How big is a Cp? Cycloheptatrienyl zirconium complexes with bulky cyclopentadienyl and indenyl ligands

Article abstract of DOI:10.1039/c2dt12132h

A combination of phase-transfer and traditional alkylation strategies has been employed to synthesise sterically encumbered 1,3-di(cyclohexyl) and 1,3-di(tert-butyl) substituted indenes in multi-gram quantities. These indenyl ligands and sterically demanding alkyl cyclopentadienyl ligands have been used to prepare a series of [(η⁷-C₇H₇) Zr(η⁵-L)] (L = Cp and Ind) complexes by straightforward salt metathesis between [(η⁷-C₇H₇)ZrCl(tmeda)] and the corresponding sodium indenide or cyclopentadienide. All of these Zr complexes have been characterized by elemental analysis, NMR spectroscopy and single crystal X-ray diffraction. The structural information derived from these studies was employed to evaluate the steric demand of these ligands in a realistic manner.

Full text of DOI:10.1039/c2dt12132h

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Dalton
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An international journal of inorganic chemistry
www.rsc.org/dalton
Volume 41 | Number 22 | 14 June 2012 | Pages 6581–6872
ISSN 1477-9226
COVER ARTICLE
Walter et al.
How big is a Cp? Cycloheptatrienyl zirconium complexes with bulky
cyclopentadienyl and indenyl ligands
1477-9226(2012)41:22;1-S

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PAPER
How big is a Cp? Cycloheptatrienyl zirconium complexes with bulky
cyclopentadienyl and indenyl ligands†
Andreas Glöckner,a Heiko Bauer,b Miyuki Maekawa,a Thomas Bannenberg,a Constantin G. Daniliuc,a
Peter G. Jones,a Yu Sun,c Helmut Sitzmann,*b Matthias Tamm*a and Marc D. Walter*a
Received 8th November 2011, Accepted 21st December 2011
DOI: 10.1039/c2dt12132h
A combination of phase-transfer and traditional alkylation strategies has been employed to synthesise
sterically encumbered 1,3-di(cyclohexyl) and 1,3-di(tert-butyl) substituted indenes in multi-gram
quantities. These indenyl ligands and sterically demanding alkyl cyclopentadienyl ligands have been used
to prepare a series of [(η7-C7H7)Zr(η5-L)] (L = Cp and Ind) complexes by straightforward salt metathesis
between [(η7-C7H7)ZrCl(tmeda)] and the corresponding sodium indenide or cyclopentadienide. All of
these Zr complexes have been characterized by elemental analysis, NMR spectroscopy and single crystal
X-ray diffraction. The structural information derived from these studies was employed to evaluate the
steric demand of these ligands in a realistic manner.
unusual η9-indenyl–metal interaction that masks and stabilizes
Introduction
low-valent zirconium centres.8–12
Cyclopentadienyl (Cp) ligands are probably the most widely
used ligand systems in organometallic chemistry since the dis-
covery of the iconic molecule ferrocene ((C5H5)2Fe).1–3 One
reason for this astonishing success story is the relatively low
intrinsic reactivity that makes them excellent spectator ligands,
e.g. in catalysis.4 Furthermore, the steric demand and electronic
properties can readily be modified by substitutions on the cyclo-
pentadienyl ring. Another very intriguing, but less extensively
explored ligand set is provided by the related indenyls. However,
most indenyl complexes show distinct η3:η2-coordination, where
two of the five metal–carbon bonds are significantly longer than
the other three. This ability of the indenyl to undergo haptotropic
shifts, thereby changing the electron count at the metal centre,
has been termed the “indenyl effect”. This behaviour leads to
enhanced and unique reactivity and is most frequently observed
in associative substitution reactions.5–7 A variant thereof is the
For both types of ligand systems, increased steric demand has
allowed the isolation of unusual and kinetically stabilized mol-
ecules, e.g. with low-coordinate metal centres, in low oxidation
states, with unusual spin-states or novel reactivity patterns.13–42
To some extent the sterically highly encumbered cyclopentadie-
nyl and indenyl ligands are related and even complementary
to the well-established scorpionate ligands,43,44 such as tris-
(pyrazolyl)-, tris(phosphino)- and tris(carbeno)borate frame-
works and derivatives thereof, but they have very different
electronic properties. Scorpionate ligands are excellent σ-donors,
whereas cyclopentadienyls are better π-donors.45 The rapid
developments in the area of low-coordinate complexes still
stimulate interest in the development of new cyclopentadienyl
and indenyl ligands, but at the same time a convenient way to
judge the steric demand of new ligands relative to established
representatives is highly desirable. For group 15 donor ligands,
especially phosphines, the work of Tolman has introduced the
concept of cone angles, in which the metal is located at the apex
of the cone, to quantify the steric demand of a ligand.46,47
Although cyclopentadienyl ligands are as frequently used as
phosphines, only a few systematic studies have been devoted to
the effect of varying the cyclopentadienyl ring substituent, R, on
the physical, chemical and catalytic properties of organometallic
complexes incorporating these ligands. For a few selected
studies the reader may refer to Ref. 12, 33, 48–52.
aInstitut für Anorganische und Analytische Chemie, Technische
Universität Braunschweig, Hagenring 30, 38106 Braunschweig,
Germany. E-mail: m.tamm@tu-bs.de, mwalter@tu-bs.de; Fax:
+49 531-391-5309
bFachbereich Chemie, Technische Universität Kaiserslautern, Erwin-
Schroedinger Strasse, 67663 Kaiserslautern, Germany. E-mail:
sitzmann@chemie.uni-kl.de; Fax: +49 631-205-4399
cFachbereich Chemie, Technische Universität Kaiserslautern, Erwin-
Schroedinger Strasse, 67663 Kaiserslautern, Germany. E-mail:
sun@chemie.uni-kl.de; Tel: +49 631-205-4333
Probably equally surprising is the fact that quantitative cone
angles for cyclopentadienyl and indenyl ligands have not been
extensively determined. There have been several scattered litera-
ture reports on cone angles of “smaller” cyclopentadienyl
ligands. Only recently, Coville published the most comprehen-
sive review in this area.53 However, the presented data show
dramatic variations associated with different reference systems
†Electronic supplementary information (ESI) available: Details of the
electronic structure calculations and the determination of Θ and Ω. Com-
parison between cone angles (Θ) for 4 based on experimental (X-ray)
and calculated (DFT) structures. CCDC reference numbers
853653–853658. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c2dt12132h
6614 | Dalton Trans., 2012, 41, 6614–6624
This journal is © The Royal Society of Chemistry 2012

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used to assemble the cone angle values, viz. (C5H4−nRn)2Fe or
(C5H4−nRn)2ZrCl2 complexes, which display very different
metal–ligand bond distances in these reference systems of 1.73 Å
and 2.20 Å, respectively. Furthermore, many of these studies
have relied on molecular modelling instead of crystallographic
data, and only very few sterically more demanding systems have
been quantified. In this manuscript, we wish to address this
oversight, and have directed our attention to the ligands tetra-
(iso-propyl)cyclopentadienyl (4Cp) and tri(tert-butyl)cyclopenta-
dienyl (Cp′′′), among others. These ligands clearly belong to
the class of extremely bulky representatives, and have already
demonstrated their exceptional synthetic potential.17,20–33,39–41
Some of us have recently introduced the concept of “soft” and
“hard” bulk in combination with these ligands and have shown
the influence of the increased flexibility and conformational
freedom of the iso-propyl groups compared to tert-butyl groups
in the context of organolanthanide complexes.31
Scheme 1 Three-step synthesis of sodium 1,3-di(tert-butyl)indenide,
Na(Ind′′).
