Di-organoiron mixed valent complexes featuring '(eta(super 2)-dppe)(eta(super 5)-C5Me5)Fe' endgroups: Smooth Class-III to Class-II transition induced by successive insertion of 1,4-phenylene units in a butadiyne-diyl bridge

The synthesis of a new redox family of symmetric dinuclear iron (II/III) complexes featuring '(eta(super 2)-dppe)(eta(super 5)-C5Me5)Fe(C triple bond C)' endgroups connected by a bis(diethynyl)-4,4,-biphenyl spacer are presented. Stepwise para-phenylene insertions in the bridge are found to produce a smooth Class III to Class-II transition for the corresponding mixed valent (MV) complexes.