2-Methylimidazole-1-(N-tert-octyl)sulfonimidoyl fluoride: A Bench-Stable Alternative to SOF4 as Precursor to N,O-Substituted S(VI) Compounds.

S(VI) compounds with multiple N or O substituents are  often difficult to make and several crucial routes, such as multimodal SuFEx (Sulfur (VI) Fluoride Exchange) chemistry, rely on the highly useful but hazardous SOF4 gas. Safety issues and inaccessibility of SOF4 strongly hamper the developments of these organic compounds. Here we describe the synthesis and applications of 2-methylimidazole-1-(N-tert-octyl)sulfonimidoyl fluoride (ImSF), a novel bench-stable analogue of SOF4. ImSF is synthesized on a gram scale via a double fluorination of t-OctNSO. We show ImSF can undergo substitution reactions with phenols and amines, which lead to sulfurimidates and sulfuramidimidates, respectively, the intrinsically chiral analogous of medicinally relevant sulfates and sulfamates in which an S=O moiety is replaced by S=NR unit. Finally we demonstrate that such substitutions can occur enantiospecifically, providing the first entry to chiral sulfurimidates and sulfuramidimidates.

Synthesis and Reactivity of Ruthenium(BINAP)(PPh3).

Ru(BINAP)(PPh3)HCl cleanly reacts with LiCH2TMS to give Ru(BINAP)(PPh3) (1) that has been fully characterized, including by X-ray diffraction (BINAP and TMS stand for (2,2'-bis(diphenylphosphino)-1,1'-binaphthyl and trimethylsilyl respectively). In sharp contrast with other carbonyl-free phosphine complexes of Ru(0), 1 demonstrates a strikingly high thermal stability and no propensity for intramolecular C-H activation (cyclometalation). Yet 1 coordinates acetonitrile and readily exchanges its PPh3 ligand with alkenes and dienes, thus behaving like a "masked" 16-e Ru(0) species. Electron-poor alkenes coordinate more readily than electron-rich ones, which testifies for the nucleophilic character of the Ru(0)-BINAP fragment. While being thermally stable, 1 is highly reactive and is capable of activating C-H and N-H bonds, and even of cleaving an inert N-Et bond. The combination of high reactivity and stability originates from the P,arene-chelation by the BINAP ligand, i.e., the coordinated π-arene stabilizes Ru(0) to prevent cyclometalation, yet it can slide upon substrate coordination, thereby enabling a variety of inert bond activation reactions to occur under mild conditions.

Rim-Based Binding of Perfluorinated Acids to Pillararenes Purifies Water.

Per- and polyfluoroalkyl substances (PFAS) pose a rapidly increasing global problem as their widespread use and high stability lead worldwide to water contamination, with significant detrimental health effects.[1] Supramolecular chemistry has been invoked to develop materials geared towards the specific capture of PFAS from water,[2] to reduce the concentration below advisory safety limits (e.g., 70 ng/L for the sum of perfluorooctane sulfonic acid, PFOS and perfluorooctanoic acid, PFOA). Scale-up and use in natural waters with high PFAS concentrations has hitherto posed a problem. Here we report a new type of host-guest interaction between deca-ammonium-functionalized pillar[5]arenes (DAF-P5s) and perfluoroalkyl acids. DAF-P5 complexes show an unprecedented 1 : 10 stoichiometry, as confirmed by isothermal calorimetry and X-ray crystallographic studies, and high binding constants (up to 106 M-1) to various polyfluoroalkyl acids. In addition, non-fluorinated acids do not hamper this process significantly. Immobilization of DAF-P5s allows a simple single-time filtration of PFAS-contaminated water to reduce the PFOS/PFOA concentration 106 times to 15-50 ng/L level. The effective and fast (<5 min) orthogonal binding to organic molecules without involvement of fluorinated supramolecular hosts, high breakthrough capacity (90 mg/g), and robust performance (>10 regeneration cycles without decrease in performance) set a new benchmark in PFAS-absorbing materials.

Synthesis of Large Macrocycles with Chiral Sulfur Centers via Enantiospecific SuFEx and SuPhenEx Click Reactions.

