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1.
Oxygenation of [Cu II(fla)(idpa)]ClO 4 (fla=flavonolate; IDPA=3,3′-iminobis( N, N-dimethylpropylamine)) in dimethylformamide gives [Cu II(idpa)( O-bs)]ClO 4 ( O-bs= O-benzoylsalicylate) and CO. The oxygenolysis of [Cu II(fla)(idpa)]ClO 4 in DMF was followed by electronic spectroscopy and the rate law −d[{Cu II(fla)(idpa)}ClO 4]/d t= kobs[{Cu II(fla)(idpa)}ClO 4][O 2] was obtained. The rate constant, activation enthalpy and entropy at 373 K are kobs=6.13±0.16×10 −3 M −1 s −1, Δ H‡=64±5 kJ mol −1, Δ S‡=−120±13 J mol −1 K −1, respectively. The reaction fits a Hammett linear free energy relationship and a higher electron density on copper gives faster oxygenation rates. The complex [Cu II(fla)(idpa)]ClO 4 has also been found to be a selective catalyst for the oxygenation of flavonol to the corresponding O-benzoylsalicylic acid and CO. The kinetics of the oxygenolysis in DMF was followed by electronic spectroscopy and the following rate law was obtained: −d[flaH]/d t= kobs[{Cu II(fla)(idpa)}ClO 4][O 2]. The rate constant, activation enthalpy and entropy at 403 K are kobs=4.22±0.15×10 −2 M −1 s −1, Δ H‡=71±6 kJ mol −1, Δ S‡=−97±15 J mol −1 K −1, respectively. 相似文献
2.
To clarify the radical-scavenging activity of butylated hydroxytoluene (BHT), a food additive, stoichiometric factors ( n) and inhibition rate constants ( kinh) were determined for 2,6-di- tert-butyl-4-methylphenol (BHT) and its metabolites 2,6-di- tert-butyl- p-benzoquinone (BHT-Q), 3,5-di- tert-butyl-4-hydroxybenzaldehyde (BHA-CHO) and 3,5-di- tert-butyl-4-hydroperoxy-4-methyl-2,5-cyclohexadiene-1-one (BHT-OOH). Values of n and kinh were determined from differential scanning calorimetry (DSC) monitoring of the polymerization of methyl methacrylate (MMA) initiated by 2,2′-azobis(isobutyronitrile) (AIBN) or benzoyl peroxide (BPO) at 70 °C in the presence or absence of antioxidants (BHT-related compounds). The n values declined in the order BHT (1–2) > BHT-CHO, BHT-OOH (0.1–0.3) > BHT-Q (0). The n value for BHT with AIBN was approximately 1.0, suggesting dimerization of BHT. The kinh values declined in the order BHT-Q ((3.5–4.6)×10 4 M −1 s −1) > BHT-OOH (0.7–1.9×10 4 M −1 s −1) > BHT-CHO ((0.4–1.7)×10 4 M −1 s −1) > BHT ((0.1–0.2)×10 4 M −1 s −1). The kinh for metabolites was greater than that for the parent BHT. Growing MMA radicals initiated by BPO were suppressed much more efficiently by BHT or BHT-Q compared with those initiated by AIBN. BHT was effective as a chain-breaking antioxidant. 相似文献
3.
