REDOX-RESPONSIVE BINUCLEAR AND TRINUCLEAR IRON/MOLYBDENUM COMPLEXES INCORPORATING THE FERROCENYL UNIT AS A REDOX SPECTATOR

Seven new ferrocene derivatives L(1)-L(7) with pendant arms containing a terminal 4-pyridyl binding site have been prepared and characterized. Six have one pendant arm. whereas the seventh has two pendant arms, one on each cyclopentadienyl ring. Two have been crystallographically characterized: (C5H5)Fe(C5H4)CH=CH(4-C5H4N) (L(1)) and (C5H5)Fe(C5H4)(4-C6H4)CH=CH(4-C5H4N) (L(4)). In both cases the conjugated side-arm is;approximately planar. Attachment of {MoL*(NO)Cl} fragments [L* = tris(3,5-dimethylpyrazolyl) hydroborate] to the vacant pyridyl sites of L(1)-L(7) afforded bimetallic complexes which contain electron-donating ferrocenyl groups attached via conjugated bridges to electron-deficient {MoL*(NO)Cl} fragments. The new ferrocenes and complexes were thoroughly characterized by electrochemical, UV/VIS and EPR spectroscopic methods, and significant inter-component interactions are evident: co-ordination of the {MoL*(NO)Cl} fragment results in a-shift of the ferrocenyl redox potential to more positive potentials by approximately 40 mV per {MoL*(NO)Cl} substituent the reductions (from 17 to 18 valence electrons) of the {MoL*(NO)Cl} groups are likewise made less negative by the presence of highly conjugated substituents on their pyridyl ligands. The electronic spectra contain transitions from both the ferrocenyl and the {MoL*(NO)Cl} components which are charge transfer in origin and therefore solvatochromic. The EPR spectra of the binuclear complexes containing one {MoL*(NO)Cl} substituent are entirely normal; however the spectrum of [{MoL*(NO)Cl}(2)L(7)], which contains two paramagnetic {MoL*(NO)Cl} groups attached to the two pendant arms of L(7), shows a weak magnetic exchange interaction between the paramagnetic centres which must be transmitted through the bridging ligand and across the ferrocenyl unit.