Ligand exchange and reaction mechanisms offluorinated compounds

Bis(perchlorocatecholato)silane—A Neutral Silicon Lewis Super Acid

“…[8] Addition of 2equivalents of tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF) led to the immediate formation of the bisfluorido(biscatecholato)silicate dianion [1-F 2 ][S(NMe 2 ) 3 ] 2 (see Figure 3b), showing at riplet ( 1 J SiF = 152 Hz) at À155 ppm in the 29 Si-NMR spectrum. [24] Importantly,i na greement with our computational results,n of luoride abstraction from [PPh 4 ][SbF 6 ]o ccurred with the weaker Lewis acid Si(cat F ) 2 . Thes olid-state structural analysis revealed a trans-arrangement of the fluorides instead, with SiÀFb ond lengths of 1.686 .…”

“…However, and similar to reactions with PF 6 − salts (see Supporting Information for details), the finally identified product contained the tris(perchlorocatecholato)antimonate anion (see Supporting Information for X‐ray diffraction), likely driven by the release of SiF 4 (for a proposed reaction scheme and the identification of all observed intermediates by 19 F‐NMR/ESI‐MS, see Supporting Information). Clearly, the neutral silicon Lewis acid 1 abstracts a fluoride ion from SbF 6 − , as the first necessary elementary step in the observed reaction cascade, serving as the experimental confirmation of its Lewis super acidity . Importantly, in agreement with our computational results, no fluoride abstraction from [PPh 4 ][SbF 6 ] occurred with the weaker Lewis acid Si(cat F ) 2 .…”

Lithium fluoride formed in situ is trapped by [TiF3(C5Me5)]2: an equilibrium with cleavage of a Ti–F–Ti bond and a model compound for molecular lithium fluoride

“…Fluorine bridging accounts for structural diversity of fluorides of main group elements and transition metals and for formation of reaction intermediates. 1 The reactivity of a Ti-F-Ti unit in fluorotitanium compounds is of particular interest since the cleavage of this unit would leave the titanium centre with high electrophilicity due to polar Ti-F bonds. 2 The catalytic activity of the fluorotitanium binaphthol complex used in the enantioselective addition of allylsilanes to aldehydes 3 was explained by cleavage of two Ti-F-Ti bonds during the catalytic cycle.…”

Silicon−Fluorine and Silicon−Carbon Bond Cleavage in Organofluorosilicates: A Molecular Orbital Study

“…The bond energies of Si−F and Si−C bonds are quite high, on the order of 565 and 318 kJ mol -1 , respectively, yet these bonds in organofluorosilanes and -silicates may be cleaved under mild conditions in the presence of fluoride ion. A mechanism which accounts for the cleavage of Si−F bonds in typical fluorosilicates such as RSiF 4 - and RSiF 5 2- , and involves a fluorine-bridged intermediate is shown in Scheme . In this mechanism the N−X−L notation of Perkins et al.…”

“…A three-stage method of analyzing reaction mechanisms has been proposed recently. ,, This method requires, first, the construction of a reaction pathway P( X , C ) which defines each elementary step of a reaction mechanism and specifies the connectivity of atoms along that pathway, taking into account their coordination number and electron count. Second, the pathway P( X , C ) is tested by carrying out molecular orbital calculations of all postulated intermediates, and that is the subject of this paper with regard to the mechanisms of Schemes and .…”