Allylic ruthenium

Chlorination of the Cp Ru(amidinate) complexes is readily achieved by treatment with CHCI3, while oxidative addition of allylic halides results in formation of cationic Ti-allyl ruthenium(IV) species (Scheme 243). °... 

Allyl methylcarbonate reacts with norbornene following a ruthenium-catalyzed carbonylative cyclization under carbon monoxide pressure to give cyclopentenone derivatives 12 (Scheme 4).32 Catalyst loading, amine and CO pressure have been optimized to give the cyclopentenone compound in 80% yield and a total control of the stereoselectivity (exo 100%). Aromatic or bidentate amines inhibit the reaction certainly by a too strong interaction with ruthenium. A plausible mechanism is proposed. Stereoselective CM-carboruthenation of norbornene with allyl-ruthenium complex 13 followed by carbon monoxide insertion generates an acylruthenium intermediate 15. Intramolecular carboruthenation and /3-hydride elimination of 16 afford the -olefin 17. Isomerization of the double bond under experimental conditions allows formation of the cyclopentenone derivative 12. 

Kondo and Watanabe developed allylations of various types of aldehydes and oximes by using nucleophilic (7r-allyl)ruthenium(ll) complexes of type 154 bearing carbon monoxide ligands (Equation (29)).345 These 73-allyl-ruthenium complexes 154 are ambiphilic reagents and the presence of the carbon monoxide ligands proved to be essential to achieve catalytic allylation reactions. Interestingly, these transformations occur with complete regioselectivity only the more substituted allylic terminus adds to the aldehyde. 

The formation as well as the reactivity of (7r-allyl)ruthenium(ll) complexes bearing phosphine ligands have been described in a series of articles. However, the main drawback in these cases is the use of non-catalytic... 

A tentative mechanism includes ruthenium-induced isomerization of the initial allylic alcohol via (hydrido) (7T-allyl)ruthenium complex 167 to the corresponding Ru-bound enol 168. This in. ( ////-generated nucleophile complex can then add to aldehydes or imines under formation of the desired products. 

Several 7] -allylic ruthenium complexes can function as both a nucleophile and an electrophile, as Watanabe and his co-workers observed. Namely, these ruthenium complexes smoothly react with a variety of carbon-centered nucleophiles such as aldehydes, alcohols, and /3-diketones under mild reaction conditions and give the corresponding allylated compounds (Scheme 22). 

Surprisingly, RuX2PR3(r 6-arene) complexes did not promote the addition of ammonium N,N-dialkyl carbamates to alkenylacetylenes. However, this reaction was catalyzed by tr-allyl ruthenium derivatives such as [Ph(CH2) PPh2]Ru(r 3-CH2=C(Me)CH2)2 (n = 1-4), and yielded 0-l-(l,3-dienyl)carbamates (4—62% yield)... 

The observation that the Ru(amidinate)C5Me5 complex could generate the first allyl ruthenium(IV) complex containing a nitrogen ligand led to the use of this complex as catalyst for simple allyl substitution of allylcarbonates [111]. Re-... 

It is noteworthy that (q3-allyl)ruthenium species, which react with nucleophiles to give nucleophilic substitution of allylic substrates, are also active for the allylation of electrophiles. Thus, allyl acetate and carbonate react with aldehydes in the presence of catalytic amounts of Ru3(CO)12 to give homoallylic alcohols in good yields [116] (Eq. 86). 

In contrast, some rr- allyl ruthenium complexes containing a chelating diphosphine ligand were the first metal complexes which favoured the anti-Markovnikov addition of carboxylic acids to terminal alkynes to form (Z)-enol and (E)-enol esters with high regioselectivity and stereoselectivity [17-19] according to Eq. (1). 

The cyclo addition of the alkene to the ruthenium vinylidene species leads to a ruthenacyclobutane which rearranges into an allylic ruthenium species resulting from / -elimination or deprotonation assisted by pyridine and produces the diene after reductive elimination (Scheme 16). This mechanism is supported by the stoichiometric C-C bond formation between a terminal alkyne and an olefin, leading to rf-butatrienyl and q2-butadienyl complexes via a ruthenacyclobutane resulting from [2+2] cycloaddition [62]. 

Other i73-allyl ruthenium complexes of type 44 have been prepared from la with allylmercury chlorides (allyl, methallyl, crotyl, 1-and 2-phenylallyl, and l-acetyl-2-methylallyl) (45). 

RuC1(OCCR=CR C3H5)(CO)2]2 arising from insertion of alkyne and CO into an allyl-ruthenium bond [28],... 

An analogous insertion reaction into the allyl-ruthenium bond occurs when (jt-C3H5)Ru(CO)3Cl is treated with butadiene at 70-80 °C in hydrocarbon solution. 

