The Bridging Acetylene to Bridging Vinylidene Rearrangement in a Triruthenium Carbonyl Cluster: A DFT Mechanistic Study

Synthesis and Chemistry of Ammonioethenyl and Phosphonioethenyl Ligands in Zwitterionic Dirhenium Carbonyl Complexes

New zwitterionic dirhenium carbonyl complexes containing ammonioethenyl and phosphonioethenyl ligands have been synthesized and studied. The reaction of Re₂(CO)₁₀ with C₂H₂ and Me₃NO yielded the dirhenium complex Re₂(CO)₉(NMe₃) (6) and the new zwitterionic complex Re₂(CO)₉[η¹-E-2-CH═CH(NMe₃)] (7). Compound 6 was characterized structurally and was found to have a NMe₃ ligand in an equatorial coordination site cis to a long Re-Re single bond, Re-Re = 3.0938(2) Å. Compound 7 can be obtained from the reaction of 6 with ethyne (C₂H₂) formally by the insertion of ethyne into the Re-N bond to the NMe₃ ligand. Compound 7 contains a 2-trimethylammonioethenyl ligand, ^-CH═CH(⁺NMe₃), that is formally a zwitterion having a positive charge on the nitrogen atom and a negative charge on the terminal carbon atom. When coordinated to rhenium by the terminal ethenyl carbon atom, the negative charge on the ^-CH═CH(⁺NMe₃) carbon atom is formally transferred to the rhenium atom. The reaction of Re₂(CO)₁₀ with C₂H₂ and NEt₃ in the presence of Me₃NO yielded the new dirhenium complex Re₂(CO)₉[η¹-E-2-CH═CH(NEt₃)] (8) together with some 6 and 7. Compound 8 is structurally similar to 7, but it contains a NEt₃ group in the ammonioethenyl ligand in the place of the NMe₃ group in 7. Reactions of 7 with PMePh₂ and PPh₃ yielded the zwitterionic 2-arylphosphonioethenyl-coordinated dirhenium carbonyl complexes, Re₂(CO)₉[η¹-E-2-CH═CH(PPh₂Me)] (9a) and Re₂(CO)₉[η¹-E-2-CH═CH(PPh₃)] (9b), and the zwitterionic 1-phosphonioethenyl ligand in the dirhenium carbonyl complexes, Re₂(CO)₉[η¹-1-C(PPh₂Me)(═CH₂)] (10a), Re₂(CO)₈[μ-η²-1-C(PPh₂Me)(═CH₂)] (11a), and Re₂(CO)₈[[μ-η²-1-C(PPh₃)(CH₂)] (11b). Compound 10a was converted to 11a and the new compound Re₂(CO)₇(μ-H)[μ-η²-1-(CH₂C)P(Ph)(Me)(o-C₆H₄)], (12) by decarbonylation using Me₃NO. Compound 12 contains an ortho-metalated phenyl ring. The new products 6,7, 8, 9b, 10a, 11a, 11b and 12 were characterized structurally by single-crystal X-ray diffraction analyses.