Transition-metal complexes containing alkynylsilyl functionalized η6-arene ligands

Article abstract of DOI:10.1021/om400378s

Six transition-metal arene complexes containing alkynylsilyl groups have been synthesized. Direct complexation of the corresponding arenes yielded the alkynylsilylarene complexes PhC≡CMe₂SiPhCr(CO)₃ (1), n-PrC≡CMe₂SiPhCr(C

Full text of DOI:10.1021/om400378s

Article
pubs.acs.org/Organometallics
Transition-Metal Complexes Containing Alkynylsilyl Functionalized
η6‑Arene Ligands
Florian Hoffmann, Jorg Wagler, and Gerhard Roewer*
̈
Institut fur Anorganische Chemie, Technische Universitat Bergakademie Freiberg, Leipziger Straße 29, 09596 Freiberg, Germany
̈
̈
S
* Supporting Information
ABSTRACT: Six transition-metal arene complexes containing
alkynylsilyl groups have been synthesized. Direct complexation
of the corresponding arenes yielded the alkynylsilylarene
complexes PhCCMe2SiPhCr(CO)3 (1), n-PrC
CMe2SiPhCr(CO)3 (2), n-PrCCMe2Si−SiMe2−
SiMe2PhCr(CO)3 (4), and PhCCMe2SiPhMo(CO)3 (6),
while PhCCMe2Si−SiMe2PhCr(CO)3 (3) and (PhC
CMe2SiPh)2Cr (7) were synthesized by modification of
precomplexed arenes. The reactivity of the CC triple
bonds of the synthesized alkynylsilyl compounds toward
complexation and carbon−carbon bond-forming reactions was
studied. The alkynyl groups of 1 and 6 underwent
intermolecular complexation to yield the trinuclear compounds 1·Ni2Cp2 (8) and 6·Cp2Mo2(CO)4 (9), respectively, while
reaction of 7 with CpCo(PPh3)2 led to intramolecular [2 + 2] cycloaddition of its two alkynyl groups with formation of the
dinuclear cyclobutadiene complex CpCo(PhCCSiMe2Ph)2Cr (10). All of these complexes were characterized by NMR, IR, and
mostly also UV/vis (1, 2, 6−10) spectroscopy. The molecular and crystal structures of compounds 1, 2, and 6−10 were
determined by single-crystal X-ray diffraction.
threne),5,7 and alkenylalkylarene complexes.8 Alkenylsilylarene
INTRODUCTION
■
complexes have been used to synthesize metal-containing
dendrimers and polymers by hydrosilylation.7g,h Alkynyl-
alkoxyalkylarenes6 as well as alkenylalkylarenes8 acted as
chelating ligands and corresponding chromium complexes
have been prepared. Finally, two highly interesting chromi-
um−iron−silicon cluster compounds can be regarded as related
(ferrasilaalkenyl)silylarene chelate complexes of chromium.9
Herein we present the first transition-metal alkynylsilylarene
complexes as well as reactions of their alkyne triple bonds
which finally lead to multinuclear complexes and carbon−
carbon bond coupling reactions.10
The alkynyl group is a useful building block for metal-organic
synthesis, e.g. for preparing multinuclear complexes with
conjugated metal centers,1 because of its various coordination
modes, its ability to participate in delocalized systems, and its
versatile reactivity.2 Recently we reported the synthesis of some
transition-metal alkynylsilyl complexes with a metal−silicon
bond as well as mild subsequent reactions preserving this
reactive bond.3a As an alternative approach toward alkynylsilyl-
functionalized complexes, which circumvents the sensitivity
issue associated with a direct metal−silicon bond, we
successfully inserted a cyclopentadienyl spacer unit between
metal and silicon.3b The metal−carbon and carbon−silicon
bonds are more robust than a direct metal−silicon bond, while
the silyl group prevents side reactions which could occur if the
alkynyl residue were bound directly to the aromatic ring
(conjugated π system) or via one carbon atom (activation of
propargylic C−H bonds). Thus, an aromatic hydrocarbon
spacer unit should also allow the complexes to resist less mild
conditions when they are employed as starting materials in
further reactions.
RESULTS AND DISCUSSION
■
Transition-Metal η6-Arene Complexes with Alkynylsi-
lylbenzenes. Similarly to the analogous alkynylsilyl-
cyclopentadienyl compounds,3b the number of synthetic
pathways to arene complexes bearing alkynylsilyl groups is
larger than that for silyl complexes with a direct metal−silicon
bond, because the Si−C bond is kinetically inert and the arene
metal complex moieties are quite robust. Thus, the alkynyl
group, the silyl group, and the arene metal complex fragment
can be connected in several sequences depending on the
reactivity of the intermediate and final complexes. In contrast,
transition-metal silyl compounds are relatively sensitive to
To our surprise, a literature search revealed that transition-
metal complexes bearing alkynylsilyl-functionalized η6-arene
ligands are hitherto completely unknown. Of course, complexes
with alkynylalkyl groups (such as propargyl) are known and
have found application in organic synthesis.4 Furthermore,
there are some related alkynylsilylalkylsilylarene,5 alkynyl-
alkoxyalkylarene,6 alkenylsilylarene (including silaphenan-
Received: April 30, 2013
Published: August 15, 2013
© 2013 American Chemical Society
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metal−silicon bond scission and their synthetic access is largely
limited to nucleophilic substitution of halosilanes with metalate
ions or oxidative addition of hydrosilanes to suitable metal
complexes.11
For the synthesis of arenetricarbonylchromium complexes,
the methods comprise complexation of alkynylsilylarenes with
hexacarbonylchromium (Cr(CO)6; Scheme 1, route 1), or
the reaction was stopped at this stage and workup gave yellow
crystals of 1 in 42% yield.14 They were air-stable for at least
some days and well soluble in all common organic solvents,
forming air-sensitive yellow solutions. The NMR and IR
spectroscopic data were consistent with the molecular structure
of 1.
Apart from a CH···π contact between an ortho phenyl
hydrogen and the silicon-bound carbon atom of the CC
triple bond, the molecule does not exhibit any striking bonding
parameters (Figure 1). Neighboring molecules arrange in a
Scheme 1. Retrosynthetic Pathways to
(Alkynylsilylarene)tricarbonylchromium Complexes
Figure 1. Molecular structure of 1 with an intramolecular CH···π
interaction (hydrogen atoms except H8 omitted for clarity). Bond
lengths and angles can be found in the Supporting Information. HPh···
CCC (CPh···CCC) distances (pm): H8−C12 = 283 (C8−C12 =
323), H8−C13 = 330 (C8−C13 = 394). Sum of the van der Waals
radii: 300 (370) pm.15
presubstituted tricarbonylchromium complexes Cr(CO)3L3
(route 2) as well as introduction of alkynylsilyl groups (route
3) or protected silyl groups (route 4) into benzenetricarbonyl-
chromium ((C6H6)Cr(CO)3).
structural motif that was observed also in compounds 2, 6, and
two related rhodium alkynylsilyl3a and titanium alkynylsilylcy-
clopentadienyl3b complexes (Figure S8; Supporting Informa-
tion). This indicates CH···π interactions between the methyl
hydrogens and neighboring CC triple bonds, but the
distances are near or somewhat above the sum of the van der
Waals radii. Nevertheless, this mutual arrangement of molecules
appears to be especially favorable, thus representing a
noteworthy feature of complexes containing a dimethyl-
(phenylethynyl)silyl group.
In order to evaluate the influence of the organic substituent
at the CC triple bond, tricarbonyl[dimethyl(pent-1-yn-1-
yl)(η6-phenyl)silane]chromium(0) (n-PrCCMe2SiPhCr-
(CO)3, 2) was synthesized from dimethyl(pent-1-yn-1-yl)-
phenylsilane (n-PrCCMe2SiPh) and fac-tris(acetonitrile)-
tricarbonylchromium(0) (Cr(CO)3(MeCN)3) (Scheme 1
(route 2) and Scheme 2).14 With 1 equiv of Cr(CO)3(MeCN)3
in cyclohexane, silane conversion stopped at 67% after 16 h
under reflux conditions because of thermal decomposition of
the starting complex. Workup gave low-melting yellow crystals
in 55% yield. In order to reduce the loss of silane, the synthesis
was repeated with 2 equiv of Cr(CO)3(MeCN)3 and complete
silane conversion was achieved after 24 h reflux in heptane.
Compound 2 was then isolated in 80% yield referenced to n-
PrCCMe2SiPh. It is quite soluble in all common organic
solvents. The solutions were more sensitive than those of 1;
e.g., 2 decomposed in chloroform (under argon) while 1 did
not. The NMR and IR data were in agreement with the
molecular structure of 2.
The first attempt to synthesize tricarbonyl[dimethyl(η6-
phenyl)phenylethynylsilane]chromium(0) (PhC
CMe2SiPhCr(CO)3, 1) via the reaction of lithiated (C6H6)Cr-
(CO)3 (−78 °C, exclusion of light)12 with chlorodimethyl-
(phenylethynyl)silane (PhCCMe2SiCl; route 3) resulted
only in a mixture of compounds, showing this route to be
inefficient.
