Arduengo-type Carbenes Research Articles

Electronic Structure and Excited-State Dynamics of an Arduengo-Type Carbene and its Imidazolone Oxidation Product.

We describe an investigation of the excited-state dynamics of isolated 1,3-di-tert-butyl-imidazoline-2-ylidene (tBu2 Im, C11 H20 N2 , m/z=180), an Arduengo-type carbene, by time- and frequency-resolved photoionization using a picosecond laser system. The energies of several singlet and triplet excited states were calculated by time-dependent density functional theory (TD-DFT). The S1 state of the carbene deactivates on a 100 ps time scale possibly by intersystem crossing. In the experiments we observed an additional signal at m/z=196, that was assigned to the oxidation product 1,3-di-tert-butyl-imidazolone, tBu2 ImO. It shows a well-resolved resonance-enhanced multiphoton ionization (REMPI) spectrum with an origin located at 36951 cm-1 . Several low-lying vibrational bands could be assigned, with a lifetime that depends strongly on the excitation energy. At the origin the lifetime is longer than 3 ns, but drops to 49 ps at higher excess energies. To confirm formation of the imidazolone we also performed experiments on benzimidazolone (BzImO) for comparison. Apart from a redshift for BzImO the spectra of the two compounds are very similar. The TD-DFT values display a very good agreement with the experimental data.

Singlet–triplet energy differences in divalent five membered cyclic conjugated Arduengo-type carbenes XC2HN2M (M = C, Si, Ge, Sn, and Pb; X = F, Cl, Br, and I)

Singlet-triplet energy differences in Arduengo-type carbenes XC2HN2C compared and contrasted with their sila, germa, stana and plumba analogues; at B3LYP/6-311++G** level of theory. Free Gibbs energy differences between triplet (t) and singlet (s) states (ΔG(t–s)) change in the following order: plumbylenes > stannylenes > germylenes > silylenes > carbenes. The singlet states in XC2HN2C are generally more stable when the electron withdrawing groups such as–F was used at β-position. However, the singlet states in XC2N2HM (M = Si, Ge, Sn, and Pb) are generally more stable when the withdrawing groups such as–F was placed. The puckering energy is investigated for each the singlet and triplet states. The DFT calculations found the linear correlation to size of the group 14 divalent element (M), the ∠N–M–N angle, and the Δ(LUMO–HOMO) of XC2HN2M.

Crystal structure of 1,3-bis-(2,6-diiso-propyl-phen-yl)-4,5-dimethyl-1H-imid-azol-3-ium bromide di-chloro-methane disolvate.

The title solvated salt, C29H41N2 +·Br−·2CH2Cl2 was obtained from the reaction of the Arduengo-type carbene 1,3-bis­(2,6-diiso­propyl­phen­yl)-1,3-dihydro-4,5-dimethyl-2H-imidazol-2-ylidene with Si2Br6 in di­chloro­methane. The complete cation is generated by a crystallographic mirror plane and the dihedral angle between the five-membered ring and the benzene ring is 89.8 (6)°; the dihedral angle between the benzene rings is 40.7 (2)°. The anion also lies on the mirror plane and both di­chloro­methane mol­ecules are disordered across the mirror plane over two equally occupied orientations. In the crystal, the cations are linked to the anions via C—H⋯Br hydrogen bonds.

Erratum to: “Heteroatom effects in XC5H5C Arduengo-type carbenes (X = CH, N, P, and As) in singlet and triplet states”

Erratum to: “Heteroatom effects in XC5H5C Arduengo-type carbenes (X = CH, N, P, and As) in singlet and triplet states”

Heteroatom effects in XC5H5C Arduengo-type carbenes (X = CH, N, P, and As) in singlet and triplet states

Internal energy difference, ΔEs-t; enthalpy difference, ΔHs-t; Gibbs free energy difference, ΔGs-t, between the singlet (s) and triplet states (t) of XC5H5C, 1X (X = CH, N, P, and As) were computed at B3LYP/6-311++G** and MP2/6-311++G**//B3LYP/6-311++G** levels of theory. The ΔGs-t between the singlet and triplet states of 1X were changed in the order: 1P > 1As > 1N.

