Cyclization Accompanied with 1,2-Phenyl Migration in the Protonation of Ruthenium Acetylide Complex Containing an Allenyl Group

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Reaction of the ruthenium allenylidene complex [Ru]═C═C═CPh 2 ( 1, [Ru] = Cp(PPh 3 ) 2 Ru) with the propargylic Grignard reagent R-C≡CCH 2 MgBr (R = CH 3, CH 2 CH 3, Ph) yielded a mixture of two acetylide complexes. The major products, [Ru]C≡CCPh 2 C(R)═C═CH 2 ( 2a, R = CH 3; 2b, R = CH 2 CH 3; 2c, R = Ph), have an allenyne moiety, and the minor ones, [Ru]C≡CCPh 2 CH 2 C≡CR ( 3a, R = CH 3; 3b, R = CH 2 CH 3; 3c, R = Ph), have a diyne ligand. The reaction of similar propargyl Grignard reagent HC≡CCH 2 MgBr with 1 yielded only the diyne complex 3d . Treatment of complexes 2a − 2c with HBF 4 afforded the cyclization complexes 5a − 5c, respectively, proceeding via a vinylidene intermediate. The cyclization of the allenyl and the vinylidene groups is accompanied with a phenyl group migration. Complex 5b is fully characterized by a single-crystal X-ray diffraction analysis. Similar cyclization of complexes 2a and 2b, catalyzed by a Au phosphine complex, gave the ruthenium vinylidene complexes 6a and 6b, respectively, with different selectivity from that of the protonation reaction. Au-catalyzed cyclization of the diyne complex 3d yielded 6d, which is fully characterized by a single-crystal X-ray diffraction analysis.