Synthesis of a stable crystalline nitrene.

Nitrenes are a highly reactive, yet fundamental compound class. They possess a mono-valent nitrogen atom and usually a short life span, typically in the nanosecond range. Here, we report on the synthesis of a stable nitrene by photolysis of the arylazide MSFluindN3 (1), which gave rise to the quantitative formation of the arylnitrene MSFluindN (2) (MSFluind = dispiro[fluorene-9,3'-(1',1',7',7'-tetramethyl-s-hydrindacen-4'-yl)-5',9''-fluorene]), that remains unchanged for at least 3 days when stored under argon atmosphere at room temperature. The extraordinary life span permitted the full characterization of 2 by single crystal x-ray crystallography, EPR spectroscopy and SQUID magnetometry, which supported a triplet ground state. Theoretical simulations suggest in addition to the kinetic stabilization conferred by the bulky MSFluind aryl substituent, that electron delocalization across the central aromatic ring contributes to the electron stabilization of 2.

Synthesis and crystal structure of 2-(anthracen-9-yl)-1-(tert-butyl-dimethyl-sil-yl)-3,6-di-hydro-1λ4,2λ4-aza-borinine.

The title compound, C24H30BNSi (I), is an asymmetric 1,2,3,6-tetra-hydro-1,2-aza-borinine consisting of a BN-substituted cyclo-hexa-diene analog with a B-anthracenyl substituent. A ring-closing metathesis with subsequent substitution of the obtained BCl 1,2-aza-borinine using anthracenyl lithium yielded the title compound I. The asymmetric unit (Z = 8) belongs to the ortho-rhom-bic space group Pbca and shows an elongated N-C bond compared to previously reported BN-1,4-cyclo-hexa-diene [Abbey et al. (2008 ▸) J. Am. Chem. Soc. 130, 7250-7252]. The primarily contributing surface inter-actions are H⋯H and C⋯H/H⋯C (as elucidated by Hirshfeld surface analysis) which are dominated by van der Waals forces. Moreover, the non-aromatic BN heterocycle and the protecting group exhibit intra- and inter-molecular C-H⋯π inter-actions, respectively, with the anthracenyl substituent.

Heavier bis(m-terphenyl)element phosphaethynolates of group 13.

The synthesis and reactivity of the heavier group 13 phosphaketene complexes (2,6-Mes2C6H3)2EPCO (1, E = Ga; 2, E = In) were reported. The reaction of 1 and 2 with 1,2,3,4-tetramethylimidazolin-2-ylidene, IMe4, gave rise to the formation of (2,6-Mes2C6H3)2EP(O)C(IMe4) (3, E = Ga; 4 E = In; Mes = mesityl). Subsequent addition of elemental tellurium proceeded via insertion into the E-P bond and provided (2,6-Mes2C6H3)2ETeP(O)C(IMe4) (5, E = Ga; 6, E = In) comprising five-membered ETePCO-heterocycles. Compounds 1-6 were fully characterized by X-ray crystallography and heteronuclear NMR spectroscopy. The electronic structures of 1-6 were studied by DFT calculations and analyses of a complementary set of real-space bonding indicators (AIM, ELI-D, NCI) derived from the electron and pair densities, with focus on the bond characteristics of the PCO fragment.

Nickel and Palladium Complexes of a PP(O)P Pincer Ligand Based upon a peri-Substituted Acenaphthyl Scaffold and a Secondary Phosphine Oxide.

A PP(O)P pincer ligand based upon a peri-substituted acenaphthyl (Ace) scaffold and a secondary phosphine oxide, (5-Ph2P-Ace-6-)2P(O)H, was prepared and fully characterized including a neutron diffraction study. The reaction with [Ni(H2O)6]Cl2 and PdCl2 produced ionic metal(II) complexes [κ3-P,P',P''((5-Ph2P-Ace-6-)2P(OH))MCl]Cl, which upon addition of Et3N gave rise to zwitterionic metal(II) complexes κ3-P,P',P''((5-Ph2P-Ace-6-)2P(O))MCl (M = Ni, Pd). The reaction with Ni(COD)2 (COD = cyclooctadiene) provided the η3-cyclooctenyl Ni(II) complex κ3-P,P',P''((5-Ph2P-Ace-6-)2P(O))Ni(η3-C8H13). A detailed complementary bonding analysis of the P-H, P-O, and P-M interactions was carried out (M = Ni, Pd).

