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The reaction of alpha,alpha'-bis(3,5-bis(bromomethyl)phenoxy-p-xylene (3) with 4 equiv of the monolithium salt of 1-Ph-1,2-C2B10H11 or 1-Me-1,2-C2B10H11 gave the corresponding neutral carboranyl-functionalized aryl ether derivatives closo-4 and closo-5, respectively. These compounds contain four closo clusters that were degraded using basic conditions with KOH in EtOH, affording the corresponding nido-6 and nido-7 as potassium salts. Nido species were also isolated with tetramethylammonium as cation giving compounds nido-8 and nido-9 in good yield. The potassium salts showed good solubility in water and polar solvents. All these compounds were characterized by 1H, 11B and 13C NMR spectroscopy and UV-vis. The electronic data in different solvents indicated a solvatochromic shift for all compounds and a red shift of the absorption maxima for the nido species with respect to the closo derivatives. These neutral and anionic carboranyl-functionalized aryl ether derivatives represent a new family of high boron content luminescent compounds that show strong fluorescence emission in different solvents at room temperature. This phenomenon is very interesting considering the fact that none of the precursors have such a property. The fluorescence emission depends on the cluster substituent (Ph or Me) and the solvent polarity. Additionally, the fluorescence emission intensity was clearly dependent on the solvent polarity; the closo species showed strongest fluorescence intensities in the non-polar solvents, while anionic species were highly emissive in polar solvents.

Five new boronates of the type 2-phenyl-6-aza-1,3-dioxa-2- borabenzocyclononenes (6a-e) were prepared from substituted 2-[(2- hydroxyethylamino)methyl]phenols (4a-e) and phenylboronic acid (5) in benzene-EtOH (4:1) mixtures. Tridentate ligands 4a-e and boronates 6a-e were characterized by [sup.1]H, [sup.13]C, [sup.15]N, and 2D-NMR (HETCOR, NOESY, and COLOC) experiments, FT-IR, mass spectra, and elemental analysis, as well as [sup.11]B NMR for the boron derivatives. Suitable monocrystals of 2-[(2-hydroxyethylamino)methyl]phenol hydrochloride (4a), cis-2-phenyl-6-aza-1,3-dioxa-2- borabenzocyclononene (6a), (2S,5R,6S)-2,5-diphenyl-6-aza-1,3-dioxa-2- borabenzocyclononene (6b), and (2S,4R,5R,6S)-2,4-dipbenyl-5-methyl-6- aza-1, 3-dioxa-2-borabenzocyclononene (6e) were obtained and their structures are discussed. The X-ray structures of 6a, 6b, and 6e, as well as the NMR data established that the configurations at the nitrogen and boron atoms are both "S" and the transannular fusion is cis. A semi-empirical (SAM1) study was used to calculate the energy for all possible stereoisomers, showing that the stabilization increases as the THC (tetrahedral character of the boron atom) increases and also as the N [right arrow] B bond distance decreases, in agreement with the experimental results and previous work related to amino acid boronates. Key words: boron compounds, X-ray structures, NMR, boronates, synthesis.

The reaction of N-salicylidene-2-aminophenolate (SAP-[H.sub.2]) derivatives with phenyl boronic acid afforded five new boron bicyclic species in moderate yields, as confirmed by an X-ray study of the boron heterocycle derived from 2-amino-4-chlorophenol. The results also showed that the boron complexes derived from Schiff bases undergo an acetolysis reaction to give the corresponding dioxazaborocines containing all substituents on the same side also in good yields. The structure of one of the addition products was established by X-ray analysis showing that, in the solid state, it exists as a dimeric structure formed by hydrogen bonds. Key words: borocines, tridentate ligands, imines, boronic acids.

Fluorescent star-shaped molecules and dendrimers with a 1,3,5-triphenylbenzene moiety as the core and 3 or 9 carborane derivatives at the periphery, have been prepared in very good yields by following different approaches. One procedure relies on the nucleophilic substitution of Br groups in 1,3,5-tris(4-(3-bromopropoxy)phenyl)benzene with the monolithium salts of methyl and phenyl- o-carborane. The second method is the hydrosilylation reactions on the peripheral allyl ether functions of 1,3,5-tris(4-allyloxy-phenyl)benzene and 1,3,5-tris(4-(3,4,5-trisallyloxybenzyloxy)phenyl)benzene with suitable carboranyl-silanes to produce different generations of dendrimers decorated with carboranyl fragments. This approach is very versatile and allows one to introduce long spacers between the fluorescent cores and the boron clusters, as well as to obtain a high loading of boron clusters. The removal of one boron atom from each cluster leads to high-boron-content water-soluble macromolecules. Thermogravimetric analyses show a higher thermal stability for the three-functionalized compounds than for those containing 9 clusters. All compounds exhibit photoluminescent properties at room temperature under ultraviolet irradiation with high quantum yields; these depend on the nature of the cluster and the substituent on the Ccluster. Cyclic voltammetry indicates that there is no electronic communication between the core and the peripheral carboranyl fragments. Due to the high boron content of these molecules, we currently focus our research on their biocompatibility, biodistribution in cells cultures, and potential applications for boron neutron capture therapy (BNCT). [ABSTRACT FROM AUTHOR]

