Mesityl Ring Research Articles

High-spin Cyclopentadienyl Complexes, Part 7. Ambivalent Interpretation of the Bonding in Iron-Copper Complexes: Metalated Arene versus Carbocyclic Carbene

The electron distribution within a mesityl ligand bridging a cyclopentadienyliron fragment attached to the mesityl π system and a second metal fragment connected to the ipso carbon of the mesityl ring has been probed using a copper(I) halide as a component in [CpmFe (μ,η5 :η1-C6H2Me3)CuCl] (2) and its copper bromide derivative 3. This approach minimizes steric effects and allows for DFT calculations the results of which are in very good agreement with structural data. The calculations show a significant carbene character already for the bare phenyl anion as a result of electrostatic repulsion of the lone pair pushing the π electrons away from the ipso carbon towards the para carbon atom of the aromatic ring. π Coordination of a cyclopentadienyliron(II) fragment to the phenyl anion to form a hypothetical sandwich complex does not change this situation. The iron center rather follows the unsymmetric distribution of π charge with an unsymmetrical coordination to the π system. Coordination of a copper(I) chloride moiety to the phenyl anion or to the hypothetical π complex [CpFe(C6H5)] in both cases equally lowers that carbene character by attracting the lone pair of the ipso carbon and thus decreasing its repulsive influence on the π electrons.

Tetra-kis{2,4-bis-[(1-oxo-2-pyridyl)-sulfanyl-methyl]mesitylene} acetone hemisolvate 11.5-hydrate.

In the crystal structure of the title compound, 4C21H22N2O2S2·0.5C3H6O·11.5H2O, there are four crystallographically independent mol­ecules (A, B, C, D) with similar geometries, 11 water mol­ecules and a solvent acetone mol­ecule which is disordered with a water mol­ecule with occupancy factors of 0.5:0.5. The dihedral angles formed by the mesitylene ring with the two pyridyl rings are 82.07 (3) and 78.39 (3)° in mol­ecule A, 86.20 (3) and 82.29 (3)° in mol­ecule B, 81.05 (3) and 76.0 (4)° in mol­ecule C, 86.0 (3) and 80.9 (3)° in moleule D. The two pyridyl rings form dihedral angles of 41.17 (4), 64.01 (3), 81.9 (3) and 82.25 (3)° in mol­ecules A, B, C and D, respectively. The crystal structure is stabilized by inter­molecular O—H⋯O hydrogen bonds and possible weak C—H⋯π inter­actions. Some short intra­molecular S⋯O contacts are apparent [2.684 (4)–2.702 (4) Å].

π‐Face Donor Properties of N‐Heterocyclic Carbenes in Grubbs II Complexes

The electron-donating properties of eighteen N-heterocyclic carbenes (N,N'-bis(2,6-dimethylphenyl)imidazol)-2-ylidene and the respective dihydro ligands) with 4,4'-R substituted aryl rings (4,4'-R = NEt2, OMe, Me, H, SMe, F, Cl, Br, I) in the respective Grubbs II complexes were studied using electrochemical techniques. The nature of the 4-R substituent has a strong influence on the RuII/III redox potentials ranging between DeltaE1/2= +0.196 and +0.532 V. Three unsymmetrical Grubbs II complexes with 4-R not equal to 4-R' were also synthesized. Dynamic NMR spectroscopy revealed the restricted rotation around the (NHC)C-Ru bond (DeltaG = 89 kJ mol(-1) at 333 K) resulting in two atropisomers, respectively, with an isomer ratio close to unity. Each of the isomers, that is the two orientations of the 4-R/4-R' substituted mesityl ring with respect to the R=CHPh unit, gives rise to different redox potentials (4-R = NEt2, 4-R' = Br: DeltaE1/2= +0.232 and +0.451 V). In the oxidized Grubbs II complex (4-R = NEt2, H) and in the cathodic isomer the electron rich aryl ring is located above the Ru=CHPh unit. This orientational effect provides clear evidence for strong pi-pi through-space interactions in the RuIII complexes, assuming that the alternative through-bond transfer of electron density is equally efficient in both isomers.

2,4,6-Tris(1-oxo-2-pyridylsulfanylmeth-yl)mesitylene methanol solvate.

In the title compound, C27H27N3O3S3·CH4O, the dihedral angles formed by the mesitylene ring with the three oxopyridyl rings are 89.6 (1), 75.5 (1) and 80.69 (1)°, indicating that all three are nearly perpendicular to the mesitylene ring. Intra­molecular C—H⋯S hydrogen bonds generate S(6) ring motifs. The crystal structure is stabilized by intra­molecular C—H⋯S and inter­molecular C—H⋯O hydrogen bonds and weak C—H⋯π inter­actions.

