Oxygen reaction with lanthanides

Nearly all of the information available on the kinetics of heterogeneous reactions with lanthanide oxides concerns the C-type sesquioxides or the fluorite-related higher oxides. As stated in the section above, in these materials oxygen mobility is very high, whereas, metal-atom movement is extremely limited below 1200°C. Table 19 suggests the type of experiments that were done and the phenomenological mechanisms proposed before 1980 (Eyring 1979). 

Cyclic 1,2-diketones, such as3-methylcyclopentane-l,2-dione, act as oxygen nucleophiles in palladium(0)-catalyzed reactions with a range of cyclic and acyclic allylic esters. The products of these reactions were subjected to a lanthanide-catalyzed Claisen rearrangement to access the C-alkylated products. 

As in the case with oxygen separation materials, lanthanum is the preferred lanthanide. Strontium, calcium and barium are all possible dopants, although the susceptibility of barium to reaction with CO2 Hmits its use. Efforts to make the materials A-site deficient are also common. 

The polymerization undergoes coordination-insertion mechanism. The initiation step involves nucleophilic attack of the active group, such as hydride, alkyl, amide, or alkoxide group, on the carbonyl carbon atom of a lactide or lactone to form a new lanthanide alkoxide species via acyl-oxygen cleavage. The continued monomer coordination and insertion into the active metal-alkoxo bond formed completes the propagation step as shown in Scheme 27. The reactions with stereoselectivity proceed by means of a chain-end control mechanism , which is the chirality of the propagating... 

The lanthanide and actinide ions react with oxygen donor molecules. Recently, four selected lanthanide and actinide ions have been reacted with several sources of oxygen including 02. The formation of [MO]+ and [M02]+ ions were observed by the reactions of Ce+, Nd+, Th+, and U+ with 02. All reactions produced [MO]+ but [MOH]+ was a common minor product and [Th02]+ and [U02]+ ions were also obtained by the reaction of M+ with 02 (101). 

The lanthanide oxide cations [LnO]+ and the bare lanthanide ions Ln+ react differently with butadiene (162). Some bare Ln+ ions (La, Ce, Pr, Gd) activate butadiene but their oxide cations are inert toward butadiene. The lanthanides with weak M-O bonds, EuO and YbO, react by oxygen transfer to the butadiene. The oxide cations of Dy, Ho, Er, and Tm activate butadiene, whereas the bare metals of these lanthanides are unreactive with butadiene. The [HoO]+ ion has been studied in detail and is able to polymerize butadiene the mechanism of this reaction has been discussed. 

Hoppe D, Marr F, Bruggemann M (2003) Enantioselective Synthesis by Lithiation Adjacent to Oxygen and Electrophile Incorporation. 5 61-138 Hou Z, Wakatsuki Y (1999) Reactions of Ketones with Low-Valent Lanthanides Isolation and Reactivity of Lanthanide Ketyl and Ketone Dianion Complexes. 2 233-253 Hoveyda AH (1998) Catalytic Ring-Closing Metathesis and the Development of Enantioselective Processes. 1 105-132 Huang M, see Wu GG (2004) 6 1-36... 

The reduction of imines can be performed with zinc powder in 5% aq. NaOH solution without any organic solvents under mild conditions (Tsukinoki et al., 1998). In comparison with other conventional methods, some advantages of this method are the fact that, since the reaction can be done in water at room temperature under atmospheric pressure, it is safe, and that hydrogen gas is not necessary because the proton source is water. Furthermore, Zn powder is cheap compared with metal hydrides, hydrogenation catalyst, and lanthanides, and is not sensitive to oxygen and water. 

---