Iterative Synthesis of Oligosilanes Using Methoxyphenyl- or Hydrogen-Substituted Silylboronates as Building Blocks: A General Synthetic Method for Complex Oligosilanes.

Abstract

Organosilanes have attracted the attention of researchers for more than 150 years due to their unique properties, and they have become indispensable industrial assets. However, many synthesized oligosilanes with multiple Si-Si bonds are relatively simple, i.e., they often only contain a single repeating unit. More laborious customized synthetic routes can lead to more complex oligosilanes, but compared to carbon-based molecules, their structural diversity remains limited. The development of effective and practical synthetic routes to complex oligosilanes that contain mixed substituents constitutes a long-standing challenge. Here, we describe an iterative synthesis of oligosilanes using methoxyphenyl- or hydrogen-substituted silylboronates, which were obtained via transition-metal-catalyzed Si-H borylation reactions. The first key reaction is a cross-Si-Si bond-forming reaction between chloro(oligo)silanes and silylboronates activated by MeLi. The second key reaction is the selective chlorination of the methoxyphenyl group or the hydrogen atom at the terminal of the oligosilanes. Iteration of these two key reactions enables the synthesis of various oligosilanes that are otherwise difficult to access. As a demonstration of the synthetic utility of this iterative synthetic approach, oligosilanes with different sequences were prepared by simply changing the order of the reaction of four different silicon units. Furthermore, a bespoke tree-shaped oligosilane is easily obtained via the present iterative synthesis. The solid-state structures of several of these oligosilanes were unequivocally determined using single-crystal X-ray diffraction analysis.