Novel zirconium complexes containing a bidentate phenoxybenzotriazole ligand

Treatment of CpZrCl₃ with 1 equiv of 2-(2H-benzo[d][1,2,3]triazol-2-yl)-4,6-di-tert-pentylphenol (LigH) in THF or toluene affords the monomeric complex C₃₁H₄₁Cl₂N₃O₂Zr (1) or the dimeric complex C₅₄H₆₆Cl₄N₆O₂Zr₂ (2), respectively. THF can transform the dimeric 2 into monomeric 1 within a few minutes at room temperature. The reaction between LigH and 2 equiv of CpZrCl₃ gave the novel dinuclear complex C₃₂H₃₈Cl₅N₃OZr₂ (3), linked by three bridging chlorides. The monomeric complex C₄₄H₅₆Cl₂N₆O₂Zr (4), containing two Lig and two Cl ligands, could be obtained by the reaction between 2 equiv of LigH and Zr(NMe₂)₄ in toluene and subsequent addition of Me₃SiCl. The molecular structures of the complexes were determined by the single crystal X-ray crystallographic method. In the presence of methylalumoxane (MAO) as a cocatalyst, the four complexes synthesized were highly active for the polymerization of ethylene.     

Olefin metathesis featuring ruthenium indenylidene complexes with a sterically demanding NHC ligand

The synthesis and characterization of two new ruthenium indenylidene complexes [RuCl(2)(SIPr)(Py)(Ind)] 6 and [RuCl(2)(SIPr)(3-BrPy)(Ind)] 7 featuring the sterically demanding N-heterocyclic carbene 1,3-bis(2,6-di isopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr) are reported. Remarkable activity was observed with these complexes in ring closing, enyne, and cross metathesis of olefins at low catalyst loadings. The performance of SIPr-bearing complexes 6 and 7 as well as [RuCl(2)(SIPr)(PCy(3))(Ind)] 5 in ring opening metathesis polymerization is also disclosed. This work highlights the enormous influence of the neutral "spectator" ligands on catalyst activity and stability.     

Six-coordinate titanium complexes of a tripodal aminetris(phenoxide) ligand: synthesis, structure, and dynamics

The five-coordinate titanium(IV) alkoxide LTi(O(t)Bu) (LH(3) = tris(2-hydroxy-3,5-di-tert-butylbenzyl)amine) is protonolyzed readily by the conjugate acids of monoanionic bidentate ligands, both symmetrical (tropolone, acetylacetone, di-p-toluoylmethane) and unsymmetrical (8-hydroxyquinoline, salicylaldehyde, 2,6-diformyl-p-cresol, anthrarufin). The geometry of these complexes, which is pseudo-octahedral with the tripodal ligand adopting a chiral, propeller-like conformation, has been confirmed in four cases by X-ray crystallography. Variable-temperature NMR spectroscopy indicates that the six-coordinate complexes undergo two dynamic processes. First, the ligands undergo a twisting motion that results in racemization, a process which is over 10(4) times faster than in five-coordinate complexes. The rate acceleration upon binding of an equatorial ligand is ascribed to steric repulsions with one of the cis phenoxides; the dynamics of a binuclear dibenzyl phosphate-bridged compound, which has a unique conformation of the tripodal ligand, indicates that flexing the cis phenoxide is the rate-limiting step in racemization. Second, the complexes undergo a process that interchanges the inequivalent arms of the tripodal ligand. This process involves a trigonal twist that shifts the bidentate ligand between clefts in the tripod. The intermediate geometry in the reaction appears to be a transition state and not a long-lived intermediate, as judged from the relative rates of interconversion of tripod arms and chelate ends in the ditoluoylmethane complex. Tripod arm interchange takes place without partial dissociation of the bidentate chelate, a reaction that has been observed on a slower time scale in one case.     

