(MeQn2SiH)Fe[N(SiMe3)2]2 (Qn = 8-quinolyl): An unusual δ-agostic iron complex containing an η1-SiH interaction

Article abstract of DOI:10.1039/c0nj00554a

Reaction of MeQn₂SiH (Qn = 8-quinolyl) (1) with Fe[N(SiMe ₃)₂]₂ at room temperature afforded (MeQn ₂SiH)Fe[N(SiMe₃)₂]₂ (2), which is an unusual example of a δ-agostic iron complex containing an η¹-H-Si interaction. Treatment of 2 with excess 3-pentanone at 60 °C produced MeQn₂SiOCHEt₂ (3) in ca. 80% yield.

Full text of DOI:10.1039/c0nj00554a

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LETTER
www.rsc.org/njc | New Journal of Chemistry
(MeQn2SiH)Fe[N(SiMe3)2]2 (Qn = 8-quinolyl): an unusual d-agostic
iron complex containing an g1-SiH interactionw
Jian Yang, Meg Fasulo and T. Don Tilley*
Received (in Montpellier, France) 15th July 2010, Accepted 10th August 2010
DOI: 10.1039/c0nj00554a
Reaction of MeQn2SiH (Qn = 8-quinolyl) (1) with Fe[N(SiMe3)2]2
at room temperature afforded (MeQn2SiH)Fe[N(SiMe3)2]2 (2),
which is an unusual example of a d-agostic iron complex
containing an Z1-H–Si interaction. Treatment of 2 with excess
3-pentanone at 60 1C produced MeQn2SiOCHEt2 (3) in
ca. 80% yield.
The chemistry of s-silane complexes has attracted much
interest because such species are highly relevant to Si–H bond
activation and are frequently invoked as intermediates for
catalytic silylation reactions.1,2 Understanding the coordination
of the Si–H bond to first row metals is particularly interesting
since it can provide insights into catalytic Si–H activation
processes utilizing these inexpensive metals. Indeed, two notable
Fig. 1 Molecular structure of 2 with thermal ellipsoids drawn at the
examples of olefin hydrosilylation catalyzed by first row metals
seem to involve s-silane complexes as intermediates.3 Further-
50% probability level. Key bond distances (A) and angles (1):
Fe(1)–H(1) = 1.926(17), Si(1)–H(1) = 1.464(17), Si(1)ꢁ ꢁ ꢁFe(1) =
more, most of the isolable s-silane complexes exhibit Z2-H–Si
3.06(2), Fe(1)–N(1)
Fe(1)–N(4)
N(4)–Fe(1)–N(3)
N(3)–Fe(1)–N(1) = 101.46(6).
=
2.1486(16), Fe(1)–N(3)
1.9550(15), Fe(1)–H(1)–Si(1)
136.46(7), N(4)–Fe(1)–N(1)
=
1.9656(15),
interactions with significant metal–silicon interaction.2 In this
contribution, we report the synthesis and structural charac-
terization of an unusual d-agostic iron complex incorporating
an Z1-H–Si interaction.4,5
=
= 128.6(7),
=
=
115.72(7),
iron center is a highly distorted tetrahedron, as indicated by
the nearly planar arrangement of donor nitrogen atoms
[S(N–Fe–N) = 353.651]. The most interesting feature of 2 is
the coordinated Si–H bond. The Si–H bond length of
1.464(17) A is normal; however, the Fe–H bond of 1.926(17)
A is rather long. The Feꢁ ꢁ ꢁSi distance of 3.06(2) A is well
beyond the sum of covalent radii for Fe and Si (2.63 A)8
and the Fe–H–Si angle is about 128.6(7)1, suggesting an
Z1-H–Si coordination mode with no appreciable Feꢁ ꢁ ꢁSi inter-
action. A very similar bonding situation has been reported
for [(POCOP)Ir(H)(Et3SiH)]+[B(C6F5)4]ꢀ (POCOP = 2,6-
[OP(tBu)2]2C6H3),4 in which Z1-coordination of Et3SiH to
the cationic Ir center has been investigated by structural,
spectroscopic, and computational studies.
In most transition-metal Z2-silane complexes, the metal–
silicon distances remain relatively short and the silicon–
hydrogen bond is substantially elongated.2 For example,
Sabo-Etienne et al. have recently described the agostic
Ru complex Ru{Z2-H–SiMe2CH(o-C6H4)PPh2}2 with Ru–Si
(ca. 2.45 A) and Si–H (ca. 1.71 A) bond distances that are
typical for Z2-H–Si interactions.9 Also for comparison,
ð1Þ
Reaction of bis(8-quinolyl)methylsilane6 (1) with
Fe[N(SiMe3)2]27 at room temperature afforded a paramagnetic
complex 2 in 86% isolated yield (eqn (1)). X-Ray quality
crystals of 2 were obtained from a concentrated Hexanes
solution at ꢀ30 1C. The ORTEP diagram is shown in
Fig. 1.z The bis(8-quinolyl)methylsilane ligand is coordinated
to the Fe(II) center in a chelate fashion via donation from a
quinolyl group and from an agostic Si–H bond. The other
quinolyl group is not bound to the iron center, presumably
because of the steric crowding imposed by two bis(trimethyl-
silyl)amide ligands. The coordination geometry for the
Chirik’s iron s-silane complex
(
two Z2-H–Si bonds are coordinated to iron, exhibits a short
Fe–Si bond [2.3266(8) A] and a long Si–H bond [1.82(3) A],
while the other coordinated silane is less activated and associated
with a longer Fe–Si bond [2.4733(7) A] and a shorter Si–H
(
iPrPDI)Fe(Z2-PhSiH3)2
iPrPDI = (2,6-CHMe2)2C6H3NQCMe)2C5H3N), in which
Department of Chemistry, University of California, Berkeley,
California 94720, USA. E-mail: tdtilley@berkeley.edu
w CCDC reference number 784610. For crystallographic data in CIF
or other electronic format see DOI: 10.1039/c0nj00554a
c
2528 New J. Chem., 2010, 34, 2528–2529 This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010

