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A bifunctional iminophosphorane (BIMP)-catalyzed, enantioselective intramolecular oxa-Michael reaction of alcohols to tethered, low electrophilicity Michael acceptors is described. Improved reactivity over previous reports (1 day vs 7 days), excellent yields (up to 99%), and enantiomeric ratios (up to 99.5:0.5 er) are demonstrated. The broad reaction scope, enabled by catalyst modularity and tunability, includes substituted tetrahydrofurans (THFs) and tetrahydropyrans (THPs), oxaspirocycles, sugar and natural product derivatives, dihydro-(iso)-benzofurans, and iso-chromans. A state-of-the-art computational study revealed that the enantioselectivity originates from the presence of several favorable intermolecular hydrogen bonds between the BIMP catalyst and the substrate that induce stabilizing electrostatic and orbital interactions. The newly developed catalytic enantioselective approach was carried out on multigram scale, and multiple Michael adducts were further derivatized to an array of useful building blocks, providing access to enantioenriched biologically active molecules and natural products.

The first metal-free catalytic intermolecular enantioselective Michael addition to unactivated α,β-unsaturated amides is described. Consistently high enantiomeric excesses and yields were obtained over a wide range of alkyl thiol pronucleophiles and electrophiles under mild reaction conditions, enabled by a novel squaramide-based bifunctional iminophosphorane catalyst. Low catalyst loadings (2.0 mol %) were achieved on a decagram scale, demonstrating the scalability of the reaction. Computational analysis revealed the origin of the high enantiofacial selectivity via analysis of relevant transition structures and provided substantial support for specific noncovalent activation of the carbonyl group of the α,β-unsaturated amide by the catalyst.

To improve the field of catalysis, there is a substantial and growing need for novel high-performance catalysts providing new reactivity. To date, however, the set of reactions that can be reliably performed to prepare chiral compounds in largely one enantiomeric form using chiral catalysts still represents a small fraction of the toolkit of known transformations. In this context, chiral Brønsted bases have played an expanding role in catalyzing enantioselective reactions between various carbon- and heteroatom-centered acids and a host of electrophilic reagents. This Account describes our recent efforts developing and applying a new family of chiral Brønsted bases incorporating an H-bond donor moiety and a strongly basic iminophosphorane, which we have named BIMPs (Bifunctional IMinoPhosphoranes), as efficient catalysts for reactions currently out of reach of more widespread tertiary amine centered bifunctional catalysts. The iminophosphorane Brønsted base is easily generated by the Staudinger reaction of a chiral organoazide and commercially available phosphine, which allows easy modification of the catalyst structure and fine-tuning of the iminophosphorane p K BH+ . We have demonstrated that BIMP catalysts can efficiently promote the enantioselective addition of nitromethane to low reactivity N -diphenylphosphinoyl (DPP)-protected imines of ketones (ketimines) to access valuable chiral diamine and α-quaternary amino acid building blocks, and later extended this methodology to phosphite nucleophiles. Subsequently, the reaction scope was expanded to include the Michael addition of high p K a alkyl thiols to α-substituted acrylate esters, β-substituted α,β-unsaturated esters, and alkenyl benzimidazoles as well as the challenging direct aldol addition of aryl ketones to α-fluorinated ketones. Finally, BIMP catalysts were shown to be used in key steps in the synthesis of complex alkaloid natural products (-)-nakadomarin A and (-)-himalensine A, as well as in polymer synthesis. In most cases, the predictable nature of the BIMP promoted reactions was demonstrated by multigram scale-up while employing low catalyst loadings (down to 0.05 mol%). Furthermore, it was shown that BIMP catalysts can be easily immobilized onto a solid support in one-step for increased catalyst recycling and flow chemistry applications. Alongside our own work, this Account also includes elegant work by Johnson and co-workers utilizing the BIMP catalyst system, when alternative catalysts proved suboptimal.

