Simple organometallic alcohols: Synthesis of (C5H4OH)Mn(CO)3 (Hydroxycymantrene) and (C5H4OH)W(CO)3CH3

Article abstract of DOI:10.1021/om960611t

The reaction of tert-butyldimethylsilyl triflate with cyclopent-2-enone and 3,4-dimethylcyclopentenone, respectively, gives siloxycyclopentadienes in yields >90%, whose deprotonation and reaction with BrMn(CO)₃(py)₂ or W(CO)₃

Full text of DOI:10.1021/om960611t

5066
Organometallics 1996, 15, 5066-5068
Sim p le Or ga n om eta llic Alcoh ols: Syn th esis of
(C5H4OH)Mn (CO)3 (Hyd r oxycym a n tr en e) a n d
(C5H4OH)W(CO)3CH3
Herbert Plenio*,† and Andre´ Warnecke
Institut fu¨r Anorganische und Analytische Chemie, Universita¨t Freiburg,
Albertstrasse 21, 79104 Freiburg, Germany
Received J uly 23, 1996X
Summary: The reaction of tert-butyldimethylsilyl triflate
with cyclopent-2-enone and 3,4-dimethylcyclopentenone,
respectively, gives siloxycyclopentadienes in yields >90%,
whose deprotonation and reaction with BrMn(CO)3(py)2
or W(CO)3(CH3CN)3/ MeI generates (CpOSitBuMe2)-
Mn(CO)3 and (CpOSitBuMe2)W(CO)3Me. Cleavage of
the organometallic silyl ether with NBu4F results in the
formation of the previously unknown alcohols (C5H4OH)-
Mn(CO)3 and (C5H4OH)W(CO)3Me in 80-90% yield,
from which the corresponding ethers can be synthesized.
oxygen-substituted cyclopentadienes. The reactions of
cyclopentenones with silylating reagents result in the
formation of the corresponding silyl enol ethers
()siloxycyclopentadienes) in almost quantitative yields,
which can be easily transformed into the respective
ferrocenyl silyl ethers.10
We wish to report on the synthesis of novel cyclo-
pentadienyl-tert-butyldimethylsilyl ethers and (R2CpO-
SitBuMe2)Mn(CO)3 (3a , R ) H; 3b, R ) Me) and
(R2CpOSitBuMe2)W(CO)3Me (4a , R ) H; 4b, R ) Me)
as well as the previously unknown alcohols (C5H4OH)-
Mn(CO)3 (5a ) and (C5H4OH)W(CO)3Me (6a ).
Cyclopentadienyl ligands continue to be most impor-
tant in organometallic chemistry, and consequently an
enormous number of such compounds with different
substituents have been synthesized.1 However, cyclo-
pentadienes and cyclopentadienyls substituted with
heteroatoms of high electronegativity are not very
common2,3 and even simple aminometallocenes and
hydroxymetallocenes used to be available only via
multistep reactions.4
Aminocyclopentadienes in which a nitrogen atom is
directly linked to the five-membered ring have become
easily available lately via the enamine reaction of sec-
amines with 3,4-diphenylcyclopentenone.5 Numerous
η5-bound complexes such as aminoferrocenes,6,7 amino-
cobaltocenes,6,7 aminocymantrenes,8 or aminozirconocene
dichlorides9 could thus be synthesized.
