Polycarbon Ligand Chemistry: Electronic Interactions between a Mononuclear Ruthenium Fragment and a Cobalt-Carbon Cluster Core

Article abstract of DOI:10.1021/om990290w

The preparation, characterization, and electrochemical response of the complexes Co₂(μ-Me₃SiC≡CC₂C≡CSiMe ₃)(CO)₄(dppm) (2) and Co₂(μ-Me₃SiC₂C≡CC≡CSiMe ₃)(CO)₄(dppm) (3) are described. Metalation of one of the pendant alkynyl groups in each complex has been achieved, yielding Co₂{μ-Me₃SiC≡CC₂C≡C[Ru(PPh ₃)₂Cp]}(CO)₄(dppm) (4) and Co₂{μ-Me₃-SiC₂C≡CC≡C[Ru(PPh ₃)₂Cp]}(CO)₄(dppm) (5). The spectral and electrochemical properties of the heterometallic complexes indicate a significant electronic interaction between the mononuclear fragment and the metallocarbon cluster core. The electronic structure of these compounds has been modeled using DFT, ZINDO, and ELF calculations, and an explanation of the nature of the electronic interaction between the heterometallic fragments is presented.

Full text of DOI:10.1021/om990290w

Organometallics 1999, 18, 3885-3897
3885
P olyca r bon Liga n d Ch em istr y: Electr on ic In ter a ction s
betw een a Mon on u clea r Ru th en iu m F r a gm en t a n d a
Coba lt-Ca r bon Clu ster Cor e
Paul J . Low,† Roger Rousseau,† Pikka Lam,† Konstantin A. Udachin,†
Gary D. Enright,† J ohn S. Tse,*,† Danial D. M. Wayner,† and Arthur J . Carty*,†,‡
Steacie Institute for Molecular Sciences, 100 Sussex Drive,
Ottawa, Ontario, K1A 0R6, Canada, and Ottawa-Carleton Research Institute,
Department of Chemistry, University of Ottawa, 1125 Colonel By Drive,
Ottawa, Ontario, K1S 5B6, Canada
Received April 22, 1999
The preparation, characterization, and electrochemical response of the complexes Co2(µ-
Me3SiCtCC2CtCSiMe3)(CO)4(dppm) (2) and Co2(µ-Me3SiC2CtCCtCSiMe3)(CO)4(dppm) (3)
are described. Metalation of one of the pendant alkynyl groups in each complex has been
achieved, yielding Co2{µ-Me3SiCtCC2CtC[Ru(PPh3)2Cp]}(CO)4(dppm) (4) and Co2{µ-Me3-
SiC2CtCCtC[Ru(PPh3)2Cp]}(CO)4(dppm) (5). The spectral and electrochemical properties
of the heterometallic complexes indicate a significant electronic interaction between the
mononuclear fragment and the metallocarbon cluster core. The electronic structure of these
compounds has been modeled using DFT, ZINDO, and ELF calculations, and an explanation
of the nature of the electronic interaction between the heterometallic fragments is presented.
In tr od u ction
sition metal centers,8 and transition metal clusters.9
Unbranched polyyndiyl ligands -(CtC)n- appear to be
especially efficient in promoting electronic interactions,
as connection between the end-capping groups is largely
unaffected by the relative orientation10 or aromaticity11
of a spacing group.
Electronic “communication” between organometallic
fragments linked by pure polyynyl ligands, -(CtC)n-,
has been described by Gladysz,12 Lapinte,13 and Bruce14
for mononuclear systems and by Osella15 and Robinson16
for multimetallic systems. Several theoretical studies
The construction of molecules in which redox-active
subunits are linked by a bridging ligand capable of
transmitting electronic effects has become an area of
immense interest in recent years. It is thought that
these compounds may find application in the construc-
tion of molecular scale electronic devices1 or display
useful bulk properties, including magnetism,2 electron
transfer,3 and large nonlinear optical response.4
Acetylene-based bridging ligands have been exten-
sively examined during the course of these studies as
the acetylene group is compatible with a wide range of
redox probes, such as substituted organic aromatic
groups,5 porphyrins,6 metallocenes,7 mononuclear tran-
(5) (a) Brandsma, L. Preparative Acetylenic Chemistry, 2nd ed.;
Elsevier Science Publishers: New York, 1988. (b) March, J . Advanced
Organic Chemistry, 3rd ed.; Plenum: New York, 1985.
(6) (a) Anderson, H. L. Inorg. Chem. 1994, 33, 972. (b) Arnold, D.
P.; Nitschinsk, L. Tetrahedron 1992, 48, 8781. (c) Arnold, D. P.; Heath,
G. A.; J ames, D. A. New J . Chem. 1998, 12, 1377. (d) Anderson, H. L.
Tetrahedron Lett. 1992, 33, 1101.
(7) (a) Rosenblum, M.; Brawn, N.; Papenmeier, J .; Applebaum, M.
J . Organomet. Chem. 1966, 6, 173. (b) Hsung, R. P.; Chidsey, C. E. D.;
Sita, L. R. Organometallics 1995, 14, 4808.
* Corresponding author. E-mail: Arthur.Carty@nrc.ca. Fax: +1 613
957 8850.
† Steacie Institute for Molecular Sciences.
‡ Ottawa-Carleton Research Institute.
(1) (a) Ward, M. D. Chem. Soc. Rev. 1995, 121. (b) Ward, M. Chem.
Ind. 1997, 640. (c) Grosshenny, V.; Harriman, A.; Hissler, M.; Ziessel,
R. Platinum Met. Rev. 1996, 40, 26. (d) Petty, M. C.; Bryce, M. R.;
Bloor, D. Introduction to Molecular Electronics; Oxford University
Press: New York, 1995.
(2) (a) Posselt, D.; Badur, W.; Steiner M.; Baumgarten, M. Synth.
Met. 1993, 55, 3299. (b) Hmyene, M.; Yassar, A.; Escorne, M.; Perchon-
Gue´gan, A.; Garnier, F. Adv. Mater. 1994, 6, 564. (c) Cargill Thompson,
A. M. W.; Gatteschi, D.; McCleverty, J . A.; Navas, J . A.; Rentschler,
E.; Ward, M. D. Inorg. Chem. 1996, 35, 2701. (d) Ung, V. A.; Cargill
Thompson, A. M. W.; Bardwell, D. A.; Gatteschi, D.; J effery, J . C.;
McCleverty, J . A.; Totti, F.; Ward, M. D. Inorg. Chem. 1997, 36, 3447.
(3) (a) Carter, F. L. In Electronic Devices II; Marcel Dekker: New
York, 1987. (b) Goppel, W., Zeigler, C., Eds. Nanostructures Based on
Molecular Materials; VCH: Weinheim, 1992. (c) Lehn, J . M. Supramo-
lecular Chemistry; VCH: Weinheim, 1995. (d) Tour, J . M. Chem. Rev.
1996, 96, 537.
(8) (a) Nast, R. Coord. Chem. Rev. 1982, 47, 89. (b) Manna, J .; J ohn,
K. D.; Hopkins, M. D. Adv. Organomet. Chem. 1995, 38, 79.
(9) (a) Sappa, E.; Tiripicchio, A.; Braunstein, P. Chem. Rev. 1983,
83, 203. (b) Sappa, E.; Tiripicchio, A.; Braunstein, P. Coord. Chem.
Rev. 1985, 65, 219. (c) Bruce, M. I. J . Organomet. Chem. 1985, 257,
417.
(10) Woitellier, S.; Launay, J . P.; J oachim, C. Chem. Phys. 1989,
131, 481.
(11) Taylor, P. N.; Wylie, A. P.; Huuskonen, J .; Anderson, H. L.
Angew. Chem., Int. Ed. Engl. 1998, 37, 986.
(12) (a) Brady, M.; Weng, W.; Zhou, Y.; Seyler, J . W.; Amoroso, A.
J .; Arif, A. M.; Bo¨hme, M.; Frenking, G.; Gladysz, J . A. J . Am. Chem.
Soc. 1997, 119, 775. (b) Bartik, T.; Bartik, B.; Brady, M.; Dembinski,
R.; Gladysz, J . A. Angew. Chem., Int. Ed. Engl. 1996, 35, 414. (c) Brady,
M.; Weng, W.; Gladysz, J . A. J . Chem. Soc., Chem. Commun. 1994,
2655.
(13) (a) Le Narvor, N.; Toupet, L.; Lapinte, C. J . Am. Chem. Soc.
1995, 117, 7129. (b) Coat, F.; Lapinte, C. Organometallics 1996, 15,
477.
(4) (a) Long, N. J . Angew. Chem., Int. Ed. Engl. 1995, 34, 21. (b)
Kanis, D. R.; Ratner, M. A.; Marks, T. J . Chem. Rev. 1994, 94, 195. (c)
Whittal, I. R.; McDonagh, A. M.; Humphrey, M. G.; Samoc, M. Adv.
Organomet. Chem. 1998, 42, 291.
(14) Bruce, M. I.; Denisovich, L. I.; Low, P. J .; Peregudova, S. M.;
Ustynyuk, N. A. Mendeleev Commun. 1996, 200.
10.1021/om990290w CCC: $18.00 © 1999 American Chemical Society
Publication on Web 09/13/1999

