NCN Pincer Ligand Research Articles

New cyclometalated Ir(iii) complexes with NCN pincer and meso-phenylcyanamide BODIPY ligands as efficient photodynamic therapy agents

A new class of cyclometalated iridium(iii) with NCN pincer andmeso-phenylcyanamide BODIPY ligands has been synthesized and studied for photodynamic therapy.

Synthesis and Structure of Bis- and Tris-Benzyl Bismuth Complexes

The first crystallographic characterization of bismuth complexes containing benzyl ligands is reported. The NCN pincer ligand complex, Ar′BiCl2 [Ar′ = 2,6-(Me2NCH2)2C6H3], reacts with (PhCH2)MgCl to form Ar′Bi(η1-CH2Ph)2 in high yield. X-ray crystallography and spectroscopic studies confirm η1-bonding of the benzyl ligands in Ar′Bi(η1-CH2Ph)2 as well as in the homoleptic Bi(η1-CH2Ph)3.

Hemilabile and bimetallic coordination in Rh and Ir complexes of NCN pincer ligands.

Two new pincer ligands have been developed that contain a central N-heterocyclic carbene (NHC) moiety linked to two pendant pyrazole groups by either a methylene (NCN(me)) or ethylene (NCN(et)) chain. The coordination of these two ligands to rhodium and iridium resulted in a variety of binding modes. Tridentate coordination of the ligands was observed in the complexes [Rh(NCN(me))(COD)]BPh4 (8), [Ir(NCN(me))(COD)]BPh4 (10), [Rh(NCN(et))(CO)2]BPh4 (13), and [Ir(NCN(me))(CO)2]BPh4 (14), and monodentate NHC coordination was observed for [Ir(NCN(me))2(COD)]BPh4 (11) and [Ir(NCN(et))2(COD)]BPh4 (12). Both tridentate and bidentate coordination modes were characterized for [Rh(NCN(et))(COD)]BPh4 (9) in the solution and solid state, respectively, while an unusual bridging mode was observed for the bimetallic complex [Rh(μ-NCN(me))(CO)]2(BPh4)2 (15). The impact of this diverse coordination chemistry on the efficiency of the complexes as catalysts for the addition of NH, OH, and SiH bonds to alkynes was explored.

An NCN-pincer ligand dysprosium single-ion magnet showing magnetic relaxation via the second excited state.

Single-molecule magnets are compounds that exhibit magnetic bistability purely of molecular origin. The control of anisotropy and suppression of quantum tunneling to obtain a comprehensive picture of the relaxation pathway manifold, is of utmost importance with the ultimate goal of slowing the relaxation dynamics within single-molecule magnets to facilitate their potential applications. Combined ab initio calculations and detailed magnetization dynamics studies reveal the unprecedented relaxation mediated via the second excited state within a new DyNCN system comprising a valence-localized carbon coordinated to a single dysprosium(III) ion. The essentially C2v symmetry of the DyIII ion results in a new relaxation mechanism, hitherto unknown for mononuclear DyIII complexes, opening new perspectives for means of enhancing the anisotropy contribution to the spin-relaxation barrier.

Self‐Assembly Properties of NCN Pincer Palladium(II) Complexes Bearing a Uracil Moiety

AbstractNCN pincer palladium(II) complexes bearing a 6‐ethynyl‐1‐octyluracil moiety were designed by the combination of an NCN pincer palladium(II) complexes as an organometallic compound and a uracil derivative as a nucleobase to afford bioorganometallic compounds. The reaction of the NCN pincer ligand with Pd(dba)2 (dba = dibenzylideneacetone) led to the formation of the NCN pincer palladium(II) complex Pd‐Br. The crystal structure of the cationic complex Pd‐MeCN, which was prepared by the treatment of Pd‐Br with AgOTf (OTf = trifluoromethanesulfonate) in acetonitrile, revealed that a dimeric structure formed through intermolecular hydrogen bonds between the uracil moieties of two independent molecules. The self‐assembly properties of the NCN pincer palladium(II) complexes were found to depend on the ancillary ligands. Each hydrogen‐bonded dimer was connected through an intermolecular hydrogen‐bonding bridge between the coordinated water molecule and the triflate anion in the cationic complex Pd‐H2O. Intermolecular hydrogen bonding between the uracil moiety and the triflate anion bound to the palladium center was observed in the NCN pincer palladium(II) complex Pd‐OTf, although a dimeric structure between the uracil moieties was formed in the NCN pincer palladium(II) complex Pd‐O2CCF3, which was obtained by the abstraction of the bromide ion from Pd‐Br with AgO2CCF3.

