Fischer-type tungsten acyl (carbeniate), carbene and carbyne complexes bearing C5-attached thiazolyl substituents: Interaction with gold(I) fragments

Article abstract of DOI:10.1039/b9nj00413k

2-(1-Piperidinyl)thiazole and 2-phenylthiazole were deprotonated at C5 of the thiazole rings and both reacted with [W(CO)₆] to form Fischer-type tungsten carbeniate complexes 1a and 1b of the type [(CO ₅)WC(O){C=CHN=C(R)S}] (R = 1-pi

Full text of DOI:10.1039/b9nj00413k

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Fischer-type tungsten acyl (carbeniate), carbene and carbyne complexes
bearing C5-attached thiazolyl substituents: interaction with
gold(I) fragmentsw
Christoph E. Strasser, Stephanie Cronje and Helgard G. Raubenheimer*
Received (in Montpellier, France) 18th August 2009, Accepted 26th October 2009
First published as an Advance Article on the web 12th January 2010
DOI: 10.1039/b9nj00413k
2-(1-Piperidinyl)thiazole and 2-phenylthiazole were deprotonated at C5 of the thiazole rings and
both reacted with [W(CO)6] to form Fischer-type tungsten carbeniate complexes 1a and 1b of the
type [(CO5)WC(O){
carbeniate 1b with [(Ph3P)AuCl] afforded by acyl ligand transfer a tungstenoxycarbene complex
of gold(I), [(Ph3P)AuQC{OW(CO)5}{ }] (2), in which the W(CO)5 fragment
remains coordinated to the acyl oxygen atom. Alkylation of 1a and 1b with [Me3O][BF4]
afforded the carbene complexes [(CO)5WQC(OMe){ }], 3a and 3b. A rare
example of a hydroxycarbene complex of 1a stabilised by a hydrogen bond to 1a,
[NMe4][{ }C{QW(CO)5}OH...(O)C{W(CO)5}{ }], 4,
}] (R = 1-piperidinyl for 1a and phenyl for 1b). Reaction of
(R = 1-piperidinyl) was crystallised while attempting to prepare 3a by a different route.
Reaction of 3b with [ClAu(tht)] (tht = tetrahydrothiophene) furnished the corresponding
alkoxycarbene gold(I) complex [ClAuQC(OMe){
of 1a and 1b with bis(trichloromethyl)carbonate and pyridine yielded the carbyne complexes
[Cl(CO)2(py)2WRC{ }], 6a and 6b. Reaction of 6a with [ClAu(tht)] afforded an
}], 5. Subsequent reaction
unstable addition compound, 7, in which the gold atom is coordinated to the formal carbyne
triple bond. Interaction between gold and the proton of the thiazole ring in this complex was
observed by variable temperature NMR. The crystal and molecular structures of complexes 1a,
1b, 2, 3b, 4, 5, 6a and 6b were all determined by single crystal X-ray diffraction.
using N-heterocyclic precursors, have been carried out by
various other groups.10–13
Introduction
Fischer-type carbene complexes of chromium and tungsten
bearing five-membered heterocyclic rings as the organic group
R1 in the general formula [(CO)5MQC(OR2)R1] have been
prepared and characterised before. Some of them have been
utilised as starting materials in the synthesis of more complex
heteroaromatic systems.1 Such complexes with side chains
derived from thiophenes or polythiophenes2–4 and those with
2- or 3-furyl groups5,6 were prepared with an eye on possible
application in non-linear optics, new materials, organic
conductors and in fine-tuning of carbene reactivity. Using the
Fischer-method, we have previously prepared 2-benzothiazolyl,7
5-pyrazolyl8 and 4-methylthiazolyl carbene complexes of
group 6 metals and could also show that the precursor acyl
complex of the latter is an excellent ligand, well suited for
coordination to mainly hard metal centres while affording
complexes of complexes.9 Related carbene syntheses, also
Despite the fact that five-membered heterocyclic rings have
been shown to stabilise the rather elusive Fischer-type carbene
complexes of molybdenum,14 rather few heterocyclic groups
have found application in Fischer-type carbyne methodology
and only 2-furyl15 and 2-thienyl15,16 have been utilised. Further-
more, we have established, in a preliminary investigation,17 that
decomposition occurs immediately when attempts are made to
convert acylmetallate complexes obtained from 2-lithio-
benzothiazole or 2-lithio-4-methylthiazole into carbyne complexes.
Recently, so-called ‘‘abnormal’’ N-heterocyclic carbene
complexes and isomers of the more general Ofele-Wanzlick-
type were discovered. They belong to a class of ligands with
reduced heteroatom stabilisation18 while simultaneously being
excellent s-donors. The carbene carbon in imidazolylidenes is
C4/C5 whereas in thiazolylidenes, it is usually C5. In azoles,
the precursors for such ligands, for example, the C2-position
(normal), is more acidic than the other positions by as much as
9 pKa units—a difference that could be rationalised in simple
terms as being a result of much better charge delocalisation
upon deprotonation in the 2-position than in the others. These
results prompted us to investigate the use of 5-deprotonated
thiazoles in the preparation of Fischer-type carbenes and
carbynes.
Department of Chemistry and Polymer Science, Stellenbosch
University, Private Bag X1, Matieland, 7602, South Africa.
E-mail: hgr@sun.ac.za; Fax: +27 21 808 3849;
Tel: +27 21 808 3850
w Electronic supplementary information (ESI) available: Synthesis of
2-phenylthiazole, the molecular structures of compound 7 and of the
tungsten p-tolylcarbyne complex. CCDC reference numbers 710165
(1b), 710167 (2), 744822–744829 (1a, 3b, 4, 5, 6a, 6b, 7 and 8). For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/b9nj00413k
Acyl ligand transfer from tungsten(0) to gold(I) has been
investigated.19 Despite the fact that a working mechanism has
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been proposed for such (so called aurolysis) reactions,20
convincing confirmation for initial O-coordination to the
liberated W(CO)5 fragment is still lacking. Although carbene
ligand transfer to gold fragments is also known,21 Fischer-type
carbene complexes of gold and structural data thereof remain
rare.22 Heterocyclic substituents on such carbene ligands could
offer alternative coordination possibilities for the W(CO)5
fragments during ligand transfer or to a gold(I) unit if ligand
transfer does not occur.
Here, we report the synthesis and physical characterisation
of tungsten carbeniate, carbene, and carbyne complexes
bearing not the normal 2-deprotonated, but rather the unusual
5-thiazolyl side chains, as well as the interaction of these
products with AuI fragments while focusing on the bonding
mode of the W(CO)5 fragment after the reactions. The role
of an electron-donating piperidinyl group attached to the
5-membered ring in comparison to a phenyl group in the same
position, is also assessed.
