Coupling of acetylide ligands on an electron-rich tetraruthenium diphosphido framework: Synthesis, structure, and reactivity studies of Ru4(CO)9(μ-PPh2)2(C 2But)2 and Ru4(CO)8(μ-PPh2)2(C 4Bu2t)

Article abstract of DOI:10.1021/om960507b

Thermolysis of Ru₂(CO)₆(μ-PPh₂)(C₂Bu ^t) (1) in toluene afforded Ru₄(CO)₉(μ-PPh₂)₂(C ₂Bu^t)₂ (2) in which the acetylide ligands are coordinated to a novel 64-electron butterfly platform. Upon thermolysis, this complex underwent C-C bond coupling to give the diyne complexes Ru₄(CO)₈(μ-PPh₂)₂(C ₄Bu₂^t) (3) and Ru₃(CO)₇(μ-PPh₂)₂(C ₄BU₂^t) (4) through sequential CO elimination and fragmentation, respectively.

Full text of DOI:10.1021/om960507b

Organometallics 1996, 15, 5269-5271
5269
Cou p lin g of Acetylid e Liga n d s on a n Electr on -Rich
Tetr a r u th en iu m Dip h osp h id o F r a m ew or k : Syn th esis,
Str u ctu r e, a n d Rea ctivity Stu d ies of
Ru 4(CO)9(µ-P P h 2)2(C2Bu t)2 a n d Ru 4(CO)8(µ-P P h 2)2(C4Bu t )
2
Yun Chi,*,† Arthur J . Carty,*,‡ Peter Blenkiron,‡ Esther Delgado,‡
Gary D. Enright,‡ Weibin Wang,‡ Shie-Ming Peng,*,§ and Gene-Hsiang Lee§
Department of Chemistry, National Tsing Hua University, Hsinchu 30043, Taiwan, Steacie
Institute for Molecular Sciences, National Research Council of Canada, 100 Sussex Drive,
Ottawa, Ontario K1A 0R6, Canada, and Department of Chemistry, National Taiwan
University, Taipei 10764, Taiwan
Received J une 24, 1996X
Summary: Thermolysis of Ru2(CO)6(µ-PPh2)(C2But) (1)
in toluene afforded Ru4(CO)9(µ-PPh2)2(C2But)2 (2) in
which the acetylide ligands are coordinated to a novel
64-electron butterfly platform. Upon thermolysis, this
complex underwent C-C bond coupling to give the diyne
the formation of diynes from intermolecular coupling
of acetylides is, to our knowledge, rare.7
Thermolysis of 1 in toluene solution at reflux for 4 h
afforded a 1:1 mixture of diacetylide complex Ru4(CO)9(µ-
PPh2)2(C2But)2 (2) and diyne metal complex Ru4(CO)8(µ-
complexes Ru4(CO)8(µ-PPh2)2(C4But ) (3) and Ru3(CO)7(µ-
PPh2)2(C4But ) (3) as a mixture of red crystalline
2
2
PPh2)2(C4But ) (4) through sequential CO elimination
2
materials in 57% yield after recrystallization from CH2-
Cl2 and methanol at room temperature. Attempts to
separate these cluster complexes by chromatography
proved fruitless because of the similar Rf values and the
rapid decomposition of 3 on contact with silica gel.
However, thermolysis of the mixture in toluene for 1 h
led to the isolation of 3 with g95% purity and in nearly
quantitative yield. This suggested that complex 2 is an
intermediate prior to the formation of 3. Accordingly,
pure 2 was obtained by treatment of the mixture with
carbon monoxide in toluene (1 atm, 80 °C) for 5 min.
Under such conditions, complex 3 present in the mixture
was found to convert into triruthenium cluster
and fragmentation, respectively.
