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Studies on metal—metal bonds
321
Journal of Organometallic Chemdy, @ Elsevier Sequoia S.A., Lausanne -
STUDIES
139 (1977) 321-336 Printed in The Netherlands
ON METAL--METAL
BONDS
II *_ THE CRYSTAL AND MOLECULAR STRUCTURES PHYSICAL PROPERTIES OF (~s-c~H~)~cO,(NO)~,(CO), A COMMENT ON THE EAN RULE
IVAN
BERNAL
Department
**, JAMES
of Chemistry.
and WOLFGANG
Institut
fiir Chemie.
(Received
D. KORP, University
GEORGE of Houston,
AND OTHER (;r = 1,O).
M. REISNER Houston.
Texas 77004
(USA_)
A_ HERRMANN
Universita^t Regensburg,
Uniwrsif~tstmsse
31. 84 Regensburg
(Germany)
March 29th, 19fi)
5 -ary l The compounds ($-C5Hs),Co,(NO),,(CO), (x = LO) crystallize in space group P2,/c with 2 = 2 molecules per unit cell. The unit celI constants for the former (x = 1) are: u 7.878(5), b 6.121(l), c 12_080(4) A and p 105_46(2)“; while those for the latter (x = 0) are: a 7.833(l), b 6.117(l), c 12.119(3) A and fl= 105.44(2)“. In both cases the fragment Co-~z-(NO),-x(CO),Co is planar, with a maximum deviation of any atom in that fragment from its least squares plane of 0.004 A_ The Cp rings are planar and have normal C-C distances. The perpendiculars to the Cp planes make angles of 90” with the normals to the Co(NO),,(CO),Co planes. In what followes the values given in parentheses refer to the x = 0 derivative, the other values refer to the carbonylnitrosyl derivative (x = 1). The range of Co-C(Cp) distances is 2.0’71 to 2.103 a, mean 2.088 A (2.086 to 2.115 A, mean 2.101 A). The Cp ring C-C distances range from 1.379 to 1.401 A, mean 1.388 A (1.381 to 1.445 A, mean 1.411 A). The Co-N (or C) distances are 1.829 and 1.831 ft (1.824 and 1.827 A). The N-Co-N (or C) angle is 99.3” (99.0”). The two independent values of the Co-N (or Q-0 angles are 139.5 and 139.8” (139.4 and 139.6”) while the value of the Co-N(or Q-Co angle is 80.7” (81.1”). The Co-Co distance is 2.370 (2.372) A, The EAN rule is discussed with regard to these and related observations. The paramagnetic carbonylnitrosyl derivative gives a 15 line ESR spectrum (room temperature, benzene) of which the lines have, approximately,
322
intensityratios of l/2/3/---7/8/7---3/2/1,. as expected for an unpaired electron distributed equally over two s9Conuclei The s9Cohyperfiie splitting is 47-4 Oe, the g value is 2.0539 and the linewidth is ca. 29 Oe. At room temperature there is no evidence of a 14N hyperfiie splitting from the bridging nitrosyl.
IntrcKiuction
In 1968, Brunner [2] prepared the novel compound Cp,Fez(NO)z for which the existence of a double Fe-Fe bond had to be postulated if the substance were to obey the EAN rule, a fact later verified in the structural study of Calderon et al_[3], who found an Fe-Fe distance of 2.326(4) A (compared with 2_59-2.70 a normally found for Fe-Fe single bonds)_ Later, Brunner [4] prepared the Co analogue by direct nitrosylation of CpCo(CO), using NO gas, Cp,Coz(NO)z being the only NO-containing product which could be isolated. Very recently, Miiller and Schmitt [ 51 annouuced the synthesis of Cp,Coz(CO)(NO) obtained by reaction (reflex) of C~,CO~(NO)~ and cobalt carbonyls, and for which no structural data were presented. In an independent study, using N-nitrosourea derivatives (ie., N-methyl- or N-ethyl-N-nitrosourea), Herrmann and Bemal [6] showed smooth, partial nitrosylation of COCOS (boiling benzene) to Cp,Co,(CO)(NO). Finally, two recent notes from Bergman [ ‘7,8 J gave the eiectrochemical preparation [‘I] and the structural details of Cp,Coz(CO)*- which is isoelectronic with Cp&02(CO)(NO). In this report, we give the &ructural parameters of CpzCo2(CO)(NO) (III) and Cp2Co,(NO)z (II), the ESR of III and IR spectra of II and III, as well es the usual analytical data. An electrochemical study (cyclic voltammetry) of the carbonylnitrosyl and the dinitrosyl compounds is also presented. In what follows, it will be desirable to label the various compounds discussed by simple reman numerals: n
0
i Cp-M
(I)
/E’\ \E2/M-cp
1
0
Cp =
(Q5-C5H3
M =
Fe
; E’ =
E2=
N;n
(n)M
=
Co;E’=
E2=
N;n
mM
=
Co;
El =
N;E2
=
(m)M
=
Co;
E’=
E2=
C;n=
=
0
= C;n
0 =
0
-1
1
Experimental Crystallography
The procedures of data collection and processing were so nearly identical that we will describe only that for III; below we give only those details of data collection for II which differ from those of III. Crystals of both substam& were obtained by cooling (-35%) solutions (diethyl ether/methylene.chloride; 2/l) of the compounds. In both cases, the crystals chosen had six:sided plate morphology, which upon indexing turned out to be: (100 and iO0; the large .faceof the
flat plates); the six edges of the pkite~ (010 and Oio); (001 and.OOij -&id (011 end Oii). A crystal of III was n~unted.tith its [Olo] direction pm~II&&i the-: -: _ .-
:
.~.
,_ --
-. .::
323
$Baxis of the diffractometer_ Its dimensions were 0.336 mm along the [OOl] direction; 0.296 mm along the [OlO] direction; 0.296 mm along the [Oil] direction and 0.104 mm along the [loo] direction_ The crystal was mounted on a computer-controlled CAD-4 diffractometer using MO-K, radiation together with a dense graphite monochromator. A total of 23 high-angle reflections (24O < 28 < 30”) were centered automatically and used to define the cell constants. Intensity data were collected using a scan range of 2.40” + O-80” tg 0 (8 = calculated pe& center) and scan speed between 0.4 to 5.0 deg min-’ _The scan speed was decided by a pre-scan of 5 deg min- ’ in which, if the reflection had more than 60 net counts above background, the reflection was deemed observed and r&-scanned at a rate such that a minimum of 2000 counts above background were achievedThe maximum time allowed was five minutes_ All of the data between 5” =G20 < 50.0” were scanned_ Some of the data between 50.0 and 56.0” were also sampled. In total 1444 reflections were collected of which 1158 were used in the refinement of the structural parameters_ The data were corrected for Lorentz and polarization effects which include the effect of the graphite crystal used for monochromatization- They were also corrected for absorption, and the transmission coefficients ranged from O-44 to O-73. Solution of the structure was derived from program MIJLTAN. Refinement of the structural parameters of III gave: R,(F)
= Cl(lF,I
R*(F) = [Cw(F,
-
IF,I)ICIFOl -
Error of fit = [cw(F,,
IF,l)z/c -
= o-0031 wlF,l’]
lF,l)2/(N0
Ii2 = 0.0034 -NV)]“*
= l-12
where the weights, w, were set at l/o’(F) and a(F,) = a(l)/ZpF, where a(&,), a(r), Lp and F, are the standard deviations of F and I, the Lorentr-polarization factor and F observed respectively_ The o(f) were calculated from simple Poisson statistics. NO and NV are, respectively, the number of observations and the number of variables in the refinement_ The only differences between the above and the details of data collection of II are the following: the crystal was mounted parallel to the 10121 direction; and while its morphology was the same as that of III, the crystal dimensions were 0.414 mm along the [OOl] d irection; 0.344 mm along the [Oil] direction and 0.112 mm along the [loo] direction_ The-transmission coefficients ranged from 0.38 to 0.71 for this crystal_ A total of 1557 reflections were collected in the range of 5” =G20 < 56” using MO-& radiation, as described above (i.e., scan lengths, etc. were identical for both cases)_ The structure was solved by Patterson methods and reflmement converged to final discrepancy indices of R,(F) = 0.049 and R,(F) = 0.054, error of fit = 0.86. In both cases the scattering curves used for Co were corrected for anomalous dispersion_ Data decollation was accomplished with a locally written program (Houston) and all other data processing and calculations were carried out with the X-ray ‘72 system of programs [9]_ The X-ray crystallographic data are given in Table 1. Refinement of the-positional and isotropic thermal parameters for the hydrogenla_toin$*& @&-ied,out~in the case of III, which Was not sensible in the case of IL l!Jote in Table 2 (positional and thermal parameters) that, throughout, the :_
324 TABLE1 X-RAYCRYSTAUOGRAPHICDATA III
II
C1oWoCo2WW2
Molecular
fonmlla
C~OHIOC~~(CO)~NO)
MoIeculax
weight
306.07
308.07
P-WC
PzllC
787_8<5) ppm
561 A3 1.81<2) l.SlO~~m-~
7aa_3
Space
group
UnitceUdah 0 b
612.1(l) pm 1208_0<4)pm 90.00" 105.46<2)"
c a".
90_oo”
Y V
Density
MO-K,
MO-K,
Linear absorption coefficient Crystal shape
30.66 cm-I
30.60 cm-’
see text)
Sisededplate 1444 1158 93
Six&dedplate 1557 1178 93
Numberofreffectioosmeasured Numberu+edinthefinarefmemel;t Numberofvariablesforrefinement o The
unit
accuracy
cell of
dimensions
the crystal
were
refmed
on
the assumption
the substance
was
tricUnie
in order
to test
the
centering.
thermal parameters of the crystal used for the study of II are much higher- Where as in III the hydrogens were found sharply defined in the difference Fourier map at sensible positions, this was not equally the case for II; therefore, we placed them at theoretical positions with fixed thermal parameters_ It is remarkable the degree of precision and accuracy with which they were found in the refinement of the data for III, see Table 2 for a comparison of found positions vs. calculated positions. The bond lengths and angles are listed in Table 3, least squares planes (with deviations thereof) in Table 4_ A set of tables of structure factors is availabIe for both compounds *_ In Figs. 1 and 2 the shape of molecules of II and III and the packing in the unit cell are shown, ESR studies These were carried out in benzene solutions (approximately 0.05 M) using a standard Varian 4502 spectrometer_ Magnetic field measurements were made with an NMR magnetometer and the room temperature spectrum is shown in Fig_ 3, together with the details of that run [ll]. +ontinued
*ATabl~ofS~ct~Factorrhaibeen depositedarNAPSd&&tnumbe?No.03080~th ~IS/NAPS.clo,MinofichiPu~licltio~~PvirAve~eSo~th,NeurYo~N.Y.l0016. COPY may be see+d.~+y ,&&+ d~~me&an&emitti+~ 3.00 f&r miero%be hdd 7.00 pbotocopiez-Ahvance pay&t 4 &&oiredr bf&e ebe&s &able to Miitoficbe~~k&4ifea&on*~ outsfde
the
united
s’t’p
..-__..- .-
or cc&d&
_;_’ .-.._-j
Portycir
_. -_.
