Rare-earth alkyl complexes supported by formamidinate ligands: synthesis, structure, and catalytic activity for isoprene polymerizationElectronic supplementary information (ESI) available. CCDC 982911-982916. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt00242c

A series of rare-earth metal monoalkyl complexes supported by N , N ′-di(2,6-dialkylphenyl)formamidinate ligand (L) 2 RECH 2 SiMe 3 ·thf [L 1 = HC(N-2,6-Me 2 C 6 H 3 ) 2 , RE = Y ( 1 ), L 2 = HC(N-2,6- i Pr 2 C 6 H 3 ) 2 , RE = Y ( 2 ), Er ( 3 ), Dy ( 4 ), Sm ( 5 ), and Nd ( 6 )] were synthesized by alkyl elimination reaction or by salt metathesis reaction in good yields. All complexes were characterized by elemental analyses, FT-IR spectroscopy and single crystal X-ray diffraction. In combination with [Ph 3 C][B(C 6 F 5 ) 4 ] and alkylaluminium, these complexes displayed a good activity towards isoprene polymerization to give polyisoprenes with high molecular weight ( M n > 10 4 ) and narrow molecular distribution (PDI < 2.0). The influence of alkylaluminium, central metal, temperature, sequence of addition of alkylaluminium and [Ph 3 C][B(C 6 F 5 ) 4 ] on the polymerization of isoprene was studied. It was interesting to find that addition of the cocatalysts sequence has a great influence on the regioselectivity of the polymerization. High 1,4-regioselectivity polymerizations of isoprene (as high as 98%) were observed when the catalysts were added in the order [RE]/[alkylaluminum]/[borate]. Monoalkyl rare-earth metal complexes could be highly active catalysts for 1,4-regioselective polymerization of isoprene in the presence of cocatalysts.