The rates of displacement of arene and thiophene ligands by P(n-Bu)3 in decalin and PPh3 in toluene have been studied. The reactions are first order in complex and incoming ligand. Rates of reaction increase in the order benzene < styrene < triphenylene < pyrene < phenanthrene < dimethylthiophene < naphthalene < thiophene < anthracene and span roughly 8 orders of magnitude. The thermodynamic stability of these species has also been investigated by solution calorimetry and equilibrium studies. The order of decreasing thermodynamic stability is benzene > dimethylthiophene > triphenylene > phenanthrene > thiophene > naphthalene > anthracene > pyrene and spans about 7 kcal/mol. The combination of kinetic and thermodynamic data is used to construct reaction profiles for these reactions. On the basis of the assumption that the transition state occurs on the way to formation of (η4-arene)Cr(CO)3(L) a linear correlation exists between the enthalpy of formation of the transition-state complex and changes in resonance energy of the fused arene ligands attributable to localization of the π bonds of the proposed η4 intermediate. The rate of binding of C6H6 to (THF)3Cr(CO)3 is 10% slower than for C6D6, implicating the importance of (η1-C6H6)Cr(CO)3(THF) 2 as an intermediate on the pathway to formation of (η6-C6H6)-Cr(CO)3.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry