Indenyl esters as potential electronically modified cyclopentadienyl ligands for transition metal complexes

Article abstract of DOI:10.1016/S0040-4039(02)00766-9

The preparation of two new indenyl esters 2-(2,4,6-trimethylbenzoyloxy)indene (1) and 2-(adamantanoyloxy)indene (2) is reported. Both compounds can be deprotonated with alkyllithiums such as n-BuLi and the resulting anions trapped by addition of TMSCl or iodomethane, rendering them as potential electronically modified cyclopentadienyl ligand analogues for complexation with transition metals.

Full text of DOI:10.1016/S0040-4039(02)00766-9

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 4149–4151
Indenyl esters as potential electronically modified
cyclopentadienyl ligands for transition metal complexes
Reko Leino,* Hendrik J. G. Luttikhedde, Lena La˚ngstedt and Antti Penninkangas
,
,
Laboratory of Polymer Technology, Abo Akademi University, FIN-20500 Abo, Finland
Received 22 March 2002; accepted 18 April 2002
Abstract—The preparation of two new indenyl esters 2-(2,4,6-trimethylbenzoyloxy)indene (1) and 2-(adamantanoyloxy)indene (2)
is reported. Both compounds can be deprotonated with alkyllithiums such as n-BuLi and the resulting anions trapped by addition
of TMSCl or iodomethane, rendering them as potential electronically modified cyclopentadienyl ligand analogues for complexa-
tion with transition metals. © 2002 Elsevier Science Ltd. All rights reserved.
Substituted indenes function as versatile ligand precur-
sors for a variety of transition metal complexes.1 In
particular, bridged and unbridged group 4 bis(indenyl)
metallocenes have gained attention as stoichiometric
reagents or catalyst precursors for enantioselective
organic transformations2 and catalytic olefin polymer-
ization.3 The catalytic performance of these complexes
is determined by steric and electronic effects induced by
the ancillary ligand substituents. Although synthetic
methods for preparing 1- (or 3-) and 2-alkyl/aryl substi-
tuted indenyl ligand precursors are well established,4,5
the preparation of heteroatom functionalized indenes
has remained relatively unexplored.6–9 We were inter-
ested in studying the applicability of indenyl esters as
potential electronically modified cyclopentadienyl lig-
ands for transition metal complexes. Herein we report
the simple preparation and spectroscopic characteriza-
tion of two new -OCOR ester substituted indenes,
2-(2,4,6-trimethylbenzoyloxy)indene (1) and 2-(adaman-
tanoyloxy)indene (2). Both compounds can be success-
fully deprotonated with alkyllithiums to generate the
corresponding indenyl anions.
addition, Gibson et al. have reported the preparation of
the arenetricarbonylchromium(0) complex of 2-(ace-
toxy)indene by deprotonation of tricarbonyl(indan-2-
one) with LDA followed by quenching with acetic
anhydride.13 Based on the available reactivity data,14 we
did not expect these esters to be stable under standard
deprotonation conditions. Thus, sterically more hin-
dered indenyl esters were chosen as targets for the
present study.
Synthesis of the mesitoyl and adamantanoyl esters 1
and 2 are presented in Scheme 1. Reaction of 2-
indanone with an equimolar amount of NaH in THF
generated the corresponding enolate ion15 that was
cooled to −80°C and reacted with 2,4,6-trimethylben-
zoic acid chloride (obtained by chlorination of 2,4,6-
trimethylbenzoic
acid
with
SOCl2)
and
adamantane-1-carboxylic acid chloride (Aldrich),
respectively. The reaction mixture was slowly warmed
up to room temperature, quenched by addition of
saturated aqueous ammonium chloride, washed with
water and dried over sodium sulphate. Evaporation of
the solvent and subsequent crystallization from Et2O
Only a few examples of 2-indenyl esters have been
described in the literature. 2-(Benzoyloxy)indene has
been prepared by reaction of 2-indanone with iodoben-
zene in the presence of CO (40–45 atm), Et3N and
Cl2Pd(PPh3)2 in DMF.10 2-(Acetoxy)indene has been
obtained by reaction of 2-indanone with isopropenyl
acetate11 and as a low yield byproduct of mangane-
se(III) mediated g-lactone annulation of indene.12 In
* Corresponding author. Fax: +358-2-2154866; e-mail: reko.leino@
abo.fi
Scheme 1. Synthesis of the indenyl esters 1 and 2.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00766-9

4150
R. Leino et al. / Tetrahedron Letters 43 (2002) 4149–4151
As shown in previous reports, electronic modifications
of bis(cyclopentadienyl)22 and bis(indenyl) metallocenes
may significantly influence their catalytic performance
in various applications, including olefin polymeriza-
tion.8d,23 Compounds 1–5 may thus prove to be inter-
esting ligand candidates for structural tailoring of
transition metal as well as alkali metal20 cyclopentadi-
enyl complexes.
