1.3- Diimines macrocyclic complexes

The template condensation of 2,3-butanedione dihydrazone with aldehydes or ketones affords a variety of octaazabis(a-diimine) macrocyclic complexes of nickel(II), according to the Scheme 48.2655 NH deprotonation with py or Et3N of the aforementioned cationic complexes leads to neutral NiL species. 

The hexahydropyrimidine (58), formed from l-phenylpropane-l,2-dione and propane-1,3-diamine, is an excellent precursor for the a-diimine macrocyclic complexes (60), presumably via the amino ketone (59) (Scheme 36).126 In this case, intramolecular cyclization of (59) to (58) is reversible, so that the metal ion can exert a thermodynamic template effect in formation of the complex (60). This represents a further example of a long-known phenomenon in which a metal ion can stabilize an a-diimine structure by virtue of the formation of stable five-membered chelate rings. Many 2-hydroxy- or 2-mercapto-amines undergo reaction with a-dicarbonyl compounds to yield heterocyclic compounds rather than a-diimines. However, in the presence of suitable metal... 

The zinc iodide complex of a 15-membered diamine diimine macrocycle has been structurally... 

The complex [MnL](PF6)2, where L is the pendant arm ligand (184), also based on a N5 diimine macrocycle, was obtained directly by a template procedure." . The coordination geometry is pentagonal bipyramidal with the pendant amino groups occupying the axial sites. The aqueous HNMR relaxation rate enhancement in the presence of this complex is small in comparison to... 

The polyether-diimine macrocycle (108) forms a catenate [Fe(cat)] which proved impossible to oxidize to [Fe(cat)] " but which is readily reducible, electrochemically in dichloromethane solution on a Pt or Hg surface, to [Fe(cat)]+ and to [Fe(cat)]°. " [Fe(bmpphen)2] (bmpphen = (109) can be electroreduced to [Fe(bmpphen)2] and to [Fe(bmpphen)2]. The relatively high stabilities of all three bmpphen complexes may be due to their entwined character. Here and below one should bear in mind the possibility, outlined in Section 5.4.1.3 above, that it is the ligand rather than the metal which is being reduced. 

A large amount of work has been devoted to N-binding macrocyclic complexes of Ni, Cu and Fe, which yield imine ligand products. Bidentate amine ligands, mainly ethylenediamine (en), have been used with Ru and Os complexes. The oxidation of coordinated ethylenediamine and related ligands stops at the diimine stage and does not continue to the dinitrile. The a,a -diimine entity -N=C-C = N- formed in the four-electron oxidation is particularly stable (93). 

Simple a-diimines are hydrolytically unstable, but can be stabilized as metal complexes by virtue of the formation of stable five-membered chelate rings.68 69 a-Diketones and glyoxal undergo metal template reactions with amines to yield complexes of multidentate ligands such as (34),70 (35)71 and (36).72>73 In the last case, the metal exerts its stabilizing influence on the a-diimine partner in an equilibrium process (Scheme 5). The same phenomenon occurs with amino alcohols74 75 in addition to amino thiols. The thiolate complexes (37) can be converted to macrocyclic complexes by alkylation in a kinetic template reaction (Scheme 5).76 77... 

Let us start by considering the reaction of the copper(n) complex 6.49 with formaldehyde. Initially we might expect the diimine 6.50 to be formed, but this ignores the nature of the intermediates. As we saw earlier, the reaction of an amine with an aldehyde initially produces an aminol. Consider the addition of the second molecule of formaldehyde to 6.49. The product will be 6.51, which contains an imine and an aminol (Fig. 6-43). The imine is co-ordinated to a metal ion, and the polarisation effect is likely to increase the electrophilic character of the carbon. The hydroxy group of the aminol is nucleophilic and it is correctly oriented for an intramolecular attack upon the co-ordinated imine. The result is the formation of the copper(n) macrocyclic complex 6.52. 

Metal-Directed Macrocyclic Complexes Incorporating Diimine Rhenium Tricarbonyl Moieties... 

