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Lithium 2 2-Biphenyldiyltrimethylsilicate; First Observation of Pentaorganosilicates.

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dried. Yield: 2.75 g, 97% yield of crude air-sensitive red-orange 2-4THF. Pure
2 - 2 D M E was obtained by slow diffusion ofn-hexane into a solution of 2 dissolved
in DME. C,,H,,Na,O,P,
(red-orange crystals), M , = 971.01, crystal dimensions
Pi (No. 2). a=11.909(1), h=14.819(2).
0 . 3 2 ~ 0 . 3 2 ~ 0 . 3 2 m mtriclinic,
c=16.901(2)A. rx =95.29(1). /(=101.23(1). 7 =112.58(1)", V=2654.0 ( l ) A 3 ,
Z = 2. pEllLd
= 1.215 gcm-'. j.(MoKI)= 0.71073 A. p = 2.0 cm-', F(OO0) = 1028,
7' = 123k0.5 K . Final R = 0 044, R, = 0 065 for 9550 observed unique reflections
with 2OmdX
= 60 having F: > 3.0n(F;). Solution by direct methods; 595 variables
refined using toIFol - IF,I)' by full matrix least squares. GOF =1.19.
(Ap),,,,,,, =1.05 A' in the final difference map [13].
3: Potassium metal (0.91 g, 23.3 mmol) and tetramer 1 (4.00 g, 5.38 mmol) were
heated to 70 C in freshly distilled DME (100 mL) for 12 h. The crude precipitate of
air-sensitive pale yellow needles was collected, washed with DME, and dried. Yield
of 3.4DME: 6.3Og. 93%. Crystals suitable for X-ray diffraction were grown by
dil%sion of hexane into a THF solution containing equimolar amounts of 3
and [18]crown-6. C',,,H,,,K,O,,,P,
(pale yellow crystals). M , = 2006.69, crystal
dimensions 0.20 x 0 30 x 0.34 mm, monoclinic, P2lin (No. 14). a = 17.445(2),
h = 15.783(1). c = 20 382(2)
/( = 102.2711)
V = 5483.5(2) A3, 2 = 2,
pcs,cd=1.215 gcm-3, j.(MoK.) = 0.71073
) I = 2.8cm-l.
F(OO0) = 2152,
T = 123 k0.5 K . Final K = 0.056, R, = 0.072 for 5664 observed unique reflections
with 20,,, = 6 0 having FZ > 3.0u(F:). Solution by direct methods; 595 variables
by full matrix least squares.. GOF =1.22.
refined using !-,(lFol -IF,[)'
(Ap),az,m,n= 0.57 A' in the final difference map 1131.
Received: December 11, 1995 [Z8640IE]
German version: Angen. Chem. 1996, 108, 1204-1206
Keywords: alkali metal compounds
lides phosphorus compounds
- phospho-
[l] For a recent highlight, see: D. Stdlke, Angew. Chem. 1994, 106, 2256; Angew.
Chem. I n [ . Ed. Engl. 1994. 33. 2168.
[Z] S . Harder. M. H. Prosenc, Aiigcn. Chem. 1994, 106, 1830; Angen. Chem. Inr.
Ed. Enxl. 1994. 33. 1744
131 T. Douglas. K . H . Theopold, Angew. Chem. 1989,101,1394;Angew. Chew. I n f .
Ed. Engl. 1989.28. 1367.
14) F. Laporte. F. Mercier, L. Ricard. F. Mathey. J Am. Chem. Suc. 1994. 116,
[5] J. Fischer, A. Mitschler. F. Mathey. F. Mercier. J. Chem. Suc. Dalron Trans.
1983. 841.
16) D. Baudry, M. Ephritikhine, F. Nief, L. Ricard, F. Mathey, Angew Chem.
1990, /02, 1501. Angrw. Chem. Int. Ed. Engl. 1990, 29, 1485.
[7] E. J. Padma Malar. J Org. Chem. 1992, 57, 3694 and references therein.
[8] G. Rabe. H. W. Roesky, D. Stalke. F. Pauer, G. M. Sheldrick, J. Organumet.
Chrm. 1991, 403. 11.
