Fast and reversible intramolecular cleavage of an Au-C bond in the spiked-triangular metal complexes [Fe3Au(μ4,η2-C≡CtBu) (CO)9 (PR3)] (R = Ph, iPr)

Article abstract of DOI:10.1021/om010980b

The fast and irreversible intramolecular cleavage of an Au-C bond in the spiked-triangular metal complexes was analyzed. The gold fragment was found to display an unexpected bonding mode and a fast and reversible process of oxidative addition/reductive elimination of the Au-C bond was observed in the solution. The results show that the Au-C bond cleavage equilibrium operating in the observed clusters has a low kinetic barrier and results from a subtle balance of factors.

Full text of DOI:10.1021/om010980b

780
Organometallics 2002, 21, 780-782
F a st a n d Rever sible In tr a m olecu la r Clea va ge of a n
Au -C Bon d in th e Sp ik ed -Tr ia n gu la r Meta l Com p lexes
i
[F e3Au (µ4,η2-CtCtBu )(CO)9(P R3)] (R ) P h , P r )
Esther Delgado,*,† Bruno Donnadieu,‡ M. Esther Garc´ıa,§ Silvia Garc´ıa,†
Miguel A. Ruiz,§ and Fe´lix Zamora†
Departamento de Quı´mica Inorga´nica, Facultad de Ciencias, Universidad Auto´noma de
Madrid, 28049 Madrid, Spain, Service de Cristallochimie, Laboratoire de Chimie de
Coordination CNRS, 31077 Toulouse, France, and Departamento de Qu´ımica Orga´nica e
Inorga´nica/ IUQOEM, Universidad de Oviedo, 33071 Oviedo, Spain
Received November 13, 2001
Summary: The C-S bond cleavage in the alkynethiolate
ligand of the compound Li[Fe3(µ3-SCtCtBu)(CO)9] (1a )
takes place in its reaction with [AuClPR3] (R ) Ph, iPr),
affording the complexes [Fe3Au(µ4,η2-CtCtBu)(CO)9-
process operating in the resulting Fe3Au clusters which
involves the reversible cleavage of an Au-C(alkyne)
bond. To our knowledge, there is no precedent in the
literature for this type of metal-carbon bond cleavage.
i
(PR3)] (R ) Ph (3a ), Pr (3b)). The gold fragment dis-
Reaction of Fe3(CO)12 with LiSCtCtBu in refluxing
THF yields Li[Fe3(µ3-SCtCtBu)(CO)9] (1a ) as the major
product after chromatographic work on silica gel, along
with a small amount of [Fe2(µ-SCtCtBu)2(CO)6] (2).
Complex 2 has been characterized in solution, its 1H
NMR spectrum being indicative of the presence of syn/
anti isomers (see the Supporting Information). Com-
pound 1a and the analogous (NEt4)[Fe3(µ3-SCtCtBu)-
(CO)9] (1b) exhibit a single resonance for the tert-butyl
group in the 1H NMR spectrum, and the pattern of their
C-O stretching bands is similar to those reported for
the related clusters Li[Fe3(µ3-SR)(CO)9] (R ) alkyl,
aryl).4a The FAB- mass spectrum of 1b shows peaks
corresponding to the molecular ion and those derived
from loss of the sulfur atom and up to seven carbonyls
in the latter.
plays an unexpected bonding mode, and a fast and
reversible process of oxidative addition/ reductive elimi-
nation of the Au-C bond has been observed in solution.
Transition-metal chemistry with organosulfur ligands
is an attractive subject, due to its relevance from a
biological, industrial, and environmental point of view.1
Although thiolate or alkynyl chemistry has been widely
explored, only a few complexes containing alkynethi-
olate ligands have been described.2 Within the well-
known field of mixed gold-transition-metal clusters,3
we have previously reported some Fe2Au and Fe3Au
compounds bearing alkane- or arenethiolate ligands.4
Due to the absence of data on iron-gold alkynyl
compounds, we considered it of interest to synthesize
clusters bearing RCtCS- ligands in order to know
whether the presence of a C-C triple bond in these
sulfur ligands could have an influence on the structure
of the new compounds. Unexpectedly, however, we have
found that sulfur is easily extruded from the alkynethi-
olate ligands upon reaction with suitable gold com-
plexes. Moreover, we have discovered a novel dynamic
Treatment of a THF solution of 1a with [AuClPPh3]
in the presence of TlBF4 leads5 to the formation of the
new cluster [Fe3Au(µ4,η2-CtCtBu)(CO)9(PPh3)] (3a ) and
the known complex [Fe3Au2(µ3-S)(CO)9(PPh3)2],6 to-
gether with some other unidentified compounds. The
main products are obviously derived from a C-S bond
cleavage in the alkynethiolate ligand in the starting 1a .
