Article pubs.acs.org/Organometallics
Germaester Complexes with a Ge(E)Ot-Bu Moiety (E = S or Se) Rahul Kumar Siwatch and Selvarajan Nagendran* Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India S Supporting Information *
ABSTRACT: Although germanium analogues of ketones, carboxylic acids, acid halides, and amides are known, an example of a germaester complex is still missing. Therefore, the first examples of germathioesters [(R)2ATI]Ge(S)Ot-Bu (R = t-Bu 5 and R = i-Bu 6) and germaselenoesters [(R)2ATI]Ge(Se)Ot-Bu (R = t-Bu 7 and R = i-Bu 8) stabilized through aminotroponiminate (ATI) ligands are reported here. Aminotroponiminatogermylene alkoxides [(t-Bu)2ATI]GeOt-Bu (3) and [(i-Bu)2ATI]GeOt-Bu (4) serve as starting materials for the synthesis of the aforementioned ester complexes. Compounds 5−8 were characterized by multinuclear NMR spectroscopic and single-crystal X-ray diffraction studies in the liquid and solid state, respectively. 77Se NMR spectra of compounds 7 and 8 showed a singlet resonance at −77.76 and −285.10 ppm, respectively. The germanium center in compounds 5−8 adopts a distorted tetrahedral geometry. The average GeS and GeSe bond lengths in germathioester (5 and 6) and germaselenoester (7 and 8) complexes are 2.078 and 2.219 Å, respectively.
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[η4-Me8taa]Ge with selenium and tellurium/PMe3, respectively (Me8taa = octamethyldibenzotetraaza[14]annulene).4 Tokitoh and co-workers isolated the kinetically stabilized germathione [Tbt(Tip)]GeS (IV) and germaselenone [Tbt(Tip)]GeSe (V) by the desulfurization and deselenation of tetrathiagermolane [Tbt(Tip)]GeS4 and tetraselenagermolane [Tbt(Tip)]GeSe 4 with PPh 3 , respectively (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl; Tip = 2,4,6-tris(isopropyl)phenyl).5a,b The same group also synthesized germatellurone [Tbt(R)]GeTe (R = Tip IIIb; Dis IIIc) by a reaction of germylene [Tbt(R)]Ge with elemental tellurium (Dis = bis(trimethysilyl)methyl).5c With the advent of functionalized germylene complexes with Ge−OH, Ge−Cl, and Ge−NR2 bonds2,6 the synthesis of stable germanium analogues of acids,7 acid halides,8 and amides9 has became possible using the abovementioned stabilization protocol, respectively. The oxidative addition reaction of germylene monohydroxide complex [HC{(CMe)(2,6-i-Pr2C6H3N)}2]GeOH with sulfur and selenium was exploited by Roesky and co-workers for the isolation of germathioacid [HC{(CMe)(2,6-i-Pr2C6H3N)}2]Ge(S)OH (VI) and germaselenoacid [HC{(CMe)(2,6-i-Pr2C6H3N)}2]Ge(Se)OH (VII) complexes, respectively.7a,b The groups of
INTRODUCTION Carbon, the first group 14 element, forms a double bond with oxygen (the first group 16 element), and this multiple bond is present in various organic compounds such as aldehydes, ketones, carboxylic acids, acid halides, esters, amides, lactones, lactams, enones, and quinones.1 Therefore, it is of basic interest to look at how the other group 14 elements behave in multiplebond formation with oxygen and its heavier analogues.2 In fact, the facile formation of double bonds by heavier analogues of carbon with chalcogens was encumbered by the polarity of ME bonds (where M is a heavier group 14 element and E is a chalcogen) ensuing in the spontaneous oligomerization or polymerization of the compounds containing such multiple bonds.2 A viable solution found to avert this issue concerning compounds with ME bonds (M = Si, Ge, Sn; E = S, Se, Te) is to protect such bonds kinetically with bulky substituents and/ or electronically through donor ligand systems at the heavier group 14 element centers.2 In the case of germanium, the donor ligand stabilized germathione complex [η3-{(μ-NtBu)2(SiMeNt-Bu)2}]GeS (I) was prepared by Veith and co-workers through the reaction of bis(amino)germanediyl [η3{(μ-Nt-Bu)2(SiMeNt-Bu)2}]Ge with sulfur.3 Parkin and coworker isolated the germaselenone [η4-Me8taa]GeSe (II) and germatellurone [η4-Me8taa]GeTe (IIIa) complexes by the reaction a four-coordinate germylene complex © 2012 American Chemical Society
