Dinuclear Triazole-Derived Janus-Type N‑Heterocyclic Carbene Complexes of Palladium: Syntheses, Isomerizations, and Catalytic Studies toward Direct C5-Arylation of Imidazoles
datasetposted on 26.01.2016 by Shuai Guo, Han Vinh Huynh
Datasets usually provide raw data for analysis. This raw data often comes in spreadsheet form, but can be any collection of data, on which analysis can be performed.
The dipalladium triazolidine-diylidene complex all-trans-[PdBr2(CH3CN)]2(μ-ditz) (1) (ditz = 1,2,4-trimethyltriazolidine-3,5-diylidene) was synthesized via in situ deprotonation of the precursor salt with a basic metal precursor. Ligand replacements of all-trans-1 with monodentate or chelating phosphines afforded the dicarbene-bridged complexes all-cis-[PdBr2(PPh3)]2(μ-ditz) (2) and [PdBr(DPPP)]2(μ-ditz)Br2 (3), respectively. Bromido substitution of all-cis-2 gave tetra-acetato complex all-cis-[Pd(CH3COO)2(PPh3)]2(μ-ditz) (4) with retention of the configuration as the predominant product. In addition, monopalladium triazolin-5-ylidene complexes trans-[PdBr2(CH3CN)(tazy)] (6, tazy =1,4-dimethyltriazolin-5-ylidene), cis-[PdBr2(PPh3)(tazy)] (7), [PdBr(DPPP)(tazy)]Br (8), and cis-[Pd(CH3COO)2(PPh3)(tazy)] (9) were also synthesized as the respective mononuclear equivalents for comparison. A comparative catalytic study revealed the general superiority of dinuclear complexes 1–4 over their respective mononuclear counterparts 6–9 in the direct C5-arylation reaction of 1-methylimidazoles. Overall, mixed dicarbene/diphosphine complex 3 showed the best catalytic performance.