No abstract

Die Kondensation von (‐)‐L‐N‐Benzoyl‐phenylalanin mit (‐)‐L‐Phenylalaninol in Gegenwart von Dicyclohexylcarbodiimid ergibt Aurantiamid (Ia), das mit Acetanhydrid in Pyridin zu (Ib) acetyliert wird.

The kinetics of formation and dissociation of the binuclear complex of Co H with histidinato(pentaammine)Co nI have been studied at 10.0~176176 and I = 0.3 mol dm-3 (C104)" The formation of the binuclear complex, [(NH3)sCoIIILCoU] 4+ (L = histidinate), in the 5.7-6.8pH range involves the reaction of Co(OH2) 2+ with the deprotonated, (NH3)sCoL 2+, and monoprotonated, (NH3)sCoLH 3 +, forms of the complex. The rate and activation parameters for the formation are consistent with an I a mechanism. The binuclear species undergoes dissociation to yield the parent Co m substrate and Co(OH2) 2+ via spontaneous and acid-catalysed paths. Comparison of spontaneous dissociation rate of the binuclear complex with other related systems indicated the chelate nature of the binuclear species.

The kinetics of reversible complex formation of Ni", Co" and Cu" with the pentaammine-(nitrilotriacetato)cobalt(rll) ion, [Co( NH,),( H,nta)I2+ (H,nta = nitrilotriacetic acid) have been investigated at 0.0025 < [M2+] < 0.04, 0.004 d [H ' 1 < 0.05 mol drn-,, 10.0 < T < 40.0 "C and / = 0.3 mol dm-,. The rate constants for the formation of the binuclear species are at least 10, times less than the water exchange rate constants of [M (OHJ6I2+ under comparable conditions. General base catalysis indicated that proton transfer from the N H + site of the co-ordinated ligand (nta) is involved in the rate determining step. The binuclear species undergo dissociation via spontaneous and acidcatalysed paths. The low values of spontaneous dissociation rate constants also support the chelate nature of the binuclear species. It is likely that the nta moiety of (NH,),Co(nta) acts at least as a tridentate ligand and the chelate ring closure/opening via N-M" bond formationjdissociation is rate limiting. Complex formation with Fe"' and A P has been investigated at 15-35 "C (/ = 1 .O mol drn-,) Supplementar). data available (No. Sup 57104, I 1 pp.): kobs values at different temperatures. See Instructions for Authors,

The reaction of (~fl)-(tetren)CoOH 2+ with $2 O2-in the 7.25-828 pH range at 20-40 ~ yielded S-(yellow) and O-(purple) bonded thiosulfato(tetren)cobalt(III) complexes, the former in larger quantities. The rate determining step is preceded by diffusion-controlled ion-pair [(tetren)CoOH2+,S2 O2 ] formation. Replacement of coordinated OH-by $20 ~ is interpreted in terms of an internal conjugate base mechanism: (tetren)CoOH 2 +~ (tetren-H)CoOH~ +, the reactive amido conjugate base being generated by intramolecular proton transfer from the coordinated NH site.In acid medium the S-bonded (tetren)Co(S203) + is highly stable to redox decomposition, in contrast to its pentaammine analogue. The complex however," undergoes base hydrolysis yielding the corresponding hydroxo complex. The rate and activation parameters for the base hydrolysis have been reported. Photolysis of O-and S-bonded isomers of [(tetrcn)CoS203] + in acidic medium at 254 and 313 nm, respectively, yielded aquation products accompanied by some decomposition of $20 2 -