A novel approach to the design of dirhodium(II) tetracarboxylates derived from (S)-amino acid ligands is reported. The approach is founded on tailoring the steric influences of the overall catalyst structure by reducing the local symmetry of the ligand's N-heterocyclic tether. The application of the new approach has led to the uncovering of [Rh (S- PTTL) ] as a new member of the dirhodium(II) family with extraordinary selectivity in cyclopropanation reactions. The stereoselectivity of [Rh (S- PTTL) ] was found to be comparable to that of [Rh (S-PTAD) ] (up to >99 % ee), with the extra benefit of being more synthetically accessible. Correlations based on X-ray structures to justify the observed enantioinduction are also discussed.

In this review the recent advances in the utilization of two of the most important classes of dirhodium(II) paddlewheel complexes, dirhodium(II) carboxylates and carboxamidates, as chemzymes in inter- and intramolecular asymmetric cyclopropanation, as well as cyclopropenation reactions are discussed.

Abstract:Modern experiments have offered alternative interpretations on the symmetry of chiral dirhodium(II) carboxylate complexes and its relationship to their level of enantioselectivity. So, this contribution is to provide an insight on how the knowledge around the structure of these catalysts has evolved with a particular emphasis on the impact of this knowledge on enantioselectivity prediction and catalyst design.

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The catalysis by dirhodium paddlewheel complexes has been an area of immense interest and extensive study over the past three decades -not only because most of the catalysts are highly stable to heat, moisture and ambient atmosphere but also for the asymmetric induction in the ylide generation. In this review, we attempt to provide an overview on the general preparation method for most homogeneous chiral dirhodium(II) catalysts that have appeared to date and their recent applications in asymmetric catalysis with iodonium ylides as carbenoid precursors.

A new series of dirhodium(II) tetracarboxylate was derived from N-1,2-naphthaloyl-(S)-amino acid ligands. In terms of enantioselectivity, Rh2 (S-1,2-NTTL)4 () derived from N-1,2-naphthaloyl-(S)-tert-leucine, was the best-performing catalyst among the new series in the enantioselective synthesis of cyclopropylphosphonate derivatives (up to >99% enantiomeric excess). A predictive model was proposed to justify the observed high enantiomeric induction exhibited by Rh2 (S-1,2-NTTL)4 with donor-acceptor phosphonate carbenoids.

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Enoldiazosulfones undergo [3 + 3]-cycloaddition with nitrones when catalyzed by copper­(I) catalysts, but not with dirhodium­(II) catalysts. Under mild reaction conditions with chiral bisoxazoline ligands, copper­(I) catalysts produce 1,2-oxazine-sulfone derivatives in high yields and enantioselectivities. Dirhodium­(II) catalysts form stable donor–acceptor cyclopropenes that undergo uncatalyzed [3 + 2]-cycloaddition reactions with nitrones.