pubs.acs.org/Organometallics Published on Web 01/26/2011 r 2011 American Chemical Society 1046 Organometallics 2011, 30, 1046–1058 DOI: 10.1021/om101091c Syntheses, Structures, and Electronic Properties of the Branched Oligogermanes (Ph 3 Ge) 3 GeH and (Ph 3 Ge) 3 GeX (X = Cl, Br, I) † 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* ,‡ ‡ 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 13 th International Conference on Germanium, Tin, and Lead Chemistry (GTL-13), Graz, Austria, July 2010. Received November 19, 2010 The branched oligogermanium hydride (Ph 3 Ge) 3 GeH was synthesized via a hydrogermolysis reaction from GeH 4 and Ph 3 GeNMe 2 and was converted to the halide series of compounds (Ph 3 Ge) 3 GeX (X = Cl, Br, I) upon reaction with [Ph 3 C][PF 6 ] in CH 2 X 2 solvent (X = Cl, Br, I). These species were fully characterized by NMR ( 1 H and 13 C) and UV/visible spectroscopy, cyclic voltammetry, and elemental analysis. In addition, (Ph 3 Ge) 3 GeH was analyzed by 73 Ge 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 73 Ge NMR spectrum of (Ph 3 Ge) 3 GeH. The X-ray crystal structures of (Ph 3 Ge) 3 GeH and (Ph 3 Ge) 3 GeX (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 (Ph 3 Ge) 3 GeH are short (average value 2.4310(5) A ˚ ), while those in the halide compounds (Ph 3 Ge) 3 GeX 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 synthe- ses, structures, and spectral properties of several linear and cyclic organo-oligogermanes. 1-19 In addition, the chemistry of the cyclotrigermane (Mes 2 Ge) 3 , which was first synthe- sized in 1987, 20 has been extensively investigated, and it has been demonstrated that the reactivity of (Mes 2 Ge) 3 re- sembles that of both the free germylene Mes 2 Ge: and the (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. (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.
Transcript
pubs.acs.org/Organometallics Published on Web 01/26/2011 r 2011 American Chemical Society
1046 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)†
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*,‡
‡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 workwill 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 hydrogermolysisreaction 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, cyclicvoltammetry, and elemental analysis. In addition, (Ph3Ge)3GeH was analyzed by 73Ge NMRspectroscopy and exhibits two resonances at δ -56 and -311 ppm. A Ge-H coupling constant of191Hzwas observed in the proton-coupled 73GeNMR spectrumof (Ph3Ge)3GeH. TheX-ray crystalstructures of (Ph3Ge)3GeH and (Ph3Ge)3GeX (X = Cl, Br, I) were obtained and represent the firstexamples of branched oligogermane hydrides or halides to be characterized in this fashion. TheGe-Ge bond distances in (Ph3Ge)3GeH are short (average value 2.4310(5) A), while those in thehalide 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 DFTcomputations, and excellent agreement was found between the experimental and theoretical data.
Introduction
The chemistry of singly bonded oligogermanes, which arediscrete molecules containing germanium-germaniumbonds that range in length from approximately 2.40 to 2.50A, has recently received significant new attention. The firstdetailed study of these systems was reported in a series of 19papers published during the 1980s that described the synthe-ses, structures, and spectral properties of several linear and
cyclic organo-oligogermanes.1-19 In addition, the chemistryof the cyclotrigermane (Mes2Ge)3, which was first synthe-sized in 1987,20 has been extensively investigated, and it hasbeen demonstrated that the reactivity of (Mes2Ge)3 re-sembles that of both the free germylene Mes2Ge: and the
(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.
(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.
digermeneMes2GedGeMes2.21-34 A number of compounds
containing Ge-Ge multiple bonds have also beenreported.35-47
The syntheticmethods employed for the synthesis of linearsingly bonded oligogermanes were often complicated by lowyields and/or the formation of product mixtures. A versatilesynthetic method for the preparation of these materials,allowing control over the Ge-Ge chain length and theorganic substituent pattern, proved to be elusive, despitethe potentially interesting physical properties of these sys-tems and their potential optical and electronic applications.Although germanium is frequently and mistakenly regardedas being nearly identical with its lighter congener silicon, theband gap, electron and hole mobility, and conductivity arehigher in bulk elemental germanium,48 and as the limitationsof silicon-based materials become realized, germanium willlikely play an increased role in the electronics industrydespite its higher cost.A rational method for the stepwise synthesis of oligoger-
manes, which relies on the hydrogermolysis reaction, hasbeen developed in our laboratory that allows control overboth the number of germanium atoms in the chain and thetype of organic substituents attached to the germanium-
germanium backbone.49-56 Using this method, we havesynthesized a variety of linear oligogermanes and have alsoextended it to the preparation of unusual branched systems.The first branched oligogermanes were reported in 1963 andincluded (Ph3Ge)3GeH (1) and (Ph3Ge)3GeMe.57 The for-mer oligogermane was synthesized from Ph3GeLi and GeI2and was characterized by IR spectroscopy and elementalanalysis, and the latter compoundwas obtained from 1 usingBunLi followed by quenching withMeI. The syntheses of theheteroleptic branched oligogermane (PhCl2Ge)3GePh58 andits derivatives (PhMe2Ge)3GePh58 and (Ph(X)2Ge)3GePh(X=MeO, MeS, Me2N, Et2P)
59 were subsequently de-scribed, and the preparation of the mixed group 14 metalneopentane analogues (Ph3M)4M
We recently reported the preparation of (Ph3Ge)3GePh (2)as well as (EtOCH2CH2Bu
n2Ge)3GePh.51 Compound 2 was
the first branched oligogermane to be structurally character-ized, and we demonstrated that the functionalized branchedspecies (EtOCH2CH2Bu
n2Ge)3GePh could be used for the
construction of higher branched heptagermanes using ourhydride protection/deprotection strategy combined with thehydrogermolysis reaction.51 We have also prepared thebranched system (Bun3Ge)3GePh,53 and the two dendrite-type tridecagermanes Me28Ge13 and Ph6Me22Ge13 werereported in 2005 and the photoconductive properties of thesesystems in the presence of a C60 dopant were investigated.
