Osmium complexes amides

Photoinduced and chemical oxidation of coordinated imines to amides in isomeric osmium(II) complexes of AT-arylpyridine-2-carboxaldimines has been studied by Ghosh and coworkers [34]. The complexes [Os(Br)2(Rimpy)2] (Scheme 1) were prepared and characterized structurally, indicating the pyridines of the two Rimpy ligands are trans to one another and the bromides are cis. Broadband photolysis of the complex in aerated acetonitrile resulted in oxidation of one Rimpy ligand to yield the RimOpy ligand and oxidation of the osmium to Os(III). The overall yield of the photochemical process is reported to be greater than 95%. The authors propose a mech-... 

An osmium(VI) nitrido complex with tetraanionic chelating amide ligand was prepared by the reaction of [Os(T 4-HBA-B)(PPh3)2] with phenyl azide in benzene at room temperature. The X-ray structure of [Osvi(N)(t)4-HBA-B)]- revealed a square-pyramidal structure with a measured Os=N distance of 1.64(1) A (282). 

Insertion of carbodiimides into Zr-C bonds is also observed. Zinc bis-amides insert only one equivalent of carbodiimide to give zinc guanidate complexes Ruthenium, osmium and iridium hydrides insert Ai,AI -(ji.p.tolylcarbodiitnide into their metal-hydrogen bonds to giveiV,Ai -p-tolylformamidinato derivatives . 

In subsequent studies, Esteruelas et at disclosed the synthesis of another cationic complex, [(IPr)Os(OH)(p-cymene)][OTf] 52, which was an efficient pre-catalyst for transfer hydrogenation of aldehydes with isopropanol, for hydration of nitriles into amides, and for a-alkylation of arylacetonitriles and methyl ketones with alcohols (Scheme 7.10). All these transformations were assumed to involve cationic hydrido intermediates formed by hydrogen transfer from one of the substrates to the osmium active species. 

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