Unprecedented chemical transformation of benzaldehyde semicarbazone mediated by osmium

Abstract

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.