Synthesis has been carried out of 15 examples of anionic diphenylboron complexes of arylpyruvic acids, and the structures of the compounds have been determined from spectroscopic data and from X-ray analysis of one of the compounds. Crystals of5jare monoclinic,P21/n,a= 9.5566(10),b= 15.961(3),c= 16.6382(6) Å, beta = 99.3239(10)°, andZ= 4, at 180 K. The structure was solved by direct methods and refined by full-matrix least-squares procedures toR(F2) = 0.056 for 6662 CCD data.5jcontains a triethylammonium cation and an anion containing a planar five-membered OBOCC ring, with cation and anion linked by an N-H···O hydrogen bond. Spectroscopic data and bond distances establish that the pyruvate ligand is the enol-tautomeric stat