An investigation into the Brønsted acidity of the perfluorinated alkoxy silanes {(F3C)3CO}3SiH and {(F6C5)3CO}2Si(Cl)H.

The perfluorinated alkoxy silanes {(F3C)3CO}3SiH (1) and {(F5C6)3CO}2Si(Cl)H (2) were prepared and fully characterized. Despite the high calculated Brønsted acidities, all attempts to deprotonate 1 and 2 to give the conjugate silanide ions failed due to the exceptionally short and strong Si-H bonds. In the solid state, the Si-H units are not involved in any intermolecular interactions, but instead the crystal packing consists of exceptionally short and strong F⋯F interactions. The cohesive energies are entirely comprised of London dispersion interactions, similarly as in the crystal structures of noble gases.

Lewis acid-base adducts of Al(N(C6F5)2)3 and Ga(N(C6F5)2)3 - structural features and dissociation enthalpies.

Herein we present the molecular structures of six neutral Lewis acid-base adducts of the Lewis superacid Al(N(C6F5)2)3 and its higher homolog Ga(N(C6F5)2)3 with the electron pair donors MeCN, CNtBu, THF and PMe3. The crystal structures reveal crucial structural changes compared to the free Lewis acids as a consequence of the adduct formation. Furthermore, we calculated the corresponding dissociation enthalpies of the adducts which lie between 69 and 141 kJ mol-1 and are therefore considerably lower compared to the values for the formation of the anionic fluoride or chloride metallates.

Thermally stable polyfluorinated monoalkoxysilanetriols and dialkoxydisiloxanetetrols.

The reaction of the polyfluorinated lithium triarylmethanolates Ar3COLi (Ar = C6F5, 3,5-(CF3)2C6H3) with SiCl4 provided the monosubstituted products Ar3COSiCl3 (1a, Ar = C6F5; 1b, Ar = 3,5-(CF3)2C6H3). The hydrolysis of 1a and 1b produced the silanetriols Ar3COSi(OH)3 (2a, Ar = C6F5; 2b, Ar = 3,5-(CF3)2C6H3) without the aid of an HCl scavenger. The reaction of two equivalents of Ar3COLi (Ar = C6F5, 3,5-(CF3)2C6H3) with (Cl3Si)2O afforded the disubstituted products [(C6F5)3COSiCl2]2O (3a) and {[(3,5-(CF3)2C6H3)3CO]SiCl2}2O (3b), the hydrolysis of which gave the corresponding disiloxanetetraols [(C6F5)3COSi(OH)2]2O (4a) and [(3,5-(CF3)2C6H3)3COSi(OH)2]2O (4b). At high concentrations in the presence of HCl, 2b undergoes controlled condensation to yield 4b. In the solid-state, 2a, 4a and 4b are mainly associated by hydrogen bonds of the type SiO-H⋯O(H)Si whereas the competing SiO-H⋯O(C)Si type was not observed.

Tri- and Tetranuclear Metal-String Complexes with Metallophilic d10 -d10 Interactions.

The reaction of 2,6-F2 C6 H3 SiMe3 with Ph2 PLi provided 2,6-(Ph2 P)2 C6 H3 SiMe3 (1), which can be regarded as precursor for the novel anionic tridentate ligand [2,6-(Ph2 P)2 C6 H3 ]- (PCP)- . The reaction of 1 with [AuCl(tht)] (tht=tetrahydrothiophene) afforded 2,6-(Ph2 PAuCl)2 C6 H3 SiMe3 (2). The subsequent reaction of 2 with CsF proceeded with elimination of Me3 SiF and yielded the neutral tetranuclear complex linear-[Au4 Cl2 (PCP)2 ] (3) comprising a string-like arrangement of four Au atoms. Upon chloride abstraction from 3 with NaBArF 4 (ArF =3,5-(CF3 )2 C6 H3 ) in the presence of tht, the formation of the dicationic tetranuclear complex linear-[Au4 (PCP)2 (tht)2 ](BArF 4 )2 (4) was observed, in which the string-like structural motif is retained. Irradiation of 4 with UV light triggered a facile rearrangement in solution giving rise to the dicationic tetranuclear complex cyclo-[Au4 (PCP)2 (tht)2 ](BArF 4 ) (5), which comprises a rhomboidal motif of four Au atoms. In 3-5, the Au atoms are associated by a number of significant aurophilic interactions. The atom-economic and selective reaction of 3 with HgCl2 yielded the neutral trinuclear bimetallic complex [HgAu2 Cl3 (PCP)] (6) comprising significant metallophilic interactions between the Au and Hg atoms. Therefore, 6 may be also regarded as a metallopincer complex [ClHg(AuCAu)] between HgII and the anionic tridentate ligand [2,6-(Ph2 PAuCl)2 C6 H3 ]- (AuCAu)- containing a central carbanionic binding site and two "gold-arms" contributing pincer-type chelation trough metallophilic interactions. Compounds 1-6 were characterized experimentally by multinuclear NMR spectroscopy and X-ray crystallography and computationally using a set of real-space bond indicators (RSBIs) derived from electron density (ED) methods including Atoms In Molecules (AIM), the Electron Localizability Indicator (ELI-D) as well as the Non-Covalent Interaction (NCI) Index.

