Abstract
The structure of the complex trans-[Ru(η2-H2) (H)(dppe)2] [BPh4] (1), dppe = PPh2CH2CH2PPh2, has been determined by single-crystal X-ray diffraction at 123 K and neutron diffraction at 12 K. The core of the complex has a distorted octahedral geometry about ruthenium with the dihydrogen ligand trans to hydride and eclipsing a trans-P-Ru-P axis that is bent away from the hydrogens with a P-Ru-P angle of 167.9(4)°. The crystallographically determined H-H distance is 0.83(8)(X-ray) or 0.82(3) (neutron) Å. The latter value, when corrected for the shortening caused by the torsional libration of the H2 ligand, increases to about 0.94 Å. The long Ru-(H2) distance of 1.81(2) Å (neutron), compared to the terminal hydride to ruthenium distance of 1.64(2) A (neutron), is consistent with the lability of the dihydrogen ligand, which is partially lost from the crystal by treatment with vacuum. The analogous iron complex trans-[Fe(η2-H2)(H)(dppe) 2] [BPh4] (2) has similar features except that the Fe-H(H2) distances are much shorter and the H2 ligand is correspondingly less labile. An inelastic neutron scattering study of the powder of 1 at 5 K reveals two broad inelastic peaks flanking the elastic peak. With the assumption that the dihydrogen librates in a double-minimum potential, the barrier to dihydrogen reorientation is calculated to be 1.0 to 1.4 kcal mol-1 ',depending upon which of the H-H distances is used. This barrier is less than that for the iron analog, determined for its BF4 salt, therefore suggesting that there may be less dπ-» → σ* backbonding in 1 than 2.
Original language | English |
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Pages (from-to) | 351-357 |
Number of pages | 7 |
Journal | Inorganica Chimica Acta |
Volume | 259 |
Issue number | 1-2 |
DOIs | |
State | Published - Jun 1997 |
Keywords
- Crystal structures
- Dihydrogen complexes
- Hydride complexes
- Neutron scattering
- Ruthenium complexes