The Effect of Remote Donor Substituents on the Properties of Alkoxy and Amino Fischer Carbene Complexes of Tungsten

Abstract

AbstractTungsten Fischer ethoxy‐ and dimethylaminocarbene complexes [W{C(X)(C6H4‐4‐R}(CO)5] (X=OEt: series a; or X=NMe2: series b) are synthesized from phenyl substrates containing remote tertiary amino substituents R’2N with R’=Me (2), Ph (3) or C6H4Br‐4 (4). The π‐delocalization and carbene‐stabilizing effects of the distant tertiary amine donor substituent are investigated by NMR and IR spectroscopy, electrochemistry and quantum chemical calculations. A significant transfer of electron density from the remote 4‐R’2N substituent to the carbene C atom in the ethoxycarbene complexes is supported by NMR data and the solid‐state structure of 2 a. This is strongly attenuated in the amino‐substituted carbene complex 2 c and irrelevant in the dimethylaminocarbene complexes of series b, where the electron demand of the electrophilic carbene center is satisfied by the directly attached dimethylamino substituent. Quantum chemical calculations and IR spectroelectrochemistry on complexes 1 a‐‐4 a verify carbene‐centered reductions and a ligand based oxidation of complex 2 b.