Reaction of cyclopentadienyl ruthenium complexes with a carborane anion: Effect of the spectator ligands on the substitution site

Article abstract of DOI:10.1021/om700305e

The reaction of cyclopentadienyl ruthenium complexes of the type [RuCl(Cp)L₁L₂] (L₁, L₂ = PPh ₃, PMe₂Ph, PMePh₂; L₁L₂ = dppe; L₁L₂ = COD; L₁ = CO, L₂ = PPh₃) with Licarb (Hcarb = 2-Me-1,2-dicarba-closo-dodecaborane) gives two types of complexes, [Ru(H)(C₅H₄-carb)L ₁L₂] or [Ru(carb)(Cp)-L₁L₂], depending on the nature of the coordination set. The structures of [Ru(carb)(Cp)(PMe₂Ph)₂] and [RuCl(η⁵-C ₅Me₄H)(PMe₂Ph)₂] have been determined by single-crystal crystallography. The role played by the ligand set on the site of nucleophilic attack is discussed in light of the steric crowding and electronic density at the metal center.

Full text of DOI:10.1021/om700305e

Organometallics 2007, 26, 4265-4270
4265
Reaction of Cyclopentadienyl Ruthenium Complexes with a
Carborane Anion: Effect of the Spectator Ligands on the
Substitution Site
Marino Basato,*,† Andrea Biffis,† Gabriella Buscemi,† Elena Callegaro,† Mauro Polo,†
Cristina Tubaro,† Alfonso Venzo,† Chiara Vianini,† Claudia Graiff,‡
Antonio Tiripicchio,‡ and Franco Benetollo§
Dipartimento di Scienze Chimiche, UniVersita` di PadoVa and ISTM-CNR, Via Marzolo 1, I-35131,
PadoVa, Italy, Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica,
UniVersita` di Parma, Viale G.P. Usberti 17/A, I-43100, Parma, Italy, and ICIS-CNR, Corso Stati Uniti 4,
I-35127, PadoVa, Italy
ReceiVed March 28, 2007
The reaction of cyclopentadienyl ruthenium complexes of the type [RuCl(Cp)L1L2] (L1, L2 ) PPh3,
PMe2Ph, PMePh2; L1L2 ) dppe; L1L2 ) COD; L1 ) CO, L2 ) PPh3) with Licarb (Hcarb ) 2-Me-1,2-
dicarba-closo-dodecaborane) gives two types of complexes, [Ru(H)(C5H4-carb)L1L2] or [Ru(carb)(Cp)-
L1L2], depending on the nature of the coordination set. The structures of [Ru(carb)(Cp)(PMe2Ph)2] and
[RuCl(η5-C5Me4H)(PMe2Ph)2] have been determined by single-crystal crystallography. The role played
by the ligand set on the site of nucleophilic attack is discussed in light of the steric crowding and electronic
density at the metal center.
In this context, we were surprised by the preliminary results
obtained in the reaction of [RuCl(Cp)(PPh3)2] with an ethereal
solution of Licarb (Hcarb ) 2-Me-1,2-dicarba-closo-dodecabo-
rane).5 In fact, instead of a simple Cl-/carb- exchange product,
we isolated a hydrido Ru(II) complex, [RuH(C5H4-carb)(PPh3)2]
(1), resulting from a formal nucleophilic attack of carb- on the
cyclopentadienyl group. To our knowledge, this was the first
example of a nucleophilic substitution reaction on a Cp ring
coordinated to a fairly electron-rich metal center such as
ruthenium(II). Indeed, very few examples are reported in the
literature for this type of reaction. They involve electron-poor
metal centers such as Os(IV),6 W(IV),7 and Mo(IV)7a in
cyclopentadienyl complexes and carbanions (from lithium
alkyls6 or Grignard reagents7b) or rather exotic metallophosphide
anions Li[M(PPh2)(CO)5].7a
An article was published by Xie et al., almost at the same
time of our preliminary communication, in which a similar
ruthenium complex [(η5-Me2C(C5H3)(C2B10H10))RuH(PPh3)2]
was obtained in good yield by the reaction of [RuCl2(PPh3)3]
with [Me2C(C5H4)(C2B10H10)]Li2, in which the Me2C bridge
joins a cyclopentadienyl and a carboranyl unit.8 In an extension
of this work, they reported later that the same reaction with
complexes bearing phosphines with smaller cone angles yielded
only the salt metathesis products [(η5: σ-Me2C(C5H4)(C2B10H10))-
RuL2] (L2 ) 2PPh2(OEt) or dppe).9 The observed behavior with
the PPh3 ligands was justified with a sterically induced
intramolecular coupling reaction between the o-carboranyl and
the cyclopentadienyl functionality.
Introduction
Cyclopentadienyl ruthenium(II) complexes are low spin d6
coordinatively saturated octahedral systems and, as a conse-
quence, rather inert toward substitution; for this reason, their
use as catalysts has been generally very limited. However, rather
recently, complexes of the type [RuCl(Cp)(L)2] (L ) PPh3,
PMePh2, PMe2Ph, 1/2dppe, CO, Ph2PNHPh, Ph2PNHC6H11, 1/2-
Ph2PN(Et)PPh2, 1/2Ph2PN(nPr)PPh2, 1/2Ph2PN(iPr)PPh2, and 1/2-
Ph2PN(nBu)PPh2) have been successfully employed as catalysts
in a series of C-C bond forming reactions,1-4 starting from a
variety of diazo compounds. In all cases, preliminary dissocia-
tion of one neutral ligand (phosphine or CO) was needed to
afford the effective catalytic species. We have an ongoing
research project aimed at the improvement of the reactivity of
this type of complexes by changing the steric and electronic
character of the anionic ligand. For example, substitution of a
chloride ligand with a bulky and poor electron-withdrawing
anion, like the one of 2-Me-1,2-dicarba-closo-dodecaborane
(HCC(Me)B10H10), should favor, both for steric and electronic
reasons, the dissociation of a neutral ligand in the crucial
catalytic step.