A prerequisite for the determination of quantitative cone angle
data is a well-defined organometallic complex that can accom-
modate a wide range of different ligands and that is relatively
easy to crystallize. Our system of choice is the (C7H7)Zr frag-
ment, since the precursor [(η7-C7H7)ZrCl(tmeda)] is known to
be an excellent starting material for the synthesis of [(η7-C7H7)
Zr(η5-L)] systems (“trozircenes”) where L = indenyl, pentadie-
nyl, phospholyl and cyclopentadienyl.54–58 Here, we also
describe the synthesis of several sterically very encumbered
[(η7-C7H7)Zr(indenyl)] and [(η7-C7H7)Zr(cyclopentadienyl)]
complexes and the determination of the Tolman angle and substi-
tuent size based on single crystal data. The previously described
systems will be included for a detailed comparison. In addition,
we report on improved syntheses for 1,3-di(cyclohexyl)- and
1,3-di(tert-butyl)indenyl ligands, allowing the preparation of
these ligands in multi-gram quantities.
Scheme 2 Three-step synthesis of sodium 1,3-di(cyclohexyl)indenide,
Na(IndcHexyl).
In addition, we were interested in using cyclohexyl-substituted
systems. Replacing iso-propyl by cyclohexyl does not affect the
electron-donor capabilities significantly, but can improve the
crystallization tendency of the corresponding organometallic
complexes. A similar effect has already been achieved for
cyclohexyl-substituted cyclopentadienyl complexes.68 Therefore,
we developed an efficient synthesis for 1,3-di(cyclohexyl)indene
(Scheme 2). It is now available in multi-gram quantities and
excellent overall yield (47%).69 We hope that this new ligand
will offer a useful alternative to the iso-propyl derivative.
Results and discussion
Ligand synthesis
The syntheses of iso-propyl and tert-butyl substituted cyclopen-
tadienyl ligands are well established in the literature.20,33,59,60
In contrast, the syntheses of the related indenyl derivatives such
as 1,3-di(iso-propyl)indene61 and 1,3-di(tert-butyl)indene62–64
have been rather tedious, involving multiple steps or low
yields; only a few indenyl complexes with these ligands
have been reported, although they exhibit interesting
properties.8,13,61,62,64–67 Therefore, a better synthetic protocol
would be desirable to provide reasonable quantities of these
ligands and to facilitate the exploration of the corresponding
coordination chemistry.
In contrast to previous reports, we decided to combine phase-
transfer catalysis and classic alkylation reactions, an approach
that has already been applied successfully in the synthesis of
tri(tert-butyl)cyclopentadiene (Scheme 1).33,60 The second tert-
butyl group in 1,3-di(tert-butyl)indene was introduced via the
Grignard method, which significantly increased the yield of this
step (51%) compared to literature reported routes via lithium
organyls (18%).62 These improvements are also reflected in the
overall yield of our synthesis of 1,3-di(tert-butyl)indene (42%)
when compared to the best literature procedure (11%).64
Synthesis of cycloheptatrienyl zirconium complexes
We have recently used [(η7-C7H7)ZrCl(tmeda)] (1) as an efficient
starting material for a number of [(η7-C7H7)Zr(η5-C5H4R)] com-
plexes (R = H, CH3, PPh2, SiMe3, CH2CHvCH2), and also for
the indenyl analogue [(η7-C7H7)Zr(η5-C9H7)].56 Now, with a
convenient procedure for the preparation of indenyl ligands
bearing sterically demanding substituents in hand, we first
wanted to test the incorporation of these and of bulky cyclopen-
tadienyl ligands into the cycloheptatrienyl-zirconium coordi-
nation sphere. Indeed, the salt metathesis reactions with
Na(Cp′′), Na(Cp′′′), Na(4Cp), Na(Ind′′) and Na(IndcHexyl) give
after workup [(η7-C7H7)Zr(η5-Cp′′)] (2), [(η7-C7H7)Zr(η5-Cp′′′)]
(3), [(η7-C7H7)Zr(η5-4Cp)] (4), [(η7-C7H7)Zr(η5-Ind′′)] (5) and
[(η7-C7H7)Zr(η5-IndcHexyl)] (6), respectively, in reasonable to
good yields as purple solids (Scheme 3; see Experimental
section for details). Because of the extremely high solubility of
compounds 2–6 even in hydrocarbon solvents such as pentane,
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Structural studies
Whereas only qualitative information on the steric demand of the
different cyclopentadienyl ligands can be inferred from the ten-
dency to form solvent adducts, X-ray structures allow us to
evaluate quantitatively the steric demand of a ligand within the
metal coordination sphere. For this purpose, single crystals of all
five new complexes 2–6 were grown either by slow sublimation
in a sealed glass tube or by cooling saturated pentane solutions
(Fig. 1–5).
Scheme 3 Synthesis of cycloheptatrienyl zirconium complexes.
the reaction yields are significantly higher than the isolated
yields; for instance, 170 mg of 3 may be dissolved in 0.8 ml
C6H6. Whereas the formation of 2 is indicated by an immediate
colour change from blue to the final pink–purple colour upon
addition of 1,3-di(tert-butyl)cyclopentadienide to 1 at −78 °C,
significantly slower reactions to the sterically more encumbered
complexes 3, 4 and 5 are observed, as indicated by a gradual
colour change via grey or brownish intermediate shades.
However, several independent attempts by two of our labs to
isolate the sterically extremely encumbered complex [(η7-C7H7)
Zr(η5-5Cp)] (7) from the reaction of 1 with Li(5Cp) (5Cp =
penta(iso-propyl)cyclopentadienide) have so far proved to be
unsuccessful.70 This is rather surprising, considering that DFT
calculations (vide infra) suggest 7 to be a stable compound. It is
unclear at this point whether the experimental observation can be
traced to the enhanced steric demand of the penta(iso-propyl)
cyclopentadienyl ligand or to the need for a different cyclopenta-
dienyl transfer reagent.
