Stable Compounds of Composition LGe(II)R (R = OH, PhO, C6F5O

May 15, 2009 - C6F5O, PhCO2) Prepared by Nucleophilic Addition Reactions ... LGeOTf (2) is synthesized by salt metathesis reaction of. LGeCl (1) with ...
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Organometallics 2009, 28, 3763–3766 DOI: 10.1021/om900149k

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Stable Compounds of Composition LGe(II)R (R = OH, PhO, C6F5O, PhCO2) Prepared by Nucleophilic Addition Reactions Anukul Jana, Bijan Nekoueishahraki, Herbert W. Roesky,* and Carola Schulzke :: :: :: :: Institut fur Anorganische Chemie, Universitat Gottingen, Tammannstrasse 4, 37077 Gottingen, Germany Received February 24, 2009

The stable β-diketiminate germanium(II) compounds LGeR [L = HC(CMeNAr)2, Ar = 2,6-iPr2C6H3] (R = OTf, OH, PhO, C6F5O, PhCO2) are described. LGeOTf (2) is synthesized by salt metathesis reaction of LGeCl (1) with AgOTf and can be isolated as colorless crystals in 90% yield. Compound L0 Ge (3) (L0 = CH{(CdCH2)(CMe)(2,6-iPr2C6H3N)2}) was obtained by treatment of LGeOTf (2) with 1 equiv of 1,3di-tert-butylimidazol-2-ylidene (NHC) in toluene. Reaction of 3 with H2O, PhOH, C6F5OH, and PhCO2H, respectively, in toluene provided the germanium(II) compounds 4-7 in high yield. Compounds 2-7 were characterized by microanalysis and multinuclear NMR spectroscopy. Furthermore compounds 5, 6, and 7 are confirmed by X-ray structural analysis with the result that compounds 5, 6, and 7 are monomeric and the germanium center resides in a trigonal-pyramidal environment.

Introduction In recent years we have been interested in the synthesis of compounds with low-valent germanium. We reported on the preparation and structural characterization of LGeCl,1 LGeF,2 LGeOH,3 LGeH,4 and LGeNH25 (L = CH{(CMe) (2,6-iPr2C6H3N)}2) including the reactivity of LGeH.6 These small molecules are ideal precursors for the preparation of heterometallic germylenes, which are active catalysts in olefin polymerization reations.7 All compounds were synthesized by nucleophilic substitution reactions with the exception of LGeNH2. The synthesis of LGeNH2 involved the cleavage of one N-H bond of ammonia by L0 Ge (3) (L0 = CH{(CdCH2)(CMe)(2,6-iPr2C6H3N)2}). Driess and co-workers independently demonstrated that 3 has a dipolar character.8 Herein, *To whom correspondence should be addressed. Fax: +49-551393373. E-mail: [email protected]. (1) Ding, Y.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G.; Power, P. P. Organometallics 2001, 20, 1190–1194. (2) Ding, Y.; Hao, H.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G. Organometallics 2001, 20, 4806–4811. (3) (a) Pineda, L. W.; Jancik, V.; Roesky, H. W.; Neculai, D.; Neculai, A. M. Angew. Chem. 2004, 116, 1443–1445. (b) Angew. Chem., Int. Ed. 2004, 43, 1419-1421. (4) (a) Pineda, L. W.; Jancik, V.; Starke, K.; Oswald, R. B.; Roesky, H. W. Angew. Chem. 2006, 118, 2664–2667. (b) Angew. Chem., Int. Ed. 2006, 45, 2602-2605. (5) Jana, A.; Objartel, I.; Roesky, H. W.; Stalke, D. Inorg. Chem. 2009, 48, 798–800. (6) Jana, A.; Ghoshal, D.; Roesky, H. W.; Objartel, I.; Schwab, G.; Stalke, D. J. Am. Chem. Soc. 2009, 131, 1288–1293. (7) (a) Pineda, L. W.; Jancik, V.; Roesky, H. W.; Herbst-Irmer, R. Inorg. Chem. 2005, 44, 3537–3540. (b) Yang, Y.; Roesky, H. W.; Jones, P. G.; So, C.-W.; Zhang, Z.; Herbst-Irmer, R.; Ye, H. Inorg. Chem. 2007, 46, 10860–10863. :: (8) (a) Driess, M.; Yao, S.; Brym, M.; van Wullen, C. Angew. Chem. 2006, 118, 4455 – 4458. (b) Angew. Chem., Int. Ed. 2006, 45, 4349-4352 :: (c) Yao, S.; van Wullen, C.; Driess, M. Chem. Commun. 2008, 5393–5395. r 2009 American Chemical Society

