Use of 73Ge NMR Spectroscopy and X-ray Crystallography for the

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Organometallics 2010, 29, 582–590 DOI: 10.1021/om900905c

Use of 73Ge NMR Spectroscopy and X-ray Crystallography for the Study of Electronic Interactions in Substituted Tetrakis(phenyl)-, -(phenoxy)-, and -(thiophenoxy)germanes Claude H. Yoder,*,† Tamara M. Agee,† Allison K. Griffith,† Charles D. Schaeffer, Jr.,‡ Mary J. Carroll,‡ Alaina S. DeToma,‡ Adam J. Fleisher,‡ Cameron J. Gettel,‡ and Arnold L. Rheingold§ †

Department of Chemistry, Franklin and Marshall College, Lancaster, Pennsylvania 17604-3003, Department of Chemistry and Biochemistry, Elizabethtown College, Elizabethtown, Pennsylvania 170222298, and §Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0314

‡

Received October 14, 2009

NMR chemical shifts of 1H, 13C, and 73Ge, molecular modeling, and single-crystal X-ray diffraction results are reported for a series of substituted tris- and tetrakis(phenyl)germanes of the type (XC6H4)3GeY and (XC6H4)4Ge, where X = o-, m-, and p-OCH3, o-, m-, and p-OC2H5, m- and p-CF3, H, p-C(CH3)3, p-Cl; and Y = Cl and H. Chemical shifts and X-ray data are also reported for o-CH3 and o-OCH3 tetrakis(phenoxy)- ((XC6H4O)4Ge) and thiophenoxygermanes ((XC6H4S)4Ge). For tetrakis derivatives, 73 Ge resonances are observed for all but the o-methoxyphenoxy compound, for which the inability to detect a resonance is attributed to rapid quadrupolar relaxation caused by intramolecular interactions of the methoxy oxygen with the central atom. The observation of a relatively broad, slightly upfield 73Ge resonance in the analogous phenyl and thiophenoxy derivatives suggests, as do the results of molecular modeling, that in these compounds there is some hypercoordination. The solid-state structures show bond angles at the aromatic carbon bearing the alkoxy group that suggest an interaction of the alkoxy oxygen with germanium. Oxygen-germanium bond distances are about 17% shorter than the sum of the van der Waals radii.

Introduction Our recent use of 73Ge NMR spectroscopy for the study of intra- and intermolecular coordination to germanium utilized symmetrical derivatives that contained a basic, potentially coordinating site at the end of an aliphatic chain.1 The 73 Ge resonance in these systems was found to be easily observable for all derivatives except the dialkylaminoethyl derivatives. The lack of an observable resonance was attributed to the perturbation of tetrahedral symmetry caused by hypercoordination and the consequent rapid quadrupolar relaxation. Our recent work indicates that the low-frequency shifts that so nicely characterize hypercoordination in silicon and tin are also observed with the quadrupolar 73Ge, though with greater difficulty.1-3 When the extent of hypercoordination is insufficient to cause a significant low-frequency shift, it may nevertheless produce considerable broadening due to its effect on the symmetry of the electric field surrounding the 73Ge nucleus.1 *To whom correspondence should be addressed. E-mail: claude. [email protected]. (1) Yoder, C. H.; Agee, T. M.; Schaeffer, C. D., Jr.; Carroll, M. J.; Fleisher, A. J.; DeToma, A. S. Inorg. Chem. 2008, 47, 10765–10770. (2) Marsmann, H. C.; Uhlig, F. In The Chemistry of Organic Germanium, Tin and Lead Compounds; Rappoport, Z., Ed.; Wiley-Interscience: New York, 2002; Vol. 2, Chapter 6. (3) Takeuchi, Y; Takayama, T. Annu. Rep. NMR Spectrosc. 2005, 54, 155–200. pubs.acs.org/Organometallics

Published on Web 01/11/2010

The present study is designed to explore hypercoordination in ortho-substituted tetraphenyl-, tetraphenoxy-, and tetrathiophenoxygermanes, where coordination of a basic ortho site would generate a four-membered ring for the phenyl derivatives and a five-membered ring for the phenoxy and thiophenoxy analogues.

Results and Discussion Syntheses and Characterization. Tetrakis(phenyl)germanes were prepared by Grignard reaction of the appropriate substituted phenyl bromide with GeCl4, while the tetrakis(phenoxy) and tetrakis(thiophenoxy) derivatives were prepared by reaction of the substituted phenol or thiophenol with GeCl4. The attempted syntheses of the tetrakis(o-ethoxy)-, -(o-trifluoromethyl)-, -(m-methoxy)-, and -(m-ethoxy)phenyl derivatives using the Grignard reagent with a 5-8 h reflux in THF produced primarily the tris derivatives (XC6H4)3GeCl. The use of the higher boiling solvent toluene and 30-40 h reaction times afforded the tetrakis derivatives. In one attempt (in THF using a 20% excess of magnesium to form the Grignard reagent in 8 M excess relative to GeBr4, followed by a 40 h reflux period and the usual ammonium chloride hydrolysis workup), the tris(o-ethoxyphenyl) hydride was obtained. The compounds were characterized by elemental analyses (Experimental Section) and NMR data. Carbon-13 chemical r 2010 American Chemical Society

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Organometallics, Vol. 29, No. 3, 2010

