Cationic Tungsten Imido Alkylidene N-Heterocyclic Carbene Complexes That Contain Bulky Ligands

Neutral and cationic tungsten imido alkylidene complexes of the general formulas W(NtBu)(CHR1)(OR2)Cl(NHC), W(N-2,6-bis(2,4,6-tri-iPr-C6H4)phenyl)(CHR1)Cl-2(NHC), [W(NtBu)(CHR1)(OR2)(NHC)][B(Ar-F)(4)] and [W(N-2,6-bis(2,4,6-tri-iPr-C6H4)phenyl)(CHR1)Cl(NHC)][B(Ar-F)(4)] (R-1 = CMe3, CMe2Ph; R-2 = sterically demanding alkoxide; B(Ar-F)(4) = tetrakis(3,5-(CF3)(2)-C6H3)borate; NHC = N-heterocyclic carbene) were prepared. Two electronically different NHCs, namely 1,3-dimethylimidazol-2-ylidene (IMe) and 1,3-dimethyl-4,5-dichloroimidazol-2-ylidene (IMeCl), as well as a variety of terphenolates and a chiral biphenolate were employed. Z-selective homometathesis (HM) of unfunctionalized olefins was achieved with a selectivity of up to 90% and decent turnover numbers (TON) of up to 480 in the HM of 1-dodecene. Additionally, the reactivity of the cationic tungsten tert-butylimido complexes in the reaction with vinyltrimethylsilane and ethylene was investigated, which yielded the corresponding silyl-alkylidene complex and, for the first time, a fully characterized cationic tungsten(IV) NHC ethylene complex.

Automated summary

The synthesis of tungsten imido alkylidene complexes with neutral and cationic properties was achieved, leading to successful homometathesis of unfunctionalized olefins. The reactivity of these complexes in various reactions was investigated, resulting in the first fully characterized cationic tungsten(IV) NHC ethylene complex.