Rigid NON-donor pincer ligand complexes of lutetium and lanthanum: synthesis and hydroamination catalysis

Abstract

Reaction of H₂XN₂ {4,5-bis(2,4,6-triisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene} with [Lu(CH₂SiMe₃)₃(THF)₂], and crystallization from O(SiMe₃)₂, yielded [(XN₂)Lu(CH₂SiMe₃)(THF)]·(O(SiMe₃)₂)_1.5 (1·(O(SiMe₃)₂)_1.5). Lanthanum complexes of the XN₂ dianion were also prepared by salt metathesis; treatment of H₂XN₂ with excess KH in DME produced the dipotassium salt, [K₂(XN₂)(DME)_x] (x = 2–2.5), and subsequent reaction with [LaCl₃(THF)₃] afforded [{(XN₂)LaCl(THF)}_x]·(O(SiMe₃)₂)_0.25x (2·(O(SiMe₃)₂)_0.25x; x = 1 or 2) after crystallization from O(SiMe₃)₂. Compound 2 reacted with two equivalents of LiCH₂SiMe₃, to form the dialkyl-‘ate’ complex, [Li(THF)_x][(XN₂)La(CH₂SiMe₃)₂]·Toluene·LiCl (3·toluene·LiCl; x = 3). Both 1 and 3 (x = 4) were structurally characterized, and were evaluated as catalysts for intramolecular hydroamination; while 3 showed poor activity, 1 is highly active for both intramolecular hydroamination and more challenging intermolecular hydroamination. Reactions with unsymmetrical alkenes yielded Markovnikov products, and the activity of 1 surpassed that of the previously reported yttrium analogue in the reaction of diphenylacetylene with 4-tert-butylbenzylamine.