The unusual ring scission of a quinoxaline-pyran-fused dithiolene system related to molybdopterin.

The reduction of the dithiolene ligand, qpdt2-, a mimic of the biological molybdopterin cofactor, and the corresponding (η5-cyclopentadienyl)cobalt(iii) complex [(qpdt)CoIIICp] was studied. It was found that in both cases an unprecedented ring scission reaction took place in acidic medium. All new reaction products have been spectroscopically and structurally characterized. Plausible mechanisms for the formation of these products were also proposed.