Fig. 1 ORTEP diagram of 2 with thermal displacement parameters
drawn at 50% probability. Selected bond lengths (Å): Zr–C1 2.3380(15),
Zr–C2 2.3441(16), Zr–C3 2.3472(16), Zr–C4 2.3433(15), Zr–C5 2.3438
(16), Zr–C6 2.3330(15), Zr–C7 2.3229(15), Zr–C8 2.5261(14), Zr–C9
2.5079(14), Zr–C10 2.5163(14), Zr–C11 2.4937(14), Zr–C12 2.4999
(15).
Another point of interest is the colour of THF solutions
of complexes 2–6. Moderately substituted trozircenes such as
[(η7-C7H7)Zr(η5-C5H4CH3)] give red THF solutions compared
to their purple colour in the solid state,56 which suggests that the
formation of a weak THF adduct to the Lewis-acidic zirconium
atom is feasible. This is illustrated for [(η7-C7H7)Zr(η5-
C5H4Si(CH3)3)], for which the corresponding THF adduct was
isolated on crystallization at low temperatures.56 In contrast,
complexes 2–5 preserve their colour even upon cooling to
−78 °C. This suggests that the steric shielding imposed by the
bulky cyclopentadienyl and indenyl ligands effectively prevents
even a weak THF coordination.
As expected, the diamagnetic 16-valence electron sandwich
complexes exhibit 1H NMR resonances corresponding to the
protons of the seven-membered C7H7 ring, which is slightly
shifted upfield in the indenyl complexes 5 and 6, with δ 5.02
and 5.05, respectively, in comparison to their cyclopentadienyl
congeners 2–4 (δ 5.26–5.29); the opposite effect is observed in
the 13C{1H} NMR (δ 83.2–84.0 vs. 80.9–81.6). The resonances
of the η5-ligands are also characteristic (see Experimental section
for details); for instance a distinct 2 : 9 : 18 pattern for the
protons of the tri(tert-butyl)cyclopentadienyl ligand in 3 or a
1 : 2 : 2 : 6 : 6 : 6 : 6 pattern for the tetra(iso-propyl)cyclopentadie-
nyl ligand in 4 are observed.
Fig. 2 ORTEP diagram of 3 with thermal displacement parameters
drawn at 50% probability. Selected bond lengths (Å): Zr–C1 2.3498(15),
Zr–C2 2.3508(13), Zr–C3 2.3459(13), Zr–C4 2.3407(14), Zr–C5 2.3411
(14), Zr–C6 2.3452(14), Zr–C7 2.3486(15), Zr–C8 2.5542(12), Zr–C9
2.5316(12), Zr–C10 2.4856(12), Zr–C11 2.5054(12), Zr–C12 2.5013
(12).
6616 | Dalton Trans., 2012, 41, 6614–6624
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Fig. 4 ORTEP diagram of one of the two independent molecules of 5
with thermal displacement parameters drawn at 50% probability.
Selected bond lengths (Å): Zr–C1 2.319(2), Zr–C2 2.3229(18), Zr–C3
2.3289(19), Zr–C4 2.3408(19), Zr–C5 2.3298(19), Zr–C6 2.3392(19),
Zr–C7 2.343(2), Zr–C8 2.5192(16), Zr–C9 2.5037(18), Zr–C10 2.5156
(17), Zr–C11 2.5413(17), Zr–C12 2.5395(16), C12–C13 1.434(2), C13–
C14 1.358(2) C14–C15 1.412(2), C15–C16 1.356(2), C11–C16 1.426
(2).
Fig. 3 ORTEP diagram of 4 with thermal displacement parameters
drawn at 50% probability. Selected bond lengths (Å): Zr–C1 2.338(4),
Zr–C2 2.345(4), Zr–C3 2.351(4), Zr–C4 2.346(4), Zr–C5 2.346(4), Zr–
C6 2.334(5), Zr–C7 2.324(5), Zr–C8 2.515(4), Zr–C9 2.532(4), Zr–C10
2.542(4), Zr–C1 2.522(4), Zr–C12 2.480(3).
A closer inspection of the seven-membered ring ligands in
2–6 reveals a significant tilt of the hydrogen substituents out of
the C1–C7 plane toward the metal, while this effect is only mar-
ginal for the η5-ligands. For instance, the corresponding tilt
angles are on average 5.6 and 6.4° for the C7H7 ligands vs. 0.8
and 1.7° for the η5-ligands for the di(tert-butyl) substituted com-
plexes 2 and 5, respectively. This observation is a consequence
of the large diameter of the cycloheptatrienyl, for which a tilt of
the substituents helps to improve ligand–metal orbital overlap
(Scheme 4).71,72 For this reason, we generally refine hydrogen
atoms of the seven-membered ring freely (if necessary with
restraints to C–H distances and/or with fixed U values), provided
that the data are robust enough to allow this.
Theoretically, the tetra(iso-propyl)cyclopentadienyl ligand in
[(η7-C7H7)Zr(η5-4Cp)] (4), can adopt nine different confor-
mations with either C2v or Cs symmetry, but only three of these
are thermodynamically favoured by avoiding repulsive methyl–
methyl contacts.31,73 Indeed, the X-ray structure of 4 exhibits
Fig. 5 ORTEP diagram of one of the two independent molecules of 6 with thermal displacement parameters drawn at 50% probability. Selected
bond lengths (Å): Zr–C1 2.337(5), Zr–C2 2.343(5), Zr–C3 2.342(5), Zr–C4 2.296(6), Zr–C5 2.302(6), Zr–C6 2.304(5), Zr–C7 2.318(5), Zr–C8 2.494
(4), Zr–C9 2.478(4), Zr–C10 2.506(4), Zr–C11 2.518(4), Zr–C12 2.521(4), C12–C13 1.440(5), C13–C14 1.347(5) C14–C15 1.399(5), C15–C16
1.353(5), C11–C16 1.436(5).
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 6614–6624 | 6617

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structure of the as yet synthetically inaccessible complex
[(η7-C7H7)Zr(η5-5Cp)] (7) for subsequent discussions (see ESI
for a representation†). In this case, the five iso-propyl groups
interlock with each other like cogwheels, and rotation around the
Cp–iPr bond requires high activation energies, ranging from 13.1
(1) kcal mol−1 in [(η5-5Cp)Mo(CO)3(CH3)]74 to 20.4 kcal mol−1
in [(η5-5Cp)2Co]+[PF6]−.75 Empirical force field calculations on
hexakis(dimethylsilyl)benzene suggest that the rotation in these
tightly interlocked systems occurs via a step-wise rather than a
concerted mechanism.76
Scheme 4 Improvement of ligand–metal orbital overlap.