Synthesis, Reactivity and Structural Properties of Trifluoromethylphosphoranides.

Phosphoranides are interesting hypervalent species which serve as model compounds for intermediates or transition states in nucleophilic substitution reactions at trivalent phosphorus substrates. Herein, the syntheses and properties of stable trifluoromethylphosphoranide salts are reported. [K(18-crown-6)][P(CF3 )4 ], [K(18-crown-6)][P(CF3 )3 F], and [NMe4 ][P(CF3 )2 F2 ] were obtained by treatment of trivalent precursors with sources of CF3 - or F- units. These [P(CF3 )4-n Fn ]- (n=0-2) salts exhibit fluorinating (n=1-2) or trifluoromethylating (n=0) properties, which is disclosed by studying their reactivity towards selected electrophiles. The solid-state structures of [K(18-crown-6)][P(CF3 )4 ] and [K(18-crown-6)][P(CF3 )3 F] are ascertained by single crystal X-ray crystallography. The dynamics of these compounds are investigated by variable temperature NMR spectroscopy.

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.

Lewis Superacidic Tellurenyl Cation-Induced Electrophilic Activation of an Inert Carborane.

The aryltellurenyl cation [2-(tBuNCH)C6 H4 Te]+ , a Lewis super acid, and the weakly coordinating carborane anion [CB11 H12 ]- , an extremely weak Brønsted acid (pKa =131.0 in MeCN), form an isolable ion pair complex [2-(tBuNCH)C6 H4 Te][CB11 H12 ], in which the Brønsted acidity (pKa 7.4 in MeCN) of the formally hydridic B-H bonds is dramatically increased by more than 120 orders of magnitude. The electrophilic activation of B-H bonds in the carborane moiety gives rise to a proton transfer from boron to nitrogen at slightly elevated temperatures, as rationalized by the isolation of a mixture of the zwitterionic isomers 12- and 7-[2-(tBuN{H}CH)C6 H4 Te(CB11 H11 )] in ratios ranging from 62 : 38 to 80 : 20.

Pseudocyclic bis-N-heterocycle-stabilized iodanes - synthesis, characterization and applications.

Bis-N-heterocycle-stabilized λ3-iodanes (BNHIs) based on azoles are introduced as novel structural motifs in hypervalent iodine chemistry. A performance test in a variety of benchmark reactions including sulfoxidations and phenol dearomatizations revealed a bis-N-bound pyrazole substituted BNHI as the most reactive derivative. Its solid-state structure was characterized via X-ray analysis implying strong intramolecular interactions between the pyrazole nitrogen atoms and the hypervalent iodine centre.

A Versatile Silver(I) Pentafluorooxosulfate Reagent for the Synthesis of OSF5 Compounds.

Herein, we report the preparation of silver(I) pentafluorooxosulfate from commercially available AgF and OSF4 . The compound is surprisingly stable in a MeCN solution. Apart from that, AgOSF5 has been stabilised by the addition of 2,2'-bipyridine ligands. Starting from solutions of the unstabilised silver(I) salt, OSF5 complexes with NiII , CuI , and CuII -centres have been obtained. In addition, AgOSF5 has proven to be generally capable of mediating the transfer of OSF5 groups to aryne moieties, thus furnishing a new and safe method for the preparation of OSF5 -substituted arenes. X-ray crystal structure analysis of selected transition-metal OSF5 compounds have revealed distorted octahedral [OSF5 ]- anions which are extensively stabilised by hydrogen bonding.

N-Heterocyclic Iod(az)olium Salts - Potent Halogen-Bond Donors in Organocatalysis.

