Organometallics 1995, 14, 1073-1075
1073
Synthesis and Crystal Structure of a Monomeric Tetraalkyldigallium Telluride with a Bent Ga-Te-Ga Group Werner Uhl* and Uwe Schutz Fachbereich Chemie der Universitat Oldenburg, Postfach 2503,261 11 Oldenburg, Germany
Wolfgang Hiller and Maximilian Heckel Anorganisch-chemisches Institut der Technischen Universitat Miinchen, Lichtenbergstrasse 4, 85748 Garching, Germany Received August 23, 1994@ Summary: Tetrakis[bis(trimethylsilyl)methyl]digallane(4) (1)with a gallium-gallium bond reacts under mild conditions with E t P - T e - to give the title compound RzGa-Te-GaRz (2; R = CH(SiMe& in high yield. 2 is stable in solution at room temperature and, due to the high steric shielding, a monomer even in the solid state. A crystal structure determination (orthorhombic; Pcaa; a = 2375.3(2) pm; b = 1658.4(2) pm, c = 1216.6(3) pm; Z = 4) reveals an angled Ga-Te-Ga group (109.8') and a Ga-Te bond length of 255.21(4) pm, as would be expected for a Ga-Te single bond with the atoms in low coordination numbers. There are no indications for a significant n-interaction between tellurium lone pairs and the gallium atoms, and the hindered rotation of the bulky substituents observed by low-temperature NMR is more likely caused by steric restrictions.
Introduction Recently we succeeded in the synthesis of a tetraalkyldialane(4) derivative with an aluminum-aluminum bond showing a remarkable stability toward disproportionation reaction, which is probably a result of the high steric shielding by four bulky bis(trimethylsily1)methyl substituents.lpZThis compound exhibits very interesting chemical proper tie^.^ Reactions retaining the AI-Al bond such as the formation of simple adducts415and radical anionszp6 or cleaving the Al-Al bond such as insertion reactions with CSz7and isonitriles8 have been carried out up to now. By a different synthesis starting with GazBrc2(dioxane)and 4 equiv of LiCH(SiMe3)zwe also obtained the analogous, intensively yellow compound with a Ga-Ga bond ( l h 9 Its chemical behavior has not been investigated as extensively as for the Al derivative, and we only published one metathesis reacAbstract published in Advance ACS Abstracts, December 15,1994. (1) Uhl, W. 2.Naturforsch., B 1988,43, 1113. (2) Wehmschulte,R. J.; Ruhlandt-Senge,K.; Olmstead,M. M.; Hope, H.; Sturgeon, B. E.; Power, P. P. Inorg. Chem. 1993,32, 2983. (3)Uhl, W. Angew. Chem., Int. Ed. Engl. 1993,32, 1386. (4) Uhl, W.; Vester, A. Chem. Ber. 1993,126, 941. (5) Uhl, W.; Schiitz, U.; Pohl, S.; Saak, W. 2.Naturforsch., B 1994, 49, 637. (6) (a) Uhl, W.; Vester, A.; Kaim, W.; Poppe, J. J.Organomet. Chem. 1993, 454, 9. (b) Uhl, W.; Vester, A.; Fenske, D.; Baum, G. J . Orgammet. Chem. 1994,464,23. (c) Pluta, C.; Porschke, K R.; Kriiger, C.; Hildenbrand, K. Angew. Chem., Znt. Ed. Engl. 1993,32, 388. (7) Uhl, W.; Vester, A.; Hiller, W. J. Orgunomet. Chem. 1993,443, 9. (8) Uhl, W.; Schiitz, U.; Hiller, W.; Heckel, M. Chem. Ber. 1994,127, 1587. (9) Uhl, W.; Layh, M.; Hildenbrand, T. J . Organomet. Chem. 1989, 364, 289. @
tion between 1 and the sterically highly shielded ditellurium compound RTe-TeR ( R = Si(SiMe&, yielding R2Ga-TeR.1° The gallium telluride has a monomeric structure even in the solid state, with a planar CZGaTeSi core, and shows a hindered rotation around the Ga-Te bond as determined by NMR spectroscopy. Both observations might indicate a n interaction between a tellurium lone pair and the empty p orbital a t the gallium atom. Recently Power et al. synthesized a tetraaryldigallane(4) compound shielded by four bulky triisopropylphenyl groups by a similar route,'l which interestingly shows a staggered conformation across the Ga-Ga bond in contrast t o the planar structure of 1. By reduction with lithium in diethyl ether the transfer of only one electron is observed and a black radical anion is isolated containing a one-electron Ga-Ga n bond." We wish to report here the reaction of 1 with the tellurium donor Et3P+-Te-.
