N,N'-Diaryl-Sulfurdiimides are Strongly Redox Tuned.

The synthesis and extensive characterization of nine aryl sulfur diimides (SDIs, Ar-NSN-Ar) are presented with a robust computational and experimental investigation of the fundamental properties of these important members of the thiazyl family of compounds, with particular attention paid to their highly tunable electrochemical behaviour. This is the first work to undertake a systematic comparison of the electrochemical profiles of a coherent series of SDIs to demonstrate and quantify the response of their reduction potentials to substituent electron-donating and -withdrawing properties. This effect is found to be not only exceptionally strong, but also correlates very closely with computed orbital energies. Electron paramagnetic resonance spectroscopy is used to determine the nature, localization, and qualitative lifetimes of the radical anions of SDIs. This work also addresses significant misconceptions about physical properties of SDIs. Experimental data and modern computational methods are employed to provide a resolute answer to the long-standing contention of the solution-state conformations of SDIs, and to correct historical mistakes in the assignment of infrared spectroscopic data. High-quality crystal structures of all SDIs in this work showcase the utility of the recently introduced structural refinement software NoSpherA2, enabling full anisotropic refinement of H-atoms with accurate C-H bond lengths.

Hydrogen Bonds Stabilize Chloroselenite Anions: Crystal Structure of a New Salt and Donor-Acceptor Bonding to SeO2.

The single-crystal X-ray diffraction structure characterizing a new 4-methylbenzamidinium salt of chloroselenite [C8H11N2][ClSeO2] is reported. This is only the second crystal structure report on a ClSeO2- salt. The structure contains an extended planar hydrogen bond net, including a double interaction with both O atoms of the anion (an R228 ring in Etter notation). The anion has the shortest Se-Cl distances on record for any chloroselenite ion, 2.3202(9) Å. However, the two Se-O distances are distinct at 1.629(2) and 1.645(2) Å, attributed to weak anion-anion bridging involving the oxygen with the longer bond. DFT computations at the RB3PW91-D3/aug-CC-pVTZ level of theory reproduce the short Se-Cl distance in a gas-phase optimized ion pair, but free optimization of ClSeO2- leads to an elongation of this bond. A good match to a known value for [Me4N][ClSeO2] is found, which fits to the Raman spectroscopic evidence for this long-known salt and to data measured on solutions of the anion in CH3CN. The assignment of the experimental Raman spectrum was corrected by means of the DFT-computed vibrational spectrum, confirming the strong mixing of the symmetry coordinate of the Se-Cl stretch with both ν2 and ν4 modes.

Accurate Crystal Structures of C12H9CN, C12H8(CN)2, and C16H11CN Valence Isomers Using Nonspherical Atomic Scattering Factors.

Fourteen crystal structures, mostly from good-quality datasets but including some marginal and twinned exemplars, from a series of novel polycyclic benzo- and naphtho-fused organic nitriles are presented and accurately described, including some related structures of a bromo-substituted and partially hydrogenated analogues. These structures represent a considerable increase in the number of published structures within their archetypes. This work highlights the significant advancement in structural refinement software proffered by NoSpherA2, which enables Hirshfeld Atom Refinement (HAR) of the structures within Olex2 v1.5. This results in the determination of C-H bond lengths with near to neutron diffraction accuracies at far lower experimental cost, and with an average improvement in C-C bond precision of 42% compared to Independent Atom Model refinements. H-atoms (apart from disordered components) refined well with anisotropic displacement parameters. Nonclassical H-bonding (C-H···N≡C) in this series is analyzed, and dipolar nitrile-nitrile interactions (C≡N···C≡N) in three major motifs described by (Wood, P. A. Acta Cryst. B, 2008, 64, 393-396) are found in 9 out of 13 nitrile-containing compounds of this series, a much higher proportion than the global average of 21% of nitrile-containing compounds. The HAR/NoSpherA2 approach shows increasing benefits with better data quality without apparent discontinuities.

