Arenes orthometallation

An orthometallation procedure for the preparation of condensed iso-thiazolium salts from appropriately substituted arenes has been described earlier in this Section (Scheme 117)180 an example illustrating the way in which this approach can be elaborated to the synthesis of condensed 1,2-dithiolylium perchlorates is given in Scheme 123. 

Good yields of l-arylaminoquinolin-2-ones are obtained when the azo-arene complexes 116 are treated with hexafluorobut-2-yne (Scheme 141).214 This procedure is particularly novel in the chemistry of orthometallated complexes in that the primary organometallic products (117) arise from the formal insertion of a three carbon unit [CO + C2(CF3)2] into the aryl-cobalt bond of 116. A wider study of the scope of this type of process using a variety of orthometallated complexes would be desirable. 

Several chapters deal with the synthesis of and the synthetic applications of organolithium compounds such as orthometallation, arene catalysed lithiation, addition to carbon-carbon double bonds, their reaction with oxiranes, and asymmetric deprotonation with lithium (-)-sparteine. We gratefully acknowledge the contributions of ah the authors of these chapters. 

Orthometallation of substituted arenes has been re-viewed. The ortho-directing ability of substituents in ( ) -arene)Cr(CO)3 complexes decreases as F > CONHR > NHCOR > CH2NR2 OMe CH20Me. Heavier alkali metal arenes can be formed from the reaction of phenyl lithium with sodium or potassium aUcoxides. 

A number of research groups have developed rhodium-catalyzed methods for the C-H bond arylation of arenes that likely proceed through cyclometalated intermediates. Aryl phosphites and phosphinites undergo facile orthometalation... 

An efficient catalyst for the hydrogenation of polycyclic arenes, such as anthracene, is derived from an anionic orthometallated hydride ruthen-ate complex that, according to equation (24), reacts with hydrogen to jdeld /ac-[RuH3(PPh3)3], followed by the reaction with anthracene to yield... 

In their paper describing the direct hydroxylation of arene sp C—H bonds with a ruthenium catalyst, Rao and co-workers demonstrated that a simple thiophene was also compatible with these reaction conditions (Scheme 10.21). It is proposed that under acidic conditions, [RuCl2(p-cymene)]2 facilitates C—H bond cleavage of 67 via an orthometalation process throngh chelation with the ester carbonyl group (kinetic isotope experiments also support a kinetically relevant C—H metalation step). Snbseqnent reductive elimination afforded the hydroxylated thiophene 68 in 41% yield. 

---