Synergistic Effect of a Low-Valent Cobalt Complex and a

Synergistic Effect of a Low-Valent Cobalt Complex and a Trimethylphosphine Ligand on Selective C−F Bond Activation of Perfluorinated Toluene...
0 downloads 0 Views 1MB Size
Download PDF
Organometallics 2009, 28, 5771–5776 DOI: 10.1021/om900589z

5771

Synergistic Effect of a Low-Valent Cobalt Complex and a Trimethylphosphine Ligand on Selective C-F Bond Activation of Perfluorinated Toluene Tingting Zheng,† Hongjian Sun,† Yue Chen,† Xiaoyan Li,*,† Simon D€ urr,‡ Udo Radius,‡ § and Klaus Harms †

School of Chemistry and Chemical Engineering, Shandong University, Shanda Nanlu 27, 250100 Jinan, People’s Republic of China, ‡Institut fuer Anorganische Chemie, Universit€ at W€ urzburg, Am Hubland, D-97074 W€ urzburg, Germany, and §Fachbereich Chemie, Philpps-Universitaet Marburg, Hans-Meerwein-Strasse, 35032 Marburg, Germany Received July 8, 2009

The aryne cobalt complex [Co(4-CF3-η2-C6F3)(PMe3)3] (1) was formed from the reaction of [Co(PMe3)4] and perfluorinated toluene through selective activation of two C-F bonds of perfluorotoluene. A mechanism for the formation of complex 1 is proposed and in most parts experimentally verified. Following this mechanism, a synergistic effect of an electron-rich cobalt(0) center and one of its trimethylphosphine ligands is responsible for the C-F activation of two carbon-fluorine bonds of perfluorotoluene. The detection of difluorotrimethylphoshphorane as the sole byproduct provides strong evidence for this mechanism. Complex [Co(4-CF3-C6F4)(PMe3)3] (4), an intermediate of the proposed mechanism to the aryne complex, was also isolated and structurally characterized. Complex 4 transforms to complex 1 via activation of a second C-F bond of a perfluorotolyl ligand only in the presence of trimethylphosphine in the reaction mixture. Complex 4 reacts with CO under atmospheric pressure and room temperature to give [Co(4-CF3-C6F4)(CO)2(PMe3)2] (6) and with bromobenzene via one-electron oxidative addition of the C-Br bond to give the cobalt(II) bromide [CoBr(4-CF3-C6F4)(PMe3)3] (8) and a C-C-coupling product, 4-phenylheptafluorotoluene (7). The structures of complexes 1, 4, and 8 were determined by X-ray crystallography. Introduction The activation of carbon-fluorine bonds by transition metal complexes presents a significant chemical challenge.1 The design of well-defined soluble transition metal complexes capable of selective activation and functionalization of strong carbon-fluorine bonds under mild conditions is a highly desirable goal and of considerable current interest. Few methods have been reported for the activation of carbon-fluorine bonds of fluorinated compounds by transition metal complexes.2-6 Oxidative addition at low-valent

metal centers, such as Pt(II), W(0), and Ni(0), is an effective route,3,7-9 whereas reports of carbon-fluorine bond activation mediated by cobalt complexes are scarce.10-15 Richmond et al. reported C-F bond formation with cobaltocenium fluoride as a novel fluoride source to obtain fluoroorganic compounds. Fluoride ions are mobilized by C-F bond activation in a saturated perfluorocarbon, e.g., perfluorodecalin.12 C-F bond activation and cleavage was also discovered by Hughes et al. for reactions of carbonyl cobaltates [Co(CO)3L]and [{Co(CO)3 L}2]- (L = CO, PPh3, PMe2Ph, PMe3) with