Although the complexes [M3Au(µ3,η2-CtCR)(CO)9(PPh3)]
are known for M ) Ru,7 Os,8 to our knowledge 3a
represents the first example of an Fe3Au cluster con-
taining an alkynyl group. The molecular structure of
3a (Figure 1) contains an “out-of-plane” spiked trian-
* To whom correspondence should be addressed. E-mail:
esther.delgado@uam.es.
† Universidad Auto´noma de Madrid.
‡ Service de Cristallochimie.
§ Universidad de Oviedo.
(1) (a) Adv. Inorg. Chem. 1992, 38. (b) Sanchez-Delgado, R. A. J .
Mol. Catal. 1994, 86, 287. (c) Rauchfuss, T. B. Prog. Inorg. Chem. 1991,
39, 259.
(2) (a) Weigand, W.; Weisha¨upl, M.; Robl, C. Z. Naturforsch. 1996,
B51, 501. (b) Ara, I.; Delgado, E.; Fornie´s, J .; Herna´ndez, E.; Lalinde,
E.; Mansilla, N.; Moreno, M. T. J . Chem. Soc., Dalton Trans. 1998,
3199. (c) Rosenberger, C.; Steunou, N.; J eannin, S.; J eannin, Y. J .
Organomet. Chem. 1995, 494, 17. (d) Seyferth, D.; Womack, G. B.
Organometallics 1986, 5, 2360.
(3) (a) Salter, I. D. In Comprehensive Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford,
U.K., 1995; Vol. 10, Chapter 5. (b) Salter, I. D. In Metal Clusters in
Chemistry; Braunstein, P., Oro, L. A., Raithby, P., Eds.; Wiley-VCH:
Weinheim, Germany, 1999; Vol. 1, Chapter 1.27. (c) Stra¨hle, J . In Metal
Clusters in Chemistry; Braunstein, P., Oro, L. A., Raithby, P., Eds.;
Wiley-VCH: Weinheim, Germany, 1999; Vol. 1, Chapter 1.28.
(4) (a) Delgado, E.; Herna´ndez, E.; Rossell, O.; Seco, M.; Solans, X.
J . Chem. Soc., Dalton Trans. 1993, 2191. (b) Delgado, E.; Herna´ndez,
E.; Rossell, O.; Seco, M.; Gutie´rrez, E.; Ruiz, C. J . Organomet. Chem.
1993, 445, 177.
t
gular metal core, which interacts with the C2 Bu ligand.9
Similar [M3M′(µ4,η2-CtCR)] complexes have been re-
ported.10
(5) [AuCl(PPh3)] and TlBF4 were added to a THF solution of
compound 1a . After 2 h of stirring at room temperature the solvent
was removed under vacuum. Chromatographic workup afforded 3a .
(6) Fischer, K.; Deck, W.; Schwarz, M.; Vahrenkamp, H. Chem. Ber.
1985, 118, 4946.
(7) Braunstein, P.; Predieri, G.; Tiripichio, A.; Sappa, E. Inorg. Chim.
Acta 1982, 63, 113.
(8) Deeming, A. J .; Donovan-Mtunzi, S.; Hardcastle, K. J . Chem.
Soc., Dalton Trans. 1986, 543.
(9) Crystal structure analysis (Stoe imaging plate diffraction sys-
tem): 3a , monoclinic, P21/n, a ) 15.087(5) Å, b ) 9.997(5) Å, c ) 23.272-
(5) Å, â ) 98.531(5)°, V ) 3471(2) Å3, Z ) 4, 4969 unique reflections,
548 parameters. R1 ) 0.0472, wR2 ) 0.1162 (I > 2σ(I)); R1 ) 0.0630,
wR2 ) 0.1238 (all data).
10.1021/om010980b CCC: $22.00 © 2002 American Chemical Society
Publication on Web 01/31/2002

Communications
Organometallics, Vol. 21, No. 5, 2002 781
31P spectra are observed at this temperature. When the
temperature is lowered, all resonances broaden, and
each of them eventually splits into two resonances with
ca. 2:1 relative intensities, except for the carbonyl
resonances, which exhibit a more complex behavior. The
relative intensities of the resonances assigned to each
of the two isomers change moderately with temperature,
so that the major isomer A is more abundant as the
temperature is lowered (ratio A:B ) 2.0 at 203 K, 2.2
at 188 K). From this we conclude that the minor isomer
B must be more abundant at room temperature, in
agreement with the averaged chemical shifts observed
at 291 K. In fact, from the averaged value of J (PC) of
the ipso carbon of PPh3, we can estimate a ratio A:B of
2:3 at 291 K.
