Organometallics 2009, 28, 2619–2624
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Bis- and Tris(dimethylgallyl)benzenes: Synthesis, Solid-State Structures, and Redistribution Reactions Peter Jutzi,* Joseph Izundu, Henning Sielemann, Beate Neumann, and Hans-Georg Stammler Fakulta¨t fu¨r Chemie, UniVersita¨t Bielefeld, UniVersita¨tstrasse 25, 33615 Bielefeld, Germany ReceiVed January 21, 2009
Benzene derivatives containing dimethylgallyl substituents in 1,3- (compounds 5 and 6), 1,4- (compound 9), and 1,3,5-position (compound 12) were prepared by reaction of the corresponding chloromercuriobenzenes with an excess of trimethylgallium at higher temperatures. These compounds decompose in solution at room temperature and in the solid state upon mild heating with elimination of trimethylgallium to give oligomeric condensation products of unknown detailed composition. These condensation products can be transformed back into the starting compounds by treatment with an excess of trimethylgallium at higher temperatures. Highly air-sensitive crystals of 5, 6, 9, and 12 suitable for an X-ray analysis are obtained from trimethylgallium as solvent. The X-ray crystallographic studies revealed the presence of higher coordinate gallium atoms, which lead to the formation of strand- or sheet-like polymers. A trigonalbipyramidal coordination sphere is observed for the gallium atoms in 9. A distorted tetrahedral coordination is found for the gallium atoms in 5, 6, and 12. The latter compounds possess asymmetric aryl-dimethylgallyl bridging units. 1. Introduction 1,1′-Bis(dimethylgallyl)ferrocene undergoes reversible condensation reactions due to the easy cleavage and formation of covalent Ga-C bonds.1 This phenomenon has been used synthetically within the framework of the concept of “dynamic covalent chemistry”.2 In this context, we have become interested in checking the possibility of the Ga-C cleavage and formation in comparable benzene derivatives. Multiple dimethylgallylsubstituted benzene derivatives are thus far unknown. Surprisingly, the first monodimethylgallyl-substituted benzenes were described only recently. They show the expected substituent redistribution reactions.3 Here we describe the first multiple dimethylgallyl-substituted compounds with the synthesis of the 1,3-disubstituted derivatives 5 and 6, of the 1,4-disubstituted derivative 9, and of the 1,3,5-trisubstituted derivative 12. Furthermore, we report the pronounced instability of these compounds with regard to redistribution reactions in solution and in the solid state and their structures in the solid state.
2. Results Synthesis and Characterization. The strategy for the synthesis of the dimethylgallyl-functionalized benzene derivatives is described in eq 1. The reaction sequence starts with the substitution of trimethylstannyl groups in the corresponding * Corresponding author. Phone: +49-5211066163. E-mail: peter.jutzi@ unibielefeld.de. (1) (a) Jutzi, P.; Lenze, N.; Neuman, B.; Stammler, H. G. Angew. Chem. 2001, 113, 1470. (b) Jutzi, P.; Lenze, N.; Neuman, B.; Stammler, H. G. Organometallics 2002, 21, 3018. (c) Jutzi, P.; Lenze, N.; Neuman, B.; Stammler, H. G. Organometallics 2003, 22, 2766. (d) Althof, A.; Eisner, D.; Jutzi, P.; Lenze, N.; Neumann, B.; Schoeller, W. W.; Stammler, H. G. Chem. Eur. 2006, 12, 5471. (2) Rowan, S. T.; Cantrill, S. J.; Cousins, G. R. L.; Sanders, J. K. M.; Stoddart, J. F. Angew. Chem. 2002, 114, 938; Angew. Chem. Int. Ed. 2002, 41, 898. . (3) Jutzi, P.; Izundu, J.; Neumann, B.; Stammler, H. G. Organometallics 2008, 27, 4565–4571.
trimethylstannylbenzenes by chloromercurio groups, which subsequently are replaced by dimethylgallyl groups.3 Table 1 shows the compounds involved in the synthetic procedure.
