Elongated Dihydrogen Complexes:  A Combined Electronic DFT + Nuclear Dynamics Study of the [Ru(H···H)(C₅H₅)(H₂PCH₂PH₂)]⁺ Complex

Abstract

A study on a modeled version of the complex [Ru(H···H)(C5Me5)(dppm)]+ has been performed both at electronic structure level and including quantum treatment of nuclei. Density functional theory (DFT) electronic structure calculations alone fail to reproduce the experimentally reported geometry of the elongated dihydrogen ligand of the complex, even though the rest of the complex is satisfactorily described. Quantum nuclear motion calculations manage to correctly explain the geometries found experimentally by means of neutron diffraction measurements. Isotopic effects are predicted for the hydrogen−hydrogen distance of the elongated dihydrogen ligand depending on its isotopic composition. Moreover, the temperature dependence of the J(H,D) coupling constant is also interpreted successfully on the grounds of varying population of the vibrational excited states of the Ru−H2 unit.

Performance of the semiempirical PM3 (tm) method in the geometry optimization of transition metal complexes

“…The DFT computed structure 54 shows a "normal" dihydrogen complex, the H-H distance of 0.888 Å falling 0.20 Å short from the experimental value, a discrepancy that has been partly explained by the quantum vibrational motion of the nuclei. 54 Our PM3 (tm) optimized structure for 5a is, on the other hand, even further from the experimental elongated dihydrogen complex, being clearly a dihydride with an H-H distance of 1.678 Å.…”

“…The geometry reproduction of elongated dihydrogen complexes with H-H in the range 1.0-1.2 Å has proven to be a very elusive target for theoretical calculation, with results hardly getting closer than 0.1 Å from the experiment, 52,54 often giving dihydride isomers. 45 Because of that, we decided to test PM3 (tm) on species derived from [Ru(η 5 -C 5 Me 5 )(H 2 )(PPh 2 CH 2 PPh 2 )] (5c).…”

“…45 Because of that, we decided to test PM3 (tm) on species derived from [Ru(η 5 -C 5 Me 5 )(H 2 )(PPh 2 CH 2 PPh 2 )] (5c). Neutron diffraction data are available for this species from Morris and coworkers, 46,47 and a recent theoretical study on [Ru(η 5 -C 5 H 5 )(H 2 )(PH 2 CH 2 PH 2 )] (5a) has been presented by Gelabert et al 54 at the nonlocal DFT Becke3LYP level. 54 We have computed the simple theoretical model 5a, the experimental system 5c, and the intermediate model [Ru(η 5 -C 5 Me 5 ) (H 2 )(PH 2 CH 2 PH 2 )] (5b).…”

“…Neutron diffraction data are available for this species from Morris and coworkers, 46,47 and a recent theoretical study on [Ru(η 5 -C 5 H 5 )(H 2 )(PH 2 CH 2 PH 2 )] (5a) has been presented by Gelabert et al 54 at the nonlocal DFT Becke3LYP level. 54 We have computed the simple theoretical model 5a, the experimental system 5c, and the intermediate model [Ru(η 5 -C 5 Me 5 ) (H 2 )(PH 2 CH 2 PH 2 )] (5b). The geometrical parameters from these previous experiments and calculations are presented in Table IV together with the results of our PM3 (tm) calculation on species 5a, 5b, and 5c.…”

Elongated Dihydrogen Versus Compressed Dihydride Complexes: The Temperature Dependence of the H–D Spin–Spin Coupling Constant as a Criterion To Distinguish between Them

“…[4] The substantial anharmonicity of the potential energy surface (PES) that describes the internal motion in the Ru À H 2 unit, together with the varying thermal population of excited vibrational states could explain the geometry obtained by neutron diffraction and the lengthening of R HÀH , observed indirectly through a decrease in the value of 1 J HD with temperature. The adequacy of this theoretical explanation was put to the test when it predicted a systematic shortening of the H À H distance for heavier isotopomers of the dihydrogen ligand coordinated in the complex, a prediction that was afterwards proven to be true.…”