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Experimental and Theoretical Study of Ni II ‐ and Pd II ‐Promoted Double Geminal C(sp 3 )−H Bond Activation Providing Facile Access to NHC Pincer Complexes: Isolated Intermediates and Mechanism
Author(s) -
He Fengkai,
Gourlaouen Christophe,
Pang Huan,
Braunstein Pierre
Publication year - 2022
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202200507
Subject(s) - geminal , pincer movement , chemistry , physics , palladium , medicinal chemistry , stereochemistry , catalysis , organic chemistry
We report the first examples of metal‐promoted double geminal activation of C(sp 3 )−H bonds of the N−CH 2 −N moiety in an imidazole‐type heterocycle, leading to nickel and palladium N‐heterocyclic carbene complexes under mild conditions. Reaction of the new electron‐rich diphosphine 1,3‐bis((di‐ tert ‐butylphosphaneyl)methyl)‐2,3‐dihydro‐1 H ‐benzo[ d ]imidazole ( 1 ) with [PdCl 2 (cod)] occurred in a stepwise fashion, first by single C−H bond activation yielding the alkyl pincer complex [PdCl(PCsp3H P)] ( 3 ) with two trans phosphane donors and a covalent Pd−Csp3bond. Activation of the C−H bond of the resulting α‐methine Csp3H−M group occurred subsequently when 3 was treated with HCl to yield the NHC pincer complex [PdCl(PC NHC P)]Cl ( 2 ). Treatment of 1 with [NiBr 2 (dme)] also afforded a NHC pincer complex, [NiBr(PC NHC P)]Br ( 6 ), but the reactions leading to the double geminal C−H bond activation of the N−CH 2 −N group were too fast to allow identification or isolation of an intermediate analogous to 3 . The determination of six crystal structures, the isolation of reaction intermediates and DFT calculations provided the basis for suggesting the mechanism of the stepwise transformation of a N−CH 2 −N moiety in the N−C NHC −N unit of NHC pincer complexes and explain the key differences observed between the Pd and Ni chemistries.