we report on the synthesis of different heteroleptic germanium (II) compounds by the reaction of L0 Ge (3) under nucleophilic addition of RH.

Results and Discussion In a previous communication we reported the synthesis of L0 Ge (3)5 from LGeCl (1) and 1,3-di-tert-butylimidazol-2ylidene9 (NHC) in a 65% yield. The yield can be improved when, instead of LGeCl (1), LGeOTf (2) and NHC are used. The triflate anion ([OSO2CF3]- = OTf -) has served here as an excellent leaving group, and the conversion is almost quantitative (Scheme 1). LGeOTf (2) was synthesized under salt metathesis reaction of LGeCl (1) with AgOTf in toluene and afforded colorless compound 2 in high yield. LGeOTf (2) was also reported by Driess and co-workers by the reaction of LGeP(H)SiMe3 with Me3SiOTf in the presence of Et3N.10 Unlike other β-diketiminate germanium compounds, the 1H NMR spectrum of 2 shows for the iPr substituents at room temperature only one broad singlet (CH, δ = 3.26 ppm) and one doublet for the methyl groups. This may be due to the rapid exchange of the triflate group and the lone pair at the germanium atom. Therefore we studied the temperature dependence 1H NMR between +75 and -50 °C. At -50 °C two septets appeared at 3.92 and 2.60 ppm for the CH protons (see Figure 1). However at -50 °C the exchange of the triflate group and the lone pair is slow on the NMR time scale compared to that at room temperature. The calculated exchange rate at different temperatures is the (9) (a) Arduengo, A. J.; Bock, H.; Chen, C.; Denk, M.; Dixon, D. A.; Green, J. C.; Herrmann, W. A.; Jones, N. L.; Wagner, M.; West, R. J. Am. Chem. Soc. 1994, 116, 6641–6649. (b) Scott, N. M.; Dorta, R.; Stevens, E. D.; Correa, A.; Cavallo, L.; Nolan, S. P. J. Am. Chem. Soc. 2005, 127, 3516–3526. (10) Yao, S.; Brym, M.; Merz, K.; Driess, M. Organometallics 2008, 27, 3601–3607.

Published on Web 05/15/2009

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Figure 1. 1H NMR spectrum of 2 at various temperatures. Scheme 1. Preparation of Compounds 2, 3, 4, 5, 6, and 7

following: -50 °C, 3.5 s-1; -25 °C, 28 s-1; 0 °C, 250 s-1; +25 °C, 2500 s-1; +50 °C, 26 000 s-1. In recent years we were interested in the synthesis of hydroxides, and we were able to isolate LGeOH, LAl(OH)2, and LAlMe(OH).11 Therefore we followed the reaction of L0 Ge with H2O, and we expected the formation of the LGeOH by an alternative route. The reaction of L0 Ge with H2O in a 1:1 ratio at room temperature resulted in the formation of LGeOH (4) in almost quantitative yield (Scheme 1). For a broader feasibility we extended the reaction of L0 Ge with PhOH and C6F5OH and obtained products 5 and 6, respectively (Scheme 1). 5 and 6 are colorless solids, which are soluble in n-hexane, n-pentane, THF, dichloromethane, benzene, and diethyl ether. 5 and 6 were characterized by 1H and 13C NMR spectroscopy, EI mass spectrometry, elemental analysis, and X-ray single-crystal structural analysis. The 1H NMR spectra of 5 and 6 show the expected pattern for the β-diketiminato ligand.6 The 19F NMR spectrum of 6 displays three resonances (-158.8, -166.9, -175.2 ppm) for the ortho, meta, and para fluorine atoms, respectively. The most intense peak in the EI mass spectra appeared at m/z = 491 [M - OPh]+ and 673 [M]+ for compounds 5 and 6, respectively. Compounds 5 and 6 crystallize in the orthorhombic Pnma and monoclinic P21/n space groups with one monomer in the (11) Roesky, H. W.; Walawalkar, M. G.; Murugavel, R. Acc. Chem. Res. 2001, 34, 201-211, and references therein.

