Surface organometallic chemistry: Synthesis and X-ray characterization of novel silanolate surface models [Re2(CO) 8(μ-h)(μ-OSiR2R′)] and of the first models with two homo and hetero metal carbonyl fragments linked to vicinal or geminal silanols

Article abstract of DOI:10.1021/om030075m

Reaction of [Re₂(CO)₈(THF)₂] with R ₂R′SiOH (R = Et, Ph; R′ = Et, Ph, OH, OSiPh ₂OH) gives the new molecular models [Re₂(CO) ₈(μ-H)(μ-OSiR₂R′)], which mimic a surface [Re₂(CO)₈(μ-H)(μ-OSi≡)] species anchored to isolated, geminal, or vicinal silanols. The bridging structure has been confirmed by the X-ray structure of [Re₂(CO) ₈(μ-H)(μ-OSiPh₂OH)]. Thermal treatment (70 °C) of [Re₂(CO)₈(μ-H)(μ-OH)] with excess Et ₃SiOH is another way to form [Re₂(CO) ₈(μ-H)(μ-OSiEt₃)], which can be reconverted into the hydroxo complex by addition of excess water at the same temperature. Both [Re₂(CO)₈(μ-H)(μ-OSiEt₃)] and [Re ₂(CO)₈(μ-H)(μ-OH)] are readily transformed into [Re₂(CO)₁₀] under 1 atm of CO at 150 °C. These molecular models, which are the only neutral carbonyl rhenium complexes bearing silanolate ligands reported up to now, constitute a new tool to clarify the first step of the surface chemistry of the photochemical interaction of [Re ₂(CO)₁₀] with a rather inert support such as silica. Although the free silanol OH of both [Re₂(CO) ₈(μ-H)(μ-OSiPh₂OSiPh₂OH)] and [Re ₂(CO)₈(μ-H)(μ-OSiPh₂OH)] is much less reactive than the OH of the corresponding noncoordinated silanol, it reacts at 25 °C with excess [Re₂(CO)₈(THF)₂] to give the first bimetallic models [Re₂(CO) ₈(μ-H)(μ-OSiPh₂OSiPh ₂O-μ)(μ-H)Re₂(CO)₈] and [Re ₂(CO)₈(μ-H)(μ-OSiPh ₂O-μ)(μ-H)Re₂(CO)₂], respectively. The latter complex, less stable to hydrolysis, is of particular interest because it constitutes the first molecular model of two metal carbonyl fragments linked to geminal surface silanols, thus suggesting that this kind of bimetallic system may occur also on a surface. Remarkably, the reaction of the rather unreactive [Os₃(CO)₁₀(μ-H)(μ-OSiPh₂OSiPh ₂OH)] cluster with the very reactive [Re₂(CO) ₈(THF)₂] affords [Re₂(CO) ₈(μ-H)(μ-OSiPh₂OSiPh ₂O-μ)(μ-H)Os₃(CO)₁₀], the first heterobimetallic molecular model whose structure has been determined by X-ray diffraction.

Full text of DOI:10.1021/om030075m

Organometallics 2003, 22, 3271-3278
3271
Su r fa ce Or ga n om eta llic Ch em istr y: Syn th esis a n d X-r a y
Ch a r a cter iza tion of Novel Sila n ola te Su r fa ce Mod els
[Re2(CO)8(µ-H)(µ-OSiR2R′)] a n d of th e F ir st Mod els w ith
Tw o Hom o a n d Heter o Meta l Ca r bon yl F r a gm en ts
Lin k ed to Vicin a l or Gem in a l Sila n ols
Giuseppe D’Alfonso, Virna Formaggio, Dominique Roberto,* and Renato Ugo
Dipartimento di Chimica Inorganica, Metallorganica e Analitica dell’Universita` di Milano,
Unita` di Ricerca dell’INSTM di Milano, Centro CIMAINA, and Istituto di Scienze e Tecnologie
Molecolari del CNR (ISTM), via Venezian 21, 20133 Milano, Italy
Elena Lucenti
Istituto di Scienze e Tecnologie Molecolari del CNR, Via C. Golgi 19, 20133 Milano, Italy
Lucia Carlucci
Dipartimento di Chimica Strutturale e Stereochimica Inorganica dell’Universita` di Milano,
Via G. Venezian, 21, 20133 Milano, Italy
Received J anuary 30, 2003
Reaction of [Re2(CO)8(THF)2] with R2R′SiOH (R ) Et, Ph; R′ ) Et, Ph, OH, OSiPh2OH)
gives the new molecular models [Re2(CO)8(µ-H)(µ-OSiR2R′)], which mimic a surface [Re2-
(CO)8(µ-H)(µ-OSit)] species anchored to isolated, geminal, or vicinal silanols. The bridging
structure has been confirmed by the X-ray structure of [Re2(CO)8(µ-H)(µ-OSiPh2OH)].
Thermal treatment (70 °C) of [Re2(CO)8(µ-H)(µ-OH)] with excess Et3SiOH is another way to
form [Re2(CO)8(µ-H)(µ-OSiEt3)], which can be reconverted into the hydroxo complex by
addition of excess water at the same temperature. Both [Re2(CO)8(µ-H)(µ-OSiEt3)] and [Re2-
(CO)8(µ-H)(µ-OH)] are readily transformed into [Re2(CO)10] under 1 atm of CO at 150 °C.
These molecular models, which are the only neutral carbonyl rhenium complexes bearing
silanolate ligands reported up to now, constitute a new tool to clarify the first step of the
surface chemistry of the photochemical interaction of [Re2(CO)10] with a rather inert support
such as silica. Although the free silanol OH of both [Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2OH)]
and [Re2(CO)8(µ-H)(µ-OSiPh2OH)] is much less reactive than the OH of the corresponding
noncoordinated silanol, it reacts at 25 °C with excess [Re2(CO)8(THF)2] to give the first
bimetallic models [Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-µ)(µ-H)Re2(CO)8] and [Re2(CO)8(µ-H)-
(µ-OSiPh2O-µ)(µ-H)Re2(CO)8], respectively. The latter complex, less stable to hydrolysis, is
of particular interest because it constitutes the first molecular model of two metal carbonyl
fragments linked to geminal surface silanols, thus suggesting that this kind of bimetallic
system may occur also on a surface. Remarkably, the reaction of the rather unreactive [Os3-
(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)] cluster with the very reactive [Re2(CO)8(THF)2] affords
[Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-µ)(µ-H)Os3(CO)10], the first heterobimetallic molecular
model whose structure has been determined by X-ray diffraction.
In tr od u ction
define structural aspects but also to clarify by a molec-
ular approach the chemical behavior of organometallic
Transition-metal carbonyls supported on silica are
interesting hybrid materials, which may be convenient
precursors of highly dispersed metals with unusual
catalytic properties.1 However, the surface organome-
tallic chemistry involved is not always clear. It can be
better understood from the structure and reactivity of
molecular organometallic compounds bearing silanolate
ligands to mimic the functional groups of the silica
surface. These models are an important tool not only to
species bound to silica.2 Although models of silica-
(1) For example, see the following reviews and references therein:
(a) Iwasawa, Y.; Gates, B. C. CHEMTECH 1989, 173. (b) Gates, B. C.
Catalytic Chemistry; Wiley: New York, 1992. (c) Scott, S. L.; Basset,
J . M. J . Mol. Catal. 1994, 86, 5. (d) Psaro, R.; Recchia, S. Catal. Today
1998, 41, 139. (e) Braunstein, P.; Rose´, J . In Metal Clusters in
Chemistry; Braunstein, P., Oro, L., Raithby, P., Eds.; Wiley-VCH:
Weinheim, Germany, 1999; pp 616-665. (f) Lefebvre, F.; Candy, J .-
P.; Basset, J .-M. In Metal Clusters in Chemistry; Braunstein, P., Oro,
L., Raithby, P., Eds.; Wiley-VCH: Weinheim, Germany, 1999; pp 782-
793.
* To whom correspondence should be addressed. Fax: +39-02-
50314405. E-mail: dominique.roberto@unimi.it.
(2) Lucenti, E.; Roberto, D.; Ugo, R. Organometallics 2001, 20, 1725
and references therein.
