X-ray diffraction structure of Co2(CO)4(μ-PhC≡CH)[(Z)-Ph2PCH=CHPPh2[: proof for diphosphine ligand chelation

Abstract

Treatment of the dicobalt compound Co2(CO)6(μ-PhC≡CH) (1) with the unsaturated diphosphine ligand (Z)-Ph2PCH=CHPPh2 gives the chelating diphosphine compound Co2(CO)4(μ-PhC≡CH)[(Z)-Ph2PCH=CHPPh2] (2) when the reaction is carried in refluxing 1,2-dichloroethane or in the presence of Me3NO. 2 was characterized in solution by IR and 31P NMR spectroscopy, and the molecular structure of Co2(CO)4(μ-PhC≡CH)[(Z)-Ph2PCH=CHPPh2] was established by X-ray diffraction analysis, which confirmed the chelation of the P-ligand to a single cobalt center. Co2(CO)4(μ-PhC≡CH)[(Z)-Ph2PCH=CHPPh2] crystallizes in the monoclinic space group P21/c, a = 10.151(1), b = 32.694(5), c = 11.051(5) A, β = 111.14(1)°, V = 3420.7(9) A3, Z = 4, and dcalc = 1.414. The two distinct 31P resonances found in the 31P NMR spectrum of 2 are discussed relative to the X-ray structure and other structurally similar cobalt–alkyne complexes. Thermolysis of Co2(CO)4(μ-PhC≡CH)[(Z)-Ph2PCH=CHPPh2] led only to the slow decomposition of Co2(CO)4(μ-PhC≡CH)[(Z)-Ph2PCH=CHPPh2] and not to the formation of the isomeric bridged-diphosphine complex.