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.     

Crystal structures and coordination-site exchange reactions of palladium(II) and platinum(II) complexes containing tris[2-(tert-butylthio)ethyl]amine

Palladium(II) and platinum(II) complexes, [PdX(NS₃ ¹Bu)]BPh₄ (X=Cl, Br, I; NS₃ ¹Bu=tris[2-(tert-butylthio)ethyl]amine) and [PtCl(NS₃ ¹Bu)]BPh₄, were prepared, and their structures were determined by X-ray analyses. The geometry around the palladium and platinum atoms is square planar. The NS₃ ¹Bu ligand functions as a tridentate ligand and one sulfur atom is not coordinated to the metal. The ¹H NMR spectrum of [PdCl(NS₃ ¹Bu)]BPh₄ in acetone-d₆ exhibited a dynamic behavior. At 20°C the spectrum showed a singlet signal at 1.60 ppm that can be assigned to tert-butyl protons, whereas at −70°C three singlet signals were observed at 1.36, 1.61, and 1.70 ppm with an intensity ratio of 1: 0.25: 2. The signals at 1.36 and 1.70 ppm are assigned to the tert-butyl protons in the square-planar structure, and these signals are consistent with the X-ray structure. The signal at 1.61 ppm can be assigned to the tert-butyl protons in a trigonal-bipyramidal structure where the three tert-butyl groups are magnetically equivalent. Thus, we concluded that the coordination-site exchange occurred via a trigonal-bipyramidal intermediate. The square-planar and trigonal-bipyramidal species of [PdCl(NS₃ ¹Bu)]BPh₄ are in equilibrium in acetone-d₆. The equilibrium was shifted toward the square-planar species on decreasing the temperature. The ¹H NMR spectra for [PdX(NS₃ ¹Bu)]BPh₄ (X=Cl, Br, and I) were similar to one another at the same temperature, suggesting that the site-exchange process is insensitive to the kind of coexisting halogen ligand. The site exchange reaction of [PtCl(NS₃ ¹Bu)]BPh₄ seems to occur more slowly than that of the palladium(II) analogue.     

Synthesis, structure and cytotoxicity studies of four-coordinate bis (cis-bis(diphenylphosphino)ethene) gold(I) complexes, [Au(dppey)2]X

Four-coordinate 1:2 gold(I) complex salts with cis-bis(diphenylphosphino)ethene, [Au(dppey)₂]X have been synthesized for X = PF₆⁻, CF₃SO₃⁻, BF₄⁻, Cl⁻, Br⁻ and BPh₄⁻ and characterized by NMR spectroscopy and electrospray mass spectrometry. Single crystal X-ray structure determinations show the BF₄⁻, Cl⁻ and Br⁻ complexes to be isostructural, although with different degrees of hydration, while the BPh₄⁻ complex crystallizes as an acetone solvate with two molecules in the asymmetric unit. The Au(P-P)₂ core for the BF₄⁻, Cl⁻ and Br⁻ complexes adopts D₂ symmetry with Au-P bond lengths 2.3980(7)-2.4009(7) Å and inter-ligand P-Au-P angles 114.78(2)-127.82(2))°. The Au(P-P)₂ core in the BPh₄⁻ complex is unsymmetrical with Au-P bond lengths 2.364(1)-2.420(1) Å and inter-ligand P-Au-P angles 104.76(5)-137.50(4)°. In vitro cytotoxicity studies show the PF₆⁻, CF₃SO₃⁻, BF₄⁻, Cl⁻, Br⁻ and I⁻ complexes to be potent and selective growth inhibitors of the human cell lines MCF7 (hormone-dependent breast cancer), MDA-MB-231 (hormone-independent breast cancer), MM96L (melanoma), CI80-13S (cisplatin resistant ovarian cancer) and a normal cell line NFF (neonatal foreskin fibroblasts), achieving IC₅₀ values between 13 and 196 nM. The halogen and triflate salts were approximately twice as potent towards the MCF7 and MDA-MB-231 cell lines compared to the PF₆⁻ and BF₄⁻ derivatives; while the cytotoxicity of all complexes towards the sensitive CI80-13S and MM96L cancer cell lines was approximately 10-fold greater than that displayed towards the normal human cell line (NFF).     

