The cationic AuIII pincer complex [(tBuPCP)AuIII-OH]OTf (AuOH, tBuPCP = 2,6-(CH2PtBu2)2C6H3) was prepared and characterized. In contrast to hydrogenolysis reactions of other late metal hydroxides, the hydrogenolysis of AuOH to form the corresponding AuIII-H and water is shown to require an acid catalyst. The kinetic data, collected in acetone-d6, are consistent with a reaction mechanism involving initial protonation to form the AuIII aquo complex, [(tBuPCP)AuIII-OH2](OTf)2 (AuOH2), which was isolated and characterized. Following substitution of the water by a coordinating solvent, the dicationic AuIII center undergoes electrophilic activation of H2 to generate the [(tBuPCP)AuIII-H]OTf product (AuH). The mechanism of hydrogenolysis is supported by experimental and computational (density functional theory) results. A AuIII-dihydrogen complex (Au(H2)) was located along the potential energy surface for the reaction, and computations indicate that deprotonation of Au(H2) by acetone solvent is barrierless. The bonding and properties of the proposed AuIII-H2 complex are consistent with predictions made for high-valent, electrophilic metal-dihydrogen complexes.

We report here the synthesis and characterization of a bulky titanium(IV) imido via the bimolecular deazotation of trityl azide by the Ti(II) precursor [(Tp3-tBu,5-Me)TiCl] (1, Tp3-tBu,5-Me = hydrido(tris(3-methyl-5-tert-butylpyrazolyl)borate)). The sterically encumbering trityl substituent on an azide group discourages the unimolecular deazotation pathway and allows the isolation and full characterization of a rare organic azide adduct of Ti, namely, the diazenylimide complex [(Tp3-tBu,5-Me)Ti(N3CPh3)Cl] (2). We show how free Ti(II) is a necessity to promote deazotation, thus allowing for a bimolecular conversion of 2 to a sterically crowded triphenylimido complex, [(Tp3-tBu,5-Me)Ti(NCPh3)Cl] (3). Complex 3 is the kinetic species formed from deazotation of 2, and mild thermolysis results in the formation of its isomer [{HB(pyztBu,Me)2(pyzMe,tBu)}Ti{NCPh3}Cl] (4), {HB(pyztBu,Me)2(pyzMe,tBu)} = hydrido(bis(3-methyl-5-tert-butylpyrazolyl)(5-methyl-3-tert-butylpyrazolyl)borate) via a 1,2-borotropic shift. This study demonstrates that unimolecular deazotation of 2 to 3 is significantly disfavored, and attributed to the steric bulk of the trityl substituent. By congesting the imido fragment, we also show mechanistically how conversion of 3 takes place to alleviate congestion by the CPh3 group to form 4. This process involves a rate-limiting 1,2-borotropic shift with activation parameters Ea = 30(1) kcal/mol, ΔH‡ = 30(1) kcal/mol, and ΔS‡ = 15(1) cal/mol·K as measured by VT-1H NMR spectroscopy.

A series of solvated complexes: [(C8H8)Ln(C5Me4R)(DME)] Ln = La, R = -Me; (La-2) Ln = Ce, R = -Me, -SiMe3, -H; (Ce-2, Ce-3, Ce-4), [(dbCOT)Ln(C5Me5)(DME)] (Ln-6), (dbCOT2- = dibenzocyclooctadienide; Ln = Ce, La), [(dbCOT)Ce(C5Me4H)(DME)] (Ce-7) and [(hdcCOT)Ce(C5Me5)(DME)] (Ce-8) (hdcCOT2- = hexahydrodicyclopentacyclooctatetraenide) and base-free mixed-sandwich complexes [(C8H8)Ce(C5Me5)] (Ce-9), [(C8H8)Ce(C5Me4H) (Ce-10) and [(hdcCOT)Ce(C5Me5)] (Ce-11) of the early lanthanide metals cerium and lanthanum comprising variable cyclopentadienide (Cp-) and cyclooctatetraenide (COT2-) ligands is described. To evaluate the effect of cyclopentadienide and cyclooctatetraenide ligands on the characteristics of these complexes, their solid-state structural, electrochemical, and photophysical properties were studied and accompanied by theoretical calculations. To further evaluate the effect of ligands on the topology of the complexes and the reducing properties of the complexes, syntheses of several base-free congeners were pursued, which led to isolation of the first base-free monomeric and polymeric Ce(III) mixed-sandwich compounds.

