Synthesis and characterization of osmium-containing silsesquioxanes: High-yield routes to {Os3(CO)10(μ-H)[μ-OSi 7O10(c-C6H11)7]} and the new clusters {Os3(CO)10</

Article abstract of DOI:10.1021/om060844c

The reactions of [Os₃(CO)₁₀(μ-H)(μ-OH)] (3) with the incompletely condensed silsesquioxanes [(c-C₆H ₁₁)₇Si₇O₉(OH)₃] (1) and [(c-C₆H₁₁)₈

Full text of DOI:10.1021/om060844c

Organometallics 2007, 26, 75-82
75
Synthesis and Characterization of Osmium-Containing
Silsesquioxanes: High-Yield Routes to
{Os3(CO)10(µ-H)[(µ-O)Si7O10(c-C6H11)7]} and the
New Clusters {Os3(CO)10(µ-H)[(µ-O)Si7O9(OH)2(c-C6H11)7]},
{[Os3(CO)10(µ-H)]2(µ-O)2Si7O9(OH)(c-C6H11)7},
{Os3(CO)10(µ-H)[(µ-O)Si8O11(OH)(c-C6H11)8]}, and
{[Os3(CO)10(µ-H)]2(µ-O)2Si8O11(c-C6H11)8}
Elena Lucenti,*,† Frank J. Feher,‡,§ and Joseph W. Ziller‡
Istituto di Scienze e Tecnologie Molecolari del CNR, Via C. Golgi 19, 20133 Milano, Italy, and
Department of Chemistry, UniVersity of California, IrVine, California 92697-2025
ReceiVed September 14, 2006
The reactions of [Os3(CO)10(µ-H)(µ-OH)] (3) with the incompletely condensed silsesquioxanes [(c-
C6H11)7Si7O9(OH)3] (1) and [(c-C6H11)8Si8O11(OH)2] (2) afford in high yield {Os3(CO)10(µ-H)[(µ-O)-
Si7O10(c-C6H11)7]} (4) and the new compounds {Os3(CO)10(µ-H)[(µ-O)Si7O9(OH)2(c-C6H11)7]} (5),
{[Os3(CO)10(µ-H)]2(µ-O)2Si7O9(OH)(c-C6H11)7} (6), {Os3(CO)10(µ-H)[(µ-O)Si8O11(OH)(c-C6H11)8]} (8),
and {[Os3(CO)10(µ-H)]2(µ-O)2Si8O11(c-C6H11)8} (9), which are discrete molecular models of silica-anchored
[Os3(CO)10(µ-H)(µ-OSit)]. Compounds 6 and 9 represent the first examples of complexes containing
two [Os3(CO)10(µ-H)] cluster cores. The X-ray structures of 5, 8, and 9 are reported.
hydroxylated surface sites as ligands in the same way simple
alkoxides are used to prepare solution organometallic com-
pounds. Silica is the support most extensively used for modern
surface organometallic chemistry because its surface chemistry
is relatively simple and well established compared to many other
supports (e.g., alumina, metal oxides).
Introduction
Over the past two decades, “surface organometallic chemis-
try”1-5 has emerged as an important subdiscipline in the field
of heterogeneous catalysis. Numerous systems have been studied
in great detail,6-16 and it is now quite common to view
* Corresponding author. E-mail: e.lucenti@istm.cnr.it.
† Istituto di Scienze e Tecnologie Molecolari del CNR.
‡ University of California, Irvine.
One of the early success stories in surface organometallic
chemistry was the reaction of silica with [Os3(CO)12], which
produces a structurally well-defined silica-supported cluster
attached to the surface via a single siloxy group.17-26 A variety
of techniques were used to characterize this cluster, and its
structure was assigned unambiguously as [Os3(CO)10(µ-H)-
(µ-OSit)] on the basis of IR,17,18,27 Raman,22,23 and solid-state
NMR28 spectroscopies, EXAFS,20,29 and computer model-
§ Current address: Goodyear Technical Center, P.O. Box 3531, Akron,
Ohio 44309-3531.
(1) Basset, J. M., Gates, B. C., Candy, J. P., Choplin, A., Leconte, M.,
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Smith, A. K. In Fundamental Research in Homogeneous Catalysis; Tsutsui,
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10.1021/om060844c CCC: $37.00 © 2007 American Chemical Society
Publication on Web 12/02/2006

76 Organometallics, Vol. 26, No. 1, 2007
Lucenti et al.
ing24,30,31 or on the basis of its similarity to structurally analogous
homogeneous compounds (e.g., [Os3(CO)10(µ-H)(µ-OSiR3)]
(R ) Et, Ph).17,18,21,25,32,33 This work convincingly established
that (1) silica could indeed be viewed as a ligand, (2) the reaction
of silica with an organometallic compound could be highly
selective, and (3) the characterization of silica-supported com-
plexes could be achieved with a degree of accuracy and
confidence that is approaching the corresponding solution
organometallic complexes.
As the field of surface organometallic chemistry advances
and a clearer mechanistic understanding of surface chemistry
develops, it will become increasingly important to probe subtle
effects that are capable of providing low-energy pathways for
a variety of well-established surface reactions (e.g., chemisorp-
tion of metal carbonyls). One attractive approach for identifying
these effects is to study the reactivity of structurally well defined
solution complexes that possess the functionality present on a
surface. We34-39 and others40-53 have been using incompletely
condensed silsesquioxanes (e.g., 1 and 2) for this purpose, and
the collective results from this work provide a number of new
insights into the chemistry of both silica and silica-supported
catalysts.
Si-OH groups. The goal of our work was to determine whether
Os3 clusters juxtaposed to potentially reactive Si-OH groups
could interact via hydrogen bonding or undergo low-energy
reactions not seen with simpler silanols. The springboard for
this work was the recent development of a high-yield synthesis
of [Os3(CO)10(µ-H)(µ-OH)] (3),54 which is known to react
cleanly with silanolssincluding silanols with more than one
SiOH groupsto produce osmium carbonyl clusters with the
formula [Os3(CO)10(µ-H)(µ-OSiR2R′)] (R ) Et, Ph; R′ ) Et,
Ph, OH, OSiPh2OH).55 The results from our studies, as well as
their implications for the chemistry of silica-supported com-
plexes, are discussed below.
Results and Discussion
Reaction of [Os3(CO)10(µ-H)(µ-OH)] (3) with [(c-C6H11)7-
Si7O9(OH)3] (1): Synthesis of 4, 5, and 6. Trisilanol 1 does
not react significantly with 2 equiv of [Os3(CO)10(µ-H)(µ-OH)]
(3) in hydrocarbons heated at 80 °C for 6 h. Upon heating to
140 °C in m-xylene, both reagents were consumed over a period
1
of 3 h to produce a mixture of Os hydride complexes with H
NMR resonances (CDCl3) at δ -12.31, -12.46, and -12.55
1
with relative intensities of 6:35:59. Small H resonances were
also observed at δ -11.48, -12.03, -12.98, -14.94, -20.50,
and -21.35; the latter two were observed when pure 3 was
heated to 140 °C in m-xylene. (Trisilanol 1 is stable in m-xylene
at 140 °C.) Evaporation of the solvent and elution across silica
with CH2Cl2/hexanes afforded three compounds. The first to
elute with 1:9 CH2Cl2/hexane was 4 (1H δ -12.55), which was
identical in all respects to an authentic sample prepared via
reaction of trisilanol 1 with [Os3(CO)12] in refluxing octane.33
The second compound, which eluted with 1:9 CH2Cl2/hexane,
was subsequently identified as 6 (1H δ -12.03). The third
compound eluted with 2:1 CH2Cl2/hexane. This compound,
which crystallizes as a hydrogen-bonded dimer without inter-
actions between SiOH groups and the Os3 cluster (vide infra),
was identified as 5 (1H δ -12.46). The compound responsible
In this paper we present the results from our efforts to prepare
osmium-containing clusters with potentially reactive pendent
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1
for the H NMR resonance at δ -12.31 in the reaction crude
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1994, 86, 479.
(32) Evans, J.; Gracey, B. P. J. Chem. Soc., Dalton Trans. 1982, 1123.
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The combined isolated yield of 4, 5, and 6 is typically greater
than 70% based on available Os, but the relative amount of
each compound depends strongly on the relative amounts of
trisilanol 1 and of [Os3(CO)10(µ-H)(µ-OH)] (3) used in the
(42) Maschmeyer, T.; Klunduk, M. C.; Martin, C. M.; Shephard, D. S.;
Thomas, J. M.; Johnson, B. F. G. Chem. Commun. 1997, 1847.
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Cazat, J.; Basset, J. M.; Lesage, A.; Emsley, L. Angew. Chem., Int. Ed.
2001, 40, 4493.
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W.; Edelmann, F. T. Angew. Chem., Int. Ed. 2004, 43, 4603.
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Eur. J. 2004, 10, 1657.
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metallics 2000, 19, 1051.

Osmium-Containing Silsesquioxanes
Organometallics, Vol. 26, No. 1, 2007 77
Scheme 1
reaction, as well as the reaction time and temperature. When
the reaction was performed at 115 °C for 6 h with a 2:1 mixture
of 1 and 3, approximately two-thirds of the starting Os complex
reacted to produce 4 and 5 in a ∼1:1 ratio, respectively. After
12 h, the starting Os complex was completely consumed to
produce 4 and 5 in a 3:2 ratio. At 140 °C, the reaction of 1 and
3 (2:1) produces 4 and 5 with isolated yields of 35% and 39%
after 2.5 h; the corresponding yields of 4 and 5 after 6.5 h are
17% and 73%. Increasing the ratio of 1 to 3 did not improve
the selectivity for the formation of 5 versus 4. In fact, reactions
performed at 140 °C (3 h) with 5:1 or 10:1 mixtures of 1 and
3 actually showed a modest increase in selectivity for the
formation of 4 (from 1:1 to 3:1).
our observations is shown in Scheme 1. Step A in this
mechanism produces 5 via the reaction of trisilanol 1 and 3.
Complex 5 is observed early in our reactions, and it is the major
product (48% NMR yield) when 3 is reacted with an excess of
trisilanol 1 for short reaction times. The reaction of 5 with a
second equivalent of 3 produces 6 (step B), which is the product
favored when excess 3 is present and reaction times are
relatively short. At longer reaction times, 6 undergoes cycloe-
limination to produce 3 and 4 (step C). Another route to 4, which
appears to be much more facile under most conditions, involves
cycloelimination of 5 to produce 3 and trisilanol 7 (step D),
which subsequently condenses with 3 to produce 4 (step E).
This route is probably favored because the relative bulk and
electron-withdrawing nature of the Os3 carbonyl cluster combine
to produce a good leaving group on silicon. A third route to 4
might involve reversible metathesis of 5 and 7 to produce 4
and 1 (step F), but it seems more likely that this transformation
would involve catalysis by traces of water rather than direct
reaction of an Os-substituted silsesquioxane with another large
silsesquioxane framework.
Somewhat unexpectedly, the reaction of 1 with a 10-fold
excess of [Os3(CO)10(µ-H)(µ-OH)] (3) did not favor the
formation of 6 (or a derivative of 1 with three Os3 clusters).
Instead, 6 formed in trace amounts (along with 5) and the major
product was again 4. In contrast, the reaction of 5 with a 4-fold
excess of 3 (140 °C, 11.5 h) afforded 6 in 55% NMR yield
(27% isolated yield), as well as comparable amounts of 4 (24%
NMR yield). These results suggest that the formation of 6
competes with the formation of 4 only when 5 is the major
silicon-containing species in the reaction mixture.
Reactivity of {Os3(CO)10(µ-H)[(µ-O)Si7O10(c-C6H11)7]} (4)
with Et4NOH. The recent discovery that 7 reacts cleanly with
aqueous Et4NOH to afford 1 in high yield56 suggested that it
might be possible to produce 5 via the reaction of Et4NOH with
readily available 4. Unfortunately, this is not the case. The
addition of an equimolar amount of aqueous Et4NOH (20% or
35 wt %) to a solution of 4 in THF at 25 °C produces an imme-
diate color change from yellow to orange-brown. Neutralization
of this solution with a stoichiometric amount of aqueous HCl
followed by evaporation of the solvent afforded a brown residue,
which exhibited a prominent 1H NMR resonance for [Os3(CO)10-
(µ-H)(µ-OH)] (3) and several smaller resonances for other
unidentified Os-H hydride species. These results clearly
demonstrate that cleavage of the µ-OSi ligand from the osmium
The mechanisms by which 4, 5, and 6 are produced are not
known with certainty, but it appears that [Os3(CO)10(µ-H)-
(µ-OH)] (3) is both a reagent for the formation of 4-6 and a
catalyst for the cyclodehydration of 1 to 7. In the absence of 3,
trisilanol 1 is stable in m-xylene at 140 °C; no reaction is
observed after 2.5 h. Upon addition of a catalytic amount of 3
(5 mol %), trisilanol 1 undergoes clean cyclodehydration to
produce 7 with ∼70% conversion after 16 h at 140 °C. Base-
catalyzed cyclodehydration35 seems unlikely because [Os3-
(CO)10(µ-H)(µ-OH)] (3) is poorly Bronsted basic and because
the rate of cyclodehydration is similar to the rate for reactions
between 3 and other incompletely condensed silsesquioxanes
(e.g., 2, vide infra). The mechanism most consistent with all
(56) Feher, F. J.; Terroba, R.; Ziller, J. W. Chem. Commun. 1999, 2309.

78 Organometallics, Vol. 26, No. 1, 2007
Lucenti et al.
cluster is comparably facile to base-catalyzed hydrolytic cleave
of Si3O3 rings.
Reactivity of [Os3(CO)10(µ-H)(µ-OH)] (3) with [(c-
C6H11)8Si8O11(OH)2] (2): Synthesis of 8 and 9. In contrast to
reactions of trisilanol 1 with [Os3(CO)10(µ-H)(µ-OH)] (3), the
reaction of 3 with disilanol 2 is straightforward. The reaction
of 2 with an equimolar amount of 3 occurs cleanly in m-xylene
at 140 °C to afford a mixture of 8, 9, and unreacted 2. After
1
1 h, the hydride region of the H NMR spectrum (CDCl3) of
the reaction mixture exhibited two new signals at δ -12.31
(16%) and -12.40 (61%), as well as a resonance at δ -12.60
(23%) for unreacted 3. After 3 h at 140 °C, the resonance for
1
3 was gone and the hydride region of the H NMR spectrum
was dominated by the resonances at δ -12.31 (24%) and
-12.40 (71%). Small resonances were also observed at δ
-12.35 (4%), -20.48 (<1%), -21.26 (<1%), and -21.36
(<1%)). Evaporation of the reaction mixture and chromatog-
raphy on silica using CH2Cl2/hexanes afforded two compounds
in good yield. The first compound to elute (1:4 CH2Cl2/hexanes)
was 9, which exhibited a 1H NMR resonance at δ -12.31. The
second compound to elute (1:1 CH2Cl2/hexanes) was 8, which
exhibited a 1H NMR resonance at δ -12.40. Both compounds
were unambiguously identified on the basis of multinuclear
NMR spectroscopy data and single-crystal X-ray diffraction
studies.
Figure 1. ORTEP plot of 5 with thermal ellipsoids plotted at the
50% probability level. For clarity, only the ipso carbon atoms of
the cyclohexyl groups are shown. Selected distances (Å) and angles
(deg): Os1-Os2, 2.7955(3); Os1-Os3, 2.8424(3); Os2-Os3,
2.8101(3); Os1-O12, 2.131(3); Os2-O12, 2.125(3); Si1-O1,
1.625(4); Si1-O9, 1.622(3); Si1-O12, 1.632(3); Si3-O10, 1.638-
(4); Si5-O11, 1.644(3); other Si-O, 1.607-1.634; Os2-Os1-
Os3, 59.786(7); Os1-Os2-Os3, 60.936(8); Os2-Os3-Os1, 59.278-
(7); Si1-O12-Os1, 141.44(19); Si1-O12-Os2, 129.39(19); O1-
Si1-O12, 109.35(17); O9-Si1-O12, 106.08(18); Si1-O1-Si2,
153.5(2); Si1-O9-Si6, 143.4(2); other Si-O-Si, 143-166;
O-Si-O, 107-111.
The combined isolated yield of 8 and 9 is typically greater
than 80% based on the amount of 2 available. When the reaction
is performed in refluxing xylene (140 °C, 3.5 h) with a 2.5:1
molar ratio of 2 and 3, an 89:11 mixture of 8 and 9 was obtained,
as judged by an 1H NMR spectrum of the crude product mixture;
after chromatography on silica, the isolated yields of 8 and 9
were 74% and 10%, respectively. Higher yields of 9 can be
obtained by using larger amounts of 3 and longer reaction times,
but not without some decomposition of the Os cluster. For the
reaction of 2 with 2.0 molar equiv of 3, complete consumption
of the starting Os cluster requires 18 h at 140 °C and produces
a dark black reaction mixture. Evaporation of the solvent and
purification by column chromatography on neutral alumina
afforded 8 in 11% isolated yield and 9 in 70% isolated yield.
X-ray Structures of 5, 8, and 9. The molecular structures
of 5, 8, and 9 are shown in Figures 1-3. In each case, the three
Os atoms are arranged in a nearly isosceles triangle with two
long edges (2.81-2.84 Å) and one short edge (2.78-2.79 Å).