Table 1. Carbon-13 NMR Chemical Shift Data (δ in ppm) for Phenylgermanesa δ C1

X

δ C2

δ C3

δ C4

δ C5

δ C6

128.3 120.6 113.9 120.1 129.3 114.4 125.0 128.8 129.3 125.4 129.0

135.4 136.7 136.5 137.0 127.6 136.5 135.2 136.3 134.9 135.5 135.4

129.4 120.5 129.2

127.7 135.4 127.5

120.4

136.7

120.1

121.4

120.0 126.8

121.3 119.2

A. Tetrakis(phenyl), (X-C6H4)4Ge H o-OCH3b p-OCH3c o-OC2H5d m-OC2H5e p-OC2H5f p-C(CH3)3g p-Cl m-CF3h p-CF3i p-CH3j

136.1 127.5 127.6 127.5 138.7 127.5 133.1 132.9 138.4 138.5 133.1

135.4 163.0 136.5 162.3 119.8 136.5 135.2 136.3 131.4 135.5 135.4

128.3 110.3 113.9 109.6 159.2 114.4 125.0 128.8 131.2 125.4 129.0

129.1 129.7 160.3 129.3 116.2 159.7 151.1 136.1 127.0 132.2 138.7

B. Tris(phenyl), (X-C6H4)3GeCl k

m-OCH3 o-OC2H5l m-OC2H5m

138.6 126.1 137.2

119.4 162.1 121.4

159.2 110.6 158.6

115.6 131.2 114.8

C. Tris(phenyl), (X-C6H4)3GeH o-OC2H5n

125.4

162.4

110.5

130.1

D. Tris(phenoxy), (X-C6H4O)3GeH o-OCH3

o

146.5

145.6

110.7

114.5

E. Tetrakis(phenoxy), (X-C6H4O)4Ge o-OCH3p o-CH3q

146.6 153.1

145.6 129.1

110.7 131.1

114.5 123.1

F. Tetrakis(thiophenoxy), (X-C6H4S)4Ge o-OCH3 o-CH3s

r

119.2 128.8

159.3 143.0

110.6 128.5

129.0 130.4

120.4 126.2

136.1 137.0

a Chemical shift in CDCl3 relative to external TMS. C1: germaniumbonded ring carbon, the ipso carbon. b OCH3, 55.2. c OCH3, 55.0. d OCH2, 62.8; CH3, 13.9. e OCH2, 63.0; CH3, 14.6. f OCH2, 63.1; CH3, 14.8. g C, 34.6; C(CH3) 3, 31.3. h CF3, 124.0. |J(13C-19F)| coupling: C-3, 32.3; C-4, 3.7; CF3, 272.7 Hz; others, not detected. i CF3, 123.9. |J(13C-19F)| coupling: C-3,5, 3.6; C-4, 32.5; CF3, 272.4 Hz; others, not detected. j CH3, 21.4. Lit.10,12 values. k OCH3, 54.8. l OCH2, 63.4; CH3, 14.2. m OCH2, 63.1; CH3, 14.7. n OCH2, 63.5; CH3, 14.4. o OCH3, 55.8. p OCH3, 55.7. q CH3, 16.1. r OCH3, 55.3. s CH3, 21.9.

shifts for all derivatives are reported in Table 1, where the ipso ring carbon is labeled C1. Assignments of 13C resonances were based on (1) additivity relationships; (2) off-resonance protoncoupled spectra; (3) comparison of 13C chemical shifts with those reported in previous studies of substituted tert-butylbenzenes,4 phenyltrimethylsilanes,4 phenyltrimethylgermanes,4,5 and phenyltrimethylstannanes;6,7 and (4) established trends in magnitude of J(19F-13C) coupling constants in some of (4) Schaeffer, C. D., Jr.; Zuckerman, J. J.; Yoder, C. H. J. Organomet. Chem. 1974, 80, 29–35. (5) Fleisher, A. J.; Schaeffer, C. D., Jr.; Buckwalter, B. A.; Yoder, C. H. Magn. Reson. Chem. 2006, 44, 191–194. (6) Schaeffer, C. D., Jr.; Zuckerman, J. J. J. Organomet. Chem. 1973, 47, C1–C4. (7) Schaeffer, C. D., Jr.; Zuckerman, J. J. J. Organomet. Chem. 1973, 55, 97–110. (8) Vaickus, M. J.; Anderson, D. G. Org. Magn. Reson. 1980, 14, 278– 279. (9) Batchelor, R. J.; Birchall, T. J. Am. Chem. Soc. 1983, 105, 3848– 3852. (10) (a) Charissee, M.; Mathiasch, B.; Dr€ager, M.; Russo, U. Polyhedron 1995, 14, 2429–2439. (b) Charissee, M.; Zickgraf, A.; Stenger, H.; Br€au, E.; Desmarquet, C.; Dr€ager, M.; Gerstmann, S.; Dakternieks, D.; Hook, J. Polyhedron 1998, 17, 4497–4506.

