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

Abstract

Complex OsH3(SnPh2Cl){è2-CH2dC(CH3)PiPr2}(PiPr3) (1) reacts with acetophenone and benzophenone to give OsH2(SnPh2Cl){C6H4C(O)R}(PiPr3)2 (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 ¢Hq ) 11.9 ( 0.5 kcalâmol-1 and ¢Sq ) -0.7 ( 1.2 calâmol-1âK-1 for 2 and ¢Hq ) 11.8 ( 0.2 kcalâmol-1 and ¢Sq ) -2.6 ( 1.9 calâmol-1âK-1 for 3. The reaction of 1 with perdeuterated benzophenone affords the hydridedeuteride Os(H)(D)(SnPh2Cl){C6D4C(O)C6D5}(PiPr3)2 (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 OsH2(SnPh2Cl){C6H4C(O)- C6F5}(PiPr3)2 (4) and OsH2(SnPh2Cl){C6H3FC(O)CH3}(PiPr3)2 (5). In solution, the hydride ligands of 4 and 5 also exchange their positions. In this case, the activation parameters are ¢Hq ) 12.6 ( 0.5 kcalâmol-1 and ¢Sq ) -2.9 ( 1 calâmol-1âK-1 for 4 and ¢Hq ) 11.2 ( 0.4 kcalâmol-1 and ¢Sq ) -2.8 ( 1.1 calâmol-1âK-1 for 5. The reaction of 1 with benzophenone imine leads to OsH2(SnPh2Cl){C6H4C(NH)C6H5}(PiPr3)2 (6), which has been characterized by X-ray diffraction analysis. The structure reveals an intramolecular ClâââH-N hydrogen bond between the chlorine bonded to the tin atom and the hydrogen of the imine. Treatment of 6 with KOH affords OsH2(SnPh2OH){C6H4C(NH)C6H5}(PiPr3)2 (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 OsH2{Sn(CHdCH2)2Cl}{C6H4C(O)- CH3}(PH3)2 (2t) and OsH2{Sn(CHdCH2)2X}{C6H4C(NH)CH3}(PH3)2 (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.