Structural behaviour of cobaloximes: planarity, an anomalous trans-influence and possible implications on CoC bond cleavage in coenzyme-B12-dependent enzymes

DFT Analysis of Co−Alkyl and Co−Adenosyl Vibrational Modes in B12-Cofactors

“…37 Changing the alkyl group to ethyl lengthens the Co-C bond, to 1.99 Å, due to a combination of electronic and nonbonded ethyl-corrin interactions, while increasing the steric bulk further, to propyl, lengthens the Co-C bond to 2.03 Å. Interestingly, the Co-imidazole bond lengthens in the same order, to 2.26 and 2.32 Å, illustrating what has become known as the 'inverse trans influence'. [38][39][40][41][42][43] The computed frequencies fall in the same order, as expected. The Co-C stretching frequencies are in excellent agreement with reported values for MeCbl and EtCbl; no data are available for isopropyl derivatives.…”

Trans and cis influences and effects in cobalamins and in their simple models

“…Therefore, in a series with the same L and various R ligands, the plot of Co\L distances against Co\R distances exhibits negative slope in the case of normal trans influence and positive slope in the case of inverse trans influence. A behavior similar to cobaloximes was also suggested in the alkylcobalamins, RCbl (Scheme 1a, X = R), whose structures were available at that time [18]. It was concluded that …”

“…The early extensive analysis carried by Burgi et al [18] on a series of LCo(DH) 2 R complexes revealed that both the axial distances lengthen when the electron donating ability of the R group increases. This behavior was called inverse trans influence, in contrast to the normal trans influence, which occurs when the lengthening of one axial bond corresponds to a shortening of the trans bond [1][2][3][4][5][6][7][8].…”

Electronic Properties of the Axial Co−C and Co−S Bonds in B12 Systems − A Density Functional Study

“…The ''inverse'' trans influence, derived through an analysis of structural data in several alkylcobaloximes, LCo(DH) 2 R, a simple B 12 model, [34] was attributed principally to the electronic properties of R. However, it has been shown that in these complexes the bulk of R (independently of its electronic properties) also contributes significantly in determining the CoϪR distance, because of its interaction with the equatorial ligand. [35] In fact, compared to the Me analogue, alkylcobaloximes with strong electronic withdrawing and bulky R groups, such as CH(CN)CH 2 CN, [36] and CF(CF 3 ) 2 , [37] show a significant lengthening of the CoϪC bond (up to 0.08 Å ) and a shortening of the CoϪL bond (up to 0.03 Å ).…”