Dianionic Tridentate Research Articles

Synthesis, characterization, X-ray structure and DFT calculation of two Mo(VI) and Ni(II) Schiff-base complexes

Abstract In this study, the syntheses of two new Mo(VI) and Ni(II) complexes with H2L tridentate (ONO) Schiff-base ligand have been described and fully characterized by means of elemental analysis, FT–IR, electronic, 1H-NMR spectroscopy and single-crystal X-ray diffraction. In both complexes, the Schiff-base completely deprotonates and coordinates to the metal ion as a dianionic tridentate ligand via the donor oxygens and nitrogen atoms. The coordination numbers of Mo(VI) and Ni(II) are six and four, respectively. The DFT-B3LYP/6–31 + G (d,p) and PBEPBE/6–31 + G (d,p) calculations are carried out for the determination of the optimized structures. Frequency calculations and NBO analysis are also performed for characterization. According to the theoretical analysis of the complexes, ligand-to-metal donation is greater than back donation. NBO data revealed that the main contribution of the frontier orbitals belongs to L−2.

Synthesis, characterization and antibacterial activity of a tridentate Schiff base derived from cephalothin and sulfadiazine, and its transition metal complexes

Metal(II) coordination compounds of a cephalothin Schiff base (H2L) derived from the condensation of cephalothin antibiotic with sulfadiazine were synthesized. The Schiff base ligand, mononuclear [ML(H2O)3] (M(II)=Mn,Co,Ni,Zn) complexes and magnetically diluted dinuclear copper(II) complex [CuL(H2O)3]2 were characterized by several techniques, including elemental and thermal analysis, molar conductance and magnetic susceptibility measurements, electronic, FT-IR, EPR and 1H NMR spectral studies. The cephalothin Schiff base ligand H2L behaves as a dianionic tridentate NOO chelating agent. The biological applications of complexes have been studied on two bacteria strains (Escherichia coli and Staphylococcus aureus) by agar diffusion disc method.

Synthesis, structure, characterization and study of antiproliferative activity of dimeric and tetrameric oxidomolybdenum(VI) complexes of N,N′-disalicyloylhydrazine

The in situ reaction of salicyloylhydrazide and its corresponding hydrazone with [MoO2(acac)2] afforded two novel and unusual dimeric [(MoVIO2)2L] (1) and tetrameric [{(C2H5OH)LO3Mo2VI}2(μ-O)2]·C2H5OH (2) oxidomolybdenum(VI) complexes with N,N′-disalicyloylhydrazine (H2L). The binucleating ligand was formed by the self-combination of the acid hydrazide or corresponding hydrazone. The complexes were characterized by various spectroscopic techniques (IR, UV and NMR) and also by electrochemical study. The molecular structures of both complexes have been confirmed by X-ray crystallography. The above studies indicate that the N,N′-disalicyloylhydrazine (H2L) has the normal tendency to form both dimeric and tetrameric complexes coordinated through the dianionic tridentate manner. The in vitro antiproliferative activity of complexes 1 and 2 was assayed against HeLa cell line.

Novel ruthenium sensitizers with a dianionic tridentate ligand for dye-sensitized solar cells: the relationship between the solar cell performances and the electron-withdrawing ability of substituents on the ligand

Five novel ruthenium sensitizers (TUS sensitizers) with a dianionic tridentate ligand (pyridine-2,6-dicarboxyamidato and its derivatives) have been synthesized for application to dye-sensitized solar cells (DSCs). These TUS sensitizers have much larger molar absorption coefficients in the wavelength range below 600 nm compared with those of Black dye which is a structural analog and a highly efficient ruthenium sensitizer. The energy levels of HOMOs and LUMOs of TUS sensitizers shifted to the positive direction with increasing the electron-withdrawing ability of the substituents on the dianionic tridentate ligand. The energy levels of HOMO and LUMO showed linear correlation with respect to the Hammett constant of the substituents. The DSCs with TUS sensitizers showed much lower performances than that of Black dye. Both inferior adsorptivity on the TiO2 surface and unfavorable energy levels of HOMOs and LUMOs for the effective electron transfer reactions in the DSCs are considered to be the main reasons for the much lower performances of TUS sensitizers. The conversion efficiency of the DSC with a TUS sensitizer increased with increasing the electron-withdrawing ability of the substituents on the dianionic tridentate ligand. The observed linear relationship between the conversion efficiency and the driving force of the reduction process of the oxidized form of dyes by I(-) suggests that the dye regeneration process is a rate-determining step in the DSCs with TUS sensitizers.

