Transition-metal silyl complexes

151

Journal of OrganometaIZicChemistry, 365 (1989) 151-161 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands

JOM 09602

Transition-metal silyl complexes XXVIII *. Preparation and stereochemistry of phosphitesubstituted hydride silyl complexes of iron and derived anionic complexes * * Michael Knom and Ukich Schubert * Institut fti Anorganische Chemie der UniversitLit Wiirzburg, Am Hubland O-8700 Wiirzburg (E R.G.) (Received July 26th, 1988)

Abstract Fe(CO),[P(OR’),](H)SiR, (R’ = Et,Ph) (1) and Fe(CO),[P(OEt),],(H)SiR, (2) are obtained by photochemical reaction of Fe(CO),[P(OR’),] or Fe(CO),[P(OEt),], with a number of different silanes. To avoid side reactions, triphenylphosphite derivatives Fe&O), [P(OPh), J2(H)SiR, (5) are better prepared by thermal reaction of the known o&o-metallated complex Fe(CO),[P(OPh),], with silanes. Monophosphite substituted complexes 1 have a mer arrangement of the CO ligands and a tram disposition of the SiR, and P(OR’), ligands. In the bis-phosphite derivatives 2 and 5 the CO ligands are mutually trans and the phosphite ligands cis. For Fe(CO),[P(OPh),],(H)SiMeCl, (5a) a second isomer, with cis-CO ligands and truns-P(OPh), ligands, is observed at low temperature. The hydrido silyl complexes 1, 2 and 5 are fluxional at room temperature. Deprotonation of 2 or 5 with KH gives anionic silyl complexes K[Fe(CO),(P(OPh),},SiR,] (7). The reactivity of 7 is exemplified by reactions of the Si(OEt), derivative 7b with Me&Cl, Me,SnCl, or Ph,PAuCl (L,MCl), which gives the corresponding substitution products Fe(C0)2[P(OR’),],[Si(OEt)3]ML, (9). The latter compounds have the same geometry as 2 and 5. While the Ph,PAu derivative 9c is fluxional at room temperature, the stannyl derivatives 9a,!Jb adopt static structures.

Introduction We have recently shown .that silyl-, germyl- or stannyl-substituted anionic metal complexes [MeCp(CO),MnER,](E = Si, Ge, Sn) or [Fe(CO),(PR’,)SiR,]-, which * Part XXVII see ref. 1. * * In memoriam Jerry Zuckermann. 0022-328X/89/$03.50

0 1989 Elsevier Sequoia S.A.

152

are obtaind by deprotonation of the corresponding hydrido silyl complexes, are interesting precursors for polynuclear complexes [l-3] or complexes containing metal-carbon double bonds [4]. Since the reactivity of the anionic complexes is of course influenced by the electronic and steric properties of the other ligands at the metal, we are interested in obtaining derivatives having different ligand environments. In the iron series, we have already reported on PR,- and dppe-substituted complexes (dppe= Ph,PCH,CH,PPh,), the preferred geometries of which are given in Scheme 1 [5,6]. 0

: OC

1

R3Si’

7

OC

PR,’

‘Fe’

n~,F,co

P,

p

,cO

lFelP

1 ‘H

R3Si

C 0

’

HA

) ‘H C 0

FelSiR I

PyFje1SiR3

3

H

s

(C)

(8)

(A) I

Scheme 1. (P

I

P = dppe)

This paper deals with the preparation, dynamic behaviour, structural features and reactivity of phosphite-substituted derivatives. Monosubstituted

complexes

For the preparation of the phosphine:substituted complexes A UV-irradiation of Fe(CO),PR’3 with HSiR3 in hydrocarbon or aromatic solvents is the method of choice [5]. The phosphite-substituted complexes 1 can be correspondingly obtained without difficulties (eq. 1). Despite the somewhat different electronic and steric properties of P(OR’), and PR> ligands, complexes 1 adopt the same geometry as their PR\-substituted counterparts A. The IR spectra are consistent with a mer arrangement of the three