Examination of the carbonyl resonances for 3a reveals
severe geometric differences between isomers. Isomer
B seems to have the symmetry of the hydrido complex
[Fe3(µ-H)(µ3,η2CtCtBu)(CO)9] (4) (see below), having an
AuPPh3 fragment bridging an Fe-Fe edge, as found for
[M3Au(µ3,η2-CtCtBu)(CO)9(PPh3)] (M ) Ru, Os).7,8 The
major isomer gives rise at 188 K to just two resonances
(2:1 intensity) and is consistent with the more sym-
metrical structure found for this compound in the
crystal, after allowing for rapid rotation of the Fe(CO)3
moieties of the cluster. The above proposal is consistent
with the spectroscopic properties of the alkyne reso-
nances. In fact, although chemical shifts for CR or Câ
are found in similar regions (around 185 or 140 ppm,
respectively), only the CR resonance of the major isomer
(181.3 ppm) exhibits P-C coupling (J PC ) 58 Hz).
Moreover, the large value of this coupling is fully
consistent with a carbon atom directly bonded to the
AuPPh3 fragment. Finally, the above assignment is also
consistent with the temperature dependence of the
equilibrium between isomers, as the isomer more abun-
dant at low temperature corresponds to that found in
the crystal.
F igu r e 1. View of compound 3a . Hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles
(deg): Fe(1b)-Fe(2), 2.702(8); Fe(1b)-Fe(3), 2.588(7);
Fe(2)-Fe(3), 2.476(2); Fe(1b)-Au(b), 2.672(8); Au(b)-C(1),
2.109(10); Fe(1b)-C(1), 1.808(9); Fe(2)-C(1), 2.027(8); Fe-
(3)-C(1), 2.001(9); Fe(2)-C(2b1), 1.92(4); Fe(3)-C(2b1),
2.054(16); C(1)-C(2b1), 1.348(18); C(1)-C(2b1)-C(2t),
137(2); Fe(1b)-Fe(3)-Fe(2), 64.44(18); Fe(2)-Fe(1b)-
Fe(3), 55.78(17); Fe(3)-Fe(2)-Fe(1b), 59.78(14); Fe(3)-
Fe(1b)-Au(b), 96.6(2); Fe(2)-Fe(1b)-Au(b), 91.4(2); C(1)-
Au(b)-P, 160.9(3); Fe(1b)-Au(b)-P, 156.6(3); Fe(1b)-
C(1)-Fe(3), 85.4(4); Fe(2)-C(1)-Fe(3), 75.9(3).
Sch em e 1
In all, the interconversion between isomers A and B
represents a reversible process of oxidative addition/
reductive elimination of an Au-C bond across a metal-
metal bond (Scheme 1). To our knowledge, this is the
first time that a process like that has been detected.3a,13
To gain further insight into the factors governing the
equilibrium between isomers for 3a , we have prepared
the related cluster [Fe3Au(µ4,η2-CtCtBu)(CO)9(PiPr3)]
(3b), which also exists in solution as a equilibrium
The coordination position of the gold fragment in 3a
is unexpected, as iron-gold clusters bearing one or more
AuPPh3 moieties usually display structures in which the
gold unit adopts either edge-bridging or face-capping
positions. Compound 3a appears to be the first example
of a mixed M3Au cluster (M ) Fe, Ru, Os) in which the
gold fragment displays this unexpected bonding mode.
As far as we know, [Fe2MAu2(µ4,η2-CtCPh)(CO)7-
(PPh3)2] (M ) Ir, Rh)11 are the only examples where a
similar coordination environment for the Au2(PPh3)2
unit has been previously observed. Moreover, it should
be noted that the structure of compound 3a contrasts
with those of the isoelectronic Ru and Os analogues
[M3Au(µ3,η2-CtCtBu)(CO)9(PPh3)],7,8 the latter having
the gold fragment bonded to the metal framework. Thus,
in a formal sense, replacement of Fe by Ru or Os favors
the oxidative cleavage of the Au-C(acetylide) bond.
