Synthesis, structural characterization, ligand displacement reaction, and electrochemical property of ruthenium complexes incorporating linked cyclopentadienyl-carboranyl ligands

Article abstract of DOI:10.1021/om0493816

Reactions of the dilithium salts of carbon-bridged cyclopentadienyl- carboranyl ligands with 1 equiv of [RuCl₂(COD)]_x in THF afforded the organoruthenium(II) complexes [η⁶:σ-Me ₂C-(C₅H₄)(C₂B₁₀H ₁₀)]Ru(COD) (1a), [η⁵:σ-Me₂C(C ₉H₆)(C₂B₁₀H₁₀)]Ru(COD) (2a), and [η⁵:σ-H₂C-(C₁₃H ₈)(C₂B₁₀H₁₀)]Ru(COD) (3a), respectively. Treatment of 1a with bidentate tertiary phosphines in THF gave the corresponding COD displacement complexes [η⁵:σ-Me ₂C(C₅H₄)-(C₂B₁₀H ₁₀)]Ru(dppe) (1b, dppe = 1,2-bis(diphenylphosphino)ethane), [η⁵:σ-Me₂C(C₅H₄)(C ₂B₁₀-H₁₀)]Ru(dppm) (1c, dppm = bis(diphenylphosphino)methane), [η⁵:σ-Me ₂C(C₅H₄)(C₂B₁₀H ₁₀)]-Ru(dppf) (1d, dppf = 1,1′-bis(diphenylphosphino)ferrocene) , and [η⁵:σ-Me₂C(C₅H ₄)(C₂B₁₀H₁₀)]-Ru(dppc) (1e, dppc = 1,2-(Ph₂P)₂-1,2-C₂B₁₀H ₁₀). 1a also reacted with 2,2′-bipyridine (bipy) to offer [η⁵:σ-Me₂C(C₅H₄)(C ₂B₁₀H₁₀)]Ru(bipy) (1f). However, 1a did not react with monodentate tertiary phosphines such as PPh₃ and PCy ₃, tertiary amines, and bidentate ligands with no π-acidity such as dimethoxyethane and tetramethylethylenediamine. These results imply that a bidentate ligand with π-acidity is critical to displace the COD in 1a. The electrochemical studies showed that the electron-donating power of various ligands increases in the following order: cyclopentadienyl < indenyl < fluorenyl, and COD < dppc < dppm ≈ dppe < bipy. All of these new complexes were fully characterized by various spectroscopic techniques and elemental analyses. Their molecular structures (except for 1d) were further confirmed by single-crystal X-ray analyses.

Full text of DOI:10.1021/om0493816

5864
Organometallics 2004, 23, 5864-5872
Synthesis, Structural Characterization, Ligand
Displacement Reaction, and Electrochemical Property of
Ruthenium Complexes Incorporating Linked
Cyclopentadienyl-Carboranyl Ligands
Yi Sun,† Hoi-Shan Chan,† Pierre H. Dixneuf,‡ and Zuowei Xie*,†
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories,
Hong Kong, China, and Institut de Chimie de Rennes, UMR 6509 CNRS, Universite´ de
Rennes, Organome´talliques et Catalyse, Campus de Beaulieu, 35042 Rennes, France
Received August 10, 2004
Reactions of the dilithium salts of carbon-bridged cyclopentadienyl-carboranyl ligands with
1 equiv of [RuCl2(COD)]x in THF afforded the organoruthenium(II) complexes [η5:σ-Me2C-
(C5H4)(C2B10H10)]Ru(COD) (1a), [η5:σ-Me2C(C9H6)(C2B10H10)]Ru(COD) (2a), and [η5:σ-H2C-
(C13H8)(C2B10H10)]Ru(COD) (3a), respectively. Treatment of 1a with bidentate tertiary
phosphines in THF gave the corresponding COD displacement complexes [η5:σ-Me2C(C5H4)-
(C2B10H10)]Ru(dppe) (1b, dppe ) 1,2-bis(diphenylphosphino)ethane), [η5:σ-Me2C(C5H4)(C2B10-
H10)]Ru(dppm) (1c, dppm ) bis(diphenylphosphino)methane), [η5:σ-Me2C(C5H4)(C2B10H10)]-
Ru(dppf) (1d, dppf ) 1,1′-bis(diphenylphosphino)ferrocene), and [η5:σ-Me2C(C5H4)(C2B10H10)]-
Ru(dppc) (1e, dppc ) 1,2-(Ph2P)2-1,2-C2B10H10). 1a also reacted with 2,2′-bipyridine (bipy)
to offer [η5:σ-Me2C(C5H4)(C2B10H10)]Ru(bipy) (1f). However, 1a did not react with monodentate
tertiary phosphines such as PPh3 and PCy3, tertiary amines, and bidentate ligands with no
π-acidity such as dimethoxyethane and tetramethylethylenediamine. These results imply
that a bidentate ligand with π-acidity is critical to displace the COD in 1a. The electrochemi-
cal studies showed that the electron-donating power of various ligands increases in the
following order: cyclopentadienyl < indenyl < fluorenyl, and COD < dppc < dppm ≈ dppe
< bipy. All of these new complexes were fully characterized by various spectroscopic
techniques and elemental analyses. Their molecular structures (except for 1d) were further
confirmed by single-crystal X-ray analyses.
Introduction
electron richness of the metal center and to the labile
ligands, thus favoring oxidative coupling of the unsatur-
ated molecules, and to the steric hindrance of the C5-
Me5 group favoring regioselective couplings.1 By con-
trast, (η5-C5R5)RuCl(PPh3)2 complexes underwent activa-
tion of terminal alkynes into ruthenium-vinylidene key
intermediates that controlled catalytic anti-Markovni-
kov additions to alkynes.6 These catalytic processes are
favored by electron-releasing PR3 ligands and illustrate
how simple COD/ligand exchanges can modify the action
of the catalyst.
On the other hand, ruthenium half-sandwich com-
plexes, in which a cyclopentadienyl ligand is tethered
to a donor atom, also receive much attention.7 The
tethered donor atom in Cp-D chelating ligands can
prevent rotation of the Cp ring and allow the planar
chirality to be exploited in an efficient discrimination,
through a strong coordination to the Ru atom, or can
temporarily and reversibly coordinate to a Ru atom
while stabilizing highly reactive, electronically and
sterically unsaturated species,8 to meet the require-
ments of various catalytic processes. For example, a
Ruthenium half-sandwich complexes of the type (η5-
C5R5)RuXL2 [R ) H, Me; X ) Cl, Br; L2 ) phosphines,
COD (1,5-cyclooctadiene)] are effective catalysts for C-C
bond-forming reactions.1 For example, (η5-C5H5)RuCl-
(COD) catalyzed a variety of coupling reactions of CtC
and CdC bonds for the production of functional dienes.2
(η5-C5Me5)RuCl(COD) allowed the head-to-head cou-
pling of alkynes to form dienes and cyclobutenes3 or the
sequential coupling of alkynes generating aromatic
compounds.4 (η5-C5Me5)RuCl(COD) also promoted double
addition of carbene to alkynes and to enynes to generate
dienes and bicyclo[3.1.0]hexane derivatives.5 The suc-
cess of these catalytic processes is attributed to the
* To whom correspondence should be addressed. Fax: (852)-
26035057. Tel: (852)26096269. E-mail: zxie@cuhk.edu.hk.
† The Chinese University of Hong Kong.
