Syntheses and characterization of hepta-coordinated Group 4 amidinate complexes†
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.