Electron-donating Ligands Research Articles

Low pKa Phosphido-Boranes Capture Carbon Dioxide with Exceptional Strength: DFT Predictions Followed by Experimental Validation.

We have developed a class of phosphido-boranes (BoPh's) with formula X+[R2PBH3-] that bind CO2 with exceptional strength (ΔG = -8.2 to -24.0 kcal/mol) at ambient conditions. We use quantum mechanics (QM) to determine how the choice of electron-donating versus electron-withdrawing ligand impacts the CO2 binding strength, in the presence of a donating borane moiety. We also examine the role of the cation in CO2 binding, finding that the ion position relative to the bound CO2 dramatically alters binding strength. We find that the BoPh with two ethyl ligands Li[Et2PBH3] leads to ΔG = -24.0 kcal/mol upon CO2 binding while Li[Ph2PBH3] leads to ΔG = -12.8 kcal/mol. We synthesized the BoPh with two phenyl ligands Li[Ph2PBH3] to validate the QM-predicted stability and predicted pKa.

Gold(I) Catalysis in Alkyne-Alkene Reactions: A Systematic Exploration through Molecular Electrostatic Potential Analysis.

Gold catalysis enables selective chemical transformations with catalytic activity tunable through ligand selection. This study uses the density functional theory (DFT) to explore the impact of phosphine ligands (PR3) on gold(I)-catalyzed alkyne-alkene cyclobutene formation. We analyze the following key steps: (i) PR3-Au+ complexation, (ii) alkyne binding, (iii) alkene binding, (iv) C-C coupling transition state, (v) cyclobutene formation transition state, and (vi) cyclobutene dissociation. Molecular electrostatic potential (MESP) analysis provided a deeper understanding of electronic effects and revealed a strong correlation between the change in MESP at the gold nucleus (ΔNVAu+) upon complex formation with various ligands and the corresponding complexation energy, as well as between the change in MESP at the alkyne carbon (ΔVC) and the C-C coupling step activation barrier. This establishes MESP as a powerful tool for understanding ligand influence on catalysis. Our findings suggest that electron-donating phosphine ligands, combined with electron-withdrawing alkyne substituents, enhance catalyst turnover, promote cyclobutene product dissociation from the gold(I) complex, and facilitate catalyst regeneration. Solvent effects also play a crucial role. Bulky XPhos, JohnPhos, and CyJohnPhos ligands enhance gold(I) catalysis via steric protection, electron donation, and catalyst regeneration efficiency. In conclusion, this study provides insights into ligand effects in gold(I)-catalyzed cyclobutene formation, guiding future catalyst design.

Boryloxy Titanium Complex-Enabled High Polar Monomer Contents in Catalytic Copolymerization of Olefins.

The preparation of polyolefins with high polar monomer contents (above 20 mol %) has long been a challenge. Half-titanocenes (Cp')[HC(Ar)N]2BOTiCl2 bearing bulky electron-donating N-heterocyclic boryloxy ligands have been designed and synthesized. The complexes (Cp*)[HC(Ar)N]2BOTiCl2 (2, Ar = 2,6-iPr2C6H3; 5, Ar = 2,4,6-Me3C6H2) supported by Cp* and the bulky boryloxy ligands have been shown to efficiently catalyze the copolymerization of ethylene with long chain α-olefins. In particular, precatalyst 5 enabled the controlled synthesis of poly(ethylene-co-9-decen-1-ol) with unprecedented high polar monomer contents up to 32.1 mol% while maintaining high catalytic activity. The structural analysis and DFT calculations disclosed that the bulky and strong electron-donating boryloxy ligands could effectively stabilize cationic active species. The mechanical studies on the hydroxyl-functionalized copolymers disclosed that they exhibited high strength and toughness because of the existence of hydrogen bonds in the polymer network.

Metal-Metal Redox Exchange to Produce Heterometallic Manganese-Cobalt Oxo Cubanes via a "Dangler" Intermediate.

