Synthesis and Structure of Rare-Earth-Metal Dicarbollide Complexes

Feb 11, 2011 - Manning , M. J.; Knobler , C. B.; Khattar , R.; Hawthorne , M. F. Inorg. Chem. 1991, 30, 2009. [ACS Full Text ACS Full Text ], [CAS]. 1...
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Organometallics 2011, 30, 1122–1129 DOI: 10.1021/om1011243

Synthesis and Structure of Rare-Earth-Metal Dicarbollide Complexes with an Imidazolin-2-iminato Ligand Featuring Very Short Metal-Nitrogen Bonds Alexandra G. Trambitas,† Jingying Yang,‡ Daniel Melcher,† Constantin G. Daniliuc,† Peter G. Jones,† Zuowei Xie,*,‡ and Matthias Tamm*,† †

Institut f€ ur Anorganische und Analytische Chemie, Technische Universit€ at Braunschweig, Hagenring 30, 38106 Braunschweig, Germany, and ‡Department of Chemistry, The Chinese University of Hong Kong, Shatin NT, Hong Kong, People’s Republic of China Received November 30, 2010

Several rare-earth-metal complexes involving both imidazolin-2-iminato and dicarbollide ligands were prepared by the reaction of imidazolin-2-iminato rare-earth-metal dichlorides [(ImArN)MCl2(THF)3] with 1 equiv of Na2[C2B9H11] in THF to afford the complexes [(ImArN)M(η5-C2B9H11)(THF)2] (2a, M = Sc; 2b, M = Y; 2c, M = Lu) in high yields. Treatment of [(ImArN)M(CH2SiMe3)2(THF)n] with 1 equiv of the zwitterionic [nido-(Me2NHCH2CH2)C2B9H11] in THF afforded the donor-functionalized dicarbollide complexes [(ImArN)M{σ:η5-(Me2NCH2CH2)C2B9H10}(THF)] (4a, M = Sc; 4b, M = Y; 4c, M = Lu) in good yields. In a similar manner, complexes [(ImArN)Y{σ:σ:η5-(Me2NCH2)2C2B9H9}(THF)] (5) and [(ImArN)Y{σ:σ:η5-(Me2NCH2CH2)(MeOCH2CH2)C2B9H9}] (6) with two tethered donor moieties were synthesized. All complexes were characterized by various spectroscopic techniques and elemental analyses. Their structures were further confirmed by single-crystal X-ray analyses, revealing that the metal-nitrogen bonds in these complexes are either the shortest or among the shortest ever reported for scandium-, yttrium-, or lutetium-nitrogen systems.

Introduction In recent years, considerable efforts have been devoted to the isolation of rare-earth-metal complexes containing terminal imido ligands.1 In most cases, however, the high polarity of the metal-nitrogen bond prevents the formation of complexes containing MdNR or MtNR moieties, since the imido group is usually found to bind in a bridging or capping fashion.2-4 The first evidence for the existence of a transient scandium-imido species was delivered by Mindiola and co-workers, who managed to generate and study the *To whom correspondence should be addressed. E-mail: zxie@ cuhk.edu.hk (Z.X.); [email protected] (M.T.). (1) Giesbrecht, G. R.; Gordon, J. C. Dalton Trans. 2004, 2387. (2) (a) Trifonov, A. A.; Bochkarev, M. N.; Schumann, H.; Loebel, J. Angew. Chem., Int. Ed. Engl. 1991, 30, 1149. (b) Evans, W. J.; Ansari, M. A.; Ziller, J. W.; Khan, S. I. Inorg. Chem. 1996, 35, 5435. (c) Xie, Z.; Wang, S.; Yang, Q.; Mak, T. C. W. Organometallics 1999, 18, 1578. (d) Wang, S; Yang, Q.; Mak, T. C. W.; Xie, Z. Organometallics 1999, 18, 5511. (e) Gordon, J. C.; Giesbrecht, G. R.; Clark, D. L.; Hay, P. J.; Keogh, D. W.; Poli, R.; Scott, B. L.; Watkin, J. G. Organometallics 2002, 21, 4726. (f) Cui, D.; Tardif, O.; Hou, Z. J. Am. Chem. Soc. 2004, 126, 1312. (3) Chan, H.-S.; Li, H. W.; Xie, Z. Chem. Commun. 2002, 652. The dinuclear ytterbium complex {(ArN)2Yb(μ-NAr)}2{[Li2(THF)][Na(THF)]}2 reported in this reference could be regarded as a lanthanide complex containing terminal 2,6-diisopropylphenylimido ligands (ArN), if the bridging lithium and sodium cations are ignored. (4) (a) Beetstra, D. J.; Meetsma, A.; Hessen, B.; Teuben, J. H. Organometallics 2003, 22, 4372. (b) Knight, L. K.; Piers, W. E.; FleuratLessard, P.; Parvez, M.; McDonald, R. Organometallics 2004, 23, 2087. (c) Knight, L. K.; Piers, W. E.; McDonald, R. Organometallics 2006, 25, 3289. pubs.acs.org/Organometallics

Published on Web 02/11/2011

reactivity of the mononuclear complex [(PNP)Sc(NAr)] (Ar = 2,6-diisopropylphenyl) containing the PNP pincer ligand bis(2-(diisopropylphosphino)-4-methylphenyl)amide.5 Full stabilization and structural characterization of the first rare-earth-metal terminal imido complex was achieved by Chen and co-workers by use of an ancillary amino-functionalized β-diketimido ligand (NNN), and treatment of the amido-methyl precursor [(NNN)Sc(NHAr)(CH3)] with 4(dimethylamino)pyridine (DMAP) afforded the complex [(NNN)Sc(NAr)(DMAP)] by methane elimination. Structural characterization revealed an exceptionally short scandiumnitrogen bond of 1.881(5) A˚, and theoretical calculations indicate the presence of two orthogonal (p-d)π bonds, in agreement with the dianionic imido ligand acting as a 2σ,4πelectron donor toward the scandium ion.6 This resembles the situation found for rare-earth-metal complexes containing imidazolin-2-iminato ligands such as I (ImArN),7 in which the ability of the imidazole ring to stabilize a positive charge efficiently (resonance structure IB) leads to highly basic ligands with a strong electron donating ability toward early transition metals or metals in a higher oxidation state (Scheme 1).8,9 Accordingly, these ligands can be regarded as monoanionic (5) Scott, J.; Basuli, F.; Fout, A. R.; Huffman, J. C.; Mindiola, D. J. Angew. Chem., Int. Ed. 2008, 47, 8502. (6) Lu, E.; Li, Y.; Chen, Y. Chem. Commun. 2010, 46, 4469. (7) Trambitas, A. G.; Panda, T. K.; Tamm, M. Z. Anorg. Allg. Chem. 2010, 636, 2156. (8) Tamm, M.; Petrovic, D.; Randoll, S.; Beer, S.; Bannenberg, T.; Jones, P. G.; Grunenberg, J. Org. Biomol. Chem. 2007, 5, 523. r 2011 American Chemical Society

