Anionic bromide complexes

Fig. 11 Fragment of the crystal structures of tetracyanobenzene/bromide complex showing different modes of anion coordination to the acceptor moieties (coordinates from [24])...

In a similar manner, the diffusion of hexane into dichloromethane solutions containing mixtures of the alkylammonium salts of bromide and the olefinic acceptors o-CA and TCNE result in the formation of brown-red crystals [23]. X-ray analysis reveals the (1 1) complex of bromide with o-CA, in which the anion is located over the center of the C - C bond of the acceptor moiety (Fig. 15b) and Br - C contacts are shortened by as much as 0.6 A relative to the sum of van der Waals radii (Table 3). In bromide complexes with TCNE, the location of the anion relative to the acceptor is variable. In fact, a 2 1 complex [(Br )2,TCNE] is isolated in which both anions reside over the olefinic bond when the tetraethylammonium salt of bromide is used. In comparison, if the tetrapropyl- or tetrabutylammonium salts of the same anion are employed, the (1 1) complexes [Br ,TCNE] are formed in which the bromide donors are shifted toward the cyano substituents (Fig. 15a). In both cases however, the short intermolecular separations that are characteris-... 

The crystal structure of the bromide complex of [78] has been elucidated and clearly shows bromide anions hydrogen-bonded to the amide N—H groups and, interestingly, also to the cyclopentadienyl hydrogen atoms (Fig. 40). 

The formation of the heterocycle 1 from the xylylene-bis-phosphonium salt 2 and PCI3 proceeds via a detectable intermediate 3 in a cascade of condensation reactions that is terminated by spontaneous heterolysis of the last remaining P-Cl bond in a cyclic bis-ylide-substituted chlorophosphine formed (Scheme 1) [15]. The reaction scheme is applicable to an arsenic analogue of 1 [15] and to bis-phosphonio-benzophospholides with different triaryl-, aryl-alkyl- and aryl-vinyl-phosphonio groups [16, 18, 19], but failed for trialkylphosphonio-substituted cations here, insufficient acidity prohibited obviously quantitative deprotonation of the phosphonium salts, and only mixtures of products with unreacted starting materials were obtained [19]. The cations were isolated as chloride or bromide salts, but conversion of the anions by complexation with Lewis-acids or metathesis was easily feasible [16, 18, 19] and even salts with organometallic anions ([Co(CO)4] , [CpM(CO)3] (M=Mo, W) were accessible [20]. 

The [4+1] annulation of 1-azadienes to pyrroles can also be achieved through their carbonyl iron complexes (Scheme 6). Novel complex (1,4-diphenyl-2-methyl-l-azabutadiene)tricarbonyliron (0) 24 was obtained in 40% yield from the corresponding azadiene 23 and Fe2(CO)9 then nucleophilic attack by methyl lithium and quenching with tert-butyl bromide, as the proton source, gave 2,5-dimethyl-l,3-diphenylpyrrole 26 in 70% yield, probably through the anionic intermediate complex 25 [88TL1425 90JCS(P1)761]. 

Alternatively, a more nucleophilic anionic reagent can be generated by selective cleavage of a single trimethylsilyl group with methyl lithium-lithium bromide complex. This 1ithiobutadlyne derivative will react with electrophiles such as carbonyl compounds or primary alkyl iodides. 2... 

Shur, V. B., Tikhonova, I. A., Yanovsky, A. I., et al, Compounds for anions - unusual complex of trimeric perfluoro-o-phenylenemercury with the bromide anion having a polydecker sandwich structure. J Organomet. Chem. 1991, 418, C29-C32. 

The electrochemical technique gave the possibility of obtain the to-acetonitrilc adduct of the tetrachlorides and bromides, except in those cases where gram quantities of tetra-ethylammonium halide were present when the appropriate anionic halogen complexes were obtained. Thionyl chloride proved to be the most satisfactory solvent for the preparation of the anionic chlorocomplexes. 

Unlike the interaction of bis(halodiphenylstannyl)alkanes with halide ions which lead to anionic 1 1 adducts with bridged halogen238,269, 119Sn NMR spectroscopy indicates the formation of five-coordinate dinuclear 1 2 chloride and bromide complexes 67a-d, and 68a,b, respectively, from the reactions between X3Sn(CH2)nSnX3 (X = Cl, Br n = 1, 3, 4, 8) and halide ions in CHCI3 solution (equation 13)296. 

