One‐Electron Oxidation of a Disilicon(0) Compound: An Experimental and Theoretical Study of [Si2]+ Trapped by N‐Heterocyclic Carbenes

One‐electron oxidation of the disilicon(0) compound Si₂(Idipp)₂ ( 1 , Idipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) with [Fe(C₅Me₅)₂][B(Ar^F)₄] (Ar^F=C₆H₃‐3,5‐(CF₃)₂) affords selectively the green radical salt [Si₂(Idipp)₂][B(Ar^F)₄] ( 1 ‐[B(Ar^F)₄). Oxidation of the centrosymmetric 1 occurs reversibly at a low redox potential (E_1/2=?1.250 V vs. Fc⁺/Fc), and is accompanied by considerable structural changes as shown by single‐crystal X‐ray structural analysis of 1 ‐B(Ar^F)₄. These include a shortening of the Si?Si bond, a widening of the Si‐Si‐C_NHC angles, and a lowering of the symmetry, leading to a quite different conformation of the NHC substituents at the two inequivalent Si sites in 1⁺ . Comparative quantum chemical calculations of 1 and 1⁺ indicate that electron ejection occurs from the symmetric (n₊) combination of the Si lone pairs (HOMO). EPR studies of 1 ‐B(Ar^F)₄ in frozen solution verified the inequivalency of the two Si sites observed in the solid‐state, and point in agreement with the theoretical results to an almost equal distribution of the spin density over the two Si atoms, leading to quite similar ²⁹Si hyperfine coupling tensors in 1⁺ . EPR studies of 1 ‐B(Ar^F)₄ in liquid solution unraveled a topomerization with a low activation barrier that interconverts the two Si sites in 1⁺ .     

Trapping a Silicon(I) Radical with Carbenes: A Cationic cAAC–Silicon(I) Radical and an NHC–Parent‐Silyliumylidene Cation

The trapping of a silicon(I) radical with N‐heterocyclic carbenes is described. The reaction of the cyclic (alkyl)(amino) carbene [cAAC_Me] (cAAC_Me=:C(CMe₂)₂(CH₂)NAr, Ar=2,6‐i Pr₂C₆H₃) with H₂SiI₂ in a 3:1 molar ratio in DME afforded a mixture of the separated ion pair [(cAAC_Me)₂Si:^.]⁺I⁻ ( 1 ), which features a cationic cAAC–silicon(I) radical, and [cAAC_Me−H]⁺I⁻. In addition, the reaction of the NHC–iodosilicon(I) dimer [I_Ar(I)Si:]₂ (I_Ar=:C{N(Ar)CH}₂) with 4 equiv of I_Me (:C{N(Me)CMe}₂), which proceeded through the formation of a silicon(I) radical intermediate, afforded [(I_Me)₂SiH]⁺I⁻ ( 2 ) comprising the first NHC–parent‐silyliumylidene cation. Its further reaction with fluorobenzene afforded the C_Ar−H bond activation product [1‐F‐2‐I_Me‐C₆H₄]⁺I⁻ ( 3 ). The isolation of 2 and 3 confirmed the reaction mechanism for the formation of 1 . Compounds 1 – 3 were analyzed by EPR and NMR spectroscopy, DFT calculations, and X‐ray crystallography.     

Trapping a Silicon(I) Radical with Carbenes: A Cationic cAAC–Silicon(I) Radical and an NHC–Parent-Silyliumylidene Cation