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these systems. Literature values of tetraphenylgermane8-10 and tetrakis(p-tolyl)germane10-12 are in excellent agreement with those determined here, with the exception of the 141.5 ppm carbon-13 chemical shift reported for tetraphenylgermane by Batchelor et al.9 for C1 (both Vaickus et al.8 and Dr€ ager et al.10 report 136.2 ppm). Proton shifts are reported in Table 2. Hypercoordination, 73Ge Resonances. Hypercoordination at the central germanium was explored with 73Ge NMR data, and structures were determined by X-ray diffraction. The 73 Ge NMR shifts and half-height widths are reported in Table 2, which shows relatively sharp resonances for all of the tetrakis(phenyl)germanes. Only four of the 12 derivatives have half-height widths greater than 33 Hz. Ten of these derivatives have 73Ge shifts ranging from -25 to -33 ppm, while the two ortho-alkoxy derivatives have more negative shifts of -41.6 and -39.6 ppm for the methoxy and ethoxy, respectively. Thus, the germanium resonance for both the o-alkoxy phenyl compounds is shifted upfield (to lower frequency) by 7-8 ppm relative to the other derivatives. The increase in the width of the 73Ge peak for these derivatives is noteworthy, but not large. This small shielding and increase in width could be explained by coordination of the ortho oxygen to the germanium in solution, and there is some evidence (see below) for this interaction in the solid-state structures. The tetrakis(ortho-methoxyphenoxy) derivative shows no 73Ge resonance at either -40 or 20 °C. For comparison, the resonance for the ortho-methylphenoxy derivative had a half-height width of 94 Hz, and the ortho-methyl- and orthomethoxythiophenoxy derivatives both display 73Ge resonances with half-height widths of 139 and 216 Hz, respectively. The lack of an observable 73Ge resonance in the orthomethoxyphenoxy derivative can be attributed1 to interaction of the ortho oxygen with germanium, which changes the electric field gradient sufficiently to increase the relaxation time and gives rise to a very broad and unobservable resonance. Interestingly, the thiophenoxy compounds do exhibit 73Ge resonances. The smaller extent of hypercoordination in the thio derivatives is in agreement with our previous work with the compound Ge(SCH2CH2N(CH3)2)4 and can be attributed to the lower acidity at germanium due to the lower electronegativity of sulfur relative to oxygen and also to the steric hindrance provided by the larger sulfur atoms surrounding the germanium. Not surprisingly, a 73Ge resonance could not be observed for the lower-symmetry tris derivatives. Hypercoordination, Structures. Single-crystal X-ray diffraction data for six tris- and tetrakis(germanes) are summarized in Table 3 and presented as ORTEP diagrams in Figures 1-6. The considerable number of previous X-ray (11) Charissee, M.; Roller, S.; Dr€ager, M. J. Organomet. Chem. 1992, 427, 23–31. (12) Schneider-Koglin, C.; Mathiasch, B.; Dr€ager, M. J. Organomet. Chem. 1993, 448, 39–46. (13) Takeuchi, Y.; Harazono, T.; Kakimoto, N. Inorg. Chem. 1984, 23, 3835–3836. (14) Takeuchi, Y.; Nishikawa, M.; Tanaka, K.; Takayama, T.; Imanari, M.; Deguchi, K.; Fujito, T.; Sugisaka, Y. Chem. Commun. 2000, 687–688. (15) Takeuchi, Y.; Tanaka, K.; Aoyagi, S.; Yamamoto, H. Magn. Reson. Chem. 2002, 40, 241–243. (16) Takeuchi, Y.; Nishikawa, M.; Tanaka, K.; Takayama, T. Chem. Lett. 2001, 572–573.

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Table 2. 1H and 73Ge Chemical Shifts and 73Ge Line Widths for Phenyl-, Phenoxy-, and Thiophenoxygermanes X

1

H aromatic (δ in ppm)a

1

H other (δ in ppm)a

δ 73Ge (δ in ppm)b

Δν1/2 (Hz)c

-33.0 -41.6 -27.1 -39.6 -31.1 -24.6 -29.5 -36.2 -30.4 -33.3 -32.9 -31.6

30 75 29 86 81 33 26 32 28 22 11 11

n.o. n.o. n.o.

n.o. n.o. n.o.

n.o.

n.o.

(-300)

(>1 104)

-98.5 n.o.

94 n.o.

98.0 92.4

139 216

A. Tetrakis(phenyl), (X-C6H4)4Ge H o-OCH3 p-OCH3 o-OC2H5 m-OC2H5 p-OC2H5 p-C(CH3)3 p-Cl m-CF3 p-CF3 m-CH3d p-CH3d

7.24-7.57 6.78-7.39 6.92-7.45 6.78-7.39 6.92-7.46 6.92-7.46 7.16-7.18 7.36 7.57-7.77 7.58-7.69

3.31, OCH3 3.82, OCH3 0.65, CH3; 3.65, OCH2 1.23, CH3; 5.55, OCH2 1.43, CH3; 4.05, OCH2 1.21, C(CH3) 3

B. Tris(phenyl), (X-C6H4)3GeCl m-OCH3 o-OC2H5 m-OC2H5

6.83-6.88 7.49-7.51 7.00-7.36

3.41, OCH3 1.00, CH3; 3.89, OCH2 1.42, CH3; 4.02, OCH2 C. Tris(phenyl), (X-C6H4)3GeH

o-OC2H5

6.77-7.36

1.03, CH3; 3.87, OCH2; H, 5.78 D. Tris(phenoxy), (X-C6H4O)3GeH

o-OCH3

6.61-6.97

3.76, OCH3; H, 5.73 E. Tetrakis(phenoxy), (X-C6H4O)4Ge

o-CH3 o-OCH3

6.89-7.30 6.88-7.33

2.33, CH3 3.88, OCH3 F. Tetrakis(thiophenoxy), (X-C6H4S)4Ge

o-CH3 o-OCH3

6.94-7.21 6.65-7.17

2.18, CH3 3.72, OCH3

a Chemical shift in CDCl3, relative to external TMS; n.o., not observed. b Chemical shift in CDCl3, relative to external tetramethylgermanium. c Halfheight line width for 73Ge resonances. d Lit.32 e Germanium-73 shifts for tetraphenylgermane13-15,32 and several ortho-, meta-, and para-substituted tetrakis(phenyl)germanes16,32 in solution and solid state have been reported.

structural studies on tetraphenylgermanes and tetraphenylstannanes17 indicates that most have crystallographic P 421c (S4) symmetry.18 The molecules are approximately S4 with four smaller (ca. 108-109°) and two larger bond angles (ca. 110-111°) around the central atom (M). The phenyl rings are twisted out of the plane of the C-M-C plane, giving each phenyl3M group a propeller shape.19 Tetraphenylgermane has P 421c symmetry,18,20 while tetrakis(p-tolyl)germane has the space group Pc.11,21,22 Tris(o-tert-butoxybenzyl)germane has space group P 1 with three different Ge-O distances, two of which (3.2-3.3 A˚) are about 10% shorter than the sum of the van der Waals radii (3.62 A˚).23 A series of tris[(o-methoxymethyl)phenyl]germanes containing halogens, methyl, or phenyl on germanium have been described as hypercoordinated trigonalbipyramidal structures with at least one germanium-oxygen (17) Wharf, I.; Simard, M. G. J. Organomet. Chem. 1997, 532, 1–9. (18) Chieh, P. C. J. Chem. Soc. A 1972, 1207–1208. (19) Mackay, K. M. Structural Aspect of Compounds Containing C-E (E = Ge, Sn, Pb) Bonds. In Chemistry of Organic Germanium, Tin and Lead Compounds; Patai, S., Ed.; Wiley: New York, 1995; Vol. 1, p 103. (20) Chieh, P. C. J. Chem. Soc. A 1971, 3243–3245. (21) Charissee, M.; Gauthey, V.; Dr€ager, M. J. Organomet. Chem. 1993, 448, 47–53. (22) Schneider-Koglin, C.; Mathiasch, B.; Dr€ager, M. J. Organomet. Chem. 1994, 469, 25–32. (23) Takeuchi, Y.; Yamamoto, H.; Tanaka, K.; Ogawa, K.; Harada, J.; Iwamoto, T.; Yuge, H. Tetrahedron 1998, 54, 9811–9822.

