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.本研究开发了一条以稳定二价钛（Ti(II)）前驱体为原料，合成双(CpR)配位的钛杂氮丙啶（titanaaziridines）与钛杂环氧乙烷（titanaoxiranes）的全新合成路线，并首次测定了手性钛杂氮丙啶与钛杂环氧乙烷的对映异构体互变速率常数。本研究合成了钛杂氮丙啶类化合物(CpR)₂Ti(η²-N(R¹)CHPh)(L)（其中R=H（10）、Me（12）；R¹=Ph（a）、邻甲氧基苯基（o-anisyl，b）、三甲基硅基（SiMe3，c）；L=三甲基膦（PMe3，a,c）、甲氧基（-OMe，b））与钛杂环氧乙烷类化合物Cp₂Ti(η²-Ph(R)CO)(L)（其中R=Ph（14）、H（15）；L=PMe3），并完成了光谱学表征；其中钛杂氮丙啶10a与钛杂环氧乙烷14还通过X射线晶体衍射（X-ray crystallography）完成了结构表征。本研究通过变温核磁共振（variable-temperature NMR）测定了手性钛杂氮丙啶与钛杂环氧乙烷的对映异构体互变速率常数；其中化合物10b的对映异构体互变速率常数k_inv是目前已报道的所有金属杂氮丙啶（metallaaziridine）与金属杂环氧乙烷（metallaoxirane）中最快的。钛杂氮丙啶10与12可与碳碳双键（C=C）及碳杂双键（C=X）发生交换反应，而钛杂环氧乙烷14与15则可发生插入反应。