Surface organometallic chemistry: Easy reductive carbonylation of silica-supported [Re(CO)3(OH)]4 to [Re2(CO)10] via silica-anchored [Re(CO)5(OSi≡)] and the thermal behavior of silica-supported [Re2(CO)10]

Article abstract of DOI:10.1021/om000028j

Silica-supported [Re(CO)₃(OH)]₄ is easily converted to [Re₂(CO)₁₀] by reductive carbonylation under very mild conditions (1 atm CO). This reaction does not occur in solution, suggesting that the silica surface plays a unique role via the surface-anchored species [Re-(CO)₅(OSi)].

Full text of DOI:10.1021/om000028j

2
564
Organometallics 2000, 19, 2564-2572
Su r fa ce Or ga n om eta llic Ch em istr y: Ea sy Red u ctive
Ca r bon yla tion of Silica -Su p p or ted [Re(CO) (OH)] to
3
4
[
Re (CO) ] via Silica -An ch or ed [Re(CO) (OSit)] a n d th e
2
10
5
Th er m a l Beh a vior of Silica -Su p p or ted [Re (CO) ]
2
10
Giuseppe D’Alfonso, Dominique Roberto,* and Renato Ugo
Dipartimento di Chimica Inorganica, Metallorganica e Analitica and Centro CNR
CSSSCMTBSO”, Universit a` di Milano, Via G. Venezian, 21, 20133 Milano, Italy
“
Claudia L. Bianchi
Dipartimento di Chimica Fisica ed Elettrochimica, Universit a` di Milano, Via Golgi, 19,
2
0133 Milano, Italy
Angelo Sironi
Dipartimento di Chimica Strutturale e Stereochimica Inorganica and Centro CNR
CSSSCMTBSO”, Universit a` di Milano, Via G. Venezian, 21, 20133 Milano, Italy
“
Received J anuary 13, 2000
3 4 2
Silica-supported [Re(CO) (OH)] is easily converted to [Re (CO)10] by reductive carbonyl-
ation under very mild conditions (1 atm CO). This reaction does not occur in solution,
suggesting that the silica surface plays a unique role via the surface-anchored species [Re-
(
CO)
of the type [Re(CO)
to give [Re(CO) Cl], [Re(CO)
reached for the previously proposed formation of [HRe
of silica-physisorbed [Re(CO) (OH)] . In addition, silica-supported [Re
reoxidized to [Re(CO) (OH)] on the silica surface by thermal treatment at 150-250 °C under
nitrogen. Some highly oxidized rhenium species such as ROReO (R ) H, Sit) are formed
in parallel, as suggested by an XPS study and confirmed by further treatment under 1 atm
of CO at 200 °C, which affords mixtures containing also [Re(CO) OReO ]. The latter was
5
(OSit)]. This latter intermediate, of particular interest since organometallic species
(OR)] have so far eluded isolation, reacts with HCl, HReO , and water
OReO ], and [Re(CO) (OH)] , respectively. No evidence was
(CO)14] in the reductive carbonylation
(CO)10] can be easily
5
4
5
5
3
3
4
3
3
4
2
3
4
3
5
3
isolated and fully characterized by X-ray diffraction. Obviously these oxidation reactions,
in which the silica surface plays an important positive role, are faster in air than under
nitrogen.
4
In tr od u ction
Supported metal catalysts derived from supported
In a photoacoustic infrared study, photolysis (300-
3
(
[
60 nm) at room temperature of a THF solution of [Re2-
CO)10] in the presence of silica was reported to produce
Re2(CO)9(H2O)] and a mixture of silica-supported car-
bonyl species, characterized by a complex infrared
spectrum in the carbonyl stretching region (νCO ) 2150-
w), 2101(m), 2050(m, sh), 2027(s), 1992(w, sh), 1977-
w, sh), 1921(s) cm ). By comparison with the infrared
spectra of known complexes, two strong absorptions
at 2027 and 1921 cm were tentatively assigned to the
tricarbonyl surface-anchored species [Re(CO)3(OSit)(t
SiOSit)2], whereas the other bands were associated
with minor amounts of the poorly characterized an-
chored species [Re(CO)5(OSit)] and [Re(CO)4(OSit)]2.
When a noncoordinating solvent such as benzene was
metal carbonyls can show interesting catalytic proper-
1
ties. Therefore a large amount of work has been
devoted to the investigation of the thermal and chemical
behavior of various transition metal carbonyls supported
(
(
2
on the silica surface. However, even though the indus-
-1
trial importance of supported rhenium catalysts for
reforming of petroleum naphtha and metathesis of
6,7
-1
3
alkenes is well established, the study of the behavior
of rhenium carbonyls supported on silica has received
limited attention and, to our knowledge, only two
4
,5
nonexhaustive investigations appeared.
*
Corresponding author. Fax: +39-02-2362748. E-mail: dominique.
roberto@unimi.it.
(4) McKenna, W. P.; Higgins, B. E.; Eyring, E. M. J . Mol. Catal.
1985, 31, 199.
(1) Psaro, R.; Recchia, S. Catal. Today 1998, 41, 139.
(
2) Psaro, R.; Ugo, R. In Metal Clusters in Catalysis; Gates, B. C.,
(5) Kirlin, P. S.; Gates, B. C. Inorg. Chem. 1985, 24, 3914.
(6) Brateman, P. S. Metal Carbonyl Spectra; Academic Press: New
York, 1975.
Guczi, L., Kn o¨ zinger, H., Eds.; Elsevier: Amsterdam, 1986; p 451.
3) Yermakov, Y. I.; Kuznetsov, B. N.; Zakharov, V. A. Catalysis by
Supported Complexes; Elsevier: New York, 1981.
(
(7) Gard, D. R.; Brown, T. L. J . Am. Chem. Soc. 1982, 104, 6340.
1
0.1021/om000028j CCC: $19.00 © 2000 American Chemical Society
Publication on Web 05/26/2000

Surface Organometallic Chemistry
Organometallics, Vol. 19, No. 13, 2000 2565
(OH)]
Sch em e 1. Red u ctive Ca r bon yla tion of Silica -Su p p or ted [Re(CO)
3
4
used, the photoacoustic infrared spectrum suggested
Resu lts
4
only the presence of the supposed tricarbonyl species.
Red u ctive Ca r bon yla tion of Silica -Su p p or ted
Re(CO)3(OH)]4 to [Re2(CO)10] via [Re(CO)5(OSit)]
Sch em e 1). When a slurry of SiO2, [Re(CO)3(OH)]4 (2
5
Also, it has been reported that by refluxing n-octane
[
(
and [H4Re4(CO)12] in the presence of hydrated silica,
silica-supported [Re(CO)3(OH)]4 is generated. Exposure
of this latter species to CO (1 atm) at 150 °C for 4 h
leads to the formation of a surface species characterized
by carbonyl bands at 2095(w), 2053(s, br), 1992(m, br),
wt % of Re with respect to SiO2), and CH2Cl2 is stirred
at room temperature for 2 h and evaporated to dryness,
the final white powder shows two carbonyl bands at
-1
2
028(s) and 1925(vs) cm in Nujol mull, similar to those
-1
and 1933(w) cm , similar to those reported for [HRe3-
of [Re(CO)3(OH)]4 in CH2Cl2 (νCO ) 2031(s) and 1925-
vs) cm ). The quantitative recovery of [Re(CO)3-
OH)]4 by extraction of the silica with dichloromethane
or acetone confirms a simple physisorption.
8
(
CO)14]. On the basis of the infrared evidence only, a
-
1 12
(
(
silica-mediated reductive carbonylation of [Re(CO)3-
5
(
OH)]4 to [HRe3(CO)14] was then proposed, although the
5
lack of fragmentation under CO of the supposed silica-
supported Re3 cluster to [HRe(CO)5] and [Re2(CO)10] was
When physisorbed [Re(CO)3(OH)]4 is heated at 200
°
C under 1 atm of CO in the closed cylindrical Pyrex
8
,9
unexpected.
