High-resolution liquid-and solid-state 119 Sn NMR spectroscopy was used to study the bonding envi... more High-resolution liquid-and solid-state 119 Sn NMR spectroscopy was used to study the bonding environment in the series of monomeric, two-coordinate Sn(II) compounds of formula Sn(X)C 6 H 3-2,6-Trip 2 (X) Cl, Cr(η 5-C 5 H 5)(CO) 3 , t-Bu, Sn(Me) 2 C 6 H 3-2,6-Trip 2 ; Trip) C 6 H 2-2,4,6-i-Pr 3). The trends in the principal components of the chemical shift tensor extracted from the solid-state NMR data were consistent with the structures determined by X-ray crystallography. Furthermore, the spectra for the first three compounds displayed the largest 119 Sn NMR chemical shift anisotropies (up to 3798 ppm) of any tin compound for which data are currently available. Relaxation time based calculations for the dimetallic compound 2,6-Trip 2 H 3 C 6 Sn-Sn(Me) 2 C 6 H 3-2,6-Trip 2 suggests that the chemical shift anisotropy for the two-coordinate tin center may be as much as ca. 7098 ppm, which is as broad as the 1 MHz bandwidth of the NMR spectrometer.
The "distannynes" Ar′SnSnAr′ (Ar′) C 6 H 3-2,6(C 6 H 3-2,6-Pr i 2) 2) and Ar*SnSnAr* (Ar*) C 6 H ... more The "distannynes" Ar′SnSnAr′ (Ar′) C 6 H 3-2,6(C 6 H 3-2,6-Pr i 2) 2) and Ar*SnSnAr* (Ar*) C 6 H 3-2,6(C 6 H 2-2,4,6-Pr i 3) 2) were examined by solid-state 119 Sn NMR and Mössbauer spectroscopy. The two compounds display substantially different spectroscopic parameters, while differing only in the absence (Ar′SnSnAr′) or presence (Ar*SnSnAr*) of a para-Pr i group in the flanking aryl rings of their terphenyl substituents. The spectroscopic differences can be interpreted in terms of a more trans-bent geometry and a longer Sn−Sn bond for Ar*SnSnAr* in comparison to the wider Sn−Sn−C angle (125.24(7)°) and shorter Sn−Sn bond length (2.6675(4)Å) determined from the crystal structure of Ar′SnSnAr′. The differences are consistent with previously published calculations by Nagase and Takagi for Ar*SnSnAr*.
The nature of metalmetal bonding in group 13 dimetallenes REER (E = Al, Ga, In, Tl; R = H, Me, t... more The nature of metalmetal bonding in group 13 dimetallenes REER (E = Al, Ga, In, Tl; R = H, Me, t Bu, Ph) was investigated by use of quantum chemical methods that include HF, second order Møller-Plesset perturbation theory (MP2), coupled cluster (CCSD(T)), complete active space with (CASPT2) and without (CAS) second order perturbation theory and two density functionals, namely B3LYP and M06-2X. The results show that the metalmetal interaction in group 13 dimetallenes stems almost exclusively from static and dynamic electron correlation effects: both dialuminenes and digallenes have an important singlet diradical component in their wave function, whereas the bonding in the heavier diindenes and, in particular, dithallenes is dominated by closed shell metallophilic interactions. The reported calculations represent the first systematic attempt to determine the metal and ligand dependent bonding changes in these systems.
The reduction of {ArFeBr} 2 (Ar = terphenyl) with KC 8 in the presence of excess PMe 3 afforded t... more The reduction of {ArFeBr} 2 (Ar = terphenyl) with KC 8 in the presence of excess PMe 3 afforded the Fe(I) complex 3,5-Pr i 2-Ar¢Fe(PMe 3) (1) (Ar¢-3,5-Pr i 2 = C 6 H-2,6-(C 6 H 3-2,6-Pr i 2)-3,5-Pr i 2), which has a structure very different from the previously reported, linear Cr(I) species 3,5-Pr i 2-Ar*Cr(PMe 3) (3,5-Pr i 2-Ar* = C 6 H-2,6-(C 6 H 2-2,4,6-Pr i 3) 2-3,5-Pr i 2) and features a strong Fe-h 6-aryl interaction with the flanking aryl ring of the terphenyl ligand. In sharp contrast, the reduction of {ArCoCl} 2 (Ar = 3,5-Pr i 2-Ar¢ and Ar¢) afforded the allyl complexes Co(h 3-{1-(H 2 C) 2 CC 6 H 3-2-(C 6 H 2-2,4-Pr i 2-5-(C 6 H 3-2,6-Pr i 2))-3-Pr i })(PMe 3) 3 (4) and Co(h 3-{1-(H 2 C) 2 CC 6 H 3-2-(C 6 H 4-3-(C 6 H 3-2,6-Pr i 2))-3-Pr i })(PMe 3) 3 (5) formed by an unusual triple dehydrogenation of an isopropyl group. It is proposed that the reduction initially generates an intermediate 3,5-Pr i 2-Ar¢Co(PMe 3), which is similar in structure to 1, followed by 3,5-Pr i 2-Ar¢Co(PMe 3) decomposition to a cobalt hydride intermediate and dehydrogenation of the isopropyl group via remote C-H activation induced by PMe 3 complexation. Complexes 1, 4, and 5 were characterized by X-ray crystallography. In addition, 1 was studied by NMR and EPR spectroscopy; 4 and 5 were characterized by NMR spectroscopy.
