Synthesis and properties of bis(heteroazulen-3-yl)methyl cations and bis(heteroazulen-3-yl)ketones

The synthesis and properties of a novel type of bis(heteroazulen-3-yl)methyl cations, bis(2-oxo-2H-cyclohepta[b]furan-3-yl)methyl cation salt and nitrogen analogues, (9a-c·PF₆⁻) and (9a-c·BF₄⁻), as well as bis(heteroazulen-3-yl)ketones (12a-d) are studied. The synthetic method was based on a TFA-catalyzed electrophilic aromatic substitution on the heteroazulenes (6a-d) with paraformaldehyde to afford the corresponding disubstituted methane derivatives 7a-d, followed by oxidative hydrogen abstraction with DDQ, and subsequent exchange of the counter-anion by using aq. HPF₆ or aq. HBF₄. In addition, the reaction of 7a-d with 2.2 equiv. amounts of DDQ afforded carbonyl compounds 12a-d. The delocalization of the positive charge of 9a-c was evaluated by the ¹H and ¹³C NMR spectral data. The thermodynamic stability of cations 9a-c was evaluated to be in the order 9a<9b<9c on the basis of their reduction potentials measured by cyclic voltammetry (CV) and pK_R+ values (2.6-10.3) obtained spectrophotometrically. The reduction waves of cations 9a-c were irreversible, suggesting the dimerization of the radical species generated by one-electron reduction. This was demonstrated by the reduction of 9a·BF₄⁻ with Zn powder to give dimerized product 14a. In addition, the quenching of 9a·BF₄⁻ with MeOH/NaHCO₃ gives ether derivative 15a, which is proposed for the precursor for synthesizing tris(heteroazulene)-substituted methyl cations bearing two different heteroazulene-units.     

Ruthenium monoterpyridine complexes with 2,6-bis(benzimidazol-2-yl)pyridine: Synthesis,spectral properties and structure

Ruthenium monoterpyridine complexes with the tridentate 2,6-bis(benzimidazol-2-yl)pyridine (LH₂), [Ru(trpy)(LH₂)]²⁺, [1]²⁺ and [Ru(trpy)(L²⁻)], 2 (trpy = 2,2′:6′,2″-terpyridine) have been synthesized. The complexes have been authenticated by elemental analyses, UV–Vis, FT-IR, ¹H NMR spectra and their single crystal X-ray structures. Complexes [1]²⁺ and 2 exhibit strong MLCT band near 475 and 509 nm, respectively, and are found to be very much dependent on solution pH. The successive pH dependent dissociations of the N–H protons of benzimidazole moiety of LH₂ in [1]²⁺ lead to the formation of 2. The proton induced inter-convertibility of [1]²⁺ and 2 has been monitored via UV–Vis spectroscopy and redox features. The two pK_a values, 5.75 and 7.70, for complex [1]²⁺ have been determined spectroscopically.     

Dimolybdenum complexes containing anions of N,N′-bis(pyrimidine-2-yl)formamidine and N-(2-pyrimidinyl)formamide

The reactions of Mo₂(O₂CCH₃)₄ with different equivalents of N,N′-bis(pyrimidine-2-yl)formamidine (HL1) and N-(2-pyrimidinyl)formamide (HL2) afforded dimolybdenum complexes of the types Mo₂(O₂CCH₃)(L1)₂(L2) (1) trans-Mo₂(L1)₂(L2)₂ (2) cis-Mo₂(L1)₂(L2)₂ (3) and Mo₂(L2)₄ (4). Their UV–Vis and NMR spectra have been recorded and their structures determined by X-ray crystallography. Complexes 2 and 3 establish the first pair of trans and cis forms of dimolybdenum complexes containing formamidinate ligands. The L1 ligands in 1–3 are bridged to the metal centers through two central amine nitrogen atoms, while the L2 ligands in 1–4 are bridged to the metal centers via one pyrimidyl nitrogen atom and the amine nitrogen atom. The Mo–Mo distances of complexes 1 [2.0951(17) Å], 2 [2.103(1) Å] and 3 [2.1017(3) Å], which contain both Mo?N and Mo?O axial interactions, are slightly longer than those of complex 4 [2.0826(12)–2.0866(10) Å] which has only Mo?O interactions.     

