Potassium Hydride as Nucleophile: A Practical Method for Cleavage and Functional Modification of Cr(CO)3-Ar-SiMe3 Bonds

Article abstract of DOI:10.1021/jo971856y

Potassium hydride reacts with Cr(CO)₃-aryltrimethylsilanes at room temperature to generate stabilized aryl anions which can further react with electrophiles.

Full text of DOI:10.1021/jo971856y

J . Org. Chem. 1998, 63, 1901-1905
1901
P ota ssiu m Hyd r id e a s Nu cleop h ile: A P r a ctica l Meth od for
Clea va ge a n d F u n ction a l Mod ifica tion of Cr (CO)3-Ar -SiMe3
Bon d s†
Sunil K. Mandal and Amitabha Sarkar*
Division of Organic Chemistry (Synthesis) National Chemical Laboratory Pune - 411 008, India
Received October 8, 1997
Potassium hydride reacts with Cr(CO)3-aryltrimethylsilanes at room temperature to generate
stabilized aryl anions which can further react with electrophiles.
Sch em e 1
In tr od u ction
In arene-tricarbonylchromium chemistry,1 an o-tri-
methylsilyl group has often been used as a means to
effect high diastereoselectivity at benzylic centers.1c,2 If
one begins with a homochiral substrate, high diastereo-
selectivity implies enantioselectivity as well, and desi-
lylation can afford an optically pure benzyl derivative in
a subsequent step.3 It is also possible to use SiMe3 as a
site-protecting group on the aromatic ring so that a
functionalization is directed to alternative sites.4 Cleav-
age of the Ar-Si bond at an appropriate stage by
protiolysis or conversion of a SiMe3 group to a useful
functionality has a direct impact on the efficiency of a
synthetic plan, an aspect that has been addressed in the
present report.
Sch em e 2
Resu lts a n d Discu ssion
The study originated from the following two observa-
tions5 of facile cleavage of the Ar-SiMe3 bond, while
attempting standard organic transformations such as
aldol-dehydration (Scheme 1) and anion-assisted Cope
rearrangement (Scheme 2). In both instances, desilyla-
tion could be suppressed only at low temperatures.
While the facility of Ar-Si bond cleavage can be
attributed to stabilization of an anionic aryl group
complexed with tricarbonylchromium, this observation
sounds a note of caution for the use of nucleophilic bases
in reactions with such substrates. We found that several
common bases used in organic reactions readily effected
* E-mail: sarkar@ems.ncl.res.in. Phone/FAX: 91-212-335153.
† NCL Communication No. 6426.
(1) Reviews on arene tricarbonylchromium complexes: (a) Semmel-
hack. M. F. Transition Metal Arene Complexes: Nucleophilic Addition.
In Comprehensive Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Pergamon: Oxford, 1995; Vol. 12, p 979.
(b) Semmelhack. M. F. Transition Metal Arene Complexes: Ring
Lithiation. Ibid. p 1017. (c) Davies, S. G.; McCarthy, T. D. Transition
Metal Arene Complexes: Side Chain Activation and Control of
Stereochemistry. Ibid. p 1039.
desilylation of a chromium-complexed aromatic ring
(Scheme 3). However, desilylation does not readily occur
for uncomplexed arylsilanes except with fluoride ion
catalysis,6 or when strong electron-withdrawing substit-
uents are present on the aromatic ring.7
(2) Uemura, M. Tricarbonyl (η6-arene) chromium Complexes in
Organic Synthesis. In Advances In Metal-Organic Chemistry; Liebe-
skind, L. S., Ed.; J AI Press: Greenwich, CT, 1991; Vol. 2, pp 231-240
and refs 84-110 cited therein.
We observed that potassium hydride in the presence
of a catalytic quantity of 18-crown-6 (reagent A) effected
(3) Davies, S. G.; Goodfellow, C. L. J . Chem. Soc., Perkin Trans. 1
1990, 393.
(4) (a) Mukai, C.; Hirai, S.; Kim, I. J .; Hanaoka, M. Tetrahedron
Lett. 1996, 37, 5389. (b) Bisaha, J . J .; Ph.D. Dissertation, Princeton
University, 1980. (c) Semmelhack. M. F.; Bisaha, J . J .; Czarny, M. J .
Am. Chem. Soc. 1979, 101, 768. (d) Semmelhack. M. F.; Zask, A. J .
