Chemical and thermal behavior of the molecular models [Os3(CO)10(μ-H)(μ-OSiR2R′)] (R = Et, Ph; R′ = Et, Ph, OH, OSiPh2OH): Molecular approach to the clarification of the surface chemistry of the silica-anchored cluster [Os3(CO)10(μ-H)(μ-OSi≡)]

Article abstract of DOI:10.1021/om000858x

The reactivity (e.g., toward hydrolysis, alcoholysis, reduction by CO or H₂) of various [Os₃(CO)₁₀(μ-H) (μ-OSiPh₂R′)] (R′ = Ph, OH, OSiPh₂OH) clusters and the thermal behavior of [Os₃(CO)₁₀(μ-H)(μ-OSiEt₃)] have been studied with the aim of clarifying by a molecular approach some aspects of the surface chemistry of silica-anchored [Os₃(CO)₁₀(μ-H)(μ-OSi≡)]. Their easy and selective reduction to [Os₃(CO)₁₂] (under CO) and to [H₄Os₄(CO)₁₂] (under H₂) suggests that [Os₃(CO)₁₀(μ-H)(μ-OSi≡)] does not require, as a reactive intermediate, a previous hydrolysis to the more reactive molecular species [Os₃(CO)₁₀(μ-H)(μ-OH)] in order to generate different osmium carbonyl clusters in their silica-mediated synthesis starting from OsCl₃ or [Os(CO)₃Cl₂]₂. The thermal behavior of [Os₃(CO)₁₀(μ-H)(μ-OSiEt₃)] dissolved in triethylsilanol (to mimic a silica surface with many available surface silanols) or triglyme (to mimic a highly dehydroxylated silica surface) gives an answer to the controversy on the nature of the products formed by thermal degradation on the silica surface of [Os₃(CO)₁₀(μ-H)(μ-OSi≡)]. In triethylsilanol, oxidation occurs to give a Os(II) hydrido carbonyl species which, on the basis of chemical and spectroscopic evidence, we suggest to be [Os(CO)₃(μ-OSiEt₃)₂(OSiEt₃) (H)Os(CO)₂]_n (n = probably 2), whereas in triglyme an aggregation to high-nuclearity clusters such as [H₄Os₁₀(CO)₂₄]^2- and [H₅Os₁₀(CO)₂₄]^- occurs. Therefore, it is shown for the first time that molecular models not only are a tool to define structural aspects but also may be a springboard to understand and clarify by a molecular approach aspects of the reactivity of organometallic species on the silica surface.

Full text of DOI:10.1021/om000858x

Organometallics 2001, 20, 1725-1733
1725
Ch em ica l a n d Th er m a l Beh a vior of th e Molecu la r Mod els
[Os3(CO)10(µ-H)(µ-OSiR2R′)] (R ) Et, P h ; R′ ) Et, P h , OH,
OSiP h 2OH): Molecu la r Ap p r oa ch to th e Cla r ifica tion of
th e Su r fa ce Ch em istr y of th e Silica -An ch or ed Clu ster
[Os3(CO)10(µ-H)(µ-OSit)]
Elena Lucenti, Dominique Roberto,* and Renato Ugo
Dipartimento di Chimica Inorganica, Metallorganica e Analitica and Centro CNR
“CSSSCMTBSO”, Universita` di Milano, Via G. Venezian, 21, 20133 Milano, Italy
Received October 10, 2000
The reactivity (e.g., toward hydrolysis, alcoholysis, reduction by CO or H2) of various [Os3-
(CO)10(µ-H)(µ-OSiPh2R′)] (R′ ) Ph, OH, OSiPh2OH) clusters and the thermal behavior of
[Os3(CO)10(µ-H)(µ-OSiEt3)] have been studied with the aim of clarifying by a molecular
approach some aspects of the surface chemistry of silica-anchored [Os3(CO)10(µ-H)(µ-OSit)].
Their easy and selective reduction to [Os3(CO)12] (under CO) and to [H4Os4(CO)12] (under
H2) suggests that [Os3(CO)10(µ-H)(µ-OSit)] does not require, as a reactive intermediate, a
previous hydrolysis to the more reactive molecular species [Os3(CO)10(µ-H)(µ-OH)] in order
to generate different osmium carbonyl clusters in their silica-mediated synthesis starting
from OsCl3 or [Os(CO)3Cl2]2. The thermal behavior of [Os3(CO)10(µ-H)(µ-OSiEt3)] dissolved
in triethylsilanol (to mimic a silica surface with many available surface silanols) or triglyme
(to mimic a highly dehydroxylated silica surface) gives an answer to the controversy on the
nature of the products formed by thermal degradation on the silica surface of [Os3(CO)10-
(µ-H)(µ-OSit)]. In triethylsilanol, oxidation occurs to give a Os(II) hydrido carbonyl species
which, on the basis of chemical and spectroscopic evidence, we suggest to be [Os(CO)3(µ-
OSiEt3)2(OSiEt3)(H)Os(CO)2]n (n ) probably 2), whereas in triglyme an aggregation to high-
nuclearity clusters such as [H4Os10(CO)24]2- and [H5Os10(CO)24]- occurs. Therefore, it is shown
for the first time that molecular models not only are a tool to define structural aspects but
also may be a springboard to understand and clarify by a molecular approach aspects of the
reactivity of organometallic species on the silica surface.
In tr od u ction
species [Os3(CO)10(µ-H)(µ-OSit)], the first well-de-
scribed organometallic carbonyl cluster species co-
valently bound to silica, has attracted increasing
attention.1a,2,3,6b,9 However, this approach was limited
to the identification of the structural features. Very little
is known about the surface chemistry and thermal
decomposition of [Os3(CO)10(µ-H)(µ-OSit)], which not
only is a catalyst for olefin isomerization10 and hydro-
genation11 but which also seems to be an intermediate
in the synthesis of various neutral and anionic osmium
carbonyl clusters starting from OsCl3 or [Os(CO)3Cl2]2
Because of the usefulness of molecular models for
getting a better insight into surface organometallic
species,1-9 the synthesis and structural characterization
of molecular organometallic compounds bearing silano-
late ligands as models of the silica-anchored surface
* To whom correspondence should be addressed. FAX: +39-2-
2362748. E-mail: dominique.roberto@unimi.it.
(1) (a) Psaro, R.; Ugo, R. Besson, B.; Smith, A. K.; Basset, J . M. J .
Organomet. Chem. 1981, 213, 215. (b) Smith, A. K.; Besson, B.; Basset,
J . M.; Psaro, R.; Fusi, A.; Ugo, R. J . Organomet. Chem. 1980, 192,
C31. (c) Besson, B.; Moraweck, B.; Smith, A. K.; Basset, J . M.; Psaro,
R.; Fusi, A.; Ugo, R. J . Chem. Soc., Chem. Commun. 1980, 569. (d)
Ugo, R.; Psaro, R.; Zanderighi, G. M.; Basset, J . M.; Theolier, A.; Smith,
A. K. In Fundamental Research in Homogeneous Catalysis; Tsutsui,
M., Ed.; Plenum Press: New York, 1979; Vol. 3.
(2) (a) Evans, J .; Gracey, B. P. J . Chem. Soc., Dalton Trans. 1982,
1123. (b) Calvert, R. B. Ph.D. Thesis, University of Illinois at Urbana-
Champaign, 1979.
(3) D’Ornelas, L.; Choplin, A.; Basset, J . M.; Hsu, L. Y.; Shore, S.
Nouv. J . Chim. 1985, 9, 155.
(4) (a) Zucchi, C.; Shchegolikhina, O. I.; Borsari, M.; Cornia, A.;
Gavioli, G.; Fabretti, A. C.; Rentschler, E.; Gatteschi, D.; Ugo, R.; Psaro,
R.; Pozdniakova, Y. A.; Lindeman, S. V.; Zhdanov, A. A.; Pa´lyi, G. J .
Mol. Catal. A 1996, 107, 313 and references therein. (b) Vizi-Orosz,
A.; Ugo, R.; Psaro, R.; Sironi, A.; Moret, M.; Zucchi, C.; Ghelfi, F.; Pa´lyi,
G. Inorg. Chem. 1994, 33, 4600. (c) Pa´lyi, G.; Zucchi, C.; Ugo, R.; Psaro,
R.; Sironi, A.; Vizi-Orosz, A. J . Mol. Catal. 1992, 74, 51.
(5) Puga, J .; Fehlner, T. P.; Gates, B. C.; Braga, D.; Grepioni, F.
Inorg. Chem. 1990, 29, 2376.
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Liu, J . C.; Wilson, S. R.; Shapley, J . R.; Feher, F. J . Inorg. Chem. 1990,
29, 5138. (c) Feher, F. J .; Walzer, J . F. Inorg. Chem. 1990, 29, 1604.
(d) Feher, F. J .; Gonzales, S. L.; Ziller, J . W. Inorg. Chem. 1988, 27,
3440. (e) Feher, F. J . J . Am. Chem. Soc. 1986, 108, 3850.
(7) (a) Meyer, T. Y.; Woerpel, K. A.; Novak, B. M.; Bergman, R. G.
J . Am. Chem. Soc. 1994, 116, 10290. (b) Abbenhuis, H. C. L.;
Vorstenbosch, M. L. W.; van Santen, R. A.; Smeets, W. J . J .; Spek, A.
L. Inorg. Chem. 1997, 36, 6431.
(8) Murugavel, R.; Voigt, A.; Walawalkar, M. G.; Roesky, H. W.
Chem. Rev. 1996, 96, 2205 and references therein.
(9) (a) Lucenti, E.; Roberto, D.; Roveda, C.; Ugo, R.; Sironi, A.
