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The first dimeric half-sandwich gadolinacarborane of the “carbons apart” C2B4-carborane ligand system
Inorganic Chemistry Communications 4 (2001) 104±107
www.elsevier.nl/locate/inoche
The ®rst dimeric half-sandwich gadolinacarborane of the ``carbons apart'' C2B4-carborane ligand system Narayan S. Hosmane a
a,*
, Shoujian Li
a,1
, Chong Zheng a, John A. Maguire
b
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA b Department of Chemistry, Southern Methodist University, Dallas, TX 75275, USA Received 17 October 2000; accepted 10 November 2000
Dedicated to Professor Sheldon G. Shore of The Ohio State University on the occasion of his 70th birthday
Abstract The reaction between the THF solvated ``carbons apart'' dinatracarborane, closo-exo-4,5-Na(THF)2 ±1-Na(THF)2 ±2,4(SiMe3 )2 C2 B4 H4 (1), and anhydrous GdCl3 in a 1:1 molar ratio in dry benzene at 0°C, followed by extraction and crystallization of the product from an anhydrous n-hexane/TMEDA/THF solution mixture resulted in the isolation of o-white crystals of the dimeric half-sandwich dichlorogadolinacarborane, {1,1-Cl2 [l; l0 -Na(TMEDA)]±1-(THF)-2,4-(SiMe3 )2 ±closo-g5 -1-Gd-2,4-C2 B4 H4 }2 (2) in 88% yield. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Carborane; Gadolinacarborane; Half-sandwich complex and metallacarborane
Recently, we have reported the syntheses, properties and structures of several titanium(IV), zirconium(IV) and hafnium(IV) bent-sandwich complexes of C cage trimethylsilyl-substituted C2 B4 -carborane ligands [1]. The X-ray crystal structures of these compounds show that in each complex the metal atom bonds to a Cl atom, a THF molecule and two carborane ligands resulting in a distorted tetrahedral geometry [1]. A similar metal geometry was found in the full-sandwiched yttracarborane complex despite the formal 3+ metal oxidation state [2]. The monoanionic chlorozircona- and chlorohafnacarboranes each contain a Li(THF)n (n 1 or 2) moiety that bridges the two carboranes and is oriented opposite to the metal bound Cl and THF ligands. In the dianionic chloroyttracarborane there is an additional Li (THF)4 ion that is well separated from the carborane complex [1,2]. This highlights one of the limitations in the use of the f-block metallacarboranes: because of the trivalent nature of the metal the carborane sandwich complexes bear signi®cant negative charges which can result in zwitterionic clusters and retard any reactions *
Corresponding author. Tel.: +1-815-753-3556; fax: +1-815-7534802. E-mail address: [email protected] (N.S. Hosmane). 1 On leave from Sichuan University, People's Republic of China.
involving the addition of anionic groups to the metal centers. Therefore, there is little possibility of ligand exchange reactions about the metal center after the addition of reactive anionic ligands such as alkyls. A possible solution to this problem would be to design lower charged, less sterically crowded half-sandwich complexes. However, the syntheses of such complexes are not simple; the reaction of 2,3-(SiMe3 )2 ±2,3-C2 B4 H5 in 1:1 molar ratio with Y(CH2 SiMe3 )3 , made in situ by the reaction of YCl3 and Me3 SiCH2 MgCl, resulted in complex mixtures of products and no discrete halfsandwich, closo-yttracarborane, could be isolated [3]. The syntheses of the lanthanacarboranes also shows unusual complexity. The reaction of the THF-solvated dilithium compound of the [2,3-(SiMe3 )2 C2 B4 H4 ]2ÿ dianion with anhydrous LnCl3 (Ln Nd, Sm, Gd, Tb, Dy, Ho) in a molar ratio of 2:1 in dry benzene and THF produced unusual trinuclear Ln(III)-carboranes of the form, [g5 -1-Ln±2,3-(SiMe3 )2 ±2,3-C2 B4 H4 ]3 [(l2 -1-Li±2,3(SiMe3 )2 ±2,3-C2 B4 H4 )3 (l3 -OMe)]-[l2 -Li(THF)]3 (l3 -O) [4]. These are clusters composed of three half-sandwich lithiacarboranes and lanthanacarboranes arranged about a central O atom and a MeO unit. The mechanism for their formation is not known, however, their general structures suggest that the reaction could go through an initially formed reactive monomeric half-sandwich
1387-7003/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 7 - 7 0 0 3 ( 0 0 ) 0 0 2 1 5 - X
N.S. Hosmane et al. / Inorganic Chemistry Communications 4 (2001) 104±107
105
Scheme 1.