61
In addition, the synthesis of the neopentyl system (Me3Ge)4-Ge, as well as (Me3Ge)3GeK(18-crown-6) and (Me3Ge)3-GeH obtained from (Me3Ge)4Ge, was recently described;62
however, neither (Me3Ge)4Ge nor (Me3Ge)3GeHwere struc-turally characterized.We were interested in the preparation of the related
neopentane analogue (Ph3Ge)4Ge via the hydrogermolysisreaction between GeH4 and Ph3GeNMe2. To our knowl-edge, the synthesis and full characterization of this oligoger-mane has not been described, although 13C NMR chemicalshift values for this compound were reported in the absenceof any synthetic details.19 Herein we wish to report ourattempts to synthesize (Ph3Ge)4Ge via the hydrogermolysisreaction as described above. We have found that the pre-paration of this material is not possible due to steric con-straints; however, the reaction of GeH4 with Ph3GeNMe2in acetonitrile solvent does yield the branched hydride(Ph3Ge)3GeH (1), and this species has been converted to thethree branched halide species (Ph3Ge)3GeX (X=Cl (3), Br(4), I (5)). The X-ray structures of 1 and 3-5 have beenobtained, and these four systems have been fully character-ized by NMR (1H and 13C) and UV/visible spectroscopy aswell as cyclic voltammetry. In addition, 73Ge NMR spectra
(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,
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. Organome-
tallics 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.
(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) Rivi�ere, P.; Satg�e, J. Synth. Inorg. Met.-Org. Chem. 1971, 1, 13–
20.(59) Rivi�ere, P.; Satg�e, J.; Soula, D. J. Organomet. Chem. 1974, 72,
329–338.(60) Willemsens, L. C.; van der Kerk, G. J. M. J. Organomet. Chem.
Mochida, K. Chem. Lett. 2005, 34, 1690–1691.(62) Hlina, J.; Baumgartner, J.; Marschner, C.Organometallics 2010,
29, 5289–5295.
1048 Organometallics, Vol. 30, No. 5, 2011 Samanamu et al.
of 1 were obtained, and we were able to observe 73Ge- 1Hcoupling in the 1H-decoupled spectrum.
Results and Discussion
The synthesis of (Ph3Ge)4Ge was attempted using twodifferent stoichiometric conditions. Initially, excess GeH4
was condensed into a Schlenk tube containing Ph3GeNMe2in acetonitrile at 77K. The tube was sealed, warmed to roomtemperature, and then placed in an oil bath at 90 �C, whereafter stirring for 1 h a large amount of white precipitate hadformed. The reactionmixture was cooled, and the precipitatewas filtered and washed with hexane. The 1H NMR spec-trum of the product in C6D6 solvent was clean and containedthree resonances in the aromatic region as well as a singlet atδ 4.58 ppm, which was identical with the chemical shift of(Ph3Ge)3GeH (1) prepared from (Ph3Ge)3GePh (2).51,63 Theinfrared spectrum of 1 contains a band for the ν(Ge-H)bond stretch at 1953 cm-1 which is identical with that foundpreviously for 1.51,57 The same reaction was conducted usinga 1:3.3 molar ratio of GeH4 to Ph3GeNMe2, and 1was againisolated in 66% yield as the only germanium-containingproduct (Scheme 1). The reaction ofGeH4with Ph3GeNMe2proceeds via the in situ conversion of Ph3GeNMe2 toPh3GeCH2CN, which is the active species in the Ge-Gebond forming process.49-51,54
The product obtained from the latter reaction was recrys-tallized from hot benzene to provide colorless crystals thatwere analyzed usingX-ray crystallography, which confirmedthe composition of 1. An ORTEP diagram of 1 is shown inFigure 1, and selected bond distances and angles are col-lected in Table 1. The three Ge-Ge bond distances are2.4271(5), 2.4298(5), and 2.4360(5) A for the Ge(1)-Ge(2),Ge(1)-Ge(3), andGe(1)-Ge(4) bonds, respectively, with anaverage value of 2.4310(5) A. The average Ge-Ge bonddistance in 1 is similar to those in the linear oligogermanesPh3GeGeR3 (R=Me, 2.418(1) A;64 R=Et, 2.4253(7) A;54
R=Bun, 2.421(8) A54) 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 Ge3Ph8and 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 atomat the central germanium atom in 1, which is significantly lesssterically encumbering than the phenyl substituent in 2. Thehydrogen atom at the central germanium atom was located,and the Ge-H distance is 1.45(3) A, which is comparable tothe Ge-H distance of 1.50(5) A in Ph3GeH.65
The central germanium atom in 1 is disposed in a dis-torted-tetrahedral environment, which was also found forcompound 2. The three Ge-Ge-Ge bond angles in 1 are116.11(2), 112.49(2), and 117.89(2)�with an average value of115.50(2)�. The pattern among the three bond angles in 1
mirrors that in 2, where one Ge-Ge-Ge bond angle issubstantially more acute than the other two. However, theGe(2)-Ge(1)-Ge(4) bond angle ismore acute than the othertwo 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 areallmore obtuse than the corresponding angles in 2, which hasan average Ge-Ge-Ge bond angle of 112.72(1)�, as aconsequence of the shorter Ge-Ge bond distances presentin 1.The branched hydride 1 has been characterized by NMR
(1H, 13C, and 73Ge) spectroscopy. These data can be com-pared with the corresponding data that have been obtainedfor the phenyl-substituted derivative 2 as well as the methylderivative (Me3Ge)3GeH.62 As mentioned above, the 1HNMR spectrum of 1 exhibits a Ge-H resonance at δ 4.58ppm, which is shifted upfield relative to typical resonancesfor germanium hydrides and suggests that the hydrogenatom at the central germanium atom is significantly shielded.This effect is more drastic in (Me3Ge)3GeH, where theresonance for the hydrogen atom was observed at δ 2.81ppm62 due to the presence of the more inductively electrondonating methyl groups versus the phenyl substituents in 1.In addition, all of the aromatic resonances in the 1H and 13C
Scheme 1
Figure 1. ORTEP diagram of (Ph3Ge)3GeH (1). Thermal ellip-soids are drawn at the 50% probability level.