2,4,6-Trimethyl-1,3,5-tris(morpholinomethyl)benzene

In the title compound, C24H39N3O3, the H atoms of the methyl groups are disordered over two positions, with site-occupation factors fixed at 0.5. The three morpholino groups are arranged in an asymmetrical fashion with respect to the anchoring mesitylene ring and adopt chair conformations. Inter­molecular C—H⋯π inter­actions link the mol­ecules into a one-dimensional chain structure.

Dichlorido(2-chloro-9-mesityl-1,10-phenanthroline-κ2N,N′)cobalt(II) dichloromethane hemisolvate

The title compound, [CoCl2(C21H17ClN2)]·0.5CH2Cl2, crystallizes from dichloro­methane as a 2:1 solvate [CoCl2L]2·CH2Cl2 (L is 2-chloro-9-mesityl-1,10-phenanthroline). There are two independent CoCl2 L mol­ecules in the asymmetric unit and both mol­ecules have similar conformations. They are connected by a weak C—H⋯π inter­action involving the mesityl ring. The cobalt center is four-coordinated by the two N-atom donors of the bidentate ligand and two chloride ions in a distorted tetra­hedral geometry. The packing of the mol­ecules is stabilized by weak slipped π–π stacking inter­actions between symmetry-related phenanthroline groups.

A Tungsten Complex with a Bidentate, Hemilabile N-Heterocyclic Carbene Ligand, Facile Displacement of the Weakly Bound W−(CC) Bond, and the Vulnerability of the NHC Ligand toward Catalyst Deactivation during Ketone Hydrogenation

The initial reaction observed between the N-heterocyclic carbene IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO){sub 2}(PPh{sub 3})H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMes)H]{sup +}[CpM(CO){sub 2}(PPh{sub 3})]{sup -}. At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO){sub 2}(PR{sub 3})H (M = Mo, W; R = Me, Ph) produces CpM(CO){sub 2}(IMes)H. Hydride transfer from CpW(CO)2(IMes)H to Ph{sub 3}C{sub +}B(C{sub 6}F{sub 5}){sub 4}{sup -} gives CpW(CO){sub 2}(IMes){sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -}, which was crystallographically characterized using X-ray radiation from a synchrotron. The IMes is bonded as a bidentate ligand, through the carbon of the carbene as well as forming a weak bond from the metal to a C=C bond of one mesityl ring. The weakly bound C=C ligand is hemilabile, being readily displaced by H{sub 2}, THF, ketones, or alcohols. Reaction of CpW(CO){sub 2}(IMes){sup +} with H{sub 2} gives the dihydride complex [CpW(CO){sub 2}(IMes)(H){sub 2}]{sup +}. Addition of Et{sub 2}CH-OH to CpW(CO){sub 2}(IMes){sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -} gives the alcohol complex [CpW(CO){sub 2}(IMes)(Et{sub 2}CH-OH)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -}, which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OHmore » group. Addition of H{sub 2} to the ketone complex [CpW(CO){sub 2}(IMes)(Et{sub 2}C=O)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -} produces an equilibrium with the dihydride [CpW(CO){sub 2}(IMes)(H){sub 2}]{sup +} (K{sub eq} = 1.1 x 10{sup 3} at 25 {sup o}C). The tungsten ketone complex [CpW(CO){sub 2}(IMes)(Et{sub 2}C=O)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -}- serves as a modest catalyst for hydrogenation of Et{sub 2}C=O to Et{sub 2}CH-OH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]{sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -}, indicating that these catalysts with N-heterocyclic carbene ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.« less

Iodidomesityltellurium(II) iodidotrimesitylditellurium(II)(Te—Te)

In the title compound, C9H11ITe·C27H33ITe2 or (Mes)TeI·(Mes2Te)TeI(Mes) (Mes is mesityl or 2,4,6-trimethyl­phen­yl), a strong Te⋯I inter­action of 3.3157 (9) A links the Te atom of an iodidomesityltellurium(II) moiety, (Mes)TeI, and an I atom of the iodidotrimesitylditellurium(II) unit, (Mes2Te)TeI(Mes). Further weak Te⋯I contacts of 4.0818 (9) A give rise to one-dimensional chains along the b axis in the crystal structure. An intra­molecular C—H⋯π(arene) inter­action is present in the (TeMes2)TeI(Mes) moiety, with a C⋯Cg distance of 3.497 (9) A and a C—H⋯Cg angle of 142° (where Cg is the centroid of a mesityl ring of the Mes2Te moiety).