Most of the trimethylstannyl and chloromercurio benzenes are known from the literature (see Table 1). The novel tin compound 2 was prepared by reaction of sodium trimethylstannide with the corresponding dibromobenzene (see Experimental Section). Rather drastic conditions had to be applied for the last step in the reaction sequence, the introduction of the dimethylgallyl groups, which leads to the novel dimethylgallylsubstituted benzene derivatives 5, 6, 9, and 12. The respective chloromercuriobenzenes have to be treated with an excess of trimethylgallium (using the reagent as solvent) at 100-140 °C in a pressure vessel. After cooling to room temperature and removal of the liquid components (dimethylmercury, chloro(dimethyl)gallane, and the excess of trimethylgallium), the respective dimethylgallyl-functionalized benzene derivative remained as a solid residue, which was crystallized from trimethylgallium as solvent. The crystalline compounds are extremely sensitive toward air and moisture. The use of highboiling solvents such as p-xylene together with an excess of the reagent trimethylgallium instead of the use of trimethylgallium as solvent and reagent was not successful. Redistribution Reactions in Solution and in the Solid State. We have also been unsuccessful in preparing solutions of the novel organogallium compounds 5, 6, 9, and 12 in organic solvents such as hexane, toluene, or diethyl ether. Concomitant substituent redistribution reactions were observed, which finally led to the formation of trimethylgallium and of solid condensation products of thus far unidentified composition and structure. The degree of condensation can be judged from the amount of isolated trimethylgallium and varies with the reaction conditions
10.1021/om900048c CCC: $40.75 2009 American Chemical Society Publication on Web 03/30/2009
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Jutzi et al. Table 1. Compounds 1-12
and from compound to compound. A comparable behavior is described in the literature for monodimethylgallyl-substituted benzene derivatives.3 In the redistribution reaction of compound 5 in benzene-d6/THF solution, a soluble condensation product was tentatively assigned to the first condensation step by 1H NMR spectroscopy, as described in the Experimental Section. Worth mentioning, treatment of the isolated solid condensation products with an excess of trimethylgallium in a pressure vessel at 100-140 °C regenerated the crystalline starting compounds. With halogenated solvents such as dichloromethane, decomposition reactions were observed. As a result, it was not possible to investigate the physical properties of the novel compounds in solution (for example determination of the molecular mass and of the NMR parameters). A similar behavior was observed in the solid state of the novel compounds. On treating the samples under reduced pressure ( 2σ(I)]/wR2b final R1/wR2 (all data) largest peak in final diff map, e /Å3 a
5
6
9
12
C10H16Ga2 275.67 monoclinic P21/c
C14H24Ga2 331.77 monoclinic P21/c
C10H16Ga2 275.67 monoclinic P21/n
C12H21Ga3 374.45 monoclinic C2/c
7.943(2) 14.358(2) 9.8740(3) 97.682(8) 1116.0(3) 4 0.26 × 0.20 × 0.14 1.641 552 4.776 0.3698/0.5545 multiscan 2.5 to 27.5 99.9% 22 550 2571 2293 113 0.0330, 0.0852 0.0386, 0.0901 0.568
14.3120(10) 9.9480(7) 22.5040(14) 103.736(5) 3112.4(4) 8 0.30 × 0.08 × 0.06 1.416 1360 3.438 0.4253/0.8203 multiscan 3.3 to 25.0 83.7% 12 266 4577 3342 229 0.0517, 0.1265 0.0799, 0.1445 0.775
5.5550(4) 15.4270(13) 6.5310(9) 101.849(12) 547.76(10) 2 0.30 × 0.20 × 0.16 1.671 276 4.865 0.3231/0.5099 multiscan 2.6 to 30.0 99.9% 13 910 1597 1434 57 0.0200, 0.0488 0.0239, 0.0510 0.404
17.6600(3) 10.4860(2) 15.9950(11) 104.5570(11) 2866.91(8) 8 0.30 × 0.29 × 0.27 1.735 1488 5.567 0.2859/0.3148 multiscan 3.0 to 30.0 99.8% 38 635 4175 3839 142 0.0220, 0.0529 0.0254, 0.0541 0.476
R1 ) ||Fo| - |Fc||/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}0.5.
Figure 1. Parameters (R, β, Φ, d, d*, and γ) defined to describe the crystal structures.
