Reactivity Study of a Pyridyl-1-azaallylgermanium(I) Dimer: Synthesis

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Reactivity Study of a Pyridyl-1-azaallylgermanium(I) Dimer: Synthesis of Heavier Ether and Ester Analogues of Germanium Wing-Por Leung,*,† Yuk-Chi Chan,‡,§ Cheuk-Wai So,‡ and Thomas C. W. Mak§ †

School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, China Division of Chemistry and Biological Chemistry, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore § Department of Chemistry, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China ‡

S Supporting Information *

ABSTRACT: The reactivity study of a pyridyl-1-azaallylgermanium(I) dimer LGe−GeL [1; L = N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)] with different stoichiometric ratios of elemental selenium and tellurium is described. The reactions of 1 with 1 equiv of selenium and tellurium afforded the first examples of heavier ether analogues of germanium, bis(germylene) selenide and telluride LGe(μ-E)GeL [E = Se (2) and Te (3)], respectively. Meanwhile, the reactions of 1 with 2 equiv of selenium and tellurium gave the heavier ester analogues LGe E(μ-E)GeL [E = Se (4) and (5)]. All compounds have been characterized by X-ray crystallography and multinuclear NMR spectroscopy.

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INTRODUCTION Stable heavier alkyne analogues (REER) of group 14 elements (E = Si, Ge, Sn, or Pb; R = alkyl or aryl groups) have attracted much attention in the past decade.1−4 In 2002, Power and co-workers reported the first example of digermyne RGeGeR (A; R = C6H3-2,6-Dipp2) from the reduction of Ge(Cl)C6H3-2,6-Dipp2 with potassium.2a Inspired by this work, other examples of multiply bonded digermynes2b,c,5 and a series of novel base-stabilized analogues, which are germanium(I) dimers, supported by amidinate (C),6 guanidinate (C),6a βdiketiminate (D),7 pyridyl-1-azaallyl (E),8 amido (F),9 2,6diiminophenyl (G),10 2-imino-5,6-methylenedioxylphenyl (H)10 and 1-(diethylamino)methyl-3,5-di-tert-butylphenyl (I)11 ligands have been synthesized and structurally characterized (Figure 1). The striking difference in Power’s (A) and Tokitoh’s (B)2 digermynes with other germanium(I) dimers is the bond length of the central Ge−Ge bond. X-ray diffraction studies of digermynes reveal the Ge−Ge bond lengths of 2.206−2.307 Å being shorter than the Ge−Ge bond lengths of 2.570−2.709 Å in the germanium(I) dimers. This suggests that multiple bonding is present in digermyne, whereas the germanium(I) dimer comprises a Ge−Ge single bond with a stereoactive lone pair on each germanium center. In addition, the multiple-bond character of the digermyne was supported by theoretical calculations.12 It is worth noting that digermynes adopt a transbent geometry, while germanium(I) dimers possess either trans- or gauche-bent geometry. The reactivity studies of digermynes have been well documented;13 however, those of germanium(I) dimers are still underexplored. Roesky and co© XXXX American Chemical Society

Figure 1. Structurally characterized digermynes and germanium(I) dimers.

workers reported the reactivity of an amidinate-stabilized germanium(I) dimer toward azobenzene and Fe2(CO)9 to Received: January 6, 2016

A

DOI: 10.1021/acs.inorgchem.6b00026 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

mechanism for the synthesis of 4 or 5 via an insertion reaction, followed by an oxidative addition reaction. Furthermore, it also verifies the proposed mechanism for the formation of LGe(S)(μ-S)Ge(S)L from 1 with excess sulfur.8 Attempts to prepare diseleno- and ditellurocarboxylic acid anhydride from the reactions of 1 with 3 equiv or excess selenium/tellurium were not successful, and only 4 or 5 can be obtained. Recently, Jambor and co-workers have also reported the stepwise oxidation of distannyne [2,6-(Me2NCH2)2C6H3Sn]2 with different stoichiometric ratios of selenium and tellurium, giving the insertion products and oxidative addition products, which also illustrated that the SnI−SnI bond is easily cleaved by chalcogens to produce the insertion products.19 X-ray Structures. The molecular structures of compounds 2−5 are shown in Figures 2−5, respectively. Compounds 2 and

