Synthesis, structure, and unprecedented solubility of lipophilic borate salts

The multi-gram scale preparation of halide free lipophilic borate salts from inexpensive precursor compounds 3,3′,5,5′-tetra-tert-butyl-2,2′-biphenol and tetrahydridoboranate salts is reported. The so-called “bortebate” anion is more stable against water and bases than its aluminum analog “altebate”, but bortebate formation is significantly slower. Bortebate salts are highly soluble in hydrocarbon solvents, e.g. >35 mmol/L lithium bortebate in pentane at 20 °C. Quantitative salt metathesis reactions between sodium bortebate and halide salts can be easily achieved by precipitation of the sodium halide in methylene chloride.