Carbene complexes. Part II. Thermally-induced isomerisations of trans-platinum( II ) and palladium( II ) complexes and the chemistry of the cis- and trans-isomers

trans-Dihalogenoplatinum(II) or palladium(II)(carbene) complexes are isomerised either thermally or in polar solvents to the thermodynamically more stable cis-isomers. Reactivity decreased from PdII to PtII and with increasing n-alkyl chain-length of a tertiary phosphine trans to the carbene ligand. Properties of cis- and trans-carbene complexes are compared and certain generalisations emerge. Dichloro-complexes undergo Cl– displacement (cis- more readily than trans- and PdII more than PtII) by Br–(LiBr), Me–(LiMe), H–(Et3SiH), and PR3(NaBF4/PR3). trans-Hydrido(chloro)platinum(II) and dimethylplatinum(II) carbene complexes are of particular interest.