High and low rotational barriers in metal tricarbonyl complexes of 2- and 3-indenyl anthracenes and triptycenes: Rational design of molecular brakes

Article abstract of DOI:10.1021/om300512z

Syntheses and X-ray crystal structures are reported for a series of M(CO)₃ derivatives (M = Cr, Re) of phenyl and also 2- and 3-indenyl anthracenes and triptycenes. In each case, the rotational barrier about the bond linking the two organic fragments was evaluated both experimentally by VT or 2D-EXSY NMR and by calculation at the DFT level. Attachment of the metal tripod to the indenyl moiety in an η⁶ fashion does not markedly change the barrier relative to that for the free ligand but lowers the symmetry so as to facilitate its direct measurement. Interestingly, an η⁶ → η⁵ haptotropic shift of the Cr(CO)₃ moiety in 9-indenylanthracenes led to a somewhat lowered barrier, probably attributable to an increase in the ground state energy rather than to decreased steric interactions in the transition state. In contrast, in indenyltriptycenes η⁶ → η⁵ migration of the M(CO)₃ unit along the indenyl skeleton and closer to a paddlewheel leads to a very significant increase in the rotational barrier. These effects can be rationalized in terms of angular steric strain and multiple interactions in the ground state and in the transition state. The results not only provide semiquantitative data on the steric effects of η⁶-phenyl and η⁶- or η⁵-indenyl M(CO)₃ fragments but are also discussed with relevance to their role in organometallic molecular brakes.

Full text of DOI:10.1021/om300512z

Article
pubs.acs.org/Organometallics
High and Low Rotational Barriers in Metal Tricarbonyl Complexes of
2- and 3‑Indenyl Anthracenes and Triptycenes: Rational Design of
Molecular Brakes
Kirill Nikitin,* Cornelia Bothe, Helge Muller-Bunz, Yannick Ortin, and Michael J. McGlinchey*
̈
School of Chemistry & Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland
S
* Supporting Information
ABSTRACT: Syntheses and X-ray crystal structures are
reported for a series of M(CO)3 derivatives (M = Cr, Re) of
phenyl and also 2- and 3-indenyl anthracenes and triptycenes.
In each case, the rotational barrier about the bond linking the
two organic fragments was evaluated both experimentally by
VT or 2D-EXSY NMR and by calculation at the DFT level.
Attachment of the metal tripod to the indenyl moiety in an η6
fashion does not markedly change the barrier relative to that
for the free ligand but lowers the symmetry so as to facilitate
its direct measurement. Interestingly, an η6 → η5 haptotropic shift of the Cr(CO)3 moiety in 9-indenylanthracenes led to a
somewhat lowered barrier, probably attributable to an increase in the ground state energy rather than to decreased steric
interactions in the transition state. In contrast, in indenyltriptycenes η6 → η5 migration of the M(CO)3 unit along the indenyl
skeleton and closer to a paddlewheel leads to a very significant increase in the rotational barrier. These effects can be rationalized
in terms of angular steric strain and multiple interactions in the ground state and in the transition state. The results not only
provide semiquantitative data on the steric effects of η6-phenyl and η6- or η5-indenyl M(CO)3 fragments but are also discussed
with relevance to their role in organometallic molecular brakes.
dynamic behavior of a series of related organic and organo-
metallic structures. Recent studies5,6 of the rigid rotational
systems 3−8 clearly demonstrated that the very substantial
rotational barriers in the anthracenes 3b and 5 arise from
unavoidable steric clashes of hydrogens in the indenyl or phenyl
ring with the peri positions of the anthracene fragment (Chart
1). In contrast to the situation in the anthracenes 3b and 5, the
corresponding triptycenes 4b and 6 can access an energetically
more favorable conformation whereby the planar indenyl or
phenyl moiety can bend away from the 3-fold axis of the
triptycene and slide partially into the valley between the blades,
thus alleviating the steric strain and reducing the rotational
barrier. However, further comparison with the analogous
ferrocenylanthracene and -triptycene 7 and 8, respectively,
suggests that the presence of the additional unsubstituted free-
rotating (η5-cyclopentadieny)iron fragment inverts the situation
once again, now making the rotation of the nominally C3-
symmetrical triptycene paddlewheel in 8 slower than that of the
flat anthracene moiety in 7.6
INTRODUCTION
■
Mechanical systems, and their molecular analogues, exhibit two
fundamental kinds of motion: translation and/or rotation. All
currently known examples of controlled or random intra-
molecular mechanical motion may be categorized as either
translational (shuttles) or rotational (rotors).1 The past decade
has been graced by a plethora of reports describing the design
and function of molecular machines employing either rotation
or translation.2,3 However, molecular systems explicitly
combining both types of intramolecular motion are less
commonly described.
In our recent study of the dynamic behavior of [{(η6-2-(9-
triptycyl)indene}Cr(CO)3] (1), we demonstrated how the
rotor−shuttle concept can work in such a controlled molecular
motion system, whereby the sliding movement of a metal
carbonyl tripod severely hinders the rotation of a triptycene
moiety (Scheme 1). For the first time, a directed suprafacial
migration was combined with the rotational motion of a
molecular paddlewheel in a compact molecular design.4 The
transition from an η6 to an η5 structure, 1 → 2, is accompanied
by an increase of the rotational barrier by ∼12 kcal mol−1,
corresponding at ambient temperature to a 108-fold rate
decrease.
While the observed molecular braking effect can apparently
be viewed as a simple consequence of “jamming” of the
triptycene blades by a carbonyl of the Cr(CO)3 tripod, a more
detailed understanding of this phenomenon requires theoretical
and experimental comparative analysis of the structures and
Although rotational barriers arising in the molecules
containing planar anthracenyl or paddlewheel-shaped triptycyl
fragments directly connected to an aromatic moiety bearing an
orthogonally attached organometallic group remain largely
unexplored, there is particular relevance to the structures and
dynamics of organometallic atropisomers. Thus, axially chiral
Received: June 8, 2012
Published: August 22, 2012
© 2012 American Chemical Society
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Scheme 1. Illustration of a Rotor−Shuttle Controlled Molecular Motion System
Chart 1. Intramolecular Rotation Barriers in the
Anthracenes 3, 5, and 7 and Triptycenes 4, 6, and 8
diamagnetic anisotropy,6,10 both helping to observe and
quantify the rotational barriers. Finally, since the site of
attachment of the tricarbonylchromium group can be altered by
applying a chemical stimulus, some of the systems described
also have an in-built molecular shuttle function.
Because the archetypal haptotropic molecular brake 1 can be
viewed as the juxtaposition of a paddlewheel and an indene or
indenyl moiety bearing a metal tricarbonyl group, the present
study focuses on chromium and rhenium tricarbonyl derivatives
of hydrocarbons containing an indene/indenyl fragment and/or
a C3-symmetrical paddlewheel-shaped triptycene rotor.
RESULTS AND DISCUSSION
■
Our continuing interest in the indene scaffold is primarily
driven by the fact that an organometallic moiety such as
Cr(CO)3, [Mn(CO)3]+, or [Rh(C2H4)2]+ can be attached to
the six-membered aromatic ring of an indene (as in the η6
complex Cr-10, Scheme 3). However, upon deprotonation by a
strong base, the organometallic unit undergoes a suprafacial
migration driven by its ability to delocalize the negative charge
on the five-membered ring of the indenide anion, typically
leading to the anionic η5 complex Cr-11.11 On the other hand,
an isolobal [Re(CO)3]+ moiety can be attached to the five-
membered ring of the indenide anion (as the η5 complex Re-
11, Scheme 3). Such relatively robust molecules are excellent
models for structural and dynamic studies of the isolobal
anionic chromium derivatives Cr-11. Moreover, under
appropriate protonation conditions, a neutral complex typified
by Re-11 or (η5-indenyl)Rh(C2H4)2 can undergo the reverse
sliding movement, thus forming a cationic η6 complex, as in Re-
10.11
biaryls, made by palladium-catalyzed cross-couplings, can lead
to atropisomeric mixtures.7 Typically, as illustrated in Scheme
2, the initially formed naphthyl-substituted arene-Cr(CO)3
Scheme 2. Rotation about the Single Bond Linking the
Phenyl and Naphthyl Fragments in 9, Bringing about
Diastereomerization of Chiral Atropisomers
Let us consider a C3-symmetrical triptycyl rotor connected to
a flat aromatic fragment, exemplified by phenyl or indenyl as in
Chart 1, in which the 3-fold symmetry of the triptycene is
broken and two of the blades are no longer equivalent to the
third one. This nonequivalence, at least in principle, can be
observed and used for the determination of the rotational
barrier.5 However, analysis of dynamic 500 MHz 1H NMR data
demonstrated that rotation in both 9-(2-indenyl)triptycene and
9-phenyltriptycene (4a and 6, respectively), is fast on the NMR
time scale at 193 K, and the rotational barrier is less than ∼9
kcal mol−1. In this context, we note that the much slower
internal rotation in 9-(3-indenyl)anthracene (3b) and 9-
phenylanthracene (5) cannot be directly observed, as the
terminal benzo rings (blades) of the anthracene remain
equivalent, owing to their dynamic symmetry. However,
judicious lowering of their time-averaged C2v symmetry, as in
9,10-bis(m-fluorophenyl)anthracene or 9-naphthyl-10-phenyl-
anthracene, revealed the phenyl rotation barrier to be in excess
of 20 kcal mol−1.5e
complex 9-syn undergoes axial rotation to furnish its
thermodynamically favored diastereomer 9-anti, when heated
in a high-boiling solvent.8 This phenomenon has been exploited
in the syntheses of natural products such as the alkaloids
Korupensamine A and B.9
Herein we report the syntheses, crystal structures, theoretical
modeling, and dynamic NMR behavior of a series of closely
related π-arene complexes containing tripodal M(CO)3
moieties, where M is chromium or rhenium. We show that
such organometallic fragments clearly evoke unusual additional
steric interactions and strongly influence the rotational barriers.