Pendent metals bound to heterocubanes are components of well-known active sites in enzymes that mediate difficult chemical transformations. Investigations into the specific role of these metal ions, sometimes referred to as "danglers", have been hindered by a paucity of rational synthetic routes to appropriate model structures. To generate pendent metal ions bonded to an oxo cubane through a carboxylate bridge, the cubane Co4(μ3-O)4(OAc)4(t-Bupy)4 (OAc = acetate, t-Bupy = 4-tert-butylpyridine) was exposed to various metal acetate complexes. Reaction with Cu(OAc)2 gave the structurally characterized (by X-ray diffraction) dicopper dangler Cu2Co4(μ4-O)2(μ3-O)2(OAc)6(Cl)2(t-Bupy)4. In contrast, the analogous reaction with Mn(OAc)2 produced the MnIV-containing cubane cation [MnCo3(μ3-O)4(OAc)4(t-Bupy)4]+ by way of a metal-metal exchange that gives Co(OAc)2 and [CoIII(μ-OH)(OAc)]n oligomers as byproducts. Additionally, reaction of the formally CoIV cubane complex [Co4(μ3-O)4(OAc)4(t-Bupy)4][PF6] with Mn(OAc)2 gave the corresponding Mn-containing cubane in 80% yield. A mechanistic examination of the related metal-metal exchange reaction between Co4(μ3-O)4(OBz)4(py)4 (OBz = benzoate) and [Mn(acac)2(py)2][PF6] by ultraviolet-visible (UV-vis) spectroscopy provided support for a process involving rate-determining association of the reactants and electron transfer through a μ-oxo bridge in the adduct intermediate. The rates of exchange correlate with the donor strength of the cubane pyridine and benzoate ligand substituents; more electron-donating pyridine ligands accelerate metal-metal exchange, while both electron-donating and -withdrawing benzoate ligands can accelerate exchange. These experiments suggest that the basicity of the cubane oxo ligands promotes metal-metal exchange reactivity. The redox potentials of the Mn and cubane starting materials and isotopic labeling studies suggest an inner-sphere electron-transfer mechanism in a dangler intermediate.

Photo-assisted selective oxidation of monoterpenes by a covalently supported dioxo-molybdenum complex on TiO2: Effect of electron donor ligands

High-valent dioxo-Mo species have demonstrated the ability to catalyze industrially interesting alkene-to-epoxide transformations via oxygen atom transfer (OAT) reactions. The impact of electron donor ligands of dioxo-molybdenum complexes [MoO2Ln] covalently supported on TiO2 nanotubes (MoO2Ln/TiO2NT) on OAT to α-pinene, β-pinene, (R)-limonene and camphene has been investigated through the use of UV–vis radiation and molecular oxygen. Molybdenum complexes with electron donor ligands, such as bipyridine, bispyrazole, and terpyridine, exhibited high conversion and selectivity towards epoxide formation. This suggests that electron donation enhances the efficiency of photostimulated OAT. The photonic efficiency (ξ) demonstrates a linear correlation between the ligand structure and the OAT activity, indicating that the electron donation of the ligands enhances electron mobility towards the Mo=O bond. This correlation is evident in the position of the IR and Raman νsym(O=Mo=O) and vasym(O=Mo=O) vibrations of the complex Mo.

IZCp and PZCp: Redox Non-innocent Cyclopentadienyl Ligands as Electron Reservoirs for Sandwich Complexes.