Organometallics 2000, 19, 1051. (b) Lucenti, E.; Feher, F. J .; Ziller, J .
W. Organometallics, in press.
(10) (a) Barth, R.; Gates, B. C.; Zhao, Y.; Kno¨zinger, J .; Hulse, J . J .
Catal. 1983, 82, 147. (b) Dossi, C.; Fusi, A.; Grilli, E.; Psaro, R.; Ugo,
R.; Zanoni, R. J . Catal. 1990, 123, 181.
(11) Choplin, H.; Besson, B.; D’Ornelas, L.; Sanchez-Delgado, R.;
Basset, J . M. J . Am. Chem. Soc. 1988, 110, 2783.
10.1021/om000858x CCC: $20.00 © 2001 American Chemical Society
Publication on Web 04/05/2001

1726 Organometallics, Vol. 20, No. 9, 2001
Sch em e 1. Rea ctivity of [Os3(CO)10(µ-H)(µ-OSiP h 2R′)] (R′ ) P h , OH, OSiP h 2OH)
Lucenti et al.
supported on silica in the presence of alkali-metal
carbonates.12,13 In particular, its thermal decomposition
has been first reported by one of us to give rise to
Os(II) carbonyl1 or even to Os(II) hydrido carbonyl14
species anchored to the surface of silica. In contrast,
another group suggested the thermal formation on the
surface of high-nuclearity osmium carbonyl clusters.15
Surprisingly, although the investigation of the reactivity
of simple molecular silanolate models could be a way
to mimic the complex chemical and thermal behavior
of silica-anchored [Os3(CO)10(µ-H)(µ-OSit)], to our knowl-
edge this approach has never been attempted. This lack
can be attributed to the difficulty of synthesizing
molecular models such as [Os3(CO)10(µ-H)(µ-OSiR3)]
(R ) Et, Ph)1a,2,3 and [Os3(CO)10(µ-H)(µ-OSi7O10(c-
C6H11)7)],6b which were obtained only in rather low
yields in one or more steps starting from [Os3(CO)12];
probably for this reason, the more easily prepared [Os3-
(CO)10(µ-H)(µ-OPh)] was used as a molecular model in
order to obtain mechanistic insight into the olefin
hydrogenation catalyzed by silica-anchored [Os3(CO)10-
(µ-H)(µ-OSit)].11 However, recently we found that the
direct reaction of the easily available reactive cluster
[Os3(CO)10(µ-H)(µ-OH)] with different silanols (e.g.,
HOSiR2R′, where R ) Et, Ph and R′ ) Et, Ph, OH,
OSiPh2OH) is a convenient route for a high-yield (79-
84%) preparation of molecular models of [Os3(CO)10(µ-
H)(µ-OSit)] anchored not only to a surface isolated
silanol, such as [Os3(CO)10(µ-H)(µ-OSiR3)] (where R )
Et, Ph), but also to a surface geminal silanol, such as
[Os3(CO)10(µ-H)(µ-OSiPh2OH)], or vicinal silanol, such
as [Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)].9a This method
was recently confirmed by the synthesis in good yields
of models with silsesquioxanes, including for the first
time the synthesis of {[Os3(CO)10(µ-H)]2(µ-O)2Si8O11Cy8}
carrying two “Os3(CO)10(µ-H)” moieties.9b The ready
availability in good amounts of a series of these molec-
ular models prompted us to study their reactivity and
thermal behavior in order to mimic and therefore to
clarify by an organometallic approach the still poorly
defined chemistry of silica-anchored [Os3(CO)10(µ-H)(µ-
OSit)], which up to now has been interpreted by a
rather qualitative and unsatisfactory approach.
define the strength of the bonding to the silica surface
and (ii) reduction by CO or H2 in order to confirm the
possible involvement of silica-anchored [Os3(CO)10(µ-H)-
(µ-OSit)] as an intermediate in the synthesis of various
osmium carbonyl clusters starting from OsCl3 or
[Os(CO)3Cl2]2 supported on silica in the presence of
alkali-metal carbonates12,13 and finally the thermal
transformation of [Os3(CO)10(µ-H)(µ-OSiEt3)] as a way
to clarify the real molecular nature of the species formed
on the silica surface by thermal degradation of silica-
anchored [Os3(CO)10(µ-H)(µ-OSit)]. By this approach,
molecular models not only are a tool to define structural
aspects of surface organometallic species but also may
be a springboard to better understand their reactivity
and thermal behavior, which up to now were interpreted
by starting from spectroscopic evidence,1-9 from mass
balance of gaseous products,1,14 or more recently by
using a series of methods of extraction of organometallic
species from the silica surface.16
Resu lts a n d Discu ssion
1. Hyd r olysis, Alcoh olysis, a n d Red u ction by CO
or H2 of [Os3(CO)10(µ-H)(µ-OSiP h 2R′)] (R′ ) P h , OH,
OSiP h 2OH) (Sch em e 1). We investigated first the
reactivity of the model compound [Os3(CO)10(µ-H)(µ-
OSiPh2OSiPh2OH)], because at the temperature (ca.
150-200 °C) of the synthesis of various osmium carbon-
yl clusters starting from OsCl3 or [Os(CO)3Cl2]2 sup-
ported on silica in the presence of alkali-metal carbon-
ates,12,13 ca. 62% of the total surface silanols are vicinal,
whereas ca. 25% and 13% are isolated and geminal
silanols, respectively.17 In a second experiment, to
confirm and extend the observed behavior, we investi-
(12) Cariati, E.; Roberto, D.; Ugo, R. Gazz. Chim. Ital. 1996, 126,
339.
(13) Cariati, E.; Recanati, P.; Roberto, D.; Ugo, R. Organometallics
1998, 17, 1266.
(14) Basset, J . M.; Besson, B.; Choplin, A.; Hugues, F.; Leconte, M.;
Rojas, D.; Smith, A. K.; Theolier, A.; Chauvin, Y.; Commereuc, D.;
Psaro, R.; Ugo, R.; Zanderighi, G. M. In Fundamental Research in
Homogeneous Catalysis; Giongo, M., Graziani, M., Eds.; Plenum: New
York, 1984; Vol. 4, p 19.
(15) Collier, G.; Hunt, D. J .; J ackson, S. D.; Moyes, R. B.; Pickering,
I. A.; Wells, P. B.; Simpson, A. F.; Whyman, R. J . Catal. 1983, 80,
154.
In the present work we describe the reactivity of these
models toward (i) hydrolysis and alcoholysis in order to
(16) Roberto, D.; Cariati, E.; Pizzotti, M.; Psaro, R. J . Mol. Catal. A
1996, 111, 97.

Surface Chemistry of [Os3(CO)10(µ-H)(µ-OSit)]
Organometallics, Vol. 20, No. 9, 2001 1727
gated the reactivity of [Os3(CO)10(µ-H)(µ-OSiPh3)], [Os3-
(CO)10(µ-H)(µ-OSiPh2OH)], and [Os3(CO)10(µ-H)(µ-OH)].
1.1. Hyd r olysis of [Os3(CO)10(µ-H)(µ-OSiP h 2R′)]
(R′ ) P h , OH, OSiP h 2OH). When silica-anchored [Os3-
(CO)10(µ-H)(µ-OSit)] is stirred at 95 °C under nitrogen
for ca. 6 h, in the biphasic solvent system water/toluene,
[Os3(CO)10(µ-H)(µ-OH)] is formed in 94% yield. The rate
of hydrolysis is strongly temperature dependent: for
instance, at 40 °C only traces of [Os3(CO)10(µ-H)(µ-OH)]
are formed, even after 24 h.18
(µ-OSit)] and silica-supported [Os3(CO)10(µ-H)(µ-OH)]
as intermediates in the silica-mediated synthesis of
different osmium carbonyl clusters starting from [Os-
(CO)3Cl2]2.12,13 In fact, these two potential intermediates
may interconvert under reaction conditions;12 therefore,
due to the presence of surface water, the surface species
[Os3(CO)10(µ-H)(µ-OSit)] could first hydrolyze to the
more reactive molecular species [Os3(CO)10(µ-H)(µ-OH)],
which could be the key intermediate also in the surface-
mediated synthesis of [H4Os4(CO)12] by easy hydrogena-
tion of silica physisorbed [Os3(CO)12].21,22
To clarify whether silica-anchored [Os3(CO)10(µ-H)-
(µ-OSit)] could be directly reduced to various carbonyl
clusters, without involving the intermediate formation
of [Os3(CO)10(µ-H)(µ-OH)], we studied the reduction in
anhydrous triglyme of the molecular models [Os3(CO)10-
(µ-H)(µ-OSiPh2OSiPh2OH)], [Os3(CO)10(µ-H)(µ-OSiPh2-
OH)], and [Os3(CO)10(µ-H)(µ-OSiPh3)]. For comparison,
we also studied the reduction of [Os3(CO)10(µ-H)(µ-OH)]
under similar conditions.
Red u ction u n d er CO. When an anhydrous triglyme
solution of [Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)] is
heated under a flux of CO (1 atm) at 160 °C for 2.5 h, a
yellow material precipitates. Filtration affords [Os3-
(CO)12] in 79% yield. Under the same conditions, yields
of [Os3(CO)12] are slightly lower starting from [Os3-
(CO)10(µ-H)(µ-OSiPh3)] (71% yield after 3 h) and, in a
more significant manner, from [Os3(CO)10(µ-H)(µ-OSiPh2-
OH)] (59% yield after 3.5 h). However, [Os3(CO)10(µ-H)-
(µ-OH)] is more easily reduced by CO (1 atm) than the
related silanolate derivatives: at 160 °C in anhydrous
triglyme, [Os3(CO)12] is generated in 84% yield after
only 2 h.
