(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, WCl2(=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 η2-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.