Xue Mingqiang, Zheng Yu, Hong Yubiao, Yao Yingming, Xu Fan, Zhang Yong, Shen Qi
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Dushu Lake Campus, Soochow University, Suzhou 215123, People's Republic of China.
Dalton Trans. 2015 Dec 14;44(46):20075-86. doi: 10.1039/c5dt03674g.
Reduction reactions of bis(β-diketiminate)lanthanide(III) chlorides formed in situ by reactions of anhydrous LnCl3 with 2 equiv. of sodium salt of the β-diketiminate ligand in THF with a Na/K alloy afforded a series of bis(β-diketiminate)lanthanide(II) complexes LnL2(THF)n (L = L(2,6-Me2) = [N(2,6-Me2C6H3)C(Me)]2CH(-), n = 1, Ln = Eu (1); L = L(2,4,6-Me3) = [N(2,4,6-Me3C6H2)C(Me)]2CH(-), n = 1, Ln = Eu (2); L = L(2,6-iPr2) = [N(2,6-(i)Pr2C6H3)C(Me)]2CH(-), n = 0, Ln = Eu (3), Sm (4); L = L(2,6-ipr2)(Ph) = (2,6-(i)Pr2C6H3)NC(Me)CHC(Me)N(C6H5), n = 0, Ln = Eu (5), Yb (6); L = L(2-Me) = [N(2-MeC6H4)C(Me)]2CH(-), n = 1, Ln = Yb (7)) in high yields. All the complexes, especially the complexes of Sm(II) (4) and Eu(II) (5), were found to be excellent pre-catalysts for catalytic addition of amines to carbodiimides to multi-substituted guanidines with a wide scope of substrates. The activity depends both on the central metals and the ligands with the active sequence of Yb(II) < Eu(II) and Eu(II) < Sm(II) and L(2,6-Me2) < L(2,4,6-Me3) ∼ L(2,6-iPr2) < L(2,6-ipr2)(Ph) for the ligands. The mechanistic study by the isolation of guanidinate species and their reactivity revealed that Eu(II) monoguanidinate complexes Eu(L(2,6-Me2))(C6H5N)C(NHCy)(NCy) (8) and Eu(L(2,6-ipr2)Ph)(C6H5N)C(NHCy)(NCy)2 (9) should be the key active intermediates for the systems with Eu(II) complexes and a Yb(III) bis(guanidinate) complex Yb(L(2-Me))[(C6H5N)C(NHCy)(NCy)]2 (11) for the system using a Yb(II) complex.
无水LnCl₃与2当量的β - 二酮亚胺配体的钠盐在四氢呋喃中与钠/钾合金反应原位生成的双(β - 二酮亚胺)镧系(III)氯化物的还原反应，高产率地得到了一系列双(β - 二酮亚胺)镧系(II)配合物LnL₂(THF)ₙ（L = L(2,6 - Me₂)= [N(2,6 - Me₂C₆H₃)C(Me)]₂CH⁻，n = 1，Ln = Eu (1)；L = L(2,4,6 - Me₃)= [N(2,4,6 - Me₃C₆H₂)C(Me)]₂CH⁻，n = 1，Ln = Eu (2)；L = L(2,6 - iPr₂)= [N(2,6 - (i)Pr₂C₆H₃)C(Me)]₂CH⁻，n = 0，Ln = Eu (3)，Sm (4)；L = L(2,6 - ipr₂)(Ph)= [(2,6 - (i)Pr₂C₆H₃)NC(Me)CHC(Me)N(C₆H₅)]⁻，n = 0，Ln = Eu (5)，Yb (6)；L = L(2 - Me)= [N(2 - MeC₆H₄)C(Me)]₂CH⁻，n = 1，Ln = Yb (7)）。发现所有这些配合物，特别是Sm(II) (4)和Eu(II) (5)的配合物，是用于催化胺与碳二亚胺加成生成多取代胍的优异预催化剂，底物范围广泛。活性既取决于中心金属，也取决于配体，配体的活性顺序为Yb(II) < Eu(II)、Eu(II) < Sm(II)以及L(2,6 - Me₂) < L(2,4,6 - Me₃) ∼ L(2,6 - iPr₂) < L(2,6 - ipr₂)(Ph)。通过分离胍基物种及其反应性进行的机理研究表明，Eu(II)单胍基配合物Eu(L(2,6 - Me₂))(C₆H₅N)C(NHCy)(NCy) (8)和Eu(L(2,6 - ipr₂)Ph)(C₆H₅N)C(NHCy)(NCy)₂ (9)应该是使用Eu(II)配合物的体系的关键活性中间体，而Yb(III)双(胍基)配合物Yb(L(2 - Me))[(C₆H₅N)C(NHCy)(NCy)]₂ (11)是使用Yb(II)配合物的体系的关键活性中间体。