3886 Organometallics, Vol. 18, No. 19, 1999
Low et al.
that address the issues relating to the extent of elec-
tronic interaction between metal-containing groups in
related model compounds have also been undertaken.17
It has been suggested that transition metal clusters
should function well as electron reservoirs, capable of
both accepting and releasing electrons,18 and as such
these species may find some use in the construction of
nanoscale electronic circuits.19 In addition, the redox
properties of mixed transition metal-main group cluster
cores have also attracted a great deal of attention in
their own right, as these compounds play a crucial role
in biological electron transport cycles.20 Therefore com-
pounds in which multinuclear cluster cores are linked
by polyynyl ligands would appear to have great potential
for use in the construction of large electroactive molec-
ular assemblies.
F igu r e 1. Some representative examples of cluster com-
These observations have prompted something of a
renaissance in the organometallic chemistry of polyynes.
In addition to the studies mentioned above, many other
groups have also been active in the preparation of
compounds of the general type [LnM](CtC)x[MLn].21
Examples of compounds in which a polycarbon chain is
capped at each end by a multinuclear cluster fragment
include the following: tricobalt clusters linked by µ3-
η1-carbon chains22 and related [MCo2(CO)8Cp] (M ) Mo,
W) species;17c a complex with an [MnMo(µ2-η1,η1-C2)-
MnMo] core;23 a series of compounds with M2(µ-PPh2)-
(CO)6 units (M ) Fe, Ru) linked by µ4-η1,η2-C2 and µ4-
η1,η2:η1,η2-C4 ligands;24 the hexametallic complexes
{M3(µ-PPh2)(CO)9}2(µ3-η1,η2,η2:µ3-η1,η2,η2-C4) (M ) Ru,
Os),25 and dicobaltcarbonyl complexes of conjugated
plexes bearing polyynyl ligands.
a mononuclear tungsten fragment is attached to a
triruthenium cluster via a polyyne bridge (Figure 1).29
Very recently series of related iron and iron-cobalt
clusters have also been reported.30,31
However, while the studies described above have
shown that strong electronic interactions may occur
between two identical metal-based termini through a
(CtC)n bridge, evidence for similar interactions be-
tween chemically distinct groups remains scarce. Gla-
dysz has described the synthesis of the heterobimetallic
complexes {Cp*(NO)(PPh3)Re}(µ-CtC)n{PdCl(PEt3)} (n
) 1, 2), which undergo one-electron oxidation processes
to yield Re-centered radical cations.32 The same group
has also prepared Os3(µ-H)[µ-η1-(CtC)n{Re(NO)(PPh3)-
Cp*}](CO)10 (n ) 1-3), the structures of which were
shown by crystallographic and spectroscopic measure-
ments to contain modest contributions from the
+Red(CdC)nd[Os3]- resonance form in the ground
state.33 Lapinte and colleagues have shown that the first
oxidation of the asymmetrically substituted homome-
tallic complex {Cp*(dppe)Fe}(µ-CtCCtC){Fe(CO)2Cp*}
results in the formation of a localized Fe(III)-Fe(II)
mixed-valence complex.34
diynes,16a,26 polyynes,27 and cyclo-C18 (Figure 1). In
28
addition, several complexes have been reported in which
(15) (a) Osella, D.; Rossetti, R.; Nervi, C.; Ravera, M.; Moretta, M.;
Fiedler, J .; Popsisil, L.; Samuel, E. Organometallics 1997, 16, 695. (b)
Osella, D.; Milone, L.; Nervi, C.; Ravera, M. Eur. J . Inorg. Chem. 1998,
1473.
(16) (a) Duffy, N.; McAdam, C. J .; Nervi, C.; Osella, D.; Ravera, M.;
Robinson, B. H.; Simpson, J . Inorg. Chim. Acta 1996, 247, 99. (b)
McAdam, C. J .; Duffy, N. W.; Robinson, B. H.; Simpson, J . Organo-
metallics 1996, 15, 3935. (c) Worth, G. H.; Robinson, B. H.; Simpson,
J . Organometallics 1992, 11, 3863. (d) Dellaca, R. J .; Penfold, B. R.;
Robinson, B. H.; Robinson, W. T.; Spencer, J . L. Inorg. Chem. 1970, 9,
2204.
(17) (a) Frapper, G.; Kertesz, M. Inorg. Chem. 1993, 32, 732. (b)
Belanzoni, P.; Re, N.; Sgamellotti, A.; Floriani, C. J . Chem. Soc., Dalton
Trans. 1998, 1825. (c) Re, N.; Sgamellotti, A.; Floriani, C. J . Chem.
Soc., Dalton Trans. 1998, 2521. (d) Bruce, M. I.; Halet, J .-F.; Kahlal,
S.; Low, P. J .; Skelton, B. W.; White, A. H. J . Organomet. Chem., in
press.
(18) (a) Lemoine, P. Coord. Chem. Rev. 1982, 47, 56. (b) Lemoine,
P. Coord. Chem. Rev. 1988, 83, 169. (c) Geiger, W. E. Prog. Inorg. Chem.
1985, 33, 275. (d) Drake, S. R. Polyhedron 1990, 9, 455.
(19) Andres, R. P.; Bielefeld, J . D.; Henderson, J . I.; J anes, D. B.;
Kolagunta, V. R.; Kubiak, C. P.; Mahoney, W. J .; Osifchin, R. G. Science
1996, 273, 1690.
We have recently described the synthesis and char-
acterization of several carbonyl cluster complexes con-
(26) (a) Lewis, J .; Lin, B.; Khan, M. S.; Al-Mandhury, M. R. A.;
Raithby, P. R. J . Organomet. Chem. 1994, 484, 161. (b) Duffy, N.;
McAdam, J .; Nervi, C.; Osella, D.; Ravera, M.; Robinson, B.; Simpson,
J . Inorg. Chim. Acta 1996, 247, 99. (c) Bruce, M. I.; Low, P. J .; Werth,
A.; Skelton, B. W.; White, A. H. J . Chem. Soc., Dalton Trans. 1996,
1551.
(27) (a) Magnus, P.; Becker, D. P. J . Chem. Soc., Chem. Commun.
1985, 640. (b) Agh-Atabay, N. M.; Lindsell, W. E.; Preston, P. N.; Tomb,
P. J .; Lloyd, A. D.; Raugel-Rojo, R.; Spruce, G.; Wherrett, B. S. J . Mater.
Chem. 1992, 2, 1241. (c) Lindsell, W. E.; Preston, P. N.; Tomb, P. J . J .
Organomet. Chem. 1992, 439, 201. (d) Matsumoto, T.; Kotani, S.;
Shiina, K.; Sonogashira, K. Appl. Organomet. Chem. 1993, 7, 613.
(28) Diederich, F.; Rubin, Y.; Chapman, O. L.; Goroff, N. S. Helv.
Chim. Acta 1994, 77, 1441.
(20) (a) Goh, C.; Holm, R. H. Inorg. Chim. Acta 1998, 270, 46. (b)
Noodleman, L.; Peng, C. Y.; Case, D. A.; Mouesca, J .-M. Coord. Chem.
Rev. 1995, 144, 199. (c) Golbeck, J . H. Biochim. Biophys. Acta 1987,
895, 167. (d) Cammack, R., Sykes, A. G., Eds. Iron-Sulfur Proteins;
Academic Press: San Diego, 1992, and references therein.
(21) Akita, M.; Chung, M.-C.; Sakurai, A.; Sugimoto, S.; Terada, M.;
Tanaka, M.; Moro-oka, Y. Organometallics 1997, 16, 4882, and
references therein.
(29) (a) Bruce, M. I.; Ke, M.; Low, P. J . Chem. Commun. 1996, 2405.
(b) Bruce, M. I.; Skelton, B. W.; White, A. H.; Zaitseva, N. N. J . Chem.
Soc., Dalton Trans. 1996, 3151.
(22) Osella, D.; Gambino, O.; Nevi, C.; Ravera, M.; Bertolino, D.
Inorg. Chim. Acta 1993, 206, 155.
(23) Miguel, D.; Moreno, M.; Pe´rez, J .; Riera, V.; Churchill, D. G.;
Churchill, M. R.; J anik, T. S. J . Am. Chem. Soc. 1998, 120, 417.
(24) (a) Bruce, M. I.; Snow, M. R.; Tiekink, E. R. T.; Williams, M. L.
J . Chem. Soc., Chem. Commun. 1986, 701. (b) Adams, C. J .; Bruce, M.
I.; Skelton, B. W.; White, A. H. J . Organomet. Chem. 1993, 450, C9.
(c) Blenkiron, P.; Enright, G. D.; Low, P. J .; Corrigan, J . F.; Taylor, N.
J .; Chi, Y.; Saillard, J .-Y.; Carty, A. J . Organometallics 1998, 17, 2447.
(25) Adams, C. J .; Bruce, M. I.; Horn, E.; Skelton, B. W.; Tiekink,
E. R. T.; White, A. H. J . Chem. Soc., Dalton Trans. 1993, 3299.
(30) Akita, M.; Sakura, A.; Moro-oka, Y. Chem. Commun. 1999, 101.
(31) Akita, M.; Chung, M.-C.; Terada, M.; Miyauti, M.; Tanaka, M.;
Moro-oka, Y. J . Organomet. Chem. 1998, 565, 49.
(32) Weng, W.; Bartik, T.; Brady, M.; Bartik, B.; Ramsden, J . A.;
Arif, A. M.; Gladysz, J . A. J . Am. Chem. Soc. 1995, 117, 11922.
(33) Falloon, S. B.; Szafert, S.; Arif, A. M.; Gladysz, J . A. Chem. Eur.
J . 1998, 4, 1033.
(34) Coat, F.; Guillevic, M.-A.; Toupet, L.; Paul, F.; Lapinte, C.
Organometallics 1997, 16, 5988.