Moreover, they provide versatile internal molecular labels that
lower the molecular symmetry and engender very substantial
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Scheme 3. Relationships between η5- and η6-Indene Metal Carbonyl Complexes
Scheme 4. Preparation of η6-Cr(CO)3 and η5-Re(CO)3 Complexes from the Indenes 12a,b
Figure 1. Molecular structure of the η6 complex 13. The space-filling representation shows that no close contacts are evident.
One can anticipate that further modification of the indenyl or
phenyl substituent in molecules 3−6 by incorporation of a
metal tricarbonyl moiety should lower the molecular symmetry
such that internal rotation in the anthracenes 3 and 5, and also
in the triptycenes 4 and 6, may be conveniently observed by
NMR spectroscopy. Accordingly, we have prepared and studied
the dynamic behavior of a series of organometallic derivatives of
these and other closely related hydrocarbon scaffolds. Inspired
by a theoretically predicted,12 and very recently experimentally
verified,5e high rotational barrier in 9-phenylanthracene (5), the
rotational energy profiles of these new organometallic systems
have been simulated by calculations at the DFT level.
Gratifyingly, the theoretical studies are in reasonable agreement
with the experimentally observed trends.
Internal Rotation in Metal Carbonyl Derivatives of 2-
Methyl- and 2-Phenylindenes. As shown in Scheme 3,
substituted indenes react readily with appropriate metal
carbonyls at elevated temperature, thus yielding complexes
such as Cr-10 and Re-11.13 While treatment with rhenium
carbonyl leads selectively to η5 complexes, reactions with
Cr(CO)6 furnish a mixture of several possible metalated
derivatives when multiple aromatic fragments are present as
substituents R1 and R2.14
Typically, when 2-methylindene (12a) was heated with
Cr(CO)6 in 1,4-dioxane, only the η6 complex 13 was formed
(Scheme 4). The molecular structure of 13, shown in Figure 1,
clearly suggests that, as the methyl group does not engage in
steric clashes with the rest of the molecule, the methyl
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Figure 2. Molecular structures of (a) [η6-(2-indenyl)benzene]tricarbonylchromium(0) (15) and (b) [η5-(2-phenyl)indenyl]tricarbonylrhenium(I)
(16).
Scheme 5. (a) Minimum 90° Flip of the Indenyl Ring Relative to the (phenyl)Cr(CO)3 Fragment Required to Equilibrate the
C(9) and C(13) Positions and the Methylene Hydrogens in 15 and (b) Achievement of Such Equivalence in 16 by Just a Minor
Oscillation of the Phenyl Ring Relative to the Indenyl Plane
rotational barrier should be low.11d,15 Indeed, as revealed by X-
ray crystallography, the methyl group is rotationally disordered
in the solid state.
mol−1 for a phenyl oscillation of the type illustrated in Scheme
5b.
As illustrated in Scheme 5, we note that the chromium
complex 15 and the rhenium derivative 16 can both adopt
mirror-symmetric (Cs) conformations. However, in the former
case the indenyl moiety must lie orthogonal with respect to the
phenyl ring plane (dihedral angle of 90°), whereas in 16 the
molecular mirror plane bisects both ring systems when they are
coplanar with a dihedral angle of 0°. We note parenthetically
that detection of rotation of an η5-bonded organometallic
fragment relative to an indenyl ring requires that the symmetry
be lowered further, as for example in (η5-1-methylindenyl)Rh-
(C2H4)2.17
Hence, as given in Table 1, it is evident that the
incorporation of an organometallic tripodal moiety does not
per se impose a substantial energy barrier that markedly slows
relative rotation of the adjacent aromatic systems. We now
extend our focus to more complex systems bearing an
organometallic tripod attached in an η6 or η5 fashion.
Recently, we described several interesting 2,2′-disubstituted
1,1′-biindenyls5c that can exist in both meso and racemic forms.
Rotation about the C(1)−C(1′) linkage in these molecules is
slow, owing to multiple side-to-side repulsions of the indenyl
fragments and the substituents attached to the 2- and 2′-
positions. Remarkably, when either rac- or meso-1,1′-di(2-
methylindenyl) was heated with rhenium carbonyl in decalin at
160 °C, an identical mixture of organorhenium products was
formed. The major component of this mixture was found to be
the monorhenium complex 1-(2-methylinden-3-yl)-2-methyl-
1,2,3,3a,7a-[η5-tricarbonylrhenium]indenide (17), the molec-
ular structure of which is shown in Figure 3. Formation of this
rhenium tricarbonyl η5 complex is accompanied by migration of
the double bond in the five-membered ring of the second
indenyl fragment, as seen previously in related systems.4,5a
In contrast, the reaction of 2-phenylindene (12b) with
chromium hexacarbonyl yielded two isomeric products: in the
1
η6 complex 14, H and 13C NMR data indicated that the
chromium was positioned on the six-membered ring of the
indene, while in 15 the chromium was η6-bonded to the phenyl
ring. Unfortunately, this 1/2 mixture could not be conveniently
separated on a preparative scale, but slow crystallization
furnished X-ray-quality crystals of 15, and Figure 2a shows
that the dihedral angle between the phenyl ring and the indenyl
framework is only 2°. Interestingly, even in this essentially
coplanar conformation the closest distance between the two
spatially adjacent hydrogens H(3) and H(9) is a very
comfortable 2.24 Å, (sum of vdW radii 2.05 Å).16 Moreover,
a DFT study of this molecular system revealed that a full 180°
rotation of the phenyl (Scheme 5a) would evoke a potential
barrier not exceeding 6 kcal mol−1.
Turning now to (η5-2-phenylindenyl)Re(CO)3 (16), which
can be efficiently prepared in 70% yield by transmetalation of 2-
phenyl-1-trimethylstannylindene (but, perhaps, more conven-
iently by direct metalation of 12b, as described in the
Experimental Section), one can see from Figure 2b that the
phenyl substituent is no longer coplanar with the indenyl ring.
The dihedral angle ranges from 13 to 22° in the three slightly
different conformations found in its crystal structure. Never-
theless, since the closest approach distance between H(3) and
H(9) is 2.3 Å, once again such a minimal steric interaction
would not be expected to create a significant barrier to the
1
rotation about the C(2)−C(8) bond. The 500 MHz H NMR
spectrum of 16 at 193 K exhibited no decoalescence or
significant broadening of the phenyl peaks, suggesting a
rotational barrier of less than 8 kcal mol−1. This observation
is in line with DFT calculations indicating a barrier of ca. 5 kcal
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substituted anthracenes bearing a phenyl or 3-indenyl group at
the 9-position suggest that strong double steric interactions
between spatially adjoining hydrogens of the anthracene and
phenyl or indenyl systems cause very significant rotational
hindrance. As shown in Chart 1, rotational barriers increase
rapidly in the order 3a < 5 < 3b, and we here analyze the
manner in which attachment of an organometallic tripod to
these aromatic skeletons can alter the internal rotation energy
profile.
The formation of the tricarbonylchromium derivatives 18
and 19 from 9-phenylanthracene (5) has been previously
reported to be a rather complex process.14 The initial purple
Cr@anthracene η6 complex 18 rearranges to furnish the yellow
product 19 (Scheme 6). The yield of 19 is always poor, which
Table 1. Experimental and Calculated Rotational Barriers
(kcal mol−1) for Molecules Discussed in the Present Work
exptl
(NMR)
calcd
(DFT)
a
molecule
comment
η6-[9-Cr@phenylan-
thracene] (19)
η6-[9-(2-indenyl)an-
thracene]Cr (21)
η5-[9-(2-indenyl)an-
thracene]Cr (22)
η5-[9-(2-indenyl)an-
thracene]Re (20)
17.5
14.5
13
15.5
13
11
9
in 9-phenylanthracene the barrier is
21 kcal mol−1
in 9-(2-indenyl)anthracene the bar-
rier is 12 kcal mol−1
slightly reduced barrier after η6 → η5
migration
11
isostructural with anionic chromium
complex 22
η6-[9-(3-indenyl)an-
thracene]Cr (24)
η5-[9-(3-indenyl)an-
thracene]Cr (25)
η5-[9-(3-indenyl)an-
thracene]Re (23)
η6-[9-Cr@phenyltrip-
tycene] (27)
>23
22
24
19
in 9-(3-indenyl)anthracene the bar-
rier is 24 kcal mol−1
slightly reduced barrier after η6 → η5
migration
c
21.5
b
20.5
isostructural with the anionic chro-
mium complex 25
Scheme 6. Migration of a Cr(CO)3 Moiety from a Peripheral
Benzo Ring of Anthracene in 18 onto the 9-Phenyl
Substituent in 19
9
in 9-phenyltriptycene the barrier is
<8 kcal mol−1
η6-[9-phenyl-Cr@
triptycene] (28)
<8
η6-[9-(2-indenyl)trip-
tycene]Cr (1)
η5-[9-(2-indenyl)trip-
tycene]Re (32)
8
in 9-(2-indenyl)triptycene the bar-
rier is <8 kcal mol−1
c
19.5
20
isostructural with 2, the anion
derived from 1; the η6 → η5
migration yields an effective mo-
lecular brake!
η6-[9-(3-indenyl)trip-
tycene]Cr (30)
η5-[9-(3-indenyl)trip-
tycene]Re (33)
η6-[9-(3-indenyl)
Cr@triptycene]
(31)
b
17
in 9-(3-indenyl)triptycene the bar-
rier is 12 kcal mol−1
c
20
13
16.5
isostructural with the anion derivable
from complex 30
may be attributable to the sterically shielded surroundings of
the phenyl, whose aromatic system is tightly confined between
the blades of the anthracene. In our hands, even after very
careful adjustment of reaction conditions, the yield of 19 did
not surpass 7%.
The structure of 19 has been determined by X-ray diffraction
for the first time,18 and while a substantial degree of packing
disorder prevents a precise determination of the molecular
parameters, the data are sufficient to establish the molecular
connectivity unequivocally (Figure 4). The phenyl and
11.5
data from ref 5a
a
b
Barriers evaluated at Tc, the coalescence temperature. Hypothetical
c
molecule. Calculated for the analogous Mn(CO)3 complex.
