Metathesis Reactions of Tris(adamantylimido)methylrhenium and Aldehydes and Imines

The tris(imido)methylrhenium compound CH 3 Re(NAd) 3 (Ad = 1-adamantyl) was prepared and characterized. It reacts with aromatic aldehydes ArCHO forming the imines ArCH NAd. The reaction occurs in three stages, during which CH 3 Re(NAd) 2 O and CH 3 Re(NAd)O 2 could be detected. In the third and slowest stage CH 3 ReO 3 (MTO) was formed, eventually in quantitative yield. The second-order rate constant for PhCHO in C 6 D 6 at 298 K is 1.4 × 10 - 4 L mol - 1 s - 1 . Electron-donating substituents at the para-position of ArCHO cause a significant diminution in rate. Treated by the Hammett equation, the reaction constant is ρ = +0.90. The reactions between CH 3 Re(NAd) 3 and linear aliphatic aldehydes occur much faster than do reactions of nonlinear aliphatic or aromatic aldehydes, indicating an important steric effect. Ketones do not react. The imidorhenium complex evidently undergoes a metathesis reaction with the aldehyde. Analogously, CH 3 Re(NAd) 3 reacts with imines. Imine−imine metathesis is catalyzed by MTO homogeneously and by MTO supported on Nb 2 O 5 .