Pentamethylcyclopentadienyl organoiron(II) hydrazone complexes: Synthesis, spectroscopic characterization, and second-order nonlinear optical properties. X-ray crystal structure of [formula omitted

A series of novel pentamethylated sandwich complexes based on the [Cp ∗Fe(η 6-C 6H 5)] + core (Cp ∗ = η 5-C 5Me 5) has been prepared. The new organometallic π-conjugated push–pull chromophores [ Cp ∗ Fe ( η 6 - C 6 H 5 ) -NHN CHR ] + PF 6 - (R = 2,4,6-Me 3C 6H 2, 4; (η 5-C 5H 5)Fe(η 5-C 5H 4), 5) were prepared through condensations between the organometallic hydrazine precursor [ Cp ∗ Fe ( η 6 - C 6 H 5 NHNH 2 ) ] + PF 6 - ( 3), and either the mesitaldehyde or the ferrocenecarboxaldehyde, respectively. Their original design combines the cationic mixed sandwich acceptor (A) associated with an organic or organometallic donor (D) through the asymmetric hydrazone spacer –NH–N CH–. The mesityl ring of 4 has been complexed by the arenophile Cp ∗Ru +, leading to the first η 6:η 6-coordinated dinucleating hydrazone complex, [ Cp ∗ Fe ( η 6 - C 6 H 5 ) -NHN CH- { ( η 6 - 2 , 4 , 6 - Me 3 C 6 H 2 ) Ru Cp ∗ } ] 2 + [ PF 6 - ] 2 ( 6). Both the mono- and dinuclear hydrazones were stereoselectively obtained as their trans-isomers about the N C double bond. All the new compounds were thoroughly characterized by a combination of elemental analysis and spectroscopic techniques ( 1H and 13C NMR, IR and UV–Vis). In addition, the solid-state structure of the organometallic hydrazine precursor 3 has been determined by X-ray diffraction study. Spectroscopic and electrochemical data of the organometallic hydrazones 4 and 5 clearly indicate a mutual donor–acceptor electronic influence resulting from conjugation between the end groups through the entire hydrazone backbone. Compounds 4 and 5 are strongly polarized D–π–A systems exhibiting low-lying intramolecular charge transfer bands in their electronic absorption spectra and enhanced second-order NLO properties (μβ), as measured by EFISH technique at 1.907 μm.

2-{[4-(3-Mesityl-3-methylcyclobutyl)thiazol-2-yl]hydrazono}-1,2-diphenylethanol ethanol solvate

In the title compound, C31H33N3OS·C2H6O, the dihedral angle between the least-squares planes of the thiazole and mesityl rings is 77.3 (1)°. There are intramolecular N—H...O hydrogen bonds and intermolecular O—H...N/O and C—H...O interactions.

A Monomeric Thallium(I) Amide in the Solid State: Synthesis and Structure of TlN(Me)ArMes2 (ArMes2 = C6H3-2,6-Mes2)

Reaction of TlCl and [LiN(Me)Ar(Mes)2](2) [Ar(Mes)2 = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Me(3))(2)] in Et(2)O generated the thallium amide, TlN(Me)Ar(Mes)2 (1). X-ray data showed that it has a monomeric structure with an average Tl-N distance of 2.364(3) Angstroms. There was also a Tl-arene approach [Tl-centroid = 3.026(2) Angstroms (avg)] to a flanking mesityl ring from the terphenyl substituent. DFT calculations showed that this interaction is weak and supported essentially one coordination for thallium. The electronic spectrum of 1 is hypsochromically shifted in comparison to the monomeric TlAr(Trip)2 (Trip = C(6)H(2)-2,4,6-Pr(i)(3)).

Adamantyl-Substituted N-Heterocyclic Carbene Ligands in Second-Generation Grubbs-Type Metathesis Catalysts

The N-heterocyclic carbene (NHC) ligands H2IAd (H2IAd = 1,3-di(1-adamantyl)-4,5-dihydroimidazol-2-ylidene) and H2IAdMes (H2IAdMes = 1-(1-adamantyl)-3-mesityl-4,5-dihydroimidazol-2-ylidine) were prepared and treated with [RuCl2(CHPh)(PCy3)2] (1). While H2IAd failed to react with 1, H2IAdMes readily produced [RuCl2(CHPh)(H2IAdMes)(PCy3)] (7). Only a single isomer of 7 was formed, this being that with the mesityl ring situated above the benzylidene moiety, as confirmed by an X-ray structure. Complex 7 was found to be only a very poor olefin metathesis catalyst, likely a consequence of the excessive steric crowding imparted by the 1-adamantyl moiety towards the position trans to the benzylidene group.