Experimental Section All procedures were carried out under an atmosphere of purified argon in dried solvents (n-pentane over LiAlH4; toluene and benzene over Nahenzophenone). 1 and
[email protected](toluene)(recrystallized from toluene) were prepared according to the l i t e r a t ~ r e . ~ J ~ RsGa-Te-G& (R = CH(SiMe&) (2). A solution of 0.263 g (0.9 mmol) of
[email protected](toluene) in 10 mL of toluene is added dropwise t o a solution of 0.70 g (0.9 mmol) of 1 in 60 mL of n-pentane at -30 "C. While it is slowly warmed to room temperature, the solution changes from yellow to colorless. After the mixture is stirred for a further 30 min, the solvent is removed in vacuo, and the residue is recrystallized from toluene (251-30 "C). Yield: 0.59 g (72%)colorless platelets. Anal. Calcd for Cz&I~&azSigTe:Ga, 15.4; C, 37.2; H, 8.5; mol wt, 904.64. Found: Ga, 15.3; C, 37.3; H, 8.5; mol wt, 859 (cryoscopically in benzene). Dec pt: 149 "C (closed capillary, argon). lH N M R (room temperature, C&, 300 (10) uhl, W.; Layh, M.; Becker, G.; Klinkhammer, K.-W.; Hildenbrand, T. Chem. Ber. 1992,125, 1547. (11) (a) Re, X.; Bartlett, R. A.; Olmstead, M. M.; Ruhlandt-Senge, K.; Sturgeon, B. E.; Power, P. P. Angew. Chem., Int. Ed. Engl. 1993, 32,717. (b) Veith, M.; Goffing, F.; Becker, S.; Huch, V. J.Orgunomet. Chem. 1991,406, 105. (c) Schluter, R. D.; Cowley, A. H.; Atwood, D. A.; Jones, R. A.; Bond, M. R.; Carrano, C. J. J . Am. Chem. Soc. 1993, 115,2070. (12)(a) Zingaro, R. A.; Steeves, B. H.; Irgolic, K. J . Organomet. Chem. 1965,4, 320. (b) Steigerwald, M. L.; Rice, C. E. J.Am. Chem. SOC.1988, 110, 4228. (13) Hahn, T., Ed. International Tables for Crystallography: Space Group Symmetry; Kluwer Academic: Dordrecht, Boston, London, 1989; Vol. A. (14)(a) SHELXTL PLUS REL. 4.1; Siemens Analytical X-Ray Instruments, Inc., Madison, WI, 1990. (b) Sheldrick, G. M. SHELXL93, Program for the Refinement of Structures; Universitat Gattingen, Giittingen, Germany, 1993.
