Mesityl-copper

Finally, some orgatiocopper compounds undergo diarge disproporLionation under die influence of ligands dial bind strongly to copper. Treatment of mesityl-copper witli 1,2-bis-idipbenylpbospbinoJediane iDPPE), for example, results in tlie fotniation of bisimesityljcopper anions and a copper cation to wbidi four pbos-pborus atoms of two DPPE molecules ate coordinated [75]. 

In Hght of the hahde effects, the role of the copper afkoxide and the lithium halide, derived from the transmetaUation, was probed by preparing the copper afkoxide under salt-free conditions (Tab. 10.10) [24, 51, 52]. Initially, mesityl copper, from which the metal hahde salts are removed during preparation [53], was chosen to provide the copper(I) afkoxide. Interestingly, only a trace of product was observed in the absence of hthium... 

For preparation of mesityl copper, see Tsuda, T Yazawa, T Watanabe, K. ... 

Finally some organocopper compounds undergo charge disproportionation under the influence of ligands that bind stron y to copper. Treatment of mesityl-copper with lj2-bis-(diphenylphosphino)ethane (DPPE) for example results in the formation of bis (mesityl) copper anions and a copper cation to whidi four phosphorus atoms of two DPPE molecules are coordinated [75]. 

Organocopper and -silver macrocycles are also known and it would be interesting to check their molecular recognition of anions, if any. Thus, the pentameric (jU-mesityl)copper(I) derivative [21] and the tetrameric (/i-mesityl)silver(I) derivative [22] would be interesting candidates as receptors in host-guest chemistry. 

Finally, selective hydrogenation of the olefinic bond in mesityl oxide is conducted over a fixed-bed catalyst in either the Hquid or vapor phase. In the hquid phase the reaction takes place at 150°C and 0.69 MPa, in the vapor phase the reaction can be conducted at atmospheric pressure and temperatures of 150—170°C. The reaction is highly exothermic and yields 8.37 kJ/mol (65). To prevent temperature mnaways and obtain high selectivity, the conversion per pass is limited in the Hquid phase, and in the vapor phase inert gases often are used to dilute the reactants. The catalysts employed in both vapor- and Hquid-phase processes include nickel (66—76), palladium (77—79), copper (80,81), and rhodium hydride complexes (82). Complete conversion of mesityl oxide can be obtained at selectivities of 95—98%. 

NHC ligands with a pendant group that enforces chelation have also been coordinated to copper centers. The reaction of Cu20 with pyridine fV-functionalized carbene ligand led to the formation of several compounds.91 In the case of mesityl derivatives, a dinuclear complex with a weak metal-metal interaction was isolated 60,91 whereas for the bulkier 2,6-diisopropylphenyl group, a monomeric complex was formed and characterized 61 (Figure 25).91... 

The mesityl diimine 88d was as effective a ligand in the aziridination as the 2,6-dichlorophenyl diimine 88a ( 65% ee vs 66% ee) (61). The bound face of the styrene undergoes aziridination (in contrast with Fu s selective crystallization of the wrong face of styrene in his copper-catalyzed cyclopropanation reaction, cf. Section II.A.8). Unfortunately, the potential racemization of 118 (by the mechanism... 

In the third step, the mesityl oxide is hydrogenated (hydrogen added) to MIBK by heating it to the vapor stage at 300—400°F and passing it over a copper or nickel catalyst at 50-150 psi in the presence of hydrogen. 

Hydroxy-4-methyl-4-penten-2-one (1) was prepared from 3-chloro-mesityl oxide using a modified procedure from the literature [ref.4], A reference sample of 4-methyl-4-penten-2,3-dione (2) was prepared from using the copper acetate method [ref.2], 4-methyl-pentan-2,3-dione (3) was purchased from Wiley Co. 2-Hydroxy-4-methyl-4-penten-3-one (4) was synthesized in 30% yield from 2-propenyl-magnesium bromide and 2-hydroxy-propionitrile in tetrahydrofurane. The structures of all compounds were confirmed by H-. C-NMR- and mass spectroscopy [ref. 5],... 

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