Metal-silicon triple bonds: Nucleophilic addition and redox reactions of the silylidyne complex [Cp(CO)2MoξSi-R]

Article abstract of DOI:10.1002/anie.201005794

As a silicon analogue of metal alkylidyne complexes, the title compound offers new perspectives in organosilicon chemistry. The high synthetic potential of 1 is demonstrated by a series of reactions that provide access to the first anionic silylidene complexes and dianionic silyl complexes (see scheme; Nu= Cl, N₃, CH₃; R=C₆H₃-2,6-Trip ₂).

Full text of DOI:10.1002/anie.201005794

Communications
DOI: 10.1002/anie.201005794
Organosilicon Chemistry
Metal–Silicon Triple Bonds: Nucleophilic Addition and Redox
ꢀ
Reactions of the Silylidyne Complex [Cp(CO)2Mo Si-R]**
Alexander C. Filippou,* Oleg Chernov, and Gregor Schnakenburg
Recent developments in the chemistry of low-valent main-
group element compounds have revealed that N-heterocyclic
carbenes (NHC) are particularly suitable to stabilize silicon
centers in low oxidation states.[1] Remarkable achievements
include the syntheses of stable NHC adducts of Si2,[2] SiX2
(X = Cl, Br),[3] silanones,[4] and Si(R)Cl (R = m-terphenyl).[5]
The latter compounds were shown to be useful precursors for
the preparation of complexes containing metal–silicon multi-
1438C, respectively. Chlorosilylidene complexes are very
rare[10] and azidosilylidene complexes as 3 have not been
reported to date highlighting the synthetic potential of 1.
Moreover, complex 1 undergoes selective addition reactions
with carbon-centered nucleophiles. For example, addition of
one equivalent of LiMe to a solution of 1 in diethylether at
ꢁ608C was accompanied by a rapid color change from red-
brown to orange and afforded cleanly the methylsilylidene
complex salt 4, which was isolated as a yellow, air-sensitive,
thermolabile diethylether solvate in 75% yield.[9,11] The
crystal structures of 2 and 3 were determined by single-crystal
X-ray diffraction analyses[12] and revealed the presence of
well separated tetraalkylammonium cations and silylidene
complex anions.[13] The most striking bonding features of the
ple bonds as exemplified by the synthesis of the first silylidyne
[6]
ꢀ
complex, [Cp(CO)2Mo Si-R] (1). Compound 1 offers, as
silicon analogue of metal alkylidyne complexes,[7] new
perspectives in organosilicon chemistry. The high synthetic
potential of 1 is demonstrated here by a series of reactions
providing access to new complexes containing metal–silicon
double and single bonds.
Complex 1 contains an
electrophilic silicon center
and reacts smoothly with
various anionic nucleo-
philes to give unprece-
dented anionic silylidene
complexes (Scheme 1).[8]
For example, treatment of
1 with (NMe4)Cl in 1,2-
dimethoxyethane (DME)
afforded selectively the
bright orange chlorosilyli-
dene complex salt 2 in 72%
yield, and reaction of 1 with
(NEt4)N3 gave the orange
azidosilylidene
complex
salt 3 in quantitative yield
(Scheme 1).[9] Compounds
2 and 3 were isolated as
very air-sensitive solids,
which decompose on heat-
ing at 122–1268C and
Scheme 1. Nucleophilic addition and redox reactions of 1.
three-legged piano-stool complex anions (Figures 1 and 2)
[*] Prof. Dr. A. C. Filippou, Dipl.-Chem. O. Chernov,
Dr. G. Schnakenburg
ꢁ
are: a) the short Mo Si distances (2, 2.300(1) ꢀ; 3,
ꢁ
Institut fꢀr Anorganische Chemie, Universitꢁt Bonn
Gerhard-Domagk-Strasse 1, 53121 Bonn (Germany)
E-mail: filippou@uni-bonn.de
2.287(1) ꢀ), which compare well with the Mo Si double
bond lengths of other molybdenum arylsilylidene complexes
(Mo Si 2.288(2)–2.3872(7) ꢀ);
[6,10a,14]
ꢁ
b) the trigonal planar
[**] We thank the Deutsche Forschungsgemeinschaft for the generous
financial support of this work. We also thank C. Schmidt, K.
