Stepwise construction of the Cr-Cr quintuple bond and its destruction upon axial coordination

Article abstract of DOI:10.1002/anie.201202337

Give me five! Terdentate 2,6-diamidopyridyl ligands were used to stabilize the Cr-Cr quintuple bond and have made it possible to isolate and characterize not only the Cr-Cr quintuple-bonded complex, but also the mixed-valent intermediates (Cr^I

Full text of DOI:10.1002/anie.201202337

Angewandte
Chemie
DOI: 10.1002/anie.201202337
Quintuple Bonding
ꢀ
Stepwise Construction of the Cr Cr Quintuple Bond and Its
Destruction upon Axial Coordination**
Yu-Lun Huang, Duan-Yen Lu, Hsien-Cheng Yu, Jen-Shiang K. Yu, Chia-Wei Hsu,
Ting-Shen Kuo, Gene-Hsiang Lee, Yu Wang, and Yi-Chou Tsai*
Although quadruple bonding in transition-metal chemistry
has been considered a thoroughly studied area,[1a] the concept
of multiple bonding[1b] was reinvigorated in 2005 by the
Wurtz reductive coupling reaction of the corresponding
chloride coordinated precursors.[2,3] The previously reported
quintuple-bonded dichromium examples were obtained by
alkali metal reduction of the mononuclear [LCrCl2-
ꢀ
seminal discovery of the first Cr Cr quintuple bond in the
(THF)2][3c,e] or dimeric complexes [LCr(m-Cl)]2 (L = mono-
[3]
isolable dimeric chromium compound Ar’CrCrAr’ (Ar’ = 2,6-
(2,6-iPr2C6H3-)2C6H3) by Power and co-workers.[2] Since then,
the structures of several Group 6 homobimetallic compounds
dentate or bidentate ligand). It should be noted that all these
ꢀ
precursors lack Cr Cr bonding. Besides, we have recently
ꢀ
ꢀ
with very short Cr Cr (1.73–1.75 ꢀ) and Mo Mo (2.02 ꢀ)
quintuple bonds have been characterized.[3] All these remark-
able quintuple-bonded bimetal units are supported by either
C- or N-based bridging ligands. Based on their structures,
these quintuple-bonded dinuclear compounds can be simply
classified into two types as illustrated in Figure 1. The
existence of the type I quintuple
demonstrated that the metal–metal quintuple and quadruple
bond can be constructed from the corresponding quadruple
and triple bond, respectively. For example, the d bonds in the
quintuple-bonded species [Mo2{m-h2-RC(N-2,6-iPr2C6H3)2}2]
(R = H, Ph)[3h] and quadruple-bonded complex [Mo2{m-h2-
Me2Si(N-2,6-iPr2C6H3)2}2][6] are formed by alkali metal reduc-
tion of the corresponding chloride-coordinated quadruple-
and triple-bonded species, respectively. However, the forma-
bond was recently corroborated by
experiments,[4a] and the bonding
tion mechanism of the metal metal quintuple bonds has not
ꢀ
paradigms of both types were real-
been investigated. To this end, continuing our exploration in
the field of quintuple-bond chemistry, we herein report the
ized by theoretical investigations.[4]
ꢀ
Preliminary reactivity studies on the
type I complexes show that they are
reactive towards the activation of
small molecules and display inter-
esting complexation with olefins and
alkynes.[5]
construction of a complex with a Cr Cr quintuple bond by
two subsequent one-electron-reduction steps from a halide-
free homo-divalent dichromium complex to a mixed-valent
intermediate (CrI, CrII), and then to the final quintuple-
bonded product. Structural characterization of these dichro-
mium compounds is important to shed light on the formation
mechanism of the metal–metal quintuple bonds. Moreover,
Figure 1. Two types of
quintuple-bonded com-
plexes.
Up to now, both type I and II compounds have been
exclusively synthesized by a procedure analogous to the
ꢀ
the metal metal quadruple bonds can be dramatically
elongated by intramolecular axial coordination, but such an
interaction in the quintuple-bonding system has not been
investigated. We report herein that the Cr Cr quintuple bond
can be readily cleaved by disproportionation induced by
intramolecular axial coordination.
