Unprecedented chemical transformation of benzaldehyde semicarbazone mediated by osmium

para-Nitrobenzaldehyde semicarbazone (O2N(para)-C6H4C(H)=N-NH-CO-NH2) undergoes unprecedented chemical transformation during its reaction with [Os(Pph3)(2)(CO)(2)(HCOO)(2)] in different alcoholic (R'OH, R' = CH2CH2OCH3, CH2CH3, CH2CH2CH3, and CH2CH2CH2CH3) solvents whereby the NH2 group of the semicarbazone ligand is displaced by a OR' group provided by the solvents. The transformed semicarbazone ligand binds to osmium as a bidentate N,O-donor forming five-membered chelate ring to afford complexes of type [Os(PPh3)(2)(CO)(H)(L-OR')], where L-OR' refers to the transformed semicarbazone ligand. Structure of the [Os(PPh3)(2)(CO)(H)(L-OCH2CH2OCH3)] complex has been determined by X-ray crystallography. All the [Os(PPh3)(2)(CO)(H)(L-OR')] complexes are diamagnetic and show characteristic H-1 NMR signals. They also show intense absorptions in the visible and ultraviolet region. Cyclic voltammetry on the complexes shows an irreversible oxidative response within 0.69-0.88 V versus SCE.