Step-by-step introduction of silazane moieties at ruthenium: Different extents of Ru-H-Si bond activation

Article abstract of DOI:10.1021/ic302682f

The coordination of pyridine-2-amino(methyl)dimethylsilane ligands to ruthenium has afforded access to a family of novel complexes that display multicenter Ru-H-Si interactions according to the number of incorporated ligands. The new complexes Ru[κ-Si,N-(SiMe₂)N(Me)(C ₅H₄N)](η⁴-C₈H ₁₂)(η³-C₈H₁₁) (1), Ru ₂(μ-H)₂(H)₂[κ-Si,N-(SiMe ₂)N(Me)(C₅H₄N)]₄ (2), and Ru(H)[κ-Si,N-(SiMe₂)N(Me)(C₅H₄N)] ₃ (3) were isolated and fully characterized. The complexes exhibit different degrees of Si-H activation: complete Si-H cleavage, secondary interactions between the atoms (SISHA), and η²-Si-H coordination. Reversible protonation of 3 leading to the cationic complex [RuH{(η²-H-SiMe₂)N(Me)κ-N-(C₅H ₄N)}{κ-Si,N-(SiMe₂)N(Me)(C₅H ₄N)}₂]⁺[BAr^F₄] ^- (5) was also demonstrated. The coordination modes in these systems were carefully studied with a combination of X-ray and neutron diffraction analysis, DFT geometry optimization, and multinuclear NMR spectroscopy.

Full text of DOI:10.1021/ic302682f

Article
pubs.acs.org/IC
Step-by-Step Introduction of Silazane Moieties at Ruthenium:
Different Extents of Ru−H−Si Bond Activation
Katharine A. Smart,†,‡ Mary Grellier,*,†,‡ Laure Vendier,†,‡ Sax A. Mason,§ Silvia C. Capelli,§
Alberto Albinati,∥ and Sylviane Sabo-Etienne*,†,‡
†LCC (Laboratoire de Chimie de Coordination), CNRS, 205 Route de Narbonne, F-31077 Toulouse, France
‡Universite
́
de Toulouse, UPS, INPT, F-31077 Toulouse, France
§Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9, France
∥Dipartimento di Chimica, Universita
̀
di Milano, Via C. Golgi, 19, 20133 Milan, Italy
S
* Supporting Information
ABSTRACT: The coordination of pyridine-2-amino(methyl)-
dimethylsilane ligands to ruthenium has afforded access to a
family of novel complexes that display multicenter Ru−H−Si
interactions according to the number of incorporated ligands.
The new complexes Ru[κ-Si,N-(SiMe2)N(Me)(C5H4N)](η4-
C8H12)(η3-C8H11) (1), Ru2(μ-H)2(H)2[κ-Si,N-(SiMe2)N-
(Me)(C5H4N)]4 (2), and Ru(H)[κ-Si,N-(SiMe2)N(Me)-
(C5H4N)]3 (3) were isolated and fully characterized. The
complexes exhibit different degrees of Si−H activation:
complete Si−H cleavage, secondary interactions between the
atoms (SISHA), and η2-Si−H coordination. Reversible protonation of 3 leading to the cationic complex [RuH{(η2-H-
SiMe2)N(Me)κ-N-(C5H4N)}{κ-Si,N-(SiMe2)N(Me)(C5H4N)}2]+[BArF ]− (5) was also demonstrated. The coordination modes
4
in these systems were carefully studied with a combination of X-ray and neutron diffraction analysis, DFT geometry optimization,
and multinuclear NMR spectroscopy.
substituted compound, 2-pyridinetetramethyldisilazane, to the
two ruthenium complexes RuH2(H2)2(PCy3)2 and its precursor
Ru(η4-C8H12)(η6-C8H10) gave rise to the formation of
mononuclear complexes with dangling Si−H bonds and
pyridine coordination to the ruthenium.4 Clearly modification
of the N-substituent of silazanes is a means of achieving novel
complexes displaying a large variety of coordination modes
where it is possible to modulate Si−H bond activation.
Comprehensive understanding of Si−H activation by metal
centers is indeed crucial for the tuning of catalytic processes
such as hydrosilylation.5 In the present work we focus on the
use of pyridine-2-amino(methyl)dimethylsilane to prepare
mononuclear and dinuclear ruthenium compounds incorporat-
ing one, two, or three silazane ligands in a stepwise manner.
The compounds exhibit a range of multicenter Ru−H−Si
bonding, from Si−H cleavage to Si2−H, Si3−H, and [Si3−H2]+
interactions, and we show that reversible protonation can be
achieved. The nature of the bonding in these dynamic systems
has been delineated with a combination of multinuclear NMR
spectroscopy, DFT, X-ray, and neutron structural determi-
nations.