provided 1 and 2 in 57% and 50% isolated yields,
respectively.16,17
Various conditions were examined for the deprotona-
tion of the new indenyl esters. In a typical experiment,
1 (1.04 g, 3.75 mmol) or 2 (1.10 g, 3.75 mmol) was
dissolved in THF and reacted with an equimolar
amount of n-BuLi (2.5 M solution in hexanes) at −80°C
to generate the corresponding indenyllithium salts. Stir-
ring for 5 minutes and subsequent quenching with
TMSCl gave after work-up and crystallization from
pentane the trimethylsilyl derivatives 3 and 4 in isolated
Acknowledgements
yields of 69% and 44%, respectively (Scheme 2).18,19 1
H
The authors thank Mr. Markku Reunanen and Mrs.
Pa¨ivi Pennanen for their assistance with the EIMS and
NMR-analyses.
NMR analyses of the crude products were in both cases
consistent with 85–90% conversions of 1 and 2 to the
trimethylsilyl adducts. Alternatively, the indenyl anions
could be trapped by addition of iodomethane and the
corresponding 1- (3-) methyl derivatives identified by
GC/MS analysis.
References
1. (a) Halterman, R. L. In Metallocenes; Togni, A.; Halter-
man, R. L., Eds.; Wiley-VCH: Weinheim, 1998; pp.
455–544; (b) Cadierno, V.; D´ıez, J.; Gamasa, M. P.;
Gimeno, J.; Lastra, E. Coord. Chem. Rev. 1999, 193–195,
147–205; (c) Stradiotto, M.; McGlinchey, M. J. Coord.
Chem. Rev. 2001, 219–221, 311–378.
2. (a) Halterman, R. L. Chem. Rev. 1992, 92, 965–994; (b)
Hoveyda, A. H.; Morken, J. P. In Metallocenes; Togni,
A.; Halterman, R. L., Eds.; Wiley-VCH: Weinheim, 1998;
pp. 625–683.
The analogous method can be applied to the synthesis
of 3-indenyl esters as well.20 Thus, reaction of 1-
indanone with NaH in THF followed by subsequent
addition of 2,4,6-trimethylbenzoic acid chloride at
−80°C gave, after work-up and distillation, 3-(2,4,6-
trimethylbenzoyloxy)indene (5) in 53% yield (Scheme
3).21 Compound 5 was likewise successfully deproto-
nated in THF solution at −80°C using n-BuLi or
tert-BuLi. Quenching with TMSCl gave the trimethyl-
silyl derivative as identified by GC/MS analysis. Other
promising deprotonation conditions for the 2-substi-
tuted esters include NaH/THF/ambient temperature
and n-BuLi/DMF/−80°C.
3. (a) Coates, G. W. Chem. Rev. 2000, 100, 1223–1252; (b)
Resconi, L.; Cavallo, L.; Fait, A.; Piemontesi, F. Chem.
Rev. 2000, 100, 1253–1346.
4. 1- (or 3-) Alkyl substituted indenes: (a) Meurling, L. Acta
Chem. Scand. B 1974, 28, 295–300 (addition of alkyl
halides to indenyl anions); (b) Greifenstein, L. G.; Lam-
bert, J. B.; Nienhuis, R. J.; Fried, H. E.; Pagani, G. A. J.
Org. Chem. 1981, 46, 5125–5132; (c) Adamczyk, M.;
Watt, D. S.; Netzel, D. A. J. Org. Chem. 1984, 49,
4226–4237 (addition of alkyl or aryl metals to 1-indanone
followed by acid-promoted dehydration).
