Thermodynamics organometallic chemistry

Chemistry can be viewed as a balance between thermodynamic and kinetic factors which dictate the course of chemical reactions and the stability of compounds. Chemists seeking to achieve particular goals, manipulate these factors using chemical or physical means. The papers in this symposium on "High Energy Processes in Organometallic Chemistry" describe recent attempts to apply mainly physical means to get around the thermodynamic and kinetic constraints of conventional organometallic chemistry. 

Both kinetic and thermodynamic data on organometallic hydrides should be very useful. The relative rates of proton transfer processes and other reactions determine a good deal of organometallic chemistry. For example, in our synthesis of cis-0s(C0) (CH )H> reactions 2-4, the comparative rates of... 

Less attention has been paid, however, to C02 organometallic chemistry during the past decade. Whilst many reduction or coupling reactions are known to proceed in the presence of stoichiometric or catalytic amounts of transition metal complexes, very few examples remain where the formation of a metal-C02 complex has led to an effective, catalytic reduction reaction of C02. Carbon dioxide complex photoactivation also represents an attractive route to CO bond cleavage, coupled with O-atom transfer. However, progress in the area of C02 utilization requires a better understanding of the reaction mechanisms, of the thermodynamics of reaction intermediates, and of structure-reactivity relationships. 

Organometallic chemistry does have its own distinctive flavour. Organometallic compounds are often (but not invariably) air- and moisture-sensitive and their handling requires much care and skill. In the interplay between kinetic and thermodynamic considerations, organometallic chemistry falls somewhere between inorganic and organic chemistry. Most organometallic compounds of the transition elements can also be classified as coordination compounds, and are dealt with in more detail in Chapter 8. (See also Section 10.5.)... 

Extended Hiickel Theory (EHT) uses the highest degree of approximation of any of the approaches we have already considered. The Hamiltonian operator is the least complex and the basis set of orbitals includes only pure outer atomic orbitals for each atom in the molecule. Many of the interactions that would be considered in semi-empirical MO theory are ignored in EHT. EHT calculations are the least computationally expensive of all, which means that the method is often used as a quick and dirty means of obtaining electronic information about a molecule. EHT is suitable for all elements in the periodic table, so it may be applied to organometallic chemistry. Although molecular orbital energy values and thermodynamic information about a molecule are not accessible from EHT calculations, the method does provide useful information about the shape and contour of molecular orbitals. 

Dumestre, F., Chaudret, B.,Amiens, C., Fromen, M.C., Casanove,M.J., Renaud, P.andZurcher, P. (2002) Shape control of thermodynamically stable cobalt nanorods through organometallic chemistry. Angew. Chem., 114, 4462... 

Tobin J. Marks (NAS) is the Charles E. and Emma H. Morrison Professor and Vladimir N. Iptieff Professor of Chemistry at Northwestern University. Through landmark synthetic, mechanistic, and thermodynamic investigations, he and his students opened a new portion of the Periodic Table to organometallic chemistry. He has also made major advances in solid state, polymer, bioinorganic, and boron hydride chemistry and in photochemical isotope separation. He received his B.S. from the University of Maryland and his Ph.D. from Massachusetts Institute of Technology. 

Kuntz, particularly, found no echo in the academic community. The reason may have been that the idea of organometallic complex catalysts in the presence of water seemed unnatural or even perverse, although even air-stable aquocarbonyl complexes of transition metals such as rhenium [9] were known in the meantime. In addition, metal-carbon bonds are thermodynamically unstable relative to their hydrolysis products (cf. Section 2.2), although it was well known that reaction rates could be increased by a factor of up to 1011 by aqueous media [10]. In simple terms, organometallic chemistry was not ready for aqueous operation before the early 1980s. 

This journal publishes fundamental studies in all phases of inorganic chemistry. Coverage includes experimental and theoretical reports on the synthesis, structures, and properties of new compounds quantitative studies of structure and thermodynamics, kinetics, and mechanisms of inorganic reactions bioinorganic chemistry and some aspects of organometallic chemistry, solid-state phenomena, and chemical bonding theory. Short papers (notes), full papers, and preliminary communications of an urgent nature are published. 

With growing data banks of rate constants of elementary steps, it appears that kinetics assisted design of new catalytic processes will accelerate the development of improved catalytic processes. With powerful computational methods of thermodynamic and kinetic parameters, microkinetic analysis has emerged as a mature method to describe existing processes in combustion, polymerization, homogeneous and heterogeneous catalysis. In catalysis, the method is now poised to become one of the tools of catalyst development with the help of surface science, organometallic chemistry, materials science, com-... 

The premier issue of the journal Inorganic Chemistry was published in February 1962. Much of the focus of that issue was on classic coordination chemistry, with more than half its research papers on synthesis of coordination complexes and their structures and properties. A few papers were on compounds of nonmetals and on organometallic chemistry, then a relatively new field several were on thermodynamics or spectroscopy. All of these topics have developed considerably in the subsequent half-century, but much of the evolution of inorganic chanistry has been into realms unforeseen in 1962. 

Oxidative addition reactions (and their reverse, reductive eliminations) are among the most important elementary transformations in organometallic chemistry and also play a key role in many stoichiometric and catalytic processes. Oxidative additions commonly involve the addition of a neutral molecule (X-Y) to a single metal center (M), resulting in the formation of new M-X and M-Y bonds and an increase by two units in the metal s oxidation state, electron count, and coordination number (Equation (5)). Although oxidative additions and reductive eliminations are in principle reversible reactions, the position of the equilibrium, which is governed by the overall thermodynamics of the species involved (i.e., the relative strengths of the bonds broken and formed), is often completely shifted to one of the sides. 

Electrochemical methods have diverse applications in chemistry - synthesis, catalysis, thermodynamics, kinetics, mechanistic studies, to mention a few. Electrochemistry was well developed for studies of relevance to organometallic chemistry prior to COMC (1995), but there was no separate section devoted to the topic in that work. However, excellent books and reviews have been published that summarize aspects of organometallic electrochemistry. 

In this chapter, the application of electrochemical techniques in organometallic chemistry will be presented with specific focus on utilization of electrode potential data to extract thermodynamic quantities pertaining to metal-ligand bonding energetics. Many readers may be unfamiliar with the electrochemical methods, and therefore the most widely used technique to obtain the required electrode potential data - cyclic voltammetry (CV) - will be briefly described. The derived bond energy data will be no better than the underlying electrode potential data, and therefore some issues which, in the author s view, are particularly relevant to ensure that data are obtained as accurately and correctly as possible will be discussed. For a more in-depth discussion of CV and other electrochemical techniques, the reader is referred to selected textbooks and reviews. 

The catalytic transformation of alkanes at moderate temperatures into higher and lower homologs, known as alkane metathesis, is an area in which organometallic chemistry and petrochemical chemistry find common roots [1, 2]. This reaction is thermodynamically unfavored because it requires the intermediate formation of olefins from alkanes, which is a chemical challenge considering the inertness of the sp carbon-hydrogen bond [3]. 

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