INTRODUCTION
■
Silazane (R3Si)nN(R′)3‑n compounds are implicated in many
domains, from organic chemistry to materials science.1 Silazane
derivatives bearing a Si−H function can offer additional
multicenter properties, but except for the area of ceramics
where they serve as precursors for the preparation of polymer-
derived ceramics, their chemistry remains relatively unex-
plored.2 Recently, Sadow and co-workers reported the
magnesium-catalyzed formation of Si−N bonds, promoting
the method as an alternative to the substitution reaction of
chlorosilanes with amines that is often employed in the
synthesis of silazanes.2a Silazanes employed as ligands have
been shown by Nolan, Thomas, and co-workers to increase the
activity of gold catalysts in the polymerization of rac-β-
butyrolactone.2e In the field of materials, the spectroscopic
properties of the Si−H bonds of silazanes were for example
exploited by Anwander and co-workers in the characterization
of iron silylamide-grafted periodic mesoporous silica.1c
We entered this field with the commercial disilazane
compound, (Me2HSi)2NH, and achieved catalytic, selective
deuteration to give (Me2DSi)2NH. Moreover, we showed that
(Me2HSi)2NH could substitute the two labile dihydrogen
ligands in RuH2(H2)2(PCy3)2 to form the corresponding
disilazane complex RuH2{(η2-HSiMe2)2NH}(PCy3)2 stabilized
by secondary interactions between the hydrides and the silicon
atoms (SISHA).3 In contrast, the coordination of the pyridine-
Received: December 6, 2012
Published: February 19, 2013
© 2013 American Chemical Society
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Scheme 1. Step by Step Synthesis of Complexes 1−3
RESULTS AND DISCUSSION
■
Synthesis of Complexes 1−3. Addition of pyridine-2-
amino(methyl)dimethylsilane to a solution of Ru(η4-C8H12)-
(η6-C8H10) led to the formation of Ru[κ-Si,N-(SiMe2)N(Me)-
(C5H4N)](η4-C8H12)(η3-C8H11) (1) (Scheme 1), which was
isolated as a pale yellow powder in 81% yield and characterized
by NMR spectroscopy and X-ray diffraction. Compound 1
results from the coordination of the silazane, through Si−H
bond cleavage inducing the reduction of cyclooctatriene to
form an η3-allyl system. Heteronuclear (H,C)-single quantum
coherence (HSQC) NMR spectroscopy enabled assignment of
the ligands around the metal center. The 1H NMR spectrum of
1 has a relatively high field signal at δ = −0.02 ppm for one of
the protons in the η3-C8H11 ring. A 29Si singlet at δ = 81.0 ppm
is observed in the gradient-pulsed heteronuclear (H,Si)-
multiple quantum coherence (HMQC) NMR spectrum of 1,
which can be compared to δ = −4.14 for the free ligand. The
three carbon atoms of the allyl system resonate at δ 58.55, δ
106.85, and δ 70.03. As expected, the central allyl carbon is the
most deshielded.6 The adjacent unsaturated carbons, which do
not have a bonding interaction with the ruthenium atom, are
found at δ 137.07 and δ 123.89. The two nitrogen
environments are distinguished by (H,N)-HMQC NMR
spectroscopy with δ = −168.7 ppm for the coordinating
pyridinic nitrogen and δ = −282.9 ppm for the amino nitrogen,
comparable with −104.4 ppm and −312.2 ppm for the
corresponding nitrogen atoms in the free ligand. The X-ray
structure of 1 is depicted in Figure 1, and geometrical
parameters are listed in Table 1. The carbon−carbon bond
lengths of the C8H11 ligand are indicative of five adjacent
unsaturated carbon atoms (C17−21), with three of these
carbon atoms (C17−19) providing an η3-bonding interaction
with ruthenium. The Ru−C allylic (C17−19) distances of 1 are
2.282(2), 2.227(2), and 2.442(2) Å. The presence of a CC
bond adjacent to the coordinated allyl moiety might be
responsible for the lengthening of the Ru−C19 distance. For
comparison, in [κ2P,P′-{(η3-C6H8)CyP(CH2)3PCy2}Ru(η3-
C8H13)] the corresponding Ru−C allylic distances are
2.270(4), 2.151(3), and 2.311(4).6a This instance in 1 of η3-
Figure 1. X-ray molecular structure of 1 (50% probability ellipsoids
with hydrogen atoms represented by green spheres or excluded for
clarity).
Table 1. Selected Bond Distances (Å) and Angles (deg) for 1
C9−C10
1.410(3)
1.415(3)
1.426(3)
1.414(3)
1.479(3)
1.325(4)
1.522(4)
1.542(4)
1.543(3)
78.76(5)
Ru−C9
Ru−C10
Ru−C13
Ru−C14
Ru−C17
Ru−C18
Ru−C19
Ru−Si
2.227(2)
2.207(2)
2.189(2)
2.195(2)
2.282(2)
2.227(2)
2.442(2)
2.3809(7)
2.188(2)
C13−C14
C17−C18
C18−C19
C19−C20
C20−C21
C21−C22
C22−C23
C23−C24
Si−Ru−N1
Ru−N1
coordination of five adjacent unsaturated carbon atoms to a
metal center is, to the best of our knowledge, unique.
The reaction of 1 with an equivalent of pyridine-2-
amino(methyl)dimethylsilane under a pressure of 3 bar of H2
yielded the dinuclear complex Ru2(μ-H)2(H)2[κ-Si,N-(SiMe2)-
N(Me)(C5H4N)]4 (2) (Scheme 1), which was isolated as a red
powder in 22% yield and characterized by NMR and infrared
1
spectroscopy, and X-ray diffraction. The H NMR integration
ratios are consistent with the presence of two bridging and two
terminal hydrides in comparison to four silazane ligands. The
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two high field triplet signals, at δ = −1.32 ppm (2JHH = 7.1 Hz)
directly from the reaction of Ru(η4-C8H12)(η6-C8H10) with 3.2
equiv of the ligand at 60 °C. Compound 3 can also be achieved
from 2 by heating at 50 °C with a slight excess of an equivalent
of the ligand. The 1H NMR integration ratios of 3 indicate that
there are three SiMe2 groups in comparison to a single hydride
at δ = −14.27 ppm. The hydride singlet has 29Si satellites and a
coupling constant JSiHapp = 9.0 Hz. A single silicon singlet at δ =
64.28 ppm is observed in the (H,Si)-HMQC NMR spectrum at
room temperature indicating that the SiMe2 groups are
equivalent in solution. At 173 K, no change is observed with
and δ = −9.66 ppm with 29Si satellites (2JHH = 7.2 Hz, JHSiapp
=
28.0 Hz), are attributed to the bridging and terminal hydrides,
respectively. A single singlet at δ = 51.5 ppm observed in the
(H,Si)-HMQC NMR spectra of 2 at room temperature and at
193 K indicates that the four silicon atoms are equivalent in
solution. The (H,N)-HMQC NMR spectrum distinguishes the
two nitrogen environments: δ = −171.9 ppm for the
coordinating pyridinic nitrogen and δ = −287.1 ppm for the
amino nitrogen. The X-ray structure of 2 is depicted in Figure
2, and the geometrical parameters are given in Table 2.
1
a single resonance, both for the H and the 29Si signals. The
(H,N)-HMQC NMR spectrum has a signal at δ = −151.4 ppm
for the coordinating pyridinic nitrogen and one at δ = −284.8
ppm for the amino nitrogen. The X-ray structure of 3 shown in
Figure 3 confirms the coordination of three silazane moieties
Figure 2. X-ray molecular structure of 2 (ellipsoids are shown at 50%
probability with hydrogen atoms represented by green spheres or
excluded for clarity.).
