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

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 sp(2) boron within a boronic anhydride intermediate is proposed and preliminary mechanistic studies by MALDI-TOF and (11)B 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.