Syntheses, Structures, and Electronic Properties of the Branched

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Organometallics 2011, 30, 1046–1058 DOI: 10.1021/om101091c

Syntheses, Structures, and Electronic Properties of the Branched Oligogermanes (Ph3Ge)3GeH and (Ph3Ge)3GeX (X = Cl, Br, I)† )

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Christian R. Samanamu,‡ Monika L. Amadoruge,‡ Claude H. Yoder,§ James A. Golen,^, Curtis E. Moore, Arnold L. Rheingold, Nicholas F. Materer,‡ and Charles S. Weinert*,‡ ‡

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Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, United States, § Department of Chemistry, Franklin and Marshall College, Lancaster, Pennsylvania 17604-3003, United States, Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0358, United States, and ^Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, Massachusetts 02747, United States. †A portion of this work will appear in Proceedings of the 13th International Conference on Germanium, Tin, and Lead Chemistry (GTL-13), Graz, Austria, July 2010. Received November 19, 2010

The branched oligogermanium hydride (Ph3Ge)3GeH was synthesized via a hydrogermolysis reaction from GeH4 and Ph3GeNMe2 and was converted to the halide series of compounds (Ph3Ge)3GeX (X = Cl, Br, I) upon reaction with [Ph3C][PF6] in CH2X2 solvent (X = Cl, Br, I). These species were fully characterized by NMR (1H and 13C) and UV/visible spectroscopy, cyclic voltammetry, and elemental analysis. In addition, (Ph3Ge)3GeH was analyzed by 73Ge NMR spectroscopy and exhibits two resonances at δ -56 and -311 ppm. A Ge-H coupling constant of 191 Hz was observed in the proton-coupled 73Ge NMR spectrum of (Ph3Ge)3GeH. The X-ray crystal structures of (Ph3Ge)3GeH and (Ph3Ge)3GeX (X = Cl, Br, I) were obtained and represent the first examples of branched oligogermane hydrides or halides to be characterized in this fashion. The Ge-Ge bond distances in (Ph3Ge)3GeH are short (average value 2.4310(5) A˚), while those in the halide compounds (Ph3Ge)3GeX are similar to one another and range from 2.4626(7) to 2.4699(5) A˚. The UV/visible and cyclic voltammetry data for these species have been correlated with DFT computations, and excellent agreement was found between the experimental and theoretical data.

Introduction The chemistry of singly bonded oligogermanes, which are discrete molecules containing germanium-germanium bonds that range in length from approximately 2.40 to 2.50 A˚, has recently received significant new attention. The first detailed study of these systems was reported in a series of 19 papers published during the 1980s that described the syntheses, structures, and spectral properties of several linear and (1) Dr€ ager, M.; Ross, L. Z. Anorg. Allg. Chem. 1980, 469, 115–122. (2) Dr€ ager, M.; Ross, L. Z. Anorg. Allg. Chem. 1980, 460, 207–216. (3) Dr€ ager, M.; Ross, L. Z. Anorg. Allg. Chem. 1980, 472, 109–119. (4) Dr€ ager, M.; Ross, L.; Simon, D. Z. Anorg. Allg. Chem. 1980, 466, 145–156. (5) Ross, L.; Dr€ ager, M. J. Organomet. Chem. 1980, 194, 23–32. (6) Dr€ ager, M.; Simon, D. Z. Anorg. Allg. Chem. 1981, 472, 120–128. (7) Dr€ ager, M.; Ross, L. Z. Anorg. Allg. Chem. 1981, 476, 95–104. (8) Ross, L.; Dr€ ager, M. J. Organomet. Chem. 1980, 199, 195–204. (9) Ross, L.; Dr€ ager, M. Z. Naturforsch. 1983, 38B, 665–673. (10) Ross, L.; Dr€ ager, M. Z. Anorg. Allg. Chem. 1984, 515, 141–146. (11) Simon, D.; H€ aberle, K.; Dr€ager, M. J. Organomet. Chem. 1984, 267, 133–142. (12) Dr€ ager, M.; H€aberle, K. J. Organomet. Chem. 1985, 280, 183– 196. (13) Dr€ ager, M.; Simon, D. J. Organomet. Chem. 1986, 306, 183–192. (14) H€ aberle, K.; Dr€ager, M. J. Organomet. Chem. 1986, 312, 155– 165. (15) H€ aberle, K.; Dr€ager, M. Z. Naturforsch. 1987, 42B, 323–329. (16) Roller, S.; Dr€ ager, M. J. Organomet. Chem. 1986, 316, 57–65. pubs.acs.org/Organometallics

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cyclic organo-oligogermanes.1-19 In addition, the chemistry of the cyclotrigermane (Mes2Ge)3, which was first synthesized in 1987,20 has been extensively investigated, and it has been demonstrated that the reactivity of (Mes2 Ge)3 resembles that of both the free germylene Mes 2 Ge: and the (17) Roller, S.; Simon, D.; Dr€ager, M. J. Organomet. Chem. 1986, 301, 27–40. (18) Ross, L.; Dr€ager, M. Z. Anorg. Allg. Chem. 1984, 519, 225–232. (19) H€aberle, K.; Dr€ager, M. Z. Anorg. Allg. Chem. 1987, 551, 116– 122. (20) Ando, W.; Tsumuraya, T. J. Chem. Soc., Chem. Commun. 1987, 1514–1515. (21) Baines, K. M.; Cooke, J. A.; Dixon, C. E.; Liu, H. W.; Netherton, M. R. Organometallics 1994, 13, 631–634. (22) Baines, K. M.; Cooke, J. A.; Vittal, J. J. Heteroat. Chem. 1994, 5, 293–303. (23) Baines, K. M.; Stibbs, W. G. Adv. Organomet. Chem. 1996, 39, 275–324. (24) Dixon, C. E.; Liu, H. W.; Vander Kant, C. M.; Baines, K. M. Organometallics 1996, 15, 5701–5705. (25) Dixon, C. E.; Netherton, M. R.; Baines, K. M. J. Am. Chem. Soc. 1998, 120, 10365–10371. (26) Fujdala, K. L.; Gracey, D. W. K.; Wong, E. F.; Baines, K. M. Can. J. Chem. 2002, 80, 1387–1392. (27) Kollegger, G. M.; Stibbs, W. G.; Vittal, J. J.; Baines, K. M. Main Group Met. Chem. 1996, 19, 317–330. (28) Samuel, M. S.; Baines, K. M. J. Am. Chem. Soc. 2003, 125, 12702–12703. (29) Samuel, M. S.; Baines, K. M.; Hughes, D. W. Can. J. Chem. 2000, 78, 1474–1478. r 2011 American Chemical Society