Polycarbon Ligand Chemistry
Organometallics, Vol. 18, No. 19, 1999 3887
Sch em e 1a
taining metallocarbon cores with various polyhedral
geometries bearing pendant trimethylsilylacetylene
ligands.35 As the trimethylsilyl acetylene moiety is a
protected form of the terminal acetylene functional
group, CtCH, which is in turn a traditional source of
metal acetylide complexes, it is our contention that these
metallocarbon clusters will prove to be viable reagents
in the synthesis of electronically interesting heterome-
tallic materials and molecular networks through a
combination of deprotection, oxidative coupling, and
metalation reactions as well as the direct attachment
of other substrates.
In this paper, we describe the preparation of two
complexes that contain a mononuclear Cp(PPh3)2Ru
metal fragment and a dicobalt-dicarbon cluster core
linked via acetylene-based bridging ligands. The spec-
troscopic and electrochemical properties of these com-
pounds not only demonstrate that significant electronic
interactions may be observed between vastly different
metal fragments but also indicate that subtle changes
in the nature of the bridging ligands may allow the
optical properties of these species to be tuned. A detailed
theoretical study utilizing DFT, ZINDO, and ELF
methods has been undertaken to provide an orbital-
based rationalization of the observed properties.
Resu lts a n d Discu ssion
a
(i) Co2(CO)6(dppm)/benzene/80 °C. (ii) RuCl(PPh3)2Cp/KF/
MeOH/60 °C.
Syn th eses. The synthetic and reaction chemistry
associated with alkyne-dicobalt carbonyl complexes has
been extensively examined over a period of many years,
and these compounds have found widespread applica-
tion in preparative organic chemistry.36-38 As a result,
Co2(CO)6 complexes of a great many alkyne reagents
have been prepared, and their structures and reactivity
examined.39 Reaction of the hexacarbonyl Co2-alkyne
complexes with phosphines or phosphites under rela-
tively mild thermal conditions leads to CO substitution
and formation of complexes of general form Co2(µ-η2-
RC2R)(CO)6-nLn.26a,28,39 Of particular relevance to the
current study is the observation that substitution of two
carbonyl ligands by bis(diphenylphosphino)methane
(dppm) affords complexes of increased stability which
display a simplified electrochemical response (vide
infra).16b
which one or both CtC triple bonds are coordinated
according to the stoichiometry of the reaction.16a,26,39
Given the synthetic challenges associated with the
preparation of more highly conjugated polyynes (1,3,5-
triynes, 1,3,5,7-tetraynes, etc.), it is not surprising that
the reactions of Co2(CO)8 with these species have been
much less extensively investigated. The Diederich group
examined the 1:1 reaction of Co2(CO)8 with 1,6-bis-
(triisopropylsilyl)hexa-1,3,5-triyne and found exclusive
formation of Co2(µ-η2-Pri SiCtCC2CtCSiPri )(CO)6, in
3
3
which the cobalt carbonyl fragment was coordinated to
the central carbon-carbon triple bond, which was
attributed to the presence of the bulky triisopropylsilyl
end-caps.28 A bis(dicobalt) complex of 1,8-bis(trimeth-
ylsilyl)octa-1,3,5,7-tetrayne prepared by oxidative cou-
pling of a diyyne precursor was also described. Lewis
et al. have made a similar observation.26a
Conjugated 1,3-diynes have also been shown to un-
dergo reaction with Co2(CO)8, affording complexes in
We were interested in preparing Co2(CO)4(dppm)-
triyne derivatives with a dicobalt moiety coordinated to
either the terminal or central alkyne moiety for use as
redox-active polycarbon ligands. We chose to examine
the reaction between Co2(CO)6(dppm) and 1,6-bis(trim-
ethylsilyl)hexa-1,3,5-triyne Me3SiCtCCtCCtCSiMe3
(1) on the basis that the relatively sterically undemand-
ing SiMe3 end-caps might permit coordination of the
dicobalt reagent not only to the central alkyne fragment
but also to the terminal CtC moieties.
The reaction of Co2(CO)6(dppm) with 1 in refluxing
benzene afforded two dark red crystalline complexes
Co2(µ-Me3SiC2CtCCtCSiMe3)(CO)4(dppm) (2) (15%)
and Co2(µ-Me3SiCtCC2CtCSiMe3)(CO)4(dppm) (3) (42%),
which were readily separated by chromatography on
silica gel (Scheme 1). The steric bulk of the dppm ligand
is sufficient to prevent serendipitous coordination of two
Co2 fragments to one molecule of 1, but insufficient to
(35) (a) Low, P. J .; Enright, G. D.; Carty, A. J . J . Organomet. Chem.
1998, 565, 279. (b) Low, P. J .; Udachin, K. A.; Enright, G. D.; Carty,
A. J . J . Organomet. Chem. 1999, 578, 103.
(36) (a) Davies, S. G. In Organotransition Metal Chemistry: Ap-
plications to Organic Synthesis; Pergamon: Oxford, 1986; pp 86-90.
(b) Kunz, H.; Waldmann, H. In Comprehensive Organometallic Chem-
istry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Elsevier: New
York, 1995; Vol. 6, pp 692-693.
(37) (a) Pauson, P. L. In Organometallics in Organic Synthesis; de
Meijere, A. tom Dieck, H., Eds.; Springer-Verlag: Berlin, 1987; pp 233-
246. (b) Shore, N. E. Chem. Rev. 1988, 88, 1081. (c) Shore, N. E. In
Comprehensive Organic Synthesis; Trost, B. M., Flemming, I., Eds.;
Pergamon: Oxford, 1991; Vol. 5, pp 1037-1064. (d) Shore, N. E. In
Comprehensive Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Elsevier: New York, 1995; Vol. 12, pp 703-
739.
(38) (a) Nicholas, K. M. Acc. Chem. Res. 1987, 20, 207. (b) Caffyn,
A. J . M.; Nicholas, K. M. In Comprehensive Organometallic Chemistry
II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Elsevier: New
York, 1995; Vol. 12, pp 685-702. (c) Vizniowski, C. S.; Green, J . R.;
Breen, T. L.; Dalacu, A. V. J . Org. Chem. 1995, 60, 7496.
(39) For a review of Co2(alkyne) complexes see: Dickson, R. S.;
Fraser, P. J . Adv. Organomet. Chem. 1974, 12, 323.

3888 Organometallics, Vol. 18, No. 19, 1999
Low et al.
completely restrict coordination to the alkyne moiety
adjacent to an SiMe3 group.
84.68 (t, J CP ) 9 Hz), 89.72 (t, J CP ) 5 Hz)] and the
remainder of the polycarbon ligand [C(1) δC 90.09 (t, J CP
) 16 Hz), C(2) δC 100.08, C(3) δC 89.82 and C(4) δC 64.69
(br)] by comparison of the J CP and chemical shift values
with those of 2. The atom-numbering scheme used to
describe the NMR spectra of 2-5 follows that given in
the appropriate ORTEP figure. The FAB mass spectrum
is characterized by an [M+H]+ ion at m/z 1450, which
fragmented by competitive loss of CO and PPh3 ligands
to give [M - nCO]+ (n ) 1-4) and [M - nCO - mPPh3]+
(m ) 1, 2; n ) 0, 3, 4) daughter ions.
The compounds 2 and 3 were characterized by the
usual spectroscopic methods and microanalytical data
and the structures confirmed by a single-crystal X-ray
study in each case (vide infra). The inequivalent SiMe3
groups in 2 give rise to distinct resonances at δH 0.31,
0.37 and δC 0.87, 1.57. The 13C NMR spectrum also
contains a triplet resonance at δC 37.99 (J CP ) 20 Hz)
for the dppm methylene carbon. The carbon centers of
the Co2C2 cluster core give rise to triplet resonances at
δC 75.41 (J CP ) 8 Hz) and 82.39 (J CP ) 4 Hz), while the
remaining carbon nuclei of the polyyne chain are
observed as singlets at δC 81.48, 91.34, 91.55, and 92.89.
In contrast, single SiMe3 resonances are observed at δH
0.29 and δC 0.44 for the symmetrical isomer 3. The
identical carbon centers of the tetrahedral cluster core
produced a single broad resonance at δC 70.37, while
singlet resonances at δC 103.27 and 107.85 are assigned
to the carbon centers of the pendant ethynyl moieties.
Mass spectra of 2 and 3, obtained using fast atom bom-
bardment (FAB) ionization techniques, show [M-nCO]+
ions (n ) 1-4) in each case.
A similar reaction between 3 and RuCl(PPh3)2Cp, also
in the presence of KF, gave the strikingly green-colored
complex Co2{µ-Me3SiCtCC2CtC[Ru(PPh3)2Cp]}(CO)4-
(dppm) (5) (74%). Substitution of only one SiMe3 group
in 3 by an Ru(PPh3)2Cp fragment is indicated by the
NMR data, with both SiMe3 (δH 0.47, δC 1.035) and Cp
(δH 4.55, δC 86.61) resonances being detected along with
those of the dppm (δH 3.79, 3.10; δC 34.52) ligand. Other
13C resonances are assigned to C(1) [δC 111.08 (t, J CP
)
4 Hz)], C(2) 114.78, C(5) and C(6) [δC 99.75, 95.78]. The
cluster-bound C(3) and C(4) nuclei were not detected.
The FAB-MS is similar to that of 4 and contains [M+H]+
as the highest molecular weight ion, with fragment ions
derived from loss of both CO and PPh3 ligands. Rather
surprisingly, the remaining tC-SiMe3 bond in 5 has
proven to be remarkably robust, and there was no evi-
dence for the formation of the corresponding desilylated
product, Co2{µ-HCtCC2CtC[Ru(PPh3)2Cp]}(CO)4(dppm),
even in the presence of a large excess of KF.
The many examples of known cobalt-carbonyl alkyne
complexes render 2 and 3, by themselves, rather unre-
markable. However, from our perspective, the interest
in these complexes comes from the presence of the
pendant, wirelike trimethylsilyl-capped alkynyl (2) and
diynyl (3) groups that are attached directly to the
electrochemically active Co2C2 core.
Recently, several reports have described the synthesis
of Fe(II) and Ru(II) acetylide complexes from trialkyl-
silyl-substituted alkynes and an appropriate metal
substrate in the presence of a source of the fluoride
ion.14,40 The application of similar reaction conditions
to a mixture of RuCl(PPh3)2Cp and one of the Co2(CO)4-
(dppm)-substituted hexatriynes 2 or 3 afforded good
yields of the complexes Co2{µ-Me3SiC2CtCCtC[Ru-
(PPh3)2Cp]}(CO)4(dppm) (4) and Co2{µ-Me3SiCtCC2Ct
C[Ru(PPh3)2Cp]}(CO)4(dppm) (5), respectively (Scheme
1).
Thus, treatment of 2 with 1 equiv of RuCl(PPh3)2Cp
and 1.5 equiv of KF in a thf/methanol mixture (1:1) gave
the reddish brown diynyl complex Co2{µ-Me3SiC2Ct
CCtC[Ru(PPh3)2Cp]}(CO)4(dppm) (4) in good (79%)
yield. The 1H and 13C NMR spectra contained the
anticipated resonances for the SiMe3 (δH 0.78, δC 1.21)
and Cp (δH 4.55, δC 86.41) ligands. The retention of the
SiMe3 group attached adjacent to the cluster core in 4
is perhaps not too surprising, as cleavage of the Co2C2-
SiMe3 bond is known to require somewhat more forcing
conditions than the corresponding tC-SiMe3 bond.26a,28,41
A triplet resonance at δC 36.82 is readily assigned to
the methylene group of the dppm ligand, although in
the proton spectrum only a broad, unresolved signal (δH
3.43) is observed, suggesting that at room temperature
the methylene group oscillates between the endo and
exo positions. Six low-intensity signals are assigned to
the carbon centers in the Co2C2 cluster core [C(5/6) δC
The resistance of the remaining tC-SiMe3 group in
5 to fluoride ion (i.e., nucleophile) induced cleavage
remains a curiosity at this stage. It may be that the
electron-rich Ru(PPh3)2Cp group induces a small, but
significant, increase in electron density at the silicon
center through the cluster-spaced bridging ligand,
thereby reducing the susceptibility of this group to
nucleophilic attack.
Molecu la r Str u ctu r es. Single-crystal X-ray diffrac-
tion studies were carried out on each of complexes 2, 3,
4, and 5 in order to examine the structural variation
within the series. Crystallographic details are collected
in Table 1, while important bond lengths and angles are
summarized in Table 2. ORTEP plots indicating the
atom-labeling schemes are given in Figures 2 (2), 3 (3),
4 (4), and 5 (5).
An examination of the structure of complex 2 shows
a chain of four carbon atoms [C(1-4)] with the typical
short, long, short, long bond length alternation associ-
ated with a diyne moiety. The [C(1-4)] four carbon
fragment is essentially linear, with the greatest devia-
tion from linearity being found at C(1). The C(1) end of
the chain is capped by the Si(1) trimethylsilyl group,
while C(4) is connected to the tetrahedral Co2C2 met-
allocarbon core via C(5). The Co(1)-Co(2) separation is
2.476(2) Å, which may be considered typical for this type
of cluster.26a,c Both Co centers are further connected to
C(5) [Co(1,2)-C(5) 1.964(8), 1.973(8) Å] and C(6) [Co-
(1,2)-C(6) 1.963(7), 1.977(7) Å]. Two carbonyl ligands
and a phosphine from the dppm ligand complete the
coordination geometry about each Co center. Treating
Co(1)-Co(2)-C(6) as the basal plane of the Co2C2
tetrahedron, the bidentate dppm ligand occupies the two
available pseudoequatorial positions. A connection be-
(40) (a) Lomprey, J . R.; Selegue, J . P. Organometallics 1993, 12, 616.
(b) Weyland, T.; Lapinte, C.; Frapper, G.; Calhorda, M. J .; Halet, J .-
F.; Toupet, L. Organometallics 1997, 16, 2024. (c) Bruce, M. I.; Hall,
B. C.; Kelly, B. D.; Low, P. J . Unpublished results.
(41) Bruce, M. I.; Low, P. J .; Werth, A.; Skelton, B. W.; White, A.
H. J . Chem. Soc., Dalton Trans. 1996, 1551.

