Low‐Temperature N2 Binding to Two‐Coordinate L2Fe0 Enables Reductive Trapping of L2FeN2− and NH3 Generation

The two‐coordinate [(CAAC)₂Fe] complex [CAAC=cyclic (alkyl)(amino)carbene] binds dinitrogen at low temperature (T2 complex, [(CAAC)₂Fe(N₂)], was trapped by one‐electron reduction to its corresponding anion [(CAAC)₂FeN₂]^? at low temperature. This complex was structurally characterized and features an activated dinitrogen unit which can be silylated at the β‐nitrogen atom. The redox‐linked complexes [(CAAC)₂Fe^I][BAr^F₄], [(CAAC)₂Fe⁰], and [(CAAC)₂Fe^?IN₂]^? were all found to be active for the reduction of dinitrogen to ammonia upon treatment with KC₈ and HBAr^F₄?2 Et₂O at ?95 °C [up to (3.4±1.0) equivalents of ammonia per Fe center]. The N₂ reduction activity is highly temperature dependent, with significant N₂ reduction to NH₃ only occurring below ?78 °C. This reactivity profile tracks with the low temperatures needed for N₂ binding and an otherwise unavailable electron‐transfer step to generate reactive [(CAAC)₂FeN₂]^?.     

The use of free energy relationships to rationalize kinetic data in complex solvent mixtures

The electron transfer reaction [(NH₃)₄CO^III(μ-pzCO₂)Fe^II(CN)₅]⁻ → [(NH₃)₄CO^II(μ-pzCO₂)Fe^III (CN)₅]⁻ has been studied in water-cosolvent mixtures at ionic strength of I = 0.5 mol dm⁻³ (NaClO₄). A multiparameter regression coefficients have been compared to those obtained for the same reaction to a different ionic strength (I = 2.8 10⁻³ mol dm⁻³). The magnitude of these coefficients changes with the ionic strength. An explanation is given for this behavior. © 1996 John Wiley & Sons, Inc.     

Computational study of structures and proton transfer in hydrogen‐bonded ammonia complexes using semiempirical valence‐bond approach

In this study, the seGVB method was implemented for the N H bonding system, specifically for hydrogen‐bonded ammonia complexes, and the model well reproduces the MP2 geometries and energetics. A comparison between the ammonia dimer and water dimer is given from the viewpoint of valance‐bond structures in terms of the calculated bond energies and pair–pair interactions. The linear hydrogen bond is found to be stronger than the bent bonds in both cases, with the difference in energy between the linear and cyclic structures being comparable in both cases although the NH bonds are generally weaker. The energy decomposition clearly demonstrates that the changes in electronic energy are quite different in the two cases due to the presence of an additional lone pair on the water molecule, and it is this effect which leads to the net stabilization of the cyclic structure for the ammonia dimer. Proton‐transfer profiles for hydrogen‐bonded ammonia complexes [NH₂ H NH₂]⁻ and [NH₃ H NH₃]⁺ were calculated. The barrier for proton transfer in [NH₃ H NH₃]⁺ is larger than that in [NH₂ H NH₂]⁻, but smaller than that in the protonated water dimer. The different bonding structures substantially affect the barrier to proton transfer, even though they are isoelectronic systems. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 357–367, 1999     