Air-and water-stable silicon nanocrystals were prepared by the bromine oxidation of porous silico... more Air-and water-stable silicon nanocrystals were prepared by the bromine oxidation of porous silicon nanoparticles followed by reaction with n-butyllithium. Transmission electron microscopy suggests that the vigorous oxidation of porous silicon under reflux conditions removes the porous layer from the nanoparticle to expose a crystalline silicon core that can be passivated with organic ligands. A combination of infrared, ultraviolet/visible, and photoluminescence demonstrate the presence of small crystalline silicon particles and saturated hydrocarbon ligands, while solid-and liquid-state nuclear magnetic resonance spectroscopies establish that butyl ligands are localized on the nanocrystal surface. All of these analytical methods suggest that the product of this synthesis is stable in air and water indefinitely.
Contents 1. Introduction 3877 2. Bonding 3877 3. Doubly Bonded Compounds 3882 3.1. Compounds of F... more Contents 1. Introduction 3877 2. Bonding 3877 3. Doubly Bonded Compounds 3882 3.1. Compounds of Formula REdER (E) Group 13 Element) 3882 3.2. Compounds of Formula REdE′R 2 (E Group 13, E′) Group 14 Element) and Related Species 3884 3.3. Dianions of Formula [R 2 EdER 2 ] 2-(E) Group 13 Element) 3884 3.4. Monoanions of Formula [R 2 EdE′R′ 2 ]-(E) Group 13, E′) Group 14 Element) 3885 3.5. Compounds of Formula R 2 E-Ë ′R 2 (E) Group 13, E′) Group 15 Element) and Related Species 3886 3.6. Compounds of Formula R 2 E-E′R and [R 2 E-E′]-(E) Group 13, E′) Group 16 Element) 3888 3.7. Compounds of Formula R 2 EdER 2 , [L:Ë dË :L] and [RË dË R] 2-(E) Group 14 Element) 3888 3.8. Compounds of Formula R 2 EdË ′R (E) Group 14, E′) Group 15 Element) 3896 3.9. Compounds of Formula [R 2 EdË ′R 2 ] + (E) Group 14, E′) Group 15 Element) 3900 3.10. Compounds of Formula R 2 EdË ′ (E) Group 14, E′) Group 16 Element) 3901 3.11. Compounds of Formula RË)Ë R, (E or E′) N, P, As, Sb, or Bi) 3902 3.12. Compounds of Formula RË dE′ (E) Group 15, E′) Group 16 Element) 3908 4. Triply Bonded Compounds 3908 4.1. Group 13 Derivatives 3908 4.2. Group 14 Derivatives 3909 4.3. Compounds with Potential Triple Bonding between Group 14 and Group 15 Elements 3912 4.4. Compounds with Potential Triple Bonding between Group 14 and Group 16 Elements 3913 4.5. Compounds with Triple Bonding between Group 15 Elements 3913 5. Conclusions 3914 6. List of Abbreviations 3914 7. Acknowledgments 3915 8. References 3915
6-i Pr 2 } 2), a rare metal−metal bonded cobalt−tin cluster with low-coordinate tin atoms, was pr... more 6-i Pr 2 } 2), a rare metal−metal bonded cobalt−tin cluster with low-coordinate tin atoms, was prepared by the reaction of [K(thf) 0.2 ][Co(1,5-cod) 2 ] (cod = 1,5-cyclooctadiene) with [Ar′Sn(μ-Cl)] 2. This reaction illustrates a promising synthetic strategy to access uncommon metal clusters. The structure of 1 features a rhomboidal Co 2 Sn 2 core with strong metal−metal bonds between tin and cobalt and a weaker tin−tin interaction. Reaction of 1 with white phosphorus afforded [Ar′ 2 Sn 2 Co 2 P 4 ] (2), the first molecular cluster compound containing phosphorus, cobalt and tin.
