No abstract

The ligands 2-pyridin-2-yl-1H-benzimidazole (HL(1)), 1-methyl-2-pyridin-2-ylbenzimidazole (HL(2)), and 2-(1H-imidazol-2-yl)pyridine (HL(3)) and the proligand 2-phenyl-1H-benzimidazole (HL(4)) have been used to prepare five different types of new ruthenium(II) arene compounds: (i) monocationic complexes with the general formula [(η(6)-arene)RuCl(κ(2)-N,N-HL)]Y [HL = HL(1), HL(2), or HL(3); Y = Cl or BF4; arene = 2-phenoxyethanol (phoxet), benzene (bz), or p-cymene (p-cym)]; (ii) dicationic aqua complexes of the formula [(η(6)-arene)Ru(OH2)(κ(2)-N,N-HL(1))](Y)2 (Y = Cl or TfO; arene = phoxet, bz, or p-cym); (iii) the nucleobase derivative [(η(6)-arene)Ru(9-MeG)(κ(2)-N,N-HL(1))](PF6)2 (9-MeG = 9-methylguanine); (iv) neutral complexes consistent with the formulation [(η(6)-arene)RuCl(κ(2)-N,N-L(1))] (arene = bz or p-cym); (v) the neutral cyclometalated complex [(η(6)-p-cym)RuCl(κ(2)-N,C-L(4))]. The cytototoxic activity of the new ruthenium(II) arene compounds has been evaluated in several cell lines (MCR-5, MCF-7, A2780, and A2780cis) in order to establish structure-activity relationships. Three of the compounds with the general formula [(η(6)-arene)RuCl(κ(2)-N,N-HL(1))]Cl differing in the arene moiety have been studied in depth in terms of thermodynamic dissociation constants, aquation kinetic constants, and DNA binding measurements. The biologically most active compound is the p-cym derivative, which strongly destabilizes the DNA double helix, whereas those with bz and phoxet have only a small effect on the stability of the DNA double helix. Moreover, the inhibitory activity of several compounds toward CDK1 has also been evaluated. The DNA binding ability of some of the studied compounds and their CDK1 inhibitory effect suggest a multitarget mechanism for their biological activity.

The new complex [(η 6 -p-cym)RuCl(κ 2 -N,N-dmbpy)](BF 4 ) (pcym = p-cymene; dmbpy = 4,4′-dimethyl-2,2′-bipyridine) is water-soluble and active in the catalytic transfer hydrogenation (TH) of different ketones (cyclohexanone, 2-cyclohexenone, and 3-pentanone) to the corresponding alcohols using aqueous HCOONa/HCOOH as the hydrogen source at pH 4.4. A higher activity was found for the TH of the imine N-benzylideneaniline under the same conditions. Excellent results have been obtained for catalyst recycling. Aqua, formato, and hydrido species were detected by 1 H NMR experiments in D 2 O. Importantly, when the catalytic reaction was carried out in D 2 O, selective deuteration at the C α of the alcohols was observed due to a rapid Ru−H/D + exchange, which was also deduced theoretically. This process involves a reversal of polarity of the D + ion, which is transformed into a Ru−D function ("umpolung"). Negligible deuterium labeling was observed for the imine, possibly due to the high activity in the TH process and also to the decrease in the hydrido complex concentration due to the stability of a hydrido-imine intermediate. Both facts should ensure that the TH reaction will compete favorably with the Ru−H/D + exchange. The basic nature of the imine hydrogenation product can also hinder the stated Ru−H/D + exchange. On the basis of DFT calculations, all these hypotheses are discussed. In addition, calculations at this level also support the participation of the stated aqua, formato, and hydrido intermediates in the catalytic reaction and provide a detailed microscopic description of the full catalytic cycle. In the case of the imine TH process, the formation of the hydrido complex (decarboxylation step) is clearly the limiting step of the cycle. On the contrary, in the hydrogenation of cyclohexanone, both decarboxylation and reduction steps exhibit similar barriers, and due to the limitations of the solvent model employed, a definitive conclusion on the rate-determining step cannot be inferred.

