Preparation, methylation, and coupling reaction of 1,2-dithienyl-3,4- bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutenes

Sterically protected 1,2-di(2-thienyl)- and 1,2-di(3-thienyl)-3,4-bis[(2,4, 6-tri-t-butylphenyl)phosphinidene]cyclobutenes were prepared and their properties were studied. When the dithienyldiphosphinidenecyclobutenes were allowed to react with butyllithium and then with iodomethane, the corresponding methylthienyl derivatives were obtained. The structure of (E,E)-1,2-bis(5- methyl-3-thienyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutene was analyzed by X-ray crystallography. Lithiation of the dithienyldiphosphinidenecyclobutenes, followed by treatment with CuCl ₂, afforded the corresponding coupling products on the thiophene rings.