Theoretical study on activation mechanism of fluorine substitution reactions of Keggin-MAl12 in aqueous solutions

The fluorine substitution reactions of Keggin polymeric aluminum species K-MAl₁₂ (M = Al, Ga, Ge) were investigated using density functional theory. Two substitution pathways (associative and dissociative) were simulated. The results show that the replacement of charged tetrahedral center metals causes the change in energy barrier either for associative mechanism or dissociative mechanism. The preferred activation mechanisms are proposed by comparing associative and dissociative barriers for fluorine substitution reactions of three Keggin Al species. The fluorine substitution reactions of Al₁₃ and GaAl₁₂ are inclined to dissociative mechanism and GeAl₁₂ follows an associative mode, indicating a mechanistic variation induced by the alteration of tetrahedral metals.     

Are α-alkoxyalkyl complexes special? 13CH coupling constant evidence.

Comlexes of type L_nMCH₂O₂CCMe₃ exhibit relatively large values of ¹J_CH for the α-carbon; however, unexpectedly large values are also found for the methyl analogs, L_nMCH₃. Thus technique does not provide evidence for any unusual interactions in the former. Cleavage of the ester linkage by MeLi proceeded cleanly only for L_nM = CpMo(Co)₃, leading to CpMo(CO)₃^?; with L_nM = Mn(CO)₅ or CpFe(CO)₂ electron transfer processes predominate. Such reactions are also observed for simple metal alkyls such as CpFe(CO)₂CH₃.     

Ligand exchange of metal carbonyls by chain mechanisms. Electrochemical kinetics of electron transfer catalysis

The metal carbonyl derivatives LM(CO)_n of manganese, rhenium, molybdenum and tungsten undergo facile ligand substitution by an electrode-mediated process. Phosphine, pyridine and isocyanaide substitutions are shown to be chain reactions by coulometric analysis and by cyclic voltammetry of the metal carbonyl solutions containing the added nucleophiles L. Reversible electrochemical parameters can be obtained for both LM(CO)_n and the substitution product LM(CO)_n. These allow the digital simulation of the cyclic voltammograms by Feldberg's method, which provides a detailed analysis of the kinetics of the electrocatalytic mechanism for ligand substitution. Generally, the radical cation LM(CO)_n⁺ produced initially at the anode undergoes rapid exchange with L to afford the cationic substituted species LM(CO)_n⁺. This step is followed by electron transfer with the reactant LM(CO)_n to yield the substitution product LM(CO)_n and regenerate the radical cation LM(CO)_n⁺, which completes the chain propagation sequence. Multiple repetition of this cycle is indicated by the high current efficiencies which are obtainable. The second order rate constants for the ligand exchange of the 17-electron radical cations LM(CO)_n⁺ with added L are evaluated, and found to be more than 10⁶ times larger than that for the neutral, diamagnetic precursor LM(CO)_n. The radical cations LM(CO)_n⁺ also react readily with phosphine and alkyl isocyanide nucleophiles, leading to a characteristic distortion of the CV waves. Digital simulation of such cyclic voltammograms allows the kinetics of these processes, particularly the redox catalysis in the oxidation of phosphines by LM(CO)_n⁺, to be evaluated quantitatively. The enhanced reactivity of the 17-electron radical cations LM(CO)_n⁺ is discussed in relationship to recent reports of the substitution lability in other 17- and 19-electron metal carbonyls.     

