Rhodium phosphine-phosphite catalysts in the hydrogenation of challenging N-(3,4-dihydronaphthalen-2-yl) amide derivatives

The enantioselective catalytic hydrogenation of N-(3,4-dihydronaphthalen-2- yl) amides (1) with rhodium catalysts bearing phosphine-phosphite ligands 4 has been studied. A wide catalyst screening, facilitated by the modular structure of 4, has found a highly enantioselective catalyst for this reaction. This catalyst gives a 93% ee in the hydrogenation of 1a and also produces high enantioselectivities, ranging from 83 to 93% ee, in the hydrogenation of several OMe- and Br-substituted substrates. In contrast, the structurally related enol esters 2 are very reluctant to undergo hydrogenation. A coordination study of the representative enamide 1d has shown an unusual η6-arene coordination mode, over the typical O,C,C chelating mode for enamides, as the preferred one for this substrate in a Rh(I) complex. Deuteration reactions of 1c,d indicate a clean syn addition of deuterium to the double bond without an isotopic effect on the enantioselectivity. © 2013 American Chemical Society.Peer Reviewe

A Local Pair Natural Orbital Coupled Cluster Study of Rh Catalyzed Asymmetric Olefin Hydrogenation

The recently developed local pair natural orbital coupled cluster theory with single and double excitations (LPNO−CCSD) was used to study the rhodium-catalyzed asymmetric hydrogenation of two prochiral enamides. The method was carefully calibrated with respect to its accuracy. According to calculations on a truncated model system, the effects of perturbative triples (T) on the reaction energetics are very limited, the LPNO approximation is accurate, and complete basis set extrapolation (CBS) causes only minor changes in the relative energies computed with a standard basis set (def2-TZVP). The results for the full system are thus believed to be within 1−2 kcal/mol of the CCSD(T)/CBS limit for the present systems. Relativistic effects were treated by a scalar relativistic Hamiltonian using the zeroth order regular approximation (ZORA). The results of the study were compared to density functional calculations on the same systems and with calculations available in the literature. All calculations predict the correct stereochemical outcome of the reaction that is determined by the relative energies of the transition states in the early stages of the catalytic cycle. In general, DFT calculations using the B3LYP functional are in reasonable agreement with the LPNO−CCSD results, although deviations of 3−5 kcal/mol exist that are also not entirely systematic in the minor and major reaction branches. The present case study thus demonstrates that catalytic reactions, which are well described by single-reference electronic structure theory, can now be routinely studied with confidence in systems with 50−100 atoms applying local correlation methods that are as easy to use as DFT methods