Organometallic turnstiles: acid and base locking and unlocking

A symmetrical organometallic Pt(II) based molecular turnstile 1, composed of a rotor bearing two benzonitrile units as coordinating sites and a stator equipped with a dianionic tridentate coordinating pole, undergoes a reversible switching process between two open and one closed states. In the absence of an effector, the turnstile is in its open state defined by the free rotation of the rotor around the stator. In the presence of Pd(II), the latter is simultaneously complexed by both the rotor and the stator (1-Pd) leading to the first closed state owing to locking of the rotational movement. The turnstile can be unlocked to its second open state 1-Pd-DMAP by addition of para-dimethylaminopyridine (DMAP) behaving as an external competitive ligand replacing the bound benzonitrile in the coordination sphere of the Pd centre. Upon addition of PdCl2(CH3CN)2, a competitive metal complex to remove DMAP, the turnstile is switched back to its closed state. The same process can also be achieved upon addition of MsOH causing the protonation of DMAP into DMAP-H(+) and its decomplexation and replacement by one of the two benzonitrile groups of the rotor. Finally, the deprotonation of DMAP-H(+) by addition of Et3N as a base regenerates the second open state of the turnstile.

Synthesis, spectral and electrochemical studies of binuclear Ru(III) complexes containing dithiosemicarbazone ligand

Synthesis of several new octahedral binuclear ruthenium(III) complexes of the general composition [(EPh3)2(X)Ru-L-Ru(X)(EPh3)2] containing benzene dithiosemicarbazone ligands (where E=P or As; X=Cl or Br; L=binucleating ligands) is presented. All the complexes have been fully characterized by elemental analysis, FT-IR, UV–vis and EPR spectroscopy together with magnetic susceptibility measurements. IR study shows that the dithiosemicarbazone ligands behave as dianionic tridentate ligands coordinating through the oxygen atom of the deprotonated phenolic group, nitrogen atom of the azomethine group and thiolate sulphur. In DMF solution, all the complexes exhibit intense d-d transition and ligand-to-metal charge transfer (LMCT) transition in the visible region. The magnetic moment values of the complexes are in the range 1.78–1.82BM, which reveals the presence of one unpaired electron on each metal ion. The EPR spectra of the liquid samples at LNT show the presence of three different ‘g’ values (gx≠gy≠gz) indicate a rhombic distortion around the ruthenium ion. All the complexes exhibit two quasi-reversible one electron oxidation responses (RuIII–RuIII/RuIII–RuIV; RuIII–RuIV/RuIV–RuIV) within the E1/2 range of 0.61–0.74V and 0.93–0.98V respectively, versus Ag/AgCl.

Iridium-mediated N–H and methyl C–H bond activations in N-(2′,6′-dimethylphenyl)pyrrole-2-aldimine. Synthesis, characterization and catalytic applications

