Competitive Substitution and Electron Transfer in Reactions between Haloamminegold(III) and Halocyanoaurate(III) Complexes and Thiocyanate

Kinetics for reactions between thiocyanate and trans-Au(CN)(2)Cl(2)(-), trans-Au(CN)(2)Br(2)(-), and trans-Au(NH(3))(2)Cl(2)(+) in an acidic, 1.00 M perchlorate aqueous medium have been studied by use of conventional and diode-array UV/vis spectroscopy and high-pressure and sequential-mixing stopped-flow spectrophotometry. Initial, rapid formation of mixed halide-thiocyanate complexes of gold(III) is followed by slower reduction to Au(CN)(2)(-) and Au(NH(3))(2)(+), respectively. This is an intermolecular process, involving attack on the complex by outer-sphere thiocyanate. Second-order rate constants at 25.0 degrees C for reduction of trans-Au(CN)(2)XSCN(-) are (6.9 +/- 1.1) x 10(4) M(-)(1) s(-)(1) for X = Cl and (3.1 +/- 0.7) x 10(3) M(-)(1) s(-)(1) for X = Br. For reduction of trans-Au(CN)(2)(SCN)(2)(-) the second-order rate constant at 25.0 degrees C is (3.1 +/- 0.1) x 10(2) M(-)(1) s(-)(1) and the activation parameters are DeltaH() = (55 +/- 3) x 10(2) kJ mol(-)(1), DeltaS() = (-17.8 +/- 0.8) J K(-)(1) mol(-)(1), and DeltaV() = (-4.6 +/- 0.5) cm(3) mol(-)(1). The activation volume for substitution of one chloride on trans-Au(NH(3))(2)Cl(2)(+) is (-4.5 +/- 0.5) cm(3) mol(-)(1), and that for reduction of trans-Au(NH(3))(2)(SCN)(2)(+) (4.6 +/- 0.9) cm(3) mol(-)(1). The presence of pi-back-bonding cyanide ligands stabilizes the transition states for both substitution and reductive elimination reactions compared to ammine. In particular, complexes trans-Au(CN)(2)XSCN(-) with an unsymmetric electron distribution along the X-Au-SCN axis are reduced rapidly. The observed entropies and volumes of activation reflect large differences in the transition states for the reductive elimination and substitution processes, respectively, the former being more loosely bound, more sensitive to solvational changes, and probably not involving any large changes in the inner coordination sphere. A transition state with an S-S interaction between attacking and coordinated thiocyanate is suggested for the reduction. The stability constants for formation of the very short-lived complex trans-Au(CN)(2)(SCN)(2)(-) from trans-Au(CN)(2)X(SCN)(-) (X = Cl, Br) by replacement of halide by thiocyanate prior to reduction can be calculated from the redox kinetics data to be K(Cl,2) = (3.8 +/- 0.8) x 10(4) and K(Br,2) = (1.1 +/- 0.4) x 10(2).     

Polyoxoanions Derived from [gamma-SiO(4)W(10)O(32)](8-)-Containing Oxo-Centered Dinuclear Chromium(III) Carboxylato Complexes: Synthesis and Single-Crystal Structural Determination of [gamma-SiO(4)W(10)O(32)(OH)Cr(2)(OOCCH(3))(2)(OH(2))(2)](5-)

The previously unknown heteropolyoxometalates [gamma-SiO(4)W(10)O(32)(OH)Cr(2)(OOCR)(2)(OH(2))(2)](5-) (R = H, CH(3)) have been prepared by the reaction of [gamma-SiO(4)W(10)O(32)](8-) with [Cr(OH(2))(6)](3+) in formate or acetate buffer solution. Isolation of these new Cr(III)-substituted polyoxometalates was accomplished both as Cs(+) salts and as the Bu(4)N(+) salt for the acetate-containing anion. The compounds were characterized by elemental analysis, UV/vis, IR, and ESR spectroscopy, and cyclic voltammetry. The single-crystal X-ray structural analysis of (Bu(4)N)(3)H(2)[gamma-SiO(4)W(10)O(32)(OH)Cr(2)(OOCCH(3))(2)(OH(2))(2)].3H(2)O [P2(1)2(1)2(1); a = 17.608(12), b = 20.992(13), c = 24.464(11) ?; Z = 4; R = 0.057 for 6549 observed independent reflections] reveals that the two corner-linked CrO(6) octahedra are additionally bridged by two acetate groups, demonstrating the relationship to the well-studied oxo-centered trinuclear carboxylato complexes of Cr(III).     