Prochnicki and H. Spitz for recording the solution NMR spectra, Dr.
B. Lewall for the electroanalytical studies, and A. Martens for the
elemental analyses. Cp=h5-C5H5; R=C6H3-2,6-Trip2, Trip=2,4,6-
triisopropylphenyl.
coordination of the silicon atoms (sum of angles at Si: 2,
359.48; 3, 359.68); c) the nearly upright conformation of the
silylidene ligand with the m-terphenyl group pointing towards
the cyclopentadienyl ring;[15] d) the considerably widened
Mo-Si-Caryl angle (2, 145.0(1)8; 3, 142.2(1)8), which can be
attributed to the large steric demand of the m-terphenyl
substituent; and e) the small Cl/Nazide-Si-Caryl angle (2,
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201005794.
1122
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 1122 –1126

Si(C6H3-2,6-Trip2)H2Cl (2.032(8) ꢀ),[16] or other typical
organic chlorosilanes (2.023 ꢀ),[17] indicating a strongly
ꢁ
polarized Si Cl bond in 2. Indirect evidence for the polar-
ꢁ
ization of the Si Cl bond of 2 is also provided by the IR and
1H NMR spectra, which show that 2 dissociates to some
extent in toluene or benzene solutions to give 1 and (NEt4)Cl.
The dissociation equilibrium depends on the solvent and is
fully shifted in THF or DME to 2. In comparison, complex 3
ꢁ
contains a less polar Si Nazide bond and does not dissociate to
1 and (NMe4)N3 in toluene or benzene solutions at similar
ꢁ
concentrations. The lower polarity of the Si Nazide bond in 3 is
ꢁ
also indicated by the bonding parameters: the Si Nazide bond
of 3 (1.801(4) ꢀ) is only slightly longer than that of Si(N3)4
((Si N)calcd 1.735 ꢀ)[18] or other tetracoordinate azidosilanes
ꢁ
(1.760(3)–1.814(2) ꢀ),[19] and the difference between the Na
ꢁ
ꢁ
Nb (1.217(5) ꢀ) and Nb Ng bond length (1.124(6) ꢀ) of the
azide group in 3 (D(NN) = 9.3 pm) compares well with that of
Si(N3)4 (D(NN)calcd = 9.0 pm).[18] The Mo CO bond lengths of
ꢁ
2 (1.915(15) ꢀ)[20] and 3 (1.926(4) ꢀ)[20] are much shorter than
those of [Mo(CO)6] (2.063(3) ꢀ)[21] or 1 (1.971(3) ꢀ)[6,20] and
indicate a considerably stronger metal–carbonyl back bond-
ing in 2 and 3 in full agreement with the IR spectra (see
below).
Figure 1. Diamond plot of the structure of the silylidene complex
anion in 2·toluene. Hydrogen atoms were omitted for clarity. Selected
bond lengths [ꢂ] and angles [8]: Mo–Si 2.300(1), Mo–C37 1.930(4),
Mo–C38 1.900(4), Si–Cl 2.145(1), Si–C1 1.909(4), C37–O1 1.176(5),
C38–O2 1.188(5); Mo-Si-C1 145.0(1), Mo-Si-Cl 120.81(5), Cl-Si-C1
93.6(1), Si-Mo-C37 79.5(1), Si-Mo-C38 85.8(1), C37-Mo-C38 83.8(2).
The IR and NMR spectra corroborate the structures of
the silylidene complex salts 2–4. Thus, the 29Si{1H} NMR
spectra of 2–4 display a distinctive downfield-shifted signal at
d = 228.2, 228.5, and 138.0 ppm, respectively. The 29Si NMR
chemical shifts of the silylidene complexes 2–4 lie between
that of the silylidyne complex 1 (d = 320.1 ppm) and those of
the silyl complexes 5 and 6 (d = 27.4 and 50.8 ppm, respec-
1
tively). Further structural information is provided by the H
and 13C{1H} NMR spectra, which reveal that complexes 2–4
are on average Cs symmetric in solution. The NMR spectra
also show, that rotation of the m-terphenyl substituent about
ꢁ
the Si Caryl bond is fast on the NMR timescale at room
temperature. The IR spectrum of 3 in DME shows a
distinctive, very strong nas(N3) absorption band at 2109 cmꢁ1.
