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Abstract Hofmann coordination polymers (CPs) that couple the well-studied spin transition of the FeII central ion with electron-responsive ligands provide an innovative strategy toward multifunctional metal-organic frameworks (MOFs). Here, we developed a 2D planar network consisting of metal-cyanide-metal sheets in an unusual coordination mode, brought about by infinitely π-stacked redox-active bipyridinium derivatives as axial ligands. The obtained family of materials show vivid thermochromism attributed to electron transfer and/or electronic spin state change processes that can occur either independently or concomitantly. Importantly, the redox activity of the ligands within the structure leads to the quasi-reversible electrochemical reduction reaction on a spin-crossover complex at solid state. These observations have been confirmed via temperature-dependent single-crystal X-ray diffraction, magnetic measurements, Mössbauer, EPR, optical and vibrational spectroscopies as well as quantum chemical calculations.

In the early 1990s, the seminal work by B [...]

Hydrazone compounds represent an important area of research that includes, among others, synthetic approaches and biological studies. A series of 17 hydrazones have been synthesized by mechanochemical means. The fragments chosen were phenolic and furanyl aldehydes coupled with 12 heterocyclic hydrazines or hydrazinamides. All compounds can be obtained quantitatively when operating on a planetary ball mill and a maximum reaction time of 180 min (6 cycles of 30 min each). Complete spectroscopic analyses of hydrazones revealed eight compounds (3–5, 8–11, 16) present in one geometric form, six compounds (1, 2, 13–15) present in two isomeric forms, and three compounds (6, 7, 12) where one rotation is restricted giving rise to two different forms. The single crystal X-ray structure of one of the hydrazones bearing the isoniazid fragment (8) indicates a crystal lattice consisting of two symmetry-independent molecules with different geometries. All compounds obtained were tested for anti-infectious and antibacterial activities. Four compounds (1, 3, 5 and 8) showed good activity against Mycobacterium tuberculosis, and one (7) was very potent against Staphylococcus aureus. Most interesting, this series of compounds displayed very promising antileishmanial activity. Among all, compound 9 exhibited an IC50 value of 0.3 µM on the Leishmania donovani intramacrophage amastigote in vitro model and a good selectivity index, better than miltefosine, making it worth evaluating in vivo.

The coordination chemistry of the N-heterocyclic carbene ligand IMes(NMe2)2, derived from the well-known IMes ligand by substitution of the carbenic heterocycle with two dimethylamino groups, was investigated with d6 [Mn(I), Fe(II)], d8 [Rh(I)], and d10 [Cu(I)] transition-metal centers. The redox behavior of the resulting organometallic complexes was studied through a combined experimental/theoretical study, involving electrochemistry, EPR spectroscopy, and DFT calculations. While the complexes [CuCl(IMes(NMe2)2)], [RhCl(COD)(IMes(NMe2)2)], and [FeCp(CO)2 (IMes(NMe2)2)](BF4) exhibit two oxidation waves, the first oxidation wave is fully reversible but only for the first complex the second oxidation wave is reversible. The mono-oxidation event for these complexes occurs on the NHC ligand, with a spin density mainly located on the diaminoethylene NHC-backbone, and has a dramatic effect on the donating properties of the NHC ligand. Conversely, as the Mn(I) center in the complex [MnCp(CO)2 ((IMes(NMe2)2)] is easily oxidizable, the latter complex is first oxidized on the metal center to form the corresponding cationic Mn(II) complex, and the NHC ligand is oxidized in a second reversible oxidation wave.

In the title compound, [RuCl(C18H15P)(C26H31N2OP)](CF3O3S)·2C3H6O, the RuII ion is coordinated in a three-legged piano stool, half-sandwich-type geometry by a chlorido ligand, a triphenylphosphine and a tethered η6-(phenyl-p-O-methoxy) κ1-P N-diphenylphosphino N′-diisopropyl amidine ligand charge-balanced by a trifluormethansulfonate counter-anion. The η6-coordination mode of the arene incorporated into the structure was generated in situ after addition of methyl trifluoromethanesulfonate to the neutral η5-arene tethered precursor complex [RuCl(PPh3)(η5:κ1-OC6H4C(NiPr2)=N-PPh2)] in dichloromethane solution.

