Synthesis, characterization of some organolanthanide complexes containing 2-pyridylmethyl substituted fluorenyl ligand and catalytic activity of organolanthanide(II) complexes

A series of organolanthanide complexes with 2-pyridylmethyl substituted fluorenyl ligand were synthesized via reaction of [(Me₃Si)₂N]₃Ln^III(μ-Cl)Li(THF)₃ (Ln = Yb, Eu, Nd, Y) with the functionalized fluorene compound. Treatment of [(Me₃Si)₂N]₃Ln^III(μ-Cl)Li(THF)₃ (Ln = Yb, Eu) with 2 equiv. of C₅H₄NCH₂C₁₃H₉ (1) at 60-80 °C in toluene afforded the corresponding organolanthanide(II) complexes with formula [η⁵:η¹- C₅H₄NCH₂C₁₃H₈]₂Ln [Ln = Yb (2), Eu (3)] via tandem silylamine elimination/homolysis of the Ln-N bond reaction. Reaction of [(Me₃Si)₂N]₃Ln^III(μ-Cl)Li(THF)₃ (Ln = Y, Nd) with 2 equiv. of C₅H₄NCH₂C₁₃H₉ in toluene at 80 °C produced the corresponding organolanthanide(III) complexes with formula [η⁵:η¹-C₅H₄NCH₂C₁₃H₈]₂LnCl [Ln = Y (4), Nd (5)]. Complexes 4 and 5 could also be prepared by treatment of 2 equiv. of lithium fluorenide [η⁵:η¹-C₅H₄NCH₂C₁₃H₈]Li(THF)₂ (6) with corresponding LnCl₃. All compounds were fully characterized by spectroscopic methods and elemental analyses. The structures of complexes 4 and 6 were additionally determined by single-crystal X-ray analyses. The catalytic properties of the divalent organolanthanide complexes 2 and 3 on the ring-opening polymerization of ε-caprolactone (CL) have been studied. The temperatures, solvents effects on the catalytic activities of the complexes were examined.     

Synthesis, characterization and ethylene polymerization activity of titanium aminopyridinato complexes

Three titanium complexes derived from 2-(2,6-difluoroanilino)pyridine and 2-(2-chloroanilino)pyridine were synthesized and characterized by X-ray diffraction or spectroscopic methods. All titanium complexes have been used to catalyze the polymerization of ethylene in the presence of MAO as cocatalyst. The mono(2,6-difluorophenylaminopyridinato) titanium catalyst was found to be more active in ethylene polymerization than the bis(2,6-difluorophenylaminopyridinato) and bis(2-chlorophenylaminopyridinato) titanium catalysts. ortho-Halogens disturbed the β-elimination transition state of ethylene polymerization and formed higher molar mass polyethylene than their unhalogenated congener. Due to fluxionality, the bis(2-chlorophenylaminopyridinato) titanium catalyst formed broader molar mass distribution than the bis(2,6-difluorophenylaminopyridinato) titanium catalysts.     

Synthesis and characterization of divalent metal complexes containing the heteroscorpionate ligand dihydrobis(3-carboxyethyl-5-methylpyrazolyl)borate

The dihydrobis(3-carboxyethyl-5-methylpyrazolyl)borate ligand, Bp^COOET,Me, reacts with divalent metals to yield complexes of general type [(Bp^COOET,Me)₂M], where M = Mn(II), Fe(II), Co(II), Ni(II), Zn(II), Cu(II), Pb(II) and Cd(II). All complexes have been fully characterized by elemental analyses and FT-IR in the solid state and by NMR (¹H and ¹¹³Cd NMR) spectroscopy and electrospray ionization mass spectrometry in solution. A single crystal structural characterization is reported for [Cu(Bp^COOET,Me)₂] and [Zn(Bp^COOET,Me)₂]. In the two complexes, both metals are four-coordinated and they are only bound to the nitrogen atoms of the bis(pyrazolyl)borate ligand; however, while the environment of the copper atom is square planar, that of the zinc center shows a tetrahedral distorted conformation.     

