Cyclohexadiene complexes with ruthenium

Cycloheptene complexes with gold, 12 348 Cyclohexadiene complexes with cobalt, 12 286 with group VIB metals, 12 225-227 with group VIIB metals, 12 240, 241 with iron, 12 264 with palladium, 12 313 with ruthenium, 12 278 with silver, 12 340... 

A more general route to make bis(cyclophane)ruthenium(II) complexes involves a reduction of 263 (arene = benzene) with Red-Al to afford the [ 174-1,3-cyclohexadiene)(tf-cyclophane)]ruthenium(O) derivatives 271 (Scheme 28, p. 224). Treatment of 271 with hydrochloric acid gives the dimeric chloride complexes 272, which lead the desired bis(r)6-[2 ]cyclo-phane)ruthenium(II) complexes 274 via Bennett s procedure (145). Synthesis of the oligomer 275a is also achieved in quantitative yield by heating 274 with the solvated complex 7 (arene = C6Me6) in neat trifluoroacetic acid. 

The reactions of Ru3(CO)i2 with diolefins to give (diene)Ru(CO)3 derivatives does not proceed as well as the corresponding reactions of Fe3(CO)i2f since the ruthenium triangle is more stable than the iron triangle. Nevertheless, the 1,3-cyclohexadiene complex C6H0Ru(CO)3 can be prepared in reasonable yield by heating 1,3-cyclohexadiene with RU3(CO)j2 (221). Cyclooctatetraene reacts with RU3(00) 2 boiling... 

Organoruthenium compounds tend to form complexes coordinated by the 10 electrons of cyclic unsaturated compounds similar to ferrocene in organoiron compounds, for example, ruthenocene (r/ -C5H5)2Ru and tf( / -C6Hx)Ru. As shown in Scheme 16.1, ruthenium chloride 3H20 reacts with unsaturated cyclic compounds in the presence of zinc metal to afford cyclic compounds coordinated by 10 electrons by dehydrogenation [15-18]. In the case of cyclopentadiene, ruthenocene is formed by the coordination of two five-electron rings. In the case of 1,3-cyclohexadiene, the complex is obtained to be coordinated with 4-electron 1,3-cyclohexadiene and with 6-electron benzene. In the case of 1,3-cycloheptadiene... 

Although mechanistic details are still unclear, an open-form triruthenium complex 43, which adopted a ruthena-benzene structure, was derived from the bimetallic 1,4-cyclohexadiene complex 42 (Equation (14)). On the basis of the fact that complex 43 was dicationic, the trimetallic skeleton is most likely formed by the reaction of 42 with a cationic monometallic species, [Cp Ru], generated by the partial decomposition of 42. The X-ray diffraction study of 43 showed that the central ruthenabenzene moiety was coordinated to one of the peripheral ruthenium atoms in an 7 -fashion and to the other in an 7 -fashion. This nonsymmetrical structure arises from the hydrido ligand bridging on one of the Ru-Ru bonds. 

The dichlororuthenium arene dimers are conveniently prepared by refluxing ethanolic ruthenium trichloride in the appropriate cyclohexadiene [19]. The di-chloro(pentamethylcyclopentadienyl) rhodium dimer is prepared by refluxing Dewar benzene and rhodium trichloride, whilst the dichloro(pentamethylcyclo-pentadienyl)iridium dimer is prepared by reaction of the cyclopentadiene with iridium trichloride [20]. Alternatively, the complexes can be purchased from most precious-metal suppliers. It should be noted that these ruthenium, rhodium and iridium arenes are all fine, dusty, solids and are potential respiratory sensitizers. Hence, the materials should be handled with great care, especially when weighing or charging operations are being carried out. Appropriate protective clothing and air extraction facilities should be used at all times. 

RuCl2(arene)]2 complexes (1) react with 1,5-cyclooctadiene and 1,3- or 1,4-cyclohexadiene in the presence of ethanol and Na2C03 or zinc dust to give Ru°(776-arene)(V diene) compounds of type 196-198 in 60% yield [Eq. (20)] thus, this reaction appears to be the reverse of the 198-> 1 reaction [Eq. (19)]. The same reaction with ethylene leads to the bis-ethylene ruthenium(O) complex 205 (37%) (131,10). The norbornadiene complex 207 is prepared similarly from derivative 206 (125). Combination of transformations 206 - 207 [Eq. (21)] or 1 - 198 [Eq. (20)] with trans-... 

Tj -Cyclohexadienyl ruthenium complexes have been obtained either by addition of nucleophiles to the arene ring of arene ruthenium(II) complexes or by protonation of ruthenium(O) complexes. The first complex prepared, the benzene cyclohexadienyl ruthenium cation 236a, has been obtained together with the zero-valent arene cyclohexadiene ruthenium(O) complex 196a, by reaction of 235a with lithium aluminum hydride (118) [Eq. (27)]. 