Table 1 Comparison of experimental vs. calculated bond distances (Å)
for 4, and calculated bond distances (Å) for 7
The characteristic bonding parameters for the cyclopen-
tadienyl derivatives 2–4 resemble those of related [(η7-C7H7)
Zr(η5-Cp)] complexes (Table 2). An interesting point concerns
a potential ring-slippage toward an η3-coordination in the
indenyl derivatives 5 and 6. The fold angle is one measurement
of structural distortions in indenyl complexes,77 and is defined
as the angle between the planes of the six-membered ring and
of the other three atoms of the indenyl group. In our complexes,
the angles between the planes C8–C10 and C11–C16 are 3.9(2),
2.4(2) and 3.6(5), 5.6(3)° for the two independent molecules
of 5 and 6, which compare well to the value of 3.7° for the
unsubstituted complex [(η7-C7H7)Zr(η5-C9H7)] (13).56 Further-
more, a distinct long–short–long–short–long pattern of bond
lengths is observed within the C12–C13–C14–C15–C16–
C11 moiety, indicating a reasonably unperturbed η5-coordination
mode.
4 (exp.)
4 (calc.)
7 (calc.)
Zr–C1
Zr–C2
Zr–C3
Zr–C4
Zr–C5
Zr–C6
Zr–C7
Zr–C8
Zr–C9
Zr–C10
Zr–C11
Zr–C12
2.338(4)
2.345(4)
2.351(4)
2.346(4)
2.346(4)
2.334(5)
2.324(5)
2.515(4)
2.532(4)
2.542(4)
2.522(4)
2.480(3)
2.342
2.350
2.365
2.370
2.364
2.351
2.345
2.520
2.541
2.549
2.528
2.499
2.364
2.356
2.357
2.364
2.359
2.357
2.363
2.540
2.543
2.546
2.544
2.545
one of these forms, whereby three iso-propyl groups are oriented
in the same direction (the methine C–H vectors lie approxi-
mately in the plane of the five-membered ring and correspond to
the same rotational sense) while one (at C8) is turned in the
opposite direction. Density functional theory (DFT) calculation
at the M06 level of theory (see ESI for details†) suggest that this
conformation is stabilized by ΔE0 = 2.0 and 2.7 kcal mol−1 in
comparison to the only C2v symmetrical conformer without
methyl–methyl contacts or to the conformer with all iso-propyl
groups located in the same direction, respectively. Furthermore,
the calculated bonding parameters for 4 nicely reproduce the
experimental data (Table 1), which motivated us to calculate the
With six additional structures of trozircenes in hand, we now
have a useful library of twelve complexes for the assessment of
the steric bulk of various cyclopentadienyl and indenyl ligands
based on experimental data.56 The ligands range from unsubsti-
79
tuted (C5H5)78 to pentasubstituted in C5(CH3)5 or 5Cp; the
latter is the only calculated structure included in the discussion
(Scheme 5). For several reasons, the (C7H7)Zr fragment appears
to be advantageous for the determination of cone angles: 1) The
complexes are readily available by a straightforward synthetic
procedure (vide supra), which facilitates extensions of this
Table 2 Comparison of structural parameters for complexes 2–13 (distances in Å, angles in °)a
Nr.
Cp
Zr–Cht
Zr–Cp
Zr–Chtcent
Zr–Cpcent
Cht–Zr–Cp
α
Ref.
8
9
10
11
2
3
4
12
7
C5H5
2.323(2)–2.3416(15)
2.316(2)–2.340(2)
2.316(4)–2.347(4)
2.322(3)–2.332(3)
2.3229(15)–2.3472(16)
2.3407(14)–2.3508(13)
2.324(5)–2.351(4)
2.328(3)–2.377(6)
2.356–2.364
2.494(2)–2.5037(15)
2.477(2)–2.523(2)
2.485(3)–2.516(3)
2.487(2)–2.517(2)
2.4937(14)–2.5261(14)
2.4856(12)–2.5542(12)
2.480(3)–2.542(4)
2.483(3)–2.488(3)
2.540–2.546
1.664
1.659
1.667
1.663
1.667
1.681
1.677
1.663
1.699
2.195
2.188
2.193
2.193
2.198
2.204
2.207
2.172
2.234
175.4
175.7
175.3
178.8
175.6
176.0
175.4
170.3
179.5
5.33
4.05
4.56
2.16
5.21
5.13
6.39
9.59
0.36
78
56
56
56
C5H4(CH3)
C5H4Si(CH3)3
C5H4(allyl)
Cp′′
This work
This work
This work
79
Cp′′′
4Cp
C5(CH3)5
5Cp
This workb
Nr.
Indenyl
Zr–Cht
Zr–Cp
2.488(4)–2.554(3)
2.5045(18)–2.5414(17)
2.5111(19)–2.5446(16)
2.481(4)–2.521(4)
Zr–Chtcent
Zr–Cpcent
Cht–Zr–Cp
α
Ref.
13
5
C9H7
Ind′′
2.302(5)–2.335(5)
2.319(2)–2.344(2)
2.318(2)–2.355(2)
2.299(5)–2.348(5)
2.280(6)–2.3446(5)
1.648
1.665
1.667
1.655
1.674
2.205
2.211
2.215
2.193
2.203
175.4
179.5
169.3
166.1
160.7
3.16
0.83
10.65
14.15
21.63
56
This workc
6
IndcHexyl
This workc
2.491(4)–2.531(4)
a Cht = cycloheptatrienyl; Cht–Zr–Cp represents the angle between the centroid of the cycloheptatrienyl ring, the metal and the centroid of the five-
membered ligand; α = angle between the two ligand planes. b Data for complex 7 are based on a calculated structure. c There are two independent
molecules in the asymmetric unit. Therefore the structural parameters of both molecules are given.
6618 | Dalton Trans., 2012, 41, 6614–6624
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Scheme 5 Drawings of the cycloheptatrienyl zirconium sandwich complexes 2–13 (“trozircenes”).
