1,3-Cyclopentadiene ruthenium complex

Ruthenium complexes have also been reported as active species for enan-tioselective Diels-Alder reactions. Faller et al. prepared a catalyst by treatment of (-)-[( ] -cymene)RuCl(L)]SbF6 with AgSbFe resulting in the formation of a dication by chloride abstraction [95]. The ligand was (-l-)-IndaBOx 69 (Scheme 36) and the corresponding complex allowed the condensation of methacrolein with cyclopentadiene in 95% conversion and 91% ee. As another example, Davies [96] prepared the complex [Ru(Fl20)L ( i -mes)] [SbFe]2 (with 70 as L in Scheme 36), and tested its activity in the same reaction leading to the expected product with similar activity and lower enan-tioselectivity (70%). 

Ruthenium reacts with cyclopentadiene in ether to form a sandwich complex, a yellow crystalline compound, bis(cyclopentadiene) ruthenium(0), also known as ruthenocene. 

C4H 2OSi, Silane, methoxytrimethyl-, 26 44 CH4N, Propane, 2-isocyant-2-methyl-ruthenium complex, 26 275 C][l,4]-dithiin-2-thione, 26 389 CHfc, 1,3-Cyclopentadiene cobalt complex, 26 191-197, 309 chromium, molybdenum, and tungsten complexes, 26 343 iron complex, 26 232-241 mercury-molybdenum-ruthenium complex, 26 333... 

In 1971, a preparation of 1 from 2 using thallium cyclopentadienide was reported (I) but the toxicity of thallium and the mass of the reagent needed render this procedure unsuitable for large-scale preparations. An improved method was reported by Bruce et al. (3,4), using cyclopentadiene, ruthenium trichloride hydrate (3), and triphenylphosphine, which gives the desired complex in high yield [Eq. (2)]. The primary advantage of this latter method is formation of the complex in one pot. 

With cyclopentadiene ruthenium 7t-complex [C5Me5Ru(MeCN)3](OTf), tellurophene reacts to form a stable sandwich Jt-complex 22 in 82% yield (Equation 10) <1998BKC706>. The -coordination of the tellurophene ring is confirmed by the strong high field shift of the Te NMR signal (107 ppm to be compared with 782 ppm signal of tellurophene). 

CgHu, Cyclooctene, iridium complex, 21 102 C10H4, Benzene, l-isopropyl-4-methyl-, ruthenium complex, 21 75 CioHit, 1,3-Cyclopentadiene, 1,2,3,4,5-penta-methyl-, 21 181... 

C,2H, )N2, Azobenzene, cobalt and palladium complexes, 26 175,176 manganese complex, 26 173 C,2H N, Pyridine, 2-(phenylmethyl)-, palladium complex, 26 208-210 C,2H, P, Phosphine, diphenyl-, manganese complex, 26 158,226-230 ruthenium complex, 26 264 C 2H,2, Toluene, a-2,4-cyclopentadiene-l-yl-, chromium, molybdenum and tungsten hexacaibonyl complexes, 28 148... 

Kiindig et al [14] have reported the synthesis of the new chiral ruthenium complexes, [CpRu(biphop-F)] (45) and [(Indenyl)Ru(biphop-F)] (46), and have shown their efficiency as Lewis acids in Diels-Alder reactions of methacrolein (24a) with cyclopentadiene (Scheme 16.14, Table 16.3). The corresponding cycloadduct (25) was observed in high exo selectivities. They found that the rate of Diels-Alder reaction varied with the catalyst counteranion and it increased in order BF4 < SbF6 < TFPB (tetrakis[3,5-bis(trifluoromethyl)phenylj borate). 

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. 

As mentioned earlier, ruthenium cymene, rhodium and iridium pentamethyl-cyclopentadiene are good metal complexes, to start with, in a screen. It is diffi-... 

The common metathesis reactions for the preparation of metallocenes, treating a metal salt MX2 with NaCp, are hampered in the case of ruthenium by the lack of suitable Ru salts. (Rul2 is commercially available, but is still not commonly used in the synthesis of rathenocene.) Thus, ruthenocene has been obtained from Ru(acac)3 and NaCp in very low yield and later from RuCb and NaCp in 50-60% yield. It has now become apparent that alkene polymers, in particular [Ru(nbd)Cl2]x, but also [Ru(cod)Cl2]x and hydrazine derivatives (Section 3.1), can serve as Ru precursors. Equally successful in many cases is reductive complexation of cyclopentadiene in ethanol in the presence of Zn (Section 3.2), which furnishes the metallocene in about 80% yield. Decamethylruthenocene (82) was first obtained by the Zn reduction route in 20% yield, but can now be prepared conveniently from halide complexes [Cp RuCl2]2 or [Cp RuCl]4, a common method for the preparation of symmetrical and unsymmetrical sandwich compounds of ruthenium featuring one alkyl-substituted ligand. 

The trinuclear pentahydride complex [Cp Ru]3(/w-H)3(/x3-H)2 (105) in Scheme 26 consists of ruthenium centers tightly bound by bridging hydrides. Treatment of the pentahydride complex with excess butadiene in THF results in a trinuclear 1-methyl-1,3-dimetalloallyl complex [Cp"Ru]3(H)4[/x3- ] -C(Me)CHCH] (106). This interaction shows the cooperation of all three ruthenium centers as either coordination sites or activation sites. Similar results are found by treating (105) with isoprene. Treatment of (105) with five equivalents of cyclopentadiene results in bond cleavage of the cyclopentadiene to form a dark purple crystalline solid [Cp Ru(/u.-H)]3[/x3- j4-C(Me)=CHCH=CH] (107). In this complex, two of the ruthenium centers act as a coordination site, while the third is an activation... 

Suzuki et al. reported an interesting example of a C-C bond cleavage of an ordinary non-strained diene substrate with a multimetallic complex [62]. The Csp2-Csp3 bond of cyclopentadiene is cleaved by trinuclear ruthenium pentahydride complex 40 to afford ruthenacyclohexadiene 41, which then rearranges to 2-methylruthenacyclopentadiene complex 42. The three metal centers cooperate for cleavage two of the three centers act as coordination sites for the diene moiety and the third is inserted into the C-C bond. 

Further examples also show particularly impressive selectivity. Kiindig has used the cationic iron catalyst (8.83) in the Diels-Alder reaction to give cycloadduct (8.85). The ruthenium (BINAP) catalyst (8.86) effects the Diels-Alder reaction of cyclopentadiene with 2-substituted acrylates with ees up to 99%. Kobayashi has shown that lanthanide and scandium triflate complexes of BINOL with 1,2,6-trimethylpiperidine, formulated as complex (8.87), are effective with oxazohdinone-based substratesand gives good selectivity in the formation of the Diels-Alder product (8.52). 

The chloro complex is prepared by adding a mixture of ruthenium trichloride and cyclopentadiene to an excess of triphenylphosphine, which acts as the reducing agent as well as a ligand ... 

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... 

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