Results and discussion
Thiazoles can be readily lithiated at the 5-position if the
2-position is blocked by suitable substituents.23 Furthermore,
electron donating substituents could have
a stabilising
influence upon subsequent complex formation. As precursors,
2-(1-piperidinyl)thiazole, offering additional electron density
at the 5-position in the thiazole ring and, for comparison,
2-phenylthiazole, a more rigid substituent that is electron
attracting, were selected. The carbeniate complexes 1a and
1b (Scheme 1) were then synthesised in moderate to good
yields by reacting the 5-lithiated azoles with [W(CO)6]
followed by cation exchange to afford [NMe4]+ salts of the
anionic complexes.
Scheme 1 Reagents and conditions: (i) [(Ph3P)AuCl], thf, ꢁ50 1C;
(ii) [Me3O][BF4], CH2Cl2–CH3CN, 0 1C; (iii) [ClAu(tht)], thf, ꢁ5 1C.
single crystals dark orange. While attempting to crystallise
crude 3a prepared according to the former method, crystals
of 4, a rare hydroxycarbene complex, stabilised by a hydrogen
bond to its carbeniate precursor, were isolated (Scheme 2).
The gold alkoxycarbene complex, 5 (Scheme 1), was formed
in fair yield by carbene transfer from 3b using the labile
complex [ClAu(tht)]. The crude product is readily soluble in
CH2Cl2 whereas once crystallised, solubility of 5 is poor in
most standard solvents.
To establish whether the 5-thiazolyl carbeniate complex 1b
would react in the expected manner with [(Ph3P)AuCl] by
transfer of the acyl ligand to gold and what then would happen
to the liberated W(CO)5 fragment, or whether coordination of
a gold fragment to the imine nitrogen atom would simply
occur, 1b was reacted with the gold(I) starting material
(Scheme 1). A gold acyl (carbeniate) complex formed and,
unexpectedly, the extricated W(CO)5 fragment remained
bonded to the acyl oxygen yielding the complex, 2, that could
also be formulated as a zwitterionic tungstenoxycarbene
complex of gold (Scheme 1). Why this unusual O-coordination
of W(CO)5 is preferred to potential N-coordination at the
thiazole ring cannot readily be explained. It was nevertheless
satisfying to see our previous assumption of weak acylgold
coordination to M(CO)5-fragments19 in related products
vindicated.
The suitability of (a somewhat modified) protocol for the
one developed by Mayr and coworkers25 for conversion
of oxycarbene complexes (carbeniates) into carbyne
complexes, while replacing phosgene or oxalyl halides with
solid bis(trichloromethyl)carbonate, was verified by the
successful preparation of the known carbyne complex
[Cl(CO)2(py)2WRCC6H4-4-Me].26 The initial tetracarbonyl
species was stabilised by substitution of a set of cis-CO ligands
with pyridine (py).
The same reactions worked well when starting with the
5-thiazolyl carbeniates 1a and 1b (Scheme 3). The carbyne
complexes 6a and 6b were isolated in moderate yields
(49 and 54%, respectively) after purification by flash
Since Fischer-type alkoxycarbene complexes bearing
5-thiazolyl side chains are unknown, preparation of 3a and
3b from the carbeniate complexes 1a and 1b was attempted
(Scheme 1). To circumvent the problem of competing
N-alkylation in the classic method, an indirect route that
involves acetylation of the carbeniate and subsequent methanolysis
was first followed.24 Later, direct alkylation with [Me3O][BF4]
was found to be simpler and to give similar yields. The colour
of 3b is noteworthy in that it forms dark red solutions whilst
the microcrystalline solid is purplish-black and the isolated
Scheme 2 Connectivity within compound 4, R = 1-piperidinyl.
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Scheme 3 Reagents and conditions: i: (Cl3CO)2CO, CH2Cl2, ꢁ78 1C,
py, r.t.
Scheme 4 Reagent and conditions: i: [ClAu(tht)], thf, ꢁ10 1C.
Fig. 1 Expansion of a segment of the 1H NMR spectra of 5 at
different temperatures.
chromatography under inert conditions. The compounds
are stable as solids at low temperature. Stability at room
temperature is somewhat lower and the products decompose
slowly in solution even at temperatures below 0 1C.
Interaction of the new carbyne complexes 6a and 6b with
AuI reagents was then examined. Both compounds readily
react with [ClAu(tht)] but, unfortunately, complex mixtures
resulted and only intergrown crystals of the addition product 7
(Scheme 4) could eventually be obtained by crystallisation
from thf–pentane. The molecular structure clearly indicated
coordination of AuI to the carbyne functionality as well as
further stabilisation by Auꢂ ꢂ ꢂS intramolecular interaction.
10.5 Hz at 10 1C to 0.93 Hz at ꢁ55 1C which proved to be the
solubility limit of 5 in CD2Cl2 (Fig. 1). This signal has its
highest value at ꢁ10 1C and moves towards higher field
both upon warming (dd/dT E 7 ꢃ 10ꢁ4
K
ꢁ1) or cooling
(ꢁ6 ꢃ 10ꢁ4 Kꢁ1). Concomitantly, the other signals experience
only small and monotonic upfield changes on cooling.
The carbene carbon atoms in 3a and 3b resonate at d 274.3
and 291.6, respectively. They appear at higher field compared
to that of [(CO)5WQC(OMe)Ph] (d 321.9)28 which can be
attributed to the more electron-rich 5-thiazolyl substituent
compared to a phenyl group. Even the larger shielding effected
by the piperidinyl substituent in the 2-position of the hetero-
cyclic ring compared to phenyl substitution is obvious. The
carbene resonance of compound 5 (d 248.6) is observed at
higher field than that of its precursor, 3b, while the opposite is
true for the thiazole resonances. The C-4 resonance at d 160 is
also broadened at room temperature. A similar decrease in the
chemical shift of the carbene resonance of tungsten complexes
when compared to the gold analogues has been observed for
rNHC complexes as well.29
Infrared spectroscopy
The complexes that contain a W(CO)5 fragment (1a, 1b, 2, 3a
and 3b) exhibit signals expected for a pentacarbonyl group. In
most instances, the A1(2) vibration is obscured by the E and/or
acyl vibration. The wavenumbers of the A1(1) vibrations of the
piperidinyl-substituted complexes, which are readily assign-
able, always seem lower (by 2 and 12 cmꢁ1 for pairs 1 and 3)
than those of the phenyl-substituted compounds showing the
greater electron-donating effect of the former substituent. The
(1)
A1
Notably, the carbyne carbon signal in complex 6a (d 245.1)
appears at a somewhat lower field strength than that of the
more electron-poor ligand in 6b (d 240.8).
vibration of [(CO)5WQC(OMe)Ph]27 is observed at
2068 cmꢁ1 in CH2Cl2 solution and thus comparable to the
value found for 3b and 2.