library. 2) As noted earlier,48 cone angles depend on metal–
centroid distances, and in the present case these span a narrow
range of 2.172–2.234 Å (Table 2). 3) Because of the sandwich
structure, free rotation of the ligands is possible, which is not
always the case when only bulky cyclopentadienyl ligands are
involved; otherwise more complicated patterns in the room temp-
erature NMR spectra are to be expected (see Experimental
section).34,60 4) As a consequence of 3), the substituents on the
η5-ligand are not sterically hindered by other ligands in their
adoption of any configuration. 5) Zirconium as the largest tran-
sition metal is a viable model for “large” metals such as the
lanthanides and actinides.80
this we define the angle Ω for a given substituent (Scheme 5,
Table 3). Its determination for the complexes 2–12 gives
H ꢂ CH3 < allyl < cHexyl ꢁ iso ꢃ propyl < SiðCH3Þ3
< tert ꢃ butyl
ð3Þ
and shows that a substitution of an iso-propyl group by cHexyl
does not affect the size, although it might improve the crystalli-
zation process. The use of Ω as a second parameter also helps
to rationalize some other observations: 1) Although eqn (2)
Similarly to previous studies,48,53 we have measured the cone
angle Θ according to
Θ ¼ ðθ1 þ θ2 þ θ3 þ θ4 þ θ5Þ ꢀ 2=5
ð1Þ
with θi as the maximum half cone angles of each substituent
(Scheme 6). For the determination of θi the centres of each outer-
most hydrogen atom, and not the van der Waals radii, were used,
and therefore the resulting cone angle Θ is a lower limit (see ESI
for all θi†). Table 3 lists the values obtained for each ligand,
which results in the following order of size:
C5H5 < C5H4CH3 < C9H7 ꢁ C5H4SiðCH3Þ3
ꢁ C5H4ðallylÞ < Cp00 < C5ðCH3Þ5 < Ind00
4
5
ꢁ IndcHexyl ꢁ Cp000 < Cp < Cp
ð2Þ
However, Θ does not take into account that some of the substi-
tuents are not rotationally symmetric, and consequently their
“real” steric demand may be smaller than that estimated from the
maximum half cone angle. Therefore, Θ is a good descriptor for
the steric bulk in the xy direction parallel to the ring, but an
additional measure for the ligand size in the z-dimension is
needed to indicate the shielding of a (reactive) metal atom. For
Scheme 6 Measurement of the angles θi and ωi leading to Θ (top) and
Ω (bottom). The large sphere represents the metal and the small spheres
the methyl hydrogens. The relevant group is not necessarily directly
bonded to the ring, nor does it necessarily lie in the ring plane. For each
substituent the outermost methyl hydrogen, corresponding to the largest
θi value, is chosen.
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Table 3 Measured cone angles (°) for 2–13
di(tert-butyl) substituted indenes are now available in multi-
gram quantities. These indenyl and sterically demanding alkyl
cyclopentadienyl ligands have been employed to synthesize an
extensive series of [(η7-C7H7)Zr(η5-L)] (L = Cp and Ind) com-
plexes by straightforward salt metathesis between [(η7-C7H7)
ZrCl(tmeda)] and the corresponding sodium indenide or cyclo-
pentadienide. All of these Zr complexes have been characterized
by elemental analysis, NMR spectroscopy and single crystal
X-ray diffraction. The structural information derived from these
studies was employed to evaluate realistically the steric demand
of these ligands, some of which have already been exploited in
previous studies to stabilize very unusual molecules. Further
studies exploring the coordination chemistry of these ligands are
the subject of ongoing investigations.
Nr.
Cp
Θ
Ωa
8
9
10
11
2
C5H5
88.2
95.1
0
C5H4CH3
C5H4Si(CH3)3
C5H4(allyl)
Cp′′
49.0
95.6
68.6
100.7
99.8
85.9
51.2
88.6
104.3
106.0
116.2
132.0
146.4
122.4
167.4
3
4
Cp′′′
4Cp
12
7
C5(CH3)5
5Cp
Nr.
Indenyl
Θ
Ωa
13
5b
6b
C9H7
102.6
130.7/131.8
131.0/131.7
0
Ind′′
101.3/100.2
84.9/84.2
IndcHexyl
a Calculated for a given substituent by measuring the maximum cone
angle of each group on the α-C of the substituent with the ipso-C atom
as the apex, then averaged. In the case of iPr and cHexyl the C–H proton
was included in the calculation. b Two independent molecules in the
asymmetric unit.
Experimental section
General
All synthetic and spectroscopic manipulations were carried out
under an atmosphere of prepurified nitrogen or argon, either in a
Schlenk apparatus or in a glovebox. Solvents were dried and
deoxygenated either by distillation under a nitrogen atmosphere
from sodium benzophenone ketyl (THF) or by an MBraun
GmbH solvent purification system. NMR spectra were recorded
on Bruker DPX 200, AV 300 and Bruker DRX 400 spec-
trometers. The chemical shifts are expressed in parts per million
suggests Ind′′ and IndcHexyl to be of similar size, the former is to
be regarded as bulkier because of the noticeably greater Ω angle.
A similar argument applies to C5H4Si(CH3)3 vs. C9H7. 2) Ben-
zanellation of Cp′′ gives Ind′′, which naturally has a greater Θ
angle. However, the additional contribution to the bulk in the
z-dimension is only marginal. 3) Whenever the expansion in all
three dimensions becomes crucial, the size of Ind′′ is exceeded
by Cp′′′ – despite similar Θ values, which is exemplified by a
rotation barrier of ΔG‡ = 14.2 kcal mol−1 for [(η5-Cp′′′)2Fe]34 vs.
11.8 kcal mol−1 for [(η5-Ind′′)2Fe].81 4) Undoubtedly, 5Cp
represents the bulkiest ligand in this series; the trozircene
[(η7-C7H7)Zr(η5-5Cp)] (7) has as yet not been synthesised (vide
supra), nor does the reaction of Na(5Cp) with FeCl2 afford the
corresponding ferrocene, but instead the stable 5Cp˙ radical.82
However, the order in size of the two C17H29− isomers, Cp′′′ and
1
(ppm) and are referenced to residual H or 13C of the solvent or
tetramethylsilane. A Bruker Vertex 70 spectrometer was used for
recording IR spectra. Elemental analyses were performed by
combustion and gas chromatography analysis with an Elementar
varioMICRO
instrument.
[(η5-C7H7)ZrCl(tmeda)]
(1),55
Na(Cp′′′),33 and Na(4Cp)20 were synthesized by a published pro-
cedure, whereas all other reagents were obtained commercially.
X-Ray diffraction studies
4Cp, can be questioned since [(η5-4Cp)2Fe] has with ΔG‡
=
Single crystals of each compound were examined under inert oil.
Data collection was performed on various Oxford Diffraction
diffractometers using monochromated Mo Kα or mirror-focussed
Cu Kα radiation (Table 4). Absorption corrections were per-
formed on the basis of multi-scans. The data were analyzed
using the SHELXL97 program.90 In all cases, the non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were either
located and refined isotropically (for all hydrogen atoms directly
attached to a 5- or 7-membered ligand), incorporated as idealised
methyl groups allowed to rotate but not tip, or were allowed to
ride on their attached carbon atoms. Compounds 5 and 6 crystal-
lised with two independent molecules per asymmetric unit.
Exceptions and special features: For compound 4, the absorption
correction was based on indexed faces. The structure was refined
as a pseudo-merohedral twin (formed by rotation of 180° about
the a axis).
