作者:Tobias N. Hoheisel、Stephen Schrettl、Roman Marty、Tanya K. Todorova、Clémence Corminboeuf、Andrzej Sienkiewicz、Rosario Scopelliti、W. Bernd Schweizer、Holger Frauenrath
DOI:10.1038/nchem.1575
日期:2013.4
Packing constraints and precise placement of functional groups are the reason that organic molecules in the crystalline state often display unusual physical or chemical properties not observed in solution. Here we report a single-crystal-to-single-crystal dimerization of a bromodiacetylene that involves unusually large atom displacements as well as the cleavage and formation of several bonds. Density functional theory computations support a mechanism in which the dimerization is initiated by a [2Â +Â 1] photocycloaddition favoured by the nature of carbonâcarbon short contacts in the crystal structure. The reaction proceeded up to the theoretical degree of conversion without loss of crystallinity, and it was also performed on a preparative scale with good yield. Moreover, it represents the first synthetic pathway to (E)-1,2-dibromo-1,2-diethynylethenes, which could serve as synthetic intermediates for the preparation of molecular carbon scaffolds. Our findings both extend the scope of single-crystal-to-single-crystal reactions and highlight their potential as a synthetic tool for complex transformations. The photochemical-induced dimerization of bromine-terminated oligo(ethynylene)s in the solid state is shown to give 1,2-dibromoeneynes on a preparative scale. This single-crystal-to-single-crystal transformation proceeds through a multistep reaction that involves the making and breaking of several bonds in addition to large atom displacements. The reaction represents an atom-efficient and catalyst-free pathway towards functional carbon-rich molecular scaffolds.
有机分子在结晶状态下往往会显示出在溶液中无法观察到的不寻常物理或化学性质,原因就在于填料的限制和官能团的精确定位。在此,我们报告了溴二乙烯的单晶-单晶二聚反应,其中涉及异常大的原子位移以及多个键的裂解和形成。密度泛函理论计算支持这样一种机理,即二聚化是由晶体结构中碳碳短接触的性质促成的[2Â +Â 1]光环加成反应引发的。反应进行到理论转化程度时,结晶度没有降低,而且在制备规模上进行的反应产率也很高。此外,它还代表了(E)-1,2-二溴-1,2-二乙炔基乙烯的第一条合成途径,可作为制备分子碳支架的合成中间体。我们的发现既扩大了单晶到单晶反应的范围,又突出了其作为复杂转化合成工具的潜力。光化学诱导的固态溴端低聚(乙炔)二聚化反应可制备出 1,2-二溴乙炔。这种单晶到单晶的转化是通过多步反应进行的,除了大原子位移外,还涉及多个键的生成和断裂。该反应代表了一种原子高效、无催化剂的富碳功能分子支架途径。