Exclusive C−Si Bond Formation upon Reaction of a Platinum(II) Alkyl with Silanes

Abstract

An unusual, highly selective C−Si coupling reaction takes place upon treating the platinum(II) alkyl complex cis-(DIPPIDH)(DIPPID)PtMe (2) (DIPPIDH = α2-(diisopropylphosphino)isodurene, 1) with HSiR3 (R3 = Et3, EtMe2, Me2Ph), leading to formation of MeSiR3 and the hydrido complex trans-(DIPPIDH)(DIPPID)PtH (5). The overall process involves activation of a Si−H bond, reverse-cyclometalation of the phosphine ligand DIPPIDH (1), and C−Si elimination. The resulting thermally stable platinum(II) hydride complex 5 was independently prepared by thermolysis of a platinum(II) dihydride, trans-(DIPPIDH)2PtH2 (6), which was obtained by reaction of 2 with H2. In the absence of silane, the cis complex 2 isomerizes thermally to trans-(DIPPIDH)(DIPPID)PtMe (3), which does not react productively with silanes. Our results indicate that opening of the metallacycle of 2 by benzylic C−H formation is kinetically preferred over formation of CH4 or CH3SiR3.

σ‐Silane Platinum(II) Complexes as Intermediates in C−Si Bond‐Coupling Processes

“…The reactions presented above are processes that take place under very mild conditions, in contrast to previous observations concerning related Pt II complexes (usually requiring heating to induce the C−Si bond‐coupling process) . Presumably, the vacant site in the platinum‐NHC systems reduces the energy barrier for the coupling process (dissociation of one of the ligands is generally a prerequisite for coupling processes).…”

“…For example, Milstein et al. reported that addition of silanes to platinum(II) methyl complexes can lead to methane and a platinum‐silyl derivative, or to C−Si reductive coupling species and a Pt−H complex, or mixtures containing all of the possible coupling products . The effect of the electronic nature of the substituents on the silane has been investigated in iridium systems and found to be a key factor in directing the reactivity towards C−H or C−Si bonds, with electron‐withdrawing substituents favoring the former…”

Carbon−Carbon vs Carbon−Hydrogen Bond Activation by Ruthenium(II) and Platinum(II) in Solution

“…No C−C bond activation took place and no intermediates were observed under these conditions. As is well documented, cyclometalation can be a highly reversible process. ,,− A rare case of catalytic benzylic C−H bond activation involving a Ru(II)/Ru(0) mechanism was reported. , …”

“…A lower yield (∼50%) of 8 is obtained with (MeCN) 2 PtCl 2 and 1 in CH 2 Cl 2 . Activation of benzylic C−H bonds by Pt(II) has been reported. ,,, Displacement of COD from (COD)PtCl 2 by the analogue of 1 in THF at room temperature results in the quantitative formation of a compound with two coordinated phosphines to one metal center Pt(Cl 2 ){1,3,5-(CH 3 ) 3 -2,6-(Ph 2 PCH 2 ) 2 C 6 H} . Such a species is likely to be an intermediate in the reaction of 1 as well.…”

Transition Metal Silyl Complexes. 60.,1 Enhanced Reactivity of a Platinum Dimethyl Complex toward Trimethoxysilane Due to a P,N-Chelating Co Ligand

“…A C 6 D 6 solution of [(κ 2 -P,N)-Me 2 NCH 2 CH 2 PPh 2 ]PtMe 2 ( 1 ), synthesized from (nbd)Pt(CH 3 ) 2 (nbd = 2,5-norbornadiene) and 2-(diphenylphosphino)ethyldimethylamine (eq 1), was reacted with 3.5 equiv of trimethoxysilane at room temperature in an NMR tube. The tube was equipped with a poly(tetrafluoroethylene) (PTFE) liner to exclude the possibility of metal-catalyzed reactions of the silane with adsorbed water or Si−OH groups of the glass surface …”