Synthesis and reactivity of Bis(η5:η1- pentafulvene)zirconium complexes

Article abstract of DOI:10.1021/om500031s

Here we present the first synthetic route to bis(η⁵: η¹-pentafulvene)zirconium complexes as well as investigations of several consecutive reactions. Sodium amalgam reduction of ZrCl₄ in the presence of a bulky substituted pentafulvene in THF leads to the formation of [η⁵:η¹-C₅H₄=CR ₂]₂Zr(THF) (2a, R = p-tol; 2b, R = Ph). The molecular structure of 2a has been determined by single-crystal X-ray diffraction and exhibits an unusually large Zr-C_exo distance (2.708(2) A) caused by the bulky substituents at the exocyclic carbon, which allows THF coordination. The reaction of 2a with H-acidic compounds such as hydrogen chloride, amines, and water were examined: addition of HCl leads to the dichloride complex [η⁵-C₅H₄-CH(p-tol) ₂]₂ZrCl₂ (3) and treatment of 2a with p-methylaniline forms the bis-amide complex [η⁵-C ₅H₄-CH(p-tol)₂]₂Zr(NH-p-tol) ₂ (4), whereas addition of the sterically more demanding dicyclohexylamine furnishes the monoamide complex [η⁵: η¹-C₅H₄=C(p-tol)₂] [η⁵-C₅H₄-CH(p-tol)₂]Zr(NCy ₂) (5). The cyclotrimeric compound {[η⁵-C ₅H₄-CH(p-tol)₂]₂Zr(μ-O)} ₃ (6) is obtained by reaction of 2a with water. Moreover, insertion reactions of CX multiple bonds (X = N, O) into the Zr-C_exo(Fv) bond of 2a result in the formation of the zirconacycles [η⁵: η¹-C₅H₄-C(p-tol)₂-C(C ₆H₄Cl)=N-]₂Zr (7), [η⁵: η¹-C₅H₄-C(p-tol)₂-MeC ₄H₆N-]₂Zr (8), and [η⁵: η¹-C₅H₄-C(p-tol)₂-C(Ph) ₂O-]₂Zr (9). Finally, 2a is a valuable agent for the activation of molecular hydrogen under ambient conditions. In this regard, only one pentafulvene ligand per zirconium atom is protonated and the dinuclear zirconium hydride complex {[η⁵:η¹-C ₅H₄=C(p-tol)₂][η⁵-C ₅H₄-CH(p-tol)₂]Zr(μ-H)}₂ (10) is isolated. All compounds were confirmed by single-crystal X-ray diffraction and NMR spectroscopic measurements.

Full text of DOI:10.1021/om500031s

Article
pubs.acs.org/Organometallics
Synthesis and Reactivity of Bis(η5:η1‑pentafulvene)zirconium
Complexes
Hanna Ebert, Vanessa Timmermann, Tim Oswald, Wolfgang Saak, Marc Schmidtmann,
Marion Friedemann, Detlev Haase, and Rudiger Beckhaus*
̈
Institute of Chemistry, Carl von Ossietzky University Oldenburg, D-26111 Oldenburg, Germany
S
* Supporting Information
ABSTRACT: Here we present the first synthetic route to
bis(η5:η1-pentafulvene)zirconium complexes as well as inves-
tigations of several consecutive reactions. Sodium amalgam
reduction of ZrCl4 in the presence of a bulky substituted
pentafulvene in THF leads to the formation of [η5:η1-C5H4
CR2]2Zr(THF) (2a, R = p-tol; 2b, R = Ph). The molecular
structure of 2a has been determined by single-crystal X-ray
diffraction and exhibits an unusually large Zr−Cexo distance
(2.708(2) Å) caused by the bulky substituents at the exocyclic
carbon, which allows THF coordination. The reaction of 2a
with H-acidic compounds such as hydrogen chloride, amines,
and water were examined: addition of HCl leads to the
dichloride complex [η5-C5H4-CH(p-tol)2]2ZrCl2 (3) and treatment of 2a with p-methylaniline forms the bis-amide complex [η5-
C5H4-CH(p-tol)2]2Zr(NH-p-tol)2 (4), whereas addition of the sterically more demanding dicyclohexylamine furnishes the
monoamide complex [η5:η1-C5H4C(p-tol)2][η5-C5H4-CH(p-tol)2]Zr(NCy2) (5). The cyclotrimeric compound {[η5-C5H4-
CH(p-tol)2]2Zr(μ-O)}3 (6) is obtained by reaction of 2a with water. Moreover, insertion reactions of CX multiple bonds (X = N,
O) into the Zr−Cexo(Fv) bond of 2a result in the formation of the zirconacycles [η5:η1-C5H4-C(p-tol)2-C(C6H4Cl)N−]2Zr
(7), [η5:η1-C5H4-C(p-tol)2-MeC4H6N−]2Zr (8), and [η5:η1-C5H4-C(p-tol)2-C(Ph)2O−]2Zr (9). Finally, 2a is a valuable agent
for the activation of molecular hydrogen under ambient conditions. In this regard, only one pentafulvene ligand per zirconium
atom is protonated and the dinuclear zirconium hydride complex {[η5:η1-C5H4C(p-tol)2][η5-C5H4-CH(p-tol)2]Zr(μ-H)}2
(10) is isolated. All compounds were confirmed by single-crystal X-ray diffraction and NMR spectroscopic measurements.
Scheme 1. Bis(pentafulvene)titanium Complexes I and II:22
INTRODUCTION
■
(A) Dianionic π-η5:σ-η1 Resonance Structure; (B) Neutral
In organometallic chemistry, pentafulvenes are well-known for
Olefinic π-η6 Resonance Structure
being versatile ligands.1−3 The coordination mode depends on
the metal fraction as well as on the substitution patterns of the
pentafulvene. Due to their partial dipolar character, pentaful-
venes are excellent π acceptors and are thus able to stabilize
low-valent metal centers. Pentafulvenes can be bound to a
transition metal in η2, η4, and η6 coordination modes.4−12 The
most common bonding mode of a pentafulvene ligand to early
transition metals is η6 coordination, which occurs in two
different resonance structures. On the one hand, a pentafulvene
can be bound in a neutral olefinic π-η6 coordination (Mn)
venes with less bulky substituents at the exocyclic carbon atom
(Scheme 1, B). On the other hand, the dianionic π-η5:σ-η1
structure (Mn+2) can be formed, resulting from stronger M−
Cexo(Fv) π back-bonding (Fv = pentafulvene) (Scheme 1,
A).4,12 Furthermore, a change of polarity appears at the
exocyclic carbon atom of pentafulvene metal complexes. To be
more precise, free pentafulvenes possess an electrophilic
exocyclic carbon atom and in pentafulvene metal complexes
the exocyclic carbon has a nucleophilic character.
leads to a C−C coupling reaction at the exocyclic positions,
resulting directly in the formation of an ansa-zirconocene
complex. Therefore, bulky substituents appear to be essential to
avoid C−C coupling.15 In this regard, in 1985 Green and co-
workers developed the first known bis(η5:η1-pentafulvene)-
titanium complex by using a sterically demanding pentaful-
vene.21 First, bis(η6-toluene)titanium(0) was synthesized by a
cocondensation of titanium and toluene. Subsequent reaction
An area of application for pentafulvenes is the preparation of
ansa-metallocenes, particularly for group 4 metals in a
direct13−16 or indirect way.17−20 The direct use of pentaful-
Received: January 15, 2014
Published: March 12, 2014
© 2014 American Chemical Society
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with diphenylfulvene leads to the formation of bis(η5:η1-
diphenylfulvene)titanium, due to the fact that the pentafulvene
ligand is a better π-acceptor ligand than toluene. In 2006 the
synthesis of bis(η5:η1-pentafulvene)titanium complexes was
made more easily accessible by our group.22 The bis(η5:η1-
pentafulvene)titanium complexes [η5:η1-C5H4CR2]2Ti (R =
p-tol (I), CR2 = adamantyl (II); Scheme 1) could be isolated by
reaction of TiCl3(THF)3 with the appropriate pentafulvene and
magnesium turnings as reducing agent. Furthermore, bis(η5:η1-
pentafulvene)titanium complexes serve as catalysts for intra-
molecular hydroamination reactions of geminally disubstituted
amino alkenes.23
with other donors such as pyridine, 2,6-lutidine, 2-fluorpyridine,
and thiophene have been unsuccessful so far. A nonselective
mixture of compounds was formed, which was not possible to
separate.
Of particular interest is the chiral center at the zirconium
atom, resulting from the two bidentate pentafulvene ligands.