Complex 1 was finally synthesized along route 1, starting
from Cr(CO)6 and dimethylphenyl(phenylethynyl)silane
(PhCCMe2SiPh; Scheme 2).13 The reaction was rather
slow; a conversion of 73% was achieved only after 93 h, as
judged by 29Si NMR. Because of increasing byproduct
formation (complexation of the alkyne-bound phenyl group)
Scheme 2. Synthesis of Complexes 1, 2, 4, and 6
The molecular conformation of 2 is similar to that of 1,
including the CH···π contact between an ortho phenyl
hydrogen and the silicon-bound carbon atom of the CC
triple bond (Figure 2). The propyl group is disordered with
two different conformations in a ratio of about 2:1.
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(SiMe2)4−PhCr(CO)3, 5).18 This was confirmed by single-
crystal X-ray structure analysis. The molecule possesses
inversion symmetry with the central Si−Si bond being located
on a crystallographic center of inversion (Figure 3). The
Figure 2. Molecular structure of 2 with an intramolecular CH···π
interaction (30% probability thermal ellipsoids; only the more
predominant of the two propyl conformations shown, hydrogen
atoms except H4 omitted for clarity). Bond lengths and angles can be
Figure 3. Molecular structure of 5 (only the more predominant of the
two tetrasilane conformations shown, hydrogen atoms omitted for
clarity). Bond lengths and angles can be found in the Supporting
Information.
found in the Supporting Information. HPh···CCC (CPh···CCC
)
distances (pm): H4−C12 = 277 (C4−C12 = 323), H4−C131 =
320 (C4−C131 = 389). Sum of the van der Waals radii: 300 (370)
pm.15
tetrasilane chain is disordered with two conformations in the
approximate ratio 4:1. Unfortunately, the amount of crystalline
product was too small for further spectroscopic and elemental
analyses.
The disilane compound tricarbonyl[tetramethyl-1-(η6-phe-
nyl)-2-phenylethynyldisilane]chromium(0) (PhCCMe2Si−
SiMe2PhCr(CO)3, 3) was synthesized via consecutive
introduction of the disilyl and alkynyl groups into the metal
complex fragment (Scheme 1 (route 4) and Scheme 3). The
Further workup of the reaction mixture finally gave a brown
oil in 65% yield with acceptable analytical data. As in the case of
3, attempts at “recrystallization” did not lead to a pure or solid
product. The IR spectroscopic data indicated the presence of
minor amounts of uncomplexed trisilane ligand but were
consistent with the proposed structure of 4. However, its
Scheme 3. Synthesis of 3
1
identity was finally confirmed by the H, 13C, and 29Si NMR
spectra, which indicated the presence of impurities, as well
(purity ∼90%).
Arenetricarbonylmolybdenum complexes are less stable than
the analogous chromium compounds. Consequently, generally
applicable synthetic routes toward these types of compounds
are very limited. The recommended route comprises the
substitution of the pyridine ligands in tricarbonyltris(pyridine)-
molybdenum (Mo(CO)3(py)3) by the arene in the presence of
boron trifluoride−diethyl ether (BF3·Et2O).19
Thus, BF3·Et2O was added to a mixture of Mo(CO)3py3 and
PhCCMe2SiPh in diethyl ether at room temperature to
s y n t h e s i z e t r i c a r b o n y l [ d i m e t h y l ( η 6 - p h e n y l ) -
phenylethynylsilane]molybdenum(0) (PhCCMe2SiPhMo-
(CO)3, 6) (Scheme 2). Workup afforded yellow-brown crystals
(light yellow under the microscope) in 46% yield. They were
air-stable for at least a few days. The 1H, 13C, and 29Si NMR as
well as the IR spectra were consistent with the molecular
structure of 6. A special feature was the observation of 95Mo
satellites at the carbonyl 13C NMR signal (1JMoC = 95 Hz, lit.20
60−208 Hz). The 95Mo NMR signal appeared at δ −2079 ppm
with a very narrow line width (Δν1/2 = 4 Hz), which is typical
for arenetricarbonylmolybdenum derivatives.21 Complex 6
crystallizes with four molecules of nearly identical conformation
in the asymmetric unit (Figure 4). In contrast to the related
chromium complex 1, compound 6 does not establish
intramolecular CH···π contacts in the crystal.
Unlike mono(arene)tricarbonylchromium complexes, bis-
(arene)chromium compounds are very sensitive toward
oxidation.22a,b There are three entries into this class of
complexes: (1) co-condensation of arene and chromium
vapor, (2) Fischer−Hafner synthesis, and (3) modification of
the arene ligands in a bis(arene)chromium complex.22c−e While
the co-condensation requires expensive equipment, the harsh
conditions of the Fischer−Hafner synthesis would lead to
rearrangement or decomposition of the alkynylphenylsilanes
used. The only promising pathway to alkynylsilyl derivatives of
multistep reaction consisted of initial lithiation of (C6H6)Cr-
(CO)3, which was then reacted with 1-chloro-2-N,N-
diethylaminotetramethyldisilane (Et2NMe2Si−SiMe2Cl) to in-
troduce the disilane chain. Subsequently, the amino protecting
group was transformed into a methoxy and then a chloro
substituent by methanol and acetyl chloride, respectively.16
Final addition of phenylethynylmagnesium bromide (PhC
CMgBr) gave 3 as a viscous brown oil in 57% total crude yield.
Details about the assumed intermediates, which were not
isolated, can be found in the Supporting Information.
Admittedly, the NMR spectra of the product indicated a
“purity” of only ∼75%.17 Unfortunately, attempts at recrystal-
lization did not afford a pure or solid product, probably because
of the flexible disilane chain, which prevented crystallization.
Therefore, satisfying elemental analyses could not be obtained.
1
Nevertheless, the identity was verified by the H, 13C, and 29Si
NMR as well as the IR spectroscopic data, which were in good
agreement with the proposed structure concerning position,
number, intensity, and coupling patterns of the signals.
Although it appeared unlikely to obtain a crystalline
compound (cf. 3), the trisilane complex tricarbonyl-
[hexamethyl-1-(pent-1-yn-1-yl)-3-(η6-phenyl)trisilane]-
chromium(0) (n-PrCCMe2Si−SiMe2−SiMe2PhCr(CO)3, 4)
was synthesized from hexamethyl-1-(pent-1-yn-1-yl)-3-phenyl-
trisilane (n-PrCCMe2Si−SiMe2−SiMe2Ph) and Cr(CO)6
(Scheme 1 (route 1) and Scheme 2). As in the case of the
synthesis of 1 the reaction was very slow, the conversion being
93% only after 150 h. Unexpectedly, workup yielded at first a
small amount of yellow crystals. However, their NMR spectra
suggested them to be [μ-octamethyl-1,4-bis(η6-phenyl)-
tetrasilane]bis[tricarbonylchromium(0)] ((OC)3CrPh−
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Figure 4. Molecular structure of 6 (only one of the four molecules
with nearly identical conformations in the asymmetric unit shown,
hydrogen atoms omitted for clarity). Bond lengths and angles can be
found in the Supporting Information.
Figure 5. Molecular structure of 7 with an intramolecular CH···π
interaction (hydrogen atoms except H1 and H1i omitted for clarity).
Bond lengths and angles can be found in the Supporting Information.
HPh···CCC (CPh···CCC) distances (pm): H1−C9 = 280 (C1−C9 =
324), H1−C10 = 329 (C1−C10 = 395). Sum of the van der Waals
radii: 300 (370) pm.15
bis(benzene)chromium ((C6H6)2Cr) seemed to be its lithiation
and subsequent reaction with an alkynylchlorosilane. This
sequence should result in 1,1′-disubstituted compounds since
1,1′-dilithiation is preferred (like in ferrocene).23
Thus, in order to synthesize bis[dimethyl(η6-phenyl)-
phenylethynylsilane]chromium(0) ((PhCCMe2SiPh)2Cr,
7), (C6H6)2Cr was dilithiated with n-butyllithium/N,N,N′,N′-
tetramethylethylenediamine (n-BuLi/TMEDA) in cyclohexane
under reflux (Scheme 4).24 Subsequent addition of PhC
reactions, especially the synthesis of multinuclear compounds,
we explored their reactivity toward complexation (inter- and
intramolecular) and bond-forming reactions of the CC triple
bond.
