Cyclopentadienyl-type ruthenium complexes

From the mechanistic point of view, the observed competitive reactions can be explained by considering two different pathways (Scheme 114). The intermediacy of ruthenacyclopentadiene 453 or biscarbenoid 452, formed from the reaction of a diyne and a ruthenium(ll) complex, is postulated in the proposed mechanism. Cyclopropanation of the alkene starts with the formation of ruthenacyclobutane 456, which leads to the generation of the vinylcarbene 457. Then, the second cyclopropanation occurs to afford the biscyclopropyl product 458. Insertion of the alkene 459 into the ruthenacyclopentadiene 453 affords the ruthenacycloheptadiene 454. The subsequent reductive elimination gives the cyclotrimerization product 455. The selectivity toward the bis-cyclopropyl product 458 is improved with an increasing order of haptotropic flexibility of the cyclopentadienyl-type ligand. 

Compound 127 is a useful starting material in preparing a variety of arene cyclopentadienyl ruthenium complexes of type 125 by... 

This type of sandwich complex, first reported with iron as the central metal, has now become widespread with ruthenium as well. Early routes to ruthenium complexes were modeled on iron chemistry, and used the AICI3-catalyzed exchange of a cyclopentadienyl ligand for an arene in ruthenocene, or reaction of CpRu(CO)2Cl with AlCb/arene. These methods are less successful with ruthenium than with iron, however, owing to the greater stability of ruthenocene. A mixture of arene, pentamethylcyclopentadiene, and RuCls in the Zn reduction method gives good yields of the mixed-sandwich cations. A... 

To date, two types of metallocene complexes have been used in the polymerization of olefins at CNT surfaces by PFT a ruthenium alkylidene complex anchored by two routes onto SWCNTs via a pyrene derivative spacer [94], and zirconium complexes of general formula [(R)2ZrCl2], R being a derivative of cyclopentadienyl or indenyl, anchored onto CNTs modified with MAO [97]. 

Although benezene and benzene type complexes are much less common than those with cyclopentadienyl ligands, a number of such complexes are known for chromium and ruthenium. The bis benzene complex (// -C6H6)2Cr is photochemi-... 

---