chlorolanthanacarborane complex which reacts further with the remaining lithiacarborane precursors in the presence of degraded fragments of the THF solvent to yield the corresponding trinuclear Ln(III) cluster [4]. The recent report on the synthesis and crystal structure of a half-sandwich samaracarborane, {1,1-(tC4 H9 OH)2 ±1-(t-C4 H9 O)±2,3-(SiMe3 )2 ±4,5-[Li(THF)Cl]closo-g5 -1-Sm-2,3-C2 B4 H4 } THF, lends support the assumption of an initially formed half-sandwich lanthanacarborane [5]. When TMEDA was substituted for THF, the courses of the reactions were quite dierent in that full-sandwiched dichlorolanthanacarboranes were the only discernable products [6]. All of the above reactions have been carried out using the ``carbons adjacent'', 2,3-C2 B4 -carboranes in which the cage carbons occupy adjacent positions on the C2 B3 bonding face of the carborane. There is another possible arrangement of the facial atoms in which the carborane cage carbons are separated by a boron atom, to give the 2,4-C2 B4 or ``carbons apart'' isomers. These have been shown to form metallacarboranes with several early transition metals, similar to those in the ``carbons adjacent'' system [1e,3]. However, neither a half-sandwich species nor a trinuclear lanthanacarborane cluster have been reported in the ``carbons apart'' C2 B4 -cage system. In order to establish a reactivity pattern in the design of the ``carbons apart'' half-sandwich lanthanacarborane species and also to investigate further the role of the coordinating solvents in the lanthanacarborane syntheses, anhydrous GdCl3 was reacted with 1 equivalent of dinatracarborane, closo-exo-5,6-
Na(THF)2 ±1-Na(THF)2 ±2,4-(SiMe3 )2 C2 B4 H4 (1) [7], in dry benzene at 0°C for 24 h. After removal of the solvents, followed by repeated washing of the residue with a n-hexane (60%)/TMEDA (30%)/THF (10%) mixture, and the subsequent removal of solvents from the ®ltrate, a pale-yellow solid was isolated. After recrystallization of this solid from dry TMEDA o-white crystals of {1,1-Cl2 [l; l0 -Na(TMEDA)]±1-(THF)±2,4(SiMe3 )2 -closo-g5 -1-Gd±2,4-C2 B4 H4 }2 (2) were obtained in 88% yield (Scheme 1). 2 A magnetic moment leff of 7.44 lB for 2 is consistent with a formal 3+ oxidation state of Gd in the complex [8]. Due to its paramagnetic nature, the NMR spectra of 2 are of no use in elucidating its solution 2
A 2.50 mmol (2.76 g) sample of dinatracarborane, closo-exo-5,6Na(THF)2 ±1-Na(THF)2 ±2,4-(SiMe3 )2 C2 B4 H4 (1) [7], was allowed to react with 2.50 mmol of anhydrous GdCl3 (0.66 g) in dry benzene (25 ml) at 0°C for 24 h, during which time the color of the solution turned to pale yellow. At this point, the heterogeneous product mixture was ®ltered through a frit in vacuo and the solvent was removed from the ®ltrate to collect a pale yellow solid. This solid was then washed repeatedly with a solvent mixture of n-hexane(60%), TMEDA (30%) and THF (10%), to collect a clear, pale-yellow ®ltrate. After slow removal of the solvents from the second ®ltrate in vacuo, and subsequent recrystallization of the resulting solid from dry TMEDA gave o-white crystals of {1,1-Cl2 [l; l0 -Na(TMEDA)]±1-(THF)-2,4(SiMe3 )2 ±closo-g5 -1-Gd-2,4-C2 B4 H4 }2 (2) in 88% yield [2.87 g, 2.19 mmol; soluble in polar and slightly soluble in non-polar organic solvents; m.p.> 240° C]. Analytical and spectroscopic data for 2: Anal. calc. for C18 H43 OB4 Si2 Cl2 GdN2 Na: C, 33.05; H, 6.63; Cl, 10.84. Found: C, 33.15; H, 6.86; Cl, 10.66. IR (cmÿ1 ; C6 D6 vs. C6 D6 ): 2593 (vs), 2285 (vs, s) [m(BH)].
