Ortho-CH Activation of Aromatic Ketones, Partially Fluorinated Aromatic Ketones, and Aromatic Imines by a Trihydride-Stannyl-Osmium(IV) Complex

Abstract

Complex (1) reacts with acetophenone and benzophenone to give (R = CH3 (2), Ph (3)). In the solid state, the structure of 2 determined by X-ray diffraction analysis can be described as a pentagonal bipyramid with the phosphorus atoms of the phosphines occupying axial positions. In solution the hydride ligands of 2 and 3 undergo a thermally activated site exchange process. The activation parameters for the exchange are ΔH⧧ = 11.9 ± 0.5 kcal·mol-1 and ΔS⧧ = −0.7 ± 1.2 cal·mol-1·K-1 for 2 and ΔH⧧ = 11.8 ± 0.2 kcal·mol-1 and ΔS⧧ = −2.6 ± 1.9 cal·mol-1·K-1 for 3. The reaction of 1 with perdeuterated benzophenone affords the hydride-deuteride (3-d10), suggesting that the activation takes place on the monohydride intermediate OsH(SnPh2Cl)(PiPr3)2. The reaction pathway for the formation of this intermediate is evaluated by DFT calculations. Complex 1 also reacts with 2,3,4,5,6-pentafluorobenzophenone, 2-fluoroacetophenone, and benzophenone imine. The reactions with the partially fluorinated ketones give (4) and (5). In solution, the hydride ligands of 4 and 5 also exchange their positions. In this case, the activation parameters are ΔH⧧ = 12.6 ± 0.5 kcal·mol-1 and ΔS⧧ = −2.9 ± 1 cal·mol-1·K-1 for 4 and ΔH⧧ = 11.2 ± 0.4 kcal·mol-1 and ΔS⧧ = −2.8 ± 1.1 cal·mol-1·K-1 for 5. The reaction of 1 with benzophenone imine leads to (6), which has been characterized by X-ray diffraction analysis. The structure reveals an intramolecular Cl···H−N hydrogen bond between the chlorine bonded to the tin atom and the hydrogen of the imine. Treatment of 6 with KOH affords (7). The X-ray diffraction analysis of 7 shows a intramolecular O···H−N hydrogen bond and intermolecular HO···H interactions between the oxygen and the O−H hydrogen atom of two adjacent molecules in the crystal. DFT calculations on the model compounds (2t) and (X = Cl (6t), OH (7t)) have allowed the complete determination of the hydride positions in 2, 6, and 7 and the full characterization of the hydrogen bonds in 6 and 7.