[Pt(η 2 -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(η 2 -alkene)(η 2 -norbornene) 2 ]. X-ray crystal structures of [Pt(η 2 -maleic anhydride)-(η 2 -norbornene) 2 ] and [Pt(η 2 -diphenyl fumarate)(η 2 -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(η 2 -maleic anhydride)(η 2 -norbornene)(σ-N-pyridine)]. Whereas in the case of [Pt(η 2 -norbornene) 3 ] no coordination of pyridine is observed, the complex [Pt(σ-N-pyridine) 2 (η 2 -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.

Dimethyl fumarate, C 6 H 8 O 4 , crystallizes in the fully stretched planar conformation. The molecule is located on a crystallographic inversion centre and has local symmetry 2/m. The fumarate molecules aggregate in layers coinciding with the (111) lattice planes. Comment Dimethyl fumarate, (I), is frequently used as a coordinating ligand. The January 2004 update of the Cambridge Structural Database (CSD; Allen, 2002) contains 62 crystal structures of compounds with dimethyl fumarate acting as a ligand coordinated to a metal atom, mostly Ru and Pt. Knaggs & Lonsdale (1942) reported the unit-cell parameters of the crystal structure of the isolated molecule. Up until now, the full crystal structure determination of this compound has not been reported. The only other diester of fumaric acid reported in the CSD is diphenyl fumarate (Albano et al., 2003).