Experimental and theoretical studies on the platinum-mediated selective C(sp)-Si bond cleavage of alkynylsilanes

A series of cis-alkynyl(silyl)platinum(II) complexes was prepared via the chemoselective C(sp)-Si bond cleavage of alkynylsilanes by a platinum(0) complex ligated with the P-N hemilabile bidentate ligand. The coordination of the triple bond to the platinum center triggers selective C(sp)-Si bond cleavage. Hammett plots of the ³¹P{¹H} NMR spectroscopic properties (δ and J values) reflect an electronic effect on platinum(II) complexes; trans substituents of arylethynyl groups are influenced, but cis-positioned silyl groups are not affected, as evidenced by ²⁹Si{¹H} NMR. In comparison, Hammett plots show that C(sp)-Si bond cleavage rates are accelerated by electron-rich alkynylsilanes, which is opposite to the ordinary oxidative addition of aryl halides to transition metals often observed in catalytic cross-coupling reactions. A DFT calculation reveals that intermediates and transition states are stabilized by electron-rich alkynylsilanes and that the five-membered hemilabile P-N ligand is essential, in which a reactive electron-deficient 14-electron platinum(0) species is produced via the dissociation of nitrogen, giving rise to a monodentate phosphine coordination. Electron-rich alkynylsilanes allow decreased π back-donation from the platinum center to the ligand, accelerating the dissociation of the more labile nitrogen. Steric congestion between diisopropylphosphino and silyl groups thermodynamically disfavors C(sp)-Si bond cleavage.