The coupling of terminal or functionalized metal
acetylides via methodologies such as oxidative1 or
Cadiot-Chodkiewicz2 coupling has been extensively
exploited recently to generate polycarbon ligand com-
plexes and new molecular materials possessing ex-
tended carbon unsaturation.3 In principle, it should be
possible to effect head-to-head or tail-to-tail linkage of
acetylides or polyacetylides coordinated in a multisite
fashion on a binuclear or cluster framework to synthe-
size new multimetallic polycarbon complexes in which
the full potential of σ- and π-electrons of the alkynyl
fragments are used in bonding. This strategy has as
yet been little exploited in organometallic chemistry.4
In this communication, we describe the stereospecific
high-yield head-to-head intermolecular coupling of µ-η1:
η2-alkynyl groups in Ru2(CO)6(µ-PPh2)(CtCBut)5 (1)
molecules to produce an eight-electron-donor butadiyne
ligand on an Ru4 framework. Although the cleavage of
diynes by transition-metal clusters has been reported,6
Ru3(CO)7(µ-PPh2)2(C4But ) (4) in 90% yield, leaving 2
2
intact. The clusters 2 and 4 can then be separated using
chromatographic workup followed by recrystallization.
These stepwise transformations can be summarized:
2Ru2(CO)6(µ-PPh2)(C2But) f
1
Ru4(CO)9(µ-PPh2)2(C2But)2 f
† National Tsing Hua University.
2
‡ National Research Council of Canada.
Ru4(CO)8(µ-PPh2)2(C4But ) f
§ National Taiwan University.
2
X Abstract published in Advance ACS Abstracts, November 1, 1996.
(1) (a) Hay, A. S. J . Org. Chem. 1962, 27, 3320. (b) Zhou, Y.; Seyler,
J . W.; Weng, W.; Arif, A. M.; Gladysz, J . A. J . Am. Chem. Soc. 1993,
115, 8509. (c) Brady, M.; Weng, W.; Gladysz, J . A. J . Chem. Soc., Chem.
Commun. 1994, 2655. (d) Yuan, Z.; Stringer, G.; J obe, I. R.; Kreller,
D.; Scott, K.; Koch, L.; Taylor, N. J .; Marder, T. B. J . Organomet. Chem.
1993, 452, 115.
3
Ru3(CO)8(µ-PPh2)2(C4But ) + Ru3(CO)12
2
4
The reaction sequences 2 f 3 f 4 were further verified
by conversion of a pure sample of 2 in toluene and by
treatment of a pure sample of 3 with CO under identical
conditions.
(2) (a) Chodkiewicz, W.; Cadiot, P. C. R. Hebd. Seances Acad. Sci.
1955, 241, 1055. (b) Worth, G. H.; Robinson, B. H.; Simpson, J .
Organometallics 1992, 11, 501. (c) Bartik, T.; Bartik, B.; Brady, M.;
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414.
(3) Lagow, R. J .; Kampa, J . J .; Wei, H.-C.; Battle, S. L.; Genge, J .
W.; Laude, D. A.; Harper, C. J .; Bau, R.; Stevens, R. C.; Haw, J . F.;
Munson, E. Science 1995, 267, 362.
Compounds 2-4 were initially characterized by spec-
tral methods.8 Single-crystal X-ray diffraction studies
(4) (a) Akita, M.; Sugimoto, S.; Terada, M.; Moro-oka, Y. J . Orga-
nomet. Chem. 1993, 447, 103. (b) Crescenzi, R.; Sterzo, C. L. Organo-
metallics 1992, 11, 4301. (c) Hwang, D.-K.; Lin, P.-J .; Chi, Y.; Peng,
S.-M.; Lee, G.-H. J . Chem. Soc., Dalton Trans. 1991, 2161. (d) Wu,
C.-H.; Chi, Y.; Peng, S.-M.; Lee, G.-H. J . Chem. Soc., Dalton Trans.
1990, 3025. (e) Matsuzaka, H.; Hirayama, Y.; Nishio, M.; Mizobe, Y.;
Hidai, M. Organometallics 1993, 12, 36. (f) J eannin, S.; J eannin, Y.;
Robert, F.; Rosenberger, C. Inorg. Chem. 1994, 33, 243. (g) Heeres, H.
J .; Nijhoff, J .; Teuben, J . H.; Rogers, R. D. Organometallics 1993, 12,
2609.