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Scheme 1. Mesomeric Structures for Imidazolin-2-iminato Ligands I and Resulting Rare-Earth-Metal Cyclooctatetraenyl Complexes II

Figure 1. nido-C2B9 systems for the preparation of imidazolin2-iminato rare-earth-metal complexes.

imido-like ligands, and the resulting rare-earth-metal complexes, e. g. cyclooctatetraenyl (COT) complexes of type II,10,11 might serve as models for mononuclear rare-earth-metal imido complexes. Indeed, a strong metal-nitrogen interaction was evidenced by the observation of very short metal-nitrogen bonds,10-13 and it could be demonstrated that the reactivity along the metal-nitrogen bond in the scandium complex [(η8C8H8)Sc(NImAr)(THF)] (II, M=Sc, n=1) is similar to that of isolobal “pogo-stick” titanium imido complexes of the type [(η8-C8H8)TidNR)].11,14 In the complexes of type II, the dinegative 10-electron C8H82- (COT) ligand is involved in a δ interaction with the metal atoms,10 which should have an impact on the M-N π bond, since significant mixing of COT and ImArN orbitals was observed for [(ImArN)Sc(η8-C8H8)(THF)].11 If the C8H82ligand were replaced by dinegative 6-electron dicarbollyl (9) (a) Tamm, M.; Randoll, S.; Bannenberg, T.; Herdtweck, E. Chem. Commun. 2004, 876. (b) Tamm, M.; Beer, S.; Herdtweck, E. Z. Naturforsch. 2004, 59b, 1497. (c) Tamm, M.; Randoll, S.; Herdtweck, E.; Kleigrewe, N.; Kehr, G.; Erker, G.; Rieger, B. Dalton Trans. 2006, 459. (d) Beer, S.; Hrib, C. G.; Jones, P. G.; Brandhorst, K.; Grunenberg, J.; Tamm, M. Angew. Chem. 2007, 119, 9047; Angew. Chem., Int. Ed. 2007, 46, 8890. (e) Beer, S.; Brandhorst, K.; Grunenberg, J.; Hrib, C. G.; Jones, P. G.; Tamm, M. Org. Lett. 2008, 10, 981. (f) Stelzig, S. H.; Tamm, M.; Waymouth, R. M. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 6064. (g) Beer, S.; Brandhorst, K.; Hrib, C. G.; Wu, X.; Haberlag, B.; Grunenberg, J.; Jones, P. G.; Tamm, M. Organometallics 2009, 28, 1534. (h) Sharma, M.; Botoshanskii, M.; Bannenberg, T.; Tamm, M.; Eisen, M. S. C. R. Chim. 2010, 13, 767. (i) Haberlag, B.; Wu, X.; Brandhorst, K.; Grunenberg, J.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Chem. Eur. J. 2010, 16, 8868. (10) Panda, T. K.; Randoll, S.; Hrib, C. G.; Jones, P. G.; Bannenberg, T.; Tamm, M. Chem. Commun. 2007, 5007. (11) Panda, T. K.; Trambitas, A. G.; Bannenberg, T.; Hrib, C. G.; Randoll, S.; Jones, P. G.; Tamm, M. Inorg. Chem. 2009, 48, 5462. (12) Panda, T. K.; Hrib, C. G.; Jones, P. G.; Tamm, M. J. Organomet. Chem. 2010, 695, 2768. (13) Trambitas, A. G.; Panda, T. K.; Bannenberg, T.; Hrib, C. G.; Daniliuc, C. G.; Jones, P. G.; Jenter, J.; Roesky, P. W.; Tamm, M. Inorg. Chem. 2010, 49, 2435. (14) (a) Dunn, S. C.; Hazari, N.; Jones, N. M.; Moody, A. G.; Blake, A. J.; Cowley, A. R.; Green, J. C.; Mountford, P. Chem. Eur. J. 2005, 11, 2111. (b) Dunn, S. C.; Hazari, N.; Cowley, A. R.; Green, J. C.; Mountford, P. Organometallics 2006, 25, 1755. (15) (a) Hawthorne, M. F.; Young, D. C.; Wegner, P. A. J. Am. Chem. Soc. 1965, 87, 1818. (b) Hawthorne, F. M.; Dunks, G. B. Science 1972, 178, 462. (c) Hawthorne, M. F.; Young, D. C.; Andrews, T. D.; Howe, D. V.; Pilling, R. L.; Pitts, A. D.; Reintjes, M.; Warren, L. F., Jr.; Wegner, P. A. J. Am. Chem. Soc. 1968, 90, 879. (16) Manning, M. J.; Knobler, C. B.; Khattar, R.; Hawthorne, M. F. Inorg. Chem. 1991, 30, 2009. (17) Bazan, G. C.; Schaefer, W. P.; Bercaw, J. E. Organometallics 1993, 27, 2126. (18) (a) Saxena, A. K.; Hosmane, N. S. Chem. Rev. 1993, 93, 1081. (b) Hosmane, N. S. Pure Appl. Chem. 2003, 75, 1219. (c) Hosmane, N. S.; Maguire, J. A. Eur. J. Inorg. Chem. 2003, 3989. (19) (a) Xie, Z.; Liu, Z.; Chiu, K.-Y.; Xue, F.; Mak, T.C. W. Organometallics 1997, 16, 2460. (b) Chiu, K.; Zhang, Z.; Mak, T. C. W.; Xie, Z. J. Organomet. Chem. 2000, 614, 107.

Scheme 2. Synthesis of the Dicarbollide Complexes 2a-c via the Salt Metathesis Route

ligands as shown in Figure 1,15-20 metal-dicarbollyl interactions relatively weaker than metal-COT interactions would be expected, leading to stronger metal-nitrogen interactions in the resultant imidazolin-2-iminato rare-earth-metal dicarbollide complexes. To test this assumption, we report herein on the preparation and structural characterization of imidazolin-2iminato complexes containing the C2B9H112- dicarbollyl ligand present in III. We also used donor-functionalized dicarbollyl ligands derived from the zwitterions IV-VI;21,22 these have been successfully employed in both rare-earth- and early-transitionmetal chemistry.23,24

