Carbon Monoxide-Induced Dinitrogen Cleavage with Group 4 Metallocenes: Reaction Scope and Coupling to N-H Bond ormation and CO Deoxygenation

摘要

The scope of CO-induced N_2 cleavage in a series of zirconocene and hafnocene complexes containing activated, side-on bound dinitrogen ligands has been studied. In each case, bridging oxamidide ligands, [N_2C_2O_2]~4-, were formed from N-N bond cleavage coupled to N-C and C-C bond assembly. For the zirconium examples, [(η~6-C_5Me_4H)_2Zr]_2(μ2,η~2,η~2-N_2) and [Me_2Si(η~5-C_5Me_4)(η~5-C_5H_3-3-(~t)Bu)Zr]_2(u2,η~2,η~2-N_2), dinitrogen loss became competitive with N_2 carbonylation, and significant quantities of the zirconocene dicarbonyl accompanied oxamidide formation. In contrast, the hafnocene complex [(η~5-C_sMe_4H)_2Hf]_2(μ_2,η~2,η ~2-N_2) underwent clean carbonylative dinitrogen cleavage with no evidence of N_2 loss. CO-induced N2 cleavage was also coupled to N-H bond formation by hydrogenation and C-H bond activation, as carbonylation of the zirconocene and hafnocene dinitrogen complexes in the presence of H_2 or phenylacetylene furnished isocyanato metallocene complexes with bridging imido (μ-NH) ligands. In the case of the ansa-hafnocene dinitrogen complex, replacing the dihydrogen atmosphere with various primary silanes yielded an isocyanato hafnocene μ-oxo hydride resulting from cleavage of N_2 and CO, the diatomics with the two strongest bonds in chemistry.