The electrochemical behaviour of electron deficient benzoheterocycle triosmium clusters

The electrochemical behaviour of the electron deficient clusters [Os-3(CO)(9)(mu(3)-eta(2)-(L-H)) (mu-H)] (L = quinoline (1); 3-amino-quinoline (2); 5-amino quinoline (3); 6-methoxy quinoline (4); phenanthridine (5); 5,6-benzoquinoline (6); quinoxaline (7); 2-methyl benzimidazole (8); 2-methyl benzotriazole (9); 2-methyl benzothiazole (10); benzothiazole (11); 2-methyl benzoxazole (12)) is reported. The complexes all exhibit two one-electron electrochemically quasi-reversible reduction processes and in the case of 5 and 6 stable radical anions are formed following a one-electron reduction that is both electrochemically and chemically reversible. The electrochemical behaviour of the electron precise decacarbonyl analogues of 4-12 (4'-12') was also studied in order to gain some insight into changes in the nature of the lowest unoccupied molecular orbital (LUMO) on going from the electron deficient to the electron precise cluster for a given ligand. The observed electrochemical potentials for 1-12 correlate with n to sigma* electronic transitions (excluding 3 and 6) but not with the other absorptions for two series of complexes and the free ligands. The infrared spectroelectrochemistry, and ESR of 5(-) was also studied in an attempt to confirm the stability of these radical anions and to further elucidate their electronic and molecular structure. (C) 2000 Elsevier Science S.A. All rights reserved.