Acetonitrile Ligands Research Articles

Luminescent Rhenium(I) Phenanthroline Complexes with a Benzoxazol-2-ylidene Ligand: Synthesis, Characterization, and Photophysical Study

A series of luminescent rhenium(I) phenanthroline complexes containing benzoxazol-2-ylidene ligands with the general formula {Re(CO)3(phen)[CN(X)C6H4-2-O]}+ and cis,trans-{Re(CO)2(phen)(L)[CN(H)C6H4-2-O]}+ (X = H, methyl; phen = 1,10-phenanthroline; L = PPh3, PPh2Me, P(OEt)3) have been synthesized and characterized. The X-ray crystal structures of most of the carbene complexes and some of their synthetic precursors have also been determined. A new synthetic methodology for the preparation of dicarbonyl rhenium diimine synthetic precursors with a labile acetonitrile ligand, [Re(CO)2(phen)(PR3)(MeCN)]+, was developed. Photophysical study shows that these carbene complexes display a green to red 3MLLCT [dπ(Re) → π*(N–N)] phosphorescence at room temperature. The N-deprotonations of the benzoxazol-2-ylidene ligand in these complexes were investigated.

Synthesis and Charac terization of New Complexes of (N-4-Methoxy Phenyl) Amino Phenyl Acetonitrile Ligand with Some Divalent Transition Metal Ions

The synthesis and characterization of new complexes of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) with bidentate (N-4-methoxy phenyl) amino phenyl acetonitrile ligand which was prepared from benzaldehyde and 4-methoxy aniline in the presence of KCN and acidic medium have been described. The complexes were synthesized by treating an ethanolic solution of the ligand with appropriate amount of metal salts [1:2] [M:L] ratio. The complexes were characterized by metal and elemental analysis, infrared and electronic spectra, molar conductivity, magnetic susceptibility, and mole ratio method. According to obtained data the probable coordination geometries of Manganese, Cobalt, Nickel, Copper, and Zinc in these complexes with N2-donor of ligand atoms are octahedral. All complexes were found to be non-electrolyte in absolute ethanol, and the complexes were formulated as [ML2Cl2].XH2O.

Pyrazolin-5-ylidene Palladium(II) Complexes: Synthesis, Characterization, and Application in the Direct Arylation of Pentafluorobenzene

Ten palladium(II) complexes bearing a pyrazolin-5-ylidene ligand have been synthesized by oxidative addition and silver carbene transfer pathways. The weakly bound acetonitrile ligand in the initially obtained trans-[PdBr2(MeCN)(Pyry)] complex (6, Pyry = 1-phenyl-2,3-dimethylpyrazolin-5-ylidene) could be replaced by other donor ligands, and additional NHC ligands were introduced either by silver carbene transfer reactions or via reaction with in situ generated free carbenes. Using our previously reported 13C NMR-based electronic parameter, the pyrazolin-5-ylidene ligand is estimated to be among the most strongly donating ligands on our scale so far. The complexes obtained were employed as catalysts for the direct arylation of pentafluorobenzene with moderate to good yields under optimized conditions.

Conductometric studies of the thermodynamics complexation of Li+, Na+, K+, Mg2+, and Ba2+ ions with 4′,4″(5″)-Di-tert-butyldibenzo-18-crown-6 ligand in acetonitrile, ethanol and methanol solutions

The complexation reaction between 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6, ligand and Li+, Na+, K+, Mg2+, and Ba2+ ions were studied conductometrically in acetonitrile, ethanol, and methanol solutions. The formation constants of the 1:1 and 2:1 complexes (metal to ligand) were calculated from the computer fitting of the molar conductance in various mole ratios at 10, 20, 30, and 40 °C. The enthalpy and entropy changes of the complexation reactions in acetonitrile, ethanol, and methanol were estimated at four different temperatures.

