First Order In Complex Research Articles

Synthesis of Cyclic Carbonates Catalysed by Aluminium Heteroscorpionate Complexes.

New aluminium scorpionate based complexes have been prepared and used for the synthesis of cyclic carbonates from epoxides and carbon dioxide. Bimetallic aluminium(heteroscorpionate) complexes 9-14 were synthesised in very high yields. The single-crystal X-ray structures of 12 and 13 confirm an asymmetric κ(2)-NO-μ-O arrangement in a dinuclear molecular disposition. These bimetallic aluminium complexes were investigated as catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide in the presence of ammonium salts. Under the optimal reaction conditions, complex 9 in combination with tetrabutylammonium bromide acts as a very efficient catalyst system for the conversion of both monosubstituted and internal epoxides into the corresponding cyclic carbonates showing broad substrate scope. Complex 9 and tetrabutylammonium bromide is the second most efficient aluminium-based catalyst system for the reaction of internal epoxides with carbon dioxide. A kinetic study has been carried out and showed that the reactions were first order in complex 9 and tetrabutylammonium bromide concentrations. Based on the kinetic study, a catalytic cycle is proposed.

Reaction of the Ruthenium(II) Indenyl Complex [Ru(η5-C9H7){κ3(P,C,C)-PPh2(CH2CHCH2)}(PPh3)][PF6] with Terminal Alkynes. Mechanisms of 1-Alkyne to η1-Vinylidene Transformation and Kinetic Detection of Hemilability of the Allylphosphine Ligand

The reaction of the complex [Ru(η5-C9H7){κ3(P,C,C)-PPh2(CH2CHCH2)}(PPh3)][PF6] (1) with p-XC6H4C⋮CH (X = H, Cl) yields the transient and observable vinylidene species [Ru(η5-C9H7){κ1(P)-PPh2(CH2CHCH2)}(PPh3)(CCH(p-XC6H4))]+, which react further by an intramolecular [2 + 2] cycloaddition process, forming bicyclic alkylidene compounds. The formation of the vinylidene intermediates, associated with a change of the binding mode of the allylphosphine ligand from κ3(P,C,C) to monodentate κ1(P) coordination, has been investigated by kinetic measurements carried out in chloroform-d at 38 °C. Plots of first-order kobs values vs concentration of arylalkyne are linear with a positive intercept on the y axis. The reaction proceeds via two parallel pathways, one which is first order in complex 1 and first order in arylalkyne, second order overall, and one which is zero order in arylalkyne, overall first order. The second-order pathway implies rate-determining nucleophilic attack of the arylalkyne on complex 1, k2 = [5.5(±0.4)] × 10-4 (X = H) and [2.8(±0.3)] × 10-4 M-1 s-1 (X = Cl) being the corresponding rate constants, associated with displacement of the allylic double bond or a haptotropic shift of the indenyl ring. The first-order pathway involves rate-determining formation of a transient 16-electron intermediate arising from complex 1 by reversible decoordination of the allylic double bond and rapid reaction with the incoming arylalkyne. The rate of this route is independent of the concentration and nature of the alkyne (k1 = [9.5(±2.5)] × 10-5 s-1 for X = H; [6.9(±1.5)] × 10-5 s-1 for X = Cl) and corresponds to the rate of formation of the intermediate species [Ru(η5-C9H7){κ1(P)-PPh2(CH2CHCH2)}(PPh3)]+. The vinylidene complexes [Ru(η5-C9H7)(CCRR‘){κ1(P)-PPh2(CH2CHCH2)}(PPh3)][BF4] (R‘ = H, R = Ph (3a), p-MeC6H4 (3b), p-ClC6H4 (3c); R‘ = Me, R = Ph (4a), p-MeC6H4 (4b)) have been independently synthesized by electrophilic attack of HBF4 or MeSO3CF3 on the alkynyl derivatives [Ru(η5-C9H7)(C⋮CR){κ1(P)-PPh2(CH2CHCH2)}(PPh3)] (R = Ph (2a), p-MeC6H4 (2b), p-ClC6H4 (2c)), obtained in turn from [Ru(η5-C9H7)Cl{κ1(P)-PPh2(CH2CHCH2)}(PPh3)].

