Lanthanide complexes amine oxides

Complexes of the lanthanides with amine oxides, nitroso compounds, and nitroxide radicals fall under this category. However, only the complexes with the amine oxides have received wide attention. Four comprehensive reviews have appeared on the complexes of amine oxides with various metal ions 142-145). Only a few complexes of the lanthanides have been quoted in these reviews. 

Complexes of monodentate aliphatic amine oxides with the lanthanides have not been extensively investigated. The only series of complexes with a ligand of this type, Et3NO, has been reported by Pavlenko et al. (181). The complexes have the formula [Ln(Et3N0)6][Cr(NCS)6]-2H20. 

The reaction is catalyzed by lanthanide complexes CpjfLnR,41 although noble metal catalysts, notably rhodium, are most widely applied, particularly in asymmetric hydroboration,42 The mechanism is likely to be similar to hydrosilylation. The products may be oxidized with H202 and converted to alcohols or amines. 

CCC (1987) contains a section on sulfoxides, amide, amine oxides, and related ligands that have sections on phosphine oxides and arsine oxides.159 Phosphine and arsine oxide complexes of yttrium and the lanthanides were highlighted in CCC (1987).1 Scandium and yttrium phosphine oxide complexes have been reinvestigated and characterized by multinuclear NMR and X-ray... 

Solutions of alkali metals in ammonia have been the best studied, but other metals and other solvents give similar results. The alkaline earth metals except- beryllium form similar solutions readily, but upon evaporation a solid ammoniste. M(NHJ)jr, is formed. Lanthanide elements with stable +2 oxidation states (europium, ytterbium) also form solutions. Cathodic reduction of solutions of aluminum iodide, beryllium chloride, and teUraalkybmmonium halides yields blue solutions, presumably containing AP+, 3e Be2, 2e and R4N, e respectively. Other solvents such as various amines, ethers, and hexameihytphosphoramide have been investigated and show some propensity to form this type of solution. Although none does so as readily as ammonia, stabilization of the cation by complexation results in typical blue solutions... 

The preparation of urethanes from primary aliphatic and aromatic amines by oxidative carbonylation has been described in which - instead of Pd salts or complexes - lanthanide compounds, particularly of cerium, and promoters comprising alkali metal salts or quaternary ammonium salts, are used [133]. 

The hydroamination of olefins has been shown to occur by the sequence of oxidative addition, migratory insertion, and reductive elimination in only one case. Because amines are nucleophilic, pathways are available for the additions of amines to olefins and alkynes that are unavailable for the additions of HCN, silanes, and boranes. For example, hydroaminations catalyzed by late transition metals are thought to occur in many cases by nucleophilic attack on coordinated alkenes and alkynes or by nucleophilic attack on ir-allyl, iT-benzyl, or TT-arene complexes. Hydroaminations catalyzed by lanthanide and actinide complexes occur by insertion of an olefin into a metal-amide bond. Finally, hydroamination catalyzed by dP group 4 metals have been shown to occur through imido complexes. In this case, a [2+2] cycloaddition forms the C-N bond, and protonolysis of the resulting metallacycle releases the organic product. 

Amine activatitMi pathway has been well studied in catalysis by lanthanides, early transition metals, and alkali metals. In metal amide chemistry of late transition metals, there are mainly two pathways to synthesize metal amide complexes applicable under hydroamination conditions [54], One is oxidative addition of amines to produce a metal amide species bearing hydride (Scheme 8a). The other gives a metal amide species by deprotonation of an amine metal intermediate derived from the coordination of amines to metal center, and it often occurs as ammonium salt elimination by the second amine molecule (Scheme 8b). Although the latter type of amido metal species is rather limited in hydroamination by late transition metals, it is often proposed in the mechanism of palladium-catalyzed oxidative amination reaction, which terminates the catalytic cycle by p-hydride elimination [26]. Hydroamination through aminometallation with metal amide species demands at least two coordination sites on metal, one for amine coordination and another for C-C multiple bond coordination. Accordingly, there is a marked difference between the hydroamination via C-C multiple bond activation, which demands one coordination site on metal, and via amine activation. 

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