1,4,7-Triazacyclononane cobalt complexes

The medium-ring cyclic triamines, 1,4,7-triazacyclononane (tacn), 1,4,7-triazacyclodecane (tacd), 1,4,8-triazacycloundecane (tacud), and 1,5,9-triaza-cyclododecane (tacdd) have been synthesized and the cobalt complexes [Co(tacn)2]Br3, [Co(tacd)2]Br3,H20 and [Co(tacud)BrCl2] isolated. It has been suggested that the structures are of the sandwich type [viz. (95) and (96) "] and, for this reason, the reporter looks forward to publication of X-ray structural analyses. 

A cooperative effect of two mononuclear complexes has been observed in the hydrolysis of phosphate mono- or diesters, the reaction order being then two with respect to the metal (343-348). Hydrolysis of methyl para-nitrophenylphosphate diester doubly coordinated to a di-nuclear cobalt(III) complex was reported, and a crystalline compound of dimethylphosphate coordinated to the same cobalt complex was characterized [Co2 (l,4,7-triazacyclononane)2 (0H)2 02P(0CH3)2 ] ... 

The CD spectra of bis[(R)-2-methyl-l,4,7-triazacyclononane]cobalt(III), [Co(R-metacn)2], were studied by Mason and Peacock For this complex, five... 

Cobalt complexes have been also extensively studied as artificial hydrogenases for the reductive side of water splitting.It has been recently demonstrated that the cobalt(ii) complex of the pentadentate ligand l,4-di(picolyl)-7-(p-toluenesulfonyl)-l,4,7-triazacyclononane (iy2T stacn) displays excellent H2 photoproduction catalytic activity, in the presence of [Ir(ppy)2(bpy)]PF6 as photosensitiser, and EtgN as electron donor. Under the same conditions, the corresponding complex of nick-el(ii) presents low photochemical activity, while the iron(n) analogue is inactive. 

Heterostannenes, preparation and characteristics, 3, 870 Heterosubstituted arenes, metallation, 9, 17 Hexaaryldiplumbanes, preparation, 3, 887 Hexabutyldistannane, preparation, 3, 856 Hexacarbenes, in cobalt(III) complexes, 7, 19 Hexacarbonyl complexes, with molybdenum kinetics and reactivity, 5, 395 photochemistry, 5, 393 solid-support studies, 5, 394 spectroscopic and theoretical studies, 5, 392 Hexadentate iV-substituted triazacyclononane, synthetic applications, 1, 70... 

Another way of bringing reactants into close proximity, which is encountered commonly in transition metal chemistry, is through metal ion complexation. The coordination of a reactant to a metal ion complex often activates its reactivity and can bring the reactant into close proximity with a second reactant or with a catalytic group. One example, shown in Fig. 6, is a zinc (11) complex of 1,5,9-triazacyclononane, as a model for the enzyme carbonic anhydrase, which contains a zinc (11) cofactor in its active site (4). In the aqua complex, the bound water molecule has a dramatically reduced pKa value of 7.3, which is similar to the pKa of the active site nucleophihc water. The corresponding cobalt (111) complex catalyzed ester hydrolysis at twice the rate because Co(lll) can coordinate both the hydroxide nucleophile and the ester carbonyl via a... 

The first [M Dm3(ttnFe)2](C104)2 complexes of this type were obtained [79] by the interaction of iron(II) acetate and copper, zinc, nickel, cobalt, and manganese acetates with dimethylglyoxime and 1,4,7-trimethyl-1,4,7-triazacyclononane ttn) in methanol in the presence of triethylamine (Reaction 20). In this case, a triazamacrocycle served as the protecting group in the octahedral capping nFe "03 fragment. 

Fe- and Co-complexes of pyridines and triazacyclononane as synthetic analogs of cysteinate-ligated non-heme iron and non-corrinoid cobalt enzymes 04CRV825. 

Polyamines. New cobalt(iii) complexes of 1,4,7-triazacyclononane (TACN), [Co(TACN)X3] (X = Cl, NO2, or Br), have been made as precursors to amino-alcohol complexes, [Co(TACN)tmOH] (tmOH = 2,3-diaminopropan-l-ol and... 

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