Anti-Markovnikov addition ruthenium

In 1998, Wakatsuki et al. reported the first anti-Markonikov hydration of 1-alkynes to aldehydes by an Ru(II)/phosphine catalyst. Heating 1-alkynes in the presence of a catalytic amount of [RuCljlCgHs) (phosphine)] phosphine = PPh2(QF5) or P(3-C6H4S03Na)3 in 2-propanol at 60-100°C leads to predominantly anti-Markovnikov addition of water and yields aldehydes with only a small amount of methyl ketones (Eq. 6.47) [95]. They proposed the attack of water on an intermediate ruthenium vinylidene complex. The C-C bond cleavage or decarbonylation is expected to occur as a side reaction together with the main reaction leading to aldehyde formation. Indeed, olefins with one carbon atom less were always detected in the reaction mixtures (Scheme 6-21). 

Rhodium(I) and ruthenium(II) complexes containing NHCs have been applied in hydrosilylation reactions with alkenes, alkynes, and ketones. Rhodium(I) complexes with imidazolidin-2-ylidene ligands such as [RhCl( j -cod)(NHC)], [RhCl(PPh3)2(NHC)], and [RhCl(CO)(PPh3)(NHC)] have been reported to lead to highly selective anti-Markovnikov addition of silanes to terminal olefins [Eq. 

The hydrative cyclization involves the formation of a ruthenium vinylidene, an anti-Markovnikov addition of vater, and cyclization ofan acylmetal species onto the alkene. Although the cyclization may occur through a hydroacylation [32] (path A) or Michael addition [33] (path B), the requirement for an electron- vithdra ving substituent on the alkene and lack of aldehyde formation indicate the latter path vay to be the more likely mechanism. Notably, acylruthenium complex under vent no decarbonylation in this instance. 

Anti-Markovnikov Additions of 0-, N-, P-Nucleophiles to Triple Bonds with Ruthenium Catalysts... 

Success was obtained with Ru3(CO)i2 as catalyst precursor [6], but the most efficient catalysts were found in the RuCl2(arene)(phosphine) series. These complexes are known to produce ruthenium vinylidene spedes upon reaction with terminal alkynes under stoichiometric conditions, and thus are able to generate potential catalysts active for anti-Markovnikov addition [7]. Similar results were obtained by using Ru(r]" -cyclooctadiene)(ri -cyclooctatriene)/PR3 as catalyst precursor [8]. (Z)-Dienylcarba-mates were also regio- and stereo-selectively prepared from conjugated enynes and secondary aliphatic amines (diethylamine, piperidine, morpholine, pyrrolidine) but, in this case, RuCl2(arene) (phosphine) complexes were not very efficient and the best catalyst precursor was Ru(methallyl)2(diphenylphosphinoethane) [9] (Scheme 10.1). 

Scheme 10.5 Some ruthenium catalysts leading to anti-Markovnikov addition of carboxylic acids to terminal alkynes.

The formation of metal vinylidene complexes directly from terminal alkynes is an elegant way to perform anti-Markovnikov addition of nucleophiles to triple bonds [1, 2], The electrophilic a-carbon of ruthenium vinylidene complexes reacts with nucleophiles to form ruthenium alkenyl species, which liberate this organic fragment on protonolysis (Scheme 1). 

Several ruthenium complexes are able to promote the classical Markovnikov addition of O nucleophiles to alkynes via Lewis-acid-type activation of triple bonds. Starting from terminal alkynes, the anti-Markovnikov addition to form vinyl derivatives of type 1 (Scheme 1) is less common and requires selected catalysts. This regioselectivity corresponding to the addition of the nucleophile at the less substituted carbon of the C=C triple bond is expected to result from the formation of a ruthenium vinylidene intermediate featuring a highly reactive electrophilic Ca atom. 

The most efficient catalyst precursors were found in the RuCl2(arene)(phos-phine) series. These complexes are known to produce ruthenium vinylidene species upon reaction with terminal alkynes under stoichiometric conditions, and thus are able to generate potential catalysts active for anti-Markovnikov addition [8]. Dienylcarbamates could also be selectively prepared from conju-... 

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 regioselective anti-Markovnikov addition of benzoic acid to phenyl-acetylene has also been carried out with success at 111 °C in the presence of ruthenium complexes containing a tris(pyrazolyl)borate (Tp) ligand [RuCl(Tp)(cod), RuCl(Tp)(pyridine), RuCl(Tp)(N,N,Ar,AT-tetramethylethyl-enediamine )] with a stereoselectivity in favour of the (E)-enol ester isomer [22]. The o-enynyl complex Ru(Tp)[PhC=C(Ph)C=CPh](PMe/-Pr2) (C) efficiently catalyses the regioselective cyclization of a,cu-alkynoic acids to give en-docyclic enol lactones [23] (Eq. 2). 

