Cyclopentadienyl ruthenium(II) complexes with bridging alkynylphosphine ligands: Synthesis and electrochemical studies

The reaction of [CpRuCl-(PPh3)2] (Cp= cyclopentadienyl) and [CpRuCl(dppe)] (dppe=Ph2PCH2CH 2PPh2) with bis-and trisphosphine ligands 1,4-(Ph 2PC= C)2C6H4 (1) and 1,3,5-(Ph 2PC= C)3C6H3 (2), prepared by Ni-catalysed cross-coupling reactions between terminal alkynes and diphenylchlorophosphine, has been investigated. Using metal-directed self-assembly methodologies, two linear bimetallic complexes,[CpRuCl(PPh 3)2(μ-dppab)] (3) and[CpRu(dppe)2(μ- dppab)](PF6)2 (4), and the mononuclear complex [CpRuCl(PPh3)(η1-dppab)] (6), which contains a dangling arm ligand, were prepared (dppab=1,4-bis[(diphenylphosphino) ethynyl]benzene). Moreover, by using the triphosphine 1,3,5- tris[(diphenylphosphino)ethynyl]benzene (tppab), the trimetallic [CpRuCl-(PPh3)3(μ3-tppab)] (5) species was synthesised, which is the first example of a chiral-at-ruthenium complex containing three different stereogenic centres. Besides these open-chain complexes, the neutral cyclic species [CpRuCl(μdppab)2] (7) was also obtained under different experimental conditions. The coordination chemistry of such systems towards supramolecular assemblies was tested by reaction of the bimetallic precursor 3 with additional equivalents of ligand 2. Two rigid macrocycles based on cis coordination of dppab to [CpRu-(PPh 3)] were obtained, that is, the dinuclear complex [CpRu(PPh 3)(mdppab)2](PF6)2 (8) and the tetranuclear square [CpRu(PPh3)(mdppab)3](PF 3)3 (9). The solid-state structures of 7 and 8 have been determined by X-ray diffraction analysis and show a different arrangement of the two parallel dppab ligands. All compounds were characterised by various methods including ESIMS, electrochemistry and by X-band ESR spectroscopy in the case of the electrogenerated paramagnetic species. © 2009 Wiley-VCH Verlag GmbH& Co