Internal, linear alkenes

The hydroalumination of alkenes with BujAlCl catalyzed by Cp2ZrCl2 produces higher dialkylaluminum chlorides, which cannot be prepared by non-catalytic hydroalumination (Scheme 2-12) [63-65]. Terminal alkenes, internal linear alkenes and cycloalkenes can serve as substrates at reaction temperatures increasing in this order. 1,5-Dienes react to give cyclized products. 

Further processing of the product a-alkenes involves separation into the desired product fractions in a series of distillation columns. First the lower C4—C10 a-al-kenes are stripped off. In a heavy-ends column the C20+ a-alkenes are removed from the desired C12— C20 a-alkenes. Finally the middle-range products meeting the market needs are separated into the desired cuts and blends. The very high flexibility of the SHOP results from the following steps. The c4-c10 and the C20+ fractions are combined to be isomerized to internal linear alkenes and then subjected to a metathesis reaction. Both steps require about 80-140°C and 0.3-... 

Early attempts by Asinger to enlarge the scope of hydroalumination by the use of transition metal catalysts included the conversion of mixtures of isomeric linear alkenes into linear alcohols by hydroalumination with BU3AI or BU2AIH at temperatures as high as 110°C and subsequent oxidation of the formed organoaluminum compounds [12]. Simple transition metal salts were used as catalysts, including tita-nium(IV) and zirconium(IV) chlorides and oxochlorides. The role of the transition metal in these reactions is likely limited to the isomerization of internal alkenes to terminal ones since no catalyst is required for the hydroalumination of a terminal alkene under these reaction conditions. 

Bis(diamino)alanes (R2N)2A1H were used for the hydroalumination of terminal and internal alkenes [18, 19]. TiCb and CpjTiCb are suitable catalysts for these reactions, whereas CpjZrCb exhibits low catalytic activity. The hydroaluminations are carried out in benzene or THF soluhon at elevated temperatures (60°C). Internal linear cis- and trans-alkenes are converted into n-alkylalanes via an isomerization process. Cycloalkenes give only moderate yields tri- and tetrasubstituted double bonds are inert. Hydroaluminahon of conjugated dienes like butadiene and 1,3-hexa-diene proceeds with only poor selechvity. The structure of the hydroaluminahon product of 1,5-hexadiene depends on the solvent used. While in benzene cyclization is observed, the reaction carried out in THF yields linear products (Scheme 2-10). 

Addition of carbon monoxide and water to an alkene, i.e. hydrocarboxylation, is catalyzed by a variety of transition metal complexes, including [Ni(CO)4], [Co2(CO)s] and [HaPtClg]. Unfortunately this reaction usually leads to mixtures of products due to both metal-catalyzed alkene isomerization and the occurrence of Irath Markownikov and anti-Markownikov addition of the metal hydride intermediate to the alkene. The commercially available zirconium hydride [(C5Hs)2Zr(H)Cl] can be used as a stoichiometric reagent for conversion of alkenes to carboxylic acids under mild conditions (equation 23). In this case the reaction with linear alkenes gives exclusively terminal alkyl complexes even if the alkene double bond is internal. Insertion of CO followed by oxidative hydrolysis then leads to linear carboxylic acids in very good yield. 

The Rh/TPPTS catalyst system is only applicable to the hydroformylation of terminal linear alkenes. With branched or internal alkenes as substrates only very low conversion rates are achieved. Exceptions include strained cyclic alkenes such as cyclopentene and norbornene, which are hydroformylated at moderate rates under Ruhrchemie/Rhone-Poulenc conditions. 

Phosphites have been extensively studied for their use as ligands in rhodium-catalyzed hydroformylation (see Chapter 3). The first publication on the use ofphosphites is from Pruett and Smith, from Union Carbide [31]. The first exploitation of bulky monophosphites was reported by van Leeuwen and Roobeek [32]. They found that very high rates can be obtained for internal and terminal alkenes, but selectivities were low for linear alkenes. The bulky phosphites not only gave higher rates than less bulky phosphites, but they are also more resistant to hydrolysis. Bryant and coworkers [33] introduced even more stable, bulky phosphites by the... 