In summary, we have demonstrated the compatibility
of sterically congested ester substituents with indenyl
derived anions. These new ligand precursors are avail-
able in good yields from commercial starting materials.
5. 2-Alkyl and 2-arylsubstituted indenes: See for example,
Ref. 4b and (a) Ribakove, E. C.; Kerber, R. C.
Organometallics 1990, 9, 531–534; (b) Hauptman, E.;
Waymouth, R. M.; Ziller, J. W. J. Am. Chem. Soc. 1995,
117, 11586–11587 (addition of alkyl or aryl metals to
2-indanone followed by dehydration). Ref. 4c and (c)
Schumann, H.; Karasiak, D. F.; Mu¨hle, S. H.; Halter-
man, R. L.; Kaminsky, W.; Weingarten, U. J.
Organomet. Chem. 1999, 579, 356–372 (cross coupling of
Grignard reagents with 2-bromoindene). (d) Lappert, M.
F.; Martin, T. R.; Raston, C. L.; Skelton, B. W.; White,
A. H. J. Chem. Soc., Dalton Trans. 1982, 1959–1963; (e)
Ellis, W. W.; Hollis, T. K.; Odenkirk, W.; Whelan, J.;
Ostrander, R.; Rheingold, A. L.; Bosnich, B.
Organometallics 1993, 12, 4391–4401; (f) Witte, P.; Lal,
T. K.; Waymouth, R. M. Organometallics 1999, 18, 4147–
4155 (reaction of 1,2-di(magnesiomethyl)benzene dichlo-
ride with a carboxylic acid methyl ester; (g) Halterman,
R. L.; Zhu, C. Tetrahedron Lett. 1999, 40, 7445–7448
(Ni-catalyzed Cr(II)-promoted addition of aryl bromides
to a tethered ketone carbonyl); (h) Ijpeij, E. G.; Beijer, F.
H.; Arts, H. J.; Newton, C.; de Vries, J. G.; Gruter, G.-J.
Scheme 2. Synthesis of the trimethylsilyl derivatives 3 and 4.
Scheme 3. Synthesis of the indenyl ester 5.

R. Leino et al. / Tetrahedron Letters 43 (2002) 4149–4151
4151
M. J. Org. Chem. 2002, 67, 169–176 (Suzuki coupling of
2-bromoindene with diboronic acid).
123.44 (CH); 121.05 (CH); 115.04 (CH); 37.95 (CH2);
21.18 (CH3); 20.03 (2C, CH3).
6. 2- and 3-Methoxyindene: (a) Paquette, L. A.; Varadara-
jan, A.; Bay, E. J. Am. Chem. Soc. 1984, 106, 6702–6708;
(b) Keeffe, J. R.; Kresge, A. J.; Yin, Y. J. Am. Chem.
Soc. 1988, 110, 8201–8206.
17. Compound 2: 14.7 g (50%) of white crystals. Anal. calcd
for C20H22O2 (294.4): C, 81.60; H, 7.53. Found: C, 82.01;
1
H, 7.52. EIMS calcd/found: 294.1620/294.1616. H NMR
(CDCl3, l): 7.34–7.31 (m, 1H, CH); 7.29–7.20 (m, 2H,
CH); 7.14–7.10 (m, 1H, CH); 6.58 (m, long range cou-
plings, 1H, CH); 3.55 (m, long range couplings, 2H,
CH2); 2.08–2.06 (m br., 3H, adam.); 2.01–2.00 (m, 6H,
adam.); 1.80–1.71 (m br., 6H, adam.). 13C NMR (CDCl3,
l): 174.91 (CꢀO); 156.20 (C-O); 143.04 (Cq); 137.24 (Cq);
126.57 (CH); 124.14 (CH); 123.32 (CH); 120.79 (CH);
114.53 (CH); 41.21 (Cq, adam.); 38.65 (3C, CH2, adam.);
37.78 (CH2); 36.38 (3C, CH2, adam.); 27.84 (3C, CH2,
adam.).
7. 3-(Methylthio)indene: Ready, T. E.; Chien, J. C. W.;
Rausch, M. D. J. Organomet. Chem. 1996, 519, 21–28.
8. 2-Dialkylaminoindenes: (a) Edlund, U. Acta. Chem.