This article describes the application of N-heterocyclic iod(az)olium salts (NHISs) as highly reactive organocatalysts. A variety of mono- and dicationic NHISs are described and utilized as potent XB-donors in halogen-bond catalysis. They were benchmarked in seven diverse test reactions in which the activation of carbon- and metal-chloride bonds as well as carbonyl and nitro groups was achieved. N-methylated dicationic NHISs rendered the highest reactivity in all investigated catalytic applications with reactivities even higher than all previously described monodentate XB-donors based on iodine(I) and (III) and the strong Lewis acid BF3 .

Experimental and Theoretical Studies of a Spirostannole and Formation of a Pentaorganostannate.

A new spirostannole, 1,1',3,3'-tetrakis(5-methylthiophen-2-yl)-4,4',5,5',6,6',7,7'-octahydro-2,2'-spirobi[benzo[c]stannole] (4), is synthesised and the molecular structure is compared with the optimised geometry from DFT calculations. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are twice degenerated and show a small HOMO-LUMO energy gap of 3.2 eV. In addition, cyclic voltammetry measurements are conducted and three redox processes are observed. Absorption and emission spectra show maxima at λabs,max 436 nm and λem,max 533 nm, respectively. Spirostannole 4 is a strongly absorbing material, but an extremely weak emitter in solution at 295.15 K. However, when the solution is cooled from 280 to 80 K, the emission becomes visible. The reaction of spirostannole 4 with methyllithium is monitored by NMR spectroscopy at 238.15 K. The 119Sn{1H} NMR signal shifts from -36.0 (4) to -211.0 ppm, which is indicative of the formation of the lithium pentaorganostannate 5. The complex is thermally instable at 295.15 K, but insights into the molecular structure and electronic behaviour are obtained by DFT and TD-DFT calculations.

Iodolopyrazolium Salts: Synthesis, Derivatizations, and Applications.

The synthesis of iodolopyrazolium triflates via an oxidative cyclization of 3-(2-iodophenyl)-1H-pyrazoles is described. The reaction is characterized by a broad substrate scope, and various applications of these novel cyclic iodolium salts acting as useful synthetic intermediates are demonstrated, in particular in site-selective ring openings. This was finally applied to generate derivatives of the anti-inflammatory drug celecoxib. Their application as highly active halogen-bond donors is shown as well.

Aggregation induced emission - emissive stannoles in the solid state.

The optoelectronic and structural properties of six stannoles are reported. All revealed extremely weak emission in solution at 295 K, but intensive fluorescence in the solid state with quantum yields (ΦF) of up to 11.1% in the crystal, and of up to 24.4% (ΦF) in the thin film.

Clickable azide-functionalized bromoarylaldehydes - synthesis and photophysical characterization.

Herein, we present a facile synthesis of three azide-functionalized fluorophores and their covalent attachment as triazoles in Huisgen-type cycloadditions with model alkynes. Besides two ortho- and para-bromo-substituted benzaldehydes, the azide functionalization of a fluorene-based structure will be presented. The copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) of the so-synthesized azide-functionalized bromocarbaldehydes with terminal alkynes, exhibiting different degrees of steric demand, was performed in high efficiency. Finally, we investigated the photophysical properties of the azide-functionalized arenes and their covalently linked triazole derivatives to gain deeper insight towards the effect of these covalent linkers on the emission behavior.

Symmetry Effects in Photoinduced Electron Transfer in Chlorin-Quinone Dyads: Adiabatic Suppression in the Marcus Inverted Region.

In donor-acceptor dyads undergoing photoinduced electron transfer (PET), a direction or pathway for electron movement is usually dictated by the redox properties and the separation distance between the donor and acceptor subunits, while the effect of symmetry is less recognized. We have designed and synthesized two isomeric donor-acceptor assemblies in which electronic coupling between donor and acceptor is altered by the orbital symmetry control with the reorganization energy and charge transfer exothermicity being kept unchanged. Analysis of the optical absorption and luminescence spectra, supported by the DFT and TD-DFT calculations, showed that PET in these assemblies corresponds to the Marcus inverted region (MIR) and has larger rate for isomer with weaker electronic coupling. This surprising observation provides the first experimental evidence for theoretically predicted adiabatic suppression of PET in MIR, which unambiguously controlled solely by symmetry.

One-Pot Synthesis and Conformational Analysis of Six-Membered Cyclic Iodonium Salts.

