MECHANISM AND STERIC COURSE OF OCTAHEDRAL AQUATION .12. KINETICS AND STERIC COURSE OF AQUATION OF SOME OSOMERS OF DICHLORO(1,4,8,11-TETRAAZAUNDECANE)COBALT(3) CATION

The kinetics and steric course of the aquations of the isomeric trans-(RR,SS)-Co(2,3,2-tet)Cl2+ and trans-(RS)-Co(2,3,2-tet)Cl2+ (2,3,2-tet = 1,4,8,11-tetraazaundecane; R and S refer to the chirality of the coordinated secondary nitrogens) in dilute acid are reported. The more labile (RR, SS) isomer (k25 = 2.9 × 10-4 sec-1, ∆H≠ = 25.9 kcal mol-1, ∆S≠ = 12 cal deg-1 mol-1) initially forms a mixture of trans- and β-cis-(RR,SS)-Co(2,3,2-tet)H2OCl2+ containing 50 ± 20% of the unstable trans isomer which then rapidly changes to the β-cis form. The trans-(RS)-Co(2,3,2-tet)Cl2+ cation (fes= 1.5 × 10-5 sec-1, ∆H≠ = 24.3 kcal mol-1, ∆S≠ = 1 cal deg-1 mol-1) aquates with complete retention of configuration. The mercuric ion catalyzed aquation of the trans-(RR,SS)-dichloro isomer yields initially 30 ± 5% trans- and 70 ± 5% β-cischloroaquo complex, whereas the analogous reaction of the trans-(RS) isomer yields 100% trans product. A cis-dichloro isomer (presumed to be β-cis-(RR-SS)-dichloro) aquates with complete retention of configuration (k25 = 1.1 × 10-3 sec1 ∆H≠ = 22.3 kcal mol-1, ∆S≠ = 2 cal deg-1 mol-1). The β-cis-(RR,SS)-chloroaquo complex undergoes chloride anation in hydrochloric acid to give only the trans-(RR,SS)-dichloro complex, but in less acid solution it isomerizes at a rate inversely proportional to [H+], to the more stable trans-(RS) form. These reactions are discussed in connection with those of analogous complexes of the cyclic 1,4,8,11-tetraazacyclotetradecane (cyclam) and 1,4,7,10-tetraazadecane (trien). A dissociative mechanism is assigned in all cases and some conclusions are drawn concerning the nature of the five-coordinate intermediate. © 1969, American Chemical Society. All rights reserved.