Quantum chemistry studies on the Ru-M interactions and the P NMR in [Ru(CO)3(Ph2Ppy)2(MCl2)] (M = Zn, Cd, Hg)

To study the Ru-M interactions and their effects on ³¹P NMR, complexes [Ru(CO)₃(Ph₂Ppy)₂] (py = pyridine) (1) and [Ru(CO)₃(Ph₂Ppy)₂MCl₂] (M = Zn, 2; Cd, 3; Hg, 4) were calculated by density functional theory (DFT) PBE0 method. Moreover, the PBE0-GIAO method was employed to calculate the ³¹P chemical shifts in complexes. The calculated ³¹P chemical shifts in 1-3 follow 2 > 3 > 1 which are consistent to experimental results, proving that PBE0-GIAO method adopted in this study is reasonable. This method is employed to predict the ³¹P chemical shift in designed complex 4. Compared with 1, the ³¹P chemical shifts in 2-4 vary resulting from adjacent Ru-M interactions. The Ru → M or Ru ← M charge-transfer interactions in 2-4 are revealed by second-order perturbation theory. The strength order of Ru → M interactions is the same as that of the P-Ru → M delocalization with Zn > Cd > Hg, which coincides with the order of ³¹P NMR chemical shifts. The interaction of Ru → M, corresponding to the delocalization from 4d orbital of Ru to s valence orbital of M²⁺, results in the delocalization of P-Ru → M, which decreases the electron density of P nucleus and causes the downfield ³¹P chemical shifts. Except 2, the back-donation effect of Ru ← M, arising from the delocalization from s valence orbital of M²⁺ to the valence orbital of Ru, is against the P-Ru → M delocalization and results in the upfield ³¹P chemical shifts in 4. Meanwhile, the binding energies indicate that complex 4 is stable and can be synthesized experimentally. However, as complex [Ru(CO)₃(Ph₂Ppy)₂HgCl]⁺5 is more stable than 4, the reaction of 1 with HgCl₂ only gave 5 experimentally.     

Formation and crystal structures of [(alkoxy)bis(pyridin-2-yl)methanolato-N,O,N]tin(IV) complexes

Reactions of bis(pyridin-2-yl)ketone with tin tetrahalides, SnX₄ (X = Cl or Br), or organotin trichlorides, R^′SnCl₃ (R^′ = Ph, Bu or CH₂CH₂CO₂Me), in ROH (R = Me or Et) readily produces RObis(pyridin-2-yl)methanolato)tin complexes, [5: RO(py)₂C(OSnX₃)] (5: R,X = Me,Cl; Et,Cl; Et,Br) or [6: MeO(py)₂C(OSnCl₂R^′)] (R^′ = Ph, Bu, CH₂CH₂CO₂Me). In addition, halide exchange reaction between SnI₄ and (5: R,X = Me,Cl) occurred to give (5: R,X = Me,I). The crystal structures of six tin(IV) derivatives indicated, in all cases, a monoanionic tridentate ligand, [RO(py)₂C(O⁻)-N,O,N], arranged in a fac manner about a distorted octahedral tin atom. The Sn–O and Sn–N bonds lengths do not show much variation amongst the six complexes despite the differences in the other ligands at tin.     

Hypervalent triphenyl and diphenyl tin coordination compounds derived from 2-(1H-benzimidazol-2-yl)phenol

