2015
DOI: 10.1002/anie.201508659
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Tetraalkylammonium Salts as Hydrogen‐Bonding Catalysts

Abstract: Although the hydrogen-bonding ability of the α-hydrogens on tetraalkylammonium salts is often discussed in the chemistry of phase-transfer catalysts, the catalysis that utilizes the hydrogenbond donor properties of tetraalkylammonium salts remains unknown. In the present work, we demonstrated hydrogen-bonding catalysis with newly designed tetraalkylammonium salt catalysts in Mannich-type reactions. Both the structure and the hydrogenbonding ability of the new ammonium salts were investigated via Xray diffracti… Show more

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Cited by 88 publications
(46 citation statements)
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“…Surmising that even stronger binding was possibly being masked by tight ion-pairing,o ther capsule salts, 1·4 X, were then prepared either directly from the relevent Pd II source (X À = BF 4 À )orbyadding excess NaX or KX to 1·4 OTf( X À = PF 6 À ,S bF 6 À ,B ArF À [BArF = B-(3,5-(CF 3 ) 2 C 6 H 3 ) 4 À ]). [12] Non-capsule salts were removed by exploiting the low solubility of 1·4 Xi ne ither methanol or water, while 19 FNMR spectroscopy confirmed anion metathesis.I nterestingly,c omparing the 1 HNMR spectra of 1·4 X (see Figures S3, S27 in the Supporting Information) indicates that the stronger coordinating anions,O Tf À and BF 4 À in particular,are likely to reside within the cavity of the capsule, with internal signals H a and H e being notably deshielded by up to 0.2 ppm in the case of both 1·4 OTfa nd 1·4 BF 4 . [13] The affinity of 1 4+ for the different anions was also qualitatively observed using ESI-MS; 1·4 OTfexhibited dominant 2 + and 3 + charge states with two and one associated anions, respectively,w hile the "naked" 1 4+ was the major ion with 1·4 BArF (Figures S28-32).…”
mentioning
confidence: 99%
“…Surmising that even stronger binding was possibly being masked by tight ion-pairing,o ther capsule salts, 1·4 X, were then prepared either directly from the relevent Pd II source (X À = BF 4 À )orbyadding excess NaX or KX to 1·4 OTf( X À = PF 6 À ,S bF 6 À ,B ArF À [BArF = B-(3,5-(CF 3 ) 2 C 6 H 3 ) 4 À ]). [12] Non-capsule salts were removed by exploiting the low solubility of 1·4 Xi ne ither methanol or water, while 19 FNMR spectroscopy confirmed anion metathesis.I nterestingly,c omparing the 1 HNMR spectra of 1·4 X (see Figures S3, S27 in the Supporting Information) indicates that the stronger coordinating anions,O Tf À and BF 4 À in particular,are likely to reside within the cavity of the capsule, with internal signals H a and H e being notably deshielded by up to 0.2 ppm in the case of both 1·4 OTfa nd 1·4 BF 4 . [13] The affinity of 1 4+ for the different anions was also qualitatively observed using ESI-MS; 1·4 OTfexhibited dominant 2 + and 3 + charge states with two and one associated anions, respectively,w hile the "naked" 1 4+ was the major ion with 1·4 BArF (Figures S28-32).…”
mentioning
confidence: 99%
“…In light of the recent studies by Shirakawa and Maruoka [5051], we propose that catalysts L13 could act not only through Coulombic interactions, but also as hydrogen bond donors. While various factors including Coulombic interactions between the pyridinium (or ammonium) salt and the chloride undoubtedly play an important role in promoting substrate ionization and chloride complexation, the provided X-ray data are consistent with L13 acting as hydrogen bond donors (Scheme 10).…”
Section: Reviewmentioning
confidence: 86%
“…The existence of alpha C–H hydrogen bonds has also been invoked in the computational studies rationalizing the outcome of various asymmetric phase-transfer reactions [4649]. However, despite these developments until recently [5051] the use of tetraalkylammonium salts as hydrogen bond donor catalysts has not been explored.…”
Section: Reviewmentioning
confidence: 99%
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