Synthesis, stereodynamics, and reactivity of isonitrile derivatives of dodecacarbonyltetrairidium

Abstract

Abstract The reaction of Ir 4( CO) 12 with t-BuNC or MeNC in the presence of trimethylamine oxide in refluxing tetrahydrofuran provides the substituted iridium clusters Ir 4 (CO) 12-x (RNC) x ] (χ  14; R  t-Bu, Me). The infrared and 13 C NMR spectra of these molecules indicate that most of them adopt structures related to Ir 4 (CO) 12 , i.e., they have only terminal carbonyl ligands. The variable temperature 13 C NMR spectra for Ir 4 (CO) 11 (t-BuNC) establish a carbonyl scrambling process which is the formal inverse of the C 3v → T d scrambling mechanism proposed for Rh 4 (CO) 12 . The kinetics of substitution of Ir 4 (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 PPh 3 . The observed differences between t-BuNC and PPh 3 , can be rationalized on the basis of steric differences between the two ligands.