Here we report the first asymmetric synthesis of large chiral macrocycles with chiral sulfur atoms. Building on stereospecific SuFEx and SuPhenEx click chemistries, this approach utilizes disulfonimidoyl fluorides and disulfonimidoyl p-nitrophenolates─which are efficient building blocks with two chiral sulfur centers, and diphenols to efficiently form novel S-O bonds. Characteristic results include the enantiospecific one-step synthesis of rings consisting of 21-58 members and characterization of both enantiomers (R,R and S,S) by e.g. X-ray crystallography.

Experimental and Computational Studies of Ruthenium Complexes Bearing Z-Acceptor Aluminum-Based Phosphine Pincer Ligands.

Reaction of [Ru(C6H4PPh2)2(Ph2PC6H4AlMe(THF))H] with CO results in clean conversion to the Ru-Al heterobimetallic complex [Ru(AlMePhos)(CO)3] (1), where AlMePhos is the novel P-Al(Me)-P pincer ligand (o-Ph2PC6H4)2AlMe. Under photolytic conditions, 1 reacts with H2 to give [Ru(AlMePhos)(CO)2(µ-H)H] (2) that is characterized by multinuclear NMR and IR spectroscopies. DFT calculations indicate that 2 features one terminal and one bridging hydride that are respectively anti and syn to the AlMe group. Calculations also define a mechanism for H2 addition to 1 and predict facile hydride exchange in 2 that is also observed experimentally. Reaction of 1 with B(C6F5)3 results in Me abstraction to form the ion pair [Ru(AlPhos)(CO)3][MeB(C6F5)3] (4) featuring a cationic [(o-Ph2PC6H4)2Al]+ ligand, [AlPhos]+. The Ru-Al distance in 4 (2.5334(16) Å) is significantly shorter than that in 1 (2.6578(6) Å), consistent with an enhanced Lewis acidity of the [AlPhos]+ ligand. This is corroborated by a blue shift in both the observed and computed νCO stretching frequencies upon Me abstraction. Electronic structure analyses (QTAIM and EDA-ETS) comparing 1, 4, and the previously reported [Ru(ZnPhos)(CO)3] analogue (ZnPhos = (o-Ph2PC6H4)2Zn) indicate that the Lewis acidity of these pincer ligands increases along the series ZnPhos < AlMePhos < [AlPhos]+.

Zinc-Promoted ZnMe/ZnPh Exchange in Eight-Coordinate [Ru(PPh3 )2 (ZnMe)4 H2 ].

The syntheses, reactivity and electronic structure analyses of [Ru(PPh3 )2 (ZnMe)4 H2 ], 1 a, and [Ru(PPh3 )2 (ZnPh)4 H2 ], 2 b, are reported. 1 a exhibits an 8-coordinate Ru centre with axial phosphines and a symmetrical (2 : 2) arrangement of ZnMe ligands in the equatorial plane. The ZnMe ligands in 1 a undergo facile, sequential exchange with ZnPh2 to give 2 b, which shows a 3 : 1 arrangement of ZnPh ligands. Both 1 a and 2 b exist in equilibrium with their respective 3 : 1 and 2 : 2 isomers. Mechanisms for ZnMe/ZnPh exchange and isomerisation are proposed using DFT calculations. The relationships of these {Ru(ZnR)4 H2 } species to isoelectronic Group 8 transition metal polyhydrides and related Schlenk equilibria in the Negishi reaction are discussed.

Sulfur-Phenolate Exchange: SuFEx-Derived Dynamic Covalent Reactions and Degradation of SuFEx Polymers.

The products of the SuFEx reaction between sulfonimidoyl fluorides and phenols, sulfonimidates, are shown to display dynamic covalent chemistry with other phenols. This reaction was shown to be enantiospecific, finished in minutes at room temperature in high yields, and useful for both asymmetric synthesis and sustainable polymer production. Its wide scope further extends the usefulness of SuFEx and related click chemistries.

Bonding and Reactivity of a Pair of Neutral and Cationic Heterobimetallic RuZn2 Complexes.

