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(mu-F)(CO)(3)](4) [M = Ru (1a), Os (1b)] with the alkynylphosphane, Ph2PC CPh, 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)(mu-eta(1):eta(2)-PPh2CCPh)(2){Co-2(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 degrees C results in fluoride dissociation to give [RuF(CO)(2)(mu-eta(1):eta(2)-PPh2CCPh)(2){Co-2(CO)(6)}(2)](+) (4), while no reaction occurred with the osmium analogue. Prolonged thermolysis at 120 degrees C in a sealed vessel of both 3a and 3b gave only insoluble decomposition products. (C) 2007 Elsevier B.V. All rights reserved.