Research in the Power group is focused on expanding knowledge concerning the more exotic chemistries of main group and transition metal chemistry. This includes the synthesis of compounds containing multiple bonds between metal centers and the investigation of their reactivity patterns with an emphasis on their interactions with small molecules. Much of this work is accomplished using the extremely bulky, anionic m-terphenyl ligands. These ligands, by virtue of their considerable steric bulk, stabilize low-coordinate compounds while allowing interactions between the metal center and small molecules.
One of the more interesting uses of the m-terphenyls was the synthesis of Ar’CrCrAr’ which shows evidence of a Cr–Cr quintuple bond. This has been shown to react with N2O and AdN3. Ar#CrPMe3 and Ar#Cr(THF) were also synthesized by the reduction of Ar#CrCl in THF with or without the presence of PMe3, respectively. M-terphenyl ligands have also been used to isolate the products of other low-coordinate transition metals with reactive small molecules, two examples of which are also shown below.
Our group has been able to use m-terphenyl ligands to support low oxidation state compounds of group 13 elements. These include the terminal aryl gallium(I) and the Hückel aromatic [Ar’Al]3. Our main interest in this area, however, lies in the interaction of the compounds with small molecules. In our aluminum example, the as yet uncharacterized intermediate “Na2[Ar’AlAlAr’] undergoes a Diels-Alder-like [2+4] cyclization to give a six-membered ring containing an Al-Al double bond, de-aromatizing the reactant toluene. On the other hand, the gallium(I) species can react with diphenylacetylene to give an antiaromatic ring system (hence the puckered arrangement) which upon a 2e- reduction gives the 6π electron aromatic system.
Our research into the chemistry of low valent Ge and Sn chemistry has also yielded interesting details on their behavior towards H2. The dimer Ar’SnSnAr’ reacts with H2 to give a hydrogen-bridged species, while Ar” gives an unsymmetrical molecule where one of the Sn atoms is bonded to both H atoms. This appears to be due to the increased steric hindrance from the Ar” ligands compared to Ar’. Both reactions are shown below.