DFT 2H quadrupolar coupling constants of ruthenium complexes: a good probe of the coordination of hydrides in conjuction with experiments

Abstract

Transition metal (TM) hydrides are of great interest in chemistry because of their reactivity and their potential as catalysts for hydrogenation reactions. 2H solid-state NMR can be used in order to get information about the local environment of hydrogen atoms, and more particularly the coordination mode of hydrides in such complexes. In this work we will show that it is possible to establish at the level of density functional theory (DFT) a viable methodological strategy that allows the determination of 2H NMR parameters, namely the quadrupolar coupling constant (C(Q)) respectively the quadrupolar splitting (deltanuQ) and the asymmetry parameter (etaQ). The reliability of the method (B3PW91-DFT) and basis set effects have been first evaluated for simple organic compounds (benzene and fluorene). A good correlation between experimental and theoretical values is systematically obtained if the large basis set cc-pVTZ is used for the computations. 2H NMR properties of five mononuclear ruthenium complexes (namely Cp*RuD3(PPh3), Tp*RuD(THT)2, Tp*RuD(D2)(THT) and Tp*RuD(D2)2 and RuD2(D2)2(PCy3)2) which exhibit different ligands and hydrides involved in different coordination modes (terminal-H or eta2-H2), have been calculated and compared to previous experimental data. The results obtained are in excellent agreement with experiments. Although 2H NMR spectra are not always easy to analyze, assistance by quantum chemistry calculations allows unambiguous assignment of the signals of such spectra. As far as experiments can be achieved at very low temperatures in order to avoid dynamic effects, this hybrid theoretical/experimental tool may give useful insights in the context of the characterization of ruthenium surfaces or nanoparticles with solid-state NMR.

2H NMR calculations on polynuclear transition metal complexes: on the influence of local symmetry and other factors

“…This is consistent with experimental data, as already shown in a previous article, 9 -[45-85] kHz can be assigned to Ru-(m-D), according to the Ru-Ru bond length. This is consistent with experimental data, as already shown in a previous article, 9 -[45-85] kHz can be assigned to Ru-(m-D), according to the Ru-Ru bond length.…”

“…We also considered strongly electron-deficient H 4 Ru 4 (CO) 9 clusters, in order to roughly mimic electron-deficient surfaces of NPs. 9 This synergy between experiments and theory seemed in particular very promising for elucidating the coordination mode of deuterides with metal atoms as well as the origin (Ru-D vs. D in ligands) of all the features of experimental spectra. Although m-H cannot be easily distinguished from m 3 -H or subsurfacic m 4 -H due to similar shieldings, it seems possible to identify subsurfacic m 6 -H and terminal hydrides which turn out to be significantly unshielded.…”

“…Getting knowledge of their structure would be very helpful, but their structure may often not be characterized at the same level as well-defined molecular species. [8][9][10] The coordination of hydrogen to metal nanoparticles synthesized by organometallic techniques is especially important. 7 In most cases, spectra assignment is not obvious, so that there is a need for providing reference data.…”

“…Although m-H cannot be easily distinguished from m 3 -H or subsurfacic m 4 -H due to similar shieldings, it seems possible to identify subsurfacic m 6 -H and terminal hydrides which turn out to be significantly unshielded. 9,23 However one has to pay attention to temperature effects which may significantly modify experimental quadrupolar splittings, as it is the case with the rotational motion of D 2 ligands. Since periodic boundary calculations with plane wave basis sets are tools of choice for the description of organometallic compounds, calculation of NMR properties with standard periodic DFT packages is desirable in order to bring another point of view.…”

Revisiting NMR composite pulses for broadband 2 H excitation

“…Although the quadrupolar couplings of spin-1 2 H nuclei are far smaller than those of most half-integer spin nuclei, their values (typically in the range of C Q = e 2 qQ = 50-180 kHz) [5,6] are comparable with the maximum RF field strength that can be achieved by modern NMR probes. Therefore, high RF fields for efficient excitation are strongly desired to cover the wide spectral widths encountered in deuterium experiments.…”