In an attempt to circumvent the harsh reaction conditions
hitherto applied in the synthesis of complexes of the type
Cp2Ni2·RCCR,28 a new synthetic procedure starting from
alkyne, nickelocene (Cp2Ni), sodium, and a small amount of
naphthalene (as electron-transfer catalyst) at room temperature
was developed. Tests with diphenylethyne (tolane, PhC
CPh) gave good results (80−90% crude yield of Cp2Ni2·PhC
CPh, 40−50% after recrystallization); therefore, this reaction
was used to synthesize the complex tricarbonyl-1κ3C-
dicyclopentadienyl-2(η5),3(η5)-{μ3-dimethyl[phenyl-1(η6)]-
(phenylethynyl-2κ2C,C′:3κ2C,C′)silane}-1-chromium(0)-2,3-
bis[nickel(I)](Ni−Ni) ((OC)3CrPhSiMe2CCPh·Ni2Cp2, 8)
from compound 1 (Scheme 5). The reaction product was
Scheme 4. Synthesis of 7
CMe2SiCl furnished 7 in a slow but clean reaction in 79% yield
after workup as very air-sensitive, dark red crystals. The
oxidation product was supposed to be the bis(arene)chromium
monocation.22c,d However, when we attempted to synthesize it
on a preparative scale by aerobic oxidation under either acidic
or basic conditions and precipitation with aqueous sodium
tetraphenylborate (NaBPh4) solution, complete desilylation
occurred and the bis(benzene)chromium salt
Scheme 5. Synthesis of Di- and Trinuclear Complexes 8−10
(C6H6)2Cr+BPh4 was obtained.25 Only upon oxidation in a
−
neutral aqueous medium (phosphate buffer) could a mixture of
silylated cations and (C6H6)2Cr+ be detected by IR spectros-
copy and elemental analysis.26
The spectroscopic characterization of 7 was complicated by
its air sensitivity. While the organosilyl groups furnished the
1
expected signals in the H, 13C, and 29Si NMR spectra, the
peaks of the chromium-bound phenyl groups were severely
broadened in benzene-d6 (C6D6). This is quite common for
bis(arene)chromium complexes and is caused by exchange
processes with traces of their oxidation products.27 Never-
theless, in cyclohexane these exchange processes were sup-
pressed due to the insolubility of the cationic oxidation
products and the missing signals could be observed. The stretch
of the CC triple bond was detected by IR spectroscopy in
solution at 2157 cm−1. A solid-state IR spectrum of 7 could not
be measured because of decomposition.
In the solid state the chromium atom of 7 is situated on a
crystallographic inversion center. The phenylethynyl groups are
oriented in opposite directions, leading to an elongated shape
of the molecule (Figure 5). As in 1 and 2 there is a CH···π
contact between an ortho phenyl hydrogen and the silicon-
bound carbon atom of the CC triple bond.
obtained after four tedious recrystallizations in 24% yield as a
dark green microcrystalline solid, which showed no signs of
decomposition in contact with air for at least 1 day. X-ray
crystal structure analysis revealed the presence of 0.25 mol of
naphthalene per 1 mol of 8 (8·0.25C10H8). In addition to the
high solubility of 8 in organic solvents this may be an
Reactivity of the CC Triple Bond. In order to examine
the synthetic potential of the alkynylsilyl complexes in further
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explanation for the low yield: the amount of naphthalene used
for catalysis was too small for complete crystallization of 8 as 8·
0.25C10H8. The IR and NMR data were consistent with the
proposed molecular structure.
The asymmetric unit of 8·0.25C10H8 contains two molecules
of 8 (with very similar conformations) and a half molecule of
naphthalene, which is situated on a crystallographic inversion
center (Figure 6). The former triple bond (C12−C13) has a
Figure 7. Molecular structure of 9 (hydrogen atoms omitted for
clarity). Bond lengths and angles can be found in the Supporting
Information. Mo···CO distances (pm): Mo3−C25 = 286, Mo3−C26 =
346, Mo2−C32 = 348, Mo2−C33 = 441. Sum of the van der Waals
radii: 360 pm (310 pm based on the metallic radius of
molybdenum).15,32
With appropriate transition-metal moieties, e.g. bis-
(triphenylphosphane)(η5-cyclopentadienyl)cobalt(I) (CpCo-
(PPh3)2), the reaction does not stop at the alkyne complex
stage and carbon−carbon bond coupling reactions occur.33
Reaction of the bis(arene)chromium complex 7 with CpCo-
(PPh3)2 at room temperature afforded an unprecedented
dinuclear bis(arene)chromium−cyclobutadienecobalt complex
instead of the expected cobaltacyclopentadiene compound
(Scheme 5).34 It was isolated in 8% yield and identified by X-
ray crystallography. Considering the harsh conditions hitherto
reported for the formation of cyclobutadiene cobalt complexes,
the mild reaction temperature is remarkable.35 The product,
2(η5)-cyclopentadienyl-{μ-3,4-diphenyl-1,2-bis{dimethyl-
[phenyl-1(η6)]silyl}-cyclobutadiene-2(η4)}-1-chromium(0)-2-
cobalt(I) (CpCo[PhCCSiMe2Ph]2Cr, 10), formed large dark
brown crystals which were air stable for at least a few hours. In
contrast, solutions were very air sensitive. Thus, as with 7, the
NMR spectroscopic characterization was hampered by
exchange processes with oxidation products (line broadening).
However, analytical and spectral data were consistent with the
anticipated molecular structure.
Figure 6. Molecular structure of 8·0.25C10H8 (only one of the two
complex molecules with nearly identical conformations in the
asymmetric unit shown, hydrogen and naphthalene carbon atoms
omitted for clarity). Bond lengths and angles can be found in the
Supporting Information.
length of 134 pm, corresponding to a double-bond character in
this complex. The crystal packing contains voids along the a
axis between the silicon-bound methyl groups and the
noncomplexed phenyl substituents of the former triple bonds
which accommodate the naphthalene molecules.29
Compound 6 reacted with tetracarbonyldi(η5-
cyclopentadienyl)dimolybdenum (Cp2Mo2(CO)4), resulting
in the homotrinuclear complex heptacarbonyl-
1κ3C,2κ2C,3κ2C-dicyclopentadienyl-2(η5),3(η5)-{μ3-dimethyl-
[phenyl-1(η6)](phenylethynyl-2κ2C,C′:3κ2C,C′)silane}-1-
molybdenum(0)-2,3-bis[molybdenum(I)](Mo2−Mo3)
((OC)3MoPhSiMe2CCPh·Cp2Mo2(CO)4, 9) in 23% yield as
a dark reddish brown microcrystalline solid which could be
handled in air (Scheme 5).
The molecular structure shows that the fixation of the alkynyl
groups by the bis(arene)chromium unit apparently hampers the
formation of a cobaltacyclopentadiene moiety and favors the
formation of a cyclobutadiene cobalt moiety instead by forcing
the phosphane out of the complex (Figure 8).36 The former
alkyne triple bonds are elongated to 147−148 pm. The
compound features helical chirality with the chirality axis along
the 6-fold symmetry axis of the bis(arene)chromium unit.
The IR and NMR spectral features were consistent with the
molecular structure of 9. The 95Mo NMR spectrum showed
two signals at δ −2071 ppm (Δν1/2 = 6 Hz) and δ −1870 ppm
(Δν1/2 = 1200 Hz), which were assigned to the arene and the
alkyne complex moiety, respectively, on the basis of literature
data21 and comparative measurements of the analogous tolane
complex.30 However, the H and 29Si NMR spectra indicated
1
the presence of ∼5% tetracarbonyl-1κ2C,2κ2C-dicyclopenta-
dienyl-1(η5),2(η5)-[μ-dimethyl(phenyl)(phenylethynyl-
1κ2C,C′:2κ2C,C′)silane]-1,2-bis[molybdenum(I)](Mo−Mo)
(PhSiMe2CCPh·Cp2Mo2(CO)4) (29Si NMR (C6D6): δ +0.6
ppm), formed by demetalation of the phenyl group.
The bond length of the former alkyne triple bond (138 pm)
is comparable to that of an aromatic C−C bond (Figure 7).
While three of the carbonyl ligands of the Cp2Mo2(CO)4
moiety form nearly linear Mo−C−O axes, the carbon atom of
the fourth ligand (C25−O4) is markedly displaced toward the
opposite molybdenum atom (Mo3), their distance being below
the sum of the corresponding van der Waals radii. This can be
regarded as a partially bridging carbonyl ligand, as already
described in the literature for other alkyne complexes of
Cp2Mo2(CO)4.31
Figure 8. Molecular structure of 10 (M isomer, hydrogen atoms
omitted for clarity). Bond lengths and angles can be found in the
Supporting Information.
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However, it crystallizes as a racemate (space group type Cc, Z =
4).
Thus, alkynylsilylarene complexes are useful precursors to
multinuclear homo- or heterometallic compounds, which may
find application in the fields of catalysis (tailored catalysts) or
materials science (metal- and silicon-containing polymer-
s).3a,7g,h
Whereas the preceding experiments aimed at intermolecular
reactions of the triple bond to form multinuclear complexes,
intramolecular reactions of the alkynylsilyl group with the
transition-metal complex moiety are also possible.6,37
Irradiation-induced ligand substitutions are quite common
also for silyl38 and stannyl39 complexes with unsaturated
hydrocarbons. Admittedly, oligosilane chains rearrange and
shorten under these conditions.38b,c,40 Even cyclic benzene-
tricarbonylchromium−alkyne derivatives with alkyl ether
bridges are known.6 Consequently, solutions of compounds
1, 3, 4, and 6 were irradiated with UV light6a,41 and the progress
of the reaction was monitored with IR and NMR spectroscopy.
