Synthesis, structure, and electrochemistry of mononuclear and face-to-facebinuclear orthometalated complexes of palladium(II) with N-monodentate or N(1),N(3)-bridging 1,3-di-p-tolyltriazenido ligands. Dependence on geometrical arrangement of the electronic communication between two equivalent redox sites

The synthesis, electrochemistry, and structural characterization of the mon onuclear complex [Pd{C6H4N(H)N=C(CH3)C5H4N}(p-tolN-N=Np-tol)] (1) containin g the monodentate 1,3-di-p-tolyltriazenido ligand is described. Compound 1 is an example of a stable species containing a Pd-N amido bond cis to a Pd- C aryl bond. Kinetic parameters for the dynamic intramolecular N(1)-N(3) ex change of the monodentate ligand in complex 1 have been calculated. The cis and trans isomers of the orthometalated face-to-face complex [{Pd(C6H4N=NC 6H5)(mu -p-tolNNNp-tol)}(2)] (2) have also been prepared, and-the crystal s tructure of the trans isomer is reported. There are noticeable differences in the electrochemical behavior of the mononuclear and binuclear species. F rom the electrochemical experiments on both isomers of 2 it is possible to recognize different redox sites, to calculate the electronic coupling betwe en them, and to suggest where the reversible electron transfers occur. Each isomers of 2 undergoes two one-electron oxidations and two one-electron re ductions. The electronic coupling (DeltaE = 0.40 V) at oxidizing potentials is identical for both isomers of complex 2, suggesting that the oxidations occur on the Pd(mu -triazenido)(2)Pd framework which is common to both iso mers. By contrast, the electronic coupling at reducing potentials is greate r for cis-a (DeltaE = 0.33 V) than for trans-a (DeltaE = 0.25 V), suggestin g that the reduction processes occur on the orthopalladated fragments, whic h are arranged differently on the two isomers. Thus, electronic communicati on between two equivalent redox centers in the same molecule depends not on ly on the nature of the bridging ligand but also on the geometrical arrange ment of the redox centers.