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digermene Mes2GedGeMes2.21-34 A number of compounds containing Ge-Ge multiple bonds have also been reported.35-47 The synthetic methods employed for the synthesis of linear singly bonded oligogermanes were often complicated by low yields and/or the formation of product mixtures. A versatile synthetic method for the preparation of these materials, allowing control over the Ge-Ge chain length and the organic substituent pattern, proved to be elusive, despite the potentially interesting physical properties of these systems and their potential optical and electronic applications. Although germanium is frequently and mistakenly regarded as being nearly identical with its lighter congener silicon, the band gap, electron and hole mobility, and conductivity are higher in bulk elemental germanium,48 and as the limitations of silicon-based materials become realized, germanium will likely play an increased role in the electronics industry despite its higher cost. A rational method for the stepwise synthesis of oligogermanes, which relies on the hydrogermolysis reaction, has been developed in our laboratory that allows control over both the number of germanium atoms in the chain and the type of organic substituents attached to the germanium(30) Samuel, M. S.; Jennings, M. C.; Baines, K. M. J. Organomet. Chem. 2001, 636, 130–137. (31) Tsumuraya, T.; Kabe, Y.; Ando, W. J. Organomet. Chem. 1994, 482, 131–138. (32) Valentin, B.; Castel, A.; Riviere, P.; Mauzac, M.; Onyszchuk, M.; Lebuis, A. M. Heteroat. Chem. 1999, 10, 125–132. (33) Baines, K. M.; Cooke, J. A.; Payne, N. C.; Vittal, J. J. Organometallics 1992, 11, 1408–1411. (34) Baines, K. M.; Cooke, J. A. Organometallics 1991, 10, 3419– 3421. (35) Cui, C.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 2004, 126, 5062–5063. (36) Kishikawa, K.; Tokitoh, N.; Okazaki, R. Chem. Lett. 1998, 239– 240. (37) Leung, W.-P.; Wang, Z.-X.; Li, H.-W.; Mak, T. C. W. Angew. Chem., Int. Ed. 2001, 40, 2501–2503. (38) Pu, L.; Phillips, A. D.; Richards, A. F.; Stender, M.; Simons, R. S.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 2003, 125, 11626–11636. (39) Pu, L.; Senge, M. O.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 1998, 120, 12682–12683. (40) Richards, A. F.; Brynda, M.; Power, P. P. Chem. Commun. 2004, 1592–1593. (41) Richards, A. F.; Phillips, A. D.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 2003, 125, 3204–3205. (42) Stender, M.; Phillips, A. D.; Power, P. P. Chem. Commun. 2002, 1312–1313. (43) Stender, M.; Phillips, A. D.; Wright, R. J.; Power, P. P. Angew. Chem., Int. Ed. 2002, 41, 1785–1787. (44) Stender, M.; Pu, L.; Power, P. P. Organometallics 2001, 20, 1820– 1824. (45) Takagi, N.; Nagase, S. Organometallics 2001, 20, 5498–5500. (46) Tokitoh, N.; Kishikawa, K.; Okazaki, R.; Sasamori, T.; Nakata, N.; Takeda, N. Polyhedron 2002, 21, 563–577. (47) Weidenbruch, M.; St€ urmann, M.; Kilian, H.; Pohl, S.; Saak, W. Chem. Ber. 1997, 130, 735–738. (48) Sze, S. M.; Ng, K. K. Physics of Semiconductor Devices, 3rd ed.; Wiley: Hoboken, NJ, 2007. (49) Amadoruge, M. L.; DiPasquale, A. G.; Rheingold, A. L.; Weinert, C. S. J. Organomet. Chem. 2008, 693, 1771–1778. (50) Amadoruge, M. L.; Gardinier, J. R.; Weinert, C. S. Organometallics 2008, 27, 3753–3760. (51) Amadoruge, M. L.; Golen, J. A.; Rheingold, A. L.; Weinert, C. S. Organometallics 2008, 27, 1979–1984. (52) Amadoruge, M. L.; Short, E. K.; Moore, C.; Rheingold, A. L.; Weinert, C. S. J. Organomet. Chem. 2010, 695, 1813–1823. (53) Amadoruge, M. L.; Yoder, C. H.; Conneywerdy, J. H.; Heroux, K.; Rheingold, A. L.; Weinert, C. S. Organometallics 2009, 28, 3067– 3073. (54) Subashi, E.; Rheingold, A. L.; Weinert, C. S. Organometallics 2006, 25, 3211–3219.

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germanium backbone.49-56 Using this method, we have synthesized a variety of linear oligogermanes and have also extended it to the preparation of unusual branched systems. The first branched oligogermanes were reported in 1963 and included (Ph3Ge)3GeH (1) and (Ph3Ge)3GeMe.57 The former oligogermane was synthesized from Ph3GeLi and GeI2 and was characterized by IR spectroscopy and elemental analysis, and the latter compound was obtained from 1 using BunLi followed by quenching with MeI. The syntheses of the heteroleptic branched oligogermane (PhCl2Ge)3GePh58 and its derivatives (PhMe2Ge)3GePh58 and (Ph(X)2Ge)3GePh (X = MeO, MeS, Me2N, Et2P)59 were subsequently described, and the preparation of the mixed group 14 metal neopentane analogues (Ph3M)4M0 (M=Pb, M0=Ge, Sn, Pb; M = Sn, M0 = Ge, Sn, Pb; M = Ge, M0 = Sn, Pb) has also been reported.60 We recently reported the preparation of (Ph3Ge)3GePh (2) as well as (EtOCH2CH2Bun2Ge)3GePh.51 Compound 2 was the first branched oligogermane to be structurally characterized, and we demonstrated that the functionalized branched species (EtOCH2CH2Bun2Ge)3GePh could be used for the construction of higher branched heptagermanes using our hydride protection/deprotection strategy combined with the hydrogermolysis reaction.51 We have also prepared the branched system (Bun3Ge)3GePh,53 and the two dendritetype tridecagermanes Me28Ge13 and Ph6Me22Ge13 were reported in 2005 and the photoconductive properties of these systems in the presence of a C60 dopant were investigated.61 In addition, the synthesis of the neopentyl system (Me3Ge)4Ge, as well as (Me3Ge)3GeK(18-crown-6) and (Me3Ge)3GeH obtained from (Me3Ge)4Ge, was recently described;62 however, neither (Me3Ge)4Ge nor (Me3Ge)3GeH were structurally characterized. We were interested in the preparation of the related neopentane analogue (Ph3Ge)4Ge via the hydrogermolysis reaction between GeH4 and Ph3GeNMe2. To our knowledge, the synthesis and full characterization of this oligogermane has not been described, although 13C NMR chemical shift values for this compound were reported in the absence of any synthetic details.19 Herein we wish to report our attempts to synthesize (Ph3Ge)4Ge via the hydrogermolysis reaction as described above. We have found that the preparation of this material is not possible due to steric constraints; however, the reaction of GeH4 with Ph3GeNMe2 in acetonitrile solvent does yield the branched hydride (Ph3Ge)3GeH (1), and this species has been converted to the three branched halide species (Ph3Ge)3GeX (X=Cl (3), Br (4), I (5)). The X-ray structures of 1 and 3-5 have been obtained, and these four systems have been fully characterized by NMR (1H and 13C) and UV/visible spectroscopy as well as cyclic voltammetry. In addition, 73Ge NMR spectra (55) Amadoruge, M. L.; Weinert, C. S. Chem. Rev. 2008, 108, 4253– 4294. (56) Weinert, C. S. Dalton Trans. 2009, 1691–1699. (57) Glockling, F.; Hooton, K. A. J. Chem. Soc. 1963, 1849–1854. (58) Riviere, P.; Satge, J. Synth. Inorg. Met.-Org. Chem. 1971, 1, 13– 20. (59) Riviere, P.; Satge, J.; Soula, D. J. Organomet. Chem. 1974, 72, 329–338. (60) Willemsens, L. C.; van der Kerk, G. J. M. J. Organomet. Chem. 1964, 2, 260–264. (61) Seki, S.; Acharya, A.; Koizumi, Y.; Saeki, A.; Tagawa, S.; Mochida, K. Chem. Lett. 2005, 34, 1690–1691. (62) Hlina, J.; Baumgartner, J.; Marschner, C. Organometallics 2010, 29, 5289–5295.

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Samanamu et al. Scheme 1

of 1 were obtained, and we were able to observe 73Ge- 1H coupling in the 1H-decoupled spectrum.

Results and Discussion The synthesis of (Ph3Ge)4Ge was attempted using two different stoichiometric conditions. Initially, excess GeH4 was condensed into a Schlenk tube containing Ph3GeNMe2 in acetonitrile at 77 K. The tube was sealed, warmed to room temperature, and then placed in an oil bath at 90 C, where after stirring for 1 h a large amount of white precipitate had formed. The reaction mixture was cooled, and the precipitate was filtered and washed with hexane. The 1H NMR spectrum of the product in C6D6 solvent was clean and contained three resonances in the aromatic region as well as a singlet at δ 4.58 ppm, which was identical with the chemical shift of (Ph3Ge)3GeH (1) prepared from (Ph3Ge)3GePh (2).51,63 The infrared spectrum of 1 contains a band for the ν(Ge-H) bond stretch at 1953 cm-1 which is identical with that found previously for 1.51,57 The same reaction was conducted using a 1:3.3 molar ratio of GeH4 to Ph3GeNMe2, and 1 was again isolated in 66% yield as the only germanium-containing product (Scheme 1). The reaction of GeH4 with Ph3GeNMe2 proceeds via the in situ conversion of Ph3GeNMe2 to Ph3GeCH2CN, which is the active species in the Ge-Ge bond forming process.49-51,54 The product obtained from the latter reaction was recrystallized from hot benzene to provide colorless crystals that were analyzed using X-ray crystallography, which confirmed the composition of 1. An ORTEP diagram of 1 is shown in Figure 1, and selected bond distances and angles are collected in Table 1. The three Ge-Ge bond distances are 2.4271(5), 2.4298(5), and 2.4360(5) A˚ for the Ge(1)-Ge(2), Ge(1)-Ge(3), and Ge(1)-Ge(4) bonds, respectively, with an average value of 2.4310(5) A˚. The average Ge-Ge bond distance in 1 is similar to those in the linear oligogermanes Ph3GeGeR3 (R =Me, 2.418(1) A˚;64 R = Et, 2.4253(7) A˚;54 R=Bun, 2.421(8) A˚54) and Ph3GeGeMe2GePh3 (dav=2.429(1) A˚)13 but is significantly shorter than those in 2 (dav=2.469(4) A˚)51 and the perphenylated linear oligogermanes Ge3Ph8 and Ge4Ph10 (dav =2.440(2) and 2.462(2) A˚, respectively).17 The Ge-Ge distances in 1 are all shorter than those in 2, which can be attributed to the presence of the hydrogen atom at the central germanium atom in 1, which is significantly less sterically encumbering than the phenyl substituent in 2. The hydrogen atom at the central germanium atom was located, and the Ge-H distance is 1.45(3) A˚, which is comparable to the Ge-H distance of 1.50(5) A˚ in Ph3GeH.65 (63) Amadoruge, M. L.; Golen, J. A.; Rheingold, A. L.; Weinert, C. S. Organometallics 2009, 28, 4628. (64) P ark anyi, L.; Kalman, A.; Sharma, S.; Nolen, D. M.; Pannell, K. H. Inorg. Chem. 1994, 33, 180–182. (65) McGrady, G. S.; Odlyha, M.; Prince, P. D.; Steed, J. W. Cryst. Eng. Commun. 2002, 4, 271–276.

