Studies of ligand additions to coordinatively unsaturated dirhenium complexes containing the bulky PBu₃^t ligand

Five new complexes were obtained from the reaction of Re ₃(CO)₁₂(μ-H)₃ with PBu₃ ^t. These are Re₂(CO)₈(μ-PBu₂ ^t)(μ-H), 1, Re₂(CO)₇(μ-PBu ₂^t)(PBu₂^tH)(μ-H), 2, HRe(CO) ₄(PBu₃^t), 3, Re₂(CO) ₆(PBu₃^t)(μ-PBu₂ ^t)(μ-H), 4, and Re₂(CO)₅(PBu ₃^t)(PBu₂^tH)(μ-PBu ₂^tO)(μ-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 Re₂(CO) ₇(PBu₃^t)(μ-PBu₂ ^t)(μ-H), 6, Re₂(CO)₆(NCMe)(PBu ₃^t)(μ-PBu₂^t)(μ-H), 7, and Re₂(CO)₆(NCPh)(PBu₃^t)(μ-PB ₂^t)(μ-H), 8, respectively. ¹³CO 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 Re₂(CO)₆(PBu₃ ^t)(PBu₂^tH)(μ-PBu₂ ^tO)(μ-H), 9.¹³CO 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.