Chemistry of molybdenum. Part 9. Non-oxomolybdenum(IV) and mononuclear oxomolybdenum(V) complexes with dithioacid ligands

Abstract

The syntheses and characterisation of a series of non-oxomolybdenum(IV) and mononuclear oxomolybdenum(V) complexes are described with 2-aminocyclopent-1 -ene-1 -carbodithioate (acda) and its N-alkyl derivatives [aacda; alkyl = ethyl (eacda), propyl (pacda) or butyl (bacda)] as the bidentate (S–S)^– donor ligands. The molybdenum(IV) complexes [Mo(ox)(aacda)(acda)](ox = oxalate) are feebly paramagnetic (ca. 0.9 µ_B) with a spin-paired d² ground state. They exhibit rich electrochemistry consisting of two reversible one-electron couples: Mo^IV–Mo^III(E_1/2≈–0.45 V) and Mo^IV–Mo^V(E_½+0.54 V), indicating conservation of the six-co-ordinated structure in [Mo(ox)(aacda)(acda)]^Z(z=–1, 0 or +1). The molybdenum(V) complexes [MoOCl(L)₂](L = acda 2a, eacda 2b, pacda 2c or bacda 2d) are paramagnetic (1.56 – 1.68 µ_B) with one unpaired electron. Their electronic spectra in the visible region are dominated by high intensity multiple bands arising from S(π)→ Mo(d_π) charge transfers. The cyclic voltammograms of the complexes show a reversible, one-electron Mo^V–Mo^IV reduction and an irreversible Mo^V–Mo^IV oxidation. In frozen solution (80 K), 2a has an axially anisotropic ESR spectrum indicating axial co-ordination of Cl. For the remaining compounds 2b–2d the features are much more complicated due to the hyperfine interactions from the chloro ligand providing evidence for possible equatorial co-ordination of Cl.