Product rates cobalt catalysis

In contrast to triphenylphosphine-modified rhodium catalysis, a high aldehyde product isomer ratio via cobalt-catalyzed hydroformylation requires high CO partial pressures, eg, 9 MPa (1305 psi) and 110°C. Under such conditions alkyl isomerization is almost completely suppressed, and the 4.4 1 isomer ratio reflects the precursor mixture which contains principally the kinetically favored -butyryl to isobutyryl cobalt tetracarbonyl. At lower CO partial pressures, eg, 0.25 MPa (36.25 psi) and 110°C, the rate of isomerization of the -butyryl cobalt intermediate is competitive with butyryl reductive elimination to aldehyde. The product n/iso ratio of 1.6 1 obtained under these conditions reflects the equihbrium isomer ratio of the precursor butyryl cobalt tetracarbonyls (11). 

In addition to OH , other nucleophiles such as BH4 ,318 CN-319,320 and N3-321 also add at the nitrile carbon of cobalt(III)-nitrile complexes at rates which are = 104 times those of the corresponding reactions of the free ligands. Catalysis by C032 in the hydration of [(NH3)5RuNCMe]3+,316 and of the acrylonitrile complex [(NH3)5CoNCCH=CH2]3+,322 has been observed. In the latter complex, a direct nucleophilic pathway results in the incorporation of oxygen from C032 into the amide product with elimination of C02. 

A common feature of all catalysis for F-T synthesis, whether they are cobalt or iron based, is that the catalytic activity is reduced due to the oxidation of active species. Under the typical reaction conditions, this oxidation may be caused by water, which is one of the primary products in the F-T process. On the other hand, at low partial pressure water can also help to increase the product quality by increasing the chain growth probability. Thus, in situ removing some of the water from the product and keeping the water pressure at an optimal value may improve the catalysis activity and promote the reaction rate. Zhu and coworkers [22] have evaluated the potential separation using NaA zeolite membrane to in situ removal of water Irom simulated F-T product stream. High selectivity for water removal from CO, H2 and CH4 were obtained. This result opened an opportunity for in situ water removal from F-T synthesis under the reaction conditions. 

Lim derivative was also studied using HP-NMR, and a mechanism for the formation of branched aldehyde products was proposed. Further work published by Crause et a described the effect of variation of the Lim alkyl chain. HP-NMR and HP-IR studies, combined with molecular modeling and autoclave experiments, showed that the primary factor governing performance of these ligands was the extent of phosphine-modified versus unmodified catalysis. Control of catalyst equilibria in favor of cobalt—phosphine species resulted in improved product linearities, but slower reaction rates. 

The palladium complex, [Pd(PPh3)4], was found to catalyze the decomposition of r-BuOOH in chlorobenzene at 35 °C [337], The rate of oxygen evolution was found to be directly proportional to the catalyst concentration. The rate of radical production (R ) was measured by the inhibition method [338] using 2,6-di-f-butyl-4-methylphenol. The chain length of the reaction [d02ldt/Rr] was found to be 10 in agreement with other studies [339,340]. Thus, decomposition is a normal radical induced reaction as in the case of catalysis by cobalt compounds. 

Reduction of complexes [(NHsjsCoCIIIjL], where L is a reducible ligand by Eu " and is subject to catalysis by the L/L° couple when the ligand is released from the cobalt(II) product.These catalysts have a variety of fates. Addition of excess Eu " or suppresses catalysis " by oxidation of the active species L and allows examination of the uncatalyzed reaction. For the 4-carboxamide derivative (5) a positive hydrogen dependence in the rate law is... 

Catalysed Aquation.— In 1971 Rudakov and Kozhevnikov reported a correlation between the rate constants for metal-ion (M +) catalysed solvolysis of t-butyl halides and the stability constants of the respective complexes Now these authors have shown that a similar correlation applies, albeit rather approximately, to metal-ion catalysis of aquation of halogeno-cobalt(ra), -chromium(ni), and -rhodium(in) complexes. In fact the catalysts mentioned include not only metal ions such as Hg , Tl +, and Ag+, but also complexes such as HgCl+ and T1C1 +. This correlation can be improved by making an allowance for the different coulombic repulsions in systems of different charge products. If the rate constant for the catalysed aquation is ki and that for uncatalysed aquation Ato, the stability constant of the metal-ion complex produced K, the product of the charges on the reactants zazb, and C is a coulombic interaction constant, then the correlation conforms to the equation... 

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