Reversible Redox Chemistry of Anionic Imidazole-2-thione-Fused 1,4-Dihydro-1,4-diphosphinines.

Anionic 1,4-dihydro-1,4-diphosphinines were synthesized from tricyclic 1,4-diphosphinines and isolated as blue powdery salts M[2a-2c]. Reaction of solutions of these monoanions with iodomethane led to P-methylated compounds 3a-3c. An oxidation/reduction cycle was examined, starting from solutions of K[2a] via P-P coupled product 4a and back to K[2a], and the recyclability and redox chemistry of this cycle were confirmed by experimental and simulated cyclic voltammetry analysis, which is proposed as a potential 2-electron cathode for rechargeable cells. TD-DFT studies were used to examine species that might be involved in the process.

Lewis Acid Behavior of MoF5 and MoOF4: Syntheses and Characterization of MoF5(NCCH3), MoF5(NC5H5)n, and MoOF4(NC5H5)n (n = 1, 2).

The Lewis acid-base adducts MoF5(NC5H5)n and MoOF4(NC5H5)n (n = 1, 2) were synthesized from the reactions of MoF5 and MoOF4 with C5H5N and structurally characterized by X-ray crystallography. Whereas the crystal structures of MoF5(NC5H5)2 and MoOF4(NC5H5)2 are isomorphous containing pentagonal-bipyramidal molecules, the fluorido-bridged, heptacoordinate [MoF5(NC5H5)]2 dimer differs starkly from monomeric, hexacoordinate MoOF4(NC5H5). For the weaker Lewis base CH3CN, only the 1:1 adduct, MoF5(NCCH3), could be isolated. All adducts were characterized by Raman spectroscopy in conjunction with vibrational frequency calculations. Multinuclear NMR spectroscopy revealed an unprecedented isomerism of MoOF4(NC5H5)2 in solution, with the pyridyl ligands occupying adjacent or nonadjacent positions in the equatorial plane of the pentagonal bipyramid. Paramagnetic MoF5(NC5H5)2 was characterized by electron paramagnetic resonance (EPR) spectroscopy as a dispersion in solid adamantane as well as in a diamagnetic host lattice of MoOF4(NC5H5)2; EPR parameters were computed using ZORA with the BPW91 functional using relativistic all-electron wave functions for Mo and simulated using EasySpin. Density functional theory calculations (B3LYP) and natural bond orbital analyses were conducted to elucidate the distinctive bonding and structural properties of all adducts reported herein and explore fundamental differences observed in the Lewis acid behavior of MoF5 and MoOF4.

Gram-Scale Synthesis and Highly Regioselective Bromination of 1,1,9,9-Tetramethyl[9](2,11)teropyrenophane.

An improved synthetic pathway to the nanobelt-like 1,1,9,9-tetramethyl[9](2,11)teropyrenophane has been developed, and enables the synthesis of gram quantities of material. Key innovations are the development of a sequential chlorination/Friedel-Crafts alkylation reaction, a sequential iodination/Wurtz coupling reaction, and a room-temperature teropyrene-forming reaction. The teropyrenophane was found to form a very stable radical cation and undergo a completely regioselective fourfold bromination reaction.

Mono- and Bis(imidazolidinium ethynyl) Cations and Reduction of the Latter To Give an Extended Bis-1,4-([3]Cumulene)-p-carboquinoid System.

An extended π-system containing two [3]cumulene fragments separated by a p-carboquinoid and stabilized by two capping N-heterocyclic carbenes (NHCs) has been prepared. Mono- and bis(imidazolidinium ethynyl) cations have also been synthesized from the reaction of an NHC with phenylethynyl bromide or 1,4-bis(bromoethynyl)benzene. Cyclic voltammetry coupled with synthetic and structural studies showed that the dication is readily reduced to a neutral, singlet bis-1,4-([3]cumulene)-p-carboquinoid as a result of the π-accepting properties of the capping NHCs.

The First Lanthanide Complexes with a Redox-Active Sulfur Diimide Ligand: Synthesis and Characterization of [LnCp*2 (RN=)2 S], Ln=Sm, Eu, Yb; R=SiMe3.