(63) Amadoruge, M. L.; Golen, J. A.; Rheingold, A. L.; Weinert,C. S. Organometallics 2009, 28, 4628.(64) P�ark�anyi, L.; K�alm�an, 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.
spectrum of 1 are shifted upfield relative to the correspond-ing peaks in the spectrum of 2.The use of 73Ge NMR spectroscopy for the characteriza-
tion of oligogermanium compounds is uncommon,66-68 butseveral species containing germanium-germanium bondshave been characterized by this method.53,68 The 73GeNMR spectrum of 2 exhibits a single feature at δ -202ppm corresponding to the central germanium atom in thismaterial,53 and a peak for the peripheral Ph3Ge- atoms wasnot observed. However, the 73Ge NMR spectrum of 1
contains two resonances, including one for the three Ph3Ge-groups at δ-56 ppm (Δν1/2=35Hz) and a second feature atδ -311 ppm (Δν1/2= 210 Hz) for the central germaniumatom; the latter is consistent with a previously reportedvalue.68 Consistent with the 1H NMR spectrum of 1, thefeature for the central germanium atom in 1 is shifted upfieldrelative to that for 2, since the central germanium atomof 1 ismore shielded due to the presence of the hydrogen atomversus the phenyl group in 2. In addition, the resonance atδ-311ppm in the 1H-coupled 73GeNMRspectrumof 1 splitsinto a doublet with a coupling constant of 191 Hz, as shownin Figure 2. This coupling constant is nearly twice those
observed for several monomeric arylgermanium hydrides,including p-(MeOC6H4)GeH3 (1JGeH = 97 Hz), p-(CH3-C6H4)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 fewother one-bond Ge-H coupling constants have been re-ported, with the exception of GeH4
70 and Et3GeH.70,71 Noother examples of data for compounds having hydrogenbound to a catenated germanium atom have been reported,but it is possible that the connectivity at the central germa-nium atom of 1 is responsible for the large magnitude of theGe-H coupling constant.The synthesis of (Ph3Ge)4Ge from 1 was attempted by
treating 1with 1 equiv of Ph3GeNMe2 in CH3CN solution at90 �C for an extended reaction time of 7 days (Scheme 1).However, the 1H NMR spectrum of the products obtainedafter removing the volatile components in vacuo still exhib-ited a resonance at δ 4.58 ppm for the hydrogen atom of 1 aswell as a singlet at δ 1.98 ppm corresponding to the methyl-ene protons of Ph3GeCH2CN
49 generated from Ph3Ge-NMe2 during the course of the reaction. There was noevidence for the generation of the desired neopentane analo-gue (Ph3Ge)4Ge, indicating that steric limitations about thecentral germanium atom might prevent the attachment of afourth -GePh3 group.
Table 1. Selected Bond Distances (A) and Angles (deg) for(Ph3Ge)3GeH (1)
Figure 2. Proton-coupled 73Ge NMR spectrum of (Ph3Ge)3GeH (1) at 17.43 MHz, referenced to external GeMe4.