Table 2. Selected Bond Distances (Å) and Angles (deg) for 2
N1−Ru
Si−Ru
Ru−Ru′
Ru−Hy1
Ru−Hy2
2.112(1)
2.3283(5)
2.8850(3)
1.80(2)
Si−Hy2
1.96(2)
N1−Ru−N1′
N1−Ru−Si
Si−Ru−Si′
173.14(7)
81.93(4)
113.01(3)
1.51(3)
Complex 2 possesses a motif unusual in ruthenium chemistry,
namely two bridging hydrides together with two terminal
hydrides positioned between two silyl groups. The only other
ruthenium complex with two bridging and two terminal
hydrides to be found on searching the Cambridge Structural
Database is Ru2H4(PMe3)6, although here not all of the
hydrides were located.7 The asymmetric unit of 2 contains a
single Ru−Si−(H)2 moiety, and the dimeric bridged structure
is generated from the symmetry elements of the P42212 space
group. The terminal hydrides of 2 are located in the same plane
as Ru(μ-H)2Ru as confirmed by DFT optimization. The
terminal hydrides are equidistant between the silicon atoms
with a relatively short silicon−hydride distance of 1.96(2) Å
(1.996 Å by DFT), which implies the presence of “strong”
secondary interactions (SISHA).8 The expected range for
SISHA is 1.9−2.4 Å. Further evidence for a rather strong Si−H
interaction is provided by the relatively large coupling constant
JHSiapp = 28.0 Hz.9 η2-Si−H coordination to a metal center
results in reduced JSiH values relative to an unbound silane (ca.
200 Hz), and it is generally considered that values lower than
20 Hz are characteristic of very weak interactions. For small
values (a few Hz) oxidative addition can be inferred.5a,9,10
Reaction of 1 with 2.5 equiv of pyridine-2-amino(methyl)-
dimethylsilane at 60 °C leads to Ru(H)[κ-Si,N-(SiMe2)N-
(Me)(C5H4N)]3 (3) (Scheme 1), which was isolated as a
yellow powder in 91% yield. Compound 3 can be accessed
Figure 3. Top: X-ray molecular structure of 3 (ellipsoids are shown at
50% probability with hydrogen atoms represented by green spheres or
excluded for clarity). Bottom: Optimized DFT strutures of 3a (left)
and 3b (right).
together with the single hydride. The geometric parameters of 3
obtained by X-ray and DFT calculations are listed in Table 3.
Complex 3, similarly to the previously reported complex
Ru(H)[κ-Si,N-(SiMe2)N(C5H4N)(SiMe2H)]3 (4),4 incorpo-
rates three bidentate pyridylsilazane ligands and a hydride in
the coordination sphere of ruthenium. However, 4 was found
to be symmetric by X-ray and neutron diffraction with the
hydride ligand positioned in the middle of three symmetry-
related silicon atoms (three equal Si−H distances: 2.120(9) Å
by X-ray, 2.154(8) Å by neutron, and 2.162 Å by DFT). In
contrast, the X-ray structure of 3 indicates two Si−H distances
shorter than the third with the corresponding Ru−Si distances
longer as one would expect if there were two Si−H interactions
stronger than the other. The N−Ru−Si angles are also unequal,
further reflecting the lower degree of symmetry of the molecule.
A DFT study found that the two structures, 3a and 3b, the
former symmetric and the latter less regular, are degenerate.
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again no decoalescence could be observed at 173 K, both for
1H and 29Si NMR. The (H,N)-HMQC NMR spectrum has a
signal at δ = −168.2 ppm for the coordinating pyridinic
nitrogen and a signal at δ = −290.2 ppm for the amino
nitrogen. The molecular structure of 5 was obtained by X-ray
and neutron diffraction (Figure 4) enabling us to compare the
Table 3. Comparison between Selected Bond Distances (Å)
and Angles (deg) for the Experimental and Calculated
Structures of 3
X-ray
DFT
3
3b
3a
Ru−Ha
Sia−Ha
Sib−Ha
Sic−Ha
Ru−Sia
Ru−Sib
Ru−Sic
Na−Ru−Sia
Nb−Ru−Sib
Nc−Ru−Sic
1.42(3)
1.586
1.891
2.042
2.929
2.351
2.359
2.33
1.558
2.16
1.97(3)
2.00(3)
2.33(3)
2.3213(5)
2.3264(5)
2.3117(5)
168.93(4)
170.46(4)
172.12(4)
2.34
163.90
168.39
172.67
169.75
Geometrical parameters are given in Table 3. Thus, we note
that, in a Ru−H−Si3 system, it is equally energetically favorable
for there to be two strong silicon hydrogen interactions as for
there to be three equivalent yet slightly weaker silicon hydrogen
interactions. The potential energy surface is very flat, coherent
with the description of weak Si−H interactions and a highly
delocalized hydride.11 The experimental structure geometry is
intermediate between those of the two lowest energy calculated
geometries 3a and 3b. In solution, NMR data are consistent
with a symmetrical environment.
The Ru−H−Si2 interaction of the dimeric species 2 is
interesting in relation to the Ru−H−Si3 system of 3. The two
short Si−H distances of 3 are identical, 1.97(3) and 2.00(3) Å,
and the same as the Si−H distance in 2, 1.96(2) Å reaffirming
that it is favorable for the hydride to be located equidistant
between two silicon atoms even in the presence of a third. In
solution, however, the silicon hydrogen coupling constants of 2,
28.0 Hz, and 3, 9.0 Hz, are significantly different suggesting a
weaker Si−H interaction in 3.9 However, care must be taken
when using these coupling constants as indicators of the
strength of the interaction between the atoms because the
Figure 4. Neutron molecular structure of 5 (ellipsoids are shown at
50% probability with hydrogen atoms represented by green spheres
and other hydrogens excluded for clarity.).
two sets of structural parameters and to assess the importance
of the contribution made by DFT calculations to the reliable
description of metal−hydride compounds in general, bearing in
mind that only five neutron studies of M−H−Si systems have
been reported.12 Table 4 displays selected geometrical
parameters of 5 determined by X-ray and neutron diffraction
and by DFT calculations.
