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Crystal structure of the strongly hydrogen bonded complex anion [(C6F5)3B(H3O2)B(C6F5)3]−
Inorganica Chimica Acta 340 (2002) 207 /210 www.elsevier.com/locate/ica
Note
Crystal structure of the strongly hydrogen bonded complex anion [(C6F5)3B(H3O2)B(C6F5)3] Mark J. Drewitt, Martina Niedermann, Michael C. Baird * Department of Chemistry, Queen’s University, Kingston, Ont., Canada K7L 3N6 Received 20 February 2002; accepted 2 May 2002
Abstract The highly electrophilic borane B(C6F5)3 reacts with water to form the aqua complex H2OB(C6F5)3 ×/2H2O, which is deprotonated by 1,8-bis(dimethylamino)naphthalene (proton sponge) to form the salt [C10H6(NMe2)2H][(C6F5)3B(H3O2)B(C6F5)3]. The complex anion is characterized crystallographically and asymmetry is found, suggesting that this is the first example of the theoretically predicted asymmetrically hydrogen bonded [H3O2] ion. There also appears to be evidence for significant CF HO hydrogen bonding in the complex anion that may be responsible in part for the overall structure of the anion. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Crystal structures; Complex anion; Hydrogen bonding
1. Introduction The use of tris(pentafluorophenyl)borane, B(C6F5)3, as an activator of substituted cyclopentadienyl group 4 metals complexes for alkene polymerization has become common in recent years [1]. In the most studied catalyst systems, the active species are generated from dimethylmetallocenes of the type Cp2ZrMe2 by abstraction of methide groups from the metal by B(C6F5)3 to give species of the type Cp2ZrMe(m-Me)B(C6F5)3. In contrast, the chemistry relating to the Lewis acid/base complexes formed with this strong Lewis acid has until recently received little attention [2]. The aqua complex, H2OB(C6F5)3, has been used as a Brønsted acid, with the anionic portion of the salt formed being [(C6F5)3B(H3O2)B(C6F5)3] [3a]. The [H3O2] portion of this anion has been of theoretical interest with regard to the position of the central hydrogen atom, being symmetrically or asymmetrically distributed between the two oxygen atoms depending on the method of calculation [4]. Although theory suggests that the central hydrogen atom should move from being symmetrically
* Corresponding author. Tel.: /1-613-533-2616; fax: /1-613-5336669 E-mail address: [email protected] (M.C. Baird).
to asymmetrically distributed as the O O distance increases [5], asymmetry has not in fact been observed in any structurally characterized compounds containing the [H3O2] anion [3a,6,7]. We now report the structural characterization of the compound [C 10H 6(NMe2) 2H][(F5 C6 )3 B(H 3O 2)B(C6F 5) 3] ×/CH 2Cl 2 (1), prepared via the protonation of 1,8-bis(dimethylamino)naphthalene (proton sponge) by H2OB(C6F5)3 ×/ 2H2O and in which asymmetry seems to be clearly established.
2. Experimental All operations were performed under purified argon using normal Schlenk techniques or an MBraun Labmaster glove box. Solvents were purified by standard methods, and distilled and degassed before use. All 1D 1 H, 13C{1H} and 19F NMR spectra and 2D COSY, HMQC and HSQC spectra, (used for assignment), were recorded using Bruker Avance 400 or 500 spectrometers, chemical shifts being determined by reference to residual 1 H and 13C solvent peaks for 1H and 13C{1H} studies, and external CFCl3 for 19F studies. The compound B(C6F5)3 [8] was prepared according to published procedures. 1,8-(Dimethylamino)naphthalene was purchased from Aldrich and sublimed before use. CD2Cl2