[*] Y.-L. Huang, D.-Y. Lu, H.-C. Yu, C.-W. Hsu, Prof. Dr. Y.-C. Tsai
Department of Chemistry and Frontier Research Center on
Fundamental and Applied Sciences of Matters
ꢀ
National Tsing Hua University, Hsinchu 30013 (Taiwan)
E-mail: yictsai@mx.nthu.edu.tw
As illustrated in Scheme 1, treatment of CrCl2 in THF
with 1 equiv of dilithiated 2,6-diamidopyridine Li2[2,6-(2,6-
iPr2C6H3-N)2-4-CH3C5H2N] (1) and Li2[2,6-(iPr3SiN)2-C5H3N]
(2), prepared by adding 2 equiv of nBuLi to the correspond-
ing 2,6-diaminopyridine in n-hexane, yields two dark green
dimeric complexes [{(THF)Cr(m-k1:k2-2,6-(2,6-iPr2C6H3-N)2-
4-CH3C5H2N)}2] (3) and [{(THF)Cr(m-k1:k2-2,6-(iPr3Si-
N)2C5H3N)}2] (4), respectively, in good yields (62% for 3
and 74% for 4). The 1H NMR spectra of 3 and 4 display broad
signals in the range of 20 and ꢀ10 ppm, so little useful
information could be obtained.
The dinuclear nature of 3 and 4 was confirmed by single-
crystal X-ray crystallography[7] and their molecular structures
are depicted in Figure 2 and Figure S2 in the Supporting
Information). It is interesting to note that although these two
dinuclear species bear the same number of ligands, they
exhibit very different structural conformations. In compound
3, each Cr atom is five-coordinate, ligated by four nitrogen
Prof. Dr. J.-S. K. Yu
Institute of Bioinformatics and Systems Biology and
Department of Biological Science and Technology
National Chiao Tung University, Hsinchu, 30010 (Taiwan)
T.-S. Kuo
Department of Chemistry
National Taiwan Normal University, Taipei 11677 (Taiwan)
Dr. G.-H. Lee, Prof. Dr. Y. Wang
Department of Chemistry
National Taiwan University, Taipei 10617 (Taiwan)
[**] We are grateful to the National Science Council, Taiwan for financial
support under grants NSC 99-2113M-007-012-MY3 (Y.C.T.) and 100-
2627-B-009-001 (J.S.K.Y.), and the “Center for Bioinformatics
Research of Aiming for the Top University Program” of NCTU and
MoE, Taiwan.
Supporting information for this article (including experimental
details for the synthesis and characterization of complexes 3–8) is
available on the WWW under http://dx.doi.org/10.1002/anie.
201202337.
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[(Et2O)Kꢁ[18]crown-6][Cr{m-k1:k2-2,6-(2,6-iPr2C6H3-N)2-4-
CH3C5H2N}2Cr] (5) (43% yield) and brown [(THF)2K-
ꢁ[18]crown-6][Cr{m-k1:k2-2,6-(iPr3Si-N)2C5H3N}2] (6) (35%
1
yield), respectively. Like 3 and 4, the H NMR spectra of 5
and 6 are also not diagnostic because of the extreme line
broadening caused by their nondiamagnetic properties.
Fortunately, the formulation of 5 and 6 was corroborated
by X-ray crystallography,[7] and their molecular structures are
depicted in Figure 3 ([(Et2O)Kꢁ18-crown-6][5]) and Fig-
Scheme 1. Synthesis of complexes 3–7.
Figure 3. Molecular structure of the Cr-containing anion of 5 with
thermal ellipsoids at 35% probability. The counter cation
[(Et2O)Kꢁ[18]crown-6]+, diethyl ether solvate, and hydrogen atoms
have been omitted for clarity.
Figure 2. Molecular structure of 3 with thermal ellipsoids at 35%
probability. Hydrogen atoms have been omitted for clarity.