Syntheses and structural characterizations of novel mono- and dinuclear iridium hydrido complexes with polydentate nitrogen donor ligands

New five mono- and dinuclear Ir hydrido complexes with polydentate nitrogen ligands, [Ir(H)₂(PPh₃)₂(tptz)]PF₆ (1), [Ir₂(H)₄(PPh₃)₄(tptz)](PF₆)₂ · 2H₂O (2 · 2H₂O), [Ir(H)₂(PPh₃)₂(tppz)]BF₄ (3), [Ir₂(H)₄(PPh₃)₄(tppz)](BF₄)₂ (4) and [Ir₂(H)₄(PPh₃)₄(bted)](BF₄)₂ · 6CHCl₃ (5 · 6CHCl₃), were systematically prepared by the reactions of the precursor Ir hydrido complex [Ir(H)₂(PPh₃)₂(Me₂CO)₂]X (X=PF₆ and BF₄) with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) and 1,4-bis(2,2^′:6^′,2″-terpyridine-4^′-yl)benzene (bted), and their structures and properties were characterized in the solid state and in solution. Each of the Ir hydrido complexes with polydentate nitrogen ligands crystallographically described a unique coordination mode. Their ¹H NMR spectra demonstrated unusual ¹H NMR chemical shifts of pyridyl rings that are likely induced by the ring current effect of neighboring ligands.     

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.     

Platinum group metal complexes of bis(2-(diphenylphosphino)ethyl benzylamine and bis(2-(diphenylarsino)ethyl)benzylamine

Rh(I), Ir(I), Pd(II) and Pt(II) metal complexes of bis(2-diphenylphosphino)ethyl)benzylamine(DPBA) and bis(2-diphenylarsino)ethyl)benzylamine (DABA) have been synthesized using various starting materials. Reaction of RhCl(CO)(AsPh₃)₂ with DPBA or DABA in methanol resulted in the formation of cationic complexes of the composition, [Rh(CO)(L)]Cl (L = DPBA or DABA). Interaction of [IrCl(COD)]₂ with DPBA in benzene resulted in the formation of a neutral complex [IrCl(DPBA)]. Reaction of [PdCl₂(COD)] with the ligand DPBA in benzene resulted in a cationic complex of the composition [PdCl(DPBA)]Cl. Interaction of [PdCl(DPBA)]BPh₄ with SnCl₂ gave the complex [Pd(SnCl₃)(DPBA)]BPh₄. The ligands DPBA and DABA react with PtCl₂(COD) in acetone to give neutral, Pt(II) complexes of the type, [PtCl₂L] (L = DPBA or DABA). All the complexes were fully characterized by elemental analysis, conductivity measurements, IR and far-IR and ³¹P{¹H} NMR spectral data.     

Nickel(II) complexes of di- and tri-substituted thiourea mono- and di-anions

Reaction of nickel(II) acetate, 1,2-bis(diphenylphosphino)ethane (dppe), and a di- or tri-substituted thiourea R¹NHC(S)R²R³ (R³ = H or alkyl) with trimethylamine in hot methanol gave cationic nickel(II) complexes containing N,S-chelated thiourea monoanion ligands [Ni{SC(NR²R³)NR¹}(dppe)]⁺, which can be readily isolated as their BPh₄⁻ salts. The X-ray crystal structure of [Ni{SC(NMe₂)NPh}(dppe)]⁺BPh₄⁻ is reported.     

