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Key Laboratory of Organic Synthesis of Jiangsu Province, Department of Chemistry and Chemical Engineering, Dushu Lake Campus, Suzhou 215123, People's Republic of China
; Fax: +(86) 512-65880305
; Tel: +(86) 512-65882806
Dalton Trans., 2013,42, 5890-5901
21 Dec 2012,
01 Feb 2013
First published online
04 Feb 2013
Various lanthanide aryloxide complexes supported by bridged bis(amidinate) ligand L, LLnOAr(DME) (L = Me3SiNC(Ph)N(CH2)3NC(Ph)NSiMe3, DME = dimethoxyethane, Ln = Y, Ar = 2,6-(Me)2C6H3 (1), 2,6-(iPr)2C6H3 (2), 2,6-(tBu)2-4-(Me)C6H2 (3); Ar = 2,6-(tBu)2-4-(Me)C6H2, Ln = Nd (4), Sm (5), Yb (6)) were synthesized, and complexes 1, 2 and 4–6 were characterized by single crystal X-ray diffraction. All the complexes are efficient precatalysts for catalytic addition of amines to carbodiimides. The catalytic activity is influenced by lanthanide metals and the aryloxide groups (Nd (4) Sm (5) < Y (3) Yb (6) and -2,6-(Me)2C6H3 < -2,6-(iPr)2C6H3 < -2,6-(tBu)2-4-(Me)C6H2). The catalytic addition reaction with 3 showed a good scope of substrates. The mechanism investigation revealed the real active intermediate being the monoguanidinate complexes supported by an aryloxide and an amidine-functionalized amidinate group, L′Ln[O2,6-(tBu)2-4-(Me)C6H2][RNCNHRN(Ar′)] (L′ = Me3SiNHC(Ph)N(CH2)3NC(Ph)NSiMe3, R = iPr, Ar′ = phenyl, Ln = Yb (8), Y (11); R = Cy, Ar′ = phenyl, Ln = Yb (10), Y (12); R = iPr, Ar′ = 4-ClC6H4, Ln = Yb (9)), which were isolated from the reactions of 6 (or 3) with amine and carbodiimide in a molar ratio of 1:1:1 and structurally characterized. The Ln-active group in the present precatalyst is a Ln–amidinate species, not the Ln–OAr group.
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