The carbyne complexes 6a and 6b, each comprising a pair of
cis-CO ligands, show bands of A0 and A00 symmetry in their
infrared spectra, as expected for local Cs symmetry. Both
bands of 6a are observed at lower wavenumbers than those
found for 6b, highlighting the electron-donating influence of
the piperidine substituent at the thiazole ring.
Solid-state CP-MAS 13C NMR spectroscopy
The acylmetallate 1b crystallised with two unique molecules in
the asymmetric unit (vide infra) and the question arose whether
their different environments could cause separate 13C NMR
signals in the solid state.30 A sample of the crystalline solid was
measured with the cross-polarisation magic angle spinning
(CP-MAS) technique utilising spinning frequencies of
5 to 11 kHz for identification of the strong spinning side
bands. Data are summarised in Table 1 and Fig. 2 portrays an
expansion of a measured spectrum.
NMR spectroscopy
1
In the H NMR spectra of all the products, only the single
proton of the thiazole ring is of some use to gain information
about the electronic situation within the heterocyclic ligand.
The resonances for the complexes are found at ca. d 8.7 with
the exception of 6b where it appears at a more shielded
7.79 ppm. A routine spectrum of the gold carbene complex 5
revealed an unusually broad signal for this proton at ambient
temperature, indicating a potential Auꢂ ꢂ ꢂH interaction and
thus prompting us to investigate its behaviour at lower
temperatures. The signal half-width drastically decreases from
The signals for the thiazole and ipso-phenyl carbon atoms
are well resolved while the resonances for the other phenyl
carbon signals do not allow identification of each unique
carbon atom, owing to small chemical shift differences. The
differences between the individual chemical shifts of the NCS
carbon of the thiazole rings (Dd 2.9, signals 6 in Fig. 2) and the
ipso-C of the phenyl rings (Dd 2.2, signals 3 in Fig. 2),
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Table 1 13C NMR data (d) of 1b
Solid-state CP-MAS (126 MHz, 11 kHz spinning)
Solution (101 MHz, CD2Cl2)
268.2 (s)
207.2 (s, d, JWC 134.0)
203.1 (s, d, JWC 127.4)
168.7 (s)
C(carbeniate)
trans-CO
cis-CO
C-2 thiazole
C-4 thiazole
C-5 thiazole
i-Ph
Not detected
Not detected
1
202.8a
1
171.0, 168.1 (D 367 Hz)
160.7, 160.0 (D 82 Hz)
148.3, 147.7 (D 82 Hz)
134.7, 132.5 (D 284 Hz)
130.2, 129.2, 128.6, 127.3, 125.7, 124.4
56.1, 54.4 (D 204 Hz)
160.9 (s)
147.9 (s)
135.1 (s)
130.6 (s), 129.4 (s), 127.0 (s)
p-, m-, o-Ph
[NMe4]+
1
56.9 (t, JNC 3.8)
a
Observed only without cross-polarisation.
loss of CO and pyridine. A number of fragment ions are
observed both as protonated and radical cationic species.
Crystallography
The ease with which single crystals of the compounds were
obtained varied considerably; while crystals of 1a, 1b, 3b and
6a suitable for X-ray diffraction formed readily, 3a gave no
crystals of sufficient quality and 6b only crystallised as a
dichloromethane solvate. Selected bond lengths and angles
within the molecular structures determined, are summarised in
Table 2.
Compound 1a (Fig. 3) crystallises with only one molecule in
the asymmetric unit. The relative position of the [NMe4]+
cation is similar in the two acyl complexes (1a and 1b): it
approaches the negatively charged carbeniate oxygen atom.
The piperidine ring is in the chair conformation with the
thiazole ring as an equatorial substituent. Bond lengths of 1a
and 1b are comparable, indicating no appreciable influence of
the 2-substituent at the thiazole ring, in contrast to the results
obtained from the IR and 13C NMR investigations.
Fig. 2 Solid-state CP-MAS 13C NMR (126 MHz) spectrum of 1b;
spinning frequency 11 kHz; unassigned peaks are spinning side-bands.
respectively, are much larger than the differences within the
other signal groups. C-2 of the thiazole, as well as the ipso-
carbon of the phenyl group, are affected the most by different
interplanar angles of the benzene and thiazole rings, which is
indeed one of the most significant differences between the
asymmetric molecules in the solid state (vide infra). Two
signals are observed for the [NMe4]+ counter ions which we
believe stem from different carbons within the unique cations
rather than being one each for two unique cations. Signals for
the pentacarbonyl metal fragment could not be identified
in the CP experiments. But in an experimental run without
cross-polarisation, the cis-CO carbons appear as a broad
resonance at d 202.8 while the intensities of the thiazolyl and
phenyl signals are much weaker. The carbeniate carbon and
trans-CO, however, could not be identified in any spectrum.
Compound 1b (Fig. 4) crystallises as two independent
molecules (designated A and B) per unit cell. The main
differences within the molecules are the respective interplanar
angles of the essentially flat phenyl and thiazolyl groups [5.2(2)
and 16.3(2)1]. The [NMe4]+ cations are located adjacent to the
carbeniate oxygen atoms forming Oꢂ ꢂ ꢂH contacts in the range
of 2.27 to 2.40 A. The C–O bond distances of the acyl groups
in the anionic complexes 1a and 1b are somewhat longer
[1.248(5) and 1.246(4) A, respectively] than in the neutral
complex [(Ph3P)AuC(O)Ph] [1.200(7) A].19
The product of an acyl (or anionic carbene) transfer to a AuI
fragment, 2, was isolated as red crystals of a pentane solvate.
The Ph3PAu+ group is coordinated to what essentially
amounts to be an acyl carbon, while the displaced W(CO)5
fragment is bonded to the acyl oxygen atom. Compound
2ꢂC5H12, shown in Fig. 5, confirms the existence of the
proposed intermediate during the preparation of tungsten-free
gold acyls.19 As mentioned above, the W(CO)5 unit
surprisingly prefers O-coordination to imine bonding. When
compared to 2ꢂC5H12, the Au–C bond in the free benzoyl-
gold complex, [(Ph3P)AuC(O)Ph],19 is found to be shorter
[1.200(7) A] than the respective value of 1.247(8) A for
2ꢂC5H12. The Au–C bonds are similar in both structures
[2.085(5) A in the free acyl and 2.053(7) A in 2], and both
are longer than those found in the Fischer-type carbene
Mass spectrometry
Except for compounds 2 and 5, fast atom bombardment gave
the best results and molecular peaks were observed for all the
other complexes. Loss of the piperidinyl group of the carbene
complex 3a, but not of the carbyne complex 6a, was observed.
