Synthesis, structures, and cytotoxicity insights of organotin(IV) complexes with thiazole-appended pincer ligand.

Diorganotin complexes of the compositions [Me2Sn(L)] (1), [n-Bu2Sn(L)] (2), [Ph2Sn(L)]⋅C6H6 (3), [Bz2Sn(L)]⋅C6H6 (4) and [n-Oct2Sn(L)] (5) were synthesized by reacting R2SnO (R = Me, n-Bu, Ph, Bz or n-Oct) with the N2,N6-di(thiazol-2-yl)pyridine-2,6-dicarboxamide (H2L, where H2 denotes the two acidic protons) in refluxing toluene. Additionally, the mono-n-butyltin complex [n-BuSn(HL)Cl2]·H2O (6) was synthesized from n-BuSnCl3 and H2L in acetonitrile. Compounds were characterized by FT-IR, 1H, 13C and 119Sn NMR spectroscopy, while their solid-state structures were examined using single-crystal X-ray diffraction studies. In diorganotin compounds 1-5, the dianionic tridentate ligands (Npy, N-, N-) act as κ-N3 chelators. In 6, the L moiety (O, Npy, N-) acts as a κ-ON2 tridentate chelator, with involvement of one of the carboxamide oxygen atoms. The coordination polyhedron around the Sn(IV) ion is completed either by two axial Sn-R ligands in compounds 1-5 or by n-Bu and Cl ligands in compound 6, giving rise to distorted trigonal bipyramid or octahedral structures, respectively. The tin NMR results show that the penta-coordinated structures of compounds 1-5 and the hexacoordinated structure of compound 6, observed in the solid-state, are retained in solution. The in vitro antitumor activities of 1-5 were tested on T-47D breast cancer cells. Of these, diphenyltin compound 3 showed the highest anti-proliferative effect, with an IC50 of 10 ± 1.60 µM. Compound 3 exhibited selective toxicity, potentially inducing apoptosis via reactive oxygen species generation and nuclear changes, indicating promise as a breast cancer treatment. This study is the first to explore thiazole-appended organotin compounds for cytotoxicity.

Crystal structures of the (η2:η2-cyclo-octa-1,5-diene)(η6-toluene)-iridium(I) cation and µ-chlorido-iridium(III) complexes of 2-(phosphinito)- and 2-(phosphinometh-yl)anthra-quinone ligands.

When reacted in dry, degassed toluene, [Ir(COD)Cl]2 (COD = cyclo-octa-1,5-diene) and 2 equivalents of 2-(di-tert-butyl-phosphinito)anthra-quinone (tBuPOAQH) were found to form a unique tri-iridium compound consisting of one monoanionic dinuclear tri-µ-chlorido complex bearing one bidentate tBuPOAQ ligand per iridium, which was charge-balanced by an outer sphere [Ir(toluene)(COD)]+ ion, the structure of which has not previously been reported. This product, which is a toluene solvate, namely, (η2:η2-cyclo-octa-1,5-diene)(η6-toluene)-iridium(I) tri-µ-chlorido-bis-({3-[(di-tert-butyl-phosphan-yl)-oxy]-9,10-dioxoanthracen-2-yl}hydridoiridium(III)) toluene monosolvate, [Ir(C7H8)(C8H12)][Ir2H2(C22H24O3P)2Cl3]·C7H8 or [Ir(toluene)(COD)][Ir(κ-P,C-tBuPOAQ)(H)]2(µ-Cl)3]·toluene, formed as small orange platelets at room temperature, crystallizing in the triclinic space group P. The cation and anion are linked via weak C-H⋯O inter-actions. The stronger inter-molecular attractions are likely the offset parallel π-π inter-actions, which occur between the toluene ligands of pairs of inverted cations and between pairs of inverted anthra-quinone moieties, the latter of which are capped by toluene solvate mol-ecules, making for π-stacks of four mol-ecules each. The related ligand, 2-(di-tert-butyl-phosphinometh-yl)-anthra-quinone (tBuPCAQH), did not form crystals suitable for X-ray diffraction under analogous reaction conditions. However, when the reaction was conducted in chloro-form, yellow needles readily formed following addition of 1 atm of carbon monoxide. Diffraction studies revealed a neutral, dinuclear, di-µ-chlorido complex, di-µ-chlorido-bis-(carbon-yl{3-[(di-tert-butyl-phosphan-yl)-oxy]-9,10-dioxoanthracen-2-yl}hydridoiridium(I)), [Ir2H2(C23H26O2P)2Cl2(CO)2] or [Ir(κ-P,C-tBuPCAQ)(H)(CO)(µ-Cl)]2, Ir2C48H54Cl2O6P2, again crystallizing in space group P. Offset parallel π-π inter-actions between anthra-quinone groups of adjacent mol-ecules link the mol-ecules in one dimension.

