Reversing Lewis acidity from bismuth to antimony

Abstract

Investigations on the boundaries between the neutral and cationic models of (Mesityl)2EX (E = Sb, Bi and X = Cl―, OTf―) have facilitated reversing the Lewis acidity from bismuth to...

Lewis Superacidic Heavy Pnictaalkene Cations: Comparative Assessment of Carbodicarbene-Stibenium and Carbodicarbene-Bismuthenium Ions

“…Interestingly, the AN for the Sb compound 3 (78) is much higher than 8 (65)the bismuth analogue of 4 . This reversal in expected Lewis acidity moving down the periodic table was recently observed in a set (mesityl) 2 PnOTf (Pn = Sb or Bi) complexes reported by Venugopal . Pellois and Gabbaï have also observed a reversal in Lewis acidity in a set of pnictogenium cations as evaluated using fluoride anion affinity .…”

“…Venugopal and co-workers observed a reversal in the Lewis acidity of bis(mesityl) antimony and bismuth compounds when the chloride substituent was replaced with triflate (Figure 4a). 46 They also observed an increase in Lewis acidity as the ligand bite angle decreased, whereby the AN of b increased from 55 to 69 when the chelating ligand decreases from a fiveto four-membered ring. 67 Venugopal has also prepared an acidic bismuth dication coordinated to a tridentate trispyrazolylborate ligand (c), which catalyzes the hydrosilylation of olefins under mild conditions.…”

“…This reversal in expected Lewis acidity moving down the periodic table was recently observed in a set (mesityl) 2 PnOTf (Pn = Sb or Bi) complexes reported by Venugopal. 46 Pellois and Gabbai ̈have also observed a reversal in Lewis acidity in a set of pnictogenium cations as evaluated using fluoride anion affinity. 45 Addition of one equivalent of O�PEt 3 to the stibenium trication 11 resulted in a sharp peak at 90.5 ppm in the 31 P NMR spectrum, which corresponds to an exceptionally high AN of 109.…”

“…Not only is this the first quantitative assessment of Lewis acidity for heavy element carbone-pnictenium ions, but CSb + , CSb 2+ , and CSb 3+ compounds with strong multiple bond character are hitherto unknown, with antimony representing the only missing element from the cationic pnictaalkene family. Considering the reports from Pellois and Gabbaï and Venugopal who observed a reversal in the Lewis acidity trend for Sb and Bi, we were particularly interested in accessing these molecules. Notably, the Gutmann−Beckett acceptor numbers (AN) for the pyridyl-substituted CDC-Sb 3+ and CDC-Bi 3+ complexes are among the highest observed for any cationic antimony or bismuth compound in the literature, and based on fluoride ion affinities (FIAs) they may be considered Lewis superacids.…”

Binuclear Triphenylantimony(V) Catecholates through N-Donor Linkers: Structural Features and Redox Properties

“…Organoantimonials represent a very diverse class of antimony compounds, attracting growing attention from scientists because of the variety of structural motifs offered by this type compounds (including acting as ligands in different complexes) [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ], various and sometimes unusual reactivity [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ], and prospective applications in biochemistry and medicine [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. So, some tetraarylstibonium cations, as well as cationic stibine–palladium complexes, may be used as sensors for the toxic fluoride anion, even in water [ 31 , 32 , 33 , 34 ], can activate the Element–Fluorine bond and promote the hydrodefluorination of fluoroalkanes in the presence of Et 3 SiH [ 35 ], or activate the Ag–Cl bond in gold chloride complex to catalyze the cyclization of propargyl amides [ 36 ].…”