Photochemistry of nitrogen ligand substituted dinuclear rhenium carbonyl compounds

Article abstract of DOI:10.1021/om00069a007

The reactions of eq-Re₂(CO)₉ L (L = CH₃CN, pyridine, CH₃NH₂, or CaHgNH₂) and of 1,2-eq,eq-Re₂(CO)₈L₂ (L = CH₃CN, pyridine (py)) have been examined under sunlamp irradiation. 1,2-eq,eq-Re₂(CO)₈(CH₃CN)₂ is observed as the primary photoproduct under continuous photolysis of Re₂(CO)₉(CH₃CN). Re₄(CO)₁₂(OH)₄ is formed from a side photochemical reaction of the CH₃CN compounds with residual H₂o in the THF or heptane solvent. The initial rhenium-containing products of the photochemical reaction of eq-Re₂-(CO)₉(pyridine) or of 1,2-eq,eq-Re₂(CO)₈(pyridine)₂ under continuous photolysis in THF are Re₂(CO)₁₀, Re(CO)₃(py)₃⁺, HRe₄(CO)₁₆^-, and 1,1-(μ-H)Re₂(CO)₇(py)(NC₅H₄) (formed in similar yields with either starting compound). Flash irradiation of eq-Re₂(CO)₉(py) in THF allows detection of the intermediate 1,2-eq-eq-Re₂(CO)₈(py)₂·(μ-H)Re ₂(Co)₈(NC₆H₄) can be prepared in a thermal reaction from 1,2-eq,eq-Re₂(CO)₈(py)₂. It reacts slowly with pyridine to yield 1,1-(μ-H)Re₂(CO)₇(py)(NC₅H₄). Photolysis of eq-Re₂(CO)₉(RNH₂) (R = CH₃, C₂H₅) in heptane yields Re₂(CO)₁₀ and a precipitate of 1,1-Re₂(CO)₈(RNH₂)₂. Mechanisms are proposed for the photochemical reactions of the nitrogen-base compounds. The primary photoprocess in all cases is homolytic cleavage of the Re-Re bond. Loss of CO or L from the Re(CO)₄L· radicals allows formation of Re(CO)₅· and Re(CO)₃L₂· species. The rate of dissociation of L from photogenerated Re(CO)₄L· appears to be comparable to that of CO. Analogies to the photochemical reaction of Re₂(CO)₁₀ with H₂o are noted.