Synthesis, structure, and solution behaviour of the compound trans-bis(dimethylglyoximato)(ethyl)(methyl 4-pyridinecarboximidate)cobalt(III)
Abstract
The synthesis of the title compound [CO(mpyim)(Hdmg)2Et](1), starting from [Co(4CN-py)(Hdmg)2Cl](mpyim = methyl 4-pyridinecarboximidate, 4CN-py = 4-cyanopyridine, and Hdmg = dimethylglyoximate monoanion) is reported. The compound crystallizes in the space group P212121 with cell parameters a= 12.776(6), b= 9.606(5), c= 16.884(7)Å, and Z= 4. The structure was solved by Patterson and Fourier methods and refined by block-diagonal anisotropic least-squares methods to a final R value of 0.039 using 1 968 independent reflections having I > 3σ(I) and using Mo-Kα radiation to a maximum 2θ= 56°. The N–Co–CH2CH3 fragment is characterized by N–Co–C and Co–C–C angles of 177.1(2) and 117.8(4)° respectively and by Co–N, Co–C, and C–C distances of 2.081 (3), 2.035(5), and 1.519(8)Å respectively. Of the two possible configurations, E and Z, the imidate ester appears to prefer the E configuration in the solid state. 1H N.m.r. lineshape analysis suggests that both the E and Z isomers are present in CDCl3 solution, with relative populations (E:Z) of 4:1. These interconvert at a rate of 1.1 × 102 s–1 at 25 °C. Trace acid and base increase the rate of isomerization. The ligand exchange rate for the substitution of mpyim by P(OMe)3 in CH2Cl2 shows that the reactivity of (1) is similar to that of the pyridine analogue.