Influence of Media and Homoconjugate Pairing on Transition Metal Hydride Protonation. An IR and DFT Study on Proton Transfer to CpRuH(CO)(PCy₃)

Abstract

The interaction of the ruthenium hydride complex CpRuH(CO)(PCy(3)) (1) with proton donors HOR of different strength was studied in hexane and compared with data in dichloromethane. The formation of dihydrogen-bonded complexes (2) and ion pairs stabilized by hydrogen bonds between the dihydrogen ligand and the anion (3) was observed. Kinetics of the interconversion from 2 to 3 was followed at different (CF(3))(3)COH concentrations between 200 and 240 K. The activation enthalpy and entropy values for proton transfer from the dihydrogen-bonded complex 2 to the (eta(2)-H(2))-complex 3 (DeltaH() = 11.0 +/- 0.5 kcal/mol and DeltaS() = -19 +/- 3 eu) were obtained for the first time. The results of the DFT study of the proton transfer process, taking CF(3)COOH and (CF(3))(3)COH as a proton donors and introducing solvent effects in the calculation with the PCM method, are presented. The role of homoconjugate pairs [ROHOR](-) in the protonation is analyzed by means of the inclusion of an additional ROH molecule in the calculations. The formation of the free cationic complex [CpRu(CO)(PCy(3))(eta(2)-H(2))](+) is driven by the formation of the homoconjugated anionic complex [ROHOR](-). Solvent polarity plays a significant role stabilizing the charged species formed in the process. The theoretical study also accounts for the dihydrogen release and production of CpRu(OR)(CO)(PCy(3)), observed at temperatures above 250 K.

Experimental and Computational Studies of Hydrogen Bonding and Proton Transfer to [Cp*Fe(dppe)H]

“…The geometrical parameters that describe the hydrogen bond are quite similar to those computed previously [20] for [25] compared to E j = 1.02 for [CpRuH(CO)(PCy 3 )]. [12] The formation of the hydrogen bonds is reflected in the lengthening of the OH bond lengths (Dd(OH)) from their values in the isolated proton donors and consequently by the shift of n(OÀH), see Table 3.…”

“…[19] Some of us have studied the kinetics of the transformation of the dihydrogen-bonded complex I into the nonclassical complex II in the case of [CpRuH(CO)(PCy 3 )] by using fluorinated alcohols as proton donors. [20] The activation enthalpy and entropy of the proton transfer process as well as the thermodynamic parameters for the dihydrogen bond formation step have been obtained for the protonation by perfluoro-tert-butanol (PFTB) in hexane. The low solubility of the ion-paired complex in hexane prevented us from determining the equilibrium thermodynamic parameters of the proton transfer step.…”

“…[20] Although the trifluoroacetate anion is colorless preventing the use of UV/Vis spectroscopy, IR spectroscopy can be conveniently used in this case because the n as (OCO) bands are sufficiently diagnostic of the hydrogen bonding state of the TFA anion. The IR spectrum in the carbonyl stretching region for a 2:1 [Cp*FeH(dppe)]/TFA mixture is shown in Figure 5 a.…”

“…[20] The presentation of the theoretical results is divided in two parts. The first one will be devoted to the thermodynamics of the formation of the initial hydrogenbonded complexes, both in the gas phase and in dichloromethane (DCM).…”

Solvent‐Dependent Dihydrogen/Dihydride Stability for [Mo(CO)(Cp*)H2(PMe3)2]+[BF4]− Determined by Multiple Solvent⋅⋅⋅Anion⋅⋅⋅Cation Non‐Covalent Interactions

“…[17,18] The solvent polarity effect on the proton-transfer thermodynamics and energy barrier has been shown for the protonation of [Ru(CO)(Cp)H-A C H T U N G T R E N N U N G (PCy 3 )] [19] and [RuH 2 A C H T U N G T R E N N U N G (PP 3 )] [20] [PP 3 =P(CH 2 CH 2 PPh 2 ) 3 ]. For the latter system, the ability of the hydrogen-bond-donating solvent to interfere with the formation of hydrogen bonds in the [ …”