X-ray Structural Analysis of Tetramethylammonium Fluorochromate(VI). A Link between Reactivity and the Extent of Symmetry

Abstract

The crystal and molecular structure of tetramethylammonium fluorochromate(VI), (CH 3 ) 4 N[CrO 3 F] has been determined at 130(2) K by X-ray diffraction. X-ray data clearly demonstrate inequality between the CrÀO and the CrÀF bonds that is responsible for the higher reactivity of this compound over similar oxidizing agents in terms of the amount of oxidant and solvent required, short reaction times and high yields. The reason for this inequality is due to the CHÁ Á ÁF hydrogen bond that forms between the methyl hydrogen of the cation and the fluoride atom of the anion. The IR spectrum and hydrogen bonding of this compound is similar to the tetramethylammonium perchlorate salt and shows the existence of hydrogen bonding.

Some aspects of tetramethylammonium fluorochromate (VI) oxidations and identification of the reduced chromium species

“…This accord with the earlier observations with pyridinium fluoro and chloro chromates [15,16]. According to previous studies this mechanism is proposed to involve the formation of a chromate ester in a fast preequilibrium step and then a disproportion of the ester in a subsequent slow step via a cyclic concerted symmetrical transition state leading to the product (Scheme 2).…”

“…This type of hydrogen bonding in tetramethylammonium salts has been studied by Harmon et al [20]. The IR spectrum and hydrogen bonding of this compound is similar to the tetramethylammonium perchlorate salt and shows the existence of hydrogen bonding [15,21]. The oxidation of alcohols results in the formation of corresponding aldehydes or ketones.…”

“…Oxo complexes of transition metals are also as general purpose, stoichiometric oxidant in synthetic organic chemistry and a variety of reaction pathways including both atom-transfer and electron-transfer are involved [15,16]. (CH 3 ) 4 N[CrO 3 F] was prepared by the reaction of (CH 3 ) 4 NF and CrO 3 in a 1:1 ratio in acetonitrile solvent as follows:…”

Chromium Oxide Tetrafluoride and Its Reactions with Xenon Hexafluoride; the [XeF5]+ and [Xe2F11]+ Salts of the [CrVIOF5]−, [CrVOF5]2−, [CrV2O2F8]2−, and [CrIVF6]2− Anions

“…The chromium(VI) oxide fluorides, CrO 2 F 2 [1,2] and CrOF 4 , [3][4][5] and salts of the [CrO 3 F] À , [6][7][8] [CrO 2 F 3 ] À , [9] cis-[CrO 2 F 4 ] 2À , [3,10,11] and [CrOF 5 ] À [4,5] anions have been synthesized and characterized. Synthetic and structural studies have shown that CrOF 4 is sufficiently Lewis acidic to form stable adducts with the noble-gas difluorides NgF 2 (Ng = Kr, [5,12] Xe [12] )( vide infra).…”

Synthesis and characterization of new bromomolybdate complex (C6H13)4N MoO3Br

“…When halochromates of type CrO 3 X -(X = F, Cl, Br) having isolated tetrahedral anions, known for some time and are readily accessible by reaction in solution (Brauer, 1960;Ghammami and Sadjadi, 2005;Mahjoub et al, 2003) the corresponding molybdates are not found in similar way. We had prepared and reported synthesis of some [CrO 3 F]and [CrO 3 Cl]anions with tetralkylammonium counter ion previously (Ghammamy et al, 2006;Mahjoub et al, 2000). We have managed to prepare a new bromo compound of molybdenum which is analog of the above chromium compounds.…”