The first total synthesis of the potent antibiotic berkeleylactone A is described in 10 steps with an overall yield of 9.5%. A key step of our concise route is a late-stage, highly diastereoselective, sulfa-Michael addition. The 16-membered macrocyclic lactone was formed via ring closing metathesis and subsequent chemoselective reduction. The absolute stereochemical configuration was confirmed by single-crystal X-ray analysis. Synthetic berkeleylactone A was tested against several methicillin-resistant Staphylococcus aureus strains, and its potent antibacterial activity was verified.

We synthesized and characterized the ligand N,N'-bis[(2,2'-dihydroxybiphen-3-yl)methyl]-N,N'-dimethylethylenediamine (L), which contains two biphenol moieties linked as side arms to an N,N'-dimethylethylenediamine scaffold. The ligand is highly soluble in a 50/50 (v/v) water/ethanol mixture and, in its deprotonated form H-2L(2-), is able to coordinate transition-metal ions such as Ni(II), Zn(II), Cu(II), Cd(II), and Pd(II). The crystal structures of [Ni(H-2L)·2n-BuOH], [Ni(H-2L)·2MeOH], [Cd(H-2L)·2DMF], [Cu(H-2L)(DMF)], and [Pd(H-2L)(DMF)] were also determined and described. Potentiometric titrations were carried out in a mixed solvent with Zn(II), Cu(II), and Ni(II) metal ions to determine the acid-base and stability constants. L was highly fluorescent in the visible range (400 nm). Moreover, its emission intensity increased upon the addition of Zn(II) or Cd(II) ions in an ethanol/water solution and behaved as a chemosensor for the presence of these ions in the solution.

Ligand L (2,6-bis{[7-(7-nitrobenzo[1,2,5]oxadiazole-4-yl)-3,10-dimethyl-1,4,7,10-tetraazacyclododeca-1-yl]methyl}phenol) is a fluorescent sensor that is useful for detecting Cu(II), Zn(II), and Cd(II). Some of the complexes formed are able to sense the presence of halides in solution. L passes through the cellular membrane, becoming fluorescent inside cells. The H(-1)L- species is able to form dinuclear complexes with [M(2)H(-1)L]3+ stoichiometry with Cu(II), Zn(II), and Cd(II) ions, experiencing a CHEF effect upon metal coordination in an acetonitrile/water 95:5 (v/v) solution. In all three of the complexes investigated, the metal cations are coordinatively unsaturated and can therefore bind secondary ligands as anionic species. The crystal structure of [Cd(2)(H(-1)L)Cl(2)](ClO(4))·4H(2)O is discussed. The Zn(II) complex behaves as an OFF-ON sensor for fluoride and chloride anions.

The N,N'-bis[(3-hydroxy-4-pyron-2-yl)methyl]-N,N'-dimethylethylendiamine (malten) and 4,10-bis[(3-hydroxy-4-pyron-2-yl)methyl]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (maltonis) were synthesized and characterized. The acid-base behavior, structural characterizations, and biochemical studies in aqueous solution were reported. Each compound contains two 3-hydroxy-2-methyl-4-pyrone units (maltol) symmetrically spaced by a polyamine fragment, the 1,4-dimethylethylendiamine (malten), or the 1,7-dimethyl-1,4,7,10-tetraazacyclododecane (maltonis). They are present at physiological pH 7.4 in the form of differently charged species: neutral but in a zwitterion form for malten and monopositive with an internal separation of charges for maltonis. Malten and maltonis are both able to alter the chromatin structure inducing the covalent binding of genomic DNA with proteins, a feature consistent with the known antiproliferative activity exerted by this class of molecules. Solid-state results and MD simulations in water show that malten, because of its molecular topology, should be more prone than maltonis to act as a donor of H-bonds in intermolecular contacts, thus it should give a better noncovalent approach with the negatively charged DNA. Crystal structures of [H(2)malten](2+) and [H(2)maltonis](2+) cations were also reported.

