Probing the Electron Accepting Ability of Phosphaphenalenes.

Phosphaphenalenes, extended π conjugates with the incorporation of phosphorus, are attractive avenues towards molecular materials for the applications in organic electronics, but their electron accepting ability have not been investigated. In this study, we present systematic studies on the reductive behavior of a representative phosphaphenalene and its oxide by chemical and electrochemical methods. The chemical reduction of the phosphaphenalene by alkali metals reveals the facile P‒C bond cleavage to form phosphaphenalenide anion, which functions as a transfer block for structure modification on the phosphorus atom. In contrast, the pentavalent P-oxide reacts with one or two equivalents of elemental sodium to form stable radical anion and dianion salts, respectively.

Platinum(II) N-heterocyclic carbene complexes arrest metastatic tumor growth.

Vimentin is a cytoskeletal intermediate filament protein that plays pivotal roles in tumor initiation, progression, and metastasis, and its overexpression in aggressive cancers predicted poor prognosis. Herein described is a highly effective antitumor and antimetastatic metal complex [PtII(C^N^N)(NHC2Bu)]PF6 (Pt1a; HC^N^N = 6-phenyl-2,2'-bipyridine; NHC= N-heterocyclic carbene) that engages vimentin via noncovalent binding interactions with a distinct orthogonal structural scaffold. Pt1a displays vimentin-binding affinity with a dissociation constant of 1.06 µM from surface plasmon resonance measurements and fits into a pocket between the coiled coils of the rod domain of vimentin with multiple hydrophobic interactions. It engages vimentin in cellulo, disrupts vimentin cytoskeleton, reduces vimentin expression in tumors, suppresses xenograft growth and metastasis in different mouse models, and is well tolerated, attributable to biotransformation to less toxic and renal-clearable platinum(II) species. Our studies uncovered the practical therapeutic potential of platinum(II)‒NHC complexes as effective targeted chemotherapy for combating metastatic and cisplatin-resistant cancers.

Cyanide-Bridged Rope-like Chains Based on Trigonal-Bipyramidal [Fe2Cu3] Subunits.

Extending a selected cyanometalate block into a higher dimensional framework continues to present intriguing challenges in the fields of chemistry and material science. Here, we prepared two rope-like chain compounds of {[(Tp*Me)Fe(CN)3]2Cu2X2(L)}·sol (1, X = Cl, L = (MeCN)0.5(H2O/MeOH)0.5, sol = 2MeCN·1.5H2O; 2, X = Br, L = MeOH, sol = 2MeCN·0.75H2O; Tp*Me = tris(3, 4, 5-trimethylpyrazole)borate) in which the cyanide-bridged trigonal-bipyramidal [Fe2Cu3] subunits were linked with the adjacent ones via two vertex Cu(II) centers, providing a new cyanometallate chain archetype. Direct current magnetic study revealed the presence of ferromagnetic couplings between Fe(III) and Cu(II) ions and uniaxial anisotropy due to a favorable alignment of the anisotropic tricyanoiron(III) units. Moreover, compound 1 exhibits single-chain magnet behavior with an appreciable energy barrier of 72 K, while 2 behaves as a metamagnet, likely caused by the subtle changes in the interchain interactions.

An anticancer gold(III)-activated porphyrin scaffold that covalently modifies protein cysteine thiols.

Cysteine thiols of many cancer-associated proteins are attractive targets of anticancer agents. Herein, we unequivocally demonstrate a distinct thiol-targeting property of gold(III) mesoporphyrin IX dimethyl ester (AuMesoIX) and its anticancer activities. While the binding of cysteine thiols with metal complexes usually occurs via M-S bond formation, AuMesoIX is unique in that the meso-carbon atom of the porphyrin ring is activated by the gold(III) ion to undergo nucleophilic aromatic substitution with thiols. AuMesoIX was shown to modify reactive cysteine residues and inhibit the activities of anticancer protein targets including thioredoxin, peroxiredoxin, and deubiquitinases. Treatment of cancer cells with AuMesoIX resulted in the formation of gold-bound sulfur-rich protein aggregates, oxidative stress-mediated cytotoxicity, and accumulation of ubiquitinated proteins. Importantly, AuMesoIX exhibited effective antitumor activity in mice. Our study has uncovered a gold(III)-induced ligand scaffold reactivity for thiol targeting that can be exploited for anticancer applications.

