Synthesis and structures of bimetallic and polymeric zinc coordination compounds supported by salicylaldiminato and anilido–aldimine ligands

Abstract

A series of bimetallic zinc complexes bearing salicylaldiminato (1b-3b) or anilido-aldimine (4c-5c) ligand frameworks, in which the metal centres are separated by aliphatic spacer groups containing 3-6 methylene units, were targeted. X-Ray analysis of salicylaldiminato derivative 2b, with a 4 carbon spacer group, revealed a coordination polymer in the solid state where each zinc centre is ligated by two salicylaldiminato ligands. Contrastingly, the structure of the anilido-aldimine complex 4c, with a 3 carbon methylene spacer group, was found to be a discrete bimetallic complex. These differences are attributed to the differing steric protection at the anilido vs phenoxy donors, the latter more readily facilitating bridges between metal centres.

Zinc Complexes of Piperazinyl‐Derived Aminephenolate Ligands: Synthesis, Characterization and Ring–Opening Polymerization Activity

“…These were recrystallized from methanol by cooling to 0 °C. Their characterization by 1 Hand 13 C{ 1 H} NMR studies afforded well resolved resonances for all proton and carbon environments, while elemental analysis showed that the compounds were obtained in pure form. Single crystals of L2H suitable for X-ray crystallography were grown via slow evaporation of a saturated methanol solution at ambient temperature.…”

“…The Zn-C, Zn-N and Zn-O bond distances are within the ranges previously reported for zinc complexes. [1,26,39,43] The ethyl groups on each of the two metal centres lay trans to each other. Presumably, the larger tert-butyl group in the 4-position of the phenolate donor in 3, although distant from the metal coordination sphere, causes the ethyl groups to orientate themselves in a trans arrangement in contrast to the syn-(cis) arrangement in 2, where the 4-position of the phenolate group is a methyl.…”

“…The more acute bond angles around Zn, O(1)-Zn(1)-N(1) 96.82(5)°, can most probably be associated with the bite of the six-membered C 3 NZnO chelate ring. This ring adopts a legless chair [34] or slight sofa [1] conformation with the C(6) atom forming the backrest and lies ca.…”

“…Various ligands of this type have been used in main group and early transition metal chemistry (including lithium, [2][3] magnesium, [4][5][6][7][8][9][10] calcium, [11] rare-earths, [12,13] , zinc, [1,[14][15][16][17]19] aluminum, [18,20] zirconium [21,22] and titanium. [23] ) Many of these complexes have been reported to be excellent initiators for ring-opening polymerization (ROP) of cyclic esters such as rac-lactide.…”

Aluminum Methyl and Chloro Complexes Bearing Monoanionic Aminephenolate Ligands: Synthesis, Characterization, and Use in Polymerizations

“…Thus, amine-phenolate and related ligands possessing a mixed set of N-and O-donor atoms have emerged as attractive candidates due to their ability to stabilize a wide range of metal centers and the ease of systematic steric manipulation by variation of the backbone and phenol substituents. 9 A number of main-group and transition metal complexes including lithium, [10][11][12][13][14][15][16] magnesium, [17][18][19][20][21][22][23] larger alkaline earths, 24 rare-earths, 25,26 zinc, [27][28][29][30][31][32][33][34][35][36] aluminum, [37][38][39][40][41][42][43][44] , tin, 45 zirconium 46,47 and titanium 48 complexes stabilized by these and related ligands have been prepared and some are effective initiators for ROP of cyclic esters such as lactide and ε-caprolactone (e.g., I-IV, Figure 1). Among the catalysts/initiators studied, aluminum complexes with N,O-chelate and related ligands have attracted much attention due to their high activity and good polymer molecular weight control.…”