Protonation of γ-Butyrolactone and γ-Butyrolactam

Abstract : γ-Butyrolactone and γ-butyrolactam were reacted in the superacidic systems XF/MF₅ (X=H, D; M=As, Sb). Salts of the monoprotonated species of γ-butyrolactone were obtained in terms of [(CH₂)₃OCOH]⁺[AsF₆]⁻, [(CH₂)₃OCOH]⁺[SbF₆]⁻ and [(CH₂)₃OCOD]⁺[AsF₆]⁻ and the analogous lactam salts in terms of [(CH₂)₃NHCOH]⁺[AsF₆]⁻, [(CH₂)₃NHCOH]⁺[SbF₆]⁻ and [(CH₂)₃NDCOD]⁺[AsF₆]⁻. The salts were characterized by low temperature Raman and infrared spectroscopy and for both protonated hexafluoridoarsenates, [(CH₂)₃OCOH]⁺[AsF₆]⁻ and [(CH₂)₃NHCOH]⁺[AsF₆]⁻, single-crystal X-ray structure analyses were conducted. In addition to the experimental results, quantum chemical calculations were performed on the B3LYP/aug-cc-pVTZ level of theory. As in both crystal structures C⋅⋅⋅F contacts were observed, the nature of these contacts is discussed with Mapped Electrostatic Potential as a rate of strength.     

One-Step Synthesis and Schlenk-Type Equilibrium of Cyclopentadienylmagnesium Bromides

In the in situ Grignard metalation method (iGMM), the addition of bromoethane to a suspension of magnesium turnings and cyclopentadienes [C₅H₆ (HCp), C₅H₅-Si(iPr)₃ (HCp^TIPS)] in diethyl ether smoothly yields heteroleptic [(Et₂O)Mg(Cp^R)(μ-Br)]₂ (Cp^R=Cp ( 1 ), Cp^TIPS ( 2 )). The Schlenk equilibrium of 2 in toluene leads to ligand exchange and formation of homoleptic [Mg(Cp^R)₂] ( 3 ) and [(Et₂O)MgBr(μ-Br)]₂ ( 4 ). Interfering solvation and aggregation as well as ligand redistribution equilibria hamper a quantitative elucidation of thermodynamic data for the Schlenk equilibrium of 2 in toluene. In ethereal solvents, mononuclear species [(Et₂O)₂Mg(Cp^TIPS)Br] ( 2’ ), [(Et₂O)_nMg(Cp^TIPS)₂] ( 3’ ), and [(Et₂O)₂MgBr₂] ( 4’ ) coexist. Larger coordination numbers can be realized with cyclic ethers like tetrahydropyran allowing crystallization of [(thp)₄MgBr₂] ( 5 ). The interpretation of the temperature-dependency of the Schlenk equilibrium constant in diethyl ether gives a reaction enthalpy ΔH and reaction entropy ΔS of −11.5 kJ mol⁻¹ and 60 J mol⁻¹, respectively.     

Protonation of CO2, COS,CS2: Proton affinities and the structures of the protonated species

The geometric structures of a number of isomers of the ions formed by protonation of CO₂, COS and CS₂, and of the parent molecules themselves, have been fully optimized using ab initio quantum chemical methods. Stable minima have been found both for molecules protonated at the terminal atom and at the central carbon atom; ions of the latter type show strong near-degeneracy effects which have been ignored in previous calculations. Proton affinities of CO₂, COS and CS₂ have been calculated: for CO₂ the theoretical result (565 kJ mol⁻¹) is in excellent agreement with experiment (540 kJ mol⁻¹), given that the experimental proton affinity includes a contribution from zero-point vibration of ≈ −27 kJ mol⁻¹. For COS, for which no experimental value is available, the calculations give almost identical results for both O and S protonated species (619 and 636 kJ mol⁻¹, respectively). It may not therefore be possible to distinguish these two isomers experimentally. The theoretical result for CS₂ (678 kJ mol⁻) suggests that the current experimental value of the proton affinity (699 kJ mol⁻¹) is too high, since this value includes a zero-point vibration contribution of some −19 kJ mol⁻¹).     