give the oxidative addition product R′GeN(Ph)N(Ph)GeR′ [R′ = PhC(tBuN)2] and the Lewis acid−base adduct R′Ge[Fe(CO)4]Ge[(Fe(CO)4]R′, in which the former product involves cleavage of the Ge−Ge bond.14 So and co-workers reported the synthesis of germylidenide anions from the reduction of the 2,6-diiminophenyl- or 2imino-5,6-methylenedioxylphenyl-stabilized germanium(I) dimer with potassium graphite.10 More recently, Jones et al. reported the facile activation of small molecules, e.g., dihydrogen, carbon dioxide, olefins, etc., by the amidodigermyne.9,15,16 The unprecedented amidodigermyne is due to the very narrow HOMO−LUMO energy gap. We have communicated the synthesis of a germanium analogue of dithiocarboxylic acid from the reaction of a pyridyl-1-azaallylgermanium(I) dimer with excess sulfur.8 The reactions toward azobenzene and Fe2(CO)9 were also reported recently.17 It would be of interest to further investigate the reactivity of the germanium(I) dimer for fundamental reasons and for potential applications in small-molecule activations. Herein, we report the reactivity study of the pyridyl-1-azaallylgermanium(I) dimer LGe−GeL [1; L = N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)] with different stoichiometric ratios of elemental selenium and tellurium, leading to the formation of the first examples of heavier ether and ester analogues of germanium.

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RESULTS AND DISCUSSION Reactions of 1 with 1 equiv of selenium and tellurium in the absence of light afforded the insertion products bis(germylene) selenide and telluride LGe(μ-E)GeL [E = Se (2) and Te (3); Scheme 1], respectively.. Compound 3 can be considered as the Scheme 1. Reactions of 1 toward Selenium and Tellurium Figure 2. Molecular structure of 2 (30% ellipsoid probability). Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ge1−Se1 2.417(3), Ge2−Se1 2.453(4), Ge1−N1 1.957(2), Ge1−N2 2.041(2), Ge2−N3 1.946(2), Ge2−N4 2.068(2); Ge1−Se1−Ge2 88.8(1), N1−Ge1−N2 86.0(8), N1−Ge1−Se1 98.9(6), N2−Ge1−Se1 95.6(6), N3−Ge2−N4 86.9(8), N3−Ge2− Se1 99.9(6), N4−Ge2−Se1 91.0(6).

3 are the first examples of structurally characterized bis(germylene) selenide and telluride complexes (Figures 2 and 3). The Ge1−Se1 [2.417(3) Å] and Ge2−Se2 [2.453(4) Å] bond lengths in 2 are similar and comparable to those fourcoordinate germanium(IV) compounds containing a Ge−Se single bond in [Tbt(Mes)Ge(μ-Se)]2 [2.397(1) and 2.433(1) Å],20 [RGe(μ-Se)3GeR] [R = C(SiMe3)3; average Ge−Se bond length = 2.406 Å],21 and [(Me3SiNPPh2)2CGe(μ-Se)]2 [2.357(4) and 2.370(4) Å].22 Meanwhile, the Ge1−Te1 [2.632(4) Å] and Ge2−Te2 [2.664(4) Å] bond lengths in 3 are also similar and show good agreement with those fourcoordinate germanium(IV) compounds containing Ge−Te single bonds, [R 4 Ge 4 Te 6 ], [R 2 Ge(μ-Te)GeR 2 ] (R = 2,4,6-iPr3C6H2; Ge−Te bond lengths = 2.5885−2.6107 Å),23 and [(Me 3 SiNPPh 2 ) 2 CGe(μ-Te)] 2 [2.585(4) and 2.577(4) Å].22 The pyridyl-1-azaallyl ligands are bonded to the germanium atoms in a N,N′-chelating fashion. The Ge1− Se1−Ge2 [88.8(1)°] and Ge1−Te1−Ge2 [90.1(1)°] bond angles in 2 and 3 are significantly smaller than the lighter congener bis(germylene) oxides [{tBuC(NAr)2Ge}2(μ-O)] [Ar = 2,6-iPr2C6H3, 147.2(3)°],18a [{Ar′Ge}2(μ-O)] [Ar′ = C6H32,6-(C6H3-2,6-iPr2)2, 154.8(2)],13m [{Ar*N(SiMe3)Ge}2(μO)] [Ar* = C6H2{C(H)Ph2}2Me-2,6,4, 122.30(9)°],15 and

