Structure and reactivity of palladium and platinum arylazooximates

Abstract

The structure and selected reactions of the title compounds are reviewed. Some highlights are as follows (L = conjugate base of phenylazoacetaldoxime). While PtL₂ exist in cis and trans forms, PdL₂ occurs only in thetrans form. In the crystalline state cis-PtL₂ consists of weakly held dimers (Pt. Pt 3.151 Å) buttrans-PtL₂ consists of stacks of discrete molecules in the solid state.Trans- PdL₂ displays a surprisingly large tetrahedral distorsion. The different metal-ligand bonds undergo selective cleavage by different reagents. Thus HCl and tertiary phosphines respectively cleave the M-N (oxime) and M-N (azo) bonds. Phosphine cleavage leads to interesting situations such as cone angle-dependent equilibria and fluxional behaviour. A rich redox chemistry consisting of successive reductions of the azo groups and of the metal are revealed electrochemically.Cis-PtL₂ unliketrans- PtL₂ undergoes a facile one-electron oxidation at low potentials. Another very curious reaction of cis-PtL₂ is the process in which an aromatic ring is thermally hydroxylated at the expense of an oximato oxygen atom. The meaning and significance of the observations are discussed.