UNUSUAL NMR SPECTRAL PROPERTIES OF THE 1,2-DICYANOETHYL ALKYL LIGAND IN ORGANOCOBALOXIMES - STRUCTURE OF THE ORGANOCOBALT COMPLEX TRANS-BIS(DIMETHYLGLYOXIMATO)(1,2-DICYANOETHYL)(1,5,6-TRIMETHYLBENZIMIDAZOLE)COBALT(III)

The 1,2-dicyanoethyl ligand has been reported to exhibit unusual dynamic processes in certain organocobaloxime complexes. The crystal and molecular structures of the complex trans-bis(dimethyl-glyoximato)(l,2-dicyanoethyl)(l,5,6-trimethylbenzimidazole)cobalt(III)-0.5-ethanol, Me3BzmCo-(DH)2CH(CN)CH2CN, are reported. The compound crystallizes in space group P1, triclinic, with a = 7.721 (1) Å, b = 11.845 (2) Å, c = 15.078 (3) Å, α = 79.09 (2)°, β = 80.65 (2)°, γ = 75.65 (2)°, V = 1320.0 Å3, Z = 2. Dmeasd = 1.38 g cm-3, = 1.39 g cm-3, and R = 0.051 for 5261 independent reflections. The Co‒C bond distance of 2.061 (3) Å is slightly shorter than that of 2.076 (2) Å found in the structure of the isopropyl analogue, whereas the Co‒N(Me3Bzm) bond length (2.031 (3) Å) is shorter than that in the isopropyl analogue (2.097 (2) Å). Hence, the 1,2-dicyanoethyl and isopropyl groups have similar bulk properties but different trans influences. The rate constants, k1 were determined for dissociation of Me3Bzm from six Me3BzmCo(DH)2R complexes where R ranges from weak donors such as CH2CF3 to strong donors and CH(CH3)2. High-field1H NMR spectroscopy showed that the CH(CN)CH2CN proton pattern, which is distorted by second-order effects, is greatly affected by temperature and the trans influence of L. A deuteration study in pyridine-d5/D2O revealed no exchange of the -CH(CN)CH2CN after 2 months at ambient temperature. These results militate against any unusually rapid dynamic processes involving the CH(CN)CH2CN group. Rather, previous NMR spectral observations at low field could be understood as arising from the peculiar1H NMR spectral characteristics of these compounds. © 1990, American Chemical Society. All rights reserved.