distance of about 2.8 A˚, except when the substituent is methyl or phenyl (the phenyl derivative is tetrahedral, while the methyl derivative has one germanium-oxygen distance of 3.15 A˚ and was described as monocapped tetrahedral24). The structures of the ortho-substituted tetrakis(phenyl) derivatives studied in this work show P 1, P2(1)/n, or C2/c crystallographic symmetry (Table 3). Table 4 summarizes bond angles around germanium and alkoxy-oxygen to germanium distances for these compounds. Tris(o-ethoxyphenyl)chlorogermane has two independent molecules in the unit cell and therefore two different sets of bond angles. The angles around germanium are close to tetrahedral values with variations from 105° to 112° for all but the tris(o-ethoxyphenyl)chlorogermane. The tetrakis(ortho-alkoxy) compounds have one angle at germanium that is significantly larger than the average and one angle that is significantly smaller. For example, for the o-methoxyphenyl derivative the angles are 112.0°, 110.4°, 110.4°, 109.3°, 108.5°, and 106.3°. All of the ortho derivatives have structures with the alkyl group of the ortho substituent pointed away from the germanium, thereby placing the lone pairs at oxygen in a position to interact with the germanium. This orientation is not necessarily adopted because of (24) Sugiyama, Y.; Matsumoto, T.; Yamamoto, H.; Nishikawa, M.; Kinoshita, M.; Takei, T.; Mori, W.; Takeuchi, Y. Tetrahedron 2003, 59, 8689–8696.

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an intramolecular interaction, but may be a result of the steric requirements of groups relative to the rest of the structure. Another structural feature suggestive of hypercoordination is the presence of a smaller bond angle at the aromatic carbon attached to the alkoxy oxygen toward the germanium

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relative to the angle at the same atom away from the germanium. For example, Figure 7 shows that in tetrakis(o-methoxyphenyl)germane the average angles at each of the four aromatic carbons bearing the methoxy substitutent are 114.9° and 123.6°, with the smaller angle being toward the germanium. This is particularly interesting given the

Table 3. Crystal and Structural Refinement Data

formula fw T, K wavelength, A˚ cryst syst space group a, A˚ b, A˚ c, A˚ R, deg β, deg γ, deg V, A˚3 Z d(calcd), g cm-3 abs coeff, mm-1 F(000) cryst size, mm θ range, deg index ranges no. of reflns collected no. of indep reflns completeness to θ = 25° abs corr transmn, max/min ref method no. of data/restr/params goodness-of-fit on F2 final R indices [I > 2θσ(I)] R indices (all data) largest diff peak and hole, e A˚-3


(o-CH3OC6H4)4Ge

(o-C2H5OC6H4)4Ge

C28H28GeO4 501.09 208(2) 0.71073 triclinic P1 8.5326(9) 8.8304(9) 16.6832(16) 80.6290(10) 82.1780(10) 89.6300(10) 1228.5(2) 2 1.355 1.278 520 0.28 0.28 0.10 2.34-28.67 -11 e h e 10, -10 e k e 11, -22 e l e 22 16 960 5651 (R(int) = 0.0439) 99.7% multiscan 0.8828/0.7161 full-matrix least-squares on F2 5651/0/302 0.992 R1 = 0.0361, wR2 = 0.0806 R1 = 0.0535, wR2 = 0.0890 0.357 and -0.340

C32H36GeO4 557.20 100(2) 0.71073 monoclinic C2/c 13.6906(12) 12.5077(11) 16.1770(14) 90 92.7420(10) 90 2766.9(4) 4 1.338 1.142 1168 0.28 0.24 0.20 2.21-25.35 -16 e h e 16, -15 e k e 15, -19 e l e 13 9388 2530 (R(int) = 0.0308) 100% multiscan 0.8038/0.7404 full-matrix least-squares on F2 2530/0/330 1.036 R1 = 0.0266, wR2 = 0.0612 R1 = 0.0329, wR2 = 0.0640 0.481 and -0.176

(o-CH3OC6H4S)4Ge

(o-CH3C6H4S)4Ge

C28H28GeO4S4 629.33 100(2) 1.54178 monoclinic P2(1)/n 18.619(2) 7.7442(9) 19.302(2) 90 101.550(7) 90 2726.8(5) 4 1.533 4.668 1296 0.24 0.20 0.14 3.69-68.27 -22 e h e 22, -7 e k e 9, -22 e l e 22 11 692 4697 (R(int) = 0.0331) 97.6% multiscan

C28H28GeS4 565.33 150(2) 0.71073 monoclinic C2/c 7.414(2) 25.203(8) 14.182(4) 90 104.424(3) 90 2566.5(13) 4 1.463 1.535 1168 0.38 0.34 0.30 1.62-25.54 -8 e h e 8, -30 e k e 30, -17 e l e 17 13 651 2367 (R(int) = 0.0541) 98.9% multiscan 0.6560/0.5932 full-matrix least-squares on F2 2367/0/152 1.027 R1 = 0.0243, wR2 = 0.0627 R1 = 0.0263, wR2 = 0.0644 0.445 and -0.289

full-matrix least-squares on F2 4697/0/339 1.098 R1 = 0.0374, wR2 = 0.0882 R1 = 0.0443, wR2 = 0.0910 0.617 and -0.430

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Yoder et al. Table 3. Continued