The first row transition metal(II) dithiolates M(SAr iPr 4)2 (Ar iPr 4 = C6H3-2,6-(C6H3-2,6-iPr2)... more The first row transition metal(II) dithiolates M(SAr iPr 4)2 (Ar iPr 4 = C6H3-2,6-(C6H3-2,6-iPr2)2, M = Cr (1), Mn (3), Fe (4), Co (5), Ni (6), and Zn (7)), Cr(SAr Me 6)2 (2) (Ar Me 6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) and the ligand transfer reagent (NaSAr iPr 4)2 (8) are described. In contrast to their M(SAr iPr 6)2 (M = Cr, Mn, Fe, Co, Ni, and Zn; Ar iPr 6 = C6H3-2,6-(C6H2-2,4,6-iPr3)2) congeners, which differ from 1 and 3-6 in having para-isopropyl groups on the flanking aryl rings of the terphenyl substituents, compounds 1 and 4-6 display highly bent coordination geometries with S-M-S angles of 109.802(2) (1), 120.2828(3) (4), 91.730(3) (5), and 92.68(2)° (6) as well as relatively close metal-flanking aryl ring η 6 interactions with metal-centroid distances of 2.11477(6) (1), 1.97188(3) (2), 2.15269(6) (4), 1.62058(9) (5), and 1.724(8) Å (6). However, the d 5 (Mn) and d 10 (Zn) complexes 3 and 7 display linear or near-linear coordination with no close metal-ligand distances. The non-linear geometries of 1 and 4-6 also contrast with those of their Ar iPr 4 substituted alkoxo and amido congeners, which have strictly linear coordination. Complexes 1-7 were synthesized by the reaction of lithium or sodium thiolate salt with the metal dihalide or, in the case of 3, by the reaction of the thiol with the amido complex Mn[N(SiMe3)2]2. All compounds were characterized by electronic spectroscopy, X-ray crystallography, and magnetic measurements using Evans' method and SQUID magnetometry. It was concluded that, despite the large bulk of the Ar iPr 4 substituents, the absence of paraisopropyl groups on the flanking rings of the ligand permits close secondary metal-flanking ring distances. The compounds are characterized by more intense colors and display magnetic moments that are generally lower than the spin-only values, in agreement with the covalent character of the close metal-flanking ring η 6 interactions.
Chemical communications (Cambridge, England), Jan 4, 2015
The reduction of Mn{C(SiMe3)3}2 with KC8 in the presence of crown ethers yielded the d(6), Mn(I) ... more The reduction of Mn{C(SiMe3)3}2 with KC8 in the presence of crown ethers yielded the d(6), Mn(I) salts [K2(18-crown-6)3][Mn{C(SiMe3)3}2]2 and [K(15-crown-5)2][Mn{C(SiMe3)3}2], that have near-linear manganese coordination but almost completely quenched orbital magnetism as a result of 4s-3dz(2) orbital mixing which affords a non-degenerate ground state.
We used a novel experimental setup to conduct the first synchrotron-based (61)Ni Mössbauer spectr... more We used a novel experimental setup to conduct the first synchrotron-based (61)Ni Mössbauer spectroscopy measurements in the energy domain on Ni coordination complexes and metalloproteins. A representative set of samples was chosen to demonstrate the potential of this approach. (61)NiCr2O4 was examined as a case with strong Zeeman splittings. Simulations of the spectra yielded an internal magnetic field of 44.6 T, consistent with previous work by the traditional (61)Ni Mössbauer approach with a radioactive source. A linear Ni amido complex, (61)Ni{N(SiMe3)Dipp}2, where Dipp = C6H3-2,6-(i)Pr2, was chosen as a sample with an "extreme" geometry and large quadrupole splitting. Finally, to demonstrate the feasibility of metalloprotein studies using synchrotron-based (61)Ni Mössbauer spectroscopy, we examined the spectra of (61)Ni-substituted rubredoxin in reduced and oxidized forms, along with [Et4N]2[(61)Ni(SPh)4] as a model compound. For each of the above samples, a reasonable...
Indium(I)chloride reacts with LiAr Me 6 (Ar Me 6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) in THF to give thr... more Indium(I)chloride reacts with LiAr Me 6 (Ar Me 6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) in THF to give three new mixed-valent organoindium subhalides. While the 1:1 reaction of InCl with LiAr Me 6 yields the known metal-rich cluster In8(Ar Me 6)4 (1), the use of freshly prepared LiAr Me 6 led to incorporation of iodide, derived from the synthesis of LiAr Me 6 , into the structures, to afford In4(Ar Me 6)4I2 (2) along with minor amounts of In3(Ar Me 6)3I2 (3). When the same reaction was performed in 4:3 stoichiometry, the mixedhalide compound In3(Ar Me 6)3ClI (4) was obtained. Further increasing the chloride:aryl ligand ratio resulted in the formation of the known mixed-halide species In4(Ar Me 6)4Cl2I2 that can also be obtained from the reaction of InCl with in situ prepared LiAr Me 6 in toluene. The new compounds 2 and 4 were characterized in the solid state by X-ray crystallography and IR spectroscopy, and in solution by UV/Vis and 1 H/ 13 C{ 1 H} NMR spectroscopies. The structural characterization of 2 and 4 was supported by electronic structure calculations at the density functional level of theory which were also performed to rationalize the cluster-type bonding in 1.