Reaction of N-(2′,6′-dimethylphenyl)pyrrole-2-aldimine (L-Me2) with Ir(PPh3)3Cl in refluxing toluene affords two organometallic complexes (1 and 2), where the imine-ligand (L-Me2) is coordinated to the metal center, via N–H and methyl C–H activations, as a di-anionic tridentate NNC-donor, along with two triphenylphosphines. In 1 the sixth coordination site is occupied by a hydride, while in 2 by a chloride. In both cases the hydride or chloride is trans to the coordinated imine-nitrogen, and the two triphenylphosphines are mutually trans. Similar reaction of N-(2′-methylphenyl)pyrrole-2-aldimine (L-Me) with Ir(PPh3)3Cl affords 3, where the imine-ligand is coordinated to the metal center as a mono-anionic bidentate NN-donor, along with two triphenylphosphines, a hydride and a chloride. Structures of 1, 2 and 3 have been determined by X-ray crystallography. DFT analyses have been carried out to understand the formation of the complexes. All the complexes show characteristic 1H NMR signals and, intense transitions in the visible and ultraviolet regions. Cyclic voltammetry on all three complexes shows two irreversible oxidations within 0.89–1.34 V vs. SCE and a reduction within −1.31 to −1.40 V vs. SCE. Complexes 1, 2 and 3 have been found to efficiently catalyze the Oppenauer oxidation of alcohols.

Copper(II) and molybdenum(VI) complexes with 5-bromosalicylaldehyde S-allylisothiosemicarbazone: Syntheses, characterizations and crystal structures

A new tridentate Schiff base, 5-bromosalicylaldehyde S-allylisothiosemicarbazone hydrobromide (H2L), and several new mononuclear complexes of copper(II) and molybdenum(VI) of this ligand with general formulas ([Cu(L)Im] (1)), ([Cu(L)NH3]·4H2O (2)), and ([MoO2(L)1-MeIm] (3), Imidazole: Im, 1-methylimidazole: 1-MeIm) were prepared and characterized by elemental analyses, IR, proton magnetic resonance Spectroscopy, and ultraviolet–visible techniques. The physico-chemical results suggested that the H2L coordinates in the dianionic tridentate form. Crystal structures of the Cu(II) complexes reveal a square planar configuration surrounded by the dianionic tridentate isothiosemicarbazone (ONN) and Im and NH3 for 1 and 2, respectively. The L2-, two oxo, and 1-methylimidazole are coordinated to molybdenum(VI) in a distorted octahedral geometry in 3. Formation of pure metal oxide residues was confirmed by thermal degradation of the complexes.

Controlled interaction of benzaldehyde thiosemicarbazones with palladium: formation of bis-complexes with cis-geometry and organopalladium complexes, and their catalytic application in C–C and C–N coupling

Reaction of a 1 : 1 mixture of 4-R-benzaldehyde thiosemicarbazone (R = OCH3, CH3, H, Cl and NO2) and 2-picolinic acid with an equivalent quantity of Na2[PdCl4] in ethanolic medium, under relatively mild reflux, affords a group of complexes of type [Pd(NS–R)2] as the major product and another family of complexes of type [{Pd(CNS–R)}n] as the minor product (where NS–R and CNS–R denote the N,S- and C,N,S-coordinated thiosemicarbazone, respectively). The [{Pd(CNS–R)}n] complexes are conveniently obtained in good yields from similar reactions carried out under prolonged reflux. The sulfur-bridge in the [{Pd(CNS–R)}n] complexes undergoes facile cleavage upon their reaction with triphenylphosphine to yield complexes of type [Pd(CNS–R)(PPh3)]. Crystal structures of [Pd(NS–OCH3)2], [Pd(NS–CH3)2], [Pd(NS–Cl)2], [Pd(CNS–CH3)(PPh3)], [Pd(CNS–H)(PPh3)] and [Pd(CNS–Cl)(PPh3)] have been determined. In the [Pd(NS–R)2] complexes the thiosemicarbazones are coordinated to the metal center, via dissociation of the acidic proton, as monoanionic bidentate N,S-donors forming five-membered chelate rings, while in the [Pd(CNS–R)(PPh3)] complexes they are coordinated to palladium, via dissociation of the acidic proton and activation of an ortho C–H bond, as dianionic tridentate C,N,S-donors forming two adjacent five-membered chelate rings. The [Pd(NS–R)2] and [Pd(CNS–R)(PPh3)] complexes show characteristic 1H NMR signals, and in dichloromethane solution they all display intense absorptions in the visible and ultraviolet regions. The [Pd(NS–R)2] and [Pd(CNS–R)(PPh3)] complexes have shown notable efficiency in catalyzing C–C and C–N coupling reactions.

