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 ZnOC₆H₂tBu₂-2,4-{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.