Ana Guerrero

New studies on the apparent allyl rotation in scorpion-like palladium complexes. The influence of non-directly bonded groups. X-ray molecular structures of [Pd(η3-2-Me-C3H4)L]TfO, L = bpzmArOMe and bpz*mCy

Abstract New cationic 2-Me-allylpalladium complexes were prepared with the N,N-donor chelate ligands bis(pyrazol-1-yl)(R)methane (R=anisol-2-yl, bpzmArOMe; 2-hydroxyphenyl, bpzmArOH) and bis(3,5-dimethylpyrazol-1-yl)(R)methane (R=anisol-2-yl, bpz*mArOMe; cyclohexyl, bpz*mCy and ferrocenyl, bpz*mFc). The bpz′mR ligands adopt a rigid boat conformation after coordination to the Pd center and the R group is in the axial position of the metallacycle. The new complexes exhibit two isomeric forms in solution that differ in the relative orientation of the 2-Me-allyl group with respect to the bpz′mRPd fragment. The fluxional behavior of the new complexes, mainly in the context of the isomerization process, has been analyzed. Conclusions concerning the influence on this isomerization of the R group and the pyrazole substituents in positions 3 and 5 are discussed. The isomerization process was found to be affected by the presence of coordinating anions (Cl−) or by a change in the complex concentration. The molecular structures of the complexes [Pd(η3-2-Me-C3H4)(bpzmArOMe)]TfO and [Pd(η3-2-Me-C3H4)(bpz*mCy)]TfO have been determined by X-ray diffraction studies.

New palladium and platinum polyfluorophenyl complexes with pyrazolyl N-donor ligands. Analysis of the restricted rotation of the polyfluorophenyl rings

The new N-donor chelate ligands bis(pyrazol-1-yl)(anisol-2-yl)methane, bpzmArOMe, bis(3,5-dimethylpyrazol-1-yl)hydrocarbylmethane (hydrocarbyl = anisol-2-yl, bpz*mArOMe; cyclohexyl, bpz*mCy) and bis(3,5-dimethylpyrazol-1-yl)ferrocenylmethane, bpz*mFec, have been prepared and characterized. New palladium and platinum polyfluorophenyl complexes were prepared with these ligands and those previously described: bis(pyrazol-1-yl)(phenol-2-yl)methane, bpzmArOH; bis(3,5-dimethylpyrazol-1-yl)(phenol-2-yl)methane, bpz*mArOH; 2-(pyrazol-1-yl)-pyridine, pzpy and 2-(pyrazol-1-yl)-pyrimidine, pzpm. For the bpzmR or bpz*mR complexes only one isomer has been found with the R group in an axial orientation. The fluxional behaviour of the new complexes, mainly the polyfluorophenyl rotation, has been analyzed. For the complexes with the nonplanar ligands, derived from bis(pyrazol-1-yl)methane, rotation of the pentafluorophenyl groups has been found to occur with different energy barriers. The presence of methyl groups in position 3 of the pyrazole rings reduces this barrier. The process is not affected by the presence of coordinating solvents or anions (Cl−) or by a change in the complex concentration. For the derivative Pd(2,3,4,6-C6HF4)2(pzpm), containing a planar ligand, two atropisomers are observed even at high temperature, which excludes the existence of polyfluorophenyl rotation. Processes of Pd–N bond rupture or cis,trans-isomerization have not been observed for this complex on the NMR time scale. The molecular structure of complex Pd(C6F5)2(bpz*mFec) has been determined by an X-ray diffraction study.

New catalysts for the alternating copolymerization of 4-tert-butylstyrene/CO

New cationic palladium(II) complexes, containing CS-nitrogen chelate ligands with pyrazol moieties, catalyze the copolymerization of styrene with CO under mild conditions, to produce a syndiotactic copolymer. Molecular weight and polydispersity for the obtained polymers are among the best reported for bisnitrogen planar ligands.

New hybrid ditopic ligands containing fused phenanthroline and crown ether units

Reaction of 5,6-dihydroxy-1,10-phenanthroline with various poly(ethylene)glycol-ditosylates affords, in good yield, a series of ligands in which a phenanthroline binding site is attached to an adjacent crown ether unit; the NN chelating site may be coordinated to {Ru(bipy)2}2+ units to afford [Ru(bipy)3]2+ derivatives with pendant crown ether units, which can bind alkali metal ions.

Variety in the Coordination Modes of the Ligand Hexakis(pyrazol-1-yl)benzene (Hpzb) to PdII, PtII and CuI 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(C6F5)2, [Pd(η3-2-Me-C3H4)]+, PtCl2 and Cu(PMe3)+] coordinate with two adjacent pyrazole residues yielding complexes with one, two or three metallic centres. The crystal and molecular structures of [{Pd(C6F5)2}2(hpzb)], [{Pd(η3-C4H7)}2(hpzb)](TfO)2, [{Cu(PMe3)}2(hpzb)](BF4)2 and [{Pd(η3-C4H7)}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(PMe3)]2(hpzb)}(BF4)2 and probably [{Pd(η3-C4H7)}2(hpzb)](TfO)2 exhibit metallotropy on the NMR time scale. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Multinuclear NMR solution studies on complexes of hexakis(pyrazol-1-yl)benzene (hpzb) with Ag(I)

Abstract The reaction of the polydentate N-donor ligand hexakis(pyrazol-1-yl)benzene (hpzb) with AgSbF6/PPh3 or AgClO4PPh3 in a 1:1 ratio leads to the complexes [Ag(PPh3)(hpzb)]SbF6 (1) or [Ag(PPh3)(hpzb)]ClO4 (3). When two or three equivalents of the silver derivatives are used the species [Ag(PPh3)2]X are formed in addition to 1 or 3. In the case of SbF6− the remaining Ag+ competes with AgPPh3+ for coordination to hpzb and the derivative [Ag(hpzb)]SbF6 (2) is also obtained, while in the case of ClO4− the insoluble salt AgClO4 is formed. The same reactions performed with hpzb–15N12 confirmed the presence of the N-donor ligand in 1–3. At room temperature a Ag–P dissociation process is observed for all the derivatives containing Ag–PPh3 fragments. Complexes 1–3 show in solution an intramolecular argentotropic shift that makes the six pyrazolyl rings of the hpzb ligand equivalent on the 1H NMR time scale. When the amount of counteranion present in solution is sufficiently high, an intermediate of lower coordination number (stabilized with the anion) is observed for complexes 1 and 3 in the low temperature 31P NMR spectra in addition to the three-coordinated species. This intermediate is more stable in the case of ClO4− due to the higher coordinating ability of this anion.

The Structure of Tris(3',5'-dimethylpyrazol-1-yl)-s-triazine and Its Use as a Ligand in Coordination Chemistry

The crystal and molecular structure of the title compound (Me2-TPzT) has been determined by X-ray analysis. The observed molecular conformation presents the nitrogen atoms of three pyrazole rings in the same relative positions. The molecules are joined through intermolecular contacts forming chains that are arranged in a distorted hexagonal symmetry. Two complexes containing this ligand have been prepared: [{Pd(en)}3(Me2-TPzT)](PF6)6 and [{Ag(PPh3)}3(Me2-TPzT)](ClO4)3, which, due to their insolubility, have been characterized only by microanalysis, IR, 1H NMR and, in the latter case, by mass spectrometry.