Jana et al.

asymmetric unit, respectively (Table 1). Single crystals of both 5 and 6 were obtained from saturated n-hexane solution at -32 °C after two days. These compounds are stable in the solid state as well as in solution for a long time without any decomposition under inert atmosphere. The coordination polyhedron around the germanium atom features a distorted trigonal-pyramidal geometry (Figures 2, 3). The germanium is attached to two nitrogen atoms from the backbone of the chelating ligand and the oxygen atom from the OPh and OC6F5 group, respectively. The Ge-N bond lengths and N-Ge-N angles are comparable with those of related compounds.12 The Ge-O bond length of 5 (1.860 A˚) can be compared with that of LGeOH3 (1.828 A˚), but in 6 it is a slightly longer Ge-O bond (1.9515 A˚), when compared with the latter one. Subsequently after the successful reaction of L0 Ge with H2O, PhOH, and C6F5OH, respectively, we used a carboxylic acid as precursor. Treatment of 3 with PhCO2H in toluene at room temperature after 1 h afforded the corresponding benzoic acid derivative, germylene benzoate HC(CMeNAr)2GeOC(O)Ph (Ar = 2,6-iPr2C6H3) (7), in high yield (85%) (Scheme 1). Compound 7 is thermally stable. No decomposition was observed at temperatures below the melting point (167 °C) under an inert atmosphere. Compound 7 is a white solid that is soluble in benzene, toluene, n-hexane, and THF. 7 was characterized by 1 H and 13C NMR spectroscopy, EI mass spectrometry, elemental analysis, and X-ray structural analysis. The 1H NMR spectrum of compound 7 shows a singlet (δ = 5.16 ppm) for the γ-CH protons and two septets (δ = 3.61, 3.17 ppm) corresponding to the two different types of CH protons of the iPr moieties. EI-MS of 7 gave the corresponding monomeric molecular ion peak M+ at m/z 612. The molecular structure of 7 has been determined by singlecrystal X-ray diffraction analysis (Figure 4), which demonstrates that the complex exists as a monomer. Colorless crystals of 7 were obtained from an n-hexane solution at -30 °C after one day in a freezer. Compound 7 crystallizes in the monoclinic space group P21/c, with one monomer in the asymmetric unit. The coordination polyhedron around the germanium atom exhibits a distorted trigonal-pyramidal geometry. The sum of angles around the germanium atom is 268.59°. The Ge-O bond distance (1.9462 A˚) in 7 is quite large when compared with that of 5 (1.860 A˚), and it is similar to that of 6 (1.9515 A˚).

Summary and Conclusion In this contribution, we report the syntheses and characterization of three monomeric germanium(II) compounds supported by the bulky β-diketiminate ligand. The synthetic strategy takes advantage of the easy access of [CH{(CdCH2)(CMe)(Ar)}2Ge] (Ar = 2,6-iPr2C6H3) (3), which is formed by elimination of CF3SO3H with 1,3-di-tert-butylimidazol-2-ylidene. The concept of nucleophilic addition of RH was applied using H2O, PhOH, C6F5OH, and PhCO2H, respectively, to afford the monomeric organogermanium(II) compounds 4-7 in high yield. Compounds 5-7 are highly soluble in common organic solvents.

Experimental Section General Considerations. All manipulations were performed in a dry and oxygen-free atmosphere (N2 or Ar) by using Schlenk-line and glovebox techniques. Solvents were purified with the M-Braun (12) Nagendran, S.; Roesky, H. W. Organometallics 2008, 27, 457–492.

