10.1021/om500139b.s002
Shuai Guo
Shuai
Guo
Han Vinh Huynh
Han Vinh
Huynh
Dinuclear Triazole-Derived Janus-Type N‑Heterocyclic Carbene Complexes of Palladium: Syntheses, Isomerizations, and Catalytic Studies toward Direct C5-Arylation of Imidazoles
American Chemical Society
2016
PdBr
Catalytic Studies
metal precursor
Bromido substitution
ci
chelating phosphines
precursor salt
Ligand replacements
complex
2016-01-26 12:08:35
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Dinuclear_Triazole_Derived_Janus_Type_N_Heterocyclic_Carbene_Complexes_of_Palladium_Syntheses_Isomerizations_and_Catalytic_Studies_toward_Direct_C5_Arylation_of_Imidazoles/2067588
The
dipalladium triazolidine-diylidene complex <i>all-trans</i>-[PdBr<sub>2</sub>(CH<sub>3</sub>CN)]<sub>2</sub>(μ-ditz) (<b>1</b>) (ditz = 1,2,4-trimethyltriazolidine-3,5-diylidene) was
synthesized via <i>in situ</i> deprotonation of the precursor
salt with a basic metal precursor. Ligand replacements of <i>all</i><b>-</b><i>trans</i><b>-1</b> with
monodentate or chelating phosphines afforded the dicarbene-bridged
complexes <i>all-cis</i>-[PdBr<sub>2</sub>(PPh<sub>3</sub>)]<sub>2</sub>(μ-ditz) (<b>2</b>) and [PdBr(DPPP)]<sub>2</sub>(μ-ditz)Br<sub>2</sub> (<b>3</b>), respectively.
Bromido substitution of <i>all-cis</i><b>-2</b> gave
tetra-acetato complex <i>all-cis</i>-[Pd(CH<sub>3</sub>COO)<sub>2</sub>(PPh<sub>3</sub>)]<sub>2</sub>(μ-ditz) (<b>4</b>) with retention of the configuration as the predominant product.
In addition, monopalladium triazolin-5-ylidene complexes <i>trans</i>-[PdBr<sub>2</sub>(CH<sub>3</sub>CN)(tazy)] (<b>6</b>, tazy
=1,4-dimethyltriazolin-5-ylidene), <i>cis</i>-[PdBr<sub>2</sub>(PPh<sub>3</sub>)(tazy)] (<b>7</b>), [PdBr(DPPP)(tazy)]Br
(<b>8</b>), and <i>cis</i>-[Pd(CH<sub>3</sub>COO)<sub>2</sub>(PPh<sub>3</sub>)(tazy)] (<b>9</b>) were also synthesized
as the respective mononuclear equivalents for comparison. A comparative
catalytic study revealed the general superiority of dinuclear complexes <b>1</b>–<b>4</b> over their respective mononuclear
counterparts <b>6</b>–<b>9</b> in the direct C5-arylation
reaction of 1-methylimidazoles. Overall, mixed dicarbene/diphosphine
complex <b>3</b> showed the best catalytic performance.