Methanol Ligands Research Articles

Oxidation of dimethyldi(2-pyridyl)borato PtIIMen complexes, n = 1, 0, with H2O2: tandem B-to-Pt methyl group migration and formation of C–O bond

New dimethyldi(2-pyridyl)borato (dmdpb) platinum(II) complexes, (dmdpb)Pt(II)Me(SMe(2)) (1), (dmdpb)Pt(II)(L)(SMe(2))(+), L = MeOH (2), MeCN (3), supported by dimethylsulfide ligand and featuring one (1) or no hydrocarbyls at the metal (2, 3) were prepared and their oxidation with hydrogen peroxide was studied. Both complex 1 bearing the formal charge of +1 on the metal and the methanol complex 2 capable of losing the proton of the methanol ligand to form the methoxide derivative 4 charged similarly to 1, are reactive towards H(2)O(2). However, the cationic complex 3 with a formal charge of +2 on the metal does not react with H(2)O(2). The oxidation of the monomethyl platinum(II) complex 1 leads to the B-to-Pt methyl transfer and formation of a robust dimethyl Pt(IV) species 5 which does not undergo C-O reductive elimination up to 100 °C. By contrast, oxidation of 2 in methanol-d(4) leads to quantitative formation of dimethyl ether-d(3), CD(3)OCH(3). It was presumed that the latter reaction involves the B-to-Pt methyl transfer and formation of a highly reactive cationic monomethyl Pt(IV) species whose methyl group carbon atom can accept nucleophilic attack by the methanol-d(4) solvent to form dimethyl ether-d(3).

Catena-Poly[[bis-(2,4-dichloro-benzoato)bis-(methanol-κO)cobalt(II)]-μ-4,4'-bipyridine-κN:N'

In the title compound, [Co(C7H3Cl2O2)2(C10H8N2)(CH3OH)2]n, the CoII ion lies on a twofold rotation axis and is in a slightly distorted octa­hedral CdO4N2 environment, formed by two O atoms from monodentate dichloro­benzoate ligands, two O atoms from methanol ligands, and two N atoms from trans-related 4,4′-bipyridine ligands. The bipyridine ligands also lies on a twofold rotation axis and bridge the CoII ions, forming chains extending along [010]. An intra­chain O—H⋯O hydrogen bond is observed.

Bis(methanol-κO)bis-(quinoline-2-carboxyl-ato-κN,O)nickel(II).

In the title complex, [Ni(C10H6NO2)2(CH3OH)2], the NiII ion lies on an inversion center and is coordinated by two quinoline-2-carboxyl­ate ligands in the equatorial sites and two axial methanol ligands, forming a distorted octa­hedral environment. In the crystal, mol­ecules are linked via O—H⋯O hydrogen bonds into a two-dimensional network parallel to (10).

μ-Acetato-aqua-μ-(5-bromo-2-{1,3-bis[2-(5-bromo-2-oxidobenzylideneamino)ethyl]imidazolidin-2-yl}phenolato)methanoldinickel(II) methanol disolvate monohydrate

The crystal structure of the title compound, [Ni2(C27H24Br3N4O3)(CH3CO2)(CH3OH)(H2O)]·2CH3OH·H2O contains [L(OAc){(CH3OH)Ni}{(H2O)Ni}] mol­ecules {H3 L = 2-(5-bromo-2-hy­droxy­phen­yl)-1,3-bis­[4-(5-bromo-2-hy­droxy­phen­yl)-3-aza­but-3-en­yl]-1,3-imidazolidine} with additional water and two methanol solvent mol­ecules. In this instance, one of the two Ni atoms is coordinated to a water and the other to a methanol mol­ecule. The Ni—O and Ni—N distances, as well as the angles about the metal atoms, show quite regular octa­hedra around the central ions. The Ni—Ophenol—Ni and Ni—Oacetate—Ni angles are not similar [95.26 (13) and 97.34 (13)°, respectively], indicating that this subtle solvate exchange induces significant differences in the conformation adopted. The coordinated methanol ligand is involved in an intra­molecular hydrogen bond to the uncoordinated O atom of the bridging acetate ligand, while the coordinated water mol­ecule forms a hydrogen bond with the one of the methanol solvent mol­ecules. The water solvent mol­ecule forms strong hydrogen bonds to both phenolate O atoms. The remaining methanol solvent mol­ecule also forms a hydrogen bond with this solvent water mol­ecule.

The “Missing Link”: The Gas-Phase Generation of Platinum-Methylidyne Clusters PtnCH+ (n=1, 2) and Their Reactions with Hydrocarbons and Ammonia

Electrospray ionization (ESI) of tetrameric platinum(II) acetate, [Pt(4)(CH(3)COO)(8)], in methanol generates the formal platinum(III) dimeric cation [Pt(2)(CH(3)COO)(3)(CH(2)COO)(MeOH)(2)](+), which, upon harsher ionization conditions, sequentially loses the two methanol ligands, CO(2), and CH(2)COO to form the platinum(II) dimer [Pt(2)(CH(3)COO)(2)(CH(3))](+). Next, intramolecular sequential double hydrogen-atom transfer from the methyl group concomitant with the elimination of two acetic acid molecules produces Pt(2)CH(+) from which, upon even harsher conditions, PtCH(+) is eventually generated. This degradation sequence is supported by collision-induced dissociation (CID) experiments, extensive isotope-labeling studies, and DFT calculations. Both PtCH(+) and Pt(2)CH(+) react under thermal conditions with the hydrocarbons C(2)H(n) (n=2, 4, 6) and C(3)H(n) (n=6, 8). While, in ion-molecule reactions of PtCH(+) with C(2) hydrocarbons, the relative rates decrease with increasing n, the opposite trend holds true for Pt(2)CH(+). The Pt(2)CH(+) cluster only sluggishly reacts with C(2)H(2), but with C(2)H(4) and C(2)H(6) dihydrogen loss dominates. The reactions with the latter two substrates were preceded by a complete exchange of all of the hydrogen atoms present in the adduct complex. The PtCH(+) ion is much less selective. In the reactions with C(2)H(2) and C(2)H(4), elimination of H(2) occurs; however, CH(4) formation prevails in the decomposition of the adduct complex that is formed with C(2)H(6). In the reaction with C(2)H(2), in addition to H(2) loss, C(3)H(3)(+) is produced, and this process formally corresponds to the transfer of the cationic methylidyne unit CH(+) to C(2)H(2), accompanied by the release of neutral Pt. In the ion-molecule reactions with the C(3) hydrocarbons C(3)H(6) and C(3)H(8), dihydrogen loss occurs with high selectivity for Pt(2)CH(+), but in the reactions of these substrates with PtCH(+) several reaction routes compete. Finally, in the ion-molecule reactions with ammonia, both platinum complexes give rise to proton transfer to produce NH(4)(+); however, only the encounter complex generated with PtCH(+) undergoes efficient dehydrogenation of the substrate, and the rather minor formation of CNH(4)(+) indicates that C-N bond coupling is inefficient.

Solution stability of Cu(II) metal–organic polyhedra

In this report the structural stability of self assembled Cu(II) hydroxylated nanoballs (CuOH NB) [Cu 2+ 2(5-OH-bdc) 2L 2] 12 ((5-OH-bdc) 2− = 5-hydroxybenzene-1,3-dicarboxylate; L = dimethyl sulfoxide, methanol or water ligand) are investigated using optical absorption and emission spectroscopies. Specifically, the effects of temperature, hydrostatic pressure, and solvent conditions on the CuOH NB stability were determined by monitoring both the ligand emission intensity and the metal to ligand charge transfer (MLCT) absorption band of the complex under different solution conditions. The results of temperature and pressure variation suggest that the CuOH NB is stable in solution with minimal perturbations between 10 and 60 °C and from ambient pressure up to 3.5 kbar. Degradation of the CuOH NB occurs with increasing concentrations of water with complete dissociation in methanol solutions containing ⩾0.7 mole fraction water. In methanolic solutions containing <0.7 mole fraction water the CuOH NB is stable over a pH range from 5 to 10 while at low pH (i.e., <4.5) the CuOH NB dissociates presumably due to protonation of the carboxylic groups associated with the ligand. The corresponding degradation at high pH (i.e., >10.5) is likely due to coordination of hydroxide ions to the Cu 2+ ions resulting in disruption of the nanoball structure. Finally addition of imidazole disrupts the CuOH NB due to competition between the OH-bdc and imidazole for coordination to the Cu 2+ ions. Overall these results provide important insights into the range of conditions required for the general solution stability of metal–organic polyhedra.