*Corresponding author. E-mail: [email protected]. (1) For reviews on C-F activation see: (a) Doherty, N. M.; Hoffmann, N. W. Chem. Rev. 1991, 91, 553. (b) Burdeniuc, J.; Jedlicka, B.; Crabtree, R. H. Chem. Ber./Recl. 1997, 130, 145. (c) Kiplinger, J. L.; Richmond, T. G.; Osterberg, C. E. Chem. Rev. 1994, 94, 373. (d) Murphy, E. F.; Murugavel, R.; Roesky, H. W. Chem. Rev. 1997, 97, 3425. (e) Mazurek, U.; Schwarz, H. Chem. Commun. 2003, 1321. (f) Braun, T.; Perutz, R. N. Chem. Commun. 2002, 2749. (g) Torrens, H. Coord. Chem. Rev. 2005, 249, 1957. (h) Jones, W. D. Dalton Trans. 2003, 3991. (i) Perutz, R. N.; Braun, T. In Comprehensive Organometallic Chemistry III, Vol. 1; Crabtree, R. H., Mingos, M. P., Eds.; Elsevier: Oxford, 2007; p 725. (2) B€ ohm, V. P. W.; Gst€ ottmayr, C. W. K.; Weskamp, T.; Herrmann, W. A. Angew. Chem., Int. Ed. 2001, 40, 3387–89. (3) (a) Schaub, T.; Radius, U. Chem.;Eur. J. 2005, 11, 5024. (b) Schaub, T.; Backes, M.; Radius, U. J. Am. Chem. Soc. 2006, 128, 15964– 15965. (c) Schaub, T.; Fischer, P; Steffen, A.; Braun, T; Radius, U; Mix, A. J. Am. Chem. Soc. 2008, 130, 9304–9317. (4) Richmond, T. G. Angew. Chem., Int. Ed. 2000, 39, 3241–3244. (5) Mazurek, U.; Schwarz, H. Chem. Commun. 2003, 1321–1326. (6) Young, R. J.; Grushin, V. V. Organometallics 1999, 18, 294–296.

(7) (a) Lopez, O.; Crespo, M.; Font-Bardia, M.; Solans, X. Organometallics 1997, 16, 1233. (b) Bennett, M. A.; Wenger, E. Chem. Ber. 1997, 130, 1029–1042. (8) Kiplinger, J. L.; King, M. A.; Arif, A. M.; Richmond, T. G. Organometallics 1993, 12, 3382. (9) (a) Ceder, R.; Granell, J.; Muller, G.; Font-Bardia, M.; Solans, X. Organometallics 1995, 14, 5544. (b) Keen, A. L.; Doster, M.; Johnson, S. A. J. Am. Chem. Soc. 2007, 129, 810–819. (c) Keen, A. L.; Johnson, S. A. J. Am. Chem. Soc. 2006, 128, 1806–1807. (10) Hughes, R. P.; Doig, S. J.; Hemond, R. C.; Smith, W. L.; Davis, R. E.; Gadol, S. M.; Holland, K. D. Organometallics 1990, 9, 2745–2753. (11) Doig, S. J.; Hughes, R. P.; Davis, R E.; Gadol, S. M.; Holland, K. D. Organometallics 1984, 3, 1921–1922. (12) Bennett, B. K; Harrison, R. G.; Richmond, T. G. J. Am. Chem. Soc. 1994, 116, 11165–11166. (13) Kiplinger, J. L; Richmond, T. G.; Osterberg, C. E. Chem. Rev. 1994, 94, 373–431. (14) Li, X.; Sun, H; Yu, F.; Floerke, U.; Klein, H.-F. Organometallics 2006, 25, 4695–4697. (15) Hughes, R. P.; Lindner, D. C.; Rheingold, A. L.; Yap, G. P. A. Organometallics 1995, 15, 5678–5686.

r 2009 American Chemical Society

Published on Web 09/09/2009

pubs.acs.org/Organometallics

5772

Organometallics, Vol. 28, No. 19, 2009

octafluorocyclooctatetraene.10 We reported the synthesis of the first organo cobalt(III) complex containing a [C-Co-F] fragment through a cyclometalation reaction involving carbonfluorine bond activation at a cobalt(I) center using azine as an anchoring group (eq 1).14

Zheng et al. Scheme 1

cobalt(II) bromide [CoBr(4-CF3-C6F4)(PMe3)3] (8) under C-C coupling, which gives 4-phenylheptafluorotoluene (7). The structures of complexes 1, 4, and 8 were determined by X-ray crystallography.

Results and Discussion Selective C-F Bond Activation of Octafluorotoluene. The reaction of [Co(PMe3)4] with perfluorinated toluene in diethyl ether results in the formation of the benzyne cobalt complex 1 (eq 2).

