A Vanadium Methylidene.

Examples of stable 3d transition metal methylidene complexes are extremely rare. Here we report an isolable and stable vanadium methylidene complex, [(PNP)V(=NAr)(=CH2)] (PNP = N[2-PiPr2-4-methylphenyl]-, Ar = 2,6-iPr2C6H3), via H atom transfer (HAT) from [(PNP)V(NHAr)(CH3)] or [(PNP)V(=NAr)(CH3)] using two or one equivalents of the TEMPO radical (TEMPO = (2,2,6,6-tetramethylpiperidin-1-yl)oxyl), respectively. Alternatively, the vanadium methylidene moiety can also be formed via the treatment of transient [(PNP)V=NAr] with the Wittig reagent, H2CPPh3. Structural and spectroscopic analysis, including 13C enriched labeling of the methylidene ligand, unequivocally confirmed the terminal nature of a rare 3d methylidene complex, featuring a V=CH2 bond distance of 1.908(2) Å and a highly downfield 13C NMR spectral shift at 298 ppm. In the absence of the ylide, intermediate [(PNP)V=NAr] activates dinitrogen to form an end-on bridging N2 complex, [(PNP)V(=NAr)]2(µ2-η1:η1-N2), having a singlet ground state. Complex [(PNP)V(=NAr)(=CH2)] reacts with H3COTf to form [(PNP)V(=NAr)(OTf)], accompanied by the release of ethylene as evidenced by 1H NMR spectroscopy, and reactivity studies suggest a ß-hydride elimination pathway.

Vanadium Alkylidyne Initiated Cyclic Polymer Synthesis: The Importance of a Deprotiovanadacyclobutadiene Moiety.

Reported is the catalytic cyclic polymer synthesis by a 3d transition metal complex: a V(V) alkylidyne, [(dBDI)V≡CtBu(OEt2)] (1-OEt2), supported by the deprotonated ß-diketiminate dBDI2- (dBDI2- = ArNC(CH3)CHC(CH2)NAr, Ar = 2,6-iPr2C6H3). Complex 1-OEt2 is a precatalyst for the polymerization of phenylacetylene (PhCCH) to give cyclic poly(phenylacetylene) (c-PPA), whereas its precursor, complex [(BDI)V≡CtBu(OTf)] (2-OTf; BDI- = [ArNC(CH3)]2CH, Ar = 2,6-iPr2C6H3, OTf = OSO2CF3), and the zwitterion [((C6F5)3B-dBDI)V≡CtBu(OEt2)] (3-OEt2) exhibit low catalytic activity despite having a neopentylidyne ligand. Cyclic polymer topologies were verified by size-exclusion chromatography (SEC) and intrinsic viscosity studies. A component of the mechanism of the cyclic polymerization reaction was probed by isolation and full characterization of 4- and 6-membered metallacycles as model intermediates. Metallacyclobutadiene (MCBD) and deprotiometallacyclobutadiene (dMCBD) complexes (dBDI)V[C(tBu)C(H)C(tBu)] (4-tBu) and (BDI)V[C(tBu)CC(Mes)] (5-Mes), respectively, were synthesized upon reaction with bulkier alkynes, tBu- (tBuCCH) and Mes-acetylene (MesCCH), with 1-OEt2. Furthermore, the reaction of the conjugate acid of 1-OEt2, [(BDI)V≡CtBu(OTf)] (2-OTf), with the conjugated base of phenylacetylene, lithium phenylacetylide (LiCCPh), yields the doubly deprotio-metallacycle complex, [Li(THF)4]{(BDI)V[C(Ph)CC(tBu)CC(Ph)]} (6). Protonation of the doubly deprotio-metallacycle complex 6 yields 6-H+, a catalytically active species toward the polymerization of PhCCH, for which the polymers were also confirmed to be cyclic by SEC studies. Computational mechanistic studies complement the experimental observations and provide insight into the mechanism of cyclic polymer growth. The noninnocence of the supporting dBDI2- ligand and its role in proton shuttling to generate deprotiometallacyclobutadiene (dMCBD) complexes that proposedly culminate in the formation of catalytically active V(III) species are also discussed. This work demonstrates how a dMCBD moiety can react with terminal alkynes to form cyclic polyalkynes.

