Synthesis and Structural Characterization of Group 10 Metal

Sep 23, 2010 - ... of Hong Kong, Shatin, New Territories, Hong Kong, People's Republic of China ... with Li2C2B10H10−nXn (M = Ni, Pd, Pt; X = Br, I,...
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Organometallics 2010, 29, 4541–4547 DOI: 10.1021/om100669x

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Synthesis and Structural Characterization of Group 10 Metal-Carboryne Complexes Zaozao Qiu,† Liang Deng,† Hoi-Shan Chan,† and Zuowei Xie*,†,‡ †

Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, People’s Republic of China, and ‡State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin, People’s Republic of China Received July 9, 2010

A series of group 10 metal-carboryne complexes were prepared from an equimolar reaction of MCl2(PR3)2 with Li2C2B10H10-nXn (M = Ni, Pd, Pt; X = Br, I, Ph; n = 0, 1, 2). They were fully characterized by various spectroscopic techniques, elemental analyses, and X-ray diffraction studies. These complexes have similar solid-state structures, in which the metal atom is bonded to two cage carbon atoms and coordinated to two phosphorus atoms in a planar geometry. The coordinated phosphines are labile and can be replaced by other Lewis bases. The bonding interactions between the metal and the carboryne unit can be described as a resonance hybrid of both the M-C σ- and M-C π-bonding forms. These complexes can be viewed as 16e species.

Introduction Carboryne (1,2-dehydro-o-carborane), a three-dimensional relative of benzyne, was first reported in 1990 as a very reactive intermediate.1 Subsequent reactivity studies showed that it can react with alkenes, dienes, alkynes, and aromatics in [2þ2] and [4þ2] cycloaddition and ene-reaction patterns,2 similar to that of benzyne.3 These carboryne reactions are usually complicated and not in a controlled manner. On the other hand, metalcarboryne complexs can react efficiently with various unsaturated molecules to produce organic and organometallic compounds incorporating a carboranyl unit. For example, nickel-carboryne complex (η2-C2B10H10)Ni(PPh3)24 can undergo regioselective [2þ2þ2] cycloaddition reactions with 2 equiv of alkynes to afford benzocarboranes,5 react with

1 equiv of alkenes to generate alkenylcarborane coupling products,6 and undergo three-component [2þ2þ2] cyclotrimerization with 1 equiv of activated alkene and 1 equiv of alkyne to give dihydrobenzocarboranes.7 The reaction of carboryne with alkynes can also proceed in a catalytic manner using Ni species as catalyst.8 In contrast, the zirconium-carboryne precursor Cp2Zr(μ-Cl)(μ-C2B10H10)Li(OEt2)2 reacts with only 1 equiv of alkynes9 or polar unsaturated organic substrates such as isonitrile, nitrile, and azide to give monoinsertion products even in the presence of excess substrates.10 The aforementioned results suggest that the reactivity patterns of metal-carboryne complexes are largely dependent upon the nature of the transition metals. Although one Ni-carboryne4 and several Zr-carboryne complexes11,12 have been structurally characterized, other transition metalcarboryne complexes are either unknown or partially characterized without NMR data.13 As an ongoing project, we are interested in the effects of cage substituents, co-ligands, and the nature of transition metals on the formation, structure, and stability of metal-carboryne complexes. We report here the synthesis and structural characterization of a variety of group 10 metal-1,2-o-carboryne complexes

*To whom correspondence should be addressed. Fax: (852)26035057. Tel: (852)26096269. E-mail: [email protected]. (1) Gingrich, H. L.; Ghosh, T.; Huang, Q.; Jones, M., Jr. J. Am. Chem. Soc. 1990, 112, 4082. (2) (a) Ghosh, T.; Gingrich, H. L.; Kam, C. K.; Mobraaten, E. C. M.; Jones, M., Jr. J. Am. Chem. Soc. 1991, 113, 1313. (b) Huang, Q.; Gingrich, H. L.; Jones, M., Jr. Inorg. Chem. 1991, 30, 3254. (c) Cunningham, R. T.; Bian, N.; Jones, M., Jr. Inorg. Chem. 1994, 33, 4811. (d) Ho, D. M.; Cunningham, R. J.; Brewer, J. A.; Bian, N.; Jones, M., Jr. Inorg. Chem. 1995, 34, 5274. (e) Barnett-Thamattoor, L.; Zheng, G.; Ho, D. M.; Jones, M., Jr.; Jackson, J. E. Inorg. Chem. 1996, 35, 7311. (f) Atkins, J. H.; Ho, D. M.; Jones, M., Jr. Tetrahedron Lett. 1996, 37, 7217. (g) Jeon, J.; Kitamura, T.; Yoo, B.-W.; Kang, S. O.; Ko, J. Chem. Commun. 2001, 2110. (h) Lee, T.; Jeon, J.; Song, K. H.; Jung, I.; Baik, C.; Park, K.-M.; Lee, S. S.; Kang, S. O.; Ko, J. Dalton Trans. 2004, 933. (i) Wang, S. R.; Qiu, Z.; Xie, Z. J. Am. Chem. Soc. 2010, 132, 9988. (3) (a) Dyke, A. M.; Hester, A. J.; Lloyd-Jones, G. C. Synthesis 2006, 24, 4093. (b) Pellissier, H.; Santelli, M. Tetrahedron 2003, 59, 701. (c) Hoffmann, R. W. Dehydrobenzene and Cycloalkynes; Academic Press: New York, 1967. (d) Franzen, V.; Joschek, H. I. Ann. 1967, 703, 90. (e) Jones, M., Jr.; Levin, R. H. J. Am. Chem. Soc. 1969, 91, 6411. (4) Only the X-ray structure was reported and no NMR data were available; see: Sayler, A. A.; Beall, H.; Sieckhaus, J. F. J. Am. Chem. Soc. 1973, 95, 5790. (5) Deng, L.; Chan, H.-S.; Xie, Z. J. Am. Chem. Soc. 2006, 128, 7728. (6) Qiu, Z.; Xie, Z. Angew. Chem., Int. Ed. 2008, 47, 6572.

