Reducing zirconium(IV) phthalocyanines and the structure of a Pc(4-)Zr complex

The synthesis and characterization of the ring-unsubstituted zirconium phthalocyanine PcZrCl2 (; Pc(x-) = phthalocyaninato(x-)) and its reduction products are described. X-ray analysis of (crystallized from hot 1-chloronaphthalene) reveals that is a chloride-bridged dimer [PcZrCl]2(μ-Cl)2 in the solid-state; was also characterized by UV-vis/MCD spectroscopy and cyclic voltammetry, which indicated reduction potentials at -0.55, -0.95 and -1.28 V. Although attempts to access these Pc-ring reduced species with KC8 led to mixtures of reduced products due to the insolubility of both starting materials, one equivalent of the reducing agent KEt3BH reacted with to generate Pc(3-)-containing species, as indicated by visible Q-band spectral changes (from λmax = 686 for to 589/611 nm), a single ESR peak (g = 2.001) and paramagnetically shifted (1)H NMR resonances consistent with the presence of a Pc-radical anion. Addition of two equivalents of KEt3BH to generated Pc(4-)-containing species, confirmed by a shift in λmax to 522 nm and upfield-shifted (1)H NMR peaks relative to . Reaction of with one and two equivalents of LiCp* did not generate Cp*-substituted products but also effected reduction to analogous Pc(3-) and Pc(4-) species. This latter material, the air-sensitive ring di-reduced "ate"-complex Pc(4-)Zr(LiCl)1.5(DME)3, of the form [LiCl(DME)4]0.5[Pc(4-)ZrClLi(DME)] was structurally characterized, illustrating partial bond localization in the Pc(4-) ring, which also adopts a saddle-shape vs. the more typical dome-configuration found in . This represents a rare example of an isolated and structurally characterized Pc(4-) complex.