‡ Universite´ de Rennes.
(1) (a) Trost, B. M.; Toste, F. D.; Pinkerton, A. B. Chem. Rev. 2001,
101, 2067. (b) De´rien, S.; Dixneuf, P. H. J. Organomet. Chem. 2004,
689, 1382.
(2) Trost, B. M. Acc. Chem. Res. 2002, 35, 695.
(3) (a) Paih, J. Le.; Monnier, F.; De´rien, S.; Dixneuf, P. H.; Clot, E.;
Eisenstein, O. J. Am. Chem. Soc. 2003, 125, 11964. (b) Paih, J. Le.;
De´rien, S.; Bruneau, C.; Demerseman, B.; Toupet, L.; Dixneuf, P. H.
Angew. Chem., Int. Ed. 2001, 40, 2912.
(6) (a) Bruneau, C.; Dixneuf, P. H. Acc. Chem. Res. 1999, 32, 311.
(b) Trost, B. M.; Martinez, J. A.; Kulawiec, R. J.; Indolese, A. F. J.
Am. Chem. Soc. 1993, 115, 10402. (c) Je´roˆme, F.; Monnier, F.; Lawicka,
H.; De´rien, S.; Dixneuf, P. H. Chem. Commun. 2003, 696.
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(8) Ganter, C. Chem. Soc. Rev. 2003, 32, 130.
(4) Yamamoto, Y.; Ogawa, R.; Itoh, K. Chem. Commun. 2000, 549.
(5) (a) Paih, J. Le.; De´rien, S.; O¨ zdemir, I.; Dixneuf, P. H. J. Am.
Chem. Soc. 2000, 122, 7400. (b) Monnier, F.; Castillo, D.; De´rien, S.;
Toupet, L.; Dixneuf, P. H. Angew. Chem., Int. Ed. 2003, 42, 5474.
10.1021/om0493816 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 10/21/2004

Cyclopentadienyl-Carboranyl Ligands
Organometallics, Vol. 23, No. 24, 2004 5865
1,1′-bis(diphenylphosphino)ferrocene20 were prepared accord-
ing to literature methods. All other chemicals were purchased
from either Aldrich or Acros Chemical Co. and used as received
unless otherwise noted. Cyclic voltammetric measurements
were performed using a BAS CV-50W voltammetric analyzer.
The electrochemical cell comprised a platinum-wire working
electrode, a silver-wire reference electrode, and a platinum-
disk counter electrode. All measurements were made in a dry
N2 atmosphere. All sample solutions (CH2Cl2) contained n-Bu4-
NPF6 (0.15 M) as supporting electrolyte and complex (2.0 ×
10-3 M). Chemical potentials were internally referenced to the
ferrocenium/ferrocene redox system. Infrared spectra were
obtained from KBr pellets prepared in the glovebox on a
Perkin-Elmer 1600 Fourier transform spectrometer. 1H and
13C NMR spectra were recorded on a Bruker DPX 300
spectrometer at 300 and 75 MHz, respectively. 11B and 31P
NMR spectra were recorded on a Varian Inova 400 spectrom-
eter at 128 and 162 MHz, respectively. All chemical shifts are
reported in δ units with references to the residual protons of
the deuterated solvents for proton and carbon chemical shifts,
to external BF3‚OEt2 (0.0 ppm) for boron chemical shifts, and
to external 85% H3PO4 (0.0 ppm) for phosphorus chemical
shifts. Mass spectra were recorded on a Thermo Finnigan MAT
95 XL spectrometer. Elemental analyses were performed by
either MEDAC Ltd. U.K. or Shanghai Institute of Organic
Chemistry, CAS, China.
phosphine-tethered Cp ligand was used in the recon-
stitutive addition of alkynes and allyl alcohols,9 since a
rigid (Cp-PPh2)Ru+ moiety was required in catalysis.
In contrast, a hemilabile amido-appended Cp ligand was
employed in direct derivatization of peptides and pro-
teins10 or proton transfer reactions.11 In the case where
a substrate is more coordinating than the tethered donor
atom, the functionalized side-arm will lose its function
as a coordinating unit, which in turn will change the
properties of the resulting Ru catalysts. To solve this
problem, a new bidentate ligand system is desired.
We have recently developed a novel class of linked
cyclopentadienyl-carboranyl ligands which are finding
many applications in rare earth and early transition
metal chemistry.12 Recent work showed that the [η5:σ-
Me2C(C5H4)(C2B10H10)]M (M ) Ti, Zr, Hf) moiety re-
mains intact in ethylene polymerization and multiple
insertion reactions of unsaturated molecules due to the
presence of the sterically bulky carboranyl unit.13 It is
anticipated that the [η5:σ-Me2C(C5H4)(C2B10H10)]Ru
moiety will be stable and remain intact in catalysis and
the electronic property of the metal center should be
tunable by variation of the structures of the π ligands.
It is hoped that the rigidity of this type of ligand and
unique property of the carborane molecule would add
some new features to organoruthenium chemistry,
especially as the σ(alkyl) carbon-ruthenium bond in
such systems is not stable via either â elimination or
insertion reaction. With this in mind, we have extended
our research to include the late transition metals and
report herein the syntheses, X-ray structures, and
electrochemical properties of [η5:σ-R2C(L)(C2B10H10)]Ru-
(COD) (R ) CH3, L ) C5H4, C9H6; R ) H, L ) C13H8)
and their phosphines derivatives generated from COD
displacement reactions.
Preparation of H2C(C13H9)(C2B10H11) (3). To a solution
of o-C2B10H12 (1.00 g, 6.90 mmol) in a dry toluene/diethyl ether
(2:1, 15 mL) mixture was added dropwise a 1.60 M solution of
n-BuLi in n-hexane (8.70 mL, 13.90 mmol) at -78 °C with
stirring, and the mixture was warmed to room temperature
and stirred for 3 h. This solution was then cooled to 0 °C, and
a solution of dibenzofulvene (2.45 g, 13.80 mmol) in a toluene/
diethyl ether (2:1, 15 mL) mixture was slowly added. The
reaction mixture was stirred at 80 °C overnight, quenched with
20 mL of a saturated NH4Cl aqueous solution at 0 °C,
transferred to a separatory funnel, and then diluted with 30
mL of diethyl ether. The organic layer was separated, and the
aqueous layer was extracted with Et2O (3 × 15 mL). The
combined ether solutions were dried over anhydrous MgSO4
and concentrated to give a crude yellow solid, which was
purified by column chromatography (SiO2, hexane/ether, 4:1)
Experimental Section
1
to yield 3 as pale yellow crystals (1.90 g, 85%). H NMR (300
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. THF and n-hexane were freshly
distilled from sodium benzophenone ketyl immediately prior
to use. CH2Cl2 was freshly distilled from CaH2 and P2O5,
respectively, immediately prior to use. Me2C(C5H5)(C2B10H11),14
Me2C(C9H7)(C2B10H11),15 dibenzofulvene,16 6,6′-dimethyldiben-
zofulvene,17 [RuCl2(COD)]x,18 1,2-(Ph2P)2-1,2-C2B10H10,19 and
MHz, CDCl3): δ 7.75 (d, J ) 6.9 Hz, 2H, aryl H), 7.52 (d, J )
7.5 Hz, 2H, aryl H), 7.44-7.33 (m, 4H, aryl H), 4.12 (t, J )
4.5 Hz, 1H, sp3-CH in fluorenyl), 3.46 (s, 1H, CH of cage), 3.05
(d, J ) 4.5 Hz, 2H, CH2). 13C NMR (75 MHz, CDCl3): δ 145.9,
141.3, 128.5, 128.3, 124.8, 120.9 (aryl C), 75.3, 61.8 (cage C),
47.8 (sp3-C in fluorenyl), 42.2 (CH2). 11B NMR (128 MHz,
CDCl3): δ -2.1 (1B), -5.4 (1B), -9.3 (2B), -11.1 (2B), -11.8
(2B), -12.9 (2B). IR (KBr, cm-1): νBH 2574 (vs). Anal. Calcd
for C16H22B10: C, 59.60; H, 6.88. Found: C, 60.27; H, 6.82. HR-
FABMS: m/z calcd for C16H22B10, 322.2719; found, 322.2726.