(7) Qiu, Z.; Xie, Z. J. Am. Chem. Soc. 2009, 131, 2084. (8) Qiu, Z.; Wang, S. R.; Xie, Z. Angew. Chem., Int. Ed. 2010, 49, 4649. (9) (a) Ren, S.; Chan, H.-S.; Xie, Z. J. Am. Chem. Soc. 2009, 131, 3862. (b) Ren, S.; Chan, H.-S.; Xie, Z. Organometallics 2009, 28, 4106. (10) Deng, L.; Chan, H.-S.; Xie, Z. J. Am. Chem. Soc. 2005, 127, 13774. (11) Wang, H.; Li, H.-W.; Huang, X.; Lin, Z.; Xie, Z. Angew. Chem., Int. Ed. 2003, 42, 4347. (12) Ren, S.; Deng, L.; Chan, H.-S.; Xie, Z. Organometallics 2009, 28, 5749. (13) (C2B10H10)MLn (M = Pd, Pt, L = PPh3, n = 2; M = Co, L = bipy, n = 1) were reported without NMR data; see: (a) Zakharkin, L. I.; Kovredov, A. I. Izv. Akad. Nauk. SSSR, Ser. Khim. 1975, 2619. (b) Ol'dekop, Yu. A.; Maier, N. A.; Erdman, A. A.; Prokopovich, V. P. Zh. Obshch. Khim. 1982, 52, 2256. (c) Ol'dekop, Yu. A.; Maier, N. A.; Erdman, A. A.; Prokopovich, V. P. Dokl. Akad. Nauk. SSSR 1981, 257, 647.

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Scheme 1. Synthesis of Group 10 Metal-Carboryne Complexes

with different cage B-substituents or different phosphine ligands.

Results and Discussion Synthesis. Salt metathesis between Li2C2B10H10 and metal halides is a useful method for the preparation of metalcarboryne complexes. Treatment of Li 2C2B10H10 with 1 equiv of MCl2(PPh3)2 in THF or diethyl ether at 0 °C gave, after workup, (η2-C2B10H10)M(PPh3)2 (M = Ni (1), Pd (2), Pt (3)) as red or yellow crystals in 60-72% isolated yields (Scheme 1).4,13 In a similar manner, complexes (η2-C2B10H10)Ni(PMe3)2 (4) and (η2-C2B10H10)Ni(dppe) (5) (dppe = 1,2bis(diphenylphosphino)ethane) were also synthesized as yellow crystals from the interaction of Li2C2B10H10 with 1 equiv of NiCl2(L)n (L = PMe3, n = 2; L = dppe, n = 1) in diethyl ether at 0 °C in 83% and 45% isolated yields, respectively (Scheme 1). To gain information on the effects of cage substituents on the formation, structure, and stability of metal-carboryne complexes, several B-substituted carboranes were selected as the starting materials. Treatment of 9-I-1,2-C2B10H11 or 9,12-I21,2-C2B10H10 with 2 equiv of n-BuLi in THF at 0 °C, followed by reaction with 1 equiv of NiCl2(PPh3)2 at room temperature, afforded (η2-9-I-1,2-C2B10H9)Ni(PPh3)2 (6) as a yellow solid in 55% isolated yield or (η2-9,12-I2-1,2-C2B10H8)Ni(PPh3)2 (7) as yellow crystals in 72% isolated yield, respectively. No intermolecular interactions were observed between the Ni center and the B-I unit of the second molecule (vide infra). Under the same reaction conditions, reaction of 3-Br-1,2-Li2-1,2-C2B10H9 with 1 equiv of NiCl2(PPh3)2 did not produce the expected Nicarboryne complex; rather, 3-Br-1,2-C2B10H11 and Ni(0) species were generated probably due to the decomposition of the Ni-carboryne at room temperature. However, if NiCl2(PMe3)2 was used as the starting material, the expected complex (η2-3Br-1,2-C2B10H9)Ni(PMe3)2 (8) was isolated as yellow crystals in 31% isolated yield. These results suggested that steric factors play a role in the formation and stability of the Ni-carboryne complexes, and the fewer steric interactions between 3-Br and PMe3 moieties lead to the successful isolation of 8. In the case of 3-Ph-1,2-C2B10H11, both complexes (η2-3-C6H5-1,2-C2B10H9)Ni(PMe3)2 (9) and (η2-3-C6H5-1,2-C2B10H9)Ni(PPh3)2 (10) were isolated as yellow or orange crystals in 42% or 76% isolated yields from an equimolar reaction of 3-C6H5-1,2-Li21,2-C2B10H9 with NiCl2(PMe3)2 or NiCl2(PPh3)2 in THF (Scheme 2). Complexes 1-9 are sensitive to moisture and air, whereas 10 is air- and moisture-stable in both solid state and solution. Complex 10 is also very thermally stable, and no decomposition is observed even after prolonged heating in THF. However, complexes 1-9 decompose partially into neutral

