X-ray structure and theoretical studies of RuH2(η2-H2)(η2-H-SiPh3) (PCy3)2, a complex with two different η2-coordinated σ bonds

Article abstract of DOI:10.1039/a901558b

Weak interactions between the silicon and the hydrides are responsible for the stabilization of the title complex bearing two different coordinated σ-bonds, (η²-H₂) and (η²-H-SiPh₃).

Full text of DOI:10.1039/a901558b

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X-Ray structure and theoretical studies of RuH2(h -H2)(h -H-SiPh3)(PCy3)2, a
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complex with two different h -coordinated s bonds
Khansaa Hussein,a† Colin J. Marsden,a Jean-Claude Barthelat,a Venancio Rodriguez,b Salvador Conejero,b
Sylviane Sabo-Etienne,*b Bruno Donnadieub and Bruno Chaudretb
a Laboratoire de Physique Quantique, IRSAMC (UMR 5626), Université Paul Sabatier, 118 route de Narbonne,
31062 Toulouse Cedex 4, France
b Laboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne, 31077 Toulouse Cedex 04, France.
E-mail: sabo@lcc-toulouse.fr
Received (in Basel, Switzerland) 25th February 1999, Accepted 11th June 1999
Weak interactions between the silicon and the hydrides are
responsible for the stabilization of the title complex bearing
1.66(2) Å with the two Ru–H distances involving the di-
hydrogen ligand markedly higher. The dihydrogen ligand is
characterized by a H1–H2 distance of 0.82(2) Å, a value in
agreement with an unstretched dihydrogen complex as high-
lighted by its high reactivity [addition of H2 or N2 results in
immediate elimination of the silane and formation of the
corresponding bis(dihydrogen) or bis(dinitrogen) complex].
The Si…H4 distance of 1.83(3) Å is below the limit of 2 Å
normally admitted for s-Si–H bonds. Thus the silicon is almost
symmetrically bonded to H5 and H4, as can be seen from the H–
Ru–Si angles of 45.9(11) and 50.2(10)°. In addition the Si…H3
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two different coordinated s-bonds, (h -H2) and (h -H–
SiPh3).
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2
Nowadays the existence of h -dihydrogen or h -silane coor-
dination to a metal centre is well established.1–3 These h -H–X
2
species (X = H, Si) are often considered as a representation of
the arrested oxidative addition of dihydrogen or silanes to a
metal center. They are thus often invoked in many catalytic
reactions such as hydrogenation or hydrosilylation.1–4 When
considering the small number of complexes accommodating
two s-HX bonds, one important question is to determine the
factors that promote the formation of such species. Indeed, there
are only two thermally stable bis(dihydrogen) complexes3
[RuH2(H2)2(PCy3)2] 1 and [Tp*RuH(H2)2], and we have
recently described a new family of bis(silane) complexes
2
[RuH2{(h -H–SiR2)2X}(PRA3)2] in which the disilane ligand
acts as a chelate and is coordinated to the ruthenium via two s-
H–Si bonds.5
Here, we present the first structural characterization of a
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mixed s-(H–H) and s-(H–Si) complex RuH2(h -H2)(h -H–
SiPh3)(PCy3)2 2 as well as theoretical studies highlighting the
importance of weak formally non-bonding interactions between
the silicon and the classical hydrides.
In 1994, we reported our first results concerning the reactivity
of 1 toward weakly coordinating ligands such as N2 and HEPh3
(E = Si, Ge).6 Substitution of two or one dihydrogen ligands
2
was observed leading to RuH2(N2)2(PCy3)2 and RuH2(h -
2
H2)(h -H–EPh3)(PCy3)2 respectively. The silane complex 2
was obtained by addition of 1 equiv. of HSiPh3 to a pentane
suspension of 1. On the basis of NMR data and T1 measure-
ments, we proposed a formulation for 2 in which the two
phosphine ligands were in a trans position, in agreement with
the presence of such bulky phosphines. However, we have now
succeeded in growing crystals and have obtained new informa-
tion from the X-ray diffraction study. The molecular structure is
shown in Fig. 1 and the principal distances and angles are listed
in Table 1.‡ Two molecules are found in the asymmetric unit;
however, as no significant differences are observed, we present
here only the data concerning one molecule. Surprisingly, the
phosphines are in a cis configuration with a P1–Ru–P2 angle of
109.71(5)°. The classical hydride H4 is trans to one phosphine
with a P1–Ru–H4 angle of 166.5(14)° whereas the hydrogen H5
involved in the s-H–Si bond is trans to the other phosphine with
a P2–Ru–H5 angle of 170.7(11)°. The second classical hydride
H3 is trans to the dihydrogen ligand H1–H2 with H3–Ru–H1
and H3–Ru–H2 angles of 163(2) and 168(2)°, respectively.
Fig. 1 ORTEP12 drawing of compound 2.
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Table 1 Calculated geometrical parameters for the RuH2(h -H2)(h -H–
SiH3)(PH3)2 ground-state isomer and X-ray data for 2a
B3LYP X-ray
B3LYP X-ray
Ru–H1
Ru–H3
Ru–H5
Si…H3
H1–H2
Ru–P1
H3…H4
1.807
1.626
1.643
2.116
0.849
2.370
2.301
1.66(2)
Ru–H2
Ru–H4
Si–H5
Si…H4
Ru–Si
1.785
1.641
1.946
2.071
2.394
2.367
1.64(2)
1.47(4)
1.72(3)
1.83(3)
2.3846(18)
2.3921(16)
1.49(4)
1.54(4)
2.40(4)
0.82(2)
2.4058(17) Ru–P2
2.22(2)
P1–Ru–P2 98.9
P2–Ru–H5 177.6
Si–Ru–H3 60.0
H1–Ru–H2 27.4
P1–Ru–Si 114.4
a
109.71(5)
P1–Ru–H4 171.8
166.5(14)
170.7(11)
72.6(14)
28.9(8)
Si–Ru–H5 53.8
Si–Ru–H4 58.3
H2–Ru–H3 162.9
P2–Ru–Si 124.9
45.9(11)
50.2(10)
168(2)
2
The (h -Si–H) coordination is confirmed by a significant
lengthening of the Si–H5 bond: 1.72(3) Å (ca. 1.49 Å in
free silanes). The Ru–H bond lengths vary from 1.47(4) to
118.49(6)
124.85(6)
See Fig. 1 for labelling of the atoms. Distances are in Å and angles
† Permanent address: Department of Chemistry, Faculty of Sciences,
University Al Baath, Homs, Syria.
in °.
Chem. Commun., 1999, 1315–1316
1315

