Synthesis and Characterization of OsX{NHC(Ph)C₆H₄}H₂(PⁱPr₃)₂ (X = H, Cl, Br, I):  Nature of the H₂ Unit and Its Behavior in Solution

Abstract

The hexahydride OsH6(PiPr3)2 (1) reacts with benzophenone imine to give the trihydride derivative (2). The three hydride ligands and the bidentate group of 2 are situated in the equatorial plane of a pentagonal-bipyramidal arrangement of ligands around the metallic center. In solution, two thermally activated exchange processes take place between these hydride ligands, one of them faster than the other one. The reaction of 2 with HCl leads to OsH3Cl(NHCPh2)(PiPr3)2 (3), which evolves in solution into the elongated dihydrogen compound (4). Complex 4 and the related compounds (X = Br (5), I (6)) can be also prepared by protonation of 2 with HBF4·OEt2 in dichloromethane and subsequent treatment with NaX (X = Cl, Br, I). The structure of 4 has been determined by X-ray diffraction. The geometry around the osmium atom can be described as a distorted octahedron, with the triisopropylphosphine ligands occupying two relative trans positions. The remaining perpendicular plane is formed by the mutually cis disposed chloro and dihydrogen ligands and the metalated benzophenone imine group, which has a bite angle of 75.1(1)°. The H2 unit of 4−6 shows a restricted rotational motion in solution. Thus, the 1H NMR spectra in the high-field region are a function of the temperature. Lowering the sample temperature leads to a broadening of the dihydrogen resonances. At 213 K, decoalescence occurs, and at 193 K, two signals are clearly observed. Theoretical calculations suggest that the transition states for the hydrogen exchanges in 2 and 4−6 present dihydrogen-like nature.

The Activation of Dihydrogen

“…Lluch, Lledos and coworkers have shown that the potential energy surface for elongation or contraction of the H-H distance is remarkably flat in the case of elongated dihydrogen complexes [58][59][60][61][62]. Heinekey and coworkers state, ".…”

Iron‐Mediated Coupling of Two Ethyl Anions to Form a 2‐Butyne Ligand

“…The hydrogen elimination may proceed by several α‐H abstraction steps in dinuclear intermediates to produce dihydrogen complexes. Dihydrogen complexes are known for the heavier congeners of iron, for example, the cyclopentadienylruthenium complexes [CpRu(dmpe)(H 2 )] + [dmpe = 1,2‐bis(dimethylphosphino)ethane]33,34 and [Cp*Ru(dppm)(H 2 )] + [dppm = 1,1‐bis(diphenylphosphino)methane],35,36 the cationic osmium complexes [Os(en) 2 (CH 3 COO)(H 2 )] + (en = ethylenediamine)37,38 and [Os(dppe) 2 Cl(H 2 )] + [dppe = 1,2‐bis(diphenylphosphino)ethane],39 the imine complexes [OsCl 2 (NH=CPh 2 )(P i Pr 3 ) 2 (H 2 )],40 and its ortho ‐metalated relative [OsCl{NH=C(Ph)C 6 H 4 }(H 2 )(P i Pr 3 ) 2 ] 41. These complexes possess dihydrogen ligands, the energy of which is almost independent of the H–H distance.…”

Chlorido(2-iminomethyl-3-fluorophenyl-κ2C1,N)tris(trimethylphosphane-κP)iron

“…Related crystal structures of iron compounds have not yet been reported in the literature. For substituted phenylmethanimine coordinated dihydride complexes of osmium, see: Schloerer et al (2006); Barea et al (1998).…”