Alkynylphosphanes as supports for mixed-metal Co4M (M = Ru, Os) fluoride complexes: Syntheses, structures and thermolysis studies

Treatment of the tetrameric group eight fluoride complexes [MF(μ-F)(CO)3]4 [M = Ru (1a), Os (1b)] with the alkynylphosphane, Ph2PCtriple bond; length of mdashCPh, results in fluoride-bridge cleavage and the formation of the air-sensitive monomeric octahedral complexes [MF2(CO)2(PPh2CCPh)2] [M = Ru (2a), Os (2b)] in high yield. The molecular structure of 2b reveals a cis, cis, trans configuration for each pair of ligands, respectively. The free alkyne moieties in 2 can be readily complexed to hexacarbonyldicobalt fragments by treatment with dicobalt octacarbonyl to afford [MF2(CO)2(μ-η1:η2-PPh2CCPh)2{Co2(CO)6}2] [M = Ru (3a), Os (3b)]. Evidence for an intramolecular non-bonded contact between a bound fluoride and a cobalt carbonyl carbon atom is seen in the molecular structure of 3a. Thermolysis of 3a at 50 °C results in fluoride dissociation to give [RuF(CO)2(μ-η1:η2-PPh2CCPh)2{Co2(CO)6}2]+ (4), while no reaction occurred with the osmium analogue. Prolonged thermolysis at 120 °C in a sealed vessel of both 3a and 3b gave only insoluble decomposition products.