Reexamining Oxidation States during the Synthesis of 2‑Rhodaoxetanes from Olefins

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.