The coordination properties and photochemical responses of three fluorescent polyamine macrocycles, 9,12,15,24,25-pentaaza-26-oxatetracyclo[21.2.1.0(2,7).0(17,22)]hexaicosa-2,4,6,17,19,21,23,25(1)-octaene (L1), 9,12,15,18,27,28-hexaaza-29-oxatetracyclo[24.2.1.0(2,7).0(20,25)]enneicosa-2,4,6,20,22,24,26,28(1)-octaene (L2), and 9,12,15,18,21,30,31-heptaaza-32-oxatetracyclo[27.2.1.0(2,7).0(23,28)]diatriconta-2,4,6,23,25,27,29,31(1)-octaene (L3), toward Cu(II), Zn(II), Cd(II), and Pb(II) are reported. Each ligand contains the 2,5-diphenyl[1,3,4]oxadiazole (PPD) moiety inserted in a polyamine macrocycle skeleton. The stability constants were determined by means of potentiometric measurements in aqueous solution. L1 forms mononuclear complexes only with Cu(II). L2 and L3 form stable mononuclear species with all of the metals, while L3 is able to form dinuclear Cu(II) species. The fluorescence of all ligands was totally quenched by the presence of Cu(II). L2 behaves as an OFF-ON sensor for Zn(II) under physiological conditions, even in the presence of interfering species such as Cd(II) and Pb(II). This ligand combines selective binding of Zn(II) with a highly specific fluorescent response to Zn(II) due to the chelating enhancement of fluorescence (CHEF) effect. The interaction of Zn(II), Cd(II), and Pb(II) with L3 does not produce an appreciable enhancement of fluorescence at the same pH. The different behavior is attributed to the cavity size of the macrocycle and to the number of amine functions. L2 possesses the best arrangement of these two characteristics, allowing a full participation of all of the amine functions in metal coordination, as shown by the crystal structures of [CuL2(ClO(4))](ClO(4))·H(2)O and [ZnL2Br]Br·H(2)O species; this prevents the PET effect and supplies the higher CHEF effect. The interaction between L2 and Zn(II) can also be observed with the naked eye as an intense sky blue emission.

The synthesis and characterization of the new polytopic ligands 1,14-bis(3,6,9-triaza-15-hydroxybicyclo[9.3.1]pentadeca-11,13,1(15)-trien-6-yl)-3,6,9,12-tetraazatetradecane L1, 1,15-bis(3,6,9-triaza-15-hydroxybicyclo[9.3.1]pentadeca-11,13,1(15)-trien-6-yl)-3,6,10,13-tetraazapentadecane L2, and 1,16-bis(3,6,9-triaza-15-hydroxybicyclo[9.3.1]pentadeca-11,13,1(15)-trien-6-yl)-3,7,10,14-tetraazahexadecane L3, containing two equal amino-phenol macrocycles spaced by several linear tetraamines, are reported. The basicity and coordination behavior toward the Cu(II) ion were potentiometrically determined in aqueous solution at 298.1 K. All the ligands show similar acid-base properties behaving as octaprotic bases in the examined pH range (pH = 2-12). The acid protons of L1-L3 cannot be removed under the experimental conditions used; thus, the main deprotonated species obtainable in aqueous solution are the neutral ligands, having amphionic character as demonstrated by UV-vis experiments. These species are able to form mono-, di-, and trinuclear Cu(II) complexes having stoichiometry [CuL](2+), [Cu(2)L](4+), and [Cu(3)L](6+), respectively, that can lose one or two protons giving rise to [CuH(-1)L](+), [Cu(2)H(-2)L](2+), and [Cu(3)H(-2)L](4+). Depending on the used ligand to metal molar ratio, the mono-, di-, or trinuclear species prevail over the others in solution. Both di- and trinuclear complexes are able to add secondary ligands (such as OH(-)), and in some cases two Cu(II) can cooperate to stabilize them by coordinating the guest in a bridged conformation. The structure of the [Cu(2)L3](4+) cation was resolved by X-ray analysis of the {[Cu(2)L3](ClO(4))(4) x 3 H(2)O}(2) x H(2)O crystalline complex. It shows that each Cu(II) is penta-coordinated by one phenolate oxygen, two amine functions, belonging to one macrocyclic unit, and two amine functions of the spacer; in this species the distance between the two Cu(II) is about 5.3 A.

