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

This work describes the preparation of a series of platinum-aminocarbene complexes [PtCl{C(N=C (C₆R²R³R⁴R⁵CON ))=N(H)R¹}(CNR¹)] (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-MeC₆H₃ 4) with 3-iminoisoindolin-1-ones HN=C (C₆R²R³R⁴R⁵CON H) (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=C (C₆H₃(5-Me)CON ))=N(H)(2-Cl-6-MeC₆H₃)}{CN(2-Cl-6-MeC₆H₃)}] (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.