* Corresponding author. E-mail: marino.basato@unipd.it; phone: +39
049 8275217; fax: +39 049 8275223.
† Universita` di Padova.
‡ Universita` di Parma.
§ ICIS-CNR.
(1) Trost, B. M.; Toste, F. D.; Pinkerton, A. B. Chem. ReV. 2001, 101,
2067.
(2) Guerchais, V. Eur. J. Inorg. Chem. 2002, 783.
(3) (a) Baratta, W.; Del Zotto, A.; Rigo, P. Chem. Commun. 1997, 2163.
(b) Baratta, W.; Del Zotto, A.; Rigo, P. Organometallics 1999, 18, 5091.
(c) Baratta, W.; Herrmann, W. A.; Kratzer, R. M.; Rigo, P. Organometallics
2000, 19, 3664. (d) Del Zotto, A.; Baratta, W.; Verardo, G.; Rigo, P. Eur.
J. Org. Chem. 2000, 2795.
(5) Basato, M., Biffis, A.; Tubaro, C.; Graiff, C.; Tiripicchio, A. Dalton
Trans. 2004, 4092.
(6) Baya, M.; Crochet, P.; Esteruelas, M. A.; On˜ate, E. Organometallics
2001, 20, 240.
(4) (a) Tutusaus, O.; Delfosse, S.; Demonceau, A.; Noels, A. F.; Nun˜ez,
R.; Vin˜as, C.; Teixidor, F. Tetrahedron Lett. 2002, 43, 983. (b) Priya, S.;
Balakrishna, M. S.; Mobin, S. M.; McDonald, R. J. Organomet. Chem.
2003, 688, 227. (c) Simal, F.; Demonceau, A.; Noels, A. F.; Knowles, D.
R. T.; O’Leary, S.; Maitlis, P. M.; Gusev, O. J. Organomet. Chem. 1998,
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(7) (a) Comte, V.; Blacque, O.; Kubicki, M. M.; Mo¨ıse, C. Organome-
tallics 2001, 20, 5432. (b) Forschner, T. C.; Cooper, N. J. J. Am. Chem.
Soc. 1989, 111, 7420.
(8) Sun, Y.; Chan, H.-S.; Dixneuf, P. H.; Xie, Z. Chem. Commun. 2004,
2588.
(9) Sun, Y.; Chan, H.-S.; Xie, Z. Organometallics 2006, 25, 4188.
10.1021/om700305e CCC: $37.00 © 2007 American Chemical Society
Publication on Web 07/13/2007

4266 Organometallics, Vol. 26, No. 17, 2007
Basato et al.
35%). Anal. Calcd for C24H40B10P2Ru (M ) 599.7): C, 48.07; H,
6.72. Found: C, 48.31; H, 6.79.
We present here the results obtained in the reaction of the
anion of 2-Me-1,2-dicarba-closo-dodecaborane with a number
of ruthenium cyclopentadienyl complexes characterized by
different sets of neutral ligands, [RuCl(Cp)L1L2] (L1, L2 ) PPh3,
PMe2Ph, PMePh2; L1L2 ) dppe; L1L2 ) COD; L1 ) CO, L2 )
PPh3). The main purpose is to obtain information on how steric
and electronic variations of the spectator ligands can direct this
peculiar substitution reaction and, on the basis of this informa-
tion, to propose a possible mechanism. The role of steric
hindrance furthermore has been checked by replacing the Cp
ring with the tetramethyl analogue C5Me4H.
[Ru(carb)(Cp)(PMePh2)2] (3). The NMR data and elemental
analysis indicate that the isolated solid is the substitution product
[Ru(carb)(Cp)(PMePh2)2] (3), together with small quantities of the
starting materials Hcarb (ca. 5%) and [RuCl(Cp)(PMePh2)2] (ca.
10%). Characterization of 3: 1H NMR (CDCl3): δ 1.99 (s, 3H,
CH3), 1.83 (t, 6H, CH3 PMePh2, 2JPH ) 3.6 Hz), 1.2-3.0 (br, 10H,
BH), 4.57 (s, 5H, C5H5), 7.04-7.76 (m, 10H, Ph). 31P NMR
(CDCl3): δ 24.9 (s, PMePh2). 13C NMR (CDCl3): δ 16.1 (CH3
PMePh2), 17.1 (CH3), 79.9 (t, C5H5, 2JPC ) 2.1 Hz), 82.1 (CH3-C),
86.1 (t (br), Ru-C), 128.6-133.4 (Ph). MS (ESI) m/z: 567 ([Ru-
(Cp)(PMePh2)2]+, 15%), 367 ([Ru(Cp)(PMePh2)]+, 100%).