Due to the fact that the exocyclic carbon atom can coordinate
in two different stereochemical ways, a racemate is formed
(Figure 1). The same effect has already been described for the
bis(η5:η1-pentafulvene)titanium complexes.22
In the past, the pentafulvene chemistry of zirconium has
attracted little attention. (Pentafulvene)zirconium complexes
reported in the literature have arisen from the spontaneous C−
H activation of a pentamethylcyclopentadienyl ligand under
thermolytic conditions (Cp*(C5Me4CH2)ZrX; X = Ph, Cl, I,
2-butenyl)24−26 and reductive conditions (Cp*Zr[−C(C
CHtBu)-CHtBu-CH-η5-C5Me3-CH2−]; Cp*Zr(H)-
[η5:η2(C,P)(CH2)C5Me3CH2CH2PMe2]27,28), leading to sub-
sequent formation of a Zr−C σ bond. To the best of our
knowledge, bis(pentafulvene)zirconium complexes are un-
known up to now. In light of the large variety of chemical
reactions of bis(η5:η1-pentafulvene)titanium complexes and
their application in catalysis, we decided to carry out
investigations in order to obtain analogous zirconium
complexes. Herein, we present the first known route to
bis(η5:η1-pentafulvene)zirconium complexes. In addition, vari-
ous consecutive reactions with H-acidic compounds and CX
multiple bonds (X = N, O) are discussed, and the successful
activation of molecular hydrogen is shown.
Figure 1. Chirality of the bis(η5:η1-pentafulvene)zirconium complex 2.
Ct = centroid of the five-membered ring, and Cexo = exocyclic carbon
atom of the five-membered ring of the pentafulvene ligand.
Compound 2a was characterized by NMR spectroscopy, and
the obtained signals are quite similar to those of the analogous
titanium compound I. Table 1 summarizes selected 1H and 13
C
RESULTS AND DISCUSSION
■
Bis(η5:η1-pentafulvene)zirconium. The bis(η5:η1-
pentafulvene)zirconium complexes 2a,b are synthesized by
reaction of freshly sublimated ZrCl4 with 2 equiv of the
appropriate pentafulvene 1a,b and 4 equiv of sodium amalgam
(20% Na) in THF (Scheme 2). After purification the rather
Table 1. Selected 1H NMR (C6D6, 500 MHz, 300 K) and 13
NMR (C6D6, 126 MHz, 300 K) Data of Complex 2a in
Comparison to Those of I and 1a
C
2a
1H NMR Data (ppm)
I22
1a22
Scheme 2. Synthesis of the Bis(η5:η1-pentafulvene)zirconium
Complexes 2a,b
C5H4
4.17
4.39
5.72
6.43
4.20
6.57
6.65
4.96
5.88
6.53
13C NMR Data (ppm)
C5H4
92.2
108.8
110.0
116.5
121.7
132.6
112.0
124.8
99.1
102.6
114.7
129.2
103.4
132.4
Cipso
Cexo
144.2
152.2
moisture and air sensitive compounds 2a,b can be isolated as
dark red solids (2a, yield 47%; 2b, yield 14%). The purification
of 2b is difficult, owing to its poor solubility in aliphatic
solvents. When 6,6-di-p-tolylfulvene (1a) is used instead of
diphenylfulvene (1b), the solubility of the bis(η5:η1-pentaful-
vene)zirconium complex increases and the yield is improved.
Thus, further investigations have been conducted with the
bis(η5:η1-pentafulvene)zirconium complex 2a. One THF
molecule is coordinated to the zirconium atom, in contrast to
the analogous bis(η5:η1-pentafulvene)titanium complex I. The
different behavior is due to the higher covalent radius of
zirconium. In solution, 2a,b are stable up to a temperature of
approximately 60 °C, above which it decomposes. Attempts to
obtain a more stable compound by replacing the THF ligand
NMR data of 2a in comparison to those of I and the free
pentafulvene 1a. NMR spectra of 2a indicate that the
pentafulvene ligands are identical; therefore, only one set of
signals is observed. Four separated broadened signals found at
0.42, 0.62, 2.53, and 2.96 ppm are assigned to the coordinated
THF ligand. When a small amount of THF-d8 is added to a
benzol-d6 solution of 2a, an exchange of coordinated THF with
free THF can be observed: the signals of the coordinated THF
ligand disappear and, consequently, signals corresponding to
free THF appear (Figure 2), suggesting that the THF ligand is
only weakly bound to the zirconium center. The characteristic
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1
○
○
Figure 2. H NMR spectra of 2a: (top) benzene-d6 ( ), 300 K, 500 MHz, coordinated THF (*), n-pentane (+); (bottom) benzene-d6 ( ) + THF-
d8 (*), 300 K, 500 MHz.
four separated signals of the pentafulvene ring protons appear
at 4.17, 4.39, 5.72, and 6.43 ppm and are slightly shifted upfield
in comparison with those of I. In addition, the 13C NMR data
of 2a are similar to those of I and a slight upfield shift is
observed as well (Table 1). Upon coordination of the
pentafulvene 1a to the zirconium center the signals of the
pentafulvene ligand experience a considerable upfield shift. The
1H NMR of 2a shows a significant shift up to 2.4 ppm, and in
particular the Cexo atom shows a difference of 49 ppm,
suggesting a noticeable electron transfer from the zirconium
center to the pentafulvene.
Single crystals of 2a suitable for X-ray diffraction were
obtained from a saturated n-hexane solution after several days
at 0 °C. The molecular structure is shown in Figure 3, and
selected bond lengths and angles in comparison with those of I
and other known pentafulvene zirconium complexes are
summarized in Table 2. The bis(η5:η1-pentafulvene)zirconium
Figure 3. Solid-state molecular structure of 2a (50% probability
complex 2a crystallizes in the monoclinic space group P21/c.
The observed Zr−O bond length (2.3135(11) Å) corresponds
to a dative bond and lies within the expected range of typical
weakly bound THF molecules (Cp2Zr[η2-N(Ph)CHPh]-
(THF), 2.34 Å;29 Cp2Zr(η2-Me3SiCCSiMe3)(THF), 2.39
Å30), which is in accordance with the aforementioned NMR
investigations. Due to the additional THF ligand the Ct1−Zr−
ellipsoids). Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (deg): Zr1−O1 2.3135(11), Zr1−C1
2.3266(16), Zr1−C2 2.4109(16), Zr1−C3 2.5278(17), Zr1−C4
2.5322(17), Zr1−C5 2.4058(17), Zr1−C6 2.7084(17), Zr1−C21
2.3266(16), Zr1−C22 2.3867(16), Zr1−C23 2.5273(17), Zr1−C24
2.5637(17), Zr1−C25 2.4316(16), Zr1−C26 2.7007(16), C1−C6
1.443(2), C21−C26 1.450(2), Zr1−Ct1 2.121, Zr1−Ct2 2.129; Ct1−
Zr1−Ct2 133.9, C6−Zr1−C26 160.22(5), O1−Zr1−C6 80.26(5),
O1−Zr1−C26 79.97(5), C1−C6−Zr1 59.21(8), C21−C26−Zr1
59.43(8) (Ct1 = centroid of C1−C5; Ct2 = centroid of C21−C25).