The pressure tunning Raman and IR spectral studies on the multinuclear metal carbyne complexes

The Raman and infrared (IR) spectra of four tungsten metal carbyne complexes I, II, IV and V [Cl(CO) 2(L)W CC 6H 4 (C CC 6H 4) n N C ] 2M (L = TMEDA, n = 0, M = PdI 2 or ReCl(CO) 3; L = DPPE, n = 1, M = PdI 2 or ReCl(CO) 3) were studied at high external pressure. Their pressure-induced phase transitions were observed near 20 kbar (complexes I), 15 kbar (complexes II), 25 kbar (complex IV) and 30 kbar (complex V). The pressure-induced phase transition likely is first order in complex I and the pressure-induced phase transitions of complexes II, IV and V are mostly second order. The pressure sensitivities d ν/d p of ν(W C) are high in the low-pressure phase area and very low in the high-pressure phase area due to the pressure strengthening π back-bonding from metal W to π * orbital of C O in fragment Cl(CO) 2(L)W C. The pressure strengthening metal π back-bonding from metal Re or Pd to π * orbital of C O or C N also happened to both of central metal centers of NCPd(I 2)CN in complex I and NCReCl(CO) 3CN in complex II.

Kinetic Evidence of an Arm-Off Mechanism in Complexes of Hemilabile Hybrid Ligands. Oxidative Addition of Methyl Iodide to the Rhodium(I) Complex [Rh(2,6-bis(benzylthiomethyl)pyridine)(CO)]PF6 via Competitive Pathways

Kinetic experiments of the oxidative addition of methyl iodide to the cationic rhodium(I) carbonyl complex [Rh(L)(CO)]PF6 (1; L = 2,6-bis(benzylthiomethyl)pyridine) forming the observable rhodium(III) methyl species [RhI(L)(CO)Me)]PF6 have been performed by FT-IR. The reaction yields the isolable rhodium acyl complex [RhI(L)(COMe)]PF6. Plots of kobs versus concentration of methyl iodide indicate that the reaction proceeds by two parallel pathways, one which is first order in complex 1 and zero order in MeI (k1) and one which is first order in complex 1 and first order in MeI (k2). The first-order pathway displays scarce dependence on the nature of the solvent (k1 (31 °C): 6.7 × 10-6 s-1, acetone; 1.1 × 10-5 s-1, dichloromethane; 1.7 × 10-5 s-1, acetonitrile), while a larger solvent effect is observed for the second-order pathway (k2 (31 °C): 6.4 × 10-6 M-1 s-1, dichloromethane; 5.9 × 10-5 M-1 s-1, acetone; 1.4 × 10-4 M-1 s-1, acetonitrile), in agreement with the dissociative and associative character of...

Intermolecular Hydroamination of Terminal Alkynes Catalyzed by Organoactinide Complexes. Scope and Mechanistic Studies

Organoactinide complexes of the type Cp*2AnMe2 (An = Th, U) have been found to be efficient catalysts for the hydroamination of terminal alkynes with aliphatic primary amines. The chemoselectivity and regioselectivity of the reactions depend strongly on the nature of the catalyst and the nature of the amine and show no major dependence on the nature of the alkyne. The hydroamination reaction of the terminal alkynes with aliphatic primary amines catalyzed by the organouranium complexes produces the corresponding imines where the amine and the alkyne are regioselectively disposed in a syn-regiochemistry, whereas for similar reactions with the organothorium complex besides the methyl alkylated imine, dimeric and trimeric alkyne oligomers are also produced. For (TMS)C⋮CH and EtNH2 both organoactinides produced the same imine compounds when the reaction is carried out in THF or toluene. In benzene, both imines E and Z (TMS)CH2CHNEt are obtained, the earlier undergo a 1,3-silyl Brook sigmatropic rearrangement toward the enamine, whereas the latter remains unchanged. Mechanistic studies on the hydroamination of (TMS)C⋮CH and EtNH2 promoted by the organouranium complex show that the first step in the catalytic reaction is the formation of the bis(amido) complex, found in equilibrium with the corresponding bisamido−amine complex, which loses an amine, yielding a uranium−imido complex. Insertion of the alkyne into the imido bond with subsequent amine protonolysis, isomerization, and product release comprise the primary steps in the catalytic cycle. The kinetic rate law was found to follow an inverse kinetic order in amine, a first order in complex, and a zero order in alkyne, with ΔH⧧ = 11.7(3) kcal mol-1, ΔS⧧ = −44.5(8) eu. The turnover-limiting step is the release of an amine from the bisamido complex yielding the imido complex. The key organoactinide intermediate for the intermolecular hydroamination reaction was found to be the corresponding actinide−imido complexes. For both actinides the complexes have been characterized, and for thorium the single-crystal X-ray diffraction was studied. A plausible mechanistic scenario is proposed for the hydroamination of terminal alkynes and aliphatic primary amines.