Except for the UV treatment of compound 4, only
decomposition occurred and the free silane ligands were
detected.
EXPERIMENTAL SECTION
■
General Remarks. All operations were carried out under purified
argon using standard Schlenk line or glovebox techniques. If possible,
reactions were monitored by NMR or IR spectroscopy. The NMR
spectra were recorded at 22 °C using tetramethylsilane (Me4Si) as
1
internal standard for H (400.13 MHz), 13C (100.63 MHz), and 29Si
(79.49 MHz). The external standards for 31P (161.98 MHz), 59Co
(94.65 MHz), and 95Mo (26.02 MHz) were 85% H3PO4, 0.1 mol/L
K3[Co(CN)6] in D2O, and 1 mol/L Na2MoO4 in H2O, respectively.43
For 29Si NMR spectra the INEPT44 pulse sequence was employed.
Melting points were determined between thin glass plates (air) or in
sealed capillaries (argon) on a Boetius type heating microscope with a
̈
Upon irradiation of complex 4 a low-field shift of the 29Si
NMR signal of the silicon atom bearing the alkyne group by
about 10 ppm suggested that complexation of the CC bond
had taken place.42 However, the anticipated main product
dicarbonyl{hexamethyl-1-[(1,2-η)-pent-1-yn-1-yl]-3-(η6-
phenyl)trisilane}chromium(0) (n-PrCCMe2Si−SiMe2−
SiMe2PhCr(CO)2, Scheme 6) could not be isolated. Instead,
heating rate of about 4 K/min. The UV irradiation experiments were
performed in a Narva UVS 125 quartz photoreactor with 125 W
irradiation power and 150 mL volume.45
Chemicals. Solvents were dried and deoxygenated by distillation
under argon from sodium−benzophenone (benzene, diethyl ether,
hexane, THF, toluene), calcium hydride (acetonitrile, dibutyl ether,
chloroform-d (CDCl3), cyclohexane, heptane, propionitrile, pyridine,
TMEDA), lithium aluminum hydride (pentane), sodium−potassium
alloy (C6D6), or magnesium (methanol) and stored under argon until
use. Acetyl chloride was distilled from iron powder under argon and
stored under argon until use. Et2NMe2Si−SiMe2Cl was synthesized
analogously to Et2NMe2SiCl.46 The other silanes were synthesized as
previously published.31c Mo(CO)3(py)3 was prepared from Mo-
(CO)3(MeCN)3 and pyridine in THF.47 CpCo(PPh3)2·0.5(C6H14/
C7H8) was obtained as already described.33 The other chemicals were
prepared after common procedures or purchased from commercial
suppliers and were used as received.
Scheme 6. Intramolecular Reaction of Complex 4 upon UV
Irradiation As Indicated by 29Si NMR Spectroscopy
Crystal Structure Analyses. The X-ray single-crystal structure
analyses were performed on a “Bruker-Nonius X8” diffractometer
using Mo Kα radiation (λ = 71.073 pm) and an APEX2-CCD area
detector. For solution, refinement, and visualization of the structures
the programs Bruker SMART,48a Bruker SAINT,48a Bruker
SHELXTL,48b SHELXS-97,48c SHELXL-97,48d and ORTEP3248e
were used. The thermal ellipsoids are drawn at the 50% probability
level unless otherwise stated. The data of 9 were collected from a twin
with domains of similar diffraction power (56:44 ratio, Rint = 0.0246
and 0.0247). Equivalent reflections were merged before scaling.
Structure refinement was carried out with a HKLF5 file containing
data of both domains.
a mixture of 4 and the free trisilane ligand n-PrCCMe2Si−
SiMe2−SiMe2Ph was obtained. These were most likely formed
by decomposition of the irradiation product, as the 29Si NMR
spectrum had indicated that they were present after irradiation
only in minor amounts. Nevertheless, this indicates that the
trisilane backbone is maintained throughout the irradiation
without rearrangement.
CONCLUSIONS
■
Tricarbonyl[dimethyl(η6-phenyl)phenylethynylsilane]-
chromium(0) (1). Cr(CO)6 (2.23 g, 10.1 mmol) and PhC
CMe2SiPh (2.29 g, 9.7 mmol) were refluxed in a mixture of dibutyl
ether (45 mL) and THF (5 mL) for 93 h. From time to time Cr(CO)6
subliming into the condenser was pushed back into the flask with a
long spatula. After it was cooled to room temperature, the mixture was
evaporated in vacuo. The oily residue was dissolved in diethyl ether
and filtered. The filtrate was evaporated in vacuo and the residue
extracted with hexane (50 mL) by stirring overnight. The extract was
concentrated in vacuo to 10 mL and cooled to −20 °C, whereupon a
brown-yellow solid deposited. Repetition of extraction and cooling
furnished yellow needlelike crystals, which were separated, washed
with hexane (2 × 5 mL), and dried in vacuo. These needles were
suitable for X-ray crystallography. 1 is air-stable for several days but
should be stored under argon.
Alkynylsilylarene complexes can be synthesized with good
results both by direct complexation of substituted benzenes or
silylation of preformed arene complexes (except for the
reaction of lithiated (C6H6)Cr(CO)3 with an alkynylchlor-
osilane). Therefore, derivatives of (C6H6)Cr(CO)3 are more
easily to synthesize than the corresponding CpMn(CO)3
derivatives.3b In case of direct arene complex formation of a
silane bearing phenylethynyl and phenyl substituents, complex-
ation of the silicon-bound phenyl group is preferred.
Complexes with an n-propyl substituent at the CC triple
bond are more sensitive to decomposition than those with a
phenyl substituent. This is likely to be more an electronic than
a steric effect, as their molecular structures are very similar
including a weak CH···π contact.
The alkynyl groups undergo further complexation reactions
with additional metal compounds leading to various hetero-
and homomultinuclear compounds. With appropriate reagents,
such as CpCo(PPh3)2, complexation is accompanied by
carbon−carbon bond coupling reactions resulting, e.g., in a
dinuclear cyclobutadiene complex.
Yield: 1.53 g, 4.11 mmol, 42%. Mp: 47−48 °C (argon), 48−50 °C
(air). Solubility: hexane, diethyl ether, THF, chloroform. Anal. Found
(calcd) for C19H16CrO3Si (372.416): C, 61.32 (61.28); H, 4.44 (4.33).
1H NMR (0.13 mol/L in CDCl3): δ 7.51 (m, 2 H, Phortho), 7.32 (m, 3
3
3
H, Phmeta+para), 5.61 (d, JHH = 6.4 Hz, 2 H, PhCrortho), 5.55 (t, JHH
=
3
6.4 Hz, 1 H, PhCrpara), 5.17 (“t”, JHH = 6.4 Hz, 2 H, PhCrmeta), 0.52
(s, JHC = 121 Hz, 6 H, SiMe2) ppm. 13C NMR (0.13 mol/L in
1
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CDCl3): δ 232.8 (s, 3 C, CO), 132.2 (s, 2 C, Phortho), 129.1 (s, 1 C,
Phpara), 128.3 (s, 2 C, Phmeta), 122.4 (s, 1 C, Phipso), 108.0 (s, 2JCSi = 17
Hz, 1 C, CCSi), 99.7 (s, 2 C, PhCrortho), 95.8 (s, 1JCSi = 70 Hz, 1 C,
PhCripso), 95.5 (s, 1 C, PhCrpara), 90.1 (s, 2 C, PhCrmeta), 89.8 (s, 1JCSi
= 92 Hz, 1 C, CCSi), −0.9 (s, 1JCSi = 60 Hz, 2 C, SiMe2) ppm. 29Si
(29Si NMR (THF): δ +14.6 (s, 1 Si, −SiMe2OMe), −20.1 (s, 1 Si,
−SiMe2PhCr(CO)3) ppm).
This solution was evaporated in vacuo, and the residue was
redissolved in hexane (20 mL). After this solution was cooled to 0 °C,
acetyl chloride (7.0 mL, 7.73 g, 98.6 mmol) diluted with hexane (5
mL) was added. The mixture was stirred at room temperature for 2
days. Then it was filtered and the filtrate evaporated in vacuo,
furnishing a dark yellow oil (29Si NMR (hexane): δ +18.1 (s, 1 Si,
−SiMe2Cl), −19.4 (s, 1 Si, −SiMe2PhCr(CO)3) ppm).
1
NMR (0.13 mol/L in CDCl3): δ −18.3 (s, JSiC(Me) = 59 Hz (2 C),
1JSiC(Ph) = 71 Hz (1 C), JSiC(CC) = 92 Hz (1 C), JSiC(CC) = 17 Hz
1
2
(1 C)) ppm. IR (hexane): ν
̃
2160 (w, ν(CC)), 1978 (s, ν(CO)),
1912 (s, ν(CO)) cm−1. IR (KBr): ν
2157 (m, ν(CC)), 1965 (vs,
̃
ν(CO)), 1888 (vs, ν(CO)) cm−1 (see the Supporting
Information for complete data). UV/vis (hexane): λ (ε) 222 (br,
16000, PhCr(CO)3), 238 (15000, PhCC), 248 (18000, PhCC),
259 (15000, PhCC), 319 (br, 7400, PhCr(CO)3) nm (L/(mol
cm)).49
This oil was dissolved in diethyl ether (15 mL), and PhCCMgBr
in diethyl ether (prepared from magnesium (75 mg, 3.09 mmol), 1,2-
dibromoethane (1 droplet), ethyl bromide (300 μL, 438 mg, 4.02
mmol), phenylacetylene (330 μL, 307 mg, 3.01 mmol), and diethyl
ether (10 mL), 3 h reflux)50 was added slowly at room temperature.