Although in principle transition metals can form bonds with six shared electron pairs, only quadr... more Although in principle transition metals can form bonds with six shared electron pairs, only quadruply bonded compounds can be isolated as stable species at room temperature. Here we show that the reduction of {Cr(μ-Cl)Ar′}2 [where Ar′ indicates C6H3-2,6(C6H3-2,6-Pri2)2 and Pr indicates isopropyl] with a slight excess of potassium graphite has produced a stable compound with fivefold chromium-chromium (Cr–Cr) bonding. The very air- and moisture-sensitive dark red crystals of Ar′CrCrAr′ were isolated with greater than 40% yield. X-ray diffraction revealed a Cr–Cr bond length of 1.8351(4) angstroms (where the number in parentheses indicates the standard deviation) and a planar transbent core geometry. These data, the…
The synthesis and characterization of a stable, acyclic two-coordinate silylene, Si(SAr Me 6)2, (... more The synthesis and characterization of a stable, acyclic two-coordinate silylene, Si(SAr Me 6)2, (Ar Me 6 = C6H3-2,6(C6H2-2,4,6-Me3)2) by reduction of Br2Si(SAr Me 6)2 with a magnesium(I) reductant is described. It features a v-shaped silicon coordination with a S-Si-S angle of 90.519(2)° and an average Si-S distance of 2.158(3) Å. Although it reacts readily with an alkyl halide, it does not react with hydrogen under ambient conditions probably as a result of the ca. 4.3 eV energy difference between the frontier silicon lone pair and 3p orbitals.
The synthesis, spectroscopic and structural characterization of an extensive series of acyclic, m... more The synthesis, spectroscopic and structural characterization of an extensive series of acyclic, monomeric tetrylene dichalcogenolates of formula M(ChAr)2 (M = Si, Ge, Sn, Pb; Ch = O, S, or Se; Ar = bulky m-terphenyl ligand) are described. They were found to possess several unusual features-the most notable of which is their strong tendency to display acute interligand, Ch-M-Ch, bond angles that are often well below 90°. Furthermore, and contrary to normal steric expectations, the interligand angles were 2 found to become narrower as the size of the ligand was increased. Experimental and structural data in conjunction with high-level DFT calculations, including corrections for dispersion effects, led to the conclusion that dispersion forces play a key role in stabilizing their acute interligand angles.
An experimental and DFT investigation of the mechanism of the coupling of methylisocyanide and C-... more An experimental and DFT investigation of the mechanism of the coupling of methylisocyanide and C-H activation mediated by the germylene (germanediyl) Ge(Ar Me6)2 (Ar Me6 = C6H2-2,6(C6H2-2,4,6-Me3)2) showed that it proceeded by initial MeNC adduct formation and sequential insertions of two MeNC molecules into a Ge-C bond. Insertion of a third MeNC leads to methylisocyanide methyl group C-H activation to afford an azagermacyclopentadienyl complex. The Xray crystal structures of the 1:1 (Ar Me6)2GeCNMe adduct, the first and final insertion products (Ar Me6)GeC(NMe)Ar Me6 and (Ar Me6)GeC(NHMe)C(NMe)C(Ar Me6)NMe were obtained. The DFT calculations on the reaction pathway represent the first detailed mechanistic study of isocyanide oligomerization by a p-block element species.
The mechanism of the reaction of olefins and hydrogen with dimetallenes ArMMAr (Ar = aromatic gro... more The mechanism of the reaction of olefins and hydrogen with dimetallenes ArMMAr (Ar = aromatic group; M = Al or Ga) was studied by density functional theory calculations and experimental methods. The digallenes, for which the most experimental data are available, are extensively dissociated to gallanediyl monomers :GaAr in hydrocarbon solution, but we found that they do not react as the more open dissociated The computational findings are in agreement with experimental observations that the digallene Ar iPr 4 GaGaAr iPr 4 (Ar iPr 4 = C6H3-2,6-(C6H3-2,6-i Pr2)2), reacts readily with two equivalents of olefin or hydrogen to give 1-4-digallacyclohexane or aryl gallium dihydride products, whereas the stable monomer, :GaAr iPr 8 (Ar iPr 8 = C6H-2,6-(C6H3-2,4,6i Pr3)2-3,5-i Pr2), does not react with ethylene or hydrogen. Calculations on the reaction of propene to ArAlAlAr show that, in contrast to the digallenes, addition involves an openshell transition state consistent with the higher singlet diradical character of dialuminenes.
High-resolution liquid-and solid-state 119 Sn NMR spectroscopy was used to study the bonding envi... more High-resolution liquid-and solid-state 119 Sn NMR spectroscopy was used to study the bonding environment in the series of monomeric, two-coordinate Sn(II) compounds of formula Sn(X)C 6 H 3-2,6-Trip 2 (X) Cl, Cr(η 5-C 5 H 5)(CO) 3 , t-Bu, Sn(Me) 2 C 6 H 3-2,6-Trip 2 ; Trip) C 6 H 2-2,4,6-i-Pr 3). The trends in the principal components of the chemical shift tensor extracted from the solid-state NMR data were consistent with the structures determined by X-ray crystallography. Furthermore, the spectra for the first three compounds displayed the largest 119 Sn NMR chemical shift anisotropies (up to 3798 ppm) of any tin compound for which data are currently available. Relaxation time based calculations for the dimetallic compound 2,6-Trip 2 H 3 C 6 Sn-Sn(Me) 2 C 6 H 3-2,6-Trip 2 suggests that the chemical shift anisotropy for the two-coordinate tin center may be as much as ca. 7098 ppm, which is as broad as the 1 MHz bandwidth of the NMR spectrometer.