Electronic properties of polyoxometalate derivatives [(C2B9H11) M'M5O18]n‐ (M' = TiIV,MoVI, WVI; M = MoVI,WVI): Protonation,Electronic Spectra,and Redox Properties

Density functional theory is used to study the electronic structures and properties of Lindqvist‐type polyoxometalates‐supported organometallic compounds [LM'M₅O₁₈]^n– (L = [C₂B₉H₁₁]^2– (Cb), [C₅H₅]^– (Cp); M' = Ti^IV, Mo^VI, W^VI; M = Mo^VI, W^VI). [(Cb)M'M₅O₁₈]^n– are a series of novel compounds designed in this work, based on related experiment. The calculated results reveal that the Cb ligand is able to form a σ, 2π triple bond with M', which is similar to the bond character in [(Cp)M'M₅O₁₈]^n–. However, comparing with the protonation, electronic spectra and redox properties of [(Cp)M'M₅O₁₈]^n– and [M'M₅O₁₉]^n–, [(Cb)M'M₅O₁₈]^n– species show the advantageous electronic properties owning to the superior electron donating ability of the Cb ligand. © 2015 Wiley Periodicals, Inc.     

Absolute Rate Constants for the Addition of the 1‐(tert‐Butoxy)carbonylethyl Radical to Alkenes in Solution

Absolute rate constants and some of their Arrhenius parameters are reported for the addition of the 1‐[(tert‐butoxy)carbonyl]ethyl radical (MeC . HCO₂Me₃) to several mono‐ or 1,1‐disubstituted alkenes in acetonitrile as obtained by time‐resolved electron spin resonance spectroscopy. At 295 K, the rate constants range from 470 M ⁻¹ s⁻¹ (but‐1‐ene) to 2.4⋅10⁵ M ⁻¹ s⁻¹ (1,1‐diphenylethene), the experimental activation energies range from 26.8 kJ/mol (but‐1‐ene) to 14.7 kJ/mol (styrene), and the frequency factors obey on the average log (A/M ⁻¹ s⁻¹)=7.9±0.5. The rate constants of the secondary 1‐[(tert‐butoxy)carbonyl]ethyl radical are close to the geometric mean of those of the related primary [(tert‐butoxy)carbonyl]methyl and the tertiary 2‐(methoxycarbonyl)propan‐2‐yl radicals. The activation energies for addition of these three carboxy‐substituted alkyl radicals are mainly governed by the addition enthalpy but are also substantially lowered by ambiphilic polar effects. The results support a previously derived predictive analysis, and relations to rate constants of acrylate polymerizations are discussed.     

High-level computational study on the thermochemistry of saturated and unsaturated three- and four-membered nitrogen and phosphorus rings

The heats of formation and strain energies for saturated and unsaturated three- and four-membered nitrogen and phosphorus rings have been calculated using G2 theory. G2 heats of formation (ΔH_f298) of triaziridine [(NH)₃], triazirine (N₃H), tetrazetidine [(NH)₄], and tetrazetine (N₄H₂) are 405.0, 453.7, 522.5, and 514.1 kJ mol⁻¹, respectively. Tetrazetidine is unstable (121.5 kJ mol⁻¹ at 298 K) with respect to its dissociation into two trans-diazene (N₂H₂) molecules. The dissociation of tetrazetine into molecular nitrogen and trans-diazene is highly exothermic (ΔH₂₉₈ = −308.3 kJ mol⁻¹ calculated using G2 theory). G2 heats of formation (ΔH_f298) of cyclotriphosphane [(PH)₃], cyclotriphosphene (P₃H), cyclotetraphosphane [(PH)₄], and cyclotetraphosphene (P₄H₂) are 80.7, 167.2, 102.7, and 170.7 kJ mol⁻¹, respectively. Cyclotetraphosphane and cyclotetraphosphene are stabilized by 145.8 and 101.2 kJ mol⁻¹ relative to their dissociations into two diphosphene molecules or into diphosphene (HP(DOUBLE BOND)PH) and diphosphorus (P₂), respectively. The strain energies of triaziridine [(NH)₃], triazirine (N₃H), tetrazetidine [(NH)₄], and tetrazetine (N₄H₂) were calculated to be 115.0, 198.3, 135.8, and 162.0 kJ mol⁻¹, respectively (at 298 K). While the strain energies of the nitrogen three-membered rings in triaziridine and triazirine are smaller than the strain energies of cyclopropane (117.4 kJ mol⁻¹) and cyclopropene (232.2 kJ mol⁻¹), the strain energies of the nitrogen four-membered rings in tetrazetidine and tetrazetine are larger than those of cyclobutane (110.2 kJ mol⁻¹) and cyclobutene (132.0 kJ mol⁻¹). In contrast to higher strain in cyclopropane as compared with cyclobutane, triaziridine is less strained than tetrazetidine. The strain energies of cyclotriphosphane [(PH)₃, 21.8 kJ mol⁻¹], cyclotriphosphene (P₃H, 34.6 kJ mol⁻¹), cyclotetraphosphane [(PH)₄, 24.1 kJ mol⁻¹], and cyclotetraphosphene (P₄H₂, 18.5 kJ mol⁻¹), calculated at the G2 level are considerably smaller than those of their carbon and nitrogen analog. Cyclotetraphosphene containing the P(DOUBLE BOND)P double bond is less strained than cyclotetraphosphane, in sharp contrast to the ratio between the strain energies for the analogous unsaturated and saturated carbon and nitrogen rings. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62 : 373–384, 1997     