Softer Is Better for Titanium: Molecular Titanium Arsenido Anions Featuring Ti≡As Bonding and a Terminal Parent Arsinidene.

We introduce the arsenido ligand onto the TiIV ion, yielding a remarkably covalent Ti≡As bond and the parent arsinidene Ti═AsH moiety. An anionic arsenido ligand is assembled via reductive decarbonylation involving the discrete TiII salt [K(cryptand)][(PN)2TiCl] (1) (cryptand = 222-Kryptofix) and Na(OCAs)(dioxane)1.5 in thf/toluene to produce the mixed alkali ate-complex [(PN)2Ti(As)]2(µ2-KNa(thf)2) (2) and the discrete salt [K(cryptand)][(PN)2Ti≡As] (3) featuring a terminal Ti≡As ligand. Protonation of 2 or 3 with various weak acids cleanly forms the parent arsinidene [(PN)2Ti═AsH] (4), which upon deprotonation with KCH2Ph in thf generates the more symmetric anionic arsenido [(PN)2Ti(As){µ2-K(thf)2}]2 (5). Experimental and computational studies suggest the pKa of 4 to be ∼23, and the bond orders in 2, 3, and 5 are all in the range of a Ti≡As triple bond, with decreasing bond order in 4.

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 of metal complexes, complexes where the proton has been substituted with a methyl group (NMe) are often investigated. An alternative strategy would involve 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. The different CO stretching frequencies of all four Rh-complexes suggest that substitutions of NH with NMe, as well as O, lead to significant electronic differences, and these differences are further demonstrated to lead to different ligand addition/substitution reactivities of the four isoelectronic Rh-complexes. Overall, the results suggest that the electronic differences arising due to NH substitutions can be significant and must be accounted for prior to invoking the participation of the proton.

Synthesis and Luminescence Studies of a Tethered, Trigonal, Silver(I) Tris(alkyne) Complex.

The synthesis and characterization of a tris(alkyne) ligand, tris[2-(trimethylsilyl)ethynyl-4-tert-butylbenzyl]amine (1), and its silver(I) hexafluorophosphate complex, 1-Ag, are reported. The solid-state structure and luminescence properties of 1-Ag indicate relatively strong silver(I)-alkyne interactions between the metal cation and 1. No significant changes in the bond angles or lengths were observed upon metalation of 1 with Ag+, indicating a relatively unstrained ligand-metal motif. The luminescence properties of 1 and 1-Ag are also disclosed, showing attenuation in the luminescence intensity upon Ag+ metalation, with Stokes shifts of ∼3700 and ∼3200 cm-1 for 1 and 1-Ag, respectively. The lifetimes of 1-Ag (τ1 = 8.383 ± 0.053 ns and τ2 = 4.665 ± 0.061 ns) were longer than those of 1 (τ1 = 6.708 ± 0.085 ns and τ2 = 3.689 ± 0.025 ns), possibly indicating multiple conformers of 1-Ag in solution. This new silver alkyne platform has potential applications in studies of catalysis, luminescent compounds, and sensing.

Reversible O-H Bond Activation by Tripodal tris(Nitroxide) Aluminum and Gallium Complexes.

Herein, we report the preparation and characterization of the Group 13 metal complexes of a tripodal tris(nitroxide)-based ligand, designated (TriNOx3-)M (M = Al (1), Ga (2), In (3)). Complexes 1 and 2 both activate the O-H bond of a range of alcohols spanning a ∼10 pKa unit range via an element-ligand cooperative pathway to afford the zwitterionic complexes (HTriNOx2-)M-OR. Structures of these alcohol adduct products are discussed. We demonstrate that the thermodynamic and kinetic aspects of the reactions are both influenced by the identity of the metal, with 1 having higher reaction equilibrium constants and proceeding at a faster rate relative to 2 for any given alcohol. These parameters are also influenced by the pKa of the alcohol, with more acidic alcohols reacting both to more completion and faster than their less acidic counterparts. Possible mechanistic pathways for the O-H activation are discussed.