Ruthenium derivatives of the type [RuCl(arene)(NN)][BPh 4 ] (arene = benzene, p-cymene) have been synthesized with NN = 2-hydroxyphenylbis(pyrazol-1-yl)methane (bpzmArOH) or 2-hydroxyphenylbis(3,5-dimethylpyrazol-1-yl)methane (bpz*mArOH). In the p-cymene derivative containing bpzmArOH, activation of the hydroxy group is observed and a scorpionate complex is obtained with the ligand behaving in a tridentate manner, [Ru(bpzmArO-κThe structure of this derivative and that of [RuCl(p-cymene)(bpz*mArOH)][BPh 4 ] were determined by X-ray diffraction. The new derivatives, along with other compounds previously described by us that contain similar ligands, were tested in the transfer hydrogenation of benzophenone and other carbonyl compounds under base-free conditions without any other additive to promote the reaction. The precursors were active in this process, and the p-cymene derivatives exhibited a higher activity than the benzene complexes. For the p-cymene complexes the activity was even higher than that found in the presence of base (KOH). The effect of the substituents on the methylene carbon was also studied. Mechanistic and kinetic studies were carried out, and hydride species were observed after a pretreatment of the precatalyst in 2-propanol. Taking into account all of the results, a proposal for the mechanism taking place during the hydrogenation of carbonyl groups under base-free conditions has been made.

The new ligands bis(pyrazol-1-yl)(pyridine-4yl)methane (bpzm4py) (L1) and bis(3,5-dimethylpyrazol-1yl)(pyridine-4-yl)methane (bpz*m4py) (L2) were synthesized and were made to react with different metallic starting materials. In the case of Pd(II), chloride or allyl trinuclear complexes were synthesized, in which the central palladium is bonded to two ligands through the pyridine moiety. Mononuclear [Pd(allyl)L]X complexes were also isolated. On using other M(II) centers (M = Co, Ni, Zn), which could adopt an octahedral geometry, box-like cyclic dimers formed by the self-assembly of two metal centers and two ligands in a head-to-tail disposition were obtained. All metal ions exhibited a distorted octahedral geometry. A complex of Ag(I) with similar cyclic dimers connected through difluorophosphate anions to generate zigzag chains was also crystallized. The silver center was five-coordinate and the chain interactions gave rise to the formation of sheets. In the solid state, different noncovalent interactions were present in the molecular and supramolecular structures, including hydrogen bonds, π−π stacking and anion−π or CH−π interactions. Examples of possible synergy between some of these interactions were found. Where possible, the solution chemistry was analyzed and correlated with the solid state structure. The existence of polynuclear species in solution was evaluated and the effect of some noncovalent interactions on the NMR resonances was observed.

(Aminoferrocenyl)phosphine ligands 2-(1-(dimethylamino)ethyl)-1-(diphenylphosphino)ferrocene (PPFA) and [η5-cyclopentadienyl][η5-4-(endo-dimethylamino)-3-(diphenylphosphino)-4,5,6,7-tetrahydro-1H-indenyl]iron(II) (PTFA), were used as ligands in palladium(0) and -(II) complexes. The reaction of Pd2(dba)3·CHCl3 with PPFA or PTFA in the presence of the electron-withdrawing olefins maleic anhydride (MA) and dimethyl fumarate (DMFU) gave the complexes Pd(PTFA)(DMFU) (2), Pd(PPFA)(MA) (3), and Pd(PPFA)(DMFU) (4). Allylic complexes [Pd(η3-2-Me-C3H4)(PTFA)]Tf (5) and [Pd(η3-2-Me-C3H4)(PPFA)]Tf (6) (Tf = triflate) were obtained by reaction of PTFA or PPFA with [Pd(η3-2-Me-C3H4)Cl]2 in the presence of AgTf. In solution all these compounds exist as mixtures of two diastereomers, with either the alkene or the allyl group differently oriented with respect to the aminophosphine ligand. 1H NMR variable-temperature studies have been carried out for 2−6 and for Pd(PTFA)(MA) (1). Rotation of the alkene was observed for complexes 1−4 on the NMR time scale. ΔG ⧧ c has been calculated and values between 57.6 kJ mol -1 (298 K) and 76.6 kJ mol -1 (373 K) have been obtained. A Pd−N bond rupture which interchanges the two amino methyl groups is observed (ΔG ⧧ 328 = 63.9 kJ mol-1 to ΔG ⧧ 368 = 74.9 kJ mol-1) for derivatives of PPFA, but not for complexes containing PTFA. An EXSY experiment carried out on complex 5 has evidenced a selective η3−η1−η3 (carbon cis to phosphorus) allyl isomerization. Molecular structures of 4 and 6 were determined by X-ray structure analysis.

