Syntheses and characterization of hepta-coordinated Group 4 amidinate complexes

Abstract

Tri-amidinate chloride complexes M[MeC(NⁱPr)₂]₃Cl [M = Zr (1), Hf (2)] have been prepared from MCl₄ and lithium amidinate Li[MeC(NⁱPr)₂]. The uncommon hepta-coordinated complexes Zr–Cl (1) and Hf–Cl (2) undergo metathesis reactions with 1 equiv. of MeLi and EtMgCl to give alkyl derivatives M[MeC(NⁱPr)₂]₃R [R = Me, M = Zr (3), Hf (4); R = Et, M = Zr (5), Hf (6)]. The dynamic behaviors of Zr–Cl (1) and Hf–Cl (2) in solution have been studied using variable-temperature ¹H NMR (VT ¹H NMR), giving activation parameters ΔH^‡, ΔS^‡, and ΔG^‡ for several exchange processes in Zr–Cl (1) and Hf–Cl (2). ¹H–¹⁵N gHMBC NMR spectroscopy gives the chemical shifts of the N atoms in 1–6. The ¹H–¹⁵N gHMBC NMR spectra of 1–4 at elevated temperatures are needed to obtain signals. Crystal structures of Zr–Cl (1), Hf–Cl (2), Zr–Et (5), and Hf–Et (6) have been determined via X-ray diffraction. DART-MS studies of Zr–Cl (1) and Hf–Cl (2) in air give MS of 1–2, cations M[MeC(NⁱPr)₂]₃⁺ [M = Zr (7), Hf (8)], and hydroxyl complexes M[MeC(NⁱPr)₂]₃OH [M = Zr (9), Hf (10)]. In comparison, DART-MS spectra of 3–6 in air show only 7–8 and 9–10, indicating lability of the alkyl ligands and/or their fast hydrolysis by moisture.