Diphosphine and diarsine complexes of chromium(III). Crystal and molecular structure of [NPrn 4][Cr(cis-Ph2PCHCHPPh2)Cl4]

Abstract

cis-[Cr(L–L)X4]– ions (X = Cl, Br, or I; L–L = diphosphine or diarsine) have been isolated as tetra-alkylammonium salts by reaction of [NR4]X, [Cr(thf)3X3](thf = tetrahydrofuran), and L–L. The reaction of [Cr(thf)3X3] with L–L′ in CH2Cl2 gave Cr(L–L′)1,5X3[L–L′=o-C6H4(AsMe2)2, o-C6H4(AsMe2)(PMe2), o-C6H4(NMe2)(PMe2), or o-C6H4(PMe2)(SbMe2)], which are formulated as trans-[Cr(L–L′)2X2]cis-[Cr(L–L′)X4]. In the case of o-C6H4(PMe2)2 only, it is possible to isolate both Cr[o-C6H4(PMe2)2]1,5X3 and [Cr{o-C6H4(PMe2)2}2X2]X depending upon the Cr : L–L ratio. The ligand Me2As(CH2)3AsMe2 gave Cr(L–L)1,5X3(X = Cl or Br) complexes for which a ligand-bridged structure is proposed [X3(L–L)Cr(L–L)Cr(L–L)X3]. Weaker donors (Ph2PCH2CH2PPh2, cis-Ph2PCHCHPPh2, or Ph2AsCH2CH2AsPh2) react with [Cr(thf)3X3] to give [Cr(L–L)2X3] which contain one uni- and one bi-dentate diphosphine or diarsine, and in the presence of moisture [Cr(L–L)(H2O)X3] can be isolated. The complexes [Cr(L–L)2X2]Y [X = Cl or Br; Y = ClO4– or PF6–; L–L =o-C6H4(AsMe2)2 or o-C6H4(PMe2)2] have also been obtained The complexes have been characterised by analysis, conductance, i.r. and electronic spectroscopy, and the electronic spectra analysed (d3) to produce Dq, B′, and β35. The title complex is triclinic, a= 17.534(3), b= 11.930(2), c= 11.108(3)Å, α= 116.30(2), β= 75.12(2), γ= 110.61(1)°, and Z= 2; space group P(no. 2). 1 757 Reflections were refined to R= 0.0656 (R′= 0.0658). The structure consists of tetrahedral NPrn4+ cations, and pseudo-octahedral [Cr(Ph2PCHCHPPh2)Cl4]– anions. In the anion Cr–P = 2.485(4) and 2.511(4)Å; Cr–Cl = 2.331 (4), 2.31 9(4), 2.31 8(4), and 2.31 6(4)Å; P–Cr–P = 81.2°. The diphosphine does not exert any trans influence, consistent with weak binding to the hard CrIII ion.