Phosphorus-Based Functional Groups as Hydrogen Bonding Templates for Rotaxane Formation

We report on the use of the hydrogen bond acceptor properties of some phosphorus-containing functional groups for the assembly of a series of [2]rotaxanes. Phosphinamides, and the homologous thio– and selenophosphinamides, act as hydrogen bond acceptors that, in conjunction with an appropriately positioned amide group on the thread, direct the assembly of amide-based macrocycles around the axle to form rotaxanes in up to 60% yields. Employing solely phosphorus-based functional groups as the hydrogen bond accepting groups on the thread, a bis(phosphinamide) template and a phosphine oxide–phosphinamide template afforded the corresponding rotaxanes in 18 and 15% yields, respectively. X-ray crystallography of the rotaxanes shows the presence of up to four intercomponent hydrogen bonds between the amide groups of the macrocycle and various hydrogen bond accepting groups on the thread, including rare examples of amide-to-phosphinamide, -thiophosphinamide, and -selenophosphinamide groups. With a phosphine oxide–phosphinamide thread, the solid-state structure of the rotaxane is remarkable, featuring no direct intercomponent hydrogen bonds but rather a hydrogen bond network involving water molecules that bridge the H-bonding groups of the macrocycle and thread through bifurcated hydrogen bonds. The incorporation of phosphorus-based functional groups into rotaxanes may prove useful for the development of molecular shuttles in which the macrocycle can be used to hinder or expose binding ligating sites for metal-based catalysts.

本研究报道了若干含磷官能团的氢键受体特性在一系列[2]轮烷组装中的应用。次磷酰胺（phosphinamide）及其同系物硫代次磷酰胺、硒代次磷酰胺均可作为氢键受体，与轮烷轴上位置适宜的酰胺基团协同作用，引导轴周侧的酰胺基大环组装形成轮烷，产率最高可达60%。若仅以含磷官能团作为轴上的氢键受体基团，双次磷酰胺模板与氧化膦（phosphine oxide）-次磷酰胺模板分别以18%和15%的产率得到对应轮烷。轮烷的X射线晶体学分析表明，大环的酰胺基团与轴上各类氢键受体基团之间最多可形成4组组分间氢键，其中不乏罕见的酰胺与次磷酰胺、硫代次磷酰胺、硒代次磷酰胺之间的氢键相互作用。当采用氧化膦-次磷酰胺轴时，该轮烷的固态结构颇为特殊：其组分间不存在直接氢键，而是通过水分子构建氢键网络——该水分子以分叉氢键分别连接大环与轴的氢键作用基团。将含磷官能团引入轮烷结构中，或可助力分子梭的开发：此类轮烷的大环可用于遮蔽或暴露金属催化剂的配位结合位点。