Issue 13, 2019

Magnesium, calcium and zinc [N2N′] heteroscorpionate complexes

Abstract

A new family of sterically demanding N2N′ heteroscorpionate pro-ligands (HC(tBu2pz)2SiMe2N(H)R (R = iPr, tBu, Ph, Xyl)) has been prepared via a straightforward modular synthetic route. An extensive study into the synthesis and characterisation of lithium, magnesium, calcium and zinc complexes supported by both 3,5-tBu and 3,5-Me substituted N2N′ ligand families has been conducted. Attempted deprotonation of the pro-ligands with nBuLi afforded the corresponding lithium salts Li{HC(tBu2pz)2SiMe2NR} (R = iPr (1), tBu (2), Ph (3) and Xyl (4)) but air- and thermal-sensitivity limited the yields of these potentially useful precursors; only the sterically encumbered ligand system allowed clean reactivity. Magnesium methyl complexes Mg{HC(tBu2pz)2SiMe2NR}Me (R = iPr (5) and R = Ph (6)) were prepared using an excess of the Grignard reagent MeMgCl. Magnesium butyl complexes were synthesised in good yields using the dialkyl precursor MgnBu2 to afford Mg{HC(R′2pz)2SiMe2NR}nBu (R′ = Me; R = iPr (7), tBu (8), Ad (9), Ph (10). R′ = tBu; R = iPr (11), Ph (12)). Protonolylsis reactions were used to synthesise magnesium and calcium amide complexes Mg{HC(R′2pz)2SiMe2NR}{N(SiHMe2)2} (R′ = Me; R = iPr (13), tBu (14), Ph (15). R′ = tBu; R = Ph (16)) or Mg{HC(R′2pz)2SiMe2NR}{N(SiMe3)2} (R′ = Me; R = iPr (17), tBu (18), Ph (19). R′ = tBu; R = Ph (20)), and Ca{HC(R′2pz)2SiMe2NR}{N(SiMe2)2} (L) (R′ = Me; L = thf; R = iPr (21), tBu (22), Ph (23). R′ = tBu; L = none; R = Ph (24). Zinc methyl complexes Zn{HC(R′2pz)2SiMe2NR}Me (R′ = Me; R = iPr (25), tBu (26), Ph (27). R′ = tBu; R = Ph (28)) were prepared by reaction of the N2N′ heteroscorpionate pro-ligands with ZnMe2. In preliminary studies, magnesium amide complexes 16 and 20 were evaluated as initiators for the ring-opening polymerisation (ROP) of ε-caprolactone (ε-CL) and rac-lactide (rac-LA). Although the overall polymerisation control was poor, 16 and 20 were found to be active initiators.

Graphical abstract: Magnesium, calcium and zinc [N2N′] heteroscorpionate complexes

Supplementary files

Article information

Article type
Paper
Submitted
18 dez 2018
Accepted
07 jan 2019
First published
08 jan 2019
This article is Open Access
Creative Commons BY license

Dalton Trans., 2019,48, 4124-4138

Magnesium, calcium and zinc [N2N′] heteroscorpionate complexes

M. Luna Barros, M. G. Cushion, A. D. Schwarz, Z. R. Turner and P. Mountford, Dalton Trans., 2019, 48, 4124 DOI: 10.1039/C8DT04985H

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