1050 Organometallics, Vol. 30, No. 5, 2011 Samanamu et al.
We also attempted to synthesize the branched germaniumcation (Ph3Ge)3Geþ from 1 using tritylium hexafluorophos-phate [Ph3C
þ][PF6-] as the hydrogen-abstracting reagent
(Scheme 2). However, [Ph3Cþ][PF6
-] is not soluble in non-polar solvents, and therefore the reaction was carried out indichloromethane. The product isolated after the reactionmixture was stirred at room temperature for 36 h was not thedesired [(Ph3Ge)3Geþ][PF6
-] but rather the chlorinated oli-gogermane (Ph3Ge)3GeCl (3). However, it is clear that(Ph3Ge)3Geþ was generated in the reaction, since the 1HNMR spectrum of the crude product mixture exhibited aresonance at δ 5.43 ppm that matches exactly with that for acommercial sample of Ph3CH. The cation (Ph3Ge)3Geþ
generated in the reaction subsequently abstracts a chlorineatom from the CH2Cl2 solvent to provide 3, with [CH2-Clþ][PF6
-] being generated as a byproduct. The [CH2Clþ]
cation has been identified by infrared spectroscopy as adiscrete molecule in an argon matrix.72
The crude product mixture was suspended in benzene andfiltered to remove excess [Ph3C
þ][PF6-] and the [CH2-
Clþ][PF6-] containing byproduct, and after evaporation of
the benzene the resulting solid was washed with hexane toremove Ph3CH.The product 3was isolated in 68%yield, andthe 1Hand 13CNMRspectra of 3 are very similar to that of 1,although the resonance for the ortho protons of 3 (δ 7.34ppm) is shifted downfield relative to that for 1 (δ 7.26 ppm).In light of the successful conversion of 1 to 3 using thereaction conditions described above, we prepared (Ph3Ge)3-GeBr (4) and (Ph3Ge)3GeI (5) from 1 using [Ph3C
þ][PF6-]
and dibromo- or diiodomethane, respectively, as thesolvent (Scheme 3). Compound 4was obtained in 56% yield,while 5 was obtained in 59% yield, and the chemical shiftsobserved for the phenyl groups in the 1H and 13C NMRspectra of these two species are very similar to those of thechloride 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 3wereobtained as the monobenzene solvate (Ph3Ge)3GeCl 3C6H6
(3a). However, when a 5/1 (v/v) mixture of benzene tocyclohexane was used as the crystallization medium,crystals of the tris(benzene) mono(cyclohexane) solvate(Ph3Ge)3GeCl 3 3C6H6 3C6H12 (3b) were obtained. Figure 3containsORTEPdiagramsof3a,b, and selectedbonddistances
andangles are collected inTables 2 and3. In the structure of 3a,theGe(1)-Cl(1) distance is 2.230(1) A and the averageGe-Gebond distance is 2.4626(7) A. The Ge-Ge distances in 3a arelonger than those in the hydride 1 but are slightly shorter thanthose in 2. The Ge-Ge-Ge bond angles in 3a average116.22(2)�, and as observed for both 1 and 2, the Ge(2)-Ge-(1)-Ge(4) bond angle in 3a is more acute thanthe other two bond angles by an average value of 5.2�. Theaverage Ge-Ge-Cl angle in 3a is 101.34(4)�; therefore, theenvironment about the central germanium atom in 3a canbe regarded as distorted tetrahedral.
Scheme 3
Figure 3. ORTEP diagrams of the two morphologies of 3,including the benzene solvate (Ph3Ge)3Cl 3C6H6 (3a, top) andthe tris(benzene) mono(cyclohexane) solvate (Ph3Ge)3GeCl 3 3-C6H6 3C6H12 (3b, bottom). Thermal ellipsoids are drawn at the50% probability level.
(66) Mackay, K. M.; Thomson, R. A.Main GroupMet. 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–
The structure of 3b adopts the P63 space group that has aC3 axis of rotation located along the Ge(1)-Cl(1) bond. Theunit cell of 3b incorporates three molecules of benzene andone molecule of cyclohexane from the solvent system usedfor crystallization, and the single cyclohexane molecule islocated on the C3 axis. The metric parameters of 3b differvery slightly from those from 3a, due in part to the highersymmetry of 3b. The Ge(1)-Cl(1) bond length of 2.215(2) Ais shorter than that of 3a by 0.015 A, and the Ge-Ge bonddistance of 2.4699(5) A is identical within error with the
averageGe-Ge bond distance in 3a. TheGe-Cl distances inboth structures of 3 are slightly elongated relative to those inthe chloro-substituted linear oligogermanes ClPh2GeGePh2-GePh2Cl and ClPh2GePh2GePh2GePh2Cl, which measure2.193(5) and 2.134(7) A, respectively,14 due to the branchedstructure of 3. The bond angles about the central germaniumatom in 3b are slightly different from those in 3a. TheGe-Ge-Ge bond angle in 3b is slightly more acute thanthe average angle in 3a and measures 115.96(2)�, while theCl-Ge-Ge bond angle is slightly more obtuse than theaverage 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 inFigure 4, and selected bond distances and angles are col-lected in Table 3. As found for 3, compound 4 3 3C6H6 alsocrystallizes in theP63 space group and has aC3 axis along theGe(1)-Br(1) bondwhichmeasures 2.3796(9) A. TheGe-Gebond distances in 4 3 3C6H6 are 2.4698(4) A and are nearly thesame as those in both structures obtained for 3. The envir-onment about the central germanium atom in 4 3 3C6H6 isalso very similar to that of 3, which is consistent withthe similarity observed between their NMR spectra. TheGe-Ge-Ge and the Br-Ge-Ge bond angles in 5 measure
Table 2. Selected Bond Distances (A) and Angles (deg) for(Ph3Ge)3GeCl 3C6H6 (3a)