Polycarbon Ligand Chemistry
Organometallics, Vol. 18, No. 19, 1999 3889
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta for 2-5
2
3
4
5
formula
fw
crystal size (mm)
crystal system
space group
a, Å
C
41H40Co2O4P2Si2
C41H40Co2O4P2Si2
832.74
0.30 × 0.30 × 0.30
triclinic
P1h
11.2289(5)
11.7570(5)
16.6934(8)
95.01(1)
91.67(1)
106.84(1)
2097.8(2)
2
1.318
860
0.962
2.46-57.46
25025
10776
7818
C79H66Co2O4P4RuSi.0.5C6H14
C79H66Co2O4P4RuSi.2C3H6O
1566.44
832.74
1493.37
0.20 × 0.10 × 0.01
monoclinic
P21/c
18.436(1)
25.607(2)
17.349(1)
90
111.40(2)
90
7625(1)
4
1.301
3076
0.773
4.34-50
47221
13171
8197
0.15 × 0.10 × 0.03
monoclinic
P21/c
12.177(1)
23.160(3)
29.993(3)
90
91.86(3)
90
8454(1)
8
1.308
3440
0.954
2.72-45
58380
10754
4550
0.20 × 0.20 × 0.30
triclinic
P1h
12.314(6)
15.3649(7)
22.370(1)
96.00 (1)
104.08(1)
106.53(1)
3866.5(3)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
Dc, g.cm-3
F(000)
1.345
1616
0.767
2.82-57.46
45969
19845
14512
µ, mm-1
2θ range, deg
no. of reflns measd
no. of unique reflns
no. of obsd reflns
no. of params refined
final R, Rw
GOF
972
461
880
878
0.0789, 0.0689
0.902
0.0425, 0.0851
0.900
0.0511, 0.1003
0.893
0.0389, 0.0885
1.015
max, min residual
+0.370, -0.392
+0.945, -0.659
+0.689, -0.464
+0.610, -0.681
density, e Å-3
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles (d eg) for Com p lexes 2, 3, 4, 5, a n d Ru (CtCP h )(P P h 3)2Cp (6)
2
3
4
5
6f
Co(1)-Co(2)
Co(1)-C(5)
Co(1)-C(6)
Co(2)-C(5)
Co(2)-C(6)
Co(1)-P(1)
Co(2)-P(2)
Co(1)-C(13)
Co(1)-C(14)
Co(2)-C(15)
Co(2)-C(16)
C-O(av)
2.476 (2)
1.964(8)
1.963(7)
1.973(8)
1.977(7)
2.223(2)
2.213(2)
1.77(1)
1.799(10)
1.814(10)
1.779(10)
1.147
2.4684(4)
1.958(2)a
1.964 (2)b
1.954(2)a
1.951 (2)b
2.2387(6)
2.2217(6)
1.784(2)
1.786(2)
1.796(2)
1.783(2)
1.138
1.843(2)
1.208(3)
1.409(3)
1.367(3)
1.402(3)
1.201(3)
1.841(2)
2.4856(8)
1.979(4)
1.966(4)
1.970(4)
1.979(4)
2.209(1)
2.220 (1)
1.777(6)
1.789(6)
1.796(5)
1.758(6)
1.136
2.4763(5)
1.954(2)a
1.981(2)b
1.964(2)a
1.965(2)b
2.2315(6)
2.2277(7)
1.773(3)
1.774(3)
1.786(3)
1.778(3)
1.142
1.830(3)
1.211(3)
1.407(3)
1.370(3)
1.395(3)
1.217(3)
Si(1)-C(1)
C(1)-C(2)
1.86(1)
1.19 (1)
1.37 (1)
1.203(10)
1.398(10)
1.376(9)
1.847(7)
1.230(6)
1.359(6)
1.219(6)
1.382(6)
1.361(6)
1.831(5)
1.981(4)
2.297 (1)
2.296 (1)
2.232
1.214(7)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(1)-Si(2)
Ru(1)-C(1)
Ru(1)-P(3)
Ru(1)-P(4)
Ru(1)-Cp(av)
1.997(2)c
2.2855(7)
2.2836(7)
2.239
2.017(5)
2.229(3)
2.228(3)
2.239
Si(1)-C(1)-C(2)
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(3)-C(4)-C(5)
C(4)-C(5)-C(6)
C(5)-C(6)-Si(2)
P(3)-Ru(1)-P(4)
175(2)
177.8 (2)
171.9(4)d
175.7(2)
176.7(17)
176.8(9)
177.4(9)
141.6(8)
138.7(6)
174.6(2)
140.2(2)
139.5(2)
178.1(2)
176.9(2)
178.7(5)
178.1(5)
176.2(5)
140.5(4)
141.6(3)
103.73(5)
176.7(2)
138.6(2)
143.9(2)
176.1(2)
178.0(2)e
102.08(2)
100.9(1)
a
b
d
Read C(3) for C(5). Read C(4) for C(6). c Read C(6) for C(1). Read Ru(1) for Si(1). e Read Ru(1) for Si(2). f Reference 42.
tween C(6) and Si(2) [1.847(7) Å] completes the coordi-
nation about the metallocarbon cluster core.
greater electron-donating character of SiMe3 (2) when
measured against CtCSiMe3 (3). In keeping with this
notion, it may also be noted that the average C-O bond
distance in 2 [1.147 Å] is greater than in 3 [1.138 Å].
The expansion of the Co2C2 core in 2 relative to that in
3 may also be enhanced by the shorter and stronger
Co-P bonds in 2 (Co-P av 2.218 Å 2; 2.231 Å 3).
Figure 4 shows that complex 4 is derived from 2 by
substitution of the Si(1)Me3 group by a Ru(PPh3)2Cp
fragment. In general the structural parameters of the
common fragments are the same, within experimental
error. However, the following trends are worth noting.
Figure 3 clearly shows that complex 3 is a simple
structural isomer of 2, in which the Co2 group has
coordinated to the central C(3)-C(4) CtC group in 1.
The C(1)-C(2) and C(5)-C(6) separations are charac-
teristic of alkyne moieties and are equivalent, within
error, at 1.208(3) and 1.201(3) Å, respectively. Overall,
the dimensions of the Co2C2 core in 2 appear to be
somewhat greater than in 3. Since these molecules
contain a cluster-based HOMO which is bonding in
nature (vide infra), this discrepancy may be due to the

3890 Organometallics, Vol. 18, No. 19, 1999
Low et al.
F igu r e 4. Molecular structure of 4 indicating the atom-
labeling scheme. Only the ipso-carbons of the C(30)-C(35)
and C(72)-C(77) phenyl groups are shown for clarity.
F igu r e 2. Molecular structure of 2 indicating the atom-
labeling scheme. Thermal ellipsoids in this and all subse-
quent figures are drawn at the 30% probability level.
F igu r e 5. Molecular structure of 5 indicating the atom-
labeling scheme.
erometallic complex 4 are significantly elongated in
comparison to those in 6. Similar structural trends were
noted between 6 and Ru(CtCC6H4NO2-p)(PPh3)2Cp.42b
A molecule of complex 5 is illustrated in Figure 5. The
mononuclear fragment has substituted the SiMe3 moiety
attached at C(6), on the opposite side of the Co(1,2)-
C(3,4) cluster to the dppm ligand, a fact that can be
attributed to steric influences. Similar trends are ap-
parent between 3 and 5 as has been indicated for 2
and 4, notably that the dimensions of the Co2C2 cluster
core in 5 are greater than found in 3. The mononuclear
fragment in 5 is almost identical with that of the
comparable fragment in 4, and therefore as noted above
for 4 the Ru(1)-P(3,4) separations are longer than in
6. The tC(1)-Si(1) bond is the shortest in this series
at 1.830(3) Å, a fact that may be related to the surpris-
ing resilience of this bond toward cleavage (vide supra).
In summary, there is some indication that for both 4
and 5 the mononuclear fragment donates electron
density through the carbon bridging ligand to the Co2C2
cluster core, which expands as a result. The increased
electron density at the cluster core is then relieved to a
certain extent through π-back-bonding into the carbonyl
ligands. However, for the Ru-C and C-C distances
these trends are at the borderline of statistical signifi-
cance, and it should be noted that the bonding param-
eters of acetylenic linkages are notoriously insensitive
to electronic effects.8b
F igu r e 3. Molecular structure of 3 indicating the atom-
labeling scheme.
Within the C(1-4) diyne moiety, the separations of the
triple-bonded carbons C(1)-C(2) and C(3)-C(4) are
greater in 4 than 2 [1.230(6), 1.219(6) Å (4) vs 1.19(1),
1.20(1) Å (2)], while the C-C single bonds C(2)-C(3)
and C(4)-C(5) are shorter [1.359(6), 1.382(6) Å (4) vs
1.37(1), 1.40(1) Å (2)]. On average, there is an increase
in the dimensions of the Co(1)-Co(2)-C(5)-C(6) cluster
core in 4 when compared to 2.
When the bonding parameters of the mononuclear
ruthenium fragment are compared with the correspond-
ing data from the prototypical acetylide complex Ru-
(CtCPh)(PPh3)2Cp (6), some further trends become
apparent (Table 2).42 The Ru(1)-C(1) distance in 4 is
shorter than in 6, while the opposite is true for the
C(1)-C(2) distance. The Ru-P separations in the het-
(42) (a) Bruce, M. I.; Humphrey, M. G.; Snow, M. R.; Tiekink, E. R.
T. J . Organomet. Chem. 1986, 314, 213. (b) Whittall, I. R.; Humphrey,
M. G.; Persoons, A.; Houbrechts, S. Organometallics 1996, 15, 1935.