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was dried over CaH2 and vacuum transferred prior to use. 2.1. Synthesis of [C10H6(NMe2)2H][(F5C6)3B(H3O2)B(C6F5)3]×/ CH2Cl2 (1) To B(C6F5)3 (80 mg, 0.156 mmol) in 5 ml dichloromethane, 1.4 ml of degassed water (0.078 mmol) was added at room temperature (r.t.) via a 10-ml syringe. After 5 min stirring, proton sponge (16.7 mg, 0.078 mmol) was added as a solid, and the mixture was stirred until all solids had dissolved. The solution was then layered with 5 ml hexane and maintained at /20 8C overnight. Isolation of the resulting crystals afforded 89.7 mg of the product (0.067 mmol, 86% yield with respect to proton sponge). Prior to submission for microanalysis, the crystals were subjected to drying in vacuo which removed the dichloromethane of crystallization from the crystal lattice. Anal. Calc. for C50H22B2F30N2O2: C, 47.1; H, 1.7; N, 2.2. Found C, 47.1; H, 1.7; N, 2.1%. 1H NMR (293 K, CD2Cl2): d 19.40 (s, 1H, NH); 8.04 (dd, 2H, JHH /8.3, 2.4 Hz, CH); 7.77 (m, 4H, CH ); 6.55 (br s, 3H, H3O2); 3.14 (d, 12H, JHH /2.5 Hz, JCH /141 Hz, N(CH3)2). 13C{1H} NMR (293 K, CD2Cl2): d 148.2 (dm, JFC /235.6 Hz, ortho C F); 141.7 (dm, JFC /231.1 Hz, para C F); 136.99 (dm, JFC /235.6 Hz, meta C F) 122.3 (broad, ipso C ); 143.29, 135.9, 130.47, 127.64, 121.44, 118.8 (naphthyl), 46.73 (s, N(C H3)2), 19F NMR: (293 K, CD2Cl2) / 137.17 (d, JFF /21.2 Hz, 2F, ortho ); /162.42 (t, JFF /18.9 Hz, 1F, para ); /167.14 (br, t, JFF /18.9 Hz, 2F, meta ). MS (FAB, nitrobenzyl alcohol) FAB m /e 215.1 [C10H6(NCH3)2H] ; FAB m /e 1058.6 [H3O2{B(C6F5)3}2] .
Table 1 Crystal data for compound 1 1 Empirical formula fw Temperature (K) Crystal system Crystal size (mm3) Space group Unit cell dimensions ˚) a (A ˚) b (A ˚) c (A a (8) b (8) g (8) ˚ 3) V (A Z Dcalc (g cm 3) m (mm 1) 2u Range (8) F (000) Index range No. of reflections collected No. of unique reflections, n Goodness-of-fit on F2, S R1 [I 2s (I )] wR2 (all data) Largest difference peak and ˚ 3) hole (e A
C51H24B2Cl2F30N2O2 1359.22 296(2) triclinic 0.1 0.1 0.2 P 1¯ 13.054(8) 14.374(8) 14.779(9) 87.319(12) 70.169(9) 84.422(11) 2596(3) 2 1.735 0.279 2.845 2u 5 56.90 1348 17 5 h 5 15, 195 k 5 18, 18 5 l 5 19 17779 11863 (Rint 0.0411) 1.028 0.0672 0.1169 0.444 and 0.438
were directly located and successfully refined isotropically. Crystallographic data are summarized in Table 1. The figure was prepared using ORTEP-3 for Windows [11].
3. Results and discussion 2.2. X-ray crystallography A crystal of 1 was mounted on a glass fiber with epoxy glue. The data were collected on a CCD-detectorequipped SMART system with graphite monochromated ˚ ) operated at 50 kV and Mo Ka radiation (l /0.71073 A 30 mA at 23 8C over the 2u range of 2.84 /56.908. No significant decay was observed for the crystal. The data were processed on a Pentium PC using Siemens SHELXTL (version 5.0) software package [9]. A semiempirical absorption correction was applied from C scans. Neutral atoms scattering factors were taken from Cromer and Waber [10]. The structure was solved by direct method in the space group P 1¯ (no. 2). Full-matrix least-square refinements minimizing the function S w (Fo2 /Fc2)2 were applied to the compound. All non-hydrogen atoms were refined with anisotropic displacement parameters. The positions of hydrogen atoms were directly located or calculated and refined successfully. In the case of H(8), H(9) and H(10), they
The range of compounds in which the H3O2 anionic unit is found falls into two categories. The first contains ‘very strong’ hydrogen bonds in which the O O ˚ ) are very short [12], and in which distances (2.29 /2.34 A the hydrogen has been generally assumed to be symmetrically distributed. For the other, into which the anion [(F5C6)3B(H3O2)B(C6F5)3] belongs, the O O dis˚ although the tances are generally greater, 2.40 /2.52 A hydrogen bonds involved may still be quite strong [12]. The complex anion [(F5C6)3B(H3O2)B(C6F5)3] was synthesized as a CH2Cl2 solvate of the [C10H6(NMe2)2H] salt by reaction in CH2Cl2 of 1,8(dimethylamino)naphthalene, (C10H6(NMe2)2, proton sponge) with H2OB(C6F5)3 ×/2H2O, generated in situ [2b,3]. After removal of the solvent molecule under reduced pressure, the compound was satisfactorily characterized by elemental analyses, multinuclear NMR spectroscopy and mass spectrometry. The FAB mass spectrum (nitrobenzyl alcohol) exhibited
