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.