Metallacycles conjugated dienes

The stoichiometric head-to-head oxidative coupling of alkynes with CpRuBr(COD) affords a metallacyclic biscarbene complex [22], This process has been used to initiate catalytic formation of the RCH=CH-CH=C(Y)R backbone, to produce Junctional dienes from alkynes by addition of H-Y. The complex [Cp RuCl(COD)[ successfully catalyzes this new chemical transformation, involving the combination of two molecules of alkynes and one molecule of carboxylic acid to afford functional conjugated dienes (Scheme 4) [23]. 

Conjugated dienes and C02 react with Ni(0) complexes to yield nickel allylcarboxylates.49 (Butadiene)Fe(PMe3)3 reacted with C02 to provide an allylcarboxylate metallacycle.50 The anionic (butadiene)Mn(CO)3 reacted readily with C02 to give the anionic allylcarboxylate.51 Similarly, 1,2-dienes reacted with C02 on some Ni(0) complexes.52... 

The seven-membered metallacycles 89 (formed by ketone addition to [(butadiene)ZrCp2] cleanly add a nitrile molecule at elevated temperatures to yield the respective nine-membered metallacyclic products 96. Their hydrolysis then yields the 6-hydroxy-substituted non-conjugated unsaturated imines 97 under kinetic control. Within a few hours at room temperature these rearrange to the thermodynamically favored primary dienamine products 98.107 In this case the thermochemical diene conjugational energy makes the primary dienamines more stable than their conjugated imine tautomers (Scheme 32). 

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