Metallacyclobuta-(2,3)-diene: A Bidentate Ligand for Stream-line Synthesis of First Row Transition Metal Catalysts for Cyclic Polymerization of Phenylacetylene.

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{κ2 -C,C-(Me3 SiC3 SiMe3 )}] (2-M) (BDI=[ArNC(CH3 )]2 CH- , Ar=2,6-i Pr2 C6 H3 ; M=Ti, V). Catalysts are prepared in one step by the treatment of [(BDI)MCl2 ] (1-M, M=Ti, V) with 1,3-dilithioallene [Li2 (Me3 SiC3 SiMe3 )]. 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 (N2 O) cleanly yields a [VV ] alkylidene-alkynyl oxo complex [(BDI)V(=O){κ1 -C-(=C(SiMe3 )CC(SiMe3 ))}] (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.

Divalent Titanium via Reductive N-C Coupling of a TiIV Nitrido with π-Acids.

The nitrido-ate complex [(PN)2Ti(N){µ2-K(OEt2)}]2 (1) (PN-=(N-(2-PiPr2-4-methylphenyl)-2,4,6-Me3C6H2) reductively couples CO and isocyanides in the presence of DME or cryptand (Kryptofix222), to form rare, five-coordinate TiII complexes having a linear cumulene motif, [K(L)][(PN)2Ti(NCE)] (E=O, L=Kryptofix222, (2); E=NAd, L=3 DME, (3); E=NtBu, L=3 DME, (4); E=NAd, L=Kryptofix222, (5)). Oxidation of 2-5 with [Fc][OTf] afforded an isostructural TiIII center containing a neutral cumulene, [(PN)2Ti(NCE)] (E=O, (6); E=NAd (7), NtBu (8)) and characterization by CW X-band EPR spectroscopy, revealed unpaired electron to be metal centric. Moreover, 1e- reduction of 6 and 7 in the presence of Kryptofix222cleanly reformed corresponding discrete TiII complexes 2 and 5, which were further characterized by solution magnetization measurements and high-frequency and -field EPR (HFEPR) spectroscopy. Furthermore, oxidation of 7 with [Fc*][B(C6F5)4] resulted in a ligand disproportionated TiIV complex having transoid carbodiimides, [(PN)2Ti(NCNAd)2] (9). Comparison of spectroscopic, structural, and computational data for the divalent, trivalent, and tetravalent systems, including their 15N enriched isotopomers demonstrate these cumulenes to decrease in order of backbonding as TiII→TiIII→TiIV and increasing order of π-donation as TiII→TiIII→TiIV, thus displaying more covalency in TiIII species. Lastly, we show a synthetic cycle whereby complex 1 can deliver an N-atom to CO and CNAd.

Mediating Photochemical Reaction Rates at Lewis Acidic Rare Earths by Selective Energy Loss to 4f-Electron States.

Manifesting chemical differences in individual rare earth (RE) element complexes is challenging due to the similar sizes of the tripositive cations and the corelike 4f shell. We disclose a new strategy for differentiating between similarly sized Dy3+ and Y3+ ions through a tailored photochemical reaction of their isostructural complexes in which the f-electron states of Dy3+ act as an energy sink. Complexes RE(hfac)3(NMMO)2 (RE = Dy (2-Dy) and Y (2-Y), hfac = hexafluoroacetylacetonate, and NMMO = N-methylmorpholine-N-oxide) showed variable rates of oxygen atom transfer (OAT) to triphenylphosphine under ultraviolet (UV) irradiation, as monitored by 1H and 19F NMR spectroscopies. Ultrafast transient absorption spectroscopy (TAS) identified the excited state(s) responsible for the photochemical OAT reaction or lack thereof. Competing sensitization pathways leading to excited-state deactivation in 2-Dy through energy transfer to the 4f electron manifold ultimately slows the OAT reaction at this metal cation. The measured rate differences between the open-shell Dy3+ and closed-shell Y3+ complexes demonstrate that using established principles of 4f ion sensitization may deliver new, selective modalities for differentiating the RE elements that do not depend on cation size.

