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

The trihydride complex ( 1 ) reacts with HBF 4 ·H 2 O 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 [ON C(CH 3 ) 2 ]}(⋮CCH 2 R)(P i Pr 3 ) 2 ]BF 4 (R = Ph ( 4 ), Cy ( 5 ), t Bu ( 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 HBF 4 ·Et 2 O. The reactions with KOH afford the vinylidene derivatives OsH{κ- N,κ- O [ON C(CH 3 ) 2 ]}( C CHR)(P i Pr 3 ) 2 (R = Ph ( 7 ), Cy ( 8 ), t Bu ( 9 )), whereas the reactions with HBF 4 ·Et 2 O give the fluoro-oxime compounds (R = Ph ( 10 ), Cy ( 11 ), t Bu ( 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 ( J H - 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.