Magnesium derivatives

The reaction of nitrofurazans with IV-magnesium derivatives of amines is a pathway to unsymmetrical azoxyfurazans (Scheme 152). Yields are in the region of 30-50% (92BAU1500, 92IZV1916). 

Addilion of benzophenone to the lithium derivative 2 (M = Li) proceeds in a stereorandom fashion, which is attributed to the participation of radicals, detected by ESR and produced by single-electron transfer (SET)12. The magnesium derivative reacts with 90% diastereoselectivity with no SET being recorded. Benzaldehyde as the carbonyl compound affords the [1/, 1(1S)]-and [15,1(1/ )]-diastereomers in a 70 30 mixture, with 40% de12. Enhanced selectivities are achieved with camphor-derived 2-(2-oxazolyl)isoquinolines12a. 

Organotin enamines can be prepared by treating organotin halides with the lithium or magnesium derivatives of enamines, and also by treating distannazanes with tin enolates (222,223). 

As with the magnesium derivatives, the reaction between Me2Be and Tl[TpBut] is accompanied by the deposition of T1 metal because the decomposition of the by-product [T1R], thereby providing an efficient driving force (53,54). In this regard, it is noteworthy that [TpBut]BeMe was not isolated from the reactions of [TpBut]BeX (X = Cl, Br) with MeLi (52). 

The reactivity of the zinc alkyl derivatives [TpBut]ZnR is typically lower than that of the corresponding magnesium derivatives (Section III,A,2,c.). For example, whereas [TpBut]MgMe undergoes insertion of C02 into the Mg-C bond at room temperature, no reaction is observed between [TpBut]ZnMe and C02 at 140°C. Similarly, whereas the magnesium alkyl derivatives [TpBut]MgR (R = Me, Et, Pr1, Bul) react immediately with 02 at room temperature to give alkylperoxo derivatives [TpBut]MgOOR, solutions of the zinc derivative [TpBut]ZnEt are stable in the presence of 02 at 100°C. 

Early reports document the use of Zn(OR)2 and EtZn(OR), (R = CH2Br, CH2CH2CH = CH2, CH2CH2NEt2)817 for well-controlled polymerizations of CL. Subsequently, the use of zinc(II) lactate and related carboxylates was described.818,819 For simple magnesium derivatives, low activities and epimerization are generally observed.820 In more recent years, research in this field has been directed towards the development of single-site initiators. 

The only other known transition metal terphenyl derivative is the blue, crystalline cobalt species Co(ju.-Br)C6H3-2,6-Mes2(THF) 239 (Fig. 12). It is isostructural to the corresponding magnesium derivative discussed earlier. It was synthesized via the reaction of CoCl2 with the Grignard reagent,... 

The successful utilization of alkoxo Zn- and Mg-tris(pyrazolyl) borate initiators in the lactide polymerization inspired the synthesis of sterically bulky B-diketiminates (BDls) (Fig. 5) and their zinc and magnesium derivatives [60-62]. Replacing the ancillary ligands resulted in the production of several mono- and dinuclear complexes of Mg" and Zn" 24-39 (Fig. 6), which demonstrated excellent catalytic activity for the polymerization of l- and rac-lactide [62-66]. 

Magnesium derivatives are less common than with pyridine, although... 

The potentially bidentate a-(2-pyridyl)-a,a-bis(trimethylsilyl)methyl monoanionic ligand also has been used in a variety of organometallic derivatives. Its magnesium derivative bis[a-(2-pyridyl)-a,a-bis(trimethylsilyl)methyl]magnesium (70) has been structurally characterized by X-ray crystallography (Figure 41) ° . 

Reaction of aLkyknagnesium reagents with sterically hindered amines leads to the formation of magnesium amides 110-112 °, reacting much faster than the parent alkyl-magnesium derivatives with C—H acidic substrates (Scheme 9). 

---