Reactions of 2-(1H-benzimidazol-2-yl)phenol (1) and SnPh₃Cl, SnPh₂Cl₂ and SnCl₄ were investigated. One tetracoordinated triphenyltin(IV) compound: triphenyltin-2-(1H-benzimidazol-2-yl)phenolate] (3) and its adducts: [O → Sn] dimethylsulfoxide triphenyltin-[2-(1H-benzimidazol-2-yl)phenolate] (4), [O → Sn] aqua triphenyltin-[2-(1H-benzimidazol-2-yl)phenolate] (5) [O → Sn] ethanol triphenyltin-[2-(1H-benzimidazol-2-yl)phenolate] (6), [N → Sn] pyridine triphenyltin-[2-(1H-benzimidazol-2-yl)phenolate] (7), where 1 acts as a monodentate ligand bound through the phenol oxygen, were obtained. In the pentacoordinated compounds 4-7, the tin atom has tbp geometry. The three phenyl groups are in equatorial positions, whereas the benzimidazole and the Lewis base are in apical positions. Two hexacoordinated tin compounds: diphenyltin-bis[2-(1H-benzimidazol-2-yl-κN)phenolate-κO] (8), dichlorotin-bis[2-(1H-benzimidazol-2-yl-κN)phenolate-κO] (9) bearing two bidentate ligands are reported. The coplanar ligands in 8 and 9 form six membered rings by oxygen and nitrogen coordination. The tin geometry is all-trans octahedral. In 8 the two phenyl groups, and in 9 the two chlorine atoms are perpendicular to the plane of the ligands. Compounds were identified in solution mainly by ¹H, ¹³C and ¹¹⁹Sn NMR and in the solid state by X-ray diffraction analysis.     

Coordination studies of 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine towards Cu cation. X-ray studies,spectroscopic characterization and DFT calculations

The reactions of 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine with CuCl₂ · 2H₂O, Cu(NO₃)₂ · 3H₂O and CuSO₄ · 5H₂O have been examined, and four [CuCl₂(dppt)] (1), [CuCl₂(dppt)₂] · 2MeOH (2), [Cu(dppt)₂(H₂O)₂](NO₃)₂ (3) and [Cu(SO₄)(dppt)(H₂O)]_n · nH₂O (4) complexes have been obtained. All the complexes have been structurally and spectroscopically characterized, and compound 4 has been additionally studied by magnetic measurements. The electronic structure of 1 has been calculated with the density functional theory (DFT) method, and the time-dependent DFT calculations have been employed to calculate the electronic spectrum of 1.     

Dinuclear copper(I) complexes of tris(3,5-dimethylpyrazol-1-yl)methane: Synthesis, structure, and reactivity

The reaction of [Cu(NCMe)₄](BF₄) with equimolar amounts of the tris(substituted-pyrazolyl)methane ligand HCPz₃ or HC(3,5-Me₂Pz)₃ yields the respective salts [Cu(HCPz₃)(NCMe)](BF₄) (1a) or [Cu(HC(3,5-Me₂Pz)₃)(NCMe)](BF₄) (1). The acetonitrile ligand of 1 can be replaced by prazine, 4,4′-dipyridine or 1,4-diisocyanobenzene to yield related mononuclear complexes [Cu(HC(3,5-Me₂Pz)₃)(pyrazine)](BF₄) (2), [Cu(HC(3,5-Me₂Pz)₃)(4,4′-bipyridine)] (BF₄) (3) or [Cu(HC(3,5-Me₂Pz)₃)(1,4- CNC₆H₄NC)](BF₄) (7), respectively. A series of binuclear copper(I) complexes {[Cu(HC(3,5-Me₂Pz)₃)]₂(μ -BL)}(BF₄)₂ (4, BL = pyrazine; 5, BL = 4,4′-dipyridine; 8, BL = 1,4-diisocyanobenzene) were prepared by treating equal molar ratio of 1 with related mononuclear complexes 2, 3 and 7. In addition, binuclear copper(I) complexes were also prepared from treatment of 2 equiv of 1 with the related bridge ligand. Both of 4 and 5 reformed mononuclear starting complex 1 in acetonitrile solution. However, the more robust complex 8 was stable in acetonitrile solutions. The structure of complexes 1a, 4, 5, and 7 were confirmed by X-ray crystallography. The redox properties of 4 and 8 were examined by cyclic voltammetry and exhibited two quasi-reversible waves suggesting that no significant structural reorganization occurs during the redox process on the electrochemical time scale.     