μ-Acetato-μ-(5-chloro-2-{1,3-bis[2-(5-chloro-2-oxidobenzylideneamino)ethyl]imidazolidin-2-yl}phenolato)-bis[methanolnickel(II)] methanol monosolvate monohydrate

The crystal structure shows that the title compound, [Ni2(CH3CO2)(C27H24Cl3N4O3)(CH4O)2]·CH3OH·H2O, con­tains [Ni2 L(OAc)(CH3OH)2] mol­ecules in the unit cell {H3 L = 5-chloro-2-{1,3-bis[2-(5-chloro-2-oxidobenzylideneimino)-ethyl]imidazolidin-2-yl}phenolate} with water and methanol as solvates. The title compound is a neutral dinuclear compound, in which the L 3− Schiff base acts as a hepta­dentate ligand, using each one of its N2O compartments to coordinate a nickel atom. The acetate anion bridges the two nickel atoms via one O while the distorted octahedral coordination sphere for each nickel atom is completed by a coordinated methanol ligand. One of the coordinated methanol ligands is involved in an intra­molecular hydrogen bond to the uncoordinated O atom of the bridging acetate ligand while the other forms a hydrogen bond with the methanol solvate. The solvate water mol­ecule forms strong hydrogen bonds to both terminal phenolato O atoms. The methanol solvate mol­ecule also forms a hydrogen bond with the water solvate mol­ecule.

(Methanol-κO)(2-methyl-3,5-dinitrobenzoato-κO)triphenyltin(IV)

In the title complex, [Sn(C6H5)3(C8H5N2O6)(CH3OH)], the Sn(IV) ion is coordinated in a slightly distorted trigonal–bipyramidal geometry by three phenyl ligands in the equatorial plane and by a 2-methyl-3,5-dinitro­benzene­carboxyl­ato ligand and a methanol ligand at the apical sites. In the crystal, complex mol­ecules are linked via inter­molecular O—H⋯O hydrogen bonds, forming chains along [100].

Hydrogen and Methanol Exchange Processes for (TMP)Rh-OCH3(CH3OH) in Binary Solutions of Methanol and Benzene

Tetramesityl porphinato rhodium(III) methoxide ((TMP)Rh-OCH(3)) binds with methanol in benzene to form a 1:1 methanol complex ((TMP)Rh-OCH(3)(CH(3)OH)) (1). Dynamic processes are observed to occur for the rhodium(III) methoxide methanol complex (1) that involve both hydrogen and methanol exchange. Hydrogen exchange between coordinated methanol and methoxide through methanol in solution results in an interchange of the environments for the non-equivalent porphyrin faces that contain methoxide and methanol ligands. Interchange of the environments of the coordinated methanol and methoxide sites in 1 produces interchange of the inequivalent mesityl o-CH(3) groups, but methanol ligand exchange occurs on one face of the porphyrin and the mesityl o-CH(3) groups remain inequivalent. Rate constants for dynamic processes are evaluated by full line shape analysis for the (1)H NMR of the mesityl o-CH(3) and high field methyl resonances of coordinated methanol and methoxide groups in 1. The rate constant for interchange of the inequivalent porphyrin faces is associated with hydrogen exchange between 1 and methanol in solution and is observed to increase regularly with the increase in the mole fraction of methanol. The rate constant for methanol ligand exchange between 1 and the solution varies with the solution composition and fluctuates in a manner that parallels the change in the activation energy for methanol diffusion which is a consequence of solution non-ideality from hydrogen bonded clusters.