Figure 3. Molecular structure of the η5-Re(CO)3 complex 17.
Figure 4. Molecular structure of [η6-(9-anthracenyl)benzene]-
tricarbonylchromium (19).
1
The H−1H 2D EXSY analysis of complex 17 at 323 K
indicates a dynamic exchange process with a rotational barrier
of ca. 20 kcal mol−1. This value is in good agreement with a
DFT computational study of 17, which revealed that a 360°
rotation about the C(1)−C(11) single bond would evoke two
substantial energy barriers, 20 and 24 kcal mol−1, depending on
whether the uncomplexed indenyl blade passes the C(8)
methyl or the C(7) H in the complexed indenyl, thus making
rotation in this system at room temperature very slow on the
NMR time scale.
anthracenyl rings adopt a dihedral angle of approximately
60°, which may be compared to the structure of the related
system 9-ferrocenylanthracene, in which the interplanar angle
between the cyclopentadienyl and anthracene rings is 45°.6 We
note that, were the solid state conformation of 19 to be
retained in solution, the H(1) and H(8) positions of the
anthracene should be rendered magnetically nonequivalent, and
likewise for the H(12) and H(16) positions of the phenyl. The
Internal Rotation in Metal Carbonyl Derivatives of
Phenyl- and Indenylanthracenes. Our recent findings on
1
500 MHz H NMR spectrum of 19 at 25 °C revealed that the
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resonances assignable to the H(1) and H(8) nuclei are
separated by 1.42 ppm, a difference that can be attributed to
the very significant diamagnetic anisotropy of the Cr(CO)3
group.10 However, H(12) and H(16), the ortho protons of the
phenyl ring, remained isochronous. This nonequivalence of the
anthracene blades, together with the apparent mirror symmetry
of the phenyl ring, is consistent with a dynamic process
whereby the phenyl-Cr(CO)3 unit is rapidly oscillating relative
to the plane of the anthracene framework, as depicted in
Scheme 7a. Since the 180° rotation of Cr(CO)3@Ph19 relative
When 9-(2-indenyl)anthracene (3a) was heated with
rhenium carbonyl in decalin at 160 °C, the η5 derivative 20
was isolated in 22% yield. Analogously, the η6-Cr(CO)3
complex 21 was prepared in 95% yield by heating 3a with
Cr(CO)6 in 1,4-dioxane at 120 °C. The structures of both
complexes (Figure 5) display a slight twisting from planarity of
the anthracene framework: by 11° in 20 and by 3° in 21. Such
minor perturbations may arise through π-stacking or other
crystal-packing effects. The interplanar indenyl−anthracene
angles are 52° (20) and 62° (21), thus rendering the peripheral
blades of the anthracene nonequivalent in the solid state.
1
As shown in Figure 6a, at 193 K the 500 MHz H NMR
spectrum of the rhenium complex 20 in CD2Cl2 exhibited
Scheme 7. Proposed Dynamics of 19: (a) Oscillation of the
Anthracene Close to the Perpendicular Orientation Leaves
H(1) and H(8) Nonequivalent but Equilibrates the Edges of
the Phenyl Ring and (b) Equilibration of the Terminal
Benzo Rings of the Anthracene Requires a 180° Rotation of
the Phenyl Ring To Generate Time-Averaged C2v Symmetry
to the plane of the anthracene in 19 (Scheme 7b) would be
expected to have to overcome a rather substantial energy
1
barrier, this dynamic process was investigated by 2D H−1H
EXSY spectroscopy, which revealed an exchange process, H(1)
↔ H(8), characterized by an activation energy of 17.5 0.5
kcal mol−1. It is noteworthy that this value is markedly lower
than the corresponding barrier (21 kcal mol−1) found in the
parent hydrocarbon 9-phenylanthracene (5).5e
It is apparent that rotation about the C(9)−C(11) single
bond linking the phenyl and anthracene fragments in 19 is
associated with strong steric interactions in the plane of the
anthracene. Moreover, and somewhat contrary to expectations,
the data available at present suggest that the presence of an η6-
bonded tricarbonylchromium tripod in fact reduces the height of
the barrier. This interesting finding will be considered further in
the context of steric and electronic interactions in other metal
tricarbonyl derivatives, as discussed below.
1
Figure 6. Sections of the 500 MHz H NMR spectra of (a) the η5-Re
complex 20 at 193 K in CD2Cl2 and (b) the η6-Cr complex 21 at 243
K in acetone (atom numbering as in Figure 5).
Figure 5. Molecular structures of [η5-2-(9-anthracenyl)indenyl]tricarbonylrhenium (20) and [η6-2-(9-anthracenyl)indene]tricarbonylchromium
(21).
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doublets for the anthracene protons H(1) and H(8) at 8.35 and
8.85 ppm, respectively. This very marked chemical shift
difference can be attributed to the large diamagnetic anisotropy
of the adjacent Re(CO)3 tripod. Coalescence of these peaks at
anthracene (3)5e and also in 9-ferrocenylanthracene (7)6 that
as the dihedral angle between the rotating fragments
approaches 0, the molecular geometry of the hydrocarbon
framework is forced to deviate quite significantly from
coplanarity.
243 K indicated a barrier of 11.1
0.5 kcal mol−1 for
anthracene rotation. However, no broadening of the indenyl
five-membered-ring signals at H(12)/H(17) was observed even
at 193 K, indicating that oscillation of the indenyl-Re(CO)3
unit about the mirror plane containing the anthracene
framework remains fast on the NMR time scale, analogously
to the behavior of 9-phenylanthracene-Cr(CO) (19), as
depicted in Scheme 7.
Furthermore, and in line with our recent findings,5,6 it has
been shown that the rotational barriers themselves appear to
arise from the interactions of the peri-oriented H(1) and H(8)
atoms of the anthracene with the five- or six-membered ring
rather than with the metal tricarbonyl unit attached to the
scaffold in a perpendicular direction. This phenomenon may
also provide a simple rationale for a longstanding observation of
the relative barriers to rotation in ferrocenylpentaphenylben-
zene22 and (hexaphenylbenzene)tricarbonylchromium, where
the Cr(CO)3 is π-bonded to one of the peripheral phenyls.23 In
the latter case, the barrier to rotation of the (C6H5)Cr(CO)3
substituent is 12 kcal mol−1,23 whereas in the former system the
barrier to rotation of the ferrocenyl group relative to the central
ring was too low to be determined by variable-temperature
NMR measurements.22 Discussion at that time focused on the
cone angles swept out by the phenyl-Cr(CO)3 and ferrocenyl
groups, but a more prosaic explanation merely involves the fact
that the five-membered ring poses less steric interaction than
the six-membered ring as it approaches coplanarity with the
central ring; in these cases, the organometallic fragment
Fe(C5H5) or Cr(CO)3merely serves as a label to lower the
symmetry and so allows the dynamic process to be monitored.
(η6-2-(9-Anthracenyl)indene)tricarbonylchromium(0)
(21) as a Molecular Shuttle. The known ability of a
tricarbonylchromium unit to undergo an η6 to η5 haptotropic
shift across an indenyl framework prompted us to investigate
the possibility of molecular shuttling in 21. In principle, such a
process (Scheme 8) would furnish 22, the anionic Cr(CO)3
analogue of the η5-Re(CO)5 complex 20.
In the chromium complex 21 the degeneracy of the
anthracenyl H(1) and H(8) protons is again split at low
temperature; however, the shift separation is now only 0.07
ppm, reflecting the greater distance from the M(CO)3 moiety.
Peak coalescence data (see the Supporting Information) yield a
barrier of 14.7 0.5 kcal mol−1 for equilibration of the outer
rings of the anthracene. The placement of the π-bonded
organometallic fragment on one face of the indene “paints the
faces different colors”20 and so renders diastereotopic the
methylene protons at C(12). It is well established that the
diamagnetic anisotropy of the Cr(CO)3 tripod preferentially
deshields the endo proton relative to its exo counterpart,21 thus
allowing their ready attribution as H(12)exo and H(12)endo at
3.98 and 4.26 ppm, respectively. Subsequent NOE measure-
ments indicated pairwise interactions between the peaks at 4.26
and 8.01 ppm and those at 3.98 and 8.08 ppm, thus allowing
the attribution of H(8) as being more shielded than H(1). It
appears likely that the favored conformation in solution
parallels that found in the solid state, whereby the dihedral
angle between the indenyl and anthracenyl ring planes is 62°.
It is particularly noteworthy that the barrier for anthracene
rotation in the rhenium η5 complex 20 is approximately 3.5 kcal
mol−1 lower than that found in the closely related chromium η6
complex 21, despite the fact that the metal tripod is
considerably closer to the anthracene system in the former
case. Interestingly, this finding is in good agreement with DFT
calculations showing that the rotational barrier is 4.4 kcal mol−1
lower for the η5-Re system 20 than for the η6-Cr complex 21.
However, one should recall that the NMR experiment merely
yields a value for the energy separation between the ground
state and the transition state for the dynamic process. One
cannot assume that moving the metal tripod closer to the
rotating group actually lowers the energy of the transition state;
it is perhaps more likely that steric interactions raise the energy
of the ground state.
These findings on the organometallic systems 19−21,
whereby a five- or six-membered ring bearing a metal
tricarbonyl tripod is attached to the 9-position of anthracene,
may be compared to the previously reported molecules 3a,b, 5,
and 7 (Chart 1), as these relationships have important
implications for the understanding of the function of
haptotropic molecular brakes such as 1. The new data reveal
that the introduction of a metal carbonyl moiety does not in
itself lead to an increase of the rotational barrier; indeed, in (9-
phenylanthracene)Cr(CO)3 (19, with Cr@Ph), the value of ca.