Ansa-metallocene derivatives XXXVI. Dimethylsilyl-bridged permethyl chromocene carbonyl complexes — syntheses, crystal structures and interconversion reactions

The ring-bridged chromocene carbonyl complex Me 2Si(C 5Me 4) 2Cr(CO) 1 is obtained by reaction of Me 2Si(C 5Me 4) 2Li 2 with CrCl 2 · THF in the presence of CO. Reaction with CO transforms the monocarbonyl complex 1 to a dicarbonyl complex Me 2Si(C 5Me 4)(C 5( endo-3-H)(2-CH 2)Me 3)Cr(CO) 2 2; in this reaction, a hydrogen atom is shifted from one of the α-CH 3 groups to the adjacent β-position of a C 5 ring ligand. The rate of this reaction is first order in complex and CO concentration, with an activation enthalpy of H ≠ = 51 ± 3 kJ mol −1 and an activation entropy of S ≠ = 136 ± 10 J mol −1 K −1. In toluene solution at 50°C, complex 2 isomerizes to Me 2Si(C 5Me 4)(C 5( exo-3-H)(2-CH 2)Me 3)Cr(CO) 2 3, then to Me 2Si(C 5Me 4)(C 5( exo-1-H)(2-CH 2)Me 3)Cr(CO) 2 4 and further to Me 2Si(C 5Me 4)(C 5 ( endo-5-H)(2-CH 2)Me 3)Cr(CO) 2 5. The kinetics of these isomerizations, which involve hydrogen migrations and ring rotation reactions, indicate monomolecular reactions. Possible reaction paths and transition states are discussed. The structures of complexes 1–5 were determined by 1H NMR spectroscopy, those of 1, 2, 4 and 5 also by single-crystal X-ray diffraction. Complex 1: space group P2 1/ n, a = 13.257(7)Å, b = 10.186(5)Å, c = 14.739(7) Å, β = 90.89(4)°; V = 1990.1(7)Å 3; Z = 4. Complex 2: space group Pbca, a = 8.699(3) Å, b = 14.713(6) Å, c = 32.801(14)Å; V = 4198(3)Å 3; Z = 8. Complex 4: space group P2 1, a = 9.497(2)Å, b = 9.895(3) Å, c = 11.371(2)Å, β = 103.919(8)°; V = 1037.1(4) Å 3; Z = 2. Complex 5: space group P2 1/ c, a = 16.555(4)Å, b = 13.036(3)Å, c = 10.044(2)Å, β = 107.45(1)°; V = 2067.8(8)Å 3; Z = 4.

Carbonyl ligand substitution at rhodium in the heterometallic cluster [PPN] 2[Re 7C(CO) 21Rh(CO) 2]. A reactivity comparison with mononuclear ( n5-C 5H 5Rh(CO) 2 and related compounds

The heteometallic cluster compound [PPN] 2[Re 7C(CO) 21Rh(CO) 2] reacts with tertiary phosphines and phosphites selectively at the rhodium center to form the mono-substituted products [PPN] 2[Re 7C(CO) (L)]. Isolated compounds have been characterized by standard analytical and spectroscopic methods. Kinetics studies have shown that the reaction proceeds by an overall second-order process, first order in complex and first order in nucleophile. The second-order rate constants have been analysed in terms of electronic and steric effects. The substitution rates at the rhodium center in the cluster are compared with those for the analogous mononuclear complexes ( n 5-C 5 H 4 X) Rh( CO) 2 previously studied by Basolo and co-workers.