Furthermore, the solution IR spectra of all silylidene com-
plexes show in DME two very strong n(CO) absorption bands,
which appear at considerably lower wavenumbers (2, 1840
and 1762 cmꢁ1; 3, 1826 and 1756 cmꢁ1; 4, 1824 and 1695 cmꢁ1
)
than those of 1 (1937 and 1875 cmꢁ1 in toluene) and of the
=
zwitterionic silylidene complex [Cp(CO)2Mo Si(C6H3-2,6-
Trip2)(Im-Me4)] (1859 and 1785 cmꢁ1 in toluene).[6] This
suggests that the s-donor/p-acceptor ratio increases in the
ligand series SiR+ < SiR(Im-Me4)+ < Si(R)Cl < Si(R)N3 <
Si(R)Me leading to a strengthening of the metal–carbonyl
back bonding.
Transition-metal silyl complexes are a well-studied class of
compounds.[22] The majority of silyl complexes are neutral.
Anionic transition metal silyl complexes are less common and
have been shown to be useful building blocks in coordination
chemistry.[23] In comparison, dianionic silyl complexes are
extremely rare and structural characterization has been
lacking so far.[24] The silylidyne complex 1 enables general
synthetic access to dianionic silyl complexes by two routes.
The first route involves double addition of strong nucleo-
philes to the electrophilic silicon center of 1. For example,
treatment of 1 with two equivalents of LiMe in DME/hexane
Figure 2. Diamond plot of the structure of the silylidene complex
anion in 3·2(toluene)·pentane. Hydrogen atoms were omitted and the
2,4,6-tris(isopropyl)phenyl rings were faded for clarity. Selected bond
lengths [ꢂ] and angles [8]: Mo–Si 2.287(1), Mo–C37 1.922(5), Mo–C38
1.929(5), Si–N1 1.801(4), Si–C1 1.919(4), N1–N2 1.217(5), N2–N3
1.124(6); Mo-Si-C1 142.2(1), Mo-Si-N1 126.3(1), N1-Si-C1 91.1(2), Si-
Mo-C37 90.9(1), Si-Mo-C38 81.4(1), C37-Mo-C38 83.3(2).
93.6(1)8; 3, 91.1(2)8), which reflects the low tendency of the
doubly-bonded silicon atom for hybridization.
ꢁ
The Si Cl bond of 2 (2.145(1) ꢀ) is slightly shorter than
that of the SiII chloride Si(R)Cl(Im-Me4) (2.1836(8) ꢀ; R =
C6H3-2,6-Trip2; Im-Me4 = tetramethylimidazol-2-ylidene),[5]
but considerably longer than that of the arylchlorosilane
Angew. Chem. Int. Ed. 2011, 50, 1122 –1126
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
1123

Communications
(1:4) at ꢁ708C followed by warming to room temperature
affords selectively the silyl complex salt 5, which was isolated
as a yellow, extremely air-sensitive DME/hexane solvate in
88% yield (Scheme 1).[9] The second approach to dianionic
silyl complexes was discovered studying the redox properties
of 1. In fact, reduction of 1 with slightly more than two
equivalents of potassium graphite in DME/pentane (1:1)
ꢁ
resulted in an unusual insertion of silicon into the C C bond
of one of the peripheral 2,6-positioned isopropyl substituents
to give the silafluorenyl complex 6. The dianionic silyl
complex 6 was isolated as an orange, highly air-sensitive
dipotassium salt in 90% yield (Scheme 1).
Cyclic voltammetric studies of 1 provided further insight
ꢁ
into this C C bond activation reaction induced by electron
transfer. They showed that the silylidyne complex 1 under-
goes in THFat ambient temperature an irreversible reduction
at Ecpð1Þ ¼ꢁ2060 mV to give probably a silafluorenyl radical
Figure 3. Diamond plot of the structure of the one independent
contact ion-pair dimer of 6·1.5(DME)·0.5(Et2O). Hydrogen atoms and
the DME and Et2O molecules bonded to K2 and K2# were omitted for
clarity. Selected distances [ꢂ] and angles [8]: K1–O1 2.806(7), K1–O2
2.950(7), K1–O2# 2.913(6), K1–C7 3.329(8), K1–C8 3.151(8), K1–C9
3.080(8), K1–C10 3.144(8), K1–C11 3.173(9), K1–C12 3.259(9), K2–O1
2.627(6), K2–O2# 2.652(7), Mo1–Si1 2.480(2), Mo1–C37 1.910(9),
Mo1–C38 1.891(11), Si1–C1 1.934(9), Si1–C8 1.920(9), Si1–C34
1.944(9), C37–O1 1.204(11), C38–O2 1.220(11); Mo1-Si1-C1 121.8(3),
Mo1-Si1-C8 115.6(3), Mo1-Si1-C34 119.9(3), C1-Si1-C8 87.2(4), C1-Si1-
C34 102.4(4), C8-Si1-C34 104.3(4).
