Rearrangement and scission of terminal alkynes in dimolybdenum complexes on reaction with ruthenium carbonyl: Formation of trinuclear vinylidene and hexanuclear bis(alkylidyne) clusters

Article abstract of DOI:10.1021/om960235c

The reaction of the dimolybdenum alkyne complexes Mo₂(CO)₄(μ-R¹C≡CR²)Cp ₂ (Cp = η-C₅H₅; R¹= H, R² = H, Me, Ph, CO₂Me; 1a-d) with Ru₃(C

Full text of DOI:10.1021/om960235c

+
+
4182
Organometallics 1996, 15, 4182-4189
Rea r r a n gem en t a n d Scission of Ter m in a l Alk yn es in
Dim olybd en u m Com p lexes on Rea ction w ith Ru th en iu m
Ca r bon yl: F or m a tion of Tr in u clea r Vin ylid en e a n d
Hexa n u clea r Bis(a lk ylid yn e) Clu ster s
Harry Adams, Louise J . Gill, and Michael J . Morris*,†
Department of Chemistry, University of Sheffield, Sheffield S3 7HF, U.K.
Received March 27, 1996X
The reaction of the dimolybdenum alkyne complexes Mo2(CO)4(µ-R1CtCR2)Cp2 (Cp )
η-C5H5; R1) H, R2 ) H, Me, Ph, CO2Me; 1a -d ) with Ru3(CO)12 in refluxing toluene or heptane
affords reasonable yields of the orange µ3-vinylidene clusters [Mo2Ru(µ3-CdCHR2)(CO)7Cp2]
(2a -d ). The crystal structure of Mo2Ru(µ3-CdCHMe)(CO)7Cp2 (2b) has been determined
and shows that the metal triangle is capped by a vinylidene ligand which is formally σ-bound
to the two molybdenum atoms and π-bound to the ruthenium. Low to moderate yields of
the blue-turquoise hexanuclear bis(alkylidyne) clusters Mo2Ru4(µ3-CR1)(µ3-CR2)(CO)12Cp2
(3a -d ) are formed in addition to the vinylidene clusters, especially if the reaction is carried
out in heptane. The synthesis of 3a is particularly noteworthy, as it represents the first
example of the scission of ethyne into two methylidyne fragments on a metal cluster. The
disubstituted alkyne complex 1e (R1 ) R2 ) Me) leads to the corresponding hexanuclear
cluster 3e in either solvent, but complexes of bulkier disubstituted alkynes 1f and 1g (R1 )
R2 ) Et, CO2Me) do not give analogous products. The X-ray crystal structure of the cluster
Mo2Ru4(µ3-CMe)2(CO)12Cp2‚CH2Cl2 (3e‚CH2Cl2) reveals an octahedral metal core in which
the two MoCp fragments occupy adjacent positions, with the two alkylidyne groups formed
by scission of the alkyne ligand capping the two Mo2Ru faces. Unusually for octahedral
clusters, complexes of type 3 have 84 cluster valence electrons.
Sch em e 1
In tr od u ction
The interaction of alkynes with di- and polynuclear
metal carbonyls has been under investigation for over
35 years now and is still a subject of considerable
research interest.1 In such complexes, alkynes almost
always coordinate as bridging ligands, such as the well-
known µ3,η2- and µ3,η2-| bonding modes observed on
metal triangles (Scheme 1, path a). Apart from simple
coordination, however, they are known to undergo a
variety of additional activation processes, e.g. coupling
reactions with other ligands present on the cluster, most
commonly hydride, CO, or further alkynes, but also
alkylidynes and phosphinidenes.1 Moreover, terminal
alkynes often undergo rearrangement to form cluster-
bound vinylidenes (i.e. HCtCR f dCdCHR) or oxida-
tive addition to form alkynyl hydrides (HCtCR f
HMCtCR) (Scheme 1, path b).2
A much rarer form of activation involves the cleavage
of the CtC bond of disubstituted alkynes to produce two
alkylidyne ligands (Scheme 1, path c). About 15 ex-
amples of this process have been reported since it was
first observed; they encompass reactions on, or at least
leading to, dinuclear, trinuclear, tetranuclear, hexa-
nuclear, and heptanuclear clusters with both homo- and
heterometallic frameworks.3-5 The reverse process
(coupling of two alkylidynes to form an alkyne) is also
known,6 and indeed some of the alkyne scission reac-
tions are reversible. Often the CtC bond rupture is
induced by elimination of a CO ligand from the cluster,
either by heating or by use of Me3NO, and can subse-
quently be reversed simply by exposure to CO. Re-
cently, the scission of an acetylide ligand into alkylidyne
† E-mail: M.Morris@sheffield.ac.uk.
X Abstract published in Advance ACS Abstracts, September 1, 1996.
(1) (a) Hu¨bel, W. In Organic Syntheses via Metal Carbonyls; Wender,
I., Pino, P., Eds.; Wiley-Interscience: New York, 1968; Chapter 2, p
273. (b) Sappa, E.; Tiripicchio, A.; Braunstein, P. Chem. Rev. 1983,
83, 203. (c) Sappa, E.; Tiripicchio, A.; Braunstein, P. Coord. Chem. Rev.
1985, 65, 219. (d) Raithby, P. R.; Rosales, M. J . Adv. Inorg. Chem.
Radiochem. 1985, 29, 169.
(2) (a) Bruce, M. I.; Swincer, A. G. Adv. Organomet. Chem. 1983,
22, 59. (b) Bruce, M. I. Chem. Rev. 1991, 91, 197.
S0276-7333(96)00235-X CCC: $12 00 © 1996 American Chemical Society

+
+
Vinylidene and Bis(alkylidyne) Clusters
Organometallics, Vol. 15, No. 20, 1996 4183
and carbide has been described in the reaction of
WRu2(µ3-CtCPh)(CO)8Cp with Ru3(CO)12 to give WRu4-
(µ5-C)(µ-CPh)(CO)12Cp and WRu5(µ6-C)(µ-CPh)(CO)14Cp;
this can also be reversed under CO pressure.7
behavior of this important species on the catalyst
surface during the Fischer-Tropsch reaction, where it
is thought to be formed by the reduction of the surface
carbide resulting from the cleavage of CO;10 for example,
surface methylidyne ligands have been directly detected
after hydrogenation of predeposited carbide on a Ru(001)
surface.11 Few general routes to methylidyne clusters
exist and usually involve reduction of a CO ligand,
modification of a methylene group, or dehalogenation
of a C1 halocarbon such as CHCl3.12
This paper reports thermal reactions of the dimolyb-
denum alkyne complexes 1 with Ru3(CO)12 which ap-
parently involve competing processes of CsH and CsC
activation. By control of the conditions, alkyne scission
can be induced in several terminal alkynes, including
acetylene itself, to give octahedral Mo2Ru4 clusters with
methylidyne ligands, albeit in fairly modest yields. A
preliminary account of this work has appeared as a
communication.13
Prior to the work we describe here, only one instance
was known of the scission of a terminal alkyne on a
metal cluster, specifically the thermal reaction of Co-
(CO)2Cp with HCtCSiMe3 to give Co3(µ3-CH)(µ3-CSi-
Me3)Cp3, from which the parent bis(methylidyne) cluster
Co3(µ3-CH)2Cp3 could be obtained by protodesilylation.8
In most cases, activation of the C-H bonds of terminal
alkynes is evidently much more favorable than CtC
scission. One would instinctively expect this on bond
strength grounds,9 but it is somewhat unfortunate, as
scission reactions would provide a useful route to
clusters containing the simplest hydrocarbon frag-
ment: the methylidyne ligand, µ3-CH. Methylidyne
complexes are of interest as model systems for the
(3) Examples on, or leading to, trinuclear clusters are as follows.
Co3: (a) Fritch, J . R.; Vollhardt, K. P. C.; Thomson, M. R.; Day, V. W.
