3-[4-Phenoxyphenyl]pyrazole (Hpz(pp)) and 3-[4-butoxyphenyl]pyrazole (Hpz(bp)) in rhodium chemistry - Crystal structures of 3-[4-phenoxyphenyl]pyrazole, [Rh(mu-pz(pp))(COD)](2)center dot 1/2CH(2)Cl(2) and [Rh(mu-pz(bp))(COD)](2)

The novel pyrazoles containing 3-[4-phenoxyphenyl] (pp) and 3-[4-butoxyphenyl] (bp) substituents, Hpz(pp) and Hpz(bp), have been synthetized and characterized, and the crystalline structure of 3-[4-phenoxiphenyl]pyrazole (Hpa(pp)) is also reported. Rh(I) compounds [Rh(Cl)(Hpz(R))(LL)] and [Rh(mu-pz(R))(LL)](2) (LL = NBD, COD, 2CO; R = pp, bp) have been prepared in order to explore the influence of the alkoxy- or aryloxyphenyl substituents on the pyrazol ring of some features such as the presence of dynamic processes or the preference of determined isomers in the complexes. The molecular structures of complexes [Rh(Cl)(Hpz(R))(LL)] and [Rh(mu-pz(R))(LL)](2) (LL = NBD, COD, 2CO; R = pp, bp) have been studied by IR and H-1 and C-13 NMR spectroscopies. H-1 NMR spectra of compounds [Rh(Cl)(Hpz(R))(LL)] (LL = NBD, COD, 2CO; R = pp, bp) indicate that the presence of a metallotropic equilibrium only depends on the steric characteristics of the ancillary ligands. On the other hand, complexes [Rh(mu-pz(R))(CO)(2)](2) (R = pp, bp) are formed as a mixture of the head-to-head (H-H) and head-to-tail (H-T) configurational isomers. By contrast, [Rh(mu-pz(R))(LL)](2) (LL = NBD, COD; R = pp, bp) have been obtained as only one isomer in both the solid state and the solution. The crystalline structures of complexes [Rh(mu-pz(pp))(COD)](2) . 1/2CH(2)Cl(2) and [Rh(mu-pz(bp))(COD)](2) have been solved, showing the presence of the H-T configurational isomer in both cases. The H-1 NMR spectra of [Rh(mu-pz(R))(LL)](2) (LL = NBD, COD, 2CO; R = pp, bp) show that the ortho protons of the C6H4 group of the substituents on the pyrazol ring are considerably deshielded. Furthermore, the X-ray structures of [Rh(mu-pz(pp))(COD)](2) . 1/2CH(2)Cl(2) and [Rh(mu-pz(bp))(COD)](2) complexes show an Rh-H(ortho) distance of ca. 2.7 Angstrom, characteristic of a weak preagostic interaction.