Reactions of Phenylhydrosilanes with Pincer-Nickel Complexes: Evidence for New Si-O and Si-C Bond Formation Pathways

摘要

This contribution presents evidence for new pathways manifested in the reactions of the phenylhydrosilanes Ph_nSiH_(4-n) with the pincer complexes (POC_(sp~2)OP)Ni(OSiMe_3), 1-OSiMe_3, and (POC_(sp~3)OP)Ni(OSiMe_3), 2-OSiMe_3 (POC_(sp~2)OP = 2,6-(i-Pr_2PO)_2C_6H_3; POC_(sp~3)OP = (i-Pr_2POCH_2)_2CH). Excess PhSiH_3 or Ph_2SiH_2 reacted with 1-OSiMe_3 to eliminate the disilyl ethers Ph_nH_(3-n)SiOSiMe_3 (n = 1 or 2) and generate the nickel hydride species 1-H. Subsequent reaction of the latter with more substrate formed corresponding nickel silyl species 1-SiPhH_2 or 1-SiPh_2H and generated multiple Si-containing products, including disilanes and redistribution products. The reaction of 1-OSiMe_3 with excess Ph_2SiH_2/Ph_2SiD_2 revealed a net KIE of ca. 1.3-1.4 at room temperature. Treating 1-OSiMe_3 with excess Ph_3SiH also gave 1-H and the corresponding disilyl ether Ph_3SiOSiMe_3, but this reaction also generated the new siloxide 1-OSiPh_3 apparently via an unconventional σ-bond metathesis pathway in which the Ni center is not involved directly. The reaction of excess PhSiH_3 and 2-OSiMe_3 gave polysilanes of varying solubilities and molecular weights; NMR investigations showed that these polymers arise from Ni(0) species generated in situ from the reductive elimination of the highly reactive hydride intermediate, 2-H. The stoichiometric reactions of 2-OSiMe_3 with Ph_2SiH_2 and Ph_3SiH gave, respectively, siloxides 2-OSiPh_2(OSiMe_3) and 2-OSiPh_3. Together, these results demonstrate the strong influence of pincer backbone and hydrosilane sterics on the different reactivities of 1-OSiMe_3 and 2-OSiMe_3 toward Ph_nSiH_(4-n) (dimerization, polymerization, and redistribution vs formation of new siloxides). The mechanisms of the reactions that lead to the observed Si-O, Si-C, and Si-Si bond formations are discussed in terms of classical and unconventional σ-bond metathesis pathways.