0276-733319512314-1073$09.00/0 0 1995 American Chemical Society
Notes
1074 Organometallics, Vol. 14, No. 2, 1995
Table 1. Crystal Data and Data Collection Parameters for RzGa-Te-GaR2 (2; R = CH(SiMed2) formula: CzsH76GazSisTe cryst syst; space group: orthorhombic;Pcca (No. 54)13 2 4 temp ("C): 20 dcdc(glcm3):1.254 a (pm): 2375.3(2) b (pm): 1658.4(2) c (pm): 1216.6(3) V( m3): 4792 p (lo2m-I): 19.37 cryst size (mm): 0.5 x 0.5 x 0.4 diffractometer;radiation: 4-cycle CAD4; Mo K a 26 range (deg): 6 5 28 5 50 reciprocal space: 0 5 h 5 28, -19 5 k 5 0,O 5 1 5 14 scan mode: w-26 indep rflns; no. of rflns with F > 4a(F): 4177; 3423 program: SHELXL-93;I4 solution by direct methods; full-matrix refmement with all indep structure factors params: 189 R = CllFol - IFcll/xIFoI ( F > 40(F)): 0.034 wR2 = {Cw(lFolz- IFE12)2/C~(Fn2)2)1n (all data): 0.090 largest residuals (IO3O elm3):+1.006/-0.727
Table 2. Atomic Coordinates and Equivalent Isotropic mZ)for the Atoms of the Displacement Parameters Asymmetric Unit in RzGa-Te-GaRz (2; R = CH(SiMed2) xla
Te Ga c1 Si1 c11 c12 C13 Si2 c 21 c22 C23 c2 Si3 C3 1 C32 c33 Si4 C4 1 C42 c43
0.5000 0.5808( 1)
0.6042(1) 0.6209(1) 0.6769(2) 0.5565(2) 0.6429(3) 0.6552(1) 0.7308(2) 0.6450(2) 0.6437(2) 0.6173(1) 0.5674(1) 0.5256(2) 0.5167(2) 0.6076(2) 0.6589(1) 0.7242(2) 0.6195(2) 0.6819(2)
Ylb 0.6466(1) 0.7351(1) 0.8262(2) 0.9222(1) 0.9079(3) 0.9606(3) 1.0039(3) 0.7922(1) 0.8043(3) 0.8520(3) 0.6847(2) 0.6970(2) 0.7008(1) 0.6068(3) 0.7861(3) 0.7207(4) 0.60 11(1) 0.6224(3) 0.5190(2) 0.5621(3)
dC 0.2500 0.1823(1) 0.2761(3) 0.2011(1) 0.0965(4) 0.1304(5) 0.2963(4) 0.3850(1) 0.3412(4) 0.5143(4) 0.4228(4) 0.0465(2) -0.073 1(1) -0.0863(3) -0.0573(4) -0.2034(3) 0.0602(1) 0.1397(4) 0.1301(4) -0.0761(3)
5.2(1) 3.9(1) 4.8(1) 6.2(1) 9.6(2) 10.8(2) 11.0(2) 5.7(1) 9.2(2) 9.1(2) 8.0(1) 4.5(1) 6.0(1) 8.4(1) 10.2(2) 9.6(2) 5.5(1) 8.8(1) 8.1(1) 9.2(2)
MHz): 6 1.05 (s, GaCH), 0.33 (s, SiMe3). 'H NMR (-63 "C, toluene-&, 500 MHz): 6 1.21 and 0.96 (8, each 2 H, GaCH), 0.37 and 0.35 (s, each 36 H, SiMe3). l3C " I R (CsD6, 75.5 MHz): 6 26.4 (GaC), 4.5 @Me& IR (paraffin, CsBr, cm-'): 1298 vw, 1260 m, 1246 s (d(CH3));1169 vw, 1155 vw,1121 vw; 1013 m (6(CH));964 w, 943 vw,843 vs, 772 m, 758 m, 727 w (e(CHs(Si)));687 sh, 667 m (v=(SiC)); 629 vw, 619 vw (vs(Sic)); 513 m, 490 vw (v(GaC)). Crystal Structure. Single crystals of 2 were obtained from pentane at -30 "C. Relevant crystal and data collection parameters are given in Table 1 and atomic coordinates in Table 2. 2 crystallizes in space group Pcca isotypic to the appropriate compounds with AI-S-Al,' Al-Te-Al,15 or AlCHz-AP bridges with the bridging atoms located on a 2-fold crystallographic rotation axis.
