PHOTOCHEMISTRY OF 2,5,7,7-TETRAPHENYL-7-BORATABICYCLO[4.1.0]HEPTA-2,4-DIENE (A BORATANORCARADIENE ANION) - NO EVIDENCE FOR DIPHENYLBORENE ANION

Irradiation of 2,5,7,7-tetraphenyl-7-boratabicyclo[4.1.0]hepta-2,4-diene anion (1, a boratanorcaradiene, as its potassium or tetramethylammonium salt) with UV light leads to formation of p-terphenyl in high yield. This observation led us to consider the possibility that diphenylborene anion (Ph2B-, an analogue of diphenylcarbene) might also be formed in this reaction. We designed and carried out a series of spectroscopic and chemical experiments to detect and characterize the borene. None of these experiments provides evidence for the formation of diphenylborene from this reaction. We suggest that the formation of p-terphenyl from the photolysis of 1 is initiated by an electron-transfer (photoionization) process. We also reexamined experiments reported earlier that were claimed to show that diphenylborene is formed from the irradiation or overirradiation of tetraphenylborate. Each of these experiments is ambiguous and cannot be relied upon to demonstrate the formation of the borene by this route. © 1990, American Chemical Society. All rights reserved.