Dinitrogen activation by a titanium hydride complex supported by 2-butene ligand

Abstract

The activation of dinitrogen by a titanium hydride complex with two bridging hydrides located between metal Ti and Li was investigated. Exposing cyclic bis-alkylidene titanium complex 1 to H₂ in THF solution yielded titanium hydride 2, {[(2-butene)(C₅H₅)Ti](μ-H)₂Li(THF)₃}. 2 aggregated into dimer 3 in hexane, accompanied by the release of LiH. Treatment of 2 with N₂ (1 atm) in THF resulted in ionic end-on bridged dinitrogen dititanium complex 4, {[((2-butene)(C₅H₅)Ti)₂(μ₂-η¹,η¹-N₂)][Li(THF)₄]}, without using external reducing agents. Furthermore, 4 could be oxidized to yield the binuclear complex 5, {[(2-butene)(C₅H₅)Ti]₂(μ₂-η¹,η¹-N₂)}. The solid-state structures of 4 and 5, as revealed by X-ray crystallographic studies, exhibit relatively short N–N bond distances of 1.198(2) Å and 1.179(2) Å, respectively. These results align with the observed N–N Raman stretching frequencies at 1699 cm⁻¹ and 1704 cm⁻¹. The N₂ moiety bridging two titanium atoms could be converted into ammonia and hydrazine upon treatment with a proton source and reductant.