Studies of ligand additions to coordinatively unsaturated dirhenium complexes containing the bulky PBu3t ligand

Five new complexes were obtained from the reaction of Re-3(CO)(12)(mu-H)(3) with PBu3t. These are Re-2(CO)(8)(mu-PBu2t)(mu-H), 1, Re-2(CO)(7)(mu-PBu2t)((PBu2H)-H-t)(mu-H), 2, HRe(CO)(4)(PBu3t), 3, Re-2(CO)(6)(PBu3t)(mu-PBu2t)(mu-H), 4, and Re-2(CO)(5)(PBu3t)((PBu2H)-H-t)(mu-(PBu2O)-O-t)(mu-H), 5. Compounds 4 and 5 are electronically unsaturated by the amount of two electrons; namely, one of the metal atoms has an 18-electron configuration and the other metal atom has a 16-electron configuration. Compound 4 adds CO and the nitriles MeCN and PhCN, reversibly, to form the electronically saturated 1:1 adducts Re-2(CO)(7)(PBu3t)(mu-PBu2t)(mu-H), 6, Re-2(CO)(6)(NCMe)(PBu3t)(mu-PBu2t)(mu-H), 7, and Re-2(CO)(6)(NCPh)(PBu3t)(mu-PBu2t)(mu-H), 8, respectively. (CO)-C-13 labeling studies have shown that the CO ligand that is added to 4 to form 6 is added at the electronically saturated metal atom and one of the originally coordinated CO ligands is shifted to the unsaturated metal atom. Compound 5 also adds 1 equiv of CO to form the complex Re-2(CO)(6)(PBu3t)((PBu2H)-H-t)(mu-(PBu2O)-O-t)(mu-H), 9.(CO)-C-13 labeling studies have shown that the added CO ligand was added to the unsaturated metal atom in this case. All of the new compounds were characterized structurally by single-crystal X-ray diffraction analyses.