ure S4 ([(THF)2Kꢁ18-crown-6][6]). Unlike 3 and 4 and their
striking structural difference, compounds 5 and 6 display
strongly similar structures. In contrast to 3, the two 2,6-
diamidopyridyl units in 5 are no longer parallel; the dihedral
angle between these two supporting ligands is 33.4(2)8. In 6,
the torsion angle between two pyridyl units is 52.7(3)8. Both
compounds consistently show two chromium atoms in differ-
ent coordination environments. One chromium atom is
ligated by two N donors (amido) and thus shows a linear
geometry with the bond angle N1-Cr1-N6 of 178.00(17)8 in 5
and N3-Cr2-N3A of 177.8(2)8 in 6, while the other chromium
atom is embraced by the other four nitrogen atoms and thus
displays a roughly planar conformation. In comparison with
two structurally characterized monomeric two-coordinate
monovalent chromium complexes [(2,6-(2,4,6-iPr3C6H2)2-3,5-
iPr2C6H1)Cr(L)] (L = THF, PMe3), in which the central Cr
atom has five unpaired electrons described by Power and co-
workers,[8] a + 1 oxidation state is accordingly assigned to the
two-coordinate chromium centers, while the four-coordinate
chromium centers are divalent. The distances between two Cr
atoms are 3.1036(11) (5) and 2.9277(15) ꢀ (6), indicative of
donors and a molecule of THF, but the Cr atoms in 4 are four-
coordinate, surrounded by three nitrogen atoms and a THF
molecule. In 3, the two 2,6-diamidopyridyl ligands are parallel
to each other and two THF ligands are arranged in an anti
conformation. The two much more sterically encumbered
silyl-substituted 2,6-diamidopyridyl ligands in 4, however, are
arranged in a nearly orthogonal orientation with a torsion
angle of 77.5(1)8 with two THF ligands in a syn conformation.
Each Cr atom in 3 adopts a square-pyramidal geometry, but
the geometry at each Cr atom in 4 is approximately planar. As
ꢀ
a result, compound 3 has a shorter Cr Cr distance of
2.8513(25) ꢀ, while the separation between two chromium
centers is 3.1151(7) ꢀ in 4. Despite the significant structural
differences, 3 and 4 display similar magnetic properties. The
room-temperature solution magnetic moments of 3 and 4 are
4.22 and 3.89 mB, respectively, which are both less than the
spin-only value expected for two uncoupled Cr2+ ions (meff
=
ꢀ
6.93 for S1 = S2 = 2), indicative of antiferromagnetic coupling.
Subsequent one-electron reduction of dark green 3 and 4
in THF by 1 equiv of KC8 in the presence of 1 equiv of
[18]crown-6 and recrystallization from diethyl ether and THF
gives the reddish brown mixed-valent dinuclear complex
no Cr Cr bond. Besides the structural resemblance, 5 and 6
also possess similar magnetic properties. They both exhibit an
antiferromagnetic exchange between two Cr spin centers. The
room-temperature solution magnetic moments of 5 and 6 are
5.00 and 3.53 mB, respectively, which are less than the spin-only
2
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value expected for two noninteracting Cr+ and Cr2+ ions
(meff = 7.68 for S1 = 5/2 and S2 = 2).
cleavage of the Cr Cr quintuple bond and gives 3 in
quantitative yield.
ꢀ
Interestingly, when a solution of 3 in diethyl ether is
treated with 2.5 equiv of KC8, the diamagnetic burgundy
The magnetic susceptibility of 7 was measured between 2
and 300 K. Simulation based on a best fit of the data points
yielded a temperature-independent paramagnetism (TIP) =
768 ꢁ 10ꢀ6 emu (Figure S6), which is consistent with Powerꢂs
quintuple-bonded dichromium compounds with TIP values of
680 ꢁ 10ꢀ6 to 1500 ꢁ 10ꢀ6 emu.[2,3a] This magnetic behavior
indicates an S = 0 ground state, which supports strongly
coupled d5–d5 bonding electrons.
On the theoretical side, the DFT calculations at the BP86
level with triple-z quality basis sets gave a theoretical
structure for 7 in good agreement with the X-ray data (see
Table S13 in the Supporting Information). As indicated by the
molecular orbital (MO) studies, there is no significant N–Cr
p-bonding interactions. Attention is next drawn to five
occupied metal-based MOs, namely, HOMO, HOMO-1,
HOMO-4, HOMO-6, and HOMO-10 (see Figure S7 in the
Supporting Information). These orbitals have their electron
densities concentrated on the metal atoms rather than the
supporting ligands and thus may be assumed to be responsible
ꢀ
Cr Cr quintuple-bonded complex [{(Et2O)K}2{Cr2(m-
k1:k1:k1:h3:h6-2,6-(2,6-iPr2C6H3-N)2-4-CH3C5H2N)2}] (7) is iso-
lated (43% yield) after recrystallization from diethyl ether. In
contrast, treatment of 4 with an excess amount (4 equiv) of
ꢀ
KC8 does not engender the formation of the analogous Cr Cr
quintuple-bonded species. Complex 7 can be prepared alter-
natively by reduction of 5 in THF with KC8 (3 equiv), but the
yield of isolated product is poor (6%). It is, however,
interesting to note that the yield of 7 can be dramatically
improved to 82%, if 5 equiv of potassium iodide is added.