anion, which then takes up
a
second electron at
Ecpð2Þ ¼ꢁ2270 mV to give the silafluorenyl complex dianion
6 (potentials vs. the [Fe(C5Me5)2]/[Fe(C5Me5)2]+redox couple/
0.1m (NBu4)PF6 in THF; scan rate = 100 mVsꢁ1).[9,25] The
complex salts 5 and 6 were fully characterized.[9] The IR
spectra of DME solutions of 5 and 6 display two very strong
n(CO) absorption bands at comparable low energy (5: 1677
and 1589 cmꢁ1; 6: 1685 and 1593 cmꢁ1) as those of highly
reduced metal carbonyls (e.g. [M(CO)4]3ꢁ (M = Mn, Re);
n(CO) = 1670, 1690 cmꢁ1; [M(CO)3]3ꢁ (M = Rh, Ir); n(CO) =
1664, 1666 cmꢁ1).[26] The 29Si{1H} NMR spectra of 5 and 6
show a distinctive 29Si NMR signal at d = 27.4 ppm and
50.8 ppm, respectively. The 29Si NMR chemical shifts of 5 and
6 are typical for transition metal silyl complexes, which
usually display 29Si NMR signals in the range of ꢁ50 to
+ 70 ppm.[22,27] The 1H and 13C{1H} NMR spectra of 5 show a
single set of resonance signals for the m-terphenyl substituent
and one CO signal at d = 248.9 ppm, as expected for an
overall Cs symmetric silyl complex dianion, in which rotation
of two silafluorenyl complex dianions through short K···O
ꢁ
ꢁ
isocarbonyl
bridges
(K2 O1
2.627(6) ꢀ,
K2 O2#
2.652(7) ꢀ)[30] to form a twelve-membered ring, which con-
sists of three planes arranged in a chair-like conformation
(plane 1: Mo1, C37, O1, C38, O2; plane 2: O1, K2, O2#, O1#,
K2#, O2; plane 3: Mo1#, C37#, O1#, C38#, O2#).[31] The other
two potassium cations (K1, K1#) are located above and below
the central ring plane (plane 2), display slightly longer
ꢁ
interionic contacts to three carbonyl O atoms (K1 O1
[30]
ꢁ
ꢁ
ꢁ
of the m-terphenyl substituent about the Si Caryl single bond
2.806(7) ꢀ, K1 O2 2.950(7) ꢀ, K1 O2# 2.913(6) ꢀ), and
ꢁ
is fast on the NMR time scale. In comparison, 6 contains a
stereogenic silicon center, which renders the methyl groups of
all isopropyl substituents diastereotopic, and gives rise to two
CO signals in the 13C{1H} NMR spectrum at d = 245.7 and
248.3 ppm.[9] The CO signals of the dianionic silyl complexes 5
and 6 appear in the 13C{1H} NMR spectra at even lower field
than those of the anionic silylidene complexes 2–4 (d = 240.4–
243.2 ppm) indicating an even stronger metal–carbonyl back-
bonding in 5 and 6 than in 2–4, which is further demonstrated
by the position of the n(CO) absorption bands in the IR
are coordinated in an asymmetric fashion to the C C bond
activated arene ring (K Carene 3.080(8)–3.329(8) ꢀ).[32,33] Iso-
ꢁ
carbonyl bridging leads in 6·1.5(DME)·0.5(Et2O) to even
ꢁ
shorter Mo Ccarbonyl bonds (1.900 ꢀ) than those of 2 (1.915 ꢀ)
ꢁ
and 3 (1.926 ꢀ) and correspondingly to even longer C O
bonds (1.208 ꢀ) than those of 2 (1.182 ꢀ) and 3 (1.181 ꢀ).[34]
Finally, the silafluorenyl complex anions in 6·1.5(DME)·0.5
(Et2O) feature a distorted tetrahedral coordinated silicon
ꢁ
center and a Mo Si single bond (2.480(2) ꢀ), which is ca.
