Hydroformylation, relative rates

The composition of the products of reactions involving intermediates formed by metaHation depends on whether the measured composition results from kinetic control or from thermodynamic control. Thus the addition of diborane to 2-butene initially yields tri-j iAbutylboraneTri-j -butylborane. If heated and allowed to react further, this product isomerizes about 93% to the tributylborane, the product initially obtained from 1-butene (15). Similar effects are observed during hydroformylation reactions however, interpretation is more compHcated because the relative rates of isomerization and of carbonylation of the reaction intermediate depend on temperature and on hydrogen and carbon monoxide pressures (16). 

By analogy with hydroformylation, dicobalt octacarbonyl has been examined as a hydrosilylation catalyst. Various silanes and a-olefins react, often exothermically. Thermal deactivation occurs above 60° C hence, large exotherms and high temperatures must be avoided (56, 57,130). Isomerization is more pronounced than for the bridged olefin complexes of Pt(II) and Rh(I) (see below) it even occurs with trialkoxysilanes (57). Though isomerization is faster than hydrosilylation, little variation in the relative rates of these two processes with the nature of the silane is observed this is in marked contrast to the bridged systems (55). 

Although Eq. (3) indicates that CO absorption is required for aldehyde formation, it has been shown by Karapinka and Orchin 18) that at 25° and with a moderate excess of olefin the rate of reaction and the yield of aldehyde are similar when either 1 atm of CO or 1 atm of Nj is present. Obviously CO is not essential for the reaction and a CO-deficient intermediate, probably an acylcobalt tricarbonyl, can be formed under these conditions. The relative rates of HCo(CO)4 cleavage of tricarbonyl and tetracarbonyl are not known, and thus the stage at which CO is absorbed in the stoichiometric hydroformylation of olefins under CO is not known with certainty. Heck (19) has shown conclusively that acylcobalt tetracarbonyls are in equilibrium with the acylcobalt tricarbonyl ... 

Table 1 Hydroformylation of Alkenes Relative Rate and Isomer Ratios...

Table 1. Relative Rates of Hydroformylation of Various Olehn ...

CH3CH=CH(CH2)3CH3 (2-heptene) Comparison of cis- and Irans- hydrocarboxylation rates 14.6.4.3. Relative rate of hydroformylation (table) 14.6.3.2. 

Comparison of cis- and trans-hydrocarboxylation rates 16, 14.6.4.3 Relative rate of hydroformylation 16,... 

Figure 6.5. Relative rates of hydroformylation of 1-hexene catalyzed by benzene solutions containing [HRh(CO)(PPh3)3] and various amounts of the diphosphine Ph2P(CH2) PPh2 (n-2-4). Reproduced, with permission, from Reference 72.

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