Heterobimetallic reagents

A novel and highly efficient synthesis of 1,1-diiodo-, 1,1-dibromo-, and mixed (Z)- or ( )-1-iodo-l-bromo-l-alkenes using the 1,1-heterobimetallic reagents obtained by hydrozirconation of stannylacetylenes has also been described [155], The hydrozirconation and halo-genolysis steps were carried out at room temperature in THF under a nitrogen atmosphere. It is noteworthy that the developed route is compatible with various functionalities... 

Some other sp3 organogembismetallic compounds were reported as the synthesis of 1,3 dizinc derivatives using the boron-zinc exchange24 (Protocol 11), or the synthesis of l,n-heterobimetallic reagents.25 In the latter case, the reactivity of these derivatives is mainly the same as that of the monometallic compound. 

Heterobimetallic reagents. Reagents of this type can be prepared from primary l,n-diiodoalkanes by reaction with zinc (2 equiv.) followed by transmetalation with CuCN 2LiCI (1 equiv.). When separated by 4-6 CH2 groups, these reagents undergo... 

The second part of the chapter deals with several kinds of asymmetric reactions catalyzed by unique heterobimetallic complexes. These reagents are lanthanoid-alkali metal hybrids which form BINOL derivative complexes (LnMB, where Ln = lanthanoid, M = alkali metal, and B = BINOL derivative). These complexes efficiently promote asymmetric aldol-type reactions as well as asymmetric hydrophosphonylations of aldehydes (catalyzed by LnLB, where L = lithium), asymmetric Michael reactions (catalyzed by LnSB, where S = sodium), and asymmetric hydrophosphonylations of imines (catalyzed by LnPB, where P = potassium) to give the corresponding desired products in up to 98% ee. Spectroscopic analysis and computer simulations of these asymmetric reactions have revealed the synergistic cooperation of the two different metals in the complexes. These complexes are believed to function as both Brpnsted bases and as Lewis acids may prove to be applicable to a variety of new asymmetric catalytic reactions.1,2... 

Although heterobimetallic complexes with alkylated rare-earth metal centers were proposed to promote 1,3-diene polymerization via an allyl insertion mechanism, details of the polymerization mechanism and of the structure of the catalytically active center(s) are rare [58,83,118-125]. Moreover, until now, the interaction of the cationizing chloride-donating reagent with alkylated rare-earth metal centers is not well-understood. Lanthanide carboxylate complexes, which are used in the industrial-scale polymerization of butadiene and isoprene, are generally derived from octanoic, versatic, and... 

Scheme 24 Formation of a structurally characterized heterobimetallic Nd(III)/A1 complex from Nd(Oi-Pr)3 and alkylaluminum reagents. Three different types of metal environments are realized for six structurally independent neodymium cations Ndl-Nd6 [170]...

Aryloxide (phenolate) ligands provide rigid and versatile ancillary ligand sets in order to study the multifunctional reactivity of alkylaluminum and alkylmagnesium reagents toward Ln-OR moieties. Several types of symmetrically substituted phenolate ligands — summarized in Chart 4 — were employed for the synthesis of a variety of heterobimetallic lanthanide(III) and lanthanide(II) metal complexes. Alkylation reactions revealed the preferred... 

Lanthanide(III) complexes demand special attention in view of the specific spectra-structure relationship for biological applications, chiral catalysis, molecular magnetism and luminescence. One unique chiral stereochemistry is realized by the combination of labile Ln complexes and weak Na+-fluorocarbon interactionwhich show intense CD (circular dichroism) with variation of Ln(III) and/or M(I) ions to chiroptical spectra-structure relations and an important role in configurational chirality for chemical sensors, NMR shift reagents or chiral catalysis. Trivalent lanthanides are also found to be incorporated into heterobimetallic complexes showing intramolecular energy transfer processes. 

The nature of the reagents is crucial to formation of the heterobimetallic complex, as shown in the following reactions ... 

---