Organometallic complexes of the platinum metals: Synthesis, structure, and catalytic applications

Reaction of a group of N-(aryl)picolinamides (pic-R) with [Ru(PPh3)2(CO)2Cl2] in refluxing 2-methoxyethanol in the presence of a base affords hydrido complexes of two types (1-R and 2-R), which are geometric isomers. Similar reaction with N-(naphthyl)picolinamide (pic-nap) yields an organoruthenium complex (3) via formation of a hydrido intermediate. Reaction of 2-(arylazo)phenols (ap-R) with [Ir(PPh3)3Cl] in refluxing ethanol affords a mono-hydrido intermediate (4-R), a di-hydrido intermediate (5-R) and an organoiridium complex (6-R) as the final product, where the azo-ligand is coordinated as CNO-donor. Reaction of ap-R ligands with [Rh(PPh3)3Cl] yields organorhodium complexes (7-R) analogous to 6-R, but without any hydrido intermediate. N-(2′-hydroxyphenyl)benzaldimines (hpbz-R) react with [Rh(PPh3)3Cl] to yield a group of organorhodium complexes (8-R), where the hpbz-R ligands are coordinated in CNO-fashion. Upon interaction with [Ir(PPh3)3Cl] 2-(2′,6′-dimethylphenylazo)-4-methylphenol (dmap) undergoes a methyl C–H activation and affords organoiridium complex 9, while 2-(2′-methylphenylazo)-4-methylphenol (mmap) undergoes a phenyl C–H activation and gives organoiridium complex 10. Reaction of benzaldehyde thiosemicarbazones (bztsc-R) with [Pd(PPh3)2Cl2], carried out with the expectation of inducing CNS-mode of coordination, actually has yielded complexes (11-R) where the bztsc-R is coordinated in an uncommon NS-mode forming a five-membered chelate ring associated with a restricted rotation around the imine (C=N) bond. These palladium complexes are found to catalyse C–C cross coupling reactions very efficiently. Crystal structures of selected complexes of each type have been determined by X-ray crystallography.