Supported Catalysis

Grafting onto silica affords materials containing well-identified surface species. The neodymium-decorated silica converts the b-butyrolactone monomer into highly isotactic poly(hydroxybutyrate). Under similar conditions, the molecular precursor gives rise to an atactic polymer. The neodymium borohydride complex exhibits the highest stereoselectivity for isospecific polymerization of rac-BBL to date. The most notable feature of the grafted borohydride initiators described in these studies, and in particular of the neodymium complex, is to give significantly improved selectivities compared to homogeneous catalysts.

Key Words: Supported Catalysis, Silica, Microstructure, Enantioselective Catalysts, Tacticity

Supported Neodymium Catalysts for Isoprene and rac-b-Butyrolactone Polymerization: Modulation of Reactivity by Controlled Grafting

M. Terrier, E. Brulé, M. J. Vitorino, N. Ajellal, C. Robert, R. M. Gauvin,* C. M. Thomas,* Macromol. Rapid Commun. 201132, 215.

A series of hybrid materials, bearing neodymium silylamide initiating groups, have been shown to mediate isoprene polymerization when combined with alkyl aluminum activators [methylaluminoxane, AlEt2Cl, Al(iBu)3]. The surface species nature and relative distribution were correlated with isoprene polymerization activity and selectivity. This approach to stereocontrol modulation has been extended to racemic β-butyrolactone isoselective ring opening polymerization.

Design of a well-defined, silica-supported chiral Zn scaffold for enantioselective catalysis

J. Ternel, L. Delevoye, F. Agbossou-Niedercorn, T. Roisnel, R. M. Gauvin*, C. M. Thomas* Dalton Trans. 201039, 3802.

New compound Zn[(S,S)-iPr-pybox](Et)2 (1) was fully characterized, including by X-ray diffraction structural studies. Its grafting onto partially dehydroxylated silica affords material 2, which bears well-defined chiral ([triple bond, length as m-dash]SiO)Zn[(S,S)-iPr-pybox](Et) sites. Hybrid material 2 displays significantly better catalytic performances than 1 in enantioselective silylcyanation, thus demonstrating a beneficial grafting effect.

Polymerization of racemic β-butyrolactone using supported catalysts: a simple access to isotactic polymers

N. Ajellal, G. Durieux, L. Delevoye, G. Tricot, C. Dujardin, C. M. Thomas*, R. M. Gauvin* Chem. Commun. 201046, 1032.

Grafting of [Ln(BH4)3(THF)3] (Ln= La, Nd) onto silica affords materials containing well-identified bis(borohydride) surface species. The neodymium-decorated silica converts the b-butyrolactone monomer into highly isotactic poly(hydroxybutyrate). Under similar conditions, the molecular precursor gives rise to an atactic polymer. The neodymium borohydride complex exhibits the highest stereoselectivity for isospecific polymerization of rac-BBL to date. The most notable feature of the grafted borohydride initiators described in this study, and in particular of the neodymium complex, is to give significantly improved selectivities compared to homogeneous catalysts. It can be anticipated that this class of neodymium complexes should continue to provide new and interesting results.