Intramolecular activation of pendant alkenyl group as a tool for modification of the zirconocene framework

Article abstract of DOI:10.1016/j.ica.2011.03.061

The diphenyl zirconocene [(η⁵-C₅H ₅){η⁵-C₅H₄CMe ₂(CH₂)₂CHCH₂}ZrPh₂] (2) was readily obtained from the corresponding zirconocene dichlo

Full text of DOI:10.1016/j.ica.2011.03.061

Inorganica Chimica Acta 373 (2011) 291–294
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Note
Intramolecular activation of pendant alkenyl group as a tool for modification
of the zirconocene framework
⇑
ˇ
ˇ
ˇ
ˇ
Martin Lamac, Michal Horácek, Jirí Kubišta, Jirí Pinkas
´
J. Heyrovsky Institute of Physical Chemistry of ASCR, v.v.i., Dolejškova 2155/3, 182 23 Prague 8, Czech Republic
a r t i c l e i n f o
a b s t r a c t
The diphenyl zirconocene [(g g
5-C5H5){ 5-C5H4CMe2(CH2)2CH@CH2}ZrPh2] (2) was readily obtained from
the corresponding zirconocene dichloride 1 and two equivalents of phenyllithium. Upon thermal treat-
Article history:
Received 11 January 2011
Received in revised form 23 March 2011
Accepted 26 March 2011
Available online 1 April 2011
ment at 80 °C, complex 2 released benzene, with concomitant activation of the pendant double bond
and formation of intramolecularly
CHCH2C6H4}Zr] (3). Both Zr–C -bonds in 3 easily undergo nucleophilic reactions with two equivalents
of HCl or one equivalent of Cl2PPh giving rise to zirconocene dichlorides with pendant phenyl group
[(
5-C5H5){ 5-C5H4CMe2(CH2)4Ph}ZrCl2] (4) or with 1-phenylphosphindolinyl moiety [( 5-C5H5)-
5-C5H4CMe2(CH2)2cyclo-CHCH2C6H4P(Ph)}ZrCl2] (5), respectively.
a-tethered zirconaindane [(g , ,g
5-C5H5){g5 g1 1-C5H4CMe2(CH2)2-
r
Keywords:
Metallocenes
Zirconium
Benzyne complexes
Metallacycles
g
g
g
{g
Ó 2011 Published by Elsevier B.V.
Functionalized cyclopentadienyl ligands
Pendant alkenyl group
1. Introduction
complex [(g g
5-C5H5){ 5-C5H4CMe2(CH2)2CH@CH2}ZrPh2] (2), and
to use the resulting, intramolecularly tethered zirconaindane 3 as
a precursor for nucleophilic attack by Cl2PPh. This introduces teth-
ered 1-phenylphosphinindolinyl functionality into the bent zirco-
nocene dichloride framework.
Bent group 4 metallocenes have found numerous applications
as reagents in organic synthesis and as catalyst components in ole-
fin oligo/polymerization [1,2]. The main current interest is focused
on design of complexes with targeted structures and their struc-
ture modification to enhance the catalytic performance. Neverthe-
2. Results and discussion
less, high reactivity of metal–ligands
r-bonds in bent metallocenes
precludes simple synthetic modifications on their cyclopentadienyl
rings, that is feasible for metallocenes of late transition metals (e.g.
ferrocene). Generally, an appropriate functionality is introduced
during the ligand synthesis and the modified ligand is then
transferred to early transition metal (by transmetallation, amine
elimination). On the other hand, there are only rare examples of
transformations of functional group at the bent metallocene frame-
work [3–8].
Particularly, group 4 metallocenes bearing cyclopentadienyl
rings modified with a pendant phosphino functionality represent
interesting systems capable of reversible intramolecular coordina-
tion or in the intermolecular formation of early–late complexes
[9,10].