Molecular Structures of Dipeptide–Palladium(II) Conjugated Complexes

AbstractThe chiral tridentate 2,6‐pyridinedicarboxamide ligand L1H2 bearing two dipeptide chains (‐L‐Ala‐L‐Pro‐NHBu) was designed. Complexation of L1H2 with Pd(OAc)2 was demonstrated to afford the dipeptide–palladium(II) conjugated complex [(L1)Pd(MeCN)] (1) with an ancillary acetonitrile ligand. In the crystal packing of 1, a right‐handed helical‐like molecular arrangement was observed, wherein each assembly is connected through continuous intermolecular hydrogen bonds together with water molecules. The dipeptide–palladium(II) conjugated complex 1 was studied as a metalloreceptor through metal coordination to accommodate a guest ligand, 4‐aminopyridine, resulting in the formation of the dipeptide–palladium(II) conjugated complex [(L1)Pd(4APy)] (2). Each preorganized helical molecule of 2 is packed in a right‐handed helical‐like molecular arrangement in the crystal packing. The dipeptide–palladium(II) conjugated complex 2 was found to exhibit emission with a maximum at 652 nm in the solid state.

Neutral Pentacoordinate Halogeno‐ and Pseudohalogenosilicon(IV) Complexes with a Tridentate Dianionic O,N,O or N,N,O Ligand: Synthesis and Structural Characterization in the Solid State and in Solution

AbstractA series of neutral pentacoordinate silicon(IV) complexes with an SiFO2NC, SiBrO2NC, SiO2NC2, SiO2N2C, SiFON2C, SiBrON2C, SiON2C2, or SiON3C skeleton was synthesized and structurally characterized by multinuclear NMR spectroscopy in the solid state and in solution and by single‐crystal X‐ray diffraction. The compounds studied contain a tridentate dianionic O,N,O or N,N,O ligand, a phenyl ligand, and a (pseudo)halogeno ligand (F, Br, CN, N3, NCS). The structures, NMR spectroscopic parameters, and chemical properties of these silicon(IV) complexes were compared with those of related compounds that contain an analogous tridentate dianionic S,N,O ligand instead of the O,N,O or N,N,O ligand (comparison of S/O/NMe analogues). In addition, two cationic pentacoordinate silicon(IV) complexes with an SiO2N2C and SiON3C skeleton, respectively, were synthesized (isolated as iodides) and structurally characterized. These compounds contain a tridentate O,N,O or N,N,O ligand, a phenyl ligand, and an acetonitrile ligand. The experimental investigations reported in this article were complemented by computational studies to better understand the different properties of some of the S/O/NMe analogues studied.

Reactivity of bulky tris(phenylpyrazolyl)methanesulfonate copper(I) complexes towards small unsaturated molecules

Reaction of the tris(3-phenylpyrazolyl)methane sulfonate species (TpmsPh)Li with the copper(I) complex [Cu(MeCN)4][PF6] affords [Cu(TpmsPh)(MeCN)] 1. The latter, upon reaction with equimolar amounts of cyclohexyl- (CyNC) or 2,6-dimethylphenyl (XylNC) isocyanides, or excess CO, furnishes the corresponding Cu(I) complexes [Cu(TpmsPh)(CNR)] (R = Cy 2, Xyl 3) or [Cu(TpmsPh)(CO)] 4. The ligated isocyanide in 2 or 3 (or the acetonitrile ligand in 1) is displaced by 3-iminoisoindolin-1-one to afford 5, the first copper(I) complex containing an 3-iminoisoindolin-1-one ligand. The ligated acetonitrile in 1 undergoes nucleophilic attack by methylamine to give the amidine complex [Cu(TpmsPh){MeC(NH)NHMe}] 6, whereas only the starting materials were recovered from the attempted corresponding reactions of 2 and 3 with methylamine. Complexes 1 or 6 form the trinuclear hydroxo-copper(II) species [(μ-Cu){Cu(μ-OH)2(TpmsPh)}2] 7 upon air oxidation in moist methanol. In all the complexes the scorpionate ligand facially caps the metal in the N,N,O-coordination mode.