Al(OCArF3)3 - a thermally stable Lewis superacid.

The adduct free Lewis superacid Al(OCArF3)3 was obtained by the reaction of ArF3COH with AlEt3 and fully characterized (ArF = C6F5). It comprises a high thermal stability up to 180 °C and a distinct reactivity towards Lewis bases, as exemplified by the isolation of the neutral adducts Al(OCArF3)·D (D = MeCN, THF, Et2O, pyridine, OPEt3), the fluoride complexes [Q][FAl(OCArF)3] (Q+ = Cs+, Ag+, Tl+, [S(NMe2)3]+, [Ph3C]+, Li+, [NBu4]+, [FeCp2]+) and the chloride complex [Ph3C][ClAl(OCArF)3].

Bis(dipyrrinato)zinc(II) Complex Chiroptical Wires: Exfoliation into Single Strands and Intensification of Circularly Polarized Luminescence.

One-dimensional (1D) coordination polymers (CPs) experiences limitations in exfoliation into individual strands, which hamper their utility as functional 1D nanomaterials. Here we synthesize chiral 1D-CPs that feature the bis(dipyrrinato)zinc(II) complex motif. They can be exfoliated into single strands upon sonication in organic media, retaining lengths of up to 3.19 µm (ca. 2600 monomer units). Their chiroptical structure allows the exfoliated wires to show circularly polarized luminescence at an intensity 5.9 times that of reference monomer complexes.

Structural Characterization of Neutral Saccharides by Negative Ion MALDI Mass Spectrometry Using a Superbasic Proton Sponge as Deprotonating Matrix.

The superbasic proton sponge 1,8-bis(tripyrrolidinylphosphazenyl)naphthalene (TPPN) has been successfully employed for the structural characterization of neutral saccharides, cyclodextrins, and saccharide alditols by matrix assisted laser desorption/ionization tandem mass spectrometry (MALDI-MS/MS). Owing to its inherently high basicity, TPPN is capable of deprotonating neutral carbohydrates (M) providing an efficient and simple way to produce gas-phase [M - H]- ions. Highly informative negative ions MS/MS spectra showing several diagnostic fragment ions were obtained, mainly A-type cross-ring and C-type glycosidic cleavages. Indeed, cross-ring cleavages of monosaccharides with formation of 0,2A, 0,3A, 2,4A, 2,5A, 3,5A, and 0,3X product ions dominate the MS/MS spectra. A significant difference between reducing (e.g., lactose, maltose) and non-reducing disaccharides (e.g., sucrose, trehalose) was observed. Though disaccharides with the anomeric positions blocked give rise to deprotonated molecules, [M - H]-, at m/z 341.1, reducing ones exhibited a peak at m/z 340.1, most likely as radical anion, [M - H•- H]-•. The superiority of TPPN was clearly demonstrated by comparison with well recognized matrices, such as 2,5-dihydroxybenzoic acid and 2',4',6'-trihydroxyacetophenone (positive ion mode) and nor-harman (negative ion mode). MALDI MS/MS experiments on isotopically labeled sugars have greatly supported the interpretation of plausible fragmentation pathways. Graphical Abstract ᅟ.

A Phosphorus Bisylide: Exploring a New Class of Superbases with Two Interacting Carbon Atoms as Basicity Centers.