Zirconocene diphenyl complex 2 was conveniently prepared in
high yield from the corresponding dichloride 1 and PhLi in diethyl
ether (Scheme 1). The compound 2 showed C2v symmetry in C6D6
solution as revealed by 1H and 13C NMR spectra (see Section 4).
The pendant alkenyl chain remained uncoordinated (@CH2: dH
=
4.87–4.95 ppm; dC = 114.13 ppm; @CH: dH = 5.55–5.70 ppm; dC =
139.19 ppm) and the Zr–Cipso signal appeared at dC = 183.35 ppm
showing the phenyl group
r-bonding to zirconium center. The EI-
MS measurements showed limited thermal stability of 2, as the
molecular ion at m/z 470 could be observed only at the beginning
of experiment. As the measurement proceeded the fragment at m/
z 470 ceased, fragment at m/z 392 [M-PhH]+ became the ion with
the highest m/z and the spectrum apparently corresponded to 3 (vide
infra).
Storing C6D6 solution of 2 in a sealed NMR tube for 14 days at
room temperature led to ca 2% conversion of 2–3. Further heating
of the tube to 80 °C (see Supplementary data) for 20 h led to com-
plete vanishing of signals corresponding to 2 with concomitant for-
mation of benzene (singlet signal at dH = 7.15 ppm). Nevertheless,
the expected product 3 was formed only in ca 80% purity being
Herein, we describe
a synthetic pathway for simple and
straightforward modification of the zirconocene framework with
a phosphine functionality. Our strategy is to employ a thermally
induced intramolecular activation of pendant alkenyl chain in
⇑
Corresponding author.
E-mail address: pinkas@jh-inst.cas.cz (J. Pinkas).
0020-1693/$ - see front matter Ó 2011 Published by Elsevier B.V.
doi:10.1016/j.ica.2011.03.061

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M. Lamac et al. / Inorganica Chimica Acta 373 (2011) 291–294
292
Chart 1.
Scheme 1.
zirconocene dichloride 4 with pendant phenyl group (Scheme 3).
Complex 4 restored C2v symmetry and the presence of phenyl group
was unambiguously revealed from 1H and 13C NMR spectra. An
attempt to perform a silicon transfer to zirconacycle by reacting 3
with Cl2SiMe2 did not succeed even when prolonged reaction
heating was used. Indeed, the difficulty of silacycle formation from
reaction of zirconacycles with either SiCl4 [19] or Cl2Me2Si [20]
was reported.
contaminated by at least two side products arising probably from
the exchange of -bonded Zr–Ph group with C6D6 [11]. Therefore,
the thermolysis of diphenylzirconocene 2 in a preparative scale
was conducted in heptane at 80 °C and proceeded smoothly to give
the tethered zirconaindane 3 in high yield (Scheme 2).
r
The reaction is an intramolecular analogue to known [2 + 2]
cycloadditions of zircona-g g
2-benzyne [12–14] and titana- 2-ben-
zyne [15] intermediates with terminal olefines. The formation of
On the other side, Cl2PPh reacted smoothly with 3 in toluene-d8
with a formation of zirconocene dichloride 5 bearing 1-phenyl-
3 proceeded regioselectively with a formation of zirconaindane
tethered in
metallaindanes, where b-substitution was reported [12–15].
Noticeably, thermal activation of
5-{(C5H3-3-allyl)Si-
Me2(C5H4)}ZrPh2] at 80 °C led to a zirconaindane with an intramo-
lecular tethering in b-position [16]. The -tethering in 3 is
a-position contrary to the intermolecularly formed
phosphindolinyl framework connected at
a-position via the
a
[ ,g
g5
(CH2)2CMe2 spacer to one cyclopentadienyl ring. The molecule
possesses a stereogenic centre at phosphorus atom giving rise to
a diastereotopic set of signals for CMe2 group (dH: 1.24 and
1.28 ppm; dC: 26.91 and 27.45 ppm) and CH2 groups which is most
representatively shown for benzylic C6H4CH2 group (dH: 2.51 and
3.11 ppm). The phosphorus atom remained uncoordinated to the
zirconium centre giving rise to a signal at dP = 10.0 ppm close to
values known for similar ‘‘organic’’ 2-phospholene derivatives
(dP = 10–11 ppm) [21].
