Dehydrogenative Double C—H Bond Activation in a Germylene-Rhodium Complex

Abstract

Transition metal tetrylene complexes offer great opportunities for molecular cooperation due to the ambiphilic character of the group 14 element. Here we focus on the coordination of germylene [(Ar<sup>Mes2</sup>)<sub>2</sub>Ge:] (Ar<sup>Mes</sup> = C<sub>6</sub>H<sub>3</sub>-2,6-(C<sub>6</sub>H<sub>2</sub>-2,4,6-Me<sub>3</sub>)<sub>2</sub>) to [RhCl(COD)]<sub>2</sub> (COD = 1,5-cyclooctadinene), which yields a neutral germyl complex in which the rhodium center exhibits both <i>η</i><sup>6</sup>- and <i>η</i><sup>2</sup>-coordination to two mesityl rings in an unusual pincer-type structure. Chloride abstraction from this species triggers a singular dehydrogenative double C—H bond activation across the Ge/Rh motif. We have isolated and fully characterized three rhodium-germyl species associated to three C—H cleavage events along this process. The reaction mechanism has been further investigated by computational means, supporting the key cooperative action of rhodium and germanium centers.Transition metal tetrylene complexes offer great opportunities for molecular cooperation due to the ambiphilic character of the group 14 element. Here we focus on the coordination of germylene [(Ar<sup>Mes2</sup>)<sub>2</sub>Ge:] (Ar<sup>Mes</sup> = C<sub>6</sub>H<sub>3</sub>-2,6-(C<sub>6</sub>H<sub>2</sub>-2,4,6-Me<sub>3</sub>)<sub>2</sub>) to [RhCl(COD)]<sub>2</sub> (COD = 1,5-cyclooctadinene), which yields a neutral germyl complex in which the rhodium center exhibits both <i>η</i><sup>6</sup>- and <i>η</i><sup>2</sup>-coordination to two mesityl rings in an unusual pincer-type structure. Chloride abstraction from this species triggers a singular dehydrogenative double C—H bond activation across the Ge/Rh motif. We have isolated and fully characterized three rhodium-germyl species associated to three C—H cleavage events along this process. The reaction mechanism has been further investigated by computational means, supporting the key cooperative action of rhodium and germanium centers.