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B. J . Chem. Soc., Chem. Commun. 1987, 461. (b) Deeming, A. J .; Felix,
M. S. B.; Nuel, D. Inorg. Chim. Acta 1993, 213, 3. (c) Maekawa, M.;
Munakata, M.; Kuroda-Sowa, T.; Hachiya, K. Inorg. Chim. Acta 1995,
233, 1. (d) Rosenthal, U.; Pulst, S.; Arndt, P.; Ohff, A.; Tillack, A.;
Baumann, W.; Kempe, R.; Burlakov, V. V. Organometallics 1995, 14,
2961.
(7) (a) Ustynyuk, N. A.; Vinogradova, V. N.; Korneva, V. N.;
Kravtsov, D. N.; Andrianov, V. G.; Struchkov, Y. T. J . Organomet.
Chem. 1984, 277, 285. (b) Bruce, M. I.; Zaitseva, N. N.; Skelton, B.
W.; White, A. H. J . Cluster Sci. 1996, 7, 109 and references therein.
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Taylor, N. J . Carty, A. J . Organometallics 1988, 7, 969.
S0276-7333(96)00507-9 CCC: $12.00 © 1996 American Chemical Society

5270 Organometallics, Vol. 15, No. 25, 1996
Communications
F igu r e 1. Molecular structure of 2 and the atomic
numbering scheme. The phenyl groups of the phosphido
ligands are omitted for clarity. Selected bond lengths (Å):
Ru(1)-Ru(2) ) 3.0207(4), Ru(1)-Ru(3) ) 2.7815(4), Ru-
(1)-Ru(4) ) 3.0437(4), Ru(2)-Ru(4) ) 3.0974(4), Ru(3)-
Ru(4) ) 2.8575(4), Ru(1)-P(1) ) 2.366(1), Ru(2)-P(1) )
2.344(1), Ru(2)-P(2) ) 2.358(1), Ru(4)-P(2) ) 2.302(1), Ru-
(1)-C(10) ) 2.052(4), Ru(2)-C(10) ) 2.293(4), C(10)-C(11)
) 1.209(6), Ru(1)-C(16) ) 2.222(4), Ru(3)-C(16) ) 2.205-
(4), Ru(4)-C(16) ) 1.968(4), Ru(1)-C(17) ) 2.324(4), Ru-
(3)-C(17) ) 2.214(4), C(16)-C(17) ) 1.296(6).
F igu r e 2. Molecular structure of 3 and the atomic
numbering scheme. Selected bond lengths (Å): Ru(1)-Ru-
(2) ) 2.814(1), Ru(1)-Ru(3) ) 2.875(1), Ru(2)-Ru(3) )
2.924(1), Ru(2)-Ru(4) ) 2.844(1), Ru(3)-Ru(4) ) 2.821-
(1), Ru(1)-P(1) ) 2.319(1), Ru(3)-P(1) ) 2.352(2), Ru(2)-
P(2) ) 2.331(1), Ru(4)-P(2) ) 2.313(2), Ru(1)-C(10) )
2.053(5), Ru(2)-C(10) ) 2.430(5), Ru(1)-C(11) ) 2.361-
(5), Ru(2)-C(11) ) 2.183(5), Ru(3)-C(11) ) 2.363(5), Ru-
(2)‚‚‚C(12) ) 2.700(5), Ru(3)-C(12) ) 2.186(5), Ru(4)-C(12)
) 2.247(5), Ru(3)-C(13) ) 2.371(5), Ru(4)-C(13) ) 2.106-
(5), C(10)-C(11) ) 1.332(7), C(11)-C(12) ) 1.366(7),
C(12)-C(13) ) 1.321(7).
