RESUMO
A series of 2-biphenyl bismuth(iii) compounds of the type (2-PhC6H4)3-nBiXn [n = 0 (1); n = 1, X = Cl (2), Br (3), I (4), Me (5); n = 2, X = Cl (6), Br (7), I (8)] has been synthesized and analyzed with focus on intramolecular London dispersion interactions. The library of the compounds was set up in order to investigate the Biπ arene interaction by systematic variation of X. The structural analysis in the solid state revealed that the triarylbismuth(iii) compound 1 shows an encapsulation of the metal atom but the distances between the bismuth atom and the phenyl centroids amount to values close to or larger than 4.0 Å, which is considered to be a rather week dispersion interaction. In the case of monomeric diorganobismuth(iii) compounds 2-5 the moderate crowding effectively hinders the formation of intermolecular donor-acceptor interactions, but allows for intramolecular dispersion-type interactions with the 2-biphenyl ligand. In contrast, the structures of the monoorganobismuth compounds 6-8 show the formation of Bi-XBi donor-acceptor bonds leading to the formation of 1D ribbons in the solid state. These coordination bonds are accompanied by intermolecular dispersion interactions with BiPhcentroid distances < 4.0 Å. In solution the diorganobismuth(iii) halides 2-4 show a broadening of their NMR signals (H-8, H-8' and H-9, H-9' protons of the 2-biphenyl ligand), which is a result of dynamic processes including ligand rotation. For further elucidation of these processes compounds 2, 4 and 7 were studied by temperature-dependent NMR spectroscopy. Electronic structure calculations at the density functional theory and DLPNO-coupled cluster level of theory were applied to investigate and quantify the intramolecular London dispersion interactions, in an attempt to distinguish between basic intramolecular interactions and packing effects and to shed light on the dynamic behavior in solution.
RESUMO
New diorganobismuth(iii) bromides of type [RN(CH2C6H4)2]BiBr [R = C6H5CH2 (1), C6H5CH2CH2 (2), and CH3OCH2CH2 (3)], based on the heterocyclic butterfly-like tetrahydro-dibenzo[c,f][1,5]azabismocine framework, were prepared starting from the corresponding RN(CH2C6H4Br-2)2 in a succession of reactions including ortho-lithiation and treatment of the dilithio derivative with BiBr3 in a 1 : 1 molar ratio. Further exchange reactions between bromides and appropriate metal halides or ammonium fluoride resulted in the formation of [RN(CH2C6H4)2]BiX [X = Cl and I for R = C6H5CH2 (4 and 5) and C6H5CH2CH2 (6 and 7) and X = F (8), Cl (9), and I (10) for R = CH3OCH2CH2]. All ten compounds were structurally characterized in solution by NMR and in the solid state by single-crystal X-ray diffraction. Strong transannular NâBi interactions were observed in all the investigated diorganobismuth(iii) halides, thus giving rise to hypervalent 10-Bi-4 species in 1, 2, 4-7 and 12-Bi-5 species in 3, 8-10, where the oxygen atom in the pendant arm is intramolecularly coordinated to bismuth. The molecules are associated in dimeric units by strong Biπ arene interactions in 3, 4, and 10 (approx. 3.50 Å) and by BiX interactions in 1, 5, and 7. Bromide 1, chloride 4, and iodide 5 are isostructural, but stronger polarization of the Bi-Cl bond favors Biπ arene interaction in 4 over Bihalide interactions, as observed in 1 and 5. In the isostructural series [RN(CH2C6H4)2]BiX (R = CH3OCH2CH2), Bioxygen interactions compensate the electron deficiency at bismuth in fluoride 8 and chloride 9, whereas the coordination sphere of bismuth is completed by a combination of Biπ arene and Bihalide interactions in bromide 3 and only by Biπ arene interactions in iodide 10. Moreover, weak Hπ arene and HX intermolecular interactions, mainly of dispersion type, contribute to supramolecular networks in all three series of compounds.
