Synthesis and coordination chemistry of an enantiomerically pure pentadienyl ligand

Article abstract of DOI:10.1021/om301189g

The coordination chemistry of the enantiomerically pure dimethylnopadienyl ligand (Pdl) with early to late transition metals is presented. Dimethylnopadiene is prepared by a Wittig reaction from (1R)-(-)-myrtenal, which is readily available from the chiral pool. Deprotonation of dimethylnopadiene with a Schlosser base gives K(Pdl), which is a good starting material for the preparation of the early- to late-transition-metal open metallocenes [M(η⁵-Pdl)₂] (M = Ti, V, Cr, Fe) and mono(pentadienyl) complexes [(η⁵-Cp′)Fe(η⁵-Pdl)] (Cp′ = 1,2,4-(Me₃C)₃C₅H₂), [(η⁷-C₇H₇)Zr(η⁵-Pdl)], and [(η⁴-COD)Ir(η⁵-Pdl)]. These complexes have been fully characterized by several spectroscopic techniques, elemental analysis, and X-ray crystallography. In all of these cases the Pdl* ligand exhibits excellent face selectivity upon metal coordination, because it coordinates exclusively from the sterically less hindered site of the bicyclic ligand framework. Within the series of open metallocenes [M(η⁵-Pdl) ₂] (M = Ti, V, Cr, Fe) the open ferrocene is the least thermally stable molecule and degrades to iron metal in solution. This instability is attributed to the severe steric demand of this ligand system in combination with the relatively small Fe²⁺ center.

Full text of DOI:10.1021/om301189g

Article
pubs.acs.org/Organometallics
Synthesis and Coordination Chemistry of an Enantiomerically Pure
Pentadienyl Ligand
Ann Christin Fecker, Andreas Glo
and Marc D. Walter*
†
̈
ckner, Constantin G. Daniliuc, Matthias Freytag, Peter G. Jones,
Institut fu
Germany
̈
̈
r Anorganische und Analytische Chemie, Technische Universitat Braunschweig, Hagenring 30, 38106 Braunschweig,
*
S Supporting Information
ABSTRACT: The coordination chemistry of the enantiomerically pure
dimethylnopadienyl ligand (Pdl*) with early to late transition metals
is presented. Dimethylnopadiene is prepared by a Wittig reaction
from (1R)-(−)-myrtenal, which is readily available from the chiral
pool. Deprotonation of dimethylnopadiene with a Schlosser base gives
K(Pdl*), which is a good starting material for the preparation of the
5
early- to late-transition-metal open metallocenes [M(η -Pdl*) ] (M =
2
5
5
7
5
Ti, V, Cr, Fe) and mono(pentadienyl) complexes [(η -Cp′)Fe(η -Pdl*)] (Cp′ = 1,2,4-(Me C) C H ), [(η -C H )Zr(η -Pdl*)],
3
3
5
2
7
7
4
5
and [(η -COD)Ir(η -Pdl*)]. These complexes have been fully characterized by several spectroscopic techniques, elemental analysis,
and X-ray crystallography. In all of these cases the Pdl* ligand exhibits excellent face selectivity upon metal coordination, because it
coordinates exclusively from the sterically less hindered site of the bicyclic ligand framework. Within the series of open metallocenes
M(η -Pdl*) ] (M = Ti, V, Cr, Fe) the open ferrocene is the least thermally stable molecule and degrades to iron metal in solution.
This instability is attributed to the severe steric demand of this ligand system in combination with the relatively small Fe center.
5
[
2
2
+
INTRODUCTION
enforced by an optically active pentadienyl ligand. Despite
these advantageous properties, it is remarkable that chiral
■
Metal cyclopentadienyl (Cp) and allyl complexes are well-known
and have attracted significant attention over the years. While the
cyclopentadienyl ligand is one of the most prominent spectator
ligands in organometallic chemistry, the allyl ligand is often used
in synthetic and catalytic applications. However, pentadienyls
Pdl) are well-established ligands for transition-metal complexes
and they are interesting, as they can be considered as “open”
cyclopentadienyl congeners. In contrast to cyclopentadienyl,
this class of ligands can readily adopt multiple hapticities. This
13
pentadienyl complexes have not been explored extensively. In
contrast, enantiomerically pure cyclopentadienyl ligands have
14
been known since 1978, and their development was primarily
motivated by the belief that such ligands could play a valuable
role in catalytic enantioselective synthesis, particularly for
reactions or substrates where chiral phosphines are ineffective.
To date, considerable success has been achieved with chiral
metallocene complexes that catalyze the polymerization of
1
(
2
−9
1
3
5
15,16
17
ability to isomerize between the η , η , and η coordination
modes may be very beneficial chemically as well as catalytically,
offering great flexibility to facilitate ligand association and
dissociation processes in a manner similar to that displayed by
alkenes,
the hydrogenation of nonfunctionalized alkenes,
18
and the hydrosilylation of ketones and act as chiral Lewis acid
19
catalysts.
Over the years a large number of pentadienyl complexes have
been prepared, but these investigations have mainly focused on
the parent ligand, C H , or alkyl- or trimethylsilyl-substituted
1
0−12
5
indenyl ligands.
Since the η -bound pentadienyl is a better
chelate than allyl, a wide variety of thermally stable complexes are
accessible. In comparison to the cyclopentadienyl ring, the open
pentadienyl system is a stronger δ acceptor for geometric and
5
7
derivatives such as 2,4-dimethylpentadienyl (2,4-Me C H ) and
2
5
5
2−9
1
,5-(Me Si) C H . Additionally, a number of so-called edge-
bridged pentadienyl ligands such as cyclooctadienyl are known.
6
3 2 5 4
electronic reasons. With the open edge, the area enclosed by
20
five pentadienyl carbon atoms is much larger than that of the
cyclopentadienyl ring and the bond formation to these widely
spread carbon atoms requires the metal atom to move more
closely to the pentadienyl plane, thereby enhancing the orbital
overlap. The pentadienyl LUMO is of low energy and is well
suited for δ-type back-bonding interactions with metal orbitals
of matching symmetry. If the terminal carbon atoms of the
pentadienyl system approach each other, the LUMO is shifted to
higher energy, because the corresponding orbital lobes are out of
phase. These stronger bonding interactions in comparison to the
cyclopentadienyl ligand might facilitate chiral introduction
However, the only enantiomerically pure pentadienyl ligand
reported in the literature is dimethylnopadienyl (Pdl*), which has
5
been used to prepare the half-open ruthenocene [(η -C Me )-
5
5
5
13
Ru(η -Pdl*)]. Intrigued by this fact, we set out to explore the
coordination chemistry of this ligand in greater detail. Herein, we
report on the preparation and characterization of chiral open
metallocenes with early to late transition metals and present a
Received: December 10, 2012
Published: January 30, 2013
©
2013 American Chemical Society
874
dx.doi.org/10.1021/om301189g | Organometallics 2013, 32, 874−884

Organometallics
Article
Scheme 1
Table 1. Crystallographic Data
4
5
6
7
8
9
10
11
chem formula
formula mass/amu
cryst syst
a/Å
C H KO
C H Ti
C H V
C H Cr
C H Fe
C H Fe
C H Zr
C H Ir
21 31
2
5
43
6
26 38
26 38
26 38
26 38
30 48
20 26
478.69
398.46
401.50
402.56
406.41
464.53
357.63
475.66
orthorhombic
9.6598(3)
13.2279(3)
20.7805(7)
90
orthorhombic
12.1532(2)
14.9904(4)
24.2244(6)
90
orthorhombic
12.0837(2)
14.9805(2)
24.2167(2)
90
orthorhombic monoclinic
orthorhombic
9.5922(2)
14.8818(4)
18.3651(4)
90
orthorhombic monoclinic
12.0216(2)
14.8368(2)
24.5563(2)
90
8.7907(2)
11.5333(2)
11.5809(2)
90
8.0907(2)
10.9532(2)
18.8076(4)
90
8.3693(2)
24.3239(2)
9.5464(2)
90
b/Å
c/Å
α/deg
β/deg
90
90
90
90
111.230(2)
90
90
90
115.328(2)
90
γ/deg
unit cell vol/Å3
90
90
90
90
90
90
2655.29(14)
100(2)
4413.23(18)
100(2)
4383.70(10)
100(2)
4379.91(10)
100(2)
P2 2 2
1094.45(4)
100(2)
P21
2621.60(11)
100(2)
1666.71(6)
100(2)
P2 2 2
1756.59(6)
100(2)
P21
temp/K
space group
P2 2 2
P2 2 2
P2 2 2
P2 2 2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1 1 1
no. of formula units
per unit cell, Z
4
8
8
8
2
4
4
4
radiation type
Mo Kα
0.235
Mo Kα
0.396
Cu Kα
3.807
Cu Kα
4.322
Cu Kα
5.548
Mo Kα
0.590
Mo Kα
0.652
Mo Kα
7.597
−
1
abs coeff, μ/mm
no. of rflns measd
no. of indep rflns
Rint
93305
6551
165691
10516
0.0844
0.0347
76005
8976
84454
8931
10522
3548
101445
6242
66370
4670
82625
8312
0.0651
0.0371
0.0297
0.0187
0.0331
0.0197
0.0223
0.0243
0.0633
0.0279
0.0308
0.0142
0.0236
0.0236
final R1 values
(
I > 2σ(I))
2
final wR2(F ) values
0.0683
0.0553
0.0743
0.0652
0.0458
0.0684
0.0501
0.0188
0.0502
0.0521
0.0199
0.0522
0.0615
0.0248
0.0619
0.0594
0.0334
0.0614
0.0350
0.0149
0.0353
0.0128
0.0130
0.0305
(
I > 2σ(I))
final R1 values
all data)
(
2
Final wR2(F ) values
all data)
(
Flack parameter
goodness of fit on F
Δρ/e Å−
0.00(3)
−0.017(13)
1.042
0.000(2)
1.039
−0.002(2)
1.026
−0.008(2)
1.055
−0.022(10)
1.045
−0.010(18)
1.061
−0.003(4)
1.158
2
1.015
3
0.171/−0.182
0.265/−0.218
0.182/−0.169
0.180/−0.259 0.227/−0.273 0.314/−0.218
0.269/−0.186 0.920/−0.685
5
comparison to the nonchiral analogues [M(η -Pdl) ] and the
lithium pentadienyl complex [(tmeda)Li(1,5-(Me Si) -3-
3 2
2
5
22
5
classical metallocenes [M(η -Cp) ].
