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)3MLn (Fc: ferrocenyl. pz: 1-pyrazolyl. MLn: 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)3MLn]2 (fc: ferrocenylene. MLn: 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]22- 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