Ethylene complexes with ruthenium

Intermolecular enyne metathesis has recently been developed using ethylene gas as the alkene [20]. The plan is shown in Scheme 10. In this reaction,benzyli-dene carbene complex 52b, which is commercially available [16b], reacts with ethylene to give ruthenacyclobutane 73. This then converts into methylene ruthenium complex 57, which is the real catalyst in this reaction. It reacts with the alkyne intermolecularly to produce ruthenacyclobutene 74, which is converted into vinyl ruthenium carbene complex 75. It must react with ethylene, not with the alkyne, to produce ruthenacyclobutane 76 via [2+2] cycloaddition. Then it gives diene 72, and methylene ruthenium complex 57 would be regenerated. If the methylene ruthenium complex 57 reacts with ethylene, ruthenacyclobutane 77 would be formed. However, this process is a so-called non-productive process, and it returns to ethylene and 57. The reaction was carried out in CH2Cl2 un-... 

The course of the condensation of ethylene glycol with secondary amines (Me2NH, Et2NH, pyrrolidine or morpholine) depends on the catalyst used. Triphenylphosphine complexes of ruthenium, e.g. RuCl2(PPh3)3, give hydroxyalkylamines while hydrated ruthenium(III) chloride yields diamines (equation 24)62. 

The reaction rate of enyne 107j having a terminal alkyne is very slow, and the starting material is recovered [Eq. (6.80)]. ° Presumably, the terminal alkene of the product 108j should further react with ruthenium carbene complex Ih to form XVII, whose ruthenium carbene should be coordinated by the olefin in the pyrrolidine ring. Thus, the catalytic activity of Ih should be decreased. If complex XVII reacts with ethylene, 108j and methylidene ruthenium carbene complex Ih should be regenerated. On the basis of this idea, the reaction was carried out under ethylene... 

Reduction of ammonium chlororuthenate with titanous chloride gives a solution containing divalent ruthenium which will absorb ethylene or propylene to give a 1 1 ruthenium-olefin complex which was not isolated (108). Ethylene was previously reported not to form stable complexes on treatment with ruthenium halides (97). 

Ruthenium complexes mediate the hydroamination of ethylene with pyridine.589 The reaction, however, is not catalytic, because of strong complexation of the amine to metal sites. Iridium complexes with chiral diphosphine ligands and a small amount of fluoride cocatalyst are effective in inducing asymmetric alkene hydroamination reaction of norbomene with aniline [the best enantiomeric excess (ee) values exceed 90%].590 Strained methylenecyclopropanes react with ring opening to yield isomeric allylic enamines 591... 

Detailed mechanistic studies with respect to the application of Speier s catalyst on the hydrosilylation of ethylene showed that the process proceeds according to the Chalk-Harrod mechanism and the rate-determining step is the isomerization of Pt(silyl)(alkyl) complex formed by the ethylene insertion into the Pt—H bond.613 In contrast to the platinum-catalyzed hydrosilylation, the complexes of the iron and cobalt triads (iron, ruthenium, osmium and cobalt, rhodium, iridium, respectively) catalyze dehydrogenative silylation competitively with hydrosilylation. Dehydrogenative silylation occurs via the formation of a complex with cr-alkyl and a-silylalkyl ligands ... 

Along with diene and diyne metathesis, ene-yne metathesis has also been employed to form macrocycles. This type of metathesis is performed with the catalysts used for olefin metathesis, and the yields are improved in the presence of ethylene, which forms the highly reactive [Ru]=CH2 species. Shair and coworkers took advantage of this reaction twice in the course of their total synthesis of longithorone A [40]. When ene-ynes 51 and 52 are treated with ruthenium complex G1 under an atmosphere of... 

Consiglio and Morandini (98) have determined that the formation of the ethylene complex 129 from the chloro epimer 34 proceeds stereo-specifically with retention of configuration at ruthenium (Scheme 15). The alkene complex, however, did epimerize in solution over a period of days to give an equilibrium mixture of the two epimers 129 and 130. As in the similar reaction of 34 with CH3CN discussed in Section V,D, the stereochemical integrity of the ruthenium center is maintained in the co-ordinatively unsaturated intermediate formed on loss of CP. 

Cleavage of Ru—CH3 bonds by acids has been used by Werner et al. for the selective introduction of small molecules at the ruthenium center. Addition of HBF4 to complex 33, in the presence of carbon monoxide or ethylene, allows the coordination of these molecules in complexes 48,49, and 50 (43). Complexes of type 33 give carboxylate complexes 34,35, and 38 on treatment with carboxylic acids (42,43). A bis(alkyl)ruthenium(II) complex (52) was also obtained by addition of PMe3 to the ethylene complex 51 (24,26). 