13.6 kcal mol−1 a smaller rotation barrier than its tri(tert-butyl)
cyclopentadienyl analogue.20 The higher conformational flexi-
4
bility of Cp can be ascribed to the smaller Ω in comparison to
Cp′′′, although the Θ values are reversed (Table 3); this phenom-
enon has recently been described as “soft” vs. “hard bulk”.31
5
4
Nevertheless, together with Cp, Cp′′′ and Cp clearly approach
the upper limit of possible steric bulk in this series. It is worth
mentioning that penta(aryl)cyclopentadienyls (“CpBIG”) also
belong to the class of superbulky ligands,83 and they can give
unusual, but unexpectedly stable metallocenes associated with
attractive Ar5Cp⋯Ar5Cp interactions.84–87 Similarly, pentadienyl
(“open Cp”) ligands are also known to present a severe steric
demand,88,89 and the Θ value of 113° for [(η7-C7H7)Zr(η5-
C7H11)] places the 2,4-dimethylpentadienyl ligand between
C5H4Si(CH3)3 and Cp′′.55
3-(tert-Butyl)indene. The synthesis was adapted from Ref. 33.
Adogen 464 (5 mL), indene (50 g, 0.39 mol) and tert-butyl
bromide (160 g, 1.17 mol) were added to an aqueous solution of
potassium hydroxide (1 kg KOH in 750 mL degassed water).
The reaction mixture was stirred vigorously at 80 °C for 2 days
Conclusions
The syntheses of sterically demanding indenyl ligands have been
reported using a combination of phase-transfer and traditional
alkylation strategies. By this method 1,3-di(cyclohexyl) and 1,3-
6620 | Dalton Trans., 2012, 41, 6614–6624
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Table 4 Crystallographic data for complexes 2–6
2
3
4
5
6
Empirical formula
Formula weight
Temperature (K)
Wavelength, λ (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
C20H28Zr
359.64
100(2)
1.54184
monoclinic
P21/c
14.3641(2)
9.9629(2)
12.1930(2)
90
91.555(2)
90
1744.27(5)
4
C24H36Zr
415.75
100(2)
0.71073
monoclinic
P21/n
10.0111(2)
21.1152(4)
10.1725(2)
90
100.199(2)
90
2116.35(7)
4
C24H36Zr
415.75
150(2)
1.54184
monoclinic
P21/c
15.0646(6)
8.6396(4)
16.4412(6)
90
90.047(4)
90
2139.86(15)
4
C24H30Zr
409.70
100(2)
0.71073
triclinic
ˉ
P1
10.0987(4)
14.0383(6)
15.6547(10)
66.262(6)
82.216(4)
84.290(4)
2010.38(19)
4
C28H34Zr
461.77
100(2)
0.71073
monoclinic
P21/c
13.6123(8)
21.0921(12)
16.3638(10)
90
106.805(6)
90
γ (°)
Volume (Å3)
Z
4497.6(5)
8
Reflections collected
Independent reflections
Goodness of fit on F2
15095
3610 (Rint = 0.0171)
1.106
1.370
5.072
87658
5041 (Rint = 0.0515)
0.892
1.305
0.523
14356
3422 (Rint = 0.0492)
1.002
1.290
4.202
63302
8815 (Rint = 0.0572)
0.910
1.354
0.550
140503
9188 (Rint = 0.1569)
0.931
1.364
0.500
ρcalcd (g cm−3
)
μ (mm−1
)
R(Fo), [I > 2σ(I)]
0.0202
0.0526
0.400/−0.506
0.0202
0.0421
0.330/−0.228
0.0348
0.0886
1.541/−0.297
0.0277
0.0307
0.748/−0.375
0.0483
0.0781
1.405/−0.678
2
Rw (Fo )
Δρ (e Å−3
)
and the reaction progress was monitored by GC. The reaction
mixture was cooled to ambient temperature and then diluted with
diethyl ether (ca. 100 mL). The organic layer was separated and
washed with 2 M HCl (100 mL). The aqueous layer was
extracted twice with diethyl ether (ca. 200 mL). The combined
organic phases were dried over MgSO4. After filtration the
diethyl ether was removed under reduced pressure and the
product was distilled at 60 °C (0.06 mbar). 3-(tert-Butyl)indene
was obtained as a pale yellow liquid. Yield: 54.77 g (0.32 mol,
82%). The 1H and 13C{1H} NMR spectroscopic data agreed
with those reported previously.63,91 1H NMR (CDCl3, ambient):
δ 7.76 (d, 1 H, C(7)-H), 7.58 (d, 1 H, C(4)-H), 7.40 (dd, 1 H,
C(5)-H), 7.30 (ddd, 1 H, C(6)-H), 6.31 (t, 1 H, C(2)-H), 3.40
(d, 2 H, C(1)-H), 1.52 (s, 9 H, tBu-H). 13C{1H} NMR (CDCl3,
ambient): δ 153.45, 146.85, 144.09 (3 Cipso), 126.10, 125.64,
124.10, 124.01, 122.21 (5 C, C9H6), 37.28 (1 C, C9H6), 33.22
(Cipso, tBu), 29.53 (3 C, tBu). GC-MS: m/z = 172 (M+), 157
(M+ − Me), 142 (M+ − 2 × Me), 116 (M+ − tBu). IR (ATR;
cm−1): 2961 (m), 1597 (w), 1569 (w), 1477 (m), 1460 (m), 1392
(m), 1363 (m), 765 (s), 721 (s).
purification. 3-(tert-Butyl)indene (24.70 g, 143 mmol) was
added dropwise to a suspension of ethylmagnesium bromide
(18.66 g, 140 mmol) in toluene (40 mL). The reaction mixture
was slowly heated to 140 °C (oil bath temperature) whereby gas
formation was observed, and it was vigorously stirred for 8 h.
After this time the reaction mixture was cooled to 0 °C, and tert-
butyl chloride (15.55 mL, 143 mmol) was added dropwise to
this suspension. After complete addition, the temperature was
allowed to reach room temperature and the reaction mixture was
stirred for 8 h. A saturated aqueous solution of ammonium chlor-
ide (50 mL) was mixed with ice (250 g) and the reaction mixture
was slowly added (a very exothermic reaction). The aqueous
layer was separated and extracted twice with diethyl ether (ca.
150 mL). The ether extracts were combined with the organic
layer, washed with water and dried over sodium sulfate. The
solvent was removed under reduced pressure and the residue was
purified by distillation (at 70 °C under 0.06 mbar) to give the
product as a colourless liquid. Yield: 16.27 g (71 mmol, 51%).
The 1H and 13C{1H} NMR spectroscopic data agreed with those
previously reported for this compound.63,64 1H NMR (CDCl3,
ambient): δ 7.68 (m, 2 H, C(4,7)-H), 7.38 (m, 1 H, C(5)-H),
7.25 (m, 1 H, C(6)-H), 6.32 (d, 1 H, C(2)-H), 3.27 (d, 1 H,
C(1)-H), 1.51 (s, 9 H, tBu-H), 1.14 (s, 9 H, tBu-H). 13C{1H}
NMR (CDCl3, ambient): δ 152.70, 147.91, 144.66 (3 Cipso),
130.19, 125.86, 125.11, 123.64, 122.07 (5 C, C9H6), 58.73 (1 C,
C9H6), 34.41, 33.19 (2 Cipso, tBu), 29.69 (3 C, tBu), 28.70 (3 C,
tBu). GC-MS: m/z = 228 (M+), 172 (M+ − tBu), 157 (M+ − tBu
− Me), 142 (M+− tBu − 2 × Me), 116 (M+ − 2 × tBu). IR
(ATR; cm−1): 2953 (m), 1602 (w), 1571 (w), 1458 (m), 1391
(m), 1363 (m), 762 (s), 724 (s).
