Sodium cyanoboranate

See Sodium chlorate Cyanoborane oligomer See related BORANES, cyano compounds... 

Cyanoborohydride and its modified reagents have been used for reductive dehalogenations. Thus, the combination of sodium or tetrabutylammonium cyanoborohydride, sodium or potassium 9-cyano-9-hydro-9-borabicyclo[3.3.1]nonanate [9-BBNCN] (2) or polymeric cyanoborane (3) in HMPA furnishes an efficient and mild system for the reduction of alkyl halides. The reagents are selective in that other functional groups, including ester, carboxylic acid, amide, cyano, alkene, nitro, sulfone, ketone, aldehyde and epoxide, are essentially inert under the reduction conditions thus, the reduction procedure is attractive for synthetic schemes which demand minimum damage to sensitive portions of the molecule. 

The preparation of cyanoborane derivatives produced sodium chloride by-product (to be discussed in a different section). Attempts to remove the salt from the polymeric derivatives were made using dialysis for high molecular weight derivatives and ultrafiltration for the lower molecular weight material. 

The cyanoborane derivatives were prepared from the corresponding polyamine hydrochlorides in aqueous media using a procedure similar to that described in ref [7]. Hydrogen evolved in the reaction between the hydrochloride and sodium cyanotrihydroborate was measured with a wet test meter. An alternative synthetic approach to prepare the cyanoborane derivative of PEI that did not produce sodium chloride by-product used a transamination reaction between neutral PEI and pyridine cyanoborane. 

Reaction of the hydrochloride derivative of the PEI fraction of a MW of 1800 liberated 94% of the anticipated hydrogen within a few hours. In contrast with this the 10000 MW fraction produced only 86% of the theoretical amount of H2. These two materials were obtained as free flowing powders after solvent evaporation which retained the sodium chloride by-product. Attempts to separate the salt by ultrafiltration or dialysis were partially effective because the polymers behaved as ion exchangers and retained chloride ions. An alternate synthetic approach to the cyanoborane derivatives which would not produce salt as a byproduct was explored. In this case, previously formed pyridine.BH2CN was used in a transamination reaction with neutral PEI producing a derivative that showed 59% derivatization. Attempts to derivatize polyallylamine hydrochloride, PAA, by reaction with NaBH3CN failed even in boiling water under reflux. Apparently this marked difference with PEI stems from differences in pKa values of the two hydrochlorides which was measured to be about 5.0 for PEI and 7.0 for PAA. 

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