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Manganese complexes of the types [Mn(PNP′)(Br)(CO)2] and [Mn(PNP′)(H)(CO)2] containing a tridentate ligand with a planar chiral ferrocene and a centro chiral aliphatic unit were synthesized, characterized, and tested in the enantioselective transfer hydrogenations of 13 ketones. The catalytic reactions proceeded with conversions up to 96 % and ee values up to 86 %. The absolute configuration of all products was determined to be (S). Notably, the presence of dihydrogen (up to 20 bar) did not affect the reduction. On the basis of DFT calculations, preliminary mechanistic details including the origin of the (S) selectivity are presented. The molecular structure of [Mn(PNP′)(Br)(CO)2] was studied by X‐ray diffraction.

The mechanism of asymmetric hydrogenation of alpha-(acylamino)acrylic esters with Ru(CH(3)COO)(2)[(S)-binap] (BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl), giving the S saturated products in >90% ee, has been investigated by means of a kinetic study, deuterium labeling experiments, isotope effect measurements, and NMR and X-ray analysis of certain Ru complexes. The hydrogenation in methanol under a low H2 pressure proceeds via a monohydride-unsaturate mechanism that involves the initial RuH formation followed by a reaction with an olefinic substrate. The migratory insertion in the enamide-RuH chelate complex occurs reversibly and endergonically in an exo manner, giving a five-membered metallacycle intermediate. The cleavage of the Ru-C bond is achieved with either H2 (major) or CH3OH (minor). Both of the pathways result in overall cis hydrogenation products. The hydrogen at C3 is mainly from an H2 molecule, and the C2 hydrogen is from another H2 or protic CH3OH. The major S and minor R enantiomers are produced via the same mechanism involving diastereomeric intermediates. The turnover rate is limited by the step of hydrogenolysis of a half-hydrogenated metallacyclic intermediate. The participation of two different hydrogen donor molecules is in contrast to the pairwise dihydrogenation using a single H2 molecule in the RhI-catalyzed reaction which occurs via a dihydride mechanism. In addition, the sense of asymmetric induction is opposite to that observed with S-BINAP-RhI catalysts. The origin of this phenomenon is interpreted in terms of stereocomplementary models of the enamide/metal chelate complexes. A series of model stoichiometric reactions mimicking the catalytic steps has indicated that most NMR-observable Ru complexes are not directly involved in the catalytic hydrogenation but are reservoirs of real catalytic complexes or even side products that retard the reaction.

The phosphorus-chiral diphosphine 1,1‘-bis(1-naphthylphenylphosphino)ferrocene (1a) and its new electronically modified derivatives 1b−d bearing methoxy and/or trifluoromethyl groups in para positions of the phenyl rings were investigated as ligands in rhodium-catalyzed (asymmetric) hydroformylation. Depending on ligand basicity, high-pressure NMR and IR characterization of the respective (diphosphine) rhodium dicarbonyl hydride precursor complexes revealed subtle differences in the occupation of bis-equatorial (ee) and equatorial−apical (ea) coordination geometries. The high ee:ea ratio of the four complexes contrasted with the clear ea preference observed for the related achiral compound dppf (1,1‘-bis(diphenylphosphino)ferrocene). In the hydroformylation of styrene the best result (50% ee) was obtained by employing the best π-acceptor ligand 1c, incorporating two p-trifluoromethyl substituents. Substrate electronic variations using 4-methoxystyrene and 4-chlorostyrene showed a pronounced influence on turnover frequencies, branched/linear aldehyde product ratios, and enantiodiscrimination, whereas in the hydroformylation of 1-octene ligand electronic perturbations did affect only the rate, but not the selectivity of the reaction.