Variety in the Coordination Modes of the Ligand Hexakis(pyrazol‐1‐yl)benzene (Hpzb) to Pd II , Pt II and Cu I Centres

The structure and conformational analysis of eight complexes derived from hexakis(pyrazol‐1‐yl)benzene (hpzb) have been carried out by means of X‐ray crystallography and NMR spectroscopy. The metallic fragments [Pd(C 6 F 5 ) 2 , [Pd(η 3 ‐2‐Me‐C 3 H 4 )] + , PtCl 2 and Cu(PMe 3 ) + ] coordinate with two adjacent pyrazole residues yielding complexes with one, two or three metallic centres. The crystal and molecular structures of [{Pd(C 6 F 5 ) 2 } 2 (hpzb)], [{Pd(η 3 ‐C 4 H 7 )} 2 (hpzb)](TfO) 2 , [{Cu(PMe 3 )} 2 (hpzb)](BF 4 ) 2 and [{Pd(η 3 ‐C 4 H 7 )} 3 (hpzb)](TfO) 3 have been determined. The structure of each of the complexes depends on the fact that the metal atoms, when two or three are present, prefer to be situated on opposite faces of the benzene ring. Evidence for restricted rotation of the uncoordinated pyrazolyl groups has been found for the free ligand and monometallic derivatives, while free rotation of these groups at room temperature has been observed for the dimetallic complexes. Furthermore, the derivative {[Cu(PMe 3 )] 2 (hpzb)}(BF 4 ) 2 and probably [{Pd(η 3 ‐C 4 H 7 )} 2 (hpzb)](TfO) 2 exhibit metallotropy on the NMR time scale. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)