Synthesis and X-ray characterization of 15- and 16-vertex closo-carboranes

Fangrui Zheng,Jiji Zhang,Zuowei Xie,Tsz Hin Yui

doi:10.1038/s41467-020-19661-5

Abstract

Carboranes are a class of carbon-boron molecular clusters with three-dimensional aromaticity, and inherent robustness. These endowments enable carboranes as valuable building blocks for applications ranging from functional materials to pharmaceuticals. Thus, the chemistry of carboranes has received tremendous research interest, and significant progress has been made in the past decades. However, many attempts to the synthesis of carboranes with more than 14 vertices had been unsuccessful since the report of a 14-vertex carborane in 2005. The question arises as to whether these long sought-after molecules exist. We describe in this article the synthesis and structural characterization of 15- and 16-vertex closo-carboranes as well as 16-vertex ruthenacarborane. Such a success relies on the introduction of silyl groups to both cage carbons, stabilizing the corresponding nido-carborane dianions and promoting the capitation reaction with HBBr2·SMe2. This work would shed some light on the preparation of carboranes with 17 vertices or more, and open the door for studying supercarborane chemistry.

Highlights

Carboranes are a class of carbon-boron molecular clusters with three-dimensional aromaticity, and inherent robustness
A 13-vertex closo-carborane accepted one electron to give a stable carborane radical anion with [2n + 3] framework electrons[30,31]; it reacted with various nucleophiles to afford the cage carbon and/or cage boron extrusion products closoCB11−, nido-CB10−, closo-CB10−, and closo-C2B10, depending on the nature of the nucleophiles[32,33,34,35]
It was documented that silyl groups can stabilize carboanions and the stabilization is approximately additive for the number of silyl groups[36]

Summary

Introduction

Carboranes are a class of carbon-boron molecular clusters with three-dimensional aromaticity, and inherent robustness. A number of 13- and 14vertex closo-carboranes were prepared and structurally characterized[20,21,22,23,24,25,26,27,28,29]. Insertion of a metal fragment into a 14-vertex CAd nido-carborane was successful, resulting in the isolation and structural characterization of a 15-vertex metallacarborane 1,4-(CH2)3-7-(p-cymene)-7,1,4-RuC2B12H1223.

Results

Conclusion