A unique entry into mononuclear titanium complexes bearing phosphinidene and phosphide ligand moieties is reported. Reaction of [K(crypt)][(PN)2TiCl] (1, crypt = 2.2.2-cryptand) with [Na(OCP)] results in [K(crypt)][(PN)2Ti(OCP)] (2) and such species can be oxidized to the derivative [(PN)2Ti(OCP)] (3), both of which do not undergo decarbonylation. However, the reaction of 1 and [NaP(SiMe3)2] leads to an unprecedented TiIII phosphinidene, [K(crypt)][(PN)2Ti═PSiMe3] (4), through an oxidative phosphorylation reaction. To promote the formation of a Ti≡P bond, complex 4 was treated with 0.5 equivalent XeF2, resulting in an oxidative desilylation step forming a molecular titanium phosphide complex, [K(crypt)][(PN)2Ti≡P] (5), which showed a characteristic downfield chemical shift at 1449.8 pmm in the 31P NMR spectrum. Complex 5 can be further functionalized to generate a terminal TiIV phosphinidene, [(PN)2Ti═PSiMe3] (6), and the latter can be independently accessed through oxidation of 4. All new complexes were characterized structurally and as appropriate by multinuclear NMR, CW X-band EPR (for TiIII), and HFEPR (for TiII) spectroscopies.

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. Ancillary NH groups contained within ligands can participate in reactions through metal-ligand cooperation. Substitution of the NH moiety by NMe or O can be used in the evaluation of its role. This study investigates how such substitutions also affect the electronics and the binding strengths of the ligand. image

Described here is a direct entry to two examples of 3d transition metal catalysts that are active for the cyclic polymerization of phenylacetylene, namely, [(BDI)M{κ 2 - C , C -(Me 3 SiC 3 SiMe 3 )}] ( 2-M ) (BDI=[ArNC(CH 3 )] 2 CH − , Ar=2,6- i Pr 2 C 6 H 3 ; M = Ti, V ). Catalysts are prepared in one step by the treatment of [(BDI)MCl 2 ] ( 1-M , M = Ti , V ) with 1,3-dilithioallene [Li 2 (Me 3 SiC 3 SiMe 3 )]. Complexes 2-M have been spectroscopically and structurally characterized and the polymers that are catalytically formed from phenylacetylene were verified to have a cyclic topology based on a combination of size-exclusion chromatography (SEC) and intrinsic viscosity studies. Two-electron oxidation of 2-V with nitrous oxide (N 2 O) cleanly yields a [V V ] alkylidene-alkynyl oxo complex [(BDI)V(=O){κ 1 - C -(=C(SiMe 3 )CC(SiMe 3 ))}] ( 3 ), which lends support for how this scaffold in 2-M might be operating in the polymerization of the terminal alkyne. This work demonstrates how alkylidynes can be circumvented using 1,3-dianionic allene as a segue into M−C multiple bonds.

Herein we report the discovery of an azabicyclo[2.1.1]hexane piperazinium methanesulfonate salt from an unexpected rearrangement reaction in the preparation of ligand-directed degraders (LDDs). This bench-stable compound was found to be a versatile electrophile in a ring-opening reaction with various types of nucleophiles. Its utility as a versatile medicinal chemistry building block is further demonstrated in the synthesis of an LDD compound targeting degradation of the androgen receptor.

During the synthesis of a new family of diimine-dioxime acenaphthene cobalt complexes a novel cis coordination mode was observed for (DABn)Co(Py)Br (4), along with the expected trans coordination mode for [(DAEn)Co(L)2]BPh4 (2). The new coordination mode for this class of compounds is fully characterized. We explore the influence of linker length, ligand protonation, and supporting ligands on the preference for the cis vs. trans coordination mode using experimental and computational methods. Increased flexibility, increased acidity, and large supporting ligands all support the preference for the cis coordination mode.

Quaternary ammonium compounds have served as a first line of protection for human health as surface disinfectants and sanitizers for nearly a century. However, increasing levels of bacterial resistance have spurred the development of novel QAC architectures. In light of the observed reduction in eukaryotic cell toxicity when the alkyl chains on QACs are shorter in nature (<= 10 C), we prepared 47 QAC architectures that bear multiple short alkyl chains appended to up to three cationic groups, thus rendering them "bushy-tailed" multiQACs. Antibacterial activity was strong (often similar to 1-4 mu M) in a varied set of bushy-tailed architectures, though observed therapeutic indices were not significantly improved over QAC structures bearing fewer and longer alkyl chains.

