Premium
C−H Activation and Olefin Insertion in d 8 and d 0 Complexes: Same Elementary Steps, Different Electronics
Author(s) -
Bumberger Andreas E.,
Gordon Christopher P.,
Trummer David,
Copéret Christophe
Publication year - 2020
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.201900278
Subject(s) - chemistry , olefin fiber , alkyl , cycloaddition , regioselectivity , crystallography , transition metal , stereochemistry , catalysis , organic chemistry
Metallocene alkyl complexes with d 0 electron configuration and d 8 ‐configured square planar α ‐diimine late transition metal alkyl complexes show activity in both C−H activation through σ ‐bond metathesis and olefin insertion. Herein, we show by analysis of their M− C H 3 13 C chemical shift tensors that these reactions involve a π (M−C) interaction in the horizontal plane of the complex for both d 0 and d 8 systems. While in the case of d 0 systems the interaction of an empty metal d‐orbital and a filled carbon p‐orbital causes partial alkylidene character of the M−C bond, the corresponding metal d‐orbital is filled in d 8 systems, thus generating a filled π *(M−C) orbital that increases the anionic character of the methyl group. This entails fundamentally different reaction mechanisms for d 0 and d 8 systems, which are reflected in the structures of the transition states: While d 0 olefin insertion can be viewed as a [2+2] cycloaddition reaction, d 8 olefin insertion rather resembles methyl group migration onto a positively polarized olefin, thus explaining the observed differences in regioselectivity. These findings are translated to σ ‐bond metathesis, a reaction which is isolobal to olefin insertion for both early and late transition metals.