Reactivity of N-heterocyclic carbene, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, towards heavier halogens (Br2 and I2) (original) (raw)
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The Journal of Physical Chemistry A, 2014
A theoretical study of the halogen-bonded complexes (A−X···C) formed between halogenated derivatives (A−X; A = F, Cl, Br, CN, CCH, CF 3 , CH 3 , H; and X = Cl, Br) and a nitrogen heterocyclic carbene, 1,3-dimethylimidazole-2ylidene (MeIC) has been performed using MP2/aug′-cc-pVDZ level of theory. Two types of A−X:MeIC complexes, called here type-I and -II, were found and characterized. The first group is described by long C−X distances and small binding energies (8−54 kJ·mol −1 ). In general, these complexes show the traditional behavior of systems containing halogen-bonding interactions. The second type is characterized by short C− X distances and large binding energies (148−200 kJ·mol −1 ), and on the basis of the topological analysis of the electron density, they correspond to ion-pair halogen-bonded complexes. These complexes can be seen as the interaction between two charged fragments: A − and + [X−CIMe] with a high electrostatic contribution in the binding energy. The charge transfer between lone pair A(LP) to the σ* orbital of C−X bond is also identified as a significant stabilizing interaction in type-II complexes.
Activation of N-Heterocyclic Carbenes by {BeH2} and {Be(H)(Me)} Fragments
Organometallics, 2015
A stable three-coordinate dimethylberyllium species coordinated by the 1,3-bis-(2,4,6trimethylphenyl)imidazol-2-ylidene (IMes) ligand is readily converted to the corresponding methylhydrido derivative through metathetical reaction with phenylsilane. Attempts to synthesise the corresponding molecular dihydrides are, however, unsuccessful and result in ring opening of an IMes ligand through hydride transfer to the donor carbon atom and the consequent formation of a heterocyclic beryllium organoamide. In agreement with previous calculations, we suggest that this process occurs via a Schlenk-type equilibration process and formation of a four-coordinate bis-NHC beryllium dihydride. These species are not observed, however, as the steric pressure exerted by coordination of the two sterically demanding IMes ligands is sufficient to induce hydride transfer. This latter deduction is supported by the observation that a similar ring opened product, but derived from methyl and hydride transfer, is available through the introduction of a further equivalent of IMes to the isolated beryllium methyl hydride species. In this latter case the ring opening process is more facile, which we ascribe to the increased steric pressure achieved upon the formation of four-coordinate beryllium. In a further striking reaction under more forcing thermal conditions, the carbene carbon center of an IMes ligand is observed to be completely eliminated with selective formation of a three-coordinate diamidoberyllium species.
Experimental and computational study of the HXeI⋯HY complexes (Y = Br and I)
The Journal of Chemical Physics, 2013
The complexes of HXeI with hydrogen halides HY (Y = Br and I) are studied computationally and experimentally in a xenon matrix. The calculations at the CCSD(T)/def2-TZVPPD level of theory predict several energy minima for the HXeI· · ·HY complexes with interaction energies from −4.69 to −0.23 kcal mol −1 . We have identified three bands of the HXeI· · ·HI complexes in the H−Xe stretching region with the monomer-to-complex blue shifts from +37 to +96 cm −1 , and three bands of the HXeI· · ·HBr complexes with blue shifts from +88 to +157 cm −1 . The structural assignments are done on the basis of the strong H−Xe and HY stretching bands and the decomposition rates upon broadband IR irradiation. The experimental bands with larger shifts are assigned to the most stable structures of the HXeI· · ·HY complexes with the Y−H· · ·I hydrogen bond.
Journal of Organometallic Chemistry, 2014
a b s t r a c t C 2 -Symmetric normal and mesoionic bis-N-heterocyclic carbenes (NHCs) derived from 1,1 0 -((1,1 0biphenyl)-2,2 0 -diylbis(methylene))bis(3-methyl-4-phenyl-1H-1,2,3-triazol-3-ium) diiodide (5) and 3,3 0 -((1,1 0 -biphenyl)-2,2 0 -diylbis(methylene))bis(1-phenyl-1H-imidazol-3-ium) dibromide (6) were used as ligands for the synthesis of the corresponding Pd(II) complexes. 2,2 0 -Disubstituted 1,1 0 -biphenyl moiety was used as the C 2 -symmetric backbone for the synthesis. 2,2 0 -Bis(bromomethyl)-1,1 0 -biphenyl was used as a common precursor for the synthesis of both 5 and 6. These salts were treated with Ag 2 O for the insitu generation of the corresponding NHCeAg(I) complexes which were transmetallated to the corresponding Pd(II) chloro and acetate complexes. The bis(1,2,3-triazol-5-ylidene) derivative gave structurally well-defined mono nuclear chelate complexes that were characterized by spectroscopic and single crystal XRD data. The bis(imidazol-3-ylidene) derivative gave polymeric complex and not the expected mono nuclear chelate complex. These complexes were compared for their reactivity in SuzukieMiyaura coupling reaction.
