Synthesis, characterization, and complexation of tetraarylborates with aromatic cations and their use in chemical sensors

Five aromatic borate anions, namely tetrakis(4-phenoxyphenyl)borate (1). tetrakis(biphenyl)borate (2), tetrakis(2-naphthyl)borate (3), tetrakis(4-phenylphenol)borate (4), and tetrakis(4-phenoxy)borate (5), have been prepared and tested as ion-recognition sites in chemical sensors for certain aromatic cations and metal ions. To gain further insight into the complexation of the cations, some complexes have been prepared and structurally characterized. The complexation behavior of 1 and 2 towards N-methylpyridinium (6), 1-(ethyl-4-(methoxycarbonyl)pyridinium) (7), tropylium (8), imidazolium (9), and 1-methylimidazolium (10) cations has been studied, and the stability constants of the complexes of 1 with cations 6 and 8 have been measured to compare them with the values for the previously studied complexes of tetraphenylborate. The structures of the borate anions and their complexes have been characterized by NMR and mass spectrometric methods. X-ray crystal structures have been determined for potassium tetrakis(4-phenoxyphenyl)borate (K(+.)1), N-methylpyridinium tetrakis(4-phenoxyphenyl)borate (6(.)1), 1-ethyl-4-(methoxycarbonyl)pyridinium tetrakis(4-phenoxyphenyl)borate (7(.)1), tropylium tetrakis(4-phenoxyphenyl)borate (8(.)1), and imidazolium tetrakis(biphenyl)borate (9(.)2). The results show that borate derivatives are potential candidates for a completely new family of charged carriers for use in cation-selective electrodes.