After it was stirred overnight, the mixture was refluxed for 2 h. After
cooling it was cautiously hydrolyzed with 10% NH4Cl solution (4 × 10
mL), washed with water (3 × 10 mL), and dried over Na2SO4.
Removal of the ether furnished 3 as a dark brown oil.
Tricarbonyl[dimethyl(pent-1-yn-1-yl)(η6-phenyl)silane]-
chromium(0) (2). (a). Synthesis in the Ratio 1:1 in Cyclohexane. n-
PrCCMe2SiPh (300 mg, 330 μL, 1.48 mmol), Cr(CO)3(MeCN)3
(420 mg, 1.62 mmol), and cyclohexane (17 mL) were refluxed for 16
h. After it was cooled to room temperature, the solution was filtered
and concentrated in vacuo to 1 mL and hexane (1.5 mL) was added.
Cooling to −78 °C afforded a yellow solid, which was separated,
washed with pentane (2 × 1.5 mL), and dried in vacuo. It was
recrystallized once from hexane (5 mL) to give bright yellow crystals.
Crystals suitable for X-ray crystallography were grown from hexane by
slow warming of a concentrated solution from −78 to −20 °C. The
product is air-stable for some time but should be stored under argon in
a refrigerator. Yield: 275 mg, 0.81 mmol, 55%.
1
Yield: 745 mg, 1.73 mmol, 57%. Solubility: hexane, benzene. H
NMR (0.7 mol/L in C6D6): δ 7.38 (m/br, 2 H, Phortho), 6.98 (m/br, 3
3
H, Phmeta+para), 4.98 (d/br, JHH = 4.8 Hz, 2 H, PhCrortho), 4.69 (t/br,
3
3JHH = 5.9 Hz, 1 H, PhCrpara), 4.40 (“t”/br, JHH = 5.9 Hz, 2 H,
PhCrmeta), 0.38 (s/br, 6 H, SiMe2), 0.24 (s/br, 6 H, SiMe2) ppm. 13C
NMR (0.7 mol/L in C6D6): δ 233.7 (s, 3 C, CO), 132.1 (s, 2 C,
Phortho), 128.9 (s, 1 C, Phpara), 128.6 (s, 2 C, Phmeta), 123.5 (s, 1 C,
Phipso), 109.1 (s, 2JCSi = 14 Hz, 1 C, CCSi), 99.2 (s, 2 C, PhCrortho),
98.5 (s, 1 C, PhCripso), 94.8 (s, 1 C, PhCrpara), 92.1 (s, 1 C, CCSi),
91.0 (s, 2 C, PhCrmeta), −2.8 (s, 2 C, SiMe2), −4.3 (s, 2 C, SiMe2)
ppm. 29Si NMR (0.7 mol/L in C6D6): δ −16.5 (s, 1JSiC(Me) = 48 Hz (2
C), 1JSiC(Ph) = 53 Hz (1 C), 2JSiC(CC) = 18 Hz (1 C), 1JSiSi = 90 Hz, 1
(b). Synthesis in the Ratio 1:2 in Heptane. n-PrCCMe2SiPh
(595 mg, 660 μL, 2.94 mmol), Cr(CO)3(MeCN)3 (1.520 g, 5.86
mmol), and heptane (30 mL) were refluxed for 24 h. After it was
cooled to room temperature, the solution was filtered and evaporated
in vacuo. The brown oily residue was dissolved in hexane (4 mL) and
cooled to −78 °C. The precipitated solid was separated, washed with
pentane (500 μL), and dried in vacuo (815 mg, 82% crude yield). It
was recrystallized once from hexane (3 mL), yielding brownish yellow
crystals. Yield: 800 mg, 2.36 mmol, 80% referenced to n-PrC
CMe2SiPh, 40% referenced to Cr(CO)3(MeCN)3.
Si, −SiMe2PhCr(CO)3), −36.9 (s, 1JSiC(Me) = 50 Hz (2 C), 1JSiC(CC)
=
2
1
76 Hz (1 C), JSiC(CC) = 16 Hz (1 C), JSiSi = 90 Hz, 1 Si,
−SiMe2CCPh) ppm. IR (hexane): ν 2152 (w, ν(CC)), 1972 (s,
̃
ν(CO)), 1906 (s, ν(CO)) cm−1.
Tricarbonyl[hexamethyl-1-(pent-1-yn-1-yl)-3-(η6-phenyl)-
trisilane]chromium(0) (4) and [μ-octamethyl-1,4-bis(η6-
phenyl)tetrasilane]bis[tricarbonylchromium(0)] (5). Cr(CO)6
(1.220 g, 5.54 mmol), n-PrCCMe2Si−SiMe2−SiMe2Ph (1.475 g,
4.63 mmol), dibutyl ether (45 mL), and THF (6 mL) were refluxed
for 150 h. From time to time Cr(CO)6 subliming into the condenser
was pushed back into the flask with a long spatula. After it was cooled,
the mixture was evaporated in vacuo, the oily residue was redissolved
in diethyl ether, and this solution was filtered. The filtrate was again
evaporated in vacuo, leaving a yellow-brown oil which was dissolved in
hexane (5 mL). On cooling to −20 °C a greenish yellow solid
precipitated (5), which was separated, washed with hexane (3 × 1
mL), and dried in vacuo. Crystals suitable for X-ray crystallography
were grown from hexane at 5 °C. The mother liquor was evaporated to
two-thirds of its volume and cooled to −78 °C, whereupon a brownish
red oil deposited (4). It was separated, washed with hexane (1 mL),
and dried in vacuo.
Mp: 21−23 °C (argon), 24−25 °C (air). Solubility: hexane,
pentane, heptane, benzene, diethyl ether, chloroform (dec). Anal.
Found (calcd) for C16H18CrO3Si (338.399): C, 57.05 (56.79); H, 5.18
(5.36). 1H NMR (0.3 mol/L in C6D6): δ 5.10 (d, 3JHH = 5.5 Hz, 2 H,
PhCrortho), 4.70 (t, 3JHH = 5.5 Hz, 1 H, PhCrpara), 4.33 (“t”, 3JHH = 5.5
Hz, 2 H, PhCrmeta), 2.01 (t, 3JHH = 6.4 Hz, 2 H, −CH2CH2CH3), 1.37
(“sextet”, 3JHH = 7 Hz, 2 H, −CH2CH2CH3), 0.85 (t, 3JHH = 6.9 Hz, 3
1
H, −CH2CH2CH3), 0.32 (s, JHC = 120 Hz, 6 H, SiMe2) ppm. 13C
NMR (0.3 mol/L in C6D6): δ 233.3 (s, 3 C, CO), 111.2 (s, 2JCSi = 18
Hz, 1 C, CCSi), 99.6 (s, 2 C, PhCrortho), 96.5 (s, 1 C, PhCripso), 95.3
(s, 1 C, PhCrpara), 90.1 (s, 1JCC = 46 Hz, 2 C, PhCrmeta), 81.0 (s, 1JCSi
=
95 Hz, 1 C, CCSi), 22.1 (s, 1 C, CH2), 22.0 (s, 1 C, CH2), 13.4 (s, 1
1
C, CH3), −0.7 (s, JCSi = 59 Hz, 2 C, SiMe2) ppm. 29Si NMR (0.3
mol/L in C6D6): δ −19.3 (s, 1JSiC(Me) = 59 Hz (2 C), 1JSiC(Ph) = 71 Hz
1
2
Data for 4 are as follows. Yield: 1.360 g, 2.99 mmol, 65%. Anal.