The ruthenium complex (C5H5)RuCl(PPh3)2 with NH4PF6 catalyzes the addition of allylic alcohols to terminal alkynes, yielding /3,y-unsaturated ketones (Eq. 5.23) [38]. This process involves the nucleophilic attack of allylic alcohols to a (vinylide-ne)ruthenium intermediate, leading to the formation of an (acyl)(jr-allyl)ruthenium intermediate. 

In this reaction, carbon monoxide is not needed. The key intermediate is an (acyl)(jt-allyl)ruthenium complex that undergoes reductive elimination to give the corresponding /3,y-unsaturated ketones. 

A series of easily prepared and exceptionally active ruthenium catalysts for ringopening metathesis polymerization (ROMP) have been reported. As mentioned previously, the reaction of isoprene with RuCh gave a bis(jt-allyl)ruthenium(IV) complex of [RuC1(m-C1)( -CioHi6)]2, which was converted into cationic bis(jt-allyl)-ruthenium(IV) complexes by treatment with silver tetrafluoroborate. All of these complexes are stable in air and in solution for several hours. Although alone they... 

The intermediacy of bis(jt-allyl)ruthenium complexes has been strongly suggested by the fact that a similar reaction of (C5Me5)RuCl(>/ -l,3-pentadiene) with 1,3-penta-diene in the presence of AgOTf affords [(C5Me5)Ru 4-methyl-(l-3->/ 6-8-> )-nona-dienediyl ]OTf via a regioselective tail-to-head dimerization reaction (Eq. 5.43). 

The reaction of allyl carbonates with 2-norbornene under 3 atm of CO catalyzed by [RuCl2(CO)3]2 gives cyclopentenones. A reaction mechanism involving successive insertion of 2-norbornene and CO into a Jt-allyl-ruthenium bond is proposed (Eq. 11.39) [83], the details of which discussed in Chapter 5. 

On the other hand, a nucleophilic addition reaction of a jt(-allyl)ruthenium complex to a ketone is also reversible. The deallylation of a tertiary homoallylic... 

Ruthenium-catalyzed hydroacylation of 1,3-dienes with aromatic and heteroaromatic aldehydes occurs in relatively good yields to afford the corresponding fi, /-unsaturated ketones . Isoprene and benzaldehyde were treated with 4 mol% Ru(COD)(COT) (COD = 1,5-cyclooctadiene, COT = 1,3,5-cyclooctatriene) and 4 mol% PPhs under argon for 40 hours to give 54% 80 (equation 41). The key intermediate is an acyl- ) -(allyl)ruthenium complex which undergoes reductive elimination to give the corresponding... 

The (7T-allyl )ruthenium complex Ru(t -C,H5)(OAc)(CO)3, which is a model for a possible kev intermediate of Ru3(CO)p catalyzed allylations, shows ambiphilic reactivity... 

Allyl sulhdes react with Ru(cod)(cot)/DEPE to give cationic r/ -allyl-ruthenium(II) complexes (Eq. 3.36) [143]. Allyl phenyl sulhde gives a much higher yield of the 17 -allyl complex than allyl methyl sulhde. 

Other reversible y6-alkyl eliminations cause the transformation of ruthenacy-clobutanes to methyl allyl ruthenium derivatives (Eq. 6.26) [152], or alkyl exchange by a rare formal -alkyl elimination in a metal alkenyl complex (Scheme 6.52) [153]. Reversible propene extrusion by /1-alkyl elimination has also been described for some zirconium metallacycles [154]. 

Water-soluble bis(allyl)ruthenium hydrate catalysts (1 and 2) initiate emulsion polymerization of norbomene, yielding surprisingly specific cis polymers (85-90% cis) [10]. 

Starting with a dimeric bis(allyl)ruthenium complex, the precatalyst Id was synthesized by complexation with tricyclohexylphosphane. After addition of trimethylsilyldiazomethane, the basic bisallylic ligands were displaced from the coordination sphere of the metal to form the catalytically active ruthenium(Il)-alkylidene species IdTMS [10]. Although the ruthenium-alkylidene complex generated in situ is easy to obtain, the structure of catalytically active species is poorly defined. Therefore, a control over the activity is difficult, and reproducible experimental results are almost impossible to achieve. 

The 5 2 allylic substitution of cinnamyl chloride by water in the presence of an (5)-Cp Ru catalyst and NaHC03 in aqueous THF at room temperature occurs with complete regiospeciflcity, giving a 93-99% yield of the branched allylic alcohol, with between 89 and 94% eeP A r-allyl-ruthenium complex is believed to form during the reaction. A tracer study using H2 0 showed that water is the nucleophile in the hydrolysis reaction. 

Carbon-Carbon Bond Formation Reactions Involving Allyl-Ruthenium Intermediates. Unlike many other allylmetal complexes, r-allyl-ruthenium complexes demonstrate both nucleophilic and electrophilic behavior. Two postulated mechanisms are presented side by side in Figure 23. The first scheme shows the mechanism for nucleophilic addition of primary alcohols to allyl... 

---