Norman Govan

A metallomicelle catalysed hydrolysis of a phosphate triester, a phosphonate diester and O-isopropyl methylfluorophosphonate (Sarin)

Abstract A metallomicelle based on the copper(II) complex of N,N,N′ -trimethyl-W-tetradecylethylenediamine is shown to be an excellent catalyst for the hydrolysis of 2,4-dinitrophenyl diethyl phosphate (DNPDEP), 2,4-dinitrophenyl ethyl methylphosphonate (DNPEMP) and O -isopropyl methylfluorophosphonate (Sarin). At pH 8 and35 °C the hydrolysis of DNPDEP is accelerated by 1.3 × 10 5 fold, while that of of DNPEMP is increased by 6.6 × 10 4 fold. The micelle is also an active catalyst for the hydrolysis of the nerve agent Sarin. A mechanism involving binding of the phosphoryl oxygen to copper(II) and intramolecular attack by coordinated hydroxide at the phosphorus centre is consistent with the kinetic data.

A lanthanum macrocycle catalysed hydrolysis of 2,4-dinitrophenyl diethyl phosphate and O-isopropyl methylfluorophosphote (Sarin)

Abstract The lanthanum complex of a hexa-aza macrocycle is shown to be an effective catalyst for the hydrolysis of the water soluble phosphate triester 2,4-dinitrophenyl diethyl phosphate. At pH 9, using a catalyst concentration of 2.5 × 10 −3 mol dm −3 at 25°C, the rate enhancement is ca 10 3 fold. The reaction is shown to be catalytic rather than stoichiometric and possible mechanisms involving a metal-bound hydroxide nucleophile are considered to account for the catalysis. The macrocyclic complex is alswn to be an effective catalyst for the hydrolysis of the anticholinesterase agent O-isopropyl methylfluorophosphate (Sarin).

The [CoN4(OH)(OH2)]2+ (N4 = trpn, cyclen and tren) promoted hydrolysis of the phosphotriester 2,4–dinitrophenyl diethyl phosphate

The [CoL(OH2)2]3+ (L=trpn, cyclen and␣tren)␣promoted hydrolysis of the phosphotriester 2,4–dinitrophenyl diethyl phosphate to give diethyl phosphate and 2,4–dinitrophenolate has been studied in detail over the pH range 3–7.5. The pK values of the various complexes have been determined at 25°C and I=0.1moldm−3 by potentiometric titration. The pH-rate profiles for the reactions are consistent with the hydroxoaqua complex [CoL(OH)(OH2)]2+ being the active species in the hydrolysis. No evidence for saturation kinetics was obtained and values of kcat determined at pH 7 and 25°C (I=0.1moldm−3) are 4.24×10−3dm3mol−1 s−1 (tren)<3.05×10−2dm3mol−1 s−1 (cyclen)<7.5 × 10−1dm3mol−1s−1 (trpn). Studies involving the more reactive phosphonate ester 2,4–dinitrophenyl ethyl methylphosphonate suggest that the rate-determining step in the reaction is the decomposition of the ternary complex between the cobalt(III) complex and the phosphotriester. The rate enhancement using 0.01mol dm−3 Co(trpn)3+ is some 4.6×104 fold at pH␣7 and 25°C.

The [Cu([9]aneN3)(OH)(OH2)]+ catalysed hydrolysis of the phosphotriester 2,4-dinitrophenyl diethyl phosphate ([9]aneN3 = 1,4,7-triazacyclononane)

Abstract The hydrolysis of the phosphotriester 2,4-dinitrophenyl diethyl phosphate to diethyl phosphate is catalysed by the macrocyclic complex [Cu([9]aneN3)(OH2)2]2+ ([9]aneN3 = 1,4,7-triazacyclononane). The pH dependence of the hydrolysis over the pH range 6.2 to 8.7 establishes that the active catalyst is the hydroxoaqua complex. The pK for the equilibrium [Cu([9]aneN3)(OH2)2]2+ ⇌ [Cu([9]aneN3)(OH)(OH2)]+ + H+ determined by potentiometric titration is 7.5 at 35°C and I = 0.1 mol dm−3 so that catalysis at pH values close to neutrality is observed. Hydrolysis occurs by intramolecular attack of coordinated hydroxide on the phosphate triester which is bonded via the phosphoryl oxygen to the copper centre.

The reactivity of metal-hydroxo nucleophiles and a range of bases in the hydrolysis of the phosphate triester 2,4-dinitrophenyl diethyl phosphate

Abstract The reaction of 16 different nucleophiles with the water-soluble phosphate triester, 2,4-dinitrophenyl diethyl phosphate (1 = DNPDEP) has been studied at 35°C and I = 0.1 mol dm −3 (KNO 3 ). The nucleophiles studied included a number of metal-hydroxo complexes, such as [M(NH 3 ) 5 OH] 2+ (M = Co III , Cr III ), the macrocyclic complexes [Zn(CR)OH] + , [Co([15]aneN 5 )OH] 2+ , and the hydroxoaqua complex [Cu (tmen) (OH)(OH 2 )] + (tmen = N, N, N′,N′-tetramethylethylenediamine). The Bronsted plot of log k n versus p K a shows good linearity with a slope β of 0.39. The monohydroxo complexes lie on the line, but the hydroxo-aqua complex shows enhanced reactivity due to intramolecular hydrolysis taking place.

