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

Abstract

Reaction of the ruthenium allenylidene complex [Ru]═C═C═CPh2 (1, [Ru] = Cp(PPh3)2Ru) with the propargylic Grignard reagent R-C≡CCH2MgBr (R = CH3, CH2CH3, Ph) yielded a mixture of two acetylide complexes. The major products, [Ru]C≡CCPh2C(R)═C═CH2 (2a, R = CH3; 2b, R = CH2CH3; 2c, R = Ph), have an allenyne moiety, and the minor ones, [Ru]C≡CCPh2CH2C≡CR (3a, R = CH3; 3b, R = CH2CH3; 3c, R = Ph), have a diyne ligand. The reaction of similar propargyl Grignard reagent HC≡CCH2MgBr with 1 yielded only the diyne complex 3d. Treatment of complexes 2a−2c with HBF4 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.