Half-sandwich Rh(Cp*) and Ir(Cp*) complexes with oxygen atom transfer reagents as ligands

Abstract

Rhodium(Cp*) and iridium(Cp*) complexes with bidentate ligands and a coordinated oxygen atom transfer reagent as the final ligand in the d6 coordination sphere are described (Cp* = η5-pentamethylcyclopentadienyl). A Rh(Cp*) cation with a pyridyl-benzamide bidentate ligand resistant to insertion and a coordinated oxygen atom transfer reagent, 2-tert-butylsulfonyliodosylbenzene (sPhIO), was isolated in the solid state. In anhydrous solution, the sPhIO ligand was reduced over 24 h, and a solvent-stabilized, 16-electron rhodium complex was formed. Oxygen atom transfer either led to unobserved oxidative degradation of a small fraction of the rhodium species, or formed the iodoxyarene, sPhIO2, via a known disproportionation reaction. The reduced oxidant, sPhI, did not coordinate to rhodium, but the 16-electron cation was readily trapped by water. The organometallic Ir(Cp*) backbone with cyclometalated 2-phenylpyridine (phpy) formed stable complexes with the mild oxygen atom transfer reagents pyridine-N-oxide and 4-methoxy-pyridine-N-oxide. Oxygen atom transfer from the coordinated N-oxides was induced by thermolysis or photolysis and initially led to decomposition of a small fraction of the samples. The liberated pyridine derivatives displaced coordinated N-oxides and somewhat limited decomposition of the Ir(Cp*)(phpy) backbone. Neither oxygen atom insertion into the metal–carbon bond of coordinated phpy nor metal-oxo complexes were observed.