[Ru(carb)(Cp)(dppe)] (4). The NMR data indicate that the
substitution product [Ru(carb)(Cp)(dppe)] (4) is contaminated by
the starting materials Hcarb and [RuCl(Cp)(dppe)]. By repeated
treatment of the solid with small portions of hexane (up to 159
mL) and of diethyl ether (up to 100 mL), 4 can be obtained pure
in low yield (25 mg, 10%). 1H NMR (CDCl3): δ 1.32 (s, 3H, CH3),
2.65 (m, 2H, CH2), 3.16 (m, 2H, CH2), 1.2-3.0 (br, 10H, BH),
4.79 (s, 5H, C5H5), 6.75-7.80 (m, 20H, Ph). 31P NMR (CDCl3):
δ 77.2 (s, dppe). 13C NMR (CDCl3): δ 23.8 (m, CH2), 27.6 (CH3),
Experimental Procedures
General Comments. The reagents (Aldrich-Chemie) were high
purity products and generally used as received. All solvents were
dried by standard procedures and distilled under nitrogen im-
mediately prior to use. The reaction apparatus was carefully
deoxygenated, the reactions were performed under argon, and all
operations were carried out under an inert atmosphere. The
complexes [RuCl(Cp)(PPh3)2],10 [RuCl(Cp)(PMe2Ph)2],11 [RuCl-
(Cp)(PMePh2)2],12 [RuCl(Cp)(dppe)],13 [RuCl(Cp)(COD)],14 [RuCl-
(Cp)(CO)(PPh3)],15 and [RuH(C5H4-carb)(PPh3)2] (1)5 and 1-methyl-
1,2-dicarba-closo-dodecaborane (Hcarb)16 were prepared according
to published methods. The solution 1H, 13C{1H}, and 31P{1H}-NMR
spectra were acquired on a Bruker DRX-400 (400.13 MHz for 1H,
100.62 MHz for 13C, and 121.5 MHz for 31P) at room temperature.
The chemical shifts (δ) are reported in units of parts per million
relative to the residual solvent signals, using tetramethylsilane as
an internal standard, for proton and carbon chemical shifts and to
external 85% H3PO4 (0.0 ppm) for phosphorus chemical shifts.
2
84.1 (t, C5H5, JPC ) 2.1 Hz), 80.4 (CH3-C), 85.5 (br, Ru-C),
126.1-137.1 (Ph). MS (ESI) m/z: 465 ([Ru(Cp)(dppe)]+, 100%).
Anal. Calcd for C34H42B10P2Ru (M ) 721.8): C, 56.57; H, 5.87.
Found: C, 56.21; H, 5.62.
[RuH(C5H4-carb)(COD)] (5). Complex 5 obtained with the
general procedure is contaminated by the presence of free Hcarb
and can be obtained NMR pure in very low yield (3-5%) by careful
washing with small quantities of cold diethyl ether. 1H NMR
(C6D6): δ -5.26 (s, 1H, Ru-H), 0.8-3.6 (br, 10H, BH), 1.21 (s,
3H, CH3), 1.79 (m, 2H, CH2), 1.86 (m, 2H, CH2), 2.13 (m, 2H,
CH2), 2.30 (m, 2H, CH2), 3.27 (m, 2H, CH), 3.67 (m, 2H, CH),
4.22 (m, 2H, C5H4), 5.12 (m, 2H, C5H4). 13C NMR (C6D6): δ 22.4
(CH3), 31.4 (CH2), 32.5 (CH2), 60.8 (CH), 61.4 (CH), 77.0 (CH3-
C), 79.3 (C-C5H4), 82.1 (C5H4), 88.9 (C5H4), 89.9 (C5H4). Complex
5 is unstable in CDCl3 so that the initial NMR pattern [1H NMR
(CDCl3): δ -5.44 (s, 1H, Ru-H), 1.2-3.1 (br, 10H, BH), 1.82 (s,
3H, CH3), 2.15 (m, 6H, CH2), 2.30 (m, 2H, CH2), 3.15 (m, 2H,
CH), 3.75 (m, 2H, CH), 4.78 (m, 2H, C5H4), 5.49 (m, 2H, C5H4)]
evolves in a few days to that corresponding to the H/Cl exchange
complex [RuCl(C5H4-carb)(COD)]: 1H NMR (CDCl3): δ 0.96-
3.5 (br, 10H, BH), 1.82 (s, 3H, CH3), 2.18 (m, 6H, CH2), 2.72 (m,
2H, CH2), 4.51 (m, 2H, CH), 4.83 (m, 2H, C5H4), 5.29 (m, 2H,
C5H4), 5.39 (m, 2H, CH). 13C NMR (CDCl3): δ 22.5 (CH3), 26.7
(CH2), 31.1 (CH2), 76.6 (C5H4), 79.3 (CH), 89.6 (CH), 96.3 (C5H4);
CH3-C, C-C5H4, and C-C5H4 were not observed.
General Procedure for Reaction of Complexes [RuCl(Cp)-
L1L2]with n-LiBu. Complexes 2-6 were obtained by reaction of
[RuCl(Cp)L1L2] with carb- in a 1:1.5 molar ratio, in anhydrous
toluene, at room temperature for 3 days.