High-resolution liquid-and solid-state 119 Sn NMR spectroscopy was used to study the bonding envi... more High-resolution liquid-and solid-state 119 Sn NMR spectroscopy was used to study the bonding environment in the series of monomeric, two-coordinate Sn(II) compounds of formula Sn(X)C 6 H 3-2,6-Trip 2 (X) Cl, Cr(η 5-C 5 H 5)(CO) 3 , t-Bu, Sn(Me) 2 C 6 H 3-2,6-Trip 2 ; Trip) C 6 H 2-2,4,6-i-Pr 3). The trends in the principal components of the chemical shift tensor extracted from the solid-state NMR data were consistent with the structures determined by X-ray crystallography. Furthermore, the spectra for the first three compounds displayed the largest 119 Sn NMR chemical shift anisotropies (up to 3798 ppm) of any tin compound for which data are currently available. Relaxation time based calculations for the dimetallic compound 2,6-Trip 2 H 3 C 6 Sn-Sn(Me) 2 C 6 H 3-2,6-Trip 2 suggests that the chemical shift anisotropy for the two-coordinate tin center may be as much as ca. 7098 ppm, which is as broad as the 1 MHz bandwidth of the NMR spectrometer.
The "distannynes" Ar′SnSnAr′ (Ar′) C 6 H 3-2,6(C 6 H 3-2,6-Pr i 2) 2) and Ar*SnSnAr* (Ar*) C 6 H ... more The "distannynes" Ar′SnSnAr′ (Ar′) C 6 H 3-2,6(C 6 H 3-2,6-Pr i 2) 2) and Ar*SnSnAr* (Ar*) C 6 H 3-2,6(C 6 H 2-2,4,6-Pr i 3) 2) were examined by solid-state 119 Sn NMR and Mössbauer spectroscopy. The two compounds display substantially different spectroscopic parameters, while differing only in the absence (Ar′SnSnAr′) or presence (Ar*SnSnAr*) of a para-Pr i group in the flanking aryl rings of their terphenyl substituents. The spectroscopic differences can be interpreted in terms of a more trans-bent geometry and a longer Sn−Sn bond for Ar*SnSnAr* in comparison to the wider Sn−Sn−C angle (125.24(7)°) and shorter Sn−Sn bond length (2.6675(4)Å) determined from the crystal structure of Ar′SnSnAr′. The differences are consistent with previously published calculations by Nagase and Takagi for Ar*SnSnAr*.
The nature of metalmetal bonding in group 13 dimetallenes REER (E = Al, Ga, In, Tl; R = H, Me, t... more The nature of metalmetal bonding in group 13 dimetallenes REER (E = Al, Ga, In, Tl; R = H, Me, t Bu, Ph) was investigated by use of quantum chemical methods that include HF, second order Møller-Plesset perturbation theory (MP2), coupled cluster (CCSD(T)), complete active space with (CASPT2) and without (CAS) second order perturbation theory and two density functionals, namely B3LYP and M06-2X. The results show that the metalmetal interaction in group 13 dimetallenes stems almost exclusively from static and dynamic electron correlation effects: both dialuminenes and digallenes have an important singlet diradical component in their wave function, whereas the bonding in the heavier diindenes and, in particular, dithallenes is dominated by closed shell metallophilic interactions. The reported calculations represent the first systematic attempt to determine the metal and ligand dependent bonding changes in these systems.
The reduction of {ArFeBr} 2 (Ar = terphenyl) with KC 8 in the presence of excess PMe 3 afforded t... more The reduction of {ArFeBr} 2 (Ar = terphenyl) with KC 8 in the presence of excess PMe 3 afforded the Fe(I) complex 3,5-Pr i 2-Ar¢Fe(PMe 3) (1) (Ar¢-3,5-Pr i 2 = C 6 H-2,6-(C 6 H 3-2,6-Pr i 2)-3,5-Pr i 2), which has a structure very different from the previously reported, linear Cr(I) species 3,5-Pr i 2-Ar*Cr(PMe 3) (3,5-Pr i 2-Ar* = C 6 H-2,6-(C 6 H 2-2,4,6-Pr i 3) 2-3,5-Pr i 2) and features a strong Fe-h 6-aryl interaction with the flanking aryl ring of the terphenyl ligand. In sharp contrast, the reduction of {ArCoCl} 2 (Ar = 3,5-Pr i 2-Ar¢ and Ar¢) afforded the allyl complexes Co(h 3-{1-(H 2 C) 2 CC 6 H 3-2-(C 6 H 2-2,4-Pr i 2-5-(C 6 H 3-2,6-Pr i 2))-3-Pr i })(PMe 3) 3 (4) and Co(h 3-{1-(H 2 C) 2 CC 6 H 3-2-(C 6 H 4-3-(C 6 H 3-2,6-Pr i 2))-3-Pr i })(PMe 3) 3 (5) formed by an unusual triple dehydrogenation of an isopropyl group. It is proposed that the reduction initially generates an intermediate 3,5-Pr i 2-Ar¢Co(PMe 3), which is similar in structure to 1, followed by 3,5-Pr i 2-Ar¢Co(PMe 3) decomposition to a cobalt hydride intermediate and dehydrogenation of the isopropyl group via remote C-H activation induced by PMe 3 complexation. Complexes 1, 4, and 5 were characterized by X-ray crystallography. In addition, 1 was studied by NMR and EPR spectroscopy; 4 and 5 were characterized by NMR spectroscopy.
