ABSTRACT
The reactions of water with a number of iridium(III) complexes relevant to the mechanism for catalytic methanol carbonylation are reported. The iridium acetyl, [Ir(CO)2I3(COMe)](-), reacts with water under mild conditions to release CO2 and CH4, rather than the expected acetic acid. Isotopic labeling and kinetic experiments are consistent with a mechanism involving nucleophilic attack by water on a terminal CO ligand of [Ir(CO)2I3(COMe)](-) to give an (undetected) hydroxycarbonyl species. Subsequent decarboxylation and elimination of methane gives [Ir(CO)2I2](-). Similar reactions with water are observed for [Ir(CO)2I3Me](-), [Ir(CO)2(NCMe)I2(COMe)] and [Ir(CO)3I2Me] with the neutral complexes exhibiting markedly higher rates. The results demonstrate that CO2 formation during methanol carbonylation is not restricted to the conventional water gas shift mechanism mediated by [Ir(CO)2I4](-) or [Ir(CO)3I3], but can arise directly from key organo-iridium(III) intermediates in the carbonylation cycle. An alternative pathway for methane formation not involving the intermediacy of H2 is also suggested. A mechanism is proposed for the conversion MeOH + CO â CO2 + CH4, which may account for the similar rates of formation of the two gaseous by-products during iridium-catalysed methanol carbonylation.
ABSTRACT
BACKGROUND: There is an ongoing discussion about age limits for deep brain stimulation (DBS). Current indications for DBS are tremor-dominant disorders, Parkinson's disease, and dystonia. Electrode implantation for DBS with analgesia and sedation makes surgery more comfortable, especially for elderly patients. However, the value of DBS in terms of benefit-risk ratio in this patient population is still uncertain. METHODS: Bilateral electrode implantation into the subthalamic nucleus (STN) was performed in a total of 73 patients suffering from Parkinson's disease. Patients were analyzed retrospectively. For this study they were divided into two age groups: group I (age <65 years, n = 37) and group II (age > or = 65 years, n = 36). Examinations were performed preoperatively and at 6-month follow-up intervals for 24 months postoperatively. Age, UPDRS motor score (part III) on/off, Hoehn & Yahr score, Activity of Daily Living (ADL), L-dopa medication, and complications were determined. RESULTS: Significant differences were found in overall performance determined as ADL scores (group I: 48/71 points, group II: 41/62 points [preoperatively/6-month postoperatively]) and in the rate of complications (group I: 4 transient psychosis, 4 infections in a total of 8 patients, group II: 2 deaths [unrelated to surgery], 1 intracerebral hemorrhage, 7 transient psychosis, 3 infections, 2 pneumonia in a total of 13 patients), (p < 0.05). Interestingly, changes in UPDRS scores, Hoehn & Yahr scores, and L-dopa medication were not statistically different between the two groups. CONCLUSION: DBS of the STN is clinically as effective in elderly patients as it is in younger ones. However, a more careful selection and follow-up of the elderly patients are required because elderly patients have a higher risk of surgery-related complications and a higher morbidity rate.