10.1021/om030075m CCC: $25.00 © 2003 American Chemical Society
Publication on Web 07/04/2003

3272 Organometallics, Vol. 22, No. 16, 2003
Sch em e 1. Syn th esis a n d Rea ctivity of Novel Sila n ola te Com p lexes
D’Alfonso et al.
anchored carbonyl species of various metals (e.g. Rh,3
Os,2,4 Ru5) have been prepared and characterized, in the
case of Re only recently has the anionic species [Re2-
(CO)6(µ-OH)3-x(µ-OSiEt3)x]- (x ) 1-3) been obtained.6
Yet, there is a need for neutral rhenium carbonyl species
bearing silanolate ligands as models to understand and
confirm the proposed chemistry of silica-supported
rhenium carbonyl species such as [Re2(CO)10] and [Re-
(CO)3OH]4. This specific surface organometallic chem-
istry is not well-known,7 particularly with respect to the
industrial relevance of Re catalysts supported on inor-
ganic oxides for reactions such as olefin metathesis8a
and epoxidation,8b hydrogenation,8c dehydrogenation,8d
and petroleum refining.8e Therefore, to produce a better
insight into the organometallic chemistry of Re carbonyl
species supported on silica, we studied the preparation
of neutral Re carbonyl silanolate complexes such as [Re2-
(CO)8(µ-H)(µ-OSiR2R′)] (R ) Et, Ph; R′ ) Et, Ph, OH,
OSiPh2OH), which, by analogy with the known activa-
tion of [Os3(CO)12] by silica to give silica-anchored
[Os3(CO)10(µ-H)(µ-OSit)],9a could be models of [Re2-
(CO)8(µ-H)(µ-OSit)], first formed by thermal interaction
of [Re2(CO)10] with silica. This surface species, never
clearly identified, could also be the key intermediate in
the formation of [Re2(CO)10] upon treatment of silica-
supported [Re(CO)3(OH)]4 with CO (1 atm, 150-200
°C)7c by analogy with the well-known reductive carbon-
ylation of silica-anchored [Os(CO)x(OSit)2]n (x ) 2,3)9a
or silica-supported [Os(CO)3(OH)2]n9b to give [Os3(CO)12]
via [Os3(CO)10(µ-H)(µ-OSit)].
[Re2(CO)8(THF)2] is a very reactive species derived
from [Re2(CO)10], capable of activating different H-Y
bonds (e.g. Y ) H, Cl, CtCPh, CHdCHPh, CH2C(O)-
OEt, OH) to give the corresponding [Re2(CO)8(µ-H)(µ-
Y)] complexes.10 Therefore we investigated its reactivity
with different types of molecular silanols: (i) R3SiOH
(R ) Et, Ph) to mimic surface-isolated silanols, (ii) Ph2-
Si(OH)2 to mimic surface geminal silanols, and (iii)
HOSiPh2OSiPh2OH to mimic surface vicinal silanols.
In this work we present the results of this investigation
(Scheme 1).
(8) For example, see the following papers and references therein:
(a) Danilyuk, A. F. Kinet. Katal. 1983, 24, 926. Herrmann, W. A.;
Wagner, W.; Flessner, U. N.; Volkhardt, U.; Komber, H. Angew. Chem.,
Int. Ed. Engl. 1991, 30, 1636. Hietala, J .; Root, A.; Knuuttila, P. J .
Catal. 1994, 150, 46. Mol, J . C. Catal. Today 1999, 51, 289. Chabanas,
M.; Baudoin, A.; Cope´ret, C.; Basset, J .-M. J . Am. Chem. Soc. 2001,
123, 2062. (b) Zhu, Z.; Espenson, J . H. J . Mol. Catal. A: Chem. 1997,
121, 139. Dallmann, K.; Buffon, R. Catal. Commun. 2000, 1, 9.
Mandelli, D.; van Vliet, M. C. A.; Arnold, U.; Sheldon, R. A.; Schu-
chardt, U. J . Mol. Catal. A: Chem. 2001, 168, 165. (c) Iizuka, T.;
Kojima, M.; Tanabe, K. Y. J . Chem. Soc., Chem. Commun. 1983, 638.
Komiyama, M.; Ogino, Y.; Akai, Y.; Goto, M. J . Chem. Soc., Faraday
Trans. 1983, 79, 1719. Komiyama, M.; Okamoto, T.; Ogino, Y. J . Chem.
Soc., Chem. Commun. 1984, 618. Kirlin, P. S.; Gates, B. C. Nature
1987, 325, 38. Nacheff, M. S.; Kraus, L. S.; Ichikawa, M.; Hoffman, B.
M.; Butt, J . B.; Sachtler, W. M. H. J . Catal. 1987, 106, 263. Braca, G.;
Raspolli Galletti, A. M.; Sbrana, G.; Lami, M.; Marchionna, M. J . Mol.
Catal. 1995, 95, 19. (d) Fung, A. S.; Kelley, M. J .; Koningsberger, D.
C.; Gates, B. C. J . Am. Chem. Soc. 1997, 119, 5877. (e) Sinfelt, J . H.
Acc. Chem. Res. 1987, 20, 134. Hao, L.; Xiao, J .; Vittal, J . J .;
Puddephatt, R. J . Organometallics 1997, 16, 2165.
(3) (a) The´olier, A.; Smith, A. K.; Leconte, M.; Basset, J .-M.;
Zanderighi, G. M.; Psaro, R.; Ugo, R. J . Organomet. Chem. 1980, 191,
415. (b) Vizi-Orosz, A.; Marko´, L. Transition Met. Chem. 1982, 7, 216.
(c) Pa´lyi, G.; Zucchi, C.; Ugo, R.; Psaro, R.; Sironi, A.; Vizi-Orosz, A. J .
Mol. Catal. 1992, 74, 51. (d) Vizi-Orosz, A.; Ugo, R.; Psaro, R.; Sironi,
A.; Moret, M.; Zucchi, C.; Ghelfi, F.; Pa´lyi, G.; Inorg. Chem. 1994, 33,
4600.
(4) (a) Psaro, R.; Ugo, R. Besson, B.; Smith, A. K.; Basset, J . M. J .
Organomet. Chem. 1981, 213, 215. (b) Evans, J .; Gracey, B. P. J . Chem.
Soc., Dalton Trans. 1982, 1123. (c) D’Ornelas, L.; Choplin, A.; Basset,
J . M.; Hsu, L. Y.; Shore, S. Nouv. J . Chim. 1985, 9, 155. (d) Feher, F.
J . J . Am. Chem. Soc. 1986, 108, 3850. (e) Feher, F. J .; Gonzales, S. L.;
Ziller, J . W. Inorg. Chem. 1988, 27, 3440. (f) Feher, F. J .; Walzer, J . F.
Inorg. Chem. 1990, 29, 1604. (g) Lucenti, E.; Roberto, D.; Roveda, C.;
Ugo, R.; Sironi, A. Organometallics 2000, 19, 1051. (h) Lucenti, E.;
Feher, F. J .; Ziller, J . W. Submitted for publication in Organometallics.
(i) Liu, J . C.; Wilson, S. R.; Shapley, J . R.; Feher, F. J . Inorg. Chem.
1990, 29, 5138.
(5) Puga, J .; Fehlner, T. P.; Gates, B. C.; Braga, D.; Grepioni, F.
Inorg. Chem. 1990, 29, 2376.
(6) Roberto, D.; D’Alfonso, G.; Ugo, R.; Vailati, M. Organometallics
2001, 20, 4307.
(7) To our knowledge, the only papers on the chemistry of rhenium
carbonyl species supported on silica are ref 6 and the following: (a)
Kirlin, P. S.; Gates, B. C. Inorg. Chem. 1985, 24, 3914. (b) McKenna,
W. P.; Higgins, B. E.; Eyring, E. M. J . Mol. Catal. 1985, 31, 199. (c)
D’Alfonso, G.; Roberto, D.; Ugo, R.; Bianchi, C. L.; Sironi, A. Organo-
metallics 2000, 19, 2564.
(9) (a) 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. (b) Cariati, E.; Recanati, P.; Roberto, D.; Ugo,
R. Organometallics 1998, 17, 1266.
(10) (a) Carlucci, L.; Proserpio, D. M.; D’Alfonso, G. Organometallics
1999, 18, 2091. (b) Carlucci, L.; Proserpio, D. M.; D’Alfonso, G. XXVII
Congresso di Chimica Inorganica, Como, Italy, 1999. (c) Carlucci, L.;
Proserpio, D. M.; D’Alfonso, G. Manuscript in preparation.