$ i.-w
‘0’”
&3hotocop+:or~jl~ko
f&i .:-:
on 0. 327)
A f&r-. :-
fiche. :ii -.: i. -. .__. .-
-
‘,
:
‘,
;
’
B(2)
7(2)
11(3)
ll(3)
--
8(2)
1156(8R)
i111(3) 460(12) OG7(27) 1108(63) UO3(24) OG3(40) 767(30) (JBG(70) 1034(G3) 1202(04) 400(3(i) G34(57) llGG(G0) llBR(80) 814I43) 303(3) GG(4) 48(b) 386(8) 033(20) -110(20) 1070(47) -00(37) 6W22) RB(23) O(34) 066(37) GlO(20) 172(30) 107(02) 687(42) GGG(34) 108(40) 02(71) 64O(GG) 603(4(i) 87(3D) 918(70) 44UiO) 631(46) 670(3G) 63G(G4) , 601(7G) 744(3G) 3Gf34) 7G(G8) 7G1(GO)
60(2) 3G(7) 371(20) 366(34) 107(10) 23(31) -112(27) -62(47) 138(32) 118(63) -1 G6(37) -176(00) 40(34) 44(64) -27(27) O(3b)
-27(3) -42(3) 308(22) 307(42) O(22) G(33) -103(32) -G6(Gl) 31G(38) 287(63) Ol(38) 230(85) -102(3S) -74(GS) 152(40) 203(60)
104 023 104 Ujj 104 u12 104 u12 104U11 ..,_^,.,... __..._ ,_,_ -...__,..__ -WI_ .._,___ ......._.l,__.._.” __..._..-__..- . . . _ .._._.. “..,..,..,... ..._.. .. _...,e,
_ __
-
-
--
_
___-...-
’ Note that In thle compound CO end NO ore dlaorde~tl In the crystal lnttlce. In the Ilntof coordlnotes “N” la the ovcro~e posltlon of C and Ni see text for dctellr of rulincment, b Thcae coordlnetcs shoultl hnve 1,O orldetl to them In order for tho otoms In rlucatlon to be locotcd In thu nnme molecule us the other onas, a Position, of hydrogens for III arc theoretlcnl due to hlghcr thermnl motion, see text,
WN
H(4)
wu
1w
Ii(l) c
C(b)
C(4)
(x3)
....,
331(3) 444(G) 487(20) OQZ(44) 414(21) 672(3G) 640(3G) 8l17(66) G17(36) 883(71) 7GB(4G) Ob4(74) 713(34) OOE(80) 383(27) GO4(48) S(2)
104 LIII
...-.“,”.. .
O.O06G8(4) O.OOS40(7) -0,075G(3) -6.0760(o) -0.0410(3) -0,0417(O) 0.232bf4) 0.2331(7) 0.2253(53 0,2278(D) 0.1412(6) 0,1428(O) 0,0031(5) 0,0000(8) 0.1487(6) 0,148G(0) 0,2AO(4) 0,2842 0,2UG(5) 0,2167 0,122(b) 0,1243 0,043(d) 0,0296 0,100(4) 081324
I .._.. .--. ,,...,_ _._.I _-,_-.
0,0073G~D) 0,00601(15) 0,2000(6) b 0,1067(12) 0,1070(6) b O,lOG8(11) 0,0210(11) 0.0264(18) 0,7473(13) 0,7GO2(22) 0,0043(11) 0,6023(17) 0,6004(13) 0,6004(22) 0,8042(12) O,SO48(21) O-047(8) b 0,0467 0,720(10) 0.72DG 0,488(10) 0,4003 0,630(7) 0,8286 0,010(8) b 0,9014
x 1 _,.-.._-_.-“_._C-.____”
Atom
0,1126fl(7) 0,11814(12) 0,2371(4) 0,2331(S) 0,1272(b) 0,1264(e) 0,2016(8) 0,2003(14) 0,1800(0) 0,1780(1b) 0,2028(10) 0,203xlG) 0,3270(O) 0,3247(16) 0,3821(7) 0,3822(12) 0,302(O) 093332 0,117(7) O,Ofi27 0,147(7) 0,145S 0357(O) 0,3627 0,481(G) 0,4670
_
-
____.____,_ .,.._ _...____.I _,,,._._ ....... .._,.____.,.__“._. ... . ..__..._ ___.. _.”. .._.I ..__.._..-_.. ..__.1_ .. .,-_.-..--__-._..__...__...
l&h entry II double, the top one concaponda to x 511’. Stondnrd dcvlatlons In porentheees,
\‘, ‘I TABLE2 ,’ ‘,’ ,‘, POSITIONAL AND TllEltMAL PARAMETERS OF TIlli ELEMENTS IN (~s~C~ll~)~Co~~CO)~-,(Co)x (x m 0, 1)
\’
TABLE3 DISTANCES
(A) ANDANGLES~o)WITHESTIMATEDSTANDARDDEVIATIONSINPARENTHESES
A_ Distcnceabetween
heavy
atom
BOXId
II
III
Bond
II
III
CO-CO CO-NO Co-N Co-al) Co-a2) Co--c<3) co-a4)
2-372(l) 1.827(7) l-824(7) 2.113(8) 2.095<11) 2.115(10) 2094(13)
2370(l) l-829(4) l-831(4) 2.103(5) 2071(7) 2.093(7) 2084(8)
Co--c<5) N-0 c(l)--c<2> C(l)-C<5) C(2)--c<3) C<2)-C(4) c<4)--cc5)
2.086(S) 1.187<10) 1.381<17) 1.415<16) 1.424(17) 1.385(19) 1.44X18)
2.089(5) 1.290(5) 1.379(10) 1.386(S) 1.389(10) 1.384(11) 1.4oluo)
C(l)-H(l) c<2)_m2> C<3)_-H<3) Cc4)_H<4) C<5)_H<5> C.
0.95<5) O-80(7) .0.84(6) 0_79(5) 1.02<5)
Angles
APgk
II
III
An&
II
III
N-Co-N= Co-N-Co= Co-N-G=. Co-N-G= Cw-C<1l-C(2)
99.0(3) 81.1<3) 139.4s) 139.6<5) 107.6<10)
99.3(2) 80.7(2) 139.5(3? 139.8(3) 167_6(6)
C
108.8(10) 108.8(10) 106.6(10) 108.1(10)
109.6<6) 107.1(6) 108.0(73 107.8(6)
=DisorderedN.Cin
III.
--
TABLE4 LEASTSQUARESPLANESTHROUGHSELECTEDATOMS=. DEVIATIONS THESEPLANES.ANGLES(O)BETWEENTHENORMALSOFPAIRSOFTHESEPLANES:Equatiolu givecarbonylnitrosyltbendinitrosyl) l-Plane defined byCo.~Cpria~) 0.56247x-0_48338~+0_67079z=+XG5067 0.56816~ -0_47453y+0.67232z=+9.00675 0.00914 0.99753 cc11 C(4) '-c!(S) C(2) -0.01079 .-AL01343 mm818 .0.01~16 .: _ co_ cc31 3.An~lebetween~Isncrlaind
2 i~8Zi.64~foiCO.NO;and
-0_00001 -Q.o0201 0.00381
ATOMS
FROM
-C.OOOOl -0.00153 0.00285
-0.00257 +MlO940 -0.00398~ 0.00&14. ..+_72317 : _ -1_72_408 89_Sl"or
._-..>-.
~- ~. I- ;_ ::.:
'.
327
Fii 1. The shape of both molecules showing the numbering System used in the crysttallographic study. This is a stereo pair drawn with 50% probability envclopcs for the thermal dlipsoidS of tbe heavy atoms.
of II and III Both compounds were prepared and purified according to Brunner (II) 143 and Herrmann (III) [6], respectively.
Preparation
Description of the molecules and discussion The distances and angles, as well as the planes, listed in Tables 3 &and4 show that the two molecules are essentially identical. They consist of a pair of cobalt
328
3177.61
ot
(bl
_ldLl reLInt_ t
Fig.
3. The
2
ESR
IcIdystron frequency
scanca_3177.61
3
spectrum was
L
5
of
a benzene
9.13469679
I
676765L321 solution GHz.
the
of
0.05 the
I
I
iV) of CP+OZ(CO)
the
Oe.
atoms held together by two bridging groups (CO or NO) so as to form a planar CO~(NO)~-~(CO)~ moiety. The four-membered ring is really diamond shaped, having angles at the Co atom (X-Co-Y; and Y = C or N) of approximately 99” while the Co-(X,Y)+o angles are only 81” in both cases. The Co-(X,Y) distances and Co-Co distances are, approximately, Z-11 and 2.37 A in both cases. The average Co-(Cp) distance and the Co-(ring centroid) for II and III are 2.09 and 2.10, and 1.723 and 1.724 A, respectively. Finally, the normal to the cyclopentadienyl ring makes angles of 89.64 and 89.91” with the normal to the plane of CO(NO)~C!O and Co(CO)(NO)Co respectively_ If the cyclopentadienyl ring is counted as a single ligand, the coordination around the cobalt atom is a distorted trigonal planar arrangement with one angle (X-Co-Y) of 99” _ Ekecisely the same kind of arrangement prevails in Cp,Fe2(NO)z [3] and Cp,Co,(CO); [S]. It is proper at this point to discuss the effect of the crystallographic disorder of CO and NO in Cp,C&(CO)(NO) (III) on the strucl+ral data presented here. From the fact that B ergman’s f8] anion, Cp,+(CO)z(Iv); &S the same molecular dimensions as our (ordered) CpzCo2(NO)~~(II jderiktive; one must conclude that th~e~cryst.alI~gr&$&disckder in no’ibay cahsei $Ablems in the. accurate deskiption ok the &n&&l parameters of III.‘.& fact, sz5& the 1 metal-metal dis@qc& tid$hk detai% of t@ knic_&ur& ox the b&ing CO .tid NO groups seem ti ~~.the~sau.ie~-_*th ne@gibk&fftie&es, :&c&i I&M+UI@& I _-~: _; -. _:__ .._..~_ _:: ._z.-.,‘I_ ‘__( ___..T.‘1.. l..-._ ._. _:-. .; ._--:_-_ ‘.‘-i:_. -- .;.: _’ .__. . _.. .-‘, ._:.i ._ __._-._ _____.. ._.: ~.- .: :_ ~I.-~. ..~ .._._ ._ .TT”. -‘Tr.._.: __.:..~_.~ . -c_
329
stand why compound III crystallizes so readily as disordered molecules_ From this point on, we neglect completely the disorder in III, since we can point, further, that thermally speaking the crystals of III are better behaved than those of II. The CJr,-co fmgment. So as to facilitate the discussion of the structural parameters of this fragment, we prepared Table 5 in which the various compounds entered are arranged in decreasing order of the Co-C(Cp) distance, the philosophy being that as this distance varies, we may see its effect on the other molecular parameters, or vice versa. The twelve compounds listed in Table 5 are easily divided into two classes; namely, those with sandwich arrangements of metal plus two hydrocarbons or metal plus hydrocarbon plus carborane. All these Co-(ring centroid) distances under 1.7 A. The second class contains one cyclopentadienyi ring plus two bridging ligands opposite the CsHS group. These have @-(ring centroid) distances longer than 1.7 A, except in the case of XIV. Within one given class, the average Co-C(Cp) distance varies even though the Co-(ring centroid) distance is the same. For instance, take VII and XI with Co-C(Cp) distances ranging from 2.051(6) to 2.081(5) while the Cp C-C distances range from 1.426(S) to l-402(9) (in VII) while in XI the Co-C(Cp) range from 2.042(3) to 2.057(4) and the Cp C-C distances from l-373(6) to l-408(6) A_ It is clear this is the result of ring vibrations, as demonstrated earlier [ 37-43]_ As a result, discussion concerning variations in the individual Co-C(Cp) distances and in the C-C(Cp) distances is unproductive since all of these quantities are unreliable to different degrees_ However, since the equations for the least squares planes are reliable in all cases [37-431, the variations in the Co-(ring centroid) distances are useful in gauging variations in bonding between the metal and the Cp rings. These vary according to the pattern described above, which is the same pattern one observes in going from ferrocenes to CpFeL -(contim-d TABLE
on &a_33’)
5
COMPAR~SONOFBONDINGPARAMETERS
FORVARIOUSSTRUCTURESCONTAININGTHE (~5CsHs)CoFRAGhlEh~(Thev~uesLiztedaremeanvaluesandthenumbersin wrenthesesarethe deviations
from the ____----
mean)
-.