(o-C2H5OC6H4)3GeH

(o-C2H5OC6H4)3GeCl

C24H28GeO3 437.05 100(2) 0.71073 triclinic P1 8.8594(8) 11.4220(9) 11.5301(9) 78.028(2) 80.456(2) 69.1880(10) 1061.48(15) 2 1.367 1.464 456 0.33 0.10 0.08 1.81-28.26 -11 e h e 11, -15 e k e 15, -14 e l e 15 12 833 4752 (R(int) = 0.0266) 99.5% semiempirical form equivalents 0.8919/0.6436 full-matrix least-squares on F2 4752/0/257 1.052 R1 = 0.0388, wR2 = 0.0996 R1 = 0.0452, wR2 = 0.1040 0.595 and -0.316

C24H27ClGeO3 471.50 100(2) 0.71073 triclinic P1 9.2445(10) 11.2180(12) 23.106(3) 94.474(2) 98.982(2) 106.334(2) 2252.5(4) 4 1.390 1.500 976 0.22 0.20 0.08 1.91-28.31 -11 e h e 12, -14 e k e 14, -30 e l e 30 18 495 9722 (R(int) = 0.0249) 97.4% multiscan 0.8894/0.7337 full-matrix least-squares on F2 9722/0/523 1.036 R1 = 0.0425, wR2 = 0.0952 R1 = 0.0571, wR2 = 0.1020 0.981 and -0.340

Figure 2. Thermal ellipsoid diagram of tetrakis(o-ethoxyphenyl)germane with 50% probability. Figure 1. Thermal ellipsoid diagram of tetrakis(o-methoxyphenyl)germane with 50% probability.

mean angles at the same atom reported for tetrakis(o-methylphenyl)germane.25 In the o-methyl case the angle closest to the germanium is the larger one, with a mean of 123.0°, relative to the angle of 118.3° away from the germanium. These two angles (along with a widening of the angle at the ipso carbon on the side of the methyl group) were attributed to steric repulsions between the germanium and methyl.25 The angles at the aromatic carbon bearing the methoxy group are therefore suggestive of movement of the methoxy oxygen toward the germanium, presumably to strengthen the dative interaction to that atom. (25) Belsky, V. K.; Simonenko, A. A.; Reikhsfeld, V. O. J. Organomet. Chem. 1984, 265, 141–143.

Figure 3. Thermal ellipsoid diagram of tetrakis(o-methoxythiophenoxy)germane with 50% probability.

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Table 4. XRD Data for Tetrakis(phenyl)germanium Compounds

compound tetrakis(o-methoxyphenyl)Ge

tetrakis(o-ethoxyphenyl)Ge

Figure 4. Thermal ellipsoid diagram of tetrakis(o-methylthiophenoxy)germane with 50% probability. tetrakis(o-methoxythiophenoxy)Ge

tris(o-ethoxyphenyl)GeH

tris(o-ethoxyphenyl)GeCl

Figure 5. Thermal ellipsoid diagram of tris(o-ethoxyphenyl)germane with 50% probability.

Ge-O distance (A˚)

average Ge-O distance (A˚)

112.04(9)

2.963(2)

3.001(2)

110.40(9) 110.36(9) 109.29(9) 108.45(9) 106.29(9) 111.48(14)

2.996(2) 3.011(2) 3.032(2)

R-Ge-R bond anglesa (R = C or O, deg)

109.65(14) 109.60(13) 109.49(15) 108.79(14) 107.77(14) 112.31(3) 110.41(3) 110.13(3) 109.32(3) 109.29(3) 105.29(3) 111.4(8) 111.43(10) 110.85(10) 108.94(10) 107.8(8) 106.2(8) 114.32(12), 112.81(11) 114.13(12), 112.17(12) 110.50(12), 111.76(11) 107.21(9), 110.62(8) 105.47(9), 105.24(8) 104.25(10), 103.70(9)

2.918(7)

2.984(7)

2.967(7) 3.016(7) 3.034(7) 3.167(4)

3.334(4)

3.278(4) 3.341(4) 3.551(4) 2.978(3)

2.994(3)

2.992(3) 3.013(3)

2.950(3), 2.871(4) 2.983(3), 3.013(4)

3.002(4), 2.944(4)

3.073(3), 2.948(4)

a For the last two compounds, bond angles are R-Ge-H and R-Ge-Cl, respectively.

Figure 6. Thermal ellipsoid diagram of tris(o-ethoxyphenyl)chlorogermane with 50% probability.

The bond distances shown in Table 4 for the o-methoxy and o-ethoxy derivatives are less than the sum of the van der Waals radii26 of 3.63, but not sufficiently small (the sum of covalent radii27 is 1.86) to suggest a strong interaction between the oxygen and germanium. (26) Mantina, M.; Chamberlin, A. C.; Valero, R.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. A 2009, 113, 5806–5812. (27) Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, M.; Echeverria, J.; Cremades, E.; Barragan, F.; Alvarez, S. Dalton Trans. 2008, 2832–2838.

Figure 7. Average angles at the aromatic carbon bearing the methoxy group in tetrakis(o-methoxyphenyl)germane.

The argument for weak hypercoordination at germanium is also supported by the results of our DFT calculations (Table 5), which are in good agreement with the X-ray structural data for tetrakis(o-methoxyphenyl)germane. The DFT results for the o-methoxyphenoxy derivative suggest the presence of two bonds of about 2.2 A˚ in length with angles that may indicate five- or six-coordination. Hence, it seems reasonable to conclude that there may be weak hypercoordination in the tetrakis- and tris(orthoalkoxyphenyl) derivatives that leads to slightly broader 73Ge NMR line widths, and stronger hypercoordination for

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Table 5. DFT Calculations for o-Methoxy(tetrakisphenyl)-, -(phenoxy)-, and -(thiophenoxy)germanes R-Ge-R angle (deg) (R = C, O, or S)

compound tetrakis(o-methoxyphenyl)Ge

O-Ge distances (A˚)

