Bulky Aminotroponiminate-Stabilized Germylene Monochloride and Its

Mar 14, 2011 - bulky substituents.1,4,5 The most widely used monoanionic and bidentate ... valent compounds of germanium,11,13,15 tin,11,13,15c,16 and...
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Bulky Aminotroponiminate-Stabilized Germylene Monochloride and Its Alkyne Derivatives† Rahul Kumar Siwatch, Subrata Kundu, Dinesh Kumar, and Selvarajan Nagendran* Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110 016, India

bS Supporting Information ABSTRACT: By means of a two-step synthetic route, aminotroponimine [(t-Bu)2ATI]H (3) with a tert-butyl substituent on the nitrogen atoms has been synthesized from 2-(tosyloxy)tropone. Lithiation of 3 with n-BuLi in THF afforded the lithium salt [(t-Bu)2ATI]Li 3 (THF)2 (4). Reaction of 4 with GeCl2 3 (1,4-dioxane) resulted in the germylene monochloride complex [(t-Bu)2ATI]GeCl (5). Treatment of 5 with the lithium derivative of ethynyl ferrocene [(C5H5)Fe(C5H4)CtCH] (6) and phenyl acetylene (C6H5CtCH) (7) gave the corresponding alkynyl germylene complexes [(t-Bu)2ATI]GeCtC(C5H4)Fe(C5H5) (8) and [(t-Bu)2ATI]GeCtCC6H5 (9), respectively. Compounds 3, 4, 5, 8, and 9 have been characterized by elemental analysis and various spectroscopic (multinuclear NMR, mass, and IR) techniques. Further confirmation came from the single-crystal X-ray structural studies on all these compounds. The structure of the alkynyl germylenes reveals the presence of a slightly bent Ge(II)-CtC moiety [bond angle in 8 168.4(3)° and 9 170.8(2)°].

’ INTRODUCTION Recent years have witnessed a tremendous growth in lowvalent germanium chemistry, which is mainly due to the availability of sophisticated synthetic routes and starting materials.1 The synthesis of a digermanium compound (NHCfGed GerNHC) stabilized by an N-heterocyclic carbene [NHC = :C{N(Ar)CH}2, Ar = 2,6-(i-Pr)2C6H3] containing a GedGe double bond with a formal oxidation state of zero on germanium atoms can be suggested as an example.2a Jones and co-workers isolated this compound by reducing the germanium dichlorideNHC adduct (NHCfGeCl2) with a dimagnesium compound (LMg-MgL) [L = HC{C(Me)N(Ar)}2, Ar = 2,6-(i-Pr)2C6H3 or 2,4,6-(Me)3C6H2] that contained a direct Mg(I)-Mg(I) bond.2b-d The isolation of LGeOC(O)H [L = HC{C(Me) N(Ar)}2, Ar = 2,6-(i-Pr)2C6H3], a germanium(II) ester of formic acid,3a through the hydrogermylation of CO2 using a germylene hydride complex3b (LGeH) in the absence of any catalyst at room temperature by Roesky and co-workers, further reveals the maturity of germylene chemistry. The synthesis of the aforementioned compounds and various other unusual subvalent compounds of germanium4 would not have been possible without the proper choice of ligands that generally offer profuse thermodynamic and/or kinetic stabilization through the donor sites and/or bulky substituents.1,4,5 The most widely used monoanionic and bidentate ligands in the low-valent group 14 chemistry possessing nitrogen donors with bulky substituents are the 6π electron β-diketiminate6,7 and 4π electron amidinate8,9 systems. Notable examples of low-valent germanium compounds stabilized through the latter ligand system include the germanium(I) dimers r 2011 American Chemical Society

L0 Ge-GeL0 [L0 = RC(NAr)2, Ar = 2,6-(i-Pr)2C6H3, R = t-Bu or N(i-Pr)2]8a and L00 Ge-GeL00 [L00 = (Ph)C{N(t-Bu)}2]8b that contain a Ge(I)-Ge(I) single bond. Interestingly, another monoanionic and bidentate ligand system, namely, the aminotroponiminate (ATI) with a distinct 10π electron backbone, is also known.10-16 Dias and co-workers have used various aminotroponimine (R2ATIH, R = Me,12 n-Pr,13 i-Pr14) to synthesize lowvalent compounds of germanium,11,13,15 tin,11,13,15c,16 and lead.11 Nevertheless, it is surprising to note that to develop the chemistry further, low-valent group 14 complexes stabilized by ATI ligands with bulky substituents beyond isopropyl groups are not available until now.11-16 Therefore, we became interested in the synthesis of a germylene monochloride complex supported on an ATI ligand with substituents having a bulkiness greater than that of isopropyl groups. Furthermore, to reveal the reaction potential of such a complex, we planned to react it with the lithium derivative of terminal alkynes with the objective of isolating hitherto unknown ATI-based alkynyl germylene derivatives. Though various germylene derivatives are known,1,3,4,6,8,11,17-19 to the best of our knowledge, the alkynyl germylene derivatives as such are very scarce, and only very few structurally characterized examples are known to date.20-22 Some of the known complexes (Chart 1) include MamxGeCtCR (Mamx = methylaminomethyl-m-xylyl, R = H I; Ph II) and LGeCtCPh III [L = HC{C(Me)N(Ar)}2, Ar = 2,6-(i-Pr)2C6H3] reported by the groups of Jutzi20 and Driess,21 respectively. Received: January 15, 2011 Published: March 14, 2011 1998

dx.doi.org/10.1021/om200035z | Organometallics 2011, 30, 1998–2005

Organometallics Chart 1. Alkynyl Germylene Complexes I-III

Accordingly, we report herein the facile synthesis and characterization of [(t-Bu)2ATI]H (3), its lithium derivative [(t-Bu)2 ATI]Li 3 (THF)2 (4), the germylene monochloride complex [(tBu)2ATI]GeCl (5), and the first alkynyl germylene complexes [(t-Bu)2ATI]GeCtC(C5H4)Fe(C5H5) (8) and [(t-Bu)2ATI] GeCtCC6H5 (9) stabilized by an ATI ligand.