The first lanthanide complexes with a redox-active sulfur diimide ligand, [LnCp*2 (Me3 SiN=)2 S] (Ln=Sm, Eu, Yb; Cp*=η5 -C5 Me5 ), are reported. The complexes were synthesized by using [LnCp*2 (THF)2 ] and (Me3 SiN=)2 S and have been thoroughly characterized by single-crystal X-ray diffraction, EPR spectroscopy, UV/Vis/NIR electronic absorption spectroscopy and SQUID magnetometry. The results, as interpreted by CASSCF/SOC-RASSI calculations providing a non-perturbative treatment of spin-orbit coupling, indicate that these paramagnetic complexes are best described as Ln3+ and [(Me3 SiN=)2 S]-. adducts. As such, these complexes contain the first isolated and structurally characterized acyclic [(RN=)2 S]-. radical anions.

On the oxidation of the three-dimensional aromatics [B(12)X(12)](2-) (X=F, Cl, Br, I).

The perhalogenated closo-dodecaborate dianions [B12 X12 ](2-) (X=H, F, Cl, Br, I) are three-dimensional counterparts to the two-dimensional aromatics C6 X6 (X=H, F, Cl, Br, I). Whereas oxidation of the parent compounds [B12 H12 ](2-) and benzene does not lead to isolable radicals, the perhalogenated analogues can be oxidized by chemical or electrochemical methods to give stable radicals. The chemical oxidation of the closo-dodecaborate dianions [B12 X12 ](2-) with the strong oxidizer AsF5 in liquid sulfur dioxide (lSO2 ) yielded the corresponding radical anions [B12 X12 ](⋅-) (X=F, Cl, Br). The presence of radical ions was proven by EPR and UV/Vis spectroscopy and supported by quantum chemical calculations. Use of an excess amount of the oxidizing agent allowed the synthesis of the neutral perhalogenated hypercloso-boranes B12 X12 (X=Cl, Br). These compounds were characterized by single-crystal X-ray diffraction of dark blue B12 Cl12 and [Na(SO2 )6 ][B12 Br12 ]⋅B12 Br12 . Sublimation of the crude reaction products that contained B12 X12 (X=Cl, Br) resulted in pure dark blue B12 Cl12 or decomposition to red B9 Br9 , respectively. The energetics of the oxidation processes in the gas phase were calculated by DFT methods at the PBE0/def2-TZVPP level of theory. They revealed the trend of increasing ionization potentials of the [B12 X12 ](2-) dianions by going from fluorine to bromine as halogen substituent. The oxidation of all [B12 X12 ](2-) dianions was also studied in the gas phase by mass spectrometry in an ion trap. The electrochemical oxidation of the closo-dodecaborate dianions [B12 X12 ](2-) (X=F, Cl, Br, I) by cyclic and Osteryoung square-wave voltammetry in liquid sulfur dioxide or acetonitrile showed very good agreement with quantum chemical calculations in the gas phase. For [B12 X12 ](2-) (X=F, Cl, Br) the first and second oxidation processes are detected. Whereas the first process is quasi-reversible (with oxidation potentials in the range between +1.68 and +2.29 V (lSO2 , versus ferrocene/ferrocenium (Fc(0/+) ))), the second process is irreversible (with oxidation potentials ranging from +2.63 to +2.71 V (lSO2 , versus Fc(0/+) )). [B12 I12 ](2-) showed a complex oxidation behavior in cyclic voltammetry experiments, presumably owing to decomposition of the cluster anion under release of iodide, which also explains the failure to isolate the respective radical by chemical oxidation.

A variable temperature X-ray diffraction investigation of [PPN+][S4N5-]: supramolecular interactions governing an order/disorder transformation and the first high resolution X-ray structure of the anion.

