Methyl-palladium(II) complexes of pyridine-bridged bis(nucleophilic heterocyclic carbene) ligands: Substituent effects on structure,stability, and catalytic performance

A series of discrete, mononuclear palladium(II)–methyl complexes, together with several palladium(II)–chloro analogues, of pyridine-functionalised bis-NHC ligands have been prepared via ligand transmetallation from the silver(I)-NHC complexes. The reported complexes comprise examples with both the methylene-bridged 2,6-bis[(3-R-imidazolin-2-yliden-1-yl)methyl]pyridine (_RC^∧N^∧C; R = Mes, dipp, ^tBu) and planar 2,6-bis(3-R-imidazolin-2-yliden-1-yl)pyridine (_RCNC; R = Mes, dipp) ligands and, when combined with the previously reported _MeC^∧N^∧C/_MeCNC examples, cover a broad spectrum of ligand substituent steric and electronic properties, including the bulky Mes and dipp groups frequently used in catalytic applications. The palladium(II) complexes have been characterised by a variety of methods, including single crystal X-ray crystallography, with the shielding of the Pd–Me groups in the proton NMR spectra of some of the N-aryl substituted examples correlated with the proximity of the aryl rings to the methyl group in the solid state structures. The [PdMe(_RC^∧N^∧C/_RCNC)]⁺ complexes undergo thermal degradation via reductive methyl-NHC coupling to give 2-methyl-3-R-imidazolium-1-yl species with relative stabilities in the order of [PdMe(_MesC^∧N^∧C)]BF₄ > [PdMe(_MeC^∧N^∧C)]BF₄ ≈ [PdMe(_MesCNC)]BF₄ > [PdMe(_MeCNC)]BF₄ > [PdMe(_tBuC^∧N^∧C)]BF₄ ≫ [PdMe(_tBuCNC)]BF₄ (not isolable). A comparison of the activity of the complexes as precatalysts in a model Heck coupling reaction shows greatest activity in those species bearing bulkier N-substituents, with complexes bearing _RC^∧N^∧C ligands generally more efficient precatalysts than those bearing _RCNC ligands.     

The isolation and structural characterization of copper(II) complexes obtained by oxidation of the 2,6-bis(dicyclohexylphosphinomethyl)pyridine and 2-(diisopropylphosphinomethyl)-1-methylimidazole ligands

The reactions of [Cu(NCCH₃)₄]BF₄ with 2,6-(dicyclohexylphosphinomethyl)pyridine and 2-(diisopropylphosphinomethyl)-1-methylimidazole afford Cu(I) species that convert slowly to the Cu(II) complexes [CuCl{Cy₂P(O)CH₂pyCH₂P(O)Cy₂}(H₂O)]BF₄ and [Cu{MelmCH₂P(O)Prⁱ₂}₂](BF₄)₂, respectively, when their solutions are exposed to air. The structures of the Cu(II) complexes have been established by X-ray crystallography.     

Synthesis, structures and spectroscopic properties of palladium(II) complexes with tridentate piperidyl-containing pincer ligands

A new series of square planar palladium(II) complexes with pincer ligands, pip₂NCN⁻ (pip₂NCNH = 1,3-bis(piperidylmethyl)benzene) and pip₂NNN (2,6-bis(piperidylmethyl)pyridine), has been prepared: Pd(pip₂NCN)X (X = Cl, Br, I), [Pd(pip₂NCN)(L)](BF₄) (L = pyridine, 4-phenylpyridine), and [Pd(pip₂NNN)Cl]Cl. The X-ray crystal structures of Pd(pip₂NCN)Br, [Pd(pip₂NCN)(L)]BF₄, and [Pd(pip₂NNN)Cl]Cl confirm the tridentate coordination geometries of the pincer ligands. For the pip₂NCN⁻ complexes, each piperidyl ring adopts a chair conformation with the metal center at an equatorial position on the N(piperidyl) atom. However, one of the piperidyl groups of Pd(pip₂NNN)Cl⁺ adopts a previously unobserved coordination geometry, effectively placing the metal center at an axial position on the N(piperidyl) atom. ¹H NMR and UV-Vis absorption measurements provide additional insight into the electronic structures of these complexes. The ¹H NMR spectra of Pd(pip₂NCN)X (X = Cl, Br, I) are consistent with deshielding of the pip₂NCN⁻ ligand resonances along the Cl < Br < I series, in opposition to the relative halogen electronegativities. It is suggested that this trend is consistent with decreasing filled/filled repulsions between the dπ orbitals of the metal center and the lone pair orbitals of the halide ligands along this series. Electronic absorption spectra support the notion that ligand-to-metal charge-transfer states are stabilized in these palladium(II) complexes relative to their platinum(II) analogues.     

