Di-, tetra-, penta- and polynuclear zinc complexes supported by a flexible tetradentate Schiff base ligand

摘要

When treated with Et _2Zn, the tetradentate Schiff base N,N′-ethylenebis(4-iminopentan-2-one) (H _2L) led to the formation of dimers, [L _2Zn _2], a tetranuclear complex, [L _4Zn _4] (1) and a polymeric material [LZn(Et)] _n (2), thus highlighting the coordinative versatility of the ligand. Halogenation of 1 with SO _2Cl _2 or Br _2 afforded in moderate yield the dinuclear zinc complexes [LZn(thf)·ZnCl _2] (3) and [LZn(thf)·ZnBr _2] (4). [LZn·ZnI(μ-OEt)] _2 (5) was isolated from the reaction of an in situ generated mixture of 1 and 2 with iodine. This product likely results from adventitious oxygen in the reaction mixture. This was seemingly confirmed by the diffusion of air into a solution of 2 in toluene, thereby resulting in a pentanuclear zinc complex, [(LZn·ZnEt) _2{Zn(μ-OEt) _4}] (6). Complex 6 features a central Zn(OEt) _4 unit, in which the ethoxide groups bridge two dinuclear fragments. The identities of complexes 1-6 were conclusively identified by X-ray crystallography, thereby revealing similar structural features that were confirmed by spectroscopic data and, for 1-5, supported by DFT calculations. The coordination preferences of the tetradentate Schiff base N,N′-ethylenebis(4-iminopentan-2-one), H _2L, with Et _2Zn under various stoichiometries were investigatedand the reactivity of the resultant products was explored. These reactions afforded a series of di-, tetra- and polynuclear zinc complexes.