Synthesis and Properties of Subphthalocyanine–Tetracyanobutadiene–Ferrocene Triads

A series of boron subphthalocyanine–tetracyanobutadiene–ferrocene
(SubPc–TCBD–Fc) triads was synthesized by subjecting
SubPcs with a ferrocenylethynyl substituent at either the axial or
peripheral position to a [2 + 2] cycloaddition reaction with tetracyanoethylene
followed by retroelectrocyclization. The ferrocenylethynyl unit was
introduced at the axial position (at the boron atom) by a simple aluminum
chloride-mediated alkynylation reaction, while functionalization at
the SubPc periphery was accomplished by a Sonogashira coupling reaction.
The conversion of one alkyne unit into a TCBD unit in combination
with the location of the resulting TCBD–Fc moiety was found
to have a strong influence on the optical and redox properties, which
is ascribed to very different ground-state interactions between the
individual donor/acceptor systems. The first electrochemical oxidation
could thus be anodically shifted by as much as 0.4 V from the strongest
donor molecule (with most unperturbed ferrocene character) to the
poorest donor molecule (with strongly perturbed ferrocene character).
Six redox states could be reached reversibly for the SubPc–TCBD–Fc
triads, −3, −2, −1, 0, + 1, + 2, and for one
compound the formation of a tetraanion persistent at the time scale
of slow scan voltammetry was observed.