Regioselective addition of mixed-chalcogenide iron carbonyl clusters Fe2(CO)6(μ-EE′) (E ≠ E′, E, E′ = S, Se, Te) to a carbon-carbon triple bond activated by a metal carbene fragment.

Article abstract of DOI:10.1021/om9702237

From the room-temperature reaction of the transition-metal alkynyl Fischer carbene complexes (CO)₅M=C(OEt)(C≡CPh) (M = Cr, W) with the mixed-chalcogenide compounds Fe₂(CO)₆(μ-EE′) (E ≠ E′, E, E′ = S, Se, Te), the following new trimetallic adducts were obtained: Fe₂(CO)₆{μ-EC(Ph)=C(E′)[(OEt)C=M(CO) ₅]} 1-6 (1, 85%, E = S, E′ = Se, M = Cr; 2, 82%, E = S, E′ = Se, M = W; 3, 84%, E = S, E′ = Te, M - Cr; 4, 80%, E = S, E′ = Te, M = W; 5, 83%, E = Se, E′ = Te, M = Cr; 6, 81%, E = Se, E′ = Te, M = W). In addition, trace amounts of the corresponding alkenyl Fischer carbene complexes (CO)₅M=C(OEt)-{(CH=C(OMe)Ph} 7-8 (7, M = Cr; 8, M = W) were also formed in each case. Compounds 1-6 were characterized by IR and ¹H, ¹³C, ⁷⁷Se, and ¹²⁵Te NMR spectroscopy. Crystallographic analyses of the compounds 2, 3, and 6 were carried out. The structures of 2, 3, and 6 can be described as Fe₂EE′ (E, E′ = S, Se, Te) tetrahedral butterfly cores containing the alkynyl Fischer carbene as a bridge between the two wingtip chalcogens with three terminally bonded carbonyl groups on each Fe atom.

Full text of DOI:10.1021/om9702237

3536
Organometallics 1997, 16, 3536-3540
Regioselective Ad d ition of Mixed -Ch a lcogen id e Ir on
Ca r bon yl Clu ster s F e2(CO)6( -EE′) (E * E′, E, E′ ) S, Se,
Te) to a Ca r bon -Ca r bon Tr ip le Bon d Activa ted by a
Meta l Ca r ben e F r a gm en t. Str u ctu r a l Ch a r a cter iza tion
of New Tr im eta llic Ad d u cts
F e2(CO)6{ -SC(P h )dC(Te)[(OEt)CdCr (CO)5]}, F e2(CO)6-
{ -SC(P h )dC(Se)[(OEt)CdW(CO)5]}, a n d
F e2(CO)6{ -SeC(P h )dC(Te)[(OEt)CdW(CO)5]}
Pradeep Mathur* and Sundargopal Ghosh
Chemistry Department, Indian Institute of Technology, Powai, Bombay 400076, India
Amitabha Sarkar
Division of Organic Chemistry (Synthesis), National Chemical Laboratory, Pune 411008, India
C. V. V. Satyanarayana
Regional Sophisticated Instrumentation Center, Indian Institute of Technology,
Powai, Bombay 400 076, India
Arnold L. Rheingold and Louise M. Liable-Sands
Department of Chemistry, University of Delaware, Newark, Delaware 19716
Received March 19, 1997X
From the room-temperature reaction of the transition-metal alkynyl Fischer carbene
complexes (CO)5MdC(OEt)(C≡CPh) (M ) Cr, W) with the mixed-chalcogenide compounds
Fe2(CO)6(µ-EE′) (E * E′, E, E′ ) S, Se, Te), the following new trimetallic adducts were
obtained: Fe2(CO)6{µ-EC(Ph)dC(E′)[(OEt)CdM(CO)5]} 1-6 (1, 85%, E ) S, E′ ) Se, M )
Cr; 2, 82%, E ) S, E′ ) Se, M ) W; 3, 84%, E ) S, E′ ) Te, M ) Cr; 4, 80%, E ) S, E′ ) Te,
M ) W; 5, 83%, E ) Se, E′ ) Te, M ) Cr; 6, 81%, E ) Se, E′ ) Te, M ) W). In addition,
trace amounts of the corresponding alkenyl Fischer carbene complexes (CO)5MdC(OEt)-
{(CHdC(OMe)Ph} 7-8 (7, M ) Cr; 8, M ) W) were also formed in each case. Compounds
1
1-6 were characterized by IR and H, 13C, 77Se, and 125Te NMR spectroscopy. Crystal-
lographic analyses of the compounds 2, 3, and 6 were carried out. The structures of 2, 3,
and 6 can be described as Fe2EE′ (E, E′ ) S, Se, Te) tetrahedral butterfly cores containing
the alkynyl Fischer carbene as a bridge between the two wingtip chalcogens with three
terminally bonded carbonyl groups on each Fe atom.