Two Zn(II)-dinuclear systems were studied as receptors for phosphates; they were obtained by using the two polyamino-phenolic ligands 3,3'-bis[N,N-bis(2-aminoethyl)aminomethyl]-2,2'-dihydroxybiphenyl (L1) and 2,6-bis[N,N-bis(2-aminoethyl)aminomethyl]phenol (L2) in which the difference lies in the spacers between the two dien units, biphenol or phenol in L1 and L2, respectively. The metallo-receptors obtained are able to selectively discriminate phosphate (Pi) from pyrophosphate (PPi) and vice versa in aqueous solution in a wide range of pH (6 < pH < 10). The L1 receptor system shows selectivity toward PPi over Pi, and on the contrary the L2 system exhibits opposite selectivity. This different selectivity is ascribed to the different Zn(II)-Zn(II) distances between the two metal centers which, showing a similar coordination requirement and binding phosphate in a bridge disposition, fit in a different way with the different guests. Furthermore, NMR studies supported the model of interaction proposed between guests and receptors, highlighting that they are also able to bind biological phosphates such as G6P and ATP at physiological pH. Fluorescence studies showed that the receptor system based on L1 is able to signal the presence in solution of Pi and PPi at physiological pH; the presence of Pi is detected by a quenching of the emission, that of PPi by an enhancement of it. With the aid of an external colored sensor (PCV), the receptors were then used to produce simple signaling systems for phosphates based on the displacement method; the two chemosensors obtained are able to signal and quantify these anions at physiological pH, preserving the selectivity between phosphate and pyrophosphate and extending it to G6P and ATP.

A new and efficient synthetic protocol for the preparation of unsymmetrical difunctionalized cyclen and its close derivatives using a modified Ugi reaction (N-split Ugi) is described. The scope of this methodology is further extended by the successful use of various isocyanides, highly functionalized carboxylic acids, and aldehydes.

The synthesis and characterization of the new ligand 2,9-bis[N,N-bis(2-aminoethyl)aminomethyl]-1,10-phenanthroline (L) are reported. L contains two diethylenetriamine units connected on the central nitrogen atom by a 1,10-phenanthroline group forming a symmetrical branched ligand. The basicity and binding properties of L toward Cu(II) and Zn(II) in aqueous solution were determined by means of potentiometric, UV-vis, fluorescence, and 1H and 13C NMR techniques. L behaves as pentaprotic base under the experimental conditions used; from HL+ to H4L4+ species it is the secondary amine functions that are protonated while in the H5L5+ species also the phenanthroline is involved in protonation. L does not show fluorescence properties in the range of pH (0-14) investigated. It forms both mono- and dinuclear stable species where the phenanthroline is directly involved with both nitrogens in the coordination of the first metal which is coordinated in a pentacoordination environment also by one dien unit. The other dien unit undergoes easy protonation in the mononuclear complex while it binds the second metal in the dinuclear species. For this reason, L, in providing two different binding areas for metal coordination, behaves as an unsymmetrical compartmental ligand; one area is formed by one dien unit and by the phenanthroline, and the other by the remaining dien unit. This produces unsymmetrical metal complexes both for the mono- and dinuclear species; however, the role of the binding areas is fast exchanging in aqueous solution, at least on the NMR time scale. Solution studies and the three crystal structures of the [Zn(H2L)]4+, [[Cu(H2L)](ClO4)]3+, and [[Cu2LCl2](ClO4)]+ species highlight the unsymmetrical compartmental behavior of L as well as the host properties of the complexes in adding exogenous ligands such as hydroxide, pherchlorate, and chloride anions.

