Platina-β-diketones as catalysts for hydrosilylation and their reactivity towards hydrosilanes

The platina-β-diketones [Pt2{(COMe)2H}2(μ-Cl)2] (1), [PPh4][Pt{(COMe)2H}Cl2] (2) and [Pt{(COMe)2H}-(acac)] (3) were found to catalyze the hydrosilylation of alkynes (hex-1-yne, hex-2-yne, hex-3-yne) and alkenes (hex-1-ene, styrene, trimethylvinylsilane) with methyldiphenylsilane (nsilane:nsubstrate:nPt = 3000:3000:1, T = 27 °C, in C6D6). The comparison with the well-established catalysts from Speier (4) and Karstedt (5) exhibited up to twice as high activities for catalyst 1 and comparable regioselectivities. To get insight into the mechanism of the hydrosilylation, Si–H oxidative addition reactions towards the dinuclear platina-β-diketone 1 have been explored. Reactions of 1 with 2-picolyl substituted hydrosilanes of the type NSiMe2H and NSiMeHN resulted in decomposition with the formation of platinum black, only. On the other hand, the analogous reaction with the 8-quinolyl substituted silane of the type NSiMeHN was found to proceed under loss of H2 with the formation of a diacetyl(silyl)platinum(IV) complex [Pt(COMe)2Cl(NSiMeN-κ2N,N′,κSi)] (23). DFT calculations gave insight into the reason for this different reactivity and into the course of reaction. For comparison, the reaction of 1 with bis(2-picolyl)amine was performed resulting under proton shift in the sense of an oxidative addition reaction in the formation of the diacetyl(hydrido)platinum(IV) complex [Pt(COMe)2Cl(NNHN-κ3N,N′,N′′)] (25). The complexes 23 and 25 were fully characterized spectroscopically (1H, 13C, 195Pt, 29Si NMR, IR) and by single-crystal X-ray structure determinations.

Platina-β-diketones were found to catalyze the hydrosilylation of alkynes and alkenes such as hexynes, hex-1-ene, styrene and trimethylvinylsilane showing up to twice as high activities in comparison with the well-established catalysts from Speier and Karstedt. To get insight into the mechanism of the hydrosilylation, Si–H oxidative addition reactions towards the dinuclear platina-β-diketone [Pt2{(COMe)2H}2(μ-Cl)2] have been explored resulting with an 8-quinolyl substituted silane under loss of H2 in the formation of a diacetyl(silyl)platinum(IV) complex [Pt(COMe)2Cl-(NSiMeN-κ2N,N′,κSi)].Figure optionsDownload as PowerPoint slideFigure optionsDownload as PowerPoint slideFigure optionsDownload as PowerPoint slide