Preparation of benzophenone imine complexes of transition metals

Benzophenone imine [M(η¹-NHCPh₂)(CO)_nP_5-n]BPh₄ [M = Mn, Re; n = 2, 3; P = P(OEt)₃, PPh(OEt)₂, PPh₂OEt, PPh₃] complexes were prepared by allowing triflate M(κ¹-OTf)(CO)_nP_5-n compounds to react with an excess of the imine. Hydride-imine [MH(η¹-NHCPh₂)P₄]BPh₄ (M = Ru, Os), triflate-imine [Os(κ¹-OTf)(η¹-NHCPh₂)P₄]BPh₄ and bis(imine) [Ru(η¹-NHCPh₂)₂P₄](BPh₄)₂ [P = P(OEt)₃] derivatives were also prepared. The complexes were characterized spectroscopically (IR, ¹H, ³¹P, ¹³C NMR) and a geometry in solution was also established. Hydride-benzophenone imine [IrHCl(η¹-NHCPh₂)L(PPh₃)₂]BPh₄and [IrHCl(η¹-NHCPh₂)L(AsPh₃)₂]BPh₄ [L = P(OEt)₃ and PPh(OEt)₂] complexes were prepared by reacting hydride IrHCl₂L(PPh₃)₂ and IrHCl₂L(AsPh₃)₂ precursors with an excess of imine. Dihydride IrH₂(η¹-NHCPh₂)(PPh₃)₃ complex was also obtained and a geometry in solution was proposed.     

Insertion of heteroallenes into the rhenium-hydride bond

Dithioformato [Re{η²-SC(H)S}(NO)P₃]BPh₄ (1), thioformamido [Re{η²-RNC(H)S}(NO)P₃]BPh₄ (2) (R = Et, p-tolyl), formamido [Re{η²-PhNC(H)O}(NO)P₃]BPh₄ (3) and formamidinato [Re{η²-p-tolylNC(H)Np-tolyl}(NO)P₃]BPh₄ (4) (P = PPh₂OEt) complexes were prepared by allowing the hydride ReH₂(NO)P₃ to react first with triflic acid and then with the appropriate heteroallene CS₂, RNCS, PhNCO and p-tolylNCNp-tolyl. Treatment of the ReH₂(NO)L(PPh₃)₂ [L = P(OEt)₃, PPh(OEt)₂] and ReH₂(NO)(PPh₃)₃ hydrides first with triflic acid and then with isothiocyanate RNCS (R = Et, p-tolyl) gave the [Re{η²-RNC(H)S}(NO){P(OEt)₃}(PPh₃)₂]BPh₄ (5, 6) and [Re(η²-RNC(H)S)(NO)(PPh₃)₃]BPh₄ (7) derivatives. Depending on the nature of the phosphite, instead, the reaction of ReH₂(NO)L(PPh₃)₂ and ReH₂(NO)(PPh₃)₃ hydrides first with CF₃SO₃H and then with isocyanate R1NCO (R1 = Ph, p-tolyl) gave the chelate [Re{η²-R1NC(H)O}(NO){P(OEt)₃}(PPh₃)₂]BPh₄ (8) and [Re{η²-R1NC(H)O}(NO)(PPh₃)₃]BPh₄(10) complexes with P(OEt)₃ or PPh₃, while the η¹-coordinate [Re{η¹-RNC(H)S}(NO){PPh(OEt)₂}₂(PPh₃)₂]BPh₄ (9) derivative was obtained with the PPh(OEt)₂ phosphite ligand. η¹-Coordinate dithioformato [Re{η¹-SC(H)S}(NO){PPh(OEt)₂}₂(PPh₃)₂]BPh₄ (11) and formato [Re{η¹-OC(H)O}(NO){PPh(OEt)₂}₂(PPh₃)₂]BPh₄ (12) complexes, as well as the formamidinato [Re{η²-p-tolylNC(H)Np-tolyl}(NO){P(OEt)₃}(PPh₃)₂]BPh₄ (13) derivative were also prepared.     

