Journal of Organometallw Chemistq, 82 (1971) 421-430 0 Eisevier Sequoia S.A., Lausanne - Printed in The Netherlands
REACTIONS OF METHOXYENYLPALLADIUILI ISOCYANIDES
COMPLEXES
WlTH
G. CARTURAN
Centro
dl Chimica
e Tecnologia
de1 C. N. R.. Calle Larga S. Jlarta R. ZAXELLA,
M. GRAZIANI
Facoltti dl Chimica (Received
July
Indusiriale,
lOth,
dei Composti Metallorganwi 2 137, i’cnezia (Ito1.v)
degli Element1
dr Transizrone
and U. BELLUCO
The Uniuerslt_y, \,‘enezia (Italy)
1971)
Summary
The reactions of [Pd(C,,,H,,OCH,)LCI], (L = PPh,, C,H,,NC or CH,NC) with RNC (R = C,Hll, CH3) proceed in mild co!lditions in benzene to give a l/l adduct. The products of the reactions, formulated on the basis of spectroscopic properties, may be looked upon as models for the intermediate that was proposed for the transanularcarbonylation of 1,5xyclooctadiene. The reactions of isocyanides with methosyenyl dimers of palladium are also reported.
Introduction Insertion reactions of carbon monoside or isocyanides across the metalcarbon o-bond m alkosyenyl compleses of palladium and platinum lead to different products, depending on the metal, the diolefin, and the ancillary ligands [ l]. Thus, dicyclopentadienyl derivatives of Pd” and Ptrfi give acyl carbonyl products (eqn. 1) [ 2,3]. Analogous products are obtained from insertion reactions of isocyanides, although the reaction intermediates observed suggest. different mechanisms of format.i.zm ]4]. OChj
c- Y
The dependence of the course of insertion on the nature of the diolefm is borne out in the case of the cyclooctadienyl-Pt” comples which reacts with carbon monoxide to give a carbomethosyl species (eqn. 2) [ 51.
0CH3
6
Pt(COJCI
-
Carbon monoside
catalyzed
h
Pt’
COOC Hj (21
insertions are involved in the carbonylation of diolefins in which formation of a ketone of the type A [S]
by Pd” compleses,
(A1
has been observed
along with esters (in the case of 1,5cyclooctadiene).
No
in which the organic moiety has undergone transannuiar carbonyl&ion has yet been detected in the carbonylation of alkosyenyl metal compleses. With a view to investigating the mechanism of this unusual reaction we have therefore carried out a series of reactions of isocyanides with the alkosydienyl Pd” compleses I, II and III. We also hoped to be able to trap some model intermediate
(L = PPhJ, C,H, ,NC and CHjNC) intermediates having relevance to the palladium-catalyzed transannular carbonylations by taking advantage of the generally greater stability of isocyanideover carbon monoxide-met& complexes. Results
and discussion
Reactions of [Pd(C,oHj20CH3)LC1] (I) (L = PPh3, C,H, JVC, CHJVC) with RNC (R = GH, I, CHJ We studied reaction 3, which proceeds under mild conditions in CH2C12_ Compound IV (monomeric in benzene, non-conductiqg in CH:Cl:) was characterized and formulated on the basis of elemental analysis, IR, PIPER, md mass spectra. Proton absorption data are presented in Table 1. In some cases the complexity of the spectrum prevented assignment of all the signals. The NMR spectrum shows no signal attributable to either free or coordinated olefinic protons, as shown by integration and comparison with the signals from the phenylic protons. Based on this evidence we rule out structures V and VI, both of which
423
(+ZRNC)
are in agreement
with molecular weight and IR spectrum. The imino group protons have been assigned, in particular, for compound IVc (Table 1) on the basis of the different intensities of the terminal iso-cyanide protons (6H, 7 6.58 ppm) from those of imino protons (3H, T 6.66 ppm). We recall that rhe cyclohesyl a-proton in systems which have an amino nitrogen coordinated to palladium, has been found to absorb at 7 6.5 ppm [S], a value very close to our observed Sigtld.