(MeOC H )C H )]. In [(tmeda)K(η -2,4-Me C H )] the
2
2 4 5 4 2 5 5
5
U-shaped η -2,4-dimethylpentadienyl anion is coordinated by
two potassium cations to form a zigzag polymeric chain in the
solid state. Unfortunately, the same crystallization strategy
failed to provide single crystals of 3. Therefore, to increase the
solubility of 3 in noncoordinating hydrocarbon solvents and also
to derive structural information, the crown ether 18-crown-6 was
RESULTS AND DISCUSSION
■
21
Ligand Synthesis. The natural product (1R)-(−)-myrtenal
1) was treated with the Wittig salt [Ph PCH(CH ) ]I and
(
3 3 2
NaNH to give the enantiomerically pure dimethylnopadiene
2
1
3
(
(
2). Deprotonation of 2 with potassium tert-pentoxide
t
added to a suspension of 3 in toluene and [K(18-crown-6)-
KO Pe) and n-butyllithium (n-BuLi) yields the potassium
5
(
η -Pdl*)] (4) was isolated as orange single crystals (Table 1).
salt K(Pdl*) (3) as an extremely pyrophoric yellow powder
Scheme 1). Alternatively, a traditional Schlosser base (KO Bu
t
An ORTEP diagram of 4 is shown in Figure 1, and selected
bond distances and angles are given in the figure caption. The
(
and n-BuLi) can also be used to deprotonate 2. However, the low
+
t
pentadienyl anion is coordinated to one K cation in a U-shaped
solubility of KO Bu in aliphatic solvents can cause product
5
η -coordination mode, and the 18-crown-6 ether prevents the
contamination with unreacted KOtBu and this problem is
t
formation of a polymeric chain structure. The C−C distances
(C1−C5) within the pentadienyl system exhibit a distinct short−
long−long−short pattern, and the central carbon atom C3 has
the shortest distance to the metal center: 3.0923(16) Å. The
other distances are progressively longer: 3.1156(16) Å (C2),
3.1694(18) Å (C1), 3.2332(16) Å (C4), and 3.3063(18) Å (C5).
These observations are consistent with a substantial contribution
of the resonance structure (a) shown in Figure 2. The distance
between the terminal carbon atoms C1 and C5 is 3.255 Å, and
the metal−(ligand plane) separation is 2.758 Å.
overcome by the very soluble KO Pe derivative. In addition, salt
t
metathesis reactions with 3 prepared from KO Pe and n-BuLi are
cleaner and give increased yields.
Compound 3 is soluble in coordinating solvents, such as
tetrahydrofuran, in which it forms dark red solutions, but it is
only sparingly soluble in aromatic hydrocarbons and insoluble
in aliphatic hydrocarbons. It is interesting to note that only
very few group 1 complexes with pentadienyl fragments have
5
been structurally authenticated, such as [(tmeda)K(η -2,4-
2
1
Me C H )] and more recently the donor-functionalized
2
5
5
8
75
dx.doi.org/10.1021/om301189g | Organometallics 2013, 32, 874−884

Organometallics
Article
1
3
1
Table 3. C{ H} NMR Data of 3, 4, 5 (Major), 5′ (Minor),
and 8−11 at Ambient Temperature in C D
6
6
compd
C1
C2
C3
C4
C5
a
3
4
5
5
8
9
1
1
75.7
77.5
64.2
68.4
46.0
43.0
78.0
51.7
143.0
143.0
118.3
113.1
98.7
82.5
83.1
149.4
150.1
134.3
136.6
115.2
111.5
144.4
122.9
84.1
82.0
87.5
86.7
67.9
54.3
86.0
48.5
(major)
112.6
114.8
84.1
b′ (minor)
89.8
82.0
0
1
129.9
99.3
93.6
96.4
a
b
In THF-d . In C H .
8
7
8
Figure 1. ORTEP diagram of 4 with thermal displacement parameters
drawn at the 50% probability level. Selected bond lengths (Å) and angles
18-electron rule. Because of the straightforward synthesis, most
studies on open metallocenes have focused on the 2,4-
3
,4,6,7,27−30
(
deg): K−O(18-C-6) = 2.8242(11)−3.0343(12), K−C1 = 3.1693(18),
dimethylpentadienyl ligand, 2,4-Me C H .
However,
2
5
5
K−C2 = 3.1156(16), K−C3 = 3.0923(16), K−C4 = 3.2332(16),
K−C5 = 3.3063(18), C1−C2 = 1.369(3), C2−C3 = 1.423(2), C3−C4 =
1
the preparation of other open metallocenes of the first-row
transition metals with the sterically more demanding and chiral
pentadienyl ligand 3 should also be feasible.
.418(2), C4−C5 = 1.371(2); C1−C2−C3 = 128.04(17), C2−C3−
C4 = 129.62(16), C3−C4−C5 = 131.00(15).
Open Titanocene/Vanadocene/Chromocene. The reaction
of [TiCl (thf) ] or [VCl (thf) ] with 3 equiv of 3 in a toluene/
3
3
3
3
THF solvent mixture gives deep green solutions (Scheme 2).
5
Single crystals of the open titanocene [Ti(η -Pdl*) ] (5) and open
2
5
vanadocene [V(η -Pdl*) ] (6) were grown from concentrated
2
pentane solutions at −30 °C. The reduction of the metal(III)
chloride to a divalent species is induced by 1 equiv of 3, which
presumably results in the corresponding coupled bis(pentadiene),
Figure 2. Resonance structures of a metal-bound pentadienyl ligand.
1
13
1
30
The H and C{ H} NMR spectra of 3 and 4 were recorded in
THF-d and C D , respectively (see Tables 2 and 3). The crown
as in many other cases. In addition, we have found that the
5
analogous open chromocene [Cr(η -Pdl*) ] (7) can readily be
8
6
6
2
1
ether in 4 exhibits a single resonance at δ 3.23 and 70.0 in the H
prepared as a green crystalline compound starting from CrCl and
2
13
1
and C{ H} NMR spectra, respectively. The terminal hydrogen
atom H5 is observed as a multiplet at δ 4.39−4.44, whereas those
for the terminal carbon atom C1 and the central carbon atom C3
are shifted further downfield (H1a, 4.03 ppm; H1b, 3.81−3.85 ppm;
H3, 3.74 ppm). This observation is consistent with the resonance
structure shown in Figure 2a.
2 equiv of 3. These open metallocenes 5−7 are air and moisture
sensitive but can be stored without degradation under a dry
nitrogen atmosphere.
The open sandwich structure of these molecules was
confirmed by single-crystal X-ray diffraction studies. Complexes
5−7 are isostructural and crystallize in the orthorhombic space
group P2 2 2 with two independent molecules in the
No trace of the other possible diastereomer, in which the metal
coordinates from the sterically more hindered site, was detected
by NMR spectroscopy. This is accord with the coordination
1
1 1
asymmetric unit (Table 1). The open metallocenes 5−7 have
approximate (noncrystallographic) C symmetry; as a represen-
2
23
chemistry developed for the dimethylnopadiene ligand, since
in most cases the neutral ligand and its functionalized derivatives
react with complete diastereoselectivity to produce only a single
transition-metal complex. Paquette and co-workers reported a
similar π-facial selectivity with respect to Diels−Alder cyclo-
additions and metallocene formation of related cyclopentadienyl
tative example, the molecular structure of 5 is shown in Figure 3
and selected bond distances and angles are given in Table 4 (see
the Supporting Information for the molecular structures of 6
and 7, Figures S1 and S2). To the best of our knowledge, these
complexes represent the first structurally characterized enantio-
merically pure open metallocenes.
To differentiate the mutual orientations of two pentadienyl
moieties, the conformation angle χ is defined as the angle
between the two planes (centroid (C1−C5)−C3−M) and
(centroid (C14−C18)−C16−M) (Scheme 3). In 5 the
2
4−26
ligands.
