Photolysis of in frozen Nujol Matrices

Article abstract of DOI:10.1016/S0022-328X(98)00512-9

A series of compounds, (η⁵-C5H4C4H9)2Mo2(CO)4(μ-η^2:2-acetylene), where acetylene = 3-hexyne, diphenylacetylene, phenylacetylene and 1-phenylpropyne, was prepared and characterized by IR, 1H- and 13C-NMR spectroscopies and MS.Photolysis of these compounds was carried out in frozen Nujol at 77 K.IR spectra established the presence of two isomeric carbonyl-loss species, (η⁵-C5H4C4H9)2Mo2(CO)2(μ-η^2:2-acetylene), A, and (η⁵-C5H4C4H9)2Mo2(μ-CO)3(μ-η^2:2-acetylene), B.A is formed by photolysis into low energy electronic transitions associated with the tetrahedrane core of the parent molcule, while B is formed by either photolysis into electronic bands associated with A, or photolysis into the high energy charge-transfer bands of the parent molecule.These photointermediates are likely to be involved in the formation of 'fly-over' compounds, resulting from thermally or photochemically induced multiple substitution of acetylenes. - Keywords: Molybdenum; Carbonyls; Cyclopentadienyls; Photochemistry; Matrices

Full text of DOI:10.1016/S0022-328X(98)00512-9

Journal of Organometallic Chemistry 561 (1998) 49–56
Photolysis of (p5-C5H4C4H9)2Mo2(CO)4(v-p2:2-RCꢀCR%) in frozen
Nujol matrices
Thomas E. Bitterwolf *, J. Timothy Bays
Department of Chemistry, Uni6ersity of Idaho, Moscow, ID 83844-2343, USA
Received 20 October 1997; received in revised form 2 January 1998
Abstract
A series of compounds, (p5-C5H4C4H9)2Mo2(CO)4(v-p2:2-acetylene), where acetylene=3-hexyne, diphenylacetylene, pheny-
1
lacetylene and 1-phenylpropyne, was prepared and characterized by IR, H- and 13C-NMR spectroscopies and MS. Photolysis of
these compounds was carried out in frozen Nujol at 77 K. IR spectra established the presence of two isomeric carbonyl-loss
species, (p5-C5H4C4H9)2Mo2(CO)2(v-p1,p2-CO)(v-p2:2-acetylene), A, and (p5-C5H4C4H9)2Mo2(v-CO)3(v-p2:2-acetylene), B. A is
formed by photolysis into low energy electronic transitions associated with the tetrahedrane core of the parent molecule, while B
is formed by either photolysis into electronic bands associated with A, or photolysis into the high energy charge-transfer bands
of the parent molecule. These photointermediates are likely to be involved in the formation of ‘fly-over’ compounds, resulting
from thermally or photochemically induced multiple substitution of acetylenes. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Molybdenum; Carbonyls; Cyclopentadienyls; Photochemistry; Matrices
1. Introduction
Knox et al. [4] found that reaction of the tetrahe-
drane compounds with excess acetylene in refluxing
heptane or octane resulted in sequential addition and
linking of the acetylenes to yield products with up to
four acetylene units coupled into a chain. These multi-
ple acetylene-substituted products have been given the
general name of ‘fly-over’ compounds. It was suggested
Thermolysis or photolysis of the group VI bimetallic
compounds (p5-C5H5)2M2(CO)6 forms the triply-
bonded species, (p5-C5H5)2M2(v-CO)4. For molybde-
num, photolysis has been shown to proceed via
photochemical loss of carbon monoxide to form (p5-
C5H5)2Mo2(CO)4(v-p1,p2-CO), which undergoes ther-
that acetylene might add to (p5-C5H5)2M2(CO)4(v-p2:2
RCꢀCR) by either concerted addition to
-
a
a
mal
loss
of
carbon
monoxide
to
give
(p5-C5H5)2Mo2(v-CO)4 [1]. Subsequent reaction of
Mꢁacetylene bond, or by loss of carbon monoxide to
yield an unsaturated intermediate that might subse-
quently react with acetylene. Somewhat later work by
Green et al. [5] on indenyl molybdenum compounds,
(p5-C9H7)2Mo2(CO)4, yielded the expected tetrahedrane
derivatives, and also a series of ‘fly-over’ compounds. A
complex reaction sequence involving dihapto-acetylene
units and p5 to p3 indenyl shifts was proposed to
account for the formation of the ‘fly-over’ species.
Recently, Kreiter et al. [6] have demonstrated that
photolysis of (p5-C5H5)2M2(CO)4(v-p2:2-HCꢀCH) in
these unsaturated species with acetylenes gives the te-
trahedrane compounds, (p5-C5H5)2M2(CO)4(v-p2:2
-
RCꢀCR) [2]. Amer and Po¨e [3] established that the
thermal reaction of (p5-C5H5)2M2(CO)6 and acetylenes
proceeds through carbon monoxide loss and not via
radical processes.
* Corresponding author. Tel.: +1 208 8856361; fax: +1 208
8856173; e-mail: bitterte@idaho.edu
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00512-9

50
T.E. Bitterwolf, J.T. Bays / Journal of Organometallic Chemistry 561 (1998) 49–56
the presence of excess acetylene yielded (p5-
C5H5)2M2(CO)2(v-p1:3:3:1-C6H6), where M=Mo or W,
and (p5-C5H5)2Mo2(CO)(v-p1:4:1-C4H4). These workers
proposed the reaction sequence in which initial photoly-
sis of (p5-C5H5)2M2(CO)4(v-p2:2-HCꢀCH) results in loss
of carbon monoxide to form a coordinatively unsatu-
rated intermediate that adds acetylene. Subsequent pho-
tochemical steps result in loss of carbon monoxide and
these samples. Further, in the case of 2, a trace of 1
remained in the sample, even after careful chromato-
graphic purification.
Fast atom bombardment (FAB) MS was carried out
on compounds 2–5, with molecular ions being observed
in all cases. Although no fragment associated with loss
of only a single carbon monoxide ligand was observed,
loss of two carbon monoxide ligands was found to be the
dominant fragmentation process.
either rearrangement to give (p5-C5H5)2M2(CO)(v-p1:4:1
C4H4), or addition of a third acetylene to yield (p5-
C5H5)2M2(CO)2(v-p1:3:3:1-C6H6). Clearly, such
-
1H- and 13C-NMR spectra of the tetrahedrane com-
pounds were consistent with those of analogous nonsub-
stituted cyclopentadienyl compounds. Carbonyl
resonances were observed for compounds 2–4, but not
for 5. Compounds 2 and 3 were found to have a single
carbonyl resonance, while compound 4 had two carbonyl
resonances, consistent with the presence of an asymmet-
ric acetylene in 4. In all cases, carbonyl groups shuttle
between terminal and semibridging carbonyl positions at
a rate that must be fast on the NMR time scale.
a
sequence could also account for the thermal formation
of the ‘fly-over’ compounds.
We have been examining the photochemistry of
bimetallic compounds in both gas and frozen Nujol
matrices and recognized that matrix photolysis of tetra-
hedrane compounds offered a simple way of establishing
the identity of the photointermediates in these reactions.
In this paper we present the synthesis and Nujol glass
matrix photolysis of a series of tetrahedrane compounds
and demonstrate a facile photochemical transformation
between two isomeric forms of the carbonyl-loss pho-
tointermediate. These results are discussed in the light of
the growing literature on photointermediates of bimetal-
lic compounds.
3. Photochemical studies in frozen Nujol at 77 K
We have previously reported the photolysis of (p5-
C5H5)2Mo2(CO)6 in frozen gas matrices at 12 K [8].
