Nature of the Rh−H₂ Bond in a Dihydrogen Complex Stabilized Only by Nitrogen Donors. Inelastic Neutron Scattering Study of Tp^Me₂RhH₂(η²-H₂) (Tp^Me₂ = Hydrotris(3,5-dimethylpyrazolyl)borate)

Abstract

The tunnel splitting of the librational ground state and the torsional frequencies of the dihydrogen ligand in Tp(Me)()2RhH(2)(eta(2)-H(2)) (Tp(Me)()2 = hydrotris(3,5-dimethylpyrazolyl)borate) were measured using inelastic neutron scattering spectroscopy. The barrier for the rotation of the H(2) ligand and its H-H separation, calculated from these data, are 0.56(2) kcal/mol and 0.94 Å, respectively. These values indicate that pi-back-donation from the Tp(Me)()2RhH(2) fragment to H(2) is relatively weak and/or the interaction between the coordinated dihydrogen molecule and the two cis-hydride ligands significantly lowers the barrier for H(2) rotation.

Effect of the Spinning Motion of the Dihydrogen Ligand on the Properties of an Elongated Dihydrogen Complex. A Theoretical Study of the trans-[Os(H···H)Cl(H2PCH2CH2PH2)2]+ Complex

“…Hence, the low value of the rotational barrier in the osmium complex is consistent with the complex being between the fast and slow spinning limits, whereas the ruthenium complex, having a higher rotational barrier, is in fact a slow spinning dihydrogen complex. The value of the barrier is comparable to the values found by inelastic neutron scattering (INS) in complexes Mo(CO)(η 2 -H 2 )(dppe) 2 ,24a [FeH(η 2 -H 2 )(dppe) 2 ] + ,24b and Tp Me2 Rh(η 2 -H 2 )H 2 ,24c which was in all cases below 2.5 kcal/mol. As a final note, the energy of dissociation of H 2 from the rest of the complex has been calculated to be 34.9 kcal/mol.…”

“…Due to symmetry reasons, a new identical minimum appears when θ = π, and a further transition state structure exists when θ = 3π/2. We have chosen the following simple functional form for function W (θ), which fulfills these simple requirements: Parenthetically, we note that a similar functional form has been previously used for V libration by several authors when studying the librational dynamics of the H 2 unit in dihydrogen complexes. 24c, Finally, to determine the dependence of the librational potential energy barrier on the H−H stretch, V ⧧ ( r ), we have opted for determining the energy barriers along the minimum energy path that leads from the minimum (an elongated dihydrogen) to the area of the PES corresponding to the dihydride, and also from the minimum to the area in which the H 2 unit dissociates from the complex. This has been done by optimizing the structure of the complex for different values of r , and then determining the librational potential energy barrier for each of them, keeping fixed the geometry of the Os−H 2 unit but making the phase of the librational motion to be π/2, and allowing the rest of the geometrical parameters of the complex to vary in the optimization.…”

Polyhydrides of Platinum Group Metals: Nonclassical Interactions and σ-Bond Activation Reactions

“…The Tp Me2 -derivative RhH 2 Tp Me2 (η 2 -H 2 ) ( 738 ) is, however, stable in the solid state. , DFT calculations have confirmed the dihydride-dihydrogen structure, which presents a near octahedral arrangement of the ligands around the metal center . The barrier for the rotation of the dihydrogen ligand and the separation between the hydrogen atoms, calculated from data of inelastic neutron scattering spectroscopy, are 0.56(2) kcal mol –1 and 0.94 Å, respectively …”

“…358 The barrier for the rotation of the dihydrogen ligand and the separation between the hydrogen atoms, calculated from data of inelastic neutron scattering spectroscopy, are 0.56(2) kcal mol −1 and 0.94 Å, respectively. 359 The salt [Rh{Ph 2 P(CH 2 ) 2 PPh 2 }{PCyp 2 (η 2 -C 5 H 7 )}][BAr F 4 ] (739), which is quantitatively formed by reaction of NaBAr F 4 with RhCl{Ph 2 P(CH 2 ) 2 PPh 2 }(PCyp 3 ) (740), is easily hydrogenated under 1 atm of H 2 to give the dihydride-dihydrogen complex [RhH 2 (η 2 -H 2 ){Ph 2 P(CH 2 ) 2 PPh 2 }(PCyp 3 )][BAr F 4 ] (741; d H2 ≈ 0.9 Å), according to Scheme 126. 360 The hydrogenation of the Osborn-type complexes [Rh(η 4 -NBD)(PR 3 ) 2 ][BAr 4 ] 2 (PR 3 = PCy 3 (750), P i Pr 3 (751)), with 16 hydrogen atoms surrounding the metal core.…”

Ligand Effect on the Structures and Acidities of [TpOs(H2)(PPh3)2]BF4and [CpOsH2(PR3)2]BF4

“…It is interesting to note that although Cp - and Tp - are both 6e - donors, trans- [CpOsH 2 (PPh 3 ) 2 ] + and trans- [CpOsH 2 (CO)(P( i -Pr) 3 )] + are classical dihydride complexes, but the analogous Tp complexes [TpOs(H 2 )(PPh 3 ) 2 ] + and [TpOs(H 2 )(CO)(P( i -Pr) 3 )] + are dihydrogen complexes. That the Tp ligand has a higher tendency to stabilize the dihydrogen ligand relative to Cp has also been noted for other analogous Tp and Cp (or Cp*) complexes, − as exemplified by the structures of Cp*RuH 3 (PCy 3 ) vs TpRuH(H 2 )(PCy 3 ), [Cp*IrH 3 (PMe 3 )] + vs [TpIrH(H 2 )(PMe 3 )] + , and trans- [CpRuH 2 (PPh 3 ) 2 ] + vs [TpRu(H 2 )PPh 3 ) 2 ] + 16b…”