Enthalpy organometallic chemistry

In general, although the results of microcalorimetric studies do not pretend to provide enthalpy values of the very highest accuracy presently attainable by macroscale combustion calorimetry, they do offer a basis for application on a wide scale and are sufficiently precise for most purposes. The conflicting claims of accuracy and usefulness are particularly acute in the area of transition metal organometallic chemistry this review will attempt to follow a middle way between them. 

The breaking or formation of metal-hydrogen and metal-alkyl bonds is an integral part of most elementary reaction steps in organometallic chemistry. As a consequence, considerable efforts have been directed toward the determination of M-H (15b) and M-alkyl bond strength (23) as a prerequisite for a full characterization of the reaction enthalpies of elementary steps in organometallic chemistry. 

Nolan, S. P. Bonding Energetics of Organometallic Compounds. In Encyclopedia of Inorganic Chemistry, John Wiley New York, 1994. A review on application of metal-ligand bond dissociation enthalpy data to discuss several aspects of organometallic chemistry. 

Strontium enolate chemistry is almost nonexistent barium enolate chemistry is rare radium enolate chemistry is unknown. Allyl chlorides react with barium to form the corresponding organometallics, which in turn react with o ,/ -unsaturated ketones to form the metal enolate . These enolates may also be formed in situ by the reaction of a-chloroketones with barium metal in the presence of an aldehyde, resulting in addition products. These reactions and the enthalpies of formation of the precursor a-haloketones and enones are seemingly ideal candidates for calorimetric investigation. 

In some cases experimental values of A,//°and AA are available, but in general these data are calculated using experimental or estimated values of the standard enthalpies of formation, AfH°, and entropies, S°, of all species involved in the reaction. It should also be pointed out that most organometallic reactions of interest occur in solution at temperatures not far from ambient, and that under these conditions the enthalpy term in Equation (6) is often dominant. Therefore, thermodynamic stability trends of organometallic compounds can frequently be analyzed solely in terms of A H°. When necessary, however, computational chemistry calculations or simple estimation schemes can normally be used to predict A, ° with an acceptable accuracy. " ... 

Chickos, J. S. Acree, W. E., Jr. Enthalpies of sublimation of organic and organometallic compounds 1920-2001, J. Phys. Chem. Ref. Data 2002, 31, 537-698 H. Y. Afeefy, J. F. Liebman and S. E. Stein, Neutral Thermochemical Data and J. S. Chickos, Heat of Sublimation Data, in NIST Chemistry Web-Book, NIST Standard Reference Database Number 69, Edited by Linstrom, P. J. Mallard, W. G. March 2003, National Institute of Standards and Technology, Gaithersburg MD, 20899 (http //webbook.nist.gov). 

---