1
0a
vessel previously described,
some [Re2(CO)10] sub-
This relatively easy surface reactivity under CO of
limes onto the cold walls of the reaction vessel. After 2,
, and 5 days, extraction of both the sublimate and the
silica powder with anhydrous pentane affords [Re2-
CO)10] in 47%, 60%, and 71% yields, respectively. By
[
Re(CO)3(OH)]45 was suggestive of a new way to syn-
3
thesize rhenium carbonyl clusters as it occurs with less
1
0
oxophilic metals such as Rh, Ir, Ru, or Os. In this area,
as a preliminary result, it has only been reported that
reductive carbonylation of ammonium perrhenate sup-
ported on silica affords [Re2(CO)10] in ca. 40% yield, but
by working under high pressures of CO (ca. 20 atm) and
H2 (ca. 130 atm) at 150 °C.11 This latter result prompted
us to study more deeply the reductive carbonylation of
(
stopping the reaction after 2 days, the infrared spectrum
of the remaining silica powder, as a Nujol mull, shows
the presence of some unreacted [Re(CO)3(OH)]4, a weak
-
1
carbonyl band at 2089 cm , and two carbonyl bands
-
1
at 2049(s) and 1991(m) cm , which we tentatively
assign to a surface pentacarbonyl Re(I) species by
analogy with the infrared spectrum of [Re(CO)5Cl] or
[Re(CO)3(OH)]4 and to investigate in parallel the ther-
mal stability of [Re2(CO)10], both supported on the silica
surface.
1
3
[
Re(CO)5Br].
Attempts to convert quantitatively [Re(CO)3(OH)]4
into this latter intermediate surface species, by working
under milder conditions, failed due to its relatively easy
conversion into [Re2(CO)10], although it is produced in
good amounts by working at 150 °C. After 4 days under
CO at this temperature, some [Re2(CO)10] sublimes,
whereas the infrared spectrum of the silica powder, as
Nujol mull, shows carbonyl bands at 2089(w), 2069(w),
(
8) Fellmann, W.; Kaesz, H. D. Inorg. Nucl. Chem. Lett. 1966, 2,
6
3.
(
(
9) Harril, R. W.; Kaesz, H. D. Inorg. Nucl. Chem. Lett. 1966, 2, 69.
10) (a) Roberto, D.; Psaro, R.; Ugo, R. Organometallics 1993, 12,
2
1
292. (b) Roberto, D.; Cariati, E.; Psaro, R.; Ugo, R. Organometallics
994, 13, 734. (c) Roberto, D.; Cariati, E.; Ugo, R.; Psaro, R. Inorg.
Chem. 1996, 35, 2311. (d) Roberto, D.; Cariati, E.; Lucenti, E.; Respini,
M.; Ugo, R. Organometallics 1997, 16, 4531. (e) Roberto, D.; Lucenti,
E.; Roveda, C.; Ugo, R. Organometallics 1997, 16, 5974. (f) Cariati, E.;
Lucenti, E.; Roberto D.; Ugo R. In Supported Reagents and Catalysts
in Chemistry; Hodnett, B. K., Kybett, A. P., Clark, J . H., Smith, K.,
Eds.; The Royal Society of Chemistry: London, 1998; pp 214-219. (g)
Cariati, E.; Roberto, D.; Ugo, R. J . Cluster Science 1998, 9, 329. (h)
Cariati, E.; Lucenti, E.; Roberto, D.; Ugo, R. In Metal Clusters in
Chemistry; Braunstein, P., Oro, L., Raithby, P., Eds.; Wiley-VCH
Verlag: Weinheim, 1999; pp 860-876.
2049(vs), 2028(m), 2012(m), 1991(m), 1974(w), and
-1
1
925(s) cm
due to a mixture of [Re2(CO)10] (νCO )
(12) (a) Herberhold, M.; S u¨ ss, G. Angew. Chem., Int. Ed. Engl. 1975,
14, 4, 700. (b) Herberhold, M.; S u¨ ss, G.; Ellermann, J .; Gabelein, H.
Chem. Ber. 1978, 111, 2931.
(13) Schmidt, S. P.; Trogler, W. C.; Basolo, F. Inorg. Synth. 1985,
23, 41.
(11) Marchionna, M.; Lami, M.; Raspolli Galletti, A. M.; Braca, G.
Gazz. Chim. Ital. 1993, 123, 107.

2
2
566 Organometallics, Vol. 19, No. 13, 2000
D’Alfonso et al.
069(w), 2012(m), and 1974(w) cm-1), [Re(CO)3(OH)]4
+ H O
2
νCO ) 2028(m) and 1925(s) cm- ), traces of still uni-
1
[Re(CO) (OSit)]/SiO - HOSit8
(
5
2
dentified rhenium carbonyl species (νCO ) 2089(w) and
1
[Re(CO) (OH)]/SiO 2CO8
5
2
-
-1
927(w) cm ), and the supposed surface pentacarbonyl
-1
1/4[Re(CO) (OH)] /SiO
3 4 2
Re(I) species (νCO ) 2049(vs) and 1991(m) cm ), which
appears to be the major component of the mixture. Such
assignments are confirmed by extraction of both the
sublimate and silica with anhydrous pentane, which
affords [Re2(CO)10] (18% yield), whereas successive
extraction with anhydrous CH2Cl2 gives [Re(CO)3(OH)]4
It has been reported17 that reaction of [Re(CO)5FBF3]
with aqueous sodium hydroxide results in the precipita-
tion of a product of analytical composition “Re(CO)5-
(
OH)”, which was proposed, by infrared spectroscopy
only, to be [(OC)4(HO)Re-C(OH)O-Re(CO)5], easily
converted in organic solvents (e.g., acetone, dichlo-
romethane, or tetrahydrofuran) into [(OC)4Re(CO2)Re-
CO)5]2 with µ3-CO2 bridges, as evidenced by X-ray
structural analysis. However, we could not isolate these
species during the hydrolysis of the proposed [Re(CO)5-
OSit)] species, the final product being always [Re(CO)3-
OH)]4.
Also, during our study on the reductive carbonylation
(24-27% yields) and leaves, on the silica surface, the
traces of an unidentified carbonyl rhenium species
together with the supposed pentacarbonyl Re(I) species
as the major component. These latter two species cannot
be extracted even by further treatment of the silica
powder with donor solvents such as acetone or THF,
suggesting that they are strongly interacting with the
silica surface. The supposed pentacarbonyl Re(I) species
could interact with a surface silanolate either bound
covalently (as in [Re(CO)5(OSit)]) or attached by ion-
(
(
(
of silica-supported [Re(CO)3(OH)]4, we could not reach
5
evidence of the formation of [HRe3(CO)14] since extrac-
+
-
pairing (as in [Re(CO)5(HOR)] tSiO where R ) H or
tion with pentane failed to give this cluster, even in
traces, although we proved that silica-supported [HRe3-
CO)14] can be easily removed from the silica surface
1
4
tSi). We found that the pentacarbonyl Re(I) species
cannot be extracted even by treatment with [NBu4]Cl
dissolved in dichloromethane. This observation allows
rejection of a cationic formulation of the carbonyl
rhenium species and is in agreement with a covalent
bonding to a surface silanolate.
(
by extraction with pentane.
In fact, when a slurry of SiO2, [HRe3(CO)14] (2 wt %
of Re with respect to SiO2), and pentane is stirred at
room temperature for 2 h and evaporated to dryness, a
pale yellow powder is obtained. Its infrared spectrum,
as Nujol mull, shows carbonyl bands at 2146(vw), 2100-
(w), 2046(vs), 2013(m), 1991(s), 1974(w), 1965(w), 1955-
We added further evidence to the proposed formula-
tion [Re(CO)5(OSit)] by the well-established method of
cleavage of M-OSit (M ) metal) bonds by reaction
under mild conditions with an acid such as HCl(aq)
followed by solvent extraction.14 For instance, silica-
anchored [HOs3(CO)10(OSit)] reacts with HCl(aq) af-
fording [HOs3(CO)10Cl], which can be easily extracted
with CH2Cl2.15 The silica powder, after extractions as
above, is then treated with CH2Cl2 acidified with a few
drops of HCl(aq), producing pure [Re(CO)5Cl] (43% yield
with respect to the initial silica-supported [Re(CO)3-
-
1
(vw), and 1932(w) cm , similar to those of [HRe (CO) ]
3
14
dissolved in cyclohexane (νCO ) 2143(vw), 2100(w),
2045(s), 2014(m), 1992(m), 1975(w), 1966(w), 1956(vw),
-
1 8
and 1936(w) cm ). The cluster can be quantitatively
recovered by extraction of the silica powder with pen-
tane, as expected for a simple physisorption.
