Synthesis and Crystal Structures of Zerovalent Platinum η²-Fumarate Bis(norbornene) Complexes and Their Application as Hydrosilylation Catalysts

[Pt(η2-norbornene)3] reacts with a series of electron-poor alkenes, such as dimethyl maleate, maleic anhydride, several fumarates, and fumaric acid, to give platinum complexes of the type [Pt(η2-alkene)(η2-norbornene)2]. X-ray crystal structures of [Pt(η2-maleic anhydride)(η2-norbornene)2] and [Pt(η2-diphenyl fumarate)(η2-norbornene)2] have been obtained. Using di-tert-butylfumaramide and diethyl dithiofumarate does not yield pure complexes. Addition of an excess of pyridine to [Pt(maleic anhydride)(norbornene)2] yields the complex [Pt(η2-maleic anhydride)(η2-norbornene)(σ-N-pyridine)]. Whereas in the case of [Pt(η2-norbornene)3] no coordination of pyridine is observed, the complex [Pt(σ-N-pyridine)2(η2-tetracyanoethylene)] is readily obtained by the addition of 1 equiv of tetracyanoethylene concomitant with or immediately after the addition of pyridine. The complexes have been employed as precatalysts in the hydrosilylation of styrene by triethylsilane. The maleate and fumarate complexes are the most stable catalysts, and the various fumarate complexes do not exhibit significant differences in their catalytic behavior.