Phosphino-alkyne

Unlike the late metal chemistry reviewed above, these reactions did not require Michael acceptor substrates, but the reactions were rather slow (turnover frequencies range from 2 to 13 h at 22°C). For phosphino-alkenes (Scheme 5-15, Eqs. 1-3), a competing uncatalyzed reaction gave six-membered phosphorinane rings (Scheme 5-15, Eq. 6) this could be minimized by avoiding light and increased temperature. For phosphino-alkynes (Scheme 5-15, Eqs. 4 and 5), the products were unstable and could not be isolated [14]. 

In another copper-catalyzed reaction, cross-coupling of alkynes with phosphi-ne-boranes was followed by surprising oxidation to yield ketones (Scheme 69) [122]. The active species was proposed to be a copper phosphido-borane complex, formed by proton transfer to a Cu-OH group. Formation of a Cu-acetylide followed by P-C reductive elimination would then yield a phosphino-alkyne, whose subsequent Cu-mediated air oxidation yields the ketone. 

Electrophilic attack on alkene or alkyne complexes can be a route to cr-organonickel derivatives. One example is the reaction of a cyclohexyne compound with iodomethane shown in Equation (43). The reaction of 77 -phosphino-alkyne complexes with HGl gives a mixture of two isomeric phosphinovinyl compounds with iy//-stereoselectivity (Equation (44)). The regioselectivity of the protonation depends on the electronic properties of the alkyne substituents, and has been correlated with the chemical shift of the G resonances of the two acetylenic carbon atoms. ... 

Stable zirconate complexes of type 31 have also been described by the [3 + 2] cycloaddition of a-phosphino zirconaindene with alkyne derivatives, and the method has been extended to the synthesis of zirconium complexes from various heterocumulenes X=C=Y (X,Y=0,S,CyN) (Scheme 15) [69,70]. 

Marks and Douglass recently reported organolanthanide-catalyzed hydrophosphina-tion/cyclization of phosphino-alkenes and -alkynes (Scheme 5-15). 

Arylation of alkynes via addition of arylboronic acids to alkynes represents an attractive strategy in organic synthesis. The first addition of arylboronic acids to alkynes in aqueous media catalyzed by rhodium was reported by Hayashi et al.89 They found that rhodium catalysts associated with chelating bisphosphine ligands, such as 1,4-Ws(diphenyl-phosphino)butane (dppb) and 1,1 -/ E(diphenylphospliino)fcrroccnc... 

Dinuclear palladium complexes catalyze m-hydroarylation of alkynes with arenes.56 The reaction of 3-hexyne with benzene in the presence of a dinulear palladium complex Pd2R2(M-OH)(//-dpfam) [dpfam = j/V,Ar -bis[2-(diphenyl-phosphino)phenyl]formamidinate, R=/>-Tol] and tri(/z-butyl)borane at 100 °C for 4h affords ( )-3-phenyl-3-hexene quantitatively (Equation (53)). The hydroarylation of 3-hexyne with monosubstituted benzenes ( )-3-aryl-3-hexenes with a 2 1 ratio of the meta- and ra -isomers. This regioselectivity is different from that of the hydroarylation of diphenylacetylene catalyzed by Rh4(GO)12.57... 

Ir-complexes also demonstrate catalyhc achvity in the intermolecular [2+2+2] cycloaddition of three monoalkynes, when Takeuchi examined the mixed cyclotrimerization of two alkynes. In this situation the choice of ligand was shown to determine the excellent chemoselechvity for example, when the Ir-dppe complex was used, 2 1 cycloadducts of DM AD and mono- or disubstituted alkynes were obtained, but when Ir-F-dppe (l,2-bis[bis(pentafluorophenyl)phosphino]eth ane) one was used, a 1 2 cycloadduct of DMAD and l,4-dimethoxybut-2-yne was obtained (Schemes 11.7 and 11.8) [15]. A regioselective cyclotrimerizahon of three alkynes was achieved by [lrH(cod)(dppm)] (bis(diphenylphosphino)methane), and 1,2,4-triarylbenzenes were obtained exclusively (Scheme 11.9) [16]. 

Thus examples such as 16 that have a phosphino substituent on the N atom are more nucleophilic in character and react readily with electron-poor alkenes and alkynes (see above) but fail to react with those that are electron rich. In contrast, the ones with a phosphonio substituent (e.g., 24) were found to react readily with... 

The amide [Sm(45a) N(SiMe3)2 ] was a catalyst for an aUene-based hydroamination/ cyclisation. As an illustration, one such product upon hydrogenation yielded a naturally occurring alkaloid. Scheme 4.8. " " The same samarium(lll) amide was also active for the intramolecular hydrophosphination/cyclisation of phosphino-alkenes or -alkynes e.g., H2P(CH2)3C=CPh was transformed into 76. " ... 

On reaction with hydroxyallenes, a variety of terminal alkynes led selectively to 1,3-disubstituted conjugated enynes in good yields in the presence of the catalyst RuH2(PPh3)4 and the ligand l,T-bis(di(p-methylphenyl)phosphino)fer-rocene [83] (Eq. 62). The selectivity may result from the interaction of the al-lene hydroxyl group with the ruthenium catalyst. 

The best catalyst precursors are Ru(methallyl)2( l,4-bis(diphenylphosphino)bu-tane) (A) and Ru(methallyl)2(dppe) (B), where dppe is l,2-bis(diphenyl-phosphino)ethane, the choice of the appropriate complex depending on the steric demand of both the alkyne and the carboxylic acid. A large variety of carboxylic acids and alkynes have been used, including AT-protected amino acids, a-hydroxy acids and functionalized alkynes such as enynes and propargylic ethers (Table 1) [20,21]. 

Phospha-alkyne systems have continued to attract interest. The phosphino-phospha-alkyne (324) arises as a transient intermediate in the thermolysis of a phosphino-phosphiranyl-diazo system.A convenient synthetic route to substituted phosphavinyl Grignard reagents (325) is provided by the regio- and stereo-selective addition of Grignard reagents to the phospha-alkyne... 

As already mentioned in the introduction, anionic early transition metallocene complexes of the type [Cp2Zr(R1)(R2)(R3)] with R, R2, R3 = alkyl, alkenyl, or alkynyl, are unstable. Most of them exhibit electrostatic anion-cation pairing resulting in dimer, trimer, oligomer, or polymeric structures [21-25]. In marked contrast, stable 18 electron-zirconate complexes were prepared via a formal [3 + 2] cycloaddition reaction between 2-phosphino-zirconaindene 16a and alkyne derivatives (Scheme 5) [26,27]. 

The first examples of phosphirenium salts (129) have been prepared from the reactions of alkynes with the aluminium trichloride adducts of dichlorophos-phines. The reactions of phosphines with fluorotrihalogenomethanes lead to the first examples of fluorine-containing phosphoranium salts (130). The related nitrogen-bridged salt (131) is formed in the reactions of lithium bis(diphenyl-phosphino)amide with iodomethane. ... 

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