The phosphinoalkenes Ph 2P(CH 2) nCH=CH 2 ( n= 1, 2, 3) and phosphinoalkynes Ph 2P(CH 2) n C≡CR (R = H, N = 2, 3; R = CH 3, N = 1) have been prepared and reacted with the dirhodium complex (η−C 5H 5) 2Rh 2(μ−CO) (μ−η 2−CF 3C 2CF 3). Six new complexes of the type (ν−C 5H 5) 2(Rh 2(CO) (μ−η 1:η 1−CF 3C 2CF 3)L, where L is a P-coordinated phosphinoalkene, or phosphinoalkyne have been isolated and fully characterized; the carbonyl and phosphine ligands are predominantly trans on the Rh---Rh bond, but there is spectroscopic evidence that a small amount of the cis-isomer is formed also. Treatment of the dirhodium-phosphinoalkene complexes with (η−CH 3C 5H 4)Mn(CO) 2thf resulted in coordination of the manganese to the alkene function. The Rh 2---Mn complex [(η−C 5H 5) 2Rh 2(CO) (μ−η 1:η 1−CF 3C 2CF 3) {Ph 2P(CH 2) 3CH=CH 2} (η−CH 3C 5H 4)Mn(CO) 2] was fully characterized. Simi treatment of the dirhodium-phosphinoalkyne complexes with Co 2(CO) 8 resulted in the coordination of Co 2(CO) 6 to the alkyne function. The Rh 2---Co 2 complex [(η−C 5H 5) 2Rh 2(CO) (μ−η 1:η 1−CF 3C 2CF 3) {Ph 2PCH 2C≡CCH 3}Co 2(CO) 2], C 37H 25Co 2F 6O 7PRh 2, was fully characteriz spectroscopically, and the molecular structure of this complex was determined by a single crystal X-ray diffraction study. It is triclinic, space group
( Ci1, No. 2) with a = 18.454(6), B = 11.418(3), C = 10.124(3) Å, = 112.16(2), β = 102.34(3), γ = 91.62(3)°, Z = 2. Conventional R on | F| was 0.052 fo observed ( I > 3σ( I)) reflections. The Rh 2 and Co 2 parts of the molecule are distinct, the carbonyl and phosphine are mutually trans on the Rh---Rh bond, and the orientations of the alkynes are parallel for Rh 2 and perpendicular for Co 2. Attempts to induce Rh 2Co 2 cluster formation were unsuccessful. 相似文献
4.
The trinuclear clusters [Pd 3(μ-dppm) 3(CO)] 2+ and [PtPdCo(μ-dppm) 2(CO) 3(CN tBu)] + exhibit a large and a small cavity, respectively, formed by the phenyl rings of the bridging diphosphine ligands. Their binding constants ( K11) with halide ions (X −) were obtained by UV-Vis spectroscopy. The binding ability varies as I − > Br − > Cl −, and [Pd 3(μ-dppm) 3(CO)] 2+ > [ptPdCo(μ-dppm) 2-(CO) 3(CN tBu)] +. The MO diagram for the related cluster [Pd 2Co(μ-dppm) 2(CO) 4] + has been addressed theoretically in order to predict the nature of the lowest energy electronic bands. For this class of compounds, the lowest energy bands are assigned to charge transfers from the Co center to the Pd 2 centers. 相似文献
5.
The reaction of [N(PPh 3) 2] 2[Ni 6(CO) 12] with Cu(PPh 3) xCl ( x=1, 2), as well as the degradation of [N(PPh 3) 2] 2[H 2Ni 12(CO) 21] with PPh 3, affords the new and unstable dark orange–brown [N(PPh 3) 2] 2[Ni 9(CO) 16].THF salt in low yields. This salt has been characterized by a CCD X-ray diffraction determination, along with IR spectroscopy and elemental analysis. The close-packed two-layer metal core geometry of the [Ni 9(CO) 16] 2− dianion is directly related to that of the bimetallic [Ni 6Rh 3(CO) 17] 3− trianion and may be envisioned to be formally derived from the hcp three-layer geometry of [Ni 12(CO) 21] 4− by the substitution of one of the two outer [Ni 3(CO) 3(μ−CO) 3] 2− layers with a face-bridging carbonyl group. 相似文献
6.