J . Am. Chem. Soc. 1979, 101, 2768. (b) Eaton, B.; O’Connor, J . M.;
Vollhardt, K. P. C. Organometallics 1986, 5, 394. (c) King, R. B.;
Murray, R. M.; Davis, R. E.; Ross, P. K. J . Organomet. Chem. 1987,
330, 115. (d) Yamazaki, H.; Wakatsuki, Y.; Aoki, K. Chem. Lett. 1979,
1041. (e) Quenec’h, P.; Rumin, R.; Pe´tillon, F. Y. J . Organomet. Chem.
1994, 479, 93. Co3 and Rh3: (f) King, R. B.; Harmon, C. A. Inorg. Chem.
1976, 15, 879. Co3, Rh3 and Ir3: (g) Clauss, A. D.; Shapley, J . R.; Wilker,
C. N.; Hoffmann, R. Organometallics 1984, 3, 619. Fe3: (h) Cabrera,
E.; Daran, J . C.; J eannin, Y. J . Chem. Soc., Chem. Commun. 1988,
607. W2Os: (i) Chi, Y.; Shapley, J . R. Organometallics 1985, 4, 1900.
W2Ru: (j) Stone, F. G. A.; Williams, M. L. J . Chem. Soc., Dalton Trans.
1988, 2467.
(4) Examples on, or leading to, tetranuclear clusters are as follows.
WOs3: (a) Park, J . T.; Shapley, J . R.; Churchill, M. R.; Bueno, C. J .
Am. Chem. Soc. 1983, 105, 6182. (b) Park, J . T.; Shapley, J . R.; Bueno,
C.; Ziller, J . W.; Churchill, M. R. Organometallics 1988, 7, 2307. (c)
Park, J . T.; Woo, B. W.; Chung, J .-H.; Shim, S. C.; Lee, J .-H.; Lim,
S.-S.; Suh, I.-H. Organometallics 1994, 13, 3384. W2Ir2: (d) Shapley,
J . R.; McAteer, C. H.; Churchill, M. R.; Biondi, L. V. Organometallics
1984, 3, 1595. WIr3: (e) Shapley, J . R.; Humphrey, M. G.; McAteer, C.
H. ACS Symp. Ser. 1993, No. 517, 127. Co2Fe2: (f) Rumin, R.; Robin,
F.; Pe´tillon, F. Y.; Muir, K. W.; Stevenson, I. Organometallics 1991,
10, 2274. Mo2Ni2 and Mo4Co3: (g) Shaposhnikova, A. D.; Drab, M. V.;
Kamalov, G. L.; Pasynskii, A. A.; Eremenko, I. L.; Nefedov, S. E.;
Struchkov, Y. T.; Yanovsky, A. I. J . Organomet. Chem. 1992, 429, 109.
(h) Pasynskii, A. A.; Eremenko, I. L.; Nefedov, S. E.; Kolobkov, B. I.;
Shaposhnikova, A. D.; Stadnitchenko, R. A.; Drab, M. V.; Struchkov,
Y. T.; Yanovsky, A. I. New J . Chem. 1994, 18, 69.
Exp er im en ta l Section
General experimental techniques were as described in
recent papers from this laboratory.14,15 Infrared spectra were
recorded in CH2Cl2 solution on a Perkin-Elmer 1600 FT-IR
machine using 0.5 mm NaCl cells. UV/visible spectra were
recorded in CH2Cl2 solution on a Unicam UV2 spectrometer
in glass cuvettes of path length 1 cm. 1H and 13C NMR spectra
were obtained in CDCl3 solution on a Bruker AC250 machine
with automated sample changer or an AMX400 spectrometer.
Chemical shifts are given on the δ scale relative to SiMe4 (0.0
ppm). The 13C{1H} NMR spectra were routinely recorded
using an attached proton test technique (J MOD pulse se-
quence). Mass spectra were recorded on a Fisons/BG Prospec
3000 instrument operating in the fast atom bombardment
mode with m-nitrobenzyl alcohol as matrix. Elemental analy-
ses were carried out by the Microanalytical Service of the
Department of Chemistry.
The complex Mo2(CO)6Cp2 was prepared by a literature
method.16 The alkyne complexes 1a -g were prepared by a
slight modification of the literature procedure, described
below.17
Syn th esis of Mo2(CO)4(µ-R1C2R2)Cp 2 (1a -g). A solution
of Mo2(CO)6Cp2 (3 g, 6.12 mmol) in toluene (200-300 mL) was
refluxed for 24 h with a stream of argon bubbling slowly
through it to form Mo2(CO)4Cp2. After the mixture was cooled
to room temperature, 5 equiv of the appropriate alkyne was
added; gaseous alkynes (HCtCH, HCtCMe) were bubbled
through the solution for a few minutes. After this mixture
was stirred overnight, the solvent was removed and the
products isolated by column chromatography. Small amounts
of unreacted Mo2(CO)6Cp2 can sometimes be separated before
elution of the product as a dark red band. Typical yields are
75-80%; we find that improved yields are consistently ob-
(5) Examples leading to higher nuclearity clusters are as follows.
Ru6: (a) Haggitt, J . L.; J ohnson, B. F. G.; Blake, A. J .; Parsons, S. J .
Chem. Soc., Chem. Commun. 1995, 1263. Os6: (b) Gomez-Sal, M. P.;
J ohnson, B. F. G.; Kamarudin, R. A.; Lewis, J .; Raithby, P. R. J . Chem.
Soc., Chem. Commun. 1985, 1622. (c) Fernandez, J . M.; J ohnson, B.
F. G.; Lewis, J .; Raithby, P. R. Acta Crystallogr., Sect. B 1978, 34B,
3086. (d) Eady, C. R.; Fernandez, J . M.; J ohnson, B. F. G.; Lewis, J .;
Raithby, P. R.; Sheldrick, G. M. J . Chem. Soc., Chem. Commun. 1978,
421. Os7: (e) J ohnson, B. F. G.; Lewis, J .; Lunniss, J . A.; Braga, D.;
Grepioni, F. J . Chem. Soc., Chem. Commun. 1988, 972. (f) Braga, D.;
Grepioni, F.; J ohnson, B. F. G.; Lewis, J .; Lunniss, J . A. J . Chem. Soc.,
Dalton Trans. 1991, 2223. (g) Braga, D.; Grepioni, F.; J ohnson, B. F.
G.; Lewis, J .; Lunniss, J . A. J . Chem. Soc., Dalton Trans. 1992, 1101.
(6) For examples on closely related W2Ru clusters see: (a) Busetto,
L.; Green, M.; Hessner, B.; Howard, J . A. K.; J effery, J . C.; Stone, F.
G. A. J . Chem. Soc., Dalton Trans. 1983, 519. (b) Howard, J . A. K.;
Laurie, J . C. V.; J ohnson, O.; Stone, F. G. A. J . Chem. Soc., Dalton
Trans. 1985, 2017. Other examples: (c) Nuel, D.; Dahan, F.; Mathieu,
R. Organometallics 1985, 4, 1436. (d) Lentz, D.; Michael, H. Angew.
Chem. Int. Ed. Engl. 1988, 27, 845. (e) Vollhardt, K. P.; Wolfgruber,
M. Angew. Chem., Int. Ed. Engl. 1986, 25, 929.
(10) (a) Muetterties, E. L.; Rhodin, T. N.; Band, E.; Brucker, C. F.;
Pretzer, W. R. Chem. Rev. 1979, 79, 91. (b) Muetterties, E. L.; Stein,
J . Chem. Rev. 1979, 79, 479. (c) Rofer-DePoorter, C. K. Chem. Rev.
1981, 81, 447. (d) Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1982,
21, 117.
(7) Chiang, S.-J .; Chi, Y.; Su, P.-C.; Peng, S.-M.; Lee, G.-H. J . Am.
Chem. Soc. 1994, 116, 11181.
(8) Fritch, J . R.; Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl.
1980, 19, 559. A further example was observed in solution, but the
product was not isolated: Hriljac, J . A.; Shriver, D. F. J . Am. Chem.
Soc. 1987, 109, 6011.
(11) Barteau, M. A.; Feulner, P.; Stengl, R.; Broughton, J . Q.;
Menzel, D. J . Catal. 1985, 94, 51.
