om500342z_si_003.xyz (22.46 kB)
Palladium(II) Complexes of 1,2,4-Triazole-Based N‑Heterocyclic Carbenes: Synthesis, Structure, and Catalytic Activity
dataset
posted on 2014-06-23, 00:00 authored by Jan Turek, Illia Panov, Miloslav Semler, Petr Štěpnička, Frank De Proft, Zdeňka Padělková, Aleš RůžičkaSix
palladium(II) complexes bearing three different triazole-based
N-heterocyclic carbene (NHC) ligands, [1-tert-butyl-4-{2-[(N,N-dimethylamino)methyl]phenyl}-3-phenyl-1H-1,2,4-triazol-4-ium-5-ide, 1-tert-butyl-4-(2-methoxyphenyl)-3-phenyl-1H-1,2,4-triazol-4-ium-5-ide, and 1-tert-butyl-4-(4-methylphenyl)-3-phenyl-1H-1,2,4-triazol-4-ium-5-ide],
were synthesized and fully characterized. NMR spectroscopy and X-ray diffraction
analysis revealed that the amino-group-substituted
NHC ligand is coordinated in bidentate fashion, forming a monocarbene
chelate complex with an additional intramolecular Pd ← N bond
with the nitrogen donor atom. The 4-methylphenyl- and 2-methoxyphenyl-substituted
NHC ligands coordinate as C-monodentate donors, forming simple biscarbene
Pd(II) complexes. The evaluation of the catalytic performance in the
Suzuki–Miyaura cross-coupling reaction revealed very promising
performance of the intramolecularly coordinated monocarbene complexes
under relatively mild conditions even in direct comparison with the
commercially available PEPPSI catalyst. In contrast, the biscarbene
complexes proved inactive in this catalytic process. According to
theoretical calculations (EDA and NOCV analysis), functionalization
of the 1,2,4-triazole-based NHC with the 2-[(N,N-dimethylamino)methyl]phenyl group has a significant effect
on the stability of the NHC–metal bond.