Figure 2. Solid-state structure of 5 with the thermal ellipsoids given at the 50% probability level. Bridging at Ga(1A) and Ga(2B) is not shown; hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and bond angles [deg]: Ga(1) environment: Ga(1)-C(7) 1.961; d ) 1.991; d* ) 2.718; R ) +7.5; β ) 6.8, Φ ) 355.8; γ ) 98.4; Ga(2) environment: Ga(2)-C(9) 1.956; d ) 1.997, d* ) 2.706, R ) -7.2, β ) 8.1, Φ ) 356.2, γ ) 84.2.
values for the angle R and by only a small deviation of the angle Φ from 360°. As expected, the Ga-C(methyl) distances are shorter than the Ga-C(aryl) distances, because the Ga-C(aryl) bonds are part of the bridging units. The structural changes in the benzene unit of 5 are discussed in a later section.
Figure 3. Solid-state structure of 6, with the thermal ellipsoids given at the 50% probability level. Bridging at Ga(4A) and Ga(2A) is not shown; also hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and bond angles [deg]: Ga(1) environment: Ga(1)-C(11) 1.952(7); d ) 1.995; d* ) 2.689; R ) +6.6; β ) 16.2, Φ ) 356.4, γ ) 87.7; Ga(2) environment: Ga(2)-C(13) 1.961(5); d ) 2.000, d* ) 2.741, R ) -9.9, β ) 11.6, Φ ) 355.7, γ ) 97.7; Ga(3) environment: Ga(3)-C(25) 1.969(6); d ) 2.010, d* ) 2.737, R ) -7.6; β ) 11.7, Φ ) 355.9, γ ) 98.8; Ga(4) environment: Ga(4)-C(27) 1.973(6); d ) 1.999, d* ) 2.761, R ) +3.2; β ) 10.9, Φ ) 356.9, γ ) 82.4.
Compound 6 crystallizes as colorless needles in the space group P21/c with two molecules in the asymmetric unit and with translation along the b-axis under formation of a strand-like coordination polymer (see Figure 3). The overall bonding situation is comparable to that observed for compound 5, as concluded from the structural parameters defined in Figure 1. The additional butyl group on the benzene ring does not have a pronounced influence on the asymmetric bridging situation. Compound 9 crystallizes as colorless needles in the space group P21/n with one-half of the monomer in the asymmetric unit and with an inversion center located in the monomer. A strand-like polymer chain is formed by translation along the a-axis. These strands are connected by weak contacts between gallium atoms in one strand and methyl groups from dimeth-
2622 Organometallics, Vol. 28, No. 8, 2009
Figure 4. Solid-state structure of 9, with the thermal ellipsoids given at the 50% probability level. Full coordination is shown only for Ga(1); also hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and bond angles [deg]: Ga(1)-C(1) 1.9594, Ga(1)-C(3) 1.9777, R ) +2.5, β ) 11.1, Φ ) 359.7, Ga(1)-C(4B) 3.04, Ga(1)-C(Ga(1D) 3.448.
ylgallyl units in another (see Figure 4). Interestingly, the coordination behavior of 9 differs from that observed for 5 and 6 and corresponds partly to that observed for monodimethylgallyl-substituted arenes3 and partly to that found in trimethylgallium.10,11 The molecular unit possesses a nearly planar structure (see values for R, β, and Φ) with sp2-hybridized gallium atoms. An overall only weakly distorted trigonal-bipyramidal coordination geometry at the gallium atoms is observed, arising from a further π-type coordination to a neighboring arene unit [see Ga(1)-C(4B) distance in Figure 4] and a further weak contact (based on polarization forces) to a methyl group from a dimethylgallyl unit of another neighbor [see Ga(1)-C(Ga1D) distance in Figure 4]. Compound 12 crystallizes as colorless sheet-like crystals in the space group C2/c with one molecule in the asymmetric unit. The molecular structure of 12 is portrayed in Figure 5 without the coordination and in Figure 1* in the Supporting Information with coordination to other molecules. All three GaMe2 groups are involved in the formation of asymmetric bridging units by interaction with aryl-GaMe2 groups from neighboring molecules. Based on these intermolecular interactions, a coordination polymer is formed, which consists of undulated sheets built by weakly connected strands of doublebridged monomers. In more detail, the atoms Ga(1)Ga(2A) and Ga(2)Ga(1B), which form less asymmetric bridging units (greater values of R, smaller values of Φ), connect the benzene rings within the strand structure. These strands are connected via a more asymmetric interaction including the Ga(3)Ga(3C) atoms (smaller value of R, greater value of Φ) to give the final sheet structure. The formation of strands with the benzene rings positioned in two planes is schematically described in Figure 6 by the view from two different perspectives. The sheet formation is portrayed in Figure 7 by a view in the direction of the b-axis from the unit cell. For a rudimentary understanding of the bonding in the molecules 5, 6, 9, and 12, the influence of the GaMe2 (10) Mitzel, N. W.; Lustig, C.; Berger, R. J. F.; Runeberg, N. Angew. Chem., 2002, 114, 2629–2632; Angew. Chem. Int. Ed. 2002, 41, 25192522. . (11) Boese, R.; Downs, A. J.; Greene, T. M.; Wall, A. W.; Morrison, C. A.; Parsons, S. Organometallics 2003, 22, 2450–2457.