[Ru(carb)(Cp)(PMe2Ph)2] (2). In this prototype reaction, n-BuLi
(1 mL of a 1.6 M solution in hexane, 1.6 mmol) was added to
Hcarb (0.126 g, 0.79 mmol, in 10 mL of diethyl ether). The resulting
light yellow suspension was left under stirring for ca. 30 min and
then added to a solution of [RuCl(Cp)(PMe2Ph)2] (0.240 g, 0.50
mmol, in 25 mL of toluene). The suspension was stirred for 3 days
at room temperature, after which LiCl was filtered off. The volatiles
were removed under reduced pressure from the clear solution, and
the residue was treated at 0 °C with hexane to give a yellow solid,
which was filtered, washed with hexane, and dried (188 mg, yield
1
63%). H NMR (CDCl3): δ 1.59 (s, 3H, CH3), 1.67 (t, 6H, CH3
2
2
PMe2Ph, JPH ) 4.0 Hz), 1.89 (t, 6H, CH3 PMe2Ph, JPH ) 4.0
Hz), 1.2-3.0 (br, 10H, BH), 4.37 (s, 5H, C5H5), 7.10-7.40 (m,
10H, Ph). 31P NMR (CDCl3): δ 8.3 (s, PMe2Ph). 13C NMR
[RuH(C5H4-carb)(CO)(PPh3)] (6). Complex 6 was obtained as
1
a light maroon solid (215 mg, yield 65%). H NMR (toluene-d8):
δ -11.05 (d, 1H, Ru-H, 2JPH ) 30 Hz), 1.30 (s, 3H, CH3), 1.20-
3.00 (br, 10H, BH), 4.19 (m, 1H, C5H4), 4.25 (m, 1H, C5H4), 5.03
1
(CDCl3): δ 21.5 (t, CH3 PMe2Ph, JPC ) 13.0 Hz), 22.0 (t, CH3
1
2
(m, 1H, C5H4,), 5.05 (m, 1H, C5H4), 7.50-7.60 (m, 15H, Ph). 31
P
PMe2Ph, JPC ) 13.5 Hz), 28.4 (CH3), 83.4 (t, C5H5, JPC ) 2.0
2
NMR (toluene-d8): δ 66.72 (s, PPh3).13C NMR (toluene-d8): δ
22.6 (s, CH3), 75.3 (s, CH3-C), 77.8 (s, C-C5H4), 83.4 (d, C5H4,
2JPC ) 1.0 Hz), 86.5 (d, C5H4, 2JPC ) 1.4 Hz), 87.4 (d, C5H4, 2JPC
Hz), 83.8 (CH3-C), 87.2 (t (br), Ru-C, JPC ) 12.3 Hz), 127.0-
145 (Ph). FT IR (KBr, cm-1): 3103-2853, 2527 (ν(B-H)), 1433,
1279, 908, 746. MS (ESI) m/z: 429 ([Ru(Cp)(PMe2Ph)(PMePh)]+,
30%), 305 ([Ru(Cp)(PMe2Ph)]+, 100%), 288 ([Ru(Cp)(PMePh)]+,
2
) 0.7 Hz), 90.4 (d, C5H4, JPC ) 1.7 Hz), 98.1 (s, C5H4), 127.9-
2
133.3 (Ph), 204.4 (d, CO, JPC ) 14.85 Hz). FT IR (KBr, cm-1):
3056-2857, 2569 (ν(B-H)), 1927, 1480, 1435, 1095, 745. Anal.
Calcd for C27H33B10OPRu (M ) 613.7): C, 52.70; H, 5.36.
Found: C, 52.35; H, 5.25.
Synthesis of [RuCl(η5-C5Me4H)(PPh3)2] (7). This complex was
prepared in two steps, employing the procedure already reported
for the Cp* analogue.17 A mixture of RuCl3‚nH2O (2.10 g, 9.3
mmol) and C5Me4H (2.7 mL, 1.85 g, 15.0 mmol), dissolved in
ethanol (60 mL), was refluxed for 4 h; the resulting reddish brown
(10) (a) Bruce, M. I.; Windsor, N. J. Aust. J. Chem. 1997, 30, 1601. (b)
Bruce, M. I.; Hameister, C.; Swincer, A. G., Wallis, R. C. Inorg. Synth.
1982, 21, 78.
(11) Lomprey, J. R.; Selegue, J. P. J. Am. Chem. Soc. 1992, 114, 5518.
(12) Treichel, P. M.; Komar, D. A.; Vincenti, P. J. Synth. React. Inorg.
Met.-Org. Chem. 1984, 14, 383.
(13) Ashby, G. S., Bruce, M. I.; Tomkins, I. B.; Wallis, R. C. Aust. J.
Chem. 1979, 32, 1003.
(14) Albers, M. O.; Robinson, D. J.; Shaver, A.; Singleton, E. Organo-
metallics 1986, 5, 2199.
(15) Davies, S. G.; Simpson, S. J. J. Chem. Soc., Dalton Trans. 1984,
993.
(16) Bregadze, V. I. Chem. ReV. 1992, 22, 209.
(17) (a) Oshima, N.; Suzuki, H.; Moro-Oka, Y. Chem. Lett. 1984, 1161.
(b) Chinn, M. S.; Heinekey, D. M. J. Am. Chem. Soc. 1990, 112, 5166.

RuII Cyclopentadienyl Complexes
Organometallics, Vol. 26, No. 17, 2007 4267
solved by Patterson methods (2)18 and by direct methods (8)19 and
refined against F2 with SHELXL-97,18 with anisotropic thermal
parameters for all non-hydrogen atoms. Idealized geometries were
assigned to the hydrogen atoms.
