Transfer hydrogenation of ketones catalyzed by nickel complexes bearing an NHC [CNN] pincer ligand

Four NHC [CNN] pincer nickel (II) complexes, [^iPrCNN (CH₂)₄‐Ni‐Br] ( 5a ), [^nBuCNN (CH₂)₄‐Ni‐Br] ( 5b ), [^iPrCNN (Me)₂‐Ni‐Br] ( 6a ) and [^nBuCNN (Me)₂‐Ni‐Br] ( 6b ), bearing unsymmetrical [C (carbene)N (amino)N (amine)] ligands were synthesized by the reactions of [CNN] pincer ligand precursors 4 with Ni (DME)Cl₂ in the presence of Et₃N. Complexes 5a and 5b are new and were completely characterized. The transfer hydrogenation of ketones catalyzed by the four pincer nickel complexes were explored. Complexes 5a and 6a have better catalytic activity than 5b and 6b . With a combination of NaO^tBu/ⁱPrOH/80 °C and 2% catalyst loading of 5a , 77–98% yields of aromatic alcohols could be obtained.     

Lanthanide and uranium complexes with an SPS-based pincer ligand

Reactions of Ln(BH4)3(THF)n and [Li(Et2O)]SPS(Me)], the lithium salt of an anionic SPS pincer ligand composed of a central hypervalent lambda4-phosphinine ring bearing two ortho-positioned diphenylphosphine sulfide sidearms, led to the monosubstituted compounds [Ln(BH4)2(SPS(Me))(THF)2] [Ln = Ce (1), Nd (2)], while the homoleptic complexes [Ln(SPS(Me))3] [Ln = Ce (3), Nd (4)] were obtained by treatment of LnX3 (X = I, BH4) with [K(Et2O)][SPS(Me)]. The [UX2(SPS(Me))2] complexes [X = Cl (5), BH4 (6)] were isolated from reactions of UX4 and the lithium or potassium salt of the [SPS(Me)]- anion. The X-ray crystal structures of 1.1.5THF, 2.1.5THF, 3.2THF.2Et2O, and 5.4py reveal that the flexible tridentate [SPS(Me)]- anion is bound to the metal as a tertiary phosphine with electronic delocalization within the unsaturated parts of the ligand.     

A new class of transition metal pincer ligand: tantalum complexes that feature a [CCC] X3-donor array derived from a terphenyl ligand

A new class of [CCC] X(3)-donor pincer ligand for transition metals has been constructed via cyclometalation of a 2,6-di-p-tolylphenyl ([Ar(Tol(2))]) derivative. Specifically, addition of PMe(3) to [Ar(Tol(2))]TaMe(3)Cl induces elimination of methane and formation of the pincer complex, [κ(3)-Ar(Tol'(2))]Ta(PMe(3))(2)MeCl (Tol' = C(6)H(3)Me), which may also be obtained by treatment of Ta(PMe(3))(2)Me(3)Cl(2) with [Ar(Tol(2))]Li. Solutions of [κ(3)-Ar(Tol'(2))]Ta(PMe(3))(2)MeCl undergo ligand redistribution with the formation of [κ(3)-Ar(Tol'(2))]Ta(PMe(3))(2)Me(2)and [κ(3)-Ar(Tol'(2))]Ta(PMe(3))(2)Cl(2), which may also be synthesized by the reactions of [κ(3)-Ar(Tol'(2))]Ta(PMe(3))(2)MeCl with MeMgBr and ZnCl(2), respectively. Reduction of [κ(3)-Ar(Tol'(2))]Ta(PMe(3))(2)Cl(2) with KC(8) in benzene gives the benzene complex [κ(3)-Ar(Tol'(2))]Ta(PMe(3))(2)(η(6)-C(6)H(6)) that is better described as a 1,4-cyclohexadienediyl derivative. Deuterium labeling employing Ta(PMe(3))(2)(CD(3))(3)Cl(2) demonstrates that the pincer ligand is created by a pair of Ar-H/Ta-Me sigma-bond metathesis transformations, rather than by a mechanism that involves α-H abstraction by a tantalum methyl ligand.     

