CNC-Pincer Rare-Earth Metal Amido Complexes with a Diarylamido Linked Biscarbene Ligand: Synthesis, Characterization, and Catalytic Activity
作者:Xiaoxia Gu、Xiancui Zhu、Yun Wei、Shaowu Wang、Shuangliu Zhou、Guangchao Zhang、Xiaolong Mu
DOI:10.1021/om500354s
日期:2014.5.12
In preparation of CNC-pincer rare-earth metal amido complexes with a diarylamido linked biscarbene ligand, it is found that conditions have a key influence on final products. Reaction of a THF suspension of bis[2-(3-benzylimidazolium)-4-methylphenyl]amine dichlorides (H3LCl2) with [(Me3Si)(2)N](3)RE(mu-Cl)Li(THF)(3) (RE = Yb, Eu, Sm) in THF at room temperature afforded the only unexpected fused-heterocyclic compound 8,9-dibenzyl-3,14-dimethyl-8a,9-dihydro-8H-benzo[4,5]imidazo-[2',1':2,3]imidazo[1,2-a]imidazo[2,1-c]quinoxaline (1) containing an imidazolyl ring and a piperidyl ring, which formed through carbene C-C and C-N coupling. However, the reaction of H3LCl2 with [(Me3Si)(2)N](3)Er(mu-Cl)Li(THF)(3) in toluene afforded the CNC-pincer erbium amido complex incorporating a diarylamido linked biscarbene ligand LEr[N(SiMe3)(2)](2) (2) in low yield and the above fused-heterocyclic compound 1. The stepwise reaction of H3LCl2 with strong bases (n-BuLi or LiCH2SiMe3) in THF for 4 h, followed by treatment with [(Me3Si)(2)N](3)RE(mu-Cl)Li(THF)(3), generated zwitterion complexes [L2RE][REClN(SiMe3)(2)}(3)] (L = [4-CH3-2-(C6H4CH2-[N(CH)(2)CN]}C6H3](2)N; RE = Y (3), Er (4), Yb (5)) in less than 20% yields together with fused-heterocyclic compound 1. Additionally, the reaction of H3LCl2 with 6 equiv of NaN(SiMe3)(2) in THF for 4 h, followed by treatment with YbCl3, generated a novel discrete complex [L2Yb][Na(mu-N(SiMe3)(2))}(5)(mu(5)-Cl)] (6). The one-pot reaction of H3LCl2 with n-BuLi, followed by reaction with [(Me3Si)(2)N](3)RE(mu-Cl)Li(THF)(3) in THF at -78 degrees C, generated the CNC-pincer lanthanide bisamido complexes LRE[N(SiMe3)(2)](2) (RE = Er (2), Y (7), Sm (8), Eu (9)) in moderate yields. These kinds of biscarbene supported pincer bisamido complexes could also be prepared by a one-pot reaction of bis(imidazolium) salt (H3LCl2) with 5 equiv of NaN(SiMe3)(2), followed by treatment with RECl3, in good yields at -78 degrees C. Investigation of the catalytic activity of complexes 2 and 7-9 indicated that all complexes showed a high activity toward the addition of terminal alkynes to carbodiimides producing propiolimidines, which represents the first example of rare-earth metal CNC-pincer-type catalysts applied for catalytic C-H bond addition of terminal alkynes to carbodiimides at room temperature.