Structural Characterization, Solution Dynamics, and Reactivity of Palladium Complexes with Benzimidazolin‐ 2‐ylidene N‐Heterocyclic Carbene Ligands. Issue 12 (13th March 2014)

• Record Type: Journal Article
• Authors: Hohloch, Stephan; Deibel, Naina; Schweinfurth, David; Frey, Wolfgang; Sarkar, Biprajit
• Is Part Of: European journal of inorganic chemistry. Issue 12(2014)
• Page Start: 2131
• Page End: 2139
• Publication Date: 2014-03-13
• Subjects: Carbene ligands -- Structure elucidation -- Palladium -- Click chemistry -- Cross coupling; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201301339
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract: Mononuclear and halide‐bridged dinuclear palladium(II) complexes with symmetrically (1 and3 ) and nonsymmetrically (2, 4 –6 ) substituted benzimidazolin‐2‐ylidene N‐heterocyclic carbene ligands were synthesized and characterized by 1 H and 13 C 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 complexes4 –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 1 H 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. Abstract : Pd II complexes with symmetrically and nonsymmetrically substituted benzimidazolylidene ligands are presented. The complexes exist as various isomers and rotamers in solution and exhibit C–H··· Pd interactions in the solid state and in solution. All of the complexes are potent (pre)catalysts for the Suzuki–Miyaura cross‐coupling reaction in water and the hydrodehalogenation reactions of haloarenes.