Synthesis and Reactions with CO and C2H4 of Cobalt(I) Complexes Containing Trimethylphosphine and Chelating o-Diphenylphosphanyl- phenolate Ligands

In tetracoordinate cobalt(I) halide compounds CoX(Ph2P⌒O H)(PMe3)2 (X = CI, Br) o-phos-phanylphenols PhaP⌒OH are coordinated as phosphane ligands. In the presence of base chelat­ ing anions Ph2P⌒O- give rise to pentacoordinate com plexes Co(Ph2P⌒O)(PMe3)3. Molecular structures are presented for both types of compounds. The five-membered chelate ring in Co(Ph2P⌒O)(PMe3)3 is resistant to protonation, and ring-opening is not observed in the presence of CO or C2H4. Replacing one of the trimethylphosphanes by one of the π-acceptor ligands affords fluxional complex molecules which upon cooling attain definite ground-state geometries out of a multitude of possible isomers.