’ EXPERIMENTAL SECTION All the manipulations were performed under an atmosphere of dry N2 using either standard Schlenk or glovebox techniques. For the latter purpose, either a Mbraun or Jacomex glovebox equipped with a lowtemperature refrigerator (ca. -36 °C) was used. Dry solvents were either prepared using the conventional procedures or purchased directly from Aldrich. 2-(Tosyloxy)tropone23 1 and ethynyl ferrocene24 6 were prepared according to the literature procedures. t-Butylamine, Et3O 3 BF4, n-BuLi (1.6 M solution in hexane), GeCl2 3 (1,4-dioxane), and phenyl acetylene 7 were purchased from Aldrich and used without any further purification. Thin-layer chromatography (TLC) was performed over precoated silica gel plates purchased from Merck (TLC silica gel 60 F254). The plates were treated with triethylamine and dried before use. Melting points were recorded using an Ambassador melting point apparatus by sealing the samples in a glass tube and are uncorrected. Also, the nature of the resolidified substances obtained during the cooling of molten materials was not analyzed. Elemental analyses were performed using a Perkin-Elmer CHN analyzer. 1H and 13C NMR spectra were recorded on a 300 MHz Bruker Topspin NMR spectrometer using dry CDCl3 or C6D6. The chemical shifts δ are reported in ppm with respect to the residual solvent resonances as internal reference.25 IR spectroscopic studies in the solid state were carried out by means of a Nicolet spectrometer as either KBr pellets or Nujol mulls. EI mass spectroscopic studies were carried out using a Finnigan MAT 8230 mass spectrophotometer, and only the characteristic fragments are reported. Synthesis of [2-{(t-Bu)HN}C7H5(O)] (2). In a 100 mL RB flask, 2-(tosyloxy)tropone 1 (1.86 g, 6.73 mmol) was refluxed with an excess of tert-butylamine until the complete disappearance of 1. After that, all volatiles were removed in vacuo to afford a yellow residue. It was extracted using diethyl ether, and the combined ether extracts were filtered through a G-4 frit. The filtrate was concentrated under reduced pressure to obtain 2 as a yellow solid. Further purification by column chromatography over basic alumina gave the analytically pure sample of 2-(tert-butylamino)tropone, 2. Single crystals of 2 suitable for X-ray diffraction studies were obtained from its hexane solution at -15 °C. Yield: 0.83 g (4.68 mmol), 69.6%. Mp: 63 °C. Anal. Calcd for C11H15NO (M = 177.24): C, 74.54; H, 8.53; N, 7.90. Found: C, 74.21; H, 8.49; N, 7.98. 1H NMR (300 MHz, C6D6): δ 0.99 (s, 9H, C(CH3)3), 6.26 (t, 3JHH = 9.3 Hz, 1H, CH), 6.54 (d, 3JHH = 10.2 Hz, 1H, CH), 6.72-6.83 (m, 2H, CH), 7.38 (d, 3JHH = 11.7 Hz, 1H, CH), 7.73