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Notes and references
‡ Crystal data for 2: C58H91OP2SiRu, M = 995.59, triclinic, space group
P1, T = 160(2) K, a = 12.7694(16), b = 20.991(3), c = 21.691(2) Å, a
= 94.763(14), b = 103.677(14), g = 98.202(15)°, V = 5550.0(12) Å3, Z
= 4, m = 0.342 mm21, reflections collected/unique = 44792/16676, R1 =
0.0381, wR2 = 0.0626. The H1–H5 atoms were located on difference
Fourier syntheses; their coordinates were refined with isotropic thermal
parameters. CCDC 182/1287. See http://www.rsc.org/suppdata/cc/
1999/1315/ for crystallographic files in .cif format.
§ All calculations were performed with the Gaussian 94 program.8 The Si
and P atoms were described by standard pseudo-potentials developed in
Toulouse9 with a double-zeta plus polarization basis set. A double-zeta plus
polarization basis was used for the hydrogen atoms, except for those of the
phosphine ligands (DZ only).
Fig. 2 The B3LYP-optimized structures of isomers A and B.
¶ We obtain non-negligible positive overlap populations between Si and H3
or H4 of 0.05 and between Si and H5 of 0.09 (0.40 in free SiH4).
∑ The energy differences between the products and the reactants are 292.7
kJ mol21 for SiH4 and 273.8 kJ mol21 for H2. Further details on related
complexes will be published elsewhere.
distance is 2.40(3) Å, allowing further Si…H interactions as
also found by theoretical calculations. Similar interactions are
also responsible for the cis geometry for the two PCy3 ligands
2
in the ruthenium complexes RuH2{(h -H–SiR2)2X}(PRA3)2
accommodating two s-Si–H bonds.5b
** Intramolecular hydrogen bonding between a hydride and a hydrogen
bond donor.
DFT/B3LYP calculations using a relativistic small-core
pseudopotential and a [5s,5p,3d] contracted Gaussian basis for
1 For reviews on dihydrogen complexes chemistry: G. J. Kubas, Acc.
Chem. Res., 1988, 21, 120; R. H. Crabtree, Acc. Chem. Res., 1990, 23,
95; P. G. Jessop and R. H. Morris, Coord. Chem., Rev., 1992, 121, 155;
D. M. Heinekey and W. J. Oldham Jr., Chem. Rev., 1993, 93, 913; R. H.
Crabtree, Angew. Chem., Int. Ed. Engl., 1993, 32, 789; M. A. Esteruelas
and L. A. Oro, Chem. Rev., 1998, 98, 577.
2 For reviews on silane complexes: (a) U. Schubert, Adv. Organomet.
Chem., 1990, 30, 151; (b) J. Y. Corey and J. Braddock-Wilking, Chem.
Rev., 1999, 99, 175.
3 S. Sabo-Etienne and B. Chaudret, Coord. Chem. Rev., 1998, 178–180,
381.
4 M. L. Christ, S. Sabo-Etienne and B. Chaudret, Organometallics, 1995,
14, 1082; F. Delpech, S. Sabo-Etienne, B. Donnadieu and B. Chaudret,
Organometallics, 1998, 17, 4926.
5 (a) F. Delpech, S. Sabo-Etienne, B. Chaudret and J. C. Daran, J. Am.
Chem. Soc., 1997, 119, 3167; (b) F. Delpech, S. Sabo-Etienne, B.
Chaudret, J. C. Daran, K. Hussein, C. J. Marsden and J.-C. Barthelat
J. Am. Chem. Soc., 1999, in press.
6 S. Sabo-Etienne, M. Hernandez, G. Chung, B. Chaudret and A. Castel,
New J. Chem., 1994, 18, 175.
7 V. Rodriguez, S. Sabo-Etienne, B. Chaudret, J. Thoburn, S. Ulrich,
H.-H. Limbach, J. Eckert, J.-C. Barthelat, K. Hussein and C. J. Marsden,
Inorg. Chem., 1998, 37, 3475.
8 Gaussian 94, M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill,
B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. A. Keith, G. A.
Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G.
Zakrewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski, B. B. Stefanov, A.
Nanayakkara, M. Challacombe, C. Y. Peng, P. Y. Ayala, W. Chen,
M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin,
D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-