The short edge in the triosmium triangle is bridged by the
µ-oxygen-bonded silsesquioxane ligand and a hydrogen atom,
which was not located or refined. The short edge length is
coherent with the average Os-Os distance of 2.68 Å found by
EXAFS investigation of the silica-anchored cluster [Os3(CO)10-
(µ-H)(µ-OSit)].17 The average Os-O lengths of 2.08-2.13 Å
for the two osmium atoms bridged by µ-oxygen in clusters 5,
8, and 9 are in agreement with the Os-O distance of 2.16 Å
measured for the alumina-supported cluster [Os3(CO)10(µ-H)-
(µ-OAl<)].29 The interatomic distances and intrabond angles
within the Os3 clusters are not significantly different from those
in other crystallographically characterized Os3(CO)10-containing
clusters, including [Os3(CO)10(µ-H)(µ-Y)] with Y) OSiEt3,21
OSi7O10(c-C6H11)7,33 OSiPh2OH,55 and OSiPh2OSiPh2OH.55
Figure 2. ORTEP plot of 8 with thermal ellipsoids plotted at the
50% probability level. For clarity, only the ipso carbon atoms of
the cyclohexyl groups are shown. Selected distances (Å) and angles
(deg): Os1-Os2, 2.7841(11); Os1-Os3, 2.8175(11); Os2-Os3,
2.8206(10); Os1-O1, 2.085(13); Os2-O1, 2.095(11); Si1-O1,
1.684(13); Si1-O2, 1.653(14); Si1-O5, 1.603(14); Si7-O13,
1.655(15); other Si-O, 1.58-1.68; Os2-Os1-Os3, 60.47(3);
Os1-Os2-Os3, 60.35(3); Os1-Os3-Os2, 59.18(3); Si1-O1-
Os1, 128.6(7); Si1-O1-Os2, 132.0(7); O2-Si1-O1, 104.3(6);
O5-Si1-O1, 108.0(7); Si1-O2-Si2, 145.0(9); Si1-O5-Si4,
147.3(8); other Si-O-Si, 142-155; O-Si-O, 105-113.
Metrical data for the silsesquioxane framework are also within
their generally accepted ranges. In fact, there is no evidence
for distortion of the Si/O frameworks due to steric compression

Osmium-Containing Silsesquioxanes
Organometallics, Vol. 26, No. 1, 2007 79
complexes, the osmium clusters are unperturbed by the presence
of neighboring SiOH groups, which clearly prefer to avoid the
Os cluster by hydrogen bonding to each other (as well as SiOH
groups from a second molecule in the solid state). The stability
and unexceptional spectroscopic data for 6 also demonstrate that
osmium clusters are unperturbed by the presence of other
osmium clusters. Collectively, the results from the work
described here parallel the known surface organometallic
chemistry of triosmium clusters on silica, and neither the
presence of potentially reactive SiOH groups nor neighboring
triosmium clusters appear to influence the reactivity or spec-
troscopic features of [Os3(CO)10(µ-H)(µ-OSit)] groups. The
current description of [Os3(CO)10(µ-H)(µ-OSit)] on silica as
isolated triosmium clusters therefore appears to be accurate
regardless of whether the clusters are indeed isolated from each
other or additional to surface SiOH groups.
Although the reactions of [Os3(CO)10(µ-H)(µ-OH)] (3) with
incompletely condensed silsesquioxanes did not uncover any
new coordination environments for triosmium clusters, the
observation that 3 catalyzes the cyclodehydration of 1 has
interesting implications for the surface organometallic chemistry
of silica. In particular, it appears that metal complexes chemi-
sorbed via M-O-Si linkages may be susceptible to desorption
via reaction with adjacent SiOH groups and that the resulting
MOH species may be capable of catalyzing further dehydration
of the surface. This pathway is unlikely to be significant on
dehydrated surfaces with isolated SiOH groups, but it could
become important with more extensively hydroxylated surfaces
possessing substantial populations of vicinally hydrogen-bonded
SiOH groups.
Figure 3. ORTEP plot of 9 with thermal ellipsoids plotted at the
50% probability level. For clarity, only the carbon atoms of the
cyclohexyl groups are shown. Selected distances (Å) and angles
(deg): Os1-Os2, 2.7830(4); Os1-Os3, 2.8200(5); Os2-Os3,
2.8275(5); Os1-O1, 2.133(5); Os2-O1, 2.125(5); Si1-O1, 1.636-
(6); Si1-O2, 1.619(5); Si1-O5, 1.611(5); other Si-O, 1.62-1.64;
Os2-Os1-Os3, 60.609(11); Os1-Os2-Os3, 60.343(11); Os1-
Os3-Os2, 59.048(10); Si1-O1-Os1, 128.3(3); Si1-O1-Os2,
138.8(3); O2-Si1-O1, 104.2(3); O5-Si1-O1, 109.2(3); Si1-
O2-Si2, 143.8(4); Si1-O5-Si4, 153.9(4); other Si-O-Si, 142-
156; O-Si-O, 107-110.
by the large triosmium cluster. In the case of 8 and 9, the Si-O
distances, as well as O-Si-O and Si-O-Si angles, are
comparable to those observed for the bis-triphenyltin derivative
of disilanol 2.34 In the case of 5, which possesses two Si-OH
groups, the molecule adopts a symmetry-related (1h) dimeric
structure with extensive hydrogen bonding. Although the
hydrogen atoms for the SiOH groups could not be located in
the final difference map, the Si-O distances and intrabond
angles for 5 are remarkably similar to those observed for the
hydrogen-bonded dimer of (c-C6H11)7Si7O9(OH)2(OSiMe2Ph).57
Both compounds clearly adopt the same hydrogen-bonded
arrangement of SiOH groups, and there is no evidence in the
structure of 5 for interaction between SiOH groups and the Os3-
(CO)10 cluster.