Silica Supported Organometallic IrI Complexes Enable Efficient Catalytic Methane Borylation.

Catalytic C-H borylation is an attractive method for the conversion of the most abundant hydrocarbon, methane (CH4), to a mild nucleophilic building block. However, existing CH4 borylation catalysts often suffer from low turnover numbers and conversions, which is hypothesized to result from inactive metal hydride agglomerates. Herein we report that the heterogenization of a bisphosphine molecular precatalyst, [(dmpe)Ir(cod)CH3], onto amorphous silica dramatically enhances its performance, yielding a catalyst that is 12-times more efficient than the current standard for CH4 borylation. The catalyst affords over 2000 turnovers at 150 °C in 16 h with a selectivity of 91.5% for mono- vs diborylation. Higher catalyst loadings improve yield and selectivity for the monoborylated product (H3CBpin) with 82.8% yield and >99% selectivity being achieved with 1255 turnovers. X-ray absorption and dynamic nuclear polarization-enhanced solid-state NMR spectroscopic studies identify the supported precatalyst as an IrI species, and indicate that upon completion of catalysis, multinuclear Ir polyhydrides are not formed. This is consistent with the hypothesis that immobilization of the organometallic Ir species on a surface prevents bimolecular decomposition pathways. Immobilization of the homogeneous IrI fragment onto amorphous silica represents a unique and simple strategy to improve the TON and longevity of a CH4 borylation catalyst.

Electronic Structure Studies and Photophysics of Luminescent Th(IV) Anilido and Imido Complexes.

A series of thorium anilide compounds [ThNHArR(TriNOx)] (R = para-OCH3 (1-ArOMe), para-H (1-ArH), para-Cl (1-ArCl), para-CF3 (1-Ar4-CF3), TriNOx3- = tris(2-tert-butylhydroxylaminato)benzylamine), and their corresponding imido compounds [Li(DME)][Th═NArR(TriNOx)] (2-ArR) as well as the alkyl congeners [ThNHAd(TriNOx)] (1-Ad) and [Li(DME)][Th═NAd(TriNOx)] (2-Ad), have been prepared. The para-substituents on the arylimido moiety were introduced for systematic variation of their electron-donating and withdrawing abilities, changes that were evident in measurements of the 13C{1H} NMR chemical shifts of the ipso-C atom of the ArR moiety. Room temperature, solution-state luminescence of the four new thorium imido compounds, along with the previously reported [Li(THF)2][Th═NAr3,5-CF3(TriNOx)] (2-Ar3,5-CF3) and [Li(THF)(Et2O)][Ce═NAr3,5-CF3(TriNOx)] (3-Ar3,5-CF3) have been described. Among these complexes, 2-Ar3,5-CF3 demonstrated the most intense luminescence feature with excitation at 398 nm and emission at 453 nm. The luminescence measurements, together with a time-dependent density functional theory (TD-DFT) study, helped uncover an intra-ligand n → π* transition that was assigned as the origin of the bright blue luminescence; 3-Ar3,5-CF3 has an 1.2 eV redshift in excitation energy compared with its proligand. The weak luminescence of other derivatives (2-ArR and 3-Ar3,5-CF3) was attributed to non-radiative decay from low-lying excited states originating from inter-ligand transitions (2-ArR) or ligand-to-metal charge transfer bands (3-Ar3,5-CF3). Overall, the results expand the range of the thorium imido organometallic compounds and demonstrate that thorium(IV) complexes can support strong ligand luminescence. The results also demonstrate the utility of applying a Th(IV) center for tuning the n → π* luminescence energy and intensity of an associated imido moiety.

