Mixed Allyl–Borohydride Lanthanide Complexes: Synthesis of Ln(BH₄)₂(C₃H₅)(THF)₃ (Ln = Nd, Sm), Characterization, and Reactivity toward Polymerization

Abstract

New mixed allyl−borohydrido lanthanide complexes Ln(BH 4 ) 2 (C 3 H 5 )(THF) 3 (Ln = Nd (1), Sm (2)) could be prepared in good yield by reacting Ln(BH 4 ) 3 (THF) 3 (Ln = Sm, Nd) with 1/2 equiv of Mg(C 3 H 5 ) 2 (THF) x . X-ray structure analysis revealed monomeric structures with two terminal BH 4 ligands, one π-allyl ligand, and three THF molecules. In an assessment of isoprene polymerization, 1 afforded trans-1,4-polyisoprene in good yield, as a single component or in combination with Mg cocatalyst. Both 1 and 2 were found to be extremely active toward ε-caprolactone polymerization.

Mixed Allyl Rare‐Earth Borohydride Complexes: Synthesis, Structure, and Application in (Co‐)Polymerization Catalysis of Cyclic Esters

“…[c] Determined by SEC in THF at 40 °C against polystyrene standards with the correction M n(exp) = M n PS ×0.56, Ð = M w / M n . [d] Taken from reference .…”

“…The synthesis of the neodymium and samarium complexes of the type [RE(BH 4 ) 2 (C 3 H 5 )(thf) 3 ] [RE=Nd ( 4 ) and Sm ( 5 )] was reported in a preliminary work from our group . In this work, we reported that the attempt to substitute one of the borohydrides groups of [Nd(BH 4 ) 3 (thf) x ] by an allyl ligand by using the classical Grignard reagents (C 3 H 5 )MgX (X=Cl, Br) led to untraceable mixtures, although Taube et al.…”

“…We explored the potential of the mixed allyl–borohydride complexes 1 – 3 toward the ring‐opening polymerization of ϵ‐caprolactone (ϵ‐CL). We previously reported the very high activity of their neodymium and samarium congeners 4 and 5 , respectively, as ROP initiators, exhibiting an unprecedented huge activity (TOF up to 700 000 h −1 ) with complex 4 . This study was herein extended to the three new complexes 1 – 3 (Scheme , Table ).…”

“…Recently, we reported the first mixed allyl–borohydrido rare‐earth‐based complexes [RE(BH 4 ) 2 (C 3 H 5 )(thf) 3 ] [RE=Nd ( 4 ) and Sm ( 5 )] and we demonstrated the ability of the neodymium derivative to polymerize isoprene in a highly trans manner without the need of a co‐catalyst . We also highlighted the exceptionally high activity of these complexes towards the polymerization of ϵ‐CL at room temperature, the highest one ever reported toward this monomer with a lanthanide‐based catalyst to the best of our knowledge (turnover frequency (TOF)=700 000 mol ϵ‐CL mol Nd −1 h −1 ).…”

Recent Advances in Rare Earth Complexes Bearing Allyl Ligands and Their Reactivity towards Conjugated Dienes and Styrene Polymerization

“…Bonnet, Visseaux, and co-workers synthesized the first RE complexes bearing both allyl and borohydride ligands, RE(BH 4 ) 2 (η 3 -C 3 H 5 )(THF) 3 (8 RE , RE = Nd, Sm, Scheme 4) by reacting RE(BH 4 ) 3 (THF) 3 with half an equivalent of Mg(C 3 H 5 ) 2 (L) n (L = THF, dioxane) in THF at room temperature [29]. From 1 H NMR analysis, the allyl moiety appeared as a 1H/2H/2H set of resonances for both 8 RE complexes, revealing no dynamic behavior at the 1 H NMR timescale.…”