An Isolable Radical Anion Featuring a 2-Center-3-Electron π-Bond without a Clearly Defined σ-Bond.

Featuring an extra electron in the π* antibonding orbital, species with a 2-center-3-electron (2c3e) π bond without an underlying σ bond are scarcely known. Herein, we report the synthesis, isolation and characterization of a radical anion salt [K(18-C-6)]+ {[(HCNDipp)2 Si]2 P2 }⋅- (i.e. [K(18-C-6)]+ 3⋅- ) (18-C-6=18-crown-6, Dipp=2,6-diisopropylphenyl), in which 3⋅- features a perfectly planar Si2 P2 four-membered ring. This species represents the first example of a Si- and P-containing analog of a bicyclo[1.1.0]butane radical anion. The unusual bonding motif of 3⋅- was thoroughly investigated via X-ray diffraction crystallography, electron paramagnetic resonance spectroscopy (EPR), and calculations by density functional theory (DFT), which collectively unveiled the existence of a 2c3e π bond between the bridgehead P atoms and no clearly defined supporting P-P σ bond.

Self-Assembly of Molecular Trefoil Knots Featuring Pentadecanuclear Homoleptic AuI -, AuI /AgI -, or AuI /CuI -Alkynyl Coordination.

Metal-free and metal-containing molecular trefoil knots are fascinating ensembles that are usually covalently assembled, the latter requiring the rational design of di- or multidentate/multipodal ligands as connectors. In this work, we describe the self-assembly of pentadecanuclear AuI trefoil knots [Au15 (C≡CR)15 ] from monoalkynes HC≡CR (R=9,9-X2 -fluorenyl with X=nBu, n-hexyl) and [AuI (THT)Cl]. Hetero-bimetallic counterparts [Au9 M6 (C≡CR)15 ] (M=Cu/Ag) were self-assembled by reactions of [Au15 (C≡CR)15 ] with [Cu(MeCN)4 ]+ /AgNO3 and HC≡CR. The type of pentadecanuclear trefoil knots described herein is characterized by X-ray crystallography, 2D NMR and HR-ESI-MS. [Au9 Cu6 (C≡CR)15 ] is relatively stable in hexane; its excited state properties were investigated. DFT calculations revealed that non-covalent metal-metal and metal-ligand interactions, together with longer alkyl chain-strengthened inter-ligand dispersion interactions, govern the stability of the trefoil knot structures.

Copper-Catalyzed Enantioconvergent Cross-Coupling of Racemic Alkyl Bromides with Azole C(sp2 )-H Bonds.

The development of enantioconvergent cross-coupling of racemic alkyl halides directly with heteroarene C(sp2 )-H bonds has been impeded by the use of a base at elevated temperature that leads to racemization. We herein report a copper(I)/cinchona-alkaloid-derived N,N,P-ligand catalytic system that enables oxidative addition with racemic alkyl bromides under mild conditions. Thus, coupling with azole C(sp2 )-H bonds has been achieved in high enantioselectivity, affording a number of potentially useful α-chiral alkylated azoles, such as 1,3,4-oxadiazoles, oxazoles, and benzo[d]oxazoles as well as 1,3,4-triazoles, for drug discovery. Mechanistic experiments indicated facile deprotonation of an azole C(sp2 )-H bond and the involvement of alkyl radical species under the reaction conditions.

Azido-Cyanide Mixed-Bridged FeIII-NiII Complexes.

The successful introduction of azide ions as secondary bridges into the FeIII-NiII cyanide system afforded two clusters and one unique 4(3),2-ribbon chain: [(bpzpy)2Ni2(µ2-1,1-N3)2{(pzTp)Fe(CN)3}2]·3H2O [1; bpzpy = 2,6-bis(pyrazol-1-yl)pyridine, and pzTp = tetrakis(pyrazolyl)borate], [(L1)2Ni4(µ3-1,1,1-OCH3)2(µ2-1,1-N3)2(H2O)2{(Tp)Fe(CN)3}2]·2CH3OH·H2O [2; Tp = hydrotris(pyrazolyl)borate, and HL1 = 2,6-bis{(2-hydroxypropylimino)methyl}-4-methylphenol], and [(L2)2Ni3(µ2-1,1-N3)4{(pzTp)Fe(CN)3}2]n (3; L2 = 2-{[phenyl(pyridin-2-yl)methylene]amino}ethan-1-amine). Both 1 and 2 feature the centrosymmetric {FeIII-NiII2-FeIII} and {FeIII-NiII4-FeIII} rodlike structures in which the two peripheral [(TpR)Fe(CN)3]- anions act as monodentate ligands via one cyanide group to link the central azide-bridged [Ni2] and [Ni4] subunit, respectively, while 3 displays an extended structure of the double-zigzag (4,2-ribbon) chain in which the double end-on azide-bridged trinuclear [Ni3] subunits serve as the 4-connected nodes. Magnetic study revealed that intramolecular ferromagnetic coupling is dominated by the azide or cyanide bridges in all of the complexes. Remarkably, complex 1 behaves as a single-molecule magnet with an effective energy barrier of 16.5 cm-1 at zero dc field, while complex 3 exhibits metamagnetism with a hidden spin canting property below 12 K.