Am. Chem. Soc. 1983, 105, 2034. (e) Clough, J . M.; Mann, I. S.;
Widdowson, D. A. Synlett 1990, 469.
(6) For fluoride-induced desilylation from uncomplexed aromatic
ring: (a) Hayes, M. A. One or More dCH Bond(s) Formed by
Substitution or Addition. In Comprehensive Organic Functional Group
Transformations; Katritzky, A. R., Meth-Cohn, O., Rees, C. W., Eds.;
Pergamon: Oxford, 1995; Vol. 1, pp 447-448 and refs cited therein.
(b) Snieckus, V. Chem. Rev. 1990, 90, 922.
(5) Sur, S.; Mandal, S. K.; Sarkar, A. Unpublished result.
S0022-3263(97)01856-2 CCC: $15.00 © 1998 American Chemical Society
Published on Web 02/20/1998

1902 J . Org. Chem., Vol. 63, No. 6, 1998
Mandal and Sarkar
Sch em e 3
Sch em e 4
Ta ble 2.
Ta ble 1.
sub-
strate
time
(h) product
yield
R
EX
E
(%)a
1a
H
DMFb
1.0
1.5
1.5
1.0
8.0
10.0
7.0
10.0
2a
2b
2c
2d
2e
2f
CHO
CHO
CHO
CHO
CO2Me
CO2Et
CO2Ph
70 (15)
70 (10)
84 (6)
90 (<5)
81 (13)
73 (9)
1d 2-OMe
1e 4-OMe
DMFb
DMFb
1f
1a
1a
1a
1a
4-Me
H
H
H
H
DMFb
(MeO)2CO
(EtO)2CO
(PhO)2CO
ethylene
carbonate
Ph2CO
2g
2h
75 (10)
CO2(CH2)2OH 78 (10)
1a
1a
H
H
12.0
4.0
2.5
2i
2j
2k
C(OH)Ph2
C(OH)PhCF3 80 (10)
CHO 74 (15)
85 (<5)
PhCOCF3
1g 2,6-(OMe)2 DMFb
a
Numbers in parentheses indicate percentage yields of pro-
tiodesilylated products. b DMF was used as solvent.
tetrasubstituted silicon to initiate desilylation. In com-
plex 1h , SiMe3 on the uncomplexed ring survives during
desilylation of the complexed ring. Under biphasic
conditions (reagent B), desilylation was found to reach
completion within 3 to 6 h. Other mild bases such as
K2CO3, KOH, and NaOMe can also be used for desilyla-
tion (Table 1; compounds 1a ,b). Tertiary amines such
as triethylamine, DBU, or DABCO were not effective.
Destannylation was also observed when an SnMe3 group
was present on the complexed aromatic ring instead of
SiMe3 group (Table 1; complex 1i).
The aryl anion stabilized by coordination with a
Cr(CO)3 group was expected to be trapped regiospecifi-
cally by electrophiles. In absence of any other electro-
phile, solvent DMF itself reacts with the aryl anion to
afford the corresponding aromatic aldehyde complex in
good yield (67-90%), along with some protiodesilylated
product (5-20%), as presented in the Scheme 4 and Table
2.
Direct complexation of aromatic aldehydes with Cr-
(CO)6 using conventional thermal method9 is difficult due
to thermal instability of the organic ligands and electron-
withdrawing nature of formyl group.10 The present
method of formylation is, therefore, a clearly acceptable
solution to this problem. Tricarbonylchromium com-
plexes of a wide range of substituted aromatic aldehydes
can now be conveniently prepared.4a,11
a
A ) KH/18-crown-6/ether; B ) 50% aq NaOH/TBAB/CH2Cl2;
C ) K2CO3/18-crown-6/acetone; D ) KOH/EtOH; E ) NaOMe/
ether.
This method was readily adapted for introduction of
other electron-withdrawing functional groups to the
aromatic nucleus. When tricarbonylchromium complex
of phenyltrimethylsilane (1a ) was allowed to react with
electrophiles such as ketone or dialkyl or diaryl carbonate
in the presence of KH/18-crown-6 in ether, carbinol and
ester complexes were obtained in moderate to good yield
(see Table 2). However, protiodesilylation could not be
completely suppressed. Although this reaction proceeded
desilylation in ether in a short period of time. In a typical
run, a suspension of potassium hydride in ether was
added dropwise to a stirred solution of the arene-
chromium complex and 18-crown-6 (10 mol %) in ether.
