Alkenes lanthanides

Lanthanide triflates catalyze the Diels-Alder reaction of imines, generated from anilines and aldehydes, with both dienes and alkenes [26]. Thus N-benzyl-ideneaniline in the presence of Yb(OTf)3 (Scheme 6.16) reacts in organic solvent with open-chain dienes, such as Danishefsky s diene, to give tetrahy-dropyridine derivatives, while with cyclopentadiene and vinylethers and vinylthioethers it works like azadiene in both organic solvent and aqueous medium, affording tetrahydroquinoline derivatives. 

Secondary amines can be added to certain nonactivated alkenes if palladium(II) complexes are used as catalysts The complexation lowers the electron density of the double bond, facilitating nucleophilic attack. Markovnikov orientation is observed and the addition is anti An intramolecular addition to an alkyne unit in the presence of a palladium compound, generated a tetrahydropyridine, and a related addition to an allene is known.Amines add to allenes in the presence of a catalytic amount of CuBr " or palladium compounds.Molybdenum complexes have also been used in the addition of aniline to alkenes. Reduction of nitro compounds in the presence of rhodium catalysts, in the presence of alkenes, CO and H2, leads to an amine unit adding to the alkene moiety. An intramolecular addition of an amine unit to an alkene to form a pyrrolidine was reported using a lanthanide reagent. 

The proposed mechanism for the metallocene complexes of Group 5 metals and lanthanides involves the coordination of alkene to the metal hydride (51), followed... 

As in the P(III) chemistry above, both late metal (Pd) and lanthanide catalysts have been used for P(V)-H additions to alkynes, alkenes, aldehydes, and imines. In addition, titanium, aluminum, and zinc catalysts have been employed. Typical P(V) substrates include dialkyl phosphites P(0R)2(0)H and phosphine oxides PR2(0)H. 

In 2003, Livinghouse et al. also reported that chelating bis(thiophosphonic amidates) complexes of lanthanide metals, such as yttrium or neodymium, were able to catalyse intramolecular alkene hydroaminations. These complexes were prepared by attachment of the appropriate ligands to the metals by direct metalation with Ln[N(TMS)2]3- When applied to the cyclisation of 2-amino-5-hexene, these catalysts led to the formation of the corresponding pyrrolidine as a mixture of two diastereomers in almost quantitative yields and diastereos-electivities of up to 88% de (Scheme 10.81). 

As in the case of Diels-Alder reactions, aqueous aza-Diels-Alder reactions are also catalyzed by various Lewis acids such as lanthanide triflates.113 Lanthanide triflate-catalyzed imino Diels-Alder reactions of imines with dienes or alkenes were developed. Three-component aza-Diels-Alder reactions, starting from aldehyde, aniline, and Danishefsky s diene, took place smoothly under the influence of HBL4 in aqueous media to afford dihydro-4-pyridone derivatives in high yields (Eq. 12.46).114... 

Abstract Significant advances have been made in the study of catalytic reductive coupling of alkenes and alkynes over the past 10 years. This work will discuss the progress made in early transition metal and lanthanide series catalytic processes using alkyl metals or silanes as the stoichiometric reductants and the progress made in the use of late transition metals for the same reactions using silanes, stannanes and borohydrides as the reductant. The mechanisms for the reactions are discussed along with stereoselective variants of the reactions. 

Metal complexes of lanthanides beyond lanthanocenes were used to catalyze the reductive coupling reaction of dienes. La[N(TMS)2h was found to effect the cyclization of 1,5-hexadiene in the presence of PhSiH3 (Eq. 13) [50]. Cyclized products 88 and 89 were isolated in a combined yield of 95% (88 89 = 4 1). It was suggested that the silacycloheptane 89 resulted from competitive alkene hydrosilylation followed by intramolecular hydrosilylation. 

Although transition metal-mediated P-H addition across ordinary alkenes proceeds well only with five-membered cyclic hydrogen phosphonates, addition across the olefinic linkage of a,P-unsaturated compounds occurs readily with a range of phosphorus species and catalytic agents. Of particular note are the reaction systems involving platinum,96-107 palladium,108-115 and the lanthanides.116-122... 

Recently, another type of catalytic cycle for the hydrosilylation has been reported, which does not involve the oxidative addition of a hydrosilane to a low-valent metal. Instead, it involves bond metathesis step to release the hydrosilylation product from the catalyst (Scheme 2). In the cycle C, alkylmetal intermediate generated by hydrometallation of alkene undergoes the metathesis with hydrosilane to give the hydrosilylation product and to regenerate the metal hydride. This catalytic cycle is proposed for the reaction catalyzed by lanthanide or a group 3 metal.20 In the hydrosilylation with a trialkylsilane and a cationic palladium complex, the catalytic cycle involves silylmetallation of an alkene and metathesis between the resulting /3-silylalkyl intermediate and hydrosilane (cycle D).21... 