Conformational studies by dynamic NMR. 94.1 cogwheel pathway for the stereomutations of durene derivatives containing the mesityl ring.

The low-temperature NMR spectra of 1,4-bis(mesitoyl)durene, 1, and of 1,4-bis(mesitylethenyl)durene, 2, reveal the presence of syn and anti rotamers at the equilibrium, their relative proportions depending on the dielectric constant of the solvent. In solution the more stable rotamer of 1 is the anti whereas, in the case of 2, the more stable is the syn. Depending on the crystallization solvent employed the more (anti) and the less stable (syn) rotamers were both observed (X-ray diffraction) in the solid state of 1. On the other hand, only the less stable rotamer (anti) was found to be present in the solid state of 2. As shown by MM calculations, the syn-to-anti interconversion occurs via a correlated process (cogwheel pathway) involving the mesityl-C and durene-C bond rotations: the dynamic NMR technique yields an experimental barrier of 8.2 kcal mol(-)(1) for 1 and 13.1 kcal mol(-)(1) for 2. In the case of derivative 2 a second barrier, due to a second type of correlated rotation process (torsion), was also determined (8.6 kcal mol(-)(1)). As a consequence of the restriction of this second torsional motion the anti rotamer of 2 displays two distinguishable NMR spectra at -133 degrees C, corresponding to a pair of conformers with different symmetry (anti C(i)() and anti C(2)).

Infrared and Raman features of a series of α,ω-bis(arylthio)oligothiophenes as molecular wires. A π-electron delocalization efficiency study

Fourier transform infrared and Raman spectra of a novel series of neutral α,ω-bis(mesitylthio)oligothiophenes and some α,ω-bis(mesitylthio)oligothiophenes containing ethylenedioxy groups at the β positions, with various chain lengths have been investigated. Because these compounds contain carbon-sulfur linkages they can be viewed as models for prototypical surface-bound molecular wires in which the oligomer is linked to the surface by a thiol-metal bond. Thus, interactions between the conjugated moiety and the metallic surface or cluster can be simulated. These studies are very important in order to apply molecular systems in micro and optoelectronic devices. The statements of effective conjugation coordinate theory and density functional theory calculations let us describe the specific electronic interactions between the mesitylthio groups and the oligothiophene backbone. An increased π-electron delocalization or conjugation length with respect to the α,ω-bis(alkyl)oligothiophenes of the same length has been noticed. The inclusion of C–S bridges between the end groups and the central π-conjugated backbone increases the π-electron delocalization within the oligomeric chain and precludes the oligothiophene moiety from conjugative interactions with the mesityl rings.

A 95Mo and 13C solid-state NMR and relativistic DFT investigation of mesitylenetricarbonylmolybdenum(0) – a typical transition metal piano-stool complex

The chemical shift (CS) and electric field gradient (EFG) tensors in the piano-stool compound mesitylenetricarbonylmolybdenum(0), 1, have been investigated via95Mo and 13C solid-state magic-angle spinning (MAS) NMR as well as relativistic zeroth-order regular approximation density functional theory (ZORA-DFT) calculations. Molybdenum-95 (I = 5/2) MAS NMR spectra acquired at 18.8 T are dominated by the anisotropic chemical shift interaction (Ω = 775 ± 30 ppm) rather than the 2nd-order quadrupolar interaction (CQ = −0.96 ± 0.15 MHz), an unusual situation for a quadrupolar nucleus. ZORA-DFT calculations of the 95Mo EFG and CS tensors are in agreement with the experimental data. Mixing of appropriate occupied and virtual d-orbital dominated MOs in the region of the HOMO-LUMO gap are shown to be responsible for the large chemical shift anisotropy. The small, but non-negligible, 95Mo quadrupolar interaction is discussed in terms of the geometry about Mo. Carbon-13 CPMAS spectra acquired at 4.7 T demonstrate the crystallographic and magnetic nonequivalence of the twelve 13C nuclei in 1, despite the chemical equivalence of some of these nuclei in isotropic solutions. The principal components of the carbon CS tensors are determined via a Herzfeld–Berger analysis, and indicate that motion of the mesitylene ring is slow compared to a rate which would influence the carbon CS tensors (i.e. tens of μs). ZORA-DFT calculations reproduce the experimental carbon CS tensors accurately. Oxygen-17 EFG and CS tensors for 1 are also calculated and discussed in terms of existing experimental data for related molybdenum carbonyl compounds. This work provides an example of the information available from combined multi-field solid-state multinuclear magnetic resonance and computational investigations of transition metal compounds, in particular the direct study of quadrupolar transition metal nuclei with relatively small magnetic moments.

