Schlenk reagents

The study of the Schlenk equilibrium for organozinc compounds represents a major chapter in the understanding of these reagents in general [26]. Before elaborating the studies on zinc carbenoids, it is appropriate to briefly review the definitive investigations on organozinc halides themselves. 

By reaction of zinc-copper couple with diiodomethane 2 an organozinc species 4 is formed, similar to a Grignard reagent. Its structure cannot be fully described by a single structural formula. The actual structure depends on the reaction conditions—e.g. the solvent used this corresponds to the Schlenk equilibrium as it is observed with the Grignard reaction ... 

Boiling-point elevation and freezing-point depression measurements have demonstrated that at all concentrations in THF and at low concentrations in ether (up to 0.1M) Grignard reagents prepared from alkyl bromides and iodides are monomeric, that is, there are few or no molecules with two magnesium atoms. Thus, part of the Schlenk equilibrium is operating... 

However, Grignard reagents prepared from alkyl bromides or iodides in ether at higher concentrations (0.5-1 M) contain dimers, trimers, and higher polymers, and those prepared from alkyl chlorides in ether at all concentrations are dimeric, so that 24 is in solution, probably in equilibrium with RMgX and R2Mg that is, the complete Schlenk equilibrium seems to be present. 

Reagents and diy solvents were purchased from Aldrich or VWR and used without further treatment. Synthetic preparation of the complexes was done using standard Schlenk techniques (diy aigon) unless otherwise stated. Standard rathenium(ll) precursors were prepared as described in the literature or via internal routes. 

As noted, sol-gel syntheses for materials based on water-sensitive reagents, such as titanium isoproproxide, must be carried out under low pH20 conditions, which are typically achieved using either an inert atmosphere box (glove box) or under laboratory conditions using a Schlenk-line.73 The Schlenk-line, shown in Fig. 2.4,71 consists of a dual manifold arrangement with one line... 

Sixty years ago, organic chemists were struggling with the preparation and observation of properties of organolithiums today, metallation chemistry is routinely executed on gram and multi-ton scale. Since chemists are recognized for their intense level of curiosity and pride in experimental achievement, the real or apparent intricacies associated with the preparation and use of Zr and Ti reagents that appear to be bizarre, unavailable, and/or relegated to the Schlenk tube will be overcome. May this volume be a hallmark in this quest. 

The following operations are all carried out under oxygen-free nitrogen using standard Schlenk techniques.9,10 Solvents and liquid reagents are degassed before use. 

On a different note, Schlenk s work on alkylmetals, e.g. alkyllithiums, was deemed interesting, but these reagents were judged not to become of any greater use ( ) in the service of organic synthetic chemistry because of the extreme difficulty in handling them. 

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