Reduction of the previously reported Iron (III) complex PhCC4MeFeCl with sodium naphthalide forms the square pyramidal complex PhCC4MeFe (1), cleanly in moderate yield with short reaction times. The related diamagnetic complex PhCC4MeFe(CNtBu) (2) was prepared by addition of an equivalent of tert-butylisocyanide to a solution of 1. XRD of 2 reveals a rare bent form of the isocyanide moiety with a C-N-C bond angle of 142.67(18)degrees consistent with sp2 hybridization at the N-atom while IR spectroscopy reveals an atypically broadened isocyanide stretch at nu CNR=1981 cm-1; taken together these metrics are demonstrative of the excellent donor ability of the dianionic penta-carbene framework and point to a degree of metal-to-ligand pi-backbonding rarely seen at isocyanide complexes of iron. Combined results from single crystal X-ray diffractometry and Infrared spectroscopy are consistent with a rare bent carbenic resonance form of isocyanide bonding to iron supported in a dianionic tetrapodal pentadentate N-heterocyclic carbene framework; thereby illustrating the strong donor ability of this new ligand class. image

We report the first mononuclear TiIII complex possessing a terminal imido ligand. Complex [TptBu,MeTi{NSi(CH3)3}(THF)] (2) (TptBu,Me = hydridotris(3-tert-butyl-5-methylpyrazol-1-yl)borate) is prepared by reduction of [TptBu,MeTi{NSi(CH3)3}(Cl)] (1) with KC8 in high yield. The connectivity and metalloradical nature of 2 were confirmed by single crystal X-ray diffraction studies, Q- and X-band EPR, UV-Vis and 1H NMR spectroscopies. The d1 complex [(TptBu,Me)TiCl(OEt2)][B(C6F5)4] (3), was prepared to spectroscopically compare it to 2. Electrochemical studies of 1 and 2 reveal a reversible 1e- process, and chemical oxidants ClCPh3 or 1/2 eq. XeF2 react cleanly with 2 yielding 1 or the fluoride derivative [TptBu,MeTi{NSi(CH3)3}(F)] (4), respectively.

Quaternary ammonium compounds (QACs) serve as a first line of defense against infectious pathogens. As resistance to QACs emerges in the environment, the development of next-generation disinfectants is of utmost priority for human health. Balancing antibacterial potency with environmental considerations is required to effectively counter the development of bacterial resistance. To address this challenge, a series of 14 novel biscationic quaternary phosphonium compounds (bisQPCs) have been prepared as amphiphilic disinfectants through straightforward, high-yielding alkylation reactions. These compounds feature decomposable or "soft" amide moieties in their side chains, anticipated to promote decomposition under environmental conditions. Strong bioactivity against a panel of seven bacterial pathogens was observed, highlighted by single-digit micromolar activity for compounds P6P-12A,12A and P3P-12A,12A. Hydrolysis experiments in pure water and in buffers of varying pH revealed surprising decomposition of the soft QPCs under basic conditions at the phosphonium center, leading to inactive phosphine oxide products; QPC stability (>24 h) was maintained in neutral solutions. The results of this work unveil soft QPCs as a potent and environmentally conscious new class of bisQPC disinfectants.

The Front Cover shows selected tetrapodal-pentadentate “butterflies” taking flight. First noted as bearing resemblance to butterflies by Paine and Nordlander, these 5-coordinate frameworks have found applications in areas such as H2 evolution catalysis, N2 reduction chemistry, and as scaffolds to support high-valent metal-oxo compounds. Our contribution to this topology consists of a carbon butterfly composed of five N-heterocyclic carbene donors bridged by arylborate linkers to provide a dianionic framework upon removal of five protons. More information can be found in the Research Article by J. J. Scepaniak and co-workers.

The title compound crystallizes with Z = 6 in space group P21/m.

Substituted oxazoles and imidazoles are synthesized in one pot from the isocyanide building block Asmic (anisylsulfanylmethyl isocyanide), an alkyl halide, and an acid chloride or nitrile, respectively. The modular assembly employs sequential deprotonation-alkylation and deprotonation-acylation or imination of Asmic, followed by an unusual carbon-sulfur bond cleavage to construct the azole. The strategy is robust, highly efficient, and affords C4-C5 disubstituted oxazoles or imidazoles in a single operation.

SiCl4 promotes isocyanide additions to oxoalkenenitriles to selectively generate 3-acylpyrroles, 2-aminofurans, or pyrrolidinones. Cyclic oxoalkenenitriles add 2 equiv of an isocyanide that installs the two core atoms of an acylpyrrole and a nitrile substituent, whereas acyclic oxoalkenenitriles add 1 equiv of an isocyanide to afford 2-aminofurans; subsequent air oxidation generates pyrrolidinones via a furan oxygenation-cleavage-cyclization sequence. The syntheses proceed under mild conditions to rapidly access three richly decorated heterocycles.

Naphthalene converts magnesiated ω-alkenylnitriles into bi- and tricyclic ketones via a polar-radical addition-cyclization cascade. One-electron oxidation of magnesiated nitriles generates nitrile-stabilized radicals that cyclize onto a pendant olefin and then rebound onto the nitrile through a reduction-cyclization sequence; subsequent hydrolysis affords a diverse array of bicyclo[3.2.0]heptan-6-ones. Combining the polar-radical cascade with a 1,2:1,4-carbonyl-conjugate addition generates complex cyclobutanones containing four new carbon-carbon bonds and four chiral centers in one synthetic operation.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.