1052 Organometallics, Vol. 30, No. 5, 2011 Samanamu et al.
116.21(1) and 101.38(2)�, respectively. Crystals of the iodidecompound 5 were also analyzed by X-ray crystallography;an ORTEP diagram of 5 3
1/3C6H6 is shown in Figure 5, andselected bond distances and angles are collected in Table 4.Two of the Ge-Ge bond distances in 5 3
1/3C6H6 are slightlyelongated relative to those in 3a,b and 4 3 3C6H6, measuring2.4728(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 inthe chloride and bromide derivatives. The germanium-iodidebond length is 2.5868(5) A, which is within the range
(2.45-2.85 A) of the ca. 40 crystallographically character-ized compounds containing a Ge-I bond. The Ge-Ge-Gebond angles in 5 3
1/3C6H6 have an average value of116.54(2)�, and the Ge-Ge-I bond angles have an averagevalue of 100.80(2)�, both of which are similar to the averageGe-Ge-Ge andGe-Ge-X (X=Cl, Br) angles in 3a,b and4 3 3C6H6. Therefore, the structures of the three halide species3-5 are very similar, despite the increasing size and decreas-ing electronegativity of the halogen atom.The electronic properties of compounds 1- 5 were investi-
gated using UV/visible spectroscopy and cyclic voltammetry
Figure 6. UV/visible spectrum (top) and cyclic voltammogram (bottom) of (Ph3Ge)3GeH (1) in dichloromethane solvent.
coupled with density functional theory (DFT) calcula-tions. The UV/visible spectrum of 1 shown in Figure 6exhibits 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 theλmax features for 1 and 2 are red-shifted relative to thosefor (Bun3Ge)3GePh 53 and (Me3Ge)3GeH, 62 which wereobserved at 233 nm (ε=1.38� 10 4M-1 cm-1) and 198 nm
Figure 7. UV/visible spectra of (Ph3Ge)3GeCl (3, green line), (Ph3Ge)3GeBr (4, brown line), and (Ph3Ge)3GeI (5, purple line) indichloromethane solvent.
Figure 8. Cyclic voltammograms of (Ph3Ge)3GeCl (3, green line), (Ph3Ge)3GeBr (4, brown line), and (Ph3Ge)3GeI (5, purple line) indichloromethane solvent.
1054 Organometallics, Vol. 30, No. 5, 2011 Samanamu et al.
(ε=5.0 � 10 4 M-1 cm-1), due to the presence of the phenylsubstituents in 1 and 2. The cyclic voltammogram of 1 isshown in Figure 6 and contains an irreversible oxidationwave at 1921( 8mV,while that for 2was observed at 1435(14mV, indicating that 1 ismore difficult to oxidize than 2. Asfound for several other oligogermanes,50,73-75 compounds 1and 2 each exhibit a single irreversible oxidation wavecorresponding to loss of an electron from the HOMO ofthemolecule followed by decomposition, which likely occursdue to germylene extrusion. However, multiple oxidationwaves were observed for the perphenyl-substituted linearoligogermanes GenPh2nþ2 (n=3, 4) as well as the tolyl-containing species Tol3GeGePh2GeTol3, Tol3GeGeTol2Ge-Tol3, and Tol3GeGePh2GePh2GeTol3,
52 indicating the spe-cies generated after oxidation were stable enough to undergofurther oxidative processes. This appears not to be the case in1 and 2, however, which is common for oligomeric germa-nium systems.A composite UV/visible spectrum for the three halide
comounds 3-5 is shown in Figure 7, and an overlaid CVplot for 3-5 is shown in Figure 8. The UV/visible spectra forthese three oligogermanes are similar and exhibit absorbancemaxima at 245 nm (3, ε=2.8� 104M-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 withdecreasing electronegativity of the halide is expected, sinceprevious findings indicated that more inductively electrondonating groups lead to a destabilization of the HOMO inoligogermane systems.51 Compounds 3-5 each exhibit asingle oxidation wave in their cyclic voltammograms atnearly the same potential (Figure 9). The oxidation wavefor the branched chloride 3 was observed at 1668 ( 11 mV,while those for the bromide and iodide species 4 and 5 wereobserved at 1656 ( 14 and 1645 ( 16 mV, respectively.Therefore, these three species have the same oxidationpotential within experimental error.The electronic structures of 1-5 were investigated using
density functional theory computations. The 6-31G* basisset was used for all of the atoms, except for the iodine atom in5, where the LanL2DZ basis set, combined with Hay and
Wadt’s effective core potential,76 was employed. Table 5contains the computed HOMO and LUMO energies, as wellas the energy of the HOMO-LUMO transition (in nm), theprimary orbital contribution with the largest oscillatorstrength and the predicted UV/visible maximum (λtheory),and the experimental UV/visible maximum (λmax) and oxi-dation potential (Eox) values.As expected, the HOMO-LUMO transition energies
computed from the B3LYP/6-31G(d) ground state orbitalsare greater than the theoretical values computed using time-dependent density functional theory to optimize the excitedstate. The molecular orbitals involved in the UV/visibletransitions with the largest oscillator strength are fundamen-tally different for 1 compared to those for the other fourcompounds. The electronic transition in 1 occurs between abonding and antibonding orbital between the central germa-nium atom and the peripheral germanium atoms, as shownin Figure 9. For 2 and 3-5, the transition occurs between thep or π orbital on the halide or phenyl ligand, respectively,which is antibonding in nature with the central germaniumatom, to a diffuse orbital localized over the rest of themolecule (Figure 10). For 4 and 5, the HOMO-1 and theHOMO orbitals are very similar in energy, and both havecontributions from the p orbitals on the halogen. TheLUMO orbital is a σ-halogen-germanium antibondingorbital with significant density on the halogen and the centralgermanium atom. The LUMOþ1 orbitals correspond tocomplete charge transfer to the Ge4 framework.The experimental data correlate with the theoretical find-
ings, 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 stabilizedrelative to that of compound 2, which is consistent with thefinding that compound 1 is more difficult to oxidize than 2.The HOMO orbital energies of the halide series 3-5 are allnearly identical, which correlates with the similarity in theirobserved oxidation potentials, and the red shift in theirabsorbance maxima are also consistent with the calculatedHOMO-LUMO gap for these species.The amide 6was 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 spec-trum of 6 exhibits a resonance at δ 2.73 ppm correspondingto the protons of the dimethylamido group. Compound 6
Figure 9. Frontier orbitals of (Ph3Ge)3GeH (1): (a) theHOMO, containing a p orbital located on the central germanium atoms; (b) theLUMO, drawn to show the transfer of this p-orbital density into the Ge4 framework.