ꢁ
20 pm longer than the Mo Si double bonds of the silylidene
ꢁ
ꢁ
ꢁ
spectra and the Mo C and C O bond lengths (see below).
complexes 2 and 3, but shorter than the Mo Si single bonds of
Compound 6 crystallizes in the space group P1 and is
all silyl complexes reported so far (2.487–2.669 ꢀ).[35]
The general, expandable access to unprecedented anionic
silylidene complexes and dianionic silyl complexes presented
in this work illustrates the high synthetic potential of the
silylidyne complex 1 resulting from the high polarity of the
ꢀ
composed of two independent, centrosymmetric ion-pair
dimers containing two molybdenum silafluorenyl dianions
and four potassium cations (Figure 3).[12] Each ion-pair dimer
is hold together by electrostatic interactions between the
potassium cations and the carbonyl oxygen atoms, which are
typical of alkali metal salts of metal carbonyl anions and
isocarbonyl compounds.[28] Two potassium cations (K2 and
ꢁ
Mo Si triple bond. Further studies are currently underway to
explore the scope of this new chemistry.
ꢁ
K2#) are bound to one diethylether (K2 O3 2.715(13) ꢀ) and
Received: September 15, 2010
Revised: October 31, 2010
Published online: December 22, 2010
ꢁ
ꢁ
one chelating DME ligand (K2 O4 2.827(9) ꢀ, K2 O5
2.639(9) ꢀ)[29] and link the molybdenum dicarbonyl moieties
1124
www.angewandte.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 1122 –1126

[15] The nearly upright conformation of the silylidene ligand in the
complex anions 2 and 3 is best indicated by the dihedral angle of
21.0 (2) and 17.68 (3) between the silylidene ligand plane (least-
square plane passing through the atoms Mo, Si, Caryl, and Cl/
Nazide) and the plane defined by the atoms Mo, Si, and Cg, where
Cg denotes the center of gravity of the cyclopentadienyl ring.
[16] N. Weidemann, G. Schnakenburg, A. C. Filippou, Z. Anorg. Allg.
Chem. 2009, 635, 253.
[17] E. Lukevics, O. Pudova, R. Sturkovich in Molecular Structure of
Organosilicon Compounds, Ellis Horwood, New York, 1989.
[18] P. Portius, A. C. Filippou, G. Schnakenburg, M. Davis, K.-D.
Wehrstedt, Angew. Chem. 2010, 122, 8185 – 8189; Angew. Chem.
Int. Ed. 2010, 49, 8013 – 8016.
Keywords: molybdenum · silicon · silylidenes · silylidynes ·
triple bonds
.
[1] Y. Wang, G. H. Robinson, Chem. Commun. 2009, 5201.
[2] Y. Wang, Y. Xie, P. Wei, R. B. King, H. F. Schaeffer III, P. von R.
Schleyer, G. H. Robinson, Science 2008, 321, 1069.
[3] a) R. S. Ghadwal, H. W. Roesky, S. Merkel, J. Henn, D. Stalke,
Angew. Chem. 2009, 121, 5793; Angew. Chem. Int. Ed. 2009, 48,
5683; b) A. C. Filippou, O. Chernov, G. Schnakenburg, Angew.
Chem. 2009, 121, 5797; Angew. Chem. Int. Ed. 2009, 48, 5687.
[4] Y. Xiong, S. Yao, M. Driess, J. Am. Chem. Soc. 2009, 131, 7562.
[5] A. C. Filippou, O. Chernov, B. Blom, K. W. Stumpf, G. Schna-
kenburg, Chem. Eur. J. 2010, 16, 2866.
[19] a) S. S. Zigler, K. J. Haller, R. West, M. S. Gordon, Organo-
metallics 1989, 8, 1656; b) M. Denk, R. K. Hayashi, R. West, J.
Am. Chem. Soc. 1994, 116, 10813.
[6] A. C. Filippou, O. Chernov, K. W. Stumpf, G. Schnakenburg,
Angew. Chem. 2010, 122, 3368; Angew. Chem. Int. Ed. 2010, 49,
3296.