Carbonylation of the anionic iridium(III) methyl complex, [MeIr(CO) 2I 3] − (1) is an important step in the new iridium-based process for acetic acid manufacture. A model study of the migratory insertion reactions of 1 with P-donor ligands is reported. Complex 1 reacts with phosphites to give neutral acetyl complexes, [Ir(COMe)(CO)I 2L 2] (L = P(OPh) 3 (2), P(OMe) 3 (3)). Complex 2 has been isolated and fully characterised from the reaction of Ph 4As[MeIr(CO) 2I 3] with AgBF 4 and P(OPh) 3; comparison of spectroscopic properties suggests an analogous formulation for 3. IR and 31P NMR spectroscopy indicate initial formation of unstable isomers of 2 which isomerise to the thermodynamic product with trans phosphite ligands. Kinetic measurements for the reactions of 1 with phosphites in CH 2Cl 2 show first order dependence on [1], only when the reactions are carried out in the presence of excess iodide. The rates exhibit a saturation dependence on [L] and are inhibited by iodide. The reactions are accelerated by addition of alcohols (e.g. 18× enhancement for L = P (OMe) 3 in 1:3 MeOH-CH 2Cl 2). A reaction mechanism is proposed which involves substitution of an iodide ligand by phosphite, prior to migratory CO insertion. The observed rate constants fit well to a rate law derived from this mechanism. Analysis of the kinetic data shows that k1, the rate constant for iodide dissociation, is independent of L, but is increased by a factor of 18 on adding 25% MeOH to CH 2Cl 2. Activation parameters for the k1 step are Δ H≠ = 71 (±3) kJ mol −, Δ S≠ = −81 (±9) J mol −1 K −1 in CH 2Cl 2 and Δ H≠ = 60(±4) kJ mol −1, Δ S≠ = −93(± 12) J mol −1 K −1 in 1:3 MeOH-CH 2Cl 2. Solvent assistance of the iodide dissociation step gives the observed rate enhancement in protic solvents. The mechanism is similar to that proposed for the carbonylation of 1. 相似文献
7.
The trinuclear complexes [Ag(PR 3) 2] 2[Ni(mnt) 2] and [AgL] 2[Ni(mnt) 2] have been prepared by reactions of (NEt 4) 2[Ni(mnt) 2] and Ag 2SO 4 with alkyl phosphines (PR 3=P(CH 3) 3 (PMe 3) for 1, P(C 2H 5) 3 (PEt 3) for 2 and P(C 6H 11) 3 (PCy 3) for 3), or with chelating diphosphines (L=1,1′-bis(diphenylphosphino)ferrocene (dppf) for 4 and bis(diphenylphosphino)methane (dppm) for 5). The structures of all the complexes have been determined by X-ray crystallography. Interactions between the [Ag(PR 3) 2] + and [Ni(mnt) 2] 2− groups occur in compounds 1 and 2 with Ni---Ag distances of 3.063(4) and 2.9311(6) Å, respectively. Only one sulfur atom of each mnt ligand bridged [Ag(PR 3) 2] + cations and [Ni(mnt) 2] 2− anions in compound 1 through 3 with Ag---S distances of about 2.7 Å. There is no interaction between Ag and Ni in compound 3 due to the flexibility of the cyclohexyl groups. Interactions between [AgL] + and [Ni(mnt) 2] 2− groups also occur in compound 4 with a much shorter Ag---Ni distance of 2.7213(7) Å, while silver atoms and the NiS 4 plane in compound 4 make a chair conformation with Ag---S distances of about 2.8 Å. In compound 5, dppm bridges two silver atoms, and interaction between silver atoms occurs at a distance of 2.9859(11) Å, and only one sulfur atom of mnt is used to bridge Ni and Ag atoms with Ag---S distances of 2.582(3) and 2.663(3) Å. 相似文献
8.
Analogy with the isolable oxo cluster [Fe 3(CO) 9(μ 3-O)] 2−, which is structurally interesting and synthetically useful, prompted the present attempt to synthesize its ruthenium analog. Although the high reactivity of [Ru 3(CO) 9(μ 3-O)] 2− (I) prevented its isolation, the reaction of this species with [M(CO) 3(NCCH 3)] +, where M = Mn or Re, yields [PPN][MRu 3(CO) 12(η 2-μ 3-NC(μ-O)CH 3] −. The high nucleophilicity of the oxo ligand in [Ru 3(CO) 9(μ 3-O)] 2− (I) appears to be responsible for the conversion of acetonitrile to an acetamidediato ligand and for the instability of I. The crystal structure of [PPN][MnRu 3(CO) 12(η 2-μ 3-NC(μ-O)CH 3)]] reveals a hinged butterfly array of metal atoms in which the acetamidediato ligand bridges the two wings with μ 3-N bonding to an Mn and two Ru atoms, and μ-O bonding to an Ru atom. 相似文献
9.
