An yttrium hydride-silane complex as a structural model for a σ-bond metathesis transition state

Article abstract of DOI:10.1002/anie.201300638

A structural model for the transition state of the σ-bond metathesis between Si-H and M-E bonds (M: d⁰ transition metal) was obtained through the formation of an yttrium hydride-silane complex (see picture). The silane moiety can be either retained or released during the reactions of the complex with other substrates. Copyright

Full text of DOI:10.1002/anie.201300638

Angewandte
Chemie
DOI: 10.1002/anie.201300638
Transition States
An Yttrium Hydride–Silane Complex as a Structural Model for a s-
Bond Metathesis Transition State**
Jiliang Zhou, Jiaxiang Chu, Yanyan Zhang, Guang Yang, Xuebing Leng, and Yaofeng Chen*
À
The transition-metal-promoted Si H bond cleavage is a piv-
otal step in several important catalytic processes, such as
hydrosilylation, hydrosilane dehydropolymerization, and
dehydrogenative silylation.[1–4] There are two different mech-
based tetradentate ligand, which can stabilize a scandium
complex with the terminal imido group.[8] To explore further
applications of this powerful multidentate ligand, we sought
to synthesize an yttrium dihydride supported by this ligand.
During this study, we obtained an unprecedented yttrium
hydride–PhSiH3 complex, which represents the first structural
À
anisms for the metal-mediated Si H bond cleavage: a) oxi-
À
dative addition of Si H bond toward a low-valent electron-
À
rich metal, in which a s-complex is believed to be the key
model for the s-bond metathesis transition state of a Si H
intermediate; and b) s-bond metathesis of Si H and M E
bonds (E = C, N, H, etc.) via a four-center transition state
(Scheme 1).[5] As evidence for the oxidative addition mech-
bond cleavage mediated by a d0 transition metal. Further
studies showed that the coordinated PhSiH3 molecule in the
complex can be either retained or released during the
reactions with other substrates.
À
À
A
salt elimination of LiL (L = [MeC(N(Dipp))CH-
C(Me)NCH2CH2N(Me)CH2CH2NMe2]À, Dipp = 2,6-(iPr)2-
C6H3) with anhydrous YCl3 in toluene gave an yttrium
dichloride [LYCl2] (1) in 88% yield. This yttrium dichloride
was treated with two equivalents of MeLi in toluene to afford
an yttrium dimethyl complex [LYMe2] (2) in 68% yield. The
1H NMR spectrum of 2 in C6D6 clearly shows two signals at
À
Scheme 1. Two commonly accepted mechanisms for Si H bond cleav-
age: a) oxidative addition through an intermediate s-silane–metal
complex, and b) s-bond metathesis via a four-center transition state.
À
d = À0.43 and À0.98 ppm for two unequal Y Me groups.
Complex 2 (shown in the Supporting Information, Figure S1).
is a monomer, in which the yttrium center adopts a distorted
octahedral geometry with three nitrogen atoms of L and
a methyl ligand forming the equatorial plane, and the
remaining nitrogen atom of L and the other methyl ligand
occupying the axial positions. The reaction of 2 with two
anism, s-silane transition-metal complexes have been well
documented.[5] For d0-transition-metal complexes, the oxida-
À
tive addition is impossible, and the Si H bond cleavage
1
proceeds through the s-bond metathesis mechanism. How-
ever, to the best of our knowledge, there has been no report of
such a d0-transition-metal complex, which can be considered
as a model for the s-bond metathesis transition state. On the
other hand, b-agostic interactions between metal ions and Si
H bonds are commonly observed in the coordinative unsatu-
equivalents of PhSiH3 was monitored by H NMR spectros-
copy in C6D6 at room temperature, showing the formation of
a complicated mixture of products and PhSiH2Me. Surpris-