The gold complex, 5, only afforded interpretable signals from
the loss of chloride, a methyl group and the associated
decarbonylation peak. Notably, the carbyne complexes 6a
and 6b fragment via two pathways, either by loss of chloride,
which seemingly precludes further fragmentation, or sequential
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Table 2 Selected bond lengths (A) and angles (1)
1a
1b A/B
2ꢂC5H12
3b
4
5 A/B
6a
6bꢂCH2Cl2
M(1)–C(1)
W(1)–C(COtrans
2.251(5)
1.994(5)
2.035
2.251(3)/2.248(3) 2.053(7)
1.994(4)/2.019(4) 1.953(7)
2.195(5) 2.246(7)
2.029(5) 2.012(7)
1.976(4)/1.959(4)
—
—
1.841(4)
—
1.996(4)/
1.990(4)
—
1.411(5)
2.523(2)
176.7(2)e
175.1(3)
—
1.822(3)
—
2.001(3)/
1.993(3)
—
1.418(5)
2.5107(8)
170.9(1)e
169.4(3)
—
)
a
W(1)–C(COcis
)
2.035/2.035
2.033
2.047
2.024
C(1)–O(1)
C(1)–C(10)
M(1)–Cl(1)
1.248(5)
1.467(6)
—
1.245(5)/1.245(5) 1.247(8)
1.495(5)/1.507(4) 1.460(9)
1.330(5) 1.284(8)
1.447(7) 1.437(9)
1.296(5)/1.302(5)
1.430(6)/1.433(6)
2.289(1)/2.279(2)
174.8(2)/177.5(2)d
119.9(3)/122.6(3)
127.9(3)/125.9(3)
—
—
—
—
—
C(1)–W(1)–C(2) 173.6(2)
M(1)–C(1)–C(10) 125.0(3)
M(1)–C(1)–O(1) 121.9(3)
177.7(2)/174.4(2) 175.0(2)c
115.8(5)
122.9(2)/123.8(2) 127.1(5)
175.2(2) 178.9(3)
124.6(3) 124.4(5)
129.4(3) 125.2(5)
N(2)–eb
0.185(5)
—
5.2(2)/16.3(2)
—
5.2(4)
—
8.2(2)
0.146(8)
—
0.074(5)
—
—
21.9(2)
Interplanar angle —
C3HNS–C6H5
1.9(3)/13.8(3)
Others
—
—
Au(1)–P(1)
2.301(2)
W(1)–O(1)–C(1)
132.1(4)
—
2.418(9)
3.3866(3)
2.276(3)
2.246(3)
[O(1)ꢂ ꢂ ꢂO(1)0] [Au(1A)ꢂ ꢂ ꢂAu(1B)] [W(1)–N(3)], [W(1)–N(3)],
3.09(1)
3.4871(4)
2.269(3)
2.254(3)
[C(7)ꢂ ꢂ ꢂN(1)] [Au(1B)ꢂ ꢂ ꢂAu(1B0 0)] [W(1)–N(4)] [W(1)–N(4)]
a
b
c
d
e
Average values. e corresponds to the plane of C(12), C(13), C(17). O(1)–W(1)–C(2) angle. Cl(1)–Au(1)–C(1) angles. Cl(1)–W(1)–C(1)
0
0 0
angles. Symmetry operators: 1 ꢁ x, y, 3/2 ꢁ z; 2 ꢁ x, 1 ꢁ y, –z.
include an acylgold complex coordinated to a dirhenium
fragment with similar bond lengths in the acyl moiety32 and
a compound wherein [BrW(CO)5]ꢁ, diethyl ether and two
[(Ph3P)AuC(O)Ph] molecules are coordinated to one Li+
ion, again with closely related geometry.19 Complex 2ꢂC5H12
is one of very few examples comprising a W(CO)5 group
coordinated to an oxygen donor. Such compounds are usually
of very limited stability. [(CO)5W(OPPh3)] is presently the
only neutral example in the literature that has been crystallo-
graphically authenticated.33 Its W–O bond [2.244(3) A] is
slightly longer than the one in 2ꢂC5H12 [2.205(5) A]. Both
molecules, however, share a considerably shorter W–COtrans
distance [1.942(5) A in the literature example and 1.953 A in
2ꢂC5H12] compared to the corresponding values for the cis-CO
ligands [2.048 vs. 2.033 A on average]. The W–O–C angle of
132.1(4)1 in 2ꢂC5H12 indicates sp2-hybridisation at the oxygen
atom in contrast to group 4 bis(cyclopentadienyl)metal
Fig. 3 Molecular structure of 1a.
complexes of gold, such as the recently described chloro-
(pyrazolin-3-ylidene)gold compounds [Au–C 1.981(6) and
1.991(5) A].31 Structurally related metaloxycarbene complexes
Fig. 4 Molecular structure of 1b.
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complicated N-heterocyclic azolyl as a substituent can be
inferred from the structure of the carbene complex 3b (Fig. 6).
The bond lengths most influenced are W(1)–C(1)—which is
shortened in view of the formal metal–carbene double bond
formation [2.195(5) A in 3b, 2.251(3) and 2.248(3) A in 1b]—
and, obviously, C(1)–C(10) [1.447(7) A vs. 1.495(5) and
1.507(4) A] is shortened owing to a participation of the
heterocyclic ring in decreasing the carbocationic character of
C(carbene). As expected, the C(1)–O(1) bond is elongated
considerably [1.330(5) A vs. 1.246(4) A]. In the comparable
phenylcarbene complex,35 the C(carbene)–C(phenyl) bond of
1.59 A is ca. 0.1 A longer than C(1)–C(10) in 3b.
As mentioned previously, a crystal of 4 (Scheme 2) was
isolated during an attempt to purify crude 3a by recrystallisa-
tion from CHCl3–hexane. It represents only the second
example of a tungsten hydroxycarbene complex that is stabi-
lised by a carbeniate moiety; another example was previously
reported by us.36 Compound 4 (Fig. 7) crystallises in the
monoclinic space group C2/c and is ordered around a C2 axis
passing between the oxygen atoms of the carbene groups.
The bridging proton is distributed evenly between the two
molecules and stabilises the arrangement by a strong hydrogen
bond [Oꢂ ꢂ ꢂO0 2.418(9) A, 0 = 1 ꢁ x, y, 3/2 ꢁ z]. The basicity of
the imine nitrogen atom in the thiazole ring, enhanced by the
piperidinyl substituent, is demonstrated by the CHCl3
molecules engaging in weak hydrogen bonds. The piperidine
nitrogen N(2) is essentially sp2-hybridised. Comparison to the
other example in the literature that contains a phenyl
substituent reveals the same structural parameters except for
the C(1)–C(10) bond, which is shorter in 4 than in the phenyl
analogue [1.437(9) A vs. 1.505(7) A]; additional electron
delocalisation from the heterocycles may be responsible for
this observation.
