Benzo annulated cycloheptatriene PCP pincer iridium complexes

Abstract

The benzo annulated cycloheptatriene PCP pincer ligand 5 was prepared in five steps. Treatment of 5 with Ir(CO)₃Cl gave the meridional cyclometalated chlorohydrido carbonyl iridium complexes 6a–c which differ in their arrangement of the H, Cl, and CO ligands around iridium. Storing 6 in THF led to isomerization processes. Hydrogen shifts from the sp³-CH carbon bound to iridium into the ligand backbone produced the three isomers 7a–c. Reductive elimination of HCl from these complexes resulted in the square planar Ir(I) carbonyl complexes 8a–c. Abstraction of the hydrogen from the sp³-CH–Ir fragment could be achieved either by treatment of 6 with Ph₃CBF₄ or by the elimination of H₂ which is initiated by CF₃SO₃H. The mass spectrometric characterisation of 6 using fast atom bombardment reveals a complex fragmentation pattern. These different “fragment” ions were further investigated by electro-spray ionisation (tandem) mass spectrometry in high and low resolution. The identified compounds were attributed to structures by DFT calculations.