Ferrocene-Based Tris(1-pyrazolyl)borates:  A New Approach to Heterooligometallic Complexes and Organometallic Polymers Containing Transition Metal Atoms in the Backbone

Starting from mono- and bifunctional ferrocene-based tris(1-pyrazolyl)borates, a novel route to oligonuclear complexes is presented, which incorporates transition metal centers differing substantially in their chemical nature. Both binuclear organometallics FcB(pz)₃ML_n (Fc:  ferrocenyl. pz:  1-pyrazolyl. ML_n:  Tl, 1-Tl; Mo(CO)₃Li, 1-MoLi; Mo(CO)₂(η³-methylallyl), 1-Mo; ZrCl₃, 1-Zr) and trinuclear complexes 1,1‘-fc[B(pz)₃ML_n]₂ (fc:  ferrocenylene. ML_n:  Tl, 2-Tl; Mo(CO)₃Li, 2-MoLi; Mo(CO)₂(η³-methylallyl), 2-Mo) have been prepared. The trinuclear compound [FcB(4-SiMe₃pz)₃]₂Fe, 1-FeSi, has been investigated as a model system for organometallic coordination polymers, consisting of the bifunctional linker 1,1‘-fc[B(pz)₃]₂^2- and transition metal ions Mⁿ⁺. X-ray crystallography shows 1-Tl to establish a polymeric structure in the solid state, while 1-Mo features the usual tridentate coordination mode of the scorpionate ligand (C₂₅H₂₅BFeMoN₆O₂; a = 8.756(1) Å, b = 12.154(1) Å, c = 12.927(1) Å, α = 105.26(1)°, β = 102.29(1)°, γ = 105.09(1)°; triclinic space group P1̄; Z = 2). With the exception of 1,2-Tl, the anodic oxidation of the ferrocene moiety is generally reversible; cyclic voltammetry measurements indicate the two Mo centers in 2-Mo and the two Fc moieties in 1-FeSi to be noncommunicating.