Herein we present the first superbase MHPN with two interacting P-ylide entities. Unlike classical proton sponges, this novel compound class has carbon atoms as basicity centers which are forced into close proximity by a naphthalene scaffold. The bisylide exhibits an experimental pKBH+  value of 33.3±0.2 on the MeCN scale and a calculated gas-phase proton affinity of 277.9 kcal mol-1 (M062X/6-311+G**//M062X/6-31G*+ZPVE method) exceeding that of the corresponding monoylide by nearly 15 kcal mol-1 . The origin of the unexpectedly high basicity of the new bisylide was investigated by NMR spectroscopic methods, single-crystal X-ray diffraction as well as theoretical calculations and can be partly attributed to the rapid exchange of the "acidic" proton between the two basic carbon atoms after protonation.

Chelating P2-Bis-phosphazenes with a (R,R)-1,2-Diaminocyclohexane Skeleton: Two New Chiral Superbases.

The linkage of two P2 -phosphazenyl groups through a C2 -symmetric (R,R)-1,2-diaminocyclohexane (DACH) backbone yielded the new chiral superbases DACH-P2 NMe2 and DACH-P2 Pyr (Pyr=pyrrolidinyl). These bases were prepared by a Kirsanov reaction and studied with respect to their spectroscopic and structural characteristics. Theoretical calculations concerning their basicity properties revealed remarkable pKBH+ values of 38.1 and 39.9 on the acetonitrile scale; this makes them the strongest nonionic chiral superbases known to date.

Dissymmetric Bis(dipyrrinato)zinc(II) Complexes: Rich Variety and Bright Red to Near-Infrared Luminescence with a Large Pseudo-Stokes Shift.

Bis(dipyrrinato)metal(II) and tris(dipyrrinato)metal(III) complexes have been regarded as much less useful luminophores than their boron difluoride counterparts (4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes, BODIPYs), especially in polar solvent. We proposed previously that dissymmetry in such metal complexes (i.e., two different dipyrrinato ligands in one molecule) improves their fluorescence quantum efficiencies. In this work, we demonstrate the universality and utility of our methodology by synthesizing eight new dissymmetric bis(dipyrrinato)zinc(II) complexes and comparing them with corresponding symmetric complexes. Single-crystal X-ray diffraction analysis, (1)H and (13)C NMR spectroscopy, and high-resolution mass spectrometry confirm the retention of dissymmetry in both solution and solid states. The dissymmetric complexes all show greater photoluminescence (PL) quantum yields (ϕPL) than the corresponding symmetric complexes, allowing red to near-infrared emissions with large pseudo-Stokes shifts. The best performance achieves a maximum PL wavelength of 671 nm, a pseudo-Stokes shift of 5400 cm(-1), and ϕPL of 0.62-0.72 in toluene (dielectric constant εs = 2.4), dichloromethane (εs = 9.1), acetone (εs = 21.4), and ethanol (εs = 24.3). The large pseudo-Stokes shift is distinctive considering BODIPYs with small Stokes shifts (∼500 cm(-1)), and the ϕPL values are higher than or comparable to those of BODIPYs fluorescing at similar wavelengths. Electrochemistry and density functional theory calculations illustrate that frontier orbital ordering in the dissymmetric complexes meets the condition for efficient PL proposed in our theory.

Experimental Basicities of Phosphazene, Guanidinophosphazene, and Proton Sponge Superbases in the Gas Phase and Solution.

Experimental gas-phase superbasicity scale spanning 20 orders of magnitude and ranging from bicyclic guanidine 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene to triguanidinophosphazenes and P3 phosphazenes is presented together with solution basicity data in acetonitrile and tetrahydrofuran. The most basic compound in the scale-triguanidinophosphazene Et-N═P[N═C(NMe2)2]3-has the highest experimental gas-phase basicity of an organic base ever reported: 273.9 kcal mol(-1). The scale includes besides the higher homologues of classical superbasic phosphazenes and several guanidino-substituted phosphazenes also a number of recently introduced bisphosphazene and bis-guanidino proton sponges. This advancement was made possible by a newly designed Fourier transform ion cyclotron resonance (ICR) mass spectrometry setup with the unique ability to generate and control in the ICR cell sufficient vapor pressures of two delicate compounds having low volatility, which enables determining their basicity difference. The obtained experimental gas-phase and solution basicity data are analyzed in terms of structural and solvent effects and compared with data from theoretical calculations.