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Table 1. Crystallographic Data for the Structural Analyses of Compounds 5, 6, and 7 empirical formula CCDC No. T [K] cryst syst space group a [A˚] b [A˚] c [A˚] R [deg] β [deg] γ [deg] V [A˚3] Z Dcalcd [g cm-3] μ [mm-1] F(000) θ range [deg] reflns collected indep reflns data/restraints/params reflns collected/unique R1, wR2 [I > 2σ(I)]a R1, wR2 (all data) a GoF ΔF(max), ΔF(min) [e A˚-3] a

R1 =

5

6

7

C35H46GeN2O 715867 133(2) orthorhombic Pnma 16.597(3) 20.695(4) 9.2831(19) 90 90 90 3188.5(11) 4 1.215 0.989 1240 1.97-25.95 11 672 3120 3010/0/192 11 672/3120[R(int) = 0.0839] 0.0747, 0.1429 0.1107, 0.1557 1.062 2.084, -0.699

C35H41F5GeN2O 715868 133(2) monoclinic P21/n 13.162(3) 19.533(4) 13.519(3) 90 103.49(3) 90 3379.8(12) 4 1.323 0.963 1400 1.87-26.99 30 456 7330 7330/0/431 30 456/7330[R(int) = 0.0506] 0.0329, 0.0740 0.0482, 0.0784 0.942 0.495, -0.499

C36H46GeN2O2 715869 133(2) monoclinic P21/c 18.371(4) 10.627(2) 16.940(3) 90 96.28(3) 90 3287.4(11) 4 1.235 0.965 1296 2.22-26.96 31 397 7131 7131/0/383 31 397/7131[R(int) = 0.0802] 0.0478, 0.0867 0.0746, 0.0939 1.025 0.631, -0.588

P P P P ||Fo| - |Fc||/ |Fo|. wR2 = [ w(F2o - F2c )2/ w(F2o)2]0.5.

Figure 2. Molecular structure of 5. Selected bond lengths [A˚] and angles [deg]; anisotropic displacement parameters are depicted at the 50% probability level and all restrained refined hydrogen atoms are omitted for clarity: Ge1-O1 1.860(4), Ge1N1 2.008(3), N1-C17 1.314(5), O1-C1 1.360(7); N1-Ge1N1A 88.67(16), N1-Ge1-O1 93.88(12), Ge1-O1-C1 117.5(4). solvent drying system. Compound LGeCl (1) was prepared by a literature procedure.1 Other chemicals were purchased commercially and used as received.1H, 13C, and 19F NMR spectra were recorded on a Bruker 500 MHz instrument and referenced to the deuterated solvent in the case of the 1H and 13C NMR spectra. 19F NMR spectra were referenced to CFCl3. Elemental analyses were performed by the :: Analytisches Labor des Instituts fur Anorganische Chemie der :: :: Universitat Gottingen. Mass spectra were obtained on a Finnigan Mat 8230 instrument. Melting points were measured in a sealed glass tube and are not corrected. Synthesis of [{HC(CMeNAr)2}Ge(II)OSO2CF3] (Ar = 2,6iPr2C6H3) (2). A solution of 1 (0.52 g, 1 mmol) in toluene (15 mL) was added drop by drop to a stirred suspension of AgOSO2CF3 (0.26 g, 1 mmol) in toluene (10 mL) at room remperature. The solution was stirred for an additional 2 h. After filtration the filtrate was concentrated to about 10 mL and stored in a -30 °C freezer.

