Chloride abstraction

As well as the neutral compounds, also cationic complexes are available from chlorosilyl compounds by chloride abstraction. One example 12 has been characterized by x-ray structure analysis (Fig. 2). 

Ruthenium complexes have also been reported as active species for enan-tioselective Diels-Alder reactions. Faller et al. prepared a catalyst by treatment of (-)-[( ] -cymene)RuCl(L)]SbF6 with AgSbFe resulting in the formation of a dication by chloride abstraction [95]. The ligand was (-l-)-IndaBOx 69 (Scheme 36) and the corresponding complex allowed the condensation of methacrolein with cyclopentadiene in 95% conversion and 91% ee. As another example, Davies [96] prepared the complex [Ru(Fl20)L ( i -mes)] [SbFe]2 (with 70 as L in Scheme 36), and tested its activity in the same reaction leading to the expected product with similar activity and lower enan-tioselectivity (70%). 

Co(Y)CP and Co(HY)Cl react with Fe " " at comparable rates. Comparisons are instructive between this redox reaction and other cation-catalysed chloride-abstraction reactions which occur without simultaneous oxidation-reduction. The intimate mechanisms are likely to be... 

The aforementioned reactive cationic zirconocene species can react with chlorinated solvents by chloride abstraction. However, an even more pronounced property of cationic zirconocenes is their ability to abstract and bind fluoride. Cationic complexes [Cp2ZrMe(thf)]+ are unstable with BF4 and PF6 counterions [14], and the reaction of Cp2ZrCl2 with AgBF4 directly affords Cp2ZrF2 [7]. The use of Cp2ZrCl2/AgC104 as an... 

A mechanism involving the generation of a cationic alk(en)ylzirconocene (I X = R ) through chloride abstraction by silver(I) has been postulated (Scheme 8.22). This cationic intermediate is capable of activating the carbonyl group towards addition (II). Irrespective of whether an alk(en)yl group is added intra- or intermolecularly, a new cationic species is generated (either by R -transfer or Cl-abstraction from III) and the reaction thus proceeds in a zirconium-catalyzed manner [50]. 

A strategy to accelerate p-BL formation was therefore developed, consisting of the synthesis of unsymmetrical tridentate Ci Schiff base) complexes (Fig. 44) that might open a reaction channel for this particular sequence after chloride abstraction with Na[Co(CO)4]. 

Scheme 6.53 Proposed mechanism for the 53-catalyzed asymmetric Pictet-Spengler-type cyclization of P-indolyl ethyl hydroxylactams Hydroxylactam (1) forms chlorolactam (2) followed by chiral N-acyliminium chloride-thiourea complex (3) and the observed product generated by intramolecular cyclization catalysis and enantioinduction result from chloride abstraction and anion binding.

Trust s group has shown that another selective reaction involving C—O bond formation followed by rearrangement and C—C bond formation occurred when Cp-containing ruthenium complexes were used as catalytic precursors. With RuCl(Cp)(PPh3)2 in the presence of NH4PF6, an additive known to facilitate chloride abstraction from the metal center, the addition of allylic alcohols to terminal alkynes afforded unsaturated ketones [46, 47]. It has been shown that the key steps are the... 

Mg+" reacts with alkyl halides in the gas phase via a range of substrate-dependent pathways Not all halides are reactive—examples of unreactive substrates include methyl chloride, vinyl chloride, trichloro and tetrachloro ethylene. Reaction with ethyl chloride proceeds via an elimination reaction (equation 18) followed by a displacement reaction (equation 19). For larger alkyl halides, such as isopropyl chloride, chloride abstraction also occurs (equation 20). For multiply halogenated substrates such as carbon tetrachloride, oxidative reactions occur (equations 21 and 22), although organometallic... 

Birkett and co-workers506 have applied a different approach using chloride abstraction with A1C13 from Ar5C6oCl to generate pentaarylated fullerene cations... 

Subsequent NMR experiments indicate that the monocationic species (24) is formed initially as a donor-acceptor complex and then a second chloride abstraction could provide the dication (25). At temperatures above — 60° C... 

The only targeted preparation of a lA3,2A3-diphosphete complex is based on a thermal-induced chloride abstraction by a transition metal and rearrangement of the isolable intermediate (/ra t-l,2-dichloro-lA3,2A3-diphosphete)Fe2(CO)8 cr-complex lg which leads to the (lA3,2A3-diphosphete)Fe(CO)3 Jt-complex 112 <1999OM2021>. Bis-trimethylsilyl-l,3-diphosphetane-2,4-diyl 6e <1999AGE3028> may be reduced by K or Li to form aromatic 1,3-diphosphetediide salts, for example, 20 (Scheme 36) <2004AGE637, 2004PS779>. 

In the latter, the alkynylation proved to be effective only in the presence of dichlorozirconocene and catalytic amounts of silver triflate, suggesting a complex mechanism in which Ag-Zr transmetallation and chloride abstraction by the added silver triflate occurred (Scheme 10.63).8 Nevertheless, this reaction proved quite general.98... 

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