Moreover, we investigated the behavior of silica-
supported [HRe (CO) ] under CO.
3
14
(
OH)]4; Scheme 1), which dissolves in CH2Cl2. Similarly,
Treatment under CO (1 atm) at room temperature of
physisorbed [HRe (CO) ] in the closed cylindrical Pyrex
use of HReO4 instead of HCl leads to the quantitative
conversion of the surface species into [Re(CO)5OReO3],
which is soluble in dichloromethane (51% yield with
respect to the initial silica-supported [Re(CO)3(OH)]4;
Scheme 1). Following the above extraction processes, the
combined isolated yields of [Re2(CO)10], [Re(CO)5X]
3
14
1
6
10a
vessel previously described
affords, as it occurs in
8
solution, [Re (CO) ] and [HRe(CO) ], which are ex-
2
10
5
tracted with CHCl and characterized by infrared and
3
1
H NMR spectroscopies. By working under 1 atm of CO
at 150 °C for 4 h (i.e., the same conditions used by Kirlin
5
(
8
X ) Cl or OReO3), and unreacted [Re(CO)3(OH)]4 are
8-96%, whereas traces of still unidentified surface
et al. to obtain what they proposed to be [HRe (CO) ]
3
14
physisorbed on the silica surface) the pale yellow silica
powder turns white while some [Re (CO) ] sublimes
rhenium carbonyl species (νCO as Nujol mull ) 2089(w)
and 1927(w) cm- ) are not extracted even after treat-
ment with CH2Cl2 acidified with HCl(aq).
The proposed [Re(CO)5(OSit)] species is readily (less
than 1 h) converted back to silica-physisorbed [Re(CO)3-
2
10
1
onto the cold walls of the reaction vessel. Treatment of
the sublimate and silica powder with anhydrous pen-
tane affords pure [Re2(CO)10], whereas no carbonyl
rhenium species remains on the silica surface, as
expected due to the known formation of [Re2(CO)10] by
thermal treatment at 100 °C of [HRe(CO)5].18 Our
obvious conclusion is that [HRe3(CO)14] is not stable on
the silica surface by working under 1 atm of CO at 150
°C; therefore the conclusion of Kirlin et al.5 is not
confirmed by our experimental evidence.
(OH)]4 either by addition of a few drops of water at room
temperature or by leaving the silica powder in air
overnight. This behavior is in agreement with an
expected easy hydrolysis of a Re-OSit bond and could
reasonably involve the unknown “Re(CO)5(OH)” species
as intermediate, which would be readily converted to
[
Re(CO)3(OH)]4:
The infrared spectrum of the surface species (νCO as
silica wafer ) 2095(w), 2053(s, br), 1992(m, br), 1933-
(
14) Roberto, D.; Cariati, E.; Pizzotti, M.; Psaro, R. J . Mol. Catal. A
996, 111, 97, and references therein.
15) Roberto, D.; Pizzotti, M.; Ugo, R. Gazz. Chim. Ital. 1995, 125,
33.
1
1
3
(17) Beck, W.; Raab, K.; Nagel, U. Steimann, M. Angew. Chem., Int.
Ed. Engl. 1982, 21, 526. (b) Raab, K.; Beck, W. Chem. Ber. 1985, 118,
3830.
(18) Beck, V. W.; Hieber, W.; Braun, G. Z. Anorg. Allg. Chem. 1961,
308, 23.
(
(16) Heidrich, J .; Loderer D.; Beck, W. J . Organomet. Chem. 1986,
12, 329.

Surface Organometallic Chemistry
Sch em e 2. Th er m a l Beh a vior of Silica -Su p p or ted [Re
Organometallics, Vol. 19, No. 13, 2000 2567
2
(CO)10] a t Atm osp h er ic P r essu r e
(
w) cm-1) obtained by these authors5 by reductive
Silica physisorbed [Re2(CO)10] does not react when
heated at 100 °C under nitrogen in the closed cylindrical
carbonylation of silica-supported [Re(CO)3(OH)]4, and
proposed to be [HRe3(CO)14], is much simpler than that
of silica-supported [HRe3(CO)14] and is quite similar to
that of the sample (νCO as Nujol mull ) 2089(w), 2049-
1
0a
Pyrex vessel previously described for 16 h; an increase
of the temperature to 150 °C leads to the sublimation
of some [Re2(CO)10] onto the cold walls of the reaction
vessel and to the formation of traces of physisorbed [Re-
(CO)3(OH)]4. After 17 h at the same temperature, almost
all [Re2(CO)10] sublimes, whereas the infrared spectrum
of the remaining silica powder shows the presence of
only traces of physisorbed [Re2(CO)10] and [Re(CO)3-
(OH)]4, which can be easily separated by selective
extraction first with pentane (which gives [Re2(CO)10])
and then with dichloromethane (which gives [Re(CO)3-
(OH)]4).
-1
(s), 1991(m), and 1927(w) cm ) obtained in the present
work under analogous conditions by treatment of silica-
supported [Re(CO)3(OH)]4 under 1 atm of CO at 150 °C
followed by solvent extractions to remove some minor
amounts of [Re2(CO)10] and [Re(CO)3(OH)]4. The slight
difference in the carbonyl stretching frequencies (by ca.
-1
4
-6 cm ) is expected on going from silica wafer to Nujol
1
9
mull, as confirmed by us in the case of silica-supported
Re(CO)3(OH)]4. Therefore the infrared spectrum of
[
5
Kirlin et al. could be interpreted as well as a mixture
of surface carbonyl species containing as major compo-
nent the intermediate [Re(CO)5(OSit)] (νCO as silica
Only a further increase of the temperature to 200 °C
leads to a large oxidation of [Re (CO) ] to physisorbed
2
10
[Re(CO) (OH)] . After 17 h at this temperature, only
3
4
-
1
wafer ) 2053(s), 1992(m) cm ).
2 10
11% of the starting [Re (CO) ] sublimes, whereas the
Th e Th er m a l Beh a vior of Silica -Su p p or ted [Re2-
CO)10] (Scheme 2). When a slurry of SiO2, [Re2(CO)10]
infrared spectrum, as Nujol mull, of the resulting beige
silica powder shows carbonyl bands at 2028(s) and 1925-
(
-
1
(2 wt % of Re with respect to SiO2), and CH2Cl2 is stirred
3 4
(vs) cm , typical of physisorbed [Re(CO) (OH)] . Ex-
at room temperature for 2 h and evaporated to dryness,
traction of this beige silica powder with acetone affords
[Re(CO) (OH)] in 45% yield. After the extraction pro-
the final white powder shows three carbonyl bands, in
3
4
Nujol mull, at 2070(m), 2013(vs), and 1975(m) cm-
1
,
cess, no carbonyl species remains on the silica surface,
as evidenced by infrared spectroscopy. However, since
rhenium oxides such as Re O ‚xH O and ReO are black
similar to those of [Re2(CO)10] dissolved in CH2Cl2
νCO ) 2071(m), 2013(vs), and 1967(m) cm- ); [Re2-
1
(
(
2
1
3
2
2
2
CO)10] can be quantitatively recovered by extraction
and brown, respectively, the beige color of the silica
powder suggests the presence on the silica surface of
some oxidized rhenium species totally decarbonylated.
The oxidation process is faster at 250 °C: after 30
min only, traces of [Re2(CO)10] sublimes onto the cold
walls of the reaction vessel (ca. 1% of the starting
complex), whereas the infrared spectrum of the result-
ing beige silica powder shows the presence of [Re(CO)3-
with dichloromethane or pentane.