: FeICOIL[P~OR’)3

]

OC \

hv

+

HSiR3

co

1 ,P(OR’)3

+

(1) R 3 Si/;e\H r

L

0 (1)

t

R’

SiR3

a

Ph

SiMePh2

b

Ph

Si (OEt

C

Et

Si Ph3

13

2062(w),1995(s,sh),1990(vs) 2063(w),2OW(s,sh),l998(vs) 2056(w),2OOO(s,sh),l984(vs) 2009(w),1971(s) ’ - ‘,1952(s) (I - P,1953(s) h 1996 0 2036(m),1985(vs) h 2016(w),1977(vs) ’ 2009(w),197qvs) b 2004(w),1963(vs) h 2004(w),1959(vs) = 2OOO(w),1955(vs)n 192qm),1865(s,sh),1846(vs) 1914@),1852(vs),1829(s) ’ 1902@),1845(s),1812(vs) D 1903(s),1842(vs),1815(s) ’ 1897(m),1841(s),1814(vs) ’ 1884(m),182qvs),1795(m) ’ 1943 = 1960” 1952(w),19Oqvs) b

’

Q a a

and 9 ( + 25 ’ C)

19.6(t)

-86.1(t)

26.8

a(Si) (ppm)

155.2(J(AB) 55.1 Hz) 0 152.4(J(AB) 56.6 Hz) ’ see text o

168.0 m 169.4 m

168.8 m

169.9 b 169.6 * 168.2 * 164.1 b 170.4 o 173.4 * 179.5 i*0 157.1 j 162.9 b 158.6 j 160.6 j 162.8 * 163.5 b

s(P) (ppm)

7.4

81.4

27.0

J( PFeSi) (Hz) -9.4(d) -9.7(d) -9.2(d) -10.1(t) -10.0(t) -10.5(t) -12.3(t) -9.9(t) - 10.2(t) -9.9(t) -10.2(t) -10.5(t) - 10.6(t)

&FeW

(ppm)

37 34 36 30.0 25.1 26.9 18.1 19.4 n.k 17.0 14.0 15.0 13.5 16.5

J( PFeH) (Hz) *

o Petroleum ether. * Benzene. ’ Cyclohexane. d Only spectroscopically identified. e Second band hidden by lc. g Second band hidden by 3. h Et,O. i Off-resonance: quartet. j Acetone-d,. k trans-5h: - 9.2 ppm, 62.0 Hz. ’ THF. m THF/benzene-d,. ’ 104’ C in toluene-d,. ’ Benzene-d,. P 13C NMR (C,D,) 8 210.3(t, CO, J(PFeC), 17.1 Hz), 58.3(s, OCH,), 18.5(s, CH,).

51 d 7a 7b 7c 7d 7e 7f !h 9b !k

5e

5d

scp

5b

cis-5a

2bd 2cd 3d

2a

lC

la lb

v(C0) (cm-‘)

IR and NMR data of l-3,5,7

Table 1

154

carbonyl ligands and the magnitude of the 2J(PFeH) c&disposition of H and P(OR’), (Table 1).

coupling constants indicates a

Disubstituted complexes While a variety of complexes of the type A, B, C or 1 was prepared by the photochemical route, this method proved to be less efficient for bis-phosphite complexes. On irradiation of Fe(CO),[P(OEt),], with HSiMeCl,, HSi(OEt), or HSiPh,, only the SiMeCl,-substituted complex 2a was obtained without complications (eq. 2). : Fe(C0)3[P(OEt

J312

+

HSiMeC12

-

(EtOj3P

hv

co

+

1

H

1

LSiMeClz

‘Fe’ Va0)3P

’

(2)

C 0

(Pa)

Reaction with HSiPh, is extremely slow and gives both the mono-phosphite (lc) and the bis-phosphite complex (2b) due to competitive phosphite or CO dissociation (es. 3). CO + Fe(CO)z[ P(OEt)3],(H)SiPh, (2b) Fe(CO),[P(OEt),]