heaviest ether analogue of germanium. These results suggest that the GeI−GeI bond is relatively weak and is prone to cleavage by a weak oxidizing agent. Lighter congeners bis(germylene) oxide13m,15,18 and sulfide15,18a were reported recently. Meanwhile, the treatment of 1 with 2 equiv of selenium or tellurium gave the oxidative addition products LGe(E)(μ-E)GeL [E = Se (4) and (5)]. Compound 5 is the first heaviest ester analogue of germanium. The formation of compounds 2−5 from the reactions of 1 with different stoichiometric ratios of selenium or tellurium support the B

DOI: 10.1021/acs.inorgchem.6b00026 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 3. Molecular structure of 3 (30% ellipsoid probability). Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ge1−Te1 2.632(4), Ge2−Te1 2.664(4), Ge1−N1 2.042(3), Ge1−N2 1.944(2), Ge2−N3 2.047(2), Ge2−N4 1.956(2); Ge1−Te1−Ge2 90.1(1), N1−Ge1−N2 86.8(1), N1−Ge1−Te1 97.5(7), N2−Ge1−Te1 98.5(7), N3−Ge2−N4 85.9(1), N3−Ge2− Te1 91.3(6), N4−Ge2−Te1 102.0(7).

Figure 5. Molecular structure of 5 (30% ellipsoid probability). Hydrogen atoms and solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ge1−Te1 2.6957(3), Ge2−Te1 2.5530(3), Ge2−Te2 2.4385(3), Ge1−N1 2.051(2), Ge1− N2 1.941(2), Ge2−N3 1.995(2), Ge2−N4 1.896(2); Ge1−Te1−Ge2 92.714(10), N1−Ge1−N2 86.77(9), N1−Ge1−Te1 90.10(6), N2− Ge1−Te1 99.15(6), N3−Ge2−N4 89.51(9), N3−Ge2−Te1 104.77(6), N4−Ge2−Te1 102.90(6), Te1−Ge2−Te2 121.342(13).

around the germanium atom, which also suggests the existence of a stereoactive lone pair at each germanium atom. The Ge1− Se2 [2.216(2) Å] bond length in 4 (Figure 4) is significantly shorter than those of Ge1−Se1 [2.337(2) Å] and Ge2−Se1 [2.486(2) Å]. It is comparable to the GeSe double bonds in [{(tBu)2(ATI)GeSe}2(μ-O)] [2.2124(8) Å]18b and other germaneselones Tbt(Tip)GeSe [2.180(4) Å],24 Tbt(Dis)GeSe [2.173(3) Å],20 and [{(C5H4N-2)C(SiMe3)2}2Ge Se] [2.2472(7) Å].25 The results suggest that Ge1−Se2 should possess some double-bond character. The shortening of the Ge1−Se1 bond rather than the Ge2−Se1 bond may have resulted from the higher oxidation state of the Ge1 atom. Similarly, the Ge2−Te2 [2.4385(3) Å] bond length in 5 (Figure 5) is significantly shorter than those of Ge1−Te1 [2.6957(3) Å] and Ge2−Te1 [2.5530(3) Å]. It shows a good agreement with the GeTe bonds in [{(iBu)2(ATI)Ge Te}2(μ-O)] (average 2.43 Å)26 and other germanetellones Tbt(Tip)GeTe [2.398(1) Å], Tbt(Dis)GeTe [2.384(2) Å],27 and [{(C5H4N-2)C(SiMe3)2}2GeTe] [2.4795(5) Å].25 The sums of the bond angles at the Ge2 atom in 4 and the Ge1 atom in 5 are 276.9° and 276.0°, respectively, which indicate the presence of stereoactive lone pairs on the germanium atoms. Spectroscopic Properties. Compounds 2−5 were isolated as air- and moisture-sensitive yellow and orange crystalline solids. Compounds 3 and 5 decompose slowly in the solution state in the presence of light. The 1H and 13C{1H} NMR spectra of 2−5 display two sets of signals assignable to the ligand backbone. Compounds 2 and 3 seem to be centrosymmetric; however, from their X-ray crystallographic structures, the two ligands chelating to two germanium centers are slightly unsymmetric. Hence, two sets of ligand signals are observed from 1H and 13C {1H} NMR for 2 and 3. In addition, variable-temperature (from −80 to +60 °C) 1H NMR of compounds 2 and 3 has been preformed, and the signals remain unchanged, suggesting the presence of two different

