A Heteroleptic Dirhodium Catalyst for Asymmetric Cyclopropanation with α‐Stannyl α‐Diazoacetate. “Stereoretentive” Stille Coupling with Formation of Chiral Quarternary Carbon Centers

Abstract

The heteroleptic dirhodium paddlewheel catalyst 7 with achiral carboxylate/acetamidate ligand sphere is uniquely effective in asymmetric [2+ +1] cycloadditions with a-diazo-atrimethylstannyl (silyl, germyl) acetate.O riginally discovered as at race impurity in as ample of the homoleptic parent complex [Rh 2 ((R)-TPCP) 4 ](5), it is shown that the protic acetamidate ligand is quintessential for rendering 7 highly enantioselective.The-NH group is thought to lock the ensuing metal carbene in place via interligand hydrogen bonding.The resulting stannylated cyclopropanes undergo "stereoretentive" cross coupling, whichs hows for the first time that even chiral quarternary carbon centers can be made by the Stille-Migita reaction. Scheme 1. Conceptualo utline.

Triple Resonance Experiments for the Rapid Detection of 103Rh NMR Shifts: A Combined Experimental and Theoretical Study into Dirhodium and Bismuth–Rhodium Paddlewheel Complexes

“…This finding has implications for catalysis, as a chiral relative of 16 was recently shown to be uniquely effective in asymmetric cyclopropanation reactions of α-stannyl(silyl) α-diazoesters. 49 Indirect evidence suggested that these reactions proceed at the rhodium face carrying the protic −NH group, which according to the shift data is the (much) less electrophilic site; this conclusion clearly mandates further scrutiny. In any case, 103 Rh NMR makes it unambiguously clear that carboxylate- and carboxamidate-based paddlewheel complexes are very distinct types of catalysts in electronic terms.…”

A New Ligand Design Based on London Dispersion Empowers Chiral Bismuth–Rhodium Paddlewheel Catalysts

“…3a , b as the parent complexes of this series excel in cyclopropanation, cyclopropenation, and certain insertion reactions; as many variations of the conceptually new design can be envisaged, one may have high expectations for future generations of catalysts of this type. Opportunities along these and related lines 99 , 100 are actively pursued in our laboratory.…”

[Rh2(MEPY)4] and [BiRh(MEPY)4]: Convenient Syntheses and Computational Analysis of Strikingly Dissimilar Siblings

“…Future work must hence try to gain deeper understanding for and better control over this particular parameter. For our long‐standing interest in various aspects of metal carbene chemistry in general, [41–49] we are committed to doing so; encouraging lead findings along these lines have recently been disclosed [50]…”