In tr od u ction
bonding modes to transition metals, relatively little is
known about the addition of acetylenes on main group
elements.4 The use of certain main group elements as
bridging and stabilizing ligands in designed cluster
growth reactions has been extensively demonstrated in
recent years.5
In the course of our investigations on the addition of
inorganic and organic species to Fe2(µ-EE′)(CO)6 (where
E or E′ ) S, Se, or Te), we prepared, under facile
conditions, the acetylene adducts Fe2(CO)6{µ-
EC(H)dC(R)E′} (where R ) Ph, CH2OH, and H).1,2 The
addition of the C-C triple bonds across the reactive
E-E′ bonds was found to depend on the E, E′ combina-
tion in Fe2(µ-EE′)(CO)6 (where E or E′ ) S, Se, or Te).
Bonding and reactivity studies of alkynes attached to
metal centers is of current interest because of the
potential of the coordinated alkynes to be transformed
into useful organic species.3 In contrast to the large
number of reports on the different types of acetylene
The compounds Fe2(µ-EE′)(CO)6 are highly reactive
species, and different combinations of the chalcogen
ligands in these provide versatility in their reactions
with organic and inorganic moieties. Reaction between
phenylacetylene and these clusters leads to the forma-
tion of regioisomeric products. Diaryl, alkylaryl, or
dialkylacetylenes did not undergo similar addition reac-
tion. Initially, it appeared that the steric factor alone
precluded the addition to disubstituted alkynes, but use
X Abstract published in Advance ACS Abstracts, J uly 1, 1997.
(1) (a) Mathur, P.; Hossain, M. M.; Umbarkar, S.; Satyanarayana,
C. V. V.; Tavale, S. S.; Puranik, V. G. Organometallics 1995, 14, 959.
(b) Mathur, P.; Hossain, M. M. Organometallics 1993, 12, 2398. (c)
Mathur, P.; Dash, A. K.; Hossain, M. M.; Umbarkar, S.; Satya-
narayana, C. V. V.; Chen, Y.-S.; Holt, E.; Rao, S. N.; Soriano, M.
Organometallics 1996, 15, 1356.
(3) Katz, T. J .; Hacker, S. M. J . Am. Chem. Soc. 1985, 107, 2182.
(4) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry;
Wiley: New York, 1988; p 1157.
(5) (a) Whitmire, K. H. J . Coord. Chem. 1988, 17, 95. (b) Linford,
L.; Raubenheimer, H. G. Adv. Organomet. Chem. 1991, 32, 1. (c)
Compton, N. A.; Errington, R. J .; Norman, N. C. Adv. Organomet.
Chem. 1990, 31, 91.
(2) Mathur, P.; Hossain, M. M.; Umbarkar, S.; Satyanarayana, C.