Fig. 5 Molecular structure of 2ꢂC5H12; the solvent molecule is
omitted for clarity.
fragments that cause the M–O–C angle to approach
linearity.34 The thiazole ring in 2ꢂC5H12 is oriented in such
a way that the hydrogen atom is close to the gold centre
[Auꢂ ꢂ ꢂH 2.84 A] in what could amount to an attractive
interaction, as was found for complex 5 (vide infra). In
contrast to 5, no evidence of such an interaction was found
by NMR measurements in solution.
The structural effects of O-alkylation on the molecular
a carbeniate such as 1b that contains a
structure of
The alkoxycarbene 5 (Fig. 8) crystallises as two asymmetric
molecules (A and B) that form chains of four complex units
linked by aurophilic interactions, two of them asymmetric and
the others related by a centre of inversion. Molecule A forms
Fig. 6 Molecular structure of 3b.
one contact to molecule
B of the crossed-sword type
Fig. 7 Molecular structure of 4; H(1) is arbitrarily located in one position; primed atoms are related by a C2 rotation; disordered [NMe4]+ is not
shown.
ꢀc
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Fig. 8 Molecular structure of 5; primed atoms are related by a centre of inversion located between Au(1B) and Au(1B)0.
[Cl(1A)–Au(1A)ꢂ ꢂ ꢂAu(1B)–Cl(1B) 88.20(4)1] while B is further
linked to its symmetry-generated image by a longer, antiparallel
metallophilic bond [Cl(1B)–Au(1B)ꢂ ꢂ ꢂAu(1B)00–Cl(1B)0 0 1801;
00
symmetry operator = 2 ꢁ x, 1 ꢁ y, –z]. Only a few other
examples are known in which four gold centres form a chain of
intermolecular aurophilic interactions.37 It is remarkable that
by substituting W(CO)5 in 3b by isolobal AuCl in 5 only minor
changes occur in the bond distances and angles of the carbene
complex. The structures of [ClAuQC(NMe2)Ph],22 a cationic
combined NHC/Fischer alkoxycarbene AuI complex,22 and a
series of gold pyrazolin-3-ylidene complexes31 have been
reported. The Au–C distances in all of these are comparable
to those in 5; in the cationic alkoxycarbene complex, the Au–C
may be longer, as was observed for neutral and cationic AuI
rNHC complexes.29 Notably, the interplanar angle between
the phenyl group and the heterocycle in 5 is much smaller
[1.9(3)1 and 13.8(3)1] than in the pyrazolinylidene complexes
which show angles of 45.91 and 47.71.31 The thiazole in 5 is
arranged to enable close Auꢂ ꢂ ꢂH contacts of 2.87 A and 2.97 A
Fig. 9 Molecular structure of 6a.
1
which can also be observed in the H NMR spectrum of the
compound (vide supra). Auꢂ ꢂ ꢂH interactions in the solid state
have also been initially reported as ranging between 2.6 A and
3.0 A.38 Later, it was found that in thione complexes, such
Auꢂ ꢂ ꢂH distances could vary between 2.80–3.07 A,39 and in a
recent study employing pyridinethiolates, distances between
2.83 A and 2.88 A were observed.40
Fig. 10 Molecular structure of 6bꢂCH2Cl2; the solvent molecule is
The crystal structures of both tungsten carbyne complexes
6a (Fig. 9) and 6b (Fig. 10) were determined; they crystallise
in rather similar triclinic lattices. Compound 6b (Fig. 10)
co-crystallises with a CH2Cl2 solvent molecule per formula
unit. In complex 6a, the piperidine nitrogen atom is essentially
planar, possibly showing increased delocalisation of its lone
pair compared to the situation in the structure of 1a and
in accordance with the increased electron-withdrawing
power of theꢁ–CRWCl(CO)2(py)2 unit over the anionic
–C(O)W(CO)5 fragment. The effect of the piperidine lone
pair can be observed in the elongated W(1)–Cl(1) bond in 6a
[2.523(2) A] compared to 6bꢂCH2Cl2 [2.5107(8) A] (Scheme 5).
Again, comparison to other tungsten carbyne complexes
is complicated by the fact that only one complex exhibiting
cis-bis(pyridine) substitution, [Cl(CO)2(Z2-Ppyr3)WRCPh]
(pyr = 2-pyridyl), has so far been structurally characterised.41
omitted for clarity.
Scheme 5 Electron delocalisation in 6a effects a longer W(1)–Cl(1)
bond length than in the Ph-substituted analogue.
Its W(1)–C(1) bond length of 1.806(6) A is similar to that in
6bꢂCH2Cl2 but shorter than in 6a. The W–N separations are
similar. To supplement this example, the crystal and molecular
structure of [Cl(CO)2(py)2WRCC6H4-4-Me], 8, was also
determined and is included in the ESIw to this article. The
angle at the carbyne carbon [169.4(3)1] as well as the
ꢀc
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Cl(1)–W(1)–C(1) angle [170.9(1)1] in 6bꢂCH2Cl2 deviate from
2-Phenylthiazole was synthesised in 75% yield following a
modified methodw to the one described in the literature.47
Melting points were determined with a Stuart Scientific
SMP3 instrument or with a Fischer Scientific (Pittsburgh
PA, St. Louis MO) and Eimer & Amend (New York NY)
hot stage apparatus and are uncorrected. FAB mass spectra
(nitrobenzyl alcohol matrices) were performed on a VG 70
SEQ mass spectrometer by the University of the Witwatersrand.
linearity.
Conclusions
Although group 6 metalcarbonyl carbeniates from standard
2-lithiated thiazoles cannot be converted into carbyne
complexes, the ‘abnormal’ 5-deprotonated analogs produce
relatively stable carbene and carbyne complexes. No appreci-
able stability difference is effected by changing the substituent
IR spectra were recorded at
4 a
cmꢁ1 resolution on
Nicolet Avatar 300 FT-IR instrument equipped with a Smart
Performer ZnSe disk ATR accessory; spectra were corrected
for ATR effects using Omnic software supplied with the
spectrometer. 1H, 13C and 31P NMR spectra were recorded
at the indicated frequency on a Varian VNMRS 300 or Varian
Unity Inova 400 spectrometer. 1H and 13C spectra were
referenced to residual solvent peaks and the 31P spectrum is
externally referenced to 85% H3PO4. Elemental analyses were
performed by the University of Cape Town or Stellenbosch
University.
in the
2 position of such complexes. Nevertheless, a
1-piperidinyl substituent clearly transfers more electron
density onto the rest of the carbene ligand than a phenyl
group. Treatment of the carbeniate and corresponding
carbene complexes with gold(I) fragments leads to ligand
transfer reactions and, in the former example, the liberated
W(CO)5 group is trapped by the acyl ligand bonded to gold.