Experimental Section
General experimental protocols and procedures have been
reported earlier.58 Methods and procedures for the synthesis of [(c-
C6H11)7Si7O9(OH)3] (1), [(c-C6H11)8Si8O11(OH)2] (2), and [Os3-
(CO)10(µ-H)(µ-OH)] (3) appear elsewhere.34,54 Unless otherwise
noted, reagent-grade chemicals were used without further purifica-
tion for all work described here; m-xylene was dried over activated
4 Å molecular sieves prior to use. The NMR spectra were recorded
on General Electric GN-500 (1H, 500.03 MHz; 13C, 125.75 MHz;
29Si, 99.37 MHz) and Omega-500 (1H, 500.22 MHz; 13C, 125.79
MHz; 29Si, 99.34 MHz) spectrometers, infrared spectra were
recorded on a Mattson Galaxy Series FTIR 5000 spectrometer, and
mass spectra were recorded on a VG Analytical Autospec E double-
focusing spectrometer or a Perceptive Biosystems matrix-assisted
laser desorption ionization-time-of-flight (MALDI-TOF) Voyager
DE STR spectrometer and a Micromass LCT electrospray ioniza-
tion-time-of-flight (ESI) spectrometer. Combustion analyses (C, H)
were measured at Atlantic Microlab Inc.
General Procedure for Reactions of Incompletely Condensed
Silsesquioxanes (i.e., 1, 2, and 5) with [Os3(CO)10(µ-H)(µ-OH)]
(3). Reactions were performed under nitrogen in a small flask (5
mL) fitted with a fritted-glass funnel (diameter ) ca. 3 cm; height
) ca. 25 cm) containing P2O5 (2 g). The distance between the
reaction solution and the fritted disk was ca. 12 cm, and the flask
was heated by immersion in a thermostated oil bath maintained at
140 °C. In a typical reaction, a solution of 3 (50-100 mg) and the
incompletely condensed silsesquioxane in anhydrous m-xylene
(0.5-1.0 mL; in order to have a concentration of 3 equal to 0.1 M)
was heated at 140 °C. Evaporation of the volatiles (25 °C, 0.1 Torr)
afforded a residue, which was analyzed by 1H NMR spectroscopy
(CDCl3) to determine the relative amounts of compounds containing
Os-H bonds. The crude product mixture was usually separated by
Conclusions
The reactions of [Os3(CO)10(µ-H)(µ-OH)] (3) with incom-
pletely condensed silsesquioxanes produce osmium-substituted
Si/O frameworks via metathesis of the SiOH for the bridging
OH group. In the case of disilanol 2, which possesses two SiOH
groups that are separated by more than 6 Å, reaction with 3
can occur at either or both SiOH groups to produce Si/O
frameworks with one or two [Os3(CO)10(µ-H)(µ-OSit)] groups.
In the case of trisilanol 1, which possesses three mutually
hydrogen-bonded SiOH groups, reaction with 3 is considerably
more complicated and the product mixture depends greatly on
the reaction stoichiometry and conditions. Three major products
have been isolated from the reaction. Two of these products (5
and 6) are derived from condensation of 3 with one or two SiOH
groups from 1; the third (4) appears to form via Os-catalyzed
cyclodehydration of 1 and condensation of the resulting mono-
silanol (i.e., 7) with 3. Both 5 and 6 juxtapose potentially
reactive SiOH and [Os3(CO)10(µ-H)(µ-OSit)] groups, but there
is no evidence for interaction of SiOH groups from either 5 or
6 with neighboring [Os3(CO)10(µ-H)(µ-OSit)] groups. As is
the case for stoichiometrically analogous silica-supported
(58) Feher, F. J.; Schwab, J. J.; Tellers, D. M.; Burstein, A. Main Group
Chem. 1998, 2, 169.
(57) Feher, F. J.; Newman, D. A. J. Am. Chem. Soc. 1990, 112, 1931.

80 Organometallics, Vol. 26, No. 1, 2007
Lucenti et al.
column chromatography on silica using CH2Cl2/hexanes as eluent.
Evaporation of the eluent typically afforded products that were
spectroscopically pure (1H, 13C, 29Si). Analytically pure samples
were obtained as described below.
2057 (s), 2020 (vs), 1998 (m), 1982 (m, sh) cm-1. MS (ESI): m/e
2698 (M + Na+), 2676 (M + H+).
Reaction of 3 with Disilanol 2: Synthesis of {Os3(CO)10-
(µ-H)[(µ-O)Si8O11(OH)(c-C6H11)8]} (8) and {[Os3(CO)10(µ-H)]2-
(µ-O)2Si8O11(c-C6H11)8} (9). As described above, 3 (110.0 mg;
0.126 mmol), disilanol 2 (349.6 mg; 0.318 mmol), and m-xylene
(1.25 mL) were reacted at 140 °C for 3.5 h. The 1H NMR spectrum
of the crude product mixture exhibited prominent resonances at δ
-12.31 and -12.40 (11:89), as well as three smaller signals at δ
-11.52, -20.48, and -21.35. Chromatography on silica with CH2-
Cl2/hexanes (1:4, v/v) first afforded 9 (17.6 mg; 10% yield);
continued elution with 1:1 CH2Cl2/hexanes afforded 8 (182.3 mg;
74% yield). When the same reaction was performed at 140 °C for
18.5 h using a 1:2 molar ratio of disilanol 2 (68.6 mg; 0.062 mmol)
and 3 (107.4 mg; 0.124 mmol), the crude mixture exhibited
prominent 1H NMR resonances (CDCl3) at δ -12.31, -12.40, and
-12.61 (80:14:6), and the isolated yields of 8 and 9 were 11%
(13.8 mg) and 70% (121.3 mg), respectively. Analitically pure 8
was obtained by allowing CH3OH to diffuse into a CH2Cl2 solution
of 8 at 25 °C. Pure 9 can be obtained by recrystallization from hot
1,2-dichloroethane.
For 8: 1H NMR (500.1 MHz, CDCl3, 25 °C): δ -12.40 (s,
1 H, HOs), 0.78 (vbr, m, 8 H), 1.26 (vbr, m, 40 H), 1.72 (vbr, m,
40 H), 2.11 (s, 1 H, HO). 13C{1H} NMR (125.03 MHz, CDCl3,
25 °C): δ 182.48, 180.58, 176.20, 175.63, 173.56, 173.52, 171.26,
171.11 (s, for CO); δ 27.78, 27.61, 27.54, 27.51, 27.47, 27.42,
27.36, 26.86, 26.74, 26.69, 26.61, 26.58, 26.54, 26.49, 26.28
(s, for CH2); δ 23.98, 23.84, 23.66, 23.52, 23.48, 23.38, 23.20 (s,
1:1:1:1:1:1:2 for CH). 29Si{1H} NMR (99.35 MHz, CDCl3,
25 °C): δ -54.75, -57.44, -65.59, -65.84, -67.82, -68.01,
-69.05, -69.16 (s, 1:1:1:1:1:1:1:1). IR (CDCl3), ν(CO): 2110 (w),
2070 (vs), 2059 (m), 2021 (vs), 2003 (s), 1983 (m, sh) cm-1. MS
(ESI): m/e 1973 (M + Na+), 1951 (M + H+). Anal. Calcd for
C58H90O23Si8Os3 (found): C, 35.71 (36.96); H, 4.65 (4.76).