(1 C), JSiC(CC) = 95 Hz (1 C), JSiC(CC) = 18 Hz (1 C)) ppm. IR
Found (calcd) for C20H30CrO3Si3 (454.711): C, 54.23 (52.83);51a H,
(hexane): ν 2174 (w, ν(CC)), 1980 (s, ν(CO)), 1908 (s, ν(C
̃
1
O)) cm−1. IR (neat liquid): ν
̃
2173 (s, ν(CC)), 1970 (vs, ν(C
6.89 (6.65). Solubility: hexane, benzene, diethyl ether. H NMR (0.9
3
4
O)), 1893 (vs, ν(CO)) cm−1 (see the Supporting Information for
complete data). UV/vis (hexane): λ (ε) 218 (br, 21000, PhCr(CO)3),
260 (br, 7000, PhCr(CO)3), 319 (br, 11000, PhCr(CO)3) nm (L/
(mol cm)).49
mol/L in C6D6): δ 4.98 (dd, JHH4 = 6.4 Hz, JHH = 1 Hz, 2 H,
3
PhCrortho), 4.78 (tt, JHH = 6.4 Hz, JHH = 1 Hz, 1 H, PhCrpara), 4.51
3
3
(“t”, JHH = 6.4 Hz, 2 H, PhCrmeta), 2.00 (t, JHH = 7.0 Hz, 2 H,
3
−CH2CH2CH3), 1.36 (“sextet”, JHH = 7.1 Hz, 2 H, −CH2CH2CH3),
0.86 (t, 3JHH = 7.3 Hz, 3 H, −CH2CH2CH3), 0.40 (s, 2JHSi = 6 Hz, 6 H,
T r i c a r b o n y l [ t e t r a m e t h y l - 1 - ( η 6 - p h e n y l ) - 2 -
phenylethynyldisilane]chromium(0) (3). A 2.5 mol/L solution of
n-BuLi in hexane (1.3 mL, 3.25 mmol) was diluted with hexane (5
mL) and added to a solution of (C6H6)Cr(CO)3 (645 mg, 3.01 mmol)
in THF (30 mL) cooled to −78 °C with exclusion of light. After 2.5 h
of stirring at −78 °C Et2NMe2SiSiMe2Cl (900 μL, 800 mg, 3.58
mmol) in hexane (5 mL) was added slowly. Warming to room
temperature and stirring overnight furnished a yellow-brown solution
(29Si NMR (THF): δ −3.9 (s, 1 Si, −SiMe2NEt2), −19.8 (s, 1 Si,
−SiMe2PhCr(CO)3) ppm).
2
2
SiMe2), 0.17 (s, JHSi = 6 Hz, 6 H, SiMe2), 0.11 (s, JHSi = 6 Hz, 6 H,
SiMe2) ppm. 13C NMR (0.9 mol/L in C6D6): δ 233.7 (s, 3 C, CO),
110.5 (s (1H coupled: m), 1 C, CCSi), 100.2 (s (1H coupled: s/br),
1 C, PhCripso), 99.1 (s (1H coupled: dt, 1JCH = 171 Hz, 3JCH = 7 Hz), 2
C, PhCrortho), 94.8 (s (1H coupled: dt, 1JCH = 173 Hz, 3JCH = 6 Hz), 1
C, PhCrpara), 91.0 (s (1H coupled: dd, 1JCH = 174 Hz, 3JCH = 6 Hz), 2
C, PhCrmeta), 83.0 (s (1H coupled: m), 1 C, CCSi), 22.3 (s (1H
2
coupled: tm, 1JCH = 129 Hz, JCH = 5−6 Hz), 1 C, CH2), 22.2 (s (1H
coupled: tm, 1JCH = 129 Hz, JCH = 5−6 Hz), 1 C, CH2), 13.5 (s (1H
2
1
2
This solution was cooled to 0 °C, and methanol (1.0 mL, 0.79 g,
24.7 mmol) was added. Stirring for 1.5 h yielded a brown solution
coupled: qt, JCH = 126 Hz, JCH = 4 Hz), 1 C, CH3), −1.7 (s (1H
1 3 1
coupled: qq, JCH = 121 Hz, JCH = 2 Hz), JCSi = 49 Hz, 2 C,
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1
3
SiMe2CC-n-Pr), −3.5 (s (1H coupled: qq, JCH = 121 Hz, JCH = 2
Hz), 1JCSi = 47 Hz, 2 C, SiMe2PhCr(CO)3), −6.9 (s (1H coupled: qq,
1JCH = 122 Hz, 3JCH = 3 Hz), 1JCSi = 39 Hz, 2 C, −SiMe2−) ppm. 29Si
−20 °C. After removal of the supernatant liquid the dark red crystals
were washed with pentane (3 × 2.5 mL) and dried in vacuo. These
crystals were suitable for X-ray crystallography. The complex is very air
sensitive and must be stored under argon.
1
NMR (0.9 mol/L in C6D6): δ −13.2 (s, JSiC(Me) = 46 Hz (2 C),
1JSiC(Ph) = 54 Hz (1 C), JSiSi = 73 Hz, JSiSi = 8 Hz, 1 Si,
1
2
Yield: 830 mg, 1.58 mmol, 79%. Mp: 131−134 °C (argon).
Solubility: benzene, toluene, THF; sparingly in hexane, cyclohexane.
Anal. Found (calcd) for C32H32CrSi2 (524.776): C, 73.21 (73.24); H,
1
1
−SiMe2PhCr(CO)3), −35.5 (s, JSiC(Me) = 49 Hz (2 C), JSiC(CC)
=
76 Hz (1 C), 2JSiC(CC) = 15 Hz (1 C), 1JSiSi = 82 Hz, JSiSi = 8 Hz, 1
2
1
Si, −SiMe2CC-n-Pr), −47.0 (s, 1JSiC(Me) = 38 Hz, 1JSiSi = 73 Hz, 1JSiSi
6.13 (6.15). H NMR (0.5 mol/L in C6D6): δ 7.56 (m, 4 H, Phortho),
6.94 (m, 6 H, Phmeta+para), 4.7 (vbr, Δν1/2 = 900 Hz, 10 H, PhCr), 0.52
= 81 Hz, 1 Si, −SiMe2−) ppm. IR (hexane): ν
̃
2169 (w, ν(CC)),
1
1
1975 (s, ν(CO)), 1909 (s, ν(CO)) cm−1. IR (neat liquid): ν
̃
(s, JHC = 120 Hz, 12 H, SiMe2) ppm. H NMR (0.03 mol/L in
cyclohexane): δ 7.47 (m/br, 4 H, Phortho), 7.19 (m/br, 6 H, Phmeta+para),
4.54 (m/br, 4 H, PhCrortho/meta), 4.49 (m/br, 4 H, PhCrortho/meta), 4.26
(m/br, 2 H, PhCrpara), 0.43 (s/br, 12 H, SiMe2) ppm. 13C NMR (0.5
mol/L in C6D6): δ 132.3 (s, 4 C, Phortho), 128.8 (s, 2 C, Phpara), 128.6
(s, 4 C, Phmeta), 123.7 (s, 2 C, Phipso), 107.1 (s, 2 C, CCSi), 93.4 (s, 2
C, CCSi), 80−75 (br, PhCr), −0.04 (s, 4 C, SiMe2) ppm. 13C NMR
(0.03 mol/L in cyclohexane): δ 132.5 (s, 4 C, Phortho), 128.6 (s, 2 C,
Phpara), 128.4 (s, 4 C, Phmeta), 124.5 (s, 2 C, Phipso), 106.8 (s, 2 C, C
CSi), 92.9 (s, 2 C, CCSi), 79.4 (s, 4 C, PhCrortho/meta), 77.4 (s, 4 C,
PhCrortho/meta), 75.5 (s, 2 C, PhCrpara), 76−74 (s, 2 C, PhCripso), 0.0 (s,
4 C, SiMe2) ppm. 29Si NMR (0.5 mol/L in C6D6): δ −15.5 (vbr, Δν1/2
= 200 Hz) ppm. 29Si NMR (0.03 mol/L in cyclohexane): δ −15.6 (s)
̃
2166 (m, ν(CC)), 1969 (vs, ν(CO)), 1890 (vs, ν(CO)) cm−1
(see the Supporting Information for complete data).
Data for 5 are as follows. Yield: 90 mg, 0.14 mmol. Solubility: THF,
chloroform (dec), diethyl ether, hexane. 1H NMR (CDCl3): δ 5.5 (br,
2 H, PhCrpara), 5.3 (br, 4 H, PhCrortho/meta), 5.2 (br, 4 H, PhCrortho/meta),
0.4 (br, 12 H, SiMe2), 0.1 (br, 12 H, SiMe2) ppm. 13C NMR (CDCl3):
δ 233 (s, 3 C, CO), 100 (s, 2 C, PhCripso), 99 (s, 4 C, PhCrortho), 95 (s,
2 C, PhCrpara), 91 (s, 4 C, PhCrmeta), −3 (s, 4 C, −SiMe2PhCr(CO)3),
−5 (s, 4 C, −SiMe2−) ppm. 29Si NMR (CDCl3): δ −13 (s, 2 Si,
−SiMe2PhCr(CO)3), −44 (s, 2 Si, −SiMe2−) ppm.
