Structural and spectroscopic characterization of five coordinate iron and cobalt bis(dithiolene)-trimethylphosphine complexes

Heteroleptic bis(dithiolene)-phosphine iron and cobalt complexes [Fe(adt)(2)(PMe3)] (1) and [Co(adt)(2)(PMe3)] (2) (adt = para-anisyldithiolene) have been synthesized from corresponding bis(dithiolene) dimers [M-2(adt)(4)](2) (M = Fe, Co) by reacting with excess PMe3 in dichloromethane. Solid-state structures of 1 and 2 have been determined by single crystal X-ray crystallography, and the dithiolene ligands C-S (approximate to 1.72 angstrom) and C-C (approximate to 1.37 angstrom) bond distances reveal the coordination of pi-radical monoanionic dithiolene (adt center dot(1-)) ligands to metal centers. Intense low energy ligand-to-ligand-charge transfer (LLCT) absorption band (743 nm for 1; 905 nm for 2) in UV vis spectra and characteristic nu(C=S center dot) (1168 cm(-1) for 1; 1170 cm(-1) for 2) in IR spectra affirms coordination of pi-radical monoanionic dithiolenes to divalent metal ions. The cyclic voltammogram of 1 and 2 shows reversible oxidation and reduction waves attributed to M-II -> M-III + e(-) (+0.52 V for 1; +0.29 V for 2) and adt center dot(1-) + e(-) -> adt(2-) (-0.63 V for 1; -0.46 V for 2) redox process respectively. Comprehensive structural and spectroscopic investigations conclude, [M-2(III)(adt(2-))(2)(adt center dot(1-))(2)] -> 2 [M-II(adt center dot(1-))(2)(PMe3)] intramolecular redox interplay during phosphine coordination induced cleavage of homoleptic bis(dithiolene) dimers to produce square pyramidal complexes. (C) 2017 Elsevier B.V. All rights reserved.