Organometallics 1995, 14, 5472-5474
5472
Polysilyl Group Isomerization via Migrations in Rhodium and Iridium Derivatives (Me3P)sMSi(SiMe& Gregory P. Mitchell and T. Don Tilley” Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460
Glenn P. A. Yap and Arnold L. Rheingold” Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716-2522 Received August 15, 1995@ Summary: Reaction of (Me3P)3RhCl with (THFj3LiSi(SiMe3)3 generates the thermally unstable complex (Me3P)8hSiMe~SiMe(SiMe3)~ (l),probably via a series of 1,2- and 2,3-migrations. The analogous iridium reaction results in a similar rearrangement to give the I
I
iridacycle (Me3P)3(H)IrSiMe~SiMe(SiMe3)SiMezCHz as a mixture of diastereomers (2a,b),which is catalytically converted to an equilibrium mixture by hydrogen. Intramolecular 1,2- and 1,3-migrations appear to pervade transition metal-silicon chemistry and are thought to mediate many important pathways for silicon-element bond reactivity.’ For example, such processes have been invoked in proposed mechanisms for metal-mediated redistributions at silicon2and silane dehydro~oupling.~ Although neither type of migration has been directly observed, convincing evidence for such steps has been amassed by Pannell, Ogino, and Turner for reactions involving the Cp(C0)Fe f r a g n ~ e n tThese .~ photochemically-driven processes result in rearrangement of silyl ligands, possibly by series of migration steps as generalized in eq 1. An interesting example of ,SIR’,
1,2-mig
L,M-SiR,SiR’3
L,M+ SIR,
-
of Berry, the 1,3-migration of methyl groups in Cp2W(SiMes)(SiR’aOTf)complexes has been probede5 In attempts to study this important and fundamental rearrangement chemistry, we have sought t o observe isolated migrations that might be amenable to further scrutiny. One approach involves the generation of coordinatively unsaturated silyl derivatives which could rearrange t o more stable l&electron, silyl-silylene complexes via a 1,2-migration. We have previously employed a related strategy in the synthesis of y2-silene complexes.6 Here we report an attempt to observe such transformations in rhodium and iridium systems of the type LsM-SiRs, which has led to observation of rather dramatic migratory rearrangements. Reaction of (THF)3LiSi(SiMe3)37with (Me3P)3RhC18in pentane resulted in a deep red solution, from which dark red crystals were obtained in 53% yield. Complete characterization of this compound was complicated by its thermal instability (t112 = 6 h in benzene-ds), but the NMR data strongly support formulation of the compound as (Me3P)3RhSiMezSiMe(SiMe& (1, eq 2h9 A
1,3-mig
+ (THF),LiSi(SiMe,),
-LiCI
+SiR’, LM ,,
-3THF
(Me,P),RhCI (1)
SiR,R’
Me,P-
SiMe(SiMe3),
I Rh-
/ Si ...,,
I
this chemistry is the photochemical conversion of Cp(C0)2Fe(SiMe2)3SiMe3to Cp(CO)zFeSi(SiMes)s,for which 1,2- and 1,3-migrations are inferred.4c In recent work Abstract published in Advance ACS Abstracts, November 1, 1995.