Lately, several mechanistic studies on transition metal complex mediated C-F bond activation have been published. Perutz and co-workers employed both experimental and computational methods to rationalize the diverse reactivity of bis(phosphine)Pt(0) complexes toward fluoropyridines.16 In a computational study on the reaction of C6F6 with [IrMe(PEt3)3], phosphine-assisted C-F activation was proposed as a novel mechanism just recently.17 Johnson et al. presented important results on the selectivity of C-F versus C-H bond activation using a bis(trimethylphosphine)nickel(II) system. Although C-H bond activation is thermodynamically disfavored, it seems to be more easily accessible kinetically.18 In many cases C-F/C-H bond activations are competing reactions. The catalytic hydrodefluorination of aromatic fluorocarbons was carried out by ruthenium N-heterocyclic carbene complex. On the basis of the kinetic investigation, the hydrodefluorination mechanisms of C6F6 and C6F5H were proposed and discussed.19 Herein, we report the selective activation of two C-F bonds of perfluorinated toluene by a trimethylphosphinesupported cobalt(0) complex to afford a perfluoro benzyne cobalt complex, [Co(4-CF3-η2-C6F3)(PMe3)3] (1), and propose a mechanism of its formation. As an intermediate, perfluorotolyl complex [Co(4-CF3-C6F4)(PMe3)3] (4) was successfully isolated and structurally characterized. The formation of difluorotrimethylphosphorane, where the activated fluoride in this process winds up, provides powerful evidence for a synergistic effect of an electron-rich low-valent complex center and one of its trimethylphosphine ligands in the C-F bond activation process. Furthermore, the reactions of complex 4 with trimethylphosphine, carbon monoxide, and bromobenzene have been studied. Complex 4 reacts with bromobenzene via one-electron oxidative addition of the C-Br bond at the cobalt(I) center to produce the (16) Nova, A.; Erhardt, S.; Jasim, N. A.; Perutz, R. N.; Macgregor, S. A.; McGrady, J. G.; Whitwood, A. C. J. Am. Chem. Soc. 2008, 130, 15499–15511. (17) Erhardt, S.; Macgregor, S. A. J. Am. Chem. Soc. 2008, 130, 15490–15498. (18) Johson, S. A.; Huff, C. W.; Mustafa, F.; Saliba, M. J. Am. Chem. Soc. 2008, 130, 17278–17280. (19) Reade, S. P.; Mahn, M. F.; Whittlesey, M. K. J. Am. Chem. Soc. 2009, 131, 1847-1861.

Red crystals of complex 1, which are very sensitive to air, have been obtained from recrystallization in pentane. The molecular structure of complex 1 reveals a perfluoroaryne complex of zerovalent cobalt (Figure 1). Two modes of coordination, A and B, can represent complex 1 (Scheme 1). Form A is referred to as a π-bonded benzyne complex, while form B describes a di-σ-bonded complex of an ortho-phenylene. The bonding state of 1 is somewhere between these two extremes. Complex 1 exhibits a pseudotetrahedral coordination geometry made up of three P-donors and the centroid of the C1-C2 bond. The metal-carbon bond lengths of 1.919(5) and 1.914(5) A˚ are in the region expected for (sp2)C-Co bonds. The distance of the coordinated bond C1-C2 of 1.345(7) A˚ is significantly shorter compared to the corresponding distance (1.374(7) A˚) in a tetrafluoro-benzyne-iridium complex, [Ir(η5-C5Me5)(PMe3)(η2-C6F4)],20 but closer to that observed for an η2-benzyne nickel complex (1.332(6) A˚).21 The bite angle (C1-Co-C2 = 41.1(2)o) is typical for this type of three-membered chelate ring, which is coplanar with the aromatic ring. The CF3 group shows rotational disorder. Co-P3 (2.2370(12) A˚) is remarkably longer than Co-P1 (2.1867(14) A˚) and Co-P2 (2.1865(13) A˚), and the angle P1-Co-P2 (103.74(5)o) is larger than P1-Co-P3 (101.31(5)o) and P2-Co-P3 (101.78(15)o). The (20) Hughes, R. P.; Williamson, A.; Sommer, R. D.; Rheingold, A. L. J. Am. Chem. Soc. 2001, 123, 7443–7444. (21) Bennett, M. A.; Hambley, T. W.; Roberts, N. K. Organometallics 1985, 4, 1992–2000.