It is known that thermal treatment of many silica-
supported metal carbonyls leads to the formation of
oxidized silica-anchored carbonyl species. For example,
thermal degradation of silica-supported [Ru3(CO)12] and
2
[
Os3(CO)12], at ca. 100 and 200 °C, respectively, affords
silica-anchored species such as [M(CO)x(OSit)2]n (M )
Ru, Os; x ) 2 or 3).2 A similar oxidation process occurs
with [Re2(CO)10] dissolved in tetrahydrofuran in the
,20
(OH)]4, which can be easily extracted with acetone (63%
yield). By heating for a longer time (17 h), further
degradation takes place, resulting in a dark gray silica
powder showing the presence of only traces of physi-
sorbed [Re(CO)3(OH)]4.
4
presence of silica under photolytic conditions. These
results prompted us to study the possible formation of
oxidized species anchored to silica by thermal treatment
under nitrogen of silica-supported [Re2(CO)10].
As expected, the oxidation of silica-supported [Re2-
(
CO)10] is much faster by working in air instead of
(
19) Cook, S. L.; Evans, J .; McNulty, G. S.; Greaves, G. N. J . Chem.
Soc., Dalton Trans. 1986, 7.
20) (a) Psaro, R.; Ugo, R.; Zanderighi, G. M.; Besson, B.; Smith, A.
nitrogen, although it does not take place at tempera-
tures lower than 100 °C. After 10 min at 250 °C, only
(
K.; Basset, J . M. J . Organomet. Chem. 1981, 213, 215. (b) Zanderighi,
G. M.; Dossi, C.; Ugo, R.; Psaro, R.; Theolier, A.; Choplin, A.; D′Ornelas,
L.; Basset, J . M. J . Organomet. Chem. 1985, 296, 127.
(21) Pacer, R. A. J . Inorg. Nucl. Chem. 1976, 38, 817.

2
568 Organometallics, Vol. 19, No. 13, 2000
D’Alfonso et al.
Ta ble 1. Bon d Len gth s (Å) a n d An gles (d eg) for
(
5 3
CO) ReOReO
molecule A
molecule B
Re(1)-C(15)
Re(1)-C(14)
Re(1)-C(13)
Re(1)-C(11)
Re(1)-C(12)
Re(1)-O(21)
C(11)-O(11)
C(12)-O(12)
C(13)-O(13)
C(14)-O(14)
C(15)-O(15)
Re(2)-O(24)
Re(2)-O(23)
Re(2)-O(22)
Re(2)-O(21)
1.923(7)
1.995(7)
2.003(7)
2.033(7)
2.052(7)
2.135(4)
1.118(7)
1.117(7)
1.132(7)
1.133(7)
1.140(7)
1.682(5)
1.691(5)
1.704(5)
1.752(4)
1.915(7)
1.994(7)
2.000(7)
2.007(8)
2.034(7)
2.146(4)
1.123(7)
1.134(7)
1.146(8)
1.105(7)
1.143(7)
1.667(6)
1.682(6)
1.706(5)
1.744(4)
C(15)-Re(1)-C(14)
C(15)-Re(1)-C(13)
C(14)-Re(1)-C(13)
C(15)-Re(1)-C(11)
C(14)-Re(1)-C(11)
C(13)-Re(1)-C(11)
C(15)-Re(1)-C(12)
C(14)-Re(1)-C(12)
C(13)-Re(1)-C(12)
C(11)-Re(1)-C(12)
C(15)-Re(1)-O(21)
C(14)-Re(1)-O(21)
C(13)-Re(1)-O(21)
C(11)-Re(1)-O(21)
C(12)-Re(1)-O(21)
O(11)-C(11)-Re(1)
O(12)-C(12)-Re(1)
O(13)-C(13)-Re(1)
O(14)-C(14)-Re(1)
O(15)-C(15)-Re(1)
O(24)-Re(2)-O(23)
O(24)-Re(2)-O(22)
O(23)-Re(2)-O(22)
O(24)-Re(2)-O(21)
O(23)-Re(2)-O(21)
O(22)-Re(2)-O(21)
Re(2)-O(21)-Re(1)
88.8(3)
87.9(3)
90.3(3)
92.0(3)
88.3(3)
178.6(3)
93.4(3)
177.8(3)
89.6(3)
91.8(3)
178.5(2)
89.8(2)
91.4(2)
88.6(2)
87.9(2)
176.8(6)
177.4(6)
174.6(6)
177.3(6)
176.8(7)
108.5(3)
109.1(3)
107.8(3)
109.7(2)
110.3(3)
111.3(2)
161.9(3)
92.0(3)
89.1(3)
90.4(3)
88.4(3)
89.9(3)
177.5(3)
92.1(3)
175.5(3)
91.4(3)
88.4(3)
178.5(2)
88.2(2)
89.4(2)
93.1(2)
87.7(2)
176.4(6)
179.1(6)
176.2(6)
177.7(7)
176.9(7)
107.9(4)
107.7(3)
110.5(3)
110.9(3)
109.9(3)
109.9(2)
151.2(3)
F igu r e 1. ORTEP diagrams (with thermal ellipsoids
drawn at the 50% of probability level) of the two indepen-
dent molecules in the asymmetric unit of [(CO)
ReO ]. The C atoms of the CO groups bear the same
numbering of the corresponding O atoms.
5
Re(µ-O)-
low), and traces of a surface species characterized by a
3
-
1
carbonyl band at 2087 cm is formed (Scheme 2). [Re2-
CO)10] and [Re(CO)5OReO3] can be easily removed from
(
traces of [Re(CO)3(OH)]4 are left on the dark gray silica
surface. On the contrary, by working under 1 atm of
CO at 250 °C for 30 min, only traces of [Re(CO)3(OH)]4
are formed, but almost all [Re2(CO)10] sublimes on the
cold walls of the reaction vessel (Scheme 2). Finally,
some [Re(CO)3(OH)]4 is obtained also by thermal treat-
ment of silica-supported [Re2(CO)10] under H2 at 150-
the silica surface by selective extraction with pentane
and dichloromethane, respectively. Successive extrac-
tion with acetone affords traces of a species character-
-
1
ized by a carbonyl band at 2081 cm , which could be
[Re(CO)6][ReO4] by analogy with the known complex
-1 23
[Re(CO)6][AlCl4] (νCO in acetone ) 2081 cm ), whereas
only the silica-anchored [Re(CO)5(OSit)] species re-
mains on the surface.
2
00 °C, although at 150 °C most [Re2(CO)10] sublimes.
Under these latter conditions neither [H3Re3(CO)12] nor
H4Re4(CO)12] is formed, although these clusters are
readily generated by hydrogenation (1 atm) of [Re2-
We confirmed the formation of [Re(CO)5OReO3] both
by mass spectrometry (its FAB+ mass spectrum shows
the molecular ion peak at 578) and by X-ray diffraction
of suitable crystals. [(CO)5Re(µ-O)ReO3] crystallizes in
the monoclinic space group P21/c with two independent
molecules in the asymmetric unit separated by normal
van der Waals interactions. The molecular stereochem-
istry together with the pertinent labeling for the two
molecules are shown in Figures 1a and 1b, respectively.
Relevant bond distances and angles are listed in Table
[
(
CO)10] in Decaline or dodecane solution at 150-170
2
2
°
C.
When an oxidized silica sample containing both [Re-
CO)3(OH)]4 and the decarbonylated oxidized rhenium
(
species (obtained by thermal treatment under nitrogen
at 250 °C for 30 min of silica-supported [Re2(CO)10]) is
treated under 1 atm of CO at 200 °C for 24-48 h, a
mixture of the above-described [Re(CO)5(OSit)], [Re2-
1
. By comparison of Figures 1a and 1b, it appears that
CO)10], [Re(CO)5OReO3]16 (fully characterized, see be-
the two independent molecules in the asymmetric unit
have a slightly different conformation; that is, they are
(
(
22) Kaesz, H. D.; Knox, S. A. R.; Koepke, J . W.; Saillant, R. B.
Chem. Commun. 1971, 477.
(23) Hieber, V. W.; Kruck, T. Z. Naturforsch. 1961, 166, 709.

Surface Organometallic Chemistry
Organometallics, Vol. 19, No. 13, 2000 2569
different rotamers about the Re1-O21 and O21-Re2
single bonds.