Investigating Metal-Metal Bond Polarization in a Heteroleptic Tris-Ylide Diiron System.

This article describes the synthesis, characterization, and S-atom transfer reactivity of a series of C3v-symmetric diiron complexes. The iron centers in each complex are coordinated in distinct ligand environments, with one (FeN) bound in a pseudo-trigonal bipyramidal geometry by three phosphinimine nitrogens in the equatorial plane, a tertiary amine, and the second metal center (FeC). FeC is coordinated, in turn, by FeN, three ylidic carbons in a trigonal plane, and, in certain cases, by an axial oxygen donor. The three alkyl donors at FeC form through the reduction of the appended N═PMe3 arms of the monometallic parent complex. The complexes were studied crystallographically, spectroscopically (NMR, UV-vis, and Mössbauer), and computationally (DFT, CASSCF) and found to be high-spin throughout, with short Fe-Fe distances that belie weak orbital overlap between the two metals. Further, the redox nature of this series allowed for the determination that oxidation is localized to the FeC. S-atom transfer chemistry resulted in the formal insertion of a S atom into the Fe-Fe bond of the reduced diiron complex to form a mixture of Fe4S and Fe4S2 products.

Observing Similarities and Differences in the Properties of Isostructural Niobium(V)/Tantalum(V) Coordination Compounds with Strong Pi-Donor Ligands.

While niobium and tantalum are found together in their mineral ores, their respective applications in technology require chemical separation. Nb/Ta separations are challenging due to the similar reactivities displayed by these metals in the solution phase. Coordination complexes of these metals have been studied in the contexts of catalysis, small-molecule activation, and functional group insertion reactivity; relatively few studies exist directly comparing the properties of isostructural Nb/Ta complexes. Such comparisons advance the development of Nb/Ta separation chemistry through the potential for differential reactivity. Here, we explore fundamental physicochemical properties in extensively characterized Nb/Ta coordination complexes [Na(DME)3][MClamp], (Clamp6- = tris-(2-(3',5'-di-tert-butyl-2'-oxyphenyl)amidophenyl)amine; M = Nb, Ta) to advance the understanding of the different electronic, optical, and excited-state properties that these metals exhibit in pi-loaded coordination complexes.

C-C σ-Bond Oxidative Addition and Hydrofunctionalization by a Macrocycle-Supported Diiron Complex.

This report describes the first examples of unassisted C(sp)-C(sp2) and C(sp)-C(sp3) bond oxidative addition reactions to give thermodynamically favorable products. Treatment of a diiron complex supported by a geometrically and electronically flexible macrocyclic ligand, (3PDI2)Fe2(µ-N2)(PPh3)2 ([Fe2N2]0), with stoichiometric amounts of various 4,4'-disubstituted diphenylacetylenes (ArX-C≡C-ArX; X = OMe, H, F, CF3) yielded C(sp)-C(sp2) bond oxidative addition products. When Ph-C≡C-R substrates were used as substrates (R = Me, Et, iPr, tBu), products of either C(sp)-C(sp2) or C(sp)-C(sp3) bond activation were obtained, with the less sterically encumbering alkynes exclusively undergoing C(sp)-C(sp3) bond activation. Treatment of the C-C activation species with either H2 or HBpin was found to form products of C-C σ-bond hydrofunctionalization. In both the hydrogenation and hydroboration schemes, the diiron species was observed to return to [Fe2N2]0, thereby completing synthetic cycles for C-C σ-bond functionalization.

Metal-Ligand-Anion Cooperation in C-H Bond Formation at Platinum(II).

