Platinum Complexes with Chelating Acyclic Aminocarbene Ligands Work as Catalysts for Hydrosilylation of Alkynes.

Abstract

This work describes the preparation of a series of platinum–aminocarbene complexes [PtCl{C(N=Ca(C6R2R3R4R5CONb))=N(H)R1}(CNR1)]a–b (8–19, 65–75% isolated yield) via the reaction of cis-[PtCl2(CNR1)2] (R1 = Cy 1, t-Bu 2, Xyl 3, 2-Cl-6-MeC6H34) with 3-iminoisoindolin-1-ones HN=Ca(C6R2R3R4R5CONbH) (R2–R5 = H 5; R3 = Me, R2, R4, R5 = H 6; R3, R4 = Cl, R2, R5 = H 7). New complexes 17–19 were characterized by elemental analyses (C, H, N), ESI+-MS, Fourier transform infrared spectroscopy (FT-IR), one-dimensional (1H, 13C{1H}), and two-dimensional (1H,1H correlation spectroscopy (COSY), 1H,13C heteronuclear multiple quantum correlation (HMQC)/1H,13C heteronuclear single quantum coherence (HSQC), 1H,13C heteronuclear multiple bond correlation (HMBC)) NMR spectroscopy, and authenticity of known species 8–16 was confirmed by FT-IR and 1H and 13C{1H} NMR. Complexes 8–19 were assessed as catalysts for hydrosilylation of terminal alkynes with hydrosilanes to give vinyl silanes, and complex [PtCl{C(N=Ca(C6H3(5-Me)CONb))=N(H)(2-Cl-6-MeC6H3)}{CN(2-Cl-6-MeC6H3)}]a−b (18) showed the highest catalytic activity. The catalytic system proposed operates at 80–100 °C for 4–6 h in toluene and with catalyst loading of 0.1 mol %, enabling the reaction of a number of terminal alkynes (PhC≡CH, t-BuC≡CH, and 4-(t-Bu)C6H4C≡CH) with hydrosilanes (Et3SiH, Pr3SiH, i-Pr3SiH, and PhMe2SiH). Target vinyl silanes were prepared in 48–95% yields (as a mixture of α/β isomers) and with maximum turnover number of 8.4 × 103. Hydrosilylation of internal alkynes (PhC≡CPh, Me(CH2)2C≡C(CH2)2Me, and PhC≡CMe) with hydrosilanes (Et3SiH, PhMe2SiH) led to the corresponding trisubstituted silylated alkenes in 86–94% yields. Initial observations on the mechanism of the catalytic action of platinum–ADC catalysts 8–19 suggested a molecular catalytic cycle.