Inorg. Chem. 1983, 22, 421-433 kinetics identical with that of the reaction of [Fe(CO),NO]and Me1 alone; i.e., the phosphine reacts with an intermediate in a step following the rate-determining reaction between the metalate and MeI. No reaction may be observed between the metalate and Ph,P.47 Using Occam's Razor, in conjunction with the very high yields of the phosphine product, we have assigned the intermediate the structure of the alkyliron complex. It is not surprising that we are unable to isolate or observe this species since it is electronically equivalent to the [Co(CO),CH,] complex, which decomposes at temperatures in excess of -30 0C.48 We have made no attempts to discover (47) This comment refers to thermal reactions. If the metalate is treated with triphenylphosphine and irradiation, we have observed facile CO displacement. We are examining the new metalate formed under these conditions.
427
the fate of the alkyl group in the reactions performed in the absence of phosphine ligand. Acknowledgment. We thank the Robert A. Welch Foundation, Houston, TX, the National Science Foundation, Washington, DC, and the Patriomonie of the University of Liege, Liege, Belgium, for support of this research. Registry No. [Fe(CO),(NO)]-Na+, 25875-18-7; [Fe(CO),(NO)]-PPN', 6 1003-17-6; [Fe(CO)3(NO)]-K+, 25875- 19-8; PPh3, 603-35-0; 18-C-6, 17455-13-9; (NH2),DBC, 60016-77-5; Br,DBC, 62667-75-8; (NO,),DBC, 29721-41-3; MeI, 74-88-4. Supplementary Material Available: Comments relating to the treatment of the disorder problem and a listing of calculated and observed structure factors (16 pages). Ordering information is given on any current masthead page. (48) W. Beck and R. E. Nitzschmann, Chem. Ber., 97, 2098 (1964).
Contribution from the Guelph-Waterloo Centre for Graduate Work in Chemistry, Guelph Campus, University of Guelph, Guelph, Ontario, Canada N l G 2W1
Role of the Trichlorostannyl Ligand in Homogeneous Catalysis. 2. Spectroscopic Studies of the Reaction of cis-[PtC12(CO)(PR,)] with SnC12-2H20: Ligand Rearrangement Reactions in the Formation of an Olefin Hydroformylation Catalyst Precursor GORDON K. ANDERSON, HOWARD C. CLARK,* and JULIAN A. DAVIES Received February 12, 1982
The complex cis-[PtCI,(CO)(PPh,)] reacts with SnCI2.2H20in acetone to yield solutions that are active in the catalytic 31P{lH),'I9Sn('H),and 195PtNMR spectroscopy, including experiments hydroformylation of olefins. Studies by I3C('H), utilizing "C-labeled carbon monoxide, have shown that cis-[PtCl,(CO)(PPh,)] reacts with SnC1,.2H20 via a ligand rearrangement process. A cationic complex, trans-[PtC1(CO)(PPh3)z]+, and four anionic complexes, three of which are are formed. One minor anionic identified as [Pt(SnC1,),I3-, trans-[PtC1(SnC13)2(CO)]-,and tr~ns-[PtCI(SnCl,)~(PPh~)]-, product remains unidentified. Similar chemistry occurs with the analogous P(p-MeC6H4), and P(p-FC6H4), complexes, but the rearrangement reaction occurs much more slowly with the basic PEt, ligand. Some conclusions concerning the mechanism of the reaction are presented; SnCI2.2Hz0not only serves as a source of SnC1, moieties, which undergo insertion reactions, but also generates secondary cationic species, which maintain electroneutrality in the system. Attempted isolation of the ionic species leads to a further rearrangement reaction, ultimately yielding cis-[PtC12(PPh3),] as the only isolable product.
