Ring‐Opening Polymerization of Cyclic Esters by an Enantiopure Heteroscorpionate Rare Earth Initiator

Abstract

With a sting in its tail: An enantiopure neodymium complex (see scheme) acts as an efficient single-site initiator for the controlled ring-opening polymerization of rac-lactide, forming isotactic polyester. The heteroscorpionate complex was characterized spectroscopically and by X-ray diffraction.

Synthesis of new bulky bis(pyrazolyl)methane carboxylate (heteroscorpionate) ligands and their complexes with iron, manganese and nickel

“…This may be attributable to either the planarity of the aryl rings allowing closer approach than for the tertbutyl system which has more three-dimensional bulk. Alternatively, it could be an influence of the ortho-methoxyl groups, which have close approach in the range of 2.762 (2) The coordination achieved by these ligand systems is very sensitively balanced, as the isopropoxyl ethers resulted in pseudo-octahedral coordination to all metals in this study and did not participate in any type of stabilisation. In fact, in all complexes containing L 1c the aryl rings were orientated with the isopropoxyl groups directed away from the metal.…”

“…There was no evidence for dimeric complexes with this Fe(II) precursor. Alteration of the iron precursor to FeCl 2 (Fig. 7), respectively.…”

“…The bpmc ligands HL 1a-1c were then reacted directly with a selection of transition metal chlorides or tetrafluoroborates under the conditions outlined in Scheme 4 to give either neutral or cationic pseudo-octahedral ML 2 The resulting complexes were characterized predominantly by X-ray crystallography but supported by HPLC, mass spectrometry, elemental analysis and infra-red spectroscopy. Initially, it was anticipated that using stoichiometric amounts of metal salt and ligand could control the outcome, however, it was found that the same result was obtained regardless of the ratio of LH to MX n .…”

“…13 6.01 (2H, s, 2 × pzCH), 7.14 (1H, s, CH), 9.91 (1H, s, CHO). 13 General procedure for metal complex formation for type ML 2 or (ML) 2 …”

“…Their coordination chemistry has been explored with metals such as Zn, Y, Ti and Sc in the context of catalysis 1,2 whereas with Tc and Re 3-6 the focus moved in part to radiopharmaceuticals. The coordination chemistry of this class of ligand has been the subject of several reviews.…”