Syntheses and molecular structures of mono(guanidinate) lanthanide borohydrides and their catalytic activity for MMA-polymerization

The mono(guanidinate) lanthanide borohydride complexes of [(Me3Si)2NC(NCy)2]Ln(BH4)2(THF)2 (Ln = Yb (1), Er (2)) have been synthesized by the reactions of corresponding Ln(BH4)3(THF)3 with sodium guanidinate of [(Me3Si)2NC(NCy)2]Na in a 1:1 molar ratio in THF. They were characterized by elemental analysis, infrared spectrum and X-ray diffraction analysis. 1 and 2 have similar structures. The lanthanide ion was bonded by an η2-guanidinate ligand, two η3-BH4 ligands and two THF molecules as a distorted octahedron. The two BH4 ligands in a complex are equivalent and cis to each other. The structure of solvated sodium guanidinate of {[(Me3Si)2NC(NCy)2]Na(THF)}2 (3) was also presented. In a dimeric molecule of 3, each Na atom is bound to three nitrogen atoms from two guanidinate groups and one oxygen atom from the THF molecule. 1 and 2 displayed moderate high catalytic activity for the polymerization of methyl methacrylate. The Er complex is more active than the Yb complex.