A critical assessment of coupled cluster method in quantum chemistry

Mechanisms of Nucleophilic Organocopper(I) Reactions

The metal-carbon bond-dissociation energies (D0) and geometries for the first- and second-row transition-metal methyl neutrals and positive ions are determined. The computed D0 values for the positive ions compare favorably with experiment, except for RuCH3(+), RhCH3(+), and PdCH3(+), where the experimental values are 10-15 kcal/mol larger. The computed D0 values for the hydride and methyl positive ions are similar for all metals in both transition rows, except for Cu and Ag. However, for the neutral systems, the D0 values for the methyls are smaller, especially on the right-hand side of both transition rows, where the differences approach 15 kcal/mol.

Theoretical studies of the first- and second-row transition-metal methyls and their positive ions

For species as simple as atomic transition-metal ions, organometallic transformations usually involve multistep processes. These transformations have been studied with the entire arsenal of experimental techniques developed for the study of ion-molecule chemistry: conventional tandem mass spectrometry, flowing afterglow (FA) techniques, and ion cyclotron resonance (ICR) mass spectrometry and its Fourier transform adaptation (FT-ICR). In this Account, the authors limit ourselves to those methods in which motion along the reaction coordinate is the key dynamic variable that can be controlled as reactants approach and measured as the products recede. In our laboratories, guided ion beam techniques have been developed and highly refined for studies of the variation of reaction probabilities with E{sub T}. Complementing this work are measurements of product kinetic energy release distributions (KERDs).

The chemistry of atomic transition-metal ions: insight into fundamental aspects of organometallic chemistry

Cobalamin cofactors play critical roles in radical-catalyzed rearrangements and in methyl transfers. This Account focuses on the role of methylcobalamin and its structural homologues, the methylcorrinoids, as intermediaries in methyl transfer reactions, and particularly on the reaction catalyzed by cobalamin-dependent methionine synthase. In these methyl transfer reactions, the cobalt(I) form of the cofactor serves as the methyl acceptor. Biological methyl donors to cobalamin include N5-methyltetrahydrofolate, other methylamines, methanol, aromatic methyl ethers, acetate, and dimethyl sulfide. The challenge for chemists is to determine the enzymatic mechanisms for activation of these unreactive methyl donors and to mimic these amazing biological reactions.

R. Georgiadis

Papers

Periodic trends in gas phase MH and MC bond energies