Scand. 1973, 27, 4027–4029; (b) Plenio, H.; Burth, D.
Organometallics 1996, 15, 4054–4062; (c) Plenio, H.;
Burth, D. J. Organomet. Chem. 1996, 519, 269–272; (d)
Barsties, E.; Schaible, S.; Prosenc, M.-H.; Rief, U.; Ro¨ll,
W.; Weyand, O.; Dorer, B.; Brintzinger, H.-H. J.
Organomet. Chem. 1996, 520, 63–68; (e) Luttikhedde, H.
J. G.; Leino, R. P.; Wile´n, C.-E.; Na¨sman, J. H.;
Ahlgre´n, M. J.; Pakkanen, T. A. Organometallics 1996,
15, 3092–3094; (f) Carter, C. A. G.; McDonald, R.;
Stryker, J. M. Organometallics 1999, 18, 820–822; (g)
Faure´, J.-L.; Erker, G.; Fro¨hlich, R.; Bergander, K. Eur.
J. Inorg. Chem. 2000, 2603–2606; (h) Knu¨ppel, S.; Faure´,
J.-L.; Erker, G.; Kehr, G.; Nissinen, M.; Fro¨hlich, R.
Organometallics 2000, 19, 1262–1268. (i) Greidanus, G.;
McDonald, R.; Stryker, J. M. Organometallics 2001, 20,
2492–2504.
9. 2- and 3-Trialkylsiloxyindenes: See for example, Ref. 6b
and (a) Parham, W. E.; Roosevelt, C. S. Tetrahedron
Lett. 1971, 14, 923–926; (b) Conde-Frieboes, K.; Hoppe,
D. Tetrahedron 1992, 48, 6011–6020; (c) Suginome, H.;
Takeda, T.; Itoh, M.; Nakayama, Y.; Kobayashi, K. J.
Chem. Soc., Perkin Trans. 1 1995, 49–61; (d) Leino, R.;
Luttikhedde, H.; Wile´n, C.-E.; Sillanpa¨a¨, R.; Na¨sman, J.
H. Organometallics 1996, 15, 2450–2453; (e) Luttikhedde,
H. J. G.; Leino, R.; Lehtonen, A.; Na¨sman, J. H. J.
Organomet. Chem. 1998, 555, 127–134; (f) Leino, R.;
Luttikhedde, H. J. G.; Lehtonen, A.; Ekholm, P.; Na¨s-
man, J. H. J. Organomet. Chem. 1998, 558, 181–188.
10. (a) Shimoyama, I.; Zhang, Y.; Wu, G.; Negishi, E. Tetra-
hedron Lett. 1990, 31, 2841–2844; (b) Negishi, E.; Liou,
S.-Y.; Xu, C.; Shimoyama, I.; Makabe, H. J. Mol. Catal.
A: Chem. 1999, 143, 279–286.
18. Compound 3: 0.91 g (69%) of an off-yellow solid. Anal.
calcd for C22H26O2Si (350.5): C, 75.38; H, 7.48. Found:
C, 75.78; H, 7.63. EIMS calcd/found: 350.1702/350.1704.
1H NMR (CDCl3, l): 7.28–7.26 (m, 1H, CH); 7.22–7.19
(m, 1H, CH); 7.13–7.09 (m, 1H, CH); 7.04–7.00 (m, 1H,
CH); 6.79 (overlapping singlets, 3H, CH); 3.55 (m, 1H,
CH); 2.28 (s, 6H, CH3); 2.19 (s, 3H, CH3); −0.12 (s, 9H,
Si(CH3)3). 13C NMR (CDCl3, l): 167.11 (CꢀO); 157.61
(C-O); 142.24 (Cq); 139.89 (Cq); 138.72 (Cq); 135.63 (2C,
Cq); 130.00 (Cq); 128.67 (2C, CH); 125.25 (CH); 123.34
(CH); 122.65 (CH); 121.00 (CH); 112.41 (CH); 44.19
(CH); 21.18 (CH3); 20.07 (2C, CH3); −2.60 (3C,
Si(CH3)3).
19. Compound 4: 0.61 g (44%) of an off-yellow solid. Anal.
calcd for C23H30O2Si (366.6): C, 75.36; H, 8.25. Found:
C, 75.22; H, 8.27. EIMS calcd/found: 366.2015/366.2013.