Hafnium chloride and hafnium methyl complexes bearing substituted pyrrolyl ligands: synthesis, characterization, and ethylene polymerization

Reactions of HfCl₄ with 2 and 3 equiv. of Li[C₄H₃N(CH₂NMe₂)-2] in toluene afford HfCl₂[C₄H₃N(CH₂NMe₂)-2]₂ (1) and HfCl[C₄H₃N(CH₂NMe₂)-2]₃ (2), respectively. Transmetallation reaction of 1 with 2 equiv. of MeLi results in a hafnium dimethyl compound HfMe₂[C₄H₃N(CH₂NMe₂)-2]₂ (3). A variable-temperature ¹H NMR spectroscopic study shows that the activation energy for the dissociation/association of the NMe₂ units of compound 2 in solution is ca. 13.6 kcal/mol. Compounds 1-3 are characterized by NMR spectroscopy and single crystal X-ray diffraction. A polymerization study shows that compounds 1 and 3 exhibit moderate activity toward ethylene in the presence of TIBA and MAO.     

Synthesis and characterization of yttrium complexes bearing a bulky arylamido ancillary ligand

Reaction of anhydrous YCl₃ with 1 equiv. of arylamido lithium 2,6-ⁱPr₂C₆H₃NSiⁱPr₃Li in THF gave an anionic mono-arylamido-ligated yttrium dichloride complex {[2,6-ⁱPr₂C₆H₃NSiⁱPr₃]YCl₂(THF)}₂[LiCl(THF)₂] (1). Alkylation of 1 with 4 equiv. of LiCH₂SiMe₃ afforded an anionic arylamido-ligated yttrium tris(alkyl) complex [2,6-ⁱPr₂C₆H₃NSiⁱPr₃]Y(CH₂SiMe₃)₃Li(THF)₂ (2). Both complexes were characterized by NMR, elementary analysis, and X-ray structural determination.     

Synthesis and spectroscopic investigations of four-coordinate nickel complexes supported by a strongly donating scorpionate ligand

Two four-coordinate nickel complexes, HB(^tBuIm)₃NiBr and HB(^tBuIm)₃NiNO, were prepared by reaction of a bulky tris(carbene)borate ligand with NiBr₂(PPh₃)₂ and NiBr(NO)(PPh₃)₂, respectively, and structurally and spectroscopically characterized. In addition to standard techniques, high-frequency and -field electron paramagnetic resonance (HFEPR) was employed to understand the spin triplet (S = 1) ground state of the bromo complex. HFEPR, combined with electronic absorption spectroscopy allows comparison of this novel complex with other paramagnetic four-coordinate Ni(II) species. The tris(carbene)borate ligand is a stronger σ-donor than corresponding tris(pyrazolyl)borates (traditional “scorpionate” ligands). The tris(carbene)borate ligand may also act as a π-acceptor, in contrast to tris(pyrazolyl)borates, which show relatively little π-bonding interactions. The influence of tris(carbene)borate substituents on the donor strength of the ligand have been elucidated from IR spectroscopic investigations of {NiNO}¹⁰ derivatives. HFEPR spectra of HB(^tBuIm)₃NiBr exhibit hyperfine coupling from Br, which indicates the strong electronic interaction between Ni(II) and this halide ligand, consistent with studies on tris(pyrazolyl)borate Ni(II) complexes.     

Synthesis and characterization of heteroscorpionate dioxo-tungsten(VI) complexes

Twelve new dioxo W(VI) complexes of a family of heteroscorpionate ligands of the type [(L)WO₂Y], where L = N₂X ligand and Y = Cl or OR, have been synthesized and characterized. With the more sterically bulky ligands we show that these complexes exist as isolable cis and trans isomers and compare the rate of such isomerization with their corresponding dioxo Mo(VI) analogs.     

Reactivity of a new family of diamido-diamine cyclam-based zirconium complexes in ethylene polymerization

Compounds of general formula [(^∗Bn₂Cyclam)ZrCl₂] (^∗Bn = 4-^tBuC₆H₄CH₂, (4) and 4-CF₃C₆H₄CH₂, (5)) were synthesised using Zr(CH₂SiMe₃)₂Cl₂(Et₂O)₂ and the corresponding ligand precursors 1,8-(4-^tbutylbenzyl)-1,4,8,11-tetraazacyclotetradecane (H₂(4-^tBuBn)₂Cyclam), (4a), and 1,8-(4-trifluoromethylbenzyl)-1,4,8,11-tetraazacyclotetradecane (H₂(4-CF₃Bn)₂Cyclam), (5a). Complexes 4 and 5, in addition to other [(^∗Bn₂Cyclam)ZrCl₂] compounds previously described by some of us (^∗Bn = PhCH₂, (1), 3,5-Me₂C₆H₃CH₂, (2) and 3,5-^tBu₂C₆H₃CH₂, (3)) were tested in the polymerization of ethylene in the presence of MAO. System 4/MAO presents the highest activity (2790 g PE molZr⁻¹ h⁻¹ atm⁻¹). The polymers formed are slight to moderately branched polyethylenes with a percentage of branching ranging between 1.2% and 3.3%. The melting points obtained by differential scanning calorimetry (DSC) ranging from 128 to 140 °C, are consistent with rather high average molecular weight polymers with crystallinity close to 50%.     

