Gold vinylidene intermediate

Scheme 17 The benzofulvene products more directly reflect the gold vinylidene intermediate. The em-diaurated species as an instant dual activation precatalyst shows three times the activity of other gold catalysts...

Scheme 18 The dibenzopentalaie products also are good indicators for a gold vinylidene intermediate...

Vinylidene" Gold(l) Intermediates 93 Figure 4.4 Gold acetylide 31 as a stable compound. 

Based on the analysis of the electronic structure of vinylidene intermediates, we wanted to test whether allenylidene complexes of gold(I) could be prepared. First, the gold acetylides 49 were prepared then an alkylation delivered 50 (Scheme 4.20). A detailed structure investigation, based on experimental and computational methods, followed [43]. The strong donors, which allow 50 to be isolated, stabilize the carbenium ion with the lone pair of the heteroatom (O or N). Thus no significant Au-C double bond character could be detected. 

More recently, Au(I)-catalyzed ring-closure reactions of 1,2-diethynylbenzenes 158-160 bearing a terminal acetylene unit afford benzofulvene and dibenzopen-talene derivatives 161-163, as illustrated in Scheme 6.37 [79]. Gold vinylidene complexes are postulated to generate the respective reaction intermediates. These reactions are of importance for the construction of asymmetric polycyclic systems. 

---