Complete conversion of the substrate was observed (TLC)
in all cases. The reaction course remained virtually
unchanged when an ether solution of the complex was
added to a suspension of potassium hydride in ether
containing 10 mol % 18-crown-6. Sodium hydride can
replace potassium hydride. Potassium or sodium hydride
is believed to act as a nucleophile8 which reacts with the
(8) Potassium hydride as nucleophile: Pinnick, H. W. Org. Prepn.
Proc. Int. 1983, 15(3), 199.
(9) (a) Mahaffy, C. A. L.; Pauson, P. L. Inorg. Synth. 1979, 19, 154.
(b) Top, S.; J aouen, G. J . Organomet. Chem. 1979, 182, 381.
(10) (a) Davies, R.; Kane-Maguire, L. A. P. Chromium Compounds
with η2-η8 Carbon Ligands. In Comprehensive Organometallic Chem-
istry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon:
Oxford, 1982; Vol. 3, p 1001 and refs 214, 216 cited therein.
(7) For desilylation of electron defficient aromatic ring using potas-
sium tert-butoxide: (a) Effenberger, F.; Spiegler, W. Chem. Ber. 1985,
118, 3900. (b) Effenberger, F.; Schollkopf, K. Angew. Chem., Int. Ed.
Engl. 1981, 20, 226. (c) Streitweiser, A.; Boerth, D. W. J . Am. Chem.
Soc. 1978, 100, 755.

Potassium Hydride As Nucleophile
J . Org. Chem., Vol. 63, No. 6, 1998 1903
Sch em e 5
formyl group by the procedure described in this paper,
so that the complex 3f, isomer of complex 3c, was
obtained. This sequence uses the trimethylsilyl unit as
a site-protective group as well as a precursor of formyl
function.
Su m m a r y
In summary, we have disclosed a facile cleavage of an
Ar-SiMe3 bond where the aromatic ring is complexed
with tricarbonylchromium, by nucleophilic bases. Potas-
sium or sodium hydride effects a clean reaction in aprotic
medium. It is possible to trap the intermediate anionic
species by different electrophiles to prepare metal-
complexed arenes with electron-withdrawing functional
groups. This should prove to be a useful synthetic
method for such complexes since these are not readily
obtainable by direct complexation route. The mild condi-
tion should tolerate a wide range of sensitive functional-
ity as well. Further exploration of the scope and syn-
thetic potential of this transformation is currently under
way in our laboratory.
much faster when DMF was used as solvent,12 formyla-
tion (20-50%) was always a competing reaction in DMF.
Direct thermal complexation of a substrate containing
more than one aromatic ring with Cr(CO)6 always gives
a mixture of products.13 For instance, attempted mono-
complexation of phenyl benzoate by thermolysis with
Cr(CO)6 yielded about 1:1 mixture of isomeric com-
plexes.14 In contrast, using the present method, pure
complex 2g could be readily obtained. Similarly, by
proper choice of substrate and electrophile, it is possible
to prepare a compound in which only the desired aro-
matic ring is complexed to tricarbonylchromium (see
Table 2, complex: 2i,2j).
One important aspect of this method of functionaliza-
tion is its complete regioselectivity. Scheme 5 sum-
marizes two routes to regioisomeric aromatic products.
Normal ortho-lithiation of complex 3a occurred at the
sterically less congested site, and addition of methyl
iodide led to the corresponding methyl substituted de-
rivative 3b. Subsequent treatment with BuLi generated
aryl anion at the alternative site (adjacent to OMe group),
where formylation could be readily effected to produce
aldehyde 3c. To obtain a regioisomer of this aldehyde,
the first ortho-lithiated derivative from 3a was treated
with Me3SiCl so that a silylated product 3d was obtained.
A second lithiation-alkylation led to the derivative 3e.