The hydrolysis of [Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2-
OH)] mimics quite well that of silica-anchored [Os3-
(CO)10(µ-H)(µ-OSit)]. No reaction occurs when [Os3-
(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)] dissolved in toluene
is stirred in the presence of water, at 25 °C under
nitrogen for a few days. When the reaction is carried
out at 95 °C for 9 h, the hydrolysis is fast, affording [Os3-
(CO)10(µ-H)(µ-OH)] in quantitative yield. As expected,
the hydrolysis is even faster at higher temperatures:
it is complete in ca. 4 h by working at 125 °C with the
biphasic solvent system water/anisole. Similarly, under
the latest conditions, [Os3(CO)10(µ-H)(µ-OSiPh3)] and
[Os3(CO)10(µ-H)(µ-OSiPh2OH)] are also readily hydro-
1
lyzed, as shown by H NMR spectroscopy.
1.2. Rea ction of [Os3(CO)10(µ-H)(µ-OSiP h 2R′)] (R′
) P h , OH, OSiP h 2OH) w ith 1-Bu ta n ol. When a
slurry of silica-anchored [Os3(CO)10(µ-H)(µ-OSit)] in a
given alcohol, ROH, is refluxed under nitrogen, the
molecular species [Os3(CO)10(µ-H)(µ-OR)] is obtained
and easily extracted from the surface, the reaction being
faster when high-boiling alcohols are used, due to the
higher temperatures.18 Similarly, when a solution of
[Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)] in anhydrous 1-
butanol is stirred under nitrogen at reflux temperature
(118 °C) for 5 h, [Os3(CO)10(µ-H)(µ-OBun)] is formed in
80% yield. Under these conditions, [Os3(CO)10(µ-H)(µ-
OSiPh3)] and [Os3(CO)10(µ-H)(µ-OSiPh2OH)] also react
These results confirm the already observed higher
reactivity of silica-supported [Os3(CO)10(µ-H)(µ-OH)] and
clearly show that silica-anchored [Os3(CO)10(µ-H)(µ-
OSit)] could be directly reduced to [Os3(CO)12] without
involving a preliminary hydrolysis.12
1
to generate [Os3(CO)10(µ-H)(µ-OBun)], as shown by H
NMR spectroscopy.
In the easy reductive carbonylation (1 atm of CO, 150
°C) of silica-physisorbed [Os(CO)3Cl2]2 to K[H3Os4-
(CO)12] in the presence of K2CO3 (molar ratio K2CO3:
Os ) 10:1),19 silica-anchored [Os3(CO)10(µ-H)(µ-OSit)]
and silica-supported [Os3(CO)10(µ-H)(µ-OH)] were sug-
gested as possible intermediate species.12,13 To confirm
the involvement of these species as reactive intermedi-
ates, we tried a model homogeneous reaction. When an
anhydrous ethylene glycol solution of [Os3(CO)10(µ-H)-
(µ-OSiPh2OSiPh2OH)] is heated under a flux of CO (1
atm) at 160 °C for 14 h in the presence of K2CO3 (molar
ratio K2CO3:Os ) 10:1), K[H3Os4(CO)12] is formed
selectively, as shown by infrared spectroscopy of the
resulting solution. Extraction with a dichloromethane
solution of [NBu4]I gives [NBu4][H3Os4(CO)12] in 72%
yield. However, the same yields are obtained under
similar reaction conditions starting from [Os3(CO)10-
(µ-H)(µ-OH)], because both [Os3(CO)10(µ-H)(µ-OSiPh2-
OSiPh2OH)] and [Os3(CO)10(µ-H)(µ-OH)] are readily
converted to the same species [Os3(CO)10(µ-H)(µ-OCH2-
CH2OH)] prior to reduction, as confirmed by mass
spectrometry (molecular ion peak m/e 914). Unfortu-
1.3. Red u ction of [Os3(CO)10(µ-H)(µ-OSiP h 2R′)]
(R′ ) P h , OH, OSiP h 2OH) a n d [Os3(CO)10(µ-H)(µ-
OH)]. Recently some of us reported that both silica-
anchored [Os3(CO)10(µ-H)(µ-OSit)] and silica-supported
[Os3(CO)10(µ-H)(µ-OH)] can be selectively reduced to
various carbonyl clusters ([Os3(CO)12], [H4Os4(CO)12],
[H3Os4(CO)12]-, [H2Os4(CO)12]2-, [Os5C(CO)14]2-, and
[Os10C(CO)24]2-) by reductive carbonylation or hydro-
genation, under appropriate conditions, in the presence
of alkali-metal carbonates.12,13 For a given set of reaction
parameters (nature and quantity of alkali-metal car-
bonate, temperature, gas-phase composition), the se-
lectivity starting from silica-anchored [Os3(CO)10(µ-H)(µ-
OSit)] and silica-supported [Os3(CO)10(µ-H)(µ-OH)] is
similar to that observed starting from silica-supported
[Os(CO)3Cl2]2.19,20 This evidence does not allow us to
discriminate between silica-anchored [Os3(CO)10(µ-H)-
(17) Vansant, E. F.; Van Der Voort, P.; Vrancken, K. C. In
Characterization and Chemical Modification of the Silica Surface in
Studies in Surface Science and Catalysis; Delmon, B., Yates, J . T., Eds.;
Elsevier: Amsterdam, 1995; Vol. 93.
(18) Roberto, D.; Lucenti, E.; Roveda, C.; Ugo, R. Organometallics
1997, 16, 5974.
(19) Roberto, D.; Cariati, E.; Psaro, R.; Ugo, R. Organometallics
1994, 13, 734.
(20) Roberto, D.; Cariati, E.; Ugo, R.; Psaro, R. Inorg. Chem. 1996,
35, 2311.
(21) Dossi, C.; Psaro, R.; Roberto, D.; Ugo, R.; Zanderighi, G. M.
Inorg. Chem. 1990, 29, 4368.
(22) Roberto, D.; Pizzotti, M.; Ugo, R. Gazz. Chim. Ital. 1995, 125,
133.

1728 Organometallics, Vol. 20, No. 9, 2001
Sch em e 2. Th er m a l Degr a d a tion of [Os3(CO)10(µ-H)(µ-OSiEt3)]
Lucenti et al.
nately the reactive ethylene glycol was the only avail-
able solvent which could dissolve K2CO3 under the
reaction conditions, unlike, for instance, triglyme.
Red u ction u n d er H2. When an anhydrous triglyme
solution of [Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)] is
heated under a flux of H2 (1 atm) at 160 °C for 30 min,
a yellow material precipitates. Filtration affords [H4-
Os4(CO)12] in 61% yield. Under similar conditions, [Os3-
(CO)10(µ-H)(µ-OSiPh2OH)] and [Os3(CO)10(µ-H)(µ-OS-
iPh3)] are also converted to [H4Os4(CO)12] in similar
yields (63-64%). These results give some evidence of a
conversion of silica-anchored [Os3(CO)10(µ-H)(µ-OSit)]
into [H4Os4(CO)12]22 which does not require the inter-
mediate formation of [Os3(CO)10(µ-H)(µ-OH)], although
the latter is also reduced to [H4Os4(CO)12] in 65% yield,
by working in an anhydrous triglyme solution as above.
2. Th er m a l Beh a vior of [Os3(CO)10(µ-H)(µ-OSi-
Et3)] a s a Mod el of th e Th er m a l Degr a d a tion of
Silica -An ch or ed [Os3(CO)10(µ-H)(µ-OSit)] (Sch em e
2). Metal clusters supported on inorganic oxides con-
stitute an interesting class of hybrid materials, and their
use as catalyst precursors may provide activities and
selectivities often different from those displayed by the
usual supported metallic catalysts.23-25 Since a thermal
treatment of these materials is generally required to
promote their catalytic activity, this aspect cannot be
limited to the evidence of thermal rearrangements of
surface species,15 but it may involve a complex surface
organometallic chemistry originated by reaction with
the OH groups of the support.1,23-24,26 With silica-
supported [Os3(CO)12], it is now well established that
thermal treatment (at 100-150 °C) causes, as the first
step of chemisorption, oxidative addition of a surface
silanol group into an Os-Os bond of the triangular
frame with formation of silica-anchored [Os3(CO)10-
(µ-H)(µ-OSit)].1,23,24 Further thermal treatment (at
150-250 °C) leads to new surface species of interest in
view of their catalytic activity;10b,14,27 however, their
nature has been, as already pointed out, the subject of
some controversy.1,14-15,28-29
On a hydroxylated or partially dehydroxylated silica
surface under vacuum (4-72 h; 150-250 °C)1,29,31,32 or
under oxygen (1-2 h; 150-200 °C),10b,31 both physi-
sorbed [Os3(CO)12] and silica-anchored [Os3(CO)10(µ-H)-
(µ-OSit)] (2.0 wt % Os with respect to SiO2) are
converted to new surface species characterized by three
broad carbonyl bands (for instance, in Nujol, νCO 2126
(m, br), 2036 (s, br), and 1952 (m, br) cm-1) in their
infrared spectrum. The relative intensities of these
bands is dependent upon temperature, time of treat-
ment, and further addition of a CO atmosphere.1 The
real nature and structure of these surface species, which
are also obtained by refluxing a n-decane27 or nonane30
solution of [Os3(CO)12] in the presence of silica, is still
an open question. The similarities of their infrared
spectra with those of known complexes of Os(II) such
as [Os(CO)3X2]2 (X ) Cl, Br, I) and [Os(CO)2I2]n, the K3
Fourier transform of their EXAFS spectra, which showed
the absence of any ordered Os-Os bond, and the
observation that an oxygen atmosphere favors this kind
of surface transformation first suggested complete
rupture of the original cluster cage with formation of
mononuclear oxidized Os(II) surface species such as [Os-
(CO)x(OSit)2]n (x ) 2, 3) which were in equilibrium of
carbonylation/decarbonylation.1 An x value of about 2.7
was proposed by a temperature-programmed decompo-
(23) Basset, J . M.; Choplin, A. J . Mol. Catal. 1983, 21, 95.