Air-and water-stable silicon nanocrystals were prepared by the bromine oxidation of porous silico... more Air-and water-stable silicon nanocrystals were prepared by the bromine oxidation of porous silicon nanoparticles followed by reaction with n-butyllithium. Transmission electron microscopy suggests that the vigorous oxidation of porous silicon under reflux conditions removes the porous layer from the nanoparticle to expose a crystalline silicon core that can be passivated with organic ligands. A combination of infrared, ultraviolet/visible, and photoluminescence demonstrate the presence of small crystalline silicon particles and saturated hydrocarbon ligands, while solid-and liquid-state nuclear magnetic resonance spectroscopies establish that butyl ligands are localized on the nanocrystal surface. All of these analytical methods suggest that the product of this synthesis is stable in air and water indefinitely.
Contents 1. Introduction 3877 2. Bonding 3877 3. Doubly Bonded Compounds 3882 3.1. Compounds of F... more Contents 1. Introduction 3877 2. Bonding 3877 3. Doubly Bonded Compounds 3882 3.1. Compounds of Formula REdER (E) Group 13 Element) 3882 3.2. Compounds of Formula REdE′R 2 (E Group 13, E′) Group 14 Element) and Related Species 3884 3.3. Dianions of Formula [R 2 EdER 2 ] 2-(E) Group 13 Element) 3884 3.4. Monoanions of Formula [R 2 EdE′R′ 2 ]-(E) Group 13, E′) Group 14 Element) 3885 3.5. Compounds of Formula R 2 E-Ë ′R 2 (E) Group 13, E′) Group 15 Element) and Related Species 3886 3.6. Compounds of Formula R 2 E-E′R and [R 2 E-E′]-(E) Group 13, E′) Group 16 Element) 3888 3.7. Compounds of Formula R 2 EdER 2 , [L:Ë dË :L] and [RË dË R] 2-(E) Group 14 Element) 3888 3.8. Compounds of Formula R 2 EdË ′R (E) Group 14, E′) Group 15 Element) 3896 3.9. Compounds of Formula [R 2 EdË ′R 2 ] + (E) Group 14, E′) Group 15 Element) 3900 3.10. Compounds of Formula R 2 EdË ′ (E) Group 14, E′) Group 16 Element) 3901 3.11. Compounds of Formula RË)Ë R, (E or E′) N, P, As, Sb, or Bi) 3902 3.12. Compounds of Formula RË dE′ (E) Group 15, E′) Group 16 Element) 3908 4. Triply Bonded Compounds 3908 4.1. Group 13 Derivatives 3908 4.2. Group 14 Derivatives 3909 4.3. Compounds with Potential Triple Bonding between Group 14 and Group 15 Elements 3912 4.4. Compounds with Potential Triple Bonding between Group 14 and Group 16 Elements 3913 4.5. Compounds with Triple Bonding between Group 15 Elements 3913 5. Conclusions 3914 6. List of Abbreviations 3914 7. Acknowledgments 3915 8. References 3915
6-i Pr 2 } 2), a rare metal−metal bonded cobalt−tin cluster with low-coordinate tin atoms, was pr... more 6-i Pr 2 } 2), a rare metal−metal bonded cobalt−tin cluster with low-coordinate tin atoms, was prepared by the reaction of [K(thf) 0.2 ][Co(1,5-cod) 2 ] (cod = 1,5-cyclooctadiene) with [Ar′Sn(μ-Cl)] 2. This reaction illustrates a promising synthetic strategy to access uncommon metal clusters. The structure of 1 features a rhomboidal Co 2 Sn 2 core with strong metal−metal bonds between tin and cobalt and a weaker tin−tin interaction. Reaction of 1 with white phosphorus afforded [Ar′ 2 Sn 2 Co 2 P 4 ] (2), the first molecular cluster compound containing phosphorus, cobalt and tin.