The title salt, triphenyl(P,P,P-triphenylphosphineimidato-kN)-phosphorus(1+) 1,3,5,7-tetrathia(1,5-SIV)-2,4,6,8,9-pentaazabicyclo[3.3.1]nona-1,4,6,7-tetraene(1-), CAS [48236-06-2], prepared by the literature method, is found by crystallography to be a 1:1 CH3CN solvate. Disorder exists for the N atoms of the anion. A VT crystal structure study was conducted at 100 K, 120 K, 140 K, 172 K, 200 K, 240 K and 280 K. The 100 K structure is superior, with only 10% of a second anion position oppositely-oriented w.r.t the diad axis of point group 2mm. At 120 K, an adjacent two-site disorder is encountered, but at higher temperatures three-site disorder with both opposite and adjacent placements of S4N5- ions is required w.r.t. the primary component. At 240 and especially 280 K, the anion nitrogen atoms appear fully scrambled amongst the six possible sites on the edges of an S4 tetrahedron with 83.3% occupancy for each. The PPN+ geometry does not show strong cation-cation interactions. However, there are numerous supramolecular contacts corresponding mostly to non-classical H-bonds between PPN+ ions and S4N5- as well as CH3CN. The geometry of the anion is corroborated from B3LYP/6-311++G(3df) DFT calculations, and the infra-red spectrum was assigned with excellent agreement between experimental and calculated frequencies.

4-Thio-carbamoylpyridin-1-ium iodide.

The title salt, C6H7N2S(+)·I(-), crystallizes with two independent cations and two anions in the asymmetric unit. In one of the cations, the dihedral angle between the pyridinium ring and the thioamide group is 28.9 (2)°; in the other it is 33.5 (2)°. In the crystal, N-H⋯S and C-H⋯S hydrogen bonds link the independent cations into pairs. These pairs form a three-dimensional network through additional N-H⋯I and C-H⋯I hydrogen bonds to the anions.

Synthesis, characterization, and electrochemical studies of PPh(3-n)(dipp)(n) (dipp = 2,6-diisopropylphenyl): steric and electronic effects on the chemical and electrochemical oxidation of a homologous series of triarylphosphines and the reactivities of the corresponding phosphoniumyl radical cations.

Activation barriers to the electrochemical oxidation for the series PPh3-n(dipp)n (dipp = 2,6-diisopropylphenyl) in CH2Cl2/Bu4NPF6 were measured using large amplitude FT ac voltammetry. Increasing substitution across this series, which offers the widest range of steric requirements across any analogous series of triarylphosphines reported to date, increases the energetic barrier to electron transfer; values of 18, 24, and 25 kJ mol(-1) were found for compounds with n = 1, 2, and 3, respectively. These values are significantly greater than those calculated for outer sphere activation barriers, with deviations between observed and calculated values increasing with the number of dipp ligands. This suggests that the steric congestion afforded by these bulky substituents imposes significant reorganizational energy on the electron transfer processes. This is the first investigation of the effect of sterics on the kinetics of heterogeneous electron transfer across a structurally homologous series. Increased alkyl substitution across the series also increases the chemical reversibility of the oxidations and decreases the oxidation peak potentials. As the compounds for which n = 1 and 2 are novel, the synthetic strategies employed in their preparation are described, along with their full spectroscopic, physical, and crystallographic characterization. Optimal synthesis when n = 1 is via a Grignard reagent, whereas when n = 2 an aryl copper reagent must be employed, as use of a Grignard results in reductive coupling. Chemical oxidation studies were performed to augment the electrochemical work; the O, S, and Se oxidation products for the parent triarylphosphines for which n = 1 and 2 were isolated and characterized.

Quantum-chemical and electrochemical investigation of the electrochemical windows of halogenated carborate anions.

