[Show abstract][Hide abstract] ABSTRACT: Digermene, the germanium analogue of ethylene, has a multiple bonding
motif that differs greatly from that of alkenes and exhibits no pure
σ or π type bonds. The electronic structure of digermenes is
difficult to study experimentally due to their reactivity, and is
computationally challenging because of their shallow potential energy
surfaces. Using X-ray absorption near edge structures at both the
germanium K and L edges we have been able to directly probe the
unoccupied electronic states, or the lowest unoccupied molecular orbital
(LUMO), and LUMO+ etc. in the Ge=Ge bond of tetramesityldigermene. We
have demonstrated that the LUMO, LUMO+, etc. are composed of hybrid Ge
4s and 4p orbitals. Additionally, our data suggest that the LUMO
exhibits relatively more Ge 4s character, whereas the LUMO+ and LUMO+2
exhibit relatively more Ge 4p character. An X-ray excited optical
luminescence study of Ge2Mes4 revealed one broad
optical emission band at 620 nm, which is significantly red shifted
compared to the known energy gap of this molecular germanium compound.
Journal of Physics Conference Series 05/2013; 430(1). DOI:10.1088/1742-6596/430/1/012046
[Show abstract][Hide abstract] ABSTRACT: A series of cationic cryptand complexes of tin(II), [Cryptand[2.2.2]SnX][SnX(3)] (10, X = Cl; 11, X = Br; 12, X = I) and [Cryptand[2.2.2]Sn][OTf](2) (13), were synthesized by the addition of cryptand[2.2.2] to a solution of either tin(II) chloride, iodide, or trifluoromethanesulfonate. The complexes could also be synthesized by the addition of the appropriate trimethylsilyl halide (or pseudohalide) reagent to a solution of tin(II) chloride and cryptand[2.2.2]. The complexes were characterized using a variety of techniques including NMR, Raman, and temperature-dependent Mössbauer spectroscopy, mass spectrometry, and X-ray diffraction.
[Show abstract][Hide abstract] ABSTRACT: The reaction of the anionic gallium(I) N-heterocyclic carbene (NHC) analogue 3 with the solution stable digermene 5 results in the formation of the gallium NHC – germylene complex 8. The gallium NHC – germylene complex 8 was derivatized with CH3I and (CH3)3SiCl.Key words: digermene, carbene analogue, germylene, gallium(I).
Canadian Journal of Chemistry 02/2011; 85(2):141-147. DOI:10.1139/v07-002 · 1.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The chemistry of three N-heterocyclic carbene (NHC) complexes of GeR2, where R = Cl (1), OtBu (2), Mes (3) (Mes = 2,4,6-trimethylphenyl), toward 2,3-dimethylbutadiene (DMB), 3,5-di-tert-butylorthoquinone, methyl iodide, pivalic acid, and benzophenone is reported. Upon heating, 2 and 3 cyclize with DMB to yield a germacyclopentene and free NHC. In contrast, 1 does not react with DMB. PB1PBE/6-311+G(d,p) model chemistry shows that the cycloaddition reactions of NHC-GeX2 (X = F, Cl) with butadiene are not thermodynamically favorable. 3,5-Di-tert-butylorthoquinone reacts rapidly with 1−3 to form cyclic products; in the case of 1 and 2, the NHC remains coordinated to the germanium, resulting in a hypervalent species. Compounds 1−3 react with methyl iodide by displacement of I−; in each case [NHC-GeR2Me]+ is produced. Only compound 3 reacts in a controlled fashion with pivalic acid; both 1:1 and 1:2 adducts were characterized. Benzophenone failed to react with 1 or 2 but did undergo cycloaddition with 3. In comparison with uncomplexed GeR2 species, the NHC-GeR2 complexes are less reactive. The prospect of using NHC-GeR2 as a synthon for GeR2 appears to be reaction specific.
[Show abstract][Hide abstract] ABSTRACT: Measurement of the ionic nature of [Ge(cryptand[2.2.2])](2+) by XANES has provided direct experimental evidence that the germanium center is best described as a nearly-naked dication encased within an electron rich cryptand cage.