Jutzi et al.
Figure 5. Structure of the monomeric unit of 12 with the thermal ellipsoids given at the 50% probability level. Bridging of Ga(1) with Ga(2A), Ga(2) with Ga(1B), and Ga(3) with Ga(3C) is not shown; also hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and bond angles [deg]: Ga(1) environment: Ga(1)-C(7) 1.966, d ) 2.103; d* ) 2.307; R ) +28.8; β ) 16.3, Φ ) 344.3, γ ) 85.2; Ga(2) environment: Ga(2)-C(9) 1.970, d ) 2.105, d* ) 2.321, R ) +27.3, β ) 21.2, Φ ) 345.4, γ ) 91.5; Ga(3) environment: Ga(3)-C(11) 1.964, d ) 2.007, d* ) 2.681, R ) -13.3; β ) 9.8, Φ ) 354.7, γ ) 95.0.
Figure 6. Sketch of the structure of the coordination polymer 12 viewed in the direction of (top) and perpendicular to (bottom) the benzene-ring planes.
Figure 7. Sketch of the structure of the coordination polymer 12 viewed in the direction of the b-axis of the unit cell; the dashed lines represent nonbonding Ga-Ga distances in bridging units between adjacent chains represented in Figure 6.
substituents on the bonding parameters of the C6 perimeter of the corresponding benzene unit was investigated. In this context, the measured C-C bond lengths and CCC bond angles in these compounds are presented in Table 1* of the Supporting Information. The CCC angles at the carbon atoms connected with dimethylgallyl substituents are smaller than 120° (∼116°), and the corresponding C-C bonds are somewhat longer. These changes do not indicate a pronounced carbocation character of carbon atoms in the C6 perimeter. Thus, the electron deficiency is mainly located in the bonds to the dimethylgallyl units.
Bis- and Tris(dimethylgallyl)benzenes
Organometallics, Vol. 28, No. 8, 2009 2623
in relation to the plane of the benzene rings (see type III in Figure 8 and parameter γ in Figure 1). The asymmetry parameters are different for each of the bridging dimethylgallyl units. It is evident from our investigations that dimethylgallylsubstituted benzene derivatives find quite different ways to avoid the low coordination at gallium, presumably for steric reasons.
Experimental Section
Figure 8. Schematic presentation of the coordination modes in dimethylgallyl-substituted benzene derivatives (benzene rings are given as thicker black lines).
Discussion and Conclusion In this paper, the syntheses of benzene derivatives containing dimethylgallyl substituents in 1,3- (compounds 5 and 6), 1,4(compound 9), or 1,3,5-position (compound 12) are described. These highly air-sensitive compounds are thermolabile in solution and to a smaller extent even in the solid state. They decompose with elimination of trimethylgallium to give oligomeric condensation products of unknown detailed composition. These condensation products can be retransformed into the starting compounds by treatment with an excess of trimethylgallium at higher temperatures. Unfortunately, the observed cleavage and linking processes do not lead to molecularly defined condensation products (for example ring structures containing benzene units and trigonal-planar coordinate gallium atoms) as desirable for a synthetic method in the frame of the concept of “dynamic covalent chemistry”.2 This might be due to the fact that in the desired condensation products the galliumbridged benzene rings cannot form energetically favored planar ring systems, which are further stabilized by intermolecular π-contacts. The interference of ortho-hydrogen atoms of the benzene units might prevent the formation of such structures. Crystalline samples of the compounds 5, 6, 9, and 12 are obtained from trimethylgallium as solvent. X-ray crystal structure investigations show that all compounds form coordination polymers, whereby old and novel structural features for higher coordinated organogallium compounds are observed. Figure 8 gives a schematic presentation of the different coordination modes. In compound 9 a structural motif is observed that resembles on one hand that found for monodimethylgallylsubstituted benzenes (type I)3 and on the other hand that observed for trimethylgallium.10,11 In more detail, a coordination number of five in a trigonal-bipyramidal geometry is realized at the gallium atoms by formation of a π-contact to a neighboring aryl system and of a van der Waals contact to a methyl group from a neighboring dimethylgallyl unit (see type II). Another structural feature is found for the compounds 5, 6, and 12. A coordination number of four at the gallium atoms is realized by the formation of highly asymmetric electron-deficient bridge bonds involving the ipso-carbon atoms of the benzene and the gallium atoms from the dimethylgallyl units. The asymmetry concerns on one hand the different Ga-C(ipso) bond lengths and on the other hand the position of the Ga-Ga vector