The trapping of a silicon(I) radical with N-heterocyclic carbenes is described. The reaction of the cyclic (alkyl)(amino) carbene [cAAC_Me] (cAAC_Me=:C(CMe₂)₂(CH₂)NAr, Ar=2,6-iPr₂C₆H₃) with H₂SiI₂ in a 3:1 molar ratio in DME afforded a mixture of the separated ion pair [(cAAC_Me)₂Si:^.]⁺I⁻ ( 1 ), which features a cationic cAAC–silicon(I) radical, and [cAAC_Me−H]⁺I⁻. In addition, the reaction of the NHC–iodosilicon(I) dimer [I_Ar(I)Si:]₂ (I_Ar=:C{N(Ar)CH}₂) with 4 equiv of I_Me (:C{N(Me)CMe}₂), which proceeded through the formation of a silicon(I) radical intermediate, afforded [(I_Me)₂SiH]⁺I⁻ ( 2 ) comprising the first NHC–parent-silyliumylidene cation. Its further reaction with fluorobenzene afforded the C_Ar−H bond activation product [1-F-2-I_Me-C₆H₄]⁺I⁻ ( 3 ). The isolation of 2 and 3 confirmed the reaction mechanism for the formation of 1 . Compounds 1 – 3 were analyzed by EPR and NMR spectroscopy, DFT calculations, and X-ray crystallography.     

Untersuchungen an Polyhalogeniden. XXIII. Kristallstrukturen der N-Alkylurotropiniumtriiodide UrRI3 mit R = Methyl,Ethyl, n-Propyl und n-Butyl

Studies on Polyhalides. 23. Crystal Structures of N-Alkylurotropinium Triiodides UrRI₃ with R = Methyl, Ethyl, n-Propyl, and n-Butyl The salts UrRI₃ may be prepared by the reaction of N-alkylurotropinium iodides UrRI with iodine I₂ at room temperature from aqueous solution. N-methylurotropinium triiodide C₇H₁₅N₄I₃ crystallizes monoclinically in P2₁/c with a = 1300.8(2) pm, b = 1276.0(3) pm, c = 859.3(2) pm, β = 94.75(2)° and Z = 4. The crystal structure is built up from layers of cations UrMe⁺ and of linear symmetric triiodide ions I₃^? alternating along [100]. N-ethylurotropinium triiodide C₈H₁₇N₄I₃ crystallizes orthorhombically in Pnma with a = 1397.3(5) pm, b = 1221.3(2) pm, c = 886.2(2) pm and Z = 4. The cationic (UrEt⁺) and anionic (I₃^?) layers alternate along [0 10]. N-propylurotropinium triiodide C₉H₁₉N₄I₃ crystallizes monoclinically in P2₁/c with a = 1885.7(5) pm, b = 1657.1(5) pm, c = 1700.5(4) pm, β = 112.39(2)° and Z = 12. The three independent cations and anions are slightly, but differently distorted. N-butylurotropinium triiodide C₁₀H₂₁N₄I₃ crystallizes monoclinically in P2₁/m with a = 991.8(3) pm, b = 757.8(2) pm, c = 1128.2(2) pm, β = 90.73(2)° and Z = 2. The crystal structure is stacked by alternating cationic and anionic layers along [001]. The triiodide ion is asymmetric and linear.     

Synthesis and fluorescence properties of DMCX+—a stable oxygen-bridged [4]helicenium dye

A one-step synthesis of the stable [4]helicenium dye, 1,13-dimethoxy-chromeno[2,3,4-kl]xanthenium hexafluorophosphate (DMCX⁺) from the readily available tris(2,6-dimethoxyphenyl)carbenium ion is reported. The crystal structure, the chemical stability, and dye properties of the DMCX⁺ helicenium system are described.     

Liquid-liquid extraction of metal ions with tris (2,6-dimethoxyphenyl) phosphine and its quaternary phosphonium salts