Figure 1. ORTEP diagram of (Ph3Ge)3GeH (1). Thermal ellipsoids are drawn at the 50% probability level.

The central germanium atom in 1 is disposed in a distorted-tetrahedral environment, which was also found for compound 2. The three Ge-Ge-Ge bond angles in 1 are 116.11(2), 112.49(2), and 117.89(2) with an average value of 115.50(2). The pattern among the three bond angles in 1 mirrors that in 2, where one Ge-Ge-Ge bond angle is substantially more acute than the other two. However, the Ge(2)-Ge(1)-Ge(4) bond angle is more acute than the other two bond angles in 1 by an average value of 4.5, while in 2 this difference is 8.0. The Ge-Ge-Ge bond angles in 1 are all more obtuse than the corresponding angles in 2, which has an average Ge-Ge-Ge bond angle of 112.72(1), as a consequence of the shorter Ge-Ge bond distances present in 1. The branched hydride 1 has been characterized by NMR (1H, 13C, and 73Ge) spectroscopy. These data can be compared with the corresponding data that have been obtained for the phenyl-substituted derivative 2 as well as the methyl derivative (Me3Ge)3GeH.62 As mentioned above, the 1H NMR spectrum of 1 exhibits a Ge-H resonance at δ 4.58 ppm, which is shifted upfield relative to typical resonances for germanium hydrides and suggests that the hydrogen atom at the central germanium atom is significantly shielded. This effect is more drastic in (Me3Ge)3GeH, where the resonance for the hydrogen atom was observed at δ 2.81 ppm62 due to the presence of the more inductively electron donating methyl groups versus the phenyl substituents in 1. In addition, all of the aromatic resonances in the 1H and 13C

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spectrum of 1 are shifted upfield relative to the corresponding peaks in the spectrum of 2. The use of 73Ge NMR spectroscopy for the characterization of oligogermanium compounds is uncommon,66-68 but several species containing germanium-germanium bonds have been characterized by this method.53,68 The 73Ge NMR spectrum of 2 exhibits a single feature at δ -202 ppm corresponding to the central germanium atom in this material,53 and a peak for the peripheral Ph3Ge- atoms was not observed. However, the 73Ge NMR spectrum of 1 contains two resonances, including one for the three Ph3Gegroups at δ -56 ppm (Δν1/2=35 Hz) and a second feature at δ -311 ppm (Δν1/2 = 210 Hz) for the central germanium atom; the latter is consistent with a previously reported value.68 Consistent with the 1H NMR spectrum of 1, the feature for the central germanium atom in 1 is shifted upfield relative to that for 2, since the central germanium atom of 1 is more shielded due to the presence of the hydrogen atom versus the phenyl group in 2. In addition, the resonance at δ -311 ppm in the 1H-coupled 73Ge NMR spectrum of 1 splits into a doublet with a coupling constant of 191 Hz, as shown in Figure 2. This coupling constant is nearly twice those Table 1. Selected Bond Distances (A˚) and Angles (deg) for (Ph3Ge)3GeH (1) Ge(1)-H(1) Ge(1)-Ge(2) Ge(1)-Ge(3) Ge(1)-Ge(4) Ge(2)-C(1) Ge(2)-C(7) Ge(2)-C(13) Ge(2)-Ge(1)-H(1) Ge(3)-Ge(1)-H(1) Ge(4)-Ge(1)-H(1) Ge(2)-Ge(1)-Ge(3) Ge(2)-Ge(1)-Ge(4) Ge(3)-Ge(1)-Ge(4) Ge(1)-Ge(2)-C(1) Ge(1)-Ge(2)-C(7)

1.45(3) 2.4271(5) 2.4298(5) 2.4360(5) 1.953(3) 1.950(3) 1.951(3) 104(1) 102(1) 101(1) 116.11(2) 112.49(2) 117.89(2) 106.58(8) 110.27(9)

Ge(3)-C(19) Ge(3)-C(25) Ge(3)-C(31) Ge(4)-C(37) Ge(4)-C(43) Ge(4)-C(49) Ge(1)-Ge(2)-C(13) Ge(1)-Ge(3)-C(19) Ge(1)-Ge(3)-C(25) Ge(1)-Ge(3)-C(31) Ge(1)-Ge(4)-C(37) Ge(1)-Ge(4)-C(43) Ge(1)-Ge(4)-C(49)

1.948(3) 1.953(3) 1.949(3) 1.948(3) 1.947(3) 1.951(3)

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observed for several monomeric arylgermanium hydrides, including p-(MeOC6H4)GeH3 (1JGeH = 97 Hz), p-(CH3C6H4)GeH3 (1JGeH = 96 Hz), MesGeH3 (1JGeH = 95 Hz), PhGeH3 (1JGeH = 98 Hz), Ph2GeH2 (1JGeH = 94 Hz), and Ph3GeH (1JGeH = 98 Hz).69 Aside from these data, very few other one-bond Ge-H coupling constants have been reported, with the exception of GeH470 and Et3GeH.70,71 No other examples of data for compounds having hydrogen bound to a catenated germanium atom have been reported, but it is possible that the connectivity at the central germanium atom of 1 is responsible for the large magnitude of the Ge-H coupling constant. The synthesis of (Ph3Ge)4Ge from 1 was attempted by treating 1 with 1 equiv of Ph3GeNMe2 in CH3CN solution at 90 C for an extended reaction time of 7 days (Scheme 1). However, the 1H NMR spectrum of the products obtained after removing the volatile components in vacuo still exhibited a resonance at δ 4.58 ppm for the hydrogen atom of 1 as well as a singlet at δ 1.98 ppm corresponding to the methylene protons of Ph3GeCH2CN49 generated from Ph3GeNMe2 during the course of the reaction. There was no evidence for the generation of the desired neopentane analogue (Ph3Ge)4Ge, indicating that steric limitations about the central germanium atom might prevent the attachment of a fourth -GePh3 group. Scheme 2

111.04(8) 108.68(8) 107.63(9) 115.50(9) 107.78(9) 112.07(9) 112.81(9)

Figure 2. Proton-coupled 73Ge NMR spectrum of (Ph3Ge)3GeH (1) at 17.43 MHz, referenced to external GeMe4.