The first row transition metal(II) dithiolates M(SAr iPr 4)2 (Ar iPr 4 = C6H3-2,6-(C6H3-2,6-iPr2)... more The first row transition metal(II) dithiolates M(SAr iPr 4)2 (Ar iPr 4 = C6H3-2,6-(C6H3-2,6-iPr2)2, M = Cr (1), Mn (3), Fe (4), Co (5), Ni (6), and Zn (7)), Cr(SAr Me 6)2 (2) (Ar Me 6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) and the ligand transfer reagent (NaSAr iPr 4)2 (8) are described. In contrast to their M(SAr iPr 6)2 (M = Cr, Mn, Fe, Co, Ni, and Zn; Ar iPr 6 = C6H3-2,6-(C6H2-2,4,6-iPr3)2) congeners, which differ from 1 and 3-6 in having para-isopropyl groups on the flanking aryl rings of the terphenyl substituents, compounds 1 and 4-6 display highly bent coordination geometries with S-M-S angles of 109.802(2) (1), 120.2828(3) (4), 91.730(3) (5), and 92.68(2)° (6) as well as relatively close metal-flanking aryl ring η 6 interactions with metal-centroid distances of 2.11477(6) (1), 1.97188(3) (2), 2.15269(6) (4), 1.62058(9) (5), and 1.724(8) Å (6). However, the d 5 (Mn) and d 10 (Zn) complexes 3 and 7 display linear or near-linear coordination with no close metal-ligand distances. The non-linear geometries of 1 and 4-6 also contrast with those of their Ar iPr 4 substituted alkoxo and amido congeners, which have strictly linear coordination. Complexes 1-7 were synthesized by the reaction of lithium or sodium thiolate salt with the metal dihalide or, in the case of 3, by the reaction of the thiol with the amido complex Mn[N(SiMe3)2]2. All compounds were characterized by electronic spectroscopy, X-ray crystallography, and magnetic measurements using Evans' method and SQUID magnetometry. It was concluded that, despite the large bulk of the Ar iPr 4 substituents, the absence of paraisopropyl groups on the flanking rings of the ligand permits close secondary metal-flanking ring distances. The compounds are characterized by more intense colors and display magnetic moments that are generally lower than the spin-only values, in agreement with the covalent character of the close metal-flanking ring η 6 interactions.
Chemical communications (Cambridge, England), Jan 4, 2015
The reduction of Mn{C(SiMe3)3}2 with KC8 in the presence of crown ethers yielded the d(6), Mn(I) ... more The reduction of Mn{C(SiMe3)3}2 with KC8 in the presence of crown ethers yielded the d(6), Mn(I) salts [K2(18-crown-6)3][Mn{C(SiMe3)3}2]2 and [K(15-crown-5)2][Mn{C(SiMe3)3}2], that have near-linear manganese coordination but almost completely quenched orbital magnetism as a result of 4s-3dz(2) orbital mixing which affords a non-degenerate ground state.
We used a novel experimental setup to conduct the first synchrotron-based (61)Ni Mössbauer spectr... more We used a novel experimental setup to conduct the first synchrotron-based (61)Ni Mössbauer spectroscopy measurements in the energy domain on Ni coordination complexes and metalloproteins. A representative set of samples was chosen to demonstrate the potential of this approach. (61)NiCr2O4 was examined as a case with strong Zeeman splittings. Simulations of the spectra yielded an internal magnetic field of 44.6 T, consistent with previous work by the traditional (61)Ni Mössbauer approach with a radioactive source. A linear Ni amido complex, (61)Ni{N(SiMe3)Dipp}2, where Dipp = C6H3-2,6-(i)Pr2, was chosen as a sample with an "extreme" geometry and large quadrupole splitting. Finally, to demonstrate the feasibility of metalloprotein studies using synchrotron-based (61)Ni Mössbauer spectroscopy, we examined the spectra of (61)Ni-substituted rubredoxin in reduced and oxidized forms, along with [Et4N]2[(61)Ni(SPh)4] as a model compound. For each of the above samples, a reasonable...
Indium(I)chloride reacts with LiAr Me 6 (Ar Me 6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) in THF to give thr... more Indium(I)chloride reacts with LiAr Me 6 (Ar Me 6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) in THF to give three new mixed-valent organoindium subhalides. While the 1:1 reaction of InCl with LiAr Me 6 yields the known metal-rich cluster In8(Ar Me 6)4 (1), the use of freshly prepared LiAr Me 6 led to incorporation of iodide, derived from the synthesis of LiAr Me 6 , into the structures, to afford In4(Ar Me 6)4I2 (2) along with minor amounts of In3(Ar Me 6)3I2 (3). When the same reaction was performed in 4:3 stoichiometry, the mixedhalide compound In3(Ar Me 6)3ClI (4) was obtained. Further increasing the chloride:aryl ligand ratio resulted in the formation of the known mixed-halide species In4(Ar Me 6)4Cl2I2 that can also be obtained from the reaction of InCl with in situ prepared LiAr Me 6 in toluene. The new compounds 2 and 4 were characterized in the solid state by X-ray crystallography and IR spectroscopy, and in solution by UV/Vis and 1 H/ 13 C{ 1 H} NMR spectroscopies. The structural characterization of 2 and 4 was supported by electronic structure calculations at the density functional level of theory which were also performed to rationalize the cluster-type bonding in 1.