Two one-pot procedures for the construction of carbon-bridged diaryliodonium triflates and tetrafluoroborates are described. Strong Brønsted acids enable the effective Friedel-Crafts alkylation with diversely substituted o-iodobenzyl alcohol derivatives, providing diphenylmethane scaffolds, which are subsequently oxidized and cyclized to the corresponding dibenzo[b,e]iodininium salts. Based on NMR investigations and density functional theory (DFT) calculations, we could verify the so-far-undescribed existence of two stable isomers in cyclic iodonium salts substituted with aliphatic side chains in the carbon bridge.

Proximity enforced oxidative addition of a strong unpolar σ-Si-Si bond at rhodium(i).

The new bidentate bisphosphino ligand (5-Ph2P-Ace-6-SiMe2)2 (1) binds rhodium(i) chloride and brings it into close proximity to a strong unpolar σ-Si-Si bond, in which it immediately inserts. In the spirocyclic Rh(iii) product of the oxidative addition, (5-Ph2P-Ace-6-SiMe2)2RhCl (2), the two Si atoms are still close enough to engage in weak non-covalent interactions.

Synthesis and Thermal Investigations of Eleven-Membered Ring Systems Containing One of the Heavier Group 14 Element Atoms Si, Ge, and Sn.

Unique eleven-membered rings containing silicon, germanium, and tin were synthesized in good yields by the reactions of the corresponding 1,2-bis((2-bromothiophen-3-yl)methoxy)benzenes with (C6H5)2ECl2 where E = Sn, Ge, Si. The Sn and Ge congeners were crystallized, but the conformers that these rings crystallized in, were quite different. As confirmed by Density Functional Theory (DFT) calculations, (C28H22O2S2Sn) assumes a unique crystal structure that leaves more room around the tetrel atom as compared to the crystal structure of the corresponding Ge compound. In the latter, the central cavity is quite open, whereas in the former, one of the methylene groups can fold inwards. Another consequence is the influence on the planes of the aromatic rings flanking the heterocycle. In the Ge case, the benzene ring is folded away from the central cavity, whereas in the Sn case, it is almost parallel to the imaginary axis through the center of the ring. Thermal analysis investigations (TGA and DSC methods) of these eleven-membered rings suggested the loss of a phenyl group in the first decomposition step. The decomposition temperature decreased from the Si containing heterocycle to Ge and was lowest for the Sn containing heterocycle.

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.

Non-Oxido-Vanadium(IV) Metalloradical Complexes with Bidentate 1,2-Dithienylethene Ligands: Observation of Reversible Cyclization of the Ligand Scaffold in Solution.

Derivatives of 1,2-dithienylethene (DTE) have superb photochromic properties due to an efficient reversible photocyclization reaction of their hexatriene structure and, thus, have application potential in materials for optoelectronics and (multi-responsive) molecular switches. Transition-metal complexes bearing switchable DTE motifs commonly incorporate their coordination site rather distant from the hexatriene system. In this work the redox active ligand 1,2-bis(2,5-dimethylthiophen-3-yl)ethane-1,2-dione is described, which reacts with [V(TMEDA)2 Cl2 ] to give a rare non-oxido vanadium(IV) species 3(M,M/P,P). This blue complex has two bidentate en-diolato ligands which chelate the VIV center and give rise to two five-membered metallacycles with the adjacent hexatriene DTE backbone bearing axial chirality. Upon irradiation with UVA light or prolonged heating in solution, the blue compound 3(M,M/P,P) converts into the purple atropisomer 4(para,M/para,P). Both complexes were isolated and structurally characterized by single-crystal X-ray diffraction analysis (using lab source and synchrotron radiation). The antiparallel configuration (M or P helicity) present in both 3(M,M/P,P) and 4(para,M/para,P) is a prerequisite for (reversible) 6π cyclization reactions. A CW EPR spectroscopic study reveals the metalloradical character for 3(M,M/P,P) and 4(para,M/para,P) and indicates dynamic reversible cyclization of the DTE backbone in complex 3(M,M/P,P) at ambient temperature in solution.