Table 1. Crystallographic Data for [Ru(carb)(Cp)(PMe2Ph)2]
(2) and [Ru(η5-C5Me4H)Cl(PMe2Ph)2] (8)
2
8
chemical formula
C24H40B10P2Ru
599.67
C25H35ClP2Ru
533.99
fw (g mol-1
)
T (K)
203(2)
1.5418
monoclinic
P21/n
14.519(5)
13.791(3)
14.581(5)
94.09(5)
2912(2)
4
1.368
54.75
1232
5727
5511
5077
494
293(2)
0.71073
Results and Discussion
wavelength (Å)
cryst syst
space group
a (Å)
b (Å)
c (Å)
orthorhombic
Pna21
17.090(3)
16.233(3)
9.215(1)
The cyclopentadienyl complexes [RuCl(Cp)L1L2] (L1, L2 )
PPh3, PMe2Ph, PMePh2; L1L2 ) dppe; L1L2 ) COD; L1 ) CO,
L2 ) PPh3) react with o-methyl carborane (Hcarb) in the
presence of excess butyl lithium (Ru/Hcarb/LiBu 1:1.5:3) in
toluene/diethyl ether to give substitution at the cyclopentadienyl
ring or at the metal center depending on the nature of the
coordination set (Scheme 1).
The resulting complexes are stable solids, which can be stored
safely under an inert atmosphere. They are soluble in organic
solvents, such as toluene, CH2Cl2, and CHCl3, but mostly
insoluble in n-hexane or diethyl ether. They have been fully
characterized by elemental analysis and by standard spectro-
scopic techniques, and in the case of complexes [RuH(C5H4-
carb)(PPh3)2] (1)5 and [Ru(carb)(Cp)(PMe2Ph)2] (2), also by
X-ray structure determination.
â (deg)
volume (Å3)
Z
2556.4(7)
4
1.387
8.52
1104
3205
3077
3020
271
R1 ) 0.0362,
wR2 ) 0.0872
R1 ) 0.0376,
wR2 ) 0.0887
D
calc (mg/m3)
µ(cm-1
F(000)
)
reflns collected
reflns unique
obsd reflns [I > 2σ(I)]
Params
final R indices [I > 2σ(I)]a
R1 ) 0.0249,
wR2 ) 0.0644
R1 ) 0.0277,
wR2 ) 0.0659
final R indices all dataa
1
2
2
2
a R1 ) Σ||Fo| - |Fc||/Σ|Fo|; wR2 ) [Σ[w(Fo - Fc )2]/Σ[w(Fo )2]]1/2
.
The H NMR spectra of the hydrido complexes 1, 5, and 6
exhibit a characteristic hydride signal at negative fields (δ ca.
-10 ppm), the multiplicity of which depends on the set of
coordinated ligands: a triplet (2JPH 34 Hz) for complex 1, a
doublet (2JPH 30 Hz) for 6, and a singlet for 5. Furthermore,
two pseudotriplets of signals for the cyclopentadienyl protons
are present in the spectra of 1 and 5, as expected for a C5H4X
system;20 the corresponding 13C NMR spectra are consistent
with the proton ones, and in particular, they show three signals
for the Cp carbon atoms. The cyclopentadienyl region in the
1H and 13C spectra of 6 is more complex, due to the chirality at
the ruthenium center; as a consequence, each CH group of the
substituted Cp ligand resonates at different chemical shifts. The
31P signals of 1 and 6 are observed at ca. 67 ppm, in the typical
range of hydride phosphino complexes.20,21
suspension was filtered, giving a brown solid, which was washed
with hexane (2 × 10 mL) and dried in vacuo (yield 63%). A
solution of PPh3 (2.10 g, 7.9 mmol) and the solid isolated in the
previous step (1.0 g, 3.4 mmol) was refluxed for 12 h. The resulting
suspension was filtered, and the isolated yellow solid was purified
by recrystallization from a dichloromethane/hexane 1:1 mixture
(yield 76%). H NMR (CDCl3): δ 0.90 (t, 6H, CH3, JPH ) 0.8
Hz), 1.11 (t, 6H, CH3, 4JPH ) 1.8 Hz), 3.76 (s, 1H, C5Me4H), 7.00-
7.70 (m, 30H, Ph). 31P NMR (CDCl3): δ 40.4 (s, PPh3). 13C NMR
(CDCl3): δ 8.9 (CH3), 9.5 (CH3), 80.4 (s, C5Me4H), 85.3 (s, C5-
Me4H), 94.0 (s, C5Me4H), 127.0-142.0 (Ph). FT IR (KBr, cm-1):
3052-2900, 1433, 1088, 698, 519. Anal. Calcd for C45H43ClP2Ru
(M ) 782.31): C, 69.09; H, 5.54. Found: C, 68.82; H, 5.48.
1
4
Synthesis of [RuCl(η5-C5Me4H)(PMe2Ph)2] (8). The complex
was prepared by displacement of the triphenylphosphine ligands
from [RuCl(C5Me4H)(PPh3)2] (7) (0.25 g, 0.33 mmol) with a slight
excess of PMe2Ph (0.10 g, 0.70 mmol) in toluene (25 mL) under
reflux for 8 h. The reaction mixture was then evaporated to small
volume under reduce pressure; treatment with diethyl ether afforded
a yellow solid, which was filtered and dried under vacuum (yield
63%). 1H NMR (CDCl3): δ 1.23 (br, 6H, CH3), 1.32 (br, 6H, CH3),
1.62 (m, 12H, CH3 PMe2Ph), 3.70 (s, 1H, C5Me4H), 7.25-7.65
(m, 10H, Ph). 31P NMR (CDCl3): δ 14.3 (s, PMe2Ph). 13C NMR
(CDCl3): δ 9.1 (CH3), 18.2 (t, CH3 PMe2Ph), 18.9 (t, CH3 PMe2-
Ph), 81.3 (s, C5Me4H), 84.8 (m, C5Me4H), 93.2 (m, C5Me4H),
127.8-132.0 (Ph). FT IR (KBr, cm-1): 3054-2902, 1433, 1101,
903, 700. Anal. Calcd for C25H35ClP2Ru (M ) 534.02): C, 56.23;
H, 6.61. Found: C, 55.83; H, 6.49.
