Relative Binding Energies of Sterically Demanding Tertiary Phosphine Ligands to the Cp*RuCl (Cp* = .eta.5-C5Me5) Moiety. Thermochemical Investigation of Coordinatively Unsaturated Organoruthenium Complexes

Abstract

The enthalpies of reaction of (Cp*RuCl)4 (Cp* = i/5-C5Me5) with two sterically demanding monodentate tertiary phosphine ligands, leading to the formation of Cp*Ru(PR3)Cl (PR3 = P(CeHn)3 and ' 3) complexes, have been measured by anaerobic solution calorimetry in THE at 30 °C. The enthalpies of reaction associated with the rapid and quantitative reaction of the (Cp*RuCl)4 complex allow for a determination of relative ruthenium-phosphorus bond energy terms and, for the first time, enable a direct solution calorimetric measurement of the relative donating properties of large cone-angle phosphine ligands. Reaction of Cp*Ru-(PR3)C1 with excess phosphine ligand, at 30 °C, has been shown to quantitatively yield the corresponding Cp*Ru(PR'3)2Cl complex and allows for the design of thermochemical cycles, assuring the internal consistency of the thermochemical data. The ruthenium-phosphine bond energy in Cp*Ru(PCy3)Cl was found to be 1.4 ± 0.5 kcal/mol more stable than in the Cp*Ru(P* iPrs)Cl complex.

Structure and Reactivity of Coordinatively Unsaturated Half‐Sandwich Iron, Ruthenium and Osmium Complexes

“…These reactions have been the subject of very detailed thermochemical investigations, which have shown that sterically demanding phosphane ligands exhibit the weakest RuϪPR 3 bonds. [31] There is an upper limit for the phosphane cone angle which allows the stabilization of [Cp*RuCl(PR 3 )] species. If the cone angle is too large this results in an inefficient RuϪPR 3 interaction.…”

Electrochemical oxidation of H2 catalyzed by ruthenium hydride complexes bearing P2N2 ligands with pendant amines as proton relays

“…Cp*Ru(dmpm)Cl (where dmpm ¼ bis(dimethylphosphino) methane) is expected to have an electronic inuence at the metal center similar to P 2 N 2 ligands. Cp*Ru(dmpm)Cl was synthesized according to a published procedure, 75,76 and converted to Cp*Ru(dmpm)H by a reaction with excess NaBH 4 in ethanol.…”

Competitive Ligand Exchange and Dissociation in Ru Indenyl Complexes

“…Those quantitative studies involved collision-induced dissociation (CID) of mass-selected ions within the FTICR cell, and provided a lower limit for the Ru–PPh 2 H BDE of 16.6 kcal/mol. We noted the difficulty in comparing this absolute, gas phase value for an η 5 -indenyl system with BDE values for Ru–PR 3 available from solution calorimetry studies of tertiary phosphine substitutions at {Ru­(η 5 -Cp*)­Cl} 4 , given the dependence of the calorimetry-derived values on solvent and temperature, and the observed strong correlation of BDEs for the η 5 -Cp* system with steric, as opposed to electronic, properties of the tertiary phosphines studied . Ideally, a clearer picture of the relative binding energies of phosphines could be obtained by performing these painstaking CID studies on a broad range of analogous cationic complexes for a given half-sandwich system.…”