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[(F5C6)3B(H3O2)B(C6F5)3] (m /e 1058.5) as the major ion, with a minor species being identified as [(HO)B(C6F5)3] (m /e 528.3). We may expect that [(HO)B(C6F5)3] is formed by the breaking of the hydrogen bond to give [(HO)B(C6F5)3] and [(H2O)B(C6F5)3]. Crystals suitable for single crystal X-ray diffraction were obtained by recrystallization from CH2Cl2-n hexane and were studied as the CH2Cl2 solvate. The crystal structure shows the compound to be [C10H6(NMe2)2H][(F5C6)3B(H3O2)B(C6F5)3]×/CH2Cl2, and is illustrated in Fig. 1, with a list of the pertinent bond lengths and angles. As can be seen, the anion consists of two borane molecules bridged by an [H3O2] anion. The structure of the complex anion is similar to those reported elsewhere for this anion in a variety of other environments [3a,7], but a distinct asymmetry can be observed by considering a variety of bond lengths and angles. The problems associated with locating hydrogen atoms by single crystal X-ray diffraction are well known, and the estimated standard deviations for the O /H bond lengths (Fig. 1) are sufficiently large as to not provide any information regarding the symmetric or asymmetric nature of the [H3O2] unit. With the heavy atom positions being better defined, however, a comparison of characteristic bond lengths and angles can be carried out. Indeed, examination of the boron oxygen bond
Fig. 1. Structure of the [(F5C6)3B(H3O2)B(C6F5)3] anion in 1, with ˚ ), bond angles (8) and torsions (8). O(1) /H(9) selected bond lengths (A 1.24(6), O(1) /H(10) 0.61(5), O(2) /H(8) 0.79(3), O(2) /H(9) 1.17(6), B(1) /O(1) 1.529(6), B(2) /O(2) 1.509(5), H(8) /F(20) 2.02(4), H(8) / F(21) 2.51(4), H(10) /F(10) 2.69(6), H(10) /F(15) 2.27(6), H(9) /O(1) / H(10) 110(7), H(8) /O(2) /H(9) 118(4), O(1) /H(9) /O(2) 179(4), H(8) / O(2) /O(1) /H(10) 75(7). For clarity, the numbering scheme for all carbon atoms and most of the fluorine atoms are omitted and the anion is with 30% probability thermal ellipsoids. The dashed lines indicate possible CF HO hydrogen bonds.
209
lengths in combination with the degree to which the B(C6F5)3 unit is distorted from planarity, as measured by the sum of the three Cipso /B /Cipso bond angles, allows us to identify clear asymmetry in the [(F5C6)3B(H3O2)B(C6F5)3] anion. More useful information becomes apparent on examination of the geometric parameters of (H2O)B(C6F5)3 and Et3NH [(HO)B(C6F5)3] , the other structurally characterized aqua and hydroxide complexes of B(C6F5)3. Interestingly, the B /O bond length shortens and the sum of the Cipso /B /Cipso bond angles decreases (indicating a greater degree of pyramidalization) as the group becomes more electron donating, i.e. aqua to hydroxy complex. For (H2O)B(C6F5)3, ˚ and the sum of the three the B /O distance is 1.597(2) A Cipso /B /Cipso bond angles is 341.3(2)8 [3b], compared to Et3NH [(HO)B(C6F5)3] where the B /O distance is ˚ and the sum of the three Cipso /B /Cipso bond 1.495(5) A angles is 333.0(5)8 [13]. In 1, there is a small but significant difference between the two boron oxygen ˚ and B(2) /O(2) / bond lengths; B(1) /O(1) /1.529(6) A ˚ 1.509(5) A. In addition, the sum of the Cipso /B /Cipso bond angles around B(1) is 335.5(6)8, higher than the sum of the Cipso /B /Cipso bond angles around B(2) 333.0(6)8. These differences suggest a structure better described as [HO H2O] than as [HO H OH] . Thus the [H3O2] unit, supported by O-coordination to two B(C6F5)3 molecules, can be thought of as a [HOB(C6F5)3] anion with an apparently almost linear (179(4)8) hydrogen bond to a molecule of H2OB(C6F5)3. ˚ , is at the lower end The O(1)/O(2) distance, 2.409(2) A ˚ ) for H3O2 in of the range of those found (2.40/2.52 A a variety of environments [3a,7], such as bridging between two [Co(en)2]2 