Structural distortions in alkylcobaloximes containing triphenylphosphine as axial ligand. The X-ray structures of trans-bis(dimethylglyoximoto)(bromomethyl)(triphenylphosphine)cobalt(III) and trans-bis(dimethylglyoximato)(cyanomethyl)(triphenylphosphine)cobalt(III)

Add time:09/02/2019    Source:sciencedirect.com

The crystal structure of two cobaloximes, [Co(CH2Br)(Hdmg)2(PPh3)] (1) and [Co(CH2CN)(Hdmg)2(PPh3)] (2) (H2dmg = dimethylglyoxime), are reported and discussed. Compound (1) crystallizes in the space group P21/c with cell parameters a = 10.221(7), b = 15.23(1), c = 19.27(1) Å β = 108.0(1)°, Z = 4; (2) crystallizes in the space group P22/c with cell parameters a = 8.653(4), b = 16.55(1), c = 19.99(1) Å, β = 104.7(1)°, Z = 4. Both structures have been solved by Patterson and Fourier methods and refined by least-squares methods to final R values of 0.057(1) and 0.028(2), using 1746(1) and 2950(2) independent reflections. The cobalt atom is displaced 0.065(1) and 0.084(2) Å above the (Hdmg)2 4-N equatorial donors towards PPh3, the two Hdmg planes making dihedral angles of 2.7(1) and 11.1° (2) and bending towards the alkyl group. The PPh3CoCH2Br fragment of (1) is characterized by a PCoC angle of 175.1(4)° and CoP and CoC bond lenghts of 2.399(3) and 1.998(15) Å respectively; the corresponding figures for (2) are 177.7(1)°, 2.391(1) and 2.043(3) Å respectively. The CoCH2Br angle is 125.2(9)° and the CBr distance is 1.84(1), significantly shorter (∼0.1 Å) than values reported for bromoalkyls. The CoCH2CN angle is 116.5(3)° and the CCN distance is 1.424(5) Å, slightly but significantly shorter (∼0.04 Å) than those reported for R3CCN compounds. The present results are compared with those reported for the analogues [Co(CH2X)Co(Hdmg)2(PPh3)], (X = H, t-C4H9, CF3) and discussed in terms of steric and electronic influences. Comparison with the [Co(CH2X)Co(Hdmg)2(py)] series is discussed, pointing out the differences provoked by substitution of PPh3 with py on the geometry of the Co(CH2X)(Hdmg)2 moiety.

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