Effect of nitrogen-donor ancillary ligand on oxidation behavior of Co(III) binuclear complexes with conjugated bis(catecholate) ligands

Two binuclear complexes of cobalt(III) have been prepared with 3,3′,4,4′-tetrahydroxy-5,5′-di-tert-butylbenzaldazine (H₄thBu) as bis(catecholate) ligand and two different ancillary ligands, 2,2′-bipyridine (bpy) or 2,2′-dipyridylamine (dpa). These compounds were characterized by ¹H NMR spectra, electrochemical measurements and UV–Vis spectra. In one case, [Co₂(dpa)₄(thBu)]²⁺, electrochemical oxidation of the complexes occurs at the bridges as two closely spaced one-electron couples (E_1/2 = 1 mV and 168 mV versus Fc/Fc⁺). Chemical oxidation of [Co₂(dpa)₄(thBu)]²⁺ using Ag⁺ is observed to occur as a stepwise two-electron process forming [Co₂(dpa)₄(thBu^Cat,SQ)]³⁺ or [Co₂(dpa)₄(thBu^SQ,SQ)]⁴⁺ by UV–Vis spectrum. However, [Co₂(bpy)₄(thBu)]²⁺ shows no change in electronic spectrum under the same conditions of oxidation. This illustrates the dependence of redox properties of the binuclear Co(III) complexes on the nature of the nitrogen-donor ancillary ligands. In this report we discuss the effect of two different nitrogen-donor ancillary ligands on the0 oxidation behavior of binuclear Co(III) complexes.     

Synthesis of new palladium(II) complexes containing tetradentate-nitrogen donor ligands: Combined structural studies by NMR spectroscopy and X-ray crystallography

Treatment of the tetradentate (NN′N′N) N-alkylaminopyrazole ligands 3,6-dimethyl-1,8-(3,5-dimethyl-1-pyrazolyl)-3,6-diazaoctane (ddad) and 1,4-bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl]piperazine (bedp) with [PdCl₂(CH₃CN)₂] in a 1:1 M/L ratio in acetonitrile produces [Pd₂Cl₄(L)] and [PdCl₂(L)] (L = ddad and bedp). Treatment of the corresponding complex [PdCl₂(L)] (L = ddad, bedp) in the presence of AgBF₄ in CH₂Cl₂/methanol (2:1) or NaBF₄ in acetonitrile gives [Pd(L)](BF₄)₂. The Pd(II) complexes have been characterised by elemental analyses, conductivity measurements, IR and ¹H and ¹³C{¹H} NMR spectroscopies when possible. The X-ray structure of the complex [Pd(ddad)]Cl₂ · 3H₂O has been determined. The Pd(II) is coordinated to the ddad ligand by two nitrogen atoms of pyrazolyl groups and two nitrogen atoms of the amine groups, in a slightly distorted square-planar geometry.     

Syntheses and characterization of Co(III) binuclear complexes with bis(catecholate) ligands containing an acetylene linker

Three binuclear Co(III) complexes with 5,5′-(buta-1,3-diyne-1,4-diyl)bis(3-tert-butylcatechol) (L1), 5,5′-(2,5-dimethoxy-1,4-phenylene)bis(ethyne-2,1-diyl)bis(3-tert-butyl-catechol) (L2) and 5,5′-(4,4′-(buta-1,3-diyne-1,4-diyl)bis(2,5-dimethoxy-4,1-phenylene))bis(ethyne-2,1-diyl)bis(3-tert-butyl-catechol) (L3) have been prepared. The triple bond-containing L1, L2 and L3 ligands were synthesized by a cross-coupling reaction. These complexes were characterized by elemental analyses, electrochemical measurements, ¹H NMR and UV-Vis spectra. In [Co₂(bpy)₄(L1)]²⁺, electrochemical oxidation of the complexes occurs at the bridges as two closely spaced one-electron couples. UV-Vis spectra reveal that chemical oxidation of [Co₂(bpy)₄(L1)]²⁺ using Ag⁺ occurs as a two-electron process forming [Co₂(bpy)₄(L1^Cat,SQ)]³⁺ or [Co₂(bpy)₄(L1^SQ,SQ)]⁴⁺. On the other hand, [Co₂(bpy)₄(L2)]²⁺ and [Co₂(bpy)₄(L3)]²⁺ exhibit different oxidation behavior under the same experimental conditions. In this report we discuss the role of the distance between the two metal atoms on the oxidative behavior of binuclear Co(III) complexes.     

