Solution structure investigation of Ru(II) complex ion pairs: quantitative NOE measurements and determination of average interionic distances.

The structure of the Ru(II) ion pairs trans-[Ru(COMe)[(pz(2))CH(2)](CO)(PMe(3))(2)]X (X(-) = BPh(4)(-), 1a; BPh(3)Me(-), 1b; BPh(3)(n-Bu)(-), 1c; BPh(3)(n-Hex)(-), 1d; B(3, 5-(CF(3))(2)(C(6)H(3)))(4)(-), 1e; PF(6)(-), 1f; and BF(4)(-), 1g; pz = pyrazol-1-yl-ring) was investigated in solution from both a qualitative (chloroform-d, methylene chloride-d(2), nithromethane-d(3)) and quantitative (methylene chloride-d(2)) point of view by performing 1D- and 2D-NOE NMR experiments. In particular, the relative anion-cation localization (interionic structure) was qualitatively determined by (1)H-NOESY and (19)F, (1)H-HOESY (heteronuclear Overhauser effect spectroscopy) NMR experiments. The counteranion locates close to the peripheral protons of the bispyrazolyl ligand independent of its nature and that of the solvent. In complexes 1c and 1d bearing unsymmetrical counteranions, the aliphatic chain points away from the metal center as indicated by the absence of NOE between the terminal Me group and any cationic protons. An estimation of the average interionic distances in solution was obtained by the quantification of the NOE build-up versus the mixing time under the assumption that the interionic and intramolecular correlation times (tau(c)) are the same. Such an assumption was checked by the experimental measurements of tau(c) from both the dipolar contribution to the carbon-13 longitudinal relaxation time T(DD-1)and the comparison of the intramolecular and interionic cross relaxation rate constant (sigma) dependence on the temperature. Both the methodologies indicate that anion and cation have comparable tau(c) values. The determined correlation time values were compared with those obtained for the neutral trans-[Ru(COMe)[(pz(2))BH(2)](CO)(PMe(3))(2)] complex (2), isosteric with the cation of 1. They were significantly shorter (approximately 3.8 times), indicating that the main contribution to dipolar relaxation processes comes from the overall ion pair rotation. As a consequence, the determined average interionic distances appear to be accurate. By using such interionic distances, it was possible to verify that the counteranion in complex 1b also orients the BMe group far away from the metal center.

Fluxional behavior of the dinitrogen ligand 2,9-dimethyl-1,10-phenanthroline in cationic methyl platinum(II) complexes.

The ionic methylplatinum(II) complexes [Pt(Me)(L)(dmphen)]X (dmphen = 2,9-dimethyl-1,10-phenanthroline, L = Me(2)SO, X = PF(6)(-) 1a, BF(4)(-) 1b, CF(3)SO(3)(-) 1c, ClO(4)(-) 1d, B(C(6)H(5))(4)(-) 1e, [B(3,5-(CF(3))(2)C(6)H(3))(4)](-) 1f; L = n-Bu(2)SO, X = CF(3)SO(3)(-) 1g; L = PPh(3), X = PF(6)(-) 2a, BF(4)(-) 2b, CF(3)SO(3)(-) 2c, ClO(4)(-) 2d, B(C(6)H(5))(4)(-) 2e, [B(3,5-(CF(3))(2)C(6)H(3))(4)](-) 2f; X = CF(3)SO(3)(-), L = CyNH(2) 3a, i-PrNH(2) 3b, 2,6-Me(2)py 3c, EtNH(2) 3d, AsPh(3) 3e, dimethylthiourea (Me(2)th) 3f and the uncharged [Pt(Me)(X)(dmphen)] (X = SCN(-) 4a, SeCN(-) 4b) complexes have been synthesized and fully characterized. In chloroform, as well as in acetone or methanol, complexes 1a-1g, 2a-2h (X = Cl(-) g, NO(2)(-) h, formed "in situ"), and 3e show dynamic behavior due to the oscillation of the symmetric chelating ligand dmphen between nonequivalent bidentate modes. All the other compounds feature a static structure in solution. The crystal structure of 2a shows a tetrahedral distortion of the square planar coordination geometry, a loss of planarity of the dmphen ligand, and, most notably, a rotation of the dmphen moiety, around the N1-N2 vector, to form a dihedral angle of 42.64(8) degrees with the mean coordination plane. The hexafluorophosphate ion lies on the side of the phenanthroline ligand. The interionic structures of 2a, 2b, and 2f were investigated in CDCl(3) at low temperature by (1)H-NOESY and (19)F[(1)H]-HOESY NMR spectroscopies. Whereas PF(6)(-) (2a) and BF(4)(-) (2b) show strong contacts with the cation [Pt(Me)(PPh(3))(dmphen)](+), being located preferentially on the side of the phenanthroline ligand, the [B(3,5-(CF(3))(2)C(6)H(3))(4)](-) (2f) ion does not form a tight ion pair. The dynamic process was studied by variable-temperature NMR spectroscopy for 1a-1f and 2a-2h in CDCl(3). The activation energies DeltaG(298) for the sulfoxide complexes 1a-1f are lower than those of the corresponding phosphine complexes 2a-2f by approximately 10 kJ mol(-)(1). The nature of the counteranion exerts a tangible influence on the fluxionality of dmphen in both series of complexes 1 and 2. The sequence of energies observed for 2a-2h encompasses an overall difference of about 16 kJ mol(-)(1), increasing in the order Cl(-) approximately NO(2)(-) << CF(3)SO(3)(-) < ClO(4)(-) < B(C(6)H(5))(4)(-) < BF(4)(-) approximately PF(6)(-) < B(3,5-(CF(3))(2)C(6)H(3))(4)(-). Acetone and methanol have an accelerating effect on the flipping. Concentration-dependent measurements, carried out in CDCl(3) for 2a with n-Bu(4)NPF(6) and the ligands dmphen, n-Bu(2)SO, sec-Bu(2)SO, and sec-Bu(2)S showed that the rate of the fluxional motion is unaffected by added n-Bu(4)NPF(6), whereas in the other cases this increases linearly with increasing ligand concentration, according to a pattern of behavior typical of substitution reactions. Dissociative and associative mechanisms can be envisaged for the observed process of flipping. Dissociation can be prevalent within the ion pair formed by a "noncoordinating" anion with the metallic cationic complex in chloroform. Among the possible associative mechanisms, promoted by polar solvents or by relatively strong nucleophiles, a consecutive displacement mechanism is preferred to intramolecular rearrangements of five-coordinate intermediates.

Phenolic compounds of olive fruit: one- and two-dimensional nuclear magnetic resonance characterization of Nüzhenide and its distribution in the constitutive parts of fruit.

The phenolic composition of peel, pulp, and seed of the olive fruit was studied for several Italian cultivars used for oil extraction. The seed contained a compound never previously detected in peel and in pulp. The spectroscopic characterization of this compound proved, for the first time, the presence of nüzhenide in the olive seed. Study of the phenolic composition showed that oleuropein, demethyloleuropein, and verbascoside were present in all of the constitutive parts of the fruit; by contrast, nüzhenide was exclusively present in the seeds of all the cultivars at all ripening stages studied.