Elena Pinilla

Chemistry of Rh(I) complexes based on mesogenic 3,5-disubstituted pyrazole ligands. X-ray crystal structures of 3,5-di(4-n-butoxyphenyl)pyrazole (Hpzbp2) and [Rh(μ-pzR2)(CO)2]2 (R = C6H4OCnH2n+1, n = 10, 12) compounds. Part II

Abstract Four new 3,5-disubstituted pyrazoles Hpz R2 containing long-chain 4- n -alkyloxyphenyl substituents [R=C 6 H 4 OC n H 2 n +1 ; n =4 ( 1 ), 6 ( 2 ), 12 ( 5 ), 14 ( 6 )] have been prepared and characterised. All of them showed mesomorphic behaviour, the stability and the range of the mesophases increasing with the length of the chain on the pyrazole. The X-ray structure of Hpz bp2 ( 1 ) showed a highly linear molecular shape. Related results were deduced for the remained Hpz R2 and the structural consequences agree with the observed mesomorphic properties. The mesogenic pyrazoles Hpz R2 ( 1 – 6 ) were used as ligands towards [RhCl(CO) 2 ] and [Rh(CO) 2 ] fragments. [RhCl(CO) 2 (Hpz R2 )] complexes ( 7 – 12 ) showed some physical properties dependant on the long-chained pyrazoles, and related to different molecular arrays in the solid state. In all cases these compounds evolved to [Rh(μ-pz R2 )(CO) 2 ] 2 in solution. The pyrazolate Rh(I) complexes [Rh(μ-pz R2 )(CO) 2 ] 2 ( 13 – 18 ) had the usual boat conformation, as deduced by the crystal structure of two of these derivatives [ n =10 ( 16 ), 12 ( 17 )]. The packing arrangement has both layer and columnar characteristics. No mesophases have been detected for any of the Rh(I) complexes.

The structure of halogeno-1,2,4-triazoles in the solid state and in solution

The X-ray molecular structures of two halogenotriazoles, 3-chloro- and 3-bromo-1H-1,2,4-triazole, have been determined, thus ending a controversy that made these compounds an exception to a general rule concerning their annular tautomerism. 13C and 15N NMR experiments in the solid state are complex because of the dipolar couplings with the halogens. The complex signal of the carbon atom bearing the halogen has been analysed and the residual 13C–X dipolar couplings determined. However, since the tautomeric structures are known, the spectra can be analysed. Solution NMR, at low temperatures (178 K) at which the tautomerism of triazoles is blocked, and using as models 1,2,4-triazole itself and its 1-methyl derivative, allowed us to determine that the same tautomers, 3-halo-1H-1,2,4-triazole, are present in methanol.

3-[4-Phenoxyphenyl]pyrazole (Hpzpp) and 3-[4-butoxyphenyl]pyrazole (Hpzbp) in rhodium chemistry crystal structures of 3-[4-phenoxyphenyl]pyrazole, [Rh(μ−pzpp)(COD)]2⋅12CH2C12 and [Rh(μ-pzbp)(COD)]2

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.

Mesogenic Pd(II) complexes based on 3-substituted pyrazol ligands

Abstract A new family of linear Pd(II) complexes based on pyrazoles containing long-chain substituents at the third position has been prepared and their mesomorphic properties studied. The crystalline structure of one of these compounds is described as a representative example of a very elongated and straight molecule.

Polymorphism and metal–metal interactions on [Rh(Cl)(CO)2(HpzR)] complexes

The novel pyrazoles containing 3-[4- n -hexyloxyphenyl] (hp), 3-[4- n -octyloxyphenyl] (op) and 3-[4- n -decyloxyphenyl] (dp) substituents, Hpz R (R=hp, op, dp; 1 – 3 ), and their corresponding Rh(I) compounds [Rh(Cl)(LL)(Hpz R )] (LL=2,5-norbornadiene NBD, 1,5-cyclooctadiene COD, 2CO; R=hp, op, dp; 4 – 12 ) have been prepared and characterised. The influence of the pyrazol substituent on the properties of the Rh(I) complexes has been analysed. Two crystalline polymorphs (yellow and red) have been isolated for [Rh(Cl)(CO) 2 (Hpz dp )] ( 12 ) in contrast to the single red crystalline form isolated for the related complexes [Rh(Cl)(CO) 2 (Hpz R )] (R=hp, op; 10 and 11 ). X-ray crystal structures of the red forms of 10 – 12 as well as the yellow one of 12 have been solved. The red compounds display one-dimensional stacking of square-planar molecules with metal–metal interactions along the c -axis. The yellow form consists of dimeric unities held together by Cl bridges, and without the one-dimensional metal–metal contacts. In both cases an intramolecular hydrogen bond was present, being stronger in the yellow form than in the red one. Thermochromic behaviour has also been observed for these dicarbonyl complexes. No liquid crystals properties were found for the new compounds, however, the double melting behaviour observed for 10 – 12 could be closely related to mesomorphism.