Models of vitamin B6 enzymes. 3. Steric and electronic effects in carbon-hydrogen bond breaking reactions of bis(salicylideneglycinato)cobaltate(III) anions

Salicylaldehydes readily Schiff bases with glycine. These schiff bases form bis(salicylideneglycinato) cobaltate (III) complexes. Twelve cobalt (III) complexes have been synthesized with substituents variously on the 3-, 4-, 5-, and 6-positions of the aromatic ring of the salicylaldehyde moiety. The carbon-hydrogen bond breaking reactions of the two gem-methylenic protons of the glycine moiety have been studied by deuterium exchange. Rates are first order in complex and first order in hydroxide ion. Rates differ for the exchange of the two protons, and their ratio varies from 0.81 to 4.7. This demonstrates a reversal of stereoselectivity, depending on ring substituents. Rates vs substituents generally follow Hammett behavior. The structural and electronic features that lead to stereoselectivity are discussed

The mechanism of amination of η 3-allylpalladium complexes. An exploratory kinetic study

A kinetic study of the amination of chloro(η 3-methyl-2-butenyl)(triphenylphosphine)palladium ( 1) with dimethylamine shows that the rate is first order in complex 1 and second order in dimethylamine. At high amine concentrations this is also true for the amination of acetonitrile(η 3-3-methyl-2-butenyl)(triphenylphospine)palladium tetrafluoroborate ( 2b) with benzylamine. These kinetic data, together with structural information from NMR during the reaction, suggest a common mechanism for the two reactions which involves rapid addition of the first equivalent of amine to the η 3-allyl system, followed by rate determining deprotonation of the intermediate.

Dihydride transfer: a bimolecular mechanism in the isomerization of cis-dihydridobromo(carbonyl)[bis(diphenylphosphino)ethane]iridium, IrH2Br(CO)(dppe)

Abstract : The oxidative addition of H2 to IrBr(CO) (doppe), 2, (dppe - 1,2-bis(diphenyphosphino)ethane) yields a kinetic dihydride species, 3, which then isomerizes to a more stable isomer 4. This isomerizatoin of 3 to 4 has been studied kinetically as a function of initial H2 pressure. Two pathways are operative at ambient temperature. The first is a reductive elimation/oxidative addition sequence which is first order in complex, while the second is a bimolecular pathway involving dihydride transfer from 3 to 20 to produce 4 and regenerate 2. The dihydride transfer pathway is second order in complex and becomes the dominant isomerizatoin mechanism when less than one equivalent of H2 relative to 2 has been added to the system. All of the kinetic data have been fit to a complete rate law which leads to a bimolecular rate constant for dihydride transfer of 0.21/M.min. Below -20C, the dhydride transfer pathway for isomerization is the only one operating.

Alkylation of organoiron thiolate complexes

The iron thiolate complexes Fe(SPh)(CO)(L)(η-C 5H 5 (L  PMe 3, PPh 2Me, PPh 3, PPh 2OMe, PPh(OMe) 2, P(OMe) 3, P(OPh) 3) react with EtBr in CHCl 3 (21°C) to produce the cationic sulfide complexes, [Fe(PhSEt)(CO)(L)(η-C 5H 5)]Br. A study of the kinetics of these reactions shows that these reactions are first order in complex and in EtBr; however the rates are largely insensitive to the nature of L in the precursor. After prolonged periods of time, or upon heating, a further reaction ensues in which bromide ion displaces the sulfide ligand to yield FeBr(CO)(L)(η-C 5H 5). Reactions between Fe(SPh)(CO) 2(η-C 5H 5) and EtBr, and between Fe(SPh)(CO)(PMe 3)(η-C 5Me 5) and EtBr, give FeBr(CO) 2(η-C 5H 5) and FeBr(CO)(PMe 3)(η-C 5Me 5) directly. These reactions presumably also occur via facile ligand loss from the intermediate sulfide complexes.