2 + HSiPh3

hv

(3)

-I

P(OEt),

+ lc

Photochemical reaction of Fe(CO),[P(OEt),], with HSi(OEt), is complicated by the formation of Fe(CO)[P(OEt),]2(H)3Si(OEt), (3) from 2c (eq. 4). We were not able to prevent this subsequent reaction or to separate 2e from 3. Fe(CO),[P(OEt),],

+ HSi(OEt),

$$

Fe(C0)2[P(OEt),]2(H)Si(OEt),

(4)

@) hv

I

Fe@)

+ HSi(OEt)3

b’(OJ%]

,(I-%Si(OEth

The spectra of 3 (Table 1) clearly show that this complex is related to the trihydride complexes Fe(CO)(dppe)(H),SiR,, which we described recently [7]. Because photochemical preparation of the complexes 2 was less straightforward than anticipated, we looked for another route to prepare bis-phosphite complexes of this type. Grant and Manning showed that the 16-electron species Fe(CO),[P(OPh),], (4a), which generated by of Fe(CO),[P(OPh),],, stabiorthometallated form (4b) is in lized intramolecular orthometallation. equilibrium with 4a and can therefore be used for oxidative addition reactions [8].

155

”

(Ph012P OC ,I’@

+HSiR3

_ _

Fe oC’I

----Id

Fe(C012

[P(OPh)j]2

(pho)3p\ i

FeAH

(5)

[ ‘SiR3

P/

(PtlO)a (4a)

C 0

P(OPhl3 (5)

(4b)

SiR3

cis-a b

Si

MeCl

z

SKOEtl,

c

si Phj

6

Si MePh2

C

SiMezPh

f

SiMe3

Since the 16-electron species 4a is thermally generated from the orthometallated complex 4b, complications arising from photochemical side-reactions can be avoided. By thermal reaction of 4b with HSiR, a number of new hydrido silyl complexes were prepared (eq. 5). The time required for completion of ‘the reaction at room temperature strongly depends on the silane: it increases from 3-4 h for HSiMeCl, to about 20 h for HSiPh, and HSiMePh,. There are two limitations for this reaction: (i) with HSiCl, not the corresponding hydridosilyl complex but the chloro complex Fe(CO),[P(OPh),] ,(H)Cl (6) is obtained. 6 has previously been prepared by oxidative addition of HCl to 4 [8]. Since we can exclude that the HSiCl, we used contained HCl, the silane acts as a chlorinating agent in this reaction. Complex 6 is also formed as a byproduct (20%) in the reaction of 4a with HSiMeCl,. We and others have observed similar reactions before (see e.g. ref. 6,9,10). In 6, the two P(OPh), ligands are trans and the two CO ligands cis to each other. Melting point and spectroscopic data of 6, obtained by reaction of 4 with HSiCl,, agree with the values reported in ref. 8 except for G(FeW), which we observe at - 5.9 ppm (instead of - 9.9 ppm). (ii) Complexes Se and, partially, 5f with electron-donating silyl ligands are prone to a subsequent reaction, in which (particularly in the presence of excess HSiR,) the silyl group is replaced by a second hydride ligand and the known dihydride complex WC%PW%lA PI is formed. This reaction is discussed in more detail in another paper of this series [ll]. There are six possible isomers for octahedral complexes of the type Fe(CO),L,XY. For 2 and 5 the four isomers having c&CO ligands can be excluded on grounds of the v(C0) bands in the infrared spectra. A very weak absorption between 2CKKI and 2036 cm-’ and a very strong one between 1955 and 1985 cm-’ indicate that the two CO ligands are in a distorted tram arrangement. Rather strong deviations from an ideal octahedral geometry are not uncommon for transition-metal silyl complexes [6]. Two bands of about equal intensity would be expected for octahedral ci.s-dicarbonyl complexes. Among the two isomers having tram CO ligands, D appears more likely than E because a hydride ligand usually avoids being trun.s to a silyl ligand. A distinction