---
Co--c
C-C
C-C-C
M-CP
(A)
(A)
(9
1_411<20> l-388(8) l-38%12> 1_415<14~ 1.417<10) l-413(8) 1.387(S) 1.407(2)
108.2~10~ 108.0(9~ 108.0<7) 108.0(9) 108_0~8) 108.0(3) 108.0(8) 108<1)
l-i24 Li23 1.714 1.682 1.682 1.674 = =
=
RMCcrrIlrr
II
Z
III V VI VII VIII IX X
(C$-W~Coz
2.101<12) 2_088(:2) 2.081(S) 2.07q91 2.066(11) 2.061(X1) 2_064(8) 2.049<13)
2.056<4)
1.400<6)
108.0<10)
1.676
19
XI
CSHsCotC4~C~Hs)2(Si~~rej)21
XII xnt XIV
2049(7J 2_038<15) 2.03600) 2029(18)
l-389(17) 1_405(14> 1.390(6) l-402(23)
108.0(S) 108(2) lOB.O
1.673 1.651 1.660 1.642
15 16 17 18
~C5~5~~~S2C2~CN~21
Thisstudy Thisstudy 10 11 12 13 14
,,,‘,,
‘.
/,
.
;‘Xx,‘,,:‘~1~O);Coe2~CO)1Co(CO)(Nbd)
25
co
__
co
Fc
Fc
Fc
Fe
22
__ .--__-
c
C
c
C
C
Ni
Fe
Co
21
C
Nf
co
Co
20
.,‘;,,,; ; .I,:’ <, , ,, ‘, , ‘: :.: : 23 ,.XVHl: i(r140Nbd)(OC)(Co.cI~~CO)2~ ;‘.:,.'. '>:.' *; :Fa(COt(r$GsH~)] 24 ,; Xl? :: ‘~~I.[(~~~~HJ)F~(CO)~J~ ‘,I.j,,,1 /./ i ‘, 2, I, ;, ) I, ::J, _; ‘,‘.I
,‘Xk’: [(~5~5~~)NlCo(CC),(PEcJ)1 t, ::,‘,, T’,’ : ,a ‘: ‘,,Xy’;’ I(rls.CP~jNICo(C0,4(PR3!1 :...I ’ R’=jbFC,$ir) +ll [Cd(~*~~l2~Mc)l(C0)132 ,,’ : ~’ ,,‘,,.I 0 ,.
-
..
2,531(l)
2,831(2)
1
1
2+530(l)
2,1)10(l)
1
1
2.426(2)
2,418(2)
1
1
.- -
1,657(4) 1.675(4) 1,663(5) 1,580(r))
1,629(10) l,Q28(lO) 1,004(11) 2+026(12) 1,682w 1,816(B) 1,626(3) X,028(3) 1,606(4) 1,618(4) 1,006(T) 1.625(7)
_
_
_
06,0(3) OOtO(3)
Ob,1(2)
D&6(3) 06,4(3)
81i,B(6)
87,3(4)
1,113(a) 91.1(2) 1,164(5) 84,5(l)
1,163(6) 1‘17tm) 1.178(O) i.i8a(fu
1.160(12) 1,167(11) 1,176(12) 1,145(14) 1,170(9) 1,177w
- .~
61,0(2) 62,0(2)
83,2(2) 32.7(2) 62.qa) 02,4(3)
79,7(4) 70,3(4) 79,4(/r) 77,9(b) ei,z(a) 6l,b(3)
__
(X,Y)E-0
-
130,3(0) 143,5(8) 14a,4(lo) 138,0(11) 138,8(7) 130,9(7) 138,0(7) 13%6(6) x36,6(4) 136&(4) 137,Ei6) ’ 130*4(6) 189,2(6) 138,4(6) 142,0(4) 141,3(4) 136,1(4) 136X4)
.‘:Mih,l!&ii,~R PARAMETERS REPORTED FOR SPECIES OF THE TYPE X.~~'OY.E~O~Y WITH X AND Y m METALS AND IS’ AND E2 EITHER C OR N ,i (D~ihkIh A and ander In degrees. Only Co or Fc data Wed hero) *I b _.__“,_~-r”___.“_~.-“_.~__~._‘~---~--~.-..-----_ p--E'-fX,Y).X_(E'J). Rclar- x Y El I32 Band X-Y (X,Y)-13 E-O ~.,;cwIlpbund ",,,i, '9" -Y -22 cnce order c i ).’ 1, 3 ...--,“l.----_“.--l~__“,_._I *_p._,” _-._-_-.-. I
‘iT&E’@,
,,
;
,(t15*C5ti5)2C02(No)2
” ;;15~5,~~)$02~~o)l_-
‘,
Co
Fe Co
Fc Co
3 thlc ctudy co
co
co
30
Co
co
co
29
co
Co
Fc
28
8 thb
Fe
Fo
27
C
1
2,54G
c
c
C
N
c
N C
N
c
N N
Clorrc
c
c
C
1,5 1,O
2 1-G
1
1
1
2,372(2) 2,372(l)
2,32fJO) 2,370(l)
2,aoB(a)
2,640(l)
2$46(l)
Clot8 IJ, Plonnrderlunflucr C C 1 2,834(2)
C
1.82(2) 1,826(7)
1.708(O) 1,82B(7)
l.Bll(lO)
l.BlO(G) 1,918(a) 1,806(7) l,B33(0) l,B31(4)
2,036(7) 1,882(7)
1,21(4) l.l8Lt(lO)
1,264(12) 1.200(10)
1,102(17)
1,160(8) 1,166(8) 1,165(b)
l*la8(0)
1,147(E)
e&a(a) O&O(3)
07.7(4) BO,3(2)
Bb,B(O)
07,1(4)
Ob,7(3)
07,1(4)
87,6(3) f&8(3)
61,2(6) fllJ(3)
82,3(4) fJQ,7(2)
84,1(5)
82,5(3) 82,8(3) 82,0(2)
82,0(2)
80,0(3)
130,6(a)
138.8(8) 130,4(3)
13&E(4) 138,4(4) 13O,b(6) 138,0(5) 130,6(3) 137,0(3) 13&O(3)
134,6(O) 144,6(O)
‘1
..“.
,’
‘, ‘:anly tha date for tho CpCo bcarlng frcgmcnt II glvcn. In XX data for (Nbd)Co and (OC)$o nrc given for cmphaslr: ccc footnote e snd tho Dlscueslon, ’ Calculated .‘accordltig !o the EAN Nle. cl Whenever rclcvant, lha (Nbd)Co data am rlvcn first, followctl by thnt for the (OC)$o portlon, ’ P.ntrica on the upper holf o! each column belopg tb,the Co rtom of lhe (Nbd)Co fragment. .,
.____..__._._______,_______.,___._.____ .._. __.___.__... _..,..___.. . ... ,___..“_.._.. ..._.“_”._......-+..I..-M-M ..-- I----‘:’ a Whenever e mlxcd Fe, Co compound occurs, only the Co InformalIon IaIlstcd, Nbd - norbornadleno. b When a Cp-mctnl fragment occult wlth II metal boar@ no CP rlnu,
“,
‘I Iv .I:, 1’
,,’
Co
Fc
20
332
derivatives [44] (L = a suitable set of ligands such as (CO)*I, (CO)(PPhs)Cl, etc.). It is interesting to note, however, that there is no variation in the Co-(ring centroid) distance between II and III since the former has one electron more, and, consequently, a single Co-Co bond whereas the latter has, according to the EAN rule, a 1.5 order bond between the two metals. The Co[p,-(CO)JCo fragment. A comment on the EALV rule. Briefly stated, the EAN rule says that a transition metal atom will combine with a set of donor ligands such that the total number of electrons (metal plus electrons donated by ligands) add to that of the nearest rare gas configuration. Thus, the metal has a total number of electrons equivalent to the number contained in the stable, rare gas, configuration. This rule is undoubtedly very useful, and it is generally obeyed_ As such, it correctly predicts that certain *&gments, such as CpFe(CO),, will be unstable unless they are (a) reduced to CpFe(CO);, (b) treated with a one-electron donor such as Cl-, etc. to form CpFe(CO)zCl, etc., (c) allowed to dime&e to Cp,Fe,(CO),, in which case there is a two-electron(single) metalmetal bond. The argument is exactly that used to expiain why the halide elements are diatomic. We have prepared Table 6 which shows that, for the general classes of compounds labelled class A and class B, this rule is not only obeyed but that the length of the metal-metal bonds remains very close despite the marked changes involved. Note that this observation is valid for both the cis and Pans isomers, where relevant, and that changing from one isomer to the other changes the picture very little. The variations in metal-metal bond lengths can be explained, easily, by the variations in metal covalent radii (i.e., Fe vs. Co vs. Ni) and by the changes in ligands, which are quite drastic in some cases. Overall, the length of metal-metal bonds in class A compounds ranges from 2.418(2) to 2_559(3) A, which amounts to a 6% change_ It is equally true that the variations in the metal to bridging carbonyl (M-C) distance, the C-O distance and the angles of the entire fragments change very little, as well. Thus, the M[l.r-(C0)2]M fragment seems to be largely invariant and it would appear that this rule can safely predict approximate values for the length of metal-metal bonds. As long as we are dealing with a single metal-metal bond (class A compounds) the expectation is that the bond length of M-M’ should be about 2.5 A, irrespective of the nature of M and/or M’ (M, M’ = Fe, Co or Ni) (Table 6). Recently, Calderon et al. [3] studied the structure of Cp,Fe,(NO)z (I) and found, according to the EAN rule prediction, that there is a short Fe-Fe distance of 2.326(4) A, which was readily explained on the basis that a compound with that composition should have a four electron (double bond) between the two iron atoms. Comparison of their result with those of Bergman et al. [8] for CP~CO~(CO)~- (IV has a 1.5 bond order between Co atoms, according to the EAN.rule), our study of CpsCol(CO)(NO) (III) which is isoelectronic with IV and, most importantly, with Cp,Co,(NO), (II), which shouId have a single Co-Co bond, show that the metal to metal bonds are of nearly the same length in all four cases. It is important to stress, that not only are I, II, III, and IV molecularly identical (see Table 6, class C for details of the molecular parameters) but, more important, I, II and IIIare isomorphous and is’ostructural. Therefore, all crystallographic effects are identical for these three species. Further, according to Pauling [44], the difference in radii between Fe and Co ’ is 0.01 A - This difference,. if used, .would predict a larger Co-@ distance for the I~ .:. _.~.. -. ., -- .:-. (__ . __, .~ .; .v-. -, ,.-._ : _: _. .:. -..~’ ,. :-:: ._ --
333 same bond order- However, the point is that the EAN rule predicts a single bond for II and a double bond for I. We must conclude at this point that the EAN rule is unreliable as a criterion for predicting finer details such as bond orders end bond lengths. The bonding details (Table 6) for I, II, III and IV demonst.rate this point amply. Early in our search of the literature, we were struck by the homogeneity of the values for metal-metal bonds for compounds in class A and class B and attributed the change in metal-metal bond between the isoelectronic species III and IV and those compounds of class A and B to a change in bond order. In fact, our carbonylnitrosyl (III) and Bergman’s anion (IV) are predicted -to have a 1.5 Co-Co bond order. However, we then determined the structure of the dinitrosyl (II) and found the result of Calderon et al. [3], and realized that this was not a valid explanation for these results. Finally, we must comment that the differences in metal-metal bond lengths observed for classes-A and B, on the one hand, and those on class C cannot be simply explained on a change in structure because (a) there are equally drastic structural changes within the compounds of classes A and B, (b) the compounds in class C have the identical same structure and bonding parameters and for them the EAN rule would predict a smooth increase in metal-metal bond length from I to (III and IV) to II. In conclusion, when we go from Cp&0z(N0)~ to either Cp&o,(CO)(NO) or its isoelectronic anions C~,CO,(CO)~- and, finally, to Cp,Fe,(NO), the successive increase in bond order predicted by the EAN rule is not observed. The implication is that the electrons associated with these changes must come from orbitals which are non-bonding in character, as far as the dinuclear metal framework is concerned. Our research is directed currently to probe further into this interesting question_
The ESR spectrum of Cp,Co,(NOI(CO) Given the composition of this substance, one expects it to be pararnagnetic (S = l/2). In fact, this had been recently demonstrated by Miiller and Schmitt [5] who measured its magnetic moment (lS6 BM) compound III is isoelectronic with the anion IV as shown by ESR spectroscopy [S]. As a fine tool for probing electron distribution and because it seemed desirable to compare III and IV, we recorded the ESR spectrum of III. The results are shown in Fig. 3 where it is clear that there are 15 lines having relative intensity ratios of approximately 1/2/3/---7/8/7---3/2/l_ This is, of course, a classic pattern already found in [(HaN)&oOOCo(NH3),] 5* [31,32] and in IV [8], and is associated with an unpaired electron equally delocalized over two 59Co nuclei (I = 7/2; abundance ca. 100%). It is also clear that there is no evidence of further splitting by the N nucleus of the nitrosyl bridge. One must, however, note that while the splitting due to the Co nuclei is 47.4 Oe, the linewidth is ca. 29 Oe. In order to place these numbers in perspective, we have prepared Table 7 in which a number of ESR spectral parameters of relevant molecules are listed. From these data, the parameters ofthe ESR spectra of III and IV are .the same, to the-accuracy quoted. Tbis is not very surprising since the structural parameters in III and IV are essentially identical In particular, note that the CO-CO, cO-_N or Co-C distances are identical within stated accuracy- Therefore, one expects the unpaired electron to be distributed, approximately, equally-in_t.he twq-sub&ances. This-isan interesting observation-which agreeswell :
334 TABLE
x
7
COMPARISON OF ESR PARAMETERS
WITH SOME
Comsmimd
in
RELEVANT
g-factor
Reference
140
2.0539
This reference 8 33 34 35 31.32
47.4 Ea.50
f.cj-RCCojKO)g
ca35 12.7
xxx
CF3(NO)Co(DMG)
a Estimated
vahe
from linewidths.
