Biphenylic Bisphosphines through ortho-Metalation of Aryldiphenylphosphine Oxides

Diphenyl-(2-trifluoromethyl)phosphine oxide was metalated next to the diphenylphosphinoyl group with LITMP. Upon iodination and Ullmann coupling, the corresponding 3,3'-disubstituted bis(phosphine oxide) was obtained. When phenyllithium was used as metalating agent, aryl/phenyl group exchange occurred. The torsional barrier for the planarization of the biaryl moiety was equal to 22 ± 1 kcal/mol.