Reaction of 3 with Trisilanol 1: Synthesis of {Os3(CO)10-
(µ-H)[(µ-O)Si7O10(c-C6H11)7]} (4) and {Os3(CO)10(µ-H)[(µ-O)-
Si7O9(OH)2(c-C6H11)7]} (5). As described above, trisilanol 1 (140.7
mg; 0.144 mmol) and 3 (62.3 mg; 0.072 mmol) were reacted in
1
m-xylene for 6.5 h at 140 °C. A H NMR spectrum of the crude
product mixture exhibited prominent 1H NMR resonances (CDCl3)
at δ -12.31, -12.46, and -12.55 (4:19:77), as well as small reso-
nances at δ -12.95, -14.92, -20.48, and -21.35. Column chroma-
tography on silica using CH2Cl2/hexanes (1:9 then 2:1 v/v) afforded
two yellow fractions. The first compound to elute was 4 (94.6 mg;
73% yield); the second was 5 (22.8 mg; 17% yield). When the
same reaction was performed at 140 °C for 2.5 h using a 2:1 molar
ratio of trisilanol 1 (170.4 mg; 0.175 mmol) and 3 (75.6 mg; 0.087
1
mmol), the H NMR resonances (CDCl3) at δ -12.31, -12.46,
and -12.55 had relative intensities of 9:48:43 and the isolated yields
of 4 and 5 were 35% (55.4 mg) and 39% (61.9 mg), respectively.
Both 4 and 5 were obtained as spectroscopically pure, yellow
microcrystalline powders after evaporation of the eluent. Analyti-
cally pure 4 can be obtained by crystallization from CH2Cl2/hexane
at -10 °C. Analytically pure 5 was obtained by allowing CH3OH
to diffuse into a solution of 5 in CH2Cl2 at 25 °C.
For 4: 1H NMR (500.1 MHz, CDCl3, 25 °C): δ -12.55 (s,
1 H, HOs), 0.89 (vbr, m, 7 H), 1.26 (vbr, m, 35 H), 1.71 (vbr, m
35 H). 13C{1H} NMR (125.03 MHz, CDCl3, 25 °C): δ 182.46,
180.70, 176.41, 175.82, 173.31, 173.25, 170.95 (s, for CO); δ 27.98,
27.72, 27.52, 27.46, 27.42, 27.38, 27.33, 26.86, 26.70, 26.56, 26.43,
26.39, 26.20 (s, for CH2); δ 24.41, 23.64, 23.49, 22.96, 22.52 (s,
1:2:1:2:1 for CH). 29Si{1H} NMR (99.35 MHz, CDCl3, 25 °C): δ
-56.02, -56.39, -59.08, -66.73, -68.20 (s, 1:1:2:1:2). IR (C6H12),
ν(CO): 2110 (w), 2072 (vs), 2059 (s), 2019 (vs), 2000 (s), 1986
(m), 1982 (m), 1952 (vw) cm-1. MS (ESI): m/e 1829 (M + Na+),
1807 (M + H+).
For 5: 1H NMR (500.1 MHz, CDCl3, 25 °C): δ -12.46 (s,
1 H, HOs), 0.78 (vbr, m, 7 H), 1.26 (vbr, m, 35 H), 1.72 (vbr, m
35 H), 3.65 (s, 2 H, HO). 13C{1H} NMR (125.03 MHz, CDCl3,
25 °C): δ 182.58, 180.62, 176.32, 175.59, 173.27, 171.14 (s, for
CO); δ 28.02, 27.67, 27.62, 27.55, 27.48, 26.82, 26.77, 26.73, 26.63
(s, for CH2); δ 24.47, 24.27, 23.97, 23.22 (s, 2:1:2:2 for CH).
29Si{1H} NMR (99.35 MHz, CDCl3, 25 °C): δ -56.64, -59.35,
-67.11, -67.29, -68.98 (s, 1:2:1:1:2). IR (C6H12), ν(CO): 2111
(w), 2073 (vs), 2059 (s), 2021 (vs), 2000 (s), 1986 (m) cm-1. MS
(ESI): m/e 1847 (M + Na+), 1825 (M + H+). Anal. Calcd for
C52H80O22Si7Os3 (found): C, 34.23 (34.44); H, 4.65 (4.53).
For 9: 1H NMR (500.1 MHz, CDCl3, 25 °C): δ -12.31 (s,
1 H, HOs), 0.76 (vbr, m, 8 H), 1.24 (vbr, m, 40 H), 1.73 (vbr, m
40 H). 13C{1H} NMR (125.03 MHz, CDCl3, 25 °C): δ 182.44,
180.50, 176.05, 175.47, 173.62, 171.53, 171.34 (s, for CO); δ 27.70,
27.59, 27.50, 27.43, 27.31, 27.06, 26.80, 26.72, 26.66, 26.57, 26.48,
26.34, 26.00 (s, for CH2); δ 24.00, 23.92, 23.71, 23.41 (s, 2:2:2:2
for CH). 29Si{1H} NMR (99.35 MHz, CDCl3, 25 °C): δ -55.74,
-65.84, -67.71, -71.51 (s, 2:2:2:2). IR (CDCl3), ν(CO): 2110
(w), 2069 (vs), 2060 (s), 2017 (vs), 2003 (s), 1983 (m, sh) cm-1
.