Protonation versus Oxonium Salt Formation: Basicity and Stability Tuning of Cyanoborate Anions

Anhydrous H[BH₂(CN)₂] crystallizes from acidic aqueous solutions of the dicyanodihydridoborate anion. The formation of H[BH₂(CN)₂] is surprising as the protonation of nitriles requires strongly acidic and anhydrous conditions but it can be rationalized based on theoretical data. In contrast, [BX(CN)₃]⁻ (X=H, F) gives the expected oxonium salts (H₃O)[BX(CN)₃] while (H₃O)[BF₂(CN)₂]/H[BF₂(CN)₂] is unstable. H[BH₂(CN)₂] forms chains via N−H⋅⋅⋅N bonds in the solid state and melts at 54 °C. Solutions of H[BH₂(CN)₂] in the room‐temperature ionic liquid [EMIm][BH₂(CN)₂] contain the [(NC)H₂BCN−H⋅⋅⋅NCBH₂(CN)]⁻ anion and are unusually stable, which enabled the study of selected spectroscopic and physical properties. [(NC)H₂BCN−H⋅⋅⋅NCBH₂(CN)]⁻ slowly gives H₂ and [(NC)H₂BCN−BH(CN)₂]⁻. The latter compound is a source of the free Lewis acid BH(CN)₂, as shown by the generation of [BHF(CN)₂]⁻ and BH(CN)₂⋅py.     

Superelectrophilic Behavior of an Anion Demonstrated by the Spontaneous Binding of Noble Gases to [B12Cl11]−

It is common and chemically intuitive to assign cations electrophilic and anions nucleophilic reactivity, respectively. Herein, we demonstrate a striking violation of this concept: The anion [B₁₂Cl₁₁]⁻ spontaneously binds to the noble gases (Ngs) xenon and krypton at room temperature in a reaction that is typical of “superelectrophilic” dications. [B₁₂Cl₁₁Ng]⁻ adducts, with Ng binding energies of 80 to 100 kJ mol⁻¹, contain B−Ng bonds with a substantial degree of covalent interaction. The electrophilic nature of the [B₁₂Cl₁₁]⁻ anion is confirmed spectroscopically by the observation of a blue shift of the CO stretching mode in the IR spectrum of [B₁₂Cl₁₁CO]⁻ and theoretically by investigation of its electronic structure. The orientation of the electric field at the reactive site of [B₁₂Cl₁₁]⁻ results in an energy barrier for the approach of polar molecules and facilitates the formation of Ng adducts that are not detected with reactive cations such as [C₆H₅]⁺. This introduces the new chemical concept of “dipole-discriminating electrophilic anions.”     

