Synthesis, Structural Characterization, and Reactivity of Cp2- and (CpMe)2‑Ligated Titanaaziridines and Titanaoxiranes with Fast Enantiomer Interconversion Rates

A new synthetic route to (CpR)2-ligated titanaaziridines and titanaoxiranes from stable Ti­(II) precursors has been developed, and the enantiomer interconversion rate constants for chiral titanaaziridines and titanaoxiranes have been measured for the first time. The titanaaziridines (CpR)2Ti­(η2-N­(R1)­CHPh)­(L) (R = H (10), Me (12); R1 = Ph (a), o-anisyl (b), SiMe3 (c); L = PMe3 (a, c), −OMe (b)) and titanaoxiranes Cp2Ti­(η2-Ph­(R)­CO)­(L) (R = Ph (14), H (15); L = PMe3) have been synthesized and characterized spectroscopically; titanaaziridine 10a and titanaoxirane 14 have been characterized by X-ray crystallography. The enantiomer interconversion rate constants for the chiral titanaaziridines and titanaoxiranes have been measured by variable-temperature NMR; kinv for 10b is the fastest enantiomer interconversion rate constant reported for any metallaaziridine or metallaoxirane to date. Titanaaziridines 10 and 12 undergo exchange reactions with CC and CX bonds, whereas the titanaoxiranes 14 and 15 undergo insertions.