General Comments. All experiments were conducted under a purified argon atmosphere using standard Schlenk techniques. All solvents were commercially available, purified by conventional means, distilled, and stored under argon prior to use. The NMR spectra were recorded on a Bruker Avance DRX 500 spectrometer at 300 K (1H NMR, 500.1 MHz; 13C NMR, 125.8 MHz; 119Sn NMR, 186.5 MHz; 199Hg NMR, 89.6 MHz). The chemical shift values are reported in ppm. The Microanalytical Laboratories of the University of Bielefeld and Beller & Matthies, Goettingen, performed the CH elemental analyses. Crystallographic data were collected with a BrukerNonius KappaCCD diffractometer with Mo KR radiation (graphite monochromator, λ ) 0.71073 Å) at 100 K. Crystallographic programs used for structure solution and refinement were from SHELXS-97 and SHELXL-97. The structures were solved by direct methods and were refined by using full-matrix least-squares on F2 of all unique reflections with anisotropic thermal parameters for all non-hydrogen atoms. Starting Materials. The bromobenzenes were purchased from Merck Chemicals and Fluka Chemicals. The trimethyltin and chloromercurio derivatives were prepared according to the cited literature procedures. Caution! Trimethylgallium is a pyrophoric liquid and should be handled with care. Dimethylmercury is poisonous to the central nervous system and has a long latency period before the characteristic symptoms appear. It is necessary to use a combination of gloves as suggested by Blaney et al.12-15 Dimethylmercury is destroyed by treating it with aqua regia. The resulting mercury dichloride is precipitated as the oxide under basic conditions before it was appropriately disposed. 1,3-Bis(trimethylstannyl)-5-n-butylbenzene (2). A THF solution of sodium trimethylstannide16 (13.46 g, 72.0 mmol) in a Schlenk flask was cooled to 0 °C. 1,3-Dibromo-5-n-butylbenzene (7.10 g, 24.31 mmol) in 10 mL of THF was added to the solution dropwise within 30 min. A rusty-brown suspension appeared after a while. The reaction mixture was stirred at 0 °C for 5 h, allowed to warm to room temperature, and stirred for a further 12 h. Thereafter, 20 mL of degasified distilled water was added, and the organic layer was separated. The aqueous layer was extracted three times, each with 30 mL of diethyl ether. The combined organic layer was dried over sodium sulfate to give a colorless solution. The solvents were removed at reduced pressure to give a colorless liquid. Fractional distillation of the liquid at reduced pressure (0.01 mbar; 105 °C) yielded 2 (5.40 g, 10.94 mmol, 45%) as a colorless liquid. 1H NMR (CDCl3) [δ/ppm]: 0.31 (s, 18H Sn(CH3)3, 2JSn-H ) 46/53 Hz), 0.97 (t, 3H, 3JHH ) 8 Hz, CH2CH3), 1.42 (m, CH2CH3, 3 JHH ) 8 Hz), 1.63 (m, 2H, 3JHH ) 8 Hz, CH2CH2CH3), 2.60 (t, 2H, 3JHH ) 8 Hz, CH2CH2CH2CH3), 7.29 (s, 2H, C-4/6, 3JSn-H ) 47 Hz), 7.58 (s, 1H, C-2, 3JSn-H ) 41 Hz). 13C NMR (CDCl3) [δ/ppm]: -9.5 (Sn(CH3)3, 1JSn-13C ) 331/346 Hz), 14.1 (CH2CH3), 22.7 (CH2CH3), 34.0 (CH2CH2CH3), 36.0 (CH2CH2CH2CH3), 140.4 (12) Nierenberg, D. W.; Nordgren, R. E.; Chang, M. B.; Siegler, R. W.; Blayney, M. B.; Hochberg, F.; Toribara, T. Y.; Cernichiari, E.; Clarkson, T. New Engl. J. Med. 1998, 338 (23), 1672. (13) Blayney, M. B. Appl. Occup. EnViron. Hyg. 2001, 16 (2), 233. (14) Florea, A.; Buesselberg, D. BioMetals 2006, 19 (4), 419. Lockwood, A. H.; Landrigan, P. J. New Engl. J. Med. 1998, 339 (17), 1243. (15) Blayney, M. B.; Winn, J. S.; Nierenberg, D. W. Chem. Eng. News 1997, (May 12), 7. (16) Bickelhaupt, F. J. Organomet. Chem. 2000, 593-594, 369.
