Amidation catalyst activation

Reactions of amines with alkenes have been reviewed298,299. Alkali metal amides are active homogeneous catalysts for the amination of olefins. Thus diethylamine and ethylene yield triethylamine when heated at 70-90 °C at 6-10 atm in the presence of lithium diethylamide and /V./V./V. /V -tetrarncthylcthylcncdiaminc. Solutions of caesium amide promote the addition of ammonia to ethylene at 100 °C and 110 atm to give mixtures of mono-, di- and triethylamines300. The iridium(I)-catalysed addition of aniline to norbomene affords the anilinonorbomane 274301. Treatment of norbomene with aniline... 

In general, amino-containing compounds are poor partners in CM due to their tendency to coordinate to the metal catalyst, even when late-transition metal systems are employed. To preserve catalyst activity, amino groups are therefore typically masked as cyanides, carbamates, amides, or phthalimides. In substrates where iV-coordination to the catalyst is less favored, such as with hindered /V-aryl-/V-allylamines, no protecting group is required. 

The work on the AlR3-aeid amide catalyst system has its origin in the studies on the AlR3-ketone catalyst system (35). In the course of studies on the latter catalyst, we speculated that the dialkylaluminum monoenolate [X] might be superior to dialkylaluminum monoalcoholate [XI] as a stereospecific polymerization catalyst (35). Although the speculation on the active species of the AlR3-ketone catalyst system was disproved later by our more detailed studies, fortunately we could find out about the AlR3-acid amide catalyst system (35). 

An analogous propargylation can be attained with allenyl tributyl stannane however, this reaction is catalyzed by SiCU that is activated by a bisphosphor-amide catalyst. Note that in this case, the role of the Lewis basic phosphoramide is to increase the Lewis acidity of SiCU rather than to increase the nucleophilicity of the stannane [51b]. A discussion of these effects is provided in Section 7.4. 

Not surprisingly, chiral formamides emerged as prime candidates for the development of an asymmetric variant of this reaction. A selection of the most efficient amide catalysts based on amino acids is shown in Figure 7.4 representative examples of enantioselective hydrosilylation are collected in Tables 7.7 and 7.8. Proline-derived anilide 82a and its naphthyl analogue 82b, introduced by Matsu-mura [3c], produced moderate enantioselectivity in the reduction of aromatic ketimines with trichlorosilane at 10 mol% catalyst loading (Table 7.7, entries 1 and 2). Formamide functionality proved to be crucial for the activation of the silane, as the corresponding acetamides failed to initiate the reaction. 

The solubility of NdX3 catalysts is improved by the addition of electron donors (D). Catalyst activity is remarkably increased without substantial deterioration of the cis- 1,4-content. Typical donor ligands applied in NdX3 Dn/AlR3 type systems are alcohols such as EtOH [92,112,113], 2-ethylhexanol [114] or various pentanol isomers [115]. Furthermore, tetrahydrofuran (THF) [35], tributyl phosphate (TBP) [116-119], alkyl sulfoxides [116,117,120,121], propion amide [122,123], B(0-CH2-CH2-0-CH2-CH2-0H)3/B(0-CH2-CH2-0-C2H5)3 [124,125], pyridine [126] and dioxides [127,128] are applied as donors. The increase in catalyst activity by donor ligands is attributed to the improved solubility of the active species in hydrocarbon solvents [129,130]. 

Table 14 Polymerization of butadiene with neodymium amide catalysts utilizing borate activators...

Similar catalytic activity for the hydroamination with amines could be realized under low pressures (<10 MPa) by the use of metal amide catalysts preformed before the alkylation step. The metal amide can be prepared in situ by reacting the metal, e. g., sodium, with the amine in the presence of 1,3-butadiene, whereby the sodium amide is produced and the diene hydrogenated to 2-butene. 

Any basic or alkaline material can react with a zeolite to effectively neutralize the acidic active sites, which generally results in irreversible loss of catalyst activity. Basic compounds found in the ethylene or benzene feedstocks can include amines, amides, nitriles, and trace metal cations such as sodium and potassium. Of particular concern are nitrogen-containing organic compormds typically present in the benzene feed. 

In 2006 Palomo and coworkers tested several prolinamides in the asymmetric Michael addition of aliphatic aldehydes to nitroalkenes. Hydroxy-proline-derived amides 13 were found to be the most active catalysts for this transformation, establishing the importance of the hydrojy group not only for reaction stereocontrol, but also for catalyst activity. However, 3-hydro>y-prolinamide 13b gave less satisfactory results in terms of stereocontrol, compared to the 4-hydro>y-prolinamide analogue 13a (Scheme 11.11). 

Compared with the amides, the amine commiomers 24—31 were much better tolerated by the catalyst system. In ethylene copolymerizations, the catalyst activity remained at a moderate level, i.e., 1,000-3,000 kg polymer/(mol Zr h), when Al/comonomer ratios were 4—10 mol/mol. In the comparison of different amines. 

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