Luminescent Neutral Platinum Complexes Bearing an Asymmetric N^N^N Ligand for High‐Performance Solution‐Processed OLEDs

The synthesis and full characterization of new platinum complexes bearing a bulky asymmetric dianionic tridentate ligand is reported. The hindrance of the ligand prevents detrimental intermolecular interactions yielding to highly emitting species in both crystalline state and thin-film. Such properties prompted their successful use in solution-processed OLEDs, showing remarkable external quantum efficiency up to 5.6%.

Synthesis, structural characterization, electrochemistry and catalytic transfer hydrogenation of ruthenium(II) carbonyl complexes containing tridentate benzoylhydrazone ligands

Convenient synthesis of eight new octahedral ruthenium(II) carbonyl benzoylhydrazone complexes having the general molecular formula [Ru(L)(CO)(EPh3)2] (where E = P or As; H2L = benzoylhydrazone ligand, the two H's representing the two dissociable protons) has been described. The substituted benzoylhydrazone ligands behave as a dianionic tridentate O, N and O donors (L) and coordinates to ruthenium via the phenolate oxygen, the azomethine nitrogen and the deprotonated amide oxygen. The compositions of the complexes have been established by elemental analysis and spectral methods (FT-IR, 1H NMR, 13C NMR, UV–vis). The crystal structure of one of the complexes, [Ru(L2)(CO)(PPh3)2] (2), has been solved by single crystal X-ray crystallography and it indicates the presence of a distorted octahedral geometry in these complexes. All the complexes exhibit metal-to-ligand charge transfer (MLCT) transitions in the visible region and display one quasi-reversible reduction and two irreversible oxidations. Further, the catalytic efficiency of the complexes has been investigated in the case of transfer hydrogenation of ketones to the corresponding secondary alcohols. The influence of base, reaction temperature and catalyst loading in transfer hydrogenation reaction was also evaluated. The complexes were found to be efficient catalysts with conversion up to 99.5% in presence of iso-propanol/KOH.

Benzaldehyde thiosemicarbazone complexes of platinum: Syntheses, structures and cytotoxic properties

The reaction of 4-R-benzaldehyde thiosemicarbazones (denoted in general as H2L-R, where H2 stands for the two dissociable protons and R (R=OCH3, CH3, H, Cl and NO2) for the substituent on the phenyl ring) with [Pt(PPh3)2Cl2] in the presence of NEt3 afforded a family of organometallic complexes of platinum(II) of the type [Pt(PPh3)(L-R)]. Reaction of the same group of ligands with K2[PtCl4] in the presence of NEt3 afforded complexes of the type [Pt(HL-R)2]. The crystal structure of [Pt(PPh3)(L-CH3)] and [Pt(HL-CH3)2] have been determined. In the [Pt(PPh3)(L-R)] complexes, the benzaldehyde thiosemicarbazones are coordinated to platinum as dianionic tridentate C,N,S-donors. In the [Pt(HL-R)2] complexes, the benzaldehyde thiosemicarbazones are coordinated to the metal center as bidentate N,S-donors, forming five-membered chelate rings, and with reference to the structure of the uncoordinated thiosemicarbazone ligand, this coordination mode is associated with a change in stereochemistry around the CN bond. All the [Pt(PPh3)(L-R)] and [Pt(HL-R)2] complexes display intense absorptions in the visible and ultraviolet regions. The cytotoxic effects of these complexes, examined on the human leukemia cell line HL-60 and human lymphoma cell line U-937, have shown that all the [Pt(PPh3)(L-R)] and [Pt(HL-R)2] complexes are cytotoxic in nature and their IC50 values indicate their potential use as antitumor agents.

