New complexes of rhenium-(V) or -(III) with various diphosphines or bis(diphenylphosphino)methane monoxide: crystal structure of mer-[ReCl3(dppm-PP′)(dppom-P)][dppm = Ph2PCH2PPh2, dppom = Ph2PCH2P(O)Ph2]

Abstract

Treatment of [ReOCl₃(AsPh₃)₂] or [ReOBr₃(AsPh₃)₂] with the diphosphines, Ph₂PCH₂PPh₂(dppm), Ph₂PC(CH₂)PPh₂(vdpp), cis-Ph₂PCHCHPPh₂(dppen), or Ph₂PCHMePPh₂(1,1′-dppe) gave complexes of the type [ReOX₃(L–L)](L–L = chelating diphosphine, X = Cl or Br), in high yield. Treatment of [ReOCl₃(AsPh₃)₂] with an excess of dppm at 20°C caused some reduction to give a mixture of two rhenium(III) complexes [ReCl₃(dppm-PP′)(dppom-P)]2a[dppom = Ph₂PCH₂P(O)Ph₂] and [ReCl₃(dppm-PP′)(dppm-P)]3a, which was difficult to separate. Treatment of [ReOCl₃(AsPh₃)₂] with 2 mol of dppm in hot benzene gave pure 2a, whilst treatment of [ReCl₃(NCMe)(PPh₃)₂] with 4–5 mol equivalents of dppm in hot benzene gave 3a in excellent yield. The tribromide analogue [ReBr₃(dppm-PP′)(dppom-P)] was prepared by heating [ReOBr₃(dppm-PP′)] with dppm. On treating [ReBr₃(NCMe)(PPh₃)₂] with dppm, [ReBr₃(dppm-PP′)(dppm-P)] was formed but this was contaminated with the isomeric salt [ReBr₂(dppm-PP′)₂]Br from which it could not be separated; however the NMR parameters for both components were assigned. The pure salt [ReBr₂(dppm-PP′)₂]BPh₄ was prepared from the mixture. In their ¹H NMR spectra, these rhenium(III) complexes show large paramagnetic shifts for the methylene protons of the chelated dppm and for some of the ortho-protons. Some of these resonances were assigned using two-dimensional correlation spectroscopy and nuclear Overhauser effect experiments. Crystals of complex 2a are monoclinic, space group P2₁/n, with a= 1147.7(4), b= 2315.5(6), c= 2069.7(6) pm, β= 91.76(3)° and Z= 4; final R factor 0.0465 for 6150 observed reflections. The structure shows octahedral co-ordination with a mer arrangement of chlorines, a chelated dppm and a monodentate dppm monoxide, with the PO group unco-ordinated.