on 2 and 3 were carried out to confirm their molecular
structures. As indicated in Figure 1,9 the cluster
framework of 2 shows a flattened-butterfly geometry
with the Ru-Ru distances adopting a pattern of two
normal Ru-Ru bonds (2.7815(4)-2.8575(4) Å) and three
elongated Ru-Ru bonds (3.0207(4)-3.0974(4) Å). This
skeletal arrangement is similar to that of the 64e,
electron-rich cluster compounds Ru4(CO)13(µ-PR2)2 (R )
Ph, Et, Cy, Pri).10 In addition, the cluster contains two
multisite-bound acetylide ligands. The acetylide C(16)-
C(17), which possesses a µ3-η2-bonding mode,11 lies on
the Ru(1)-Ru(3)-Ru(4) triangle with its R-carbon con-
nected to the Ru(4) atom via a σ-bond and with the C-C
vector perpendicular to the Ru(1)-Ru(3) bond. The
other, C(10)-C(11), which adopts the less common µ2-
η2-mode,12 resides on the Ru(1)-Ru(2) bond and pushes
the phosphido bridge away from the triangular plane
defined by Ru(1), Ru(2), and Ru(4) atoms. The lengths
of the -CtC- bonds in the acetylide ligands reflect the
coordination mode5,11,12 with the more highly coordi-
nated µ3-η2-bond (C(16)-C(17) ) 1.296(6) Å) being
longer than the µ2-η2-bond (C(10)-C(11) ) 1.209(6) Å).
Interestingly, the acetylide ligands also align in a
configuration with the sterically bulky tert-butyl sub-
stituents pointing away from each other.
The molecular structure of the diyne complex 3 is
shown in Figure 2.13 The cluster, with 62 valence
electrons, adopts a butterfly geometry similar to that
of 2. The four peripheral Ru-Ru bonds span the narrow
range 2.814(1)-2.875(1) Å and are shorter than the
hinge Ru(2)-Ru(3) bond (2.924(1) Å). Although the
basic cluster framework is retained, one phosphido
ligand has migrated to the Ru-Ru edge parallel to the
(8) Spectral data for 2: MS (FAB, 102Ru), m/z 1192 (M+); IR (C6H14
ν(CO) 2068 (vs), 2031 (vs), 2014 (s), 1999 (s), 1993 (m), 1962 (m), 1952
(m), 1936 (w) cm-1 1H NMR (300 MHz, CDCl3) δ 8.22 (m, 2H), 7.96
)
;
(m, 2H), 7.58-7.44 (m, 6H), 7.30 (m, 2H), 7.10-7.06 (m, 6H), 6.58 (m,
2H), 1.53 (s, 9H, But), 0.31 (s, 9H, But); 31P NMR (121.5 MHz, CDCl3)
δ 138.3 (d, J P-P ) 177 Hz, 1P), 135.8 (d, J P-P ) 177 Hz, 1P). Anal.
Calcd for C45H38O9P2Ru4: C, 45.46; H, 3.22. Found: C, 45.43; H, 3.22.
Spectral data for 3: MS (FAB, 102Ru), m/ z 1164 (M+); IR (C6H14): ν-
(CO), 2032 (vw), 2009 (vs), 1997 (m), 1971 (s), 1961 (w), 1949 (m) cm-1
;
1H NMR (200 MHz, CDCl3) δ 7.28-7.11 (m, 16H), 7.01-6.93 (m, 4H),
1.63 (s, 18H, 2But); 31P NMR (121.5 MHz, CDCl3) δ 194.8 (s, 2P). Anal.
Calcd for C44H38O8P2Ru4: C, 45.52, H, 3.30. Found: C, 45.30; H, 3.17.
Spectral data for 4: MS (FAB, 102Ru), m/ z 1034 (M+); IR (C6H14) ν-
(CO) 2056 (s), 2028 (s), 2013 (vs), 1993 (s), 1987 (m), 1973 (m), 1948
(w) cm-1; 1H NMR (300 MHz, CDCl3, 293 K) δ 7.92-7.88 (m, 4H), 7.72-
7.67 (m, 4H), 7.42-7.40 (m, 6H), 7.33-7.29 (m, 6H), 1.13 (s, 9H, But),
0.69 (s, 9H, But); 31P NMR (121.5 MHz, CDCl3, 203 K) δ 275.8 (d, J P-P
) 152 Hz, 1P), 188.3 (J P-P ) 152 Hz, 1P). Anal. Calcd for C43H38O7P2-
Ru3: C, 50.05; H, 3.71. Found: C, 49.99, H, 3.75.
(11) (a) Hwang, D.-K.; Chi, Y.; Peng, S.-M.; Lee, G.-H. Organome-
tallics 1990, 9, 2709. (b) Sappa, E.; Tiripicchio, A.; Braunstein, P. Chem.
