Mono- and heterodimetallic FeII and RuII complexes based on a novel heteroditopic 4’,-{bis(phosphino)aryl}-2,2’:6’,2”-terpyridine ligand

In the search for a versatile building block that allows the preparation of heteroditopic tpy-pincer bridging ligands, the synthon {4 -[C6H3(CH2Br)2-3,5]-2,2 :6 ,2 -terpyridine} was synthesized. Facile introduction of diphenylphosphanyl groups in this synthon gave the ligand {4 -[C6H3(CH2- PPh2)2-3,5]-2,2 :6 ,2 -terpyridine} ([tpyPC(H)P]). The asymmetric mononuclear complex [Fe(tpy){tpyPC(H)P}](PF6)2, prepared by selective coordination of [Fe(tpy)Cl3] to the tpy moiety of [tpyPC(H)P], was used for the synthesis of the heterodimetallic complex [Fe(tpy)(tpyPCP)Ru(tpy)](PF6)3, which applies the “complex as ligand” approach. Coordination of the ruthenium centre at the PC(H)P-pincer moiety of [Fe(tpy){tpyPC(H)P}](PF6)2 has been achieved by applying a transcyclometallation procedure. The ground-state electronic properties of both complexes, investigated by cyclic and square-wave voltammetries and UV/Vis spectroscopy, are discussed and compared with those of [Fe(tpy)2](PF6)2 and [Ru(PCP)(tpy)]Cl, which represent the mononuclear components of the heterodinuclear species. An in situ UV/Vis spectroelectrochemical study was performed in order to localize the oxidation and reduction steps and to gain information about the FeII–RuII communication in the heterodimetallic system [Fe(tpy)(tpyPCP)Ru(tpy)](PF6)3 mediated by the bridging ligand [tpyPCP]. Both the voltammetric and spectroelectrochemical results point to only very limited electronic interaction between the metal centres in the ground state.