1
apparent JSiHapp is most likely a combination of JSiH, always
2
negative, with JSiH, sometimes negative, and it is difficult to
meaningfully separate the contributions made to JSiHapp by the
different orders.5a,10
Protonation of 3. Single Crystal Neutron Diffraction
Structure of 5. The reaction of 3 with an equivalent of
[H(OEt2)2]+[(3,5-(CF3)2C6H3)4B]− gave [RuH{(η2-H-
SiMe2)N(Me)κ-N-(C5H4N)}{κ-Si,N-(SiMe2)N(Me)-
(C5H4N)}2]+[BArF ]− (5) (BArF = B(3,5-(CF3)2C6H3)4),
Table 4. Comparison between Selected Distances (Å) and
Angles (deg) for the X-ray, Neutron, and Calculated
Structures of 5
4
4
which was isolated as a brown powder in 76% yield (Scheme
2). In this case, the 1H NMR integration ratios show that there
are two hydrides at δ = −15.23 ppm in comparison to the three
SiMe2 groups. The hydride singlet has 29Si satellites and a
coupling constant of JSiHapp = 17.6 Hz. The (H,Si)-HMQC
NMR spectrum of 5 at 298 K has a signal at δ = 50.8 ppm, and
X-ray
Neutron
DFT
Ru−Ha
Ru−Hb
Ru−Sia
Ru−Sib
Ru−Sic
Sia−Ha
Sib−Ha
Sic−Ha
Sia−Hb
Sib−Hb
Sic−Hb
Na−Ru−Sia
Nb−Ru−Sib
Nc−Ru−Sic
1.55(5)
1.600(8)
1.587(7)
2.459(6)
2.408(6)
2.400(6)
1.74(1)
1.596
1.579
2.472
2.431
2.414
1.750
3.300
2.282
3.103
1.921
2.060
163.07
169.99
164.73
1.47(4)
2.4560(9)
2.4105(9)
2.3941(9)
1.62(4)
Scheme 2. Reversible Protonation of 3 Leading to 5
3.20(5)
3.28(1)
2.37(5)
2.29(1)
3.07(4)
3.057(9)
1.95(1)
2.03(4)
1.89(4)
2.00(1)
162.58(7)
169.94(7)
164.06(7)
162.8(2)
169.9(2)
164.2(2)
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The Si−H neutron diffraction distances allow the for-
mulation of 5 with an η2-Si−H interaction (Sia−Ha = 1.74(1)
Å) together with two secondary interactions between the
second hydride and the remaining two silicon atoms (Sib−Hb
= 1.95(1) and Sic−Hb = 2.00(1) Å). This is consistent with the
differences in Ru−Si bond lengths, the longest one for the
silicon involved in the η2-Si−H bonding (Ru−Sia = 2.459 (6) Å
compared to Ru−Sib = 2.408 (6) Å and Ru−Sic = 2.400 (6) Å).
There is no interaction between the two hydride atoms as
indicated by an interhydride distance of 1.98(2) Å and the
chemistry, one that can be expressed in the absence or presence
of a transition metal.
EXPERIMENTAL SECTION
■
General Methods. Manipulations were carried out following
standard Schlenk line and glovebox techniques, with O2 < 1 ppm, and
Ar as the inert gas. Solvents were dried using a MBraun SPS column.
Deuterated solvents were freeze−pump−thaw degassed and stored
under Ar and over 4 Å molecular sieves. THF-d8 was dried over
17
sodium. Ru(η4-C8H12)(η6-C8H10
)
and [H(OEt2)2]+[[3,5-
18
(CF3)2C6H3]4B]− were prepared by previously published methods.
Unless otherwise indicated, commercially available reagents were used
as supplied and for the most part were purchased from Aldrich or
AlfaAesar. NMR spectra were collected on several machines; a Bruker
500 MHz Avance, a Bruker 400 MHz Avance, a Bruker 300 MHz
Avance, and a Bruker 300 MHz DPX. Chemical shifts are given in
units of ppm, with coupling constants in Hz. Mass spectroscopy was
carried out using a TSQ 7000 Thermo Electron mass spectrometer.
Infrared spectroscopy was carried out using a Perkin-Elmer 1725
spectrometer for nujol mulls pressed between KBr disks and a Bruker
Alpha P spectrometer for ATR measurements. Microanalyses were
performed at the Laboratoire de Chimie de Coordination on a Perkin-
Elmer 2400 Series II analyzer.
T
1 min value of 620 ms at 183 K and 500 MHz, both parameters
being too long to postulate a dihydrogen complex.13
Interestingly, the reaction of 5 with a slight excess of LiEt3BH
in THF regenerated 3.
CONCLUSION
■
The family of complexes presented here demonstrates the
versatility in the nature of Ru−H−Si interactions that can be
achieved from the reactivity of pyridine-2-amino(methyl)-
dimethylsilane. The combination of two labile alkenyl ligands
with the silazane in the coordination sphere of 1 endows it with
great potential as a precursor to other ruthenium−silazane
complexes. Accordingly, it has been possible to modulate the
number of silazane ligands coordinated to ruthenium by control
over stoichiometry and reaction conditions enabling useful
comparisons to be drawn within a series of related complexes
displaying multicenter interactions. Fine tuning of the
coordination sphere of the metal has been well illustrated by
the reversible protonation reaction. Studies of the effect of N-
substituent modification of silazane ligands will continue with
the aim of creating a series of compounds with varying basicity
and electrochemical properties.