The synthesis of octahedral copper and zinc coordination complexes containing ligands of the type 6R,2,4-bis(3,5-dimethylpyrazol-1-yl)triazine is described. They exhibit the simultaneous presence of C-H/pi and anion-pi interactions on both sides of the same triazine ring. When the pyrazolyl groups are not methylated, lone pair-pi and anion-pi interactions coexist on the same triazine ring. In addition, the interplay between C-H/pi and anion-pi interactions is studied by means of high level correlation ab initio calculations. They demonstrate that synergistic effects are present when both interactions coexist. These synergistic effects have been evaluated using the genuine non-additivity energies and symmetry adapted perturbation theory (SAPT).

Complexes of formula [RuCl 2 (arene)(κ 1 -dpim)] (dpim ) 2-(diphenylphosphino)-1-methylimidazole) (arene ) p-cymene, 1a; C 6 H 6 , 1b) were prepared by the reaction of [RuCl 2 (pcymene)] 2 or [RuCl 2 (C 6 H 6 )(CH 3 CN)] with dpim. Complexes 1a and 1b were structurally characterized by NMR spectroscopy and X-ray diffraction. The reaction of these precursors with BF 4salts led, in dichloromethane, to cationic complexes of formula [RuCl(arene)(κ 2dpim)]BF 4 (arene ) p-cymene, 2a; C 6 H 6 , 2b). However, in methanol the products were unexpected phosphinite derivatives of the type [RuCl(arene)(HImMe){κ 1 -PPh 2 (OMe)}]A (A ) BF 4 , arene ) p-cymene, 3a; C 6 H 6 , 3b; A ) BPh 4 , arene ) p-cymene, 3d) (ImMe ) methylimidazole). This transformation implies the existence of an easy P-C bond cleavage and phosphine functionalization with methanol at room temperature. The precursors 1a,b or the analogous derivative with 2-(diphenylphosphino)pyridine (PPh 2 py), [RuCl 2 (p-cymene)-(κ 1 -PPh 2 py)], 1c, reacted with HBF 4 to give cationic derivatives by protonation of the imidazole or the pyridine fragment, [RuCl 2 (arene)(κ 1 -PNH)]BF 4 (PNH ) dpimH, arene ) p-cymene, 4a; C 6 H 6 , 4b; PNH ) PPh 2 pyH, arene ) p-cymene, 4c). In these compounds the existence of an asymmetric and bifurcated hydrogen bond NH‚‚‚Cl 2 has been structurally determined (even by X-ray studies for 4a,b). Complexes 2a and 4a also yield the corresponding and analogous phosphinite derivatives in the presence of methanol-d 4 but at a markedly slower rate. NMR and spectrophotometric studies provided information concerning the formation of the phosphinite derivatives. It was concluded that the phosphine is not functionalized if it is not coordinated and that, very probably, a methanol solvatesintermediate between 1a and 2asparticipates in the P-C bond cleavage and allows the aforementioned transformation. Some preliminary catalytic tests involving the transfer hydrogenation of cyclohexanone and the hydrogenation of phenylacetylene have also been carried out.