Diphenylacetylene metal reaction products

The reactivity of carbene-metal complexes, amongst others the reactivity with respect to alkenes and alkynes, has been reviewed by Dotz Just like free carbenes the coordinated carbenes add to triple bonds to give cyclopropene derivatives. Other reaction products, however, are also possible. For instance, the carbene ligand of chromium complex 23 reacts with diphenylacetylene to a mixture of products, including naphthalene derivative 24 and furan derivative 25 (equation 18). A carbonyl ligand has participated. Molecular orbital calculations by Hofmann and Hammerle " on this system reveal that the reaction would pass through an y-vinylcarbene type of complex (26) instead of through a planar chromacyclobutene 27. The subsequent steps to yield either phenol or furan could involve vinylketene 28, but this still is a matter of debate. Similar, but more selective, furan syntheses have been observed for carbene complexes based on iron and cobalt. ... 

Disilanes connected via both the Si-Si bond and an organic or an organo-metallic linkage are activated toward reaction with unsaturated substrates to form cyclic bis(silyl) products. Reactions of 3,4-benzo-l,l,2,2-tetraethyl-1,2-disilacyclobutene with diphenylacetylene or benzaldehyde catalyzed by Ni(PEt3)4 proceed with addition across the multiple bond to form the ring-expanded product.54 A second product is formed in a lesser amount in the case of diphenylacetylene, with insertion into the Si-C bond [Eq. (13)]. 

Generally, insertion of the alkyne into a metal-P bond is observed (Scheme 10).188,190 When aminoalkynes are used, the formation of a C=N double bond inhibits the interaction of that carbon with the metal centers of the cluster.186 187 When two PR groups are present, the alkyne has been observed to bridge between them as seen in Scheme 10.195,285 A second equivalent of diphenylacetylene can substitute for two carbonyl groups on the iron triangle.195 The hetero-main group element species Fe3(CO)9(NPh) (P Bu) and Fe3(CO)9(NPh)2 have been reacted with diphenylacetylene.273 Some of the products involved in the acetylene addition reaction are shown here (241-243). 

The zirconium complex 315 reacts with diphenylacetylene to give the coupling product 326 [Eq. (55)].116 The regiochemistry of the reaction parallels that of an acyclic allene complex.133 Complex 315 also reacts with stilbene, but in this case, the seven-membered ring is displaced from the metal. The fate of the seven-membered ring is unknown. 

In addition to monocyclopentadienyl dimers, various molybdenocene derivatives can form dimers, as shown in equation (33). This is one example of a vast range of organic ligands that bridge metal-metal bonded complexes. Another example is one of the several products obtained by reaction of diphenylacetylene and molybdenum carbonyl (equation 34). 

The reaction of alkyl-substituted tungsten-carbene complexes of the type (88b) have been reported by Macomber to react with alkynes to give dienes of the type (319). One mechanism that has been proposed to account for this product is a 3-hydride elimination from the metallacyclobutene intermediate (320) and subsequent reductive elimination in the metal hydride species (321). An additional example of this type of reaction has been reported by Rudler, also for an alkyl tungsten carbene complex. Chromium complexes have not been observed to give diene products of this type the reaction of the analogous chromium complex (88a) with diphenylacetylene gives a cyclobutenone as the only reported product (see Scheme 31). Acyclic products are observed for both tungsten and chromium complexes in their reactions with ynamines. These reactions produce amino-stablized carbene complexes that are the result of the formal insertion of the ynamine into the metal-carbene bond. ... 

Although catalytic preparations of cyclopentadienones with other metal systems are known, chemose-lectivity is often a problem. For example, the reactions of 2-butyne, 3-hexyne and diphenylacetylene with [(CO)2RhCl]2 at 80 °C give mixtures of hexasubstituted benzenes, metal-complexed, tetrasub-stituted cyclopentadienones and quinones. An exception is the preparation of the stable tetrakis(trifluo-romethyl)cyclopentadienone from the alkyne the unusual electronic properties of the product make this result lack generality. 

A comprehensive treatment of the benzannulation of Fischer carbene complexes with alkynes is not possible in this review, and thus instead the material presented here will hopefully serve to give the reader an overview of its scope and limitations. The first report of this reaction was in 1975 by Dotz in which he describes the formation of the naphthol chromium tricarbonyl complex (236) from the reaction of the phenyl chromium complex (la) with diphenylacetylene. In the intervening years over 100 papers have been published describing various aspects of this reaction.The reaction of the generic cartene complex (233 Scheme 34) with alkynes will serve to focus the organization of the scope and limitations of the benzaimulation reaction. The issues to be considered are (i) the regioselectivity with unsymmetri-cal alkynes (ii) possible mechanisms (iii) applications in natural product syntheses (iv) the effect of substitution on the aryl or alkenyl substituent of the carbene carbon (v) functionality on the alkyne (vi) effects of the solvent and the concentration of the alkyne (vii) tandem applications with other reactions of carbene complexes (viii) reactions where aromatization is blocked (cyclohexadienone annulation) (ix) annulation of aryl versus alkenyl carbene complexes (x) the effect of the ligands L on the metal (xi) the effect of the ancilliary substituent RX and (xii) reactions with —C X functionality. 

The sequential addition of a proton and a hydride to a metal complex may be considered equivalent to an oxidative addition of hydrogen. With this in mind, the cationic hydrido derivative [Ru3(//-H)(/t3-ampy)(/<-PhC=CHPh)(CO)8][BF4] (42) (Fig. 11) was made and subsequently treated with [PPN] BH4]. This latter reaction was found to lead to Z- and -stilbene and to a mixture of cluster decomposition products. However, the cluster 40 is reformed when it is sequentially treated with HBF4 and [PPN][BH4] in the presence of diphenylacetylene. Z- and -stilbene are also produced in this reaction.It should be noted that complex 42 is coor-dinatively saturated and that a vacant site is needed before its reaction with [BH4]. ... 

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