Organometallic Rhodium(III) and -(I) Complexes with 1,3-Diniethyllumazine(DML). The Crystal Structure of [(η2- (O4,N5)DML)(η5-C5Me5)ClRh](PF6)

The crystal structure determination of the new rhodium(III)-complex [(DML)(C5Me5)ClRh](PF6). DML = 1,3-dimethyllumazine, reveals O4,N5 coordination of the metal to DML with not very different bond lengths of 213.0(2) pm (Rh-N) and 219.2(2) pm (Rh-O). This result stands in contrast to the previously reported structure of a cationic dihydrobiopterin bound to [Mo(O)Cl3]- which exhibited a very unsymmetrical chelate ar­rangement. Chemical and electrochemical two-electron reduction of the Rh(III) complex led to a very labile Rh(I) species (DML)(C5Me5)Rh which is distinguished by an intense charge transfer band in the visible. The results confirm the characterization of DML as a weak σ donor/π acceptor ligand with a rather low-lying π* orbital.