106
N.S. Hosmane et al. / Inorganic Chemistry Communications 4 (2001) 104±107
Fig. 1. Perspective view of 2 with the thermal ellipsoids of the heavy atoms, excluding Si and Na, drawn at the 50% probability level and showing the selective atom numbering scheme. For clarity the SiMe3 moiety, TMEDA and THF molecules are drawn with lines. The disordered B(2) atom in the cage is shown as a sphere. All atoms with ``A'' notations are symmetry #1 equivalents of those atoms without ``A'' label. Pertinent parameters include Gd±C(1) 2.703 (13), Gd±C(3) 2.718 (13), Gd±B(2) 2.696 (16), Gd±B(4) 2.750 (14), Gd±B(5) 2.755 (16), Gd±O(THF) 2.552 (10), Gd±Cl(1) 2.658 (3), Gd±Cl(2) 2.680 (3), Gd±Cnt 2.375 (16),Gd±B(4a) 2.742 (15), Gd±B(5a) 2.699 (16), Cl(1)± Na 2.36 (7), Cl(2)±Na 2.37 (6), Na±N(31) 2.08 (5), Na±N(32) 2.09 (6), ; O±Gd±Cnt 174.5 (4), Cl(1)±Gd±Cnt 106.6 (4), Cl(2)±Gd±Cnt 106.8 A (4), Cl(1)±Gd±Cl(2) 86.79 (11), O±Gd±Cl(1) 78.5 (2), O±Gd±Cl(2) 75.1 (2), O±Gd±B(5a) 76.5 (4), O±Gd±B(4a) 74.6 (4), Cl(1)±Gd±B(4a) 138.4 (3), Cl(2)±Gd±B(4a) 115.6 (3), Cl(1)±Gd±B(5a) 107.8 (4), Cl(2)±Gd± B(5a) 144.6 (3), N(31)±Na±N(32) 89 (2) .
geometry. However, the solution IR spectrum of 2 exhibits two well-resolved terminal B±H stretches. 2 The ®ne structure of the B±H stretch has been previously observed in the IR spectra of other known closo- and commo-lanthanacarboranes and has been explained on the basis of M±H±B interactions where M is a metal other than the one in that particular complex [4±6,9]. The unambiguous structure of the title compound was determined by X-ray diraction studies 3 and is shown in Fig. 1. To the best of our knowledge, this constitutes
3 Crystal data for 2: [C18 H43 B4 Cl2 GdN2 NaOSi2 ], fw 654.10, monoclinic, P 21 =n, a 10:8619 8, b 23:3042 16, c 12:1105 8 b 93:2470 10°; V 3060:6 4 A 3 , Z 4, Dcalc: 1:420 mg/m3 , A, l 2:447 mmÿ1 . Of 13746 data collected on a Siemens SMART CCD PLATFORM diractometer (MoKa, 2h 2:07±23.26°, at 198 (2) K), 4346 re¯ections were independent and all were used for re®nement I > 2:0r I. Data were corrected for Lorentz, polarization, and absorption eects (G.M. Sheldrick, SADABS, Program for Empirical Absorption Correction of Area Detector Data, University of G ottingen, Germany, 1996). The structure was solved by heavy-atom methods and re®ned by full-matrix least-squares techniques using SHELXL 97 (G.M. Sheldrick, SHELXL, Version 5.1, Bruker Analytical X-ray Systems, Madison, WI, 1997). All non-H atoms were re®ned anisotropically. Cage-H atoms were located in the dierence Fourier maps, and methyl and methylene H atoms were calculated. The ®nal re®nement of 2 converged at R1 0.0984, wR2 0.1467, and GOF 1.370 for observed re¯ections.
the ®rst report on a half-sandwich ``carbons apart'' gadolinacarborane complex. The crystal structure of 2 shows that the gadolinacarborane is a dimer in which each Gd metal interacts exo-polyhedrally with the two basal B±H terminal units of the neighboring cage and the two Gd-bound chlorine atoms bridge the Na(TMEDA) moiety (Fig. 1) 3. The Na(TMEDA) unit was originally exo-polyhedrally bridged to two adjacent basal B±H terminal groups in the carborane precursor (1), but have migrated to the two Cl sites in the ®nal product. This migration may be due to a stronger ionic interaction of the Na with a Cl moiety than with a H±B unit or to the fact that stronger Gd±H± B bridging bonds replace the Na±H±B ones in (2). Such behavior in the formation of a number of lanthanacarborane derivatives has been observed previously [4±6]. The C2 B4 -carborane ligand in each complex unit is essentially g5 -bonded to the Gd metal with the distances ranging from 2.696 (16) to 2.755 (16), and no systematic variations consistent with a slip distortion noted. The in 2 is quite reaGd-centroid distance of 2.375 (16) A sonable for a Gd(III)-carborane complex when com found in the pared to the average value of 2.42 A structure of an anionic, ``carbons adjacent'' Gd(III)sandwiched complex, [1-Cl-1-(l-Cl)±2; 20 ; 3; 30 -(SiMe3 )4 ± 5,6-[(l-H)2 Li(TMEDA)]±4; 40 ; 50 -[(l-H)3 Li(TMEDA)]1; 10 -commo-Gd(2,3-C2 B4 H4 )2 ]ÿ [5]. In addition to the carborane ligand, two Cl atoms [Gd±Cl 2.658 (3) A and 