NOPR Collection:

Photochemical reactions of cobalt(III)-amine complexes innon-aqueous solvents: Mechanistic details of oxygenation reaction of cobalt(III) systems-II]

Mon, 01 Jan 1990 00:00:00 GMT

Title: Photochemical reactions of cobalt(III)-amine complexes innon-aqueous solvents: Mechanistic details of oxygenation reaction of cobalt(III) systems-II] Authors: Ramamurthy, P; Radhakrishnan, A; Vijayaraghavan, R; Natarajan, P Abstract: Flash photolysis and steady-state photolysis studies of a series [Co(Am)(NO₂)₂^- (Am = 2 en, trien) of complexes have been carried out in acetonitrile. Photolysis of the complexes in air-equilibrated acetonitrile medium produces mononuclear superoxo, dinuclear superoxo and dinuclear peroxo complexes sequentially. Transient absorptions are observed for the formation of mononuclear and dinuclear superoxo complexes at 400 and 700 nm respectively during flash photolysis. Steady state photolysis results in the dinuclear peroxo complex as the final product. Page(s): 1-5

Reactions of oxygen-bonded and sulphur-bonded (sulphito)(amine)cobalt(III) complexes in solution:Part II1 - kinetics and mechanism of reactions of cis(diaquo) - bis(ethylenediamine) cobalt(III) and cis(diaquo)bis- (trimethylenediamine)cobalt(III) cations with aqueous sulphur dioxide

Mon, 01 Jan 1990 00:00:00 GMT

Title: Reactions of oxygen-bonded and sulphur-bonded (sulphito)(amine)cobalt(III) complexes in solution:Part II1 - kinetics and mechanism of reactions of cis(diaquo) - bis(ethylenediamine) cobalt(III) and cis(diaquo)bis- (trimethylenediamine)cobalt(III) cations with aqueous sulphur dioxide Authors: Dash, Anadi C; Padhy, Bishnu P Abstract: Kinetics of title reactions have been investigated at 35-50°C and I = 0.3 mol dm ^-3. In the presence of excess sulphite and at pH = 4.5-6.7, the diaquo complexes are completely transformed to the O-bonded disul-phito complexes, cis-[Co(AA)₂(OSO₂)₂]^- (AA = en, tmd) which undergo two kinetically identifiable reactions: (i) intramolecular reduction to Co(II); and (ii) isomerisation to O- and S-bonded sulphito complexes, Cis-[Co(AA)₂(OSO₂)(SO)]^-. This mixed sulphito complexes also undergo intramolecular reduction to Co(II) at rates much slower than those of their bis-O-sulphito congeners. The observed biphasic kinetics have been resolved. The rates and activation parameters for these three kinetic processes are reported. Rate comparison with similar other systems establishes the reactivity sequence for intramolecular reduction process as: trans-[CO(en)₂(OSO₂H)(OSO₂)] » cis-[Co(en)₂(OH₂)(OSO₂)]⁺ > cis-[Co(AA)₂(OSO₂)₂]^-(AA = en, tmd) > cis-[Co(AA)₂(OSO₂)(SO₃)] > cis-[Co(en)₂(OSO₂)⁺ (B = NH₃, imidazole). The activation enthalpy and entropy data for the partial intramolecular isomerisation of cis-[Co(AA)₂(OSO₂)₂]^- to cis- [Co(AA)₂(OSO₂)(SO₃)]^‑ are significantly lower than those for the intramolecular reduction of bis-O-sulphito or (O -, S - ) sulphito species. Page(s): 6-10

1H and 13C NMR spectral studies on dicyclopentadiene complexes of rhodium(I) containing N-heterocycles

Mon, 01 Jan 1990 00:00:00 GMT

Title: 1H and 13C NMR spectral studies on dicyclopentadiene complexes of rhodium(I) containing N-heterocycles Authors: Ramaswamy, Y S; Gowda, N M N; Reddy, G K N Abstract: The bridge cleavage reaction of [Rh(μ-CI)(DCPD)]₂ (DCPD = endo-dicyclopentadiene) with exo-bidentate N-he-terocycles (N - N) yields binuclear complexes of the type [{RhCl(DCPD)₂(μ-N-N)] [where N-N =pyrazine(pyz), 4,4'-bipyridyl(bpy) or trans-1,2-bis(4-pyridyl)ethylene(bpel)]. The ¹H NMR spectral assignments of DCPD and [Rh(μ -Cl)(DCPD)]₂ have been unequivocally confirmed by two-dimensional NMR spectroscopy. The stereochemical aspects of the latter are reflected in selective homonuclear ¹H{¹H} nuclear overhauser enhancement studies. The N-N bridged structure for the complexes [{RhCl(DCPD}]₂ (μ-N-N)] has been proposed based on the recurrence of spectral features of their precursor in addition to those of the uncoordinated N-heterocycles. The synergistic effect in the metal-olefin bonding in these complexes in manifested in the upfield shifts of olefinic proton and carbon resonances as compared with those of free DCPD. The complexes, [{RhCl(DCPD)}₂(μ -N-N)] undergo facile substitution of DCPD with carbon monoxide to afford carbonyl complexes retaining the [Rh(μ -N-N)Rh] unit. Page(s): 11-17

Electrochemical studies on (η5-C5H5)Ru(PPh3)(L)X(L= PPh3, pyridine; X =H, CI) and (η5-C5H5) Ru{P(OMe)3}2 CI in non-aqueous solvents

Mon, 01 Jan 1990 00:00:00 GMT

Title: Electrochemical studies on (η5-C5H5)Ru(PPh3)(L)X(L= PPh3, pyridine; X =H, CI) and (η5-C5H5) Ru{P(OMe)3}2 CI in non-aqueous solvents Authors: Mandal, Sisir K; Chakravarty, Akhil R Abstract: The redox properties of a series of cyclopentadienylruthenium compounds, (η⁵-C₅H₅)Ru(PPh₃)(L)X(L= PPh₃, pyridine; X = H, Cl) and (η⁵-C₅H₅)Ru{p(OMe)₃}₂Cl, have been studied in different nonaqueous solvents (MeCN, THF, CH₂Cl₂). The ruthenium(II)/ruthenium(III) couple is observed in the potential range of + 0.05 V to + 0.70 V (vs SCE) depending upon the type of ligands and the solvent medium. The E values vary in the order THF> CH₂CI₂ > MeCN. While the couple is nearly reversible in MeCN, the electron transfer is sluggish (i.e., quasireversible) in other solvents. The E values follow the order: (η-Cp)Ru-{p(OMe)₃}₂Cl > (η-Cp)Ru(PPh₃)(py)Cl ≥ (η-Cp)Ru(PPh₃)₂Cl > (η-Cp)Ru(PPh₃)₂H- (η-Cp = η⁵-C₅H₅). Page(s): 18-21