A Two-Dimensional Zinc(II)–Schiff Base Coordination Polymer Formed by Six-Membered Metallacyclic Repeating Motif: Structural Aspects, Thermal and Photophysical Properties

Abstract A dicyanoamide-bridged 2D polynuclear zinc(II) complex having formula [Zn2(L)(μ-dca-κN1κN5)2]n, 1 has been synthesized using the Schiff base ligand N,N′-bis(salicylidene)-1,3-diaminopentane, (H2L) and sodium dicyanoamide [Na(dca)]. The complex presents a 2D hexagonal structure formed by 1,5-dca singly bridged helical chains connected through double 1,5-dca bridges. The ligand and the complex are well characterized by elemental analyses, IR and UV–vis spectroscopy. Thermogravimetric analysis is performed to investigate the thermal stability of the metal–organic framework. Photoluminescence studies of the Schiff base ligand in methanol and of the zinc(II) complex 1 in solid state show the presence of blue emission. The emission of the ligand occurs from an excited state involving an intramolecular proton-transfer process as a result of keto–enol tautomerisation and the zinc(II) complex emits from a ligand-centered excited state.

Di-μ-methanolato-κ4O:O-bis[trichlorido(dimethylformamide-κO)tin(IV)

The title compound, [Sn2(CH3O)2Cl6(C3H7NO)2], contains two hexa­coordinated SnIV atoms symmetrically bridged by two deprotonated methanol ligands, with an inversion center in the middle of the planar Sn2O2 ring. The other sites of the distorted octa­hedral coordination geometry of the SnIV atom are occupied by three Cl atoms and one O atom from a dimethyl­formamide mol­ecule. The complex mol­ecules are connected by weak C—H⋯Cl hydrogen bonds into a two-dimensional supra­molecular network parallel to (10).

Copper(ii) carboxylate tetramers formed from an enantiopure ligand containing a π-stacking supramolecular synthon: single-crystal to single-crystal enantioselective ligand exchange

An enantiopure ligand built from connecting the π···π stacking 1,8-naphthalimide supramolecular synthon with L-asparagine, L(asn)(-), forms tetrameric [Cu(4)(L(asn))(8)(py)(MeOH)]. The methanol ligand, located in a chiral pocket, is replaced enantioselectively when exposed to racemic ethyl lactate vapor to yield [Cu(4)(L(asn))(8)(py)((S)-ethyl lactate)], in a single-crystal to single-crystal gas/solid transformation.

Pyrazolyl methyls prescribe the electronic properties of iron(ii) tetra(pyrazolyl)lutidine chloride complexes

A series of iron(II) chloride complexes of pentadentate ligands related to α,α,α',α'-tetra(pyrazolyl)-2,6-lutidine, pz(4)lut, has been prepared to evaluate whether pyrazolyl substitution has any systematic impact on the electronic properties of the complexes. For this purpose, the new tetrakis(3,4,5-trimethylpyrazolyl)lutidine ligand, pz**(4)lut, was prepared via a CoCl(2)-catalyzed rearrangement reaction. The equimolar combination of ligand and FeCl(2) in methanol gives the appropriate 1:1 complexes [FeCl(pz(R)(4)lut)]Cl that are each isolated in the solid state as a hygroscopic solvate. In solution, the iron(II) complexes have been fully characterized by several spectroscopic methods and cyclic voltammetry. In the solid state, the complexes have been characterized by X-ray diffraction, and, in some cases, by Mössbauer spectroscopy. The Mössbauer studies show that the complexes remain high spin to 4 K and exclude spin-state changes as the cause of the surprising solid-state thermochromic properties of the complexes. Non-intuitive results of spectroscopic and structural studies showed that methyl substitution at the 3- and 5- positions of the pyrazolyl rings reduces the ligand field strength through steric effects whereas methyl substitution at the 4-position of the pyrazolyl rings increases the ligand field strength through inductive effects.

