SYNTHESIS AND MOLECULAR-STRUCTURE OF TETRARUTHENIUM CLUSTER ISOMERS WITH DIFFERENT ELECTRON COUNTS

The two novel cluster species Ru-4(CO)(12)(mu(4)-eta(2)-C8H10) (1) and Ru-4(CO)(12)(mu(4)-eta(2):eta(2)-C8H10) (2) have been isolated from t he thermolysis of RU(3)(CO)(12) in octane in the presence of cycloocta -1,3-diene. The two clusters are isomers of formula Ru-4(CO)(12)(C8H10 ), differing only in the overall electron donation from the C8H10 liga nd to the cluster. Clusters 1 and 2 possess 60 and 62 electrons, respe ctively, and both are based on a butterfly framework of metal atoms, a s shown by single-crystal X-ray diffraction experiments. The bonding i nteraction between the ligand and the cluster as well as the effect of the extra pair of electrons in 2 with respect to 1 has been investiga ted by extended Huckel molecular orbital calculations.