156

(R’013

R3Si

CR’013

CD)

’

I C 0

‘P(OPW

3

(E)

between both isomers is possible by NMR spectroscopy, because the two phosphorus nuclei are equivalent in E, but not in D. The room temperature NMR spectra of 2 and 5 show triplets for both the hydride ligand and the silicon nucleus, and a singlet (off-resonance: doublet) for the phosphorus nuclei (Table 1). However, broadening of the phosphorus signal and the center line of the hydride triplet in 2a and 5b-5d indicates, that a dynamic process is responsible for the equivalence of the phosphorus atoms rather then a static structure E. This is confirmed by low temperature 31P{1H} and ‘H NMR spectra of these compounds. At -60 *C the phosphorus resonance splits into an AB-type signal (2a: J(AB) 88 Hz), and in the ‘H NMR spectra of Sc,Sd a virtual doublet (J - 50 Hz) is observed at - 40 o C for the hydride ligand. Coalescence temperatures are lower for 2b,zC and 5e,5f. The low-temperature spectra are consistent with structure D. Fluxional behaviour is very typical for octahdral hydridosilyl complexes of iron. In fact, all derivatives of type A, B, C, 2 or 5, which we prepared until the present time [5,6], are dynamic at room temperature. The SiMeCl, derivative 5a exhibits a strucural feature, which is unique among complexes of this type: At + 104” C the hydride signal of 5a appears as a sharp triplet at - 9.9 ppm (J(PFeH) 19.4 Hz) due to the dynamic process discussed above. On cooling, the lines get broader (particularly the low-field signal of the triplet) and coalesce to an unsymmetrical, structureless broad signal at room temperature. However, contrary to the other derivatives, a weak new triplet appears at lower field (- 9.3 ppm, J(PFeH) 62 Hz), which becomes stronger and sharper at - 50 o C. This phenomenon is reversible. The temperature dependence of the 31P{1H} NMR spectrum of 5a provides additional information: The sharp singulet observed at + 80 o C at 157.2 ppm gets broad at room temperature. At - 70 * C the four lines of the AB spectrum at 159.6 ppm (static structure D) are superimposed by a singlet at 157.8 ppm. Clearly, the additional signals in the low-temperature spectrum of 5a are due to a second isomer (“tram-5a”), which is in thermal equilibrium with cisda. The spectroscopic data of transda are consistent with the structure given in equ. 6. In particular, the high value of J(PFeH), which is similar to J(PFeH) in Fe(CO),[P(OPh),],HX (X = H, Cl; - 63 Hz), is indicative for a hydride cis to both phosphite ligands [12]. Thus, frans-5a has the same geometry as Fe(CO), [P(OPh), ] *Hz (SiMeCl, replaced by a second hydride) or Fe(CO),[P(OPh),] 2(H)C1 (6, SiMeCl 2 replaced by Cl).

157

0 P(OPh ( Ph013

P

)3

i \ ’

(Ph013P

(6)

FeHH

1 \SiMeCLz C 0

( frans-5a

(cis-5a)

)

The isomer with trans-P(OPh)3 ligands but trans-CO ligands, which would also be in agreement with the observed NMR data for trunsda, appears rather unlikely, because a truns arrangement of the hydride and the silyl ligand is less favourable in this type of complexes. At this point a comparison between the structures of Fe(CO),[P(OR’),] 2(H)SiR3 (2, 5) and Fe(CO),(dppe)(H)SiR, seems appropriate. While a geometry of that of trms-5a is not possible for dppe-substituted complexes, a structure corresponding to D would be. In fact, the latter geometry is adopted by bis-silyl complexes Fe(C0) 2(dppe)(SiR 3) 2 (a second SiR 3 being in place of H) [6]. For Fe(CO),(dppe)(H)SiR, only structure C is observed. The hydride ligand obviously avoids being tram to a phosphine ligand in Fe(CO),(dppe)(H)SiR,, while it tolerates a less electron-donating phosphite ligand in a trans position. By this, the sterically more favourable arrangement of ligands in isomer D (the smaller hydride being in the same plane as the bulky phosphite and silyl ligands) becomes possible. Anionic complexes The bis-phosphite substituted complexes 2 and 5 are easily deprotonated by KH in THF (eq. 7). Although the derived anionic silyl complexes 7 can be crystallized