ingly, when the amount of PhSiH3 was increased to three
equivalents, complex 2 was nearly quantitatively converted
into complex 3 with some unreacted PhSiH3. Subsequently,
the reaction of 2 with three equivalents of PhSiH3 was scaled
up in toluene, the unreacted PhSiH3 was removed under
vacuum after the reaction was completed, and 3 was isolated
as a pale yellow solid in 77% yield (Scheme 2). The NMR
spectral data of 3 in C6D6 were intriguing and inconsistent
with what we expected for an yttrium dihydride [LYH2]2. For
example, the 1H NMR spectrum of 3 shows a distinct triplet at
d = 5.37 ppm with a 1JY-H coupling constant of 21.2 Hz for the
Y-H-Y unit of the complex, but this triplet integrates for 3H
atoms rather than 4H atoms; in addition, an unexpected
À
rated d0-transition-metal complexes.[6]
Rare-earth-metal hydrides attract intense interest
because of their fascinating structural features and high
reactivity.[7] Recently, we have developed a b-diketiminato-
[*] J. L. Zhou, J. X. Chu, Dr. X. B. Leng, Prof. Dr. Y. F. Chen
State Key Laboratory of Organometallic Chemistry, Shanghai
Institute of Organic Chemistry, Chinese Academy of Sciences
345 Lingling Road, Shanghai 200032 (P.R. China)
E-mail: yaofchen@mail.sioc.ac.cn
Y. Y. Zhang, G. Yang
Shanghai Key Laboratory of Magnetic Resonance
Department of Physics, East China Normal University
3663 North Zhongshan Road, Shanghai 200062 (P.R. China)
[**] This work was supported by the National Natural Science
Foundation of China (Grant Nos. 21072209, 21132002 and
21121062), the State Key Basic Research & Development Program
(Grant No. 2011CB808705), and Chinese Academy of Sciences.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201300638.
Scheme 2. Synthesis of complex 3.
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doublet was observed at d = 8.17 ppm (d, 3JHH = 6.8 Hz). The
proton-coupled 29Si DEPT 45 spectrum of 3 shows a triplet at
can be viewed as a coordination of the H3M atom to the
Lewis acidic Y ion and the Si atom to the electronegative N,
1
À
d = À124.8 ppm with a JSi-H coupling constant of 220 Hz,
which causes a polarization and weakening of the Si H3M
À
which is very different from that of PhSiH3 (d = À59.5 ppm, q,
bond. It is also noteworthy that, in comparison with the Y N1
1JSi-H = 200 Hz).
and Y N5 bonds (2.367(2) and 2.389(2) ꢁ), the Y N2 and Y
N6 bonds are slightly stretched (2.420(2) and 2.416(2) ꢁ). A
fast exchange of H3M with H1M and H2M was observed in
the room-temperature 1H NMR spectrum, which shows
a triplet at d = 5.37 ppm for these three hydrogen atoms.
Lowering the temperature to À908C only led to a broadened
resonance and the resonance decoalescence did not occur,
thus indicating a very small energy barrier for the observed
hydride exchange in solution. Although complex 3 may be
racemic or have meso forms, only the racemic form that
minimizes steric interactions between the bulky Dipp sub-
stituents is observed.
À
À
À
The single-crystal structure of the yttrium hydride–PhSiH3
complex 3 was determined and the high-quality data set
allowed us to locate the H atoms on Y/Si, H1M to H5M, from
the Fourier map. Complex 3 has some rather remarkable
structural features (Figure 1). The tetradentate monoanionic
We also examined the reactivity of the complex 3. The
=
reaction of 3 with triphenylphosphine selenide (Ph3P Se)
gave an yttrium selenide–PhSiH3 complex 4 (Scheme 3).
Figure 1. Molecular structure of 3 with thermal ellipsoids set at 30%
probability level. Isopropyl groups of Dipp and hydrogen atoms
(except those bound to yttrium and silicon) have been omitted for
clarity.
=
Scheme 3. Reaction of 3 with Ph3P Se.