The carbene transfer affords rare alkoxycarbene complexes of
gold and while no tungsten carbonyl fragments remain in the
products, agostic-type Auꢂ ꢂ ꢂH interactions may be studied by
NMR spectroscopy and verified by crystal and molecular
structure determination. One of the carbyne complexes forms
an adduct with the gold AuCl fragment that is stabilised by an
Auꢂ ꢂ ꢂS interaction.
Tetramethylammonium pentacarbonyl{[2-(1-piperidinyl)thiazol-
5-yl]carbonyl}tungstate(1–), 1a. A solution of 2-(1-piperidinyl)-
thiazole (1.068 g, 6.35 mmol) in thf (30 cm3) was cooled to
ꢁ78 1C. Butyllithium (6.1 cm3, 1.05 M in hexanes, 6.41 mmol)
was added dropwise by syringe and after stirring for 1 h, solid
[W(CO)6] (2.172 g, 6.17 mmol) was added, whereupon the
light yellow solution slowly turned brownish-red. After 2.5 h,
the temperature had risen to –25 1C and the cooling bath was
removed. The suspension was stirred for another 1.5 h at room
temperature, whereupon the solvents were removed in vacuo.
A golden-red foam of the lithium salt was obtained, which was
washed with pentane (60 cm3) to remove excess [W(CO)6].
In an extraction funnel under inert atmosphere, [NMe4]Cl
(819 mg, 7.47 mmol) was dissolved in deoxygenised water
(20 cm3) and CH2Cl2 (100 cm3) was added. The lithium salt
was dissolved in deoxygenised water (50 cm3), affording a
blood-red solution which was filtered through a pad of Celite
into the extraction funnel. A first black-red organic phase was
separated, a yellow precipitate of 1a remained in the extraction
funnel. Another extraction with CH2Cl2–acetonitrile (4 : 1)
yielded a red organic phase. Both fractions were evaporated
to dryness. The CH2Cl2 extract formed an ochre precipitate
while the MeCN–CH2Cl2 fraction yielded an orange
crystalline solid. Crystals suitable for X-ray diffraction were
grown from the MeCN–CH2Cl2 fraction in acetonitrile
layered with diethyl ether. Yield of 1a: 55%, 2.00 g, mp
145 1C (dec.). Found: C, 36.4; H, 3.9; N, 7.1. C18H23N3O6SW
requires C, 36.4; H, 3.9; N, 7.1%. dH (400 MHz, CD3OD) 7.80
(1 H, s, CH thiazole), 3.48 (4 H, m, NCH2), 3.18 (12 H, t, 2JNH
0.59, NMe4) and 1.66 (6 H, m, NCH2(CH2)3). dC (101 MHz,
Experimental
Crystallography
Data associated with the crystal structures are summarised in
Table 3. Intensity data were collected at T = 100 K with
a Bruker SMART Apex diffractometer42 with graphite mono-
chromated Mo Ka radiation (l = 0.71073 A). Intensities were
measured using the o-scan mode and were corrected for
Lorentz and polarisation effects. The structures were solved
by direct methods and refined by full-matrix least-squares on
F2 using the SHELXL-97 software package within the X-Seed
environment.43 All non-hydrogen atoms were refined with
anisotropic displacement parameters and all hydrogens were
placed in calculated positions. Ellipsoids were drawn at the
50% probability level throughout. Hydrogen atoms in Figures
were omitted for clarity except when noted otherwise. In the
crystal structure of 4, H(1) was refined with an occupancy
factor of 0.5 resembling the bulk average and the N–C bond
distances involving C(21), C(22) and C(23) in the tetramethyl-
ammonium cation were restrained to have equal lengths.
Syntheses
All work was performed under an atmosphere of dry argon
using standard Schlenk- and vacuum line techniques. All
solvents were distilled under a dry dinitrogen atmosphere,44
MeOH was distilled from Mg(OMe)2, CH2Cl2 from CaH2,
pentane, hexane, hexanes (commercial mixture of isomers) and
toluene from sodium and diethyl ether and thf from sodium
wire and sodium benzophenone ketyl radical. Flash chromato-
graphic separations were performed at low temperature
with ‘‘flash grade’’ silica gel (230–400 mesh) under inert
atmosphere. [ClAu(Me2S)], [ClAu(tht)]45 and 2-(1-piperidinyl)-
thiazole46 were prepared according to literature procedures.
1
1
CD3OD) 271.8 (s, d, JWC 85.8, carbene), 206.8 (s, d, JWC
1
133.1, trans-CO), 203.1 (s, d, JWC 127.3, cis-CO), 174.7
1
(s, C2 thiazole), 150.8 (s, d, JWC 21.2, C4/C5 thiazole),
2
148.8 (s, C5/C4 thiazole), 55.9 (t, JNC 4, NMe4), 50.3
(s, NCH2CH2CH2), 26.2 (s, NCH2CH2CH2) and 25.0
(1)
CO),
(s, NCH2CH2CH2). nmax/cmꢁ1 (ATR) 2044s (A1
(2)
1949m (B1 CO), 1881, 1859vs (E and A1 CO) and 1840vs
(acyl group). m/z 667 [(M + NMe4)+, 12%], 520 [(M–NMe4 +
H)+, 12], 519 [(M–NMe4)+, 5], 492 [(M–NMe4–CO + H)+, 7],
ꢀc
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ꢀc
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491 [(M–NMe4–CO)+, 7], 464 [(M–NMe4–2CO + H)+, 17],
463 [(M–NMe4–2CO)+, 2], 436 [(M–NMe4–3CO + H)+, 7],
435 [(M–NMe4–3CO)+, 7], 408 [(M–NMe4–4CO + H)+, 8]
and 407 [(M–NMe4–4CO)+, 10].
721 {[Au(PPh3)2]+, 22}, 648 [(M–W(CO)5 + H)+, 25] and 459
{[Au(PPh3)]+, 100}.
Pentacarbonyl{methoxy[2-(1-piperidinyl)thiazol-5-yl]methylidene}-
tungsten, 3a. In a Schlenk flask, 1a (927 mg, 1.56 mmol) was
suspended in CH2Cl2 (20 cm3) and the suspension cooled to
0 1C. A solution of [Me3O][BF4] (250 mg, 1.69 mmol, 1.1 mol
eq.) in acetonitrile (40 cm3) was slowly added via a dropping
funnel. After stirring for 3 h, all volatiles were removed
in vacuo and the crude product was subjected to flash
chromatography (column dimensions 9 ꢃ 5 cm) at ꢁ20 1C,
eluting with 150 cm3 CH2Cl2–pentane (1 : 1) and 150 cm3
CH2Cl2–diethyl ether (1 : 1). Two fractions were collected.
