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Synthesis and structures of mono- and di-nuclear aluminium and zinc complexes bearing α-diimine and related ligands, and their use in the ring opening polymerization of cyclic esters

Xiao, Lin; Zhao, Yanxia; Qiao, Sijie; Sun, Ziyue; Santoro, Orlando; Redshaw, Carl

Authors

Lin Xiao

Yanxia Zhao

Sijie Qiao

Ziyue Sun

Orlando Santoro

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Professor Carl Redshaw C.Redshaw@hull.ac.uk
Professor of Inorganic Materials Chemistry and REF Lead for Chemistry



Abstract

A series of organoaluminium imino-amido complexes of the type {[ArNC(Me2)C(Me)NAr]AlMe2} (Ar = 2,6-iPr2C6H3 (1), Ar = 2,6-Et2C6H3 (2); Ar = 2,6-Me2C6H3 (3) have been prepared via reaction of AlR3 and the respective α-diimine. Similar reaction of the bis(α-diimine) [ArNC(Me)C(Me)N-]2 (Ar = 2,6-iPr2C6H3) with AlMe3 afforded the bimetallic complex [ArN-C(Me)2C(Me)NAlMe2]2 (4), whilst reaction of the acetyl-imino compound [OC(Me)C(Me)NAr] (Ar = 2,6-Et2C6H3) with AlMe3 afforded the bimetallic complex {[OCMe2CH(Me)NAr]AlMe2}2 (5). In related organozinc chemistry, we have isolated {[ArNC(Me)(Et)C(Me)NAr]ZnEt} (Ar = 2,6-iPr2C6H3, 6) and the trinuclear complex {[ArNC(Me)COCHCO(Me)C(Me)NAr][OCH(Me)C(Me)NAr](ZnEt)3} (Ar = 2,6-iPr2C6H3, 7) from reactions of ZnEt2 with ArNC(Me)C(Me)NAr or [OC(Me)C(Me)NAr], respectively. Reaction of the bis(α-diimine), LiPr-N2-ArCH2Ar-N2, derived from 4,4′-methylenebis(2,6-diisopropylaniline), with ZnCl2 affords [LiPr-N2-ArCH2Ar-N2(ZnCl2)2] (8). The molecular structures of complexes 1-8 are reported. Preliminary results of the ability of 1-8, along with the previously reported metal-metal bonded complex {[ArNC(Me)C(Me)NAr]Al(THF)}2 (9), to act as catalysts for the ring opening polymerization (ROP) of the cyclic esters ϵ-caprolactone (ϵ-CL), δ-valerolactone (δ-VL) and rac-lactide (r-LA) are presented. For ϵ-CL and δ-VL, best results were obtained using the metal-metal bonded complex 9. For r-LA, the Al-based systems exhibited moderate activity affording only liquid oligomers, whilst the Zn-based systems performed better affording at 80 °C isotactic PLA with Mnca. 10 kDa with conversions of up to 66%. The co-polymerization of ϵ-CL with δ-VL was also examined, and differing preferences were noted for monomer incorporation.

Citation

Xiao, L., Zhao, Y., Qiao, S., Sun, Z., Santoro, O., & Redshaw, C. (2020). Synthesis and structures of mono- and di-nuclear aluminium and zinc complexes bearing α-diimine and related ligands, and their use in the ring opening polymerization of cyclic esters. Dalton Transactions : an international journal of inorganic chemistry, 49(5), 1456-1472. https://doi.org/10.1039/c9dt04332b

Journal Article Type Article
Acceptance Date Dec 28, 2019
Online Publication Date Dec 30, 2019
Publication Date Feb 7, 2020
Deposit Date Jan 2, 2020
Publicly Available Date Jan 3, 2020
Journal Dalton Transactions
Print ISSN 1477-9226
Electronic ISSN 1477-9234
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 49
Issue 5
Pages 1456-1472
DOI https://doi.org/10.1039/c9dt04332b
Keywords Inorganic Chemistry
Public URL https://hull-repository.worktribe.com/output/3340444
Publisher URL https://pubs.rsc.org/en/content/articlelanding/2020/DT/C9DT04332B#!divAbstract
Additional Information : This document is Similarity Check deposited; : Supplementary Information; : Single-blind; : Received 8 November 2019; Accepted 28 December 2019; Accepted Manuscript published 30 December 2019

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