cis Influence in Models of Cobalt Corrins by DFT and TD-DFT Studies

Abstract

Time-dependent density-functional theory and density-functional theory are applied to study the cis influence of the equatorial macrocycle in vitamin B(12) derivatives. A series of dicyanocobalt corrinoids, CN-[Co(III)-corrin]-CN, where the C(10)H of the corrin ring is replaced by different substituents, X, is considered. The calculated UV-visible absorption spectra, the charge distribution obtained from a Bader QTAIM analysis of the electron density, the CN stretch frequencies of the axial cyano ligands and the electron densities at some bond critical points are compared. The main absorption bands in the UV-visible spectra depend on the electron donating or withdrawing power of X, as assessed from its Hammett σ(p) constants. For X with a stronger electron donating power than H, the other properties do not change appreciably. However, when σ(p)(X) > σ(p)(H), these properties vary linearly with the electron withdrawing power of the substituent. This helps explain the experimental observation that substitution of the axial ligand is more difficult and proceeds more slowly with the increase of the electron withdrawing power of the C(10) substituent.

Vitamin B12 Catalysis: Probing the Structure/Efficacy Relationship

“…Firstly, we focused on derivatives modified at the meso ‐position because it is known that such modifications, through the cis effect, influence the nature of the central cobalt atom . The presence of meso ‐Br− ( 10 ), −Cl ( 11 ) or −NH 2 ( 13 ) substituents in the catalyst structure had little to no effect on the model reaction yield, but fluctuation in the ratio of products ( 5 / 6 ) was observed (Table , entries 2, 3 and 5).…”

Probing the nature of the Co(III) ion in cobalamins: The ligand substitution reactions of aquacyanocobester, aquacyano(10-nitro)cobester and aquacyano(10-amino)cobester

“…Interactions with |V b |/G b < 1 are characteristic of ionic interactions; those with |V b |/G b > 2 are typically covalent interactions; and 1 < |V b |/G b < 2 is diagnostic of interactions of intermediate character. As we have shown for a wide variety of compounds [24,[59][60][61][62][63][64][65], metal-ligand bonds are usually intermediate in character. Focusing on the four compounds in Table 4 with Z = H, we note that |V b |/G b varies from 1.118 for the Co-OH 2 bond, to 1.129 for Co-N(Im), 1.203 for Co-NO 2 À , to 1.375…”

“…Generally, there is a greater discrimination between [ACCbs] + and [AC(10-NO 2 )Cbs] + than between it and [AC(10-NH 2 )Cbs] + . We have noted [64] in a BP86/6-311+G(d,p) study of complexes of the type [(CN) 2 (10-Z)corrin] that properties such as the charge on the CN ligands, the symmetric and anti-symmetric NCCoCN stretching frequency, and the strength of the CoCN bond (as assessed from the electron density at the bond critical point), respond linearly with values of the Hammett para constant, r p , for Z provided r p > 0, but are generally insensitive when r p < 0.…”

A stress tensor and QTAIM perspective on the substituent effects of biphenyl subjected to torsion

“…This includes, in particular, the work of Popelier who used a similarity measure in the form of a BCP (bond critical point) space to accurately predicted the Hammett σ p and σ m values for benzoic acids . Other more recent work has also provided QTAIM perspectives on Hammett constants …”

“…[29] Other more recent work has also provided QTAIM perspectives on Hammett constants. [30][31][32][33][34] The biphenyl molecule is larger than the substituted benzene, C 6 H 5 -x, compounds used to determine the Hammett constants. Therefore, changes to the total charge density distribution q(r) must propagate across a greater number of bonds compared with smaller benzenwie compounds.…”