I k
/’
LC/Pa~CNP
H&O
+I\ i ,CI
A,,, /Pd\CNQ
CH3O
II
N -R
N-R
CY)
(523)
Protons bound to the a-carbon in an imino group in platinum compleses were found to absorb at lower fields than in their palladium analogues and this appears to be a rather general trend. In fact, in Pd” and Pt” tetracyanocyclopropane compleses, the methylene protons of the organic ligand zue shifted downfield upon coordination by ca. 0.5 ppm for palladium and ca. 1 ppm for platinum [9]. To the estent that a relationship between chemical shift and electron density esists, this suggests a higher electron acceptor ability from ligands for platinum(U) than for palladium(I1). The IR spectrum of IV shows v(C=N) absorptions m the range 1642-1633 cm-’ (Table 2). These v(C=N) values are general!y higher, albeit to a small estent than those for isocyanides inserted across the palladium-carbon o-bond, which fall in the range 1630-1515 cm-’ in phosphine derivatives [8] *. In the products of the reactions of n-ally1 palladium complexes with isocyanides, u(C=N) is about 1575 cm-’ [lo]; higher values (1660-1652 cm-‘) were found for other PdI’ imino derivatives [ 113. The mass spectrum of IVb was compared with that of the platinum(I1) analog VII, and the comparison suggests the presence (confinued * A possible coordrnntion of nitrogen atom to platinum has been recently trans-~odobls(triethylphosphine)-(lrhloropheoslunmo)meLhylplatmum~lI) xlaiysis 171.
on p. 16)
eucludcd in the case oi on tie bass of .X-m>
m) m)
G.D2(1H. bs): 6.22(2H. m): G.64(0ClI.1. s); 7.42(1H. b#); 7.7G(lH, bs); 8.24*8.79(14H. 6.90(111. bs); 6.24(28.
6.2C(211. m):6,72(OCH~.
XI
XII
s); 8.18~8.60(391~, m)
m): G.G8(OCH~. 9): 7.68(lH,
bs); 7.90(1H. bs): 8.13.8.78(268.
m); 8.20.8.60(38H.
X
bs): 7.68(18.
6.14.G.28(211. m); 6.69(0CH~.
IVd
9): 7,00(111, bs); 7.23(38.
fi.‘?R(l H. m); G.40(111, m); 6.68(GII.C11 I-NC. bs): 6 fM (C=NCHJ. bs): 6.74(OCIi~. s); 7.00 (1H. bs); 7.19(3H. bs): 7.32(18. m): 7AG(lH. m); 7.97(1H, m): 8.03(111. m): 8.30(21-I. m)
7.00(1H. bs): 7.26 (3% bs): 7.74(1h
IVr
INC)(C~.H,INC)(PPII))CII
2.30~2.G0(16H. br): 0.16-G.SO(211. m): 6.70(0CH1.9); m). 8.20.8.80(27H, m)
(Pd(CI[,HI:OCH&,H,
1Vb
7,02(3H. bs):
In): CAZ(CIIrNC.bs); 6.57(lH. m): 6.74(0CH~. 8): bs): 7.21(38. bs): 7,34(lH, m); 7.73(121. m); KOO(lH. a):
3.18(CH=CII. bs); 6.43 (1H. bs); G.GG(CIIJNC. 9): 8.73(OCl1~.8); 7.45~7.7fMW, m): 8.31%A RO(3H. m) 2 30.2.Gl(lGH, bs); 6.14(lH. 6.87 (C=NCIIl, bs)i 7.02(lH. 8.OG(lH. s): 8.31(211. m)
lPd(C~~H,~OCM~)(CNCH;1)CII
IVll
IC
SELECTED NMR DATAa
TAULE 1
m)
[Pd(C,Hk,OCHJC,.HI
INC)KIMI INC~CH
IPd(CI,IMI2OCHSC,.HI lNC)(Cr,H, ,NC)$II
a All compounds multlng with dccomposlllon.
XII
Xl
X
IVd
83
90
122
206
1RCI
103
IVIJ
WC
101
7.1
(Oc)a
m.p.
