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C(sp n )-X (n=1-3) Bond Activation by Palladium.

Authors :: Hansen T
Sun X
Dalla Tiezza M
van Zeist WJ
Poater J
Hamlin TA
Bickelhaupt FM
Source :: Chemistry (Weinheim an der Bergstrasse, Germany) [Chemistry] 2022 May 06; Vol. 28 (26), pp. e202103953. Date of Electronic Publication: 2022 Jan 31.
Publication Year :: 2022
Abstract: We have studied the palladium-mediated activation of C(sp <superscript>n</superscript> )-X bonds (n = 1-3 and X = H, CH <subscript>3</subscript> , Cl) in archetypal model substrates H <subscript>3</subscript> C-CH <subscript>2</subscript> -X, H <subscript>2</subscript> C=CH-X and HC≡C-X by catalysts PdL <subscript>n</subscript> with L <subscript>n</subscript> = no ligand, Cl <superscript>-</superscript> , and (PH <subscript>3</subscript> ) <subscript>2</subscript> , using relativistic density functional theory at ZORA-BLYP/TZ2P. The oxidative addition barrier decreases along this series, even though the strength of the bonds increases going from C(sp <superscript>3</superscript> )-X, to C(sp <superscript>2</superscript> )-X, to C(sp)-X. Activation strain and matching energy decomposition analyses reveal that the decreased oxidative addition barrier going from sp <superscript>3</superscript> , to sp <superscript>2</superscript> , to sp, originates from a reduction in the destabilizing steric (Pauli) repulsion between catalyst and substrate. This is the direct consequence of the decreasing coordination number of the carbon atom in C(sp <superscript>n</superscript> )-X, which goes from four, to three, to two along this series. The associated net stabilization of the catalyst-substrate interaction dominates the trend in strain energy which indeed becomes more destabilizing along this same series as the bond becomes stronger from C(sp <superscript>3</superscript> )-X to C(sp)-X.<br /> (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)