Interestingly, the reaction of 6 and 3 equiv of KC8 in the
ꢀ
presence of 5 equiv of potassium iodide does not give the Cr
Cr quintuple-bonded species, either.
The formulation of 7 is supported by the 1H NMR
spectrum. For example, signals corresponding to only one
ligand environment are observed at room temperature. Two
different meta protons of the pyridine backbone resonate at
d = 4.89 and 4.61 ppm with an integration ratio of 1:1. The
ratio of the K+ ion bound diethyl ether to 2,6-diamidopyridyl
ligand is 1:1 as well. The solid-state molecular structure of 7
was established by X-ray crystallography[7] and is presented in
Figure 4. Complex 7 displays C2h symmetry with the Cr2 unit
lying on the crystallographically imposed center of symmetry.
ꢀ
for the metal–metal bonding. Among these five occupied Cr
Cr bonding MOs, HOMO-10 (dyzꢀdyz) and HOMO-6
ꢀ
ꢀ
(dxzꢀdxz) represent two Cr Cr p bonds, while the Cr Cr
s character is found at HOMO-4 (ðdz2 þ dz2 Þ). The contour
À
Á
plots of HOMO (dxy + dxy) and HOMO-1 ( sdx2ꢀy2 þ sdx2ꢀy2
)
ꢀ
unambiguously indicate two Cr Cr d bonds. Overall, the
pattern of these five occupied metal–metal bonding MOs
leads to an effective bond order (eBO) of 4.54.[9] The Cr Cr
ꢀ
bond in 7 is formally quintuple, because five orbitals and five
electrons on each Cr atom are involved in the bonding.
Another striking structural feature of 7 is the presence of
two potassium counter cations, which are ligated by amido
nitrogen atoms and capped by neighboring phenyl rings. In
fact, the encapsulated K+ ions in 7 play a critical role in the
ꢀ
formation of the Cr Cr quintuple bond. In contrast to ligand
1, the lack of two N(amido)-substituted aryl groups, which can
stabilize the K+ ions, renders ligand 2 unable to support the
quintuple-bonded Cr2 unit. Presumably, over the course of the
reduction of 5, the coordination of the lone pairs of the
pendant amido nitrogen atoms to K+ ions, by which the
interaction between Cr atoms and pendant nitrogen atoms
can be blocked, makes further one-electron reduction of 5
and formation of 7 possible. The presence of two K+ ions in 7
is thus of vital importance towards the stabilization the
quintuple-bonded Cr2 unit. This speculation is corroborated
by the following experiment.
Figure 4. Molecular structure of 7 with thermal ellipsoids at 35%
probability. The diethyl ether solvate and hydrogen atoms have been
omitted for clarity.
In principle, the core structure of 7 belongs to the type I
conformation. Each ligand uses two of its three nitrogen
atoms to coordinate with the Cr2 unit. The third nitrogen,
located near one of the two chromium atoms in an off-axis
position, is blocked by coordinating with a K+ ion. Thus, the
directions of the two pendant arms alternate around the
dichromium unit. One striking feature is the extremely short
Compound 7 is stable in n-hexane and diethyl ether.
However, addition of 1 equiv of [18]crown-6 ether to
a burgundy suspension of 7 in n-hexane unexpectedly elicited
ꢀ
Cr Cr bond length of 1.7443(10) ꢀ, comparable to those of
the type I 2-amidopyridine- and amidinate-stabilized quintu-
ple-bonded dichromium complexes.[3c,e] The Cr Cr quintuple
ꢀ
bond is sensitive to oxidation. Two-electron oxidation of 7
upon treatment with 2 equiv of AgOTf in THF results in the
Scheme 2. The reaction of 7 and 1 equiv of [18]crown-6.
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formation of a dark brown precipitate (Scheme 2). After
recrystallization from toluene, the brown mononuclear tetra-
coordinate divalent chromium complex [(h3-CH3C6H5)K-
ꢁ[18]-crown-6][K{m-h1:k1:h1:k2-2,6-(2,6-iPr2C6H3-N)2-4-CH3-
C5H2N}2Cr] (8) was isolated in very good yield (89%). The
molecular structure of 8 was established by X-ray crystallo-
graphy (see Figure S8 in the Supporting Information). It is not
clear as to how compound 7 undergoes Cr22+ disproportiona-
tion to produce 8. Two possible pathways are proposed for
this reaction. One is that the crown ether first coordinates one
of the chromium atoms, which consequently becomes more
electron-rich, and is able to reduce the other chromium atom.