A reaction of 3 with 2 equivalents of ClPPh2 in toluene-d8 was
attempted with the aim to introduce two diphenyl phosphine
functionalities into the zirconocene backbone. Nevertheless, the
reaction is less selective in comparison to the reaction with Cl2PPh.
The 1H and 13C NMR spectra showed a cleavage of the Zr–CH bond
with concomitant preservation of Zr–C6H4 bond (a characteristic
signal at dC = 178.43 ppm). Moreover, a range of new phosphorus
signals was detected in 31P NMR spectra besides the signal of unre-
acted ClPPh2. The main products showed singlets at À13.2 and
À8.9 ppm. Unfortunately, we have failed in isolation of any pure
product from the reaction. Therefore, we could only tentatively
propose the structure of a potential product as depicted in
Chart 1 on the basis of NMR data. The optimalisation of reaction
a
probably preferred due to its ansa-character, since the C4 spacer
between zirconium and cyclopentadienyl ring is more common
than the C5 spacer [17]. The 1H and 13C NMR spectra revealed
the absence of olefinic group and particularly low symmetry of
complex 3 with diastereotopic CH2 and CMe2 groups in the spacer.
The five-membered zirconacycle gave rise to characteristic signals
for the methine ZrCH group (dH: 2.67–2.78 ppm; dC: 55.11 ppm)
benzylic C6H4CH2 group (dH: 2.75–2.87 ppm and 3.04 ppm; dC:
38.19 ppm), and for two quaternary carbons in C6H4 group (dC
(ZrC): 182.38 ppm; dC (CCH2): 144.89 ppm). The EI-MS spectrum
showed a highly abundant molecular peak at m/z 392 and a base
peak of uncertain composition at m/z 259.
The use of nucleophilic attack on zirconacycles as a tool for
synthesis of various functionalised organic species (mainly
heterocycles) was widely reported [18]. In this respect, complex 3
presented an ideal precursor for a wide variety of nucleophilic reac-
tions leading to functionalised zirconocene dichlorides. A reaction of
3 with 2 equivalents of dry HCl in diethyl ether led to immediate
cleavage of both Zr–C bonds and afforded the corresponding
Scheme 2.
Scheme 3.

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M. Lamac et al. / Inorganica Chimica Acta 373 (2011) 291–294
293
conditions and investigations into reactivity of 3 towards other
nucleophiles is currently under progress.
470 (M+Å, 10); 396 (22); 394 (26); 393 (28); 392 ([M–PhH]+, 64);
261 (67); 260 (58), 259 (60); 245 (23); 233 (40); 205 (28); 154
(33); 115 (17); 78 ([PhH]+, 100); 77 (89). Anal. Calc. for C29H32Zr
(471.77): C 73.83, H 6.84. Found C 74.15, H 6.97%.
3. Conclusion
4.2. Preparation of zirconaindane [(g , , -
5-C5H5){g5 g1 g1
C5H4CMe2(CH2)2CHCH2C6H4}Zr] (3)
The present study has shown an intramolecular activation of
pendant alkenyl group at the zirconium centre leading to a forma-
tion of new Zr–C bond in the tethered zirconaindane moiety. The
both Zr–C bonds in the zirconaindane could be cleaved with HCl
or Cl2PPh to give zirconocene dichlorides with phenyl or 1-phenyl-
phosphindolinyl functionality. The reaction has a synthetic poten-
tial for the preparation of diverse functionalised zirconocene
dichlorides. Versatility of the reaction arises from a wide family
of potential zirconocene precursors (e.g. zirconocenes featuring
Compound 2 (300 mg, 0.64 mmol) in heptane (10 ml) was stir-
red at 80 °C for 17 h. The mixture gradually changed its colour from
slightly yellow to orange-brown as the reaction proceeded. The
resulting mixture was filtered and the filtrate was concentrated
by slow evaporation of the solvent. The resulting orange solution
was evaporated to dryness, washed with minimum of heptane
and dried in vacuum. Yield of the yellowish waxy solid was
220 mg (87%).
g
5-cyclopentadienyl- 1-ansa-bridges [17]) and many commer-
g
cially available nucleophiles RnECl2 (where E is a heteroatom e.g.