(24) Psaro, R.; Ugo, R. In Metal Clusters in Catalysis; Gates, B. C.,
Guczi, L., Knozinger, H., Eds.; Elsevier: Amsterdam, 1986; p 427, and
references therein.
(25) (a) Psaro, R.; Recchia, S. Catal. Today 1998, 41, 139. (b)
Knozinger, H.; Zhao, Y. J . Catal. 1981, 71, 337. (c) Ichikawa, M. J .
Catal. 1979, 59, 67.
(27) Deeba, M.; Gates, B. C. J . Catal. 1981, 67, 303.
(28) Psaro, R.; Dossi, C.; Fusi, A.; Ugo, R. Res. Chem. Intermed. 1991,
15, 31.
(29) Dossi, C.; Fusi, A.; Grilli, E.; Psaro, R.; Ugo, R.; Zanoni, R. Catal.
Today 1988, 2, 585.
(30) Cook, S. L.; Evans, J .; McNulty, G. S.; Greaves, G. N. J . Chem.
Soc., Dalton Trans. 1986, 7.
(26) (a) Scott, S. L.; Basset, J . M. J . Mol. Catal. 1994, 86, 5. (b)
Basset, J . M.; Candy, J . P.; Choplin, A.; Leconte, M.; Theolier, In
Aspects of Homogeneous Catalysis; Ugo, R., Ed.; Kluwer Academic:
Dordrecht, The Netherlands, 1990; Vol. 7, p 85. (c) Lamb, H. H.; Gates,
B. C.; Kno¨zinger, H. Angew. Chem., Int. Ed. Engl. 1988, 27, 1127.
(31) Dossi, C.; Fusi, A.; Psaro, R.; Ugo, R.; Zanoni, R. In Structure
and Reactivity of Surfaces; Morterra, C., Zecchina, A., Costa, G., Eds.;
Elsevier: Amsterdam, 1989; p 375.
(32) Dossi, C.; Fusi, A.; Psaro, R.; Zanderighi, G. M. Appl. Catal.
1989, 46, 145.

Surface Chemistry of [Os3(CO)10(µ-H)(µ-OSit)]
Organometallics, Vol. 20, No. 9, 2001 1729
sition and oxidation study,31,32 whereas the formation
of Os(II) surface species, by treatment under O2 at 200
°C of [Os3(CO)10(µ-H)(µ-OSit)], was confirmed by XPS
spectroscopy.29 However, a careful investigation of the
mass balance showed that the amount of the evolved
hydrogen was less than that required (3 mol of H2/mol
of [Os3(CO)10(µ-H)(µ-OSit)]) for the surface reaction
can be purified by column chromatography and that we
propose to be [Os(CO)3(µ-OSiEt3)2(OSiEt3)(H)Os(CO)2]n
(52% isolated yield) on the basis of elemental analysis
1
and infrared, H NMR, 13C NMR, 29Si NMR, and mass
spectra (see Experimental Section). The infrared spec-
tral pattern of this new species (in CH2Cl2, νCO 2115
(s), 2021 (vs, br), 2008 (s), 1921 (s) cm-1; in hexane, νCO
2112 (s), 2020 (sh), 2017 (vs), 1933 (s) cm-1), which is
quite similar to that reported for the surface species
formed by thermal degradation of silica-anchored [Os3-
(CO)10(µ-H)(µ-OSit)], would suggest the presence of
both fac-(CO)3OsII (νCO in CH2Cl2 2115 (s) and 2021 (vs,
br) cm-1) and cis-(CO)2OsII (νCO in CH2Cl2 2008 (s) and
1921 (s) cm-1) moieties,35 as confirmed both by its easy
reaction with aqueous HCl to produce equimolar amounts
of fac-[Os(CO)3Cl3]- and cis-[Os(CO)2Cl4]2- (see later)
and by the 13C NMR spectrum, carried out in CDCl3,
which shows three signals in a 2:1:2 ratio, one at δ (ppm)
181.16 attributed to cis-Os(CO)2 and two at 169.99 and
169.63 attributed to fac-(CO)3Os, by analogy with the
13C NMR spectrum of fac-[Os(CO)3Cl2(acetone)], which
shows two signals at δ (ppm) 167.75 and 166.34. The
1H NMR spectrum, carried out in CDCl3, shows the
presence of a hydridic signal (Os-H, δ -14.68 ppm)
characterized by a 187Os-1H coupling constant of 94 Hz,
a value that is quite high36 but is not too far from the
value of the 187Os-1H coupling constant of 76.2 Hz
reported for the terminal hydrogen in [(η5-Cp)H(PMe3)2-
Os].37 The hydridic signal is coupled selectively to the
C signal of the CO’s at 181.16 ppm, as evidenced by
heteronuclear multiple quantum correlation (HMQC)
spectroscopy with the bilinear rotation decoupling (BIRD)
technique, giving evidence for a cis-HOs(CO)2 moiety.
The presence of two kinds of “Et3SiO-” groups, in a 1:2
ratio as expected for one terminal Et3SiO- and two
bridging Et3SiO- groups, is confirmed by the two
signals in the 29Si NMR spectrum (in CDCl3, δ 27.57
and 29.71 ppm; see Experimental Section). Finally both
the EI and FAB mass spectra show a peak at m/e 916
corresponding to the fragment “Os(CO)3(µ-OSiEt3)2-
(OSiEt3)(H)Os(CO)2”, whereas the ESI+ mass spectrum
in CH3CN evidences peaks at m/e 1914 and 998 corre-
sponding to “[Os(CO)3(µ-OSiEt3)2(OSiEt3)(H)Os(CO)2]2‚
2CH3CN” and “[Os(CO)3(µ-OSiEt3)2(OSiEt3)(H)Os(CO)2]‚
2CH3CN”, respectively. On the basis of all this spectro-
scopic evidence, a possible structure can be proposed for
this new carbonyl species based on “Os(CO)3(µ-OSiEt3)2-
(OSiEt3)(H)Os(CO)2” units such as
[Os3(CO)10(µ-H)(µ-OSit)] + 5HOSit f
3Os(CO)3(OSit)2 + CO + 3H2
suggesting that the oxidation process could occur with
complete breaking of the cluster framework but with
parallel formation of some hydridocarbonylosmium(II)
species covalently bound to the silica surface such as
[HOs(CO)3(OSit)(HOSit)].14 The latter species could
then to some extent, particularly under oxygen, lose H2
to give the previously proposed [Os(CO)x(OSit)2]n (x )
2, 3) species.1
In addition, it has been reported that, on a highly
dehydroxylated silica surface, thermal treatment up to
250 °C of physisorbed [Os3(CO)12] (2.0 wt % Os with
respect to SiO2) affords new surface species also char-
acterized by three broad carbonyl bands (in Nujol, νCO
2122 (m, br), 2030 (s, br), and 1950 (s, br) cm-1) in their
infrared spectrum.15 On the basis of UV/visible reflec-
tance spectra, which evidenced retention of Os-Os
bonding, temperature-programmed decomposition, and
high-resolution transmission electron microscopy, the
authors suggested a thermal process of cluster growth
to produce high-nuclearity surface species such as [Osn-
(CO)2.8nC0.1nZ0.3n] (n ) ca. 12), where Z represents
adsorption sites. In this particular study, the formation
of high-nuclearity species, instead of carbonylosmium-
(II) species, was attributed15,28 to the use of a high rate
of heating, high [Os3(CO)12] surface loadings, and highly
dehydroxylated silica, which would inhibit an easy
interaction of [Os3(CO)12] with surface silanols and
therefore could lead to its simple well-known pyrolysis
to produce high-nuclearity carbonyl species.33 The con-
version of silica-anchored [Os3(CO)10(µ-H)(µ-OSit)] to
high-nuclearity species, by thermal treatment under an
inert atmosphere, was not experimentally studied under
conditions reported in ref 15, but it is well-known that
this latter species is easily formed as the first step of
chemisorption by heating [Os3(CO)12] physisorbed on
silica at 150-200 °C.1
To contribute to this still-open controversy, we inves-
tigated the thermal reactivity, in air or under nitrogen,
of the molecular model [Os3(CO)10(µ-H)(µ-OSiEt3)] dis-
solved in triethylsilanol (to mimic a silica surface with
available surface silanols) or triglyme (to mimic a highly
dehydroxylated silica surface). This latter cluster was
chosen as a molecular model because its reactivity is
particularly easy to monitor by 1H and 13C NMR
spectroscopy.
When a solution of [Os3(CO)10(µ-H)(µ-OSiEt3)] in pure
anhydrous triethylsilanol is heated in dried air at 200
°C for ca. 4 h in the closed reaction vessel previously
described,34 some [H4Os4(CO)12] (11% isolated yield) is
formed, along with a new osmium carbonyl species that
These units may aggregate via OSiEt3 bridges, in
(35) (a) J ohannsen, F. H.; Preetz, W. J . Organomet. Chem. 1976,
104, 79. (b) J ohannsen, F. H.; Preetz, W.; Scheffler, A. J . Organomet.
Chem. 1975, 102, 527. (c) Preetz, W.; J ohannsen, F. H. J . Organomet.