Ligand substitution kinetics in M(CO)4(η-norbornadiene) complexes (M=Cr, Mo, W): displacement of norbornadiene by bis(diphenylphosphino)alkanes

The thermal substitution kinetics of norbornadiene (NBD) by bis(diphenylphosphino)alkanes (PP), (C₆H₅)₂P(CH₂)_nP(C₆H₅)₂ (n=1, 2, 3) in M(CO)₄(η^2:2-NBD) complexes (M=Cr, Mo, W), were studied by quantitative FT-IR spectroscopy. The reaction rate exhibits first-order dependence on the concentration of the starting complex, and the observed rate constant depends on the concentration of the leaving NBD ligand and on the concentration and the nature of the entering PP ligand. In the proposed mechanism there are two competing initial steps: an associative reaction involving the attachment of the entering PP ligand to the transition metal center and a dissociative reaction involving the stepwise detachment of the diolefin ligand from the transition metal center. A rate law is derived from the proposed mechanism. The activation parameters are obtained from the evaluation of the kinetic data. It is found that at higher concentrations of the entering ligand, the associative path is dominant, while at lower concentrations the contribution of the dissociative path becomes significant. Both the observed rate constant and the activation parameters show noticeable variation with the chain length of the diphosphine ligand.     

Stibinidenkomplexe: Verbindungen mit trigonal planar koordiniertem antimon

Intensively coloured stibinidene complexes (L_nM)₂SbR (L_nM = (CO)₅Cr; R = ^tBu, Cl, I, EtS. L_nM = C₅H₅(CO)₂Mn; R = Cl. L_nM = CH₃C₅H₄(CO)₂Mn; R = Br) which contain trigonally planar coordinated Sb(+1) with the stibanediyl ligand stabilized by M $\text{?}$ Sb(R) $\text{?}$ M-π-bonding have been obtained. Their synthesis and properties as well as an X-ray structure determination of [CH₃C₅H₄(CO)₂Mn]₂SbBr are described.     

Zur kenntnis der chemie der metallcarbonyle und der cyanokomplexe in flüssigem ammoniak : XXXIII. Über die darstellung neuer carbamoylcarbonyl-komplexe aus bekannten und neuen kationischen carbonylverbindungen des mangans und rheniums

The covalent carbamoyl carbonyl compounds Re(CO)₅COHN₂, cis-M(CO)₄(L)CONH₂, M(CO)₃(L)₂CONH₂ and M(CO)₃(D)CONH₂ (M = Mn, Re; L = PPh₃, PEt₃; D = bipy, phen) are formed by reactions of the cationic complexes [Re(CO)₆]⁺, [M(CO)₅L]⁺, [M(CO)₄L₂]⁺ and [M(CO)₄D]⁺ (M = Mn, Re; L = PPh₃, PEt₃; D = bipy, phen) with liquid NH₃ with concomitant deprotonation: [M(CO)_6?nL_n]⁺ + 2 NH₃ → M(CO)_5?nL_nCONH₂ + NH₄⁺ (n = 0, 1, 2) and [M(CO)₄D]⁺ + 2 NH₃ → M(CO)₃(D)CONH₂ + NH₄⁺ The stability of the above-mentioned carbamoyl carbonyl complexes increases from the penta- to the tetra- to the tri-carbonyl derivatives. In all cases the rhenium compounds are much more stable than the corresponding manganese complexes. Whereas the carbamoyl compound Re(CO)₄(PEt₃)CONH₂ can be isolated by reaction of [Re(CO)₅PEt₃]⁺ with NH₃, the corresponding manganese complex undergoes Hofmann degradation of amides even at ?70°C to form HMn(CO)₄PEt₃ and NH₄NCO. The IR and some mass and ¹H NMR spectra of the new hexacoordinated carbamoyl carbonyl complexes are discussed and the reactions of these compounds with liquid NH₃, HCl and CH₃OH are described.     

Diorganothallium-übergangsmetall-komplexe,R2Tl—Mln

Diorganothallium transition metal complexes of the general formula R₂Tl—ML_n with ML_n = M(CO)₂LCp (M = Mo, W; L = CO, PPh₃) are obtained by protolytic reactions, redistribution reactions or by methatetic reactions, and are characterized spectroscopically and by chemical reactions. For ML_n = Cr(CO)₃Cp, Fe(CO)₂Cp and Co(CO)₄ R₃Tl and Tl(ML_n)₃ can always be isolated. In the case of Me₂Tl—M(CO)₃Cp (M = Mo, W) variable temperature NMR measurements gave evidence for a symmetrisation—redistribution equilibrium 3 R₂Tl—ML_n—ML_n ? R₃Tl + Tl(ML_n, which generally determines the stability of the diorganomthallium transition metal complexes.     