17.5 kcal mol−1 is noticeably less than that reported (21 kcal
mol−1) for the uncomplexed hydrocarbon 3.5e While this result
may be related to a somewhat raised value for complex 19 in its
minimum energy conformation, one must also consider
possible stabilization of its highly distorted transition state by
the metal carbonyl. We have shown previously in 9-phenyl-
Scheme 8. Haptotropic Shift from the η6-Indene Complex 21
to the η5-Indenyl Anion 22
Indeed, when sodium tert-butoxide was added to a solution
1
of 21 in DMSO, the H NMR spectrum (Figure 7) recorded
after 12 h clearly revealed the formation of the anticipated η5-
Cr(CO)3 anionic complex 22. Since the doublet resonance at 9
ppm attributable to H(1) and H(8) is not significantly
Figure 7. 500 MHz 1H NMR spectrum of Na+[{η5-2-(9-anthracenyl)-
indenyl}Cr(CO)3]− (22) (atom numbering as for molecule 20 in
Figure 5).
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broadened at 303 K, this may imply a lower rotational barrier in
the η5 complex 22 than in the parent η6 complex 21; however,
in this case the barrier cannot be precisely determined, as the
DMSO solvent freezes at 290 K. Strikingly, the behavior of the
potential anthracene-based molecular brake, 21/22, contrasts
with that of the triptycene-based molecular brake, 1/2, for
which the η5 complex has an enormously enhanced rotational
barrier. Hence, even though both systems incorporate the same
molecular actuator, i.e. a sliding chromium tricarbonyl moiety
attached to the 2-indenyl fragment, this demonstrates the very
different behavior of the two-bladed (anthracenyl) and three-
bladed (triptycyl) molecular rotors.
Chromium and Rhenium Tricarbonyl Derivatives of 3-
Indenylanthracenes. Analogously to the reactions of 2-
indenylanthracene (3a) with metal carbonyls, isomeric 3-
indenylanthracene (3b) was also converted into its rhenium η5-
Re(CO)3 complex 23 (12% yield) and the η6-Cr(CO)3
derivative 24 (57% yield). Interestingly, although the solid-
state structures of 23 and 24 are superficially very similar
(Figure 8), there are some significant differences. If one were to
imagine the anthracenyl unit initially positioned orthogonally to
the plane of the indenyl/indene framework, then in the
rhenium complex 23 the proximal face of the indenyl-Re(CO)3
unit has rotated 56.5° toward the anthracene, whereas in the
chromium system the indenyl fragment has rotated 75.5° away
from the plane of the anthracene.
1
The 500 MHz H NMR spectra of 23 and 24 are shown in
Figure 9. In the rhenium complex 23, the anthracene peri
protons, H(1) and H(8), are widely separated (9.42 and 7.25
ppm, respectively). The lower field resonance, H(1), is clearly
in the deshielding region of the Re(CO)3 tripod and shows an
NOE interaction with H(12) in the indenyl six-membered ring.
Concomitantly, H(8) is proximate to H(17), the five-
membered-ring proton adjacent to the C(9)−C(11) bond
linking the indenyl and anthracenyl units. Since the X-ray
crystal structure reveals the distance between these NOE-
connected pairs of protons to be ca. 2.47 Å, it is apparent that
the conformations found in the solid state are also favored in
solution.
We have previously reported that rotation of the 3-indenyl
moiety in the parent hydrocarbon 3b has a barrier of 25 kcal
mol−1, and so NMR peak coalescence is unattainable at
accessible temperatures.5d Assuming comparable barriers for 23
or 24, their dynamics were probed by using 2D EXSY at 323 K.
Gratifyingly, rotation of the anthracene moiety in the η5-
Re(CO)3 complex 23 was detectable at this temperature, and
off-diagonal exchange peaks for H(1) ↔ H(8) and H(2) ↔
H(7) were clearly evident. Quantitative analysis of the data
yielded a rotational barrier of 21.5 0.5 kcal mol−1, noticeably
lower than in 3-indenylanthracene itself. In contrast, a 2D-
EXSY study of the η6-Cr(CO)3 derivative 24 failed to identify
any exchange process even at 323 K, thus indicating a rotational
barrier in excess of 23 kcal mol−1.
Figure 8. Molecular structures of [η5-3-(9-anthracenyl)indenyl]-
tricarbonylrhenium (23) and [η6-3-(9-anthracenyl)indene]-
tricarbonylchromium (24).
Continuing our study of haptotropic shuttling of metal
tricarbonyl moieties from a six- to a five-membered ring, as
depicted in Scheme 9, when sodium tert-butoxide was added to
a DMSO solution of 24, the η6-Cr(CO)3 derivative of 3-
Figure 9. 500 MHz 1H NMR spectra and proposed conformations in solution of the Re and Cr complexes 23 and 24, as determined by 2D 1H−1H
NOESY measurements at 303 K.
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the η5 complexes relative to that of their noncomplexed
precursors may be a consequence of raising the energy of the
ground state and/or metal carbonyl stabilization of the highly
distorted transition state. The DFT calculated rotational
barriers in these systems (Table 1) indicate that the barrier
in the η6 complex 24 is very similar to that of the parent
hydrocarbon 3b, whereas the calculated barrier in the η5
analogue 23 is lower by ca. 3.5 kcal mol−1.
Scheme 9. Haptotropic Shift of the Cr(CO)3 Unit in 24 To
Form 25 Also Accompanied by a Conformational Change
Internal Rotation in Metal Carbonyl Derivatives of
Aryl-Substituted Three-Blade Systems. It has been shown
in the previous section that haptotropic translational movement
of a metal tricarbonyl unit from the six- to the five-membered
ring of an indenyl fragment attached to anthracene at the 9-
position does not increase the barrier to the rotation; indeed,
there are indications that this barrier is somewhat reduced. In
contrast, in the analogous indenyltriptycene complexes, the
same metal tricarbonyl moiety effectively blocks rotation of the
paddlewheel, as the barrier in the η5 complex is at least 12 kcal
mol−1 higher than that in the η6 counterpart.
indenylanthracene, the 13C NMR spectra recorded after 12 h
(Figure 10) clearly showed the formation of a new anionic
As shown in Chart 1, the barrier to rotation about the 3-fold
axis in 9-substituted triptycenes increases markedly from the 2-
indenyl derivative 4a to the isomeric angular system 4b, in
which the six-membered ring of the indene is directly adjacent
to the blades of the triptycene. However, this increase in the
height of the barrier is even greater when the 9-substituent
possesses an orthogonally attached fragment, such as Re(CO)3
in 2 or Fe(C5H5) in 8. To probe more deeply into this
phenomenon, we have synthesized and characterized several
systems in which an aryl-M(CO)3 moiety is connected to a
nominally C3-symmetrical rigid hydrocarbon skeleton, namely
triptycene or [2.2.2]bicyclooctane. In addition, their dynamic
behavior was investigated by experiment, by NMR spectrosco-
py, and also by means of DFT calculations.
When 1,4-diphenylbicyclo[2.2.2]octane (1,4-diphenyl-BCO)
and Cr(CO)6 were heated in dioxane at 120 °C for 24 h, the
monochromium derivative 26 was obtained in 45% yield. Its
molecular structure appears in Figure 11, from which it is
Figure 10. Spectroscopic 13C NMR (DMSO, 303 K) observation of a
rearrangement of the chromium complex 24 into the anionic system
25, isostructural with the rhenium complex 23.
complex, 25, isostructural with the rhenium complex 23.
1
Moreover, the H 2D NOESY study revealed that complex 25
adopted a conformation very similar to that of the η5-rhenium
complex 23 (Figure 8), in which H(17) at 5.10 ppm is proximal
to H(8) at 7.46 ppm; likewise, H(12) and H(1) at 6.68 and
10.60 ppm, respectively, are close neighbors in space. 2D EXSY
data on 25 revealed exchange peaks for H(1) ↔ H(8) and
H(2) ↔ H(7); the rotational barrier was found to be 22 0.5
kcal mol−1, slightly lower than in the precursor η6 complex 24
and close to the value (21.5 kcal mol−1) previously seen in the
η5-Re analogue 23.
Figure 11. Molecular structure of (η6-1,4-diphenylbicyclo[2.2.2]-
octane)Cr(CO)3 (26).
Our results on the systems 23−25 can be compared to those
for the parent hydrocarbon, 3-indenylanthracene (3b), in which
the rotation of the indenyl moiety, although not directly
measurable, is believed to be slow with a 25 kcal/mol barrier.5d
As in the case of 2-indenyl derivatives, our findings appear to
suggest that the introduction of a metal carbonyl moiety
attached at the five-membered ring of 3b significantly decreases
the rotational barrier. It is reasonable to assume that, similarly
to the 2-indenylanthracene metal complexes 20 and 22, the
rotational barriers in 23 and 24 also arise from the interactions
of the peri-oriented H(1) and H(8) of the anthracene with the
five- and six-membered rings rather than the metal tricarbonyl
unit attached to the scaffold in a perpendicular direction. As
noted above, the apparent decrease of the rotational barrier in
apparent that rotation of the C6H5−Cr(CO)3 unit would not
evoke contacts shorter than 2.2 Å between the hydrogen atoms
of the BCO core and the coordinated phenyl ring. Additionally,
the hydrocarbon backbone of the molecule, i.e. C(9)−C(1)−
C(4)−C(15), deviates only 2° from linearity. Accordingly, one
would anticipate a barrier to rotation about the C(1)−C(9)
single bond of less than 8 kcal mol−1; a DFT calculation yielded
1
a value of ca. 6 kcal mol−1, and the 500 MHz H NMR
spectrum at 193 K did not exhibit peak decoalescence. One
may conclude that incorporation of a Cr(CO)3 tripod to an
aromatic group directly linked to the C3-symmetrical BCO
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scaffold does not bring about a substantial increase in the aryl
rotational barrier.
This observation contrasts with the situation previously
reported in the reaction of Cr(CO)6 with 9-(2-indenyl)-
triptycene (4a), for which two complexes have been isolated.