Trialkylsilyl groups are among the most popular
protecting groups for alcohols. The stability of the silyl
ethers crucially depends on the steric demand of the
alkyl group (-SiMe3 < -SiEt3 < SitBuMe2 < SiiPr3) and
thus governs the yield of the desired product as well as
the conditions for silyl ether cleavage.11
The -SiMe3 and -SiEt3 protecting groups which work
well for the synthesis of the siloxyferrocenes fail in the
synthesis of (R2CpOSiR3)Mn(CO)3 or (R2CpOSiR3)-
W(CO)3Me. A more robust choice for the siloxycyclo-
pentadienes therefore was -SitBuMe2 protection. The
reactions of cyclopentenone (1a , R ) H) and 3,4-
dimethylcyclopentenone (1b, R ) Me) with CF3SO3-
SitBuMe2 in petroleum ether (30-50 °C) and NEt3
yielded the respective silyl enol ethers 2a ,b in almost
quantitative yields (Scheme 1) as a mixture of three
isomers. 2b is a stable compound, whereas 2a is prone
toward dimerization but can be stored for several weeks
at -20 °C without significant decomposition. Deproton-
ation of 2a or 2b with BuLi at 0 °C and reaction with
BrMn(CO)3(py)2 gave the respective cymantrenes 3a ,b
in yields of 45-50%. For the synthesis of (R2CpO-
SiR3)W(CO)3Me the siloxycyclopentadienes 2a ,b were
reacted first with NaN(SiMe3)2 and then with
W(CO)3(CH3CN)3 and MeI, resulting in the formation
of 4a ,b in modest yields of 30-40% (Scheme 1). The
manganese as well as the tungsten compound is very
stable, and the silyl ether could not be cleaved in
strongly acidic or basic media. However, treatment of
solutions of 3a ,b, and 4a ,b in anhydrous THF with
NBu4+F-‚3H2O cleaves the organometallic silyl ethers
within 15 min at room temperature. After evaporation
of the solvent the pure alcohol is isolated by simply
filtering a 2:1 cyclohexane/ethyl acetate solution of the
residue over a short silica plug. Evaporation of the
Very recently we have discovered that cyclopenten-
ones can also serve as excellent starting materials for
† E-mail: plenio@ruf.uni-freiburg.de.
X Abstract published in Advance ACS Abstracts, October 15, 1996.
(1) (a) Haltermann, R. Chem. Rev. 1992, 92, 965. (b) Okuda, J . Top.
Curr. Chem. 1991, 160, 97. (c) J aniak, C.; Schumann, H. Adv.
Organomet. Chem. 1991, 33, 291.
(2) (a) Macomber, D. W.; Hart, W. P.; Rausch, M. D. Adv. Organomet.
Chem. 1982, 21, 1. (b) J utzi, P.; Schwartzen, K.-H.; Mix, A. Chem. Ber.
1990, 123, 837. (c) J utzi, P.; Schwartzen, K.-H. Chem. Ber. 1989, 122,
287. (d) Kohl, F. X.; Schwarzen, K.-H.; J utzi, P. Zh. Org. Khim. 1988,
24, 1109. (e) Paprott, G.; Lentz, D.; Seppelt, K. Chem. Ber. 1984, 117,
1153.
(3) (a) Benson, R. E.; Lindsey, R. V. J . Am. Chem. Soc. 1957, 79,
5471. (b) Egger, H.; Nikiforov, A. Monatsh. Chem. 1969, 100, 1069. (c)
Su¨nkel, K.; Blum, A. Z. Naturforsch. 1995, B50, 1307. (d) Klauck, A.;
Seppelt, K. Angew. Chem., Int. Ed. 1994, 33, 93.
(4) (a) Herberhold, M. In Ferrocenes; Togni, A., Hayashi, T., Eds.;
VCH: Weinheim, Germany, 1995. (b) Kirchner, K.; Meriter, K.;
Schmid, R.; Taube, H. Inorg. Chem. 1993, 32, 5553. (c) Sheats, J . E.;
Hlatky, G.; Dickson, R. S. J . Organomet. Chem. 1979, 173, 107. (d)
Kur, S. A.; Rheingold, A. L.; Winter, C. H. Inorg. Chem. 1995, 34, 414.
(e) Han, Y. H.; Heeg, M. J .; Winter, C. H. Organometallics 1994, 13,
3009.
(5) Plenio, H.; Burth, D. Angew. Chem. 1995, 107, 881; Angew.
