Search

The reaction of three [FeII(TSC)2] complexes, where TSC is a pyridine-substituted thiosemicarbazone of the HDpT or HBpT families, with H2O2 in acetonitrile solution does not result in the accumulation of the corresponding [FeIII(TSC)2]+ complexes. Instead, a mixture of diamagnetic low-spin FeII species is generated. According to the MS spectra, those species result from the sequential addition of up to five oxygen atoms to the complex. This capability for the addition of oxygen atoms suggested that oxygen atom transfer to external substrates may be possible, and these TSC complexes were tested in the oxidation of thioanisole and styrene with H2O2. As hypothesized, the complexes are active in both the oxidation of thioanisole to its sulfoxide and styrene to benzaldehyde, with time scales indicating the participation of the species containing added oxygen atoms. Interestingly, the free thiosemicarbazone ligands and the [Zn(Dp44mT)2] complex also catalyse the selective sulfoxidation of thioanisole, but they are ineffective in catalysing styrene oxidation to benzaldehyde. These findings open up new directions for the development of thiosemicarbazone-based metal catalysts for oxidation processes. [ABSTRACT FROM AUTHOR]

Two oxoiron(IV) isomers (R2a and R2b) of general formula [FeIV(O)(RPyNMe3)(CH3CN)]2+ are obtained by reaction of their iron(II) precursor with NBu4IO4. The two isomers differ in the position of the oxo ligand, cis and trans to the pyridine donor. The mechanism of isomerization between R2a and R2b has been determined by kinetic and computational analyses uncovering an unprecedented path for interconversion of geometrical oxoiron(IV) isomers. The activity of the two oxoiron(IV) isomers in hydrogen atom transfer (HAT) reactions shows that R2a reacts one order of magnitude faster than R2b, which is explained by a repulsive noncovalent interaction between the ligand and the substrate in R2b. Interestingly, the electronic properties of the R substituent in the ligand pyridine ring do not have a significant effect on reaction rates. Overall, the intrinsic structural aspects of each isomer define their relative HAT reactivity, overcoming changes in electronic properties of the ligand. [ABSTRACT FROM AUTHOR]

The anion pairs formed during the reaction between a dihydrogen-iron complex and ammonia in presence of anionic salts accelerate the reaction rate. The proton transfer also does not involve any energy transfer and the reaction pathway provided by the anions is more efficient than in presence of unpaired complexes.

The formation of the dihydrogen complex has been discussed. The reaction between cis-[RuH (sub)2 (Ph (sub)2 PCH (sub)2 CH (sub)2 PPh (sub)2) (sub)2 and acids in the THF solution is described.

The novel [W3S4H3(edpp)3]+ (edpp=(2‐aminoethyl)diphenylphosphine) (1+) cluster hydride with an acidic −NH2 functionality has been synthetized and studied. Its crystal structure shows the characteristic incomplete W3S4 cubane core with the outer positions occupied by the P and N atoms of the edpp ligands. Although no signal due to the hydride ligands is observed in the 1H NMR spectrum, hydride assignment is supported by 1H‐15N HSQC techniques, the changes in the 31P{1H} NMR chemical shift, and FT‐IR spectra in the W−H region of the deuterated [W3S4D2H(edpp)3]+ (1+‐d2) samples. Moreover, all NMR evidences suggest that one of the hydrogen atoms of the NH2 group in 1+ is rapidly exchanging with the hydride. The reaction of 1+ with acids (HCl, HBr and DCl) features complex polyphasic kinetics with zero‐order dependence with respect to the acid concentration, being also independent of the solvent nature. This behavior differs from that of their diphosphino analogues, suggesting a different mechanism. [ABSTRACT FROM AUTHOR]

Substitution reactions for dihydrogen in tittle complex were investigated to determine the activation and kinetic parameters of the reaction. Results indicate that the reaction is not a direct substitution of the dihydrogen group by the incoming ligand. Rather, the coordination of the incoming group follows a conversion step in the parent compound that generates a reactive intermediate. This conversion step probably opens a chelate ring.

