Ferrocenylpyrazolyl bridging rhodium dimers. Crystal structure of [Rh(mu-pz(Fc))(COD)](2)

The ability of pyrazolato ligands to form dinuclear complexes has been used to prepare a family of rhodium(I) complexes of the type [Rh(mu-pz(Fc))(L-2 )](2) (L-2 = 2,5-norbornadiene (NBD) (1); 1,5-cyclooctadiene (COD) (2); 2CO (3)) containing ferrocenylpyrazolate (pz(Fc)) as a bridging ligand. The di olefinic compounds 1 and 2 were obtained as the head-to-tail (H-T) isomer, whereas the tetracarbonyl derivative 3 was formed as a mixture of the head- to-tail (H-T) and head-to-head (H-H) isomers, as deduced by NMR studies in solution. The crystal structure determination of [Rh(mu-pz(Fc))(COD)](2) co nfirmed its identity as the H-T isomer having the boat conformation for the six-membered Rh(NN)(2)Rh ring in the solid state. Important structural par ameters were Rh ... Rh and Rh ... H10 distances of 3.189(1) and 2.877 Angst rom, respectively, according to the presence of weak intermolecular interac tions. Electronic and electrochemical studies were also performed. (C) 1999 Elsevier Science S.A. All rights reserved.