Salt-elimination reactions

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],... 

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

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

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 %. 

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. 

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. 

The clusters described so far have in common, that the number of metal atoms is less or equal than the number of substituents. However, there is a still growing number of both neutral and anionic clusters in which the number of metal atoms is larger than the number of substituents. As a consequence, these metal-rich clusters contain naked metal centers which are only bonded to other metal centers. Schnockel referred these ones to as metalloid clusters. Several metalloid A1 and Ga clusters were prepared by standard salt elimination reactions using metastable solutions of metal subhalides MX (M = Al, Ga X = Cl, Br) as well as solutions of Gal. Since the metal subhalides were found to play the key role for the successful synthesis of this particular class of compounds, they will be discussed first. (For excellent review articles see Refs 273 and 274.)... 

Salt elimination reactions proved to be very effective for the synthesis of closo-heteroborates with the heavy elements of this group. Todd and co-workers prepared for the first time the lead, tin and germanium cluster dianions [EBnHn]2 as shown in Scheme 3.3-5 [17]. 

Apart from incorporation of a silicon vertex into the decaborane skeleton by salt elimination reactions, the controlled nucleophilic degradation of the disilaborane Me2Si2BioHio with NaOH is another versatile method for the preparation of the nido-silaborate, [MeSiBioHi2], which is depicted in Scheme 3.3-9 [29]. 

The synthesis of heterocyclic group 13/15 compounds of the type [R2MER 2]jc has been investigated for many years [21]. General synthetic pathways such as dihydrogen, alkane and salt elimination reactions as summarized in Scheme 3... 

A fascinating feature of the chemistry of boron-phosphorus heterocycles is the existence of stable singlet biradicals, e.g. fBuBP Pr2)2 (for a discussion of the electronic structure, see Section 5.4.2.2). The synthesis of this four-membered ring is illustrated in Scheme 5.2. Related derivatives of the type (RBPR 2)2 are also prepared by a salt-elimination reaction of the appropriate lithium phosphide with a 1,2-dichlorodiborane or, in the case of the perphenylated derivative (PhBPPh2)2, by reduction of the cyclic dimer [Ph(Cl)BPPh2]2 with lithium naphthalenide (Scheme 9.11). ... 

As an alternative to the hydrocarbon-elimination method, salt-elimination reactions involving an organometallic halide, which can be generated in situ, and an alkali-metal pnictide have also been used (Scheme 9.15a). The elimination of a volatile triorganosilyl halide is viable in cases where the steric bulk... 

A different class of four-membered Su2P2 ring 10.39 is obtained as orange-red crystals from the salt-elimination reaction of potassium di-tert-butyl phosphide with the triethylphosphine adduct of tin(II) dichloride [eqn (10.27)] the dimeric structure was deduced from multinuclear NMR spectra and solution molecular weight measurements. The Sn NMR spectrum exhibits a doublet-of-triplets... 

The simple, salt elimination reaction of Equation (8.1) has been employed for amides of all the group 13 metals. In addition, it is currently the only well-established route to M(I) metal amides where M = Ga or Tl. The alkane elimination route of eqn. (8.2) is generally employed only for M = Al or Ga. This synthetic approach is also used for the metal imides (RMNR )n where a primary amine H2NR is the reactant. The use of metal hydrides, of which Equation (8.3) is but one example, is limited mainly to aluminium and, to a lesser extent, gallium because of the decreased stability of the heavier metal hydrides. 

The aluminium is coordinated by three silylamido nitrogens in an essentially trigonal planar fashion ( °A1 = 359.7(3)) with coordination by the amine nitrogen in an axial position. The Al—N(amido) bond lengths average 1.809(3) A and the axial Al—N(amine) distance is 1.983(6) A The related podand derivatives [ HC(SiMe2NR)3 Al thf] (R CHsPh or C6H4Me-4 2), synthesized by salt elimination reactions, were reported recently. 

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