Now, the trimethylsilyl group was transformed to a
Exp er im en ta l Section
All reactions were performed under an inert atmosphere of
argon, using freshly distilled, degassed solvents. DMF was
purified by distillation over calcium hydride under reduced
pressure. Diethyl ether, dibutyl ether, and THF were freshly
distilled over sodium benzophenone ketyl. Chromium hexa-
carbonyl and 18-crown-6 were purchased from Aldrich and
used as received. Potassium hydride and sodium hydride were
also purchased from Aldrich and washed with portions of
hexane and anhydrous diethyl ether prior to use. Chlorotri-
methylsilane was distilled over zinc powder under argon prior
to use. Dimethyl and diethyl carbonate were distilled under
reduced pressure. n-BuLi in hexane (ca. 1.5 M) was prepared
using standard procedure and titrated prior to use. For
descriptions of analytical instruments, spectral data formats
and standard calibrations see ref 16. Analytical data of liquid
samples (2h , 3c, and 4-(trimethylsilyl)phenyl ether) were
unsatisfactory.
Gen er a l P r oced u r e for P r ep a r a tion of Tr ica r bon yl-
(η6-a r en e)-ch r om iu m (0) Com p lexes. Parent arenes of all
five complexes15a,b (1a , 1d -f, and 1i) were prepared from
corresponding bromo compounds via Grignard reaction fol-
lowed by quenching with chlorotrimethylsilane (in case of 1a ,
1d , 1e, 1f) or chlorotrimethyltin (in case of 1i). The arene and
chromium hexacarbonyl were thermolyzed in a mixture of
dibutyl ether-THF (10:1) (bath temperature: 150 °C) for 12-
24 h to prepare the complexes, as described in standard
procedure.9 The complexes 1b and 1c were prepared following
reported procedures.3
P r ep a r a tion of Tr ica r bon yl[η6-2-(tr im eth ylsilyl)r esor -
cin ol d im eth yl eth er ]ch r om iu m (0) (1g). n-BuLi (1.56 M,
1.3 mL, 2.0 mmol) was added dropwise to a cooled (-78 °C)
THF solution of tricarbonyl[η6-resorcinol dimethyl ether]-
chromium(0)15c (548 mg, 2.0 mmol), and the mixture was
stirred at -78 °C for 2 h. Chlorotrimethylsilane (218 mg, 0.3
mL, 2 mmol) was added, and stirring was continued ( -78 °C,
2 h). Degassed methanol (5 mL) was slowly added to quench
the reaction, and the mixture was allowed to reach room
temperature. Solvent was evaporated to afford the crude
complex, which was purified by column chromatography.
Recrystallization from dichloromethane-hexane gave the title
compound as yellow crystals (554 mg, 80%), mp 145 °C; 1H
NMR (CDCl3): 0.35 (s, 9H), 3.70 (s, 6H), 4.72 (d, 2H, J ) 6.5
Hz), 5.73 (t, 1H, J ) 6.5 Hz); 13C NMR (CDCl3): 1.8, 55.6, 70.0,
(11) Synthetic uses of some substituted aromatic aldehyde com-
plexes: (a) Sur, S.; Mandal, S. K.; Sarkar, A. Unpublished results. (b)
Reference 1c pp 1044-1048 and refs cited therein. (c) Taniguchi, N.;
Kaneta, N.; Uemura, M. J . Org. Chem. 1996, 61, 6088. (d) Mukai, C.;
Hirai, S.; Kim, I. J .; Hanaoka, M. Tetrahedron Lett. 1996, 37, 5389.
(12) When DMF was used as the solvent, reaction was complete
within 2 h. In ether it took more than 5 h for completion.
(13) Reference 10, p 1010.
(14) Thermal complexation of phenyl benzoate resulted in a mixture
of three products (15:10:1). In first major product Cr(CO)3 anchored
on the electron rich phenoxy ring and the second major product is the
same as 2g, and in the minor product both rings complexed to Cr-
(CO)3.
(15) (a) Seyferth, D.; Alleston, D. L. Inorg. Chem. 1963, 2, 417. (b)
Effenberger, F.; Schollkopf, K. Chem. Ber. 1985, 118, 4356. (c)
Mcfarlane, W.; Grim, S. O. J . Organomet. Chem. 1966, 5, 147. (d)
Nicholls, B.; Whiting, M. C. J . Chem. Soc. 1959, 551. (e) Davies, S. G.;
Goodfellow, C. L. J . Chem. Soc., Perkin Trans. 1 1989, 192. (f) Mahaffy,
C. A. L.; Hamilton, J . Synth. React. Inorg. Met. Org. Chem. 1987, 17,
43. (g) Mahaffy, C. A. L. Ibid. 1984, 14, 679.