A combined experimental and computational study of the structure and reactivity of two [RuZn2Me2] complexes, neutral [Ru(PPh3)(Ph2PC6H4)2(ZnMe)2] (2) and cationic [Ru(PPh3)2(Ph2PC6H4)(ZnMe)2][BArF4] ([BArF4] = [B{3,5-(CF3)2C6H3}4]) (3), is presented. Structural and computational analyses indicate these complexes are best formulated as containing discrete ZnMe ligands in which direct Ru-Zn bonding is complemented by weaker Zn···Zn interactions. The latter are stronger in 2, and both complexes exhibit an additional Zn···Caryl interaction with a cyclometalated phosphine ligand, this being stronger in 3. Both 2 and 3 show diverse reactivity under thermolysis and with Lewis bases (PnBu3, PCy3, and IMes). With 3, all three Lewis bases result in the loss of [ZnMe]+. In contrast, 2 undergoes PPh3 substitution with PnBu3, but with IMes, loss of ZnMe2 occurs to form [Ru(PPh3)(C6H4PPh2)(C6H4PPhC6H4Zn(IMes))H] (7). The reaction of 3 with H2 affords the cationic trihydride complex [Ru(PPh3)2(ZnMe)2(H)3][BArF4] (12). Computational analyses indicate that both 12 and 7 feature bridging hydrides that are biased toward Ru over Zn.

Zn-Promoted C-H Reductive Elimination and H2 Activation via a Dual Unsaturated Heterobimetallic Ru-Zn Intermediate.

Reaction of [Ru(PPh3)3HCl] with LiCH2TMS, MgMe2, and ZnMe2 proceeds with chloride abstraction and alkane elimination to form the bis-cyclometalated derivatives [Ru(PPh3)(C6H4PPh2)2H][M'] where [M'] = [Li(THF)2]+ (1), [MgMe(THF)2]+ (3), and [ZnMe]+ (4), respectively. In the presence of 12-crown-4, the reaction with LiCH2TMS yields [Ru(PPh3)(C6H4PPh2)2H][Li(12-crown-4)2] (2). These four complexes demonstrate increasing interaction between M' and the hydride ligand in the [Ru(PPh3)(C6H4PPh2)2H]- anion following the trend 2 (no interaction) < 1 < 3 < 4 both in the solid-state and solution. Zn species 4 is present as three isomers in solution including square-pyramidal [Ru(PPh3)2(C6H4PPh2)(ZnMe)] (5), that is formed via C-H reductive elimination and features unsaturated Ru and Zn centers and an axial Z-type [ZnMe]+ ligand. A [ZnMe]+ adduct of 5, [Ru(PPh3)2(C6H4PPh2)(ZnMe)2][BArF4] (6) can be trapped and structurally characterized. 4 reacts with H2 at -40 °C to form [Ru(PPh3)3(H)3(ZnMe)], 8-Zn, and contrasts the analogous reactions of 1, 2, and 3 that all require heating to 60 °C. This marked difference in reactivity reflects the ability of Zn to promote a rate-limiting C-H reductive elimination step, and calculations attribute this to a significant stabilization of 5 via Ru → Zn donation. 4 therefore acts as a latent source of 5 and this operational "dual unsaturation" highlights the ability of Zn to promote reductive elimination in these heterobimetallic systems. Calculations also highlight the ability of the heterobimetallic systems to stabilize developing protic character of the transferring hydrogen in the rate-limiting C-H reductive elimination transition states.

Impact of the Novel Z-Acceptor Ligand Bis{(ortho-diphenylphosphino)phenyl}zinc (ZnPhos) on the Formation and Reactivity of Low-Coordinate Ru(0) Centers.

The preparation and reactivity with H2 of two Ru complexes of the novel ZnPhos ligand (ZnPhos = Zn(o-C6H4PPh2)2) are described. Ru(ZnPhos)(CO)3 (2) and Ru(ZnPhos)(IMe4)2 (4; IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene) are formed directly from the reaction of Ru(PPh3)(C6H4PPh2)2(ZnMe)2 (1) or Ru(PPh3)3HCl/LiCH2TMS/ZnMe2 with CO and IMe4, respectively. Structural and electronic structure analyses characterize both 2 and 4 as Ru(0) species in which Ru donates to the Z-type Zn center of the ZnPhos ligand; in 2, Ru adopts an octahedral coordination, while 4 displays square-pyramidal coordination with Zn in the axial position. Under photolytic conditions, 2 loses CO to give Ru(ZnPhos)(CO)2 that then adds H2 over the Ru-Zn bond to form Ru(ZnPhos)(CO)2(µ-H)2 (3). In contrast, 4 reacts directly with H2 to set up an equilibrium with Ru(ZnPhos)(IMe4)2H2 (5), the product of oxidative addition at the Ru center. DFT calculations rationalize these different outcomes in terms of the energies of the square-pyramidal Ru(ZnPhos)L2 intermediates in which Zn sits in a basal site: for L = CO, this is readily accessed and allows H2 to add across the Ru-Zn bond, but for L = IMe4, this species is kinetically inaccessible and reaction can only occur at the Ru center. This difference is related to the strong π-acceptor ability of CO compared to IMe4. Steric effects associated with the larger IMe4 ligands are not significant. Species 4 can be considered as a Ru(0)L4 species that is stabilized by the Ru→Zn interaction. As such, it is a rare example of a stable Ru(0)L4 species devoid of strong π-acceptor ligands.

