Double Bond Character Research Articles

Tetraimido Sulfuric Acid H2 S(NtBu)4 -Valence Isoelectronic to H2 SO4.

The valence isoelectronic imido analog H2S(NtBu)4 (1) of sulfuric acid H2SO4 was synthesized, isolated, and characterized by NMR spectroscopy and high‐resolution X‐ray charge density analysis. The latter reveals strongly polarized Sδ+−Nδ− bonds with virtually no double bond character. The easy‐to‐polarize S−N bonds are an advantageous and versatile feature of sulfur nitrogen ligands, which enables them to adapt to different electron requirements of various metal cations.

Twofold C-H Activation Enables Synthesis of a Diazacoronene-Type Fluorophore with Near Infrared Emission Through Isosteric Replacement.

The synthesis and photophysical properties of a soluble amide-embedded coronene is reported. The key step in this synthesis is the twofold C-H activation of diazaperylene by a rhodium(III)Cp* catalyst. This unprecedented structural motif shows intense fluorescence in the near infrared region with a small Stokes shift and a distinct vibronic structure, which exhibits a slight extent of negative solvatochromism. Comparison of this compound with some relevant compounds revealed the importance of the amide incorporation in the peripheral concave region including an angular position to retain high aromaticity reflecting that of parent coronene. Treatment of this compound with Lewis acid B(C6 F5 )3 formed a bis-adduct, which exhibited enhanced aromaticity as a consequence of the increased double bond character of the amide C-N bonds.

Synthesis and electronic structure analysis of the actinide allenylidenes, [{(NR2)3}An(CCCPh2)]- (An = U, Th; R = SiMe3).

The reaction of [AnCl(NR2)3] (An = U, Th, R = SiMe3) with in situ generated lithium-3,3-diphenylcyclopropene results in the formation of [{(NR2)3}An(CH Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CCPh2)] (An = U, 1; Th, 2) in good yields after work-up. Deprotonation of 1 or 2 with LDA/2.2.2-cryptand results in formation of the anionic allenylidenes, [Li(2.2.2-cryptand)][{(NR2)3}An(CCCPh2)] (An = U, 3; Th, 4). The calculated 13C NMR chemical shifts of the Cα, Cβ, and Cγ nuclei in 2 and 4 nicely reproduce the experimentally assigned order, and exhibit a characteristic spin–orbit induced downfield shift at Cα due to involvement of the 5f orbitals in the Th–C bonds. Additionally, the bonding analyses for 3 and 4 show a delocalized multi-center character of the ligand π orbitals involving the actinide. While a single–triple–single-bond resonance structure (e.g., An–C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C–CPh2) predominates, the AnCCCPh2 resonance form contributes, as well, more so for 3 than for 4.

A novel structural type of conformationally fixed, mixed phosphonium-iodonium ylides based on phenoxaphosphinine

A synthetic approach to a novel type of phosphonium and mixed phosphonium-iodonium ylides containing a conformationally fixed phosphonium fragment is developed. New representatives of these families of chemical compounds based on cyclic phenoxaphosphinine were synthesized. One compound was structurally characterized by single-crystal X-ray diffraction. Based on the 1H NMR data, one can state that phosphonium ylide exists in solution in the form of two geometric isomers even at room temperature. This is indicative of pronounced double-bond character of the bond between the ylide carbon atom and the stabilizing carbomethoxy group.

Synthesis and Reactivity of Heteroleptic Ga‐P‐C Allyl Cation Analogues

AbstractOxidative addition of cyclic alkyl(amino)carbene‐coordinated phosphinidenes (MecAAC)PX to LGa affords gallium‐coordinated phosphinidenes LGa(X)‐P(MecAAC) (L=HC[C(Me)N(2,6‐i‐Pr2C6H3)]2; X=Cl 1, Br 2), which react with NaBArF4 and LiAl(ORF)4 to [LGaP(MecAAC)][An] (An=B(C6H3(CF3)2)4 3, B(C6F5)4 4, Al(OC(CF3)3)4 5). The cations in 3–5 show substantial Ga−P double bond character and represent heteronuclear analogues of allyl cations according to quantum chemical calculations. The reaction of 4 with 4‐dimethylaminopyridine (dmap) to adduct 6 confirms the strong electrophilic nature of the gallium center, whereas 5 reacts with ethyl isocyanate with C−C bond formation to the γ‐C atom of the β‐diketiminate ligand and formation of compound 7.