V. V.; Puranik, V. G. J . Organomet.Chem. 1996, 506, 313.
S0276-7333(97)00223-9 CCC: $14.00 © 1997 American Chemical Society

Addition of Mixed-Chalcogenide Iron Carbonyl Clusters
Organometallics, Vol. 16, No. 15, 1997 3537
Ta ble 1. Exp er im en ta l Con d ition s Used for P r ep a r a tion of F e2(CO)6{ -EC(P h )dC(E′)[(OEt)CdM(CO)5]}
(M ) Cr , W a n d E * E′; E ) S, Se; E′ ) Se, Te) (1-6)
(CO)5MdC(OEt)(C≡CPh)
(CO)6Fe2(µ-EE′)
reaction
[g, (mmol)]
[g, (mmol)]
time (min)
product
yield, g (%)
0.25 (85)
anal. calcd (found)
mp, °C
(CO)5CrdC(OEt)(C≡CPh)
(CO)6Fe2(µ-SSe)
[0.20, (0.51)]
(CO)6Fe2(µ-SSe)
[0.15, (0.38)]
(CO)6Fe2(µ-STe)
[0.24, (0.54)]
(CO)6Fe2(µ-STe)
[0.23, (0.52)]
(CO)6Fe2(µ-SeTe)
[0.19, (0.39)]
(CO)6Fe2(µ-SeTe)
[0.20, (0.41)]
35
35
40
45
45
40
1
C, 35.6 (35.7); H, 1.35 (1.44)
128-130 dec
[0.14, (0.40)]
(CO)5WdC(OEt)(C≡CPh)
[0.14, (0.30)]
2
3
4
5
6
0.21 (82)
0.31 (84)
0.35 (80)
0.25 (83)
0.29 (81)
C, 30.2 (30.4); H, 1.14 (1.26)
C, 33.4 (33.6); H, 1.26 (1.38)
C, 28.6 (28.8); H, 1.08 (1.18)
C, 31.5 (31.7); H, 1.03 (1.10)
C, 27.2 (27.4); H, 1.03 (1.16)
136-138 dec
132-134 dec
142-144 dec
138-140 dec
146-148 dec
(CO)5CrdC(OEt)(C≡CPh)
[0.16, (0.47)]
(CO)5WdC(OEt)(C≡CPh)
[0.23, (0.48)]
(CO)5CrdC(OEt)(C≡CPh)
[0.13, (0.37)]
(CO)5WdC(OEt)(C≡CPh)
[0.18, (0.38)]
Ta ble 2. Cr ysta llogr a p h ic Da ta for C22H10F e2O12SeTeW (6), C22H10F e2O12S0.7Se1.3W (2), a n d
C22H10Cr F e2O12STe (3)
6
2
3
formula
fw
C22H10Fe2O12SeTeW
968.41
C22H10Fe2O12S0.7Se1.3
886.94
W
C22H10CrFe2O12STe
789.66
space group
a, Å
b, Å
Pbca
Pbca
Pbca
13.797(2)
18.742(3)
21.490(2)
5557(1)
13.910(3)
18.444(4)
21.289(2)
5462(1)
13.713(5)
18.309(7)
21.427(1)
5380(4)
c, Å
V, Å3
Z
8
8
8
cryst color/habit
D(calc), g cm-3
(Mo KR), cm-1
T, K
deep red block
2.315
75.58
deep red block
2.157
70.96
deep red block
1.950
26.62
240(2)
240(2)
244(2)
T(max)/T(min)
radiation
R(F)[I > 2σ(I)],a
0.275/0.214
0.284/0.169
Mo KR (λ ) 0.710 73 Å)
4.23
0.889/0.560
%
4.26
7.46
3.86
18.51
R(wF2)[I > 2σ(I)],a
%
10.11
a
2
R ) ∑∆/∑(Fo), ∆ ) |(Fo - Fc)|; quantity minimized ) R(wF2) ) ∑[w(Fo - Fc2)2]/∑[(wFo2)2]1/2
.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (Deg) for 2, 3, a n d 6
ated immediately prior to use. Reactions were monitored by
FT-IR spectroscopy and thin-layer chromatography. Infrared
spectra were recorded on a Nicolet-Impact 400 FTIR spec-
trometer as an n-hexane solution in a sodium chloride cell at
0.1 mm path length. Elemental analyses were performed
using a Carlo Erba 1106 automatic analyzer. 1H, 13C, 77Se,
and 125Te NMR spectra were recorded on a Varian VXR 300S
spectrometer in CDCl3 at 25 °C. The operating frequency for
77Se NMR was 57.23 MHz with a pulse width of 15 µs and a
delay of 1.0 s, and the operating frequency for 125Te was 94.70
MHz with a pulse width of 9.5 µs and a delay of 1 s. 77Se NMR
spectra were referenced to Me2Se (δ ) 0 ppm), and 125Te NMR
spectra were referenced to Me2Te (δ ) 0 ppm).
