Properties of Ion Clusters: Interactions of [Ru(NH₃)₅H₂O]³⁺ and [Ru(NH₃)₆]³⁺ with [Ru(CN)₆]^4- and [Fe(CN)₆]^4-

Properties of Ion Clusters:  Interactions of [Ru(NH3)5H2O]3+ and [Ru(NH3)6]3+ with [Ru(CN)6]4- and [Fe(CN)6]4-</sup

Kinetic Effects in Outer Sphere Ion Clusters: Interactions of [Ru(NH₃)₅H₂O]³⁺ with [Ru(CN)₆]^4-, [Fe(CN)₆]^4-, [Os(CN)₆]^4- and [Co(CN)₆]^3-

A study of the kinetics of substitution in [Ru(NH3)5H2O]3+ by the nucleophiles [Fe(CN)6]4-, [Ru(CN)6]4-, [Os(CN)6]4-, and [Co(CN)6]3- in the absence of indifferent electrolyte shows that k for substitution (in every case first order in cation concentration) increases as the ratio of the concentration of the nucleophile to the aquo ion increases, and then it abruptly becomes independent of this ratio. When the reaction medium is 1.5 × 10-2 M H+ (chosen to eliminate catalysis by the formation of [Ru(NH3)5H2O]2+ when [Fe(CN)6]4- is the nucleophile), the critical values of R are ca. 4 for [M(CN)6]4-, but 8 for [Co(CN)6]3-. In a reaction medium adjusted to pH = 3.1, the [M(CN)6]4- species are less fully protonated. Again, approximately constant values of k are reached as R increases, but now at higher values of R. Short of these values of R, maxima in k are observed, which, as in the case of earlier studies of oscillator strength of the intervalence absorption bands, are attributed to structural changes, the anions rearranging from positions on the apices of the cation octahedron, to the faces. A study of catalysis of substitution by extrinsic [Ru(NH3)5H2O]2+ and, in the case of [Fe(CN)6]4-, intrinsic Ru(II) reveals some unusual kinetic effects which also have their origin in ion clustering

Inner-Sphere Cluster Formation by [Ru(NH₃)₅H₂O]³⁺ or [Os(NH₃)₅H₂O]³⁺ in Combination with [M(CN)₆]^4- (M = Fe, Ru, or Os)

When the cations [M‘(NH3)5H2O]3+ or [M‘(NH3)5H2O]2+ (M‘ = Ru, Os) are added in excess of the co-reactants [M(CN)6]4- (M = Fe, Ru, Os), inner-sphere binding ends abruptly at the 4:1 ratio. The [M(CN)6]4- → [M‘(NH3)5]3+ charge transfer (CT) absorption shifts slightly to higher energy as the cations accumulate in the cluster, and there is a progressive decrease in intensity per additional oscillator introduced. The absorption bands and the electrochemical properties reveal the presence of isomeric forms in complexes of order 2 and above. The successive stages of reduction of [Ru(NH3)5)]3+ take place in a narrow range of potentials, despite the close proximity of the peripheral cations in a cluster. Clusters containing Ru(II) and Ru(III) show also the [Ru(NH3)5]2+ → [Ru(NH3)5]3+ CT transition. While [Ru(NH3)5]2+ has little effect on M(II) → M‘(III) CT absorption, accumulation of M‘(III) in a cluster containing the M‘(II) → M‘(III) oscillator, despite an increase in the number of these oscillators, leads to no significant increase in the intensity. The energy of the [Ru(NH3)5]2+ → [Ru(NH3)5]3+ transition is 1500 cm-1 greater when M = Ru than when it is Fe or Os, for which it appears at 8000 cm-1. This difference is attributed to rapid isomerization of the RuIICNRuIII linkage causing a shift to higher energy. This interpretation is in accord with the deep seated degradation of the clusters which occurs whenever [Ru(NH3)5]2+ is present (complete loss of the M‘(II) → M‘(III) and M(II) → M‘(III) oscillators), which is most rapid when M = Ru(II)

Anti-Markovnikov Olefin Arylation Catalyzed by an Iridium Complex

Anti-Markovnikov Olefin Arylation Catalyzed by an Iridium Comple

Cooperative Ligation, Back-Bonding, and Possible Pyridine−Pyridine Interactions in Tetrapyridine−Vanadium(II): A Visible and X-ray Spectroscopic Study