(1)(a) Tilley, T. D. In The Chemistry oforganic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989; Chapter 24, p 1415. (b) Tilley, T. D. In The Silicon-Heteroatom Bond; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1991; Chapters 9 and 10, pp 245 and 309. (ci Pannell, K. H.; Sharma, H. K. Chem. Reu. 1995,95, 1351. (2) (a) Curtis, M. D.; Epstein, P. S. Adu. Organomet. Chem. 1981, 19, 213. (b) Kobayashi, T.: Hayahi, T.; Yamashita, H.; Tanaka, M. Chem. Lett. 1988, 1411. (c) Okinoshima, H.; Yamamota, K.; Kumada, M. J . Organomet. Chem. 1971,27, C31. (3) Tilley, T. D. Comments Inorg. Chem. 1990, I O , 37. (4) (a) Pannell, K. H.; Cervantes, J.; Hernandez, C.; Cassias, J.; Vincenti, S. Organometallics 1986,5, 1056. (b) Pannell, K. H.; Rozell, J. M., Jr.; Hernandez, C. J . Am. Chem. SOC.1989, 111, 4482. (c) Pannell, K. H.: Wang, L.-J.: Rozell, J . M. Organometallics 1989,8,550. (d) Jones, K. L.; Pannell, K. H. J . Am. Chem. SOC.1993, 115, 11336. (e)Hernandez, C.; Sharma, H. K.; Pannell, K. H. J . Organomet. Chem. 1993, 462, 259. (D Pannell, K. H.; Brun, M.-C.: Sharma, H.; Jones, K.: Sharma, S. Organometallics 1994, 13, 1075. (g)Tobita, H.: Ueno, K.; Ogino, H. Bull. Chem. Soc. Jpn. 1988, 61, 2797. (h) Ueno, K.; Tobita, H.; Ogino, H. Chem. Lett. 1990, 369. (1) Haynes, A,: George, M. W.; Haward, M. T.; Poliakoff, M.; Turner, J. J.;Boag, N. M.; Green, M. J . A m . Chem. SOC.1991,113,2011. Pannell, K. H.; Sharma, H. Organometallics 1991,10,954. (k) Ueno, K.; Hamashima, N.; Shimoi, M.; Ogino, H. Organometallics 1991, 10, 959.
Q276-7333/95/2314-5472$Q9.QQlQ
PMe,
\ Me Me
(2)
1
single resonance at 1.16 ppm is assigned to the fluxional PMe3 ligands.I0 The SiMe groups give rise to resonances a t 0.73, 0.44, and 0.36 ppm, in a relative intensity ratio of 2:6:1. The 29Si{1H}NMRspectrum contains resonances a t 6 -80.7, -11.9, and -4.9, which may be attributed to the p, y , and a silicon atoms, respectively, on the basis of relative intensities and published chemical shift data.lJ’ Compound 1 decomposes to several uncharacterized products (by NMR spectroscopy), but the appearance of a resonance in the hydride region (6 -9.63) suggests that a major decomposition pathway involves metalation of the silyl ligand. The analogous reaction of “(Me3P)3IrCl”,generated in THF by addition of PMe3 to [(COE)2IrC112 (COE = (5) Pestana, D. C.; Koloski, T. S.; Berry, D. H. Organometallics 1994, -I.?. - , 4173. -~ -
(6) Campion, B. K.; Heyn, R. H.; Tilley, T. D. J . Am. Chem. SOC. 1988, 110, 7558. (7) Gutekunst, G.; Brook, A. G. J . Organomet. Chem. 1982,225, 1. ( 8 )Jones, R. A.; Real, F. R.; Wilkinson, G.; Galas, A. M. R.; Hursthouse, M. B.; Malik, K. M. A. J . Chem. Soc., Dalton Trans. 1980, 511
0 1995 American Chemical Society
Organometallics, Vol. 14, No. 12, 1995 5473
Communications
Scheme 1
PMe,
2a
2b