Synthesis and Characterization of Novel Iron(II) Complexes with Tetradentate Bis(N-heterocyclic carbene)–Bis(pyridine) (NCCN) Ligands

Three novel iron(II) complexes bearing tetradentate ligands of the type pyridine–bis(N-heterocyclic carbene)–pyridine (NCCN) have been synthesized. The compounds trans-diacetonitrile[bis(o-imidazol-2-ylidenepyridine)alkane]iron(II) hexafluorophosphate (alkane = methane (2a), ethane (2b)) and cis-diacetonitrile[1,3-bis(o-imidazol-2-ylidenepyridine)propane]iron(II) hexafluorophosphate (2c) have been characterized by single-crystal X-ray diffraction (XRD), nuclear magnetic resonance spectroscopy (NMR), and infrared spectroscopy (IR). Cyclic voltammetry (CV) measurements show reversible oxidation of Fe(II) to Fe(III). The rotational barrier of the bridge has been determined via variable-temperature NMR (VT-NMR) studies of 2b. In all complexes, the Fe centers coordinate—in addition to the NCCN ligands—two acetonitrile ligands in the solid state as well as in solution. The alkylene bridge connecting the two NHCs has an influence on the coordination mode of the NCCN ligands. Whereas the methylene- and ethylene-bridged NHC moieties lead to a nearly planar geometry of the NCCN ligand and two trans-positioned acetonitrile ligands, the propylene-bridged complex 2c exhibits a sawhorse-type coordination mode, with two cis-oriented acetonitrile ligands. The reactivity of the synthesized complexes toward substitution of the solvent ligands was investigated, showing that acetonitrile is readily substituted by benzonitrile. Upon addition of carbon monoxide, one acetonitrile ligand is replaced by CO to yield complexes 3a–c, as shown by NMR and IR spectroscopy, as well as by XRD in the case of compound 3c.

Pyridine-substituted calix[4]pyrrole: a new cation receptor

Novel pyridine-substituted calix[4]pyrrole (CP), has been synthesised and characterised by different analytical techniques (1H NMR, microanalysis and mass spectroscopy). The cation-binding behaviour of this receptor was investigated by proton NMR spectroscopy, conductometric and UV titrations. 1H NMR measurements reveal the sites of interaction of the ligand with metal cations in deuterated acetonitrile (CD3CN). The results show that introduction of one pyridine group to the pendent arm of the modified CP enables the produced hybrid to bind with metal cations [Cd(II), Pb(II), Hg(II)] in acetonitrile. No interaction was observed between this ligand and other metal cations in acetonitrile. The composition of the anion complexes was established through conductance measurements. In all cases, 1:1 complexes are formed. The thermodynamics of metal cations complexation in acetonitrile is discussed.

Perrhenate Complexation by Uranyl in Traditional Solvents and in Ionic Liquids: A Joint Molecular Dynamics/Spectroscopic Study

The complexation of perrhenate (ReO(4)(-)) anions by the uranyl (UO(2)(2+)) cation has been investigated by joint molecular dynamics simulations and spectroscopic (UV-vis, TRLFS, and EXAFS) studies in aqueous solution, acetonitrile, and three ionic liquids (ILs), namely, [Bmi][Tf(2)N], [Me(3)BuN][Tf(2)N], and [Bu(3)MeN][Tf(2)N] that are based on the same Tf(2)N(-) anion (bis(trifluoromethylsulfonyl)imide) and either Bmi(+) (1-butyl,3-methylimidazolium), Me(3)BuN(+), or Bu(3)MeN(+) cations. They show that ReO(4)(-) behaves as a weak ligand in aqueous solution and as a strong ligand in acetonitrile and in the ILs. According to MD simulations in aqueous solution, the UO(2)(ReO(4))(2) complex quickly dissociates to form UO(2)(H(2)O)(5)(2+), while in acetonitrile, a stable UO(2)(ReO(4))(5)(3-) species forms from dissociated ions. In the ILs, the UO(2)(ReO(4))(n)(2-n) complexes (n = 1 to 5) remained stable along the dynamics, and to assess their relative stabilities, we computed the free energy profiles for stepwise ReO(4)(-) complexation to uranyl. In the two studied ILs, complexation is favored, leading to the UO(2)(ReO(4))(5)(3-) species in [Bmi][Tf(2)N] and to UO(2)(ReO(4))(4)(2-) in [Bu(3)MeN][Tf(2)N]. Furthermore, in both acetonitrile and [Bmi][Tf(2)N] solutions, MD and PMF simulations support the formation of dimeric uranyl complexes [UO(2)(ReO(4))(4)](2)(4-) with two bridging ReO(4)(-) ligands. The simulation results are qualitatively consistent with spectroscopic observations in the different solvents, without firmly concluding, however, on the precise composition and structure of the complexes in the solutions.

