Rare earth metal complexes carbodiimide addition

Zhang, W.X., Nishiura, M., and Hou, Z.M. (2005) Catalytic addition of terminal alkynes to carbodiimides by half-sandwich rare earth metal complexes. Journal of the American Chemical Society, 127, 16788. 

An interesting organolanthanide-catalyzed reaction which has been studied in recent years is the addition of terminal alkynes to carbodiimides leading to the novel class of ,A -disubstituted propiolamidines. It was found that half-sandwich rare earth metal complexes bearing silylene-linked cyclopentadienyl-amido ligands can act as excellent catalysts in this addition reaction. As illustrated in Scheme 58, a rare earth amidinate species has been confirmed to be a true catalytic species [68]. 

W.-X. Zhang, M. Nishiura, Z. Hou, Catalytic addition of amine N-H bonds to carbodiimides by halfsandwich rare-earth metal complexes efficient synthesis of substituted guanidines through amine protonolysis of rare-earth metal guanidinates. Chem. Eur. J. 13, 2007 4037. 

Rare earth metal NHC complexes have primarily been applied in polymerization reactions, addition of terminal alkynes and amines to carbodiimides, as well as catalytic C-N coupling. Although a relatively limited amount of research has been carried out in this area, these preliminary investigations have proven the utility of REM NHC complexes as catalysts. 

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