Jean M. Pearson

Cis–trans isomerism in [M(CO)2I4]− (M=Rh, Ir): Kinetic, mechanistic and spectroscopic studies

Infrared spectroscopic studies show that the cis–trans isomerisation of [Rh(CO)2I4]− (1) reaches an equilibrium in solution favouring the trans isomer (Keq≈10 in CH2Cl2 at 25°C). The approach to equilibrium obeys a first order rate law with a half life of ca. 40 min at 25°C. Activation parameters for the isomerisation are ΔH‡ 103 (±3) kJ mol−1, ΔS‡ +32 (±9) J mol−1 K−1 in CH2Cl2 and ΔH‡ 99 (±2) kJ mol−1, ΔS‡+25 (±4) J mol−1 K−1 in THF. In polar coordinating solvents, formation of monocarbonyl complexes [Rh(CO)I4(sol)]− occurs in competition with cis–trans isomerisation, and in the presence of added iodide salt, [Rh(CO)I5]2− is formed. Isotopic labelling experiments show that added 12CO is incorporated into trans-1 on isomerisation of cis-[Rh(13CO)2I4]−. Addition of CO to the monocarbonyls, [Rh(CO)I4(sol)]− and [{Rh(CO)I4}2]2− gives predominantly trans-[Rh(CO)2I4]−. A mechanism is proposed for cis–trans isomerisation involving dissociation of a CO ligand. Elemental and infrared spectroscopic analysis of crystals obtained from the residues of carbonylation experiments on [Ir(CO)2I3(Me)]− are consistent with a new trans isomer of [Ir(CO)2I4]−. The same species is formed in the reaction of [{Ir(CO)I4}2]2− with CO. Isomerisation to cis-[Ir(CO)2I4]− only occurs in the presence of added CO. The ν(CO) frequencies for isotopomers of cis- and trans-[M(CO)2I4]− (M=Rh, Ir) are analysed using C–O factored force-fields. The force constants obtained indicate stronger metal–CO back-donation for the cis relative to the trans isomers and also for iridium relative to rhodium.

Model reactions of a carbonylation catalyst: phosphite induced migratory CO insertion in [MeIr(CO)2I3]−

Carbonylation of the anionic iridium(III) methyl complex, [MeIr(CO)2I3]− (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)I2L2] (L = P(OPh)3 (2), P(OMe)3 (3)). Complex 2 has been isolated and fully characterised from the reaction of Ph4As[MeIr(CO)2I3] with AgBF4 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 CH2Cl2 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-CH2Cl2). 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 CH2Cl2. Activation parameters for the k1 step are ΔH≠ = 71 (±3) kJ mol−, ΔS≠ = −81 (±9) J mol−1 K−1 in CH2Cl2 and ΔH≠ = 60(±4) kJ mol−1, ΔS≠ = −93(± 12) J mol−1 K−1 in 1:3 MeOH-CH2Cl2. 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.

Dramatic acceleration of migratory insertion in [MeIr(CO)2I3]– by methanol and by tin(II) iodide

Carbonylation of [MeIr(CO)2I3]– to [MeCOIr(CO)2I3]– requires temperatures >80 °C in chlorobenzene, but is dramatically accelerated on addition of methanol (×104 at 33 °C) or of the Lewis acid Snl2(× 200 at 93 °C); the acceleration is proposed to arise from activation of an Ir–I bond.

Acceptability of post-mortem imaging among Muslim and non-Muslim communities

OBJECTIVE: Peoples views regarding autopsy vary according to their cultural and religious beliefs. This paper aims to determine the opinions towards this procedure among Muslims resident in Libya and Muslims and non-Muslims resident in the UK. Our long-term goal is to improve autopsy rates; whether conventional or through the use of post-mortem imaging. METHODS: 400 questionnaires were distributed to the three communities, interrogating belief about post-mortem investigations. Descriptive statistics and non-parametric statistics were used to analyse the data. RESULTS: Of the 400 distributed questionnaires, there was a high return rate of 320 (80%). All groups felt that children should be buried sooner than adults(p < 0.001), but 77% of Libyan Muslims thought that children should be buried within 12 h of death compared to 16% of UK Muslims and only 7% of UK non-Muslims (p < 0.001). More non-Muslims were unconcerned about a negative impact of traditional autopsy on the dignity of the corpse than Muslims (p < 0.001) and more Muslims responded that autopsy has a negative emotional effect on the family (p < 0.001). Type of death altered what sort of investigations were desired. In the case of homicide, Libyan Muslims were less likely to prefer CT (p < 0.001) or MRI (p = 0.001). Sex had no effect on the results of the survey. CONCLUSION: Post-mortem imaging is acceptable to both Muslims and non-Muslims in Libya and the UK, but Muslims have a significant preference for post-mortem imaging compared to autopsy, except in homicidal cases. ADVANCES IN KNOWLEDGE: (1) The ability of post-mortem imaging to preserve the dignity of the corpse is independent of religion, however, significantly more Muslims feel that autopsy has a negative emotional effect on the family of the deceased. (2) A significant majority of Muslims in Libya prefer to bury children within 12 h of death, while a delay of up to a week is acceptable in UK. (3) Muslims resident in UK have an attitude closer to that of the indigenous (non-Muslim) population and therefore, educational programmes may be successful in changing attitudes of Muslims in Libya and other predominantly Muslim countries.