A series of (allyl)palladium(II)
complexes of anionic N-heterocyclic
carbenes that contain a weakly coordinating borate moiety (WCA-NHC)
were prepared by deprotonation of the carbene IPr with n-butyllithium in the 4-position, which was followed by addition of
B(C6F5)3 and reaction of the resulting
lithium carbene–borate with [(η3-allyl)Pd(μ-Cl)]2 (allyl = 2-propenyl, 2-butenyl, 2-methyl-2-propenyl, 1-phenyl-2-propenyl).
In polar solvents such as tetrahydrofuran, chloropalladate complexes
of the type [Li(THF)3][(WCA-NHC)PdCl(η3-allyl)] were formed, whereas the reactions in toluene afforded
neutral complexes of the type [(WCA-NHC)Pd(η3-allyl)],
which exhibit an intramolecular interaction with the N-aryl groups
of the carbene ligands. The allyl-palladium complexes were employed
as catalysts for the Buchwald–Hartwig amination of various
aryl halides with morpholine.
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