(12) Akita, M.; Noda, K.; Moro-oka, Y. Organometallics 1994, 13,
4145 and references therein.
(13) Adams, H.; Gill, L. J .; Morris, M. J . J . Chem. Soc., Chem.
Commun. 1995, 899; see also correction on p 1309.
(14) Adams, H.; Gill, L. J .; Morris, M. J . Organometallics 1996, 15,
464.
(15) Adams, H.; Bailey, N. A.; Gill, L. J .; Morris, M. J .; Wildgoose,
F. A. J . Chem. Soc., Dalton Trans. 1996, 1437.
(16) King, R. B. Organometallic Syntheses; Academic Press: New
York, 1965; Vol. 1, p 109.
(9) Estimates of the CsH and CtC bond strengths in acetylene are
535 and 960 kJ mol-1, respectively. Even when allowance is made for
the weakening of the CtC bond on coordination of the alkyne to a
dimolybdenum center, it is still the stronger of the two; for example
in complexes 1 the CtC bond length is around 1.33 Å, similar to that
in ethylene (1.337 Å), where the CdC bond strength is 719 kJ mol-1
.
Data from: Weast, R. C., Ed. Handbook of Chemistry and Physics;
CRC Press: Boca Raton, FL, 1977.
(17) Bailey, W. I., J r.; Chisholm, M. H.; Cotton, F. A.; Rankel, L. A.
J . Am. Chem. Soc. 1978, 100, 5764.

+
+
4184 Organometallics, Vol. 15, No. 20, 1996
Adams et al.
2d : IR ν(CO) 2062 s, 2006 s, 1989 m, 1967 m, 1923 w cm-1
tained by stirring the second stage of the reaction overnight
as opposed to the 4 h recommended previously.17
;
1H NMR δ 5.29 (s, 5 H, Cp), 5.17 (s, 5 H, Cp), 5.11 (s, 1 H,
CH), 3.69 (s, 3 H, Me); 13C NMR δ 299.1 (µ3-C), 231.5, 229.4,
228.8, 222.3 (all MosCO), 197.8, 196.5, 193.1 (all RusCO),
172.0 (CO2Me), 93.2 (Cp), 90.8 (Cp), 79.5 (CH), 51.6 (Me); MS
m/ e 705 (M+). Anal. Calcd for C21H14O9Mo2Ru‚CH2Cl2: C,
33.50; H, 2.03. Found: C, 33.92; H, 1.78.
Syn th esis of Mo2Ru (µ3-CdCH2)(CO)7Cp 2 (2a ). A solu-
tion of 1a (250 mg, 0.543 mmol) and Ru3(CO)12 (521 mg, 0.815
mmol) in 175 mL of toluene was heated to reflux. The reaction
was monitored by TLC until the starting material had disap-
peared. After 22 h, silica (5 g) was added, the solvent was
removed on a rotary evaporator, and the residue was loaded
onto a chromatography column. Elution with petroleum ether
and then petroleum ether/CH2Cl2 (19:1) removed a yellow band
containing Ru3(CO)12 followed by faint orange, pink, pink, and
blue bands, the last of these consisting of minute quantities
of 3a . Careful elution with petroleum ether/CH2Cl2 (9:1)
produced an orange band of 2a (137 mg, 0.212 mmol, 39.0%)
followed by a darker red-brown zone of Ru6(µ6-C)(CO)14(η-C6H5-
Me) (31 mg, 0.028 mmol, 7.0%).
3d : IR ν(CO) 2071 w, 2046 s, 2019 s, 1980 w, 1955 w cm-1
;
UV/vis λmax 312 nm (ꢀ 14 430 dm3 mol-1 cm-1), 589 nm (ꢀ 2290
1
dm3 mol-1 cm-1); H NMR δ 16.32 (s, 1 H, µ3-CH), 5.16 (s, 10
H, Cp), 3.96 (s, 3 H, Me); 13C NMR δ 324.7 (µ3-CH), 317.3 (µ3-
CCO2Me), 204.9 (CO), 203.8 (CO), 201.7 (6 CO), 192.6 (2 CO),
192.5 (2 CO), 182.6 (CO2Me), 96.1 (Cp), 52.7 (Me); MS m/ e
1147 (M+). Anal. Calcd for C26H14O14Mo2Ru4: C, 27.23; H,
1.22. Found: C, 27.14; H, 1.23.
Syn th esis of Mo2Ru 4(µ3-CH)2(CO)12Cp 2 (3a ). A solution
of 1a (1.00 g, 2.17 mmol) and Ru3(CO)12 (1.389 g, 2.17 mmol)
in heptane (175 mL) was heated to reflux for 24 h. After this
time TLC indicated the presence of unreacted dimolybdenum
complex; a further 0.5 equiv of Ru3(CO)12 was added and
heating continued for a further 20 h. The mixture was then
absorbed onto silica and chromatographed. Elution with
petroleum ether gave a yellow band of Ru3(CO)12 followed by
an orange band of H4Ru4(CO)12 (351 mg, 0.471 mmol, 10.9%).
After a faint pink band, the blue cluster 3a (106.3 mg, 0.098
mmol, 4.5%) was separated by careful elution with petroleum
ether/CH2Cl2 (19:1). Orange 2a (538.1 mg, 0.834 mmol, 38.4%)
was then eluted with petroleum ether/CH2Cl2 (5:1).
2a : IR ν(CO) 2058 s, 2001 s, 1983 m, 1961 m, 1916 w, 1840
1
m cm-1; H NMR δ 5.21 (s, 10 H, Cp), 4.61 (s, 2 H, CH2); 13C
NMR δ 295.9 (µ3-C), 231.0 (MosCO), 226.9 (MosCO), 198.5
(RusCO), 195.2 (2 RusCO), 91.1 (Cp), 71.2 (CH2); MS m/ e
646 (M+). Anal. Calcd for C19H12O7Mo2Ru: C, 35.35; H, 1.75.
Found: C, 35.18; H, 1.75.
Syn th esis of Mo2Ru (µ3-CdCHMe)(CO)7Cp 2 (2b). In a
manner similar to that above, a mixture of 1b (1.95 g, 4.07
mmol) and Ru3(CO)12 (2.56 g, 4.00 mmol) in toluene (150 mL)
was heated to reflux for 18 h. Chromatography, with petro-
leum ether as eluent, gave a small amount of Ru3(CO)12
followed by H2Ru4(CO)13 (117.4 mg). Subsequent elution with
petroleum ether/CH2Cl2 (19:1) afforded a blue band of 3b
(114.1 mg, 0.103 mmol, 2.6%). Elution with petroleum ether/
CH2Cl2 (4:1 and then 3:1) produced two major fractions,
orange-red 2b (1.1684 g, 1.77 mmol, 44.3%) and red-brown
Ru6(µ6-C)(CO)14(η-C6H5Me) (155.3 mg, 0.142 mmol, 3.6%). A
large black band (300 mg), which presumably consists of higher
nuclearity ruthenium clusters judging from the absence of any
Cp signals in its 1H NMR spectrum, could be eluted in CH2-
Cl2 but was not investigated further.
3a : IR ν(CO) 2068 w, 2039 s, 2012 s, 1980 w, 1949 w cm-1
;
UV/vis λmax 317 nm (ꢀ 8700 dm3 mol-1 cm-1), 589 nm (ꢀ 1440
1
dm3 mol-1 cm-1); H NMR δ 16.58 (s, 2 H, µ3-CH), 5.06 (s, 10
H, Cp); 13C NMR δ 323.4 (µ3-CH), 204.7 (2 CO), 202.3 (6 CO),
192.8 (4 CO), 94.2 (Cp); MS m/ e 1089 (M+). Anal. Calcd for
C
24H12O12Mo2Ru4: C, 26.47; H, 1.10. Found: C, 25.99; H, 1.03.