Easy Access to Hydride Chemistry on a Tripodal P-Based Rhodium Scaffold

The TBPY-5 rhodium complex [(PhBP3)Rh(CH2═CH2)(NCMe)] (1; PhBP3 = PhB(CH2PPh2)3), which contains ethylene in the equatorial plane and a labile acetonitrile ligand at one of the axial positions, provides a simple entry into the chemistry of the fac-[P3Rh] scaffold. DFT calculations using the model compound [(MeB(CH2PMe2)3)Rh(CH2═CH2)(NCMe)] (1′) reproduce well the crystallographic geometry of 1 and converge to the isolated conformer, in which the strong π back-donation from the metal to the π* orbital of ethylene fixes it coplanar with the equatorial plane. Oxidation of 1 is electrochemically irreversible (at 0.080 V vs SCE), and 1 was effectively oxidized with [Cp2Fe]+ in acetonitrile to [(PhBP3)Rh(NCMe)3]2+. Reaction of 1 with hydrogen in toluene gives the dihydride [(PhBP3)Rh(H)2(NCMe)] (3), which loses acetonitrile to give the insoluble hydride [{(PhBP3)Rh(H)(μ-H)}2] (4), while 1 in THF with BHT (2,6-bis(1,1-dimethylethyl)-4-methylphenol) results in the mixed-valence paramagnetic hydride [{(PhBP3)Rh}2(...

Water versus Acetonitrile Coordination to Uranyl. Effect of Chloride Ligands

Optimizations at the BLYP and B3LYP levels are reported for the mixed uranyl chloro/water/acetonitrile complexes [UO(2)Cl(n)(H(2)O)(x)(MeCN)(5-n-x)](2-n) (n = 1-3) and [UO(2)Cl(n)(H(2)O)(x)(MeCN)(4-n-x)](2-n) (n = 2-4), in both the gas phase and a polarizable continuum modeling acetonitrile. Car-Parrinello molecular dynamics (CPMD) simulations have been performed for [UO(2)Cl(2)(H(2)O)(MeCN)(2)] in the gas phase and in a periodic box of liquid acetonitrile. According to population analyses and dipole moments evaluated from maximally localized Wannier function centers, uranium is less Lewis acidic in the neutral UO(2)Cl(2) than in the UO(2)(2+) moiety. In the gas phase the latter binds acetonitrile ligands more strongly than water, whereas in acetonitrile solution, the trend is reversed due to cooperative polarization effects. In the polarizable continuum the chloro complexes have a slight energetic preference for water over acetonitrile ligands, but several mixed complexes are so close in free energy ΔG that they should exist in equilibrium, in accord with previous interpretations of EXAFS data in solution. The binding strengths of the fifth neutral ligands decrease with increasing chloride content, to the extent that the trichlorides should be formulated as four-coordinate [UO(2)Cl(3)L](-) (L = H(2)O, MeCN). Limitations to their accuracy notwithstanding, density functional calculations can offer insights into the speciation of a complex uranyl system in solution, a key feature in the context of nuclear waste partitioning by complexant molecules.

Hybridization vs. bond stretching isomerism in Ru(II) cyclometalated complexes of 2-phenylpyridine.