Qiu et al. Scheme 2. Synthesis of B-Substituted Nickel-Carboryne Complexes

carboranes and the Ni(0) species in refluxing THF. It is suggested that both 3-phenyl and the sterically demanding PPh3 ligands contribute to the exceptional stability of 10. Complexes 1-10 are highly soluble in THF and slightly soluble in ether and toluene. All complexes were fully characterized by various spectroscopic techniques and elemental analyses. The 1H and 13C NMR spectra, which displayed only the signals of cage substituents and phosphine ligands, do not give much information on the solution structures. The cage carbons were not observed for all complexes. The 11B NMR spectra exhibited 2:4:4, 2:1:3:4, 3:4:3, 2:2:6, 2:2:6, 3:6:1, 2:6:2, 1:1:3:1:2:2, 1:1:1:2:5, and 1:1:1:3:4 patterns for 1-10, respectively. In addition, one singlet at -22.9 ppm corresponding to the BI vertex in 6 and one resonance at -21.6 ppm assignable to the two BI vertices in 7 were observed in their 1H coupled 11B NMR spectra. The BBr signal of 8 was observed as a singlet at -11.6 ppm. The BPh signal was exhibited as a singlet at -3.8 and -0.8 ppm in 9 and 10, respectively. The 31P NMR spectra showed one singlet at ca. -9 ppm for PMe3 ligands in 4, 8, and 9, one singlet at ca. 30 ppm for PPh3 ligands in 1, 2, 6, 7, and 10, one singlet at 63 ppm for the dppe ligand in 5, and satellite peaks (1:5:1) at 19.7 ppm with a JP-Pt coupling constant of 1788 Hz for 3. Displacement of PPh3 in 1. NMR reactions of 1 with various phosphines were examined in order to gain information on the lability of PPh3 ligands in 1. These reactions were closely monitored by 11B and 31P NMR spectra. The results showed that the PPh3 ligands in 1 can be completely substituted by dppe, P(OEt)Ph2, and P(OEt)3 at room temperature to give (η2C2B10H10)Ni(dppe) (5), (η2-C2B10H10)Ni[P(OEt)Ph2]2 (11), and (η2-C2B10H10)Ni[P(OEt)3]2 (12), respectively. However, the substitution reaction between 1 and 4 equiv of PCy3 was not complete, giving a mixture of (η2-C2B10H10)Ni(PPh3)(PCy3) (13) and (η2-C2B10H10)Ni(PCy3)2 in a molar ratio of 1:0.11 as measured by 31P NMR spectrum. X-ray-quality crystals of 13 were obtained from the NMR solution, and its molecular structure was characterized by X-ray analyses (vide infra). The above reactions are outlined in Scheme 3. These results indicated that the PPh3 ligands in 1 are very labile, which can be displaced by other Lewis bases. Steric factors play a role in these substitution reactions.14 This is consistent with our early observations that 1 cannot mediate the reaction of highly bulky alkynes such as tBuCtCnBu5 and TMSCtCTMS.7 Structure. The solid-state structures of 2-5 and 7-10 were further confirmed by single-crystal X-ray analyses. A better resolution of the molecular structure of 1 was also obtained4 and is included in the discussion. Complexes 1-3 are isostructural, and their representative structure of 2 is shown in Figure 1. Molecular structures of 4, 5, and 7-10 are shown in Figures 2-7, respectively. As illustrated in the figures, the (14) Sun, Y.; Chan, H.-S.; Dixneuf, P. H.; Xie, Z. Organometallics 2004, 23, 5864.

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Figure 2. Molecular structure of (η2-C2B10H10)Ni(PMe3)2 (4).

Figure 1. Molecular structure of (η2-C2B10H10)Pd(PPh3)2 (2). Scheme 3. Phosphine Exchange Reactions of 1

Figure 3. Molecular structure of (η2-C2B10H10)Ni(dppe) (5).

metal atom in all structures is bonded to two cage C atoms and coordinated to two phosphorus atoms in an essentially planar geometry. Selected bond distances and angles around the metal atoms are listed in Table 1 for comparison. The C(cage)-C(cage) bond distances (1.52-1.57 A˚) found in all structures are generally shorter than those observed in the Zr-carboryne complexes (1.61-1.71 A˚)11,12 and in o-carborane (1.63 A˚). The average Ni-C(cage) distances fall in the range 1.91-1.94 A˚. It is interesting to note that the shortest C(cage)C(cage) distance of 1.523(3) A˚ observed in 10 is associated with the longest Ni-C(cage) distance of 1.937(2) A˚ in 10, which is consistent with that observed in metal-alkyne(alkene) π complexes.15 This suggests some π interactions between the Ni atom and carboryne unit in Ni-carboryne complexes. These observations can be explained using a resonance hybrid bonding mode of both the M-C σ- and M-C π-bonding forms (Chart 1) proposed on the basis of DFT calculations on the Zr-carboryne model complex.11 Zr(II) has a higher tendency (15) (a) Elschenbroich, C.; Salzer, A. Organometallics. A Concise Introduction; VCH: New York, 1992; Chapter 15, p 256. (b) Jemmis, E. D.; Roy, S.; Burlakov, V. V.; Jiao, H.; Klahn, M.; Hansen, S.; Rosenthal, U. Organometallics 2010, 29, 76.

than group 10 metals to donate its d electrons to the π* orbital of the carboryne ligand,16 resulting in much longer C(cage)C(cage) bond distances observed in Zr-carboryne complexes.11,12 In other words, the interactions between the group 10 metal atom and carboryne have more π character than those observed in Zr-carboryne complexes. The M-P distances are in the range 2.15-2.32 A˚ (Table 1), which compare well with the 2.200(1) A˚ in (η2-C6H4)Ni(PCy3)2,17 2.140(1) and 2.152(1) A˚ in (η2-C6H4)Ni(Cy2PCH2CH2PCy2),18 2.151(2) and 2.176(2) A˚ in (η2-PhCtCSiMe3)Ni(PPh3)2,19 2.328(1) and 2.342(1) A˚ in (η2-C6H4)Pd(PCy3)2,17 2.290(1) and 2.281(1) A˚ in (η2-PhCtCPh)Pt(PPh3)2,20 and 2.264(1) and 2.271(1) A˚ in (η2-cyclohexyne)Pt(PPh3)2.21 The M 3 3 3 B(6)/B(3) distances in 1-5 and 7-10 fall in the region 2.58-2.81 A˚. These values are significantly longer than those observed in Ni2(CO)2(η5-2,7-Me2-2,7-C2B9H9)2 (2.261(11) A˚),22 1,3,6-{Pd(dppe)}3,6-(μ-H)2-1,1,1-(CO)3-2-Ph-closo-1,2-MnCB9H7 (2.257(5) and (16) Crabtree, R. H. The Organometallic Chemistry of the Transition Metals; Wiley: NJ, 2005; Chapter 2, p 47. (17) Retbøll, M.; Edwards, A. J.; Rae, A. D.; Willis, A. C.; Bennett, M. A.; Wenger, E. J. Am. Chem. Soc. 2002, 124, 8348. (18) Bennett, M. A.; Hambley, T. W.; Roberts, N. K.; Robertson, G. B. Organometallics 1985, 4, 1992. (19) Bartlk, T.; Happ, B.; Iglewsky, M.; Bandmann, H.; Boese, R.; Heimbach, P.; Hoffmann, T.; Wenschuh, E. Organometallics 1992, 11, 1235. (20) Harris, K. J.; Bernard, G. M.; McDonald, C.; McDonald, R.; Ferguson, M. J.; Wasylishen, R. E. Inorg. Chem. 2006, 45, 2461. (21) Robertson, G. B.; Whimp, P. O. J. Am. Chem. Soc. 1975, 97, 1051. (22) Carr, N.; Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A. Inorg. Chem. 1994, 33, 1666.

