11B NMR Together with IR Spectroscopy Provides Insight into Structural Elucidation of Quadrivalent Diazaborines & Cyclic Boronate Esters: The Chemist’s Perspective

Imidazo-fused diazaborines which serve as intermediary structures somewhat along benzene and borazine had been of particular interest to Dewar and Snyder more than 60 years ago. To this end, Dewar utilised his ‘π- complex theory’ so as to represent ‘borazaros’ as ‘quadrivalent’ species; however, sadly modern representations have deviated and leapt into ‘trivalent’ counterparts. Inasmuch as bonding in boron species has never been straightforward to such an extent that the orthodox ‘ethane’ like diborane i.e. H3B–BH3 which conferred to the paradigmatic rules of molecular structure, in particular, hybridisation and electronegativity was later evolved to a more realistic ‘3-centre 2-electron’ bonding, so as to give the lie to the purported diborane structures of X-ray diffractors, herein 11B NMR together with IR spectroscopy sheds light on the nature of bonding in borazaros and ‘caged’ cyclic oxazaborons so as to reenforce and reinvigorate the old literature which could be of interests to the synthetic and medicinal chemist alike.