The structure and conformation of N,N'-bis[(2-hydroxy)phenyl]oxamide (1 ); N,N'-bis[(2-methoxy)phenylloxamide (2); NN-bis(pheny1)oxamide (3); N,N'-bis[(l R,2S)-( -)-norephedrineloxamide (4); N,N'-bis[ (1 R,2R)-( -)-norpseudoephedrine]oxamide ( 5 ) ; N-[(2-hydroxy)phenyl]methylamide (6); N-[ (2-methoxy)phenyl]methylamide (7); N-phenylmethylamide (8); N-[ ( -) -norephedrine1methylamide ( 9 ) and N-[( -) -norpseudoephedrine]methylamide (1 0) were unambiguously established by 'H, 13C, 15N, 2 0 and variable temperature NMR spectroscopy. A careful NMR investigation of the conformational behaviour in these systems was relevant. It has been found that the dicarbonylic group in compounds 1-5 has a trans geometry, stabilized by intramolecular hydrogen bonding and that they possess a C2 axis. Compounds 1 and 2 are planar and compounds 1,2,4 and 5 present the amidic proton coordinated by two oxygen atoms.

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Protic-fluoride interactionsThe preparation, NMR and X-ray diffraction studies of a series of azolylboron hydrides derived from pyrrole, indole, and carbazole coordinated with tetrahydrofuran, pyridine, and imidazole are reported. The azolyl substituents are very electroattractive leading to a n acidic boron atom which strongly coordinates with the Lewis bases. The stabilization of the -BH2-groups against disproportionation could be explained in terms of the interactions found between the acidic hydrogen atoms of the heterocycles (C-H'+ acceptor) and the hydrides (B-H6-donors).There are few examples of aminoboron hydrides NBH2 derived from aromatic nitrogen heterocycles [',2], in part because free XBH2 boron dihydrides are not stable compounds, the XBH2 group disproportionating to BH3 and BX,; however, the acidic boron atom of these compounds can be stabilized in a cycle by coordination as in the case of pyrazaboles[2c-dl and other XBH2 compounds (X = O)w. It is relevant to understand the nature of the N-B bondC4] and the structural factors for stabilization of the N -BH2 group which could include the donating ability of the nitrogen atoms, the ring aromaticity and the charge distribution. The (dialky1amino)boranes derived from pyrrole, indole, and carbazole were studied by "B-NMR spectro~copy[~>~1.Herein, the preparation and the study by NMR and Xray diffraction analyses of a series of azolylboron hydrides derived from pyrrole, indole, and carbazole coordinated with tetrahydrofuran, pyridine, and imidazole is reported (Scheme 1). The imidazole-BF, adduct was also prepared in order to compare it with the azolylborane-irnidazole adducts. We wanted to know the structural and electronic reasons for the stability of these boron compounds and how coordination affects their behaviour. Results and DiscussionThe azolylborane-THF complexes (Scheme 1) were synthesized from the equimolar reaction of the azole (1-3) and BH3 . THE The reactions were followed by measuring the hydrogen evolution. When the reactions had finished the coordinating nitrogen heterocycles were added. The adducts were isolated by crystallization or precipitation from saturated THF solutions.

cis-and trans-1,2-chdcaH 2 , 1,3-chdcaH 2 , and 1,4-chdcaH 2 (chdcaH 2 = cyclohexanedicarboxylic acid) as well as cis,cis-1,3,5-chtcaH 3 (chtcaH 3 = cyclohexanetricarboxylic acid) have been treated with dimethyl-and di-n-butyltin reagents, and for the case of 1,4-chdcaH 2 additionally with ditert-butyltin dichloride, to determine whether macrocyclic or polymeric diorganotin dicarboxylates are formed dependent of the spatial orientation of the coordinating ligand functions and the organic substituents at the metal atom and to analyze conformational and topological variations in the resulting supramolecular aggregates. The single-crystal X-ray diffraction studies showed that besides the ligand geometry the substituents at the metal center are key elements for the formation of either monomeric, cyclo-oligomeric, or polymeric assemblies. Two of the compounds characterized by X-ray diffraction analysis exhibited macrocyclic ring structures, [{Me 2 Sn(cise,a-1,4-chdca)} 2 ] and [{nBu 2 Sn(cis-e,a-1,4-chdca)} 4 ]. For most of the remaining compounds, one-dimensional polymeric solidstate structures of composition [{R 2 Sn(1,x-chdca)(H 2 O) y } n ] (R = Me, nBu, tBu; x = 2, 3, 4; y = 0, 1) were observed, which had varying topologies, and for the case of the Me 2 Sn and nBu 2 Sn derivatives were further linked to two-or three-dimensional supramolecular architectures, either through intermolecular Sn•••O or O−H•••O hydrogen-bonding interactions.