Synthesis, characterization, and ethylene polymerization behavior of [(RR′-admpzp)2Ti(OPr)2] complexes (RR′-admpzp = 1-dialkylamino-3-(3,5-dimethyl-pyrazol-1-yl)-propan-2-olate)

[(RR′-admpzp)₂Ti(OPrⁱ)₂] complexes (2a-c), synthesized from reaction of Ti(OPrⁱ)₃Cl (0.5 equiv) with 1-dialkylamino-3-(3,5-dimethyl-pyrazol-1-yl)-propan-2-ol compounds in the presence of triethylamine (0.5 equiv), are pseudo-octahedral with each RR′-admpzp ligand κ²-O,N(pyrazolyl) coordinated to the titanium center. In solution, 2a-c adopt isomeric structures that are in dynamic equilibrium. At 23 °C, 2a-c/1000 MAO catalyst systems furnished high molecular weight polymers with narrow molecular weight distributions (M_w/M_n = 2.7-2.8). At 100 °C, 2a-c/MAO catalyst systems exhibited increased polymerization activity and 2c/1000 MAO system furnished high molecular weight polyethylene with a molecular weight distribution (M_w/M_n = 2.1) that is close to that found for single-site catalysts.     

Ruthenium(II), rhodium(III) and iridium(III) based effective catalysts for hydrogenation under aerobic conditions

The new cationic mononuclear complexes [(η⁶-arene)Ru(Ph-BIAN)Cl]BF₄ [η⁶-arene = benzene (1), p-cymene (2)], [(η⁵-C₅H₅)Ru(Ph-BIAN)PPh₃]BF₄ (3) and [(η⁵-C₅Me₅)M(Ph-BIAN)Cl]BF₄ [M = Rh (4), Ir (5)] incorporating 1,2-bis(phenylimino)acenaphthene (Ph-BIAN) are reported. The complexes have been fully characterized by analytical and spectral (IR, NMR, FAB-MS, electronic and emission) studies. The molecular structure of the representative iridium complex [(η⁵-C₅Me₅)Ir(Ph-BIAN)Cl]BF₄ has been determined crystallographically. Complexes 1–5 effectively catalyze the reduction of terephthaldehyde in the presence of HCOOH/CH₃COONa in water under aerobic conditions and, among these complexes the rhodium complex [(η⁵-C₅Me₅)Rh(Ph-BIAN)Cl]BF₄ (4) displays the most effective catalytic activity.     

Kinetics and mechanistic studies of the interaction of thiosulfate with cis-diaqua-bis[1-alkyl-2-(arylazo)imidazole]ruthenium(II) complexes

The nucleophilic substitution reaction of S₂O₃²⁻ with [Ru(HaaiR′)₂(OH₂)₂](ClO₄)₂ (1) [HaaiR′ = 1-alkyl-2-(phenylazo)imidazole] and [Ru(ClaaiR′)₂(OH₂)₂](ClO₄)₂ (2) [ClaaiR′ = 1-alkyl-2-(chlorophenylazo)imidazole] [where R′ = Me(a), Et(b) or Bz(c)] in acetonitrile–water (50% v/v) medium to yield Na₂[Ru(HaaiR′)₂(S₂O₃)₂] (3a, 3b or 3c) and Na₂[Ru(ClaaiR′)₂(S₂O₃)₂] (4a, 4b or 4c) has been studied. The products were characterized by microanalytical data and spectroscopic techniques (UV–Vis, NMR and mass spectroscopy). The reaction proceeds in two consecutive steps (A → B → C); each step follows first order kinetics with respect to each complex and S₂O₃²⁻, and the first step second order rate constant (k′₂) is greater than the second step one (k″₂). An increase in the π-acidity of the ligand increases the rate. Thermodynamic parameters, the standard enthalpy of activation (Δ^‡H⁰) and the standard entropy of activation (Δ^‡S⁰), have been calculated for both steps using the Eyring equation from variable temperature kinetic studies. The low Δ^‡H⁰ and large negative Δ^‡S⁰ values indicate an associative mode of activation for both aqua ligand substitution processes.     