Synthesis and Reactivity of Heteroleptic Ga-P-C Allyl Cation Analogues.

Oxidative addition of cyclic alkyl(amino)carbene‐coordinated phosphinidenes (MecAAC)PX to LGa affords gallium‐coordinated phosphinidenes LGa(X)‐P(MecAAC) (L=HC[C(Me)N(2,6‐i‐Pr2C6H3)]2; X=Cl 1, Br 2), which react with NaBArF 4 and LiAl(ORF)4 to [LGaP(MecAAC)][An] (An=B(C6H3(CF3)2)4 3, B(C6F5)4 4, Al(OC(CF3)3)4 5). The cations in 3–5 show substantial Ga−P double bond character and represent heteronuclear analogues of allyl cations according to quantum chemical calculations. The reaction of 4 with 4‐dimethylaminopyridine (dmap) to adduct 6 confirms the strong electrophilic nature of the gallium center, whereas 5 reacts with ethyl isocyanate with C−C bond formation to the γ‐C atom of the β‐diketiminate ligand and formation of compound 7.

Structural Changes Induced by Quinones: High-Resolution Microwave Study of 1,4-Naphthoquinone.

1,4‐Naphthoquinone (1,4‐NQ) is an important product of naphthalene oxidation, and it appears as a motif in many biologically active compounds. We have investigated the structure of 1,4‐NQ using chirped‐pulse Fourier transform microwave spectroscopy and quantum chemistry calculations. The rotational spectra of the parent species, and its 13C and 18O isotopologues were observed in natural abundance, and their spectroscopic parameters were obtained. This allowed the determination of the substitution r s, mass‐weighted r m and semi‐experimental r e SE structures of 1,4‐NQ. The obtained structural parameters show that the quinone moiety mainly changes the structure of the benzene ring where it is inserted, modifying the C−C bonds to having predominantly single or double bond character. Furthermore, the molecular electrostatic surface potential reveals that the quinone ring becomes electron deficient while the benzene ring remains a nucleophile. The most electrophilic areas are the hydrogens attached to the double bond in the quinone ring. Knowledge of the nucleophilic and electrophilic areas in 1,4‐NQ will help understanding its behaviour interacting with other molecules and guide modifications to tune its properties.

Donor-Acceptor Conjugated Macrocycles with Polyradical Character and Global Aromaticity.

SummaryPolyradical character and global aromaticity are fundamental concepts that govern the rational design of cyclic conjugated macromolecules for optoelectronic applications. Here, we report donor-acceptor (D−A) conjugated macromolecules with and without π-spacer derivatives to tune the antiferromagnetic couplings between the unpaired electrons. The macromolecules without π-spacer have a closed-shell electronic configuration and show global nonaromatic character in the singlet and lowest triplet states. However, the derivatives with π-spacer develop a nearly pure open-shell diradical and a very high polyradical character, not reported for D−A type macromolecules. Furthermore, the π-spacer derivatives display global nonaromaticity in the singlet ground state, but global aromaticity in the lowest triplet state, according to Baird's rule. The absorption spectra of the open-shell macromolecules calculated with time-dependent density functional theory indicate intensive light absorption in the near-infrared region and broadening to 2,500 nm, making these materials suitable for numerous optoelectronic applications.

Synthesis and Reactivity of Heterotrinuclear Platinum Cyclometalated Complexes Containing Bridging Nitrido Ligands

AbstractThe treatment of [M(LOEt)(N)Cl2] (LOEt−=[Co(η5‐C5H5){P(O)(OEt)2}3]−) with the Pt(II) bis(cyclometalated) complex [Pt(C N CBu)(DMSO)] (H2C N CBu=2,6‐di(4‐tert‐butylphenyl)pyridine; DMSO=dimethylsulfoxide) afforded the heterotrinuclear nitrido complexes [LOEtCl2M(μ‐N)Pt(C N CBu)] (M=Ru (1‐Ru), Os (1‐Os)). The Pt−N(nitrido) (1.821(5) Å) and Ru−N (1.673(5) Å) distances in 1‐Ru are consistent with the Ru=N=Pt bonding description. The Pt−N(nitrido) distance in 1‐Os (1.859(7) Å) is longer than that in 1‐Ru, suggesting the π interaction between Pt(II) and Os≡N is weaker than that for the Ru counterpart. Oxidation of 1‐Ru with PhICl2 afforded the Pt(IV) dichloride complex [LOEtCl2Ru(μ‐N)Pt(C N CBu)Cl2] (2) that has a longer Pt−N distance (1.893(3) Å) than that in 1‐Ru, indicating the weakening of the Pt−N(Ru) π bonding upon oxidation of Pt(II) to Pt(IV). Treatment of [Pt(C N CBu)(DMSO)] with [nBu4N][Ru(N)Cl4] in tetrahydrofuran (THF) afforded [nBu4N][(THF)Cl4Ru(μ‐N)Pt(C N CBu)] (3), which reacted with K[N(Ph2PS)2] and K[N(iPr2PO)2] to yield [Cl{N(Ph2PS)2}2Ru(μ‐N)Pt(C N CBu)] (4) and [nBu4N][Cl3{N(iPr2PO)2}Ru(μ‐N)Pt(C N CBu)] (5), respectively. The short Pt−N(nitrido) distances in 3 (1.816(5) Å) and 4 (1.809(2) Å) are indicative of Pt=N double bond character.

