Synthesis and characterization of rhenium(I) complexes with the polypyridinic quinone functionalized electron acceptor ligand [3,2-a:2′,3′-c]-benzo[3,4]-phenazine-11,16-quinone, Nqphen

Abstract

In this work, the synthesis and characterization of fac-[Re(CO)3(Nqphen)(L)]PF6 complexes is reported. Nqphen is the quinone substituted acceptor ligand [3,2-a:2′,3′-c]-benzo[3,4]-phenazine-11,16-quinone, and L represents the donor monodentate pyridine substituted ligands 4-tert-butylpyridine (t-Bupy), 4-methoxypyridine (MeO-py) or 10-(4-picolyl)phenothiazine (py-PTZ). The complexes were synthesized by refluxing in methanol the metal precursor fac-Re(CO)3(Nqphen)TfO (TfO=trifluoromethanesulphonate anion) with the corresponding L ligand. The UV–Vis spectra of the complexes are dominated by intense intraligand (IL) bands, and less intense metal ligand charge transfer (MLCT) bands with maxima in the 380–400nm region. The IR shows the typical pattern for tricarbonyl Re complexes with facial (fac) geometry. An additional v(CO) stretching band, attributed to the quinone fragment of Nqphen, is observed.Electrochemical data indicate that the acceptor capacity of Nqphen is increased in the complexes with regard to the free ligand. This effect is sensitive to the nature of the L ligand, following the order: MeO-py<t-Bupy<py-PTZ, indicating therefore that the donor capacity of L affects the rest of the molecule. The results obtained for the fac-[Re (CO)3(Nqphen)(pyPTZ)]PF6 complex here reported were compared with those observed for the homologous complex fac-[Re(CO)3(Aqphen)(L)]0/+, with Aqphen=12,17-dihydronaphtho[2,3-h]dipyrido[3,2-a:2′,3′-c]-phenazine-12,17-dione, and L=Cl−, TfO−, py-PTZ.