Mono‐ and Heterodimetallic Fe II and Ru II Complexes Based on a Novel Heteroditopic 4′‐{Bis(phosphanyl)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′‐[C 6 H 3 (CH 2 Br) 2 ‐3,5]‐2,2′:6′,2″‐terpyridine} was synthesized. Facile introduction of diphenylphosphanyl groups in this synthon gave the ligand {4′‐[C 6 H 3 (CH 2 PPh 2 ) 2 ‐3,5]‐2,2′:6′,2″‐terpyridine} ([ tpyPC(H)P ]). The asymmetric mononuclear complex [Fe(tpy){ tpyPC(H)P }](PF 6 ) 2 , prepared by selective coordination of [Fe(tpy)Cl 3 ] to the tpy moiety of [ tpyPC(H)P ], was used for the synthesis of the heterodimetallic complex [Fe(tpy)( tpyPCP )Ru(tpy)](PF 6 ) 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 }](PF 6 ) 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 ](PF 6 ) 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 Fe II –Ru II communication in the heterodimetallic system [Fe(tpy)( tpyPCP )Ru(tpy)](PF 6 ) 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)