Metallacyclopentadiene complex

Bis(phenylethynyl)-l,6-methanocycIodeca-l,3,5,7,9-pentaene (45) reacted with cyclopen-tadienylbis(triphenylphosphane)cobalt to form an intermediate metallacyclopentadiene complex 46 (with the methanocyclodecapentaene 45 converted to its norcaradiene valence tautomer) which gave the corresponding iminocyclopentadiene complex of 47 upon treatment with an... 

Recently the oxidative coupling of olefins and alkynes, not only with late transition metal complexes, but also with low valent early transition metal complexes to give metallacyclopentane or metallacyclopentadiene complexes is attracting increasing attention. For example, titanium(II) and zirconium(II) complexes react with olefins and form metallacycles. Various stoichiometric processes to produce useful compounds that are otherwise unavailable can be produced by exploit-... 

Oxidative coupling - Example M"(t -C2H4)2 gives a metallacyclopentane and, more commonly, addition of 2 equiv. alkyne to M" yields metallacyclopentadiene complexes or the bis-carbene mesomers. 

A f/oro-mthenacyclopentadiene complex 55 was obtained by the reaction of 7 with linear alkanes (Equation (18))." During this reaction, six C-H bonds of alkane were successively cleaved. Such multiple C-H bond cleavage was rationalized by the cooperative action of the neighboring ruthenium centers of the ttimetallic framework, which promotes the incorporation of alkane into the reaction field of the cluster. Such closo-typc metallacyclopentadiene complexes have been intensively studied using carbonyl clusters, and often prepared by the coupling reaction between the two alkyne ligands of the bis(/r3-7 ( )-alkyne) complex, so-called violet isomer.The /i3-sulfido complex 9 obtained by the reaction of 7 with thiophenol also reacts with alkane to yield a /ts-alkylidyne complex. ... 

A myriad of metallacyclopentadiene complexes relevant to cyclotrimerization have been isolated representativeruthenacyclopentadienes are depicted in Table 3.16. Except for 91, these complexes are not only reactive intermediates but also competent catalysts for relevant [2 -i- 2 -i- 2] cycloadditions. For example, carbonyl complexes 1 and 90 catalyze the cyclotrimerization of electron-deficient alkynes [8a,20], and... 

Metallacyclopentadiene is a common intermediate in the [2 -b 2 -b 2] cycloaddition of alkynes. The oxidative cyclization of alkynes to a metal center gives metaUacyclopen-tadiene. Various metallacyclopentadiene complexes are formed by this reaction. It is generally accepted that there are two mechanisms for the reaction of metallacyclopentadiene with alkynes to give benzenes a Diels-Alder type of mechanism to give l-metallabicyclo[2.2.0]hepta-3,6-diene intermediate and an insertion mechanism to give metallacycloheptatriene (Scheme 5.23). 

---