A new class of easily tunable N,N,N-pyridinebisimidazoline (pybim) ligands have been synthesized. The synthesis and tunability of these chiral tridentate ligands are much easier and flexible compared to the popular pyboxes, making the former a suitable ligand tool box for various asymmetric transformations. Ruthenium complexes of the new ligands were synthesized and applied in the asymmetric epoxidation of olefins using hydrogen peroxide as the oxidant. Excellent yields and moderate to good enantioselectivities were achieved in the epoxidation of aromatic olefins.

Synthesis of a novel class of chiral N,N,N-tridentate pyridinebisimidazoline ligands and their application in Ru-catalyzed asymmetric epoxidations

A new method is presented for metalation of a wide range of free-base, neutral, cationic, and anionic porphyrins in refluxing dimethylformamide (DMF) using an easily prepared [Ru(DMF)6](OTf)3 complex, and comparisons are made with the more familiar metalation procedure using Ru3(CO)12. Both procedures generate RuII(porp)(CO)L complexes (L = solvent); use of the RuIII-triflate precursor gives yields comparable to, or greater than, those obtained with the carbonyl, and generates no Ru-chlorin impurities. Mechanistic studies on the meso-tetraphenylporphyrin system reveal that the DMF furnishes the CO, which in the presence of essential water reduces the metal, and metalation likely occurs via a RuII−CO species. Corresponding metalation of tetradentate Schiff-bases gives trans-[RuIII(Schiff- base)(DMF)2]OTf complexes in yields of ∼50%, a limitation being the accompanying hydrolysis of the Schiff-base through the presence of trace water.

Synthetic and mechanistic aspects of a new method for ruthenium-metalation of porphyrins and Schiff-bases.

The ruthenium(II) 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin carbonyl complex has been covalently attached to a 3 - aminoporpyl functionalized silica gel. This supported complex is found to efficiently catalyze the epoxidation of the Δ 5 -unsaturated steroid derivatives with high conversion, epoxide yield and β-selectivity. High β-selectivity is also observed for the epoxidation of a Δ 4 -unsaturated steroid though the conversion and derivative are low. This new silica-supported polyhalogenated metalloporphrin catalyst can be easily recovered after reaction and has shown high stability over repeated uses. No catalyst leaching is detected in these reactions.

Highly β-selective epoxidation of the Δ5- and Δ4-unsaturated steroids catalyzed by the silica-supported polyhalogenated ruthenium porphyrin

Chapter 3.2 – Three-membered ring systems (2005)

Ruthenium, Carbonyl[5,10,15,20‐tetraphenyl‐21H,23H‐porphinato(2–)‐κN21,κN22,κN23,κN24]‐

Protected α-amino epoxides were successfully obtained in high threo-selectivity (up to 99%) under mild reaction conditions by using carbonyl 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrin ruthenium(II) [Ru(TDCPP)CO] as catalyst and 2,6-dichloropyridine N-oxide (Cl2PyNO) as oxidant.

Highly diastereoselective epoxidation of protected α-amino alkenes catalyzed by ruthenium porphyrin/Cl2PyNO system

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Highly diastereoselective epoxidation of protected α-amino alkenes catalyzed by ruthenium porphyrin/Cl2PyNO system