Chem. 1975, 86, 397. (d) Cleare, M. J .; Griffith, W. P. J . Chem. Soc. A
1969, 372.
(33) Braga, D.; Lewis, J .; J ohnson, B. F. G.; McPartlin, M.; Nelson,
W. J . H.; Vargas, M. D. J . Chem. Soc., Chem. Commun. 1983, 241.
(34) Roberto, D.; Psaro, R.; Ugo, R. Organometallics 1993, 12, 2292.

1730 Organometallics, Vol. 20, No. 9, 2001
Lucenti et al.
agreement with the 18-electron rule. The evidence of a
dimer, given by the ESI+ mass spectrum, would suggest
a cubane structure similar to that of the Os(II) complex
under nitrogen, being complete in ca. 3 h and affording
Os(II) silica-anchored carbonyl species only.
It is remarkable that the species proposed as [Os-
(CO)3(µ-OSiEt3)2(OSiEt3)(H)Os(CO)2]n perfectly repro-
duces the behavior toward aqueous HCl of silica-
anchored dicarbonyl- and tricarbonylosmium(II) species
obtained by thermal degradation of [Os3(CO)10(µ-H)(µ-
OSit)]. In fact, when this species is dissolved in hexane
or CHCl3, it reacts with aqueous HCl, affording Et3-
SiOSiEt3 and a mixture of fac-[Os(CO)3Cl3]- and cis-
[Os(CO)2Cl4]2- (molar ratio 1:1) which can be easily
separated by column chromatography (see Experimental
Section). In addition, when a solution of [Os(CO)3(µ-
OSiEt3)2(OSiEt3)(H)Os(CO)2]n in triethylsilanol is heated
under CO (1 atm) at 200 °C in the closed reaction vessel
previously described,34 [Os3(CO)12] is slowly formed
(yield 50% after 5 days), mimicing the well-known
reductive carbonylation of the silica-anchored dicarbon-
yl- and tricarbonylosmium(II) species to regenerate [Os3-
(CO)12].24
Unfortunately, the proposed [Os(CO)3(µ-OSiEt3)2-
(OSiEt3)(H)Os(CO)2]n species (where n is probably 2),
obtained by thermal degradation of [Os3(CO)10(µ-H)(µ-
OSiEt3)] in triethylsilanol, is oily (probably with a low
melting point). Therefore, it was impossible to confirm
the proposed structure by X-ray crystallography, but the
body of spectroscopic evidence produced is in good
agreement with the main features of the proposed
structural arrangement.
38
[(CO)3OsO]4 and common to many complexes with a
metal having a low-spin d6 configuration such as
Pt(IV) ([Me3PtCl]4,39 [Me3PtOH]440), Mn(I) ([(CO)3Mn-
SR]441), and Re(I) ([(CO)3ReSR]4,41 [(CO)3ReOH]442).
The same species, which we propose to be [Os(CO)3-
(µ-OSiEt3)2(OSiEt3)(H)Os(CO)2]n, is formed, along with
traces of [H4Os4(CO)12], also by thermal degradation
under N2 of [Os3(CO)10(µ-H)(µ-OSiEt3)] dissolved in
triethylsilanol. The reaction is slower than when carried
out in air, being incomplete even after 19 h. In both
cases, minor amounts of Et3Si(OSiEt2)nOSiEt3 (n ) 0-2)
species are also formed, as evidenced by mass spectrom-
etry43 and 29Si NMR spectroscopy, due to thermal
condensation of triethylsilanol as confirmed by a blank
experiment (see Experimental Section).
In pure anhydrous triglyme under N2 at 200 °C, [Os3-
(CO)10(µ-H)(µ-OSiEt3)] is rapidly (less than 2 h) con-
verted to mixtures of [H4Os4(CO)12] and [H5Os10(CO)24]-
1
only (identified by infrared and H NMR spectroscopy;
see Experimental Section), confirming that the presence
of excess silanol groups inhibits the formation of high-
nuclearity clusters such as [H5Os10(CO)24]- which occurs
by simple thermal pyrolysis.33
The above observations prompted us to reinvestigate
in great detail the already studied thermal degradation,
under N2 at 200 °C and using the now well-established
so-called extraction methodology developed in our labo-
ratory,16 of [Os3(CO)10(µ-H)(µ-OSit)] (1.7 wt % Os with
respect to SiO2) anchored to a silica surface having
enough available surface silanols (Degussa Aerosil 200,
number of surface silanols equal ca. 4.9 OH/nm2). After
88 h, the reaction is complete, affording the expected
silica surface species characterized by three broad
carbonyl bands (in Nujol: νCO 2121 (m, br), 2035 (s, br),
and 1955 (m, br) cm-1) along with small traces of [H4-
Os4(CO)12], [H4Os10(CO)24]2-, and [H5Os10(CO)24]-, which
were easily removed from the silica surface by extraction
with dichloromethane (neutral cluster) and acetonitrile
(anionic clusters) and then identified by infrared and
1H NMR spectroscopy (see Experimental Section). The
remaining silica-anchored osmium carbonyl species
were extracted with aqueous HCl, affording a mixture
of fac-[Os(CO)3Cl3]- and cis-[Os(CO)2Cl4]2-, which con-
firms the presence of Os(II) surface species and the
parallel presence of both (CO)3OsII and (CO)2OsII moi-
eties as first proposed.1 As in the homogeneous models,
this thermal degradation is much faster in air then
Con clu sion
The information obtained in this work (see Schemes
1 and 2), through the study of the reactivity and thermal
behavior of surface molecular models such as [Os3(CO)10-
(µ-H)(µ-OSiR2R′)] (R ) Et, Ph; R′ ) Et, Ph, OH, OSiPh2-
OH), led to a clarification of aspects of the surface
chemistry of the silica-anchored species [Os3(CO)10(µ-
H)(µ-OSit)] still to be fully defined.
Remarkably, the study of the thermal behavior of
[Os3(CO)10(µ-H)(µ-OSiEt3)] dissolved in triethylsilanol
(to mimic a silica surface with available surface silanols)
or triglyme (to mimic a highly dehydroxylated silica
surface) clarifies definitively the controversy on the
nature of the products formed by thermal degradation
of silica-anchored [Os3(CO)10(µ-H)(µ-OSit)].28 In the
absence of silanol groups only a thermal degradation
occurs, to produce by pyrolysis some high-nuclearity
clusters, including anionic clusters, confirming that the
growth to high-nuclearity osmium species reported to
occur on the surface by Wells et al.15 was due, as also
suggested by one of us,28 not only to the high rate of
heating but also mainly to the very low concentration
on the surface of reactive silanol groups. In addition,
we produced direct evidence that on a silica surface
having enough reactive silanol groups, the breakdown
of the cluster structure occurs easily by oxidative
addition of the silanol groups with formation of both
(CO)3OsII and (CO)2OsII surface anchored fragments, as
one of us proposed for the first time.1 In fact, the
isolation in excellent yields by thermal degradation of
[Os3(CO)10(µ-H)(µ-OSiEt3)] in triethylsilanol of a mo-
lecular species that, on the basis of an extended
spectroscopic and chemical evidence, we propose to be
[Os(CO)3(µ-OSiEt3)2(OSiEt3)(H)Os(CO)2]n, where n is
(36) Granger, P.; Harris, R. K. Eds. Multinuclear Magnetic Reso-
nance in Liquids and Solids-Chemical Applications; NATO ASI Series
C: Mathematical and Physical Sciences; Kluwer Academic: Amster-
dam, 1990; Vol. 322.
(37) Benn, R.; Brenneke, H.; J oussen, E.; Lehmkuhl, H.; Ortiz, F.
L. Organometallics 1990, 9, 756.
(38) Nyholm, R. S.; Truter, M. R.; Bradford, C. W. Nature 1970, 228,
648.
(39) Rundle, R. E.; Sturdivant, J . H. J . Am. Chem. Soc. 1947, 69,
1561.
(40) (a) Spiro, T. G.; Templeton, D. H.; Zalkin, A. Inorg. Chem. 1968,
7, 2165. (b) Preston, H. S.; Mills, J . C.; Kennard, C. H. L. J . Organomet.
Chem. 1968, 14, 447.
(41) Braterman, P. S. J . Chem. Soc. A 1968, 2907.
(42) Herberhold, M.; Suss, G.; Ellermann, J .; Gabelein, H. Chem.
Ber. 1978, 111, 2931.
(43) Mysov, E. I.; Akhrem, I. S.; Avetisyan, D. V. Org. Mass
Spectrom. 1976, 11, 358.