Results and Discussion When a solution of Et3P+-Te- in toluene is added to the yellow solution of the tetraalkyldigallane(4) derivative 1 in n-pentane, the resulting reaction mixture becomes slowly colorless on warming to room tempera(15)Uhl, W.; Schutz, U.2.Naturforsch., B 1994,49, 931. (16)Layh, M.;Uhl, W. Polyhedron 1990,9,277.
ture, and Et3P is detected by its characteristic 31PNMR resonance. After removal of the solvent and recrystallization from toluene or n-pentane colorless crystals of the tellurium insertion product 2 (eq 1)are isolated in
over 70% yield. 2 shows a higher thermal stability in solution than the Al-Te-Al analogue, which decomposes slowly at room temperature in benzene, precipitating black elemental te1luri~m.l~ For 2 we observe a comparable decomposition reaction only by contact to oxygen. Molecular weight determination in benzene gives the monomeric formula unit. Surprisingly, the NMR spectra of 2 are similar to those of the educt 1, and chemical shifts of both compounds are nearly indistinguishable. The protons in positions a to the gallium atoms reveal a resonance a t 6 1.05 ppm with an unusual downfield shift of about 0.8 ppm compared to the trialkylgallium derivative Ga[CH(SiMe&b. Similar chemical shifis for the inner CH(SiMea)~protons are usually observed in neutral bis(trimethylsily1)methyl compounds with Al-Al,I GaGa,9 and In-In bonds.17 When the temperature is lowered to -60 "C in toluene, the resonance of the trimethylsilyl groups splits into two signals corresponding to the comparable compounds with Al-S-A17 or AlTe-Al15 bridges. In agreement with the crystal structure discussed below, we believe that this is not an indication for a n interaction between a lone pair at Te and an empty p orbital at Ga but more probably the result of a hindered rotation of the bulky substituents caused by steric restrictions and also observed in a derivative with an Al-CH2-M group,16 where no n interactions are expected. Power et al. published a similar discussion for the monomeric gallium-sulfur compound Ga(SMes*)3(Mes* = C&b(CMe3)3), where the short Ga-S distance is attributed to an electrostatic attraction between the electropositive Ga and the electronegative S atom rather than to a Ga-S n bond.ls A significant spectroscopic difference between the yellow digallane(4) compound 1 and the colorless insertion product 2 is observed in the U V l v i s spectra, where the absorption at 370 nm, characteristic for compounds with Al-Al,9 Ga-Ga,g or In-In bonds,17 is absent in the spectrum of 2. Figure 1 shows an ORTEP diagram of one molecule of 2, as obtained by a crystal structure determination. The angle at the central Te atom (109.8'), as well as the molecular conformation with the substituents in a staggered arrangement for the minimization of sterical repulsions, clearly excludes a significant n interaction between Ga and Te, as observed in tellurium-bridged transition-metal compounds19 and possibly also existing (17) Uhl, W.; Layh, M.; Hiller, W. J.Organomet. Chem. 1989,368, 139. (18)Ruhlandt-Senge, R; Power, P. P. Inorg. Chem. 1991,30,2633. For the Se analogue see: Ruhlandt-Senge, K.; Power, P. P. Inorg. Chem. 1991,30,3683.
Organometallics, Vol. 14, No. 2, 1995 1075
Notes
only one example with a dimeric Ga-Te unit showing, as expected, very much elongated Ga-Te bond lengths (274-276 pmhZ1 Typical solid-state structures such as GaTe and GazTes with higher coordination numbers at Ga and Te usually show values between 253 and 269 pm.22 The Ga-C distances (197.2pm) are only slightly shortened in comparison to the values found in 1 (199.6 pm); however, a more significant shortening up to 5 pm is observed for the Al-C bond lengths in all bridged dialuminum compounds with Al-S-Al,7 Al-Te-Al,15 or Al-CHz-Al16 groups derived from the dialane(4) system similar to 1. This might be a consequence of the larger charge separation and a more effective electrostatic attraction in compounds with the less electronegative Al atom.