Results and Discussion Preparation and Structural Characterization of Imidazolin2-iminato Rare-Earth-Metal Complexes Containing the Dicarbollide Ligand C2B9H112-. The sodium salt Na2[C2B9H11] (III) can be conveniently prepared from the ammonium salt [Me3NH][C2B9H12] by treatment with 2 equiv of sodium hydride (NaH).15c A salt metathesis reaction between III and the dichlorides 1a-c at 60 °C in THF solution furnished the dicarbollide complexes [(ImArN)M(η5-C2B9H11)(THF)2] (2a, M=Sc; 2b, M=Y; 2c, M=Lu) in high yields as white solids after extraction with toluene (Scheme 2). The compounds readily dissolve in polar organic solvents such as THF and pyridine but are insoluble in toluene or n-hexane. The 1H NMR spectra of 2a-c exhibit two doublet resonances, as expected for one set of diastereotopic isopropyl (20) (a) Xie, Z. Coord. Chem. Rev. 2002, 231, 23. (b) Xie, Z. Acc. Chem. Res. 2003, 36, 1. (21) Cheung, M.-S.; Chan, H.-S.; Xie, Z. Dalton Trans. 2005, 2375. (22) (a) Lee, Y.-J.; Lee, J.-D.; Ko, J.; Kimb, S.-H.; Kang, S. O. Chem. Commun. 2003, 1364. (b) Lee, J.-D.; Kim, H.-Y.; Han, W.-S.; Kang, S. O. Organometallics 2010, 29, 2348. (23) Cheung, M.-S.; Chan, H.-S.; Xie, Z. Organometallics 2005, 24, 4207. (24) (a) Shen, H.; Chan, H.-S.; Xie, Z. Organometallics 2006, 25, 5515. (b) Shen, H.; Chan, H.-S.; Xie, Z. Organometallics 2007, 26, 2694. (c) Shen, H.; Xie, Z. Organometallics 2008, 27, 2685. (d) Shen, H.; Xie, Z. J. Organomet. Chem. 2009, 694, 1652. (e) Shen, H.; Xie, Z. J. Am. Chem. Soc. 2010, 132, 11473.

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Trambitas et al. Scheme 3. Preparation of Dicarbollide Complexes 4a-c via the Acid-Base Route

Figure 2. ORTEP diagram of 2b with thermal displacement parameters drawn at the 50% probability level. Table 1. Selected Bond Lengths (A˚) and Angles (deg) in 2a,b 2a (M = Sc)

2b (M = Y)

M-N1 M-O1 M-O2 M-C28 M-C29 M-B1 M-B2 M-B3

1.9466(12) 2.1963(11) 2.1854(11) 2.5021(15) 2.4967(15) 2.4821(18) 2.4991(18) 2.4782(18)

2.0829(14) 2.3319(12) 2.318(12) 2.6564(18) 2.6461(19) 2.604(2) 2.631(2) 2.621(2)

M-N1-C1 O1-M-O2

172.45(10) 82.06(4)

175.11(13) 81.93(5)

CH3 groups, indicating that rotation around the CN-metal axes is fast on the NMR time scale. Introduction of the dicarbollide ligand induces a pronounced low-field shift of the NCH resonances in comparison with the resonances observed for the dichlorides 1a-c.11 The BH hydrogen atoms give rise to broad, unresolved signals in the range between -2.5 and -3.5 ppm, whereas the resonances for the two cage CH hydrogen atoms in 2a-c are found as broad singlets at 1.47, 1.60, and 1.49 ppm, respectively. This assignment is backed up by two-dimensional 1H-13C HSQC experiments, which result in a correlation of these signals with the corresponding 13C NMR resonances for the cage CH carbon atoms at 42.4, 42.5, and 42.7 ppm. The 11B NMR spectra of all three complexes exhibit six resonances in a 2:2:1:2:1:1 ratio, in agreement with the data reported for related compounds.16-19 The solid-state structures of complexes 2a,b were determined by X-ray diffraction analyses; they are isostructural and crystallize in the space group P21/c. In addition to the C2B9H112- and ImArN ligands, the coordination spheres at the metal atoms (Sc and Y) are completed by two THF ligands to give three-legged piano-stool geometries (Figure 2). As expected,16-19 the dicarbollide ligands are η5-bound through the pentagonal C2B3 bonding face of the carborane, while the imidazolin-2-iminato ligands coordinate in an almost linear fashion (Sc-N1-C1 = 172.45(10)°, Y-N1C1=175.11(13)°) and form very short metal-nitrogen bonds of 1.9466(12) A˚ (Sc-N1) and 2.0829(14) A˚ (Y-N1) (Table 1), which are considerably shorter than the corresponding bond lengths in the COT complexes of type II: viz., Sc-N=1.982(2)/ 1.965(2) A˚ for two independent molecules of [(ImArN)Sc(η8C8H8)(THF)] and Y-N=2.163(2) A˚ in [(ImArN)Y(η8-C8H8)(THF)2].11 Sc-N distances smaller than that in 2a are only

seen in 4a (vide infra), in the AlMe3 adduct of Mindiola’s scandium-imido complex (1.9366(14) A˚), and in Chen’s “true” terminal scandium-imido complex (1.881(5) A˚) (vide supra).5,6 In contrast, the Y-N bond in 2b represents the shortest ever observed for yttrium-nitrogen systems, and the previous shortest bond length of 2.116(6) A˚ was found in a tetranuclear cyclopentadienyl-yttrium complex containing μ3-ethylimido ligands.25 Short Y-N distances have also been reported for related yttrium-phosphoraneiminato complexes.26 Preparation and Structural Characterization of Imidazolin2-iminato Rare-Earth-Metal Complexes with Donor-Functionalized Dicarbollide Ligands. The zwitterions IV-VI offer the possibility of preparing dicarbollide complexes through an acid-base route, and the bis(neosilyl) complexes 3 were expected to be well suited for the twofold deprotonation and generation of the resulting donor-functionalized dicarbollide ligands.13 The additional coordination of the functional side arm is expected to stabilize the resulting carboranyl complexes and to prevent ligand redistribution reactions.23 Accordingly, the reactions of [(ImArN)M(CH2SiMe3)2(THF)n] (3a, M=Sc, n=1; 3b, M = Y, n=2; 3c, M=Lu, n = 2) with [nido-(Me2NHCH2CH2)C2B9H11] (IV) in THF solution at room temperature afforded, after elimination of 2 equiv of tetramethylsilane, the desired products [(ImArN)M{σ:η5(Me2NCH2CH2)C2B9H10}(THF)] (4a-c) in good yields (Scheme 3). Coordination of the planar chiral dicarbollide ligand and of the pendant donor group leads to the formation of chiral-at-metal complexes,27 and accordingly, the 1H and 13C NMR spectra of 4a,c exhibit two sets of resonances for the diastereotopic isopropyl groups of the ImArN ligand. In contrast, complex 4b, containing the larger yttrium ion,28 shows a higher degree of fluxionality, as indicated by the appearance of only one set of isopropyl 1H and 13C NMR resonances. The 11B NMR spectra of 4a-c, recorded in pyridine-d5, exhibit broad unresolved peaks for the nine inequivalent boron atoms.23 Compounds 4a-c were additionally characterized by X-ray diffraction analyses. The scandium complex 4a crystallizes in the monoclinic space group P21/n (Figure 3), whereas 4b,c crystallize as isostructural THF-solvated complexes in the triclinic space group P1; Figure 4 shows the molecular structure of 4b. In all cases, the dicarbollyl ligand binds in a chelating fashion, with the metal atoms being η5 coordinated by the pentagonal C2B3 bonding face and (25) Cui, D.; Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. 2005, 44, 959. (26) Dehnicke, K.; Greiner, A. Angew. Chem. 2003, 115, 1378; Angew. Chem., Int. Ed. 2003, 42, 1340. (27) (a) Brunner, H. Angew. Chem., Int. Ed. 1999, 38, 1194. (b) Brunner, H. Eur. J. Inorg. Chem. 2001, 905. (c) Brunner, H.; Tsuno, T. Acc. Chem. Res. 2009, 42, 1501. (28) Shannon, R. D.; Prewit, C. T. Acta Crystallogr., Sect. B 1969, B25, 925.