The extraction of various metal ions from hydrochloric acid solutions with tris(2,6-dimethoxyphenyl)phosphine, [2,6-(MeO)₂C₆H₃]₃P, abbreviated to (2,6-MeOPh)₃P, and its tertiary and quaternary phosphonium salts were studied. A series of phosphonium salts, [(2,6-MeOPh)₃PH]⁺ClO^?₄, [(2,6-MeOPh)₃PR]⁺Br^? and {[(2,6-MeOPh)₃P]₂R′}²⁺ (Br^?)₂, where R = C₁₂H₂₅, C₁₈H₃₇ or C₆H₅CH₂ and R′ = p-CH₂C₆H₄CH₂, (CH₂)₃ and (CH₂)₁₀, were synthesized and applied to an anion exchanger for chloro complex anions of various metal ions. (2,6-MeOPh)₃P and [(2,6-MeOPh)₃PR]⁺Br^? were found to be effective for the extraction of metal ions such as iron(III), gold(III) and gallium(III), forming tetrachloro complex anions of the M^IIICl^?₄ type. The extractabilities of the doubly charged cationic quaternary phosphonium salts [{(2,6-MeOPh)₃P}₂R′]²⁺ (Br^?₂, were found to be superior to those of the singly charged cationic phosphonium salts for metal ions such as cadmium(II), platinum(II) and palladium(II), forming a tetrachloro complex doubly charged aion of the M^IICl^2?₄ type. Most of the metal ions are extracted through ion-pair formation between their chloro complex anions and the phosphonium cations.     

Structural Snapshots of π-Arene Bonding in a Gold Germylene Cation

Heavier group 14 element cations exhibit a remarkable reactivity that has typically hampered their isolation. For the few available examples, the role of π-arene interactions is crucial to provide kinetic stabilization, but dynamic and structural information on those contacts is yet limited. In this study we have accessed the metalogermylenium cation [(PMe₂Ar^Dipp2)AuGe(Ar^Dipp2)Cl]⁺ ( 4⁺ ) (Ar^Dipp2=C₆H₃-2,6-(C₆H₃-2,6-iPr₂)₂) that has been structurally characterized with three different non-coordinating counter anions. These studies provide for the first time dynamic information about the conformational rearrangement that characterizes π-arene bonding thorough a series of X-ray diffraction structural snapshots. Computational studies reveal the weak character of the π-arene bonding (ca. 2 kcal mol⁻¹) that can be described as the donation from a π_C=C bond toward the empty p valence orbital of germanium.     

Crystal and molecular structure of diphenyliodonium triiodide

A new salt diphenyliodonium triiodide (C₁₂H₁₀I₄) was obtained. The [C₁₂H₁₀I⁺][I₃⁻] compound was isolated as red brown crystals and studied by single-crystal X-ray diffraction. The structure of diphenyliodonium triiodide consists of separate, virtually linear I₃⁻ anions and C₁₂H₁₀I⁺ cations. Strong intermolecular anion-anion (I₃⁻…I₃⁻) and anion-cation (I₃⁻…I⁺) interactions in the crystal structure leads to a change in the symmetry of triiodide ions. The complex formation in the system organic cation iodide-elementary iodine was studied by spectrophotometry. The complex composition was found (1: 1), and the stability constant of the complex in chloroform was determined (loggB = 3.91).     

Indyllithium and the Indyl Anion [InL]−: Heavy Analogues of N‐Heterocyclic Carbenes

Reduction of the indate complex In(NON^Ar)(μ‐Cl)₂Li(OEt₂)₂ (NON^Ar=[O(SiMe₂NAr)₂]^2?; Ar=2,6‐iPr₂C₆H₃) with sodium generates the In^II diindane species [In(NON^Ar)]₂. Further reduction with a mixture of potassium and [2.2.2]crypt affords the In^I N‐heterocyclic indyl anion [In(NON^Ar)]^?, which crystallizes with a non‐contacted [K([2.2.2]crypt)]⁺ cation. The indyl anion can also be isolated as the indyllithium compound In(NON^Ar)(Li{THF}₃), which contains an In?Li bond. Density functional theory calculations show that the HOMO of the indyl anion is a metal‐centred lone pair, and preliminary reactivity studies confirm its nucleophilic behaviour.     