Transition metal pincer catalysts for formic acid dehydrogenation: a mechanistic perspective.

The storage and transportation of hydrogen gas, a non-polluting alternative to carbon-based fuels, have always been challenging due to its extreme flammability. In this regard, formic acid (FA) is a promising liquid organic hydrogen carrier (LOHC), and over the past decades, significant progress has been made in dehydrogenating FA through transition metal catalysis. In this review, our goal is to provide a detailed insight into the existing processes to expose various mechanistic challenges associated with FA dehydrogenation (FAD). Specifically, methodologies catalyzed by pincer-ligated metal complexes were chosen. Pincer ligands are preferred as they provide structural rigidity to the complexes, making the isolation and analysis of reaction intermediates less challenging and consequently providing a better mechanistic understanding. In this perspective, the catalytic activity of the reported pincer complexes in FAD was overviewed, and more importantly, the catalytic cycles were examined in detail. Further attention was given to the structural modifications, role of additives, reaction medium, and their crucial effects on the outcome.

Loading Lewis Acid/Base Pair on Metal Nanocluster for Catalytic Ugi Reaction.

Constructing structurally robust and catalytically active metal nanoclusters for catalyzing multi-component reactions is an interesting while challenging task. Inspired by Lewis acid and Lewis base catalysis, we realized the combination of both Lewis acid and Lewis base sites on the surface of a stable gold nanocluster Au35Cd2. The catalytic potential of Au35Cd2 in four-component Ugi reaction was explored, demonstrating high activity and exceptional recyclability. In-depth mechanism studies indicate that the catalytic synergy of the Lewis acid/base pair is crucial for the high efficiency of Au35Cd2-catalyzed Ugi reaction. Bearing the stable structure, multiple activation sites and hierarchical chirality, Au35Cd2 is expected to display further interesting catalytic performance such as asymmetric catalysis.

From Simple Probe to Smart Composites: Water-Soluble Pincer Complex With Multi-Stimuli-Responsive Luminescent Behaviors.

Water-soluble smart materials with multi-stimuli-responsiveness and ultra-long room-temperature phosphorescence (RTP) have garnered broad attention. Herein, a water-soluble terpyridine zinc complex (MeO-Tpy-Zn-OAc), featuring a simple donor-π-acceptor (D-π-A) structure is presented, which responds to a variety of stimuli, including changes in solvents, pH, temperature, and the addition of amino acids. Notably, MeO-Tpy-Zn-OAc functions as a fluorescence probe, capable of visually and selectively discriminating aspartate or histidine among other common amino acids in water. Additionally, when incorporated into polyvinyl alcohol (PVA) to form the composite MeO-Tpy-Zn-OAc@PVA, the material exhibits reversible writing, photochromism, and a prolonged RTP with a 14 s afterglow. These unique properties enable the composite to be utilized in potential applications such as secure data encryption and inkless printing.

Anterior Cervical Discectomy and Fusion for the Treatment of Pincer Cervical Spondylotic Myelopathy: A Single-Center Retrospective Study.

BACKGROUND: Anterior and posterior compression of the cervical spinal cord is usually called pincer cervical spondylotic myelopathy (p-CSM), and surgery is generally recommended; however, there is some controversy about the choice of surgical approach because single anterior or posterior surgery cannot effectively relieve contralateral compression, and combined surgery may cause problems related to trauma and effects on cervical spine function. OBJECTIVE: To investigate the feasibility and indications of single anterior cervical discectomy and fusion (ACDF) for the treatment of p-CSM. METHODS: The data of 21 p-CSM patients who were treated with ACDF at a single center from 2019 to 2022 were collected. Neurologic status was evaluated by the Japanese Orthopedic Association scoring system. The radiologic parameters included the percentage of space occupied by the spinal canal, the cervical sagittal Cobb angle, and the cross-sectional area of the spinal cord before and after the operation. Complications and spinal cord compression rates were also observed. Correlations between the decompressive effects and various prognostic factors were statistically analyzed. RESULTS: The mean follow-up period was 24.1 ± 3.55 months. The average Japanese Orthopedic Association score significantly increased, with a mean recovery rate of 65.88 ± 8.97%. The fusion rate was satisfactory. Correlation analysis revealed that the number of operation segments and age were important predictors of decompressive effects. There was no further deterioration of spinal cord function after the operation. CONCLUSIONS: ACDF is an effective method for treating pincer spinal cord compression in terms of neurologic recovery, radiologic parameters, fusion rates, and complications, especially for patients younger than 60 years of age with single operative segments.

