Chem. Eur. J. [LCC/LCQ]

Abstract:

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 NHC 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 stepwise, first by single C–H bond activation yielding the alkyl pincer complex [PdCl(PC sp3 H P)] ( 3 ) with two trans phosphane donors and a covalent Pd–C sp3 bond. Activation of the C–H bond of the resulting α-methine C sp3 H–M group occurred subsequently when 3 was reacted with HCl to yield the NHC pincer complex [PdCl(PC NHC P)]Cl ( 2 ). The reaction 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.

Graphical abstract:

 

First examples of stepwise (Pd) or direct (Ni) metal-promoted double geminal activation of C_sp3–H bonds leading to imidazole-type NHC metal pincer complexes under mild conditions.

Reference :

Fengkai He, Christophe Gourlaouen, Huan Pang, Pierre Braunstein

Experimental and Theoretical Study of the Ni(II)- and Pd(II)-Promoted Double Geminal C(sp3)–H Bond Activation Providing Facile Access to NHC Pincer Complexes: Isolated Intermediates and Mechanism

Chem. Eur. J. 2022, 28, e202200507- DOI: https://doi.org/10.1002/chem.202200507

Contact:

Pierre Braunstein (braunstein@unistra.fr), ancien Directeur du Laboratoire de Chimie de Coordination (LCC),Institut de Chimie de Strasbourg, UMR 7177.