Synthesis of Pyridine-2-amino(methyl)dimethylsilane. 2-
(Methylamino)-pyridine (4.00 g, 37.0 mmol) was dissolved in Et2O
(80 mL) and cooled to −35 °C before n-BuLi (14.8 mL, 2.5 M in
hexane, 37.0 mmol) was added dropwise. After 1 h of stirring at −35
°C, an Et2O solution (10 mL) of HSiMe2Cl (4.02 mL, 37.0 mmol)
was added to the yellow suspension giving rise to the formation of a
white precipitate. A yellow solution was obtained after filtration
through Celite and the solvent evaporated. The resulting yellow oil
was purified by trap-to-trap distillation at 75 °C to afford a colorless oil
1
(4.97 g, 81%). H NMR (400.12 MHz, C6D6, 298 K): 8.20 (dd, 1 H,
Pyr, 3JHH = 4.8, 4JHH = 1.1), 7.26 (ddd, 1 H, Pyr, 3JHH = 8.8, 3JHH = 7.2,
3
3
4JHH = 2.0), 6.47 (dd, 1 H, Pyr, JHH = 7.0, JHH = 5.0), 6.28 (d, 1 H,
Structural studies are essential for the identification of η2-
complexes and the establishment of secondary interactions. Si−
H bond distances are useful parameters with the upper limit for
an η2-Si−H bond being 1.90 Å whereas the range for SISHA is
1.90−2.40 Å. However, the location of hydrogen atoms by X-
ray diffraction is subject to systematic errors that lead to an
underestimate of any distance involving a hydrogen. Con-
sequently, DFT calculations are often used, and our study
confirms that DFT structural parameters are in close agreement
to those obtained by neutron diffraction, a technique able to
irrefutably locate hydrogen atoms.14 It is noteworthy that the
neutron structure of 5 allows unambiguous characterization of
η2-Si−H and SISHA bonds with different Si−H distances at the
same metal center (1.74(1) Å for η2-Si−H and 1.96(1)−
2.29(1) Å for SISHA).
3
3
1
Pyr, JHH = 8.4), 5.02 (sept, 1 H, SiH, JHH = 3.6, JSiH = 197.1), 2.16
(s, 3H, NMe), 0.61 (dd, 6 H, SiMe, 2JSiH = 10.2, 3JHH = 3.1). 13C{1H}
NMR (100.62 MHz, C6D6, 298 K): 161.74 (Pyr quaternary), 147.33
(Pyr), 137.44 (Pyr), 112.88 (Pyr), 105.63 (Pyr), 33.01(NMe), −0.89
(SiMe). 15N NMR (40.55 MHz, C6D6, 298 K): −104.4 (Pyr), −312.2
(NMe). 29Si DEPT NMR (79.50 MHz, C6D6, 298 K): −4.14 (s). IR
(Nujol mull, cm−1) 2115 weak (νSi−H). Positive CI-MS: m/z 167 [M +
1]+ (100%). Negative CI-MS: m/z 107 [C6H7N2]− (100%).
Synthesis of Ru[κ-Si,N-(SiMe2)N(Me)(C5H4N)](η4-C8H12)(η3-
C8H11) (1). A pentane solution (1 mL) of pyridine-2-amino(methyl)-
dimethylsilane (0.240 g, 1.425 mmol) was added to a pentane solution
(6 mL) of Ru(η4-C8H12)(η6-C8H10) (0.300 g, 0.951 mmol) at room
temperature and the solution stirred for 10 min after which time the
formation of a yellow precipitate was observed. The suspension was
allowed to stir for 15 h. The precipitate was isolated by filtration and
rinsed with pentane (3 mL) to afford the pure product, a lemon yellow
powder (0.370 g, 81%). Yellow crystals suitable for X-ray analysis were
Finally, there are a few published examples of the interaction
1
grown from a pentane solution. H NMR (500.33 MHz, C6D6, 301
of two silicon atoms with a single hydrogen. Muller and co-
̈
K): (see Figure S1 for (H,C)-HSQC NMR spectrum; see below for
atom numeration) 7.58 (dd, 1 H, H3 Pyr, 3JHH = 6.0, 4JHH = 1.5), 6.84
workers reported the structural characterization of a disilyl
cation with a bridging hydrogen and naphthyl backbone.15 The
disilyl cation 29Si NMR resonance at δ = 54.4 ppm is interesting
to compare with the values of 2 (δ = 51.5 ppm) and 5 (δ = 50.8
ppm) suggesting that the electronic environment of the silicon
atoms in these three compounds is similar. In addition, the
experimental molecular structure of the disilyl cation is
asymmetric with Si−H bond distances elongated (1.583(5)
and 1.677(4) Å), in relation to a classical Si−H bond (1.481(5)
Å).4 A further example of the hydride-bridged silicon motif is
provided by Reed and co-workers who have structurally
characterized [Me3Si−H−SiMe3][CHB11Cl11], a moiety with
statistically identical Si−H distances (1.60(2) and 1.62(2) Å).16
Multicenter bonding is an often encountered feature of silicon
3
3
4
(ddd, 1 H, H5 Pyr, JHH = 9.0, JHH = 7.0, JHH = 2.0), 6.71 (dd, 1 H,
H20 η3-C8H11, 3JHH = 10.5, 3JHH = 2.5), 5.92 (dd, 1 H, H4 Pyr, 3JHH
=
4
3
6.0, JHH = 1.0), 5.78 (d, 1 H, H6 Pyr, JHH = 8.5), 5.45 (ddd, 1 H,
H21 η3-C8H11, 3JHH = 10.0, 3JHH = 8.5, 3JHH = 1.0), 5.30 (dd, 1 H, H19
η3-C8H11, 3JHH = 8.5, 3JHH = 2.0), 3.36 (dddd, 1H, H11 η4-C8H12, 2JHH
3
3
3
= 13.7, JHH = 10.8, JHH = 10.8, JHH = 5.4), 3.06 (dd, 1 H, H10 η4-
C8H12, 3JHH = 9.0, 3JHH = 5.5), 3.00 (m, 1 H, H22 η3-C8H11), 2.98 (m,
1 H, H18 η3-C8H11), 2.97 (m, 1 H, H15 η4-C8H12), 2.91 (dd, 1 H,
H11 η4-C8H12, JHH = 14.5, JHH = 9.0), 2.77 (dd, 1 H, H9 η4-C8H12,
2
3
3JHH = 8.5, JHH = 4.0), 2.68 (m, 1 H, H17 η3-C8H11), 2.66 (m, 1 H,
3
H14 η4-C8H12), 2.62 (s, 3 H, NMe), 2.44 (dd, 1 H, H15 η4-C8H12,
2JHH = 14.0, JHH = 8.5), 2.33 (m, 1 H, H16 η4-C8H12), 2.27 (m, 1 H,
3
H12 η4-C8H12), 2.21 (m, 1 H, H22 η3-C8H11), 1.74 (dddd, 1 H, H16
η4-C8H12, 2JHH = 13.3, 3JHH = 8.8, 3JHH = 8.8, 3JHH = 4.3), 1.52 (m, 1 H,
2658
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Inorganic Chemistry
Article
H24 η3-C8H11), 1.50 (m, 1 H, H12 η4-C8H12), 1.47 (m, 1 H, H13 η4-
C8H12), 1.43 (m, 1 H, H23 η3-C8H11), 1.30 (ddddd, 1 H, H23 η3-
crystals suitable for X-ray analysis were grown from a C6D6 solution.