THE LITERATURE _
O(N)
2*2
’
FROM
MC01
IV xxv XXVI XXVII XXVIII XXIX
CF~(NO)CO(CN)S
VALUES
2.091
-
11.75 12 -
Not given 2.0149 2.006 2.037
10.25
13.92
2.0066
36
10.1
13.6
2.0065
36
--___ See
texL.
b DMG
= dimethylglyoximato.
with the commonly accepted idea that in organometallics the change from one group (effectively CO- for NO) having the same number of electrons to contribute to the bonding, results in the same total electronic distribution around the core atom_ We note, next, that the spectroscopic splitting factor for III is g = 2.0539, which is higher than 2-0023 (the free electron value) by a significant amount. This is expected for a transition element compound of the 3d series due to the spin-orbit contribution; it is also in accord with the measured value of the magnetic moment for III given by Miiller and Schmitt [5] which is larger than the value of 1.73 BM expected for a free electron. The fact that the g factor for III exceeds the free radical value implies a negative value for the spin-orbit coupling constant, which is to be expected of any cobalt compound whose effective charge is less than 5+ and which is certainly the case for III and IV, no matter how electrons are counted. Concerning the magnitude of the 14N hyperfme constant, the results quoted in Table 7 show that for a relevant number of compounds having the fragment: ? R-N-(3d-transition
metal)
it does not exceed 12-14 Oe [ 34-361. These substances have g values that are consistent with their formulation as “free radical-like” and contain an unpaired electron which can be labelled as “ligand based”. The SpCo hyperfine splitting constant for these substances is approximately l/4 those observed for III and IV_ Also, note that they are approximately the same as those observed in p-peroxodecaaminodicobalt [31,32] for which Weil and Kinnaird [ 323 estimate that the unpaired electron spends 90% of the time on the 0, bridge_ Thus, it is quite likely that the 14N splitting is lost in the.29 Oe linewidth, whose large value may be due to stereochemical non-rigidity and/or solvent perturbations in the open ; Co-(bridge)-Co fragment. A careful stud* of the line shapes as a.function &f temperature may still reveal the magnitude of the‘ 14N intera&&; &til sukh’ : time, nothing defiit&can b& saic+bo~t.the path of the tip&re&&ctr&ti~ %. moving between the two-cobalt atoms over:which-ii is de&al&d~~~‘t~~&~~ -i ' -.-. moment
12-14
we
only
&;ofithe
bm
of_~&i&&j~&@,
&
Upljeriimit_oi:.'_:'---:.~~‘
:
Oe to the %I hyperfine s&ting: Coti&e+ig.&e -5_pC;, a.&~~_(X2/ jZ:Zi._..i(: ;. :, .._ ._ ... : .a._.. _ .- “:_A:.._ ._ I _,.. -. I ._..-:,~r_, .-;: ..-: -.._ 1 ,_: :.:: :: .. ._ .--, f_ __
335 TABLE
8
SPECTRAL.
ANALYTICAL.
AND
POLAROGRAPkIlC
DATA
spectrum
Mass
IR
1545 cm-’
WNO)):
1819 em-’
(v
Anolyticol doto: Found: C. 43.25: H. 3.59; N. 4.50; Co. 37.09: moL weight. 345 (osmometricaIIy in benzene). CI IHIoColN02 caled.: C. 43.17; H. 3.29: N. 4.58; Co. 38.51%: moL weight 306.07. The compound has no melting point up to 250-C. but decomposition starts out slowly at ca_ 30°C and is complete at ca. 160°C
reported by Katz et al. 1331, we see that both the g factors and the hyperfine splittings, consistently, point to these species as having a more “metal based” unpaired electron than the other enfries of Table 7_ Using Weil and Kinnaird’s [32] estimate of ca. 10% for the distribution of the unpaired electron over the two “Co nuclei of [(H,N)&o-02-Co(NH,).$+ and assuming a roughly linear change, the unpaired electron spends about 40% of the time on the metals of III. Finally, we want to call the reader’s attention to the fact that in the anions of Kotx et al. 1331 there are three cobalt atoms and that the 5gCo splitting is ca. 2/3 the value found in either III or IV. Since the sum of the individual spin densities at all atoms of a species with spii l/2 must addd to unity, the obvious conclusion is that for HI, IV, and XXV, the fraction of the time the unpair electron spends on the metal framework and on the bridging framework are about the same. Electrochemistry of II and III The electrochemical processes described by the data of Table 8 indica+tethat the dinitrosyl derivative II can easily be oxidized to its cation, Cp2Cp2(NO)z’, which would be isoelectronic with the known, stable, species III and IV. Consequently, it is not surprising to find that this is a reversible process. The same comment8 can be made about the reduction of III to Cp,Co,(CO)(NO)-. Oxidation of III to its cation and reduction of II to it8 anion are both irreversible processes and would correspond to the formation of CplCo,(CO)(NO)+ and Cp2Col(NO)z-, respectively_ The former, III’, would be isoelectronic with Cp2Col(CO)s which has been isolated recently [l]. The anion, IT, probably undergoes a bridge splitting reduction similar with those known to OCCUTin specie8 of the type Cp2Fe2(CO), and Cp2Mo.2(CO)6, etc. Our observations for II and III parallel the recent experiences described by Bergman and associates with C&C&(CO)~[7,8]. Acknowledgeme.nts
‘.
.
I, Es&& JDy’ K&p, Itid G_M_ X+sner thank the Welch Foundation and the :I@ Nat&&&en& F&$I_$ttion for support and funds for the purchase of :_:t_ _..-.;-~i ..::.. -:....z. <7-:;..r_ =,.:_ ,-_..;t_?.Y_‘_ ,_.__ _. -. :. ;:--_ ‘.I.:_‘. ._.:‘._._ .._ ,.:.. I-- L I _ _’ __. ‘_.. .--_.;z;--.-:-_ ‘.- _:. ._. _,. __.. :
336
the diffractometer_ We also thank the Computer Center of the University of Houston for a generous supply of free ctimpiiting time. W_A_ Herrman n thanks Prof. H. Bnmner as well as the Deutsche Forschungsgemeinschaft for generous support of this study_ Finally, we thank Dr. B. Kaly anaraman (Univzsity of Alabama) for running a calibrated ESR spectrum and Dr_ A_ Merz (llniversitit Regensburg) for performing the electrochemical measurements_
Chem.. 127 (1977) 87. 1 W.S_ Lee and H_ ~rintziiger. J. OaanometaL 2 H. Brunner. J_ OrgamxnetaL Cbem.. 14 (1968) I73_ 3 J-L_ CaIdemn. S_ Fontana. E_ Frauendorfer. V-W_ Day and DA. Iske. J_ OrganomeLal Chem.. 64 (1974) Cl6. 4 H_ Bmnner. J_ OrgarmmetaL Chem, 14 (1968) 517. 5 J. Mtlllcr and S. Schmitt, J. OrganometaL Chem.. 97 (1975) C54. 6 W.A. Herrman n and 1. Bernal, Angela. Chem.. 89 (1977) 186; Angew. Chem. Internat. Edit. En& 16 (1977) in press. 7 CS_ ILznda. N-E. Shore. and R-G. Beaman. J. Amer. Chem_ Sot.. 98 (1976) 255. 8 N.B_ Shore. CS. Ilenda.and R_G_ Bergman. J_ Amer. Chem. Sot_. 98 0976) 256. 9 JM. Steward. G. Kruger. H.L. Amon. C. Dickinson and S.R. Hall (Ed%;. The Xjay System of ckystalIographic Programs. Technical Report No. 192. Computer Center. University of Man-land 1972. 10 G_ Evrrrd. R. Thomas. B.R. Davis and I. Bernal. J. Organometal. Chem.. 124 (1977) 59. 11 KS. Calkhan. C.E. Stmuse. A.L. Sims and M-F. Hawthorne. Inorg. Chem.. 13 (1974) 1393. 12 E.L. Hoel. C.E. Stmuse and M.F. Hawthorne. Inorg. Chem, 13 (1974) 1388. 13 G. Evrard. JS. Ricd. Jr, I. Bern& W_J. Eva. D.F. Dustin and M.F. Hawthorne. Chem. Commun.. (1974) 234. F_Y_ Lo. CR_ Strouse, A-L. Sii and hi_E. Hawthome. Inorg_ Chem, 13 (1974) 2842. 14 K-P_ &U&an_ 15 M-D_ E+sch. I. Bernal. B.R. Davfs. A_ Siegel. F.A. Highie and G.F. Westover. J. Coord. Chem.. 3 (1973) 149_ 16 hf_R_ Churcbilland B_G_ De Boer. Inorg_ Chem.. 13 0974) 1411. Chem.. 113
B&id. Ithaca. %Y..
