One-pot synthesis of four-coordinate boron(III) complexes by the ligand-promoted organic group migration between boronic acids

Venkata S Sadu,Kee-In Lee,Hye-Rin Bin,Do-Min Lee

doi:10.1038/s41598-017-00236-2

Venkata S Sadu, Kee-In Lee + Show 2 more

Open Access

https://doi.org/10.1038/s41598-017-00236-2

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Abstract

Multidisciplinary applications of four-coordinate boron(III) complexes make them very attractive and challenging research field in chemistry, biology and material sciences. The dual role played by boron atom in stabilising the chelate ligand and enhancing the π-conjugation makes them very useful as luminescent materials for organic electronics and photonics, and sensing and imaging probes for biomedical purposes. The conventional methods involve the use of diarylborinic acids or anhydrides and triaryl boranes, which are made from organometallic reagents. The strong nucleophilicity of these reagents limits the peripheral modifications onto the boron cores. Here, we report a metal-free one-pot synthesis of four-coordinate organoborons using boronic acids, which represents the first instance of ligand assisted organic group migration between boronic acids. A tetrahedral boron ‘ate’ complex capable of transferring an organic group to the adjacent sp2 boron within a boronic anhydride intermediate is proposed and preliminary mechanistic studies by MALDI-TOF and 11B NMR support this proposal. The products are available from a series of N,O-, N,N- and O,O-bidentate ligands upon a wide array of boronic acids. We anticipate that this reaction will impact the way of producing the four-coordinate organoborons, and propel a new discovery of such materials for optoelectronic and biomedical applications.

Highlights

Boronic acids are ubiquitous components in organic synthesis, chemical biology, and material sciences[1]
After the pioneering work by Petasis and co-workers, multi-component reaction employing a boronic acid with an amine and an aldehyde has been extensively studied, where aryl, alkenyl, and alkynylboronic acids served as the nucelophilic component[6]
There are a decent number of publications in which the boronic acids act as organic group donors under transition metal-free conditions

Summary

Introduction

Boronic acids are ubiquitous components in organic synthesis, chemical biology, and material sciences[1]. Along with the Petasis boronic acid-Mannich reactions, 1,2-migration of alkyl groups from boron to carbon have been developed utilising anionotropic rearrangement of tetra-substituted boron ‘ate’ complexes (Fig. 1b)[7]. We report formation of four-coordinate boron(III) complexes via an organic group migration between boronic acids in the presence of a bidentate ligand under the basic conditions (Fig. 1d).

Results

Conclusion