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

摘要

The scope of CO-induced N₂ 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, [N₂C₂O₂]4−, were formed from N−N bond cleavage coupled to N−C and C−C bond assembly. For the zirconium examples, [(η5-C₅Me₄H)₂Zr]₂(μ₂,η2,η2-N₂) and [Me₂Si(η5-C₅Me₄)(η5-C₅H₃-3-tBu)Zr]₂(μ₂,η2,η2-N₂), dinitrogen loss became competitive with N₂ carbonylation, and significant quantities of the zirconocene dicarbonyl accompanied oxamidide formation. In contrast, the hafnocene complex [(η5-C₅Me₄H)₂Hf]₂(μ₂,η2,η2-N₂) underwent clean carbonylative dinitrogen cleavage with no evidence of N₂ 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 H₂ 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 N₂ and CO, the diatomics with the two strongest bonds in chemistry.