Ruthenium complexes of C,C′-bis(ethynyl)carboranes: An investigation of electronic interactions mediated by spherical pseudo-aromatic spacers

Article abstract of DOI:10.1021/ja0779755

The complexes [Ru(1-C≡C-1, 10-C₂B₈H ₉)(dppe)Cp*] (3a), [Ru(1-C≡C-1,12-C₂B ₁₀H₁₁)(dppe)-Cp*] (3b), [{Ru(dppe)Cp*} ₂{μ-1,10-(C≡C)₂-1,10-C₂B ₈H₈}] (4a) and [{Ru(dppe)Cp*}₂{μ-1,12- (C≡C)₂-1,12-C₂B₁₀H₁₀}] (4b), which form a representative series of mono- and bimetallic acetylide complexes featuring 10- and 12-vertex carboranes embedded within the diethynyl bridging ligand, have been prepared and structurally characterized. In addition, these compounds have been examined spectroscopically (UV-vis-NIR, IR) in all accessible redox states. The significant separation of the two, one-electron anodic waves observed in the cyclic voltammograms of the bimetallic complexes 4a and 4b is largely independent of the nature of the electrolyte and is attributed to stabilization of the intermediate redox products [4a]⁺ and [4b]⁺ through interactions between the metal centers across a distance of ca. 12.5 A. The mono-oxidized bimetallic complexes [4a] ⁺ and [4b]⁺ exhibit spectroscopic properties consistent with a description of these species in terms of valence-localized (class II) mixed-valence compounds, including a unique low-energy electronic absorption band, attributed to an IVCT-type transition that tails into the IR region. DFT calculations with model systems [4a-H]⁺ and [4b-H]⁺ featuring simplified ligand sets reproduce the observed spectroscopic data and localized electronic structures for the mixed-valence cations [4a]⁺ and [4b]⁺.

Full text of DOI:10.1021/ja0779755

Published on Web 02/23/2008
Ruthenium Complexes of C,C′-Bis(ethynyl)carboranes: An
Investigation of Electronic Interactions Mediated by Spherical
Pseudo-aromatic Spacers
Mark A. Fox,† Rachel L. Roberts,† Thomas E. Baines,† Boris Le Guennic,‡,§
Jean-Franc¸ois Halet,‡ Frantisˇek Hartl,| Dmitri S. Yufit,† David Albesa-Jove´,†
Judith A. K. Howard,† and Paul J. Low*,†
Department of Chemistry, Durham UniVersity, South Rd, Durham, DH1 3LE, UK, Laboratoire
des Sciences Chimiques de Rennes, UMR 6226 CNRS-UniVersite´ de Rennes 1, 35042 Rennes
cedex, France, Laboratoire de Chimie, UMR CNRS 5182, Ecole Normale Supe´rieure de Lyon,
46 alle´e d’Italie, 69364 Lyon cedex 07, France, and Van ’t Hoff Institute for Molecular
Sciences, UniVersity of Amsterdam, Nieuwe Achtergracht 166,
1018WV Amsterdam, The Netherlands
Received October 17, 2007; E-mail: p.j.low@durham.ac.uk
Abstract: The complexes [Ru(1-CtC-1,10-C2B8H9)(dppe)Cp*] (3a), [Ru(1-CtC-1,12-C2B10H11)(dppe)-
Cp*] (3b), [{Ru(dppe)Cp*}2{µ-1,10-(CtC)2-1,10-C2B8H8}] (4a) and [{Ru(dppe)Cp*}2{µ-1,12-(CtC)2-
1,12-C2B10H10}] (4b), which form a representative series of mono- and bimetallic acetylide complexes
featuring 10- and 12-vertex carboranes embedded within the diethynyl bridging ligand, have been prepared
and structurally characterized. In addition, these compounds have been examined spectroscopically (UV-
vis-NIR, IR) in all accessible redox states. The significant separation of the two, one-electron anodic waves
observed in the cyclic voltammograms of the bimetallic complexes 4a and 4b is largely independent of the
nature of the electrolyte and is attributed to stabilization of the intermediate redox products [4a]+ and [4b]+
through interactions between the metal centers across a distance of ca. 12.5 Å. The mono-oxidized bimetallic
complexes [4a]+ and [4b]+ exhibit spectroscopic properties consistent with a description of these species
in terms of valence-localized (class II) mixed-valence compounds, including a unique low-energy electronic
absorption band, attributed to an IVCT-type transition that tails into the IR region. DFT calculations with
model systems [4a-H]+ and [4b-H]+ featuring simplified ligand sets reproduce the observed spectroscopic
data and localized electronic structures for the mixed-valence cations [4a]+ and [4b]+.
Introduction
bridge structures and many bimetallic complexes featuring, for
example, diethynyl aromatic3 and polyyndiyl4 bridging ligands
The study of bridge-mediated electronic interactions between
organic, organometallic and inorganic probe groups has been
spurred by interest in the fundamentals of the electron (or hole)-
transfer process,1 and the prospect of using such systems in the
construction of the highly functionalized molecules necessary
for the realization of molecular electronic devices.2 The ethynyl
moiety, which offers a linear geometry, polarizable π-electron
system and cylindrical symmetry, is often incorporated into the
are now known.
(3) For a selection of examples of this burgeoning field see: (a) Field, L. D.;
George, A. V.; Laschi, F.; Malouf, E. Y.; Zanello, P. J. Organomet. Chem.
1992, 435, 347. (b) Khan, M. S.; Kakkar, A. K.; Ingham, S. L.; Raithby,
P. R.; Lewis, J.; Spencer, B.; Wittmann, F.; Friend, R. H. J. Organomet.
Chem. 1994, 472, 247. (c) Faulkner, C. W.; Ingham, S. L.; Khan, M. S.;
Lewis, J.; Long, N. J.; Raithby, P. R. J. Organomet. Chem. 1994, 482,
139. (d) Le Narvor, N.; Lapinte, C. Organometallics 1995, 14, 634. (e)
Lavastre, O.; Plass, J.; Bachmann, P.; Guesmi, S.; Moinet, C.; Dixneuf, P.
H. Organometallics 1997, 16, 184. (f) Paul, F.; Lapinte, C. Coord. Chem.
ReV. 1998, 178-180, 431. (g) Bruce, M. I.; Hall, B. C.; Low, P. J.; Skelton,
B. W.; White, A. H. J. Organomet. Chem. 1999, 592, 74. (h) Albertin, G.;
Antoniutti, S.; Bordignon, E.; Granzotto, M. J. Organomet. Chem. 1999,
585, 83. (i) Albertin, G.; Antoniutti, S.; Bordignon, E.; Bresolin, D. J.
Organomet. Chem. 2000, 609, 10. (j) Weyland, T.; Ledoux, I.; Brasselet,
S.; Zyss, J.; Lapinte, C.; Organometallics 2000, 19, 5235. (k) Werner, H.;
Bachmann, P.; Martin, M. Can. J. Chem. 2001, 79, 519. (l) Hurst, S. K.;
Ren, T. J. Organomet. Chem. 2002, 660, 1. (m) Long, N. J.; Williams, C.
K. Angew. Chem., Int. Ed. 2003, 42, 2586. (n) Wong, K. M. C.; Lam, S.
C. F.; Ko, C. C.; Zhu, N. Y.; Yam, V. W. W.; Roue, S.; Lapinte, C.;
Fathallah, S.; Costuas, K.; Kahlal, S.; Halet, J.-F. Inorg. Chem. 2003, 42,
7086. (o) Yam, V. W. W. J. Organomet. Chem. 2004, 689, 1393. (p) Saha,
R.; Qaium, Md. A.; Debnath, D.; Younis, M.; Chawdhury, N.; Sultana,
N.; Kociok-Kohn, G.; Ooi, L.; Raithby, P. R.; Kijima, M. Dalton Trans.
2005, 2760. (q) de Montigny, F.; Argouarch, G.; Costuas, K.; Halet, J.-F.;
Roisnel, T.; Toupet, L.; Lapinte, C. Organometallics 2005, 24, 4558. (r)
Low, P. J.; Roberts, R. L.; Cordiner, R. L.; Hartl, F. J. Solid State
Electrochem. 2005, 9, 717.
† Durham University.
‡ UMR 6226 CNRS-Universite´ de Rennes 1.
§ UMR CNRS 5182, Ecole Normale Supe´rieure de Lyon.
| University of Amsterdam.
(1) (a) Brunschwig, B. S.; Creutz, C.; Sutin, N. Coord. Chem. ReV. 1998, 177,
61. (b) Creutz, C. Prog. Inorg. Chem. 1983, 30, 1. (c) Lambert, C.; Risko,
C.; Coropceanu, V.; Shelter, J.; Amthor, S.; Gruhn, N. E.; Durivage, J. C.;
Bredas, J. L. J. Am. Chem. Soc. 2005, 127, 8508. (d) Lambert, C.; Amthor,
S.; Schelter, J. J. Phys. Chem. A 2004, 108, 6474. (e) Karafiloglou, P.;
Launay, J.-P. Chem. Phys. 2003, 289, 231. (f) Launay, J.-P. Chem. Soc.
ReV. 2001, 30, 386.
(2) (a) Adams, D. M.; et al. J. Phys. Chem. B 2003, 107, 6668. (b) Low, P. J.
Dalton Trans. 2005, 2821. (c) Ren, T. Organometallics 2005, 24, 4854.
(d) Benniston, A. C. Chem. Soc. ReV. 2004, 33, 573. (e) Coe, B. J.; Curati,
N. R. M. Comments Inorg. Chem. 2004, 25, 147. (f) Carroll, R. L.; Gorman,
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9
3566
J. AM. CHEM. SOC. 2008, 130, 3566-3578
10.1021/ja0779755 CCC: $40.75 © 2008 American Chemical Society

