Organometallic reagents low-valent

The mechanistic data on the N-arylations are separated into data on reactions of hypervalent organometallic reagents, reactions of low-valent organometallic reagents, reactions of low-valent organometallic reagents with a co-oxidant, that are catalytic in copper, and reactions of aryl halides (I, Br, Cl). 

Mechanism of the reactions with low-valent organometallic reagents... 

In the past few years, the application of low-valent organometallic reagents to carbohydrate chemistry has attracted much interest largely due to the mild reaction conditions required and the excellent diastereoselectivities obtained due to the control of the process through chelation to proximal hydroxyl, amino, and keto substituents [14],... 

Huffman MA, Liebeskind LS, Pennington WT (1992) Reaction of cyclobutenones with low-valent metal reagents to form.eta.4- and.eta.2-vinylketene complexes. Reaction ofeta.4-vinylketene complexes with alkynes to form phenols. Organometallics ll(l) 255-266. doi 10.1021/om00037a047... 

Metal-promoted reductive p-elimination reactions in 1,2-difunctionalized substrates have been one of the most important means of generating C=KZ bonds [9]. In the past few years, a number of reductive elimination reactions of 1,2-difunctionalized compounds have been reported under various organometallic reagents, such as Sml2 [10], Zn [11], or In [12], In addition, those low-valent organometallic species exhibit excellent properties for sequential organic reactions and several examples have been described in which a metal-promoted ehmination reaction occurs as a step of a sequential process [13],... 

In principle, organometallic complexes are also highly interesting candidates for efficient HAT reagents. This is because M-H bonds are usually much weaker than C-H bonds [14-16]. Also, it has been established for a number of cases that HAT from organometallic complexes can be very fast. Still, the rates of the processes can be modulated by the introduction of steric bulk around the metal center. Moreover, low valent hydrido metal complexes can also act as chain carrying reagents because... 

The most important organometallic reagents used for the carbon-carbon bond formation in carotenoid synthesis are the metal acetylides, metal alkenyls and the Gngnard reagents. However the Reformatsky reaction has also been applied and recently also transition metals such as Pd, Ni, Cu and especially low valent Ti have been used. The application of organometallic reactions for the synthesis of carotenoids and retinoids has recently been reviewed [39]. 

Another possible synthetic route to introduce ligands into an organometallic complex is the reaction of one of its low-valent species with radicals. Thus, an O- or N-centered radical is reduced to a monoanionic ligand while the metal center is oxidized. However, some apphcations of the radical-like properties of titanium(III) species are known in the literature. In that way, the free radical-like properties of CpTi Cb derivatives are observed in reactions, for example, with quinones [36] as well as with azo and diazo compounds [32], whereas the intermediately generated Cp2Ti Cl reagent is well introduced in organic reactions [37]. 

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