Introduction Platinum(I1) halide complexes are known to react with tin(I1) chloride2" to produce solutions, usually intensely colored, that are often catalytically active in the homogeneous hydrogenation3s4and hydroformylation5,6 of olefins. It has been appreciated for some years7 that SnC12 will react with certain (1) Part 1: Anderson, G. K.; Clark, H. C.; Davies, J. A. Organometallics 1982. 1 . 64. (2) Hartiey, F. R. "The Chemistry of Platinum and Palladium"; Wiley: New York, 1973: (a) p 93;(b) p 96. (3) Billard, C.; Clark, H. C.; Wong, C. S . IXth International Conference on Organometallic Chemistry, Dijon, France, 1979,Abstract No. C3; J. Orghnomet. Chem. 1980, -190,-C3. (4) See for examples: Cramer, R. D.; Jenner, E. L.; Lindsey, R. V.; Stolberg, U. G. J . Am. Chem. SOC.1963, 85, 1691. Tayim, H . A,; Bailar, J. C . , Jr. J . Am. Chem. SOC.1967, 89, 3420. Bailar, J. C., Jr.; Itatani, H.; Crespi, M. J.; Geldard, J. Adv. Chem. Ser. 1967, No. 62, 103. Bailar, J. C., Jr. Platinum Met. Rev. 1971, 15, 2. Itatani, H.; Bailar, J. C., Jr. Ind. Eng. Chem. Prod. Res. Deu. 1972,11, 146. James, B. R."Homogeneous Hydrogenation"; Wiley: New York, 1973. (5) Clark, H.C.; Davies, J. A. J . Organomet. Chem. 1981, 213, 503. (6) Schwager, I.; Knifton, J. F., German Patent 2322751, 1973. Hsu, C. Y.; Orchin, M. J . Am. Chem. SOC.1975, 97, 3553. Consiglio, G.; Pino, P. Helu. Chim. Acta 1976, 59, 642. Schwager, I.; Knifton, J. F. J . Catal. 1976, 45, 256. (7) Meyer, A. S.; Ayres, G. H. J. Am. Chem. Sor. 1955, 77, 2671. Davies, A. G.; Wilkinson, G.; Young, J. F. Ibid. 1963, 85, 1692.
0020-1669/83/1322-0427$01.50/0
transition-metal complexes containing a M-Cl bond to yield trichlorostannyl complexes, via migratory insertion reactions. Such complexes are believed to be key intermediates in the homogeneous catalytic activation of organic unsaturates. Support for these ideas has become available in recent years through the application of multinuclear magnetic resonance techniques,8 which allow complex systems such as the [PtC12(PR3),]/SnC12~2H20 catalyst precursor to be probed by 'H, 31P,117,119Sn, and 195PtNMR methods and much structural information to be acquired concerning the species present in solution. Extensive NMR studies by Pregosin and co-workers" * have shown that halocarbon solutions of [PtCl,(PR,),] complexes react with tin(I1) chloride according to eq 1. The geometry of 1 may be either cis or trans, depending upon the nature of R, whereas 2 is always of trans geometry and reacts with H2 (8) Davies, J. A. In "The Chemistry of the Metal-Carbon Bond"; Hartley, F. R., Patai, S . , Eds.; Wiley: New York, in press. (9) Pregosin, P. S.;Sze, S. N. Helu. Chim. Acta 1979, 61, 1848. (10) Ostaja-Starzewski, K. A,; Pregosin, P. S.; Ruegger, H. Inorg. Chim. Acta~1979, 36, L445. ( 1 1) Pregosin, P. S. Biennial Inorganic Chemistry Symposium of the Chemical Institute of Canada and the American Chemical Society, Guelph, Canada, 1980. ~~
0 1983 American Chemical Society
428 Inorganic Chemistry, Vol. 22, No. 3, 1983
Anderson, Clark, and Davies
SnQ
bient temperature after the addition of 1.0, 2.0, 2.5, and 5.0 equiv of SnC12.2H20. The disappearance of the starting material (6(P) = 9.05, 1J(195Pt,31P) = 3057 Hz)17 was accompanied by the formation of a single observable new phosphorus-containing species (6(P) = 18.50, 1J(1g5Pt,3'P) = 2034 Hz). After the addition of 2.0 equiv of SnCl2*2H20,the resonances associated with cis-[PtCl,(CO)(PPh,)] were no longer present and no change in the spectrum was observed upon further additions. If chemistry analogous to eq 1 had occurred, the expected products would be [PtCl(SnCl,)(CO)(PPh3)] and/or [Pt(SnCl,),(CO)(PPh,)], and yet the 3'P(LHJ NMR spectra showed no evidence of coupling between ,lP and 1173119Sn, even when recorded at 213 K.I8 It was found that samples prepared in the absence and in the presence of air had identical 31P(lH}NMR spectra and that sealed samples could be stored for several days without any deterioration being apparent. Purging solutions of cis[PtC12(CO)(PPh,)] with molecular oxygen during the slow addition of SnC12.2H20 considerably retarded the reaction, however,19 and indeed, it has been shown20 that SnCl, is oxidized by dioxygen in the presence of donor solvents according to eq 3 (where x = 1, 2). Under the conditions normally