Unified Total Synthesis of Pyrroloazocine Indole Alkaloids Sheds Light on Their Biosynthetic Relationship.

The total synthesis of seven members of the lapidilectine and grandilodine family of alkaloids has been accomplished in racemic and enantiopure form without protection/deprotection of functional groups. The two key steps, an 8- endo-dig hydroarylation and a 6- exo-trig photoredox cyclization, were catalyzed using gold. A rationale for the formation of the cyclopropane ring of the lundurines is also provided.

Exceedingly Facile Ph-X Activation (X = Cl, Br, I) with Ruthenium(II): Arresting Kinetics, Autocatalysis, and Mechanisms.

[(Ph3P)3Ru(L)(H)2] (where L = H2 (1) in the presence of styrene, Ph3P (3), and N2 (4)) cleave the Ph-X bond (X = Cl, Br, I) at RT to give [(Ph3P)3RuH(X)] (2) and PhH. A combined experimental and DFT study points to [(Ph3P)3Ru(H)2] as the reactive species generated upon spontaneous loss of L from 3 and 4. The reaction of 3 with excess PhI displays striking kinetics which initially appears zeroth order in Ru. However mechanistic studies reveal that this is due to autocatalysis comprising two factors: 1) complex 2, originating from the initial PhI activation with 3, is roughly as reactive toward PhI as 3 itself; and 2) the Ph-I bond cleavage with the just-produced 2 gives rise to [(Ph3P)2RuI2], which quickly comproportionates with the still-present 3 to recover 2. Both the initial and onward activation reactions involve PPh3 dissociation, PhI coordination to Ru through I, rearrangement to a η(2)-PhI intermediate, and Ph-I oxidative addition.

Well-defined CuC2F5 complexes and pentafluoroethylation of acid chlorides.

Four new well-defined Cu(I) complexes bearing a C2 F5 ligand have been prepared and fully characterized: [(Ph3 P)2 CuC2 F5 ] (2), [(bpy)CuC2 F5 ] (3), [(Ph3 P)Cu(phen)C2 F5 ] (4), and [(IPr*)CuC2 F5 ] (5). X-ray structures of all four have been determined, showing that the C2 F5 -ligated Cu atom can be di- (5), tri- (2 and 3), and tetracoordinate (4). The mixed phen-PPh3 complex 4 is a highly efficient fluoroalkylating agent for a broad variety of acid chlorides. This high-yielding transformation represents the first general method for the synthesis of RCOC2 F5 from the corresponding RCOCl.

The Trifluoromethyl Anion.

First evidence for the existence of free trifluoromethyl anion CF3 (-) has been obtained. The 3D-caged potassium cation in [K(crypt-222)](+) is inaccessible to CF3 (-) , thus rendering it uncoordinated ("naked"). Ionic [K(crypt-222)](+) CF3 (-) has been characterized by single-crystal X-ray diffraction, solution NMR spectroscopy, DFT calculations, and reactivity toward electrophiles.

A Platform for the Liebeskind-Srogl Coupling of Heteroaromatic Thioethers for Medicinal-Chemistry-Relevant Transformations.

General and robust conditions for the Liebeskind-Srogl coupling were developed and used in functionalization of medicinal-chemistry-relevant heterocyclic substrates. Applicability in HTE and library synthesis, combined with its orthogonality to other cross-coupling reactions, make it highly attractive for discovery chemistry workflows. Additionally, the results suggest that the nature of the Cu(I)-carboxylate plays a more prominent role in the reaction performance than the nature of Pd-catalysts, which is rather uncommon for Pd-catalysis and can be used in further optimization of Liebeskind-Srogl coupling.

2D and 3D Self-Assembly of Fluorine-Free Pillar-[5]-Arenes and Perfluorinated Diacids at All-Aqueous Interfaces.