2.680 (3) A] and a THF molecule [Gd±O 2.552 are also bound to the metal atom, as shown in (10) A] Fig. 1. With the additional interactions of the Gd metal and with the two B±H units [Gd±B(4A) 2.742 (15) A Gd±B(5A) 2.699 (16) A] of the neighboring cage, each Gd can be considered to be octahedrally coordinated by the two H±B units, two Cl atoms, the THF molecule and carborane ligand. Thus, 2 represents the ®rst halfsandwiched, dimeric ``carbons apart'' Gd(III)-carborane complex of any kind of which we are aware. It is of interest to note that the reactivity of the ``carbons apart'' C2 B4 -carborane ligands is quite dierent from that of the corresponding ``carbons adjacent'' carborane ligands. The formation of a less complicated gadolinacarborane complex suggests that the ``carbons apart'' C2 B4 -carborane ligands might be less sensitive to the nature of the solvents and hence be able to exhibit a general synthetic pattern. At present, we are not sure whether the nature of the group 1 metal cation in the precursor, 1, or the separation of the cage carbons on the open C2 B3 bonding face is responsible for the formation of such a simple lanthanacarborane product. If the ``carbons apart'' carboranes turn out to be better ligands for lanthanacarboranes, their conversion to the corresponding dialkylgadolinacarboranes would be of great interest in the study of Ziegler±Natta type ole®n polymerizations. Such studies are currently underway in our laboratories.
N.S. Hosmane et al. / Inorganic Chemistry Communications 4 (2001) 104±107
Supplementary material available Summary of crystallographic data, tables of positional and thermal parameters, bond distances, bond angles and a listing of observed and calculated structure factors (24 pages) are available from the authors on request. Acknowledgements This work was supported by grants from the National Science Foundation (CHE-9988045), the donors of the Petroleum Research Fund, administered by the American Chemical Society, and the Robert A. Welch Foundation (N-1322).
[2] [3] [4]
[5] [6] [7]
References [1] [a] U. Siriwardane, H. Zhang, N.S. Hosmane, J. Am. Chem. Soc. 112 (1990) 9637; [b] C.J. Thomas, L. Jia, H. Zhang, U. Siriwardane, J.A. Maguire, Y. Wang, K.A. Brooks, V.P. Weiss, N.S. Hosmane, Organometallics 14 (1995) 1365; [c] H. Zhang, L. Jia, N.S. Hosmane, Acta Crystallogr. Cryst. Struct. Commun. C49 (1993) 453; [d] N.S. Hosmane, Y. Wang, H. Zhang, J.A. Maguire, E. Waldh or, W. Kaim, H. Binder, R.K. Kremer, Organometallics 13 (1994) 4156;
[8]
[9]
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[e] N.S. Hosmane, Y. Wang, H. Zhang, K.-J. Lu, J.A. Maguire, T.G. Gray, K.A. Brooks, E. Waldh or, W. Kaim, R.K. Kremer, Organometallics 16 (1997) 1365; [f] N.S. Hosmane, H. Zhang, L. Jia, T.J. Colacot, J.A. Maguire, X. Wang, S.N. Hosmane, K.A. Brooks, Organometallics 18 (1999) 516. A.R. Oki, H. Zhang, N.S. Hosmane, Organometallics 10 (1991) 3964. N.S. Hosmane, D. Zhu, H. Zhang, A.R. Oki, J.A. Maguire, Organometallics 17 (1998) 3196. [a] N.S. Hosmane, Y. Wang, A.R. Oki, H. Zhang, J.A. Maguire, Organometallics 15 (1996) 626; [b] C. Zheng, N.S. Hosmane, H. Zhang, D. Zhu, J.A. Maguire, Internet J. Chem. 2 (1999) 10, URL: http://www.ijc.com/ articles/1999v2/10/. N.S. Hosmane, A.R. Oki, H. Zhang, Inorg. Chem. Commun. 1 (1998) 101. N.S. Hosmane, Y. Wang, H. Zhang, J.A. Maguire, M. McInnis, T.G. Gray, J.D. Collins, R.K. Kremer, H. Binder, E. Waldh or, W. Kaim, Organometallics 15 (1996) 1006. N.S. Hosmane, L. Jia, H. Zhang, J.W. Bausch, G.K.S. Prakash, R.E. Williams, T.P. Onak, Inorg. Chem. 30 (1991) 3793. The temperature-dependent magnetic susceptibility of 2 was determined using the Faraday balance, as described in J.C. Dobson, J.H. Helms, P. Doppelt, B.P. Sullivan, W.E. Hat®eld, T.J. Meyer, Inorg. Chem. 28 (1989) 2200; The room temperature eective magnetic moment of 7.44 lB for 2 is well within the reported range observed for other Gd(III) pcomplexes.J.M. Birmingham, G. Wilkinson, J. Am. Chem. Soc. 78 (1956) 42, see also [5]. [a] M.J. Manning, C.B. Knobler, M.F. Hawthorne, J. Am. Chem. Soc. 110 (1988) 4458; [b] M.J. Manning, C.B. Knobler, R. Khattar, M.F. Hawthorne, Inorg. Chem. 30 (1991) 2009.