In the cation of the title complex, [Ru(C31H32N3P2)(C10H8N2)2](PF6)(Br)2·2CH2Cl2·H2O, the ruthenium ion is coordinated in a distorted octahedral geometry by two 2,2′-bipyridine (bpy) ligands and a chelating cationic N-diphenylphosphino-1,3,4,6,7,8-hexahydro-2-pyrimido[1,2-a]pyrimidine [(PPh2)2-hpp] ligand. The tricationic charge of the complex is balanced by two bromide and one hexafluoridophosphate counter-anions. The compound crystallized with two molecules of dichloromethane (one of which is equally disordered about a Cl atom) and a water molecule. In the crystal, one of the Br anions bridges two water molecules via O—H...Br hydrogen bonds, forming a centrosymmetric diamond-shaped R42(8) motif. The cation and anions and the solvent molecules are linked via C—H...F, C—H...Br, C—H...Cl and C—H...O hydrogen bonds, forming a three-dimensional network.

The ten-membered fused ring of the title compound, C12H10N2O, is essentially planar in the two independent molecules of the asymmetric unit (r.m.s. deviations = 0.012 and 0.015 Å).

The asymmetric unit of the title compound, C11H12N2O, contains two independent molecules. In the crystal structure, intermolecular C—H...O hydrogen bonds link the molecules. There are π–π contacts between the quinoxaline rings [centroid–centroid distances = 3.446 (2), 3.665 (2), 3.645 (3) and 3.815 (3) Å]. There also exist C—H...π contacts between the methyl groups and the quinoxaline rings.

The methyl cyclopropyl hydrotris(3,5-dimethylpyrazolyl)borate complex TpMe2NbMe(c-C3H5)(MeCCMe) reacts smoothly with different alkylaromatics XH at 308 K to yield methane and TpMe2NbX(c-C3H5)(MeCCMe). NMR data show that for mesitylene and 1,4-dimethylbenzene, selective benzylic CH bond activation is observed, giving the benzyl cyclopropyl complexes TpMe2Nb(CH2Ar′)(c-C3H5)(MeCCMe) (Ar′ = 3,5-Me2C6H3, 4-MeC6H4, respectively). Selective arene CH bond activation is observed with 1,2-dimethylbenzene, yielding TpMe2Nb(3,4-Me2C6H3)(c-C3H5)(MeCCMe). With 1,3-dimethylbenzene, a 3:1 mixture of arene and benzylic CH activated products, TpMe2Nb(3,5-Me2C6H3)(c-C3H5)(MeCCMe) and TpMe2Nb(CH2-3-MeC6H4)(c-C3H5)(MeCCMe), is observed, translating to a 18:1 preference for aromatic versus benzylic CH bond activation on a per CH bond basis. Kinetic studies are consistent with rate-limiting intramolecular β-H abstraction of methane to yield a transient unsaturated η2-cyclopropene intermediate. This intermediate reacts rapidly with the aromatic or benzylic CH bond of the arene via 1,3-addition across a Nb(η2-cyclopropene) bond. DFT calculations suggest that the observed selectivities are a result of the steric influence of the methyl groups on the arene ring, which blocks activation of an orthoC–H bond. [ABSTRACT FROM AUTHOR]

Methyleneaminophosphine ligands R′C(Ph)N−PPh2(R′ = H (1), Ph (4)) are unable to form tethered η6-arene-η1-Pruthenium(II) complexes 3and 6starting from their corresponding η1-Pmetallic precursors 2and 5. In marked contrast, straightforward high-yield synthesis of tethered η6-arene-η1-Pruthenium(II) complexes 9a,bwas achieved upon addition of methylenaminophosphine-type ligands i-Pr2N−C(Ph)N−PR27(R = Ph (a), i-Pr (b)) on the ruthenium precursor [(p-cymene)RuCl2]2at 80 °C. We have observed by X-ray crystallographic analyses the unprecedented structural adaptive behavior of the N-phosphino amidine ligands 7a,bupon the untethered η1-P8a,bor tethered η6-arene-η1-P9a,bcoordination mode in ruthenium(II) complexes. The imino nitrogen atom of the amidine moiety in 7a,bbehaves as a “universal joint”. In order to minimize the steric hindrance in the second coordination sphere of complexes 8a,b, the value of the C1−N1−P1 bond angle of the amidine moiety widened from 119−122° in 7a,bto 133°, which corresponds to a dramatic change in the geometry of the N-phosphino amidine ligands. Moreover, in order to reduce the strain induced by the tethered coordination mode, the value of the C1−N1−P1 bond angle in the amidine moiety in ruthenium(II) complexes 9a,bdecreases to 116°. DFT calculations have been carried out in order to gain more insight into the structural and electronic properties of the methylenaminophosphine ligands R′-C(Ph)N-PPh2as well as the tethered and untethered ruthenium complexes. Moreover, the reaction feasability has also been theoretically discussed. [ABSTRACT FROM AUTHOR]