(16) Chowdhury, S. K.; Samanta, U.; Puranik, V. G.; Sarkar, A.
Organometallics 1997, 16, 2618.

1904 J . Org. Chem., Vol. 63, No. 6, 1998
Mandal and Sarkar
81.1, 93.6, 148.7, 234.5; IR (CHCl3): 1960, 1860 cm-1. Anal.
Calcd for C14H18O5SiCr: C: 48.55, H: 5.24. Found: C: 48.51,
H: 5.32.
water at ice cold temperature and extracted with ether. Crude
complex obtained after evaporation of solvent was purified by
chromatography. Some products have been reported earlier.
viz, com p lex 2a : ref 15b, com p lex 2b: ref 15e, com p lex
2e: ref 15d, com p lex 2f: ref 15f, com p lex 2i: ref 15b.
Com p lex 2c: eed crystalline solid; mp 108-110 °C; 1H
NMR (CDCl3): 3.80 (s, 3H), 5.22 (d, 2H, J ) 6.7 Hz); 6.08 (d,
2H, J ) 6.7 Hz), 9.40 (s, 1H); 13C NMR (CDCl3): 55.9, 76.8,
90.6, 94.6, 144.8, 186.6, 230.0; IR (CHCl3): 1985, 1915 (br),
1690 cm-1. Anal. Calcd for C11H8O5Cr: C: 48.54, H: 2.96.
Found: C: 48.63, H: 2.97.
P r ep a r a tion of Tr ica r bon yl[η6-4-(tr im eth ylsilyl)p h en -
yl eth er ]ch r om iu m (0) (1h ). Grignard reaction of 4-bro-
mophenyl ether (10 g, 0.03 mol) and magnesium (0.063 mol)
in ether followed by quenching with trimethylsilyl chloride (7
g, 0.065 mol) gave 4-(trimethylsilyl)phenyl ether as colorless
1
oil (7 g, 73%), bp 150 °C (Kugelrohr bath temp)/1.0 mm; H
NMR (CDCl3): 0.45 (s, 18H), 7.17 (d, 4H, J ) 8.6 Hz), 7.66 (d,
4H, J ) 8.6 Hz); 13C NMR (CDCl3): -0.68, 129.90, 134.60,
135.10, 158.13; IR (CHCl3): 3020, 1580, 1480 cm-1; mass: M+
) 314. 4-(Trimethylsilyl)phenyl ether was (3 g, 9.55 mmol)
subjected to complexation under standard condition using
chromium hexacarbonyl (3 g, 13.6 mmol), dibutyl ether (100
mL), and THF (10 mL) to yield the title compound 1h as yellow
Com p lex 2d : red crystalline solid; mp 90 °C; 1H NMR
(CDCl3): 2.35 (s, 3H), 5.17 (d, 2H, J ) 6.4 Hz); 6.00 (d, 2H, J
) 6.4 Hz), 9.46 (s, 1H); 13C NMR (CDCl3): 20.6, 90.4, 93.0,
95.1, 112.1, 187.3, 230.2; IR (CHCl3): 1985, 1915 (br), 1690
cm-1
.
Anal. Calcd for C11H8O4Cr: C: 51.56, H: 3.15.
1
crystals (1.85 g, 43%), mp 93-95 °C; H NMR (CDCl3): 0.29
Found: C: 51.49, H: 3.14.
(s, 9H), 0.31 (s, 9H), 5.10 (d, 2H, J ) 6.4 Hz), 5.54 (d, 2H, J )
Com p lex 2g: orange crystalline solid; mp 100 °C; 1H NMR
(CDCl3): 5.35 (t, 2H, J ) 6.6 Hz); 5.65 (t, 1H, J ) 6.6 Hz),
6.27 (d, 2H, J ) 6.6 Hz), 7.21 (d, 2H, J ) 8.4 Hz), 7.29 (t, 1H,
J ) 8.4 Hz), 7.45 (t, 2H, J ) 8.4 Hz); 13C NMR (CDCl3): 88.4,
89.9, 95.0, 121.7, 126.5, 129.8, 150.6, 164.5, 230.8; IR
(CHCl3): 1980, 1910 (br), 1730 cm-1. Anal. Calcd for C16H10O5-
Cr: C: 57.49, H: 3.03. Found: C: 57.51, H: 3.13.
