Insertion in hydrogenation

Fig. 23. When lithium inserts in hydrogen-containing carbon, some lithium atoms bind on the hydrogen-terminated edges of hexagonal carbon fragments. This causes a change from sp to sp bonding [37].

Zheng, T., Zhong, Q., and Dahn, J.R. (1996). Hysteresis during insertion in hydrogen-containing carbons./. Electrochem. Soc., 143, 2137-45. 

Formed in superacid media species exhibiting electrophilic properties are able to attack alkanes primarily via electrophilic addition to C-H bond followed by other reactions. In particular, Olah et al. observed O atom insertion in hydrogen peroxide reaction with methane in Magic Acid above 0 °C to produce methanol with very high (>95%) selectivity [54a]. The particle (OH)"", which may be considered to be a protonated oxygen atom in the singlet state is apparently the active species in the reaction. Methyl alcohol formed is immediately protonated to methyloxonium ion, and this prevents further... 

All samples heated at 700 and 800°C show significant hysteresis that is, lithium is inserted in the materials near zero volts and removed at about one volt. We have shown that the amount of lithium which can be inserted in 700°C materials is directly proportional to their hydrogen (H) content. Table 4 shows that materials heated to 700 and 800°C retain substantial hydrogen. Upon heating to 900 C, the hydrogen is predominantly eliminated and so is the hysteresis. The samples then show substantial recharge capacity at low voltages. 

How does oxygen insert in between the B—bonds Let s take a closer look at the reagents— a hydroxide ion can deprotonate hydrogen peroxide to form a hydroperoxide anion ... 

ESCA Sample Pretreatment. Samples were pelleted and cut to fit into a rectangular depression in an ESCA sample probe similar in design to one used by Hercules (16). The portion of the probe holding the catalyst sample could be withdrawn into an outer cylinder and sealed under an atmosphere of the pretreatment gas. For pretreatment the calcined samples were exposed to a hydrogen flow at one atmosphere and heated to AOO C. After this pretreatment the sanqile was withdrawn into the insertion tube, sealed in the pretreatment gas, inserted into the ESCA, evacuated, and then the ESCA spectra were recorded. A similar procedure was followed for the uncalcined catalysts except that the temperature was first increased in hydrogen flow to SOO C and held at this temperature for 3 to 4 hours the sample was then heated to 400 C and held at this temperature for 18 hours. 

The gas-phase reaction of cationic zirconocene species, ZrMeCp2, with alkenes and alkynes was reported to involve two major reaction sequences, which are the migratory insertion of these unsaturated hydrocarbons into the Zr-Me bond (Eq. 3) and the activation of the C-H bond via er-bonds metathesis rather than /J-hydrogen shift/alkene elimination (Eq. 4) [130,131]. The insertion in the gas-phase closely parallels the solution chemistry of Zr(R)Cp2 and other isoelec-tronic complexes. Thus, the results derived from calculations based on this gas-phase reactivity should be correlated directly to the solution reactivity (vide infra). 

Interception of the reaction sequence at the alkylcobalt carbonyl stage before carbonyl insertion, and hydrogenation of this intermediate, produces an alkane. This undesired side reaction is only minor (1-3%) in cobalt-catalyzed hydroformylation of a nonfunctional olefin, but may become predominant with phenyl- or acyl-substituted olefins. Ethylbenzene has been obtained in >50% yield from styrene (37), and even more alkane was obtained from a-methylstyrene (35). 

---