The phenomenon of formation of two isomers, yellow and orange, of the cyclometalated Ru(II) complex, [Ru(o-C6H4-py)(MeCN)4]+, was investigated by EELS spectroscopy and theoretical calculations. Both forms show very similar structures and spectroscopic properties, but slight differences in X-ray data and absorption between them were noted. No double minimum on the potential energy surface was found and thus these two forms cannot be considered as bond stretching isomers. However, the DFT study revealed the change in the hybridization of the carbon in trans-position of one of acetonitrile ligands. This effect can be responsible for the difference in colour. The results of the theoretical modelling coincide well with the experimental EELS data.

Dinucleating Naphthyridine‐Based Ligand for Assembly of Bridged Dicopper(I) Centers: Three‐Center Two‐Electron Bonding Involving an Acetonitrile Donor

Unusual bonding: A ligand system that promotes formation of a rare μ-η1:η1 acetonitrile-bridged dicopper(I) complex (see picture) has been developed. The acetonitrile ligand is involved in a three-center two-electron bond supported by a cuprophilic interaction. The labile acetonitrile ligand can be substituted with xylyl isocyanide or CO.

Di-μ-chlorido-bis[diacetonitrilechloridooxidovanadium(IV)

The title compound, [V2Cl4O2(CH3CN)4], is a centrosymmetric dinuclear VIV complex associated with four mol­ecules of acetonitrile. The coordination around both VIV atoms is essentially square-planar, involving three Cl atoms and one O atom [maximum deviation = 0.017 (3) Å for the O atom]. The augmented octahedral coordination of the metal atom is completed by the N atoms of acetonitrile ligands. The VIV atoms are linked by two Cl atoms, acting as bridging atoms. The crystal studied was a non-merohedral twin with a ratio of the two twin components of 0.8200 (3):0.1800 (3). Although Cl and O atoms are present as potential acceptors in the title compound, no hydrogen bonds were observed in the crystal structure.

Dinuclear macrocyclic palladium complexes having pincer coordinating groups and their catalytic properties in Mizoroki–Heck reactions

An improved synthetic method of palladium(II) dinuclear macrocyclic complexes have been described. Each of the two isomers of the complexes [Pd 2LBr 2] has a macrocyclic ligand L in which two 2,6-bis(diaminomethyl)phenyl units coordinate to the Pd(II) centers with N, C, N donor atoms. Substitution of the bromo ligands of one of the isomer of the complexes with acetonitrile ligands affords a new dinuclear complex. Catalytic activities of these complexes were studied for the Mizoroki–Heck type reactions of iodobenzene and styrene. High turnover number up to 30,000 was achieved using one of the isomer of the complexes.

Simultaneous End-On/Side-On Coordination Modes of a Diphosphorus Tetrahedral Complex Imposed by Pre-organization of Oligometallic CuI Acceptors

The reaction of the [{CpMo(CO)(2)}(2)(μ,η(2):η(2)-P(2))] (Cp=cyclopentadienyl) metallo-ligand 2 with pre-organized Cu(I) bi- and trimetallic precursors afforded new coordination complexes with unprecedented coordination modes for a Mo(2)P(2) complex. Variable-temperature solution and solid-state (31)P NMR spectroscopy measurements were performed and X-ray diffraction studies revealed an η(2):η(1) coordination mode for the Mo(2)P(2) unit of 2 in the Cu(I) bimetallic complexes 3 and 4. DFT calculations were carried out to highlight the bonding situation of this unprecedented coordination mode in the Cu(I) bimetallic compound 3. It is built up from a side-on coordination of the P-P σ bond to one copper ion and from the interaction of the lone pair of one phosphorus atom with the second copper ion. The remaining available lone pair of the second phosphorus atom can be involved as well to interact with an additional metal centre, as evidenced in the Cu(I) trimetallic compound 5 in which an η(2):η(1):η(1) coordination mode of the ligand 2 is observed. Derivative 3 can be used as a molecular clip to obtain discrete π-stacked dimers through a ligand exchange reaction between acetonitrile ligands and cyano-capped π-conjugated systems, indicating the stability of the new η(2):η(1) coordination mode.