Ct2 angle is 12° smaller and the Cexo−Zr−Cexo angle (Cexo
=
C6, C26) is 21° larger than in the analogous titanium
compound I. Characteristic of a dianionic π-η5:σ-η1 structure
(Scheme 1, A) is the deviation (bend angle θ) of the Cexo−Cipso
bond from the plane of the five-membered ring toward the
metal center as well as the ring slippage (Δ) toward the Cipso
atom of the five-membered ring (Table 2). In this respect,
evidence for weaker M−Cexo π back-bonding of 2a in
comparison to I are the smaller bend angles θ (26.9° vs
34.1/35.3°) and the shorter ring slippage Δ (0.236/0.262 Å vs
0.282/0.267 Å). Additionally, the M−Cexo bond in 2a is
approximately 0.3 Å longer than that in I, because of the higher
covalent radius of zirconium (Zr, 1.45 Å;31 Ti, 1.32 Å32) and
the weaker M−Cexo π back-bonding. The Zr−Cexo bonds are
approximately 2.7 Å and are considerably longer than those of
other reported pentafulvene zirconium complexes (2.37−2.39
Å; Table 2).24,27,33−35 The weak Zr−Cexo contact is best
compared with the pentafulvene titanium complex Cp*-
[C5H4C(p-tol)2]2TiCl (III), which also exhibits an unusually
large Ti−Cexo distance (2.535(5) Å) and consequently a small
bend angle θ (29.2°).36 This effect is evoked by the bulky
substituents at the exocyclic carbon; hence, π-donor sub-
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Table 2. Selected Bond Lengths (Å) and Angles (deg) of 2a, I, III, and Other Known Pentafulvene Zirconium Complexes
Ct1−M−
Cexo−M−
a
a
compd
M−Cexo
Cipso−Cexo
Ct2
Cexo
θ
Δ
[η5:η1-C5H4C(p-tol)2]2Zr(THF) (2a)
[η5:η1-C5H4C(p-tol)2]2Ti (I)22
Cp*[C5H4C(p-tol)2]2TiCl (III)36
Cp*FvZrPh24
2.708(2), 2.701(2) 1.443(2), 1.450(2)
2.408(2), 2.392(2) 1.453(3), 1.453(3)
133.9
145.9
137.8
143.6
142.8
141.6
144.9
160.22(5)
139.25(8)
26.9, 26.9 0.236, 0.262
34.1, 35.3 0.282, 0.267
2.535(5)
2.389(8)
2.371(5)
2.366(4)
2.389(5)
1.428(7)
1.468(9)
1.432(8)
1.457(5)
1.475(8)
29.2
36.3
36.3
36.7
35.5
0.290
0.370
0.382
0.377
0.390
Cp*FvZr(C6F5)33
35
[Cp*FvZr(THF)]BPh4
[Cp*Zr{−C(CCHtBu)-CHtBu−CH2-η5-C5Me-
CH2−}]27
a
Fv: = C5Me4CH2. The values θ and Δ are defined as
stituents on Cexo decrease the bend angle θ and increase the
Zr−Cexo bond length.24 Moreover, the Cipso−Cexo distances
(Cipso = C1, C21; Cexo = C6, C26) are elongated to 1.443(2)/
1.450(2) Å in comparison to the corresponding bond length in
the free pentafulvene ligand 1a (1.36 Å)36 and lie in the same
range as for I (1.45 Å) and III (1.43 Å). The Cipso−Cexo bonds
Scheme 3. Reactions of 2a with H-Acidic Compounds (R =
p-tol): HCl (3), p-Toluidine (4), Dicyclohexylamine (5),
H2O (6)
2
3
are shorter than a typical Csp −Csp single bond (1.51 Å) but
2
2
also longer than a characteristic Csp −Csp double bond (1.32
Å).37 Thus, the Cexo atom lies between sp2 and sp3
hybridization. A further argument against a pure sp3 hybrid-
ization are the angles C1−C6−C7 (122.6°), C1−C6−C14
(117.0°), and C7−C6−C14 (113.0°), which deviate from an
ideal sp3 bond angle (109°) and are similar to those of typical
sp2-hybridized carbon atoms (120°), except for the angle C7−
C6−C14. To sum up, the bonding situation of the pentafulvene
ligand of 2a is best described as coordination between olefinic
and dianionic forms (Scheme 1, A and B).4
Reactions of 2a with H-Acidic Compounds. The
treatment of pentafulvene complexes of early transition metals
with H-acidic compounds generally leads to a 1,2-addition
reaction to the M−Cexo bond due to the nucleophilic character
of the exocyclic carbon atom.22,23,36,38 The following section
demonstrates the reaction of bis(η5:η1-pentafulvene)zirconium
2a with electrophiles such as hydrogen chloride, amines, and
water (Scheme 3).
Bis(di-p-tolylcyclopentadienyl)zirconium dichloride (3) was
prepared using a method similar to that described for the
synthesis of the analogous titanium compound [η5-C5H4-
CH(p-tol)2]2TiCl2.22 Addition of 2 equiv of HCl/Et2O to a
THF solution of 2a, followed by stirring at ambient
temperature for 2 h and subsequent purification, leads to 3 as
a yellow solid (yield 78%) (Scheme 3). In 1999, Bochmann et
al. reported a different synthetic procedure to obtain bis-
(diphenylcyclopentadienyl)zirconium dichloride, using
ZrCl4(THF)2 and Li[C5H4CHPh2].39 In contrast to this
synthesis route we can carry out the preparation of 3 with a
considerably higher yield and in a salt-free way. Recrystalliza-
tion from a saturated n-hexane solution provided colorless
RCp)2ZrCl2 complexes published previously.40 Also, the Cl−
Zr−Cl (98.2°) and Ct−Zr−Ct (123.3°) bond angles lie within
the range for known zirconocene derivatives.41−48
The 1H NMR spectrum of 3 shows two characteristic signals
for the cyclopentadienyl protons at δ 5.77 and 6.01 ppm. In
addition, the typical singlet of the exocylic CH proton is located
at δ 5.53 ppm. These values are in close agreement with those
obtained for the analogous titanium compound.22
crystals of 3, which were solved in the triclinic space group P1
̅
(Figure 4). The metal center adopts a pseudotetrahedral
geometry, and the five-membered rings form a staggered
conformation. The Zr−Cl (average. 2.44 Å) and Zr−Ct
(average 2.21 Å) bond lengths are consistent with (η5-
Furthermore, the reactivity of 2a with N−H acidic
compounds, in particular primary and secondary amines, was
examined. By treatment of 2a with p-toluidine or dicyclohexyl-
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Figure 4. Solid-state molecular structure of 3 (50% probability
ellipsoids). Hydrogen atoms and solvent molecules are omitted for
clarity. Selected bond lengths (Å) and angles (deg): Zr1−Cl1
2.4388(3), Zr1−Cl2 2.4356(3), C1−C6 1.5143(15), C21−C26
1.5097(15), Zr1−Ct1 2.214, Zr1−Ct2 2.208; Ct1−Zr1−Ct2 123.3,
Cl1−Zr1−Cl2 98.225(12) (Ct1 = centroid of C1−C5; Ct2 = centroid
of C21−C25).
Figure 5. Solid-state molecular structure of 4 (50% probability
ellipsoids). Solvent molecules and hydrogen atoms bonded to carbon
are omitted for clarity. Selected bond lengths (Å) and angles (deg):
Zr1−N1 2.114(2), Zr1−N2 2.123(2), C1−C6 1.511(3), C21−C26
1.519(3), N1−C48 1.404(3), N2−C41 1.398(3), Zr1−Ct1 2.242,
Zr1−Ct2 2.239; Ct1−Zr1−Ct2 127.5, N1−Zr1−N2 98.98(8), Zr1−
N1−C48 130.27(17), Zr1−N1−H1 117.6(19), H1−N1−C48
108.0(2), Zr1−N2−C41 133.24(17), Zr1−N2−H2 114.6(18), H2−
N2−C41 110.2(18) (Ct1 = centroid of C1−C5; Ct2 = centroid of
C21−C25).
amine a color change from red to yellow occurs. The resulting
zirconocene amides could be obtained in yields of 97% (4) and
59% (5), respectively (Scheme 3). The air- and moisture
sensitive compounds are highly soluble in THF and aromatic
hydrocarbons but only moderately soluble in aliphatic solvents.
Independent of the stoichiometric ratios (1:1 or 1:2) of 2a to
the appropriate amine, only one product is formed. The
treatment with p-toluidine leads to the zirconocene bis(amide)
complex 4, whereas the sterically more demanding dicyclohex-
ylamine results in protonation of only one pentafulvene ligand
with consequent formation of the zirconium monoamide
complex 5. Compounds 4 and 5 were characterized by means
of NMR spectroscopy. Characteristic values for 4 are the two
signals of the cyclopentadienyl protons, which are located at δ
5.33 and 5.83 ppm. Additionally, a typical singlet is found at δ
5.27 ppm for the exocyclic CH group. These data compare
favorably with those reported for the analogous titanium
compound [η5-C5H4-CH(p-tol)2]2Ti(NHp-tol)2.23 An excep-
tion is the chemical shift of the NH singlet in 4 (δ 6.24 ppm),
which is shifted upfield in comparison to that for the titanocene
bis(amide) complex (δ 7.84 ppm). The 1H NMR spectrum of 5
shows four separated multiplets for the substituted Cp
derivative (δ 4.78, 5.06, 6.48, 6.57 ppm) as well as for the
coordinated pentafulvene ligand (δ 4.70, 5.04, 5.79, 6.63 ppm).
Single crystals of 4 and 5 suitable for X-ray diffraction were
obtained from a saturated n-hexane solution. Compound 4
crystallizes in the monoclinic space group P21/c and complex 5
angles, in agreement with other zirconocene derivatives.49 The
Zr−C6(Fv) distance in 5 (2.496(4) Å) is shorter than in 2a
(average 2.70 Å). Moreover, the larger bend angle θ (33.3°)
and ring slippage Δ (0.323 Å) in compound 5 imply a stronger
π back-donation than in 2a (26.9°, 0.236/0.262 Å). The Zr−N
distances in 4 (average 2.12 Å) as well as in 5 (2.084(3) Å) are
comparable to those of other zirconocene amide com-
plexes.50−60 As expected, the C−N bond lengths in 4 (average
2
1.40 Å) correlate well with Csp −N single bonds (1.38 Å) and
3
those in 5 (average 1.48 Å) with Csp −N single bonds (1.47
Å).37 Furthermore, the N atoms have a nearly planar geometry,
with the sum of the angles about 357° in 4 and 360° in 5.
However, the individual angles at each N atom deviate
considerably from the ideal trigonal-planar arrangement of
120° ranging from 109° to 133° in 4 and from 108° to 140° in
5. Group 4 metal Cp2M(NR2)X complexes with a d0
configuration can form a M−N dπ−pπ interaction, if the
plane defined by R−N−R has a perpendicular orientation to
the N−M−X plane. A parallel orientation of these planes
renders the overlap of the nitrogen lone pair with an acceptor
orbital of the zirconium center impossible.23,55,61 The dihedral
angles in compounds 4 and 5 are approximately 54 and 73°,
respectively. It can thus be concluded that a partial double-
bond character can be expected for the Zr−N bonds, especially
for complex 5. It should be noted that the p orbitals of both
in the triclinic space group P1. The molecular structures are
̅
shown in Figures 5 and 6, respectively. The zirconium atoms
exhibit the typical pseudotetrahedral coordination sphere,
owing to the Ct−Zr−Ct (127.5° (4)/ 126.7° (5)) bond
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hexane at room temperature. After purification, 7 (yield 88%)
can be isolated as a red solid and compounds 8 (yield 37%) and
9 (yield 61%) as colorless solids. The corresponding insertion
products are shown in Scheme 4.