[PtCl,(PR,),]
SnCI,
-
[PtCl(SnC13)(PR3)2] 1
[Pt(SnCl3)2(PR3)21 ( 1) 2
to yield tr~ns-[PtH(SnCl,)(PR,)~]. The hydrido complex reacts with activated acetylenes to yield insertion products.I0 This reaction sequence is a stoichiometric series that reproduces the chemistry expected to occur in a catalytic cycle for the activation of unsaturated hydrocarbons. Studies of the [PtC12(PEt3),]/SnC12 system by 31Pand IL7SnNMR techniques have shown12that the use of acetone as a solvent causes the chemistry described by eq 1 to be complicated by equilibria, as exemplified by eq 2, involving the elimination of SnCl, from a M-SnCl, bond.
trans-[PtCl(SnCl,)(PEt,),] + cis- [PtCl,(PEt,),]
+ SnC1, (2)
Nonetheless, the simple insertion of SnC1, into a M-Cl bond is often assumed to yield the primary intermediate in a catalytic cycle, although this is by no means proven under the conditions employed for actual catalytic syntheses. Such reactions are generally performed under elevated conditions of temperature and pre~sure,~"and yet catalytic cycles derived from simple stoichiometric reaction series and equilibria, of the types shown in eq 1 and 2, are described in even the most modern critical texts on homogeneous c a t a l y ~ i s . ~ ~ ~ ' ~ In a recent paper' we described the development of a new series of catalyst precursors for olefin hydroformylation. The precursors were formed by the reaction of cis- [PtCl,(CO)(PR,)] (R = p-FC6H4,Ph, p-MeC6H4,Et, n-Bu, C-HX)'~ with SnC12.2H20. In addition to the expected variations in catalytic activity with CO/H2 ratios, total pressures, and operating temperatures, marked dependences on the Pt(II)/Sn(II) ratio, the nature of the R group in the PR3 ligand, and the nature of the solvent were observed. Catalytic activity was approximately constantL6with Pt(II)/Sn(II) ratios of 1/2 to 1/10 but declined rapidly when ratios employing less SnCl,.2H20 were used. No correlation of activity with either steric or electronic parameters associated with the PR, ligands was observed, and efficient catalysis was obtained with use of only acetone or acetonitrile as solvent; use of both methanol and tetrahydrofuran resulted in a total loss of activity.' This behavior is so markedly different from that of the well-known [PtCl,(PR,),] /SnC12 catalyst system6that it seemed possible that chemistry of the type described by eq 1 and 2, although taken to be entirely general for such Pt(II)/Sn(II) reaction systems, may not be operative in the present case. Results and Discussion For many of our catalytic studies5 we employed the complex cis-[PtCl,(CO)(PPh,)] as a model catalyst precursor and utilized acetone as the solvent; accordingly, it was this system that we first investigated by N M R spectroscopy. The addition of SnC12.2H20 to acetone suspensions of cis-[PtCl,(CO)(PPh,)] generates an immediate bright red coloration, and the evolution of gas could be visually detected in clear solutions of the more concentrated samples. The 3LP(1H) NMR spectra of such solutions were recorded at am(12) Koch, B. R.; Fazakerley, G. V.; Dijkstra, E. Inorg. Chim. Acta 1980, 45, L51. (1 3) Masters, C 'Homogeneous Transition-Metal Catalysis-A Gentle Art"; Chapman and Hall: London, 1981; p 131 (paperback edition). (14) Kahn, M. M. T.; Martell, A. E. "Homogeneous Catalysis by Metal Complexes"; Academic Press: New York, 1974; Vol. I, p 60. (1 5) Abbreviations are as follows: Ph = C6H5,Me = CHI, Et = C2H5, n-Bu = CH2(CH2)2CH3,c-Hx = cyclohexane. (16) Catalytic activity was found to be constant within experimental error for Pt(II)/Sn(II) ratios of 1/2 and 1/5 with possibly a very slight decrease upon changing to a ratio of 1/10, See ref 5 for discussion.