The annular tautomerism of the curcuminoid NH-pyrazoles

The structures of four NH-pyrazoles, (E)-3,5-bis[β-(4-hydroxy-3-methoxyphenyl)-ethenyl]-1H-pyrazole (3), (E)-3(5)-[β-(4-hydroxy-3-methoxyphenyl)-ethenyl]-5(3)-methyl-1H-pyrazole (4), (E)-3(5)-[β-(4-hydroxy-3-methoxyphenyl)-ethenyl]-4,5(3)-dimethyl-1H-pyrazole (5) and (E)-3(5)-[β-(3,4-dimethoxyphenyl)-ethenyl]-4-methyl-5(3)-phenyl-1H-pyrazole (8), have been determined by X-ray crystallography. Compounds that have a phenol residue crystallize forming sheets that are stabilized by a complex pattern of hydrogen bonds between a unique tautomer (4), or by a 2 : 1 mixture of both tautomers (5) (these tautomers being identical in the case of 3). Pyrazole 8, which lacks OH groups, crystallizes in cyclic dimers that are stabilized by N–H⋯N hydrogen bonds. The tautomerism in solution and in the solid state was determined by 13C and 15N CPMAS NMR spectroscopy. For compounds 4, 5 and 8, the solid state results agree with those observed by crystallography; the most abundant tautomer in solution coincides with the tautomer present in the solid state (4 and 8) or with the most abundant tautomer in the crystal (5).

2-Anilinopyridinate of Cu(I) and adducts of 2-anilinopyridine and metal acetates.: Crystal structure of Cu2(μ-OAc)4(PhNHpy)2

Abstract The adducts of M(OAc)2·nH2O (M=Cu, Co, Ni, Zn) with 2-anilinopyridine, M(OAc)2(PhNHpy), have been synthesized and characterized. The X-ray crystal structure of Cu2(μ-OAc)4(PhNHpy)2 shows the dimer structure of Cu2(μ-OAc)4(H2O)2 with the PhNHpy ligand in the axial positions of the water molecules. It is antiferromagnetic (2J=−286 cm−1). Signals of the triplet state are observed in its EPR spectrum and the zero field splitting parameter (D=0.33 cm−1) has been calculated. The electronic spectra and the strong antiferromagnetism of the cobalt (2J=−324 cm−1) and nickel (2J=−382 cm−1) compounds allow to propose also a dimeric structure for them. By excess of ligand, in the anionic form, the Cu(I) compound Cu(PhNpy) was obtained for which a dinuclear structure with a lineal coordination in Cu(I) is proposed.

Bulky pyrazole as ligands in rhodium(I) complexes. Crystal structure of chlorodicarbonyl (3-p-methoxyphenylpyrazole)rhodium(I)

Abstract A new family of complexes containing bulky pyrazoles substituted in the 3 or the 3 and 5 positions, [RhCl(L2)(HpzR′,R″)] (L2  NBD, 2CO; R′  But, Ph, p-CH3OC6H4 (An), R″  H; R′  But, Ph, R″  CH3; R′  R″  H, CH3), has been obtained. A dynamic behaviour has been observed only in complexes with the less demanding pyrazole ligands, relating with a metallotropic equilibrium when R′  R″  H, Me, or a diolefin reorientation when R′  But, Ph, An, R″  H. The X-ray crystal structure of [RhCl(CO)2(HpzAn)] has been solved, showing a molecular stacking with a RhRh separation of 3.398(3) A along the one-dimensional chain.

Tetraphenylborate complexes of rhodium(I)

Abstract Addition of B(C6H5)4− as precipitating counteranion to cationic four-coordinate rhodium(I) complexes with nitrogen donor ligands of the type [(NBD)- RhL2]+ results in a competition between coordination by the tetraphenylborate group (via π-interaction of an arene ring) and the nitrogen donor ligands. The stoichiometry of the precipitated complexes depends on the nature of these ligands.

Copper Complexes with New Pyridylpyrazole Based Ligands

We report the synthesis, characterization, and crystal structures of new ligands of the pyridinylpyrazole type, i.e., 3,5-bis(4-butoxyphenyl)-1-(pyridin-2-yl)-1H-pyrazole (L1) and 3,5-bis(4-phenoxyphenyl)-1-(pyridin-2-yl)-1H-pyrazole (L2) (Scheme 1), and the study of their coordination behavior towards CuI and CuII. The versatility of this type of ligand, which can give access to different coordination spheres about the metal center, depending on the nature of the copper starting material used in the preparation of the complexes (Scheme 2), is illustrated. Thus, pseudo-tetrahedral CuI as well as six-coordinated tetragonal and distorted tetragonal pyramidal CuII derivatives were obtained for [Cu(L)2]PF6, [Cu(Cl)2(L)2] (L=L1, L2), and [Cu(Cl)(L1)2]PF6, respectively. We also present a crystallographic support of a distorted octahedral cis-bis(tetrafluoroborato-κF)copper(II) compound found for [Cu(BF4)2(L1)2] (3).