SYNTHESIS OF O-CO-ORDINATED PLATINUM(II) COMPLEXES OF CARBONYL-STABILIZED ARSONIUM YLIDES AND THE MECHANISM OF CONVERSION TO THEIR C-CO-ORDINATED ISOMERS

The reaction of [{PtCl(dppe)}2][BF4], [dppe=1,2-bis(diphenylphosphino)ethane] with ylides Ph3AsCHCOR (R = Me, Ph or OMe) led to novel platinum(II) complexes [PtCl(dppe){OC(R)CH(AsPh3)}]BF4 (R = Me 1, Ph 2 or OMe 3) in which the carbonyl stabilized arsonium ylides are co-ordinated to the metal centre via the oxygen carbonyl atom. These derivatives are not stable in chlorinated solvents and slowly undergo isomerization to their C-co-ordinated analogues 4-6 following a first-order rate law. The mechanism proposed for this rearrangement implies both intramolecular and free-ylide promoted intermolecular paths with k(obs) values of the whole process depending on the basicity of the ylide.