(Trimethylphosphine)cobalt(I) Complexes. 1. Reactivity with Ethylene and Crystal Structure of BPh4*MeCN

Article abstract of DOI:10.1021/ja00378a018

The reaction of Co^IBr(PMe3)3 with ethylene in various solvents was investigated at -80 and 35 deg C by 31P<1H> NMR spectroscopy.In toluene, acetone, and methanol, ethylene adds reversibly to the paramagnetic tetrahedral d⁸ Co^I complex to give the diamagnetic CoBr(C2H4)(PMe3)3 species with C2H4 and Br in equatorial positions.Adding acetonitrile (1:1) to acetone or methanol leads to a mixture of two pentacoordinate diamagnetic compounds: Br (where L= C2H4 or MeCN) and Br.In the former, L cannot be unambiguosly identified, but both L and C2H4 have to be equatorial.In the latter species, the ligand distribution is the same as found in the crystals of the corresponding BPh4^- salt, i. e., C2H4 equatorial and MeCN axial.The same spectrum was obtained with BPh4*MeCN, which confirms that Br has been expelled from the coordination sphere of cobalt.The affinity of MeCN for Co^I in this system is evidenced by the formation of the rigonal-bipyramidal (TBP) adducts ⁺ and ⁺ in acetonitrile solutions of CoBr(PMe3)3 and BPh4, respectively, at -80 deg C.The reaction of ethylene with BPh4 yields a TBP adduct BPh4 with equatorial C2H4.The crystals of BPh4, MeCN belong to space group P2₁/c with a=12.738 Angstroem, b=28.52 Angstroem, c=11.891 Angstroem, and β=106.85 deg.The structure contains a distorted TBP ⁺ cation in which MeCN and PMe3 are axial, whereas C2H4 and two PMe3 ligands are equatorial.The ethylene double bond lies on the equatorial plane, and it undergoes the usual structural changes upon coordination.The distortions in the TBP are related to the individual steric requirements of each type of ligand.