Complexation reactions metal exchange

Reductive lithiation of allyl phenyl sulfides.1 This reagent is particularly useful for preparation of allyllithium reagents at temperatures at which the anions are stable. Moreover, regioselectivity in reactions can be achieved by conversion to allyltitanium(IV) complexes by metal exchange with Ti(0-/-Pr)4. Thus the un-symmetrical anion formed from the allyl sulfide 1 with LDMAN reacts with cro-tonaldehyde to give a mixture of 1,2- and 1,4-adducts. The 1,2-adduct 2 can be obtained in high yield as two diastereomers (9 1) by use of the allyltitanium complex (equation I). 

This square planar zinc complex is an excellent intermediate for the preparation of other BZO4 [16] octaene N4 complexes by metal exchange, and its use alleviates the problem of separating the desired complex from other reaction side products when o-aminobenzaldehyde is condensed in the presence of the appropriate metal ion. Complexes of nickel, cobalt, iron, and palladium have been prepared from this zinc compound. 

Intramolecular zinc-ene reaction. Metal exchange of a 7r-allylpalladium complex to form a cr-bonded organozinc species permits ene reaction with a proximal alkene unit. The cyclic product can be functionalized. 

A transmetalation of the styrylcarbene chromium complex 62 in the presence of stoichiometric amounts of [Ni(cod)2] to give the nickel carbene intermediate 63 was applied to the synthesis of Cr(CO)3-coordinated cycloheptatriene 64 upon reaction with terminal alkynes [57] (Scheme 37). The formation of pen-tacarbonyl(acetonitrile)chromium is expected to facilitate the metal exchange. 

Yields in the above reactions can often be improved by the addition of 1 mole of triphenylphosphine directly to the trifluoroacetic acid solution of the reactants immediately before final work-up. It would appear that the triphenylphosphine functions as a scavenger for TTFA released in the metal-metal exchange reaction, thus protecting the final phenol from further electrophilic thallation and/or oxidation. Validation of the metal-metal exchange mechanism was obtained indirectly by isolation and characterization of an ArTlX2/LTTFA complex directly from the reaction mixture. NMR analysis revealed that this complex still possessed an intact aryl-thallium bond, indicating that it was probably the precursor to the transmetallation products, an aryllead tristrifluoroacetate and TTFA. 

This reaction has been observed for porphyrins, and used to establish relative stabilities.51,53 It is of practical use in the preparation of metal complexes, e.g., metallophthalocyanines by metal exchange with dilithium(I) phthalocyanine.54... 

Dissociation of a ligand from a complex may be spontaneous, acid-catalyzed, or consequent on the addition of an appropriate metal ion or ligand. Metal exchange, viz. ML+M ->M L+M, involves either dissociation of a complex (ML M+L) followed by formation of a new complex (M +L M L), or reaction through a... 

Materials such as humates, fulvates, and melanins are related to, or contain, peptide or protein molecules or moieties. Kinetic patterns for their interactions with metal ions may be complicated by the probability that more than one complex species will be involved. Thus it has been demonstrated that Ni2+-fulvate solutions contain at least four kinetically distinct species, i.e. Ni2+aq and three complexes, as indicated in reactions of such solutions with for example par (514). Moreover in a metal-exchange reaction the metal ions M and M may complex at some... 

The surface characteristics of kaolinite was discussed in Chapter 3.4 and in Fig. 3.9. While the siloxane layer may - to a limited extent - participate in ion exchange reactions. The functional OH-groups at the gibbsite and edge surfaces are able to surface complex heavy metal ions. (Schindler et al., 1987). 

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