Synthesis and structures of some sterically hindered zinc complexes containing 6-membered and rings

Zinc β-diketiminates containing the N,N′-chelating ligand [{N(SiMe3)C(Ph)}2CH]− (≡LL−) [Zn(LL)(μ-Cl)]2 (1) and [ZnEt(LL)thf] (2) were prepared from 2ZnCl2 + [Li(LL)]2 and ZnEt2 + H(LL), respectively. The new phenols 2-(N-R-piperazinyl-N′-methyl)-4,6-di-tert-butylphenol [R = Ph (3a), Me (3b)] and 2,2-[μ-N,N′-piperazindiyldimethyl]-bis(4,6-di-tert-butylphenol) (4) were obtained from 2,4-tBu2C6H3OH, (CH2O)n and the appropriate piperazine. Zinc phenoxides 5, 7 and 8 were derived from 2ZnEt2 with 2(3a), 2(3b) and 4, respectively. Controlled methanolysis of 5 furnished the bis(phenoxo)zinc compound Zn[OC6H2tBu2-2,4-{CH2N(CH2CH2)2NPh}-6]2 (6). The X-ray structures of the crystalline zinc compounds 1, 2, 5, 6, 7 and 8, are presented; each of 5–8 contains two six-membered rings. The centrosymmetric molecule 1 has a rhomboidal (ZnCl)2 core with exceptionally different Zn–Cl and Zn–Cl′ bond lengths of 2.248(1) and 2.509(1) Å, respectively. None of 1, 2 or 5–8 was an effective catalyst for the copolymerisation of an oxirane and CO2.

Graphical abstractThe synthesis and structures of six crystalline zinc β-diketiminates and 2-(piperazinyl-N-methyl)-4,6-di-tert-butylphenoxides, including 2 and 8, potential candidates for copolymerisation of epoxides and carbon dioxide, are reported.Figure optionsDownload full-size imageDownload as PowerPoint slide