Cu aq+ forms stable complexes with carbon monoxide in aqueous solutions. Furthermore it reacts very fast with aliphatic radicals. The reaction of Cu(CO) maq+ with methyl radicals, •CH 3 was studied using the pulse-radiolysis technique. The results point out that methyl radicals react with Cu(CO) aq+ to form an unstable intermediate with a Cu II-C σ bond identified as (CO)Cu II-CH 3+, k = (1.1±0.2) × 10 9 M −1 s −1. This intermediate has a strong LMCT charge transfer band (λ max = 385 nm, max = 2500 M −1 cm −1) which is similar to the absorption bands of other transient complexes with Cu II-alkyl σ bonds. The coordinated carbon monoxide in (CO)Cu II-CH 3+ inserts into the copper—carbon bond (or rather the coordinated methyl migrates to the coordinated carbon monoxide ligand) at a rate of (3.0±0.8) × 10 2 s −1 to form the copperacetyl complex (CO) mCu II-C(CH 3)=O + (λ max = 480 nm, max = 2100 M −1 cm −1). The rate of formation of (CO)Cu II-CH 3+ and of the insertion reaction are pH independent. The complex (CO) mCu II-C(CH 3)=O + is also unstable and decomposes heterolytically to yield acetaldehyde and Cu aq2+ as the final stable products. This reaction is slightly pH dependent. The same reactivity pattern has been observed for the Cu(CO naq+ complexes ( n = 2 or 3). The results clearly point out that CO remains coordinated to transient complexes of the type Cu II-alkyl. 相似文献
10.
Manganese tricarbonyl complexes (η 5-C 5H 4CH 2CH 2Br)Mn(CO) 3 (3) and (η 5-C 5H 4CH 2CH 2I)Mn(CO) 3 (4), with an alkyl halide side chain attached to the cyclopentadienyl ligand, were synthesized as possible precursors to chelated alkyl halide manganese complexes. Photolysis of 3 or 4 in toluene, hexane or acetone-d 6 resulted in CO dissociation and intramolecular coordination of the alkyl halide to manganese to produce (η 5:η 1-C 5H 4CH 2CH 2Br)Mn(CO) 2 (5) and (η 5:η 1-C 5H 4CH 2CH 2I)Mn(CO) 2 (6). Low temperature NMR and IR spectroscopy established the structures of 5 and 6. Photolysis of 3 in a glass matrix at 91 K demonstrated CO release from manganese. Low temperature NMR spectroscopy established that the coordinated alkyl halide complexes are stable to approximately −20°C. 相似文献
11.
The reaction of meso-tetrakis (4-dimethoxyphenyl) porphinatomanganese(II), MnTP OMeP, with TCNE (TCNE = tetracyanoethylene) leads to the formation of [MnTP OMeP] + [TCNE] − and [MnTP OMeP] +[OC(CN)C(CN) 2] −. The single-crystal X-ray structures of the latter as well as [Cu(bipy) 2Cl] + [OC(CN)C(CN) 2] − were determined. The former has a disordered [OC(CN)C(CN) 2] − bridging via C and O between a pair of Mn III sites, whereas the latter has an isolated [OC(CN)C(CN) 2] − unbound to Cu II. The IR characterization for μ 2-C,O bound [OC(CN)C(CN) 2] − is at 2219m and 2196s (νCN) cm −1 and at 1558s (νCO) cm −1 while for unbound [OC(CN)C(CN) 2] − it is at 2210m, 2203m, 2181m (νCN) cm −1 and at 1583s (νCO) cm −1. 相似文献
12.