Ta ble 2. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
5 3
for (CO) ReOReO
Although [Re(CO)5OReO3] was prepared a few years
ago by reacting [Re(CO)5Br] with AgReO4, to our
empirical formula
fw
temperature
wavelength
cryst syst
C5 O9 Re2
576.45
293(2) K
0.71073 Å
monoclinic
1
6
knowledge the coordination of the perrhenate ion to the
+
[
Re(CO)5] moiety was not firmly established up to
2
4
now. This bonding is easily cleaved by addition of a
few drops of 37% aqueous HCl to a solution of [Re-
space group
unit cell dimens
P2 /c
1
a ) 11.8801(10) Å, R ) 90°
b ) 13.932(2) Å, â ) 95.256(5)°
c ) 12.984(2) Å, γ ) 90°
2140.1(5) Å3
(
CO)5OReO3] in dichloromethane, at room temperature,
with formation of [Re(CO)5Cl] in quantitative yield. The
perrhenate anion, which is a relatively strong ligand
volume
Z
density (calcd)
abs coeff
F(000)
cryst size
θ range for data collection
index ranges
8
-
-
- 16
3
with respect to [ClO4] , [SO3CF3] , and [BF4] , can
3.578 Mg/m
22.635 mm
2016
-
1
be displaced even by a large excess of acetone, as
evidenced by both infrared spectroscopy2
5,26
and con-
3
0.35 × 0.20 × 0.20 mm
ductivity measurements of an acetone solution of [Re-
CO)5OReO3]:
1.72-27.86°
(
-15 e h e 15, -18 e k e 18,
-
16 e l e 16
25 483
-
+
acetone
] [Re(CO) (acetone)][ReO ]
5 4
acetone
no. of reflns collected
no. of ind reflns
completeness to θ ) 27.86°
refinement method
[
Re(CO) OReO ] [
5
3
4732 [R(int) ) 0.0434]
92.8%
full-matrix least-squares on F
4732/0/289
0.953
2
As expected for an equilibrium reaction, evaporation of
the acetone solution gives back [Re(CO)5OReO3], while,
no. of data/restraints/params
goodness-of-fit on F2
in agreement with the behavior of [Re(CO)5O3SCF3]
final R indices [I > 2σ(I)]
R1 ) 0.0234, wR2 ) 0.0444
dissolved in dichloromethane,27 the addition of a few
R indices (all data)
R1 ) 0.0397, wR2 ) 0.0467
-
3
largest diff peak and hole
1.196 and -1.244 e Å
drops of acetone to a solution of [Re(CO)5OReO3] in
dichloromethane is not enough to cause the formation
of [Re(CO)5(acetone)][ReO4], as evidenced by infrared
spectroscopy.
The isolation and full characterization of [Re(CO)5-
OReO3] add further evidence to our suggestion that
highly oxidized species such as ROReO3 (R ) H, Sit)
are formed on the silica surface by silica-mediated
oxidation at 250 °C of [Re(CO)3(OH)]4 even working
under nitrogen.
from the total amount actually supported on silica (ca.
wt % of Re with respect to SiO2). This discrepancy is
2
explained by a nonhomogeneous distribution of rhenium
on the silica surface, as shown by a SEM investigation
of the various samples.
A disadvantage of XPS investigations is the require-
ment of ultrahigh-vacuum conditions, which, in some
cases, could change in situ the original nature of the
14
surface organometallic species. We found that, while
Additional evidence for a process of oxidative decom-
position of [Re2(CO)10] or even [Re(CO)3(OH)]4 with total
decarbonylation was given by X-ray photoelectron spec-
troscopy (XPS) studies. In the case of rhenium species
supported on alumina, the reported binding energy (Eb)
of the Re 4f7/2 peak in the different valence states are
as follows: (0) 40.6 eV; (+1) 41.0 eV; (+4) 42.9 eV; (+6)
silica-supported [Re2(CO)10] is stable under XPS condi-
-9
tions (P ) 10 Torr), silica-supported [Re(CO)3(OH)]4
turns out to be easily oxidized, affording selectively a
4+
Re
species which could be anchored to the silica
7+
surface by analogy with alumina-supported Re spe-
cies, which were proposed to have several ReOAl
bonds. The demolition of [Re(CO)3(OH)]4 to an oxidized
28
4
4.4 eV; (+7) 46.5 eV.28 Similar values are reported for
the Re 4f7/2 peak of silica-supported [NH4][ReO4] before
46.0 eV) and after reduction to metal (40.9 eV) under
non-carbonyl rhenium species was confirmed by infrared
spectroscopy of the sample after the XPS measurements.
(
4+
The easy oxidation with formation of Re
surface
2
9
hydrogen at 500 °C. We investigated by XPS the
following samples: (i) silica-supported [Re2(CO)10] (2 wt
species can be attributed to a strong decrease of the
amount of physisorbed water due to the high-vacuum
conditions, because it is known that refluxing a slurry
of octane, [H4Re4(CO)12], and uncalcined silica affords
%
of Re with respect to SiO2); (ii) silica-supported [Re-
(CO)3(OH)]4 (2 wt % of Re with respect to SiO2); (iii)
silica sample obtained by thermal oxidative treatment,
for 30 min at 250 °C under nitrogen of silica-supported
[
1
Re(CO)3(OH)]4, whereas the use of calcined (700 °C for
2 h) silica leads to the selective formation of a Re
6+
[Re2(CO)10] (2 wt % of Re with respect to SiO2). The Eb
decarbonylated species, showing clearly that a decrease
of physisorbed water favors the oxidation and decar-
bonylation of rhenium carbonyl species on the silica
of the Re 4f7/2 peaks, the weight percentage of Re with
respect to SiO2, and the percentage of the different
rhenium species in a given oxidation state with respect
to the total rhenium are reported in Table 3.
XPS quantitative results give a wt % of total Re with
respect to SiO2 (1.38-2.44%), which can be different
5
surface.
The XPS analysis of the powder obtained by thermal
treatment, at 250 °C under nitrogen for 30 min, of silica-
supported [Re2(CO)10] shows the total absence of Re(0)
species and the presence of oxidized rhenium species
in the (+1) valence state (corresponding to 6.8% of the
total rhenium species), (+4) valence state (correspond-
ing to 56.6% of the total rhenium species), and (+7)
valence state (corresponding to 36.6% of the total
(
(
24) Chakravorti, M. C. Coord. Chem. Rev. 1990, 106, 205.
25) Raab, K.; Olgemoller, B.; Schloter, K.; Beck, W. J . Organomet.
Chem. 1981, 214, 81.
(
26) Horn, E.; Snow, M. R. Aust. J . Chem. 1984, 37, 1375.
(27) Nitschke, J .; Schmidt, S. P.; Trogler, W. C. Inorg. Chem. 1985,
2
4, 1972.
(28) Zsoldos, Z.; Beck, A.; Guczi, L. Stud. Surf. Sci. Catal. 1988, 48,
4+
rhenium species). If the Re species is formed in situ
9
55.
under the XPS conditions from silica-supported [Re-
(CO)3(OH)]4, the percentage of [Re(CO)3(OH)]4 sup-
(29) Shpiro, E. S.; Avaev, V. I.; Antoshin, G. V.; Ryashentseva, M.
A.; Minachev, Kh. M. J . Catal. 1978, 55, 402.

2
570 Organometallics, Vol. 19, No. 13, 2000
Ta ble 3. XP S Mea su r em en ts
D’Alfonso et al.
%
Re in various oxidation states
samplea
Re2(CO)10]/SiO2
Re(CO)3(OH)]4/SiO2
Re2(CO)10]/SiO2 after 30 min
under N2 at 250 °C
% Re/SiO2 (wt %)
Eb Re 4f7/2 (eV)
40.55
42.26
41.09; 42.39; 46.50
(0)
(+1)
(+4)
(+7)
[
[
[
1.38
2.44
1.60
100
0
0
0
0
6.8
0
100
56.6
0
0
36.6
a
Sample prepared with ca. 2 wt % of Re with respect to SiO2.
ported on the silica surface before the XPS measurement
should be ca. 63.4% (corresponding to 6.8% + 56.6%),
in excellent agreement with the amount of [Re(CO)3-
topological arrangement of surface silanols, which pre-
vents the aggregation of [Re(CO)5(OSit)] by bridging
silanolate or hydroxo bonds and loss of carbon monoxide
to give dinuclear surface species of the type [(CO)3Re-
(OH)]4 actually extracted with acetone from the silica
-
surface (63%, see above). The XPS analysis confirms the
presence, in 36.6% yield, of Re7 species which could
be of the type ROReO3 (R ) H, Sit), as suggested by
the formation of [Re(CO)5OReO3)] by successive treat-
ment under 1 atm of CO and at 200 °C of the silica
powder (Scheme 2).