Intramolecular Nitrene Insertion into Saturated C-H-Bond-Mediated C-N Bond Cleavage of a Coordinated NHC Ligand.

Ruthenium(II) complexes bearing a tridentate bis(N-heterocyclic carbene) ligand reacted with iminoiodanes (PhI=NR) resulting in the formation of isolable ruthenium(III)-amido intermediates, which underwent cleavage of a C-N bond of the tridentate ligand and formation of an N-substituted imine group. The RuIII -amido intermediates have been characterized by 1 H NMR, UV/Vis, ESI-MS, and X-ray crystallography. DFT calculations were performed to provide insight into the reaction mechanism.

An Azido-Cyanide Mixed-Bridged [Fe4Ni4] Single-Molecule Magnet.

Taking advantages of both azide and cyanide bridges in magnetism and synthesis, an azido-cyanide mixed-bridged octanuclear [FeIII4NiII4] SMM of [{(enbzpy)Ni2(µ1,1-N3)2·(DMF)}{Tp*Fe(CN)3}2]2·2DMF·14H2O (1) was explored and characterized, which exhibits slow relaxation of the magnetization and an S = 6 ground state benefit from the end-on azido bridges.

Solvent-Induced Cluster-to-Cluster Transformation of Homoleptic Gold(I) Thiolates between Catenane and Ring-in-Ring Structures.

Supramolecular ensembles adopting ring-in-ring structures are less developed compared with catenanes featuring interlocked rings. While catenanes with inter-ring closed-shell metallophilic interactions, such as d10 -d10 AuI -AuI interactions, have been well-documented, the ring-in-ring complexes featuring such metallophilic interactions remain underdeveloped. Herein is described an unprecedented ring-in-ring structure of a AuI -thiolate Au12 cluster formed by recrystallization of a AuI -thiolate Au10 [2]catenane from alkane solvents such as hexane, with use of a bulky dibutylfluorene-2-thiolate ligand. The ring-in-ring AuI -thiolate Au12 cluster features inter-ring AuI -AuI interactions and underwent cluster core change to form the thermodynamically more stable Au10 [2]catenane structure upon dissolving in, or recrystallization from, other solvents such as CH2 Cl2 , CHCl3 , and CH2 Cl2 /MeCN. The cluster-to-cluster transformation process was monitored by 1 H NMR and ESI-MS measurements. Density functional theory (DFT) calculations were performed to provide insight into the mechanism of the "ring-in-ring⇌ [2]catenane" interconversions.

Arylruthenium(III) Porphyrin-Catalyzed C-H Oxidation and Epoxidation at Room Temperature and [RuV(Por)(O)(Ph)] Intermediate by Spectroscopic Analysis and Density Functional Theory Calculations.

The development of highly active and selective metal catalysts for efficient oxidation of hydrocarbons and identification of the reactive intermediates in the oxidation catalysis are long-standing challenges. In the rapid hydrocarbon oxidation catalyzed by ruthenium(IV) and -(III) porphyrins, the putative Ru(V)-oxo intermediates remain elusive. Herein we report that arylruthenium(III) porphyrins are highly active catalysts for hydrocarbon oxidation. Using catalyst [RuIII(TDCPP)(Ph)(OEt2)] (H2TDCPP = 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin), the oxidation of C-H bonds of various hydrocarbons with oxidant m-CPBA at room temperature gave alcohols/ketones in up to 99% yield within 1 h; use of [ nBu4N]IO4 as a mild alternative oxidant avoided formation of lactone from cyclic ketone in C-H oxidation, and the catalytic epoxidation with up to 99% yield and high selectivity (no aldehydes as side product) was accomplished within 5 min. UV-vis, electrospray ionization-mass spectrometry, resonance Raman, electron paramagnetic resonance, and kinetic measurements and density functional theory calculations lend evidence for the formation of Ru(V)-oxo intermediate [RuV(TDCPP)(O)(Ph)].