Syn th esis of Mo2Ru 4(µ3-CH)(µ3-CMe)(CO)12Cp 2 (3b). A
solution of 1b (850 mg, 1.79 mmol) and Ru3(CO)12 (1.71 g, 2.69
mmol) in heptane (200 mL) was refluxed for 33 h. Chromato-
graphic separation of the product mixture, with petroleum
ether as eluent, gave a small amount of Ru3(CO)12 and 400
mg of H2Ru4(CO)13. Careful elution with petroleum ether/CH2-
Cl2 (19:1) produced a blue band of 3b (182 mg, 0.165 mmol,
9.2%). Finally, an orange band of 2b (656.9 mg, 1.00 mmol,
55.8%) was removed with petroleum ether/CH2Cl2 (4:1).
2b: IR ν(CO) 2056 s, 1998 s, 1982 m, 1962 m, 1909 w, 1841
1
m cm-1; H NMR δ 5.21 (q, J ) 6 Hz, 1 H, CH), 5.15 (s, 5 H,
Cp), 5.08 (s, 5 H, Cp), 1.83 (d, J ) 6 Hz, 3 H, Me); 13C NMR δ
290.6 (µ3-C), 233.8, 230.7, 229.5, 222.8 (all MosCO), 198.4,
197.2, 193.5 (all RusCO), 91.5 (Cp), 91.1 (CHMe), 90.5 (Cp),
29.3 (Me); MS m/ e 660 (M+). Anal. Calcd for C20H14O7Mo2-
Ru: C, 36.42; H, 2.12. Found: C, 36.42; H, 1.99.
3b: IR ν(CO) 2064 m, 2036 s, 2013 s, 1980 w, 1949 w cm-1
;
UV/vis λmax 313 nm (ꢀ 15 360 dm3 mol-1 cm-1), 589 nm (ꢀ 2550
1
dm3 mol-1 cm-1); H NMR δ 16.60 (s, 1 H, µ3-CH), 5.04 (s, 10
Syn th esis of Mo2Ru (µ3-CdCHP h )(CO)7Cp 2 (2c). A solu-
tion of 1c (0.75 g, 0.93 mmol) and Ru3(CO)12 (0.894 g, 1.40
mmol) in toluene was heated to reflux for 18 h. The reaction
mixture was subjected to chromatographic workup as before.
Petroleum ether eluted small amounts of Ru3(CO)12 and H2-
Ru4(CO)13. After descent of a faint pink band, a blue band of
3c (35 mg, 0.03 mmol, 3.2%) was eluted with petroleum ether/
CH2Cl2 (9:1), followed by an unidentified yellow-green zone
and then orange 2c (204 mg, 0.28 mmol, 30.4%). Finally, a
small amount of Ru6(µ6-C)(CO)14(η-C6H5Me) was collected.
2c: IR ν(CO) 2058 s, 2001 s, 1983 m, 1964 m, 1911 w, 1845
m cm-1; 1H NMR δ 7.40-7.19 (m, 5 H, Ph), 6.28 (s, 1 H, CH),
5.25 (s, 5 H, Cp), 5.12 (s, 5 H, Cp); 13C NMR δ 290.6 (µ3-C),
233.7, 229.9, 229.6, 222.5 (all MosCO), 198.3, 197.7, 192.2 (all
RusCO), 143.9 (Cipso), 128.1, 127.7, 127.0 (all Ph), 98.9 (CHPh),
92.5 (Cp), 91.2 (Cp); MS m/ e 722 (M+). Anal. Calcd for
C25H16O7Mo2Ru: C, 41.61; H, 2.22. Found: C, 41.58; H, 2.13.
H, Cp), 4.07 (s, 3 H, Me); 13C NMR δ 353.3 (µ3-CMe), 323.1
(µ3-CH), 206.2 (CO), 204.0 (CO), 202.4 (6 CO), 194.6 (2 CO),
192.4 (2 CO), 95.7 (Cp), 51.4 (Me); MS m/ e 1103 (M+). Anal.
Calcd for C25H14O12Mo2Ru4: C, 27.22; H, 1.27. Found: C,
27.06; H, 1.18.
Syn th esis of Mo2Ru 4(µ3-CH)(µ3-CP h )(CO)12Cp 2 (3c). A
solution of 1c (500 mg, 0.93 mmol) and Ru3(CO)12 (894 mg,
1.40 mmol) in heptane (150 mL) was heated to reflux for 30 h
and subjected to chromatographic workup as above. After
elution of Ru3(CO)12 and 1c, cluster 3c was eluted with CH2-
Cl2/petroleum ether (1:4) as a blue band (81 mg, 0.07 mmol,
7.5%). Further elution with a 2:3 mixture of the same solvents
produced an orange band of 2c (402 mg, 37.0%).
3c: IR ν(CO) 2066 m, 2038 s, 2016 s, 1986 w, 1922 w cm-1
;
UV/vis λmax 308 nm (ꢀ 17 820 dm3 mol-1 cm-1), 605 nm (ꢀ 3670
dm3 mol-1 cm-1); 1H NMR δ 16.86 (s, 1 H, CH), 7.31-6.68 (m,
5 H, Ph), 4.96 (s, 10 H, Cp); 13C NMR δ 348.5 (µ3-CPh), 327.7
(µ3-CH), 207.4 (CO), 202.6 (CO), 202.1 (6 CO), 195.3 (2 CO),
192.1 (2 CO), 166.6 (Cipso), 128.2, 125.4 (Ph), 97.1 (Cp); MS
m/ e 1163 (M+). Anal. Calcd for C30H16O12Mo2Ru4: C, 30.93;
H, 1.37. Found: C, 30.63; H, 1.31.
Syn th esis of Mo2Ru (µ3-CdCHCO2Me)(CO)7Cp2 (2d) an d
Mo2Ru 4(µ3-CH)(µ3-CCO2Me)(CO)12Cp 2 (3d ). A solution of
1d (300 mg, 0.58 mmol) and Ru3(CO)12 (550 mg, 0.86 mmol)
in heptane was heated to reflux for 24 h. Column chroma-
tography of the products yielded two major fractions: blue 3d
(110.3 mg, 0.10 mmol, 16.6%), which was eluted by petroleum
ether/CH2Cl2 (3:1), and then orange 2d (177.5 mg, 0.25 mmol,
43.6%), which was eluted by a 3:2 mixture of the same
solvents.
Syn th esis of Mo2Ru 4(µ3-CMe)2(CO)12Cp 2 (3e). A solution
of 1e (250 mg, 0.51 mmol) and Ru3(CO)12 (491 mg, 0.77 mmol)
in toluene was refluxed for 18 h. Chromatography produced
a weak red band of dimolybdenum starting material followed
by a blue band due to 3e (158.7 mg, 0.14 mmol, 27.8%), which

+
+
Vinylidene and Bis(alkylidyne) Clusters
Organometallics, Vol. 15, No. 20, 1996 4185
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta for Com p lexes 2b a n d 3e‚CH2Cl2
2b 3e‚CH2Cl2
identification code
formula
lg123x
20H14Mo2O7Ru
lg514
C27H18Cl2Mo2O12Ru4
C
fw
659.26
1201.47
temp, K
293(2)
293(2)
wavelength, Å
cryst syst
space group
unit cell dimens
0.710 73
monoclinic
P21/n
0.710 73
monoclinic
P21/n
a ) 9.3070(10) Å, b ) 16.190(2) Å,
a ) 15.126(3) Å, b ) 14.672(2) Å,
c ) 13.9550(10) Å, â ) 96.350 (10)°
c ) 15.196(2) Å, â ) 91.810(10)°
V, Å3
2089.8 (4)
3370.7 (9)
Z
4
4
density (calcd), Mg/m3
abs coeff, mm-1
2.095
1.934
2.368
2.685
F(000)
1272
2280
cryst size, mm
θ range for data collection, deg
index ranges
0.65 × 0.44 × 0.35
0.65 × 0.40 × 0.40
1.93-22.5
1.87-22.51
-1 e h e 10, -1 e k e 17, -15 e l e 15
3435
2715 (Rint ) 0.0450)
full-matrix least squares on F2
2715/0/271
-1 e h e 14, -1 e k e 15, -16 e l e 16
5365
4316 (Rint ) 0.0233)
full-matrix least squares on F2
4315/0/424
no. of rflns collected
no. of indep rflns
refinement method
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
largest diff peak and hole, e Å-3
1.274
1.224
R1 ) 0.0476, wR2 ) 0.1205
R1 ) 0.0498, wR2 ) 0.1225
0.722 and -2.711
R1 ) 0.0384, wR2 ) 0.0985
R1 ) 0.0436, wR2 ) 0.1018
0.683 and -2.035
was eluted in petroleum ether/CH2Cl2 (9:1). A small band of
Ru6(µ6-C)(CO)14(η-C6H5Me) was also collected. The reaction
can also be performed in heptane with no significant change
in yield.
phosphines, thiols, or elemental sulfur and that the
products obtained often retain the alkyne ligands.20
Moreover, their identities depend on the electronic and
steric properties of R1 and R2, the alkyne substituents.
