The photodecarboxylation of [N,N-bis(2-pyridylmethyl)amino acidato]phenanthrolinecobalt(III) complexes: – formation and decomposition of metallacyclic species

Abstract

Photolysis of [N,N-bis(2-pyridylmethyl)amino acidato]phenanthrolinecobalt(III) complexes (amino acidato = glycinato (dpg) or alaninato (dpa) or 2-cyclopropylglycinato (dpc)) with UV light led to elimination of carbon dioxide from the amino acidato chelate and the formation of cobalt(III) complexes which contain a Co–C–N metallacycle. These photolysis products were characterised by NMR and UV-vis spectroscopy and, in the case of dpg, by X-ray crystallography. The eventual decomposition reactions of the photolysis products were monitored by NMR spectroscopy in both D₂O and dilute DCl. The decomposition products included bis(2-pyridylmethyl)amine (bpa) and an aldehyde derived from the carbon atom of the metallacycle and its alkyl substituents. A μ-peroxo dinuclear cobalt(III) complex, [(bpa)(phen)(Co(O₂)Co(phen)(bpa)]⁴⁺, was formed from the decomposition products and its structure determined by X-ray crystallography. Experiments with a cyclopropyl derivative demonstrate that any intermediates with a radical centre on what was the α-carbon of the amino acid must be very short-lived.