Neutral and cationic rare-earth metal alkyl complexes that contain bis(2-methoxyethyl)(trimethylsilyl)amine, a neutral [ONO]-type ligand

Neutral tris(trimethylsilylmethyl) complexes [Ln(CH₂SiMe₃)₃(L)] (Ln = Sc (1), Lu (2)) and cationic bis(trimethylsilylmethyl) complexes [Ln(CH₂SiMe₃)₂(L)(THF)]⁺[BPh₄]⁻, (Ln = Sc (3), Lu (4)) that contain bis(2-methoxyethyl)(trimethylsilyl)amine (L = Me₃SiN(CH₂CH₂OMe)₂) as a neutral, tridentate ligand were synthesized and characterized by NMR spectroscopy. X-ray structural analysis was performed for the scandium complex 1 and exhibited a distorted octahedral coordination geometry with a facially arranged ligand at the neutral scandium center. NMR spectroscopy corroborated the coordination of the tertiary amine function of the ligand to the metal. Complexes 3 and 4 expand the still limited range of cationic rare-earth metal alkyl complexes with known neutral, multidentate ligands.     

Synthesis, characterization and emission properties of yttrium(III) and europium(III) complexes of a tripodal heptadentate Schiff-base ligand N[CH2CH2NCH(2-OH-3-MeC6H3)]3

The preparation and characterization of yttrium(III) and europium(III) complexes of tripodal heptadentate Schiff-base ligand N[CH₂CH₂NCH(2-OH-3-MeC₆H₃)]₃ (H₃L¹) have been studied. These complexes were prepared by the reaction of tris(2-aminoethyl)amine with 3-methylsalicylaldehyde in presence of M(CF₃SO₃)₃ (M = Y, Eu) in methanol. The molecular structures of [YL¹] (1) and [EuL¹] (2) were determined by X-ray crystallography. The crystal structure analysis revealed that the Schiff-base behaves as a tri-deprotonated heptadentate ligand encapsulating the metal ion within the N₄O₃ cavity. Under the excitation of UV light, the solid state of these complexes exhibited blue and red emission, respectively. The optical properties of 1 and 2 in solution and in the solid state were examined.     

Palladium(II) complexes bearing a salicylaldiminato ligand with a hydroxyl group: Synthesis, structures, deprotonation, and catalysis

Palladium complexes with a salicylaldiminato ligand bearing a hydroxyl group (1a and 1b) have been synthesized and characterized. The structures of these complexes were confirmed by X-ray crystallography. A reversible deprotonation/protonation of the hydroxyl moiety on 1b was observed, while such behaviour was impossible with a related palladium complex (1c) bearing a methoxyl group in place of the hydroxyl group. The deprotonation affected its catalytic behaviour: the activity for polymerization of methyl acrylate catalyzed by 1b considerably decreased in the presence of 1 equiv. of ^tBuOK.     

Nickel(II) complexes bearing pyrazolylimine ligands: Synthesis, characterization, and catalytic properties for ethylene oligomerization

