Cyclopropylidene complexes

Transition metals 172 a-bonded to cyclopropanes, substituted on the a-carbon with a halogen atom, are interesting intermediates for cyclopropylidene complexes 173 or allene ones 174 [88]. The former complexes are also supposed to be precursors of the above-mentioned nickel enolates. (Scheme 65)... 

Cyclopropylidene complexes are rare. In fact, there is only one report of isolated (/(-cyclo-propylidene)diiron complexes which are stable in the solid state at room temperature vide infray. More recently, a labile cyclopropylidene tungsten complex has been isolated which decomposes above -40 °C42. In all other reports21,110 cyclopropylidene complexes are proposed as transient intermediates. 

Unusual bridging (//-cyclopropyIidene)diiron complexes having a tetrahedral carbene carbon have been studied as model intermediates in carbon-carbon bond formation in the Fischer-Tropsch synthesis248. The cyclopropylidene complexes cis- and trans-[Cp(Co)Fe]2(/(-Co)(//-C,H4) were readily prepared by cyclopropanation in ether, of the corresponding cis- and mww-vinylidene complexes [CpCoFe](//-CO)(//-CH2) with diazomethane in the presence of CuCl (equation 181). Both isomers are air stable in the solid state. Solutions of the complexes are air stable for several hours, provided they are kept in the dark. The pure //-cyclopropylidene isomers slowly interconvert in solution, like their parent /z-vinylidene and other alkylidene complexes. The final equilibrium ratio cis .trans = 4.8 1 is reached after two weeks. 

Cyclopropylidene complexes have been reported to undergo ring opening to allene or allyl complexes. ... 

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