Article

Figure 1. Molecular structure of 1. Selected distances [A˚] and angles [deg]: Co-C1 1.914(5), Co-C2 1.919(5), C1-C2 1.345(7), C2-C3 1.350(7), C3-C4 1.425(7), C4-C5 1.395(7), C5-C6 1.373(7), C1-C6 1.341(7), Co-P1 2.1867(14), CoP2 2.1865(13), Co-P3 2.2370(12); C1-Co-C2 41.1(2), P1-Co-P2 103.74(5), P1-Co-P3 101.31(5), P2-Co-P3 101.78(5).

donor atom P3 appears to be subject to a stronger transinfluence of the C1,C2-donor/acceptor. A proposed mechanism for the formation of complex 1 is given in Scheme 2. The first likely step is the precoordination of the aromatic system to the Co(0) center under elimination of a phosphine ligand and formation of a complex with a η2coordinated perfluorotoluene ligand.3c The bond activation of the first C-F bond of the substrate is facilitated by the nucleophilicity of the low-valent Co(PMe3)3 group. Selective oxidative addition of the carbon-fluorine bond of perfluorinated toluene at the para position at the cobalt(0) center should lead to a cobalt(II) intermediate, 3, which comproportionates with PMe3 to give the cobalt(I) complex 4 and difluorotrimethylphosphorane, F2PMe3. The oxidative addition of the second carbon-fluorine bond generates intermediate 5, which transfers the fluoride ligand to PMe3 and results in the formation of the end product 1 and F2PMe3. The formation of F2PMe3 in solution was verified via 31P NMR.22 The intermediate 4 was successfully isolated as green crystals suitable for single-crystal X-ray diffraction from the reaction mixture through variation of the reaction conditions employed. As the structure reveals (Figure 2), the cobalt atom in 4 is located at the center of a distorted tetrahedron. The Co1-C bond distance is 2.036(3) A˚, which is longer than those observed in complex 1, but in the range expected for a (sp2)C-Co bond. The three Co-P bond lengths are close to an average value of 2.2381 A˚ and unexceptional. The outcome of the reaction of [Co(PMe3)4] and perfluorotoluene to give complexes 1 and 4 strongly depends on the reaction conditions. The yield of complex 4 was improved from 18% to 57% if the reaction was carried out in pentane instead of in diethyl ether under the same reaction conditions. At the same time the yield of complex 1 was reduced from 37% to 11%. On the other hand, the yield of complex 1 was improved from 11% to 44% in pentane if the reaction time was changed from 18 h to (22) Doxsee, K. M.; Hanawalt, E. M.; Weakley, T. J. R. Inorg. Chem. 1992, 31, 4420–4421.

Organometallics, Vol. 28, No. 19, 2009

5773

Figure 2. Molecular structure of 4 (the hydrogen atoms were omitted for clarity). Selected distances [A˚] and angles [deg]: Co1C1 2.036(3), Co1-P1 2.2244(12), Co1-P2 2.2434(10), Co1-P3 2.2465(11); C1-Co1-P1 110.28(9), C1-Co1-P2 116.46(10), C1-Co1-P3 119.47(10), P1-Co1-P2 102.48(4), P1-Co1-P3 104.06(5), P2-Co1-P3 102.11(4). Scheme 2. Suggested Pathway for Formation Mechanism of Complex 1

48 h at room temperature. In this case the yield of complex 4 was reduced from 57% to 6%. Therefore, complex 4 may be regarded as the kinetically controlled product, whereas complex 1 is the thermodynamically stable product. We have also observed that the green solution of complex 4 is thermally very stable, and for the transformation of complex 4 to complex 1 the presence of trimethylphosphine (under formation of difluorotrimethylphosphorane, according to eq 3) is required. Therefore, in the C-F bond activation and formation of complex 1 the free trimethylphosphine ligand and the low-valent cobalt complex [Co(PMe3)4] display a synergistic effect. The mechanism proposed here is significantly different from other phosphine-assisted C-F activation pathway suggested earlier, in which a metallophosphorane is regarded to be an intermediate and a fluorodialkylphosphine alkyl metal complex

5774

Organometallics, Vol. 28, No. 19, 2009

Zheng et al.

is formed.16,17 Due to our investigations, the formation of difluorotrimethylphosphorane plays a crucial role in the C-F activation process.