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Figure 3. ORTEP diagram of 4a with thermal displacement parameters drawn at the 50% probability level.

Figure 4. ORTEP diagram of 4b with thermal displacement parameters drawn at the 50% probability level.

additionally σ bound to the nitrogen atom of the Me2N functional group. The coordination spheres are completed by coordination of one ImArN ligand and one THF molecule to afford pseudotetrahedral geometries. It is interesting to note that the dicarbollide ligand in complexes 4 is bound in a significantly more asymmetric fashion than in complexes 2 and shows a slip distortion with the metal-cage distances in the ranges 2.458(2)-2.567(2) A˚ (in 4a), 2.585(3)-2.772(2) A˚ (in 4b), and 2.541(3)-2.737(3) A˚ (in 4c), respectively (Table 2). These distortions are even more pronounced than those observed for related complexes, e.g. Y-C2B3 = 2.647(5)-2.729(4) A˚ in [{σ:η5-(Me2NCH2CH2)C2B9H10}YCl(THF)2],23 which could be ascribed to the steric impact of the ImArN ligand. Steric congestion might also account for the marked deviation of the M-N1-C1 angles from linearity, with Sc-N1-C1 = 151.35(15)°, Y-N1-C1 = 162.27(18)°, and Lu-N1-C1 = 162.4(2)°. Nonetheless, this bending does not result in any significant elongation of the metal-nitrogen bonds; on the contrary, the Sc-N1 bond of 1.9441(17) A˚ in 4a is even shorter than in 2a, whereas the Y-N1 bond of 2.097(2) A˚ is longer than that observed for 2b (vide supra, Tables 1 and 2). The Lu-N1 bond in 4c, however, is the shortest ever observed for lutetium-nitrogen systems. The previous shortest Lu-N distances were observed in other

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imidazolin-2-iminato lutetium complexes7 and-prior to our investigations-in amido and benzamidinate complexes.29,30 The reactivity of the yttrium bis(neosilyl) complex 3b toward the zwitterionic compounds V and VI, containing two pendant donor groups, was also studied.21,22 At first, the reaction of 3b with V in toluene solution at room temperature afforded the dicarbollide complex 5 in satisfactory yield (70%) as a colorless, crystalline material by vapor diffusion of n-hexane into the concentrated reaction mixture (Scheme 4). In agreement with the presence of a Cs-symmetric complex with two identical diaminomethyl groups, the 1H NMR spectrum of 5 (in pyridine-d5) exhibits two doublets at 3.23 and 2.82 ppm (2JH,H = 14.2) for the diastereotopic methylene hydrogen atoms (CH2NMe2), indicating either coordination of both amino groups or rapid fluxional behavior on the NMR time scale. In fact, X-ray diffraction analysis reveals that both nitrogen donor atoms are coordinated to yttrium (Figure 5), although the coordination of an additional THF ligand to afford [(ImArN)Y{σ:σ:η5-(Me2NCH2)2C2B9H9}(THF)] (5) leads to the formation of a C1-symmetric, pseudopentacoordinate complex in the solid state. It should be noted that 5 represents the first example in which this dicarbollide ligand displays a σ:σ:η5 coordination mode, since one amino side arm in related titanium(IV) amido complexes generally remains uncoordinated in the solid state. The geometry about the yttrium atom can be described either as distorted trigonal bipyramidal with the nitrogen atom N4 and the oxygen atom in the axial positions or as square pyramidal with the dicarbollide ligand adopting the apical position. For structures that are intermediate between the idealized square-pyramidal and trigonal-bipyramidal extremes, Addison and Reedijk have introduced the structural index parameter τ = (R - β)/60, in which R and β represent the two largest angles around the metal atom. Accordingly, a τ value of zero is obtained for perfect tetragonal geometry, while it becomes unity for a perfect trigonal bipyramid.31 The largest angles in 5 are O-Y-N4 = 152.1(1)° and N5-Y-N1 = 137.3(1)°, and the resulting τ value of 0.25 thus points toward a strongly distorted square pyramidal geometry. Pentacoordination in 5 induces a noticeable elongation of the Y-N1 bond (2.136(3) A˚) in comparison with the values determined for tetracoordinate 2b and 4b (2.0829(14) and 2.097(2) A˚) (Tables 1 and 2). As a result of the short methylene tethers in 5, the slip distortion is less pronounced than in 4b, with the Y-C2B3 distances ranging from 2.645(5) to 2.706(5) A˚, Y-B2 being the longest. Finally, the zwitterionic compound VI containing appended amino and ether functionalities was treated with 3b in toluene solution, and following the protocol for the preparation of 5, complex 6 was isolated in 77% yield (Scheme 5). The NMR spectra give no indication of additional THF ligands and are thus in agreement with the formation of [(ImArN)Y{σ:σ:η5-(Me2NCH2CH2)(MeOCH2CH2)C2B9H9}] (6). The molecular structure was confirmed by X-ray diffraction analysis (Figure 6), revealing the coordination of both N- and O-donor groups to afford a distorted-pseudotetrahedral geometry around the metal atom. The orientation of the bifunctional dicarbollide ligand toward yttrium is similar to (29) Cui, D.; Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. 2005, 44, 959. (30) Nishiura, M.; Hou, Z.; Wakatsuki, Y.; Yamaki, T.; Miyamoto, T. J. Am. Chem. Soc. 2003, 125, 1184. (31) Addison, A. W.; Rao, T. N.; Reedijk, J.; van der Rijn, J.; Verschoor, G. C. J. Chem. Soc., Dalton Trans. 1984, 1349.