(µ-OSit)3Re(CO)3] . In fact the related alkoxy deriva-
+
tives of the type [Re(CO)5(OR)] have so far eluded
3
0b,31
isolation,
due to (i) the strong tendency of OR
groups to function as bridging ligands, (ii) the relative
lability of mutually transoid CO ligands, and (iii) the
low steric hindrance of OR ligands against the aggrega-
3
1
tion of “Re(CO)3(OR)” fragments. Even [Re(CO)5-
t
t
(
[
(
OBu )] could not be isolated, by reaction of NaOBu with
Discu ssion a n d Con clu sion
Re(CO)5Br], due to the easy formation of Na[(CO)3Re-
µ-OBu )3Re(CO)3].
The facile reduction of [Re(CO)3(OH)]4 to [Re2(CO)10]
on the silica surface and under relatively mild conditions
t
30b
The reduction with CO (1 atm) of silica-anchored [Re-
(
150-200 °C and 1 atm CO) is a remarkable new
observation showing that silica-supported [Re(CO)3-
OH)]4, which does not sublime, could be a useful
(CO)5(OSit)] to give [Re2(CO)10] is a new example of
the known easy reductive carbonylation of silica-
(
anchored oxidized metal carbonyl species such as [Os-
starting material for the synthesis of Re(0) carbonyl
clusters. Surely the silica surface plays a unique role
in this easy reduction of [Re(CO)3(OH)]4 to a Re(0)
species because working in n-octanol (a high-boiling
hydroxylated solvent that could mimic surface silanols)
as reaction medium the reduction does not occur at all.
Treatment of an n-octanol solution of [Re(CO)3(OH)]4
with a flux of CO (1 atm) at 170 °C does not generate
32
(CO)x(OSit)2]n (x ) 2, 3), which affords [Os3(CO)12].
Since the original goal of our investigation was that of
defining reaction conditions for the silica-mediated
synthesis of Re(0) carbonyl clusters, we have shown that
a simple Re(0) carbonyl cluster such as [Re2(CO)10] is
relatively stable on silica, unexpectedly even under 1
atm of H2. Only at 200-250 °C under nitrogen it is
transformed into [Re(CO)3(OH)]4, as occurs when a
suspension of [Re2(CO)10] in water is heated at 200 °C
[Re2(CO)10], which is stable under these reaction condi-
tions, as confirmed by a blank experiment. The treat-
ment leads to the slow formation of a carbonyl rhenium
complex characterized by an infrared spectrum (νCO )
12
under nitrogen in an autoclave. However, on silica, the
relatively high temperature (200-250 °C) necessary to
generate silica-supported [Re(CO)3(OH)]4 with respect
to the sublimation of [Re2(CO)10] produces even under
-
1
1
995(s) and 1882(vs) cm ) typical of the [(CO)3Re(µ-
-
30
OR)3Re(CO)3] (R ) alkyl group) anion.
7+
nitrogen some further oxidation up to Re , as confirmed
The facile reduction on the silica surface is probably
due to a specific stabilization under a CO atmosphere
of the [Re(CO)5]+ moiety by anchoring to the surface.
We have produced a large amount of evidence that this
moiety can be covalently bound to the silica surface
probably via a Re-OSit bond, which, as expected, can
be easily cleaved by H2O, HCl, or HReO4, as shown by
the use of the “extraction method”,14 which allows the
chemical characterization of complex mixtures of surface
metal carbonyl species, which cannot be easily defined
by infrared spectroscopy only.
by XPS and by treatment of these oxidized surface
rhenium species with CO, which affords some [Re-
(CO)5OReO3]. Because solid [Re(CO)3(OH)]4 oxidizes
with decomposition in air only at temperatures higher
5
than 360 °C, it appears that the silica surface must
play an important role in favoring a more facile oxida-
tion process.
In conclusion, our work clarified and unveiled some
new aspects of the surface organometallic chemistry of
silica-supported [Re(CO)3(OH)]4 and [Re2(CO)10], con-
firming the importance of the “extraction method” as a
tool to fully identify supported organometallic species
The proposed species [Re(CO)5(OSit)] is of particular
interest since complexes of the type [Re(CO)5(OR)]
1
4
and their mixtures. We have shown in particular that
the silica surface plays quite a relevant role in the
increased reactivity of [Re(CO)3(OH)]4 toward oxidation
even under nitrogen or vacuum, when compared to its
behavior in solution or in the solid state. In addition
its high tendency to be reduced with CO to [Re2(CO)10],
by cleavage of Re-O bonds and formation of a Re-Re
(R ) alkyl or aryl) have never been reported to be stable
up to now, therefore its stability on the surface is
noteworthy. It could be attributed to the rigidity of the
(
30) (a) Ginsberg, A. P.; Hawkes, M. J . J . Am. Chem. Soc. 1968, 90,
930. (b) Ioganson, A. A.; Lokshin, B. V.; Kolobova, E. E.; Anisimov,
K. N. J . Gen. Chem. 1974, 20, 20. (Translated from Zh. Obshch. Khim.
974, 44, 23). (c) Albano, V. G.; Ciani, G.; Freni, M.; Romiti, P. J .
5
1
Organomet. Chem. 1975, 96, 259. (d) Ciani, G.; D’Alfonso, G.; Freni,
M.; Romiti, P.; Sironi, A. J . Organomet. Chem. 1978, 152, 85. (e) Ciani,
G.; Sironi, A.; Albinati, A. Gazz. Chim. Ital. 1979, 109, 615. (f)
Herrmann, W. A.; Mihalios, D.; Ofele, K.; Kiprof, P.; Belmedjahed, F.
Chem. Ber. 1992, 125, 1795.
(31) J iang, C.; Wen, Y. S.; Liu, L. K.; Hor, T. S. A.; Yan, Y. K.
Organometallics 1998, 17, 173.
(32) Dossi, C.; Fusi, A.; Grilli, E.; Psaro, R.; Ugo, R.; Zanoni, R. Catal.
Today 1988, 2, 585.

Surface Organometallic Chemistry
Organometallics, Vol. 19, No. 13, 2000 2571
CO at 150 °C for 4 days, some [Re (CO)10] sublimed, whereas
the infrared spectrum of the silica powder showed carbonyl
bands at 2089(w), 2069(w), 2049(vs), 2028(m), 2012(m), 1991-
bond, is noteworthy for an oxophilic metal and encour-
aging in further attempts to investigate the synthesis
of rhenium(0) carbonyl clusters from oxidized Re species
mediated by the silica surface.
2
-
1
(
m), 1974(w), and 1925(s) cm . Treatment of the sublimate
and silica powder with anhydrous pentane afforded [Re (CO)10
33 mg; 0.050 mmol; 18% yield), whereas successive extraction
of the silica powder with anhydrous CH Cl gave [Re(CO)
OH)] (44 mg; 0.038 mmol; 27% yield) and left the proposed
[Re(CO) (OSit)] species and traces of unidentified rhenium
2
]
(
Exp er im en ta l Section
2
2
3
-
(
4
Gen er a l Com m en t s. SiO
2
(Aerosil 200 Degussa, with a
2
5
nominal surface area of 200 m /g) was used as the support
-1
-
2
carbonyl species (νCO ) 2089(w) and 1927(w) cm ) on the silica
after treatment in vacuo (10 Torr) at 25 °C for 3 h. [Re
CO)10] and HReO were purchased from INALCO and Sigma-
Aldrich, respectively. [Re(CO) (OH)] was prepared according
to the literature and characterized by infrared and H NMR
2
-
surface.
