A unique coordination of SiH4: Isolation, characterization, and theoretical study of (PR3)2>H2Ru(SiH4)RuH2(PR3)2 [15]

Full text of DOI:10.1021/ja000223p

5664
J. Am. Chem. Soc. 2000, 122, 5664-5665
A Unique Coordination of SiH4: Isolation,
Characterization, and Theoretical Study of
(PR3)2H2Ru(SiH4)RuH2(PR3)2
Isabelle Atheaux,† Bruno Donnadieu,† V. Rodriguez,†,§
Sylviane Sabo-Etienne,*,† Bruno Chaudret,†
Khansaa Hussein,‡,| and Jean-Claude Barthelat‡
Laboratoire de Chimie de Coordination du CNRS
205 route de Narbonne, 31077 Toulouse Cedex 04, France
Laboratoire de Physique Quantique, IRSAMC (UMR 5626)
UniVersite´ Paul Sabatier, 118 route de Narbonne
31062 Toulouse Cedex 4, France
ReceiVed January 21, 2000
Since the report of the first silane σ-complex in 1969,1 the
activation of Si-H bonds has been the focus of intense research
effort.2,3 Hydrosilylation, dehydrogenative silylation, and dehy-
drogenative polymerization of silanes represent the most important
applications and involve a wide variety of silanes.4 However, the
scarcity of publications on reactions using SiH4, the simplest
silane, and transition metals is probably the result of safety
concerns. The only transition metal η2-SiH4 complex Mo(η2-
SiH4)(CO)(R2PC2H4PR2)2 was reported in 1995 by Luo, Kubas
et al.5 This compound was obtained by direct reaction of SiH4
on the molybdenum complex Mo(CO)(R2PC2H4PR2)2. To cir-
cumvent any hazard associated with the use of SiH4, its in situ
generation by catalytic redistribution of HSi(OEt)3 by Cp2TiMe2
was exploited by Harrod et al.6 Such alkoxyhydrosilane redistri-
butions were also catalyzed by zirconium and hafnium complexes
as shown by Tilley et al.7
Within the last three years, we have made a lot of progress on
the isolation of unusual complexes involving in particular more
than one σ-bond. We have described a series of bis(silane)
mononuclear complexes [RuH2{(η2-H-SiR2)2X}(PR′3)2] with two
σ-Si-H bonds and demonstrated that these compounds are
stabilized by secondary H‚‚‚Si interactions.8 These additional
interactions are also responsible for the stability of another
complex incorporating two different σ-bonds RuH2(η2-H2)(η2-
Figure 1. ORTEP drawing of compound 2b.
H-SiPh3)(PCy3)2 (1).9 We present in this contribution our first
studies on the reactivity of dihydrogenosilanes with ruthenium
complexes, and the isolation of the two complexes (PR3)2H2Ru-
i
(SiH4)RuH2(PR3)2 (R) Cy, 2a; R ) Pr, 2b) with a SiH4 ligand
trapped by two dihydridobis(phosphine)ruthenium units.
Addition at room temperature of 2 equiv of H2SiPhMe to a
suspension of the bis(dihydrogen) complex RuH2(H2)2(PCy3)2 (3)10
in pentane results in immediate gas evolution, and (PCy3)2H2Ru-
(SiH4)RuH2(PCy3)2 (2a) is isolated as a white powder in 32%
1
yield.11 The H NMR spectrum of 2a in C6D6 solution at room
temperature exhibits a pseudotriplet at δ -7.89 that transforms
into a singlet upon phosphorus decoupling with satellites due to
coupling to a single silicon (JSi-H ) 36 Hz). Upon cooling, two
separate broad signals of equal intensities are observed at δ -6.0
and δ -8.6. The 29Si{1H} NMR shows a singlet at δ 290.2, and
the 29Si INEPT spectrum shows a nonet (JSi-H ) 36 Hz) in
agreement with eight hydrogen atoms (in fast exchange) coupled
to the silicon. We were able to obtain an X-ray structure of the
analogous complex 2b with the triisopropylphosphine in place
of PCy3.11,12 2b and 2a display the same basic NMR features.
An ORTEP plot is shown in Figure 1. 2b is a dinuclear ruthenium
complex with each ruthenium in a roughly octahedral geometry.