5
Preparation of [M(η -Pdl*) ] Complexes. In contrast to
their Cp analogues, open metallocenes of the first-row elements
2
can exhibit enhanced stability even when they do not obey the
1
Table 2. H NMR Data of 3, 4, 5 (Major), 5′ (Minor), and 8−11 at Ambient Temperature in C D
6
6
compd
H1a (endo)
H1b (exo)
H3
H5
a
3
4
5
5
8
9
1
1
2.76, “d”, 1 H, J = 2.76 Hz
4.03, “d”, 1 H, J = 3.26 Hz
−1.35, “d”, 2 H, J = 5.27 Hz
1.81−1.80, m, 2 H
−2.07, br s, 2 H
−1.21, “d”, 1 H, J = 3.52 Hz
1.87−1.82, m, 1 H
3.27−3.22, m, 1 H
3.85−3.81, m, 1 H
3.11, “d”, 1 H, J = 2.01 Hz
3.74, “d”, 1 H, J = 2.01 Hz
6.32, “d”, 2 H, J = 2.51 Hz
6.58, “d”, 2 H J = 2.26 Hz
4.09, br s, 2 H
3.78−3.73, m, 1 H
4.44−4.39, m, 1 H
(major)
0.56, dd, 2 H, J = 5.15 Hz, J = 2.64 Hz
3.50, dd, 2 H, J = 5.64 Hz, J = 2.38 Hz
1.17−0.99, m, 2 H
1.91, “d”, 2 H, J = 3.76 Hz
−1.28, “d”, 2 H, J = 5.77 Hz
2.14−1.98, m, 2 H
0.32, “d”, 1 H, J = 7.28 Hz)
2.78, “d”, 1 H, J = 4.9 Hz
1.73−1.66, m, 1 H
b′ (minor)
2
4
3.05, dd, 1 H, J = 3.60 Hz, J = 1.40 Hz
5.44, s, 1 H
0
1
3.81, s, 1 H
3.84, m, 1 H
1.86−1.83, m, 1 H
3.62, “t”, 1 H, J = 1.64 Hz
5.42−5.39, m, 1 H
a
b
In THF-d . In C H .
8
7
8
8
76
dx.doi.org/10.1021/om301189g | Organometallics 2013, 32, 874−884

Organometallics
Article
Scheme 2
Figure 3. ORTEP diagrams of 5 (left) and 8 (right) with thermal displacement parameters drawn at 50% probability. Only one of the two independent
molecules in the asymmetric unit is shown for 5.
Table 4. Selected Bond Distances (Å) and Angles (deg) for 5−8
5
5
5
5
[
Ti(η -Pdl*) ] (5)
[V(η -Pdl*) ] (6)
[Cr(η -Pdl*) ] (7)
[Fe(η -Pdl*) ] (8)
2
2
2
2
Molecule 1
χ
84.7
82.0
84.2
72.5
M−C(1/14)
M−C(2/15)
M−C(3/16)
M−C(4/17)
M−C(5/18)
M−C(av)
2.2264(18)/2.2246(18)
2.2698(17)/2.2809(18)
2.2912(17)/2.3019(18)
2.3050(17)/2.3000(17)
2.2370(17)/2.2894(18)
2.273 ± 0.032
2.1803(11)/2.1809(11)
2.2434(11)/2.2462(11)
2.2604(11)/2.2583(11)
2.2672(11)/2.2537(10)
2.2027(11)/2.2485(11)
2.234 ± 0.032
2.1928(12)/2.1968(12)
2.2124(11)/2.2004(12)
2.1997(12)/2.1952(12)
2.2115(11)/2.2059(11)
2.2144(12)/2.2470(11)
2.208 ± 0.016
2.134(2)/2.134(2)
2.0688(18)/2.0642(18)
2.0698(17)/2.0702(17)
2.1162(16)/2.1155(16)
2.1961(17)/2.1957(17)
2.117 ± 0.043
a
M−Pdl*plane
C(1/14)−C(5/18)
1.585/1.542
1.5046/1.5401
1.538/1.553
1.494/1.492
b
3.166/3.208
3.123/3.095
3.0227/3.0207
2.847/2.853
c
Molecule 2
χ
86.1
87.4
89.0
M′−C′(1/14)
M′−C′(2/15)
M′−C′(3/16)
M′−C′(4/17)
M′−C′(5/18)
M′−C′(av)
2.2117(18)/2.2182(17)
2.2762(17)/2.2610(17)
2.2872(18)/2.2722(18)
2.2790(17)/2.2836(16)
2.2684(18)/2.2801(18)
2.264 ± 0.027
2.1694(11)/2.1820(11)
2.2487(11)/2.2290(10)
2.2517(11))/2.2338(11)
2.2324(10)/2.2401(10)
2.2298(11)/2.2426(11)
2.226 ± 0.028
2.1847(11)/2.1929(11)
2.2036(12)/2.1907(11)
2.1917(11)/2.1726(11)
2.1862(11)/2.1910(11)
2.2305(12)/2.2466(11)
2.199 ± 0.023
a
M−Pdl*plane
C′(1/14)−C′(5/18)
1.560/1.579
1.5177/1.5427
1.542/1.556
b
3.140/3.109
3.102/3.064
3.0012/2.9850
a
b
M−Pdl*
is defined as the distance between the metal atom and the plane formed by C1−C5 and C14−C18, respectively. C(1/14)−C(5/18)
plane
c
describes the distance of the open edges of the Pdl* ligand, i.e. the distances between C(1) and C(5) and C(14) and C(18), respectively. The prime
′) denotes the second independent molecule in the asymmetric units.
(
orientation of the pentadienyl fragments is approximately
staggered with χ = 84.7 and 86.1° for both independent
molecules, respectively. For 6 and 7 the conformation angles are
indicates a rather flat potential energy surface with respect to the
conformation angle χ.
The carbon atoms of the pentadienyl fragments (C1−C5/
C1′−C5′ and C14−C18/C14′−C18′) lie in an almost perfect
plane, but steric interactions between the two pentadienyl ligands
5
5
also very similar ([V(η -Pdl*) ]/[V′(η -Pdl*) ], χ = 82.0/87.4°;
2
2
5
5
[
Cr(η -Pdl*) ]/[Cr′(η -Pdl*) ], χ = 84.2/89.0°). Overall, this
2
2
8
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dx.doi.org/10.1021/om301189g | Organometallics 2013, 32, 874−884

Organometallics
Article
Scheme 3
are responsible for a pronounced tilting of the two ligand planes
with respect to each other. The tilt angles α for the two
independent molecules of 5 in the asymmetric unit are 18.7 and
the presence of another diastereomer in which the titanium is
coordinated to the more sterically hindered site of the pentadienyl
ligand (i.e., syn to the CMe bridge). The terminal hydrogen atom
2
1
3.4°, respectively. However, for 6 and 7 the α values are
H5 (major) is observed as a pseudodoublet at δ 1.91, whereas the
signal for the terminal hydrogen atom H5′ (minor) is shifted
further upfield (δ −1.28). The protons attached to the terminal
carbon atom C1 have also very different chemical shifts in both
isomers δ −1.35 (H1a-major) and 0.56 (H1b-major), in
comparison to δ 1.81 (H1a′ minor) and 3.50 (H1b′ minor).
VT NMR studies were carried out on 5 to investigate if these two
isomers interconvert on the NMR time scale. However, no
5
5
significantly smaller ([V(η -Pdl*) ]/[V′(η -Pdl*) ], α = 14.7/
2
2
5
5
1
0.6°; [Cr(η -Pdl*) ]/[Cr′(η -Pdl*) ], α = 15.4°/11.3°). In
2
2
addition, the methyl (β-Me) groups at the C2/C2′ and C15/
C15′ positions are rotated slightly out of the ligand plane
toward the metal atom to realize a better metal−ligand overlap
5
5
5
(
[Ti(η -Pdl*) ]/[Ti′(η -Pdl*) ], β-Me-2 = 8.8/8.4°; [V(η -
2
2
5
5
Pdl*) ]/[V′(η -Pdl*) ], β-Me-2 = 8.9/5.0°; [Cr(η -Pdl*) ]/
2
2
2
5
5
5
1
[
Cr′(η -Pdl*) ], β-Me-2 = 8.3/6.8°; [Ti(η -Pdl*) ]/[Ti′(η -
significant line broadening of the H NMR resonances was
2
2
5
5
Pdl*) ], β-Me-15 = 11.2/7.2°; [V(η -Pdl*) ]/[V′(η -Pdl*) ],
observed when the sample was heated to 90 °C, but exchange
peaks between these isomers can be identified in an EXSY NMR
experiment (Figure 4). This suggests that these two species are
2
2
2
5
5
β-Me-15 = 7.2/6.5°; [Cr(η -Pdl*) ]/[Cr′(η -Pdl*) ], β-Me-15 =
2
2
9
.4/6.8°). Furthermore, the distances between the terminal
carbon atoms C1−C5/C1′−C5′ and C14−C18/C14′−C18′ are
significantly longer than the ca. 1.40 Å edge length of a cyclo-
pentadienyl ligand. In addition, the average separation between
the terminal carbon atoms decreases smoothly from 3.156 Å for
5
5
[
[
Ti(η -Pdl*) ] to 3.096 Å for [V(η -Pdl*) ] and 3.007 Å for
2
2
5
Cr(η -Pdl*) ]. This difference can be explained by the smaller
2
31
atomic radii of the last two. However, as a direct geometric
consequence the pentadienyl planes C1−C5/C1′−C5′ and
C14−C18/C14′−C18′ must approach the metal center more
closely in order to realize comparable M−C bond distances as in
classic metallocenes. The average Ti−C distances are 2.273(32)/
2
.264(27) Å and are longer than in 6 (2.234(33)/2.226(28) Å)
and 7 (2.208(16)/2.199(23) Å). It is instructive to compare the
metal−ligand plane separations in these open metallocenes to
those of the corresponding metallocenes. These distances are
1
1
.522/1.530 Å for 6 and 1.546/1.549 Å for 7 in comparison to
5
5
.928(6) and 1.798(4) Å for [V(η -C H ) ] and [Cr(η -C H ) ],
5
5 2
5
5 2
5
respectively. [Cr(η -C H ) ] and 7 have two unpaired electrons
5
5 2
(
S = 1). The difference between the open vanadocene and
5
[
V(η -C H ) ] is quite remarkable but can be rationalized by the
5 5 2
different spin states of these molecules. The low-spin configura-
tion of 6, μ (300 K) = 2.1 μ , results in stronger metal−
eff
B
pentadienyl bonds (see the Supporting Information for details,
1
Figure 4. H EXSY NMR spectrum of 5 recorded at 90 °C in C D . The
Figure S3). This is also reflected in substantially shorter average
7
8
5
prime (′) denotes resonances corresponding to the minor isomer 5′.