As shown in Scheme 10, in 29 the Cr(CO)3 is bonded to a
triptycene blade; in 1, the tripod is η6 linked to the six-
membered ring of the indenyl substituent.4 However, the
reactivity of 9-(3-indenyl)triptycene (4b) parallels that of 9-
phenyltriptycene (6), such that it does not form the Cr@
indene complex 30 but instead yields the blade-bonded isomer
31.5a Apparently, spatial proximity of the target benzene ring to
the triptycene paddlewheel unit sterically precludes the
formation of chromium tricarbonyl complexes 27 and 30.
Unfortunately, the alternative route to these hypothetical
complexes via benzyne addition to their corresponding
precursor anthracenes was not successful, and mixtures of
unidentified products were obtained.
With the goal of extending this topic from a bicyclo[2.2.2]-
octane to the bulkier triptycene system, an attempt was made to
prepare (η6-9-phenyltriptycene)Cr(CO)3 such that the metal
was π-bonded to the phenyl substituent, as in 27. However,
when the reaction was performed, it yielded only the isomeric
complex 28, whereby the Cr(CO)3 fragment was attached to a
blade of the triptycene (Figure 12). In unsubstituted
Upon examination of the molecular structure of 28, the
triptycene blade bonded Cr(CO)3 complex shown in Figure 12,
one would not anticipate a substantial barrier toward the
rotation of the 9-phenyl substituent. The position and
orientation of the phenyl are almost identical with those
recently found in the parent structure 6;5d for example, the
C(10)−C(9)−C(17) angle is 174° in both cases. Accordingly,
NMR measurements revealed that, while all three blades of the
triptycene are, of course, nonequivalent, the phenyl substituent
displays dynamic C2v symmetry, showing that it is freely
rotating about the C(9)−C(17) axis on the NMR time scale.
Similar structural and dynamic relationships have previously
been reported for the blade-bonded Cr(CO)3 complex 31 and
its parent compound 9-(3-indenyl)triptycene (4b), which both
displayed rotational barriers of ∼12.5 kcal mol−1.5a
Figure 12. Molecular structure of the chromium complex 28.
triptycenes bearing tricarbonylchromium fragments, breaking
the 3-fold symmetry did not greatly change the interblade
angles, which ranged only from 117.7 to 121.9°.13a,24 However,
as previously noted in η6-[9-(3-indenyl)Cr@triptycene],5a the
3-fold symmetry in 28 is indeed seriously perturbed; the valley
containing the organometallic unit widens to 134.5°, while the
other two diminish accordingly, with dihedral angles of 102.1
and 123.4°.
Having established the experimental inaccessibility of the
chromium derivatives 27 and 30, whereby the metal was
positioned on the 9-phenyl or 9-(3-indenyl) substituent of the
Scheme 10. Possible Metal Carbonyl Derivatives of the Triptycenes 4a,b and 6
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triptycenes 4b and 6, respectively, we turned instead to η5
complexes such that a tricarbonylrhenium tripod is located on
the five-membered ring of the indenyl (see Scheme 1). Indeed,
the [η5-2-indenyltriptycene]M(CO)3 complex 32 (M =
rhenium, manganese) has previously served as a convenient
isolobal, structural, and dynamic model of the anionic
chromium species 2 (Scheme 1).4
Prolonged heating of 9-(3-indenyl)triptycene (4b) with
Re2(CO)10 in decalin at 180 °C furnished the complex 33 in
7% yield; the structure, shown in Figure 13, clearly illustrates
steric interaction between the triptycene moiety and the metal
tricarbonyl tripod.
The dynamic behavior of the triptycene paddlewheel in the
η5-Re(CO)3 complex 33 was further probed by 1H NMR
spectroscopy at 303 K, which revealed the expected non-
equivalence of the three triptycene blades. As a result of the
diamagnetic anisotropy of the cyclopentadienyl-Re(CO)3
moiety, the chemical shifts of the three ortho hydrogens
H(1), H(8), and H(13) are widely separated: H(8) located
under the five-membered ring is at 5.85 ppm, while the two
remaining hydrogens resonate at 8.15 and 7.77 ppm.
As these three proton environments do not exhibit
coalescence even at 363 K, the 2D-EXSY spectrum of 33 was
recorded at 323 K with a 1 s mixing time. As shown in Figure
14, the existence of the relevant off-diagonal peaks unequiv-
Figure 13. Molecular structure of the η5-rhenium complex 33 and
DFT-optimized structure of the experimentally unavailable η6-
chromium complex 30. These views illustrate the spatial relationships
between the two molecules and are also consistent with the EXSY data
shown in Figure 14.
the nonequivalence of the three aromatic blades of the
triptycene. Unlike in the parent system 4b, where the plane
of the indenyl is almost coplanar with one of the triptycene
blades, instead in 33 the indenyl ring is now perpendicular to
one of the blades, thus aligning the Re(CO)3 tripod with a
valley between the other two blades. In the solid state, two of
the three carbonyl ligands are pointing toward their adjacent
blades, thus engendering steric strain, as evidenced by the
deviation of the indenyl plane from the nominal 3-fold axis of
the triptycene by 21° (this deviation is only 9° in 4b). Since the
observed molecular structure of 33 is in good agreement with
that predicted by DFT, the structure of the hypothetical
Cr(CO)3 complex 30 was also optimized by calculation and is
shown in Figure 13 (lower structure). In this case, although the
orientation of the indene relative to the triptycene blades is
similar to that seen in complex 33, the deviation of the indene
plane from the triptycene axis is negligible, indicating very little
1
Figure 14. 2D H−1H EXSY spectrum of [η5-3-(9-triptycyl)indenyl]-
Re(CO)3 (33) (323 K, Tm = 1000 ms, CDCl3) exhibiting cross-peaks
showing exchange between all three nonequivalent aromatic blades of
the triptycene paddlewheel.
ocally demonstrates exchange between these sites via 120°
rotations. Quantification of 2D-EXSY data over the temper-
ature range 303−323 K yielded a rotational barrier of 20 0.5
kcal mol−1.
Comparing the results of the DFT calculated rotational
barriers for the anthracenes and triptycenes and their metal
tricarbonyl complexes, it is evident that the values for the
hydrocarbons can be predicted with a substantial degree of
accuracy. However, comparison of the DFT B3LYP calculated
values and experimental free energies for the metal tricarbonyl
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Scheme 11. On Account of the Higher Ground State Energy of the η5 Complexes, an η6 → η5 Haptotropic Migration of the
Metal Tricarbonyl Unit in 9-Anthracene Derivatives Resulted in a Slight Lowering of the Observed Paddlewheel Rotational
Barrier; Conversely, η6 → η5 Haptotropic Shifts in the Analogous 9-Triptycene Derivatives Led to a Marked Increase of This
Barrier
derivatives 19−34 (Table 1) suggests that in most cases the
calculated energy barriers are lower than the experimental
values. This difference ranges from 1.5 to 3.0 kcal mol−1 for the
anthracene derivatives 19−25 but more significantly up to 3.5
kcal mol−1 for the triptycene derivative 31, possibly owing to
considerable distortion of the metal carbonyl fragment in the
transition state. Indeed, in those cases with large barriers the
molecules may become significantly more crowded at the
rotational transition states, thus decreasing the entropy, making
−TΔS positive, and increasing the free energies of activation.
Nevertheless, comparison of the rotational barriers within
either the experimental or the calculated data set shows that
attachment of a metal tricarbonyl fragment to 9-arylanthracene
and 9-aryltriptycene systems does not significantly alter their
rotational freedom unless the metal carbonyl tripod is
connected in such a fashion that it is adjacent to the 9-position
of the anthracene or triptycene. One may summarize as follows.
(1) Rotational barriers in the η5 derivatives of 9-indenylan-
thracenes 20, 22, 23, and 25 are somewhat lower than in
their parent hydrocarbons or the corresponding η6-
complexes 21 and 24, possibly rationalizable in terms of a
higher ground state energy rather than a reduced energy
transition state. Consequently, an η6 → η5 haptotropic
migration of the metal tricarbonyl fragment closer to the
rotatable single bond leads to a relatively somewhat
diminished braking effect or “brake release” effect, as
shown in Scheme 11.
indenyl moiety with the adjacent H(1), H(8), and H(13)
positions of the triptycene. Experimentally, as shown in
Scheme 1, the rotation of the triptycene paddlewheel is
slowed by a factor of ca. 108.
To conclude, polycyclic hydrocarbons in which two aromatic
or rigid aliphatic moieties are connected by a single C−C bond
provide interesting molecular systems for the study of
rotational barriers. A series of η6- and η5-M(CO)3 derivatives
of such hydrocarbons have been synthesized and characterized
by X-ray crystallography and their dynamic behavior has been
studied both by experiment and by means of DFT calculations.
Several of these systems are potential candidates as
mechanically controlled intramolecular rotation systems
(molecular brakes). Somewhat unexpectedly, for indenylan-
thracenes slightly reduced rotational barriers were found for the
η5 complexes relative to their η6 precursors or the respective
uncomplexed hydrocarbons. The rotational barriers in such
systems are controlled largely by strong double steric clashes
between the quasi-planar indenyl moiety and the peri positions
of the anthracene. In contrast, in the 2- and 3-indenyltripty-
cenes, significantly higher barriers (ca. 20 kcal mol−1) have
been observed and/or calculated for the η5-M(CO)3 complexes
than for the corresponding η6-M(CO)3 complexes (8−10 kcal
mol−1). This very pronounced molecular braking effect
attributable to multiple steric interactions between the
triptycene paddlewheel and the indenyl-metal tricarbonyl
moiety has so far been established only for triptycene
derivatives, but work is underway to extend this fascinating
effect to other three-bladed molecular paddlewheels.
