麻豆淫院

When it comes to chemical bonding, boron has a reputation for being unconventional. While covalent bonds are usually formed by sharing two electrons between two atoms, some compounds鈥攊ncluding diboranes (B₂H₆) 鈥攃ontain B鈥揌鈥揃 bonds in which an electron pair is distributed over three sites. The electron-deficient nature of these 鈥�3-center, 2-electron鈥� bonds can generate a variety of distinct chemical structures, some of which鈥攕uch as triple-bonded diborane derivatives鈥攈ave only been seen theoretically.

Kohei Tamao and colleagues from the RIKEN Advanced Science Institute in Wako and Kyoto University, Japan, have now isolated the first stable diborane molecule with butterfly-shaped B鈥揌鈥揃 bonds and a boron鈥揵oron link with triple bond characteristics. This discovery unlocks new insights into the workings of 3-center, 2-electron boron interactions and puts scientists one step closer to synthesizing the elusive boron鈥揵oron triple bond.

The key to this approach is a bulky molecule known as 鈥楨ind鈥� that contains a rigid core of fused hydrocarbon rings covered with ethyl side chains. Previously, the researchers used Eind ligands to stabilize heavy elements into multiply bonded species. This time, the team hoped to generate a neutral boron鈥揵oron double bond by substituting Eind groups for hydrogen atoms in diborane.

However, after characterizing the structure of the diborane鈥揈ind compound鈥攁 difficult task requiring synchrotron x-rays to detect hydrogen atom positions鈥攖he researchers saw a previously unidentified arrangement at the B2H2 core: a central boron鈥揵oron connection nearly as short as a theoretical triple bond, flanked by two symmetric B鈥揌鈥揃 鈥榳ings鈥� (Fig. 1). 鈥淲e did not expect this butterfly-shaped structure at first, and finding it was a kind of serendipity,鈥� says co-author Yoshiaki Shoji.

Quantum computations revealed that the Eind ligands enforced a linear bonding geometry upon the boron atoms, creating molecular energy levels closely related to the triple-bond species. Furthermore, the bridging hydrogen atoms enhanced the multiple bonding characteristics. 鈥淏ased on this analysis, it is possible to consider triple bonding interactions between the two boron atoms,鈥� says team-member Tsukasa Matsuo.

Matsuo notes that the butterfly-shaped molecule already displays unique chemical reactivity, and the insights gained from this new structure could lead to additional multiply-bonded diboranes. 鈥淲e may be able to synthesize a more triply bonded species in the near future by replacing the bridging hydrogen atoms with alkali metals,鈥� he says. 鈥淎t the moment, this compound is just a dream but I think we have a chance to obtain it.鈥