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Borabenzene
A borabenzene is a heteroaromatic compound that has a boron atom instead of the carbon atom of a benzene molecule. A free borabenzene, which has no donor ligand on the boron atom, has not yet been isolated despite its simple structure and the chemical robustness of boron-carbon bonds. The instability of this molecule results from the high Lewis acidity of the boron atom due to its electron deficiency. All attempts to create a free borabenzene have resulted in formations of complexes with anionic or neutral ligands (even a nitrogen molecule can coordinate to a borabenzene). However, the complexes with anionic ligands, called boratabenzenes, show rich chemistry including the coordination chemistry as anionic ''π''-type ligands. Borabenzene also forms stable adducts with electron donor molecules such as pyridine (the adduct with which is isoelectronic with biphenyl) or triphenylphosphine (the adduct with which is isoelectronic with tetraphenylsilane).
==Properties as ligands==
Boratabenzenes have a negative charge on their six-membered rings and act as strong ''π''-donating ligands like a cyclopentadienyl anion, which is often used in transition metal complexes. In fact, sandwich or half-sandwich type complexes of many transition metals have been reported using boratabenzenes, and the zirconium sandwich complexes exhibit catalytic activity in ethylene polymerization similar to zirconocenes, which are the cyclopentadienyl counterparts.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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