Hydrothermal Synthesis and Structure Analysis of a Chromium Complex [Cr(aea)]2(OH)2(aea=N-(2-Aminoethyl)aspartate)

A dimeric chromium compound has been synthesized by hydrothermal method and characterized by IR,EPR spectra and TG-DTA technique.The title compound [Cr(aea)]2(OH)2(aea=N-(2-aminoethyl)aspartate)crystallizes in monoclinic,space group P21/c with a=8.9393(10),b=6.7198(7),c=14.6791(16)(A),β=91.0580(10)°,V=881.63(17)(A)3,Z=2,Mr=486.34,Dc=1.832g/cm3,F(000)=500,μ=1.296 mm-1,R=0.0271 and wR=0.0756.Single-crystal X-ray structural analysis indicates that the title compound consists of two Cr(aca)units linked by two bridging hydroxyl groups.The geometry around each chromium center is approximately octahedral and completed by two hydroxyls and a quadridentate ligand which is formed when ethylenediamine reacts with maleie acid.     

Two Mercury Chloro Thiocyanate Complexes: NH4[HgCl2(SCN)] and NH4[HgCl(SCN)2]

Single crystals of NH₄[HgCl₂(SCN)] ( 1 ) and NH₄[HgCl(SCN)₂] ( 2 ) are obtained by slow evaporation of ethanol solutions of HgCl₂ and NH₄SCN or Hg(SCN)₂ and NH₄Cl. 1 crystallizes in the monoclinic space group P2₁ (a = 9.297(1), b = 4.171(1), c = 9.198(1)Å, β = 92.827(5)°). The structure consists in HgCl₂(SCN) linear chains, extending along the twofold axis, connected through the ammonium ions. 2 crystallizes in the monoclinic space group C2/c (a = 7.088(1), b = 19.986(2), c = 5.958(1)Å, β = 100.718(5)°). The structure consists of HgCl(SCN)₂ molecules connected through the ammonium ions. The second order non linear optical properties of 1 are discussed.     

Solid-Phase Substitution of Ammonia in Hexaamine Heteroligand Complexes of Chromium(III) with Cyclic Tetraamines

The solid-phase substitution of ammonia in heteroligand hexaamine complexes of chromium(III) with cyclic tetraamines was studied. The kinetic stability of these compounds, determined from the value of the activation energy, is lower than for other hexaamine compounds of chromium(III). This is due to the weakening of the Cr—NH₃ bonds and to the less close packing of the ions in the crystal lattice. For complexes with the trans structure the thermal stability increases in the series of tetraazamacrocyclic ligands teta < cyclam < TMC.     

Kinetics and mechanism of the [Ru(III)(edta)(H2O)](-)-mediated oxidation of cysteine by H2O2

