Catalytic addition of amines to carbodiimides by bis(β-diketiminate)lanthanide(ii) complexes and mechanistic studies. Issue 46 (3rd November 2015)

• Record Type: Journal Article
• Authors: Xue, Mingqiang; Zheng, Yu; Hong, Yubiao; Yao, Yingming; Xu, Fan; Zhang, Yong; Shen, Qi
• Is Part Of: Dalton transactions. Volume 44:Issue 46(2015)
• Page Start: 20075
• Page End: 20086
• Publication Date: 2015-11-03
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c5dt03674g
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Bis(β-diketiminate)lanthanide(ii ) complexes L2 Ln(THF) n were found to be excellent pre-catalysts for catalytic addition of amines to carbodiimides and a possible catalytic mechanism was proposed on the basis of the isolation of monoguanidinate Eu(ii ) and bis(guanidinate) Yb(iii ) species. Abstract : 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-Me2 C6 H3 )C(Me)]2 CH −, n = 1, Ln = Eu (1 ); L = L 2, 4, 6-Me3 = [N(2, 4, 6-Me3 C6 H2 )C(Me)]2 CH −, n = 1, Ln = Eu (2 ); L = L 2, 6-iPr2 = [N(2, 6- i Pr2 C6 H3 )C(Me)]2 CH −, n = 0, Ln = Eu (3 ), Sm (4 ); L = L 2, 6-ipr2 Ph = [(2, 6- i Pr2 C6 H3 )NC(Me)CHC(Me)N(C6 H5 )] −, n = 0, Ln = Eu (5 ), Yb (6 ); L = L 2-Me = [N(2-MeC6 H4 )C(Me)]2 CH −, 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 )[(C6 H5 N)C(NHCy)(NCy)](DME) (8 ) and Eu(L 2, 6-ipr2 Ph )[(C6 H5 N)C(NHCy)(NCy)](THF)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 )[(C6 H5 N)C(NHCy)(NCy)]2 (11 ) for the system using a Yb II complex.