Ru Complexes of C,C
′
-Bis(ethynyl)carboranes
A R T I C L E S
Scheme 1. Preparation of Monoruthenium (3a, 3b) and
Diruthenium Complexes (4a, 4b) via In Situ Metalation/Desilylation
Reactions
reported the first experimental steps in this area and described
the preparation and electrochemical properties of [{Fe(CO)2Cp}2-
(µ-1,12-(CtC)2-1,12-C2B10H10}].14 Unfortunately, the limited
thermodynamic stability of the mono-oxidized derivative [{Fe-
(CO)2Cp}2(µ-1,12-(CtC)2-1,12-C2B10H10}]+ with respect to
disproportionation hampered efforts to probe this interesting
species more thoroughly.
Half-sandwich complexes with supporting phosphine ligands
have proven to be particularly useful probe groups in studies
of bimetallic systems featuring ethynyl-based bridging ligands,
often giving rise to radical derivatives with appreciable chemical
and thermodynamic stability.15 With this in mind, we have
prepared the complexes [Ru(1-CtC-1,10-C2B8H9)(dppe)Cp*]
(3a), [Ru(1-CtC-1,12-C2B10H11)(dppe)Cp*] (3b), [{Ru(dppe)-
Cp*}2{µ-1,10-(CtC)2-1,10-C2B8H8}] (4a) and [{Ru(dppe)-
Cp*}2{µ-1,12-(CtC)2-1,12-C2B10H10}] (4b), which form a
representative series of mono- and bimetallic acetylide com-
plexes featuring 10- and 12-vertex carboranes embedded within
the diethynyl bridging ligand. We have used these systems to
address the role of the polyhedral p-carborane cages in promot-
ing electronic interactions between remote sites, the nature of
the formally mixed-valence compounds that may be derived
from them, and a DFT-based study of the electronic structure
in each of the electrochemically accessible redox states.
The intriguing possibilities that arise from combination of
the ethynyl moiety with the interesting and potentially useful
physical and electronic properties offered by the p-carboranyl
moiety, such as high symmetry along the C‚‚‚C axis, high
thermal and chemical stability, and spherical or “three-
dimensional” aromaticity,5 has sparked considerable interest in
the use of diethynylcarborane-based ligands as structural ele-
ments in multimetallic assemblies.6 This interest can only be
expected to increase now that convenient synthetic routes to
10- and 12-vertex diethynyl-p-carboranes 1,10-(Me3SiCtC)2-
1,10-C2B8H8 (2a) and 1,12-(Me3SiCtC)2-1,12-C2B10H10 (2b)
have been reported (Scheme 1).7-12 The rigid geometry of the
diethynyl carboranes together with the potential for the p-
carborane cage to mediate electronic effects between groups
located at the 1 and 10 (2a) or 1 and 12 (2b) positions has
prompted consideration of diethynyl carboranes as conduits for
electronic interactions between remote metal centers.13 Indeed,
on the basis of computational results, it has been suggested that
the degree of electronic communication between the apical
substituents of the 10-vertex carborane cage may be comparable
to that of para-substituted benzenes.11 Hawthorne’s group
Results and Discussion
Syntheses. Acetylide complexes of half-sandwich group 8
bis(phosphine) fragments such as Ru(dppe)Cp* are conveniently
prepared from terminal acetylenes, via intermediate vi-
nylidenes,16,17 or by fluoride-induced desilylmetallation of
trimethylsilyl-protected acetylenes.18,19 The parent mono- and
diethynyl carboranes are highly volatile,7-9 and so for conven-
ience the trimethylsilyl derivatives 1-Me3SiCtC-1,10-C2B8H9
(1a), prepared by copper(I)-mediated cross-coupling of BrCt
CSiMe3 with 1,10-C2B8H10,9 1-Me3SiCtC-1,12-C2B10H11
(1b),9 1,10-(Me3SiCtC)2-1,10-C2B8H8 (2a)7 and 1,12-(Me3-
SiCtC)2-1,12-C2B10H10 (2b)7 were used in the preparation of
complexes 3a, 3b, 4a and 4b, respectively (Scheme 1).
The ruthenium complexes 3a, 3b, 4a and 4b were character-
ized by the usual spectroscopic methods and single-crystal X-ray
diffraction. The phosphine ligands gave rise to singlet resonances
in the 31P NMR spectra near 81.6 ppm, which compare well
(5) (a) Aihara, J. J. Am. Chem. Soc. 1978, 100, 3339. (b) Schleyer, P. v. R.;
Maerker, C.; Dransfield, A.; Jiao, H.; Hommes, N. J. R. v. E. J. Am. Chem.
Soc. 1996, 118, 6317.
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Hawthorne, M. F. Organometallics 2004, 23, 482.
(6) (a) Vicente, J.; Chicote, M.-T.; Alvarez-Falco´n, M. M.; Fox, M. A.; Bautista,
D. Organometallics 2003, 22, 4792. (b) Jude, H.; Disteldorf, H.; Fischer,
S.; Wedge, T.; Hawkridge, A. M.; Arif, A. M.; Hawthorne, M. F.;
Muddiman, D. C.; Stang, P. J. J. Am. Chem. Soc. 2005, 127, 12131.
(7) Fox, M. A.; Baines, T. E.; Albesa-Jove´, D.; Howard, J. A. K.; Low, P. J.
J. Organomet. Chem. 2006, 691, 3889.
(15) (a) Cordiner, R. L.; Feroze, M. P.; Albesa-Jove´, D.; Yufit, D. S.; Howard,
J. A. K.; Low, P. J. Inorg. Chim. Acta 2006, 359, 3459. (b) Bruce, M. I.;
Low, P. J.; Hartl, F.; Humphrey, P. A.; de Montigny, F.; Jevric, M.; Lapinte,
C.; Perkins, G. J.; Roberts, R. L.; Skelton, B. W.; White, A. H.
Organometallics 2005, 24, 5241. (c) Bruce, M. I.; Costuas, K.; Davin, T.;
Ellis, B. G.; Halet, J.-F.; Lapinte, C.; Low, P. J.; Smith, M. E.; Skelton, B.
W.; Toupet, L.; White, A. H. Organometallics 2005, 24, 3864. (d) Bruce,
M. I.; Low, P. J.; Costuas,. K.; Halet, J.-F.; Best, S. P.; Heath, G. A. J.
Am. Chem. Soc. 2000, 122, 1949. (e) Jiao, H. J.; Costuas, K.; Gladysz, J.
A.; Halet, J.-F.; Guillemot, M.; Toupet, L.; Paul, F.; Lapinte, C. J. Am.
Chem. Soc. 2003, 125, 9511. (f) Paul, F.; Meyer, W. E.; Toupet, L.; Jiao,
H. J.; Gladysz, J. A.; Lapinte, C. J. Am. Chem. Soc. 2000, 122, 9405. (g)
Dembinski, R.; Bartik, T.; Bartik, B.; Jaeger, M.; Gladysz, J. A. J. Am.
Chem. Soc. 2000, 122, 810. (h) Paul, F.; Lapinte, C. Coord. Chem. ReV.
1998, 178, 431.
(8) Batsanov, A. S.; Fox, M. A.; Howard, J. A. K.; MacBride, J. A. H.; Wade,
K. J. Organomet. Chem. 2000, 610, 20.
(9) Fox, M. A.; Cameron, A. M.; Low, P. J.; Paterson, M. A. J.; Batsanov, A.
S.; Goeta, A. E.; Rankin, D. W .H.; Robertson, H. E.; Schirlin, J. T. Dalton
Trans. 2006, 3544.
(10) Kaszynski, P.; Pakhomov, S.; Young, V. G., Jr. Collect. Czech. Chem.
Commun. 2002, 67, 1061.
(11) Pakhomov, S.; Kaszynski, P.; Young, V. G., Jr. Inorg. Chem. 2000, 39,
2243.
(12) Herzog, A.; Jalisatgi, S. S.; Knobler, C. B.; Wedge, T. J.; Hawthorne, M.
F. Chem. Eur. J. 2005, 11, 7155.
(16) Paul, F.; Ellis, B. G.; Bruce, M. I.; Toupet, L.; Roisnel, T.; Costuas, K.;
Halet, J.-F.; Lapinte, C. Organometallics 2006, 25, 649.
(13) (a) Fox, M. A.; MacBride, J. A. H.; Peace, R. J.; Wade, K. J. Chem. Soc.,
Dalton Trans. 1998, 401. (b) Allis, D. G.; Spencer, J. T. Inorg. Chem.
2001, 40, 3373. (c) Allis, D. G.; Spencer, J. T. J. Organomet. Chem. 2000,
614-615, 309. (d) Fox, M. A.; Paterson, M. A. J.; Nervi, C.; Galeotti, F.;
Puschmann, H.; Howard, J. A. K.; Low, P. J. Chem. Commun. 2001, 1610.
(e) Le Guennic, B.; Costuas, K.; Halet, J.-F.; Nervi, C.; Paterson, M. A. J.;
Fox, M. A.; Roberts, R. L.; Albesa-Jove´, D.; Puschmann, H.; Howard, J.
A. K.; Low, P. J. C. R. Chimie 2005, 8, 1883.
(17) Bitcon, C.; Whiteley, M. W. J. Organomet. Chem. 1987, 336, 385.
(18) Bruce, M. I.; Hall, B. C.; Kelly, B. D.; Low, P. J.; Skelton, B. W.; White,
A. H. J. Chem. Soc., Dalton Trans. 1999, 3719.
(19) (a) Bruce, M. I.; Kelly, B. D.; Skelton, B. W.; White, A. H. J. Organomet.
Chem. 2000, 604, 150. (b) Coat, F.; Thominot, P.; Lapinte, C. J. Organomet.
Chem. 2001, 629, 39. (c) Bruce, M. I.; de Montigny, F.; Jevric, M.; Lapinte,
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689, 2860.
9
J. AM. CHEM. SOC. VOL. 130, NO. 11, 2008 3567

