Synthesis and structures of titanium and yttrium complexes with N,N′-tetramethylguanidinate ligands: different reactivity of the M–N bonds toward phenyl isocyanate

Abstract

A salt elimination reaction of bis(cyclopentadienyl)titanium dichloride (C₅H₅)₂TiCl₂ with one equiv. of N,N′-tetramethylguanidinate lithium [LiNC(NMe₂)₂] proceeded in THF at room temperature to yield a bis(cyclopentadienyl)titanium mono-guanidinate chloride (C₅H₅)₂TiCl(NC(NMe₂)₂) (1). However, treatment of two equiv. of LiNC(NMe₂)₂ with (C₅H₅)₂TiCl₂ under the same conditions resulted in the elimination of one cyclopentadienyl ring to form an unexpected mono(cyclopentadienyl)titanium bis(guanidinate) chloride (C₅H₅)TiCl[NC(NMe₂)₂]₂ (2), in which only one Ti–Cl bond is broken, with the other Ti–Cl bond retained. Reaction of [(C₅H₅)₂YCl]₂ with LiNC(NMe₂)₂ gave the corresponding product {(C₅H₅)₂Y[μ-η¹:η²-NC(NMe₂)₂]}₂ (3). On further investigations on the reactivity of 1–3 toward phenyl isocyanate, we found phenyl isocyanate only inserts into the Y–N(μ-Gua) bonds of 3 to yield [(C₅H₅)₂Y(μ-η¹:η²-OC(NC(NMe₂)₂)NPh)]₂ (4). Complexes 1–4 were characterized by elemental analysis and spectroscopic properties and their solid-state structures were determined by X-ray single-crystal diffraction.