Synthesis and metal complexes of 2,6-bis(1-triazolo)pyridine: X-ray structure of 2,6-bis(1-triazolo)pyridine dihydrochloride

2,6-Bis(1-triazolo)pyridine (1) was synthesized and characterized via IR and NMR. The regiochemistry of the compound was confirmed via single crystal X-ray analysis of the hydrochloride salt. A series of insoluble complexes of the general formulae M(1)₂(X)₂ or M(1)(X)₂ [M=Co(II), Ni(II), Cu(II); X=ClO₄, BF₄, Cl] were prepared and their structures interpreted in light of infrared spectra and composition analysis. The results suggest that first row transition metals are not chelated by 1, but rather form extended coordination polymeric networks. A second family of complexes was prepared using 2,6-bis(1-imidazolo)pyridine to support this interpretation.     

Heterodinuclear Cu(II)Zn(II) complexes: F NMR as a versatile tool to control the synthesis

The dinucleating ligands 2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4-methylphenol (H-BPMP) and 2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4-fluorophenol (H-BPFP) were used to synthesize heterodinuclear (μ-phenoxo)(μ-hydroxo) Cu(II)Zn(II) complexes. The labeled ligand with a fluorine atom allows the use of ¹⁹F NMR spectroscopy, which turned to be a rapid and powerful tool to tune the synthesis of the heterodinuclear paramagnetic complex [CuZnBPFP(μOH)](ClO₄)₂ and avoid mixing of complexes with statistical distribution. When applied to the non-fluorinated ligand, this experimental procedure leads to prepare and isolate easily the complex [CuZnBPMP(μOH)](ClO₄)₂. The X-ray structure is described.     

S versus O alkylation and coordination in zinc complexes containing the bulky heteroscorpionate alkoxy ligand bis(3,5-dimethylpyrazol-2-yl) diphenylmethanol

A series of zinc complexes containing the tripodal heteroscorpionate ligand bis(3,5-dimethylpyrazol-2-yl)diphenylmethanol (L2H) have been synthesized and characterized by X-ray crystallography. The L2H/Zn complexes were designed to model the N₂OX coordination (with the zinc-bound O being a reactive nucleophile) that is characteristic of many protease and amidase zinc enzymes. The pseudotetrahedral mononuclear complexes characterized include [(L2)ZnI] (1), [(L2)Zn(CH₃)] (2), and [(L2)Zn(SPh)] (3). Alkylation of (1) with methyl iodide has revealed a modest nucleophilicity of the chelated zinc-bound alkoxide, and produces the penta-coordinate [(L2OCH₃)ZnI₂] (4) which contains a weakly bound ether in the fifth coordination site. However, when the coordination sphere also includes a thiolate sulfur as in (3), reaction with methyl iodide produces exclusive alkylation at the sulfur to produce thioanisole and (1). The coordination of the ether in the neutral (4) can be strengthened by reaction with various silver salts, Ag⁺X⁻, to produce other penta-coordinate complexes [(L2OCH₃)ZnI(Tf)] (5) and [(L2OCH₃)ZnI(H₂O)]BF₄ (6) which show enhanced coordination of the ether.     