1,3-Di(tert-butyl)indene. The synthesis was adapted from Ref.
60. Ethylmagnesium bromide was prepared from magnesium
and ethyl bromide in diethyl ether. A 3-neck 250 mL well-dried
round-bottom flask equipped with a dropping funnel and a reflux
condenser was charged with magnesium turnings (3.40 g,
140 mmol), I2 (50 mg) and diethyl ether (15 mL). This mixture
was stirred until the purple I2 colour faded indicating the acti-
vation of the Mg. At this point an ethereal solution of EtBr
(11.00 mL, 144 mmol diluted in 35 mL of diethyl ether) was
slowly added under stirring to ensure gentle reflux of the diethyl
ether solvent. After complete addition of the ethyl bromide the
reaction mixture was heated under gentle reflux for 12 h. After
the reaction mixture was allowed to cool to room temperature
and taken to dryness, the crude product was dried for 8 h under
dynamic vacuum, and used for further reaction without
(1,3-Di(tert-butyl)indenyl)sodium. The sodium salt of 1,3-
di(tert-butyl)indene (11.42 g, 50 mmol) was prepared by reac-
tion with NaNH2 (1.87 g, 48 mmol) in THF (120 mL) for 18 h
under reflux. The reaction mixture was allowed to cool to room
temperature, filtered and the precipitate was washed with THF
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(ca. 30 mL). The THF solutions were taken to dryness, the red–
brown crude product was suspended in pentane (150 mL) and
filtered. The residue was washed with pentane (ca. 100 mL) and
dried in vacuo, affording the product, Na(Ind′′), as an ivory-
coloured solid. Yield: 8.57 g (34 mmol, 71%).
extracted twice with ether (100 mL). The combined organic
phases were dried over MgSO4. Solvent was removed and the
residue distilled (130 °C, 0.1 mbar) to remove unreacted 3-
(cyclohexyl)indene, the residue contained 1,3-di(cyclohexyl)
indene as a viscous oil (95% purity). Yield: 61.7 g (0.22 mol,
65%). 1,3-Di(cyclohexyl)indene was used for the metallation
1
3-(Cyclohexyl)indene. This phase transfer procedure was
slightly modified compared to the original report by Dehmlow
and co-workers.59 Aqueous KOH (50%; 0.75 L, ca. 10 mol) and
Adogen 464 (5 g) were placed in a 2 L three-neck round-bottom
flask fitted with a condenser, mechanical stirrer, heating mantle,
and a dropping funnel. Indene (100 g, 101 mL, 0.86 mol) and
cyclohexyl bromide (700 g, 526 mL, 4.3 mol) were slowly
added via the dropping funnel, with vigorous stirring. The
mixture turned dark green and became warm (40 °C). The vigor-
ously stirred mixture was maintained at 50 °C overnight,69 after
which the contents of the flask were decanted into a 1 L separ-
ating funnel, and the flask and remaining solid were washed with
diethyl ether (3 × 100 mL). The washings were combined with
the contents of the separating funnel and the layers separated.
The diethyl ether layer was washed with dilute HCl (0.1 M,
20 mL) and with water (2 × 100 mL). The organic layer was
dried over MgSO4, and filtered through a layer of celite (5 ×
5 cm). The solvent was evaporated, leaving a dark orange oil,
which was distilled under dynamic oil pump vacuum at
119–125 °C to give 122.93 g (0.62 mol, 72%) of a yellow oil.
Only the 3-(cyclohexyl)indene isomer was obtained by this pro-
cedure, in contrast to a previous report in which a mixture of
1-(cyclohexyl)indene and 3-(cyclohexyl)indene was reported on
step without further purification. H NMR (200 MHz, CDCl3,
ambient): δ 7.50 (m, 2 H, C(4,7)-H), 7.32 (m, 1 H, C(5)-H),
7.25 (m, 1 H, C(6)-H), 5.21 (m, 1 H, C(2)-H), 3.38 (m, 1 H,
C(1)-H), 2.55 (m, 2 H, cyclohexyl-CH), 2.15–1.25 (m, 20 H,
cyclohexyl-CH2). 13C{1H} NMR (CDCl3, ambient): δ 149.4,
147.7, 145.2 (3 Cipso), 128.9, 125.9, 124.2, 123.1, 119.0 (5 C,
C9H6), 54.6 (1C, C9H6), 40.6 (1 C, cyclohexyl-CH), 37.0 (1 C,
cyclohexyl-CH), 32.8 (1 C, cyclohexyl-CH2), 32.5 (1 C, cyclo-
hexyl-CH2), 32.2 (1 C, cyclohexyl-CH2), 28.2 (1 C, cyclohexyl-
CH2), 27.0 (1 C, cyclohexyl-CH2), 26.8 (2C, cyclohexyl-CH2),
26.6 (3C, cyclohexyl-CH2). GC-MS: m/z = 281 (M+).
(1,3-Di(cyclohexyl)indenyl)sodium. The sodium salt of 1,3-
di(cyclohexyl)indene (50.5 g, 0.18 mol) was prepared by reac-
tion with NaNH2 (7.8 g, 0.20 mol) in THF (400 mL) for 5 h
under reflux. The reaction mixture was allowed to cool to room
temperature, and filtered. The THF solution was taken to
dryness, and the brown residue was suspended in pentane
(300 mL) and filtered off. The solid was washed with pentane
(ca. 100 mL) and dried in vacuo, affording sodium 1,3-di-
(cyclohexyl)indenide, Na(IndcHexyl), as a beige solid. Yield:
45.6 g (0.14 mmol, 78%).
