Kinetic hydricity of silane hydrides in the gas phase

Abstract

Herein, gas phase studies of the kinetic hydricity of a series of silane hydrides are described. An understanding of hydricity is important as hydride reactions figure largely in many processes, including organic synthesis, photoelectrocatalysis, and hydrogen activation. We find that hydricity trends in the gas phase differ from those in solution, revealing the effect of solvent. Calculations and further experiments, including H/D studies, were used to delve into the reactivity and structure of the reactants. These studies also represent a first step toward systematically understanding nucleophilicity and electrophilicity in the absence of solvent. Fig. 1 General hydride transfer reaction studied herein. † Electronic supplementary information (ESI) available: Cartesian coordinates for all calculated species, full citations for references with greater than 16 authors, and representative mass spectra are available. See

Nucleophilicity and Electrophilicity in the Gas Phase: Silane Hydricity

“…We also noted previously, and note here again, that for Et 3 SiH ( 5 ) and i Pr 3 SiH ( 12 ), the former reacts more quickly in solution but the latter reacts faster in the gas phase . The gas-phase results of 12 reacting more quickly than 5 are consistent with the increased polarizability (calculated to be 20.3 × 10 –24 cm 3 for 12 but 15.0 × 10 –24 cm 3 for 5 ) as well as the Taft σ I parameter (−0.064 for 12 and −0.055 for 5 ). − , The reversal of the trend in solution, where 5 reacts more quickly than 12 , is similar to the well-known reversal in relative acidity between tert -butanol and methanol in solution as compared to the gas phase .…”

“…The rate constants for the reactions of benzhydryl cations 1 with silanes 2–15 are compiled in Table . A few of these reactions were studied in our prior work, as indicated in Table …”

“… a All values are in kcal mol −1 . b Calculated at B3LYP/6-31+G­(d), at 298 K. c Calculated at B3LYP-D3­(BJ)/6-311++G­(2d,p), at 298 K. d To form the singlet carbene (triplet carbene). e From ref . …”

Reduction of CO2 by Hydrosilanes in the Presence of Formamidinates of Group 13 and 12 Elements

“…Thus, the following hydrosilane reactivity trend was revealed: PhMe 2 SiH > Et 3 SiH > PhSiH 3 > Ph 2 SiH 2 > Ph 3 SiH > (EtO) 3 SiH. The observed trend is only partially in agreement with both thermodynamic hydricity (Ph 3 SiH = PhMe 2 SiH > Et 3 SiH > Ph 2 SiH 2 > PhSiH 3 ) and kinetic nucleophilicity (PhMe 2 SiH > Et 3 SiH > Ph 3 SiH > Ph 2 SiH 2 > PhSiH 3 > (EtO) 3 SiH) tendencies and is inconsistent with those for the series of relatively bulkier hydrosilanes Ph 3 SiH, Ph 2 SiH 2 , and PhSiH 3 , which demonstrate quite the opposite corresponding trends. Given that the observed trend can only be rationalized in part in terms of the thermodynamic and kinetic stability of the corresponding R 3 SiH·LA adducts (LA = Lewis acid, e.g.…”

Ruthenium‐Catalyzed Coupling Reactions of CO2 with C2H4 and Hydrosilanes towards Silyl Esters

“…In the present study,w ea imed at identifying-using highthroughput screening( HTS) techniques-effective catalytic systems for the carboxylation of ethylene in the presence of alternative, readily availablec o-reagents,n amely hydrosilanes (Scheme 2). [37] The favored formation of the SiÀOb ond [bond dissociation energy (BDE) = 460 kJ mol À1 ] [38] and the relatively facile activation of the SiÀHb ond( BDE = 314 kJ mol À1 )m ake hydrosilanes (such as Et 3 SiH) [38] good reductants under relatively mild conditions. We thus envisioned that such reactants may enable releaseo ft he free acrylate product from ap utative metallalactone intermediate, formed by the activation of CO 2 via oxidative cyclization with ethylene.…”