Figure 4. Molecular structure of 4 (30% ellipsoid probability). Hydrogen atoms and solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ge1−Se1 2.337(2), Ge2−Se1 2.486(2), Ge1−Se2 2.216(2), Ge1−N1 1.968(7), Ge1−N2 1.892(6), Ge2−N3 2.013(7), Ge2−N4 1.928(6); Ge1−Se1−Ge2 91.6(7), N1−Ge1−N2 89.1(3), N1−Ge1−Se1 103.1(2), N2−Ge1− Se1 104.9(2), N3−Ge2−N4 88.8(3), N3−Ge2−Se1 93.5(2), N4− Ge2−Se1 94.6(2), Se1−Ge1−Se2 118.7(9).

[{( tBu) 2 (ATI)Ge} 2(μ-O)] [ATI = aminotroponiminato, 154.4(2)°] 18b and the bis(germylene) sulfides [{PhC(NtBu) 2Ge} 2(μ-S)] [101.4(6)°] 18a and [{Ar*N(SiMe 3)Ge}2(μ-S)] [98.21(3)°].15 The reduced Ge1−E1−Ge2 (E = Se or Te) bond angles are probably because of the stronger lone-pair repulsion on the selenium and tellurium atoms. In addition, the small Ge1−E1−Ge2 and N−Ge−E [91.0(6)− 102.0(7)°] angles indicate the bonding between germanium(II) centers and the chalcogen atom via the p orbitals rather than the hybrid orbitals. The sums of the bond angles at the Ge1 and Ge2 atoms in 2 and 3 are 282.8° and 279.2°, respectively. These values are consistent with the three-coordinate chlorogermylene and adopt a trigonal-pyramidal geometry C

DOI: 10.1021/acs.inorgchem.6b00026 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry ligand-packing environments in 2 and 3. The 77Se{1H} NMR spectrum of 2 gives a signal at −214 ppm, which is downfieldshifted to the reported bridging selenium signal in the germaacid anhydride [{iBu2(ATI)GeSe}2(μ-Se)] (−324.1 ppm).28 The 125Te{1H} NMR resonance of 3 at −227 ppm is comparable to the reported bridging tellurium signal in the germaacid anhydride [{iBu2(ATI)GeTe}2Te] (−217.9 ppm).28 The 77Se{1H} NMR spectrum of 4 displays two signals at −164.0 and −638.3 ppm, which correspond to the bridging and terminal selenium signals, respectively. The signal for terminal selenium atom in 4 is downfield-shifted to that reported in [{iBu2(ATI)GeSe}2(μ-Se)] (−324.1 ppm), whereas the terminal selenium signal in 4 is upfield-shifted compared to that in [{iBu2(ATI)GeSe}2(μ-Se)] (−370.4 ppm). The 125Te{1H} NMR spectrum of 5 displays two resonances at −231 and −480 ppm, which are assignable to the bridging and terminal tellurium signals. The bridging tellurium signal in 5 is comparable to that reported in the germaacid anhydride [{iBu2(ATI)GeTe}2(μ-Te)] (−217.9 ppm); however, the terminal tellurium signal in 5 is downfield-shifted compared to those in [{iBu2(ATI)GeTe}2(μ-O)] (−884.1 ppm)26 and [{iBu2(ATI)GeTe}2(μ-Te)] (−933.2 ppm).28

