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

Ferrocene-based tris(1-pyrazolyl)borate ligands 1R-Li and 1R-Tl have been synthesized and used to generate a variety of heterotrinuclear transition metal complexes, 3R-M [R = H, SiMe(3), cyclohexyl, (cyclohexyl)methyl, phenyl; M(II) = Mn, Fe, Co, Ni, Cu, Zn]. The poor solubility of 3H-M is greatly enhanced by the introduction of large organic substituents into the 4-positions of all pyrazolyl rings. The unsubstituted ligand 1H-Li and the trinuclear complex 3Cym-Cu [Cym = (cyclohexyl)methyl] have been investigated by X-ray crystallography. 1H-Li, which represents the first example of a structurally characterized lithium tris(1-pyrazolyl)borate, forms centrosymmetric dimers in the solid state. A severe Jahn-Teller distortion was observed for the (Bpz(3))(2)Cu fragment in 3Cym-Cu. Compared to the parent compounds [(HBpz(3))(2)M], the presence of uncharged ferrocenyl substituents in 3R-M tends to shift the M(2+)/M(3+) redox potential to significantly more cathodic values. The opposite is true if the ferrocenyl fragments are in their cationic state, which results in an anodic shift of the M(2+)/M(3+) transition. Most interestingly, the two ferrocenyl fragments in 3R-Cu appear to be electronically communicating.