Polycarbon Ligand Chemistry
Organometallics, Vol. 18, No. 19, 1999 3891
Ta ble 3. IR a n d UV-Vis Da ta for Com p lexes 2, 3,
4, a n d 5 (ν in cm -1, E in cm -1 M-1
)
ν(CtC)a
ν(CO)a
UV/vis abs (ꢀ)b
2
3
2160
2030vs, 2009vs,
2004sh, 1982vs,
1962w
216 (72500), 278 (34060),
354 (10690), 448 (1532),
548 (1050)
218 (85000), 288 (36560),
354 (14000), 446 (1587),
542 (1160)
2118, 2105 2037vs, 2019vs,
1994vs, 1972w
4
5
2124
2104
2018s, 1998vs,
1970vs, 1952w
2036s, 2015sh,
2000vs, 1975vs,
1954w
214 (105840), 294 (44520),
348 (32400), 572 (1703)
220 (134,700), 268 (61530),
358 (45400), 600 (2300)
a
b
Measured in cyclohexane. Measured in thf.
In fr a r ed Sp ectr a . The ν(CO) spectrum of each
complex 2, 3, 4, and 5 is characterized by a pattern of
three strong bands and other much weaker features
(Table 3). The conjugated CtC moieties in 2 give rise
to a single ν(CtC) band at 2160 cm-1. In the case of
the “V”-shaped molecule 3, both the symmetric and
antisymmetric vibrations result in an oscillation of the
molecular dipole moment. Consequently both modes are
IR active and two absorption bands are observed (2118,
2105 cm-1).
The spectra of the heterometallic complexes 3 and 4
display a pattern of ν(CO) bands similar to that found
in the precursors 2 and 3. For 4 however only a single
ν(CtC) band was observed. On average, the ν(CO)
bands of 4 are shifted to lower energy by ca. 10 cm-1
when compared with the parent complex 2. In 5, the
highest energy A1 ν(CO) band (2036 cm-1) is broader
and less intense than the corresponding band in 3. The
other strong ν(CO) bands in 5 appear at lower frequen-
cies than the analogous bands in the precursor. The
decrease in the frequency of the ν(CO) bands in the
heterometallic complexes 4 and 5 relative to 2 and 3
suggests an increase in the electron density at the Co2C2
core in these compounds following substitution of an
SiMe3 group by the electron-rich Ru(PPh3)2Cp fragment.
A decrease in the ν(CtC) band of 36 cm-1 in 4 compared
to 2 is consistent with a small decrease in the CtC bond
strength in this complex.
UV-Vis Sp ectr a . The most visually apparent dis-
tinction between the complexes 2-5 is the color, which
ranges from dark red (2 and 3) through green-brown
(4) to striking dark green (5), prompting an examination
of the UV-vis spectra across the series.
The spectra of 2 and 3 closely resemble that of the
protio derivative Co2(µ-η2-HCtCC2CtCH)(CO)4(dppm),28
and a series of weak, overlapping d-d bands are
observed in the visible region (Figure 6, Table 3). In the
case of 4 and 5 bands at 572 nm (4) and 600 nm (5)
dominate the visible region, which account for the color
of these complexes (Figure 6). This band displays modest
solvatochromatic behavior, with a shift in λmax of 12 nm
found for 5 in cyclohexane and dimethylformamide. It
would therefore appear more likely that these visible
absorption bands in 4 and 5 are d-d in origin rather
than Ru-Co2C2 charge-transfer transitions.
F igu r e 6. Visible spectra of complexes 2-5 in thf (6.5 ×
10-4 M).
) H [λmax 306 nm (cyclohexane)] for R ) NO2 [λmax 437
nm (cyclohexane)], a fact that was attributed to the
increased stabilization of the charge-separated form in
the nitro-substituted derivative. In each complex 2-5
an intense absorption, presumably arising from π-π*
transitions in the Ph groups of the dppm ligand, is
observed at highest energy in the UV region (Table 3).
Electr och em istr y. The hexacarbonyl complexes Co2-
(alkyne)(CO)6 undergo one-electron, diffusion-controlled
reduction processes, followed by a series of fast chemical
reactions which lead to Co-Co bond rupture and/or loss
of a Co2(CO)6 fragment.26a The net result is rapid
decomposition of the radical anions [Co2(alkyne)(CO)6]•-
at room temperature. Chemical reversibility of the
electrochemical process is improved by the presence of
electron-withdrawing or bulky substituents on the
alkyne.43 Oxidation processes have not been observed
for the hexacarbonyl compounds within the potential
windows examined.44
However, in the case of the substituted derivatives
Co2(RC2R′)(CO)6-n(L)n [n ) 1-3, L ) P(OMe3); n ) 2,4
L2 ) dppm] the Co2C2 core was found to be sufficiently
electron rich to be oxidized at readily accessible poten-
tials in CH2Cl2.16b,43b For the dppm derivatives, the
oxidation process is reversible, a trait that has been
attributed to stabilization of the Co-Co bond by the
bridging bisphosphine ligand, although fast chemical
complications were reported to hamper the study of the
reduction process in these complexes.43b Mononuclear
acetylide complexes containing electron-rich metal cen-
ters are well-known to undergo one-electron oxidation
processes to give 17e radical cations [LnM-CtCR]•+,45
the stability of which depends greatly on the steric bulk
of the supporting ligands.13a,46
(43) (a) Osella, D.; Fiedler, J . Organometallics 1992, 11, 3875. (b)
Duffy, N. W.; McAdam, C. J .; Robinson, B. H.; Simpson, J . J .
Organomet. Chem. 1998, 565, 19.
(44) Arewgoda, C. M.; Robinson, B. H.; Simpson, J . J . Am. Chem.
Soc. 1983, 105, 1893.
(45) (a) Connelly, N. G.; Gamasa, M. P.; Gimeno, J .; Lapinte, C.;
Lastra, E.; Maher, J . P.; Le Narvor, N.; Rieger, A. L.; Rieger, P. H. J .
Chem. Soc., Dalton Trans. 1993, 2575. (b) Adams, J . S.; Bitcon, C.;
Brown, J . R.; Collison, D.; Cunningham, M.; Whiteley, M. W. J . Chem.
Soc., Dalton Trans. 1987, 3049. (c) Beddoes, R. L.; Bitcon, C.; Whiteley,
M. W. J . Organomet. Chem. 1991, 402, 85. (d) Whittall, I. R.;
Humphrey, M. G.; Hockless, D. C. R.; Skelton, B. W.; White, A. H.
Organometallics 1995, 14, 3970.
The Ru-containing complexes also displayed MLCT
bands at 348 nm (4) and 358 nm (5). Similar MLCT
bands have been noted for a series of related Ru-
acetylide complexes Ru(CtCC6H4R)(PR′3)2Cp.42 The
energy of these bands decreased upon substitution of R

3892 Organometallics, Vol. 18, No. 19, 1999
Low et al.
Ta ble 4. Cyclic Volta m m etr y Da ta a
response was observed for the related diyne complex
Co2(µ-η2-PhC2CtCPh)(CO)4(dppm), although the reduc-
tion wave was irreversible in CH2Cl2.16b
ERed° (ipa/ipc) [∆Ep]
EOx1° (ipa/ipc) [∆Ep]
EOx2° [∆Ep]
2
3
4
5
-1.09 (1.0) [0.33]
-1.06 (1.0) [0.36]
-1.29 (1.0) [0.31]
-1.36 (1.0) [0.29]
1.49 (1.0) [0.35]
1.60 (1.0) [0.38]
0.96 (0.87)b [0.30]
0.86 (0.93)b [0.29]
For each of the heterometallic complexes 4 and 5 a
single, reversible, one-electron reduction wave was
observed (-1.29 V 4, -1.36 V 5) as well as two quasi-
reversible oxidation processes EOx1° (+0.96 V 4, +0.86
V 5) and EOx2° (+1.16 V 4, +1.14 V 5) (Table 4, Figure
7). The close spacing of the oxidation waves hindered
meaningful determination of the peak current ratio for
1.16 [0.27]
1.14 [0.30]
a
All data collected from thf solutions containing 0.05
M
[nBu4N]BF4 as supporting electrolyte, at -50 °C, scan rate 100
mV s-1, analyte concentration 1 × 10-3, Pt disk working electrode,
Ag wire pseudo reference, Pt wire counter electrode. Internal Fc/
Fc+ reference at E° 0.99V, ipa/ipc, ∆Ep 0.38 V. Measured from the
b
isolated wave.
E
Ox2. However, in both cases, chemical reactions fol-
lowed EOx2, and minor product reduction processes were
observed at Epc(A) 0.31 V (4) and at Epc(B) 0.52 V and
E
pc(C) 0.12 V (5). These reduction waves A, and B and C
are not observed when the reverse sweep in the cyclic
voltammograms were initiated prior to the generation
of [4]2+ or [5]2+ at potentials near EOx2. The identifica-
tion of these electrogenerated chemical species must
await the results of a more detailed spectroelectro-
chemical study.
It is reasonable to attribute the reduction processes
in 4 and 5 to the [Co2C2]0/- couple, although these
reductions occur at a more negative potential than the
analogous process in the parent complexes 2 and 3
(Table 4). On this basis 4 and 5 are predicted to have a
Co2C2-centered LUMO, which is somewhat raised in
energy when compared with 2 and 3.
More information about the nature of the electronic
interaction between the metal fragments is contained
in the oxidative sweep, as model compounds for each of
the isolated parts of the molecule (2 or 3 and 6) display
an oxidation wave. Both oxidation processes in 4 and 5
occur at much less positive potentials than the [Co2C2]0/+
couple in the precursors 2 and 3, respectively, and also
at a less positive potential than the RuII/III couple of the
model complex Ru(CtCPh)(PPh3)2Cp (E° +1.10 V)
(Table 4).
Consider a hypothetical case in which the redox-active
centers are completely independent (i.e., there are no
interactions between the Ru(PPh3)2Cp and Co2C2 moi-
eties). In such a case, the E° values for the RuII/III and
[Co2C2]0/+ couples in 4 or 5 would be essentially identical
to the E° values observed for the isolated components,
with small differences due to the modified solvent
interactions about each redox-active core resulting from
the new molecular shape. It is apparent from the data
collected in Table 4 that this is not the case, and the
organometallic moieties in 4 and 5 must therefore
interact in some fashion.
F igu r e 7. Cyclic voltammograms of (a) 2 and 4 and (b) 3
and 5.
The presence of both of these types of redox-active site
encouraged an examination of the electrochemical re-
sponse of 2-5, using cyclic votammetry techniques. The
results obtained are gathered in Table 4. In thf solvent
at -50 °C the parent cobalt-carbon clusters 2 and 3
have reversible one-electron oxidation and reduction
waves, corresponding to the formation of the radical
cations [2]•+ (EOx1° +1.49 V) and [3]•+ (EOx1° +1.60 V)
If the Ru and Co2C2 oxidation centers are considered
to interact via a simple through-space (i.e., Coulombic)
mechanism, the first oxidation process, which yields a
positively charged pendant group, should result in a less
thermodynamically favorable second oxidation when
compared to the isolated parent species. Again, this
simple model fails to satisfy the experimental data.
and radical anions [2]•- (ERed° -1.09 V) and [3]•- (ERed
°
-1.06 V), respectively (Figure 7). Peak to peak separa-
tions for each process are comparable to that of the
ferrocene/ferrocenium couple under identical conditions,
and the ipa/ipc ratio in each case is unity. Linear plots
of ipa against the square of the scan rate were also
obtained. As indicated above, a similar electrochemical
We find that a more subtle, through-bond mechanism
of interaction is required to explain the presence of two
one-electron oxidation processes in 4 and 5, both of
which are thermodynamically more favorable than in
the isolated model complexes 2 or 3 and 6. To resolve
this issue, and address the broader issues about the
nature of the electronic interactions occurring between
(46) (a) Beddoes, R. L.; Bitcon, C.; Ricalton, A.; Whiteley, M. W. J .
Organomet. Chem. 1989, 367, C21. (b) Bitcon, C.; Whiteley, M. W. J .
Organomet. Chem. 1987, 336, 385.