ARTICLE

(bs, 1H, NH). 1H NMR (300 MHz, CDCl3): δ 1.51 (s, 9H, C(CH3)3), 6.64 (t, 3JHH = 9.3 Hz, 1H, CH), 6.91 (d, 3JHH = 10.5 Hz, 1H, CH), 7.12-7.23 (m, 3H, CH), 7.46 (bs, 1H, NH). 13C{1H} NMR (75 MHz, CDCl3): δ 28.80 (C(CH3)3), 51.41 (C(CH3)3), 110.40 (C2), 121.75 (C6), 127.92 (C4), 135.63 (C3), 137.08 (C5), 154.70 (C7), 177.04 (C1). IR (KBr, cm-1): 3256 (N-H). EI-MS: m/z (%) 177 (54, [M]þ), 162 (14, [M - Me]þ), 121 (100, [M - C4H8]þ). Synthesis of [(t-Bu)2ATI]H (3). A solution of Et3O 3 BF4 (4.42 g, 23.26 mmol) in dichloromethane (25 mL) was transferred to a solution of 2 (3.75 g, 21.16 mmol) in dichloromethane (25 mL) and stirred for 5 h. After that, tert-butylamine (35 mL) was added slowly and the reaction mixture was stirred for a further 5 h. All the volatile materials were then removed under reduced pressure to obtain a dark brown solid. This was purified by column chromatography using basic alumina to get N-tert-butyl-2-(tert-butylamino)troponimine 3 as a yellow solid. Single crystals of 3 suitable for X-ray diffraction studies were grown from its ether solution at -15 °C. Yield: 3.46 g (14.87 mmol), 70.4%. Mp: 72 °C. Anal. Calcd for C15H24N2 (M = 232.36): C, 77.53; H, 10.41; N, 12.06. Found: C, 77.74; H, 10.48; N, 12.27. 1H NMR (300 MHz, C6D6): δ 1.34 (s, 18H, C(CH3)3), 6.12 (t, 3JHH = 8.1 Hz, 1H, CH), 6.57-6.67 (m, 4H, CH), 8.59 (bs, 1H, NH). 1H NMR (300 MHz, CDCl3): δ 1.43 (s, 18H, C(CH3)3), 6.07 (t, 3JHH = 9.0 Hz, 1H, CH), 6.52-6.71 (m, 4H, CH), 8.24 (bs, 1H, NH). 13C{1H} NMR (75 MHz, CDCl3): δ 29.54 (C(CH3)3), 51.96 (C(CH3)3), 111.77 (C4), 116.53 (C2,6), 131.41 (C3,5), 151.61 (C1,7). IR (KBr, cm-1): 3047 (N-H). EI-MS: m/z (%) 232 (34, [M]þ), 217 (30, [M - Me]þ), 161 (100, [M - N(C(CH3)3]þ). Synthesis of [(t-Bu)2ATI]Li 3 (THF)2 (4). To a solution of 3 (7.07 g, 30.43 mmol) in THF (160 mL) was added n-BuLi (19.97 mL, 1.6 M solution in hexane) at -78 °C. After 30 min, the reaction mixture was brought slowly to room temperature and stirred for 2 h. Then the volatile materials were removed under vacuum to yield 4 as a yellow solid. Single crystals of 4 suitable for X-ray diffraction studies were grown by cooling its THF solution at -32 °C. Yield: 11.52 g (30.12 mmol), 98.9%. Mp: 134-136 °C. Anal. Calcd for C23H39LiN2O2 (M = 382.51): C, 72.22; H, 10.28; N, 7.32. Found: C, 72.35; H, 10.15; N, 7.09. 1H NMR (300 MHz, C6D6): δ 1.29-1.34 (m, 8H, CH2), 1.50 (s, 18H, C(CH3)3), 3.41 (t, 3 JHH = 6.6 Hz, 8H, CH2), 6.09 (t, 3JHH = 8.7 Hz, 1H, CH), 6.62 (d, 3JHH = 11.4 Hz, 2H, CH), 6.95 (dd, 3JHH = 11.4 Hz, 2H, CH). 13C{1H} NMR (75 MHz, C6D6): δ 25.15 (CH2), 30.49 (C(CH3)3), 52.76 (C(CH3)3), 67.88 (CH2), 108.43 (C4), 110.53 (C2,6), 130.61 (C3,5), 163.52 (C1,7). 7 Li NMR (117 MHz, C6D6): δ 1.76 (s, 1Li). EI-MS: m/z (%) 232 (36, [M - Li(THF)2 þ H]þ), 217 (30, [M - (CH2)Li(THF)2]þ), 161 (100, [M - N(C4H8)Li(THF)2]þ). Synthesis of [(t-Bu)2ATI]GeCl (5). A solution of 4 (4.28 g, 11.18 mmol) in THF (100 mL) was transferred to a suspension of GeCl2 3 (1,4dioxane) (2.59 g, 11.18 mmol) in THF (100 mL) at -78 °C. After 30 min, the reaction mixture was brought to room temperature and stirred overnight. Then THF was removed under reduced pressure to yield an orange solid, which was extracted using toluene (100 mL) and filtered through a G4 frit. The filtrate was dried under reduced pressure to yield compound 5 as an orange solid. Single crystals of 5 suitable for X-ray diffraction studies were grown by keeping its toluene solution at -32 °C overnight. Yield: 3.74 g (11.02 mmol), 98.5%. Mp: 122-124 °C. Anal. Calcd for C15H23ClGeN2 (M = 339.45): C, 53.07; H, 6.83; N, 8.25. Found: C, 52.96; H, 6.69; N, 8.37. 1H NMR (300 MHz, C6D6): δ 1.56 (s, 18H, C(CH3)3), 6.27 (t, 3JHH = 9.0 Hz, 1H, CH), 6.69 (dd, 3JHH = 11.7 Hz, 2H, CH), 6.89 (d, 3JHH = 11.7 Hz, 2H, CH). 13C{1H} NMR (75 MHz, C6D6): δ 30.36 (C(CH3)3), 56.97 (C(CH3)3), 119.48 (C4), 122.35 (C2,6), 134.91 (C3,5), 160.76 (C1,7). IR (KBr, cm-1): 2937, 2840, 1587, 1468, 1378, 1213, 1184, 1097, 846, 801, 731. EI-MS: m/z (%) 340 (100, [M]þ), 305 (82, [M Cl]þ), 269 (15, [M - NC(CH3)3]þ), 231 (59, [M - GeCl]þ). Synthesis of [(t-Bu)2ATI]GeCtC(C5H4)Fe(C5H5) (8). To a solution of ethynyl ferrocene 6 (0.50 g, 2.38 mmol) in THF (40 mL) 1999

dx.doi.org/10.1021/om200035z |Organometallics 2011, 30, 1998–2005

R = 90° β = 114.442(3)° γ = 90° 4577.7(1)

1680.0 0.504  0.312  0.154

R = 90° β = 94.747(2)° γ = 90° 2884.4(5) 8 1.070 0.063 1024.0

volume, Å3

Z

density (calcd), Mg/m3

absorption coefficient, mm-1

F(000)

2000

R1 = 0.0897, wR2 = 0.1431

0.260 and -0.186

largest diff peak and hole, e Å-3

0.546 and -0.355

R1 = 0.0572, wR2 = 0.1302

R1 = 0.0527, wR2 = 0.1201 R1 = 0.0576, wR2 = 0.1230

final R indices [I > 2σ(I)]

