Chromium(III) complexes of multidentate phosphines, arsines, and thioethers. Crystal and molecular structure of the complex mer-[Cr{P(CH2CH2PPh2)3}Cl3]

Abstract

Octahedral chromium(III) complexes mer-[CrLX₃]{X = Cl or Br; L = PPh(CH₂CH₂PPh₂)₂, P(CH₂CH₂PPh₂)₃, [–CH₂P(Ph)CH₂CH₂PPh₂]₂, or S(CH₂CH₂CH₂SMe)₂} and fac-[CrLX₃][L = CMe(CH₂PPh₂)₃, CMe(CH₂AsMe₂)₃, CMe(CH₂SMe)₃, AsMe(CH₂CH₂CH₂AsMe₂)₂, or As(CH₂CH₂CH₂AsMe₂)₃] have been prepared from [Cr(thf)₃X₃](thf = tetrahydrofuran) and L in CH₂Cl₂ under anhydrous conditions. Chromium(III) fluoride complexes [CrLF₃][L = PPh(CH₂CH₂PPh₂)₂, P(CH₂CH₂PPh₂)₃, or CMe(CH₂AsMe₂)₃] are obtained by reaction of [Cr(thf)₃Cl₃] with AgF in thf, followed by addition of the ligand. The reactions with [Cr(thf)₃I₃] differ in that both [CrLI₃][L =e.g. PPh(CH₂CH₂PPh₂)₂ or CMe(CH₂AsMe₂)₃] and CrL₂l₃ can be isolated depending upon the Cr : L ratio. The [CrLX₃] complexes, which have been characterised by i.r. and electronic spectroscopy, conductance and molecular weight measurements, have P₃X₃, As₃X₃, or S₃X₃(X = F, Cl, Br, or l) donor sets. The electronic spectra were analysed to produce Dq, B′, and β₃₅. Treatment of [CrLCl₃]{L = P(CH₂CH₂PPh₂)₃, As(CH₂CH₂CH₂AsMe₂)₃, or [–CH₂P(Ph)CH₂CH₂PPh₂]₂} with AgBF₄ in CH₂Cl₂ produced cis-[CrLCl₂]BF₄(P₄Cl₂ or As₄Cl₂ donor sets). The title complex is monoclinic, a= 14.787(6), b= 21.617(4), c= 14.474(4)Å, β= 113.43(3)°, and Z= 4; space group p2₁/a(no. 14). 2101 Reflections were refined to R= 0.075 (R′= 0.079). The molecular complex has a mer octahedral structure (P₃Cl₃ co-ordination) with Cr–P(Ph₂) 2.466(5) and 2.489(6); Cr–P(CH₂)₃ 2.399(4); Cr–Cl 2.306(4), 2.292(6), and 2.320(5)Å. The long Cr–P bonds are due both to the steric crowding, and the relatively weak binding of the phosphorus donors to the hard metal, and both these points are also evident in the electronic spectral parameters.