Norbornadiene complexes with ruthenium

RuCl2(arene)]2 complexes (1) react with 1,5-cyclooctadiene and 1,3- or 1,4-cyclohexadiene in the presence of ethanol and Na2C03 or zinc dust to give Ru°(776-arene)(V diene) compounds of type 196-198 in 60% yield [Eq. (20)] thus, this reaction appears to be the reverse of the 198-> 1 reaction [Eq. (19)]. The same reaction with ethylene leads to the bis-ethylene ruthenium(O) complex 205 (37%) (131,10). The norbornadiene complex 207 is prepared similarly from derivative 206 (125). Combination of transformations 206 - 207 [Eq. (21)] or 1 - 198 [Eq. (20)] with trans-... 

One of the first examples of ruthenium-catalyzed C-C bond formation afforded the synthesis of cyclobutenes, from norbornene derivatives with dimethyl acetylenedicarboxylate, and was reported by Mitsudo and coworkers [45, 46] by using various catalysts such as RuH2(CO)[P(p-C6H4F)3]3 or RuH2(PPh3)4. More recently, the complex Cp RuCl(COD) has shown to be an excellent catalyst for the [2+2] cycloaddition of norbornenes with various internal alkynes [45] (Eq. 33) and with a variety of substituted norbornenes and norbornadienes [47]. The ruthenacycle intermediate, formed by oxidative coupling, cannot undergo /1-hydride elimination and leads to cyclobutene via a reductive elimination. 

Norbornene or norbornadiene-type substrates with nickel, ruthenium or cobalt catalysts undergo stereoselective dimerization or codimerizations with other substrates. Numerous examples have been reported15. Stoichiometric use of an iridium complex in the cyclodimerization of norbornadiene results in an isolable c.vo-rrans-c.ro-metallacyclopentane 7, formed from two norbornadiene units18. Upon heating in the presence of triphenylphosphanc, the exo-trans-e.YO-dimer 8 is liberated from complex 7. 

More polar functional groups such as ketones are hydrogenated effectively with homogeneous cationic rhodium and ruthenium complexes. Polymer catalysts active for both olefin and ketone hydrogenation activity were synthesized from ionic precursors such as Rh(norbornadiene)(acac) + HCIO4 or Rh(norbornadiene)(PE 3)2 + C104. Two types of coordination were observed, depending on the method of attachment " ... 

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