A series of tetrakis(trimethylsilylethyne) derivatives of Group 14 metals (2–4) was prepared. Co 2(CO) 6 complexes 5–10 were synthesised by the reaction of 2–4 with Co 2(CO) 8. From the silyl and germyl based compounds 2 and 3, either one or two alkynes could be complexed with Co 2(CO) 6. In contrast, the tin derived compound 4 could accommodate up to four Co 2(CO) 6 complexes. The longest wavelength UV-Vis absorbances of the silicon and germanium-based complexes were consistent with multiple, non-conjugated Co 2(CO) 6 chromophores. The tetrakis Co 2(CO) 6 complex 10, however, absorbs at a much longer wavelength suggesting conjugation of Co 2(CO) 6 complexes through the tin. The reactivity towards protonolysis of the uncomplexed alkynes 2–4 is a consequence of the hyperconjugative stabilisation of the intermediate β-vinyl cation (the β-effect): Sn(CCSiMe 3) 3>SnOTf(CCSiMe 3) 2>SiMe 3>Ge(CCSiMe 3) 3. The reactivity of the Co 2(CO) 6 complexes, however, was quite different from the reactions of 2–4 and from analogous all-carbon systems. Treatment of 5–10 with strong acid led neither to protiodemetallation of the complexed or non-complexed alkynes but to decomplexation of the cobalt. Similarly, ligand metathesis reactions between 10 and Ph 2SiCl 2 were not observed. The normal reactivity of silylalkynes towards electrophiles, which was expected to be enhanced by the presence of the cobalt complex, was diminished by the particular steric environment of the molecules under examination (5–10). As a result, the favoured reaction under these conditions was decomplexation of the cobalt. 相似文献
13.
Two new spin-crossover complexes, [Fe(Medpq)(py) 2(NCS) 2] · py · 0.5H 2O (1) and [Fe(Medpq)(py) 2(NCSe) 2] · py (2) (Medpq = 2-methyldipyrido[3,2- f:2′,3′- h]-quinoxaline, py = pyridine), have been synthesized. The crystal structures were determined at both room temperature (298 K) and low temperature (110 K). Complexes 1 and 2 crystallize in the orthorhombic space group Pbca and monoclinic space group P2 1/ n, respectively. In both complexes, the distorted [FeN 6] octahedron is formed by six nitrogen atoms from Medpq, the trans pyridine molecules and the cis NCX − groups. The thermal spin transition is accompanied by the shortening of the mean Fe–N distances by 0.194 Å for 2. The mononuclear [Fe(Medpq)(py) 2(NCS) 2] and [Fe(Medpq)(py) 2(NCSe) 2] neutral species interact each other via π-stacking, resulting in a one-dimensional extended structure for both 1 and 2. There exist C–HX (X = S, Se) hydrogen bonds for both complexes. Variable-temperature magnetic susceptibility measurements and Mössbauer spectroscopy reveal the occurrence of a gradual spin transition. The transitions are centered at T1/2 = 120 K for 1 and T1/2 = 180 K for 2, respectively. 相似文献
14.
Kinetic results are reported for intramolecular PPh 3 substitution reactions of Mo(CO) 2(η 1-L)(PPh 3) 2(SO 2) to form Mo(CO) 2(η 2-L)(PPh 3)(SO 2) (L = DMPE = (Me) 2PC 2H 4P(Me) 2 and dppe=Ph 2PC 2H 4PPh 2) in THF solvent, and for intermolecular SO 2 substitutions in Mo(CO) 3(η 2-L)(η 2-SO 2) (L = 2,2′-bipyridine, dppe) with phosphorus ligands in CH 2Cl 2 solvent. Activation parameters for intramolecular PPh 3 substitution reactions: Δ H≠ values are 12.3 kcal/mol for dmpe and 16.7 kcal/mol for dppe; Δ S≠ values are −30.3 cal/mol K for dmpe and −16.4 cal/mol K for dppe. These results are consistent with an intramolecular associative mechanism. Substitutions of SO 2 in MO(CO) 3(η 2-L)(η 2-SO 2) complexes proceed by both dissociative and associative mechanisms. The facile associative pathways for the reactions are discussed in terms of the ability of SO 2 to accept a pair of electrons from the metal, with its bonding transformations of η 2-SO 2 to η 1-pyramidal SO 2, maintaining a stable 18-e count for the complex in its reaction transition state. The structure of Mo(CO) 2(dmpe)(PPh 3)(SO 2) was determined crystallographically: P2 1/ c, A=9.311(1), B = 16.344(2), C = 18.830(2) Å, ß=91.04(1)°, V=2865.1(7) Å 3, Z=4, R( F)=3.49%. 相似文献
15.