V−C distances in 6 in comparison to those in [V(η -C H ) ]
5
5 2
3
2a
(
2.280(5) Å). However, shorter V−C distances for pentadienyl
vs cyclopentadienyl are also observed in the half-open vanadocene
(η -C H )V(η -C H )(L)] (L = CO, PEt ), which suggests
conformational isomers and that there is a significant barrier for
their interconversion. In addition, the ratio between 5 and 5′ is
temperature dependent and the minor isomer 5′ is favored when
the temperature is increased. The thermodynamic parameters of
this equilibrium (K = [5]/[5′]) were derived from the ln K vs
5
5
32b
[
5 7 5 5 3
that the bonding between V and pentadienyl is stronger
independent of spin states). The larger size and lower nuclear
(
charges of the early transition metals seem especially important
for generating stronger interactions with these metals.
eq
eq
−1
T
plot (see the Supporting Information for details): ΔH° =
1
13
1
The H and C{ H} NMR spectra of the diamagnetic open
−1.0(1) kcal/mol and ΔS° = 1.1(2) eu. The entropy value ΔS° is
close to zero and therefore consistent with an intramolecular
process. Unfortunately, attempts to obtain structural information
on the minor isomer by X-ray diffraction have so far been
unsuccessful.
titanocene 5 are interesting (see Tables 2 and 3), since two
different C -symmetric species, 5 (major) and 5′ (minor), are
2
observed in a 10:1 ratio in solution. These species are also present
in the crude reaction mixture. NOESY NMR experiments rule out
8
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Organometallics
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All attempts to coordinate PMe or CO to the open meta-
Scheme 4
3
llocenes 5−7 failed, and only unreacted starting material was
recovered. We attribute this to the significant steric hindrance
imposed by the pentadienyl ligand system and hence the effective
shielding of the metal atoms.
Open Ferrocene. The open ferrocene [Fe(η -Pdl*) ] (8)
5
2
suffers from a significantly reduced thermal stability, and metallic
iron is also formed during the synthesis of 8 starting from
[
FeBr (dme)] (dme = dimethoxyethane) and 2 equiv of 3 in
2
THF. Hence, crystals of 8 were only obtained in low yield from a
saturated pentane solution. It is noteworthy that crystallized 8
decomposes at ambient temperature in solution and that, even
in freshly prepared solutions, broadened NMR resonances are ob-
served because of the presence of iron nanoparticles. In view of the
1
5
33
synthesis of [Fe(η -C H P) ] from [Fe(η -2,4-Me C H ) ]
5
5
5
2
5
5 2
5
34
and [Fe(PF ) ] from [Fe(η -C H ) ], the open ferrocene 8
3
5
5
7 2
might also serve as a suitable precursor for the preparation of
low-valent iron complexes or nanoparticles under mild
3
5
5
conditions. Bis(pentadienyl)iron ([Fe(η -C H ) ]) and bis-
5
7 2
5
(
3-methylpentadienyl)iron ([Fe(η -3-C H ) ]) also form met-
6 9 2
29
1
allic iron particles, but at slower rates. The H NMR spectrum
of 8 displays the terminal hydrogen atom H5 as a multiplet at δ
1
.98−2.14. The hydrogen atom H3 is shifted downfield (δ 4.09),
whereas the terminal hydrogen atoms at C1 are shifted further
upfield (H1a, δ −2.07; H1b, δ 0.99−1.17) (see Tables 2 and 3). In
contrast to the other chiral open metallocenes 5−7, 8 crystallizes
in a different chiral space group (monoclinic, P2 ) with only one
1
molecule in the asymmetric unit (Table 1 and Figure 3), and
selected bond distances and angles are given in Table 4. The
conformation angle χ is, at 72.46°, very different from those
observed for 5−7. For comparison a nearly gauche-eclipsed
5
29
5
conformation is adopted in [Fe(η -2,4-Me C H ) ], [Fe(η -1-
2
5
5 2
36
5
37
Me Si-3-CH C H ) ], and [Fe(η -c-C H ) ] However, the
3
3
5
5 2
7
9 2
5
5
average Fe−C distance of 2.117(43) Å is significantly longer than
with those of Cp′, the half-open ferrocene [(η -Cp′)Fe(η -Pdl*)]
5
38
5
47
2
that in [Fe(η -C H ) ] (2.064(3) Å) and in the open ferrocene
(9) was prepared from [(η -Cp′)FeI] and 3 in THF (Scheme 4).
5
5 2
5
29
[
Fe(η -2,4-Me C H ) ] (2.089(3) Å), probably because of the
Despite the presence of two bulky π ligands, 9 exhibits an enhanced
thermal stability in comparison to the open ferrocene 8 and was
isolated in good yield.
2
5
5 2
steric strain imposed by the bulky pentadienyl ligand, Pdl*. For
the same reasons as discussed above, a very close approach of the
ligand plane to the metal is observed (1.493 Å), resulting in an
increased interligand repulsion in comparison to that in the
corresponding metallocenes. The van der Waals radii for carbon
The molecular structure of 9 is shown in Figure 5, and selected
bond distances and angles are given in the figure caption. The
carbon atoms of the pentadienyl (C1−C5) and the Cp′ (C14−
C18) fragments form almost perfect planes. To reduce the steric
interactions of the pentadienyl ligand with the sterically
demanding CMe groups, the two planes are tilted with respect
to each other by 7.3°. As shown for 8, the methyl group at the C2
position is displaced toward the iron center, but the tilt angle
39
atoms and methyl groups are 1.7 and 2.0 Å, respectively, and
.
..
therefore a series of nonbonded C C contacts (C1−C17 = 3.093
Å, C1−C16 = 3.256 Å, C2−C16 = 3.199 Å, C2−C15 = 3.24 Å,
C3−C15 = 3.181 Å, C3−C14 = 3.244 Å, C4−C14 = 3.079 Å,
C5−C18 = 3.098 Å, C8−C14 = 3.173 Å, C1−C21 = 3.169 Å) are
found in 8, which might explain the thermal instability and the
formation of iron metal. Steric repulsion has also been invoked for
3
(6.5°) is less pronounced than in 8. In contrast, the CMe groups
3
point away from the iron atom (by 12.7, 4.0, and 11.2°) to
minimize steric repulsions. The average Fe−C(Pdl*) bond
distance is 2.121(72) Å, longer than the Fe−C(Cp′) bond length
at 2.107(27) Å but quite similar to the 2.117(43) Å found in 8.
However, because of the unique properties of the pentadienyl
ligand, the metal−(ligand plane) separation for the pentadienyl
system (1.506 Å) is significantly shorter than for the cyclo-
•
the formation of the stable cyclopentadienyl radical [C (CHMe ) ]
5
2 5
40
from the reaction of FeCl with [Li(OEt )][C (CHMe ) ].
2
2
5
2 5
Half-Open Ferrocene. Half-open metallocenes offer the
possibility of direct comparison between conventional Cp
ligands and their open congeners within one molecule, thereby
revealing the unique properties of pentadienyl ligands. However,
the synthesis of half-open ferrocenes is usually hampered by the
fact that “CpFeX” complexes are thermodynamically unstable;
ligand redistribution to Cp Fe and FeX takes place, and a
12,37
pentadienylsystem(1.718Å), consistent with previous results.
In contrast to 8, H and C{ H} NMR spectra recorded in C D
1
13
1
6
6
solution are resolved (see Tables 2 and 3), and the terminal
hydrogen atom H5 is observed upfield at δ 0.32, whereas the
resonances for H1a and H1b are shifted to δ −1.21 and 3.05,
respectively.
2
2
mixture of compounds is usually obtained. In contrast, sterically
demanding cyclopentadienyl ligands kinetically stabilize “CpFeX”
complexes and facilitate the exploration of their reaction
4
1−49
Half-Open Trozircene. It was recently shown that [(η7-
C H )Zr(tmeda)Cl] is an ideal complex fragment for the
chemistry.
Cp′), which stabilizes unusual and low-coordinate molecules.
To compare the features of the chiral pentadienyl ligand (Pdl*)
Our ligand of choice is 1,2,4-(Me C) C H
3 3 5 2
4
6−54
(
7
7
incorporation of various monoanionic ligands, including achiral
8
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Organometallics
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The Zr−C distances are uniform and range between 2.335(11)
and 2.369(11) Å. In contrast, the Zr−C distances of the
pentadienyl system are different, with the shortest distance of
2
.429(10) Å being found between C10 and Zr, whereas the others
become progressively longer. This short−longer−longest pattern
is characteristic of pentadienyl ligands coordinated to a metal in a
high oxidation state, and it is also reflected in a typical short−
long−long−short pattern of the Pdl* C−C bond distances.