Palladium catalyzed direct C-2 arylation of indoles

The synthesis and catalytic evaluation of palladium complexes containing NCN Pincer ligand is reported. The pincer palladium complexes as (pre)catalyst showed efficient catalytic activity for the C–H arylation of N-substituted indoles, allowing the synthesis of 2-arylindoles with moderate to good yields and excellent regioselectivities.

Bismuth-based cyclic synthesis of 3,5-di-tert-butyl-4-hydroxybenzoic acid via the oxyarylcarboxy dianion, (O2CC6H2tBu2O)2−

3,5-Di-tert-butyl-4-hydroxybenzoic acid can be made under mild conditions in a cyclic process from carbon dioxide and 3,5-di-tert-butyl-4-phenol using bismuth-based C-H bond activation and CO2 insertion chemistry starting with the Bi(3+) complex, Ar'BiCl2, of the NCN pincer ligand, Ar' = 2,6-(Me2NCH2)2C6H3. Complexes of the recently discovered oxyaryl dianion, (C6H2(t)Bu2-3,5-O-4)(2-), and the oxyarylcarboxy dianion, [O2C(C6H2(t)Bu2-3,5-O-4)](2-), are intermediates in the process. Further studies of the oxyarylcarboxy dianion in Ar'Bi[O2C(C6H2(t)Bu2-3,5-O-4)-κ(2)O,O'], show that it undergoes decarboxylation upon reaction with I2 and it reacts with trimethylsilyl chloride to produce the trimethylsilyl ether of the trimethylsilyl ester of 3,5-di-tert-butyl-4-hydroxybenzoic acid and the Ar'BiCl2 starting material.

Synthesis, characterization, and cyclometalation studies of benzo[1,2-h: 5,4-h′]diquinolines with palladium and platinum

Benzo[1,2-h: 5,4-h′]diquinoline( 1a) represents a new family of tridentate NCN pincer ligand. We report the synthesis of the parent ligand ( 1a) and its derivatives ( 1b R = Me, 1c R = t-Butyl, 1d R = Phenyl). The ligands were characterized by 1H and 13C NMR, as well as mass spectral analysis, and X-ray structural determination. They readily undergo cyclometalation with LiPdCl 4, Pd(OAc) 2, and K 2PtCl 4 to form the cyclometalated Pd(NCN)Cl ( 2a– c, 3a), and Pt(NCN)Cl ( 4a) pincer complexes. These complexes have been characterized through NMR, and mass spectrometry. PdNCNCl ( 2a) structure was determined by single crystal X-ray diffraction. Complex 2a has shown to catalyze the Heck coupling reaction between bromobenzene and n-butylacyrlate in NMP at 140 °C, TON of 2506 were observed.

Mono N,C,N-pincer complexes of titanium, vanadium and niobium. Synthesis, structure and catalytic activity in olefin polymerisation

Transmetallation of 4,4'-bis{(2,6-bis[(dimethylamino)methyl]phenylgold)diphenyl-phosphino}biphenyl (3) with MCl(4) (M = Ti, NbCl, V) in benzene gave the corresponding transition metal pincer complexes (4) and insoluble 4,4'-bis[P-(chloro gold(I))diphenylphosphino]biphenyl (2), which can be quantitatively recovered and recycled. Interestingly, 3 did not react with TiCl(3). However, reaction of 2,6-bis[(dimethylamino)methyl]phenyllithium (1) with TiCl(3) resulted in formation of the novel diaryltitanium(IV) compound 5 (16% yield), comprising one N,C,N-mer bound NCN-pincer ligand and a second NCN-pincer ligand that is rearranged from a 1,2,6-isomer to a 1,2,4 one. The latter NCN-ligand is dianionic and is bidentate bonded; one of the CH(2)NMe(2) substituents (para to C'(ipso)) is non-coordinated, while the second CH(2)NMe(2) group, after C-H activation of one of the Me groups, is η(2)-C,N-bonded to the titanium centre trans to C(ipso) of the mer-NCN ligand. The new NCN-pincer metal complexes 2,6-bis[(dimethylamino)methyl]phenylTiCl(3) (4a) and 2,6-bis[(dimethylamino)methyl]-phenylVCl(2) (4d) gave, after immobilization on MgCl(2)-based supports, very high activity in ethene polymerisation.

Formation of organorhodium complexes via C–H bond activation of 1,3-di(phenylazo)benzene

Reaction of a potential NCN-pincer ligand, viz. 1,3-di(phenylazo)benzene (L), with [Rh(PPh(3))(3)Cl] affords, via a C-H bond activation, an interesting dinuclear Rh(II) complex (1), and with RhCl(3)·3H(2)O affords a mononuclear Rh(III) complex (2) containing a catalytically useful Rh-OH(2) fragment.

