Rhodium complexes of 3,5-di-terl-butylcatechol synthesis, structure and, spectral and electrochemical properties

Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata-700 032, India

E-mail : samaresh_b@hotmail.com

Manuscript received online 11 April 2012, revised 23 April 2012, accepted 23 April 2012

Reaction of [Rh(PPh₃)₃CI] with 3,5-di-tert-butylcatechol (H₂DBC) in dry benzene affords a bis-semiquinonato rhodium(III) complex, [Rh(PPh₃)(DBSQ)₂CI]. A similar reaction of [Rh(PPh₃)₃CI] with a mixture of H₂DBC and quinolin8-ol (Hq) in 1 : 1 : 1 mole ratio affords a mixed-his complex of rhodium(III), [Rh(PPh₃)(DBSQ)(q)CI]. Formation of complexes [Rh(PPh₃)(DBSQ)₂CI] and [Rh(PPh₃)(DBSQ)(q)CI] is believed to proceed through the intermediacy of a reactive hydrido complex, generated in the initial step via oxidative insertion of rhodium into the acidic O-H fragment of the ligand. Reaction of H₂DBC with RhCI₃.3H₂0 in ethanol yields a tris-semiquinonato complex of rhodium(III), [Rh(DBSQ)₃]. Formation of this [Rh(DBSQ)₃] complex proceeds through simple displacement reaction. Structures of all the three complexes have been determined by X-ray crystallography. The [Rh(PPh₃)(DBSQ)₂CI] complex is diamagnetic and shows characteristic ¹H NMR spectrum, while complexes [Rh(PPh₃)(DBSQ)(q)CI] and [Rh(DBSQ)₃] are one-electron paramagnetic, and show sharp ESR signal with g ~2.0. All the complexes show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry on all the three complexes shows an oxidation on the positive side of SCE and a reduction on the negative side, both of which are irreversible and ligand (DBSQ/q)-based.