The synthesis and characterization of the new polyamino-phenolic ligand 3,3'-bis[N,N-bis(2-aminoethyl)aminomethyl]-2,2'-dihydroxybiphenyl (L) are reported. L contains two diethylenetriamine units linked by a 1,1'-bis(2-phenol) group (BPH) on the central nitrogen atom which allows two separate binding amino subunits in a noncyclic ligand. The basicity and binding properties of L toward Cu(II) and Zn(II) were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm-3). L behaves as a pentaprotic base and as a monoprotic acid under the experimental conditions used, yielding the H5L5+ or H-1L- species, respectively. L forms both mono- and dinuclear species with both metal ions investigated; the dinuclear species are largely prevalent in aqueous solution with a L/M(II) molar ratio of 1:2 at pH higher than 7. L shows different behavior in Cu(II) and Zn(II) binding, affecting the dinuclear species formed and the distance between the two coordinated metal ions, which is greater in the Zn(II) than in the Cu(II) dinuclear species. This difference can be attributed to the different degree of protonation of BPH which influences the angle between the phenyl rings in the two systems. In this way, it is possible to modulate the M(II)-M(II) distance by the choice M(II) and to space the two M(II) farther away than was possible with the previously synthesized ligands. L does not saturate the coordination sphere of the coordinated M(II) ions in the dinuclear species, and thus, these latter species are prone to add guests. 1H and 13C NMR experiments carried out in aqueous solution, as well as the crystal structures of the dinuclear Cu(II) and Zn(II) species formed in aqueous solution, aided in elucidating the involvement of L and BPH in Zn(II) and Cu(II) stabilization.

The synthesis and characterization of the new polyaza-phenolic-macrobicycle 32-hydroxy-1,4,7,10,13,16,19,22-octaazatricyclo-[11.11.7.1(26,30)]-diatriconta-26,28,Delta(30,32)-triene (L) are reported. L incorporates a 2,6-dimethyl-phenolic unit bridging two opposite amine functions of the [24]aneN(8) polyazamacrocyclic base to obtain a large cage. The basicity and binding properties of L toward Cu(II), Zn(II), and Cl(-) were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm(-3)). L can add up to six acidic protons, yielding the H(5)L(5+) species or the H(6)L(6+) species, depending on the ionic medium used. The molecular topology of L permits the formation of a highly positive three-dimensional cavity in the polyprotonated species that is able to host the chloride anion. This was detected both using potentiometric data, log K = 41.33 for the reaction L + 6H(+) + Cl(-) = H(6)LCl(5+), and in (35)Cl NMR experiments that showed interactions also with the H(5)L(5+) and H(4)L(4+) species. The anion is probably hosted inside the three-dimensional cavity of L, and stabilized by H-bonding interactions with the ammonium groups, as depicted in the crystal structure of the H(6)L(6+) cation reported. L forms mono- and dinuclear complexes with all the metal ions investigated; the dinuclear species are the only existing species with an L:M(II) molar ratio of 1:2 at pH higher than 6. The phenolate oxygen atom coordinates the two metal ions in a bridged disposition, drawing them inside the macrobicyclic cavity. The two metals were found to be quite isolated by the medium, and were coordinated by all the amine groups of L, as shown by the crystal structure of the dinuclear [Zn(2)H(-1)L](3+) species. This species can bind guests such as hydroxide and phosphate anions. Studies of anion binding in aqueous solution using pyrochatecol violet as the sensing guest revealed that the [Zn(2)H(-1)L](3+) species is able to bind one phosphate at physiological pH.