A R T I C L E S
Fox et al.
Table 1. Selected NMR Spectroscopic Data for Compounds and Complexes 1,10-R,R′-1,10-C2B8H8
R
R
′
C1a
C10
C10H
B2−5
B6−9
B2
−5H
B6−9H
H
H
H
H
H
101.7
104.1
117.8
120.5
99.8
7.00
6.85
6.01
7.01
-12.7
-9.3
2.00
2.31
1.66
2.56
2.35
2.30
1.70
Me3SiCC
Cp*(dppe)RuCC
C2B8H9
HCC
Me3SiCC
1a
3a
98.3
82.8
97.8
-13.3
-15.7
-12.8
2.03
1.83
2.18
-11.3
-8.8
HCC
Me3SiCC
Cp*(dppe)RuCC
-9.8
-10.0
-13.4
2a
4a
100.7
99.3
Cp*(dppe)RuCC
a See Figures 1-5 for atom labeling schemes used in this and all other tables.
Table 2. Selected NMR Spectroscopic Data for Compounds and Complexes 1,12-R,R′-1,12-C2B10H10
R
R
′
C1
C12
C12H
B2−6
B7−11
B2
−6H
B7−11H
H
HCC
Me3SiCC
Cp*(dppe)RuCC
HCC
H
H
H
H
63.5
67.9
69.6
78.7
65.3
66.0
69.3
2.74
2.61
2.61
2.28
-14.9
-11.6
-11.5
-11.1
-11.9
-11.9
-12.2
2.10
2.41
2.44
1.82
2.49
2.44
1.96
60.4
59.9
53.4
-15.1
-15.2
-16.3
2.16
2.22
2.14
1b
3b
HCC
Me3SiCC
Cp*(dppe)RuCC
Me3SiCC
Cp*(dppe)RuCC
2b
4b
Table 3. Selected Bond Lengths (Å) and Angles (deg) Associated with 1a, 1b, 2a, 2b, 3a, 3b, 4a and 4b
1a
1ba,9
2ac,11
2b9
3a
3bb(A)
3bb (B)
4ad
4bc
Si(1)-C(3)
1.847(2)
1.840(5)
1.848(2), 1.845(2)
1.856(2)
Ru(1)-C(3)
1.999(2)
2.2745(6)
2.2587(7)
1.214(3)
1.443(3)
1.619(3)
1.846(4)
1.808(4)
1.844(4)
1.595(4)
172.6(2)
169.9(2)
83.61(2)
2.003(2)
2.2620(4)
2.2602(4)
1.212(2)
1.437(2)
1.721(3)
1.775(6)
1.757(6)
1.770(9)
1.696(6)
176.6(2)
176.0(2)
81.16(2)
2.004(2)
2.2463(4)
2.2656(4)
1.217(2)
1.440(2)
1.731(4)
1.784(4)
1.764(4)
1.779(4)
1.707(4)
172.6(2)
173.3(2)
82.45(2)
2.000(3)
2.2548(7)
2.2738(7)
1.213(4)
1.427(4)
1.623(5)
1.846(5)
1.802(5)
1.843(5)
1.621(4)
173.9(3)
175.3(3)
83.30(3)
12.643
1.991(4)
2.2509(10)
2.2638(11)
1.205(4)
1.454(5)
1.726(6)
1.774(6)
1.756(6)
Ru(1)-P(1)
Ru(1)-P(2)
C(2)-C(3)
1.197(3)
1.436(3)
1.611(3)
1.853(3)
1.810(3)
1.850(4)
1.597(4)
176.6(2)
179.4(2)
1.227(5)
1.442(5)
1.725(6)
1.789(6)
1.765(8)
1.792(7)
1.708(7)
180.0
1.199(2), 1.200(3)
1.439(2), 1.434(2)
1.614(3)
1.856(3)
1.809(3)
1.854(3)
1.614(3)
177.1(2), 175.2(2)
178.1(2), 177.1(2)
1.204(2)
1.453(2)
1.728(2)
1.793(3)
1.769(2)
C(1)-C(2)
C(1)-B(2-5/6)
B(2)-B(3)
B(2)-B(6/7)
B(6/7-7/8)
C(10/12)-B
Si(1)/Ru(1)-C(3)-C(2)
C(1)-C(2)-C(3)
P(1)-Ru(1)-P(2)
Ru(1)‚‚‚Ru(2)
177.9(2)
179.4(2)
172.4(3)
171.8(4)
83.52(4)
12.373
180.0
a Gas-phase electron diffraction. b Two independent molecules in the unit cell. c Molecule in a special position at the center of symmetry. d Also Ru(2)-
C(5) 1.999(3) Å, Ru(2)-P(3) 2.2732(8) Å, Ru(2)-P(4) 2.2716(7) Å, C(5)-C(4) 1.215(4) Å, C(4)-C(10) 1.435(4) Å, Ru(2)-C(5)-C(4) 172.9(3)°, C(5)-
C(4)-C(10) 174.9(3)°, P(3)-Ru(2)-P(4) 83.12(3)°.
with the values found for other acetylide complexes of this metal
fragment.16 In the 13C NMR spectrum, resonances from the
acetylide carbons were detected near 100 and 120 ppm, attrib-
uted to C(3) and C(2), respectively, on the basis of the JCP
coupling constants (ca. 25 Hz) associated with C(3) (Table 1).
Tables 1 and 2 list additional NMR spectroscopic data
associated with the cage for compounds synthesized here
together with data from related systems previously reported.7-9,20,21
The resonances associated with the cage carbons were sensitive
to the presence of the metal center. In the case of the
monometallic systems, the carbon remote from the ethynyl group
was sensitive to the antipodal effect of the electron-donating
metal acetylide fragment.22 For example, the acetylide carbon
resonances were found at 117.8 (C1) and 82.8 (C10) ppm in
3a, compared with 104.1 (C1) and 98.3 (C10) in the pro-ligand
1a. This effect is also evident in the cage C-H 1H NMR
resonances. The 11B NMR spectra are characterized by two (3a,
3b) or one (4a, 4b) resonance, as expected for the symmetry of
these molecules. Metalation has a notable effect on the electronic
environment of the 11B nuclei, with these characteristic 11B
NMR resonances being found at higher field in the C2B8
complexes than in the appropriate trimethylsilyl-protected pro-
ligands. It can be concluded that the presence of the metal center,
a good electron donor, is reflected in the NMR parameters
associated with the atoms of the carborane cage.
X-ray Crystallographic Studies. Single crystals of the new
compounds reported here (1a, 3a, 3b, 4a, 4b) were obtained
and the compounds structurally characterized (Table 3). The
structures of the ethynyl carborane derivatives 1b,9 2a11 and
2b9,10,12 have been reported on previous occasions, and selected
data are included here for purposes of comparison. Plots of
single molecules of 1a, 3a, 3b, 4a (as the dichloromethane
solvate) and 4b (as a benzene hexasolvate) are shown in Figures
1-5, and selected parameters are summarized in Table 3.
Critical bond parameters associated with the ethynyl carbo-
rane 1a are similar to those found in the closely related diethynyl
analogue 2a; for example, the acetylenic CtC distances are
indistinguishable (Table 3). The C2B8 cage in 1a is distorted
from an idealized decahedron, with the cage C-B distances
being significantly shorter than the various meridional and
(20) Turner, A. R.; Robertson, H. E.; Borisenko, K. B.; Rankin, D. W. H.; Fox,
M. A. Dalton Trans. 2005, 1310.
(21) Fox, M. A.; Greatrex, R.; Greenwood, N. N.; Kirk, M. Collect. Czech.
Chem. Commun. 1999, 64, 806.
(22) Hermanek, S. Chem. ReV. 1992, 92, 325.
9
3568 J. AM. CHEM. SOC. VOL. 130, NO. 11, 2008

Ru Complexes of C,C
′
-Bis(ethynyl)carboranes
A R T I C L E S
Figure 5. Molecular structure of [{Ru(dppe)Cp*}2{µ-1,12-(CtC)2-
1,12-C2B10H10}] (4b) showing the atom labeling scheme. Hydrogen atoms
are omitted for clarity.
Figure 1. Molecular structure of 1a showing the atom labeling scheme.
In this and all subsequent Figures, displacement ellipsoids shown at the
50% probability level.
Figure 6. Crystal packing of 1a illustrating the C-H‚‚‚π(CtC) hydrogen-
bonding motif. Selected distances (Å): C10-H10A, 0.89; H10A‚‚‚C2, 2.81;
H10A‚‚‚C3, 2.82; C10A‚‚‚C2, 3.66; C10A‚‚‚C3, 3.71.
Figure 2. Molecular structure of [Ru(1-CtC-1,10-C2B8H9)(dppe)Cp*]
(3a) showing the atom labeling scheme. Hydrogen atoms are omitted for
clarity.
Table 4. Electrochemical Data for Complexes 3a, 3b, 4a and 4ba
Eo (ox1)
Eo (ox2)
∆
Eo
Kc
3a
3b
4a
4b
0.35
0.39
0.27
0.32
0.39
0.41
0.12
0.09
116
35
a All E values in V vs SCE. Conditions: 10-1 M NBu4BF4 in CH2Cl2,
glassy carbon working electrode, Pt wire counter and pseudo-reference
electrodes, 20 °C, V ) 0.1 V s-1. The decamethylferrocene/decamethyl-
ferrocenium couple (Fc*/Fc*+ ) -0.08 V vs SCE) was used as an internal
reference. The observed peak-to-peak separations for each couple are
comparable with those from the Fc*/Fc*+ internal standard.
Figure 3. Molecular structure of [Ru(1-CtC-1,12-C2B10H11)(dppe)Cp*]
(3b) showing the atom labeling scheme. Hydrogen atoms are omitted for
clarity.
of the Ru-P bond lengths reveal average distances of 2.26 Å,
with no statistically significant variation as a function of the
acetylide substituent. The P-Ru-P angles are similar within
the series of complexes reported here, and entirely consistent
with values observed for a range of phenyl acetylide complexes
reported previously [83.01(2)-84.02(5)°].16 The Ru-C(1)
distances are equivalent within error and marginally shorter than
that found in [Ru(CtCC6H4NH2-4)(dppe)Cp*] [2.026(3) Å],
which could be argued as evidence for the electron-withdrawing
nature of the carborane moieties.16 The distances between the
two ruthenium atoms in the bimetallic complexes 4a and 4b
are 12.6 and 12.4 Å, respectively. This arises from the
considerably longer intracage C‚‚‚C distance in the 10-vertex
cage of 4a than the 12-vertex cage of 4b in spite of the shorter
C(ethynyl)-C(cage) bonds found in 4a compared to those in
4b (Table 3).
The C(2)tC(3) bond lengths are worthy of comment, given
the significant discussion of metal-acetylide back-bonding
interactions that has often accompanied reports of this param-
eter.16,24,25 On the basis of the data obtained from single-crystal
X-ray diffraction, replacement of the trimethylsilyl groups in
the trimethylsilylethynyl carborane precursors by the half-
sandwich ruthenium centers is found to be accompanied by a
Figure 4. Molecular structure of [{Ru(dppe)Cp*}2{µ-1,10-(CtC)2-1,-
10-C2B8H8}] (4a) showing the atom labeling scheme. Hydrogen atoms are
omitted for clarity.
tropical B-B distances. Within the extended solid-state structure
a C-H‚‚‚π hydrogen-bonding motif is clearly observed (Figure
6).23
The structures of the mono- and bimetallic ruthenium
complexes may be compared with those of the trimethylsilyl-
protected pro-ligands and representative metal arylacetylide
complexes [Ru(CtCAr)(dppe)Cp*].16 The Ru-C(Cp*) dis-
tances vary little, falling in the ranges 2.220(2)-2.266(2) Å (3a),
2.228(2)-2.265(2) Å (3b), 2.213(3)-2.263(3) and 2.215(3)-
2.282(3) Å (4a) and 2.220(4)-2.258(4) Å (4b). Comparisons
(24) Koentjoro, O. F.; Rousseau, R.; Low, P. J. Organometallics 2001, 20, 4502.
(25) (a) McGrady, J. E.; Lovell, T.; Stranger, R.; Humphrey, M. G. Organo-
metallics 1997, 16, 4004. (b) Delfs, C. D.; Stranger, R.; Humphrey, M.
G.; McDonoagh, A. M. J. Organomet. Chem. 2000, 607, 208.
(23) Fox, M. A.; Hughes, A. K. Coord. Chem. ReV. 2004, 248, 457.
9
J. AM. CHEM. SOC. VOL. 130, NO. 11, 2008 3569

