Design of new heteroscorpionate ligands and their coordinative ability toward Group 4 transition metals; an efficient synthetic route to obtain enantiopure ligands

Abstract

The reaction of different types of bis(pyrazol-1-yl)methane derivatives with BuⁿLi and alkyl or aryl-containing-isocyanates or isothiocyanates, some of these as chiral reagents, gives rise to the preparation of new heteroscorpionate ligands in the form of the lithium derivatives [Li(NNE)]₂ (1–10), although a similar process with trimethylsilyl isocyanate or isothiocyanate gave the complexes [Li(NCX)(bdmpzs)(THF)] (X = O, 11; X = S, 12) [bdmpzs = bis(3,5-dimethylpyrazol-1-yl)trimethylsilylmethane]. Compounds 1–8 reacted with [TiCl₄(THF)₂] or [MCl₄] (M = Zr, Hf) to give a series of cationic complexes [MCl₃{κ³-NNE(H)}]Cl (13–36) where the heteroscorpionate ligand contains either an acetamide or thioacetamide group resulting from the protonation of the corresponding acetamidate or thioacetamidate. However, under appropriate experimental conditions neutral Ti complexes were isolated—namely [TiCl_x(NMe₂)_3−x(S-mbbpam)] (37–39) [S-mbbpam = (S)-(−)-N-α-methylbenzyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamidate]. Finally, two alkoxide-containing titanium complexes [TiCl_x(OR)_3−x(S-mbbpamH)]Cl (40–41) were also prepared. The structures of these complexes have been determined by spectroscopic methods and, in addition, the X-ray crystal structures of 1, 12, and 19 were also established.