Single crystals suitable for X-ray structure determination
were obtained from n-hexane as well as n-hexane/THF
solutions. The insertion product 7 crystallizes in the monoclinic
space group P2/n, 8 in C2/c ,and 9 in the triclinic space group
P1. Thermal ellipsoid plots of 7−9 are shown in Figures 8−10,
respectively. As for the bis(η5:η1-pentafulvene)zirconium
complex 2a, the insertion products are enantiomeric mixtures.
The insertion of 2-methyl-1-pyrroline leads to the formation of
a stereospecific product. Due to the newly formed chiral center
in the five-membered heterocycles, the molecular structure of 8
contains a pair of enantiomers in the unit cell, which are found
to be R,R,R and S,S,S. In addition, the molecular structure of
the benzophenone insertion product 9 shows a stereospecific
product as well; hence, only one enantiomer R is observed. The
zirconium atom exhibits the typical pseudotetrahedral coordi-
nation feature with Ct−Zr−Ct angles of 134.9° (7), 130.9° (8)
and 130.1° (9) as well as X−Zr−X angles of 95.13(9)° (7),
106.72(6)° (8) and 103.39(4)° (9). The Zr−Ct distances of
2.208 Å (7), 2.219 Å (8), and 2.22 Å (9) correspond well to
those of other Cp2Zr(IV) complexes.40 In addition, the Zr−N
bond distances in 7 (2.090(2) Å) and 8 (2.111(1) Å) are
comparable to known Zr−N single bonds.50−56 The C−N
bond length in 7 (1.266(2) Å) is within the range expected for
Figure 6. Solid-state molecular structure of 5 (50% probability
ellipsoids). Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (deg): Zr1−N1 2.084(3), Zr1−C6 2.496(4),
C1−C6 1.459(5), C21−C26 1.516(5), N1−C47 1.474(4), N1−C41
1.486(5), Zr1−Ct1 2.147, Zr1−Ct2 2.274; Ct1−Zr1−Ct2 126.7, Zr1−
N1−C41 140.4(2), Zr1−N1−C47 108.3(2), C41−N1−C47 111.0(3),
N1−Zr1−C6 111.11(11) (Ct1 = centroid of C1−C5; Ct2 = centroid
of C21−C25).
2
a Csp N double bond (1.28 Å), and that in 8 (1.489(2) Å) is
37
3
typical of a Csp −N single bond (1.47 Å). The Zr−O bond
amido ligands in 4 compete for the same π-acceptor orbital on
the zirconium atom. This effect does not occur in the
zirconocene monoamide complex 5, which is an additional
reason for the shorter Zr−N bond in 5 in comparison to that in
4.
The reaction of 2a with H2O leads to the cyclotrimeric
compound {[η5-C5H4-CH(p-tol)2]2Zr(μ-O)}3 (6) in the form
of colorless crystals, which were suitable for X-ray diffraction
distances in 9 (2.023(1), 2.008(1) Å) are shorter than a typical
Zr−O single bond (∼2.2 Å),68 indicating a partial double-bond
character owing to the pπ−dπ interaction between the free
electron pair of the oxygen and the zirconium atom. Moreover,
3
the Csp −O distances of 9 (average 1.422 Å) are in accordance
37
3
with a Csp −O single bond (1.43 Å). Of significance is the
length of the newly formed C6−C21 bond (1.575(2) Å (7),
1.599(2) Å (8), 1.629(2)/1.635(2) Å (9)), which is
considerably longer than a typical C−C single bond; that for
especially 9 is comparable to other reported extremely long
alkane C−C single bonds.69 This elongation can be attributed
to the strong ring strain of the metallacycles, whereas the steric
effects of the substituents at C6 and C21 have a minimal
impact.67
(Scheme 3). 6 crystallizes in the triclinic space group P1, and
̅
the molecular structure is given in Figure 7. The similar
compound [Cp2Zr(μ-O)]3 was first reported by Floriani et al.,
obtained from the reaction of Cp2Zr(CO)2 with CO2.62 The
bond lengths and angles of complex 6 are in agreement with
those of [Cp2Zr(μ-O)]3 and other known oxo-zircono-
cenes.63,64 The Zr3O3 unit forms a nearly planar six-membered
ring with an average displacement of 0.021 Å. 6 contains rather
short Zr−O bond distances (1.965−1.985 Å) resulting from the
metal−oxygen partial double-bond character (dπ−pπ inter-
action). In addition, the Zr−O−Zr angles (average 142.3°) are
close to the values observed in other Zr3O3 cycles.
Unfortunately, the complete insolubility in common organic
solvents prevented its NMR spectroscopic characterization.
Reactions of 2a with CX Multiple Bonds (X = N, O). In
recent years, complexes with functionalized cyclopentadienyl
chelate ligands have received considerable attention due to their
application in several catalytic processes.65−67 Therefore, the
reactivity of 2a toward polar multiple bonds was investigated.
Insertion reactions of polar CX multiple bonds into the Zr−
Cexo(Fv) bond are feasible due to the nucleophilic character of
the exocyclic carbon atom and the electrophilic zirconium
center. Consequently, metallacycles can be generated by
forming σ−π chelate ligands.
As expected, the NMR spectra of the enantiomeric
compounds 7 and 8 show one set of signals; in addition, the
values are within the anticipated range. In contrast, the spectra
of 9 indicate a 1:2 mixture of products. One set of signals can
be assigned to the expected complex 9, which contains equal
chelate ligands and therefore shows four signals for the C5H4
protons. The additional set of signals exhibit eight signals for
the C5H4 protons, which indicates the existence of an
asymmetric compound. Because of the rather long CexoCp
−
C
keto (CexoCp = C6, Cketo = C21) bond it can be assumed that 9
partially exists in solution in another coordination mode; more
precisely, the cleavage of the newly formed bond may lead to a
dative coordinated benzophenone and a η6-coordinated
pentafulvene ligand 9a/9a′ (Scheme 5).
1
Furthermore, high-temperature H NMR studies show only
broadened signals, which points to a CexoCp−Cketo bond
cleavage of both chelate ligands. Owing to the poor solubility
of 9, no evaluable 13C NMR spectrum could be obtained for
detailed investigations. Some years ago, we reported the
reaction of Cp*(C5H4C(p-tol)2)TiCl (III) with benzophe-
Complexes 7−9 are obtained by reaction of 2a with 2 equiv
of the CX multiple bond compounds p-chlorobenzonitrile, 2-
methyl-1-pyrroline, and benzophenone, respectively, in n-
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Figure 7. Solid-state molecular structure of 6 (50% probability ellipsoids). Hydrogen atoms and solvent molecules are omitted for clarity. Selected
bond lengths (Å) and angles (deg): Zr1−O1 1.9734(17), Zr1−O3 1.9670(18), Zr2−O2 1.9654(17), Zr2−O1 1.9718(17), Zr3−O3 1.9846(18),
Zr3−O2 1.9739(17); Zr1−O1−Zr2 140.00(10), Zr2−O2−Zr3 144.61(10), Zr1−O3−Zr3 142.34(9), O1−Zr1−O3 99.38(7), O1−Zr2−O2
97.80(7), O2−Zr3−O3 95.60(7).
Scheme 4. Reaction of 2a with p-Chlorobenzonitrile (7), 2-
Methyl-1-pyrroline (8), and Benzophenone (9)
Figure 8. Solid-state molecular structure of 7 (50% probability
ellipsoids). Solvent molecules and hydrogen atoms are omitted for
clarity. Selected bond lengths (Å) and angles (deg): Zr1−N1
2.0904(15), N1−C21 1.266(2), C1−C6 1.536(2), C6−C21
1.575(2), Zr1−Ct1 2.208; Ct1−Zr1−Ct1′ 134.9, N1−Zr1−N1′
95.13(9), Zr1−N1−C21 124.71(12), N1−C21−C6 121.57(15),
C1−C6−C21 105.94(13) (Ct1 = centroid of C1−C5).
none, resulting in the insertion product Cp*[C5H4-C(p-tol)2-
C(Ph)2O−]TiCl, as identified by an X-ray structure determi-
nation.36 It is notable that the newly formed CexoCp−Cketo bond
(1.657(2) Å) was even longer than in 9 (1.629(2)/1.635(2) Å).
