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-pi interaction in the major product is proposed