Reactions of the carbonyl complexes M(CO)3(L)3 (L = py,M = Mo,W; L = NH3, M = Mo) and M(CO)4(2-Mepy)2 (M = Mo,W) with HgX2 (X = Cl,CN, SCN)

The reactions of the substituted Group VI metal carbonyls of the type M(CO)₄(2-Mepy)₂ (M = Mo, w) and M(CO)₃(L)₃ (L = py, M = Mo, W; L = NH₃, M = Mo) with mercuric derivatives HgX₂ (X = Cl, CN, SCN) have given rise to three series of tricarbonyl complexes: M(CO)₃(py)HgCl₂ · 1/2HgCl₂ (M = Mo, W); 2[M(CO)₃(L)]Hg(CN)·nHg(CN)_x (L = py, M = Mo, W, n = $\text{1}\text{2}$, × = 2; L = 2- Mepy, × = 1; M = Mo, n = 3; M = W, n = 1); and [M(CO)₃(L)Hg(SCN)₂ · nHg(SCN)₂] (L = py, M = Mo,W, n = 0; L = 2-Mepy, M = Mo, W, n = $\text{1}\text{2}$; L = NH₃, M = Mo, n = 0) depending on which mercuric compound is employed. All the reactions with Hg(SCN)₂ give isolable products whereas those with Hg(CN)₂ and HgCl₂ did so far only the reactions with [M(CO)₄(2-Mepy)₂] and M(CO)₃(py)₃. The greater reactivity of Hg(SCN)₂ than of Hg(CN)₂ and HgCl₂ is consistent with the various acceptor capacities of the groups bonded to the mercury atom.The reactions studied always involve displacement of the N-donor ligand of the original complex and partial or total displacement of the halide or pseudohalide groups of the mercury compound to give in all cases compounds containing MHg bonds. In addition, elimination of a CO group in the tetracarbonyl complexes M(CO)₄(2-Mepy)₂occurs.     

Complexes containing phosphorus lignads—161: New phosphinite,phosphonite and phosphite derivatives of ruthenium,osmium and iridium

The complexes [MHCl(CO)(PPh₃)₃] (M = Ru or Os) readily undergo substitution at the site trans to the hydride ligand to afford phosphinite-, phosphonite-, or phosphite-containing products [MHCI(CO)(PPh₃)₂L] [L = P(OR)Ph₂, P(OR)₂Ph or P(OR)₃ respectively; R = Me or Et]. The ruthenium complexes alone undergo further substitution to afford complex cations [RuH(CO)(PPh₃)_nL_4?n]⁺ [n = 2, L = P(OMe)₃; n = 1, L = P(OR)₃; n = 0, L = P(OR)₂Ph or P(OR)Ph₂] which were isolated and characterised as their tetraphenylborate salts. Synthesis of the cationic complexes [IrHL₅][BPh₄]₂ [L = P(OR)₃, R = Me or Et] is also reported. Stereochemical assignments based on NMR data are given, and second order ³¹P and high field ¹H NMR patterns are analysed.     