For this reason we always tend to explore the reactions
of a range of such compounds rather than just a single
example.
3e: IR ν(CO) 2063 m, 2034 s, 2012 s, 1980 w, 1949 w cm-1
;
UV/vis λmax 310 nm (ꢀ 15 430 dm3 mol-1 cm-1), 582 nm (ꢀ 3030
dm3 mol-1 cm-1); H NMR δ 5.15 (s, 10 H, Cp), 4.11 (s, 6 H,
1
Me); 13C NMR δ 353.9 (µ3-C), 205.5 (2 CO), 202.5 (6 CO), 194.4
(4 CO), 97.3 (Cp), 52.4 (Me); MS m/ e 1117 (M+). Anal. Calcd
for C26H16O12Mo2Ru4: C, 27.96; H, 1.43. Found: C, 27.81; H,
1.36.
One of the established routes to higher nuclearity
alkyne clusters is the reaction of preformed alkyne
complexes with suitable metal fragments. Initially our
objective in this work was to explore whether com-
pounds of type 1 could be used as precursors to higher
nuclearity alkyne clusters, since similar cluster-forming
reactions are already known for related alkyne com-
plexes such as Co2(CO)6(µ-R1C2R2), Ni2(µ-C2Ph2)Cp2, and
recently Ru2(µ-CO)(µ-C2R2)Cp2 (R ) Ph, CF3).3e,4f-h,21
Scheme 2 shows the reactions carried out in the
present work. Heating the terminal alkyne complexes
1a -d (R1 ) H, R2 ) H, Me, Ph, CO2Me) in toluene with
1-1.5 equiv of Ru3(CO)12 resulted in the gradual disap-
pearance of the red dimolybdenum compound and the
formation of two major products (one orange and one
slightly darker red), as monitored by TLC. Separation
by careful column chromatography provided the vi-
nylidene clusters Mo2Ru(µ3-CdCHR2)(CO)7Cp2 (2a -d )
as air-stable orange-red solids in moderate yields (30-
45%). In each case the second product obtained was the
hexanuclear carbido cluster Ru6(µ6-C)(CO)14(η-C6H5Me),
which is known to be formed when Ru3(CO)12 is heated
Cr ysta l Str u ctu r e Deter m in a tion s of 2b a n d 3e. The
crystal data for the two structures are summarized in Table
1. Three-dimensional, room-temperature X-ray data were
collected on a Siemens P4 diffractometer by the ω-scan method.
The independent reflections for which |F|/σ(|F|) > 4.0 were
corrected for Lorentz and polarization effects, but not for
absorption. The structures were solved by direct methods and
refined by full-matrix least squares on F2. Hydrogen atoms
were included in calculated positions and refined in the riding
mode. Refinement converged at the final R values shown with
allowance for the thermal anisotropy of all non-hydrogen
atoms. Weighting schemes w ) 1/[σ2(Fo2) + (0.0748P)2
+
1.57P] (for 2b) and w ) 1/[σ2(Fo2) + (0.0564P)2 + 2.98P] (for
3e), where P ) (Fo2 + 2Fc2)/3, were used in the latter stages of
refinement. Complex scattering factors were taken from the
program package SHELXL93,18 as implemented on the Viglen
486dx computer.
Resu lts a n d Discu ssion
Syn th esis of Vin ylid en e Clu ster s 2a -d . The
dimolybdenum alkyne complexes Mo2(CO)4(µ-R1CtCR2)-
Cp2 (1a -g) can be conveniently prepared in 75-80%
yield by a one-pot process from Mo2(CO)6Cp2.17 The
incorporation of the alkyne ligand greatly modifies the
reactivity of the dimolybdenum center compared to
Mo2(CO)6Cp2 and Mo2(CO)4Cp2, both of which have been
extensively studied.19 As a result, we and others have
shown previously that the alkyne compounds can act
as useful starting materials for further reactions with
(19) (a) Curtis, M. D. Polyhedron 1987, 6, 759. (b) Winter, M. J . Adv.
Organomet. Chem. 1989, 29, 101. (c) Morris, M. J . In Comprehensive
Organometallic Chemistry II; Wilkinson, G., Stone, F. G. A., Abel, E.
W., Eds.; Pergamon: Oxford, U.K., 1995; Vol. 5, Chapter 7.
(20) (a) Doel, G. R.; Feasey, N. D.; Knox, S. A. R.; Orpen, A. G.;
Webster, J . J . Chem. Soc., Chem. Commun. 1986, 542. (b) Conole, G.;
Hill, K. A.; McPartlin, M.; Mays, M. J .; Morris, M. J . J . Chem. Soc.,
Chem. Commun. 1989, 688. (c) Conole, G.; McPartlin, M.; Mays, M.
J .; Morris, M. J . J . Chem. Soc., Dalton Trans. 1990, 2359. (d) Adams,
H.; Bailey, N. A.; Gay, S. R.; Hamilton, T,; Morris, M. J . J . Organomet.
Chem. 1995, 493, C25. (e) Abbott, A.; Bancroft, M. N.; Gill, L. J .; Morris,
M. J .; Hogarth, G.; Redmond, S. Manuscript in preparation.
(21) (a) Robin, F.; Rumin, R.; Pe´tillon, F. Y.; Foley, K.; Muir, K. W.
J . Organomet. Chem. 1991, 418, C33. (b) Adams, K. J .; Barker, J . J .;
Charmant, J . P. H.; Ganter, C.; Klatt, G.; Knox, S. A. R.; Orpen, A. G.;
Ruile, S. J . Chem. Soc., Dalton Trans. 1994, 477.
(18) Sheldrick, G. M. SHELXL93, an Integrated System for Solving
and Refining Crystal Structures from Diffraction Data (Revision 5.1);
University of Go¨ttingen: Go¨ttingen, Germany, 1993.

+
+
4186 Organometallics, Vol. 15, No. 20, 1996
Adams et al.
Sch em e 2
in toluene.22 In some reactions (particularly those of
1c), low yields (i.e. traces) of the hexanuclear bis-
(alkylidyne) clusters 3 described below were also ob-
tained.
The vinylidene clusters 2a -d were characterized by
their IR, 1H and 13C NMR, and mass spectra. All show
a similar pattern of six peaks in the IR spectrum
consisting of two sharp absorptions, which we ascribe
to the Ru(CO)3 unit, and four broader peaks at lower
wavenumber, which we assign to the MosCO groups.
The presence of the vinylidene ligand is evident from
the NMR spectra; thus, the 1H NMR spectrum of 2b
shows a doublet and a quartet (J ) 6 Hz) characteristic
of a dCHMe group, and the 13C spectra of all four
compounds contain a peak between 290 and 296 ppm
due to the µ3-C atom and a peak between 70 and 100
ppm due to the â-carbon. The spectra were recorded
with an attached proton test technique (J MOD spec-
trum), which enabled this peak to be identified as a CH2
(for 2a ) or CHR2 carbon (for 2b-d ) as appropriate. In
addition, the 13C NMR spectra display two groups of
carbonyl peaks, those between 220 and 235 ppm as-
signed to the Mo-CO groups and others in the range
190-200 ppm assigned to the CO ligands on Ru.