Although in principle transition metals can form bonds with six shared electron pairs, only quadr... more Although in principle transition metals can form bonds with six shared electron pairs, only quadruply bonded compounds can be isolated as stable species at room temperature. Here we show that the reduction of {Cr(μ-Cl)Ar′}2 [where Ar′ indicates C6H3-2,6(C6H3-2,6-Pri2)2 and Pr indicates isopropyl] with a slight excess of potassium graphite has produced a stable compound with fivefold chromium-chromium (Cr–Cr) bonding. The very air- and moisture-sensitive dark red crystals of Ar′CrCrAr′ were isolated with greater than 40% yield. X-ray diffraction revealed a Cr–Cr bond length of 1.8351(4) angstroms (where the number in parentheses indicates the standard deviation) and a planar transbent core geometry. These data, the…
The synthesis and characterization of a stable, acyclic two-coordinate silylene, Si(SAr Me 6)2, (... more The synthesis and characterization of a stable, acyclic two-coordinate silylene, Si(SAr Me 6)2, (Ar Me 6 = C6H3-2,6(C6H2-2,4,6-Me3)2) by reduction of Br2Si(SAr Me 6)2 with a magnesium(I) reductant is described. It features a v-shaped silicon coordination with a S-Si-S angle of 90.519(2)° and an average Si-S distance of 2.158(3) Å. Although it reacts readily with an alkyl halide, it does not react with hydrogen under ambient conditions probably as a result of the ca. 4.3 eV energy difference between the frontier silicon lone pair and 3p orbitals.
The synthesis, spectroscopic and structural characterization of an extensive series of acyclic, m... more The synthesis, spectroscopic and structural characterization of an extensive series of acyclic, monomeric tetrylene dichalcogenolates of formula M(ChAr)2 (M = Si, Ge, Sn, Pb; Ch = O, S, or Se; Ar = bulky m-terphenyl ligand) are described. They were found to possess several unusual features-the most notable of which is their strong tendency to display acute interligand, Ch-M-Ch, bond angles that are often well below 90°. Furthermore, and contrary to normal steric expectations, the interligand angles were 2 found to become narrower as the size of the ligand was increased. Experimental and structural data in conjunction with high-level DFT calculations, including corrections for dispersion effects, led to the conclusion that dispersion forces play a key role in stabilizing their acute interligand angles.
An experimental and DFT investigation of the mechanism of the coupling of methylisocyanide and C-... more An experimental and DFT investigation of the mechanism of the coupling of methylisocyanide and C-H activation mediated by the germylene (germanediyl) Ge(Ar Me6)2 (Ar Me6 = C6H2-2,6(C6H2-2,4,6-Me3)2) showed that it proceeded by initial MeNC adduct formation and sequential insertions of two MeNC molecules into a Ge-C bond. Insertion of a third MeNC leads to methylisocyanide methyl group C-H activation to afford an azagermacyclopentadienyl complex. The Xray crystal structures of the 1:1 (Ar Me6)2GeCNMe adduct, the first and final insertion products (Ar Me6)GeC(NMe)Ar Me6 and (Ar Me6)GeC(NHMe)C(NMe)C(Ar Me6)NMe were obtained. The DFT calculations on the reaction pathway represent the first detailed mechanistic study of isocyanide oligomerization by a p-block element species.
The mechanism of the reaction of olefins and hydrogen with dimetallenes ArMMAr (Ar = aromatic gro... more The mechanism of the reaction of olefins and hydrogen with dimetallenes ArMMAr (Ar = aromatic group; M = Al or Ga) was studied by density functional theory calculations and experimental methods. The digallenes, for which the most experimental data are available, are extensively dissociated to gallanediyl monomers :GaAr in hydrocarbon solution, but we found that they do not react as the more open dissociated The computational findings are in agreement with experimental observations that the digallene Ar iPr 4 GaGaAr iPr 4 (Ar iPr 4 = C6H3-2,6-(C6H3-2,6-i Pr2)2), reacts readily with two equivalents of olefin or hydrogen to give 1-4-digallacyclohexane or aryl gallium dihydride products, whereas the stable monomer, :GaAr iPr 8 (Ar iPr 8 = C6H-2,6-(C6H3-2,4,6i Pr3)2-3,5-i Pr2), does not react with ethylene or hydrogen. Calculations on the reaction of propene to ArAlAlAr show that, in contrast to the digallenes, addition involves an openshell transition state consistent with the higher singlet diradical character of dialuminenes.
High-resolution liquid-and solid-state 119 Sn NMR spectroscopy was used to study the bonding envi... more High-resolution liquid-and solid-state 119 Sn NMR spectroscopy was used to study the bonding environment in the series of monomeric, two-coordinate Sn(II) compounds of formula Sn(X)C 6 H 3-2,6-Trip 2 (X) Cl, Cr(η 5-C 5 H 5)(CO) 3 , t-Bu, Sn(Me) 2 C 6 H 3-2,6-Trip 2 ; Trip) C 6 H 2-2,4,6-i-Pr 3). The trends in the principal components of the chemical shift tensor extracted from the solid-state NMR data were consistent with the structures determined by X-ray crystallography. Furthermore, the spectra for the first three compounds displayed the largest 119 Sn NMR chemical shift anisotropies (up to 3798 ppm) of any tin compound for which data are currently available. Relaxation time based calculations for the dimetallic compound 2,6-Trip 2 H 3 C 6 Sn-Sn(Me) 2 C 6 H 3-2,6-Trip 2 suggests that the chemical shift anisotropy for the two-coordinate tin center may be as much as ca. 7098 ppm, which is as broad as the 1 MHz bandwidth of the NMR spectrometer.
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