Stereochemistry and exchange processes in five-coordinate cobalt(I) complexes containing one of three triphosphine ligands

Six extensive series of five-coordinate complexes of the types [Co(triphos)(CO)₂]X and [Co(triphos)L(CO)]X (X = BF₄, PF₆; L = P(OMe)₃, PPh₂H, PPh₂Me, PEt₃, PPh₃; triphos = either bis(3-diphenylphosphinopropyl)phenylphosphine (ttp), bis(2-diphenylphosphinoethyl)phenylphosphine (etp), or 1,1,1-tris(diphenylphosphinomethyl)ethane (tripod-P₃)) were synthesized and their stereochemistry and dynamic behavior studied principally by ³¹P{₁H} NMR. The details of the stereochemistry and exchange processes depend both on the monodentate ligand and on the triphosphine ligand. For example, the [Co(etp)L(CO)]X and [Co(etp)(CO)₂]X complexes are trigonal bipyramidal with the equatorial positions occupied by a carbonyl ligand and the two terminal phosphorus atoms of the triphosphine ligand; the axial positions are occupied by the central phosphorus atom and either a monophosphine or a carbonyl ligand, respectively. The [Co(ttp)L(CO)]X complexes have square-pyramidal structures with L located at the axial position. A trigonal-bipyramidal structure is assigned to the dicarbonyl complexes [Co(ttp)(CO)₂]X. The complexes [Co(tripod-P₃)L(CO)]X are stereochemically nonrigid, whereas those of [Co(etp)L(CO)]X are stereochemically rigid at room temperature. A large number of ²J_PP coupling constants are presented for these complexes.