Iridium Complexes of Macrocyclic Tetraamine Ligands. Preparation, Characterization and Crystal Structure of a Macrocyclic Iridium(III) Complex Coordinated with the 4-Cycloocten-1-yl Anion.

The reaction between [Ir(cod)Cl]₂ and cyclam (cod= cycloocta-1,5-diene, cyclam= 1,4,8,11-tetraazacyclotetradecane) results in oxidation of iridium(I) to iridium(III) and reduction of cycloocta-1,5-diene to cyclooctene. The product of the reaction is a diastereomeric mixture of octahedral cis-tetraamineiridium(III) complexes coordinated with a cyclam ligand and a 4-cycloocten-1-ide ligand (coei), isolated as the perchlorate salt. The molecular structure of the trifluoromethanesulfonate salt of the dominant diastereomer [Ir(cyclam)(coei)](CF₃SO₃)2 was determined by a single-crystal X-ray investigation. The compound crystallizes in the monoclinic space group P2₁/c with a=9.227(4), b=24.838(6), c=12.537(3) Å, β=107.59(3)° and Z= 4. The cyclam ligand adopts the cis configuration, while the coei ligand is coordinated via a σ-bond to the deprotonated carbon atom and by a π-bond to the double bond, giving a distorted octahedral coordination geometry around the iridium atom. Addition of strong base to the complex causes further deprotonation of the cyclooctenide ligand. This process has been investigated in some detail by deuterium labelling experiments using ¹H and ¹³C NMR.