(9) Trost, B. M.; Vidal, B.; Thommen, M. Chem. Eur. J. 1999, 5,
1055.
(10) Grotjahn, D. B.; Joubran, C.; Combs, D.; Brune, D. C. J. Am.
Chem. Soc. 1998, 120, 11814.
(11) (a) Ayllon, J. A.; Sayers, S. F.; Sabo-Etienne, S.; Donnadieu,
B.; Chaudret, B.; Clot, E. Organometallics 1999, 18, 3981. (b) Chu, H.
S.; Lau, C. P.; Wong, K. Y. Organometallics 1998, 17, 2768.
(12) Xie, Z. Acc. Chem. Res. 2003, 36, 1.
Preparation of [η5:σ-Me2C(C5H4)(C2B10H10)]Ru(COD)
(1a). A 1.60 M solution of n-BuLi in n-hexane (1.25 mL, 2.00
mmol) was slowly added to a THF solution (15 mL) of Me2C-
(C5H5)(C2B10H11) (1; 0.25 g, 1.00 mmol) at -78 °C with stirring,
and the mixture was warmed to room temperature and stirred
overnight. The powder of [RuCl2(COD)]x (0.28 g, 1.00 mmol)
was added to the resulting solution, and the mixture was
stirred at room temperature for 48 h. After removal of the
solvent and addition of CH2Cl2 (20 mL), the precipitate was
filtered off, and the clear solution was concentrated to about
10 mL. 1a was obtained as orange crystals after slow evapora-
(13) (a) Wang, H.; Wang, Y.; Li, H.-W.; Xie, Z. Organometallics 2001,
20, 5110. (b) Wang, H.; Li, H.-W.; Xie, Z. Organometallics 2003, 22,
4522. (c) Wang, Y.; Wang, H.; Wang, H.; Chan, H.-S.; Xie, Z. J.
Organomet. Chem. 2003, 683, 39. (d) Wang, J.; Zheng, C.; Maguire, J.
A.; Hosmane, N. S. Organometallics 2003, 22, 4839.
(14) Chui, K.; Yang, Q.; Mak, T. C. W.; Xie, Z. Organometallics 2000,
19, 1391.
1
tion of the solvent (0.38 g, 82%). H NMR (300 MHz, CDCl3):
(15) Wang, S.; Yang, Q.; Mak, T. C. W.; Xie, Z. Organometallics 2000,
19, 334.
δ 5.07 (m, 2H, C5H4), 4.79 (m, 2H, CH of COD), 4.57 (m, 2H,
C5H4), 3.68 (m, 2H, CH of COD), 2.63 (m, 2H, CH2 of COD),
2.02 (m, 4H, CH2 of COD), 1.76 (m, 2H, CH2 of COD), 1.38 (s,
(16) Nakano, T.; Takewaki, K.; Yade, T.; Okamoto, Y. J. Am. Chem.
Soc. 2001, 123, 9182.
(17) Kice, J. L. J. Am. Chem. Soc. 1958, 80, 348.
(18) Albers, M. O.; Ashworth, T. V.; Oosthuizen, H. E.; Singleton,
E. Inorg. Synth. 1989, 26, 68.
(20) Bishop, J. J.; Davison, A.; Katcher, M. L.; Lichtenberg, D. W.;
Merrill, R. E.; Smart, J. C. J. Organomet. Chem. 1971, 27, 241.
(19) Alexander, R. P.; Schroeder, H. Inorg. Chem. 1963, 2, 1107.

5866 Organometallics, Vol. 23, No. 24, 2004
Sun et al.
6H, C(CH3)2). 13C NMR (75 MHz, CDCl3): δ 87.8, 86.4 (C5H4),
74.8, 74.7 (CH of COD), 39.8 (C(CH3)2), 33.1, 28.1 (CH2 of
COD), 31.9 (CH3). 11B NMR (128 MHz, CDCl3): δ -4.3 (1B),
-5.1 (1B), -6.6 (2B), -8.9 (4B), -9.8 (2B). IR (KBr, cm-1): νBH
2570 (vs). Anal. Calcd for C18H32B10Ru: C, 47.24; H, 7.05.
Found: C, 46.82; H, 6.88.
cm-1): νBH 2578 (vs). Anal. Calcd for C35H42B10P2Ru: C, 57.28;
H, 5.77. Found: C, 57.55; H, 5.94.
Preparation of [η5:σ-Me2C(C5H4)(C2B10H10)]Ru(dppf)
(1d). A THF solution (10 mL) of [η5:σ-Me2C(C5H4)(C2B10H10)]-
Ru(COD) (1a; 0.23 g, 0.50 mmol) and a THF solution (5 mL)
of dppf (0.31 g, 0.60 mmol) were mixed at room temperature
and then refluxed for 24 h, followed by the identical procedures
Preparation of [η5:σ-Me2C(C9H6)(C2B10H10)]Ru(COD)
(2a). This complex was prepared as red-brown crystals from
n-BuLi in n-hexane (1.60 M, 1.25 mL, 2.00 mmol), Me2C(C9H7)-
(C2B10H11) (2; 0.30 g, 1.00 mmol), and [RuCl2(COD)]x (0.28 g,
1.00 mmol) in THF (15 mL) using the identical procedures
reported for 1a: yield 0.33 g (64%). 1H NMR (300 MHz,
CDCl3): δ 7.76 (d, J ) 8.7 Hz, 1H, aryl H), 7.39 (dd, J ) 8.7
and 6.6 Hz, 1H, aryl H), 7.11 (d, J ) 8.7 Hz, 1H, aryl H), 6.91
(dd, J ) 8.7 and 6.6 Hz, 1H, aryl H), 5.60 (d, J ) 2.7 Hz, 1H,
indenyl), 4.80 (d, J ) 2.7 Hz, 1H, indenyl), 4.62 (m, 1H, CH of
COD), 3.70 (m, 1H, CH of COD), 2.80 (m, 2H, CH of COD),
2.72 (m, 2H, CH2 of COD), 2.50 (m, 2H, CH2 of COD), 2.25 (m,
2H, CH2 of COD), 1.86 (m, 2H, CH2 of COD), 1.68 (s, 3H,
C(CH3)2), 1.43 (s, 3H, C(CH3)2). 13C NMR (75 MHz, CDCl3): δ
131.5, 129.7, 125.5, 123.2, 118.4, 112.7, 87.8, 84.3, 84.2
(indenyl), 82.0, 79.0, 77.2, 75.3 (CH of COD), 42.7 (C(CH3)2),
38.0, 27.6, 27.4, 26.3 (CH2 of COD), 33.7, 32.7 (CH3). 11B NMR
(128 MHz, CDCl3): δ -3.8 (1B), -4.3 (1B), -6.5 (2B), -9.1
(6B). IR (KBr, cm-1): νBH 2570 (vs). Anal. Calcd for C22H34B10-
Ru: C, 52.04; H, 6.75. Found: C, 51.76; H, 6.56.
