Competition studies and stereochemistry of base hydrolysis of (dimethyl sulfoxide)- and (trimethyl phosphate)amminebis(ethylenediamine)cobalt(III) ions

The preparation, properties, and base hydrolysis of (+)589-[Co(en)2NH3(Me2SO)](C104)2(N03) (1) and (+)5g9-[Co-(en)2NH3(TMP)](C104)3(2) (Me2SO = dimethyl sulfoxide; TMP = trimethyl phosphate) are reported; fc0H(l) = 2.35 X 102 and k0H(2) = 2.5 x 103 mol dm3 s1 in 1.0 mol dm3 NaC104 at 25C. Base hydrolysis of 1 involves 100% Co-0 bond breaking, and Cl2 oxidation gives 100% optical retention in the (+)589-[Co(en)2NH3(OH2)]3+ product. Base hydrolysis of (+)589-[Co(en)2NH3X]2+,3+ (X = Br, Me2SO, TMP) gives 77% trans and 23% cis hydroxo products, but the retention in the cis ion varies with X (78% (Br), 83.5% (Me2SO), 85% (TMP)); these ratios are independent of both the electrolyte (NaN3, NaC104) and its concentration (0-2 mol dm3). The relative amounts of cis-and irani-[Co(en)2NH3N3]2+ formed in the presence of N3 are independent of N3 concentration (66% cis, 34% trans), but the retention in the cis azide also depends on X (73.5% (Br), 83% (Me2SO), 85% (TMP)); marginally more (3%) azide products are formed for X = Me2SO and TMP than for X = Br. The results are interpreted in terms of an ion-pairing mechanism for base hydrolysis. © 1979, American Chemical Society. All rights reserved.