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.