| Abstract
| - Functionalization of the N2 ligand in the side-on bound dinitrogen complex, [(η5-C5Me4H)2Zr]2(μ2,η2,η2-N2), has been accomplished by addition of terminal alkynes to furnish acetylide zirconocenediazenido complexes, [(η5-C5Me4H)2Zr(C⋮CR)]2(μ2,η2,η2-N2H2) (R = nBu, tBu, Ph). Characterization of [(η5-C5Me4H)2Zr(C⋮CCMe3)]2(μ2,η2,η2-N2H2) by X-ray diffraction revealed a side-on bound diazenido ligand inthe solid state, while variable-temperature 1H and 15N NMR studies established rapid interconversion betweenη1,η1 and η2,η2 hapticity of the [N2H2]2- ligand in solution. Synthesis of alkyl, halide, and triflato zirconocenediazenido complexes, [(η5-C5Me4H)2ZrX]2(μ2,η1,η1-N2H2) (X = Cl, I, OTf, CH2Ph, CH2SiMe3), afforded η1,η1coordination of the [N2H2]2- fragment both in the solid state and in solution, demonstrating that stericallydemanding, in some cases π-donating, ligands can overcome the electronically preferred side-on bondingmode. Unlike [(η5-C5Me4H)2ZrH]2(μ2,η2,η2-N2H2), the acetylide and alkyl zirconocene diazenido complexesare thermally robust, resisting α-migration and N2 cleavage up to temperatures of 115 °C. Dinitrogenfunctionalization with [(η5-C5Me4H)2Zr]2(μ2,η2,η2-N2) was also accomplished by addition of proton donors.Weak Brønsted acids such as water and ethanol yield hydrazine and (η5-C5Me4H)2Zr(OH)2 and (η5-C5Me4H)2Zr(OEt)2, respectively. Treatment of [(η5-C5Me4H)2Zr]2(μ2,η2,η2-N2) with HNMe2 or H2NNMe2 furnished amidoor hydrazido zirconocene diazenido complexes that ultimately produce hydrazine upon protonation withethanol. These results contrast previous observations with [(η5-C5Me5)2Zr(η1-N2)]2(μ2,η1,η1-N2) where lossof free dinitrogen is observed upon treatment with weak acids. These studies highlight the importance ofcyclopentadienyl substituents on transformations involving coordinated dinitrogen.
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