Anal. Calcd for C68H90O33Si8Os6 (found): C, 29.16 (29.06); H, 3.24
(3.28).
Catalytic Cyclodehydration of 1 to 7 by 3. As described above,
a solution of trisilanol 1 (211.5 mg; 0.217 mmol) was heated in
m-xylene (1.10 mL) for 16 h at 140 °C with 5 wt % of 3 (9.1 mg;
0.010 mmol). Evaporation of the volatiles afforded a 7:3 mixture
of 7 and unreacted trisilanol 1 as determined by 29Si NMR
spectroscopy.
For 1: 29Si{1H} NMR (99.35 MHz, CDCl3, 25 °C): δ -60.42,
-68.18, -69.76 (3:1:3).
For 7: 29Si{1H} NMR (99.35 MHz, CDCl3, 25 °C): δ -56.18,
-57.25, -57.66, -67.06 (1:1:2:3). (Note: In the absence of 3, the
cyclodehydration of 1 to 7 does not occur to any significant extent
under the same conditions.)
Reaction of 3 with 5: Synthesis of {[Os3(CO)10(µ-H)]2-
(µ-O)2Si7O9(OH)(c-C6H11)7} (6). As described above, 3 (103.3
mg; 0.119 mmol), 5 (52.0 mg; 0.028 mmol), and m-xylene (0.55
mL) were reacted at 140 °C under N2 for 11.5 h. The crude product
1
mixture exhibited prominent H NMR resonances at δ -12.03,
-12.31, -12.55, and -12.60 (22:8:10:60), as well as much smaller
resonances at δ -12.95, -14.92, -20.48, and -21.35. Chroma-
tography on silica with CH2Cl2/hexanes (1:9, v/v) first afforded 4.
Further elution with 1:9 CH2Cl2/hexanes afforded spectroscopically
pure 6 (20.2 mg; 27% yield), and continued elution with 1:1
CH2Cl2/hexanes recovered unreacted 3.
For 6: 1H NMR (500.1 MHz, CDCl3, 25 °C): δ -12.03 (s,
1 H, HOs), 0.75 (vbr, m, 7 H), 1.26 (vbr, m, 35 H), 1.77 (vbr, m
35 H)), 3.55 (s, 1 H, HO). 13C{1H} NMR (125.03 MHz, CDCl3,
25 °C): δ 183.42, 180.70, 176.63, 176.46, 175.73, 175.64, 173.39,
173.29, 172.95, 172.63 (s, for CO); δ 27.91, 27.70, 27.60, 27.56,
27.51, 27.46, 27.36, 26.85, 26.72, 26.69, 26.58, 26.47 (s, for CH2);
δ 25.74, 24.62, 24.44, 23.13 (s, 1:3:2:1 for CH). 29Si{1H} NMR
(99.35 MHz, CDCl3, 25 °C): δ -56.25, -60.96, -66.71, -68.87,
-69.50 (s, 2:1:1:1:2). IR (CH2Cl2), ν(CO): 2110 (w), 2072 (vs),
Thermolysis of 5 (NMR Tube Reaction). An NMR tube
containing 5 (10.8 mg; 0.006 mmol) in toluene-d8 (0.4 mL) was
progressively heated and periodically monitored by 1H NMR
spectroscopy. After 1 h at 60 °C, no changes were observed in the
spectrum. At 90 °C, the Os-H resonance for 3 began to appear at
δ -13.30 (versus -12.60 in CDCl3) and grow at the expense of
the resonance for 5. The percentage of 3 relative to total Os-H
was 3%, 12%, and 27% after 1, 4, and 12 h, respectively. An
electrospray ionization mass spectrum of the crude reaction mixture

Osmium-Containing Silsesquioxanes
Organometallics, Vol. 26, No. 1, 2007 81
Table 1. Details of the X-ray Structure Determinations
5
8
9
empirical formula
fw
C
104H160O44Os6Si14‚CH2Cl2
C
116H180O46Os6Si16
C68H90O33Os6Si8‚C2H4Cl2
2900.27
3733.71
3901.24
temperature, K
wavelength, Å
cryst syst
space group
a, Å
158(2)
0.71073
monoclinic
C2/c
a ) 15.8524(7)
b ) 25.8552(12)
c ) 33.6161(15)
R ) 90
â ) 90.6020(10)
γ ) 90
13777.4(11)
4
1.800
5.750
7312
0.26 × 0.22 × 0.11
1.21 to 28.29
-20 e h e 21,
-34 e k e 34,
-44 e l e 44
73 141
163(2)
0.71073
monoclinic
C2/c
a ) 51.535(2)
b ) 12.9064(5)
c ) 24.7552(10)
R ) 90
â ) 107.8740(10)
γ ) 90
15670.8(11)
4
1.654
5.041
7696
0.25 × 0.12 × 0.05
0.83 to 28.31
-68 e h e 68,
-17 e k e 17,
-32 e l e 32
83 561
158(2)
0.71073
monoclinic
C2/c
a ) 29.3568(18)
b ) 13.3023(8)
c ) 24.8330(16)
R ) 90
â ) 106.3810(10)
γ ) 90
9304.0(10)
b, Å
c, Å
R, deg
â, deg
γ, deg
volume, Å3
Z
4
density(calc), g/cm3
absorp coeff, mm-1
F(000)
2.071
8.400
5520
0.27 × 0.11 × 0.04
1.45 to 28.32
-39 e h e 38,
-17 e k e 17,
-33 e l e 32
47 919
cryst size, mm3
θ, deg
index ranges
no. of reflns collected
no. of indep reflns
completeness to θ max.