Gordon, C. Gonzalez and J. A. Pople, Gaussian, Inc., Pittsburgh PA,
1995.
9 Y. Bouteiller, C. Mijoule, M. Nizam, J.-C. Barthelat, J.-P. Daudey, M.
Pélissier and B. Silvi. Mol. Phys., 1988, 65, 2664.
10 G. I. Nikonov, L. G. Kuzmina, D. A. Lemenovskii and V. V. Kotov,
J. Am. Chem. Soc., 1995, 117, 10 133; M.-F. Fan and Z. Lin,
Organometallics, 1998, 17, 1092.
11 See, for example, R. H. Crabtree, P. E. M. Siegbahn, O. Eisenstein,
A. L. Rheingold and T. F. Koetzle, Acc. Chem. Res., 1996, 29, 348; S.
Park, A. J. Lough and R. H. Morris, Inorg. Chem., 1996, 35, 3001; J. A.
Ayllon, S. Sabo-Etienne, B. Chaudret, S. Ulrich and H.-H. Limbach,
Inorg. Chim. Acta, 1997, 259, 1; A. Castellanos, J. A. Ayllon, S. Sabo-
Etienne, B. Donnadieu, B. Chaudret, W. Yao, K. Kavallieratos and R. H.
Crabtree, C. R. Acad. Sci. 1999, in press.
2
ruthenium7 were performed on the model complex RuH2(h -
2
H2)(h -H–SiH3)(PH3)2.§ Geometry optimizations followed by
vibrational frequency analyses allow identification of five
singlet local minima. The structure of the most stable isomer A
in Fig. 2 (C1 symmetry) closely resembles that found by X-ray
diffraction for 2; we note that location of H atoms by X-ray
diffraction is subject to considerable uncertainties, and that the
computed P1–Ru–P2 bond angle would increase by about 7° if
the PH3 ligands were replaced by a more realistic model, such
as PMe3.5b Optimized geometrical parameters are listed in
Table 1 for comparison. The origin of the unusual cis geometry
for the two phosphines can be found in the presence of two
attractive non-bonded interactions between the silicon atom and
the two classical hydrides H3 and H4;10 the attractive nature
of these interactions is shown by the Mulliken population
analysis.¶ Indeed, the calculated Si…H3 and Si…H4 distances,
2.116 and 2.071 Å, respectively, are much shorter than the
sum of the van der Waals radii of silicon and hydrogen (3.3 Å).
Such interactions are precluded geometrically in the four other
isomers (all having trans phosphines). The lowest-energy of
these is better described as a hydrido(silyl) complex RuH-
2
(SiH3)(h -H2)2(PH3)2 (B in Fig. 2); it is only 8 kJ mol21 above
A [17 kJ mol21 by single-point CCSD(T) calculations].
Relative B3LYP energies of the other isomers vary from 16 to
41 kJ mol21. Binding energies of the SiH4 and H2 ligands have
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been calculated from the RuH2(h -H2)(PH3)2 and RuH2(h -H–
SiH3)(PH3)2 fragments.∑
As pointed out very recently by Corey and Braddock-Wilking
in their impressive review on the reactions of hydrosilanes with
transition-metal complexes, ‘Several variations of interactions
seem to occur between silanes and metals, from full oxidative
addition to that of arrested addition with an interaction between
a metal orbital and a Si–H sigma bond’.2b We have shown here
how important additional Si…H interactions are; they control
the coordination geometry at the metal centre. This type of
bonding deserves special attention for future studies, given that
it involves energies comparable to those in the ‘dihydrogen
bonds’** recently described by several groups,11 and that it
might well be of primary importance in catalytic silicon
transformations.
12 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National
Laboratory, Oak Ridge, TN, 1976.
This work is supported by the CNRS. We thank the Centre
National Universitaire Sud de Calcul, Montpellier, France
(project irs 1013) for a generous allocation of computer time.
Communication 9/01558B
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Chem. Commun., 1999, 1315–1316