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Table 2. Selected Bond Lengths (A˚) and Angles (deg) in 4a-c, 5, and 6

M-N1 M-O M-N4 M-N5 M-C28 M-C29 M-B1 M-B2 M-B3 M-N1-C1 O-M-N1 N4-M-N1 N5-M-N1

4a (M = Sc)

4b 3 THF (M = Y)

4c 3 THF (M = Lu)

1.9441(17) 2.1577(14) 2.30336(18)

2.097(2) 2.3288(18) 2.432(2)

2.068(2) 2.2759(18) 2.377(3)

2.567(2) 2.491(2) 2.530(2) 2.480(3) 2.458(2)

2.772(2) 2.739(3) 2.604(3) 2.585(3) 2.646(3)

2.737(3) 2.692(3) 2.562(3) 2.541(3) 2.594(3)

151.35(15) 100.94(6) 101.46(7)

162.27(18) 100.81(7) 101.16(7)

162.4(2) 100.35(8) 100.73(9)

Figure 5. ORTEP diagram of 5 with thermal displacement parameters drawn at the 30% probability level. Scheme 4. Preparation of the Dicarbollide Complex 5

that previously reported for the related cyclopentadienylyttrium complex [{σ:σ:η5-(Me2NCH2CH2)(MeOCH2CH2)C2B9H9}Y{η5-C5H3(SiMe3)2}].23 Similar to the slip distortion observed for 4b, the Y-C2B3 bond lengths show considerable variation between 2.542(8) and 2.708(5) A˚, with the longest bonds being Y-C28 and Y-C29. The Y-N1 distance of 2.085(5) A˚ in 6 is significantly shorter than that observed for the diamino-functionalized dicarbollide complex 5 (2.136(4) A˚), and it adopts an intermediate position between the values found for 2b (2.0829(14) A˚) and 4b (2.097(2) A˚, which contain an unfunctionalized (2b) or monofunctionalized dicarbollide ligand (4b), respectively.

Conclusions Several imidazolin-2-iminato rare-earth-metal complexes incorporating various dicarbollyl ligands were synthesized via salt metathesis or alkane elimination reactions and structurally characterized. The present study showed that the rare-earth-metal dichlorides 1 and the bis(neosilyl) complexes 3 are convenient starting materials for the preparation

5 (M = Y)

6 (M = Y)

2.136(4) 2.355(3) 2.680(4) 2.660(4) 2.645(5) 2.681(4) 2.700(5) 2.707(5) 2.652(5)

2.085(5) 2.376(5) 2.363(6)

174.0(3) 85.98(12) 92.86(12) 137.31(13)

2.703(6) 2.708(7) 2.611(7) 2.542(8) 2.576(7) 171.6(4) 104.14(19) 99.53(19)

Figure 6. ORTEP diagram of 6 with thermal displacement parameters drawn at the 15% probability level. Scheme 5. Preparation of the Dicarbollide Complex 6

of dicarbollide complexes with various Lewis base functionalized side arms. It is suggested that the steric bulk of the ImArN ligand (I) supports the formation of mononuclear rare-earth-metal complexes, which, under an inert atmosphere, are easy to handle and stable in solution and in the solid state. X-ray structural data show that the metal-nitrogen bonds in these new rare-earth-metal dicarbollide complexes are very short, giving further evidence of the ability of imidazolin-2-iminato ligands to form particularly strong “imido-type” metal-nitrogen bonds. Future studies will be directed toward exploiting the reactivity along the strongly polarized M-N bond in these systems, as described for related cyclooctatetraenyl imidazolin-2-iminato rareearth-metal complexes11 and their isolobal cyclooctatetraenyl imido titanium and zirconium congeners.14

Experimental Section General Procedures. All manipulations of air-sensitive materials were performed with the rigorous exclusion of oxygen and

Article moisture in flame-dried Schlenk-type glassware either on a dual manifold Schlenk line, interfaced to a high-vacuum (10-4 Torr) line, or in an argon-filled glovebox (MBraun 200B). All solvents were purified by a solvent purification system from MBraun and stored over molecular sieves (4 A˚) prior to use. Deuterated solvents were obtained from Sigma Aldrich (all g99 atom % D) and were degassed, dried, and stored in the argon-filled glovebox. NMR spectra were recorded on Bruker DPX 200 and Bruker DRX 400 devices. The chemical shifts are expressed in parts per million (ppm) using tetramethylsilane (TMS) as internal standard (1H, 13C). 11B NMR spectra were obtained on a Bruker-400 spectrometer and were externally referenced to BF3 3 Et2O. Elemental analysis (C, H, N) was performed by combustion and gas chromatographic analysis with an Elementar vario MICRO instrument. 1,3-Bis(2,6-diisopropylphenyl)imidazolin-2-iminato rare-earth-metal complexes [(ImArN)MCl2(THF)3] (1a-c; M = Sc, Y, Lu)11 and [(ImArN)M(CH2SiMe3)2(THF)2] (3a-c; M = Sc, Y, Lu),13 Na2[C2B9H11] (III),15c [7-Me2NHCH2CH2-7-C2B9H10] (IV), [7-Me2NHCH2-8-Me2NCH2-7,8-C2B9H10] (V),21 and [7-Me2NHCH2CH2-8-MeOCH2CH2-7,8-(C2B9H10)] (VI)22 were prepared according to published procedures. Procedure for the Preparation of [(ImArN)Sc(η5-C2B9H11)(THF)2] (2a). To a THF (10 mL) solution of [(ImArN)ScCl2(THF)3] (1a; 192.4 mg, 0.265 mmol) was added dropwise 47.5 mg (0.265 mmol) of Na2[C2B9H11] (III) in THF (5 mL) at ambient temperature, and then the reaction mixture was stirred at 60 °C for 12 h. The solvent was evaporated, and the compound was extracted with toluene, which in turn was removed in vacuo. The compound was recrystallized from THF at room temperature. Yield: 94% (199.2 mg, 0.250 mmol). 1H NMR (THF-d8, 400 MHz, 25 °C): δ 7.35-7.25 (m, 6H, m-H, p-H), 6.69 (s, 2H, NCH), 2.86 (sept, 4H, CHMe2), 1.47 (br, 1H, BCH), 1.23 (d, 12H, CHCH3), 1.19 (d, 24H, CHCH3) ppm; the BH signals are very broad from -2.6 to -3.3 ppm. 13C{1H} NMR (THF-d8, 100 MHz, 25 °C): δ 153.3 (NCN), 148.6 (o-C), 132.72 (ipso-C), 130.8 (p-C), 124.2 (m-C), 116.3 (NCH), 42.4 (BCH), 29.6 (CHMe2), 24.3 (CHCH3), 23.88 (CHCH3) ppm. 11B{1H} NMR (THF-d8, 96 MHz, 25 °C): δ -34.2 (1B), -29.44 (1B), -18.6 (2B), -13.8 (1B), -13.0 (2B), -7.12 (2B) ppm. Anal. Calcd for C33H55B9N3OSc: C, 60.79; H, 8.50; N, 6.44. Found: C, 60.24; H, 8.35; N, 5.96. Procedure for the Preparation of [(ImArN)Y(η5-C2B9H11)(THF)2] (2b). To a THF (10 mL) solution of [(ImArN)YCl2(THF)3] (1b) (230.0 mg, 0.295 mmol) was added dropwise 51.7 mg (0.295 mmol) of Na2[C2B9H11] (III) in THF (5 mL) at ambient temperature, and then the reaction mixture was stirred for 12 h at 60 °C. The solvent was evaporated, and the compound was extracted with toluene, which in turn was removed in vacuo. The compound was recrystallized from THF at room temperature. Yield: 91% (206 mg, 0.268 mmol). 1 H NMR (THF-d8, 400 MHz, 25 °C): δ 7.35-7.23 (m, 6H, m-H, p-H), 6.47 (s, 2H, NCH), 3.02 (sept, 4H, CHMe2), 1.60 (br, 1H, BCH), 1.22 (d, 12H, CHCH3), 1.20 (d, 12H, CHCH3) ppm; the BH signals are very broad from -2.5 to -3.5 ppm. 13C{1H} NMR (THF-d8, 100 MHz, 25 °C): δ 154.9 (NCN), 149.1 (o-C), 129.9 (ipso-C), 129.6 (p-C), 124.6 (m-C), 114.7 (NCH), 42.5 (BCH), 29.5 (CHMe2), 24.9 (CHCH3), 24.1 (CHCH3) ppm. 11 B{1H} NMR (THF-d8, 96 MHz, 25 °C): δ -37.9 (1B), -33.2 (1B), -22.2 (2B), -17.2 (1B), -16.7 (2B), -10.64 (2B) ppm. Anal. Calcd for C37H63B9N3O2Y: C, 57.86; H, 8.27; N, 5.47. Found: C, 57.67; H, 7.64; N, 5.87. Procedure for the Preparation of [(ImArN)Lu(η5-C2B9H11)(THF)2] (2c). To a THF (10 mL) solution of [(ImArN)LuCl2(THF)3] (1c; 245.8 mg, 0.284 mmol) was added dropwise 59.8 mg (0.284 mmol) of Na2[C2B9H11] (III) in THF (5 mL) at ambient temperature, and then the reaction mixture was stirred for 12 h at 60 °C. The solvent was evaporated, and the compound was extracted with toluene, which in turn was removed in vacuo. The compound was recrystallized from