Chem., Int. Ed. Engl. 1995, 34, 800.
(6) Plenio, H.; Burth, D. Organometallics 1996, 15, 1151.
(7) Plenio, H.; Burth, D. Organometallics 1996, 15, 4054.
(8) Plenio, H.; Burth, D. Z. Anorg. Allg. Chem. 1996, 622, 225.
(9) (a) Plenio, H.; Burth, D. J . Organomet. Chem. 1996, 519, 269.
(b) Leino, R.; Luttikhedde, H.; Wilen, C. E.; Sillanpaa, R.; Nasman, J .
H. Organometallics 1996, 15, 2450.
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Synthesis; J . Wiley & Sons: New York, 1991.
S0276-7333(96)00611-5 CCC: $12.00 © 1996 American Chemical Society

Notes
Organometallics, Vol. 15, No. 23, 1996 5067
Sch em e 1a
pentenone all workup was performed without delay. The
remaining oil, which may still contain small amounts of
ammonium salt, was removed from the flask with a syringe.
2a may be distilled (only data of main isomer listed), yield
>90%: 1H NMR (CDCl3) δ ) 0.19 (s, SiCH3, 6H), 0.95 (s, C4H9,
9H), 2.90-2.93 (m, CH2, 2H), 5.22-5.25 (m, CH, 1H), 6.24-
6.38 (m, CH, 2H). 2b: yield >90%, complex isomer mixture.
Silyl Cym a n tr en yl Eth er s 3a ,b. An ice-cooled solution
of the siloxycyclopentadiene (2 mmol) in THF (25 mL) was
treated with BuLi (2 mmol, 0.8 mL). After 10 min BrMn-
(CO)3(py)2 (2 mmol, 754 mg) was added and the reaction
mixture stirred for 4 h. The volatiles were evaporated in
vacuum, and the remaining solid was extracted with cyclo-
hexane. The extract was filtered over a silica plug (5 cm) and
extracted with cyclohexane. The filtrate was evaporated and
dried in vacuum yielding pale-yellow oils, which slowly
crystallize. 3a : 1H NMR (C6D6) δ 0.00 (s, SiCH3, 6H), 0.84 (s,
C4H9, 9H), 3.74 (br, CpH, 2H), 3.86 (br, CpH, 2H); 13C NMR
(C6D6) δ -5.03, 17.98, 25.39, 69.35, 76.82, 137.21, 225.45; IR
a
Reagents and conditions: (a) petroleum ether (30/50), 1.1
equiv of Et3N, 0.98 equiv of CF3SO3SitBuMe2, 2a , R ) H, 2b,
R ) Me; (b) 1.0 equiv of BuLi, 1.0 equiv of BrMn(CO)3(py)2 or
1.0 equiv of NaN(SiMe3)2, 1.0 equiv of W(CO)3(CH3CN)3, 1.5
equiv of MeI; (c) 1.5 equiv of NBu4F in THF; 7 from 5a +
PhCH2Br/Na2CO3.
ν(CO) ) 1935, 2019 cm-1. Yield: 48%. Anal. Calcd for C14H19
-
MnO4Si (335.24): C, 50.16; H, 5.71. Found: C, 49.88; H, 5.85.
3b: Yield 45%; 1H NMR (C6D6) δ 0.63 (s, SiCH3, 6H), 0.89 (s,
C4H9, 9H), 1.45 (s, CH3, 6H), 3.95 (s, CpH, 2H); 13C NMR (C6D6)
δ -4.87, 11.60, 18.07, 25.47, 69.77, 92.41, 135.24, 226.1; IR
ν(CO) ) 1921, 2012 cm-1
. Anal. Calcd for C16H23MnO4Si
(363.29): C, 52.90; H, 6.38. Found: C, 52.50; H, 6.31.
volatiles gives the previously unknown alcohols as
yellow crystalline materials (5a ,b) or as almost colorless
solids (6a ) in >80% yield. Somewhat to our surprise
none of these compounds is very stable, and after 24 h
in the flask the alcohols have darkened significantly.