A long-sustained effort of systematic steric and electronic modification of cyclopentadienyl (Cp) ligands has enabled them to find wide-ranging, valuable applications. Herein, we present two novel Cp ligands: imidazolium- and pyrrolinium-substituted zwitterionic Cps (IZCp and PZCp), whose key utility is redox non-innocence─the ability to participate cooperatively with the metal center in redox reactions. Through the simple metalation of ZCps, the Cr(0) and Mo(0) half-sandwich complexes (IZCp)Cr(CO)3, (PZCp)Cr(CO)3, (IZCp)Mo(CO)3, and (PZCp)Mo(CO)3, respectively, as well as the Ru(II) sandwich complexes [(IZCp)RuCp]PF6 and [(PZCp)RuCp]PF6 were prepared. The sandwich complexes were fully characterized and showed by cyclic voltammetry reversible one-electron reduction at E1/2 potentials ranging from -1.7 to -2.7 V vs Fc/Fc+. These values are unusually low and have not been observed with other Cp ligands due to the instability of the reduced complexes. Density functional theory (DFT) calculations for the reduced sandwich derivatives with IZCp and PZCp showed their spin densities to be highly delocalized over their ZCp ligand moieties (70-90%). Electron paramagnetic resonance (EPR) analysis of the isolated K[(PZCp)Mo(CO)3] and (PZCp)RuCp also indicated a high degree of ligand-localized radical character. Thus, the IZCp and PZCp ligands act as electron reservoirs to sustain these sandwich complexes in highly reduced states. At the same time, the CO stretching frequencies of K[(PZCp)Mo(CO)3]: νCO 1871, 1748, and 1699 cm-1, rank the [PZCp]- ligand as the strongest electron-donating Cp ligand among the reported CpMo(CO)3 derivatives, whose νCO > 1746 cm-1. In addition, these redox non-innocent Cps were obtained in high yields and found to be practically air- and moisture-stable, unlike typical Cps.

Biosynthesis of NIR-II Ag2Se Quantum Dots with Bacterial Catalase for Photoacoustic Imaging and Alleviating-Hypoxia Photothermal Therapy.

Developing the second near-infrared (NIR-II) photoacoustic (PA) agent is of great interest in bioimaging. Ag2Se quantum dots (QDs) are one kind of potential probe for applications in NIR-II photoacoustic imaging (PAI). However, the surfaces with excess anions of Ag2Se QDs, which increase the probability of nonradiative transitions of excitons benefiting PA imaging, are not conducive to binding electron donor ligands for potential biolabeling and imaging. In this study, Staphylococcus aureus (S. aureus) cells are driven for the biosynthesis of Ag2Se QDs with catalase (CAT). Biosynthesized Ag2Se (bio-Ag2Se-CAT) QDs are produced in Se-enriched environment of S. aureus and have a high Se-rich surface. The photothermal conversion efficiency of bio-Ag2Se-CAT QDs at 808 and 1064nm is calculated as 75.3% and 51.7%, respectively. Additionally, the PA signal responsiveness of bio-Ag2Se-CAT QDs is ≈10 times that of the commercial PA contrast agent indocyanine green. In particular, the bacterial CAT is naturally attached to bio-Ag2Se-CAT QDs surface, which can effectively relieve tumor hypoxia. The bio-Ag2Se-CAT QDs can relieve heat-initiated oxidative stress while undergoing effective photothermal therapy (PTT). Such biosynthesis method of NIR-II bio-Ag2Se-CAT QDs opens a new avenue for developing multifunctional nanomaterials, showing great promise for PAI, hypoxia alleviation, and PTT.

A Survey of the Angular Distortion Landscape in the Coordination Geometries of High-Spin Iron(II) 2,6-Bis(pyrazolyl)pyridine Complexes.

Reaction of 2,4,6-trifluoropyridine with sodium 3,4-dimethoxybenzenethiolate and 2 equiv of sodium pyrazolate in tetrahydrofuran at room temperature affords 4-(3,4-dimethoxyphenylsulfanyl)-2,6-di(pyrazol-1-yl)pyridine (L), in 30% yield. The iron(II) complexes [FeL2][BF4]2 (1a) and [FeL2][ClO4]2 (1b) are high-spin with a highly distorted six-coordinate geometry. This structural deviation from ideal D2d symmetry is common in high-spin [Fe(bpp)2]2+ (bpp = di{pyrazol-1-yl}pyridine) derivatives, which are important in spin-crossover materials research. The magnitude of the distortion in 1a and 1b is the largest yet discovered for a mononuclear complex. Gas-phase DFT calculations at the ω-B97X-D/6-311G** level of theory identified four minimum or local minimum structural pathways across the distortion landscape, all of which are observed experimentally in different complexes. Small distortions from D2d symmetry are energetically favorable in complexes with electron-donating ligand substituents, including sulfanyl groups, which also have smaller energy penalties associated with the lowest energy distortion pathway. Natural population analysis showed that these differences reflect greater changes to the Fe-N{pyridyl} σ-bonding as the distortion proceeds, in the presence of more electron-rich pyridyl donors. The results imply that [Fe(bpp)2]2+ derivatives with electron-donating pyridyl substituents are more likely to undergo cooperative spin transitions in the solid state. The high-spin salt [Fe(bpp)2][CF3SO3]2, which also has a strong angular distortion, is also briefly described and included in the analysis.