Heteroleptic [Bis(oxazoline)](dipyrrinato)zinc(II) Complexes: Bright and Circularly Polarized Luminescence from an Originally Achiral Dipyrrinato Ligand.

Heteroleptic zinc(II) complexes synthesized using achiral dipyrrinato and chiral bis(oxazoline) ligands show bright fluorescence with quantum efficiencies of up to 0.70. The fluorescence originates from the (1)π-π* photoexcited state localized exclusively on the dipyrrinato ligand. Furthermore, the luminescence is circularly polarized despite the achirality of the dipyrrinato ligand. Single-crystal X-ray structure analysis discloses that the chiral bis(oxazoline) ligand undergoes intramolecular π-π stacking with the dipyrrinato ligand, inducing axial chirality in the dipyrrinato moiety.

Fluoro- and perfluoralkylsulfonylpentafluoroanilides: synthesis and characterization of NH acids for weakly coordinating anions and their gas-phase and solution acidities.

Fluoro- and perfluoralkylsulfonyl pentafluoroanilides [HN(C6F5)(SO2X); X = F, CF3, C4F9, C8F17] are a class of imides with two different strongly electron-withdrawing substituents attached to a nitrogen atom. They are NH acids, the unsymmetrical hybrids of the well-known symmetrical bissulfonylimides and bispentafluorophenylamine. The syntheses, the structures of these perfluoroanilides, their solvates, and some selected lithium salts give rise to a structural variety beyond the symmetrical parent compounds. The acidities of representative subsets of these novel NH acids have been investigated experimentally and quantum-chemically and their gas-phase acidities (GAs) are reported, as well as the pKa values of these compounds in acetonitrile (MeCN) and DMSO solution. In quantum chemical investigations with the vertical and relaxed COSMO cluster-continuum models (vCCC/rCCC), the unusual situation is encountered that the DMSO-solvated acid Me2SO-H-N(SO2CF3)2, optimized in the gas phase (vCCC model), dissociates to Me2SO-H(+)-N(SO2CF3)2(-) during structural relaxation and full optimization with the solvation model turned on (rCCC model). This proton transfer underlines the extremely high acidity of HN(SO2CF3)2. The importance of this effect is studied computationally in DMSO and MeCN solution. Usually this effect is less pronounced in MeCN and is of higher importance in the more basic solvent DMSO. Nevertheless, the neglect of the structural relaxation upon solvation causes typical changes in the computational pKa values of 1 to 4 orders of magnitude (4-20 kJ mol(-1)). The results provide evidence that the published experimental DMSO pKa value of HN(SO2CF3)2 should rather be interpreted as the pKa of a Me2SO-H(+)-N(SO2CF3)2(-) contact ion pair.

Superbasic alkyl-substituted bisphosphazene proton sponges: synthesis, structural features, thermodynamic and kinetic basicity, nucleophilicity and coordination chemistry.

Herein we describe an easily accessible class of superbasic proton sponges based on the 1,8-bisphosphazenylnaphthalene (PN) proton pincer motif and P-alkyl substituents ranging from methyl (TMPN) to n-butyl (TBPN), isopropyl (TiPrPN) and cyclopentyl (TcyPPN). These neutral bases with a pK(BH)(+) value (MeCN) of ~30 were accessible via a Kirsanov condensation using commercially available 1,8-diaminonaphthalene, and in case of TMPN and TBPN, simple one-pot procedures starting from trisalkylphosphanes can be performed. Furthermore, the known pyrrolidinyl-substituted superbase TPPN previously synthesized via a Staudinger reaction could also be prepared by the Kirsanov strategy allowing its preparation in a larger scale. The four alkyl-substituted proton sponges were structurally characterized in their protonated form; molecular XRD structures were also obtained for unprotonated TiPrPN and TcyPPN. Moreover, we present a detailed description of spectroscopic features of chelating bisphosphazenes including TPPN and its hyperbasic homologue P2-TPPN on which we reported recently. The four alkyl-substituted superbases were investigated with respect to their basic features by computational means and by NMR titration experiments revealing unexpectedly high experimental pK(BH)(+) values in acetonitrile between 29.3 for TMPN and 30.9 for TBPN. Besides their thermodynamic basicity, we exemplarily studied the kinetic basicity of TMPN and TPPN by means of NMR-spectroscopic methods. Furthermore, the competing nucleophilic versus basic properties were examined by reacting the proton sponges with ethyl iodide. Insight into the coordination chemistry of chelating superbases was provided by reacting TMPN with trimethylaluminum and trimethylgallium to give cationic complexes of Group XIII metal alkyls that were structurally characterized.