The kinetics and mechanism of the [Ru(III)(edta)(H(2)O)](-)-mediated oxidation of cysteine (RSH) by hydrogen peroxide (edta(4-) = ethylenediaminetetraacetate), were studied in detail as a function of both the hydrogen peroxide and cysteine concentrations at pH 5.1 and room temperature. The kinetic traces reveal clear evidence for a catalytic process in which hydrogen peroxide reacts directly with cysteine coordinated to the Ru(III)(edta) complex in the form of [Ru(III)(edta)SR](2-). A parallel process in which [Ru(III)(edta)(H(2)O)](-) first reacts with H(2)O(2) to produce [Ru(V)(edta)O](-) and subsequently oxidizes cysteine, is orders of magnitude slower than the [Ru(III)(edta)(H(2)O)](-)-mediated oxidation in which cysteine rapidly coordinates to [Ru(III)(edta)(H(2)O)](-) prior to the reaction with H(2)O(2). HPLC product analyses revealed the formation of cystine (RSSR) as major product along with cysteine sulfinic acid (RSO(2)H) in the reaction system, and established the catalytic role of [Ru(III)(edta)(H(2)O)](-). Simulations were performed to account for the rather complex kinetic traces in terms of the suggested reaction mechanism. The results of the simulations support the proposed reaction mechanism that involves the oxidation of coordinated cysteine to cysteine sulfenic acid (RSOH), which subsequently rapidly reacts with H(2)O(2) and RSH to form RSO(2)H and RSSR, respectively.     

Reactions of Chromium(III)- and Cobalt(III)-amine-complexes with Starburst(PAMAM)dendrimers

The starburst(PAMAM)dendrimer of generation 0 was reacted with pentaammine-triflato-chromium(III) and -cobalt(III). The products were separated by ion exchange chromatography and characterized by elemental analysis, UV-VIS-, IR-, ¹³C-spectroscopy or cyclic voltammetry. The dendrimer forms five membered chelate rings containing amine and amide nitrogens and binds one or two metal ions.     

Hydrothermal Synthesis and Structure Analysis of a Chromium Complex [Cr（aea）]2（OH）2 （aea = N-（2-Aminoethyl）aspartate）

A dimeric chromium compound has been synthesized by hydrothermal method and characterized by IR, EPR spectra and TG-DTA technique. The title compound [Cr（aea）]2（OH）2 （aea = N-（2-aminoethyl）aspartate） crystallizes in monoclinic, space group P21/c with a = 8.9393（10）, b = 6.7198（7）, c = 14.6791（16） A, β = 91.0580（10）°, V= 881.63（17） A3, Z= 2, Mr = 486.34, De= 1.832 g/cm3, F（000） = 500,μ = 1.296 mm-1, R = 0.0271 and wR = 0.0756. Single-crystal X-ray structural analysis indicates that the title compound consists of two Cr（aea） units linked by two bridging hydroxyl groups. The geometry around each chromium center is approximately octahedral and completed by two hydroxyls and a quadridentate ligand which is formed when ethylenediamine reacts with maleic acid.     

Elucidation of the solution structure and water-exchange mechanism of paramagnetic [Fe(II)(edta)(H(2)O)](2-)

The lability and structural dynamics of [Fe(II)(edta)(H(2)O)](2-) (edta = ethylenediaminetetraacetate) in aqueous solution strongly depend on solvent interactions. To study the solution structure and water-exchange mechanism, (1)H, (13)C, and (17)O NMR techniques were applied. The water-exchange reaction was studied through the paramagnetic effect of the complex on the relaxation rate of the (17)O nucleus of the bulk water. In addition to variable-temperature experiments, high-pressure NMR techniques were applied to elucidate the intimate nature of the water-exchange mechanism. The water molecule in the seventh coordination site of the edta complex is strongly labilized, as shown by the water-exchange rate constant of (2.7 +/- 0.1) x 106 s(-1) at 298.2 K and ambient pressure. The activation parameters DeltaH(not equal), DeltaS(not equal), and DeltaV(not equal) were found to be 43.2 +/- 0.5 kJ mol(-1), +23 +/- 2 J K(-1) mol(-1), and +8.6 +/- 0.4 cm(3) mol(-1), respectively, in line with a dissociatively activated interchange (Id) mechanism. The scalar coupling constant (A/h) for the Fe(II)-O interaction was found to be 10.4 MHz, slightly larger than the value A/h = 9.4 MHz for this interaction in the hexa-aqua Fe(II) complex. The solution structure and dynamics of [Fe(II)(edta)(H(2)O)](2-) were clarified by (1)H and (13)C NMR experiments. The complex undergoes a Delta,Lambda-isomerization process with interconversion of in-plane (IP) and out-of-plane (OP) positions. Acetate scrambling was also found in an NMR study of the corresponding NO complex, [Fe(III)(edta)(NO(-))](2-).     

