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

Abstract

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, PPhzMe, PEt3, PPh3; triphos = either bis(3-dipheny1phosphinopropyl)phenylphosphine (ttp), bis(2-dipheny1phosphinoethyl)phenylphosphine (etp), or l,l,l-tris(diphenylphosphinomethy1)ethane (tripod-P3)) were synthesized and their stereochemistry and dynamic behavior studied principally by 31P(1H] K M R . 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)(C0)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)(C0)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 2Jpp coupling constants are presented for these complexes