Palladium and platinum complexes of trans-coordinating bidentate phosphine ligands
Two ditertiary phosphine ligands, 1,6.-bis(diphenylphosphino)-hexane, (dPh), and 3,31_bis(diphenylphosphinomethyl)biphenyl, (PP), have been used in the preparation of complexes described in this work. Construction of molecular models proved useful in predicting the likely geometries of the complexes. For example, the ligand PP is capable of chelating trans- but not cis- in a mononuclear fourcoordinate square-planar complex because of the steric constraints due to a rigid back bone in its structure. However, the ligand dPh, with the more flexible chain of methylene groups, is capable of spanning cis- and trans-positions. Preparations of palladium (0) and platinum (0) complexes gave, in low yield, solids which analysed for [Pd(dPh) 2 ]; [Pd(PP)(H 20)] and [Pt(Pp)]. The solids were stable in air for short periods of time, but in organic solvents they appeared to undergo changes, presumably to either the diphosphine dioxide complexes or to the metal and the corresponding ligand dioxide, as evidenced from I H n.rn.r. and infrared studies. This behaviour precluded the determination of molecular weights of the complexes in solution. A series of nickel (11) palladium (II) and platinum (II) complexes of the ligands were prepared; and although the compounds analysed for [MLx2 ] , CX = Cl, Br; I), the nature of the complexes, whether mononuclear of polynuclear, could not be ascertained as they were too insoluble in organic solvents for their molecular weights to be determined. The palladium (II) and platinum (II) complexes were so stable that they could only be decomposed by wet oxidation using perchioric acid and concentrated sulphuric acid mixture. Cisor trans-coordination in the complexes was distinguished by the far infrared studies of the (M-.X) stretching frequencies. The perchlorate complexes of palladium (II) and platinum (II) prepared analysed for [M(L) 2 (clo4 ) 2 ]. From infrared studies and, conductance measurements it was concluded that the complexes were 2:1 electrolytes of the type [ML2 ](Clo 4 ) 2 . Molecular models of the square planar cation, [ML2]2+, show that, when L = dPh, non-bonding interactions are less if the ligand chelates cis- rather than trans-.
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