Preparation and characterization of the argentates: [Ag[P(CF(3))(2)](2)](-), [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-) (M = Cr, W), and [Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)](-): X-ray crystal structure of [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)

The first example of a mononuclear diphosphanidoargentate, bis[bis(trifluoromethyl)phosphanido]argentate, [Ag[P(CF(3))(2)](2)](-), is obtained via the reaction of HP(CF(3))(2) with [Ag(CN)(2)](-) and isolated as its [K(18-crown-6)] salt. When the cyclic phosphane (PCF(3))(4) is reacted with a slight excess of [K(18-crown-6)][Ag[P(CF(3))(2)](2)], selective insertion of one PCF(3) unit into each silver phosphorus bond is observed, which on the basis of NMR spectroscopic evidence suggests the [Ag[P(CF(3))P(CF(3))(2)](2)](-) ion. On treatment of the phosphane complexes [M(CO)(5)PH(CF(3))(2)] (M = Cr, W) with [K(18-crown-6)][Ag(CN)(2)], the analogous trinuclear argentates, [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-), are formed. The chromium compound [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)] crystallizes in a noncentrosymmetric space group Fdd2 (No. 43), a = 2970.2(6) pm, b = 1584.5(3) pm, c = 1787.0(4), V = 8.410(3) nm(3), Z = 8. The C(2) symmetric anion, [Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)](-), shows a nearly linear arrangement of the P-Ag-P unit. Although the bis(pentafluorophenyl)phosphanido compound [Ag[P(C(6)F(5))(2)](2)](-) has not been obtained so far, the synthesis of its trinuclear counterpart, [K(18-crown-6)][Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)], was successful.     

Observation of hysteretic bistability in [Co(III)Cp(2)](+)[Fe(III)I(4)](-)

[Co(III)Cp(2)](+)[Fe(III)I(4)](-) (Cp = cyclopentadienyl) prepared by the double oxidation of FeI(2) and CoCp(2) with iodine exhibits a 30 degrees C thermal hysteresis in magnetic susceptibility between 134 and 164 K that is attributed to a phase transition to a disordered triclinic unit cell from an ordered monoclinic unit cell upon cooling.     

Reactions of 3-[N-chloroacetylamino-N-(4-nitrophenyl)]-2-formylindole with alkylamines

The reactions of 3-[N-chloracetylamino-N-(4-nitrophenyl)]-2-formylindole (1a) with 2-(N, N-dialkylamino)ethylamines afford complex condensation products 7b,c consisting of two similar but not identical diazepinoindole fragments. For the reaction of compound 1a with 3-(N,N-diethylamino)propylamine, the process occurs in a different manner, and the predominant product is 4-ethylaminopropyl-1-(4-nitrophenyl)-2-oxo-1,2,3,4,5,6-hexahydro[1,4]diazepino[6,5-b]indole hydrocloride (14). Two routes of these unexpected transformations were proposed. The structures of the synthesized products were proved by the ¹sH and ¹³C NMR, HMBC, and HSQC (direct proton-carbon correlation) spectra. Dedicated to Academician V. A. Tartakovsky on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1536–1542, August, 2007.     

