Methyl B12Models Containing Unsubstituted Imidazole As an Axial Ligand Investigated by Structural and NMR Spectroscopic Methods. Evidence that μ-Imidazolato-Bridged Dimers Are Formed by Base Addition to Some Analogues with Macrocyclic Equatorial Ligands Incorporating BF2

Abstract

Imidazole (imH)-containing B12 model complexes that could possibly be deprotonated at the imidazole NH to form the corresponding imidazolato (im) complexes were investigated. Organomethyl complexes of cobaloxime and imine/oxime (I/O) analogues with equatorial ligands possessing an O−BF2−O moiety in place of each deprotonatable O−H- - -O moiety of standard models were prepared. In some cases, NMR spectroscopy revealed formation of μ-imidazolato (μ-im) dimers in methanol-d4 on addition of methoxide. The desired monomeric imidazolato species was not formed at a characterizable level. We present the X-ray crystal structures of LCo(DBF2)2CH3 (where L = imH, 4-t-BuimH) and [AsPh4][(μ-im)(Co(DBF2)2CH3)2] (DBF2 = the BF2-substituted monoanion of dimethylglyoxime). The latter confirms the NMR solution studies and is the first structure of a B12 model species bridged by an imidazolato moiety. We have also structurally characterized the related I/O complexes, [imHCo((DO)(DOBF2)pn)CH3]PF6 and [imHCo((DO)(DOH)pn)CH3]I...