1H NMR (CDCl3, l): 7.32–7.27 (m, 2H, CH); 7.20–7.16
(m, 1H, CH); 7.12–7.08 (m, 1H, CH); 6.63 (d, 4J=0.7 Hz,
1H, CH); 3.63 (m, 1H, CH); 2.07–2.05 (m br., 3H,
adam.); 2.04–2.00 (m, 6H, adam.); 1.79–1.70 (m br., 6H,
adam.); 0.01 (s, 9H, Si(CH3)3). 13C NMR (CDCl3, l):
175.00 (CꢀO); 158.19 (C-O); 142.14 (Cq); 139.07 (Cq);
125.07 (CH); 123.08 (CH); 122.52 (CH); 120.74 (CH);
112.45 (CH); 44.07 (CH); 41.22 (Cq, adam.); 38.77 (3C,
CH2, adam.); 36.39 (3C, CH2, adam.); 27.87 (3C, CH,
adam.); −2.37 (3C, Si(CH3)3).
&
20. Preparation of 3-(N,N-diisopropylcarbamoyloxy)indene
from 1-indanone and N,N-diisopropylcarbamoyl chloride
in pyridine has been reported previously, see: Heinl, T.;
Retzow, S.; Hoppe, D.; Fraenkel, G.; Chow, A. Chem.
Eur. J. 1999, 5, 3464–3470. This compound was success-
fully deprotonated with n-BuLi in the presence of (−)-
sparteine followed by addition of iodomethane or TMSCl
to produce the corresponding Me or TMS-substituted
derivatives.
21. Light yellow oil (bp 154–156°C/0.02 mbar) identified by
its EIMS and NMR spectra. Crystallization of the dis-
tilled product from acetone yields a white crystalline
solid.
22. (a) Deck, P. A.; Jackson, W. F.; Fronczek, F. R.
Organometallics 1996, 15, 5287–5291; (b) Thornberry, M.
P.; Slebodnick, C.; Deck, P. A.; Fronczek, F. R.
Organometallics 2000, 19, 5352–5369; (c) Thornberry, M.
P.; Slebodnick, C.; Deck, P. A.; Fronczek, F. R.
Organometallics 2001, 20, 920–926.
23. Lehmus, P.; Kokko, E.; Ha¨rkki, O.; Leino, R.; Lut-
tikhedde, H. J. G.; Na¨sman, J. H.; Seppa¨la¨, J. V. Macro-
molecules 1999, 32, 3547–3552.
11. Stavber, S.; Sket, B.; Zajc, B.; Zupan, M. Tetrahedron
1989, 45, 6003–6010.
12. Fristad, W. E.; Peterson, J. R. J. Org. Chem. 1985, 50,
10–18.
13. Cowton, E. L. M.; Gibson, S. E.; Schneider, M. J.;
Smith, M. H. J. Chem. Soc., Perkin Trans. 1 1995,
2077–2078.
14. Greene, T. W.; Wuts, P. G. M. Protective Groups in
Organic Synthesis, 3rd ed.; John Wiley and Sons: New
York, 1999; pp. 712–713.
15. Baierweck, P.; Simmross, U.; Mu¨llen, K. Chem. Ber.
1988, 121, 2195–2200.
16. Compound 1: 9.20 g (57.5%) of light yellow crystals. Anal.
calcd for C19H18O2 (278.4): C, 81.99; H, 6.52. Found: C,
1
82.24; H, 6.68. EIMS calcd/found: 278.1307/278.1309. H
NMR (CDCl3, l): 7.37–7.31(m, 2H, CH); 7.28–7.24 (m,
1H, CH); 7.18–7.14 (m, 1H, CH); 6.90 (s, 2H, CH); 6.78
(m, long range couplings, 1H, CH); 3.67 (m, long range
couplings, 2H, CH2); 2.39 (s, 6H, CH3); 2.30 (s, 3H,
CH3). 13C NMR (CDCl3, l): 166.97 (CꢀO); 155.67 (C-O);
142.87 (Cq); 140.15 (Cq); 137.15 (Cq); 135.81 (2C, Cq);
129.72 (Cq); 128.69 (2C, CH); 126.75 (CH); 124.47 (CH);