Polycarbon Ligand Chemistry
Organometallics, Vol. 18, No. 19, 1999 3893
Ta ble 5. Selected Bon d Len gth s (Å) Obta in ed fr om
Op tim ized Str u ctu r e Mod els, a n d Ch a r ges on
Va r iou s F r a gm en tsg
Ru-C
CtCa
C-Cb Co-Co
1.35 2.47
(1.34) (2.46)
1.37 2.47
(1.36) (2.48)
1.37 2.47
(1.37) (2.48)
1.38
(1.37) (2.47)
∑qD
∑qB
∑qA
A
B
C
D
1.99
(1.98)
1.99
(1.99)
2.01
1.25
(1.23)
1.25
(1.22)
1.24
+0.50 -0.37 -0.13
+0.52 -0.34 -0.18
E
F
+0.43 -0.54 +0.21
+0.45 -0.38 -0.07
2.02
1.24
F igu r e 8. Calculated UV/vis spectra of model compounds
B, C, and D. Intensities are in arbitrary units.
(2.01)c (1.21)c
G
H
2.00
1.25
+0.49 -0.34 -0.15
(1.99)d (1.23)d
1.22
The calculated UV/vis absorption spectra in the region
of 400-800 nm are presented in Figure 8. The visible
region of the spectrum for B, C, and D each contains
three distinct absorptions. For B these absorptions (445,
485, and 525 nm) all correspond to excitations from the
Co2C2 cluster HOMO to an unoccupied Co2C2-based
orbital. In C, the transitions that give rise to the optical
bands arise from an orbital that has the same gross
shape as the corresponding orbital in B, but also
contains a small, yet significant, contribution from the
Ru-CtCCtC moiety. This secondary mixing leads to
a destabilization of this essentially Co2C2-centered
orbital in C with respect to that in B. Consequently,
the UV-vis spectrum of C also contains three similar
transitions (512, 575, and 683 nm) which are strongly
red shifted relative to those observed in B. Furthermore,
the intensity ratio of the peaks has also changed due to
a remixing of the orbitals. However, one fact does
remain consistent: the transitions remain localized on
orbitals centered on the Co2C2 cluster core and have no
contribution either in the occupied or unoccupied states
from Ru. These same three transitions also occur in the
spectrum of D (529, 595, and 766 nm) and are even more
red shifted then those of C, as a result of a greater
contribution from the acetylenic moiety. The trend in
these spectral shifts is strongly correlated with those
observed in the experimental species. More quantitative
agreement between the experimental data and the
computed spectra should not be expected due to the use
of the approximated structural models in the gas phase.
However, the qualitative agreement between the ex-
perimental and computational results strongly suggests
that the observed change in color is due primarily to a
reorganization of the energy levels of the Co2C2 cluster
core rather than a Ru cluster charge-transfer process.
A schematic MO diagram of the frontier orbitals of
A-E is presented in Figure 9. The frontier orbitals of
the model complex A have been well established by
Hoffman, Hoffmann, and Fisel47 and others. These
orbitals are reproduced by the current DFT treatment,
although there is a small discrepancy in the ordering
of the occupied orbitals below the HOMO. These orbitals
retain their overall shape and order in compound B but
(1.205e,
1.218f)
a
b
CtC of acetylene directly attached to Ru. C-C of the Co2C2
cluster. c From ref 42. From ref 48. e Callomon, J . H.; Stoicheff,
B. P. Can. J . Phys. 1957, 35, 373. Tanimoto, M.; Kuchitsu, K.;
Morino, Y. Bull. Chem. Soc. J pn. 1971, 44, 386. Average values
of the experimental parameters are included in parentheses where
appropriate. See text for chemical formula of model species and
definition of symbolism.
d
f
g
the organometallic fragments in more detail, a thorough
theoretical analysis was undertaken.
Th eor etica l Stu d ies. To facilitate theoretical analy-
sis, several simplified structural models have been
adopted. Thus, calculations have been performed on Co2-
(µ-HC2H)(CO)6 (A) and Co2(µ-HC2H) (CO)4(H2PCH2PH2)
(B), which serve as structural models for 2 and 3, and
Co2{µ-H3SiC2CtCCtC[Ru(PH3)2Cp]}(CO)4(H2PCH2-
PH2) (C) and Co2{µ-H3SiCtCC2CtC[Ru(PH3)2Cp]}-
(CO)4(H2PCH2PH2) (D), which model 4 and 5, respec-
tively. In addition, Ru(CtCR)(PH3)2Cp (R ) H (E); Ph
(F ); C6H4NO2-p (G)) and HCtCCtCH (buta-1,3-diyne)
(H) were also modeled as reference compounds. The
model compounds were subjected to geometry optimiza-
tion, as detailed in the Experimental Section. Quantita-
tive agreement between the observed and calculated
data is not expected due to the nature of the theoretical
and structural approximations. However, the model
compounds do provide an effective method for probing
the electronic structures and spectroscopic and electro-
chemical properties of the experimental compounds and
provide an indication of the various structure-property
relationships.
Several relevant structural parameters obtained from
the optimized structures of A-H are compared with the
experimental data in Table 5. The computed Ru-C
distance in C and D is found to be relatively short (1.99
Å), while the corresponding CtC separation is some-
what long (1.25 Å). However, the calculations reproduce
the increase in C-C length in the cluster backbone upon
substitution of two CO ligands in A (1.35 Å) for H2PCH2-
PH2 in B (1.37 Å), C (1.37 Å), and D (1.38 Å) found in
the experimental analogues. The Co-Co bond length in
all of the model compounds was found to be unaffected
by phosphine substitution (2.47 Å). It is notable that
the absolute values of these parameters, as well as the
trends across the series, are in excellent agreement with
the crystallographically determined parameters. This
observation provides a measure of confidence in the
accuracy of the computations and, hence, the conclu-
sions that are drawn from them.
(47) (a) Hoffman, D. F.; Hoffmann, R.; Fisel, C. R. J . Am. Chem.
Soc. 1982, 82, 3858. For further discussion see for example: (b) Thron,
D. L.; Hoffmann, R. Inorg. Chem. 1978, 17, 126. (c) DeKock, R. L.;
Lubben, T. V.; Hwang, J .; Fehlner, T. P. Inorg. Chem. 1981, 20, 1627.
(d) Baert, F.; Guelzim, A.; Poblet, J . M.; Wiest, R.; Demuynck, J .;
Bunard, M. Inorg. Chem. 1986, 25, 1830. (e) Pepermans, H.; Hoogzand,
C.; Geerlings, P. J . Organomet. Chem. 1986, 306, 395. (f) Halet, J .-F.;
Saillard, J .-Y. J . Organomet. Chem. 1987, 327, 365. (g) Yuan, P.; Don,
M.-J .; Richmond, M. G.; Schwartz, M. Inorg. Chem. 1992, 31, 3491.

3894 Organometallics, Vol. 18, No. 19, 1999
Low et al.
F igu r e 10. Electronic interactions between the Ru(PPh3)2-
Cp fragment and Co2C2(CO)4(dppm) cluster core repre-
sented in terms of (a) a bonding electron delocalized model
and (b) an inductive model.
of the UV/vis absorption as obtained from ZINDO
calculations (vide supra) and also matches the observa-
tion of characteristic ν(CtC) bands in the IR spectra of
4 and 5 (Table 3).
To provide further support for this conclusion, a
description of the electron density about the acetylenic
CtC moieties that link the organometallic fragments
was undertaken using the electron localization function
(ELF), which is defined as49
F igu r e 9. Schematic MO diagram of frontier orbitals of
compounds A-E.
1
are increased in energy about 1 eV, which is consistent
with the presence of the electron-donating H2PCH2PH2
ligand. This shift also correlates well with the lower
oxidation and higher reduction potentials observed in
the electrochemical measurements on related systems
(vide supra).
η(r) )
2
(∇F)2
F
1
2
|∇Ψ | -
∑
i
4
i
1 +
3
(3π2)5/3F5/3
(
(
) )
The frontier orbitals of E are also well established,48
and these earlier results are essentially reproduced by
the DFT scheme employed in this work. The HOMOs
and SHOMOs of C and D are, approximately, the same
as found for E (Figure 9). However, two important
differences must be highlighted. First, the energy of the
HOMO increases in the order E < C < D, which,
assuming that electrochemical oxidation involves re-
moval of electrons from the HOMO, is in good agree-
ment with the electrochemical measurements (Table 4
and above discussion). Second, these HOMOs include
significant contributions from not only the Ru(PH3)2Cp
fragment and the acetylenic moiety but also the Co2C2
cluster core. As a result, the HOMO is actually delo-
calized across the entire molecule. However, it is
important to note that in both C and D the HOMO is
not bonding in nature, but consists primarily of a Ru-
C(acetylene) antibonding interaction and a similar
antibonding interaction between the acetylene backbone
and the Co2C2 cluster. This orbital picture suggests that
there is very little direct “communication” between the
Ru center and the Co2C2 cluster core in terms of a
delocalized bonding model (Figure 10a). Instead, a
description involving a more inductive interaction be-
tween the two fragments passed on via a filled orbital-
filled orbital repulsive interaction along the acetylenic
bridge (Figure 10b) appears to be more justified. This
also correlates well with our interpretation of the trends
5
The ELF method puts electron localization onto a
quantitative footing while managing to avoid some of
the inherent difficulties that may arise in traditional
orbital-based analysis. The ELF function, η(r), is large
in regions where two electrons with antiparallel spin
are paired in space, and hence its maxima can be
associated with attractor basins due to electron pairing.
The ELF is normalized between zero and unity, with
the value for a uniform electron gas being 1/2. This
normalization scale allows for the direct comparison of
electron localization between similar atoms in different
chemical systems and thus places the concept of the
localization of electrons on a semiquantitative footing.
Consequently, the ELF has met with great success when
used as a tool to locate and interpret chemical bonding
in a variety of different systems.50 To understand the
information contained in this function in greater detail,
one may consider, for example, a core state in an atom
as a typical localized electronic state. The local kinetic
2
energy density ∑i|∇φ| will be very high, but so will the
gradient of the electronic density ∇ F(r). In such a case
(49) Becke, A. D.; Edgecombe, K. E. J . Chem. Phys. 1990, 92, 5397.
(50) (a) Silvi, B.; Savin, A. Nature (London) 1994, 371, 683. (b) Savin,
A.; J epsen, O.; Flad, J .; Andersen, O. K.; Preu, H.; von Schnering, H.
G. Angew. Chem., Int. Ed. Engl. 1992, 31, 187. (c) Savin, A.; Nesper,
R.; Wengert, S.; Fo˜ssler, T. F. Angew. Chem., Int. Ed. Engl. 1997, 36,
1808. (d) Savin, A.; Becke, A. D.; Flad, J .; Nesper, R.; Preuss, H.; von
Schnering, H. G. Angew. Chem., Int. Ed. Engl. 1991, 30, 409. (e) Marx,
D.; Savin, A. Angew. Chem., Int. Ed. Engl. 1997, 36, 2077.
(48) McGrady, J . E.; Lovell, T.; Stranger, R.; Humphrey, M. G.
Organometallics 1997, 16, 4004.