Ligand oxygenation (112 -> 113) of Fe11 complexes of bis(/ -diimine) macrocycles by molecular oxygen has also been observed. Again, an Feni-mediated radical mechanism has been suggested for this oxidation.397... 

The achiral 14-membered trans-diimine macrocycle (f , S )-102, in the presence of trifluoroacetic acid, rearranges quantitatively into the chiral seven-membered monoimine ( )-103 (Section Ill.C.l.h)". If the rearrangement of (i , S )-102 is carried out in methanol containing a suspension of ( )-(—)-78, an orange solution is obtained from which pure [I ,(Sas,I as)] ( )-1 6 can be isolated by the addition of ammonium hexafluorophosphate. The yield of the complex was ca 50%. The addition of more acid and halide in an attempt to facilitate racemization of the free arsine and thereby promote the further crystallization of the complex by second-order asymmetric transformation was unsuccessful. Nevertheless, this highly stereoselective synthesis of [H,(Sas,IIas)] ( ) 106 is a more expedient route to (R,I )-(—)-102 than the one involving resolution of the benzyl alcohol complex (R, SA.)-(-)-92a. 

The condensation of 2V,A -bis(3-aminopropyl)ethylenediamine (7V,A -ethylene-bis[l,3-propanediamine]) as its acid salt with 2,3-butanedione (biacetyl) in the presence of cobalt(II) or nickel(II) acetate gives complexes of 2,S-Mej [14] - 1,3-diene-l,4,8,11-N4 containing one a-diimine linkage. Experiments have shown that the presence of H ion determines whether or not a macrocyclic complex forms and that, in the presence of H, the time at which the metal acetate is added to the reaction mixture influences the yield of the complex. Unlike the reaction between biacetyl and 1,3-propanediamine to form 2,3,9,10-Me4[14]-1,3,8,10-tetraene-l,4,8,11-N4 (Sec. 4), the condensation of biacetyl withTVA -bis(3-aminopropyl)ethylenediamine is particularly sensitive to excess acetate so that the procedures given use the optimized conditions. 

The complex [Ni(2,3-Me2[14]-l,3-diene-l,4,8,lI-N4)] [ZnCU] is square planar and low-spin. The visible spectra show bands near 21.3 kK (characteristic of square planar nickel(II)), near 26.1 kK (due to the imine functions), and near 35.1 kK. The infrared spectra of all of the nickel complexes prepared show absorptions near 3195 and 1595 cm assignable to the N—H stretching vibration and to the symmetric imine vibration, respectively. A strong sharp band also occurs near 1210 cm and is characteristic of the a-diimine function. The NMR spectrum of the perchlorate complex in nitromethane shows a methyl singlet at 2.33 ppm. The ligand can be hydrogenated on nickel(II) with Raney nickel and hydrogen to produce the fully saturated macrocyclic complex [Ni(2,3-Me2[14]-ane-1,4,8,1 1-N4] ... 

Complexes of Ni11 or Cu11 with 1,2- 1,3- or 1,4-diamines react with acetone in 2+2 condensations to form [14]-, [15]-, [16]-, or [18]-membered diamine-diimine macrocycle compounds, e.g., (15) and (16), formed from en, or with 3,3-tri or tetraamines in 1 + 1 condensations to form a diamine-monoimine or triamine-monoimine macrocycle compounds, respectively, e.g., (19) formed from 2,2,2-tet (Scheme 5).31... 

The template condensation of a-diketones with 1,3-propanediamine in the presence of divalent iron, cobalt, nickel, or copper leads to 14-membered-ring macrocyclic complexes containing two a-diimines. A number of complexes of this class, derived from 2,3-butanedione,1-3 1-phenyl-1,2-propanedione,4,5 benzil,6 and substituted benzils,5 have been prepared. Preparation of the Ni(II)... 

Ligand oxygenation (112 113) of Fe complexes of bis(/ -diimine) macrocycles by molecular... 

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