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THF at room temperature. Yield: 81% (196.4 mg, 0.230 mmol). H NMR (THF-d8, 400 MHz, 25 °C): δ 7.33-7.25 (m, 6H, m-H, p-H), 6.61 (s, 2H, NCH), 2.84 (sept, 4H, CHMe2), 1.49 (br, 1H, BCH), 1.16 (d, 12H, CHCH3), 1.11 (d, 12H, CHCH3) ppm; the BH signals are very broad from -2.7 to -3.4 ppm. 13C{1H} NMR (THF-d8, 100 MHz, 25 °C): δ 148.6 (o-C), 136.7 (ipso-C), 129.7 (p-C), 125.2 (m-C), 114.8 (NCH), 42.7 (BCH), 29.6 (CHMe2), 24.6 (CHCH3), 24.2 (CHCH3) ppm; the resonances for NCN were not observed. 11B{1H} NMR (THF-d8, 96 MHz, 25 °C): δ -37.6 (1B), -32.9 (1B), -21.9 (2B), 17.1 (1B), -16.4 (2B), -10.5 (2B) ppm. Anal. Calcd for C33H55B9LuN3O: C, 50.61; H, 6.91; N, 5.68. Found: C, 50.68; H, 7.09; N, 5.37. Procedure for the Preparation of [(ImArN)Sc{σ:η5-(Me2NHCH2CH2)C2B9H10}(THF)] (4a). To a THF (10 mL) solution of [(ImArN)Sc(CH2SiMe3)2(THF)] (3a; 246.0 mg, 0.354 mmol) was added dropwise 73.8 mg (0.284 mmol) of [nido-Me2NHCH2CH2-C2B9H11] (IV) in THF (10 mL) at ambient temperature, and then the reaction mixture was stirred for 12 h at room temperature. The THF was removed in vacuo. The compound was recrystallized from THF at room temperature. Yield: 79% (202.9 mg, 0.279 mmol). 1H NMR (pyridine-d5, 400 MHz, 25 °C): δ 7.41-7.17 (m, 6H, m-H, p-H), 6.63 (s, 2H, NCH), 3.71 (br, 1H, BCH), 3.62 (THF), 3.56 (sept, 2H, CHMe2), 3.37 (sept, 2H, CHMe2), 2.77-2.45 (br, 4H, CH2CH2NMe2), 2.00 (s, 6H, N(CH3)2), 1.58 (THF), 1.40 (d, 6H, CHCH3), 1.37 (d, 6H, CHCH3), 1.22 (d, 6H, CHCH3), 1.15 (d, 6H, CHCH3) ppm. 13C{1H} NMR (pyridine-d5, 100 MHz, 25 °C): δ 148.5 (o-C), 148.3 (o-C), 140.5 (NCN), 135.9 (ipso-C), 129.7 (p-C), 124.63 (m-C), 124.2 (m-C), 114.87 (NCH), 67.8 (CH2CH2NMe2), 60.43 (THF) 50.5 (cage C), 47.6 (cage C), 36.8 (CH2CH2NMe2), 29.0 (CHMe2), 28.8 (CHMe2), 25.44 (THF), 24.9 (NMe2), 25.12 (CHCH3), 23.5 (CHCH3), 22.9 (CHCH3), 22.4 (CHCH3) ppm. 11B{1H} NMR (pyridine-d5, 96 MHz, 25 °C): δ -33.9, -27.6, -8.0 (broad), -1.6 (broad) ppm. Anal. Calcd for C37H64B9N4OSc: C, 61.45; H, 8.92; N, 7.75. Found: C, 61.79; H, 9.03; N, 7.59. Procedure for the Preparation of [(ImArN)Y{σ:η5-(Me2NHCH2CH2)C2B9H10}(THF)] (4b). To a THF (10 mL) solution of [(ImArN)Y(CH2SiMe3)2(THF)3] (3b; 207.8 mg, 0.257 mmol) was added dropwise 52.6 mg (207.8 mmol) of [nido-Me2NHCH2CH2-C2B9H11] (IV) in THF (10 mL) at ambient temperature, and then the reaction mixture was stirred for 12 h. The THF was removed in vacuo and the compound recrystallized from THF at room temperature. Yield: 83% (164.5 mg, 0.214 mmol). 1H NMR (THF-d8, 400 MHz, 25 °C): δ 7.35-7.27 (m, 6H, m-H, p-H), 6.36 (s, 2H, NCH), 3.37 (sept, 4H, CHMe2), 3.31 (br, 1H, BCH), 2.67-2.41 (m, 4H, CH2CH2NMe2), 2.05 (s, 6H, N(CH3)2), 1.33 (d, 12H, CHCH3), 1.20 (d, 12H, CHCH3); BH signals are very broad from -2.5 to -4 ppm. 13C{1H} NMR (THF-d8, 400 MHz, 25 °C): δ 149.1 (o-C), 140.1 (NCN), 137.3 (ipso-C), 128.9 (p-C), 124.4 (m-C), 114.5 (NCH), 61.9 (CH2CH2NMe2), 46.24 (cage C), 45.9 (cage C), 37.2 (CH2CH2NMe2), 29.5 (CHMe2), 24.7 (NMe2), 24.3 (CHCH3), 23.5 (CHCH3) ppm. 11B{1H} NMR (THF-d8, 96 MHz, 25 °C): δ -37.2 (1B), -30.9 (broad, 2B), -18.0 (1B), -10.6 (broad, 3B), -6.6 (2B), -5.0 (2B) ppm. 1H NMR (pyridine-d5, 400 MHz, 25 °C): δ 7.29-7.17 (m, 6H, m-H, p-H), 6.58 (s, 2H, NCH), 3.61 (THF), 3.42 (sept, 4H, CHMe), 3.19 (br, 1H, BCH), 2.83-2.35 (br., 4H, CH2-CH2-NMe2), 1.78 (s, 6H, N(CH3)2), 1.57 (THF), 1.21 (d, 12H, CHCH3), 1.14 (d, 12H, CHCH3) ppm. 13 C{1H} NMR (Pyridine-d5, 100 MHz, 25 °C): δ 148.7 (o-C), 141.1 (NCN), 137.8 (ipso-C), 131.4 (p-C), 125.3 (m-C), 116.5 (NCH), 69.9 (CH2CH2NMe2), 61.8 (THF), 38.6 (cage C), 31.6 (CH2CH2NMe2), 28.8 (CHMe2), 27.8 (THF), 27.7 (NMe2), 24.7 (CHCH3), 23.4 (CHCH3) ppm. 11B{1H} NMR (pyridine-d5, 96 MHz, 25 °C): δ -34.7, - 32.9, -29.3, -9.8 (broad), -5.9 (broad), -4.4 (broad) ppm. Anal. Calcd for C41H72B9N4O2Y: C, 58.68; H, 8.62; N, 6.68. Found: C, 58.26; H, 8.42; N, 6.65. Procedure for the Preparation of [(ImArN)Lu{σ:η5-(Me2NHCH2CH2)C2B9H10}(THF)] (4c). To a THF (10 mL) solution 1