1
reported for 1b to give 1d as yellow solids (0.38 g, 84%). H
NMR (300 MHz, CDCl3): δ 7.61-7.29 (m, 20H, aryl H), 4.98,
4.46, 4.34, 4.29, 4.19, 3.88 (br, 2H each, C5H4), 1.38 (s, 6H,
CH3) 13C NMR (75 MHz, CDCl3): δ 135.3, 134.8, 131.5, 129.9,
129.7, 127.6 (aryl C), 81.9, 76.6, 75.6, 74.9, 71.4, 70.6 (C5H4),
40.2 (C(CH3)2), 32.1 (CH3). 11B NMR (128 MHz, CDCl3): δ -3.7
(2B), -6.5 (8B). 31P NMR (162 MHz, CDCl3): δ 41.47. IR (KBr,
cm-1): νBH 2545 (vs). Anal. Calcd for C44H48B10FeP2Ru: C,
58.47; H, 5.36. Found: C, 58.70; H, 5.37.
Preparation of [η5:σ-Me2C(C5H4)(C2B10H10)]Ru(dppc)‚
THF (1e‚THF). A THF solution (10 mL) of [η5:σ-Me2C(C5H4)-
(C2B10H10)]Ru(COD) (1a; 0.23 g, 0.50 mmol) and a THF
solution (5 mL) of dppc (1,2-(Ph2P)2-1,2-C2B10H10) (0.31 g, 0.60
mmol) were mixed at room temperature and then refluxed for
48 h, followed by the identical procedures reported for 1b to
1
give 1e‚THF as yellow crystals (0.64 g, 68%). H NMR (300
MHz, CDCl3): δ 8.00-7.00 (m, 20H, aryl H), 4.64 (m, 2H,
C5H4), 4.26 (m, 2H, C5H4), 3.63 (m, 4H, THF), 1.61 (m, 4H,
THF), 1.32 (s, 6H, CH3). 13C NMR (75 MHz, CDCl3): δ 136.6,
136.4, 136.2, 135.6, 131.2, 129.0, 127.4 (aryl C), 90.5, 90.2, 88.3
(C5H4), 39.7 (C(CH3)2), 32.0 (CH3). 11B NMR (128 MHz,
CDCl3): δ -3.6 (6B), -5.9 (2B), -8.4 (12B). 31P NMR (162
MHz, CDCl3): δ 99.84. IR (KBr, cm-1): νBH 2566 (s). Anal.
Calcd for C40H58B20OP2Ru: C, 51.43; H, 6.26. Found: C, 51.48;
H, 5.96.
Preparation of [η5:σ-H2C(C13H8)(C2B10H10)]Ru(COD) (3a).
This complex was prepared as dark red crystals from n-BuLi
in n-hexane (1.60 M, 1.25 mL, 2.00 mmol), H2C(C13H9)-
(C2B10H11) (3; 0.32 g, 1.00 mmol), and [RuCl2(COD)]x (0.28 g,
1.00 mmol) in THF (15 mL) using the identical procedures
reported for 1a: yield 0.28 g (52%). 1H NMR (300 MHz,
C6D6): δ 7.06-6.88 (m, 4H, aryl H), 6.89 (d, J ) 8.7 Hz, 2H,
aryl H), 6.49 (dd, J ) 8.7 and 6.3 Hz, 2H, aryl H), 3.33 (d, J )
5.7 Hz, 2H, CH2), 3.10 (m, 4H, CH of COD), 2.32 (m, 4H, CH2
of COD), 1.71 (m, 4H, CH2 of COD). 13C NMR (75 MHz, C6D6):
δ 156.5, 130.7, 127.5, 127.2, 126.8, 126.5, 125.6, 124.5, 124.2,
120.4, 119.9, 119.2, 109.4 (aryl C), 88.8, 77.5, 68.2, 65.1 (CH
of COD), 45.9 (CH2), 35.8, 31.0, 28.7, 25.1 (CH2 of COD). 11B
NMR (128 MHz, C6D6): δ -2.8 (2B), -5.5 (4B), -8.1 (4B). IR
(KBr, cm-1): νBH 2550 (vs). Anal. Calcd for C22H34B10Ru: C,
52.04; H, 6.75. Found: C, 52.00; H, 6.55.
Preparation of [η5:σ-Me2C(C5H4)(C2B10H10)]Ru(bipy)
(1f). A toluene solution (10 mL) of [η5:σ-Me2C(C5H4)(C2B10H10)]-
Ru(COD) (1a; 0.23 g, 0.50 mmol) and a THF solution (5 mL)
of 2,2′-bipyridine (0.08 g, 0.50 mmol) were mixed at room
temperature and then refluxed for 48 h, followed by the
identical procedures reported for 1b to give 1f as purple
1
crystals (0.18 g, 71%). H NMR (300 MHz, CDCl3): δ 9.37 (d,
J ) 5.4 Hz, 2H, bipy), 8.03 (d, J ) 8.1 Hz, 2H, bipy), 7.66 (dd,
J ) 8.1 and 7.6 Hz, 2H, bipy), 7.27 (dd, J ) 7.6 and 5.4 Hz,
2H, bipy), 4.41 (m, 2H, C5H4), 3.99 (m, 2H, C5H4), 1.59 (s, 6H,
CH3). 13C NMR (75 MHz, CDCl3): δ 153.8, 132.5, 124.4, 122.0
(bipy), 80.1, 77.2 (C5H4), 41.7 (C(CH3)2), 31.9 (CH3). 11B NMR
(128 MHz, CDCl3): δ -3.1 (1B), -3.8 (1B), -5.2 (1B), -7.5
(2B), -8.5 (2B), -10.2 (1B), -12.7 (2B). IR (KBr, cm-1): νBH
2570 (vs). Anal. Calcd for C20H28B10N2Ru: C, 47.51; H, 5.58;
N, 5.54. Found: C, 47.60; H, 5.60; N, 5.60.