Figure 3. Molecular structure of 6. Selected bond lengths [A˚] and angles [deg]; anisotropic displacement parameters are depicted at the 50% probability level and all restrained refined hydrogen atoms are omitted for clarity: Ge1-O1 1.9515(14), Ge1-N1 1.9785(16), N1-C19 1.338(2), O1-C1 1.319(2); N1-Ge1-N2 90.85(6), N1-Ge1-O1 91.11(6), Ge1-O1-C1 129.25(12). Colorless crystals of 2 were formed after two days. Yield: 0.575 g (90%); mp 216 °C. 1H NMR (500 MHz, C6D6): δ 7.06-7.15 (m, 6H, Ar-H), 5.58 (s, 1H, γ-CH), 3.27 (sept, 4H, CH(CH3)2), 1.68 (s, 6H, CH3), 1.19 (d, 12H, CH(CH3)2), 1.15 (d, 12H, CH(CH3)2) ppm. 13 C{1H} NMR (125.75 MHz, C6D6): δ 167.45 (CN), 145.75, 137.91, 125.63 (Ar-C), 120.9 (CF3), 106.39 (γ-C), 25.81 (CHMe2), 24.27 (CHMe2), 23.03 (Me) ppm. 19F{1H} NMR (188.28 MHz, C6D6): δ -76.5 ppm. EI-MS: m/z (%) 640 (100) [M+]. Anal. Calcd for C30H41F3GeN2O3S (640.20): C, 56.36; H, 6.46; N, 4.38; S, 5.02. Found: C, 56.55; H, 6.93; N, 4.35; S, 5.02.10 Synthesis of [CH{(CdCH2)(CMe)(Ar)}2Ge] (Ar = 2,6iPr2C6H3) (3). 1,3-Di-tert-butylimidazol-2-ylidene (0.360 g, 2.0 mmol) and 2 (1.280 g, 2.0 mmol) were dissolved in toluene (30 mL) at room temperature. The reaction mixture was stirred, and the color of the solution changed from colorless to brown-red. A white

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Jana et al. CH(CH3)2), 1.10 (d, 6H, CH(CH3)2), 1.06 (d, 6H, CH(CH3)2) ppm. C{1H} NMR (125.77 MHz, C6D6): δ 164.23 (CN), 162.34 (CO), 146.64, 143.91, 140.19, 129.34, 125.11, 124.26, 119.94, 118.46 (Ar-C), 98.38 (γ-C), 29.15 (CH(CH3)2), 28.37 (CH(CH3)2), 25.85 (CH(CH3)2), 25.29 (CH(CH3)2), 24.64 (CH(CH3)2), 24.59 (CH(CH3)2), 23.26 (CH3) ppm. EI-MS (70 eV): m/z (%) 491 (100) [M - OPh]+. Anal. Calcd for C35H46GeN2O (583.39): C, 72.06; H, 7.95; N, 4.80. Found: C, 71.00; H, 7.53; N, 4.76. 6. C6F5OH (0.190 g, 1 mmol) and 3 (0.490 g, 1 mmol). Yield: 0.540 g (80%); mp 155 °C. 1H NMR (500 MHz, C6D6): δ 6.99-7.10 (m, 6H, Ar-H ), 5.10 (s, 1H, γ-CH), 3.48 (sept, 2H, CH(CH3)2), 3.05 (sept, 2H, CH(CH3)2), 1.55 (s, 6H, CH3), 1.18 (d, 6H, CH(CH3)2), 1.11 (d, 6H, CH(CH3)2), 1.03 (d, 6H, CH(CH3)2), 0.88 (d, 6H, CH(CH3)2) ppm. 13C{1H} NMR (125.77 MHz, C6D6): δ 164.69 (CN), 146.15, 143.91, 143.78, 139.89, 137.83, 129.27, 128.50, 125.63, 125.09, 124.33, 123.54 (Ar-C), 100.71 (γ-C), 29.27 (CH(CH3)2), 28.03 (CH(CH3)2), 25.49 (CH(CH3)2), 24.79 (CH(CH3)2), 24.44 (CH(CH3)2), 24.09 (CH(CH3)2), 23.38 (CH3) ppm. 19F{1H} NMR (188.31 MHz, C6D6): δ -158.8 (d, 6F, o-F), -166.9 (t, 6F, m-F), -175.2 (t, 3F, p-F ). EI-MS (70 eV): m/z (%) 673 (100) [M]+. Anal. Calcd for C35H41F5GeN2O (673.34): C, 62.43; H, 6.14; N, 4.16. Found: C, 62.24; H, 6.05; N, 4.16. 7. PhCO2H (0.122 g, 1 mmol) and 3 (0.490 g, 1 mmol). Yield: 0.520 g (85%); mp 167 °C. 1H NMR (500 MHz, C6D6): δ 6.99-8.44 (m, 11H, Ar-H ), 5.16 (s, 1H, γ-CH ), 3.61 (sept, 2H, CH(CH3)2), 3.17 (sept, 2H, CH(CH3)2), 1.61 (s, 6H, CH3), 1.21 (d, 6H, CH(CH3)2), 1.13 (d, 6H, CH(CH3)2), 1.07 (d, 6H, CH(CH3)2), 1.05 (d, 6H, CH(CH3)2) ppm. 13C{1H} NMR (125.77 MHz, C6D6): δ 165.00 (CN), 161.49 (CCO), 146.45-123.55 (Ar-C), 99.76 (γ-C), 94.24 (CO), 29.35 (CH(CH3)2), 28.60 (CH(CH3)2), 26.52 (CH(CH3)2), 24.67 (CH(CH3)2), 24.53 (CH(CH3)2), 24.08 (CH(CH3)2), 23.44 (CH3) ppm. EI-MS (70 eV): m/z (%) 612 (100) [M]+. Anal. Calcd for C36H46GeN2O2 (611.40): C, 70.72; H, 7.58; N, 4.55. Found: C, 70.11; H, 7.52; N, 4.55. Crystallographic Details for Compounds 5, 6, and 7. Suitable crystals of 5, 6, and 7 were mounted on a glass fiber, and data were collected on an IPDS II Stoe image-plate diffractometer (graphitemonochromated Mo KR radiation, λ = 0.71073 A˚) at 133(2) K. The data were integrated with X-Area. The structures were solved by direct methods (SHELXS-97)13 and refined by full-matrix leastsquares methods against F2 (SHELXL-97).13 All non-hydrogen atoms were refined with anisotropic displacement parameters. Crystallographic data are presented in Table 1. 13

