M. R. H. Siddiqui

Thermodynamics of homogeneous hydrogenation: Part III. Oxidative addition of H2 to Rh(I) complexes: correlation of dihydrides structure to the thermodynamics of the catalysed homogeneous hydrogenation of cyclohexane

Abstract The oxidative addition of H2 to the Rh(I) chelates RhCl(PPh3)31, [RhCl(diphos)]22 and RhCl(NP2) (NP2 = H-N(CH2CH2PPh2)2 proceeds at 30 °C and 1 atm of molecular hydrogen in ethanol-benzene with the formation of exclusively cis-dihydride products elucidated by their proton and 31P {1H} NMR spectra in situ. Complex 1 affords the cis-dihydrides RhCl-(H)2 (PPh3)2(S) 1a and RhCl(H)2(PPh3)31b with the preponderance of 1a over 1b. Complex 2 dissociates in solution to form an active RhCl(diphos)(S) species which oxidatively adds H2 to form the isomeric dihydrido complexes RhCl(diphos)(H)2(S) 2a – 2c. Complex 2a is the kinetically controlled dihydride isomer with both H−trans to P, whereas 2b and 2c are more stable isomers with the hydrides trans to P and (S) in 2b and P and (Cl) in 2c, respectively. Complex 2a is completely converted to 2b + 2c in about 24 h. Complex 3 afford the most stable mer-Rh(NP2)Cl(H)23a with H−trans to N and (Cl). The less stable fac-Rh(NP2)Cl(H)23c species in which one H− is trans to P and the other to N and the least stable 3b where both H− are trans to P. The homogeneous hydrogenation of cyclohexene catalyzed by complexes 1 – 3 was investigated in the temperature range 10 – 40 °C at 0.6 – 1 atm of hydrogen partial pressure. Thermodynamic parameters for the formation of the dihydrido complexes of 1, 2 and 3 and the monoolefin complexes of Rh(I) were computed. The activation parameters corresponding to the rate constant k for the homogeneous hydrogenation of cyclohexene were also calculated. The enthalpy of formation of the dihydrido complexes ΔH0 is more favourable (exothermic) for those hydrido species where there are minimal changes in the configuration of the dihydrido complex in oxidative addition reaction. The enthalpies ΔH0 increase in the order 3

Nitrosyl ethylenediaminetetraacetato ruthemium(III) — an efficient oxygen atom transfer agent for the oxidation of olefins by molecular O2 and PhIO through ligand-mediated nitrosyl/nitro couple

The complexes [RuIII(EDTA—H)NO]BF4 1 and [RuIII(EDTA)(NO)] 1a were synthesized and characterised by elemental analysis, IR and UV—Vis spectroscopy, conductivity, magnetic susceptibility, EPR and electrochemical studies. Complex 1a catalyses the oxidation by molecular oxygen of 1-hexene to 2-hexanone and cyclohexene to cyclohexene oxide through the ligand-mediated RuIII—EDTA—NO 1a/Ruv—EDTA—NO2 2 oxygen atom transfer. The oxidation reactions were studied in 7:3 ethanol—water medium in the temperature range 30–45 °C (μ=0.1 M KCl). The oxidation of 1-hexene and cyclohexene proceeds with a turnover number of 50 and 44 moles product per mole catalyst per hour. The rate of oxidation is first order with respect to catalyst concentration and one-half order with respect to molecular oxygen concentration. At higher substrate concentrations, the reaction rate was found to be independent of substrate concentration. 18O2 studies indicate that the source of O atom transferred to the substrate is from molecular O2. The formation of an organometallic metallocyclic intermediate is proposed for the reaction. The rate of oxygenation of cyclohexene by iodosyl benzene catalyzed by 1a was found to be identical with that obtained with O2 as oxidant. The rate of oxygenation of 1a to 2 was studied independently by an O atom transfer from iodosyl benzene.

Formation of a rhodium(II) monohydrido complex derived from wilkinson's complex RhCl(PPh3)3 in the interlamellar spaces of montmorillonite and catalytic hydrogenation of cyclohexene

Abstract The interaction of molecular hydrogen with [Rh(PPh 3 ) 3 ] + ( 1a ) “immobilized” in the interlamellar spaces of montmorillonite resulted in the formation of a monohydrido complex, [Rh II H(PPh 3 ) 3 ] ( 2a ), characterized by electrochemical data of the clay-loaded electrode, IR, EPR and hydrogen absorption studies. Heterogenized homogeneous catalytic hydrogenation of cyclohexene catalysed by 1a was investigated in the temperature range 283–313 K. The order of reaction with respect to cyclohexene and hydrogen concentration is fractional and first order with respect to catalyst concentration. Thermodynamic parameters Δ H 0 and Δ S 0 corresponding to the formation of the monohydrido species were found to be 18 kcal mol −1 and 61 e.u., respectively. The activation enthalpy, Δ H ‡ , and entropy, Δ S ‡ , for the hydrogenation of cyclohexene by the Rh II —H complex in clay are more negative by about 2 kcal mol −1 and 7 e.u. compared to Wilkinsons catalyst, RhCl(PPh 3 ) 3 ( 1 ), in homogeneous solution.

