Divalent Lanthanide Complexes: Highly Active Precatalysts for the Addition of N−H and C−H Bonds to Carbodiimides
Various divalent lanthanide complexes with the formula LnL2(sol) x (L = N(TMS)2, sol = THF, x = 3, Ln = Sm (I), Eu (II), Yb (III); L = MeC5H4, sol = THF, x = 2, Ln = Sm (IV); L = ArO(Ar = [2,6-( t Bu)2-4-MeC6H2]), sol = THF, x = 2, Ln = Sm (V)), especially complexes I−III, serve as excellent catalys...
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Veröffentlicht in: | Journal of organic chemistry 2008-11, Vol.73 (22), p.8966-8972 |
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Sprache: | eng |
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Zusammenfassung: | Various divalent lanthanide complexes with the formula LnL2(sol) x (L = N(TMS)2, sol = THF, x = 3, Ln = Sm (I), Eu (II), Yb (III); L = MeC5H4, sol = THF, x = 2, Ln = Sm (IV); L = ArO(Ar = [2,6-( t Bu)2-4-MeC6H2]), sol = THF, x = 2, Ln = Sm (V)), especially complexes I−III, serve as excellent catalyst precursors for catalytic addition of various primary and secondary amines to carbodiimides, efficiently providing the corresponding guanidine derivatives with a wide range of substrates under solvent-free condition. The reaction shows good functional groups tolerence. Complexes I−III are also excellent precatalysts for addition of terminal alkynes to carbodiimides yielding a series of propiolamidines. The active sequence of Yb < Eu < Sm for metal and MeC5H4 < ArO < N(TMS)2 for ligand around the metal was observed for both reactions. The first step in both reactions was supposed to include the formation of a bimetallic bisamidinate samarium species originating from the reduction-coupling reaction of carbodiimide promoted by lanthanide(II) complex. The active species is proposed to be a lanthanide guanidinate and a lanthanide amidinate. |
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ISSN: | 0022-3263 1520-6904 |
DOI: | 10.1021/jo801693z |