Figure 4. Molecular structure of 7. Selected bond lengths [A˚] and angles [deg]; anisotropic displacement parameters are depicted at the 50% probability level and all restrained refined hydrogen atoms are omitted for clarity: Ge1-O1 1.9462(19), Ge1-N1 1.978(2), O1-C1 1.311(3), C1-O2 1.216(3); N1-Ge1-N2 90.48(9), N1-Ge1-O1 89.43(8), O1-C1-O2 125.0(3). precipitate was formed. The reaction mixture was stirred for another hour, then the white precipitate was separated by filtration and the remaining red solution was evaporated. The residue was dissolved in nhexane (20 mL). Storage of this solution at -30 °C for one day in a freezer yielded brown-red crystals. Yield: 0.880 g (90%).5,8a Synthesis of [{HC(CMeNAr)2}Ge(II)OH] (Ar = 2,6-iPr2C6H3) (4). Water (18 μL, 1 mmol) was added to a red solution of 3 (0.490 g, 1 mmol) in toluene (20 mL) under stirring at room temperature. The reaction mixture became yellow. Stirring of the reaction mixture was continued for about 15 min. After that, the solvent was removed under vacuum and the residue was extracted with n-hexane (15 mL). The solution was reduced to half of the volume. Storage of the solution at -30 °C for one day in a freezer yielded yellow crystals. Yield: 0.480 g (95%).3 Synthesis of Compounds 5, 6, and 7. Compounds 5-7 are prepared in a similar way using different RH precursors. 5. A 10 mL toluene solution of phenol (0.095 g, 1 mmol) was added to a solution of 3 (0.490 g, 1 mmol) in toluene (20 mL) under stirring at room temperature, and the color of the solution changed immediately from red to colorless. After 30 min all the volatiles were removed under vacuum and the residue was extracted with n-hexane (30 mL) and concentrated to give colorless crystals of 5 after two days, which were suitable for X-ray structural analysis. Yield: 0.475 g (82%); mp 203 °C. 1H NMR (500 MHz, C6D6): δ 6.63-7.13 (m, 11H, Ar-H ), 4.98 (s, 1H, γ-CH ), 3.77 (sept, 2H, CH(CH3)2), 3.27 (sept, 2H, CH(CH3)2), 1.60 (s, 6H, CH3), 1.28 (d, 6H, CH(CH3)2), 1.18 (d, 6H,

Acknowledgment. We are thankful to Dr. Michael John for NMR measurements and the Deutsche Forschungsgemeinschaft for financial support. Supporting Information Available: X-ray data for 5, 6, and 7 (CIF). This material is available free of charge via the Internet at http://pubs.acs.org. (13) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112–122.