Thermolysis of [H(BPI)Pt(CH3)][OTf] (BPI = 1,3-bis(2-(4-tert-butyl)pyridylimino)isoindole) to release methane and form (BPI)Pt(OTf) is reported. Kinetic, mechanistic, and computational studies point to an unusual anion-assisted pathway that obviates the need for a higher oxidation state intermediate to couple the metal-bound methyl group with the ligand-bound hydrogen. Leveraging this insight, a triflimide derivative of the (BPI)Pt complex was shown to activate benzene, highlighting the role of the counteranion in controlling the activity of these complexes.

An Isolable Azide Adduct of Titanium(II) Follows Bifurcated Deazotation Pathways to an Imide.

AdN3 (Ad = 1-adamantyl) reacts with the tetrahedral TiII complex [(TptBu,Me)TiCl] (TptBu,Me = hydrotris(3-tert-butyl-5-methylpyrazol-1-yl)borate) to generate a mixture of an imide complex, [(TptBu,Me)TiCl(NAd)] (4), and an unusual and kinetically stable azide adduct of the group 4 metal, namely, [(TptBu,Me)TiCl(γ-N3Ad)] (3). In these conversions, the product distribution is determined by the relative concentration of reactants. In contrast, the azide adduct 3 forms selectively when a masked TiII complex (N2 or AdNC adduct) reacts with AdN3. Upon heating, 3 extrudes dinitrogen in a unimolecular process proceeding through a titanatriazete intermediate to form the imide complex 4, but the observed thermal stability of the azide adduct (t1/2 = 61 days at 25 °C) is at odds with the large fraction of imide complex formed directly in reactions between AdN3 and [(TptBu,Me)TiCl] at room temperature (∼50% imide with a 1:1 stoichiometry). A combination of theoretical and experimental studies identified an additional deazotation pathway, proceeding through a bimetallic complex bridged by a single azide ligand. The electronic origin of this deazotation mechanism lies in the ability of azide adduct 3 to serve as a π-backbonding metallaligand toward free [(TptBu,Me)TiCl]. These findings unveil a new class of azide-to-imide conversions for transition metals, highlighting that the mechanisms underlying this common synthetic methodology may be more complex than conventionally assumed, given the concentration dependence in the conversion of an azide into an imide complex. Lastly, we show how significantly different AdN3 reacts when treated with [(TptBu,Me)VCl].

Ditelluride, Terminal Tellurido, and Bis(tellurido) Motifs of Titanium.

Highly modular and rational syntheses of titanium compounds containing ditelluride, terminal telluride, and bis(telluride) structural motifs are disclosed in this study. Titanate anions bearing two cis and terminal telluride functionalities bound to the same metal center represent a unique example of a group 4 transition metal bis(chalcogenide) ion and are accessed in a simple, single-step procedure from Ti(III) bis(alkyl) complexes in the presence of an outer-sphere reductant and at least 3 equiv of Te0 powder. These compounds have been characterized crystallographically and spectroscopically with some preliminary reactivity reported for the anionic Ti(═Te)2 motif. We also report solution 125Te NMR spectral data in addition to theoretical studies addressing the bonding and structure for these titanate bis(tellurido) systems.

Tale of Three Molecular Nitrides: Mononuclear Vanadium (V) and (IV) Nitrides As Well As a Mixed-Valence Trivanadium Nitride Having a V3N4 Double-Diamond Core.

