Issue 44, 2021

N-Donor stabilized tin(ii) cations as efficient ROP catalysts for the synthesis of linear and star-shaped PLAs via the activated monomer mechanism

Abstract

α-Iminopyridine ligands L1 (2-(CH[double bond, length as m-dash]N(C6H2-2,4,6-Ph3))C5H4N), L2 (2-(CH[double bond, length as m-dash]N(C6H2-2,4,6-tBu3))C5H4N) and L3 (1,2-(C5H4N-2-CH[double bond, length as m-dash]N)2CH2CH2) differing by the steric demand of the substituent on the imine CH[double bond, length as m-dash]N group and by the number of donating nitrogen atoms were utilized to initiate a Lewis base mediated ionization of SnCl2 in an effort to prepare ionic tin(II) species [L1–3 → SnCl][SnCl3]. The reaction of L1 and L2 with SnCl2 led to the formation of neutral adducts [L1 → SnCl2] (2) and [L2 → SnCl2] (3). The preparation of the desired ionic compounds was achieved by subsequent reactions of 2 and 3 with an equivalent of SnCl2 or GaCl3. In contrast, ligand L3 containing four donor nitrogen atoms showed the ability to ionize SnCl2 and also Sn(OTf)2, yielding [L3 → SnCl][SnCl3] (7) and [L3 → Sn(H2O)][OTf]2 (8). The study thus revealed that the reaction is dependent on the type of the ligand. The prepared complexes 4–8 together with the previously reported [{2-((CH3)C[double bond, length as m-dash]N(C6H3-2,6-iPr2))-6-CH3O-C5H3N}SnCl][SnCl3] (1) were tested as catalysts for the ROP of L-lactide, which could operate via an activated monomer mechanism. Finally, a DFT computational study was performed to evaluate the steric and electronic properties of the ionic tin(II) species 1 and 4–8 together with their ability to interact with the L-lactide monomer.

Graphical abstract: N-Donor stabilized tin(ii) cations as efficient ROP catalysts for the synthesis of linear and star-shaped PLAs via the activated monomer mechanism

Supplementary files

Article information

Article type
Paper
Submitted
10 Aug. 2021
Accepted
01 Okt. 2021
First published
01 Okt. 2021

Dalton Trans., 2021,50, 16039-16052

N-Donor stabilized tin(II) cations as efficient ROP catalysts for the synthesis of linear and star-shaped PLAs via the activated monomer mechanism

M. Novák, J. Turek, Y. Milasheuskaya, Z. Růžičková, Š. Podzimek and R. Jambor, Dalton Trans., 2021, 50, 16039 DOI: 10.1039/D1DT02658E

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