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bond [1.59(2) A].3b Note that complex 2, characterized by a
much longer Feꢁ ꢁ ꢁSi distance, a normal Si–H bond, a long
Fe–H bond, and a large Fe–H–Si angle, may model a very early
stage of oxidative addition of a Si–H bond to a transition-
metal center.2d
for X-ray analysis were grown from a concentrated hexanes
solution of 2 at ꢀ30 1C.
Dow Corning is gratefully acknowledged for financial
support of this research. The authors wish to acknowledge
the National Science Foundation for partial support, and
Richard Taylor, Binh Nguyen and Misha Tzou (Dow Corning)
are thanked for valuable discussions. J. Y. sincerely thanks
Dr Robert J. Wright for experimental assistance.
The reactivity of 2 toward a few organic molecules has been
briefly explored. While no reaction was observed between 2
and 1-hexene at 23 1C over 1 d in benzene-d6, addition of
aniline to 2 resulted in rapid formation of HN(SiMe3)2 and
1
release of free 1, as observed by H and 13C NMR spectro-
Notes and references
scopy (eqn (2)). Similarly, treatment of a benzene-d6 solution
of 2 with 3-pentanone (4.15 equiv.) at 23 1C resulted in
formation of 1 and HN(SiMe3)2. Heating this reaction mixture
to 60 1C for 6 d afforded the corresponding hydrosilylation
product Qn2MeSiOCHEt2 (3) in ca. 80% yieldy (eqn (3)).10
The paramagnetic iron-containing products for these reactions
have yet to be identified.
z Crystal data for 2: C31H52FeN4Si5, M = 677.07, triclinic, space
86.7540(10)1, b = 85.8280(10)1, g = 83.0680(10)1, V = 1928.2(2) A3,
Z = 2, T = 138(2) K, 49 035 reflections collected, 7057 unique (Rint =
0.0397), R1 = 0.0329, wR2 = 0.0912, R indices based on 7057
reflections with I > 2s(I) (refinement on F2).
ꢀ
group P1, a = 11.3439(8), b = 11.7230(8), c = 14.6618(0) A, a =
y Determined by 1H NMR relative to Me4Si as an internal standard.
Characterization data of 3: dH (600 MHz; C6D6) 8.58 (2H, dd, J 4 and
2), 8.30 (2H, dd, J 7 and 2), 7.53 (2H, dd, J 8 and 2), 7.45 (2H, dd, J 8
and 2), 7.25 (2H, dd, J 8 and 7), 6.70 (2H, dd, J 8 and 4) (aryl
hydrogens, total 12H), 4.39 (1H, quintet, J 6), 1.73–1.62 (4H, m), 1.60
(3H, s, SiCH3), 0.93 (6H, t, J 8). dC (151 MHz; C6D6): 153.6, 149.5,
141.1, 138.9, 136.3, 129.7, 126.9, 120.9 (aryl carbons, one resonance is
obscured by C6D6), 76.2, 30.2, 10.5, 2.79 (Si–CH3). dSi (119 MHz;
C6D6): ꢀ4.5. GC-MS m/z 386 (M+), 371, 315, 299, 283, 272, 256, 242,
228, 215, 207, 188.
ð2Þ
1 (a) G. J. Kubas, Metal Dihydrogen and s-Bond Complexes,
Kluwer/Plenum, New York, 2001; (b) G. J. Kubas, Adv. Inorg.