The FTIR spectra of the hydrido compounds show, in
particular, two bands: a narrow one with low intensity at 1970
cm-1 (stretching Ru-H) and a rather broad one centered at 2570
cm-1 (stretching B-H). The whole of these data, together with
2-D NMR spectra and NOE correlations, allows us to propose
for 5 and 6 the same structure determined for 1: a three-legged
piano-stool structure with the hydride located under the carbo-
ranyl substituent and the neutral ligands positioned opposite to
it.5
In the ESI-MS spectrum, 1 gives an ion at 585 m/z that
corresponds to the loss of the hydride and of one triphenylphos-
phine ligand, to give [Ru(C5H4-carb)(PPh3)]+; further support
is also given by the simulation of the isotopic pattern of the
mass ion, which perfectly matches the experimental one.
The hydrido phosphine compounds slowly decompose in
chlorinated solvents, to give phosphine oxides, whereas in
toluene, they exhibit a very high stability, also at high
temperatures (90-100 °C). The hydrido cyclooctadiene complex
Reactions of [RuCl(η5-C5Me4H)L2] (L ) PPh3, PMe2Ph) with
Licarb. The reactions were conducted using variable Licarb
excesses (Ru/Hcarb/LiBu ratios 1:1.5:3 or 1:2:4) without any
evidence of the formation of new products.
Crystal Structure Determination of 2 and 8. Crystals of 2 and
8 suitable for X-ray analysis were grown by slow crystallization at
0 °C of solutions in dichloromethane/hexane 1:1. Data of 2 were
collected at 203 K on a Enraf Nonius CAD 4 single-crystal
diffractometer (Cu- KR radiation, λ ) 1.5418 Å) and those of 8
at room temperature on a Philips PW1100 single-crystal diffrac-
tometer (FEBO system, Mo- KR radiation, λ ) 0.7107 Å). Details
for the X-ray data are summarized in Table 1. The structures were
(18) Sheldrick, G. M. SHELX-97. Programs for Crystal Structure
Analysis (Release 97-2); University of Go¨ttingen: Go¨ttingen, Germany,
1997.
(19) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.
SIR92: A program for crystal structure solution. J. Appl. Crystallogr. 1993,
26, 343.
(20) Ayllon, J. A.; Sayers, S. F.; Sabo-Etienne, S.; Donnadieu, B.;
Chaudret, B.; Clot, E. Organometallics 1999, 18, 3981.
(21) Wilczewski, T.; Bochenska, M.; Biernat, J. F. J. Organomet. Chem.
1981, 215, 87.

4268 Organometallics, Vol. 26, No. 17, 2007
Scheme 1. Synthesis of Ruthenium Cyclopentadienyl Complexes 1-6
Basato et al.
Table 2. Selected Bond Distances (Å) and Angles (deg) in Cyclopentadienyl Complexes 1, 2, and 8, [RuCl(Cp)(PMe2Ph)2], and
[RuCl(Cp*)(PMe2Ph)2]
1
2
8
[RuCl(Cp)(PMe 2Ph)2]a
[RuCl(Cp*)(PMe2Ph)2]
Ru-Xb
1.55(2)
2.266(1)
2.274(1)
1.907(2)
97.38(2)
74.2(7)
2.226(2)
2.312(1)
2.331(1)
1.881(2)
94.45(2)
94.40(6)
101.46(6)
120.71(7)
118.82(6)
121.11(8)
2.458(2)
2.283(2)
2.293(2)
1.871(2)
95.49(7)
89.78(6)
88.95(6)
122.9(2)
128.5(2)
120.6(2)
2.455(2)-2.436(2)
2.292(2)-2.283(2)
2.277(2)-2.288(2)
1.846-1.852
94.47(6)-96.14(6)
90.83(6)-91.34(6)
90.70(5)-86.40(5)
123.8-124.3
125.2-126.1
122.4-121.9
2.451(2)
2.297(1)
Ru-P(1)
Ru-P(2)
Ru-Cp#c
1.896(5)
94.5(2)
89.62(5)
89.62(5)
125.4(2)
125.4(2)
P(1)-Ru-P(2)
X-Ru-P(1)
X-Ru-P(2)
Cp#-Ru-P(2)
Cp#-Ru-P(1)
Cp#-Ru-X
87.3(7)
126.3(3)
129.9(3)
124.7(7)
a Two independent molecules per unit cell. b X ) D (1), C(6) (2), Cl (8), [RuCl(Cp)(PMe2Ph)2], and [RuCl(Cp*)(PMe2Ph)2]. c Cp# refers to the centroid
of the cyclopentadienyl ring.