In solution, 3a exists as an equilibrium mixture of
two isomers12 (labeled A and B in Scheme 1). Intercon-
version between isomers is fast at room temperature
(12) Data for 3a are as follows. 1H NMR: at 291 K in CDCl3 δ 7.61-
7.47 (m, 15H, C6H5), 1.57 (s, 9H, C(CH3)3); in CD2Cl2 at 223 K δ 7.70-
7.35 (m, 30H, C6H5), 1.54, 1.49 (2 × s, br, 2 × 9H, C(CH3)3). 13C{1H}
NMR in CD2Cl2 at 291 K: δ 214.2 (br, 6CO), 213.3 (br, 3CO), 134.3 (d,
J PC ) 14 Hz, C6H5), 132.4 (s, 4C(C6H5)), 129.8 (d, J PC ) 12 Hz, C6H5),
129.7 (d, J PC ) 55 Hz, 1C(C6H5)), 39.9 (s, C(CH3)3), 35.4 (s, CH3), alkynyl
signals are too broad to be observed. 31P{1H} NMR in CD2Cl2: at 291
K δ 50.6 (PPh3); at 223 K δ 52.2, 46.6 (PPh3). Data for isomer A are as
follows. 13C{1H} NMR in CD2Cl2 at 188 K: δ 214.9 (s, 6CO), 211.7 (s,
3CO), 181.3 (d, J PC ) 58 Hz, CR(CtCtBu)), 144.9 (s, Câ(CtCtBu)), 134.4
(d, J PC ) 14 Hz, C6H5), 132.8 (s, 4C(C6H5)), 129.9 (d, J PC ) 11 Hz, C6H5),
128.2 (d, J PC ) 59 Hz, 1C(C6H5)), 41.1 (s, C(CH3)3), 35.9 (s, CH3). Data
for isomer B are as follows. 13C{1H} NMR in CD2Cl2 at 188 K: δ 219.5
(s, 2CO), 216.7 (br, 2CO), 215.5 (s, CO), 211.7 (s, 2CO), 210.3 (s, 2CO),
193.4 (s, CR(CtCtBu)), 134.3 (d, J PC ) 15 Hz, C6H5), 132.0 (s, 4C(C6H5)),
130.9 (s, Câ(CtCtBu)), 130.2 (d, J PC ) 52 Hz (obtained from the
spectrum recorded at 223 K), 1C(C6H5)), 129.6 (d, J PC ) 11 Hz, C6H5),
38.5 (s, C(CH3)3), 33.5 (s, CH3).
1
on the NMR time scale, so that averaged H, 13C, and
(13) (a) Farrugia, L. J .; Orpen, A. G. In Metal Clusters in Chemistry;
Braunstein, P., Oro, L. A., Raithby, P., Eds.; Wiley-VCH: Weinheim,
Germany, 1999; Vol. 2, Chapter 3.4. (b) Dyson, P. J .In Metal Clusters
in Chemistry; Braunstein, P., Oro, L. A., Raithby, P., Eds.; Wiley-
VCH: Weinheim, Germany, 1999; Vol. 2, Chapter 3.5.
(10) Deabate, S.; Giordano, R.; Sappa, E. J . Cluster Sci. 1997, 8,
407.
(11) Bruce, M. I.; Koutsantonis, G. A.; Tiekink, E. R. T. J . Orga-
nomet. Chem. 1991, 408, 77.

782 Organometallics, Vol. 21, No. 5, 2002
Communications
mixture14 of isomers A and B. The ratio A:B is now
much higher (ca. 8:1 at 203 K) and also increases
slightly at lower temperatures. The equilibrium between
CtCtBu)(CO)9] (4) in good yield.16 Compound 4 is also
obtained from 1 and HBF4‚OEt2, thus completing the
+
H+/AuPPh3 analogy. The ν(CO) pattern and chemical
i
isomers seems to be also somewhat slower for the Pr
shift of the hydrido ligand are similar to those found
for the compound [Fe3(µ-H)(µ3,η2-CtCSiMe3)(CO)9].17 As
deduced from NMR data,18 compound 4 exhibits dy-
namic behavior in solution, which is similar to that well
established for the related ruthenium cluster [Ru3(µ-
H)(µ3,η2-CtCtBu)(CO)9].19
The preliminary results reported in this paper show
that the Au-C bond cleavage equilibrium operating in
clusters 3 has a low kinetic barrier and results from a
subtle balance of factors. Further studies are now in
progress in order to evaluate the influence that the
nature of phosphine, alkyne, or group 11 metal has on
this novel Au-C cleavage process.
derivative, as judged from the fact that at room tem-
perature the 31P resonance for 3b is much broader than
that for 3a , while the relevant chemical shift difference
is similar (ca. 900 Hz). Apart from this, spectroscopic
data for both isomers in 3b are similar to those for 3a
and need no further comment. Fehlner and co-workers15
have studied the related tautomeric equilibrium E-H-M
T M-H-M observed in some main-group-transition-
metal atom clusters.