Tricarbonyl[dimethyl(η6-phenyl)phenylethynylsilane]-
molybdenum(0) (6). BF3·Et2O (1.22 mL, 1.376 g, 9.69 mmol) was
added to Mo(CO)3(py)3 (1.340 g, 3.21 mmol) and PhCCMe2SiPh
(790 mg, 790 μL, 3.34 mmol) in diethyl ether (40 mL) at room
temperature with exclusion of light. After 1 h the molybdenum starting
complex had dissolved and the orange-yellow solution had turned dark
brown. It was evaporated in vacuo, and the residue was extracted with
hexane (15 × 10 mL). The extract was evaporated to half its volume in
vacuo and cooled to −78 °C. The precipitated solid was separated,
washed with hexane (3 × 2 mL), and dried in vacuo, yielding brownish
yellow crystals. Crystals suitable for X-ray crystallography were grown
from hexane at −20 °C. The complex is air-stable for several days but
should be stored under argon.
ppm. IR (toluene): ν 2157 (m, ν(CC)) cm−1. UV/vis (hexane): λ
(ε) 238 (18000, PhCC), 248 (25000, PhCC), 258 (19000,
PhCC), 312 (br, 11000, Ph2Cr), 407 (br/sh, 750, Ph2Cr), 520 (br/
sh, 170, Ph2Cr), 700 (br, 24, Ph2Cr) nm (L/(mol cm)).53
Tricarbonyl-1κ3C-dicyclopentadienyl-2(η5),3(η5)-{μ3-
dimethyl[phenyl-1(η6)](phenylethynyl-2κ2C,C′:3κ2C,C′)silane}-
1-chromium(0)-2,3-bis[nickel(I)](Ni−Ni)−Naphthalene (4:1) (8·
0.25C10H8). Cp2Ni (530 mg, 2.81 mmol), 1 (540 mg, 1.45 mmol),
and naphthalene (a few mg) were dissolved in THF (18 mL) and
stirred with sodium metal (70 mg, 3.04 mmol) at room temperature,
whereupon the green solution quickly became dark. The next day ethyl
bromide (500 μL, 730 mg, 6.70 mmol) was added, resulting in a
detectable rise of the temperature of the solution. After it was stirred
overnight, the mixture was evaporated in vacuo and the solid black-
green residue extracted with hexane (15 × 10 mL). The extract was
again evaporated in vacuo, leaving a dark green semisolid mass (760
mg, 88% crude yield referenced to 8, 80% crude yield referenced to 8·
0.25C10H8). Fourfold recrystallization from 1/1 diethyl ether/pentane
(or diethyl ether/hexane; 2−5 mL each, slow cooling to −78 °C)
yielded dark green microcrystals, which were washed with hexane (3 ×
0.5 mL) and dried in vacuo. These crystals were suitable for X-ray
crystallography. 8·0.25C10H8 is air-stable for at least 1 day but should
be stored under argon.
Yield: 620 mg, 1.49 mmol, 46%. Mp: 72−75 °C (argon), 72−74 °C
(air). Solubility: benzene, diethyl ether, hexane. Anal. Found (calcd)
for C19H16MoO3Si (416.360): C, 53.71 (54.81);51b H, 3.88 (3.87). 1H
NMR (0.17 mol/L in C6D6): δ 7.51 (m, 2 H, Phortho), 6.93 (m, 3 H,
Phm3eta+para), 5.24 (dd, 3JHH = 6.4 Hz, 4JHH = 1 Hz, 2 H, PhMoortho), 4.83
4
3
(tt, JHH = 6.4 Hz, JHH = 1 Hz, 1 H, PhMopara), 4.50 (“t”, JHH = 6.5
Hz, 2 H, PhMometa), 0.32 (s, 1JHC = 122 Hz, 2JHSi = 7 Hz, 6 H, SiMe2)
ppm. 13C NMR (0.17 mol/L in C6D6): δ 221.1 (s, 1JCMo = 95 Hz, 3 C,
CO), 132.4 (s, 1JCC = 56 Hz, 2 C, Phortho), 129.3 (s, 1 C, Phpara), 128.6
(s, 2 C, Phmeta), 122.9 (s, 1 C, Phipso), 108.6 (s, 2JCSi = 16 Hz, 1 C, C
CSi), 100.3 (s, 2 C, PhMoortho), 98.5 (s, 1JCSi = 70 Hz, 1 C, PhMoipso),
95.9 (s, 1 C, PhMopara), 91.7 (s, 2 C, PhMometa), 90.3 (s, 1JCSi = 92 Hz,
1 C, CCSi), −0.6 (s, JCSi = 60 Hz, 2 C, SiMe2) ppm. 29Si NMR
1
Yield: 230 mg, 0.35 mmol, 24%. Mp: 108−111 °C (argon), 114−
116 °C (air). Solubility: hexane, pentane, benzene, diethyl ether. Anal.
Found (calcd) for C31.5H28CrNi2O3Si (652.030): C, 57.90 (58.03); H,
1
1
(0.17 mol/L in C6D6): δ −18.8 (s, JSiC(Me) = 59 Hz (2 C), JSiC(Ph)
=
1
2
70 Hz (1 C), JSiC(CC) = 92 Hz (1 C), JSiC(CC) = 18 Hz (1 C))
1
ppm. 95Mo NMR (0.17 mol/L in C6D6): δ −2078.7 (s, Δν1/2 = 4 Hz)
4.44 (4.33). Calcd for 8 (C29H26CrNi2O3Si): C, 56.18; H, 4.23. H
NMR (0.03 mol/L in C6D6): δ 7.62 (d, 3JHH = 6.6 Hz, 1JHC = 160 Hz,
2 H, Phortho), 7.25 (m, C10H8), 7.14 (“t”, 3JHH = 8 Hz, 1JHC = 159 Hz, 2
ppm. IR (hexane): ν
̃
2161 (w, ν(CC)), 1984 (s, ν(CO)), 1913
(s, ν(CO)) cm−1. IR (KBr): ν
2157 (s, ν(CC)), 1964 (vs, ν(C
̃
3
O)), 1881 (vs, ν(CO)) cm−1 (see the Supporting Information for
complete data). UV/vis (hexane): λ (ε) 216 (10000, PhMo(CO)3),
238 (12000, PhCC), 248 (14000, PhCC), 259 (11000, PhC
C), 325 (br, 9100, PhMo(CO)3), 375 (br/sh, 960, PhMo(CO)3) nm
(L/(mol cm)).49b,52
H, Phmeta), 7.09 (t, JHH = 7.3 Hz, 1 H, Phpara), 7.14−7.09 (C10H8),
3
1
5.13 (d, JHH = 5.9 Hz, 2 H, PhCrortho), 5.04 (s, JHC = 174 Hz, 10 H,
Cp), 4.66 (t, 3JHH = 6 Hz, 1 H, PhCrpara), 4.33 (“t”, 3JHH = 6.2 Hz, 2 H,
PhCrmeta), 0.60 (s, JHC = 121 Hz, 6 H, SiMe2) ppm. 13C NMR (0.03
1
mol/L in C6D6): δ 233.6 (s, 3 C, CO), 138.8 (s, 1 C, Phipso), 134.1 (s,
C, C10H8), 131.2 (s, 2 C, Phortho), 128.6 (s, 2 C, Phmeta), 126.0 (s, CH,
C10H8), 113.4 (s, 1 C, CCSi·Ni2), 99.4 (s, 2 C, PhCrortho), 98.5 (s, 1
C, PhCripso), 95.2 (s, 1 C, PhCrpara), 90.3 (s, 2 C, PhCrmeta), 89.1 (s, 1
Bis[dimethyl(η6-phenyl)phenylethynylsilane]chromium(0)
(7). (C6H6)2Cr (416 mg, 2.00 mmol), TMEDA (700 μL, 540 mg, 4.65
mmol), and cyclohexane (20 mL) were heated to reflux, and 2.5 mol/
L n-BuLi in hexane (2.0 mL, 5.00 mmol) diluted with cyclohexane (8
mL) was added within 1.5 h. Refluxing was stopped 30 min after the
addition of n-BuLi had ended, and the red-brown suspension was
stirred overnight. The cyclohexane was then removed with a syringe
and replaced by hexane (30 mL), and the suspension was cooled to
−78 °C. PhCCMe2SiCl (845 mg, 4.34 mmol) in hexane (8 mL) was
added slowly. After it was warmed to room temperature overnight, the
mixture was stirred for 6 days. It was then evaporated in vacuo and the
residue extracted with toluene (16 mL). The extract was evaporated in
vacuo, furnishing a red oil which crystallized to a great extent on
standing. The solid was layered with pentane (5 mL) and cooled to
1
C, CCSi·Ni2), 87.7 (s, 10 C, Cp), −0.1 (s, JCSi = 58 Hz, 2 C,
SiMe2) ppm. 13C NMR (0.15 mol/L in diethyl ether): δ 233.1 (s, 3 C,
CO), 138.5 (s, 1 C, Phipso), 134.0 (s, C, C10H8), 131.0 (s, 2 C, Phortho),
128.2 (s, 2 C, Phmeta), 127.9 (s, CH, C10H8), 127.6 (s, 1 C, Phpara),
125.7 (s, CH, C10H8), 113.5 (s, 1 C, CCSi·Ni2), 99.8 (s, 2 C,
PhCrortho), 98.2 (s, 1 C, PhCripso), 95.7 (s, 1 C, PhCrpara), 90.4 (s, 2 C,
PhCrmeta), 88.4 (s, 1 C, CCSi·Ni2), 87.4 (s, 10 C, Cp), −0.3 (s, 2 C,
SiMe2) ppm. 29Si NMR (0.03 mol/L in C6D6): δ −8.9 (s, 1JSiC(Me) = 58
Hz (2 C), 1JSiC(PhCr) = 73 Hz (1 C), 1JSiC(CC·Ni2) = 67 Hz (1 C)) ppm.