Effects of equatorial ligand bulk on the orientation of axial ligands in methyl organocobalt B12 models assessed by X-ray and NMR methods

We prepared two new analogues of ([CH₃Co((DO)(DOH)pn)L]⁺) [(DO)(DOH)pn = N²,N^2′-propane-1,3-diylbis(2,3-butanedione-2-imine-3-oxime)] B₁₂ models but with an O-BF₂-O unit replacing the O-H?O unit as follows: [CH₃Co((DO)(DOBF₂)pn)L]PF₆ with L = pyridine (py) and 1,5,6-trimethylbenzimidazole (Me₃Bzm). Our goal was to compare the properties of these new O-BF₂-O complexes with the well-established O-H?O analogues. The Co-CH₃¹H NMR shifts indicate that the BF₂ group makes the Co(III) less electron rich. The X-ray crystal structures determined for the new compounds were compared to the one known structure with L = imidazole (Im). With increasing size of L, in the series Im < py < Me₃Bzm, the plane of L orients so as to avoid the bulky BF₂ group. This orientation effect becomes apparent in the L ¹H NMR shifts, which are not sensitive to Co(III) electronic properties. Thus, in the O-BF₂-O versus the O-H?O analogue, the Me₃Bzm H4 signal shifts 0.41 ppm upfield from the anisotropic effect of the equatorial ligand double bonds. We advance the concept (applicable to a broad series of complexes) that steric interactions between L and the equatorial ligands are alleviated by a combination of Co-N_ax bond elongation and opening of the N_eq-Co-N_ax angles.     

Synthesis, and characterization of cobalt(III) complexes with Schiff bases derived from 2-hydroxynaphthaldehyde, (naph)2dien and (naph)2dpt, and monodentate amine ligands: Crystal structure, spectral and redox properties

Two series of complexes of the type [Co^III{(naph)₂dien}(amine)]BPh₄ {(naph)₂dien = bis-(2-hydroxy-1-naphthaldimine)-N-diethylenetriamine dianion, and amine = piperidine (pprdn) (1), pyrrolidine (prldn) (2), pyridine (py) (3), N-methylimidazole (N-MeIm) (4)}, and [Co^III{(naph)₂dpt}(amine)]BPh₄ {(naph)₂dpt = bis-(2-hydroxy-1-naphthaldimine)-N-dipropylenetriamine dianion, and amine = piperidine (pprdn) (5), 3-methylpyridine (3-Mepy) (6)} have been synthesized and characterized by elemental analyses, IR, UV-Vis, and ¹H NMR spectroscopy. The crystal structures of (2) and (6) have been determined by X-ray diffraction. The redox potentials of the central cobalt ion show a relatively good correlation with the σ-donor ability of the axial ligands. The spectroscopic and electrochemical properties of these complexes are also influenced by the mutual steric hindrance between the pentadentate Schiff base and the ancillary ligands.     

Novel carbon-centered heteroscorpionate ligands: Cu(I) complexes and luminescence properties