Perfluormethyl-Element-Liganden. XVIII. Darstellung und spektroskopische Untersuchung von M(CO)5L und M(CO)4L2-Komplexen [L = MenP(CF3)3−n; n = 0–3; M = Cr,Mo, W]

Perfluoromethyl-Element-Ligands. XVIII. Preparation and Spectroscopic Investigation of M(CO)₅L and M(CO)₄L₂ Complexes [L = Me_nP(CF₃)_3?n; n = 0–3; M = Cr, Mo, W] M(CO)₅L and cis-M(CO)₄L₂ complexes, respectively [M = Cr, Mo, W; L = Me_nP(CF₃)_3?n; n = 0–3] are prepared reacting M(CO)₅ · THF or M(CO)₄norbor with L at room temperature. The cis-compounds isomerize above 50°C yielding the trans-complexes; the rate of isomerization increases with increasing number of CF₃ groups. Thermal reaction of M(CO)₆ (M = Cr, Mo, W) with P(CF₃)₃ yields M(CO)₅P(CF₃)₃ and trans-M(CO)₄[P(CF₃)₃]₂. Introduction of three P(CF₃)₃ ligands by reaction with M(CO)₃(cycloheptatriene) (M = Cr, Mo) proves unsuccessful; besides little M(CO)₅P(CF₃)₃ trans-M(CO)₄[P(CF₃)₃]₂ is formed. The new compounds are characterized by analytical and spectroscopic (n.m.r., i.r., MS) methods.     

New synthesis and low temperature13C n.m.r. spectra of some anionic seven-coordinate complexes of molybdenum(II) and tungsten(II) of the type [NBu 4 n ][MI2X(CO)3L]

Summary The bisacetonitrile complexes [MI₂(CO)₃(NCMe)₂] react with an equimolar amount of L in CH₂Cl₂ at room temperature to give [MI₂(CO)₃(NCMe)L] which when mixedin situ with an equimolar amount of [NBu ₄ ⁿ ]X affords the anionic seven-coordinate compounds [NBu ₄ ⁿ ][MI₂X(CO)₃L][M=Mo or W,X=I, L=PPh₃ (for M=W only), AsPh₃ or SbPh₃ (for M=Mo only); M=Mo and W, X=Br₃ or Br₂I, L=PPh₃, AsPh₃ or SbPh₃]. These reactions are likely to occurvia the stepwise dissociative displacement of two acetonitrile ligands. Low-temperature (–70° C, CD₂Cl₂)¹³C n.m.r. spectra (CO resonances) are reported for several of the complexes in order to infer the likely stereochemistry of these compounds.     

Mo(CO)5L的氧原子转移反应动力学和机理研究

近期我们报道了M(CO)_2(M=Cr,Mo,W)与Me_2NO反应的动力学研究结果。 本文报道在CH_2Cl_2,-CH_2CN(体积比1:1)混合溶剂中,三甲胺氧化物存在下的二取代反应: Mo(CO)_5L Me_3NO L→顺-Mo(CO)_4L_2 Me_3N CO_3 (1)式中L=P(c-hx)_3,P(n-Bu)_3,NMe_3Pyr,PPh_3,AsPh_3,P(OEt)和P(OMe)_3,在金属原子不变的情况下对配体的电子效应(以Mo(CO)_5L的羰基伸缩振动频率表现出来)和立体效应做探讨。     

TR-FTIR absorption spectroscopy of transition metal carbonyl radicals generated by photodissociation of metal-metal bonds, by halogen abstraction or by radical ligand substitution

Three methods of obtaining time-resolved Fourier-Transform infrared (TR-FTIR) absorption spectra of transition metal carbonyl radicals in hexane are reported here. For the first method, CpM(CO)₂L and Cp*M(CO)₂L (M = Mo, W; L = CO, PR₃) radicals have been generated by photodissociation of the corresponding metal-metal bonded dimers. Radicals of formula M(CO)₄L (M = Mn, Re; L = CO, PR₃, AsPh₃, SbPh₃) and CpM(CO)_n (M = Fe, Mo; n = 2, 3) have been produced via the second method which is halogen abstraction of the transition metal carbonyl halides using CpMo(CO)₃ radical. For the third method, fast radical ligand substitution kinetics has been exploited to generate CpMo(CO)₂PR₃ radicals from CpMo(CO)₃ in the presence of free phosphines. An assessment of the three methods with respect to TR-FTIR spectroscopic detection of radicals was also discussed.     

