Salt eliminations

Recently the first examples of complexes between the four-membered amidinato-Group 13 metal(l) heterocycles and transition metal fragments were reported. Complexes of the type CpFe(CO)2[M(X) But(NR)2 ] (M = Al, Ga, In X = Cl, Br R = Pri, Gy) were formed in salt-elimination reactions between Na[CpFe(CO)2] and [But(NR)2]MX2. A series of complexes between the four-membered amidinato-Group 13 metal(l) heterocycles and Group 10 metal(O) fragments have been prepared according to Scheme 35. ... 

Group 13/15 heterocycles of the type [R2MER2]x and [RMER ]x containing the lighter elements of group 15, N and P, are usually synthesized by alkane, hydrogen or salt elimination reactions, as can be seen in Scheme 6 [8b, 11],... 

West et al. have recently described the synthesis and reactions of a 1-germaallene. Germaallene 76 (Eq. (7)) is analogous to silaallene 59a and is synthesized by intermolecular addition of f-butyllithium to precursor 75, followed by salt elimination at —78 C. This germaallene is not stable above 0 C in solution, but remains intact until heated above 90°C in the solid state. In either case, the... 

The major synthetic routes to transition metal silyls fall into four main classes (1) salt elimination, (2) the mercurial route, a modification of (1), (3) elimination of a covalent molecule (Hj, HHal, or RjNH), and (4) oxidative addition or elimination. Additionally, (5) there are syntheses from Si—M precursors. Reactions (1), (2), and (4), but not (3), have precedence in C—M chemistry. Insertion reactions of Si(II) species (silylenes) have not yet been used to form Si—M bonds, although work may be stimulated by recent reports of MejSi 147) and FjSi (185). A new development has been the use of a strained silicon heterocycle as starting material (Section II,E,4). 

Salt Elimination-. Reaction of a Transition Metal Anion with a Silicon... 

Salt elimination was used by Piper, Lemal, and Wilkinson 203) to obtain the first compound containing an Si—M bond [Eq. (1)]. The same procedure... 

Salt Elimination Reaction of an Alkali Metal Silyl with a Transition Metal Halide... 

Equations (5)-(8) illustrate the use of this reverse salt elimination procedure. 

Limitations common to both salt elimination methods 1 and 2 are (a) the required product may be difficult to separate from the alkali metal halide, (b) reactions are best carried out in the solvent (usually an ether) in which the initial alkali metal derivative is prepared, (c) difficulties may arise through metal-halogen exchange (207), and (d) the range of starting anions is limited [e.g., X3Si compounds are only readily formed when X = H or Ar,... 

Meat products have to be stabilised in some cases, as meat lipids contain no natural antioxidants or only traces of tocopherols. Most muscle foods contain, however, an efficient multi-component antioxidant defence system based on enzymes, but the balance changes adversely on storage. The denaturation of muscle proteins is the main cause of the inbalance as iron may be released from its complexes, catalysing the lipid oxidation. Salting contributes to the negative effects of storage, as it enhances oxidation. Using encapsulated salt eliminates the deleterious effect of sodium chloride. 

R2Sp=C(SiMej)2 (3a) Salt elimination from R2SiX—C(SiMe3)jLi R = Me, Ph 28-32... 

Salt Elimination Forming R2Si—C(SiMei)(SiRJ)... 

By far the most important reaction is the salt elimination reaction (a). Most of the known monomeric stannylenes have been synthesized via this route which is unaffected by the bulkiness of the substituent. In all cases, tin(II) chloride is taken as the tin component, because it dissolves quite well in ethers. The yields of the stannylenes are relatively high and may attain 95 %. 

In the synthesis of the boron-containing four-membered cycle 26 the reaction is started by a salt elimination of type (a) followed by an intramolecular condensation... 