_ .. . ..: .:.
Cornell U&ersity
‘--I-. -_.._
-..-
_w.
3rd. Ed.. i973.
..-
_. -.
Journal of Organometallic Chemdy, @ Elsevier Sequoia S.A., Lausanne -
STUDIES
139 (1977) 321-336 Printed in The Netherlands
ON METAL--METAL
BONDS
II *_ THE CRYSTAL AND MOLECULAR STRUCTURES PHYSICAL PROPERTIES OF (~s-c~H~)~cO,(NO)~,(CO), A COMMENT ON THE EAN RULE
IVAN
BERNAL
Department
**, JAMES
of Chemistry.
and WOLFGANG
Institut
fiir Chemie.
(Received
D. KORP, University
GEORGE of Houston,
AND OTHER (;r = 1,O).
M. REISNER Houston.
Texas 77004
(USA_)
A_ HERRMANN
Universita^t Regensburg,
Uniwrsif~tstmsse
31. 84 Regensburg
(Germany)
March 29th, 19fi)
5 -ary l The compounds ($-C5Hs),Co,(NO),,(CO), (x = LO) crystallize in space group P2,/c with 2 = 2 molecules per unit cell. The unit celI constants for the former (x = 1) are: u 7.878(5), b 6.121(l), c 12_080(4) A and p 105_46(2)“; while those for the latter (x = 0) are: a 7.833(l), b 6.117(l), c 12.119(3) A and fl= 105.44(2)“. In both cases the fragment Co-~z-(NO),-x(CO),Co is planar, with a maximum deviation of any atom in that fragment from its least squares plane of 0.004 A_ The Cp rings are planar and have normal C-C distances. The perpendiculars to the Cp planes make angles of 90” with the normals to the Co(NO),,(CO),Co planes. In what followes the values given in parentheses refer to the x = 0 derivative, the other values refer to the carbonylnitrosyl derivative (x = 1). The range of Co-C(Cp) distances is 2.0’71 to 2.103 a, mean 2.088 A (2.086 to 2.115 A, mean 2.101 A). The Cp ring C-C distances range from 1.379 to 1.401 A, mean 1.388 A (1.381 to 1.445 A, mean 1.411 A). The Co-N (or C) distances are 1.829 and 1.831 ft (1.824 and 1.827 A). The N-Co-N (or C) angle is 99.3” (99.0”). The two independent values of the Co-N (or Q-0 angles are 139.5 and 139.8” (139.4 and 139.6”) while the value of the Co-N(or Q-Co angle is 80.7” (81.1”). The Co-Co distance is 2.370 (2.372) A, The EAN rule is discussed with regard to these and related observations. The paramagnetic carbonylnitrosyl derivative gives a 15 line ESR spectrum (room temperature, benzene) of which the lines have, approximately,
322
intensityratios of l/2/3/---7/8/7---3/2/1,. as expected for an unpaired electron distributed equally over two s9Conuclei The s9Cohyperfiie splitting is 47-4 Oe, the g value is 2.0539 and the linewidth is ca. 29 Oe. At room temperature there is no evidence of a 14N hyperfiie splitting from the bridging nitrosyl.
IntrcKiuction
In 1968, Brunner [2] prepared the novel compound Cp,Fez(NO)z for which the existence of a double Fe-Fe bond had to be postulated if the substance were to obey the EAN rule, a fact later verified in the structural study of Calderon et al_[3], who found an Fe-Fe distance of 2.326(4) A (compared with 2_59-2.70 a normally found for Fe-Fe single bonds)_ Later, Brunner [4] prepared the Co analogue by direct nitrosylation of CpCo(CO), using NO gas, Cp,Coz(NO)z being the only NO-containing product which could be isolated. Very recently, Miiller and Schmitt [ 51 annouuced the synthesis of Cp,Coz(CO)(NO) obtained by reaction (reflex) of C~,CO~(NO)~ and cobalt carbonyls, and for which no structural data were presented. In an independent study, using N-nitrosourea derivatives (ie., N-methyl- or N-ethyl-N-nitrosourea), Herrmann and Bemal [6] showed smooth, partial nitrosylation of COCOS (boiling benzene) to Cp,Co,(CO)(NO). Finally, two recent notes from Bergman [ ‘7,8 J gave the eiectrochemical preparation [‘I] and the structural details of Cp,Coz(CO)*- which is isoelectronic with Cp&02(CO)(NO). In this report, we give the &ructural parameters of CpzCo2(CO)(NO) (III) and Cp2Co,(NO)z (II), the ESR of III and IR spectra of II and III, as well es the usual analytical data. An electrochemical study (cyclic voltammetry) of the carbonylnitrosyl and the dinitrosyl compounds is also presented. In what follows, it will be desirable to label the various compounds discussed by simple reman numerals: n
0
i Cp-M
(I)
/E’\ \E2/M-cp
1
0
Cp =
(Q5-C5H3
M =
Fe
; E’ =
E2=
N;n
(n)M
=
Co;E’=
E2=
N;n
mM
=
Co;
El =
N;E2
=
(m)M
=
Co;
E’=
E2=
C;n=
=
0
= C;n
0 =
0
-1
1
Experimental Crystallography
The procedures of data collection and processing were so nearly identical that we will describe only that for III; below we give only those details of data collection for II which differ from those of III. Crystals of both substam& were obtained by cooling (-35%) solutions (diethyl ether/methylene.chloride; 2/l) of the compounds. In both cases, the crystals chosen had six:sided plate morphology, which upon indexing turned out to be: (100 and iO0; the large .faceof the
flat plates); the six edges of the pkite~ (010 and Oio); (001 and.OOij -&id (011 end Oii). A crystal of III was n~unted.tith its [Olo] direction pm~II&&i the-: -: _ .-
:
.~.
,_ --
-. .::
323
$Baxis of the diffractometer_ Its dimensions were 0.336 mm along the [OOl] direction; 0.296 mm along the [OlO] direction; 0.296 mm along the [Oil] direction and 0.104 mm along the [loo] direction_ The crystal was mounted on a computer-controlled CAD-4 diffractometer using MO-K, radiation together with a dense graphite monochromator. A total of 23 high-angle reflections (24O < 28 < 30”) were centered automatically and used to define the cell constants. Intensity data were collected using a scan range of 2.40” + O-80” tg 0 (8 = calculated pe& center) and scan speed between 0.4 to 5.0 deg min-’ _The scan speed was decided by a pre-scan of 5 deg min- ’ in which, if the reflection had more than 60 net counts above background, the reflection was deemed observed and r&-scanned at a rate such that a minimum of 2000 counts above background were achievedThe maximum time allowed was five minutes_ All of the data between 5” =G20 < 50.0” were scanned_ Some of the data between 50.0 and 56.0” were also sampled. In total 1444 reflections were collected of which 1158 were used in the refinement of the structural parameters_ The data were corrected for Lorentz and polarization effects which include the effect of the graphite crystal used for monochromatization- They were also corrected for absorption, and the transmission coefficients ranged from O-44 to O-73. Solution of the structure was derived from program MIJLTAN. Refinement of the structural parameters of III gave: R,(F)
= Cl(lF,I
R*(F) = [Cw(F,
-
IF,I)ICIFOl -
Error of fit = [cw(F,,
IF,l)z/c -
= o-0031 wlF,l’]
lF,l)2/(N0
Ii2 = 0.0034 -NV)]“*
= l-12
where the weights, w, were set at l/o’(F) and a(F,) = a(l)/ZpF, where a(&,), a(r), Lp and F, are the standard deviations of F and I, the Lorentr-polarization factor and F observed respectively_ The o(f) were calculated from simple Poisson statistics. NO and NV are, respectively, the number of observations and the number of variables in the refinement_ The only differences between the above and the details of data collection of II are the following: the crystal was mounted parallel to the 10121 direction; and while its morphology was the same as that of III, the crystal dimensions were 0.414 mm along the [OOl] d irection; 0.344 mm along the [Oil] direction and 0.112 mm along the [loo] direction_ The-transmission coefficients ranged from 0.38 to 0.71 for this crystal_ A total of 1557 reflections were collected in the range of 5” =G20 < 56” using MO-& radiation, as described above (i.e., scan lengths, etc. were identical for both cases)_ The structure was solved by Patterson methods and reflmement converged to final discrepancy indices of R,(F) = 0.049 and R,(F) = 0.054, error of fit = 0.86. In both cases the scattering curves used for Co were corrected for anomalous dispersion_ Data decollation was accomplished with a locally written program (Houston) and all other data processing and calculations were carried out with the X-ray ‘72 system of programs [9]_ The X-ray crystallographic data are given in Table 1. Refinement of the-positional and isotropic thermal parameters for the hydrogenla_toin$*& @&-ied,out~in the case of III, which Was not sensible in the case of IL l!Jote in Table 2 (positional and thermal parameters) that, throughout, the :_
324 TABLE1 X-RAYCRYSTAUOGRAPHICDATA III
II
C1oWoCo2WW2
Molecular
fonmlla
C~OHIOC~~(CO)~NO)
MoIeculax
weight
306.07
308.07
P-WC
PzllC
787_8<5) ppm
561 A3 1.81<2) l.SlO~~m-~
7aa_3
Space
group
UnitceUdah 0 b
612.1(l) pm 1208_0<4)pm 90.00" 105.46<2)"
c a".
90_oo”
Y V
Density
MO-K,
MO-K,
Linear absorption coefficient Crystal shape
30.66 cm-I
30.60 cm-’
see text)
Sisededplate 1444 1158 93
Six&dedplate 1557 1178 93
Numberofreffectioosmeasured Numberu+edinthefinarefmemel;t Numberofvariablesforrefinement o The
unit
accuracy
cell of
dimensions
the crystal
were
refmed
on
the assumption
the substance
was
tricUnie
in order
to test
the
centering.
thermal parameters of the crystal used for the study of II are much higher- Where as in III the hydrogens were found sharply defined in the difference Fourier map at sensible positions, this was not equally the case for II; therefore, we placed them at theoretical positions with fixed thermal parameters_ It is remarkable the degree of precision and accuracy with which they were found in the refinement of the data for III, see Table 2 for a comparison of found positions vs. calculated positions. The bond lengths and angles are listed in Table 3, least squares planes (with deviations thereof) in Table 4_ A set of tables of structure factors is availabIe for both compounds *_ In Figs. 1 and 2 the shape of molecules of II and III and the packing in the unit cell are shown, ESR studies These were carried out in benzene solutions (approximately 0.05 M) using a standard Varian 4502 spectrometer_ Magnetic field measurements were made with an NMR magnetometer and the room temperature spectrum is shown in Fig_ 3, together with the details of that run [ll]. +ontinued
*ATabl~ofS~ct~Factorrhaibeen depositedarNAPSd&&tnumbe?No.03080~th ~IS/NAPS.clo,MinofichiPu~licltio~~PvirAve~eSo~th,NeurYo~N.Y.l0016. COPY may be see+d.~+y ,&&+ d~~me&an&emitti+~ 3.00 f&r miero%be hdd 7.00 pbotocopiez-Ahvance pay&t 4 &&oiredr bf&e ebe&s &able to Miitoficbe~~k&4ifea&on*~ outsfde
the
united
s’t’p
..-__..- .-
or cc&d&
_;_’ .-.._-j
Portycir
_. -_.