Surface Chemistry of [Os3(CO)10(µ-H)(µ-OSit)]
Organometallics, Vol. 20, No. 9, 2001 1731
FAB- MS), Hewlett-Packard 5988 (ESI+ MS). Elemental
analyses were carried out in the analytical laboratory of our
department.
probably 2, not only confirms the degradation of the
original cluster to silica-anchored (CO)3OsII and (CO)2-
OsII fragments linked by bridging silanolates, as orig-
inally proposed,1 but also gives additional direct evi-
dence that the process of thermal degradation of
[Os3(CO)10(µ-H)(µ-OSit)] produces surface hydridic
osmium species as suggested by one of us.14
The presence on the silica surface of stable hydridic
species would explain some aspects of the catalytic
properties toward olefin isomerization of the Os(II)
carbonyl species anchored to silica produced by thermal
degradation of [Os3(CO)10(µ-H)(µ-OSit)]; this isomer-
ization was reported to increase by working in the
presence of hydrogen.10b
Another remarkable observation reached in the course
of this work is the evidence that, as reported for [Os3-
(CO)10(µ-H)(µ-OSit)],1 the thermal degradation of the
model [Os3(CO)10(µ-H)(µ-OSiEt3)] occurs more easily
under oxygen than under nitrogen, producing a molec-
ular Os(II) carbonyl species with a ratio of CO to Os of
2.5, not too far from the value of 2.7 obtained by a
temperature-programmed decomposition and oxidation
of the Os(II) carbonyl species generated on the silica
surface by thermal degradation of [Os3(CO)10(µ-H)-
(µ-OSit)].32
Finally, we produced strong chemical evidence that
not only is the silica-anchored species [Os3(CO)10(µ-H)-
(µ-OSit)] easily attacked by water or alcohols but it can
also be the intermediate in the silica-mediated synthesis
of different osmium carbonyl clusters, starting from
OsCl3 or [Os(CO)3Cl2]2.12,13
Hyd r olysis of [Os3(CO)10(µ-H)(µ-OSiP h 2R′)] (R′ ) P h ,
OH, OSiP h 2OH). [Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)]9a (20
mg, 0.016 mmol) was dissolved in toluene (10 mL) in a two-
necked flask, equipped with a magnetic stirrer, a condenser,
and a thermometer and stirred under nitrogen in the presence
of water (5 mL). After a few days at room temperature, no
1
reaction occurred, as shown by H NMR spectroscopy. When
the reaction mixture was heated at reflux temperature (95 °C),
the hydrolysis took place, affording [Os3(CO)10(µ-H)(µ-OH)]18
in quantitative yield (1H NMR) after 9 h. The hydrolysis was
complete in less than 4 h by working at 125 °C with the
biphasic solvent system water (1 mL)/anisole (20 mL). Under
these conditions, [Os3(CO)10(µ-H)(µ-OSiPh3)]9a and [Os3(CO)10-
(µ-H)(µ-OSiPh2OH)]9a were also readily hydrolyzed, as shown
1
by the appearance of the typical H NMR hydridic signal at δ
-12.64 ppm (in CDCl3).18
Rea ction of [Os3(CO)10(µ-H)(µ-OSiP h 2OSiP h 2OH)] w ith
1-Bu ta n ol. A solution of [Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2-
OH)]9a (49.0 mg, 0.039 mmol) in anhydrous 1-butanol (8 mL)
was heated under nitrogen at 118 °C in a two-necked flask
equipped with a magnetic stirrer, a condenser, and a ther-
mometer. After 5 h, evaporation to dryness of the solution,
followed by recrystallization (pentane), afforded pure [Os3-
(CO)10(µ-H)(µ-OBun)]18 (28.6 mg, 0.031 mmol; 80% yield).
Under these conditions, [Os3(CO)10(µ-H)(µ-OSiPh3)]9a and [Os3-
(CO)10(µ-H)(µ-OSiPh2OH)]9a also reacted to generate [Os3-
1
(CO)10(µ-H)(µ-OBun)], as shown by H NMR spectroscopy.18
R ed u ct ion of [Os3(CO)10(µ-H)(µ-OSiP h 2OSiP h 2OH)],
[Os3(CO)10(µ-H)(µ-OSiP h 3)], [Os3(CO)10(µ-H)(µ-OSiP h 2OH)],
a n d [Os3(CO)10(µ-H)(µ-OH)] u n d er CO. (i) Red u ction of
[Os3(CO)10(µ-H)(µ-OSiP h 2OSiP h 2OH)]. A solution of [Os3-
(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)]9a (55.6 mg, 0.044 mmol) in
anhydrous triglyme (28 mL) was heated under a flux of CO (1
atm) at 160 °C in a three-necked flask equipped with a
condenser, a thermometer, and a magnetic stirrer. The reac-
tion was followed by infrared spectroscopy in the carbonyl
region by monitoring the appearance of the bands character-
istic for [Os3(CO)12]. After 2.5 h the reaction was complete. The
solution was cooled at -20 °C in order to precipitate [Os3-
(CO)12]. Filtration followed by washing with pentane (ca. 3
mL), to remove the last drops of triglyme eventually present,
afforded pure [Os3(CO)12] (31.4 mg, 0.035 mmol; 79% yield).
[Ph2SiO]4 was present in the triglyme solution, since the EI
mass spectrum showed the molecular ion peak of the tet-
rameric species at m/e 792 [M]+. As a consequence, during the
reductive carbonylation, the silanolate ligand is converted to
the tetrameric species [Ph2SiO]4 and some water is evolved in
this condensation process; however, traces of [Os3(CO)10(µ-H)-
(µ-OH)] could not be detected by 1H NMR or by mass
spectrometry even in the first stage of the reaction: for
example, by stopping the reaction after 30 min. This latter
observation confirms that the reduction does not proceed via
previous hydrolysis of the silanolate ligand.
In conclusion, for the first time, molecular silanolate
models of surface species such as [Os3(CO)10(µ-H)-
(µ-OSit)] are used not only as tools to define structural
aspects but also as springboards to understand their
surface chemistry on the silica surface. Work is in
progress in our laboratory to prepare and characterize
new Os(II) compounds by thermal degradation of sil-
anolate models with more complex silanolate ligands9b
that mimic even better the complexity of the silica
surface and could give crystalline compounds good for
a full X-ray characterization of their structure.
Exp er im en ta l Section
Gen er a l Com m en ts. [Os3(CO)10(µ-H)(µ-OH)]18 and [Os3-
(CO)10(µ-H)(µ-OSit)]10,18 were prepared according to the lit-
erature. [Os3(CO)10(µ-H)(µ-OSiPh2R′)] (R′ ) Ph, OH, OSiPh2-
OH) molecular models were prepared as recently reported9a
by heating, at 138 °C under N2, an anhydrous m-xylene
solution of [Os3(CO)10(µ-H)(µ-OH)] and the corresponding
R′Ph2SiOH (molar ratio (Ph3SiOH or HOSiPh2OSiPh2OH):[Os3-
(CO)10(µ-H)(µ-OH)] ) 2:1, reaction time 4 h; molar ratio Ph2-
Si(OH)2:[Os3(CO)10(µ-H)(µ-OH)] ) 60:1, reaction time 50 min),
whereas [Os3(CO)10(µ-H)(µ-OSiEt3)] was prepared by heating,
at 138 °C under N2 for 2.5 h, an anhydrous Et3SiOH solution
of [Os3(CO)10(µ-H)(µ-OH)] (molar ratio Et3SiOH:[Os3(CO)10(µ-
H)(µ-OH)] ) 9:1). Most gases (N2, CO, H2) were dried by
flowing over Drierite, whereas air was dried by flowing over
molecular sieves (4 Å) at -78 °C and then over P2O5. For some
reactions (see below) N2 was deoxygenated on a copper BASF
catalyst. The organic solvents were usually dried over molec-
ular sieves (3 Å). Products were purified by recrystallization
or by column chromatography using silica gel 60. Spectroscopic
data were obtained by use of the following spectrometers:
Bruker-Vector 22 or J asco FT-IR 420 (IR), Bruker DRX-300
(1H NMR, 13C NMR, and 29Si NMR), Varian VG9090 (EI and
Red u ction in th e P r esen ce of K2CO3. A suspension of
[Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)]9a (55.6 mg, 0.044 mmol)
in anhydrous ethylene glycol (25 mL) added to K2CO3 (185 mg,
1.34 mmol; molar ratio K2CO3:Os ) 10:1) was heated under a
flux of CO (1 atm) at 160 °C in a three-necked flask equipped
with a condenser, a thermometer, and a magnetic stirrer. The
reaction was followed by infrared spectroscopy in the carbonyl
region by monitoring the appearance of the bands character-
istic for [H3Os4(CO)12]-. After 14 h the reaction was complete.
The solution was extracted with [NBu4]I (35.0 mg, 0.095 mmol)
dissolved in CH2Cl2 (35 mL). The dichloromethane solution
was evaporated to dryness, affording a brown residue which
was washed twice with water (2 × 5 mL), to remove the excess
of [NBu4]I, and then purified by column chromatography on

1732 Organometallics, Vol. 20, No. 9, 2001
Lucenti et al.
silica using CH2Cl2 as eluent, to obtain pure [NBu4][H3Os4-
(CO)12] (31.8 mg, 0.024 mmol; 72% yield).
afforded pure [H4Os4(CO)12] (24.3 mg, 0.022 mmol; 61% yield).
Traces of [H4Os10(CO)24]2- and [H5Os10(CO)24]- were present
in the filtered triglyme solution, as suggested by infrared
spectroscopy in the carbonyl region.33,44 Even in the first stage
of the reaction, traces of [Os3(CO)10(µ-H)(µ-OH)] could not be
detected by 1H NMR or by mass spectrometry, suggesting that
the reduction does not proceed via preliminary hydrolysis of
the silanolate ligand.
(ii) Red u ction of [Os3(CO)10(µ-H)(µ-OSiP h 2OH)]. A solu-
tion of [Os3(CO)10(µ-H)(µ-OSiPh2OH)]9a (72.8 mg, 0.068 mmol)
in anhydrous triglyme (10 or 14 mL) was heated under a flux
of CO (1 atm) at 160 °C in a three-necked flask equipped with
a condenser, a thermometer, and a magnetic stirrer. The
reaction was followed by infrared spectroscopy in the carbonyl
region by monitoring the appearance of the bands character-
istic for [Os3(CO)12]. After 3.5 h, the solution was cooled at -20
°C in order to precipitate [Os3(CO)12]. Filtration followed by
washing with pentane (ca. 3 mL), to remove the last drops of
triglyme eventually present, afforded pure [Os3(CO)12] (36.7
mg, 0.040 mmol; 59% yield). The triglyme solution was
evaporated to dryness, and the residue was analyzed by mass
spectrometry; both EI and FAB- mass spectra showed the
molecular ion peak of the trimer [Ph2SiO]3 at m/e 594.