7
The (η -C H )Zr fragment provides an excellent platform to
7
7
5
assess the size of η -bound monoanionic ligands in a realistic
manner, and cone angle measurements on a series of [(η -
C H )Zr(η -L)] (L= Cp, Ind, pyrrolyl (Pyr), imidazolyl (Im))
complexes were undertaken.
7
5
7
7
6
1,65
For this purpose the angle θ,
which describes the size of the ligand in the xy dimension, was
61
defined. Interestingly, Pdl* is significantly larger than 2,4-
Me C H with θ = 134 vs 113°, and it is also slightly larger than
2
5
5
Figure 5. ORTEP diagram of 9 with thermal displacement parameters
drawn at the 50% probability level. Selected bond distances (Å) and angles
Cp′ ligand (θ = 133°).
Complex 10 and the other pentadienyl complexes are volatile
enough to obtain EI mass spectra and, in addition to the
(
deg): Pdl* ligand, Fe−C(1) = 2.0961(15), Fe−C(2) = 2.0602(15), Fe−
C(3) = 2.0753(15), Fe−C(4) = 2.1307(14), Fe−C(5) = 2.2410(16), Fe−
C(av) = 2.121 ± 0.072, Fe−plane(C(1)−C(5)) = 1.506; Cp′ ligand, Fe−
C(14) = 2.1375(15), Fe−C(15) = 2.1236(15), Fe−C(16) = 2.0863(15),
Fe−C(17) = 2.1132(14), Fe−C(18) = 2.0715(16), Fe−C(av) = 2.106 ±
molecular ion, species resulting from H loss were also observed,
2
suggesting a pentadienyl-to-cyclopentadienyl conversion (see
the Experimental Section for details). This is consistent with
previous experiments describing such a conversion under high-
0.027, Fe−plane(C(14)−C(18)) = 1.718; α(Pdl*−Cp′ planes) = 7.3.
6
6−70
energy conditions such as mass spectroscopy and thermolysis.
7
5
7
5
However, [(η -C H )Zr(η -C H )] converts to [(η -C H )Zr(η -
7
7
5
7
7
7
pentadienyl ligands, into the cycloheptatrienyl (Cht) coordina-
5
5−65
C H )] and H under relatively mild conditions on sublimation
5 5 2
55
tion sphere.
With the Pdl* ligand in hand, we set out to
or on heating in solution. Unfortunately, no pentadienyl-to-
cyclopentadienyl conversion was observed on heating of 10 in the
solid state at 120 °C for several weeks followed by sublimation.
extend this series to chiral derivatives. The potassium salt 3 reacts
cleanly with [Zr(η -C H )(Cl)(tmeda)] in THF to give [(η -
7
7
7
7
5
C H )Zr(η -Pdl*)] (10) as a wine red solid in moderate yield
7
7
Iridium(I) Pentadienyl Complex. Attempts to prepare
after sublimation at 135 °C (0.1 mbar) (Scheme 4). Single
5
open cobaltocenes [Co(η -Pdl) ] have been unsuccessful, and
2
crystals were grown from concentrated pentane solutions at
71
instead reduction to Co(I) has been observed. However,
cationic pentadienyl Co(III) complexes can be stabilized by a
η -C H )Co or (η -C Me )Co fragment.
−30 °C. The molecular structure of 10 is shown in Figure 6, and
5
5
72,73
(
For the heavier
5
5
5
5
cobalt congener iridium, iridium(I) heteropentadienyl com-
7
4
4
plexes such as [(η -COD)Ir(μ -1-2,5-η-CH CHCHCHSO)]
2
2
2
75
5
and cationic iridium(III) pentadienyl complexes such as [(η -
C H )Ir(η -C H Me -2,4)][BF ] have only recently been
5
5
5
5
5
2
4
reported.
Complex 3 was treated with [(η -COD)Ir(μ-Cl)] in THF,
4
2
4
5
forming the heteroleptic complex [(η -COD)Ir(η -Pdl*)] (11).
Single crystals were grown from concentrated pentane solution
at −30 °C (Scheme 4). Complex 11 crystallizes in space group
P2 with two independent, but similar, molecules in the
1
asymmetric unit. Figure 7 shows the molecular structure of one
of these independent molecules, and selected bond distances and
angles are given in the figure caption.
No COD replacement was observed on addition of PMe or
3
Figure 6. ORTEP diagram of 10 with thermal displacement parameters
drawn at the 50% probability level. Selected bond lengths (Å) and angles
tris(2,4,6-trimethoxyphenyl)-phosphine to 11. However, pre-
liminary experiments suggest that the COD moiety can be
replaced by CO, and further experiments regarding the reaction
chemistry are ongoing and will be reported in due course.
(
deg): Pdl* ligand, Zr−C(8) = 2.5994(11), Zr−C(9) = 2.5131(10),
Zr−C(10) = 2.4291(10), Zr−C(11) = 2.5513(10), Zr−C(12) =
2
2
C(3) = 2.3411(12), Zr−C(4) = 2.3353(11), Zr−C(5) = 2.3571(13),
Zr−C(6) = 2.3689(11), Zr−C(7) = 2.3361(12), Zr−C(av) = 2.353 ±
0
.6464(11), Zr−C(av) = 2.548 ± 0.083, Zr−plane(C(1)−C(5)) =
.019; Cht ligand, Zr−C(1) = 2.3682(12), Zr−C(2) = 2.3651(12), Zr−
CONCLUSIONS
A series of open metallocenes [M(η -Pdl*) ] (M = Ti, V, Cr, Fe)
■
5
2
5
5
.015, Zr−plane(C(1)−C(7)) = 1.690; α(Pdl*−Cht planes) = 21.6.
and mono(pentadienyl) complexes [(η -Cp′)Fe(η -Pdl*)]
7
5
(
Cp′ = 1,2,4-(Me C) C H ), [(η -C H )Zr(η -Pdl*)], and
3
3
5
2
7
7
4 5
selected bond distances and angles are given in the figure caption.
As was found for the half-open ferrocene, the Pdl* ligand
exclusively coordinates from the sterically less hindered site to
avoid repulsive interactions with the seven-membered Cht ring.
The carbon atoms C1−C7 of the Cht ligand form an almost
[(η -COD)Ir(η -Pdl*)] can be prepared with the enantiomeri-
cally pure dimethylnopadienyl ligand. It is noteworthy that, in
all of these complexes, the Pdl* ligand exhibits excellent face
selectivity upon metal coordination, since it coordinates ex-
clusively from the sterically less hindered site of the bicyclic
ligand framework. Because of the severe steric demand of Pdl* in
7
perfect plane and coordinate in a η fashion to the zirconium atom.
8
80
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Organometallics
Article
Synthesis of Dimethylnopadiene (2).
1
3
Compound 2 had been previously reported, but we utilized a slight
variation of the reported procedure for its isolation. A suspension of
[
Ph PCH(CH ) ]I (24.5 g, 56.7 mmol) and NaNH (2.21 g, 56.7
3 3 2 2
mmol) in THF (250 mL) was stirred at ambient temperature. The
suspension turned brown after a few minutes, and stirring was continued
for 4 h until no further NH evolution was observed. (1R)-(−)-Myrtenal
3
(
1; 8.51 g, 56.7 mmol) was added, and the solution was stirred for 12 h at
Figure 7. ORTEP diagram of 11 with thermal displacement para-
meters drawn at the 50% probability level. Selected bond lengths (Å)
and angles (deg) of molecule 1: Ir−C1 = 2.266(3), Ir−C2 = 2.249(3),
Ir−C3 = 2.302(3), Ir−C4 = 2.285(3), Ir−C5 = 2.193(3), Ir−C(av) =
ambient temperature. The orange solution was poured into a diethyl
ether/water mixture (100 mL/100 mL). The ether phase was separated,
and the water phase was extracted with three portions of diethyl ether
(30 mL). The collected organic phases were washed with a 40% aqueous
2
.259 ± 0.042, Ir−plane(C(1)−C(5)) = 1.634, C1−C2 = 1.369(3),
NaHSO solution (20 mL) and dried over NaHCO , yielding a pale
yellow solution. After removal of the solvent, pentane (250 mL) was
added to precipitate Ph PO. Filtration, removal of the solvent, and
column chromatography (silica) (pentane, R = 0.860) yielded a colorless
C2−C3 = 1.423(2), C3−C4 = 1.418(2), C4−C5 = 1.371(2); C1−C2−
3
3
C3 = 128.04(17), C2−C3−C4 = 129.62(16), C3−C4−C5 =
131.00(15).
