Synthesis and structural characterization of scandium SALEN complexes

Abstract

A series of heteroleptic scandium SALEN complexes, [(SALEN)Sc(µ-Cl)]₂ and (SALEN)Sc[N(SiHMe₂)₂] is obtained via amine elimination reactions using [Sc(NⁱPr₂)₂(µ-Cl)(THF)]₂ and Sc[N(SiHMe₂)₂]₃(THF) as metal precursors, respectively. H₂SALEN ligand precursors comprising H₂Salen [(1,2-ethandiyl)bis(nitrilomethylidyne)bis(2,4-di-tert-butyl)phenol], H₂Salpren [(2,2-dimethylpropanediyl)bis(nitrilomethylidyne)bis(2,4-di-tert-butyl)phenol], H₂Salcyc [(1R,2R)-(−)-1,2-cyclohexanediyl)bis(nitrilomethylidyne)bis(2,4-di-tert-butyl)phenol] and H₂Salphen [((1S,2S)-(−)-1,2-diphenylethandiyl)bis(nitrilomethylidyne)bis(2,4-di-tert-butyl)phenol] are selected according to solubility and ligand backbone variation (“N–(R)–N” bite angle) criteria. Consideration is given to the feasibility of [Cl → NR₂] and [N(SiHMe₂)₂ → OSiR₃] secondary ligand exchange reactions. X-ray crystal structure analyses of donor-free (Salpren)Sc(NⁱPr₂), (R,R)-(Salcyc)Sc[N(SiHMe₂)₂], (Salen)Sc(OSi^tBuPh₂) and (Salphen)Sc(OSiH^tBu₂) reveal (i) a very short Sc–N bond distance of 2.000(3) Å, (ii) weak β(Si–H)_amido–Sc agostic interactions and (iii) an exclusive intramolecularly tetradentate and intrinsically bent coordination mode of the SALEN ligands with ∠(Ph,Ph) dihedral angles and Sc–[N₂O₂] distances in the 124.27(9)–127.7(3)° and 0.638(1)–0.688(1) Å range, respectively.