2, M ) W
3, M ) Cr
6, M ) W
Fe(1)-Fe(2)
Fe(2)-S/Se
2.507(2)
2.304(2)
1.316(11)
2.5445(13)
2.572(2)
C(7)-C(8)
1.330(6)
2.5272(12)
2.5226(10)
1.324(11)
2.5322(14)
2.5291(13)
2.365(2)
Fe(1)-Te
Fe(2)-Te
Fe(1)-Se
2.383(2)
2.373(2)
Fe(2)-Se
2.375(2)
Fe(1)-S
2.249(2)
2.255(2)
Fe(2)-S
W-C(9)
2.161(9)
1.965(9)
2.152(8)
Cr-C(9)
2.014(5)
2.165(4)
Se-C(8)
Te-C(8)
2.186(8)
65.73(5)
56.95(5)
57.32(4)
59.51(4)
61.09(4)
Chromium hexacarbonyl, tungsten hexacarbonyl, and phe-
nylacetylene were purchased from Aldrich Chemical Co., and
these were used without further purification. The mixed
chalcogenide iron carbonyl clusters Fe2(µ-SSe)(CO)6, Fe2(µ-
Fe(1)-Se-Fe(2)
Fe(1)-Fe(2)-Se
Fe(2)-Fe(1)-Se
Fe(1)-Fe(2)-Te
Fe(1)-Te-Fe(2)
Cr-C(9)-C(8)
Fe(1)-S-Fe(2)
Fe(1)-Fe(2)-S
Te-C(8)-C(7)
Se-C(7)-C(8)
W-C(9)-C(8)
Se-Fe(2)-S/Se
Fe(1)-S/Se-Fe(2)
63.63(6)
58.38(5)
57.99(5)
59.83(3)
60.51(3)
125.8(3)
68.78(4)
55.50(4)
114.2(3)
6
STe)(CO)6, and Fe2(µ-SeTe)(CO)6 and the alkynyl Fischer
carbene complexes were prepared as previously reported.7
P r ep a r a tion of F e2(CO)6{ -EC(P h )dC(E′)[C(OEt)dM-
(CO)5}] (1-6) (E ) S, Se; E ) Se, Te a n d M ) Cr , W). Table
1 summarizes the conditions used for the preparation of 1-6.
In a typical preparation, equimolar amounts of a solution of
(CO)6Fe2(µ-EE′) and (CO)5MdC(OEt)(C≡CPh) in methanol
were stirred at room temperature for 35-45 min. The stirring
was stopped when all the (CO)6Fe2(µ-EE′) had been consumed,
as monitored by TLC. The solvent was removed in vacuo, and
the residue was chromatographed on a silica gel column.
Elution with hexane yielded in each case a major red band
followed by trace amounts of a yellow band. The red band
118.1(6)
124.3(6)
124.2(6)
81.73(7)
65.95(7)
of a highly polarized carbon-carbon triple bond in
alkynyl Fischer carbene complexes dispelled this ap-
prehension. Addition of Fe2(µ-EE′)(CO)6 (E * E′ and
E, E′ ) S, Se, or Te) occurred on this C-C triple bond
with high facility and yield to provide highly regiose-
lective trimetallic adducts. This paper describes the
preparation and structural characterization of these
new, functional metal clusters.
(6) (a) Mathur, P.; Chakrabarty, D.; Hossain, M. M.; Kumar, R. K.
J . Organomet. Chem. 1991, 410, 143. (b) Mathur, P.; Chakrabarty, D.;
Hossain, M. M. J . Organomet. Chem. 1991, 401, 167. (c) Mathur, P.;
Chakrabarty, D.; Hossain, M. M.; Rashid, R. S. J . Organomet. Chem.
1991, 420, 79. (d) Mathur, P.; Chakrabarty, D.; Hossain, M. M. J .
Organomet. Chem. 1991, 418, 415.
(7) (a) Fischer, E. O.; Kreissl, F. R. J . Organomet. Chem. 1972, 35,
C47-C51. (b) Fischer, E. O.; Kalder, H. J . J . Organomet. Chem. 1977,
131, 57-64.
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions and other manipula-
tions were carried out under an argon or nitrogen atmosphere,
using standard Schlenk techniques. Solvents were deoxygen-

3538 Organometallics, Vol. 16, No. 15, 1997
Sch em e 1. F or m a tion of Com p ou n d s 1-6
Mathur et al.