www.elsevier.nl/locate/inoche
The ®rst dimeric half-sandwich gadolinacarborane of the ``carbons apart'' C2B4-carborane ligand system Narayan S. Hosmane a
a,*
, Shoujian Li
a,1
, Chong Zheng a, John A. Maguire
b
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA b Department of Chemistry, Southern Methodist University, Dallas, TX 75275, USA Received 17 October 2000; accepted 10 November 2000
Dedicated to Professor Sheldon G. Shore of The Ohio State University on the occasion of his 70th birthday
Abstract The reaction between the THF solvated ``carbons apart'' dinatracarborane, closo-exo-4,5-Na(THF)2 ±1-Na(THF)2 ±2,4(SiMe3 )2 C2 B4 H4 (1), and anhydrous GdCl3 in a 1:1 molar ratio in dry benzene at 0°C, followed by extraction and crystallization of the product from an anhydrous n-hexane/TMEDA/THF solution mixture resulted in the isolation of o-white crystals of the dimeric half-sandwich dichlorogadolinacarborane, {1,1-Cl2 [l; l0 -Na(TMEDA)]±1-(THF)-2,4-(SiMe3 )2 ±closo-g5 -1-Gd-2,4-C2 B4 H4 }2 (2) in 88% yield. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Carborane; Gadolinacarborane; Half-sandwich complex and metallacarborane
Recently, we have reported the syntheses, properties and structures of several titanium(IV), zirconium(IV) and hafnium(IV) bent-sandwich complexes of C cage trimethylsilyl-substituted C2 B4 -carborane ligands [1]. The X-ray crystal structures of these compounds show that in each complex the metal atom bonds to a Cl atom, a THF molecule and two carborane ligands resulting in a distorted tetrahedral geometry [1]. A similar metal geometry was found in the full-sandwiched yttracarborane complex despite the formal 3+ metal oxidation state [2]. The monoanionic chlorozircona- and chlorohafnacarboranes each contain a Li(THF)n (n 1 or 2) moiety that bridges the two carboranes and is oriented opposite to the metal bound Cl and THF ligands. In the dianionic chloroyttracarborane there is an additional Li (THF)4 ion that is well separated from the carborane complex [1,2]. This highlights one of the limitations in the use of the f-block metallacarboranes: because of the trivalent nature of the metal the carborane sandwich complexes bear signi®cant negative charges which can result in zwitterionic clusters and retard any reactions *
Corresponding author. Tel.: +1-815-753-3556; fax: +1-815-7534802. E-mail address: [email protected] (N.S. Hosmane). 1 On leave from Sichuan University, People's Republic of China.
involving the addition of anionic groups to the metal centers. Therefore, there is little possibility of ligand exchange reactions about the metal center after the addition of reactive anionic ligands such as alkyls. A possible solution to this problem would be to design lower charged, less sterically crowded half-sandwich complexes. However, the syntheses of such complexes are not simple; the reaction of 2,3-(SiMe3 )2 ±2,3-C2 B4 H5 in 1:1 molar ratio with Y(CH2 SiMe3 )3 , made in situ by the reaction of YCl3 and Me3 SiCH2 MgCl, resulted in complex mixtures of products and no discrete halfsandwich, closo-yttracarborane, could be isolated [3]. The syntheses of the lanthanacarboranes also shows unusual complexity. The reaction of the THF-solvated dilithium compound of the [2,3-(SiMe3 )2 C2 B4 H4 ]2ÿ dianion with anhydrous LnCl3 (Ln Nd, Sm, Gd, Tb, Dy, Ho) in a molar ratio of 2:1 in dry benzene and THF produced unusual trinuclear Ln(III)-carboranes of the form, [g5 -1-Ln±2,3-(SiMe3 )2 ±2,3-C2 B4 H4 ]3 [(l2 -1-Li±2,3(SiMe3 )2 ±2,3-C2 B4 H4 )3 (l3 -OMe)]-[l2 -Li(THF)]3 (l3 -O) [4]. These are clusters composed of three half-sandwich lithiacarboranes and lanthanacarboranes arranged about a central O atom and a MeO unit. The mechanism for their formation is not known, however, their general structures suggest that the reaction could go through an initially formed reactive monomeric half-sandwich
1387-7003/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 7 - 7 0 0 3 ( 0 0 ) 0 0 2 1 5 - X
N.S. Hosmane et al. / Inorganic Chemistry Communications 4 (2001) 104±107
105
Scheme 1.