(73) Mochida, K.; Hodota, C.; Hata, R.; Fukuzumi, S. Organo-metallics 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. (76) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270–283.
was combined with 1 equiv of Ph3GeH in acetonitrile solventand was heated for 72 h at 90 �C. A 1H NMR spectrumof the crude product indicated the presence of a mixtureof products and also that 6 and Ph3GeH had beencompletely consumed during the course of the reaction.Recrystallization of the crude product mixture from a hotbenzene solution yielded crystals of two organic compounds,identified to be 3-aminocrotononitrile (7) and 2,6-dimethyl-4-aminopyrimidine (8), which canbe regarded as a dimer anda trimer of acetonitrile, respectively. Additionally, 7 wasgenerated exclusively as the E isomer, as shown in the 1HNMR spectrum of the bulk material recovered from thereaction mixture. Crystallographic data for 7 and 8 can befound in the Supporting Information.The attempted synthesis of But3GeGePh3 from But3-
GeNMe2 and Ph3GeH produced a similar result, where noevidence for the formation of the desired digermane wasobserved. Rather, only the 3-amidocrotononitrile-substitutedgermaneBut3Ge(NHC(CH3)dCHCN),alongwithBut3CH2CN
and Ph3GeH, were recovered from the reaction.49 The 3-amidocrotononitrile ligand in But3Ge(NHC(CH3)dCHCN)was also found to adopt the E conformation exclusively, asshown by its 1H NMR spectrum. Therefore, both of theseprocesses involve the insertion of the acetonitrile into theGe-C bond of the R-germyl nitrile at the bottom face of theincoming CH3CN molecule. Furthermore, it appears thatsterically encumbering conditions at the reactive germa-nium site promote the oligomerization of the acetonitrilesolvent and that this process likely occurs at the germaniumcenter, since the 3-amidocrotononitrile ligandwas shown tobe attached to the germanium atom in But3Ge(NHC(CH3)dCHCN).The branched amide 6 decomposes during the course of
the reaction that generates 7 and 8, as indicated by the 1Hand13C NMR spectra of the product mixture, which did notexhibit any of the resonances corresponding to 6 or the R-germyl nitrile species (Ph3Ge)3GeCH2CN. Both 7 and 8werecompletely removed from the crude product mixture by
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) -6.003 -0.576 228 HOMO f LUMO 253 251 1921( 8(Ph3Ge)3GePh (2) -5.907 -0.593 233 HOMO f LUMO 262 256 1435( 14(Ph3Ge)3GeCl (3) -6.069 -0.990 244 HOMO f LUMOþ1 259 245 1668( 11(Ph3Ge)3GeBr (4) -6.050 -0.950 243 HOMO-1 f LUMOþ1 261 264 1656( 14(Ph3Ge)3GeI (5) -5.977 -1.315 266 HOMO-1 f LUMOþ1 270 271 1643( 16
aFor 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
1056 Organometallics, Vol. 30, No. 5, 2011 Samanamu et al.
crystallization from hot benzene, and analysis of the crudeproduct mixture retained in the mother liquor by NMR (1Hand 13C) spectroscopy and mass spectrometry indicated thepresence of hexaphenyldigermane Ph3GeGePh3 by compar-ison of these data with those obtained for a commercialsample of this material. The material obtained from thereaction of 6 with Ph3GeH exhibited an fragmentationpattern identical with that for Ph3GeGePh3, including amolecular ion peak at m/z 608 with the correct isotopepattern.
