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 zirconocene diazenido complexes, [(η5-C5Me4H)2Zr(C≡CR)] 2(μ2,η2,η2-N 2H2) (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 in the solid state, while variable-temperature 1H and 15N NMR studies established rapid interconversion between η1,η1 and η2,η2 hapticity of the [N2H 2]2- ligand in solution. Synthesis of alkyl, halide, and triflato zirconocene diazenido complexes, [(η5-C 5Me4H)2ZrX]2(μ2, η1,η1-N2H2) (X = Cl, I, OTf, CH2Ph, CH2SiMe3), afforded η1,η1 coordination of the [N2H 2]2- fragment both in the solid state and in solution, demonstrating that sterically demanding, in some cases π-donating, ligands can overcome the electronically preferred side-on bonding mode. Unlike [(η5-C5Me4H)2ZrH] 2(μ2,η2,η2-N 2H2), the acetylide and alkyl zirconocene diazenido complexes are thermally robust, resisting α-migration and N2 cleavage up to temperatures of 115 °C. Dinitrogen functionalization with [(η5-C5Me4H)2Zr] 2(μ2,η2,η2-N 2) was also accomplished by addition of proton donors. Weak Bronsted acids such as water and ethanol yield hydrazine and (η5-C 5Me4H)2Zr(OH)2 and (η5-C5Me4H)2-Zr(OEt) 2, respectively. Treatment of [(η5-C 5Me4H)2Zr]2(μ2, η2,η2-N2) with HNMe2 or H2NNMe2 furnished amido or hydrazido zirconocene diazenido complexes that ultimately produce hydrazine upon protonation with ethanol. These results contrast previous observations with [(η5-C 5Me5)2Zr(η1-N2)] 2(μ2,η1,η1-N 2) where loss of free dinitrogen is observed upon treatment with weak acids. These studies highlight the importance of cyclopentadienyl substituents on transformations involving coordinated dinitrogen.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry