The enantioselective addition of aliphatic thiols to α,β-unsaturated N-acylpyrazoles catalyzed by a bis-cyclometalated iridium(III) complex with fine-tuned Brønsted basicity was investigated. Good to excellent yields (71–99 %) and enantioselectivities (86–98 % ee) were achieved at catalyst loadings of 0.2–2.5 mol-%. In this metal-templated catalyst design, the metal serves as a structural center and the catalysis is executed by the organic ligand sphere through a combination of proton transfer, hydrogen-bond formation, and electrostatic interactions.

The enantioselective addition of aromatic thiols to α,β-unsaturated γ-oxoesters bearing an imidazole substituent in the δ position and catalyzed by an inert octahedral bis-cyclometalated iridium(III) complex is reported. High enantioselectivity down to catalyst loadings of 0.05 mol % is achieved mediated by the formation of well-arranged hydrogen bonds within the ligand sphere of the catalyst after the initial proton transfer. This work highlights the manifold opportunities provided by this metal-templated design strategy in which the metal exerts a purely structural role whereas catalysis occurs through the organic ligand sphere (metal-templated organocatalysis).

A sustainable CC bond formation is merged with the catalytic asymmetric generation of one or two stereocenters. The introduced catalytic asymmetric cross-coupling of two CH groups with molecular oxygen as the oxidant profits from the oxidative robustness of a chiral-at-metal rhodium(III) catalyst and exploits an autoxidation mechanism or visible-light photosensitized oxidation. In the latter case, the catalyst serves a dual function, namely as a chiral Lewis acid for catalyzing enantioselective enolate chemistry and at the same time as a visible-light-driven photoredox catalyst.

A sustainable CC bond formation is merged with the catalytic asymmetric generation of one or two stereocenters. The introduced catalytic asymmetric cross-coupling of two CH groups with molecular oxygen as the oxidant profits from the oxidative robustness of a chiral-at-metal rhodium(III) catalyst and exploits an autoxidation mechanism or visible-light photosensitized oxidation. In the latter case, the catalyst serves a dual function, namely as a chiral Lewis acid for catalyzing enantioselective enolate chemistry and at the same time as a visible-light-driven photoredox catalyst.

A bis-cyclometalated chiral-at-metal rhodium complex catalyzes the Diels–Alder reaction between N-Boc-protected 3-vinylindoles (Boc=tert-butyloxycarbonyl) and β-carboxylic ester-substituted α,β-unsaturated 2-acyl imidazoles with good-to-excellent regioselectivity (up to 99:1) and excellent diastereoselectivity (>50:1 d.r.) as well as enantioselectivity (92–99 % ee) under optimized conditions. The rhodium catalyst serves as a chiral Lewis acid to activate the 2-acyl imidazole dienophile by two-point binding and overrules the preferred regioselectivity of the uncatalyzed reaction.

Various ligands, such as (Z)-1-phenyl-2-[(4S)-4-phenyl-4,5-dihydro-1,3-oxazol-2-yl]ethen-1-ol ((S)-1a) and (Z)-1-phenyl-2-[(4S)-4-phenyl-4,5-dihydro-1,3-thiazol-2-yl]ethen-1-ol ((S)-1c), were investigated as auxiliaries for the asymmetric synthesis of chiral ruthenium(II) complexes. The reaction of these chiral auxiliary ligands with [RuCl₂(dmso)₄], 2,2′-bipyridine (bpy, 2.2 equiv), and triethylamine (10 equiv) in DMF/PhCl (1:8) at 140 °C for several hours diastereoselectively provided the complexes Λ-[Ru(bpy)₂{(S)-1aH}] (Λ-(S)-2a, 52 % yield, 56:1 d.r.) and Λ-[Ru(bpy)₂{(S)-1cH}] (Λ-(S)-2c, 48 % yield, >100:1 d.r.) in a single step after purification. Both Λ-(S)-2a and Λ-(S)-2c could be converted into Λ-[Ru(bpy)₃](PF₆)₂ by replacing the bidentate enolato ligands with bpy, under retention of configuration, induced by either NH₄PF₆ as a weak acid (from Λ-(S)-2a: 73 % yield, 22:1 e.r.; from Λ-(S)-2c: 77 % yield, 22:1 e.r.), TFA as a strong acid (from Λ-(S)-2a: 72 % yield, 52:1 e.r.; from Λ-(S)-2c: 85 % yield, 25:1 e.r.), methylation with Meerwein′s salt (from Λ-(S)-2a: 59 % yield, 46:1 e.r.; from Λ-(S)-2c: 86 % yield, 37:1 e.r.), ozonolysis (from Λ-(S)-2a: 56 % yield, 22:1 e.r.; from Λ-(S)-2c: 43 % yield, 6.3:1 e.r.), or oxidation with a peroxy acid (from Λ-(S)-2a: 72 % yield, 45:1 e.r.; from Λ-(S)-2c: 79 % yield, 8.5:1 e.r.). This study shows that, except for the reaction with NH₄PF₆, oxazoline-enolato complex Λ-(S)-2a provides Λ-[Ru(bpy)₃](PF₆)₂ with higher enantioselectivities than analogous thiazoline-enolato complex Λ-(S)-2c, which might be due to the higher coordinative stability of the thiazoline-enolato complex, thus requiring more prolonged reaction times. Thus, this study provides attractive new avenues for the asymmetric synthesis of non-racemic ruthenium(II)-polypyridyl complexes without the need for using a strong acid or a strong methylating reagent, as has been the case in all previously reported auxiliary methods from our group.