σ-Bonded organotransition metal ions. Part XV. Preparation and fluorine-19 nuclear magnetic resonance spectra of some monomeric anionic, cyanide-bridged dimeric anionic, and related fluorobenzylcobalt(III) complexes

Abstract

Fluorobenzylcobalt(III) complexes of the type (i) 4-FC₆H₄CH₂Co(dmgH)₂B^–, where dmgH is the conjugate base of dimethylglyoxime and B = CN, N₃, NCO, Cl, Br, I, NO₂, NCS; (ii) 4-FC₆H₄CH₂Co(dmgH)₂CNCo(dmgH)₂R^–, where R = Me, CH₂C₆H₄F, CH₂C₆H₄NO₂; (iii) RCo(dmgH)₂CNCo(dmgH)₂CH₂C₆H₄F^–, where R = Me, CH₂C₆H₄NO₂, CCPh; (iv) 4-FC₆H₄CH₂Co(dmgH)(dmgH₂)B, where B = CNCo(dmgH)₂CH₂C₆H₄F, CNCo(dmgH)₂CH₂C₆H₄NO₂, CF₃CO₂; (v) 4-FC₆H₄CH₂Co(dotnH)B, where dotnH is the conjugate base of 4,8-diaza-3,9-dimethylundeca-3,8-diene-2,10-dione dioxime and B = CF₃CO₂, CN; (vi) 4-FC₆H₄CH₂Co(dotnH)B⁺, where B = aq, py, Ph₃P; have been prepared and isolated and/or characterised in solution. The fluorine-19 spectra have been measured and the substituent chemical shifts relative to that of fluorobenzene have been related to the electron-donating capacity of the substituent CH₂Co(ligands). The electron-donating capacity of substituents of type (i) depend markedly upon the nature of the anionic ligand B, cyanide ion being particularly effective in promoting this electron donation. Cyanide ion is also very effective in the bridged cyanide complexes of types (ii) and (iii). Protonation of one of the dioximato-ligands of complexes of types (i), (ii), and (iii), or replacement of the two dioximato-ligands by the tetradentate ligand dotnH, more than outweighs the electron-donating influence of the monomeric or bridged cyanide ligand.