An interesting aspect of the bis(methyl)ruthenium complexes 33 is their tendency to allow hydride abstraction with (Ph3C)PF6. They lead to ethylene complexes 55 and 56 (46,47).The X-ray structure of 55 shows bond distances of 1.411(13) A for C=C and 1.50 A for Ru—H (46,47). The reaction probably proceeds via intermediates 53 and 54, although it was not established whether the transformation 33 - 53 involves a mono-electronic process as with WMe2(C5H5)2 (48). A similar reaction from the deuterated derivative 57 gives exclusively complex 58, configurationally... 

Ruthenium square species where the bridging ligands are in cis positions were also obtained by the authors, starting from the [RuCl2(dppb)PPh3] complex with alterdentate ligands such as pyrazine, 4,4 -bipyridine and l,2-bis-trans-(4-pyridyl)-ethylene (Fig. 14.20) [68]. 

Further investigations are needed to clarify this point. It shonld also be noted that when the homobimetallic ruthenium-ethylene complex 4 was treated with a stoichiometric amount of acetylene in THF, the p-carbide complex 11 was formed, presumably via the intermediate ratheninm-vinyhdene complex 10 (Scheme 6) (75). 

Scheme 11. Reaction ofhomobimetallic ruthenium-benzylidene 17 and indenylidene 18 complexes with ethylene...

A few cyano phosphine and arsine complexes of ruthenium(II) have been reported. These include tra s-[RuH(CN)(dmpe)2] (dmpe = Me2P(CH2)2PMe2) obtained from the corresponding chloro complex and aqueous KCN or more recently by treatment of [RuH(2-np)(dmpe)2] (2-np = 2-naphthyl) with HCN. The latter gives a 85% cis, 15% trans isomer mixture ( H NMR evidence). The complex rranj-[Ru(CN)2(eda)2] eda = ethylene-l,2-bis(diphenylarsine) and quadriden-tate tertiary phosphine and arsine complexes such as Ru(CN)2[E(o-C5H4EPh2)3l (E = P, As) are... 

The complex ion [Ru(bpy)(trpy)Cl] was first prepared as the perchlorate salt by the reaction of Ru(bpy)Cl4 with trpy in 25% aqueous ethanol, and more recently in 75% aqueous ethanol. It has also been prepared from Ru(CO)2(bpy)Cl2, trpy, and trimethylamine oxide in 2-methoxyethanol. A method in which the readily prepared RuftrpylClj complex is used as an intermediate is more convenient, and it is this new method that is described here. (2,2 -Bipyridine-A(,A( )chloro(2,2 6, 2"-terpyridine-Al,Al, N")osmium(II) chloride has been reported and is prepared from Os(bpy)Cl4" and trpy in ethylene glycol. (2,2 -Bipyridine-N,Al )chloro 2,2 6, 2"-terpyridine-Al,N, yV")osmium(II) chloride may also be prepared by the reaction of Os(trpy)Cl3 with bpy in ethylene glycol. However, the insolubility of Os(trpy)Cl3 in this solvent makes the procedure used for the ruthenium analog less desirable, and the literature method has been used without major modification. Reaction of the chloro complexes With hot... 

In enantioselective hydrogenation, rhodium and ruthenium complexes with chiral diphosphines bound to poly(ethylene oxide)s 40-42 have been described. 

Treatment of an alkyne/alkene mixture with ruthenium carbene complexes results in the formation of diene derivatives without the evolution of byproducts this process is known as enyne cross-metathesis (Scheme 22). An intramolecular version of this reaction has also been demonstrated, sometimes referred to as enyne RCM. The yield of this reaction is frequently higher when ethylene is added to the reaction mixture. The preferred regiochemistry is opposite for enyne cross-metathesis and enyne RCM. The complex mechanistic pathways of Scheme 22 have been employed to account for the observed products of the enyne RCM reaction. Several experiments have shown that initial reaction is at the alkene and not the alkyne. The regiochemistry of enyne RCM can be attributed to the inability to form highly strained intermediate B from intermediate carbene complex A in the alkene-first mechanism. Enyne metathesis is a thermodynamically favorable process, and thus is not a subject to the equilibrium constraints facing alkene cross-metathesis and RCM. In a simple bond energy analysis, the 7r-bond of an alkyne is... 

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