In hydrogenation, early transition-metal catalysts are mainly based on metallocene complexes, and particularly the Group IV metallocenes. Nonetheless, Group III, lanthanide and even actinide complexes as well as later metals (Groups V-VII) have also been used. The active species can be stabilized by other bulky ligands such as those derived from 2,6-disubstituted phenols (aryl-oxy) or silica (siloxy) (vide infra). Moreover, the catalytic activity of these systems is not limited to the hydrogenation of alkenes, but can be used for the hydrogenation of aromatics, alkynes and imines. These systems have also been developed very successfully into their enantioselective versions. 

Hydrogenation of Alkenes with Croup III Metal and Lanthanide Complexes... 

The hydrogenation of unfunctionalized alkenes is readily performed by Group III and lanthanide cyclopentadienyl hydride derivatives, one key feature being the high TOFs of these systems (up to 120000 IT1 for hydrogenations catalyzed by Lu, Tables 6.8 and 6.9) [119, 120]. The reaction rate depends heavily on the metal and the ligands. It is inversely proportional to the metal radius (Lu>Sm>Nd>La), and it is faster for the Cp M derivatives than for the ansa di-... 

Table 6.8 Rate constants for the catalytic hydrogenation of alkenes catalyzed by Group III and lanthanide complexes.3 ...

Marks and coworkers developed a series of cyclopentadienyl-lanthanide complexes. In the initial investigations on achiral catalysts 36a and 36b (Fig. 29.21), TOFs greater than 100000 IT1 were observed in the hydrogenation of 1,2-disub-stituted unfunctionalized alkenes [48]. 

Selection of those metals where the metal alkyl complexes are stable with respect to hydride and liberated alkene. For the metals on the left-hand side of the periodic table, the Early Transition Metals and the Lanthanides, the alkyls are relatively stable. Therefore it is not surprising that the best alkene polymerisation catalysts are found amongst these metals. 

Neutral lanthanide complexes are convenient models for the cationic zirconocene systems and avoid complications due to the presence of counteranions and the limited solubility of ionic compounds. Dynamic NMR studies on yttrium complexes 44-46 has allowed the determination of the alkene binding enthalpy, the activation enthalpy of alkene dissociation, and the relative rates of dissociation and alkyl site exchange (site epimerisation) (Scheme 8.20). Compared to the Zr... 

Many other groups further studied the utility of bis(oxazolines) including Ikeda s use of biaryl bis(oxazolines) such as 250 (Fig. 9.75) in the zinc-catalyzed asymmetric alkylation of benzaldehyde with diethylzinc. " This reaction proceeded in yields up to 92% with ee up to 88%. Kodama and co-workers used a biaryl bis(oxazoline) ligand, namely, [l,l -]binaphthalenyl-2,2 -diol (BlNOL)-box 251, in the lanthanide-catalyzed asymmetric 1,3-dipolar cycloaddition of nitrones to alkenes. ... 

Widenhoefer has developed methods for Pd-catalyzed addition of 1,3-dicarbonyl nucleophiles to alkenes [ 171-173]. Most of these reactions employ stoichiometric copper as the oxidant however, Yang and coworkers recently reported a modified procedure that employs cocatalytic lanthanide Lewis acids to achieve direct dioxygen-coupled turnover (Eq. 39) [174], The Lewis acid is thought to activate the carbon nucleophile, P-keto amide, toward attack on the tethered alkene. 

Amdduri B,Boutevin (1997) Telomerisation Reactions of Fluorinated Alkenes. 192 165-233 Anwander R (1996) Lanthanide Amides. 179 33-112... 

Alkene hydroamination has been known for many years, but has been little used as a method in organic synthesis. Tobin Marks of Northwestern recently published a series of three papers that will make this transformation much mote readily accessible. In the first (J. Am. Chem. Soc. 125 12584,2003) he describes the use of a family of lanthanide-derived catalysts for intermolecular hydroamination of alkynes (to make imines, not illustrated) and alkenes. With aliphatic amines, the branched (Markownikov) product is observed, 1 — 2. With styrenes, the linear product is formed. When two alkenes are present, the reaction can proceed (3 —> 4) to form a ring, with impressive regioselectivity. 

In 1975, it was reported that while lanthanide shift reagents could not be used directly to simplify the NMR spectra of alkenes, when coupled with silver salts substantial shifts could be induced.232 Since then, a number of studies have reported the use of both chiral and achiral lanthanide(III)-silver(I) binuclear shift reagents,233-237 where the ligands were generally fluorinated /3-diketones. 

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