Cationic Tungsten Oxo Alkylidene N-Heterocyclic Carbene Complexes via Hydrolysis of Cationic Alkylidyne Progenitors

Abstract

A route to cationic tungsten alkylidyne N-heterocyclic carbene (NHC) complexes of the general formula [W(CR)X2(NHC)(tBuCN)y+B(ArF)4-] (R = tBu, C6H4-4-OMe; X = Br, Cl, OTf; NHC = 1,3-dimesityl-1,3-dihydro-2H-imidazol-2-ylidene, IMes; 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene, IDipp; 1,3-dimesityl-4,5-dichloro-1,3-dihydro-2H-imidazol-2-ylidene, IMesCl2; y = 1, 2; ArF = 3,5-bis(trifluoromethyl)phenyl) is presented. Addition of 1 equiv of water to cationic tungsten benzylidyne and neopentylidyne NHC complexes results in the formation of the corresponding cationic tungsten oxo alkylidene complexes; however, only the resulting neopentylidene complexes were isolated as stable compounds and tested in selected olefin metathesis reactions. Interestingly, even though a strongly basic ligand in the form of the NHC is coordinated to the metal center, this bond is unaffected by the reaction with 1 equiv of water. The hydrolysis of cationic tungsten alkylidyne NHC complexes represents one pathway to cationic tungsten oxo alkylidene NHC complexes and enables the synthesis of complexes, which were so far not easily accessible by previously published procedures.