Transition metal complexes of the novel hexadentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine

The novel polydentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine, bimptz, has been synthesized and its coordination chemistry was investigated. Bimptz is neutral and contains a central phthalazine unit, to which two di-(N-methylimidazol-2-yl)methyl groups are attached in the 1,4-positions. This ligand therefore provides up to 6 donor sites for coordination to metal ions. A series of metal complexes of bimptz was prepared and their molecular structures were determined by X-ray diffraction. Upon reaction of bimptz with two equivalents of MnCl(2)·4H(2)O, CoCl(2)·6H(2)O and [Ru(dmso)(4)Cl(2)], the dinuclear complexes [Mn(2)(bimptz)(µ-Cl)(2)Cl(2)] (1), [Co(2)(bimptz)(CH(3)OH)(2)(µ-Cl)(2)](PF(6))(2) (3) and [Ru(2)(bimptz)(dmso)(2)(µ-Cl)(2)](PF(6))(2) (4), respectively, were isolated. The latter were found to have similar solid state structures with octahedrally coordinated metal centers bridged by the phthalazine unit and two chloro ligands. The cobalt and ruthenium complexes 3 and 4 were isolated as PF(6)(-) salts and contain neutral methanol and dmso ligands, respectively, at the terminal coordination sites of the metal centres. The mononuclear ruthenium complex [Ru(Hbimptz)(2)](PF(6))(4) (6) was obtained from the reaction of two equivalents bimptz with [Ru(dmso)(4)Cl(2)]. In complex 6, three donor sites per ligand molecule are used for coordination of the Ru(ii) center. In each bimptz ligand, one of the remaining, dangling N-methylimidazole rings is protonated and forms a hydrogen bond with the unprotonated N-methylimidazole ring of the other bimptz ligand.

Rhodium(i) complexes bearing N-donor ligands: catalytic activity towards intramolecular cyclization of alkynoic acids and ligand lability

The structures of rhodium(I) complexes bearing tris(pyrazol-1-yl)toluidine (tpt) and tris(N-methylimidazol-2-yl)methanol (tim) ligands were examined in the solid state using single crystal X-ray diffraction, and in the solution state using variable temperature NMR spectroscopy. The solid state structures of the rhodium(I) tpt and rhodium(I) tim complexes showed that the ligands are bound to the rhodium(I) centre in the κ2 binding mode, rather than the κ3 binding mode. In the solution state, rhodium(I) complexes bearing the tpt ligand undergo fluxional behaviour at room temperature, which was attributed to rotation of the toluidine substituent about the C–C bond or the equilibrium between κ2 and κ3 binding modes. At low temperatures, rhodium(I) complexes bearing the tpt ligand adopted the κ2 binding mode, consistent with the coordination mode in the solid state structures. The efficiency of the complexes as catalysts for the intramolecular hydroalkoxylation of 4-pentynoic acid and 5-hexaynoic acid to form the corresponding lactone was established. The presence of the third unbound N-donor was shown to reduce the catalytic efficiency of the complexes with tridentate ligands when compared to their counterparts bearing bidentate ligands, due to either the steric hindrance or competitive binding of the third N-donor with the substrate during the catalytic cycle.

Structures and magnetism of {Ni2Na2}, {Ni4} and {Ni6IINiIII} 2-hydroxy-3-alkoxy-benzaldehyde clusters