Chemical Communications 10/2010; 46(37):7016-8. DOI:10.1039/c0cc01925a · 6.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The ultrahigh field natural abundance (73)Ge solid-state wide-line NMR study of germanium dichloride complexed with 1,4-dioxane and tetraphenylgermane yields the largest (73)Ge quadrupolar coupling constant determined by NMR spectroscopy to date and the first direct observation of (73)Ge chemical shift anisotropy.
Chemical Communications 04/2010; 46(16):2817-9. DOI:10.1039/b926071d · 6.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A series of N-heterocyclic carbene (NHC) complexes of Ge(II) were synthesized and structurally characterized. Unlike previous observations, the carbenic carbon−germanium bond length does not vary systematically with the electronic demands of the substituents on the germanium center. Computational analysis of the energetic and structural metrics of model compounds is consistent with a lack of a substituent effect on the carbenic carbon−germanium bond length.
[Show abstract][Hide abstract] ABSTRACT: Fit for a king: Cationic complexes of Ge(II) can be prepared by using crown ethers to stabilize and protect the germanium center. Three different crown ethers were employed: crown-4 (see structure, Ge teal, O red, C gray), crown-5, and crown-6. The structures of the cationic complexes depend on the cavity size of the crown ether and on the substituent on germanium.
[Show abstract][Hide abstract] ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
[Show abstract][Hide abstract] ABSTRACT: Unlike cations of metals such as sodium or calcium, oxidized silicon and germanium centers generally require strongly bound covalent ligands. We report the synthesis and characterization of a germanium(II) dication in the form of the salt (Ge.cryptand[2.2.2])(O3SCF3)2. The salt is isolated in 88% yield from the reaction of cryptand [2.2.2] and an N-heterocyclic carbene complex of GeCl(O3SCF3) as an air-sensitive, white solid. The crystal structure of the salt shows minimal interaction between the cryptand-encapsulated germanium(II) ion and the two -O3SCF3 counterions. These results suggest a widely expanded role of cryptands and related molecules in stabilizing nonmetallic cations.
[Show abstract][Hide abstract] ABSTRACT: The synthesis and structural characterization of a series of N-heterocyclic carbene (NHC) complexes of GeR1R2 are reported, where R1 = R2 = Mes (Mes = 2,4,6-trimethylphenyl) (1), R1 = R2 = F (5), R1 = R2 = Br (6), R1 = Cl, R2 = OTf (OTf = O3SCF3) (7), R1 = R2 = OtBu (10), and R1 = R2 = NCS (11). The bond length between the carbenic carbon and the germanium is observed to vary in accordance with the π-donating ability of the substituent on Ge. Efforts to synthesize stable complexes with small alkyl or aryl substituents were not successful; evidence for oligomerization of the GeR2 fragment is presented. The reaction between 1 and 3 (R1 = R2 = Cl) resulted in the formation of an NHC-coordinated germylgermylene (13). The 1H NMR spectra of 3−7, 10, and 11 display broad signals at room temperature. To rationalize the 1H NMR spectra, mechanisms for conformational interchange, as well as intermolecular exchanges, are discussed.
[Show abstract][Hide abstract] ABSTRACT: The dicationic 4(2+) complex with three N-heterocyclic carbenes coordinated to a germanium center is reported. The complex was characterized by H-1 NMR and FT Raman spectroscopy, and the structure was determined by single-crystal X-ray diffraction. Electronic structure calculations reveal a partial positive charge at germanium and that the germanium lone pair shows no evidence for pi bonding.
Journal of the American Chemical Society 01/2008; 129(49):15138-9. DOI:10.1021/ja0775725 · 11.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Tetramesityldigermene (1) can be synthesized cleanly and quantitatively by photolysis of hexamesitylcyclotrigermane (2) in THF at low temperature. A solution of tetramesityldigermene (1) in THF is stable for several weeks at room temperature; the digermene does not dissociate or rearrange. The molecular structure of tetramesityldigermene (1) has been determined using X-ray crystallography. The effectiveness of the new protocol for the synthesis of tetramesityldigermene (1) and its derivatives has been demonstrated in the study of the addition of carboxylic acids to tetramesityldigermene (1).
[Show abstract][Hide abstract] ABSTRACT: The synthesis of a carbene-stabilized transient germylene is presented; the resulting complex liberates free germylene upon heating, forms a stable adduct with BH3, and reacts with MeLi to displace the carbene.