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The Transition‐Metal‐Like Behavior of B 2 (NHC) 2 in the Activation of CO: HOMO–LUMO Swap Without Photoinduction
Author(s) -
Zhang Huaiyu,
Cao Zexing,
Wu Wei,
Mo Yirong
Publication year - 2018
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201805952
Subject(s) - homo/lumo , chemistry , transition metal , excited state , steric effects , atomic orbital , ground state , swap (finance) , crystallography , photochemistry , catalysis , stereochemistry , molecule , electron , physics , atomic physics , organic chemistry , finance , quantum mechanics , economics
It is a current trend to explore multi‐bonded and unsaturated main group compounds that can interact with small molecules, in order to find non‐metal catalysts. Notably, Braunschweig et al. found that diboryne stabilized by N ‐heterocyclic carbenes (NHCs) can bind and activate CO. Here we explore the bonding nature of B 2 (NHC) 2 and its activation mechanism for CO from a novel theoretical perspective. While the ground state of B 2 is of a single bond, the approach of NHCs excites B 2 to its third excited state of a triple bond with two significant σ‐holes at the two ends. The subsequent electrostatic attraction drives the formation of B 2 (NHC) 2 . However, only one of the two π bonds (HOMOs) of B 2 (NHC) 2 fits to one of the degenerate LUMOs of CO. Interestingly, the strong steric repulsion between CO and B 2 (NHC) 2 leads to the HOMO–LUMO swap in the latter. Subsequently, both HOMO and HOMO−1 of B 2 (NHC) 2 can effectively interact with the two π* anti‐bonding orbitals (LUMO and LUMO+1) of CO, resulting in substantial electron back‐donation and the ultimate activation of CO.