The coordination chemistry of guanidines and guanidinates

Species containing the Y-shaped CN₃ unit have recently attracted increasing attention as electronically and sterically flexible ligands. Neutral guanidines [(R₂N)₂CNR], guanidinates(−1) [(RN)₂CNR₂]⁻ and guanidinates(2) [(RN)₂CNR]²⁻ are capable of exhibiting a variety of coordination modes and a range of donor properties leading to compatibility with a remarkably wide range of metal ions from all parts of the periodic table. The coordination chemistry of these species is reviewed up to July 2000, and aspects of their electronic structures and metal-ligand bonding characteristics discussed.     

Structural and Oxidation State Alternatives in Platinum and Palladium Complexes of a Redox-Active Amidinato Ligand

Reaction of [Pt(DMSO)₂Cl₂] or [Pd(MeCN)₂Cl₂] with the electron-rich LH=N,N’-bis(4-dimethylaminophenyl)ethanimidamide yielded mononuclear [PtL₂] ( 1 ) but dinuclear [Pd₂L₄] ( 2 ), a paddle-wheel complex. The neutral compounds were characterized through experiments (crystal structures, electrochemistry, UV-vis-NIR spectroscopy, magnetic resonance) and TD-DFT calculations as metal(II) species with noninnocent ligands L⁻. The reversibly accessible cations [PtL₂]⁺ and [Pd₂L₄]⁺ were also studied, the latter as [Pd₂L₄][B{3,5-(CF₃)₂C₆H₃}₄] single crystals. Experimental and computational investigations were directed at the elucidation of the electronic structures, establishing the correct oxidation states within the alternatives [Pt^II(L⁻)₂] or [Pt^.(L )₂], [Pt^II(L^0.5−)₂]⁺ or [Pt^III(L⁻)₂]⁺, [(Pd^II)₂(μ-L⁻)₄] or [(Pd^1.5)₂(μ-L^0.75−)₄], and [(Pd^2.5)₂(μ-L⁻)₄]⁺ or [(Pd^II)₂(μ-L^0.75−)₄]⁺. In each case, the first alternative was shown to be most appropriate. Remarkable results include the preference of platinum for mononuclear planar [PtL₂] with an N-Pt-N bite angle of 62.8(2)° in contrast to [Pd₂L₄], and the dimetal (Pd₂⁴⁺→Pd₂⁵⁺) instead of ligand (L⁻→L ) oxidation of the dinuclear palladium compound.     

Salt forms of the pharmaceutical amide dihydrocarbamazepine

Carbamazepine (CBZ) is well known as a model active pharmaceutical ingredient used in the study of polymorphism and the generation and comparison of cocrystal forms. The pharmaceutical amide dihydrocarbamazepine (DCBZ) is a less well known material and is largely of interest here as a structural congener of CBZ. Reaction of DCBZ with strong acids results in protonation of the amide functionality at the O atom and gives the salt forms dihydrocarbamazepine hydrochloride {systematic name: [(10,11‐dihydro‐5H‐dibenzo[b,f]azepin‐5‐yl)(hydroxy)methylidene]azanium chloride, C₁₅H₁₅N₂O⁺·Cl⁻}, dihydrocarbamazepine hydrochloride monohydrate {systematic name: [(10,11‐dihydro‐5H‐dibenzo[b,f]azepin‐5‐yl)(hydroxy)methylidene]azanium chloride monohydrate, C₁₅H₁₅N₂O⁺·Cl⁻·H₂O} and dihydrocarbamazepine hydrobromide monohydrate {systematic name: [(10,11‐dihydro‐5H‐dibenzo[b,f]azepin‐5‐yl)(hydroxy)methylidene]azanium bromide monohydrate, C₁₅H₁₅N₂O⁺·Br⁻·H₂O}. The anhydrous hydrochloride has a structure with two crystallographically independent ion pairs (Z′ = 2), wherein both cations adopt syn conformations, whilst the two hydrated species are mutually isostructural and have cations with anti conformations. Compared to neutral dihydrocarbamazepine structures, protonation of the amide group is shown to cause changes to both the molecular (C=O bond lengthening and C—N bond shortening) and the supramolecular structures. The amide‐to‐amide and dimeric hydrogen‐bonding motifs seen for neutral polymorphs and cocrystalline species are replaced here by one‐dimensional polymeric constructs with no direct amide‐to‐amide bonds. The structures are also compared with, and shown to be closely related to, those of the salt forms of the structurally similar pharmaceutical carbamazepine.     

