Issue 2, 1992

Chemistry of molybdenum. Part 8. Syntheses, spectroscopy and electrochemical properties of molybdenum complexes containing dithioacid ligands

Abstract

Complexes cis-[MoVIO2(aacda)2][aacda = 2-(alkylamino)cyclopent-1-ene-1-carbodithioate; alkyl = propyl (pacda) or butyl (bacda)] react with acids HX (X = BF4 or PF6) to form species [MoVIO(aacda)3]X 1a–1d, which contain an MoVIO core. Reactivity of the terminal oxo ligand of this core towards electron-donor reagents has been investigated. Non-oxo monomeric molybdenum(V) compounds [MoV(acda)(aacda)3]BF42a, 2b and [MoV(abt)(aacda)3]BF42c, 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 [MoIV(PPh3)(aacda)3]BF43a, 3b. In frozen solution [dimethylformamide–MeCN (1 : 10 v/v), 140 K], compounds 2a–2d show ESR spectra with axial symmetry. The g and A tensor parameters (g≈ 1.977, g≈ 1.975, A≈ 51.5 × 10–4 cm–1 and A≈ 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 E½=–0.24 and –0.45 V vs. saturated calomel electrode (SCE), which correspond to MoV–MoIV and MoIV–MoIII redox couples respectively. The molybdenum(IV) compounds 3a and 3b are seven-co-ordinate with a spin-triplet ground state (µeff, 2.48 and 2.53) and show two distinct redox waves due to the interconversion of the three [Mo(PPh3)(aacda)3]z(z=+1, 0 or –1) species. Half-wave potentials, E1/2, for these processes are at –0.36 (MoIV–MoIII) and –0.90 V (MoIII–MoII)vs. SCE. The presence of the strongly π-acceptor phosphine ligand facilitates the electrochemical generation of relatively scarce molybdenum(II) species.

Article information

Article type
Paper

J. Chem. Soc., Dalton Trans., 1992, 269-274

Chemistry of molybdenum. Part 8. Syntheses, spectroscopy and electrochemical properties of molybdenum complexes containing dithioacid ligands

S. B. Kumar and M. Chaudhury, J. Chem. Soc., Dalton Trans., 1992, 269 DOI: 10.1039/DT9920000269

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