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.