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-K_α 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.