Titanium and niobium imido complexes stabilized by heteroscorpionate ligands

Abstract

The reaction of [Ti(NR)Cl₂(py)₃] (R = ^tBu, p-tolyl, 2,6-C₆H₃ⁱPr₂) with [{Li(bdmpza)(H₂O)}₄] [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate] and [{Li(bdmpzdta)(H₂O)}₄] [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate] affords the corresponding complexes [Ti(NR)Cl(κ³-bdmpzx)(py)] (x = a, R = ^tBu 1, p-tolyl 2, 2,6-C₆H₃ⁱPr₂3; x = dta, R = ^tBu 4, p-tolyl 5, 2,6-C₆H₃ⁱPr₂6), which are the first examples of imido Group 4 complexes stabilized by heteroscorpionate ligands. The solid-state X-ray crystal structure of 1 has been determined. The titanium centre is six-coordinate with three fac-sites occupied by the heteroscorpionate ligand and the remainder of the coordination sphere being completed by chloride, imido and pyridine ligands. The complexes 1–6 are fluxional at room temperature. The pyridine ortho- and meta-proton resonances show evidence of dynamic behaviour for this ligand and variable-temperature NMR studies were carried out in order to study their dynamic behaviour in solution. The complexes [Nb(NR)Cl₃(py)₂] (R = ^tBu, p-tolyl, 2,6-C₆H₃ⁱPr₂) reacted with [{Li(bdmpza)(H₂O)}₄] and (Hbdmpze) [bdmpze = 2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide], the latter with prior addition of ⁿBuLi, to give the complexes [Nb(NR)Cl₂(κ³-bdmpzx)] (x = a, R = ^tBu 7, p-tolyl 8, 2,6-C₆H₃ⁱPr₂9; x = e, R = ^tBu 10, p-tolyl 11, 2,6-C₆H₃ⁱPr₂12) and these are the first examples of imido Group 5 complexes with heteroscorpionate ligands. The structures of these complexes have been determined by spectroscopic methods.