eluting first was characterized spectroscopically as Fe2(CO)6-
{µ-EC(Ph)dC(E′)[C(OEt)dM(CO)5}] (1-6), and the second
band was identified as the corresponding alkenyl Fischer
carbene complex [(CO)5MdC(OEt){CHdC(OMe)Ph] (7, M )
Cr; 8, M ) W).8
over silica gel followed by crystallization from hexane
at -4 °C. The chromium-containing complexes (1, 3,
and 5) were obtained as deep red crystals, while the
tungsten derivatives (2, 4, and 6) were orange-red
crystalline solids. In each case, trace amounts of the
corresponding known alkenyl Fischer carbene com-
plexes (CO)5MdC(OEt){CHdC(OMe)Ph} (7, M ) Cr; 8,
M ) W) were also obtained, and these were identified
on the basis of comparison with IR and 1H NMR spectral
data reported in the literature.8
Gen er a l Tr en d s. Unlike simple monosubstituted
alkynes, addition of Fe2(µ-EE′)(CO)6 (E * E′, E, E′ ) S,
Se, Te) to the triple bond of the Fischer carbene
complexes occurred readily and in high yield. Even with
complexes like Fe2(µ-S2)(CO)6 and Fe2(µ-Te2)(CO)6 that
are reluctant to add to alkynes, addition readily occurs
to the triple bond of acetylenic carbene complexes.9
Such facility of reaction can be attributed to the high
reactivity of the acetylenic bond in alkynyl Fischer
carbene complexes.10 Owing to the strong electron-
withdrawing M(CO)5 fragment attached to the carbene
carbon, the alkyne bond is considerably polarized. The
13C chemical shift difference of more than 40 ppm
between the R- and the â-alkynyl carbons11a would
attest to this effect. While a consequence of such
polarization of the alkyne bond is facile nucleophilic
attack by the chalcogen atom, a strong regiochemical
preference is also to be expected when two different
chalcogenide atoms are present in the iron cluster. The
smaller chalcogenide atom would accommodate a de-
veloping negative charge better and react preferentially
at the electron-deficient â-acetylenic carbon. True to
this expectation, with all the heterochalcogenide clus-
ters, only one regioisomer of the product was obtained
Cr ysta l Str u ctu r e Deter m in a tion of 2, 3, a n d 6. Red
crystals of 2, 3, and 6 were selected and mounted with epoxy
cement to glass fibers. Single-crystal X-ray data were collected
on a Siemens P4 diffractometer using Mo KR radiation. The
unit cell parameters were obtained by the least-squares
refinement of the angular settings of 24 reflections (20° e 2θ
e 25°). Pertinent crystallographic data for 2, 3, and 6 are
summarized in Table 2. The systematic absences in the
diffraction data for 2, 3, and 6 are uniquely consistent for the
space group Pbca. The structures were solved using direct
methods and completed by subsequent difference Fourier
syntheses and by full-matrix least-squares procedures. Semiem-
pirical ellipsoid absorption corrections were applied. The S
atom in 2 is compositionally disordered with selenium 70/30
and is refined as an oversized sulfur atom. All non-hydrogen
atoms were refined with anisotropic displacement coefficients,
and hydrogen atoms were treated as idealized contributions.
The largest remaining peaks in the difference map (1.01-1.47
e Å-3 for 6) and (1.10-1.12 e Å-3 for 2) occur at a chemically
unreasonable positions (0.75-0.97 Å from tungsten for 6 and
1.10-1.12 Å from tungsten for 2) and were considered as noise.
All software and sources of the scattering factors are
contained in the SHELXTL (5.3) program library (Sheldrick,
G. Siemens XRD, Madision, WI). Selected bond lengths and
bond angles for 2, 3, and 6 are listed in Table 3.
Resu lts a n d Discu ssion
Syn th esis of 1-6. The alkynyl Fischer carbene
complexes of tungsten and chromium were prepared
following reported procedures.7 In a typical reaction, a
freshly prepared solution of Fe2(µ-EE′)(CO)6 (E * E′, E,
E′ ) S, Se, Te) in methanol was added to an equimolar
amount of solid Fischer carbene complex under a
blanket of argon at room temperature. On stirring at
room temperature for 30-45 min, the adduct Fe2(CO)6-
{µ-EC(Ph)dC(E′)[(OEt)CdM(CO)5]} (E * E′, E ) S, Se,
E′ ) Se, Te, and M ) Cr, W) was obtained as an air-
stable solid in 80-85% yield (Scheme 1). The products
were isolated as single regioisomers by chromatography
(9) Details of the trimetallic adducts and their chemistry have been
the subject of a separate manuscript submitted for publication:
Mathur, P.; Ghosh, S.; Sarkar, A.; Satyanarayana, C. V. V.; Puranik,
V. G. Organometallics, submitted.
(10) (a) Wulff, W. D.; Yang, D. C. J . Am. Chem. Soc. 1984, 106,
7565-7567. (b) Segundo, A.; Moreto, J . M.; Vinas, J . M.; Ricart, S.;
Molins, E. Organometallics 1994, 13, 2467.