The range of electrochemical stability of a series of weakly coordinating halogenated (Hal=F, Cl, Br, I) 1-carba-closo-dodecaborate anions, [1-R-CB(11)X(5)Y(6)](-) (R=H, Me; X=H, Hal, Me; Y=Hal), has been established by using quantum chemical calculations and electrochemical methods. The structures of the neutral and dianionic radicals, as well as the anions, have been optimized by using DFT calculations at the PBE0/def2-TZVPP level. The calculated structures are in good agreement with existing experimental data and with previous calculations. Their gas-phase ionization energies and electron affinities were calculated based on their optimized structures and were compared with experimental (cyclic and square-wave) voltammetry data. Electrochemical oxidation was performed in MeCN at room temperature and in liquid sulfur dioxide at lower temperatures. All of the anions show a very high resistance to the onset of oxidation (2.15-2.85 V versus Fc(0/+)), with only a minor dependence of the oxidation potential on the different halogen substituents. In contrast, the reduction potentials in MeCN are strongly substituent dependent (-1.93 to -3.32 V versus Fc(0/+)). The calculated ionization energies and electron affinities correlate well with the experimental redox potentials, which provide important verification of the thermodynamic validity of the mostly irreversible redox processes that are observed for this series. The large electrochemical windows that are afforded by these anions indicate their suitability for electrochemical applications, for example, as supporting electrolytes.

Electrochemically informed synthesis: oxidation versus coordination of 5,6-bis(phenylchalcogeno)acenaphthenes.

Chalcogen dications: Facile synthesis of E--E bonded dications can be readily achieved. Radical cations are identified as the intermediates.

A tetrabromo-1,4-ethanonaphthalene and related dibromo-1,4-ethenonaphthalene.

(1RS,3RS,4RS,10SR)-2,2,3,10-Tetrabromo-1,2,3,4-tetrahydro-1,4-ethanonaphthalene, C12H10Br4, (I), is the first structure to be reported with four Br atoms bound to a 1,4-ethanonaphthalene framework and also the first which possesses three Br atoms in exo positions. Interactions between the Br atoms [three short intramolecular Br...Br distances of 3.1094 (4), 3.2669 (4) and 3.4415 (5) Å] have little effect on the C-C bond lengths but lead to significant twisting of the cage structure compared with the parent hydrocarbon, which is expected to be fully eclipsed at the two saturated C2H4 bridge positions. Chemically related (1SR,4RS)-2,3-dibromo-1,4-ethenonaphthalene, C12H8Br2, (II), obtained by double dehydrobromination of (I), represents the first structure of any halogen-substituted benzobarrelene. This cis-dibromide shows little evidence of steric congestion at the double bond [Br...Br = 3.5276 (8) Å] as a consequence of the large C-C-Br angles [average C=C-Br angle = 126.15 (10)°].

A study of the pyramidality index in tris(2,4,6-triisopropylphenyl)phosphonium perchlorate.

The title compound, C45H70P(+)·ClO4(-) or [Tripp3PH(+)][ClO4(-)], was produced from the perchlorate salt of the corresponding radical cation Tripp3P(·+) through very slow H-atom abstraction reactions in a solution of 1,2-dimethoxyethane (Tripp is 2,4,6-triisopropylphenyl). The H atom on the P atom was located in a difference map and was freely refined with an isotropic displacement consistent with full occupancy [P-H = 1.37 (3) Å]. It is the most sterically congested triarylphosphonium salt yet to be reported and has a `propeller' arrangement of the three Tripp groups around the P atom, with the protonation site located along the molecular threefold axis. There are short contacts between the flanking isopropyl methine H atoms and the P atom [P···H = 1.99 (2)-2.17 (2) Å]. The sum of the angles around the P atom [Σ(C-P-C) = 349.9 (6)°] is a convenient index of pyramidality for tricoordinate centres. This value is significantly larger than in analogous Mes3PH(+) salts (Mes is mesityl or 2,4,6-trimethylphenyl), for which the average of the three reported structures in the literature is Σ(C-P-C) = 345.3 (6)°. For comparison, in the ubiquitous Ph3PH(+) salts, this parameter has a typical average value of only 333.3 (9)°. The value of Σ(C-P-C) in the title compound is midway between that of the neutral phosphane Tripp3P [334.4 (6)°] and the phosphoniumyl radical cation Tripp3P(·+) [359.8 (2)°]. This geometrical feature provides additional support for the assignment as a phosphonium salt.

