Transmetallation, redox

Figure 3. Schematic illustration of core/shell nanoparticle formation via redox transmetalation process. Metal ions (Mu) of reactant metal complexes (Mn-L ) are reduced on the surface of Mi nanoparticles while neutral Mi atoms are oxidized to Mi " by forming a Mi-ligand complex (Mi-Lj) as a resultant reaction byproduct. Repeating this process results in the complete coverage of shell layers on core metals. (Reprinted from Ref [145], 2005, with permission from American Chemical Society.)...

Therefore, for small-scale laboratory synthesis it seemed promising to develop alternative methods which avoid the inconvenient high temperature and yield the reactive, solvated form. For example, the THF adducts can readily be synthesized by treating lanthanide powders with CHC13 under ultrasonic conditions, as described by Eq. (1) [100], Redox transmetallation between lanthanide metals and mercury(II) halides are carried out in refluxing THF (Eq. 2) [108]. Recently ammonia was employed as an alternative solvent, e.g. in the synthesis... 

Reactions of Allylindium Prepared by Redox Transmetallation with Pd or Ni 698... 

Deacon, G.B., Fallon, G.D., Forsyth, C.M., Harris, S.C., Junk, PC., Skelton, B.W., and White, A.H. (2006) Manipulation of reaction pathways in redox transmetallation-ligand exchange syntheses of lanthanoid 11/111 aryloxide complexes. Dalton Transactions, 802—812. 

Deacon, GB. and Forsyth, C.M. (2003) A half-sandwich perfluoroorganoytterbium(ll) complex from a simple redox transmetalation/ligand exchange synthesis. Organometallics, 22, 1349. 

Anhydrous lanthanide trihalides, particularly the trichlorides, are important reactants for the formation of a variety of lanthanide complexes, including organometallics. Routes for the syntheses of anhydrous lanthanide trihalides generally involve high temperature procedures or dehydration of the hydrated halides.The former are inconvenient and complex for small scale laboratory syntheses, while dehydration methods may also be complex and have limitations, for example, use of thionyl chloride. - Moreover, the products from these routes may require purification by vacuum sublimation at elevated temperatures. Redox transmetalation between lanthanide metals and mercury(II) halides was initially carried out at high temperatures. However, this reaction can be carried out in tetrahydrofuran (THF, solvent) to give complexes of lanthanide trihalides with the solvent. These products are equally as suitable as reactants for synthetic purposes as the uncomplexed... 

E)etailed syntheses of four representative lanthanide trihalide-tetrahydro-furan (thf, ligand) complexes, YbCl3(thf)j, ErCljlthflj j, SmClj(thf)2, and NdCl3(thf), 5 by redox transmetalation are described. The first three compounds have previously been prepared by direct reaction of anhydrous lanthanide trihalides with but the composition of the last differs... 

Organolanthanide chemistry is dominated by the trivalent compounds. " Compounds in oxidation state (II) are restricted to derivatives of europium, samarium, and ytterbium, but they have considerable importance in both organic and organometallic syntheses because of their reducing properties. " Redox transmetalation reactions of organomercurials with lanthanide metals provide convenient syntheses of a number of diorganolanthanides, for example, R2M, R = CgFj or PhCC, M = Yb or Eu. " °... 

Details of the redox transmetalation synthesis of bis(phenylethynyl)-ytterbium(II) are presented here. This diorganoytterbium(II) compound has a rich reaction chemistry, which is currently being developed. The compound is highly air and moisture sensitive and must be handled under purified nitrogen or argon. Bis(phenylethynyl)ytterbium(II) can be stored indefinitely in an inert atmosphere at room temperature. ... 

Other small-scale laboratory procedures have been developed for the direct synthesis of the more reactive THF adducts, avoiding inconvenient high temperature treatment [59-62]. For example, the preparation of LnCl3(thf)x from metal powder and hexachloroethane is facilitated by sonication [Eq. (1)] [59]. Additional metal-based synthetic routes include the redox transmetallation with mercury(II) halides [Eq. (2)] [60] and the reaction with trimethylsilyl chloride and anhydrous methanol [Eq. (3)] [61]. Ammonia has been employed as an alternative donating solvent in the synthesis of lanthanide alkoxides starting from lanthanide chlorides [63]. 

The spontaneous deposition of noble metals onto less noble metal particles or metal surfaces is emerging as a viable technic ne for creating new catalyst architectures as well as allowing one to introduce single noble metal sites over the surface of a non-noble metal phase. A schematic representation of the spontaneons deposition of a high-valent metal via redox transmetalation is shown in Fig. 6 for a hypothetical non-noble metal phase supported on a condnctive material. 

Figure 6. Schematic metal n deposition onto metal n particles via redox transmetalation.

Preparation of Pt shells on Co cores has also been explored via a redox-transmetalation process, where Pt " in Pt(hfac)2 is reduced to Pt, while surface Co atoms on the Co core are oxidized via migration of the hfac ligand repeated cycles of the reaction are required to generate the Pt shell [43] (hfac = hexafluoroacetylacetonate). 

---