6 86 (6.88) 7.66 (7.48)
M-73 (54.66) 68.69 (68.78)
5.79 (5 92)
(7 65)
(60.75) 18.09
7.76
60.78
(18.14)
G-70 (6.W)
‘17-M (47.72)
6.77 (6.67)
66.79 (6G.73)
6.26 (0.68)
68.60 (61.02)
G.30 (6.24)
46.03 (46.10)
11
C
(7.09)
7.OG
(5.79)
5.83
(3.74)
3.69
uM4)
b.16
(9 82)
9.94
(3.GG)
1.11
(4.31)
4.12
(4.04)
4.08
N
Annlysis found (cnlrd.) (%I
(6.38)
G.88
(7 33)
7.27
(3.47)
9.74
(6.60)
5.30
(8.28)
8.40
(4.Gl)
4.30
(6.46)
6.GO
(10.24)
10.66
Cl
2198 vs
2198 vs
2198 v3
2196 vs
2226 vs
2197 vs
2226 VB
2226 vs
u(C=N)
1638 s
1646 5
1642 s
1637B
1633 s
MC=N)
260 m
275 s
2GR m
300 m
258 m
260 m
268 m
260 m
256 m
(748)
760
(428)
440
630 (649j
In CJII,
M.W.
COMPLESES
I’(l’d-CI)
Infrorcd frequcncics (1 3 cm-‘)
FOR THE REACTION PRODUCTS OF ISOCYANIDES WI’III ME?‘HOXYENYI.PhLLADIUM(II)
IP~(CI~HI~OCH\C~,HIINC)(C~,HI INC)(PPh_K.II
DATA
IVrr
IC
Compound
IR SPECTRA AND ANALYTICAL
TADLE 2
0CH3
R’
PPh3
C-PPt II
I
N\R
1
-Cl
I
CNR
of the organic moiety as depicted in IV. In fact, the mass shows very strong peaks both at 272 [(C,oHI,OCH,)(C,H, (272 - C,H, ,NC), whereas for IVb the peak at 163 is very is maintained), in line with a less easy rupture of the C,H, the organic moiety in the latter case.
spectrum of VII ,NC)] and at 163 weak (the 272 peak ,NC grouping from
CH,O
-F’d- % I
An alternative, B, ako in accord with the mass spectrum, may be ruled out by the IR spectrum, as iJ(C=N) for cyclopropane derivatives is generaUy higher than 1700 cm-’ 1121. These results throw some light on the mechanism of carbonyiation of olefins catalyzed by palladium(II) complexes. In fact, in a most general way, competition is likely to occur between two reaction modes. Initial insertion of CO across the palladium--carbon bond, leading to an acyl intermediate, may be followedby reaction 4, which involves formation of transannukr carbonylation products [6] via insertion of the olefinic bond across the paUadium--acyl bond.
A tematively,
nucleophilic
attack at the acyl carbon
may occur, leading to car-
bonylation products, according to reaction 5 [13]. The path which is actually operative depends on the basicity of the medium 1141.
tIZO3,
lixl
(%l
We think that reaction 3 may be written more fully as reaction 6, on the basis of the isolation of products VIII and LX from the analogous reaction with platinum [S]. For palladium complexes, even with complex/RNC molar ratios less than 1, a mixture of reactants and products is always obtained. At any rate, it cannot be ruled out that the first step of reaction is the insertion of isocyanide followed by displacement of the olefinic grouping, by analogy with observations on both platinum [2] and palladium [3] in carbonylation reactions. In principle, these complexes may be looked upon as models for the intermediate that has been proposed for carbonylation of 1,5-cyclooctadiene catalyzed by palladium phosphine compleres [6]. This reaction gives the final carbonylated product via P-extraction (eqn. 7).
Reaction of {Pd(C7H,0CH,)Clj2 with C&l, JVC Ln order to investigate the effect of the diolefin
on this type of reaction, we effected reaction 8. The first step, III 9 X, is not a bridge-splitting reaction as observed when the entering ligand is an amine [ 151 but instead, prior formation of dimer (X) takes place, by analogy with the reaction with carbon monoxide [ 51. By the use of an escess of isocyanide, bridge-sphtting occurs as the second step, X --r XI. The insertion of CNR in compound XI proceeds only under more stringent conditions (benzene at reflus). The strong tendency of norbomadiene to give palladium--carbon bonded compounds has been traced back to the peculiar homoallylic structure of this diolefin [ 161. The nortricyclene configuration has been established by a study of the stereochemistry of carbonylation of norbomadiene in methanol catalyzed by Pdrr (which gives 3-sndo-carbethoxy-5-exe-methoxynortricyclene [ 171) and by an X-ray structure determination on the analog-tie of XI with pyridine coordinated [18]. It should be noted that the same type of compound (XII) may also be obtained by the above sequence of reactions, even when bridgesplitting precedes the rearrangement of the norbornadiene moiety. Therefore, these possible reaction paths are ma-keclly affected by the nature of the neutral reacting ligand and a systematic study of related electronic and steric factors is currently in progress.
