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 1H 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.