Diphenylacetylene, reaction with complexes

The reaction of alkoxyarylcarbene complexes with alkynes mainly affords Dotz benzannulated [3C+2S+1C0] cycloadducts. However, uncommon reaction pathways of some alkoxyarylcarbene complexes in their reaction with alkynes leading to indene derivatives in a formal [3C+2S] cycloaddition process have been reported. For example, the reaction of methoxy(2,6-dimethylphenyl)chromium carbene complex with 1,2-diphenylacetylene at 100 °C gives rise to an unusual indene derivative where a sigmatropic 1,5-methyl shift is observed [60]. Moreover, a related (4-hydroxy-2,6-dimethylphenyl)carbene complex reacts in benzene at 100 °C with 3-hexyne to produce an indene derivative. However, the expected Dotz cycloadduct is obtained when the solvent is changed to acetonitrile [61] (Scheme 19). Also, Dotz et al. have shown that the introduction of an isocyanide ligand into the coordination sphere of the metal induces the preferential formation of indene derivatives [62]. 

Complex 12 was found to be a good reactant in the double-silylation reaction. Thus, thermolysis of a toluene solution of 12 and diphenylacetylene at 120°C for 12 h afforded 5,6-carboranylene-1,1,4,4-tetramethyl-2,3-diphenyl-1,4-disilacyclohex-2-ene 13. When 1-hexyne was employed in the reaction with 12 under the same reaction conditions, the five-membered disila ring compound 18 was isolated. A key feature in the h NMR spectrum of 18 includes a singlet at 6.24 ppm assigned to the vinyl proton. A characteristic high-frequency 13C NMR resonance at 138.50ppm provides evidence for a tethered sp2 carbon atom between the two silicon atoms. 

Reaction of the isomers IV with phenylacetylene yields a range of complexes, of which Os3(CO)7L3 is one. This is related to the complex Os3(CO)7[C2(CsHs)2]3, obtained in the corresponding diphenylacetylene reaction and shown to be an intermediate in the cyclotrimerization of diphenylacetylene to hexaphenylbenzene 124). The structure of this complex is discussed in Section III,F. 

The Pt2Ru4(CO)i8 cluster reacts with H2 to form Pt3Ru6(CO)2i(/i3-H)-(jt-H)3 in which the platinum and ruthenium atoms are arranged in triangular layers of the pure elements.10 This complex can be converted to Pt3Ru6(CO)20(/i3-C2Ph2X/i-H)2 by reaction with diphenylacetylene.10 The latter complex was found to be an active catalyst for the hydrogenation... 

Diphenylacetylene reacted with both complexes by insertion into the aziridine moiety as shown for the eg complex in Scheme 8.11. Both reactions were inhibited by addition of external PMe3 showing that the dissociation of PMe3 was required for both, even though the eg complex is electronically unsaturated and may have been expected to react by an associative mechanism. 

The reaction mechanism can be explained by the formation of a dimethylsilylene intermediate which is able to undergo an insertion reaction into a Si—H bond (for more about this type of reaction, see Chapter 7 Silylenes). The formation of the silylene can be explained by an a elimination from the n metal-complexed disilane. The presence of the silylene has been proved by a capture reaction with diphenylacetylene, when the expected 1,1,4,4-tetramethyl-1,4-disilacyclohexa-diene could be isolated. 

The full report of the crystal structure of Cp3Ti has appeared.1 la Diphenylacetylene reacts with CpTi(CO)2 in the cold to give the yellow monoacetylene complex Cp2Ti(CO)PhC2Ph the acetylene is readily displaced by CO and the complex is an active catalyst for the hydrogenation of olefins and acetylenes. Under more vigorous reaction conditions the metallocycle (1) is formed.12... 

The major product of the reaction of [(rj -CplaTiMea] with dimethylacetylene is the titanacyclopentene 161 (R = Me) <2000POL879>. With diethylacetylene metallacycle, 161 (R = Et) is formed. Thermolysis of bis(methylcy-clohexenyljzirconocene in the presence of trimethylphosphine and further reaction with diphenylacetylene gives 162. Allene complex 163 reacts with 2-butyne or diphenylacetylene to yield the titanacyclopentenes 164 (R = Me, Ph). 

Most of the reported reactions between tetranuclear clusters and alkynes involve mixed-metal cluster species. In these systems hydride and carbon monoxide substitution generally occurs [Eq. (11)] (194-200), although in some cases Me3NO has been used to activate the starting material (201, 202), and in still others cluster breakdown takes place even under mild reaction conditions (203). Rh4(CO)12 (204) and Ir4(CO)12 (205) retain their nuclearity in reactions with alkynes, but in the latter case the metal framework geometry is altered (Fig. 7). The use of [Ir4(CO)11Br] instead of Ir4(CO)12 in reactions with alkenes produces alkene-substituted tetranuclear complexes (189), as shown in Fig. 7. Few other homonuclear clusters have been found to react with alkynes (206-208). In the reaction between the tetranuclear cluster Cp2W2Ir2(CO) 0 and diphenylacetylene two independent processes... 

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. ... 

Representative reactions with (jt-C3H5)Ru(CO)3X are as follows. Alkynes, such as acetylene, phenylacetylene, and diphenylacetylene, react with (jr-C3H5)Ru(CO)3Cl at 60-90 °C in aromatic hydrocarbons to give acyl complexes with a formula of... 

Titanacycle derivatives (Scheme 543) are obtained predominantly as one isomer of the probably expected products, as a result of the reaction between a titanium aryne intermediate, generated in the pyrolysis of bis-Cp diaryl complexes with diphenylacetylene. The reaction with Cr(CO)3(CH3CN)3 affords a heterobinuclear Ti-arene-Cr... 

Grigg has utilized the Heck reaction in several ways, from the simple cyclization of A -(2-iodobenzoyl )pyrrole (203) to afford tricyclic lactam (204) [124] to the complex cascade transformation of pyrrole 205 with diphenylacetylene to tetracycle 208 [125]. The initial intermediate 206 undergoes a second Heck reaction with the pendant alkene to furnish 207. A final insertion into the appropriate phenyl C-H bond completes the sequence. 

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