Copper(II) compounds of the planar-tridentate ligand 2,6-bis(pyrazol-3-yl)pyridine

The tridentate ligand 2,6-bis(pyrazol-3-yl)pyridine (dPzPy) renders coordination compounds with halide, nitrate and tetrafluoroborate salts of copper. The complexes, which have the form [Cu(dPzPy)X₂] with X=Br and Cl, [Cu(dPzPy)(NO₃)₂](H₂O), and [Cu(dPzPy)₂](BF₄)(SiF₆)_0.5(MeOH)₃ have been characterized by elemental analysis and by IR, EPR and ligand field spectroscopy. The single-crystal X-ray structure of [Cu(C₁₁H₉N₅)Br₂] shows the copper(II) ion to be coordinated by three N atoms of 2,6-bis(pyrazol-3-yl)pyridine and two bromides in a geometry exactly in between a trigonal-bipyramid and a square-pyramid. Each molecule lies on a crystallographic C₂-symmetry axis. They are coupled to one another by a two-dimensional network through NH to Br hydrogen bonds. The crystal structure of [Cu(C₁₁H₉N₅)Cl₂] is analogous to the bromide. The single-crystal X-ray structure of [Cu(dPzPy)₂](BF₄)(SiF₆)_0.5(MeOH)₃ shows the copper ion to be in a Jahn-Teller distorted octahedral N₆ environment of two mer-oriented tridentate ligands.     

Mononuclear and dinuclear bromo bridged iridium(I) complexes with N-allyl substituted imidazolin-2-ylidene ligands

The reaction of 1-methyl-3-(2-propenyl)imidazolium bromide (1) or 1,3-bis(2-propenyl)-imidazolium bromide (2) with [Ir(μ-OMe)(cod)]₂ afforded the five coordinated iridium(I) carbene complexes [IrBr(L)(cod)] (3) (L=1-methyl-3-(2-propenyl)imidazolin-2-ylidene) and (4) (L=1,3-bis(2-propenyl)imidazolin-2-ylidene). The reaction proceeds via an in situ deprotonation of the imidazolium salt. Molecular structure determinations on 3 and 4 confirmed the coordination of the carbene ligands via the carbene carbon atom and one allyl group in both complexes. Treatment of complex 3 with an excess of AgBF₄ gave the dinuclear bromo bridged complex [(Ir(μ-Br)(L)(cod)]₂BF₄ (5) (L=1-methyl-3-(2-propenyl)imidazolin-2-ylidene). The reaction of complex 4 with an excess of AgBF₄ led to the mononuclear complex [Ir(L)(cod)]BF₄ (6) (L=1,3-bis(2-propenyl)imidazolin-2-ylidene) where both N-allyl substituents are coordinated to the iridium(I) center.     

Heteropolymetallic complexes of 1,1′-bis(diphenylphosphino)ferrocene (dppf). IV. Solvolytic behavior and cytostatic properties towards the KB cell-line of dppf and 1,2-bis(diphenylphosphino)ethane cis-complexes of Pt(II) and Pd(II)

The novel cis-platinum(II) complexes [(dppe)Pt(μ-OH)]₂(BF₄)₂ and [(dppe)Pt(DMF)₂](BF₄)₂ have been prepared and characterized by ³¹P NMR, together with cis-[(dppe)Pt(μ-Cl)]₂(BF₄)₂, both in poorly and strongly coordinating solvents (dppe = 1,2-bis(diphenylphosphino)ethane). All these complexes and their dppf analogs (dppf = 1,1′-bis(diphenylphosphino)ferrocene) as well as (dppf)PtCl₂, (dppe)PtCl₂, (dppf)PdCl₂, [(dppf)Pd(μ-Cl)]₂(BF₄)₂ and [(dppf)Pd(μ-OH)]₂(BF₄)₂ have been tested as antiproliferating agents towards Eagle's KB cell-line. Their activity is compared with that of free diphosphine ligands. For Pt(II) complexes, the ID₅₀ figures are found to be higher than those observed for free dppf and dppe. On the contrary, the activity of the palladium dppf complexes is substantially identical to that of free diphosphine.     

