Amides, Alkoxides and Thiolates

Compounds U(NR2)j and U(OR)j have been synthesized in oxidation states +3 to +6 (though the hexavalent amides are not well characterized). A limited number of thiolates U(SR)4 are also known. These largely molecular species occupy a borderline between classical coordination chemistry and organometallic chemistry. 

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Monomeric amide, alkoxide and thiolate derivatives of germanium(II), tin(II) and lead(II) are only obtained with very sterically crowded ligands. Thus, bis(2,2,6,6-... 

Detailed reviews on the structures of organomagnesium compounds and the constitution of their solutions have been published [D, 1, 2]. These references, especially the first two, also cover alkylmagnesium hydrides, amides, alkoxides and thiolates. However, while all of these compounds are of intrinsic interest, they are little used in synthesis. 

Pyrazine is more reactive than pyridine towards nucleophiles. Although the Chichibabin amination is unsatisfactory, substitution of the halogen in 2-halopyrazine occurs readily by ammonia, amines, amide, cyanide, alkoxide and thiolate. 

During the cross-couplings to form C—N, C—O, C—S, and C—P bonds, the arylpalladium halide complexes are converted to arylpalladium amide, alkoxide, thiolate, and phosphide complexes. Examples of each type of complex have now been isolated, and the reductive elimination of the organic products has been studied. Although the reductive elimination to form carbon-hydrogen and carbon-carbon bonds is common, reductive elimination to form carbon-heteroatom bonds has been studied only recently. This reductive elimination chemistry has been reviewed.23... 

Alcohols and thiols also react rapidly with most amides to give alkoxide or thiolate ligands with liberation of amine. Steric factors can be sufficiently important to limit this exchange (e.g. equation 66) and in some instances redox reactions may occur (equation 67).212 Salt formation is also possible in some cases (equation 68).213... 

Such a charge transfer from the ligated arene can lead to (a) nucleophilic addition or substitution, (b) electron transfer, and (c) proton elimination/transfer, thus revealing the dose relationship between all of these processes. The reactivity of the arene ligands towards nudeophiles in (arene)ML complexes depends on the electrophilidty of the metal fragments [MLn], this increasing in the order [Cr(CO)3] < [Mo(CO)3] [FeCp]+ < [Mn(CO)3]+ [2]. For example, in (arene)FeCp+, which is widely used for synthetic purposes, a chloro or nitro substituent on the arene is readily substituted by such nudeophiles as amides, eno-lates, thiolates, alkoxides, and carbanions [45]. 

These are formed mainly between metal atoms in d3-cP dinuclear complexes for which perhaps the most important group comprises the ethane-like X3M=MX3 (Dm) compounds, where X = alkyl, amide, alkoxide, thiolate, selenate, and mixtures thereof.115 The synthetic entry into these compounds involves principally the reactions of M2(NMe2)6, as shown in Fig. 18-C-20, and these in turn are made by metathetic reactions involving either MoC13 or WCL, and LiNMe2. 

M. N. Bochkarev, L.N. Zakharov and G.S. Kalinina, Organoderivatives of Rare Earth Elements, Kluwer, Dordrecht, 1995 (amides, alkoxides, thiolates). 

One of the main interests in indium amides has been their potential utility as single-source precursors for indium nitride materials. They also serve as starting materials in the synthesis of various other indium compounds. For instance, amides such as In(NEt2)3 and In[N(SiMe3)t-Bu]3 react with alcohols or thiols to produce indium(III) alkoxides or thiolates, respectively. 

Reductive elimination is the product-forming step in some of the most important catalytic cycles, including hydrogenation, the Monsanto acetic acid process, and various types of cross-couplings. For this reason, detailed studies of this process have been conducted. Hrese studies have revealed examples of reductive eliminations to form H-H and C-H bonds, as well as reductive eliminations to form C-G and C-X bonds (in which X = halide, amide, alkoxide, thiolate, and phosphide). The mechanisms of these processes include the same pathways as have been deduced for oxidative addition (i.e., concerted, ionic, and radical), because reductive elimination is the same as oxidative addition, but in the reverse direction. 

Although in principle any base can be made to induce an E2 reaction under appropriate experimental conditions, chemists commonly employ particularly strong bases such as hydroxide, alkoxides, and amide anions (NR ). These bases have conjugate acids with above 11. When we use other bases whose conjugate acid p. s are near or below 11 (e.g., carboxylates, thiolates, and cyanide, the intention is to effect a substitution reaction via using these reactants as nucleophiles. Therefore, one simplifying aspect of the competition between substitution and elimination is to consider an E2 pathway only when hydroxide, alkoxides, acetylides, and amide anions are used. 

Each and every arrow must start at an electron source and end at an electron sink. Therefore, before analyzing electron-flow procedures, a list of common electron sources and sinks is useful. Table A5.1 shows several electron sources and sinks. The sources are listed first. They often consist of lone pairs of electrons on heteroatoms, and the atoms can be either negative or neutral. The neutrals include, but are not limited to, alcohols, water, amines, and thiols. The anionic examples include, but are not limited to, alkoxides, amide anions, hydroxide, and thiolates. In all of these examples the lone pairs of electrons are the actual electron source, not the entire chemical structure itself. 

Many other lanthanide-based initiators have been shown to polymerize MMA, including lanthanocene amides,464 168 alkoxides,469 substituted indenyl and fluorenyl bivalent ytterbocenes,470,471 hexamethylphosphoric triamide thiolates,472 and allyl, azaallyl, and diazapentadienyl complexes.473... 

The Michael addition followed by Intramolecular Ring Closure (MIRC) reactions have been recognized as a general synthetic approach to carbocyclic three-membered ring derivatives [1]. The enhanced Michael reactivity of methyl 2-chloro-2-cyclopropylideneacetate (1-Me) towards thiolates, alkoxides, lithiated amides and cyclohexadienolates (see below) allows one to perform highly efficient assemblies of spiropentane, tricyclo [3.2.1.0 ]octane, bicyclo [2.2.2] octane... 

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