Dirhodium tetraacylate complexes and monovalent ligands. Adduct formation in solution as monitored by NMR spectroscopy

Evidences of adduct formation between the dirhodium complex Rh2[(R)-MTPA4](Rh–Rh; MTPA-H = Mosher acid) and various monovalent ligands L were obtained in solution by using NMR spectroscopy. Strongly binding ligands, e.g. selenoethers or nitriles, prefer LRh–RhL adducts whereas weaker ligands, e.g. olefins with low steric hindrance, tend to form oligomers with bridging L molecules: Rh–RhLRh–Rh. Larger steric congestion forces olefins to avoid bridge situations or even prohibits adduct formation at all.