Despite the sensitivity of 5a synthesis of the cyman-
trenyl benzyl ether 7 was possible in good yields.
One application of these systems could be the use as
aqueous IR-active organometallic pH probes as de-
scribed recently by Creaser, Stephenson, et al.12 Pre-
liminary tests have shown that upon changing the pH
the ν(CO) varies between 1930, 2016 cm-1 (pH ) 1) and
1910, 2000 cm-1 (pH ) 13). The pK value of the alcohol
which determines the useful range of such potential
sensor molecules can be changed easily by using differ-
ent cyclopentenones as starting materials for the syn-
thesis of the cymantrenes.
(Siloxycyclop en ta d ien yl)tu n gsten Tr ica r bon yl Meth -
yls 4a ,b. An ice-cooled solution of the siloxycyclopentadiene
(2 mmol) in THF (25 mL) was treated with NaN(SiMe3)2 (2.2
mmol, 403 mg). After 10 min W(CO)3(CH3CN)3 (782 mg, 2
mmol) was added and stirring continued at room temperature.
After 2 h CH3I (3 mmol, 429 mg) was added and 30 min later
the reaction mixture evaporated to dryness. The solid residue
was extracted with cyclohexane. The solution was filtered over
a silica plug (5 cm) and extracted with cyclohexane. The
filtrate was evaporated and dried in vacuum yielding yellow
solids that are pure products. 4a : Yield 37%; 1H NMR (CDCl3)
δ 0.23 (s, SiMe2, 6H), 0.95 (s, C4H9, 9H), 4.83 (“t”, 2.4 Hz, CpH,
2H), 5.00 (“t”, 2.4 Hz, CpH, 2H). 13C NMR (CDCl3) -20.71,
-4.43, 18.22, 25.51, 77.99, 78.05, 141.82, 216.74, 229.62; IR
ν(CO) ) 1920, 2011 cm-1
. Anal. Calcd for C15H22O4SiW
(478.28): C, 37.67; H, 4.64. Found: C, 37.54; H, 4.62. 4b:
1
Yield 33%; H NMR (C6D6) δ 0.00 (s, SiCH3, 6H), 0.56 (s,
We are currently exploring the synthetic potential of
3a and 4a with a view to the chemistry of the organic
phenols and are attempting the synthesis of new organo-
metallic alcohols.
WCH3, 3H), 0.85 (s, C4H9, 9H), 1.61 (s, CH3, 6H), 4.56 (s, CpH,
2H); 13C NMR (C6D6) δ -21.27, -4.70, 11.95, 18.16, 25.51,
30.16, 78.81, 96.72, 137, 218.74, 232.51. IR ν(CO) ) 1916, 2005
cm-1
. Anal. Calcd for C17H26O4SiW (506.33): C, 40.33; H,
5.18. Found: C, 39.89; H, 5.30.
Or ga n om eta llic Alcoh ols 5a ,b a n d 6a . One equivalent
of the silyl ethers 3a ,b or 4a was dissolved in anhydrous THF
and 1.5 equiv of NBu4+F-‚3H2O added. After the mixture was
stirred at room temperature for 15 min, the volatiles were
evaporated. The residue was dissolved in cyclohexane/ethyl
acetate (2:1) and filtered over a silica plug. The filtrate was
evaporated to dryness with the alcohols staying behind in good
purity but may be purified further by chromatography. Yields
were between 80 and 90%. 5a : 1H NMR (C6D6) δ 3.59-3.65
(m, CpH, 4H); 13C NMR (C6D6) δ 66.45, 76.74, 138.05, 225.4;
Exp er im en ta l Section
Commercially available solvents and reagents were purified
according to literature procedures. All reactions were carried
out in dry solvents under a nitrogen atmosphere. NMR
spectra were recorded at 300 K with a Bruker AC200 F (1H
NMR 200 MHz, 13C NMR 50.3 MHz). 1H NMR were refer-
enced to residual 1H impurities in the solvent and 13C NMR
to the solvent signals: CDCl3 (7.26 ppm, 77.0 ppm), C6D6 (7.16,
128.0 ppm), CD3CN (1.93 ppm, 1.30 ppm). IR spectra: Bruker
IFS-25 with solids as CHCl3 solutions between KBr disks or
in aqueous solution between CaF2 plates. Elemental analy-
ses: Mikroanalytisches Laboratorium der Chemischen Labo-
ratorien, Universita¨t Freiburg.