Synthesis of di-, tri-, tetra- and pentacyclic arene complexes of ruthenium(II):[Ru(η-polycyclic arene)-(1-5-η-cyclooctadienyl)]PF6 and their reactions with NaBH4

The phenanthrene complex of ruthenium(II), [Ru(η⁶-phenanthrene)(1,5-η⁵-cyclooctadienyl)]PF₆ (2c), is prepared by the reaction of Ru(η⁴-1,5-COD)(η⁶-1,3,5-COT) (1) with phenanthrene and HPF₆ in 65% yield. Similar treatments with di- tri-, tetra- and pentacyclic arenes give corresponding polycyclic arene complexes, [Ru(η⁶-polycyclic arene)(1-5-η⁵-cyclooctadienyl)]PF₆ [polycyclic arene = naphthalene (2b), anthracene (2d), triphenylene (2e), pyrene (2f) and perylene (2g)] in 46-90% yields. The molecular structure of the perylene complex 2g is characterized by X-ray crystallography. Reaction of 2c with NaBH₄ gives a mixture of the 1,5- and 1,4-COD complexes of ruthenium(0), Ru(η⁶-phenanthrene)(η⁴-1,5-COD) (3c) and Ru(η⁶-phenanthrene)(η⁴-1,4-COD) (4c) in 76% in 1:8 molar ratio. The arene exchange reactions among cationic complexes [Ru(η⁶-arene)(1-5-η⁵-cyclooctadienyl)]PF₆ (2) showed the coordination ability of arenes in the following order: benzene ∼ triphenylene > phenanthrene > naphthalene > perylene ∼ pyrene > anthracene, suggesting the benzo fused rings, particularly those of acenes, decreasing thermal stability of the arene complex.     

Synthesis, structures and electrochemical properties of ruthenium (II) complexes bearing bidentate 1,8-naphthyridine and terpyridine analogous (N,N,C)-tridentate ligands

1,8-Naphthyridine (napy) and terpyridine-analogous (N,N,C) tridentate ligands coordinated ruthenium (II) complexes, [RuL(napy-κ²N,N′) (dmso)](PF₆)₂ (1: L=L¹=N″-methyl-4′-methylthio-2,2′:6′,4″-terpyridinium, 2: L = L² = N″-methyl-4′-methylthio-2,2′:6′,3″-terpyridinium) were prepared and their chemical and electrochemical properties were characterized. The structure of complex 1 was determined by X-ray crystallographic study, showing that it has a distorted octahedral coordination style. The cyclic voltammogram of 1 in DMF exhibited two reversible ligand-localized redox couples. On the other hand, the CV of 2 shows two irreversible cathodic peaks, due to the Ru-C bond of 2 containing the carbenic character. The IR spectra of 1 in CO₂-saturated CH₃CN showed the formation of Ru-(η¹-CO₂) and Ru-CO complexes under the controlled potential electrolysis of the solution at −1.44 V (vs. Fc/Fc⁺). The electrochemical reduction of CO₂ catalyzed by 1 at −1.54 V (vs. Fc/Fc⁺) in DMF-0.1 M Me₄NBF₄ produced CO with a small amount of HCO₂H.     

2-(Benzimidazol-2-yl)-1,10-phenanthrolyl metal (Fe and Co) complexes and their catalytic behaviors toward ethylene oligomerization

The N^∧N^∧N-tridentate metal complexes, LMCl₂ (M = Fe or Co; L represents a ligand of 2-(benzimidazol-2-yl)-1,10-phenanthrolines), were synthesized and fully characterized with spectroscopic and elemental analysis. The single-crystal X-ray crystallographic analyses revealed complex 1a with a distorted octahedron geometry due to incorporating one methanol molecule, and complexes 5a and 9b with a distorted trigonal-bipyramidal geometry. Upon activation with modified methylaluminoxane (MMAO), these complexes showed good to high catalytic activities toward ethylene oligomerization. The detailed investigations were carried out to disclose the influences of various reaction conditions and nature of ligands on their performing activities of metal complexes.     

Novel hydridotris(pyrazolyl)borate ruthenium(II) complexes containing the water-soluble phosphane 1,3,5-triaza-7-phosphaadamantane: Synthesis and evaluation of DNA binding properties