Surface Organometallic Chemistry
Organometallics, Vol. 22, No. 16, 2003 3273
Ta ble 1. Selected 1H a n d 29Si NMR Sign a ls in Tolu en e-d 8 of Va r iou s Sila n ola te Com p lexes
silanolate complex
1H NMR δ(µ-H) (ppm)
29Si NMR δ (ppm)
[Re2(CO)8(µ-H)(µ-OSiPh3)]
-10.87
-2.12
[Re2(CO)8(µ-H)(µ-OSiEt3)]
-10.67
+34.38
[Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2OH)]
[Re2(CO)8(µ-H)(µ-OSiPh2OH)]
[Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-µ)(µ-H)Re2(CO)8]
[Re2(CO)8(µ-H)(µ-OSiPh2O-µ)(µ-H)Re2(CO)8)]
[Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-µ)(µ-H)Os3(CO)10
[Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)]4g
-10.79
-28.77; -37.31
-22.53
-10.81
-10.79
-29.80
-14.86
-10.85
]
-10.83; -11.96
-12.20
-28.69; -29.60
-29.11; -36.78
Resu lts a n d Discu ssion
P r ep a r a tion a n d Ch a r a cter iza tion of Molecu la r
Mod els of t h e Typ e [R e2(CO)8(µ-H )(µ-OSiR 2R ′)].
The activation of H-Y bonds by [Re2(CO)8(THF)2] often
proceeds only in solvents other than tetrahydrofuran.10
No reaction takes place in THF, even in the presence
of a 7-fold excess of R2R′SiOH (R ) Et, Ph; R′ ) Et, Ph,
OH, OSiPh2OH). However, when working in anhydrous
toluene instead of tetrahydrofuran, the corresponding
dinuclear species [Re2(CO)8(µ-H)(µ-OSiR2R′)] are readily
formed, in a few minutes, even at 0 °C and using a
stoichiometric amount of R2R′SiOH, as evidenced by 1H
and 29Si NMR spectroscopy. Thus, the addition of [Re2-
(CO)8(THF)2] to a solution of Ph3SiOH (molar ratio 1:1)
in anhydrous deuterated toluene, working at 0 °C under
1
nitrogen, can be followed by H NMR spectroscopy (by
the appearance of a signal at δ -10.87 ppm assigned to
a hydride bridging two Re atoms)10a and by 29Si NMR
spectroscopy (by the decrease of the intensity of the
signal at δ -14.26 ppm due to free Ph3SiOH and the
parallel formation of a signal at lower field, δ -2.12
ppm, attributable to a silanolate bound to rhenium6).
Evaporation to dryness followed by recrystallization
from dichloromethane/hexane gives [Re2(CO)8(µ-H)(µ-
OSiPh3)]. Similarly, treatment at 0 °C of an anhydrous
toluene solution of Et3SiOH, HOSiPh2OSiPh2OH, or
Ph2Si(OH)2 with a stoichiometric amount of [Re2(CO)8-
(THF)2] gives the corresponding dinuclear species [Re2-
(CO)8(µ-H)(µ-OSiEt3)] or [Re2(CO)8(µ-H)(µ-OSiPh2R′)]
(R′ ) OH, OSiPh2OH), which can be purified by the
same process of recrystallization. These new silanolate
compounds have been fully characterized by infrared
F igu r e 1. ORTEP diagram of the complex [Re2(CO)8(µ-
H)(µ-OSiPh2OH)] with a partial labeling scheme. Thermal
ellipsoids are drawn at the 30% probability level. The
hydrogen atoms of the phenyl groups are omitted for
clarity.
Ta ble 2. Su m m a r y of Cr ysta l Da ta a n d Str u ctu r e
Refin em en t P a r a m eter s for
[Re2(CO)8(µ-H)(µ-OSiP h 2OH)] a n d
[Re2(CO)8(µ-H)(µ-OSiP h 2OSiP h 2O-µ)(µ-H)Os3(CO)10
]
C
20H12O10Re2Si C42H22O21Os3Re2Si2
fw
812.79
1861.78
monoclinic
P21/c (14)
12.597(1)
14.044(1)
28.693(2)
96.58(1)
5042.5(6)
4
2.452
12.438
2-26
40 323
cryst syst
space group (No.)
a (Å)
b (Å)
c (Å)
monoclinic
P21/c (14)
7.624(1)
35.861(6)
8.689(2)
98.68(1)
2348.5(7)
4
2.299
10.402
2-26
21 515
1
and H NMR and 29Si NMR spectroscopy, by elemental
analysis, and, in some cases, by mass spectrometry (EI)
(see Table 1 and Experimental Section). In the particu-
lar case of [Re2(CO)8(µ-H)(µ-OSiPh2OH)] the molecular
structure was established by X-ray crystallography
(Figure 1). Crystal data and details of the structure
refinement are reported in Table 2, and relevant bond
distances and angles are listed in Table 3. The molecule
can be seen as being formed by two “Re(CO)4” fragments
bridged by a µ-OSiPh2OH ligand and a µ-H (hydride)
atom so that each rhenium atom shows an almost
octahedral geometry. The Re-Re bond distance of
3.0226(8) Å is nearly coincident with that found for the
precursor compound [Re2(CO)8(THF)2] (3.0224(4) Å)10a
and is not much different from that of related species
such as [Re2(CO)6(µ-H)(µ-OH)(dppm)]11 (dppm ) bis-
(diphenylphosphino)methane) (3.030(1) Å) with a simi-
lar “Re(µ-H)(µ-O)Re” core. The structural trend observed
in other “M(µ-H)(µ-O)M” cores thus seems confirmed:
the lengthening effect, which usually accompanies the
â (deg)
V (Å3)
Z
D(calcd), g cm-3
abs coeff, mm-1
θ range, deg
no. of rflns collected
no. of indep rflns
4694 (R(int) )
0.0466)
none
9904 (R(int) )
0.0496)
none
cryst decay, %
no. of data/restraints/
params
4694/0/298
9904/0/633
2
goodness of fit on Fo
1.360
1.061
R indices (Fo > 4σ(Fo))a,b R1, 0.0577;
R1, 0.0282;
wR2, 0.0597
R1, 0.0429;
wR2, 0.0655
wR2, 0.1149
R1, 0.0657;
wR2, 0.1173
R indices (all data)a,b
largest diff peak and
hole, e Å3
2.095 and -3.086 1.580 and -1.240
R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑(Fo - Fc2)2/∑wFo
]
.
a
b
2
4 1/2
formation of a three-center two-electron bond upon H
bridging, is counterbalanced by an effect in the opposite
direction due to the bridging µ-OR ligand. The equato-
(11) Lee, K.-W.; Penningthon, W.; Cordes, A. W.; Brown, T. L.
Organometallics 1984, 3, 404.

3274 Organometallics, Vol. 22, No. 16, 2003
D’Alfonso et al.
Ta ble 3. Selected Bon d Len gth s (Å) a n d
An gles (d eg)
O-Os angle reported when the same silanol is bridging
two Os atoms as in [Os3(CO)10(µ-H)(µ-OSiPh2OH)]
(82.65°).4g The two “Re(CO)4” fragments adopt an eclipsed
conformation, and apart from the -Si(Ph)2OH group the
molecule conforms to an idealized C2v point symmetry.
Finally, similarly to [Os3(CO)10(µ-H)(µ-OSiPh2OH)],4g no
evidence has been found for inter- or intramolecular
hydrogen bonds originated by the free silanol of the
µ-OSiPh2OH bridge.
[Re2(CO)8(µ-H)(µ-OSiPh2OH)]
Re(1)-C(3)
Re(1)-C(4)
Re(1)-C(2)
Re(1)-C(1)
Re(1)-O(10)
Re(1)-Re(2)
Re(2)-C(7)
1.905(14)
1.926(16)
1.961(14)
2.005(14)
2.141(8)
Re(2)-C(8)
Re(2)-C(6)
Re(2)-C(5)
Re(2)-O(10)
Si-O(10)
1.943(14)
1.964(15)
2.018(13)
2.160(8)
1.633(8)
1.635(9)
3.0226(8)
1.924(16)
Si-O(9)
Alter n a tive Syn th esis a n d Rea ctivity of [Re2-
(CO)8(µ-H)(µ-OSiR2R′)]. It is known that some com-
plexes or clusters bearing a metal-OH bond react more
or less easily with silanol groups of the silica surface to
anchor an organometallic species by a metal-OSit
bond.12 With regard to mimicking the reactivity of the
silica surface,12b it was recently reported by some of us
that the OH ligand of the cluster [Os3(CO)10(µ-H)(µ-OH)]
exchanges with silanol molecules such as R2R′SiOH
(R ) Et, Ph; R′ ) Et, Ph, OH, OSiPh2OH), when
working in anhydrous m-xylene at 138 °C, to afford the
related osmium cluster with a silanolate bridge.4g This
seems to be a quite general reaction.4h For instance,
some of us have described the reaction of [NEt4][Re2-
(CO)6(µ-OH)3] with excess triethylsilanol to give the
related silanolate species [NEt4][Re2(CO)6(µ-OH)3-x(µ-
OSiEt3)x] (working at 25 °C, x ) 1; working at 150 °C,
x ) 2, 3 depending on the reaction time).6 We thus
investigated the reactivity with Et3SiOH of the hydroxo
complex [Re2(CO)8(µ-H)(µ-OH)], recently prepared by
some of us,10b,c as another way to produce the bridging
rhenium silanolates described above.
