Chiral Heterobimetallic Bismuth–Rhodium Paddlewheel Catalysts: A Conceptually New Approach to Asymmetric Cyclopropanation

Abstract

Cyclopropanation reactions of styrene derivatives with donor–acceptor carbenes formed in situ are significantly more enantioselective when catalyzed by the heterobimetallic bismuth–rhodium complex 5 a endowed with N‐phthalimido tert‐leucine paddlewheel ligands rather than by its homobimetallic dirhodium analogue 1 a. This virtue is likely the result of two synergizing factors: the conical shape of 5 a translates into a narrower calyx‐like chiral binding site about the catalytically active Rh center; the Bi atom, although fully solvent exposed, does not decompose aryl diazoacetates and is hence incapable of promoting a racemic background reaction. Moreover, ligand variation proved that successful catalyst design mandates that the anisotropy of the conical heterobimetallic core be matched by proper directionality of the ligand sphere.

Chiral Bismuth‐Rhodium Paddlewheel Complexes Empowered by London Dispersion: The C−H Functionalization Nexus

“…[29,30] As long as the narrower pore surrounds the catalytically active Rh(+ 2) site of [BiRh((S)-PTTL) 4 ] (6 a), improved asymmetric induction will ensue. [31] The directionality, however, is a derivative of the ligand structure and cannot be taken for granted. To warrant this critically important parameter, the tert-butyl residues in 6 a were replaced in a next design step by phenyl rings carrying lateral À Si(iPr) 3 substituents, which get close enough to each other to entertain a large number of attractive interligand London dispersion (LD) interactions [32,33] that stabilize the desired calyx of the resulting complex 7 a (R = H).…”

Catalytic Asymmetric Fluorination of Copper Carbene Complexes: Preparative Advances and a Mechanistic Rationale

“…As part of our studiesi nto structure,b onding and reactivity of organotransitionm etal carbene complexes, [13][14][15][16][17][18] we sought to improveo nt hese lead findings. We were fully apprehensive that the small size of the fluoride ion constitutes af ormidable and inherent challenge for asymmetricc atalysis;m oreover,a ny Scheme1.Lead finding of ac opper catalyzedformation of a-fluoroesters.…”

Density Functional Theoretical Study on the Electronic Structure of Rh2O7+ with Low Oxidation States

“…Rh is regarded as an important active center, which is widely applied in various syntheses and their catalysis. 1 − 4 In numerous syntheses, it has been used as a catalyst for cyclopropanation, 5 , 6 hydroformylation, 7 , 8 and C–H bond activation; 9 , 10 what is more, it has also been used for manufacturing acetic acid 11 and β2-amino acid. 12 In particular, Shan et al 13 reported a mononuclear rhodium species, which was anchored on a zeolite or titanium dioxide support suspended in an aqueous solution; they catalyzed the direct conversion of methane to methanol and acetic acid using oxygen and carbon monoxide under mild conditions.…”