Metalloradical complexes of manganese and chromium featuring an oxidatively rearranged ligand

Redox events involving both metal and ligand sites are receiving increased attention since a number of biological processes direct redox equivalents toward functional residues. Metalloradical synthetic analogues remain scarce and require better definition of their mode of formation and subsequent operation. The trisamido-amine ligand [(RNC6H4)3N]3-, where R is the electron-rich 4-t-Bu Ph, is employed in this study to generate redox active residues in manganese and chromium complexes. Solutions of [(L1)Mn(II)-THF]- in THF are oxidized by dioxygen to afford [(L1re-1)Mn(III)-(O)2-Mn(III)(L1 re-1)]2-as the major product. The rare dinuclear manganese (III,III) core is stabilized by a rearranged ligand that has undergone an one-electron oxidative transformation, followed by retention of the oxidation equivalent as a pi radical in ano-diiminobenzosemiquinonate moiety. Magnetic studies indicate that the ligand-centered radical is stabilized by means of extended antiferromagnetic coupling between the S ) 1/2 radical and the adjacent S ) 2 Mn(III) site, as well as between the two Mn(III) centers via the dioxo bridge. Electrochemical and EPR data suggest that this system can store higher levels of oxidation potency. Entry to the corresponding Cr(III) chemistry is achieved by employing CrCl3 to access both[(L1)Cr(III)-THF] and [(L1re-1)Cr(III)-THF(Cl)], featuring the intact and the oxidatively rearranged ligands, respectively. The latter is generated by ligand-centered oxidation of the former compound. The rearranged ligand is perceived to be the product of an one-electron oxidation of the intact ligand to afford a metal-bound aminyl radical that subsequently mediates a radical 1,4-(N-to-N) aryl migration.     

A terminal nickel(II) anilide complex featuring an unsymmetrically substituted amido pincer ligand: synthesis and reactivity

This work describes preparation and reaction chemistry of a terminal nickel(II) anilide complex supported by an unsymmetrically substituted diarylamido diphosphine ligand, [N(o-C(6)H(4)PPh(2))(o-C(6)H(4)P(i)Pr(2))](-) ([Ph-PNP-(i)Pr](-)). Treatment of NiCl(2)(DME) with H[Ph-PNP-(i)Pr] in THF at room temperature produced [Ph-PNP-(i)Pr]NiCl as green crystals in 82% yield. Salt metathesis of [Ph-PNP-(i)Pr]NiCl with LiNHPh(THF) in THF at -35 °C generated cleanly [Ph-PNP-(i)Pr]NiNHPh as a greenish blue solid. The anilide complex deprotonates protic (e.g., PhOH and PhSH) and aprotic (e.g., trimethylsilylacetylene, phenylacetylene, and acetonitrile) acids in benzene at room temperature to give quantitatively [Ph-PNP-(i)Pr]NiX (X = OPh, SPh, C≡CSiMe(3), C≡CPh, CH(2)CN). In addition, [Ph-PNP-(i)Pr]NiNHPh also behaves as a nucleophile to react with acetyl chloride to yield [Ph-PNP-(i)Pr]NiCl and N-phenylacetamide quantitatively. Carbonylation of [Ph-PNP-(i)Pr]NiNHPh with carbon monoxide affords cleanly the carbamoyl derivative [Ph-PNP-(i)Pr]Ni[C(O)NHPh]. The relative bond strengths of Ni-E in [Ph-PNP-(i)Pr]NiEPh (E = NH, O, S, C≡C) are assessed and discussed.     

Synthesis and characterization of three new organotin complexes containing piperazine as a bidentate ligand

The reaction of dichlorostannanes R₂SnCl₂ (R=Me 1, Buⁿ 2) with piperazine ligand in molar ratio 1:2, in dry methylene dichloride, in an inert atmosphere leads to the synthesis of R₂Sn(C₄H₉N₂)₂(R=Me 1, Buⁿ 2). In a similar manner, The reaction between Ph₂SnCl₂ and piperazine in dry ethanol in molar ratio 1:1 produces [Ph₂Sn(C₄H₈N₂)]₂ (3). The yields of these new products were excellent and they have been fully characterized by FT-IR, UV–Vis, multinuclear (¹H, ¹³C, ¹¹⁹Sn) NMR spectroscopy and mass spectrometry, as well as elemental analysis. The spectroscopic results indicate that the piperazine ligand is coordinated to tin atom of organotin moieties, through the nitrogen atoms. Furthermore, the ligand behaves as a bidentate fashion in (1) and (2) and gives 1:2 substitution products, while in the complex (3) the two six-membered rings bind in bidentate-chelate forms between the two Sn atoms.     

