M. Cano, J. Heras, M. Maeso
Apr 1, 1997
Citations
0
Influential Citations
34
Citations
Journal
Journal of Organometallic Chemistry
Abstract
Abstract The novel pyrazoles containing 3-[4-phenoxyphenyl] (pp) and 3-[4-butoxyphenyl] (bp) substituents, Hpzpp and Hpzbp, have been synthetized and characterized, and the crystalline structure of 3-[4-phenoxiphenyl]pyrazole (Hpzpp) is also reported. Rh(I) compounds [Rh(Cl)(HpzR)(LL)] and [Rh(μ-pzR)(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)(HpzR)(LL)] and [Rh(μ-pzR)(LL)]2 (LL = NBD, COD, 2CO; R = pp, bp) have been studied by IR and 1H and 13C NMR spectroscopies. 1H NMR spectra of compounds [Rh(Cl)(HpzR)(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(μ-pzR)(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(μ-pzR)(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 ( μ − pz pp ) ( COD ) ] 2 ⋅ 1 2 CH 2 C1 2 and [Rh(μ-pzbp)(COD)]2 have been solved, showing the presence of the H-T configurational isomer in both cases. The 1H NMR spectra of [Rh(μ-pzR)(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 ( μ − pz pp ) ( COD ) ] 2 ⋅ 1 2 CH 2 C1 2 and [Rh(μ-pzbp)(COD)]2 complexes show an Rh-H(ortho) distance of ca. 2.7 A, characteristic of a weak preagostic interaction.