Reaction example using lithium chemistry

The first example is a reaction which used lithium chemistry (Scheme 1). 

The chemistry of cyclopropenyl ions is dominated by reactions which lead to cyclopropenes, usually either by reduction or by their reactions with nucleophiles. For example, triphenylcyclopropenyl cations, as well as some other derivatives, can be reduced in good yield to the corresponding cyclopropene using lithium aluminum hydride (equation 11)27,28 however, diphenylcyclopropene which is produced in the analogous reduction of... 

Reaction with organo-lithium compounds works well with all three examples one molecule of formaldehyde is lost but a CH2OH group is retained in the products 56, 57, and 58 from addition of vinyl, phenyl, and butyl lithium. This chemistry was used to make bertyodionol.7... 

Compare your results to the experimental values of -34.0 2 kcal mol for the lithium reaction and -3.6 .5 kcal mol" for the water dimer reaction. Use the same model chemistry as in Example 8.2 B3LYP/6-311+G(2df,2p) // B3LYP/6-31G(d). 

An example where the presence of a counterion makes a difference between the gas phase and solution phase pathways involves the intriguing carbanion produced on deprotonation of 1,3-dithiane at C-2. In solution, this species, almost invariably produced by reaction of the dithiane with butyllithium, is widely used as an acyl anion equivalent in synthetic chemistry. Its importance for the present work is that this is a configurationally stable lithiated species in solution the carbanion stays sp -hybridized, and the lithium prefers the equatorial position, even to the extent of driving a terr-butyl group on the same acidic C-2 carbanion to the axial position in the lithiocarbon species. The carbanion is thought to be stabilized primarily by orbital overlap with the C-S antibonding orbitals, as opposed to more conventional polar and 7t-resonance stabilization. ... 

In reactions requiring palladium 0), formation of the active complex may be achieved more conveniently by reduction of a palladium(ll) complex, for example, Pd 0Ac)2- Any phdsphine may then be used in the reaction, without the need to synthesize and isolate the corresponding palladium 0)-phosphine complex. Only 2-3 equivalents of phosphine may be needed, making the palladium(O) complex coordinatively unsaturated and therefore very reactive. The reduction of palladium li)to palladium(o) can be achieved with amines, phosphines, alkenes, and organometailics such as DIBAL-H, butyl lithium, or trialkyl aluminium. The mechanisms are worth giving as they illustrate the basic steps of organometallic chemistry. 

Iodine — Iodine, L, is a halogen which occurs naturally mainly as iodide, I- [i]. Iodine (Greek ioeides for colored violet ) is a black solid with a melting point of 113.6 °C which is readily undergoing sublimation to form a violet gas. Iodine occurs in the oxidation states -1,0, +1, +3, +5, +7 and it possesses a rich redox chemistry [ii]. In aqueous solution the formation of I2 from I- occurs with a standard potential of 0.621V vs. SHE and this oxidation process is preceded by the formation of I3 with a standard potential of 0.536 V vs. SHE. For the reaction I2(cryst) + 2e - 21 E = 0.535 V. The I—/I3 redox couple is employed, for example, in solar cells [iii] and in long-lived lithium-iodine battery systems. The oxidation of I2 in organic solvents results formally in I+ intermediates which is a powerful oxidant and useful, for example, in electro-synthetic chemical processes [ii]. 

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