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Samanamu et al. Scheme 3

We also attempted to synthesize the branched germanium cation (Ph3Ge)3Geþ from 1 using tritylium hexafluorophosphate [Ph3Cþ][PF6-] as the hydrogen-abstracting reagent (Scheme 2). However, [Ph3Cþ][PF6-] is not soluble in nonpolar solvents, and therefore the reaction was carried out in dichloromethane. The product isolated after the reaction mixture was stirred at room temperature for 36 h was not the desired [(Ph3Ge)3Geþ][PF6-] but rather the chlorinated oligogermane (Ph3Ge)3GeCl (3). However, it is clear that (Ph3Ge)3Geþ was generated in the reaction, since the 1H NMR spectrum of the crude product mixture exhibited a resonance at δ 5.43 ppm that matches exactly with that for a commercial sample of Ph3CH. The cation (Ph3Ge)3Geþ generated in the reaction subsequently abstracts a chlorine atom from the CH2Cl2 solvent to provide 3, with [CH2Clþ][PF6-] being generated as a byproduct. The [CH2Clþ] cation has been identified by infrared spectroscopy as a discrete molecule in an argon matrix.72 The crude product mixture was suspended in benzene and filtered to remove excess [Ph3Cþ][PF6-] and the [CH2Clþ][PF6-] containing byproduct, and after evaporation of the benzene the resulting solid was washed with hexane to remove Ph3CH. The product 3 was isolated in 68% yield, and the 1H and 13C NMR spectra of 3 are very similar to that of 1, although the resonance for the ortho protons of 3 (δ 7.34 ppm) is shifted downfield relative to that for 1 (δ 7.26 ppm). In light of the successful conversion of 1 to 3 using the reaction conditions described above, we prepared (Ph3Ge)3GeBr (4) and (Ph3Ge)3GeI (5) from 1 using [Ph3Cþ][PF6-] and dibromo- or diiodomethane, respectively, as the solvent (Scheme 3). Compound 4 was obtained in 56% yield, while 5 was obtained in 59% yield, and the chemical shifts observed for the phenyl groups in the 1H and 13C NMR spectra of these two species are very similar to those of the chloride 3. Compound 3 crystallizes in two different morphologies, depending on the solvent system used for recrystallization. When a hot benzene solution was employed, crystals of 3 were obtained as the monobenzene solvate (Ph3Ge)3GeCl 3 C6H6 (3a). However, when a 5/1 (v/v) mixture of benzene to cyclohexane was used as the crystallization medium, crystals of the tris(benzene) mono(cyclohexane) solvate (Ph3Ge)3GeCl 3 3C6H6 3 C6H12 (3b) were obtained. Figure 3 contains ORTEP diagrams of 3a,b, and selected bond distances

Figure 3. ORTEP diagrams of the two morphologies of 3, including the benzene solvate (Ph3Ge)3Cl 3 C6H6 (3a, top) and the tris(benzene) mono(cyclohexane) solvate (Ph3Ge)3GeCl 3 3C6H6 3 C6H12 (3b, bottom). Thermal ellipsoids are drawn at the 50% probability level.

(66) Mackay, K. M.; Thomson, R. A. Main Group Met. Chem. 1987, 10, 83–108. (67) Takeuchi, Y.; Takayama, T. Annu. Rep. NMR Spectrosc. 2005, 54, 155–200. (68) Thomson, R. A.; Wilkins, A. L.; Mackay, K. M. Phosphorus, Sulfur, Silicon Relat. Elem. 1999, 150-151, 319–324. (69) Riedmiller, F.; Wegner, G. L.; Jockisch, A.; Schmidbaur, H. Organometallics 1999, 18, 4317–4324. (70) Mackay, K. M.; Watkinson, P. J.; Wilkins, A. L. J. Chem. Soc., Dalton Trans. 1984, 133–139. (71) Wilkins, A. L.; Watkinson, P. J.; Mackay, K. M. J. Chem. Soc., Dalton Trans. 1987, 2365–2372. (72) Ma, R.; Chen, M.; Zhou, M. J. Phys. Chem. A 2009, 113, 12926– 12931.

and angles are collected in Tables 2 and 3. In the structure of 3a, the Ge(1)-Cl(1) distance is 2.230(1) A˚ and the average Ge-Ge bond distance is 2.4626(7) A˚. The Ge-Ge distances in 3a are longer than those in the hydride 1 but are slightly shorter than those in 2. The Ge-Ge-Ge bond angles in 3a average 116.22(2), and as observed for both 1 and 2, the Ge(2)-Ge(1)-Ge(4) bond angle in 3a is more acute than the other two bond angles by an average value of 5.2. The average Ge-Ge-Cl angle in 3a is 101.34(4); therefore, the environment about the central germanium atom in 3a can be regarded as distorted tetrahedral.

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Table 2. Selected Bond Distances (A˚) and Angles (deg) for (Ph3Ge)3GeCl 3 C6H6 (3a) Ge(1)-Cl(1) Ge(1)-Ge(2) Ge(1)-Ge(3) Ge(1)-Ge(4) Ge(2)-C(1) Ge(2)-C(7) Ge(2)-C(13) Ge(2)-Ge(1)-Cl(1) Ge(3)-Ge(1)-Cl(1) Ge(4)-Ge(1)-Cl(1) Ge(2)-Ge(1)-Ge(3) Ge(2)-Ge(1)-Ge(4) Ge(3)-Ge(1)-Ge(4) Ge(1)-Ge(2)-C(1) Ge(1)-Ge(2)-C(7)

2.230(1) 2.4608(7) 2.4631(6) 2.4638(7) 1.955(4) 1.951(4) 1.950(4) 100.88(4) 101.73(3) 101.42(4) 119.68(2) 112.78(2) 116.20(2) 106.3(1) 115.8(1)

Ge(3)-C(19) Ge(3)-C(25) Ge(3)-C(31) Ge(4)-C(37) Ge(4)-C(43) Ge(4)-C(49)

1.947(5) 1.955(4) 1.961(4) 1.959(4) 1.949(4) 1.957(4)

Ge(1)-Ge(2)-C(13) Ge(1)-Ge(3)-C(19) Ge(1)-Ge(3)-C(25) Ge(1)-Ge(3)-C(31) Ge(1)-Ge(4)-C(37) Ge(1)-Ge(4)-C(43) Ge(1)-Ge(4)-C(49)

110.3(1) 108.3(1) 112.3(1) 106.3(1) 109.3(1) 113.5(1) 111.5(1)

Table 3. Selected Bond Distances (A˚) and Angles (deg) for (Ph3Ge)3GeCl 3 3C6H6 3 C12H12 (3b) and (Ph3Ge)3GeBr 3 3C6H6 (4 3 3C6H6) 3b (X(1) = Cl(1))

4 3 3C6H6 (X(1) = Br(1))

Ge(1)-X(1) Ge(1)-Ge(2) Ge(2)-C(1) Ge(2)-C(7) Ge(2)-C(13)

2.215(2) 2.4699(5) 1.968(5) 1.959(5) 1.947(5)

2.3796(9) 2.4698(4) 1.964(4) 1.957(4) 1.965(4)

X(1)-Ge(1)-Ge(2) Ge(2)-Ge(1)-Ge(20 ) C(1)-Ge(2)-Ge(1) C(7)-Ge(2)-Ge(1) C(13)-Ge(2)-Ge(1)

101.75(2) 115.96(2) 110.0(2) 114.2(2) 110.4(2)

101.38(2) 116.21(1) 109.9(1) 110.4(1) 113.5(1)

Figure 5. ORTEP diagram of (Ph3Ge)3GeI 3 1/3C6H6 (5 3 1/3C6H6). Thermal ellipsoids are drawn at the 50% probability level. Table 4. Selected Bond Distances (A˚) and Angles (deg) for (Ph3Ge)3GeI 3 1/3C6H6 (5 3 1/3C6H6) Ge(1)-I(1) Ge(1)-Ge(2) Ge(1)-Ge(3) Ge(1)-Ge(4) Ge(2)-C(1) Ge(2)-C(7) Ge(2)-C(13) Ge(2)-Ge(1)-I(1) Ge(3)-Ge(1)-I(1) Ge(4)-Ge(1)-I(1) Ge(2)-Ge(1)-Ge(3) Ge(2)-Ge(1)-Ge(4) Ge(3)-Ge(1)-Ge(4) Ge(1)-Ge(2)-C(1) Ge(1)-Ge(2)-C(7)

Figure 4. ORTEP diagram of (Ph3Ge)3GeBr 3 3C6H6 (4 3 C6H6). Thermal ellipsoids are drawn at the 50% probability level.