A series of half-sandwich ruthenium(II) complexes containing κ³(N,N,N)-hydridotris(pyrazolyl)borate (κ³(N,N,N)-Tp) and the water-soluble phosphane 1,3,5-triaza-7-phosphaadamantane (PTA) [RuX{κ³(N,N,N)-Tp}(PPh₃)_2−n(PTA)_n] (n = 2, X = Cl (1), n = 1, X = Cl (2), I (3), NCS (4), H (5)) and [Ru{κ³(N,N,N)-Tp}(PPh₃)(PTA)L][PF₆] (L = NCMe (6), PTA (7)) have been synthesized. Complexes containing 1-methyl-3,5-diaza-1-azonia-7-phosphaadamantane(m-PTA) triflate [RuCl{κ³(N,N,N)-Tp}(m-PTA)₂][CF₃SO₃]₂ (8) and [RuX{κ³(N,N,N)-Tp}(PPh₃)(m-PTA)][CF₃SO₃] (X = Cl (9), H (10)) have been obtained by treatment, respectively, of complexes 1, 2 and 5 with methyl triflate. Single crystal X-ray diffraction analysis for complexes 1, 2 and 4 have been carried out. DNA binding properties by using a mobility shift assay and antimicrobial activity of selected complexes have been evaluated.     

Comparative structural study of the complexation behaviour of silver(I), cadmium(II), mercury(II), and palladium(II) with a 17-membered N3O2-donor macrocycle

A comparative investigation of the coordination behaviour of the 17-membered, N₃O₂-donor macrocycle, 1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane, L, with the soft metal ions Ag(I), Cd(II), Hg(II), and Pd(II) is reported. The X-ray structures of 12 complexes have been determined and a range of structural types, including both mononuclear and dinuclear species, shown to occur. In particular cases the effect of anion variation on the resulting structures has been investigated; L reacts with AgX (X = NO₃, ClO₄, PF₆, OTf and CN) to yield related 2:2 (metal:ligand) complexes of types [Ag₂L₂(NO₃)₂] (1), [Ag₂L₂](ClO₄)₂ · 2DMF (2), [Ag₂L₂](PF₆)₂ · 2DMF (3), [Ag₂L₂](OTf)₂ (4) and [Ag₂L₂(μ-CN)][Ag(CN)₂] · H₂O (5). In all five complexes the ether oxygens of each ring are unbound. In 1–4 the macrocycles are present in sandwich-like arrangements that shield the dinuclear silver centres, with each silver bonded to two nitrogen donors from one L and one nitrogen from a second L. A Ag···Ag contact is present between each metal centre such that both centres can be described as showing distorted tetrahedral geometries. In the case of 5 a rare single μ₂-κC:κC symmetrically bridging two-electron-donating cyano bridge links silver ions [Ag···Ag distance, 2.7437(10) Å]; the macrocyclic ligands are orientated away from the dinuclear metal centres. In contrast to the behaviour of silver, reaction of cadmium(II) perchlorate with L resulted in a mononuclear sandwich-like complex of type [CdL₂](ClO₄)₂ · CH₃CN (6). Again, the ether oxygens do not coordinate, with each L binding to the cadmium centre only via its three nitrogen donors in a facial arrangement such that a distorted octahedral coordination geometry is attained. Reaction of L with HgX₂ (X = ClO₄, SCN and I) yielded the monomeric species [HgL(ClO₄)₂] (7), [HgL(SCN)₂]·CH₃CN (8) and [Hg₂L₂](HgI₄)₂ · 2L (9), in which all five donors of L are bound to the respective mercury centres. However, reaction of L with Hg(NO₃)₂ in dichloromethane/methanol gave a mononuclear sandwich-like complex [HgL₂](NO₃)₂ · 2CH₃OH (10) without anion coordination. Reaction of K₂PdCl₄ and Pd(NO₃)₂ with L yielded the 1:1 complexes [PdLCl]Cl · H₂O (11) and [PdL(NO₃)]NO₃ · CH₃OH (12), respectively, in which the metal is bound to three nitrogen donors from L along with the corresponding chloride or nitrate anion. Each palladium adopts a distorted square-planar coordination geometry; once again the ether oxygens are not coordinated.     