The reactions of various proton donors (phenol, hexafluoro-2-propanol, perfluoro-2-methyl-2-propanol, monochloroacetic acid, and tetrafluoroboric acid) with the rhenium (I) hydride complex [(triphos)Re(CO) 2H] (1) have been studied in dichloromethane solution by in situ IR and NMR spectroscopy. The proton donors from [(triphos)Re(CO) 2H…HOR] adducts exhibiting rather strong H…H interactions. The enthalpy variations associated with the formation of the H-bonds (−Δ H = 4.4–6.0 kcal mol −1) have been determined by IR spectroscopy, while the H…H distance in the adduct [(triphos)Re(CO) 2H…HOC(CF 3) 3] (1.83 Å) has been calculated by NMR spectroscopy through the determination of the T1min relaxation time of the Re---H proton. It has been shown that the [(triphos)Re(CO) 2H…HOR] adducts are in equilibrium with the dihydrogen complex [(triphos)Re(CO) 2(η 2-H 2)] +, which is thermodynamically more stable than any H-bond adduct. 相似文献
16.
The thermolysis of trans-IrL 2(CO)Cl(H)(C 6H 5) (1abd; L=P(i-Pr) 3; H trans to CO) produces benzene and the Vaska-type complex IrL 2(CO)Cl. A mechanistic study of the reaction has shown that 1a reversibly loses CO at 120 °C (as evidenced by the incorporation of 13CO) and isomerizes to the previously unreported 1b (H trans to Cl). It was found that 1b is the complex primarily responsible for the formation of benzene upon thermolysis under CO atmosphere; direct loss of benzene from 1a was determined to be, at most, a minor pathway. Benzaldehyde was also formed as a product of thermolysis of 1a under CO atmosphere. The first-order rate constant for benzene elimination in the absence of CO was found to be 8.5 × 10 −5 s −1. The presence of only 5 Torr CO results in a decrease to 2.0 × 10 −5 s −1, but little further inhibition is observed above 5 Torr CO. Added dihydrogen (100 Torr) was found to effect a novel catalysis of benzene elimination from 1a in the absence of CO atmosphere; it is suggested that trace amounts of dihydrogen, present in solutions of 1a, are responsible for the enhanced rate of elimination in the absence of CO. The thermolysis of 1-d 6 in toluene was found to proceed without any toluene incorporation, implying that arene loss is irreversible. 相似文献
17.
The solution of [RhCl(PPh 3) 3] in acidic 1-ethyl-3-methylimidazolium chloroaluminate(III) ionic liquid (AlCl 3 molar fraction, xAlCl3=0.67) was investigated by 1H and 31P{ 1H} NMR. One triphenyl phosphine is lost from the complex and is protonated in the acidic media, and cis-[Rh(PPh 3) 2ClX], (2), where X is probably [AlCl 4] −, is formed. On, standing, 2 is converted to trans-[Rh(H)(PPh 3) 2X], (3). The reaction of 2 and H 2 also produces trans-[Rh(H)(PPh 3) 2X], (3). 1H and 31P{ 1H} NMR support the suggestion that a weak ligand such as [AlCl 4] −, present in solution may interact with the metal centre. When [RhCl(PPh 3) 3] is dissolved in CH 2Cl 2/AlCl 3/HCl for comparison, two exchanging isomers of what is probably [RhH{(μ-Cl) 2AlCl 2}{(μ-Cl)AlCl 3}(PPh 3) 2], (6) and (7), are formed. 相似文献
18.