A R T I C L E S
Fox et al.
Figure 7. IR spectra obtained in the ν(B-H) and ν(CtC) regions for the monometallic complexes 3b (solid line [blue]) and [3b]+ (dashed line [red]) in
CH2Cl2/10-1 M NBu4BF4 at 293 K within an OTTLE cell.
small elongation of the acetylide bond length, which is on the
borderline of statistical significance (Table 3). Similar structural
variations are observed in comparisons made from DFT-
optimized geometries of both the carborane precursors and
model metal complexes (vide infra).
characterization of both [4a]+ and [4b]+ we therefore turned to
UV-vis-NIR and IR spectroelectrochemical methods, and
employed 3a and 3b as mononuclear model systems for
comparative purposes.
IR Spectroelectrochemical Studies. The complexes 3a, 3b,
4a and 4b offer ν(CtC) and ν(B-H) bands in the IR region
near 2080 and 2600 cm-1, respectively. These characteristic,
strong absorptions provide suitable spectroscopic probes through
which to study the effect of oxidation on the structure of the
ligand using spectroelectrochemical methods. The IR spectra
of 3a and 3b in CH2Cl2/10-1 M NBu4BF4 are similar, with
ν(CtC) and ν(B-H) bands at 2083 and 2595 cm-1 for 3a, and
2082 and 2605 cm-1 for 3b. Oxidation to the 17-electron
monocations, [3a]+ and [3b]+, caused the ν(CtC) bands to shift
to lower frequency (2008 cm-1, [3a]+; 2014 cm-1, [3b]+),
indicating a significant decrease in the C-C bonding character,
with a large drop in intensity (Figure 7). In contrast, the
Electrochemical Studies. The cyclic voltammograms of the
mononuclear complexes 3a and 3b in CH2Cl2/10-1 M NBu4-
BF4 are each characterized by a single, reversible one-elec-
tron anodic wave [Eo ) 0.35 V (3a); 0.39 V (3b)] (Table 4).
These values are close to the oxidation potentials found for
[Ru(CtCC6H4CN)(dppe)Cp*] (0.36 V) and [Ru(CtCC6H4-
NO2)(dppe)Cp*] (0.40 V).16 Equally, the oxidation of 3a and
3b is less thermodynamically favorable than oxidation of [Ru-
(CtCC6H5)(dppe)Cp*] (0.25 V) under the same conditions,
providing a qualitative measure of the electron-withdrawing
ability of the carborane cage. The bimetallic complexes 4a and
4b displayed two sequential reversible waves that were best
resolved by square wave voltammetry at 0.27 and 0.39 V (4a),
and 0.32 and 0.41 V (4b). The difference between the potentials
gives comproportionation constants Kc ) exp(∆EoF/RT) ) 116
and 35 (at 20 °C) associated with [4a]+ and [4b]+, respectively,
which relate to the stability of these compounds with respect
to disproportionation under the conditions of the voltammetry
measurement, but not necessarily to the “electronic interactions”
between the metal centers.26
In an effort to gauge the factors such as ion-pairing in the
electrolyte solution that contribute to the stabilization of [4a]+
and [4b]+, as distinct from inherent electronic factors such as
charge delocalization, the voltammetry measurements with 4b
were also carried out using CH2Cl2 solutions containing 10-1
M NBu4[B(ArF)4] and NBu4Cl, as examples of electrolytes with
weakly and strongly interacting anions, respectively.27 Differ-
ences in the anodic potentials were found to be 70 mV in NBu4-
Cl and 80 mV in NBu4[B(ArF)4]. This small decrease in ∆E
values indicates that ion pairing is not the only factor contribut-
ing to the stability of [4b]+ in solution. To assist in the
ν(B-H) band moved to only slightly higher energy (2605 cm-1
,
[3a]+; 2614 cm-1, [3b]+), consistent with only a small reduction
in electron density in the carborane cage.
The bimetallic compounds 4a and 4b behaved in manner
distinct from that of the mononuclear models. Thus, while oxi-
dation to [4a]+/[4b]+ resulted in a small shift in the ν(B-H)
bands [ν(B-H): 4a/[4a]+, 2592/2602 cm-1; 4b/[4b]+, 2602/
2609 cm-1], the single ν(CtC) bands associated with 4a
(2081 cm-1) and 4b (2082 cm-1) were replaced by two new
bands at 2065, 1990 cm-1 ([4a]+) and 2074, 2002 cm-1 ([4b]+)
(Figure 8). These vibrational bands are superimposed on the
low-energy tail of an electronic absorption band (not shown
in Figure 8, see below). Subsequent oxidation to [4a]2+ and
[4b]2+ was accompanied by a collapse in the electronic
absorption band, a further shift of the ν(B-H) band to higher
energy ([4a]2+, 2607 cm-1; [4b]2+, 2617 cm-1), and in each
case the ν(CtC) region exhibited only one weak ν(CtC) band
at 2006 ([4a]+) or 2012 cm-1 ([4b]+) (Figure 8). The changes
in the IR spectra of 3a, 3b, 4a and 4b upon the oxidation are
consistent with the description of [4a]+ and [4b]+ in terms of
a localized mixed-valence model in which the organometallic
ethynyl moieties are distinct, at least on the IR time scale (10-13
s-1) (Table 5).
(26) (a) Richardson, D. E.; Taube, H. Coord. Chem. ReV. 1984, 60, 107. (b)
Arnold, D. P.; Heath, G. A.; James, D. A. J. Porphyrins Phthalocyanines
1999, 3, 5. (c) Barrie`re, F.; Camire, N.; Geiger, W. E.; Mueller-Westerhoff,
U. T.; Sanders, R. J. Am. Chem. Soc. 2002, 124, 7262.
(27) Barriere, F.; Geiger, W. E. J. Am. Chem. Soc. 2006, 128, 3980.
9
3570 J. AM. CHEM. SOC. VOL. 130, NO. 11, 2008

Ru Complexes of C,C
′
-Bis(ethynyl)carboranes
A R T I C L E S
Figure 8. IR spectra obtained in the ν(B-H) and ν(CtC) regions upon oxidation of (a) 4a and (b) 4b in CH2Cl2/10-1 M NBu4BF4 at 293 K within an
OTTLE cell. For clarity, the low-energy tail from the IVCT band has been subtracted (see Figure 11).
Table 5. Observed and Calculated IR Absorptions for Complexes
characterized by intense transitions in the UV region (ν˜ > 35000
[3a]n+, [3b]n+ (n ) 0, 1), [4a]n+ and [4b]n+ (n ) 0, 1, 2)
cm-1) that tail into the visible region (Figure 9). A pronounced
b
b
obs.
(C C)
calc.a
(C C)
∆
(C
obs.
(B H)
calc.a
(B H)
∆
lower-energy band was also observed for 3a that proved to be
solvatochromic, being observed at 30000 cm-1 in acetonitrile
and, coincidently, in 10-1 M NBu4BF4/CH2Cl2 but blue-shifted
and obscured by the higher-energy bands in pure CH2Cl2. In
general, the electronic absorption spectra of the 17-electron
monocations [3a]+ and [3b]+ are similar to each other and
characterized by bands near 20000, 15000, and 7000 cm-1
(Figure 9). It is notable, however, that oxidation of 3a to the
17-electron species [3a]+ resulted in the collapse of the
characteristic absorption band present in 3a (Figure 9), consistent
with the assignment as a metal (or metal ethynyl) to the
carborane charge-transfer process. The three absorption features
observed in the spectra of [3a]+ and [3b]+ below 20000 cm-1
are attributable to a dπ-(dπ)* transition and two pseudo-
interconfiguration (IC) bands associated with the formally 17-
electron, d5 Ru(III) centers present in these organometallic
radical cations. However, given the significant shift in ν(CtC)
frequencies that accompany oxidation of 3a and 3b, the
description of transitions in [3a]+ and [3b]+ in “metal-centered”
ν
t
ν
t
ν
t
C)
ν
−
ν
−
ν(B−H)
3a
2083
2008
2082
2014
2081
2065
1990
2006
2124
1983
2133
1979
2131
2055
1987
1991(HS)
1962(LS)
2134
+41
-25
+51
-35
+50
-10
-3
-15
-44
+52
+17
-15
-12
-50
2595
2605
2605
2614
2592
2602
2595
2605
2603
2611
2593
2605
0
0
-2
-3
+1
+3
[3a]+
3b
[3b]+
4a
[4a]+
[4a]2+
2607
2610(HS)
2616(LS)
2601
+3
+9
-1
+2
4b
2082
2074
2002
2012
2602
2609
[4b]+
2091
1987
2000(HS)
1962(LS)
2611
[4b]2+
2617
2616(HS)
2616(LS)
-1
-1
a At MPW1K/3-21G* with frequency correction of 0.92 using the
appropriate model system. b Difference between observed and computed
shifts (calc. - obs.).
UV-vis-NIR Spectroelectrochemical Studies. The elec-
tronic spectra of the mononuclear complexes 3a and 3b were
9
J. AM. CHEM. SOC. VOL. 130, NO. 11, 2008 3571

