π-Bond Character in Metal–Alkyl Compounds for C–H Activation: How, When, and Why?

Christopher T Gordon (1) , Damien Culver (2) , Matthew Conley , Odile Eisenstein (3) , Richard A Andersen (4) , Christophe Copéret (1)

1 ETH Zürich - Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich]
2 Department of Chemistry and Biochemistry, University of California
3 ICGM - Institut Charles Gerhardt Montpellier - Institut de Chimie Moléculaire et des Matériaux de Montpellier
4 UC Berkeley - University of California [Berkeley]

C–H bond activation via σ-bond metathesis is typically observed with transition-metal alkyl compounds in d0 or d0fn electron configurations, e.g., biscyclopentadienyl metal alkyls. Related C–H activation processes are also observed for transition-metal alkyls with higher d-electron counts, such as W(II), Fe(II), or Ir(III). A σ-bond metathesis mechanism has been proposed in all cases with a preference for an oxidative addition–reductive elimination pathway for Ir(III). Herein we show that, regardless of the exact mechanism, C–H activation with all of these compounds is associated with π-character of the M–C bond, according to a detailed analysis of the 13C NMR chemical shift tensor of the α-carbon. π-Character is also a requirement for olefin insertion, indicating its similarity to σ-bond metathesis. This observation explains the H2 response observed in d0 olefin polymerization catalysts and underlines that σ-bond metathesis, olefin insertion, and olefin metathesis are in fact isolobal reactions.

Domaines: Chimie inorganique

Christopher T Gordon, Damien Culver, Matthew Conley, Odile Eisenstein, Richard A Andersen, et al.. π-Bond Character in Metal–Alkyl Compounds for C–H Activation: How, When, and Why?. Journal of the American Chemical Society, 2019, 141 (1), pp.648-656. ⟨10.1021/jacs.8b11951⟩. ⟨hal-01979945⟩