Synthesis and characterization of para-nitro substituted 2,6-bis(phenylimino)pyridyl Fe(II) and Co(II) complexes and their ethylene polymerization properties

Four iron(II) and cobalt(II) complexes ligated by 2,6-bis(4-nitro-2,6-R₂-phenylimino)pyridines, LMCl₂ (1: R = Me, M = Fe; 2: R = iPr, M = Fe; 3: R = Me, M = Co; 4: R = iPr, M = Co) have been synthesized and fully characterized, and their catalytic ethylene polymerization properties have been investigated. Among these complexes, the iron(II) pre-catalyst bearing the ortho-isopropyl groups (complex 2) exhibited higher activities and produced higher molecular weight polymers than the other complexes in the presence of methylaluminoxane (MAO). A comparison of 2 with the reference non-nitro-substituted catalyst (2,6-bis(2,6-diisopropylphenylimino)pyridyl)FeCl₂ (FeCat 5) revealed a modest increase of the catalytic activity and longer lifetime upon substitution of the para-positions with nitro groups (activity up to 6.0 × 10³ kg mol⁻¹ h⁻¹ bar⁻¹ for 2 and 4.8 × 10³ kg mol⁻¹ h⁻¹ bar⁻¹ for 5), converting ethylene to highly linear polyethylenes with a unimodal molecular weight distribution around 456.4 kg mol⁻¹. However, the iron(II) pre-catalyst 1 on changing from ortho-isopropyl to methyl groups displayed much lower activities (over an order of magnitude) than 2 under mild conditions. As expected, the cobalt analogues showed relatively low polymerization activities.     

Synthesis,structure, and electrochemistry of pyridinecarboxamide cobalt(III) complexes; the effect of bridge substituents on the redox properties

Two series of complexes of the types trans-[Co^III(Mebpb)(amine)₂]ClO₄ {Mebpb²⁻ = N,N-bis(pyridine-2-carboxamido)-4-methylbenzene dianion, and amine = pyrrolidine (prldn) (1a), piperidine (pprdn) (2a), morpholine (mrpln) (3a), benzylamine (bzlan) (4a)}, and trans-[Co^III(cbpb)(amine)₂]X {cbpb²⁻ = N,N-bis(pyridine-2-carboxamido)-4-chlorobenzene dianion, and amine = pyrrolidine (prldn), X = PF₆ (1b), piperidine (pprdn), X = PF₆ (2b), morpholine (mrpln), X = ClO₄ (3b), benzylamine (bzlan), X = PF₆ (4b)} have been synthesized and characterized by elemental analyses, IR, UV–Vis, and ¹H NMR spectroscopy. The crystal structure of 1a has been determined by X-ray diffraction. The electrochemical behavior of these complexes, with the goal of evaluating the effect of axial ligation and equatorial substitution on the redox properties, is also reported. The reduction potential of Co^III, ranging from −0.53 V for (1a) to −0.31 V for (3a) and from −0.48 V for (1b) to −0.22 V for (3b) show a relatively good correlation with the σ-donor ability of the axial ligands. The methyl and chloro substituents of the equatorial ligand have a considerable effect on the redox potentials of the central cobalt ion and the ligand-centered redox processes.     

Dimeric and polymeric silver(I) saccharinato complexes of two bis(pyridine) ligands: Synthesis,structural, spectroscopic,fluorescent and thermal properties

The reaction of silver(I) with 1,2-bis[1-(pyridin-2-yl)ethylidene]hydrazine (bpeh) and N,N-bis(pyridin-2-ylmethyl)amine (bpma) in the presence of Na(sac) (sac = saccharinate) yielded [Ag₂(sac)₂(bpeh)] (1) and [Ag(sac)(bpma)]_n (2) with conformational chirality. Both complexes have been characterized by elemental analysis, IR, thermal analysis and X-ray single crystal diffraction. Complex 1 displays a binuclear composition, in which each silver(I) ion is bound to one monodentate sac ligand and one of the bidentate pyridylimino groups of the bpeh ligand in a distorted trigonal coordination geometry. Complex 2 is a one-dimensional helical polymer, in which silver(I) centers are bridged by tridentate bpma ligands, and each silver(I) ion is coordinated in a distorted tetrahedral geometry by one monodentate sac ligand, a bidentate pyridylamine group of one bpma ligand, and a py group of another bpma ligand. Weak intermolecular C–H?O hydrogen bonds and C–H?π interactions lead to assembly of 1 and 2 into three-dimensional supramolecular frameworks. Spectral and thermal analysis data for 1 and 2 are in agreement with the crystal structures. In addition, both complexes in the solid state display intraligand π–π∗ fluorescence.