Michael W. Cooke

Structure and electrochemistry of a tetrakis(ferrocenecarboxylato)diruthenium(II,III) diadduct: evidence for ferrocenyl–ferrocenyl communication

Abstract 1-Propanol and ethanol adducts of tetrakis(ferrocenecarboxylato)diruthenium(II,III) hexafluorophosphate have been synthesized and the 1-propanol diadduct has been characterized by X-ray crystallography. The cyclopentadienyl rings of all four ferrocenyl groups showed on average a 13° deviation from the eclipsed conformation. Cyclic voltammetry measurements in 1,2-dichloroethane show an irreversible RuIIIRuII/RuIIRuII reduction and four partially superimposed one-electron ferrocenyl-centred electron transfer processes. The existence of ferrocenyl-based mixed-valent intermediate states posessing FeIII and FeII sites are implied by the splitting of the ferrocenyl wave into two observable cathodic and anodic peaks. The first cathodic wave shows typical desorption behaviour. Osteryoung Square Wave Voltammetry (OSWV) supports the above findings.

Synthesis and crystal structures of urea and thiourea derivatives of diruthenium(II,III) tetraacetate

Diadduct complexes of the mixed-valent form of diruthenium tetraacetate, [Ru-2(mu-O2CCH3)(4)L-2](PF6), with L = urea (1), 1,1,3,3-tetramethylurea (tmu) (2) and 1,1,3,3-tetramethyl-2-thiourea (tmtu) (3) have been synthesized and characterized by elemental analysis, IR and UV-Vis spectroscopy, magnetic susceptibility, cyclic voltammetry and X-ray crystallography. Compound 1 crystallizes as a co-diadduct system from 1-propanol in which both [Ru-2(mu-O2CCH3)(4)(urea)(2)](+) and [Ru-2(mu-O2CCH3)(4)(1-propanol)(2)](+) cations are present in the unit cell. Complex 3 displays a very long Ru-S bond of 2.610(2) Angstrom and is only the second example of a sulfur-donor adduct of a diruthenium tetracarboxylate that has been structurally characterized. Electrochemical measurements on 2 and 3 show them to have reduction potentials of -487 and -541 mV (vs. Fc/Fc(+)), respectively, which is in the range of moderate to strong axial donor adducts despite the long Ru-S bond in 3. Reaction of [Ru-2(mu-O2CCH3)(4)(H2O)(2)](PF6) with thiourea yields a 1:1 complex, [Ru-2(mu-O2CCH3)(4)(thiourea)](PF6), which from solubility and infrared evidence appears to be a polymer in which the thiourea bridges through the sulfur and one of the amine nitrogens.

Synthesis and structure of trans-dimethylammonium bis(oxalato)diaquaruthenate(III) tetrahydrate

Abstract Trans-Dimethylammonium bis(oxalato)diaquaruthenate(III) tetrahydrate, trans-[(CH3)2NH2][Ru(C2O4)2(H2O)2]·4H2O, was synthesized by diffusion of dimethylamine (from dimethylformamide) into a refluxed aqueous solution of diruthenium(II,III) tetraacetate and oxalic acid. The structure of the complex was determined by X-ray diffraction. The RuO (oxalate) and RuO (water) distances are 2.041(3) and 1.994(3) A, respectively and the oxalate bite angle is 80.6(2)°. The complex displays an intricate pattern of inter- and intra-chain hydrogen bonding involving the axial water molecules, the water molecules of hydration, the dimethylammonium cation, and the carbonyl and carboxyl oxygens of the oxalate groups. Additional characterization using infrared and UV–Vis spectroscopies, magnetic susceptibility (isothermal and variable temperature), and cyclic voltammetry is also reported.

Synthesis, X-ray crystal structure and reactivity of the di-µ-carbene complex [Ru2(CO)2(µ-CHMe)(µ-CMe2)(η-C5H5)2]

Treatment of [Ru2(CO)2(µ-CO)(µ-CMe2)(η-C5H5)2] with methyl-lithium and HBF4 in succession provides the carbyne–carbene-bridged cation [Ru2(CO)2(µ-CMe)-(µ-CMe2)(η-C5H5)2]+ which may be converted into di-µ-carbene complexes [Ru2(CO)2(µ-CCH2)(µ-CMe2)(η-C5H5)2] and [Ru2(CO)2(µ-CHMe2)(µ-CMe2)(η-C5H5)2]; the latter, whose structure has been determined by X-ray diffraction, releases Me2CCHMe at 200 °C as the major volatile product.

Organic chemistry of dinuclear metal centres. Part 5. Generation of hydrocarbons from methylene chains linking two metal centres. Evidence for a dimetallacycle intermediate

The hydrocarbon products of the thermal and photochemical decompositions of the complexes [(η-C5H5)(CO)2M1{µ-(CH2)n}M2(CO)2(η-C5H5)](M1= M2= Fe, n= 3–5; M1= M2= Ru, n= 3 or 4; M1= Fe, M2= Ru, n= 3) have been determined and the results interpreted in terms of a transient dimetallacycle which undergoes decomposition viaβ-elimination and reductive elimination processes. Decomposition of the compounds containing three-carbon bridges yields cyclopropane and propene in a ratio strongly dependent upon the identity of the metal atoms and the conditions, factors which are rationalised by the proposed mechanism. But-1-ene, and cis- and trans-but-2-ene are obtained from the decomposition of complexes containing four-carbon chains, but only but-1-ene and trans-but-2-ene are produced from the thermolysis of [(η-C5H5)(CO)2Fe{µ-CH(Me)CH2CH2}Fe(CO)2(η-C5H5)]. This is attributed to a methyl-substituted dimetallacyclopentane intermediate adopting for steric reasons a conformation which does not allow the formation of cis-but-2-ene. The low proportion of but-1-ene can also be traced to crowding in the dimetallacyle. Pentane is preferentially evolved from [(η-C5H5)(CO)2Fe{µ-(CH2)5}Fe(CO)2(η-C5H5)], with smaller amounts of pent-1-ene, and cis- and trans-pent-2-ene, interpreted as due to a predominantly radical mechanism for the decomposition of this compound. The organometallic products of the decompositions are the dimers [M2(CO)4(η-C5H5)2](M = Fe or Ru) and, where appropriate, those of the subsequent photolysis of [Ru2(CO)4(η-C5H5)2]. Carbon–carbon bond fission occurs on heating [(η-C5H5)(CO)2Ru{µ-(CH2)3}Ru(CO)2(η-C5H5)] with Me3NO in tetrahydrofuran, giving a low yield of [Ru2(CO)2(µ-CO)(µ-CH2)(η-C5H5)2].