Preparation of [η5:σ-Me2C(C5H4)(C2B10H10)]Ru(dppe)
(1b). A THF solution (10 mL) of [η5:σ-Me2C(C5H4)(C2B10H10)]-
Ru(COD) (1a; 0.23 g, 0.50 mmol) and a THF solution (5 mL)
of dppe (0.24 g, 0.60 mmol) were mixed at room temperature
and stirred for 24 h. After removal of THF, the resulting solid
was washed with n-hexane. Recrystallization from CH2Cl2 (10
1
mL) gave 1b as yellow crystals (0.30 g, 81%). H NMR (300
X-ray Structure Determination. All single crystals were
immersed in Paraton-N oil and sealed under N2 in thin-walled
glass capillaries. Data were collected at 293 K on a Bruker
SMART 1000 CCD diffractometer using Mo KR radiation. An
empirical absorption correction was applied using the SADABS
program.21 All structures were solved by direct methods and
subsequent Fourier difference techniques and refined aniso-
tropically for all non-hydrogen atoms by full-matrix least
squares calculations on F2 using the SHELXTL program
package.22a For noncentrosymmetric structure 1b, the ap-
propriate enantiomorph was chosen by refining Flack’s pa-
rameter x toward zero.22b Most of the carborane hydrogen
atoms were located from difference Fourier syntheses. All other
hydrogen atoms were geometrically fixed using the riding
model. Crystal data and details of data collection and structure
MHz, CDCl3): δ 7.92-6.74 (m, 20H, aryl H), 5.32 (m, 2H,
C5H4), 4.30 (m, 2H, C5H4), 2.87 (t, J ) 9.0 Hz, 2H, CH2), 2.48
(t, J ) 9.0 Hz, 2H, CH2), 1.48 (s, 6H, CH3). 13C NMR (75 MHz,
CDCl3): δ 132.4, 131.6, 130.8, 129.5, 128.9, 128.4, 128.0, 127.6
(aryl C), 82.7, 74.6 (C5H4), 39.8 (C(CH3)2), 31.6 (CH3), 24.6 (d,
JCP ) 21.2 Hz, PCH2CH2P). 11B NMR (128 MHz, CDCl3): δ
-4.2 (2B), -7.5 (4B), -9.6 (4B). 31P NMR (162 MHz, CDCl3):
δ 81.03. IR (KBr, cm-1): νBH 2563 (s). Anal. Calcd for
C36H44B10P2Ru: C, 57.82; H, 5.93. Found: C, 57.70; H, 5.79.
Preparation of [η5:σ-Me2C(C5H4)(C2B10H10)]Ru(dppm)
(1c). A THF solution (10 mL) of [η5:σ-Me2C(C5H4)(C2B10H10)]-
Ru(COD) (1a; 0.23 g, 0.50 mmol) and a THF solution (5 mL)
of dppm (0.23 g, 0.60 mmol) were mixed at room temperature
and then refluxed for 24 h, followed by the identical procedures
reported for 1b to give 1c as yellow crystals (0.28 g, 75%). 1H
NMR (300 MHz, CDCl3): δ 7.67-6.99 (m, 20H, aryl H), 5.30
(m, 2H, C5H4), 5.06 (m, 1H, PCH2P), 4.38 (m, 2H, C5H4), 4.01
(m, 1H, PCH2P), 1.60 (s, 6H, CH3). 13C NMR (75 MHz,
CDCl3): δ 139.0, 133.9, 131.7, 131.2, 129.9, 129.2, 128.7, 128.0
(aryl C), 81.0, 71.3 (C5H4), 43.90 (PCH2P), 40.1 (C(CH3)2), 32.1
(CH3). 11B NMR (128 MHz, CDCl3): δ -4.0 (2B), -7.0 (4B),
-9.2 (4B). 31P NMR (162 MHz, CDCl3): δ 13.23. IR (KBr,
(21) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen: Germany,
1996.
(22) (a) Sheldrick, G. M. SHELXTL 5.10 for Windows NT: Structure
Determination Software Programs; Bruker Analytical X-ray Systems,
Inc.: Madison, WI, 1997. (b) Flack, H. D. Acta Crystallogr. 1983, A39,
876.

Cyclopentadienyl-Carboranyl Ligands
Organometallics, Vol. 23, No. 24, 2004 5867
Table 1. Crystal Data and Summary of Data Collection and Refinement for 1a-3a and 3
1a
2a
3a
3
formula
cryst size (mm)
fw
C
18H32B10Ru
C22H34B10Ru
0.60 × 0.40 × 0.15
507.7
C24H32B10Ru
0.40 × 0.35 × 0.30
529.7
C16H22B10
0.30 × 0.25 × 0.20
322.4
0.80 × 0.55 × 0.40
457.6
triclinic
P1h
cryst syst
space group
a, Å
monoclinic
Cc
orthorhombic
Pnma
monoclinic
P21/c
9.236(1)
10.181(1)
12.537(1)
86.31(1)
74.17(1)
69.23(1)
1059.9(1)
2
7.278(1)
21.082(2)
15.304(2)
90
10.219(2)
11.867(2)
20.697(4)
90
11.681(2)
23.528(5)
13.623(3)
90
b, Å
c, Å
R, deg
â, deg
98.88(1)
90
90
90
90
90
γ, deg
V, Å3
2320.0(4)
4
2509.8(9)
4
3744(1)
8
Z
Dcalcd, Mg/m3
radiation (λ) Å
2θ max, deg
µ, mm-1
F(000)
1.434
1.453
1.402
1.144
Mo KR (0.71073)
56.0
Mo KR (0.71073)
56.0
Mo KR (0.71073)
51.0
Mo KR (0.71073)
50.0
0.742
0.686
0.638
0.056
468
1040
1080
1344
no. of obsd reflns
no. of params refnd
goodness of fit
R1
5002
4765
2214
4296
262
299
170
471
1.113
1.061
1.175
1.046
0.061
0.057
0.039
0.084
wR2
0.175
0.134
0.111
0.259
Table 2. Crystal Data and Summary of Data Collection and Refinement for 1b, 1c, 1e, and 1f
1b
1c
1e‚THF
1f
formula
cryst size (mm)
fw
C
36H44B10P2Ru
C35H42B10P2Ru
0.40 × 0.30 × 0.20
733.8
C40H58B20OP2Ru
0.20 × 0.10 × 0.05
934.1
C20H28B10N2Ru
0.40 × 0.30 × 0.20
505.6
0.20 × 0.10 × 0.05
747.8
monoclinic
P21
cryst syst
space group
a, Å
monoclinic
P21/c
monoclinic
P21/n
triclinic
P1h
9.142(1)
17.669(1)
11.253(1)
90
9.167(1)
18.141(1)
21.169(1)
90
11.303(1)
31.324(2)
13.287(1)
90
9.142(1)
9.550(1)
14.199(2)
105.91(1)
91.42(1)
102.02(1)
1161.5(2)
2
b, Å
c, Å
R, deg
â, deg
91.48(1)
90
95.09(1)
90
96.93(1)
90
γ, deg
V, Å3
1817.2(1)
2
3506.7(3)
4
4669.9(4)
4
Z
Dcalcd, Mg/m3
radiation (λ), Å
2θ max, deg
µ, mm-1
F(000)
1.367
1.390
1.329
1.446
Mo KR (0.71073)
50.0
Mo KR (0.71073)
56.1
Mo KR (0.71073)
50.0
Mo KR (0.71073)
56.0
0.547
0.565
0.439
0.688
768
1504
1920
512
no. of obsd reflns
no. of params refnd
goodness of fit
R1
5972
8468
8229
5472
442
433
577
298
1.221
1.054
1.140
1.048
0.048
0.060
0.044
0.046
wR2
0.111
0.126
0.111
0.106
refinements are given in Tables 1 and 2, respectively. Further
details are included in the Supporting Information.
