PALLADIUM(II) COMPLEXES OF HYBRID PHOSPHINE PHOSPHINE OXIDE LIGANDS

Complexes of the type [L2PdCl2], where L = Ph2PCH2P(O)Ph-2 (dppmO), Ph 2P(CH2)(2)P(O)Ph-2 (dppeO), Ph2P(CH2)(3)P(O)Ph-2 (dpppO), Ph2P(CH2)(4) P(O)Ph-2 (dppbO), and Ph2PC5H4FeC5H4P(O)Ph-2 (dppfcO), were prepared i n high yield from Na-2[PdCl4] and 2 equiv, of the corresponding L in d ichloromethanemethanol. All complexes, except for [(dppfcO)(2)PdCl2], can exist as the cia and trans isomers, or mixtures of both, with the cis/trans ratio decreasing in media of low polarity. The ferrocene con taining complex, [(dppfcO)(2)PdCl2], appeared to be exclusively trans in both the solid state and solution, as established by single crystal X-ray diffraction of its 1 :3 benzene solvate. The ion exchange extra ction of dichloromethane solutions of [(dppmO)(2)PdCl2] and [(dppeO)(2 )PdCl2] with aqueous NaBF4 furnished the corresponding cationic P,O-ch elates, cis-[(dppmO)(2)Pd](2+) (BF4-)(2) and cis-[(dppeO)(2)Pd](2+) (B F4-)(2). Alternatively, these cations can be generated by the reaction between the chloro complexes, [(dppmO)(2)PdCl2] and [(dppeO)(2)PdCl2] , with Ag+. Single crystal X-ray diffraction of cis-[(dppeO)(2)Pd](2+) (BF4-)(2) revealed distinct conformations (a puckered chair and a dis torted sofa) for the two chelate rings situated around each Pd atom. A polymeric, poorly soluble material, {[(dpppO)(2)Pd](2+) (BF4-)(2)}(n) , was isolated from the reaction between [(dppO)(2)PdCl2] and AgNO3/Na BF4, with both coordinated and free phosphoryl groups being present in the product (IR). In dilute solutions of the {[(dpppO)(2)Pd](2+) (BF4 -)(2)}(n), depolymerization occurred, giving rise to the monomeric cat ionic chelate, cis-[(dpppO)(2)Pd](2+) (BF4-)(2). (C) 1998 Published by Elsevier Science Ltd. All rights reserved.