Carbon−Carbon Double Bond Formation from Two <i>o-</i>Methyl Groups in Osmium Phosphine Complexes

The osmium complex [(NH4)2OsCl6] reacts with PPh2(2,6-Me2C6H3) in a 2-propanol−water mixture at reflux to give quantitatively a cyclometalated osmium(II) complex containing a tridentate trans-stilbene-type ligand, which forms via a dehydrogenative carbon−carbon coupling of two phosphine o-methyl groups. The structure of this complex has been determined by an X-ray investigation. Carbon−carbon double bond formation has also been observed in the reaction of the osmium(II) precursor [OsCl2(PPh3)3] with PPh2(2,6-Me2C6H3) in toluene, leading to a hydrido osmium(II) complex containing the same tridentate stilbene-type ligand.