The other possibility is that upon removal of one K+ ion by
the crown ether, the lone pair of the pendant amido nitrogen
atom binds the nearby chromium atom, which renders the
three-coordinate chromium atom more electron-rich, and
then reduces the two-coordinate chromium atom to give 8.
Such axial coordination is possible because the distance
between chromium and the potassium-bound nitrogen atom
is 3.079(3) ꢀ, which is comparable to the distances (2.734(3)–
3.089(6) ꢀ) between Cr and the pendant nitrogen atoms in
the quadruple-bonded dichromium complexes [Cr2(DPhIP)4]
and [Cr2(dpa)4] (DPhIP = 2,6-di(phenylimino)piperidinate,
dpa = 2,2’-dipyridiylamide).[10] These short Cr···N contacts in
the latter two compounds result in remarkable elongation of
dure starting form a halide-free precursor. The employment
of the terdentate 2,6-diamidopyridyl ligands has not only
allowed for the isolation and X-ray structural characterization
of the quintuple-bonded Cr2 compound 7, but also the mixed-
valent (CrI and CrII) intermediates 5 and 6. The character-
ization of 5 and 6 is of importance to elucidate the formation
mechanism of the type I quintuple-bonded complexes.
Besides, the 2,6-diamidopyridine ligand provides a platform
to investigate how an axial interaction affects the length of the
ꢀ
Cr Cr quintuple bond. In contrast to the elongation of the
ꢀ
ꢀ
Cr Cr quadruple bonds caused by axial coordination, the Cr
Cr quintuple bond of 7 can be ruptured by disproportionation
induced by axial ligation. Reactivity studies on 5, 6, and 7 are
currently underway.
Received: March 24, 2012
Revised: May 9, 2012
Published online: && &&, &&&&
Keywords: amidinate · axial coordination · chromium ·
.
formation mechanism · quintuple bonds
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ꢀ
ꢀ
the Cr Cr quadruple bonds. For instance, the Cr Cr distance
is 2.2652(9) ꢀ in [Cr2(DPhIP)4]·THF, while it is 1.858(1) ꢀ in
[Cr2(PhIP)4]
(PhIP = phenyliminopiperidinate)
without
[3] a) R. Wolf, C. Ni, T. Nguyen, M. Brynda, G. J. Long, A. D.
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Gagliardi, P. P. Power, M. Brynda, J. Am. Chem. Soc. 2008, 130,
5104; f) G. La Macchia, F. Aquilante, V. Veryazov, B. O. Roos, L.
Gagliardi, Inorg. Chem. 2008, 47, 11455; g) M. Brynda, L.
Gagliardi, B. O. Roos, Chem. Phys. Lett. 2009, 471, 1; h) G.
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[5] a) A. Noor, G. Glatz, R. Mꢃller, M. Kaupp, S. Demeshko, R.
Kempe, Nat. Chem. 2009, 1, 322; b) C. Ni, B. D. Ellis, G. J. Long,
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6900; d) C. Schwarzmaier, A. Noor, G. Glatz, M. Zabel, A. Y.
pendant nitrogen atoms.[10]
In the chemistry of complexes with quadruple metal–
metal bonds, axial coordination usually results in significant
elongation of the metal–metal bond lengths.[1a] For example,
[11]
ꢀ
ꢀ
the Cr Cr distances range from 2.688(1) ꢀ
(no Cr Cr
bonding) in complexes having strong axial coordination to
1.773(1) ꢀ[12] in those without it. This is also the case in the
chemistry of complexes with quintuple metal–metal bonds.