1H NMR (400.13 MHz, C6D6, 298 K): 8.75 (dd, 4 H, Pyr, 3JHH = 5.9,
2
3
3
3
3
3
3
4
4JHH = 1.7), 6.70 (ddd, 4 H, Pyr, JHH = 8.7, JHH = 7.1, JHH = 1.9),
C8H11, JHH = 12.7, JHH = 11.2, JHH = 5.6, JHH = 5.6, JHH = 2.1),
1.06 (s, 3 H, SiMe), 0.88 (s, 3 H, SiMe), −0.02 (dddd, 1 H, H24 η3-
3
3
4
5.82 (d, 4 H, Pyr, JHH = 8.3), 5.49 (dd, 4 H, Pyr, JHH = 6.4, JHH
=
2
3
3
3
C8H11, JHH = 18.7, JHH = 13.8, JHH = 11.0, JHH = 5.2). 13C {1H}
NMR (125.81 MHz, C6D6, 301 K): 163.73 (C7 Pyr), 149.80 (C3
Pyr), 137.07 (C20 η3-C8H11), 136.46 (C5 Pyr),123.89 (C21 η3-
C8H11), 111.96 (C4 Pyr), 106.85 (C18 η3-C8H11), 105.67 (C6 Pyr),
74.32 (C13 η4-C8H12), 70.17 (C9 η4-C8H12), 70.03 (C19 η3-C8H11),
69.70 (C10 η4-C8H12), 67.76 (C14 η4-C8H12), 58.55 (C17 η3-C8H11),
37.18 (C15 η4-C8H12), 35.68 (C11 η4-C8H12), 31.87 (NMe), 28.13
(C16 η4-C8H12), 27.05 (C12 η4-C8H12), 26.23 (C22 η3-C8H11), 25.45
(C23 η3-C8H11), 23.56 (C24 η3-C8H11), 6.99 (SiMe), 3.22 (SiMe).
15N HMQC NMR (50.7 MHz, C6D6, 301 K): −168.7 (Pyr), −282.9
(NMe). 29Si HMQC NMR (99.4 MHz, C6D6, 301 K): 81.0. Anal.
Calcd for C24H56N2SiRu: C, 59.84; H, 7.53; N, 5.82. Found: C, 59.72;
H, 7.67; N, 5.70.
1.2), 2.77 (s, 12 H, NMe), 1.34 (s, 12 H, SiMe), 0.57 (s, 12 H, SiMe),
2
2
−1.32 (t, 2 H, μ-H, JHH = 7.1), −9.66 (t, 2 H, Hterminal, JHH = 7.2,
JHSiapp = 28.0). 1H NMR (500.32 MHz, THF-d8, 193 K): no
decoalesence, −1.72 (t, 2 H, μ-H, 2JHH = 13), −10.20 (t, 2 H, Hterminal
,
2JHH = 14, JHSiapp = 28.0). 13C{1H} NMR (100.61 MHz, C6D6, 298 K):
166.16 (Pyr quaternary) 157.55 (Pyr), 133.98 (Pyr), 110.02 (Pyr),
104.87 (Pyr), 31.74 (NMe), 9.94 (SiMe), 9.36 (SiMe). 15N HMQC
NMR (40.55 MHz, C6D6, 298 K): −171.9 (Pyr), −287.1 (NMe). 29Si
HMQC NMR (79.49 MHz, C6D6, 298 K): 51.5. 29Si HMQC NMR
(99.40, MHz, THF-d8, 193 K): 50.0. IR ATR measured (cm−1) 2068
(υRu−H, weak). IR DFT and corrected with a coefficient factor of 0.96
(cm−1) 2040 (υRu−H). Anal. Calcd for C32H56N8Si4Ru: C, 44.31; H,
6.51; N, 12.99. Found: C, 44.24; H, 6.75; N, 12.80.
Synthesis of Ru(H)[κ-Si,N-(SiMe2)N(Me)(C5H4N)]3 (3). A THF
solution (2 mL) of pyridine-2-amino(methyl)dimethylsilane (0.841 g,
5.06 mmol) was added to a THF solution (15 mL) of Ru[κ-Si,N-
(SiMe2)N(Me)(C5H4N)](η4-C8H12)(η3-C8H11) (0.950 g, 2.024
mmol). The resulting yellow solution was stirred for 3 h at 60 °C.
After cooling to room temperature, the solvent was evaporated to leave
a yellow solid that was dried under vacuum for 0.75 h and washed with
cold pentane (2 × 4 mL, −20 °C) to afford the pure product, a yellow
powder (0.991 g, 91%). Yellow crystals suitable for X-ray analysis were
1
grown from a pentane solution. H NMR (400.13 MHz, C6D6, 298
3
4
K): 7.58 (dd, 3 H, Pyr, JHH = 5.7, JHH = 1.5), 7.09 (ddd, 3 H, Pyr,
3JHH = 8.8, 3JHH = 6.9, 4JHH = 1.9), 6.23 (d, 3 H, Pyr, 3JHH = 8.7), 6.03
(ddd, 3 H, Pyr, 3JHH = 6.9, 3JHH = 5.8, 4JHH = 1.2), 2.70 (s, 9 H, NMe),
0. 87 (s, 9 H, SiMe), 0.14 (s, 9 H, SiMe), −14.27 (s, 1 H, Ru−H,
1
JSiHapp = 9.0). H NMR (500.32 MHz, THF-d8, 298 K): 7.45 (ddd, 3
Synthesis of Ru2(μ-H)2(H)2[κ-Si,N-(SiMe2)N(Me)(C5H4N)]4 (2).