Theoretical Investigation of Linear Relationships between the Dihedral Torsion Angles and Diosmium Bond Distances in Diosmium Sawhorse Complexes.

Strong linear relationships between their Ceq-Os-Os-Ceq dihedral angles and their Os-Os bond distances in diosmium sawhorse complexes Os2(u-O2CR)2(CO)4L2 (L = CO and/or PR3) form two trendlines depending upon the presence or absence of terminal phosphines. These trends appear unrelated to the basicity of the bridging ligand or the number of phosphines. The mathematical derivation of the relationship between the O-Os-Os-O dihedral angle and the Os-Os bond distance shows how the other geometric parameters affect this relationship. Optimized density functional theory (DFT) structures reveal a similar strong linear correlation, where more electron-donating ligands render shorter Os-Os bond distances and larger dihedral angles, but these results form a single trendline. Computational scans of individual parameters show that the Os-Os bond responds strongly to changes in the dihedral angles, but the dihedral angles only respond weakly to changes in the Os-Os bond distance because the Os-Os-O bond angle links and modifies their direct coupling. Solid-state analysis of their structures, including DFT geometry optimizations, shows that phosphines protect the Os-Os bond distance from packing influences along the Os-Os axis, while in complexes without phosphines, packing compresses the Os-Os bond and the weak dihedral responses create the second trendline.

Thermally Stable Monoruthenium Acetylide Radical Species

AbstractControl of radical reactivity is regarded as an important concern in the fields of catalysis and materials sciences. Radical species generated from monoruthenium acetylide complexes are, in general, highly reactive, and therefore structural characterization of these species has remained elusive. In this paper, a spectroscopic and structural characterization of the cationic radical species of a monoruthenium diacetylide bearing a Ru tetraphosphine fragment, [trans-(Ar–SC≡C)2Ru(dppe)2]SbCl6 ([1]+SbCl6) [Ar: p-t-BuC6H4; dppe: 1,2-bis(diphenylphosphino)ethane], is presented. The formation of the radical species [1]+ is supported by the vis-NIR, IR, and ESR studies. Furthermore, the solid-state structure of [1]+ reveals a significant contribution of the cumulenic Ru=C=C=S resonance structure. Remarkably, the thermal stability of [1]+ results from the incorporation of the electron-donating (arylsulfanyl)ethynyl ligands and the highly sterically demanding dppe ligands as compared with a monoruthenium complex with less-bulky and less-electron-rich derivatives.

Siloxide tripodal ligands as a scaffold for stabilizing lanthanides in the +4 oxidation state.