(2) Rotational barriers in the η5 complexes of the 9-
indenyltriptycenes 29 and 31 and the hypothetical 34
are considerably higher than in their precursor η6
complexes, thus leading to a pronounced braking effect
due to simultaneous multiple steric interactions of the
metal carbonyl tripod and the five-membered ring of the
EXPERIMENTAL SECTION
General Methods. All reactions were carried out under a nitrogen
atmosphere unless otherwise stated. Column chromatography
■
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separations were carried out on a Buchi Sepacor machine with UV
absorbance detector using silica gel (particle size 40−63 mm). NMR
spectra were acquired on Varian VnmrS 400, 500, and 600 MHz
spectrometers at 30 °C unless otherwise stated; dynamic variable-
temperature studies within the temperature range 193−363 K were
carried out on a Varian Inova 500 MHz instrument. Assignments were
Preparation of [η6 -(9-Anthracenyl)benzene]-
tricarbonylchromium (19). 9-Phenylanthracene (254 mg, 1
mmol) was heated with Cr(CO)6 (220 mg, 1 mmol) in the presence
of a catalytic amount of Zn powder in dioxane (5 mL) at 125 °C
(sealed tube) for 2 days, during which time formation of a deep purple
solution was observed. After further heating for 1 day at 80 °C, the
reaction mixture turned yellow and the products were separated
chromatographically (eluent ethyl acetate/cyclohexane) to give 19 (27
mg, 7%) as a very bright yellow solid whose characteristics were
consistent with the reported data.14 1H NMR (500 MHz, DMSO-d6,
numbering in accord with Figure 4): δ 9.30 (1H, d, J = 8 Hz, H1), 8.77
(1H, s, H10), 8.16 (2H, d, J = 8 Hz, H4,5), 7.88 (1H, d, J = 8 Hz, H8),
7.59 (2H, t, J = 7 Hz, H3,6), 7.53 (1H, t, J = 7 Hz, H2,7), 6.13 (2H, d, J
= 7 Hz, H12,16), 6.06 (1H, t, J = 6 Hz, H14), 5.96 (2H, t, J = 6 Hz,
H13,15). 13C NMR (125 MHz): δ 234.1 (Cr-CO’s), 131.9 (C8a), 131.2
(C4a,10a), 129.7 (C10), 129.4 (C4,5), 128.8 (C9), 128 (C9a), 125.8
(C2,3,6,7), 125.6 (C8), 125.5 (C1), 110.0 (C11), 101.2 (C12,16), 93.7
(C13,15), 96.6 (C14).
1
1
based on standard H−1H and H−13C two-dimensional techniques
and NOE measurements. Melting points were determined on a
Gallenkamp instrument in air and are uncorrected. Elemental analyses
were carried out by the Microanalytical Laboratory at University
College Dublin.
Compounds 3a,b, 4b, 5, 6, 2-phenylindene (35), and 2,2′-dimethyl-
1,1′-biindenyl (36) were prepared as described elsewhere.5,6
Synthesis of (η6-2-Methylindene)tricarbonylchromium (13).
2-Methylindene (65 mg, 0.5 mmol) was heated with Cr(CO)6 (220
mg, 1 mmol) in dioxane (2 mL) at 125 °C in a sealed tube for 1 day,
and the products were separated chromatographically (eluent ethyl
acetate/cyclohexane) to give 13 (70 mg, 0.26 mmol, 52%) as a yellow
S y n t h e s i s o f [ η 5 - 2 - ( 9 - A n t h r a c e n y l ) i n d e n y l ] -
tricarbonylrhenium (20). 2-(9-Anthracenyl)indene (3a; 116 mg,
0.4 mmol) was heated with Re2(CO)10 (326 mg, 0.5 mmol) in decalin
(2 mL) at 160 °C in a sealed tube for 2 days, and the products were
separated chromatically (eluent dichloromethane/cyclohexane) to give
20 (50 mg, 22%) as a yellow solid. Mp: 180 °C. 1H NMR (500 MHz,
CDCl3, numbering in accord with Figure 5): δ 8.60 (2H, d, J = 9 Hz,
H1,8), 8.51 (1H, s, H10), 8.00 (2H, d, J = 8 Hz, H4,5), 7.66 (2H, m,
H13,16), 7.53 (2H, t, J = 7 Hz, H2,7), 7.47 (2H, t, J = 7 Hz, H3,6), 7.18
(2H, m, H14,15), 6.35 (2H, s, H12,17). 13C NMR (125 MHz): δ 193.3
(Re-CO’s), 131.3 (C4a,8b), 130.3 (C4b,8a), 129.8 (C10), 129.0 (C4,5),
126.9 (C9), 126.5 (C14,15), 126.1 (C2,7), 126.0 (C1,8), 125.0 (C3,6),
123.8 (C13,16), 112.6 (C11), 106.6 (C12a,16a), 77.5 (C12,17). Anal. Calcd
for C26H15ReO3: C, 55.60; H, 2.69. Found: C, 55.8; H, 2.95.
1
solid. H NMR (400 MHz, DMSO-d6, 30 °C, numbering in accord
with Figure 1): δ 6.27 (1H, s, H3), 6.19 (1H, d, J = 6 Hz, H7), 6.02
(1H, d, J = 6 Hz, H4), 5.55 (1H, t, J = 6 Hz, H5), 5.53 (1H, d, J = 6 Hz,
H6), 3.57 and 3.28 (2H, each d, J = 23 Hz, H1, H1′), 2.06 (3H, s, H8).
13C NMR (100 MHz): δ 235.6 (Cr-CO’s), 151.6 (C2), 124.1 (C3),
119.6 (C7a), 115.2 (C3a), 93.6 (C5), 93.0 (C6), 92.3 (C7), 89.8 (C4),
42.9 (C1), 17.0 (C8). Anal. Calcd for C13H10CrO3: C, 58.65; H, 3.79.
Found: C, 58.71; H, 3.88.
Synthesis of [η6-(2-Indenyl)benzene]tricarbonylchromium
(15). 2-Phenylindene (96 mg, 0.5 mmol) was heated with Cr(CO)6
(110 mg, 0.5 mmol) in dioxane (2.5 mL) at 125 °C in a sealed tube for
2 days. The products were not separable chromatographically, but slow
crystallization from ethyl acetate gave 14 and an X-ray quality sample
of 15 (21 mg, 13%). Data for 15 are as follows. MS (ES) (m/z): [M −
H]¯ 327.06, 100%. 1H NMR (400 MHz, CDCl3, numbering in accord
with Figure 2): δ 7.53 (1H, d, J = 7 Hz, H4), 7.46 (1H, d, J = 7 Hz,
H7), 7.38 (1H, t, J = 7 Hz, H5), 7.23 (1H, t, J = 7 Hz, H6), 7.16 (1H, s,
H3) 5.70 (2H, d, J = 6 Hz, H9,13), 5.45 (2H, t, J = 6 Hz, H10,12), 5.33
(1H, t, J = 6 Hz, H11), 3.66 (2H, s, H1,1′). 13C NMR (100 MHz): δ
232.8 (Cr-CO’s), 142.2 (C2), 129.2 (C3), 126.4 (C4), 125.9 (C6),
123.8 (C7), 121.3 (C5), 104.1 (C8), 92.3 (C10,12), 91.4 (C11), 90.4
(C9,13), 39.1 (C1). Anal. Calcd for C13H10CrO3: C, 65.86; H, 3.68.
Found: C, 66.40; H, 3.98.
S y n t h e s i s o f [ η 6 - 2 - ( 9 - A n t h r a c e n y l ) i n d e n e ] -
tricarbonylchromium (21). 2-(9-Anthracenyl)indene (3a; 116 mg,
0.4 mmol) was heated with Cr(CO)6 (110 mg, 0.5 mmol) in dioxane
(2 mL) at 125 °C in a sealed tube for 2 days, and the products were
separated chromatographically (eluent ethyl acetate/cyclohexane) to
give 21 (72 mg, 42%) as a yellow solid. 1H NMR (500 MHz, DMSO-
d6, numbering in accord with Figure 5): δ 8.66 (1H, s, H10), 8.13 (2H,
d, J = 6.4 Hz, H4,5), 7.94 (2H, d, J = 7 Hz, H1,8), 7.54 (2H, t, J =, H3,6),
7.47 (2H, t, J =, H2,7), 6.41 (2H, d, J = 7 Hz, H13,16), 5.79 (2H, t, J =
H14,15), 6.95 (1H, s, H17), 4.17 and 3.87 (2H, both d, = 22 Hz,
J
Preparation of (η5-2-Phenylindenyl)tricarbonylrhenium (16).
2-Phenylindene (96 mg, 0.5 mmol) was heated with Re2(CO)10 (326
mg, 0.5 mmol) in decalin (2 mL) at 160 °C in a sealed tube for 2 days,
and the products were separated chromatographically (eluent
dichloromethane/cyclohexane) to give 16 (28 mg, 12%) as an off-
H
12,12′). 13C NMR (125 MHz): δ 235.5 (Cr-CO’s), 149.0 (C11), 131.5
(C17); 131.2 (C4a,8b), 131.1 (C9), 129.7 (C4b,8a), 129.0 (C4,5), 127.6
(C10), 126.4 (C2,7), 126.0 (C1,8), 126.0 (C3,6), 117.5 (C16a), 115.9
(C12a), 93.8 (C14,15), 93.2 (C16), 91.5 (C13), 44.8 (C12). Anal. Calcd for
C26H16CrO3: C, 72.89; H, 3.76. Found: C, 72.66; H, 4.00.
1
S y n t h e s i s o f [ η 5 - 3 - ( 9 - A n t h r a c e n y l ) i n d e n y l ] -
tricarbonylrhenium (23). 3-(9-Anthracenyl)indene (3b; 116 mg,
0.4 mmol) was heated with Re2(CO)10 (130 mg, 0.2 mmol) in decalin
(2 mL) at 180 °C in a sealed tube for 2 days, and the products were
separated chromatographically (eluent dichloromethane/cyclohexane)
to give 23 (27 mg, 12%) as a yellow solid. Mp: 165 °C. 1H NMR (600
MHz, CDCl3, numbering in accord with Figure 8): δ 9.42 (1H, d, J = 9
Hz, H1), 8.60 (1H, s, H10), 8.10 (1H, d, J = 8 Hz, H4), 8.03 (1H, d, J =
8 Hz, H5), 7.68 (1H, t, J = 9 Hz, H2), 7.67 (1H, d J = 9 Hz, H12), 7.55
(1H, t, J = 7 Hz, H3), 7.42 (1H, m, H6), 7.25 (2H, m, H7,8), 7.12 (1H,
m, H13), 7.01 (2H, m, H14,15), 6.12 (1H, d, J = 2.7 Hz, H16), 5.99 (1H,
d, J = 2.7 Hz, H17). 13C NMR (150 MHz): δ 193.2 (Re-CO’s), 131.9
(C8a), 131.4 (C4b), 131.2 (C4a), 129.3 (C8b), 129.2 (C10), 128.9 (C4,5),
126.8 (C1), 126.7 (C14), 126.6 (C8), 126.1 (C7), 125.7 (C13), 125.5
(C2), 125.4 (C3), 124.9 (C12), 124.5 (C9), 124.3 (C6), 122.7 (C15),
111.3 (C15a), 105.1 (C11), 95.2 (C17), 90.5 (C11a), 71.6 (C1). Anal.
