Betainic and ionic tungsten (VI) imido alkylidene N-heterocyclic olefin complexes

A series of betainic and ionic tungsten (VI) imido alkylidene N-heterocyclic olefin (NHO) complexes W2 - W7 of the general formulae [W(N-2,6-iPr(2)-C6H3)(CHCMe2Ph)(X)(n)(NHO)(m)] and [W(N-2,6-iPr(2)-C6H3)(CHCMe2Ph)(X)(n)(NHO)(m) (B(Ar-F)(4))(x)] (NHO = 2-methylene-1,3,4,5-tetramethyl-4,5-dihydro-1H-imidazol-3-ium, 2-methylene-1,3-dimethyl-1H-benzo[d]imidazolium; X = CF3SO3, OCMe(CF3)(2), n, m = 1, 2; x = 0,1) have been prepared. By adapting the number and type of NHO ligands, catalysts W2 and W7 show an improved activity in ring-closing metathesis compared to a previous system. In particular, the ionic and tetra-coordinated W7, which is ligated by only one NHO ligand, displays promising catalytic behavior. The results indicate that the overall still moderate performance can be further optimized by ligand tuning, suggesting less basic NHOs as promising candidates for further investigations. (c) 2023 Elsevier B.V. All rights reserved.