Vinyl C−F Cleavage by Os(H)₃Cl(PⁱPr₃)₂

Abstract

Os(H)(3)ClL(2) (L = P(i)Pr(3)) reacts at 20 degrees C with vinyl fluoride in the time of mixing to produce OsHFCl([triple bond]CCH(3))L(2) and H(2). In a competitive reaction, the liberated H(2) converts vinyl fluoride to C(2)H(4) and HF in a reaction catalyzed by Os(H)(3)ClL(2). A variable-temperature NMR study reveals these reactions proceed through the common intermediate OsHCl(H(2))(H(2)C=CHF)L(2), via OsClF(=CHMe)L(2) and OsHCl(H(2))(C(2)H(4))L(2), all of which are detected. DFT(B3PW91) calculations of the potential energy and free energy at 298 K of possible intermediates show the importance of entropy to account for their thermodynamic accessibility. Calculations of unimolecular C-F cleavage of coordinated C(2)H(3)F confirms the high activation energy of this process. Catalysis by HF is thus suggested to account for the fast observed reactions, and scavenging of HF with NEt(3) changes the product to exclusively Os(H)(2)Cl(CCH(3))L(2). The analogous reaction of Os(H)(3)ClL(2) with H(2)C=CF(2) produces exclusively OsHFCl(=CCH(3))L(2) and HF, and the latter is again suggested to catalyze C-F scission via the observed intermediates Os(H)(2)Cl(CF(2)CH(3))L(2) and OsHCl(=CFMe)L(2).

Selectivity of C–H Activation and Competition between C–H and C–F Bond Activation at Fluorocarbons

“…While preferred C−F activation of fluoroalkenes is not surprising with early d 0 transition metal complexes, an experimental-computational study shows that similar selectivity can be observed with late transition metal complexes, but for different reasons. 243 The reaction of OsH 3 ClL 2 (L = PiPr 3 ) with vinyl fluoride in toluene at 20 °C gives H 2 and a compound that is identified as an alkylidyne complex, OsH(Cl)(F)(CMe)L 2 . The release of H 2 leads to another reaction that is competitive for vinyl fluoride in which ethylene and HF are produced by the reaction of CH 2 CHF with H 2 in the presence of the osmium complex.…”

“…This interpretation was consistent with the reaction of OsH 3 ClL 2 with CH 2 CF 2 where HF is released and OsH(Cl)(F)( CMe)L 2 is the only observed osmium product, and no ethylene, vinyl fluoride, or ethyl fluoride are detected. 243 Other complexes showed similar preferences for C−F activation. Catalytic dehalogenation (F/Cl) of fluorinated/ chlorinated ethylene by (PPh 3 ) 3 RhCl in the presence of Et 3 SiH at 35 °C gives ethylene as the final product with the intermediate formation of monohalogenated (F/Cl) ethylene.…”

“…Late transition metal complexes. While preferred C-F activation of fluoroalkenes is not surprising with early d 0 transition metal complexes, an experimental-computational study shows that similar selectivity can be observed with late transition metal complexes, but for different reasons 243. The reaction ofOsH 3 ClL 2 (L = PiPr 3 ) with vinyl fluoride in toluene at 20° C gives H 2 and a compound that is identified as an alkylidyne complex, OsH(Cl)(F)(CMe)L 2 .…”

Activation of Aromatic, Aliphatic, and Olefinic Carbon–Fluorine Bonds Using Cp*2HfH2

“…While an olefin insertion prior to β-fluoride elimination mechanism seems to be operative for other non-cyclic olefins, [4,[12][13][14][15] such a process cannot be responsible for the formation of observed products in this case, because the product predicted by the mechanism is not observed [Equation (11)]. Consequently, a new mechanism must be postulated for this facile olefinic hydrogenolysis.…”

“…Furthermore, olefinic fluorocarbons have been shown to participate in β-fluoride elimination following insertion into metal-hydride bonds, leading to the generation of a new fluorocarbon or small fluorine-containing molecule. [12][13][14][15] For perfluoroalkyl-metal complexes, α-fluoride elimination has been shown to be operative in several systems, many of which feature the use of Group 9 metals.…”