Exploring the structure and redox activity of hexacoordinate bis(bipyridyl)silicon(IV) complexes

Abstract A series of hexacoordinate bis(bipyridyl)silicon(IV) complexes was synthesized by allowing [Si(bpy) 2 I 2 ]I 2 to react with the alcohols or phenols: methanol, ethylene glycol, phenol, 2,2′-biphenol, or 1,2-benzendiol. Crystal structures were obtained for the corresponding complexes: [Si(bpy) 2 (OMe) 2 ] (I)(I 3 ) ( 1 ), [Si(bpy) 2 (-OCH 2 CH 2 O-)]I 2 ( 2 ), [Si(bpy) 2 (OPh) 2 ](I 3 ) 2 ( 3 ), [Si(bpy) 2 (bph)](PF 6 ) 2 ( 4 ), and [Si(bpy) 2 (cat)](PF 6 ) 2 ( 5 ), (bpy = 2,2′-bipyridine, cat = 1,2-benzenediolato, bph = 2,2′-biphenolato ligand). All five complexes exist as distorted octahedral dications with readily exchangeable counterions. The hexafluorophosphate salts of each complex cation exhibit a reversible, first reduction wave around −1 V (versus Fc + /Fc) in acetonitrile, nearly independent of the alkoxide or diolate substituent. This is consistent with DFT calculations indicating a LUMO localized on the bipyridyl ligands. The complexes with bidentate diolate ligands possess multiple reversible reduction waves.