Structural studies on diaryl selenide dihalides in solution: molecular complex formation of substituted diphenyl selenides with bromine
作者:Warô Nakanishi、Satoko Hayashi、Yoshiaki Kusuyama
DOI:10.1039/b108556e
日期:2002.1.23
Diaryl selenides that yield molecular complexes (MC) with bromine are prepared by modulating the effective electronegativity of the selenium atom and the steric environment around the atom in diphenyl selenide (1) with various substituents at the 2-, 3- and/or 4-positions. Halogen induced 1H and 13C NMR chemical shifts of the diaryl selenides are examined. The chlorine and iodine adducts of the selenides are shown to be trigonal bipyramidal adducts (TB) and MC, respectively. In the case of bromine adducts, the structures of (3- and 4-YC6H4)2SeBr2 are demonstrated to be MC if Y is CN and NO2, contrary to the general rule: they are TB if Y is less electron-withdrawing than the ethoxycarbonyl group. The CN and NO2 groups increase the effective electronegativity of the Se atom in (3- and 4-YC6H4)2Se and do not give
TB with bromine. The four chloro groups at all meta-positions in 1 are also effective for MC formation. However, 3,5-(O2N)2C6H3SeBr2Ph is TB. Ab initio MO calculations show that the structures of (3-O2NC6H4)2Se and 3,5-(O2N)2C6H3SePh are close to the C2 and Cs symmetries, respectively, which reveals that the conformational change is also important when the structures of the bromine adducts are determined. The steric congestion must be more severe for TB formation than for MC formation. The structures of 2,6-Cl2C6H3SeBr2C6H4Y-p (Y = H and Br) are MC, which shows that the steric effect of 2,6-Cl2C6H3 group is effective for MC formation. (2-MeC6H4)2SeBr2
and (2-ClC6H4)2SeBr2 are TB and MC, respectively: the electronic effect of the Cl group must play an additional role in the MC formation since the bulkiness of the Me and Cl groups are expected to be similar. The bromine adduct of (2,4,6-Me3C6H2)2Se is also concluded to be MC: the steric effect of the four Me groups at the ortho-positions is large enough to give MC with bromine. The oxidation potentials (Eox) of the diaryl selenides explain well the structures of the bromine adducts: the electronic effect is directly correlated with Eox and the importance of the steric effect has been brought into sharp relief by Eox. Results of MO calculations support the outline of the observations. The structural behavior of some halogen adducts such as 2,6-Cl2C6H3SeCl2C6H4Y-p
(TB: Y = H and Br) is also discussed in some detail.
通过调节二苯基硒化物(1)中硒原子的有效电负性以及硒原子周围的立体环境,并在 2、3 和/或 4 位上添加各种取代基,制备出了能与溴生成分子络合物(MC)的二芳基硒化物。研究了卤素诱导的二芳基硒化物的 1H 和 13C NMR 化学位移。结果表明,硒化物的氯加合物和碘加合物分别是三叉双金字塔加合物(TB)和 MC。就溴加合物而言,如果 Y 是 CN 和 NO2,则 (3- 和 4-YC6H4)2SeBr2 的结构被证明是 MC 型,这与一般规则相反:如果 Y 的吸电子性小于乙氧羰基,则它们是 TB 型。CN 和 NO2 基团增加了 (3- 和 4-YC6H4)2Se 中 Se 原子的有效电负性,与溴一起不会产生 TB。1 中所有元位置上的四个氯基对 MC 的形成也很有效。但 3,5-(O2N)2C6H3SeBr2Ph 是 TB。Ab initio MO 计算显示,(3-O2NC6H4)2Se 和 3,5-(O2N)2C6H3SePh 的结构分别接近 C2 和 Cs 对称性,这表明在确定溴加合物的结构时,构象变化也很重要。形成 TB 时的立体拥塞一定比形成 MC 时更为严重。2,6-Cl2C6H3SeBr2C6H4Y-p(Y = H 和 Br)的结构为 MC,这表明 2,6-Cl2C6H3 基团的立体效应对 MC 的形成是有效的。(2-MeC6H4)2SeBr2和(2-ClC6H4)2SeBr2分别是TB和MC:由于Me和Cl基团的体积预计相似,因此Cl基团的电子效应一定在MC形成过程中起到了额外的作用。(2,4,6-Me3C6H2)2Se的溴加合物也被断定为 MC:位于正交位置的四个 Me 基团的立体效应大到足以与溴形成 MC。二芳基硒化物的氧化电位(Eox)很好地解释了溴加合物的结构:电子效应与 Eox 直接相关,而立体效应的重要性则因 Eox 而凸显出来。MO 计算的结果支持观察到的轮廓。我们还详细讨论了一些卤素加合物的结构行为,如 2,6-Cl2C6H3SeCl2C6H4Y-p(TB:Y = H 和 Br)。