Consistent with the formation of 4, monitoring of the reaction
ligand L in 2 was converted into a dianionic ligand Lꢀ by
in C6D6 by NMR spectroscopy showed a release of H2
1
À
addition of the Y H bond of the initially formed yttrium
(4.47 ppm in the H NMR spectrum) and Ph3P (À5.4 ppm in
hydride to the C N bond of the b-diketiminate backbone. The
the 31P{1H} NMR spectrum). Therefore, the reaction is
a hydride-based reduction.[10] During the reaction, two HÀ
=
most intriguing structural features are related to the PhSiH3
À
moiety, which coordinates to a [L’YH]2 dimer through Y H
ligands in 3 are oxidatively coupled to form an H2 molecule
2À
À
À
À
À
À
=
(Y1 H3M, Y2 H3M) and Si N (Si N2, Si N6) interactions.
The distances from the yttrium centers to the H3M atom
(both 2.09(2) ꢁ) are close to those from the yttrium centers to
the H1M and H2M atoms (2.12(3)–2.24(3) ꢁ), and fall in the
and reduce Ph3P Se to Se and Ph3P. It is noteworthy that
only two of Y-bound H atoms in the Y2H3 moiety take part in
the reaction, while the other one stays intact. The molecular
structure of 4 is shown in Figure 2. The H atoms on Y/Si, H1M
to H3M, were also located from the Fourier map. In 4, the two
À
range of 2.00 to 2.30 ꢁ observed for the Y H bonds in
reported dimeric yttrium–m-hydrido complexes.[7] The Si N
yttrium centers are bridged by a m-Se2À ligand. Y1 Se and
À
À
À
distances, 1.916(2) and 1.925(2) ꢁ, are longer than normally
Y2 Se bond lengths are 2.7584(4) and 2.7260(4) ꢁ, respec-
À
observed for Si N single bonds in aminosilyl complexes
tively. The PhSiH3 moiety was retained during the reaction,
and the Y-N-Si-H four-membered rings were retained in 4,
with only minor deviations of structural parameters from the
parent complex 3. In the 1H NMR spectrum of 4, the Si-H-Y
(1.70–1.78 ꢁ),[6h] but significantly shorter than the sum of
their van der Waals radius (3.65 ꢁ; the van der Waals radius of
Si is 2.10 ꢁ, and that of N is 1.55 ꢁ).[9] The Si H3M bond
À
(1.82(2) ꢁ) is about 0.4 ꢁ longer than the Si H4M and Si
signal displays as a triplet of triplets at d = 6.90 ppm (1JYH
=
À
À
2
H5M bonds (1.47(2) and 1.42(2) ꢁ) and the Si H bond in
12.4 Hz, 2JHH = 4.4 Hz, 1H), the JHH value is remarkably
smaller than that reported for the two diastereotopic hydro-
gen atoms of the Ti-N-SiH2Ph unit in the titanium complex
[Cp*Ti{MeC(NiPr)2}(H) {N(NMe2)SiH2Ph}] (8.0 Hz).[11] As
for 3, the 1H–29Si HSQC experiment with J = 7 Hz shows
coupling of Si with H1M–H3M, whereas that with J = 200 Hz
only shows the coupling of Si with H2M and H3M. The
INEPT experiment also shows that the coupling of Si with
H1M is very small, so that its value was not determined. In
À
hydrosilanes (1.425 ꢁ in average),[5d] indicating that the Si
À
À
H3M bond is apparently activated. The elongation of the Si
H3M bond is also supported by the solution NMR spectrum.
The H–29Si HSQC experiment with J = 200 Hz only shows
1
the coupling of Si with H4M and H5M. The coupling of Si
with H3M was observed in the experiment with J = 7 Hz. The
INEPT experiment is unable to give a coupling constant of Si
with H3M (see the Supporting Information). The interaction
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Figure 3. Molecular structure of 5 with thermal ellipsoids set at 30%
probability level. Isopropyl groups of Dipp and hydrogen atoms
(except H38) have been omitted for clarity.
Figure 2. Molecular structure of 4 with thermal ellipsoids set at 30%
probability level. Isopropyl groups of Dipp and hydrogen atoms
(except those bound to yttrium and silicon) have been omitted for
clarity.
Ph2CO by controlling using a molar ratio of 2:1 of Ph2CO:3
were unsuccessful; the reaction gave a mixture of 5 and 6 with
some unreacted 3.