Synthetic strategies to isolate molecular complexes of lanthanides, other than cerium, in the +4 oxidation state remain elusive, with only four complexes of Tb(iv) isolated so far. Herein, we present a new approach for the stabilization of Tb(iv) using a siloxide tripodal trianionic ligand, which allows the control of unwanted ligand rearrangements, while tuning the Ln(iii)/Ln(iv) redox-couple. The Ln(iii) complexes, [LnIII((OSiPh2Ar)3-arene)(THF)3] (1-LnPh) and [K(toluene){LnIII((OSiPh2Ar)3-arene)(OSiPh3)}] (2-LnPh) (Ln = Ce, Tb, Pr), of the (HOSiPh2Ar)3-arene ligand were prepared. The redox properties of these complexes were compared to those of the Ln(iii) analogue complexes, [LnIII((OSi(OtBu)2Ar)3-arene)(THF)] (1-LnOtBu) and [K(THF)6][LnIII((OSi(OtBu)2Ar)3-arene)(OSiPh3)] (2-LnOtBu) (Ln = Ce, Tb), of the less electron-donating siloxide trianionic ligand, (HOSi(OtBu)2Ar)3-arene. The cyclic voltammetry studies showed a cathodic shift in the oxidation potential for the cerium and terbium complexes of the more electron-donating phenyl substituted scaffold (1-LnPh) compared to those of the tert-butoxy (1-LnOtBu) ligand. Furthermore, the addition of the -OSiPh3 ligand further shifts the potential cathodically, making the Ln(iv) ion even more accessible. Notably, the Ce(iv) complexes, [CeIV((OSi(OtBu)2Ar)3-arene)(OSiPh3)] (3-CeOtBu) and [CeIV((OSiPh2Ar)3-arene)(OSiPh3)(THF)2] (3-CePh), were prepared by chemical oxidation of the Ce(iii) analogues. Chemical oxidation of the Tb(iii) and Pr(iii) complexes (2-LnPh) was also possible, in which the Tb(iv) complex, [TbIV((OSiPh2Ar)3-arene)(OSiPh3)(MeCN)2] (3-TbPh), was isolated and crystallographically characterized, yielding the first example of a Tb(iv) supported by a polydentate ligand. The versatility and robustness of these siloxide arene-anchored platforms will allow further development in the isolation of more oxidizing Ln(iv) ions, widening the breadth of high-valent Ln chemistry.

Stabilization of Diborynes versus Destabilization of Diborenes by Coordination of Lewis Bases: Unravelling the Dichotomy.

We have quantum chemically investigated the boron-boron bonds in B2 , diborynes B2 L2 , and diborenes B2 H2 L2 (L=none, OH2 , NH3 ) using dispersion-corrected relativistic density functional theory at ZORA-BLYP-D3(BJ)/TZ2P. B2 has effectively a single B-B bond provided by two half π bonds, whereas B2 H2 has effectively a double B=B bond provided by two half π bonds and one σ 2p-2p bond. This different electronic structure causes B2 and B2 H2 to react differently to the addition of ligands. Thus, in B2 L2 , electron-donating ligands shorten and strengthen the boron-boron bond whereas, in B2 H2 L2 , they lengthen and weaken the boron-boron bond. The aforementioned variations in boron-boron bond length and strength become more pronounced as the Lewis basicity of the ligands L increases.

Effect of Ligand Attachment at Ag11 for CO Oxidation: A Computational Investigation.

Heterogeneous CO oxidation is a demanding reaction at room temperature due to the high activation energy required to break the O=O bond. While several metal clusters are reported to oxidize CO successfully, they fall short of their selectivity for the reaction and recyclability. In this regard, there is a need for economic catalysts with high catalytic activity, low activation barrier, and reusability. In this study, we have investigated the catalytic activity of the neutral pristine and ligated Ag11 cluster toward CO oxidation. We investigated the attachment effect of three organic donor ligands: trimethylphosphine, triethylphosphine, and N-ethyl pyrrolidone to the Ag11 cluster. Our results show that including donor ligands on the Ag11 cluster surface can significantly reduce the barrier heights for CO oxidation. The minimum barrier heights with the system coordinated with triethylphosphine showed the lowest activation barrier of 1.06 kcal/mol compared to the high activation barrier of 14.77 kcal/mol recorded for the pristine cluster. Exploration of the reaction mechanism and charge analysis showed that the electron donor ligands activate O2 via charge donation, thereby reducing the barrier heights of CO oxidation.

Heme-copper and Heme O2-derived synthetic (bioinorganic) chemistry toward an understanding of cytochrome c oxidase dioxygen chemistry

