A Study on Zr–Ir Multiple Bonding Active for C–H Bond Cleavage

Zr–Ir hydrido complexes with ansa-(cyclopentadienyl)­(amide) as the supporting ligand in the zirconium fragment, e.g., (L1ZrR)­(Cp*Ir)­(μ-H)3 [L1 = Me2Si­(η5-C5Me4)­(NtBu), R = Cl (5), Ph (7), Me (10), alkyl, and aryl] were designed, synthesized, and isolated as tractable early–late heterodinuclear complexes. Despite the presence of the three supporting hydride ligands, Zr–Ir distances in the crystal structures of 5, alkyl, and aryl complexes [2.74–2.76 Å] were slightly longer than the sum of the element radii of Zr and Ir [2.719 Å]. These hydrocarbyl complexes displayed the thermolytic C–H activation of a variety of aromatic compounds and several organometallic compounds. Also, the substrate scope and limitation in the Zr–Ir system were studied. The regiochemical outcomes during the C–H activation of pyridine derivatives and methoxyarenes suggested the in situ generation of a Lewis acidic active intermediate, i.e., (L1Zr)­(Cp*IrH2) (III). The existence of III and relevant σ-complex intermediates {L1Zr­(η2-R–H)}­(Cp*IrH2) (IIR) (R = Me, Ph) in the ligand exchange was demonstrated by the direct isolation of a Et3PO-adduct of III (39b) from 7 and kinetic studies. The structure of the direct Zr–Ir bonds in IIPh, IIMe, III, and 39b were probed using computational studies. The unprecedented strong M–M′ interactions in the early–late heterobimetallic (ELHB) complexes have been proposed herein.