units and attests to strong hydrogen bonding in 1. As discussed above, the asymmetry in the central O /H bond distances is predicted in theoretical calculations on the free [H3O2] anion [4], but the structure reported here appears to be the first in which asymmetry has been established. Further inspection of the structure of the [(F5C6)3B(H3O2)B(C6F5)3] anion also reveals a number of apparently short intramolecular OH FC dis˚ ), H(8) /F(21) (2.51(4) tances, e.g. H(8) /F(20) (2.02(4) A ˚ ˚ ). ˚ A), H(10)/F(10) (2.69(5) A, H(10)/F(15) (2.27(5) A These fall within the range of distances found for ‘moderate’ O H interactions [14a], and are considerably less than have been reported for many ‘weak’ [14b] O H interactions. Little seems to be known about CF HO hydrogen bonding [14] but, given the close similarities in the van der Waals radii of oxygen and fluorine [15], the CF HO bond length data for the [(F5C6)3B(H3O2)B(C6F5)3] anion do seem to imply significant interactions. A similar anion involving the B(C6F5)3 group, [(F5C6)3B(NH2)B(C6F5)3] , also shows
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extensive CF HN hydrogen bonding with bond distances and angles similar to those noted above [15]. Further analysis of the geometric parameters of the anion reveals that the CF HO interactions may influence the overall structure of the complex anion. The CF HO interactions, which involve the ortho fluorine atoms of two of the pentafluorophenyl groups, force the rings to rotate towards the hydrogen atom. As a consequence of this, the third pentafluorophenyl group is bent away from these two. We can observe this effect in the O /B /Cipso angles which are compressed substantially to 101.9(4) and 104.1(4)8 for B(1) and B(2), respectively, compared to the other O /B / Cipso angles which are in the range 107.7(4) /112.5(4)8.
[3]
[4]
[5]
Acknowledgements
[6]
Financial support from Bayer Inc. and the Natural Sciences and Engineering Research Council made this research possible. We would like to thank Dr. David Watkin for discussions regarding the crystal structure.
[7]
References [1] (a) For useful reviews see: P.C. Mo¨hring, N.J. Coville, J. Organomet. Chem. 479 (1994) 1; (b) V.K. Gupta, S. Satish, I.S. Bhardwaj, J. Macromol. Sci., Rev. Macromol. Chem. Phys. C34 (1994) 439; (c) H.H. Brintzinger, D. Fischer, R. Mu¨lhaupt, B. Rieger, R.M. Waymouth, Angew. Chem., Int. Ed. Engl. 34 (1995) 1143; (d) M. Bochmann, J. Chem. Soc., Dalton Trans. (1996) 255; (e) W. Kaminsky, M. Arndt, Adv. Polym. Sci. 127 (1997) 143; (f) J.C.W. Chien, in: T.J. Marks, J.C. Stevens (Eds.), Topics in Catalysis, vol. 7, Baltzer Science Publishers, Delft, 1999, p. 125; (g) H.G. Alt, A. Ko¨ppl, Chem. Rev. 100 (2000) 1205; (h) G.W. Coates, Chem. Rev. 100 (2000) 1223; (i) L. Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 100 (2000) 1253; (j) K. Angermund, G. Fink, V.R. Jensen, R. Kleinschmidt, Chem. Rev. 100 (2000) 1457; (k) J. Scheirs, W. Kaminsky (Eds.), Metallocene-based Polyolefins, Wiley, UK, 1999. [2] (a) H. Jacobsen, H. Berke, S. Do¨ring, G. Kehr, G. Erker, R. Fro¨hlich, O. Meyer, Organometallics 18 (1999) 1724; (b) C. Bergquist, B.M. Bridgewater, C.J. Harlan, J.R. Norton,
[8] [9] [10] [11] [12] [13] [14]
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R.A. Friesner, G. Parkin, J. Am. Chem. Soc. 122 (2000) 10581; (c) C. Janiak, L. Braun, T.G. Scharmann, F. Girgsdies, Acta. Crystallogr., Sect. C 54 (1998) 1722; (d) A.R. Siedle, W.M. Lamanna, U.S. Patent 5416177, 1995 (Minnesota Mining and Manufacturing Co); (e) D.R. Neithamer, U.S. Patent 5721183, 1998 (The Dow Chemical Company). (a) L.H. Doerrer, M.L.H. Green, J. Chem. Soc., Dalton Trans. (1999), 4325; (b) A.A. Danopoulos, J.R. Galsworthy, M.L.H. Green, S. Cafferkey, L.H. Doerrer, M.B. Hursthouse, J. Chem. Soc., Chem. Commun. (1998) 2529; (c) J.L. Priego, L.H. Doerrer, L.H. Rees, M.L.H. Green, J. Chem. Soc., Chem. Commun. (2000) 