Under these conditions, photolysis results in loss of
carbon monoxide to yield (p5-C5H5)2Mo2(CO)2(v-
CO)2(v-p1,p2-CO), Fig. 1, having terminal, semibridg-
ing, and four-electron bridging carbonyl groups. This
species has also been observed in flash photolysis studies
[1]. For comparison we examined the photolysis of
(p5-C5H4C4H9)2Mo2(CO)6 in frozen Nujol at 77 K. In
frozen Nujol, 1 was found to have three bands at 1956,
1913 and 1906 cm−1, as shown in Fig. 2(a). Photolysis
resulted in a decrease in the bands of 1 and growth of
new bands at 2132 (w), 1976 (m), 1933 (s), 1892 (w), 1861
(m) and 1665 (m) cm−1, Fig. 2(b). Bands at 2132 cm−1
are associated with ‘free’ carbon monoxide in Nujol
matrices. The pattern and positions of the remaining
bands associated with the photolysis product are quite
similar to those of (p5-C5H5)2Mo2(CO)2(v-CO)2(v-
p1,p2-CO) in frozen methane, Table 1, and indicate that
the presence of butyl substituents on the cyclopentadi-
enyl ring do not alter the photochemical behavior of the
compound.
2. Synthesis and characterization of
(
5-C5H4C4H9)2Mo(CO)4(¦- 2:2-RꢁCꢀCR%)
As noted in Section 1, tetrahedrane acetylene com-
pounds may be prepared by reaction of the triply-bonded
derivatives, (p5-C5H5)2M2(v-CO)4, with acetylenes. For
the current photolysis study, it was recognized that it was
crucial to have tetrahedrane derivatives that would be
soluble in Nujol at concentrations sufficient to obtain
clear IR spectra. Preliminary experiments established
that tetrahedrane compounds containing the unsubsti-
tuted cyclopentadienyl ligand were functionally insoluble
in Nujol. To overcome this limitation (p5-
C5H4C4H9)2Mo2(CO)6, 1, was prepared as described in
the literature [7]. Reaction of 1 with an acetylene in
refluxing xylene yielded the desired tetrahedrane deriva-
tives. By this route a series of compounds, (p5-
C5H4C4H9)2Mo2(CO)4(v-p2:2-acetylene),
where
acetylene=3-hexyne (2), diphenylacetylene (3), pheny-
lacetylene (4), and 1-phenylpropyne (5), was prepared.
IR spectra recorded during the reaction established the
presence of (p5-C5H4C4H9)2Mo2(CO)4.
All of the tetrahedrane derivatives were isolated as
either amorphous solids or as oils. As anticipated, these
compounds had excellent solubility in Nujol. Unfortu-
nately, this very property also made it difficult to remove
all of the petroleum ether from the compounds, thus
elemental analyses were poor. Residual traces of
petroleum ether were observed in the NMR spectra of
Fig. 1. Proposed structure of (p5-C5H5)2Mo2(CO)2(v-CO)2(v-p1,p2-
CO).

T.E. Bitterwolf, J.T. Bays / Journal of Organometallic Chemistry 561 (1998) 49–56
51
Fig. 2. (a) IR spectrum of (p5-C5H4C4H9)2Mo2(CO)6 in Nujol glass at ca. 77 K. (b) 30 min photolysis (400970 nm)-starting material. (c) 15 min
anneal to ca. 173 K-30 min photolysis.
pounds, thus it is likely that two central bands overlap
in compounds 3 and 5.
In Nujol at 77 K, the IR spectra of compounds 3 and
5 in the carbonyl region contain three bands, while
those of 2 and 4 contain four. In each case, one of these
bands (1833–1843 cm−1) may be attributed to a
semibridging carbonyl, while the remaining bands are
associated with terminal carbonyl stretching modes.