Synthesis, Structure, and Reactivities of [eta(2)-P(7)M(CO)(4)](3)(-), [eta(2)-HP(7)M(CO)(4)](2)(-), and [eta(2)-RP(7)M(CO)(4)](2)(-) Zintl Ion Complexes Where M = Mo, W

Ethylenediamine (en) solutions of [eta(4)-P(7)M(CO)(3)](3)(-) ions [M = W (1a), Mo (1b)] react under one atmosphere of CO to form microcrystalline yellow powders of [eta(2)-P(7)M(CO)(4)](3)(-) complexes [M = W (4a), Mo (4b)]. Compounds 4 are unstable, losing CO to re-form 1, but are highly nucleophilic and basic. They are protonated with methanol in en solvent giving [eta(2)-HP(7)M(CO)(4)](2)(-) ions (5) and are alkylated with R(4)N(+) salts in en solutions to give [eta(2)-RP(7)M(CO)(4)](2)(-) complexes (6) in good yields (R = alkyl). Compounds 5 and 6 can also be prepared by carbonylations of the [eta(4)-HP(7)M(CO)(3)](2)(-) (3) and [eta(4)-RP(7)M(CO)(3)](2)(-) (2) precursors, respectively. The carbonylations of 1-3 to form 4-6 require a change from eta(4)- to eta(2)-coordination of the P(7) cages in order to maintain 18-electron configurations at the metal centers. Comparative protonation/deprotonation studies show 4 to be more basic than 1. The compounds were characterized by IR and (1)H, (13)C, and (31)P NMR spectroscopic studies and microanalysis where appropriate. The [K(2,2,2-crypt)](+) salts of 5 were characterized by single crystal X-ray diffraction. For 5, the M-P bonds are very long (2.71(1) ?, average). The P(7)(3)(-) cages of 5 are not displaced by dppe. The P(7) cages in 4-6 have nortricyclane-like structures in contrast to the norbornadiene-type geometries observed for 1-3. (31)P NMR spectroscopic studies for 5-6 show C(1) symmetry in solution (seven inequivalent phosphorus nuclei), consistent with the structural studies for 5, and C(s)() symmetry for 4 (five phosphorus nuclei in a 2:2:1:1:1 ratio). Crystallographic data for [K(2,2,2-crypt)](2)[eta(2)-HP(7)W(CO)(4)].en: monoclinic, space group C2/c, a = 23.067(20) ?, b = 12.6931(13) ?, c = 21.433(2) ?, beta = 90.758(7) degrees, V = 6274.9(10) ?(3), Z = 4, R(F) = 0.0573, R(w)(F(2)) = 0.1409. For [K(2,2,2-crypt)](2)[eta(2)-HP(7)Mo(CO)(4)].en: monoclinic, space group C2/c, a = 22.848(2) ?, b = 12.528(2) ?, c = 21.460(2) ?, beta = 91.412(12) degrees, V = 6140.9(12) ?(3), Z = 4, R(F) = 0.0681, R(w)(F(2)) = 0.1399.     

Reactions of Alkynes with [RuCl(cyclopentadienyl)] Complexes: The Important First Steps

Cyclopentadienyl–ruthenium half‐sandwich complexes with η²‐bound alkyne ligands have been suggested as catalytic intermediates in the early stages of Ru‐catalyzed reactions with alkynes. We show that electronically unsaturated complexes of the formula [RuCl(Cp^)(η²‐RC≡CR′)] can be stabilized and crystallized by using the sterically demanding cyclopentadienyl ligand Cp^ (Cp^=η⁵‐1‐methoxy‐2,4‐tert‐butyl‐3‐neopentyl‐cyclopentadienyl). Furthermore we demonstrate that [RuCl₂(Cp^)]₂ is an active and regioselective catalyst for the [2+2+2] cyclotrimerization of alkynes. The first elementary steps of the reaction of mono(η²‐alkyne) complexes containing {RuCl(Cp*)} (Cp*=η⁵‐C₅Me₅) and {RuCl(Cp^)} fragments with alkynes were investigated by DFT calculations at the M06/6‐31G* level in combination with a continuum solvent model. Theoretical results are able to rationalize and complement the experimental findings. The presence of the sterically demanding Cp^ ligand increases the activation energy required for the formation of the corresponding di(η²‐alkyne) complexes, enhancing the initial regioselectivity, but avoiding the evolution of the system towards the expected cyclotrimerization product when bulky substituents are present. Theoretical results also show that the electronic structure and stability of a metallacyclic intermediate is strongly dependent on the nature of the substituents present in the alkyne.     