The complex [Re2(CO)8(µ-H)(µ-OH)] does not react in
the presence of a 10-fold amount of Et3SiOH, working
at room temperature in anhydrous deuterated toluene.
However, an increase of the temperature to 70 °C leads
to the formation of [Re2(CO)8(µ-H)(µ-OSiEt3)], as evi-
denced by 1H NMR spectroscopy (see the Experimental
Section). After 2 h the reaction is complete. The bridging
OH ligand of [Re2(CO)8(µ-H)(µ-OH)] exchanges with Et3-
SiOH at a temperature lower than that for the hydroxo
group of [Os3(CO)10(µ-H)(µ-OH)] but at a temperature
higher than that for the first bridging hydroxo group of
the anionic species [Re2(CO)6(µ-OH)3]-. In addition,
whereas [Re2(CO)6(µ-OH)3-x(µ-OSiEt3)x]- (x ) 1-3) spe-
cies are immediately converted back to [Re2(CO)6(µ-
OH)3]- by addition of a few drops of water at room
temperature,6 hydrolysis of [Re2(CO)8(µ-H)(µ-OSiR3)]
(R ) Et, Ph) to give [Re2(CO)8(µ-H)(µ-OH)] occurs when
working at higher temperature (70 °C for 20 min) only
(see the Experimental Section). The reversible exchange
reaction between the bridging hydroxo and the bridging
silanolate ligand is general: addition of a 10-fold
amount of Ph3SiOH to a solution of [Re2(CO)8(µ-H)(µ-
OSiEt3)] in anhydrous toluene, followed by stirring at
80 °C for 1 h, leads to the formation of [Re2(CO)8(µ-H)-
(µ-OSiPh3)].
Re(1)-O(10)-Re(2)
C(3)-Re(1)-C(4)
C(3)-Re(1)-C(2)
C(4)-Re(1)-C(2)
C(3)-Re(1)-C(1)
C(4)-Re(1)-C(1)
C(2)-Re(1)-C(1)
C(3)-Re(1)-O(10)
C(4)-Re(1)-O(10)
C(2)-Re(1)-O(10)
C(1)-Re(1)-O(10)
C(7)-Re(2)-C(8)
C(7)-Re(2)-C(6)
89.3(3) C(8)-Re(2)-C(6)
90.8(6) C(7)-Re(2)-C(5)
88.8(6) C(8)-Re(2)-C(5)
89.7(6) C(6)-Re(2)-C(5)
90.0(6)
88.4(6)
90.2(5)
174.7(6)
88.3(5) C(7)-Re(2)-O(10) 169.9(5)
90.0(6) C(8)-Re(2)-O(10)
177.0(6) C(6)-Re(2)-O(10)
168.2(5) C(5)-Re(2)-O(10)
100.9(5) O(10)-Si-O(9)
89.8(5) O(10)-Si-C(21)
93.2(4) O(9)-Si-C(21)
90.1(6) O(10)-Si-C(11)
86.4(7) O(9)-Si-C(11)
99.9(5)
92.4(5)
92.7(4)
108.5(5)
108.3(5)
111.6(5)
111.8(5)
104.9(5)
[Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-µ)(µ-H)Os3(CO)10
]
Os(1)-Os(3)
Os(1)-Os(2)
Os(2)-Os(3)
Re(1)-Re(2)
Os(1)-C(12)
Os(1)-C(11)
Os(1)-C(9)
Os(1)-C(10)
Os(2)-C(17)
Os(2)-C(14)
Os(2)-C(16)
Os(2)-O(21)
Os(3)-C(18)
Os(3)-C(15)
Os(3)-C(13)
2.8162(4)
2.8317(4)
2.7863(4)
3.0144(4)
1.926(9)
1.936(8)
1.940(7)
1.960(7)
1.878(8)
1.900(7)
1.960(6)
2.129(4)
1.873(7)
1.916(9)
1.922(9)
Os(3)-O(21)
Re(1)-C(4)
Re(1)-C(3)
Re(1)-C(1)
Re(1)-C(2)
Re(1)-O(20)
Re(2)-C(8)
Re(2)-C(7)
Re(2)-C(5)
Re(2)-C(6)
Re(2)-O(20)
Si(1)-O(19)
Si(1)-O(21)
Si(2)-O(20)
Si(2)-O(19)
2.154(4)
1.909(8)
1.927(7)
1.983(8)
1.990(9)
2.155(4)
1.919(8)
1.944(7)
1.995(9)
1.996(8)
2.184(4)
1.630(4)
1.644(4)
1.626(4)
1.639(4)
Re(1)-O(20)-Re(2) 88.00(14) C(1)-Re(1)-C(2)
Os(2)-O(21)-Os(3) 81.17(13) C(4)-Re(1)-O(20)
C(12)-Os(1)-C(11) 101.8(3)
C(12)-Os(1)-C(9)
C(11)-Os(1)-C(9)
176.3(3)
166.0(2)
104.7(2)
90.0(3)
93.7(2)
89.5(3)
85.6(4)
91.0(3)
87.0(3)
89.8(3)
172.5(3)
167.9(3)
102.6(2)
93.7(2)
93.4(2)
C(3)-Re(1)-O(20)
C(1)-Re(1)-O(20)
C(2)-Re(1)-O(20)
C(8)-Re(2)-C(7)
C(8)-Re(2)-C(5)
C(7)-Re(2)-C(5)
C(8)-Re(2)-C(6)
C(7)-Re(2)-C(6)
C(5)-Re(2)-C(6)
C(8)-Re(2)-O(20)
C(7)-Re(2)-O(20)
C(5)-Re(2)-O(20)
93.4(3)
92.7(3)
C(12)-Os(1)-C(10) 93.3(3)
C(11)-Os(1)-C(10) 92.8(3)
C(9)-Os(1)-C(10) 170.2(3)
C(17)-Os(2)-C(14) 91.6(3)
C(17)-Os(2)-C(16) 88.4(3)
C(14)-Os(2)-C(16) 97.6(3)
C(17)-Os(2)-O(21) 167.9(2)
C(14)-Os(2)-O(21) 97.9(2)
C(16)-Os(2)-O(21) 97.7(2)
Os(3)-Os(2)-Os(1) 60.163(10) C(6)-Re(2)-O(20)
C(18)-Os(3)-C(15) 91.4(3)
C(18)-Os(3)-C(13) 88.9(3)
C(15)-Os(3)-C(13) 94.1(4)
C(18)-Os(3)-O(21) 165.2(3)
C(15)-Os(3)-O(21) 98.0(3)
C(13)-Os(3)-O(21) 101.7(3)
O(19)-Si(1)-O(21) 107.9(2)
O(19)-Si(1)-C(121) 111.7(3)
O(21)-Si(1)-C(121) 106.5(2)
O(19)-Si(1)-C(111) 106.8(2)
O(21)-Si(1)-C(111) 111.2(2)
O(20)-Si(2)-O(19) 108.2(2)
O(20)-Si(2)-C(211) 107.9(2)
O(19)-Si(2)-C(211) 107.9(2)
O(20)-Si(2)-C(221) 106.6(3)
O(19)-Si(2)-C(221) 112.4(2)
C(4)-Re(1)-C(3)
C(4)-Re(1)-C(1)
C(3)-Re(1)-C(1)
C(4)-Re(1)-C(2)
C(3)-Re(1)-C(2)
89.1(3)
88.1(4)
88.5(3)
88.4(4)
90.2(3)
rial carbonyls (C8, C7, C4, C3) are coplanar with the
two rhenium atoms, the bridging oxygen O10, and
hydride atoms with a maximum deviation from the
plane not exceeding 0.01 Å. The µ-OSiPh2OH group
bridges the two rhenium atoms in an almost symmetric
way, the two distances Re1-O10 and Re2-O10 being
2.141(8) and 2.160(8) Å, respectively. The Re1-O10-
Re2 angle, 89.3(3)°, is close to that found for [Re2(CO)6-
(µ-H)(µ-OH)(dppm)], 88.6(2)°, but larger than the Os-
Besides, [Re2(CO)10] is formed (slowly at 25-80 °C
and rapidly at 150 °C) by bubbling CO into an anisole
or triethylsilanol solution of either [Re2(CO)8(µ-H)(µ-
OSiEt3)] or [Re2(CO)8(µ-H)(µ-OH)]. After 7 h at 150 °C
the conversion is complete. This kind of reductive
(12) (a) Meyer, T. Y.; Woerpel, K. A.; Novak, B. M.; Bergman, R. G.
