SPECTROELECTROCHEMISTRY OF AROMATIC LIGANDS AND THEIR DERIVATIVES .3. BINUCLEAR TRANSITION-METAL COMPLEXES OF CU(I), MO(0), AND RE(I) WITH 2,2'-BIPYRIMIDINE

The binuclear complexes [Mo(CO)4]2(bpym) (I), [Re(CO)3Cl]2(bpym) (II), and [[Cu(PPh3)2]2(bpym)]2+ (III) were subjected to one- and (for I, III) two-electron reduction, and the products studied in situ by UV-Vis-NIR spectroscopy. The spectra were assigned in terms of a simple Huckel molecular orbital scheme, in which the reduction orbital is ligand pi-(7), related to pi-(7) of biphenyl, the transition pi-(6) --> pi-(7) moves to lower energy on successive reduction, and bands observed in the near IR-visible region are due to transitions from pi-(7) to higher unoccupied orbitals. Detailed assignments are directly related to those of other singly and doubly reduced azabiphenyls; the bpym dianion has been characterized for the first time.