P, As, Sb, Bi ...) known to be involved in heteroatom transfer reac-
tions to metallacycles.
1H NMR (C6D6): 0.62, 1.20 (2 Â s, 2 Â 3H, CMe2); 1.17–1.30 (m,
1H, CMe2CH2, Ha); 1.17–1.30 (m, 1H, CMe2CH2CH2, Ha); 1.76–1.86
(m, 1H, CMe2CH2CH2, Hb); 2.29–2.41 (m, 1H, CMe2CH2, Hb); 2.67–
2
3
2.78 (m, 1H, ZrCH); 2.82 (dd, JHH = 16.2 Hz, JHH = 6.6 Hz, 1H,
2
3
4. Experimental
C6H4CH2, Ha); 3.04 (dd, JHH = 16.2 Hz, JHH = 11.7 Hz, C6H4CH2,
Hb); 5.05–5.09 (m, 1H, C5H4, H ); 5.19–5.23 (m, 1H, C5H4, Hb);
5.89 (s, 5H, C5H5); 5.98–6.03 (m, 1H, C5H4, Hb); 6.50–6.54 (m, 1H,
a
All reactions with moisture- and air-sensitive compounds were
carried out under argon (99.998%) using standard Schlenk tech-
niques. Solvents were dried (by sodium/benzophenone), distilled
C5H4, H ); 6.80–6.84 (m, 1H, C6H4); 6.96–7.01 (m, 1H, C6H4);
a
7.06–7.11 (m, 2H, C6H4). 13C{1H} (C6D6): 25.29 (CMe2); 31.81
(CMe2CH2CH2); 33.36 (CMe2); 35.71 (CMe2); 38.19 (C6H4CH2);
40.04 (CMe2CH2); 55.11 (ZrCH); 102.60, 104.60, 108.54 (CH,
C5H4); 112.16 (C5H5); 116.05 (CH, C5H4); 124.04, 125.99, 128.57,
136.94 (CH, C6H4); 137.61 (Cipso, C5H4); 144.89 (CCH2, C6H4);
182.38 (ZrC, C6H4). EI-MS, m/z (relative abundance): 396 (37);
395 (11); 394 (41); 393 (47); 392 (M+Å, 92); 263 (37); 262 (40);
261 (95); 260 (91); 259 (100); 246 (24); 233 (21); 91 (35). Anal.
Calc. for C23H26Zr (393.66): C 70.17, H 6.66. Found C 70.31, H 6.81%.
