Alkenylation of 2-Methylpyridine via Pyridylidene-Osmium Complexes

Complex [OsTp(kappa(1)-OCMe2)(2)((PPr3)-Pr-i)]BF4 (1; Tp = hydridotris(pyrazolyl)borate) reacts with 2-methylpyridine and pyridine, in acetone, at room temperature to give the N-coordinated heterocyclic derivatives (OsTp{kappa(1)-N[NC5H4Me]} (kappa(1)-OCMe2)((PPr3)-Pr-i)]BF4 (2) and [OsTp{kappa(1)-N[NC5H5]}(kappa(1)-OCMe2)((PPr3)-Pr-i)BF4 (3). However, in fluorobenzene, at 100 degrees C, the reaction of 1 with 2-methylpyridine leads to the pyridylidene compound [OsTp{kappa(1)-C[HNC5H3Me]} (kappa(1)-OCMe2)((PPr3)-Pr-i)BF4 (4). The addition of phenylacetylene and cyclohexylacetylene to the fluorobenzene solutions of the latter affords the pyridylidene-vinylidene complexes [OsTp(kappa(1)-C[HNC5H3Me])(=C=CHR)(PiPr(3)))BF4 (R = Ph (5), Cy (6)), which undergo selective deprotonation at the Cp atom of the vinylidene ligand to generate the alkynyl-pyridylidene derivatives OsTp(C CR){kappa(1)-C[HNC5H3Me]-((PPr3)-Pr-i) (R = Ph (7), Cy (8)). Heating of toluene solutions of 7 and 8 at temperatures higher than 50 degrees C produces the hydrogen transfer from the nitrogen atom to the Cp atom of the alkynyl ligands to afford the pyridyl-vinylidene intermediates [OsTp{kappa(1)- C[NC5H3Me]}(=C=CHR)((PPr3)-Pr-i)]BF4 (R = Ph (7a), Cy (8a)), which evolve by 1,2-migratory insertion of the vinylidene ligands into the Os pyridyl bond to give the alkenylation products OsTptic2-C,N[C(=CHR)C5(Me)H3ND(PiPr3) (R = Ph (9), Cy (10)). Protonation of 9 and 10 with HBF4 center dot EtO2 yields [OsTp{kappa(2)-C,N[=C(CH2R)C-5(Me)H3ND((PPr3)-Pr-i)]BF4 (R = Ph (11), Cy (12)). Complexes 7-9 have been characterized by X-ray diffraction analysis.