Diphenylacetylene, reaction with iron complexes

Bis(imino)pyridine iron complex 5 acts as a catalyst not only for hydrogenation (see 2.1) but also for hydrosilylation of multiple bonds [27]. The results are summarized in Table 10. The reaction rate for hydrosilylations is slower than that for the corresponding hydrogenation however, the trend of reaction rates is similar in each reaction. In case of tra s-2-hexene, the terminal addition product hexyl (phenyl)silane was obtained predominantly. This result clearly shows that an isomerization reaction takes place and the subsequent hydrosilylation reaction dehvers the corresponding product. Reaction of 1-hexene with H2SiPh2 also produced the hydrosilylated product in this system (eq. 1 in Scheme 18). However, the reaction rate for H2SiPh2 was slower than that for H3SiPh. In addition, reaction of diphenylacetylene as an atkyne with phenylsilane afforded the monoaddition product due to steric repulsion (eq. 2 in Scheme 18). 

The reaction between acetylenes and ruthenium carbonyls produces a series of n complexes with cyclic ligands which, as in the iron system, have either the metal or a CO group incorporated into the ring. Accordingly, 3-hexyne 536) and hexafluoro-2-butyne 90) react with Ru3(CO)i2 to give the (substituted cyclopentadienone)tricarbonylruthenium complexes with structures presumably comparable to those of the iron complexes (93-95). Although diphenylacetylene will not react directly with Ru3(CO)i2 to produce this type of complex 536), it can be prepared 90) by treating Ru3(CO)i2 with tetracyclone in benzene under reflux. 

This is a general reaction for alkynes (acetylene, phenylacetylene, diphenylacetylene, cyclodecyne, etc.) that occurs at RT, producing 75% yields of products. The two cobalt atoms and two carbons form a tetrahedron. Analogous iron complexes are prepared in low yield by reaction of diphenylacetylene with Fe3(CO)i2 . Similar molybdenum complexes are prepared by addition of alkynes to molybdenum multiple bonds ... 

From the reaction of iron tetracarbonyl with diphenylacetylene, Schrauzer isolated a rr-complex incorporating only one molecule of carbon monoxide, a tetraphenylcyclopentadienone derivative. 

The reactions of iron carbonyls with alkynes however can often lead to a range of products that are difficult to separate. Manning and co-workers have found that photolysis of Fe(GO)3 P(OPh)3l2 with alkynes gives products Fe(GO)2 P(OPh)3 2( 7 -alkyne) 5 via the orthometallated iron-hydride intermediate HFe(GO)2 P(OPh)3 - (PhO)2POG6H4 4. Maleoyl complexes 6 are also formed with internal alkynes. However, the ferrole derivative 7 is obtained by reaction with the terminal alkyne HG=GPh (see Scheme 8). Grystal structures of the complexes 5a and 6c have been determined and confirm their formulations. The alkyne carbon-carbon distance in 5a is 1.274(4) A which lies toward the shorter end of the range of reported carbon-carbon distances of coordinated diphenylacetylene (1.24-1.35 A). 

One of the complexes formed in the reaction of diphenylacetylene and iron dodecacarbonyl is a red, crystalline compound of the composition [Fe2(CO)6(PhC2Ph)], which, on reduction with sodium in liquid ammonia, gives dibenzyl (117). By analogy with the cobalt carbonyl complex, structure (XXXV M = Fe) is proposed, in which the 7r-elcctrons of the triple... 

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. ... 

The cycloruthenated complex 13 reacts with disubstituted alkynes to afford the novel Ti -aiene Ru(0) complexes 49 which were isolated, characterized by X-ray methods, and oxidatively demetallated by treatment with Cu(II) salts to afford metal-free(7i0"isoquinolium salts 43 (with PF as counterion). Kinetic studies have revealed that the reaction proceeds via insertion of the alkyne into the Ru-C bond and that for this process the rate-limiting step is very similar to that found for the analogous palladium compound. Irradiation or thermal treatment of the cycloruthenated complex 50 with diphenylacetylene yields diphenylindole 51 as product. A similar reaction is observed with the corresponding iron or molybdenum complexes. ... 

Knox and co-workers synthesized a triruthenium cluster by the reaction of the coordinatively unsaturatcd diruthenium alkyne complex (CpRu)2(/r-CO)(/r-RCCR) 39 with a monometallic carbonyl complex M(CO)4(L) (M = Fe, Ru). Two isomers, 40 and 41, were formed in the reaction of 39 with Ru(CO)4(CH2 = CH2) (Equation (13)). The ratio between 40 and 41 was shown to be dependent on the nature of the substituents of the alkyne. In the case of diphenylacetylene complex, coalescence of the H signals of these isomers, 40a and 41a, was observed. This shows that isomerization between the two isomers took place at considerable rate. In contrast, the reaction of 39 with Fe(CO)4(thf) exclusively afforded a 3- ( )-alkyne complex, in which the alkyne moiety was 7r-coordinated to an iron center. Knox and co-workers also reported the syntheses of triruthenium /i3-alkylidyne complexes by the photolysis of a bimetallic /r-alkylidene complex and a bimetallic diruthenacy-clopentenone complex. In these reactions, formation of the triruthenium frameworks was rationalized by the coupling reaction of the monometallic coordinatively unsaturated species generated by the photolysis with the starting bimetallic complexes. 

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