Cp*[C5H4-C(p-tol)2-C(Ph)2O−]TiCl is unstable in solution
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Figure 9. Solid-state molecular structure of 8 (50% probability ellipsoids). Solvent molecules and hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) and angles (deg): Zr1−N1 2.1112(11), N1−C21 1.4890(18), N1−C24 1.4658(18), C1−C6 1.5283(18), C6−C21 1.5987(19),
Zr1−Ct1 2.220; Ct1−Zr−Ct1′ 130.9, N1−Zr1−N1′ 106.72(6), Zr1−N1−C21 126.27(8), N1−C21−C6 108.54(10), C1−C6−C21 106.63(10)
(Ct1 = centroid of C1−C5).
Figure 10. Solid-state molecular structure of 9 (50% probability ellipsoids). Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and
angles (deg): Zr1−O1 2.0230(10), Zr1−O2 2.0077(10), O1−C21 1.4273(18), C1−C6 1.530(2), C6−C21 1.629(2), O2−C54 1.4169(17), C34−
C39 1.538(2), C39−C54 1.635(2), Zr1−Ct1 2.222, Zr1−Ct2 2.210; Ct1−Zr1−Ct2 130.1, O1−Zr1−O2 103.39(4), Zr1−O1−C21 130.35(9), O1−
C21−C6 104.87(11), C1−C6−C21 104.41(12), Zr1−O2−C54 134.47(9), O2−C54−C39 104.82(11), C34−C39−C54 104.20(11) (Ct1 =
centroid of C1−C5; Ct2 = centroid of C34−C38).
(C6D6), and elimination of free pentafulvene occurs. This result
corroborates the facile CexoCp−Cketo bond cleavage in 9.
Activation of Molecular Hydrogen. Zirconium hydride
complexes have received a great deal of attention due to their
application as valuable reagents and catalysts for the synthesis
of several organic substrates and for CO reduction.49,70−76 In
general, zirconium hydride complexes can be prepared by
treating zirconium dihalide compounds with hydride sources
such as LiAlH(O-t-Bu)3, LiAlH4, LiBH4, and NaBHEt3.71,74,77
Another possible synthetic route is the hydrogenation of the
corresponding dimethyl and aryl complexes.75,78−81 These
preparations involve the formation of a leaving group. Here we
report a method to obtain dinuclear zirconium hydride
complexes without any leaving groups.
Scheme 5. CexoCp−Cketo Bond Cleavage of 9 in Solution
(C6D6)
Hydrogenolysis of 2a with H2 in n-hexane at room
temperature for 30 min leads to the heterolytic cleavage of
the molecular hydrogen, resulting in the formation of the
dinuclear zirconium hydride complex {[η5:η1-C5H4C(p-
tol)2][η5-C5H4-CH(p-tol)2]Zr(μ-H)}2 (10; yield 38%)
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(Scheme 6). The Zr2H2 core consists of three-center/two-
electron Zr−H−Zr bonding interactions. Surprisingly, only one
Scheme 6. Reaction of 2a with Molecular Hydrogen
pentafulvene ligand per zirconium atom is protonated. Even
though the hydrogen gassing has been carried out over a longer
period, only complex 10 can be isolated directly from the
reaction solution in the form of orange crystals. Metal hydride
complexes are well-known for their direct reaction with
molecular nitrogen, which is an attractive route to dinitrogen
complexes.78,80 However, in the presence of molecular
dinitrogen 10 remains stable; thus, no generation of a
dinitrogen complex occurs.
1H NMR investigation of 10 shows one singlet for the
bridging hydrides (δ −3.24 ppm). These data are similar to
those reported for other complexes containing a Zr2H2 unit
(Table 3). In addition, four characteristic signals of the
pentafulvene coordinated ligand C5H4 (Fv) (δ 4.37, 4.67,
6.51, and 6.96 ppm) and four signals of the protonated ligand
C5H4 (Cp) (δ 4.77, 4.79, 4.85, and 4.88 ppm) are found.
Crystals suitable for an X-ray structure determination were
obtained directly from the reaction solution after a few days at
room temperature. Compound 10 crystallizes in the monoclinic
space group C2/c, and the molecular structure is shown in
Figure 11. The X-ray data are of high quality, allowing the
location and free refinement of all hydrogen atoms, including
the zirconium hydrides. The Zr···Zr distance (3.4393(3) Å) is
comparable to known complexes which contain a Zr2H2 unit
(average. 3.46 Å, Table 3). In this regard, previous studies have
indicated that Zr−Zr interactions can only be assumed at
shorter distances. For instance, Gambarotta82 and Bochmann83
have reported the formation of Zr−Zr interactions with bond
distances of 3.23 and 3.15 Å, respectively. Also, the Zr−H
distance (1.99(2) Å) is quite similar to those found in other
dinuclear zirconium hydride complexes, which are known from
the literature (Table 3). The planar, rhombic Zr2H2 core shows
a Zr1−H1−Zr′ angle of 120° and a H1−Zr1−H1′ angle of 60°,
which are in line with data from dimeric zirconium dihydride
compounds given in Table 3. The C1−C7 bond length
(1.4466(19) Å) of the pentafulvene coordinated ligand is
comparable to the values for 2a (1.45 Å) and lies between sp2
and sp3 hybridization. The most striking observation to emerge
from the data comparison is that the Zr−C7 distance in 10
Figure 11. Solid-state molecular structure of 10 (50% probability
ellipsoids). Hydrogen atoms bonded to carbon are omitted for clarity.
Selected bond lengths (Å) and angles (deg): Zr1−Zr1′ 3.4393(3),
Zr1−H1 1.99(2), Zr1−C7 2.5494(14), C1−C7 1.4466(19), C22−
C27 1.5163(19), Zr1−Ct1 2.125, Zr1−Ct2 2.223; Ct1−Zr1−Ct2
130.0, Zr1−H1−Zr1′ 120.4, H1−Zr1−H1′ 59.5 (Ct1 = centroid of
C1−C5; Ct2 = centroid of C22−C26).
(2.5494(14) Å) is shorter than that in in 2a (average 2.70 Å).
Moreover, 10 possesses a larger deviation angle θ (32.45°) and
ring slippage Δ (0.278 Å) than for 2a (26.9°, 0.236/0.262 Å).
Thus, these results point to a stronger Zr−C7 π back-donation
in 10 and the bonding situation of the pentafulvene ligand
shifts toward the dianionic π-η5:σ-η1 coordination mode.
CONCLUSION
■
To sum up, our investigations present a convenient preparative
access to the first-known chiral bis(η5:η1-pentafulvene)
zirconium complexes. The bonding situation of the fulvene
ligand can best be described as a coordination between an π-η6
olefinic and π-η5:σ-η1 dianionic mode. On the basis of the
nucleophilic exocyclic carbon atom of the coordinated
pentafulvene, subsequent 1,2-addition reactions were carried
out with H-acidic compounds as well as 1,2-insertion reactions
of CX multiple bonds (X = N, O), resulting in the formation of
zirconacycles. In particular the benzophenone insertion product
exhibits a considerably long C−C single bond; hence, the
CexoCp−Cketo bond cleavage occurs in solution with subsequent
formation of a benzophenone adduct. Finally, it has been
demonstrated that the bis(η5:η1-pentafulvene)zirconium com-
Table 3. Selected Bond Lengths (Å), Angles (deg), and 1H NMR Data (ppm) of 10 in Comparison with Those of Other Known
Dinuclear Zirconium Hydride Complexes
compd
Zr···Zr
Zr−(μ-H)
1H NMR μ-H
10
3.4393(3)
3.4599(2)
3.4708(7)
3.437(2)
3.4502(5)
3.467(2)
3.462(1)
1.99(2)
−3.24
−2.98
−3.17
−3.77
−3.89
n.a.
71
[(η5-C5H4CH3)2ZrH(μ-H)]2
2.05(3), 1.94(2)
72,84
[{η5-C5H4C(Me3)3}2ZrH(μ-H)]2
[(η5-C5H4SiMe3)2ZrH(μ-H)]2
1.99(4), 2.00(4)
84
1.95, 2.00, 2.02, 2.05
1.75(4), 2.05(4), 2.08(4), 1.84(4)
1.939(8), 2.161(8)
85
[SiMe2(C5H4)2][(C5H5)ZrCl(μ-H)]2
86
[(C5H5)2ZrMe(μ-H)]2
74
[HN(SiMe2C5H4)2ZrH(μ-H)]2
1.930, 2.207, 2.148, 2.014
−3.94
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Synthesis of [η5-C5H4-CH(p-tol)2]2Zr(NH-p-tol)2 (4). 2a (300
mg, 0.441 mmol) and 94.6 mg (0.882 mmol) of p-methylaniline were
placed in a Schlenk tube. A 15 mL amount of n-hexane was added, and
the resulting light yellow suspension was stirred overnight. The
mother liquor was decanted, and the solid was washed twice with 10
mL of n-hexane. Drying in vacuo afforded 350 mg (97%) of 4 as a
yellow solid. Single crystals suitable for X-ray diffraction were obtained
from a saturated n-hexane solution of 4 after few days at room
plex is a valuable reagent for the activation of molecular
hydrogen under mild conditions, leading in a selective manner
to a zirconium dihydride. The new compounds should be
investigated in C−H, Si−H, C−F, and N2activation reactions.