2SnC1,
+ 0, + 2x(solvent)
-+
SnC14(solvent),
-
2SnOC12(solvent), SnO, 2(x - 1)solvent (3)
+
employed during this study (see Experimental Section), such oxidation of SnC12.2H20 was not observed. The Ig5PtNMR spectrum of an acetone solution of cis[PtCl,(CO)(PPh,)] to which 2.0 equiv of SnCl,.2H20 had been addedz1was recorded at 213 K. The spectrum showed the presence of a single species in the range +2800 to -4400 ppm (relative to KzPtC14(aq)) as a 1/2/1 triplet (6(Pt) = -2822, 1J('95Pt,3'P)= 2063 Hz). No coupling to 117,1'9Sn was observed. The 31P(LH) and Ig5PtNMR data indicate that a single observable platinum/phosphine complex is formed that contains two equivalent PPh, ligands per metal center. The magnitude of 1J('95Pt,31P)indicates that the two equivalent PPh, ligands are trans to groups of relatively high trans influence,22 which tends to rule against CO or C1- as possible candidates. As the presence of the high-trans-influenceSnC1,ligand is eliminated by the absence of coupling to 117J19Sn, the magnitude of 1J(L95Pt,31P) suggests that the two PPh3 ligands are mutually trans. In order to probe the nature of the rearrangement product further, we prepared a sample of c i ~ - [ P t C l ~ ( ~ ~ C 0 ) ( P Pbyh , ) ] cleavage of the dimeric complex, [Pt2(p-C1)2C12(PPh3),1,with carbon-13 monoxide. The carbonyl region of the 13C('HJ NMR spectrum of an acetone solution of cis-[PtCl2(I3CO)(PPh,)] showed the expected doublet,23exhibiting coupling to Ig5Pt(6(C) = 157.7, 1J(195Pt,L3C) = 1766 Hz, 2J(31P,'3C)
(17) Data as previously reported: Anderson, G. K.; Clark, H. C.; Davies, J. A. Inorg. Chem. 1981, 20, 1636. (18) Tin has three isotopes of I = l/2, II9Sn (8.68%), "'Sn (7.67%), and "SSn (0.35%). The low abundance of 115Snmakes the observation of coupling to this isotope uncommon. (19) Purging solutions with molecular oxygen was also found to inhibit the catalytic activity of such precursors during olefin hydroformylation. See ref 5 for discussion. (20) Messin, G.; Janier-Dubry, J. L. Inorg. Nucl. Chem. Lett. 1979, I S , 409. (21) The '95Pt NMR spectrum of cis-[PtCI (CO)(PPh,)] itself consists of a doublet resonance (S(Pt) = -3517, 7J(19sPt,31P)= 3112 Hz for a Me2C0 solution). (22) The values of IJ(195Pt,"1P)in typical square-planar platinum(I1) complex- vary with the nature of the trans ligand, L, according to the series L = P(II1) ligand < sp C ligand < Cl-. (a) For examples, see: Anderson, G. K.; Clark, H.C.; Davies, J. A. Inorg. Chem. 1981, 20, 944. (b) For a discussion of the NMR trans influence, see: Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Reu. 1973, 10, 355. (23) Data as previously reported: Anderson, G. K.; Cross, R. J.; Rycroft, D. S . J . Chem. Res., Miniprint 1979, 1601.
Inorganic Chemistry, Vol. 22, No. 3, 1983 429
Role of the SnC1; Ligand in Homogeneous Catalysis Table I.