Constrained-geometry bisphosphazides derived from 1,8-diazidonaphthalene: synthesis, spectroscopic characteristics, structural features, and theoretical investigations.

Investigations on the Staudinger reaction between 1,8-diazidonaphthalene and phosphorous(III) building blocks, a key step in the synthesis of superbasic bisphosphazene proton sponges, yielded a set of bisphosphazides with a constrained geometry 1,8-disubstituted naphthalene backbone. This compound class has attracted our interest not only due to their surprisingly high stability, but in particular because of their theoretically predicted basicity in the range of their bisphosphazene analogues that can be referred to the constrained geometry interaction of two highly basic nitrogen atoms. Eleven new bisphosphazides bearing simple P-amino groups as well as P-guanidino substituents, azaphosphatrane moieties, P2 building blocks, or chiral P-amino substituents derived from L-proline are presented. They were studied concerning their spectroscopic properties and partly also their chromophoric and structural features. In the case of the pyrrolidino-substituted TPPN(2N2) (TPPN = 1,8-bis(trispyrrolidinophosphazenyl)naphthalene), the stepwise nitrogen elimination is investigated theoretically and experimentally, which led to the isolation and structural characterization of TPPN(1N2) bearing a phosphazide and a phosphazene functionality in one molecule. Attempts to protonate the obtained bisphosphazides and to prove the computationally predicted pKBH(+) values through NMR titration reactions resulted in their decay, which again was rationalized by theoretical calculations. Altogether we present the so far most extensive spectroscopic, structural and theoretical investigation of constrained geometry bisphosphazides and their Brønsted and Lewis basic properties.

Two C2-symmetric chelating P2-bisphosphazene superbases connected via a binaphthyl backbone--synthesis, structural features and preparation of a cationic alkyl aluminum complex.

Two P2-phosphazenyl groups were linked via a C2-symmetric binaphthyl backbone resulting in two novel chiral superbases with dimethylamino and pyrrolidino substituents. We investigated their basic properties and coordination chemistry towards a cationic alkyl aluminum fragment. The outstanding basicity of the chiral tetrasphosphazenes presented herein leads to interesting perspectives for application in asymmetric Brønsted base catalysis.

The new NH-acid HN(C6F5)(C(CF3)3) and its crystalline and volatile alkaline and earth alkaline metal salts.

Herein we report on the new NH-acid N-(2,3,4,5,6-pentafluorophenyl)-N-nonafluoro-tert-butylamine, HN(C6F5)(C(CF3)3), bearing two different sterically demanding and strongly electron-withdrawing perfluorinated amine substituents. The title compound and seven of its alkaline and alkaline earth metal salts were synthesized and investigated concerning their thermal, spectroscopic, and structural properties. The Li, Na, K, Cs, and Mg salts were investigated by single-crystal XRD analysis. The molecular structures reveal interesting motifs such as manifold fluorine metal secondary interactions. The lithium and magnesium compounds exhibit a remarkable thermal stability and an unexpectedly high volatility. We believe that this report will provoke investigations to apply the corresponding anion in ionic liquids, in lithium electrolytes, and as a weakly electron-donating ligand in the preparation of highly Lewis-acidic main group, rare earth, or transition metal complexes.

A new synthetic pathway to the second and third generation of superbasic bisphosphazene proton sponges: the run for the best chelating ligand for a proton.

We present the up to now strongest chelating neutral pincer ligand for the simplest electrophile of chemistry, the proton. Two novel bisphosphazene proton sponges, 1,8-bis(trispyrrolidinophosphazenyl)naphthalene (TPPN) and its higher homologue P2-TPPN, were obtained via a Staudinger reaction and investigated concerning their structural features and basic properties by experimental and computational means. They exhibit experimental pK(BH)(+) values in acetonitrile of 32.3 and 42.1, respectively, exceeding the existing basicitiy record for proton sponges by more than 10 orders of magnitude. We show that Schwesinger's concept of homologization of phosphazene bases and Alder's concept of proton chelation in a constrained geometry regime of basic centers can be combined in the design of highly basic nonionic superbases of pincer type.