Three polynuclear complexes, [NiNa(μ(1,1,1)-N(3))(μ-hmb)(2)(DMF)](2), (1), [Ni(4)(μ(3)-OMe)(4)(heb)(4)(MeOH)(1.05)(H(2)O)(2.95)], (2) and [Ni(III)(OH)(6)(hmb)(6)Ni(II)(6)]·(ClO(4))(3) (3) (Hhmb = 2-hydroxy-3-methoxy-benzaldehyde; Hheb = 2-hydroxy-3-ethoxy-benzaldehyde), were prepared by reaction of the appropriate ligand with nickel(II) perchloride hexahydrate under solvothermal conditions. All compounds were characterized by elemental analysis, IR spectroscopy and X-ray single-crystal diffraction. Compound 1 exhibits a centrosymmetric heterotetranuclear cluster which represents the first nickel complex to possess two connected face-sharing cubes structure {Ni(2)Na(2)N(2)O(4)}. Compound 2 has a tetranuclear Ni cluster with a cubane topology in which the Ni(II) and the oxygen atoms from the methanol ligands occupying alternate vertices of the cube. Compound 3 consisits of a mixed-valence [Ni(III)(OH)(6)(hmb)(6)Ni(II)(6)](3+) subunits and it represents the first nickel {Ni(II)(6)Ni(III)} complex to possess a planar hexagonal disc-like structure. The results show that the minor ligand modifications or solvent change have a key role in the structural control of the self-assembly process. Magnetic properties of 1-3 in the 300-2 K have been discussed. The {Ni(2)Na(2)} (1) and {Ni(4)} (2) core display dominant ferromagnetic interactions from the nature of the binding modes through μ(3)-N(3)(-) or μ(3)-OCH(3)(-), while {Ni(II)(6)Ni(III)} core (3) displays dominant anti-ferromagnetic interactions from the nature of the binding modes through μ(3)-OH(-).

Structure and Heme-Independent Peroxidase Activity of a Fully-Coordinated Mononuclear Mn(II) Complex with a Schiff-Base Tripodal Ligand Containing Three Imidazole Groups

New complex [Mn(II)H1.5L]2[Mn(II)H3L]2(ClO4)5·3H2O (1), where H3L is tris{2-(4-imidazolyl)methyliminoethyl} amine (imtren), has been prepared by reacting manganese(II) perchlorate hexahydrate with the imtren ligand in methanol. X-ray crystallographic study revealed that the imtren ligand hexadentately binds to Mn(II) ion through the three Schiff-base imine N atoms and three imidazole N atoms with a distorted octahedral geometry, and the apical tertiary amine N atom of the ligand pseudo-coordinates to Mn(II), forming overall a pseudo-seven coordination environment. The hydrogen-bonds between imidazole and imidazolate of [Mn(II)H1.5L] 0.5+ complex ions are extended to build a 2D puckered network with trigonal voids. [Mn(II)H3L] 2+ complex ions constitutes another extended 2D puckered layer without hydrogen bonds. Two layers are wedged each other to constitute overall stack of the crystal. Peroxidase activity of complex 1 was examined by observing the oxidation of 2,2'-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) with hydrogen peroxide in the presence of complex 1. Generation of ABTS

Diazido(2,2′-bipyridyl)dimethanolnickel(II)

The title complex, [Ni(N3)2(C10H8N2)(CH3OH)2], lies on a twofold roation axis which runs through the NiII ion and the mid-point of the bipyridine ligand. The NiII ion is coordinated in a distorted octa­hedral environment by two azide ligands in a trans configuration. The methanol ligands are in a cis configuration and their hy­droxy groups form intra­molecular O—H⋯(N,N) hydrogen bonds with the azide ligands.

Bis[(2-aminophenyl)methanol-κ2N,O]bis(nitrato-κO)cobalt(II)

The asymmetric unit of the title compound, [Co(NO3)2(C7H9NO)2], contains one-half of the mol­ecule. The CoII atom (site symmetry 2) is six-coordinate in a distorted octahedral configuration bonded by two N and two O atoms from two (2-amino­phen­yl)methanol ligands and two O atoms from the two nitrate anions. Crystal packing is stabilized by inter­molecular N—H⋯O, O—H⋯O and C—H⋯O hydrogen-bonding inter­actions.

Bis[(2-aminophenyl)methanol-κ2O,N]bis(nitrato-κO)manganese(II)

In the title compound, [Mn(NO3)2(C7H9NO)2], the MnII atom (site symmetry 2) is coordinated by two N,O-bidentate (2-amino­phen­yl)methanol ligands and two monodentate nitrate anions in a distorted cis-MnN2O4 octa­hedral coordination geometry. In the crystal, N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds help to establish the packing.