Electronically Tuned Chiral Ruthenium Porphyrins: Extremely Stable and Selective Catalysts for Asymmetric Epoxidation and Cyclopropanation

We report the use of three enantiomerically pure and electronically tuned ruthenium carbonyl porphyrin catalysts for the asymmetric cyclopropanation and epoxidation of a variety of olefinic substrates. The D4‐symmetric ligands carry a methoxy, a methyl or a trifluoromethyl group at the 10‐position of each of the 9‐[anti‐(1,2,3,4,5,6,7,8‐octahydro‐1,4:5,8‐dimethanoanthracene)]‐substituents at the meso‐positions of the porphyrin. Introduction of a CF3‐substituent in this remote position resulted in greatly improved catalyst stability, and turnover numbers of up to 7 500 were achieved for cyclopropanation, and up to 14 200 for epoxidation, with ee values typically >90 % and ≈80 %, respectively. In one example, the axial CO ligand at the ruthenium was exchanged for PF3, resulting in the first chiral ruthenium porphyrin with a PF3 ligand reported to date. In cyclopropanations with ethyl diazoacetate, the latter catalyst performed exceedingly well, and gave a 95 % ee in the case of 1,1‐diphenylethylene as substrate. An efficient catalyst must provide high selectivities at low catalyst loadings. We herein present a new generation of electronically tuned chiral ruthenium porphyrins—designed to fulfill both requirements. In particular the tetrakis‐CF3‐substituted catalyst 1 shows unmatched performance: Total turnover numbers of >14 000 and > 7 500 were achieved in asymmetric epoxidation and cyclopropanation of terminal olefins, respectively, with high trans/cis and enantioselectivities.