The second orange fraction contained 62 mg (7.4%) of 3a.
mp 106 1C (decomp.). Found: C, 33.8; H, 2.9; N, 5.4.
C15H14N2O6SW requires C, 33.7; H, 2.6; N, 5.2%. dH
Tetramethylammonium pentacarbonyl[(2-phenylthiazol-5-yl)-
carbonyl]tungstate(1–), 1b. Compound 1b was obtained
following the same procedure as described for 1a, employing
2-phenylthiazole (1.681 g, 10.4 mmol), butyllithium in hexanes
(7.0 cm3, 1.4 M, 9.8 mmol) and [W(CO)6] (3.71 g, 10.5 mmol).
The product was extracted with CH2Cl2–MeCN (4 : 1) yielding
a blood-red solution. Upon removal of the solvents, the blood-
red (purple when wet with solvent) crystals were washed with
toluene to remove residual [W(CO)6] and free 2-phenylthi-
azole. Crystals suitable for X-ray diffraction were grown from
CH2Cl2 layered with hexanes. Yield: 75%, 5.78 g, mp 80 1C
(dec.). Found: C, 38.6; H, 3.5; N, 4.8. C19H18N2O6SW requires
C, 38.9; H, 3.1; N, 4.8%. dH (400 MHz, CD2Cl2) 8.38 (1 H, s,
CH thiazole), 7.98 (2 H, m, o-Ph), 7.42 (3 H, m, m- and p-Ph)
and 3.35 (12 H, m, NMe4). dC see Table 1. nmax/cmꢁ1 2046s
1
(400 MHz, CDCl3) 8.50 (1 H, s, d, JCH 184.0, CH thiazole),
1
4.49 (3 H, s, d, JCH 146.7, OMe), 3.67 [4 H, m, NCH2 and
1.73 (6 H, m, NCH2(CH2)3)]. dC (101 MHz, CDCl3) 274.3
(s, d, JWC 97.4, carbene), 202.1 (s, d, JWC 124.2, trans-CO),
1
1
1
198.1 (s, d, JWC 126.7, cis-CO), 176.6 (s, C2 thiazole), 163.5
(1)
(A1 CO), 1941sh (B1 CO), 1870vs (E CO) and 1835vs
(br s, C4 thiazole), 140.2 (s, C5 thiazole), 67.2 (s, OMe), 49.9
(s, NCH2), 25.3 (s, NCH2CH2CH2) and 23.8 (s, NCH2CH2CH2).
(acyl group). nmax/cmꢁ1 (CH2Cl2) 2050s (A1(1)), 1955m (B1)
and 1907vs (E, A1(2) and acyl group). m/z 660 [(M + NMe4)+,
8%], 512 [(M–NMe4)+, 2], 485 [(M–NMe4–CO + H)+, 1],
484 [(M–NMe4–CO)+, 1], 457 [(M–NMe4–2CO + H)+, 1]
and 456 [(M–NMe4–2CO)+, 2].
n
max/cmꢁ1 2058 (A1 CO), 1969m, (B1 CO) and 1981vs
(1)
(E and A1 CO). m/z 535 [3%, (M + H)+], 534 (3, M+),
506 [3, (M–CO)+], 478 [8, (M–2CO)+], 450 [1, (M–C5H11
H)+], 449 [1, (M–C5H11)+] and 422 [3, (M–C5H11–CO)+].
(2)
+
Pentacarbonyl[methoxy(2-phenylthiazol-5-yl)methylidene]-
tungsten, 3b. In a preparation similar to 3a, compound 1b
(1.140 g, 1.94 mmol) and [Me3O][BF4] (293 mg, 1.98 mmol,
1.02 eq.) were used. Inert flash chromatography (11 ꢃ 5 cm,
ꢁ20 1C) was performed, eluting with 150 cm3 CH2Cl2–hexane
(1 : 1) and subsequently 200 cm3 CH2Cl2–diethyl ether–hexane
(2 : 1 : 1). The second, dark purple fraction afforded 356 mg
(35%) of a purplish-black microcrystalline solid. Crystals
suitable for X-ray diffraction were grown from CH2Cl2 layered
with hexane. mp 147 1C. Found: C, 36.7; H, 1.9; N, 2.7.
C16H9NO6SW requires C, 36.5; H, 1.7; N, 2.7%. dH
Pentacarbonyl-2j5C-[l-(2-phenylthiazol-5-yl)carbonyl-1jC:2jO]-
(triphenylphosphine-1jP)goldtungsten, 2.
A
solution of
[(Ph3P)AuCl] in thf, prepared from PPh3 (202 mg, 0.77 mmol)
and [(Me2S)AuCl] (227 mg, 0.77 mmol), was cooled to ꢁ50 1C
and 1b (568 mg, 0.97 mmol) was added as a solid. After 2 h,
the mixture had reached 10 1C and Na[BF4] (88 mg,
0.80 mmol) was added to aid the abstraction of chloride from
[(Ph3P)AuCl]. The slightly turbid orange solution was stirred
for another hour at room temperature. TLC analysis (silica
plate with CH2Cl2 as eluent) of the reaction mixture revealed
two products. The solvent was removed in vacuo affording an
orange-brown oil, which was subjected to column chromato-
graphy under inert conditions on Florisil (15 ꢃ 5 cm) at
ꢁ30 1C, eluting with CH2Cl2 (200 cm3), CH2Cl2/thf 19 : 1
(100 cm3) and CH2Cl2/thf 12 : 1. Two product fractions were
obtained; the first one contained a mixture of two products,
the second contained 2. Crystals suitable for X-ray diffraction
were obtained from a thf solution layered with pentane. Yield:
57%, 0.414 g, mp 90 1C (dec.). Found: C, 40.8; H, 2.3; N, 1.2.
C33H21AuNO6PSW requires C, 40.8; H, 2.2; N, 1.4%.
1
(400 MHz, CDCl3) 8.83 (1 H, s, d, JCH 187.0, CH thiazole),
8.07 (2 H, m, o-Ph), 7.51 (3 H, m, m/p-Ph) and 4.70 (3 H, s, d,
1
1JCH 147.8, OMe). dC (101 MHz, CDCl3) 291.6 (s, d, JWC
103.8, carbene), 202.1 (s, d, JWC 117.2, trans-CO), 197.1
1
1
(s, d, JWC 127.4, cis-CO), 174.8 (s, C2 thiazole), 156.7
(s, C4 thiazole), 152.7 (s, C5 thiazole), 132.8 (s, i-Ph), 131.9
(s, p-Ph), 129.2 (s, m-Ph), 127.1 (s, o-Ph) and 68.7 (s, OMe).
n
max/cmꢁ1 2070s (A1(1) CO), 1969s (B1 CO) and 1880vs (E and
(2)
A1 CO). m/z 528 [10%, (M + H)+], 527 (8, M+), 499
[16, (M–CO)+], 472 [7, (M–2CO
[11, (M–2CO)+] and 443 [12, (M–3CO)+].