Herein, we describe the synthesis of N,N′,S donor ligands 2-(1-(3,5-diisopropyl-1H-pyrazol-1-yl)-3-(methythio)propyl)-4-methoxy-3,5-dimethylpyridine (L1) and 2-(1-(3,5-diisopropyl-1H-pyrazol-1-yl)-2-(methythio)ethyl)-4-methoxy-3,5-dimethylpyridine (L2). Cu(I) complexes were prepared by reacting L1 or L2 with [Cu(CH₃CN)₄]BF₄ or CuCl. The coordination behavior of the thioether arm of the ligands was found to determine the nuclearity of the resulting complexes, in which [Cu(L1)PPh₃]BF₄ (1) is polynuclear, [Cu(L2)PPh₃]BF₄ (2) is mononuclear, while [Cu(L1)]₂(BF₄)₂ (3), [Cu(L2)CH₃CN]₂(BF₄)₂ (4), and [Cu(L1)Cl]₂ (5) are dinuclear. In the dimeric complex [Cu(L2)Cl]₂ (6), the sulfur atoms are not metal-bound. Rather, the two bridging chloride ions link the two copper centers. Compounds 4-6 are luminescent in the solid state, and exhibit emission bands centered at 490 nm (4), 544 nm (5), and 562 nm (6), respectively. Their excitation spectra display bands at 280 nm and 380 nm. According to DFT calculations, the HOMO is distributed partially over the metal centers and partially over the chloride anions (5 and 6) or the sulfur atoms (4) of the ligands, while the LUMO is a π∗ antibonding pyridine orbital. This suggests that the emission properties are derived from metal-to-ligand charge-transfer (MLCT), halide-to-ligand charge-transfer (XLCT), and ligand-to-ligand charge-transfer (LLCT) excited states.     

Syntheses, structures, and properties of Co(III) complexes derived from polypyridine ligands containing one carboxamido nitrogen donor

Four cobalt(III) complexes containing the polypyridine pentadentate ligands N,N-bis(2-pyridylmethyl)amine-N′-ethyl-2-pyridine-2-carboxamide (PaPy₃H), N,N-bis(2-pyridylmethyl)amine-N′-[1-(2-pyridylethyl)acetamide (MePcPy₃H), and N,N-bis(2-pyridylmethyl)amine-N′-(2-pyridylmethyl)acetamide (PcPy₃H), have been synthesized. All three ligands bind the Co(III) center in the same fashion with the exception of loss of conjugation between the carboxamide moiety and the pyridine ring in the latter two. The structures of [(PaPy₃)Co(OH)][(PaPy₃)Co(H₂O)](ClO₄)₃ · 3H₂O (1), [(PaPy₃)Co(NO₂)](ClO₄) · 2MeCN (2), [(MePcPy₃)Co(MeCN)](ClO₄)₂ · 0.5MeCN (3), and [(PcPy₃)Co(Cl)](ClO₄) · 2MeCN (4) have been determined. These ligands with strong-field carboxamido N donor stabilize the +3 oxidation state of the Co center as demonstrated by the facile oxidation of the corresponding Co(II) complexes (prepared in situ) by H₂O₂, [Fe(Cp)₂](BF₄), or nitric oxide (NO). The Co-N_amido bond distances of 1-4 lie in the narrow range of 1.853-1.898 Å. ¹H NMR spectra of these complexes confirm the low-spin d⁶ ground states of the metal centers.     

Ruthenium complexes of furan- and thiophene-thiolates: Structure of CpRu(dppe)SThi

Complexes of ruthenium containing 2-furan- and 2-thiophene-thiolates with phosphine ligands have been prepared and characterized. The bis(triphenylphosphine) complexes CpRu(PPh₃)₂SR (R = C₄H₃O: Fu (1a), C₄H₃S: Thi (1b)) were prepared by the reaction of thiolato anions (FuS^? or ThiS^?) with CpRu(PPh₃)₂Cl. The one-pot reaction of CpRu(PPh₃)₂Cl, thiolato anions and L ligands gave CpRu(L)SR (L = bis(diphenylphosphino)methane: dppm (2); bis(diphenylphosphino)ethane: dppe (3)). The newly prepared complexes have been characterized by spectroscopic techniques (FT-IR, ¹H NMR and ³¹P NMR) and by elemental analysis. The crystal structure of CpRu(dppe)SThi (3b) has been determined by X-ray diffraction.     