The figure clearly depicts the unique geometry of the SiH4 ligand.
The two ruthenium and the silicon atoms are linear (z axis) with
one of the shortest Ru-Si distances ever reported (2.1875(4) Å),2
even slightly shorter than in [Cp*(PMe3)2RudSiMe2]+ (2.238(2)
Å).13 Moreover, highly downfield 29Si NMR resonances have been
associated with the presence of a silylene ligand.13b The four
hydrogen atoms H1, H2, H3, and H4 are in a plane (xz) perpen-
dicular to the plane (yz) containing the four other ones (H1′-
H4′). The Si-H3 and Si-H4 distances, 1.69(3) and 1.73(3) Å
respectively, indicate significant Si-H bond lengthening (1.48
Å for organosilicon compounds).2,3 If we consider a complex
† Laboratoire de Chimie de Coordination du CNRS.
‡ Universite´ Paul Sabatier.
§ Permanent address: Departamento de Qu´ımica Inorga´nica, Facultad de
Qu´ımica, 30071-Murcia, Spain.
| Permanent address: Faculty of Sciences, University Al Baath, Homs,
Syria.
(1) Hoyano, J. K.; Elder, M.; Graham, W. A. G. J. Am. Chem. Soc. 1969,
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(2) Corey, J. Y.; Braddock-Wilking, J. Chem. ReV. 1999, 99, 175.
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Schubert, U. AdV. Organomet. Chem. 1990, 30, 151.
(4) (a) Speier, J. L. AdV. Organomet. Chem. 1979, 17, 407. (b) Brown, S.
S.; Kendrick, T. C.; McVie, J.; Thomas, D. R. In ComprehensiVe Organo-
metallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.;
Pergamon press: New York, 1994; Vol. 2, Chapter 4. (c) West, R. In The
Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; John
Wiley & Sons: New York, 1989; Chapter 19. (d) Ojima, I. In The Chemistry
of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; John Wiley &
Sons: New York, 1989; Chapter 25. (e) Lapointe, A. M.; Rix, F. C.; Brookhart,
M. J. Am. Chem. Soc. 1997, 119, 906. (f) Woo, H. G.; Waltzer, J. F.; Tilley,
T. D. J. Am. Chem. Soc. 1992, 114, 7047. (g) Procopio, L. J.; Carroll, P. J.;
Berry, D. H. J. Am. Chem. Soc. 1994, 116, 177.
(5) Luo, X.-L.; Kubas, G. J.; Burns, C. J.; Bryan, J. C.; Unkefer, C. J. J.
Am. Chem. Soc. 1995, 117, 1159.
(6) (a) Xin, S.; Aitken, C.; Harrod, J. F.; Mu, Y.; Samuel, E. Can. J. Chem.
1990, 68, 471. (b) Hao, L.; Lebuis, A.-M.; Harrod, J. F.; Samuel, E. Chem.
Commun. 1997, 2193. (c) Hao, L.; Lebuis, A.-M.; Harrod, J. F. Chem.
Commun. 1998, 1089.
(7) Woo, H. G.; Heyn, R. H.; Tilley, T. D. J. Am. Chem. Soc. 1992, 114,
5698.
(8) (a) Delpech, F.; Sabo-Etienne, S.; Chaudret, B.; Daran, J. C J. Am.
Chem. Soc. 1997, 119, 3167. (b) Delpech, F.; Sabo-Etienne, S.; Chaudret, B.;
Daran, J. C.; Hussein, K.; Marsden, C. J.; Barthelat, J.-C. J. Am. Chem. Soc.
1999, 121, 6668.
1
incorporating four σ-Si-H bonds (4 JSi-H) and four classical
hydrides (4 2JSi-H), one can estimate a Jσ-Si-H value in the range
50-70 Hz.14 This is in perfect agreement with the Si-H distances
found by X-ray and can be compared to previous data.2,3,5,8
To better understand the nature of the bonding between SiH4
and the two metal-containing units, we have performed DFT/
(9) Hussein, K.; Marsden, C. J.; Barthelat, J.-C.; Rodriguez, V.; Conejero,
S.; Sabo-Etienne, S.; Donnadieu, B.; Chaudret, B. Chem. Commun. 1999, 1315.