Penta-arylcyclopentadienyl complexes

This review covers the coordination and general chemistry of the 1,2,3,4,5-penta-arylcyclopentadiene system, as anion, C₅Ar₅^?, radical, C₅Ar₅, and cation, C₅Ar₅⁺, as well as the neutral diene, C₅Ar₅H, and its derivatives. The structural rigidity and steric saturation offered by the penta-arylcyclopentadienyl ligand give rise to definite structural and geometric properties in its complexes that distinguish its chemistry from that of the parent cyclopentadiene.     

Tetraiodide von Tris(1,2‐ethandiamin)komplexen der Metalle Zink und Nickel

The isotypic compounds tris(1,2‐ethanedi­amine‐N,N′)­zinc(II) triiodide iodide, [Zn(C₂H₈N₂)₃](I₃)I, and tris(1,2‐ethanedi­amine‐N,N′)­nickel(II) triiodide iodide, [Ni(C₂H₈N₂)₃](I₃)I, contain the octahedral [M(en)₃]²⁺ cation, with M = Zn and Ni, in both enantiomeric forms, an essentially linear triiodide anion and an iodide anion. The geometries of the complex ions are as expected, e.g.d(Ni—N) = 2.123 (5), 2.127 (6) and 2.134 (5) Å, and d(Zn—N) = 2.176 (4), 2.193 (4) and 2.210 (4) Å. The shortest contact between the triiodide and iodide ions is 3.979 (1) Å for the nickel compound and 4.013 (1) Å for the zinc compound.     

Isolation and Characterization of a Bismuth(II) Radical

More than 80 years after Paneth’s report of dimethyl bismuth, the first monomeric Bi^II radical that is stable in the solid state has been isolated and characterized. Reduction of the diamidobismuth(III) chloride Bi(NON^Ar)Cl (NON^Ar=[O(SiMe₂NAr)₂]²⁻; Ar=2,6‐iPr₂C₆H₃) with magnesium affords the Bi^II radical ^.Bi(NON^Ar). X‐ray crystallographic measurements are consistent with a two‐coordinate bismuth in the +2 oxidation state with no short intermolecular contacts, and solid‐state SQUID magnetic measurements indicate a paramagnetic compound with a single unpaired electron. EPR and density functional calculations show a metal‐centered radical with >90 % spin density in a p‐type orbital on bismuth.     

Reactivity of Diarylnitrenium Ions

Hydride abstraction from diarylamines with the trityl ion is explored in an attempt to generate a stable diarylnitrenium ion, Ar₂N⁺. Sequential H-atom abstraction reactions ensue. The first H-atom abstraction leads to intensely colored aminium radical cations, Ar₂NH^.+, some of which are quite stable. However, most undergo a second H-atom abstraction leading to ammonium ions, Ar₂NH₂⁺. In the absence of a ready source of H-atoms, a unique self-abstraction reaction occurs when Ar=Me₅C₆, leading to a novel iminium radical cation, Ar=N^.+Ar, which decays via a second self H-atom abstraction reaction to give a stable iminium ion, Ar=N⁺HAr. These products differ substantially from those derived via photochemically produced diarylnitrenium ions.     

β‐Diketiminatoytterbium aryloxides: synthesis,structural characterization,and catalytic activity for addition of amines to carbodiimides

The steric effect of an aryloxido group on the synthesis and molecular structures of ytterbium aryloxides supported by β‐diketiminato ligand L (L = [N(2,6‐Me₂C₆H₃)C(Me)]₂CH^?) is reported. Reactions of β‐diketiminatoytterbium dichloride, LYbCl₂(THF)₂, with NaOAr¹ in THF (Ar¹ = [2,6‐^tBu₂‐4‐MeC₆H₂], THF = tetrahydrofuran) at 60°C gave the corresponding ytterbium complexes LYb(OAr¹)Cl(THF) ( 1 ) and LYb(OAr¹)₂ (1), depending on the molar ratio of dichloride to sodium aryloxide, respectively, while the same reactions with NaOAr² and NaOAr³ (Ar² = [2,6‐ⁱPr₂C₆H₃], Ar³ = [2,6‐Me₂C₆H₃]) in 1:1 or 1:2 molar ratio in THF afforded only bisaryloxide complexes LYb(OAr²)₂(THF) (1) and LYb(OAr³)₂(THF) ( 4 ) in good yields, respectively. Complexes 1 , 2 , 3 , 4 were fully characterized, including X‐ray crystal structure analyses. All the complexes are efficient pre‐catalysts for the catalytic addition of amines to carbodiimides giving guanidines. Copyright © 2013 John Wiley & Sons, Ltd.     