(SiMe3), 3.4 (SiMe3), 3.6 (SiMe3), 114.6, 114.7 (CSiMe3), 118.3, 118.4, 124.9, 125.0, 127.0, 127.2, 129.0, 129.2, 130.2, 130.3, 133.0, 133.1, 137.2, 137.3, 143.3, 143.4, 146.1, 146.4, 156.8, 157.0 (Ph and Py), 169.6, 169.7 (NCPh). 77Se{1H} NMR (C6D6, 25 °C): δ −214. Synthesis of [LGe(μ-Te)GeL] (3). A dark-green solution of 1 (226 mg, 0.274 mmol) in THF (20 mL) was added to a gray suspension of tellurium (37.4 mg, 0.293 mmol) in THF (10 mL) at 0 °C. The reaction mixture was stirred at room temperature for 2 days, and a yellow solution was formed. All of the volatiles in the reaction mixture were removed under reduced pressure, and the residue was extracted with Et2O (20 mL) and hexane (5 mL). After filtration and concentration of the filtrate, compound 4 was isolated as orange crystals. Yield: 139 mg (53.3%). Mp: 208.1 °C (dec). Anal. Found: C, 47.21; H, 5.95; N, 5.78. Calcd for C38H54Ge2N4TeSi4: C, 47.94; H, 5.72; N, 5.88. 1H NMR (C6D6, 25 °C): δ 0.01 (s, 9H, SiMe3), 0.02 (s, 9H, SiMe3), 0.11 (s, 9H, SiMe3), 0.24 (s, 9H, SiMe3), 6.17 (br, 1H, Py), 6.31 (br, 1H, Py), 6.86 (t, 3JHH = 7.9 Hz, 1H, Ph), 6.77 (t, 3JHH = 7.9 Hz, 1H, Ph), 6.99−7.27 (m, 7H, Ph), 7.38 (t, 3JHH = 7.9 Hz, 1H, Ph), 7.52 (br, 1H, Py), 7.59 (d, 3JHH = 7.9 Hz, 1H, Py), 7.81 (d, 3JHH = 7.9 Hz, 1H, Py), 8.25 (d, 3JHH = 7.9 Hz, 1H, Py), 8.58 (br, 1H, Py), 8.77 (br, 1H, Py). 13C{1H} NMR (C6D6, 25 °C): δ 2.6 (SiMe3), 2.7 (SiMe3), 3.5 (SiMe3), 3.7 (SiMe3), 115.5, 115.6 (CSiMe3), 118.7, 118.9, 124.7, 124.9, 127.2, 127.3, 129.2, 129.5, 130.3, 130.5, 131.2, 132.8, 132.9, 137.6, 142.8, 143.0, 145.6, 145.8, 157.2 (Ph and Py), 171.5, 171.6 (NCPh). 125Te{1H} NMR (C6D6, 25 °C): δ −227. Synthesis of [LGe(Se)(μ-Se)GeL] (4). A dark-green solution of 1 (351 mg, 0.426 mmol) in THF (20 mL) was added to a suspension of selenium (68.8 mg, 0.871 mmol) in THF (10 mL) at 0 °C. The reaction mixture was stirred at room temperature for 2 days, and a yellow solution was formed. All of the volatiles in the reaction mixture were removed under reduced pressure, and the residue was extracted with Et2O (20 mL) and hexane (5 mL). After filtration and concentration of the filtrate, compound 3 was isolated as yellow crystals. Yield: 284 mg (66.7%). Mp: 237.5 °C (dec). Anal. Found: C, 49.92; H, 5.85; N, 5.83. Calcd for C38H54Ge2N4SeSi4: C, 50.52; H, 6.02; N, 6.20. 