Received: March 1, 2012 Published: April 9, 2012 3389
dx.doi.org/10.1021/om300173s | Organometallics 2012, 31, 3389−3394
Organometallics
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Synthesis of [(i-Bu)2ATI]GeOt-Bu (4). To a solution of [(iBu)2ATI]GeCl (2) (1.00 g, 2.95 mmol) in hexane (25 mL) was added KOt-Bu (0.33 g, 2.95 mmol) at −40 °C, and the mixture stirred. It was then allowed to come to room temperature, stirred for 12 h, and filtered through a G4 frit. Removal of hexane from the filtrate gave compound 4 as a red solid. Yield: 1.05 g (2.78 mmol), 94%. Mp: 55 °C. Anal. Calcd for C19H32GeN2O (M = 377.11): C, 60.51; H, 8.55; N, 7.43. Found: C, 60.44; H, 8.49; N, 7.45. 1H NMR (300 MHz, C6D6): δ 0.87 (d, 3JHH = 6.6 Hz, 6H, CH(CH3)2), 0.95 (d, 3JHH = 6.3 Hz, 6H, CH(CH3)2), 1.57 (s, 9H, C(CH3)3), 2.13−2.22 (m, 2H, CH(CH3)3), 3.27 (dd, 3JHH = 13.5, 7.2 Hz, 2H, CH2), 3.43 (dd, 3JHH = 13.5, 5.7 Hz, 2H, CH2), 6.17 (t, 3JHH = 9.3 Hz, 1H, CH), 6.31 (d, 3JHH = 11.4 Hz, 2H, CH), 6.71 (t, 3JHH = 10.4 Hz, 2H, CH). 13C{1H} NMR (75 MHz, C6D6): δ 21.24 (CH(CH3)2), 21.39 (CH(CH3)2), 27.76 (CH(CH3)2), 34.49 (C(CH3)3) 53.84 (CH2), 69.95 (C(CH3)3), 113.86 (C4), 119.47 (C2,6), 135.93 (C3,5), 160.87 (C1,7). Synthesis of [(t-Bu)2ATI]Ge(S)Ot-Bu (5). To a solution of 3 (0.50 g, 1.33 mmol) in THF (25 mL) was added elemental sulfur (0.043 g, 1.33 mmol) at room temperature, the mixture was stirred for 2 h, and all volatiles were removed under reduced pressure. The residue obtained was washed with hexane (15 mL) and dried to get compound 5 as a yellow solid. Single crystals of compound 5 suitable for X-ray diffraction studies were obtained by the slow evaporation of solvent from its chloroform solution. Yield: 0.53 g (1.30 mmol), 98%. Mp: 178 °C (dec). Anal. Calcd for C19H32GeN2OS (M = 409.15): C, 55.77; H, 7.88; N, 6.85. Found: C, 55.73; H, 7.90; N, 6.79. 1H NMR (300 MHz, CDCl3): δ 1.56 (s, 9H, C(CH3)3), 1.87 (s, 18H, C(CH3)3), 6.80 (t, 3 JHH = 8.7 Hz, 1H, CH), 7.22−7.36 (m, 4H, CH). 13C{1H} NMR (75 MHz, CDCl3): δ 30.60 (C(CH3)3), 32.99 (C(CH3)3), 58.49 (C(CH3)3), 77.79 (C(CH3)3), 118.42 (C4), 124.25 (C2,6), 136.02 (C3,5), 155.74 (C1,7). Synthesis of [(i-Bu)2ATI]Ge(S)Ot-Bu (6). To a solution of 4 (0.40 g, 1.06 mmol) in THF (20 mL) was added elemental sulfur (0.034 g, 1.06 mmol) at room temperature, the mixture was stirred for 2 h, and all volatiles were removed under reduced pressure. The residue obtained was washed with hexane (15 mL) and dried to get compound 6 as a yellow solid. Single crystals of compound 6 suitable for X-ray diffraction studies were obtained by the slow evaporation of solvent from its THF solution. Yield: 0.43 g (1.04 mmol), 98%. Mp: 100 °C (dec). Anal. Calcd for C19H32GeN2OS (M = 409.15): C, 55.77; H, 7.88; N, 6.85. Found: C, 55.70; H, 7.86; N, 6.71. 1H NMR (300 MHz, CDCl3): δ 1.05 (d, 3JHH = 6.6 Hz, 12H, CH(CH3)2), 1.50 (s, 9H, C(CH3)3), 2.33−2.42 (m, 2H, CH(CH3)2), 3.54 (dd, 3JHH = 13.8, 7.2 Hz, 2H, CH2), 3.67 (dd, 3JHH = 14.1, 6.3, 2H, CH2), 6.86 (t, 3JHH = 9.3 Hz, 1H, CH), 6.97 (d, 3JHH = 11.1 Hz, 2H, CH), 7.40 (t, 3JHH = 10.4 Hz, 2H, CH). 