cyclooctene),12also gave a deep red solution; however, the color dissipated over a period of 3 h. Workup of the solution produced colorless crystals from pentane, which were subsequently characterized as a mixture of diastereomers 2a,b (Scheme l). The observed ratio of diastereomers in isolated material is variable but generally close to 1:l. Crystals of 2a contain enantiomeric pairs related by a crystallographic inversion center (Figure 1). The substitution pattern about Ir is the same as that observed previously for (Me3P)3Ir(C6&)SiPh2(H), which forms via orthometalation of (Me3P)3IrSiPh3.13 The hydride ligand was located and refined at a distance of 1.74(3) from Ir, and the Ir-Si bond length of 2.441(3) is quite n0rmal.l This silairidacycle is strongly folded, such that the angle between the C(8l)-Ir-Si( 1)and the C(Sl)-Si(3)-Si(2)-Si(l) planes is 124.7'. A likely mechanism for the formation of 2, shown in Scheme 1, involves rearrangement of an initially formed (9) Selected data are as follows. 1: 'H NMR (benzene&, 400 MHz) d 0.36 (s, 3H), 0.44 (s, 18 HI, 0.73 (5, 6 H), 1.16 (s, 27 HI; l3C{IH} NMR (benzene-ds, 100.6 MHz) 8 -6.20 (s, P-SiMe), 1.86 (s, y-SiMe), 9.92 (s, a-SiMe), 22.88 (m, PMe3); 31P{1H}NMR (benzene-&, 162.0 MHz) d 20.00 (d, l J p p = 145 Hz); =Si{lH} NMR (benzeneds, 59.63 MHz) b -80.7 (s, p-Si), -11.9 (s,psi!,-4.9 (s, a-Si). 2 (more stable diastereomer): 'H NMR (benzene-&, 300 MHz) 8 -12.46 (dt, 2 J ~ p= 136 Hz, 17.6 Hz, 1 H), -0.25 (m, 1 HI, -0.01 (m, 1 H), 0.42 ( 8 , 3 H), p 3 Hz), 0.86 cd, 0.49 (s,3 H) 0.51 (5, 9 H) 0.70 (s, 3 HI, 0.77 (d, 4 J ~ = 4 J ~= p 3 Hz), 1.06 (d, 2 J ~ = p 7.2 Hz), 1.09 (d, 2 J ~ = p 7.2 Hz), 1.25 (d, 2 J ~= p 7.8 Hz); 3P{1H}NMR (benzene-ds, 121.5 MHz) d -64.22 (dd, 2Jpp = 19.0 Hz, 15.7 Hz), -59.58 (dd, 2Jpp = 14.9 Hz), -57.19 (t). 2 (less stable diastereomer): 1H NMR (benzene-&, 300 MHz) b -13.41 (ddd,2 J ~ = p 140 Hz, 18.2 Hz, 17.0 Hz, 1 HI, -0.24 (m, 1 HI, -0.04 (m, 1 H), 0.45 (s,3 H), 0.46 (s,9 H) 0.58 (s,3 H) 0.63 (s,3 HI, 0.66 (d, 4 J ~ p = 3 Hz), 0.69 (d, 4 J ~ = p 3 Hz), 1.16 (d, 2 J ~ = p 7.4 Hz), 1.20 (d, 2 J ~ = p 7.4 Hz), 1.31 (d, 2 J ~ = p 8.0 Hz);31P{IH}NMR (benzeneds, 121.5 MHz) d -69.30 (dd, 2Jpp = 24.0 Hz, 18.2 Hz), -66.29 (dd, 2Jpp = 16.2 Hz), -65.75 (dd). Anal. (C, HI. 3: 31P{'H} NMR (toluene-&, 162.0 MHz, -83 "C) 0 -20.50 (d, 2Jpp = 30 Hz), -14.5 (t). lH NMR resonances for 3 were largely obscured by those for the product. (10)A similar observation was made for (Me3P13RhSiPh3: Thorn, D. L.; Harlow, R. L. Inorg. Chem. 1990,29, 2017. (11) Williams, E. A. Annu. Rep. NMR Spectrosc. 1983,15, 235. (12) (a) Bleeke, J. R.; Haile, T.; Chiang, M. Y. Organometallics 1991, IO, 19. (b) Herskovitz, T.; Guggenberger, L. J. J . Am. Chem. Soc. 1976, 98, 1615. (13)Aizenberg, M.; Milstein, D. Angew. Chen., Znt. Ed. Engl. 1994, 33, 317. (14)Crystal data for 2a: ClsH~IrPsSi4, fw = 668.1, colorless, triclinic, Pi, a = 10.585(3) A, b = 10.822(3)A, c = 14.692(5) A, a = 83.82(3)",/j = 84.99(3)",y = 77.16(2)",V = 1627.9(9)A3,.Z = 2, p(Mo Ka) = 44.0 cm-1, T = 298 K. Of 4553 empirically absorptioncorrected data (20,,, = 45"),3380 were independent and observed. The H atom bonded to Ir was located and refined. R(F) = 3.76%;R(wF) = 4.01%.