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Figure 4. Molecular structure of (η2-9,12-I2-1,2-C2B10H8)Ni(PPh3)2 (7).

Figure 5. Molecular structure of (η2-3-Br-1,2-C2B10H9)Ni(PPh3)2 (8).

2.356(5) A˚),23 3,6-{Pt(dppe)}-3,6-(μ-H)2-1,1,1-(CO)3-2-Ph-closo1,2-MnCB9H7 (2.205(7) and 2.365(7) A˚),23 1,3-{Pt(dppe)}-3-(μH)-1,1,1-(CO)3-2-Ph-closo-1,2-ReCB9H8 (2.266(11) A˚),24 and (η6-Me2C2B10H10)MoPt(CO)4(PPh3) (2.313(8) A˚),25 in which the B-H 3 3 3 M interactions have been identified. On the other hand, neither a high-field signal in the 1H NMR spectra nor significantly reduced JBH values or a very deshielded signal in the 11B NMR spectra was observed in complexes 1-10.26 The (23) Du, S.; Jeffery, J. C.; Kautz, J. A.; Lu, X. L.; McGrath, T. D.; Miller, T. A.; Riis-Johannessen, T.; Stone, F. G. A. Inorg. Chem. 2005, 44, 2814. (24) Du, S.; Kautz, J. A.; McGrath, T. D.; Stone, F. G. A. Organometallics 2003, 22, 2842. (25) Dossett, S. J.; Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A.; Went, M. J. J. Chem. Soc., Dalton Trans. 1993, 281. (26) The B-H 3 3 3 M interactions in late transition metal complexes usually lead to a significantly reduced JBH value, a very deshielded 11B signal, and a very high-field 1H resonance; see: (a) Brew, S. A.; Stone, F. G. A. Adv. Organomet. Chem. 1993, 35, 135. (b) Franken, A.; McGrath, T. D.; Stone, F. G. A. J. Am. Chem. Soc. 2006, 128, 16169. (c) McGrath, T. D.; Du, S.; Hodson, B. E.; Lu, X. L.; Stone, F. G. A. Organometallics 2006, 25, 4444. (d) McGrath, T. D.; Du, S.; Hodson, B. E.; Stone, F. G. A. Organometallics 2006, 25, 4452. (e) Hodson, B. E.; McGrath, T. D.; Stone, F. G. A. Organometallics 2005, 24, 3386. (27) Crowther, D. J.; Borkowsky, S. L.; Swenson, D.; Meyer, T. Y.; Jordan, R. F. Organometallics 1993, 12, 2897.

Qiu et al.

Figure 6. Molecular structure of (η2-3-C6H5-1,2-C2B10H9)Ni(PMe3)2 (9).

Figure 7. Molecular structure of (η2-3-C6H5-1,2-C2B10H9)Ni(PPh3)2 (10).

solid-state IR spectra (KBr) exhibited only one very strong and broad νB-H stretching band at about 2500 cm-1.27 These experimental data suggest that there are very weak or no obvious B-H 3 3 3 M interactions in complexes 1-10. Therefore, they are best described as 16e species. The relatively short M 3 3 3 B distances observed in the above structures might also partially result from crystal packing forces. It is noteworthy that as all B-H hydrogen atoms are in calculated positions, a detailed discussion of the B-H distances is not warranted.

Conclusion Salt metathesis between dilithiocarborane and metal halides has proved to be a general method for the preparation of metal-carboryne complexes. A series of group 10 metal-carboryne complexes are thus synthesized and structurally characterized. The phosphine ligands in these metal complexes are labile and can be displaced by other Lewis bases, which is important for their possible applications in organometallic reactions. This work shows that the bonding interactions between the transition metal and carboryne have more π character in group 10 metal complexes than group 4 metal ones probably due to a strong back-donation

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Table 1. Selected Bond Distances (A˚) and Angles (deg) compd (M)

Ccage-Ccage

av M-Ccage

M 3 3 3 B(3)

M 3 3 3 B(6)

av M-P

Ccage- M-Ccage

P-M-P

1 (Ni) 2 (Pd) 3 (Pt) 4 (Ni) 5a (Ni)

1.556(5) 1.564(5) 1.572(6) 1.576(4) 1.553(6) [1.561(5)] 1.550(6) 1.595(14) 1.565(5) [1.576(4)] 1.523(3) 1.551(4)

1.923(4) 2.085(4) 2.090(5) 1.913(3) 1.915(5) [1.922(4)] 1.922(4) 1.918(6) 1.923(3) [1.926(3)] 1.937(2) 1.931(3)

2.628(5) 2.780(5) 2.800(6) 2.622(7) 2.618(6) [2.635(6)] 2.647(6)

2.628(5) 2.809(5) 2.810(6) 2.626(6) 2.616(6) [2.632(5)] 2.626(6) 2.721(20) 2.631(4) [2.583(4)] 2.581(3) 2.623(3)

2.195(1) 2.323(1) 2.283(2) 2.153(1) 2.160(1) [2.155(1)] 2.202(1) 2.169(2) 2.168(1) [2.164(1)] 2.218(1) 2.212(1)

47.7(2) 44.1(2) 44.2(2) 48.7(1) 47.8(2) [47.9(2)] 47.6(2) 49.1(4) 48.1(1) [48.3(1)] 46.3(1) 47.4(1)

108.9(1) 104.0(1) 102.6(1) 112.1(1) 89.8(1) [89.8(1)] 110.0(1) 110.8(1) 104.4(1) [107.5(1)] 111.7(1) 107.2(1)

7 (Ni) 8 (Ni) 9a (Ni) 10 (Ni) 13 (Ni) a

2.680(3)

Numbers in brackets are those of a second molecule.