Reaction of Complex 4 with Carbon Monoxide. Complex 4 slowly reacts in a pentane solution with CO under atmospheric pressure and room temperature to give the dicarbonyl complex [Co(4-CF3-C6F4)(CO)2(PMe3)2], 6, which was isolated in the form of yellow crystals (eq 4). Complex 6 was characterized by IR and NMR spectroscopy as well as C, H, N analysis. In the IR spectrum of 6 there are two strong absorptions of terminal carbonyl ligands at 1920 and 1895 cm-1. The 31P NMR data show a singlet at 30.4 ppm for the two trans-PMe3 ligands. Similar carbonyl cobalt complexes have been reported earlier.23

C,C-Coupling Reaction of Complex 4 with Bromobenzene. Complex 4 reacts with bromobenzene through a one-electron oxidative addition to afford C-C-coupling product 7 and complex 8 according to eq 5.

Figure 3. Molecular structure of 8. Selected distances [A˚] and angles [deg]: C1-Co1 1.973(6), P1-Co1 2.2228(16), P2-Co1 2.3069(17), P3-Co1 2.2240(16), Co1-Br1 2.4607(10); C1Co1-P1 87.96(16), C1-Co1-P2 111.82(19), C1-Co1-P3 87.87(17), P1-Co1-P2 96.01(6), P1-Co1-P3 167.84(7), P2Co1-P3 96.14(6). C1-Co1-Br1 141,40(19), P1-Co1Br1 87.62(5), P2-Co1-Br1 106.78(5), P3-Co-Br1 88.53(5).

the equatorial plane, the large angle C1-Co-Br (141.44(19)°) is caused by in-plane orientation of the perfluorinated 4trifluoromethylphenyl ligand and F, Br repulsions. For the same steric reason the equatorial bond P2-Co1 (2.3069(17) A˚) is considerably longer than axial P1-Co1 (2.2228(17) A˚) and P3-Co1 (2.2240(16) A˚). The distance Co-Br1 (2.4607(10) A˚) is in the normal range.24 The demetalated coupling product 7 forms white crystals suitable for an X-ray structure analysis.3b For the formation of the coupling product 7 and complex 8 we propose a one-electron oxidative addition of bromobenzene to the cobalt atom of 4 in a first step under the formation of complex 8 and an intermediate complex 9 (Scheme 3). As a diorgano cobalt(II) species, complex 9 is not stable and eliminates to form coupling product 7 (reductive elimination) with regeneration of [Co(PMe3)4], which was identified in solution by IR spectroscopy.

Conclusions In summary, the benzyne cobalt complex [Co(4-CF3-η2C6F3)(PMe3)3], 1, is formed via a selective activation of two C-F bonds of perfluorotoluene using a synergistic effect of the electron-rich low-valent cobalt center [Co(PMe3)4] and trimethylphosphine. The formation mechanism of complex 1 is proposed and supported by experiment. The formation of difluorotrimethylphosphorane during this process provides evidence for this mechanism. As an intermediate, [Co(4-CF3C6F4)(PMe3)3] (4) was isolated and structurally characterized. Furthermore, we have shown that 4 converted to 1 through the second C-F bond activation process only in

Complex 8 attains a trigonal-bipyramidal molecular geometry (Figure 3). Two trimethylphosphine ligands are located in axial positions with an angle of P1-Co1-P3 = 167.84(7)°. In

(23) Jiao, G.; Li, X.; Sun, H.; Xu, X. J. Organomet. Chem. 2007, 692, 4251–4258. (24) Suzuki, H.; Abe, Y.; Ishiguro, S. Acta Crystallogr. 2001, C57, 721–722.

