The chemistry of niobium and tantalum halides, MX5, with haloacetic acids and their related anhydrides: Anhydride C–H bond activation promoted by MF5

Abstract

Niobium and Tantalum pentahalides, MX 5 (1), react with acetic acid and halo-substituted acetic acids, in 1:1 ratio, to give the dinuclear complexes [MX 4 (µ-OOCMe)] 2 [M = Nb, X = Cl, 2a; M = Ta, X = Cl, 2b, Br, 2c] and [MCl 4 (µ-OOCR)] 2 [M = Nb, R = CH 2 Cl, 4a, CHCl 2 , 4c, CCl 3 , 4e, CF 3 , 4g, CHBr 2 , 4i, CH 2 I, 4j; M = Ta, R = CH 2 Cl, 4b, CHCl 2 , 4d, CCl 3 , 4f, CF 3 , 4h]. The solid state structures of 2b and 4e have been ascertained by X ray diffraction studies. The reactions of 1 with acetic anhydride and halo-substituted acetic anhydrides result in CO bond activation and afford 2 and 4 respectively, with concomitant formation of acetyl halides. Moreover, the complexes MCl 5 [OC(Cl)Me] [M = Nb, 3a; M = Ta, 3b] have been detected in significant amounts within the mixtures of the reactions of MCl 5 with acetic anhydride. TaI 5 is unreactive, at room temperature, towards both CH 3 COOH and (CH 3 CO) 2 O. MF 5 react with RCOOH (R = Me, CH 2 Cl) in 1:1 molar ratio, to afford the ionic compounds [MF 4 (RCOOH) 2 ][MF 6 ], 5a-d, in high yields. The additions of (RCO) 2 O (R = Me, CH 2 Cl) to MF 5 give 5, suggesting that anhydride C-H and CO bonds activation is operative during the course of these reactions.

Synthesis and Dual-Mode Electrochromism of Anisotropic Monoclinic Nb12O29Colloidal Nanoplatelets

“…A similar complex was reportedly formed by mixing NbCl 5 and acetic acid to form niobium chloro carboxylate, with one carboxylate ion coordinating to two Nb 5+ ions in a bridging configuration. 29 Upon converting the NbP-40 to NbP-120, we hypothesize that the quenching of LMCT absorption is due to the conversion from a complex-like composition to an oxide-like composition, consistent with NbP-120 having absorption residing largely in the UV region. NbP-120, behaving similarly to an oxide, is referred to as a niobium oxo cluster for the remaining discussion.…”

“…It was reported that niobium chloro carboxylate will react with acid anhydride to form acyl chloride. 38 In our reaction environment, the analogues would be oleic anhydride and oleoyl chloride. In the IR and 1 H-NMR spectra of NbP-40 ( Figure 2d and 2e), the C=O stretch (1802 cm -1 ) and triplet resonance at 2.88 ppm can be assigned to oleoyl chloride.…”

“…(1)). 38 At the same time, a small amount of OA condenses into oleic anhydride with water as byproduct ( Figure 3, Eq. (2)), and subsequently, oleic anhydride reacts with the remaining NbCl5 to form oleoyl chloride and niobium chloro oleate (Figure 3, Eq.…”

“…(3)), as suggested in literature. 38 Heating to 120 o C further drives reaction (2) to generate more water that reacts with niobium chloro oleate via hydrolysis to form niobium oxo clusters (Figure 3, Eq. (4)).…”

Interaction of niobium and tantalum pentahalides with O-donors: coordination chemistry and activation reactions

“…36 These reactions preserve altogether the highly energetic M-F bonds, thus preventing the activation of O-H bonds. On the other hand, it has been known since many years that the heavier pentahalides MX 5 (M = Nb, Ta; X = Cl, Br, I) react with alcohols/phenols 1,34,75 or carboxylic acids, 76,77 in variable molar ratios, giving alcoholato/carboxylato derivatives via O-H bond cleavage and HX release. The latter derivatives generally maintain the dinuclear structure typical of the starting materials, unless additional donor atom is present in the organic moiety.…”