Die Kinetik der Spaltung dinuklearer Tri‐μ‐hydroxo‐kobalt(III)‐Komplexe N3Co(Oh)3CoN33+ (triole) mit Säure

Abstract

AbstractThe kinetics of formation of dinuclear di‐μ‐hydroxo‐diaquo‐bis‐cobalt(III) complexes from the corresponding tri‐μ‐hydroxo complexes: equation image has been investigated with three different compounds to start with: Ammonia‐Triol [N3 = (NH3)3], Dien‐Triol [N3 = H2N—CH2—CH2—NH—CH2—CH2—NH2] and Tach‐Triol [N3 = C6H9(NH2)3 = cis‐cis‐1,3,5‐triaminocyclohexane]. With respect to the otherwise very inert cobalt(III)‐complexes, reaction (1) is unusually rapid and takes place in two steps, the first being about 100 times faster than the second. The process begins with an exceptionally slow proton transfer to one of the bridging OH with half life of 0,2, 0,03 and 0,025 sec. respectively (perchlorate medium μ 1 M, 20°, pH = 0). The rate of the back reaction could also be determined, yielding ratios of the two rate constants corresponding to pK‐values between 0 and 1,5. Whereas Tach‐Triol is protonated to the di‐μ‐hydroxo‐μ‐aquo complex at about pH 1, it is deprotonated to the di‐μ‐hydroxo‐μ‐oxo complex at about pH 14 (Siroky [16]). The second step of (1), the aquation of the di‐μ‐hydroxo‐μ‐aquo species to the di‐μ‐hydroxo‐diaquo complex (Diol) takes place with half lives between 4 and 9 sec.The final cleavage to the mononuclear triaquo complex needs many hours to go half way and is again initiated by protonation of one of the remaining two OH‐bridges. Neither the μ‐aquo complex produced thereby, nor the Mono‐ol [mono‐μ‐hydroxo‐tetraaquo complex] formed as an intermediate cause any observable changes of the spectrum. The Mono‐ol aquates at a rate which is inverse in [H+] because of the labilisation brought about by deprotonation of its aquo ligands.