Intramolecular Interactions between Chalcogen Atoms: Organoseleniums Derived from 1-Bromo-4-<i>tert</i>-butyl-2,6-di(formyl)benzene

The synthesis and characterization of a series of low-valent organoselenium compounds derived from 1-bromo-4-tert-butyl-2,6-di(formyl)benzene (22) is described. The synthesis of diselenide 25 was achieved by the lithiation route whereas bis(4-tert-butyl-2,6-di(formyl)phenyl) diselenide (26) was synthesized by treating 22 with disodium diselenide. A series of monoselenides (27, 28, and 29) was obtained by facile nucleophilic substitution of bromine in 22, using the corresponding selenolates as nucleophiles. The halogenation reactions of bis(4-tert-butyl-2,6-di(formyl)phenyl) diselenide (26) did not afford the corresponding selenenyl halides but resulted in the isolation of an unexpected cyclic selenenate ester 34 as a product. The selenide 32 was synthesized by the treatment of dimethoxymethyl diselenide with trilithiated 2-bromo-5-tert-butyl-N,N‘-di(phenyl)isophthalamide. The existence of potential Se···O intramolecular nonbonding interactions was examined by IR, 1H, and 77Se NMR spectroscopy, X-ray crystallography, and computational studies. The X-ray crystal structures of 26 and 27, having two ortho formyl groups, reveal the absence of any Se···O interactions. However, the Se···O interactions were observed in the selenenate ester 34 where one of the formyl groups has been utilized for the selenenate ring formation. The crystal structures of 26 and 27 exhibited intermolecular short-range C−H···Se interactions (hydrogen bonding). Although there are four heteroatoms in carbamoyl moieties ortho to selenium capable of forming a five-membered ring on intramolecular coordination, no such intramolecular Se···X (X = N, O) interaction was observed in the crystal structure of 32. The density functional theory calculations at the B3LYP/6-31G* level predicted that for all the diformyl systems (47a−c, 48a−c), the anti,anti conformer (when both formyl oxygen atoms point away from the selenium) is more stable. This preference was found to be reversed in the monoformyl-substituted systems (50a,b, 51a,b), where the syn conformer (when formyl oxygen is near the selenium) is energetically more favorable than the anti conformer.本文报道了一系列由1-溴-4-叔丁基-2,6-二(甲酰基)苯(22)衍生得到的低价态有机硒化合物的合成与表征。二硒化物25的合成采用锂化路线完成，而双(4-叔丁基-2,6-二(甲酰基)苯基)二硒化物(26)则通过将22与二硒化二钠反应制得。以相应的硒醇盐作为亲核试剂，通过对22中溴原子的简便亲核取代反应，得到了一系列单硒化物(27、28和29)。对双(4-叔丁基-2,6-二(甲酰基)苯基)二硒化物(26)的卤代反应并未得到对应的硒卤化物，而是分离得到了一种意外的环状硒烯酸酯34作为产物。硒化物32的合成是通过将二甲氧基甲基二硒化物与三锂化的2-溴-5-叔丁基-N,N'-二(苯基)间苯二甲酰胺反应实现的。通过红外(IR)光谱、1H核磁共振(1H NMR)、77Se核磁共振(77Se NMR)谱学、X射线晶体学以及计算研究，考察了潜在的Se···O分子内非键相互作用。带有两个邻位甲酰基的26和27的X射线晶体结构显示，不存在任何Se···O相互作用。然而，在其中一个甲酰基参与形成硒烯酸酯环的硒烯酸酯34中，却观察到了Se···O相互作用。26和27的晶体结构表现出分子间短程C-H···硒相互作用（氢键）。尽管在硒邻位的氨基甲酰基部分存在四个可参与分子内配位以形成五元环的杂原子，但在32的晶体结构中并未观察到此类分子内Se···X（X=N、O）相互作用。在B3LYP/6-31G*水平下进行的密度泛函理论计算表明，对于所有的二甲酰基体系(47a−c、48a−c)，反式-反式构象（当两个甲酰基氧原子均远离硒原子时）更为稳定。而在单甲酰基取代的体系(50a,b、51a,b)中，这一偏好发生了反转：顺式构象（当甲酰基氧原子靠近硒原子时）在能量上比反式构象更有利。