Recrystallization of the quintuple-bonded dimeric chromium
amidinate [{Cr(m-k1:k1-HC(N-2,6-Me2C6H3)2)}2] (9), where
[3e]
ꢀ
the Cr Cr bond length is 1.7404(8) ꢀ,
from weakly
coordinating THF and 2-methylfuran (2-MeTHF) afforded
the axially ligated complexes [(THF)Cr(m-k1:k1-HC(N-2,6-
Me2C6H3)2)]2 (10) and {(2-MeTHFCr)Cr[(m-k1:k1-HC(N-2,6-
Me2C6H3)2)]2} (11), respectively. The molecular structures of
10 and 11 were determined by X-ray crystallography[7] and are
depicted in Figures S9 and S10, respectively. It is interesting to
note that the ligated THF and 2-MeTHF in 10 and 11 are very
labile. As assayed by 1H NMR spectroscopy, upon dissolution
of 10 and 11 in C6D6, the THF and 2-MeTHF ligands
completely dissociate from the Cr2 unit. The high lability of
both poor s-donors is also supported by the long Cr···O
distances, 2.579(4) (10) and 2.305(7) ꢀ (11). Interestingly, the
ꢀ
strength of the Cr Cr quintuple bond is indeed weakened by
axial coordination. As indicated by the structural parameters,
the separation between two Cr centers in 10 and 11 is
1.8115(12) and 1.7634(5) ꢀ, respectively, which are signifi-
cantly longer than that of 9.
ꢀ
In conclusion, the new type I Cr Cr quintuple-bonded
compound 7 supported by two terdentate 2,6-diamidopyridyl
ligands has been prepared by a sequential reduction proce-
4
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Timoshkin, B. M. Cossairt, C. C. Cummins, R. Kempe, M.
Scheer, Angew. Chem. 2011, 123, 7421; Angew. Chem. Int. Ed.
2011, 50, 7283; e) J. Shen, G. P. A. Yap, J.-P. Werner, K. H.
Theopold, Chem. Commun. 2011, 47, 12191.
indices [I > 2s(I)]: R1 = 0.0625, wR2 = 0.1598, R indices (all
data): R1 = 0.0990, wR2 = 0.1983; 8·C7H8: C86H115N6CrK2O6:
Mr = 1459.04, T= 200(2) K, triclinic, space group P1, a =
14.5434(8), b = 15.8602(9), c = 22.8046(11) ꢀ, a = 78.569(3),
[6] Y.-C. Tsai, Y.-M. Lin, J.-S. K. Yu, J.-K. Hwang, J. Am. Chem. Soc.
2006, 128, 13980.
b = 72.312(3), g = 63.613(3)8, V= 4477.0(4) ꢀ3, Z = 2, 1calcd
=
1.082 Mgmꢀ3
, , reflections collected: 37371,
m = 0.270 mmꢀ1
[7] Crystallographic data for 3·n-C6H14: C74H108N6Cr2O2, Mr =
1217.66, T= 200(2) K, triclinic, space group P1, a =
10.9399(15), b = 13.3874(19), c = 14.825(2) ꢀ, a = 70.668(2),
independent reflections: 15709 (Rint = 0.0530), final R indices
[I > 2s(I)]: R1 = 0.0978, wR2 = 0.2947, R indices (all data): R1 =
0.1806, wR2 = 0.3296; 10: C42H54N4Cr2O2: Mr = 750.89, T=
200(2) K, triclinic, space group P1, a = 8.6139(3), b =
10.8806(3), c = 11.6811(4) ꢀ, a = 83.5650(10), b = 81.9330(10),
b = 70.474(2), g = 79.147(2)8, V= 1923.6(5) ꢀ3, Z = 1, 1calcd
=
1.051 Mgmꢀ3
, , reflections collected: 11009,
m = 0.325 mmꢀ1
independent reflections: 6687 (Rint = 0.0267), final R indices
[I > 2s(I)]: R1 = 0.0603, wR2 = 0.18084, R indices (all data): R1 =
0.0844, wR2 = 0.1981; 4: C54H106N6Cr2O2Si4, Mr = 1097.81, T=
200(2) K, monoclinic, space group P21/c, a = 15.6863(3), b =
g = 68.575(2)8, V= 1006.87(6) ꢀ3, Z = 1, 1calcd = 1.238 Mgmꢀ3
,
m = 0.578 mmꢀ1
, reflections collected: 13674, independent
reflections: 3627 (Rint = 0.0759), final R indices [I > 2s(I)]: R1 =
0.0679, wR2 = 0.1686, R indices (all data): R1 = 0.0959, wR2 =
