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.