A R T I C L E S
Fox et al.
Figure 10. Electronic absorption spectra of 4a, [4a]+ and [4a]2+ (upper)
and 4b, [4b]+ and [4b]2+ (lower) in CH2Cl2/10-1 M NBu4BF4 at 293 K,
collected within an OTTLE cell.
Figure 9. Electronic absorption spectra of 3a and [3a]+ (upper) and 3b
and [3b]+ (lower) in CH2Cl2/10-1 M NBu4BF4 at 293 K, collected within
an OTTLE cell. The insets show an expansion of the lower energy region
of the monocationic species.
terms is an approximation at best. These electronic spectra are
discussed in more detail below; however, the qualitative
assignments given here are broadly consistent with the results
of time-dependent density functional theory (TD-DFT) calcula-
tions.
In a manner that tracks the trends established from the IR
spectroscopic work, the electronic spectra of [4a]n+ and [4b]n+
(n ) 0, 2) were similar to the spectra of the mononuclear models
[3a]n+ and [3b]n+ (n ) 0, 1). Thus, the electronic spectra of
the bimetallic complex 4a exhibited an unresolved band with a
low-energy edge near 25000 cm-1 assigned to a dπ to carborane
cage transition (Figure 10). The experimental spectra of the
dications [4a]2+ and [4b]2+ were similar to those of the related
mononuclear complexes [3a]+ and [3b]+, with bands near
19000, 14000 and 7000 cm-1 clearly observed, and assigned
to dπ-(dπ)* and IC-type transitions. The NIR bands in [4a]2+
and [4b]2+ are well described by a single Gaussian function
and are of approximately the same energy, but twice the
intensity, of the lowest-energy IC band observed in [3a]+ and
[3b]+. Interestingly, the relatively high-energy dπ-to-cage
transitions associated with the d6 metal fragments are not
observed in the spectra of [4a]2+ and [4b]2+, and are likely
shifted deeper into the UV region, as one would expect on the
basis of the lowering of the metal d orbital energies following
oxidation.
Figure 11. Representative plot showing the low-energy electronic and IR
transitions in [4a]+ and [4a]2+
.
the spectrum (Figure 11). These broad absorption bands can be
deconvoluted into the sum of two Gaussian components centered
at 6870 cm-1 (ε ) 590 M-1 cm-1) and 6660 cm-1 (ε ) 250
M-1 cm-1) ([4a]+), and at 5980 cm-1 (ε ) 350 M-1 cm-1) and
6640 (ε ) 200 M-1 cm-1) ([4b]+). On the basis of the assign-
ments made from the mononuclear analogue, they may be
regarded as representing the intervalence charge transfer (IVCT)
transition and a localized Ru(III) IC transition, respectively.
The more intense, presumably IVCT components of the NIR
bands in [4a]+ (νjmax ) 6870 cm-1) and [4b]+ (νjmax ) 5980
cm-1 ([4b]+) offer half-height band widths, ∆νj1/2, ([4a]+ 6400
cm-1, [4b]+ 5040 cm-1) considerably larger than that predicted
from the Hush relationship ∆νj1/2 ) (2310 νjmax
)
1/2 ([4a]+ ≈ 4000
cm-1, [4b]+ ≈ 3410 cm-1), consistent with class II behavior.
From these data, and taking the Ru‚‚‚Ru distance obtained from
the optimized geometries as an approximation of the electron-
transfer distance ([4a]+ 12.56 Å, [4b]+ 12.32 Å), coupling
The compounds [4a]+ and [4b]+ display spectroscopic
characteristics of the analogous neutral and dicationic com-
pounds, as well as an additional component within the lowest-
energy (NIR) band envelope that extends into the IR region of
9
3572 J. AM. CHEM. SOC. VOL. 130, NO. 11, 2008

Ru Complexes of C,C
′
-Bis(ethynyl)carboranes
A R T I C L E S
Table 6. Comparison of Selected Bond Lengths (Å) and Dihedral Angle (deg) of X-ray Structures of 3a and 3b and from the MPW1K/
3-21G* Optimized Structures of [3a-H]n+ and [3b-H]n+ (n ) 0, 1)
3a
3a-H
[3a-H]+
3b
3b-H
[3b-H]+
Ru-C(3)
C(3)-C(2)
C(2)-C(1)
C(1)-Ba
B-B′b
1.999(2)
1.214(3)
1.443(3)
1.619(3)
1.845(4)/1.808(4)
1.595(4)
2.267(1)
1.998
1.217
1.409
1.629
1.863/1.809
1.613
2.254
1.940
1.230
1.404
1.625
1.875/1.804
1.613
2.300
2.003(2)
1.214(2)
1.439(2)
1.726(4)
1.778(9)/1.760(6)
1.700(6)
2.259(1)
1.997
1.216
1.419
1.734
1.791/1.767
1.714
2.255
1.937
1.233
1.419
1.737
1.808/1.769
1.720
2.305
C(10/12)-Ba
Ru-P
a Averaged values. b The two values represent the two distinct B-B bonds in the p-carborane geometries; see Table 3.
Table 7. Comparison of Selected Bond Lengths (Å) and Dihedral Angle (deg) of X-ray Structures of 4a and 4b and from the MPW1K/
3-21G* Optimized Structures of [4a-H]n+ and [4b-H]n+ (n ) 0, 1, 2)
4a
4a-H
[4a-H]+
[4a-H]2+ (LS)
[4a-H]2+ (HS)
Ru-C(3)
C(3)-C(2)
C(2)-C(1)
C(1)-Ba
B-B′b
2.000(3)
1.214(4)
1.431(4)
1.622(5)
1.845(5)/1.802(5)
2.268(2)
133.5
1.999
1.217
1.409
1.628
1.861/1.805
2.254
179.9
1.976/1.931
1.223/1.232
1.396
1.920
1.241
1.379
1.640
1.881/1.800
2.285
179.2
1.947
1.227
1.407
1.627
1.873/1.805
2.313
158.6
1.630
1.871/1.802
2.261/2.294
167.6
Ru-P
θc
4b
4b-H
[4b-H]+
[4b-H]2+ (LS)
[4b-H]2+ (HS)
Ru-C(3)
C(3)-C(2)
C(2)-C(1)
C(1)-Ba
B-B′ b
1.991(4)
1.205(4)
1.454(5)
1.726(6)
1.774(6)/1.756(6)
2.257(2)
180.0
1.998
1.216
1.420
1.733
1.790/1.766
2.254
179.9
1.984/1.932
1.220/1.230
1.412
1.926
1.238
1.399
1.738
1.801/1.764
2.285
180.0
1.950
1.225
1.420
1.731
1.803/1.765
2.314
160.4
1.730
1.795/1.766
2.260/2.300
163.6
Ru-P
θc
a Averaged values. b The two values represent the two distinct B-B bonds in the p-carborane geometries, see Table 3. c The angle θ is defined as the
dihedral angle C(0)-Ru‚‚‚Ru-C(0), where C(0) represents the centroid of the Cp ring.
Table 8. Energy (ꢀ/eV), Occupancy (occ) and Composition (%) of
Selected Frontier Orbitals for 3a-H and 3b-H
parameters Hab of 260 cm-1 ([4a]+) and 140 cm-1 ([4b]+) can
be estimated.1
HOMO
−2
HOMO
−1
HOMO
LUMO
LUMO
+1
LUMO
+2
LUMO+3
DFT-Optimized Geometries and Vibrational Spectros-
copy. DFT calculations (MPW1K/3-21G*) have been performed
without symmetry constraints, using models that employ Ru-
(PH3)2Cp fragments rather than the Ru(dppe)Cp* moiety to
reduce computational effort, and are denoted [3a-H]n+, [3b-
H]n+, [4a-H]n+ and [4b-H]n+. The critical geometric features
of 3a-H, 3b-H, 4a-H and 4b-H are similar and are also broadly
in keeping with geometries of other half-sandwich ruthenium
acetylides such as [Ru(CtCR)(PH3)2Cp] (R ) H, Ph)15d,24,25,29
and the crystallographically determined structures of 3a, 3b,
4a and 4b (Tables 6 and 7). Comparisons between the structures
of 3a-H and [3a-H]+, and also between 3b-H and [3b-H]+,
reveal variations in keeping with previous studies on related
systems.29 Thus, there is an elongation of the C(3)tC(2) and
Ru-P bonds and a complementary contraction of the Ru-C(3)
bond as a consequence of the loss of a single electron from the
neutral compounds. Interestingly, the geometric parameters
associated with the carborane cages in each pair of compounds
[3a-H]n+ and [3b-H]n+ (n ) 0, 1) are largely unchanged,
although some small expansion of the cage is evidenced (Table
6).
3a-H
-6.42 -0.35
ꢀ
-7.14
2
-6.70
2
7
-0.35
0
0
1
2
4
0
92
0.21
0
24
27
49
0
0.56
0
1
12
86
1
occ
Cp
PH3
Ru
C(3)
C(2)
C2B8
2
11
5
0
0
1
29
11
31
12
12
4
4
51
10
22
6
40
10
27
7
2
4
0
93
0
0
0
1
3b-H
ꢀ
-7.22
2
-6.78
-6.51
0.17
0.52
0
1
10
79
1
0.64
0
1
2
7
7
2
81
0.67
0
1
4
12
7
occ
Cp
PH3
Ru
C(3)
C(2)
C2B10
2
10
5
54
8
2
12
6
41
9
0
23
28
49
0
27
10
30
13
10
4
19
4
27
6
0
0
0
10
1
76
structures in which the two metal moieties are in the same
geometric and electronic environment.30 In the present case, the
MPW1K calculations, with a significant HF component,31
optimize an asymmetric geometry for both [4a-H]+ and [4b-
H]+ that resembles the “valence-trapped” model. Thus, one of
the metal-ethynyl moieties in each cation [4a-H]+ and [4b-
H]+ displays elongated C(3)tC(2) and Ru-P bonds and a
contracted Ru-C(3) bond and closely resembles the optimized
geometry of the related mononuclear systems [3a-H]+ or [3b-
DFT-based calculations using B3LYP and related functionals
can fail to adequately model “valence-trapped” (i.e., class II)
mixed-valence systems, with geometry optimization affording
(28) (a) Hush, N. S. Prog. Inorg. Chem. 1967, 8, 391. (b) Hush, N. S. Trans.
Faraday Soc. 1961, 57, 557. (c) Hush, N. S. Electrochim. Acta 1968, 13,
1005.
(29) Fox, M. A.; Roberts, R. L.; Khairul, W. M.; Hartl, F.; Low, P. J. J.
Organomet. Chem. 2007, 692, 3277.
(30) Maurer, J.; Sarkar, B.; Schwederski, B.; Kaim, W.; Winter, R. F.; Za´lisˇ, S.
Organometallics 2006, 25, 3701.
(31) (a) Lynch, B. J.; Fast, P. L.; Harris, M.; Truhlar, D. G. J. Phys. Chem. A
2000, 104, 4811. (b) Lynch, B. J.; Zhao, Y.; Truhlar, D. G. J. Phys. Chem.
A 2003, 107, 1384.
9
J. AM. CHEM. SOC. VOL. 130, NO. 11, 2008 3573