OC 2,5

+

KH

-

H2

+

\

K

/ 0=

R’

SiR,

Ph

SiMeC12

Ph

S i (OEt

Ph

Si Ph3

Ph

Si MePh2

Ph

SiMezPh

Et

Si(OEt

j3

I3

158

from the solution at low temperatures, their isolation is not necessary if they are used for subsequent reactions. The presence of contact ion pairs is indicated by the number of Y(CO) absorptions in the IR spectra of THF solutions of 7 (Table 1). This behaviour is typical for metal carbonylates [13] and has also been observed for [Fe(CO),(PR>)SiR,][3]. On addition of an equimolar amount of l&crown-6 or [Ph3P-N-PPh,]+ to THF solutions of 7, only the two bands at higher wavenumbers remain, which therefore correspond to the undisturbed anionic metal complex. Their intensity ratio of about l/2 excludes a trigonal-bipyramidal structure with the CO ligands in an axial/axial or axial/equatorial arrangement and a square-pyramidal structure with cis-CO ligands. At room temperature, complexes 7 are fluxional and, therefore, one singulet is observed in the 31P{1H} NMR spectra (Table 1). However, the low-temperature 31P NMR spectrum of 7h (- 85 o C) shows an AX pattern (S 182.9 and 159.0 ppm, J(PFeP) 52 Hz) due to chemically non-equivalent phosphorus nuclei. A recent X-ray structure determination of isoelectronic Co(C0) z(PPh 3) 2 SiMePh 2 (8) shows that this complex, which is also fluxional at room temperature, is square pyramidal in the solid state [14]: PPh3 I

co .SiMePhz

Ph3P’ 0

C 0

OC

(8)

This geometry appears sterically more favourable than a trigonal bipyramid with two of the bulky ligands in axial positions. It is therefore not unreasonable to assume that the structures of the undisturbed anionic metal complexes 7 are similar to 8.

The reactivity of the bis-phosphite substituted anionic complexes 7 is similar to that of [Fe(CO),(PR>)SiR,][3], as exemplified by reactions of 7h with selected metal halides. On reaction with Me, SnCl z, Me, SnCl or Ph, PAuCl, the substitution products 9 are obtained within a few minutes (eq. 8).

: (PhO)IP

7b

+

L,MCI

+

KCI

\

I

+

AML, (8)

( PhO), P : (9)

159

9a,9b are rather unstable; particularly few hours to give 5b. The structures unequivocally deduced from their spectra proves a 1ran.s arrangement

in THF solution they decompose within a of the stannyl silyl complexes N9b are

spectra: A single v(C0) band in the infrared of the CO ligands. In the 31P NMR spectra an

AB pattern is observed at room temperature. The phosphite ligands are therefore inequivalent and must be cis towards each other. Although the stannyl silyl complexes are isostructural to the corresponding hydrido silyl complx 5b, they are no longer fluxional at room temperature. Contrary to that, the spectroscopic properties of 9c are very similar to those of 5b. A weak second Y(CO) band at hiher wave-numbers in the infrared spectrum suggests that the CO-Fe-CO axis is slightly bent, although the two CO ligands are still in a trans arrangement. Bending of carbonyl ligands towards the gold atom is observed in many dinuclear L,M-AuPPh, complexes with carbonyl-containing ML,, fragments [3]. Contrary to 9a,9b, but similar to 5b, the gold complex 9c is dynamic at room temperature. While the low-temperature 31P NMR spectrum is already obtained at + 5 o C (ABX pattern with 12 lines, &(AB) 172.2, 171.0, 170.7, 169.5, 163.0, 162.4, 161.6, 160.0 ppm, J(AB) 52 Hz; X-part centered around 39.0 ppm, J(AX) and J(BX) not determined), the AB part of the spectrum coalesces at 25 o C to two broad, unresolved signals. At + 95 o C there is one broad signal for the phosphite ligands and a triplet for the PPh, ligand.