J . Am. Chem. Soc. 1994, 116, 10290. (b) Cariati, E.; Roberto, D.; Ugo,
R. Gazz. Chim. Ital. 1996, 126, 339.

Surface Organometallic Chemistry
Organometallics, Vol. 22, No. 16, 2003 3275
carbonylation gives further evidence to our suggestion
that silica-anchored [Re2(CO)8(µ-H)(µ-OSit)] (or silica-
supported [Re2(CO)8(µ-H)(µ-OH)] when working with a
incompletely dehydrated silica) could be the key inter-
mediate in the reductive carbonylation of silica-sup-
ported [Re(CO)3(OH)]4 to give [Re2(CO)10].7c
above reaction for a long period because we found that
the excess of [Re2(CO)8(THF)2] reacts in parallel with
toluene, a reaction which is under investigation in our
laboratories.19 Therefore, to avoid this side reaction,
cyclohexane was used as solvent.
Addition of an excess of [Re2(CO)8(THF)2] to a solution
of [Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2OH)] in anhydrous
cyclohexane (molar ratio 2:1), at room temperature,
leads after 1.5 h to [Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-
µ)(µ-H)Re2(CO)8], as confirmed by isolation of a crude
product with the expected 29Si NMR spectrum (only one
signal at δ -29.80 ppm in deuterated toluene). The pure
compound, obtained by successive recrystallizations
(dichloromethane/hexane and then pentane), was fully
Molecu la r Mod els w ith Vicin a l or Gem in a l Si-
la n ols Con n ectin g Tw o “Re2(CO)8(µ-H)” Moieties:
[R e 2(C O )8(µ-H )(µ-O S iP h 2O S iP h 2O -µ)(µ-H )R e 2-
(CO)8] a n d [Re2(CO)8(µ-H)(µ-OSiP h 2O-µ)(µ-H)Re2-
(CO)8]. Both silanol groups of either the disilanol
HOSiPh2OSiPh2OH or the silanediol Ph2Si(OH)2 are
reported to react with various high-oxidation-state early
transition metals or main-group metals, affording cyclic
metallasiloxanes.13 For example, reaction of HOSiPh2-
OSiPh2OH with TiCl4 affords the spirocyclic complex
[Ti(OSiPh2OSiPh2O)2]14 and reaction with [Zr(CH2-
SiMe3)4] leads to the formation of [Zr(CH2SiMe3)2(OSiPh2-
OSiPh2O)] with a six-membered ZrO3Si2 ring,13,15 while
reaction with chromium trioxide affords [Cr(dO)2(OSiPh2-
OSiPh2O)]2, where the two disilanolate ligands bind to
two chromium dioxo units, generating a unique 12-
membered metallacyclic fragment.16 Ph2Si(OH)2 reacts
with Ti(OBu)4 to yield, by a self-condensation process,
the spirocyclic complex [Ti(OSiPh2(OSiPh2)3O)2],17 but
it reacts with R2GeX2 (R ) Me, Ph; X ) Cl, Br) to give
[Ph2SiO2GeR2]2, which has a Ge2Si2O4 eight-membered-
ring core structure.18 However, with a metal carbonyl
species such as [Os3(CO)10(µ-H)(µ-OH)], various at-
tempts to react both silanol groups in order to prepare
even simple bridged dinuclear species such as [Os3-
(CO)10(µ-H)(µ-OSiPh2OSiPh2O-µ)(µ-H)Os3(CO)10] and
[Os3(CO)10(µ-H)(µ-OSiPh2O-µ)(µ-H)Os3(CO)10] by reac-
tion of [Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)] and [Os3-
(CO)10(µ-H)(µ-OSiPh2OH)] with excess [Os3(CO)10(µ-
H)(µ-OH)] failed. These results suggested that the
second silanol group does not react when the disilanol
is bound to a metal carbonyl species such as an osmium
cluster. It was thus relevant to understand if this latter
point is general or is limited to the case of the “Os3-
(CO)10(µ-H)” moiety. Therefore, we investigated whether
the free silanol groups of [Re2(CO)8(µ-H)(µ-OSiPh2-
OSiPh2OH)] and [Re2(CO)8(µ-H)(µ-OSiPh2OH)] react
with excess [Re2(CO)8(THF)2].
1
characterized by infrared and H NMR and 29Si NMR
spectroscopy and by elemental analysis (see Table 1 and
the Experimental Section). Similarly, [Re2(CO)8(µ-H)-
(µ-OSiPh2O-µ)(µ-H)Re2(CO)8] is formed by addition of
an excess of [Re2(CO)8(THF)2] to a solution of [Re2(CO)8-
(µ-H)(µ-OSiPh2OH)] in anhydrous cyclohexane (molar
ratio [Re2(CO)8(THF)2]:[Re2(CO)8(µ-H)(µ-OSiPh2OH)] )
(1.5-2):1), at room temperature for 2 h (see Table 1 and
Experimental Section), as evidenced by 29Si NMR
spectroscopy (one signal at δ -14.86 ppm). However,
various attempts to isolate and purify this new complex
failed, due to its quick hydrolysis under crystallization
conditions to give back [Re2(CO)8(µ-H)(µ-OSiPh2OH)].
It appears that [Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-µ)(µ-
H)Re2(CO)8] is more stable than [Re2(CO)8(µ-H)(µ-
OSiPh2O-µ)(µ-H)Re2(CO)8], probably due to steric ef-
fects.
Not only do these new bridged complexes with two
homo metal carbonyl fragments linked by a silanediol
or a disilanol bridge constitute the first molecular
models carrying two metal carbonyl fragments but their
synthesis also confirms a large decrease of reactivity of
both vicinal and geminal silanol groups, when one of
the silanols is bound to a low-oxidation-state metal
carbonyl species. They thus produce evidence that on a
silica surface two metal fragments could be linked not
only to vicinal surface silanols but also to geminal
silanols, although in this latter case in a rather unstable
way.
Molecu la r Mod el w ith Tw o Heter on u clea r Meta l
Ca r bon yl F r a gm en ts: [Re2(CO)8(µ-H)(µ-OSiP h 2O-
SiP h 2O-µ)(µ-H)Os3(CO)10]. The formation of [Re2(CO)8-
(µ-H)(µ-OSiPh2OSiPh2O-µ)(µ-H)Re2(CO)8)] by reaction of
[Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2OH)] with [Re2(CO)8-
(THF)2] is remarkable because, as mentioned above, the
free silanol group of [Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2-
OH)] does not react with an excess of [Os3(CO)10(µ-H)-
(µ-OH)].4g Therefore, the high reactivity of [Re2(CO)8-
(THF)2] prompted us to investigate the reaction of
[Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)] with [Re2(CO)8-
(THF)2]. This reaction occurs in anhydrous cyclohexane,
affording [Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-µ)(µ-H)Os3-
(CO)10]. After the mixture is stirred for 3 h at room
temperature, evaporation of the solvent to dryness gives
a crude product purified by successive recrystallizations
(dichloromethane/pentane and then pentane) and char-
acterized by infrared and 1H NMR and 29Si NMR
spectroscopy and by elemental analysis (see Table 1 and
the Experimental Section). This is a unique new com-
Addition of an excess of [Re2(CO)8(THF)2] to a solution
of HOSiPh2OSiPh2OH in deuterated toluene (molar
ratio 2:1), at 0 or 25 °C, does not lead to the formation
of the bridged species [Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2-
O-µ)(µ-H)Re2(CO)8]. 29Si NMR spectroscopy indicated
that only [Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2OH)] is formed.
Equally, Ph2Si(OH)2 under the same reaction conditions
gives [Re2(CO)8(µ-H)(µ-OSiPh2OH)] as the only product.
