Cyclo-oligomerisation

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. 

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

Linear Homotetrasaccharides.- Cyclo-oligomerisation of the isomeric (8) and (9) under Helferich conditions gave the unbranched tetramers (lO) and (11), respectively, as well as the dimer and trimer from the latter trityl ether. 

Only non-enolizable eneones give satisfactory yields of hydrodiroer on reduction in aptotic solvents [83]. A suitable aqueous buffer is needed with enolizable eneones to control base catalysed side reactions of condensation and oligomerisation. The polarographic behaviour of eneones in buffers is illustrated using cyclo-... 

Studies [61,62] have shown that at 90°C, the adduct reacts to form a six member ring, cyclo(trimmido-hexamethyitrigallium), with the release of one methane molecule per Ga atom. The overall reaction proceeds in two steps, as indicated by EQNS (2) and (3). The first step is methane elimination to form (CH3)2Ga NH2, followed by the oligomerisation of this compound. 

Either triphenylarsonium benzoylylide or dibenzoylylide form complexes with bis(l,5-cyclo-octadiene)nickel these oligomerise ethylene under mild conditions . The dibenzoyl derivative is the more effective catalyst of the two, this being ascribed to the greater stabilization provided by the second benzoyl group the monobenzoyl derivative provides largely linear alkenes, but the dibenzoyl derivative leads to decreased linearity in the products. 

The mechanism of trimerisation of butadiene by a mixed cobalt(ii) chloride-aluminium triethyl catalyst has been inferred from the natures of the three products characterised. The determination of the enthalpy of dimerisation of aluminium triethyl provides a useful piece of thermochemical data for quantitative discussion of the role and energetics of aluminium triethyl in this type of reaction. Polymerisation of isoprene in the presence of Fe(acac)3-aluminium triethyl-pyridine derivatives mixtures has a negative apparent activation enthalpy, which can be attributed to the instability of the catalytic complex at elevated temperatures. Bis-cyclo-octatetraeneiron(o) is an effective oligomerisation catalyst. The composition of products accessible only by hydrogen migration indicates an oxidative addition-reductive elimination mechanism rather than insertion. 

Larger rhenium complexes are also the subject of a number of publications. Reaction of an excess of thietane with the thietane complex fRe3(CX))jQ(p-H)3(p-cyclo-SCH2CH2CH2)] affords a number of ring-opening oligomerisation products from which sulfur containing macrocycles such as 12-S-4, 16-S-4 and 24-S-6 can be eliminated upon addition of pyridine . Addition of... 

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