Chart 1. Bonding Interactions between Metal and Carboryne

of divalent group 4 metal species over group 10 metals. The results also indicate that there are very weak or no obvious B-H 3 3 3 M interactions in group 10 metal-carboryne complexes. Thus, they are best described as 16e species.

Experimental Section General Procedures. All experiments were performed under an atmosphere of dry dinitrogen with the rigid exclusion of air and moisture using standard Schlenk or cannula techniques, or in a glovebox. All organic solvents (except CH2Cl2) were refluxed over sodium benzophenone ketyl for several days and freshly distilled prior to use. CH2Cl2 was refluxed over CaH2 for several days and distilled immediately before use. All chemicals were purchased from either Aldrich or Acros Chemical Co. and used as received unless otherwise noted. NiCl2(PPh3)2,28 3-bromoo-carborane,29 9-iodo-o-carborane,30 9,12-diiodo-o-carborane,31 and 3-phenyl-o-carborane32 were prepared according to literature methods. Infrared spectra were obtained from KBr pellets prepared in the glovebox on a Perkin-Elmer 1600 Fourier transform spectrometer. 1H NMR spectra were recorded on either a Bruker DPX 300 spectrometer at 300 MHz or a Bruker DPX 400 spectrometer at 400 MHz. 13C{1H} NMR spectra were recorded on either a Bruker DPX 300 spectrometer at 75 MHz or a Bruker DPX 400 spectrometer at 100 MHz. 11B NMR spectra were recorded on either a Bruker DPX 300 spectrometer at 96 MHz or a Bruker DPX 400 spectrometer at 128 MHz. All chemical shifts were reported in δ units with references to the residual solvent resonances of the deuterated solvents for proton and carbon chemical shifts, to external BF3 3 OEt2 (0.00 ppm) for boron chemical shifts, and to external 85% H3PO4 (0.00 ppm) for phosphorus chemical shifts. Elemental analyses were performed by the Shanghai Institute of Organic Chemistry, CAS, China. Preparation of (η2-C2B10H10)Ni(PPh3)2 (1). A modified procedure was used.4 A 1.6 M solution of n-BuLi in n-hexane (1.30 mL, 2.1 mmol) was slowly added to a stirring solution of o-C2B10H12 (144 mg, 1.0 mmol) in THF (10 mL) at 0 °C, and the mixture was stirred at room temperature for 1 h. The (28) Venanzi, L. M. J. Inorg. Nucl. Chem. 1958, 8, 137. (29) Li, J.; Jones, M., Jr. Inorg. Chem. 1990, 29, 4162. (30) Andrew, J. S.; Zayas, J.; Jones, M., Jr. Inorg. Chem. 1985, 24, 3715. (31) Barber a, G.; Vaca, A.; Teixidor, F.; Sillanp€a€a, R.; Kivek€as, R.; Vi~ nas, C. Inorg. Chem. 2008, 47, 7309. (32) Ohta, K.; Goto, T.; Endo, Y. Inorg. Chem. 2005, 44, 8569.

Figure 8. Molecular structure of (η2-C2B10 H 10)Ni(PPh3)(PCy 3) (13). resulting Li2C2B10H10 suspension was then cooled to 0 °C, to which was added NiCl2(PPh3)2 (654 mg, 1.0 mmol). The reaction mixture was then stirred for 0.5 h at room temperature, giving a deep red solution. After removal of the solvent, the deep brown residue was extracted with hot toluene (10 mL  2). The combined toluene solutions were concentrated to 10 mL. Complex 1 was obtained as red crystals after this solution stood at -30 °C overnight (522 mg, 72%). 1H NMR (CD2Cl2): δ 7.36 (m, 6H, C6H5), 7.26 (m, 24H, C6H5). 13C{1H} NMR (CD2Cl2): δ 133.2 (t, 2JC-P = 6.0 Hz), 131.3 (d, 1JC-P = 45.3 Hz), 130.0, 128.0 (t, 3JC-P = 4.8 Hz), the cage carbons were not observed. 11 B NMR (CD2Cl2): δ -3.9 (d, J = 153.6 Hz, 2B), -13.0 (d, J = 166.4 Hz, 4B), -15.1 (br, unresolved, 4B). 31P NMR (162 MHz, CD2Cl2): δ 33.3. IR (KBr, cm-1): νBH 2559 (vs). This is a known complex,4 but no NMR data were reported. Preparation of (η2-C2B10H10)Pd(PPh3)2 (2). A 1.6 M solution of n-BuLi in n-hexane (1.30 mL, 2.1 mmol) was slowly added to a stirring solution of o-C2B10H12 (144 mg, 1.0 mmol) in diethyl ether (20 mL) at 0 °C, and the mixture was stirred at room temperature for 1 h. The resulting Li2C2B10H10 suspension was then cooled to 0 °C, and PdCl2(PPh3)2 (700 mg, 1.0 mmol) was added. The reaction mixture was then stirred for 0.5 h at room temperature, giving a yellow suspension. After filtration, the residue was further extracted with diethyl ether (10 mL  2). The diethyl ether solutions were combined and concentrated to 20 mL. Complex 2 was obtained as yellow crystals after this solution stood at room temperature overnight (464 mg, 60%). 1 H NMR (CD2Cl2): δ 7.35 (m, 6H, C6H5), 7.21 (m, 24H, C6H5). 13 C{1H} NMR (CD2Cl2): δ 133.3 (t, 2JC-P = 6.8 Hz), 131.6 (d, 1 JC-P = 42.9 Hz), 130.1, 128.2 (t, 3JC-P = 5.1 Hz), the cage

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Qiu et al.

