Crown ether complexes exhibiting unusual 1:2 macrocycle salt ratios: X-ray crystal structures of cyclohexano-15-crown-5•2LiOPh, cyclohexano-15-crown-5•2NaOPh, and 15-crown-5•2NaOPh

Watson, Kimberly A.; Fortier, Suzanne; Murchie, Michael P.; Bovenkamp, John W.

doi:10.1139/v91-103

Cited by 19 publications

(15 citation statements)

References 17 publications

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“…Further, the O atom of the oxazoline ring ortho to the coordinating CF 3 group is also coordinated to the sodium cation with a distance of 2.57 Å, while not particularly short, this is in the range of Na−O distances found in crown ether complexes of sodium cations. 72 Thus, the CF3 Phebox ligand favors the Na + -promoted dechelation of the acetate through a bidentate coordination of the acetate-bound sodium cation with both F and O atoms of the ligand backbone.…”

Section: ■ Computational Studies and Discussionmentioning

confidence: 91%

“…The Na + –F distance in CF3 TS-trans-OA·Na + is 2.33 Å, which is comparable to the shortest CF···Na + distances that have been reported in crystallographic studies, , presumably indicating a particularly strong interaction, in accord with the lowered energies of this TS. Further, the O atom of the oxazoline ring ortho to the coordinating CF 3 group is also coordinated to the sodium cation with a distance of 2.57 Å, while not particularly short, this is in the range of Na–O distances found in crown ether complexes of sodium cations . Thus, the CF3 Phebox ligand favors the Na + -promoted dechelation of the acetate through a bidentate coordination of the acetate-bound sodium cation with both F and O atoms of the ligand backbone.…”

Section: Computational Studies and Discussionmentioning

confidence: 91%

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Alkane Dehydrogenation Catalyzed by a Fluorinated Phebox Iridium Complex

et al. 2021

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We report an iridium acetate complex with a fluorinated Phebox ligand (2,6-bis(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-3,5-bis(trifluoromethyl)phenyl) that is a highly effective catalyst for acceptorless dehydrogenation of alkanes. Under typical acceptorless dehydrogenation conditions, a high turnover frequency is obtained, which is limited by the rate of expulsion of H 2 from the reaction solution. Rates and turnover numbers for acceptorless dehydrogenation are significantly greater than found for the nonfluorinated analogue. As in the case of the nonfluorinated analogue, Na + acts as a cocatalyst with the fluorinated catalyst again yielding greater rates and total turnovers. Computational studies shed light on the possible mechanistic pathways. The initial alkane activation is a net Ir−H/C−H bond metathesis leading to the formation of an Ir−alkyl bond and loss of H 2 ; this is the slowest chemical step in the cycle. The lowest-energy pathway is calculated to proceed via concerted metalated deprotonation (CMD) of the alkane. Pathways proceeding via transition states with oxidative addition (Ir(V)) character, however, are calculated to be only slightly higher in energy. These transition states can lead either to Ir(V) intermediates, which then lose H 2 , or connect directly to a dihydrogen complex. The role of Na + is largely to promote dechelation by coordinating to an acetate oxygen, opening a vacant coordination site that allows reaction with the alkane. This coordination by Na + prevents the CMD mechanism from operating, but it significantly lowers the energy of the Ir(V) TSs. NBO analysis shows a net transfer of charge from the alkane atoms to the metal complex in the Ir(V) TSs, with and without coordinated Na + . Thus, the oxidative addition is actually reductive in nature, driven in part by electrophilicity of the metal center. The Na + cation further increases electrophilicity in addition to promoting dechelation. The greater activity of the fluorinated catalyst compared with the parent complex can also be explained in terms of the electrophilic nature of the reaction. The fluorinated catalyst is also more resistant to decomposition than the nonfluorinated analogue.

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Section: ■ Computational Studies and Discussionmentioning

confidence: 91%

Section: Computational Studies and Discussionmentioning

confidence: 91%

Alkane Dehydrogenation Catalyzed by a Fluorinated Phebox Iridium Complex

et al. 2021

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“…However, there is no report on the crystal structure of a LiCl−15C5 complex despite much work in this area. A search of the Cambridge Structural Database returned only four entries, with the structures of three Li + −15C5 complexes: [Li−15C5][In(CH 3 ) 3 Cl], 3 , 7a, and two polymorphs of 15C5−2LiOPh, 4a and 4b 7b. All of them have large counteranions of low charge density.…”

Section: Introductionmentioning

confidence: 99%

Two Novel Lithium−15-Crown-5 Complexes: An Extended LiCl Chain Stabilized by Crown Ether and a Dimeric Complex Stabilized by Hydrogen Bonding with Water

Boulatov

Meyers

et al. 1999

Inorg. Chem.

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Two lithium chloride-15C5 (15C5 = 15-crown-5) complexes, [Li(15C5)(&mgr;-Cl)(2)Li](infinity), 1, and {[Li(15C5)(H(2)O)]Cl}(2), 2, were synthesized. Their structures, characterized by single-crystal X-ray diffraction analyses, are dictated by the absence of or presence of water. Complex 1, prepared in an anhydrous environment, is the first example of an extended LiCl chain structure. It contains repeating units Li(&mgr;-Cl)Li(15C5) that are connected by additional bridging Cl atoms. One Li has close contacts with one Cl and all five O atoms of 15C5 and the other Li with three Cl and one O of 15C5. However, the chain structure cannot form in the presence of water. Instead dimeric complex 2 was formed when LiCl.xH(2)O (x = 1.14) was the starting material. In this case H(2)O is coordinated to lithium through a Li-O linkage and is hydrogen bonded to Cl(-) (H.Cl). The Li(+) cation is coordinated to the five O atoms of 15C5 as well as the O atom from H(2)O, and the Cl(-) counteranion is isolated from Li(+) by two hydrogen bonds with one H atom each from two H(2)O molecules with H.Cl distances of 2.30(4) and 2.35(4) Å, respectively. A crystallographically imposed center of symmetry generates a dimer that resembles a 2:2 anion-paired encapsulate. Crystal data for 1: space group Pna2(1) (no. 33), a = 14.974(1) Å, b = 13.553(1) Å, c = 7.160(1) Å, V = 1453.0(2) Å(3), Z = 4. Crystal data for 2: space group P2(1)/n (no. 14), a = 10.353(1) Å, b = 7.9070(1) Å, c = 17.741 Å, beta = 100.50(1) degrees, V = 1427.9(2) Å(3), Z = 4.

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“…Bridging O atoms in 15-crown-5 are rare but may allow in future the preparation of a larger range of macrocyclic compounds. 42,43 Further insight in potential ways of assembling [PhAsSe 3 ] 2− anions was gained, when traces of water were present in the reaction between [(PhAs) 2 (l-Se)(l-Se 2 )] and NaS t Bu (Scheme 2). It turned out that [PhAsSe 3 ] 2− anions are stable in the presence of water and a 2D polymeric arrangement was found in 5 (Fig.…”

Section: Resultsmentioning

confidence: 99%