On the mechanism of the Hg2+ and base induced hydrolysis reactions of the β2-(RR,SS)-Co (trien) (glyOR)Cl2+ions (R = H,C2H5), evidence for the site of deprotonation in the reactive conjugate base

Acid hydrolysis of the ester function in Δ-(?)₅₈₉-β₂-(RR)-Co (trien) (glyOEt) Cl]²⁺ ((?)- 1 ) produces optically pure Δ-(?)₅₈₉-(RR)-Co (trien) (glyOH)Cl]²⁺ ((?)- 4 ). Hg²⁺ induced removal of chloride in (?)- 4 follows the rate law k_obs = k_Hg Hg²⁺] with k_Hg = (1.36 ± 0.03) × 10^?2 M^?1s^?1, 25°, μ=1.0, and produces optically pure Δ-(?)₅₈₉-β₂-(RR)-Co(trien) (glyO)]²⁺ ((?)- 2 ). Competition by NO occurs in this reaction (NO], 1M, 3%) indicating a path whereby external nucleophiles (Y?NO, H₂O) compete with the intramolecular carboxylate function for an intermediate of reduced coordination number. Rapid ring closure to 2 must ensue for Y ? H₂O. Base hydrolysis of chloride in (±)- 1 produces (±)- 2 together with its diastereoisomer β₂-(RS, SR)-Co(trien) (glyO)]²⁺, ((±)- 3 ), in which one secondary amine function has an inverted configuration. 2 and 3 incorporate ¹⁸O-labelled solvent into the Co-O position of the coordinated carboxylate moiety ( 2: 9.0%; 3: 12.3%) indicating that at least part of the product arises via intramolecular hydrolysis in β₂-hydroxo ethylglycinate intermediates (Fig. 4). Base hydrolysis of (?)- 4 follows the rate law K_obs = k_OHOH^?] with k_OH = (6.3 ± 0.6) × 10^?4M^?1 S^?1, 25°, μ = 1.0 producing (?)- 2 (37-45%) and (?)- 3 (63-55%), the ratio being somewhat medium dependent. Competition by added N (1M) occurs using (±) - 4 forming β₂-(RR, SS)-Co (trien) (glyO)N₃]⁺ (～2%) and β₂-(RS, SR)-Co (trien) (glyO)N₃]⁺ (～ 13%). Mutarotation at the secondary nitrogen centre is shown to occur after the rate determining loss of Cl^? in 1 and 4 and before the formation of 2 and 3 . It is concluded that this secondary nitrogen is the site of deprotonation in the reactive conjugate bases of 1 and 4 , and possible mechanisms for the mutarotation process are considered.