Conclusions
The reaction of Ph3GeNMe2 with GeH4 in acetonitrileproduces the germanium hydride species (Ph3Ge)3GeH, andthis material has been converted to the halide species(Ph3Ge)3GeX (X=Cl, Br, I) by hydride abstraction usingtritylium hexafluorophosphate in the corresponding dihalo-methane CH2X2 solvent. The crystal structure of (Ph3Ge)3-GeH indicates this species has short Ge-Ge bond distanceswith an average value of 2.4310(5) A and adopts a distorted-tetrahedral environment at the central germaniumatom.Thestructure and electronic properties of (Ph3Ge)3GeH can becompared to those of the related phenyl derivative (Ph3Ge)3-GePh. The phenyl compound has longer Ge-Ge distances(d(Ge-Ge)av = 2.469(4) A), has a red-shifted UV/visibleabsorbancemaximum relative to (Ph3Ge)3GeH, and is easierto oxidize than (Ph3Ge)3GeH.The structures of the three halide compounds (Ph3Ge)3GeX
(X=Cl, Br, I) have also been determined, and the chloridespecies (Ph3Ge)3GeClwas found to crystallize in two differentmorphologies, depending on the crystallization method em-ployed. The molecular structures of all three species aresimilar with regard to the Ge-Ge bond distances andGe-Ge-Ge bond angles, and their oxidation potentials werefound to be identical within the range of experimental error.TheUV/visiblemaxima of these oligogermanes undergo a redshift from (Ph3Ge)3GeCl to (Ph3Ge)3GeBr to (Ph3Ge)3GeI.Density functional theoretical calculations on these threecompounds, as well on (Ph3Ge)3GeH and (Ph3Ge)3GePh,correlate well with the experimental data. The electronictransition giving rise to the absorbance maximum for(Ph3Ge)3GeH results from electron promotion from a bond-ing to antibonding orbital, while in the phenyl- and halide-substituted species this transition corresponds to electronpromotion from a phenyl π or halide p orbital to a vacantmolecular orbital localized over the entire Ge4 framework.Attempts to synthesize the germanium neopentane analo-
gue (Ph3Ge)4Ge via two different methods were not success-ful. Reaction of (Ph3Ge)3GeH with 1 equiv of Ph3GeNMe2resulted in the recovery of Ph3GeH and the R-germyl nitrilePh3GeCH2CN, with no evidence for the formation of(Ph3Ge)4Ge. In addition, the chloride (Ph3Ge)3GeCl wasconverted to the amide (Ph3Ge)3GeNMe2 and reacted withPh3GeH in acetonitrile solvent, which resulted in the con-sumption of both reactants. Again, however, the desiredproduct (Ph3Ge)4Ge was not detected; rather, (E)-3-amino-crotononitrile and 2,6-dimethyl-4-aminopyrimidine wereisolated from the reaction mixture along with Ph3GeGePh3,which results from the decomposition of the branchedoligogermane species. Therefore, it is apparent that thesynthesis of (Ph3Ge)4Ge is not possible, most likely due tothe steric constraints of placing four triphenylgermyl groupsaround the central germanium atom.
Experimental Section
General Remarks.All manipulations were carried out under anitrogen atmosphere using standard syringe, Schlenk, andglovebox techniques.77 The reagents GeH4, Ph3GeCl, and Ph3-GeH were purchased from Gelest, Inc., and were used asreceived. Dichloromethane, dibromomethane, diiodomethane,LiNMe2, and [Ph3C][PF6] were purchased from Aldrich. Di-chloromethane, acetonitrile, and benzene were purified using aGlass Contour solvent purification system. Dibromomethaneand diiodomethane were dried over alumina, distilled, and keptover 5 A molecular sieves. The compounds Ph3GeNMe2
54 and(Ph3Ge)3GePh51,63 were prepared according to the literatureprocedures. 1H (300 MHz) and 13C NMR spectra (75.4 MHz)were recorded on a Gemini 2000 NMR spectrometer and werereferenced to benzene-d6 solvent. 73Ge NMR spectra wererecorded using a 50 mg/mL solution of 1 on a Varian INOVA500 MHz spectrometer using a 10 mm low gamma broad-bandprobe at 17.43 MHz using the Carr-Purcell-Meiboom-Gill(CPMG) pulse sequence.78,79 The following parameters wereused during acquisition: spectral width 100 000 Hz, acquisitiontime 0.01 s, delay time 0 s, line broadening factor 20, number oftransients 1 � 107. The spectra were referenced to externalGeMe4 by substitution. UV/visible spectra were obtained usinga Hewlett-Packard 8453 diode array spectrometer in CH2Cl2solvent. Cyclic voltammograms were recorded using a DigiIvyDY2112 potientiostat with 0.10M [Bu4N][PF6] inCH2Cl2 as thesupporting electrolyte, and reported data are the average of fourindependent runs. Mass spectra were obtained on a Shimadzu2010A LCMS by direct injection with a coronal dischargesource. Elemental analyses were conducted by GalbraithLaboratories (Knoxville, TN).
Synthesis of (Ph3Ge)3GeH (1). Germane gas (0.170 g, 2.22mmol) was condensed into an evacuated Schlenk tube at 77 Kusing a liquid N2 bath and was subsequently warmed to roomtemperature. A Schlenk tube was charged with Ph3GeNMe2(2.60 g, 7.47 mmol) and acetonitrile (25 mL) and was cooled to77 K, and the GeH4 was condensed in vacuo. The reactionmixture was warmed to room temperature and then was heatedwith stirring in an oil bath at 90 �C for 24 h. After cooling, thereaction mixture was transferred to a Schlenk flask and thevolatiles were removed in vacuo to yield 1 (1.457 g, 66%). 1HNMR (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. 13CNMR (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. Calcdfor C54H46Ge4: C, 65.79; H, 4.71. Found: C, 65.62; H, 4.79.
Alternate Synthesis of (Ph3Ge)3GeH (1). A Schlenk tube wascharged 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, 15.4mmol) was condensed at 77 K, and the reaction mixture waswarmed to room temperature. The reaction mixture was subse-quently heated at 85 �C for 18 h and was then transferred to aSchlenk flask. The volatiles were removed in vacuo to yield 1
(2.21 g, 74% based on Ph3GeNMe2). The spectral data for theproduct were identical with those given above.