The synthesis of the zero-valent, 1,3-cyclohexadiene benzene ruthenium complex 196a has been mentioned as a coproduct of the cyclohexadienyl complex 236a in the reduction of the benzene ruthenium dication 235 with lithium aluminum hydride. Reduction of 235 with sodium borohydride in THF, however, gives only the air-sensitive, yellow-green ruthenium(O) complex 196a (118). This reaction has been generalized to... 

Monolayered cyclophane complexes of type 263 are also reduced by sodium bis(methoxyethoxy)aluminum hydride (Red-Al) to give (i74-diene)-(i76-cyclophane)ruthenium(0) complexes (Scheme 33). If the benzene ring of 263 (arene = benzene) is converted to the (1,3-cyclohexadiene)-ruthenium(O) derivative 271, however, when the corresponding rj6-hexa-methylbenzene is reduced with Red-Al, the product is the (if-1, 4-cyclohexadiene)ruthenium(0) complex 288. Synthesis of 271 can... 

Cocondensation of ruthenium atoms with 1,3-cyclohexadiene, and then CO, at -196°C affords the cyclohexadienyi cyclohexenyl carbonyl ruthenium complex 327, which can be transformed to the benzene cyclohexenyl carbonyl ruthenium cation 328 by hydride abstraction (194) [Eq. (45)]. 

Although some cyclohexadienes are readily available, many can be obtained easily by Birch reduction, which involves reduction with solutions of alkali metals in liquid ammonia, a source of solvated electrons, in the presence of alcohol as a proton source.8-10 In previous years, the Bouveault-Blanc procedure, which uses sodium metal and alcohol in liquid ammonia, was frequently employed for direct reduction of aromatic esters however, it gave rise mainly to the corresponding substituted benzoic acid.11 Rabideau et al. reported a modified procedure 12 however, in our hands, this resulted in the reduction of the ester function to give benzoic acid. We have found that the Birch reduction of benzoic acid, followed by esterification, is an efficient procedure for the preparation of the corresponding 1,4-dihydro compound prior to the coordination of the arene to produce functionalized dimeric ruthenium-arene complexes.13... 

In the reaction of the a-amino acid derivative 73 with 1,5-cyclooctadiene catalyzed by ruthenium complex 2 depicted in Scheme 2.29, an enyne CM followed by an RCM was coupled in a domino manner with an initial ROM of the cyclic diene [17b,cj. The resulting enantiomericaUy pure 1,3-cyclohexadiene 74 was then used to construct the diketopiperazine core of the scabrosin epidithiodiketopiperazine antibiotics [17cj. 

If ruthenium chloride reacts with 1,3-cyclohexadiene or 1,4-cyclohexadiene in the absence of zinc powder, cyclohexadiene is dehydrogenated to benzene, and the dimer of a chloro-bridged benzene complex is obtained [8,19,20]. The dimer is easily substituted to afford the replacement compound by heating with a compound having a higher coordination reactivity than benzene, such as / -cymene (MeC6H4-/-Pr) and then with C Me as shown in eq. (16.9) [20],... 

The reaction of dibenzeneruthenium(II) perchlorate with lithium aluminum hydride, however, yields a mixture of di-Ti-cyclohexadienylruthenium and (benzene)(cyclohexadiene) ruthenium(O). If sodium borohydride is used, the latter is the only complexed product obtained. [(ji-C5H5) Mo -(C6H,)]PF,- is easily reduced to the Mo(0) complex by lithium aluminum hydride, equation (6-39). 

The ruthenium(ii) diene complexes [Ru(acac)2(diene)] (diene = 2,5-dimethyl-2,4-hexadiene, 1,2,4,5-tetramethyl-1,4-cyclohexadiene ), formed upon addition of free diene and zinc to [Ru(acac)3] in EtOH, exist in solution as a pair of diastereoisomers 83a and 83b. Thermolysis of [Ru(PPh3)3(GO)HGl] with neat GH2=G(Me)GH20H at 80 °G affords the ruthenium(O) complex [Ru(PPh3)2(G0) r7" -GH2=G(Me)GH=0 ]. ... 

Heating a benzene solution of 3,4-benzocyclodec-3-en-l,5-diyne 3.512 and 1,4-cyclohexadiene (CHD) at 84°C gives tetrahydroan-thracene with the half transformation period of 24 hours [258]. Complete cycloaromatization is achieved by heating the compound 3.512 at 100°C in nitromethane-d3 in the presence of 1,4-cyclohexadiene for 18 days. Scheme 3.27 [259] depicts an example of Bergman cyclization promoted by pentamethylcyclopentadienyl-ruthenium cation 3.518. Besides the formation of triflate 3.513 which has an arene fragment of enediyne complexed to the ruthenium cation 3.518, the rate of the Bergman cyclization is increased by the Ru-alkyne interaction. The more... 

The cyclopentadienylcobalt complexes CpCo(L)n are also good catalysts for co-cyclotrimerization of diynes with alkenes [79a]. Recently, it has been shown that the similar catalytic activity is exhibited by the ruthenium complex 106, which efficiently catalyzed cycloaddition of diynes with cyclic alkenes to the conjugated cyclohexadienes 174 (Scheme 77) [112]. 

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