109.7, 109.8, 109.0, 108.9, 109.8, 109.7 88.6, 96.2, 98.4, 104.0, 115.6, 154.2 103.6, 105.4, 108.1, 111.9, 113.6, 114.1

tetrakis(o-methoxyphenoxy)Ge tetrakis(o-methoxythiophenoxy)Ge

3.00, 3.00, 3.00, 3.00 2.20, 2.22, 2.85, 4.42 2.86, 2.89, 2.94, 2.97

Table 6. 13C and 73Ge NMR Chemical Shift Regression Analysis Parameters for para-Substituted Tetrakis(phenyl)germanes correlation

ra

F (ppm/σ)b

C (ppm)b

Sc

nd

δ 13C, C1 vs σ δ 13C, C1 vs σRo δ 13C, C4 vs σ δ 13C, C4 vs σRo δ 73Ge vs σ δ 73Ge vs σRo

0.778 0.999 0.723 0.909 0.730 0.761

10.49 20.17 -31.24 -58.84 -9.63 -15.06

132.87 136.34 143.36 133.21 -30.92 -33.49

2.789 0.201 9.839 5.947 2.976 2.822

7 7 7 7 7 7

a Correlation coefficient. Normal Hammett σ constants (ref 28a) except where noted (σRo: ref 28b). b Variables of the equation δ = Fσ þ c C. Standard deviation of residuals. d Number of compounds. e We employ the reported10 CDCl3 13C chemical shift values for tetrakis(p-tolyl)germane (Table 1) and the 73Ge solution chemical shifts determined32 for tetrakis(m-tolyl)- and tetrakis(p-tolyl)germane (Table 2) in the Hammett correlations.

tetrakis(o-methoxyphenoxy)germane that produces a 73Ge line width sufficiently broad to preclude observation of the resonance. The difference in degree of hypercoordination between the phenyl and phenoxy derivatives can be attributed to the steric accommodation of dative bonding as the “ring” size changes from four- to five-membered. Substituent Effects. As part of our continuing interest in electronic effects in group 14 compounds, we have also explored the effects of substituents on the NMR chemical shifts of the tetrakis(phenyl) compounds. The 13C chemical shifts of the ipso carbon (C1) for the substituted tetrakis(phenyl)germanes are 4-6 ppm lower than the shifts for the ipso carbons of the analogous substituted phenyltrimethylgermanes.5 For example, the 13C chemical shift of the ipso carbon of (C6H5)4Ge is 136.1 ppm, whereas the analogous shift for C6H5Ge(CH3)3 is 142.5 ppm. The same effect has been observed in the homologous tin compounds17 and can probably be attributed to electron release to Ge or Sn brought about by substitution of phenyl for methyl. Table 6 displays the results of regression analyses for the 13 C and 73Ge chemical shifts of para-substituted phenyl derivatives versus Hammett σ28a and Taft σR° constants.28b In general, the correlation coefficients for the regression of the carbon shifts versus normal Hammett constants were similar to those reported previously for the substituted phenyltrimethylgermanes but significantly lower for the germanium shifts.5 Use of σR° gave a good correlation for the C1 chemical shifts of the seven tetrakis(para-phenyl) derivatives (Figure 8). The good correlations with the resonance parameter σR° is consistent with the report of similar correlations with the (tetrakis)tin homologues.17 Attempts to improve the correlations with other parameters such as σI were unsuccessful (r < 0.76). The presumed influence of (28) (a) Hansch, C.; Leo, A. Subsituent Constants for Correlation Analysis in Chemistry and Biology; Wiley: New York, 1979. (b) Exner, O. A. Critical Compilation of Substituent Constants. In Correlation Analysis in Chemistry: Recent Advances; Chapman, N. B., Shorter, J., Eds.; Plenum: New York, 1978; Chapter 10.

Figure 8. Hammett plot of 73Ge chemical shifts vs σR° for para derivatives.

resonance effects on the C1 and 73Ge shifts may be related to the apparent electron-releasing effect of the phenyl groups as substituents on germanium.

Experimental Section Materials and Methods. All syntheses were performed under an argon atmosphere in glassware dried in an oven at 110 °C. Commercial solvents and reagents were first dried with Drierite and subsequently stored over Linde 4 A˚ molecular sieves. Tetrahydrofuran (THF) was dried over molecular sieves and then distilled from calcium hydride under an argon atmosphere prior to use. Tetrachlorogermane and tetraphenylgermane were purchased from Gelest and were used without further purification. Melting points were determined on a Thomas-Hoover capillary apparatus and are uncorrected. Schwarzkopf Microanalytical Laboratory, Woodside, NY, and Galbraith Laboratories, Knoxville, TN, performed elemental analyses. Purity of all compounds probably exceeds 95% as indicated by the absence of spurious resonances in the 1H and 13C NMR spectra. Syntheses. Substituted tris- and tetrakis(phenyl)-, (phenoxy)-, and (thiophenoxy)germane derivatives investigated in this study were obtained by one of two standard procedures (Scheme 1): (1) reaction of the Grignard reagent, prepared from magnesium turnings and the appropriately substituted phenyl bromides (Sigma Aldrich; used as received) in dry THF, with tetrachloroor tetrabromogermane (Gelest; used as received), followed by 5-8 h reflux, hydrolysis with saturated aqueous ammonium chloride solution, extraction of the aqueous layer with three small portions of THF, drying of the combined extracts over anhydrous magnesium sulfate, removal of THF under vacuum, and recrystallization twice from absolute ethanol or acetonitrile; (2) reaction of the substituted phenol or thiophenol (Sigma Aldrich) with GeCl4 in dry THF using triethylamine to scavenge the liberated hydrogen halide, followed by a 5-8 h reflux,