Anion-controlled circular dichroism spectral changes in Hg2+ complexes with a chiral bidentate ligand

Anion-controlled circular dichroism (CD) spectral changes in Hg(2+) complexes with a chiral bidentate ligand are reported. Although the Hg(CF(3)SO(3))(2) and Hg(CF(3)CO(2))(2) complexes with (R)-(-)-1-(naphthalen-1-yl)-N,N-bis(pyridin-4-ylmethyl)ethanamine, (R)-(-)-1, show significant CD spectral changes, no CD spectral changes were observed in the HgCl(2), HgBr(2), Hg(CN)(2), or Hg(CH(3)CO(2))(2) complexes. X-ray analysis indicates that both the (R)-(-)-1-Hg(CF(3)SO(3))(2) and (R)-(-)-1-HgCl(2) complexes form a coordination polymer and a discrete 2:3 [=(R)-(-)-1/HgCl(2)] complex with a figure-eight structure. X-ray crystallography revealed that (i) the Hg-Hg distances bridged by anions vary depending on the anions used and (ii) a coordination polymer cannot be formed when the Hg-Hg distances are too short. Therefore, the formation of a coordination polymer is required to give the observed significant CD spectral changes.     

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.     

Rhodium(III) complexes with a bidentate N-heterocyclic carbene ligand bearing flexible dendritic frameworks

Rh(III) complexes with a bidentate N-heterocyclic carbene ligand bearing flexible dendritic frameworks have been synthesized and fully characterized by X-ray crystallographic analysis, NMR measurements and theoretical calculations.     

N-H bond activation by palladium(ii) and copper(i) complexes featuring a reactive bidentate PN-ligand

The first examples of reactivity at the backbone of a bidentate PN-ligand L1H relevant to N-H activation are described, leading to novel Pd(II) and Cu(I) amido complexes. Activation of the PN-ligand backbone led to selective dearomatization of the pyridyl ring structure. In the case of Pd(II), the intermediate could be efficiently stabilized using PMe(3). Selective N-H bond cleavage of e.g. trifluorosulfonylamide resulted in facile formation of mononuclear metal-amido species 2 and 4, which have been crystallographically characterized. Hydrogen-bonding dimerization is observed in these solid state structures. The results obtained with these structurally versatile and reactive scaffolds likely open up new avenues in cooperative catalysis.     

Monomeric monooxomolybdenum(VI) complexes of arylazophenolates with one bidentate arylthiol ligand

Reaction of an excess of 2-aminobenzenethiol or thiosalicylic acid (H2T) with cis-[MoO2L] (H2L=tridentate 2,2-dihydroxyarylazo compound) causes elimination of one oxo ligand to give a monomeric monooxomolybdenum(VI) product [MoOL(T)]. These deep red complexes have been characterized by elemental analyses and spectroscopic techniques.     

Polystyrene anchored rhodium (I) bidentate ligand complexes as catalysts for hydrogenation

Polystyrene supported Rh(I) AA′ (AA′ = anthranilic acid, 2,2′-bipyridine or 1,10-phenanthroline) complexes catalyse the hydrogenation of monoolefins (terminal, cyclic and internal) and dienes. Ethyl sorbate undergoes saturation via the monoene intermediate. Thiscis olefin reacts faster than thetrans isomer. The rate law for the reaction is: Rate α [catalyst] [substrate] [H₂].     

Six-coordinate nitrato complexes of iron(III) porphyrins

The interaction of tetrahydrofuran (THF) with thin films of the nitrato complexes Fe(III)(Por)(eta(2)-O(2)NO) [Por = meso-tetraphenylporphyrinato (TPP) and meso-tetratolylporphyrinato (TTP) dianion] at low temperature leads to the formation of the six-coordinate nitrato complex Fe(Por)(THF)(NO(3)), which was characterized by IR and UV-visible spectroscopies. Formation of the THF adduct was accompanied by nitrate linkage isomerization from bidentate to monodentate coordination. The iron(III) center remains in a high spin state in contrast with the previously observed low-spin nitratonitrosyl complex Fe(TPP)(NO)(eta(10-ONO(2)). Upon warming, THF dissociates to restore the initial five-coordinate bidentate nitrato complex.     