Trispyrazolylmethane piano stool complexes of iron(II) and cobalt(II)

A series of cationic trispyrazolylmethane complexes of the general form [Tm^RM(CH₃CN)₃]²⁺ (Tm = tris(pyrazolyl)methane, 1, R = 3,5-Me₂, M = Fe(II); 2, R = 3-Ph, M = Fe(II); 3, R = 3,5-Me₂, M = Co(II); 4, R = 3-Ph, M = Co(II)) with ‘piano-stool’ structures was prepared by the reaction of the N₃tripodal ligands (Tm^R)with [(CH₃CN)₆M](BF₄)₂ in a 1:1 stoichiometric ratio. Magnetic susceptibility measurements indicate that all four complexes with BF₄⁻ counter anions are paramagnetic, high-spin systems in the solid state with μ_eff at high temperatures of 5.2 (1, S = 2), 5.4 (2, S = 2), 4.9 (3, S = 3/2) and 4.6 (4, S = 3/2) BM, respectively. Comparisons of bond lengths from the metal centre to the Tm^R nitrogen donors, and from the metal centre to the acetonitrile nitrogen donors indicate that the neutral tripodal ligands appear to be more weakly coordinated to the metal centre than are the acetonitrile ligands. Reactions of these tripodal complexes with bidentate phosphine ligands, such as 1,2-diphosphinoethane or 1,2-bis(diallylphosphino)ethane leads to displacement of the tripodal ligand, or to the formation of more thermally stable bis-ligand complexes M(Tm^R)₂ (R = 3,5-dimethyl).     

Synthesis,density functional theory calculations and luminescence of lanthanide complexes with 2,6‐bis[(3‐methoxybenzylidene)hydrazinocarbonyl] pyridine Schiff base ligand

A pyridine‐diacylhydrazone Schiff base ligand, L = 2,6‐bis[(3‐methoxy benzylidene)hydrazinocarbonyl]pyridine was prepared and characterized by single crystal X‐ray diffraction. Lanthanide complexes, Ln–L, {[LnL(NO₃)₂]NO₃.xH₂O (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Er)} were prepared and characterized by elemental analysis, molar conductance, thermal analysis (TGA/DTGA), mass spectrometry (MS), Fourier transform infra‐red (FT‐IR) and nuclear magnetic resonance (NMR) spectroscopy. Ln–L complexes are isostructural with four binding sites provided by two nitro groups along with four coordination sites for L. Density functional theory (DFT) calculations on L and its cationic [LnL(NO₃)₂]⁺ complexes were carried out at the B3LYP/6–31G(d) level of theory. The FT‐IR vibrational wavenumbers were computed and compared with the experimentally values. The luminescence investigations of L and Ln–L indicated that Tb–L and Eu–L complexes showed the characteristic luminescence of Tb(III) and Eu(III) ions. Ln–L complexes show higher antioxidant activity than the parent L ligand.     

Synthesis of new platinum(II) complexes containing hybrid thioether-pyrazole ligands: Structural analysis by H and C{H} NMR spectroscopy and X-ray crystal structures

Treatment of the ligands 1,8-bis(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane (bddo), 1,9-bis(3,5-dimethyl-1-pyrazolyl)-3,7-dithianonane (bddn), and 1,6-bis(3,5-dimethyl-1-pyrazolyl)-2,5-dithiahexane (bddh) with several platinum starting materials as K₂PtCl₄, PtCl₂, [PtCl₂(CH₃CN)₂] and [PtCl₂(PhCN)₂] was developed under different conditions. The reactions did not yield pure products. The ratio of the NSSN, NS, SS, NN, and 2NS isomers has been calculated through NMR experiments. Treatment of the mixtures of complexes with NaBPh₄ affords [Pt(NSSN)](BPh₄)₂ (NSSN = bddo, bddn). These Pt(II) complexes have been characterised by elemental analyses, conductivity measurements, IR and ¹H and ¹³C NMR spectroscopy. The X-ray structures of the complexes [Pt(NSSN)](BPh₄)₂ (NSSN = bddo, bddn) have also been determined. In these complexes, the metal atom is tetracoordinated by the two azine nitrogen atoms of the pyrazole rings and two thioether sulfur atoms. When the [Pt(NSSN)](BPh₄)₂ (NSSN = bddo, bddn) complexes were heated under reflux in a solution of Et₄NBr in CH₂Cl₂/CH₃OH (1:1), a mixture of isomers was obtained.