Synthesis and Structure of Ruthenium(IV) Complexes Featuring N-Heterocyclic Ligands with an N–H Group as the Hydrogen-Bond Donor: Hydrogen Interactions in Solution and in the Solid State

Abstract

The synthesis and characterization of novel ruthenium(IV) complexes [Ru(η(3):η(3)-C(10)H(16))Cl(2)L] [L = 3-methylpyrazole (2b), 3,5-dimethylpyrazole (2c), 3-methyl-5-phenylpyrazole (2d), 2-(1H-pyrazol-5-yl)phenol (2e), 6-azauracile (3), and 1H-indazol-3-ol (4)] are reported. Complex 2e is converted to the chelated complex [Ru(η(3):η(3)-C(10)H(16))Cl(κ(2)-N,O-2-(1H-pyrazol-3-yl)phenoxy)] (5) by treatment with an excess of NaOH. All of the ligands feature N-H, O-H, or C═O as the potential hydrogen-bonding group. The structures of complexes 2a-2c, 2e, 3, and 5 in the solid state have been determined by X-ray diffraction. Complexes 2a-2c and 3, which contain the pyrazole N-H group, exhibit intra- and intermolecular hydrogen bonds with chloride ligands [N-H···Cl distances (Å): intramolecular, 2.30-2.78; intermolecular, 2.59-2.77]. Complexes 2e and 3 bearing respectively O-H and C═O groups also feature N-H···O interactions [intramolecular (2e), 2.27 Å; intermolecular (3), 2.00 Å]. Chelated complex 5, lacking the O-H group, only shows an intramolecular N-H···Cl hydrogen bonding of 2.42 Å. The structure of complex 3, which turns out to be a dimer in the solid state through a double intermolecular N-H···O hydrogen bonding, has also been investigated in solution (CD(2)Cl(2)) by NMR diffusion studies. Diffusion-ordered spectroscopy experiments reveal an equilibrium between monomer and dimer species in solution whose extension depends on the temperature, concentration, and coordinating properties of the solvent. Preliminary catalytic studies show that complex 3 is highly active in the redox isomerization of the allylic alcohols in an aqueous medium under very mild reaction conditions (35 °C) and in the absence of a base.

Counteranion and Solvent Assistance in Ruthenium-Mediated Alkyne to Vinylidene Isomerizations

“…Strong deshielding has been recently observed for one of the NH proton resonances of 6-azauracile in the complex [Ru(η 3 :η 3 -C 10 H 16 )Cl 2 L] (L = 6-azauracile). 31 A thorough NMR study carried out on this compound, including variable-temperature measurements and DOSY experiments, confirmed the existence of an intramolecular hydrogen bond between one NH and a Cl atom of the coordination sphere of the metal. In the case of 2a-Cl and 2b-Cl, the IR spectra do not show any unusual shifts in the positions of the ν(NH) bands, which appear in the range 3300−3400 cm −1 .…”

“…Formation of 2a-Cl takes place in parallel with a highly exothermic side catalytic reaction of cyclotrimerization of HCCCOOMe, leading to mixtures of 1,3,5-and 1,2,4tris(carboxymethyl)benzene as organic side products. 33 In order to clarify these apparent contradictions, we monitored by 31 P{ 1 H} NMR spectroscopy reaction of 1 with an excess of HCCR (R = COOMe, C 6 H 4 CF 3 ) in CD 3 OD and CD 2 Cl 2 . Immediately upon sample preparation we can identify broad resonances in the 31 P{ 1 H} NMR spectrum attributable to the two diastereomers of the corresponding cationic π-alkyne complex [Cp*Ru(HCCR)( i Pr 2 PNHPy)] + with chloride as counterion (R = COOMe (3a-Cl), C 6 H 4 CF 3 (3b-Cl)).…”

“…The total volume was 0.6 mL in each case. Formation of vinylidene 2a-BPh 4 was monitored by 31 P{ 1 H} NMR spectroscopy over a period of 100 min. During this time, in the absence of added chloride ion conversion of 3a-BPh 4 into 2a-BPh 4 was small (18%), albeit more significant in the case of the rearrangement of 3b-BPh 4 to 2a-BPh 4 (28%).…”

Isomerization of allylic alcohols in water catalyzed by transition metal complexes

“…84 Despite the large efforts made to use water most of the metal 85 complexes that efficiently catalyze isomerisation processes have 86 been studied in organic solvents [11][12][13]. As an inexpensive, avail- 87 able and renewable feedstock, water is attracting more and more 88 interest both from industrial and academic perception as a replace- 89 ment for traditionally used organic solvents [14][15][16]. The catalytic 90 reactions in water mediated by hydrosoluble coordination com-91 pounds could provide an interesting solution to most of the prob-92 lems of the catalytic synthetic processes in organic solvents.…”

“…Asymmetric unit of the crystal structure of [Ru(g 3 :g 3 -C 10 H 16 )Cl 2 (6-azauracile)] (91): monoclinic (P121/c1); Ru1-Cl1 2.399(2) Å; Ru1-Cl2 2.406(2) Å; N2-H2Á Á ÁCl2 2.986(5) Å; N3-H3Á Á ÁO1 2.828(5) Å. Adapted from Ref [89]…”