Volume of reaction, energetics, and kinetics of tetrahydrothiophene displacement of solvent from Mo(CO)5(alkane)

Abstract

Laser-induced optoacoustic spectroscopy (LIOAS) was used to determine the enthalpies and volumes of reactions for each step in ligand substitution of molybdenum hexacarbonyl with tetrahydrothiophene (THT). The enthalpy for substitution of CO on Mo(CO)6 by an alkane and of coordinated alkane on Mo(CO)5(alkane) by THT are 114 and -99 kJ mol(-1), respectively. Likewise, the volumes of reaction are 13 and -16 ml mol(-1). These results allow the calculation of the bond energies for Mo-alkane (56 kJ mol(-1)) and Mo-THT (155 kJ mol(-1)). Furthers studies should reveal that, for certain cases, the volume of reaction can be neglected in the determination of enthalpies of ligand substitution by LIOAS.

Bond Energies, Reaction Volumes, and Kinetics for σ- and π-Complexes of Mo(CO)5L

“… a Values in parentheses are the errors in the last digit(s). b Determination in heptane assuming Δ V 1 = Δ V 2 = 0. c Multisolvent determination like that shown in Figure . d The relative errors for BE (bond energy) are the same as the errors for Δ H 2 : BE(M-L) = BE(M-CO) – Δ H 1avg – Δ H 2 . e Tetrahydrofuran, ref . f Tetrahydrothiophene, ref . …”

“…The fractional amplitude for the slow component of the signal likewise can be expressed (eqs and ). A series of linear alkanes were used to vary the solvent thermoelastic properties, and the calculations assume that the metal–solvent bond energy does not vary significantly for the different alkane chain lengths. , normalϕ 1 = h normalν normalχ − normalΦ normalΔ H 1 normalχ + normalΦ normalΔ V 1 h normalν normalχ h normalν normalχ false( 1 − normalϕ 1 false) normalΦ = normalΔ H 1 normalχ − normalΔ V 1 normalϕ 2 = − normalΦ false( normalΔ H 2 normalχ − normalΔ V 2 false) h normalν normalχ − h normalν normalχ normalϕ 2 normalΦ = normalΔ H 2 normalχ − normalΔ V 2 …”

“…A number of studies have presented gas-phase (experimental and computational) and solution-phase (experimental , ) strengths of metal–alkane bonds. Previously, we reported results for Mo–alkane bond energies as well as those for ligands that bond via lone pairs. , Currently, we present PAC results for π- or σ-complexes with 1-hexyne, 1-hexene, benzene, triethylsilane, and a series of linear alkanes ( n -pentane, n -hexane, n -heptane, n -octane, n -decane, and n -dodecane). Theoretical molybdenum-ligand bond energies were computed for the same ligands except the alkane series was methane, ethane, n -propane, n -butane, n -pentane, n -hexane, and n -heptane.…”