The synthesis and characterization of new polydentate ligand 2-(N),2'-(N')-bis[2-(3-hydroxy-2-oxo-2H-pyridin-1-yl)acetamido]-1(N'),2(N),2'(N')-trimethyl-2,2'-diaminodiethylamine (L3) is reported. The coordination properties of L3 and of two analogous macrocyclic ligands (L1 and L2) toward Cu(II) and Zn(II) metal ions are reported. All three ligands show the 3-hydroxy-2(1H)-pyridinone (HPO) groups attached as sidearms to a polyaza fragment, which is a macrocyclic framework in the case of L1 and L2 while it is an open chain in the case of L3. The role of the polyaza fragments in preorganizing the two sidearms was investigated. The basicity of L3 and the binding properties of L1-L3 were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm(-3)). UV-vis spectra as well 1H and 13C NMR experiments were used to understand the role of the HPO and of the polyaza fragments in the stabilization of the cations. While L1 forms stable mono- and dinuclear complexes, L2 and L3 can form only mononuclear species with each of the metal ions investigated. In the main mononuclear species of L2 and L3, the two HPO moieties stabilize the M(II) in a square planar geometry due to the two oxygen atoms of each HPO. The coordination sphere of the metal is completed by adding a secondary ligand such as water molecules in the case of Cu(II) systems or OH- in the Zn(II) systems. These results are confirmed by the crystal structures of the [CuH(-1)L2]+ and [CuH(-1)L3]+ species reported herein. Two conformations of L1 can be hypothesized in the formation of the dinuclear species, as suggested by NMR experiments on the [ZnH(-2)L1] species, which shows two conformers slowly interchanging on the NMR time scale, one of which was found to be more insoluble.

Nitric oxide is a gaseous, short-living free radical which behaves as an important signaling molecule with pleiotropic capacities including vasodilatation, neurotransmission, and microbial and tumor cell killing, as well as in tissue damage and organ-specific autoimmune disorders. Here, a synthesized, dinuclear copper complex system in vitro obtained by the simple aza-phenolic ligand 2,6-bis[[bis-(2-aminoethyl)amino]methyl]phenol (L) and Cu(II) ion has been used. The stability constants of ligand L with Cu(II) ion were determined through potentiometric measurements in aqueous solution (37.1 +/- 0.1 degrees C, I = 0.15 M of NaCl) to mimic the biological medium. The measurements demonstrated that [Cu(2)H(-1)L(OH)](2+) (DCu) is the predominant species present in solution at pH 7.4. The molecular structure of the ligand in this species permits the cooperation of the two copper ions in assembling the substrate, thus the complex can be used as a receptor for small molecules such as NO. As a biological model, we chose the production of NO catalyzed by inducible nitric oxide synthase obtained from RAW 264.7 murine macrophage cell line stimulated with LPS, which enabled us to prove that NO is coordinated by the DCu complex, modifying its EPR spectra. The coordination of NO with DCu reduces the level of nitrite in the culture medium of stimulated RAW 264.7 macrophages without any inhibition in the expression of iNOS.

The basicity behavior and ligational properties of the ligand 2-((bis(aminoethyl)amino)methyl)phenol (L) toward Ni(II), Cu(II), and Zn(II) ions were studied by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, l = 0.15 mol dm-3). The anionic L-H- species can be obtained in strong alkaline solution; this species behaves as tetraprotic base (log K1 = 11.06, log K2 = 9.85, log K3 = 8.46, log K4 = 2.38). L forms mono- and dinuclear complexes in aqueous solution with all the transition metal ions examined; the dinuclear species show a [M2(L-H)2]2+ stoichiometry in which the ligand/metal ratio is 2:2. The studies revealed that two mononuclear [ML-H]+ species self-assemble, giving the dinuclear complexes, which can be easily isolated from the aqueous solution due to their low solubility. This behavior is ascribed to the fact that L does not fulfill the coordination requirement of the ion in the mononuclear species and to the capacity of the phenolic oxygen, as phenolate, to bridge two metal ions. All three dinuclear species were characterized by determining their crystal structures, which showed similar coordination patterns, where all the single metal ions are substantially coordinated by three amine functions and two oxygen atoms of the phenolate moieties. The two metals in the dinuclear complexes are at short distance interacting together as shown by magnetic measurements performed with Ni(II) and Cu(II) complexes, which revealed an antiferromagnetic coupling between the two metal ions. The [Cu2(L-H)2]2+ cation shows a phase transition occurring by the temperature between 100 and 90 K; the characterization of the compounds existing at different temperatures was investigated using X-ray single-crystal diffraction, EPR, and magnetic measurements.