Scheme 1
Results and Discussion
Ligand. One of the objectives of this work is to study
the effects of the structures of π ligands on electron
richness of the Ru metal center and on the molecular
structures of the resulting Ru metal complexes. The
C-bridged ligands, Me2C(C5H5)(C2B10H11) (1)14 and Me2C-
(C9H7)(C2B10H11) (2),15 were developed earlier in our
laboratory. We attempted to prepare the fluorenyl
analogue, Me2C(C13H9)(C2B10H11), using the known
procedures. However, 6,6′-dimethyldibenzofulvene did
not react with Li2C2B10H10 under various reaction
conditions because of steric reasons. A less bulkier
substrate, dibenzofulvene, was then chosen instead.
Treatment of Li2C2B10H10 with 2 equiv of dibenzofulvene
in toluene/ether (2:1) gave, after hydrolysis with a
saturated NH4Cl aqueous solution, the desired product
H2C(C13H9)(C2B10H11) (3) as pale yellow crystals in 85%
isolated yield (Scheme 1). An excess amount of diben-
zofulvene was necessary since part of it was polymerized
under the reaction conditions.16
The 1H NMR spectrum of 3 showed multiplets of
aromatic protons in the range 7.33-7.75 ppm, one

5868 Organometallics, Vol. 23, No. 24, 2004
Sun et al.
Scheme 2
Figure 1. Molecular structure of H2C(C13H9)(C2B10H11) (3),
showing one of the two independent molecules in the unit
cell. Selected distances [Å] and angles [deg]: C1-C11 )
1.562(5) [1.529(5)], C11-C12 ) 1.549(5) [1.546(5)], C1-
C2 ) 1.682(5) [1.652(5)], C12-C13 ) 1.522(5) [1.520(5)],
C12-C24 ) 1.518(5) [1.519(5)], C1-C11-C12 ) 121.6(3)
[117.1(3)], C11-C12-C13 ) 117.4(3) [113.2(3)], C11-C12-
C24 ) 117.5(3) [115.2(4)], C13-C12-C24 ) 102.9(3)
[102.5(3)]. Distances and angles in brackets are those of a
second molecule.
triplet of the sp3-CH proton of the fluorenyl group at
4.12 ppm, one doublet of the bridging methylene protons
at 3.05 ppm, and one singlet of the cage CH proton at
3.46 ppm. Its 13C NMR spectrum exhibited six aromatic
carbon signals, two cage carbon resonances, one meth-
ylene, and one sp3-CH carbon peak, respectively. The
11B NMR spectrum displayed a 1:1:2:2:2:2 splitting
pattern, which differed from that of compounds 1 (1:1:
2:2:4) and 2 (1:1:3:2:3), respectively, indicating that the
11B NMR spectra are very sensitive to the cage carbon
substituents. The molecular structure of 3 was con-
firmed by an X-ray analysis and is shown in Figure 1.
The bond distances and angles are normal in compari-
son with the literature data.12
Table 3. Selected Structural Data for 1a-3aa
1a
2a
3a
Ru-Ccage
Ru-Cring
2.213(3)
2.207 (3)
2.222(4)
2.227(4)
2.238(4)
2.256(4)
2.230(4)
2.238(4)
1.386(6)
1.402(7)
1.394(7)
108.4(3)
111.8
2.219(4)
2.198(5)
2.231(9)
2.255(6)
2.338(7)
2.387(5)
2.282(9)
2.207(10)
1.383(10)
1.400(9)
1.3912(9)
108.3(4)
111.9
2.228(4)
2.202(4)
2.344(3)
2.344(3)
2.449(3)
2.449(3)
2.358(4)
2.185(4)
1.405(5)
1.405(5)
1.405(5)
111.9(4)
113.0
av Ru-Cring
av Ru-CCOD
CdC (COD)
av CdC (COD)
Cring-Cbridge-Ccage
Cent-Ru-Ccage
[η5:σ-R2C(C5R′4)(C2B10H10)]Ru(COD) Complexes.
Compounds 1-3 contain two acidic protons, cage CH
and sp3-CH of the cyclic group, which can be removed
by strong bases such as n-BuLi to give the dianionic
salts. Treatment of their dilithium salts with 1 equiv of
[RuCl2(COD)]x at room temperature in THF afforded,
respectively, [η5:σ-Me2C(C5H4)(C2B10H10)]Ru(COD) (1a)
as orange crystals in 82% isolated yield, [η5:σ-Me2C-
(C9H6)(C2B10H10)]Ru(COD) (2a) as red crystals in 64%
isolated yield, and [η5:σ-H2C(C13H8)(C2B10H10)]Ru(COD)
(3a) as dark red crystals in 52% isolated yield (Scheme
2).
Complexes 1a-3a are quite soluble in polar organic
solvents such as THF and pyridine, soluble in toluene,
CH2Cl2, and CHCl3, but insoluble in n-hexane. Their
stabilities in air follow the trend 1a > 2a > 3a. 1a is
stable in air in both solid and solution phases. 2a is
stable in air in the solid state only, whereas 3a is air-
sensitive in both solid state and solution phase. The 1H
NMR spectra of 1a-3a all showed the presence of the
linked organic-inorganic hybrid ligand and COD in a
molar ratio of 1:1. Their 13C NMR spectra were in line
with the 1H NMR ones. The 11B NMR spectra exhibited
a 1:1:2:4:2 splitting pattern for 1a, a 1:1:2:6 splitting
pattern for 2a, and a 2:4:4 splitting pattern for 3a. Their
a Cent: the centroid of the five-membered ring. Distances are
in Å and angles are in deg.
solid-state IR spectra all displayed a characteristic
terminal B-H absorption at ∼2550 cm-1
.
The molecular structures of 1a-3a were confirmed
by single-crystal X-ray analyses and are shown in
Figures 2-4, respectively. The coordination environ-
ments of the Ru atom in all three complexes are similar,
in which the Ru(II) ion is η5-bonded to the five-
membered ring of the cyclopentadienyl, or indenyl or
fluorenyl group, σ-bound to the carborane cage carbon,
and coordinated to two carbon-carbon double bonds of
the COD molecule. Thus, they are 18-electron com-
plexes. The selected bond distances and angles are
compiled in Table 3 for comparison. The average Ru-
C(C5 ring) and CdC(COD) distances are in the order
1a < 2a < 3a, whereas the average Ru-C(COD)
distances get shorter from 1a to 2a to 3a. These results
indicate that the back-bonding between Ru(II) and COD
becomes stronger from 1a to 3a, suggesting that the
electron-donating power of π ligands follows the trend
fluorenyl > indenyl > cyclopentadienyl. This observa-
tion is consistent with the literature report.23 The Cent-
Ru-C(cage) angles range from 111.8° to 113.0°, which

Cyclopentadienyl-Carboranyl Ligands
Organometallics, Vol. 23, No. 24, 2004 5869
Scheme 3
are close to the corresponding value of 112.2° found in
Cp*RuCl(COD).24 The characteristic slippage of the
indenyl and fluorenyl rings is also observed with aver-
age slip fold (∆) values of 0.136(7) Å in 2a and 0.142(3)
Å in 3a. All of these values can be compared with those
reported in the literature.25
COD Displacement Reactions. The labile nature
and relative thermodynamic stability of metal-COD
complexes are often used to stabilize a catalytically
active organometallic fragment. The first step of the
catalytic transformation involves substitution of solvent
and/or substrate molecules for the outgoing COD ligand.
