Preparation and nuclear magnetic resonance investigation of some stereochemically non-rigid derivatives of dodecacarbonyltetrairidium

Abstract

The complexes [Ir₄(CO)₈L₄][L = Ph₂PMe, PhPMe₂, Ph₂PEt, Ph₂AsMe, (PhO)₃P, and ½(Ph₂PCH₂)₂] have been prepared by direct reaction of Ir₄(CO)₁₂ with the ligand. All contain bridging carbonyl groups and in solution at ambient temperatures have one of two structures which differ in the number of bridging carbonyl groups. At temperatures above ambient the complexes were shown by ¹H and ¹³C n.m.r. spectroscopy to be stereochemically non-rigid by virtue of an intramolecular carbonyl scrambling process. They dissolve in acids to give mainly diprotonated species which were also stereochemically non-rigid, probably involving both carbonyl and proton intramolecular scrambling. Evidence is presented for initial formation of monoprotonated species for some complexes.