Cerium complexes carbene

Lithium(l) NHC adducts are extremely rare, but some examples have been isolated as stable crystalline solids when a ftmctional group is involved for their stabilization, the amino group, for instance. Since these showed to be effective in transmetallation processes, they represent an interesting alternative to the expensive silver complexes. As an example, Arnold reported the synthesis of covalently tethered lanthanide carbene complexes (214) using adduct (213) as source ofNHC (equation 39). Using (213) and the same methodology, unusual cerium complexes (215) and (216) were isolated and characterized (equation 40). ... 

The first Ce(IV) complex stabilized by an alkoxo functionalized Ai-heterocyclic carbene anion has recently been reported. The complex is made by oxidation of the corresponding trivalent cerium complex using benzoquinone (Figure 8.36). The cerium cation is coordinated by two bidentate ligands and two monodentate ligands, in which the NHC groups are unbound [123],... 

Figure 4.31 Synthesis of cerium (III) complexes of amino functionalised carbenes.

In the case of using lactones as electrophiles in the presence of cerium trichloride, spiroketals are obtained after acidic work-up (90JA6389). Cyclic Fischer-type chromium carbene complexes (21) have also been prepared when hexacarbonyl chromium was added to intermediates (18), followed by treatment with trimethyloxonium tetrafluoroborate (Scheme 7) (92JCS(CC)1623). 

Cerium salts turned out to be the most active (Ce Cu > Mn > Co > Cr > Mo Fe) in DPC synthesis in CH2CI2 solution using PdCl2, TBAB, HQ, and an ICC [50]. Though the activity of Ce and Cu acetates was comparable (yield 76%, Pd TON 250), cerium cocatalysts delivered better selectivity [50]. In the catalytic system including a Pd carbene complex, a Ce salt, NBu Br, and HQ in CH2CI2, the activity of cerium cocatalysts increased in the order Ce(OAc)g < Ce(trop) <... 

Reaction of chromium carbene complex 170 (Scheme 17.23) with isonitriles led to aminonaphthalene derivatives (e.g., 172) [70]. This transformation was a key step for the total synthesis of the calphostin natural products. The crude aminophenol was treated with cerium(IV) to afford the o-quinone derivative. The photochemical... 

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