C-C and C-H bond activation reactions in N-heterocyclic carbene complexes of ruthenium.

Thermolysis of Ru(PPh3)3(CO)H2 with the N-heterocyclic carbene bis(1,3-(2,4,6-trimethylphenyl)imidazol-2-ylidene) (IMes) results in C-C activation of an Ar-CH3 bond in one of the mesityl rings of the carbene ligand. Upon addition of IMes to Ru(PPh3)3(CO)H2 at room temperature in the presence of an alkene, C-H bond activation is observed instead. The thermodynamics of these C-C and C-H cleavage reactions have been probed using density functional theory.

Aminoketone, oxazole and thiazole synthesis. Part 15.1 2-[4-(4-halobenzenesulphonyl)-phenyl]-5-aryloxazoles

Acylaminoacylation of aromatic hydrocarbons (benzene, toluene, meta-xylene, mesitylene) with 2-(4-benzenesulfonyl-(4-halophenyl))-5-oxazolones in the presence of anhydrous aluminum chloride leads to 2-aza-1,4-diones 5 which cyclize under the action of phosphorus oxychloride yielding the corresponding 2-(4-(4-halobenzenesulphonyl)-phenyl)-5-aryloxazoles 6. The para- halogens are chloro or bromo atoms. Electronic absorption, vibrational, 1 H-NMR and 13C-NMR spectral data are presented. The UV and NMR spectra provide evidence for the non-coplanarity of the oxazole and mesityl rings.

One- and two-dimensional silver-coordination networks containing pi-sandwiched silver-silver interactions.

The self-assembly of coordination networks from reaction of 2,4,6-trimesityl-1,3,5-triazine and silver(I) trifluoroacetate is described. A one-dimensional linear polymer is formed from solutions deficient in silver while a two-dimensional, graphite-like sheet is formed from solutions containing 3 equiv of silver per triazine. The structurally similar networks both contain triazine rings separated by two trifluoroacetate-bridged silver atoms. The two silver atoms are effectively sandwiched between two mesityl rings with intermediate arene-silver interactions. The silver-silver bond lengths are 2.9731(4) and 2.9246(5) A in the one-dimensional network and 2.8842(4) A in the two-dimensional network.

First structural characterization of core modified 10,15-meso aryl azuliporphyrins: observation of C-H...pi interaction between pyrrole beta-CH and mesityl ring.

First successful syntheses and structural characterization of new core modified meso aryl azuliporphyrins by a simple [3 + 1] methodology are reported.

Attempted Isolation of Heavier Group 14 Element Ketone Analogues: Effect of O−H···π-Ar Hydrogen Bonding on Geometry

The terphenyl group 14 element gem-dihydroxy (gem-diol) derivatives Ar2M(OH)2 (Ar = C6H3-2,6-Mes2; Mes = C6H2-2,4,6-Me3), M = Ge (1); Sn (2), were synthesized and characterized by X-ray crystallography, NMR, IR spectroscopy, and combustion analysis. The synthetic route involved treatment of the divalent MAr2 compounds with N2O or Me3NO in hydrocarbon solution. The objective was the isolation of the heavier group 14 element ketone analogues Ar2MO. Despite stringent precautions to exclude moisture and oxygen during the synthesis, the products 1 and 2 were isolated in ca. 30−50% yield. These results are in contrast to the recently reported stabilization of the terphenyl-protected, essentially strain-free, species (bisap)2GeO (bisap = 2,6-di(1‘-naphthyl)phenyl). Seemingly, 1 and 2 represent the addition of H2O to Ar2MO. The identity of the other products is currently unknown. Compound 1 represents the second example of a germanium gem-diol to be structurally characterized, and it features the expected distorted tetrahedral germanium environment. Compound 2 is the first instance of a monomeric gem-dihydroxy derivative of tin. Surprisingly, the C−Sn−C angle is ca. 20° wider than the corresponding angle in 1 even though the larger size of tin is expected to reduce steric congestion and so afford a narrower C−Sn−C angle. This unanticipated result was attributed to the nonclassical hydrogen-bonding interaction of the O−H groups with the mesityl ring substituents, which for geometric reasons is more favorable in the tin compound.