Article Scheme 1. Illustrative Preparations of Substituted Tetrakis(phenyl)germanes

filtration of triethylamine hydrochloride, removal of solvent under vacuum, and recrystallization of solid products. Reacting quantities for typical Grignard preparations are presented in the following order: identity and amount of reacting substituted phenyl bromide, amount of reacting magnesium turnings, identity and quantity of germanium tetrahalide, yield in grams and percent. Reaction amounts for the phenoxides and thiophenoxides appear in the following order: identity and amount of reacting substituted phenol or thiophenol, quantity of triethylamine, identity and quantity of germanium tetrahalide, yield in grams and percent. Pure product yields ranged from 10% to 50% and were frequently determined from multiple preparations using varying conditions. Carbon-13 and proton and germanium-73 NMR data for the derivatives appear in Tables 1 and 2, respectively. Tetrakis(p-trifluoromethylphenyl)germane. From p-BrC6H4CF3 (12.83 g, 0.057 mol), Mg (1.53 g, 0.063 mol), GeCl4 (3.06 g, 0.014 mol). Yield: 1.4 g (15%), mp 170-172 °C (lit.29 mp 173174 °C). Anal. Calcd for C28H16F12Ge: C, 51.50; H, 2.47. Found: C, 50.91; H, 2.42. Tetrakis(m-trifluoromethylphenyl)germane. From m-BrC6H4 CF3 (30.60 g, 0.136 mol), Mg (3.63 g, 0.150 mol), GeCl4 (7.30 g, 0.034 mol). Yield: 6.0 g (27%), mp 119-120 °C. Anal. Calcd for C28H16F12Ge: C, 51.50; H, 2.47. Found: C, 50.63; H, 2.59. Tetrakis(p-methoxyphenyl)germane. From p-BrC6H4OCH3, (5.24 g, 0.028 mol), Mg (0.75 g, 0.031 mol), GeCl4 (1.51 g, 0.0070 mol). Yield: 0.7 g (20%), mp 175-176 °C (lit.30 mp 218222 °C; lit.31 mp not given; lit.32 mp 157-163 °C). Tetrakis(m-methoxyphenyl)germane. From m-BrC6H4OCH3 (5.24 g, 0.028 mol), Mg (0.75 g, 0.031 mol), GeCl4 (1.51 g, 0.0070 mol). Yield: 0.6 g (17%), mp 158-161 °C. Anal. Calcd for C28H28GeO4: C, 67.11; H, 5.63. Found: C, 63.71; H, 5.49. Tetrakis(o-methoxyphenyl)germane. This tetrakis derivative was secured from a modification30 of the standard procedure in which THF was replaced with toluene by distillation after formation of the Grignard reagent, followed by a 30 h reflux period, from o-BrC6H4OCH3 (2.99 g, 0.016 mol), Mg (0.43 g, 0.018 mol), and GeCl4 (0.86 g, 0.0040 mol). Yield: 0.4 g (20%), mp 188-190 °C (lit.30 mp 168-170 °C; lit.34 mp 213-214 °C). Anal. Calcd for C28H28GeO4: C, 67.11; H, 5.63. Found: C, 67.71; H, 5.87. Tetrakis(p-ethoxyphenyl)germane. From p-BrC6H4OC2H5 (30.56 g, 0.152 mol), Mg (4.07 g, 0.167 mol), GeCl4 (8.14 g, 0.038 mol). Yield: 3.2 g (15%), mp 102-108 °C. Anal. Calcd for C32H36GeO4: C, 68.98; H, 6.51. Found: C, 68.38; H, 6.46. Tetrakis(m-ethoxyphenyl)germane. From m-BrC6H4OC2H5 (20.91 g, 0.104 mol), Mg 2.78 g, 0.114 mol), GeCl4 (5.66 g, 0.026 mol). Yield: 2.5 g (17%), mp 70-72 °C. Anal. Calcd for C32O4H36Ge: C, 68.98; H, 6.51. Found: C, 68.40; H, 6.86. (29) Steward, O. W.; Dziedzic, J. E.; Johnson, J. S. J. Org. Chem. 1971, 36, 3475–3480. (30) Eaborn, C.; Singh, B. J. Organomet. Chem. 1979, 177, 333–348. (31) Klaukien, H.; Lehnig, M.; Reiche, T; Reiss, S.; Such, P. J. Chem. Soc., Perkin Trans. 2 1995, 2115–2119. (32) Takeuchi, Y.; Nishikawa, M.; Hachiya, H.; Yamamoto, H. Magn. Reson. Chem. 2005, 43, 662–664.