A THF solution (1 mL) of pyridine-2-amino(methyl)dimethylsilane
(17.0 mg, 0.104 mmol) was combined with a THF solution (2 mL) of
Ru[κ-Si,N-(SiMe2)N(Me)(C5H4N)](η4-C8H12)(η3-C8H11) (50.0 g,
0.104 mmol). The solution was stirred for 3 h under a pressure of
H2 (3 bar) after which time the solvent was evaporated and the
resultant dark red solid dried under vacuum. The solid was washed
with pentane (2 × 3 mL), and isolation of the pentane insoluble
species afforded the pure compound, a red powder (20 mg, 22%). Red
3
3
4
3
H, Pyr, JHH = 8.7, JHH = 8.6, JHH = 5.1), 7.19 (dd, 3 H, Pyr, JHH
=
5.7, 4JHH = 1.6), 6.51 (dd, 3 H, Pyr, 3JHH = 8.6, 4JHH = 1), 6.23 (d, 3 H,
Pyr, 3JHH = 5.9), 2.82 (s, 9 H, NMe), 0.40 (s, 9 H, SiMe), −0.33 (s, 9
H, SiMe), −14.69 (s, 1 H, Ru−H, JSiHapp = 9). 13C{1H} NMR (100.61
MHz, C6D6, 298 K): 165.00 (Pyr quaternary), 148.64 (Pyr), 136.69
(Pyr), 110.96 (Pyr), 107.04 (Pyr), 31.79 (NMe), 9.00 (SiMe), 3.24
(SiMe). 15N HMQC (40.55 MHz, THF-d8, 298 K): −151.4 (Pyr),
−284.8 (NMe). 29Si DEPT NMR (79.50 MHz, C6D6, 298 K): 64.28.
Table 5. Selected X-ray Data Collection and Refinement Parameters for 1, 2, 3, and 5
1
2
3
5
formula
fw
C24H36N2RuSi
481.71
C32H56N8Ru2Si4
867.35
C24H40N6RuSi3
597.96
C32H12BF24, C24 H41N6RuSi3
1462.19
monoclinic
Pn
cryst syst
space group
a (Å)
monoclinic
P21/n
tetragonal
P42212
orthorhombic
P212121
9.6790(6)
16.0690(8)
36.6520(18)
90
14.2470(10)
16.0730(10)
19.4300(10)
90
12.5360(2)
12.5360(2)
12.8809(2)
90
13.9065(3)
12.1742(3)
18.3076(4)
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
101.564(10)
90
90
90
94.385(2)
90
90
90
4359.0(5)
8
2024.25(6)
2
5700.6(5)
8
3090.41(12)
2
T (K)
100(2)
100(2)
1.423
100(2)
100(2)
1.571
ρcalcd (g cm−3
)
1.468
1.393
μ(mm−1
)
0.787
0.897
0.700
0.428
no. rflns collctd
no. indep rflns
no. params
72 183
11 004
123 481
11 635
61 811
17 633
2076
12 620
511
113
639
837
Rint
0.0778
0.0244
0.0288
0.0429
R1/wR2, I ≥ 2σ(I)
R1/wR2, all data
GOF
0.0424/0.0679
0.1080/0.0816
0.986
0.0156/0.0352
0.0188/0.0356
0.992
0.0161/0.0393
0.0169/0.0398
1.110
0.0345/0.0809
0.0399/0.0854
1.041
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Inorganic Chemistry
Article
29Si HMQC NMR (99.40, MHz, THF-d8, 173 K): 63.0. Anal. Calcd
for C24H40N6RuSi3: C, 48.21; H, 6.74; N, 14.06. Found: C, 48.21: H,
6.93; N, 13.97.
convergence the final Fourier difference map showed no significant
features. Further crystallographic data, experimental details and
geometrical parameters are given in Table 6, in the Supporting
Information, and as a CIF file (also as CCDC 905934).
Synthesis of {Ru[(η2-H−SiMe2)N(Me)κ-N-(C5H4N)[κ-Si,N-
(SiMe2)N(Me)(C5H4N)]}+{[3,5-(CF3)2C6H3]4B}− (5). A CH2Cl2 sol-
ution (2 mL) of [H(OEt2)2]+[[3,5-(CF3)2C6H3]4B]− (0.177 g, 0.167
mmol) was added to a CH2Cl2 solution (3 mL) of 3 (0.100 g, 0.167
mmol). The resulting brown solution was stirred for 1 h at 20 °C after
which time the solvent was evaporated to leave a brown solid that was
washed with pentane (4 × 2 mL) to afford the pure product, a light
brown powder (0.186 g, 76%). Green crystals suitable for X-ray
diffraction were grown from a saturated CH2Cl2 solution at −37 °C.
1H NMR (400.13 MHz, CD2Cl2, 298 K): 7.76 (s, 12 H, BArF), 7.70 (t,
Table 6. Crystal Data and Details of the Structure
Refinement for the Neutron Diffraction Study of 5
formula
C56H53 BF24N6 RuSi3
1462.19
mol wt
data coll T, K
radiation
20 (1)K
neutrons (λ = 1.1708 (1) Å)
Monoclinic
Pn (7)
3
4
3 H, Pyr, JHH = 8.4, JHH = 1.4), 7.60 (s, 6 H, BArF), 6.89 (dd, 3 H,
cryst syst
Pyr, 3JHH = 5.9), 6.78 (d, 3 H, Pyr, 3JHH = 8.7), 6.53 (t, 3 H, Pyr, 3JHH
=
space group (No.)
a, Å
13.9659 (3)
11.9966 (4)
18.2189 (5)
94.011 (2)
3045.0 (2)
2
6.4), 2.96 (s, 9 H, NMe), 0.63 (s, 9 H, SiMe), −0.03 (s, 9 H, SiMe),
−15.23 (s, 2 H, Ru−H, JSiHapp = 17.6). 1H NMR (500.32 MHz, THF-
d8, 173 K): no decoalescence, −15.21(s, 2 H, Ru−H, JSiHapp = 15.0).
