Spontaneous Bicyclometalation of a Single Cobalt(I) Complex Stabilized by a δ‐C–H Agostic Interaction

CoCH3(PMe3)4 is known for a long time for its potential to activate less reactive C–H Bonds under extremely mild conditions by methane elimination. A spontaneous second C–H bond activation at the same center of cobalt complex is not expected. In contrast to previous investigations with certain aryl‐iminophosphane chelating ligands, in this work two consecutive metalation steps at the same complex center lead to a rare example of a cobalt metallabicycle. In the first step a C–H activation results in a five‐membered chelate ring, whereas the second ring is formed by an incomplete C–H activation which stops at a stable, rarely observed δ‐C–H agostic interaction. The results are supported by NMR spectroscopy, X ray structure analysis and density functional theory (DFT) calculations. Knowledge of such agostic interactions are essential in order to understand catalytic reaction paths and studies of such molecular structures of their ring sizes, bite angles and electronic properties have shown that these ligands allow sensitive control within the metal coordination sphere. “Snapshot”: A double metalation through the coordination of an ortho‐iminophosphane anchoring group can initiate a new bicyclometalation reaction affording the mononuclear cobalt complex (16 valence electrons) (1, 2). The first ring closing step involves a C–H activation, while the second one stops at the level of a rarely observed δ‐C–H agostic interaction supported by quantum chemical calculations.