Electronic communication in oligometallic complexes with ferrocene-based tris(1-pyrazolyl)borate ligands

Ferrocene-based tris(I-pyrazolyl)borate ligands IR-Li and 1R-Tl have been s ynthesized and used to generate a variety of heterotrinuclear transition me tal complexes, 3R-M [R = H, SiMe3, cyclohexyl, (cyclohexyl)methyl, phenyl; M(II) = Mn, Fe, Co, Ni, Cu, Zn]. The poor solubility of 3H-M is greatly enh anced by the introduction of large organic substituents into the 4-position s of all pyrazolyl rings. The unsubstituted ligand III-Li and the trinuclea r complex 3Cym-Cu [Cym = (cyclohexyl)methyl] have been investigated by X-ra y crystallography. IH-Li, which represents the first example of a structura lly characterized lithium tris(I-pyrazolyl)borate, forms centrosymmetric di mers in the solid state. A severe Jahn-Teller distortion was observed for t he (Bpz(3))(2)Cu fragment in 3Cym-Cu. Compared to the parent compounds [(HB pz(3))(2)M], the presence of uncharged ferrocenyl substituents in 3R-M tend s to shift the M2+/M3+ redox potential to significantly more cathodic value s. The opposite is true if the ferrocenyl fragments are in their cationic s tate, which results in an anodic shift of the M2+M3+ transition. Most inter estingly, the two ferrocenyl fragments in 3R-Cu appear to be electronically communicating.