Some coordination complexes of cobalt III and some related X-ray crystallographic studies

Jewiss, Hilary Christina (1986) Some coordination complexes of cobalt III and some related X-ray crystallographic studies. University of Southampton, Doctoral Thesis.

Abstract

A range of cobalt (III) complexes of the type [Co(L-L)₃][BF_4]_3 (L-L = o-C₆H₄(PMe₂)₂, o-C₆H₄(PMe₂), (AsMe₂), o-C₆H₄(AsMe₂)₂, o-C₆H₄(PPh₂)₂ and Me₂PCH₂CH₂PMe₂) have been synthesised. They are unusual because coordination is only to the heavy donor phosphorus or arsenic atoms. Use of ⁵⁹Co NMR revealed the CoP₆³⁺ species to have the lowest frequency resonances so far observed for a cobalt (III) species and was in the range previously typical of Co(O) and Co(-1) complexes. The CoAs₆³⁺ environment has been shown to have a ⁵⁹Co NMR shift of about 5000 ppm more negative than was previoulsy reported. The octahedral nature of the cobalt (III) moiety was confirmed by a full X-ray structural determination of [Colbraceo-C₆H₄(AsMe₂0₂rbrace₃][BF₄]₃.2H₂O. Cobalt (III) complexes fac-[ColbracePhP(CH₂CH₂PPh₂)_2rbrace X₃], cis-[ColbraceP(CH₂CH₂PPh₂)_3rbraceX₂] C10₄ and cis-β-[Colbrace-CH_2P(Ph)CH_2CH_2PPh_2rbrace_2X_2]PF_6 (X = Cl or Br) have been prepared by halogen oxidation of the cobalt (II) analogues; failure to obtain complexes with other related ligands, and with X = I is considered. ^59Co NMR for these and related [Co(L-L)_2X_2]^+ complexes (X = Cl, Br or sometimes I) enabled identification of typical chemical shift ranges for various donor sets in the region + 1600 to + 4300 ppm. Unusual ditertiary stibine complexes [Co(L-L)_2X_2]X where L-L = o-C₆H₄(SbMe₂)₂ or Me₂SbCH₂CH₂CH₂SbMe₂, X = Cl, Br or I have been prepared and fully characterised. Mixed donor ligands o-C₆H₄(PMe₂)(SbMe₂) and o-C₆H₄(PPh₂) (EMe) (E = S or Se) form complexes [Co(L-L)₂X₂]⁺(X = Cl or Br) and again ⁵⁹Co chemical shift ranges have been identified for the donor sets present. Characterisation of the complexes involved elemental analysis, I.R., multinuclear NMR and electronic spectroscopy. Single crystal X-ray studies of other high oxidation state complexes are also reported. [Felbraceo-C₆F₄(PMe₂)_2rbraceCl₂]BF₄ (Fe-Cl 2.234(1), Fe-P 2.293(1)AA) contains a trans octahedrally coordinated iron atom and disordered BF₄ ^-anions. [AsPh₄] [Ru(DL-MeSeCH₂CH₂SeMe)Cl₄] (Ru-Se 2.452(1), Ru-Cl 2.372(2) AA) has tetrahedral AsPh₄ ⁺ cations with pseudo-octahedral cis anions; the diseleno-ether having the DL conformation and is the first example of this invertomer structually characterised. Studies were carried out on an osmium (VI) complex [Me₂HNCH₂CH₂NHMe₂][OsO₂Cl₄] (Os-O 1.723(4), Os-Cl 2.386(1) AA) with an anion of approximate D_4h symmetry, and on osmium (VIII) complex Cs[OsO₈(OH)] (Os = O 1.62(4) - 1.77(3), Os-O(H) 2.21(2)AA) in which the anions have distorted trigonal-bypyramidal coordination (O₅) about the osmium atoms, which are linked via a single bent hydroxo-bridge. (D72193/87)

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