The structure of 3b adopts the P63 space group that has a C3 axis of rotation located along the Ge(1)-Cl(1) bond. The unit cell of 3b incorporates three molecules of benzene and one molecule of cyclohexane from the solvent system used for crystallization, and the single cyclohexane molecule is located on the C3 axis. The metric parameters of 3b differ very slightly from those from 3a, due in part to the higher symmetry of 3b. The Ge(1)-Cl(1) bond length of 2.215(2) A˚ is shorter than that of 3a by 0.015 A˚, and the Ge-Ge bond distance of 2.4699(5) A˚ is identical within error with the

2.5868(5) 2.4728(5) 2.4744(6) 2.4595(6) 1.951(4) 1.956(4) 1.954(3) 101.51(2) 101.46(2) 99.44(2) 120.42(2) 116.25(2) 112.96(2) 109.00(9) 111.4(1)

Ge(3)-C(19) Ge(3)-C(25) Ge(3)-C(31) Ge(4)-C(37) Ge(4)-C(43) Ge(4)-C(49) Ge(1)-Ge(2)-C(13) Ge(1)-Ge(3)-C(19) Ge(1)-Ge(3)-C(25) Ge(1)-Ge(3)-C(31) Ge(1)-Ge(4)-C(37) Ge(1)-Ge(4)-C(43) Ge(1)-Ge(4)-C(49)

1.957(4) 1.949(4) 1.946(3) 1.960(4) 1.953(3) 1.953(4) 112.2(1) 110.6(1) 109.0(1) 112.0(1) 116.0(1) 110.1(1) 110.1(1)

average Ge-Ge bond distance in 3a. The Ge-Cl distances in both structures of 3 are slightly elongated relative to those in the chloro-substituted linear oligogermanes ClPh2GeGePh2GePh2Cl and ClPh2GePh2GePh2GePh2Cl, which measure 2.193(5) and 2.134(7) A˚, respectively,14 due to the branched structure of 3. The bond angles about the central germanium atom in 3b are slightly different from those in 3a. The Ge-Ge-Ge bond angle in 3b is slightly more acute than the average angle in 3a and measures 115.96(2), while the Cl-Ge-Ge bond angle is slightly more obtuse than the average angle in 3a and is 101.75(2). Crystals of 4 suitable for X-ray analysis were obtained from benzene; an ORTEP diagram of 4 3 3C6H6 is shown in Figure 4, and selected bond distances and angles are collected in Table 3. As found for 3, compound 4 3 3C6H6 also crystallizes in the P63 space group and has a C3 axis along the Ge(1)-Br(1) bond which measures 2.3796(9) A˚. The Ge-Ge bond distances in 4 3 3C6H6 are 2.4698(4) A˚ and are nearly the same as those in both structures obtained for 3. The environment about the central germanium atom in 4 3 3C6H6 is also very similar to that of 3, which is consistent with the similarity observed between their NMR spectra. The Ge-Ge-Ge and the Br-Ge-Ge bond angles in 5 measure

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Figure 6. UV/visible spectrum (top) and cyclic voltammogram (bottom) of (Ph3Ge)3GeH (1) in dichloromethane solvent.

116.21(1) and 101.38(2), respectively. Crystals of the iodide compound 5 were also analyzed by X-ray crystallography; an ORTEP diagram of 5 3 1/3C6H6 is shown in Figure 5, and selected bond distances and angles are collected in Table 4. Two of the Ge-Ge bond distances in 5 3 1/3C6H6 are slightly elongated relative to those in 3a,b and 4 3 3C6H6, measuring 2.4728(5) A˚ (Ge(1)-Ge(2)) and 2.4744(6) A˚ (Ge(1)-Ge(3)). However, the average Ge-Ge bond distance in 5 3 1/3C6H6 measures 2.4689(6) A˚, which is nearly identical with that in the chloride and bromide derivatives. The germanium-iodide bond length is 2.5868(5) A˚, which is within the range

(2.45-2.85 A˚) of the ca. 40 crystallographically characterized compounds containing a Ge-I bond. The Ge-Ge-Ge bond angles in 5 3 1/ 3 C6 H6 have an average value of 116.54(2), and the Ge-Ge-I bond angles have an average value of 100.80(2), both of which are similar to the average Ge-Ge-Ge and Ge-Ge-X (X = Cl, Br) angles in 3a,b and 4 3 3C6H6. Therefore, the structures of the three halide species 3-5 are very similar, despite the increasing size and decreasing electronegativity of the halogen atom. The electronic properties of compounds 1- 5 were investigated using UV/visible spectroscopy and cyclic voltammetry

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Figure 7. UV/visible spectra of (Ph3Ge)3GeCl (3, green line), (Ph3Ge)3GeBr (4, brown line), and (Ph3Ge)3GeI (5, purple line) in dichloromethane solvent.

Figure 8. Cyclic voltammograms of (Ph3Ge)3GeCl (3, green line), (Ph3Ge)3GeBr (4, brown line), and (Ph3Ge)3GeI (5, purple line) in dichloromethane solvent.

coupled with density functional theory (DFT) calculations. The UV/visible spectrum of 1 shown in Figure 6 exhibits a λmax value for the σ f σ* transition at 251 nm (ε=1.3 10 4 M-1 cm-1) which is slightly blue-shifted from

that for 2 at 256 nm (ε=5.1 10 4 M-1 cm-1).51 Both of the λ max features for 1 and 2 are red-shifted relative to those for (Bun 3Ge)3 GePh 53 and (Me 3Ge)3 GeH, 62 which were observed at 233 nm (ε=1.38 10 4 M-1 cm -1 ) and 198 nm

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Figure 9. Frontier orbitals of (Ph3Ge)3GeH (1): (a) the HOMO, containing a p orbital located on the central germanium atoms; (b) the LUMO, drawn to show the transfer of this p-orbital density into the Ge4 framework.

(ε=5.0 10 4 M-1 cm-1), due to the presence of the phenyl substituents in 1 and 2. The cyclic voltammogram of 1 is shown in Figure 6 and contains an irreversible oxidation wave at 1921 ( 8 mV, while that for 2 was observed at 1435 ( 14 mV, indicating that 1 is more difficult to oxidize than 2. As found for several other oligogermanes,50,73-75 compounds 1 and 2 each exhibit a single irreversible oxidation wave corresponding to loss of an electron from the HOMO of the molecule followed by decomposition, which likely occurs due to germylene extrusion. However, multiple oxidation waves were observed for the perphenyl-substituted linear oligogermanes Ge n Ph2nþ2 (n = 3, 4) as well as the tolylcontaining species Tol3GeGePh2GeTol3, Tol3GeGeTol2GeTol3, and Tol3GeGePh2GePh2GeTol3,52 indicating the species generated after oxidation were stable enough to undergo further oxidative processes. This appears not to be the case in 1 and 2, however, which is common for oligomeric germanium systems. A composite UV/visible spectrum for the three halide comounds 3-5 is shown in Figure 7, and an overlaid CV plot for 3-5 is shown in Figure 8. The UV/visible spectra for these three oligogermanes are similar and exhibit absorbance maxima at 245 nm (3, ε=2.8 104 M-1 cm-1), 264 nm (4, ε = 4.0 104 M-1 cm-1), and 271 nm (5, ε = 3.2 104 M-1 cm-1). The red shift in the absorbance maximum with decreasing electronegativity of the halide is expected, since previous findings indicated that more inductively electron donating groups lead to a destabilization of the HOMO in oligogermane systems.51 Compounds 3-5 each exhibit a single oxidation wave in their cyclic voltammograms at nearly the same potential (Figure 9). The oxidation wave for the branched chloride 3 was observed at 1668 ( 11 mV, while those for the bromide and iodide species 4 and 5 were observed at 1656 ( 14 and 1645 ( 16 mV, respectively. Therefore, these three species have the same oxidation potential within experimental error. The electronic structures of 1-5 were investigated using density functional theory computations. The 6-31G* basis set was used for all of the atoms, except for the iodine atom in 5, where the LanL2DZ basis set, combined with Hay and (73) Mochida, K.; Hodota, C.; Hata, R.; Fukuzumi, S. Organometallics 1993, 12, 586–588. (74) Mochida, K.; Shimizu, H.; Kugita, T.; Nanjo, M. J. Organomet. Chem. 2003, 673, 84–94. (75) Okano, M.; Mochida, K. Chem. Lett. 1990, 701–704.