Complex 2a evidently has a symmetrical structure in
solution, leading to four CO peaks in a ratio of 2:2:2:1,
whereas in the unsymmetrical compounds 2b-d , all
seven CO ligands are inequivalent. This asymmetry is
F igu r e 1. ORTEP plot of the molecular structure of Mo2-
Ru(µ3-CdCHMe)(CO)7Cp2 (2b) in the crystal.
The structure of 2b, derived from propyne, has been
determined by X-ray diffraction. A perspective view of
the molecule is shown in Figure 1 with selected bond
lengths and angles given in Table 2.
1
also reflected in the Cp signals in both H and 13C NMR
spectra. The complexes all gave clear molecular ion
peaks in their FAB mass spectra, with peaks corre-
sponding to CO losses also present.
The structure is based on a triangle of two molybde-
num atoms and one ruthenium atom. The two Mo-Ru
bonds are slightly unequal in length, with Mo(1)-Ru(1)
being slightly longer than Mo(2)-Ru(1) (2.9272(7) as
opposed to 2.8935(7) Å), but both are within the range
found in other Mo-Ru clusters.23 The Mo(1)-Mo(2)
(22) (a) J ohnson, B. F. G.; J ohnston, R. D.; Lewis, J . J . Chem. Soc.
A 1968, 2856. (b) Eady, C. R.; J ohnson, B. F. G.; Lewis, J . J . Chem.
Soc., Dalton Trans. 1975, 2606.

+
+
Vinylidene and Bis(alkylidyne) Clusters
Organometallics, Vol. 15, No. 20, 1996 4187
rearranged to the vinylidene on heating.27 In agree-
ment with this, in a study of interconvertible triply
bridging terminal alkyne, vinylidene, and (by hydroge-
nation) alkylidyne ligands on a range of trinuclear metal
cluster centers, Vahrenkamp found that the vinylidene
was the favored form.28 No evidence for the formation
of alkyne clusters was obtained in the present work,
though given the conditions of the reaction it is possible
that they were formed as intermediates.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 2b
Mo(1)-C(2)
Mo(1)-C(18)
Mo(1)-Mo(2)
Ru(1)-C(5)
Ru(1)-C(18)
Ru(1)-Mo(2)
Mo(2)-C(4)
C(18)-C(19)
1.979(7)
2.088(6)
3.0277(8)
1.911(8)
2.123(6)
2.8935(7)
1.979(8)
1.380(9)
Mo(1)-C(1)
Mo(1)-Ru(1)
Ru(1)-C(6)
Ru(1)-C(7)
Ru(1)-C(19)
Mo(2)-C(3)
Mo(2)-C(18)
C(19)-C(20)
1.992(7)
2.9272(7)
1.893(7)
1.916(8)
2.325(7)
1.956(7)
2.090(6)
1.515(9)
Syn th esis of Bis(a lk ylid yn e) Clu ster s 3a -e. Re-
alizing that dimolybdenum complexes of disubstituted
alkynes would be unable to undergo rearrangement to
form vinylidene clusters, we also investigated the
behavior of the but-2-yne complex 1e (R1 ) R2 ) Me)
toward ruthenium carbonyl under the same reaction
conditions. Two major products were formed, the second
of which was again Ru6(µ6-C)(CO)14(η-C6H5Me). The
first was royal blue and was characterized as the
hexanuclear bis(ethylidyne) cluster Mo2Ru4(µ3-CMe)2-
(CO)12Cp2 (3e), as described below. The reaction can
also be carried out in heptane with little alteration in
the yield of the product, which was a reasonable 28%.
However, when we tried to extend the reaction to
complexes of bulkier disubstituted alkynes, namely
EtCtCEt (1f) and MeO2CCtCCO2Me (1g), no tractable
products were obtained in either case.
Since the hexaruthenium toluene complex is an
unwanted side product in the synthesis of the vinylidene
clusters described above, we also investigated the reac-
tion of 1a -d with Ru3(CO)12 in heptane. As expected,
this strategy for eliminating the arene cluster was
successful, and good yields of 2a -d were still obtained;
however, an unforeseen bonus was that the blue bis-
(alkylidyne) clusters 3a-d, which were generally formed
in only trace amounts or not at all in toluene solution,
were now produced in somewhat increased yields (rang-
ing from 4.5% for 3a to 16% for 3d ), which enabled their
complete characterisation.
Ru(1)-Mo(1)-Mo(2) 58.11(2) Mo(2)-Ru(1)-Mo(1) 62.68(2)
Ru(1)-Mo(2)-Mo(1) 59.20(2) O(1)-C(1)-Mo(1)
175.6(5)
168.0(6)
177.1(7)
175.9(7)
O(2)-C(2)-Mo(1)
O(4)-C(4)-Mo(2)
O(6)-C(6)-Ru(1)
165.9(5) O(3)-C(3)-Mo(2)
173.7(6) O(5)-C(5)-Ru(1)
177.2(6) O(7)-C(7)-Ru(1)
C(19)-C(18)-Mo(1) 132.4(5) C(19)-C(18)-Mo(2) 131.7(5)
Mo(1)-C(18)-Mo(2) 92.9(2) C(19)-C(18)-Ru(1)
Mo(1)-C(18)-Ru(1)
C(18)-C(19)-Ru(1)
80.1(4)
86.7(2)
88.1(2) Mo(2)-C(18)-Ru(1)
64.1(4)
bond length is 3.0277(8) Å. The metal triangle is
spanned by a triply bridging methylvinylidene fragment
which is formally σ-bound to the two molybdenum atoms
and π-bound to ruthenium; the µ3-C atom C(18) caps
the triangle virtually symmetrically. The C(18)-C(19)
bond length of 1.380(9) Å is typical for µ3-vinylidene
ligands.2 The ruthenium atom bears three CO ligands,
which are all virtually linear. Each molybdenum atom
bears two carbonyls, one of which is closer to linearity
than the other; CO ligands C(2)-O(2) and C(3)-O(3)
are the most nonlinear with angles of 165.9(5) and
168.0(6)°, respectively. These deviations are large
enough to designate these ligands semibridging (they
have asymmetry parameters of 0.364 and 0.462, respec-
tively)24 and do not appear to result from crystal-packing
effects, since similar nonlinearity is observed in the
substituted analogue Mo2Ru(µ3-CdCHMe)(CO)6(PPh2-
Me).25 Moreover, the structure of 2b bears a striking
resemblance to that of Mo2Ru(µ3-S)(CO)7Cp2, which has
a capping sulfur atom in place of the vinylidene ligand.26
The metal frameworks of the two clusters are almost
identical, and it is interesting to note that the two Mo-
Ru bond lengths in the sulfur-capped cluster were also
unequal (2.9129(8) and 2.8989(9) Å). A slightly different
pattern of semibridging carbonyls was present, though
the maximum deviation from linearity was similar to
that in the present case.
Compounds 3a -e are all blue, air-stable solids which
were initially characterized spectroscopically. The ob-
servation of molecular ions in their mass spectra,
together with 12 successive CO loss peaks, indicated
that hexanuclear clusters had been formed. Confirma-
tion of alkyne scission in 3a -e was obtained from their
1
1H and 13C NMR spectra. The H spectra consist of one
The formation of triply bridging vinylidene ligands
by the rearrangement of alkyne ligands in dinuclear
complexes on reaction with metal carbonyls is well
established, e.g. the synthesis of FeCo2(µ3-CdCHR)(CO)9
(R ) H, Me, Ph, tBu) from Co2(µ-HCtCR)(CO)6 and Fe2-
(CO)9 or Fe3(CO)12. In some cases the initial product
was the corresponding µ3-alkyne cluster, which then
peak for the equivalent Cp ligands together with ap-
propriate signals for R1 and R2; in the symmetrical
complexes 3a and 3e the two alkylidyne substituents
are clearly equivalent. For the methylidyne complexes
3a -d , the 1H NMR peaks due to the µ3-CH groups occur
at around δ 16.5, which is typical for such ligands.12,29
The 13C NMR spectra also show the low-field resonances
characteristic of µ3-alkylidyne ligands between 320 and
360 ppm. Again for the symmetrical compounds 3a and
3e only one peak is observed, showing that the two
alkylidyne ligands are in equivalent environments. For
(23) (a) Cazanoue, M.; Lugan, N.; Bonnet, J .-J .; Mathieu, R. Orga-
nometallics 1988, 7, 2480. (b) Wang, J .-C.; Chi, Y.; Peng, S.-M.; Lee,
G.-H.; Shyu, S.-G.; Tu, F.-H. J . Organomet. Chem. 1994, 481, 143. (c)
Chi, Y.; Su, C.-J .; Farrugia, L. J .; Peng, S.-M.; Lee, G.-H. Organome-
tallics 1994, 13, 4167.
