Structural Characterization, Solution Dynamics, and Reactivity of Palladium Complexes with Benzimidazolin2-ylidene N- Heterocyclic Carbene Ligands

作者：Hohloch Stephan; Deibel Naina; Schweinfurth David; Frey Wolfgang; Sarkar Biprajit^*

来源：European Journal of Inorganic Chemistry, 2014, 2014(12): 2131-2139.

DOI：10.1002/ejic.201301339

• Carbene ligands
• Structure elucidation
• Palladium
• Click chemistry
• Cross coupling

Mononuclear and halide-bridged dinuclear palladium(II) complexes with symmetrically (1 and 3) and nonsymmetrically (2, 4-6) substituted benzimidazolin-2-ylidene N-heterocyclic carbene ligands were synthesized and characterized by H-1 and C-13 NMR spectroscopy, elemental analysis, and X-ray crystallography. The mononuclear complexes exist as a mixture of cis and trans isomers, and the identity of these was ascertained by NMR spectroscopy and structural characterization. The dinuclear complexes 4-6 with nonsymmetrically substituted benzimidazolin-2-ylidene ligands form rotamers (cis/anti, cis/syn, trans/anti, and trans/syn) at room temperature, which can be transformed to a single rotamer at higher temperatures as evidenced by H-1 NMR spectroscopy. Crystal structure analyses of representative examples show that the Pd-II centers are bound in a distorted square-planar environment by halides and carbene C ligands, and the carbene ligands are perpendicular to the Pd-halide plane. All of the complexes were tested for their efficiency as (pre)catalysts in the Suzuki-Miyaura cross-coupling reaction, as well as in hydrodehalogenation reactions, and they show good activity. The Suzuki-Miyaura coupling reactions can be performed under air and in water as an environmentally benign solvent. The most active catalyst for the Suzuki-Miyaura coupling was also used in a sequence together with a click reaction to synthesize valuable sterically demanding tripodal triazole ligands.

• 出版日期2014-4