3
f
oil. Yield: 8.16 g (46.3 mmol, 82%). Bp: 84−86 °C/7.9 mbar. Anal. Calcd
for C H : C, 88.56; H, 11.43. Found: C, 86.01; H, 10.88. The EI mass
1
3
20
1
combination with the relatively small Fe(II) ion, the open
ferrocene [Fe(η -Pdl*)] is thermally unstable and decomposes
to iron metal in solution. The synthesis of a myrtenal-derived
ligand library and its application in homogeneous catalysis are
ongoing and will be reported in due course.
spectrum showed a molecular ion at m/z 176 amu. GC: 22.64 min. H
5
NMR (400 MHz, CDCl , 298 K): δ 5.57−5.53 (m, 1 H, H3), 5.38−5.34
3
(
m, 1 H, H5), 2.42−2.37 (m, 1 H, H8a), 2.37−2.26 (m, 2 H, H6) 2.19
dt, 1 H, H9, J = 5.65 Hz, J = 1.51 Hz), 2.12−2.06 (m, 1 H, H7), 1.78 (br
(
s, 3 H, H1), 1.76 (br s, 3 H, H13), 1.23 (s, 3 H, H12), 1.21 (d, 1 H, H8b,
13
1
J = 8.53 Hz), 0.89 (s, 3 H, C-11) ppm. C{ H} NMR (101 MHz, CDCl ,
3
2
98 K): δ 145.7 (C, C4), 133.0 (C, C2), 126.4 (CH, C3), 120.7 (CH,
EXPERIMENTAL SECTION
■
C5), 47.0 (CH, C9), 40.8 (CH, C7), 37.9 (C, C10), 32.0 (CH , C6) 31.8
2
General Considerations. All experiments were carried out under
an atmosphere of purified nitrogen, either in a Schlenk apparatus or
in a glovebox. The solvents were dried and deoxygenated by distillation
under a nitrogen atmosphere from sodium benzophenone ketyl
(CH , C8), 27.0 (CH , C13), 26.6 (CH , C12), 21.4 (CH , C11), 20.1
2 3 3 3
(CH , C1) ppm. The EI mass spectrum showed a molecular ion at
3
m/z 177 amu. The parent ion isotopic cluster was simulated (calcd %,
obsd %): 176 (100, 100), 177 (14, 14).
(
(
tetrahydrofuran) and by a MBraun GmbH solvent purification system
Synthesis of K(pdl*) (3).
toluene, pentane). The following starting materials were prepared
76
77
5
47
5
according to the literature: CrCl , [FeBr (dme)], [(η -Cp′)FeI] ,
2
2
2
7
8
t
79
80
81
[
Ir(COD)Cl]2, KO Pe, [TiCl (thf) ], [VCl (thf) ], and [(η -
3
3
3
3
55
C H )Zr(tmeda)Cl]. Other commercial reagents such as n-BuLi
7
7
(
Acros), 18-crown-6 ether (Acros), [Ph PCH(CH ) ]I (Sigma
3 3 2
Aldrich), (1R)-(−)-myrtenal (1) (Sigma Aldrich), and NaNH
(
2
Acros) were used as received without further purification.
NMR spectra were recorded on a Bruker DRX 400 spectrometer at
00 MHz ( H) or 101 MHz ( C). All chemical shifts are reported in δ
1
13
A solution of potassium tert-pentoxide (4.08 g; 32.3 mmol) in pentane
4
(
3
(
250 mL) was prepared. At −78 °C dimethylnopadiene (2; 6.00 g,
4.0 mmol) was added to form a deep red suspension, to which n-BuLi
1.6 M in hexane, 22.3 mL, 35.7 mmol) was added. The reaction mixture
units with reference to the residual protons of the deuterated solvents,
which are internal standards, for proton and carbon chemical shifts. Gas
chromatography was performed with Hewlett-Packard (5890 Serie II),
using a 35 m × 0.25 mm glas capillary column coated with Cyclodex-B.
Magnetic susceptibility data were recorded from 5 to 300 K on a
was warmed to room temperature and stirred for 12 h at ambient
temperature. During this time the color of the mixture changed slowly to
yellow. After filtration, the yellow precipitate was washed with pentane
(3 × 30 mL) and dried under high vacuum. Yield: 7.23 g (33.72 mmol,
90%). Compound 3 was a highly pyrophoric yellow solid. Despite
several attempts, no reliable elemental analysis was obtained, but a
8
2
Quantum Design MPMS XL7 SQUID magnetometer. Elemental
analyses were performed on a vario MICRO cube elemental analyzer
MS Finnigan MAT 8400-MSS I and Finnigan MAT 4515).
X-ray Diffraction Studies. Data were recorded at 100 K on Oxford
(
1
Diffraction diffractometers using monochromated Mo Kα or mirror-
focused Cu Kα radiation (Table 1). The structures were refined
representative H NMR spectrum is shown in the Supporting
1
Information (Figure S5). H NMR (400 MHz, THF-d
, ambient): δ
8
83
anisotropically using the SHELXL-97 program. Hydrogen atoms at
C1, C3, and C5 of the pentadienyl ligands were located in difference
syntheses and refined isotropically, in some cases using distance
restraints. For 9 the hydrogens of the Cp′ ring and for 10 the hydrogens
of the C H ring were treated in the same way (for further details, see the
3.78−3.73 (m, 1 H, H5), 3.27−3.22 (m, 1 H, H1b), 3.11 (“d”, 1 H, H3,
J = 2.01 Hz), 3.08 (“d”, 1 H, H1a, J = 2.76 Hz), 2.58 (dt, 1 H, H6b, J =
15.81 Hz, J = 3.01 Hz), 2.46 (dt, 1 H, H6a, J = 15.73 Hz, J = 2.82 Hz),
2.26 (dt, 1 H, H8b, J = 8.20 Hz, J = 5.65 Hz), 2.07−1.99 (m, 1 H, H7),
1.78 −1.74 (m, 1 H, H9), 1.73 (s, 3 H, H13), 1.28 (d, 1 H, H8a, J =
7
7
1
3
1
Supporting Information). Other H atoms were included using rigid
methyl groups or a riding model. The absolute configuration was
confirmed by the Flack parameter.
8.28 Hz), 1.21 (s, 3 H, H12), 0.91 (s, 3 H, H11) ppm. C{ H} NMR
(101 MHz, THF-d , ambient): δ 149.4 (C, C4), 143.0 (C, C2),
8
84.1 (CH, C5), 82.5 (CH, C3), 75.7 (CH , C1), 53.9 (CH, C9), 42.5
2
8
81
dx.doi.org/10.1021/om301189g | Organometallics 2013, 32, 874−884

Organometallics
Article
(
CH, C7), 38.8 (C, C10), 32.99 (CH , C6), 32.97 (CH , C8), 28.2
green crystals (82 mg, 0.20 mmol, 43%). Mp: 178.4−178.5 °C. Anal.
2
2
(CH , C13), 27.3 (CH , C12), 21.8 (CH , C11) ppm.
Calcd for C H Cr: C, 77.57; H, 9.51. Found: C, 77.53; H, 9.51. The EI
3
3
3
26 38
Synthesis of (18-Crown-6)potassium Dimethylnopadienide
4). A saturated solution of 18-crown-6 (123 mg, 0.47 mmol) in toluene
0.5 mL) was added to 3 (100 mg, 0.47 mmol). A few drops of pentane
were carefully layered onto the toluene solution, and diffusive mixing at
30 °C overnight resulted in 48 mg (0.10 mmol, 22%) of red/orange
crystals. Anal. Calcd for C H O K: C, 62.73; H, 9.05. Found: C, 62.77;
mass spectrum (70 eV) showed a molecular ion at m/z 402 amu with the
following isotopic cluster distribution: 396 (1), 397 (1), 398 (4), 399 (1),
400 (13), 401 (5), 402 (100), 403 (41), 404 (11). Simulated distributions
(in %): for C H Cr, 400 (5), 401 (2), 402 (100), 403 (39), 404 (10);
(
(
26
38
−
for C H Cr, 398 (5), 399 (2), 400 (100), 401 (39), 402 (10); for
26 36
25
43
6
C H Cr, 396 (5), 397 (2), 398 (100), 399 (39), 400 (10).
26 34
1
5
H, 8.82. H NMR (400 MHz, C D , 298 K): δ 4.44−4.39 (m, 1 H, H5),
Synthesis of [Fe(η -Pdl*) ] (8). A solution of [FeBr (dme)] (143 mg,
6
6
2
2
4
1
.03 (“d”, 1 H, H1a, J = 3.26 Hz), 3.85−3.81 (m, 1 H, H1b), 3.74 (“d”,
H, H3, J = 2.01 Hz), 3.23 (s, 24 H, 18-crown-6), 3.15−3.01 (m, 2 H,
0.47 mmol) and 3 (200 mg, 0.93 mmol) in toluene (15 mL) and THF
(1 mL) was stirred for 4 h at ambient temperature and evaporated to
dryness. The brown solid residue was extracted with pentane (3 mL).
The extract was concentrated and cooled to −30 °C to give brown
crystals (54.2 mg, 0.13 mmol, 28%). Mp: 120 °C. Anal. Calcd for
H6), 2.55−2.46 (m, 2 H, H7 and H8a), 2.36 (br dt, 1 H, H9), 2.26 (s,
3
H11) ppm. C{ H} NMR (101 MHz, C D , ambient): δ 150.1 (C, C4),
H, H13), 1.89−1.82 (m, 1 H, H8b), 1.63 (s, 3 H, H12), 1.54 (s, 3 H,
13 1
6
6
1
1
43.0 (C, C2), 83.1 (CH, C3), 82.0 (CH, C5), 77.5 (CH , C1), 70.0
2
C H Fe: C, 76.84; H, 9.42. Found: C, 76.63; H, 9.61. H NMR (400
26
38
(
(
(
CH , 18-crown-6), 54.2 (CH, C9), 42.9 (CH, C7), 40.0 (C, C10), 33.9
2
MHz, C D , 298 K): δ 4.09 (br s, 2 H, H3), 2.92 (“d”, 2 H, H6, J = 15.08
7 8
CH , C6), 31.4 (CH , C8), 29.6 (CH , C13), 28.0 (CH , C12), 22.1
2
2
3
3
Hz), 2.54 (br s, 4 H, H6 and H8), 2.26 (br s, 2 H, H9), 2.19 (“s”, 2 H,
H7), 2.14−1.98 (m, 4 H, H5 and H8), 1.91 (br s, 6 H, H13), 1.44 (br s,
6 H, H12), 1.17−0.99 (m, 8 H, H1b and H11), −2.07 (br s, 2 H, H1a)
ppm. 13C{ H} NMR (101 MHz, C D , 298 K): δ 115.2 (2 C, C4), 98.7
CH , C11) ppm.