6.4 Hz), 7.19 (d, 2H, J ) 8.1 Hz), 7.50 (d, 2H, J ) 8.1 Hz); 13
C
NMR (CDCl3): -0.83, -0.32, 80.0, 94.14, 99.70, 120.85, 135.56,
138.47, 143.77, 153.90, 233.60; IR (CHCl3): 1960, 1880 (br),
1590, cm-1. Anal. Calcd for C21H26O4Si2Cr: C: 55.98, H: 5.82.
Found: C: 56.06, H: 5.90.
Gen er a l P r oced u r e for Desilyla tion . Usin g r ea gen t A
(KH/18-crown-6/ether): To a solution of the complex (n mmol)
and 18-crown-6 (10 mol %) in ether (5n mL) was added
dropwise a suspension of KH (1.2-1.3n mmol) in ether (3n
mL) with stirring at room temperature. After complete
consumption of starting material (TLC), the reaction was
quenched with degassed water at 0-5 °C, and the product was
extracted with ether.
Usin g r ea gen t B (50% aq NaOH/TBAB/CH2Cl2): To a
solution of the complex (n mmol) and tetrabutylammonium
bromide (TBAB, 10 mol %) in CH2Cl2 (3n mL) was added 50%
aq NaOH (n mL) dropwise with stirring at room temperature.
After completion of reaction (TLC), it was diluted with water
and extracted with dichloromethane.
Usin g r ea gen t C (K2CO3/18-crown-6/acetone): A solution
of the complex (n mmol) in acetone (5n mL) was added
dropwise to a stirred suspension of K2CO3 (1.5n mmol) and
18-crown-6 (10 mol %) in acetone (3n mL) at room tempera-
ture. After completion of the reaction (TLC), inorganic salts
were removed by filtration. Crude complex obtained after
evaporation of acetone was purified by chromatography.
Usin g r ea gen t D (KOH/EtOH): To a solution of the
complex (n mmol) in EtOH (5n mL) was added 1.5n mmol KOH
in ethanol (1 mL) dropwise with stirring at room temperature.
After completion of reaction (TLC), the reaction mixture was
diluted with water and the product was extracted with
dichloromethane.
Com p lex 2h : red oil; 1H NMR (CDCl3): 2.09 (brs, 1H), 3.94
(m, 2H), 4.48 (m, 2H), 5.32 (t, 2H, J ) 6.4 Hz), 5.58 (t, 1H, J
) 6.4 Hz), 6.15 (d, 2H, J ) 6.4 Hz); 13C NMR (CDCl3): 60.9,
67.3, 89.2, 89.6, 94.6, 94.7, 165.9, 230.8; IR (CHCl3): 3600-
3300 (br), 1980, 1910 (br), 1720 cm-1
.
Com p lex 2j: yellow crystals; mp 130 °C; 1H NMR
(CDCl3): 2.98 (s, 1H), 5.00 (t, 1H, J ) 6.7 Hz); 5.18 (m, 2H),
5.55 (t, 1H, J ) 6.7 Hz), 6.16 (d, 1H, J ) 6.7 Hz), 7.45 (m,
3H), 7.65 (m, 2H); 13C NMR (CDCl3): 87.3, 88.2, 94.9, 96.0,
96.1, 109.4, 127.1, 128.7, 129.7, 137.0, 231.8; IR (CHCl3): 1975,
1895 (br) cm-1. Anal. Calcd for C17H11O4F3Cr: C: 52.59, H:
2.86. Found: C: 52.68, H: 2.93.
Com p lex 2k : red crystalline solid; mp 130 °C dec; 1H NMR
(CDCl3): 3.81 (s, 6H), 4.82 (d, 2H, J ) 6.3 Hz), 5.82 (t, 1H, J
) 6.3 Hz), 10.1 (s, 1H); 13C NMR (CDCl3): 56.3, 68.7, 91.9,
103.9, 145.1, 185.2, 231.2; IR (CHCl3): 1975, 1895 (br), 1680
cm-1
.
Anal. Calcd for C12H10O6Cr: C: 47.68, H: 3.34.
Found: C: 47.58, H: 3.36.