779. For recent calculations and a useful overview of the literature, see: D. Wei, E.I. Proynov, A. Milet, D.R. Salahub, J. Phys. Chem. A 104 (2000) 2384. M.E. Tuckerman, D. Marx, M.L. Klein, M. Parrinello, Science 275 (1997) 817. (a) K. Abu-Dari, D.P. Freyborg, K.N. Raymond, Inorg. Chem. 18 (1979) 2427; (b) M. Schmidt, A. Schier, J. Riede, H. Schmidbaur, Inorg. Chem. 37 (1998) 3452; (c) M.I. Burguete, B. Escuder, E. Garcia-Espan˜a, J. Latorre, S.V. Luis, J.A. Ramı´rez, Inorg. Chim. Acta 300-302 (2000) 970. (a) M. Ardon, A. Bino, Inorg. Chem. 24 (1985) 1343; (b) M. Ardon, A. Bino, K. Michelsen, J. Am. Chem. Soc. 109 (1987) 1986; (c) A. Bino, D. Gibson, J. Am. Chem. Soc. 103 (1981) 6741; (d) A. Bino, D. Gibson, J. Am. Chem. Soc. 104 (1982) 4383; (e) A. Bino, D. Gibson, Inorg. Chem. 23 (1984) 109; (f) M. Ruf, K. Weis, H. Vahrenkamp, J. Am. Chem. Soc. 118 (1996) 9288; (g) C. Bergquist, G. Parkin, J. Am. Chem. Soc. 121 (1999) 6322. J.L. Pohlmann, F.E. Brinckmann, Z. Naturforsch., Teil b 20 (1965) 5. SHELXTL, version 5. Crystal Structure Analysis Package, Bruker AXS, Madison, WI, 1995. D.T. Cromer, J.T. Waber, International Tables for X-ray Crystallography, Table 2.2A, vol. 4, Kynoch Press, Birmingham, 1974. L.J. Farrugia, J. Appl. Cryst. 30 (1997) 565. P. Gilli, V. Bertolasi, V. Ferretti, G. Gilli, J. Am. Chem. Soc. 116 (1994) 909. R. Duchateau, R.A. van Santen, G.P.A. Yap, Organometallics 19 (2000) 809. (a) G.A. Jeffrey, An Introduction to Hydrogen Bonding, Oxford University Press, New York, 1997, p. 61; (b) G.A. Jeffrey, An Introduction to Hydrogen Bonding, Oxford University Press, New York, 1997, pp. 87 /89. B. Douglas, D. McDaniel, J. Alexander, Concepts and Models of Inorganic Chemistry, Wiley, New York, 1994, p. 102.
Note
Crystal structure of the strongly hydrogen bonded complex anion [(C6F5)3B(H3O2)B(C6F5)3] Mark J. Drewitt, Martina Niedermann, Michael C. Baird * Department of Chemistry, Queen’s University, Kingston, Ont., Canada K7L 3N6 Received 20 February 2002; accepted 2 May 2002
Abstract The highly electrophilic borane B(C6F5)3 reacts with water to form the aqua complex H2OB(C6F5)3 ×/2H2O, which is deprotonated by 1,8-bis(dimethylamino)naphthalene (proton sponge) to form the salt [C10H6(NMe2)2H][(C6F5)3B(H3O2)B(C6F5)3]. The complex anion is characterized crystallographically and asymmetry is found, suggesting that this is the first example of the theoretically predicted asymmetrically hydrogen bonded [H3O2] ion. There also appears to be evidence for significant CF HO hydrogen bonding in the complex anion that may be responsible in part for the overall structure of the anion. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Crystal structures; Complex anion; Hydrogen bonding
1. Introduction The use of tris(pentafluorophenyl)borane, B(C6F5)3, as an activator of substituted cyclopentadienyl group 4 metals complexes for alkene polymerization has become common in recent years [1]. In the most studied catalyst systems, the active species are generated from dimethylmetallocenes of the type Cp2ZrMe2 by abstraction of methide groups from the metal by B(C6F5)3 to give species of the type Cp2ZrMe(m-Me)B(C6F5)3. In contrast, the chemistry relating to the Lewis acid/base complexes formed with this strong Lewis acid has until recently received little attention [2]. The aqua complex, H2OB(C6F5)3, has been used as a Brønsted acid, with the anionic portion of the salt formed being [(C6F5)3B(H3O2)B(C6F5)3] [3a]. The [H3O2] portion of this anion has been of theoretical interest with regard to the position of the central hydrogen atom, being symmetrically or asymmetrically distributed between the two oxygen atoms depending on the method of calculation [4]. Although theory suggests that the central hydrogen atom should move from being symmetrically
* Corresponding author. Tel.: /1-613-533-2616; fax: /1-613-5336669 E-mail address: [email protected] (M.C. Baird).
