Hydrocarbon-metal bond

IV. The Hydrocarbon-Metal Bond in Catalytic and Organometallic Chemistry. 205... 

TABLE 4.13. Calculated Hydrocarbon-Metal Bond Energies (kJ mol ) for Ethene and Ethynyl Complexes (P = PPI13)... 

The carbon-metal bonds of organolithium and organomagnesium compounds have appreciable carbamomc character Carbanions rank among the strongest bases that we 11 see m this text Their conjugate acids are hydrocarbons—very weak acids indeed The equilibrium constants for ionization of hydrocarbons are much smaller than the s for water and alcohols thus hydrocarbons have much larger pA s... 

The metal-oxo molecular models outlined above have a quite remarkable potential for studying the metal activity in a quite unusual environment. Some of the possibilities could be (1) the generation and the chemistry of M—C, M=C, M=C functionalities (2) the interaction with alkenes, alkynes, hydrocarbons, and hydrogen (3) the activation of small molecules like N26 and CO (4) the support of metal-metal bonded functionalities and (5) the generation of highly reactive low-valent metals. 

The articles by J. R. Anderson, J. H. Sinfelt, and R. B. Moyes and P. B. Wells, on the other hand, deal with a classical field, namely hydrocarbons on metals. The pattern of modem wTork here still very much reflects the important role in the academic studies of deuterium exchange reactions and the mechanisms advanced by pioneers like Horiuti and Polanyi, the Farkas brothers, Rideal, Tw igg, H. S. Taylor, and Turkevich. Using this method, Anderson takes ultrathin metal films with their separated crystallites as idealized models for supported metal catalysts. Sinfelt is concerned with hydrogcnolysis on supported metals and relates the activity to the percentage d character of the metallic bond. Moyes and Wells deal with the modes of chemisorption of benzene, drawing on the results of physical techniques and the ideas of the organometallic chemists in their discussions. 

Atomic metal ion-hydrocarbon reactions bond dissociation energies for fragments, 15,16t endothermic reactions, 13,15,17f Atomic transition metal ion reactions development of approach for real-time measurements of dissociation kinetics, 39 ion beam apparatus, 12,14f studies of... 

The report by Resa et al. on a hydrocarbon-soluble, molecular compound of monovalent zinc, namely decamethyl-dizincocene, therefore caused considerable excitement among inorganic and organometallic chemists alike.233 Organozinc compounds with direct zinc-transition metal bonds have also been reported recently, and this area of organozinc chemistry with direct metal-metal bonds will undoubtedly witness considerable growth in the near future. 

In this paper we present a molecular view of the origin of selectivity differences based on bonding of intermediates. The suggestion is that hydrocarbon intermediates bonded to metal centers through oxygen atoms... 

It seems beyond debate that when an exchange reaction of a hydrocarbon (HC) with D2 is observed and the initial product distributions are binomial (random distribution of D atoms), single c-metal-carbon bonds are being formed. Nevertheless, this conclusion was puzzling in the period when virtually no homogeneous alkyl-metal complexes were known and the stability of alkyl-metal complexes was doubted for principal reasons (see, e.g., 169). However, it appeared that these complexes can be rather stable when one blocks a very fast and easy elimination of one of the H atoms in the jS-position, which step decomposes the alkyl-metal bond into an olefin and a bound hydrogen atom (170,171). On the other hand, this means that the transition... 

With the advent of sophisticated experimental techniques for studying surfaces, it is becoming apparent that the structure of chemisorbed species may be very different from our intuitive expectations.10 For example, ethylene (ethene, H2C=CH-2) chemisorbs on platinum, palladium, or rhodium as the ethylidyne radical, CH3—C= (Fig. 6.2). The carbon with no hydrogens is bound symmetrically to a triangle of three metal atoms of a close-packed layer [known as the (111) plane of the metal crystal] the three carbon-metal bonds form angles close to the tetrahedral value that is typical of aliphatic hydrocarbons. The missing H atom is chemisorbed separately. Further H atoms can be provided by chemisorption of H2, and facile reaction of the metal-bound C atom with three chemisorbed H atoms dif-... 

Zeise s salt, KPtCI3(//2-C2H4), exemplifies transition metal bonding to unsaturated hydrocarbons. The orbital interaction diagram for the T-shaped metal fragment PtClT and... 

The forces involved in the interaction al a good release interface must be as weak as possible. They cannot be the strong primary bonds associated with ionic, covalent, and metallic bonding neither arc they the stronger of the electrostatic and polarization forces that contribute to secondary van der Waals interactions. Rather, they are the weakest of these types of forces, the so-called London or dispersion forces that arise from interactions of temporary dipoles caused by fluctuations in electron density. They are common to all matter. The surfaces that are solid at room temperature and have the lowest dispersion-force interactions are those comprised of aliphatic hydrocarbons and fluorocarbons. 

The silver acetylides appear to have substantially covalent carbon-metal bonds and are less ionic than sodium and potassium alkynides. Silver-ammonia solution may be used to precipitate 1-alkynes from mixtures with other hydrocarbons. The 1-alkynes are regenerated easily from the silver precipitates by treatment with strong inorganic acids. It should be noted, however, that silver alkynides may be shock sensitive and can decompose explosively, especially when dry. 

---