A R T I C L E S
Fox et al.
Figure 12. Frontier orbitals of 3a-H, 3b-H, 4a-H and 4b-H. Contour values are plotted at (0.04 (e/bohr3)1/2
.
H]+. The other is more or less unchanged from the precursor
4a-H or 4b-H and the mononuclear model 3a-H or 3b-H as
appropriate (Table 7). Vibrational frequency calculations based
on these asymmetric geometries are in excellent agreement with
the IR spectroelectrochemical results (Table 5). Two ν(CtC)
bands are calculated, falling within 20 cm-1 of the observed
bands. The ν(B-H) band is largely unaffected by the number
of electrons in the model system and is calculated at ∼2600
cm-1 in agreement with the experimental observations.
Table 9. Energy (ꢀ/eV), Occupancy (occ) and Composition (%) of
Selected Frontier Orbitals for 4a-H and 4b-H
HOMO
−2
HOMO
−1
HOMO
LUMO
LUMO
+1
LUMO
+2
LUMO+3
4a-H
-6.04 -0.17
ꢀ
-6.43
2
7
3
22
4
13
5
12
3
21
3
6
-6.33
2
1
1
19
9
13
11
14
9
21
1
-0.17
0
0
1
2
4
0
86
0
4
0.35
0
23
28
49
0
0
0
0
0
0.37
0
0
0
0
0
0
0
0
0
49
28
23
occ
2
4
0
0
Cp(1)
PH3(1)
Ru(1)
C3(1)
C2(1)
C2B8
C2(2)
C3(2)
Ru(2)
PH3(2)
Cp(2)
2
1
17
7
2
4
14
9
15
7
0
86
0
The dications [4a-H]2+ and [4b-H]2+ offer two potential spin
states, namely a singlet, low-spin (LS) configuration and a
triplet, high-spin (HS) configuration. In contrast to the polyyndiyl-
4
18
2
2
1
2
0
0
0
0
0
bridged analogues [{Ru(PR3)2Cp}2{µ-(CtC)n}]2+ 15c,d
,
the triplet
(high spin, HS) configurations of [4a-H]2+ and [4b-H]2+ are
computed to be more stable ([4a-H]2+, 34 kcal mol-1
2
5
0
4b-H
;
ꢀ
-6.49
2
7
3
23
3
12
4
12
3
22
3
7
-6.48
2
2
1
24
7
13
7
13
7
24
1
3
-6.18
2
5
2
19
6
14
7
14
6
19
2
5
0.33
0.33
0
1
1
1
0
0
0
0
0.64
0
0
3
30
2
1
28
1
2
30
3
0.69
0
0
6
44
0
0
0
0
0
[4b-H]2+, 37 kcal mol-1) than the singlet (low-spin, LS) states.
While the calculated IR spectra of the HS and LS states are
similar, the HS model (θ ) 160°) provides the best agreement
with the experimental data (Table 5). Within the geometry-
optimized (HS) models [4a-H]2+ and [4b-H]2+ the environments
at both metal centers are indistinguishable, and similar to those
of the mononuclear systems [3a]+ and [3b-H]+, respectively.
The preference for the HS diradical species is perhaps an
indication that the carboranes act more effectively as physical
spacers than as strong electronic coupling elements in the
dications. Given the lower energy of the HS systems and the
better match between the calculated and observed IR data, we
will only refer to the triplet states in the following discussions.
Electronic Structures and TD-DFT Studies. An analysis
of the energies and composition of the MOs derived from
3a-H, 3b-H, 4a-H and 4b-H reveals the same general electronic
structure as has been found in previous studies of [Ru(Ct
CAryl)(PR3)2Cp′]-based systems.16,24,25,29 In all cases the two
highest-lying occupied MOs are largely centered on the Ru-
occ
0
23
27
48
0
0
0
0
0
Cp(1)
PH3(1)
Ru(1)
C3(1)
C2(1)
C2B10
C2(2)
C3(2)
Ru(2)
PH3(2)
Cp(2)
0
1
1
1
48
27
23
44
6
0
0
ethynyl groups of the molecules, being π-type in character,
nearly orthogonal to each other, antibonding with respect to
Ru-C(3), and bonding with respect to C(3)-C(2) (Table 8,
Table 9, Figure 12).
There are negligible contributions from the cage to the
HOMOs. In general, the lowest-lying unoccupied orbitals of
[Ru(CtCAryl)(PH3)2Cp] systems are metal and metal-Cp in
character, although the introduction of strongly electron-
withdrawing groups can lower an acetylide ligand-based orbital
9
3574 J. AM. CHEM. SOC. VOL. 130, NO. 11, 2008

Ru Complexes of C,C
′
-Bis(ethynyl)carboranes
A R T I C L E S
Table 10. Comparison of Electronic Transitions on Model Geometries [3a-H]n+, [3b-H]n+ (n ) 0, 1), [4a-H] and [4b-H]n+ (n ) 0, 1, 2) based
on TD-DFT Calculations (MPW1K/3-21G*) with Experimental UV-Vis-NIR Data for Complexes [3a]n+, [3b]n+ (n ) 0, 1), [4a]n+ and [4b]n+
(n ) 0, 1, 2)
a IC ) interconfigurational transition, IVCT ) inter-valence charge-transfer transition.
into this region.16,29,32 In the context of the present examples,
Table 11. Calculated Spin Densities (MPW1K/3-21G*) for Cations
[3a-H]+, [3b-H]+, [4a-H]+ and [4b-H]+ and Triplet States of
the complexes 3a-H and 4a-H, which feature the smaller
carborane cage, also offer low-lying, largely cage-centered
unoccupied orbitals, which are similar in energy to the metal-
based LUMOs. The energy of the various frontier MOs of 3a-
H, 3b-H, 4a-H and 4b-H together with the orbital composition
are summarized in Tables 8 and 9, and represented graphically
in Figure 12. Although Koopmans’ theorem ignores electron
correlation and similar effects, it is interesting to note that the
solution-phase oxidation potentials obtained from the cyclic
voltammetry data (Table 4) track the calculated HOMO energies
and show the similar trends, i.e., the ease of the first oxidation
being
[4a-H]2+ and [4b-H]2+
Ru(1)
C3(1)
C2(1)
C1(1)
Ru(2) C3(2) C2(2) C1(2)
[3a-H]+
[3b-H]+
[4a-H]+
[4b-H]+
0.683 -0.187 0.457 -0.050
0.647 -0.155 0.445 -0.042
0.012
0.006
0.517 -0.097 0.390 -0.033 0.060 0.033 0.037 0.018
0.607 -0.152 0.435 -0.041 0.029 0.017 0.018 0.008
(HS)-[4a-H]2+ 0.734 -0.211 0.428 -0.041
(HS)-[4b-H]2+ 0.749 -0.221 0.428 -0.041
the solvatochromic behavior of the experimentally observed
band at 30000 cm-1 in 3a. The analogous transitions in 3b-H
are calculated at significantly higher energy, near 45000 cm-1
,
accounting for the blue shift of this band in 3b. In the case of
the models [3a-H]+ and [3b-H]+ the highest occupied R-spin
orbitals (R-HOSO) and lowest unoccupied â-spin orbitals (â-
LUSO) offer considerable metal and ethynyl character and
have similar nodal properties and atomic composition as the
HOMOs in the 18-electron precursors. The calculated spin
densities are summarized in Table 11. The ruthenium center
and the C(2) carbon carry the largest positive spin density, the
proportions of which are largely insensitive to the nature of the
cage. These electronic structure calculations are in agreement
with the spectroelectrochemical results and indicate that the
oxidation of the mononuclear complexes is largely associated
with the removal of an electron from a metal-ethynyl-based
MO.
TD-DFT calculations involving the oxidized model species
[3a-H]+ or [3b-H]+ give good agreement with the experimen-
tally observed absorption bands. These bands may be ap-
proximately described as the dπ-(dπ)* and IC transitions
associated with the formally d5 Ru(III) center, although the
mixing of the metal orbitals with the ethynyl and other
4a (4a-H) (Eox1 (0/+) ) 0.27 V; -ꢀHOMO ) 6.04 eV) >
4b (4b-H) (Eox1 (0/+) ) 0.32 V; -ꢀHOMO ) 6.18 eV) >
3a (3a-H) (Eox1 (0/+) ) 0.35 V; -ꢀHOMO ) 6.42 eV) >
3b (3b-H) (Eox1 (0/+) ) 0.39 V; -ꢀHOMO ) 6.51 eV)
Electronic spectroscopy coupled with TD-DFT calculations
provides a convenient method through which to link the results
of electronic structure calculations with experiment. Detailed
TD-DFT results are included in the Supporting Information, and
important results are summarized in Table 10, to both aid in
the assignment of the electronic spectra and support the results
of the electronic structure calculations. The lowest-energy
absorption bands of any appreciable intensity in the mononuclear
model 3a-H, calculated to fall near 36000 cm-1, corresponds
to a (dπ)* f cage charge-transfer band, which correlates with
(32) Powell, C. E.; Cifuentes, M. P.; McDonagh, A. M.; Hurst, S. K.; Lucas,
N. T.; Delfs, C. D.; Stranger, R.; Humphrey, M. G.; Houbrechts, S.;
Asselberghs, I.; Persoons, A.; Hockless, D. C. R. Inorg. Chim. Acta 2003,
352, 9.
9
J. AM. CHEM. SOC. VOL. 130, NO. 11, 2008 3575

