Cationic Tungsten Alkylidyne <i>N</i>‐Heterocyclic Carbene Complexes: Synthesis and Reactivity in Alkyne Metathesis
Philipp M. Hauser, Melita van der Ende, Jonas Groos, Wolfgang Frey, Dongren Wang, Michael R. Buchmeiser
Abstract
The first cationic and neutral tungsten alkylidyne N ‐heterocyclic carbene (NHC) complexes bearing one triflate ligand were synthesized and tested for their reactivity in alkyne metathesis. Both types of tungsten alkylidyne complexes display a higher productivity in alkyne metathesis than the analogous neutral tungsten alkylidyne NHC trisalkoxide complexes. Reaction of W(≡CC 6 H 4 OMe)(1,3‐bis(1‐hydroxy‐1,1‐trifluoromethylethyl)‐imidazol‐2‐ylidene)Cl ( W18 ) with AgB(Ar F ) 4 (Ar F = 3,5‐bis(trifluoromethyl)phenyl) resulted in the unexpected formation of, to the best of our knowledge, the first cationic ditungstatetrahedrane W 2 (1,3‐bis(1‐hydroxy‐1,1‐trifluoromethyl‐ethyl)‐imidazol‐2‐ylidene) 2 (MeCN)( µ ‐((Ar)CC(Ar))) + (B(Ar F ) 4 ) – ( W19 , Ar = C 6 H 4 OMe), which suggests bimolecular decomposition as a possible decomposition pathway of cationic tungsten alkylidyne NHC complexes. Reaction of the cationic tungsten alkylidyne NHC complex W(≡CC 6 H 4 OMe)(1,3‐diisopropylimidazol‐2‐ylidene)(OC(CF 3 ) 2 Me) 2 (NC t Bu) + (B(Ar F ) 4 ) – ( W7 ) with 1‐phenyl‐1‐propyne allowed for the isolation of a cationic tungstacyclobutadiene W(C 3 (Ph)(Me)(C 6 H 4 OMe))(1,3‐diisopropylimidazol‐2‐ylidene)(OC(CF 3 ) 2 Me) 2 (NC t Bu) + (B(Ar F ) 4 ) – ( W20 ). Its formation strongly supports a cationic active species in the alkyne metathesis with tungsten alkylidyne NHC complexes.