Neutral Transition Metal Hydrides as Acids in Hydrogen Bonding and Proton Transfer: Media Polarity and Specific Solvation Effects Vladislava A. Levina Oleg A. Filippov Evgenii I. Gutsul Natalia V. Belkova Lina M. Epstein Agusti Lledos Elena S. Shubina 10.1021/ja103862r.s001 https://acs.figshare.com/articles/journal_contribution/Neutral_Transition_Metal_Hydrides_as_Acids_in_Hydrogen_Bonding_and_Proton_Transfer_Media_Polarity_and_Specific_Solvation_Effects/2741923 Structural, spectroscopic, and electronic features of weak hydrogen-bonded complexes of CpM(CO)<sub>3</sub>H (M = Mo (<b>1a</b>), W (<b>1b</b>)) hydrides with organic bases (phosphine oxides R<sub>3</sub>PO (R = <i>n-</i>C<sub>8</sub>H<sub>17</sub>, NMe<sub>2</sub>), amines NMe<sub>3</sub>, NEt<sub>3</sub>, and pyridine) are determined experimentally (variable temperature IR) and computationally (DFT/M05). The intermediacy of these complexes in reversible proton transfer is shown, and the thermodynamic parameters (Δ<i>H</i>°, Δ<i>S</i>°) of each reaction step are determined in hexane. Assignment of the product ion pair structure is made with the help of the frequency calculations. The solvent effects were studied experimentally using IR spectroscopy in CH<sub>2</sub>Cl<sub>2</sub>, THF, and CH<sub>3</sub>CN and computationally using conductor-like polarizable continuum model (CPCM) calculations. This complementary approach reveals the particular importance of specific solvation for the hydrogen-bond formation step. The strength of the hydrogen bond between hydrides <b>1</b> and the model bases is similar to that of the M−H···X hydrogen bond between <b>1</b> and THF (X = O) or CH<sub>3</sub>CN (X = N) or between CH<sub>2</sub>Cl<sub>2</sub> and the same bases. The latter competitive weak interactions lower the activities of both the hydrides and the bases in the proton transfer reaction. In this way, these secondary effects shift the proton transfer equilibrium and lead to the counterintuitive hampering of proton transfer upon solvent change from hexane to moderately polar CH<sub>2</sub>Cl<sub>2</sub> or THF. 2010-08-18 00:00:00 hydride proton transfer CPCM proton transfer reaction CH 2Cl THF bond phosphine oxides R 3PO 8H CH 2Cl Neutral Transition Metal Hydrides DFT NMe hexane calculation computationally CH 3CN product ion pair structure complex Specific Solvation EffectsStructural IR model proton transfer equilibrium