These results seem to confirm that the free silanol group
in these kinds of silanolate complexes is much less
reactive than the free silanol of a disilanol or of a
silanediol. However, we were unable to investigate the
(13) Murugavel, R.; Voigt, A.; Walawalkar, M. G.; Roesky, H. W.
Chem. Rev. 1996, 96, 2205.
(14) Andrianov, K. A.; Kurasheva, N. A.; Kuteinikova, L. I. Zh.
Obshch. Khim. 1976, 46, 1533; Chem. Abstr. 1976, 85, 177526g.
(15) Hrncir, D. C. Mater. Res. Symp. Proc. 1988, 121, 127.
(16) Abbenhuis, H. C. L.; Vorstenbosch, M. L. W.; van Santen, R.
A.; Smeets, W. J . J .; Spek, A. Inorg. Chem. 1997, 36, 6431.
(17) (a) Zeitler, V. A.; Brown, C. A. J . Am. Chem. Soc. 1957, 79,
4618. (b) Hursthouse, M. B.; Hossain, M. A. Polyhedron 1984, 3, 95.
(18) Puff, H.; Bo¨ckmann, M. P.; Ko¨k, T. R.; Schuh, W. J . Organomet.
Chem. 1984, 268, 197.
(19) Carlucci, L.; Proserpio, D. M.; D’Alfonso, G. Work in progress.

3276 Organometallics, Vol. 22, No. 16, 2003
D’Alfonso et al.
F igu r e 3. Comparison of the coordination around the Si
atoms in Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)] (left) and
[Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-µ)(µ-H)Os3(CO)10] (right).
F igu r e 2. ORTEP diagram of the complex [Re2(CO)8(µ-
H)(µ-OSiPh2OSiPh2O-µ)(µ-H)Os3(CO)10] with a partial la-
beling scheme. Thermal ellipsoids are drawn at the 30%
probability level. The hydrogen atoms of the phenyl groups
are omitted for clarity.
OSiR2R′)], which mimic a [Re2(CO)8(µ-H)(µ-OSit)] spe-
cies anchored to isolated, geminal, or vicinal silanols of
the silica surface, thus confirming, as first evidenced
by the reactivity of [Os3(CO)10(µ-H)(µ-OH)],4g that all
the different silanol species of the silica surface may
interact with metallic fragments. The synthesis of these
new rhenium carbonyl complexes with a bridging sil-
anolate ligand constitutes a new approach to the
understanding of the surface chemistry which occurs
during the photolysis of a solution of [Re2(CO)10] in THF
in the presence of silica. In this specific case the
formation of silica-anchored [Re2(CO)8(µ-OSit)2], [Re-
(CO)5OSit], and [tSiORe(CO)3(≡SiOSit)2] has been
suggested only on the evidence that the carbonyl bands
of the surface species are similar to those of known
compounds such as [Re2(CO)8(SPh)2], [Re(CO)5Cl], and
[Re(CO)3OH]4.7b However, it has been reported that the
photochemical transformation of [Re2(CO)10] into [Re-
(CO)3OH]4, working in wet tetrahydrofuran without the
presence of silica, could involve the reactive species [Re2-
(CO)8(H2O)2] and [Re2(CO)8(µ-H)(µ-OH)] as intermedi-
ates.20 Our models now suggest that the silica-anchored
species formed during the photolysis of [Re2(CO)10] in
THF in the presence of silica and proposed to be [Re2-
(CO)8(µ-OSit)2]7b could be [Re2(CO)8(µ-H)(µ-OSit)] gen-
erated directly or generated by reaction of [Re2(CO)8L2]
(L ) THF, H2O) or [Re2(CO)8(µ-H)(µ-OH)] with the
surface silanol groups. Its formation, even when work-
ing under nonanhydrous conditions,7b would be reason-
able, since our molecular models [Re2(CO)8(µ-H)(µ-
OSiR3)] are not easily hydrolyzed at room temperature
and in addition are easily prepared from [Re2(CO)8(µ-
H)(µ-OH)] by exchange with excess silanol ligands, as
probably may occur on an incompletely dehydrated silica
surface.
plex because it contains for the first time two very
different metal carbonyl fragments linked to the two
silanol groups of a vicinal disilanol. Its structure was
solved by X-ray diffraction and compared to those of
[Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)]4g and of [Re2-
(CO)8(µ-H)(µ-OSiPh2OH)], previously described (Figure
1).
The molecular structure of [Re2(CO)8(µ-H)(µ-OSiPh2-
OSiPh2O-µ)(µ-H)Os3(CO)10] is shown in Figure 2. Crys-
tal data and details of the structure are reported in
Table 2, and relevant bond distances and angles are
listed in Table 3. The structure can be discussed by
analyzing three components: the trinuclear osmium
cluster “Os3(CO)10(µ-H)(µ-O)”, the dimeric rhenium frag-
ment “Re2(CO)8(µ-H)(µ-O)”, and the disilanolate ligand
“µ-OSiPh2OPh2O-µ”, which helds together the two or-
ganometallic moieties. The structural features of the two
organometallic frameworks resemble those of [Re2(CO)8-
(µ-H)(µ-OSiPh2OH)] (see above) and [Os3(CO)10(µ-H)(µ-
OSiPh2OSiPh2OH)].4g The osmium cluster shows the
expected triangular arrangement of the metal core
framework, with two longer (Os1-Os2, 2.8317(4) Å;
Os1-Os3, 2.8162(4) Å) and one shorter (Os2-Os3,
2.7863(4) Å) Os-Os edge, the latter bearing the µ-H and
µ-OR bridges. The “Os3(CO)10(µ-H)(µ-O-)” core pre-
serves the idealized Cs point symmetry (with the pseudo
mirror plane passing through the Os1, H, and O21
atoms), as suggested for [Os3(CO)10(µ-H)(µ-OSiPh2-
OSiPh2OH)]. Equally the dinuclear rhenium fragment
“Re2(CO)8(µ-H)(µ-O)” preserves the idealized C2v point
symmetry previously evidenced for [Re2(CO)8(µ-H)(µ-
OSiPh2OH)]. The difference between this heterobime-
tallic species and [Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)]
is in the conformation of the -OSiPh2OSiPh2O- bridge.
In [Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)] the two sil-
anolate oxygens are “trans” (torsion angle O-Si‚‚‚Si-
O ) 177.2°), while in [Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-
µ)(µ-H)Os3(CO)10] the two oxygens are “gauche” (O21-
Si1‚‚‚Si2-O20 ) 90.5°), as illustrated in Figure 3.
In addition, we confirmed some previous observations4g
on the very low reactivity of the remaining free silanol
group of either disilanol or silanediol linked by one
silanol to a metal carbonyl fragment. Despite such a low
reactivity, the high reactivity of [Re2(CO)8(THF)2] allows
the formation of the first molecular models with two
homo or hetero metal carbonyl fragments linked to
vicinal or even geminal surface silanols, including the
first model of a rhenium/osmium bimetallic species. In
these new models we also evidenced for the first time
the low stability toward hydrolysis when two metal
carbonyl fragments are linked to a geminal system.
Con clu sion
The easy reaction of [Re2(CO)8(THF)2] with R2R′SiOH
(R ) Et, Ph; R′ ) Et, Ph, OH, OSiPh2OH) provides an
entry to the novel model complexes [Re2(CO)8(µ-H)(µ-
(20) Gard, D. R.; Brown, T. L. J . Am. Chem. Soc. 1982, 104, 6340.

Surface Organometallic Chemistry
Exp er im en ta l Section
Organometallics, Vol. 22, No. 16, 2003 3277
the formation of [Re2(CO)8(µ-H)(µ-OSiEt3)] in quantitative
1
yield, as evidenced by H NMR monitoring (disappearance of
Gen er a l Com m en ts. [Re2(CO)8(THF)2] was prepared fol-
lowing a reported procedure and was usually contaminated
with unreactive [Re3(µ-H)3(CO)12] (ca. 10%).10a [Os3(CO)10(µ-
H)(µ-OSiPh2OSiPh2OH)]4g and HOSiPh2OSiPh2OH21 were pre-
pared according to the literature, whereas Et3SiOH, Ph3SiOH,
and Ph2Si(OH)2 were purchased from Sigma-Aldrich. Ph3SiOH
and Ph2Si(OH)2 were recrystallized (CH2Cl2) before use,
whereas Et3SiOH and the organic solvents were dried over
molecular sieves (4 Å). All reactions, carried out under N2
(dried by flowing over Drierite) in anhydrous conditions, were
monitored by 1H and 29Si NMR spectroscopy. Products were
characterized by infrared and 1H NMR and 29Si NMR spec-
troscopy, by elemental analysis, and, in some cases, by mass
spectrometry (EI). Spectral data were obtained by use of the
following spectrometers: Bruker-Vector 22 or J asco FT-IR 420
(IR), Bruker AC-200 or Bruker DRX-300 (1H and 29Si NMR;
SiMe4 was used as standard), Varian VG9090 (MS). Elemental
analyses were carried out at the Universita` di Milano.