13C{ 1H} NMR (75 MHz, CDCl3): δ 21.23 (CH(CH3)2), 27.71 (CH(CH3)2), 32.50 (C(CH3)3), 53.32 (CH2), 75.17 (C(CH3)3), 116.38 (C4), 124.98 (C2,6), 138.15 (C3,5), 156.71 (C1,7). Synthesis of [(t-Bu)2ATI]Ge(Se)Ot-Bu (7). To a solution of 3 (0.50 g, 1.33 mmol) in THF (25 mL) was added selenium powder (0.11 g, 1.33 mmol) at room temperature, and the mixture was stirred for 6 h and filtered through a G4 frit. All volatiles from the filtrate were removed in vacuo to afford compound 7 as a yellow solid. Single crystals of compound 7 suitable for X-ray diffraction studies were obtained by the slow evaporation of solvent from its THF solution. Yield: 0.59 g (1.29 mmol), 97%. Mp: 186 °C (dec). Anal. Calcd for C19H32GeN2OSe (M = 456.04): C, 50.04; H, 7.07; N, 6.14. Found: C, 49.96; H, 7.01; N, 6.21. 1H NMR (300 MHz, CDCl3): δ 1.51 (s, 9H, C(CH3)3), 1.82 (s, 18H, C(CH3)3), 6.72 (t, 3JHH = 8.7 Hz, 1H, CH), 7.14−7.30 (m, 4H, CH). 13C{1H} NMR (75 MHz, CDCl3): δ 30.84 (C(CH3)3), 33.00 (C(CH3)3), 58.65 (C(CH3)3), 78.16 (C(CH3)3), 118.64 (C4), 124.35 (C2,6), 135.85 (C3,5), 155.50 (C1,7). 77Se{1H} NMR (57 MHz, CDCl3, Me2Se): δ −77.76 (GeSe). Synthesis of [(i-Bu)2ATI]Ge(Se)Ot-Bu (8). To a solution of 4 (0.40 g, 1.10 mmol) in THF (20 mL) was added selenium powder (0.08 g, 1.10 mmol) at room temperature, and the mixture was stirred for 6 h and filtered through a G4 frit. All volatiles were then removed from the filtrate under reduced pressure to result in compound 8 as a yellow solid. Single crystals of compound 8 suitable for X-ray
Barrau and Roesky described the synthesis of germaacid chloride complexes [HC{(CMe)(C6H5N)}2]Ge(E)Cl (E = S VIII; E = Se IX) and [HC{(CMe)(2,6-i-Pr2C6H3N)}2]Ge(E) Cl (E = S X; E = Se XI), respectively.8a,c Compounds VIII and IX were obtained by the reaction of the β-diketiminatogermylene monochloride [HC{(CMe)(C6H5N)}2]GeCl with sulfur and selenium, respectively. Oxidative addition reaction of the germylene monochloride complex [HC{(CMe)(2,6-iPr2C6H3N)}2]GeCl with sulfur and selenium afforded compounds X and XI, respectively. The germathioamide [{tBuN(CH2)2Nt-Bu}Si(Me)N(t-Bu)]Ge(S)N(TMS)2 (XII) and germaselenoamide [(R)C(NCy)2]Ge(Se)N(TMS)2 (R = t-Bu XIII; R = Me XIV) complexes were reported by the groups of Veith and Richeson, respectively (TMS = trimethylsilyl; Cy = cyclohexyl).9a,b The reaction of germylene hexamethyldisilazide complex [{t-BuN(CH2)2Nt-Bu}Si(Me)N(t-Bu)]GeN(TMS)2 with sulfur resulted in compound XII. The germaselenoamides XIII and XIV were obtained by the reaction of germylene hexamethyldisilazide complexes [(t-Bu)C(NCy)2]GeN(TMS)2 and [(Me)C(NCy)2]GeN(TMS)2 with selenium, respectively. These discussions portray the synthetic route for the isolation of germanium analogues of ketones, carboxylic acids, acid chlorides, and amides. Nevertheless, to the best of our knowledge there is no structurally characterized example of a germaester complex. Therefore, we report herein the successful synthesis and characterization of the first examples of germathio- (5 and 6) and germaselenoesters (7 and 8) that contain aminotroponiminate (ATI) ligands10 for their stability. As starting materials for these ester complexes 5−8, we also furnish here the details regarding the synthesis and characterization of hitherto unknown ATI ligand stabilized germylene alkoxides 3 and 4. Although germylene alkoxides stabilized by other ligand systems are known,6c,11 their oxidative addition reactions for the synthesis of germaester complexes have never been pursued.2
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EXPERIMENTAL SECTION