C(72)
Figure 1. Molecular structure of 2a. Selected bond lengths (A) and angles (deg): Ir-Si(1) 2.441(3), Ir-C(81) 2.216(9), Ir-H( 1)1.74(3),Ir-Rl) 2.355(3),Ir-P(2) 2.333(3), Ir-P(3) 2.296(3), Si(1)-Si(2) 2.354(4),Si(2)-Si(3)2.345(4), Si(3)-C(81) 1.852(8);Si(1)-1r-C(81) 79.4(2), Ir-C(81)Si(3) 115.8(5),Ir-Si(WSi(2) 103.3(1), Si(l)-Si(2)-Si(3) 93.9(l), Si(2)-Si(3)-C(81) 103.3(3). silyl complex (MesP)sIrSi(SiMe3)3 (3)to (Me3PMrSiMe2SiMe(SiMe& (4) via 1,2- and 1,3-migration steps and silyl (silylene) intermediates. Intramolecular metalation then produces the observed products 2a,b. Attempts to trap a silylene intermediate with PhCWPhl or [BwNICl failed to change the course of the reaction. Monitoring the reaction a t -80 'C by 31PNMR spectroscopy revealed the formation of an intermediate which exhibited two resonances (6 -20.5 (d) and -14.5 (t), J = 32 Hz, 2:l ratio) consistent with square-planar substitution about Ir. We tentatively assign this spectrum to the Ir(1) silyl complex 3. Variations in the observed ratio of diastereomers 2a,b (depending on reaction conditions) indicate that the distribution of products obtained is kinetically determined. Attempts to equilibrate the mixtures with heating (80 "C in benZene-d6) resulted only in decomposition. Interestingly, isomerization of the diastereomeric mixtures is catalyzed by hydrogen a t room temperature. Under 1atm of hydrogen, a 1.3:l ratio of diastereomers (in benzene-ds solution) is converted to a ratio of 1:9 within 12 h. Longer reaction times under hydrogen or nitrogen do not change this ratio, indicating that it represents the thermodynamic equilibrium. We are not sure which isomer is more stable, but we assume that it is 2a, which has the -SiMe3 group furthest removed from the Ir(H)(PMe& fragment (see Figure 1). A proposed mechanism for isomerization (illustrated for the conversion of 2b to 2a) is shown in Scheme 2. Presumably, 2b is in equilibrium with the Ir(1) silyl complex 4, and thermal isomerization (slow a t room temperature) would be accomplished via rotation about the Si,-Sip bond of 4. Given the relatively rapid effect of hydrogen, we conclude that an open coordination site is made readily available by C-H reductive elimination to form 4. The slow rate of thermal isomerization thus implies that k,t < k-1. Apparently, rotation about this Si-Si bond is facilitated by formation of an intermediate H2 adduct (which was not observed by NMR spectroscopy), for which Si,-Sip bond rotation is competitive with H2 reductive elimination (Scheme 2).
5474
Communications
Organometallics, Vol. 14, No. 12, 1995 Scheme 2
PMe,
PMe,
PMe,
4
2b
I Me.
cyc'omet.
Me.
The silyl group rearrangement reported here (Scheme
11, like the ones observed by Pannell for Cp(C0)zFe complexes, undoubtedly occurs via intramolecular processes. Because conclusive mechanistic data is still lacking in both systems, alternative mechanisms cannot be definitively ruled out. However other pathways, for example ones involving disilene intermediates or SiSi/Si-C oxidative additions of Si(SiMes), derivatives, seem less likely to US.^ Interestingly, the rearrangement of (Me3P)3IrSi(SiMe& to (Me3P)aIrSiMezSiMe-
(SiMe)s represents the elongation of a polysilyl chain, in contrast to what has typically been observed by Pannell.4 In one case, however, Pannell's group has observed the Cp(Ph3P)2RuMe-catalyzed isomerization of MesSi(SiMed3H to a mixture of (Me3Si)sSiH and (MeaSiIaSiMeSiMezH,which probably also occurs via a M-SiMezSiMe(SiMe& intermediate.4f Formation of a metalated, trivalent iridium center may provide some driving force for stabilizing the Ir product, but this is apparently not required for the analogous Rh rearrangement (to 1). Thus, while it is yet to be determined whether this difference has electronic and/or steric origins, the implications is that migrations of this kind might be used to produce linear polysilanes.
Acknowledgment is made to the National Science Foundation for support of this work. Supporting Information Available: Text giving experimental procedures and characterization data for compounds and tables of crystal, data collection, and refinement parameters, atom positional and U parameters, bond distances and angles, and anisotropic displacement parameters (11pages). Ordering information is given on any current masthead page.
OM9506431
