Carbon−Carbon Double Bond Formation from Twoo-Methyl Groups in Osmium Phosphine Complexes

The osmium complex [(NH 4 ) 2 OsCl 6 ] reacts with PPh 2 (2,6-Me 2 C 6 H 3 ) 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 [OsCl 2 (PPh 3 ) 3 ] with PPh 2 (2,6-Me 2 C 6 H 3 ) in toluene, leading to a hydrido osmium(II) complex containing the same tridentate stilbene-type ligand.