Tripodliganden mit Neopentangrundgerüst und zwei verschiedenen Donorfunktionen CH3C(CH2PPh2)2(CH2SR): Synthese, Struktur, Redoxchemie und Spektroskopie von Komplexen des Typs tripodM{ortho‐(X)(Y)C6H4}

Abstract

Tripod Ligands with Neopentane Frame and two Different Donor Groups CH3C(CH2PPh2)2(CH2SR): Synthesis, Structure, Redox Chemistry, and Spectroscopy of the Complexes tripodM{ortho‐(X)(Y)C6H4}Prof. Dr. Jörn Müller zum 60. Geburtstag gewidmet. Neopentane‐based tripod ligands CH3C(CH2PPh2)2(CH2Z) (Z = SBn, SH, S−) form pentacoordinate compounds [tripodM{ortho(X)(Y)C6H4}]m 1–4 with ortho‐phenylene‐bridged coligands (X)(Y)C6H4 (X, Y = O−, 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 [tripodCo(III){ortho‐(NH)2C6H4}]+(BF) from ortho‐phenylenediamine as the source of the coligand involves precoordination 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, cyclovoltammetric data and X‐ray structure analyses are presented where appropriate.