Monomeric macrocycles

While 1,2- and 1,3-alkanediols form only monomeric 1,3,2-dioxaborolanes and 1,3,2-dioxaborinanes with triethylborane, 1,4- and 1,5-alkanediols give mainly dimeric macrocyclic boronates 41 and 42, which are obtained in yields of 70-75% after purification by vacuum distillation. As lateral products oligo-and polymeric molecules are formed. The main products have a 14- and 16-membered heterocyclic ring, respectively (Fig. 15) [84]. 

The p a values of two systems with two intra-annular COOH groups have been measured. In Cram s study (Bell et al., 1982), the macrocyclic diacid [36] and an open-chain monomeric analogue [37] had almost identical pK values (see Table 18). In contrast, Gennari s compound [38], which contains two intra-annular COOH groups and in addition two"ethyl ester groups, has a different acidity from that of the analogues [39] and [40], as shown in Table 19 (Gennari et al., 1992). But in both systems, the difference Ap a between pK i and p a2 was comparable (ApA a [36] = 1.7, Ap/La[38] = 1.5). The increase from p ai to P a2 may occur for two... 

Bis(triazacyclononane) ligands (73) where the two macrocycles are linked with chains two to eight carbons in length have been complexed with zinc to form monomeric and dimeric... 

The coordinated macrocycle readily reacts with alkoxide ions to yield products of type (71) (Taylor, Urbach Busch, 1969). In so doing additional flexibility is imparted to the ring which may reduce ring strain and, in part, provide a driving force for the reaction. Thus the coordinated imine carbons appear predisposed to attack by such nucleophiles. Based on this knowledge, elegant template syntheses of three-dimensional derivatives have been performed. The syntheses involved the reaction of [M(taab)]2+ (M = Ni, Cu) with the dialkoxide ions derived from bis(2-hydroxyethyl)sulphide or bis(2-hydroxyethyl)methylamine (Katovic, Taylor Busch, 1969). The products were demonstrated to be monomeric square-pyramidal complexes of type (72). The condensation... 

Condensation of 2,6-diacetylpyridine with bis(3-aminopropane)amine in the presence of small ions such as Mn(n), Co(n), Ni(n) or Cu(n) readily leads to formation of the corresponding monomeric (14-membered) macrocyclic complexes of ligand (83). However, when the large Ag(i) ion is used as the template, then a dimetallic complex of a 28-membered macrocycle of type (88) is produced. This example illustrates well the importance of metal-ion size in promoting template reactions. 

Fe-arene complexes have been employed for the same purposes as their Ru counterparts, namely, in the preparation of monomeric aryl ethers,463,486-488 polyaromatic ethers,489,490 and macrocyclic aryl ethers.491... 

The sensor covalently joined a bithiophene unit with a crown ether macrocycle as the monomeric unit for polymerization (Scheme 1). The spatial distribution of oxygen coordination sites around a metal ion causes planarization of the backbone in the bithiophene, eliciting a red-shift upon metal coordination. They expanded upon this bithiophene structure by replacing the crown ether macrocycle with a calixarene-based ion receptor, and worked with both a monomeric model and a polymeric version to compare ion-binding specificity and behavior [13]. The monomer exhibited less specificity for Na+ than the polymer. However, with the gradual addition of Na+, the monomer underwent a steady blue shift in fluorescence emission whereas the polymer appeared to reach a critical concentration where the spectra rapidly transitioned to a shorter wavelength. Scheme 2 illustrates the proposed explanation for blue shift with increasing ion concentration. 

Monomeric hemes possess a mirror plane and are hence achiral (151). Incorporation of the heme macrocycle into the anisotropic protein matrix distorts the heme environment, inducing a circular dichroism spectrum (57, 152, 153). From the design standpoint, the presence of an induced heme CD spectrum qualitatively confirms intimate communication between the heme and the surrounding protein matrix, which indicates the heme is most likely specifically bound. This spectroscopic signature serves as a first indication that the heme resides within the designed protein scaffold and has been used by various groups to... 

The energetics of peptide-porphyrin interactions and peptide ligand-metal binding have also been observed in another self-assembly system constructed by Huffman et al. (125). Using monomeric helices binding to iron(III) coproporphyrin I, a fourfold symmetric tetracarboxylate porphyrin, these authors demonstrate a correlation between the hydropho-bicity of the peptide and the affinity for heme as well as the reduction potential of the encapsulated ferric ion, as shown in Fig. 12. These data clearly demonstrate that heme macrocycle-peptide hydrophobic interactions are important for both the stability of ferric heme proteins and the resultant electrochemistry. 

Batatins V (234) and VI (235) are acylated tetrasaccharide ester-t3 pe dimers isolated from Ipomoea batatas, which yielded operculinic acid C through saponification. A mild alkaline hydrolysis of both afforded compound 30, one of the monomeric units, identified by coelution in UPLC with natural batatinoside 111 (31), placing the lactonization at C-3 of the second saccharide in the macrocyclic portion. C-3 of the third saccharide unit was identified as the position for the ester linkage. Both dimers showed acylations at C-4 of the terminal rhamnose... 

Manganese(III) complexes of a number of phenolate pendant arm macrocycles related to the above have also been reported. Thus, both l,4,7-tris(2-hydroxybenzyl)-l,4,7-triazacyclononane and l,4,7-tris(3-t-butyl-2-hydroxybenzyl)-l,4,7-triazacyclononane, on tris-deprotonation, afford monomeric pseudooctahedral complexes with this ion." ... 

Traditionally, a polymer has been named by attaching the prefix poly to the name of the real or assumed monomer (the source ) from which it is derived. Thus, polystyrene is the name of the polymer made from styrene. When the name of the monomer comprises two or more words, parentheses should be used [1], as in poly(vinyl acetate), poly(methyl methacrylate), etc. Failure to use parentheses can lead to ambiguity. For example, polychlorostyrene could be the name of either a polychlorinated (monomeric) styrene or of a polymer derived from chlorostyrene similarly, polyethylene oxide could refer to the polymer 1, the polymer 2 or the macrocycle 3. 

Application of the same dendrimer 31 in the Stille coupling of iodobenzene with tributylvinyltin in DMF (Scheme 10 5mol% catalyst) showed an activity equal to that of the tetraphosphole macrocycle complex (Fu3P)4Pd(OAc)2 (31b 100% conversion after 15 min). In contrast to the monomer, the dendritic catalyst could be recycled, but when recycled it showed a decrease in activity (95% conversion after 15 min). A better performance was achieved with the in situ prepared catalyst 32 by mixing the third-generation diphosphine dendrimer with Pd(OAc)2 (P/Pd ratio = 4/1). An activity similar to that of the monomeric complex (Fu3P)4Pd(OAc)2 was observed (100% conversion after 15 min), even after three consecutive runs. 

Discrete dimers of the head-to-head type have been found in the structures of the Ag+ complex of (145)570 and the Na+ complex of (145)571 respectively. The complexes were recrystallized from carbon tetrachloride. In both complexes each metal is five-coordinated in the cavity provided by one anion, and there is an additional reaction with the second anion [through an Ag+-phenyl interaction or an Na+-carboxylate oxygen atom (Figure 32a)]. When the Na+ complex was crystallized from a solvent of medium polarity, acetone, the head-to-head dimer was recovered.571 In contrast, recrystallization from a polar medium, methanol, gave a monomeric complex in which one methanol of solvation was also present.572 In all of these complexes an intramolecular head-to-tail hydrogen bond was present to hold the ligand in its pseudo-macrocyclic conformation. 

Figure 2 Precursors of macrocyclic ligands which allow redox reactions for monomeric molybdenum centres...

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