Halide anions affect the rate of hydroformylation of internal olefins as well as the regioselective properties of the catalyst [136]. The rate of hydroformylation of thermally equilibrated internal higher alkenes increased by a factor of 6-7 by adding substoichiometric amounts (with respect to palladium) of Cl" or Br" and by a factor of 3-4 with I" [137]. When a thermally equilibrated mixture of internal Cg-Cj g olefins was subjected to isomerization-hydroformylation, a reverse effect on regioselectivity was observed [136e]. Thus, the formation of the linear aldehyde increased in the following order iodide > bromide > chloride. 

High selectivity was observed in the epoxidation of cyclic alkenes (especially cydohexene) with the important feature that allylic oxidation products were not obtained. Excellent results are reported for internal alkenes, for example, trans-2-octene and trans-4-octene, whereas terminal linear alkenes give slightly lower yields. 

After the oligomerization reactor and the liquid-liquid separator, the organic product has to undergo an intensive product wash to make sure that no catalyst enters the distillation columns. In the following series of distillations, the technically desired 1-alkene cut Ce-Cig is separated and the too light C4 and the too heavy C18+ cuts are combined and isomerized to internal linear olefins in the isomerization reactor. These internal alkenes are then converted in the metathesis reactor to form internal alkenes. The desired C -Cig fraction is isolated, whereas the lights and the heavies are again recycled into the isomerization reaction. 

The major product of ethylene oligomerization in the presence of Ni-ylide-aluminum alcoxides are linear 1-alkenes with even carbon atom numbers, from C4 to 40- In addition to 1-alkenes, linear alkenes with internal double bonds (trans and cis) are always present in the reaction product. 

Highly selective halide anion-promoted palladium-catalyzed hydroformylation of internal alkenes to linear alcohols was studied. A (bcope)Pd(OTf)2 complex (bcope) = bis(cydooctyl)phosphinoethane with substoichiometrically added halide anion was found to be a highly efficient homogeneous catalyst to selectively convert internal linear... 

Nickel catalysts promote the hydroalumination of alkenes using trialkylalanes R3AI and dialkylalanes such as BU2AIH as the aluminum hydride sources [9, 29, 30, 33]. However, exhaustive studies of the range of substrates capable of hydroalumination with these reagents has not been carried out. Linear terminal alkenes like 1-octene react quantitatively with BU3AI at 0°C within 1-2 h in the presence of catalytic amounts of Ni(COD)2 [30]. Internal double bonds are inert under these conditions, whereas with 1,5-hexadiene cycHzation occurs. 

The reaction can be combined with an alkene isomerization, which requires the use of the more electron-withdrawing XANTPHENOXAPHOS ligand. Thus, starting from internal alkenes, linear amines can be obtained in quite reasonable yields and high n/iso selectivity (Scheme 15) [60]. 

Cobalt carbonyls are the oldest catalysts for hydroformylation and they have been used in industry for many years. They are used either as unmodified carbonyls, or modified with alkylphosphines (Shell process). For propene hydroformylation, they have been replaced by rhodium (Union Carbide, Mitsubishi, Ruhrchemie-Rhone Poulenc). For higher alkenes, cobalt is still the catalyst of choice. Internal alkenes can be used as the substrate as cobalt has a propensity for causing isomerization under a pressure of CO and high preference for the formation of linear aldehydes. Recently a new process was introduced for the hydroformylation of ethene oxide using a cobalt catalyst modified with a diphosphine. In the following we will focus on relevant complexes that have been identified and recently reported reactions of interest. 

Fast, selective conversion of internal alkenes to linear esters is catalyzed by Pd11 complexes of chelating bis(phospha-adamantyl)diphosphines, e.g., the mesa (168) and racemic (169) isomers, and the catalysis is acutely sensitive to the ligand backbone and even to the diastereomer used the results are compared with those for the P Bu2 analogous.686... 

This group subsequently invented a domino reaction consisting of isomerization of internal to terminal alkenes, followed by linear selective hydroformyla-tion and reductive amination (Scheme 15.14) [89]. 

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