A theoretical study on the hydrogen adducts of diamidocarbenes and diaminocarbenes

The hybrid-meta GGA DFT functional M06-2X was used to examine the potential of N,N'-diamidocarbenes for use as hydrogen storage materials. We previously discovered that borylene, which is isoelectronic with an Arduengo-type carbene, was a suitable candidate for a hydrogen storage material. We compared the capabilities of N,N'-diamidocarbenes and N-heterocyclic carbenes as hydrogen storage materials. The results indicate that diamidocarbenes are not suitable hydrogen storage materials because the removal of H₂ is more endothermic for diamidocarbenes than for diaminocarbenes.

Do Carbenes Have a “Hidden” Carbon(0) Character? Revisiting the Electronic Structure of 2,2′‐Bipyridyl Carbene

Density functional calculations predict that 2,2'-bipyridyl carbenes have some degree of "hidden" carbon(0) character. This is supported by very high second proton affinity values and bond dissociation energies (BDEs) for the dissociation of one AuCl and one Ni(CO)(2) molecule from [(AuCl)(2)(2,2'-bipyridyl carbene)] and [{Ni(CO)(2)}(2)(2,2'-bipyridyl carbene)]. An Arduengo type carbene also showed significant BDE values for gem-dimetallation, thus indicating the possible existence of carbon(0) character. All of the dimetallated derivatives showed metallophilic interactions.

ChemInform Abstract: Zwitterionic and Donor‐Stabilized N‐Heterocyclic Silylenes (NHSis) for Metal‐Free Activation of Small Molecules

AbstractReview: 130 refs.

Zwitterionic and Donor-Stabilized N-Heterocyclic Silylenes (NHSis) for Metal-Free Activation of Small Molecules

This account describes recent progress (>2006) in the synthesis and structural characterization of isolable N-heterocyclic silylenes (NHSi's) and their fascinating reactivities with respect to an emergent topic in main-group chemistry: metal-free small-molecule activation. Since the seminal discovery of stable N-heterocyclic silicon analogues of nucleophilic Wanzlick−Arduengo-type carbenes in 1994, new types of NHSi's have emerged with unique electronic features and strikingly different reactivities. Among them, the first zwitterionic (ylide-like) silylene LSi: (L = CH[(C═CH2)CMe][NAr]2; Ar = 2,6-Pri2C6H3) and unprecedented N-heterocyclic bis(silylenes) with amidinate ligands and Si(I)−Si(I) bonds were synthesized. Their striking electronic structures open new doorways to metal-free activation of C−H, C−X, Si−X, E−H (E = group 15, group 16 elements), P−P, E−O (E = C, N), and E−E bonds (E = O, S, Se, Te).

N-Phosphorylated Imidazolium Salts as Precursors to 2- and 5-Phosphorylated Imidazoles and New Imidazol-2-ylidenes Featuring the PNCN Unit

It has been experimentally proven that the reaction of 1- or 1,2-disubstituted imidazoles with diorganylphosphorus(III) halides proceeds via initial formation of N-phosporylated imidazolium salts. Treatment of these salts with strong bases results in phosphorylation of the parent imidazoles at the 2- or 5-positions, correspondingly. In a previous case, imidazol-2-ylidenes are formed as intermediates. With both N1 and N3 atoms bearing sterically demanding or/and π-donating groups, deprotonation of 1,3-disubstituted imidazolium salts with NaN(SiMe(3))(2) afforded new stable N-phosphorus-substituted Arduengo-type carbenes.

1,3-Bis(2,6-diisopropylphenyl)imidazolidinium tetraphenylborate dichloromethane disolvate

The title compound, C27H39N2 +·C24H20B−·2CH2Cl2, is the first reported imidazolidinium cation with the sterically demanding 2,6-diisopropyl­phenyl groups in the 1,3-positions. The crystal structure is stabilized by weak inter­molecular C—H⋯π(arene) inter­actions. Due to the bulky nature of both the flanking 2,6-diisopropyl­phenyl substituents and the tetra­phenyl­borate counter-ion, anion inter­actions with the imidazolidinium H atom in the 2-position are not observed, also a first for this class of ortho-alkyl-substituted Arduengo-type carbene precursors.

Intermolecular =C–H···:C hydrogen bond in a crystalline unsaturated Arduengo-type carbene

The presence of the =C–H···:C intermolecular hydrogen bond in 1,3-di-tert-butylimidazol-2-ylidene has been demonstrated by vibrational spectroscopy and confirmed by X-ray diffraction analysis and quantum-chemical calculations.

