Department of Chemistry and Center for Nanoscience & Nanotechnology, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan.
Dalton Trans. 2010 Oct 7;39(37):8748-58. doi: 10.1039/c0dt00327a. Epub 2010 Aug 10.
A series of diarylamido phosphine ligands of the type N-(2-dihydrocarbylphosphinophenyl)-2,6-dialkylanilide 1a-d have been prepared and employed to investigate the coordination chemistry of zinc. Protonolysis of ZnMe2 with one equivalent of N-(2-diphenylphosphinophenyl)-2,6-dimethylaniline (H[1a]) produced a mixture of [1a]ZnMe (2a) and Zn[1a]2 (4a), whereas that involving ZnEt2 gave exclusively the three-coordinate [1a]ZnEt (3a). In contrast, treatment of ZnR2 (R = Me, Et) with N-(2-diphenylphosphinophenyl)-2,6-diisopropylaniline (H[1b]), N-(2-diisopropylphosphinophenyl)-2,6-dimethylaniline (H[1c]), or N-(2-diisopropylphosphinophenyl)-2,6-diisopropylaniline (H[1d]) under similar conditions generated quantitatively the corresponding three-coordinate zinc methyl 2b-d and zinc ethyl 3b-d. The bis-ligand complexes 4a,b,d were isolated by either protonolysis of alkyls 2-3 with one equivalent of H[1] or metathesis of ZnX2 (X = Cl, OAc) with the corresponding lithium derivatives 5. Attempts to prepare [1a-d]ZnX (X = Cl, OAc) were not successful regardless of stoichiometry of the starting materials employed. Alcoholysis of zinc alkyls 2-3 led undesirably to protonation on the amido nitrogen donor of 1, highlighting perhaps its higher basicity than alkyls. The reaction of ZnCl2 with H[1c] generated the phosphorus-bound adduct {H[1c]ZnCl(mu-Cl)}2 (6c). Interestingly, attempts to deprotonate 6c with n-BuLi produced unexpectedly the alkylated product [1c]Zn(n-Bu) (7c) instead of [1c]ZnCl; analogous reactions employing NEt3 led to Lewis base substitution to give H[1c] and [ZnCl2(NEt3)]2. Structural characterization of all new compounds was achieved by multi-nuclear NMR spectroscopy (1H, 13C, 31P, and 7Li) and X-ray crystallography (2c-d, 3c, 4d, 5c-d, and 6c) where appropriate. On the basis of the NMR and X-ray data, in combination with the synthetic investigations, the steric nature of these amido phosphine ligands is recognized to follow the order of 1a < 1b < 1c < 1d. Interestingly, zinc alkyls 2-3 are all active initiators for catalytic ring-opening polymerization of ε-caprolactone whereas the bis-ligand complexes 4 are not.
一系列类型为 N-(2-二氢烃基膦基苯基)-2,6-二烷基苯胺的二芳基酰胺基膦配体 1a-d 已被制备并用于研究锌的配位化学。ZnMe2 与等摩尔的 N-(2-二苯基膦基苯基)-2,6-二甲基苯胺 (H[1a]) 进行质子解，得到 [1a]ZnMe (2a) 和 Zn[1a]2 (4a) 的混合物，而 ZnEt2 则得到专一地三配位 [1a]ZnEt (3a)。相比之下，用 N-(2-二苯基膦基苯基)-2,6-二异丙基苯胺 (H[1b])、N-(2-二异丙基膦基苯基)-2,6-二甲基苯胺 (H[1c]) 或 N-(2-二异丙基膦基苯基)-2,6-二异丙基苯胺 (H[1d]) 处理 ZnR2 (R = Me, Et) 在类似条件下定量地生成相应的三配位锌甲基 2b-d 和锌乙基 3b-d。通过用等摩尔的 H[1] 对烷基 2-3 进行质子解，或者用相应的锂衍生物 5 对 ZnX2 (X = Cl, OAc) 进行复分解反应，分离出双配体配合物 4a,b,d。无论起始材料的化学计量如何，尝试制备 [1a-d]ZnX (X = Cl, OAc) 均未成功。锌烷基 2-3 的醇解导致 1 上的酰胺氮供体质子化，这可能表明其碱性高于烷基。ZnCl2 与 H[1c] 反应生成磷键合加合物 {H[1c]ZnCl(mu-Cl)}2 (6c)。有趣的是，用 n-BuLi 对 6c 进行脱质子化反应出乎意料地生成了烷基化产物 [1c]Zn(n-Bu) (7c)，而不是 [1c]ZnCl；类似地用 NEt3 进行的反应导致路易斯碱取代生成 H[1c] 和 [ZnCl2(NEt3)]2。通过多核 NMR 光谱 (1H、13C、31P 和 7Li) 和 X 射线晶体学 (2c-d、3c、4d、5c-d 和 6c) 适当对所有新化合物的结构特征进行了表征。基于 NMR 和 X 射线数据，结合合成研究，这些酰胺基膦配体的空间位阻性质被认为遵循 1a < 1b < 1c < 1d 的顺序。有趣的是，锌烷基 2-3 均是ε-己内酯开环聚合的活性引发剂，而双配体配合物 4 则不是。