The indenyl ligand effect on the rate of substitution reactions of Rh(η-C9H7)(CO)2and Mn(η-C9H7)(CO)3

Carbonyl substitution by triphenylphosphine (PPh3) in the indenyl compounds Rh(η-C9H7)(CO)2 and Mn(η-C9H7)(CO)3 proceeds by a second order rate law which is first order in complex and first order in PPh3 and in both cases the rates are much faster than for the corresponding cyclopentadienyl complexes; for rhodium a rate enhancement of 108 is found for the indenyl compound over the corresponding cyclopentadienyl compound.

The reaction of carbon dioxide with rhodium and iridium hydroxy complexes

The reactions of trans-M(OH)(CO)(PPh 3) 2 for M = Rh and Ir with CO 2 are described. The rate of reaction of Rh(OH)CO)(PPh 3) 2 in CH 2Cl 2 and in the presence of traces of water is first order in complex and independent of CO 2 and water concentrations. In the complete absence of water the reaction proceeds by a much faster pathway.

OXIDATIVE ADDITION REACTIONS OF d8COMPLEXES. I. CHLORINE OXIDATION OF TETRACHOLOROPALLADATE (II)

Abstract The reaction of Na2PdCl4 with chlorine in aqueous acid solution proceeds in two stages: oxidation of the complex to a Pd(IV) species followed by a slower substitution reaction. The oxidation reaction is first order in complex and first order in chlorine. At high chloride concentration, a six-coordinate palladium(II) intermediate is formed, which is oxidised via an outer-sphere type mechanism. Oxidation of the chloroaquopalladium(II) species present at low chloride concentration occurs via a different mechanism, probably involving coordination of the oxidant in a ‘quasiinner-sphere’ mechanism.

Kinetics and mechanisms of dissociation of metal chelates. II. The acid-catalyzed dissociation of tris(pyridine-2-acetaldehyde-N-Methylimine)iron(II)

The kinetics of the acid-catalyzed dissociation of tris(pyridine-2-acetaldehyde-N-Methylimine)iron(II) were investigated photometrically in 2 M HClLiCl mixtures, ranging from 2 × 10 −5 to 2 M in HCl. The rate of dissociation was shown to be first order in complex. Experimental rate data are in agreement with a mechanism previously suggested for related iron-diimine complexes with unsymmetric ligands. The mechanism consists of two simultaneous reaction paths differing by the sequence in which the bonds between the metal atom and the two different moieties of the ligand are broken. Values for the rate constants and activation parameters of the rate-determininig step were estimated and compared with the values reported for related iron-diimine complexes. The influence of the methyl group, present in the chromophore, on the bonding ability of the ligand is discussed on the basis of these values.

Reaction mechanisms of binuclear complexes containing a quadruple metalmetal bond. The reaction of acetic acid with potassium octachlorodimolybdate(II)

The reaction of acetic acid with equilibriated solutions of tetrapotassium octachlorodimolybdate(II) in hydrochloric acid, p-toluenesulphonic acid (HPTS) and mixtures of these two acids has been studied. In HPTS the final product is tetrakisacetato-dimolybdenate(II), but in chloride-containing media mixed chloroacetato complexes are obtained. The reaction proceeds in two observable stages in all reaction media, and the kinetics of these two reactions have been measured. Both reactions are first order in complex, and the observed rate laws are of the form ▪ These two reactions are ascribed to the introduction of the first and third acetate ligands, respectively. A dissociative mechanism bearing considerable similarity to that for substitution reactions of octahedral cobalt(III) systems, is suggested.