2624 Organometallics, Vol. 28, No. 8, 2009 (C4/6, 2JSn-13C ) 32 Hz), 141.6 (C-2, 2JSn-13C ) 37 Hz),142.0 (C1/3, 3JSn-13C ) 23 Hz), 143.2 (C-5, 3JSn-13C ) 33 Hz) 2JSn-13C ) 33 Hz). 119Sn NMR (CDCl3) [δ/ppm]: -28.26 (s, 1JSn-13C ) 335 Hz). Anal. Found: C, 41.35; H, 6.52. Calcd: C, 41.79; H, 6.57. 1,3-Bis(chloromercurio)-(5-n-butyl)benzene (4). To a solution of mercury dichloride (5.79 g, 21.32 mmol) in 70 mL of THF was added slowly a solution of 2 (4.90 g, 10.66 mmol) in 50 mL of diethyl ether at room temperature. The resulting colorless suspension was stirred for 15 h and finally refluxed for 1 h. All volatile components were removed at reduced pressure, and the colorless, amorphous solid residue was washed twice with 50 mL of n-hexane to give 5 (6.20 g, 10.30 mmol) as a colorless, amorphous solid in 97% yield. 1H NMR (DMSO-d6) [δ/ppm]: 0.88 (t, 3H, (CH2)3CH3), 1.29 (sext, 2H, (CH2)2CH2CH3), 1.51 (quint, 2H, (CH2CH2CH2CH3), 2.45 (t, 2H, CH2CH2CH2CH3), 3.34 (s, DMSO-coordinate), 7.19 (s, 2H), 7.24 (s, 1H). 13C NMR, (DMSO-d6) [δ/ppm]: 13.8 (CH2CH2CH2CH3), 21.7 (CH2CH2CH2CH3), 33.1 (CH2CH2CH2CH3), 35.0 (CH2CH2CH2CH3), 136.4 (C-4/6), 141.7 (C-2), 142.1 (C-5), 151.4 (C-1/3). 199Hg NMR (DMSO-d6) [δ/ppm]: -1,139.2. Anal. Found: Hg, 65.7; Cl, 11.2. Calcd: Hg, 66.38; Cl, 11.73. 1,3-Bis(dimethylgallyl)benzene (5). Trimethylgallium (15.69 g, 136.6 mmol) was added to 1,3-bis(chloromercurio)benzene (4) (3.23 g, 5.88 mmol) in a thick-walled Schlenk flask. The resulting gray suspension was heated at 120 °C for 7 h in the closed flask to give a colorless solution, which was cooled without stirring to 40 °C overnight. Colorless crystals separated from the solution. The liquid components were removed by syringe, and the remaining colorless crystals were washed twice with hexane (10 mL) and dried in vacuo (10 mbar) for 3 h to give 5 (1.5 g, 5.44 mmol) in 92% yield.17 Redistribution of 5 in Benzene-d6/THF solution. In an NMR tube, 0.15 g of 5 (0.54 mmol) was dissolved in 3 mL of a benzened6/THF (1:1) solution. The measured NMR data were tentatively assigned to the formation of the redistribution products bis(3dimethylgallylphenyl · THF)methylgallium · THF (13) and trimethylgallium · THF (14). 1H NMR (benzene-d6) [δ/ppm] 13: -0.06 (s, 12H, GaMe2), 0.14 (s, 3H, GaMe), 1.48 br (THF), 3.51 br (THF), 7.42 (m, 2H, aryl), 7.74 (m, 4H, aryl), 8.22 (s, 2H, aryl). 14: -0.28 (s, 9H, GaMe3), 1.48 br (THF), 3.51 br (THF). Evaporation of all volatiles led to an insoluble solid residue. Solid-State Decomposition of 5 and Its Regeneration. Two Schlenk flasks, A and B, were connected by a bent ground-glass joint. Flask A was charged with compound 5 (2.10 g, 7.61 mmol), and the system was evacuated (0.1 mbar). Flask B was then cooled with liquid nitrogen. Flask A was heated at 120 °C for a period of 30 min. Thereafter, an amorphous insoluble solid remained in flask A. Compound 5 liberated 0.79 g (7.02 mmol) of trimethylgallium, which was collected in flask B and characterized by 1H NMR spectroscopy [(benzene-d6) δ ) -0.28 ppm (s, GaMe3)]. The amorphous solid (1.31 g) was combined in a thick-walled Schlenk flask with trimethylgallium (15.00 g, 135.9 mmol). The (17) As explained in more detail in the chapter “Synthesis and Characterization”, it was not possible to get reliable elemental analyses (partial oxidation, chemisorbed trimethylgallium).