Influence of Halogen Atoms on a Homologous Series of Bis-Cyclometalated Iridium(III) Complexes
Inorganic Chemistry, 2012
A series of homologous bis-cyclometalated iridium(III) complexes Ir(2,4-di-X-phenyl-pyridine) 2-(picolinate) (X = H, F, Cl, Br) HIrPic, FIrPic, ClIrPic, and BrIrPic has been synthesized and characterized by NMR, X-ray crystallography, UV−vis absorption and emission spectroscopy, and electrochemical methods. The addition of halogen substituents results in the emission being localized on the main cyclometalated ligand. In addition, halogen substitution induces a blue shift of the emission maxima, especially in the case of the fluoro-based analogue but less pronounced for chlorine and bromine substituents. Supported by ground and excited state theoretical calculations, we rationalized this effect in a simple manner by taking into account the σp and σm Hammett constants on both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. Furthermore, in comparison with FIrPic and ClIrPic, the impact of the large bromine atom remarkably decreases the photoluminescence quantum yield of BrIrPic and switches the corresponding lifetime from mono to biexponential decay. We performed theoretical calculations based on linear-response time-dependent density functional theory (LR-TDDFT) including spin−orbit coupling (SOC), and unrestricted DFT (U-DFT) to obtain information about the absorption and emission processes and to gain insight into the reasons behind this remarkable change in photophysical properties along the homologous series of complexes. According to theoretical geometries for the lowest triplet state, the large halogen substituents contribute to sizable distortions of specific phenylpyridine ligands for ClIrPic and BrIrPic, which are likely to play a role in the emissive and nonradiative properties when coupled with the heavy-atom effect.
From Alkynes to Carbenes Mediated by [Re(Br)(H)(NO)(PR 3 ) 2 ] (R = Cy, i Pr) Complexes
Organometallics, 2009
Five-coordinate rhenium(I) hydride complexes of the type [Re(Br)(H)(NO)(PR 3 ) 2 ] (R=Cy 1a, iPr 1b) were reacted with terminal alkynes R 1 CtCH (R 1 =Ph, SiEt 3 , H), yielding 18-electron η 2 -alkyne adducts [Re(Br)(H)(NO)(PR 3 ) 2 (η 2 -HCtCR 1 )] (R 1 =Ph (R=Cy 2a, iPr 2b), SiEt 3 (R=Cy 4a, iPr 4b), H (R=Cy 6a, iPr 6b)). Alkyne insertion into the Re-H bond led to the formation of rhenium(I) η 1vinyl derivatives [Re(Br)((E)-CHdCHR 1 )(NO)(PR 3 ) 2 ] (R 1 =Ph (R=Cy 3a, iPr 3b), SiEt 3 (R=Cy 5a, iPr 5b), H (R=Cy 7a, iPr 7b)) in good yields. The rate of formation of the vinyl complexes depends on R 1 in the order SiEt 3 > Ph > H, and the reactions of 1b bearing the PiPr 3 ligand are generally faster than those of 1a with PCy 3 . 1a,b were also reacted with 2-methyl-1-buten-3-yne and 1,7octadiyne, affording dienyl derivatives [Re(Br){(E)-CHdCHC(CH 3 )dCH 2 }(NO)(PR 3 ) 2 ] (R = Cy 8a, iPr 8b) and the binuclear μ-bis-alkenyl compounds [(PR 3 ) 2 (NO)(Br)Re{(E)-CHdCH-(CH 2 ) 4 -CHdCH-(E)}Re(Br)(NO)(PR 3 ) 2 ] (R=Cy 9a, iPr 9b). The reactions of 3a,b or 5a,b with HBF 4 3 OEt 2 afforded the rhenium(I) carbene derivatives [Re(F)(Br)(dCHCH 2 Ph)(NO)(PR 3 ) 2 ] (R=Cy 10a, iPr 10b) or [Re(F)(Br)(dCHCHdC(CH 3 ) 2 )(NO)(PR 3 ) 2 ] (R = Cy 11a, iPr 11b) via protonation at the βand δ-carbon of the vinyl group, respectively. The fluorine ligands are located cis to the carbene ligand and the bromo atom cis to the nitrosyl group. The binuclear species 9a,b were also reacted with HBF 4 3 OEt 2 to afford the binuclear carbene derivatives [(PR 3 ) 2 -(NO)(Br)(F)Re{dCH-(CH 2 ) 6 -CHd}Re(F)(Br)(NO)(PR 3 ) 2 ] (R = Cy 12a, iPr 12b). The molecular structures of 3a, 5a, and 11a were established by X-ray diffraction studies.
