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

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journal contribution
posted on 22.11.1999, 00:00 by Wei-Dong Wang, James H. Espenson
The tris(imido)methylrhenium compound CH3Re(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 CH3Re(NAd)2O and CH3Re(NAd)O2 could be detected. In the third and slowest stage CH3ReO3 (MTO) was formed, eventually in quantitative yield. The second-order rate constant for PhCHO in C6D6 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 CH3Re(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, CH3Re(NAd)3 reacts with imines. Imine−imine metathesis is catalyzed by MTO homogeneously and by MTO supported on Nb2O5.