The synthesis and structure of several new early transition metal (Ti, Zr, Hf, and V) NHC complexes supported by one or two IMes ligands is described. Reaction of M(NMe2)4with IMes·HCl gives compounds VCl2(NMe2)(IMes)2(2), and MCl2(NMe2)2(IMes) (M = V (3), Zr (4), Hf (5)). Treatment of TiCl3(THF)3with 2 equiv. of IMes and 1 equiv. of LiNMe2affords the titanium(iii) compound TiCl2(NMe2)(IMes)2. Reaction of VCl3(THF)3with 2 equiv. of IMes in toluene produces the trivalent complex VCl3(IMes)2(6), while VCl2(Py)4gives the divalent compound VCl2(IMes)(Py)3(7), and ZrCl4(THF)2leads to ZrCl4(IMes)2(8). Imido compounds M(N-2,6-iPr2-C6H3)Cl2(NHMe2)(IMes) (M = V (9), Zr (10)) are prepared from V(NR)Cl2(NHMe2)2or ZrCl2(NMe2)2(IMes) synthons. Ionic imido complexes [M(N-2,6-iPr2-C6H3)Cl3(IMes)]−[HIMes]+(M = V (12), Ti (13)) are obtained in modest yields from the treatment of [M(NR)Cl2(NHMe2)2] with 2 equiv. of IMes. Treatment of a toluene solution of V(NMe2)4and an amide RC(O)NH2(R = tBu, Ph) in the presence of an excess of Me3SiCl produces the terminal oxo complex V(O)Cl2(NHMe2)2(13), which reacts with two equiv. of IMes to give the bis-NHC oxo-complex V(O)Cl2(IMes)2(14). All new compounds have been characterised by various spectroscopic techniques, elemental analyses, and magnetism studies for paramagnetic compounds. The solid-state structure of 12 of these complexes and of IMes·HCl have further been confirmed by X-ray diffraction analyses. [ABSTRACT FROM AUTHOR]

The synthesis of new ruthenium(ii) terpyridine bipyridine complexes bearing a phosphorus(iii) ligand is presented. The steric and electronic properties of the phosphorus ligand were varied using aminophosphines, alkyl and aryl phosphites and the bulky tri(isopropyl)phosphine. All complexes were characterized by multi-nuclear NMR spectroscopy, mass spectrometry and X-ray diffraction analysis. The electronic properties of the complexes were probed by cyclic voltammetry, absorption and luminescence spectroscopy. The complexes do not show luminescence at room temperature, whereas at 77 K in an alcoholic matrix, emission is observed in the range 600–650 nm with lifetimes of 3.5–5.5 μs, originating from 3MLCT states. The MLCT transition spans over 65 nm, which corresponds to a variation of 0.4 eV in the HOMO–LUMO gap. The oxidation potential of the ruthenium varies over a broad range of 290 mV, from +1.32 V vs. SCE with L = PiPr3 to +1.61 V vs. SCE with L = P(OPh)3. This range is unprecedented upon the variation of a single monodentate ligand coordinated by the same heteroatom in the same oxidation and charge states. This work underlines the specific capacity of phosphorus in bringing up a large variety of electronic properties by changing its substituents. [ABSTRACT FROM AUTHOR]

Mono-N-heterocyclic carbene (NHC) complex TiCl 2(NMe 2) 2(IMes) ( 1) (IMes = 1,3-dimesitylimidazol-2-ylidene) has been prepared through the addition of the free carbene to TiCl 2(NMe 2) 2. This procedure affords 1in higher yield than the previously reported synthesis of 1that consists in reacting Ti(NMe 2) 4with 2 equiv of the imidazolium IMes·HCl and that in some cases we demonstrated affords 1with concomitant formation of the titanium(III) bis-NHC complex TiCl 2(NMe 2)(IMes) 2( 2). Compound 1reacts with primary amines to give compounds of the type Ti(NR)Cl 2(NHMe 2)(IMes) ( 3). Alternatively, complexes 3could be prepared from imido precursors Ti(NR)Cl 2(NHMe 2) 2and IMes, whereas the pyridine adducts Ti(NR)Cl 2(Py) 3produced Ti(NR)Cl 2(Py)(IMes) ( 6). The reaction between dimeric complexes [Ti(μ-NAr)(NMe 2) 2] 2(Ar = 2,6-Pr i2-C 6H 3and 2,6-Cl 2-C 6H 3) and the salt IMes·HCl gives incomplete conversions into Ti(NAr)Cl 2(NHMe 2)(IMes) with formation of two side products when Ar = 2,6-Cl 2-C 6H 3, formulated as Ti(NAr)Cl 2(IMes) 2( 4) and Ti(NAr)Cl(NHAr)(NHMe 2)(IMes) ( 5). X-ray studies were carried out for 1, 2, 3a, 3d, 3e, 4, and 5. [ABSTRACT FROM AUTHOR]