C13
C31
Figure 1. Molecular structure of 2 (ORTEPplot). The thermal ellipsoids are drawn at the 40% probability level. Table 3. Important Bond Lengths and Angles for 2 Ga-Te Ga-C1 Ga-C2 Ga-Te-Ga’ Te-Ga-C1 Ga-Cl -Si1 Ga-C1 -Si2 Sil-Cl-Si2 (I
255.21(4) 197.4(3) 196.9(3) 109.82(2) 117.7(1) 115.3(2) 111.1(2) 117.4(2)
C1-Si1 C1-Si2 C2-Si3 C2-Si4
187.9(3) 188.1(4) 187.8(3) 187.9(3)
Cl-Ga-C2 Te-Cia-C2 Ga-C2-Si3 Ga-C2-Si4 Si3-C2-Si4
Ga’ calculated by the symmetry operation -x
127.3(1) 114.68(9) 111.2(3) 115.4(2) 115.4(2)
+ 1, y, -z + V 2 .
in the monomeric and planar derivative RzGa-TeR lo discussed above. As in this compound, the Ga-Te bond length in 2 is shorter (255.2pm, Table 3)than calculated (262 pm) from the Ga-Ga distance in 1 and the standard Te-Te bond length of 270 pm in organic ditellurium derivatives,2O but for the most part this might be due to an electrostatic attraction due t o the difference in electronegativities and the accumulation of negative charge a t the bridging atom. To our knowledge comparable monomeric organic compounds with a Ga-Te bond are hitherto unknown and there is (19)(a) Herrmann, W.A. Angew. Chem., Znt. Ed. Engl. 1986,25, 26. (b) Greenwood, N.N.; Earnshaw, A. Chemistry of the Elements; Pergamon Press: Oxford, U.R, 1984.
Acknowledgment. We are grateful to the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and Hewlett-Packard for generous support. Supplementary Material Available: Tables 51-53, giving the anisotropic displacement parameters for non-hydrogen atoms, atomic coordinates and isotropic displacement parameters of the hydrogen atoms, and bond lengths and angles for 2 (4 pages). Ordering information is given on any current masthead page.
OM9406761 (20)(a) MezTez: Becker, G.; Baumgarten, J.; Mundt, 0.; Riffel, H.; Simon, A. private communication. (b) PhzTez: Llabres, G.; Dideberg, 0.; Dupont, L. Acta Crystallogr., Sect. E 1972, 28, 2438. (c) @to1yl)zTez: Spirlet, M. R.; van den Bossche, G.; Dideberg, 0.;Dupont, L. Acta Crystallogr., Sect. B 1979,35, 1727. (d) @-MeOC&&Tez: Ludlow, S.; McCarthy, A. E. J. Organomet. Chem. 1981,219, 169. Mundt, 0.; Becker, G.; Riissler, M.; Witthauer, C. 2.Amrg.AlZg. Chem. 1983, 506, 42. (e) @-C1CsH&Te2: Kruse, F. H.; Marsh, R. E.; McCullough, J. D. Acta Crystallogr. 1957,10,201.van den Bossche, G.; Spirlet, M. R.; Dideberg, 0.;Dupont, L. Acta Crystallogr., Sect. C 1984,40, 1011. (0[(MesC)&&]~Tez: du Mont, W. W.; Lange, L.; Karsch, H. H.; Peters, K.; Peters, E. M.; von Schnering, H. G. Chem. Ber. 1988,121,ll. (21)Banks, M.A.;Beachley, 0. T., Jr.; Gysling, H. J.; Luss, H. R. Organometallics 1990,9,1979. (22)(a) GaTe: Julien-Pouzol, M.; Jaulmes, S.; Guittard, M.; Alapini, F. Acta Crystallogr., Sect. B 1979,35,2848.(b) GazTes: Julien-Pouzol, M.; Jaulmes, S.; Alapini, F. Acta Crystallogr., Sect. E 1977,33,2270. (c) [PPhJ[GaTez(en)zl: Warren, C. J.; Ho, D. M.; Haushalter, R. C.; Bocarsly, A. B. J . Chem. Soc.,Chem. Commun. 1994,361and literature cited therein. See also ref 10.