Table 2. Crystal Data and Summary of Data Collection and Refinement for 1-5 1

2

4

5

C38H40B10PtP2 861.83 P(-1) 11.538(1) 11.733(1) 16.028(1) 68.574(1) 71.865(1) 77.144(1) 1905.0(1) 2 1.502 0.71073 3.795 0.032 0.077

C8H28B10NiP2 353.05 Pnma 11.306(2) 15.471(2) 11.253(2) 90 90 90 1968.2(5) 4 1.191 0.71073 1.131 0.043 0.098

C28H34B10NiP2 599.30 P(-1) 11.812(1) 15.698(2) 17.794(2) 89.94(1) 84.81(1) 74.48(1) 3165.1(7) 4 1.258 0.71073 0.733 0.061 0.124

)

)

formula C38H40B10NiP2 C38H40B10PdP2 fw 725.45 773.14 P(-1) space group P21/n a, A˚ 14.767(3) 11.561(1) b, A˚ 16.511(3) 11.766(1) c, A˚ 16.039(3) 16.043(1) R, deg 90 111.35(1) β, deg 92.85(3) 98.55(1) γ, deg 90 102.89(1) 3906(1) 1916.6(3) V, A˚3 Z 4 2 1.234 1.340 Dcalcd, Mg/m3 radiation (λ), A˚ 0.71073 0.71073 0.606 0.596 μ, mm-1 a 0.049 0.048 R1 0.117 0.113 wR2a P P P P a R1 = Fo| - |Fc / |Fo|; wR2 = [ [w(Fo2 - Fc2)2]/ [w(Fo2)2]]1/2.

3

Table 3. Crystal Data and Summary of Data Collection and Refinement for 7-10 and 13 7

8

10

13

C14H32B10NiP2 429.15 P21 8.937(1) 15.886(1) 17.545(2) 90 104.205(2) 90 2414.9(4) 4 1.180 0.71073 0.934 0.033 0.084

C44H44B10NiP2 801.54 P21/n 12.958(1) 21.107(1) 15.398(1) 90 92.682(1) 90 4188.9(4) 4 1.271 0.71073 0.572 0.031 0.081

C38H58B10NiP2 743.59 P21/n 18.276(3) 11.582(2) 20.716(3) 90 108.34(1) 90 4162.5(30) 4 1.187 0.71073 0.126 0.048 0.089

)

)

formula C38H38B10I2NiP2 C8H27B10BrNiP2 fw 977.23 431.96 space group P(-1) Ama2 a, A˚ 12.597(2) 15.253(2) b, A˚ 12.615(2) 11.484(2) c, A˚ 14.992(2) 11.858(2) R, deg 71.936(3) 90 β, deg 78.406(3) 90 γ, deg 71.484(2) 90 2133.9(5) 2077.0(5) V, A˚3 Z 2 4 1.521 1.381 Dcalcd, Mg/m3 radiation (λ), A˚ 0.71073 0.71073 2.004 2.998 μ, mm-1 a 0.041 0.055 R1 a 0.098 0.149 wR2 P P P P a 2 R1 = Fo| - |Fc / |Fo|; wR2 = [ [w(Fo - Fc2)2]/ [w(Fo2)2]]1/2.

9

carbons were not observed. 11B NMR (CD2Cl2): δ -3.9 (d, J = 136.7 Hz, 2B), -12.2 (br, unresolved, 1B), -14.2 (d, J = 146.2 Hz, 3B), -15.6 (d, J = 174.5 Hz, 4B). 31P NMR (162 MHz, CD2Cl2): δ 30.5. IR (KBr, cm-1): νBH 2566 (vs). This is a known complex,13a but no NMR data were reported. Preparation of (η2-C2B10H10)Pt(PPh3)2 (3). This complex was prepared as yellow crystals from Li2C2B10H10 [prepared in situ from o-C2B10H12 (144 mg, 1.0 mmol) and n-BuLi (1.30 mL, 2.1 mmol, 1.6 M in hexane)] and PtCl2(PPh3)2 (789 mg, 1.0 mmol) in diethyl ether (30 mL) using the same procedure reported for 2: yield 586 mg (68%). X-ray-quality crystals of 3 were grown from a saturated THF solution at room temperature. 1H NMR (CD2Cl2): δ 7.48 (m, 12H, C6H5), 7.23 (m, 18H, C6H5). 13C{1H} NMR (CD2Cl2): δ 133.5 (d, 2JC-P = 12.8 Hz), 131.5 (d, 1JC-P = 54.9 Hz), 130.5, 128.2 (d, 3JC-P=9.2 Hz), the cage carbons were not observed. 11B NMR (CD2Cl2): δ -3.2 (d, J = 146 Hz, 3B), -9.6 (br, unresolved, 4B), -14.6 (d, J = 139 Hz, 3B). 31P NMR (CD2Cl2): δ 19.73 (JP-Pt = 1788 Hz). IR (KBr, cm-1): νBH 2557 (vs). This is a known complex,13a but no NMR data were reported. Preparation of (η2-C2B10H10)Ni(PMe3)2 (4). This complex was prepared as yellow crystals from Li2C2B10H10 [prepared in situ from o-C2B10H12 (144 mg, 1.0 mmol) and n-BuLi (1.30 mL, 2.1 mmol, 1.6 M in hexane)] and NiCl2(PMe3)2 (282 mg, 1.0 mmol) in diethyl ether (20 mL), using the same procedure reported for 2: yield 293 mg (83%). 1H NMR (CD2Cl2): δ 1.34 (s, 9H), 1.32 (s, 9H) (PCH3). 13C{1H} NMR (CD2Cl2): δ 16.7 (d, 1JC-P = 28.4 Hz), the cage carbons were not observed. 11B NMR (CD2Cl2): δ -4.1 (d, J = 140.0 Hz, 2B), -12.5 (d, J = 141.6 Hz, 2B), -15.5 (d, J = 156.7 Hz, 6B). 31P NMR (CD2Cl2): δ -6.8. IR (KBr, cm-1): νBH 2550 (vs). Anal. Calcd