5 is unstable in CDCl3 to give H/Cl exchange as already
observed in the synthesis of the parent complex [RuCl(Cp)-
(COD)].14
electron density on the metal center; the 1-methyl-1,2-dicarba-
closo-dodecaborane exhibits in fact a lower electronegativity
with respect to the chloride. In the ESI-MS spectra, complexes
2-4 exhibit a fragmentation path somewhat similar to 1; in fact,
their principal fragments correspond to [Ru(Cp)(L)]+ (L )
PMe2Ph, PMePh2, dppe), derived from a loss of a phosphine
and the anionic carboranyl ligand.
1
The NMR features of 2-4 are markedly different. The H,
13C, 31P, NMR spectra are consistent with coordination of the
carboranyl anion to the metal center. A single signal is present
in the 1H and 13C NMR spectra for the cyclopentadienyl proton
and carbon nuclei, as expected for an unsubstituted ring. The
13C NMR spectra show, in particular, the signal at δ 87.2 ppm,
relative to the carboranyl carbon bonded to ruthenium, which
appears as a triplet because of the virtual coupling with the two
phosphines and is shifted well downfield with respect to the
free ligand (δ 61.5 ppm).
These data are in agreement with the structure of [Ru(carb)-
(Cp)(PMe2Ph)2] (2) determined by X-ray diffraction methods.
A view of this complex is shown in Figure 1, and a selected
list of bond distances and angles is given in Table 2. As
expected, the complex assumes a three-legged piano-stool
structure achieved as legs by the two P atoms of the phosphine
molecules and by the C6 atom of the carboranyl ligand. By
comparing the structure of 2 with that of 1, it is possible to
note that substitution of the hydride with the carboranyl ligand
causes a slight lengthening of the Ru-P bond distances [2.3121-
(11) and 2.3312(7) Å in 2 vs 2.266(1) and 2.274(1) Å in 1] and
a slight narrowing of the P1-Ru1-P2 bond angle [94.45(2)°
in 2 and 97.38(2)° in 1] probably because of the steric hindrance
of the carboranyl ligand.
The 31P spectra show signals at higher fields with respect to
the starting chloro complexes, as a consequence of the increased
The first investigated complex was [RuCl(Cp)(PPh3)2], and
we justified the rather unexpected nucleophilic attack by the
carboranyl anion at the Cp ring on the basis of the steric
hindrance of the bulky triphenylphosphine ligands around the
metal center.5 The importance of steric factors in determining
the site of nucleophilic attack has been confirmed by the
behavior exhibited by the bis-phosphine complexes [RuCl(Cp)-
L1L2] (L1, L2 ) PPh3, PMe2Ph, PMePh2; L1L2 ) dppe). In fact,
in this series of cyclopentadienyl complexes, there is a smooth
size variation of the two neutral ligands (cone angle values from
Figure 1. View of the structure of [Ru(carb)(Cp)(PMe2Ph)2] (2).
Hydrogen atoms are omitted for clarity.

RuII Cyclopentadienyl Complexes
Organometallics, Vol. 26, No. 17, 2007 4269
145 (PPh3) to 136 (PMePh2), 122 (PMe2Ph), and 125 (dppe)),22
and as expected, with the less hindering phosphine ligand set,
the carboranyl anion coordinates the metal center via simple
substitution of the chloride ligand. The molecular structure of
2 shows that this replacement has a very limited effect on the
geometrical parameters of the coordination sphere around the
metal. In other words, the carboranyl anion behaves like more
common carbanions derived either from lithium alkyls or
Grignard reagents, which are known to react with cyclopenta-
dienyl halogen ruthenium complexes to give metal alkyl or aryl
derivatives. However, the differences in cone angle values
between PPh3 and PMePh2 seem too small to fully justify the
observed different reaction pathways. In fact, the importance
of electronic factors on determining the site attack is evidenced
by the results obtained with the complex [RuCl(Cp)(CO)(PPh3)],
where one PPh3 is replaced by one small CO ligand. Also in
this case, rather unexpectedly, the reaction with Licarb gives
substitution at the Cp ring (6). A similar result, attack at the
Cp ring, is observed when the two phosphines are replaced by
the non-hindering cyclooctadiene ligand (5). The evaluation of
the role played by steric and electronic factors on determining
the course of the reaction is not very easy; however, the whole
of these data seems to indicate that electronic effects are
predominant. In fact, the reactivity trend appears to be strictly
related to the electron density on the metal, which is higher
with the more basic phosphines (PMe2Ph, PMePh2, and dppe)
and decreases in the presence of one CO ligand or of COD.
This effect of the ligand set is quantified by electrochemical
studies on a series of [RuCl(Cp)L2] complexes, which clearly
show that their oxidation potentials diminuish as the basicity
of the ligands increases.12,23 In this view, nucleophilic attack at
the Cp ring is possible in the presence of poor electron-donor
ligands, which lower the electron density on the metal and, as
a consequence, on the coordinated Cp ring.
Figure 2. View of the structure of [RuCl(η5-C5Me4H)(PMe2Ph)2]
(8). Hydrogen atoms are omitted for clarity.
Scheme 2. Possible Reaction Mechanism for Synthesis of
Complexes 1-6
To gain further information on the role of steric factors on
the reaction course and on its possible reaction mechanism, we
have hindered the Cp ring with four methyl substituents and
maintained a C-H group capable of undergoing a nucleophilic
attack by carb-. We have synthesized two new complexes with
the tetramethyl cyclopentadienyl ligand (i.e., [RuCl(η5-C5-
Me4H)(PPh3)2] (7) and [RuCl(η5-C5Me4H)(PMe2Ph)2] (8)). The
steric hindrance of the four methyl substituents does not
introduce important modifications on the molecular structure
of the complexes as shown by the structure determination of 8
by X-ray diffraction methods. In fact, the structural features of
8 are strictly comparable with those found in 2, differing in the
nature of the cyclopentadienyl ring (C5Me4H vs C5H5) and of
the anionic ligand (Cl- vs carb-).
