Crystal structure of 5-(imidazol-1-yl)-25,26,27,28-tetrabenzyloxy- calix[4]arene (cone), C59H50N2O4

Brenner, Éric; Matt, Dominique; Toupet, Loı̈c

doi:10.1524/ncrs.2011.0201

Cited by 1 publication

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“…This is likely to arise from the unsymmetrical structure of the heterocycle which adopts a sideways orientation enabling its conjugation with the phenolic ring to which it is connected. 40 Unsurprisingly, the spectra of 2 and 9 showed the same feature.…”

Section: Palladium Complexes Derived From Monoimidazolium Salt 2 and ...mentioning

confidence: 88%

Calix[4]arenes with one and two N-linked imidazolium units as precursors of N-heterocyclic carbene complexes. Coordination chemistry and use in Suzuki–Miyaura cross-coupling

et al. 2011

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The calix[4]arene-imidazolium salts 5-(3-butyl-1-imidazolylium)-25,26,27,28-tetrabenzyloxy-calix[4]arene bromide (cone) (2), and 5,11-bis(3-alkyl-1-imidazolylium)-25,26,27,28-tetrabenzyloxycalix[4]arene diiodide (cone) (R = methyl, 3a; R = n-butyl, 3b) have been synthesised. Reaction of 2 in dioxane with PdCl(2) in the presence of CsCO(3) and KBr (80 °C, 24 h) gives the carbene complex trans-[PdBr(2)(calix-monocarbene)(2)] (14), containing two N-heterocyclic carbene ligands derived from 2 (yield: 63%). Repeating the reaction in pyridine instead of dioxane gives the mixed pyridine-carbene complex trans-[PdBr(2)(calix-carbene)(pyridine)] (15) in 75% yield. Treatment of the bis-imidazolium salt 3a with [Pd(OAc)(2)] affords a chelate complex, trans-[PdI(2){calix-bis(carbene)}] (16), in which a metallo-(bis-carbene) fragment caps the upper rim of the calixarene basket. Complex 16, as well as its analogue 17, obtained from 3b, display apparent C(s)-symmetry in solution. This is not the case in the solid state, a single X-ray diffraction study carried out for 16 revealing a pinced cone structure for the calixarene skeleton, which reduces the symmetry to C(1). The chelate complex 17 shows poor activity in Suzuki-Miyaura cross-coupling of phenyl boronic acid and p-tolyl halides, an observation that suggests the presence of a strained metallocyclic unit preventing easy stereochemical rearrangement to an active species. Unlike 17, complexes 14 and 15 show good activities in cross-coupling. A comparative study using the carbene precursor 1-butyl-3-(2,6-diisopropylphenyl)imidazolium bromide (18), which is devoid of the receptor fragment, strongly suggests that the carbene ligands of 14 and 15 operate typically as bulky NHC-ligands.

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Section: Palladium Complexes Derived From Monoimidazolium Salt 2 and ...mentioning

confidence: 88%

Calix[4]arenes with one and two N-linked imidazolium units as precursors of N-heterocyclic carbene complexes. Coordination chemistry and use in Suzuki–Miyaura cross-coupling

et al. 2011

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Crystal structure of 5-(imidazol-1-yl)-25,26,27,28-tetrabenzyloxy- calix[4]arene (cone), C59H50N2O4

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Cited by 1 publication

References 2 publications

Calix[4]arenes with one and two N-linked imidazolium units as precursors of N-heterocyclic carbene complexes. Coordination chemistry and use in Suzuki–Miyaura cross-coupling

Calix[4]arenes with one and two N-linked imidazolium units as precursors of N-heterocyclic carbene complexes. Coordination chemistry and use in Suzuki–Miyaura cross-coupling

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