to asymmetrically distributed as the O O distance increases [5], asymmetry has not in fact been observed in any structurally characterized compounds containing the [H3O2] anion [3a,6,7]. We now report the structural characterization of the compound [C 10H 6(NMe2) 2H][(F5 C6 )3 B(H 3O 2)B(C6F 5) 3] ×/CH 2Cl 2 (1), prepared via the protonation of 1,8-bis(dimethylamino)naphthalene (proton sponge) by H2OB(C6F5)3 ×/ 2H2O and in which asymmetry seems to be clearly established.
2. Experimental All operations were performed under purified argon using normal Schlenk techniques or an MBraun Labmaster glove box. Solvents were purified by standard methods, and distilled and degassed before use. All 1D 1 H, 13C{1H} and 19F NMR spectra and 2D COSY, HMQC and HSQC spectra, (used for assignment), were recorded using Bruker Avance 400 or 500 spectrometers, chemical shifts being determined by reference to residual 1 H and 13C solvent peaks for 1H and 13C{1H} studies, and external CFCl3 for 19F studies. The compound B(C6F5)3 [8] was prepared according to published procedures. 1,8-(Dimethylamino)naphthalene was purchased from Aldrich and sublimed before use. CD2Cl2
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was dried over CaH2 and vacuum transferred prior to use. 2.1. Synthesis of [C10H6(NMe2)2H][(F5C6)3B(H3O2)B(C6F5)3]×/ CH2Cl2 (1) To B(C6F5)3 (80 mg, 0.156 mmol) in 5 ml dichloromethane, 1.4 ml of degassed water (0.078 mmol) was added at room temperature (r.t.) via a 10-ml syringe. After 5 min stirring, proton sponge (16.7 mg, 0.078 mmol) was added as a solid, and the mixture was stirred until all solids had dissolved. The solution was then layered with 5 ml hexane and maintained at /20 8C overnight. Isolation of the resulting crystals afforded 89.7 mg of the product (0.067 mmol, 86% yield with respect to proton sponge). Prior to submission for microanalysis, the crystals were subjected to drying in vacuo which removed the dichloromethane of crystallization from the crystal lattice. Anal. Calc. for C50H22B2F30N2O2: C, 47.1; H, 1.7; N, 2.2. Found C, 47.1; H, 1.7; N, 2.1%. 1H NMR (293 K, CD2Cl2): d 19.40 (s, 1H, NH); 8.04 (dd, 2H, JHH /8.3, 2.4 Hz, CH); 7.77 (m, 4H, CH ); 6.55 (br s, 3H, H3O2); 3.14 (d, 12H, JHH /2.5 Hz, JCH /141 Hz, N(CH3)2). 13C{1H} NMR (293 K, CD2Cl2): d 148.2 (dm, JFC /235.6 Hz, ortho C F); 141.7 (dm, JFC /231.1 Hz, para C F); 136.99 (dm, JFC /235.6 Hz, meta C F) 122.3 (broad, ipso C ); 143.29, 135.9, 130.47, 127.64, 121.44, 118.8 (naphthyl), 46.73 (s, N(C H3)2), 19F NMR: (293 K, CD2Cl2) / 137.17 (d, JFF /21.2 Hz, 2F, ortho ); /162.42 (t, JFF /18.9 Hz, 1F, para ); /167.14 (br, t, JFF /18.9 Hz, 2F, meta ). MS (FAB, nitrobenzyl alcohol) FAB m /e 215.1 [C10H6(NCH3)2H] ; FAB m /e 1058.6 [H3O2{B(C6F5)3}2] .
Table 1 Crystal data for compound 1 1 Empirical formula fw Temperature (K) Crystal system Crystal size (mm3) Space group Unit cell dimensions ˚) a (A ˚) b (A ˚) c (A a (8) b (8) g (8) ˚ 3) V (A Z Dcalc (g cm 3) m (mm 1) 2u Range (8) F (000) Index range No. of reflections collected No. of unique reflections, n Goodness-of-fit on F2, S R1 [I 2s (I )] wR2 (all data) Largest difference peak and ˚ 3) hole (e A
C51H24B2Cl2F30N2O2 1359.22 296(2) triclinic 0.1 0.1 0.2 P 1¯ 13.054(8) 14.374(8) 14.779(9) 87.319(12) 70.169(9) 84.422(11) 2596(3) 2 1.735 0.279 2.845 2u 5 56.90 1348 17 5 h 5 15, 195 k 5 18, 18 5 l 5 19 17779 11863 (Rint 0.0411) 1.028 0.0672 0.1169 0.444 and 0.438
were directly located and successfully refined isotropically. Crystallographic data are summarized in Table 1. The figure was prepared using ORTEP-3 for Windows [11].