Wadt’s effective core potential,76 was employed. Table 5 contains the computed HOMO and LUMO energies, as well as the energy of the HOMO-LUMO transition (in nm), the primary orbital contribution with the largest oscillator strength and the predicted UV/visible maximum (λtheory), and the experimental UV/visible maximum (λmax) and oxidation potential (Eox) values. As expected, the HOMO-LUMO transition energies computed from the B3LYP/6-31G(d) ground state orbitals are greater than the theoretical values computed using timedependent density functional theory to optimize the excited state. The molecular orbitals involved in the UV/visible transitions with the largest oscillator strength are fundamentally different for 1 compared to those for the other four compounds. The electronic transition in 1 occurs between a bonding and antibonding orbital between the central germanium atom and the peripheral germanium atoms, as shown in Figure 9. For 2 and 3-5, the transition occurs between the p or π orbital on the halide or phenyl ligand, respectively, which is antibonding in nature with the central germanium atom, to a diffuse orbital localized over the rest of the molecule (Figure 10). For 4 and 5, the HOMO-1 and the HOMO orbitals are very similar in energy, and both have contributions from the p orbitals on the halogen. The LUMO orbital is a σ-halogen-germanium antibonding orbital with significant density on the halogen and the central germanium atom. The LUMOþ1 orbitals correspond to complete charge transfer to the Ge4 framework. The experimental data correlate with the theoretical findings, in that the calculated UV/visible absorbance (λtheory) and the observed maxima (λmax) are in excellent agreement. In addition, the energy of the HOMO in 1 is stabilized relative to that of compound 2, which is consistent with the finding that compound 1 is more difficult to oxidize than 2. The HOMO orbital energies of the halide series 3-5 are all nearly identical, which correlates with the similarity in their observed oxidation potentials, and the red shift in their absorbance maxima are also consistent with the calculated HOMO-LUMO gap for these species. The amide 6 was synthesized from 3 in 69% yield, as shown in Scheme 4, and was characterized by NMR (1H and 13C) spectroscopy and elemental analysis. The 1H NMR spectrum of 6 exhibits a resonance at δ 2.73 ppm corresponding to the protons of the dimethylamido group. Compound 6 (76) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270–283.

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Table 5. Theoretical and Experimental Data for Compounds 1-5a compd

HOMO (eV)

LUMO (eV)

HOMO-LUMO gap (nm)

transition

calcd λmax (nm)

λmax (nm)

Eox (mV)

(Ph3Ge)3GeH (1) (Ph3Ge)3GePh (2) (Ph3Ge)3GeCl (3) (Ph3Ge)3GeBr (4) (Ph3Ge)3GeI (5)

-6.003 -5.907 -6.069 -6.050 -5.977

-0.576 -0.593 -0.990 -0.950 -1.315

228 233 244 243 266

HOMO f LUMO HOMO f LUMO HOMO f LUMOþ1 HOMO-1 f LUMOþ1 HOMO-1 f LUMOþ1

253 262 259 261 270

251 256 245 264 271

1921 ( 8 1435 ( 14 1668 ( 11 1656 ( 14 1643 ( 16

a

For the electronic transitions, the primary orbital contribution for the transition with the largest oscillator strength is shown.

Figure 10. Molecular orbitals for (Ph3Ge)3GeI (5): (a) the HOMO-1, containing a p orbital on the iodine atom; (b) the LUMOþ1, showing the shift of density toward the Ge4 framework and away from the iodine atom. Scheme 4

was combined with 1 equiv of Ph3GeH in acetonitrile solvent and was heated for 72 h at 90 C. A 1H NMR spectrum of the crude product indicated the presence of a mixture of products and also that 6 and Ph3GeH had been completely consumed during the course of the reaction. Recrystallization of the crude product mixture from a hot benzene solution yielded crystals of two organic compounds, identified to be 3-aminocrotononitrile (7) and 2,6-dimethyl4-aminopyrimidine (8), which can be regarded as a dimer and a trimer of acetonitrile, respectively. Additionally, 7 was generated exclusively as the E isomer, as shown in the 1H NMR spectrum of the bulk material recovered from the reaction mixture. Crystallographic data for 7 and 8 can be found in the Supporting Information. The attempted synthesis of But3GeGePh3 from But3GeNMe2 and Ph3GeH produced a similar result, where no evidence for the formation of the desired digermane was observed. Rather, only the 3-amidocrotononitrile-substituted germane But3Ge(NHC(CH3)dCHCN), along with But3CH2CN

and Ph3GeH, were recovered from the reaction.49 The 3amidocrotononitrile ligand in But3Ge(NHC(CH3)dCHCN) was also found to adopt the E conformation exclusively, as shown by its 1H NMR spectrum. Therefore, both of these processes involve the insertion of the acetonitrile into the Ge-C bond of the R-germyl nitrile at the bottom face of the incoming CH3CN molecule. Furthermore, it appears that sterically encumbering conditions at the reactive germanium site promote the oligomerization of the acetonitrile solvent and that this process likely occurs at the germanium center, since the 3-amidocrotononitrile ligand was shown to be attached to the germanium atom in But3Ge(NHC(CH3)d CHCN). The branched amide 6 decomposes during the course of the reaction that generates 7 and 8, as indicated by the 1H and 13 C NMR spectra of the product mixture, which did not exhibit any of the resonances corresponding to 6 or the Rgermyl nitrile species (Ph3Ge)3GeCH2CN. Both 7 and 8 were completely removed from the crude product mixture by

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crystallization from hot benzene, and analysis of the crude product mixture retained in the mother liquor by NMR (1H and 13C) spectroscopy and mass spectrometry indicated the presence of hexaphenyldigermane Ph3GeGePh3 by comparison of these data with those obtained for a commercial sample of this material. The material obtained from the reaction of 6 with Ph3GeH exhibited an fragmentation pattern identical with that for Ph3GeGePh3, including a molecular ion peak at m/z 608 with the correct isotope pattern.

Conclusions The reaction of Ph3GeNMe2 with GeH4 in acetonitrile produces the germanium hydride species (Ph3Ge)3GeH, and this material has been converted to the halide species (Ph3Ge)3GeX (X = Cl, Br, I) by hydride abstraction using tritylium hexafluorophosphate in the corresponding dihalomethane CH2X2 solvent. The crystal structure of (Ph3Ge)3GeH indicates this species has short Ge-Ge bond distances with an average value of 2.4310(5) A˚ and adopts a distortedtetrahedral environment at the central germanium atom. The structure and electronic properties of (Ph3Ge)3GeH can be compared to those of the related phenyl derivative (Ph3Ge)3GePh. The phenyl compound has longer Ge-Ge distances (d(Ge-Ge)av = 2.469(4) A˚), has a red-shifted UV/visible absorbance maximum relative to (Ph3Ge)3GeH, and is easier to oxidize than (Ph3Ge)3GeH. The structures of the three halide compounds (Ph3Ge)3GeX (X = Cl, Br, I) have also been determined, and the chloride species (Ph3Ge)3GeCl was found to crystallize in two different morphologies, depending on the crystallization method employed. The molecular structures of all three species are similar with regard to the Ge-Ge bond distances and Ge-Ge-Ge bond angles, and their oxidation potentials were found to be identical within the range of experimental error. The UV/visible maxima of these oligogermanes undergo a red shift from (Ph3Ge)3GeCl to (Ph3Ge)3GeBr to (Ph3Ge)3GeI. Density functional theoretical calculations on these three compounds, as well on (Ph3Ge)3GeH and (Ph3Ge)3GePh, correlate well with the experimental data. The electronic transition giving rise to the absorbance maximum for (Ph3Ge)3GeH results from electron promotion from a bonding to antibonding orbital, while in the phenyl- and halidesubstituted species this transition corresponds to electron promotion from a phenyl π or halide p orbital to a vacant molecular orbital localized over the entire Ge4 framework. Attempts to synthesize the germanium neopentane analogue (Ph3Ge)4Ge via two different methods were not successful. Reaction of (Ph3Ge)3GeH with 1 equiv of Ph3GeNMe2 resulted in the recovery of Ph3GeH and the R-germyl nitrile Ph3GeCH2CN, with no evidence for the formation of (Ph3Ge)4Ge. In addition, the chloride (Ph3Ge)3GeCl was converted to the amide (Ph3Ge)3GeNMe2 and reacted with Ph3GeH in acetonitrile solvent, which resulted in the consumption of both reactants. Again, however, the desired product (Ph3Ge)4Ge was not detected; rather, (E)-3-aminocrotononitrile and 2,6-dimethyl-4-aminopyrimidine were isolated from the reaction mixture along with Ph3GeGePh3, which results from the decomposition of the branched oligogermane species. Therefore, it is apparent that the synthesis of (Ph3Ge)4Ge is not possible, most likely due to the steric constraints of placing four triphenylgermyl groups around the central germanium atom.