EXPERIMENTAL SECTION
■
General Considerations. Reactions with air- and moisture-
sensitive compounds were carried out under an inert atmosphere of
argon or nitrogen using Schlenk techniques and standard gloveboxes.
Solvents were dried according to standard procedures. 6,6-Di-p-
tolylfulvene (1a) and diphenylfulvene (1b) were prepared according
to the literature.87 The following instruments were used for
characterization of the compounds. NMR: Bruker AVANCE III 500
spectrometer (1H, 500 MHz; 13C, 126 MHz). Electron impact (EI)
mass spectra: Finnigan-MAT 95 spectrometer. Melting point: Mel-
Temp by Laboratory Devices, Cambridge. Single-crystal X-ray
diffraction: Bruker AXS X8 Apex II diffractometer with graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å). The structures
were solved by direct methods with SHELXS-97/SHELXS-2013 and
refined by full-matrix least-squares techniques against F2 with the
SHELXL-97/SHELXS-2013 program system.88
1
temperature. Mp: 139 °C. H NMR (C6D6, 500 MHz; ppm): δ 2.09
(s, 12 H, CH3 tolyl), 2.26 (s, 6 H, CH3 aniline), 5.27 (s, 2 H, CexoH),
5.33 (m, 4 H, C5H4), 5.83 (m, 4 H, C5H4), 6.24 (s, 2 H, NH), 6.93 (m,
3
8 H tolyl CH, 4 H aniline CH), 7.04 (d, JHH = 8.04 Hz, 4 H, aniline
3
CH), 7.08 (d, JHH = 7.90 Hz, 8 H, tolyl CH). 13C NMR (C6D6, 126
MHz; ppm): δ 21.2 (CH3 aniline), 21.3 (CH3 tolyl), 51.8 (Cexo), 110.6
(C5H4), 112.3 (C5H4), 119.5 (aniline CH), 127.3 (aniline C), 129.5
(Cipso), 129.6 (tolyl CH), 129.7 (tolyl CH), 130.0 (aniline CH), 136.5
(tolyl C), 142.5 (tolyl C), 153.9 (aniline C). 15N (C6D6, 51 MHz;
ppm): δ 167.7. IR (cm−1): ν
̃
3220 (w), 3018 (w), 2919 (w), 2859 (w),
2361 (w), 2341 (w), 1606 (w), 1502 (m), 1488 (w), 1377 (w), 1296
(w), 1262 (m), 1250 (m), 1204 (w), 1180 (w), 1106 (w), 1042 (w),
1022 (w), 946 (w), 879 (w), 853 (w), 809 (m), 761 (w). MS (EI, 70
eV): m/z (%) 716 (12) [M − p-toluidine]+, 607 (44) [M − 2 p-
toluidine − H]+, 260 (17) [(p-tol)2Fv + 2H]+, 107 (82) [p-toluidine]+.
Anal. Calcd for C54H54N2Zr: C, 78.88; H, 6.62; N, 3.41. Found: C,
78.39; H, 6.96; N, 2.98.
Synthesis of [η5:η1-C5H4C(p-tol)2]2Zr(THF) (2a). Freshly
sublimated zirconium(IV) chloride (3.2 g, 13.7 mmol), 6,6-di-p-
tolylfulvene (1a; 7.09 g, 27.5 mmol), and sodium amalgam (6.31 g,
54.9 mmol, 20% Na) were placed in a Schlenk tube and dissolved in
125 mL of THF. The reaction solution was stirred at room
temperature for 24 h followed by filtration (P4/Celite). The solvent
was removed in vacuo and the resulting residue extracted with 100 mL
of pentane at 55 °C. Subsequent solvent removal led to 2a as a dark
red solid (4.4 g, 47%). Single crystals suitable for X-ray diffraction were
obtained from a saturated n-hexane solution of 2a after several days at
0 °C. Mp: 154 °C dec. 1H NMR (C6D6, 500 MHz; ppm): δ 0.42 (m, 2
H, CH2-THF), 0.62 (m, 2 H, CH2-THF), 2.11 (s, 6 H, CH3), 2.23 (s,
6 H, CH3), 2.53 (m, 2 H, CH2-THF), 2.96 (m, 2 H, CH2-THF), 4.17
(m, 2 H, C5H4), 4.39 (m, 2 H, C5H4), 5.72 (m, 2 H, C5H4), 6.43 (m, 2
H, C5H4), 6.84 (d, 3JHH = 7.46 Hz, 4 H, tolyl CH), 7.04 (d, 3JHH = 7.41
Synthesis of [η5:η1-C5H4C(p-tol)2][η5-C5H4-CH(p-tol)2]Zr-
(NCy2) (5). 2a (400 mg, 0.588 mmol) was dissolved in 10 mL of n-
hexane, 0.12 mL (0.588 mmol) of dicyclohexylamine was added, and
the resulting yellow suspension was stirred overnight. The mother
liquor was decanted, and the solid was washed three times with 5 mL
of n-hexane. Drying in vacuo afforded 272 mg (59%) of 5 as a yellow
solid. Single crystals suitable for X-ray diffraction were obtained from a
saturated n-hexane solution of 5 after few days at 0 °C. Mp: 181 °C.
1H NMR (C6D6, 500 MHz; ppm): δ 0.61−1.72 (m, 20 H, Cy H), 2.07
(s, 3 H, CH3), 2.12 (s, 6 H, CH3), 2.20 (s, 3 H, CH3), 2.49 (m, 2 H,
Cy NCH), 4.70 (m, 1 H, C5H4 Fv), 4.78 (m, 1 H, C5H4 Cp), 5.04 (m,
1 H, C5H4 Fv), 5.06 (m, 1 H, C5H4 Cp), 5.34 (s, 1 H, CexoH), 5.79 (m,
1 H, C5H4 Fv), 6.48 (m, 1 H, C5H4 Cp), 6.57 (m, 1 H, C5H4 Cp), 6.63
(m, 1 H, C5H4 Fv), 6.93 (m, 4 H, tolyl CH), 6.95 (d, 3JHH = 7.79 Hz, 2
3
Hz, 4 H, tolyl CH), 7.51 (d, JHH = 7.88 Hz, 4 H, tolyl CH), 7.63 (d,
3JHH = 7.26 Hz, 4 H, tolyl CH). 13C NMR (C6D6, 126 MHz; ppm): δ
21.2 (CH3), 21.5 (CH3), 25.6 (CH2-THF), 76.1 (CH2-THF), 92.2
(FvC), 99.1 (FvC), 102.6 (FvC), 103.4 (Cexo), 114.7 (FvC), 127.1
(tolyl CH), 128.8 (tolyl CH), 128.9 (tolyl CH), 129.2 (Cipso), 132.0
(tolyl C), 133.1 (tolyl CH), 134.3 (tolyl C), 144.1 (tolyl C), 145.0
H, tolyl CH), 6.98 (d, 3JHH = 7.79 Hz, 2 H, tolyl CH), 7.03 (d, 3JHH
=
7.87 Hz, 2 H, tolyl CH), 7.12 (d, 3JHH = 7.95 Hz, 2 H, tolyl CH), 7.18
(d, below benzene, 2 H, tolyl CH), 7.69 (d, 3JHH = 7.97 Hz, 2 H, tolyl
3
CH), 7.78 (d, JHH = 8.01 Hz, 2 H, tolyl CH). 13C NMR (C6D6, 126
(tolyl C). IR (cm−1): ν
̃
3014 (w), 2962 (w), 2917 (w), 1606 (w), 1502
MHz; ppm): δ 21.3 (CH3), 26.9 (Cy CH2), 27.7 (Cy CH2), 28.1 (Cy
CH2), 35.7 (Cy CH2), 37.7 (Cy CH2), 52.5 (Cexo Cp), 58.1 (Cy
NCH), 103.4 (Cexo Fv), 107.4 (C5H4 Cp), 109.3 (C5H4 Fv), 109.5
(C5H4 Cp), 110.8 (C5H4 Fv), 111.1 (C5H4 Cp), 112.6 (C5H4 Fv),
112.8 (C5H4 Cp), 112.9 (C5H4 Fv), 123.8 (Cipso Fv), 125.3 (Cipso Cp),
129.1(tolyl CH), 129.2 (tolyl CH), 129.4 (tolyl CH), 129.6 (3x tolyl
CH), 129.7 (tolyl CH), 129.8 (tolyl CH), 134.2 (tolyl C), 134.3 (tolyl
C), 136.1 (tolyl C), 136.4 (tolyl C), 143.2 (tolyl C), 143.8 (tolyl C),
(m), 1442 (m), 1289 (w), 1248 (w), 1155 (w), 1113 (w), 1040 (m),
867 (w), 790 (s), 743 (s), 675 (m), 596 (m). MS (EI, 70 eV): m/z
(%) 606 (100) [M − THF]+, 515 (6) [M − THF − tolyl]+, 438 (53)
[M − THF − (p-tol)2Fv]+, 258 (49) [(p-tol)2Fv]+. Anal. Calcd for
C44H44OZr: C, 77.71; H, 6.52. Found: C, 77.47; H, 6.92.