New heterometallic Werner complexes have been synthesized by combining the cobalt cationic [Co(NH3)6]3+ species with a nitrato metal fragment [M(NO3)4]x− (M = Fe, Mn, Cu, Zn) or with metal oxides X2MO4 (M = Mo, W and X = Na, NH4). Depending on the metals, an organic and/or a water synthetic route was developed. X-Ray data on Mn and Cu precursors have shown the versatility of nitrate ligand coordination. TDA-TGA studies have been performed to demonstrate the energetic material character. The [Co(NH3)6]x[M(NO3)4]3 complexes display a good oxygen balance and, as shown by standard sensitivity tests, are suitable for automotive applications. [ABSTRACT FROM AUTHOR]

The X-ray structure determination of [L2Cu2Gd2(NO3)6(H2O)2](0.5H2O) (L = bis-[(2-hydroxy-3-ethoxyphenyl)methylene]-4,4′-methylenedianiline) confirms the existence of a tetranuclear double-stranded homotopic and unsaturated helicate. In each Cu–Gd pair, the reduced Cu⋯Gd distance allows ferromagnetic Cu–Gd superexchange interactions through two phenoxo oxygen atoms. Replacement of gadolinium ions by terbium ions yields the first example of a helicate behaving as a single molecule magnet (SMM). [ABSTRACT FROM AUTHOR]

The structures of three NH-indazoles (3-methyl, 3-trifluoromethyl and 3-trifluoromethyl-4,5,6,7-tetrafluoroindazoles) have been determined by X-ray crystallography. These three compounds, together with 3-methyl-4,5,6,7-tetrafluoroindazole, whose X-ray structure could not be determined, have been studied using multinuclear magnetic resonance spectroscopy, including solid-state CPMAS. They all are 1H-tautomers. In the crystal, 3-methyl-1H-indazole forms hydrogen bonded dimers, whereas 3-trifluoromethyl-1H-indazole and 3-trifluoromethyl-4,5,6,7-tetrafluoro-1H-indazole crystallize as catemers. These catemers are chiral space group P32. They are the first examples of indazoles crystallizing in the form of helices of three-fold screw axis. Attempts at rationalizing this behavior on the basis of supramolecular interactions (hydrogen bonds and aromatic interactions) and GIAO calculations are discussed. [ABSTRACT FROM AUTHOR]

Reaction of a phosphinobenzylsilane compound with ruthenium complexes leads to C–H and/or Si–H activation. The new complex Ru{η2-H–SiMe2CH(o-C6H4)PPh2}2 (5) was isolated and X-ray, NMR and DFT studies reveal that 5 displays two agostic Si–H interactions and two carbon-metallated bonds. [ABSTRACT FROM AUTHOR]

The new pyridine–borane compound (2-picolyl)BCy2, readily prepared from 2-picolyllithium and ClBCy2, adopts a head-to-tail dimeric structure in the solid state as indicated by X-ray diffraction analysis and according to NMR and DFT studies, the dimeric form equilibrates in solution with a strained monomeric structure; the ambiphilic behavior of the new compound is illustrated by its bridging coordination to the (p-cymene)RuCl2 unit. [ABSTRACT FROM AUTHOR]

Abstract L‐shape N‐Heterocyclic Carbenes (NHCs) based on the imidazo[1,5‐a]pyridine (ImPy) scaffold have recently gained considerable interest as the true carbene ligand analogues of the popular dialkylbiarylphosphines, better known as Buchwald phosphines. Nevertheless, the substitution pattern of ImPy ligands is still rather limited due to synthetic access issues. We report herein an efficient and versatile visible light photocatalytic strategy to access L‐shape bifunctional ImPy ligands laterally‐functionalized by a phenol group. Mechanistic investigations supported by density functional theory (DFT) reveal that the excited state of the iridium photocatalyst undergoes either a reductive quenching (SET process) or an energy‐transfer quenching (EnT process) depending on the nature of the counterion of the 5‐bromoimidazo[1,5‐a]pyridinium substrate salt. Moreover, the bifunctional character of these new family of L‐shape ImPy ligands is demonstrated by the preparation of a gold(I) complex exhibiting a free OH function capable of intermolecular hydrogen bonding. This work highlights the advantage of visible light photocatalysis in the synthesis of advanced NHC ligand structures, a strategy that has not yet been considered despite its potential benefits in terms of versatility, diversity and practicability.