Co-oligomerisation

Co-addition and Co-oligomerisation.—Nickel and palladium catalysts are again much in evidence. The same 7r-tetramethylcyclobutadienenickel dichloride plus alkylaluminium halide mixed catalysts which have been investigated in relation to alkene oligomerisation (see above) catalyse coaddition of ethylene and propene. Kinetic results for this reaction are reported. Product analysis and distribution permit postulation of mechanisms of addition of butadiene and but-2-yne to give 4,5-dimethyl-1- 

Mixtures containing nickel chloride, aluminium triethyl, and l,2-bis(di-phenylphosphino)ethane (dpe) or l,2-bis(diphenyIphosphino)propane (dpp) catalyse the reaction of ethylene and butadiene to give 1,4,9-decatriene vv hen the ratio of dpe or dpp to nickel is less than 1. However, when more phosphine is present [dpe Ni 1 or dpp Ni = 1-5], 1,4-hexadiene is produced. At higher ratios, dpe Ni 3, there is little reaction. Such marked discrimination is unusual even the replacement of these chelating phosphines by triphenylphosphine leads to greatly reduced selectivity.  

Addition of ethylene to butadiene is catalysed by cobalt(ii) chloride-bidentate diphosphine-aluminium triethyl mixtures [c/. similar nickel(ii) case above]. Addition of butadiene or of 1,1-dimethylallene to nor-bornadiene is catalysed by iron(o) complexes, for instance the cyclo-octene complex.  

Fujiwara, I. Moritani, R. A. Sano, H. Tanaka, and S. Teranishi, Tetrahedron, 

Takahashi, K. Tsukiyama, S. Sakai, and Y. Ishii, Tetrahedron Letters, 1970, 1913. 

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Holzhey N, Pitter S, Dinjus E (1997) Die heterogen katalysierte co-oligomerisation von 1,3-butadien und C02 mit immobilisierten Palladiumkomplexen. J Organomet Chem 541 243-248... 

Palladium compounds are also useful catalysts for oligomerisation and co-oligomerisation reactions. Dimerisation or co-dimerisation of olefins catalysed by palladium(n) chloride or, better, PdCl2(C6H5CN)2 involves a palladium(ii)-hydride intermediate as the catalytically active species. A similar reaction to dimerisation is coupling, e.g. of benzene to give biphenyl, which is also catalysed by palladium(ii) chloride and proceeds via palladium-phenyl u-bonded species. The nature of intermediates in... 

Abstract Over the past decade significant advances have been made in the fields of polymerisation, oligomerisation and telomerisation with metal-NHC catalysts. Complexes from across the transition series, as well as lanthanide examples, have been employed as catalysts for these reactions. Recent developments in the use of metal-NHC complexes in a-olefin polymerisation and oligomerisation, CO/olefm copolymerisation, atom-transfer radical polymerisation (ATRP) and diene telomerisation are discnssed in subsequent sections. 

In a closer examination of the formation of oligomers, Ferris and co-workers found that the reaction is favoured by relatively high salt concentrations (e.g. 1M NaCl), while the presence of divalent cations is not necessary. The formation of RNA oligomers was found to be temperature sensitive the yields decrease when the temperature is raised from 4°C to 50° C. The addition of meteorite material (from 3 meteorites) does not catalyse the polymerisation reaction only galena (PbS) can do this. The authors thus assume that RNA oligomers could have been formed on the young Earth in solutions of alkali metal salts in the presence of montmorillonite and a pH value of 7-9 (Miyakawa et al., 2006). Ferris (2006) has provided a short but up-to-date survey of montmorillonite-catalysed RNA oligomerisation. 

Attachment of dendritic wedges of either the carbosilane or benzylphenyl ether type to the para-hydroxy aryl site in [2,6-(ArN=CMe)2C5H3N (1 R = Me, Ar = 2-Me-4-OHC6H3), has been shown to proceed in good yield [162], Complexation with iron(II) chloride allows access to dendrimer-supported precatalyst 42 (Scheme 13). Using MAO as a co-catalyst, it was shown that 42 are active in the oligomerisation of ethylene the activity of these new catalysts is not, however, related to the type of dendritic wedge employed. 

The oligomerisation of isobutene, with and without isomerisation or fragmentation, and its polymerisation and co-polymerisation are industrial processes of considerable... 

Other systems, e.g.perfluoro-propene [54,59-61] and -cycloalkenes [62,63] (Scheme 30), may also be oligomerised by fluoride ion. A number of co-oligo-merisations have also been successfully carried out [54,64-66]. 

Fig. 21 summarizes the complexes obtained. The formation of cycloadducts XIV can be explained formally as insertion into the Fe-N bond. By analogy to the well known cyclo-oligomerisation reactions of acetylenes94 in the presence of transition metals, it seems probable that the reaction occurs stepwise and is initiated by formation of a 7r-complex of the alkyne. The necessary vacant coordination site may be formed by loss of CO or by opening of one Fe-N bond. 

For comparison, oxetanes are oligomerised in an analogous way to give intermediate polyfluoro-polyethers that are then further fluorinated to give perfluoro-polyethers in the process for the production of Demnum fluids (Daikin Co.) [188] (Figure 8.59). 

The formation of strongly adsorbed by-products is another major difficulty. Possible contaminants include condensation and oligomerisation products of carbonyl species and the decomposition of alcohol species to yield CO and adsorbed hydrocarbon, numerous examples of such deactivation scenarios exist giving a genuine challenge to both the catalyst... 

Fig.8 Synthesis of bis(trimethylsilyl)squarate from CO and SiMeaCl, with the uranium complex providing electrons for reductive oligomerisation and steric control conversion to squaric acid previously reported...

The diboronated BisP diphosphines contain two methyl groups amenable to be deprotonated and oxidatively oligomerised to afford C2-oligophosphine boranes with an even number of phosphorus atoms. This chemistry has been extensively studied by Chujo and co-workers (Scheme 5.37). ... 

Figure 6.17 Cyclo-oligomerisation of co-halogenoalkyl carboxylic acid bound to an anion...

Naked [Fe4] ions in the gas phase were shown by mass spectrometry to oligomerise ethyne to benzene via the cationic intermediate [Fe(C2H2)m] (m = 1-4)256. r was reported that the ethene ligand in [Fe(CO)2 P(OMe)3 2(Tl2-C2H4)] could be substituted by diphenylacetylene to form [Fe(CX))2 P(OMe)3 2(il -C2Ph2)]. The X-ray crystal structures of the alkene and alkyne complexes were determined257. Reaction of [CpFe P(OMe)3)2(NCMe)]+[PF6] with [PhCXH]... 

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