N,O-chelates

A variety of N-O-chelated glycine amide and peptide complexes of the type [CoN4(GlyNR R2)]3+ have been prepared and their rates of base hydrolysis studied.169 The kinetics are consistent with Scheme 8. Attack of solvent hydroxide occurs at the carbonyl carbon of the chelated amide or peptide. Amide deprotonation gives an unreactive complex. Rate constants kOH are summarized in Table 16. Direct activation of the carbonyl group by cobalt(III) leads to rate accelerations of ca. 104-106-fold. More recent investigations160-161 have dealt with... 

A numerous series of compounds containing a N,O-chelating ligand, namely the derivatives of anthranilic (157) and 3-amino-2-thiophenecarboxylic (158 and 159) acids, were prepared by the reactions of organohalogermanes with esters, amides or lithium derivatives of acids510-516. 

Peacock AFA, Parsons S, Sadler PJ (2007) Tuning the hydrolytic aqueous chemistry of osmium arene complexes with N,O-chelating ligands to achieve cancer cell cytotoxicity. J Am Chem Soc 129 3348-3357... 

It has long been known that the products of the reaction of cisplatin (1) with glycinate are the chloride salt of 9, ds-[Pt(NH3)2(gly-A/,(9)]Cl, and, with excess glycinate, m-Pt(NH3)2(gly-A02 (13) [6] [7]. Pivcova etal. [8] [9] have shown that these products are obtained when 1 reacts with glycine under physiological conditions. The crystal structure of the N, O-chelate complex 9 has been determined [10]. 

C104) crystallizes in 96% yield in a second-order asymmetric manner. The solution actually contains the equilibrium mixture A(jR) A(jR) = 7 3.1036 Both Co2, and OH- effect rapid mutarota-tion about the metal in this complex but not about the chiral carbon. With (S)-penicillamine a similar equilibrium obtains (A A[Co (S)pen (en)2]2+ = 7 3) but preferential crystallization does not occur.1037 X-Ray structures confirm equatorial and axial dangling carboxylate functions in A-[Co (R)cys (en)2](C104) and A-[Co (7 )cy s (en)2 ] (C104) H2 O respectively.1037 (N,S) bonding seems to be preferred in (N,S,0) systems (cysteine, penicillamine) but (N,0)[Co (R)cys (en)2]2+ has been prepared by reduction of the tridentate sulfenamide complex (285 equation 159).1038 This (N.O) chelate lacks the extended charge transfer absorptions in the near UV characteristic of thiolate coordination. 

Schiff-bases derived from substituted sali-cylaldehydes, 40, are very versatile ligands which form (N- O) chelates with many metals copper, nickel, palladium, vanadium and iron. 

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