Photoluminescent columnar zinc(II) bimetallomesogen of tridentate [ONO]-donor Schiff base ligand

A new zinc(II) bimetallomesogenic complex, [Zn₂L₂], of tridentate [ONO]-donor Schiff base ligand (L = N-(2-hydroxyethyl)-4-hexadecyloxysalicylaldimines) was synthesised and their mesomorphic and photoluminescence properties were investigated. The compounds were characterised by Fourier transform infrared spectroscopy (FTIR), ¹H and ¹³C nuclear magnetic resonance (NMR), ultraviolet-visible spectroscopy (UV-Vis) spectroscopy, elemental analyses and fast atom bombardment (FAB) mass spectrometry. The mesomorphic behaviour of the complex was investigated by polarised optical microscopy, differential scanning calorimetry and X-ray diffraction (XRD) study. A rectangular or oblique columnar mesophase is conjectured on the basis of powder X-ray diffraction (PXRD) study. The complex is found to be blue light emitter in solution, in solid and in condensed states with broad emission maxima at ～427–464 nm. The density functional theory (DFT) calculations revealed a distorted square planar structure around each zinc(II) centre in the dinuclear framework. Time-dependent DFT spectral correlative study was undertaken to account for the electronic transition.     

Hafnium alkyl complexes of the anionic PNP pincer ligand and possible alkylidene formation

The diarylamido-based PNP pincer ligand can be used successfully for support of organometallic Hf complexes (PNP = [(4-Me-2-ⁱPr₂P-C₆H₃)₂N]). (PNP)HfCl₃ (3) was prepared via reaction of (PNP)Li (2) with HfCl₄(OEt₂). Reactions of (PNP)HfCl₃ with alkyl Grignards led to triple alkylation to produce (PNP)HfMe₃ (4) with a small methyl or only double alkylation to give (PNP)Hf(CH₂SiMe₃)₂Cl (5) with a larger alkyl. Structures of 3, 4, and 5 in the solid state were established by X-ray diffraction studies. Structures of the alkyl complexes 4 and 5 display remarkably irregular coordination environments about Hf, while in 3 it is approximately octahedral. Compound 4 was found to be thermally stable at 75 °C. On the other hand, thermolysis of 5 at similar conditions led to a mixture of products, the major one of which is believed to be a Hf alkylidene on the basis of in situ NMR spectroscopic observations (e.g., δ 248.2 ppm in the ¹³C{¹H} NMR spectrum).     

Ruthenium complexes with ferrocene-based P,C,P pincer ligand

First ruthenium complexes with a ferrocene-based pincer ligand were synthesized. The cyclometallation of 1,3-bis[(di-tert-butylphosphino)methyl]ferrocene with RuCl₂(DMSO)₄ in 2-methoxyethanol afforded the RuCl(CO)[{2,5-(Bu^t ₂PCH₂)₂C₅H₂}Fe(C₅H₅)](RuCl(CO) ) complex (5). Complex 5 reversibly binds CO to form the RuCl(CO)₂ complex (6). The analogous reaction in the presence of NaBAr′₄ (Ar′ = 3,5-(CF₃)₂C₆H₃) produced the cationic complex {Ru(CO)₂ }BAr′₄ (7). The structures of complexes 5 and 7 were established by single-crystal X-ray diffraction. The X-ray diffraction study revealed an agostic interaction between one of the C-H bonds of the axial (exo-oriented with respect to the ferrocene iron atom) tert-butyl group and the Ru atom in complexes 5 and 7. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1695–1701, September, 2007.     

Ruthenium [NNN] and [NCN]-type pincer complexes with phosphine coligands: synthesis,structures and catalytic applications

Transition Metal Chemistry - A series of ruthenium [NNN]- or [NCN]-type complexes (3–7) bearing PPh3 ancillary ligands have been synthesized from pyridine- or phenylene-bridged bis(triazoles)...     

