Large yet flexible N-heterocyclic carbene ligands for palladium catalysis.
A straightforward and scalable eight-step synthesis of new N-heterocyclic carbenes (NHCs) has been developed from inexpensive and readily available 2-nitro-m-xylene. This process allows for the preparation of a novel class of NHCs coined ITent ("Tent" for "tentacular") of which the well-known IMes (N,N'-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IPr (N,N'-bis(2,6-di(2-propyl)phenyl)imidazol-2-ylidene) and IPent (N,N'-bis(2,6-di(3-pentyl)phenyl)imidazol-2-ylidene) NHCs are the simplest and already known congeners. The synthetic route was successfully used for the preparation of three members of the ITent family: IPent (N,N'-bis(2,6-di(3-pentyl)phenyl)imidazol-2-ylidene), IHept (N,N'-bis(2,6-di(4-heptyl)phenyl)imidazol-2-ylidene) and INon (N,N'-bis(2,6-di(5-nonyl)phenyl)imidazol-2-ylidene). The electronic and steric properties of each NHC were studied through the preparation of both nickel and palladium complexes. Finally the effect of these new ITent ligands in Pd-catalyzed Suzuki-Miyaura and Buchwald-Hartwig cross-couplings was investigated.
EaStCHEM, School of Chemistry, University of St. Andrews, Purdie Bulding, North Haugh, St. Andrews, Fife, KT16, 9ST (UK).
Sebastien
S
Meiries
Gaëtan
G
Le Duc
Anthony
A
Chartoire
Alba
A
Collado
Klaus
K
Speck
Kasun S
KS
Athukorala Arachchige
Alexandra M Z
AM
Slawin
Steven P
SP
Nolan
N-heterocyclic carbene; bulky; catalysis; flexible; palladium; tentacular