Oligothiophenes with phosphorus-based ligands

Phosphines are extremely versatile and ubiquitous ligands in transition metal chemistry [34], They possess several attributes which make them ideal as ligands, including the ability to tune the steric and electronic properties via the choice of the three substituents on the phosphine. Several studies have incorporated phosphine functionalities into oligothiophenes and metal complexes of these ligands have been prepared and studied. A series of diphenylphosphine substituted oligothiophenes (4-11, Chart 5.3) have been prepared [35, 36]. 

The terminally substituted diphosphines have also been used to prepare Au complexes (16-18, Chart 5.4) [37]. The metal does not shift the absorption maxima much relative to the free ligands however, dual emission is observed in the case of 17. This is attributed to emission from both monomer and an Au-Au bridged dimer, which is observed in the solid state. Several of the Pt and Pd complexes (19-24, Chart 5.4) have also been characterized crystallographically and some of these structures show k-k stacking interactions between thiophene rings in the solid state [38]. A third-order nonlinear optical response was obtained for the Pd and Pt complexes (21 and 24) using Z-scan measurements [39]. These complexes have nonlinear refractive index values of (—1.5 to —1.8) Hicks and co-workers have prepared a 

Molybdenum complexes containing these ligands were prepared and cyclic voltammetry was carried out, but no evidence for electropolymerization was observed. 

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