Polycarbon Ligand Chemistry
Organometallics, Vol. 18, No. 19, 1999 3895
and H at exactly the same value of ηmax ) 0.87. Thus,
while the CtC bond length is greater in D than in H
(Table 5), the localization properties of the bonds are
identical. The last two sets of attractors to appear in D
are associated with the C-O ligands (ηmax ) 0.83) and
the four Co-C bonds of the Co2C2 cluster core (ηmax
)
0.82) The cluster-based attractor basins collapse into a
single region of localization at η ) 0.8. For values of
the ELF lower than 0.8 all of the distinct regions of
electron pairing indicated above begin to collapse into
each other, forming larger domains stretching over the
various functional groups. It may be noted that the
acetylene-based bridge in D behaves in exactly the same
manner as H, with the CtC and C-C bonding regions
touching in both cases at exactly η ) 0.71, and reinforces
the claim that the electron localization along the acet-
ylenic chain is similar in D and H.
It is also important to consider the shape of the
various attractor basins.50a We note that the Co-CO
bonds in D have the shape of a ring, which is distorted
around the carbon nucleus due to the CO π* component
of the metal-carbonyl back-bond.50a Similarly, the C
p-orbital component of the CtC bonds in H results in a
ring-shaped attractor basin in this region of space. In
the case of regions of electron density void of π (or p)
character, such as the C-C single bond of H, the
attractor basins are not ring shaped, but are rather
more shaped like a solid disk (Figure 11). The bonding
attractors located between the phosphine ligands and
the metal centers are also disk-shaped, which is a
manifestation of the good σ-donating, poor π-accepting
character of the phosphine.
F igu r e 11. Electron localization function plotted as iso-
surfaces η ) 0.9, 0.8, and 0.7 for model compounds D and
H.
The shapes of the bonding attractors associated with
the Ru-CtC-Co2C2 portion of D therefore reveal a
great deal of information about the bonding within the
molecule and nature of the electronic interaction be-
tween the organometallic fragments. The attractors
associated with the Ru-C and C-Co2C2 bonds, and the
C-C bond of the metallocarbon cluster, are all disk-
shaped, indicating that these bonds have negligible
π-character. In contrast, the bonding attractor arising
from the CtC moiety has the same ring shape as found
for the analogous feature in H.
On the basis of the identical ηmax behavior and similar
shapes of the attractor basins associated with the Ru-
CtC-Co2C2 alkynyl portion of D and the acetylenic
fragments in H, we must conclude that the electron
density in each CtC moiety is localized in an identical
manner. Taken all in all, this pattern of electron
localization is entirely consistent with the interpretation
presented in Figure 10b and, moreover, rules out an
interpretation of the interaction based on the cumulenic
structure represented in Figure 10a. This assertion is
further supported by our natural bond orbital popula-
tion analysis (vide infra) that indicates no appreciable
Ru-C π-bonding or back-bonding.
these two terms effectively cancel each other and η(r)
≈ 1.0. On the other hand, a valence electron in a
conduction band of a metal, which may be regarded as
a prototypical delocalized state, will have a larger
kinetic energy density relative to the gradient of F(r)
and consequently a lower value of η(r). In essence, the
ELF will identify features such as lone electron pairs
and multiple bonds between elements and is therefore
an ideal instrument with which to probe the nature of
the bonding along the carbon bridge in C and D.
The ELF for the model compounds D and H is plotted
as a series of isosurfaces, η ) 0.9, 0.8, and 0.7, in Figure
11. The most localized bonding regions in both com-
pounds occur for spatial regions that correspond to the
C-H, P-H, and Si-H σ-bonds (ηmax ≈ 1.0), as one
would intuitively expect. For D, the next highest ELF
maxima (ηmax ≈ 0.93-0.96) correspond to the P-C and
Si-C σ-bonds and the lone pairs on the P atoms, which
are directed toward the Ru and Co centers. At lower
values of ηmax (ηmax ≈ 0.90-0.92) the C-C bonds in the
Cp ring and the Co-CO bonds in D and all of the
remaining C-C single bonds in both D and H are
identified. It is important to note that the central C-C
bond in H has exactly the same value of ηmax ) 0.91 as
both the corresponding bond in D and the C-C bond in
the Co2C2 cluster. As we move to still lower values of
ELF, the regions of space corresponding to oxygen lone
pairs and the Ru-C bond appear (ηmax ) 0.89). The next
and most striking feature of our ELF analysis is the
emergence of the ring-shaped CtC attractor in both D
Compounds C-G may be thought of as containing
three distinct portions: a donor fragment Ru(PH3)2Cp
(D), an acetylene bridge (B), and an acceptor fragment
(A) (A ) CtC(Co2C2(CO)4(H2PCH2PH2)SiH3, C; Co2C2-
(CO)4(H2PCH2PH2)CtCSiH3, D; H, E; Ph, F ; C6H4NO2-
p, G). For C-G, the net charge on each fragment ∑qD,
∑qB, and ∑qA has been derived by summation of the
atomic charges, which were in turn obtained from a

3896 Organometallics, Vol. 18, No. 19, 1999
Low et al.
measured versus a Ag/Ag+ reference electrode at -50 °C, such
that the ferrocene/ferrocenium redox couple was located at 0.99
V. Microanalyses were performed at the NRC’s Institute for
Biological Sciences, 100 Sussex Dr., Ottawa, Ontario, K1A 0R6,
Canada.
natural atomic orbital population analysis (Table 5).
With the exception of E, the net charge on the bridge B
remains relatively constant. The compounds with larger
positive charges on D also feature correspondingly large
negative charge on A, indicating that the role of the
bridge is to aid in the stabilization of a charge-transfer
state. In the case of E, the poor electron-accepting prop-
erties of the terminal hydrogen results instead in an
increase in negative charge on the bridge. A comparison
of ∑qD and the bond lengths reported in Table 5 indi-
cates that the larger the positive charge of D, the shorter
the Ru-C bond and suggests that the observed struc-
tural trends are due to an essentially electrostatic effect.
Finally we note that the computed charges indicate
that compound D will have a more effective transfer of
charge than found in C, and thus its properties will be
more significantly affected, as seen in their experimen-
tal analogues. This model of a stabilized charge-transfer
state is in line with the suggestion previously made for
G,48 and the magnitude of the effect is comparable in
C, D, and G.
Rea ction of Me3SiCtCCtCCtCSiMe3 w ith Co2(CO)6-
(d p p m ). A solution of Co2(CO)6(dppm) (660 mg, 0.98 mmol)
and Me3SiCtCCtCCtCSiMe3 (200 mg, 0.91 mmol) in ben-
zene (70 mL) was heated at reflux for 2 h. After this time TLC
analysis indicated the complete consumption of starting mate-
rial. The reaction mixture was adsorbed onto a small amount
of silica gel and the reaction mixture purified by column
chromatography on silica gel. A hexane/CH2Cl2 gradiant (0-
30% CH2Cl2) resolved two bands. The first red-brown band was
crystallized (CH2Cl2/MeOH slow evaporation) to give dark red,
needlelike crystals of Co2(µ-η2,η2-Me3SiC2CtCCtCSiMe3)-
(CO)4(dppm) (2) (125 mg, 17%). The second red band gave red,
block-shaped crystals of Co2(µ-η2,η2:µ-η2,η2-Me3SiCtCC2Ct
CSiMe3)(CO)4(dppm) (3) (348 mg, 46%) (CH2Cl2/MeOH slow
evaporation). 2 found: C, 60.34; H, 5.19. Co2Si2P2O4C41H40
requires: C, 59.13; H, 4.84. IR (cyclohexane): ν(CtC) 2160w,-
br; ν(CO) 2030vs, 2009vs, 2004sh, 1982vs, 1962w cm-1 1H
.
NMR (CDCl3): δ 0.30, 0.37 (2 × s, 2 × 9H, 2 × SiMe3); 3.11
(dt, J HP ) 12 Hz, J HH ) 10 Hz, CH2P2) 3.92 (dt, J HP ) 12 Hz,
J HH ) 10 Hz, CH2P2); 7.15-7.42 (m, 20H, Ph). 13C NMR
(CDCl3): δ 0.87, 1.57 (2 × s, 2 × SiMe3); 37.99 (t, J CP ) 20 Hz,
CH2P2); 75.41 [t, J CP ) 8 Hz, C(5/6)]; 82.39 [t, J CP ) 4 Hz, C(5/
6)]; 81.48, 91.34, 91.55, 92.89 (4 × s, 4 × CtC); 127.97-137.98
(m, Ph); 201.96, 207.88 (2 × br, CO). FAB-MS (m/z): 832 [M]+,
804-720 [M - nCO]+ (n ) 1-4). 3 found: C, 58.55; H, 4.86.
Co2Si2P2O4C41H40 requires: C, 59.13; H, 4.84. IR (cyclohex-
ane): ν(CtC) 2118w, 2105w; ν(CO) 2037s, 2019vs, 1994vs,
Con clu sion
The complexes 4 and 5 are affected to a significant
extent by the donor/acceptor character of the Ru(PPh3)2-
Cp and Co2C2(CO)4(Ph2PCH2PPh2) fragments when
linked by an acetylenic bridging ligand. The degree of
charge separation is on a par with that previously
observed between the Ru moiety and the classic organic
acceptor C6H4NO2-p and is best described using a model
based on inductive effects.
The orbital description obtained from DFT and ELF
studies suggests that the degree of interaction may be
modified in a rational manner and that increasing the
electron density at the Ru center (by substitution of
PPh3 for PMe3) or decreasing the effective electron
density at the Co2C2 core (by replacing the dppm ligand
with two CO ligands) will lead to even more pronounced
interactions. Studies along these lines are currently
being pursued.
1
1972w cm-1. H NMR (CDCl3): δ 0.29 (s, 9H, SiMe3); 3.44 (t,
J HP ) 5 Hz, 1H, CH2P2); 7.22-7.36 (m, 20H, Ph). 13C NMR
(CDCl3): δ 0.44 (s, SiMe3); 34.31 (t, J CP ) 21 Hz); 70.37 [br,
C(5/6)], 103.27, 107.85 (2 × s, 2 × CtC); 127.54-136.13 (m,
Ph); 203.83 (br, CO). FAB-MS (m/z): 832 [M]+; 804-720 [M
- nCO]+ (n ) 1-4).
Co2{µ-Me3SiC2CtCCtC[Ru (P P h 3)2Cp]}(CO)4(dppm ) (4).
A solution of RuCl(PPh3)2Cp (35 mg, 0.048 mmol) and 2 (48
mg, 0.048 mmol) in thf (7 mL)/MeOH (7 mL) was treated with
KF (ca. 5 mg) and heated at reflux for 1 h. The solvent was
removed and the residue purified by preparative TLC (10%
acetone in hexane) to give a single brown band, which was
crystallized (acetone/hexane) to afford Co2{µ-Me3SiC2CtCCt
C[Ru(PPh3)2Cp]}(CO)4(dppm) (4) (55 mg, 79%) as dark green-
ish-brown needles. Found: C, 65.65; H 4.53. RuCo2SiP4O4C79H64
requires: C, 65.46; H, 4.45. IR (cyclohexane): ν(CtC) 2124w;
Exp er im en ta l Section
1
ν(CO) 2018m, 1998vs, 1970s, 1952w cm-1. H NMR (CDCl3):
Gen er a l Con d ition s. All reactions were carried out under
dry high-purity nitrogen using standard Schlenk techniques.
Solvents were dried, distilled, and degassed prior to use.
Preparative TLC was performed on 20 × 20 cm glass plates
coated with silica gel (CAMAG DSF-5, 0.5 mm thick). Litera-
ture methods were used to prepare Me3SiCtCCtCCtCSiMe3,51
Co2(CO)6(dppm),52 and RuCl(PPh3)2Cp.53 Other reagents were
purchased and used as received.
In str u m en ta l Mea su r em en ts. Infrared spectra were re-
corded using calcium fluoride cells of 0.5 mm path length. UV-
vis spectra were recorded from thf solutions in a 1 cm path
length cuvette. NMR spectra were recorded at (1H) 400.13 MHz
and (13C) 100.61 MHz in CDCl3 and referenced against the
solvent resonances. FAB-MS were obtained using Xe as the
exciting gas, FAB gun voltage 6 kV, accelerating potential 3
kV, and m-nitrobenzyl alcohol matrix. Cyclic votammetry
experiments were carried out in thf containing 0.5 M [nBu4N]-
[BF4]. Solutions (1 × 10-3 M) were purged with nitrogen and
δ 0.78 (s, 9H, SiMe3); 3.43 (br, 2H, CH2P2); 4.55 (s, 5H, Cp);
6.87-7.80 (m, 50H, Ph). 13C NMR (CDCl3): δ 1.21 (s, SiMe3);
36.82 (t, J CP ) 20 Hz, CH2P2); 64.69 (br, C(4)); 84.68 (t, J CP
)
9 Hz, C(5/6)); 86.41 (s, Cp); 89.72 (t, J CP ) 5 Hz, C(5/6)); 89.82
(s, C(3)); 90.09 (t, J CP )16 Hz, C(1)); 100.08 (s, C(2)); 127.97-
138.99 (m, Ph); 203.19, 208.32 (2 × br, 2 × CO). FAB-MS (m/
z): 1450, [M + H]+; 1422-1338, [M - nCO]+ (n ) 1-4); 1188,
1104, 1076, [M - PPh3 - nCO]+ (n ) 0,3,4); 926, 842, 814, [M
- 2PPh3 - nCO]+ (n ) 0, 3, 4).
Co2{µ-Me3SiCtCC2CtC[Ru (P P h 3)2Cp]}(CO)4(dppm ) (5).
A solution of 3 (103 mg, 0.103 mmol) in thf (5 mL)/MeOH (10
mL) was treated with RuCl(PPh3)2Cp (75 mg, 0.103 mmol) and
KF (ca. 10 mg). The mixture was heated at reflux for 3 h,
during which time the solution color changed from red to dark
green. The solvent was removed and the residue purified by
preparative TLC (10% acetone in hexane). The major dark
green band yielded Co2{µ-Me3SiCtCC2CtC[Ru(PPh3)2Cp]}-
(CO)4(dppm) (5) (110 mg, 74%) as dark green blocks following
crystallization (acetone/hexane, slow diffusion). Found: C,
65.03; H, 4.95. RuCo2SiP4O4C79H64 requires: C, 65.46; H 4.45.
IR (cyclohexane): ν(CtC) 2104w; ν(CO) 2036s, 2015m, 2000vs,
(51) Rubin, Y.; Lin, S. S.; Knobler, C. B.; Anthony, J .; Doldi, A. M.;
Diederich, F. J . Am. Chem. Soc. 1991, 113, 6943.
(52) Chia, L. S.; Cullen, W. R. Inorg. Chem. 1975, 14, 482.
(53) Bruce, M. I.; Hameister, C.; Swincer, A. G.; Wallis, R. C. Inorg.
Synth. 1990, 28, 270.
1
1975s, 1954vw cm-1. H NMR (CDCl3): δ 0.47 (s, 9H, SiMe3);

