'Dialuminyne' debuts

The first well-characterized example of a "dialuminyne" has been prepared by Philip P. Power's group at the University of California, Davis (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200601925). As its name implies, this species-Na₂[RAlAlR], where R is a bulky terphenyl group-is the aluminum analog of an alkyne. But the nature of the bonding between the aluminum atoms (green) isn't as clear as in the typical alkyne, in part because the sodium atoms (yellow) interact with the aluminum atoms and aryl groups. Although the dialuminyne has "a formal Al-Al bond order of three, its calculated bond order is close to one," Power notes. The structural features suggest that the electron density between the aluminum atoms is depleted, weakening Al-Al σ bonding. The dialuminyne thus resembles a "digallyne" that was reported in 1997 by Gregory H. Robinson's group at the University of Georgia. The Ga-Ga bonding in that compound stirred much debate. Robinson has stirred the pot again, telling C&EN that dialuminyne and digallyne should both be regarded as having a weak triple bond.