Azido(η5-cyclopentadienyl)bis(triphenylphosphine)ruthenium(II)

The molecule [RuN 3 (C 5 H 5 ){P(C 6 H 5 ) 3 } 2 ] has a typical three-legged-piano-stool geometry; Ru-Cp o (where Cp o is the centre of the ring) is 1.843 (3) A, the three legs are 2.3293 (5) and 2.3304 (5) (Ru-P) and 2.135 (3) A (Ru-N) in length while the angles are P-Ru-P 105.22 (2), P-Ru-N 85.39 (6) and 86.65 (5) o . The azide group is almost linear [N-N-N 175.2(3)°] and is coordinated to Ru with an Ru-N-N angle of 124.5(2)°; there is a small difference between the N-N distances [1.186(3) and 1.164(3)A], the longer being adjacent to the Ru atom

Oxidation of tertiary phosphines by molecular oxygen catalysed by RuIII-EDTA complex. Electronic effect of phosphine substituent on the oxygen atom transfer reaction; X-ray crystal structure of the complex [RuIII(EDTA-H)PPh3]

Abstract The catalytic oxidation of tertiary phosphines, PR 3 (R = p -fluorophenyl, phenyl and cyclohexyl), by molecular oxygen to the corresponding phosphine oxide, (PR 3 O), catalysed by Ru III (EDTA-H)(H 2 O) is reported as a function of catalyst, substrate (PR 3 ) and molecular oxygen concentration at a constant pH 3.0 in water-dioxan (50% v/v) medium. The reactivity of PR 3 towards catalytic oxidation by molecular oxygen decreases in the order tris( p -fluorophenyl)phosphine triphenylphosphine tris-(cyclohexyl)-phosphine. A reverse reactivity order was observed in the case of stoichiometric oxidation of PR 3 by [Oue5fbRu V (EDTA)] − . The proposed mixed-ligand complex Ru III -EDTA-PR 3 intermediate in the catalytic oxidation of PR 3 with molecular oxygen has been isolated and its structure solved by single-crystal X-ray diffraction. The experimental results are discussed in terms of the σ-basic and π-acidic character of the phosphine substrates in the homolytic bond cleavage of Oue5f8O bonds of the μ-peroxo intermediate and oxygen atom transfer to the substrate. The bond dissociation energy for Oue5f8O bond cleavage is computed by the kinetic data obtained for oxygen atom transfer from the oxo complex [Oue5fbRu V (EDTA)] − .

Thermodynamics of homogeneous hydrogenation: Part VIII. effects of secondary ligand on the catalytic properties in the homogeneous hydrogenation of cyclohexene by some water soluble ruthenium complexes

Homogeneous catalytic hydrogenation of cyclohexene catalyzed by Na[Ru(EDTA-H)N3]·2H2O 1 and [Ru(EDTA-H)NO]BF42 was investigated in the temperature range 283–313 K at 0.4 to 1 atm of hydrogen partial pressure in a 7:3 alcohol-water mixture. The dependence of the rate of hydrogenation on factors such as catalyst concentration, cyclohexene concentration, hydrogen partial pressure and temperature is reported. Kinetic investigations reveal a non-linear dependence of rate on cyclohexene and molecular hydrogen concentration, and a first-order dependence on the catalyst concentration. Based on the kinetic data, a mechanism for the homogeneous catalytic hydrogenation has been proposed. Thermodynamic parameters corresponding to the formation of the monohydrido and monoolefin complexes were computed. The activation parameters corresponding to the rate constants k1 and k2 for the homogeneous hydrogenation of cyclohexene were also calculated. n nThe enthalpy of the formation of hydrido and olefin complexes decreases with an increase in the π-acidity of the coordinated secondary ligand. The large positive value of entropies for the hydride and olefin complex formations indicates that the reaction mechanism is dissociative, in accord with the removal of a coordinated carboxylate group of EDTA from the coordination sphere of the metal ion to make way for H− or olefin. n nA ligand constant PL for the secondary ligands in the complexes [Ru(EDTA—H)X]n− was calculated from the redox potential values E12 for the RuIIIRuII couple in the complexes. Taking the E12 value of [Ru(EDTA—H)(H2O)] as standard, the PL values for other π-acidic substituents were calculated by subtracting E12(H2O) from E12(X). The values of PL increase with an increase in the π-acidity of the ligand in the order N3− < H2O< PPh3 < NO < CO < SnCl3− < olefin. The catalytic activity of the complexes [Ru(EDTA—H)X]n− increases with an increase in the π-acidity of the secondary ligand. The hydride proton NMR signals of the [Ru(EDTA—H2)(H)(X)]n− hydrides shift further downfield with the positive value of PL.

