Boron Compounds with Oxygen Ligands

In 1998, Todd et al. studied the thermodynamics and mode of coordination of the reaction of tetrahydroxyborate (B ) with three different carbohydrates 

Anslyn et al used B NMR spectroscopy in conjunction with molecular modeling and X-ray crystallography analysis to distinguish between the types of modes of interaction between the nitrogen and boron atoms in a 

Further, they found that the hydrogen atom from the inserted methanol was located closer to the amine than to the methanolic oxygen, indicating ionization of the solvent and the formation of a zwitterionic species.  

Boronic Acids. Preparation and Applications in Organic Synthesis and Medicine, Wiley-VCH, Weinheim, 2005. 

Adamczyk-Wozniak, M. K. Cyrahski, M. Jakubczyk, P. Klimentowska, A. Koll, J. Kolodziejczak, G. Pojmaj, A. Zubrowska, G. Z. Zukowska and A. Sporzynski,/. Phys. Chem. A, 2010,114, 2324-2330. 

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Figure 11 A transition state with pentavalent coordination at boron would be required for the complexation of a ligand with a tetrahedral boronate anion. Yamashita et al. have recently reported the first single-crystal X-ray structure of a pentavalent boron compound, unequivocally confirming the existence of these hypervalent boron species.Atoms marked in red represent oxygen, pink boron and grey carbon. For clarity hydrogen atoms are not displayed.

Complexes of carbonyl oxygen with trivalent boron and aluminum compounds tend to adopt a geometry consistent with directional interaction with one of the oxygen lone pairs. Thus the C—O—M bonds tend to be in the trigonal (120°—140°) range and the boron or aluminum is usually close to the carbonyl plane.The structural specificity that is built into Lewis acid complexes can be used to advantage to achieve stereoselectivity in catalysis. For example, use of chiral ligands in conjunction with Lewis acids is frequently the basis for enantioselective catalysts. 

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