The current approach to improve and tune the enantioselective performances of transition-metal catalysts for asymmetric synthesis is mostly focused to modifications of the steric properties of the ancillary ligands of the active metal. Nevertheless, it is also known that electrostatic effects can have a remarkable role to promote selectivity in asymmetric synthesis. Using the Rh-catalyzed asymmetric 1,4-addition of phenylboronic acid to 2-cyclohexenone leading to chiral 3-phenylcyclohexanone as an example, we could show that high enantioselectivity can be indeed achieved using catalysts essentially based either on steric or electrostatic effects as the main source of enantioselective induction. In this contribution we suggest that the analysis of the surface of interaction between the catalyst and the substrate could be a useful tool to quantify the power of steric and electrostatic effects of catalysts.

A family of chiral C(2)-symmetric disulfoxide ligands possessing biaryl atropisomeric backbones has been synthesized by using the Andersen methodology. Complete characterization includes X-ray crystallographic studies of all ligands and some of their rhodium complexes. Their synthesis, optical purity, electronic properties, and catalytic behavior in the prototypical rhodium-catalyzed 1,4-addition of phenylboronic acid to 2-cyclohexen-1-one are presented through an in depth study of this ligand class. Density functional theory calculations on the step of the catalytic cycle that determines the enantioselectivity are presented and reinforce the first hypothetical explanations for the high levels of asymmetric induction observed.

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A new class of easily accessible and stable imidazolin-2-ylidenes has been synthesized where the side chains are comprised of substituted naphthyl units. Introduction of the naphthyl groups generates C 2 -symmetric ( rac) and C s- symmetric ( meso) atropisomers, and interconversion between the isomers is studied in detail both experimentally and computationally. Complete characterization of the carbenes includes rare examples of crystallographically characterized saturated NHC structures. Steric properties of the ligands and an investigation of their stability are also presented. In catalysis, the new ligands show versatility comparable to the most widely used NHCs IMes/SIMes or IPr/SIPr. Excellent catalytic results are obtained when either the NHC salts (ring-opening alkylation of epoxides), NHC-modified palladium compounds (C-C and C-N cross-couplings), or NHC-ruthenium complexes (ring-closing metathesis, RCM) are employed. In several cases, this new ligand family provides catalytic systems of higher reactivity than that observed with previously reported NHC compounds.

Two saturated N-heterocyclic carbene ligands with substituted naphthyl side chains were used for the preparation of Blechert-type ruthenium metathesis precatalysts. The resulting conformers of the complexes were separated and unambiguously assigned by X-ray diffraction studies. All new complexes were compared in terms of activity to the original, SIMes-derived Blechert catalyst and were shown to be superior. A study on the impact of solvent concentration in RCM reactions using the most active of these new catalysts ultimately led to the ring closing of a variety of substrates at very low catalyst loadings.

N-Dichlorophosphanyldibenzo[b,f]azepine (6) reacted with (−)-2,3-O-isopropylidene-d-threitol, (R)-taddol, (R,R)-diethyltartrate, (R,R)-diethyltartrate, (S)-binaphthol, α,α-diphenyl-l-prolinol, and (S)-proline to form the corresponding chiral P-alkene ligands 7−12. These ligands were then used to synthesize dinuclear chloro-bridged Rh(I) complexes 13−18 with the general formula [Rh(μ-Cl)(P-alkene)]2. It was shown by X-ray diffraction analyses that these P-alkenes indeed act as bidentate ligands for Rh(I). Furthermore, the crystal structures revealed a change in the hybridization state of the dibenzazepine N atom, passing from sp2 in the free ligand to sp3 when coordinated to Rh in a bidentate fashion, thus modifying the bite angle of the ligands. The Rh complexes 16 and 18, bearing the (S)-binaphthol-derived ligand 10 and the α,α-diphenyl-l-prolinol-derived ligand 12, respectively, were shown to be active and enantioselective catalysts for the 1,4 addition of arylboronic acids to enones. At 80 °C turnover numbers of up to 61 and enantiomeric excesses of up to 92% were observed.

From zero to hero? Sulfoxides are generally not considered useful ligand entities in asymmetric metal catalysis. However, a chiral disulfoxide as a chelating ligand in the rhodium-catalyzed 1,4-addition of aryl boronic acids to cyclic, alpha,beta-unsaturated ketones and esters gives impressive catalytic results, thus opening the door to future applications of this new chiral ligand class.

N-Heterocyclic carbene ligands derived from C(2)-symmetric diamines with naphthyl side chains are introduced as chiral monodentate ligands, and their palladium complexes (NHC)Pd(cin)Cl are prepared. These compounds exist as a mixture of diastereomers, and the palladium complexes can be successfully separated and their absolute stereochemistry assigned. When used in the asymmetric intramolecular alpha-arylation of amides, oxindoles with quaternary carbon centers can be obtained in high yield and selectivity when correctly matching the chirality of the NHC complexes.