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Tetrakis(o-ethoxyphenyl)germane. This tetrakis compound was secured from a 10:1 Grignard to GeCl4 ratio with replacement of THF with toluene (vide supra). Yield: 1.4 g (10%), mp 216-220 °C (lit.33 254-255 °C). Anal. Calcd for C32H36GeO4: C, 68.98; H, 6.51. Found: C, 68.66; H, 6.64. Some attempts to prepare the tetrakis derivative resulted in isolation of tris(o-ethoxyphenyl)chlorogermane. Yield: 0.8 g (ca. 50%), mp 111-113 °C. Anal. Calcd for C24H27ClGeO3: C, 61.14; H, 5.77. Found: C, 61.91; H, 6.38. Tris(o-ethoxyphenyl)germane. In a second attempt to synthesize tetrakis(o-ethoxyphenyl)germane, tris(o-ethoxyphenyl)germane was recovered. Yield: 0.4 g (25%), mp 119-122 °C. Anal. Calcd for C24H28GeO3: C, 65.95; H, 6.46. Found: C, 66.12; H, 6.90. Tetrakis(p-tert-butylphenyl)germane. From p-BrC6H4-t-C4H9 (12.79 g, 0.060 mol), Mg (1.61 g, 0.066 mol), GeCl4 (3.22 g, 0.015 mol). Yield: 1.5 g (17%), mp 297-301 °C (lit.31 mp 350 °C (dec)). Tetrakis(p-chlorophenyl)germane. From p-BrC6H4Cl (12.25 g, 0.064 mol), Mg (1.72 g, 0.070 mol), GeCl4 (3.43 g, 0.016 mol). Yield: 1.0 g (12%), mp 153-157 °C. Anal. Calcd for C24H16Cl4Ge: C, 55.56; H, 3.11. Found: C, 54.89; H, 3.41. Tetrakis(o-methylphenoxy)germane. From o-HOC6H4CH3 (12.61 g, 0.1167 mol), (C2H5)3N (12.07 g, 0.1193 mol), GeCl4 (6.38 g, 0.029 mol). Yield: 3.1 g (20%), undistillable ambercolored oil. Anal. Calcd for C28H28GeO4: C, 67.10; H, 5.63. Found: C, 68.54; H, 6.91. Tetrakis(o-methoxyphenoxy)germane. From o-HOC6H4OCH3 (5.00 g, 0.043 mol), (C2H5)3N (4.56 g, 0.0451 mol), GeCl4 (2.14 g, 0.010 mol). Yield: 2.9 g (20%), undistillable amber-colored oil. Anal. Calcd for C28H28GeO8: C, 59.51; H, 4.99. Found: C, 61.16; H, 5.52. Tris(o-methoxyphenoxy)germane. Employing the synthetic conditions for the tetrakis derivative but with diethyl ether as reaction solvent and a 3 h reflux period produced the tris germanium hydride. Yield: 1.5 g (15%), undistillable ambercolored oil. Anal. Calcd for C21H22GeO6: C, 56.93; H, 5.01. Found: C, 56.94; H, 5.52. Tetrakis(o-methylthiophenoxy)germane. From o-HSC6H4OCH3 (4.93 g, 0.0397 mol), (C2H5)3N (4.16 g, 0.0411 mol), GeCl4 (2.16 g, 0.0101 mol). Yield: 3.5 g (50%), mp 83-85 °C. Anal. Calcd for C28H28GeS4: C, 59.48; H, 4.99. Found: C, 59.49; H, 5.11. Tetrakis(o-methoxythiophenoxy)germane. From o-HSC6H4OCH3 (5.12 g, 0.036 mol), (C2H5)3N (3.64 g, 0.036 mol), GeCl4 (2.00 g, 0.093 mol). Yield: 1.9 g (36%), mp 94-96 °C. Anal. Calcd for C28H28GeO4S4: C, 53.40; H, 4.48. Found: C, 53.23; H, 4.58. NMR Spectra. 1H and 13C NMR spectra were obtained on Varian UNITY 300 MHz and INOVA 500 MHz spectrometers using conditions described previously.1,5 Samples were contained in 5 mm o.d. tubes. Proton chemical shifts were referenced to the chloroform-d residual solvent line set to the TMSbased chemical shift 7.24 ppm. Carbon chemical shifts were referenced to the 13C centerline in CDCl3, taken as 77.0 ppm. (33) Lapkin, I. I.; Dumler, V. A.; Ponosova, E. S. Zh. Obshch. Khim. 1971, 41, 133–135. (34) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; and Pople, J. A. Gaussian 03, Version 4.1.2; Gaussian, Inc.: Wallingford, CT, 2004.

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Probe temperature was 20 °C for the UNITY and 23 °C for the INOVA instruments. 1H chemical shifts are believed to be reproducible to (0.03 ppm; 13C shifts to (0.05 ppm. Germanium-73 NMR spectra were obtained on a Varian INOVA 500 MHz instrument fitted with a Low Gamma broadband probe (103Rh-15N, VT 500 NB) with samples contained in 10 mm o.d. tubes. Instrumental parameters for 73Ge on the INOVA included a transmitter frequency of 17.42 MHz, sweep width of 100 000 Hz, pulse delay of 0 s, and acquisition time of 0.1 s. The Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence (refocusing delay, 0.0001 s) was used to reduce baseline roll. This pulse sequence was found to give peak widths within ca. 5% of those obtained using the standard pulse sequence up to peak widths of ca. 800 Hz. Germanium-73 chemical shifts were referenced to external tetramethylgermane 20% in CDCl3 by substitution and were constant to within (0.1 ppm based on repeated observations of a constant sample during the course of several days. Nevertheless, because of the greater line widths associated with most of the 73Ge resonances, we estimate the error as ca. (0.5 ppm. Samples for 73Ge NMR spectra were prepared using 300-400 mg amounts dissolved in 3 mL of CDCl3; 1H and 13C spectra were recorded using the same solutions. X-ray Crystallographic Analyses. Crystallographic data are summarized in Table 4 and in the Supporting Information. Where space group choices were possible, the centrosymmetric alternative was shown to be correct by the results of refinement. Data were collected at -173 °C with a Bruker D8 platform diffractometer equipped with an APEX CCD detector. All nonhydrogen atoms were refined with anisotropic thermal parameters, and H atoms were treated as idealized contributions. All software was contained in the Bruker-AXS libraries (BrukerAXS, Madison, WI).

Yoder et al. Molecular Modeling. Optimized geometries of selected molecules were calculated using the Gaussian 03 program34 (Version 4.1.2) with density functional theory using the B3PW91 functional and either the 6-31G or 3-31G basis sets. Ten to 13 starting conformations with the alkoxy in varying positions were used to determine a global minimum. Substituent Constant Correlations. Normal Hammett σ constants28a and Taft σR° values28b were taken from the literature.

Acknowledgment. The authors are indebted to the National Science Foundation for an MRI grant supporting the acquisition of a Varian INOVA 500 MHz NMR spectrometer, to Anne and Scott Moore for the Moore Mentorship Award, to Blake Pepinsky for the Pepinsky Research Award, to Fredrick G. Schappell for the Shappell Research Award, and to William and Lucille Hackman for the Hackman Endowment. The authors also acknowledge the support of the E. Jane Valas Fund (to A.S.D. and C.J.G.), contributions of Alexandra R. Pagano and Professor Jeffrey A. Rood (Elizabethtown College), and Eugene P. Mazzola (Food and Drug Administration/Joint Institute for Food Safety & Applied Nutrition and University of Maryland). Supporting Information Available: X-ray crystallographic data including CIF files for tetrakis(o-methoxyphenyl)germane, tetrakis(o-ethoxyphenyl)germane, tetrakis(o-methoxythiophenoxy)germane, tetrakis(o-methylthiophenoxy)germane, tris(oethoxyphenyl)germane, and tris(o-ethoxyphenyl)chlorogermane are available free of charge via the Internet at http:// pubs.acs.org.

Use of 73Ge NMR Spectroscopy and X-ray Crystallography for the

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