1H NMR (C6D6, 25 °C): δ −0.01 (s, 9H, SiMe3), 0.02 (s, 9H, SiMe3), 0.24 (s, 9H, SiMe3), 0.40 (s, 9H, SiMe3), 6.14 (t, 3JHH = 7.9 Hz, 1H, Py), 6.27 (t, 3JHH = 7.9 Hz, 1H, Py), 6.71 (t, 3JHH = 7.9 Hz, 2H, Ph), 7.00 (d, 3JHH = 7.9 Hz, 2H, Ph), 7.18−7.32 (m, 3H, Ph), 7.45−7.55 (m, 3H, Ph), 7.61 (d, 3JHH = 7.9 Hz, 1H, Py), 7.83 (d, 3JHH = 7.9 Hz, 1H, Py), 8.11 (d, 3JHH = 7.9 Hz, 1H, Py), 8.24 (d, 3JHH = 7.9 Hz, 1H, Py), 8.55 (d, 3JHH = 7.9 Hz, 1H, Py), 9.61 (d, 3JHH = 7.9 Hz, 1H, Py). 13C{1H} NMR (C6D6, 25 °C): δ 2.2 (SiMe3), 3.1 (SiMe3), 3.5 (SiMe3), 4.1 (SiMe3), 115.0, 115.4 (CSiMe3), 118.7, 120.3, 124.4, 124.8, 127.3, 129.5, 130.1, 130.4, 130.8, 132.5, 133.6, 137.8, 139.0, 142.1, 144.1, 145.4, 156.5, 157.0 (Ph and Py), 166.5, 169.2 (NCPh). 77 Se{1H} NMR (C6D6, 25 °C): δ −164.0, −638.3. Synthesis of [LGe(Te)(μ-Te)GeL] (5). A dark-green solution of 1 (215 mg, 0.261 mmol) in THF (20 mL) was added to a gray suspension solution of tellurium (69.0 mg, 0.541 mmol) in THF (10 mL) at 0 °C. The reaction mixture was stirred at room temperature for 2 days, and an orange mixture was formed. All of the volatiles in the reaction mixture were removed under reduced pressure, and the residue was extracted with Et2O (20 mL) and hexane (5 mL). After filtration and concentration of the filtrate, compound 5 was isolated as orange crystals. Yield: 141 mg (50.2%). Mp: 210.2 °C (dec). Anal. Found: C, 42.37; H, 5.27; N, 5.58. Calcd for C38H54Ge2N4Te2Si4: C, 42.27; H, 5.04; N, 5.19. 1H NMR (C6D6, 25 °C): δ −0.01 (s, 9H, SiMe3), 0.01 (s, 9H, SiMe3), 0.18 (s, 9H, SiMe3), 0.34 (s, 9H, SiMe3), 6.19 (br, 1H, Py), 6.35 (br, 1H, Py), 6.73 (t, 3JHH = 7.9 Hz, 1H, Ph), 6.83 (t, 3JHH = 7.9 Hz,1H, Ph), 7.01−7.08 (m, 3H, Ph), 7.10−7.13 (m, 3H, Ph), 7.18−7.23 (m, 2H, Py), 7.37 (t, 3JHH = 7.9 Hz, 2H, Ph), 7.50 (d, 3JHH = 7.9 Hz,1H, Py), 7.57 (d, 3JHH = 7.9 Hz, 1H, Py), 7.80 (d, 3 JHH = 7.9 Hz, 1H, Py), 8.21 (d, 3JHH = 7.9 Hz, 1H, Py). 13C{1H} NMR (C6D6, 25 °C): δ 2.5 (SiMe3), 4.3 (SiMe3), 115.8 (CSiMe3), 116.0 (CSiMe3), 119.4, 124.4, 124.5, 127.3, 127.9, 128.2, 128.6, 129.8, 130.6, 131.2, 132.6, 132.9, 138.3, 143.2, 143.7, 145.1, 145.2, 156.9 (Ph and Py), NCPh (cannot be observed). 125Te{1H} NMR (C6D6, 25 °C): δ −231, −480.