Molecular structures of analogous unsubstituted cy-
clopentadienyl compounds establish that these
molecules are asymmetric in the solid-state with three
terminal carbonyl groups and one semibridging car-
bonyl group [9]. Symmetry arguments would predict a
total of four carbonyl stretching bands for these com-
Electronic spectra of compounds 2–5 contain two
distinct features at ca. 535 and 360 nm, and an ill-
defined shoulder at ca. 460 nm. By comparison, the
electronic spectrum of (p5-C5H5)2Mo2(CO)4(v-p2:2
-
HCꢀCC6H5) has been reported to have bands at 543
and 362 nm in isooctane at room temperature ([2]c). It
is likely that low temperature sharpening of the spectra
permitted the shoulders at ca. 460 nm to be observed
for compounds 2–5. The bands at 535 and 460 nm may
be associated with the tetrahedrane core of the

52
T.E. Bitterwolf, J.T. Bays / Journal of Organometallic Chemistry 561 (1998) 49–56
molecule, while the more intense absorbance at 360 nm
is most likely a metal-to-ligand charge-transfer band.
Hoffmann and coworkers have described the bonding
in perpendicular and parallel acetylene complexes and
find that the bonding within the tetrahedrane core is
delocalized [10]. At present, theory does not provide
guidance as to the actual nature of the excited states in
these compounds.
The IR spectrum of 2 is shown in Fig. 3(a). Bands at
1989, 1914, 1905 and 1833 cm−1 are attributable to
carbonyl groups of 2. The small band at 1956 cm−1 is
due to a trace of 1, which was not removed by chro-
matography. Photolysis of 2 at 550 nm (970 nm) for
30 min results in the loss of IR bands associated with 2
and the growth of new bands at 2132 (w), 1935 (m),
1917 (s), 1794 (w) and 1678 (s) cm−1, Fig. 3(b). The
photoproduct of 1 makes a small contribution to the
product band at 1935 cm−1 in Fig. 3(b). Electronic
spectra recorded on this sample revealed that the bands
associated with 2 had been bleached, while new bands
were observed at 550 and 450 nm.
decreasing in intensity, while those of the parent species
grew.
Photolysis of compounds 3–5 resulted in very similar
observations. The IR spectral data for all compounds
and photoproducts are summarized in Table 2. Elec-
tronic spectral data for compounds 2–5 are presented
in Table 3. Annealing samples of 3–5 after photolysis
resulted in the appearance of small, but reproducible,
bands ca. 2182 and 2040 cm−1. These bands appeared
only in those compounds with phenyl groups on the
acetylene, ruling out the possibility of N2 compounds
that are sometimes observed to arise from nitrogen
dissolved in the Nujol. Since absorbances in the range
of 2182 cm−1 are typical for metal-hydrides, we tenta-
tively propose that oxidative addition (ortho metalla-
tion) of a phenyl CꢁH bond into an electronically
unsaturated molybdenum results in the formation of a
species such as illustrated in Fig. 4. Oxidative addition
of cyclopentadienyl CꢁH bonds by electronically unsat-
urated metals in bimetallic species have been observed
by Riera and coworkers [11] and ourselves [12]. We are
presently examining this photolysis on the preparative
scale to clarify the identity of these new species.
In all cases, the photolysis of the parent tetrahedrane
species results in loss of carbon monoxide to yield two
photoproducts, A and B. Low energy photolysis into
the absorption bands associated with the tetrahedrane
core of the parent molecule yields A, having three
absorption bands that may be assigned to two terminal
carbonyl groups and a four-electron bridging carbonyl
group. That the absorption band of the four-electron
bridging carbonyl was not observed in the photolysis of
3 may only reflect the lower solubility of 3 in Nujol.
Photolysis into the electronic absorption bands of A
yields B with IR absorption bands between 1800 and
1750 cm−1. B appears to be a photochemical rear-
rangement product of A having only bridging carbonyl
groups. B may also be directly generated by photolysis
into the charge-transfer bonds of the parent com-
pounds, although it is not possible to preclude the
possibility that A is still the intermediary in the high
energy photolysis. These processes are summarized in
Scheme 1.
Continued photolysis of this sample at 450 nm (970
nm) for 30 min resulted in decreases of those bands
associated with 2 and those at 1935, 1917 and 1678
cm−1, while the bands at 2132 and 1794 cm−1 contin-
ued to grow, Fig. 3(c). As the band at 1794 cm−1
increased in intensity, it became apparent that it was
asymmetric with a shoulder at ca. 1760 cm−1. A new
band was found in the electronic spectrum at 490 nm.