Boron Lewis Acid‐Catalyzed Hydroboration of Alkenes with Pinacolborane: BArF3 Does What B(C6F5)3 Cannot Do!

The transition‐metal‐free hydroboration of various alkenes with pinacolborane (HBpin) initiated by tris[3,5‐bis(trifluoromethyl)phenyl]borane (BAr^F₃) is reported. The choice of the boron Lewis acid is crucial as the more prominent boron Lewis acid tris(pentafluorophenyl)borane (B(C₆F₅)₃) is reluctant to react. Unlike B(C₆F₅)₃, BAr^F₃ is found to engage in substituent redistribution with HBpin, resulting in the formation of Ar^FBpin and the electron‐deficient diboranes [H₂BAr^F]₂ and [(Ar^F)(H)B(μ‐H)₂BAr^F₂]. These in situ‐generated hydroboranes undergo regioselective hydroboration of styrene derivatives as well as aliphatic alkenes with cis diastereoselectivity. Another ligand metathesis of these adducts with HBpin subsequently affords the corresponding HBpin‐derived anti‐Markovnikov adducts. The reactive hydroboranes are regenerated in this step, thereby closing the catalytic cycle.     

A Terphenyl Supported Dioxophosphorane Dimer: the Light Congener of Lawesson's and Woollins’ Reagents

Thermolysis of a 1,3-dioxa-2-phospholane supported by the terphenyl ligand Ar^iPr4 (Ar^iPr4=[C₆H₃-2,6-(C₆H₃-2,6-iPr₂)]) at 150 °C gives [Ar^iPr4PO₂]₂ via loss of ethene. [Ar^iPr4PO₂]₂ was characterised by X-ray crystallography and NMR spectroscopy; it contains a 4-membered P−O−P−O ring and is the isostructural oxygen analogue of Lawesson's and Woollins’ reagents. The dimeric structure of [Ar^iPr4PO₂]₂ was found to persist in solution through VT NMR spectroscopy and DOSY, supported by DFT calculations. The addition of DMAP to the 1,3-dioxa-2-phospholane facilitates the loss of ethene to give Ar^iPr4(DMAP)PO₂ after days at room temperature, with this product also characterised by X-ray crystallography and NMR spectroscopy. Replacement of the DMAP with pyridine induces ethene loss from the 1,3-dioxa-2-phospholane to provide gram-scale samples of [Ar^iPr4PO₂]₂ in 75 % yield in 2 days at only 100 °C.     

Fluorocarbon derivatives of nitrogen. Part 16 [1]. Synthesis of some unsymmetrical aromatic azo-compounds via diazotisation of fluorinated aryl- and -heteroaryl-amines in hydrofluoric or sulphuric acid [2]

Coupling reactions of the type Ar_FN⁺₂ + ArH → Ar_FN=NAr + H⁺ have been accomplished between fluorinated arenediazonium ions selected from the benzenic, pyridinic and pyrimidinic classes [Ar_F = C₆F₅, 4---CF₃C₆F₄, 4---C₅F₄N, 4z.sbnd;C₅F₃N.Cl---3, 4---C₅F₂N.Cl₂---3,5, 2---C₅F₃N.CF(CF₃)2---4, 4---C₄F₃N₂] and one or more aromatic compounds activated towards electrophilic attack (ArH = 1,3,5,---ME₃C₆H₃, 1,3,5---Et₃C₆H₃, MeOC₆H₆, and napth-2-ol). The diazonium ions were generated by addition of solid sodium nitrite to solutions of the amines Ar_FNH₂ in anhydrous hydrogen fluoride, 80% hydrofluoric acid, or 98% sulphuric acid mixed with glacial acetic acid and propionic acid. This work has established that perfluorinated arenediazonium ions rank amongst the most electrophilic species of their general class.     