P r ep a r a tion of Tr ica r bon yl[η6-3-m eth yla n isole]ch r o-
m iu m (0) (3a ). 3-Methylanisole (3 g, 25 mmol) was subjected
to complexation under standard condition using chromium
hexacarbonyl (3 g, 13.6 mmol), dibutyl ether (100 mL), and
THF (10 mL) to yield the title compound 3a as yellow crystals
1
(2.2 g, 63%), mp 80 °C; H NMR (CDCl3 ): 2.25 (s, 3H), 3.69
(s, 3H), 4.75 (d, 1H, J ) 6.0 Hz), 5.03 (d, 1H, J ) 6.0 Hz), 5.08
(s, 1H), 5.56 (t, 1H, J ) 6.0 Hz); 13C NMR (CDCl3): 20.96,
55.63, 76.30, 80.76, 87.12, 95.40, 111.23, 144.00, 233.90; IR
(CHCl3): 1960, 1880 (br), cm-1. Anal. Calcd for C11H10O4Cr:
C: 51.17, H: 3.90. Found: C: 51.32, H: 4.02.
Usin g r ea gen t
E (NaOMe /ether): A solution of the
complex (n mmol) in ether (5n mL) was added dropwise to the
stirred suspension of NaOMe (1.5n mmol) in ether (3n mL) at
room temperature. After completion of reaction it was quenched
with degassed water under ice-cold conditions and extracted
with ether.
Several of the desilylated products have been reported
earlier: com p lex 1a ′: ref 15d, com p lex 1b ′: ref 15d,
com p lex 1c′: ref 3, com p lex 1d ′: ref 15d, com p lex 1e′: ref
15d, com p lex 1f′: ref 15c.
P r ep a r a tion of Tr ica r bon yl[η6-2,5-d im eth yla n isole]-
ch r om iu m (0) (3b).15g Following the same procedure as used
for 1g, it was prepared from 3a (516 mg, 2.0 m mol), using
n-BuLi (1.56 M, 1.3 mL, 2.0 mmol) and methyl iodide (300 mg,
0.15 mL, 2.1 mmol). Recrystallization from dichloromethane-
hexane gave the title compound as yellow crystals (419 mg,
77%).
Com p lex 1g′: yellow crystalline solid; mp 140 °C; 1H NMR
(CDCl3 ): 0.3 (s, 9H), 4.89 (t, 1H, J ) 6.3 Hz); 5.15 (d, 2H, J
) 6.3 Hz), 5.55 (t, 2H, J ) 6.3 Hz), 7.17 (d, 2H, J ) 8.5 Hz),
7.51 (d, 2H, J ) 8.5 Hz); 13C NMR (CDCl3): -1.20, 76.93,
85.62, 94.26, 120.31, 135.20, 136.13, 142.04, 153.48, 232.85;
IR (CHCl3): 1985, 1915 (br) cm-1. Anal. Calcd for C18H18O4-
SiCr: C: 57.13, H: 4.79. Found: C: 57.10, H: 4.85.
Gen er a l P r oced u r e for th e F u n ction a liza tion of Cr -
(CO)3-Com p lexed Ar ylsila n es. To a solution of the com-
plexed arylsilane (n mmol), electrophile (EX), (1.5n mmol), and
18-crown-6 (10 mol %) in ether (5n mL) was added a suspen-
sion of KH (1.2-1.3n mmol) in ether (3n mL) dropwise with
stirring at room temperature. When the electrophile was
DMF, it was used as the solvent also. After completion of the
reaction, the reaction mixture was quenched with degassed
P r ep a r a tion of Tr ica r bon yl[η6-2-m eth oxy-3,6-d im eth -
ylben za ld eh yd e]ch r om iu m (0) (3c). As described above it
was prepared from 3b (272 mg, 1.0 mmol) using n-BuLi (1.56
M, 0.7 mL, 1.0 mmol) and DMF (109 mg, 0.1 mL, 1.5 mmol).
Recrystallization from dichloromethane-hexane gave the title
compound as a red viscous oil (219 mg, 73%); 1H NMR
(CDCl3): 2.20 (s, 3H), 2.45 (s, 3H), 3.79 (s, 3H), 4.79 (d, 1H, J
) 6.3 Hz), 5.74 (d, 1H, J ) 6.3 Hz), 10.06 (s, 1H); 13C NMR
(CDCl3): 22.96, 30.00, 31.80, 64.30, 84.45, 89.07, 91.1, 131.48,
146.67, 188.90, 230.74; IR (CHCl3): 1975, 1900 (br), 1680 cm-1
.