Cyanide-limited complexation of molybdenum(III): synthesis of octahedral [Mo(CN)(6)](3-) and cyano-bridged [Mo(2)(CN)(11)](5-)

Octahedral coordination of molybdenum(III) is achieved by limiting the amount of cyanide available upon complex formation. Reaction of Mo(CF(3)SO(3))(3) with LiCN in DMF affords Li(3)[Mo(CN)(6)] x 6DMF (1), featuring the previously unknown octahedral complex [Mo(CN)(6)](3-). The complex exhibits a room-temperature moment of mu(eff) = 3.80 mu(B), and assignment of its absorption bands leads to the ligand field parameters Delta(o) = 24800 cm(-1) and B = 247 cm(-1). Further restricting the available cyanide in a reaction between Mo(CF(3)SO(3))(3) and (Et(4)N)CN in DMF, followed by recrystallization from DMF/MeOH, yields (Et(4)N)(5)[Mo(2)(CN)(11)] x 2DMF x 2MeOH (2). The dinuclear [Mo(2)(CN)(11)](5-) complex featured therein contains two octahedrally coordinated Mo(III) centers spanned by a bridging cyanide ligand. A fit to the magnetic susceptibility data for 2, gives J = -113 cm(-1) and g = 2.33, representing the strongest antiferromagnetic coupling yet observed through a cyanide bridge. Efforts to incorporate these new complexes in magnetic Prussian blue-type solids are ongoing.     

Aqueous telluridoindate chemistry: water-soluble salts of monomeric, dimeric, and trimeric In/Te anions [InTe(4)](5-), [In(2)Te(6)](6-), and [In(3)Te(10)](11-)

Water-soluble salts of monomeric, dimeric, and/or trimeric telluridoindate anions, [K(5)(H(2)O)(2.16)][InTe(4)] (1), [K(5)(H(2)O)(5)][InTe(4)] (2), [K(6)(H(2)O)(6)][In(2)Te(6)] (3), [K(16)(H(2)O)(9.62)][InTe(4)](2)[In(2)Te(6)] (4), [K(133)(H(2)O)(24)][In(3)Te(10)](12)Te(0.5) (5), and [Rb(6)(H(2)O)(6)][In(2)Te(6)] (6), were prepared by a fusion/extraction method starting from the elements and characterized by single-crystal X-ray diffraction as well as spectroscopic methods. The compounds are the first hydrates of telluridoindate salts and thus point toward an aqueous coordination chemistry with binary In/Te ligands. Both crystallization from the extracts as mixtures of salts as well as preliminary spectroscopic investigation of the solutions indicate the presence of an equilibrium of different anionic species. Here, the indates differ from related stannates, which also show pH-dependent aggregation, but to a much lesser extent and in a better distinguishable manner. We present syntheses and crystal structures and discuss observation of the coexistence of different anions both in the solid state and in solution.     

2-(Fur-2-yl)thiazolo[4,5-f]quinoline: Synthesis and Electrophilic Substitution Reactions

Russian Journal of General Chemistry - Condensation of quinoline-5-amine with furan-2-carbonyl chloride in propan-2-ol afforded N-(5- quinolyl)furan-2-carboxamide, treatment of which with an excess...     

Switching off electron transfer reactions in confined media: reduction of [Co(dipic)2]- and [Co(edta)]- by hexacyanoferrate(II)

