The Importance of a Conformational Equilibrium on the Reactivity of Molybdenum and Rhenium Hydroxo−Carbonyl Complexes toward Phenyl Acetate:  A Theoretical Investigation

Abstract

4 )], respectively, was investigated by using the B3LYP density functional theory methodology in conjunction with the PCM-UAHF model to take into account solvent effects. For both complexes, the most favorable reaction mechanism is concerted and takes place, for the first time in the metal-promoted ester hydrolysis, through the addition of the complex O-H bond to the ester single C-O bond. The larger reactivity of the Mo complex experimentally found is explained in terms of the interaction detected in the rate-determining TS between one of the lone pairs of the oxygen atom bearing the phenyl group and the two π-antibonding C-N of the bidentate ligand. Due to the existence of a conformational equilibrium for the Mo complex, its reaction with phenyl acetate can evolve through a rate-determining TS 2.4 kcal mol -1 lower in relative energy than that found for the Re case, thus explaining the ratio between both periods of experimental reaction time.

A Theoretical Study on the Reactivity of a Rhenium Hydroxo‐Carbonyl Complex Towards β‐Lactams

“…The mechanism related to the proposal D in Scheme 1 was not investigated here because the energy required for the cleavage of the HO-Re bond of the complex is higher than the 65.0 kcal mol Ϫ1 reported in a theoretical study of the reactivity of molybdenum and rhenium hydroxo-carbonyl complexes with phenyl acetate. [45] Figure 1 depicts the optimised structures of the species involved in the reaction mechanisms for the reaction between [Re(OH)(CO) 3 (N 2 C 2 H 4 )] and azetidin-2-one. Table S1 in the Supporting Information lists the corresponding energy data.…”

“…A relative permittivity of 8.93 was assumed in the calculations to simulate dichloromethane which was the solvent used experimentally in related reactions between [Re(OH)(CO) 3 (Me 2 -bipy)] and several organic electrophiles. [15][16][17] The computational scheme chosen in this work is similar to that used in a theoretical study on the reactivity of [Re(OH)(CO) 3 -(N 2 C 2 H 4 )] towards phenyl acetate, [45] wherein the validity of the B3LYP mechanistic predictions compared with X-ray experimental data and more sophisticated quantum-chemical computations was confirmed. Thus, a similar trend could be expected for the present investigation.…”

“…Besides, several theoretical studies have demonstrated the adequacy of replacing bidentate ligands such as phenanthroline (phen) or bipyridine (bpy) by the diimine (HN=CH-CH=NH). [45,47,48] Quantum chemical computations were carried out with the Gaussian 03 series of programs. [49] Full geometry optimisations of stable species and transition states (TS) were performed in the gas phase by employing the hybrid density functional B3LYP [50][51][52] with the 6-31+G(d,p) basis set [53] (LANL2DZ for Re augmented by f polarisation functions with exponent 0.869) [54,55] and by using the standard Schlegel algorithm.…”

Ring opening at N1–C2 bond of azetidin-2-ones by a molybdenum hydroxo-carbonyl complex: evidence from a computational study

“…62,63 This is in agreement with the diminution of the nucleophilic character of the hydroxide group due to its linkage to the Mo metal and to the destabilizing effect of the dichloromethane solvent as indicated in a previous theoretical study on the reaction between formamide and the Mo complex. 61 It is interesting to note that the comparison of TS2¢B with the analogous one TS2B indicates that the hydroxyl O-H and amidic N-C bonds are broken in a lesser extent at the former TS (0.973 and 1.989 A ˚, respectively) than at the latter one (1.092 and 2.004 A ˚, respectively), while the distance H(hydroxyl)-N(amidic) is notably larger by 0.779 A ˚. A NBO analysis reflects that at TS2¢B there are donor-acceptor stabilizing interactions of about 3.5 kcal mol -1 , which imply the bidentate ligand with the lone pair of amidic N atom (LP(N) → p*(N-C) bidentate ), the amidic N-H bond (s(N-H) → p*(N-C) bidentate ), and the amidic C-N bond (p(N-C) bidentate → s*(C-N)), but these interactions do no appear at TS2B.…”

“…A relative permittivity of 8.93 was assumed in the calculations to simulate dichloromethane as the solvent experimentally used in related reactions between [Mo(OH)(h 3 -C 3 H 4 -Me-2)(CO) 2 (phen)] and different organic electrophiles. [56][57][58][59] The computational scheme chosen in this work is similar to that used in a theoretical study on the reactivity of [Mo(OH)(h 3 -C 3 H 5 )(CO) 2 (HN=CH-CH=NH)] toward phenyl acetate, 61 wherein the validity of the B3LYP mechanistic predictions compared to Xray experimental data and more sophisticated quantum-chemical computations was confirmed. Thus, a similar trend could be expected for the present investigation.…”