+
H)+], 471
1
dH (400 MHz, CDCl3) 8.62 (1 H, s, d, JCH 184.4, CH
thiazole), 8.01 (2 H, m, o-Ph) and 7.52 (18 H, m, m-Ph,
2
p-Ph, PPh3). dC (101 MHz, CDCl3) 252.3 (d, JPC 133.7,
carbene), 202.6 (s, trans-CO), 198.7 (s, d, JWC 131.2,
cis-CO), 171.6 (s, C2 thiazole), 150.1 (s, C4 thiazole), 143.6
Chloro[methoxy(2-phenylthiazol-5-yl)methylidene]gold,
5.
1
Compound 3b (145 mg, 0.28 mmol) was dissolved in thf
(10 cm3) and the Schlenk tube was cooled to ꢁ5 1C. Solid
[ClAu(tht)] (89 mg, 0.28 mmol) was added and stirring
commenced for 1 h, whereupon the temperature reached
5 1C. All volatiles were removed in vacuo and the resulting
solid was re-dissolved in CH2Cl2 (30 cm3) followed by a
filterstick filtration. The solution was layered with hexane
(60 cm3) and stored at ꢁ20 1C. Well-defined red faceted
2
(s, C5 thiazole), 134.2 (d, JPC 13.4, o-PPh), 133.8 (s, i-Ph),
131.5 (d, 4JPC 1.3, p-PPh), 130.7 (s, p-Ph), 129.8 (d, 1JPC 50.3,
3
i-PPh), 129.2 (d, JPC 10.8, m-PPh), 128.9 (s, o-Ph) and 126.9
(s, m-Ph). dP (162 MHz, CDCl3) 38.8 (s). nmax/cmꢁ1 (CH2Cl2)
2069w (A1 CO) and 1922m (E and A1 CO). m/z 1078
(1)
(2)
[(M–W(CO)5 + AuPPh3–CO)+, 4%], 887 [(M ꢁ 3CO)+, 1],
ꢀc
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crystals of 5 (75 mg, 62%) suitable for X-ray diffraction were
isolated. mp 75 1C (dec.). Found: C, 30.0; H, 2.2; N, 3.4.
C11H9AuClNOS requires C, 30.3; H, 2.1; N, 3.2%. dH
(400 MHz, CD2Cl2) 9.21 (1 H, br s, CH thiazole), 8.14
(2 H, m, o-Ph), 7.64 (1 H, m, p-Ph), 7.54 (2 H, m, m-Ph)
and 4.84 (3 H, s, d, 1JCH 150.4, OMe). dC (101 MHz, CD2Cl2)
248.6 (s, carbene), 183.1 (s, C2 thiazole), 168.9 (br s, C4
thiazole), 144.4 (br s, C5 thiazole), 134.1 (s, p-Ph), 132.7
(s, i-Ph), 130.1 (s, m-Ph), 128.6 (s, o-Ph) and 71.7 (s, OMe).
m/z 386 [4%, (M–Cl–CH3 + H)+], 377 (3) and 358
[3, (M–Cl–CH3–CO + H)+].
43.5; H, 2.7; N, 7.8. C22H16ClN3O2SW requires C, 43.2; H,
2.8; N, 8.0%. dH (400 MHz, CDCl3) 9.09 (4 H, m, o-py), 7.91
(2 H, m, o-Ph), 7.83 (2 H, tt, 3JHH 7.65, 4JHH 1.71, p-py), 7.79
(1 H, s, CH thiazole), 7.44 (3 H, m, m/p-Ph) and 7.36 (4 H, m,
m-py). dC (101 MHz, CDCl3) 240.8 (s, d, 1JWC 205.7, carbyne),
1
220.1 (s, d, JWC 168.8, CO), 165.7 (s, C2 thiazole), 152.7
(s, o-py), 148.0 (s, C4/C5 thiazole), 143.9 (s, C5/C4 thiazole),
138.4 (s, p-py), 133.4 (s, i-Ph), 130.2 (s, p-Ph), 129.0 (s, m-Ph),
126.4 (s, o-Ph) and 125.2 (s, m-py). nmax/cmꢁ1 1972vs (A0 CO)
and 1870vs (A0 0 CO). m/z 606 [2%, (M + H)+], 605 (3, M+),
577 [16, (M–CO)+], 570 [7, (M–Cl)+], 549 [15, (M–2CO)+],
527 [3, (M–C5H5N + H)+], 526 [1, (M–C5H5N)+], 498
[5, (M–C5H5N–CO)+], 471 [2, (M–C5H5N–2CO + H)+],
470 [4, (M–C5H5N–2CO)+] and 367 {18, [W(RCH)Cl-
(C5H5N)(CO)2]+}.
cis-Dicarbonylchloro{[2-(1-piperidinyl)thiazol-5-yl]methylidyne}-
cis-bis(pyridine)tungsten, 6a. Two Schlenk tubes were prepared
containing the freshly prepared Li+-analogue of 1a (499 mg,
0.95 mmol) and (Cl3CO)2CO (104 mg, 0.35 mmol, 1.1 mol eq.)
and CH2Cl2 (30 cm3 and 10 cm3, respectively). After cooling to
ꢁ78 1C, the triphosgene solution was transferred to the lithium
acyl suspension via a Teflon cannula; the colour immediately
changed to dark red. Stirring was continued for 1.5 h at
ꢁ78 1C and 30 min at 0 1C. Freshly distilled pyridine
(3 cm3) was added with a glass pipette and stirring commenced
at room temperature for 2.3 h. Excessive triphosgene was
quenched with several drops of MeOH and all volatiles were
removed in vacuo. The crude product was subjected to inert
flash chromatography (7 ꢃ 5 cm, ꢁ30 1C), eluting with
CH2Cl2 (100 cm3), CH2Cl2–MeOH (19 : 1; 50 cm3) and
CH2Cl2–MeOH (16 : 1; 80 cm3). The orange-brown fraction
yielded 285 mg of 6a. Crystals suitable for X-ray diffraction
were grown by layering a CH2Cl2 solution with hexane. mp
73 1C (dec. with evolution of gas). Found: C, 41.3; H, 3.4; N,
9.2. C21H21ClN4O2SW requires C, 41.2; H, 3.45; N, 9.1%. dH
(300 MHz, CDCl3) 9.08 (4 H, m, o-py), 8.69 (1 H, br s, CH
Acknowledgements
The authors would like to thank the Alexander von Humboldt
Foundation (HGR and SC) and the South African National
Research Foundation for financial support, and Mintek for
the generous loan of gold.
Notes and references
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ꢀc
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