The binding of pyridine by V(II) in aqueous solution shows evidence for the late onset of cooperativity. The K1 governing formation of [V(py)]2+ (λmax = 404 nm, εmax = 1.43 ± 0.3 M-1 cm-1) was determined spectrophotometrically to be 11.0 ± 0.3 M-1, while K1 for isonicotinamide was found to be 5.0 ± 0.1 M-1. These values are in the low range for 3d M2+ ions and indicate that V(II)·py back-bonding is not significant in the formation of the 1:1 complex. Titration of 10.5 mM V(II) with pyridine in aqueous solution showed an absorption plateau at about 1 M added pyridine, indicating a reaction terminus. Vanadium K-edge EXAFS analysis of 63 mM V(II) in 2 M pyridine solution revealed six first-shell N/O ligands at 2.14 Å and 4 ± 1 pyridine ligands per V(II). UV/vis absorption spectroscopy indicated that the same terminal V(II) species was present in both experiments. Model calculations showed that in the absence of back-bonding only 2.0 ± 0.2 and 2.4 ± 0.2 pyridine ligands would be present, respectively. Cooperativity in multistage binding of pyridine by [V(aq)]2+ is thus indicated. XAS K-edge spectroscopy of crystalline [V(O3SCF3)2(py)4] and of V(II) in 2 M pyridine solution each exhibited the analogous 1s → 5Eg and 1s → 5T2g transitions, at 5465.5 and 5467.5 eV, and 5465.2 and 5467.4 eV, respectively, consistent with the EXAFS analysis. In contrast, [V(py)6](PF6)2 and [V(H2O)6]SO4 show four 1s → 3d XAS transitions suggestive of a Jahn−Teller distorted excited state. Comparison of the M(II)−Npy bond lengths in V(II) and Fe(II) tetrapyridines shows that the V(II)−Npy distances are about 0.06 Å shorter than predicted from ionic radii. For [VX2(R-py)4] (X = Cl-, CF3SO3-; R = 4-Et, H, 3-EtOOC), the E1/2 values of the V(II)/V(III) couples correlate linearly with the Hammett σ values of the R group. These findings indicate that π back-bonding is important in [V(py)4]2+ even though absent in [V(py)]2+. The paramagnetism of [V(O3SCF3)2(py)4] in CHCl3, 3.8 ± 0.2 μB, revealed that the onset of back-bonding is not accompanied by a spin change. Analysis of the geometries of V(II) and Fe(II) tetrapyridines indicates that the ubiquitous propeller motif accompanying tetrapyridine ligation may be due to eight dipole interactions arising from the juxtaposed C−H edges and π clouds of adjoining ligands, worth about −6 kJ each. However, this is not the source of the cooperativity in the binding of multiple pyridines by V(II) because the same interactions are present in the Fe(II)−tetrapyridines, which do not show cooperative ligand binding. Cooperativity in the binding of pyridine by V(II) is then assigned by default to V(II)−pyridine back-bonding, which emerges only after the first pyridine is bound

Anti-Markovnikov Olefin Arylation Catalyzed by an Iridium Complex

Anti-Markovnikov Olefin Arylation Catalyzed by an Iridium Comple

Osmium Complexes of 1,4,7-Triazacyclononane (tacn) and 1,4,7-Trimethyl-1,4,7-triazacyclononane (Me₃tacn) and the X-ray Crystal Structure of [(Me₃tacn)Os(η⁶-C₆H₅BPh₃)]BPh₄·CH₃CN

