Tetracyclopenta[def,jkl,pqr,vwx]tetraphenylene: A Potential Tetraradicaloid Hydrocarbon

A tetramesityl derivative of hitherto unknown tetracyclopenta[def,jkl,pqr,vwx]tetraphenylene (TCPTP), which is a potential tetraradicaloid hydrocarbon, was synthesized. Theoretical calculations based on spin-flip time-dependent density functional theory predict that the closed-shell D-2h form of TCPTP is more stable than the open-shell D-4h form with its slightly tetraradical character. The tetramesityl derivative (Mes)(4)-TCPTP exhibits remarkable antiaromaticity as a result of the peripheral 20-pi-electron circuit, which causes an absorption maximum at a long wavelength and a small HOMO-LUMO gap. In solution, (Mes)(4)-TCPTP most likely adopts rapidly equilibrating D-2h structures that interconvert via the D-4h transition state. X-ray crystallographic analysis showed (Mes)(4)-TCPTP as an approximate D-2h structure.