(10) Sabo-Etienne, S.; Chaudret, B. Coord. Chem. ReV. 1998, 178-180,
381.
(11) See Supporting Information for details on the synthesis and charac-
terization of 2a and 2b.
(12) Crystal data for 2b: pale yellow crystal, T ) 160 K, monoclinic,
C2/c, a ) 19.588(2) Å, b ) 12.1805(15) Å, c ) 19.823(3) Å, â ) 98.066
(15) °, Z ) 8, R1 ) 0.0281, GOF ) 1.034.
(13) (a) Grumbine, S. K.; Tilley, T. D.; Arnold, F. P.; Rheingold, A. L. J.
Am. Chem. Soc. 1994, 116, 5495. (b) Grumbine, S. K.; Mitchell, G. P.; Straus,
D. A.; Tilley, T. D.; Rheingold, A. L. Organometallics 1998, 17, 5607.
10.1021/ja000223p CCC: $19.00 © 2000 American Chemical Society
Published on Web 05/24/2000

Communications to the Editor
J. Am. Chem. Soc., Vol. 122, No. 23, 2000 5665
Table 1. Selected Optimized Geometrical Parameters for
(PH3)2H2Ru(SiH4)RuH2(PH3)2 2 and X-ray Data for
(PiPr3)2H2Ru(SiH4)RuH2(PiPr3)2 2ba
character. The nature of this Ru-Si interaction was first studied
by a natural bond orbital (NBO) analysis:18 it appears that in 2
as well as in A and B, the Ru-Si bond would be highly polar
with a bond order smaller than 1. Moreover, analysis of the
molecular orbitals reveals that the bonding interactions between
SiH4 and the two ruthenium fragments occur through the σ Si-H
bonds. In each xz and yz planes, the two Si-H hybrid orbitals
interact with the empty d orbital of one ruthenium center, whereas
a back-bonding delocalization occurs from the occupied d orbital
of the other Ru center into the σ* Si-H antibonding orbitals.
This double interaction is shown in Figure 2 where the two
molecular orbitals involving the metal orbitals of primarily dyz
character are depicted. The short Ru-Si distances cannot be
considered as classical double bonds but are the result of these
multiple σ-interactions. A high binding energy of 255 kJ.mol-1
between SiH4 and the RuH2(PH3)2 fragments is calculated.
When the reaction of two equiv of H2SiPhMe to (3) is
performed in an NMR tube in C6D6 solution, two major ruthenium
DFT/B3LYP
X-ray
Ru-H1(H2)
Ru-H3(H4)
Si-H3(H4)
Ru-Si
Ru-P1(P2)
H1-Ru-H2
H3-Ru-H4
H3-Si-H4
P1-Ru-P2
Ru-Si-Ru′
1.626
1.812
1.685
2.229
2.308
86.0
1.49(2); 1.52(3)
1.62(3); 1.62(3)
1.69(3); 1.73(3)
2.1875(4)
2.3119(7); 2.3129(7)
86.6(15)
101.4(14)
94.2(14)
155.18(2)
179.40(4)
95.9
105.9
155.4
180.0
a See Figure 1 for labeling of the atoms. Distances are in Å and
angles in degrees.
1
compounds are identified by H and 31P NMR as 2a and RuH2-
(η2-H2)(η2-H-SiPh3)(PCy3)2 (1), together with the two silicon
compounds HSiPh2Me and HSiMe2Ph in a 1:1.3:2.2:3.4 ratio,
respectively. A small amount of an unidentified hydride complex
was also detected as well as traces of HMe2SiSiMe2H. Clearly
this reaction undergoes redistribution at silicon with Si-C bond
breaking allowing the generation of SiH4 immediately trapped
by two dihydride ruthenium units. In situ generation of HSiPh3
also results in its coordination to ruthenium producing the known
complex 1. It is remarkable that formation of 2a is also observed
when using a dihydrogenosilane such as H2SiEt2.19
In summary, we report here a unique mode of coordination of
the simplest silane SiH4 to a transition metal complex. In our
system, in situ generation of SiH4 by redistribution of H2SiRR′
is catalyzed by a ruthenium complex; the redistribution mechanism
has still to be elucidated. In view of the structural and theoretical
data, (PR3)2H2Ru(SiH4)RuH2(PR3)2 can be formulated as com-
plexes in which SiH4 is trapped by two RuH2(PR3)2 units and
acts as a bridging ligand via four σ-Si-H bonds. These novel
interactions involve in each case σ-donation to a ruthenium and
back-bonding from the other ruthenium, and they are indeed
responsible for the very short Ru-Si distances. They represent
the first examples of a new mode of bonding of a silane, in
addition to full oxidative addition and to usual σ-bond coordina-
tion. Reactivity and catalytic activity studies of 2a,b are in
progress.