A R T I C L E S
Fox et al.
supporting ligands should be noted (Table 10). The R-HOSO
f R-LUSO transition is also apparent.
For each bimetallic carborane-bridged complex 4a-H and 4b-
H, the HOMO is composed of contributions from the pseudo-
linear Ru-CtC-cage-CtC-Ru assembly, with significant Ru
d and CtC π character, and is removed in energy from the
other frontier orbitals. In the case of 4a-H the lowest unoccupied
orbitals are degenerate and localized on the carborane cage, with
an almost degenerate pair of unoccupied metal-based orbitals
somewhat higher in energy. The lowest energy unoccupied
orbitals of 4b-H are more Cp-metallic in character (Table 10,
Figure 12).
The electronic spectrum of 4a exhibited an unresolved band
with a low-energy edge near 25000 cm-1, while only the tail
of this band was apparent in the spectrum of 4b. The TD-DFT
calculations on the model 4a-H indicate this band is likely due
to excitations between the largely metal-ethynyl-localized
HOMO (Figure 12) to the cage-based LUMOs. Electronic
structure calculations performed on the larger-cage model 4b-H
suggest that the analogous transitions between metal-ethynyl
HOMOs and the unoccupied orbitals on the C2B10 cage are
significantly higher in energy. In addition to this approximately
metal-ethynyl to cage charge-transfer band, the intermediate
oxidation states ([4a]+ or [4b]+) also feature bands in the visible
region near 20000 and 15000 cm-1, and a relatively broad
absorption band in the NIR region (Figure 11). These new bands
are similar in energy and intensity to the dπ-(dπ)* and IC
transitions observed for the mononuclear complexes and can
be identified as such from the TD-DFT calculations, although
the transitions do involve a considerable degree of mixing of
character from both metal moieties (Table 10).
Figure 13. â-LUSO and â-HOSO of [4b]+. Contour values are plotted at
(0.04 (e/bohr3)1/2
.
Conclusions
Trimethylsilyl-protected ethynyl 10- and 12-vertex p-carbo-
ranes are convenient reagents for use in the preparation of mono-
and bimetallic acetylide complexes containing p-carborane
cages. These four ruthenium complexes undergo one or two
sequential oxidation events at moderate potentials, which can
be observed voltammetrically, and the resulting oxidation
products are characterized by UV-vis-NIR and IR spectro-
electrochemical methods. A combination of spectroscopic data
and computational studies reveals that the carborane orbitals
do not mix significantly with the metal-ethynyl-based orbitals.
The stabilization of the mixed-valence states arises not entirely
from ion pairing with the electrolyte but also from an inherent
electronic effect. Both 10- and 12-vertex cages appear to permit
electronic communication between the two metal centers over
a distance of ca. 12.5 Å with the 10-vertex cage leading to a
slightly higher coupling parameter, based on treatment of the
data according to the Hush model. The LUMOs in the 10-vertex
cage complexes have cage character and metal-to-cage transfer
bands were observed in the UV spectra of these compounds.
The carborane cages, particularly the better-known 12-vertex
analogue, are perhaps best described as pseudo-aromatic spheri-
cal spacers, that in the cases described here permit a degree of
interaction between two metal centers. Geometries of the
“valence-localized” mixed-valence compounds [4a]+ and [4b]+,
and the other compounds reported here, were satisfactorily
modeled using the MPW1K/3-21G* level of theory, and the
spectroscopic transitions observed, including the “IVCT” band,
were successfully modelled with TD-DFT methods.
Perhaps of most interest are the transitions that comprise the
NIR band envelopes in the mixed-valence cations [4a]+ and
[4b]+. These bands are considerably broader and more intense
than the IC transitions associated with [3a]+ and [3b]+ and, as
indicated above, can be deconvoluted into a sum of two
Gaussian curves, which are associated with the IC style
transitions localized on the formally d5 Ru(III) component of
the mixed-valence compound, and the other, more intense and
broader component which is the true IVCT portion of the band
envelope (Table 10). These assignments are also supported by
the TD-DFT calculations, which predict a lower-intensity
component with a “dd” character from the “d5” site, albeit
admixed with similar orbitals on the “d6” metal fragment,
together with a transition largely composed of the â-HOSO and
â-LUSO orbitals (Figure 13) and which corresponds to the IVCT
transition.
The experimental spectra of the dications [4a]2+ and [4b]2+
were similar to those of the related mononuclear complexes
[3a]+ and [3b]+, with bands near 19000, 14000 and 7000 cm-1
clearly observed, and also reproduced in the computational
models (Table 10). Interestingly, the relatively high-energy dπ-
to-cage transitions associated with the complexes featuring
formally d6 metal fragments are not observed in the spectra of
[4a]2+ and [4b]2+, and according to the TD-DFT results should
be shifted deeper into the UV region, as one would expect on
the basis of the lowering of the metal d orbital energies following
oxidation.
Terminology such as “intervalence charge transfer” was
developed from studies of classical mixed-valence coordination
complexes and presupposes metal-centered redox processes and
assignment of well-defined metal d-electron counts. In many
organometallic complexes the mixing of metal, supporting and
bridging ligand orbitals arguably makes such terms less ap-
propriate. With the optimization of suitable geometries that
satisfactorily model the “valence-localized” case, TD-DFT
methods may be used to provide an alternative, molecular
9
3576 J. AM. CHEM. SOC. VOL. 130, NO. 11, 2008