Photolysis of a fresh sample of 2 for 60 min at 360
nm (910 nm) resulted in a decrease in the parent
bands, and appearance of the same bands as found at
550 nm, except that the bands at 1794 and 1760 cm−1
were substantially more intense than those at 1935,
1917 and 1678 cm−1
.
Annealing this sample to 157 K resulted in bands at
2132, 1935, 1917 and 1678 decreasing, while those of
the parent species and bands at 1794 and 1760 in-
creased in intensity. Finally, annealing the sample to
177 K resulted in bands at 2132, 1794 and 1760 cm−1
Table 1
Carbonyl stretching frequencies of (p5-C5H4R)2Mo2(CO)6 and their
photoproducts in cm−1
The initial photointermediate in this sequence, A, is
strikingly similar to the photoproducts of 1 and (p5-
C5H5)2Mo2(CO)6. In these cases, loss of a carbon
monoxide ligand is compensated for by one of the
remaining carbonyl groups serving as a four-electron
donor. Such a species was originally suggested by Kre-
iter et al. as an intermediate in the addition of acetylene
to the tetrahedrane species. Subsequent rearrangement
of A yields B, with all bridging carbonyl groups. Simi-
lar geometries with bridging or semibridging carbonyl
groups are known for the electron-deficient species:
(p5-C5H5)2M2(v-CO)4, where M=Cr, Mo, and W [1],
(p5-C5H5)2M2(v-CO)3, where M=Fe and Ru [13], (p5-
a
b
Compound
LꢁC5H5
LꢂC5H4C4H9
L2Mo2(CO)6
1963
1919
1912
1955
1913
1906
L2Mo2(CO)5
1982
1940
1886
1865
1667
1975
1933
1892
1861
1664
a
CH4 matrix, 12 K [8]
b Nujol glass matrix, 77 K (this work).

T.E. Bitterwolf, J.T. Bays / Journal of Organometallic Chemistry 561 (1998) 49–56
53
Fig. 3. (a) IR spectrum of (p5-C5H4C4H9)2Mo2(CO)4(v-p2:2-C2H5ꢁCꢀCꢁC2H5) in Nujol glass at ca. 77 K. (b) 30 min photolysis (550970
nm)-starting material. (c) 60 min photolysis (450970 nm)-30 min photolysis. (d) 15 min anneal to ca. 173 K-60 min photolysis. (Note: band at
1956 cm−1 is due to trace of 1.
photochemical conversion of (p5-C5H4C4H9)2Mo2-
(CO)2(v-p1,p2-CO)(v-p2:2-RCꢀCR) into (p5-C5H4C4-
H9)2Mo2(CO)3(v-p2:2-RCꢀCR).
C5Me5)2Re2(CO)3 [14], (p5-C5H5)2M2(v-CO)2, where
M=Co and Rh [15], (p5-C5H5)2Fe2(v-CO)2(v-CHCH3)
[16] and the acetylenic species, (p5-C5H5)2Ru2(v-CO)(v-
p2:2-PhꢁCꢀCꢁPh) [17].