IR ν(CO) ) 1925, 2017 cm-1
. Anal. Calcd for C8H5MnO4
(220.07): C, 43.66; H, 2.29. Found: C, 43.12; H, 2.25. 5b:
1H NMR (C6D6) δ 1.40 (s, CH3, 6H), 3.71 (s, CpH, 2H); IR ν(CO)
) 1924, 2010 cm-1. Anal. Calcd for C10H9MnO4 (248.10): C,
48.41; H, 3.66. Found: C, 48.29; H, 3.69. 6a : 1H NMR (C6D6)
δ 0.49 (s, WCH3, 3H), 3.98 (“t”, 2.2 Hz, CpH, 2H), 4.29 (“t”, 2.2
Hz, CpH, 2H); 13C NMR (C6D6) δ -20.50, 74.38, 77.59, 142.74,
217.61, 230.05; IR ν(CO) ) 1914, 2010 cm-1. Anal. Calcd for
C9H8O4W (364.01): C, 29.69; H, 2.22. Found: C, 29.26; H,
2.15.
Cym a n tr en yl Ben zyl Eth er (7). A mixture of 5a (48 mg,
0.22 mmol), benzyl bromide (42 mg, 0.24 mmol), and Na2CO3
(50 mg) in CH3CN (20 mL) was heated under reflux for 10 h.
After evaporation of the volatiles the remaining solid was
Siloxycyclop en ta d ien es 2a ,b. A solution of a cyclopent-
2-en-1-one (0.05 mol) and Et3N (7.07 g, 0.07 mol) in pentane
(75 mL) was treated with tert-butyldimethylsilyl triflate (13.2
g, 0.05 mol). After being stirred for 15 min, the oily precipitate
-
of Et3NH+CF3SO3 was removed with a syringe and the
volatiles were removed in vacuo. Due to a possible Diels-
Alder dimerization of the cyclopentadiene derived from cyclo-
(12) Anson, C. E.; Baldwin, T. J .; Creaser, C. S.; Fey, M. A.;
Stephenson, G. R. Organometallics 1996, 15, 1451.

5068 Organometallics, Vol. 15, No. 23, 1996
Notes
purified by chromatography (cyclohexane/ethyl acetate ) 5:1).
Yield: 50 mg (73%) of yellow crystals, mp 92 °C. 1H NMR
(C6D6): δ 3.78 (br, 2H, CpH), 3.87 (br, 2H, CpH), 4.23 (s, 2H,
CH2), 7.12-7.21 (m, 5H, C6H5). 13C NMR (C6D6): δ 65.54,
72.64, 76.90, 128.29, 128.62, 128.74, 135.60, 141.34, 225.3
(CO). IR: ν(CO) ) 2020, 1936. Anal. Calcd for C15H11MnO4
(310.19): C, 58.08; H, 3.57. Found: C, 57.67; H, 3.69.
Ack n ow led gm en t. We thank the Deutsche Fors-
chungsgemeinschaft (Graduiertenkolleg “Ungepaarte
Elektronen in Chemie und Physik”), the Fonds der
Chemischen Industrie, and the Landesschwerpunkt
“Molekulare Elektrochemie” for their support.
OM960611T