(iii) Red u ction of [Os3(CO)10(µ-H)(µ-OSiP h 3)]. A solution
of [Os3(CO)10(µ-H)(µ-OSiPh3)]9a (63.0 mg, 0.056 mmol) in
anhydrous triglyme (14 mL) was heated under a flux of CO (1
atm) at 160 °C in a three-necked flask equipped with a
condenser, a thermometer, and a magnetic stirrer. The reac-
tion was followed by infrared spectroscopy in the carbonyl
region by monitoring the appearance of the bands character-
istic for [Os3(CO)12]. After 3 h, the solution was cooled at -20
°C in order to precipitate [Os3(CO)12]. Filtration followed by
washing with pentane (ca. 3 mL), to remove the last drops of
triglyme eventually present, afforded pure [Os3(CO)12] (36.2
mg, 0.040 mmol; 71% yield).
(iv) Red u ction of [Os3(CO)10(µ-H)(µ-OH)]. A solution of
[Os3(CO)10(µ-H)(µ-OH)]18 (36.0 mg, 0.041 mmol) in anhydrous
triglyme (28 mL) was heated under a flux of CO (1 atm) at
160 °C in a three-necked flask equipped with a condenser, a
thermometer, and a magnetic stirrer. The reaction was fol-
lowed by infrared spectroscopy in the carbonyl region by
monitoring the appearance of the bands characteristic for [Os3-
(CO)12]. After 2 h the reaction was complete. The solution was
cooled at -20 °C in order to precipitate [Os3(CO)12]. Filtration
followed by washing with pentane (ca. 3 mL), to remove the
last drops of triglyme eventually present, afforded pure [Os3-
(CO)12] (31.4 mg, 0.035 mmol; 84% yield).
Red u ction in th e P r esen ce of K2CO3. A solution of [Os3-
(CO)10(µ-H)(µ-OH)]18 (65.0 mg, 0.075 mmol) in anhydrous
ethylene glycol (22 mL) added to K2CO3 (310 mg, 2.25 mmol;
molar ratio K2CO3:Os ) 10:1) was heated under a flux of CO
(1 atm) at 160 °C in a three-necked flask equipped with a
condenser, a thermometer, and a magnetic stirrer. The reac-
tion was followed by infrared spectroscopy in the carbonyl
region by monitoring the appearance of the bands character-
istic for [H3Os4(CO)12]-. After 14 h the reaction was complete.
The solution was extracted with [NBu4]I (46.1 mg, 0.125 mmol)
dissolved in CH2Cl2 (50 mL). The dichloromethane solution
was evaporated to dryness, affording a brown residue which
was washed twice with water (2 × 5 mL), to remove the excess
of [NBu4]I, and then purified by column chromatography on
silica using CH2Cl2 as eluent, to obtain pure [NBu4][H3Os4-
(CO)12] (45.5 mg, 0.034 mmol; 60% yield).
R ed u ct ion of [Os3(CO)10(µ-H)(µ-OSiP h 2OSiP h 2OH)],
[Os3(CO)10(µ-H)(µ-OSiP h 3)], [Os3(CO)10(µ-H)(µ-OSiP h 2OH)],
a n d [Os3(CO)10(µ-H)(µ-OH)] u n d er H2. (i) Red u ction of
[Os3(CO)10(µ-H)(µ-OSiP h 2OSiP h 2OH)]. A solution of [Os3-
(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)]9a (60.8 mg, 0.048 mmol) in
anhydrous triglyme (10 mL) was heated under a flux of H2 (1
atm) at 160 °C in a three-necked flask equipped with a
condenser, a thermometer, and a magnetic stirrer. The reac-
tion was followed by infrared spectroscopy in the carbonyl
region by monitoring the appearance of the bands character-
istic for [H4Os4(CO)12]. After 30 min the reaction was complete.
The solution was cooled at -20 °C in order to precipitate [H4-
Os4(CO)12]. Filtration followed by washing with pentane (ca.
3 mL), to remove the last drops of triglyme eventually present,
(ii) Red u ction of [Os3(CO)10(µ-H)(µ-OSiP h 2OH)]. A solu-
tion of [Os3(CO)10(µ-H)(µ-OSiPh2OH)]9a (84.0 mg, 0.079 mmol)
in anhydrous triglyme (14 mL) was heated under a flux of H2
(1 atm) at 160 °C in a three-necked flask equipped with a
condenser, a thermometer, and a magnetic stirrer. The reac-
tion was followed by infrared spectroscopy in the carbonyl
region by monitoring the appearance of the bands character-
istic for [H4Os4(CO)12]. After 1 h the reaction was complete.
The solution was cooled at -20 °C in order to precipitate [H4-
Os4(CO)12]. Filtration followed by washing with pentane (ca.
3 mL), to remove the last drops of triglyme eventually present,
afforded pure [H4Os4(CO)12] (41.3 mg, 0.037 mmol; 64% yield).
Minor traces of [H4Os10(CO)24]2- and [H5Os10(CO)24]- were
present in the filtered triglyme solution, as suggested by
infrared spectroscopy in the carbonyl region;34,44 the presence
1
of [H4Os10(CO)24]2- was confirmed also by H NMR spectros-
copy (in CD3COCD3: δ -16.4 ppm).33,44
(iii) Red u ction of [Os3(CO)10(µ-H)(µ-OSiP h 3)]. A solution
of [Os3(CO)10(µ-H)(µ-OSiPh3)]9a (44.0 mg, 0.039 mmol) in
anhydrous triglyme (14 mL) was heated under a flux of H2 (1
atm) at 160 °C in a three-necked flask equipped with a
condenser, a thermometer, and a magnetic stirrer. The reac-
tion was followed by infrared spectroscopy in the carbonyl
region by monitoring the appearance of the bands character-
istic for [H4Os4(CO)12]. After 30 min the reaction was complete.
The solution was cooled at -20 °C in order to precipitate [H4-
Os4(CO)12]. Filtration followed by washing with pentane (ca.
3 mL), to remove the last drops of triglyme eventually present,
afforded pure [H4Os4(CO)12] (20.3 mg, 0.018 mmol; 63% yield).
Minor traces of [H4Os10(CO)24]2- and [H5Os10(CO)24]- were
present in the filtered triglyme solution, as suggested by
infrared spectroscopy in the carbonyl region.33,44
(iv) Red u ction of [Os3(CO)10(µ-H)(µ-OH)]. A solution of
[Os3(CO)10(µ-H)(µ-OH)]18 (35.8 mg, 0.041 mmol) in anhydrous
triglyme (20 mL) was heated under a flux of H2 (1 atm) at 160
°C in a three-necked flask equipped with a condenser, a
thermometer, and a magnetic stirrer. The reaction was fol-
lowed by infrared spectroscopy in the carbonyl region by
monitoring the appearance of the bands characteristic for [H4-
Os4(CO)12]. After 30 min, the reaction was complete. The
solution was cooled at -20 °C in order to precipitate [H4Os4-
(CO)12]. Filtration followed by washing with pentane (ca. 3
mL), to remove the last drops of triglyme eventually present,
afforded pure [H4Os4(CO)12] (22.2 mg, 0.020 mmol; 65% yield).
Minor traces of [H4Os10(CO)24]2- and [H5Os10(CO)24]- were
present in the filtered triglyme solution, as suggested by
infrared spectroscopy in the carbonyl region.33,44
Th er m a l Degr a d a tion of [Os3(CO)10(µ-H)(µ-OSiEt3)]. A
solution of [Os3(CO)10(µ-H)(µ-OSiEt3)]9a (70.2 mg, 0.071 mmol)
in anhydrous triethylsilanol (1.8 mL), prepared under N2 in
the closed reaction vessel (height 17 cm; diameter 3 cm)
previously described,34 was treated under vacuum (10-2 Torr)
at 25 °C and then exposed to dried air at atmospheric pressure.
The bottom of the vessel (about half of the cylinder) was put
in an oven and heated at 200 °C. The reaction was monitored
by infrared spectroscopy in the carbonyl region; samples were
taken from the glass vessel at room temperature and analyzed
after dilution in dichloromethane. After ca. 4 h, the reaction
was complete and a black precipitate was present. The
triethylsilanol solution was taken from the reaction vessel,
(44) Lucenti, E.; Roberto, D.; Roveda, C.; Ugo, R.; Cariati, E. J .
Cluster Sci., in press.

Surface Chemistry of [Os3(CO)10(µ-H)(µ-OSit)]
Organometallics, Vol. 20, No. 9, 2001 1733
while the precipitate was washed with pentane (ca. 10 mL).
Further treatment of the precipitate with dichloromethane (ca.