3. Results and discussion 2.2. X-ray crystallography A crystal of 1 was mounted on a glass fiber with epoxy glue. The data were collected on a CCD-detectorequipped SMART system with graphite monochromated ˚ ) operated at 50 kV and Mo Ka radiation (l /0.71073 A 30 mA at 23 8C over the 2u range of 2.84 /56.908. No significant decay was observed for the crystal. The data were processed on a Pentium PC using Siemens SHELXTL (version 5.0) software package [9]. A semiempirical absorption correction was applied from C scans. Neutral atoms scattering factors were taken from Cromer and Waber [10]. The structure was solved by direct method in the space group P 1¯ (no. 2). Full-matrix least-square refinements minimizing the function S w (Fo2 /Fc2)2 were applied to the compound. All non-hydrogen atoms were refined with anisotropic displacement parameters. The positions of hydrogen atoms were directly located or calculated and refined successfully. In the case of H(8), H(9) and H(10), they
The range of compounds in which the H3O2 anionic unit is found falls into two categories. The first contains ‘very strong’ hydrogen bonds in which the O O ˚ ) are very short [12], and in which distances (2.29 /2.34 A the hydrogen has been generally assumed to be symmetrically distributed. For the other, into which the anion [(F5C6)3B(H3O2)B(C6F5)3] belongs, the O O dis˚ although the tances are generally greater, 2.40 /2.52 A hydrogen bonds involved may still be quite strong [12]. The complex anion [(F5C6)3B(H3O2)B(C6F5)3] was synthesized as a CH2Cl2 solvate of the [C10H6(NMe2)2H] salt by reaction in CH2Cl2 of 1,8(dimethylamino)naphthalene, (C10H6(NMe2)2, proton sponge) with H2OB(C6F5)3 ×/2H2O, generated in situ [2b,3]. After removal of the solvent molecule under reduced pressure, the compound was satisfactorily characterized by elemental analyses, multinuclear NMR spectroscopy and mass spectrometry. The FAB mass spectrum (nitrobenzyl alcohol) exhibited
M.J. Drewitt et al. / Inorganica Chimica Acta 340 (2002) 207 /210
[(F5C6)3B(H3O2)B(C6F5)3] (m /e 1058.5) as the major ion, with a minor species being identified as [(HO)B(C6F5)3] (m /e 528.3). We may expect that [(HO)B(C6F5)3] is formed by the breaking of the hydrogen bond to give [(HO)B(C6F5)3] and [(H2O)B(C6F5)3]. Crystals suitable for single crystal X-ray diffraction were obtained by recrystallization from CH2Cl2-n hexane and were studied as the CH2Cl2 solvate. The crystal structure shows the compound to be [C10H6(NMe2)2H][(F5C6)3B(H3O2)B(C6F5)3]×/CH2Cl2, and is illustrated in Fig. 1, with a list of the pertinent bond lengths and angles. As can be seen, the anion consists of two borane molecules bridged by an [H3O2] anion. The structure of the complex anion is similar to those reported elsewhere for this anion in a variety of other environments [3a,7], but a distinct asymmetry can be observed by considering a variety of bond lengths and angles. The problems associated with locating hydrogen atoms by single crystal X-ray diffraction are well known, and the estimated standard deviations for the O /H bond lengths (Fig. 1) are sufficiently large as to not provide any information regarding the symmetric or asymmetric nature of the [H3O2] unit. With the heavy atom positions being better defined, however, a comparison of characteristic bond lengths and angles can be carried out. Indeed, examination of the boron oxygen bond
Fig. 1. Structure of the [(F5C6)3B(H3O2)B(C6F5)3] anion in 1, with ˚ ), bond angles (8) and torsions (8). O(1) /H(9) selected bond lengths (A 1.24(6), O(1) /H(10) 0.61(5), O(2) /H(8) 0.79(3), O(2) /H(9) 1.17(6), B(1) /O(1) 1.529(6), B(2) /O(2) 1.509(5), H(8) /F(20) 2.02(4), H(8) / F(21) 2.51(4), H(10) /F(10) 2.69(6), H(10) /F(15) 2.27(6), H(9) /O(1) / H(10) 110(7), H(8) /O(2) /H(9) 118(4), O(1) /H(9) /O(2) 179(4), H(8) / O(2) /O(1) /H(10) 75(7). For clarity, the numbering scheme for all carbon atoms and most of the fluorine atoms are omitted and the anion is with 30% probability thermal ellipsoids. The dashed lines indicate possible CF HO hydrogen bonds.
