ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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 kobs = kHg [Hg2+] with kHg = (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 NO3- occurs in this reaction ([NO3-], 1M, 3%) indicating a path whereby external nucleophiles (Y=NO3-, 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 Kobs = kOH[OH-] with kOH = (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 N3- (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.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19780610624
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