Zhang and Brown reported a detailed examination of
the flash photolysis of (p5-C5H5)2Fe2(CO)4 and have
established the formation of two carbonyl loss species,
the known (p5-C5H5)2Fe2(v-CO)3 and (p5-C5H5)2Fe2(v-
CO)2(v-p1,p2-CO). It is proposed that the four-electron
semibridging species converts to the triply-bridged spe-
cies by a photochemical process [18]. This reaction
appears to parallel the observation reported here of the
4. Experimental
All syntheses were performed under an atmosphere
of nitrogen using standard Schlenk techniques. Sol-
vents were dried and distilled over a sodium–potas-
sium alloy or calcium hydride under an atmosphere of
nitrogen. Preparative chromatography was conducted

54
T.E. Bitterwolf, J.T. Bays / Journal of Organometallic Chemistry 561 (1998) 49–56
Table 2
Carbonyl stretching frequencies of the acetylene compounds in cm−1
Compounda
Nujol at 77 K
Dichloromethaneb
1972
Petroleum etherb
(BuCp)2Mo2(CO)4(v-p2:2-EtCꢀCEt) (2)
1980
1914
1905
1833
1935
1917
1679
1791
1759
1984
1926
1843
1943
1910
1823
1806
1982
1922
1914
1838
1947
1897
1681
1815
1797
1988
1925
1842
1936
1899
1682
1806
1903
1821
(BuCp)2Mo2(CO)3(v-p2:2-EtCꢀCEt) (2-A)
(BuCp)2Mo2(CO)3(v-p2:2-EtCꢀCEt) (2-B)
(BuCp)2Mo2(CO)4(v-p2:2-PhCꢀCPh) (3)
1981
1920
1834
(BuCp)2Mo2(CO)3(v-p2:2-PhCꢀCPh) (3-A)
(BuCp)2Mo2(CO)3(v-p2:2-PhCꢀCPh) (3-B)
(BuCp)2Mo2(CO)4(v-p2:2-PhCꢀCCH3) (4)
1978
1911
1828
(BuCp)2Mo2(CO)3(m-p2:2-PhCꢀCCH3) (4-A)
(BuCp)2Mo2(CO)3(v-p2:2-PhCꢀCCH3) (4-B)
(BuCp)2Mo2(CO)4(v-p2:2-PhCꢀCH) (5)
1985
1918
1830
1990
1929
1848
(BuCp)2Mo2(CO)3(v-p2:2-PhCꢀCH) (5-A)
(BuCp)2Mo2(CO)3(v-p2:2-PhCꢀCH) (5-B)
a BuCp=(p5-C5H4C4H9), Et=CH2CH3, Ph=C6H5.
b Room temperature.
Gary Knerr using the FAB, electron impact and chem-
ical ionization modes on a VG 7070-HS GC/MS.
1 was prepared by literature methods [7]. Acetylenes
were purchased from Strem Chemical or Aldrich, and
used as-received.
Photochemical studies were carried out in a cryostat
designed by Dr Antony Rest of the University of
Southampton. Experimental details on the use of the
cryostat have been previously described [19]. Nujol
using solvents flushed with nitrogen and neutral alu-
mina from CAMAG.
1H- and 13C-NMR spectra were recorded at 300 and
75 MHz, respectively, using a Bru¨ker NR-300 spec-
trometer or a Varian Gemini-300 spectrometer. IR
spectra of solution samples were recorded using a Bio-
Rad Qualimatic FT-IR. MS was carried out by Dr
Table 3
Electronic absorption bands of acetylene compounds in the Nujol
matrix at ca. 77 K
Compounda
Absorbance maxima
(nm)
(BuCp)2Mo2(CO)4(v-p2:2-EtCꢀCEt) (2)
360b
480c 535c
466 540
460 539
(BuCp)2Mo2(CO)4(v-p2:2-PhCꢀCPh) (3) 352
(BuCp)2Mo2(CO)4(v-p2:2-PhCꢀCCH3)
(4)
353
356
(BuCp)2Mo2(CO)4(v-p2:2-PhCꢀCH) (5)
450 533
a BuCp=(p5-C5H4C4H9), Et=CH2CH3, Ph=C6H5.
b Metal-to-ligand charge-transfer.
c Tetrahedrane core.
Fig. 4. Proposed structure of phenyl oxidative addition annealing
product.

T.E. Bitterwolf, J.T. Bays / Journal of Organometallic Chemistry 561 (1998) 49–56
55
Scheme 1. Photolysis of tetrahedrane acetylene derivatives.
4.1.1. (p5-C5H4C4H9)2Mo2(CO)4(v-p2:2-CH3CH2Cꢀ
CCH2CH3), 2
matrix isolation work was performed using a Bio-Rad
FTS 15/80 FT-IR spectrometer. Spectra were collected
using a liquid nitrogen-cooled mercury cadmium tel-
luride (MCTB) detector. Spectra were recorded using
1024 scans and a resolution of 2 cm−1. Each sample
was allowed to sit for 20 min prior to recording spectra
while the instrument and the sample compartment
purged with dry air.