10 mL) afforded yellow [H4Os4(CO)12] (6.7 mg, 0.006 mmol;
11% yield), whereas evaporation to dryness of the combined
pentane and triethylsilanol solutions gave 64.6 mg of a brown
oil. In the last drops of distillate, minor amounts of Et3-
SiOSiEt3 (29Si NMR in CDCl3, δ (ppm) 8.51; 1H NMR in CDCl3,
δ (ppm) 0.56 (q, 12 H, 6 CH2), 0.96 (t, 18 H, 6 CH3); MS (EI)
m/e 246 [M]+, 217 [M - Et]+) were present together with Et3-
SiOH (29Si NMR in CDCl3, δ (ppm) 19.28; 1H NMR in CDCl3,
δ (ppm) 0.62 (q, 12 H, 6 CH2), 0.99 (t, 18 H, 6 CH3); MS (EI)
m/e 132 [M]+, 103 [M - Et]+) and small traces of Et3SiOSiEt2-
OSiEt3 (MS (EI) m/e 319 [M - Et]+) and Et3Si(OSiEt2)2OSiEt3
(MS (EI) m/e 421 [M - Et]+).43 These Et3Si(OSiEt2)nOSiEt3
species (n ) 0-2) were also formed by heating in dried air
pure triethylsilanol in the closed reaction vessel at 200 °C for
4 h, as confirmed by 29Si NMR spectroscopy and by mass
spectrometry.
the carbonyl bands in the infrared spectrum of the organic
phase, was complete. Evaporation of the aqueous phase
afforded a mixture of fac-[Os(CO)3Cl3]- and cis-[Os(CO)2Cl4]2-
(molar ratio 1:1) as confirmed by infrared spectroscopy in
ethanol.35 Addition of [NBu4]Cl followed by evaporation of the
solvent and column chromatography on silica (eluent CH3OH)
afforded first fac-[NBu4][Os(CO)3Cl3] (IR in CH2Cl2, νCO 2115
(m), 2023 (s) cm-1) and then cis-[NBu4]2[Os(CO)2Cl4] (IR in
CH2Cl2, νCO 2012 (s), 1922 (s) cm-1) in the ratio 1:1. The
reaction of [Os(CO)3(µ-OSiEt3)2(OSiEt3)(H)Os(CO)2]n, dissolved
in CDCl3, with 36% aqueous HCl was also followed by 29Si
NMR spectroscopy: after 2 days the signals at δ 29.7 and 27.5
ppm were replaced by an intense signal at δ 8.51 ppm (due to
Et3SiOSiEt3) and a weak signal at δ 36.13 ppm (due to Et3-
SiCl). A blank experiment showed that Et3SiOH reacts with
36% aqueous HCl more rapidly (the reaction is complete in
ca. 40 min) than [Os(CO)3(µ-OSiEt3)2(OSiEt3)(H)Os(CO)2]n,
affording Et3SiCl only.
The crude brown oil was purified by column chromatography
on silica using as eluent hexane, to obtain a colorless oil (50.3
mg, 0.028 mmol; 52% yield with respect to starting [Os3(CO)10-
(µ-H)(µ-OSiEt3)]). It was characterized as [Os(CO)3(µ-OSiEt3)2-
(OSiEt3)(H)Os(CO)2]n by elemental analysis (Anal. Calcd: C,
30.18; H, 5.03. Found: C, 31.67; H, 4.92), mass spectrometry
(in both the EI and the FAB- mass spectra, there is a peak at
m/e 916 which corresponds to the fragment “Os(CO)3(µ-
OSiEt3)2(OSiEt3)(H)Os(CO)2”, followed by an intense peak at
m/e 888 that could correspond to the loss of one CO; in the
ESI+ mass spectrum in CH3CN there are peaks at m/e 1914,
998, and 970 that correspond to [Os(CO)3(µ-OSiEt3)2(OSiEt3)-
(H)Os(CO)2]2‚2CH3CN, [Os(CO)3(µ-OSiEt3)2(OSiEt3)(H)Os(CO)2]‚
2CH3CN, and [Os(CO)3(µOSiEt3)2(OSiEt3)(H)Os(CO)2]‚2CH3-
CN with loss of one CO, respectively), infrared spectroscopy
(ii) Wit h CO. A solution of [Os(CO)3(µ-OSiEt3)2(OSiEt3)-
(H)Os(CO)2]n (62.8 mg, 0,034 mmol) in anhydrous triethyl-
silanol (2.0 mL) was heated under CO (1 atm) at 200 °C in
the closed reaction vessel previously described.34 During the
reaction a yellow precipitate was formed whereas, in parallel,
a yellow powder sublimed on the cold walls of the vessel. After
5 days the triethylsilanol solution, containing some unreact-
ed [Os(CO)3(µ-OSiEt3)2(OSiEt3)(H)Os(CO)2]n, was separated,
whereas the sublimate and the precipitate were combined and
chromatographed on a silica column, affording pure [Os3(CO)12]
(20.6 mg, 0.023 mmol; 50% yield).
Th er m a l Degr a d a t ion of [Os3(CO)10(µ-H )(µ-OSit)].
Silica-anchored [Os3(CO)10(µ-H)(µ-OSit)]10,18 (1.824 g; 1.74 wt
% Os with respect to SiO2) was transferred into the closed
reaction vessel (height 17 cm; diameter 3 cm) previously
described,34 treated under vacuum (10-2 Torr) at 25 °C and
then exposed to deoxygenated N2 at atmospheric pressure. The
bottom of the vessel (about half of the cylinder) was put in an
oven and heated at 200 °C. The reaction was monitored by
infrared spectroscopy in the carbonyl region; samples were
taken from the glass vessel at room temperature and analyzed
as Nujol mulls. After 88 h, the reaction was complete, affording
silica-anchored osmium carbonyl species (in Nujol, νCO 2121
(m, br), 2035 (s, br) and 1955 (m, br) cm-1) along with traces
of [H4Os4(CO)12], [H4Os10(CO)24]2-, and [H5Os10(CO)24]-, which
were removed from the silica surface with dichloromethane
(neutral cluster) and acetonitrile (anionic clusters) and then
identified by infrared and 1H NMR spectroscopy.20,33,44 The
remaining silica-anchored osmium carbonyl species were
quantitatively extracted from the surface with aqueous HCl,
affording, after evaporation of the aqueous solution to dryness,
(in CH2Cl2, νCO 2115 (s), 2021 (vs, br), 2008 (s), 1921 (s) cm-1
;
in hexane, νCO 2112 (s), 2020 (sh), 2017 (vs), 1933 (s) cm-1),
1H NMR spectroscopy (in CDCl3: δ (ppm) 1.098 (t, 9 H, 3 CH3,
J ) 7.9 Hz), 1.078 (t, 18 H, 6 CH3, J ) 7.6 Hz), 0.809 (q, 6 H,
3 CH2, J ) 7.9 Hz), 0.800 (q, 12 H, 6 CH2, J ) 7.6 Hz), -14.68
(s, 1 H, HOs, J (187Os-1H) ) 94 Hz)), 29Si NMR spectroscopy
1
(in CDCl3, δ (ppm) 29.71 (2 OSiEt3), 27.57 (1 OSiEt3)) and 13C
NMR spectroscopy (in CDCl3, δ (ppm) 7.67 (9 CH3), 8.17 (9
CH2), 181.16 (cis-(CO)2Os); 169.99 and 169.63 (fac-(CO)3Os)
by analogy with the 13C NMR spectrum of fac-[Os(CO)3Cl2-
(acetone)], two signals at δ (ppm) 167.75 and 166.34).
Heteronuclear multiple quantum correlation (HMQC) spec-
troscopy with the bilinear rotation decoupling (BIRD) tech-
nique showed that the hydridic signal is coupled selectively
to the CO’s at 181.16 ppm.
The same species [Os(CO)3(µ-OSiEt3)2(OSiEt3)(H)Os(CO)2]n
was also formed, along with traces of [H4Os4(CO)12], by thermal
degradation under deoxygenated N2 of [Os3(CO)10(µ-H)(µ-
OSiEt3)] (15.0 mg, 0.015 mmol) dissolved in triethylsilanol
(0.75 mL). However, the reaction was slower than when it was
carried out in air, being not complete even after 19 h.
In addition, in pure anhydrous triglyme (12 mL) under
deoxygenated N2 at 200 °C, [Os3(CO)10(µ-H)(µ-OSiEt3)] (15.7
mg, 0.016 mmol) was rapidly (less than 2 h) converted to
mixtures of [H4Os4(CO)12] and [H5Os10(CO)24]-, as shown by
the infrared and 1H NMR spectra20,33 in CD3CN of the crude
residue obtained after evaporation to dryness of the triglyme
solution; the two clusters can be easily separated, since the
solubility of [H4Os4(CO)12] in dichloromethane is different from
that of [H5Os10(CO)24]-.44
a
mixture of fac-[Os(CO)3Cl3]- and cis-[Os(CO)2Cl4]2-, as
confirmed by infrared spectroscopy of the solid residue in both
ethanol and Nujol.35 The thermal degradation of silica-
anchored [Os3(CO)10(µ-H)(µ-OSit)] was much faster in air then
under N2, being complete in ca. 3 h and affording the same
dicarbonyl- and tricarbonylosmium(II) species only.
Ack n ow led gm en t. We deeply thank Dr. Matteo
Garegnani for some experimental help, Prof. Tiziana
Beringhelli (Universita` di Milano) for fruitful discus-
sions, Prof. Giovanni Galli (Universita` di Milano) for
ESI+ mass spectra, and Mr. Pasquale Illiano and Mr.
1
Americo Costantino for running H, 13C, and 29Si NMR
spectra. This work was supported by the Ministero
dell’Universita` e della Ricerca Scientifica e Tecnologica
and by the Consiglio Nazionale delle Ricerche (CNR,
Roma).
Reactivity of th e P r oposed [Os(CO)3(µ-OSiEt3)2(OSiEt3)-
(H)Os(CO)2]n . (i) With Aqu eou s HCl. In a two-necked flask,
[Os(CO)3(µ-OSiEt3)2(OSiEt3)(H)Os(CO)2]n (11.0 mg, 0.006 mmol)
was dissolved in hexane (8 mL) and stirred vigorously, at room
temperature, with 36% aqueous HCl (8 mL). After 2 days the
reaction, which was followed by monitoring the decrease of
OM000858X