Calcd for C26H15ReO3: C, 55.60; H, 2.69. Found: C, 55.35; H, 3.00.
S y n t h e s i s o f [ η 6 - 3 - ( 9 - A n t h r a c e n y l ) i n d e n e ] -
tricarbonylchromium (24). 3-(9-Anthracenyl)indene (3b; 116 mg,
0.4 mmol) was heated with Cr(CO)6 (110 mg, 0.5 mmol) in dioxane
(2 mL) at 125 °C in a sealed tube for 2 days, and the products were
separated chromatographically (eluent ethyl acetate/cyclohexane) to
give 23 (98 mg, 57%) as a yellow solid. 1H NMR (600 MHz, DMSO-
white solid. Mp: 117 °C. H NMR (400 MHz, CDCl3, numbering in
accord with Figure 2): δ 7.54 (2H, m, H4,7), 7.46 (2H, d, J = 7 Hz,
H9,13), 7.37 (2H, t, J = 7 Hz, H10,12), 7.31 (1H, t, J = 7 Hz, H11), 7.08
(2H, m, H5,6) 6.16 (2H, s, H1,3). 13C NMR (100 MHz): δ 193.3 (Re-
CO’s), 132.0 (C8), 129.1 (C11), 128.8 (C10,12), 126.7 (C9,13), 123.5
(C4,7), 126.2 (C5,6), 113.8 (C8), 107.6 (C3a,7a), 69.9 (C1,3). Anal. Calcd
for C18H11ReO3: C, 46.86; H, 2.40. Found: C, 46.70; H, 2.42.
Synthesis of [η5-1-(2-Methylinden-3-yl)-2-methylindenyl]-
tricarbonylrhenium (17). 2,2′-Dimethyl-1,1′-biindenyl (65 mg,
0.25 mmol) was heated with Re2(CO)10 (160 mg, 0.25 mmol) in
decalin (2 mL) at 160 °C in a sealed tube for 2 days, and the products
were separated chromatographically (eluent ethyl dichloromethane/
cyclohexane) to give a material containing 17 as the major component
(36 mg, 27%). 1H NMR (400 MHz, numbering in accord with Figure
3): δ 7.82 (1H, d, J = 7 Hz, H12), 7.42 (1H, t, J = 7 Hz, H13), 7.20 (1H,
t, J = 7 Hz, H14), 7.46 (1H, d, J = 7 Hz, H15) 7.52 (1H, d, J = 7 Hz,
H4), 7.08 (1H, t, J = 7 Hz, H5), 7.51 (1H, t, J = 7 Hz, H6), 7.06 (1H, d,
J = 7 Hz, H7), 5.78 (1H, s, H3), 3.67 and 3.58 (2H, each d, J = 22 Hz,
H9,9′), 2.43 (3H, s, H16), 2.13 (3H, s, H8). 13C NMR (100 MHz,
region 120−127 ppm unresolved): δ 193.9 (Re-CO’s), 144.7 (C11a),
144.3 (C10), 141.0 (C15a), 127.4 (C11), 111.7 (C2), 106.7 (C7a), 106.5
(C3a), 85.7 (C1), 70.4 (C3), 44.4 (C9), 15.8 (C16), 13.2 (C8). Anal.
Calcd for C23H17ReO3: C, 52.36; H, 3.25. Found: C, 52.50; H, 2.99.
6195
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Organometallics
Article
Table 2. Crystallographic Data for 13, 15−17, 20, and 21
13
15
16
17
20
21
formula
Mr
C13H10O3Cr
266.21
C18H12O3Cr
328.28
C18H11O3Re
461.47
C23H17O3Re
527.57
C26H15O3Re
561.58
C26H16O3Cr
428.39
cryst syst
space group (No.)
a (Å)
orthorhombic
Pnma (62)
15.649(2)
10.3612(15)
6.9097(10)
90
monoclinic
P21/n (14)
11.3264 (15)
10.9998(15)
12.2185(16)
90
orthorhombic
P212121 (19)
8.3815(4)
10.1729(4)
52.705(2)
90
monoclinic
P21/c (14)
15.186(3)
8.2628(15)
16.016(3)
90
monoclinic
P21/c (14)
8.0644(9)
24.041(3)
10.9718(12)
90
monoclinic
P21/c (14)
12.9308(17)
11.2668(15)
12.9929(17)
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
90
112.510(2)
90
90
111.483(3)
90
109.801(3)
90
98.190(4)
90
90
90
1115.5(3)
4
1406.3(3)
4
4493.8(3)
12
1870.0(6)
4
2001.4(4)
4
1873.6(4)
4
σcalcd (g cm−3
)
1.585
1.550
2.046
1.874
1.864
1.519
T (K)
100(2)
100(2)
100(2)
100(2)
100(2)
100(2)
μ (mm−1
F(000)
)
1.016
0.823
8.121
6.518
6.097
0.638
544
672
2616
1016
1080
880
θ range (deg)
2.60−28.79
−20 ≤ h ≤ 21
−13 ≤ k ≤ 13
−9 ≤ l ≤ 9
9827
2.09−28.27
−15 ≤ h ≤ 15
−14 ≤ k ≤ 14
−16 ≤ l ≤ 16
13 882
0.77−30.57
−8 ≤ h ≤ 11
−14 ≤ k ≤ 13
−74 ≤ l ≤ 73
51 259
2.58−28.29
−20 ≤ h ≤ 20
−11 ≤ k ≤ 11
−21 ≤ l ≤ 21
18 324
1.69−26.45
−10 ≤ h ≤ 10
−30 ≤ k ≤ 29
−13 ≤ l ≤ 13
17 722
1.59−24.97
−15 ≤ h ≤ 15
−13 ≤ k ≤ 13
−15 ≤ l ≤ 15
14 351
index ranges
no. of rflns measd
no. of indep rflns
1466
3460
13 490
4613
4113
3281
a
no. of data/restraints/params
1466/0/86
3460/0/247
13 490/291/596
4613/0/246
4113/0/271
3281/0/271
final R values (I > 2σ(I))
R1
wR2
0.0386
0.1005
0.0358
0.0926
0.0474
0.0950
0.0287
0.0645
0.0311
0.0703
0.0540
0.1213
R values (all data)
R1
0.0425
0.1021
1.196
0.0415
0.0959
1.056
0.0487
0.0955
1.283
0.0346
0.0667
1.048
0.0381
0.0728
1.067
0.0638
0.1252
1.129
wR2
GOF on F2
a
DELU (rigid bond) restraints applied to all thermal displacement parameters.
d6, numbering in accord with Figure 8): δ 8.71 (1H, s, H10), 8.18 (1H,
d, J = 9 Hz, H5), 8.16 (1H, d, J = 9 Hz, H4), 8.13 (1H, d, J = 9 Hz, H1),
7.67 (1H, d, J = 9 Hz, H8), 7.56 (1H, t, J = 7 Hz, H6), 7.55 (1H, t, J = 7
Hz, H3), 7.50 (1H, t, J = 7 Hz, H2), 7.47 (1H, t, J = 7 Hz, H7), 6.89
(1H, s, H17), 6.30 (1H, d, J = 6 Hz, H15), 5.90 (1H, t, J = 6 Hz, H14),
5.31 (1H, d, J = 6 Hz, H12), 5.29 (1H, t, J = 6 Hz, H13), 4.15 and 3.87
(2H, each d, J = 24 Hz, H16,16′). 13C NMR (150 MHz): δ 234.4 (Cr-
CO’s), 139.2 (C17), 138.7 (C11), 129.7 (C8a), 131.6 (C4a), 131.3 (C8b),
130.4 (C4b), 129.3 (C5), 128.0 (C10), 127.9 (C9), 126.9 (C4), 126.8
(C7), 126.6 (C1), 126.4 (C2), 126.1 (C3), 126.0 (C6,8), 118.4 (C15a),
117.5 (C11a), 96.3 (C14), 90.6 (C13), 92.5 (C12), 90.4 (C15), 39.6 (C16).
Anal. Calcd for C26H16CrO3: C, 72.89; H, 3.76. Found: C, 72.23; H,
3.96.
separated chromatographically (eluent ethyl acetate/cyclohexane) to
give 28 (60 mg, 43%) as a yellow solid. H NMR (500 MHz, CDCl3,
1
numbering in accord with Figure 12): δ 8.12 (2H, d, J = 8 Hz, H18,22),
7.80 (1H, m, H8), 7.67 (2H, t, J = 8 Hz, H19,21), 7.56 (1H, t, J = 8 Hz,
H20), 7.45 (1H, d, J = 7 Hz, H16), 7.40 (1H, m, H5), 7.15 (1H, t, J = 7
Hz, H15), 7.02 (2H, m, H6,7), 7.00 (1H, t, J = 7 Hz, H14), 6.85 (1H, d, J
= 7 Hz, H13), 5.70 (2H, d, J = 6 Hz, H4), 5.40 (1H, d, J = 6 Hz, H1),
5.18 (1H, t, J = 6 Hz, H3), 5.10 (1H, s, H10), 5.05 (1H, t, J = 6 Hz,
H2). 13C NMR (125 MHz): δ 232.0 (Cr-CO’s), 145.6 (C12), 143.5
(C11), 145. 0 (C8a), 146.5 (C8b), 134.0 (C17), 131.0 (C18,22), 128.8
(C19,21), 128.0 (C20), 126.2 (C15), 125.8 (C6), 125.6 (C14), 125.4 (C7),
124.8 (C8), 124.3 (C5), 124.2 (C13), 123.2 (C16), 120.0 (C4a), 119.0
(C4b), 92.0 (C1), 90.6 (C4), 89.8 (C2), 89.0 (C3), 58.5 (C9), 53.0
(C10). Anal. Calcd for C23H22CrO3: C, 74.67; H, 3.89. Found: C,
74.82; H, 4.10.