The 6π, phosphide-stabilised stannylene dianion [C6H4P2Sn]2−; the first member of a new class of Arduengo-type carbene analogues

Dilithiation of 1,2-(PH2)2C6H4 with nBuLi followed by reaction with Sn(NMe2)2 in the presence of the Lewis base donor tmeda [Me2NCH2CH2NMe2] gives [(C6H4P2Sn)(Li.tmeda)2] , containing the phosphide-stabilised, 6pi stannylene dianion [C6H4P2Sn]2-.

Vibrational and electronic spectra and the electronic structure of an unsaturated Arduengo-type carbene

The Raman, IR and UV spectra of 1,3-di-tert-butylimidazol-2-ylidene ((BuNCH)-N-t=CHNBut)C-II and quantum chemistry calculations of its normal mode frequencies and eigenvectors and the NICS index are reported.

Extending the Series: Synthesis and Characterization of a Dicationic N-Heterocyclic Selenium Carbene Analogue

The room-temperature reaction between the Dipp2DAB ligand, SnCl2, and SeCl4 results in the quantitative formation of a dicationic N-heterocyclic "carbenoid". This represents the first example of a chalcogenium dication that mimics the ubiquitous Arduengo-type carbenes; however, the electronic structure is significantly different.

The 2-Position of Imidazolium Ionic Liquids: Substitution and Exchange

The 2-position of imidazolium cations is known to be relatively acidic, leading to the useful Arduengo-type carbenes. At the same time, the acidity of this site can lead to undesired side reactions when using imidazolium-based ionic liquids as solvents. In this note, we describe the surprisingly facile deuterium exchange at this position and also the synthesis and exchange under modestly basic conditions (triethylamine) of a series of 2-methyl-substituted compounds.

The 1,4-diphosphabuta-1,3-diene ligand for coordination of divalent group 13 and 14 elements: a density functional study.

The 1,4-diphosphabuta-1,3-diene (DPB) ligand as a tool for stabilizing anionic group 13 (B, Al, Ga) and neutral group 14 (C, Si, Ge) cyclic Arduengo-type carbenes is studied by quantum chemical calculations at density functional level. Accordingly, for the former group this ligand is better suited than the corresponding 1,4-diazabuta-1,3-diene (DAB) ligand. It results in larger electron affinities for the corresponding doublet states. For the latter group the DPB ligand yields essentially smaller singlet-triplet separations than the DAB ligand. An exception is the anionic boron compound with relative low singlet stability for both the DAB and DPB ligands.

Preparation and structure of the first germanium(II) hydroxide: the congener of an unknown low-valent carbon analogue.

Trapping HCl with an Arduengo-type carbene was the key to preparing and isolating the first germanium(II) hydroxide [LGeOH] (L=HC{(CMe)(2,6-iPr2C6H3N)}2) by hydrolysis of the corresponding chloride. In the solid state [LGeOH] forms dimers through an interaction of the OH group with the lone pair of another Ge atom (see picture; Ar=2,6-iPr2C6H3).

Strong ligand accelerated catalysis by an Arduengo-type carbene in copper-catalysed conjugate addition

The addition of stabilised carbene ligand: CNMesCH 2CH 2N Mes (Mes=2,4,6-Me 3C 6H 2) results in a dramatic rate increase in the Cu(OTf) 2-catalysed conjugate addition of ZnEt 2 to enones (OTf=triflate anion).

Preparation, Characterization, and Reactivity of the Stable Indium Trihydride Complex [InH3{CN(Mes)C2H2N(Mes)}

Reaction of either LiInH4 or [InH3(NMe3)] with the Arduengo-type carbene :CN(Mes)C2H2N(Mes), Mes = C6H2Me3-2,4,6, affords the indium trihydride complex [InH3{CN(Mes)C2H2N(Mes)}]. This compound displays a remarkable thermal stability (dec 115 °C). In solution the products of decomposition depend on the solvent used. In toluene decomposition results in liberation of the free carbene and deposition of indium metal, and in tetrahydrofuran in the presence of indium metal hydrogen transfer occurs to give H2CN(Mes)C2H2N(Mes) and indium metal, while in dichloromethane, chloride abstraction occurs from the solvent to yield [InCl3{CN(Mes)C2H2N(Mes)}]. A number of related compounds have also been prepared and their structures and properties investigated. These include [GaH3{CN(Mes)C2H2N(Mes)}], which is the most stable gallium trihydride yet reported, and the indium hydride halide complex [InH2Cl{CN(Mes)C2H2N(Mes)}].