R indices (all data)

8057/0/517 1.037

least-squares on F2

least-squares on F2 5087/0/319 1.073

full-matrix

full-matrix

refinement method

no. of data/restraints/params goodness-of-fit on F2

semiempirical full-matrix

semiempirical

semiempirical

abs corr

0.554 and -0.375

R1 = 0.0379, wR2 = 0.0808

R1 = 0.0341, wR2 = 0.0797

1618/0/178 1.082

least-squares on F2

1618 (Rint = 0.0402)

8057 (Rint = 0.0474)

5087 (Rint = 0.0296)

no. of indep reflns

7808

-19e l e 19

-11 e h e 11, -9 e k e 11,

23 607

-21 e l e 15

-10 e l e 10

limiting indices

2.38 to 24.99

0.504  0.291  0.162

704.0

2.089

1.421

4

γ = 90° 1586.1(4)

β = 90°

R = 90°

27 284

-19 e h e 19, -20 e k e 19,

-12 e h e 12, -36 e k e 36,

θ range for data collection, deg

b = 9.986(1) Å c = 16.714(2) Å

no. of reflns collected

1.39 to 25.00

0.524  0.324  0.184 1.33 to 25.00

cryst size, mm3

0.069

1.110

8

b = 17.082(4) Å c = 18.289(3) Å

b = 30.524(3) Å c = 9.0531(9) Å

a = 9.503(1) Å

P212121

P21/c a = 16.095(3) Å

0.71073 orthorhombic

100(2)

339.41

C15H23ClGeN2

5

0.71073 monoclinic

P21/c

0.71073 monoclinic

wavelength, Å cryst syst

100(2)

a = 10.474(1) Å

100(2)

temperature, K

382.50

C23H39LiN2O2

space group

232.36

fw

4

unit cell dimens

C15H24N2

empirical formula

3

Table 1. Crystal Data and Structure Refinement for Compounds 3-5, 8, and 9

0.458 and -0.287

R1 = 0.0467, wR2 = 0.0991

R1 = 0.0371, wR2 = 0.0944

4323/0/286 1.046

least-squares on F2

full-matrix

semiempirical

4323 (Rint = 0.0181)

6464

-10 e l e 14

-12 e h e 12, -14 e k e 14,

1.88 to 25.00

0.524  0.324  0.184

532.0

1.828

1.385

2

γ = 112.164(3)° 1229.9(4)

β = 108.320(4)°

R = 104.196(3)°

c = 12.511(2) Å

b = 11.892(2) Å

a = 10.329(2)Å

P1

0.71073 triclinic

100(2)

513.01

C27H32FeGeN2

8

0.440 and -0.234

R1 = 0.0322, wR2 = 0.0675

R1 = 0.0272, wR2 = 0.0663

3566/0/241 1.067

least-squares on F2

full-matrix

semiempirical

3566 (Rint = 0.0181)

9772

-14 e l e 14

-11 e h e 11, -11 e k e 11,

1.72 to 25.00

0.523  0.332  0.162

424.0

1.515

1.323

2

γ = 98.882(2)° 1016.6(2)

β = 92.289(3)°

R = 105.409(2)°

c = 12.319(1) Å

b = 9.3511(9) Å

a = 9.2986(9) Å

P1

0.71073 triclinic

100(2)

405.08

C23H28GeN2

9

Organometallics ARTICLE

dx.doi.org/10.1021/om200035z |Organometallics 2011, 30, 1998–2005

Organometallics Scheme 1. Synthesis of Aminotroponimine 3 with a Bulky tert-Butyl Group on Nitrogen Atoms and Its Lithium Derivative 4

ARTICLE

Scheme 2. Synthesis of Aminotroponiminatogermylene Monochloride 5 and Its Conversion to Alkynyl Germylene Complexes 8 and 9

(C16), 114.65 (C17), 117.41 (C2,6), 118.33 (C4), 126.21, 127.24, 128.45, 131.92 (Ph), 135.32 (C3,5), 160.78 (C1,7).