Air-Stable Blue Phosphorescent Tetradentate Platinum(II) Complexes as Strong Photo-Reductant.

Strong photo-reductants have applications in photo-redox organic synthesis involving reductive activation of C-X(halide) and C=O bonds. We report herein air-stable PtII complexes supported by tetradentate bis(phenolate-NHC) ligands having peripheral electron-donating N-carbazolyl groups. Photo-physical, electrochemical, and computational studies reveal that the presence of N-carbazolyl groups enhances the light absorption and redox reversibility because of its involvement into the frontier MOs in both ground and excited states, making the complexes robust strong photo-reductant with E([Pt]+/ *) over -2.6 V vs. Cp2 Fe+/0 . The one-electron reduced [Pt]- species are stronger reductants with EPC ([Pt]0/- ) up to -3.1 V vs. Cp2 Fe+/0 . By virtue of the strong reducing nature of these species generated upon light excitation, they can be used in light-driven reductive coupling of carbonyl compounds and reductive debromination of a wide range of unactivated aryl bromides.

N-Heterocyclic Carbene Iron(III) Porphyrin-Catalyzed Intramolecular C(sp3 )-H Amination of Alkyl Azides.

Metal-catalyzed intramolecular C-H amination of alkyl azides constitutes an appealing approach to alicyclic amines; challenges remain in broadening substrate scope, enhancing regioselectivity, and applying the method to natural product synthesis. Herein we report an iron(III) porphyrin bearing axial N-heterocyclic carbene ligands which catalyzes the intramolecular C(sp3 )-H amination of a wide variety of alkyl azides under microwave-assisted and thermal conditions, resulting in selective amination of tertiary, benzylic, allylic, secondary, and primary C-H bonds with up to 95 % yield. 14 out of 17 substrates were cyclized selectively at C4 to give pyrrolidines. The regioselectivity at C4 or C5 could be tuned by modifying the reactivity of the C5-H bond. Mechanistic studies revealed a concerted or a fast re-bound mechanism for the amination reaction. The reaction has been applied to the syntheses of tropane, nicotine, cis-octahydroindole, and leelamine derivatives.

Tripodal S-Ligand Complexes of Copper(I) as Catalysts for Alkene Aziridination, Sulfide Sulfimidation, and C-H Amination.

Copper(I) complexes of tris(thioimidazolyl)borates (R'TmR), including [Cu(TmPh)(PR″3)] (R″ = Ph, Cu1; Cy, Cu2) and [Cu(R'TmPh)(PR″3)]+ (R' = N-methylimidazole; R″ = Ph, Cy) were prepared and characterized by spectroscopic methods. The X-ray crystal structures of Cu1 and Cu2 feature a tripodal TmPh ligand coordinated in κ3-S,S,S mode. Using Cu2 as a catalyst (loading: 1 mol %), the aziridination of styrenes and sulfimidation of thioanisoles with PhI═NTs at RT for 3 and 0.5 h, respectively, both resulted in product yields of up to 99%. Cu2 also catalyzed intramolecular amination of the aryl C-H bond of vinyl azides with up to 98% yield. DFT calculations were performed to gain insight into the mechanism of the Cu2-catalyzed aziridination reaction.

From Cluster to Polymer: Ligand Cone Angle Controlled Syntheses and Structures of Copper(I) Alkynyl Complexes.

Copper(I) alkynyl complexes have attracted tremendous attention in structural studies, as luminescent materials, and in catalysis, and homoleptic complexes have been reported to form polymers or large clusters. Herein, six unprecedented structures of Cu(I) alkynyl complexes and a procedure to measure the cone angles of alkynyl ligands based on the crystal structures of these complexes are reported. An increase of the alkynyl cone angle in the complexes leads to a modulation of the structures from polymeric [((PhC≡CC≡C)Cu)2 (NH3 )]∞ , to a large cluster [(TripC≡CC≡C)Cu]20 (MeCN)4 , to a relatively small cluster [(TripC≡C)Cu]8 (Trip=2,4,6-iPr3 -C6 H2 ). The complexes exhibit yellow-to-red phosphorescence at ambient temperature in the solid state and the luminescence behavior of the Cu20 cluster is sensitive to acetonitrile.