(
4
3 4
(iii) At 200-250 °C. When silica-supported [Re(CO) (OH)]
3
4
1
(4.28 g of powder corresponding to 0.459 mmol Re) was heated
at 200 °C under CO, a white material sublimed onto the cold
walls of the reaction vessel. After 2, 3, and 5 days, extraction
of both the sublimate and the silica powder with anhydrous
1
2
spectroscopies and by mass spectrometry (in the FAB-mass
spectrum, we observed the molecular ion peak at 1150, never
reported before). Organic solvents were dried over molecular
sieves (4 Å) prior to use. All the reaction products were
identified, after extraction from silica, by mass, infrared, and/
2
pentane afforded [Re (CO)10] in 47% (70 mg; 0.107 mmol), 60%
(90 mg; 0.138 mmol), and 71% (106 mg; 0.162 mmol) yields,
respectively. Similar yields were reached by working at 250
°C.
1
or H NMR spectroscopies, their spectra being compared to
those of pure samples. Their purity was also controlled by
elemental analysis. Spectral data were obtained by use of the
Rea ctivity of Silica -An ch or ed [Re(CO) (OSit)]. As
5
following spectrometers: Bruker-Vector 22 (IR), Bruker AC-
above-reported, a silica powder sample containing silica-
1
2
00 or Bruker DRX-300 ( H NMR), Varian VG9090 (MS).
anchored [Re(CO) (OSit)] was obtained by treatment of silica-
5
Elemental analyses were carried out in the analytical labora-
tory of our department, whereas XPS measurements were
performed using M-Probe (SSI) equipment. The source was
monochromatic Al KR radiation (1486.6 eV). The 1s level
hydrocarbon-contaminant carbon was taken as the internal
reference at 284.6 eV.
supported [Re(CO) (OH)] (5.19 g of powder corresponding to
3
4
0.556 mmol Re) under CO at 150 °C for 4 days, followed by
successive extraction under N2 with anhydrous pentane and
CH Cl to remove [Re (CO) ] and [Re(CO) (OH)] . The powder
2
2
2
10
3
4
sample was divided into two equal parts, whose reactivity with
HCl and HReO is reported below.
4
P r ep a r a tion of Silica -Su p p or ted [Re(CO)
typical preparation, a slurry of silica (8.23 g), [Re(CO)
254 mg; 0.221 mmol; 2.0 wt % Re with respect to SiO
CH Cl or acetone (300 mL) was stirred under N at 25 °C for
h. The solvent was evaporated at 25 °C under vacuum (10
Torr), affording a white powder, which was stored under N
P r ep a r a tion of Silica -Su p p or ted [Re (CO)10]. In a typi-
cal preparation, a slurry of silica (14.16 g), [Re (CO)10] (494
mg; 0.757 mmol; 2.0 wt % Re with respect to SiO ), and CH
Cl (300 mL) was stirred under N at 25 °C for 2 h. The solvent
was evaporated at 25 °C under vacuum (10 Torr), affording
a white powder, which was stored under N
P r ep a r a tion of Silica -Su p p or ted [HRe
typical preparation, a slurry of silica (1.82 g), [HRe
mg; 0.625 mmol; 2.0 wt % Re with respect to SiO
pentane (70 mL) was stirred under N at 25 °C for 2 h. The
solvent was evaporated at 25 °C under vacuum (10 Torr),
affording a pale yellow powder, which was stored under N
Red u ctive Ca r bon yla tion of Silica -Su p p or ted [Re-
CO) (OH)] . The silica powder sample containing [Re(CO)
OH)] (2.0 wt % Re with respect to SiO ) was transferred into
3
(OH)]
(OH)]
), and
4
. In a
(
5
i) With HCl. Extraction of silica-anchored [Re(CO) (OSit)]
3
4
with dichloromethane (ca. 200 mL) acidified with a few drops
of HCl(aq), followed by evaporation of the solution, afforded
Re(CO) Cl] (43 mg; 0.119 mmol; 43% yield with respect to
5
3 4
starting silica-supported [Re(CO) (OH)] ). After this extraction
process, traces of unidentified rhenium carbonyl species
(νCO ) 2089(w) and 1927(w) cm ) remained on the silica
(
2
2
2
2
13
[
-
2
2
2
.
2
-1
2
surface, as evidenced by infrared spectroscopy.
ii) With HReO . Extraction of silica-anchored [Re(CO)
OSit)] with dichloromethane (ca. 200 mL) acidified with a
few drops of HReO , followed by evaporation of the solution,
afforded crude [Re(CO)
from dichloromethane/hexane (82 mg; 0.142 mmol; 51% yield
with respect to starting silica-supported [Re(CO) (OH)] ). After
this extraction process, traces of unidentified rhenium carbonyl
2
2
-
(
4
5
-
2
2
(
-
2
4
2
.
1
6
5
3
OReO ], which was recrystallized
3
(CO)14]. In a
(CO)14] (42
), and
3
3
4
2
2
-
1
species (νCO ) 2089(w) and 1927(w) cm ) remained on the
silica surface, as evidenced by infrared spectroscopy. [Re-
CO) OReO ] was characterized by elemental analysis (calcd
5 3
C, 10.42; found C, 10.55), mass spectrometry (in the FAB+
mass spectrum, never reported before, there is the molecular
ion peak at m/e ) 578 [M] ), and infrared spectroscopy (in CH
-
2
2
.
(
(
(
3
4
3
-
4
2
+
2
-
the cylindrical Pyrex vessel (diameter 60 mm, length 350 mm)
previously described for the reductive carbonylation of silica-
-
1
Cl
2
: νCO ) 2164(w), 2057(vs), and 2002(m) cm ).
Ca r bon yla tion of Silica -Su p p or ted [HRe (CO)14]. The
silica powder sample containing [HRe (CO)14] (ca. 200 mg of
powder; 2.0 wt % Re with respect to SiO ) was transferred into
1
0a
3
supported metal chlorides at atmospheric pressure, treated
-
2
3
under vacuum (10 Torr) at 25 °C and then exposed to CO at
atmospheric pressure. The bottom of the vessel (about half of
the cylinder) was put into an oven and heated at the desired
temperature (100-250 °C). The surface reactions were moni-
tored by infrared spectroscopy; samples were taken from the
glass vessel at room temperature and studied as Nujol mull
2
the cylindrical Pyrex vessel (diameter 60 mm, length 350 mm)
previously described for the reductive carbonylation of silica-
supported metal chlorides at atmospheric pressure, treated
under vacuum (10 Torr) at 25 °C and then exposed to CO at
atmospheric pressure.
1
0a
-
2
(
see Results and Discussion sections). Extraction of the sup-
ported rhenium species was carried out under N with pentane
or dichloromethane (in the case of [Re (CO)10]) and dichlo-
romethane or acetone (in the case of [Re(CO) (OH)] ). [Re(CO)
OSit)] could not be extracted by treatment with donor
(
i) At Room Tem p er a tu r e. Silica-supported [HRe
reacted very slowly under CO at room temperature. After 7
days, a mixture of [HRe (CO)14], [Re (CO)10], and [HRe(CO)
was present on the silica surface and could be characterized
3
(CO)14]
2
2
5
-
3
2
5
]
3
4
(
1
8
by infrared and H NMR spectroscopies after extraction with
CDCl3.
solvents such as acetone or THF, as expected for a species
anchored to the surface via covalent bonds.14
(
i) At 100 °C. Silica-supported [Re(CO)
slowly when heated at 100 °C under CO with formation of only
traces of the proposed [Re(CO) (OSit)] species after 2 days.
ii) At 150 °C. When silica-supported [Re(CO) (OH)] (5.19
g of powder corresponding to 0.556 mmol Re) was heated under
3
(OH)]
4
reacted very
(ii) At 150 °C. When pale yellow silica-supported [HRe
(CO)14] was heated under CO at 150 °C for 4 h, the silica
powder color became white and some [Re (CO)10] sublimed.