Subspine Impingement of the Hip Secondary to Ossified Rectus Femoris Avulsion Injury.

This case report describes the evaluation, surgical intervention, and postoperative outcome of a 36-year-old male patient with chronic left hip pain following a rectus femoris injury which persisted despite conservative management and intra-articular steroid injection. Imaging revealed prominent ossification extending from the anterior inferior iliac spine at the proximal rectus femoris insertional, a femoral cam lesion, and tearing of the superior through anterior labrum, compatible with both subspine and femoroacetabular impingement. Subsequent arthroscopic femoroplasty, acetabuloplasty, labral repair, and excision of rectus femoris ossification provided lasting symptomatic relief. Identification of lesions resulting in subspine impingement is essential in the preoperative work up of patients with hip pain to ensure appropriate surgical management and optimize postoperative outcomes.

Electrocatalytic Hydrogen Generation by Ni-PN3P Pincer Complexes: Role of Phosphorus Substituents in Tuning the Reactivity.

Electrocatalytic hydrogen evolution reaction (eHER) is crucial in addressing the growing global energy demand. Although nickel-pincer-based molecular complexes, varying in donor atoms, were studied previously for eHER, the impact of variations in the substituents attached to the donor atoms was not investigated. Herein, three air-stable R1PN3PR2-based NiII-pincer complexes [R1=R2=Ph2 (7); R1=R2=tBu2 (9); R1= tBu2, R2=Ph2 (10)], varying solely in P-substituents, were studied in acetonitrile. While the redox potentials for NiII/I and NiI/0 couples underwent anodic shifts by ~100 mV upon progressively substituting tert-butyl by phenyl groups on each P-atom, the corresponding eHER reactivity with organic acids (acetic acid,  p-toluenesulfonic acid and trifluoromethanesulfonic acid) of different strengths followed different trends; likely influenced by the pKa of intermediate metal-hydride (M-H) species [pKa(M-H9) > pKa(M-H10) > pKa(M-H7)]. Depending on the acid strength, different oxidation states of the metal were activated to promote eHER. The catalytic rates for 9, 10, and 7 were calculated to be 85 s-1, 77 s-1 and 95 s-1 with Faradaic efficiencies of 88.5 ± 2%, 66.1 ± 1.4%, and 91.7 ± 1.5% respectively, in acetic acid. Electrochemical data supported by theoretical results reinforce a significant electronic influence of the anchoring P-substituents on the activity of these complexes.

High incidence of femoroacetabular impingement deformity in bi-column acetabular fractures.

INTRODUCTION: Dynamic interaction of cam and pincer deformities can result in pathological contact forces in femoroacetabular impingement (FAI) syndrome. Similar deformities were noted during acetabular fracture reconstruction. We hypothesise that the prevalence of FAI deformity is higher in patients sustaining acetabular fractures than in a control group. METHODS: This retrospective radiographic study compared the parameters that define FAI deformity in 100 patients consecutively admitted to a trauma unit with an acetabular fracture and a control group of 100 patients with lateral compression pelvic fracture without acetabular injury. Both underwent identical clinical imaging. Centre-edge angles (CEA) and alpha angles were used to define patients with pincer, cam, or mixed FAI deformity. RESULTS: There were significantly more patients with FAI deformity in the acetabular fracture group than in the control group (71% vs. 18%, p < 0.0001). There were considerably more fractures involving both anterior and posterior acetabular columns in patients with 'pincer' sockets (p = 0.02, OR = 2.95, 95% CI, 1.12-7.78). CONCLUSIONS: There is a high prevalence of cam and pincer deformities in patients with acetabular fractures, particularly bi-column fractures.

Scattering of a Bessel Pincer Light-Sheet Beam on a Charged Particle at Arbitrary Size.

