Photochemistry of Tetraarylborate Salts (Ar4B-): Formation of 2,5,7,7-Tetraphenyl-7-boratabicyclo[4.1.0]hepta-2,4-diene (a Boratanorcaradiene) by Irradiation of (p-Biphenylyl)triphenyl Borate

Article abstract of DOI:10.1021/ja00006a037

Irradiation of tetramethylammonium (p-biphenylyl)triphenylborate with UV light gives three isomeric boratanorcaradiene anions by a process analogous to the di-π-methane rearrangement of hydrocarbons. One of the boratanorcaradienes, tetramethylammonium 2,5,7,7-tetraphenyl-7-boratabicyclo[4.1.0]hepta-2,4-diene (1), was isolated as a deep red crystalline solid, and its structure was determined by X-ray crystallography. Borate 1 is a fluxional compound at room temperature; an electrocyclic rearrangement exchanges the two boron-bound phenyl groups. A mechanism for the photochemical rearrangement of (p-biphenylyl)triphenylborate is proposed, and the structural, chemical, and physical properties of 1 are discussed.