Synthesis and characterization of bioorganometallic conjugates composed of NCN-pincer platinum(II) complexes and uracil derivatives

The conjugation of the NCN-pincer platinum(II) complexes as an oraganometallic compound and the uracil derivatives as a nucleobase was demonstrated to give the corresponding bioorganometallics. The NCN-pincer ligands bearing the 6-ethynyl-1-octyluracil, 5-ethynyl-1-octyluracil, and the furanopyrimidine moiety were synthesized. In a crystal state, the NCN-pincer ligand bearing the 6-ethynyl-1-octyluracil moiety was found to form a hydrogen-bonded dimer through intermolecular hydrogen bonds between the uracil moieties, which was connected through π–π interaction between the uracil and benzene moieties of the NCN-pincer ligand. The reaction of the NCN-pincer ligand bearing the 6-ethynyl-1-octyluracil moiety with [Pt(tolyl-4) 2(SEt 2)] 2 led to the formation of the NCN-pincer platinum(II) complex bearing the 6-ethynyl-1-octyluracil moiety. The NCN-pincer platinum(II) complex bearing the furanopyrimidine moiety was obtained by the reaction of the NCN-pincer ligand bearing the furanopyrimidine moiety with [Pt(tolyl-4) 2(SEt 2)] 2. The single-crystal X-ray structure determination of the NCN-pincer platinum(II) complex bearing the furanopyrimidine moiety revealed the formation of the furanopyrimidine ring and the π stack dimer between the furanopyrimidine and benzene moieties of the NCN-pincer ligand in the crystal packing. The NCN-pincer platinum(II) complexes bearing the 6-ethynyl-1-octyluracil moiety or the furanopyrimidine moiety exhibited emission in both solution and solid states.

Synthesis and Structural Characterization of the First Copper(I) Complexes with Bis(imino)-N-heterocyclic Carbene NCN Pincer Ligands

A new class of bis(acyclic imino)-N-heterocyclic carbene (NCN pincer) ligand precursors was synthesized and structurally characterized. In situ deprotonation using a basic metal precursor resulted in the corresponding copper(I) complexes in good yields. Monometallic and bimetallic structures were observed in the solid state depending on the ligand substitution pattern.

Unsymmetrical, oxazolinyl-containing achiral and chiral NCN pincer ligand precursors and their complexes with palladium(II)

The unsymmetrical, achiral and chiral NCN pincer ligand precursors ( 3a-3d) with oxazoline and pyrazole as N donors as well as ( 3e) which has oxazolinyl and amino group have been synthesized in a facile manner in four steps starting from commercially available isophthalaldehyde. Direct C2 metallation of the precursors ( 3a–3e) with Pd(OAc) 2 in refluxing HOAc, followed by treatment with LiCl at room temperature provided convenient access to the corresponding pincer palladium(II) complexes ( 4a–4e). The molecular structure of complex 4e has been determined by X-ray single-crystal diffraction. The obtained Pd complexes exhibited good activities in the Suzuki reactions of aryl bromides and activated aryl chlorides with phenylboronic acid.

η6-Coordination of a Ruthenium(II) Organometallic Fragment to the Arene Ring of N,C,N-Pincer Metal Complexes

Stable heterobimetallic complexes of the type [MX(NCN)Ru(C5R5)]+ (R = H or Me), where the phenylene ring of an NCN-pincer ligand coordinates first to a platinum or palladium center via a σ-bond, and second to a ruthenium organometallic fragment via a π-bond, are synthesized in a single step involving electrophilic attack of a cationic Ru species on the aryl metal complex. X-ray crystal structures and solution NMR agree on the simultaneous presence of orthogonal η6- and η1-coordination axes. 195Pt NMR and electrochemistry show that the η6-coordinated ruthenium fragment has a strong electron-withdrawing effect on the pincer metal, which leads to a diminished nucleophilicity of the platinum center toward electrophiles such as SO2.

Synthesis and Characterization of (2,6-iPrNCN)HfCl2- and (3,5-MeNCN)2Hf2- (where NCN = 2,6-bis[phenylazanidyl]methylphenyl): New Trianionic Pincer Ligands

The synthesis, isolation, and metalation of the trianionic NCN-pincer ligand [2,6-iPrNCNLi3]2 (2) is described. The terdentate coordination ability of 2 is demonstrated in the synthesis of the hafnium dichloride anion [2,6-iPrNCNHfCl2][Li(DME)3] (3-DME). Complex 3-DME is distorted square pyramidal in the solid state, but NMR evidence indicates the complex is fluxional and trigonal bypyramidal in solution. Straightforward ligand modification provides the additional trianionic pincer ligand [3,5-MeNCNLi2]2[Li2(DME)6] (5). This sterically smaller ligand leads to the hafnium pincerate dianion complex [(3,5-MeNCN)2Hf][Li2(DME)2] (6), which contains two trianionic pincer ligands. The new compounds are characterized by elemental analysis, multinuclear NMR, and X-ray diffraction crystallography.