Structure Determination of Compounds 2-5, 8, and 9. was added n-BuLi (1.6 mL) at -78 °C with continuous stirring. After 30 min, the reaction mixture was brought to room temperature and transferred to a solution of 5 (0.80 g, 2.38 mmol) in THF (30 mL) at -78 °C with stirring. After 1 h, the reaction mixture was brought to room temperature and allowed to stir overnight. Then the solvents were removed under reduced pressure, and the resultant product was extracted using toluene. The toluene extract was filtered through a G4 frit, and the resultant filtrate was concentrated under vacuum to result in a dark red solid. This solid upon washing with hexane afforded an analytically pure sample of 7. A toluene solution of 7 was kept overnight at -32 °C to yield block-type single crystals suitable for X-ray diffraction studies. Yield: 0.79 g (1.54 mmol), 65.4%. Mp: 177 °C. Anal. Calcd for C27H32FeGeN2 (M = 513.04): C, 63.21; H, 6.29; N, 5.46. Found: C, 63.38; H, 6.44; N, 5.70. 1H NMR (300 MHz, C6D6): δ 1.60 (s, 18H, C(CH3)3), 3.89-3.90 (m, 2H, CH), 4.13 (s, 5H, C5H5), 4.43-4.44 (m, 2H, CH), 6.02 (t, 3JHH = 8.7 Hz, 1H, CH), 6.45-6.59 (m, 4H, CH). 13 C{1H} NMR (75 MHz, C6D6): δ 29.61 (C(CH3)3), 56.85 (C(CH3)3), 68.46 (CH, C5H4), 68.75 (C, C5H4), 70.09 (CH, C5H5), 71.80 (CH, C5H4), 102.22 (C16), 111.02 (C17), 117.32 (C2,6), 118.18 (C4), 135.25 (C3,5), 160.70 (C1,7). EI-MS: m/z (%) 514 (66, [M]þ), 305 (100, [M CtC(C5H4)Fe(C5H5)]þ). Synthesis of [(t-Bu)2ATI]GeCtCPh (9). To a solution of phenyl acetylene 7 (0.17 g, 1.63 mmol) in THF (10 mL) was added n-BuLi (1.12 mL) at -78 °C. After 30 min, the reaction mixture was brought to room temperature and stirred for a further 30 min. Then it was added slowly to a solution of 5 (0.55 g, 1.63 mmol) in THF (20 mL) at -78 °C. After 1 h, the reaction mixture was brought to room temperature and allowed to stir overnight. The solvents were then removed under reduced pressure to yield a dark red solid. It was extracted using toluene and filtered through a G4 frit. The filtrate was dried under reduced pressure to yield compound 9 as a deep red solid. It was recrystallized in hexane to yield an analytically pure sample of 9. Single crystals of 9 suitable for X-ray diffraction studies were grown by cooling its THF solution at -32 °C. Yield: 0.53 g (1.31 mmol), 80.7%. Mp: 103 °C. Anal. Calcd for C23H28GeN2 (M = 405.12): C, 68.19; H, 6.97; N, 6.91. Found: C, 68.48; H, 7.14; N, 6.90. 1H NMR (300 MHz, C6D6): δ 1.57 (s, 18H, C(CH3)3), 6.04 (t, 3JHH = 8.7 Hz, 1H, CH), 6.46-6.60 (m, 4H, CH), 6.94-6.99 (m, 3H, CH), 7.54 (d, 3JHH = 6.9 Hz, 2H, CH). 13C{1H} NMR (75 MHz, C6D6): δ 29.50 (C(CH3)3), 56.83 (C(CH3)3), 104.29

Single-crystal X-ray diffraction studies were carried out with a Bruker SMART APEX diffractometer equipped with 3-axis goniometer.26 Crystals were coated with a cryoprotectant and were mounted using a glass capillary. The crystals were kept under a steady flow of cold dinitrogen during the data collection. The details regarding the data collection and refinement for compounds 3-5, 8, and 9 are given in Table 1. The data were integrated using SAINT,27 and an empirical absorption correction was applied with SADABS.27 The structures were solved by direct methods and refined by full matrix least-squares on F2 using SHELXTL software.28 All the non-hydrogen atoms were refined with anisotropic displacement parameters, while the hydrogen atoms were refined isotropically on the positions calculated using a riding model.

’ RESULTS AND DISCUSSION Synthesis and Spectra. For the synthesis of the germylene monochloride complex 5, a bulky aminotroponimine with a tertbutyl group on the nitrogen atoms was prepared by following the synthetic protocol used by Dias and co-workers (for the synthesis of aminotroponimine with isopropyl groups)14 with suitable modifications. Accordingly, the reaction of 2-(tosyloxy)tropone23 1 with an excess of tert-butylamine under reflux conditions led to the isolation of yellow-colored 2-(tert-butylamino)tropone29 2 in about 70% yield (Scheme 1). The completion of this reaction was monitored periodically, by checking the disappearance of 1 through TLC. Further, the reaction of 2 with 1.1 equivalents of Et3O 3 BF4 in dichloromethane and excess tert-butylamine at room temperature afforded the desired aminotroponimine [(t-Bu)2ATI]H (3) as a yellow solid with a yield of 70.4% (Scheme 1). Treatment of 3 in THF with an equimolar amount of n-BuLi at -78 °C gave the lithium derivative 4 as a yellow solid in near quantitative yields (Scheme 1). A low-temperature reaction of 4 with GeCl2 3 (1,4-dioxane) in a 1:1 ratio afforded the desired germylene monochloride complex 5 in an excellent yield (98.5%) as a bright orange solid (Scheme 2). The red-colored alkynyl germylene derivatives 8 and 9 were synthesized through the reaction of 5 with the lithium derivative of ethynyl ferrocene 6 and phenyl acetylene 7 in a ratio of 1:1 at -78 °C, respectively (Scheme 2). Interestingly, compound 8 is 2001

dx.doi.org/10.1021/om200035z |Organometallics 2011, 30, 1998–2005

Organometallics

ARTICLE

Table 2. Selected Bond Lengths (Å) and Angles (deg) for Compounds 3-5, 8, and 9 Compound 3 (Molecule 1) C(1)-N(1)

1.296(2)

C(7)-N(2)-H(2A)

114.3

C(7)-N(2)

1.340(2)

N(1)-C(1)-C(7)

112.3(1)

C(1)-C(7)

1.515(2)

N(2)-C(7)-C(1)

110.5(1)

N(2)-H(2A)

0.860 Compound 3 (Molecule 2)

Figure 1. Molecular structure of the aminotroponimine 3 with a tertbutyl substituent on the nitrogen atoms. Except H2A all the other hydrogen atoms are omitted for clarity. One of the two molecules present in the asymmetric unit is shown.

