Syntheses and properties of tetrathio- and tetraseleno metalates [(C5Me4R)2NbE2]2M (E=S, Se; M=Cr, Mo; R=Me, Et) with peripheric niobocene ligands

Abstract Reactions of Cp* 2 Nb( η 2 -S 2 )H 1 (Cp*=C 5 Me 5 ( a ), C 5 Me 4 Et ( b )) and Cp* 2 Nb( η 2 -Se 2 H) 3 with 0.5 equivalents of M(CO) 6 (M=Cr, Mo) in boiling toluene give the CO free complexes [Cp* 2 NbE 2 ] 2 M 4–7 . X-ray diffraction analyses have been carried out for the Mo complexes 5a (E=S) and 7a (E=Se) showing that the structures contain ME 4 tetrahedral cores with two attached niobocene ligands thus forming a nearly linear trimetallic unit. Absorption spectra and electrochemical studies of complexes 4–7 are described. Characteristic of the novel CrSe 4 chromophor are four reversible one electron redox steps. Chemical oxidation of 4a and 5a with [(C 5 H 5 ) 2 Fe]PF 6 gives the salts {[Cp* 2 NbS 2 ] 2 M}PF 6 (M=Cr, Mo) 10 and 11 . A qualitative EHMO analysis provides evidence for a strong delocalisation of electron density over the whole metal–ligand system.