The synthesis and handling of air- and moisture-sensitive compounds were performed under a dry dinitrogen atmosphere using either standard Schlenk or glovebox techniques [Jacomex (GP Concept)-T2 workstation]. Solvents for synthesis and NMR spectroscopic studies were dried by conventional procedures. Sulfur, selenium, and potassium tert-butoxide were purchased from Aldrich and used without any further purification. Compounds 112 and 213 were synthesized according to literature procedures. Melting points were recorded using an Ambassador melting point apparatus by sealing the samples in glass capillaries, and the reported melting points are uncorrected. Elemental analyses were performed using a Perkin-Elmer CHN analyzer. Multinuclear NMR spectroscopic studies were carried out on a 300 MHz Bruker Topspin NMR spectrometer using dry CDCl3 or C6D6. The chemical shifts δ are reported in ppm and are referenced internally with respect to the residual solvent (1H NMR) and solvent (13C NMR) resonances.14 Synthesis of [(t-Bu)2ATI]GeOt-Bu (3). To a solution of [(tBu)2ATI]GeCl (1) (1.50 g, 4.42 mmol) in hexane (40 mL) was added KOt-Bu (0.50 g, 4.42 mmol) at −40 °C, and the mixture stirred. It was then allowed to come to room temperature, stirred for 12 h, and filtered through a G4 frit. Removal of hexane from the filtrate afforded compound 3 as a red solid. Yield: 1.62 g (4.30 mmol), 97%. Mp: 78 °C. Anal. Calcd for C19H32GeN2O (M = 377.11): C, 60.51; H, 8.55; N, 7.43. Found: C, 60.39; H, 8.47; N, 7.50. 1H NMR (300 MHz, C6D6): δ 1.56 (s, 9H, C(CH3)3), 1.61 (s, 18H, C(CH3)3), 6.22 (t, 3JHH = 8.7 Hz, 1H, CH), 6.67−6.81 (m, 4H, CH). 13C{1H} NMR (75 MHz, C6D6): δ 30.86 (C(CH3)3), 34.41 (C(CH3)3), 56.30 (C(CH3)3), 70.94 (C(CH3)3), 117.49 (C4), 119.24 (C2,6), 133.92 (C3,5), 160.24 (C1,7). 3390
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diffraction studies were obtained by the slow evaporation of solvent from its THF solution. Yield: 0.47 g (1.04 mmol), 98%. Mp: 110 °C (dec). Anal. Calcd for C19H32GeN2OSe (M = 456.04): C, 50.04; H, 7.07; N, 6.14. Found: C, 49.90; H, 7.11; N, 6.22. 1H NMR (300 MHz, CDCl3): δ 1.05 (d, 3JHH = 6.6 Hz, 12H, CH(CH3)2), 1.50 (s, 9H, C(CH3)3), 2.35−2.44 (m, 2H, CH(CH3)3), 3.53 (dd, 3JHH = 14.1, 7.5 Hz, 2H, CH2), 3.69 (dd, 3JHH = 14.1, 6.0 Hz, 2H, CH2), 6.84 (t, 3JHH = 9.3 Hz, 1H, CH), 6.95 (d, 3JHH = 11.1 Hz, 2H, CH), 7.40 (t, 3JHH = 10.4 Hz, 2H, CH). 13C{1H} NMR (75 MHz, CDCl3): δ 21.27 (CH(CH3)2), 27.69 (CH(CH3)2), 32.73 (C(CH3)3), 53.23 (CH2), 75.47 (C(CH3)3), 116.45 (C4), 125.00 (C2,6), 137.95 (C3,5), 156.61 (C1,7). 77Se{1H} NMR (57 MHz, CDCl3, Me2Se): δ −285.10 (Ge Se). X-ray Data Collection for Compounds 5−8. Suitable single crystals of compounds 5 and 6−8 were grown by slowly evaporating their chloroform and THF solutions, respectively. The crystals were coated with a layer of cryoprotectant and mounted on a glass fiber. All the data were collected on a Bruker SMART APEX CCD diffractometer with Mo Kα radiation (λ = 0.71073 Å) at room temperature.15 SAINT and SADABS were used for data integration and empirical absorption correction, respectively.16 The structures were solved and refined by direct methods and full matrix least-squares on F2 by means of the crystallographic software SHELXTL, respectively.17 All the non-hydrogen atoms were anisotropically refined. The positions of hydrogen atoms were calculated using a riding model and refined isotropically. Important crystallographic details regarding these compounds are provided in Table S1 (see Supporting Information).