u-i-
Esperimentd Instrldments. hlolecular weight determinations were carried out in benzene solution with a Vapor Pressure Osmometer, Model HP 302 B. Proton NMR spectra were obtained m-t a Bruker 90 MHz spectrometer, using CDC19 as solvent and TRIS as internal standard. Lnfrared spectra (4000-250 cm-‘) were recorded on a Perkin-Elmer Model 457 spectrophotometer. An LKJ3 9000 insttument was used to carry zmt mass spectral determinations. ILIaCerials. AJJ the s.Avents were reagent grade quality. Methyl isocyanide and cyclohesyl isocyanide were prepared by the methods reported in the Iiterature [19], as were the compleses [Pd(C,,,H,20CH~)C1]2 (II) [20], [Pd(CloH,~OCH~)(PPh,:ICIJ (Ia) 1211, [Pd(C,,H,,OCH,)(C,HI,NC)CIl (b) [4] and [Pd(C,HsOCH3 ,Ci Jz (III) [ 201. Elemental a.naJyseswere performed by Domis und Kolbe, MuJheim (Germany). IPd(C,,H,,OCHj)(CH,NC)CII(Ic). To a stirred CHzCIz solution of [Pd(C,,HizOCH,!CI], (II) (0.610 g, 1 mmol) kept at 0°C under nitrogen methyl isocyanide (0.084 g, 2 mmol) in 10 ml of the same solvent was added dropwise. After the addition the solvent was partially removed at reduced pressure and, by addition of petroleum ether, the pale yellow solid iPd(C,,H,20CH3)(CH,NC)CI ] waz obtained. It was recyrstallized from benzene/hexane. [Pd(C,& zOCH,CHJVC)(PPh ,)(CHJVC)Ci] (Wa). To B stirred CH,C12 solution of [Pd(CiOH,?,OCH~)(PPh~)CI] (Ia) (0.567 g, 1 mmol) keptat-10°C under nitrogen, methyl isocyanide (0.084 g, Io mmol) in 15 mJ of the same solvent was added dropwise. The solution turned yellow-orange and was maintained at 0°C For 1 h. The solvent was removed to give a colourless oil, which was washed with ethyl ether. The crude product was dried under vacuum and crystaJJized on cooling at - 6XC from dichJoromethane/pentane solution. IPd(C,.Z, @Xf&,H, ,IVC)(PPh,)(C,H, ,NC)Cf] (Wb). Using the same procedure, this product was obtained as an off-white solid.
IPd(C,H,OCH,)(C,H,,NC)CI]?(X!. To a stirred solution of [Pd(C,HsOCH,)Cl], (III) (0.265 g, 0.5 mmol) in CH,Cl, kept at 0°C under nitrogen, cyclohesyl isocyanide (C,H,, NC)(0.109 g, 1 mmol) in 10 ml of the same solvent was added dropwise. Partial removal of the solvent and addition of n-hesane gave the product as an off-white solid. [Pd(C,HsOCHj)(C”H, ,NC),Crj (X’Z). Th is comples was prepared either by slow addition of a CH,Cl, solution of cyclohesyl isocyanide to a solution of [Pd(C,H,OCH,)CI], (111) in the same solvent, using a molar ratio Pd/RNC of l/2, or using [Pd(CiHsOCH3)(C,H, ,NC)Cl], (X) as parent compound dissolved in CHzC12 and adding the stoichiometric amount of C,H, ,NC. In both cases the reactions were carried out at -10°C under nitrogen and the product was collected as a yellow solid after addition of ether and cooling to -60°C. [Pd(C,H,OCH,CJI, JVC)(C6H, ,NC)zCI] (XII). A solution of [ Pd(C,H, 0CH3)(CoH, ,NC)?Cl] (XI) (0.241 g, 0.5 mmol) in 20 ml of benzene was stirred and treated under nitrogen with CJ-I, ,NC (0.054 g, 0.5 mmol). The solution was reflused for 1 h, and then treated with charcoal and filtered. Evaporation of the solvent left an oily product which was washed with ether and dried under vacuum giving a yellow-brown solid. [Pd(C,oHl ?OCH,CH~C)fCH.NC)2C1] (IVc). (a) To a 1 mmol sample of [Pd(C, “HI ,0CH3)Cl12 (II) LIJ CH2C12 stirred under nitrogen, 6 mmol of CHjNC in the same solvent was gently added at -10°C. The solution turned orange-yellow, and was allowed to stand at 0°C for 4 h. The reaction mixture was tested by IR spectroscopy until no free isocyanide was detected. Evaporation to dryness gave the crude product which was washed with ether and n-hesane to give a yellow-brown solid. (b) The same compound was prepared under similar esperimental conditions using [Pd(C,,H,,OCH,)(CH,NC)Cl] (Ic) as starting material with a molar ratio Pd/CHjNC of l/2. The analogous cyclohexyl isocyanide derivative (IVd) was also prepared in the same way. References 1
2 3 4 5 6 7 8 9 10 11 12 13
14
For 9enera.l suneys. (a) P.M. hlaitlis. The Organic Chemtstry of Palladtum. Acadcmtc Press. New York.. 1971. (b) U. Belluco. Organometatlic and Coordmsrron CbcmistrV oi Plaunum. Academrc Press, London. 1974. (c) P.hl. Tretcbel. Advan. Organometaf. Chem.. 11 (1573). G. Carturan. hl. Grazuun and U. BeUuco. J. Chem. Sot. A. (1971) 2509. C. Carturan. hl. Graziam. R. Ros and U. Betfuco. J. Chem. Sot. Dalton Trans.. (1972) 262. R. ZaneUa. G. Carturan. hl. Gruiam and U. Belluco. J. Organomerat. Cbem.. 65 (1974) 417. A. Vttagliano and G. Ptiuo. J. Organometaf. Cbem.. 49 (1973) C49. S. Brews and P.R. Hughes. Chem. Commun.. (1966) 6. R.P. Wagner. P.hl. Treichel and J.C. Calabresse. J. Organometaf. Chem.. 56 (1973) C33. Y. Yamamoto and H. Yamaraki. Bult. Cbem. Sot. Jap.. 43 (1970) 2653. hl. Lenarda. R. Ros. hl. Graziam sod U. BeUuco. J. Organometat. Cbem.. 65 (197-l) 407. T. Borhr and B. Croclam. inorg. Chnn. Acti. 5 (1971) 477. S. Otsuka. A. Nakarnura and T. Yo=-bida. J. Amer. Cbem. Sot.. 91 (1969) 7196. f-t. Quast. E. Schmitt and R. Frank. Angew. Chcm. lnt. Ed. Fogf. 10 (1971) 651. (a) J. Teuti. hl. hlonhaws and J. Kni. J. Amer. Chem. Sot.. 86 (1964) 4851. fb) L.F. Hinesand J.K. Stdle. J. 4mer. Cbem. Soc..94 (1972) 458. (c) hl. Graziam. G. Carturan and R. Ros. Chnn. lnd. (Rl~Ian). 55 (1973) 775. T. Hosokawa and P.hl. hlaitbs. J. Amer. Chem. Sot.. 95 (1973) 4924.
430 15 N. Green sod R.I. Hancock J. Chem. Sot. A. (1967) 2054. 16 D.R. Cod-son. J. Amer. Chem. Sot.. 91 (1969) 200. 17 J.K. StilIe and L.F. Hines, J. Amer. Chem. Sot.. 92 (1970) 798. 18 E. Focsellmi. G. Bomb&i. B. Croclani and T. Boschi. J. Chem. Sot.
D. Chem.
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1203.
19 L. NaIatesta and F. Bonati. Isocranide Complexes of Metals. Wiley-Interscience. New 20 J. Cbatt. L.M. Valkino and L.hl. Vena~~:. J. Chem. Sot.. (1957) 3443. 22 B. Crocrani. P. UgUaghat~. T. Bosch1 and U. Belluco. J. Cbem. Sot. A. (1968) 2869.
York.
1969.