Polycarbon Ligand Chemistry
Organometallics, Vol. 18, No. 19, 1999 3897
3.10 (br, 1H, CH2P2); 3.79 (dt, J HP ) J HH ) 11 Hz); 4.55 (s,
5H, Cp); 6.87-7.91 (m, Ph). 13C NMR (CDCl3): δ 1.04 (s,
SiMe3); 34.52 (t, J CP ) 21 Hz, CH2P2); 95.78, 99.75 (2 × s, C(5/
6)); 111.08 (t, J CP ) 4 Hz, C(1)); 114.78 (s, C(2)); 127.78-139.67
(m, Ph); 203.33, 208.64 (2 × br, 2 × CO). FAB-MS (m/z): 1450,
[M + H]+; 1421-1337, [M - nCO]+ (n ) 1-3); 1103 [M - 3CO
- PPh3]+, 1075 [M - 4CO - PPh3]+.
DO calculations,60 as implemented within the Hyperchem
package,61 on the DFT optimized structures. The orbital
manifold for the UV/vis calculations was increased systemati-
cally until the spectra were converged within the 400-800 nm
range. Topological analysis on the electron density was
performed in terms of the electron localization function (ELF)
of Becke and Edgecombe,49 as implemented in the Vienna ab
initio simulation package (VASP),62 again on the static struc-
tures obtained from the geometry optimization. For these later
calculations, the local density approximation was employed,
with the core electrons replaced via Vanderbelt ultrasoft
pseudopotentials.63 The molecule was placed within a 16 Å
cubic box subject to periodic boundary conditions, and the
valence electrons expanded within a basis set of plane waves
with an energy cutoff of 30 Ry.
Cr ystallogr aph y. Data were collected on a Siemens SMART
CCD diffractometer. Unique diffractometer data sets (mono-
chromatic Mo KR radiation, λ ) 0.71073 Å; ω scan mode; T )
173 K) were measured within the specified 2θmax limit yielding
N independent reflections, No of these with I > 2.0σ(I) being
considered observed and used in the block/full-matrix least-
squares refinement after an empirical absorption correction
utilizing the SADABS routine associated with the Siemens
diffractometer. Anisotropic thermal parameters were refined
for the non-hydrogen atoms. In the final cycles of refinement
hydrogen atoms were placed in calculated positions and
constrained with a riding model. The minimized function was
Ack n ow led gm en t. We gratefully acknowledge fi-
nancial support from the National Research Council
Canada (NRC) and the Natural Sciences and Engineer-
ing Research Council (NSERC). P.J .L. holds an NSERC-
NRC Canadian Government Laboratories Visiting Fel-
lowship.
∑w(Fo - Fc2)2. Computations were performed using the
2
SHELXTL suite of programs.54 For 2, two independent mol-
ecules were contained within the unit cell. These differed only
by the relative orientation of a phenyl ring, and molecular
parameters were equivalent within error. The Si(1) trimeth-
ylsilyl fragment was disordered over two sites, which were
successfully modeled at 72:28 occupancy following trial refine-
ment. The analogous Si(21)Me3 fragment in the second mol-
ecule was treated similarly. Residual electron density in 4 was
successfully modeled as a molecule of a hexane solvate, with
50% occupancy. The unit cell of 5 contained two fully occupied
molecules of acetone, which were refined without difficulty.
In the absence of high-angle data, the 2θ range for 2 and 4
were constrained to a maximum value of 45° and 50°,
respectively.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data collection and refinement details, positional and thermal
parameters, and bond distances and angles for 2, 3, 4, and 5,
and Cartesian coordinates of all optimized geometries. This
material is available free of charge via the Internet at http://
pubs.acs.org. Structure factors are available from the authors
upon request.
OM990290W
(57) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
J ohnson, B. G.; Robb, M. A.; Cheeseman, J . R.; Keith, T.; Petersson,
G. A.; Montgomery, J . A.; Raghavachari, K.; Al-Laham, M. A.;
Zakrzewski, V. G.; Ortiz, J . V.; Foresman, J . B.; Peng, C. Y.; Ayala, P.
Y.; Chen, W.; Wong, M. W.; Andres, J . L.; Replogle, E. S.; Gomperts,
R.; Martin, R. L.; Fox, D. J .; Binkley, J . S.; Defrees, D. J .; Baker, J .;
Stewart, J . P.; Head-Gordon, M.; Gonzalez, C.; Pople, J . A. Gaussian
94, Revision B.2; Gaussian, Inc.: Pittsburgh, PA, 1995.
(58) Hay, P. J .; Wadt, W. R. J . Chem. Phys. 1985, 82, 270, 299.
(59) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88,
899.
Com p u ta tion a l Deta ils. Geometry optimization on the
model compounds was performed within the Kohn-Sham
description of density functional theory.55 In particular, the
B3LYP hybrid Hartree-Fock DFT method56 was employed as
implemented within the Gaussian 94 software package57 with
a LanL2DZ basis set.58 Criteria for optimization were chosen
as the defaults of this package. Population analysis was
performed within the formalism of natural orbitals.59 Elec-
tronic absorption spectra were simulated by performing ZIN-
(60) Anderson, W. P.; Edwards, W. D.; Zerner, M. C. Inorg. Chem.
1985, 25, 2728.
(61) Hyperchem, Release 4.5 for Silicon Graphics workstations;
Hypercube Inc.: Aug 1995.
(54) (a) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467. (b)
Sheldrick, G. M. Acta Crystallogr. 1993, A49 (Suppl.), C53.
(55) (a) Parr, R. G.; Yang, W. Density-Functional Theory of Atoms
and Molecules; Oxford University Press: Oxford, 1989. (b) J ones, R.
O.; Gunnarsson, O. Rev. Mod. Phys. 1989, 61, 689.
(62) (a) Kresse, G.; Hafner, J . Phys. Rev. B 1993, 47, 55; 1994, 49,
14251. (b) Kresse, G.; Furthmuller, J . Comput. Mater. Sci. 1995, 6,
15. Kresse, G.; Furthmuller, J . Phys. Rev. B 1996, 54, 11169.
(63) Vanderbelt, D. Phys. Rev. B 1990, 41, 7892. The pseudopoten-
tials used were those taken from the database provided with the VASP
program.
(56) Becke, A. D. J . Chem. Phys. 1993, 98, 5648.