Synthesis and Characterization of Novel Ligand for Use on Rhodium Paddlewheel Complexes

Dirhodium (II) paddlewheel complexes have proven to be useful catalysts in many transformations including C-H insertions, cyclopropanation, and silane insertion reactions. One deficiency of these catalysts is the inability to modulate the enantioselectivity with reactive diazo compounds. One avenue for potential improvement of paddlewheel complexes is coordinating ligands in the axial site to increase enantioselectivity. The axial site has been occupied by various ligands including Nheterocyclic carbenes, nitrogen compounds, and phosphorous compounds. This work examines compounds that can be used as ligands on dirhodium complexes that have a pendant chain containing a dibenzyl phosphite and dibenzyl phosphate, both of which are unpublished compounds. By having these pendant chains tethered to the oxazolidinone backbone, control is built-in due to the proximity effect and hemilability of the ligand being synthesized. This study also optimized the process for making oxazolidinones after cyclization resulted in some six-membered ring when the five-membered ring was desired. Purification of the phosphite ligand proved to be difficult due to the contamination of side products formed during the process, but was solved by using triethylamine in the eluent of the chromatography process. The ligands obtained can replace bridging ligands on dirhodium (II) complexes and can be used for diazo-mediated reactions.