Synthesis of hydridotrifluoromethyl complexes of platinum(II). A spectroscopic investigation of the trans and cis influence of ligands in hydridoplatinum(II) compounds

Abstract

The starting complex trans-[PtH(CF3)(PPh3)2] is prepared from trans-[PtCl(CF3)(PPh3)2] by treatment of the derived labile solvento cathionic species trans-[Pt(CF3)(PPh3)2(solv)]BF4(solv = acetone or CH2Cl2) with NaBH4 in EtOH at 0 °C. The hydridotrifluoromethyl complexes trans-[PtH(CF3)L2][L = PMePh2, PMe2Ph, PMe3, P(CH2Ph)Ph2, P(CH2Ph)2Ph, P(CH2Ph)3, PEtPh2, P(C6H11)3, or P (C6H4Me-4)3] are obtained by reaction of trans-[PtH(CF3)(PPh3)2] with 2 equivalents of phosphine, L, in n-heptane at room temperature. Similar exchange reactions between trans-[PtH(CF3)(PPh3)2] and equivalent amounts of diphosphine, L–L =cis-Ph2PCHCHPPh2, Ph2PCH2CH2PPh2, Me2PCH2CH2PMe2, or Ph2PCH2CH2CH2PPh2, lead to the formation of the corresponding [PtH(CF3)(L–L)] compounds. The hydridotrifluoromethyl complexes with L–L =cis-Ph2PCHCHPPh2 and Ph2PCH2CH2PPh2 can be prepared also by reaction of the parent chloro derivatives [PtCl(CF3)(L–L)] with NaBH4 in EtOH at room temperatue. The mixed isocyanide–phosphine complexes [PtH(CF3)(PPh3)(CNR)][R = 2,6-Me2C6H3, 4-MeOC6H4, or But] are obtained by reaction of trans-[PtH(CF3)(PPh3)2] with a three-fold excess of RNC in n-heptane at room temperature. All the hydridotrifluoromethyl complexes are air-stable in the sold state and in solution. They were characterized by elemental analyses and i.r., 1H, 19F, and 31P n.m.r. spectra. The data obtained for ν(PtH) and 1J(PtH) in trans-[PtH(CF3)(PPh3)2] have been used to compare the trans influence of CF3– with other σ carbon donors,R, in trans-[PtH(R)(PPh3)2] derivatives. The n.m.r.-based trans influence order is CF3– > C6H5– > C6H9– > CH2CH2CN– > CH2CH2CH2CN– > CH3– > CH2CN– > Cl–, wheras the i.r.-based trans influence order is C6H9– > CH2CH2CH2CN– > C6H5–≈ CH3– > CF3– > Cl–. The opposite position of CF3– in the two series of trans influence has been explained by the different mechanism operating on 1J(PtH) and ν(PtH). The first depends predominantly on the s character of the platinum hybrid orbital used in the Pt–H bond, while the second is sensitive also to electrostatic effects induced by the electronegative fluorine atoms. The 1J(PtP) data for the same series of complexes gives the following order of cis influence: Cl– > CH2CN– > CF3–≈ CH3–≈ C6H5–≈ CH2CH2CN– > CH2CH2CH2CN–. From the spectra of trans-[PtH(X)L2](X = CF3 or Cl), the effects of replacing two PPh3 ligands in trans-[PtH(CF3)(PPh3)2] by L on ν(PtH) and 1J(PtH) were measured. With the assumption that the cis effects are additive, the i.r. and n.m.r. parameters were correlated with the electronic χ and steric θ parameters of the phosphine ligands.