Kinetic Analysis of the Decomposition Reaction of the Mercury Jarosite in NaOH Medium

This work presents the kinetic study of the decomposition in NaOH medium of mercury jarosite whose approximate formula is [Hg_0.39(H₃O)_0.22]Fe_2.71(SO₄)_2.17(OH)_4.79(H₂O)_2.09. The reaction progress takes place on the surface of the compound with diffusion of the hydroxyl ions (OH⁻) from the solution to the particle surface moving the reaction front toward the interior of the particle, with the release of ions SO₄²⁻ and Hg²⁺ from the core to the reaction medium. The decomposition curve can be described by three kinetics stages: an induction period followed by a progressive conversion period and ending the reaction in the stabilization zone. The results of X−ray diffraction showed that as the decomposition reaction progresses the partially decomposed solids lost its crystallinity ending as amorphous solids. For the induction period, the reaction order (n ) was 0.52 for [OH⁻] < 0.0187 mol L⁻¹ and when [OH⁻] > 0.0187 mol L⁻¹ n = 1.48, whereas the calculated activation energy (E_a ) was 81.7 kJ mol⁻¹. For the progressive conversion period n = 0.99 for [OH⁻] > 0.0057 mol L⁻¹ and for lower concentrations n ≈ 0, with E_a = 56.9 kJ mol⁻¹, confirming that the decomposition process is controlled by the chemical reaction. Based on the calculated kinetic parameters, the partial and global kinetic expressions of the decomposition process were proposed. These models were compared with the experimental results, and it was favorably proven and described the decomposition process of the mercury jarosite in alkaline medium.     

Chemical relevance of the copper(II)—l-carnosine system in aqueous solution: A thermodynamic and spectrophotometric study

The copper(II)—l-carnosine (L⁻) system has been re-investigated in aqueous solution, at I = 0.1 mol dm⁻¹, different temperatures (5⩽t⩽45°C) and with metal to ligand ratios ranging from 3:1 to 1:3. Both potentiometry and visible spectrophotometry were employed. From an overall consideration of all experiments, [CuLH]²⁺, [CuL]⁺, [CuLH₋₁]°, [Cu₂L₂H₋₂]° and [Cu₂LH₋₁]²⁺ were recognized as the species which provide the best interpretation of experimental data. The complex formation constants, determined at different temperatures, allowed us to obtain reliable values of ΔH° and good estimates of ΔC°_p. From visible spectrophotometric measurements, carried out at different pH and metal to ligand ratios, it was possible to calculate the electronic spectrum of each complex formed in solution. A structure is also proposed for each species, on the basis of thermodynamic and spectral results.     

Molecular vibrations,electronic structure and conformation of diprotonated thiocarbohydrazide

The infrared spectra of diprotonated species of thiocarbohydrazide and its perdeuterated derivative have been examined in the crystalline state. A complete vibrational assignment with a full normal coordinate treatment based on a Urey—Bradley type intramolecular potential Function supplemented with a valence force function for the out of plane and torsional modes is proposed and the origin of the amide II band splittings is explained. A CNDO/2 study of diprotonated thiocarbohydrazide and its neutral molecule is undertaken and the changes in the molecular electronic structures and conformations consequent to protonation are determined and briefly discussed. The magnitude of the N—N⁺H₃ torsional barrier is estimated to be 21 kJ mol^? (5.0 kcal mol^?1) whereas the barrier for the C—N group is found to be 92 kJ mol^?1 (22.0 kcal mol^?1).     