The kinetics of reduction of two cobalt(III) complexes with similar redox potentials by hexacyanoferrate(II) were investigated in water and in reverse micelle (RM) microemulsions. The RMs were composed of water, surfactant [(sodium(bis(2-ethylhexylsulfosuccinate)), NaAOT], and isooctane. Compared to the reaction in water, the reduction rates of (ethylenediaminetetraacetato)cobaltate(III) by hexacyanoferrate(II) were dramatically suppressed in RM microemulsions whereas a slight rate increase was observed for reduction of bis-(2,6-dipicolinato)cobaltate(III). For example, the ferrocyanide reduction of [Co(dipic)(2)](-) increased from 55 M(-1) s(-1)in aqueous media to 85 M(-1) s(-1) in a w(o) = 20 RM. The one-dimensional (1-D) and two-dimensional (2-D) (1)H NMR and FT-IR studies are consistent with the reduction rate constants of these two complexes being affected by their location within the RM. Since reduction of [Co(edta)](-) is switched off, in contrast to [Co(dipic)(2)](-), these observations are attributed to the penetration of the [Co(edta)](-) into the interfacial region of the RM whereas [Co(dipic)(2)](-) is in a region highly accessible to the water pool and thus hexacyanoferrate(II). These results demonstrated that compartmentalization completely turns off a redox reaction in a dynamic microemulsion system by either reactant separation or alteration of the redox potentials of the reactants.     

Multidentate ligand exchange kinetics: Substitution reaction of polyaminocarboxylatoferrate (III) complex, [FeHPDTA(OH)]2− with 4‐(2‐pyridylazo)resorcinol

The kinetic study of ligand substitution reaction of 2‐hydroxy 1,3‐diamino propane N,N′N′‐tetraacetatoiron(III) ([FeHPDTA(OH)]^2?) complex with 4‐(2‐pyridylazo)resorcinol (Par) has been followed spectrophotometrically at pH = 9.00 ± 0.02, I = 0.1 M (NaClO₄), and temperature = 25.0 ± 0.1°C. The forward and reverse reactions have been studied at 496 nm, the λ_max of [Fe(Par)₂]^? which is identified as the final product of above reaction. The second‐order rate constants for the reaction of [FeHPDTA(OH)]^2? with Par were determined in a wide pH range viz. 8.0–11.5. It is observed from pH dependence of reaction that rate of reaction increases initially with pH and then levels off. In the case of reverse reaction between [Fe(Par)₂]^? and HPDTA^4?, the pseudo‐first‐order rate constant does not change with concentration at extremely low concentration of [HPDTA]^4? and shows zero‐order dependence in [HPDTA]^4?. At relatively higher concentration of [HPDTA]^4?, the order of reaction with respect to [HPDTA]^4? is found to be 1. An inverse first‐order dependence is also observed with respect to added [Par]^2?. The activation parameters were evaluated for forward and reverse reactions, which further supported the proposed mechanistic scheme. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 333–340, 2005     

Reactions of [Ru(H(2)O)(6)](2+) with water-soluble tertiary phosphines

In aqueous solutions under mild conditions, [Ru(H(2)O)(6)](2+) was reacted with various water-soluble tertiary phosphines. As determined by multinuclear NMR spectroscopy, reactions with the sulfonated arylphosphines L =mtppms, ptppms and mtppts yielded only the mono- and bisphosphine complexes, [Ru(H(2)O)(5)L](2+), cis-[Ru(H(2)O)(4)L(2)](2+), and trans-[Ru(H(2)O)(4)L(2)](2+) even in a high ligand excess. With the small aliphatic phosphine L = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1(3,7)]decane (pta) at [L]:[Ru]= 12:1, the tris- and tetrakisphosphino species, [Ru(H(2)O)(3)(pta)(3)](2+), [Ru(H(2)O)(2)(pta)(4)](2+), [Ru(H(2)O)(OH)(pta)(4)](+), and [Ru(OH)(2)(pta)(4)] were also detected, albeit in minor quantities. These results have significance for the in situ preparation of Ru(II)-tertiary phosphine catalysts. The structures of the complexes trans-[Ru(H(2)O)(4)(ptaMe)(2)](tos)(4)x2H(2)O, trans-[Ru(H(2)O)(4)(ptaH)(2)](tos)(4)[middle dot]2H(2)O, and trans-mer-[RuI(2)(H(2)O)(ptaMe)(3)]I(3)x2H(2)O, containing protonated or methylated pta ligands (ptaH and ptaMe, respectively) were determined by single crystal X-ray diffraction.