Metal dialkylamides reactions

Although cyclometallation reactions have seldom been observed with d° metal compounds, intramolecular metallation involving early transition metal dialkylamides with formation of azametallacyclopropane, which occurs by /3 H abstraction, has been reported.281... 

The insertion of carbon dioxide into a transition metal-oxygen bond, e.g., a metal alkoxide, results in an organic carbonate ester, coordinated in either a monodentate or bidentate manner. Only a limited number of such reactions have been observed, and little mechanistic information is available. The reactions may proceed by interaction of C02 with ROH or RO in solution followed by metal coordination, in a manner similar to the C02 reactions with the early transition metal dialkylamides. Alternatively, direct attack of C02 on the alkoxide oxygen might occur, or a C02 adduct may form as an intermediate. 

By Reactions of Metal Dialkylamides with Alcohols and Phenols 339... 

Carbamate complexes are synthesized by carbonation of metal dialkylamides (equation 20), or by reaction of the appropriate amine, carbon dioxide, and a metal halide (equation 21). In both cases, it has been suggested that the reaction involves combination of the amine and carbon dioxide to form the carbamate anion, followed by anion exchange. ... 

E. Reactions of Metal Dialkylamides and Bis(trimethylsilyl)amides with... 

During the period 1965-1975 the chemistry of the 1,2-dithiolene complexes of the transition metals was the subject of considerable study. However, during this period of great activity few complexes of the early transition metals were reported aside from those of vanadium. The problem had much to do with synthetic procedures, since reaction of, say, the anhydrous metal chlorides with the dithiolene or its sodium salt did not prove successful. However, the use of metal dialkylamides did result in clean reactions (e.g. equation 21). 

Other electrophilic heterocumulenes (e.g., CS2, RNCO, RNCS, SO2) are also subject to insertion reactions. Accordingly, the insertion of CS2 into the M-N bond in metal dialkylamides produces dithiocarbamate derivatives and the reaction of SO2 with M-C bonds gives sulfinate complexes resulting from either 1,1-insertion [M-0S(0)R] or 1,2-insertion [M-S(R)02]. Rare examples of insertion of dioxygen into Pt-H bonds to generate remarkably stable hydroperoxide derivatives L Pt-OOH have also been reported. 

In addition to the above, alcoholysis or transesterification reactions of metal alkoxides themselves have been widely used for obtaining the targeted homo- and heteroleptic alkoxide derivatives of the same metal. Since the 1960s, the replacement reactions of metal dialkylamides with alcohols has provided a highly convenient and versatile route (Section 2.9) for the synthesis of homoleptic alkoxides of a number of metals, particularly in their lower valency states. 

Reactions of Metal Dialkylamides M(NR2)x (R = Me, Et, SiMes) with Alcohols (Method I)... 

The homoleptic metal dialkylamides are an important class of compounds in inorganic chemistry. They are typically synthesized by treatment of the corresponding halide with lithium or sodium dialkylamide. Although involving an extra synthetic step, there are numerous examples where metal dialkylamide intermediates are useful in the synthesis of metal aryloxide compounds. The reaction normally involves the simple addition of the parent phenol to the metal dialkylamide in a nonprotic, typically hydrocarbon, solvent (Eqs 6.36, 6.37, and 6.38 ). 

Acylation. Aliphatic amine oxides react with acylating agents such as acetic anhydride and acetyl chloride to form either A[,A/-diaLkylamides and aldehyde (34), the Polonovski reaction, or an ester, depending upon the polarity of the solvent used (35,36). Along with a polar mechanism (37), a metal-complex-induced mechanism involving a free-radical intermediate has been proposed. 

Dialkylamino derivatives of elements located in the periodic table to the left or below those listed above cannot be prepared by the above method due to either the ionic character of some of the inorganic halides or the formation of stable metal halide-amine addition products. Therefore, other methods must be applied. Dialkylamino derivatives of tin7 and antimony8 are conveniently obtained by reaction of the corresponding halides with lithium dialkylamides. Others, such as the dialkylamino derivatives of aluminum,9 are made by the interaction of the hydride with dialkylamines. Dialkylamino derivatives of beryllium10 or lithium11 result from the reaction of the respective alkyl derivative with a dialkylamine. 

Zirconium and hafnium dialkylamides are highly reactive compounds. They undergo (i) protolytic substitution reactions with reagents such as alcohols, cyclopentadiene and bisftrimethylsilyOamine 63 64 (ii) insertion reactions with C02, CS2, COS, nitriles, phenyl isocyanate, methyl isothiocyanate, carbodiimides and dimethyl acetylenedicarboxylate 69-72 and (iii) addition reactions with metal carbonyls.73 These reactions are summarized with reference to Zr(NMe2)4 in Scheme 1. 

Relatively little mechanistic work has been reported on the insertion reactions of C02. The mechanism seems to be established only for the insertion of C02 into the dialkylamides of the early transition metals (131). We will speculate on probable mechanisms for the various types of insertion reactions that follow. Future work will undoubtedly shed more light on these processes, leading to a better understanding of the reaction, and enabling a more rational design of catalyst complexes in order to incorporate the insertion process into an efficient catalytic cycle. 

The attempted amine exchange reaction to prepare metal amides can be complicated if primary amines are used. Hence, titanium dialkylamides will react with many primary amines to produce polymeric materials (equation 38).66... 

The main idea of these techniques lies in the interaction of the active hydrogen atom of the alcohols with the anions of metal hydrides, alkyls, acetylides, nitrides, amides, dialkylamides, bis(trialkylsilyl)amides, sulfides, etc., with formation of compounds where an H atom is bonded by a strong covalent bond (usually gaseous HX). Alkaline hydrides of the most active metals (K, Rb, Cs) are used to slow down the reaction of metal with alcohol sometimes it is necessary simply to avoid explosion. 

This reaction type, known as directed ortho metalation reaction, requires strong bases, normally an alkyllithium reagent (most lithium dialkylamides are of insufficient kinetic basicity). Alkyllithium bases show high solubility in organic solvents due to association into aggregates of defined structure, typically as hexamers in hydrocarbon solvents e. g. hexane or tetramers-dimers in polar solvents e. g. THF (see Chapter 5). 

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