Diphenylacetylene dimerizations

Photolysis of Cp2TiAr2 in benzene solution yields titanocene and a variety of aryl products derived both intra- and intermolecularly (293—297). Dimethyl titan ocene photolyzed in hydrocarbons yields methane, but the hydrogen is derived from the other methyl group and from the cyclopentadienyl rings, as demonstrated by deuteration. Photolysis in the presence of diphenylacetylene yields the dimeric titanocycle (28) and a titanomethylation product [65090-11-1]. 

The molybdenum and tunsten diphenylacetylene compounds have been chemically useful primarily as precursors to the quadruple metal-metal bonded dimers [M(Por)]2, formed by solid-state vacuum pyrolysis reactions. However. Mo(TTP)()/"-PhC CPh) is also a useful substrate in atom-transfer reactions, reacting with Sx or Cp2TiS i to form Mo(TTP)=S. The reaction can be reversed by treatment of Mo(TTP)=S with PPh (which removes sulfur as PhxP=S) and PhC CPh. The order of preference for ligand binding to molybdenum 11) has been established to be PPh < PhC CPh < 4-picoline. ... 

The formation of transient 1,2-digermacyclobutadiene 9179 was postulated in the reaction of TsiGeCl LiCT 3THF78 with Mg in the presence of diphenylacetylene. This reaction could involve the formation of the digermyne intermediate 92 generated from 93 formed by dimerization of the germylene anion radical 94 [Eq. (18)]. 

Subsequent evidence from the thermolysis of the silirene (29), which gave the two silins (30) and (31) as the major products even in the presence of another alkyne, tends to support a mechanism involving silirene dimerization (77JOM(l42)C45). Indeed, the presence, albeit in trace amounts, of pentaphenyltrimethylsilylbenzene (32) supports a silacyclopentadiene intermediate (Scheme 38), while the 1,2-disilacyclobutene (33) and diphenylacetylene give the disilin in only 1.2% yield (Scheme 39) (78JOM(162)C43). 

The tetrahydro-2-quinolone (212) affords a very small yield of 1,2-cycloadduct on irradiation with diphenylacetylene in methanol.189 The two major products are the 1,4-dimer and the pentacyclic derivative (213), arising presumably by intramolecular photocycloaddition... 

Simultaneously, we have been occupied with the question as to how the carbyne ligand behaves when it is split off from the metal. Analogous to the carbene complexes, in the absence of a suitable reaction partner, one also observes dimerization, in this case to alkynes (100). The conditions for the removal are very mild. In nonpolar solvents, diphenylacetylene or dimethylacetylene are accessible in this way at 30°C. One arrives at the same result when the solid methylcarbync complex is heated to 50°C ... 

Cyclopentadienyl dicarbonyl ruthenium dimer 132 reacts with silver tetrafluoroborate and diphenylacetylene to afford the cyclobutadiene ruthenium complex 133 (Scheme 12). Irradiation of 133 in dichloro-methane in the presence of several alkynes leads to the arene cyclopentadienyl ruthenium complexes 125 in high yield. This reaction appears to be a general route to sterically crowded ruthenium arene cations (55). 

Three effects are observed in the reactions of Os6(CO)18 with diphenylacetylene and ethylene. There is modification of the metal framework, rupture of a C=C triple bond, and dimerization of ethylene (228-230). When the activated clusters Os6(CO)17(MeCN) (230) and Os6(CO)20(MeCN) (231) react with mono- and disubstituted alkynes, different penta- and hexanuclear framework geometries are obtained, and the alkyne-derived ligands adopt a range of coordination modes (Fig. 8). 

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 1,2-cycloaddition reaction can take place in an intramolecular manner (equation 63), although in this example the initial excitation involves the aromatic group . A reaction of a different type is thought to be involved in the first stage of the formation of azulene or naphthalene photodimers from diphenylacetylene (equation 64), though here it is claimed that an intermediate benzocyclobutadiene species has been detected . The intermediate isomer of diphenylacetylene is formed via the triplet state and is relatively long-lived at — 10 °C. The major dimers formed are 1,2,3-triphenylazulene and 1,2,3-triphenylnaphthalene hexaphenylbenzene and octaphenylcubane are also produced . 

Thermolysis of thione 362 contrasts with its oxygen analogue 14 in giving only small quantities of diphenylacetylene the mass spectrum of 362, unlike that of 14, shows a molecular ion peak. The photochemistry of 362 is complex depending upon the conditions employed diphenylacetylene, tetraphenylthiophenothiophene, diphenylcyc-lopropenethione dimers, thioacrylates and thietes or mixtures thereof are formed Oxidation of 362 with lead tetraacetate delivers 14 and the electrochemical reduction has... 

Eisch et al. have attempted to synthesize borirenes on reductive ring closure of the haloboration products of diphenylacetylene (35) <67JOM(8)53, 79JOM(l71)141>. The authors failed to isolate borirenes, and their occurrence was inferred from the dimerization products (36 n = 2), or from the products of deuterolysis (cf. Section 1.10.9.2.2). 

Assony and Kharasch15 effected the dimerization of diphenylacetylene (1) to 1,2,3-triphenylazulene (2) in about 25% yield with 2,4-dinitrobenzenesulfenyl chloride and aluminum chloride. 

Substitution reactions of CojfCOlg and Co4(CO)i2 occur with substances that contain C—C unsaturated bonds. Reaction of Co2(CO)g with diphenylacetylene " yields the dimeric hexacarbonyl derivative ... 

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