Spectroscopic Evidence for Intermolecular M−H···H−OR Hydrogen Bonding:  Interaction of WH(CO)₂(NO)L₂ Hydrides with Acidic Alcohols

Abstract

Intermolecular hydrogen bonding of acidic alcohols (PhOH, (CF3)2CHOH (HFIP), (CF3)3CHOH (PFTB)) to the hydride ligand of WH(CO)2(NO)L2 (L = PMe3 (1), PEt3 (2), P(OiPr)3 (3), PPh3 (4)) has been observed and characterized by IR and NMR spectroscopy in hexane, toluene-d 8, and CD2Cl2 solutions. The H-bonding is an equilibrium process with medium −ΔH° of 4.1−6.9 kcal/mol; the enthalpy increases on going from 4 to 1, i.e., the strongest bonding is found for the smallest and the most basic L = PMe3. The value of −ΔH° depends on the pK a of the proton donors, increasing as the acidity does (PhOH < HFIP < PFTB). The IR and NMR data suggest C 2 v symmetry around tungsten in the ROH···HW(CO)2(NO)L2 adduct, with the H···H distance of 1.77 Å (L = PMe3) estimated from the hydride T 1min relaxation time. The relevance of the hydrogen bonding to the mechanism of protonation of metal hydrides is suggested.

P Csp3 P and P Csp2 P Palladium(II) Hydride Pincer Complexes: Small Structural Difference—Large Effect on Reactivity

“…[25] The strength of dipolar MÀ H···HX interactions and, therefore, the longitudinal T 1 relaxation behavior, are strongly distance dependent (/ r À6 -…”

“…[23,28] The Pd À H···H À OMe hydrogen-hydrogen bond strengths were determined by NMR spectroscopy for 2/MeOH and [{C 6 H 3 -2,6-(CH 2 PtBu 2 ) 2 }Pd(H)]/MeOH and were consistent with the dihydrogen bond distances established. [25,29] The adduct formation equilibrium constants K were obtained from the temperature-dependent chemical shifts of the hydride signals (d PdÀH (1)], [25] in which a = KwÀKx + 1 K and d 2 were determined by non-linear fit of the experimental data to the above equation using the Levenberg-Marquardt algorithm. [30] d…”

Towards a Rational Design of Ruthenium CO2 Hydrogenation Catalysts by Ab Initio Metadynamics

“…[59][60][61][62][63] Figure 7 shows the FES of the H 2 insertion to the cis-monoformate complex (2 to 10) and of the backward reaction, i.e. the formic acid reaction with the cis-dihydride catalyst resulting in the formation of the formate complex and H 2 (10 to 2).…”

Solvent Control in the Protonation of [Cp*Mo(dppe)H3] by CF3COOH

“…Analogous broadening phenomena for hydride signals as a consequence of dihydrogen bonding and equilibrated proton transfer were noted previously in other cases, although the broadening effect was limited to a few Hz in most cases. [2,23] [14]…”