3,5-Diphenyl-1,2,4-dithia-zolium tetra-bromidoferrate(III).

The cation of the title salt, (C(14)H(10)NS(2))[FeBr(4)], contains a flat central NC(2)S(2) ring (r.m.s. deviation = 0.005 Å), with two attached phenyl rings that are almost coplanar [the dihedral angles between the mean planes are 2.4 (1) and 7.7 (1)° for the two phenyl rings]. The [FeBr(4)](-) anion makes short Br⋯S contacts [Br⋯S = 3.4819 (8), 3.6327 (9) and 3.5925 (9) Å] and also bridges by way of short contacts to ring H atoms of a second cation held parallel to the first by π-stacking, with a separation between the mean 1,2,4-dithia-zolium rings of 3.409 Å. The closest contacts are between a phenyl ring centroid of one cation and the ipso C atom of the phenyl ring of another cation, for which the distance is 3.489 Å. The discrete dimers are linked laterally by further Br⋯H short contacts, resulting in double sheets located parallel to the b axis and to the bis-ector of a and c.

(5Z,7Z,9Z)-5,10-Di-bromo-benzo[8]annulene.

In the structure of the title compound, C12H8Br2, the two bromine substituents are oriented exo to the boat-shaped cyclo-octa-tetra-ene at the two ring sites that are ß to the ring fusion positions. The average Br-C bond distance is 1.919 (2) Å, the average distance for C=C double bonds that are Br substituted is 1.328 (2) Å, while the other two double-bond distances are 1.327 (2) and 1.398 (2) Šfor the non-fused and fused bonds, respectively. Each type of ring inter-atomic distance is within s.u. of the average values for the four known structures, including the title compound, of benzo-fused cyclo-ocata-tetra-enes that are not coordinated to a metal atom. The crystal structure features short Br⋯Br [3.6620 (3) Å] and C⋯H [2.834 (2) and 2.841 (2) Å] contacts.

A novel access to phosphanylidene-phosphorane complexes via P-donor substitution and a detailed bonding analysis.

Phospha-Wittig reagents such as phosphanylidene-phosphoranes and their transition metal complexes are of great interest as sources of P1 building blocks but the access is still limited. Herein, we describe a new access to phosphanylidene-phosphorane complexes starting from the N-methylimidazole-to-phosphinidene complex adduct. The complexes were studied electrochemically and theoretically, also with respect to their 31P NMR data, and the P-P bonds were evaluated by various DFT-derived descriptors.

Access to and reactions of P-functional 1,4-dihydro-1,4-diphosphinines fused to two TTF units.

P-Functional phosphanylated tetrathiafulvalenes 3a-f were synthesised via stepwise lithiation and phosphanylation of TTF derivatives, and then reacted with PCl3 to form the related P-chloro compounds 4a-f. Reactions of 4c-f with LDA resulted in the formation of the corresponding 1,4-dihydro-1,4-diphosphinines 5c-f. As a case in point, P-oxidation reactions of 5d,f with elemental chalcogens were performed, and the former were also converted into 1,4-dichloro-1,4-dihydro-1,4-diphosphinine 9f. The latter was reduced to form the related 1,4-diphosphinine 10f which could not be isolated but formed the corresponding 1,4-diphosphabarrelene 11f in a [4 + 2]-cycloaddition with 1-hexene. All compounds were characterised by multinuclear NMR spectroscopy and mass spectrometry and also by single crystal X-ray diffraction studies in some cases. Intensive cyclic voltammetry studies were performed for all isolated compounds with the special focus on using TTF units as sensors to study the substituent effects on oxidation potentials and, hence, the degree of electronic communication between redox active moieties in the bis-TTF species. E.g., 5d possesses four quasi-reversible one-electron oxidation steps thus forming a tetracation species at highest potential (+0.54 V vs. Fc+/0). Additionally, high level DFT calculations were undertaken to get a deeper understanding of various aspects of this novel combination of phosphorus and TTF chemistry.