Synthesis,stereodynamics, and reactivity of isonitrile derivatives of dodecacarbonyltetrairidium |
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Authors: | Gordon F. Stuntz John R. Shapley |
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Affiliation: | Department of Chemistry, University of Illinois, Urbana, Illinois 61801 U.S.A. |
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Abstract: | The reaction of Ir4(CO)12 with t-BuNC or MeNC in the presence of trimethylamine oxide in refluxing tetrahydrofuran provides the substituted iridium clusters Ir4(CO)12-x(RNC)x] (χ 14; R t-Bu, Me). The infrared and 13C NMR spectra of these molecules indicate that most of them adopt structures related to Ir4(CO)12, i.e., they have only terminal carbonyl ligands. The variable temperature 13C NMR spectra for Ir4(CO)11(t-BuNC) establish a carbonyl scrambling process which is the formal inverse of the C3v→ Td scrambling mechanism proposed for Rh4(CO)12. The kinetics of substitution of Ir4(CO)12 by t-BuNC have been studied. Each substitution step occurs by a ligand-dependent, overall second-order reaction at a rate much greater than for substitution by PPh3. The observed differences between t-BuNC and PPh3, can be rationalized on the basis of steric differences between the two ligands. |
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