The lability of COD ligands in LRuCl(COD) (L ) C5H5,
C9H7) is able to undergo exchange reactions with
different tertiary phosphine ligands rapidly and quant-
itatively.24,25b,e The COD ligand in 1a is the most labile
among the three Ru(COD) complexes since the π back-
bonding interactions between the COD and filled d
orbitals of Ru(II) are the weakest in 1a as previously
discussed. On the other hand, cyclopentadienyl is the
smallest one among the three π ligands. Therefore, 1a
was chosen as a model complex for COD displacement
reactions.
Interestingly, the COD in 1a cannot be replaced by
PR3 (R ) Ph, Cy) even in refluxing THF solution. This
result is significantly different from LRuCl(COD) com-
plexes. 1a did not react with tertiary amines either. We
then turned our attention to bidentate tertiary phos-
phines. Treatment of 1a with 1.2 equiv of bidentate
tertiary phosphines in THF afforded the correspond-
ing COD displacement complexes [η5:σ-Me2C(C5H4)-
(C2B10H10)]Ru(dppe) (1b, dppe ) 1,2-bis(diphenylphos-
phino)ethane), [η5:σ-Me2C(C5H4)(C2B10H10)]Ru(dppm)
(1c, dppm ) bis(diphenylphosphino)methane), [η5:σ-
Me2C(C5H4)(C2B10H10)]Ru(dppf) (1d, dppf ) 1,1′-bis-
(diphenylphosphino)ferrocene), and [η5:σ-Me2C(C5H4)-
(C2B10H10)]Ru(dppc) (1e, dppc ) 1,2-(Ph2P)2-1,2-C2B10-
H10), respectively, in 68-81% isolated yields (Scheme
3). Upon coordination, the 31P NMR chemical shifts of
phosphines were downfield shifted by 35-93 ppm.
Therefore, these displacement reactions were well fol-
lowed by the 31P NMR technique.
It is noteworthy that the COD displacement reactions
were irreversible; that is, 1b-e did not react with COD
to give 1a. The 1H and 31P NMR studies indicated that
only 1b and 1a were detected in the reaction of 1a with
0.5 equiv of dppe, and no dinuclear species with mixed
COD and dppe ligands were observed. These results
may suggest that once one end (phosphine unit) of dppe
coordinates to the Ru center, the other end quickly
displaces the second CdC bond of the COD molecule
via intramolecular substitution reaction to generate the
Table 4. Selected Structural Data for 1b, 1c, 1e,
and 1f
1b
1c
1e
1f
Ru-Ccage
av Ru-Cring
av Ru-P
P-Ru-P
2.141(5) 2.144(4) 2.260(4) 2.095(3)
2.218(7) 2.211(5) 2.237(4) 2.174(3)
2.283(1) 2.293(1) 2.300(1) 2.067(3)a
82.08(5) 71.58(4) 87.93(3) 76.75(10)b
Cring-Cbridge-Ccage 108.5(5) 108.9(4) 108.6(3) 108.9(3)
Cent-Ru-Ccage 114.3 115.0 110.0 117.8
a Average Ru-N distance. b N-Ru-N angle.
final product 1b, implying that the chelating effect plays
a role in the COD displacement reactions. For mono-
phosphines such as PPh3 and PCy3, they may displace
one of the two CdC double bonds of the COD to form
[η5:σ-Me2C(C5H4)(C2B10H10)]Ru(PR3)(η2-COD), which are
unstable, leading to the formation of either [η5:σ-Me2C-
(C5H4)(C2B10H10)]Ru(η4-COD) (1a) or [η5:σ-Me2C(C5H4)-
(C2B10H10)]Ru(PR3)2 depending on the size of incoming
PR3 molecules. The presence of a carboranyl unit in the
constrained ligand not only makes the [η5:σ-Me2C-
(C5H4)(C2B10H10)]Ru moiety very rigid but also reduces
the open space of the central metal ion for the incoming
molecule. As a result, the second PR3 molecule cannot
approach the Ru center to displace the η2-COD. This
could explain why 1a did not react with PR3. Other
possibilities cannot be excluded.
Complexes 1b-e were fully characterized by various
spectroscopic techniques. Only one 31P resonance was
observed in each complex. The pseudo-Cs symmetry of
these complexes was further confirmed by single-crystal
X-ray diffraction studies.
The solid-state structures of complexes 1b, 1c, and
1e are shown in Figures 5-7, respectively. They have
similar coordination geometries. Selected bond distances
and angles are listed in Table 4 for comparison. The
average Ru-C(C5 ring) and Ru-C(cage) distances in 1b
(23) Gassman, P. G.; Winter, C. H. J. Am. Chem. Soc. 1988, 110,
6130.
(24) Serron, S. A.; Luo, L.; Li, C.; Cucullu, M. E.; Stevens, E. D.;
Nolan, S. P. Organometallics 1995, 14, 5290.
(25) (a) Alvarez, P.; Gimeno, J.; Lastra, E.; Garc´ıa-Granda, S.; Van
der Maelen, J. F.; Bassetti, M. Organometallics 2001, 20, 3762. (b) Li,
C.; Cucullu, M. E.; McIntyre, R. A.; Stevens, E. D.; Nolan, S. P.
Organometallics 1994, 13, 3621. (c) Bassetti, M.; Marini, S.; D´ıaz, J.;
Gamasa, M. P.; Gimeno, J.; Rodr´ıguez-AÄ lvarez, Y.; Garc´ıa-Granda, S.
Organometallics 2002, 21, 4815. (d) Cadierno, V.; D´ıez, J.; Pilar, G.
M.; Gimeno, J.; Lastra, E. Coord. Chem. Rev. 1999, 193-195, 147. (e)
Cucullu, M. E.; Luo, L.; Nolan, S. P.; Fagan, P. J.; Jones, N. L.;
Calabrese, J. C. Organometallics 1995, 14, 289. (f) Kamigaito, M.;
Watanabe, Y.; Ando, T.; Sawamoto, M. J. Am. Chem. Soc. 2002, 124,
9994.

5870 Organometallics, Vol. 23, No. 24, 2004
Sun et al.
Figure 3. Molecular structure of [η5:σ-Me2C(C9H6)-
(C2B10H10)]Ru(COD) (2a).
Figure 2. Molecular structure of [η5:σ-Me2C(C5H4)-
(C2B10H10)]Ru(COD) (1a).
and 1c are slightly shorter than those observed in 1a
and 1e, probably due to steric reasons. The average
Ru-P distances in the three complexes are very close
to each other and compare well with the values reported
in the literature.25 The bite angles of the chelate
bisphosphine ligands P-Ru-P show values similar to
those observed in CpRuCl(P-P) complexes.25
It was reported that an increase of the bite angle of
the chelating ligand results in an increase of the cone
angle.26 Thus the cone angles of bisphosphines decrease
in the order dppc > dppe > dppm. It is expected that a
larger cone angle would lead to a smaller Cent-Ru-
C(cage) angle, which is consistent with the experimental
results shown in Table 4. The structural data in Tables
3 and 4 also indicate that the variations in the Cent-
Ru-C(cage) angles observed in 1a-e are much smaller
than those found in CpRuCl(COD) and CpRuCl(P-P)
complexes.25 It may be concluded that the constrained
geometry of the [η5:σ-R2C(C5R′4)(C2B10H10)]Ru moiety
versus the flexible CpRuCl unit creates the differences
in the COD displacement reactions.