$ i.-w
‘0’”
&3hotocop+:or~jl~ko
f&i .:-:
on 0. 327)
A f&r-. :-
fiche. :ii -.: i. -. .__. .-
-
‘,
:
‘,
;
’
B(2)
7(2)
11(3)
ll(3)
--
8(2)
1156(8R)
i111(3) 460(12) OG7(27) 1108(63) UO3(24) OG3(40) 767(30) (JBG(70) 1034(G3) 1202(04) 400(3(i) G34(57) llGG(G0) llBR(80) 814I43) 303(3) GG(4) 48(b) 386(8) 033(20) -110(20) 1070(47) -00(37) 6W22) RB(23) O(34) 066(37) GlO(20) 172(30) 107(02) 687(42) GGG(34) 108(40) 02(71) 64O(GG) 603(4(i) 87(3D) 918(70) 44UiO) 631(46) 670(3G) 63G(G4) , 601(7G) 744(3G) 3Gf34) 7G(G8) 7G1(GO)
60(2) 3G(7) 371(20) 366(34) 107(10) 23(31) -112(27) -62(47) 138(32) 118(63) -1 G6(37) -176(00) 40(34) 44(64) -27(27) O(3b)
-27(3) -42(3) 308(22) 307(42) O(22) G(33) -103(32) -G6(Gl) 31G(38) 287(63) Ol(38) 230(85) -102(3S) -74(GS) 152(40) 203(60)
104 023 104 Ujj 104 u12 104 u12 104U11 ..,_^,.,... __..._ ,_,_ -...__,..__ -WI_ .._,___ ......._.l,__.._.” __..._..-__..- . . . _ .._._.. “..,..,..,... ..._.. .. _...,e,
_ __
-
-
--
_
___-...-
’ Note that In thle compound CO end NO ore dlaorde~tl In the crystal lnttlce. In the Ilntof coordlnotes “N” la the ovcro~e posltlon of C and Ni see text for dctellr of rulincment, b Thcae coordlnetcs shoultl hnve 1,O orldetl to them In order for tho otoms In rlucatlon to be locotcd In thu nnme molecule us the other onas, a Position, of hydrogens for III arc theoretlcnl due to hlghcr thermnl motion, see text,
WN
H(4)
wu
1w
Ii(l) c
C(b)
C(4)
(x3)
....,
331(3) 444(G) 487(20) OQZ(44) 414(21) 672(3G) 640(3G) 8l17(66) G17(36) 883(71) 7GB(4G) Ob4(74) 713(34) OOE(80) 383(27) GO4(48) S(2)
104 LIII
...-.“,”.. .
O.O06G8(4) O.OOS40(7) -0,075G(3) -6.0760(o) -0.0410(3) -0,0417(O) 0.232bf4) 0.2331(7) 0.2253(53 0,2278(D) 0.1412(6) 0,1428(O) 0,0031(5) 0,0000(8) 0.1487(6) 0,148G(0) 0,2AO(4) 0,2842 0,2UG(5) 0,2167 0,122(b) 0,1243 0,043(d) 0,0296 0,100(4) 081324
I .._.. .--. ,,...,_ _._.I _-,_-.
0,0073G~D) 0,00601(15) 0,2000(6) b 0,1067(12) 0,1070(6) b O,lOG8(11) 0,0210(11) 0.0264(18) 0,7473(13) 0,7GO2(22) 0,0043(11) 0,6023(17) 0,6004(13) 0,6004(22) 0,8042(12) O,SO48(21) O-047(8) b 0,0467 0,720(10) 0.72DG 0,488(10) 0,4003 0,630(7) 0,8286 0,010(8) b 0,9014
x 1 _,.-.._-_.-“_._C-.____”
Atom
0,1126fl(7) 0,11814(12) 0,2371(4) 0,2331(S) 0,1272(b) 0,1264(e) 0,2016(8) 0,2003(14) 0,1800(0) 0,1780(1b) 0,2028(10) 0,203xlG) 0,3270(O) 0,3247(16) 0,3821(7) 0,3822(12) 0,302(O) 093332 0,117(7) O,Ofi27 0,147(7) 0,145S 0357(O) 0,3627 0,481(G) 0,4670
_
-
____.____,_ .,.._ _...____.I _,,,._._ ....... .._,.____.,.__“._. ... . ..__..._ ___.. _.”. .._.I ..__.._..-_.. ..__.1_ .. .,-_.-..--__-._..__...__...
l&h entry II double, the top one concaponda to x 511’. Stondnrd dcvlatlons In porentheees,
\‘, ‘I TABLE2 ,’ ‘,’ ,‘, POSITIONAL AND TllEltMAL PARAMETERS OF TIlli ELEMENTS IN (~s~C~ll~)~Co~~CO)~-,(Co)x (x m 0, 1)
\’
TABLE3 DISTANCES
(A) ANDANGLES~o)WITHESTIMATEDSTANDARDDEVIATIONSINPARENTHESES
A_ Distcnceabetween
heavy
atom
BOXId
II
III
Bond
II
III
CO-CO CO-NO Co-N Co-al) Co-a2) Co--c<3) co-a4)
2-372(l) 1.827(7) l-824(7) 2.113(8) 2.095<11) 2.115(10) 2094(13)
2370(l) l-829(4) l-831(4) 2.103(5) 2071(7) 2.093(7) 2084(8)
Co--c<5) N-0 c(l)--c<2> C(l)-C<5) C(2)--c<3) C<2)-C(4) c<4)--cc5)
2.086(S) 1.187<10) 1.381<17) 1.415<16) 1.424(17) 1.385(19) 1.44X18)
2.089(5) 1.290(5) 1.379(10) 1.386(S) 1.389(10) 1.384(11) 1.4oluo)
C(l)-H(l) c<2)_m2> C<3)_-H<3) Cc4)_H<4) C<5)_H<5> C.
0.95<5) O-80(7) .0.84(6) 0_79(5) 1.02<5)
Angles
APgk
II
III
An&
II
III
N-Co-N= Co-N-Co= Co-N-G=. Co-N-G= Cw-C<1l-C(2)
99.0(3) 81.1<3) 139.4s) 139.6<5) 107.6<10)
99.3(2) 80.7(2) 139.5(3? 139.8(3) 167_6(6)
C
108.8(10) 108.8(10) 106.6(10) 108.1(10)
109.6<6) 107.1(6) 108.0(73 107.8(6)
=DisorderedN.Cin
III.
--
TABLE4 LEASTSQUARESPLANESTHROUGHSELECTEDATOMS=. DEVIATIONS THESEPLANES.ANGLES(O)BETWEENTHENORMALSOFPAIRSOFTHESEPLANES:Equatiolu givecarbonylnitrosyltbendinitrosyl) l-Plane defined byCo.
2 i~8Zi.64~foiCO.NO;and
-0_00001 -Q.o0201 0.00381
ATOMS
FROM
-C.OOOOl -0.00153 0.00285
-0.00257 +MlO940 -0.00398~ 0.00&14. ..+_72317 : _ -1_72_408 89_Sl"or
._-..>-.
~- ~. I- ;_ ::.:
'.
327
Fii 1. The shape of both molecules showing the numbering System used in the crysttallographic study. This is a stereo pair drawn with 50% probability envclopcs for the thermal dlipsoidS of tbe heavy atoms.
of II and III Both compounds were prepared and purified according to Brunner (II) 143 and Herrmann (III) [6], respectively.
Preparation
Description of the molecules and discussion The distances and angles, as well as the planes, listed in Tables 3 &and4 show that the two molecules are essentially identical. They consist of a pair of cobalt
328
3177.61
ot
(bl
_ldLl reLInt_ t
Fig.
3. The
2
ESR
IcIdystron frequency
scanca_3177.61
3
spectrum was
L
5
of
a benzene
9.13469679
I
676765L321 solution GHz.
the
of
0.05 the
I
I
iV) of CP+OZ(CO)
the
Oe.
atoms held together by two bridging groups (CO or NO) so as to form a planar CO~(NO)~-~(CO)~ moiety. The four-membered ring is really diamond shaped, having angles at the Co atom (X-Co-Y; and Y = C or N) of approximately 99” while the Co-(X,Y)+o angles are only 81” in both cases. The Co-(X,Y) distances and Co-Co distances are, approximately, Z-11 and 2.37 A in both cases. The average Co-(Cp) distance and the Co-(ring centroid) for II and III are 2.09 and 2.10, and 1.723 and 1.724 A, respectively. Finally, the normal to the cyclopentadienyl ring makes angles of 89.64 and 89.91” with the normal to the plane of CO(NO)~C!O and Co(CO)(NO)Co respectively_ If the cyclopentadienyl ring is counted as a single ligand, the coordination around the cobalt atom is a distorted trigonal planar arrangement with one angle (X-Co-Y) of 99” _ Ekecisely the same kind of arrangement prevails in Cp,Fe2(NO)z [3] and Cp,Co,(CO); [S]. It is proper at this point to discuss the effect of the crystallographic disorder of CO and NO in Cp,C&(CO)(NO) (III) on the strucl+ral data presented here. From the fact that B ergman’s f8] anion, Cp,+(CO)z(Iv); &S the same molecular dimensions as our (ordered) CpzCo2(NO)~~(II jderiktive; one must conclude that th~e~cryst.alI~gr&$&disckder in no’ibay cahsei $Ablems in the. accurate deskiption ok the &n&&l parameters of III.‘.& fact, sz5& the 1 metal-metal dis@qc& tid$hk detai% of t@ knic_&ur& ox the b&ing CO .tid NO groups seem ti ~~.the~sau.ie~-_*th ne@gibk&fftie&es, :&c&i I&M+UI@& I _-~: _; -. _:__ .._..~_ _:: ._z.-.,‘I_ ‘__( ___..T.‘1.. l..-._ ._. _:-. .; ._--:_-_ ‘.‘-i:_. -- .;.: _’ .__. . _.. .-‘, ._:.i ._ __._-._ _____.. ._.: ~.- .: :_ ~I.-~. ..~ .._._ ._ .TT”. -‘Tr.._.: __.:..~_.~ . -c_
329
stand why compound III crystallizes so readily as disordered molecules_ From this point on, we neglect completely the disorder in III, since we can point, further, that thermally speaking the crystals of III are better behaved than those of II. The CJr,-co fmgment. So as to facilitate the discussion of the structural parameters of this fragment, we prepared Table 5 in which the various compounds entered are arranged in decreasing order of the Co-C(Cp) distance, the philosophy being that as this distance varies, we may see its effect on the other molecular parameters, or vice versa. The twelve compounds listed in Table 5 are easily divided into two classes; namely, those with sandwich arrangements of metal plus two hydrocarbons or metal plus hydrocarbon plus carborane. All these Co-(ring centroid) distances under 1.7 A. The second class contains one cyclopentadienyi ring plus two bridging ligands opposite the CsHS group. These have @-(ring centroid) distances longer than 1.7 A, except in the case of XIV. Within one given class, the average Co-C(Cp) distance varies even though the Co-(ring centroid) distance is the same. For instance, take VII and XI with Co-C(Cp) distances ranging from 2.051(6) to 2.081(5) while the Cp C-C distances range from 1.426(S) to l-402(9) (in VII) while in XI the Co-C(Cp) range from 2.042(3) to 2.057(4) and the Cp C-C distances from l-373(6) to l-408(6) A_ It is clear this is the result of ring vibrations, as demonstrated earlier [ 37-43]_ As a result, discussion concerning variations in the individual Co-C(Cp) distances and in the C-C(Cp) distances is unproductive since all of these quantities are unreliable to different degrees_ However, since the equations for the least squares planes are reliable in all cases [37-431, the variations in the Co-(ring centroid) distances are useful in gauging variations in bonding between the metal and the Cp rings. These vary according to the pattern described above, which is the same pattern one observes in going from ferrocenes to CpFeL -(contim-d TABLE
on &a_33’)
5
COMPAR~SONOFBONDINGPARAMETERS
FORVARIOUSSTRUCTURESCONTAININGTHE (~5CsHs)CoFRAGhlEh~(Thev~uesLiztedaremeanvaluesandthenumbersin wrenthesesarethe deviations
from the ____----
mean)
-.