C(16)-N(3)

1.305(2)

C(22)-N(4)-H(4A)

114.2

C(22)-N(4)

1.335(2)

N(3)-C(16)-C(22)

112.2(1)

C(16)-C(22)

1.511(2)

N(4)-C(22)-C(16)

111.1(1)

N(4)-H(4A)

0.860 Compound 4 (Molecule 1)

the first alkynyl germylene derivative to have a ferrocenyl moiety on the terminal alkynyl carbon atom. The compounds 2-5, 8, and 9 are freely soluble in common organic solvents such as toluene, THF, and ether. Although compounds 2 and 3 are stable at ambient conditions, prolonged storage of the latter has to be done at low temperatures to prevent its decomposition. In contrast, compounds 4, 5, 8, and 9 are sensitive toward air and moisture and require inert atmosphere for their stability. Apart from the required N2 or Ar atmosphere for the stability of 4, low-temperature conditions are also necessary. All the compounds 2-5, 8, and 9 were characterized by elemental analysis, IR and multinuclear NMR spectroscopy (1H, 7Li, and 13 C), and mass spectrometry. A broad singlet (7.73 ppm) in the 1 H NMR spectrum of 2 shows the presence of a N-H group. It is supported by a broad band at 3256 cm-1 in the IR spectrum of 2. The 1H NMR spectrum of 3 displays a sharp (1.34 ppm) and broad singlet (8.59 ppm) due to the tert-butyl groups and N-H moiety, respectively. As anticipated, the N-H chemical shift in the 1H NMR spectrum of 3 is shifted more downfield than that present in 2 (vide supra), and in the IR spectrum of 3, a broad band due to the N-H group appears at 3047 cm-1. A singlet at 1.76 ppm in the 7Li NMR spectrum of 4 confirms the presence of a lithium center. The two THF molecules that are coordinated to the lithium center in 4 are readily identified from the 1H NMR spectrum by the appearance of a multiplet and triplet at 1.29-1.34 and 3.41 ppm, respectively. Furthermore, the equivalence of the tert-butyl groups on the nitrogen atoms is confirmed by the appearance of a sharp singlet at 1.50 ppm. A similar trend is observed in the 1H NMR spectra of the heteroleptic germylene derivatives 5, 8, and 9 [5 (1.56 ppm), 8 (1.60 ppm), and 9 (1.57 ppm)]. Also, in the 1H NMR spectra of compounds 3-5, all five protons present on the C7 seven-membered ring of these compounds appear in the range from 6.01 to 6.98 ppm. This observation matches well with the range (6.06-7.05 ppm) in which the C7 seven-membered ring protons were seen in the 1H NMR spectra of the corresponding isopropyl analogues.14,15a,30 Strikingly, the 1H NMR resonances corresponding to the C7 seven-membered ring protons in the alkynyl germylene complexes 8 and 9 also lie within the aforementioned range observed with respect to compounds 3-5. In the 13C NMR spectrum of 8 the resonances due to the alkynyl carbon atoms are found at 102.2 and 111.0 ppm. The same values for compound 9 are observed at 104.3 and 114.7 ppm. These values are evocative of a similar

Li(1)-O(1)

1.965(4)

O(1)-Li(1)-N(1)

116.6(2)

Li(1)-O(2)

1.987(4)

O(1)-Li(1)-N(2)

120.4(2)

Li(1)-N(1)

1.977(4)

O(2)-Li(1)- N(1)

117.2(2)

Li(1)-N(2)

1.987(4)

O(2)-Li(1)-N(2)

115.5(2)

C(1)-N(1)

1.311(3)

N(1)-Li(1)-N(2)

81.4(2)

C(7)-N(2)

1.312(3)

O(1)-Li(1)-O(2)

105.2(2)

C(1)-C(7)

1.522(3) Compound 4 (Molecule 2)

Li(2)-O(3)

1.989(4)

O(3)-Li(2)-N(3)

111.7(2)

Li(2)-O(4)

1.981(4)

O(3)-Li(2)-N(4)

115.0(2)

Li(2)-N(3)

1.997(4)

O(4)-Li(2)-N(3)

121.9(2)

Li(2)-N(4)

1.983(4)

O(4)-Li(2)-N(4)

118.6(2)

C(24)-N(3)

1.314(2)

N(3)-Li(2)-N(4)

81.7(1)

C(30)-N(4)

1.312(3)

O(3)-Li(2)-O(4)

106.6(2)

C(24)-C(30)

1.525(3) Compound 5

Ge(1)-Cl(1)

2.362(1)

N(1)-Ge(1)-Cl(1)

98.5(1)

Ge(1)-N(1)

1.983(3)

N(2)-Ge(1)-Cl(1)

94.91(9)

Ge(1)-N(2)

1.973(3)

N(2)-Ge(1)-N(1)

81.5(1)

C(1)-N(1)

1.323(5)

C(1)-N(1)-Ge(1)

113.4(2)

C(7)-N(2)

1.339(5)

C(7)-N(2)-Ge(1)

114.8(2)

C(1)-C(7)

1.485(5) Compound 8

Ge(1)-C(16)

1.997(3)

N(1)-Ge(1)-C(16)

96.6(1)

Ge(1)-N(1)

1.979(2)

N(2)-Ge(1)-C(16)

96.7(1)

Ge(1)-N(2)

1.993(2)

N(1)-Ge(1)-N(2)

C(1)-N(1)

1.331(4)

C(17)-C(16)-Ge(1)

168.4(3)

C(7)-N(2)

1.330(4)

C(16)-C(17)-C(18)

178.8(4)

C(1)-C(7)

1.480(4)

C(1)-N(1)-Ge(1)

115.2(2)

C(16)-C(17)

1.192(4)

C(7)-N(2)-Ge(1)

115.1(2)

C(17)-C(18)

1.443(4)

80.7(1)