QTAIM View of Os–Os Bonding in Triosmium Cluster [Os3(CO)9(µ-ɳ2-C7H3(2-CH3)NS)(µ-CH2)CH3

The topological features of the triosmium cluster [Os3(CO)9(µ-ɳ2-C7H3(2-CH3)NS)(µ-CH2)CH3], containing carbonyl and 2-methylbenzothiazol ide ligands, has been examined using density functional theory (DFT) and QTAIM-based Quantum Theory Atoms in Molecules. The topological parameters of the electron density in the cluster have been calculated. The QTAIM analysis of the topological features demonstrated that the core part Os3C1 in the cluster is significantly absence a bond critical point and its bond path between Os1-Os3. Whereas, the analysis Os1-Os2 and Os2-Os3 interactions revealed the occurrence of bond paths and bond critical points between these atoms. A multicenter 4c–5e interaction for the Os3C1 core has been proposed. The topological parameters calculation show that the interactions in the bridging 2-methylbenzothiazolide Ligand are a typical for shared shell with the existence of some double-bond character.

Nature of the Arsonium‐Ylide Ph3As=CH2 and a Uranium(IV) Arsonium–Carbene Complex

AbstractTreatment of [Ph3EMe][I] with [Na{N(SiMe3)2}] affords the ylides [Ph3E=CH2] (E=As, 1As; P, 1P). For 1As this overcomes prior difficulties in the synthesis of this classical arsonium‐ylide that have historically impeded its wider study. The structure of 1As has now been determined, 45 years after it was first convincingly isolated, and compared to 1P, confirming the long‐proposed hypothesis of increasing pyramidalisation of the ylide‐carbon, highlighting the increasing dominance of E+−C− dipolar resonance form (sp3‐C) over the E=C ene π‐bonded form (sp2‐C), as group 15 is descended. The uranium(IV)–cyclometallate complex [U{N(CH2CH2NSiPri3)2(CH2CH2SiPri2CH(Me)CH2)}] reacts with 1As and 1P by α‐proton abstraction to give [U(TrenTIPS)(CHEPh3)] (TrenTIPS=N(CH2CH2NSiPri3)3; E=As, 2As; P, 2P), where 2As is an unprecedented structurally characterised arsonium‐carbene complex. The short U−C distances and obtuse U‐C‐E angles suggest significant U=C double bond character. A shorter U−C distance is found for 2As than 2P, consistent with increased uranium‐ and reduced pnictonium‐stabilisation of the carbene as group 15 is descended, which is supported by quantum chemical calculations.

Nature of the Arsonium-Ylide Ph3 As=CH2 and a Uranium(IV) Arsonium-Carbene Complex.

Treatment of [Ph3 EMe][I] with [Na{N(SiMe3 )2 }] affords the ylides [Ph3 E=CH2 ] (E=As, 1As; P, 1P). For 1As this overcomes prior difficulties in the synthesis of this classical arsonium-ylide that have historically impeded its wider study. The structure of 1As has now been determined, 45 years after it was first convincingly isolated, and compared to 1P, confirming the long-proposed hypothesis of increasing pyramidalisation of the ylide-carbon, highlighting the increasing dominance of E+ -C- dipolar resonance form (sp3 -C) over the E=C ene π-bonded form (sp2 -C), as group 15 is descended. The uranium(IV)-cyclometallate complex [U{N(CH2 CH2 NSiPri 3 )2 (CH2 CH2 SiPri 2 CH(Me)CH2 )}] reacts with 1As and 1P by α-proton abstraction to give [U(TrenTIPS )(CHEPh3 )] (TrenTIPS =N(CH2 CH2 NSiPri 3 )3 ; E=As, 2As; P, 2P), where 2As is an unprecedented structurally characterised arsonium-carbene complex. The short U-C distances and obtuse U-C-E angles suggest significant U=C double bond character. A shorter U-C distance is found for 2As than 2P, consistent with increased uranium- and reduced pnictonium-stabilisation of the carbene as group 15 is descended, which is supported by quantum chemical calculations.