New platinum complexes with carbodiphosphorane as pincer ligand via ortho phenyl metallation

The platinum complex [Pt(η³-C₈H₁₁)(C₆H₄PPh₂CPPh₃)] (2) is a halve side o-phenyl insertion product resulting from the reaction of C(PPh₃)₂ and [I₂Pt(cod)] and is unstable in halogenated hydrocarbons. In a slow reaction 2 abstracts HCl from CH₂Cl₂, CHCl₃ or CDCl₃ (DCl) and converts the η³-C₈H₁₁ ligand into cod which is replaced by Cl⁻. Simultaneously, a second insertion of the Pt atom into an o-phenyl CH bond occurs under movement of the o-phenyl proton to the ylidic carbon atom resulting in the C,C,C-pincer complex [ClPt{CH(PC₆H₄Ph₂)₂}] (3). Surprisingly, crystals of the unusual carbonyl complex [(CO)Pt{C(PC₆H₄Ph₂)₂}] (5) were obtained upon attempts to replace Cl⁻ in 3 by PPh₃ in CHCl₃ solution. Instead, an intermediate was identified by ³¹P NMR spectroscopy in which the coordinated CH group is replaced by PPh₃; however, no crystals could be obtained. From the resulting oily material after some month crystals of 5 separated. We suggest, that hydrolysis of an intermediate CCl₂ ligand (from CHCl₃) to CO via a leaking stopcock has taken place. The compounds are characterized by X-ray analyses, ³¹P NMR, and IR spectroscopy.     

Preparation,characterizations and biological evaluations of new copper(II) complexes containing ONO pincer type ligands

A new heterocyclic Schiff bases, 6‐methyl/8methyl‐2‐oxo‐1,2‐dihydroquinoline‐3‐carboxaldehyde semicarbazones (H₂‐6MOQsc‐H) ( H ₂ L ¹ ) and (H₂‐8MOQsc‐H) ( H ₂ L ² ) and their corresponding copper(II) complexes [CuCl₂(H₂‐6MOQsc‐H)].3H₂O ( 1 ), [CuCl₂(H₂‐8MOQsc‐H)].3H₂O ( 2 ), [CuNO₃(H₂‐6MOQsc‐H)(H₂O)].NO₃ ( 3 ) and [CuNO₃(H₂‐8MOQsc‐H)(H₂O)].NO₃ ( 4 ) have been synthesized and characterized by various physicochemical techniques. The single crystal X‐ray diffraction and spectral data revealed that all of the complexes ( 1‐4 ), the ligands coordinated to the Cu(II) ion in a neutral manner via ONO donor atoms and all the complexes exhibited distorted squarepyramidal geometry. The consequence of electronegativity and ring size of nitrogen heterocyclic moiety of ONO donor type of copper(II) chelates on nucleic acid interaction and albumin binding was investigated by in vitro experiments. The interaction of compounds with calf‐thymus DNA (CT‐DNA) has been explored by absorption and emission titration, which exposed those ligands/complexes, could bind with CT‐DNA through electrostatic interaction. The results of gel electrophoresis proved the ability of complexes ( 1‐4 ) to cleave the pBR322 plasmid DNA. The interaction of serum albumin (BSA) was investigated by UV‐Vis, fluorescence, synchronous and three dimensional fluorescence spectra. In addition, radical scavenging activity, antifungal activity and cytotoxicity of the newly synthesized compounds were also evaluated. From the results of in vitro studies, it is seen that complex 3 has more potential as compared with other complexes and ligands.     

Coordination chemistry and reactivity of zinc complexes supported by a phosphido pincer ligand

The preparation and characterization of new Zn(II) complexes of the type [(PPP)ZnR] in which R = Et (1) or N(SiMe(3))(2) (2) and PPP is a tridentate monoanionic phosphido ligand (PPP-H = bis(2-diphenylphosphinophenyl)phosphine) are reported. Reaction of ZnEt(2) and Zn[N(SiMe(3))(2)](2) with one equivalent of proligand PPP-H produced the corresponding tetrahedral zinc ethyl (1) and zinc amido (2) complexes in high yield. Homoleptic (PPP)(2) Zn complex 3 was obtained by reaction of the precursors with two equivalents of the proligand. Structural characterization of 1-3 was achieved by multinuclear NMR spectroscopy ((1)H, (13)C, and (31)P) and X-ray crystallography (3). Variable-temperature (1)H and (31)P?NMR studies highlighted marked flexibility of the phosphido pincer ligand in coordination at the metal center. A DFT calculation on the compounds provided theoretical support for this behavior. The activities of 1 and 2 toward the ring-opening polymerization of ε-caprolactone and of L- and rac-lactide were investigated, also in combination with an alcohol as external chain-transfer agent. Polyesters with controlled molecular parameters (M(n), end groups) and low polydispersities were obtained. A DFT study on ring-opening polymerization promoted by these complexes highlighted the importance of the coordinative flexibility of the ancillary ligand to promote monomer coordination at the reactive zinc center. Preliminary investigations showed the ability of these complexes to promote copolymerization of L-lactide and ε-caprolactone to achieve random copolymers whose microstructure reproduces the composition of the monomer feed.     

