Model Complexes for Metallated Polythiophenes: Gold(I) and Palladium(II) Complexes of Bis(diphenylphosphino)oligothiophenes

The preparations of two new phosphinothiophene ligands, 3,3‘-bis(diphenylphosphino)-2,2‘-bithiophene (dppbt; 1)
and 3,3‘ ‘‘-dihexyl-3‘,3‘ ‘-bis(diphenylphosphino)-2,5‘:2‘,2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (hdppqt; 2) are reported. Oxidation
of 1 gives 3,3‘-bis(diphenylphosphine oxide)-2,2‘-bithiophene (3), and the crystal structure of this compound was
determined. Pd(II) and Au(I) complexes of these ligands have been synthesized and characterized. Crystal structures
of [(dppbt)PdCl2] (1-Pd), [(hdppqt)PdCl2] (2-Pd), [(dppbt)(AuCl)2] (1-Au), and [(hdppqt)(AuCl)2] (2-Au) were obtained.
[(dppbt)(AuCl)2] crystallized in two solid-state forms; crystals grown from CH2Cl2/Et2O show a gold−gold interaction
of 3.3221(4) Å, but from CH2Cl2/toluene, the molecule crystallizes as a toluene adduct (1-Au-tol) and does not
show any gold−gold interaction. All the complexes were characterized via UV−vis spectroscopy and cyclic voltammetry,
and the effect of the metal on the energy of the π−π* transition and oxidation potential was determined. These
data are correlated to the interannular torsion angles in the oligothienyl groups from the crystal structure studies.