Farther study on the reactivity of cationic dinuclear platinum trihydrido compounds with unsaturated hydrocarbons: Synthesis of μ-hydrido μ-alkylidene complexes, NMR characterization and mechanism insights

The reactivity of a series of well definite dinuclear platinum complexes [Pt2(L-L)2(H)3][X] ( L-L = dppe, X = BF4, 1a; L-L = dppp, X = BF4, 1b; L-L = dppb, X = BF4, 1c; L-L = dpase, X = BF4, 1d; L-L = dcype, X = Cl, 1e) with unsaturated hydrocarbons is investigated. Compounds 1a, 1c and 1e react with phenylacetylene under mild experimental conditions affording the corresponding μ-hydrido μ-alkylidene complexes [(L-L)Pt(µ-H,µ-CHCH2Ph)][X] 2a, 2c and 2e, independently of the steric and electronic properties of the chelating ligand. Otherwise, the reaction of trihydrides1 with olefins is more sensitive to the ancillary ligand. However, the new compounds [(dpase)2Pt2(µ-H,µ-CHCH2Ph)][BF4], 2d, and [(dppp)2Pt2(µ-H,µ-CHCH3)][BF4], 3b, are obtained in satisfactory yields by reaction of 1d and 1b with styrene and ethylene, respectively. Compound 1e reacts only in the presence of a very large excess of styrene, and it gives a complex mixture of platinum compounds containing 2e and high molecular weight polystyrene as main product. Complexes 2 and 3 are discussed on the basis of multinuclear NMR spectra in solution. 1H and 31P{1H} NMR data show that compound 2d can exist in three different forms with different cis- trans- disposition of phosphorous and arsenic atoms in respect of the bridging ligands. Possible mechanisms for the formation of compounds 2 from the reactions with phenylacetylene or styrene are discussed on the ground of experiments with deuterium labelled reagents.