(11) (a) For a detailed discussion of 13C assignments, see: Wulff,
W. D. In Advances in Metal-Organic Chemistry; Liebeskind, L. S.,
Ed.; J AI Press Inc: Greenwich, CT, 1989; Vol. 1, pp 317-319. (b) High
regioselectivity in the 3 + 2 cycloaddition of (trimethylsilyl)diaz-
omethane to acetylenic carbene complexes as a result of polarization
of triple bond has been reported: Chan, K. S.; Wulff, W. D. J . Am.
Chem. Soc. 1986, 108, 5229.
(8) (a) Llebaria, A.; Moreto, J . M.; Ricart, S.; Ros, J .; Vinas, J . M.;
Yanez, R. J . Organomet. Chem. 1992, 440, 79. (b) Aumann, R.;
Hinterding, P. Chem. Ber. 1993, 126, 421.

Addition of Mixed-Chalcogenide Iron Carbonyl Clusters
Organometallics, Vol. 16, No. 15, 1997 3539
F igu r e 1. Molecular structure of Fe2(CO)6{µ-EC(Ph)dC-
(E′)[(OEt)CdM(CO)5]} [2, M ) W, E ) S, E′ ) Se; 3, M )
Cr, E ) S, E′ ) Te; 6, M ) W, E ) Se, E′ ) Te].
in each case.11b This result may be contrasted with our
earlier finding that the room-temperature reaction of
Fe2(µ-SeTe)(CO)6 with phenylacetylene in the presence
of a trace amount of NaOAc gives rise to the formation
of two regioisomers Fe2(CO)6{µ-Se(Ph)CdC(H)Te} and
Fe2(CO)6{µ-Te(Ph)CdC(H)Se} in 23% and 21% yield,
respectively.1a
These new complexes have a close structural resem-
blance with the dicobalt-alkyne complexes widely used
in the Pauson-Khand reaction12 and chemistry of
stabilized propargylic cations.13 However, in our mol-
ecules, the alkynes are not directly complexed with the
metal carbonyl fragment; rather, they are linked to the
chalcogenide atoms. The chemistry of such an unusual
“heterocycle” is yet unexplored.
Molecu la r Str u ctu r es of 2, 3, a n d 6. Crystal
structure solutions for three representative complexes
were carried out to confirm the stated regioselectivity
pattern. It also enabled us to interpret the 77Se and
125Te NMR data with confidence. Red crystals of 2 and
orange-red crystals of 3 and 6 were grown from hexane
solutions at -4 °C for crystal structure determination.
Despite the difference in chalcogenide elements present
in different complexes, the complexes 2, 3, and 6 were
found to be isomorphous. The molecular structures of
2, 3, and 6 are shown in Figure 1.
The structure consists of a Fe2EE′ (E * E′ and E, E′
) S, Se and Te) butterfly core, and the alkynyl carbene
unit is attached to the wingtip of chalcogen atoms. The
acetylenic C-C bond distances of complexes 2, 3, and 6
are longer by at least 0.01 Å than in the corresponding
phenylacetylene adducts.1a,c The metal-carbene bond
(12) (a) Schore, N. E. Org. React. 1991, 40, 1. (b) Schore, N. E. In
Comprehensive Organometallic Chemistry; Hegedus, L. S., Ed., Per-
gamon Press: London, 1995; Vol. 12, p 703.
(13) (a) Nicholas, K. M.; Caffyn, A. J . M. In Comprehensive Orga-
nometallic Chemistry; Hegedus, L. S., Ed.; Pergamon Press: London,
1995; Vol. 12, p 685. (b) Nicholas, K. M.; Nestle, M. O.; Seyferth, D. In
Transition Metal Organometallics in Organic Synthesis; Alper, H., Ed.;
Academic Press: New York, 1978; Vol. 2, p 1. For a remarkable
application in total synthesis of a complex diterpene, see: J amison,
T. F.; Shambayati, S.; Crowe, W. E.; Schreiber, S. L. J . Am. Chem.
Soc. 1994, 116, 5505.