Syn th esis of [Re2(CO)8(µ-H)(µ-OSiR2R′)] (R ) Et, P h ;
R′ ) Et, P h , OH, OSiP h 2OH). In a typical synthesis, a
solution of R2R′SiOH (R ) Et, Ph; R′ ) Et, Ph, OH, OSiPh2-
OH) (0.027 mmol) in anhydrous toluene (3 mL) was prepared,
under N2 in a 25 mL two-neck round-bottomed flask equipped
with a magnetic bar, and cooled to 0 °C with an ice bath. [Re2-
(CO)8(THF)2] (20 mg; 0.027 mmol) was added and the resulting
orange-red solution stirred until it became yellow (ca. 5 min).
Evaporation to dryness of toluene, followed by addition of
dichloromethane (to dissolve the crude product) and repre-
cipitation with a few drops of hexane, gave pure [Re2(CO)8(µ-
H)(µ-OSiR2R′)] as a white powder. Crystals, suitable for X-ray
diffraction, of [Re2(CO)8(µ-H)(µ-OSiPh2OH)] were obtained at
-20 °C by using the biphasic system CH2Cl2/pentane.
the hydridic signal at δ -11.32 ppm, characteristic of the
hydroxo complex, and parallel appearance of an hydridic signal
at δ -10.67 ppm, characteristic of the silanolate complex). The
reaction is reversible. In fact, when a solution of [Re2(CO)8(µ-
H)(µ-OSiEt3)] (5 mg; 0.007 mmol) in anhydrous deuterated
toluene (0.5 mL) with a few drops of water was stirred at 70
°C for 20 min, [Re2(CO)8(µ-H)(µ-OH)] was formed, as confirmed
by 1H NMR and 29Si NMR spectroscopy (in the 29Si NMR
spectrum, the signal at δ 34.38 ppm, characteristic of the
triethylsilanolate complex, was replaced by a signal at δ 17.07
ppm, characteristic of free HOSiEt3). Under similar conditions,
[Re2(CO)8(µ-H)(µ-OSiPh3)] was also hydrolyzed.
Con ver sion of [Re2(CO)8(µ-H)(µ-OSiEt3)] in to [Re2-
(CO)8(µ-H)(µ-OSiP h 3)]. Addition of a 10-fold amount of Ph3-
SiOH (20.5 mg; 0.074 mmol) to a solution of [Re2(CO)8(µ-H)(µ-
OSiEt3)] (5.4 mg; 0.0074 mmol) in anhydrous deuterated
toluene (0.5 mL), followed by stirring at 80 °C for 1 h, led to
the formation of [Re2(CO)8(µ-H)(µ-OSiPh3)] in quantitative
1
yield, as evidenced by H NMR spectroscopy with disappear-
ance of the hydridic signal at δ -10.67 ppm, characteristic of
the triethylsilanolate complex, and parallel appearance of an
hydridic signal at δ -10.87 ppm, characteristic of the triphen-
ylsilanolate complex.
Red u ctive Ca r bon yla tion of [Re2(CO)8(µ-H)(µ-OSiEt3)]
a n d [Re2(CO)8(µ-H)(µ-OH)]. In a typical reaction, CO (1 atm)
was bubbled into a solution of [Re2(CO)8(µ-H)(µ-OSiEt3)] (20
mg; 0.027 mmol) dissolved in either triethylsilanol or anisole
(3-5 mL). After 7 h at 150 °C all the starting complex was
converted into [Re2(CO)10], as confirmed by IR and 1H NMR
spectroscopy. By working under similar conditions, [Re2(CO)8-
(µ-H)(µ-OH)] is also converted to [Re2(CO)10].
Syn th esis of [Re2(CO)8(µ-H)(µ-OSiP h 2OSiP h 2O-µ)(µ-H)-
Re2(CO)8] an d [Re2(CO)8(µ-H)(µ-OSiP h 2O-µ)(µ-H)Re2(CO)8].
In a typical synthesis, a solution of [Re2(CO)8(µ-H)(µ-OSiPh2-
OSiPh2OH)] (10 mg; 0.010 mmol) in anhydrous cyclohexane
(5 mL) was prepared, under dry N2 in a 25 mL two-neck round-
bottom flask equipped with a magnetic bar. [Re2(CO)8(THF)2]
(15 mg; 0.020 mmol) was added, and the resulting solution
was stirred for 1.5 h at room temperature. Evaporation to
dryness of the solvent afforded [Re2(CO)8(µ-H)(µ-OSiPh2-
OSiPh2O-µ)(µ-H)Re2(CO)8] contaminated by some [Re(CO)3-
[Re2(CO)8(µ-H)(µ-OSiP h 3)]. IR (in CH2Cl2): ν(CO) 2096
1
(w), 2016 (s), 1992 (m), 1954 (m) cm-1. H NMR (in toluene-
d8): δ (ppm) -10.87 (s, 1 H, bridging hydride), 7.22 (m, 9 H,
ortho and para H of the 3 Ph), 7.82 (m, 6 H, meta H of the 3
Ph). 29Si NMR (in toluene-d8): δ (ppm) -2.12; the 29Si NMR
signal of the free ligand HOSiPh3 in toluene-d8 is at -14.26
ppm. Anal. Calcd: C, 35.78; H, 1.83. Found: C, 35.93; H, 1.60.
[Re2(CO)8(µ-H)(µ-OSiEt3)]. IR (in CH2Cl2): ν(CO) 2097
1
(w), 2016 (s), 1990 (m), 1953 (m) cm-1. H NMR (in toluene-
22
OH)]4 and [HRe3(CO)14],23 as evidenced by IR and 1H NMR
d8): δ (ppm) -10.67 (s, 1 H, bridging hydride), 0.516 (q, 6 H,
3 CH2), 0.978 (t, 9 H, 3 CH3). 29Si NMR (in toluene-d8): δ (ppm)
34.38; the 29Si NMR signal of the free ligand HOSiEt3 in
toluene-d8 is at 17.07 ppm. Anal. Calcd: C, 23.01; H, 2.20.
Found: C, 22.92; H, 2.46. Mass spectrum: m/e 728 [M]+.
[Re2(CO)8(µ-H)(µ-OSiP h 2OSiP h 2OH)]. IR (in THF): ν(CO)
spectroscopy in deuterated toluene. Addition of dichloromethane
(to dissolve the crude product) and reprecipitation with hexane
gave traces of [Re(CO)3OH)]4. Evaporation to dryness of the
filtrate followed by dissolution of the residue in pentane and
cooling at -20 °C gave pure [Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-
µ)(µ-H)Re2(CO)8]. Similarly, when a solution of [Re2(CO)8(µ-
H)(µ-OSiPh2OH)] (23 mg; 0.029 mmol) in anhydrous cyclohex-
ane (10 mL) was stirred with [Re2(CO)8(THF)2] (32 mg; 0.043
mmol) for 2 h under dry N2 in a 25 mL two-neck round-bottom
flask equipped with a magnetic bar, [Re2(CO)8(µ-H)(µ-OSiPh2O-
µ)(µ-H)Re2(CO)8)] was formed, as evidenced by infrared and
1H NMR spectroscopy. However, various attempts to isolate
the latter complex failed, due to its facile reconversion back
to [Re2(CO)8(µ-H)(µ-OSiPh2OH)]. In these two syntheses, and
in the synthesis of [Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-µ)(µ-H)-
Os3(CO)10] reported below, it was convenient to use an excess
of [Re2(CO)8(THF)2] because, by working at room temperature,
this very reactive reagent produced some side products such
1
2096 (w), 2015 (s), 1996 (m, sh), 1955 (m) cm-1. H NMR (in
toluene-d8): δ (ppm) -10.79 (s, 1 H, bridging hydride), 3.57
(s, 1 H, OH), 7.16 (m, 12 H, ortho and para H of the 4 Ph),
7.74 (m, 8 H, meta H of the 4 Ph). 29Si NMR (in toluene-d8):
δ (ppm) -28.77 (ReOSi), -37.31 (HOSi); the 29Si NMR signal
of the free ligand HOSiPh2OSiPh2OH in toluene-d8 is at -36.99
ppm. Anal. Calcd: C, 38.02; H, 2.18. Found: C, 38.17; H, 2.34.