Compound 9

2002

Ge(1)-C(16)

2.017(2)

N(1)-Ge(1)-C(16)

95.84(7)

Ge(1)-N(1)

1.980(3)

N(2)-Ge(1)-C(16)

94.15(8)

Ge(1)-N(2)

1.970(3)

N(2)-Ge(1)-N(1)

N(1)-C(1)

1.337(3)

C(17)-C(16)-Ge(1)

80.73(7) 170.8(2)

N(2)-C(7)

1.339(3)

C(16)-C(17)-C(18)

176.4(2)

C(1)-C(7)

1.492(3)

C(1)-N(1)-Ge(1)

115.9(1)

C(16)-C(17)

1.209(3)

C(7)-N(2)-Ge(1)

116.2(1)

C(18)-C(17)

1.444(3) dx.doi.org/10.1021/om200035z |Organometallics 2011, 30, 1998–2005

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Figure 2. Molecular structure of the lithium salt 4 derived from 3. All the hydrogen atoms are omitted for clarity. One of the two molecules present in the asymmetric unit is shown. Figure 4. Molecular structure of the alkynyl germylene derivative 8 with a ferrocenyl substituent. All the hydrogen atoms are omitted for clarity.

Figure 3. Molecular structure of the aminotroponiminatogermylene monochloride 5. All the hydrogen atoms are omitted for clarity.

situation that prevails in compound III stabilized through a bulky β-diketiminate ligand where the alkynyl carbons were observed at 103.3 and 113.0 ppm.21 The resonances for the carbon atoms of the C7 seven-membered ring present in compounds 3-5, 8, and 9 appear as four singlets in the range from 108.4 to 163.5 ppm in their 13C NMR spectra, and this trend indicates the symmetric nature of molecules 3-5, 8, and 9 in solution. X-ray Crystal Structure of Compounds 2-5, 8, and 9. The formation of the compounds 2-5, 8, and 9 was further confirmed by the structural studies in the solid state. The crystals of compounds 2-5, 8, and 9 suitable for single-crystal X-ray diffraction studies were grown by cooling their concentrated solutions at low temperatures (see Experimental Section for details). The crystals of compounds 2-4, 5, and 8/9 were yellow, orange, and dark red, respectively. Details regarding the important structural parameters for compounds 3-5, 8, and 9 are summarized in Table 1. The molecular structure of compounds 3-5, 8, and 9 are shown in Figures 1-5. Selected bond lengths and angles for compounds 3-5, 8, and 9 are given in Table 2. This information for compound 2 is provided in the Supporting Information. In the structure of compound 3, the average -NdC (imine) bond length [1.309 Å] is considerably shorter (Table 2) than the average -(H)N-C (amine) bond [1.338 Å]. Further, to avoid steric repulsion with respect to the hydrogen atom on the C2 and C6 carbon atoms, the tert-butyl groups on the nitrogen atoms bend away from the C7 seven-membered ring (Figure 1). A similar trend is also observed in the molecular structure of compounds 4, 5, 8, and 9 (Figures 2-5). These features can also be seen in the

structure of the related compound [(i-Pr)2ATI]H.14 The lithium derivative 4 obtained by the lithiation of 3 has a five-membered C2N2Li ring (Figure 2). The Li atom in 4 is tetracoordinate with two nitrogen atoms of the ATI ligand and two oxygen atoms of two coordinate THF molecules, and this arrangement leads to a distorted tetrahedral geometry around it. The germylene monochloride complex 5 (Figure 3) obtained from the lithium derivative 4 has a puckered C2N2Ge fivemembered ring (vide infra). The Ge(II)-Cl [2.362(1) Å] and the average Ge(II)-N bond length (1.978 Å) in compound 5 are consistent with the corresponding values [average Ge-Cl and Ge-N bond length is 2.368 and 1.956 Å, respectively] observed in the germylene monochloride [(i-Pr)2ATI]GeCl.15a The NGe-Cl bond angles [98.5(1)° and 94.91(9)°] in 5 vary markedly, and this may be due to the puckered nature of the C2N2Ge five-membered ring. The tricoordinate germanium center has two nitrogen atoms of the ATI ligand and a chlorine atom in its coordination sphere and adopts a distorted trigonal-pyramidal geometry. This geometry reveals the presence of a stereochemically active lone pair, and this feature has been witnessed in various germylene monochloride complexes such as [HC{C(Me)N(Ar)}2] GeCl,6e [PhC{N(t-Bu)}2]GeCl,8b [t-BuC{N(Ar)}2]GeCl,8a and [(i-Pr)2ATI]GeCl.11,15a The alkynyl germylene derivatives 8 and 9 obtained from the reaction of 5 with the lithium derivative of ethynyl ferrocene and phenyl acetylene contain a C2N2Ge five-membered ring with a CtC-R moiety [8, R = (C5H4)Fe(C5H5) (Figure 4), and 9, R = Ph (Figure 5)] attached to the germanium(II) center, respectively. The Ge-CtC bond angle in 8 [168.4(3)°] and 9 [170.8(2)°] reveal a slightly bent nature of the GeC2 moiety, and this is reminiscent of the situation that prevails in the known alkynyl germylene complexes I [Ge-CtC bond angle: 171.1(5)°],20 II [Ge-CtC bond angle: 165.6(4)°],20 III [Ge-CtC bond angle: 171.0(3)°],21 and [PhCtCGe{N(SiMe3)C(Ph)C(SiMe3) (C5H4N-2)}] [Ge-CtC bond angle: 165.0(4)°]22 In view of the Ge-C [8, Ge1-C16 = 1.997(3); 9, Ge1-C16 = 2.017(2) Å] and CtC [8, C16-C17 = 1.192(4); 9, C16-C17 = 1.209(3) Å] bond lengths, which are devoid of any surprises18i,31 in these novel ATI ligand-stabilized alkynyl germylenes, it is explicit that there is no significant interaction between the Ge(II) center and the π electrons in the CtC bond. A similar condition also 2003

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Organometallics

Figure 5. Molecular structure of the alkynyl germylene derivative 9 with a phenyl substituent. All the hydrogen atoms are omitted for clarity.

