260431-63-8Relevant academic research and scientific papers
Hydride elimination from an iridium(III) alkoxide complex: A case in which a vacant cis coordination site is not required
Blum, Ofer,Milstein, David
, p. 479 - 484 (2000)
Decomposition of trans-HIr(OCH3)(C6H5)(PMe3)3 (2) formed by oxidative addition of methanol to Ir(C6H5)(PMe3)3 (1) was studied in detail. Thermolysis of this complex yields trans-H2Ir(C6H5)(PMe3)3 (2) and formaldehyde. Complex 2 is less stable than its two dihydrido isomers, showing that it is the kinetic product of this reaction. The elimination process follows first order kinetics and exhibits a kinetic isotope effect of kH/kD=3.2±0.2, the observed activation parameters are ΔH?obs=8.3±1.0 kcal mol-1; ΔS?obs=-34±3.5 e.u. and ΔG?obs (298 K)=18.4±2.0 kcal mol-1. Catalysis by methanol was observed. The process does not involve a vacant coordination site cis to the coordinated methoxide, as shown by labeling experiments and by the lack of exchange with P(CD3)3. Thus, in this case the β-hydride elimination process does not follow the usual pathway. A mechanism, in which following methoxide dissociation, C-H cleavage of free methanol takes place, is suggested.