chlorolanthanacarborane complex which reacts further with the remaining lithiacarborane precursors in the presence of degraded fragments of the THF solvent to yield the corresponding trinuclear Ln(III) cluster [4]. The recent report on the synthesis and crystal structure of a half-sandwich samaracarborane, {1,1-(tC4 H9 OH)2 ±1-(t-C4 H9 O)±2,3-(SiMe3 )2 ±4,5-[Li(THF)Cl]closo-g5 -1-Sm-2,3-C2 B4 H4 } THF, lends support the assumption of an initially formed half-sandwich lanthanacarborane [5]. When TMEDA was substituted for THF, the courses of the reactions were quite dierent in that full-sandwiched dichlorolanthanacarboranes were the only discernable products [6]. All of the above reactions have been carried out using the ``carbons adjacent'', 2,3-C2 B4 -carboranes in which the cage carbons occupy adjacent positions on the C2 B3 bonding face of the carborane. There is another possible arrangement of the facial atoms in which the carborane cage carbons are separated by a boron atom, to give the 2,4-C2 B4 or ``carbons apart'' isomers. These have been shown to form metallacarboranes with several early transition metals, similar to those in the ``carbons adjacent'' system [1e,3]. However, neither a half-sandwich species nor a trinuclear lanthanacarborane cluster have been reported in the ``carbons apart'' C2 B4 -cage system. In order to establish a reactivity pattern in the design of the ``carbons apart'' half-sandwich lanthanacarborane species and also to investigate further the role of the coordinating solvents in the lanthanacarborane syntheses, anhydrous GdCl3 was reacted with 1 equivalent of dinatracarborane, closo-exo-5,6-
Na(THF)2 ±1-Na(THF)2 ±2,4-(SiMe3 )2 C2 B4 H4 (1) [7], in dry benzene at 0°C for 24 h. After removal of the solvents, followed by repeated washing of the residue with a n-hexane (60%)/TMEDA (30%)/THF (10%) mixture, and the subsequent removal of solvents from the ®ltrate, a pale-yellow solid was isolated. After recrystallization of this solid from dry TMEDA o-white crystals of {1,1-Cl2 [l; l0 -Na(TMEDA)]±1-(THF)±2,4(SiMe3 )2 -closo-g5 -1-Gd±2,4-C2 B4 H4 }2 (2) were obtained in 88% yield (Scheme 1). 2 A magnetic moment leff of 7.44 lB for 2 is consistent with a formal 3+ oxidation state of Gd in the complex [8]. Due to its paramagnetic nature, the NMR spectra of 2 are of no use in elucidating its solution 2
A 2.50 mmol (2.76 g) sample of dinatracarborane, closo-exo-5,6Na(THF)2 ±1-Na(THF)2 ±2,4-(SiMe3 )2 C2 B4 H4 (1) [7], was allowed to react with 2.50 mmol of anhydrous GdCl3 (0.66 g) in dry benzene (25 ml) at 0°C for 24 h, during which time the color of the solution turned to pale yellow. At this point, the heterogeneous product mixture was ®ltered through a frit in vacuo and the solvent was removed from the ®ltrate to collect a pale yellow solid. This solid was then washed repeatedly with a solvent mixture of n-hexane(60%), TMEDA (30%) and THF (10%), to collect a clear, pale-yellow ®ltrate. After slow removal of the solvents from the second ®ltrate in vacuo, and subsequent recrystallization of the resulting solid from dry TMEDA gave o-white crystals of {1,1-Cl2 [l; l0 -Na(TMEDA)]±1-(THF)-2,4(SiMe3 )2 ±closo-g5 -1-Gd-2,4-C2 B4 H4 }2 (2) in 88% yield [2.87 g, 2.19 mmol; soluble in polar and slightly soluble in non-polar organic solvents; m.p.> 240° C]. Analytical and spectroscopic data for 2: Anal. calc. for C18 H43 OB4 Si2 Cl2 GdN2 Na: C, 33.05; H, 6.63; Cl, 10.84. Found: C, 33.15; H, 6.86; Cl, 10.66. IR (cmÿ1 ; C6 D6 vs. C6 D6 ): 2593 (vs), 2285 (vs, s) [m(BH)].