Synthesis of [η5-C5H4-CH(p-tol)2]2ZrCl2 (3). 2a (200 mg, 0.329
mmol) was dissolved in 10 mL of THF, and 0.66 mL (0.658 mmol) of
1 M HCl/Et2O-solution was added. During the addition the reaction
solution changed from red to yellow. The solution was stirred for 2 h
followed by removal of the solvent in vacuo. The resulting air- and
moisture-stable yellow residue was extracted with 25 mL of hot n-
hexane. Subsequent filtration and solvent removal yielded 172 mg
(78%) of 3 as a yellow solid. Single crystals suitable for X-ray
diffraction were obtained from a saturated n-hexane solution of 3 after
several days at room temperature. Mp: 125 °C. 1H NMR (CDCl3, 500
MHz; ppm): δ 2.28 (s, 12 H, CH3), 5.53 (s, 2 H, CexoH), 5.77 (m, 4
144.2 (tolyl C), 146.4 (tolyl C). IR (cm−1): ν
̃
v 3076 (m), 3018 (m),
̃
2922 (m), 2848 (m), 2360 (m), 2341 (m), 1505 (m), 1467 (m), 1445
(m), 1376 (w), 1312 (m), 1249 (m), 1184 (m), 1158 (m), 1144 (m),
1108 (m), 1021 (m), 945 (m), 891 (m), 864 (m), 847 (m), 819 (m),
802 (s), 789 (s), 761 (s), 744 (s), 667 (m), 575 (s). MS (EI, 70 eV):
m/z (%) 787 (4) [M]+, 606 (100) [M − HNCy2]+, 438 (62) [M − (p-
tol)2Fv − tol]+, 258 (8) [(p-tol)2Fv]+, 181 (6) [HNCy2]+. Anal. Calcd
for C52H59NZr: C, 79.13; H, 7.53; N, 1.77. Found: C, 79.19; H, 8.09;
N, 1.57.
Synthesis of {[η5-C5H4-CH(p-tol)2]2Zr(μ-O)}3 (6). An n-hexane
solution of 2a was treated with small amounts of water, resulting in the
formation of 6 as colorless crystals. Mp: 279 °C. Its complete
insolubility in common organic solvents prevented its NMR
3
H, C5H4), 6.01 (m, 4 H, C5H4), 6.97 (d, JHH = 8.03 Hz, 8 H, tolyl
CH), 7.05 (d, 3JHH = 7.93 Hz, 8 H, tolyl CH). 13C NMR (CDCl3, 126
MHz; ppm): δ 21.2 (CH3), 50.9 (Cexo), 115.6 (C5H4), 116.1 (C5H4),
129.0 (tolyl CH), 129.3 (tolyl CH), 136.4 (tolyl C), 137.0 (Cipso),
spectroscopic characterization. IR (cm−1): ν
̃
3726 (w), 3630 (w),
141.0 (tolyl C). IR (cm−1): ν
̃
3050 (w), 3022 (m), 2947 (s), 2919 (s),
3016 (w), 2876 (w), 1509 (m), 1039 (w), 1021(w), 791 (w), 761 (m),
717 (s), 685 (w), 646 (w), 605 (w), 574 (m). MS (EI, 70 eV): m/z
(%) 259 (100) [(p-tol)2Fv + H]+.
2855 (m), 1509 (s), 1453 (m), 1413 (m), 1375 (m), 1261 (w), 1109
(m), 1068 (m), 1040 (m), 1021 (m), 886 (w), 825 (s), 810 (s), 762
(s). MS (EI, 70 eV): m/z (%) 642 (27) [M − HCl]+, 421 (100) [M −
C5H4CH(p-tol)2]+. Anal. Calcd for C40H38Cl2Zr x 0.5 C6H14: C, 71.34;
H, 6.27. Found: C, 71.24; H, 6.15.
Synthesis of [η5:η1-C5H4-C(p-tol)2-C(C6H4Cl)N−]2Zr (7). 2a
(300 mg, 0.441 mmol) and 121.3 mg (0.882 mmol) of 4-
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1
chlorobenzonitrile were placed in a Schlenk tube. A 15 mL amount of
n-hexane was added, and the resulting orange suspension was stirred
overnight. The mother liquor was decanted, and the solid was washed
three times with 10 mL of n-hexane. Drying in vacuo afforded 371 mg
(88%) of 7 as an orange solid. Single crystals suitable for X-ray
diffraction were obtained from a THF/n-hexane solution of 7 after
room temperature. Mp: 238 °C dec. The H NMR spectra contains
1
two products in the ratio 1 (9):2 (9a/9a′); H NMR (C6D6, 500
MHz; ppm): 9, δ 2.09 (s, 6 H, CH3), 2.20 (s, 6 H, CH3), 4.72 (m, 2 H,
C5H4), 5.02 (m, 2 H, C5H4), 6.34 (m, 2 H, C5H4), 6.92 (m, 2 H,
C5H4); 9a/9a′, δ 2.03 (s, 6 H, CH3), 2.17 (s, 3 H, CH3), 2.18 (s, 3 H,
CH3), 5.12 (m, 1 H, C5H4), 5.53 (m, 1 H, C5H4), 5.56 (m, 1 H,
C5H4), 5.63 (m, 1 H, C5H4), 5.76 (m, 1 H, C5H4), 5.97 (m, 1 H,
C5H4), 6.50 (m, 1 H, C5H4), 6.75 (m, 1 H, C5H4); 9/9a/9a′, aryl H
6.64, 6.87−7.13, 7.25−7.31, 7.61, 7.75, 7.77, 7.83, 7.88, 7.94, 8.11,
8.32, 8.36, 8.59. The scarce solubility in common organic solvents
1
several days at room temperature. Mp: 197 °C. H NMR (C6D6, 500
MHz; ppm): δ 2.04 (s, 6 H, CH3), 2.16 (s, 6 H, CH3), 5.30 (m, 2 H,
C5H4), 5.44 (m, 2 H, C5H4), 5.84 (m, 2 H, C5H4), 6.93 (d, 3JHH = 8.39
Hz, 4 H, p-Cl-phenyl CH), 6.95 (m, 2 H, C5H4), 9.98 (d, 3JHH = 7.86
prevented its 13C NMR spectroscopic characterization. IR (cm−1): ν
̃
3
Hz, 4 H, tolyl CH), 7.01 (d, JHH = 7.83 Hz, 4 H, tolyl CH), 7.58 (d,
3
3JHH = 7.77 Hz, 4 H, tolyl CH), 7.71 (d, JHH = 8.37 Hz, 4 H, p-Cl-
3053 (w), 3024 (w), 2921 (w), 2846 (w), 1508 (w), 1488 (w), 1442
(w), 1149 (w), 1068 (w), 1024 (m), 1009 (s), 916 (w), 867 (w), 815
(m), 791 (m), 744 (s), 709 (s), 686 (s), 635 (m), 618 (m), 585 (m).
MS (EI, 70 eV): m/z (%) 788 (2) [M − benzophenone]+, 606 (53)
[M − 2 benzophenone]+, 258 (16) [(p-tol)2Fv]+, 182 (61)
[benzophenone]+. Anal. Calcd for C66H56O2Zr: C, 81.52; H, 5.80.
Found: C, 81.64; H, 5.98.
3
phenyl CH), 7.77 (d, JHH = 7.81 Hz, 4 H, tolyl CH). 13C NMR
(C6D6, 126 MHz; ppm): δ 21.2 (CH3), 21.3 (CH3), 69.9 (Cexo Cp),
107.0 (C5H4), 109.5 (C5H4), 109.9 (C5H4), 118.0 (C5H4), 128.2 (p-Cl-
phenyl CH), 129.2 (tolyl CH), 129.6 (tolyl CH), 130.7 (tolyl CH),
131.9 (tolyl CH), 132.4 (p-Cl-phenyl CH), 135.8 (p-Cl-phenyl C),
136.9 (tolyl C), 137.1 (tolyl C), 139.0 (p-Cl-phenyl C), 140.3 (tolyl
Synthesis of {[η5:η1-C5H4C(p-tol)2][η5-C5H4-CH(p-tol)2]Zr(μ-
H)}2 (10). 2a (330 mg, 0.485 mmol) was dissolved in 35 mL of n-
hexane. The suspension was treated with molecular hydrogen for 30
min. The resulting red-orange solution was reduced to approximately 5
mL. After several days orange crystals were formed, which were
washed three times with n-hexane. Drying in vacuo afforded 111 mg
(38%) of 10 as orange crystals. Mp: 214 °C dec. 1H NMR (C6D6, 500
MHz; ppm): δ −3.24 (s, 2 H, (μ-H)2), 2.09 (s, 6 H, CH3), 2.12 (s, 6
H, CH3), 2.14 (s, 6 H, CH3), 2.28 (s, 6 H, CH3), 4.37 (m, 2 H, C5H4
Fv), 4.67 (m, 2 H, C5H4 Fv), 4.77 (m, 2 H, C5H4 Cp), 4.79 (m, 2 H,
C5H4 Cp), 4.85 (m, 2 H, C5H4 Cp), 4.88 (m, 2 H, C5H4 Cp), 5.22 (s,
C), 140.4 (tolyl C), 148.9 (Cipso Cp), 192.4 (NC). IR (cm−1): ν
̃
3109 (w), 3015 (w), 2921 (w), 2360 (w), 1577 (m), 1559 (m), 1510
(m), 1481 (m), 1189 (m), 1168 (m), 1092 (m), 1057 (m), 1022 (m),
985 (m), 915 (w), 890 (w), 863 (w), 827 (m), 806 (m), 793 (m), 777
(s), 732 (m), 708 (m), 680 (m), 661 (m), 640 (m), 620 (m), 587 (m).