A
Bb C
DC
A
Ii9Sn q H } NMR Spectroscopic Dataa
-120.9 -141.6 -124.5 -109.4
15 815 14 960 ca. 15 850 ca. 18 600
I
6090 5810 not obsd not obsd
A
I
210 95%) when a 119Sn(1HJ NMR spectrum was obtained for an acetone solution of cis-[PtCl,(CO)(PPh,)] to which 5.0 equiv of SnC12.2H20 had been added. Resonances associated with species B and C were no longer observable. Additionally, a minor component, D (Table I), was observed. It is particularly noteworthy (28) The range of lssPt chemical shifts is very large, and resonances attributable to anionic platinum complexes encompass the entire known range, ca. 13000 ppm (Le., the [PtF6l2- and [PtI6I2- ions have resonances separated by 13 385 ppm). Accordingly, a diligent search for resonances attributable to anion rearrangement products was not considered profitable and 119Sn(lH]NMR spectroscopy was employed as an alternative. The known chemical shift range of ‘19Snis ca. 2500 ppm, and the presence of both Ii9Sn and “’Sn in a statistical percentage of molecules containing more than one tin nucleus, which leads to the generation of 119Sn/117Sn coupling, makes I19Sn(lH]NMR a most attractive technique. See ref 8 for discussion.
430 Inorganic Chemistry, Vol. 22, No. 3, 1983 that on no occasion was a resonance observed for uncomplexed tin(I1) chloride.29 Clearly, the 119Sn('H)NMR data are not straightforward, the relative proportions of species A-D being determined by the Pt(II)/Sn(II) ratio. As the three major species, A-C, were clearly observable for the case where the Pt(II)/Sn(II) ratio was 1/2, it was this system that we chose to study in greater depth. An acetone solution of cis-[PtCl,(CO)(PPh,)], to which 2.0 equiv of SnC1,.2H20 had been added, was examined 30 min after the addition of the tin(I1) chloride and again after 2.5 and 48 h of standing under a nitrogen atmosphere at room temperature. The final spectrum is shown in Figure 1A. The three species A-C are evident, with species C present in only a minor amount. The series of spectra indicated a relative increase in intensity of the resonance associated with species A, at the expense of B and C, over the first 2.5-h period, but then the relative intensities appear unchanged over the following 45.5 h. A similar series of experiments was performed with use of the carbon-13 monoxide complex, cis-[PtCl,(13CO)(PPh3)].The final spectrum is shown in Figure 1B. This spectrum clearly shows that the central resonance of species B and the satellites resulting from coupling to Is5Pt and lI7Sn appear as well-defined doublets, due to coupling to 13c.
These data allow some questions concerning the nature of the anionic species to be answered. The experiments with the carbon- 13 labeled carbonyl complex demonstrate that neither species A nor species C contains a carbonyl ligand. The 1'9Sn(1H]NMR data of species A are very similar to those reported for the [Pt(SnC13)5]3-anion. The data of Nelson et aL30for this anion include similar values of lJ( 195Pt,119Sn) and 2J(119Sn.i17Sn) (16 024 and 6230 Hz, respectively) but differ with respect to the chemical shift (-142 ppm, erroneously reported as -387 ppm in the original paper).30 Although tin chemical shifts cover a substantial range2* and changes in temperature and solvent can appreciably affect the shift of many classes of tin compounds, the external standard used by ourselves (10% Me$n in CDC13at ambient temperature) and Nelson et al. (Me4Sn, presumably neat, temperature undefined) is known to display only a minor shift dependence on the nature of the ~ o l v e n t . ~ ' Accordingly, the anion, [Pt(SnC13)5]3-, was prepared independently by the reaction of [K] [PtC13(C2H4)]with SnC12.2H20in acetone solution, and the 119S{1H) NMR spectrum was recorded at 213 K under our standard operating conditions (see Experimental Section). The spectrum obtained (s(Sn) = -121.2, 1J(195Pt,11gSn) = 15 995 Hz, 2J(*19Sn,117Sn) = 6185 Hz) confirmed that a complex identical with species A had been formed. Analysis of the satellite i n t e n ~ i t i e sconfirmed ~~ a Pt(II)/Sn(II) ratio of 1/5, defining the product conclusively as the [Pt(SnC13)5]3- anion. The data obtained for species B suggest a four-coordinate complex and allow a structure to be assigned. A single resonance is observed, demonstrating equivalence of all lI9Sn nuclei in each molecule, and the magnitudes of 1J('95Pt,119Sn) and 2J(119Sn,i'7Sn) show that there are two tin nuclei in mutually trans positions.33 The coupling to I3C is of the
(29) The "9Sn(1HJNMR spectrum of a saturated acetone solution of SnC12.2H20shows a single broad resonance (a(Sn) = -218, Y ~ ca. , ~ 1200 Hz,measured at 213 K). (30) Nelson, J. H.; Cooper, V.; Rudolph, R. W. Inorg. Nucl. Chem. Lett. 1980, 16, 263. For correct values of a(%), see: Ibid. 1980, 16, 587. (31) TupEiauskas, A. P.; Sergeyev, N. M.; Ustynyuk, Yu. A. Liet. Fiz. Rinkinys 1971, I J , 93. Smith, P. J.; TupEiauskas, A. P. Annu. Rep. NMR Spectrosc. 1978, 8, 292. (32) Rudolph, R. W.; Wilson, W. L.; Parker, F.; Taylor, R. C.; Young, D. C. J . Am. Chem. Soc. 1978, 100, 4629.
Anderson, Clark, and Davies magnitude expected for a cis arrangement of CO and SnC1,ligands. The earlier I3C(lH)NMR studies at 15.1 MHz of the reaction of ~is-[PtCl~('~C0)(PPh,)] with SnC1,.2H20 (vide supra) had allowed observation of the resonances associated with the ~rans-[PtCl(~~CO)(PPh,)~]+ cation, but the anionic species B, known to contain a carbonyl ligand from the 119Sn{'HJ NMR data, was not observed. Accordingly, these studies were repeated, with the obtainment of 13C('H}NMR spectra at 100.1 MHz, and resonances attributable to species B were indeed observed (6(C) = 152.5, 1J(195Pt,13C) = 1794 Hz), although the minor nature of this species prevented observation of "9Sn/'3C coupling in the I3C{lH]spectrum. The magnitude of 1J('95Pt,13C)is indicative of a carbonyl group trans to a ligand of relatively low trans infl~ence,,~ and accordingly, the fourth ligand is likely to be C1-. The species B is thus proposed to be the trans-[PtCI(SnCI,),(CO)]ani0n.34 The 1'9Sn('H}NMR data of species C do not allow a structure to be assigned for this complex. The minor nature of species C prevented observation of 119Sn/1'7Sncoupling, should any be present, and accordingly the Pt(II)/Sn(II) ratio cannot be defined by analysis of satellite intensities. The very broad resonances associated with species C suggest that a polynuclear structure may be possible,35although, other than the conclusion that this minor species contains no CO or PR3 ligands, further discussion would be speculative and unwarranted. Addition of further SnC12.2H20 to solutions containing trans- [PtC1(SnCI3),(C0)]-, [Pt(SnC13)5]3-, and species C caused both trans- [PtCl(SnCl,),(CO)]- and species C to be converted to the [Pt(SnC13)5]3-anion, thus resulting in the total loss of CO from the anionic rearrangement products and generating a dominant anionic species. The species D formed, in ca. 5% yield (by peak heights in the 119Sn{'H) NMR spectrum), along with the dominant anion, [Pt(SnC13)5]3-,by the reaction of an acetone solution of cis-[PtCl,(CO)(PPh,)] .with 5.0 equiv of SnC12.2H20remained unidentified. The 1'9Sn(1H] NMR data showed the presence of a doublet of separation 266 Hz, a value typical of ,J(119Sn,31P) in platinum(I1) complexes with cis PR3 and SnC1,ligand^.^,'^ The 3iP(1HJ NMR spectra of such reaction mixtures showed only resonances attributable to the trans[PtCl(CO)(PPh,),]+ cation (vide supra) until a spectrum was obtained with a S / N ratio of ca. 300, which showed the presence of a second species, in
