Dirhodium paddlewheel catalysts have been of great interest due to their ability to take part in metal-carbene mediated reactions, such as X-H insertion (e.g., X = C or Si), cyclopropanation, cycloadditions, and a wide range of ylide reactions (e.g., ylide-formation/sigmatropic rearrangements). Our research is motivated by the opportunity to theoretically investigate mechanistic aspects of these Rh-catalyzed reactions, which has so far, been mostly taken on by experimental groups. One question that has risen out of the literature is the effect of axially coordinated solvent on reactivity in these transformations. We know from the literature that axial solvent coordination occurs; many solved X-ray structures of these complexes display axial coordination by solvent,1 and their macroscopic effects can be seen in witnessing change in color due to ligand exchange at the axial position.2 What effects, then, do axially coordinated species have on reactivity for these catalysts? We address this question with a density functional theory (DFT) study, wherein we compute the barriers for carbene formation and C-H insertion into propane within various solvents, ranging in polarity, such as no solvent, dichloromethane, isopropanol, and acetonitrile. Our theoretical study will help inform future experimental design with regards to dirhodium complexes—or derivatives thereof that exploit tethered, axial ligands3—by illuminating some of the physical effects axial coordination facilitates.

Mechanistic interrogation of reactions involving dirhodium complexes: Effects of solvent coordination

ACS Fall 2021

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