Gordon F. Stuntz

Synthesis, stereodynamics, and reactivity of isonitrile derivatives of dodecacarbonyltetrairidium

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.

X-Ray crystal structure and dynamic behaviour of [Ir4(CO)11(CNBut)]

[Ir4(CO)11(CNBut)] has been prepared and shown (by X-ray crystallography and 13C n.m.r. studies) to be the first example of a derivative of Ir4(CO)12 without bridging carbonyl groups; variable temperature 13C n.m.r. spectra establish carbonyl scrambling via a triply bridged intermediate, i.e., the formal inverse of the C3v→Td scrambling mechanism proposed for [Rh4(CO)12].