Noninnocent Cyclopentadienyl Reactivity in an Al/Cr Heterobimetallic Complex

The cyclopentadienyl (Cp) ligand plays a pivotal role in organometallic chemistry. While it is traditionally regarded as an ancillary spectator ligand, increasing evidence shows that Cp and Cp* ligands can actively engage in bond-forming reactions with nucleophiles, electrophiles, and radicals to afford isolable, exo-substituted η4-cyclopentadiene complexes. Here we report that a Cp-containing Al/Cr heterobimetallic isocarbonyl complex, LdippAlMe-OC-CrCp(CO)2 (Ldipp = [HC(CMeNdipp)2], dipp = 2,6-di-iso-propylphenyl) reacts with epoxides by two mechanistically distinct pathways. With propylene oxide, frustrated Lewis pair (FLP) reactivity drives regioselective ring-opening to furnish an alkylchromium intermediate that subsequently undergoes homolytic Cr–C bond cleavage, delivering an alkyl radical to the Cp ligand in a previously unrecognized Cp functionalization pathway. In contrast, for styrene oxide, ring opening is followed exclusively by β-hydride elimination rather than radical cyclopentadienyl functionalization. These results define a new mode of Cp functionalization, clarify possible decomposition pathways for CpCr(CO)3R complexes, and broaden understanding of cooperative bond activation at earth-abundant heterobimetallic platforms.