Cytochrome c oxidase (CcO), also widely known as mitochondrial electron-transport-chain complex IV, is a multi-subunit transmembrane protein responsible for catalyzing the last step of the electron transport chain, dioxygen reduction to water, which is essential to the establishment and maintenance of the membrane proton gradient that drives ATP synthesis. Although many intermediates in the CcO catalytic cycle have been spectroscopically and/or computationally authenticated, the specifics regarding the IP intermediate, hypothesized to be a heme-Cu (hydro)peroxo species whose O−O bond homolysis is supported by a hydrogen-bonding network of water molecules, are largely obscured by the fast kinetics of the A (FeIII–O2•–/CuI/Tyr) → PM (FeIV=O/CuII–OH/Tyr•) step. In this review, we have focused on the recent advancements in the design, development, and characterization of synthetic heme-peroxo‑copper model complexes, which can circumvent the abovementioned limitation, for the investigation of the formation of IP and its O−O cleavage chemistry. Novel findings regarding (a) proton and electron transfer (PT/ET) processes, together with their contributions to exogenous phenol induced O−O cleavage, (b) the stereo-electronic tunability of the secondary coordination sphere (especially hydrogen-bonding) on the geometric and spin state alteration of the heme-peroxo‑copper unit, and (c) a plausible mechanism for the Tyr-His cofactor biogenesis, are discussed in great detail. Additionally, since the ferric-superoxide and the ferryl-oxo (Compound II) species are critically involved in the CcO catalytic cycle, this review also highlights a few fundamental aspects of these heme-only (i.e., without copper) species, including the structural and reactivity influences of electron-donating trans-axial ligands and Lewis acid-promoted H-bonding.

High-Efficiency Photoinduced Charge Separation in Fe(III)carbene Thin Films.

Symmetry-breaking charge separation in molecular materials has attracted increasing attention for optoelectronics based on single-material active layers. To this end, Fe(III) complexes with particularly electron-donating N-heterocyclic carbene ligands offer interesting properties with a 2LMCT excited state capable of oxidizing or reducing the complex in its ground state. In this Communication, we show that the corresponding symmetry-breaking charge separation occurs in amorphous films of pristine [Fe(III)L2]PF6 (L = [phenyl(tris(3-methylimidazol-2-ylidene))borate]-). Excitation of the solid material with visible light leads to ultrafast electron transfer quenching of the 2LMCT excited state, generating Fe(II) and Fe(IV) products with high efficiency. Sub-picosecond charge separation followed by recombination in about 1 ns could be monitored by transient absorption spectroscopy. Photoconductivity measurements of films deposited on microelectrode arrays demonstrated that photogenerated charge carriers can be collected at external contacts.

Investigation of the Relationship between Electronic Structures and Bioactivities of Polypyridyl Ru(II) Complexes.

Ruthenium (Ru)-based organometallic drugs have gained attention as chemotherapeutic and bioimaging agents due to their fewer side effects and excellent physical optical properties. Tuning the electronic structures of Ru complexes has been proven to increase the cytotoxicity of cancer cells and the luminescent efficiency of the analytical probes. However, the relationship between electronic structures and bioactivities is still unclear due to the potential enhancement of both electron donor and acceptor properties. Thus, we investigated the relationship between the electronic structures of Ru(II) complexes and cytotoxicity by optimizing the electron-withdrawing (complex 1), electron-neutral (complex 2), and electron-donating (complex 3) ligands through DFT calculations, bioactivities tests, and docking studies. Our results indicated that it was not sufficient to consider only either the effect of electron-withdrawing or electron-donating effects on biological activities instead of the total electronic effects. Furthermore, these complexes with electron-donating substituents (complex 3) featured unique "off-on" luminescent emission phenomena caused by the various "HOMO-LUMO" distributions when they interacted with DNA, while complex with electron-withdrawing substituent showed an "always-on" signature. These findings offer valuable insight into the development of bifunctional chemotherapeutic agents along with bioimaging ability.

The effect of replacing linker with carboxylic acid ligands on the oxygen evolution performance of metal-organic frameworks

Metal-organic frameworks (MOFs) are versatile platforms for developing various applications, owing to their structural diversity and functional tunability. The catalytic performance of metal-organic frameworks (MOFs) can be improved by introducing defects using monocarboxylate ligands, but the role of these ligands remains unclear. Herein, we show how doping MOFs with electron-withdrawing or electron-donating monocarboxylate ligands affects their oxygen evolution reaction (OER) performance. We further demonstrate that ferrocene derivatives as doped ligands can significantly enhance the OER performance of MOFs, owing to the strong synergistic effects between ferrocene derivatives and MOFs. Different from other doping MOF, ferrocene derivatives doped MOFs (1,1'-Fc-Ni-BDC) exhibit remarkable electrocatalytic activity with a low overpotential of 387 mV at 10 mA cm−2, and possess good electrochemical stability. Density functional theory (DFT) calculations reveal that the active sites are not on ferrocene derivatives, but rather on MOFs, and that ferrocene derivatives facilitate the formation of OER intermediates. Our findings provide new insights into the role of ligands in modulating the OER performance of MOFs. This work offers a new perspective to develop efficient MOF-based electrocatalysts by introducing electronegative metallocene ligands.