and stored over a sodium mirror. [(g
5-C5H5)ZrCl3], PhLi (1.8 M
solution in dibutyl ether), dry HCl (1 M solution in diethyl ether),
Cl2PPh (97%) and ClPPh2 (98%) were obtained from Aldrich and
used as received. Cl2SiMe2 was purified by refluxing over copper
turnings and distilled prior to use. Complex 1 was prepared accord-
ing to the literature procedure [22]. 1H and 13C NMR spectra were
recorded on a Varian Mercury 300 spectrometer at 300.0 and
75.4 MHz at 293 K. Chemical shifts (d/ppm) are given relative to
solvent signals (C6D6: dH 7.15 ppm, dC 128.00 ppm, toluene-d8: dH
(CH2D signal) 2.08 ppm, dC (CD3 signal) 20.40 ppm). EI-MS spectra
were obtained on a VG-7070E mass spectrometer at 70 eV. Crystal-
line samples in sealed capillaries were opened and inserted into
the direct inlet under argon. IR spectra were taken in an air-pro-
tecting cuvette on a Nicolet Avatar FTIR spectrometer in the range
400–4000 cmÀ1. KBr pellets were prepared in a glovebox Labmas-
ter 130 (mBraun) under purified nitrogen. Melting points of sam-
ples in sealed capillaries were measured on a Koffler block and
were uncorrected. Elemental analyses were carried out on a FLASH
2000 CHN-O Automatic Elemental Analyzer (Thermo Scientific).
4.3. Preparation of [(g g
5-C5H5){ 5-C5H4CMe2(CH2)4Ph}ZrCl2] (4)
Solution of 3 (45 mg, 0.11 mmol) in heptane (2 ml) was cooled
l,
to À78 °C and an excess of diethyl ether solution of HCl (300
l
1.0 M, 0.30 mmol) was added. The reaction mixture was allowed
to warm to room temperature to obtain yellow solution from
which a white solid precipitated within several minutes. The mix-
ture was stirred overnight, and then the solid was isolated, washed
with heptane (2 Â 0.5 ml), and dried in vacuum. Yield of a white
microcrystalline solid was 22 mg (47%).
M.p.: 140 °C. 1H NMR (C6D6): 0.87–1.01 (m, 2H, CMe2CH2CH2);
1.28–1.46 (m, 4H, CMe2CH2 and CMe2CH2CH2CH2); 1.32 (s, 6H,
CMe2); 2.36–2.44 (m, 2H, CH2Ph); 5.75 (pseudo t, 2H, C5H4); 5.97
(s, 5H, C5H5); 6.02 (pseudo t, 2H, C5H4); 7.01–7.22 partially over-
lapped by solvent signal (m, 5H, Ph). 13C{1H} (C6D6): 24.25
(CMe2CH2CH2); 27.22 (CMe2); 32.30 CMe2CH2CH2CH2); 36.02
(CH2Ph); 36.39 (CMe2); 46.77 (CMe2CH2); 112.51 (CH, C5H4);
115.74 (C5H5); 115.84 (CH, C5H4); 126.00 (CHpara, Ph); 128.58,
4.1. Preparation of [(g g
5-C5H5){ 5-C5H4CMe2(CH2)2CH@CH2}ZrPh2] (2)
Zirconocene dichloride 1 (400 mg, 1.03 mmol) was degassed
and dissolved in diethyl ether (20 ml). The solution was cooled to
À78 °C and a dibutyl ether solution of PhLi (1.20 ml, 1.8 M,
2.06 mmol) was slowly added during 15 min. The reaction mixture
was allowed to warm to À5 °C and then all volatiles were evapo-
rated in vacuum (without heating). Remaining yellowish wax
was extracted with heptane (130 ml). Evaporation of solvent gave
the product as a yellow waxy solid. Yield 0.385 g (79%).