Chem., 2004, 56, 127; (c) R. N. Perutz and S. Sabo-Etienne, Angew.
Chem., Int. Ed., 2007, 46, 2578.
(3)
2 Reviews: (a) J. Y. Corey and J. Braddock-Wilking, Chem. Rev.,
1999, 99, 175; (b) S. Lachaize and S. Sabo-Etienne, Eur. J.
Inorg. Chem., 2006, 2115; (c) G. I. Nikonov, Adv. Organomet.
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In summary, we report here an unusual example of a d-agostic
iron complex containing an Z1-H–Si interaction. The struc-
tural data suggest that it may model the early stage of
oxidative addition of an Si–H bond to an unsaturated metal
fragment. Further studies are ongoing to explore stoichio-
metric and catalytic reactions involving such species.
3 (a) M. Brookhart and B. E. Grant, J. Am. Chem. Soc., 1993, 115,
2151; (b) S. C. Bart, E. Lobkovsky and P. J. Chirik, J. Am. Chem.
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4 A cationic Z1-silane complex: J. Yang, P. S. White, C. K. Schauer
and M. Brookhart, Angew. Chem., Int. Ed., 2008, 47, 4141.
5 A neutral Zr dimer with a linear Si–H–Zr interaction: G. Ciruelo,
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Soc., Dalton Trans., 2001, 1657.
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2001, 1200; (b) P. Sangtrirutnugul, M. Stradiotto and T. D. Tilley,
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(MeQn2SiH)Fe[N(SiMe3)2]2 (2)
A benzene (3 mL) solution of 16 (0.086 g, 0.286 mmol) was
added to a solution of Fe[N(SiMe3)2]27 (0.108 g, 0.287 mmol) in
benzene (3 mL). The light green solution immediately turned
dark red. After stirring at room temperature for 2 h, all volatiles
were removed in vacuo. The red-violet solid was washed with
cold pentane (1 mL ꢂ 2) and dried in vacuo to yield 2 (0.166 g,
0.245 mmol, 86%). 1H NMR (C6D6, 600.13 MHz): d 28.1, 18.4,
8.2, ꢀ4.6. Anal. calcd (%) for C31H52N4Si5Fe (677.04): C,
54.99, H, 7.74, N, 8.28. Found: C, 55.27, H, 7.66, N, 8.02%.
Magnetic susceptibility: meff = 5.13 mB (C6D6). Crystals suitable
7 R. A. Andersen, K. Faegri, J. C. Green, A. Haaland,
M. F. Lappert and W.-P. Leung, Inorg. Chem., 1988, 27, 1782.
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2832.
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´
ndez, T. Ayed,
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Chem. Commun., 2007, 3963.
10 A control experiment shows that there is no appreciable reactivity
of 1 towards 3-pentanone at 60 1C over 2 d with or without the
presence of HN(SiMe3)2.
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010 New J. Chem., 2010, 34, 2528–2529 2529