Hydrogen computational studies

BW Beck, Q Xie, T Ichiye. Computational study of S—H S hydrogen bonds m [4Ee-4S]-type ferredoxm x-ray and NMR structures Characterization and implications for redox potentials. Protein Sci, submitted. 

These catalysts are activated by hydrogenation of the cyclooctadiene ligand, which releases cyclooctane and opens two coordination sites at iridium. The mechanism has been probed by computational studies.40 It is suggested that the catalytic cycle involves... 

There have been a number of computational studies of the epoxidation reaction. These studies have generally found that the hydrogen-bonded peroxy acid is approximately perpendicular to the axis of the double bond, giving a spiro structure.75 Figure 12.8 shows TS structures and Ea values based on B3LYP/6-31G computations. The Ea trend is as expected for an electrophilic process OCH3 < CH3 CH = CH2 < H < CN. Similar trends were found in MP4/6-31G and QCISD/6-31G computations. 

Jeong, H. Y., Han, Y., Comment on A Computational Study of the Structures of Van der Waals and Hydrogen Bonded Complexes of Ethene and Ethyne Chem. Phys. Lett., 263, 345. 

Sobolewski AL, Domcke W (2007) Computational studies of the photophysics of hydrogen-bonded molecular systems. J Phys Chem A 111 11725-11735... 

Computational Studies of Hydrogen-Containing Complexes in Semiconductors... 

The selectivity of the hydrogen transfer is excellent When employing a catalyst with deuterium at the a-positions of the isopropoxide ligands (17), complete retention of the deuterium was observed. A computational study using the density functional theory comparing the six-membered transition state (as in Scheme 20.3, the direct transfer mechanism) with the hydride mechanism (Scheme 20.3, the hydride mechanism) supported the experimental results obtained [36]. A similar mechanism has been proposed for the MPV alkynylations [37] and cyanations [38]. 

Status of the Computational Study of Rhodium-Complex-Catalyzed Enantioselective Hydrogenation... 

This formed a basis for the study of the H2 addition step in a precatalyst for Ir enantioselective hydrogenation [70]. By NMR, it proved possible to characterize a single diastereomer of the initial addition product at -40°C in THF, the configuration of which was defined by nOe methods. This was converted into a mixture of two diastereomers of the disolvate dihydride with release of cyclooctane at 0°C. In all cases, H trans-N is preferred over H trans-P, as was originally observed by Crabtree. The investigations were completed by DFT computational studies on the initial steps of the reaction sequence as a model for the stereose-... 

After discussing in detail each step of the hydrogenation process, we will comment here on the computational studies of the full catalytic cycle. 

For further important work on this and related concepts, see Rucker, J. and Kliman, J.P. (1999). Computational study of tunneling and coupled motion in alcohol dehydrogenase-catalyzed reactions Implication for measured hydrogen and carbon isotope effects. J. Am. Chem. Soc. 121, 1997 -2006, and Kohen, A. and Jensen, J.H. (2002). Boundary conditions for the Swain-Schaad relationship as a criterion for hydrogen tunneling. J. Am. Chem. Soc. April 17, 124(15), 3858-3864. 

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