209
lengths in combination with the degree to which the B(C6F5)3 unit is distorted from planarity, as measured by the sum of the three Cipso /B /Cipso bond angles, allows us to identify clear asymmetry in the [(F5C6)3B(H3O2)B(C6F5)3] anion. More useful information becomes apparent on examination of the geometric parameters of (H2O)B(C6F5)3 and Et3NH [(HO)B(C6F5)3] , the other structurally characterized aqua and hydroxide complexes of B(C6F5)3. Interestingly, the B /O bond length shortens and the sum of the Cipso /B /Cipso bond angles decreases (indicating a greater degree of pyramidalization) as the group becomes more electron donating, i.e. aqua to hydroxy complex. For (H2O)B(C6F5)3, ˚ and the sum of the three the B /O distance is 1.597(2) A Cipso /B /Cipso bond angles is 341.3(2)8 [3b], compared to Et3NH [(HO)B(C6F5)3] where the B /O distance is ˚ and the sum of the three Cipso /B /Cipso bond 1.495(5) A angles is 333.0(5)8 [13]. In 1, there is a small but significant difference between the two boron oxygen ˚ and B(2) /O(2) / bond lengths; B(1) /O(1) /1.529(6) A ˚ 1.509(5) A. In addition, the sum of the Cipso /B /Cipso bond angles around B(1) is 335.5(6)8, higher than the sum of the Cipso /B /Cipso bond angles around B(2) 333.0(6)8. These differences suggest a structure better described as [HO H2O] than as [HO H OH] . Thus the [H3O2] unit, supported by O-coordination to two B(C6F5)3 molecules, can be thought of as a [HOB(C6F5)3] anion with an apparently almost linear (179(4)8) hydrogen bond to a molecule of H2OB(C6F5)3. ˚ , is at the lower end The O(1)/O(2) distance, 2.409(2) A ˚ ) for H3O2 in of the range of those found (2.40/2.52 A a variety of environments [3a,7], such as bridging between two [Co(en)2]2 units and attests to strong hydrogen bonding in 1. As discussed above, the asymmetry in the central O /H bond distances is predicted in theoretical calculations on the free [H3O2] anion [4], but the structure reported here appears to be the first in which asymmetry has been established. Further inspection of the structure of the [(F5C6)3B(H3O2)B(C6F5)3] anion also reveals a number of apparently short intramolecular OH FC dis˚ ), H(8) /F(21) (2.51(4) tances, e.g. H(8) /F(20) (2.02(4) A ˚ ˚ ). ˚ A), H(10)/F(10) (2.69(5) A, H(10)/F(15) (2.27(5) A These fall within the range of distances found for ‘moderate’ O H interactions [14a], and are considerably less than have been reported for many ‘weak’ [14b] O H interactions. Little seems to be known about CF HO hydrogen bonding [14] but, given the close similarities in the van der Waals radii of oxygen and fluorine [15], the CF HO bond length data for the [(F5C6)3B(H3O2)B(C6F5)3] anion do seem to imply significant interactions. A similar anion involving the B(C6F5)3 group, [(F5C6)3B(NH2)B(C6F5)3] , also shows
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extensive CF HN hydrogen bonding with bond distances and angles similar to those noted above [15]. Further analysis of the geometric parameters of the anion reveals that the CF HO interactions may influence the overall structure of the complex anion. The CF HO interactions, which involve the ortho fluorine atoms of two of the pentafluorophenyl groups, force the rings to rotate towards the hydrogen atom. As a consequence of this, the third pentafluorophenyl group is bent away from these two. We can observe this effect in the O /B /Cipso angles which are compressed substantially to 101.9(4) and 104.1(4)8 for B(1) and B(2), respectively, compared to the other O /B / Cipso angles which are in the range 107.7(4) /112.5(4)8.
[3]
[4]
[5]
Acknowledgements
[6]
Financial support from Bayer Inc. and the Natural Sciences and Engineering Research Council made this research possible. We would like to thank Dr. David Watkin for discussions regarding the crystal structure.
[7]
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