Synthesis, Crystal Structure, and Redox and Photophysical Properties of Novel Bisphosphinoaryl RuII-Terpyridine Complexes

Novel organometallic [Ru(PCP)(tpy)]Cl complexes, containing the terdentate coordinating monoanionic bisphosphinoaryl ligands [C6H3(CH2PR2)2-2,6]- (PCP) (R = Ph (11); iPr (12)) and 2,2‘:6‘,2‘ ‘-terpyridine, have been synthesized by two different synthetic pathways in good yields. The molecular structure in the solid state of [Ru{C6H2(CH2PPh2)2-2,6}(tpy)](OTf) (14) has been determined by X-ray crystallography. The spectroscopic and electrochemical properties of the [Ru(PCP)(tpy)]Cl complexes were compared with those obtained for [Ru{C6H3(CH2NMe2)2-2,6}(tpy)](Cl) (3) containing the monoanionic bisaminoaryl ligand [C6H3(CH2NMe2)2-2,6]- (NCN). The obtained results revealed that substitution of the NCN-pincer ligand by PCP-pincer ligands offers a powerful tool to tune the redox and photophysical properties as well as the reactivity of the ruthenium(II) metal centers in the resulting photoactive monomeric species.

Synthesis of Novel Pd−NCN Pincer Complexes Having Additional Nitrogen Coordination Sites and Their Application as Catalysts for the Heck Reaction

A novel Pd−NCN pincer complex, 7, bearing two additional nitrogen atoms has been synthesized and characterized. The dynamic NMR study of 7 shows the two-site exchange reaction in the NCN pincer ligand with a relatively low ΔG⧧ value, suggesting easy interconversion in the pincer complex. The use of 7 as a catalyst in the Heck reaction was studied. Catalyst 7 is quite effective for all aryl iodides. A turnover number (TON) value of 4.3 × 106 was observed with 4-tolyl iodide. However, 7 is not an effective catalyst for nonactivated bromobenzene and chlorobenzene substrates. According to the study of the Heck reaction, the facile interconversion of the pincer ligand positively affects the catalytic activity.

Novel Chiral and Achiral NCN Pincer Complexes Based on 1,3-Bis(1H-1,2,4-triazol-1-ylmethyl)benzene

NCN pincer ligands based on 1,2,4-triazole and their corresponding palladium(II) complexes have been synthesized by the reaction of 1,3-bis(1H-1,2,4-triazol-1-ylmethyl)benzene derivatives with palladium(II) acetate. All compounds are ortho,ortho-metalated. Chiral complexes were obtained by using pincer ligands with substituents on the arms. The chiral complexes are conformationally rigid up to 150 °C.

A Bis(ortho-amine)aryl−Gold(I) Compound as an Efficient, Nontoxic, Arylating Reagent

A novel strategy for the synthesis of bis(ortho-amine)chelated monoanionic bisaminoaryl−metal complexes is presented. This method constitutes the exchange of a monoanionic, NCN-pincer ligand (NCN = [C6H3(CH2NMe2)2-2,6]-) between a stable arylgold(I) phosphine, [Au(η1-C-NCN)(PPh3)] (2), and a transition metal halide. This transmetalation results in the quantitative formation of [M(NCN)] organometallic compounds (M = AuIII, NiII, PdII, PtII, TiIV, and FeIII) and [AuCl(PPh3)] as the only coproduct that can be recovered.

Chiral platinum and palladium complexes containing functionalized C2-symmetric bisaminoaryl ‘Pincer’ ligands

The synthesis of enantiopure (oxo-functionalized) C 2-symmetric NCN pincer ligands is described. A key step is the symmetric functionalization of the benzylic positions, which was achieved by enantioselective ketone reduction and subsequent stereoselective substitution protocols. The introduction of α-alkyl substituents has a pronounced effect on the cavity for metal binding. For example, lithiation of the α-ethyl-functionalized pincer ligand afforded mixed (alkyl)(aryl)lithium aggregates rather than dinuclear bis(aryl) lithium [Li(NCN)] 2 species as usually observed for NCN–lithium complexes. Similar effects were established for the ( trans)-metalation reaction, which proceeded significantly slower when the steric demand of the α-substituent is increased. The potential of the corresponding enantiopure palladium and ruthenium complexes as enantioselective catalyst has been probed in the asymmetric aldol condensation and hydrogen transfer reactions. The low enantiomeric excess of the products of both reactions indicated that face-discrimination of substrates is not induced by these catalysts and that the chiral information must be located in closer proximity to the metal center.