The square-planar platinum(II) complexes of a series of bis(diphenylphosphine)alkanes have been synthesized and characterized by infrared and phosphorus-31 NMR spectroscopy, elemental analysis, and vapor-phase osmometry. Cis complexes are formed when the complex precursor is potassium tetrachloroplatinate(II), while the corresponding trans complexes are preferred when the starting material is Zeise's salt. An unusual trans-bonded complex with dpe has also been isolated. The trans isomers revert to their cis analogues in the presence of heat or excess bis(phosphine). The cis dimers are the most stable isomers for the majority of the cis complexes. The preferred ring sizes for the cis chelated monomers are 14-and 19-membered chelate rings. The amount of trans monomer increases with increasing chain length and reaches a maximum with a chelate ring size of 15 members and can be correlated directly with ring contributions to the chemical shift-thus ring contributions in trans monomeric complexes can be used as a measure of ring strain for these ligands. Large flexible chelate rings (19 members or above) appear to be unstable in the trans configuration.
The coordination chemistry of silver(I) with the nitrogen-bridged ligands (C(6)H(5))(2)PN(R)P(C(6)H(5))(2) [R = H (dppa); R = CH(3) (dppma)] has been investigated by (31)P NMR and electrospray mass spectrometry (ESMS). Species observed by (31)P NMR include Ag(2)(mu-dppa)(2+), Ag(2)(mu-dppa)(2)(2+), Ag(2)(mu-dppa)(3)(2+), Ag(2)(mu-dppma)(2+), Ag(2)(mu-dppma)(2)(2+), and Ag(eta(2)-dppma)(2)(+). Species observed by ESMS at low cone voltages were Ag(2)(dppa)(2)(2+), Ag(2)(dppa)(3)(2+), Ag(2)(dppma)(2)(2+), and Ag(dppma)(2)(+). (C(6)H(5))(2)PN(CH(3))P(C(6)H(5))(2) showed a strong tendency to chelate, while (C(6)H(5))(2)PN(H)P(C(6)H(5))(2) preferred to bridge. Differences in the bridging versus chelating behavior of the ligands are assigned to the Thorpe-Ingold effect, where the methyl group on nitrogen sterically interacts with the phenyl groups on phosphorus. The crystal structure of the three-coordinate dinuclear silver(I) complex (Ag(2)[(C(6)H(5))(2)PN(H)P(C(6)H(5))(2)](3))(BF(4))(2) has been determined. Bond distances include Ag-Ag = 2.812(1) A, Ag(1)-P(av) = 2.492(3) A, and Ag(2)-P(av) = 2.509(3) A. The compound crystallizes in the monoclinic space group Cc at 294 K, with a = 18.102(4)(o), Z = 4, V = 7261(3) A(3), R = 0.0503, and R(W) = 0.0670.
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