Experimental All reactions were carried out under N, in dried and N,-saturated solvents. Photochemical reactions were performed in an irradiation vessel using a cooled high-pressure mercury lamp (180 Watt, TQ 150, Heraeus). 31P NMR measurements were carried out on a Bruker WM90 (36.44 MHz, a(P) rel. ext. H, PO,), 29Si NMR measurements on a Bruker WM90 (17.6 MHz) or Jeol FX90Q (17.76 MHz) spectrometer (6(Si) rel. int. TMS). Analytical data, melting points, and yields of all isolated products are given in Table 2. Preparation of mer-Fe(CO),[P(OR’)j](H)SiR3 (1). This preparation was carried out according to the procedure given for the corresponding PR’, derivatives [5]. Colorless solids. Preparation of Fe(CO),[P(OEt),],(H)SiMeCl, (2a). A solution of 0.75 g (2 mmol) Fe(CO),[P(OEt),], and 0.81 g (7 mmol) HSiMeCl, in 150 ml methylcyclohexane is irradiated at -5OC for 4 h. The progress of the reaction is monitored by IR. The solution is then filtered and concentrated in vacua. The oily residue is extracted with petroleum ether and the extract concentrated to 5 ml. At - 20 o C 2a precipitates as pale yellow crystals. Preparation of Fe(CO), fP(OPh),],(H)SiR, (5). A solution of 2-3 mmol in 150 ml toluene is irradiated at 0 o C for about 3 h according Fe(COLV’WW,l, to ref. 8. Particularly towards the end of the reaction (monitored by IR), N, is bubbled through the solution to expel CO. After the lamp has been switched off, a 3-5 fold excess of silane is added and the temperature is allowed to raise to room temperature. The solution is then stirred at room temperature until the v(C0) bands of 4b are no longer observed (3-20 h depending on the silane). Then the solvent is removed in vacua.

160 Table 2 Analytical data, melting points and yields for 1-3, 5 and 9 (Found (calcd.) (W)) C la

C, H ,FeO,PSi

63.24

4.51 (4.72) 4.91 (5.09)

63-66

50

(62.96) 52.10 (52.77)

72 (dec)

60

56.70 (57.20)

5.83 (5.52)

llO(dec)

80

31.70 (32.23)

5.96

41-43

40

(6.13) 102-103

65

C2,H,,Fe09PSi

(614.4)

IC

C,,H,,FeO,PSi

(566.5)

2a

C,,H,,Cl,FeO,P,SI

5b

!k

(559.2)

C,,H,,CI,FeO,P,Si

(847.5)

C,H,FeO,,P,Si

(896.7)

54.90

3.96

(55.27)

(4.04) 5.26

58.84 (58.94)

70

4.82 (4.76)

87-88

75

63.38 (63.60)

4.78 (4.87)

58-6O(dec)

45

53.16

4.68 (4.67)

(930.8)

65.48 (65.81)

FeOsP,Si (868.7)

5d

C,,H,FeOsP,Si

5e

C&H,,

9a

C,,Hs4FeOllPZSiSn

9b

C,H,,ClFeO,,P,SiSn

9C

C,,H,AuFeO,,P,Si

(1059.5) (1080.0) (1355.0)

70

110-112

67.96

(992.8)

68-7O(dec)

(5.17)

(67.74)

C,,H,FeO,P,Si

Yield (W)

(648.5)

lb

!h

m.p. (O C)

H

5.01 (5.13)

65-69(dec)

50

(53.28) 51.38 (51.16)