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Experimental Section General Remarks. All manipulations were carried out under a nitrogen atmosphere using standard syringe, Schlenk, and glovebox techniques.77 The reagents GeH4, Ph3GeCl, and Ph3GeH were purchased from Gelest, Inc., and were used as received. Dichloromethane, dibromomethane, diiodomethane, LiNMe2, and [Ph3C][PF6] were purchased from Aldrich. Dichloromethane, acetonitrile, and benzene were purified using a Glass Contour solvent purification system. Dibromomethane and diiodomethane were dried over alumina, distilled, and kept over 5 A˚ molecular sieves. The compounds Ph3GeNMe254 and (Ph3Ge)3GePh51,63 were prepared according to the literature procedures. 1H (300 MHz) and 13C NMR spectra (75.4 MHz) were recorded on a Gemini 2000 NMR spectrometer and were referenced to benzene-d6 solvent. 73Ge NMR spectra were recorded using a 50 mg/mL solution of 1 on a Varian INOVA 500 MHz spectrometer using a 10 mm low gamma broad-band probe at 17.43 MHz using the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence.78,79 The following parameters were used during acquisition: spectral width 100 000 Hz, acquisition time 0.01 s, delay time 0 s, line broadening factor 20, number of transients 1 107. The spectra were referenced to external GeMe4 by substitution. UV/visible spectra were obtained using a Hewlett-Packard 8453 diode array spectrometer in CH2Cl2 solvent. Cyclic voltammograms were recorded using a DigiIvy DY2112 potientiostat with 0.10 M [Bu4N][PF6] in CH2Cl2 as the supporting electrolyte, and reported data are the average of four independent runs. Mass spectra were obtained on a Shimadzu 2010A LCMS by direct injection with a coronal discharge source. Elemental analyses were conducted by Galbraith Laboratories (Knoxville, TN). Synthesis of (Ph3Ge)3GeH (1). Germane gas (0.170 g, 2.22 mmol) was condensed into an evacuated Schlenk tube at 77 K using a liquid N2 bath and was subsequently warmed to room temperature. A Schlenk tube was charged with Ph3GeNMe2 (2.60 g, 7.47 mmol) and acetonitrile (25 mL) and was cooled to 77 K, and the GeH4 was condensed in vacuo. The reaction mixture was warmed to room temperature and then was heated with stirring in an oil bath at 90 C for 24 h. After cooling, the reaction mixture was transferred to a Schlenk flask and the volatiles were removed in vacuo to yield 1 (1.457 g, 66%). 1H NMR (C6D6, 25 C, 400 MHz): δ 7.26 (d, J=8.1 Hz, 18H, o-C6H5), 7.10 (t, J= 7.2 Hz, 9H, p-C6H5), 6.95 (t, J =6.9 Hz, 18H, m-C6H5), 4.58 (s, 1H, Ge-H) ppm. 13C NMR (C6D6, 25 C, 125.7 MHz): δ 137.0 (ipso-C), 136.0 (o-C), 127.8 (p-C), 128.4 (m-C) ppm. IR (Nujol mull): 1953 cm-1 (νGe-H). UV/visible (CH2Cl2): λmax 251 nm (ε=1.3 104 M-1 cm-1). Anal. Calcd for C54H46Ge4: C, 65.79; H, 4.71. Found: C, 65.62; H, 4.79. Alternate Synthesis of (Ph3Ge)3GeH (1). A Schlenk tube was charged with Ph3GeNMe2 (3.17 g, 9.11 mmol) and acetonitrile (35 mL). The mixture was frozen at 77 K using a liquid N2 bath, and the Schlenk tube was evacuated. Germane gas (1.18 g, 15.4 mmol) was condensed at 77 K, and the reaction mixture was warmed to room temperature. The reaction mixture was subsequently heated at 85 C for 18 h and was then transferred to a Schlenk flask. The volatiles were removed in vacuo to yield 1 (2.21 g, 74% based on Ph3GeNMe2). The spectral data for the product were identical with those given above. Synthesis of (Ph3Ge)3GeCl (3). A Schlenk tube was charged with 1 (0.105 g, 0.107 mmol) and [Ph3C][PF6] (0.045 g, 0.115 mmol) in dichloromethane (30 mL). The reaction mixture was heated in an oil bath with stirring at 90 C for 24 h. The reaction mixture was filtered through Celite into a Schlenk flask, and the volatiles were removed in vacuo to yield a pale yellow solid that was washed with hexane (4 5 mL). The solid was dried in (77) Shriver, D. F.; Drezdzon, M. A., The Manipulation of Air Sensitive Compounds, 2nd ed.; Wiley: New York, 1986. (78) Carr, H. Y.; Purcell, E. M. Phys. Rev. 1954, 94, 630–638. (79) Meiboom, S.; Gill, D. Rev. Sci. Instrum. 1958, 29, 688–691.

no. of rflns collected no, of indep rflns completeness to θ (deg) abs cor max, min transmissn refinement method no. of data/restraints/params goodness of fit on F2 final R indices (I < 2σ(I)) R1 wR2 final R indices (all data) R1 wR2 largest diff peak, hole (e A˚-3)

empirical formula formula wt temp (K) wavelength (A˚) cryst syst space group a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) V (A˚3) Z F (g cm-3) abs coeff (mm-1) F(000) cryst size (mm3) θ range for data collecn (deg) index ranges

4404/1/239 1.047

11 350/1/586 1.022 0.0431 0.0731 0.0580 0.0797 0.865, -0.668

0.0307 0.0721

0.0432 0.0771 0.643, -0.359

0.0671 0.1173 0.653, -0.710

0.0487 0.1061

C78H75ClGe4 1338.19 100(2) 0.710 73 hexagonal P63 18.679(1) 18.679(1) 9.8740(7) 90 90 120 2983.6(4) 2 1.490 2.088 1376 0.26 0.19 0.11 2.18-28.26 -24 e h e 24, -24 e k e 23, -12 e l e 12 12 563 4404 (Rint = 0.0520) θ = 25.00 (99.6%) multiscan 0.8029, 0.6129

3b

C60H51ClGe4 1097.82 150(2) 0.710 73 monoclinic P21 13.101(2) 10.443(1) 18.184(2) 90 95.740(2) 90 2475.4(6) 2 1.473 2.498 1112 0.26 0.14 0.11 1.56-28.47 -16 e h e 16, -13 e k e 13, -24 e l e 17 30 644 11 350 (Rint = 0.0546) θ = 25.00 (99.9%) multiscan 0.7707, 0.5628

3a

C54H46Ge4 985.27 120(2) 1.541 78 monoclinic P21/c 17.1845(5) 11.2369(3) 24.8346(7) 90 108.380(2) 90 4550.9(2) 4 1.438 3.309 1992 0.20 0.10 0.10 2.71-64.09 -17 e h e -19, -12 e k e 12, -26 e l e 27 30 305 7027 (Rint = 0.0334) θ = 60.00 (96.8%) none 0.7332, 0.5574 full-matrix least squares on F2 7027/0/527 1.028

1

0.0518 0.0846 0.924, -0.637

0.0375 0.0774

4797/1/198 1.044

C72H63BrGe4 1298.49 100(2) 0.710 73 hexagonal P63 18.660(2) 18.660(2) 10.054(2) 90 90 120 3031.7(6) 2 1.422 2.664 1316 0.30 0.12 0.12 1.26-28.06 -24 e h e 17, -24 e k e 23, -13 e l e 13 29 951 4797 (Rint = 0.0616) θ = 25.00 (99.9%) multiscan 0.7404, 0.5020

4 3 3C6H6

0.0457 0.0768 0.464, -0.465

0.0329 0.0689

8994/0/559 1.024

C57H48Ge4I 1150.21 100(2) 0.710 73 triclinic P1 12.755(1) 13.298(1) 15.166(2) 86.077(2) 69.500(2) 86.651(2) 2402.0(4) 2 1.590 3.159 1142 0.25 0.20 0.15 1,44-26.46 -13 e h e 15, -16 e k e 16, -18 e l e 18 20 853 8994 (Rint = 0.0394) θ = 25.00 (92.4%) multiscan/sadabs 0.6487, 0.5056

5 3 1/3C6H6

Table 6. Crystallographic Data for the Compounds (Ph3Ge)3GeH (1), (Ph3Ge)3GeCl 3 C6H6 (3a), (Ph3Ge)3GeCl 3 3C6H6 3 C6H12 (3b), (Ph3Ge)3GeBr 3 3C6H6 (4 3 3C6H6), and (Ph3Ge)3GeI 3 1/3C6H6 (5 3 1/3C6H6)