[Re2(CO)8(µ-H)(µ-OSiP h 2OH)]. IR (in pentane): ν(CO)
2097 (w), 2015 (s), 1997 (m, sh), 1965 (s) cm-1 1H NMR (in
.
toluene-d8): δ (ppm) -10.82 (s, 1 H, bridging hydride), 3.39
(s, 1 H, OH), 7.19 (m, 6 H, ortho and para H of the 2 Ph), 7.61
(m, 4 H, meta H of the 2 Ph). 29Si NMR (in toluene-d8): δ (ppm)
) -22.53; the 29Si NMR signal of the free ligand HOSiPh2OH
in toluene-d8 is at -37.34 ppm. Anal. Calcd: C, 29.56; H, 1.48.
Found: C, 29.48; H, 1.57. Mass spectrum: m/e 812 [M]+.
Rever sible Con ver sion of [Re2(CO)8(µ-H)(µ-OH)] in to
[Re2(CO)8(µ-H)(µ-OSiEt3)]. Addition of a 10-fold amount of
Et3SiOH (0.014 mL; 0.09 mmol) to a solution of [Re2(CO)8(µ-
H)(µ-OH)] (5.5 mg; 0.009 mmol) in anhydrous deuterated
toluene (0.5 mL), followed by stirring at 70 °C for 2 h, led to
22
as [Re(CO)3OH)]4 and [HRe3(CO)14].23
[Re2(CO)8(µ-H)(µ-OSiP h 2OSiP h 2O-µ)(µ-H)Re2(CO)8]. In-
frared (in THF): ν(CO) 2096 (w), 2015 (s), 1996 (m, sh), 1955
(m) cm-1 1H NMR (in toluene-d8): δ (ppm) -10.79 (s, 2 H,
.
(22) (a) Herberhold, M.; Suss, G. Angew. Chem., Int. Ed. Engl. 1975,
14, 700. (b) Herberhold, M.; Suss, G.; Ellermann, J .; Gabelein, H. Chem.
Ber. 1978, 111, 2931.
(23) Fellmann, W.; Kaesz, H. D. Inorg. Nucl. Chem. Lett. 1966, 2,
63.
(21) Burkhard, C. A. J . Am. Chem. Soc. 1945, 67, 2173.

3278 Organometallics, Vol. 22, No. 16, 2003
D’Alfonso et al.
bridging hydrides), 7.12 (m, 12 H, ortho and para H of the 4
Ph), 7.59 (m, 8 H, meta H of the 4 Ph). 29Si NMR (in toluene-
d8): δ (ppm) -29.80; the 29Si NMR signal of the free ligand
HOSiPh2OSiPh2OH in toluene-d8 is at -36.99 ppm. Anal.
Calcd: C, 29.89; H, 1.37. Found: C, 29.77; H, 1.43.
H)Os3(CO)10]. Crystal data and details of the structure
refinement are reported in Table 2; selected bond distances
and angles are given in Table 3. Suitable platelike crystals of
[Re2(CO)8(µ-H)(µ-OSiPh2OH)] (0.36 × 0.26 × 0.12 mm) and
[Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-µ)(µ-H)Os3(CO)10] (0.40 ×
0.22 × 0.10 mm) were mounted on a Bruker SMART CCD area
detector diffractometer, and the data collections were per-
formed at 293 K (graphite-monochromated Mo KR, λ )
0.710 73 Å) by the ω-scan method (∆ω ) 0.3°), with a crystal-
to-detector distance of 4 cm. An empirical absorption correction
was applied (SADABS).24 The structures were solved by direct
methods (SIR97)25 and refined by full-matrix least-squares on
Fo2 (SHELX-97).26 Anisotropic displacement parameters were
assigned to all non-hydrogen atoms. Hydride ligands were
located in the idealized positions calculated employing the
program HYDEX with dM-H ) 1.85 Å and fixed. Hydrogen
atoms of the phenyl and silanol groups were placed in the
idealized positions and refined riding on their parent atoms.
[Re2(CO)8(µ-H)(µ-OSiP h 2O-µ)(µ-H)Re2(CO)8]. IR (in pen-
1
tane): ν(CO) 2097 (w), 2015 (s), 1997 (m), 1965 (m) cm-1. H
NMR (in toluene-d8): δ (ppm) -10.85 (s, 2 H, bridging
hydrides), 7.20 (m, 6 H, ortho and para H of the 2 Ph), 7.89
(m, 4 H, meta H of the 2 Ph). 29Si NMR (in toluene-d8): δ (ppm)
-14.86; the 29Si NMR signal of the free ligand HOSiPh2OH
in toluene-d8 is at -37.34 ppm.
Syn th esis of [Re2(CO)8(µ-H)(µ-OSiP h 2OSiP h 2O-µ)(µ-
H)Os3(CO)10]. A solution of [Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2-
OH)] (33 mg; 0.026 mmol) dissolved in anhydrous cyclohexane
(15 mL) was prepared, under dry N2 in a 50 mL two-neck
round-bottom flask equipped with a magnetic bar. [Re2(CO)8-
(THF)2] (48 mg; 0.064 mmol) was added, and the resulting
solution was stirred for 3 h at room temperature. Evaporation
to dryness of the solvent, followed by addition of dichlo-
romethane (minimum amount to dissolve the crude product)
and then of hexane, leads to the precipitation of some [Re-
(CO)3(OH)]4. Evaporation of the filtrate to dryness followed
by dissolution of the residue in pentane and cooling at -78 °C
Ack n ow led gm en t. We are indebted to Dr. Matteo
Vailati for some experimental help and Mr. Pasquale
Illiano for running 1H and 29Si NMR spectra. L.C.
thanks Davide M. Proserpio for help in the crystal-
lography. This work was supported by the Ministero
dell’Istruzione, dell’Universita` e della Ricerca, and by
the Consiglio Nazionale delle Ricerche (CNR, Roma).
for
a few hours or -20 °C overnight leads first to the
precipitation of unreacted [Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2-
OH)] and then of pure [Re2(CO)8(µ-H)(µ-OSiPh2OSiPh2O-µ)-
(µ-H)Os3(CO)10]. Crystals, suitable for X-ray diffraction, of the
latter cluster were obtained at -20 °C from a pentane solution.
IR (in pentane): ν(CO) 2097 (w), 2072 (w), 2059 (w), 2017 (s),
Note Ad d ed a fter ASAP : In the version published
on the web 7/4/03, the last value in column 2 of Table 1
was incorrectly given as +12.20. In the final Web
version published 7/17/03, this value is correct as
-12.20.
1997 (m), 1965 (s) cm-1 1H NMR (in toluene-d8): δ (ppm)
.
-11.96 (s, 1 H, hydride bridging Os2), -10.83 (s, 1 H, hydride
bridging Re2), 7.13 (m, 12 H, ortho and para H of the 4 Ph),
7.63 (m, 8 H, meta H of the 4 Ph). 29Si NMR (in toluene-d8):
δ (ppm) -29.60 (OsOSi); -28.69 (ReOSi); the 29Si NMR signal
of the free ligand HOSiPh2OSiPh2OH in toluene-d8 is at -36.99
ppm, whereas [Os3(CO)10(µ-H)(µ-OSiPh2OSiPh2OH)] shows
signals at -29.11 and -36.78 ppm. Anal. Calcd: C, 27.09; H,
1.19. Found: C, 27.20; H, 1.24.
OM030075M
(24) Sheldrick, G. M. SADABS: Siemens Area Detector Absorption
Correction Software; University of Go¨ttingen, Germany, 1996.
(25) Altomare, M. C.; Burla, M.; Camalli, G.; Cascarano, C.; Giaco-
vazzo, A.; Guagliardi, A. G.; Moliterni, G.; Polidori, R.; Spagna, R. J .
Appl. Crystallogr. 1999, 32, 115.
(26) (a) Sheldrick, G. M. SHELX-97; University of Go¨ttingen,
Go¨ttingen, Germany, 1997. (b) Orpen, A. G. HYDEX. J . Chem. Soc.,
Dalton Trans. 1980, 2509.
X-r a y St r u ct u r e Det er m in a t ion of [R e2(CO)8(µ-H)(µ-
OSiP h 2OH)] a n d [Re2(CO)8(µ-H)(µ-OSiP h 2OSiP h 2O-µ)(µ-