Pentacoordinate Silicon Complexes with N‐(2‐pyridylmethyl)­salicylamide as a Dianionic (ONN′) Tridentate Chelator

AbstractThe title compound, N‐(2‐pyridylmethyl)salicylamide (1), was synthesized by ester aminolysis of methyl salicylate and 2‐picolylamine. In the presence of triethylamine as a supporting base, the salicylamide moiety reacts with the organodichlorosilanes RR′SiCl2 to form the desired six‐membered heterocycles of the type RR′Si–O–(o‐C6H4)–C(=O)N(pic), with pic being the 2‐pyridylmethyl (i.e., 2‐picolyl) moiety and RR′ = Me, Me (2a); Me, Ph (2b); Ph, Ph (2c); Bn, Bn (2d); All, Ph (2e) and Ph, H (2f). Despite the absence of notable ring strain release Lewis acidity (i.e., only a six‐membered chelate is formed by the dianion, and smaller rings are not present in the compound), the poor electron withdrawal from silicon by its C– or H– substituents and the flexible methylene bridge between the salicylamide and the pyridine moiety, the pyridine N donor atom furnishes pentacoordinate silicon coordination spheres in all of these compounds 2a–2f. The coordination number of the silicon atom was confirmed by single‐crystal X‐ray diffraction analysis for the solid state and by 29Si NMR spectroscopy for the solution state.

2-(1-{2-[Azanidyl(ethylsulfanyl)methylidene-κN]hydrazin-1-ylidene-κN1}ethyl)phenolato-κO](dimethyl sulfoxide-κO)dioxidomolybdenum(VI)

The MoVI atom in the title complex, [Mo(C11H13N3OS)O2(C2H6OS)], is N,N′,O-coordinated by the dianionic tridentate ligand, two mutually cis oxide O atoms and a dimethyl sulfoxide O atom, defining a distorted octa­hedral N2O4 donor set. The most prominent feature of the crystal packing is the formation of inversion dimers via pairs of N—H⋯O hydrogen bonds and eight-membered {⋯HNMoO}2 loops. The Schiff base ligand is disordered over two orientations of equal occupancy.

2-(1-{2-[Azanidyl(ethylsulfanyl)methylidene-κN]hydrazin-1-ylidene-κN1}ethyl)phenolato-κO](pyridine-κN)nickel(II)

The NiII atom in the title complex, [Ni(C11H13N3OS)(C5H5N)], exists within a square-planar N3O donor set provided by N,N′,O atoms of the dianionic tridentate ligand and a pyridine N atom. The maximum deviation from the ideal geometry is seen in the N—Ni—N five-membered chelate bite angle of 83.28 (12)°. The pyridine mol­ecule forms a dihedral angle of 44.43 (6)° with the N3O donor set. Supra­molecular stacks along the a axis mediated by alternating π–π inter­actions between the pyridine and five- [centroid–centroid distance = 3.4784 (16) Å] and six-membered [3.4633 (17) Å] chelate rings, feature in the crystal packing.

Iridium mediated N–H and C–H bond activation of N-(aryl)pyrrole-2-aldimines. Synthesis, structure and, spectral and electrochemical properties

Reaction of N-(4′-R-phenyl)pyrrole-2-aldimines (L-R, R = OCH3, CH3, H, Cl and NO2) with Ir(PPh3)3Cl in refluxing ethanol affords a group of yellow complexes (1-R), in which an imine-ligand (L-R) is coordinated to the metal center as a mono-anionic bidentate NN-donor along with two triphenylphosphines, a chloride and a hydride. The hydride is trans to the coordinated pyrrole-nitrogen, while the chloride is trans to the imine-nitrogen, and the two triphenylphosphines are mutually trans. Structure of the 1-OCH3 complex has been determined by X-ray crystallography. Similar reaction of N-(naphthyl)pyrrole-2-aldimine (L-nap) with Ir(PPh3)3Cl affords an organometallic complex 2, where the imine-ligand is coordinated to the metal center, via C–H activation of the naphthyl ring at the 8-position, as a di-anionic tridentate NNC-donor, along with two triphenylphosphines and a hydride. Structure of this complex 2 has also been determined by X-ray crystallography. All the complexes are diamagnetic, and show characteristic 1H NMR signals and intense transitions in the visible region. Cyclic voltammetry on all the complexes shows two irreversible oxidations within 0.97–1.46 V vs. SCE and a reduction within −0.83 to −1.40 V vs. SCE.