Scheme 2. Synthesis of Germaester Complexes 5−8
reaction of compounds 3 and 4 with elemental selenium for 6 h at room temperature in tetrahydrofuran afforded yellowcolored germaselenoester complexes 7 and 8 in about 97% yield, respectively (Scheme 2). Compounds 5−8 are the first examples of germaester complexes irrespective of the ligand used for stabilization. The germaester complexes 5−8 are stable at room temperatures in an inert atmosphere and are soluble in polar organic solvents such as chloroform, dichloromethane, and tetrahydrofuran. Compounds 3−8 were characterized by means of multinuclear NMR spectroscopy (1H, 13C, and 77Se). As anticipated, the 1H NMR spectra of compounds 3−8 displayed a sharp singlet for the tert-butoxide group in the range from 1.50 to 1.57 ppm. The tert-butyl groups present on the nitrogen atoms in compounds 3 (1.61 ppm), 5 (1.87 ppm), and 7 (1.82 ppm) appear as a singlet and indicate their chemically equivalent nature. The isobutyl groups on the nitrogen atoms in compound 4 gave five resonances and can be accounted for in the following manner: two doublets for the methyl protons, one multiplet for the methine proton, and two double doublets for the diastereotopic methylene protons. In compounds 6 and 8, the aforementioned pattern is retained except for the methyl protons, which appear as a single doublet. These features are supportive of the chemically nonequivalent nature of the isobutyl substituents in compounds 4, 6, and 8. One triplet and a multiplet in the integral ratio of 1:4 have been observed for the five C7 seven-membered-ring protons in the 1H NMR spectra of compounds 3, 5, and 7. Nevertheless, the five C7 seven-membered-ring protons in compounds 4, 6, and 8 appear as one triplet, doublet, and double doublet that merge into a triplet, in the intensity ratio of 1:2:2. In the 13C NMR spectra of compounds 3−8, two and four singlets anticipated for the tertbutoxide and C7 seven-membered-ring carbon atoms were seen clearly. The tert-butyl (in compounds 3, 5, and 7) and isobutyl (in compound 4) groups were seen as two and four singlets in their 13 C NMR spectra, respectively. Nevertheless, in compounds 6 and 8, three singlets were seen for the isobutyl substituents. In the 77Se NMR spectra of compounds 7 and 8, a singlet resonance due to the selenium center was detected at −77.76 and −285.10 ppm, respectively. These values are downfield shifted against the 77Se NMR resonance (−439 ppm) found for the β-diketiminatogermaselenoacid, [HC{(CMe)(2,6-i-Pr2C6H3N)}2]Ge(Se)OH.7b For the compound (H3Ge)2Se with a Ge−Se single bond, a 77Se NMR resonance has been observed at −612 ppm.18 Tokitoh and co-workers' germaselenones [Tbt(Tip)]GeSe and [Tbt(Dis)]GeSe, with an unperturbed GeSe bond, have shown signals at 941 and 872 ppm in their 77Se NMR spectra, respectively.5 The position of the 77Se NMR resonances for the germaselenoesters 7 and 8 in between the corresponding values found for (H3Ge)2Se and Tokitoh’s germaselenones can be taken as an indication of the presence of a polarized GeSe bond in these
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RESULTS AND DISCUSSION Synthesis and Spectra. An equimolar reaction of germylene monochloride complex 1 with KOt-Bu in hexane at low temperatures resulted in an analytically pure sample of ATI ligand stabilized germylene alkoxide 3 as a red solid in 97% yield (Scheme 1). Repetition of the aforementioned reaction Scheme 1. Synthesis of Aminotroponiminatogermylene Alkoxide Complexes 3 and 4
