Strategies for the Synthesis of Lanthanum Dialkyl Complexes with Monoanionic Ancillary Ligands

Abstract

The synthesis of lanthanum dialkyl complexes with monoanionic ancillary ligands [L]− is pursued by three different strategies: (a) in situ peralkylation of LaBr3(THF)4 with 3 equiv of LiCH2SiMe3 followed by reaction with LH; (b) reaction of isolated La(CH2Ph)3(THF)3 with LH; (c) stepwise salt metathesis on LaBr3(THF)4. Methods (a) and (b) generally work well for triazacyclononane-amide and amidinate ligands, but are unsuitable for the sterically demanding β-diketiminate [HC(MeCNAr)2]− (Ar = 2,6-iPr2C6H3) due to its high affinity for the Li cation and the sluggish reactivity of the diketimine. Nevertheless, the β-diketiminate lanthanum dibenzyl complex [HC(MeCNAr)2]La(CH2Ph)2(THF) could be obtained by first reacting LaBr3(THF)4 with K[HC(MeCNAr)2] to form [HC(MeCNAr)2]LaBr2(THF)2 and subsequent reaction of this dibromide complex with 2 equiv of PhCH2K. When this reaction mixture is warmed, the product decomposes by H-abstraction from one of the diketiminate methyl groups and ligand redistribution, forming the coordination polymer {[μ-η2:η1-ArNC(Me)CHC(CH2)NAr]2La[K(THF)4]}∞.