Electromagnetic scattering is a routine tool for rapid, non-contact characterization of particle media. In previous work, the interaction targets of scattering intensity, scattering efficiency, and extinction efficiency of Bessel pincer light-sheet beams were all aimed at dielectric spheres. However, most particles in nature are charged. Considering the boundary condition on a charged sphere, the beam shape coefficients (BSCs) (pmn,qmn) of the charged spherical particle illuminated by a Bessel pincer light-sheet beam are obtained. The extinction, scattering, and absorption efficiencies are derived under the generalized Lorenz-Mie theory (GLMT) framework. This study reveals the significant differences in scattering characteristics of Bessel pincer light-sheet beams on a charged particle compared to traditional beams. The simulations show a few apparent differences in the far-field scattering intensity and efficiencies between charged and natural spheres under the influence of dimensionless size parameters. As dimensionless parameters increase, the difference between the charged and neutral spheres decreases. The effects of refractive index and beam parameters on scattering, extinction, and absorption coefficients are different but tend to converge with increasing dimensionless parameters. When applied to charged spheres with different refractive indices, the scattering, extinction, and absorption efficiencies of Bessel pincer light-sheet beams change with variations in surface charge. However, once the surface charge reaches saturation, these efficiencies become stable. This study is significant for understanding optical manipulation and super-resolution imaging in single-molecule microbiology.

Well-Defined Highly-Coordinated Copper(III) Iodide and Pincer Tris(trifluoromethyl)copper Complexes.

Copper(III) iodide and bromide complexes representing a unique combination of highly-coordinated metal and soft polarizable anions were synthesized and fully characterized, including X-ray crystallography. Ligand substitution in well-defined highly-coordinated copper complex PyCu(CF3)3 with pincer ligands was achieved to give formally octahedral copper(III) complexes.

Bifunctional Ligands: Evaluating the Role of Acidic Protons in the Secondary Coordination Sphere.

To evaluate bifunctional ligand reactivity involving NH acidic sites in the secondary coordination sphere, complexes where the proton has been substituted with a methyl group (NMe) are often investigated. An alternative strategy involves substitution of the NH group for an O. This contribution considers and compares the merits of these approaches; the synthesis and characterization of cationic square-planar Rh carbonyl complexes bearing diprotic bispyrazole pyridine ligand L1, and the bis-methylated pyrazole pyridine ligand L1Me are described. The syntheses and characterization of the novel monoprotic pyrazole isoxazole pyridine ligand L2 and aprotic bisisoxazole pyridine ligand L3, and their corresponding Rh carbonyl complexes are also described. Comparison of the CO stretching frequencies of the four Rh complexes suggest that substitutions of NH with NMe, as well as with O, lead to significant electronic differences. These electronic differences result in different reactivities with respect to ligand addition/substitution of the Rh carbonyl complexes. Overall, the data suggest that electronic differences arising due to the NH substitutions can be significant and should be considered when the NH group is substituted in investigations of the participation of the NH proton in a reaction.

Why Are Some Pnictogen(III) Pincer Complexes Planar and Others Pyramidal?

Geometrically-constrained pnictogen pincer complexes have emerged in recent years as platforms for unique stoichiometric and catalytic chemical transformations. These complexes feature dynamic conformations ranging from fully planar at the pnictogen centre to distorted-pyramidal geometries, as well as variation between phases. Although the valued reactivity of pnictogen pincer complexes is ascribed to their geometries, there is no unified model to explain the observed conformational outcomes across different ligands and pnictogen centres. Here we propose such a model through computational analysis of more than 1300 structures across 64 complexes (16 ligands and 4 heavy pnictogens), explaining the experimental observations and making new predictions. By looking at signatures of bond stability (bond lengths, Wiberg bond indices) and delocalization (NPA charges, Hirshfeld charges), our framework posits a pnictogen-based σ-bonding effect that favours pyramidalization and exists in competition with a ligand-based π-bonding effect that favours planarity. Variations in structure as a function of pnictogen identity, ligand tethering, electronics, and aromaticity can be reconciled with reference to a balance between these two opposing forces. Careful consideration of the σ/π-bonding effects may aid in the rational design of future pnictogen pincer complexes with predictable geometries and reactivities.

Palladium(II) and Platinum(II) Complexes Bearing ONS-Type Pincer Ligands: Synthesis, Characterization and Catalytic Investigations.