128.65 (CHortho and CHmeta, Ph); 142.75 (Cipso, Ph); 143.39 (Cipso
,
C5H4). EI-MS, m/z (relative abundance): 470 (11), 468 (22), 467
(13), 466 (30), 465 (17), 464 (M+Å, 28), 433 (11), 431 (12), 430
(11), 429 ([MÀCl]+, 18), 417 (16), 414 (16), 413 (29), 403 (18),
401 (24), 399 ([MÀC5H5]+, 22), 339 (35), 338 (22), 337 (88), 336
(54), 335 (70), 334 (86), 333 (96), 332 (67), 331 ([MÀ(CH2)4Ph]+,
94), 300 (51), 299 (87), 298 (85), 297 (100), 296 (89), 295
([MÀ(CH2)4PhÀHCl]+, 97), 231 (25), 229 (44), 227 (62), 226 (17),
225 (64), 107 (47), 106 (82), 105 (85), 65 ([C5H5]+, 44). IR (KBr):
3102 (s), 3087 (m), 3060 (m), 3029 (m), 2977 (m), 2959 (s), 2927
(vs), 2899 (m), 2871 (m), 2854 (s), 1600 (w), 1496 (m), 1484 (m),
1452 (m), 1438 (m), 1412 (w), 1383 (m), 1365 (m), 1324 (vw),
1295 (vw), 1244 (vw), 1180 (vw), 1143 (w), 1052 (w), 1043 (m),
1016 (s), 913 (vw), 892 (w), 849 (s), 831 (vs), 814 (vs), 747 (s),
1H NMR (C6D6): 0.73 (s, 6H, CMe2); 1.20–1.29 (m, 2H,
CMe2CH2); 1.61–1.72 (m, 2H, CMe2CH2CH2); 4.87–4.95 (m, 2H,
@CH2); 5.55–5.70 partially overlapped (m, 1H, CH@); 5.67 pseudo
t, 2H, C5H4); 5.84 (s, 5H, C5H5); 6.04 (pseudo t, 2H, C5H4); 7.08
3
4
(tt, JHH = 6.9 Hz, JHH = 1.5 Hz, 2H, CHpara, Ph); 7.14–7.21 partially
overlapped by solvent signal (m, 4H, CHmeta, Ph); 7.34–7.39 (m,
4H, CHortho
,
Ph). 13C{1H} (C6D6): 26.85 (CMe2); 29.32
(CMe2CH2CH2); 35.33 (CMe2); 45.85 (CMe2CH2); 110.59, 112.18
(CH, C5H4); 112.58 (C5H5); 114.13 (@CH2); 125.68 (CHpara, Ph);
126.68 (CHmeta, Ph); 136.76 (CHortho, Ph); 139.15 (Cipso, C5H4);
139.19 (CH@); 183.35 (Cipso, Ph). EI-MS, m/z (relative abundance)

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M. Lamac et al. / Inorganica Chimica Acta 373 (2011) 291–294
294
735 (m), 699 (vs), 687 (w), 598 (vw), 497 (w). Anal. Calc. for
23H28ZrCl2 (466.57): C 59.20, H 6.05. Found C 59.07, H 6.09%.
of Education, Youth and Sports of the Czech Republic (Project
LC06070) is gratefully acknowledged.
C
4.4. NMR scale generation of 5 from the reaction of zirconaindane 3
with Cl2PPh
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2011.03.061.
Cl2PPh (15
(43 mg, 110
l
l, 110
lmol) was dropped by Hamilton syringe to 3
lmol) in toluene-d8 (0.8 ml). The solution slowly
changed colour from orange to yellow. The mixture was stirred
for additional 30 min, transferred to a NMR tube and degassed by
freeze–thaw process. The NMR tube was sealed off by flame and
measured directly in the NMR probe. The NMR data (see below)
show almost quantitative formation of 5.
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2
13C{1H} (toluene-d8): 26.91, 27.45 (CMe2); 29.42 (d, JPC = 24.0 Hz,
2
CMe2CH2CH2); 36.43 (CMe2); 41.00 (d, JPC = 24.0 Hz, CH2C6H4);
1
3
45.65 (d, JPC = 7.5 Hz, PCH); 46.29 (d, JPC = 12.8 Hz, CMe2CH2);
112.77, 112.90, 115.61, 115.65 (CH, C5H4); 115.71 (C5H5); 125.34,
127.12 (d, JPC = 6.8 Hz), 128.60 (d, JPC = 6.8 Hz), 128.98, 131.61 (d,
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1
1
140.19 (d, JPC = 15.8 Hz, CqP, C6H4); 140.40 (d, JPC = 30.8 Hz, CqP,
2
C6H5); 143.06 (Cipso, C5H4); 148.11 (d, JPC = 4.5 Hz, CCH2, C6H4).
31P{1H}(toluene-d8): 10.0.
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The financial support from the Czech Science Foundation (Pro-
jects GA203/09/1574 and GPP207/10/P200) and from the Ministry