---
Co--c
C-C
C-C-C
M-CP
(A)
(A)
(9
1_411<20> l-388(8) l-38%12> 1_415<14~ 1.417<10) l-413(8) 1.387(S) 1.407(2)
108.2~10~ 108.0(9~ 108.0<7) 108.0(9) 108_0~8) 108.0(3) 108.0(8) 108<1)
l-i24 Li23 1.714 1.682 1.682 1.674 = =
=
RMCcrrIlrr
II
III V VI VII VIII IX X
(C$-W~Coz
2.101<12) 2_088(:2) 2.081(S) 2.07q91 2.066(11) 2.061(X1) 2_064(8) 2.049<13)
2.056<4)
1.400<6)
108.0<10)
1.676
19
XI
CSHsCotC4~C~Hs)2(Si~~rej)21
XII xnt XIV
2049(7J 2_038<15) 2.03600) 2029(18)
l-389(17) 1_405(14> 1.390(6) l-402(23)
108.0(S) 108(2) lOB.O
1.673 1.651 1.660 1.642
15 16 17 18
~C5~5~~~S2C2~CN~21
Thisstudy Thisstudy 10 11 12 13 14
,,,‘,,
‘.
/,
.
;‘Xx,‘,,:‘~1~O);Coe2~CO)1Co(CO)(Nbd)
25
co
__
co
Fc
Fc
Fc
Fe
22
__ .--__-
c
C
c
C
C
Ni
Fe
Co
21
C
Nf
co
Co
20
.,‘;,,,; ; .I,:’ <, , ,, ‘, , ‘: :.: : 23 ,.XVHl: i(r140Nbd)(OC)(Co.cI~~CO)2~ ;‘.:,.'. '>:.' *; :Fa(COt(r$GsH~)] 24 ,; Xl? :: ‘~~I.[(~~~~HJ)F~(CO)~J~ ‘,I.j,,,1 /./ i ‘, 2, I, ;, ) I, ::J, _; ‘,‘.I
,‘Xk’: [(~5~5~~)NlCo(CC),(PEcJ)1 t, ::,‘,, T’,’ : ,a ‘: ‘,,Xy’;’ I(rls.CP~jNICo(C0,4(PR3!1 :...I ’ R’=jbFC,$ir) +ll [Cd(~*~~l2~Mc)l(C0)132 ,,’ : ~’ ,,‘,,.I 0 ,.
-
..
2,531(l)
2,831(2)
1
1
2+530(l)
2,1)10(l)
1
1
2.426(2)
2,418(2)
1
1
.- -
1,657(4) 1.675(4) 1,663(5) 1,580(r))
1,629(10) l,Q28(lO) 1,004(11) 2+026(12) 1,682w 1,816(B) 1,626(3) X,028(3) 1,606(4) 1,618(4) 1,006(T) 1.625(7)
_
_
_
06,0(3) OOtO(3)
Ob,1(2)
D&6(3) 06,4(3)
81i,B(6)
87,3(4)
1,113(a) 91.1(2) 1,164(5) 84,5(l)
1,163(6) 1‘17tm) 1.178(O) i.i8a(fu
1.160(12) 1,167(11) 1,176(12) 1,145(14) 1,170(9) 1,177w
- .~
61,0(2) 62,0(2)
83,2(2) 32.7(2) 62.qa) 02,4(3)
79,7(4) 70,3(4) 79,4(/r) 77,9(b) ei,z(a) 6l,b(3)
__
(X,Y)E-0
-
130,3(0) 143,5(8) 14a,4(lo) 138,0(11) 138,8(7) 130,9(7) 138,0(7) 13%6(6) x36,6(4) 136&(4) 137,Ei6) ’ 130*4(6) 189,2(6) 138,4(6) 142,0(4) 141,3(4) 136,1(4) 136X4)
.‘:Mih,l!&ii,~R PARAMETERS REPORTED FOR SPECIES OF THE TYPE X.~~'OY.E~O~Y WITH X AND Y m METALS AND IS’ AND E2 EITHER C OR N ,i (D~ihkIh A and ander In degrees. Only Co or Fc data Wed hero) *I b _.__“,_~-r”___.“_~.-“_.~__~._‘~---~--~.-..-----_ p--E'-fX,Y).X_(E'J). Rclar- x Y El I32 Band X-Y (X,Y)-13 E-O ~.,;cwIlpbund ",,,i, '9" -Y -22 cnce order c i ).’ 1, 3 ...--,“l.----_“.--l~__“,_._I *_p._,” _-._-_-.-. I
‘iT&E’@,
,,
;
,(t15*C5ti5)2C02(No)2
” ;;15~5,~~)$02~~o)l_-
‘,
Co
Fe Co
Fc Co
3 thlc ctudy co
co
co
30
Co
co
co
29
co
Co
Fc
28
8 thb
Fe
Fo
27
C
1
2,54G
c
c
C
N
c
N C
N
c
N N
Clorrc
c
c
C
1,5 1,O
2 1-G
1
1
1
2,372(2) 2,372(l)
2,32fJO) 2,370(l)
2,aoB(a)
2,640(l)
2$46(l)
Clot8 IJ, Plonnrderlunflucr C C 1 2,834(2)
C
1.82(2) 1,826(7)
1.708(O) 1,82B(7)
l.Bll(lO)
l.BlO(G) 1,918(a) 1,806(7) l,B33(0) l,B31(4)
2,036(7) 1,882(7)
1,21(4) l.l8Lt(lO)
1,264(12) 1.200(10)
1,102(17)
1,160(8) 1,166(8) 1,165(b)
l*la8(0)
1,147(E)
e&a(a) O&O(3)
07.7(4) BO,3(2)
Bb,B(O)
07,1(4)
Ob,7(3)
07,1(4)
87,6(3) f&8(3)
61,2(6) fllJ(3)
82,3(4) fJQ,7(2)
84,1(5)
82,5(3) 82,8(3) 82,0(2)
82,0(2)
80,0(3)
130,6(a)
138.8(8) 130,4(3)
13&E(4) 138,4(4) 13O,b(6) 138,0(5) 130,6(3) 137,0(3) 13&O(3)
134,6(O) 144,6(O)
‘1
..“.
,’
‘, ‘:anly tha date for tho CpCo bcarlng frcgmcnt II glvcn. In XX data for (Nbd)Co and (OC)$o nrc given for cmphaslr: ccc footnote e snd tho Dlscueslon, ’ Calculated .‘accordltig !o the EAN Nle. cl Whenever rclcvant, lha (Nbd)Co data am rlvcn first, followctl by thnt for the (OC)$o portlon, ’ P.ntrica on the upper holf o! each column belopg tb,the Co rtom of lhe (Nbd)Co fragment. .,
.____..__._._______,_______.,___._.____ .._. __.___.__... _..,..___.. . ... ,___..“_.._.. ..._.“_”._......-+..I..-M-M ..-- I----‘:’ a Whenever e mlxcd Fe, Co compound occurs, only the Co InformalIon IaIlstcd, Nbd - norbornadleno. b When a Cp-mctnl fragment occult wlth II metal boar@ no CP rlnu,
“,
‘I Iv .I:, 1’
,,’
Co
Fc
20
332
derivatives [44] (L = a suitable set of ligands such as (CO)*I, (CO)(PPhs)Cl, etc.). It is interesting to note, however, that there is no variation in the Co-(ring centroid) distance between II and III since the former has one electron more, and, consequently, a single Co-Co bond whereas the latter has, according to the EAN rule, a 1.5 order bond between the two metals. The Co[p,-(CO)JCo fragment. A comment on the EALV rule. Briefly stated, the EAN rule says that a transition metal atom will combine with a set of donor ligands such that the total number of electrons (metal plus electrons donated by ligands) add to that of the nearest rare gas configuration. Thus, the metal has a total number of electrons equivalent to the number contained in the stable, rare gas, configuration. This rule is undoubtedly very useful, and it is generally obeyed_ As such, it correctly predicts that certain *&gments, such as CpFe(CO),, will be unstable unless they are (a) reduced to CpFe(CO);, (b) treated with a one-electron donor such as Cl-, etc. to form CpFe(CO)zCl, etc., (c) allowed to dime&e to Cp,Fe,(CO),, in which case there is a two-electron(single) metalmetal bond. The argument is exactly that used to expiain why the halide elements are diatomic. We have prepared Table 6 which shows that, for the general classes of compounds labelled class A and class B, this rule is not only obeyed but that the length of the metal-metal bonds remains very close despite the marked changes involved. Note that this observation is valid for both the cis and Pans isomers, where relevant, and that changing from one isomer to the other changes the picture very little. The variations in metal-metal bond lengths can be explained, easily, by the variations in metal covalent radii (i.e., Fe vs. Co vs. Ni) and by the changes in ligands, which are quite drastic in some cases. Overall, the length of metal-metal bonds in class A compounds ranges from 2.418(2) to 2_559(3) A, which amounts to a 6% change_ It is equally true that the variations in the metal to bridging carbonyl (M-C) distance, the C-O distance and the angles of the entire fragments change very little, as well. Thus, the M[l.r-(C0)2]M fragment seems to be largely invariant and it would appear that this rule can safely predict approximate values for the length of metal-metal bonds. As long as we are dealing with a single metal-metal bond (class A compounds) the expectation is that the bond length of M-M’ should be about 2.5 A, irrespective of the nature of M and/or M’ (M, M’ = Fe, Co or Ni) (Table 6). Recently, Calderon et al. [3] studied the structure of Cp,Fe,(NO)z (I) and found, according to the EAN rule prediction, that there is a short Fe-Fe distance of 2.326(4) A, which was readily explained on the basis that a compound with that composition should have a four electron (double bond) between the two iron atoms. Comparison of their result with those of Bergman et al. [8] for CP~CO~(CO)~- (IV has a 1.5 bond order between Co atoms, according to the EAN.rule), our study of CpsCol(CO)(NO) (III) which is isoelectronic with IV and, most importantly, with Cp,Co,(NO), (II), which shouId have a single Co-Co bond, show that the metal to metal bonds are of nearly the same length in all four cases. It is important to stress, that not only are I, II, III, and IV molecularly identical (see Table 6, class C for details of the molecular parameters) but, more important, I, II and IIIare isomorphous and is’ostructural. Therefore, all crystallographic effects are identical for these three species. Further, according to Pauling [44], the difference in radii between Fe and Co ’ is 0.01 A - This difference,. if used, .would predict a larger Co-@ distance for the I~ .:. _.~.. -. ., -- .:-. (__ . __, .~ .; .v-. -, ,.-._ : _: _. .:. -..~’ ,. :-:: ._ --
333 same bond order- However, the point is that the EAN rule predicts a single bond for II and a double bond for I. We must conclude at this point that the EAN rule is unreliable as a criterion for predicting finer details such as bond orders end bond lengths. The bonding details (Table 6) for I, II, III and IV demonst.rate this point amply. Early in our search of the literature, we were struck by the homogeneity of the values for metal-metal bonds for compounds in class A and class B and attributed the change in metal-metal bond between the isoelectronic species III and IV and those compounds of class A and B to a change in bond order. In fact, our carbonylnitrosyl (III) and Bergman’s anion (IV) are predicted -to have a 1.5 Co-Co bond order. However, we then determined the structure of the dinitrosyl (II) and found the result of Calderon et al. [3], and realized that this was not a valid explanation for these results. Finally, we must comment that the differences in metal-metal bond lengths observed for classes-A and B, on the one hand, and those on class C cannot be simply explained on a change in structure because (a) there are equally drastic structural changes within the compounds of classes A and B, (b) the compounds in class C have the identical same structure and bonding parameters and for them the EAN rule would predict a smooth increase in metal-metal bond length from I to (III and IV) to II. In conclusion, when we go from Cp&0z(N0)~ to either Cp&o,(CO)(NO) or its isoelectronic anions C~,CO,(CO)~- and, finally, to Cp,Fe,(NO), the successive increase in bond order predicted by the EAN rule is not observed. The implication is that the electrons associated with these changes must come from orbitals which are non-bonding in character, as far as the dinuclear metal framework is concerned. Our research is directed currently to probe further into this interesting question_
The ESR spectrum of Cp,Co,(NOI(CO) Given the composition of this substance, one expects it to be pararnagnetic (S = l/2). In fact, this had been recently demonstrated by Miiller and Schmitt [5] who measured its magnetic moment (lS6 BM) compound III is isoelectronic with the anion IV as shown by ESR spectroscopy [S]. As a fine tool for probing electron distribution and because it seemed desirable to compare III and IV, we recorded the ESR spectrum of III. The results are shown in Fig. 3 where it is clear that there are 15 lines having relative intensity ratios of approximately 1/2/3/---7/8/7---3/2/l_ This is, of course, a classic pattern already found in [(HaN)&oOOCo(NH3),] 5* [31,32] and in IV [8], and is associated with an unpaired electron equally delocalized over two 59Co nuclei (I = 7/2; abundance ca. 100%). It is also clear that there is no evidence of further splitting by the N nucleus of the nitrosyl bridge. One must, however, note that while the splitting due to the Co nuclei is 47.4 Oe, the linewidth is ca. 29 Oe. In order to place these numbers in perspective, we have prepared Table 7 in which a number of ESR spectral parameters of relevant molecules are listed. From these data, the parameters ofthe ESR spectra of III and IV are .the same, to the-accuracy quoted. Tbis is not very surprising since the structural parameters in III and IV are essentially identical In particular, note that the CO-CO, cO-_N or Co-C distances are identical within stated accuracy- Therefore, one expects the unpaired electron to be distributed, approximately, equally-in_t.he twq-sub&ances. This-isan interesting observation-which agreeswell :
334 TABLE
x
7
COMPARISON OF ESR PARAMETERS
WITH SOME
Comsmimd
in
RELEVANT
g-factor
Reference
140
2.0539
This reference 8 33 34 35 31.32
47.4 Ea.50
f.cj-RCCojKO)g
ca35 12.7
xxx
CF3(NO)Co(DMG)
a Estimated
vahe
from linewidths.
