Ligand effect, deprotonated

The simplest such ligand-directed labilization is deprotonation of a hydration water (ti -OH2) to form a hydroxyl (ri -OH sites) in a dissolved monomer. This deprotonation is effectively a ligand substitution because an equilibrium concentration of such hydroxyl ligands is maintained dynamically by rapid proton exchange with the solvent. It is distinct from other substitutions, however, because no metal-oxygen bond is broken. The rates of exchange of protons are so fast that the waters convert to hydroxyls virtually instantaneously. 

The ligand effects in the formation of tertiary carbanions from substituted tertiary aromatic amides have been investigated." Reaction of 2-isopropyl-(iVA -diisopropyl)-benzamide (10) with f-BuLi in ether resulted in ortho deprotonation and the formation of a hemisolvate based on a tetranuclear dimer of (10-Li )2 Et2O (Scheme 7). Reaction of (10) with f-BuLi in the presence of the tridentate Lewis base NjNjN pentamethyldiethylenetriamine (PMDTA) or tridentate diglyme (DOME) takes a different course (Scheme 7). The soUd-state structures revealed a dimer core in which the amide oxygen atoms fail to stabilize the metal ions for the former case and a remarkable benzylic deprotonation giving the tertiary benzyllithium (lO-Li )-PMDTA for the latter. 

The intermolecular a-arylation of amides with aryl chlorides was unknown until very recently. Fortunately, the work developed by Walsh and coworkers [93] has demystified the theme. Aryl chlorides are generally less reactive than aryl bromides in oxidative additions nonetheless, aryl chlorides are less expensive and more readily accessible when compared with aryl bromides, making their use in cross-coupling reactions highly desirable. Walsh and coworkers reported the first deprotonative cross-coupling process for the intermolecular arylation of amides with aryl chlorides. Buchwald-type [94] precatalysts formed with Kwong s [95] indole-based phosphane ligand effectively catalyzes the... 

Comman CR, Zovinka EP, Boyajian YD, Geiser-Bush KM, Boyle PD, Singh P. 1995. Structural and EPR studies of vanadium complexes of deprotonated amide ligands effects on the V-51 hyperfine coupling constant. Inorg Chem 34 4213-4219. 

The analogous dimerization of alkynes over Fe(C0)5 is not applicable, so clearly a different route towards alkynylated derivatives of 25 was needed. Comparison of 25 to cymantrene suggests that metallation of the hydrocarbon ligand should be the route of choice for the synthesis of novel substituted cyclobutadienes. In the literature, addition of organolithium bases (MeLi, BuLi) to the CO ligands with concomitant rearrangement had been observed [25]. But the utilization of LiTMP (lithium tetramethylpiperidide, Hafner [26]) or sec-BuLi as effectively non-nucleophilic bases led to clean deprotonation of the cyclobuta-... 

An alternative route for stabilization of quinone methides by metal coordination involves deprotonation of a ri5-coordinated oxo-dienyl ligand. This approach was introduced by Amouri and coworkers, who showed that treatment of the [Cp Ir(oxo-ri5-dienyl)]+ B1, 22 with a base (i-BuOK was the most effective) resulted in formation of stable Cp Ir(r 4-o-QM) complexes 23 (Scheme 3.14).25 Using the same approach, a series of r 4-o-QM complexes of rhodium was prepared (Scheme 3.14)26 Structural data of these complexes and a comparison of their reactivity indicated that the o-QM ligand is more stabilized by iridium than by rhodium. 

Chelating ligands for magnesium were expected to influence the relative rate of deprotonation and addition [19], TMEDA gave a modest improvement in the reaction affording a 92 8 ratio of 3 61 under the best conditions. N,N -Dimethylimidazolidinone was not as effective in suppressing the formation of 61. No reaction was observed in DME, even on heating to 50°C. 

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