Reactions of an Osmium-Elongated Dihydrogen Complex with Terminal Alkynes: Formation of Novel Bifunctional Compounds with Amphoteric Nature

Abstract

The trihydride complex (1) reacts with HBF4·H2O to give the elongated dihydrogen derivative (2), with a separation between the hydrogen atoms of the elongated dihydrogen of 1.35 Å. The addition of acetone oxime to dichloromethane solutions of 2 produces the substitution of the water ligand by the oxime and the formation of (3), which shows a hydrogen−hydrogen distance of 1.34 Å. Complex 3 reacts with phenylacetylene, cyclohexylacetylene, and tert-butylacetylene to give acetophenone and the oximate-carbyne derivatives [OsH{κ-N,κ-O[ONC(CH3)2]}(⋮CCH2R)(PiPr3)2]BF4 (R = Ph (4), Cy (5), tBu (6)). The structure of 4 has been determined by X-ray diffraction analysis. The distribution of ligands around the osmium atom can be described as a distorted trigonal bipyramid with apical phosphines and inequivalent angles within the Y-shaped equatorial plane. Complexes 4−6 have amphoteric nature, reacting with both KOH and HBF4·Et2O. The reactions with KOH afford the vinylidene derivatives OsH{κ-N,κ-O[ONC(CH3)2]}(CCHR)(PiPr3)2 (R = Ph (7), Cy (8), tBu (9)), whereas the reactions with HBF4·Et2O give the fluoro-oxime compounds (R = Ph (10), Cy (11), tBu (12)). The structures of 7 and 11 have been determined by X-ray diffraction analysis. The distribution of ligands around the osmium atom of 7 is like that of 4, whereas the geometry around the metallic center of 11 can be rationalized as a distorted octahedron with the phosphine ligands in trans positions. Complexes 10, 11, and 12 contain a strong intramolecular F- - -H hydrogen bond between the fluorine and the OH-hydrogen atom of the oxime in the solid state and in dichloromethane solution (JH-F = 67.5 (10), 68.1 (11), and 68.7 (12) Hz). The formation of 4−12 is also discussed, on the basis of deuterium label experiments.