The more likely mechanism for the observed reactivity is
illustrated in Scheme 2.
The sequence of stages implies: (i) nucleophilic substitution
of the chloride by the carboranyl anion and precipitation of LiCl,
the resulting complex is the final product with strong electron-
donor substituents (L1, L2 ) 2 PMe2Ph, dppe, 2 PMePh2); (ii)
reductive elimination process with formation of the C-C bond
between the Cp and the carboranyl ligands favored by the poorer
electron-donor ligand sets that reduce the electron density on
the metal center; (iii) exo-1,5- shift to place a hydrogen in the
endo position, followed by (iv) oxidative addition of this endo
hydrogen to give the hydrido complexes 1, 5, and 6. Considering
in details the single stages: stage i is quite common, if we
consider that Licarb can be seen as a particular type of lithium
alkyl, which is known to give metathesis reactions with Ru-
Cl bonds;26 stage ii is very crucial and implies the migration of
the carboranyl ligand from the ruthenium to the Cp carbon: this
migration has been observed on an osmium cyclopentadienyl
A view of the structure of 8 is given in Figure 2. A selected
list of bond distances and angles is given in Table 2. The three-
legged piano-stool structure shows as legs the two P atoms of
the phosphine molecules and the Cl- anion. The Ru-P bond
distances, 2.283(2) and 2.293(2) Å, and the Ru-Cl one, 2.458-
(2) Å in 8, are in good agreement with those of some comparable
ruthenium complexes as [RuCl(Cp)(PMe2Ph)2]24 and [RuCl-
(Cp*)(PMe2Ph)2].25 The repulsions between the phosphines and
the Cp ring substituents are minimized, as a consequence of
the reciprocal orientation of the ligands. In particular, the phenyl
rings are oriented away from the plane defined by the carbons
of the cyclopentadienyl ring; however, this conformation
enhances the steric crowding around the chlorine ligand.
Unexpectedly, the reactions of 7 and 8 with Licarb do not occur
at all, and this gives indications as to a possible reaction
mechanism.

4270 Organometallics, Vol. 26, No. 17, 2007
Basato et al.
complex for a coordinated EPh3 (E ) Ge, Si) anionic ligand
and postulated for an alkyl group;6 in stage iii, the exo-1,5 shift
is also a well-known process operating in substituted and
unsubstituted cyclopentadiene rings;27 and in stage iv, intramo-
lecular oxidative addition of a C-H bond to electron-rich metal
centers is a fairly common reaction.28 This mechanism is in
agreement with the effect of the coordinated ligands and with
the lack of reactivity exhibited by 7 and 8, in which crowding
around the Cl ligand should not allow its exchange by hindering
the carboranyl ligand in step i.
An alternative mechanism involves in the first step direct
attack of the carboranyl anion to the coordinated cyclopenta-
dienyl ligand and successive oxidative addition by the C-H or
C-carb bond to the ruthenium center giving the final complex.
This mechanism, however, is more likely with an electron-poor
or cationic Cp complex29 and does not justify the behavior of
7 and 8, which should, at least on steric grounds, easily react.
(22) Tolman, C. A. Chem. ReV. 1977, 77, 313.
(23) Gamasa, M. P.; Gimeno, J.; Gonzales-Bernardo, C.; Martin-Vaca,
B. M.; Monti, D.; Bassetti, M. Organometallics 1996, 15, 302.
(24) Freeman, S. T. N.; Lemke, F. R.; Harr, C. M.; Nolan, S. P.; Petrson
J. F. Organometallics 2000, 19, 4828.
(25) Smith, D. C., Jr.; Harr, C. M.; Luo, L.; Li, C.; Cucullu, M. E.;
Mahler, C. H.; Peterson, J. F.; Marshal, J. M.; Jones, N. L.; Fagan, P. J.
Organometallics 1999, 18, 2357.
Supporting Information Available: Full listing of atomic
coordinates, bond distances and angles, and summaries of the X-ray
diffraction data for 2 and 8 and 1-D and 2-D NMR spectra for 5
and 6. This material is available free of charge via the Internet at
http://pubs.acs.org.
(26) Davies, S. G.; McNally, J. P.; Smallridge, A. J. AdV. Organomet.
Chem. 1990, 30, 1.
OM700305E
(27) Jutzi, P. Chem. ReV. 1986, 86, 983.
(28) (a) Liu, C. W.; Wen, Y.-S., Liu, L.-K. Organometallics 1997, 16,
155. (b) Kochhar, R. K.; Pettit, R. J. Organomet. Chem. 1966, 6, 272. (c)
Whitesides, T. H.; Shelly, J. J. Organomet. Chem. 1975, 92, 215. (d)
Humphries, A. P.; Knox, S. A. R. J. Chem. Soc., Dalton Trans. 1975, 1710.
(29) de Azevedo, C. G.; Calhorda, M. J.; Carrondo, M. A. A. F. de C.
T.; Dias, A. R.; Duarte, M. T.; Galva˜o, A. M.; Gamelas, C. A.; Gonc¸alves,
I. S.; da Piedade, F. M.; Roma˜o, C. C. J. Organomet. Chem. 1997, 544,
257.