Maroon amorphous solid. m.p. 46.7–47.0°C, 35.5%
yield. IR (cm−1, CH2Cl2): 1972, 1903 and 1821. H-
1
NMR (l, CDCl3): 5.02 (m, AA%BB%, 8H, Cp), 2.76 (q,
JCꢁH=7.30 Hz, 4H, EtꢁCH2), 2.28 (t, JCꢁH=7.20 Hz,
4H, BuꢁCH2), 1.44 (m, 4H, BuꢁCH2), 1.30 (m, 4H,
BuꢁCH2), 0.976 (t, JCꢁH=7.35 Hz, 6H, EtꢁCH3) and
0.849 (t, JCꢁH=7.25 Hz, 6H, BuꢁCH3). 13C-NMR (l,
CDCl3): 232 (CO), 112 (ipso Cp), 94 (Cp), 91
(acetylenic carbon), 90 (Cp), 88 (acetylenic carbon), 34
(BuꢁCH2), 30 (acetylenicꢁCH2), 29 (BuꢁCH2), 23
(BuꢁCH2), 15.6 (acetylenicꢁCH3) and 14 (BuꢁCH3).
MS: 630 (M+ +2, 2%), 628 (M+, 2%), 572 (M+-2CO,
37%), 547 (M+-RCCR, 18%), 544 (M+-3CO, 23%),
4.1. General procedures for the synthesis of
tetrahedrane acetylene compounds
A Schlenk flask was evacuated and back-filled with
nitrogen. Xylenes, 50 ml, and 1 (0.50g, 0.83 mmol) were
added to the Schlenk flask under nitrogen. One equiva-
lent of acetylene was added using a microliter syringe.
The mixture was refluxed overnight while nitrogen was
bubbled through the reaction mixture. After removal of
solvent under reduced pressure, the reaction mixture
was taken up in petroleum ether and chromatographed
using petroleum ether as an eluant. In all cases, three
bands were observed. An initial green band was ob-
served, but decomposed on the column, followed by a
light pink band that was determined to be unreacted
starting material. Continued elution recovered a dark
red band that was determined to be the desired
product. Three of the four compounds were oils, and
the fourth an amorphous solid. Extended periods under
vacuum failed to remove all of the petroleum ether
from these samples.
512 (M+-2COꢁBu,
100%),
and 425 (M+-
BuCpꢁRCCR, 13%). Anal. calc. for C28H36O4Mo2: C,
53.51; H, 5.77. Found: C, 55.19; H, 6.41.
4.1.2. (p5-C5H4C4H9)2Mo2(CO)4(v-p2:2-C6H5Cꢀ
CC6H6), 3
Dark red oil. 24.8% yield. IR (cm−1, CH2Cl2): 1981,
1
1920 and 1834. H-NMR (l, CDCl3): 7.11 (m, 10H,
Ph), 4.94 (m, AA%BB%, 8H, Cp), 2.32 (t, JCꢁH=7.47 Hz,
4H, CH2), 1.46 (m, 4H, CH2), 1.15 (m, 4H, CH2) and
0.847 (t, JCꢁH=7.03 Hz, 6H, CH3). 13C-NMR (l,
CDCl3): 231.6 (CO), 146 (ipso Ph), 129 (o-Ph), 128
(m-Ph), 125 (p-Ph), 113 (ipso Cp), 95 (Cp), 92 (Cp), 80
(acetylenic carbon), 34 (CH2), 28 (CH2), 22 (CH2) and
14 (CH3). MS: 726.5 (M+ +2, 10%), 724.5 (M+, 11%),
668 (M+-2CO, 100%), 641 (M+-3CO, 27%), 612 (M+-

56
T.E. Bitterwolf, J.T. Bays / Journal of Organometallic Chemistry 561 (1998) 49–56
2COꢁBu, 57%), 547 (M+-RCCR, 5%), 518 (M+-
COꢁRCCR, 10%), 489 (M+-BuꢁRCCR, 10%) and
423 (M+-BuCpꢁRCCR, 27%). Anal. calc. for
C36H36O4Mo2: C, 59.68; H, 5.00. Found: C, 61.10; H,
5.31.
nelius Kreiter for helpful discussions and Dr Antony
Rest for the gift of the cryostat used in these studies.