Four phenyl-substituted pyrazolylimine ligands 2-(C₃HN₂Me₂-3,5)(C(Ph)N(4-R₂C₆H₂(R₁)₂-2,6)) (L1: R₁ = ⁱPr, R₂ = H; L2: R₁ = H, R₂ = NO₂; L3: R₁ = R₂ = H; L4: R₁ = H, R₂ = OCH₃) were synthesized. The influences of steric bulk and electronic effect of pyrazolylimine ligands on the structures of their corresponding nickel complexes were investigated. Ligands with more bulky and electron withdrawing substituents on N-phenyl ring produced four-coordinate nickel complexes (2-(C₃HN₂Me₂-3,5))(C(Ph)(4-R₂C₆H₂(R₁)₂-2,6)NiBr₂ (1, R₁ = ⁱPr, R₂ = H; 2, R₁ = H, R₂ = NO₂)), whereas the ligands with less bulky and electron donating substituents on N-phenyl ring formed bis-pyrazolylimine dinickel tetrahalides (bis-2-(C₃HN₂Me₂-3,5))(C(Ph)N(4-R₂C₆H₂ (R₁)₂-2,6)Ni₂Br₄ (3, R₁ = R₂ = H; 4, R₁ = H, R₂ = OCH₃)) and six-coordinate nickel dihalides (bis-2-(C₃HN₂Me₂-3,5))(C(Ph)N(4-R₂C₆H₂(R₁)₂-2,6) NiBr₂ (5, R₁ = R₂ = H;6, R₁ = H, R₂ = OCH₃)). The solid-state structures of complexes 1, 4 and 5 have been confirmed by X-ray single-crystal analyses. Activated by methylaluminoxane (MAO), complexes 1, 2, 5 and 6 showed moderate to high activity for ethylene oligomerization, and complex 5 revealed the highest activity up to 8.96 × 10⁵ g oligomer/(mol Ni · h). The proportions of resultant oligomers were mainly C4-C8 and a little C10-C14 determined by gas chromatography/mass spectrometry.     

Mixed-ligand thiosemicarbazone complexes of nickel: Synthesis, structure and catalytic activity

Reaction of thiosemicarbazones of salicylaldehyde, 2-hydroxyacetophenone and 2-hydroxynaphthaldehyde with Ni(ClO₄)₂·6H₂O, using 2,2′-bipyridine as coligand, afforded three dinuclear complexes (1a, 1b and 1c). Similar reactions using 2,2′:6′2″-terpyridine as coligand yielded three mononuclear complexes (2a, 2b and 2c). Crystal structures of 1b and 2a have been determined. In the dinuclear complexes, one nickel center is surrounded octahedrally by a dianionic O,N,S-donor thiosemicarbazone, a bipyridine and the bridging phenolate oxygen of the other thiosemicarbazone. The second nickel center adopts a square-planar geometry created by the second O,N,S-coordinated thiosemicarbazone and the bridging sulfur of the first thiosemicarbazone. In the mononuclear complexes nickel is complexed by a monoanionic O,N,S-coordinated thiosemicarbazone and a terpyridine, and the cationic species are isolated as perchlorate salts. All these six complexes are paramagnetic (μ_eff = 2.63-2.92 B.M.) and in dimethylsulfoxide solution they show intense absorptions in the visible and ultraviolet region, origin of which has been probed through DFT calculations. Cyclic voltammetry on the complexes shows one irreversible oxidation of coordinated thiosemicarbazone on the positive side of SCE, and one irreversible reduction of the coordinated polypyridine ligand on the negative side. These nickel complexes are found to be efficient catalysts for Suzuki cross-coupling reactions.     

Synthesis and anticancer activity of [2-hydroxy-1,3-diaminopropane-kappa 2N,N'] platinum(II) complexes

A series of novel platinum(II) complexes involving a carrier with HO- peripheral functional group, 2-hydroxy-1,3-propanediamine (HO-pda), cis-[Pt(HO-dpa)X₂] (X₂ = 2Cl⁻ (1), (2), malonate (3), 1,1-cyclobutane dicarboxylate (CBDCA) (4), 3-hydroxy-1,1-cyclobutanedicarboxylate (HO-CBDCA) (5)), have been synthesized and characterized by elemental analysis and spectroscopic data along with X-ray diffraction for three representative complexes 1, 4 and 5. The Pt(II) is in a square planar environment and is coordinated in cis position by a chelating HO-pda and 2Cl⁻ for 1 and CBDCA for 4 and 5. Pt-N, Pt-Cl and Pt-O distances and coordinate bond angles of N-Pt-N, Cl-Pt-Cl and O-Pt-O are in the normal range. There are two independent molecules in the asymmetric unit of 5, held together by intermolecular hydrogen bonded chain. All the complexes show significant cytotoxicity on the sensitive cell lines SGC-7901, LNcap and A549, and are more active than carboplatin. 4 is also found to be active against the resistant cell A549/ATCC, which suggests that it has less cross-resistance with cisplatin than carboplatin. Moreover 4 shows much greater inhibition of tumor growth than carboplatin in S180-bearing mice, and is therefore worthy of further development as a potential anti-tumor platinum drug.     

