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{<u>C</u>­(NC^<i>a</i>(C₆R²R³R⁴R⁵CO<u>N</u>^<i>b</i>))N­(H)­R¹}­(CNR¹)]^<i>a–b</i> (<b>8</b>–<b>19</b>, 65–75% isolated yield) via the reaction of <i>cis</i>-[PtCl₂(CNR¹)₂] (R¹ = Cy <b>1</b>, <i>t</i>-Bu <b>2</b>, Xyl <b>3</b>, 2-Cl-6-MeC₆H₃ <b>4</b>) with 3-iminoisoindolin-1-ones HNC^<i>a</i>(C₆R²R³R⁴R⁵CON^<i>b</i>H) (R²–R⁵ = H <b>5</b>; R³ = Me, R², R⁴, R⁵ = H <b>6</b>; R³, R⁴ = Cl, R², R⁵ = H <b>7</b>). New complexes <b>17</b>–<b>19</b> 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 <b>8</b>–<b>16</b> was confirmed by FT-IR and ¹H and ¹³C­{¹H} NMR. Complexes <b>8</b>–<b>19</b> were assessed as catalysts for hydrosilylation of terminal alkynes with hydrosilanes to give vinyl silanes, and complex [PtCl­{<u>C</u>­(NC^<i>a</i>(C₆H₃(5-Me)­CO<u>N</u>^<i>b</i>))N­(H)­(2-Cl-6-MeC₆H₃)}­{CN­(2-Cl-6-MeC₆H₃)}]^{<i>a</i>−<i>b</i>} (<b>18</b>) 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, <i>t</i>-BuCCH, and 4-(<i>t</i>-Bu)­C₆H₄CCH) with hydrosilanes (Et₃SiH, Pr₃SiH, <i>i</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 <b>8</b>–<b>19</b> suggested a molecular catalytic cycle