Jutzi et al. mixture was heated at 120 °C for 5 h to give a colorless solution, which was cooled without stirring to 40 °C overnight. Colorless crystals of 5 separated from the solution. The crystals were isolated (1.85 g) and characterized by X-ray diffraction (space group determination). 1,3-Bis(dimethylgallyl)-5-n-butylbenzene (6). Trimethylgallium (5.39 g, 46.92 mmol) was added to 1,3-bis(chloromercurio)-5-nbutylbenzene (4) (1.18 g, 1.96 mmol) in a thick-walled Schlenk flask. The resulting colorless suspension was heated at 120 °C for 4 h in the closed flask to afford a colorless solution. All volatile components were removed at reduced pressure (10 mbar). To the remaining colorless amorphous solid was added trimethylgallium (1.0 mL) to give a colorless suspension, which was again heated at 70 °C for 2 h to a give a colorless solution. The solution was maintained at 40 °C without stirring overnight to give 6 as colorless crystals. The liquid components were removed by syringe, and the remaining crystals were washed with cold hexane (5 mL) at -80 °C and dried in vacuo (10 mbar) for 3 h to give 6 (0.63 g, 1.8 mmol) in 92% yield.17 1,4-Bis(dimethylgallyl)benzene (9). Trimethylgallium (16.62 g, 144.7 mmol) was added to 8 (3.31 g, 6.03 mmol) in a thick-walled Schlenk flask. The resulting colorless suspension was heated at 140 °C for 5 h in the closed flask to give a colorless solution. The solution was maintained at 40 °C without stirring for 3 days. Colorless crystals of 9 separated from the solution. The liquid components were removed with syringe, and the remaining crystals were washed with cold hexane (5 mL) and dried in vacuo (10 mbar) for 3 h to give 9 (1.42 g, 5.15 mmol) in 86% yield.17 1,3,5-Tris(dimethylgallyl)benzene (12). Trimethylgallium (7.40 g, 64.4 mmol) was added to 1,3,5-tris(chloromercurio)benzene (11) (1.19 g, 1.61 mmol) in a thick-walled Schlenk flask. The resulting gray suspension was heated at 100 °C for 7 h in the closed flask to give a colorless solution. The solution was maintained at 40 °C without stirring overnight. Colorless crystals of 12 separated from the solution. The liquid components were removed by syringe, and the remaining crystals were washed twice with hexane (10 mL) and dried at reduced pressure (10 mbar) for 3 h to give 12 (0.56 g, 1.5 mmol) in 93% yield.17
Acknowledgment. We thank Professor Lorberth, University of Marburg, Germany, for a gift of trimethylgallium. The financial support of the University of Bielefeld, the Deutsche Forschungsgemeinschaft, and the Fonds der Chemischen Industrie is gratefully acknowledged. Supporting Information Available: A figure of the structure of 12 (Figure 1*) and a table with structure parameters of the benzene rings in 5, 6, 9, and 12 (Table 1*) are deposited. The crystallographic data for compounds 5, 6, 9, and 12 are deposited, including the intramolecular distances, bond angles, and the calculated positions of hydrogen atoms. This information is available free of charge via the Internet at http://pubs.acs.org. OM900048C
