(CF₃)₃Au as a Highly Acidic Organogold(III) Fragment

Abstract

The Lewis acidity of perfluorinated trimethylgold (CF ) Au was assessed by theoretical and experimental methods. It was found that the (CF ) Au unit is much more acidic than its nonfluorinated analogue (CH ) Au, and probably sets the upper limit of the acidity scale for neutral organogold(III) species R Au. The significant acidity increase on fluorination is in line with the CF group being more electron-withdrawing than CH . The solvate (CF ) Au⋅OEt (1) is presented as a convenient synthon of the unsaturated, 14-electron species (CF ) Au. Thus, the weakly coordinated ether molecule in 1 is readily replaced by a variety of neutral ligands (L) to afford a wide range of (CF ) Au⋅L compounds, which were isolated and characterized. Most of these mononuclear compounds exhibit marked thermal stability. This enhanced stabilization can be rationalized in terms of substantially stronger [Au]-L interactions with the (CF ) Au unit. An affinity scale of this single-site, highly acidic organogold(III) fragment was calculated by DFT methods and experimentally mapped for various neutral monodentate ligands. The high-energy profile calculated for the fluorotropic [Au]-CF ⇌F-[Au]←CF process makes this potential decomposition path unfavorable and adds to the general stabilization of the fragment.

Not Only Hydrogen Bonds: Other Noncovalent Interactions

“…The higher the oxidation degree (for instance, Au(III) vs. Au(I)) the more acidic the Lewis acid; see, for instance, the complex (CF 3 ) 3 Au• • • pyridine [63]. We cited Legon in a 2014 paper [64] The higher the oxidation degree (for instance, Au(III) vs.…”

“…We cited Legon in a 2014 paper [64] The higher the oxidation degree (for instance, Au(III) vs. Au(I)) the more acidic the Lewis acid; see, for instance, the complex (CF3)3Au•••pyridine [63]. We cited Legon in a 2014 paper [64] In 2019, several papers were published on regium bonds, from which we have selected the following four Reference works [65][66][67][68].…”

The First Organosilver(III) Fluoride, [PPh4][(CF3)3AgF]

“…Non‐reductive ionic dissociation of F − is highly endergonic: Δ G 0 =74.5 kcal mol −1 . This value is the reverse of the FIA corresponding to the (CF 3 ) 3 Ag fragment, which thus appears as a molecular Lewis acid of considerable strength . The overall thermodynamic balance for the concerted reductive elimination of CF 4 or C 2 F 6 is strongly favored (Δ G 0 <−52 kcal mol −1 ).…”

“…The resultsa re shown in SchemeS1( SI) and summarized in Scheme3.N on-reductive ionic dissociation of F À is highly endergonic: DG 0 = 74.5 kcal mol À1 .This value is the reverse of the FIA corresponding to the (CF 3 ) 3 Ag fragment, which thus appears as am olecular Lewis acid of considerable strength. [28] The overall thermodynamic balance for the concertedr eductivee limination of CF 4 or C 2 F 6 is strongly favored (DG 0 < À52 kcal mol À1 ). These concerted processes,h owever,i nvolveh igh activation barriers (DG°% 40 kcal mol À1 )t hat might well hindert he occurrence of these single-step two-electronr eductions in favor of less energetically demandingp aths.…”

Evaluation of the Lewis acidity of metal complexes using ESI mass spectrometry

“…Besides, the Lewis acidity has been studied by spectroscopy and other methods. [8][9][10][11][12][13][14][15] Although some advances have been made recently, a persistent problem spanning essentially all the methods is the sample specificity. Additionally, it was suggested that the closest to actual value of Lewis acidity, in theory, involves the calculation of the enthalpy change derived from the formation or dissociation of a Lewis acid-base pair in the vapor phase.…”