Anal. Calcd for C13H12O5Cr: C: 52.00, H: 4.03. Found: C:
52.03, H: 4.06.
P r ep a r a t ion of Tr ica r b on yl[η6-2-(t r im et h ylsilyl)-5-
m eth yla n isole]ch r om iu m (0) (3d ). It was prepared from 3a
(258 mg, 1.0 m mol) following the same procedure as above

Potassium Hydride As Nucleophile
J . Org. Chem., Vol. 63, No. 6, 1998 1905
using n-BuLi (1.56 M, 0.7 mL, 1.0 m mol) and trimethylsilyl
chloride (110 mg, 0.15 mL, 1.0 mmol). Recrystallization from
dichloromethane-hexane gave the title compound as yellow
crystals (287 mg, 87%), mp 125 °C; 1H NMR (CDCl3): 0.28 (s,
9H), 2.28 (s, 3H), 3.73 (s, 3H), 4.68 (d, 1H, J ) 6.4 Hz), 4.89
(s, 1H), 5.33 (d, 1H, J ) 6.4 Hz); 13C NMR (CDCl3): -0.45,
21.20, 55.40, 76.60, 87.21, 87.42, 101.70, 111.51, 147.96,
234.25; IR (CHCl3): 1955, 1895, 1870, cm-1. Anal. Calcd for
procedure of functionalization it was prepared from 3e (172
mg, 0.5 mmol) using DMF (5 mL), 18-crown-6 (13 mg, 10 mol
%), and KH (26 mg, 0.65 mmol). Recrystallization from
dichloromethane-hexane gave the title compound as red
crystals (102 mg, 68%), mp 135 °C. 1H NMR (CDCl3): 2.21
(s, 3H), 2.40 (s, 3H), 3.85 (s, 3H), 5.00 (d, 1H, J ) 6.5 Hz),
5.99 (d, 1H, J ) 6.5 Hz), 9.90 (s, 1H); 13C NMR (CDCl3): 12.18,
19.62, 64.72, 89.12, 89.14, 90.66, 99.90, 111.10, 144.36, 185.80,
231.00. IR (CHCl3): 1945, 1870 (br), 1660 cm-1. Anal. Calcd
for C13H12O5Cr: C: 52.00, H: 4.03. Found: C: 52.03, H: 4.00.
C
14H18O4SiCr: C: 50.90, H: 5.49. Found: C: 50.88, H: 5.48.
P r ep a r a t ion of Tr ica r b on yl[η6-2,3-d im et h yl-6-(t r i-
m eth ylsilyl)a n isole]ch r om iu m (0) (3e). It was prepared
from 3d (330 mg, 1.0 mmol) following the same procedure as
above, using n-BuLi (1.56 M, 0.7 mL, 1.0 mmol) and methyl
iodide (300 mg, 0.15 mL, 2.1 mmol). Recrystallization from
dichloromethane-hexane gave the title compound as yellow
crystals (275 mg, 80%), mp 110 °C. 1H NMR (CDCl3): 0.38
(s, 9H), 2.20 (s, 3H), 2.31 (s, 3H), 3.76 (s, 3H), 4.86 (d, 1H, J )
6.7 Hz), 5.38 (d, 1H, J ) 6.7 Hz); 13C NMR (CDCl3): 0.00,
13.33, 19.33, 62.33, 90.67, 91.67, 98.67, 101.00, 112.00, 147.67,
Ack n ow led gm en t. One of us (S.K.M.) is grateful to
the Council of Scientific and Industrial Research, New
Delhi, for the award of a fellowship. The authors wish
to thank Prof. T. V. Rajanbabu, Ohio State University,
for helpful suggestions and comments, and Dr. S.
Rajappa and Dr. S. V. Pansare, NCL, for critiquing the
manuscript prior to submission.
234.33; IR (CHCl3): 1940, 1860 (br) cm-1
15H20O4SiCr: C: 52.31, H: 5.85. Found: C: 52.30, H: 5.91.
P r ep a r a tion of Tr ica r bon yl[η6-2-m eth oxy-3,4-d im eth -
ylben za ld eh yd e]ch r om iu m (0) (3f). Following the general
. Anal. Calcd for
C
J O971856Y