High TON

Contrary to the observations made previously with low TON reactions, here the homogeneous catalyst was more active than the anchored species. Once the homogeneous catalyst had been used for the high TON hydrogenation, though, it appeared to have been somewhat deactivated. The anchored catalyst, however, is capable of re-use several times. In this instance there was an increase in activity after the first use, even though the catalyst had been pre-hydrogenated. 

Another interesting comparison of the homogeneous Wilkinson catalyst with AHC-Wilk is in the high TON hydrogenation of cyclohexene in 10%... 

Table 4. Multiple high TON DMIT hydrogenations over AHC-Skew at 1000 psig.

Hydrogenation is not limited to the use of (EBTHI)MX2-type catalysts. In polymerization, linked amido-cyclopentadienyl ligands have emerged as very important systems, and the corresponding chiral derivatives have been prepared (Scheme 6.9) [113-116]. Nonetheless, whilst high TON can be achieved (500-1000), the ee-values are quite low (<25%). 

During recent years, substantial progress has been made in the hydrogenation of unfunctionalized alkenes. With iridium complexes derived from chiral phos-phino-oxazolines and related ligands, excellent enantioselectivities and high TON/TOF values can now be obtained for a wide range of unfunctionalized olefins. Most substrates studied to date have at least one aryl substituent at the... 

Most catalysts originally developed for C=C bonds show a rather poor performance for the hydrogenation of many ketones. However, this situation changed dramatically when it was found that selected Ru-binap and later Ru-binap-dia-mine complexes achieve excellent enantioselectivities, as well as very high TONs and TOFs, for a variety of ketones [92]. Since then, it has been demonstrated that many a- and yS-functionalized, as well as aromatic ketones, are suitable substrates for hydrogenation with industrially viable catalytic results. For the reduction of various ketones biocatalytic methods are an industrially viable alternative to chemocatalysts [15]. 

The two production processes using a-amino ketone substrates depicted in Figure 37.24 were developed by Boehringer-Ingelheim to improve on existing resolution syntheses for adrenaline and phenylephrine [94]. Unfortunately, few details are available but both processes are carried out with a Rh-mccpm catalyst with very high TONs and TOFs, albeit with medium ee-values of 88% which increase to >99% after precipitation of the free base. 

Phosphinite pincer iridium systems have also been shown to have a lower tendency to oxidatively add TEE to give (vinyl)(hydride) complexes similar to 3 [18]. While this has been identified as one of the major catalyst deactivation processes in phosphine pincer iridium catalysis, apparently with complexes such as 5, only olefin coordination can occur. However, this is a considerably weaker bonding and is less detrimental to catalyst activity. Eased on steric arguments, product olefin coordination (e.g. COE) is favored over TEE coordination, and therefore at a high TON and high product concentrations the phosphinite catalysts 5 are markedly less active than the phosphine analogues 1. 

Hashimoto has shown that the addition of phosphane sulfides results in higher yields and faster conversions for PKR under atmospheric pressure of CO. This mild promoter provided high TONs, and can be applied to catalyze an intermolecular PKR under 1 atm of CO. ... 

Mn, the highest TONs were observable with Zn as the countercation. Some of the high TONs observed in the Pd-catalyzed cross-coupling reactions of organozincs are shown in Scheme 2563. 

Although donor substances retard the reaction rate, significant deactivation of the catalyst by the conjugated dienamine 4 was observed. In connection with this observation, we have found that an isomeric dienamine of the substrate 2-[2-(A,. V-diethylamino)ethyl]-6-methyl-1,5-heptadiene (7). which is always present in small amounts (0.5-0.7%) in the crude commercial products 1, also acts as a deactivator (see Table 3.4). Thus, a careful and exhaustive pretreatment of the substrate and the reaction system is necessary to attain a high TON. 

The conversion of simple hydrocarbons into corresponding amine products is significantly higher than in previous reports. The authors also noted that NMR experiments showed that catalyst peaks reappeared after the completion of the reaction, demonstrating the robustness of the catalyst. A high TON may be achieved with this silver-pyrazolylborate system with further reaction optimization. 

The key intermediate of this novel convergent approach is a haloindanone, which is readily available from cheap starting materials and provides access to structurally diverse aryl- and heteroarylindanones. Yields are typically in the range from 85 % to 95 %. The facile isolation of the pure products sufficiently high TONs, excellent yields, and the choice of solvents employed in the reaction render this process technically feasible and very attractive. 

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