Coordinating Properties of Dipod and Tripod Phosphorus Ligands with Separated Donor and Acceptor Sites

Abstract

The coordinating properties of dipod and tripod phosphorus ligands L_I = R₂M′ (OCH₂PMe₂) _n(CH₂CH₂PMe₂) _2-n and L_II = RM′ (OCH₂PMe₂)_n(CH₂CH₂PMe₂)_3-n (M′ = Si, Ge) with separated donor and acceptor centres have been investigated using electron rich metal complex fragments, e. g. M(CO)_m, (M = Cr, MO, W), π-C₅H₅Co, RhCl(CO) or Ni(CO), as bonding partners.     

Redistribution reactions in the ion source of a mass spectrometer of complexes of titanium (iv), tin (iv) and germanium (iv) with 8-quinolinolato and halo or ethoxy ligands

The relative intensities of peaks in the mass spectra of the compounds MX_4?nox_n (oxH = 8-quinolinol; n = 2; M = Ti; X = F, Cl, Br or OEt; M = Sn; X = F, Cl, Br or I; M = Ge; X = Cl or Br; n = 1; M = Ti; X = OEt) depend on the insertion temperature and the residence time of the sample in the mass spectrometer. In most cases ions which cannot arise by fragmentation of the respective molecular ions are observed. These ions arise from the ionisation and fragmentation of species which are due to redistribution reactions in the mass spectrometer. The fragmentation pattern of the compounds MX₂ox₂ (X = halogen), mainly involving loss of ligand radicals, is related to the common oxidation states of the metals and reflects the metal-halogen bond strength. The molecular ions of the compounds Ti(OEt)_4?nox_n (n = 0, 1 or 2) fragment by loss of intact ligand radicals.     

Metal carbonyl catalysis of carbon monoxide and formate reactions

The water gas shift reaction (CO + H₂O = CO₂+ H₂) is catalyzed by aqueous metal carbonyl systems derived from simple mononuclear carbonyls such as Fe(CO)₅ and M(CO)₆ (M = Cr, Mo, and W) and bases in the 140–200 °C temperature range. The water gas shift reaction in a basic methanol-water solution containing Fe(CO)₅ is first order in [Fe(CO)₅], zero order in [CO], and essentially independent of base concentration and appears to involve an associative mechanism with a metallocarboxylate intermediate [(CO)₄Fe-CO₂H]^–. The water gas shift reactions using M(CO)₆ as catalyst precursors are first order in [M(CO)₆], inverse first order in [CO], and first order in [HCO₂ ^–] and appear to involve a dissociative mechanism with formatometallate intermediates [(CO)₅M-OCHO]^–.The Reppe hydroformylation of ethylene to produce propionaldehyde and 1-propanol in basic solutions containing Fe(CO)₅ occurs at 110–140 °C. This reaction is second order in [Fe(CO)₅], first order in [C₂H₄] up to a saturation pressure >1.5 MPa, and inhibited by [CO]. These experimental results suggest a mechanism where the rate-determining step involves a binuclear iron carbonyl intermediate. The substitution of Et₃N for NaOH as the base facilitates the reduction of propionaldehyde to 1-propanol but results in a slower rate for the overall reaction.The homogeneous photocatalytic decomposition of the formate ion to H₂ and CO₂ in the presence of Cr(CO)₆ appears to be closely related to the water gas shift reaction. The rate of H₂ production from the formate ion exhibits saturation kinetics in the formate ion and is inhibited by added pyridine. The infrared spectra of the catalyst solutions indicate an LCr(CO)₅ intermediate. Photolysis of the Cr(CO)₆/formate system in aqueous methanol in the presence of an aldehyde RCHO (R =n-heptyl,p-tolyl, andp-anisyl) results in catalytic hydrogenation of the aldehyde to the corresponding alcohol RCH₂OH by the formate ion. Detailed kinetic studies onp-tolualdehyde hydrogenation by this method indicates saturation kinetics in formate ion, autoinhibition by thep-tolualdehyde, and a threshold effect for Cr(CO)₆ at concentrations >0.004 mol L^–1. The presence of an aldehyde can interrupt the water gas shift catalytic cycle by interception of an HCr(CO)₅ ^– intermediate by the aldehyde.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1533–1539, September, 1994.     