Synthesis, characterization and X-ray crystal structure of [Re(L4)(CO)3]Br · 2CH3OH (L4 = N,N-bis[(2-diphenylphosphino)ethyl]methoxyethylamine): A model compound for novel cationic Tc(I)-tricarbonyl radiotracers useful for heart imaging

This report describes synthesis and evaluation of cationic complexes, [^99mTc(CO)₃(L)]⁺ (L = N-methoxyethyl-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (L1), N-[(15-crown-5)-2-yl]-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (L2) and N-[(18-crown-6)-2-yl]-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (L3)) as potential radiotracers for heart imaging. Preliminary results from biodistribution studies in female adult BALB-c mice indicated that the cationic ^99mTc(I)-tricarbonyl complex, [^99mTc(CO)₃(L2)]⁺, has a significant localization in the heart at 60 min post-injection. To understand the coordination chemistry of these bisphosphine ligands with the ^99mTc(I)-tricarbonyl core, we prepared [Re(CO)₃(L4)]Br (L4: N,N-bis[(2-diphenylphosphino)ethyl]methoxyethylamine) as a model compound. [Re(CO)₃(L4)]Br has been characterized by elemental analysis, IR, ESI-MS, NMR (¹H, ¹³C, ¹H-¹H COSY, and ¹H-¹³C HMQC) methods, and X-ray crystallography. In solid state, [Re(CO)₃(L4)]⁺ has a distorted octahedron coordination geometry with PNP occupying one facial plane. The chelator backbone adopts a “chair” conformation with phosphine-P atoms at equatorial positions and the amine-N at the apical site. In solution, [Re(CO)₃(L4)]⁺ is able to maintain its cationic nature with no dissociation of carbonyl ligands or any of the three PNP donors.     

Cyclopalladation of N-phenylbenzamides: Synthesis and structure of bimetallic palladium(II)-complexes

Three bimetallic palladium(II) complexes were generated by cyclopalladation of N-methyl-N-phenylbenzamide derivatives, substrates known to undergo oxidative intramolecular cross-coupling via palladium catalysis. These isolable Pd-complexes were characterized by X-ray crystallography. Stoichiometric and catalytic experiments with [(3-methoxy-N-methyl-N-phenylbenzamide)Pd(μ-TFA)]₂ were investigated, and this palladium complex was found to be an effective precatalyst for oxidative cross-coupling.     

Copper(II) complexes of new pentadentate bis(benzimidazolyl)-dithioether ligands: synthesis, structure, spectra and redox properties

Copper(II) complexes of a series of linear pentadentate ligands containing two benzimidazoles, two thioether sulfurs and a amine nitrogen, viz. N,N^′-bis{4^′-(2″-benzimidazolyl)(methyl)-3^′-thiabutyl}amine(L¹), N,N^′-bis{4^′-(2″-benzimidazolyl)(methyl)-3^′-thiabutyl}N-methylamine (L²), 2,6-bis{4^′-(2″-benzimidazolyl)(methyl)-3^′-thiabutyl}pyridine(L³), N,N^′-bis{4^′-(2″-benzimidazolyl)-2^′-thiabutyl}amine (L⁴), N,N^′-bis{4^′-(2″-benzimidazolyl)-2^′-thiabutyl}N-methylamine (L⁵) and 2,6-bis{4^′-(2″-benzimidazolyl)-2^′-thiabutyl}-3pyridine (L⁶) have been isolated and characterized by electronic absorption and EPR spectroscopy and cyclic and differential pulse voltammetry. Of these complexes, [Cu(L¹)](BF₄)₂ (1) and [Cu(L²)](BF₄)₂ (4) have been structurally characterized by X-ray crystallography. The coordination geometries around copper(II) in 1 and 4 are described as trigonal bipyramidal distorted square based pyramidal geometry (TBDSBP). The distorted CuN₃S basal plane in them is comprised of amine nitrogen, one thioether sulphur and two benzimidazole nitrogens and the other thioether sulfur is axially coordinated. The ligand field spectra of all the complexes are consistent with a mostly square-based geometry in solution. The EPR spectra of complexes [Cu(L¹)](BF₄)₂ (1), [Cu(L¹)](NO₃)₂ (2), [Cu(L²)](BF₄)₂ (4) and [Cu(L³)](ClO₄)₂ (6) are consistent with two species indicating the dissociation/disproportionation of the complex species in solution. All the complexes exhibit an intense CT band in the range 305-395 nm and show a quasireversible to irreversible Cu^II/Cu^I redox process with relatively positive E_1/2 values, which are consistent with the presence of two-coordinated thioether groups. The addition of N-methylimidazole (mim) replaces the coordinated thioether ligands in solution, as revealed from the negative shift (222-403 mV) in the Cu^II/Cu^I redox potential. The present study reveals that the effect of incorporating an amine nitrogen donor into CuN₂S₂ complexes is to generate an axial copper(II)-thioether coordination and also to enforce lesser trigonality on the copper(II) coordination geometry.     