This work describes the synthesis of eight new Pd(II) and Pt(II) complexes with the general formula [M(TSC)Cl], where TSC represents the 4N-monosubstituted thiosemicarbazone derived from 2-acetylpyridine N-oxide with the substituents CH3 (H4MLO), C2H5 (H4ELO), phenyl (H4PLO) and (CH3)2 (H4DMLO). These complexes have been characterized by elemental analysis, molar conductivity, IR spectroscopy, 1H, 13C, 195Pt and ESI-MS. The complexes exhibit a square planar geometry around the metallic center coordinated by a thiosemicarbazone molecule acting as a donor ONS-type pincer ligand and by a chloride, as confirmed by the molecular structures of the complexes, [Pd(4ELO)Cl] (3) and [Pd(4PLO)Cl] (5), determined by single-crystal X-ray diffraction. The 195Pt NMR spectra of the complexes of formulae [Pt(4PLO)Cl] (6) and [Pt(4DMLO)Cl] (8) in DMSO show a single signal at -2420.4 ppm, confirming the absence of solvolysis products. Complexes 3 and 5 have been tested as catalysts in the Suzuki-Miyaura cross-coupling reactions of aryl bromides with phenylboronic acid, with yields of between 50 and 90.

Activation of SO2F2 at a Rhodium PNP Pincer Complex: Ligand Supported S-F Bond Cleavage to Generate NSO2F Derivatives.

The κ2-(P,N)-phosphine ligand precursor NH(CH2CH2PCy2)2 can be used for the synthesis of the rhodium(I) complex [Rh(CO){ĸ3-(P,N,P)-Cy2PC2H4NHC2H4PCy2}][Cl] (1). The deprotonated complex [Rh(CO){ĸ3-(P,N,P)-Cy2PC2H4NC2H4PCy2}] (2) shows a cooperative reactivity of the PNP ligand in the activation reaction of SO2F2 to yield the rhodium fluorido complex trans-[Rh(F)(CO){ĸ2-(P,P)-Cy2PC2H4N(SO2F)C2H4PCy2}]2 (3) by S-F bond cleavage. It is remarkable that no reaction was observed when 3 was treated with hydrogen sources e. g. dihydrogen, organosilicon compounds such as triethylsilane or TMS-CF3 and different fluorine sources such as SF4 or Selectfluor®. However, the treatment of complex 3 with XeF2 in the presence of CsF resulted in the formation of the unique fluorido rhodium(III) complex cis,trans-[Rh(F)3(CO){ĸ2-(P,P)-Cy2PC2H4N(SO2F)C2H4PCy2}]2 (4). In the presence of pyridine(HF)X or BF3 the fluorido complex 3 converted into the dicationic complexes [Rh(CO){ĸ2-(P,P)-Cy2PC2H4N(SO2F)C2H4PCy2}]2[XF]2, X=HF (5) or BF3 (6), respectively.

Electrocatalytic Transfer Hydrogenation of 1-Octene with [(tBuPCP)Ir(H)(Cl)] and Water.

Electrocatalytic hydrogenation of 1-octene as non-activated model substrate with neutral water as H-donor is reported, using [(tBuPCP)Ir(H)(Cl)] (1) as the catalyst, to form octane with high faradaic efficiency (FE) of 96 % and a kobs of 87 s-1. Cyclic voltammetry with 1 revealed that two subsequent reductions trigger the elimination of Cl- and afford the highly reactive anionic Ir(I) hydride complex [(tBuPCP)Ir(H)]- (2), a previously merely proposed intermediate for which we now report first experimental data by mass spectrometry. In absence of alkene, the stoichiometric electrolysis of 1 in THF with water selectively affords the Ir(III) dihydride complex [(tBuPCP)Ir(H)2] (3) in 88 % FE from the reaction of 2 with H2O. Complex 3 then hydrogenates the alkene in classical fashion. The presented electro-hydrogenation works with extremely high FE, because the iridium hydrides are water stable, which prevents H2 formation. Even in strongly alkaline conditions (Bu4NOH added), the electro-hydrogenation of 1-octene with 1 also proceeds cleanly (89 % FE), suggesting a highly robust process that may rely on H2O activation, reminiscent to transfer hydrogenation pathways, instead of classical H+ reduction. DFT calculations confirmed oxidative addition of H2O as a key step in this context.

Synthesis, characterization and structural analysis of complexes from 2,2':6',2''-terpyridine derivatives with transition metals.