5.10 (4.76)

89-9O(dec)

70

56.11 (54.96)

4.65

97-99(dec)

50

(4.46)

5b, Se, 5f. The red, oily residue is extracted with warm petroleum ether (30-50 o C). On concentrating the solutions in vacua, colourless 5b and 5e precipitate. 51 was not isolated. Se is separated from Fe(CO),[P(OPh),],H, by repeated recrystallization. 5a, SC, 5d (less soluble derivatives). The oily residue is washed with a small amount of petroleum ether and then extracted with warm Et ,O. On concentrating the Et,0 solutions, colourless 5a, SC and 5d precipitate. They are recrystallized from Et ,O.

Preparation of Fe(CO), [P(OPh),] 2[Si(OEt),]SnR 3 (9q 96). To a suspension of lo-20 mm01 KH in 15-20 ml THF 1.0-l-5 mm01 7h is added. The mixture is stirred for about 1 h at room temperature until H, evolution ceases. Excess KH is then filtered off. The filtered solution is poured to a slight excess of Me,SnCl or MqSnCl,. After 10 min at O” C the solvent is removed in vacua and the solid is extracted with petroleum ether (9a) or Et,0 (9b). On concentrating the solutions, 9a and 9b precipitate as colorless solids. Preparation of Fe(CO), [P(OPh)J z [Si(OEt),]AuPPh, (94. 269 mg (0.3 mmol) 7b in 10 ml THF is deprotonated as described above. The filtered solution is added to a suspension of 173 mg (0.35 mmol) Ph,PAuCl in 2 ml THF. The mixture is stirred at 0°C for 10 min and then filtered. From the solution the solvent is removed in vacua. The residue is washed with a small quantity of petroleum ether and dissolved in a toluene/methylcyclohexane mixture. On cooling, 9e precipitates as an ocher solid.

161

Acknowledgements We thank the Deutsche Forschungsgemeinschaft for financial support of this work, Dr. W. Buchner for taking the 31P NMR spectra and Wacker-Chemie GmbH for gifts of chemicals. Literature 1 E. Kunz and U. Schubert, Chem. Ber., in press. 2 E. Kunz, M. Knot-r, J. WiIInecker and U. Schubert,

New J. Chem.,

12 (1988)

3 U. Schubert, E. Kunr, M. Knorr and J. Miier, Chem. Ber., 20 (1987) 4 U. Kirchg&sner and U. Schubert, Organometahics, 7 (1988) 784. 5 (a) M. Knot-r and U. Schubert, Transition Met. Chem., and M.S. Wrighton, Organometahics, 3 (1984) 1449;

11 (1986) (c) C.G.

467.

1079.

268; (b) D.K. Liu, C.G. Brinkley Brinkley, J.C. Dewan and MS.

Wrighton, Inorg. Chim. Acta, 121 (1986) 119. 6 M. Knorr, J. MiiIIer and U. Schubert, Chem. Ber., 120 (1987) 879. 7 M. Knox-r, S. Gilbert and U. Schubert, J. Organomet. Chem., 347 (1988)

C17.

8 S.M. Grant and A.R. Manning, J. Chem. Sot., Dalton Trans., (1979) 1789. 9 R.V. Parish and B.F. Riley, J. Chem. Sot., Dalton Trans., (1979) 482. 10 W. Jetz and W.A.G. Graham, Inorg. Chem., 10 (1971) 1159. 11 U. Schubert and M. Knot-r, Inorg. Chem., in press. 12 F.N. Tebbe, P. Meaking, J.P. Jesson and E.L. Muetterties, J. Am. Chem. Sot., 92 (1970) 1068. 13 M. Darensbourg, Progr. Inorg. Chem., 33 (1985) 221. Ion pairing in other dicarbonyl systems: PanneIl and D. Jackson, J. Am. Chem. Sot., 98 (1976) 4443. 14 U. Schubert and J. Miller, J. Organomet. Chem., 340 (1988)

101.

K.H.