Synthesis, Characterization, Photoluminescence, and Computational Studies of Monoorgano-Gallium and -Indium Complexes Containing Dianionic Tridentate ONE (E = O or S) Schiff Bases

The reactions of triorgano-gallium and -indium etherate with dianionic tridentate Schiff bases (2-hydroxy-N-salicylideneaniline (1a), 2-hydroxy-N-(2-hydroxy-3-methoxybenzylidene)aniline (1b), and 2-mercapto-N-salicylideneaniline (1c)) in benzene yielded complexes of the type [RM{O(2-C6H3R′-3)-CH═N(2-C6H4)E}] (where R = Me, Et; M = Ga, In; R′ = H, OMe; E = O, S) in nearly quantitative yields. These complexes have been characterized by elemental analysis, IR, UV–vis, and NMR (1H and 13C{1H}) spectroscopy. The molecular structures of [MeGa(−O(2-C6H4)-CH═N(2-C6H4)-O−)] (2a) and [MeGa(−O(2-C6H3OMe-3)-CH═N(2-C6H4)-O−)] (2b) were established by X-ray crystallography. Photoluminescence data of these complexes showed that the quantum yield was mainly affected by the substituent/groups attached to the phenyl moiety of the ligands rather than the metal atom. Density functional theory calculations have been used to assess all the possible structures and to evaluate the complexation energies corresponding to [MeM{O(2-...

New Di- and Triorganotin(IV) Tyrosylalaninates as Models for Metal—Protein Interactions: Synthesis, Structural Characterization, and Potentiometric Studies of Tyrosylalanine, Glycyltyrosine, and Glycylisoleucine with Di- and Trimethyltin(IV) Moieties in Aqueous Medium

Di- and triorganotin(IV) derivatives of tyrosylalanine (H2Tyr-Ala) with general formula R2Sn(Tyr-Ala) (where R = Me, n-Bu, n-Oct, and Ph) and R3Sn(HTyr-Ala) (where R = Me and Ph) have been synthesized and structurally characterized in the solid state as well as in solution on the basis of various spectroscopic techniques, namely. FT-IR, multinuclear (1H, 13C and 119Sn) NMR and 119Sn Mössbauer. These investigations suggest that tyrosylalanine in R2Sn(Tyr-Ala) acts as dianionic tridentate ligand coordinating through carboxylate oxygen [–C(O)O−], amino (–NH2), and (CO)Npeptide- nitrogen, while in the case of R3Sn(HTyr-Ala), the ligand acts as monoanionic bidentate coordinating through –C(O)O− and –NH2, and the polyhedron around tin in R2Sn(Tyr-Ala) and R3Sn(HTyr-Ala) is a distorted trigonal-bipyramidal. Equilibrium (pH-metric) studies of the interaction of Me2Sn(IV)2+ and Me3Sn(IV)+ with dipeptides namely, tyrosylalanine (H2Tyr-Ala), glycyltyrosine (H2Gly-Tyr), and glycylisoleucine (H2Gly-Ile), in aqueous solution (I = 0.1 M KNO3, 298 K) have also been carried out. The concentration distribution of the various complex species in solution has been evaluated as a function of pH. It has been found that in these dipeptides, [–C(O)O−, N−, NH2] coordinated complexes are dominant in the neutral pH range with a trigonal-bipyramidal structure. The complex species formed are water soluble in the pH range 2.7–10.5. In all of the studied systems, no polymeric species have been detected in the experimental pH range. Beyond pH 8.0, significant amounts of hydroxo species, namely. Me3Sn(OH) and Me2Sn(OH)2, are formed.