(24) (a) Curtis, M. D.; Han, K. R.; Butler, W. M. Inorg. Chem. 1980,
19, 2096; (b) Klingler, R. J .; Butler, W. M.; Curtis, M. D. J . Am. Chem.
Soc. 1978, 100, 5034. The long MsCO distances in 2b are C(2)-Ru(1)
) 2.700 Å and C(3)-Mo(1) ) 2.860 Å.
(27) Albiez, T.; Bernhardt, W.; von Schnering, C.; Roland, E.; Bantel,
H.; Vahrenkamp, H. Chem. Ber. 1987, 120, 141.
(28) Bernhardt, W.; Schacht, H.-T.; Vahrenkamp, H. Z. Naturforsch.,
B 1989, 44, 1060.
(29) For examples of Ru3(µ3-CH) complexes, see: (a) Kakigano, T.;
Suzuki, H.; Igarishi, M.; Moro-oka, Y. Organometallics 1990, 9, 2192.
(b) Keister, J . B.; Horling, T. L. Inorg. Chem. 1980, 19, 2304. (c) Morris,
M. J . Ph.D. Thesis, University of Bristol, 1984. For mixed-metal
systems, see: (d) Duffy, D. N.; Kassis, M. M.; Rae, A. D. J . Organomet.
Chem. 1993, 460, 97. (e) Schacht, H. T.; Vahrenkamp, H. J . Organomet.
Chem. 1990, 381, 261.
(25) Adams, H.; Bailey, N. A.; Gill, L. J .; Morris, M. J .; Sadler, N.
D. manuscript in preparation.
(26) (a) Richter, F.; Roland, E.; Vahrenkamp, H. Chem. Ber. 1984,
117, 2429. (b) Adams, R. D.; Babin, J . E.; Tasi, M. Organometallics
1988, 7, 219. (c) Adams, R. D.; Babin, J . E.; Tasi, M.; Wang, J .-G.
Organometallics 1988, 7, 755. (d) Adams, R. D.; Babin, J . E.; Tasi, M.
Angew. Chem., Int. Ed. Engl. 1987, 26, 685. (e) Adams, R. D.; Babin,
J . E.; Tasi, M. Organometallics 1987, 6, 2247.

+
+
4188 Organometallics, Vol. 15, No. 20, 1996
Adams et al.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 3e‚CH2Cl2
Ru(1)-C(15)
Ru(1)-Ru(3)
Ru(1)-Mo(2)
Ru(2)-Ru(4)
Ru(3)-Mo(2)
Ru(4)-C(13)
Ru(4)-Mo(1)
Mo(1)-C(15)
Mo(2)-C(13)
C(13)-C(14)
Ru-CO (av)
2.228(7)
2.8488(8)
2.9498(8)
2.8345(8)
2.8229(9)
2.221(7)
2.9398(9)
2.044(7)
2.007(7)
1.548(9)
1.897(8)
Ru(1)-Ru(2)
Ru(1)-Mo(1)
Ru(2)-Mo(1)
Ru(2)-Ru(3)
Ru(3)-Ru(4)
Ru(4)-Mo(2)
Mo(1)-C(13)
Mo(1)-Mo(2)
Mo(2)-C(15)
C(15)-C(16)
2.8316(9)
2.9451(8)
2.8126(9)
2.9484(8)
2.8337(8)
2.9256(9)
2.031(7)
2.5792(8)
2.029(6)
1.504(10)
Ru(2)-Ru(1)-Ru(3)
62.54(2) Ru(2)-Ru(1)-Mo(1) 58.23(2)
Ru(3)-Ru(1)-Mo(1) 86.02(2) Ru(2)-Ru(1)-Mo(2) 85.70(2)
Ru(3)-Ru(1)-Mo(2) 58.23(2) Mo(1)-Ru(1)-Mo(2) 51.89(2)
Mo(1)-Ru(2)-Ru(1) 62.90(2) Mo(1)-Ru(2)-Ru(4) 62.74(2)
Ru(1)-Ru(2)-Ru(4)
Ru(1)-Ru(2)-Ru(3)
95.73(2) Mo(1)-Ru(2)-Ru(3) 86.61(2)
59.02(2) Ru(4)-Ru(2)-Ru(3) 58.64(2)
Mo(2)-Ru(3)-Ru(4) 62.29(2) Mo(2)-Ru(3)-Ru(1) 62.67(2)
Ru(4)-Ru(3)-Ru(1)
Ru(4)-Ru(3)-Ru(2)
Ru(3)-Ru(4)-Ru(2)
95.36(2) Mo(2)-Ru(3)-Ru(2) 85.88(2)
58.67(2) Ru(1)-Ru(3)-Ru(2) 58.45(2)
62.69(2) Ru(3)-Ru(4)-Mo(2) 58.68(2)
Ru(2)-Ru(4)-Mo(2) 86.10(2) Ru(3)-Ru(4)-Mo(1) 86.39(2)
Ru(2)-Ru(4)-Mo(1) 58.27(2) Mo(2)-Ru(4)-Mo(1) 52.17(2)
Mo(2)-Mo(1)-Ru(2) 93.57(2) Mo(2)-Mo(1)-Ru(4) 63.63(2)
Ru(2)-Mo(1)-Ru(4) 58.99(2) Mo(2)-Mo(1)-Ru(1) 64.15(2)
Ru(2)-Mo(1)-Ru(1) 58.86(2) Ru(4)-Mo(1)-Ru(1) 91.12(2)
Mo(1)-Mo(2)-Ru(3) 93.94(2) Mo(1)-Mo(2)-Ru(4) 64.20(2)
Ru(3)-Mo(2)-Ru(4) 59.03(2) Mo(1)-Mo(2)-Ru(1) 63.96(2)
Ru(3)-Mo(2)-Ru(1) 59.09(2) Ru(4)-Mo(2)-Ru(1) 91.31(2)
C(14)-C(13)-Mo(2) 134.2(5) C(14)-C(13)-Mo(1) 133.9(5)
Mo(2)-C(13)-Mo(1) 79.4(2) C(14)-C(13)-Ru(4) 118.8(5)
F igu r e 2. ORTEP plot of the molecular structure of Mo2-
Ru4(µ3-CMe)2(CO)12Cp2 (3e) in the crystal. The dichlo-
romethane of crystallization is not shown.
the unsymmetrical complexes 3b-d , two such signals
are observed and can be distinguished by the J MOD
technique: the µ3-CH carbon consistently occurs at
approximately 325 ppm.
Mo(2)-C(13)-Ru(4)
87.4(2) Mo(1)-C(13)-Ru(4)
87.4(3)
C(16)-C(15)-Mo(2) 134.6(5) C(16)-C(15)-Mo(1) 133.1(5)
Mo(2)-C(15)-Mo(1) 78.6(2) C(16)-C(15)-Ru(1) 119.8(5)
The carbonyl regions of the 13C NMR spectra of the
symmetrical clusters 3a and 3e contain three peaks in
an approximate intensity ratio of 2:6:4, whereas the
unsymmetrical 3b-d each show five peaks in a 1:1:6:
2:2 pattern. The most likely explanation for this is that
the CO ligands bonded to the two ruthenium atoms
which are bonded to the alkylidyne ligands are static
on the NMR time scale, whereas those attached to the
other two ruthenium atoms are undergoing rapid tri-
podal rotation. The latter pair of metals remain equiva-
lent even when the two alkylidyne ligands are different,
whereas the former become inequivalent. Owing to the
limited solubility of the clusters at low temperature, we
did not investigate this phenomenon further.