THE LITERATURE _
O(N)
’
FROM
MC01
IV xxv XXVI XXVII XXVIII XXIX
CF~(NO)CO(CN)S
VALUES
2.091
-
11.75 12 -
Not given 2.0149 2.006 2.037
10.25
13.92
2.0066
36
10.1
13.6
2.0065
36
--___ See
texL.
b DMG
= dimethylglyoximato.
with the commonly accepted idea that in organometallics the change from one group (effectively CO- for NO) having the same number of electrons to contribute to the bonding, results in the same total electronic distribution around the core atom_ We note, next, that the spectroscopic splitting factor for III is g = 2.0539, which is higher than 2-0023 (the free electron value) by a significant amount. This is expected for a transition element compound of the 3d series due to the spin-orbit contribution; it is also in accord with the measured value of the magnetic moment for III given by Miiller and Schmitt [5] which is larger than the value of 1.73 BM expected for a free electron. The fact that the g factor for III exceeds the free radical value implies a negative value for the spin-orbit coupling constant, which is to be expected of any cobalt compound whose effective charge is less than 5+ and which is certainly the case for III and IV, no matter how electrons are counted. Concerning the magnitude of the 14N hyperfme constant, the results quoted in Table 7 show that for a relevant number of compounds having the fragment: ? R-N-(3d-transition
metal)
it does not exceed 12-14 Oe [ 34-361. These substances have g values that are consistent with their formulation as “free radical-like” and contain an unpaired electron which can be labelled as “ligand based”. The SpCo hyperfine splitting constant for these substances is approximately l/4 those observed for III and IV_ Also, note that they are approximately the same as those observed in p-peroxodecaaminodicobalt [31,32] for which Weil and Kinnaird [ 323 estimate that the unpaired electron spends 90% of the time on the 0, bridge_ Thus, it is quite likely that the 14N splitting is lost in the.29 Oe linewidth, whose large value may be due to stereochemical non-rigidity and/or solvent perturbations in the open ; Co-(bridge)-Co fragment. A careful stud* of the line shapes as a.function &f temperature may still reveal the magnitude of the‘ 14N intera&&; &til sukh’ : time, nothing defiit&can b& saic+bo~t.the path of the tip&re&&ctr&ti~ %. moving between the two-cobalt atoms over:which-ii is de&al&d~~~‘t~~&~~ -i ' -.-. moment
12-14
we
only
&;ofithe
bm
of_~&i&&j~&@,
&
Upljeriimit_oi:.'_:'---:.~~‘
:
Oe to the %I hyperfine s&ting: Coti&e+ig.&e -5_pC;, a.&~~_(X2/ jZ:Zi._..i(: ;. :, .._ ._ ... : .a._.. _ .- “:_A:.._ ._ I _,.. -. I ._..-:,~r_, .-;: ..-: -.._ 1 ,_: :.:: :: .. ._ .--, f_ __
335 TABLE
8
SPECTRAL.
ANALYTICAL.
AND
POLAROGRAPkIlC
DATA
spectrum
Mass
IR
1545 cm-’
WNO)):
1819 em-’
(v
Anolyticol doto: Found: C. 43.25: H. 3.59; N. 4.50; Co. 37.09: moL weight. 345 (osmometricaIIy in benzene). CI IHIoColN02 caled.: C. 43.17; H. 3.29: N. 4.58; Co. 38.51%: moL weight 306.07. The compound has no melting point up to 250-C. but decomposition starts out slowly at ca_ 30°C and is complete at ca. 160°C
reported by Katz et al. 1331, we see that both the g factors and the hyperfine splittings, consistently, point to these species as having a more “metal based” unpaired electron than the other enfries of Table 7_ Using Weil and Kinnaird’s [32] estimate of ca. 10% for the distribution of the unpaired electron over the two “Co nuclei of [(H,N)&o-02-Co(NH,).$+ and assuming a roughly linear change, the unpaired electron spends about 40% of the time on the metals of III. Finally, we want to call the reader’s attention to the fact that in the anions of Kotx et al. 1331 there are three cobalt atoms and that the 5gCo splitting is ca. 2/3 the value found in either III or IV. Since the sum of the individual spin densities at all atoms of a species with spii l/2 must addd to unity, the obvious conclusion is that for HI, IV, and XXV, the fraction of the time the unpair electron spends on the metal framework and on the bridging framework are about the same. Electrochemistry of II and III The electrochemical processes described by the data of Table 8 indica+tethat the dinitrosyl derivative II can easily be oxidized to its cation, Cp2Cp2(NO)z’, which would be isoelectronic with the known, stable, species III and IV. Consequently, it is not surprising to find that this is a reversible process. The same comment8 can be made about the reduction of III to Cp,Co,(CO)(NO)-. Oxidation of III to its cation and reduction of II to it8 anion are both irreversible processes and would correspond to the formation of CplCo,(CO)(NO)+ and Cp2Col(NO)z-, respectively_ The former, III’, would be isoelectronic with Cp2Col(CO)s which has been isolated recently [l]. The anion, IT, probably undergoes a bridge splitting reduction similar with those known to OCCUTin specie8 of the type Cp2Fe2(CO), and Cp2Mo.2(CO)6, etc. Our observations for II and III parallel the recent experiences described by Bergman and associates with C&C&(CO)~[7,8]. Acknowledgeme.nts
‘.
.
I, Es&& JDy’ K&p, Itid G_M_ X+sner thank the Welch Foundation and the :I@ Nat&&&en& F&$I_$ttion for support and funds for the purchase of :_:t_ _..-.;-~i ..::.. -:....z. <7-:;..r_ =,.:_ ,-_..;t_?.Y_‘_ ,_.__ _. -. :. ;:--_ ‘.I.:_‘. ._.:‘._._ .._ ,.:.. I-- L I _ _’ __. ‘_.. .--_.;z;--.-:-_ ‘.- _:. ._. _,. __.. :
336
the diffractometer_ We also thank the Computer Center of the University of Houston for a generous supply of free ctimpiiting time. W_A_ Herrman n thanks Prof. H. Bnmner as well as the Deutsche Forschungsgemeinschaft for generous support of this study_ Finally, we thank Dr. B. Kaly anaraman (Univzsity of Alabama) for running a calibrated ESR spectrum and Dr_ A_ Merz (llniversitit Regensburg) for performing the electrochemical measurements_
Chem.. 127 (1977) 87. 1 W.S_ Lee and H_ ~rintziiger. J. OaanometaL 2 H. Brunner. J_ OrgamxnetaL Cbem.. 14 (1968) I73_ 3 J-L_ CaIdemn. S_ Fontana. E_ Frauendorfer. V-W_ Day and DA. Iske. J_ OrganomeLal Chem.. 64 (1974) Cl6. 4 H_ Bmnner. J_ OrgarmmetaL Chem, 14 (1968) 517. 5 J. Mtlllcr and S. Schmitt, J. OrganometaL Chem.. 97 (1975) C54. 6 W.A. Herrman n and 1. Bernal, Angela. Chem.. 89 (1977) 186; Angew. Chem. Internat. Edit. En& 16 (1977) in press. 7 CS_ ILznda. N-E. Shore. and R-G. Beaman. J. Amer. Chem_ Sot.. 98 (1976) 255. 8 N.B_ Shore. CS. Ilenda.and R_G_ Bergman. J_ Amer. Chem. Sot_. 98 0976) 256. 9 JM. Steward. G. Kruger. H.L. Amon. C. Dickinson and S.R. Hall (Ed%;. The Xjay System of ckystalIographic Programs. Technical Report No. 192. Computer Center. University of Man-land 1972. 10 G_ Evrrrd. R. Thomas. B.R. Davis and I. Bernal. J. Organometal. Chem.. 124 (1977) 59. 11 KS. Calkhan. C.E. Stmuse. A.L. Sims and M-F. Hawthorne. Inorg. Chem.. 13 (1974) 1393. 12 E.L. Hoel. C.E. Stmuse and M.F. Hawthorne. Inorg. Chem, 13 (1974) 1388. 13 G. Evrard. JS. Ricd. Jr, I. Bern& W_J. Eva. D.F. Dustin and M.F. Hawthorne. Chem. Commun.. (1974) 234. F_Y_ Lo. CR_ Strouse, A-L. Sii and hi_E. Hawthome. Inorg_ Chem, 13 (1974) 2842. 14 K-P_ &U&an_ 15 M-D_ E+sch. I. Bernal. B.R. Davfs. A_ Siegel. F.A. Highie and G.F. Westover. J. Coord. Chem.. 3 (1973) 149_ 16 hf_R_ Churcbilland B_G_ De Boer. Inorg_ Chem.. 13 0974) 1411. Chem.. 113
B&id. Ithaca. %Y..
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Cornell U&ersity
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