References
4.1.3. (p5-C5H4C4H9)2Mo2(CO)4(v-p2:2-CH3Cꢀ
CC6H6), 4
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Dark red oil. 31.6% yield. IR (cm−1, CH2Cl2): 1978,
1
1911 and 1828. H-NMR (l, CDCl3): 7.11 (m, 5H, Ph),
4.97 (m, AA%BB%, 8H, Cp), 2.60 (s, 3H, acetylenic CH3),
2.24 (t, JCꢁH=7.60 Hz, 4H, CH2), 1.38 (m, 4H, CH2),
1.26 (m, 4H, CH2), and 0.91 (t, JCꢁH=7.20 Hz, 6H,
BuꢁCH3). 13C-NMR (l, CDCl3): 231.8, 231.6 (CO), 146
(ipso Ph), 129 (o-Ph), 128 (m-Ph), 125 (p-Ph), 113 (ipso
Cp), 94.4, 93.8, 91.1, 90.7 (Cp), 81.5, 80.7 (acetylenic
carbons), 34 (CH2), 28 (CH2), 24 (CH3, acetylenic), 22
(CH2), and 14 (CH3). MS: 663 (M+, 15%), 607 (M+-
2CO, 100%), 579 (M+-3CO, 11%), 550 (M+-2COꢁBu,
72%), 547 (M+-RCCR, 62%), 519 (M+-COꢁRCCR,
10%), 489 (M+-BuꢁRCCR, 8%), and 423 (M+-
BuCpꢁRCCR, 29%). Anal. calc. for C31H34O4Mo2: C,
56.21; H, 5.17. Found: C, 56.90; H, 5.22.
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4.1.4. (p5-C5H4C4H9)2Mo2(CO)4(v-p2:2-HCꢀCC6H6), 5
Dark red oil. 20.8% yield. IR (cm−1, CH2Cl2): 1985,
1918 and 1830. IR (cm−1, petroleum ether): 1990, 1929,
1848. H-NMR (l, CDCl3): 7.23 (m, 5H, Ph), 5.34 (s,
1H, acetylenic H), 5.16 (m, AA%BB%, 8H, Cp), 2.21 (t,
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3722.
1
JCꢁH=7.25 Hz, 4H, CH2), 1.40 (m, 8H, CH2CH2), and
0.864 (t, JCꢁH=7.05 Hz, 6H, CH3). 13C-NMR (l,
CDCl3): 153 (ipso Ph), 130 (o-Ph), 129 (m-Ph), 126
(p-Ph), 93 (Cp), 91 (Cp), 33 (CH2), 28 (CH2), 22 (CH2)
and 13 (CH3). MS: 650 (M+ +2, 12%), 648 (M+,
12%), 592 (M+-2CO, 100%), 564 (M+-3CO, 11%), 547
(M+-RCCR, 10%), 535 (M+-2COꢁBu, 59%), 489 (M+
-BuꢁRCCR, 11%) and 425 (M+-BuCpꢁRCCR, 35%).
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Macpherson, A.A. Mead, A.G. Orpen, J. Chem. Soc. Dalton
Trans. (1990) 761.
Acknowledgements
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(b) S. Zhang, T.L. Brown, J. Am. Chem. Soc. 115 (1993) 1779.
[19] T.E. Bitterwolf, K.A. Lott, A.J. Rest, J. Mascetti, J. Organomet.
Chem. 419 (1991) 113.
We thank Research Corporation for a generous Re-
search Opportunity Award for the purchase of an
FT-IR spectrometer. Our thanks to Professor Dr Cor-
.