Charge-transfer complexes of bromine atoms with haloalkanes and alkanes
The Journal of Physical Chemistry, 1993
Charge-transfer complexes of bromine atoms with haloalkanes and alkanes were produced by pulse radiolysis and by laser-flash photolysis in various organic solvents. Br atoms were produced by photolysis of Br, (at 351 or 248 nm), by photolysis of bromoalkanes (at 248 nm), or by radiolysis of bromoalkanes (either in liquid form or in cyclohexane solutions). The transient spectra, monitored within microseconds after the pulse, had absorption maxima that varied between 300 and 500 nm and are ascribed to complexes of Br atoms with the various solvents or other solutes present. The absorption maxima for Br atom complexes with alkanes and chloroalkanes correlate with the ionization potential of these molecules, suggesting the existence of charge-transfer complexes. The correlation for the bromoalkanes was more complex. CBrqBr and CHBryBr were observed to react rapidly (k = 108-109 L mol-' s-l) with Br, and with HBr to transfer their Br atom to these latter molecules.
International Journal of Molecular Sciences, 2022
In the current study, unexplored type IV halogen⋯halogen interaction was thoroughly elucidated, for the first time, and compared to the well-established types I–III interactions by means of the second-order Møller–Plesset (MP2) method. For this aim, the halobenzene⋯halobenzene homodimers (where halogen = Cl, Br, and I) were designed into four different types, parodying the considered interactions. From the energetic perspective, the preference of scouted homodimers was ascribed to type II interactions (i.e., highest binding energy), whereas the lowest binding energies were discerned in type III interactions. Generally, binding energies of the studied interactions were observed to decline with the decrease in the σ-hole size in the order, C6H5I⋯IC6H5 > C6H5Br⋯BrC6H5 > C6H5Cl⋯ClC6H5 homodimers and the reverse was noticed in the case of type IV interactions. Such peculiar observations were relevant to the ample contributions of negative-belt⋯negative-belt interactions within the ...
The Journal of Physical Chemistry A, 2010
The recombination reactions of CH 2 Br and CH 2 Cl radicals have been used to generate vibrationally excited CH 2 BrCH 2 Br and CH 2 BrCH 2 Cl molecules with 91 kcal mol -1 of energy in a room-temperature bath gas. The experimental unimolecular rate constants for elimination of HBr and HCl were compared to calculated statistical rate constants to assign threshold energies of 58 kcal mol -1 for HBr elimination from C 2 H 4 Br 2 and 58 and 60 kcal mol -1 , respectively, for HBr and HCl elimination from C 2 H 4 BrCl. The Br-Cl interchange reaction was demonstrated and characterized by studying the CH 2 BrCD 2 Cl system generated by the recombination of CH 2 Br and CD 2 Cl radicals. The interchange reaction was identified from the elimination of HBr and DCl from CH 2 ClCD 2 Br. The interchange reaction rate is much faster than the rates of either DBr or HCl elimination from CH 2 BrCD 2 Cl, and a threshold energy of =43 kcal mol -1 was assigned to the interchange reaction. The statistical rate constants were calculated from models of the transition states that were obtained from density functional theory using the B3PW91 method with the 6-31G(d′,p′) basis set. The model for HBr elimination was tested versus published thermal and chemical activation data for C 2 H 5 Br. A comparison of Br-Cl interchange with the Cl-F and Br-F interchange reactions in 1,2-haloalkanes is presented.