The interaction of perfluorinated molecules, also known as "forever chemicals" due to their pervasiveness, with their environment remains an important yet poorly understood topic. In this work, the self-assembly of perfluorinated molecules with multivalent hosts, pillar-[5]-arenes, is investigated. It is found that perfluoroalkyl diacids and pillar-[5]-arenes rapidly and strongly complex with each other at aqueous interfaces, forming solid interfacially templated films. Their complexation is shown to be driven primarily by fluorophilic aggregation and assisted by electrostatic interactions, as supported by the crystal structure of the complexes, and leads to the formation of quasi-2D phase-separated films. This self-assembly process can be further manipulated using aqueous two-phase system microdroplets, enabling the controlled formation of 3D micro-scaffolds.

Enantiospecific Synthesis of Aniline-Derived Sulfonimidamides.

Reaction of sulfonimidoyl fluorides with anilines and Ca(NTf2)2 results in the formation of chiral sulfonimidamides. The reaction proceeds with inversion of the stereocenter at a sulfur atom. Enantiospecificity of the reaction was observed for all studied non-heterocyclic anilines. Combined experimental and computational mechanistic studies highlight chelate-type coordination of the sulfonimidoyl group to Ca(NTf2)2 and the formation of a SN2-like transition state, in which leaving F- coordinates with the Ca2+ ion.

Structure and Reactivity of [Ru-Al] and [Ru-Sn] Heterobimetallic PPh3-Based Complexes.

Treatment of [Ru(PPh3)(C6H4PPh2)2H][Li(THF)2] with AlMe2Cl and SnMe3Cl leads to elimination of LiCl and CH4 and formation of the heterobimetallic complexes [Ru(C6H4PPh2)2{PPh2C6H4AlMe(THF)}H] 5 and [Ru(PPh3)(C6H4PPh2)(PPh2C6H4SnMe2)] 6, respectively. The pathways to 5 and 6 have been probed by variable temperature NMR studies, together with input from DFT calculations. Complete reaction of H2 occurs with 5 at 60 °C and with 6 at room temperature to yield the spectroscopically characterized trihydride complexes [Ru(PPh2)2{PPh2C6H4AlMe}H3] 7 and [Ru(PPh2)2{PPh2C6H4SnMe2}H3] 8. In the presence of CO, 6 forms the acylated phosphine complex, [Ru(CO)2(C(O)C6H4PPh2)(PPh2C6H4SnMe2)] 9, through a series of intermediates that were identified by NMR spectroscopy in conjunction with 13CO labeling. Complex 6 undergoes addition and substitution reactions with the N-heterocyclic carbene 1,3,4,5-tetramethylimidazol-2-ylidene (IMe4) to give [Ru(IMe4)2(PPh2C6H4)(PPh2C6H4SnMe2)] 10, which converted via rare N-Me group C-H activation to [Ru(IMe4)(PPh3)(IMe4)'(PPh2C6H4SnMe2)] 11 upon heating at 60 °C and to a mixture of [Ru(IMe4)2(IMe4)'(PPh2C6H4SnMe2)] 12 and [Ru(PPh3)(PPh2C6H4)(IMe4-SnMe2)'] 13 at 120 °C.

Correction: Heterobimetallic ruthenium-zinc complexes with bulky N-heterocyclic carbenes: syntheses, structures and reactivity.

Correction for 'Heterobimetallic ruthenium-zinc complexes with bulky N-heterocyclic carbenes: syntheses, structures and reactivity' by Maialen Espinal-Viguri et al., Dalton Trans., 2019, 48, 4176-4189, DOI: 10.1039/C8DT05023F.

Electrocatalytic multicomponent assembling of isatins, 3-methyl-2-pyrazolin-5-ones and malononitrile: facile and convenient way to functionalized spirocyclic [indole-3,4'-pyrano[2,3-c]pyrazole] system.

Electrochemically induced catalytic multicomponent transformation of isatins, 3-methyl-2-pyrazolin-5-ones and malononitrile in ethanol in an undivided cell in the presence of sodium bromide as an electrolyte results in the formation of spirooxindoles with fused functionalized pyrano[2,3-c]pyrazole system in 78-99} yields. The developed efficient electrocatalytic approach to medicinally relevant spirocyclic [indole-3,4'-pyrano[2,3-c]pyrazoles] is beneficial from the viewpoint of diversity-oriented large-scale processes and represents a novel example of facile environmentally benign synthetic concept for electrocatalytic multicomponent reaction strategy.