Über Reaktionen oxygenierter Kobalt(II)‐Komplexe. V. Reaktivität diastereoisomerer μ‐Peroxo‐μ‐hydroxo‐dikobalt(III)‐Ionen

On Reactions of oxygenated Cobalt(II) Complexes. V. Reactivity of diastereoisomeric μ‐peroxo‐μ‐hydroxo‐dicobalt(III) IonsThe kinetics of dissociation of μ‐peroxo‐μ‐hydroxo‐dicobalt(III) chelates have been reinvestigated using a stopped flow technique. The binuclear cations [(trien)Co(O2, OH) Co(trien)]3+, [(tren)Co(O2, OH)Co(tren)]3+ and [(en)2Co(O2, OH)Co(en)2]3+ dissociate on acidifying to Co2+ and the protonated ligand and up to 100% of the bound O2 is evolved. The dissociation is H+‐catalyzed and first order in complex. The observed rate constants at pH 2 are in the range of 10−3 to 10−1 s−1 (20°). They depend not only on the nature of the ligand and on ligand configuration but also on the diastereoisomeric structure of the binuclear cation.In the case of trien there are 8 possible chemically different isomers. On oxygenation of Co(trien)2+ in dilute solution 3 of those isomers seem to be formed preferentially. Their rate constants are separated over a factor of 50. For [(en)2 Co(O2, OH)Co(en)2]3+ there exist a meso form and a chiral structure. On oxygenation of Co(en)22+ in dilute solution the meso form and the racemate are formed to about equal amounts. The racemate dissociates about 5 times slower. Of the 3 possible achiral isomers of [(tren)Co(O2, OH)Co(tren)]3+ one is formed stereoselectively by oxygenation in solution.

Kinetics and Mechanism of the Thermal Decomposition of Hexaamminecobalt(III) and Aquopentaamminecobalt(III) Ions in Acidic Aqueous Solution

The initial step in the thermal decomposition of Co(NH3)63+ in acidic aqueous solution is the replacement of NH3 by H2O, which occurs by a hydrogen-ion independent path, first order in complex, with rate coefficient k1 = 7.9 × 10−5 s−1 (140.4°), ΔH* = 36.6 kcal mol−1 and ΔS* = 10.7 cal deg−1 mol−1 in 0.1 M HClO4. For Co(NH3)5OH23+, there is a similar initial aquation path with k1 = 12.6 × 10−5 s−1 (140.6°), ΔH* = 41.9 kcal mol−1 and ΔS* = 24 cal deg−1 mol−1 and also a path first order in complex but inverse first order in [H+] with k2′ = 6.2 × 10−1 M s−1 (140.6°), ΔH* = 43.5 kcal mol−1 and ΔS* = 26.7 cal deg−1 mol−1 in perchlorate media of ionic strength 1.0 M. The effects of electrolyte type and concentration on the rates of these reactions have been examined. Subsequent aquation steps are relatively rapid because of the predominance of inversely [H+]-dependent pathways and are followed by redox to Co(H2O)62+, NH4+, N2, N2O, and a minor amount of O2. A mechanism involving OH and NH2 radicals is proposed for the redox step.

ChemInform Abstract: CIS‐TRANS ISOMERIZATION OF BIS(DIALKYLSULFIDE)DIHALOPLATINUM(II) COMPLEXES IN SOLUTION

AbstractEnergetik und Kinetik der cis‐trans‐Isomerisierung der Pt(II)‐Komplexe (I) werden NMR‐spektroskopisch untersucht.

Cis‐trans Isomerization of bis(Dialkylsulfide)Dihaloplatinum(II) Complexes in Solution

AbstractThe equilibrium energetics and the kinetics of cis‐trans isomerization of some bis(dialkylsulfide)dihaloplatinum(II) complexes have been examined by 1H‐NMR. spectroscopy. The isomers are stable in chloroform but each form isomerizes to an equilibrium mixture when free dialkylsulfide is added. The cis to trans process is endothermic and the position of the equilibrium is markedly dependent on the nature of the donor atoms and of the solvent. The rate of isomerization of Pt(Me2S)2Cl2 is first order in complex and in Me2S. The isomerization proceeds by a double displacement mechanism as it is shown that the tris(dimethylsulfide)chloroplatinum(II) cation is an isolable intermediate of the reaction. When free Me2S is added to trans‐Pd(Me2S)2Cl2, isomerization does not occur and one observes instead a fast ligand exchange. Its mechanism is the usual associative one for substitutions in square planar d8complexes.