Enol-functionalized N-heterocyclic carbene lanthanide amide complexes: Synthesis, molecular structures and catalytic activity for addition of amines to carbodiimides

Reaction of LnCl3 (Ln = Y, Nd, Sm and Yb) with enol-functionalized imidazolium salt H2LBr (L = 4-OMe-C6H4COCH{C(NCHCHNiPr)}) and NaN(TMS)2 at a molar ratio of 1:4:1 in THF at room temperature afforded the corresponding novel enol-functionalized N-heterocyclic carbene (NHC) lanthanide amides L2LnN(TMS)2 (Ln = Y (1), Nd (2), Sm (3), Yb (4)) in 37–40% yields. Molecular structures of 1–4 were determined by X-ray structure analyses. All complexes adopt monomeric structures where each 5-coordinated metal is coordinated by two NHC ligands and one amido group.in distorted trigonal bipyramid geometry. All complexes, especially Yb complex (4), were found to be highly active precatalysts for the catalytic addition of amines to carbodiimides giving guanidines. The system with 4 shows good functional group tolerance and a wide scope of amines including primary and secondary cyclic amines.