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Facile Group IV Based C-H Bond Activation: Confirmation of Classic Benzyne Mechanism by DFT. Extension to Adamantyl Activation.
  • Motasem Suleiman,
  • Fioralba Taullaj,
  • Ulrich Fekl
Motasem Suleiman
University of Toronto
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Fioralba Taullaj
University of Toronto - Mississauga
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Ulrich Fekl
University of Toronto - Mississauga
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Abstract

Group IV organometallic complexes are promising systems for C-H bond activation. We are interested in the C-H bond activation of the CH2 positions of the adamantyl group, since these positions are particularly hard to activate and to functionalize. As a potential platform for activation of that important alkyl group, we consider the alkyl bonded to the cyclopentadienyl in a substituted bis-cyclopentadienyl group IV metal diphenyl complex. The mechanism proposed in the classic paper reporting such activation using Zr(IV) (Erker and Mühlenbernd, 1987) involves an η2-benzyne complex intermediate. This current work reports a computational analysis of the problem through Density Functional Theory (DFT). We found that the two-step mechanism proposed for activation of C(Me)2-Ph or tert-Bu groups using Zr(IV) is indeed confirmed by DFT and that it can be extended to Ti and Hf. We further found that the system can be successfully extended to the adamantyl group. The first step involves formation of the benzyne complex, which can also be described as a metallacyclopropene. In the second step, the cyclopentadienyl-bound alkyl is activated in the coordination sphere of the metal via proton transfer to the bound benzyne, which, if the metallacyclopropene description is chosen, resembles a σ-bond metathesis. The C-H bond activation of adamantyl through this approach is thermodynamically and kinetically feasible. Selective α-CH bond activation should be achievable with Ti (under thermodynamic control), and selective γ-CH bond activation with Zr (under kinetic or thermodynamic control).

Peer review status:IN REVISION

30 Sep 2020Submitted to International Journal of Quantum Chemistry
01 Oct 2020Submission Checks Completed
01 Oct 2020Assigned to Editor
19 Oct 2020Reviewer(s) Assigned
19 Oct 2020Review(s) Completed, Editorial Evaluation Pending
19 Oct 2020Editorial Decision: Revise Minor
16 Nov 20201st Revision Received
17 Nov 2020Submission Checks Completed
17 Nov 2020Assigned to Editor
17 Nov 2020Reviewer(s) Assigned
13 Dec 2020Review(s) Completed, Editorial Evaluation Pending
14 Dec 2020Editorial Decision: Revise Major
16 Jan 20212nd Revision Received