Guanidinate Lanthanide Complexes: Syntheses, Structures And Catalytic Activity

A series of guanidinate lanthanide complexes include trisguanidinates lanthanide complexes and dianionic guanidinates lanthanide complexes were synthesized and well characterized. The catalytic activity of these complexes in guanylation of amines with carbodiimides, amination of terminal alkynes with carbodiimides and amidation of aldehydes with amines, respectively, was tested. The main results obtained are as follows:(1) The methathesis reaction of LnCl3 with in situ formed Li[iPrNHC(NiPr) (N(p-R)C6H4)] [R=-Cl, -H], Li[CyNHC(NCy)(N(p-Cl)C6H4)], Na [(iPrN)2CN(TMS)2] and Li[(R''N)2CNR'2]in a 1:3 molar ratio yielded the corresponding trisguanidinate lanthanide complexes [iPrNHC(NiPr)(NC6H4p-R)]3Ln·THF (Ln=La: R=-Cl(3-1), -H(3-2); Ln=Nd: R=-Cl(3-3), -H(3-4); Ln=Y, R=-Cl(3-6)), [CyNHC(NCy) (N(p-Cl)C6H4)]3Nd(3-5), [(iPrN)2CN(TMS)2]3Nd(3-7), [(R''N)2CNR'2]3La, R'=-C6H5, R''=-Cy (3-8), -iPr (3-9); R'=-iPr, R''=-Cy (3-10). All these complexes were well characterized including IR spectroscopy, elemental analysis, 1H NMR for 3-1, 3-2, 3-6, 3-8, 3-9 and 3-10, X-ray diffraction for 3-1, 3-2, 3-3, 3-5 and 3-7.(2) These trisguanidinate lanthanide complexes are found to be active catalysts for amidation of aldehydes with amines. The present systems proceed smoothly with low catalyst loading under mild reaction conditions. Center metal has a profound effect on the reactivity: the active sequence is Yb < Sm < Nd < La, ligands also have profound effects on the reactivity: the active sequence is NiPr2 < NHC6H5 < N(C6H5)2 < NHC6H4p-Cl, Cy < iPr. The systems have the advantage of tolerance to various substrates.(3) These trisguanidinate lanthanide complexes are also excellent precatalysts for addition of terminal alkynes to carbodiimides yielding a series of propiolamidines. The active sequence of Yb < Sm < Nd < La for metal and Ph2 > p-ClAr > iPr2, Cy > iPr for ligand around Lanthanide ion was observed.(4) Reaction of triguanidinate lanthanide complexes Ln[(iPrN)(NC6H4p-Cl) C(NHiPr)]3 (Ln = Nd, Y) with 3 equiv. of nBuLi gave [Li(THF)(DME)]3 Ln[μ-η2η1(iPrN)2C(NC6H4p-R)]3 [R=-Cl, Ln=Nd(4-1), Y(4-2), La(4-3); R=H, Ln=Nd(4-4)], which represent the first structurally characterized example of the complex of lanthanide and lithium metals with dianionic guanidinate ligands.(5) These heterobimetallic complexes of lanthanide and lithium supported by dianionic guanidinate ligands are found to be active catalysts for amidation of aldehydes with amines with a wide scope of substrates. Center metal and ligands both have a profound effect on the reactivity: the active sequence is Nd > Y for centrel metal and [(iPrN)2C(NC6H4p-Cl)]2- > [(iPrN)2C(NC6H5)]2- for ligand. The activity is much higher than those found for triguanidinate lanthanide complexes.(6) These heterobimetallic complexes are also excellent precatalysts for guanylation of amines with carbodiimides yielding a series of guanidines with the active sequence of La > Nd > Y for metal and [(iPrN)2C(NC6H4p-Cl)]2- > [(iPrN)2C(NC6H5)]2- for ligand around Lanthanide ion was observed.(7) For an attempt to synthesize a heterobimetallic complex of lanthanide and lithium with one dianionic guanidinate and two monoanionic guanidinate ligands, the reaction of trisguanidinate lanthanide complex with one equiv. of nBuLi was tried. But no expected complex was isolated. Its a reason is that our aimed complexes were unstable. The reaction of carbodiimides with in situ formed a heterobimetallic complex of lanthanide and lithium with one dianionic guanidinate and two monoanionic guanidinate ligands afford a kind of new bisguanidinate heterobimetal complexes with a dicyclic skeleton.