[(η7-C7H7)Zr(η5-Cp′′)] (2). [(η7-C7H7)ZrCl(tmeda)] (0.350 g,
1.048 mmol) was dissolved in THF (25 mL). At −78 °C, a
yellow solution of Na(Cp′′) (0.220 g, 1.100 mol) in THF
(13 mL) was slowly added with a syringe, resulting in a colour
change from blue to pink–purple. After warming to room temp-
erature with stirring for 3 h, the solvent was removed. Drying at
40 °C and subsequent sublimation at 120 °C under high vacuum
(0.1 mbar) afforded a purple powder (0.243 g, 64%). Single
crystals were obtained by slow sublimation at 120 °C in a sealed
glass tube. 1H NMR (200 MHz, C6D6, ambient): δ 5.34 (m, 1 H,
Cp′′), 5.29–5.27 (m, 2 H, Cp′′), 5.28 (s, 7 H, C7H7), 1.10 (s, 18
H, CH3, tert-butyl). 13C{1H} NMR (50 MHz, C6D6, ambient): δ
134.8 (Cq, Cp′′), 97.6 (CH, Cp′′), 97.0 (CH, Cp′′), 80.9 (C7H7),
32.3 (CH3, tert-butyl), 31.9 (Cq, tert-butyl). Anal. Calcd. for
C20H28Zr (359.66): C, 66.79; H, 7.85. Found: C, 66.34; H, 7.91.
1
reaction of Li(indenide) with cyclohexyl tosylate. The H-NMR
spectroscopic data of 3-(cyclohexyl)indene agreed with those
previously reported for this compound.92 1H NMR (200 MHz,
CDCl3, ambient): δ 7.50–7.10 (m, 4 H, 4-H–7-H), 6.20 (m, 1 H,
3
2-H, J = 1.0 Hz (2-H,1-H)), 3.34 (bs, 2 H, 1,1′-H), 2.63 (m, 1
H, cyclohexyl-CH), 2.10–1.12 (m, 10 H, cyclohexyl-CH2). 13C
{1H} NMR (CDCl3, ambient): δ 150.1, 145.0, 144.7 (3 Cipso),
125.8, 125.5, 124.3, 123.8, 119.2 (5 C, C9H7), 37.6 (1 C, C9H7),
37.1 (1 C, cyclohexyl-CH), 32.5 (2 C, cyclohexyl-CH2), 26.7
(2 C, cyclohexyl-CH2), 26.6 (1 C, cyclohexyl-CH2). GC-MS:
m/z = 198 (M+).
1,3-Di(cyclohexyl)indene. 3-(Cyclohexyl)indene (122.93 g,
0.62 mol) diluted in THF (100 mL) was added dropwise over a
period of 0.5 h to a magnetically stirred suspension of NaNH2
(23 g, 0.59 mol) in THF (600 mL). The reaction mixture was
then heated to reflux for 12 h, with evolution of ammonia. The
reaction mixture was allowed to cool to room temperature, the
THF was distilled off. The residue was dried under dynamic
vacuum, suspended in pentane (300 mL), filtered and washed
with pentane (100 mL) to give Na(1-(cyclohexyl)indenide) as a
pale ivory-coloured solid. Yield: 130 g (0.59 mol, 95.2%).
Sodium 1-(cyclohexyl)indenide (75 g, 0.34 mmol) was dis-
solved in THF (400 mL) in a 1 L Schlenk tube. The reaction
mixture was cooled to 0 °C, cyclohexyl bromide (55.5 g, 42 mL,
0.34 mol) was added and the Schlenk tube was connected to a
reflux condenser and heated under reflux for 5 h. After this time
the reaction mixture was hydrolyzed with water (500 mL). Ether
(600 mL) was added and the organic layer was separated and
washed with water (3 × 100 mL). The aqueous phase was
[(η7-C7H7)Zr(η5-Cp′′′)] (3). [(η7-C7H7)ZrCl(tmeda)] (0.500 g,
1.497 mmol) was dissolved in THF (20 mL). An orange–red sol-
ution of Na(Cp′′′) (0.403 g, 1.572 mmol) in THF (13 mL) was
slowly added with a syringe at −78 °C, resulting in brownish
solution. During the slow warm-up and stirring for 3.5 h, a
colour change to purple was observed. The solvent was
removed, and the oily solid was extracted with pentane with sub-
sequent filtration through a pad of Celite. The extract was con-
centrated to ca. 3 mL yielding a purple crystalline solid (0.309 g,
50%) after storage at −30 °C overnight. Single crystals were
1
obtained by slow sublimation in a sealed glass tube. H NMR
(400 MHz, C6D6, ambient): δ 5.56 (s, 2 H, Cp′′′), 5.29 (s, 7 H,
C7H7), 1.29 (18 H, CH3, tert-butyl), 1.14 (9 H, CH3, tert-butyl).
13C{1H} NMR (100 MHz, C6D6, ambient): δ 131.5 (Cq, Cp′′′),
130.4 (Cq, Cp′′′), 81.1 (C7H7), 34.5 (CH3, tert-butyl), 33.4
6622 | Dalton Trans., 2012, 41, 6614–6624
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(Cq, tert-butyl), 32.1 (CH3, tert-butyl), 31.2 (Cq, tert-butyl).
Anal. calcd. for C24H36Zr (415.76): C, 69.33; H, 8.73. Found:
C, 69.10; H, 8.79.
(CH2, cHexyl), 33.7 (CH2, cHexyl), 27.3 (CH2, cHexyl), 27.2
(CH2, cHexyl), 26.7 (CH2, cHexyl). Anal. calcd. for C28H34Zr
(460.17): C, 72.83; H, 7.42. Found: C, 72.62; H, 7.59.
[(η7-C7H7)Zr(η5-4Cp)] (4). A solution of Na(4Cp) (0.159 g,
0.620 mmol) in THF (10 mL) was added with a pipette to a
stirred THF solution (15 mL) of [(η7-C7H7)ZrCl(tmeda)]
(0.205 g, 0.615 mmol) at −78 °C. The resulting grey reaction
mixture was warmed to room temperature within 80 min, and
stirring was continued for 3 h. The solvent was removed in
vacuo from the purple solution, and the residue was extracted
with pentane (50 mL). After filtration, the volume was reduced
to ca. 10 mL, and purple crystals were obtained after 3 days at
Acknowledgements
MDW gratefully acknowledges the current financial support by
Deutsche Forschungsgemeinschaft (DFG) through the Emmy-
Noether program (WA 2513/2-1). AG would like to express his
gratitude to the Fonds der Chemischen Industrie for a PhD
fellowship.
1
−30 °C (0.174 g, 68%). H NMR (400 MHz, C6D6, ambient): δ
5.34 (s, 1 H, 4Cp), 5.26 (s, 7 H, C7H7), 2.77 (sept., 2 H, CH-iso-
Notes and references
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4
4
4
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to a solution of [(η7-C7H7)ZrCl(tmeda)] (0.400 g, 1.198 mmol)
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[(η7-C7H7)Zr(η5-IndcHexyl)]
(6). [(η7-C7H7)ZrCl(tmeda)]
(0.400 g, 1.198 mmol) was dissolved in THF (25 mL). At
−78 °C, a yellow solution of Na(IndcHexyl) (0.220 g, 1.100 mol)
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1.79–1.65 (m, 4 H, cHexyl), 1.54–1.01 (m, 10 H). 13C{1H}
NMR (75 MHz, C6D6, ambient): δ 121.9 (CH, IndcHexyl), 121.6
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