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

Abstract

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(2)C(2)O(2)](4-), were formed from N-N bond cleavage coupled to N-C and C-C bond assembly. For the zirconium examples, [(eta(5)-C(5)Me(4)H)(2)Zr](2)(mu(2),eta(2),eta(2)-N(2)) and [Me(2)Si(eta(5)-C(5)Me(4))(eta(5)-C(5)H(3)-3-(t)Bu)Zr](2)(mu(2),eta(2),eta(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 [(eta(5)-C(5)Me(4)H)(2)Hf](2)(mu(2),eta(2),eta(2)-N(2)) underwent clean carbonylative dinitrogen cleavage with no evidence of N(2) loss. CO-induced N(2) 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 (mu-NH) ligands. In the case of the ansa-hafnocene dinitrogen complex, replacing the dihydrogen atmosphere with various primary silanes yielded an isocyanato hafnocene mu-oxo hydride resulting from cleavage of N(2) and CO, the diatomics with the two strongest bonds in chemistry.

Recent developments in the homogeneous reduction of dinitrogen by molybdenum and iron

“…In early transition metal chemistry, stoichiometric N 2 functionalisation now includes a range of N-C bond formation reactions, particularly through discoveries by Fryzuk 49 and Chirik. 50,51,52,53,54,55,56 Thus, a current challenge is to make these N-C bond forming reactions catalytic, possibly by using middle (Mo) and late (Fe) transition metals like those described above. Because these reactions can construct value-added chemical compounds, there is significantly more promise for commercialization for fine chemicals than for ammonia synthesis.…”

Molecular Pnictogen Activation by Rare Earth and Actinide Complexes

“…Related to this, the understanding of the nature of bonding of Ln-N multiple bonds is of fundamental interest and the isolation of terminal imido (Ln=NR) complexes has only recently been reported [162][163][164]. It is also significant to consider the reactivity of Ln-N2 complexes in the context of other low electron count early transition metal complexes; here, N2 cleavage or functionalisation can be achieved through ligand induced reductive cleavage [165][166][167][168][169][170][171][172][173], and more generally, N-N bond scission of reduced N2 derivatives can be attained through metal-ligand cooperativity [174,175].…”

Activation of Dinitrogen‐Derived Hafnium Nitrides for Nucleophilic NC Bond Formation with a Terminal Isocyanate

“…[1] Because of its high atmospheric abundance and non-toxicity, molecular nitrogen is an attractive synthon for the construction of N À C bonds if the kinetic and thermodynamic barriers associated with N 2 reduction can be surmounted. [4] With strongly activated zirconocene [5] and hafnocene [6] dinitrogen complexes, this approach has proven to be a general method for nitrogen-carbon bond formation using carbon monoxide as the incoming ligand. [4] With strongly activated zirconocene [5] and hafnocene [6] dinitrogen complexes, this approach has proven to be a general method for nitrogen-carbon bond formation using carbon monoxide as the incoming ligand.…”