Ru Complexes of C,C
′
-Bis(ethynyl)carboranes
A R T I C L E S
B7-11H), 2.28 (s, 1H, C12H), 2.53 (m, 2H, CH2), 7.10 (m, 4H, Ph),
7.24 (m, 6H, Ph), 7.40 (m, 6H, Ph), 7.59 (m, 4H, Ph). 31P{1H} NMR
(CDCl3): δ 81.3 (s). 11B NMR (CDCl3): δ -11.1 (d, 5B, JBH ) 164
Hz, B2-6), -16.3 (d, 5B, JBH ) 164 Hz, B7-11). 13C{1H} NMR: δ
9.8 (Me), 29.1 (m, CH2), 53.4 (C12), 78.7 (C1), 92.6 (C5Me5), 103.7
(RuCC), 119.1 (t, 24 Hz, RuC), the following peaks correspond to the
phenyl groups 127.3 (m), 127.4 (m), 128.8 (p), 133.1 (o), 133.3 (o),
136.9 (d, 47 Hz, i), 138.5 (m, i). Found: C, 56.5; H, 6.1%.
RuC40H50P2B10 requires: C, 59.9; H, 6.3%. Accurate Mass, ES(+)-
MS (m/z): 803.35103 Calculated for [{Ru(CtCC2B10H11)(dppe)Cp*}
+ H], 803.35214.
Preparation of [{Ru(dppe)Cp*}2(µ-1,10-(CtC)2-1,10-C2B8H8}]
(4a). From [RuCl(dppe)Cp*] (200 mg, 0.3 mmol), 2a (51 mg, 0.16
mmol), and KF (30 mg, 0.5 mmol) (6 h reflux), 4b was obtained (139
mg, 65%). IR (KBr disc, cm-1): 3054w phenyl CH, 2962w, 2912w,
2860w aliphatic CH, 2592s BH, 2082s CtC, 1432 m, 1095 m, 697s,
532s. 1H{11B} NMR (CDCl3): δ 1.51 (s, 30H, Me), 1.70 (s, 8H, BH),
2.03 (m, 4H, CH2), 2.68 (m, 4H, CH2), 7.14, 7.17, 7.21 (m, 32H, Ph),
7.73 (m, 8H, Ph). 31P{1H} NMR (CDCl3): δ 80.6 (s). 11B NMR
(CDCl3): δ -13.4 (d, 163 Hz). 13C{1H} NMR (CDCl3): δ 10.0 (Me),
29.5 (m, CH2), 92.7 (C5Me5), 99.3 (C1), 106.8 (RuCC), 122.0 (t, 26
Hz, RuC), the following peaks correspond to the phenyl groups 127.2
(m), 127.3 (m), 128.7 (p), 128.8 (p), 133.3 (o), 133.6 (o), 137.1 (d, 47
Hz, i), 138.7 (m, i). Found: C, 62.0; H, 5.9%. Ru2C78H86P4B8
requires: C, 65.2; H, 6.0%. Accurate Mass, ES(+)-MS (m/z): 1437.47037
Calculated for [{Ru(dppe)Cp*}2(µ-1,10-(CtC)2-1,10-C2B8H8}] + H],
1437.46796.
orbital-based description of the fascinating spectroscopic proper-
ties of “valence-localized mixed-valence” organometallic com-
pounds.
Experimental Section
All reactions were carried out under an atmosphere of dry nitrogen,
using standard Schlenk techniques. Reaction solvents were purified and
dried using an Innovative Technology SPS-400, and degassed before
use. No special precautions were taken to exclude air or moisture during
workup. The compounds [RuCl(dppe)Cp*],33 1a, 1b,9 2a7 and 2b7 were
prepared by the literature methods or minor variations as described in
the Supporting Information. Other reagents were purchased and used
as received.
Cyclic voltammograms were recorded from solutions of approxi-
mately 10-4 M in analyte in dichloromethane containing 10-1 M NBu4-
BF4 (recrystallized twice from absolute ethanol and dried overnight
under vacuum at 80 °C before use) at ν ) 100 mV s-1 in a gas-tight
single-compartment three-electrode cell equipped with glassy carbon
disk working (apparent surface area of 0.42 mm2), coiled platinum wire
auxiliary, and platinum wire pseudo-reference electrodes. All redox
potentials are reported against the SCE scale, with the decamethylfer-
rocene/decamethylferrocenium (Fc*/Fc*+) redox couple used as an
internal reference system: -0.08 V vs SCE.34 Data were collected using
a computer-interfaced EcoChemie PGSTAT-30 potentiostat.
Spectroelectrochemical experiments at room temperature were
performed with an airtight optically transparent thin-layer electrochemi-
cal (OTTLE) cell equipped with a Pt minigrid working electrode (32
wires cm-1) and CaF2 windows.35 The cell was positioned in the sample
compartment of a Nicolet Avatar FT-IR spectrometer (1 cm-1 spectral
resolution, 16 scans) or a Perkin-Elmer Lambda-900 spectrophotometer.
The controlled-potential electrolyses were carried out with a potentiostat
constructed in-house.
Preparation of [{Ru(dppe)Cp*}2(µ-1,12-(CtC)2-1,12-C2B10H10}]
(4b). From [RuCl(dppe)Cp*] (100 mg, 0.149 mmol), 2b (25 mg, 0.075
mmol), and KF (35 mg, 0.603 mmol) (3 h reflux) 4b was obtained and
crystallized from benzene (84 mg, 77%). IR (KBr disc, cm-1): 3051w
phenyl CH, 2962w, 2898w, 2856w aliphatic CH, 2597s BH, 2077s
1
CtC, 1433 m, 1094 m, 695s, 531s, 419s. H{11B} NMR (CDCl3): δ
General Procedure: Preparation of [Ru(1-CtC-1,10-C2B8H9)-
(dppe)Cp*] (3a). A suspended mixture of [RuCl(dppe)Cp*] (100 mg,
0.15 mmol), 1a (35 mg, 0.165 mmol), and KF (15 mg, 0.25 mmol) in
methanol (20 mL) was refluxed for 6 h. The yellow precipitate formed
was filtered and washed with ice-cold methanol to give 3a as a yellow
solid (75 mg, 69%). Recrystallization of the solid from dichloromethane/
methanol gave yellow crystals suitable for X-ray crystallography. IR
(KBr disc, cm-1): 3100w cage CH, 3076, 3054w phenyl CH, 2962w,
2908w, 2856w aliphatic CH, 2591s BH, 2074s CtC, 1433 m, 1095
1.43 (s, 30H, Me), 1.96 (s, 10H, BH), 2.04 (m, 4H, CH2), 2.51 (m, 4H,
CH2), 7.05 (m, 8H, Ph), 7.22 (m, 12H, Ph), 7.36 (m, 12H, Ph), 7.54
(m, 8H, Ph). 31P{1H} NMR (CDCl3): δ 80.4 (s). 11B NMR (CDCl3):
δ -12.2 (d, 160 Hz). 13C{1H} NMR (C6D6): δ 10.1 (Me), 29.5 (m,
CH2), 69.3 (C1), 92.7 (C5Me5), 104.5 (RuCC), 114.2 (t, 25 Hz, RuC),
the following peaks correspond to the phenyl groups 127.6 (m), 129.2
(p), 133.5 (o), 133.8 (o), 137.5 (m, i), 139.2 (m, i). Found: C, 60.7; H,
6.0%. Ru2C78H88P4B10 requires: C, 64.2; H, 6.1%. Accurate Mass, ES-
(+)-MS (m/z): 1461.50611 Calculated for [{Ru(dppe)Cp*}2(µ-1,12-
(CtC)2-1,12-C2B10H10}] + H], 1461.50401.
1
m, 697s, 533s. H{11B} NMR (CDCl3): δ 1.58 (s, 15H, Me), 1.66 (s,
4H, B2-5H), 1.83 (s, 4H, B6-9H), 2.12 (m, 2H, CH2), 2.75 (m, 2H,
CH2), 6.01 (s, 1H, C10H), 7.30 (m, 16H, Ph), 7.81 (m, 4H, Ph).
31P{1H} NMR (CDCl3): δ 81.6 (s). 11B NMR (CDCl3): δ -11.3 (d,
4B, JBH ) 164 Hz, B2-5), -15.7 (d, 4B, JBH ) 162 Hz, B6-9).
13C{1H} NMR: δ 10.0 (Me), 29.5 (m, CH2), 82.8 (C10), 92.8
(C5Me5), 107.1 (RuCC), 117.8 (C1), 126.6 (t, 23 Hz, RuC), the
following peaks correspond to the phenyl groups 127.3 (m), 127.4 (m),
128.9 (p), 128.7 (p), 133.3 (o), 133.5 (o), 137.0 (d, 48 Hz, i), 138.8
(m, i). Found: C, 58.1; H, 6.2%. RuC40H48P2B8 requires: C, 61.7; H,
6.2%. Accurate Mass, ES(+)-MS (m/z): 779.31600 Calculated for
[{Ru(CtCC2B8H9)(dppe)Cp*} + H], 779.31684.
Crystallography. Diffraction data were collected at 120K on a
Bruker SMART 6000 (3b, 4a,b), SMART 1K (3a) and Bruker
Proteum-M (1a) diffractometers, using graphite-monochromated Mo-
KR radiation. The structures were solved by direct-methods and refined
by full matrix least-squares against F2 of all data using SHELXTL
software.36 All non-hydrogen atoms where refined in anisotropic
approximation except the disordered ones, H atoms were placed into
the calculated positions and refined in “riding” mode. Molecule 4b is
located in the special position at the center of symmetry. Crystal of 4b
contains three independent solvent molecules of benzene; two of them
are severely disordered. Crystallographic data for the structural analyses
have been deposited with the Cambridge Crystallographic Data Centre,
CCDC Nos. 637465-637469 for compounds 1a, 3a, 3b, 4a and 4b,
respectively. Copies of this information may be obtained free of charge
from The Director, CCDC 12 Union Rd, Cambridge, CB2 1EZ, UK.
Computational Details. All computations were carried out with the
Gaussian 03 package,37 at the MPW1K/3-21G* level of theory.31
Frequency calculations on the resulting optimized geometries showed
Preparation of [Ru(1-CtC-1,12-C2B10H11(dppe)Cp*] (3b). From
[RuCl(dppe)Cp*] (160 mg, 0.224 mmol), 1b (60 mg, 0.249 mmol),
and KF (25 mg, 0.431 mmol) (2 h reflux), 3b was obtained as yellow
crystals (117 mg, 67%). IR (KBr disc, cm-1): 3080w cage CH, 3058w
phenyl CH, 2970w, 2912w, 2856w aliphatic CH, 2605s BH, 2081s
1
CtC, 1433 m, 1093 m, 699s, 533s. H{11B} NMR (CDCl3): δ 1.48
(s, 15H, Me), 1.82 (s, 5H, B2-6H), 2.08 (m, 2H, CH2), 2.14 (s, 5H,
(33) Bruce, M. I.; Ellis, B. G.; Low, P. J.; Skelton, B. W.; White, A. H.
Organometallics 2003, 22, 3184.
(36) (a) SAINT, v. 6.45; Bruker-AXS Inc.: Madison, Wisconsin, U.S.A., 2001.
(b) SADABS, v.2006/1; Bruker-AXS Inc.: Madison, Wisconsin, U.S.A.,
2006. (c) SHELXTL, v. 6.14; Bruker-AXS Inc.: Madison, Wisconsin,
U.S.A. 2000.
(37) Frisch, M. J.; et al. Gaussian 03, Revision C.02; Gaussian, Inc.: Walling-
ford, CT, 2004.
(34) (a) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877. (b) Rigaut,
S.; Perruchon, J.; Guesmi, S.; Fave, C.; Touchard, D.; Dixneuf, P. H. Eur.
J. Inorg. Chem. 2005, 447.
(35) Krejcˇ´ık, M.; Daneˇk, M.; Hartl, F. J. Electroanal. Chem. 1991, 317, 179.
9
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A R T I C L E S
Fox et al.
no imaginary frequencies. A scaling factor of 0.92 was applied to the
calculated IR frequencies.29 Electronic structure calculations and TD-
DFT calculations were also carried out at the same level of theory.
The rotation barriers between the two Ru(PH3)2Cp groups in 4a-H,
[4a-H]+, [4a-H]2+(LS) and [4a-H]2+(HS) were estimated by fixing the
dihedral angles P1-Ru1-Ru2-P3 (Figure 4) at 15° intervals.
Supporting Information Available: Full details of the
preparation of 1a, representative plots of the cyclic and square-
wave voltammograms for 4a and 4b, full details of the
computational methods employed, tables giving optimized
geometries of 1a, 1b, 2a and 2b, absolute and relative energies
of minima at the MPW1K/3-21G* level of theory, the orbital
order and composition (%) of selected orbitals, excitation
energies and oscillator strengths from TD-DFT computations
for [3a-H]n+ (n ) 0, 1), [3b-H]n+ (n ) 0, 1), [4a-H]n+ (n ) 0,
1, 2) and [4b-H]n+ (n ) 0, 1, 2), tables of the absolute and
relative energies of several minima found at the B3LYP/3-21G*
level of theory, comparison of selected bond lengths for
optimized geometries of 4b-H at various levels of theory, and
complete references 2a and 37.
Acknowledgment. P.J.L. and M.A.F. thank the EPSRC for
generous financial support. B.L.G. and J.F.H. thank the Poˆle
de Calcul Intentif de l’Ouest (PCIO) of the University of
Rennes and the Institut de De´veloppement et de Ressources en
Informatique Scientifique (IDRIS-CNRS) for computing facili-
ties. R.L.R. held a PhD scholarship from the University of
Durham, Department of Chemistry Doctoral Training Account.
These studies were facilitated by travel grants from the Royal
Society, UK (P.J.L., J.F.H., F.H.) and the CNRS, France (J.F.H.,
P.J.L.).
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