Potassium Cyclooctane-1,5-diyl dihydroborate

To a stirred suspension of (13.5 g, 337 mmole) KH in 250 mL tetrahydrofuran at room temperature (30.6 g, 125 mmole), 9-BBN-dimer is added rapidly enough that the solvent starts refluxing. The same work-up as for the Na compound is used to give 39.9 g (98%) of a colorless, THF free powdery product. 

The air-stable alkali metal (cyclooctane-1,5-diyl)dihydroborates(l-) are very moisture-sensitive. They must be stored and handled in an inert gas atmosphere. The salts are insoluble in aliphatic solvents and poorly soluble in aromatic solvents such as mesitylene. 

TABLE I Spectroscopic Parameters for Alkali Metal (Cyclooctane-1,5-diyl)dihydroborates( 1- ) 

The hydride content of both the ether-containing and solvent-free alkali metal (cyclooctane-1,5-diyl)dihydroborate is (1-) can be determined volumet-rically by measuring the hydrogen evolved after treatment with an alcohol (e.g., 2-ethyl-l-hexanol) at room temperature. 

The solvent-free salts do not melt below 250°, whereas the lithium salt slowly undergoes ligand exchange reactions at this temperature. 

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The preparations of lithium and sodium (cyclooctane-1,5-diyl)dihydro-borates(l-) in tetrahydrofuran proceed via isolable, stable etherates. These can be made solvent-free simply by heating under vacuum. 9-Borabicyclo[3.3.1 ]-nonane dimer (9-BBN) can easily be prepared from cycloocta-1,5-diene2 by reaction with tetraethyldiborane(6), tetrahydrofuran-borane8,9 or dimethyl sulfide-borane.10 The synthesis of alkali metal (cyclooctane-1,5-diyl)dihydroborates is achieved by addition of 9-BBN to a suspension of the alkali metal hydride in tetrahydrofuran. Lithium hydride reacts more slowly than sodium or potassium hydride. The reactions are brought to completion by heating under reflux. 

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