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

Abstract

A series of new trivalent rare-earth allyl-borohydride complexes with the formula [RE(BH ) (C H )(thf) ] (RE=Sc (1), x=2; RE=Y (2) and La (3), x=3) were synthesized by reaction of the corresponding rare-earth trisborohydrides [RE(BH ) (thf) ] with half an equivalent of bis(allyl)magnesium. The complexes were fully characterized by determining their X-ray structure. Similar to their previously described Nd (4) and Sm (5) analogues, these complexes display a monomeric structure with two terminal trihapto BH groups, one π-η allyl ligand, three THF molecules for complexes 2 and 3, and two THF molecules for complex 1. The catalytic behavior of complexes 1-5 toward the ring-opening polymerization (ROP) of l-lactide (l-LA) and ϵ-caprolactone (ϵ-CL) was assessed. The Nd complex featured the best activity toward l-LA (turnover frequency (TOF)=1300 h ) and the order was Nd>La>Sm>Y>Sc. Complexes 1-3 were found very active for the ROP of ϵ-CL (TOF=166 000 h ), which is in line with the already established exceptionnally high performance of complexes 4 and 5. With both monomers, it was shown that the borohydride moiety was the preferentially initiating group, rather than the allyl one. The random copolymerization of l-LA and ϵ-CL was performed with complexes 1-5, in the absence or in the presence of benzyl alcohol as a chain-transfer agent, affording copolymers with ϵ-caprolactone up to 62 % inserted. The copolymers synthesized display a variety of microstructures, that is, blocky, random, or quasi-alternating.

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

“…With aluminum-based co-catalysts, such as Al( i Bu) 3 or MAO (MethylAlumOxane), the activities were greatly improved with TOF of 1000 h −1 , however, the trans-selectivity was affected (78.7% and 68.2%, respectively). This family of complexes was recently extended to scandium (bis-THF adduct), yttrium, and lanthanum [30].…”

Random copolymerization of l‐lactide and ε‐caprolactone by aluminum alkoxide complexes supported by N2O2 bis(phenolate)‐amine ligands

“…Therefore, the development of the efficient catalysts is a significantly challenging goal to meet the requirements of various applications. Several metal catalyst systems have been reported for the copolymerization of ε‐CL and LA ranging from the traditional stannous octoate, to main group catalysts, transition metal catalysts, and rare‐earth catalysts leading to varying degree of monomer distribution. In most reports, the truly random copolymer poly(LA‐ ran ‐CL), in which the average sequence lengths of caproyl unit ( L CL ) and lactidyl unit ( L LA ) equal to 2, have been very challenging.…”

Construction of three types of lanthanide complexes based on 3,4‐dimethylbenzoic acid and 5,5′‐dimethyl‐2,2′‐bipyridine: Syntheses, Structures, Thermodynamic properties, Luminescence, and Bacteriostatic activities

“…The most important crystallographic data and selected bond length for the monocrystalline complexes were listed in Tables and , respectively. Obviously, the structures are quite different: the complex 1 is mononuclear molecule with three 3,4‐DMBA − ligands, one 5,5′‐DM‐2,2′‐bipy ligand, one Er (III) ion and one coordination water, and the molar ratio of each molecule is 3:1:1:1; complex 2 is binuclear molecule with six 3,4‐DMBA − ligands, two 5,5′‐DM‐2,2′‐bipy ligands, two Tb (III) ions and one coordination water, that is to say, the molar ratio of each molecule is 6:2:2:1; while complex 3 is binuclear molecule with six deprotonated 3,4‐DMBA − ligands, two unprotonated 3,4‐DMHBA ligand, two 5,5′‐DM‐2,2′‐bipy ligands and two Eu (III) ions, in the end, the molar ratio of each molecule is 3:1:1:1 . In order to make a comparison, the structures of single‐crystal complexes 1 – 3 will be described in detail, respectively.…”