A stable rhodium-coordinated carbene with a σ0π2 electronic configuration.

Isolable singlet carbenes have universally adopted a σ2π0 electronic state, making them σ-donors and π-acceptors. We present a rhodium-coordinated, cationic cyclic diphosphinocarbene with a σ0π2 ground state configuration. Nuclear magnetic resonance spectroscopy studies show a carbene carbon chemical shift below -30.0 parts per million. X-ray crystallography reveals a planar RhP2C configuration. Quantum chemical calculations rationalize how σ-electron delocalization/donation and π-electron negative hyperconjugation together stabilize the formally vacant σ orbital and the filled π orbital at the carbene center. In contrast to traditional carbene counterparts this carbene can undergo synthetic transformations with both a Lewis base and a silver salt, producing a Lewis acid/base adduct and a silver π-complex, respectively. Exhibiting ambiphilic reactivity, it can also form a ketenimine through reaction with an isocyanide.

Polarizability matters in enantio-selection.

The prevalence of chirality, or, handedness in biological world is a fundamental phenomenon and a characteristic hallmark of life. Thus, understanding the origin of enantio-selection, i.e., the sense and magnitude of asymmetric induction, has been a long-pursued goal in asymmetric catalysis. Herein, we demonstrated a polarizability-derived electronic effect that was shown to be capable of rationalizing a broad range of stereochemical observations made in the field of asymmetric catalysis. This effect provided a consistent enantio-control model for the prediction of major enantiomers formed in a ruthenium-catalyzed asymmetric transfer hydrogenations of ketones. Direct and quantitative linear free energy relationships between substrates' local polarizabilities and observed enantio-selectivity were also revealed in three widely known asymmetric catalytic systems covering both reductions and oxidations. This broadly applicable polarizability-based electronic effect, in conjunction with conventional wisdom mainly leveraging on steric effect considerations, should aid rational design of enantio-selective processes for better production of chiral substances.

Organophotocatalysed synthesis of 2-piperidinones in one step via [1 + 2 + 3] strategy.

Six-membered N-containing heterocycles, such as 2-piperidinone derivatives, with diverse substitution patterns are widespread in natural products, drug molecules and serve as key precursors for piperidines. Thus, the development of stereoselective synthesis of multi-substituted 2-piperidinones are attractive. However, existing methods heavily rely on modification of pre-synthesized backbones which require tedious multi-step procedure and suffer from limited substitution patterns. Herein, an organophotocatalysed [1 + 2 + 3] strategy was developed to enable the one-step access to diverse substituted 2-piperidinones from easily available inorganic ammonium salts, alkenes, and unsaturated carbonyl compounds. This mild protocol exhibits exclusive chemoselectivity over two alkenes, tolerating both terminal and internal alkenes with a wide range of functional groups.

Manipulating the spin crossover behaviour in a series of cyanide-bridged {FeIII2FeII2} molecular squares through NCE- co-ligands.

Manipulating the transition temperature (T1/2) of spin-crossover (SCO) complexes capable of fulfilling practical criteria through different synthetic strategies is one of the main focuses in the field of molecular magnetism. The reaction of the tricyanometallate precursor [(Tp*)FeIII(CN)3]- and Fe(II) salt with the "facially" tridentate ligand tris(2-pyridyl)phosphine oxide (TPPO) and NCE- anions afforded three isostructural {FeIII2FeII2} square complexes {[(Tp*)FeIII(CN)3]2[FeII(TPPO)]2[NCE]2}·Sol (E = S, Sol = 2CH3OH·6H2O, 1; E = Se, Sol = 2MeCN·2CH2Cl2·2H2O, 2; E = BH3, Sol = 4CH3OH·2MeCN, 3). Detailed structural analysis, variable-temperature IR analysis, magnetic susceptibility measurements and DFT calculations revealed that all compounds exhibit complete and one-step SCO behaviour between the {FeIII,LS2FeII,HS2} and {FeIII,LS2FeII,LS2} electronic states. As the ligand field increases from NCS- to NCSe- to NCBH3-, T1/2 shifts dramatically from 214 to 250 to 288 K for 1, 2 and 3, respectively, demonstrating another effective way to tune the SCO properties of the [FeIII-CN-FeII] systems through the introduction of NCE- co-ligands.