In summary, an yttrium hydride–PhSiH3 complex 3 has
been obtained and structurally characterized by single-crystal
X-ray diffraction and solution NMR spectroscopy. Complex 3
accord with 1H–29Si HSQC and INEPT spectra, the 29Si NMR
1
spectrum of 4 shows a triplet at d = À120.4 ppm with a JSi-H
coupling constant of 217 Hz as a result of the coupling of Si
with H2M and H3M.
À
À
From the reaction of 3 with four equivalents of benzo-
phenone (Ph2CO), two yttrium alkyloxo isomers 5 and 6 were
isolated in 56% and 26% yield, respectively (Scheme 4).
shows interactions between Y N and Si H bonds, which
represents the first structural model for s-bond metathesis
0
À
À
transition state between Si H and M E (M: d transition
metal). Further reactions of 3 have also been investigated and,
depending on substrates, the PhSiH3 moiety can be either
retained or released during the reactions.
Received: January 24, 2013
Published online: March 7, 2013
Keywords: hydrides · metathesis · silanes · transition states ·
.
yttrium
Scheme 4. Reaction of 3 with Ph2CO.
[1] a) I. Ojima, Z. Y. Li, J. W. Zhu in The Chemistry of Organic
Silicon Compounds, Vol. 2 (Ed.: Z. Rappoport, Y. Apeloig),
Wiley, Chichester, UK, 2003, chap. 29, p. 1687; b) Z. T. Ball in
Comprehensive Organometallic Chemistry III, Vol. 10 (Ed.:
R. H. Crabtree, M. Mingos), Elsevier, Oxford, UK, 2007,
p. 789; c) T. Hayashi in Comprehensive Organometallic Chemis-
try III, Vol. 10 (Ed.: R. H. Crabtree, M. Mingos), Elsevier,
Oxford, UK, 2007, p. 815; d) B. Marciniec in Hydrosilylation: A
Comprehensive Review on Recent Advances (Ed.: J. Matisons),
Springer, New York, 2009, p. 53.
[2] a) G. A. Molander, J. A. C. Romero, Chem. Rev. 2002, 102, 2161;
b) O. Riant, N. Mostefaꢂ, J. Courmarcel, Synthesis 2004, 2943;
c) S. Dꢃez-Gonzꢄlez, S. P. Nolan, Acc. Chem. Res. 2008, 41, 349.
[3] a) T. D. Tilley, Comments Inorg. Chem. 1990, 10, 37; b) T. D.
Tilley, Acc. Chem. Res. 1993, 26, 22; c) F. Gauvin, J. F. Harrod,
H. G. Woo, Adv. Organomet. Chem. 1998, 42, 363; d) J. Y. Corey,
Adv. Organomet. Chem. 2004, 51, 1.
1
Both 5 and 6 were fully characterized by H and 13C NMR
spectroscopy, elemental analysis, and single crystal X-ray
diffraction (Figure 3 and Figure S2 in the Supporting Infor-
mation).[12] Apparently, the formation of 5 and 6 involves not
only the insertion of the C O double bond into the Y H bond
but also the nucleophilic attack of the C3 atom of the
tetradentate ligand at the carbonyl carbon atom of Ph2CO.
Notably, the PhSiH3 molecule is released during the reaction,
which was evidenced by a 1H NMR spectral monitoring of the
reaction in C6D6 (4.23 ppm in 1H NMR spectrum). The X-ray
structural data clearly show the difference between the
multidentate ligands in the two isomers. In 5, the C1 C2
bond (1.516(5) ꢁ) is a single bond and the C2 N1 bond
(1.283(4) ꢁ) is a double bond, whereas in 6 the C1 C2 bond
double bond and the C2 N1 bond
(1.392(3) ꢁ) shows single-bond character. Attempts to
obtain the intermediate with only one inserted molecule of
=
À
À
À
À
[4] a) J. L. He, H. Q. Liu, J. F. Harrod, R. Hynes, Organometallics
1994, 13, 336; b) J. A. Reichl, D. H. Berry, Adv. Organomet.