The first example of anti-Markovnikov addition of 0-nucleophiles to terminal alkynes was actually the catalytic addition of ammonium carbamates generated in situ from secondary amines and carbon dioxide to give vinylcarbamates. This was also the first suggestion of a ruthenium-vinylidene intermediate as a catalytic active species for organic synthesis (Scheme 8.20) [6, 7]. 

Hydration of terminal alkynes can proceed with anti-Markovnikov addition. When 1-octyne was heated with water, isopropanol and a ruthenium catalyst, for example, the product was octanal. A similar reaction was reported in aqueous acetone using a ruthenium catalyst. The presence of certain functionality can... 

Gunnoe has also reported examples of catalytic aromatic alkylation using a ruthenium complex and olefins. With propylene and other terminal olefins, a 1.6 1 preference for anti-Markovnikov addition was seen. The proposed mechanism involved olefin insertion into the metal-aryl bond followed by a metathesis reaction with benzene to give the alkylated aromatic and a new metal-phenyl bond (Equation (26)). DFT calculations supported the proposed non-oxidative addition mechanism. The work was extended to include catalytic alkylation of the a-position of thiophene and furan. With pyrrole, insertion of the coordinated acetonitrile into the a-C-H bond was observed. Gunnoe has also summarized recent developments in aromatic C-H transformations in synthesis using metal catalysts. ... 

Progress on the addition of aromatic C-H bonds to olefins has been made by Periana with iridium catalysts - - and Gunnoe with ruthenium catalysts. - Both systems illustrate that the anti-Markovnikov addition products can be generated in larger quantities than the Markovnikov products, although mixtures of regioisomers are still observed. Intramolecular additions of the C-H bonds of electron-rich heterocycles to electron-deficient alkenes have also been reported (Equation 18.65). Most recently, Tilley has reported the addition of the C-H bond of methane across an olefin catalyzed by scandocene complexes. This reaction occurs, albeit slowly, with Markovnikov regiochemistry. 

The reaction, whose scope, limitation and mechanism we are going to review, directly yields a/r-poly(carbosilane/siloxanes) by the (Ph3p)3RuH2CO (Ru) catalyzed copolymerization of aromatic ketones and 1,3-divinyltetramethyldisiloxane, as shown in Figure 4. The key step in this process involves the ruthenium catalyzed activation of an aromatic C-H bond which is ortho to a carbonyl group for anti-Markovnikov addition across the C-C double bond of 1,3-divinyltetramethyldisiloxane. Each time... 

The transition metal catalyzed addition of amides to alkynes provides a useful approach to the preparation of enamides. In this context, Gooden and coworkers have developed efficient ruthenium catalysts, which allow the anti-Markovnikov addition of amide to terminal alkynes (Scheme 4.46) [187]. 

Scheme 4.46 Ruthenium-catalyzed anti-Markovnikov addition of amides to alkynes[187]...

The same research group also investigated the hydroarylation of the vinyl side chain of poly(vinylmethylsiloxane) via ruthenium-catalyzed alkenylation of the ortho C—H bonds of aromatic ketones with vinylsilanes (Fig. 18B), a reaction originally developed by Murai. The functionalization reaction was regioselective, giving anti-Markovnikov addition of the 10-position C—H bond of 9-acetylphenanthrene across the pendant... 

Intramolecular anti-Markovnikov addition of carboxylic acids to alkynes was also achieved using ruthenium catalysts. a,co-Alkynoic acids afford the corresponding cycloalkene lactones by intramolecular addition of the carboxylic acid to the corresponding catalytic vinylidene species obtained by treatment of the... 

Cyclizations can be initiated by a nucleophilic attack, e.g. by H2O or a carboxylic acid, to a catalytic ruthenium vinylidene followed by trapping with an electrophile. Lee and coworkers described the Ru-catalyzed hydrative cyclization of 1,5-enynes (Scheme 33) to give functionalized cyclopentanones [147]. Treatment of 1,5-enynes bearing an internal Michael acceptor with a catalytic amount of [Ru3Cl5(dppm)3]PF6 in the presence of water initially afforded the corresponding ruthenium vinylidene species. Nucleophilic anti-Markovnikov addition of water... 

The anti-Markovnikov addition of nitrogen nucleophiles to alkynes has been accomplished using ruthenium catalysts (Scheme 3.125) [137]. During the screening process, the authors discovered that when the reactions were carried out at 80 °C, moderate yields of the hydroamination products were obtained (50%) however, the stereocontrol was poor and a 4 1 ( ratio of the enamines was obtained. When the temperature was increased to 100°C, the Zi-isomer was obtained exclusively. At the higher temperatures, most substrates exclusively generated the E-isomer, although some substrate-specific reactivity was observed. 

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