for C8H28B10NiP2 (4): C, 27.22; H, 7.99. Found: C, 27.69; H, 7.68. Preparation of (η2-C2B10H10)Ni(dppe) (5). This complex was prepared as red crystals from Li2C2B10H10 (1.0 mmol) and NiCl2(dppe) (526 mg, 1.0 mmol) in diethyl ether (30 mL) using the same procedure reported for 2: yield 269 mg (45%). 1H NMR (benzene-d6): δ 7.56 (m, 8H, C6H5), 6.93 (m, 12H, C6H5), 1.76 (m, 4H, CH2). 13C{1H} NMR (benzene-d6): δ 133.0 (d, 2 JC-P = 11.2 Hz), 131.2 (d, 1JC-P = 42.4 Hz), 130.5, 129.7 (d, 3 JC-P = 10.0 Hz) (PC6H5), 26.8 (d, 1JC-P = 38.0 Hz) (PCH2), the cage carbons were not observed. 11B NMR (benzene-d6): δ -1.4 (d, J = 112.6 Hz, 2B), -9.9 (d, J = 124.2 Hz, 2B), -13.0 (br, unresolved, 6B). 31P NMR (benzene-d6): δ 63.00. IR (KBr, cm-1): νBH 2553 (vs). Anal. Calcd for C28H34B10NiP2 (5): C, 56.12; H, 5.72. Found: C, 56.48; H, 5.86. Preparation of (η2-9-I-1,2-C2B10H9)Ni(PPh3)2 (6). This complex was prepared from 1,2-Li2-9-I-C2B10H9 (prepared in situ from 9-I-1,2-C2B10H11 (135 mg, 0.5 mmol) and n-BuLi (0.63 mL, 1.0 mmol, 1.6 M in hexane)) and NiCl2(PPh3)2 (327 mg, 0.5 mmol) in THF (10 mL) using the same procedure reported for 1. Recrystallization from toluene gave 6 3 0.5toluene as a yellow solid after the solution stood at room temperature for 2 days (247 mg, 55%). 1H NMR (benzene-d6): δ 7.28 (m, 24H, PC6H5), 7.11 (m, 3H, toluene), 7.02 (m, 2H, toluene), 6.86 (m, 36H, PC6H5), 2.10 (s, 3H, toluene). 13 C{1H} NMR (benzene-d6): δ 133.7 (d, 2JC-P = 11.5 Hz, PC6H5), 131.9 (d, 1JC-P=44.5 Hz, PC6H5), 130.6 (PC6H5), 129.3 (toluene), 128.7 (d, 3JC-P=6.1 Hz, PC6H5), 128.6 (toluene), 125.7 (toluene), the cage carbons were not observed. 11B NMR (benzene-d6): δ -1.1 (br, unresolved, 3B), -13.9 (br, unresolved, 6B), -22.9 (s, 1B) (B-I). 31 P NMR (benzene-d6): δ 33.9. IR (KBr, cm-1): νBH 2578 (vs).

Article Anal. Calcd for C83H86B20Ni2P4I2 (6þ0.5toluene): C, 55.54; H, 4.83. Found: C, 55.68; H, 5.06. Preparation of (η2-9,12-I2-1,2-C2B10H8)Ni(PPh3)2 (7). A 1.6 M solution of n-BuLi in n-hexane (0.63 mL, 1.0 mmol) was slowly added to a stirring solution of 9,12-I2-1,2-C2B10H10 (198 mg, 0.5 mmol) in THF (10 mL) at 0 °C, and the mixture was stirred at room temperature for 1 h. The resulting 1,2-Li2-9,12I2-1,2-C2B10H8 suspension was then cooled to 0 °C, and NiCl2(PPh3)2 (327 mg, 0.5 mmol) was added. The reaction mixture was then stirred for 0.5 h at room temperature, giving a brown solution. After removal of the solvent, the deep brown residue was extracted with CH2Cl2 (20 mL). The brown filtrate was concentrated to 3 mL. Complex 7 was obtained as yellow crystals after this solution stood at -30 °C overnight (352 mg, 72%). 1H NMR (CD2Cl2): δ 7.40 (m, 6H, C6H5), 7.25 (m, 24H, C6H5). 13C{1H} NMR (CD2Cl2): δ 133.1 (t, 2JC-P = 6.0 Hz), 131.8 (d, 1JC-P = 37.1 Hz), 130.3, 128.2 (t, 3JC-P = 4.9 Hz), the cage carbons were not observed. 11B NMR (CD2Cl2): δ -0.5 (d, J = 140.8 Hz, 2B), -14.0 (br, unresolved, 6B), -21.6 (s, 2B) (B-I). 31P NMR (CD2Cl2): δ 32.4. IR (KBr, cm-1): νBH 2592 (vs). Anal. Calcd for C38H38B10NiP2I2 (7): C, 46.70; H, 3.92. Found: C, 47.19; H, 3.97. Preparation of (η2-3-Br-1,2-C2B10H9)Ni(PMe3)2 (8). This complex was prepared from 1,2-Li2-3-Br-C2B10H9 (prepared in situ from 3-Br-1,2-C2B10H11 (112 mg, 0.5 mmol) and n-BuLi (0.63 mL, 1.0 mmol, 1.6 M in hexane)) and NiCl2(PMe3)2 (141 mg, 0.5 mmol) in THF (10 mL), using the same procedure reported for 1. Complex 8 was obtained as yellow crystals after the solution stood at room temperature for 2 days (67 mg, 31%). 1 H NMR (benzene-d6): δ 0.73 (br, 18H, CH3). 13C{1H} NMR (benzene-d6): δ 16.7 (t, 1JC-P = 14.0 Hz), 16.4 (t, 1JC-P = 13.0 Hz), the cage carbons were not observed. 11B NMR (benzene-d6): δ -1.5 (d, J = 144.6 Hz, 1B), -8.4 (d, J = 147.6 Hz, 1B), -10.8 (d, J = 159.7 Hz, 3B), -11.6 (s, 1B) (B-Br), -12.6 (br, unresolved, 2B), -14.1 (d, J = 173.6 Hz, 2B). 31P NMR (benzene-d6): δ -9.4. IR (KBr, cm-1): νBH 2551 (vs). Anal. Calcd for C8H27B10BrNiP2 (8): C, 22.25; H, 6.30. Found: C, 22.61; H, 6.18. Preparation of (η2-3-C6H5-1,2-C2B10H9)Ni(PMe3)2 (9). This complex was prepared from 1,2-Li2-3-C6H5-C2B10H9 (prepared in situ from 3-C6H5-1,2-C2B10H11 (110 mg, 0.5 mmol) and n-BuLi (0.63 mL, 1.0 mmol, 1.6 M in hexane)) and NiCl2(PMe3)2 (141 mg, 0.5 mmol) in THF (10 mL), using the same procedure reported for 1. Complex 9 was obtained as yellow crystals after the solution stood at room temperature for 3 days (90 mg, 42%). 1H NMR (CD2Cl2): δ 7.82 (m, 2H, C6H5), 7.30 (m, 3H, C6H5), 1.16 (br, 18H, CH3). 13C{1H} NMR (CD2Cl2): δ 133.6, 127.6, 126.9 (C6H5), 16.5 (t, 1JC-P = 15.6 Hz), 16.2 (t, 1 JC-P = 14.4 Hz) (PCH3), the cage carbons were not observed. 11 B NMR (CD2Cl2): δ -2.8 (d, J = 144.6 Hz, 1B), -3.8 (s, 1B) (B-Ph), -8.2 (d, J = 137.1 Hz, 1B), -12.2 (d, J = 143.1 Hz, 2B), -15.2 (d, J = 146.0 Hz, 5B). 31P NMR (CD2Cl2): δ -9.1. IR (KBr, cm-1): νBH 2550 (vs). Anal. Calcd for C14H32B10NiP2 (9): C, 39.18; H, 7.52. Found: C, 38.96; H, 7.71. Preparation of (η2-3-C6H5-1,2-C2B10H9)Ni(PPh3)2 (10). This complex was prepared from 1,2-Li2-3-C6H5-1,2-C2B10H9 (prepared in situ from 3-C6H5-1,2-C2B10H11 (110 mg, 0.5 mmol) and n-BuLi (0.63 mL, 1.0 mmol, 1.6 M in hexane)) and NiCl2(PPh3)2 (327 mg, 0.5 mmol) in THF (10 mL), using the same procedure reported for 1. Complex 10 was obtained as orange crystals after the solution stood at room temperature for 3 days (305 mg, 76%). 1H NMR (CD2Cl2): δ 7.70 (d, J = 7.2 Hz, 2H, BC6H5), 7.45 (t, J = 7.2 Hz, 1H, BC6H5), 7.33 (m, 6H, PC6H5),

