INTRA-MOLECULAR HYDROLYSIS OF GLYCINAMIDE AND GLYCINE DIPEPTIDES COORDINATED TO COBALT(III) .1. HG2+, HOCL, AND BASE HYDROLYSIS OF CIS-[CO(EN)2BR(GLYNHR)]2+ (R=H, CH2CO2C3H7, CH2CO2-) AND PROPERTIES OF CIS-[CO(EN)2(OH2-OH)(GLYNHR)]3+/2+ AND TRANS-[CO(EN)2(OH2-OH)(GLYNHR)]3+/2+ IONS

The Hg2+-catalyzed removal of Br from cis-[Co(en)2Br(glyNHR)]2+ results in the immediate formation of [Co(en)2-(glyNHR)]3+ containing the chelated amide or dipeptide residue; full retention of configuration about the Co(III) center obtains and no intermediate aqua complex is formed. HOCl-catalyzed oxidation of cis-[Co(en)2Br(glyglyOC3H7)]2+ results in the formation of some cis-[Co(en)2(OH2)(glyglyOC3H7)]3+ as well as [Co(en)2(glyglyOC3H7)]3+, both with full retention of the configuration about the metal. Base hydrolysis (pH 9-14) results in the formation of some trans-[Co(en)2-(OH)(glyNHR)]2+ (~6.2%) as well as cis-[Co(en)2(OH)(glyNHR)]2+ (R=H, 34% d, 20% DL; R=CH2C02C3H7, 44% D, 19% DL; R=CH2CO2-, 70% d + DL + trans) and [Co(en)2(glyNHR)]3+ (R=H, 20% D, 20% DL; R=CH2CO2C3H7, 20% D, 10% DL; R=CH2CO2-, 30% D + DL). The trans-[CO(en)2(OH2/OH)(glyNHR)]3+/2+ ions cyclize to [Co-(en)2(glyNHR)]3+ according to the rate expression R=KH20[[Co(en)2(OH2)(glyNHR)]3+] + (kOH + k'OH[OH-]. [[Co(en)2(OH)(glyNHR)]2+] where kH2O=4 (±2) X 10-6 s-1, kOH=2.8 (±0.1) × 10-4 s-1, and k'OH=5.6 × 10-2 M-1 s-1 for R=H at 25 °C and µ=1.0 (NaC104); this process occurs directly and not via the monodentate cis-aqua or -hydroxo ions. The cis-[Co(en)2(OH)(glyNHR)]2+ ions cyclize to [Co(en)2(glyO)]2+ and [Co(en)2(glyNHR)]3+ via a mechanism involving retention of the coordinated hydroxo oxygen atom. In acid solution the cis-[Co(en)2(OH2)(glyNHR)]3+ ion also forms [Co(en)2(glyO)]2+ and [Co(en)2(glyNHR)]3+, but only the former retains the oxygen atom of the coordinated water molecule. © 1979, American Chemical Society. All rights reserved.