absorp corr
16 635 [R(int) ) 0.0433]
97.2%
numerical
19 118 [R(int) ) 0.1351]
98.0%
numerical
11 206 [R(int) ) 0.1068]
96.6%
numerical
max. and min. transmn
refinement method
no. of data/restraints/params
goodness-of-fit on F2 b
final R indices [I > 2σ(I)]a
R indices (all data)a
largest diff peak and
hole, e‚Å-3
0.5704 and 0.3164
full-matrix least-squares on F2
16 635/0/765
1.069
R1 ) 0.0354, wR2 ) 0.0779
R1 ) 0.0509, wR2 ) 0.0836
2.765 and -1.639
0.7867 and 0.3655
full-matrix least-squares on F2
19 118/336/539
1.057
R1 ) 0.0943, wR2 ) 0.2741
R1 ) 0.2209, wR2 ) 0.3557
3.956 and -2.183
0.7299 and 0.2101
full-matrix least-squares on F2
11 206/0/532
1.041
R1 ) 0.0450, wR2 ) 0.0876
R1 ) 0.0907, wR2 ) 0.1019
2.284 and -2.461
2
2
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑[w(Fo - Fo )2]/∑[w(Fo )]2]1/2
.
b Goof ) S ) [∑[w(Fo - Fc )2]/(n - p)]1/2 where n is the number of reflections
and p is the total number of parameters refined.
after 12 h at 90 °C revealed prominent peaks for unreacted 5 (m/e
997 (M + Na+), 974 (M + H+)) and silanol 7 (m/e 956 (M + H+)).
Reaction of 4 with 1 (NMR Tube Reaction). An NMR tube
containing 4 (42.6 mg; 0.024 mmol) and trisilanol 1 (24.1 mg; 0.024
mmol) in toluene-d8 (0.4 mL) was progressively heated and
are colleted in Table 1. The structure was solved by direct methods
(SHELXTL). Hydrogen atoms were included using a riding model.
Full-matrix least-squares refinement of positional and thermal
parameters (anisotropic for all non-H atoms) led to convergence
with R1 ) 0.0354, wR2 ) 0.0779 and GOF ) 1.069 for 765 vari-
ables refined against those 13 724 data with I > 2.0σ(I). All other
details regarding the crystal structure appear in the Supporting
Information.
1
periodically monitored by H NMR spectroscopy. No significant
changes were observed in the spectrum after 1 h at 60 °C and 1 h
at 90 °C. After 1 h at 110 °C, a very small resonance characteristic
of 3 appeared at δ -13.30 (versus -12.60 in CDCl3). No further
changes in the Os-H region of the spectrum were noted after 4.5 h
at 100 °C and 1 h at 140 °C. After 12 h at 140 °C, the Os-H
resonance for 3 is nearly gone and the 1H NMR spectrum exhibits
a prominent resonance for 4 (δ -12.65). Small resonances are also
observed at δ -9.86, -13.30 (characteristic of 3), -15.03, and
-20.70. The 13C NMR spectrum exhibits methine (SiCH) reso-
nances for 4 (δ 25.18, 24.41, 24.32, 23.77, 23.20 (1:2:1:2:1)) and
7 (δ 25.18, 23.93, 23.90, 23.77, 23.13 (1:2:1:2:1)). The characteristic
methine resonances for trisilanol 1 (δ 24.79, 24.39, 23.87 (3:3:1))
were not observed.
Reaction of 4 with NEt4OH. Aqueous 20% Et4NOH (22 µL)
was added to a solution of 4 (57.5 mg; 0.032 mmol) in THF (2 mL)
at 25 °C. Within 5 min, the color of the solution changed from
yellow to orange-brown. After 15 min, the solution was neutralized
with 0.5 N HCl. Evaporation of the volatiles afforded a dark brown
residue that exhibited the characteristic 1H NMR resonance (CDCl3)
for 3 (δ -12.60), as well as several smaller resonances for other
unidentified compounds containing Os-H. There was no resonance
attributable to 5 (δ -12.46).
Collection of X-ray Diffraction Data for 8. Well-formed but
poorly diffracting crystals were grown by allowing CH3OH to
diffuse into a CH2Cl2 solution of 8 at 25 °C. Diffraction data were
collected on a Bruker CCD platform diffractometer with Mo KR
radiation and a graphite monochromator. Relevant experimental data
are colleted in Table 1. The structure was solved by direct methods
(SHELXTL). Seven of eight cyclohexyl groups exhibit large thermal
ellipsoids when refined with anisotropic thermal parameters; these
were refined as groups without hydrogen atoms. Full-matrix least-
squares refinement of positional and thermal parameters (anisotropic
for all remaining atoms) led to convergence with R1 ) 0.0943,
wR2 ) 0.2741 and GOF ) 1.057 for 539 variables refined against
those 7750 data with I > 2.0σ(I). All other details regarding the
crystal structure appear in the Supporting Information.
Collection of X-ray Diffraction Data for 9. Crystals suitable
for X-ray diffraction studies were grown by recrystallization from
hot 1,2-dichloroethane. Diffraction data were collected on a Bruker
CCD platform diffractometer with Mo KR radiation and a graphite
monochromator. Relevant experimental data are collected in Table
1. The structure was solved by direct methods (SHELXTL).
Hydrogen atoms were included using a riding model. Full-matrix
least-squares refinement of positional and thermal parameters
(anisotropic for all non-H atoms) led to convergence with R1 )
0.0450, wR2 ) 0.0876 and GOF ) 1.041 for 532 variables refined
Collection of X-ray Diffraction Data for 5. Crystals suitable
for X-ray diffraction studies were grown by allowing CH3OH to
diffuse into a CH2Cl2 solution of 5 at 25 °C. Diffraction data were
collected on a Bruker CCD platform diffractometer with Mo KR
radiation and a graphite monochromator. Relevant experimental data

82 Organometallics, Vol. 26, No. 1, 2007
Lucenti et al.
against those 7652 data with I > 2.0σ(I). All other details regarding
Supporting Information Available: Complete details on the
X-ray analysis of 5, 8, and 9, including tables of bond distances
and angles, thermal parameters, hydrogen atom coordinates, and
ORTEP figures. This material is available free of charge via the
Internet at http://pubs.acs.org.
the crystal structure appear in the Supporting Information.
Acknowledgment. This work was supported by the National
Science Foundation (CHE-9307750 and CHE-9727870). E.L.
thanks Italian CNR for a “NATO-CNR Advanced Fellowship”
and Professor Renato Ugo (Universita` di Milano) for fruitful
discussions.
OM060844C