Hydroxyl amido complexes

D.v.a. Formation of C—N Bonds. Though Pd-catalyzed amination— the Hartwig-Buchwald reaction—is normally performed in anhydrous media in the presence of strong bases, no steps of the mechanism of this reaction strictly require the absence of water. Moreover, it has been shown that amido complexes of Pd, the key intermediates of this reaction, can easily form by ligand exchange of water or hydroxyl (Scheme 56). ... 

The crystal structure of the complex formed between carboxypeptidase Aa (abbreviated CPA) and glycyltyrosine (Gly-Tyr) has been refined to 2.0 A by Lipscomb et at. (444, 445) and it reveals (Fig. 90) interactions between the amide carbonyl oxygen and the catalytically essential Zn, and between the amide nitrogen and the hydroxyl of tyrosine-248 (Tyr-248). Scott et al. (443) synthesized both the [13C]amido (90% enriched) and amido[l3C, 15N]amido (90% and 99% enriched, respectively) isotopomers of Gly-Tyr. They then proceeded to probe the hydrolysis by a series of l3C and l5N high-resolution solid-state NMR spectra. 

X-ray structures have been worked out for the benzeneboronic and 2-phenyl-ethaneboronic acid (PEBA) complexes of subtilisin [9] and for the PEBA complex of a-chymotrypsin (a-CHT) dimer [10]. Further stabilization of the hydroxyls on boron is gained by hydrogen bonding to other amido groups lining the oxyanion hole. 

Rh(NH3)5(OH2)] and HC2O4 and C20, but not with oxalic acid. However, the rate of formation of [Rh(NH3)sC204H] is similar for each of these oxalate species so an mechanism is probable. Base hydrolysis of trans-[Rh(en)2X2] (X = Cl, Br, or I) follows both hydroxyl dependent and independent pathways. For X = Q or Br, complete trans to cis isomerization occurs and the final product is trans-[Rh(en)2(OH)2], but this isomerization only occurs to 50% for the di-iodo-complex. An S lcb mechanism can cause rearrangement once the ligand trans to an amido-group is dissociated a trigonal-bipyramidal intermediate is formed. 

Complexes of the type [Ir(bzn)(cod)(L)](C104) (bzn = benzonitrile L = tricyclohexylphosphine, neomenthyldiphenylphosphine) catalyze the homogeneous hydrogenation of tetrasubstituted prochiral amido alkenes R R C=CR N. Under very mild conditions, the catalysis occurs for N = NHCOR, R = COjMe R = R = Me, R" = Me, Ph R = Me, R- = Ph, R = Me, Ph R = Ph, R = Me, R = Ph. [Ir(cod)(PCy3)(py)](PFg) serves as a catalyst in the hydroxyl-directed hydrogenation of cyclic and acyclic alkenic alcohols, wherein the reaction shows diastereoselectivity dependent on catalyst substrate stoichiometry. Park el have noted that the iridium(I)... 

Every molecule contains several amido and hydroxyl groups and therefore every ultramicroscopic complex must contain many more. For the sake of simplicity let us consider onty one of these groups. 

Among the biopolymers worked with for adsorption of metal ions, cellulose, chitin and the derivatives of chitin have played significant role in their capacity as adsorbent and complexing agent by virtue of their hydroxyl, acetate, amido and amino groups. 

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