Syntheses and characterization of iridium and rhodium ethylene complexes containing a doubly linked cyclopentadienyl ligand

The dimerization of 6,6-dimethylfulvene with Ni(cod)₂ yields the 4,4,8,8-tetramethyl-3a,4,7a,8-tetrahydro-s-indacene isomer (1a). Heating a solution of 1a converts it to the 1,4,5,8 (1b) and 1,4,7,8 (1c) tetrahydro-s-indacene isomers. The activation energy for the isomerization is 23(1) kcal/mol. 1b and 1c can be deprotonated with n-BuLi and the reaction of the dianion with [ClIr(C₂H₄)₂]₂ gives two isomers, cis-[(η⁵-C₅H₃)(CMe₂)Ir(C₂H₄)₂]₂ (cis-2) and trans-[(η⁵-C₅H₃)(CMe₂)Ir(C₂H₄)₂]₂ (trans-2). Reaction of 1b and 1c with RhCl₃ · xH₂O in refluxing methanol yields a red-orange solid, which was consistent with the empirical formula, [(C₅H₃)(CMe₂)RhCl₂]_n (3). Reaction of 3 with C₂H₄ in a Na₂CO₃/ethanol mixture afforded cis-[(η⁵-C₅H₃)(CMe₂)Rh(C₂H₄)₂]₂ in 5% yield.     

Bioinspired FeIIICdII and FeIIIHgII complexes: synthesis, characterization and promiscuous catalytic activity evaluation

In this work we report on the synthesis, crystal structure, and physicochemical characterization of the novel dinuclear [Fe^IIICd^II(L)(μ-OAc)₂]ClO₄·0.5H₂O (1) complex containing the unsymmetrical ligand H₂L = 2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol. Also, with this ligand, the tetranuclear [Fe₂^IIIHg₂^II(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) and [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) complexes were synthesized and fully characterized. It is demonstrated that the precursor [Fe^III₂Hg^II₂(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) can be converted to (3) by the fixation of atmospheric CO₂ since the crystal structure of the tetranuclear organometallic complex [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) with an unprecedented {Fe^III(μ-O_phenoxo)₂(μ-CO₃)Fe^III} core was obtained through X-ray crystallography. In the reaction 2 → 3 a nucleophilic attack of a Fe^III-bound hydroxo group on the CO₂ molecule is proposed. In addition, it is also demonstrated that complex (3) can regenerate complex (2) in aqueous/MeOH/NaOH solution. Magnetochemical studies reveal that the Fe^III centers in 3 are antiferromagnetically coupled (J = − 7.2 cm^− 1) and that the Fe^III-OR-Fe^III angle has no noticeable influence in the exchange coupling. Phosphatase-like activity studies in the hydrolysis of the model substrate bis(2,4-dinitrophenyl) phosphate (2,4-bdnpp) by 1 and 2 show Michaelis-Menten behavior with 1 being ~ 2.5 times more active than 2. In combination with k_H/k_D isotope effects, the kinetic studies suggest a mechanism in which a terminal Fe^III-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst for 1 and 2. Based on the crystal structures of 1 and 3, it is assumed that the relatively long Fe^III…Hg^II distance could be responsible for the lower catalytic effectiveness of 2.     

Preparation, characterization, and catalytic properties of (triphenylphosphine)ruthenium complexes bearing N,O,N′-tridentate ligands

Preparation and characterization of (triphenylphosphine)ruthenium complexes bearing N,O,N′-tridentate ligands, [(L₁)RuCl(PPh₃)₂](BF₄) (L₁ = 2-[(2-pyridylmethoxy)methyl]pyridine), 1), [(L₂)RuCl(PPh₃)₂](BF₄) (L₂ = 8-(2-pyridylmethoxy)quinoline, 2) and [(L₃)RuCl₂(PPh₃)] (L₃ = 2-[(2-pyridylmethoxy)methyl]quinoline, 3) are described. Complexes 1-3 have been characterized by NMR and elemental analyses. Molecular structures of 2 and 3 have been determined by X-ray crystallography. Both compounds exhibit the octahedral geometry. L₂ adopts the facial configuration in 2 while L₃ is in a mer-arrangement in 3. Complexes 1-3 have proven to be able to catalyze the transfer hydrogenation of several ketones to alcohols in the presence of KOH and 2-propanol at refluxing, among which complex 3 was found to be the most active.     