3540 Organometallics, Vol. 16, No. 15, 1997
Mathur et al.
distances of these complexes are not significantly dif-
ferent from those reported for simple carbene com-
plexes.14
The crystal structures clearly reveal that the car-
bene-metal fragment and the phenyl ring are cis to
each other, which offers curious possibilities from the
standpoint of metal-carbene chemistry.15
singlet at δ 523 and 518 ppm, respectively, whereas
compounds Fe2(CO)6{µ-SeC(Ph)dC(Te)[(OEt)CdM(CO)5]}
show a singlet at δ 645 (M ) Cr, W). Examination of
the 77Se NMR spectra for the above series of compounds
shows that the signal shifts downfield when the site of
attachment of the Se atom changes from an R to a â
carbon. The 125Te NMR spectra of compounds 3-6
showed a singlet each at δ 965-1105 ppm.
Sp ectr a l Ch a r a cter iza tion . Spectroscopic features
of 1-6 are summarized in Table 4. The infrared spectra
in hexane of compounds 1-6 exhibit almost identical
carbonyl stretching patterns typically observed for
compounds containing the Fe(CO)3 and M(CO)5 (M )
Cr, W) units. For all six compounds, only terminally
bonded carbonyl stretching frequencies are observed.
Comparison of infrared spectra of compounds 1-6 with
the previously reported related compounds (CO)6Fe2{µ-
EC(Ph)dC(H)E′}1a (E * E′ and E, E′ ) S, Se, and Te)
shows that there is a shift of bands to lower ν(CO)
values in Fe2(CO)6{µ-EC(Ph)dC(E′)[(OEt)CdM(CO)5]}
(E * E′ and E ) S, Se, E′ ) Se, Te) for the following
combinations of EE′ ligands: SSe > STe > SeTe. The
1H NMR spectra of compounds 1-6 show one triplet and
one quartet for the ethoxy group attached to the carbene
carbon. 13C NMR spectra display two peaks between δ
133 and 156 ppm. The downfield signal has been
assigned to C(Ph) and the upfield signal to C(CdM) in
line with previous reports.11a The separation in chemi-
cal shifts of the two signals is at a maximum for
compound 4 (19.6 ppm) and at a minimum for 5 (11.5
ppm). The spectra also displayed peaks for phenyl
carbon atoms at δ 127-129 ppm. We observe three
signals in the CO region: the signal at δ 207-211 ppm
can be assigned to two Fe(CO)3 units, while the other
two correspond to cis CO and trans CO in M(CO)5 (M )
Cr, W) unit. The most deshielded signals at δ 337-
338 ppm for 1, 3, and 5 and δ 312-310 ppm for 2, 4,
and 6 were assigned to the carbene carbon atom.
Con clu sion s
We have demonstrated that mixed chalcogenide clus-
ters like Fe2(µ-EE′)(CO)6 (E,E′ ) S, Se, or Te) can readily
add to the activated carbon-carbon triple bond attached
to the carbene carbon in a Fischer carbene complex to
yield regioisomerically pure adducts. Crystal structure
determination of representative complexes established
the identity of the new trimetallic products beyond
doubt and led to unequivocal assignment of 77Se and
125Te NMR spectral patterns. A unique combination of
three metal carbonyl centers make these structurally
defined molecules readily soluble in organic solvents, a
useful criterion that permits systematic exploitation of
their chemistry. The metal-carbene fragment present
in these molecules is essentially a versatile, latent
organic functional group which provides handle to
covalently link a metal cluster to an organic molecule
or a biopolymer.16 Relevant functional group transfor-
mations will be reported in due course.
Ack n ow led gm en t. The Department of Science and
Technology, Government of India, is thanked for finan-
cial support to one of us (P.M). We are grateful to Dr.
Rasidul Amin and Mr. K. N. J ayaprakash, National
Chemical Laboratory, Pune, for their help during prepa-
ration of carbene complexes.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
details including complete tables of atomic coordinates, bond
lengths and bond angles, and anisotropic displacement pa-
rameters for 2, 3, and 6 (18 pages). Ordering information is
given on any current masthead page.
The 77Se NMR spectra of compounds Fe2(CO)6{µ-SC-
(Ph)dC(Se) [(OEt)CdM(CO)5]} (M ) Cr, W) show a
OM9702237
(14) (a) Cardin, D. J .; Cetinkaya, B.; Lappert, M. F. Chem. Rev. 1972,
72, 545. (b) Schubert, U. Coord. Chem. Rev. 1984, 55, 261.
(15) Merlic, C. A.; Xu, D.; Khan, S. I. Organometallics 1992, 11, 412.
(16) J aouen, G.; Vessieres, A.; Butler, I. S. Acc. Chem. Res. 1993,
26, 361.