with compound 2 (in place of 1) afforded aminotroponiminatogermylene alkoxide 4 as a red solid in about 94% yield (Scheme 1). Germylene alkoxide complexes stabilized by other ligand systems have been isolated by the groups of Jutzi, Barrau, Roesky, Fulton, and Zhu through a general synthetic route that uses a germylene monochloride complex and metal alkoxide.6c,11 The synthesis of compounds 3 and 4 also follows this methodology. Compounds 3 and 4 are freely soluble in common nonchlorinated organic solvents such as hexane, toluene, and tetrahydrofuran and are stable in the absence of air and moisture. Additionally, compound 4 starts to decompose very slowly at room temperature, and therefore we have used a −35 °C deep freezer for its extended storage of more than two days. Oxidative addition reaction of aminotroponiminatogermylene alkoxides 3 and 4 with elemental sulfur at room temperature for 2 h in tetrahydrofuran resulted in the desired germathioester complexes 5 and 6 as yellow solids in nearly quantitative yields, respectively (Scheme 2). Similarly, the 3391
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compounds. Therefore, the actual structure of these compounds can be described by a resonance hybrid of the canonical forms (i) and (ii) shown in Scheme 3. Scheme 3. Canonical Forms [(i) and (ii)] of Germaselenoester Complexes (7 and 8)
X-ray Crystal Structure of Compounds 5−8. All the compounds (5−8) crystallized in a monoclinic space group P21/n and are monomeric. The germanium center in these compounds is four-coordinate and adopts a distorted tetrahedral geometry. In compounds 5 (Figure 1) and 6
Figure 2. Molecular structure of germaselenoester complex 8. Thermal ellipsoids are drawn at the 40% probability level. All hydrogen atoms are omitted for clarity.
relationship to the length of the GeS bond in Tbt(Tip)GeS is illustrative of a polarized GeS bond in them.5 Therefore, the canonical forms analogous to those shown in Scheme 3 can explain the nature of the GeS bond in germathioester complexes 5 and 6 also. A trend that is similar is also seen with respect to the length of the GeSe bond in germaselenoester complexes 7 [(2.2193(7) Å] and 8 [(2.218(1) Å]. These values are near the length of the Ge Se double bond [2.18(2) Å] present in the kinetically stabilized germaselenone Tbt(Tip)GeSe and considerably shorter than the Ge−Se single bond [2.433(1) Å] in [Tbt(Mes)GeSe]2 (Mes = 2,4,6-trimethylphenyl).5 This feature gives supplementary support to the description of the structure of germaselenone complexes 7 and 8 by a resonance hybrid of forms (i) and (ii) (Scheme 3) based on NMR studies (vide supra). The average Ge−N bond length in compounds with tertbutyl (5 and 7: 1.920 Å) and isobutyl (6 and 8: 1.884 Å) substituents on the nitrogen atoms is within the expected range.2 The E−Ge−O bond angle in germaester complexes containing tert-butyl (5 and 7: 122.1av°) and isobutyl (6 and 8: 123.3av°) substituents compares well with the E−Ge−O angle of 121.4(1)° found in compounds [HC{(CMe)(2,6-iPr2C6H3N)}2]Ge(E)OH (E = S or Se).7 When tert-butyl substituents are present on the nitrogen atoms of the ATI ligand backbone (as in compounds 5 and 7), the puckering of the fused C7 seven-membered and C2N2Ge five-membered rings (Figure S3; see Supporting Information) determined as the dihedral angle between their mean planes is high [21.1(1)° and 20.85 (1)°, respectively]. In germaester complexes 6 and 8, nevertheless, due to the flexible nature of the isobutyl substituents, the dihedral angle between the aforementioned ring systems is considerably less, with a magnitude of 4.6(2)° and 4.6(1)°, respectively (Figure S3; see Supporting Information). In summary, we have demonstrated the feasible isolation of germaesters 5−8 in excellent yields through the stabilization offered by aminotroponiminate ligands. Theoretical, electronic
Figure 1. Molecular structure of germathioester complex 5. Thermal ellipsoids are drawn at the 40% probability level. All hydrogen atoms are omitted for clarity.