Electronic and steric effects in cobalt Schiff bases complexes: Synthesis, characterization and catalytic activity of some cobalt(II) tetra-halogens-dimethyl salen complexes

The synthesis, characterization and catalytic activity of a series of tetra-halogeno-dimethyl salen cobalt (II) complexes are reported in this paper. The investigated complexes of cobalt (II) with Schiff bases are: αα′-di-methyl Salen cobalt (II) [Co(dMeSalen)], 3,3′,5,5′-tetra chloro α,α′-di-methyl Salen cobalt (II), [Co(tCldMeSalen)], 3,3′-di-bromo 5,5′-di-chloro α,α′-di-methyl Salen cobalt (II), [Co(tBrdMeSalen)], 3,3′,5,5′-tetra bromo α,α′-di-methyl Salen cobalt (II), [Co(tBrdMeSalen)] and 3,3′,5,5′-tetra iodo α,α′-di-methyl Salen cobalt (II), [Co(tIdMeSalen)] (where Salen is bis(salicylaldehyde)ethylenediamine). The characterization of the complexes was performed by elemental analysis, cyclic voltammetry, UV-Vis, IR and EPR spectroscopies. The study was made in DMF, and pyridine was used for coordination as axial base. The redox potential is influenced by the substituent grafted on aromatic ring and in the azomethynic position and also by the molecules coordinating in axial position (solvent, DMF, or pyridine). The catalytic oxygenation of 2,6-di-tert-butylphenol by these complexes leads to the obtention of benzoquinone and diphenoquinone products. The cobalt (II) complexes form reversible adducts with molecular oxygen.     

Synthesis, structural characterization and electrochemical activity of oxidovanadium(IV/V) complexes of a diprotic ONS chelating ligand

The present work reports the chemistry of a few oxidovanadium(IV) and (V) complexes of the ONS chelating ligand S-benzyl-β-N-(2-hydroxyphenylethylidine) dithiocarbazate (H₂L). Major objective of this work is to arrive at some general conclusions about the influence of binding environment generated by the replacement of an O-donor center by a S-donor point in a ligand (of a similar arrangement of the other O- and N-donor points) on the redox behavior and on the structural features of comparable [VO(OEt)(ONS)] and [VO(OEt)(ONO)] complexes. Synthesis, characterization by various physicochemical techniques (UV-Vis, IR, EPR and elemental analysis), exploration of electrochemical activity of the oxidovanadium(V) complex [V^VO(OEt)L] (1), the mixed ligand complex [V^VO(N-O)L] (3) (where N-O is the mono anion of 8-hydroxyquinoline) and a binuclear complex [V^VO(OEt)L]₂(μ-4,4′-bipy) (2) are reported. Similar studies on of mixed ligand oxidovanadium(IV) complexes of the formula [V^VO(N-N)L] (4,5) (where N-N = 2,2′-bipy and o-phen) are also presented here. The [V^VO(OEt)L] complex is pentacoordinated and distorted square pyramidal, while the [V^IV(N-N)L] complexes are hexacoordinated and octahedral. Structural features of the complex 1 were compared with the corresponding aspects of the previously reported analogous complex [V^VO(OEt)(ONO)] (1′).     

Synthesis, structural characterization and catalytic activity of a palladium(II) complex bearing a new ditopic thiophene-N-heterocyclic carbene ligand

A new thiophene-functionalized benzimidazolium salt (2) has been prepared by reacting N-methylbenzimidazole with 2-bromomethylthiophene (1), which in turn was obtained by bromination of 2-thiophenemethanol with PBr₃. Subsequent reaction of salt 2 with Pd(OAc)₂ afforded the cis-configured bis(carbene) Pd(II) complex (cis-3), which in solution exists as an inseparable mixture of cis-anti and cis-syn-rotamers in a 3.5:1 ratio. All new compounds have been fully characterized by spectroscopic and spectrometric methods. A preliminary catalytic study shows that cis-3 is highly active in the Suzuki-Miyaura coupling of aryl bromides with phenylboronic acid in/on water as environmentally benign reaction media.