The complexes of osmium with tacn (1,4,7-triazacyclononane) and Me3tacn (1,4,7-trimethyl-1,4,7-triazacyclononane), [LOs (η6-C6H6)](PF6)2 (L = tacn) and LOsCl3 (L = tacn, Me3tacn), have been prepared by substitution of L on [Os(η6-C6H6)Cl2]2 or [Os2Cl8]2-, respectively. Reaction of LOsCl3 with neat triflic acid leads to partial replacement of chloride and formation of the binuclear Os(III)−Os(III) complexes [LOs(μ-Cl3)OsL](PF6)3 (L = tacn, Me3tacn). The binuclear nature was established by NMR spectroscopy and elemental analysis and, for L = tacn, a partially refined X-ray crystal structure which shows the Os−Os separation to be 2.667 Å, indicative of significant metal−metal bonding. Reduction of [LOs(μ-Cl3)OsL]3+ over zinc amalgam in either aqueous or non-aqueous solution yields the intensely colored Os(II)−Os(III) mixed-valence ions [LOs(μ-Cl3)OsL]2+. Electrochemical measurements on [LOs(μ-Cl3)OsL]3+ in CH3CN reveal the reversible formation of the mixed valence ions. These are further reduced at lower potential to the Os(II)−Os(II) binuclear species, reversibly for L = Me3tacn. (Me3tacn)OsCl3 is oxidized by persulfate ion to give [(Me3tacn)OsCl3]+; zinc amalgam reduction in an aqueous solution at high concentration produces the binuclear complex [(Me3tacn)Os(μ-Cl3)Os(Me3tacn)]3+ or, at low concentration, a solution containing an air sensitive osmium(II) species. Addition of BPh4- results in the η6-arene zwitterion [(Me3tacn)Os(η6-C6H5BPh3)]+, which was characterized by X-ray diffraction on the BPh4- salt. The compound crystallizes in the triclinic space group P1 with a = 11.829(2) Å, b = 12.480(3) Å, c = 17.155(4) Å, α = 84.42(2)°, β = 83.52(2)°, γ = 71.45(2)°, V = 2380(2) Å3, Z = 2, and R = 7.62%, and Rw = 7.39%

Activation of Thiourea Bound through Sulfur to Pentaammineruthenium(III): Structure and Reactivity

Activation of Thiourea Bound through Sulfur to Pentaammineruthenium(III):  Structure and Reactivit

Synthesis and Characterization of <i>trans</i>-[Os(en)₂py(H)]²⁺ and Related Studies

trans-[Os(en)2pyH](Otf)2, 2, is recovered from an acidic solution of trans-[Os(en)2py(H2)](OTf)2, 1, which has been subjected to one electron oxidation. The structures of both 1 and 2 have been determined by single crystal X-ray analysis. In cyclic voltammetry, 2 shows a one electron oxidation wave at 0.95 V and a one electron reduction wave at −1.2 V, neither accompanied by a signal for the reverse process. Reduction of 2 by Zn/Hg in methanol solution leads to quantitative formation of [Os(en)2(py)H2)]2+, predominantly in the trans-form. In aqueous solution, species 2 reacts rapidly with N-methylacridium ion, [MAH]+, by hydride transfer. One electron chemical oxidation of 2 to the corresponding Os(IV) is slower than that of 1 to 2 owing to the increase in coordination number when Os(IV) is produced. Treatment of 1, or the cis-form, 1‘, in DMSO by sodium t-butoxide produces mainly the corresponding isomers of the monohydrides of OsII, that derived from 1‘ is deep red in color while the trans-monohydride is colorless. Both react with [MAH]+ to form [MAH]2, and both disappear rapidly in acetone or acetonitrile, presumably by reducing the solvents. Reaction of trans-[Os(NH3)4(H2)H2O](BPh4)2, 4, in acetone-d6 as solvent with either CH3CHO or styrene leads to hydrogenation of the substrate. Reactions which compete with trans-[Os(en)2(η2-H2)(CF3SO)3]CF3SO3 release of substrate from the trans-complex before isomerization to the cis-form, required for hydrogenation to occur, result in the trans-derivative of the added solute. When H2CCHCH2SCH3 is the substrate, binding takes place at sulfur. Complete conversion to the cis-substrate isomer is observed, without hydrogenation occurring even though contact between dihydrogen and the double bond is possible

tmtacn, tacn, and Triammine Complexes of (η⁶-arene)Os^II: Syntheses, Characterizations, and Photosubstitution Reactions (tmtacn = 1,4,7-Trimethyl-1,4,7-triazacyclononane; tacn = 1,4,7-Triazacyclononane)

A series of (η6-arene)OsII complexes containing the saturated nitrogen donor ligands tmtacn, tacn, and NH3 are prepared and characterized. The electrochemical properties and photochemical reactions of these complexes are studied, and the solid-state structures for [(η6-p-cymene)Os(tacn)](PF6)2 (1) and [(η6-p-cymene)Os(tmtacn)](PF6)2 (2) are determined. Single-crystal X-ray data:  1, orthorhombic, space group Pbca- (No. 61), with a = 14.716(3) Å, b = 17.844(3) Å, c = 18.350(4) Å, V = 4819(2) Å3, and Z = 8; 2, monoclinic, space group C2− (No. 5), with a = 17.322(4) Å, b = 10.481(3) Å, c = 15.049(4) Å, β = 98.72°, V = 2701(1) Å3, and Z = 4