(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.