1-[(π-Cyclopentadienyl)dicarbonyliron]-1-methylsilacyclobutane and related iron-substituted silacyclobutanes

Silicon-transition metallic silacyclobutanes CpFe(L₂)$\text{Si(Me)CH}{}_2\text{CH}{}_2\text{C}$H₂ [L = CO or Ph₂MeP; or L₂ = (CO)(Ph₂MeP)] have been prepared and their reactions (substitution at Si or Fe, Si—Fe cleavage, or ring-opening) studied.     

Bimetallic Complexes with Bridging Dithiaalkane Ligands: Preparation and Kinetic Study

Reactions of M(CO)₅THF, which was generated photochemically from M(CO)₆ in THF, with (CH₃)₃CS(CH₂)_nSC(CH₃)₃ (=SS; n=5, 6; M=W, Cr) at room temperature afforded exclusively the bimetallic complexes (CO)₅MSSM(CO)₅. These new complexes with dithiaalkane bridging ligands have been characterized by IR and ¹H NMR spectroscopies and elemental analysis. Kinetic studies of ligand-exchange reactions in these complexes in chlorobenzene (=CB) solutions employing tri(iso-propyl)phosphite (=L) as an incoming nucleophile indicated that the bridging ligand SS is replaced by L to afford finally (CO)₅MP(O-i-Pr)₃ as the sole reaction product. The kinetic data have also confirmed that replacement of SS by L under pseudo-first-order reaction conditions is dissociative and proceeds via a mechanism which involves initial M-S bond breaking followed by other steps. First order rate constants and activation parameters for these reactions have been determined.     

Komplexe des Chroms und Molybdäns mit Aminoarsan-Liganden. III

Complexes of Chromium and Molybdenum with Aminoarsanes as Ligands. III The reaction of the norbornadien complexes (CO)₄MC₇H₈ (M = Cr, Mo) with aminoarsanes Me_mAs(NMe₂)_n (m = 2, 1; n = 1, 2) is examined. The substitution reaction results in the formation of complexes of the formula cis-(CO)₄M(aminoarsane)₂. These complexes rearrange to a mixture of hexacarbonyles M(CO)₆ and monosubstituted complexes (CO)₅M-aminoarsane. The cleavage of the As? N bond in the coordinated aminoarsane ligand with acid molecules as ethanol, thioethanol, or glycol yields complexes of the type (CO)₄M[AsMe_n)? X_m]₂.     

Addition reactions of a polynuclear osmium hydrido compound leading to associative carbonyl substitution and catalytic alkene isomerisation

The ability of H₂Os₃(CO)₁₀ to undergo addition reactions under mild conditions allows associative CO substitution via isolable intermediates of the type H₂Os₃(CO)₁₀ (L = CO, PMe₂Ph, PPh₃ or PhCN) whose spectra and structures are discussed. It is probable that simple addition of alkenes to H₂Os₃(CO)₁₀ is in part responsible for its facile catalysis of alkene isomerisation. The kinetics of catalytic conversion of terminal to internal alkenes and of allylic alcohols to aldehydes or ketones are reported and discussed. The reactions of H₂Os₃(CO)₁₀ with allylic halides to give the complexes HOs₃X(CO)₁₀ and Os₃X₂(CO)₁₀ where X = Cl, Br or I are described. Compound H₂Os₃(CO)₁₀ complies with the 18ρ-rule but nevertheless has a chemistry much like that of coordinatively unsaturated molecules.