The preparation of poly(m-carborane-siloxane) polymers has also been successfully achieved directly from the carborane monomer.22 The reaction used is shown in scheme 9. Here, the direct salt elimination reaction between dilithiocarborane and a dichlorosiloxane (e.g., 1,5-dichlorohexamethyltrisiloxane) results in the formation of linear polymers with a molecular-weight (M ) typically of 6800 dalton. However, the reported literature detailing this approach is very limited indeed, and the reaction has not found significant use. This is most probably because only relatively low molecular-weight polymers can be produced, ultimately restricting the flexibility to produce materials of controlled mechanical properties. 

A third way of synthesizing six-membered rings is the intramolecular salt elimination from metallated halofunctional trisiloxanols [10]. 

The lithium as well as the sodium derivative of 1,1,3, 3-tetra-tert-butyl- l-fluoro-3-hydroxydisiloxane should be predestined for the formation of four-membered rings by intramolecular salt elimination. The results of X-ray structural analysis seem to confirm this assumption. Each molecule of the lithiated derivative forms a six-membered ring showing intramolecular LiF-contact three molecules form a trimer, containing a central Li-O six-membered ring with three-coordinated lithium [8]. The sodium analogue of this compound reveals a surprisingly similar structure. 

In contrast, the synthesis of a four-membered (SiOSiN) ring is successful. Starting with an aminosilanol, Si-O-chains containing an amino-group can be synthesized. After metallation and salt elimination the formation of a (SiNSiO) ring occurs [10,11]. The X-ray structure shows a small Si(l)-N-Si(la) angle and therefore large Si-O bonds. 

The temperature at which a cycloaddition reaction of a neopentylsilene takes place (detected by the elimination of LiCl) has turned out to be dependent on the reaction partners added as substrate. This implies that an interaction between the substrate and A or B or the substrate and C occurs somewhere along the reaction pathway depicted above. For the system Cl3SiCH=CH2/LiBut/R2C=NR it was observed that the imine initiates and supports the salt elimination from the species A/B. Based on the knowledge that silenes are stabilized by external donors [1] we conclude that with carbon unsaturated compounds x-donor interactions instead of cr-donor complexes may be possible as well for the lithiated species (D) as for the silene itself (E). 

Dehalogenating reduction Salt elimination Disproportionation Electrochemical formation Dehydrogenative catalytic coupling... 

Reductive dehalogenation cannot be completely controlled, and mostly complicated mixtures were formed which are difficult to separate. Salt elimination opens the possibility of a reaction aimed at polysilane formation. Some examples are shown in Fig. 2. The key compounds are the alkali metal cyclosilanes, which we have isolated via the mercury compounds by the action of sodium/potassium alloy and used for the first time [13]. 

These precursors are generally prepared by alkane elimination (Equation (7a)) or—especially useful with bulkier substituents—the coupling of metal chlorides with lithium pnictides or silyl arsines (Equation (7b)) or salt elimination or silyl halide elimination reactions (Equation (7c)) ... 

Lastly, Livinghouse s approach to the tricyclic core of 4 is highlighted by an acylnitrilium spirocyclization [19d], Exposure of isonitrile 48 to thiophenyl acetyl chloride provides an intermediate chloramine (49) that, in the presence of a silver salt, eliminates the chloride to form a nitrilium ion (R-N = C+-R). The nitrilium is attacked by the nucleophilic aromatic ring to furnish spirocyclic imine 50 in high... 

Scheme 4. Synthesis of ME-heterocycles by standard hydrogen, alkane and salt elimination...

Several general pathways for the synthesis of group 13/15-heterocycles of the type [R2MER 2]X have been developed over the years. The most important are alkane, hydrogen and salt elimination reactions, as summarized in Scheme 4. 

Salt elimination, heterocycles from, 259, 260 Salts, betaine, 49-51, 61-64 Selectivity in oligomerization, 168, 169, 211-215... 

Incorporation of heavier alkali metals into ate complexes is usually disfavored because of the large lattice energies of the simple salt elimination products MX. However, Stephan et al. have reported that reaction of Cp2ZrHCl with KPH(mes ) in the presence of KH gives the... 

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