Cyclopentadienyl/scorpionate hybrid ligands

Cyclopentadienyl derivatives and tris(pyrazolyl)borates (“scorpionates”) are among the most popular ligands in transition metal chemistry. It is therefore interesting to combine both functionalities in the same ligand molecule (cf. 1; pz = 1-pyrazolyl). Two different coordination modes can be emphasized for derivatives of 1:

(1) The scorpionate and the Cp-functionality bind to different metal ions, thereby generating a (hetero)dinuclear complex. (2) Both groups coordinate to the same metal atom to give an ansa-complex. We have recently synthesized various derivatives of ferrocene- and cymantrene-based poly(pyrazolyl)borates containing the structural motif of 1 (e.g. 2, 3; R = Me, pz). These compounds have successfully been applied for the generation of oligonuclear transition metal complexes as well as multiple-decker sandwich complexes. We have shown that poly(pyrazolyl)borates of type 2 can readily be transformed into ansa-complexes 4 (R = Me, pz). This result offers promising perspectives for the design of novel constrained-geometry catalysts.