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Syntheses and Structures of Hypervalent Pentacoordinate Carbon and Boron Compounds Bearing an Anthracene Skeleton − Elucidation of Hypervalent Interaction Based on X-ray Analysis and DFT Calculation
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posted on 2005-03-30, 00:00 authored by Makoto Yamashita, Yohsuke Yamamoto, Kin-ya Akiba, Daisuke Hashizume, Fujiko Iwasaki, Nozomi Takagi, Shigeru NagasePentacoordinate and tetracoordinate carbon and boron compounds (27, 38, 50−52, 56−61)
bearing an anthracene skeleton with two oxygen or nitrogen atoms at the 1,8-positions were synthesized
by the use of four newly synthesized tridentate ligand precursors. Several carbon and boron compounds
were characterized by X-ray crystallographic analysis, showing that compounds 27, 56−59 bearing an
oxygen-donating anthracene skeleton had a trigonal bipyramidal (TBP) pentacoordinate structure with
relatively long apical distances (ca. 2.38−2.46 Å). Despite the relatively long apical distances, DFT calculation
of carbon species 27 and boron species 56 and experimental accurate X-ray electron density distribution
analysis of 56 supported the existence of the apical hypervalent bond even though the nature of the
hypervalent interaction between the central carbon (or boron) and the donating oxygen atom was relatively
weak and ionic. On the other hand, X-ray analysis of compounds 50−52 bearing a nitrogen-donating
anthracene skeleton showed unsymmetrical tetracoordinate carbon or boron atom with coordination by
only one of the two nitrogen-donating groups. It is interesting to note that, with an oxygen-donating skeleton,
the compound 61 having two chlorine atoms on the central boron atom showed a tetracoordinate structure,
although the corresponding compound 60 with two fluorine atoms showed a pentacoordinate structure.
The B−O distances (av 2.29 Å) in 60 were relatively short in comparison with those (av 2.44 Å) in 59
having two methoxy groups on the central boron atom, indicating that the B−O interaction became stronger
due to the electron-withdrawing nature of the fluorine atoms.
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Keywords
skeletonDFT Calculation Pentacoordinatepentacoordinate structureBoron Compounds Bearingboron species 56TBPunsymmetrical tetracoordinate carbonboron atomanthraceneapical distancesHypervalent Pentacoordinate Carbonapical hypervalent bondtridentate ligand precursorscarbon species 27fluorine atomsboron compoundsanalysis
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