PREPARATION AND PROPERTIES OF COBALT(II) PHOSPHINE COMPLEXES CONTAINING NITRO AND NITROSYL LIGANDS

Reactions of the tertiary phosphines PMe3, PEt3, PMe2Ph, PMePh2 and PPh3 with Co(NO2)2 are described. For PMe3 and PMe2Ph, five-coordinate Co(NO2)2(PR3)3 complexes (1, 2) are isolated. With PEt3, only Co(NO)(NO2)2(PEt3)2 (3) is obtained, whereas the Co(NO)(NO2)2(PMe3)2 (4) and Co(NO)(NO2)2(PMe2Ph)2 (5) analogs result from the reaction of 1 and 2 with NO gas. From EPR measurements, the electronic structures of 1 and 2 are found to correspond to low-spin d7 square-pyramidal complexes in the solid state. Compounds 3, 4 and 5 are pseudo-octahedral Co(III) species containing three different nitrogen oxide ligands, namely NO, O-bonded NO2 and N-bonded NO2. The reactions of 1 and 2 with CO are solvent dependent: in methanol Co(NO)(CO)(PMe3)2 is obtained, but in toluene a mixture of 5 and Co(NO)2(NO2)(PMe2Ph) precipitates. Co(NO)(NO2)2(PEt3)2 reacts with O2 to form the cobalt(II) complex Co(NO3)2(OPEt3)2 shown by X-ray diffraction to be a distorted octahedron with bidentate nitrate ligands and two OPEt3 ligands in cis positions.