Chemistry of Molybdenum. Part 8. Syntheses, Spectroscopy and Electrochemical Properties of Molybdenum Complexes containing Dithioacid Ligands

Article abstract of DOI:10.1039/DT9920000269

Complexes cis- react with acids HX (X = BF4 or PF6) to form species X 1a-1d, which contain an Mo(VI)O core.Reactivity of the terminal oxo ligand of this core towards electron-donor reagents has been investigated.Non-oxo monomeric molybdenum(V) compounds BF4 2a, 2b and BF4 2c, 2d can be obtained when 2-aminocyclopent-1-ene-1-carbodithioic acid (Hacda) and o-aminobenzenethiol (Habt) are used for oxygen abstraction.With triphenylphosphine, however, the products are non-oxo molybdenum(IV) compounds BF4 3a, 3b.In frozen solution , compounds 2a-2d show ESR spectra with axial symmetry.The g and A tensor parameters (g ca. 1.977, g ca. 1.975, A ca. 51.5*10^-4 cm^-1 and A ca. 19.5*10^-4 cm^-1) for this series of molybdenum(V) compounds are very similar to each other indicating that the unpaired electron is located in a metal-centred orbital of essentially identical composition.Complexes 2a and 2b display two consecutive reversible one-electron waves in their cyclic voltammograms at E_1/2 = -0.24 and -0.45 V vs. saturated calomel electrode (SCE), which correspond Mo(V)-Mo(IV) and Mo(IV)-Mo(III) redox couples respectively.The molybdenum(IV) compounds 3a and 3b are seven-co-ordinate with a spin-triplet ground state (μ_eff, 2.48 and 2.53) and show two distinct redox waves due to the interconversion of the three ^z (z = +1, 0 or -1) species.Half-wave potentials, E_1/2, for these processes are at -0.36 (Mo(IV)-Mo(III)) and -0.90 V (Mo(III)-Mo(II)) vs.SCE.The presence of the strongly ?-acceptor phosphine ligand facilitates the electrochemical generation of relatively scarce molybdenum(II) species.

Full text of DOI:10.1039/DT9920000269

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