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vacuo, and the resulting solid was crystallized from 5/1 benzene/ cyclohexane to yield 3 (0.071 g, 65%) as colorless crystals. 1H NMR (C6D6, 25 C, 300 MHz): δ 7.34 (d, J=6.6 Hz, 18H, oC6H5), 7.05 (t, J=7.2 Hz, 9H, p-C6H5), 6.93 (t, J=7.2 Hz, 18H, m-C6H5). 13C NMR (C6D6, 25 C, 75.5 MHz): δ 137.0 (ipso-C), 136.3 (o-C), 129.2 (p-C), 128.5 (m-C) ppm. UV/visible (CH2Cl2): λmax 245 nm (ε = 2.8 104 M-1 cm-1). Anal. Calcd for C78H75ClGe4 (3 3 3C6H6 3 C6H12): C, 69.98; H, 5.65. Found: C, 69.76; H, 5.67. Synthesis of (Ph3Ge)3GeBr (4). A Schlenk tube was charged with 1 (0.103 g, 0.105 mmol) and [Ph3C][PF6] (0.045 g, 0.115 mmol) in dibromomethane (30 mL). The reaction mixture was heated in an oil bath with stirring at 90 C for 24 h. The reaction mixture was filtered through Celite into a Schlenk flask, and the volatiles were removed in vacuo to yield a pale yellow solid that was washed with hexane (4 5 mL). The solid was dried in vacuo, and the resulting solid was crystallized from benzene to yield 4 (0.062 g, 56%) as colorless crystals. 1H NMR (C6D6, 25 C, 300 MHz): δ 7.35 (d, J=6.6 Hz, 18H, o-C6H5), 7.07 (t, J=7.8 Hz, 9H, p-C6H5), 6.94 (t, J = 7.5 Hz, 18H, m-C6H5). 13C NMR (C6D6, 25 C, 75.5 MHz): δ 137.1 (ipso-C), 136.4 (o-C), 129.2 (pC), 128.5 (m-C) ppm. UV/visible (CH2Cl2): λmax 264 nm (ε = 4.0 104 M-1 cm-1). Anal. Calcd for C54H45BrGe4: C, 60.91; H, 4.26. Found: C, 60.55; H, 4.45. Synthesis of (Ph3Ge)3GeI (5). A Schlenk tube was charged with 1 (0.100 g, 0.102 mmol) and [Ph3C][PF6] (0.045 g, 0.115 mmol) in diiodomethane (30 mL). The reaction mixture was heated in an oil bath with stirring at 90 C for 24 h. The reaction mixture was filtered through Celite into a Schlenk flask, and the volatiles were removed in vacuo to yield a pale yellow solid that was washed with hexane (4 5 mL). The solid was dried in vacuo, and the resulting solid was crystallized from benzene to yield 4 (0.067 g, 59%) as colorless crystals. 1H NMR (C6D6, 25 C, 300 MHz): δ 7.35 (d, J=7.2 Hz, 18H, o-C6H5), 7.07 (t, J= 7.2 Hz, 9H, p-C6H5), 6.95 (t, J=7.2 Hz, 18H, m-C6H5). 13C NMR (C6D6, 25 C, 75.5 MHz): δ 137.1 (ipso-C), 136.5 (o-C), 129.2 (pC), 128.5 (m-C) ppm. UV/visible (CH2Cl2): λmax 271 nm (ε=3.2 104 M-1 cm-1). Anal. Calcd for C54H45IGe4: C, 58.34; H, 4.08. Found: C, 52.22; H, 4.02. NOTE: We were unable to obtain a satisfactory carbon analysis for this compound. Synthesis of (Ph3Ge)3GeNMe2 (6). A Schlenk flask was charged with 3 (0.100 g, 0.098 mol), LiNMe2 (0.005 g, 0.100 mmol), and THF (40 mL). The reaction mixture was stirred for 24 h at room temperature and then was filtered through Celite. The resultant solution was evaporated in vacuo to yield a solid which was dissolved in hexane and filtered through Celite. The hexane was removed in vacuo to yield 6 (0.070 g, 69%) as a yellow solid. 1H NMR (C6D6, 25 C, 300 MHz): δ 7.65 (t, J=7.5 Hz, 18H, m-C6H5), 7.24 (d, J=7.5 Hz, 18H, o-C6H5), 6.93 (t, J=7.2 Hz, 9H, p-C6H5), 2.71 (s, 6H, -N(CH3)2) ppm. 13C NMR (C6D6, 25 C, 75.5 MHz): δ 138.3 (ipso-C), 135.5 (o-C), 129.7 (p-C), 127.7 (m-C) ppm. Anal. Calcd for C56H51Ge4N: C, 65.37; H, 5.00. Found: C, 64.98; H, 5.13. Attempted Synthesis of (Ph3Ge)4Ge. A Schlenk tube was charged with 6 (0.100 g, 0.097 mmol) and Ph3GeH (0.030 g, 0.098 mmol) in acetonitrile (40 mL). The reaction mixture was heated in an oil bath at 90 C with stirring for 72 h. The reaction mixture was cooled and was transferred to a Schlenk flask. The volatiles were removed in vacuo to yield 0.072 g of a brown solid, which was recrystallized from hot benzene (5 mL) to yield colorless crystals identified as 3-aminocrotononitrile (7) and 2,6-dimethyl-4-aminopyrimidine (8). The combined yield of 7 and 8 was 0.067 g. 1H NMR (C6D6, 25 C, 300 MHz): 7, δ 4.69 (br s, 2H, -NH2), 3.77 (s, 1H, CdCH), 1.89 (s, 3H, -CH3) ppm; 8, δ 5.36 (s, 1H, C6H), 3.82 (br s, 2H, -NH2), 2.61 (s, 3H, N-C(CH3)-N), 2.15 (s, 3H, N-C(CH3)-CH) ppm. X-ray Crystal Structure Determinations. Diffraction intensity data were collected with a Siemens P4/CCD diffractometer.

Samanamu et al. Crystallographic data for the X-ray analysis for 1 and 3-5 are collected in Table 6. The crystal-to-detector distance was 60 mm, and the exposure time was 20 s per frame using a scan width of 0.5. Data collection was 100% complete to 25.00 in θ, except in the case of 5, where CheckCIF indicated data coverage to only 92%. However, the protocols for data coverage indicated 100% coverage with high redundancy. Currently, we are not sure of the reason for this discrepancy. The data were integrated using the Bruker SAINT software program and scaled using the SADABS software program. Solution by direct methods (SIR2004) produced a complete heavy-atom phasing model consistent with the proposed structures. All non-hydrogen atoms were refined anisotropically by full-matrix least squares (SHELXL97). Aside from the germanium-bound hydrogen in 1, all hydrogen atoms were placed using a riding model. Their positions were constrained relative to their parent atom using the appropriate HFIX command in SHELXL-97. Computational Details. Gaussian 03 was utilized for all computations.80 Energy calculations, geometry optimizations, and frequency calculations were performed using the hybrid density functional method including Becke’s three-parameter nonlocal-exchange functional81 with the Lee-Yang-Parr correlation functional, B3LYP.82 The 6-31G* basis set83 was employed for all atoms except iodine. For iodine, the LanL2DZ basis set, which includes the D95 double-ζ basis set84 combined with Hay and Wadt’s effective core potential,76 was utilized. All atomic positions are optimized without geometry constraints. Frequency calculations were performed at a lower level to confirm that the stable geometries have real vibrational frequencies. The time-dependent density functional computations, as implemented by Gaussian 03, were utilized to explore the excited manifold and compute the possible electronic transitions and oscillator strengths.

Acknowledgment. Funding for this work was provided by a CAREER grant from the National Science Foundation (No. CHE-0844758) and is gratefully acknowledged. We are grateful to Prof. Rudolf Pietschnig (Karl-FranzensUniversit€at Graz) for helpful discussions. Supporting Information Available: CIF files giving crystallographic data for 1 and 3-5 and tables and figures giving structural details for 7 and 8. This material is available free of charge via the Internet at http://pubs.acs.org. (80) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J., J. A.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; yengar, 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.; Pople, J. A. Gaussian 03, Revision C.02; Gaussian, Inc.: Wallingford, CT, 2004. (81) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652. (82) Lee, C.; Yang, W.; G, P. R. Phys. Rev. 1988, B 37, 785–789. (83) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M. S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654–3665. (84) Dunning, T. H.; Hay, P. J. In Methods of Electronic Structure Theory; Schaefer, H. F., Ed.; Plenum Press: New York, 1977; pp 1-28.

Syntheses, Structures, and Electronic Properties of the Branched

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