| Abstrakt: |
The reactions of platinum(II) hydrides, trans-PtHXL2, where X = NO3, Cl or CH3OH, and L = PEt3or tricyclohexylphosphine, with disubstituted acetylenes, R1C≡CR2have been examined under a variety of conditions. From spectroscopic parameters, the gross geometry at platinum as well as the geometry of the resulting alkenyl groups in the products have been determined. The observation that all alkenyl groups have a cisgeometry is consistent with a migratory insertion step involving a four-centred transition state, in which the disposition of the acetylene relative to the Pt—H bond appears to be dependent on the Pt—H bond polarity. Evidence is presented to demonstrate that this polarity depends on several factors including solvent, and ligands on Pt(II). For L = tricyclohexylphosphine, the occurrence of a side reaction which competes with insertion and which leads to a Pt(0) acetylene complex is also demonstrated, and other interesting reactions are described. |