Intramolecular Nitrile C–H Bond Activation in Nickel NHC Complexes: A Route to New Nickelacycles

Cyclopentadienyl N-heterocyclic carbene (NHC) nickel complexes of general formula [Ni(NHC)XCp] (NHC = 1-(propylnitrile)-3-methylimidazol-2-ylidene, 1-(2,4,6-trimethylphenyl)-3-(butylnitrile)imidazol-2-ylidene, 1-(2,4,6-trimethylphenyl)-3-(pentylnitrile)imidazol-2-ylidene, 1-(2,4,6-trimethylphenyl)-3-(hexylnitrile)imidazol-2-ylidene; X = Cl, Br, I; Cp = η5-C5H5), which bear an alkylnitrile side chain attached to one of the nitrogen atoms of the NHC ring, were prepared by the direct reaction of nickelocene with the corresponding imidazolium salts (NHC·HX). The new complexes [Ni{Me-NHC-(CH2)2CN}ICp] (1a), [Ni{Mes-NHC-(CH2)3CN}ClCp] (1b), [Ni{Mes-NHC-(CH2)4CN}ICp] (1c), and [Ni{Mes-NHC-(CH2)5CN}BrCp] (1d) were obtained in good yields and were fully characterized by standard spectroscopic techniques and elemental analyses and, in the cases of 1a,b, by single-crystal X-ray crystallography. Structural studies established their two-legged piano-stool geometry. The cationic derivatives [Ni{Mes-NHC-(CH2)nCN}(NCMe)Cp]+ (2b–d; n = 3–5) were prepared from the reaction of their neutral homologues 1b−d with KPF6 in acetonitrile at room temperature. Upon treatment of the neutral complexes 1 or of the cationic compounds 2 with KO-t-Bu, a C–H bond α to the nitrile group in each molecule underwent a base-promoted C–H activation and the new nickelacyclic complexes [Ni{Me-NHC-CH2CH(CN)}Cp] (3a) and [Ni{Mes-NHC-(CH2)nCH(CN)}Cp] (3b–d; n = 2–4) were obtained. All of these metallacycles contain Ni–C σ-bonds, and their synthesis generated a new asymmetric carbon center. The cyclic complexes 3 were fully characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, and elemental analyses. The structures of complexes 3b and 3d, which contain six- and eight-membered metallacyclic rings, respectively, were determined by single-crystal X-ray diffraction studies. DFT studies, carried out to probe the mechanism of these cyclonickelation reactions, indicated that the mechanism of formation of these nickelacycles was similar to that observed for the formation of cyanomethyl ligands from coordinated acetonitrile. Nevertheless, the base deprotonation of an α-C–H ligand in a side arm, while thermodynamically comparable to that of a simultaneously coordinated acetonitrile ligand, is kinetically favored, and this leads to the formation of nickelacycles rather than cyanomethyl complexes in the case of the base-assisted activation of the cationic complexes 2.

Acetonitriledicarbonyl(η5-pentamethylcyclopentadienyl)iron(II) tetrafluoridoborate

In the structure of the title compound, [Fe{η5-C5(CH3)5}(NCCH3)(CO)2]BF4, the arrangement of ligands around the Fe atom is in a pseudo-octa­hedral three-legged piano-stool fashion in which the penta­methyl­cyclo­penta­dienyl (Cp*) ligand occupies three apical coordination sites, while the two carbonyl and one acetonitrile ligands form the basal axes of the coordination. The Fe—N bond length is 1.924 (3) Å and the Fe—Cp* centroid distance is 1.722 Å.

(Acetonitrile-κN)pentacarbonyltungsten(0)

The acetonitrile ligand in the title compound, [W(CH3CN)(CO)5], is coordinated end-on to a penta­carbonyl­tungsten(0) fragment with a W—N bond length of 2.186 (4) Å, completing an octa­hedral coordination environment around the W atom.