Transmetallation of [VCl3(THF)3] and [TlTptBu,Me] afforded [(TptBu,Me)VCl2] (1, TptBu,Me = hydro-tris(3-tert-butyl-5-methylpyrazol-1-yl)borate), which was reduced with KC8 to form a C3v symmetric VII complex, [(TptBu,Me)VCl] (2). Complex 1 has a high-spin (S = 1) ground state and displays rhombic high-frequency and -field electron paramagnetic resonance (HFEPR) spectra, while complex 2 has an S = 3/2 4A2 ground state observable by conventional EPR spectroscopy. Complex 1 reacts with NaN3 to form the VV nitride-azide complex [(TptBu,Me)V≡N(N3)] (3). A likely VIII azide intermediate en route to 3, [(TptBu,Me)VCl(N3)] (4), was isolated by reacting 1 with N3SiMe3. Complex 4 is thermally stable but reacts with NaN3 to form 3, implying a bis-azide intermediate, [(TptBu,Me)V(N3)2] (A), leading to 3. Reduction of 3 with KC8 furnishes a trinuclear and mixed-valent nitride, [{(TptBu,Me)V}2(µ4-VN4)] (5), conforming to a Robin-Day class I description. Complex 5 features a central vanadium ion supported only by bridging nitride ligands. Contrary to 1, complex 2 reacts with NaN3 to produce an azide-bridged dimer, [{(TptBu,Me)V}2(1,3-µ2-N3)2] (6), with two antiferromagnetically coupled high-spin VII ions. Complex 5 could be independently produced along with [(κ2-TptBu,Me)2V] upon photolysis of 6 in arene solvents. The putative {VIV≡N} intermediate, [(TptBu,Me)V≡N] (B), was intercepted by photolyzing 6 in a coordinating solvent, such as tetrahydrofuran (THF), yielding [(TptBu,Me)V≡N(THF)] (B-THF). In arene solvents, B-THF expels THF to afford 5 and [(κ2-TptBu,Me)2V]. A more stable adduct (B-OPPh3) was prepared by reacting B-THF with OPPh3. These adducts of B are the first neutral and mononuclear VIV nitride complexes to be isolated.

Counteranions at Peripheral Sites Tune Guest Affinity for a Protonated Hemicryptophane.

The affinity of small molecules for biomolecular cavities is tuned through a combination of primary and secondary interactions. It has been challenging to mimic these features in organic synthetic host molecules, however, where the cavities tend to be highly symmetric and nonpolar, and less amenable to chemical manipulation. Here, a host molecule composed of a TREN ligand and cyclotriveratrylene moiety was investigated. Size-matched polar guests were encapsulated within the cavity via triple protonation of the TREN moiety with various sulfonic acids. X-ray crystallography confirmed guest encapsulation and identified three methanesulfonates, p-toluenesulfonates, or 2-naphthalenesulfonates hydrogen-bonded with H3TREN at the periphery of the cavity. These structurally diverse counteranions were shown by 1H NMR spectroscopy to differentially regulate guest access at the three portals, and to undergo competitive displacement in solution. This work reveals "counteranion tuning" to be a simple and powerful strategy for modulating host-guest affinity, as applied here in a TREN-hemicryptophane.

Metalating 5-Methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY): Understanding the Denticity and Speciation of Complexes of the ROY Anion.

5-Methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY) is considered to be the most crystalline polymorphic organic molecule discovered to date with 12 fully characterized crystal structures present in the Cambridge Structural Database (CSD). However, metal complexes of ROY have not previously been described. Here, we explore the synthetic chemistry of ROY (denoted as H-ROY hereafter for the purpose of our study) and demonstrate that it can be deprotonated using either NaH or KH and that the resulting sodium and potassium salts of H-ROY can be cleanly isolated. Furthermore, we introduce two new metal complexes of the ROY anion (ROY-) with Co(II) and Ni(II) cations, formed by the reaction of the sodium salt of ROY, Na(ROY), with the respective transition-metal chloride salts. Solid-state X-ray diffraction studies confirm the presence of Co(II) or Ni(II) centers, with the ROY- ligand in a 1:2 ratio forming neutral trinuclear clusters of the forms [Co3ROY6] (Co-ROY) and [Ni3ROY6] (Ni-ROY) in both cases. Here, the ROY- moiety interacts with the metal center through the anionic N atom, an O atom of the -NO2 group, and the N atom of the -CN group. IR and electronic absorption spectroscopies reveal the influence of the Co(II) and Ni(II) centers on the properties of the complexes. Taken together, our results show that the metal complexes of the H-ROY proligand can be prepared with late 3d transition metals. The results of these structural chemistry studies may contribute to resolving polymorphism in H-ROY and related compounds.