Chiral Alkoxide-Functionalized Guanidinates from Ring-Opening Rearrangement of Aminooxazolinate Complexes

Treatment of Cp*M(NMe2)3 (M = Zr, Hf) with both achiral and optically pure chiral aminooxazoline
proligands HL yields metastable aminooxazolinate half-sandwich diamide complexes [Cp*ML(NMe2)2].
These species undergo clean rearrangement via oxazoline ring-opening to carbodiimides followed by
amide migratory insertion. The chiral-at-metal products contain tridentate alkoxide-functionalized
guanidinates, as confirmed by X-ray diffraction. In some of the chiral ligand systems, single diastereomer
samples can be prepared, either by direct reaction or after recrystallization. As a result of the chelate
structure, no thermal conversion between diastereomers is observed. A mechanism leading to the observed
diastereoselection involving an intramolecular CH-π interaction in the major product is proposed.