The coordination properties of the ligand 2,6-bis-[[bis-(2-aminoethyl)-amino]methyl]-phenol (L) toward the zinc ion were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm(-3)). L forms mono- and dinuclear complexes with zinc; the stable dinuclear complexes are practically the only existing species using L/Zn(II), molar ratio of 1:2. In these species, each dien subunit binds one zinc ion, while the phenolate moiety bound to both ions allows the two metal centers to be in close proximity with an incomplete coordination environment. The role of this metal-metal distance in binding secondary ligands was investigated for the dinuclear systems 2Zn/L and 2Cu/L by potentiometric (298.1 +/- 0.1 K, I = 0.15 mol dm(-3)) and NMR experiments in aqueous and methanol solution with a series of small guests having nitrogen donor atoms. The coordination sphere of the two metals was completed by adding 1 equiv of only those guests, which showed at least two contiguous donor atoms or two lone pairs on the same atom, to exactly fit the metal-metal distance without modifying the metal cluster. To do this, the imidazole molecule which shows the highest addition constants to the [M(2)H(-1)L](3+) species probably forms a mu-1,1-amino. These results are in agreement with the two crystal structures reported herein [Zn(2)(H(-1)L)(CH(3)CH(2)CH(2)CH(2)O)](ClO(4))(2) (space group P2(1)nb, a = 11.483(5), b = 14.166(5), c = 18.279(5) A, V = 2973(19) A(3), Z = 4, R = = 0.0701, wR2 = 0.1611) and [Zn(2)(H(-1)L)N(3)](ClO(4))(2) (space group C 2/c, a = 14.460(3), b = 12.814(3), c = 14.875(3) A, beta = 105.35(2) degrees, V = 2658(10) A(3), Z = 4, R = 0.0783, wR2 = 0.1806). In fact, these structures display a butanolate or azide guest linked to both Zn(II) ions of the dinuclear complex, resulting in a mu-1,1-oxo and mu-1,1-azido bridge, respectively.

The synthesis and characterization of two new polyazamacrocycles, 1,4,7,10-tetraaza[12](2,6)phenolphane (L1) and 1,4,7,10,13-pentaaza[15](2,6)phenolphane (L2), are reported. Both ligands incorporate the 2,6-phenolic unit within the cyclic framework. The basicity behavior and the ligational properties of L1 and L2 toward Ni(II), Zn(II), and Cu(II) were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm-3). UV spectra were used to understand the role of the phenolic function in the stabilization of the cations. L1 and L2 behave as pentaprotic bases under the experimental conditions used. The UV spectra showed that the deprotonation of the phenolic function occurs at low pH values for both ligands, giving rise to the simultaneous presence of positive and (one) negative charges on the macrocycle. While L1 forms only mononuclear complexes, L2 can also form binuclear species with all the metal ions investigated. In the mononuclear species of both ligands, one nitrogen atom close to the phenol remains unbound. The UV spectra revealed that the phenol, bridging the two metal ions in phenolate form, plays an important role in the stabilization of the binuclear complexes of L2. The coordination sphere of the two metals is completed by adding a secondary ligand such as water molecules or OH-, in any case preferring substrates able to bridge the two close metal ions. These results are confirmed by the crystal structure of [Ni2(C16H28ON5)(H2O)2Cl2]Cl.H2O.CH3OH (space group P21/a, a = 14.821(5) A, b = 10.270(4) A, c = 17.663(6) A, beta = 108.87(3) degrees, V = 2544(2) A3, Z = 4, R1 = 0.0973, wR2 = 0.2136). This structure displays a Ni(II) binuclear complex of L2 in which the phenolic oxygen and a chlorine ion bridge the two close Ni(II) ions.