MS (EI, 70 eV): m/z (%) 743 (0.4) [M − p-chlorobenzonitrile]+, 485
(0.4) [M − p-chlorobenzonitirile − (p-tol)2Fv]+, 258 (23) [(p-
tol)2Fv]+, 137 (100) [p-chlorobenzonitrile]+. Anal. Calcd for
C54H44Cl2N2Zr·C4H8O: C, 72.93; H, 5.49; N, 2.93. Found: C,
73.38; H, 5.65; N, 2.89.
Synthesis of [η5:η1-C5H4-C(p-tol)2-MeC4H6N−]2Zr (8). 2a (500
mg, 0.735 mmol) was placed in a Schlenk tube and dissolved in 10 mL
of n-hexane, and 0.139 mL (1.47 mmol) of 2-methyl-1-pyrroline was
added. The dark red solution was stirred overnight. The volume of the
solution was reduced, the mother liquor was decanted, and the solid
was washed three times with 5 mL of n-hexane. Drying in vacuo
afforded 210 mg (37%) of 8 as a light yellow solid. Single crystals
suitable for X-ray diffraction were obtained from a toluene/n-hexane
solution of 8 after several days at 0 °C. Mp: 200 °C. 1H NMR (C6D6,
500 MHz; ppm): δ 1.47 (s, 6 H, pyrroline CH3), 1.63 (m, 2 H, CH2),
1.74 (m, 2 H, CH2), 1.86 (m, 2 H, CH2), 2.15 (s, 6 H, tolyl CH3), 2.22
(s, 6 H, tolyl CH3), 2.55 (m, 2 H, CH2), 3.41 (m, 2 H, CH2), 3.81 (m,
2 H, CH2), 4.95 (m, 2 H, C5H4), 5.26 (m, 2 H, C5H4), 5.96 (m, 2 H,
C5H4), 6.59 (d, 3JHH = 7.62 Hz, 2 H, tolyl CH), 6.85 (m, 2 H C5H4, 2
3
2 H, CexoH), 6.51 (m, 2 H, C5H4 Fv), 6.91 (d, JHH = 7.82 Hz, 4 H,
tolyl CH), 6.95 (d, 3JHH = 8.04 Hz, 4 H, tolyl CH), 6.96 (m, 2 H, C5H4
Fv), 7.08 (d, 3JHH = 8.09 Hz, 4 H, tolyl CH), 7.11 (d, 3JHH = 7.99 Hz, 4
H, tolyl CH), 7.13 (d, 3JHH = 7.80 Hz, 4 H, tolyl CH), 7.43 (d, 3JHH
=
7.94 Hz, 4 H, tolyl CH), 7.50 (d, 3JHH = 7.81 Hz, 4 H, tolyl CH), 7.73
(d, 3JHH = 7.82 Hz, 4 H, tolyl CH). 13C NMR (C6D6, 126 MHz; ppm):
δ 21.3 (CH3), 21.3 (CH3), 21.4 (CH3), 21.5 (CH3), 52.3 (Cexo Cp),
101.3 (C5H4 Cp), 104.3 (2 × C5H4 Cp), 104.8 (C5H4 Fv), 107.2
(C5H4 Fv), 108.2 (Cexo Fv), 109.1 (C5H4 Fv), 110.6 (C5H4 Fv), 115.7
(C5H4 Cp), 124.0 (Cipso Cp), 124.6 (Cipso Fv), 128.1 (tolyl CH), 128.4
(tolyl CH), 129.2 (tolyl CH), 129.3 (tolyl CH), 129.6 (tolyl CH),
129.7 (tolyl CH), 130.1 (tolyl CH), 133.5 (tolyl CH), 133.8 (tolyl C),
134.6 (tolyl C), 135.6 (tolyl C), 136.7 (tolyl C), 142.2 (tolyl C), 143.5
(tolyl C), 144.8 (tolyl C), 147.6 (tolyl C). IR (cm−1): ν
̃
3020 (w),
H tolyl CH), 7.00 (d, 3JHH = 7.33 Hz, 2 H, tolyl CH), 7.06 (d, 3JHH
=
8.15 Hz, 2 H, tolyl CH), 7.13 (d, 3JHH = 8.06 Hz, 2 H, tolyl CH), 7.35
(d, 3JHH = 8.17 Hz, 2 H, tolyl CH), 7.77 (d, 3JHH = 7.90 Hz, 2 H, tolyl
2917 (w), 2860 (w), 2360 (w), 1505 (m), 1448 (m), 1271 (s), 1187
(m), 1158 (m), 1112 (m), 1042 (m), 1020 (m), 980 (w), 897 (w),
862 (m), 851 (m), 839 (m), 806 (s), 794 (s), 761 (s), 745 (s), 735 (s),
666 (w), 572 (s). MS (EI, 70 eV): m/z (%) 605 (100) [(C5H4C(p-
tol)2)2Zr − H]+, 259 (5) [(p-tol)2Fv + H]+, 258 (17) [(p-tol)2Fv]+.
Anal. Calcd for C80H76Zr2: C, 78.76; H, 6.28. Found: C, 78.53; H,
6.54.
3
CH), 8.15 (d, JHH = 7.71 Hz, 2 H, tolyl CH). 13C NMR (C6D6, 126
MHz; ppm): δ 20.9 (tolyl CH3), 21.0 (tolyl CH3), 27.6 (CH2), 33.8
(pyrroline CH3), 39.3 (CH2), 56.2 (CH2), 61.6 (Cexo Cp), 95.3
(pyrroline C), 101.8 (C5H4), 110.3 (C5H4), 110.6 (C5H4), 111.2
(C5H4), 126.7 (tolyl CH), 128.4 (tolyl CH), 128.8 (tolyl CH), 129.1
(tolyl CH), 130.0 (tolyl CH), 130.8 (tolyl CH), 131.3 (tolyl CH),
131.7 (tolyl CH), 135.5 (tolyl C), 135.7 (tolyl C), 144.2 (tolyl C),
145.7 (Cipso Cp), 146.2 (tolyl C). 15N NMR (C6D6, 51 MHz; ppm): δ
ASSOCIATED CONTENT
* Supporting Information
■
S
197.0. IR (cm−1): ν
̃
2963 (m), 2929 (m), 2866 (w), 2778 (w), 1508
Text, tables, figures, and CIF files giving synthesis and analytical
data of [η5:η1-C5H4C(Ph)2]2Zr(THF) (2b), 1H NMR
spectra of compounds 2a,b, 3−5, and 7−10, and selected
crystallographic data. This material is available free of charge via
the Internet at http://pubs.acs.org.
(m), 1477 (m), 1365 (w), 1313 (w), 1297 (w), 1260 (w), 1215 (w),
1191 (w), 1100 (m), 1038 (m), 1022 (m), 1022 (m), 1002 (m), 962
(w), 929 (w), 901 (w), 860 (m), 835 (m), 801 (s), 787 (s), 755 (m),
585 (w), 563 (w). MS (EI, 70 eV): m/z (%): 772 (1) [M]+, 757 (11)
[M − CH3]+, 689 (13) [M − pyrroline]+, 606 (100) [M − 2
pyrroline]+, 514 (5.9) [M − (p-tol)2Fv]+, 260 (15) [(p-tol)2Fv + 2H]+,
83 (55) [pyrroline]+. Anal. Calcd for C50H54N2Zr: C, 77.57; H, 7.03;
N, 3.62. Found: C, 77.19; H, 7.69; N, 3.39.
AUTHOR INFORMATION
Notes
■
Synthesis of [η5:η1-C5H4-C(p-tol)2-C(Ph)2O−]2Zr (9). 2a (500
mg, 0.735 mmol) and 268 mg (1.47 mmol) of benzophenone were
placed in a Schlenk tube. A 15 mL amount of n-hexane was added, and
the resulting light yellow suspension was stirred overnight. The
mother liquor was decanted, and the solid was washed four times with
10 mL of n-hexane. Drying in vacuo afforded 435 mg (61%) of 7 as a
light yellow solid. Single crystals suitable for X-ray diffraction were
obtained from a THF/n-hexane solution of 9 after several days at
The authors declare no competing financial interest.
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