Article

Organometallics, Vol. 28, No. 19, 2009

5775

Scheme 3. Formation Mechanism of Compound 7 and Complex 8

the presence of trimethylphosphine. Under 1 bar of CO at 20 °C complex 4 transforms to [Co(4-CF3-C6F4)(CO)2(PMe3)2] (6). Complex 4 reacts with bromobenzene via one-electron oxidative addition of the C-Br bond at a cobalt(I) center to produce the cobalt(II) bromide complex [CoBr(4-CF3-C6F4)(PMe3)3] (8) and the C-C-coupling product 4-phenylheptafluorotoluene (7). The structures of complexes 1, 4, and 8 have been determined by X-ray crystallography.

Experimental Section General Procedures and Materials. Standard vacuum techniques were used in manipulations of volatile and air-sensitive materials. Literature methods were used in the preparation of tetrakis(trimethylphosphine)cobalt(0).25 Octafluorotoluene was obtained from ABCR. All other chemicals were used as purchased. Infrared spectra (4000-400 cm-1), as obtained from Nujol mulls between KBr disks, were recorded on a Nicolet 5700. 1H, 13C, and 31P NMR (300, 75, and 121 MHz, respectively) spectra were recorded on a Bruker Avance 300 spectrometer. 13C and 31P NMR resonances were obtained with broadband proton decoupling. Elemental analyses were carried out on an Elementar Vario EL III. Melting points were measured in capillaries sealed under argon and are uncorrected. X-ray crystallography was performed with a Bruker Smart 1000 diffractometer. Synthesis of Complex 1 and Complex 4. Method a: A solution of octafluorotoluene (2.28 g, 8.26 mmol) in 10 mL of diethyl ether was combined with a solution of Co(PMe3)4 (3.00 g, 8.26 mmol) in diethyl ether (30 mL) at -80 °C. This mixture was allowed to warm to 20 °C and stirred for 24 h to form a redbrown, turbid mixture. The volatiles were transferred under vacuum, and the residue was extracted with pentane (20 mL) and diethyl ether (40 mL), respectively. Crystallization from pentane at -30 °C afforded red-brown single crystals of 1 (0.74 g, 37%) and green single crystals of 4 (0.37 g, 18%) suitable for X-ray analysis. Method b: The reaction was carried out in pentane instead of in diethyl ether. Yield: 1 (0.21 g, 11%); 4 (1.20 g, 57%). Method c: The reaction was carried out in pentane as in method b, but the reaction time increased from 24 to 48 h at the same reaction conditions. Yield: 1 (0.89 g, 44%); 4 (0.12 g, 6%). Analysis for 1, C16H27CoF6P3 [found (calcd)]: C, 39.20 (39.61); H, 5.98 (5.61). Analysis for 4, C16H27CoF7P3 [found (calcd)]: C, 37.87 (38.11); H, 5.48 (5.40). IR (25) Klein, H.-F.; Karsch, H. H. Chem. Ber. 1975, 108, 944.

