Titanium imido complexes of pendant arm functionalised benzamidinate ligands

Abstract

Reactions of the lithiated pendant arm functionalised benzamidinates Li{Me₂NCH₂CH₂NC(Ph)NSiMe₃} and Li{Me₂NCH₂CH₂CH₂NC(Ph)NSiMe₃} with the compounds [Ti(NR)Cl₂(py)₃] (R = ^tBu, 2,6-Me₂C₆H₃, 2,6-ⁱPr₂C₆H₃) afforded five-coordinate [Ti(NR){Me₂NCH₂CH₂NC(Ph)NSiMe₃}Cl] 1–3 and [Ti(NR){Me₂NCH₂CH₂CH₂NC(Ph)NSiMe₃}Cl] 4–6, respectively. Reaction of [Ti(N^tBu){Me₂NCH₂CH₂CH₂NC(Ph)NSiMe₃}Cl] 4 with C₆F₅NH₂ gave elimination of ^tBuNH₂ and the corresponding perfluoroarylimido complex 7. The X-ray crystal structures of [Ti(N^tBu){Me₂NCH₂CH₂NC(Ph)NSiMe₃}Cl] 1 and [Ti(N-2,6-R₂C₆H₃){Me₂NCH₂CH₂CH₂NC(Ph)NSiMe₃}Cl] (R = Me 5 or ⁱPr 6) have been determined. Reaction of either 1 or 4 with H₂N-2,6-Me₂C₆H₃ in C₆D₆ afforded the corresponding arylimido compounds 2 and 5, but this route is not amenable to easy scale-up. For better evaluation of the effects of the pendant NMe₂ donor group in 1–6, the bis(pyridine) compound [Ti(N^tBu){MeCH₂CH₂NC(Ph)NSiMe₃}Cl(py)₂] 9 was prepared from Li{MeCH₂CH₂NC(Ph)NSiMe₃} 8 and [Ti(N^tBu)Cl₂(py)₃]. The compounds 1–3 with two-carbon pendant arms are quite sensitive to adventitious protonation, and the X-ray crystal structures of the products of two such reactions, namely [Ti₂{Me₂NCH₂CH₂NC(Ph)N(H)SiMe₃}₂(N^tBu)₂Cl₂(μ-Cl)₂] 10 and [Ti₂(N-2,6-C₆H₃Me₂)₂Cl₂(μ-O){Me₂NCH₂CH₂NC(Ph)N(H)SiMe₃}₂] 11, have been determined. Both possess amidine ligands that show interesting intramolecular N–H⋯X (X = μ-Cl or μ-O) hydrogen bonds.