Abstract: The structural analogy of 1,3-dicarbonyl compounds with 2-hydroxybenzencarbonyl compounds allowed to do an analysis towards the reactivity with 3-aminophenylboronic acid, in order to evaluate the synthesis of macrocyclic boron compounds having calixarene like structures. The results indicate that the chelate form is preferred over the reaction of the amino group with carbonyl groups. Thus the reaction of 1,3-diketones (1,3-diphenyl-1,3-propanedione, 1-phenyl-1,3-butanedione and 2,4-pentanedione) with 3-aminophenylboronic acid using methanol or propanol as solvent medium, afforded the six-membered boron chelates as the only product. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of 2,6-dimethanolpyridine with arylboronic acids at room temperature led to the formation of tetrameric compounds 1a–1e in good yields. Since the tetrameric derivatives were insoluble in common organic solvents, their characterization was based on IR, mass spectrometry, as well as 13C and 11B NMR, in the solid state. Macrocyclic compounds 1a–1e can be hydrolyzed upon heating in DMSO to give adducts 2a–2e, which are only held by a coordination bond between the nitrogen and boron atoms, as demonstrated by 1H, 13C and 11B NMR, in solution. Moreover, the presence of an additional carbon atom in the aliphatic chain of the ligand, as in the case of 2,6(β-diethanolamine)pyridine, leads exclusively to the formation of the monomeric specie 4, as established by X-ray diffraction analysis. [Copyright &y& Elsevier]

Abstract: A series of substituted 2-hydroxysalicylidine benzohydrazides were converted into their phenyl-boron complexes in good yields upon reaction with phenylboronic acid. All new compounds were characterized by NMR, UV, IR, spectroscopy and mass spectrometry. The X-ray structures of two complexes demonstrate that the boron atoms adopt a tetrahedral geometry. The 11B NMR chemical shifts of the boron atom in the complexes are also consistent with the presence of tetracoordinate boron centres. The photophysical properties of the free benzohydrazide ligands and their boron complexes have been determined and display quantum yields below 1% with lifetimes in the range 10−10–10−11 s. [Copyright &y& Elsevier]

Abstract: The reactivity of 3-aminophenylboronic acid toward 3,5-disubstituted salicylaldehyde derivatives (R= tBu, MeO, I, Br, NO2) was analyzed with the aim to synthesize macrocyclic boron compounds having a calix-like structure. The three-component condensation was carried out using different aliphatic alcohols (ROH, R=Me, Et, nPr, nBu, nPn, nHex) in order to replace the free B–OH groups by B–OR moieties and their effect on the structural and physicochemical properties of the resulting compounds was analyzed. When the reaction was carried out under reflux conditions, trimeric calix-like compounds are formed for the 3,5-tButyl salicylaldehyde derivatives. The absence of alcohol molecules during the reaction lead to the condensation of two calixarenes through two of the three B(OH) groups to form two B-O-B moieties, giving place to the formation of a hexanuclear cage. Using the salicylaldehyde derivatives having I, Br and NO2 groups, the Schiff bases resulting from the condensation reaction of the aldehyde and the boronic acid were isolated providing thus evidence for the previously proposed reaction sequence for the formation of the calix-shaped compounds. [Copyright &y& Elsevier]

Abstract: The condensation of 2-[[(2-hydroxyphenyl)amino]methyl]-phenols (1a–1e) with different arylboronic acids led to 12 new monomeric boronates of the type 2-aryl-dibenzo[d,h]-6-aza-1,3-dioxa-2-boracyclononene (2a–2l). The boronates were characterized by 1H-, 13C-, 11B- and 2D-NMR experiments, FT infrared, mass spectra and elemental analyses. The stereochemistry of the H–N→B–Ph fusion is always cis, as established through the NMR spectra, as well as the X-ray structures of four boronates (2a, 2e, 2f and 2l). Hydrogen bonds between the amine proton and the oxygen ester of the five- membered ring are present in three X-ray structures (2a, 2e and 2f), while the supramolecular structure in the derivative possessing a primary amine (2l) is built up through the protons present in this moiety instead of the proton from the H–N→B–Ph fragment. [Copyright &y& Elsevier]

A series of tetradentate ligands were synthesized and their reaction with arylboronic acids was studied. Two classes of tetradentate ligands are discussed, which are mainly based on ONNO and ONOO donor sets and involve 2-aminophenol derivatives and Schiff bases. The reaction of phenylboronic acid with tetradentate ligands derived from 2-aminophenol leads to bisoxazaborolidines containing five-membered rings formed by CCNBO atoms, where the boron atoms have a trigonal geometry. In contrast, tetradentate ligands derived from Schiff bases lead to monomeric and dimeric boron complexes, in which the boron atoms have a tetrahedral geometry stabilized by an intramolecular N–B dative bond. The structures of two boron compounds were established by X-ray diffraction analysis. [Copyright &y& Elsevier]

Examines the preparation of seven-and eight-membered boron heterocycles from different salen ligands and arylboronic acids. Correlation between salicylidene moieties; Characterization of arylboronic acids; Impact of phenylboronic acid in ethanol.