This is a direct SN2 displacement of a bromide anion by a phenyl anion. Please note that the negative charge of the phenyl anion is accompanied by a magnesium bromide complex. This class of organic salt is known as a Grignard reagent and is characterized by the presence of magnesium and a halide such as chloride, bromide, or iodide. 

An anionic tin complex, five-coordinated tin enolate, is formed by the coordination of bromide anion from tetrabutylammonium bromide (Bu4NBr) to a neutral four-coordinated tin(iv) enolates (Equation (75)). 

The poorly characterized i(dddt)21 Ag,Brv product, which probably is a polymeric silver bromide containing species, behaves like a metal down to 4.3 K (167). The Pd analogue, [Pd(dddt)2]Ag1 54Br3 50, is metallic down to 1.3 K (169). Its crystal structure consists of layers of [Pd(dddt)2] moieties alternating with layers of silver bromide complex anions. A noticeable feature lies in the existence of a uniform stacking of Pd(dddt)2 in the conduction layers, instead of the stacking of dyads usually encountered in Pd complexes (9, 160, 175-177). Several other dddt Pd compounds exhibiting metal-like properties have been reported but poorly characterized (see Table III). 

Synthesis of unsubstituted mercuracarborands, as illustrated in Scheme 1, is a two-step process involving deprotonation of the acidic CH vertices of 1,2-carborane 7 followed by treatment with the appropriate mercury salt <1994JA7142, 1997ACR267>. Thus, -butyllithium efficiently deprotonates 1,2-carborane 7 giving doso-X.Z-VXz-1,2-C2BioHio 8, the pivotal intermediate. If treated with mercury acetate, neutral trimer 5 is formed. Using mercury chloride or bromide, however, leads to the formation of tetramer 9 and 10, respectively, as 1 1 anion-host complexes. 

The electron-releasing phosphine promotes oxidative addition of the bromo derivative to Pd(0) and, because of its bulkiness, readily generates free coordination sites by dissociation. Ethylene coordination and insertion then occur, followed by reductive elimination, triethylamine acting as a base to neutralize hydrogen bromide. As in most cases of transition metal-catalyzed reactions the fine details of the mechanism are still under investigation. Thus recent studies by Amatore s group suggest that the palladium(O) species formed by reduction of palladium acetate is an anionic acetato complex. 

The trivalent actinides and lanthanides form only weak chloride complexes in aqueous solution. Although the trivalent actinides are absorbed moderately strongly by anion exchange resins from concentrated LiCl, the MX2 complex appears to be the highest complex present to a measurable extent in the aqueous chloride solutions (2). The bromide complexes appear to be even weaker (3). The only other evidence for anionic trivalent actinide chloro or bromo complexes has been in the system of UCI3 in fused CsCl (4). Ryan and J0rgensen have recently prepared the trivalent lanthanide hexachloro and hexabromo complexes and studied their absorption spectra (8). 

Figure 3. Crystal structure of receptor 36 with bound bromide ions. [Reprinted from J. Organo-mel. Chem.. 418. C29. V. B. Shur, A. Tikhonova. A. I. Yanovsky, Y. T. Struchkov, P. V. Petrovskii, S. Y. Panov. G. G. Furin, and M. H. Vol pin. Crown compounds for anions. Unusual complex of tremeric perfluoro-o-phenylene mercury with the bromide anion having a polydecker sandwich structure C29, 1991, with kind permission of Elsevier Science SA, Lausanne, Switzerland.]...

The first step involves formation of an anionic acyl complex, which then undergoes intramolecular SN2 displacement of bromide to yield 23. 

Numerous elements form multicharged anionic complexes which are able to associate with hydrophobic basic dyes. They include anions of the heteropoly acids of Si, Ge, P(V), and As(V), the bromide complexes of Bi and Te(IV), and the thiocyanate complexes of Mo and W. Flotation of sparingly soluble ion-associates formed between the multicharged anionic complexes (with halides, SnC, and thiocyanate) of the platinum-group metals and... 

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