ꢁ
[20] The unweighted mean value xu of the two Mo CO bond lengths
of 1, 2, and 3 is given, respectively. The standard deviation s of xu
(value in parenthesis) was calculated using the equation s2 =
ꢁ(xiꢁxu)2/(n2ꢁn), where xi is the individual value and n = 2.
[21] S. P. Arnesen, H. M. Seip, Acta Chem. Scand. 1966, 20, 2711.
[22] For selected review articles on transition metal silyl complexes
see: a) T. D. Tilley in The Silicon-Heteroatom Bond (Eds.: S.
Patai, Z. Rappoport), Wiley, Chichester, 1991, pp. 245 – 364;
b) M. S. Eisen in The Chemistry of Organic Silicon Compounds,
Vol. 2 (Eds.: Z. Rappoport, Y. Apeloig), Wiley, Chichester, 1998,
pp. 2037 – 2128.
[7] Selected monographs and review articles on alkylidyne com-
plexes: a) E. O. Fischer, Adv. Organomet. Chem. 1976, 14, 1;
b) F. G. A. Stone, Angew. Chem. 1984, 96, 85; Angew. Chem. Int.
Ed. Engl. 1984, 23, 89; c) R. R. Schrock, Acc. Chem. Res. 1986,
19, 342; d) H. P. Kim, R. J. Angelici, Adv. Organomet. Chem.
1987, 27, 51; e) H. Fischer, P. Hofmann, F. R. Kreißl, R. R.
Schrock, U. Schubert, K. Weiss, Carbyne Complexes, VCH,
Weinheim, 1988; f) A. Mayr, H. Hoffmeister, Adv. Organomet.
Chem. 1991, 32, 227; g) R. R. Schrock, Chem. Rev. 2002, 102, 145.
[8] All silylidene complexes presently known are either neutral or
cationic: a) M. Okazaki, H. Tobita, H. Ogino, Dalton Trans.
2003, 493; b) N. J. Hill, R. West, J. Organomet. Chem. 2004, 689,
4165; c) R. Waterman, P. G. Hayes, T. D. Tilley, Acc. Chem. Res.
2007, 40, 712.
[23] U. Schubert in Organosilicon Chemistry (Eds.: N. Auner, J.
Weiss), Wiley, Chichester, 1994, pp. 205 – 211.
[24] a) S. Sharma, A. C. Oehlschlager, J. Org. Chem. 1989, 54, 5383;
b) S. Sharma, A. C. Oehlschlager, J. Org. Chem. 1991, 56, 770;
c) R. D. Singer, Sharma, A. C. Oehlschlager, J. Org. Chem. 1991,
56, 3510; d) S. Nakamura, M. Uchiyama, T. Ohwada, J. Am.
Chem. Soc. 2004, 126, 11146.
[9] The Supporting Information contains the syntheses and analyt-
ical and spectroscopic data of complexes 2–6. All compounds
were characterized by IR, 1H NMR, 13C NMR and 29Si NMR
[25] Ecpð1Þ and Ecpð2Þ are the cathodic peak potentials of the first and
1
spectroscopies, and the H and 13C NMR signals were unequiv-
second reduction step, respectively.
ocally assigned by a combination of H,H-COSY, HMQC,
HMBC, and DEPT experiments. The Supporting Information
contains also details of the cyclic voltammetric studies of 1.
[10] a) B. V. Mork, T. D. Tilley, Angew. Chem. 2003, 115, 371; Angew.
Chem. Int. Ed. 2003, 42, 357; b) P. G. Hayes, R. Waterman, P. B.
Glaser, T. D. Tilley, Organometallics 2009, 28, 5082.
[11] The yellow diethylether solvate of 4 turns brown at ambient
temperature and should be stored at ꢁ308C.
[26] a) J. E. Ellis, Adv. Organomet. Chem. 1990, 31, 1; b) J. E. Ellis,
Organometallics 2003, 22, 3322; c) J. E. Ellis, Inorg. Chem. 2006,
45, 3167.
[27] The following selected references contain 29Si NMR chemical
shifts of molybdenum silyl complexes: a) T. S. Koloski, D. C.
Pestana, P. J. Carroll, D. H. Berry, Organometallics 1994, 13, 489;
b) S. H. A. Petri, B. Neumann, H.-G. Stammler, P. Jutzi, J.