13C{1H} NMR (100.61 MHz, CD2Cl2, 298 K): 163.74 (Pyr
b, Å
c, Å
β, deg
V, Å3
1
quaternary), 161.72 (q, JBC = 49.7 BArF, i-C), 147.34 (Pyr), 140.21
(Pyr), 134.77 (BArF, o-C), 128.83 (q, 2JCF = 31.2, BArF, m-C), 123.22
Z
1
(q, CF3 JCF = 272.1), 117.45 (BArF, p-C), 114.36 (Pyr), 109.69 (Pyr),
ρcalcd, g cm−3
μ, mm-1
1.596
32.17 (NMe), 8.04 (SiMe), 2.64 (SiMe). 29Si HMQC NMR (79.50,
MHz, CD2Cl2, 298 K): 50.76. 29Si HMQC NMR (99.40, MHz, THF-
d8, 173 K): 50.60. 11B{1H} NMR (160.53 MHz, THF-d8, 301.1 K):
−6.50. 15N HMQC NMR (40.55 MHz, CD2Cl2, 298 K): −168.2,
−290.2. T1 min of the hydride signal in THF-d8 at 500.32 MHz and 183
K is 0.62 s. Anal. Calcd for C56H53N6BF24Si3Ru: C, 46.01; H, 3.65; N,
5.75. Found: C, 45.65: H, 3.25; N, 5.97.
0.183
no. data collected
θ range (deg)
no. indep data
no. obsd reflns (no)
no. params refined (nv)
Rint
27 927
4.8−61.3
9494
7647
1297
Reaction of Complex 5 with Li+[HB(C2H5)3]−. Li+[HB(C2H5)3]−
(72.8 μL of a 1 M solution in THF, 0.069 mmol) was added to a
brown solution of 5 (0.100 g, 0.053 mmol) in THF (6 mL). The
homogeneous brown solution was stirred for 2.5 h before the solvent
was evaporated and the brown solid dried under vacuum for 2.5 h. The
NMR spectrum of the resulting species in THF-d8 was compared to
the spectrum of 3 in THF-d8 to confirm the regeneration of 3 from 5.
Computational Details. DFT calculations employing the
B3PW9119 functional were performed with the GAUSSIAN03 series
of programs.20 The ruthenium and silicon atoms were represented by
the relativistic effective core potential (RECP) from the Stuttgart
group and their associated basis set,21 augmented by polarization
functions (αf = 1.235, Ru; αd = 0.284, Si).22 The remaining atoms (C,
N, H) were represented by 6-31G(d,p) basis sets.23 Full optimizations
of geometry without any constraint were performed. Calculations of
harmonic vibrational frequencies were performed to determine the
nature of each extremum. Cartesian coordinates in Å for the calculated
geometries. The contributions to the Gibbs free energy were taken at
T = 298 K and with P = 1 atm within the harmonic oscillator and rigid
rotator approximations.
0.1253
a
R(Fo) [I > 2σ(I)]
0.0617
a
2
Rw(Fo ) [I > 2σ(I)]
0.1197
a
GOF
1.063
a
2
2
2
2
Rint = Σ|Fo − ⟨Fo ⟩|/ΣFo ; R(Fo) = Σ∥Fo| − |Fc∥/Σ|Fo|; Rw(Fo ) =
[Σ[w(Fo2 − Fc2)2 ]/Σ[ w(Fo )2]]1/2 ; GOF = [Σ[w(Fo2 − Fc2)2]/(N −
P)]1/2, where N and P are the numbers of observations and
parameters, respectively.
2
ASSOCIATED CONTENT
* Supporting Information
■
S
(H,C) HSQC NMR spectrum of 1. Neutron diffraction
experimental and structural details for compound 5. Coor-
dinates of the calculated structures 1, 2, 3a, 3b, and 5. CIF data
for complexes 1, 2, 3, and 5 (X-ray and neutron). This material
is available free of charge via the Internet at http://pubs.acs.org.
X-ray Data. Important crystallographic data are given in Table 5;
the experimental procedure and relevant data are in the Supporting
Information as CIF data (also deposited at the CCDC: 1, CCDC
905933, 2, CCDC 905932, 3, CCDC 905930, and 5, CCDC 905931).
Neutron Data. A prismatic crystal, with a volume of ca. 0.82 mm3,
was mounted in an inert Ar atmosphere inside a thin-walled quartz
cryorefrigerator.24 The sample was mounted on a Displex cryorefrig-
erator on the ILL thermal-beam diffractometer D19 equipped with the
new horizontally curved “banana-shaped” position-sensitive detector25
and cooled to 20 K. The Bragg intensities were corrected for
attenuation by the vanadium Displex heat-shields and analytically for
the crystal absorption.
AUTHOR INFORMATION
Corresponding Author
*E-mail: mary.grellier@lcc-toulouse.fr (M.G.); sylviane.sabo@
lcc-toulouse.fr (S.S.-E.).
■
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
The starting structural model was based on the atomic coordinates
from the X-ray structural determination, while the positions of H
atoms bonded to the Ru center were found from a difference Fourier
map. The structure was refined by full matrix least-squares, minimizing
ACKNOWLEDGMENTS
■
We thank the CNRS for support and Johnson Matthey plc for
the generous gift of hydrated ruthenium trichloride. K.A.S.
thanks the French Ministry of Research for a Ph.D. fellowship.
Computer time was given by the HPC resources of CALMIP
(Toulouse, France) under the allocation 2012-[P0909]. A.A.
thanks MIUR (PRIN 2009) for financial support.
2
the function [∑w(Fo − (1/k)Fc2)2] and using all the independent
data. Anisotropic displacement parameters (ADPs) were used for all
atoms, while the site occupancy factors (SOF) of the hydrides were
left to refine freely in order to check that these sites were fully
occupied, and then fixed at 1.00 for the final refinement cycles. Upon
2660
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Inorganic Chemistry
Article
(13) (a) Hamilton, D. G.; Crabtree, R. H. J. Am. Chem. Soc. 1988,
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