Photochromic Supramolecular Isomers Derived from Pb(II)-Bipyridinedicarboxylate Complexes.

Photochromic metal-organic complexes (PMOCs) have received huge attention of chemists, thanks to their diverse structural characteristic and various available photo-modulate physicochemical functionalities. The organic ligand plays a crucial role in the quest of PMOCs with specific photo-responsive functionalities. The multiple coordination modes of polydentate ligands also provide possibilities for forming isomeric MOCs, which may open a new perspective on the research of PMOCs. The exploration of suitable PMOC systems is significant for the yield of isomeric PMOCs. Taking into account extant PMOCs based on polypyridines and carboxylate as electron acceptors (EAs) and donors (EDs), the covalent fusion of suitable pyridyl and carboxyl species may produce single functionalized ligands bearing ED and EA moieties for the building of novel PMOCs. In this study, the coordination assembly of bipyridinedicarboxylate (2,2'-bipyridine-4,4'-dicarboxylic acid, H2bpdc) and Pb2+ ions generate two isomeric MOCs, [Pb(bpdc)]·H2O (1 and 2), which have the same chemical compositions with main discrepancies in the coordination mode of bpdc2- ligands. As expected, supramolecular isomers 1 and 2 exhibited different photochromic performance, thanks to the distinct microscopic functional structural units. A schematic encryption and anti-counterfeiting device based on complexes 1 and 2 has also been studied. Compared with the extensively studied PMOCs supported by photoactive ligands like pyridinium and naphthalimide-derivatives and PMOCs derived from mixed electron-accepting polydentate N-ligands and electron-donating ligands, our work provides a new idea for building PMOCs based on pyridinecarboxylic acid ligands.

Ylide-Functionalized Phosphine (YPhos) Platinum Complexes: Synthesis and Application in Hydrosilylations under Mild Conditions

In the past years, highly electron-donating ligands have emerged as advantageous for the development of high-performance platinum catalysts for hydrosilylation reactions. In this work, we report on platinum precatalysts based on our recently introduced ylide-substituted phosphines (YPhos). Because of the high electron-donating ability and steric demand of the YPhos ligands, these complexes are in contrast to Karstedt’s catalysts stable under ambient conditions but still enable high activities and selectivities in the hydrosilylation of both alkenes and amides at low catalyst loadings and under mild reaction conditions.

Exploring the Effect of Pincer Rigidity on Oxidative Addition Reactions with Cobalt(I) Complexes.

Cobalt complexes containing the 2,6-diaminopyridine-substituted PNP pincer (iPrPNMeNP = 2,6-(iPr2PNMe)2(C5H3N)) were synthesized. A combination of solid-state structures and investigation of the cobalt(I)/(II) redox potential established a relatively rigid and electron-donating chelating ligand as compared to iPrPNP (iPrPNP = 2,6-(iPr2PCH2)2(C5H3N)). Based on a buried volume analysis, the two pincer ligands are sterically indistinguishable. Nearly planar, diamagnetic, four-coordinate complexes were observed independent of the field strength (chloride, alkyl, aryl) of the fourth ligand completing the coordination sphere of the metal. Computational studies supported a higher barrier for C-H oxidative addition, largely a result of the increased rigidity of the pincer. The increased oxidative addition barrier resulted in stabilization of (iPrPNMeNP)Co(I) complexes, enabling the characterization of the cobalt boryl and the cobalt hydride dimer by X-ray crystallography. Moreover, (iPrPNMeNP)CoMe served as an efficient precatalyst for alkene hydroboration likely because of the reduced propensity to undergo oxidative addition, demonstrating that reactivity and catalytic performance can be tuned by rigidity of pincer ligands.