Arenes with active hydrogen

Substituting deuterium for hydrogen gas in the reduction of BT to DHBT with the catalyst precursor [Rh(NCMe)3(Cp )](BF4)2 has shown that the stereoselective ds-deuteration of the double bond is kinetically controlled by the tj2-C,C coordination of BT. The incorporation of deuterium in the 2- and 3-positions of unreacted substrate and in the 7-position of DHBT has been interpreted in terms of reversible double-bond reduction and arene-ring activation, respectively (Scheme 16.14) [55]. 

The publication (70) in 1976 of the preparation of optically active epoxyketones via asymmetric catalysis marked the start of an increasingly popular field of study. When chalcones were treated with 30% hydrogen peroxide under (basic) phase-transfer conditions and the benzylammonium salt of quinine was used as the phase-transfer catalyst, the epoxyketones were produced with e.e. s up to 55%. Up to that time no optically active chalcone epoxides were known, while the importance of epoxides (arene oxides) in metabolic processes had just been discovered (71). The nonasymmetric reaction itself, known as the Weitz-Scheffer reaction under homogeneous conditions, has been reviewed by Berti (70). 

The earliest catalytic application of C-H bond activation and functionalisation is that of methane using platinum chlorides as the catalyst and oxidising reagent. The exchange of hydrogen atoms in arenes with D20 was... 

This chapter covers reactions in which coordination of a transition metal to the ir-system of an arene ring activates the ring toward addition of nucleophiles, to give V-cyclohexadienyl-metal complexes (1 Scheme 1). If an electronegative atom is present in the ipso position, elimination of that atom (X in 1) leads to nucleophilic aromatic substitution (path a). Reaction of the intermediate with an electrophile (E+) can give disubstituted 1,3-cyclohexadiene derivatives (path b). If a hydrogen occupies the ipso posi-... 

The possibility of coordination of a two-electron ligand, in addition to arene, to the ruthenium or osmium atom provides a route to mixed metal or cluster compounds. Cocondensation of arene with ruthenium or osmium vapors has recently allowed access to new types of arene metal complexes and clusters. In addition, arene ruthenium and osmium appear to be useful and specific catalyst precursors, apart from classic hydrogenation, for carbon-hydrogen bond activation and activation of alkynes such compounds may become valuable reagents for organic syntheses. 

Treatment of [(arene)OsCl2]2 with lithium amide in THF results in the formation of imidoosmium complexes in high yield, which react with a with wide variety of active hydrogen compounds and polar compounds (Scheme 10.28) [253]. 

There are two directions in the development of supramolecular catalytic compositions, that is, (1) creation of systans based on macrocyclic compounds as host molecules that bind substrates with their hydrophobic cavity and (2) development of the systems that bind substrates using aggregates formed by am-phiphihc compounds. Compounds that form host-guest complexes like modified cahxarenes are able to aid transport of substrates into the aqueous phase. This approach has been implemented in the Wacker oxidation [40,41], oxidation of alkylaromatic compounds [42], hydroxylation of aromatic compounds [43], hydrogenation [44,45], hydroformylation [45-48], and carbonylation [49]. In this case, the substrate is transported into the aqueous phase in the form of the corresponding inclusion complex. This not only affects the activity of the catalyst, but also provides selectivity of the process. Thus, in the Wacker oxidation of 1-alkenes the maximum yield of methyl ketone was achieved when 1-hexene is used, and for systems based on calix[6]arene with 1-octene among catalytic systems with modified calix[4]arenes [50]. 

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