Coordination mode of some polypyridyl ligands towards the platinum(II) complexes [Pt(dppf)(H2O)(2)](CF3SO3)(2) (dppf=1,1 '-bis(diphenylphosphino)ferrocene) and [Pt(Me2SO)(2)Cl-2]. Crystal structure of the seven-membered chelate ring complex [Pt(dpq)Cl-2] (dpq=2,3-di(2-pyridyl)quinoxaline)

A series of novel platinum(II) complexes were isolated through the reaction of the polypyridyl ligands 2,3,7,8-tetra(2-pyridyl)pyrazino[2,3-g]quinoxal ine (tpq), 2,3-di(2-pyridyl)pyrazine (dpp), 2,3-di(2-pyridyl)quinoxaline (d pq) and 6,7-dimethyl-2,3-di(2-pyridyl)quinoxaline (ddpq) with the heterobim etallic complex [Pt(dppf)(H2O)(2)](CF3SO3)(2) or with the dimethyl sulfoxid e complex [Pt(Me2SO)(2)Cl-2]. The di-platinum complex [(Pt(dppf)}(2)(tpq)]( CF3SO3)(4) and the mono-platinum compounds [Pt(dppf)(L)](CF3SO3)(2) (L = dp p, ddpq) and [Pt(L)Cl-2] (L = dpq, ddpq) were synthesized. As shown by H-1 NMR spectroscopy, in these complexes the bridging tpq and the mononucleatin g ligands dpp, dpq and ddpq present an uncommon bidentate chelate mode; the y are bonded to the Pt(II) centres only by the means of their pyridyl nitro gen atoms. This behaviour was corroborated through the X-ray crystallograph ic study of the [Pt(dpq)Cl-2] derivative. The redox properties of the three new dppf-based complexes, in dichloromethane solution, show in all cases t hat they undergo ferrocene-based (dppf) oxidations and that the primary cat hodic processes are tpq-centered in the tpq complex and platinum(II)-center ed in the dpp and ddpq complexes. (C) 2000 Elsevier Science S.A. All rights reserved.