Curtis reaction metal template reactions

Apart from this one-reaction type, the routine use of metal template procedures for obtaining a wide range of macrocyclic systems stems from 1960 when Curtis discovered a template reaction for obtaining an isomeric pair of Ni(n) macrocyclic complexes (Curtis, 1960). Details of this reaction are discussed later in this chapter. The template synthesis of these complexes marked the beginning of renewed interest in macrocyclic ligand chemistry which continues to the present day. 

Metal template syntheses of complexes incorporating the p-amino imine fragment have been introduced by Curtis as a result of his discovery that tris(l,2-diaminoethane)nickel(II) perchlorate reacted slowly with acetone to yield the macrocyclic complexes (40) and (41) (equation 8).81-83 In this macrocyclic structure the bridging group is diacetone amine imine, arising from the aldol condensation of two acetone molecules. This reaction is widely general, in the same way that the aldol reaction is, and can be applied to many types of amine complexes. The subject has been reviewed in detail with respect to macrocyclic complexes by Curtis.84... 

Metal ion template mediation in macrocyclic synthesis has been a part of the field since its inception, its importance having been realized early in the development of this area. Two specific roles for the metal ion in template reactions have been proposed. These are, in turn, kinetic and thermodynamic in origin." In the kinetic template effect, the arrangement of ligands already coordinated to the metal ion provides control in a subsequent condensation during which the macrocycle is formed. The thermodynamic effect serves to promote stabilization of a structure which would not be favored in the absence of a metal ion. Schiff base condensations tend to be dependent on this latter type of template effect. Some of the more routine and general synthetic procedures will be described here. A more in-depth treatment can be found in a review by Curtis, with particular emphasis on general methods as well as modifications of preformed macrocycles." ... 

The metal-ion-templated synthesis of a peraza macrocycle was reported more than 30 years ago. The macrocycle resulted from the reaction of tris(l,2-diaminoethane)nickel(ll) perchlorate with acetone to form a 14-membered macrocyclic ligand-Ni(ll) complex (5) (Curtis, 1960 Curtis and House, 1961). Numerous examples of this and other metal-ion-templated reactions have been investigated in the intervening years (Black and Hartshorn, 1972-1973 Busch, 1964 Curtis, 1968). Slightly earlier, the methyl-substituted peroxa-... 

The process of forming unsaturated macrocycles from acetone or other ketones and derivatives of 1,2-diaminoethane or 1,3-diaminopropane was first reported by Curtis and coworkers (Blight and Curtis, 1962 Curtis and House, 1961 House and Curtis, 1964a). The mechanism of this reaction involves the reaction of four acetone molecules with two diamino compounds probably as mentioned above for the similar 2 1 cyclization reactions of acetone and a diamine. The reaction can be carried out with or without a template metal ion (Hay et al., 1975). The monoprotonated salt of the amine was cyclized without the template ions. 

The cyclic tetraazadienes were first discovered by Curtis (Curtis, 1960 Curtis and House, 1961). These macrocycles were prepared by reacting 1,2-diaminoethane, 1,2-diaminopropane, or 1,3-diaminopropane with acetone, methyl ethyl ketone, propionaldehyde, n-butyraldehyde, isobutyraldehyde, or other small carbonyl compounds in the presence of Ni(II) or Cu(II) (Blight and Curtis, 1962 House and Curtis. 1962, 1964a, 1964b). Similar tetraaza macrocycles can be isolated from the reaction of triethylenetetraamine and the carbonyl compound in the presence of the metal template ions (Curtis... 

Curtis and others showed that cyclic condensation also was possible in the absence of a metal template ion, but acid was necessary for those reactions. Possibly, the protonated amines formed an internal hydrogen-bonding network that acted as a template. Cyclization was observed in yields of up to 80% (Curtis and Hay, 1966 Kolinski and Korybut-Daszkiewicz, 1969 Tait and Busch, 1978a, 1978b). The isomers of the formed cyclic Schiff bases were difficult to separate. Reduction of the unsaturated macrocycles gave cyclic polyamines with up to six chiral centers and up to 20 diastereomeric isomers (Hay and Piplani, 1977 Kolinski and Korybut-Daszkiewicz, 1969). 

Initially a great majority of tetradentate cyclic polyamines were prepared by condensation reactions assisted by a transition metal ion, typically nickel(II), which held the reacting molecules in favourable positions to facilitate their cyclic condensation (template reactions).The archetypal template reaction was due to the pioneering work of N. F. Curtis, who found that [Ni(en)3](C104)2 reacts with acetone at room temperature yielding... 

Virtually all types of metal ions have been complexed with macrocyclic ligands.2-7 Complexes of transition metal ions have been studied extensively with tetraaza macrocycles (Chapter 21.2). Porphyrin and porphyrin-related complexes are of course notoriously present in biological systems and have been receiving considerable investigative attention (Chapter 22).8 Macrocyclic ligands derived from the Schiffbase and template-assisted condensation reactions of Curtis and Busch also figure prominantly with transition metal ions.6,7 The chemistry of these ions has been more recently expanded into the realm of polyaza, polynucleating and polycyclic systems.9 Transition metal complexes with thioether and phosphorus donor macrocycles are also known.2... 

Most of the template syntheses of nonbenzenoid macrocycles originated with Curtis (39) and involve the condensation of metal-amine complexes with aliphatic carbonyl compounds, e.g., the reaction of acetone with tris(diaminoethane)nickel(II) perchlorate at ambient temperature leads to the isolation of three products, two of which may be represented as cts-XLIX and trans-L and the other is formed by a further interconversion of complex L in solution (39,143). With Cu(II) diaminoperchlorates, a mixture of cis and trans complexes analogous to XLIX and L is formed, but with Co(II) only the trans analog of L has been isolated. When ketones containing bulky groups are used, the reaction is much slower, e.g., there is only a small yield of LI from... 

Most of the templates diseussed in this chapter are kinetic templates. Some of the early examples of metal cation templated macrocyclization studied by Curtis and Busch [7,9] (Schemes 1-1 and 1-2) are thought to operate under thermodynamie eontrol. The clearest evidence for a thermodynamic template effect comes when the template-free product is not stable under the reaction conditions. For example, treatment of 1,2-dicyanoben-zene 11 with boron trichloride or uranyl chloride results in the formation of subphthalo-... 

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