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CONCLUSION In conclusion, the first heavier ether and ester analogues of germanium have been synthesized from the pyridyl-1azaallylgermanium(I) dimer with different stiochiometric ratios of selenium and tellurium. The results suggest that the Ge−Ge bond in the pyridyl-1-azaallylgermanium(I) dimer is relatively weak and prone to cleavage by chalcogens. Although the diseleno- and ditellurocarboxylic acid anhydride of germanium cannot be synthesized from the germanium(I) dimer with excess selenium or tellurium, the present results support the mechanism of the previously reported dithiocarboxylic acid anhydride.

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EXPERIMENTAL SECTION

General Procedures. All manipulations were carried out under an inert atmosphere of dinitrogen gas by standard Schlenk techniques. Solvents were dried over and distilled from CaH2(hexane) and/or sodium [Et2O, toluene, and tetrahydrofuran (THF)]. LGe−GeL was prepared according to literature procedures.8 Selenium and tellurium powders were purchased from Aldrich Chemical Co. and used without further purification. The 1H, 13C{1H}, 77Se{1H}, and 125Te{1H} NMR spectra were recorded on a JEOL ECA 400 spectrometer. The NMR spectra were recorded in C6D6, and the chemical shifts are relative to SiMe4 for 1H and 13C, 29Si, Ph2Se for 77Se, and Ph2Te for 125Te. Synthesis of [LGe(μ-Se)GeL] (2). A dark-green solution of 1 (457 mg, 0.555 mmol) in THF (20 mL) was added to a suspension of selenium (43.2 mg, 0.547 mmol) in THF (10 mL) at 0 °C. The reaction mixture was stirred at room temperature for 2 days, and a yellow solution was formed. All of the volatiles in the reaction mixture were removed under reduced pressure, and the residue was extracted with toluene (10 mL) and hexane (20 mL). After filtration and concentration of the filtrate, compound 2 was isolated as yellow crystals. Yield: 333 mg (67.5%). Mp: 206.5 °C (dec). Anal. Found: C, 50.30; H, 6.18; N, 5.96. Calcd for C38H54Ge2N4SeSi4: C, 50.52; H, 6.02; N, 6.20. 1H NMR (C6D6, 25 °C): δ −0.01 (s, 9H, SiMe3), 0.00 (s, 9H, SiMe3), 0.11 (s, 9H, SiMe3), 0.23 (s, 9H, SiMe3), 6.13 (t, 3JHH = 7.9 Hz, 1H, Py), 6.28 (br, 1H, Py), 6.75 (t, 3JHH = 7.9 Hz,1H, Ph), 6.85 (t, 3JHH = 7.9 Hz, 1H, Ph), 6.99−7.14 (m, 3H, Ph), 7.18−7.31 (m, 4H, Ph), 7.43 (t, 3JHH = 7.9 Hz, 1H, Ph), 7.55 (br, 1H, Py), 7.63 (d, 3JHH = 7.9 Hz, 1H, Py), 7.76 (d, 3JHH = 7.9 Hz, 1H, Py), 8.23 (d, 3 JHH = 7.9 Hz, 1H, Py), 8.35 (d, 3JHH = 7.9 Hz, 1H, Py), 8.55 (d, 3JHH = 7.9 Hz, 1H, Py). 13C{1H} NMR (C6D6, 25 °C): δ 2.4 (SiMe3), 2.5 D

DOI: 10.1021/acs.inorgchem.6b00026 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry X-ray Crystallography. Single crystals were sealed in Lindemann glass capillaries under nitrogen. X-ray data of 2−5 were collected on a Bruker Kappa APEXII Duo diffractometer and a Bruker APEX II diffractometer using graphite-monochromatized Mo Kα radiation (λ = 0.71073 Å) from a rotating-anode generator operating at 50 kV and 90 mA. Crystal data are summarized in Tables S1 and S2 (Supporting Information). The structures were solved by a direct-phase determination (SHELXS-97 and SHELXS-2013) and refined for all data by full-matrix least-squares methods on F2. All non-hydrogen atoms were subjected to anisotropic refinement. The hydrogen atoms were generated geometrically and allowed to ride on their respective parent atoms; they were assigned appropriate isotopic thermal parameters and included in the structure-factor calculations. Full details of the crystallographic analysis of 2−5 are given in the Supporting Information.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00026. Tables of crystal data for 2−5 (PDF) Details about the X-ray crystal structures in CIF format (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: 86 755 86920634. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by The Chinese University of Hong Kong (Direct Grant). Y.-C.C. and C.-W.S. are thankful for an AStar SERC PSF grant for financial support. They also thank Dr. Y. Li for X-ray crystallography.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.6b00026 Inorg. Chem. XXXX, XXX, XXX−XXX