1-[(<i>S</i>)-1-Phenylethyl]-1<i>H</i>-benzimidazole

Williamson, Craig; Storey, John M. D.; Harrison, William T. A.

doi:10.1107/s1600536807029637

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“…Their bond lengths and bond angles are in the normal range compared to similar reported compounds (Table 1). 50,51 The palladium(II)-N-heterocyclic carbene pyridine complexes Pd-C1, Pd-C2, and Pd-C3 were prepared in very good yields by reacting palladium(II) bromide with 1.0 equiv of the appropriate ligand precursor (NHC-1, NHC-2, and NHC-3) in an excess amount of pyridine, as shown in Scheme 4. The complexes were purified by passing through a column of silica gel layered with a short pad of celite to afford yellow solids.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Soft Heteroleptic N-Heterocyclic Carbene Palladium(II) Species for Efficient Catalytic Routes to Alkynones via Carbonylative Sonogashira Coupling

et al. 2020

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N , N ′-Substituted di-isopropyl ( NHC-1 ), benzyl-isopropyl ( NHC-2 ), and adamantyl-isopropyl ( NHC-3 ) benzimidazolium salts react with palladium(II) bromide in pyridine to afford the corresponding trans -dibromidopyridinepalladium(II) complexes Pd-C1 , Pd-C2 , and Pd-C3 in high yields. A distorted square planar geometry for Pd-C2 and Pd-C3 was confirmed by single-crystal X-ray diffraction. The palladium(II) complexes show a remarkably higher catalytic activity and selectivity, compared to the literature data, in carbonylative Sonogashira coupling reactions of aryl iodides and aryl diiodides with aryl alkynes, alkyl alkynes, and dialkynes. Excellent yields with as low as 0.03 mol % loading of the catalyst were obtained. In the series of benzimidazolium (NHC) precursors, the 1 H NMR signals of the α hydrogen show a consistent probing of the N-substituent donor strength. The density functional theory (DFT) quantum mechanical descriptors of the frontier orbitals were calculated. A linear correlation of the calculated absolute softness of the complexes versus the calculated percent buried volume (% V bur ) of their corresponding ligands was obtained. The catalytic activity experimental data are consistent with the hard soft acid base (HSAB)-predicted high affinity of the softest Pd-C3 complex for soft substrates, such as aryl iodides.

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Section: ■ Results and Discussionmentioning

confidence: 99%

“…Their bond lengths and bond angles are in the normal range compared to similar reported compounds (Table ). , …”

Section: Resultsmentioning

confidence: 99%