The First Crystal Structure of a Reactive Dirhodium Carbene Complex and a Versatile Method for the Preparation of Gold Carbenes by Rhodium‐to‐Gold Transmetalation

Abstract

The dirhodium carbene derived from bis(4‐methoxyphenyl)diazomethane and [Rh(tpa)4]⋅CH2Cl2 (tpa=triphenylacetate) was characterized by UV, IR, and NMR spectroscopy, HRMS, as well as by X‐ray diffraction. The isolated complex exhibits prototypical rhodium carbene reactivity in that it cyclopropanates 4‐methoxystyrene at low temperature. Experimental structural information on this important type of reactive intermediate is extremely scarce and thus serves as a reference point for mechanistic discussions of rhodium catalysis in general. Moreover, dirhodium carbenes are shown to undergo remarkably facile carbene transfer on treatment with [LAuNTf2] (L=phosphine). This formal transmetalation opens a valuable new entry into gold carbene complexes that cannot easily be made otherwise; three fully characterized representatives illustrate this aspect.

Effects of Axial Solvent Coordination to Dirhodium Complexes on the Reactivity and Selectivity in C–H Insertion Reactions: A Computational Study

“…49 The few reported X-ray structures of dirhodium carbenes crystallize as coordination polymers: OMe or NMe2 groups present in the carbene appendants coordinate to the rhodium not bearing the carbene carbon of the next unit. 50,51 These complexes require CH2Cl2 and toluene to be stable in crystalline form and their unit cells contain highly disordered solvent molecules. 50 In solution, axial solvent coordination to dirhodium complexes is well known, [52][53][54][55][56] and even macroscopically evident due to its effect on the electronic structure of the complex.…”

Effects of Axial Solvent Coordination to Dirhodium Complexes on Reactivity and Selectivity in C–H Insertion Reactions: A Computational Study

“…48 The few reported X-ray structures of dirhodium carbenes crystallize as coordination polymers: OMe or NMe2 groups present in the carbene appendants coordinate to the rhodium not bearing the carbene carbon of the next unit. 49,50 These complexes require CH2Cl2 and toluene to be stable in crystalline form and their unit cells contain highly disordered solvent molecules. 49 In solution, axial solvent coordination to dirhodium complexes is well known, [51][52][53][54][55] and even macroscopically evident due to its effect on the electronic structure of the complex.…”

“…49,50 These complexes require CH2Cl2 and toluene to be stable in crystalline form and their unit cells contain highly disordered solvent molecules. 49 In solution, axial solvent coordination to dirhodium complexes is well known, [51][52][53][54][55] and even macroscopically evident due to its effect on the electronic structure of the complex. Coordination by solvent molecules is comparatively much weaker than carboxylate coordination.…”

Microwave-Assisted Synthesis and Characterization of [Rh2(OAc)4(L)2] Paddlewheel Complexes: A Joint Experimental and Computational Study

“…In 2007, Gois and Jang groups reported, respectively, that the binuclear Rh(II) complex, V, containing N-Heterocyclic Carbenes (NHC) as auxiliary ligands, can be a profitable tool in (i) the arylation of aldehydes and (ii) the allylic oxidation reaction [49,50]. Recently, Werlé et al reported that acetate rhodium derivatives like compound VI can be useful carbene transfer reagents [51].…”