Kinetic studies of the addition of a wide range of tertiary phosphines and phosphites to the tropylium ring of the cation [Cr(CO) 3(η 7-C 7H 7] + (1) reveal the two-term raw, kobs = k1[PR 3] + k−1. This is consistent with the reversible equilibrium process (i) which is also confirmed from IR and 1H NMR studies. In the case of the highly basic nucleophiles PBu 3n and PEt 2Ph, the rate is dominated by the k1 term and the equilibrium lies far to the right. The first-order rate constants k1, for addition to the tropylium ring decrease markedly down the series PBu 3n>PEt 2Ph>P(4-MeOC 6H 4) 3>P(4-MeC 6H 4) 3>P(C 6H 11 3>PPh 2(4-MeC 6H 4)>PPh 3>P(2-CNC 2H 4) 3>P(OBu n) 3 (overall variation 10 4). This reactivity order parallels the decreasing electron availability at the phosphorus centres, as confirmed by the linear correlation between log k1 and the Tolman Σ χ values for the nucleophiles. Excellent Hammett and Brønsted correlations are also observed for ring addition by a range of P(4-XC 6H 4) 3 nucleophiles. The Brønsted slope, , of 0.7 conirms the major importance of basicity in determining nucleophilicity towards cation 1. Kinetic studies of the related additions of PBu 3n to the cations [M(CO) 3(η 7-C 7H 7] + (M = Mo, W) reveal the rate law, Rate = k1[M][PBu 3n, and show only a small dependence of k1 on the nature of metal (Cr>WMo; 2:1.1:1). These data, together with the associated activation parameters, support a mechanism involving direct addition ( k1) of the phosphorus nucleophiles to the tropylium ring, and are inconsistent with initial rate-determining attack at the metal centre. 相似文献
19.
The reactions of [(H 5C 6) 3P] 2ReH 6− with (CH 3CN) 3Cr(CO) 3, (diglyme)Mo(CO) 3 or (C 3H 7CN) 3W(CO) 3 led to the formation of [(H 5C 6) 3P] 2ReH 6M(CO) 3− (M = Cr, Mo, W) complexes. These have been characterized by IR and NMR spectroscopies, as well as elemental analyses. A single crystal X-ray diffraction study has also been carried out for the M = Cr complex as a K(18-crown-6) + salt. The complex crystallizes as a THF monosolvate in the monoclinic space group P2 1/ n with a = 22.323(6), B = 9.523(2), C = 27.502(5) Å, β = 104.98(2) 0 and V = 5648 Å 3 for Z = 4. The Re---Cr separation is 2.5745(12) Å, and the two phosphine ligands are oriented unsymmetrically. Although the hydride ligands were not found, the presence of three bridging hydrides and a dodecahedral coordination geometry about rhenium could be inferred. Low temperature 1H and 31P NMR spectroscopic studies did not reveal the low symmetry of the solid state structure. 相似文献
20.
The kinetics and equilibria of complex formation by Ga(III) with NCS − in aqueous solution have been measured over a range of acidities and temperatures, the contributing paths to the reaction resolved, and their rate constants and activation parameters determined. The hydrolysis equilibria required to carry out this resolution of kinetic behaviour have also been measured. Unlike the other reported complexation reactions of Ga(III) in aqueous solution, the separate reaction pathways can be assigned with no ambiguity. At 25 °C and ionic strength 0.5 M, the observed forward rate constant for the complex formation is described by {k1 + k2K1h/[H+] + k3K1hK2h/[H+]2} M−1 s−1. For these conditions, the first and second successive hydrolysis constants of Ga(H2O)63+ are given by pK1h = 3.69 ± 0.01 and pK2h = 3.74 ± 0.04. The rate constants corresponding to the reactions of the species Ga(H2O)63+, Ga(H2O)5(OH)2+ and Ga(H2O)4(OH)2+ with NCS− are k1 = 57 ± 4 M−1 −1, k2 = (1.08 ± 0.01) × 105 M−1 s−1 and k3 = 3 × 106 M−1 s−1 respectively. The complexation equilibrium quotient [GaNCS2+]/([Ga3+][NCS−]) has been independently determined by spectrophotometric titration to be 20.8 ± 0.3 M−1 at 25 °C and ionic strength 0.5 M. These kinetic results lead to an interpretation of the data, and a reinterpretation of other data for aquo-Ga(III) complex formation kinetics from the literature which support the assignment of a dissociative interchange mechanism for these reactions rather than the associative activation mode sometimes proposed. 相似文献
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