@article { , title = {Niobium and Tantalum complexes derived from the acids Ph2C(X)CO2H (X = OH, NH2): synthesis, structure and ROP capability}, abstract = {Reaction of benzilic acid, Ph2C(OH)(CO2H), L1H2, with equimolar amounts of M(OR)5 (M = Nb, Ta) led, following work-up, to the tetranuclear complexes [Nb4(OEt)8(L1)4(μ-O)2] (1) or [Ta4(OEt)8(L1)4(μ-O)2]·0.5MeCN (2·0.5MeCN), respectively. Similar use of 2,2′-diphenylglycine, Ph2C(NH2)(CO2H), L2H3, led to the isolation of the dinuclear complexes [Nb2(OEt)4(L2H2)4(μ-O)]·2MeCN (3·2MeCN) or [Ta2(OEt)4(L2H2)4(μ-O)]·2.25MeCN (4·2.25MeCN). The molecular structures of 1-4 are reported. Complexes 1-4 have been screened for their potential to act as catalysts for the ring opening polymerization (ROP) of ϵ-caprolactone (ϵ-CL) and rac-lactide (r-LA), with or without benzyl alcohol (BnOH) present. In the case of ϵ-CL, complex 1 displayed best activity with >99\% conversion at 100 °C, whilst 3 and 4 were virtually inactive under the same conditions. All complexes show moderate activities towards the ROP of r-LA at 160 °C, with 1-3 producing heterotactic enriched PLA while 4 afforded isotactic enriched PLA. Copolymerization studies revealed the most efficient system involved the initial addition of r-LA (for 6 h) followed by ϵ-CL (for 42 h), which led to 99\% conversion for each of the monomers. Block copolymers of PLA-b-CL and PCL-b-LA and random copolymers PLA-co-CL were successfully synthesized by adjusting the feed sequence.}, doi = {10.1039/d2nj02527b}, eissn = {1369-9261}, issn = {1144-0546}, journal = {New Journal of Chemistry}, publicationstatus = {Published}, publisher = {Royal Society of Chemistry}, url = {https://hull-repository.worktribe.com/output/4032928}, keyword = {Evolving a Circular Plastics Economy}, year = {2022}, author = {Zhang, Xin and Prior, Timothy J. and Redshaw, Carl} }