IR (hexane): ν
̃
1976 (s, ν(CO)), 1910 (s, ν(CO)) cm−1. IR
(KBr): ν
̃
1960 (vs, ν(CO)), 1879 (vs, ν(CO)), 1602 (m, ν(C
4538
dx.doi.org/10.1021/om400378s | Organometallics 2013, 32, 4531−4542

Organometallics
Article
C)) cm−1 (see the Supporting Information for complete data). UV/vis
(hexane): λ (ε) 221 (85000, PhCr(CO)3 + Cp2Ni2·CC), 248
(57000, PhCC), 253 (55000), 259 (52000, PhCC + PhCr(CO)3
+ Cp2Ni2·CC), 321 (br, 35000, PhCr(CO)3), 351 (br, 34000,
Cp2Ni2·CC), 462 (br, 4800, Cp2Ni2·CC), 672 (br, 1500, Cp2Ni2·
CC) nm (L/(mol cm)).49
Δν1/2 = 10 Hz, 6 H, SiMe), 0.41 (s/br, Δν1/2 = 6 Hz, 1JHC = 119 Hz, 6
H, SiMe) ppm. 13C NMR (0.008 mol/L in C6D6): δ 138.1 (s, 2 C,
Phipso), 129.3 (s, 4 C, Phortho), 126.6 (s, 2 C, Phpara), 88.0 (s, 2 C,
C4Co), 82.8 (s, 5 C, Cp), 81.6 (s, 2 C, C4Co), 75 (vbr, PhCr), 4.0 (s/
br, SiMe), 1.8 (s/br, SiMe) ppm.55a 29Si NMR (hexane/toluene): δ
−3.5 (s, JSiC(Me) = 54 Hz (2 C), JSiC(PhCr/CbCo) = 72 Hz (2 C))
ppm.55b IR (KBr): see the Supporting Information. UV/vis (hexane):
λ (ε) 213 (7400), 232 (br, 8600), 284 (br, 7500), 310 (br, 6900), 410
(br/sh, 820), 590 (br/sh, 65) nm (L/(mol cm)).53
1
1
Heptacarbonyl-1κ3C,2κ2C,3κ2C-dicyclopentadienyl-2(η5),3-
(η5)-{μ3-dimethyl[phenyl-1(η6)](phenylethynyl-2κ2C,C′:3κ2C,C′)-
silane}-1-molybdenum(0)-2,3-bis[molybdenum(I)](Mo2−Mo3)
(9). Cp2Mo2(CO)4 (221 mg, 0.51 mmol) was dissolved in toluene (10
mL), and 9 (215 mg, 0.52 mmol) in toluene (5 mL) was added. After
2 weeks of stirring at room temperature the solution was filtered,
evaporated in vacuo to a volume of 5 mL, and layered with hexane (10
mL). Solvent diffusion and cooling to −20 °C resulted in precipitation
of a solid, which was isolated, washed with hexane (4 × 1.5 mL), and
dried in vacuo (210 mg, 48% crude yield). The deep red-brown solid
was sorted under the microscope to remove some differently colored
byproducts, dissolved in toluene (5 mL), and layered with hexane (10
mL). After solvent diffusion for some days the precipitated
microcrystals were isolated, washed with hexane (3 × 2 mL), and
dried in vacuo. These crystals were suitable for X-ray crystallography.
They can be handled in air but should be stored under argon.
Yield: 100 mg, 0.12 mmol, 23%. Mp: 220−230 °C (dec, argon),
slow continuous dec (air). Solubility: benzene, toluene, THF;
sparingly in hexane. Anal. Found (calcd) for C33H26Mo3O7Si
(850.470): C, 47.96 (46.61);51c H, 3.23 (3.08). 1H NMR (0.035
mol/L in C6D6): δ 7.36 (dd, 3JHH = 8.2 Hz, 4JHH = 1 Hz, 2 H, Phortho),
7.10 (“t”, 3JHH = 7.9 Hz, 2 H, Phmeta), 6.89 (tt, 3JHH = 7.3 Hz, 4JHH = 1
Hz, 1 H, Phpara), 5.34 (dd, 3JHH = 6.4 Hz, 4JHH = 1 Hz, 2 H, PhMoortho),
ASSOCIATED CONTENT
■
S
* Supporting Information
Text, figures, tables, and CIF files giving details of the synthesis
of compound 3 (assumed intermediates, their 29Si NMR data,
1
Scheme S1, H, 13C, and 29Si NMR spectra of compound 3), a
summary of the spectroscopic properties, 29Si NMR, selected
IR, and selected UV/vis data, selected overlaid UV/vis spectra,
detailed IR data with assignments, Figure S8, crystal structure
data, bond lengths, bond angles, and torsion angles for
compounds 1, 2, and 5−10. This material is available free of
charge via the Internet at http://pubs.acs.org. The CCDC
entries 642190 (1), 642199 (2), 642203 (5), 642201 (6),
642193 (7), 642202 (8), 642206 (9), and 642209 (10) contain
supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
4.86 (tt, 3JHH = 6.4 Hz, 4JHH = 1.3 Hz, 1 H, PhMopara), 4.68 (s, 1JHC
=
3
176 Hz, 10 H, Cp), 4.56 (“t”, JHH = 6.4 Hz, 2 H, PhMometa), 0.50 (s,
AUTHOR INFORMATION
Corresponding Author
*G.R.: tel, +49 (0) 3731/39 4345; fax, +49 (0) 3731/39 4058;
e-mail, Gerhard.Roewer@chemie.tu-freiberg.de.
2
1JHC = 120 Hz, JHSi = 6.6 Hz, 6 H, SiMe2) ppm. 13C NMR (0.035
■
mol/L in C6D6): δ 231.1 (s, COMo2), 230.2 (s, COMo2), 221.4 (s,
COPhMo(CO)3), 146.9 (s, 1 C, Phipso), 129.9 (s, 2 C, Phortho), 126.5 (s, 1
C, Phpara), 113.8 (s, 1 C, CCSi·Mo2), 103.7 (s, 1 C, PhMoipso), 101.1
(s, 2 C, PhMoortho), 96.5 (s, 1 C, PhMopara), 92.1 (s, 1 C, CCSi·
Mo2), 91.9 (s, 10 C, Cp), 91.2 (s, 2 C, PhMometa), 0.8 (s, 1JCSi = 57 Hz,
2 C, SiMe2) ppm. 29Si NMR (0.035 mol/L in C6D6): δ +3.8 (s,
1JSiC(Me) = 57 Hz) ppm. 95Mo NMR (0.035 mol/L in C6D6): δ −1870
(br, Δν1/2 = 1200 Hz, Cp2Mo2(CO)4·CC), −2070.8 (s, Δν1/2 = 6
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the Deutsche Forschungsgemeinschaft and the Fonds
der chemischen Industrie for financial support.
■
Hz, PhMo(CO)3) ppm. IR (THF): ν
̃
1984 (m, ν(Mo2CO)), 1965
(s, ν(MoCO)), 1927 (s, ν(Mo2CO)), 1888 (s, ν(MoCO)),
1840 (m, ν(Mo2CO)) cm−1. IR (KBr): ν
1981 (vs, ν(Mo2CO)),
̃
1965 (vs, ν(MoCO)), 1926 (vs, ν(Mo2CO)), 1910 (vs,
ν(Mo2CO)), 1870 (vs, ν(MoCO)), 1836 (vs, ν(Mo2CO)),
1503 (m, ν(CC)) cm−1 (see the Supporting Information for
complete data). UV/vis (THF): λ (ε) 220 (26000, PhMo(CO)3 +
Cp2Mo2(CO)4·CC), 249 (sh, 20000, PhCC), 261 (sh, 17000,
PhCC + PhMo(CO)3), 327 (br, 17000, PhMo(CO)3), 375 (br/sh,
6100, PhMo(CO)3 + Cp2Mo2(CO)4·CC), 440 (br/sh, 1600,
Cp2Mo2(CO)4·CC), 565 (br, 480, Cp2Mo2(CO)4·CC) nm (L/
(mol cm)).49b,52,54
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1978 (m, ν(CO)), 1919 (s, ν(CO)), 1906
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(51) Although this elemental analysis result is outside the range
viewed as establishing analytical purity (Δ ≤ 0.4%), it is provided to
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hydrogen values are ∼3% too high. (b) Although compound 9 is pure
as judged by the spectroscopical data, its yellow-brown color indicates
the presence of some impurities (it should be light yellow). This may
explain the deviating carbon value (∼2% too low). (c) As explained in
the text, the product contains ∼5% PhSiMe2CCPh·Cp2Mo2(CO)4
(Anal. Calcd for C30H26Mo2O4Si (670.500): C, 53.74; H, 3.91%). This
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0.037 mol/L in diethyl ether + 2 vol % benzene, 2 h; 6, 0.008 mol/L in
diethyl ether, 2 h.
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(55) (a) The missing Phmeta signal is hidden by the solvent signal.
(b) The 29Si NMR data were obtained from the reaction solution, as
the measurement in C6D6 was thwarted by decomposition.
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