Herein, we report experimental, spectroscopic, and computational data that indicate that a rhodium ethylene complex, formally described as rhodium(I) and which forms a 2-rhoda(III) oxetane following reaction with H2O2, is more accurately described as a rhodium(III) metallacyclopropane. X-ray absorption spectroscopy clearly demonstrates a change in the oxidation state at rhodium following ligand coordination with tris(2-pyridylmethyl)amine. Both NMR and density functional theory studies suggest a high energy barrier to rotation of the coordinated ethylene, which is attributed to large geometric and electronic reorganization resulting from the loss of π-back-bonding. These results imply that the role of H2O2 in the formation of 2-rhoda(III) oxetanes is to oxidize the C2H4 fragment rather than the metal center, as has been previously suggested.
Bibliographical noteFunding Information:
We thank The University of British Columbia, NSERC (DG and RTI grants), and CFI for supporting this research. A.N.D. is grateful to the NSERC for a CGS-D and to the Izaak Walton Killam Foundation for a doctoral scholarship. We also thank Profs. Peter H. M. Budzelaar and Bas de Bruin for helpful discussions. Synchrotron experiments were performed at the Canadian Light Source, a national user facility supported by CFI, NSERC, WED Canada, NRC Canada, CIHR, the Government of Saskatchewan, and the University of Saskatchewan.
© 2015 American Chemical Society.