Iron pyrrole‐based PNP pincer ligand complexes as catalyst precursors

The structure of a pincer ligand consists of a backbone and two `arms' which typically contain a P or N atom. They are tridentate ligands that coordinate to a metal center in a meridional configuration. A series of three iron complexes containing the pyrrole‐based PNP pincer ligand 2,5‐bis[(diisopropylphosphanyl)methyl]pyrrolide (PN^pyrP) has been synthesized. These complexes are possible precursors to new iron catalysts. {2,5‐Bis[(diisopropylphosphanyl)methyl]pyrrolido‐κ³P ,N ,P ′}carbonylchlorido(trimethylphosphane‐κP )iron(II), [Fe(C₁₈H₃₄NP₂)Cl(C₃H₉P)(CO)] or [Fe(PN^pyrP)Cl(PMe₃)(CO)], (I), has a slightly distorted octahedral geometry, with the Cl and CO ligands occupying the apical positions. {2,5‐Bis[(diisopropylphosphanyl)methyl]pyrrolido‐κ³P ,N ,P ′}chlorido(pyridine‐κN )iron(II), [Fe(C₁₈H₃₄NP₂)Cl(C₅H₅N)] or [Fe(PN^pyrP)Cl(py)] (py is pyridine), (II), is a five‐coordinate square‐pyramidal complex, with the pyridine ligand in the apical position. {2,5‐Bis[(diisopropylphosphanyl)methyl]pyrrolido‐κ³P ,N ,P ′}dicarbonylchloridoiron(II), [Fe(C₁₈H₃₄NP₂)Cl(CO)₂] or [Fe(PN^pyrP)Cl(CO)₂], (III), is structurally similar to (I), but with the PMe₃ ligand replaced by a second carbonyl ligand from the reaction of (II) with CO. The two carbonyl ligands are in a cis configuration, and there is positional disorder of the chloride and trans carbonyl ligands.     

Spectroscopic characterization and biological activity of metal complexes with an ONO trifunctionalized hydrazone ligand

A series of Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), La(III), Ru(III), Hf(IV), Zr(IV) and U(VI) complexes of phenylamino acetoacetylacetone hydrazone have been synthesized and characterized by elemental analyses, IR, UV–Vis, magnetic moments, conductances, thermal analyses (DTA and TGA) and ESR measurements. The IR data show that the ligand is neutral bidentate, monobasic bidentate, monobasic tridentate or dibasic tridentate towards the metal ion. Molar conductances in DMF indicate that the complexes are non-electrolytes. The ESR spectra of solid [(L)(HL)Cu₂(NO₃)(H₂O)]·1/2H₂O (10) and [(H₂L)Cu(Cl)₂(H₂O)₂] (11) show axial spectra with g_∥ >?g_⊥ >?2.0023 indicating d_(x²???y²) ground state with significant covalent bond character. However, [(HL)₂Mn₂(Cl)₂(H₂O)₄·H₂O (13) shows an isotropic spectrum, indicating manganese(II) to be octahedral. Antibacterial and antifungal tests of the ligand and some of its metal complexes revealed that the complexes are more potent bactericides and fungicides than the ligand.     

A novel redox-active calix[4]arene-tetrathiafulvalene dyad

A novel redox-active calix[4]arene-TTF 5 was prepared by the reaction of p-tert-butylcalix[4]arene 4 with the tosylated TTF 3 in the presence of cesium fluoride. The structure of the dyad 5 was identified by X-ray diffraction analysis, and the preliminary electrochemical properties of 5 were investigated by cyclic voltammetry (CV), for which two reversible one-electron waves were observed. Moreover, the UV-vis absorption spectra studies show that the dyad 5 undergoes progressive oxidation at the TTF moiety in presence of increasing amounts of Cu²⁺ or Hg²⁺.      