Synthesis of (η6-1,4-Diphenylbicyclo[2.2.2]octane)-
tricarbonylchromium (26). 1,4-Diphenylbicyclo[2.2.2]octane (131
mg, 0.5 mmol) was heated with Cr(CO)6 (110 mg, 0.5 mmol) in
dioxane (2 mL) at 125 °C in a sealed tube for 2 days, and the products
were separated chromatographically (eluent ethyl acetate/cyclo-
Synthesis of [η5-3-(9-Triptycyl)indenyl]tricarbonylrhenium
(33). 9-(3-Indenyl)triptycene (123 mg, 0.3 mmol) was heated with
Re2(CO)10 (130 mg, 0.2 mmol) in decalin (2 mL) at 180 °C in a
sealed tube for 2 days, and the products were separated chromato-
graphically (eluent dichloromethane/cyclohexane) to give 33 (14 mg,
1
hexane) to give 26 (178 mg, 45%) as a yellow solid. H NMR (500
MHz, CD2Cl2, numbering in accord with Figure 11): δ 7.36 (2H, d, J
= 8 Hz, H16,20), 7.31 (2H, t, J = 7 Hz, H17,19), 7.19 (1H, t, J = 7 Hz,
H18), 5.49 (2H, d, J = 7 Hz, H10,14), 5.39 (1H, t, J = 7 Hz, H12), 5.18
1
7%) as a yellow solid. Mp: 182 °C. H NMR (500 MHz, C2D2Cl4,
numbering in accord with Figure 13): δ 8.15 (1H, d, J = 8 Hz, H1),
7.77 (1H, d, J = 7 Hz, H8), 7.69 (1H, d, J = 9 Hz, H20), 7.48 (2H, d, J
= 7 Hz, H4,16), 7.45 (1H, m, H5), 7.27 (1H, d, J = 9 Hz, H23), 7.16
(2H, t, J = 7 Hz, H2 and H21), 7.10 (2H, t, J = 7 Hz, H3 and H7), 7.05
(2H, m, H6 and H22), 7.04 (1H, m, H15), 6.76 (1H, t, J = 7 Hz, H14),
6.31 (1H, s, H18), 6.26 (1H, s, H19), 5.85 (1H, d, J = 7 Hz, H13), 5.46
(1H, s, H10); 13C NMR (125 MHz): δ 193.0 (Re-CO’s), 147.4 (C8b),
147.2 (C4a), 146.1 (C12), 145.2 (C8a), 144.6 (C11), 143.1 (C4b), 127.7
(C22), 125.2 (C23), 126.4 (C21), 124.7 (C20), 126.4 (C15), 125.5 (C6),
126.2 (C14), 124.2 (C7), 124.6 (C8), 123.6 (C5), 123.8 (C13), 126.6
(2H, t, J = 7 Hz, H11,13), 1.96 (6H, m, H2,6,7), 1.90 (6H, m, H3,5,8). 13
C
NMR (125 MHz): δ 233.6 (Cr-CO’s), 148.9 (C15), 128.2 (C17,19),
125.4 (C16,20), 125.8 (C18), 121.0 (C9), 93.9 (C12), 93.0 (C10,14), 90.4
(C11,13), 34.9 (C4), 34.4 (C1), 32.8 (C3,5,8), 32.4 (C2,6,7). Anal. Calcd
for C23H22CrO3: C, 69.34; H, 5.57. Found: C, 69.57; H, 5.60.
Preparation of [η6-(9-Phenyl)-1,2,3,4,4a,9a-triptycene]-
tricarbonylchromium (28). 9-Phenyltriptycene (100 mg, 0.3
mmol) was heated with Cr(CO)6 (110 mg, 0.5 mmol) in dioxane
(2 mL) at 125 °C in a sealed tube for 2 days, and the products were
6196
dx.doi.org/10.1021/om300512z | Organometallics 2012, 31, 6183−6198

Organometallics
Article
Table 3. Crystallographic Data for 23, 24, 26, 28, and 33
23
24
26
28
33
formula
Mr
C26H15O3Re
561.58
C26H16O3Cr
428.39
C23H22O3Cr
398.41
C29H18O3Cr
466.43
C32H19O3Re•0.805(C6H12)•0.195(CHCl3)
728.59
cryst syst
space group (No.)
a (Å)
triclinic
monoclinic
C2/c (15)
22.3421(19)
10.7303(9)
18.7235(15)
90
monoclinic
P21/n (14)
6.0013(4)
19.5708(12)
15.5061(9)
90
monoclinic
P21/c (14)
13.6588(14)
14.8955(15)
11.3118(11)
90
triclinic
P1 (2)
̅
P1 (2)
̅
7.7534(7)
9.9783(9)
12.5568(12)
85.996(2)
85.794(2)
78.929(2)
949.28(15)
2
10.2673(8)
11.5569(9)
13.1236(10)
88.489(1)
77.448(1)
70.282(1)
1429.01(19)
2
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
116.783(2)
90
98.909(1)
90
113.353(2)
90
4007.2(6)
8
1799.22(19)
4
2112.9(4)
4
σcalcd (g cm−3
)
1.965
1.420
1.471
1.466
1.693
T (K)
100(2)
293(2)
100(2)
100(2)
100(2)
μ (mm−1
F(000)
)
6.427
0.596
0.657
0.572
4.336
540
1760
832
960
720.1
θ range (deg)
2.08−30.68
−11 ≤ h ≤ 11
−14 ≤ k ≤ 14
−17 ≤ l ≤ 17
22 282
2.04−21.58
−23 ≤ h ≤ 22
−11 ≤ k ≤ 11
−19 ≤ l ≤ 19
9873
1.69−31.55
−8 ≤ h ≤ 8
−27 ≤ k ≤ 27
−22 ≤ l ≤ 22
20 902
2.12−26.58
−17 ≤ h ≤ 17
−18 ≤ k ≤ 18
−14 ≤ l ≤ 14
18 597
2.16−32.04
−15 ≤ h ≤ 15
−16 ≤ k ≤ 16
−19 ≤ l ≤ 18
34 578
index ranges
no. of rflns measd
no. of indep rflns
5765
2308
5637
4399
9245
a
no. of data/restraints/params
5765/0/271
2308/131/271
5637/0/332
4399/18/370
9245/31/414
final R values (I > 2σ(I))
R1
wR2
0.0294
0.0644
0.0431
0.1124
0.0357
0.0934
0.0566
0.1461
0.0255
0.0634
R values (all data)
R1
0.0348,
0.0664
1.048
0.0508
0.1184
1.069
0.0409
0.0964
1.062
0.0634
0.1510
1.072
0.0274
0.0641
1.085
wR2
GOF on F2
a
DELU (rigid bond) restraints applied to all thermal displacement parameters.
(C16), 124.1 (C1), 124.4 (C4), 123.7 (C2), 125.6 (C3), 111.5 (C23a),
105.7 (C19a), 95.1 (C18), 87.9 (C17), 74.3 (C19), 55.7 (C9), 54.9 (C10).
Anal. Calcd for C32H19ReO3•C6H12: C, 63.23; H, 4.33. Found: C,
63.14; H, 4.54.
Quantum Chemistry Calculations. These calculations were
performed using the SPARTAN 08 package on a Pentium PC.
Calculations of molecular geometries under vacuum were done at the
DFT B3LYP level using the 6-31G* basis set, as exemplified in the
Supporting Information. For rhenium complexes, the corresponding
manganese analogues were used as appropriate models.
X-ray Measurements for 13, 15−17, 20, 21, 23, 24, 26, 28,
and 33. Crystal data were collected using a Bruker SMART APEX
CCD area detector diffractometer. A full sphere of reciprocal space was
scanned by ψ−ω scans. Pseudoempirical absorption correction based
on redundant reflections was performed by the program SADABS.25
The structures were solved by direct methods using SHELXS-9726 and
refined by full-matrix least squares on F2 for all data using SHELXL-
97.26 Hydrogen atom treatment varied from compound to compound,
depending on the crystal quality. In 15, 26, and 28 all hydrogen atoms
were located in the difference Fourier map and allowed to refine freely.
In all other compounds hydrogen atoms were added at calculated
positions and refined using a riding model. Their isotropic temperature
factors were fixed to 1.2 times the equivalent isotropic displacement
parameters of the parent atom. CCDC 880504 (13), 880495 (15),
880496 (16), 880498 (17), 880502 (20), 880503 (21), 880501 (23),
880499 (24), 880497 (26), 880500 (28), and 880505 (33) contain
supplementary X-ray crystallographic data for this paper. These data
can be obtained free of charge from the Cambridge Crystallographic
Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Crys-
tallographic data for 13, 15−17, 20, and 21 are given in Table 2 and
for 23, 24, 26, 28, and 33 in Table 3.
ASSOCIATED CONTENT
■
S
* Supporting Information
Figures and tables giving characterization data and additional
details of the calculations and CIF files giving crystal data for
13, 15−17, 20, 21, 23, 24, 26, 28, and 33. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: kirill.nikitin@ucd.ie (K.N.); michael.mcglinchey@ucd.
ie (M.J.M.).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Science Foundation Ireland, University College
Dublin, and the Centre for Synthesis and Chemical Biology
funded by the Higher Education Authority’s Programme for
Research in Third-Level Institutions (PRTLI) for generous
financial support and the three reviewers for their perceptive
and helpful comments.
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