Synthesis and anomalous magnetic properties of heterometal dinuclear Fe(II)-Cr(III) complex bridged by 3,5-bis(pyridin-2-yl)-pyrazolate

A Cr(III)-Fe(II) dinuclear complex [(nta)Cr(μ-bpypz)Fe(dpea)]BF₄, where bpypz=3,5-bis(pyridin-2-yl)-pyazolate, nta=nitrilotriacetate and dpea=(2-aminoethyl)-bis(2-pyridylmethyl)amine, has been synthesized and structurally characterized by ESI-MS and ²H NMR spectra. The proposed structure is mostly more planar in the bridging moiety as compared to that of the previously reported [(nta)Cr(μ-bpypz)Fe(picen)]BF₄(N,N^′-bis-(2-pyridylmethyl)ethylenediamine(picen)). The dpea complex is found to be a high spin state, but to exhibit no spin-crossover by magnetic susceptibility and Mössbauer spectra measurements; showing a large antiferromagnetic interaction, which could make the spin transition temperature lower and/or destroy spin-crossover, suggesting complementarity between spin-crossover and magnetic interaction.     

Synthesis, characterization, crystal structures, and photophysical properties of a series of room-temperature phosphorescent copper(I) complexes with oxadiazole-derived diimine ligand

In this paper, we report four phosphorescent Cu(I) complexes of [Cu(OP)(PPh₃)₂]BF₄, [Cu(Me-OP)(PPh₃)₂]BF₄, [Cu(OP)(POP)]BF₄, and [Cu(Me-OP)(POP)]BF₄ with oxadiazole-derived diimine ligands, where OP = 2-(5-phenyl-[1,3,4]oxadiazol-2-yl)-pyridine, Me-OP = 2-(5-p-tolyl-[1,3,4]oxadiazol-2-yl)-pyridine, POP = bis(2-(diphenylphosphanyl)phenyl) ether, and PPh₃ = triphenylphosphane, including their synthesis, crystal structures, photophysical properties, and electronic nature. The Cu(I) center has a distorted tetrahedral geometry within the Cu(I) complexes. Theoretical calculation reveals that all emissions originate from triplet metal-to-ligand-charge-transfer excited state. It is found that the inter-molecular sandwich structure triggered by inter- and intra-molecular pi-stacking within solid state Cu(I) complexes is highly effective on restricting the geometric relaxation that occurs in excited states, and thus greatly enhances the photoluminescence (PL) performances, including PL quantum yield improvement, PL decay lifetime increase, and emission blue shift.     