Oxoiron(IV) complexes bearing tetradentate ligands have been extensively studied as models for the active oxidants in non‐heme iron‐dependent enzymes. These species are commonly generated by oxidation of their ferrous precursors. The mechanisms of these reactions have seldom been investigated. In this work, the reaction kinetics of complexes [FeII(CH3CN)2L](SbF6)2 ([1](SbF6)2 and [2](SbF6)2) and [FeII(CF3SO3)2L] ([1](OTf)2 and [2](OTf)2 (1, L=Me,HPytacn; 2, L=nP,HPytacn; R,R′Pytacn=1‐[(6‐R′‐2‐pyridyl)methyl]‐4,7‐ di‐R‐1,4,7‐triazacyclononane) with Bu4NIO4 to form the corresponding [FeIV(O)(CH3CN)L]2+ (3, L=Me,HPytacn; 4, L=nP,HPytacn) species was studied in acetonitrile/acetone at low temperatures. The reactions occur in a single kinetic step with activation parameters independent of the nature of the anion and similar to those obtained for the substitution reaction with Cl− as entering ligand, which indicates that formation of [FeIV(O)(CH3CN)L]2+ is kinetically controlled by substitution in the starting complex to form [FeII(IO4)(CH3CN)L]+ intermediates that are converted rapidly to oxo complexes 3 and 4. The kinetics of the reaction is strongly dependent on the spin state of the starting complex. A detailed analysis of the magnetic susceptibility and kinetic data for the triflate complexes reveals that the experimental values of the activation parameters for both complexes are the result of partial compensation of the contributions from the thermodynamic parameters for the spin‐crossover equilibrium and the activation parameters for substitution. The observation of these opposite and compensating effects by modifying the steric hindrance at the ligand illustrates so far unconsidered factors governing the mechanism of oxygen atom transfer leading to high‐valent iron oxo species. [ABSTRACT FROM AUTHOR]

Here, the kinetics of the concerted [3 + 2] cycloaddition reaction between the [Mo3(μ3‐S)(μ‐S)3Cl3(dmen)3]+ (dmen = N,N′‐dimethyl‐ethylenediamine) ([1]+) cluster and various alkynes to form dithiolene derivatives is thoroughly studied, with measurements at different temperatures and pressures allowing the determination of the free energies and volumes of activation. These parameters, together with the available single‐crystal X‐ray diffraction structures, are used to test a number of commonly used density functional theory (DFT) methods from Jacob's ladder, as well as the effects associated with the size of the basis sets, the way in which solvent effects are taken into account, or the inclusion of dispersion effects. Overall, a protocol that leads to average deviations between experimental and computed ΔV‡ and ΔG‡ values similar to the uncertainty of the experimental measurements is obtained. [ABSTRACT FROM AUTHOR]

The electrospray ionization mass studies was carried out to study the chemistry of the aqueous solutions of the [[Mo.sub.3][S.sub.4][Cl.sub.3][L.sub.3]]Cl cluster (L = dhmpe) in order to understand their acid-base and substitution behavior.

The structure of ([[[W.sub.3][Q.sub.4][X.sub.3][(dmpe).sub.3]].sup.+] is studied with B[F.sub.4.sup.-] and P[F.sub.6.sup.-] anions. In the case of [[[[W.sub.3][S.sub.4][H.sub.3-][(dmpe).sub.3].sup.+], B[F.sub.4.sup.-]], both the NMR spectra and theoretical calculations indicate that B[F.sub.4.sup.-] is placed closed to the coordinated hydrides, which causes a decrease in the rate of proton transfer from Hal to the cluster and the interactions with B[F.sub.4.sup.-] weaken the W-H...H-Cl dihydrogen bonds and inhibit proton transfer.

The synthesis, structure, and electrochemical properties of the A heterodimetallic [W3PdS4H3[(dmpe).sub.3].(Co)].sup.+] hydrido cubane are reported. The results demonstrate the incorporation of PD into the{{W3S4H3[(dmpe).sub.3]}.sup.+]} cluster produces air-stable heterodimetallic cubane type hybrido clusters in high yields.

The kinetics of deprotonation by NEt3 of the dihydrogen complex trans-[FeH(H2)(dppe)2]+(1) (dppe=Ph2PCH2CH2PPh2) is reported. It is demonstrated that ion pairing leads to drastic kinetic changes, the reaction being accelerated or decelerated depending on the nature of the anion.