Rev. 1983, 83, 203.
(9) Crystal data for 2: C45H38O9P2Ru4, M ) 1189.01, monoclinic,
space group P21/n, a ) 14.201(1) Å, b ) 18.009(1) Å, c ) 18.218(1) Å,
â ) 98.698(4)°, V ) 4605.6(3) Å3, Z ) 4, Fcalcd ) 1.715 g cm-3, F(000)
) 2344, λ(Cu KR) ) 1.541 Å, T ) 298 K, µ ) 11.79 mm-1. The intensities
were measured on a Nonius CAD4 diffractometer on a crystal with
dimensions 0.30 × 0.25 × 0.13 mm. Of the 8742 unique reflections
collected, 7427 reflections with I > 2.5σ(I) were used for the refinement.
The structure was solved by using the NRCC-SDP-VAX package and
refined to RF ) 0.032, Rw ) 0.044, and GOF ) 1.46 for 98 atoms and
542 parameters, weighting scheme ω-1 ) σ2(Fo) + 0.0005Fo2, and
highest ∆/σ ratio 0.14. A difference map following convergence showed
residual electron density within the range -0.61/1.33 e/Å3 (min/max).
(10) (a) Hogarth, G.; Hadj-Bagheri, N.; Taylor, N. J .; Carty, A. J . J .
Chem. Soc., Chem. Commun. 1988, 1570. (b) Corrigan, J . F.; Doherty,
S.; Taylor, N. J .; Carty, A. J . J . Am. Chem. Soc. 1992, 114, 7557. (c)
Corrigan, J . F.; Dinardo, M.; Doherty, S.; Hogarth, G.; Sun, Y.; Taylor,
N. J .; Carty, A. J . Organometallics 1994, 13, 3572.
(12) (a) Carty, A. J .; Taylor, N. J .; Smith, W. F. J . Chem. Soc., Chem.
Commun. 1979, 750. (b) Carty, A. J .; MacLaughlin, S. A.; Wagner, J .
V.; Taylor, N. J . Organometallics 1982, 1, 1013. (c) Cherkas, A. A.;
Taylor, N. J .; Carty, A. J . J . Chem. Soc., Chem. Commun. 1990, 385.
(13) Crystal data for 3: C44H38O8P2Ru4, M ) 1161.00, triclinic, space
group P1h, a ) 12.022(3) Å, b ) 12.768(4) Å, c ) 16.218(3) Å, R ) 85.42-
(2)°, â ) 86.11(2)°, γ ) 63.56(2)°, V ) 2220.6(10) Å3, Z ) 2, Fcalcd
)
1.736 g cm-3, F(000) ) 1133, λ(Mo KR) ) 0.7107 Å, T ) 298 K, µ )
14.33 cm-1. The intensities were measured on a crystal with dimen-
sions 0.20 × 0.25 × 0.25 mm. Of the 7806 unique reflections collected,
5690 reflections with I > 2σ(I) were used for the refinement. The
structure was refined to RF ) 0.029, Rw ) 0.030, and GOF ) 1.20 for
96 atoms and 524 parameters, weighting scheme ω-1 ) σ2(Fo) + 0.0001
Fo2, and highest ∆/σ ratio 0.009. A difference map following convergence
showed residual electron density within the range -0.36/0.34 e/Å3 (min/
max).

