Olefins hydrogenative dimerization

The minor products are generally 1-3% of the total yield and arose from (a) side-chain fragmentation producing hydrogen and low-molecular-weight hydrocarbons (b) addition of these fragments to the free olefin (c) dimerization and trimerization of the free olefin (d) fragmentation of the alkyl radical and cation intermediates. 

P-31 NMR was a powerful tool in studies correlating the structure of tertiary-phosphine-rhodium chloride complexes with their behavior as olefin hydrogenation catalysts. Triphenylphosphine-rhodium complex hydrogenation catalyst species (1) were studied by Tolman et al. at du Pont and Company (2). They found that tris(triphenylphosphine)rhodium(I) chloride (A) dissociates to tri-phenylphosphine and a highly reactive intermediate (B). The latter is dimerized to tetrakis(triphenylphosphine)dirhodium(I) dichloride (C). 

The effects of added triphenylphosphine and changing temperature on ligand dissociation and equilibria were studied also. The above dimer was an active hydrogenation catalyst. The equilibrium concentration of the dimer and the rate of olefin hydrogenation catalysis by the system depend inversely on the concentration of excess phosphine ligand. 

Three dimeric indole alkaloids of a new type, peceyline, peceylanine, and pelankine, have been isolated from a Sri Lankan apocynaceous plant, Petchia ceylanica Wight.876 The structures of these bases were determined mainly by n.m.r. spectroscopy. In their H spectra, all three alkaloids exhibit four aromatic singlets, one olefinic hydrogen multiplet, two methoxycarbonyl singlets, two N-methyl singlets, and two C-methyl doublets. One half of the non-aromatic carbon resonances in the 13C spectra show that one monomer unit is common to all three alkaloids, and inspection reveals that this unit must be based on vincorine... 

The process scheme is not complicated and yields on olefin feed are good. The major byproduct is paraffin from olefin hydrogenation in the reactor system. However paraffin make is low. Also some olefin remains unconverted, some dimer is formed, and traces of other byproducts are made. These include acetals, esters and diols. These other losses (excluding paraffins) total less than 5%. 

Rhodium-olefin complexes have been identified as intermediate species in rhodium-catalyzed olefin-to-olefin addition reactions (5a, 150a, 151) and olefin hydrogenation reactions (450). Although the ethylene-Rh(I) complexes are not in themselves catalysts for dimerization of ethylene, both [(C2H4)2RhCl]2 and (C2H4)2Rh( Cac) react with... 

Treatment of (PhCH2)4Ti with Hj in the presence of MejPCHjCHjPMej (L) gives LjTiHj, which catalyses the hydrogenation, dimerization, and polymerization of olefins. ... 

What follows depends on the nature of the radicals held by the metal surface and on the environment. If the R-S bond is weak, the R radical will leave the surface. If it encounters a source of hydrogen, it can be converted to the hydrocarbon RH. Or two radicals may disproportionate to form RH and the corresponding olefin. Radical dimerization may occur to give R-R. The sulfur is left combined with the iron as an inorganic iron sulfide. But if the R-S bond is strong enough and a source of hydrogen is available, the mercaptan RSH will leave the surface of the metal and enter the carrier fluid. The valence bond R-S-Fe may also be formed and the adsorbed radical will then become a mercaptide. 

The quantitative and selective transformation of the precursor into the dinuclear complex in catalytic conditions, the different catalytic performance of the mononuclear derivative [(BDPBzP)Ru(CH3CN)j]OTf (lower activity and enantioselectivity), the identical catalytic performance of the precursor and of the T12-H2 complex, and the recognized capability of the structurally related Ru(II) complex [(ri2-H2)(dppb)Ru()a.-Cl)3RuCl(dppb)] to maintain the dimeric structure in olefin hydrogenation reactions [35-37] were taken as proofs for the direct involvement of [(BDPzP)(DMSO)Ru((1-C1)3Ru(ti2-H2)(BDPBzP)] in the enantioselective hydrogenation of acetylacetone [68]. 

Asymmetric catalysis as a synthetic tool is relatively new (if enzymatic reactions are not considered) its development began 10 years ago, mainly because of the advances in coordination chemistry. Asymmetric hydrogenation started by modifying the Wilkinson catalyst (J). The early results (2,3,4) were encouraging enough to initiate a very large amount of research (5,6). Asymmetric C-C bond formation in olefin co-dimerization was observed for the first time by Wilke and his coworkers (7). Asymmetric hydroformylation (8) as well as several new asymmetric alkylation reactions appeared in the last five years (9,10). Asymmetric epoxidations were described in 1977 (11,12). 

Spectroscopic studies under catalytic olefin hydrogenation conditions without added L show the presence of RhClLs (43), H2RhClL3 (44), (RhClL2)2 (45), and H2(RhClL2)2 (46). (In the case of ethylene (C2H4)RhClL2 (47) is also observed.) The amount of the hydrides increases with H2 pressure, while the dimeric species are increased by... 

It might appear likely that electroreduction processes take place directly by electronst on metals which have high hydrogen overpotential and by H(a) on low overpotential metals. Indeed, e.g., electroreduction of acrylonitrile to adiponitrile on Pb or Hg takes place by electronation, followed by proton addition and dimerization, while electrolytic olefin hydrogenation on Pt takes place by transfer of H(a) to the organics. Nevertheless, such... 

This section lists examples of the conversion R2C=CR2 — R2CH2. Fof the hydrogenation, dimerization and alkylation of olefins see section 74 (Alkyls, Methylenes and Aryls from Olefins)... 

Studies on the dimerization and hydrogenation of olefins with transition metal catalysts in acidic chloroaluminate(III) ionic liquids report the formation of higher molecular weight fractions consistent with cationic initiation [L7, 20, 27, 28]. These... 

In addition to a-additions to isocyanides, copper oxide-cyclohexyl isocyanide mixtures are catalysts for other reactions including olefin dimerization and oligomerization 121, 125, 126). They also catalyze pyrroline and oxazoline formation from isocyanides with a protonic a-hydrogen (e.g., PhCH2NC or EtOCOCHjNC) and olefins or ketones 130), and the formation of cyclopropanes from olefins and substituted chloromethanes 131). The same catalyst systems also catalyze Michael addition reactions 119a). 

---