Mechanisms transfer involving isobutene

For isobutene polymerized in ethyl chloride by SnCl4 and H20 a transfer mechanism involving the catalytic complex has been suggested on kinetic grounds [4] ... 

However, with the former catalyst the mechanism is essentially an ionic one, with evolution to a dioxyalkylidene species which can yield either methacrolein, or a carboxylate species, precursor of methacrylic acid. No isobutene is detected among the reaction products since the dioxyalkylidene species is strongly bound to the surface. The overall process involves the transfer of 8 electrons from the organic substrate to the catalyst per molecule of methacrylic acid produced. In the case of W-containing heteropolycompounds the mechanism is essentially a radical one (analogous to that proposed for the radical-like chemistry exhbited by W-containing heteropolycompounds in liquid phase oxidations (46)). In the absence of centres able to insert O species, the radical alkoxy intermediate converts to isobutene. The process only involves 2 electrons. 

Alkyl- and aryl-acetylenes, e.g. (70), but not acetylene itself, co-dimerize with allylic halides (71) in the presence of catalytic amounts of palladium complexes to give halogenated 1,4-dienes (72) in excellent yields. " The most active catalyst appears to be the [PdX2(PhCN)2] complex. The procedure involves very careful addition of the acetylenic compound to the allylic halide solution at 20 °C to prevent polymerization in this exothermic reaction. The co-dimerization of isobutene with trichloroethylene can produce useful quantities of l,l-dichloro-4-methylpenta-1,4-diene in the presence of t-butyl peroxide at 500 °C in a gas-phase reactor. The reaction probably occurs by a radical transfer mechanism. 

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