Complex structure tri- and polyiodides of iodocyclization products of 2-allylthioquinoline

Iodocyclization products of 2-allylthioquinoline are obtained in the form of polyiodides with different stoichiometric compositions. X-ray crystallography data are analyzed for two different crystal structures of 1-iodomethyl-1,2-dihydro[1,3]thiazolo[3,2-a]quinolinium polyiodides: triiodide C₁₂H₁₁INS⁺I ₃ ^? and complex polyiodide 2(C₁₂H₁₁INS⁺I ₃ ^? )·I₂. A comparison is made of the nonbonding interactions of dihydrothiazoloquinolinium with atoms of the triiodide anion and complex polyiodide to show the crystal structure features attributed to the participation of molecular iodine.     

Crystalline Radicals Derived from Classical N‐Heterocyclic Carbenes

One‐electron reduction of C2‐arylated 1,3‐imidazoli(ni)um salts (IPr^Ar)Br (Ar=Ph, 3 a ; 4‐DMP, 3 b ; 4‐DMP=4‐Me₂NC₆H₄) and (SIPr^Ar)I (Ar=Ph, 4 a ; 4‐Tol, 4 b ) derived from classical NHCs (IPr=:C{N(2,6‐iPr₂C₆H₃)}₂CHCH, 1 ; SIPr=:C{N(2,6‐iPr₂C₆H₃)}₂CH₂CH₂, 2 ) gave radicals [(IPr^Ar)]^. (Ar=Ph, 5 a ; 4‐DMP, 5 b ) and [(SIPr^Ar)]^. (Ar=Ph, 6 a ; 4‐Tol, 6 b ). Each of 5 a , b and 6 a , b exhibited a doublet EPR signal, a characteristic of monoradical species. The first solid‐state characterization of NHC‐derived carbon‐centered radicals 6 a , b by single‐crystal X‐ray diffraction is reported. DFT calculations indicate that the unpaired electron is mainly located at the original carbene carbon atom and stabilized by partial delocalization over the adjacent aryl group.     

Synthesis and reactivity of neodymium(III) amido-tethered N-heterocyclic carbene complexes

The reaction of the heteroleptic Nd(III) iodide, [Nd(L′)(N″)(μ-I)] with the potassium salts of primary aryl amides [KN(H)Ar′] or [KN(H)Ar^*] affords heteroleptic, structurally characterised, low-coordinate neodymium amides [Nd(L′)(N″)(N(H)Ar′)] and [Nd(L′)(N″)(N(H)Ar^*)] cleanly (L′ = t-BuNCH₂CH₂[C{NC(SiMe₃)CHNt-Bu}], N″ = N(SiMe₃)₂, Ar′ = 2,6-Dipp₂C₆H₃, Dipp = 2,6-Prⁱ₂C₆H₃, Ar^* = 2,6-(2,4,6-Prⁱ₃C₆H₂)₂C₆H₃). The potassium terphenyl primary amide [KN(H)Ar^*] is readily prepared and isolated, and structurally characterised. Treatment of these primary amide-containing compounds with alkali metal alkyl salts results in ligand exchange to give alkali metal primary amides and intractable heteroleptic Nd(III) alkyl compounds of the form [Nd(L′)(N″)(R)] (R = CH₂SiMe₃, Me). Attempted deprotonation of the Nd-bound primary amide in [Nd(L′)(N″)(N(H)Ar^*)] with the less nucleophilic phosphazene superbase Bu^tNP{NP(NMe₂)₃}₃ resulted in indiscriminate deprotonations of peripheral ligand CH groups.