Cyclopropenyl complexes

Ruthenium vinylidene species can be transformed into small carbocyclic rings via carbocyclization reactions. Ruthenium vinylidene complex 2, generated from the electrophilic reaction of alkyne complex 1 with haloalkanes, was deprotonated with "BU4NOH to give the unprecedented neutral cyclopropenyl complex 3 (Scheme 6.2) [5]. Gimeno and Bassetti prepared ruthenium vinylidene species 4a and 4b bearing a pendent vinyl group when these complexes were heated in chloroform for a brief period, cyclobutylidene products 5a and Sb formed via a [2 + 2] cycloaddition between the vinylidene Ca=Cp bond and olefin (Scheme 6.3) [6]. 

Notably, early attempts to similarly prepare cyclopropenyl complexes of group 6 molybdenum and tungsten, using [CpM(CO),] anions (M = Mo, W) and [C,(Bu-/),]BF4, resulted in the electrophilic attack of the cyclopropenium cation on the peripheral cyclopentadienyl ligand, to give hydride complexes (equation 196)270. These air-sensitive hydride complexes readily react with CC14, to afford the corresponding air-stable chloro complexes. 

Since most of the >/2-cyclopropenyl complexes are obtained by ligand exchange reactions (cf Section IV.B.l.a) it is reasonable to believe that the reactions of cyclopropenes with octahedral complexes of tungsten (equation 222)287 and rhuthenium (equation 223)294, which lead directly to vinyl alkylidenes complexes, pass through an unstable >/2-cyclo-... 

In some cases, tj1-cyclopropenyl complexes may be isolated as intermediates, whilst in others, migration to a carbonyl ligand may be... 

Figure 13. Hypergraphs with the symbolic vertex and edge labels representing allylic and cyclopropenyl complexes given in Figure 12...

The vertex and edges alphabets of hypergraph H2 representing cyclopropenyl complex look like A V H2)) = CH, M and A E H2)) = [El, E2,E3,E4. The vertex labels are presented by symbols of functional chemical groups. It is easy to see that the vertex alphabets are the different for these hypergraphs. 

Jar structures of tlie 17 -cyclopropenyl complex [IVloBrjCOJilbipyXi -C3Pli3)]NCMe and tlie ij -oxocyclobutenyl complex [MoBr(CO)2 (bipy)(T7 -C4Ph30)] thf have been determined crystallographically (Table jH) 320 j pig reaction of [Mo(CO)4(phen)] with ally bromide to give [MoBr(CO)2(phen)(T -C3H5)] has been shown to obey the rate law -d[Mo (CO)4(phen)]/dr = K,[Mo(CO)4(phen)]. The mechanism of the reaction probably proceeds via slow solvent-assisted fission of a Mo—CO bond, followed by reaction with allyl bromide. - ... 

Although the initial cyclopropenyl complexes reported were with first-row transition metals, second- and third-row transition metals are now known to also form t]3-C3R3 complexes.13 In addition, second- and third-row transition metals can form unsymmetrical complexes with C3R3 in which the metal-carbon distances differ significantly. 

Cyclopropenyl systems can be formed from metallacyclobutadiene complexes. Here no decomplexation of unsaturated cyclopropanes is observed. The tungstacyclobutadiene complex 12 is converted into a cyclopropenyl complex 13 upon addition of a nitrogen nucleophile. ... 

Similar chemistry was unsuccessfully attempted using cobalt rather than rhenium. With cobalt, as with most other metals, no tj -cyclopropenyl complexes are obtained. Instead a carbonyl ligand is inserted, and -oxobutenyl complexes arc formed. ... 

Fig. 2.64. I2 attacks the cyclopropenyl complex VII, yielding the vinylidene species VIII.

The photochemistry of metal carbyne complexes is in many ways similar to the photochemistry of metal carbene complexes, but the reactions have not been developed or become as synthetically useful as the photochemistry of metal carbene complexes. Among reported reactions are couplings with ancillary CO ligands to form ketenyl complexes, protonation of the carbyne carbon, insertions into C-H bonds, addition of the carbyne carbon to an alkyne to produce a cyclopropenyl complex, and electron-transfer reactions. ... 

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