The synthesis and structural characterization of three families of coordination complexes synthesized from 4'-phenyl-2,2':6',2''-terpyridine (8, Ph-TPY), 4'-(4-chlorophenyl)-2,2':6',2''-terpyridine (9, ClPh-TPY) and 4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine (10, MeOPh-TPY) ligands with the divalent metals Co2+, Fe2+, Mn2+ and Ni2+ are reported. The compounds were synthesized from a 1:2 mixture of the metal and ligand, resulting in a series of complexes with the general formula [M(R-TPY)2](ClO4)2 (where M = Co2+, Fe2+, Mn2+ and Ni2+, and R-TPY = Ph-TPY, ClPh-TPY and MeOPh-TPY). The general formula and structural and supramolecular features were determinated by single-crystal X-ray diffraction for bis(4'-phenyl-2,2':6',2''-terpyridine)nickel(II) bis(perchlorate), [Ni(C21H15N3)2](ClO4)2 or [Ni(Ph-TPY)2](ClO4)2, bis[4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine]manganese(II) bis(perchlorate), [Mn(C22H17N3O)2](ClO4)2 or [Mn(MeOPh-TPY)2](ClO4)2, and bis(4'-phenyl-2,2':6',2''-terpyridine)manganese(II) bis(perchlorate), [Mn(C21H15N3)2](ClO4)2 or [Mn(Ph-TPY)2](ClO4)2. In all three cases, the complexes present distorted octahedral coordination polyhedra and the crystal packing is determined mainly by weak C-H...π interactions. All the compounds (except for the Ni derivatives, for which FT-IR, UV-Vis and thermal analysis are reported) were fully characterized by spectroscopic (FT-IR, UV-Vis and NMR spectroscopy) and thermal (TGA-DSC, thermogravimetric analysis-differential scanning calorimetry) methods.

Addition of Imidazolium-Based Ionic Liquid to Improve Methanol Production in Polyamine-Assisted CO2 Capture and Conversion Systems Using Pincer Catalysts.

Ionic liquids have been studied as CO2 capture agents. However, they are rarely used in combined CO2 capture and conversion processes. Utilizing imidazolium-based ionic liquids, the conversion of CO2 to methanol was greatly improved in polyamine assisted systems catalyzed by homogeneous pincer catalysts with Ru and Mn metal centers. Among the ionic liquids tested, [BMIM]OAc was found to perform the best under the given reaction conditions. Among the polyamine tested, pentaethylenehexamine (PEHA) led to the highest conversion rates. Ru-Macho and Ru-Macho-BH were the most active catalysts. Direct air capture utilizing PEHA as the capture material was also demonstrated and produced an 86 % conversion of the captured CO2 to methanol in the presence of [BMIM]OAc.

New Pyridine Dicarbene Pincer Ligands with Ring Expanded NHCs and their Nickel and Chromium Complexes.

The pincer complexes [NiIIBr(CNC)]Br (4), [CrIIIBr3(CNC)] (5 a) and [CrIIIBr2.3Cl0.7(CNC)] (5 b), where CNC=3,3'-(pyridine-2,6-diyl)bis(1-mesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene), were obtained from the novel ligand CNC, generated in situ from the precursor (CHNCH)Br2 and [NiIIBr2(PPh3)2] or from [CrII{N(SiMe3)2}2(THF)2] and (CHNCH)Br2 by aminolysis, respectively. The tetrahedrally distorted square planar (τ4≅0.30) geometry and the singlet ground state of Ni in 4 were attributed to steric constraints of the CNC backbone. Computational methods highlighted the dependence of the coordination geometry and the singlet-triplet energy difference on the size of the N-substituent of the tetrahydropyrimidine wingtips and contrasted it to the situation in 5-membered imidazolin-2-ylidene pincer analogues. The octahedral CrIII metal center in 5 a and 5 b is presumably formed after one electron oxidation from CH2Cl2. 4/MAO and 5 a/MAO were catalysts of moderate activity for the oligomerization and polymerization of ethylene, respectively. The analogous (CH^N^CH)Br2 precursor, where (CH^N^CH)=3,3'-(pyridine-2,6-diylbis(methylene))bis(1-mesityl-3,4,5,6-tetrahydropyrimidin-1-ium), was also prepared, however its coordination chemistry was not studied due to the inherent instability of the resulting free C^N^C ligand.

Understanding the Remarkable Stability of Well-Defined Dinuclear Copper(I) Carbene Complexes.

The synthesis of a well-defined dicopper carbene complex supported by the PNNP (2,7-bis(di-tert-butylphosphaneyl)methyl-1,8-naphthyridine) expanded pincer ligand is reported. This carbene complex is remarkably stable, even in the presence of air and water. The reactivity of this complex was explored towards typical carbene transfer substrates and its electronic structure was investigated. Using a combination of experiments and DFT calculations, the principles that underly the stability of dinuclear carbene complexes are probed.