0.1976; 11·2MeTHF: C44H56N4Cr2O2: Mr = 776.93, T=
150(2) K, monoclinic, space group P21/n, a = 10.7474(1), b =
19.2132(4),
6151.4(2) ꢀ3, Z = 4, 1calcd = 1.175 Mgmꢀ3, m = 0.473 mmꢀ1, reflec-
tions collected: 52063, independent reflections: 10790 (Rint
c = 20.4594(5) ꢀ,
b = 93.9640(10)8,
V=
=
22.6841(2),
c = 17.4934(2) ꢀ,
b = 104.7263(6)8,
V=
0.0532), final R indices [I > 2s(I)]: R1 = 0.0451, wR2 = 0.1116, R
indices (all data): R1 = 0.0820, wR2 = 0.1393; 5·C4H10O:
C80H122N6Cr2KO8: Mr = 1438.94, T= 200(2) K, monoclinic,
space group P21/c, a = 16.4037(2), b = 15.7947(2), c =
33.2294(5) ꢀ, b = 103.3030(10)8, V= 8378.44(19) ꢀ3, Z = 4,
4124.71(7) ꢀ3, Z = 4, 1calcd = 1.251 Mgmꢀ3
,
m = 0.567 mmꢀ1
,
reflections collected: 26280, independent reflections: 9447
(Rint = 0.0310), final R indices [I > 2s(I)]: R1 = 0.0506, wR2 =
0.1484,
R indices (all data): R1 = 0.0722, wR2 = 0.1654,
CCDC 843643 (3·n-C6H14), 843644 (4), 843645 (5·C4H10O),
843646 (6), 843647 (7·2C4H10O), 871483 (8·C7H8), 728851 (10),
728852 (11) 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.
1calcd = 1.141 Mgmꢀ3
,
m = 0.362 mmꢀ1
,
reflections collected:
41494, independent reflections: 15013 (Rint = 0.0878), final R
indices [I > 2s(I)]: R1 = 0.0720, wR2 = 0.1952, R indices (all
data): R1 = 0.1300, wR2 = 0.2612; 6: C66H132N6Cr2KO8Si4: Mr =
ꢀ
1393.24, T= 200(2) K, tetragonal, space group P421c, a =
16.9265(3) ꢀ,
7821.9(2) ꢀ3, Z = 4, 1calcd = 1.183 Mgmꢀ3, m = 0.443 mmꢀ1, reflec-
tions collected: 22457, independent reflections: 6876 (Rint
b = 16.9265(3) ꢀ,
c = 27.3011(5) ꢀ,
V=
[8] R. Wolf, M. Brynda, C. Ni, G. J. Long, P. P. Power, J. Am. Chem.
Soc. 2007, 129, 6076.
[9] The effective bond order is calculated based on electron
occupancy of bonding and antibonding orbitals.
[10] F. A. Cotton, L. M. Daniels, C. A. Murillo, I. Pascual, H.-C.
Zhou, J. Am. Chem. Soc. 1999, 121, 6856.
[11] F. A. Cotton, C. A. Murillo, H.-C. Zhou, Inorg. Chem. 2000, 39,
3728.
=
0.0360), final R indices [I > 2s(I)]: R1 = 0.0734, wR2 = 0.1985, R
indices (all data): R1 = 0.0831, wR2 = 0.2088; 7·2C4H10O:
C76H118N6Cr2K2O4: Mr = 1361.96, T= 200(2) K, monoclinic,
space group P21/n, a = 9.91160(10), b = 28.8440(3), c =
13.7416(2) ꢀ, b = 90.4560(10)8, V= 3928.46(8) ꢀ3, Z = 2,
1calcd = 1.151 Mgmꢀ3
,
m = 0.430 mmꢀ1
,
reflections collected:
[12] S. Horvath, S. I. Gorelsky, S. Gambarotta, I. Korobkov, Angew.
Chem. 2008, 120, 10085; Angew. Chem. Int. Ed. 2008, 47, 9937.
36327, independent reflections: 7199 (Rint = 0.0765), final R
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

.
Angewandte
Communications
Communications
Quintuple Bonding
Y.-L. Huang, D.-Y. Lu, H.-C. Yu, J.-S. K. Yu,
C.-W. Hsu
&&&& — &&&&
ꢀ
Stepwise Construction of the Cr Cr
Quintuple Bond and Its Destruction upon
Axial Coordination
Give me five! Terdentate 2,6-diamido-
pyridyl ligands were used to stabilize the
plex, but also the mixed-valent inter-
mediates (CrI and CrII), which are impor-
tant species in the formation of type I
quintuple-bonded complexes.
ꢀ
Cr Cr quintuple bond and have made it
possible to isolate and characterize not
ꢀ
only the Cr Cr quintuple-bonded com-
6
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!