Thermodynamics of homogeneous hydrogenation: Part VII. Thermodynamics of the homogeneous hydrogenation of cyclohexene catalyzed by some water-soluble ruthenium complexes containing π-acidic ligands

Abstract The complexes K[Ru(EDTA-H)Cl]2H2O 1, [Ru(EDTA-H)(PPh3)] 2, K[Ru(EDTA-H)(CO)] 3 and K[Ru(EDTA-H)(SnCl3-)] 4 activate molecular hydrogen at 30 °C and 1 atm H2 in 7:3 alcoholrwater mixture by heterolytic cleavage of the H-H bond to form the thermodynamically stable hydrido complexes [Ru(EDTA-H)(H)]2−5, [Ru(EDTA-H)(PPh3)(H)]2−6, [Ru(EDTA-H)(CO)(H)]2−7 and [RutEDTA-H)(SnCl3−(H)]3−8 in solution characterized by their proton NMR in situ. Complexes 6–8 form isomeric hydrides where H iscis or trans to the π-acidic group L (L = PPh3, CO, SnCl3−), the cis species being predominant in solution. The hydrido proton peaks in complexes 5 – 8 shift downfield in the order 4 > 3 > 2 > 1, in accord with the decreasing π-acidity of the coordinated group. The homogeneous hydrogenation of cyclohexene catalyzed by complexes 1 – 4 was investigated in the temperature range 10 – 40 °C at 0.4–1 atm of H2 partial pressure. Thermodynamic parameters corresponding to the formation of the monohydrido complexes 5–8 and the monoolefin complexes 1 – 5 were computed. The activation parameters corresponding to the rate constants K1 and K2 for the homogeneous hydrogenation of cyclohexene were also calculated. The enthalpy of the formation of hydrido and olefin complexes decreases with an increase in the π-acidity of the coordinated ligand. The entropies of the hydride and olefin complex formation are large positive numbers, indicating either the dissociation of a Cl− from the coordination sphere of the metal ion in 1, or removal of a coordinated carboxylate group from the coordination positions of EDTA to accommodate H− or olefin. The catalytic activity of complexes 1 – 4 decreases in the order 4 >3 >2 >1, in line with the decreasing π-acidity of the secondary group L coordinated to Ru(II). The thermodynamic parameters corresponding to the steps K1 and K2 show small exothermic values for ΔH‡ and large negative values for ΔS‡. The slow step K1 is the predominant step for the catalytic transfer of hydride proton to the olefin. There is a correlation between ΔH‡ of path A (K1) , ΔH0 of hydride formation and ΔS‡ and the hydride proton shift δ (ppm), indicating the involvement of the hydride in the rate-determining step.

Structure of potassium dichloro(ethylenediaminetetraacetato)ruthenate(III)

K[Ru(C 10 H 14 N 2 O 8 )Cl 2 ] cristallise dans P2 1 /n avec a = 10,4470, b = 13,947 et c = 11,296 A, β = 106,10 °, Z = 4; affinement jusqu a R = 0,030. Coordination tetraedrique autour de Ru. La structure presente un desordre. Elle est stabilisee par des interactions entre les ions potassium, les anions complexes et un reseau de liaisons hydrogene O-H...O.

Role of jasmonic acid in improving tolerance of rapeseed ( Brassica napus L.) to Cd toxicity

The well-known detrimental effects of cadmium (Cd) on plants are chloroplast destruction, photosynthetic pigment inhibition, imbalance of essential plant nutrients, and membrane damage. Jasmonic acid (JA) is an alleviator against different stresses such as salinity and drought. However, the functional attributes of JA in plants such as the interactive effects of JA application and Cd on rapeseed in response to heavy metal stress remain unclear. JA at 50 μmol/L was observed in literature to have senescence effects in plants. In the present study, 25 μmol/L JA is observed to be a “stress ameliorating molecule” by improving the tolerance of rapeseed plants to Cd toxicity. JA reduces the Cd uptake in the leaves, thereby reducing membrane damage and malondialdehyde content and increasing the essential nutrient uptake. Furthermore, JA shields the chloroplast against the damaging effects of Cd, thereby increasing gas exchange and photosynthetic pigments. Moreover, JA modulates the antioxidant enzyme activity to strengthen the internal defense system. Our results demonstrate the function of JA in alleviating Cd toxicity and its underlying mechanism. Moreover, JA attenuates the damage of Cd to plants. This study enriches our knowledge regarding the use of and protection provided by JA in Cd stress.概要目的本研究目的在于了解:(1)喷施外源茉莉酸对受 到镉胁迫油菜的作用;(2)是否茉莉酸能够通过增强气体交换,从而保护受到氧化胁迫的地上部分组织的叶绿体,进而通过减少镉的吸收来维持 离子平衡;(3)是否通过喷施茉莉酸来对具有减 缓镉毒害效应的抗氧化酶的活性进行调节。创新点茉莉酸能够调节响应胁迫的抗氧化酶的活性,从而通过保护叶绿体免受活性氧(ROS)伤害而提高光合产物的能力,最大限度地缓解油菜植株受到的镉毒害。方法(1)叶片气体交换;(2)叶片光合色素分析;(3) 丙二醛与抗氧化酶活性分析;(4)营养成分分析; (5)透射电镜亚细胞水平观察。结论茉莉酸对于植物受镉毒害的缓解作用的机理在于减少叶片中镉的积累,从而减轻氧化胁迫过程中产生的ROS 对于膜系统的损害程度。