Chem. 1998, 43, 197; c) S. Rendler, G. Auer, M. Oestreich,
Angew. Chem. 2005, 117, 7793; Angew. Chem. Int. Ed. 2005, 44,
À
(1.353(3) ꢁ) is
a
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4245

.
Angewandte
Communications
7620; d) H. Ito, K. Takagi, T. Miyahara, M. Sawamura, Org. Lett.
2005, 7, 3001; e) E. Peterson, A. Y. Khalimon, R. Simionescu,
L. G. Kuzmina, J. A. K. Howard, G. I. Nikonov, J. Am. Chem.
Soc. 2009, 131, 908; f) J. F. Dunne, S. R. Neal, J. Engelkemier, A.
Ellern, A. D. Sadow, J. Am. Chem. Soc. 2011, 133, 16782.
[5] a) J. Y. Corey, J. Braddock-Wilking, Chem. Rev. 1999, 99, 175;
b) Z. Lin, Chem. Soc. Rev. 2002, 31, 239; c) G. I. Nikonov, Adv.
Organomet. Chem. 2005, 53, 217; d) J. Y. Corey, Chem. Rev.
2011, 111, 863.
[7] a) C. J. Schaverien, Adv. Organomet. Chem. 1994, 36, 283; b) M.
Ephritikhine, Chem. Rev. 1997, 97, 2193; c) Z. M. Hou, M.
Nishiura, T. Shima, Eur. J. Inorg. Chem. 2007, 2535; d) M.
Konkol, J. Okuda, Coord. Chem. Rev. 2008, 252, 1577; e) A. A.
Trifonov, Coord. Chem. Rev. 2010, 254, 1327.
[8] a) E. L. Lu, J. X. Chu, Y. F. Chen, M. V. Borzov, G. Y. Li, Chem.
Commun. 2011, 47, 743; b) J. X. Chu, E. L. Lu, Z. X. Liu, Y. F.
Chen, X. B. Leng, H. B. Song, Angew. Chem. 2011, 123, 7819;
Angew. Chem. Int. Ed. 2011, 50, 7677.
[6] a) L. J. Procopio, P. J. Carroll, D. H. Berry, J. Am. Chem. Soc.
1994, 116, 177; b) W. S. Rees, Jr., O. Just, H. Schumann, R.
Weinmann, Angew. Chem. 1996, 108, 481; Angew. Chem. Int. Ed.
Engl. 1996, 35, 419; c) W. A. Herrmann, J. Eppinger, M. Spiegler,
O. Runte, R. Anwander, Organometallics 1997, 16, 1813; d) J.
Eppinger, M. Spiegler, W. Hieringer, W. A. Herrmann, R.
Anwander, J. Am. Chem. Soc. 2000, 122, 3080; e) W. Hieringer,
J. Eppinger, R. Anwander, W. A. Herrmann, J. Am. Chem. Soc.
2000, 122, 11983; f) M. Rastꢅtter, A. Zulys, P. W. Roesky, Chem.
Eur. J. 2007, 13, 3606; g) K. Yan, A. V. Pawlikowski, C. Ebert,
A. D. Sadow, Chem. Commun. 2009, 656; h) Y. Chen, H. B. Song,
C. M. Cui, Angew. Chem. 2010, 122, 9142; Angew. Chem. Int. Ed.
2010, 49, 8958.
[9] A. Bondi, J. Phys. Chem. 1964, 68, 441.
[10] a) W. E. Piers, G. Ferguson, J. F. Gallapher, Inorg. Chem. 1994,
33, 3784; b) W. J. Evans, B. M. Schmiege, S. E. Lorenz, K. A.
Miller, T. M. Champagne, J. W. Ziller, A. G. DiPasquale, A. L.
Rheingold, J. Am. Chem. Soc. 2008, 130, 8555; c) B. M.
Schmiege, J. W. Ziller, W. J. Evans, Inorg. Chem. 2010, 49, 10506.
[11] P. J. Tiong, A. Nova, A. D. Schwarz, J. D. Selby, E. Clot, P.
Mountford, Dalton Trans. 2012, 41, 2277.
[12] CCDC 918618 (2), 918619 (3), 918620 (4), 918621(5), and 918622
(6) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif.
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