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N.S. Hosmane et al. / Inorganic Chemistry Communications 4 (2001) 104±107
Fig. 1. Perspective view of 2 with the thermal ellipsoids of the heavy atoms, excluding Si and Na, drawn at the 50% probability level and showing the selective atom numbering scheme. For clarity the SiMe3 moiety, TMEDA and THF molecules are drawn with lines. The disordered B(2) atom in the cage is shown as a sphere. All atoms with ``A'' notations are symmetry #1 equivalents of those atoms without ``A'' label. Pertinent parameters include Gd±C(1) 2.703 (13), Gd±C(3) 2.718 (13), Gd±B(2) 2.696 (16), Gd±B(4) 2.750 (14), Gd±B(5) 2.755 (16), Gd±O(THF) 2.552 (10), Gd±Cl(1) 2.658 (3), Gd±Cl(2) 2.680 (3), Gd±Cnt 2.375 (16),Gd±B(4a) 2.742 (15), Gd±B(5a) 2.699 (16), Cl(1)± Na 2.36 (7), Cl(2)±Na 2.37 (6), Na±N(31) 2.08 (5), Na±N(32) 2.09 (6), ; O±Gd±Cnt 174.5 (4), Cl(1)±Gd±Cnt 106.6 (4), Cl(2)±Gd±Cnt 106.8 A (4), Cl(1)±Gd±Cl(2) 86.79 (11), O±Gd±Cl(1) 78.5 (2), O±Gd±Cl(2) 75.1 (2), O±Gd±B(5a) 76.5 (4), O±Gd±B(4a) 74.6 (4), Cl(1)±Gd±B(4a) 138.4 (3), Cl(2)±Gd±B(4a) 115.6 (3), Cl(1)±Gd±B(5a) 107.8 (4), Cl(2)±Gd± B(5a) 144.6 (3), N(31)±Na±N(32) 89 (2) .
geometry. However, the solution IR spectrum of 2 exhibits two well-resolved terminal B±H stretches. 2 The ®ne structure of the B±H stretch has been previously observed in the IR spectra of other known closo- and commo-lanthanacarboranes and has been explained on the basis of M±H±B interactions where M is a metal other than the one in that particular complex [4±6,9]. The unambiguous structure of the title compound was determined by X-ray diraction studies 3 and is shown in Fig. 1. To the best of our knowledge, this constitutes
3 Crystal data for 2: [C18 H43 B4 Cl2 GdN2 NaOSi2 ], fw 654.10, monoclinic, P 21 =n, a 10:8619 8, b 23:3042 16, c 12:1105 8 b 93:2470 10°; V 3060:6 4 A 3 , Z 4, Dcalc: 1:420 mg/m3 , A, l 2:447 mmÿ1 . Of 13746 data collected on a Siemens SMART CCD PLATFORM diractometer (MoKa, 2h 2:07±23.26°, at 198 (2) K), 4346 re¯ections were independent and all were used for re®nement I > 2:0r I. Data were corrected for Lorentz, polarization, and absorption eects (G.M. Sheldrick, SADABS, Program for Empirical Absorption Correction of Area Detector Data, University of G ottingen, Germany, 1996). The structure was solved by heavy-atom methods and re®ned by full-matrix least-squares techniques using SHELXL 97 (G.M. Sheldrick, SHELXL, Version 5.1, Bruker Analytical X-ray Systems, Madison, WI, 1997). All non-H atoms were re®ned anisotropically. Cage-H atoms were located in the dierence Fourier maps, and methyl and methylene H atoms were calculated. The ®nal re®nement of 2 converged at R1 0.0984, wR2 0.1467, and GOF 1.370 for observed re¯ections.