Mo(2)-C(15)-Ru(1)
Ru-C-O (av)
87.6(3) Mo(1)-C(15)-Ru(1)
175.0(8)
87.0(3)
though the first is formally electron deficient whereas
the latter is electron precise.25
The Mo-Ru bonds involving Ru(1) and Ru(4), which
are bonded to the capping alkylidynes, are all very
similar and lie within the range 2.9256(9)-2.9498(8) Å.
However, the Mo-Ru bonds involving Ru(2) and Ru(3)
are somewhat shorter (2.8126(9) and 2.8229(9) Å). The
Ru-Ru bonds between these two Ru atoms and Ru(1)
and Ru(4) are all virtually the same length and lie in
the range 2.8316(9)-2.8488(8) Å, whereas the Ru(2)-
Ru(3) bond itself is somewhat longer (2.9484(8) Å). The
two ethylidyne ligands symmetrically cap the two Mo2-
Ru faces of the octahedron. The C(13)-C(15) distance,
which in the alkyne complexes 1 is approximately 1.33
Å, has opened up to 2.944 Å, though it is interesting to
note that this axis remains perpendicular to the Mo-
Mo bond.
In terms of electron counting, compounds of type 3
have a total of 84 cluster valence electrons (correspond-
ing to n pairs of skeletal electrons) instead of the 86
which is usual for octahedral clusters (n + 1 pairs of
skeletal electrons, corresponding to a closo structure).
This means that the cluster as a whole obeys the 18-
electron rule rather than the Wade-Mingos rules.30 The
short Mo-Mo distance may be a consequence of this
unsaturation. It is also interesting to compare 3e with
Mo2Ru4(µ6-C)(µ-O)(CO)12Cp2, which if the oxo ligand
acts as a 2-electron donor also has 84 electrons;14 if bond
length can be considered an accurate indicator of bond
The X-ray crystal structure of the bis(ethylidyne)
cluster 3e was determined, and a view of the molecule
is shown in Figure 2. Selected bond lengths and angles
are collected in Table 3.
The molecule consists of an octahedral metal core in
which the two molybdenum atoms, each bearing a Cp
ligand, are situated in adjacent positions. The Mo(1)-
Mo(2) bond is rather short (2.5792(8) Å) compared to
that of 2.980(1) Å in the alkyne complex 1a ,17 though it
is not as short as the 2.448(1) Å found for the MotMo
bond in Mo2(CO)4Cp2.24b It may therefore be indicative
of some degree of multiple bonding, formally a double
bond, as indicated by electron counting (vide infra).
However, it should be pointed out that related Mo2Ru
clusters in which the Mo-Mo bond is bridged by organic
fragments can also display rather short Mo-Mo dis-
tances. For example, Mo2Ru{µ3-HCC(Ph)CHC(Ph)CH-
C(Ph)}(µ3-S)(CO)2Cp2 and Mo2Ru(µ-PhCCHCPh)(µ3-
HCCPhCH)(µ3-S)(CO)2Cp2, which were both made by
oligomerization of phenylacetylene on the face of Mo2-
Ru(µ3-S)(CO)7Cp2, have very similar Mo-Mo bond
lengths of 2.663(1) and 2.679(2) Å, respectively, even
(30) Mingos, D. M. P.; May, A. S. In The Chemistry of Metal Cluster
Complexes; Shriver, D. F., Kaesz, H. D., Adams, R. D., Eds.; VCH: New
York, 1990; Chapter 2, p 44.

+
+
Vinylidene and Bis(alkylidyne) Clusters
Organometallics, Vol. 15, No. 20, 1996 4189
order, the longer Mo-Mo distance of 2.9052(12) Å
observed may mean that the deficiency is made up by
further donation from the oxo ligand.
Con clu sion
This work has demonstrated for the first time that
scission of the CtC bonds of simple terminal alkynes,
including acetylene itself, to form two alkylidyne ligands
is a process which can be observed in suitable metal
clusters under appropriate conditions. A better under-
standing of the factors which influence this, as opposed
to the more common CsH bond activation, may furnish
useful routes to clusters containing the important
methylidyne ligand. A theoretical study31 has shown
that the cleavage of alkynes is facilitated by charge
transfer (M f π*) to the resulting alkylidyne ligands,
which should be more effective from the MoCp frag-
ments than from the Ru(CO)3 groups, hence the prefer-
ence of the µ3-CR ligands in 3 for the Mo2Ru faces. A
further illustration is the fact that Os3(µ3-C2R2)(CO)10
does not undergo alkyne scission whereas OsW2(µ3-
C2R2)(CO)7Cp2 does so readily to give a product in which
one alkylidyne caps the cluster but the other bridges
the WsW edge; the formation of the strong WsC bonds
is thought to drive the reaction forward.3j It seems
reasonable to suggest that future examples of alkyne
scission are most likely to be encountered by the
incorporation of such fragments, and consequently we
are currently exploring further routes to mixed-metal
clusters using the alkyne complexes 1 as precursors.
At present it is difficult to propose a mechanism for
the formation of 3a -e and we have been unable to
isolate any intermediates, but it is reasonable to suppose
that the alkyne scission occurs in a mixed-metal cluster.
The intramolecular nature of this step is demonstrated
by the fact that complexes 1b-d , which contain unsym-
metrical alkynes, give rise only to the corresponding
unsymmetrical bis(alkylidyne) complexes 3b-d with no
trace of the symmetrical scrambling products, which
would include 3a . This rules out a mechanism involving
dissociation of the starting complexes into two mono-
nuclear Mo(CO)2(tCR)Cp fragments, which would in
any case be highly unlikely. Moreover, the reactions of
the tungsten alkylidyne complexes W(CO)2(tCR)Cp (R
) p-C6H4Me, Me) with Ru3(CO)12 have already been
studied by Stone and co-workers; they give rise to the
trinuclear alkyne clusters W2Ru(µ3-C2R2)(CO)7Cp2 by
coupling of two alkylidyne fragments.6 The complete
absence of any products of this type in the current work,
especially in the case of the disubstituted alkyne
complex, indicates the operation of a mechanism in
which alkyne cleavage is the only available pathway.
The structure of 3e, and the fact that the bulkier
alkyne complexes 1f,g give no products at all, both
indicate that the initial approach of the ruthenium
atoms to the dimolybdenum center is toward the Mo2C
faces of the starting dimetallatetrahedrane. However,
the successful reactions of 1c,d show that if R1 is small,
R2 can be quite large. Clearly, attachment of one Ru-
(CO)x unit is necessary in order to obtain the vinylidene
complexes 2, but treatment of 2 with further Ru3(CO)12
does not lead to 3 and it seems plausible to propose that
initial interaction with (at least) two such Ru(CO)x
fragments is necessary to proceed instead to alkyne
scission and construction of the hexanuclear clusters 3.
Conceptually, it is easy to visualize the formation of 3
by the simple insertion of a Ru4 butterfly into the Mo-
Mo bond of 1, accompanied by the “clicking open” of the
carbon-carbon bond, but there is no evidence to suggest
that this is what actually occurs in solution.
Ack n ow led gm en t. We thank the EPSRC for a
studentship to L.J .G. and J ohnson Matthey plc for a
generous loan of ruthenium trichloride. We also thank
Dr. B. F. Taylor and Prof. B. E. Mann for assistance in
recording and interpreting the NMR spectra and Dr.
Yun Chi (National Tsing Hua University, Taiwan) for
interesting discussions.
Su p p or tin g In for m a tion Ava ila ble: Full tables of atomic
coordinates, bond lengths and angles, H atom coordinates, and
thermal parameters for complexes 2b and 3e (14 pages).
Ordering information is given on any current masthead page.
Tables of structure factors are available from the authors on
request.
OM960235C
(31) Deshmukh, P.; Dutta, T. K.; Hwang, J . L.-S.; Housecroft, C.
E.; Fehlner, T. P. J . Am. Chem. Soc. 1982, 104, 1740.