Figure 2. Isovalue representation of the 4e and 7e valence molecular
orbitals of 2 involved in the σSi-H f dyz Ru′ (top) and dyz Ru f σ*Si-H
-3 1/2
(bottom) interactions. The surfaces correspond to 0.05 (ea0
) .
B3LYP calculations on the model complex (PH3)2H2Ru(SiH4)-
RuH2(PH3)2 (2).15 A geometry optimization followed by a
vibrational frequency analysis results in a D2d geometry with no
imaginary frequencies. Optimized geometrical parameters and
X-ray data for 2b are compared in Table 1. Our calculation
confirms the overall structure found by X-ray diffraction. As
expected, X-ray Ru-H distances are found shorter than the
calculated ones. However, the calculated Ru-Si distance (2.229
Å) is in good agreement with the experimental one. The
comparison with optimized Ru-Si bond lengths in η2-silane
complexes (2.425 Å in [RuH2{(η2-H-SiH2)2(C6H4)}(PH3)2] (A),8b
2.394 Å in RuH2(η2-H2)(η2-H-SiH3)(PH3)2 (B))9 reveals an
unusual short distance in 2, suggesting some double bond
Acknowledgment. This work is supported by the CNRS. We thank
the CINES (Montpellier, France) for a generous allocation of computer
time.
Supporting Information Available: X-ray structural information on
2b. A table of natural atomic charges and bond orders for 2, A and B.
Synthesis and characterization data for 2a and 2b (PDF). An X-ray
crystallographic file (CIF). This material is available free of charge via
the Internet at http://pubs.acs.org.
JA000223P
(16) Rodriguez, V.; Sabo-Etienne, S.; Chaudret, B.; Thoburn, J.; Ulrich,
S.; Limbach, H.-H.; Eckert, J.; Barthelat, J.-C.; Hussein, K.; Marsden, C. J.
Inorg. Chem. 1998, 37, 3475.
(14) JH-Siobs ) 1/8(4 1JH-Si + 4 2JH-Si) ) 36 Hz. Assuming a 2JH-Si value
in the range 0-20 Hz for the coupling between the silicon and the classical
hydrides H1, H2, H1′, and H2′, one can estimate a JH-Si value of 52 to 72 Hz
for the coupling between the silicon and the hydrides H3, H4, H3′, and H4′.
(15) Ruthenium centers were described with a relativistic small-core
pseudopotential and a [5s,5p,3d] contracted Gaussian basis set.16 Pseudopo-
tentials developed in Toulouse17 were used to represent the 10-electron core
of the Si and P atoms. For these atoms and for the hydrogen atoms directly
attached to Si and Ru, double-ú plus polarization basis sets were used. All
calculations were carried out with the Gaussian 98 program (see Supporting
Information).
(17) Bouteiller, Y.; Mijoule, C.; Nizam, M.; Barthelat, J.-C.; Daudey, J.-
P.; Pe´lissier, M.; Silvi, B. Mol. Phys. 1988, 65, 2664.
(18) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. ReV. 1988, 88, 899.
(19) For redistributions at silicon, see refs 6, 7, and 20. Interestingly, Suzuki
t
et al. have described in 1995 the activation of Bu2SiH2 by Cp*Ru(µ-H)4-
RuCp* in which case, the dinuclear ruthenium complex [Cp*Ru(µ-H)]2(µ-
η2:η2-H2SitBu2) is obtained with the dihydrogenosilane bound to each
ruthenium via two σ-Si-H bonds.21
(20) Curtis, M. D.; Epstein, P. S. AdV. Organomet. Chem. 1981, 19, 213.
(21) Takao, T.; Yoshida, S.; Suzuki, H.; Tanaka, M. Organometallics 1995,
14, 3855.