Iridium Half-Sandwich Complexes with Di- and Tridentate Bis(pyridylimino)isoindolato Ligands: Stoichiometric and Catalytic Reactivity

A series of κ2-(N,N)-coordinated bis­(2-pyridylimino)­isoindolato
(BPI) complexes [Cp*Ir­(BPI)­Cl],
which possess “three-legged piano-stool” structures,
with the iridium atom being coordinated by the Cp* ligand 2 ×
N and Cl, were prepared via deprotonation of the BPIH ligands with
either potassium hydride or LDA and subsequent reaction with [Cp*IrCl2]2 in THF. Cationic complexes [Cp*Ir­(BPI)]+ containing κ3-(N,N,N)-coordinated BPI ligands were prepared
as well as complexes with bidentate-coordinated BPI ligands, where
the chloride ligand was substituted by either neutral or anionic ligands.
Substitution in the ortho-position of the PBI ligands
led to the formation of cycloiridated κ3-(N,N,C) species. Upon substitution
of the anionic ligand by triphenylphosphine, a product was obtained
with a hitherto unobserved κ2-(N,N) coordination of oMe-BPI to
the metal center via the deprotonated nitrogen atom of the isoindole
unit and one of the imine nitrogen atoms of the BPI ligand. A series
of (para-cymene) osmium half-sandwich complexes with
analogous structures and reactivities to their isoelectronic Cp*Ir­(BPI)
congeners were also prepared. Finally, it has been demonstrated that
both Ir and Os complexes are catalytically active in the transfer
hydrogenation of various ketones and imines.