the ®rst report on a half-sandwich ``carbons apart'' gadolinacarborane complex. The crystal structure of 2 shows that the gadolinacarborane is a dimer in which each Gd metal interacts exo-polyhedrally with the two basal B±H terminal units of the neighboring cage and the two Gd-bound chlorine atoms bridge the Na(TMEDA) moiety (Fig. 1) 3. The Na(TMEDA) unit was originally exo-polyhedrally bridged to two adjacent basal B±H terminal groups in the carborane precursor (1), but have migrated to the two Cl sites in the ®nal product. This migration may be due to a stronger ionic interaction of the Na with a Cl moiety than with a H±B unit or to the fact that stronger Gd±H± B bridging bonds replace the Na±H±B ones in (2). Such behavior in the formation of a number of lanthanacarborane derivatives has been observed previously [4±6]. The C2 B4 -carborane ligand in each complex unit is essentially g5 -bonded to the Gd metal with the distances ranging from 2.696 (16) to 2.755 (16), and no systematic variations consistent with a slip distortion noted. The in 2 is quite reaGd-centroid distance of 2.375 (16) A sonable for a Gd(III)-carborane complex when com found in the pared to the average value of 2.42 A structure of an anionic, ``carbons adjacent'' Gd(III)sandwiched complex, [1-Cl-1-(l-Cl)±2; 20 ; 3; 30 -(SiMe3 )4 ± 5,6-[(l-H)2 Li(TMEDA)]±4; 40 ; 50 -[(l-H)3 Li(TMEDA)]1; 10 -commo-Gd(2,3-C2 B4 H4 )2 ]ÿ [5]. In addition to the carborane ligand, two Cl atoms [Gd±Cl 2.658 (3) A and 2.680 (3) A] and a THF molecule [Gd±O 2.552 are also bound to the metal atom, as shown in (10) A] Fig. 1. With the additional interactions of the Gd metal and with the two B±H units [Gd±B(4A) 2.742 (15) A Gd±B(5A) 2.699 (16) A] of the neighboring cage, each Gd can be considered to be octahedrally coordinated by the two H±B units, two Cl atoms, the THF molecule and carborane ligand. Thus, 2 represents the ®rst halfsandwiched, dimeric ``carbons apart'' Gd(III)-carborane complex of any kind of which we are aware. It is of interest to note that the reactivity of the ``carbons apart'' C2 B4 -carborane ligands is quite dierent from that of the corresponding ``carbons adjacent'' carborane ligands. The formation of a less complicated gadolinacarborane complex suggests that the ``carbons apart'' C2 B4 -carborane ligands might be less sensitive to the nature of the solvents and hence be able to exhibit a general synthetic pattern. At present, we are not sure whether the nature of the group 1 metal cation in the precursor, 1, or the separation of the cage carbons on the open C2 B3 bonding face is responsible for the formation of such a simple lanthanacarborane product. If the ``carbons apart'' carboranes turn out to be better ligands for lanthanacarboranes, their conversion to the corresponding dialkylgadolinacarboranes would be of great interest in the study of Ziegler±Natta type ole®n polymerizations. Such studies are currently underway in our laboratories.
N.S. Hosmane et al. / Inorganic Chemistry Communications 4 (2001) 104±107
Supplementary material available Summary of crystallographic data, tables of positional and thermal parameters, bond distances, bond angles and a listing of observed and calculated structure factors (24 pages) are available from the authors on request. Acknowledgements This work was supported by grants from the National Science Foundation (CHE-9988045), the donors of the Petroleum Research Fund, administered by the American Chemical Society, and the Robert A. Welch Foundation (N-1322).
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[e] N.S. Hosmane, Y. Wang, H. Zhang, K.-J. Lu, J.A. Maguire, T.G. Gray, K.A. Brooks, E. Waldh or, W. Kaim, R.K. Kremer, Organometallics 16 (1997) 1365; [f] N.S. Hosmane, H. Zhang, L. Jia, T.J. Colacot, J.A. Maguire, X. Wang, S.N. Hosmane, K.A. Brooks, Organometallics 18 (1999) 516. A.R. Oki, H. Zhang, N.S. Hosmane, Organometallics 10 (1991) 3964. N.S. Hosmane, D. Zhu, H. Zhang, A.R. Oki, J.A. Maguire, Organometallics 17 (1998) 3196. [a] N.S. Hosmane, Y. Wang, A.R. Oki, H. Zhang, J.A. Maguire, Organometallics 15 (1996) 626; [b] C. Zheng, N.S. Hosmane, H. Zhang, D. Zhu, J.A. Maguire, Internet J. Chem. 2 (1999) 10, URL: http://www.ijc.com/ articles/1999v2/10/. N.S. Hosmane, A.R. Oki, H. Zhang, Inorg. Chem. Commun. 1 (1998) 101. N.S. Hosmane, Y. Wang, H. Zhang, J.A. Maguire, M. McInnis, T.G. Gray, J.D. Collins, R.K. Kremer, H. Binder, E. Waldh or, W. Kaim, Organometallics 15 (1996) 1006. N.S. Hosmane, L. Jia, H. Zhang, J.W. Bausch, G.K.S. Prakash, R.E. Williams, T.P. Onak, Inorg. Chem. 30 (1991) 3793. The temperature-dependent magnetic susceptibility of 2 was determined using the Faraday balance, as described in J.C. Dobson, J.H. Helms, P. Doppelt, B.P. Sullivan, W.E. Hat®eld, T.J. Meyer, Inorg. Chem. 28 (1989) 2200; The room temperature eective magnetic moment of 7.44 lB for 2 is well within the reported range observed for other Gd(III) pcomplexes.J.M. Birmingham, G. Wilkinson, J. Am. Chem. Soc. 78 (1956) 42, see also [5]. [a] M.J. Manning, C.B. Knobler, M.F. Hawthorne, J. Am. Chem. Soc. 110 (1988) 4458; [b] M.J. Manning, C.B. Knobler, R. Khattar, M.F. Hawthorne, Inorg. Chem. 30 (1991) 2009.