(Imido)tungsten-Alkylidene-Catalyzed [2+2+1]-Cycloaddition Reaction of 3,3-Disubstituted Cyclopropenes and Internal Alkynes Giving Multisubstituted Cyclopentadienes

Schrock-type alkylidene complexes, especially imido ligand-supported metal alkylidene complexes, have been used as catalysts and reagents for C–C multiple bond-forming reactions involving unsaturated organic compounds. Herein, we report that an imidotungsten(IV) complex, WCl 2 (=NDipp)(P(OMe) 3 ) 3, catalyzes a [2+2+1]-cycloaddition reaction of 3,3-disubstituted cyclopropenes and 2 equiv of alkynes, giving multisubstituted cyclopentadienes. The initial step of this catalytic reaction is ring-opening of a cyclopropene by the (imido)tungsten(IV) complex to form an (imido)tungsten vinylalkylidene species. Stoichiometric reactions of the (imido)tungsten vinylalkylidene complex and an η 2 -alkyne tungsten complex as well as density functional theory (DFT) calculations revealed the reaction mechanism, in which two consecutive metatheses of the (imido)tungsten vinylalkylidene species and two alkynes followed by reductive elimination afford the multisubstituted cyclopentadiene along with a regeneration of an (imido)tungsten(IV) species.