ARTICLE

slight puckering of the C7 seven-membered and C2N2Li fivemembered rings. The average dihedral angle [in molecule 1: 5.07(7)°, molecule 2: 12.03(6)] between the C7 seven-membered ring and C2N2Li five-membered ring is 8.55°. This is in contrast to that observed in [(i-Pr)2ATI]Li 3 (THF)2 where the dihedral angle is 16.9° and is evocative of a significant puckering.30 Nevertheless, the relationship between 5 and its isopropyl analogue [(i-Pr)2ATI]GeCl is exactly opposite15a to what has been seen (vide supra) between 4 and [(i-Pr)2ATI]Li 3 (THF)2. Thus, in the structure of 5 (Figure 6b) both the C7 seven-membered and C2N2Ge five-membered rings are appreciably puckered and the dihedral angle between the ring systems is 19.99(8)°. However, in compound [(i-Pr)2ATI]GeCl both ring systems are almost planar.15a The trend seen in compound 5 can also be seen in the alkynyl germylene complex 8, with a ferrocenyl moiety. Both the rings (C7 seven-membered and C2N2Ge five-membered) are puckered, but to a lesser extent than that seen in 5. Therefore, the dihedral angle [13.75(8)°] between the mean planes passing through the rings in 8 is less than the same angle found in 5. In view of the presence of a smaller and planar phenyl group, the alkynyl germylene complex 9 shows a relatively smaller degree of puckering (the dihedral angle between the C7 seven-membered and C2N2Ge five-membered rings is [7.28(4)°]) than that seen in 8. In summary, by utilizing the bulky aminotroponimine 3 (synthesized through a facile synthetic route from 1) we have isolated the novel germylene monochloride complex 5. Reaction of compound 5 with the lithium salt derived from ethynyl ferrocene 6 and phenyl acetylene 7 afforded the alkynyl germylene complexes 8 and 9, respectively. Compounds 8 and 9 are the first examples of ATI ligand-stabilized alkynyl germylenes, and efforts to study the reactivity of these novel derivatives are in progress in our research group. Also, we are exploiting various bulky ATI ligands for the stabilization of compounds with lowvalent silicon centers.

’ ASSOCIATED CONTENT Figure 6. View of the C7 seven-membered and C2N2X five-membered (X = Li, 4; X = Ge, 5, 8, 9) rings through the C1-C7 bond axis in compounds 4 (a), 5 (b), 8 (c), and 9 (d). All the hydrogen atoms and the tert-butyl groups are omitted for clarity. For 4 one of the two molecules in the asymmetric unit is shown.

prevails in the structure of the known alkynyl germylene complexes (vide supra).20-22 In contrast to the Ge-N bond lengths in compound 9 [Ge1-N1 1.980(3); Ge1-N2 1.970(3) Å], which are close to each other, the Ge-N bond lengths in compound 8 [Ge1-N1 1.979(2); Ge1-N2 1.993(2) Å] differ significantly, and this may be attributed to the spatial requirements of the larger ferrocenyl moiety in comparison to the smaller and planar phenyl group. The N-X-N bond angles in compounds 4 [X = Li; 81.4(1)°], 5 [X = Ge; 81.5(1)°], 8 [X = Ge; 80.7(1)°], and 9 [X = Ge; 80.73(7)°] are almost constant, and it matches with the same angle observed in compounds such as [(i-Pr)2ATI]Li 3 (THF)2 [81.5(2)°]30 and [(i-Pr)2ATI]GeCl [80.2(2)°].15a Since compounds 4, 5, 8, and 9 contain homocyclic C7 sevenmembered and heterocyclic C2N2X five-membered ring systems, it is interesting to analyze their relative orientation for a comparative study. For this purpose, a view of these molecules (4, 5, 8, and 9) through the C1-C7 bond axis seems to be most appropriate (Figure 6). In the case of lithium derivative 4 (Figure 6a), there is a

bS

Supporting Information. Crystal data (CIF) for compounds 2-5, 8, and 9, important structural parameters for compound 2 (Table S1), molecular structure of 2 (Figure S1), and selected bond lengths and angles for compound 2 (Table S2). This material is available free of charge via the Internet at http:// pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*Phone: þ91-11-2659 1523. Fax: þ91-11-2658 1102. E-mail: sisn@ chemistry.iitd.ac.in.

’ ACKNOWLEDGMENT R.K.S. thanks the Council of Scientific and Industrial Research (CSIR)-New Delhi, India, for a Junior Research Fellowship. S.N. thanks the Department of Science and Technology (DST)New Delhi, India, for financial support (SR/S1/IC-23/2008) and a single-crystal X-ray diffractometer under the FIST program to the Department of Chemistry, IIT Delhi, New Delhi, India.

’ DEDICATION † Dedicated to Prof. S. S. Krishnamurthy on the occasion of his 70th birthday. 2004

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dx.doi.org/10.1021/om200035z |Organometallics 2011, 30, 1998–2005