CH3CN H2O Research Articles

Preparations, NMR Spectra, and Electrochemical Properties of a (Ferrocenylcarbonyl)palladium(II) Complex and Its Derivatives with Some Chelate Groups Attached via Two Ligating Nitrogen Atoms

Abstract Oxidative addition of (chloroformyl)ferrocene to [Pd(PPh3)4] yielded a stable acylpalladium(II) compound of [Pd(COFc)Cl(PPh3)2] (1), (Fc=ferrocenyl). Complex 1 was treated with alkali metal salts of poly(1-pyrazolyl)borates (HnBPz4−n), (Pz=1-pyrazolyl) to give complexes [Pd(COFc)(HnBPz4−n)(PPh3)], (2, n=0; 3, n=1; and 4, n=2), which retained the palladium-attached ferrocenylcarbonyl structure. Reaction of 1 with 1,10-phenanthroline (phen) afforded [Pd(COFc)Cl(phen)], whereas reaction with 2,2′-bipyridine gave [{Pd(COFc)Cl(PPh3)}2] as an isolable material. Transformation of the ferrocenylcarbonyl moiety took place to the ferrocenyl group on palladium, in chlorine-abstraction from 1 with AgClO4·H2O in CH3CN. In the temperature-dependent 1H-NMR spectra, fluxional behavior was observed for the poly(1-pyrazolyl)borate groups in 2 and 3. Electrochemical experiments were carried out for 1–4 in CH3CN using platinum working electrodes, and reversible one-electron redox-couples were detected, which were attributed to the process Fe(II)\ightleftarrowsFe(III) in the ferrocenyl moiety. Furthermore, electron-withdrawing effects of the [poly(1-pyrazolyl)borato]palladiocarbonyl moieties from the Fe centers were compared among these complexes, in relation to their redox potentials.

Enantioselective catalysis of deacylation of p-nitrophenyl N-acylphenyl-alanates by mixed micelles composed of Nα-hexadecanoyl-L-histidine and a cationic surfactant

The deacylation of p-nitrophenyl N-acyl-L- and -D-phenylalanates (acyl = acetyl, decanoyl, and hexadecanoyl) with the co-micellar system composed of Nα-hexadecanoyl-L-histidine and octadecyltrimethylammonium chloride was investigated for the 20–35 °C range in CH3CN–H2O (3 : 97 v/v). The enantioselective properties of the co-micellar system effective for the deacylation of such substrates were investigated in the light of substrate-binding properties, activation parameters, and kinetic salt and organic co-solvent effects. Kinetic enantioselectivity is exclusively favoured for the L-substrates, even though the binding constants for the D-isomers are greater than those for the corresponding L-isomers in most cases. The highest enantioselectivity in terms of the apparent second-orde rate ratio (ka, obsL/ka, obsD) is 4.7 as observed for the deacylation of p-nitrophenyl N-decanoyl-L- and -D-phenylalanate at 20 °C and pH 7.6.

A Raman Spectral Study of the Kinetics of Hydrolysis of Acetonitrile Catalyzed by Hg(II)

Raman spectroscopy has been employed to follow the relatively slow rate of hydrolysis of acetonitrile, catalyzed by mercury(II). Raman lines at 2275 and 2305 cm−1 are characteristic of CH3CN bound to Hg2+, and are distinct from lines of bulk solvent. The intensities of these new lines decrease with time. From the intensities, concentrations of bound acetonitrile, [CH3CN]B were calculated for a time span of 400 min. The data fit a second order rate law: Rate = k[CH3CN]B[H2O]. The specific rate constant, k, obtained from four sets of data for the system Hg(ClO4)2–CH3CN–H2O equals 1.05 ± 0.06 × 10−4 mol−1 1 min−1 at 25 °C. The energy of activation is 18.9 kcal mol−1. In the proposed mechanism water molecules attack acetonitrile molecules which are bound to Hg2+ and form a mercury(II)–acetamide complex. Raman lines characteristic of this species are observed. This species slowly converts to mercury(II) ammine complexes and acetic acid. Anions which coordinate with Hg2+ more strongly than CH3CN, such as nitrate or acetate, slow or prevent the hydrolysis reaction.

The Reaction of the Hydroxamic Acid Group in Polymer with p-Nitrophenyl Acetate

Abstract Water-soluble copolymers containing protected hydroxamate groups were prepared by radical copolymerization of acetyl N-phenylacrylohydroxamate and acrylamide, and the hydroxamic acid group (PHA) was unmasked by treating it with hydroxylamine. In acetylation with p-nitrophenyl acetate (1.4 v/v% CH3CN–H2O, 30 °C) the PHA unit was less reactive than the corresponding monomeric compound. When the PHA content was low (3 mol%), the reactivity of a given PHA anion (true reacting species) was invariant (9.1 M−1 S−1) over a wide range of the dissociation of the PHA unit. However, in the case of the copolymer of a higher PHA content (11 mol%) the reactivity decreased as the neutralization of the PHA anion progressed. This phenomenon was attributed to the intramolecular aggregation of the undissociated PHA side chain. The deacylation rate of the acetylated PHA unit was comparable to those of the monomeric counterparts, in contrast with the acylation process. Finally, the probable role of the PHA unit as catalyst for the ester hydrolysis was discussed.