The first pincer-aryl [M-(NCN)] complexes {M = Pd(II); Pt(II)} with chiral pyridine donors: Synthesis and catalytic activity in C-C bond formation

The first chiral bis(pyridine) N-C(H)-N pincer ligand, (5S,7S)-1,3-bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanquinolin-2-yl)benzene (HL) has been synthesized and characterized by a thorough ¹H NMR analysis. Reaction of HL with K₂[PtCl₄] in acetic acid gives [Pt(L)Cl] (1), where L acts as a tridentate N-C-N pincer ligand. The analogous palladium(II) derivatives [Pd(L)Cl] (2), and [Pd(L)(OAc)] (3), were first prepared through a transmetalation reaction between Pd(OAc)₂ and the organomercury compound [Hg(L)Cl] (4). The structures of compounds 1 (Pt) and 2 (Pd), as determined by X-ray diffraction, are reported and compared. Compound 2 can also be obtained from Na₂[PdCl₄] and HL in refluxing acetic acid, i.e., under the same conditions used for compound 1. Apparently, this is the first palladium pincer derivative of a 1,3-bis(pyridyl)benzene ligand synthesized by direct C-H activation.The neutral complexes 1-3 are catalysts of modest activity, but devoid of enantioselectivity in the Heck reaction between iodobenzene and methyl acrylate and in the aldol condensation of benzaldehyde with methyl isocyanoacetate.     

Coordination polymers of 1,8-bis(2-methylthioethoxy)anthraquinone and 1,5-bis(2-methylthioethoxy)anthraquinone with Ag(I): Synthesis and X-ray crystallography

The reaction of 2-(methylthioethanol) with 1,8-dichloroanthraquinone and 1,5-dichloroanthraquinone in THF with base produces 1,8-bis(2-methylthioethoxy)anthraquinone (1) and 1,5-bis(2-methylthioethoxy)anthraquinone (2), respectively. Silver(I) complexes of 1 and 2 have been synthesized after combination with [Ag(CH₃CN)₄]BF₄ in 1:1 M ratio to yield, [(1,8-bis(2-methylthioethoxy)anthraquinone)Ag]BF₄, (3) and [(1,5-bis(2-methylthioethoxy)anthraquinone)Ag·CH₃CN]BF₄, (4). X-ray crystal structures of the free ligand (1) and the Ag(I) complexes (3 and 4) are reported. The intraannular carbonyl group forms a coordinate-covalent bond with Ag(I) and, in the solid state, both silver(I) complexes are found as coordination polymers.     

Ethylenediamine-palladium(II) complexes with pyridine and its derivatives: synthesis, molecular structure and initial antitumor studies.

The synthesis of four mononuclear palladium complexes of general formula [Pd(en)Cl(L)]NO3 (en = ethylenediamine; L = pyridine (I), 4-methylpyridine (II), 4-hydroxypyridine (III) or 4-aminopyridine (IV) has been achieved. The structure of these compounds was studied by elemental analysis, IR, far-IR and 1H NMR; complex I was analyzed by X-ray diffraction. The crystal of [Pd(en)(pyridine)Cl]NO3 is monoclinic, space group P21/c (a = 7.990(2), b = 16.058(3), c = 9.846(2) A, beta = 103.81(3) degrees, Z = 4, R = 0.067, Rw = 0.066). The Pd(II) atom exhibits an approximately square planar coordination with bond lengths in the range 2.017-2.042 A for Pd-N and 2.320 A for Pd-Cl. In order to determine the donor strength of the aromatic pyridine ligands, the stability constants of binary complex ML2+ (M = [Pd(en) (H2O)2]2+; L = pyridine, 4-Me-pyridine, 4-OH-pyridine and 4-NH2-pyridine) were determined by potentiometric pH titration in aqueous solution (T = 25 degrees C, I = 0.1 mol l-1 NaNO3). The results show that the stability constants of the binary complexes systematically increase with increasing pKa of the pyridines. The above four palladium complexes, [Pt(en)(pyridine)Cl]NO3 and cis-diamminedichloroplatinum (II) (cis-DDP) were assayed for cytotoxicity in vitro against the human leukemia cell line HL-60, and compounds I, II, III and cis-DDP show significant cytotoxic activity against HL-60.     