Building up Strain in One Step: Synthesis of an Edge‐Fused Double Silacyclobutene from an Extensively Trichlorosilylated Butadiene Dianion

The exhaustive trichlorosilylation of hexachloro‐1,3‐butadiene was achieved in one step by using a mixture of Si2Cl6 and [nBu4N]Cl (7:2 equiv) as the silylation reagent. The corresponding butadiene dianion salt [nBu4N]2[1] was isolated in 36 % yield after recrystallization. The negative charges of [1]2− are mainly delocalized across its two carbanionic (Cl3Si)2C termini (α‐effect of silicon) such that the central bond possesses largely C=C double‐bond character. Upon treatment with 4 equiv of HCl, [1]2− is converted into neutral 1,2,3,4‐tetrakis(trichlorosilyl)but‐2‐ene, 3. The Cl− acceptor AlCl3, induces a twofold ring‐closure reaction of [1]2− to form a six‐membered bicycle 4 in which two silacyclobutene rings are fused along a shared C=C double bond (84 %). Compound 4, which was structurally characterized by X‐ray crystallography, undergoes partial ring opening to a monocyclic silacyclobutene 2 in the presence of HCl, but is thermally stable up to at least 180 °C.

Reactions of Dihaloboranes with Electron-Rich 1,4-Bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadienes.

The reactions of electron-rich organosilicon compounds 1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (1), 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (2), and 1,1′-bis(trimethylsilyl)-1,1′-dihydro-4,4′-bipyridine (12) with B-amino and B-aryl dihaloboranes afforded a series of novel B=N-bond-containing compounds 3–11 and 13. The B=N rotational barriers of 7 (>71.56 kJ/mol), 10 (58.79 kJ/mol), and 13 (58.65 kJ/mol) were determined by variable-temperature 1H-NMR spectroscopy, thus reflecting different degrees of B=N double bond character in the corresponding compounds. In addition, ring external olefin isomers 11 were obtained by a reaction between 2 and DurBBr2. All obtained B=N-containing products were characterized by multinuclear NMR spectroscopy. Compounds 5, 9, 10a, 11, and 13a were also characterized by single-crystal X-ray diffraction analysis.

A Theoretical Investigation on Chemical Bonding of the Bridged Hydride Triruthenium Cluster: [Ru3 (μ-H)( μ3-κ2-Hamphox-N,N)(CO)9

Ruthenium-Ruthenium and Ruthenium–ligand interactions in the triruthenium "[Ru3(μ-H)(μ3-κ2-Hamphox-N,N)(CO)9]" cluster are studied at DFT level of theory. The topological indices are evaluated in term of QTAIM (quantum theory of atoms in molecule). The computed topological parameters are in agreement with related transition metal complexes documented in the research papers. The QTAIM analysis of the bridged core part, i.e., Ru3H, analysis shows that there is no bond path and bond critical point (chemical bonding) between Ru(2) and Ru(3). Nevertheless, a non-negligible delocalization index for this non-bonding interaction is calculated. The interaction in the core Ru3H can be described as a (4centre–4electron) type. For Ru-N (oxazoline ring) bond, the calculated topological data propose a pure σ-bond. The computed topological parameters of oxazoline ligand reveal the presence of slightly some double bond characters within ligand ring.

Sesquicarbene Complexes: Bonding at the Interface Between M–C Single Bonds and M═C Double Bonds

Allylic dimetalated complexes [M2C(vinyl)]+ (M = Au(IPr) and Cr(CO)5–) incorporate a new coordination mode of carbon. Digold complexes of this type have recently been detected experimentally. The intrinsic bond orbitals, partial charges, and structural parameters of the gold complexes and of chromium analogs were studied computationally and compared to those of the respective monometalated species and hydrocarbons. This showed that such digold complexes have a carbene character at both Au–C bonds comparable to typical carbene complexes of gold. Dichromium complexes with their stronger π-backdonation compete for interaction with carbon’s π-orbital; each of the chromium atoms partakes in double bonding that is significant but weaker than that in the carbene analogs. Containing two M–C bonds on the interface between single and double bonds, these bridged complexes can be conceived as “sesquicarbene complexes”. The π-system acted in a very adaptive manner and employed additional stabilization of the vinyl system only where needed. Significant carbene character is found simultaneously in both M–C bonds at the same carbon center. The discovery of these complexes with relatively strong double bond character between one carbon and two metal atoms could bring unusual single-carbon-centered organometallic cascade reactions to the horizon.