Organomet. Chem. 1998, 553, 317.
[12] Orange single crystals of 2·toluene and 3·2(toluene)·pentane
were obtained upon diffusion of pentane into a toluene solution
of 2 at room temperature and a toluene solution of 3 at ꢁ168C,
respectively. Orange single crystals of 6·1.5DME·0.5Et2O were
obtained upon addition of diethylether into a solution of 6 in
DME at ambient temperature. CCDC 800704 (2·toluene),
800705 (3·2(toluene)·pentane), and 800706 (6·1.5(DME)·0.5
(Et2O)) 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.
[13] The shortest interionic contacts exist in 2 and 3 between the
hydrogen atoms of the ammonium cations and the carbonyl
oxygen atoms of the anions (2: H45B···O1 2.313 ꢀ, H47C···O2
2.434 ꢀ; 3: H48A···O2 2.504 ꢀ). These CH···O contacts are
shorter than the sum of the van der Waals radii of hydrogen and
oxygen (2.70 ꢀ) and lie close to the range of short CH···O
contacts (2.045–2.399 ꢀ) found in various neutron diffraction
crystal structures: R. Taylor, O. Kennard, J. Am. Chem. Soc.
1982, 104, 5063.
[28] a) M. Y. Darensbourg, Prog. Inorg. Chem. 1985, 33, 221; b) C. P.
Horwitz, D. F. Shriver, Adv. Organomet. Chem. 1984, 23, 219;
c) M. M. Otten, H. H. Lamb, J. Am. Chem. Soc. 1994, 116, 1372.
[29] In the second independent ion-pair dimer of 6·1.5(DME)·0.5
(Et2O) the corresponding potassium cations K4 and K4# are
coordinated by two chelating DME ligands. The structure of the
second independent ion-pair dimer of 6·1.5(DME)·0.5(Et2O)
with selected bonding parameters is depicted in the Supporting
Information.
ꢁ
[30] The K Ocarbonyl distances of 6·1.5(DME)·0.5(Et2O) compare
well with those of other potassium carbonyl metalates: a) E.
Hey-Hawkins, H. G. von Schnering, Chem. Ber. 1991, 124, 1167;
b) V. Kirin, P. W. Roesky, Eur. J. Inorg. Chem. 2004, 1045.
[31] The chair-like conformation of the three planes is indicated by
the dihedral angle between plane 1 and plane 2, and plane 2 and
plane 3 of 47.98.
ꢁ
[32] The K Carene distances in 6·1.5(DME)·0.5(Et2O) compare well
with those found in other arene complexes of K+; selected
references: a) P. B. Hitchcock, M. F. Lappert, G. A. Lawless, B.
Royo, J. Chem. Soc. Chem. Commun. 1993, 554, and references
therein; b) L. Pu, M. O. Senge, M. M. Olmstead, P. P. Power, J.
Am. Chem. Soc. 1998, 120, 12682; c) G. K. Fukin, S. V. Linde-
[14] a) B. V. Mork, T. D. Tilley, A. J. Schultz, J. A. Cowan, J. Am.
Chem. Soc. 2004, 126, 10428; b) M. Hirotsu, T. Nunokawa, K.
Ueno, Organometallics 2006, 25, 1554.
Angew. Chem. Int. Ed. 2011, 50, 1122 –1126
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
1125

Communications
man, J. K. Kochi, J. Am. Chem. Soc. 2002, 124, 8329, and refs.
therein.
[33] The asymmetric coordination of the potassium cation K1 (K1#)
potassium-to-ring normal and Cg the center of the arene ring;
ꢁ
Cf Cg = 0.233 ꢀ).
[34] The mean bond lengths of 2, 3, and the two independent ion-pair
dimers of 6 are given in brackets.
ꢁ
is also evidenced by its distance from the arene ring C7 C12
ꢁ
[35] The median value of Mo Si single bond lengths is 2.5595 ꢀ
ꢁ
(K1 Cf 2.855(2) ꢀ), which is shorter than the distance from the
according to a CSD survey of molybdenum silyl complexes
(14.09.2010).
ꢁ
arene ring center (K1 Cg 2.865(4) ꢀ) (Cf denotes the foot of the
1126
www.angewandte.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 1122 –1126