Organoborane-carbonyl oxygen

It is postulated that the reaction involves an organoborane-carbonyl oxygen complex as an intermediate in the reaction. The hydride transfer, k2, is presumably the rate-determining step (Eq. 4.21) [12]. 

Protonolysis with carboxylic acids differs from that with mineral acids in that it appears to involve coordination of the carbonyl oxygen atom of the carboxylic acid to the boron atom of the organoborane, followed by intramolecular proton transfer (Scheme 14). - This is presumably the reason for the relative ease of protonolysis with carboxylic acids. 

Organoboranes do not normally react with carbonyl compounds in Grignard-like fashion with the exception of allylboranes. Aromatic aldehydes reacted with dialkylboron chloride derivatives in the presence of base to generate arylalkylmethanols in good yields (Equation (132)). On the other hand, reactions of aromatic aldehydes with dialkylboron chlorides in the presence of oxygen resulted in chlorination (Equation (133)).595... 

It is known that organoboranes readily undergo autoxidation in the presence of oxygen and this reaction has been used to prepare alcohols and alkyl hydroperoxides as well as to induce free radical reactions. Organoboranes can also be used to alkylate a,P-unsaturated carbonyl compounds through a free radical 1,4-addition reaction in the presence of oxygen. However, organoboranes do not normally react with saturated carbonyl compounds except for the reaction of formaldehyde with trialkylboranes in the presence of air. ... 

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