The [Cu(tmen) (OH) (OH2)]+ promoted hydrolysis of 2,4-dinitrophenyl diethyl phosphate and O-isopropyl methylphosphonofluoridate (Sarin) (tmen = N,N,N′,N′-tetramethyl-1,2-diaminoethane)

Abstract The hydrolysis of the phosphate triester 2,4-dinitrophenyl diethyl phosphate to diethyl phosphate is catalysed by [Cu(tmen)(OH)(OH2)]+ in the pH range 6.5 to 8.0. At pH 7 with a catalyst concentration of 2.5 × 10−3 mol dm−3 the rate enhancement is ca 104 fold. The pH dependence of the catalysis is consistent with the hydroxoaqua complex being the active species in the hydrolysis. The greater kinetic effectiveness of this weak base, compared with hydroxide ion on a molar basis, indicates a bifunctional mechanism in which bound hydroxide acts as a nucleophile in conjunction with electrophilic catalysis by copper at the phosphoryl oxygen. The copper complex is an excellent catalyst for the hydrolysis of O-isopropyl methylphosphonofluoridate (Sarin). At pH 7 and 25°C using a Sarin concentration of 4.5 × 10−2 mol dm−3 and a [Cu(tmen)(OH2)2]2+ concentration of 5 × 10−3 mol dm−3, complete hydrolysis (9 turnovers) occurs in 13 min.

Preparation ofcis-folded macrocyclic nickel(II) complexes of C-racemic-5,12-dimethylcyclam and kinetics of the base-catalysed conversion to the planar species

SummaryThe preparations of the violet foldedcis-macrocyclic complexes [NiL(en)](ClO4)2 and [NiLBr2] (L=C-racemic-5,12-dimethylcyclam) are described. Rapid isomerisation of these complexes occurs in basic solution to give an equilibrium mixture of planar [NiL]2+ andtrans-[NiL(OH2)2]2+. Kinetic studies establish that for these interconversions rate=kOH[Complex][OH−], with kOH=7.7×102M−1 s−1 at 25° C and I=0.1 M. The temperature dependence of kOH gives ΔH≠=26.8kJ mol−1 and ΔS298≠=−99JK−1 mol−1. The mechanism of the reaction is discussed.

Selective manganese(III) and vanadium(IV) catalysts for the oxidation of dialkyl sulfides in microemulsion media

The oxidation of n-Bu2S by t-BuOOH in the presence of␣the catalysts [Mn2L2(MeCO2)2 (μ-O)] (ClO4)2 (L= Me3tacn=1,4,7–trimethyl-1,4,7–triazacyclononane) and VO(acac)2 has been studied using microemulsion media (BRIJ 97 and SD2 microemulsions). In the presence of the MnIII complex oxidation to the sulfone occurs, while in the presence of the VIV complex the sulfide is oxidised to the sulfoxide. The oxidation of mustard gas, (ClCH2CH2)2S, has also been studied. The reactions have been monitored by total internal reflectance i.r. spectroscopy. The use of optically transparent microemulsions provides a useful method for carrying out oxidations involving inorganic reagents and water-insoluble substrates.

A lanthanum macrocycle catalysed hydrolysis of a phosphate triester

A lanthanum macrocycle is shown to be an effective catalyst for the hydrolysis of the phosphate triester 2,4-dinitrophenyl diethyl phosphate, at pH 9 the rate enhancement using 2.5 × 10–3 mol dm–3 catalyst at 25 °C being ca. 103-fold; the reaction is shown to be catalytic rather than stoicheiometric, and possible mechanisms are considered to account for the catalysis.

Copper(II), nickel(II) and palladium(II) complexes of the diamide ligand N,N′-bis(2-carbamoylethyl)ethylenediamine (H2L) and the crystal structure of the carbonyl-oxygen-bonded copper(II) complex [Cu(H2L)](ClO4)2

The preparation of the diamide ligand N,N′-bis(2-carbamoylethyl)ethylenediamine (H2L) by Michael addition of ethylenediamine to acrylamide is described. The copper(II) complex [Cu(H2L)](ClO4)2 and the deprotonated complex [CuL]·H2O have been prepared and characterized as has the blue octahedral nickel(II) complex [Ni(H2L)](ClO4)2. The crystal structure of the carbonyl-oxygen-bonded copper(II) complex [Cu(H2L)] (ClO4)2 has been determined (R=5.5%). The stepwise protonation equilibria of the ligand have been studied by potentiometric titration, giving values of logK1= 8.71 and logK2=5.74 at 25°C and I=0.1moldm−3 (NaClO4). The interaction of copper(II) with the ligand (H2L/Cu(II)=1:1) can be fitted to the set of equilibria:With nickel(II), only two complexes, [Ni(H2L)]2+ and [NiL], occur and they have formation constants of logβ110=7.39 and log β11−2=−11.49. With palladium- (II) the system is similar to that with copper(II) with three complex species, 110, 11−1 and 11−2, with log β110=15.48, log β11−1=11.88 and log β11−2=7.32.