In view of the H+/AuPPh3+ isolobal relationship, the
exchange process between isomers A and B found for
compounds 3 can be related to an alkyne/hydrido
alkynyl isomerization process. In fact, replacement of
AuPPh3 by H+ makes the structure of type B the
+
Ack n ow led gm en t. This work was supported by the
DGICYT of Spain (Project PB97-0020).
preferred one even for iron. This transformation can be
accomplished through treatment of 3a with hydrochloric
acid, thus giving the hydrido cluster [Fe3(µ-H)(µ3,η2-
Su p p or tin g In for m a tion Ava ila ble: Text describing the
synthesis and the characterization of the new compounds 1-4
and tables giving X-ray structural information for compound
3a . This material is available free of charge via the Internet
at http://pubs.acs.org.
(14) Data for 3b are as follows. 1H NMR in CD2Cl2 at 291 K: δ 2.38
(m, 3H, CH(CH3)2), 1.62 (s, 9H, C(CH3)3), 1.29 (d, J PH ) 7 Hz, 9H,
CH(CH3)2), 1.27 (d, J PH ) 7 Hz, 9H, CH(CH3)2). 13C{1H} NMR in
CD2Cl2 at 291 K: δ 214.4 (br, 6CO), 213.2 (br, 3CO), 40.2 (s, C(CH3)3),
35.5 (s, CH(CH3)2), 24.9 (s, CH(CH3)2), 24.6 (s, CH(CH3)2), 20.0 (s,
C(CH3)3). 31P{1H} NMR in CD2Cl2 at 291 K: δ 78.7 (vbr, PiPr3). Data
for isomer A are as follows. 1H NMR in CD2Cl2 at 203 K: δ 2.40 (m,
3H, CH(CH3)2), 1.67 (s, 9H, C(CH3)3), 1.27 (d, J HH ) 7 Hz, 9H, CH-
(CH3)2), 1.23 (d, J HH ) 7 Hz, 9H, CH(CH3)2). 13C{1H} NMR in CD2Cl2
at 188 K: δ 216.8 (s, CO), 215.1 (s, 6CO), 212.2 (s, 2CO), 181.9 (d, J PC
) 54 Hz, CR (CtCtBu)), 145.4 (s, Câ (CtCtBu)), 41.4 (s, C(CH3)3), 36.1
(s, CH(CH3)2), 24.1 (s, CH(CH3)2), 23.8 (s, CH(CH3)2), 20.3 (s, C(CH3)3).
31P{1H} NMR in CD2Cl2 at 203 K: 76.2 (PiPr3). Data for isomer B are
as follows. 1H NMR in CD2Cl2 at 203 K: δ 2.30 (m, 3H, CH(CH3)2),
1.41 (s, 9H, C(CH3)3), 1.21 (d, J HH ) 7 Hz, 9H, CH(CH3)2), 1.18 (d, J HH
) 7 Hz, 9H, CH(CH3)2). 13C{1H} NMR in CD2Cl2 at 188 K: δ 220.0,
215.6, 212.5, 212.1, 210.5 (CO), 193.7 (s, CR (CtCtBu)), 129.5 (s, Câ
(CtCtBu)), 38.3 (s, C(CH3)3), 33.7 (CH(CH3)2), 20.0 (s, C(CH3)3), other
resonances obscured by those from the major isomer. 31P{1H} NMR in
CD2Cl2 at 203 K: δ 82.4 (PiPr3).
OM010980B
(16) A solution of 3a in THF was treated with a few drops of
hydrochloric acid and stirred at room temperature for 30 min. The
solvent was removed under vacuum and the residue extracted with
n-hexane. The solution cooled at -20 °C gave compound 4.
(17) Schneider, J . J .; Nolte, M.; Kru¨ger, C. J . Organomet. Chem.
1991, 403, C4.
(18) Data for 4 are as follows. 1H NMR: in CDCl3 at 291 K δ -26.73
(s, H, FeH), 1.24 (s, 9H, C(CH3)3); in CD2Cl2 at 223 K δ -26.78 (s, H,
FeH), 1.24 (s, 9H, C(CH3)3), 1.51 (s, 9H, C(CH3)3). 13C{1H} NMR in
CD2Cl2 at 223 K: δ 214.0 (s, 2CO), 213.0 (s, CO), 211.0 (s, 2CO), 206.9
(s, 2CO), 205.2 (s, 2CO), 185.0 (s, CR (CtCtBu)), 123.2 (s, Câ
(CtCtBu)), 33.7 (s, CH3), CCH3 resonance obscured by those from the
solvent.
(15) Fehlner, T. P. Polyhedron 1990, 9, 1955 and therein.
(19) Farrugia, L. J .; Rae, S. E. Organometallics 1992, 11, 196.