Figure 4. Molecular structure of [η5:σ-H2C(C13H8)(C2B10-
H10)]Ru(COD) (3a).
Besides bisphosphines, other bidentate ligands were
also attempted. There were no reactions between 1a and
DME or TMEDA (DME ) dimethoxyethane, TMEDA
) tetramethylethylenediamine) in refluxing THF or
toluene solutions. 2,2′-Bipyridine (bipy), however, was
found to react with 1a in refluxing toluene solution,
affording [η5:σ-Me2C(C5H4)(C2B10H10)]Ru(η2-bipy) (1f) as
purple crystals in 68% isolated yield. It is noteworthy
that pyridine did not react with 1a under various
reaction conditions. These results imply that a bidentate
ligand with π-acidity is critical to displace the COD in
1a. 1f was fully characterized by various spectroscopic
data and elemental analyses. Its structure was con-
firmed by a single-crystal X-ray study.
Figure 5. Molecular structure of [η5:σ-Me2C(C5H4)-
(C2B10H10)]Ru(dppe) (1b).
N-Ru-N angle of 76.75(10)° are close to the corre-
sponding values of 2.095(6) Å and 75.8(2)° found in [Cp*-
(η2-bipy)(η2-EtO2C-CHdCHCO2Et)Ru][PF6].27 The av-
erage Ru-C(ring) and Ru-C(cage) distances are shorter
than the corresponding values observed in 1a-e, prob-
ably owing to the relatively smaller size of bipy mol-
ecule.
As shown in Figure 8, the Ru(II) is η5-bound to a
cyclopentadienyl ring, σ-bound to a cage carbon atom
and coordinated to two nitrogen atoms from a bipyridine
molecule in a three-legged piano stool geometry. The
average Ru-N bond length of 2.067(3) Å and the
(26) Van Haaren, R. J.; Goubitz, K.; Fraanje, J.; Van Strijdonck, G.
P. F.; Oevering, H.; Coussens, B.; Reek, J. N. H.; Kamer, P. C. J.; Van
Leeuwen, P. W. N. M. Inorg. Chem. 2001, 40, 3363.
(27) Balavoine, G. G. A.; Boyer, T.; Livage, C. Organometallics 1992,
11, 456.

Cyclopentadienyl-Carboranyl Ligands
Organometallics, Vol. 23, No. 24, 2004 5871
Table 5. Redox Potentials of Ruthenium
a
Complexes in CH2Cl2
complex
E1/2(RuIII/RuII) (V)
∆Ep (mV)
1a
2a
3a
1b
1c
1dc
1e
1f
0.601
0.484
0.397b
0.250
0.257
0.659
0.581
-0.149
100
91
88
93
75
102
94
81
a All potentials are given relative to ferrocenium/ferrocene. Pt
working electrode: 100 mV s-1; recorded in CH2Cl2 with n-Bu4NPF6
(0.15 M) as supporting electrolyte. b 200 mV s-1 c E1/2(FeIII/FeII)
.
) 0.232 V.
relative to ferrocenium/ferrocene are compiled in Table
5. Complexes 1a, 2a, and 3a have similar molecular
structures with different π ligands, thus allowing us to
compare the electron-donating ability of π ligands. The
first three entries in Table 5 correspond to complexes
1a, 2a, and 3a, indicating that the electron richness of
the Ru atom increases in the order 1a < 2a < 3a. This
result is consistent with that previously derived from
X-ray analyses and confirms that the electron-donating
power of π ligands increases in the following order:
cyclopentadienyl < indenyl < fluorenyl.23 The presence
of a ferrocenyl unit in 1d, reflected by the appearance
of the additional wave of the Fc+/Fc couple, causes a
relative increase of the RuIII/RuII potential,28 which
makes it less comparable with others. Therefore, 1d will
not be compared with other Ru complexes. Thus, the
electron richness of the Ru metal center increases in
the order 1a < 1e < 2a < 3a < 1c ≈ 1b < 1f, and
electron-donating abilities of the bidentate ligands
follow the trend COD < dppc < dppm ≈ dppe < bipy.
Figure 6. Molecular structure of [η5:σ-Me2C(C5H4)-
(C2B10H10)]Ru(dppm) (1c).
Figure 7. Molecular structure of [η5:σ-Me2C(C5H4)-
(C2B10H10)]Ru(dppc) (1e) (the solvated THF molecule is not
shown).
Conclusion
A new class of ruthenium complexes containing
carbon-bridged carboranyl-cyclopentadienyl (-indenyl or
-fluorenyl) ligands was synthesized and fully character-
ized. They are all 18-electron species and adopt a three-
legged piano stool geometry. These complexes showed
a different reactivity pattern in COD displacement
reactions in comparison with the classical LRuCl(COD)
(L ) Cp, indenyl) complexes presumably due to the
presence of sterically bulky and constrained organic-
inorganic hybrid ligands. For example, 1a did not react
with monodentate tertiary phosphines and amines. The
COD in 1a was replaced only by bidentate ligands with
π-acidity.
Both structural and electrochemical studies indicated
that the electron-donating ability of π ligands increases
in the order cyclopentadienyl < indenyl < fluorenyl, and
the electron-donating power of σ ligands follows the
trend COD < dppc < dppm ≈ dppe < bipy. This work
offers useful information for further investigation of this
novel class of ruthenium carborane complexes for both
stoichiometric and catalytic reactions.
Figure 8. Molecular structure of [η5:σ-Me2C(C5H4)-
(C2B10H10)]Ru(bipy) (1f).
Electrochemistry. For all complexes, the electro-
chemical study revealed that all observed redox pro-
cesses are one-electron and reversible processes at the
Acknowledgment. This work was supported by
grants from the Research Grants Council of The Hong
Kong Special Administration Region (Project No. CUHK
scan rate of 100 or 200 mV s-1, as indicated by the (iPa
/
iPc) ratios of unity and the ∆Ep peak separations in the
range 75-102 mV. The redox potentials E1/2 given
(28) Sˇteˇpnicˇka, P.; Gyepes, R.; Lavastre, O.; Dixneuf, P. H. Orga-
nometallics 1997, 16, 5089.

5872 Organometallics, Vol. 23, No. 24, 2004
Sun et al.
4026/02P), Mainline Research Scheme of The Chinese
University of Hong Kong (Project No. MR01/002), and
the PROCORE-France/Hong Kong Joint Research
Scheme sponsored by the Research Grants Council of
Hong Kong and the Consulate General of France in
Hong Kong (Reference No. F-HK15/02T). This research
is also partially supported by an anonymous donor who
made a donation to the Department of Chemistry at The
Chinese University of Hong Kong. We thank Dr. Yaorong
Wang for the preparation of complex 2a. Z.X. acknowl-
edges the Croucher Foundation for a Senior Research
Fellowship Award.
Supporting Information Available: Crystallographic
data and data collection details, atomic coordinates, bond
distances and angles, anisotropic thermal parameters, and
hydrogen atom coordinates for 3, 2a, 3a, 1a-c, 1e‚THF, and
1f as CIF files. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM0493816