Molybdenum complexes containing substituted cyclopenta[l]phenanthrenyl ligand

The synthesis of new cyclopenta[l]phenanthrenyl complexes [(η⁵-C₁₇H₁₀Me)(η³-C₃H₅)Mo(CO)₂] and [(η⁵-C₁₇H₉(COOMe)N(CH₂)₄)(η³-C₃H₅)Mo(CO)₂] is described. Although these compounds are structural analogues their reactivity is different. Protonation of [(η⁵-C₁₇H₁₀Me)(η³-C₃H₅)Mo(CO)₂] gives a stable ionic compound [(η⁵-C₁₇H₁₀Me)Mo(CO)₂(NCMe)₂][BF₄] while its analogue containing both tertiary amino and carboxylic ester groups [(η⁵-C₁₇H₉(COOMe)N(CH₂)₄)(η³-C₃H₅)Mo(CO)₂] decomposes under the same conditions. [(η⁵-C₁₇H₁₀Me)Mo(CO)₂(NCMe)₂][BF₄] reacts with cyclopentadiene to give a stable η⁴-complex [(η⁴-C₅H₆)(η⁵-C₁₇H₁₀Me)Mo(CO)₂][BF₄] that was successfully oxidized to the Mo(IV) dicationic compound [(η⁵-C₅H₅)(η⁵-C₁₇H₁₀Me)Mo(CO)₂][Br][BF₄].     

Synthesis,spectroscopic investigation and biological activity of metal complexes with ONO trifunctionalalized hydrazone ligand

Mn^II, Fe^III, Co^II, Ni^II, Cu^II, Zn^II, La^III, Ru^III, Hf^IV, Zr^IV and U^VI complexes of 4-methylphenylamino acetoacetylacetone hydrazone have been synthesized and characterized by elementals analyses, i.r., u.v.–vis. spectra, magnetic moments, conductances, thermal analyses (d.t.a and t.g.a) and e.s.r measurements. The i.r. data show that, the ligand behaves as a neutral bidentate type (10), (13) and neutral tridentate type (4), (11), (12) and (21) monobasic bidentate type (7) or monobasic tridentate type (2), (3), (5), (6), (8), (14), (15), (16), (18), (19), (20) and (22) or dibasic tridentate type (5), (9) and (17) towards the metal ion. Molar conductances in DMF solution indicate that, the complexes are non-electrolytes. The e.s.r spectra of solid complexes (8) and (10) show axial type spectra with , d(x²-y²) ground state with significant covalent bond character. However, complex (12), shows an isotropic type, indicating a octahedral manganese(II) complex. Antibacterial and antifungal tests of the ligand and some of its metal complexes are also carried out and it has been observed that, the complexes are more potent bactericides and fungicides than the ligand.     

An EPR study of the intramolecular dynamics in o-semiquinonic nickel complexes with a diphosphorous pincer ligand

Square pyramidal o-semiquinonic nickel complexes with 2,6-bis(diphenylphosphinomethyl)phenyl have a flexible coordination sphere and exist in solution as the mixture of tautomers rapidly, according to EPR time scale, interconverting at room temperature.     

Preparation of platinum complexes containing a thioamide-based SCS pincer ligand and their light emitting properties

Reaction of 1,3-bis(1-pyrrolidinothiocarbonyl)benzene with PtCl₂(PhCN)₂ afforded a platinum complex with η³-S,C,S type coordination. The molecular structure of the SCS-pincer platinum(II) complex was determined by X-ray analysis. Substitution of chloro ligand with anionic ligands such as iodo and acetylide was carried out. The complexes exhibit strong emission in a glassy frozen state as well as in the solid state. Light-emitting diodes based on the complexes displayed red electroluminescence.     

Pd, Pt, and Ru complexes of a pincer bis(amino)amide ligand

An improved synthesis of pincer ligand bis[(2-dimethylamino)phenyl]amine ((Me)N(2)NH) was reported. Reaction of the Li complex of (Me)N(2)N with suitable Pd, Pt, and Ru precursors gave the corresponding metal complexes. The structures of the Pd, Pt, and Ru complexes were determined. The Ru complex showed activity in catalytic transfer hydrogenation of aryl and alkyl ketones.