The Synthesis, Structure and (FTIR-Spectro)Electrochemistry of W(CO)5 complexes of 4-oxo-4-(2,5-dimethyl-azaferrocen-1’-yl) butanoic and 5-oxo-5-(2,5-dimethylazaferrocen-1’-yl) pentanoic acids

With the aim of developing new IR-detectable metal–carbonyl tracers for the amino function, we have synthesized W(CO)5 complexes of 4-oxo-4-(2,5-dimethylazaferrocen-1′-yl)butanoic acid (2) and 5-oxo-5-(2,5-dimethylazaferrocen-1′-yl)pentanoic acid (3) by AlCl3-catalyzed Friedel–Crafts reaction of W(CO)5–2,5-dimethylazaferrocene (1) with succinic or glutaric anhydride. Complexes 2 and 3 are thermally stable and display sharp, intense absorption bands of tungsten-coordinated CO ligands at ca. 1923 cm–1. In the crystalline state, molecules of 2 and 3 are stabilized by a network of intra- and intermolecular hydrogen bonds, as shown by single-crystal X-ray structure analysis. Complex 2 was transformed into the corresponding N-succinimidyl ester 4. Its utility toward labeling of amino acids was tested in its reaction with glycine methyl ester. Corresponding glycine amide 5 was obtained in 82 % yield and is an air/thermally stable bioconjugate exhibiting intense sharp absorption bands of the W–CO reporting group at ca. 1923 cm–1. Cyclic voltammetry of 1, 2, 3, and acetyl derivative 6 shows the presence of two redox events in each case. The first redox couple is ascribed as an azaferrocene-centered oxidation–reduction, whereas the second, irreversible process at higher potential originates from a W(CO)5-centered oxidation. FTIR spectroelectrochemistry allowed us to monitor the spectroscopic changes accompanying the 1/1·+, 2/2·+, and 6/6·+ redox transformations. Significant W–CO absorption band shifts were recorded in the course of these experiments

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

The reaction of [CpRuCl(PPh3)2] (Cp=cyclopentadienyl) and [CpRuCl(dppe)] (dppe=Ph2PCH2CH2PPh2) with bis- and tris-phosphine ligands 1,4-(Ph2PC≡C)2C6H4 (1) and 1,3,5-(Ph2PC≡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(PPh3)}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(μ-dppab)}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(PPh3)] were obtained, that is, the dinuclear complex [{CpRu(PPh3)(μ-dppab)}2](PF6)2 (8) and the tetranuclear square [{CpRu(PPh3)(μ-dppab)}4](PF6)4 (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