New Approaches to N-Heterocyclic-Carbene-Coordinated Iminoborane and Borenium Species.

The synthesis, characterization, and reactivity of an iminoborane-N-heterocyclic carbene (NHC) adduct were described. The reaction of DmpNHB(OEt)Br [1; Dmp = 2,6-bis(2,4,6-trimethylphenyl)phenyl] with 2 equiv of 1,3-diimethyl-4,5-dimethylimidazol-2-ylidene (IMe4) resulted in the formation of an iminoborane-NHC complex 2. Both X-ray analysis and density functional theory calculations revealed the double-bond character of the B═N bond in 2. Interestingly, compared with the corresponding Lewis-base-free iminoborane, 2 features a nitrogen atom with increased electron density, which could be attributed to coordination of the NHC. Similar to the isoelectronic species imine, this nitrogen center in 2 can be easily attacked by electrophiles. Indeed, the reaction of 2 with trimethylsilyl triflate (Me3SiOTf) afforded an NHC-stabilized borenium cation 3, representing a facile strategy to prepare cationic tricoordinate boron species.

Organic chemistry lecture course and exercises based on true scale models

Abstract 3D models of chemical structures are an important tool for chemistry lectures and exercises. Usually, simplified models based on standard bond length and angles are used. These models allow for a visualized discussion of (stereo)chemical aspects, but they do not represent the true spatial conditions. 3D-printing technologies facilitate the production of scale models. Several protocols describe the process from X-ray structures, calculated geometries or virtual molecules to printable files. In contrast, only a few examples describe the integration of scaled models in lecture courses. True bond angles and scaled bond lengths allow for a detailed discussion of the geometry and parameters derived therefrom, for example double bond character, aromaticity and many more. Here, we report a complete organic chemistry/stereochemistry lecture course and exercise based on a set of 37 scale models made from poly(lactic acid) as sustainable material. All models have been derived from X-ray structures and quantum chemical calculations. Consequently, the models reflect the true structure as close as possible. A fixed scaling factor of 1 : 1.8·108 has been applied to all models. Hands-on measuring of bond angles and bond length leads to an interactive course. The course has been evaluated with a very positive feedback.

Ferrocenylated Chalcogen (Se and Te)-containing N-heterocyclic carbenes: Selenones, silver and palladium complexes

New Ferrocenylated Chalcogen (Se and Te)-Containing imidazolium salts have been synthesized. These imidazolium salts have been used as precursors for the synthesis of ferrocenyl-NHC selenones, silver NHC and ionic palladium (II) complexes where the imidazolium ligand act as the cation. For the synthesis of Pd NHC(Se, CNHC) complex from appropriate imidazolium salts, the route of the silver carbene transfer reaction has been adopted and the ligand shows bidentate coordination through (Se, CNHC) atoms. All the compounds have been fully characterized by multinuclear NMR, mass spectrometry and X-ray diffraction. Molecular structures of ferrocenyl chalcogenide imidazolium salts present intra and inter cation/anion interactions. Interestingly, 77Se NMR studies of ionic palladium complexes with ferrocenyl chalcogenide imidazolium cation do not present Se coordination to Palladium in solution. The bond distance between CNHC and selenium atom in both the selenones is similar to other reported imidazolium selenones where this bond has a double bond character.

Crystalline Boragermenes

Boragermene 3 featuring a double bond between the Ge and dicoordinate B atoms has been synthesized for the first time by reacting the cyclic (alkyl)(boryl)germylene-PMe3 adduct 1 with Cl2 BN(SiMe3 )2 followed by reductive dehalogenation with KC8 . Addition of a Lewis base (Me NHC) to 3 leads to the formation of the corresponding adduct 4, which shows double bond character between the Ge and tricoordinate B atoms. Compound 3 undergoes hydrogenation with H2 concomitant with a complete scission of the Ge=B bond.