Synthesis of (Ph3Ge)3GeCl (3). A Schlenk tube was chargedwith 1 (0.105 g, 0.107 mmol) and [Ph3C][PF6] (0.045 g, 0.115mmol) in dichloromethane (30 mL). The reaction mixture washeated in an oil bath with stirring at 90 �C for 24 h. The reactionmixture was filtered through Celite into a Schlenk flask, and thevolatiles were removed in vacuo to yield a pale yellow solid thatwas washed with hexane (4 � 5 mL). The solid was dried in
(77) Shriver, D. F.; Drezdzon, M. A., The Manipulation of AirSensitive 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.
with 1 (0.103 g, 0.105 mmol) and [Ph3C][PF6] (0.045 g, 0.115mmol) in dibromomethane (30 mL). The reaction mixture washeated in an oil bath with stirring at 90 �C for 24 h. The reactionmixture was filtered through Celite into a Schlenk flask, and thevolatiles were removed in vacuo to yield a pale yellow solid thatwas washed with hexane (4 � 5 mL). The solid was dried invacuo, and the resulting solid was crystallized from benzene toyield 4 (0.062 g, 56%) as colorless crystals. 1HNMR (C6D6, 25 �C,300MHz):δ 7.35 (d, J=6.6Hz, 18H, o-C6H5), 7.07 (t, J=7.8Hz,9H, p-C6H5), 6.94 (t, J=7.5 Hz, 18H, m-C6H5).
with 1 (0.100 g, 0.102 mmol) and [Ph3C][PF6] (0.045 g, 0.115mmol) in diiodomethane (30 mL). The reaction mixture washeated in an oil bath with stirring at 90 �C for 24 h. The reactionmixture was filtered through Celite into a Schlenk flask, and thevolatiles were removed in vacuo to yield a pale yellow solid thatwas washed with hexane (4� 5 mL). The solid was dried invacuo, and the resulting solid was crystallized from benzene toyield 4 (0.067 g, 59%) as colorless crystals. 1H NMR (C6D6,25 �C, 300MHz): δ 7.35 (d, J=7.2Hz, 18H, o-C6H5), 7.07 (t, J=7.2Hz, 9H, p-C6H5), 6.95 (t, J=7.2Hz, 18H,m-C6H5).
13CNMR(C6D6, 25 �C, 75.5MHz): δ 137.1 (ipso-C), 136.5 (o-C), 129.2 (p-C), 128.5 (m-C) ppm.UV/visible (CH2Cl2):λmax 271nm(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 asatisfactory carbon analysis for this compound.Synthesis of (Ph3Ge)3GeNMe2 (6).ASchlenk flaskwas charged
with 3 (0.100 g, 0.098 mol), LiNMe2 (0.005 g, 0.100 mmol), andTHF (40 mL). The reaction mixture was stirred for 24 h at roomtemperature and then was filtered through Celite. The resultantsolution was evaporated in vacuo to yield a solid which wasdissolved in hexane and filtered through Celite. The hexane wasremoved in vacuo to yield 6 (0.070 g, 69%) as a yellow solid. 1HNMR(C6D6, 25 �C, 300MHz):δ7.65 (t, J=7.5Hz, 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. 13CNMR(C6D6, 25 �C,75.5MHz):δ138.3 (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 washeated in an oil bath at 90 �Cwith stirring for 72 h. The reactionmixture was cooled and was transferred to a Schlenk flask. Thevolatiles were removed in vacuo to yield 0.072 g of a brown solid,which was recrystallized from hot benzene (5 mL) to yieldcolorless crystals identified as 3-aminocrotononitrile (7) and2,6-dimethyl-4-aminopyrimidine (8). The combined yield of 7and 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.
Crystallographic data for the X-ray analysis for 1 and 3-5 arecollected inTable 6. The crystal-to-detector distancewas 60mm,and the exposure time was 20 s per frame using a scan width of0.5�. Data collection was 100% complete to 25.00� in θ, exceptin the case of 5, where CheckCIF indicated data coverage toonly 92%. However, the protocols for data coverage indicated100% coverage with high redundancy. Currently, we are notsure of the reason for this discrepancy. The data were integratedusing the Bruker SAINT software program and scaled using theSADABS software program. Solution by direct methods (SIR-2004) produced a complete heavy-atom phasing model consis-tent with the proposed structures. All non-hydrogen atomswererefined anisotropically by full-matrix least squares (SHELXL-97). Aside from the germanium-bound hydrogen in 1, all hy-drogen atoms were placed using a riding model. Their positionswere constrained relative to their parent atom using the appro-priate HFIX command in SHELXL-97.
Computational Details. Gaussian 03 was utilized for allcomputations.80 Energy calculations, geometry optimizations,and frequency calculations were performed using the hybriddensity functional method including Becke’s three-parameternonlocal-exchange functional81 with the Lee-Yang-Parr cor-relation functional, B3LYP.82 The 6-31G* basis set83 wasemployed for all atoms except iodine. For iodine, the LanL2DZbasis set, which includes the D95 double-ζ basis set84 combinedwith Hay andWadt’s effective core potential,76 was utilized. Allatomic positions are optimized without geometry constraints.Frequency calculations were performed at a lower level toconfirm that the stable geometries have real vibrational fre-quencies. The time-dependent density functional computations,as implemented by Gaussian 03, were utilized to explore theexcitedmanifold and compute the possible electronic transitionsand oscillator strengths.
Acknowledgment. Funding for this work was providedby a CAREER grant from the National Science Founda-tion (No. CHE-0844758) and is gratefully acknowledged.We are grateful to Prof. Rudolf Pietschnig (Karl-Franzens-Universit€at Graz) for helpful discussions.
Supporting Information Available: CIF files giving crystal-lographic data for 1 and 3-5 and tables and figures givingstructural details for 7 and 8. This material is available free ofcharge via the Internet at http://pubs.acs.org.
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