Kinetic and thermochemical characteristics of the dissociation of Mo(CO)6 and W(CO)6

The thermal dissociation of gaseous Mo(CO)₆ and W(CO)₆ in an argon carrier gas, Mo(CO)₆ → Mo(CO)₅ + CO (1) and W(CO)₆ → W(CO)₅ + CO (2), is studied over temperature ranges of ∼585–685 K for (1) and ∼690−810 K for (2) at a total gas concentrations of 4 × 10⁻⁶ and 4 × 10⁻⁵ mol/cm³ by using the shock tube technique in conjunction with absorption spectrophotometry. The measured rate constants are extrapolated to the high-pressure limit by means of a newly developed procedure, with the resultant expressions for the indicated temperature ranges reading as k_d1,∞(T),[s⁻¹] = 10^{16.12 ± 0.68}exp[(−148.8 ± 8.1 kJ/mol)/RT] and k_d2,∞(T),[s⁻¹] = 10^{15.93 ± 0.63}exp[(−171.7 ± 8.9 kJ/mol)/RT]. Comparison of the high-pressure dissociation rate constants with the published data revealed a considerable discrepancy, a tentative explanation of which is given. Based on the obtained high-pressure dissociation rate constants and the available data on the high-pressure room-temperature rate constants for the reverse reaction of recombination, the first bond dissociation energies for these molecules are evaluated and compared with previous determinations, both theoretical and experimental. The enthalpies of formation of Mo(CO)₅ and W(CO)₅ are determined: Δ_fH°(Mo(CO)₅, g, 298.15 K) = −644.1 ± 5.6 kJ/mol and Δ_fH°(W(CO)₅, g, 298.15 K) = −581.9 ± 6.6 kJ/mol. Based on the enthalpies of formation of Mo(CO)₅, W(CO)₅, Mo(CO)₆, and W(CO)₆, and the published molecular parameters of these four species, their thermochemical functions are calculated and presented in the form of NASA seven-term polynomials.     

New PF3 and Carbonyl Chemistry of Tantalum

Reduction of [TaCl₅] by six equivalents of alkali metal naphthalenide in 1,2-dimethoxyethane at −60°C followed by treatment with gaseous PF₃ provides the first homoleptic phosphane complex containing tantalum in the −1 oxidation state, [Ta(PF₃)₆]⁻. This can be protonated by concentrated sulfuric acid to yield the previously unknown highly acidic and volatile hydride [HTa(PF₃)₆]. An improved normal-pressure synthesis of [Ta(CO)₆]⁻ is described. Reduction of the latter species by sodium in liquid ammonia gives the carbonyl trianion [Ta(CO)₅]³⁻ which undergoes monoprotonation and stannylation to form [HTa(CO)₅]²⁻ and [Ph₃SnTa(CO)₅]²⁻, respectively. The hydride is a useful precursor to [(Ph₃PAu)₃Ta(CO)₅], the only known gold cluster of tantalum.     

A “Push–Pull” Stabilized Phosphinidene Supported by a Phosphine-Functionalized β-Diketiminato Ligand

The use of a bis(diphenyl)phosphine functionalized β-diketiminato ligand, [HC{(CH₃)C}₂{(ortho-[P(C₆H₅)₂]₂C₆H₄)N}₂]⁻ (PNac), as a support for germanium(II) and tin(II) chloride and phosphaketene compounds, is described. The conformational flexibility and hemilability of this unique ligand provide a versatile coordination environment that can accommodate the electronic needs of the ligated elements. For example, chloride abstraction from [(PNac)ECl] (E=Ge, Sn) affords the cationic germyliumylidene and stannyliumylidene species [(PNac)E]⁺ in which the pendant phosphine arms associate more strongly with the Lewis acidic main group element centers, providing further electronic stabilization. In a similar fashion, chemical decarbonylation of the germanium phosphaketene [(PNac)Ge(PCO)] with tris(pentafluorophenyl)borane affords a “push–pull” stabilized phosphinidene in which one of the phosphine groups of the ligand backbone associates with the low valent phosphinidene center.