Rhenium(V) and Technetium(V) Nitrido Complexes with Mixed Tridentate π-Donor and Monodentate π-Acceptor Ligands

Mixed-ligand [M(N)(SNS)(PPh(3))] complexes (M = Tc, Re) (1, 2) were prepared by reaction of the precursor [M(N)Cl(2)(PPh(3))(2)] with ligand 2,2'-dimercaptodiethylamine [H(2)SNS = NH(CH(2)CH(2)SH)(2)] in refluxing dichloromethane/ethanol mixtures. In these compounds, 2,2'-dimercaptodiethylamine acts as a dianionic tridentate chelating ligand bound to the [M≡N](2+) group through the two π-donor deprotonated sulfur atoms and the protonated amine nitrogen atom. Triphenylphosphine completes the coordination sphere, acting as a monodentate ligand. [M(N)(NS(2))(PPh(3))] complexes can assume two different isomeric forms depending on the syn and anti orientations of the hydrogen atom bound to the central nitrogen atom of the SNS ligand with respect to the M≡N moiety. X-ray crystallography of the syn isomer of complex 2 demonstrated that it has a distorted trigonal bipyramidal geometry with the nitrido group and the two sulfur atoms defining the equatorial plane, the phosphorus atom of the monophosphine and the protonated amine nitrogen of the tridentate ligand spanning the two reciprocal trans positions along the axis perpendicular to the trigonal plane. Synthesis of the analogous Tc derivatives with tris(2-cyanoethyl)phosphine, [Tc(N)(SNS)(PCN)] [(PCN = P(CH(2)CH(2)CN)(3)], required the preliminary preparation of the new precursor [Tc(N)(PCN)(2)Cl(2)](2) (3), which was prepared by reacting [n-NBu(4)][Tc(N)Cl(4)] with a high excess of PCN. The crystal structure of compound 3 consists of a noncrystallographic centrosymmetric dimer of Tc(V) nitrido complexes having an octahedral geometry. In this arrangement, the apical positions are occupied by two tris(2-cyanoethyl)phosphine groups and the equatorial positions by the nitrido group whereas the two Cl(-) anions and one cyano ligand belong to the other octahedral component of the dimer. By reacting the new precursor [Tc(N)(PCN)(2)Cl(2)](2) with the ligand H(2)SNS the complex [Tc(N)(SNS)(PCN)] (5) was finally obtained in acetonitrile solution. The new Tc(III) complex trans-[Tc(PCN)(2)Cl(4)][n-NBu(4)] (4) was also isolated from the reaction solution used for preparing complex 3 as side product and characterized by X-ray diffraction. The crystal structure of 4 consists of independent trans-[TcCl(4)(PCN)(2)](-) anions situated on crystallographic centers of symmetry and tetrabutylammonium cations in general positions.

Anilidopyridyl-Pyrrolide and Anilidopyridyl-Indolide Group 3 Metal Complexes: Highly Active Initiators for the Ring-Opening Polymerization of rac-Lactide

Three new group 3 metal complexes, bearing anilidopyridyl-pyrrolide (L1) and anilidopyridyl-indolide (L2) as dianionic tridentate ligands, with the general formula LMN(SiHMe2)2 were synthesized (complex 1, M = Y, L = L1; complex 2, M = Sc, L = L1; complex 3, M = Y, L = L2). All complexes were fully characterized and tested as initiators for the ROPs of rac-lactide. The yttrium complexes 1 and 3 resulted in highly active catalysts (TOF up to 104 mollactide molY–1 h–1), whereas the scandium complex showed moderate activities. This class of catalysts allowed a good control of the macromolecular architecture of the polymer, namely, the nature of end groups, the molecular weights, and their distribution. Moreover, the obtained PLAs showed Pr values in the range of 0.57–0.84, depending on the nature of the initiator and solvent. Well-controlled and rapid ROPs of rac-lactide were obtained in the solvent-free polymerizations at 130 °C as well, suggesting that complexes 1–3 are stable at high temperature. Finally,...