(Figure S1; see Supporting Information), the immediate environment around the germanium center contains two nitrogen, one sulfur, and one oxygen atom. A similar environment with a selenium atom instead of a sulfur atom is seen around the germanium center in compounds 7 (Figure S2; see Supporting Information) and 8 (Figure 2). The Ge−O bond distance in compounds 5 [1.768(4) Å], 6 [1.765(4) Å], and 7 [1.767(3) Å] is almost the same, and the corresponding bond distance in compound 8 [1.774(3) Å] is slightly longer. Nevertheless, in comparison to the length of the Ge−O bond present in compounds [HC{(CMe)(2,6-i-Pr2C6H3N)}2]Ge(S)OH [1.751(2) Å] and [HC{(CMe)(2,6-i-Pr2C6H3N)}2]Ge(Se)OH [1.756(1) Å],7 the Ge−O bond in compounds 5−8 is longer (vide supra). The GeS bond length in compounds 5 and 6 is 2.076(1) and 2.080(2) Å, respectively. The unperturbed GeS bond [2.049(3) Å] in Tokitoh’s germathione Tbt(Tip)GeS and the Ge−S bond [2.239(1) Å] in Meller’s tetravalent germanium compound [{(TMS)2C(2-py)}{(TMS)C(2-py)}]GeS(TMS) help in ascertaining the nature of the GeS bond in compounds 5 and 6 (py = pyridyl).5,19 A closer but slightly longer value of the GeS bond length in germathioester complexes (5 and 6) in 3392
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Table 1. Selected Bond Lengths (Å) and Angles (deg) for Compounds 5−8 Compound 5 Ge(1)−S(1) Ge(1)−O(1) Ge(1)−N(1) Ge(1)−N(2)
2.076(1) 1.768(4) 1.917(4) 1.919(4)
S(1)−Ge(1)−O(1) S(1)−Ge(1)−N(1) S(1)−Ge(1)−N(2) N(1)−Ge(1)−N(2) Compound 6
121.9(1) 121.6(1) 116.4(1) 84.7(1)
Ge(1)−S(1) Ge(1)−O(1) Ge(1)−N(1) Ge(1)−N(2)
2.080(2) 1.765(4) 1.880(5) 1.878(5)
S(1)−Ge(1)−O(1) S(1)−Ge(1)−N(1) S(1)−Ge(1)−N(2) N(1)−Ge(1)−N(2) Compound 7
123.1(2) 116.4(2) 117.9(2) 84.2(2)
Ge(1)−Se(1) Ge(1)−O(1) Ge(1)−N(1) Ge(1)−N(2)
2.2193(7) Se(1)−Ge(1)−O(1) 1.767(3) Se(1)−Ge(1)−N(1) 1.926(3) Se(1)−Ge(1)−N(2) 1.916(3) N(1)−Ge(1)−N(2) Compound 8
Ge(1)−Se(1) Ge(1)−O(1) Ge(1)−N(1) Ge(1)−N(2)
2.218(1) 1.774(3) 1.894(3) 1.882(3)
Se(1)−Ge(1)−O(1) Se(1)−Ge(1)−N(1) Se(1)−Ge(1)−N(2) N(1)−Ge(1)−N(2)
122.2(1) 116.4(1) 121.5(1) 85.0(1) 123.39(9) 115.6(1) 118.82(9) 84.3(1)
spectroscopic, and reactivity studies on these compounds are in progress and will be published elsewhere.
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ASSOCIATED CONTENT
S Supporting Information *
Crystal data and structural refinement parameters for compounds 5−8 (Table S1), molecular structure of compounds 6 and 7 (Figures S1 and S2, respectively), lateral view of the molecular structure of compounds 5−8 through the common C1−C7 bond axis (Figure S3), and crystallographic information file (CIF) for compounds 5−8. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Phone: +91-11-2659 1523. Fax: +91-11-2658 1102. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS R.K.S. thanks the Council of Scientific and Industrial Research (CSIR), New Delhi, India, for a Senior Research Fellowship. S.N. thanks the Department of Science and Technology (DST), New Delhi, India, for financial support (SR/S1/IC23/2008). S.N. also thanks DST-FIST for providing financial support to the Department of Chemistry, IIT Delhi, New Delhi, India, for establishing the single-crystal X-ray diffractometer facility.
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DEDICATION Dedicated to Prof. Dr. Dr. h.c. mult. Herbert W. Roesky. REFERENCES
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