3
5
Synthesis of [Ti(η -Pdl*) ] (5). A solution of [TiCl (thf) ] (115 mg,
.31 mmol) and 3 (200 mg, 0.93 mmol) in toluene (15 mL) and THF
2
3
3
1
0
7
8
(
1 mL) was stirred for 4 h at ambient temperature and evaporated to
(
(
(
2 C, C2), 84.1 (2 CH, C3), 67.9 (2 CH, C5), 51.7 (2 CH, C9), 46.0
dryness. The solid residue was extracted with pentane (3 mL), and the
2 CH , C1), 42.2 (2 CH, C7), 38.7 (2 C, C10), 36.2 (2 CH , C8), 32.7
2
2
filtered extract was concentrated and cooled to −30 °C to give green
2 CH , C6), 26.7 (2 CH , C12), 25.9 (2 CH , C13), 22.1 (2 CH , C11)
2
3
3
3
crystals (75 mg, 0.189 mmol, 61%). Anal. Calcd for C H Ti: C, 78.37;
26
38
ppm. The EI mass spectrum (70 eV) showed a molecular ion at m/z
06 amu with the following isotopic cluster distribution: 402 (7), 403
H, 9.61. Found: C, 77.89; H, 9.27. The NMR spectra showed two
4
1
isomers 5 and 5′ in the ratio 10:1. H NMR (400 MHz, C D , 298 K,
6
6
(1), 404 (20), 405 (3), 406 (100), 407 (25), 408 (3). Simulated distribu-
tions (in %): for C H Fe, 404 (6), 405 (2), 406 (100), 407 (30), 408
major product (5)): δ 6.32 (d, 2 H, H3, J = 2.51 Hz), 2.97 (dt, 2 H, H9,
J = 5.71 Hz, J = 1.17 Hz), 2.93−2.82 (m, 4 H, H6), 2.14 (“sept”, 2 H, H7,
J = 2.89 Hz”), 2.04 (“dt”, 2 H, H8b, J = 9.29 Hz, J = 5.96 Hz), 1.91 (“d”, 2
H, H5, J = 3.76 Hz), 1.85 (s, 6 H, H13), 1.80 (s, 6 H, H11), 1.49 (s, 6 H,
H12), 0.56 (dd, 2 H, H1b, J = 5.15 Hz, J = 2.64 Hz), −0.78 (d, 2 H, H8a,
26
38
(
4); for C H Fe, 402 (6), 403 (2), 404 (100), 405 (30), 406 (4); for
26 36
C H Fe, 400 (6), 401 (2), 402 (100), 403 (30), 404 (4).
2
6
34
5
5
Synthesis of [(η -Cp′)Fe(η -Pdl*)] (9).
13
1
J = 9.29 Hz), −1.35 (d, 2 H, H1a, J = 5.27 Hz) ppm. C{ H} NMR (101
MHz, C D , 298 K): δ 134.3 (2 C, C4), 118.3 (2 C, C2), 112.6 (2 CH,
6
6
C3), 87.5 (2 CH, C5), 64.2 (2 CH , C1), 55.4 (2 CH, C9), 40.9 (2 CH,
2
C7), 39.5 (2 C, C10), 33.8 (2 CH , C8), 32.5 (2 CH , C6), 28.7 (2 CH ,
2
2
3
1
C13), 26.5 (2 CH , C12), 22.7 (2 CH , C11) ppm. H NMR (400 MHz,
3
3
C D , 298 K, minor product (5′)): δ 6.58 (d, 2 H, H3′, J = 2.26 Hz), 3.50
6
6
(
dd, 2 H, H1b′, J = 5.64 Hz, J = 2.38 Hz), 2.59 (s, 6H, H13′), 2.38 (dt, 2
H, H9′, J = 5.64 Hz, J = 1.16 Hz), 1.88−1.86 (m, 2 H, H8b′), 1.81 − 1.80
(
(
m, 2 H, H1a′), 1.68−1.63 (m, 2 H, H7′), 1.63−1.50 (m, 4 H, H6′), 1.22
s, 12 H, H11′ and H12′), −1.17 (d, 2 H, H8a′, J = 9.03 Hz), −1.28 (d, 2
13
1
H, H5′, J = 5.77 Hz) ppm. C{ H} NMR (101 MHz, C D , 298 K): δ
1
6
3
6
6
36.6 (2 C, C4′), 114.8 (2 CH, C3′), 113.1 (2 C, C2′), 86.7 (2 CH, C5′),
8.4 (2 CH , C1′), 55.0 (2 CH, C9′), 40.6 (2 CH, C7′), 38.3 (2 C, C10′),
2
6.1 (2 CH , C8′), 31.2 (2 CH , C6′), 29.1 (2 CH , C13′), 26.3 (2 CH ,
2
2
3
3
C11′ or C12′), 22.2 (2 CH , C12′ or C11) ppm. The EI mass spectrum
To a solution of 3 (33 mg, 0.154 mmol) in THF (15 mL) was added a
3
5
(
70 eV) showed a molecular ion at m/z 398 amu with the following
isotopic cluster distribution: 392 (5), 393 (2), 394 (9), 395 (4), 396
19), 397 (15), 398 (100), 399 (32), 400 (12), 401 (2). Simulated
distributions (in %): for C H Ti, 396 (11), 397 (13), 398 (100), 399
solution of [(η -Cp′)FeI] (64 mg, 0.077 mmol) in THF (5 mL). The
2
mixture was stirred for 4 h at room temperature. The brown solution was
separated from a light yellow precipitate by filtration, the solvent was
removed under dynamic vacuum, and the remaining solid was extracted
with pentane (3 mL). The extracts were cooled overnight at −30 °C to
yield brown-red crystals (51 mg, 0.109 mmol, 71%). Mp: 174.2−
(
26
38
(
3
(
35), 400 (13), 401 (2); for C H Ti, 394 (11), 395 (13), 396 (100),
26 36
97 (35), 398 (13), 399 (2); for C H Ti, 392 (11), 393 (13), 394
26 34
100), 395 (35), 396 (13), 397 (2).
175.0 °C. Anal. Calcd for C30
H48Fe: C, 77.23; H, 10.80. Found: C,
5
1
Synthesis of [V(η -Pdl*) ] (6). A solution of [VCl (thf) ] (116 mg,
77.16; H, 10.00. H NMR (400 MHz, C , ambient): δ 5.44 (s, 1 H,
D
6 6
2
3
3
0
4
.31 mmol) and 3 (200 mg, 0.93 mmol) in THF (15 mL) was stirred for
H3), 3.91 (d, 1 H, H17 or C24, J = 2.20 Hz), 3.05 (dd, 1 H, H1b, J = 3.60
Hz, J = 1.40 Hz), 2.54−2.42 (m, 3 H, H6, H8 and H9), 2.27 (d, 1 H, H17
or H24, J = 2.08 Hz), 2.04 (s, 3 H, H13), 1.89−1.99 (m, 2 H, H6 and
H7), 1.85 (s, 1 H, H8), 1.83 (s, 9 H, H20 or H23), 1.49 (s, 9 H, H23 or
H20), 1.32 (s, 3 H, H11 or H12), 1.16 (s, 9 H, H16), 0.82 (s, 3 H, H12 or
H11), 0.32 (d, 1 H, H5, J = 7.28 Hz), −1,21 (d, 1 H, H1a, J = 3.52 Hz)
h at ambient temperature. The solvent was removed under dynamic
vacuum, and the solid residue was extracted with pentane (3 mL) and
filtered. The extract was concentrated and cooled to −30 °C to give dark
green crystals (50 mg, 0.13 mmol, 40%). Mp: 192.2−192.8 °C. Anal.
Calcd for C H V: C, 77.77; H, 9.54. Found: C, 77.41; H, 9.58. The EI
26
38
13
1
mass spectrum (70 eV) showed a molecular ion at m/z 401 amu with the
ppm. C{ H} NMR (101 MHz, C D , ambient): δ 111.5 (C, C4), 104.2
6 6
following isotopic cluster distribution: 397 (6), 398 (3), 399 (5), 400
(C, C18 or C21), 100.4 (C, C14), 97.6 (C, C21 or C18), 89.8 (C, C2),
82.0 (CH, C3), 71.2 (CH, C17 or C24), 64.7 (CH, C24 or C17), 54.3
(
3), 401 (100), 402 (26), 403 (4). Simulated distributions (in %): for
C H V, 401 (100), 402 (28), 403 (4); C H V: 399 (100), 400 (28),
(CH, C5), 51.6 (CH, C9), 43.0 (CH
2
, C1), 41.4 (CH, C7), 39.3
, C8), 33.7 (3 × CH ,
3
26
38
26 36
4
01 (4); for C H V, 397 (100), 398 (28), 399 (4).
