Tripod ligands with neopentane frame and two different donor groups CH;C(CH2PPh2)2(CH2SR): Synthesis, structure, redox chemistry, and spectroscopy of the complexes tripodM{ortto-(X)(Y)C6H4}

Article abstract of DOI:10.1002/cber.19961291229

Neopentane-based tripod ligands CH₃C(CH₂PPh₂)₂(CH₂Z] (Z = SBn, SH, S ) form pentacoordinate compounds [tripodM{or;/io(X)(Y)C₆H₄]^m 1-4 with ortho-phenylenebridged coligands (X)(Y)C₆H₄ (X, Y= Cr, S^-, NH^-) and Co(II), Co(III), Fe(II), or Fe(III) as the metal centers. The structures of these complexes are very similar to those observed for CH₃C(CH₂PPh₂)₃ as the tripod ligand. The redox potentials, however, for the corresponding one-electron oxidation and reduction processes are highly affected by the change in the tripod donor groups. Both potentials are shifted by a maximum of 700 mV upon replacement of a PPh₂ donor group by a sulfur-centered donor with the difference between the potential of the oxidation step and the potential of the reduction step staying almost constant for the whole series of compounds. This difference of around 1.7 eV nicely corresponds to the energy of the HOMO-LUMO chargetransfer bands observed around 2 eV for all of the compounds. It may be inferred therefore that both observations (electron spectroscopy and cyclic voltammetry) refer in a similar way to the HOMO-LUMO gap of the compounds. It is shown that the formation of ftripodCo(III){or/ho(NH)₂C₆H₄)]⁺ (BF₄ ) from ortho-phenylenediamine as the source of the coligand involves precoordinalion of the amine ligand followed by deprotonation of the coordinated ligand. The capability of the tripodCo(II) template to form Five-coordinate compounds with diamines is further corroborated by the characterization of [tripodCo(en)]²⁺ (5²). In addition to the standard analytical data, EPR, UV/Vis, cyclovoitamrnetric data and X-ray structure analyses are presented where appropriate. VCH Verlagsgesellschafi mbH. 1996.