Taming the shrew: [TMEDALi-Zn(C2H4)2L] as a model compound for anionic ethene polymerisation

Abstract

We describe the synthesis of the compound [(TMEDA)Li(μ-TMP)(μ-CHCH₂)Zn(C₂H₃)] (1) (TMEDA = N,N,N′,N′-tetramethylethylenediamine, TMP = 2,2,6,6-tetramethylpiperidide), which serves as a potential model compound for anionic ethene polymerisation, and its decomposition into the metallated compound [Li(μ-Me₂NCH₂CH₂N(Me)CH₂)(μ-TMP)Zn(C₂H₃)] (4). The previously reported compound [(PMDETA)K(μ-TMP)(μ-CHCH₂)-Zn(CH₂SiMe₃)] (2) (PMDETA = N,N,N′,N′′,N′′-pentamethyldiethylenetriamine) and 1 are used as potential model compounds for anionic ethene polymerisation. Detailed Density Functional Theory (DFT) at the B3LYP/6-311G(d,p) level of theory on both 1 and 2 in conjunction with Bader AIM and NBO analyses revealed a substantial interaction between the Zn–CH atom and the Li (in 1, d_Li–CH = 2.43 Å) or K (in 2, d_K–CH = 3.01 Å). In fact, in the case of 1, this interaction is even stronger (estimated to be 20–30 kJ mol⁻¹) than those reported in the previously reported DFT studies of the reaction with butyl lithium and ethene in the presence of diamino ligands. Our theoretical results are in good agreement with experimentally observed parameters.