1128

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Trambitas et al. Table 3. Crystallographic Data

empirical formula a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) V (A˚3) Z formula wt space group T (K) λ (A˚) Dcalcd (g cm-3) μ (mm-1) no. of rflns collected no. of indep rflns goodness of fit on F2 R(Fo) (I > 2σ(I)) Rw(Fo2) ΔF (e A˚-3)

2a

2b

4a

4b

4c

5

6

C37H63B9N3O2Sc

C37H63B9N3O2Y

C37H64B9N4OSc

C45H80B9N4O3Y

C45H80B9N4O3Lu

C43H77B9N5O2Y

C40H70B9N4O2Y

10.7349(2) 17.5335(4) 22.1591(4) 90 100.874(2) 90 4095.90(14) 4 724.15 P21/c 100(2) 1.54184 1.174 1.794 46 637

10.7992(2) 17.4516(4) 22.4186(4) 90 99.785(2) 90 4163.62(14) 4 768.10 P21/c 100(2) 0.71073 1.225 1.436 135 522

13.9306(4) 15.8819(4) 18.9486(4) 90 98.464(2) 90 4146.61(18) 4 723.17 P21/n 100(2) 0.71073 1.158 0.212 112 296

10.1838(4) 11.7374(4) 21.4661(8) 96.415(3) 92.025(3) 98.546(3) 2517.97(16) 2 911.33 P1 150(2) 0.71073 1.202 1.200 64 833

10.1178(4) 11.6476(4) 21.4015(10) 96.897(4) 92.090(4) 98.288(4) 2474.01(17) 2 997.39 P1 100(2) 1.54184 1.339 4.129 34 042

10.125(5) 12.243(5) 20.164(9) 96.541(8) 93.202(8) 106.821(8) 2366.7(18) 2 882.30 P1 296(2) 0.71073 1.238 1.273 12 950

39.348(6) 17.036(3) 17.959(3) 90 116.138(4) 90 10533(3) 8 825.20 C2/c 296(2) 0.71073 1.041 1.140 47 014

8516 (Rint = 0.0294) 1.084

8830 (Rint = 0.0629) 0.931

9470 (Rint = 0.0884) 0.843

10 623 10 191 (Rint = 0.0918) (Rint = 0.0481) 0.829 1.078

8297 (Rint = 0.0611) 0.904

9506 (Rint = 0.1076) 0.909

0.0404 0.1147 0.769/-0.380

0.0302 0.0692 0.784/-0.447

0.0453 0.1026 0.876/-0.381

0.0467 0.0564 0.987/-0.592

0.0611 0.1442 0.742/-0.388

0.0793 0.2256 1.414/-0.493

of [(ImArN)Lu(CH2SiMe3)2(THF)3] (3c) (215.0 mg, 0.239 mmol), 49.2 mg (0.239 mmol) of [nido-Me2NHCH2CH2C2B9H11] (IV) in THF (10 mL) were added dropwise at ambient temperature and then the reaction mixture was stirred for 12 h. The THF was removed in vacuo and the compound was recrystallized from THF at room temperature. Yield: 88% (179.0 mg, 0.210 mmol). 1H NMR (pyridine-d5, 400 MHz, 25 °C): δ 7.467.17 (m, 6H, m-H, p-H), 6.58 (s, 2H, NCH), 4.27 (br, 1H, BCH), 3.61 (THF), 3.43 (sept, 4H, CHMe2), 2.91-2.82 (m, 2H, CH2CH2NMe2), 2.74-2.64 (m, 2H, CH2CH2NMe2), 2.15 (s, 6H, N(CH3)2), 1.58 (THF), 1.41 (d, 6H, CHCH3), 1.22 (d, 6H, CHCH3), 1.14 (d, 6H, CHCH3), 0.86 (d, 6H, CHCH3) ppm. 13 C{1H} NMR (pyridine-d5, 100 MHz, 25 °C): δ 148.8 (o-C), 147.7 (o-C), 142.4 (NCN), 136.7 (ipso-C), 129.5 (p-C), 124.8 (m-C), 123.0 (m-C), 114.7 (NCH), 67.8 (CH2CH2NMe2), 60.1 (THF), 45.7 (cage C), 43.5 (cage C), 36.5 (CH2CH2NMe2), 29.4 (CHMe2), 28.9 (CHMe2), 26.7 (CHCH3), 25.4 (THF), 24.3 (NMe2), 23.5 (CHCH3), 22.3 (CHCH3), 20.8 (CHCH3) ppm. 11B{1H} NMR (pyridine-d5, 96 MHz, 25 °C): δ -34.7, -29.0, -9.3 (broad), -4.1 (broad) ppm. Anal. Calcd for C37B9H64LuN4O: C, 52.09; H, 7.56; N, 6.57. Found: C, 52.10; H, 7.54; N, 6.26. Procedure for the Preparation of [(ImArN)Y{σ:σ:η5-(Me2NCH2)2C2B9H9}(THF)] (5). 7-Me2NHCH2-8-Me2NCH2-7,8C2B9H10 (V; 41.0 mg, 0.50 mmol) was added to a toluene solution (10 mL) of 3b (405.0 mg, 0.50 mmol) at room temperature, and the suspension was stirred at room temperature overnight. After filtration, the resulting clear pale yellow solution was concentrated under vacuum to 5 mL. n-Hexane (5 mL) vapor diffusion gave 5 as colorless crystals over a period of 1 week at room temperature (283.0 mg, 70%). X-ray-quality crystals were grown from a THF/n-hexane solution. 1H NMR (pyridine-d5, 400 MHz, 25 °C): δ 7.36 (t, J = 7.7 Hz, 2H, m-H), 7.25 (d, J = 7.7 Hz, 2H, m-H), 7.14 (d, J = 7.7 Hz, 2H, p-H), 6.37 (s, 2H, NCH), 3.55 (m, 4H, CHMe2), 3.23 (d, J = 14.2 Hz, 2H, CH2N(CH3)2), 2.82 (d, J = 14.2 Hz, 2H, CH2N(CH3)2), 2.07 (s, 12H, N(CH3)2), 1.18 (d, J = 7.0 Hz, 24H, CHCH3) ppm. 13 C{1H} NMR (pyridine-d5, 100 MHz, 25 °C): δ 148.2 (o-C), 137.6 (NCN), 136.9 (ipso-C), 129.0 (p-C), 124.1 (m-C), 114.7 (NCH), 67.1 (CH2N(CH3)2), 56.0 (cage C), 49.9 (N(CH3)2), 28.8 (CHMe2), 25.6 (CHCH3), 22.7 (CHCH3) ppm. 11B{1H} NMR (pyridine-d5, 128 MHz, 25 °C): δ -7.0 (2B), -10.3 (2B), -12.7