(C, C10), 35.3 (3 × CH , C20 or C23), 34.9 (CH
3
2
26
34
5
Synthesis of [Cr(η -Pdl*) ] (7). A solution of CrCl (57 mg, 0.47
C23 or C20), 33.5 (C, C19 or C22), 33.1 (C, C22 or C19), 32.6 (CH2,
C6), 32.0 (3 × CH , C16), 30.2 (C, C15), 26.2 (CH , C11 or C12), 25.7
2
2
mmol) and 3 (200 mg, 0.93 mmol) in THF (15 mL) was stirred for 4 h
at ambient temperature. The solvent was removed under dynamic
vacuum, and the solid residue was extracted with pentane (3 mL) and
filtered. The extract was concentrated and cooled to −30 °C to give dark
3
3
(CH , C13), 21.5 (CH , C12 or C11) ppm. The EI mass spectrum
3
3
(70 eV) showed a molecular ion at m/z 464 amu with the following
isotopic cluster distribution: 460 (1), 461 (2), 462 (15), 463 (6),
8
82
dx.doi.org/10.1021/om301189g | Organometallics 2013, 32, 874−884

Organometallics
Article
4
64 (100), 465 (24), 466 (8). Simulated distributions (in %): for
material is available free of charge via the Internet at http://pubs.
acs.org.
C H Fe, 462 (6), 463 (2), 464 (100), 465 (35), 466 (5); for C H Fe,
4
30
48
30 46
60 (6), 461 (2), 462 (100), 463 (35), 464 (5).
7
5
Synthesis of [(η -C H )Zr(η -Pdl*)] (10).
7
7
AUTHOR INFORMATION
■
Corresponding Author
*
E-mail: mwalter@tu-bs.de.
Present Address
†
Westfal
isches Institut, Corrensstrasse 40, 48149 Mu
Notes
̈
ische Wilhelms-Universitat
̈
Mu
̈
nster, Organisch-Chem-
̈
nster, Germany.
7
[
(
(
(η -C H )ZrCl(tmeda)] (0.5 g, 1.497 mmol) was dissolved in THF
7 7
30 mL). Slow addition of K(Pdl*) (0.337 g, 1.572 mmol) in THF
10 mL) at −78 °C resulted in a red solution, which was stirred for 4 h.
The authors declare no competing financial interest.
After solvent removal, sublimation at 135 °C (0.1 mbar) afforded a wine
red solid (0.245 g, 0.69 mml, 46%). Single crystals were grown from a
concentrated toluene/pentane solution at −20 °C. Mp: 174.5−175.5 °C.
ACKNOWLEDGMENTS
■
M.D.W. acknowledges the current financial support by the TU
Braunschweig through the “Zukunftsfonds” and by the Deutsche
Forschungsgemeinschaft (DFG) through the Emmy-Noether
program (WA 2513/2-1). M.D.W. is grateful to W. C. Heraeus
1
Anal. Calcd for C H Zr: C, 67.2; H, 7.33. Found: C, 67.0; H, 7.44. H
20
26
NMR (400 MHz, C D , ambient temperature): δ 5.16 (s, 7 H, C H ),
6
6
7
7
.84 (m, 1 H, H3), 3.81 (s, 1 H, H1b), 2.78 (d, J = 4.9 Hz, 1 H, H5), 2.63
GmbH for a generous gift of IrCl . We thank Dr. Greg Nocton
3
(
́ ́ ́
Laboratoire Heteroelement et Coordination Ecole polytechni-
1
que/CNRS, Palaiseau Cedex) for magnetic susceptibility
measurements (SQUID).
6
6
1
4
2
29.9 (C2), 93.6 (C3), 86.0 (C5), 82.8 (C H ), 78.0 (C1), 51.7 (C9),
1.1 (C7), 39.2(C10), 35.3 (C8), 32.4 (C6), 27.7 (C13), 26.2 (C12),
1.3 (C11) ppm. The EI mass spectrum (70 eV) showed a molecular ion
7 7
REFERENCES
■
at m/z 356 amu with the following isotopic cluster distribution: 354 (47),
(
1) Hartwig, J. F. Organotransition Metal Chemistry: From Bonding to
Catalysis; University Science: Sausalito, CA, 2010.
2) Kreiter, C. G. Adv. Organomet. Chem. 1986, 26, 297.
3) Ernst, R. D. Chem. Rev. 1988, 88, 1255.
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6) Ernst, R. D. Comments Inorg. Chem. 1999, 21, 285.
7) Ernst, R. D. Acc. Chem. Res. 1985, 18, 56.
3
55 (22), 356 (100), 357 (43), 358 (49), 359 (11), 360 (33), 361 (6),
362 (5), 363 (0). Simulated distributions (in %): for C H Zr, 356
20
26
(
(
(
(
100), 357 (43), 358 (40), 359 (7), 360 (34), 361 (7), 362 (5), 363 (1);
for C H Zr, 354 (100), 355 (43), 356 (40), 357 (7), 358 (34), 359 (7),
20
24
3
60 (5), 361 (1).
Synthesis of [(η -COD)Ir(η -Pdl*)] (11).
4
5
(
(
(
(
(
8
(
(
8) Powell, P. Adv. Organomet. Chem. 1986, 26, 125.
9) Stahl, L.; Ernst, R. D. Adv. Organomet. Chem. 2007, 55, 137.
̃
10) Calhorda, M. J.; Romao, C. C.; Veiros, L. F. Chem. Eur. J. 2002, 8,
68.
11) Veiros, L. F.; Calhorda, M. J. Dalton Trans. 2011, 40, 11138.
12) Glockner, A.; Bannenberg, T.; Ibrom, K.; Daniliuc, C. G.; Freytag,
̈
A solution of [(COD)Ir(μ-Cl)] (85 mg, 0.13 mmol) and 3 (54 mg,
M.; Jones, P. G.; Walter, M. D.; Tamm, M. Organometallics 2012, 31,
2
0.25 mmol) in 15 mL of THF was stirred for 24 h at ambient temperature
4480.
and then evaporated to dryness. The brown solid residue was extracted
with 3 mL of pentane. Concentration of the extract and cooling to
(13) Bosch, H. W.; Hund, H.-U.; Nietlispach, D.; Salzer, A.
Organometallics 1992, 11, 2087.
−
30 °C resulted in orange crystals. Yield: 72 mg (0.15 mmol, 61%). Mp:
(14) Cesarotti, E.; Kagan, H. B.; Goddard, R.; Kru
Chem. 1978, 162, 297.
̈
ger, C. J. Organomet.
1
5
22.8−123.1 °C. Anal. Calcd for C H Ir: C, 53.2; H, 6.57. Found: C,
21
31
1
2.87; H, 6.55. H NMR (400 MHz, C D , 298 K): δ 5.42−5.39 (m, 1 H,
(15) Giardello, M. A.; Eisen, M. S.; Stern, C. L.; Marks, T. J. J. Am.
Chem. Soc. 1995, 117, 12114.
(16) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Rieger, B.;
̈
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
(17) Giardello, M. A.; Conticello, V. P.; Brard, L.; Gagne, M. R.; Marks,
T. J. J. Am. Chem. Soc. 1994, 116, 10241.
(18) Willhoughby, C. A.; Buchwald, S. L. J. Am. Chem. Soc. 1994, 116,
2642.
(19) Odenkirk, W.; Bosnich, B. J. Chem. Soc., Chem. Commun. 1995,
1181.
(20) Kulsomphob, V.; Tomaszewski, R.; Yap, G. P. A.; Liable-Sands, L.
M.; Rheingold, A. L.; Ernst, R. D. J. Chem. Soc., Dalton Trans. 1999, 3995.
(21) Gong, L.; Hu, N.; Jin, Z.; Chen, W. J. Organomet. Chem. 1988, 352,
62.
6
6
H3), 4.24 (br s, 2 H, COD), 3.76−2.16 (br m, 6 H, COD), 3.62 (t, 1 H,
H1b, J = 1.64 Hz), 2.67−2.60 (m, 1 H, H8b), 2.37 (t, 1 H, H9, J = 5.90
Hz), 2.02 (br s, 2 H, COD), 1.98−1.91 (m, 2 H, H7 and H8a), 1.86−1.83
(
m, 1 H, H1a), 1.82−1.75 (“ddd”, 1 H, H6b), 1.73−1.66 (m, 2 H, H6a
and H5), 1.52 (br s, 2 H, COD), 1.32 (s, 3 H, H13), 1.31 (s, 3 H, H12),
0
1
.98 (s, 3 H, H11) ppm. 13C{ H} NMR (101 MHz, C D , 298 K): δ
22.9 (C, C4), 99.3 (C, C2), 96.4 (CH, C3), 51.7 (CH , C1), 50.9 (CH,
1
6
6
2
C9), 48.5 (CH, C5), 43.2 (CH, C7), 39.2 (C, C10), 38.1 (CH , C8), 26.3
2
(
CH , C12), 25.1 (CH , C6), 22.8 (CH , C13), 22.2 (CH , C11) ppm.
3 2 3 3
The EI mass spectrum (70 eV) showed a molecular ion at m/z 476 amu
with the following isotopic cluster distribution: 472(29), 473 (19), 474
(
(
78), 475 (25), 476 (100), 477 (22), 478 (3). Simulated distributions
in %): for C H Ir, 474 (60), 475 (14), 476 (100), 477 (23), 478 (3);
21
31
for C H Ir, 472 (60), 473 (14), 474 (100), 475 (23), 476 (3).
21
29
(22) Solomon, S. A.; Bickelhaupt, F. M.; Layfield, R. A.; Nilsson, M.;
Poater, J.; Sola,
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ASSOCIATED CONTENT
Supporting Information
■
1
(
*
S
CIF files giving crystallographic data for 4−11 and figures giving
1
the H NMR spectrum of 3, an ln K vs T plot for 5/5′, and
solid-state magnetic susceptibility vs T data for 6 and 7. This
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