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7.18 (m, 14H, BC6H5 and PC6H5), 7.06 (m, 12H, PC6H5). 13 C{1H} NMR (CD2Cl2): δ 135.3, 134.0 (m, JC-P unresolved), 131.9 (d, 1JC-P = 44.2 Hz), 130.5, 128.6 (m, JC-P unresolved), 128.1, the cage carbons were not observed. 11B NMR (CD2Cl2): δ -0.8 (s, 1B) (B-Ph), -1.0 (d, J = 124.8 Hz, 1B), -7.7 (d, J = 132.8 Hz, 1B), -11.9 (d, J = 124.8 Hz, 3B), -13.4 (d, J = 153.6 Hz, 4B). 31P NMR (CD2Cl2): δ 29.6. IR (KBr, cm-1): νBH 2557 (vs). Anal. Calcd for C44H44B10NiP2 (10): C, 65.93; H, 5.53. Found: C, 66.12; H, 5.54. Reactions of 1 with Phosphines. An NMR tube was loaded with 1 (25 mg, 0.035 mmol) and THF (0.5 mL). Phosphine (0.138 mmol) was then added to the NMR tube at room temperature in a glovebox. These reactions were monitored by 11B and 31P NMR spectra at room temperature. 31P NMR spectra indicated the quantitative formation of (η2-C2B10H10)Ni(dppe) (5), (η2-C2B10H10)Ni[P(OEt)Ph2]2 (11), and (η2-C2B10H10)Ni[P(OEt)3]2 (12) after one hour. (η2-C2B10H10)Ni(PPh3)(PCy3) (13) was observed as a major product. For 11: 11B NMR (THF): δ -2.8 (2B), -11.2 (2B), -14.1 (6B). 31P NMR (THF): δ 134.6. For 12: 11B NMR (THF): δ -2.8 (2B), -10.6 (2B), -13.5 (4B), -15.0 (2B). 31P NMR (THF): δ 160.1. For 13: 11B NMR (THF): δ -2.8 (2B), -11.6 (2B), -13.4 (4B), -14.2 (2B). 31P NMR (THF): δ 42.90 (1P), 31.18 (1P). X-ray Structure Determination. All single crystals were immersed in Paraton-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 Mo KR radiation (0.71073 A˚). An empirical absorption correction was applied using the SADABS program.33 All structures were solved by direct methods and subsequent Fourier difference techniques and refined anisotropically for all nonhydrogen atoms by full-matrix least-squares on F2 using the SHELXTL program package.34 For the non-centrosymmetric structures, the appropriate enantiomorph was chosen by refining Flack’s parameter x toward zero.35 All hydrogen atoms were geometrically fixed using the riding model, so that a detailed discussion of the B-H distances was not warranted. Crystal data and details of data collection and structure refinements are given in Tables 2 and 3, respectively. Further details were included in the Supporting Information.

Acknowledgment. This work was supported by grants from the Research Grants Council of the Hong Kong SAR (Project No. 404108), The Chinese University of Hong Kong, and State Key Laboratory of Elemento-Organic Chemistry, Nankai University (Project No. 0314). Note Added after ASAP Publication. In the version of this paper published on Sep 23, 2010, the designation of group 8 was incorrectly given in the title, abstract, and text. The correct designation of group 10 now appears in the version published on Oct 1, 2010. Supporting Information Available: Crystallographic data in CIF format for 1-5, 7-10, and 13. This material is available free of charge via the Internet at http://pubs.acs.org. (33) Sheldrick, G. M. SADABS: Program for Empirical Absorption Correction of Area Detector Data; University of G€ottingen: Germany, 1996. (34) Sheldrick, G. M. SHELXTL 5.10 for Windows NT: Structure Determination Software Programs; Bruker Analytical X-ray Systems, Inc.: Madison, WI, USA, 1997. (35) Flack, H. D. Acta Crystallogr. 1983, A39, 876.