Iron(II) complexes based on electron-rich,bulky PNN- and PNP-type ligands

Reaction of the PNN ligand ((2-(di-tert-butylphosphinomethyl)-6-diethylaminomethyl)pyridine) with 1 equiv. of anhydrous FeCl₂ in THF results in the formation of (PNN)FeCl₂ (1). The cationic complex [(PNN)Fe(THF)Cl](PF₆) (2) was obtained by chloride abstraction from 1 with 1 equiv. of TlPF₆. Similarly, the PNP-type complexes 3 and 4 were obtained from FeCl₂ with 1 equiv. of t-Bu-PNP (2,6-bis(di-tert-butylphosphinomethyl)pyridine) and i-Pr-PNP (2,6-bis(di-iso-propylphosphinomethyl)pyridine), respectively. Complexes 1 and 3 were characterized by X-ray diffraction and elemental analyses. In both structures the Fe(II) centers exhibit a distorted square pyramidal geometry comprising two chloride ligands and one tridentate PNN or PNP ligand. The magnetic properties of the paramagnetic complexes 1–4 are discussed.     

Two new 4′,4′′-disubstituted dipyrazolylpyridine derivatives, and the structures and spin states of their iron(II) complexes

Reaction of 2 equiv of the sodium salt of ethyl pyrazole-4-carboxylate, with 1 equiv of 2,6-dibromopyridine, in diglyme at 130 °C for 5 days yields 2,6-di[4-(ethylcarboxy)pyrazol-1-yl]pyridine (L¹), with 2-bromo-6-[4-(ethylcarboxy)pyrazol-1-yl]pyridine (L²) as a significant byproduct. Reduction of L¹ with excess NaBH₄ in thf affords 2,6-di[4-(hydroxymethyl)pyrazol-1-yl]pyridine (L³) in low yield. The crystalline complex [Fe(L¹)₂][BF₄]₂ · 2CF₃CH₂OH is low-spin at 150 K, while bulk samples with this formula are approximately 10% high-spin and 90% low-spin at room temperature. This ratio does not vary significantly on cooling from its magnetic susceptibility, suggesting that the material might be contaminated by a second, minor high-spin phase. Single crystals of [Fe(L³)₂][BF₄]₂·1.4CH₃CN have a mixed spin-state population, with the low-spin state predominating at 150 K. The [Fe(L³)₂(BF₄)]⁺ moieties in the lattice associate into 1-D chains through intermolecular O-H?O and O-H?F hydrogen bonding. Bulk samples of [Fe(L³)₂][BF₄]₂ · H₂O are fully low-spin below 200 K, but the magnetic data imply the onset of a gradual thermal spin-transition centred above room temperature. DSC and TGA measurements imply that this transition is centred at 322 K, and involves loss of lattice water. Both complexes undergo spin-crossover in (CD₃)₂CO solution, with transition midpoints near 250 K.     

Preparation, characterization, and catalytic properties of (triphenylphosphine)ruthenium complexes bearing N,O,N′-tridentate ligands

Preparation and characterization of (triphenylphosphine)ruthenium complexes bearing N,O,N′-tridentate ligands, [(L₁)RuCl(PPh₃)₂](BF₄) (L₁ = 2-[(2-pyridylmethoxy)methyl]pyridine), 1), [(L₂)RuCl(PPh₃)₂](BF₄) (L₂ = 8-(2-pyridylmethoxy)quinoline, 2) and [(L₃)RuCl₂(PPh₃)] (L₃ = 2-[(2-pyridylmethoxy)methyl]quinoline, 3) are described. Complexes 1-3 have been characterized by NMR and elemental analyses. Molecular structures of 2 and 3 have been determined by X-ray crystallography. Both compounds exhibit the octahedral geometry. L₂ adopts the facial configuration in 2 while L₃ is in a mer-arrangement in 3. Complexes 1-3 have proven to be able to catalyze the transfer hydrogenation of several ketones to alcohols in the presence of KOH and 2-propanol at refluxing, among which complex 3 was found to be the most active.