0.0329 0.0844 1.039/-1.376

(4B), -32.5 (1B) ppm. Anal. Calcd for C39H69B9N5OY: C, 57.81; H, 8.58; N, 8.64. Found: C, 58.16; H, 8.36; N, 8.98. Procedure for the Preparation of [(ImArN)Y{σ:σ:η5-(Me2NCH2CH2)(MeOCH2CH2)C2B9H9}] (6). This complex was prepared as colorless crystals from 7-Me2NHCH2CH2-8MeOCH2CH2-7,8-C2B9H10 (VI; 66.5 mg, 0.25 mmol) and 3b (202.5 mg, 0.25 mmol) in toluene using the same procedure as reported for 5: yield 144.0 mg (77%). 1H NMR (pyridine-d5, 400 MHz, 25 °C): δ 7.45 (t, J = 7.7 Hz, 2H, m-H), 7.33 (m, 2H, m-H), 7.26 (m, 2H, p-H), 6.53 (s, 2H, NCH), 3.61 (m, 4H, CH2CH2OCH3 þ CHMe2), 3.43 (m, 2H, CHMe2), 3.34 (s, 3H, OCH3), 2.79 (m, 2H, CH2CH2N(CH3)2), 2.32 (m, 4H, CH2CH2N(CH3)2 þ CH2CH2OCH3), 1.95 (s, 6H, N(CH3)2), 1.35 (d, J = 6.8 Hz, 6H, CHCH3), 1.21 (m, 18H, CHCH3) ppm. 13C{1H} NMR (pyridine-d5, 100 MHz, 25 °C): δ 148.3 (o-C), 138.3 (NCN), 136.6 (ipso-C), 128.9 (p-C), 124.3 (m-C), 114.1 (NCH), 79.5 (CH2CH2OCH3), 62,7 (CH2CH2NCH3), 60.9 (CH2CH2N(CH3)2), 46.2 (OCH3), 34.6 (N(CH3)2), 29.0 (CHMe2), 28.6 (CHMe2), 25.9 (CHCH3), 25.3 (CHCH3), 23.0 (CHCH3), 22.6 (CHCH3) ppm; the resonances for BC were not observed. 11 B{1H} NMR (pyridine-d5, 128 MHz, 25 °C): δ -5.2 (1B), -8.5 (2B), -10.8 (5B), -31.3 (1B) ppm. Anal. Calcd for C36H62B9N4OY: C, 57.41; H, 8.30; N, 7.44. Found: C, 57.55; H, 8.35; N, 7.39. X-ray Structure Determinations. Intensity Measurements. For compounds 2a,b and 4a-c, crystals were mounted in inert oil on glass fibers and transferred to the cold gas stream of an Oxford Diffraction diffractometer (2a and 4c: Nova A using mirror-focused Cu KR radiation; others, Xcalibur E using monochromated Mo KR radiation). Data were registered at 100 K, except for 4b (150 K because the crystals shatter at lower temperatures). For compounds 5 and 6, crystals were immersed in Paratone-N oil and sealed under nitrogen in thin-walled glass capillaries. Data were collected at 293 K on a Bruker SMART 1000 CCD diffractometer using monochromated Mo KR radiation. Empirical absorption corrections were applied using the multiscan method. Structure Solution and Refinement. All structures were solved by direct methods refined anisotropically for all non-hydrogen atoms by full-matrix least squares on F2 using SHELXL.32

(32) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.

Article Hydrogen atoms were included using rigid methyl groups or a riding model. Special Features and Exceptions. In the B3C2 open faces, B and C atoms were distinguished where necessary by inspection of bond lengths and angles and/or by mixed B/C site refinement, where one component refined to occupation zero. For compound 2a, hydrogens of the carbollide ligand were refined freely but B-H distances were restrained to be equal. Both coordinated THF groups are disordered over two positions; appropriate restraints were employed to improve refinement stability, but the dimensions of disordered groups should be interpreted with caution. For compounds 2b and 4a-c, B3C2 open face hydrogens were refined as for 2a. For compounds 4b, c, one of the two noncoordinated THF molecules was badly disordered and could not be satisfactorily refined. The program SQUEEZE (A. L. Spek, University of Utrecht, Utrecht, The Netherlands) was therefore used to mathematically remove the effect of the solvent. For compound 6, one of the methylene

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units of the Me2NCH2CH2 fragment is disordered. Numerical details are summarized in Table 3.

Acknowledgment. This work was supported by grants from the Deutsche Forschungsgemeinschaft (DFG) through the program “Lanthanoidspezifische Funktionalit€ at in Molek€ ul und Material” (SPP 1166) and from the Research Grants Council of the Hong Kong SAR (Project No. 403907). Exchange of personnel was made possible through the Germany/Hong Kong Joint Research Programme funded by the German Academic Exchage Council (DAAD) and the Research Grants Council of the Hong Kong SAR (D/09/00534 to M.T. and G_HK010/08 to Z.X.). Supporting Information Available: CIF files giving crystallographic data for 2a,b, 4a-c, 5, and 6. This material is available free of charge via the Internet at http://pubs.acs.org.