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Issue 27, 2012
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Synthesis, characterization of bridged bis(amidinate) lanthanide amides and their application as catalysts for addition of amines to nitriles for monosubstituted N-arylamidines

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Abstract

A series of lanthanide amide complexes supported by bridged bis(amidinate) ligand L, LLnNHAr1(DME) (L = [Me3SiNC(Ph)N(CH2)3NC(Ph)NSiMe3], Ar1 = 2,6-iPr2C6H3, DME = dimethoxyethane, Ln = Y (1), Pr (2), Nd (3), Gd (4), Yb (5)), [Yb(μ2-NHPh)]22-L)2 (6) and [LYb]22-NHAr2)2 (7) (Ar2 = (o-OMe)C6H4), were synthesized by reaction of LLnCl(THF)2 with the corresponding lithium amide in good yields and structurally characterized by X-ray crystal structure analyses. All complexes were found to be precatalysts for the catalytic addition of aromatic amines to aromatic nitriles to give monosubstituted N-arylamidines. The catalytic activity was influenced by lanthanide metals and the amido groups with the active sequence of Y (1) < Gd (4) < Nd (3) < Pr (2) ∼ Yb (5) for the lanthanide metals and –NHAr2 < –NHPh < –NHAr1 for the amido groups. The catalytic addition reaction with complex 5 showed a good scope of aromatic amines. Some key reaction intermediates were isolated and structurally characterized, including the amidinate complexes LLn[NPhCNAr1](PhCN) (Ln = Y (8), Ln = Yb (9)), LYb[NAr2CNAr1](Ar2CN) (10), and amide complex 5 prepared by protonation of 9 by Ar1NH2. Reactivity studies of these complexes suggest that the present catalytic formation of monosubstituted N-arylamidines proceeds through nucleophilic addition of an amido species to a nitrile, followed by amine protonolysis of the resultant amidinate species.

Graphical abstract: Synthesis, characterization of bridged bis(amidinate) lanthanide amides and their application as catalysts for addition of amines to nitriles for monosubstituted N-arylamidines

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Publication details

The article was received on 20 Feb 2012, accepted on 15 Mar 2012 and first published on 16 Mar 2012


Article type: Paper
DOI: 10.1039/C2DT30400G
Dalton Trans., 2012,41, 8252-8260

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    Synthesis, characterization of bridged bis(amidinate) lanthanide amides and their application as catalysts for addition of amines to nitriles for monosubstituted N-arylamidines

    W. Li, M. Xue, F. Xu, J. Tu, Y. Zhang and Q. Shen, Dalton Trans., 2012, 41, 8252
    DOI: 10.1039/C2DT30400G

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