Metallopolymers featuring boratabenzene iron complexes

Boratabenzene-derived metallocene analogues are introduced as versatile new building blocks for metallopolymers. Bis(borinato)iron(II) complexes of the type Fe(C(5)H(5)B-R)(2) (R: C≡CH, C≡CSiMe(3), 4-(1-benzyl-1,2,3-triazolyl) were synthesized and spectroscopically, structurally, and electrochemically characterized. Polymerization via Sonogashira-Hagihara coupling of the alkynyl-substituted derivative Fe(C(5)H(5)B-C≡CH)(2) with 2,5-bis(dodecyloxy)-1,4-diiodobenzene yields a film-forming polymer in 50-69% yield. Polymer batches were obtained with number-average molecular weights (M(n)) of 11.7 and 20.5 kDa and polydispersity indices (PDI) of 1.55 and 2.65, respectively, as determined by gel permeation chromatography relative to polystyrene standards. Click-type polymerization of Fe(C(5)H(5)B-C≡CH)(2) through azide-alkyne cycloaddition with 1,4-bis(4-azidobutoxy)benzene gives the corresponding metallopolymer with an M(n) of 5.7 kDa and a PDI of 2.29 in 87% yield.     

Preparation and structural characterization of transition-metal complexes featuring the cymantrenyl(bromo)boryl ligand

In the present paper, we describe the first structural characterization of cymantrenyl(dihalo)borane and report on its use for the synthesis of novel cymantrenylboryl complexes.     

Synthesis and reactivity of uranium(IV) amide complexes supported by a triamidotriazacyclononane ligand

Reaction of [U{(SiMe2NPh)3-tacn}Cl] with LiNEt2 or LiNPh2 affords the corresponding amide compounds, [U{(SiMe2NPh)3-tacn}(NR2)] (R = Et (1), R = Ph (2)). The complexes have been fully characterized by spectroscopic methods and the solid-state structure of 1 was determined by single-crystal X-ray diffraction analysis. The six nitrogen atoms of the tris(dimethylsilylanilide)triazacyclononane ligand are in a trigonal prismatic configuration with the nitrogen atom of the diethylamide ligand capping one of the trigonal faces of the trigonal prism. Crystallization of 2 from CH3CN solution gave crystals of the six-membered heterocycle [U{(SiMe2NPh)3-tacn}{kappa2-(HNC(Me))2CC[triple bond]N}] (3). The reactivity of the amides was investigated. Both compounds undergo acid-base reactions with protic substrates such as HOC6H2-2,4,6-Me3, 3,5-Me2pzH (pz = pyrazolyl) and HSC5H4N to give the corresponding [U{(SiMe2NPh)3-tacn}X] (X = OC6H2-2,4,6-Me3 (4), 3,5-Me2pzH (5), kappa2-SC5H4N (6)) complexes. The solid-state structures of and were determined by single-crystal X-ray diffraction and revealed that the compounds are eight-coordinate with dodecahedral geometry.     

Cyclooctatetraenide-based single-ion magnets featuring bulky cyclopentadienyl ligand

We report a family of organometallic rare-earth complexes with the general formula (COT)M(Cp^ttt) (where (COT)²⁻ = cyclooctatetraenide, (Cp^ttt)⁻ = 1,2,4-tri(tert-butyl)cyclopentadienide, M = Y(iii), Nd(iii), Dy(iii) and Er(iii)). Similarly to the prototypical Er(iii) analog featuring pentamethylcyclopentadienyl ligand (Cp*)⁻, (COT)Er(Cp^ttt) behaves as a single-ion magnet. However, the introduction of the sterically demanding (Cp^ttt)⁻ imposes geometric constraints that lead to a simplified magnetic relaxation behavior compared to the (Cp*)⁻ containing complexes. Consequently, (COT)Er(Cp^ttt) can be viewed as a model representative of this organometallic single-ion magnet architecture. In addition, we demonstrate that the increased steric profile associated with the (Cp^ttt)⁻ ligand permits preparation, structural characterization and interrogation of magnetic properties of the early-lanthanide complex, (COT)Nd(Cp^ttt). Such a mononuclear derivative could not be obtained when a (Cp*)⁻ ligand was employed, a testament to larger ionic radius of this early lanthanide ion.

Application of steric control principles allows for simplification of the magnetic behavior of an iconic single-ion magnet architecture as well as the preparation of its previously inaccessible representative.