Treatment of the sublimate and silica powder with anhydrous
pentane afforded pure [Re (CO)10], whereas no carbonyl rhe-
3
-
5
2
(
3
4
2

2
572 Organometallics, Vol. 19, No. 13, 2000
D’Alfonso et al.
nium species remained on the silica surface, as evidenced by
infrared spectroscopy.
carbonyl bands of [Re(CO)
5
OReO
3
] were shifted to lower
frequencies by using pure acetone (νCO ) 2043(s) and 1989(m)
-1
Th er m a l Beh a vior of Silica -Su p p or ted [Re
2
(CO)10]. The
cm ) instead of dichloromethane (νCO ) 2164(w), 2057(vs), and
1
-
silica-supported [Re (CO)10] (2.0 wt % Re with respect to SiO
2
2
)
2002(m) cm ) as solvent due to the formation of [Re(CO)
(acetone)][ReO ]. This shift is in agreement with that observed
going from [Re(CO) FBF ] (νCO in CH Cl ) 2166(w), 2066(s),
and 2008(m) cm ) to [Re(CO) (H O)][BF ] (νCO in CH Cl
2160(w), 2057(s), and 2004(s) cm-1).
The formation of [Re-
(CO) (acetone)][ReO ] was confirmed by conductive measure-
5
-
was transferred into the cylindrical Pyrex vessel (diameter 60
mm, length 350 mm) previously described for the reductive
carbonylation of silica-supported metal chlorides at atmo-
4
5
3
2
2
-
1
5
2
4
2
2
)
1
0a
-2
25,26
spheric pressure, treated under vacuum (10 Torr) at 25
C, and then exposed to N , CO, H , or air at atmospheric
°
2
2
5
4
pressure. The bottom of the vessel (about half of the cylinder)
was put into an oven and heated at the desired temperature
ments using a Amel 160 conductivity meter. The conductivity
of pure acetone was 0.23 µS, whereas that of a solution of
-
3
-4
(100-250 °C). The surface reactions were monitored by
[NBu
4
]OH (10 M) and [Re(CO)
5
OReO
3
] (6.2 × 10 M) in
infrared spectroscopy; samples were taken from the glass
vessel at room temperature and studied as Nujol mull (see
Results section). Extraction of the supported rhenium species
acetone was 121.5 and 60.11 µS, respectively. A dichlo-
romethane solution of [Re(CO)
-
4
5
OReO
3
] (6.2 × 10 M) did not
conduct.
was carried out under N
2
with pentane or dichloromethane
(CO)10]) and dichloromethane or acetone
in the case of [Re(CO) (OH)] ).
Th er m a l Beh a vior of Silica -Su p p or ted [Re
u n d er N a t 250 °C. In a typical preparation, silica-supported
Re (CO)10] (6.59 g of powder corresponding to 0.704 mmol Re)
was heated under N at 250 °C for 30 min. Treatment with
X-r a y Str u ctu r e Deter m in a tion of [(CO)
5
Re(µ-O)ReO ].
3
(in the case of [Re
2
A suitable crystal of the title compound was chosen and
mounted, in air, on a glass fiber onto a goniometer head and
collected at RT on a Siemens SMART CCD area-detector
diffractometer. Crystal data are reported in Table 2. Graphite-
monochromatized Mo KR (λ ) 0.71073 Å) radiation was used
with the generator working at 45 kV and 40 mA. Cell
parameters and orientation matrix were obtained from least-
squares refinement on reflections measured in three different
sets of 15 frames each. The data collection was performed by
measuring 2500 frames (15 s per frame; ω scan method,
∆ω ) 0.3°; sample-detector distance fixed at 5.5 cm), which,
upon data reduction, afforded almost all reflections belonging
to the sphere with 2θ < 56°. The first 100 frames were
recollected at the end to monitor crystal decay, which was not
observed; an absorption correction was applied (SADABS,
(
3
4
2
(CO)10]
2
[
2
2
pentane of the silica powder and of the sublimate, formed
during the reaction onto the cold walls of the vessel, afforded
[
Re
extraction of the silica powder with acetone, followed by
evaporation of the solution to dryness, afforded crude [Re(CO)
OH)] , which was recrystallized from dichloromethane/pen-
2
(CO)10] in ca. 1% yield (ca. 2 mg; ca. 0.003 mmol). Further
3
-
(
4
tane at -30 °C (128 mg; 0.111 mmol; 63% yield).
Th er m a l Beh a vior of Silica -Su p p or ted [Re (CO)10]
2
u n d er N
powder sample containing [Re
respect to SiO
the cylindrical Pyrex vessel,
Torr) at 25 °C, and then exposed to N
2
a t 250 °C F ollow ed by Ca r bon yla tion . The silica
3
3
2
(CO)10] (2.0 wt % Re with
minimum relative effective transmission factor 0.404).
2
; 3.02 g of silica powder) was transferred into
A total of 25 483 reflections were collected (4732 unique,
1
0a
-2
34
treated under vacuum (10
Rint ) 0.0434; Rσ ) 0.0377). The structure was solved by
3
5
2
at atmospheric pressure.
direct methods (SIR97) and refined with full-matrix-block
least-squares (SHELX97);36 anisotropic temperature factors
were assigned to all atoms.
The bottom of the vessel (about half of the cylinder) was put
into an oven and heated at 250 °C for 30 min. The vessel was
cooled to room temperature, treated under vacuum (10 Torr),
exposed to CO at atmospheric pressure, and then heated at
-2
Ack n ow led gm en t. We deeply thank Dr. Stefano
Barbieri, Dr. Barbara Migliazza, Dr. Carmen Roveda,
and Matteo Vailati for some experimental help and Dr.
Mirka Bergamo (University of Milan) for a loan of
2
00 °C. After either 24 or 48 h, the infrared spectrum of the
silica powder, as Nujol mull, showed carbonyl bands at 2087-
-
1
(
w), 2069(w), 2049(vs), 2012(m), 1991(m), and 1974(w) cm
The extraction of the supported rhenium species was carried
out under N . Treatment of the sublimate and silica powder
with anhydrous pentane afforded [Re (CO)10], whereas suc-
cessive extraction of the silica powder with anhydrous CH
Cl gave [Re(CO) OReO ]. Successive extraction with acetone
afforded traces of a species characterized by a carbonyl band
.
[
HRe3(CO)14]. This work was supported by the Ministero
2
dell’Universit a` e della Ricerca Scientifica e Tecnologica
and by the Consiglio Nazionale delle Ricerche (CNR,
Roma).
2
2
-
2
5
3
-1
at 2081 cm , which could be [Re(CO)
the known complex [Re(CO) ][AlCl ] (νCO in acetone ) 2081
cm ), whereas silica-anchored [Re(CO) (OSit)] remained on
the gray silica surface, as confirmed by infrared spectroscopy
6
][ReO
4
] by analogy with
Su p p or tin g In for m a tion Ava ila ble: Refined atoms co-
ordinates (Table S1), anisotropic thermal parameters (Table
S2). This material is available free of charge via the Internet
at http://pubs.acs.org.
6
4
-1 23
5
-1
(ν
CO as Nujol mull ) 2049(vs) and 1991(m) cm ) of the sample.
Rea ctivity of [Re(CO) OReO ]. (i) With HCl. Addition
of a few drops of 37% aqueous HCl to a solution of [Re-
CO) OReO ] in dichloromethane, at room temperature, af-
forded [Re(CO)
OM000028J
5
3
(33) Sheldrick, G. M. SADABS; University of G o¨ ttingen: Germany,
(
5
3
1
996.
1
3
5
Cl] in quantitative yield. The reaction was
(
34) Rint ) ∑|F
2
- Fmean |/∑F
2
2; R
) ∑σ(F
1/2
2)/∑F
2; R
) ∑||F | -
o
o
σ
o
o
1
o
2
2
2
complete in less than 5 min, as evidenced by infrared spec-
troscopy.
|F
c
||/∑|F
o
|; wR
2 o c o
) (∑(F - F ) /∑wF
4)
(35) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J . Appl. Crystallogr. 1994, 24,
35.
36) Sheldrick, G. M. SHELX97-Program for the refinement of crystal
structure; University of G o¨ ttingen: Germany, 1997.
(
ii) With Aceton e. No change occurred in the infrared
spectrum of [Re(CO) OReO ] in dichloromethane upon addition
of a few drops of either acetone or water. However, the
4
5
3
(