Communications
Organometallics, Vol. 15, No. 25, 1996 5271
Sch em e 1
second phosphido ligand, and the phosphido-bridged
Ru-Ru bonds (2.875(1) and 2.844(1) Å) are noticeably
shorter than those of 2, consistent with an increase of
bond order through alleviation of excess electrons from
the metal-metal antibonding orbital.14 The butadiyne
ligand, generated from the end-to-end coupling of acetyl-
ide ligands, now acts as a µ4-bridge across the Ru4
surface. The diyne C4 backbone is slightly nonlinear
with angles C(10)-C(11)-C(12) ) 158.9(5)° and C(11)-
C(12)-C(13) ) 156.2(5)°. The C-C bond lengths within
this C4 unit are consistent with the parameters observed
for other coordinated diynes,15 where the net effect of
coordination is to elongate the outer formal triple bonds
(C(10)-C(11) ) 1.332(7) Å and C(12)-C(13) ) 1.321(7)
Å in 3) and shorten the inner Csp-Csp single bond
(C(11)-C(12) ) 1.366(7) Å). In fact, C(10)-C(11) and
C(12)-C(13) in 3 are both longer than the acetylenic
triple bonds in 2 from which they are derived. It is of
interest to note that the Ru(2)-C(12) bond (2.700(5) Å)
is significantly longer than the rest of the Ru-C
distances (2.053(5)-2.430(5) Å), indicating the absence
of direct bonding. However, if we ignore this nonbond-
ing interaction, the cluster core skeleton can be consid-
ered to possess a C2 axis passing through the center of
the diyne ligand and the middle of the hinge Ru(2)-
Ru(3) bond. In fact, the observation of only one 1H NMR
signal at δ 1.63 due to the But groups and one 31P NMR
signal at δ 194.8 even at 190 K indicates the formation
of such dynamic C2 symmetry in solution.
The isolation and characterization of complexes 2 and
3 provide an opportunity to explore the reactions taking
place at the Ru2 metal centers. We propose that
dimerization with CO loss leads to the formation of an
intermediate (A) via a side-by-side and head-to-head
alignment of 1 and the formation of two Ru-Ru interac-
tions (Scheme 1). Upon further removal of a CO ligand
the intermediate A would strengthen the bonding
between each Ru2(µ-PPh2)(CCBut) unit through the
simultaneous generation of a third Ru-Ru bond at the
hinge position. Phosphido ligand migration, and forma-
tion of one µ3-η2-acetylide ligand, eventually leads to the
formation of 2. With loss of CO from 2 the acetylide
ligands then undergo head-to-head coupling to afford
the diyne ligand on cluster 3. This diyne ligand is
considered as an eight-electron donor and is bonded to
all four ruthenium atoms, but in an almost linear
fashion, quite different from that observed in other
diyne clusters such as Ru4(CO)10(µ4-PR)(C4R′2) (R ) C2-
But, Ph; R′ ) But, Ph, SiMe3),15 which contains a square-
planar metal framework with a highly distorted C4
skeleton.
The degradation of 3 and formation of 4 is somewhat
unexpected but may involve the conversion of the
butterfly metal framework to a 64-electron spiked-
triangular geometry via addition of CO, followed by
removal of the pendant “Ru(CO)4” unit as Ru3(CO)12.
The assignment of 4 follows directly from the similarity
of spectroscopic data with those of the related, structur-
ally characterized derivatives Ru3(CO)7(µ-PPh2)2(RC4R′)
(R ) R′ ) Ph and R ) H, R′ ) Ph, But, and Pri).16 The
dynamic process of the diyne ligand of 4, which is
similar to the windshield wiper motion of the µ3-η2-
alkynes,17 was revealed by the observation of only two
doublets at δ 275.8 and 188.3 with a coupling constant
2J P-P of 152 Hz at the limiting temperature of 203 K
and one broad 31P NMR resonance at δ 230 at room
temperature.
The high-yield head-to-head intermolecular coupling
of µ-η-alkynyl groups in converting dinuclear 1 to
tetranuclear diyne cluster 3 may be applicable to the
generation of other polyyne ligands on a polymetallic
framework from µ-η2-butadiynyl or higher polyynyl
complexes.18 We are currently exploring the synthesis
of clusters bearing polyunsaturated R(CtC)nR hydro-
carbyls via such reactions.
Ack n ow led gm en t. This work was supported by
grants from the National Research Council of Canada,
the Natural Sciences and Engineering Research Council
of Canada (to A.J .C.), and the National Sciences Council
of Taiwan (to Y.C. and S.-M.P.; NSC 85-2113-M007-
008).
Su p p or tin g In for m a tion Ava ila ble: Text describing the
experimental details for complexes 2 and 3 and 13C NMR data
for 2 and full details of crystal structure analyses, including
tables of bond distances, atomic coordinates, and anisotropic
thermal parameters (14 pages). Ordering information is given
on any current masthead page.
OM960507B
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