Synthesis and characterization of novel Pd(II) and Pt(II) complexes with 5-ring chelating iminoylcarbene ligands

Synthesis of chiral imino- and amino-imidazolium salts and of chelating amino-N-heterocyclic carbene palladium(II) complexes

“…The direct condensation of 1-(2-oxo-ethyl)-imidazolium 3 with amines was reported to give undesired decomposition reactions [25]. Imidazolium salts 4 were prepared by reaction of iminoyl chlorides with imidazoles [26,27,31,32].…”

“…Several metal complexes (Pd, Pt, Rh, Ni) with non enolisable imino-NHC ligands have been reported [17,26,28,32,44]. Such complexes could be synthesized either from the corresponding silver complex or from the free carbene obtained by treatment of the imidazolium salt with an appropriate base [28,44].…”

“…Most of these complexes were obtained from iminoylimidazolium salts 4 ( Fig. 1) [26,28,32] or from aromatic aldimines [44]. By contrast, complexes with enolisable imino-NHC ligands, derived from azolium salts of type 2 (Fig.…”

“…1), could not be synthesized through the free carbene. Several of these complexes have been obtained by prior formation of the silver complex [23,26].…”

“…Several other achiral or chiral racemic palladium(II) complexes with chelating NHC-N ligands have been reported, including NHC-pyridyl [18][19][20][21][22][23], NHC-amino [23,24], NHC-amido [24], NHC-imino [25][26][27][28] and NHC-enamino complexes [29].…”