(Nujol, cm-1): complex 1, 1555 s, ν(CdC), 941 vs, ν (PMe3); complex 4, 1558 s, ν(CdC); 938 vs, ν (PMe3). Transformation of Complex 4 to 1. A solution of 4 (0.36 g, 0.71 mmol) in 30 mL of pentane at -80 °C was combined with a solution of PMe3 (0.20 g, 2.63 mmol) in 10 mL of pentane. This reaction mixture was allowed to warm to 20 °C and stirred for 18 h, and the green solution slowly turned red-brown. Crystallization from pentane at -30 °C yielded 1 (0.23 g, 67%). Synthesis of Complex 6. A solution of 4 (0.50 g, 0.99 mmol) in 50 mL of pentane was stirred under 1 bar of CO for 36 h, and the green solution slowly turned yellow. Upon filtration and cooling to 4 °C, complex 6 was obtained as yellow cubic crystals (0.33 g, yield 70%). Analysis for 6, C15H18CoF7O2P2 [found (calcd)]: C, 37.61 (37.21); H, 3.38 (3.47). IR (Nujol): 1920 vs, ν(CO), 1895 vs, ν(CO), 936 vs, ν(PMe3). 1H NMR (300.1 MHz, C6D6, 300 K): δ 1.30 (br, 18H, PCH3). 31P NMR (121.5 MHz, C6D6, 300 K): δ 30.4 (s). Synthesis of Complex 8 and Compound 7. To the solution of 4 (0,50 g, 1.00 mmol) in 30 mL of pentane was added bromobenzene (0.46 g, 3.00 mmol) with stirring at -80 °C. This reaction mixture was allowed to warm to 20 °C and stirred for 48 h. The color changed from green to yellow-brown. The reaction mixture was filtered. The solid residue was extracted with 20 mL of diethyl ether. Complex 8 as yellow-brown crystals was obtained from pentane/diethyl ether at -30 °C. Yield: 0.14 g (48%). Analysis for 8, C16H27CoBrF7P3 [found (calcd)]: C, 32.71 (32.90); H, 4.38 (4.66). IR (Nujol): 1556 s, ν(CdC); 941 vs, ν (PMe3). Compound 7 as white crystals was obtained from pentane at -30 °C. Yield: 0.08 g (55%). Crystallographic data of complex 1: C16H27CoF6P3, 485.22 g/mol, 0.30  0.25  0.10 mm, monoclinic, P21/n, a = 9.4302(7) A˚; b = 18.4173(17) A˚; c = 12.9476(12) A˚, R = 90°; β = 92.450(10)°; γ = 90°, V = 2246.7(3) A˚3, Z = 4, Dcalcd = 1.435 g-3, μ(Mo KR) = 1.024 mm-1, temperature = 203(2) K, data coll. range 3.84 < 2θ < 49.72°, -10 e h e 10; -21 e k e 21; -13 e l e 15, no. reflns measured = 11 169, no. unique data = 3610 (Rint = 0.1087), parameters 271, GoF on F2 = 1.042, R1 (I g 2σ(I)) = 0.0852, wR2 = 0.1585. Crystallographic data of complex 4: C16H27CoF7P3, 504.22 g/mol, 0.15  0.12  0.10 mm, orthorhombic, P212121, a = 11.887(3) A˚; b = 13.135(4) A˚; c = 15.418(4) A˚, V = 2407.5 (11) A˚3, Z = 4, Dcalcd = 1.391 g-3, μ(Mo KR) = 0.964 mm-1, temperature = 273(2) K, data coll. range 4.08 < 2θ < 50.10°, -14 e h e 12; -15 e k e 15; -18 e l e 18, no. reflns measured = 27 645, no. unique data = 4248 (Rint = 0.0403), parameters 272, GoF on F2 = 1.027, R1 (I g 2σ(I)) = 0.0327, wR2 = 0.0810. Crystallographic data of complex 8: C16H27BrCoF7P3, 584.13 g/mol, 0.330.310.05 mm, monoclinic, C2/c, a=15.0898(14)

5776

Organometallics, Vol. 28, No. 19, 2009

A˚; b=9.2174(8) A˚; c=33.644(4) A˚, R=90°; β=91.620(12)°; γ= 90°, V=4677.6(8) A˚3, Z=8, Dcalcd =1.659 g-3, μ(Mo KR)= 2.703 mm-1, temperature=193(2) K, data coll. range 2.42 < 2θ < 25.00°, -17 e h e 17; -10 e k e 10; -39 e l e 39, no. reflns measured=14 255, no. unique data=3925 (Rint=0.0618), parameters 289, GoF on F2 =1.095, R1 (I g 2σ(I))=0.0485, wR2 = 0.1224. Crystallographic data for compounds 1, 4, and 8 have been deposited with the Cambridge Crystallographic Data Centre as supplementary publications CCDC-718813 (1), CCDC-718814 (4), and CCDC-699824 (8). Copies of the data can be can be obtained free of charge on application to CCDC, 12 Union

Zheng et al. Road, Cambridge CB2 1EZ, UK (fax:(þ44)1223-336-033; e-mail: [email protected]).

Acknowledgment. We gratefully acknowledge support by NSF China No. 20772072. U.R. acknowledges the Deutsche Forschungsgemeinschaft for generous support. Supporting Information Available: Crystallographic data for 1, 4, and 8. This material is available free of charge via the Internet at http://pubs.acs.org.