A study on Zr-Ir multiple bonding active for C-H bond cleavage.

Abstract

Zr-Ir hydrido complexes with ansa-(cyclopentadienyl)(amide) as the supporting ligand in the zirconium fragment, e.g., (L(1)ZrR)(Cp*Ir)(μ-H)3 [L(1) = Me2Si(η(5)-C5Me4)(N(t)Bu), 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., (L(1)Zr)(Cp*IrH2) (III). The existence of III and relevant σ-complex intermediates {L(1)Zr(η(2)-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.