[9] S . Holand, F. Gandolfo, L . Ricard, F. Mathey. Bull. Suc. Chim. France, 1996,
133. 33 For a discussion of the validity of the (C,C,-C,C,.) criterion see also:
P. von R. Schleyer. P. K. Freeman. H. Jiao. B. Goldfuss, Angew. Chem. 1995,
107, 332; 411giwC'hrm. Inl. Ed. Engl. 1995, 34, 337.
[lo] F. G. N Cloke. P. B. Hitchcock, A. McCamley. J Chem. Suc. Chem. Cummun.
1993, 248.
[ l l ] I n very recent work, in which the existence of the natrocene anion was demonstrated crystallographically, a kalocene anion was also reported. However, no
structural data were given. See: 3. Wessel, E. Lork, R. Mews, Angen. Chrm.
1995. 107, 2565; Angeu. Chem. I n f . Ed. Engl. 1995, 34, 2376. The crystal
structure of a triple-decker cesocene complex has also been reported since
submission of the present paper: S . Harder, M. H. Prosenc, Angew. Chem.
1996. /ON. 101; Angetr. Chem. 1111.Ed. EngI. 1996. 35. 97.
[12] M. Andrianarison. D. Stalke. U. Klingebiel, Chem. Ber. 1990, 123, 71.
[13] Crystallographic data (excluding structure factors) for the structures reported
in this paper have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-179-25. Copies of the data can
be obtained free of charge on application to The Director, CCDC. 12 Union
Road, Cambridge CB2 lEZ, UK (fax: int. code +(1223) 336-033; e-mail:
Lithium 2,2'-Biphenyldiyltrimethylsilicate;
First Observation of Pentaorganosilicates
Adrianus H. J. F. de Keijzer, Franciscus J. J. de Kanter,
Marius Schakel, Robert F. Schmitz, and
Gerhard W. Klumpp*
In studies of nucleophilic substitution on silicon and nucleophilic activation of organosilicon compounds,['] organosilicates
with pentavalent silicon bonded to one or several atoms more
electronegative than carbon have become very important. By
contrast, the addition product of 1,I -dimethylsilacyclobutane
and ally1 anion, observed in a flowing afterglow experiment, is
the only case in which the structure of a pentaorganosilicate (1)
has been proposed.[21
Otherwise, pentaorganoh,s,h
silicates figure, as yet,
only as unproven
in the intrainter%J e
molecular and intermolecular transfer of tri1
organosilyl groups from
neutral to anionic carbon centers. Thus, according to Kumada and co-w~rkers,[~"l
transmetalation of 9,9-diorgano-9H,9-silafluorenes such as 2
with organolithiums proceeds via lithium pentaorganosilicates.
We now report that we have observed these species at low temperatures by NMR spectroscopy. At higher temperatures they
decompose into tetraorganosilane and organolithium. This can
result in carbanion exchange between the starting compounds.
Treatment of bromide 314]with tert-butyllithium at - 80 "C in
THF generated a species whose exceptionally high-field 29Si
NMR signal (6 = - 116.9) was indicative of pentavalent siliApparently, the lithium compound 4 rearranges instantaneously to the title compound 5J6'whose composition was de-
3:X = Br
4: X = Li
duced from the 8:9 ratio of the intensities of the biphenylene
and methyl proton signals.['] Raising the temperature converts
5 reversibly into methyllithium and 9,9-dimethyl-9H,9-silafluorene (2), which was identified in situ by comparison of its 29Si
(6 = 0.6), 'H, and 13C NMR spectra with those of authentic
material. Conversely, cooling T H F solutions of methyllithium
plus 2 generates 5,which is the only species present at approximately - 100 "C. Cryoscopy indicated that under these conditions 5 is undissociated: After addition of 2 (0.53 mmol) to a
solution in THF of Me,Li4 (0.14 mmol), the number ofparticles
contained in the solution (0.52 i0.01 mmol 5 ) corresponded to
the amount of 2 that had been added. In the presence of ten
equivalents of hexamethylphosphoric triamide (HMPA), which
strongly complexes lithium, the splitting of the 'Li NMR signal
by 7Li-31P coupling (-120°C, 6(7Li) = - 2.l.['] quintet,
Angeu. Chcm
E d Enpl. 1996, 35. Nu. 10
Prof. Dr. G. W. Klumpp. Drs. Ing. A. H. J. F. de Keijzer, Dr. F. J. J. de Kanter,
Dr. M. Schakel, R. F. Schmitz
Scheikundig Laboratorium Vrije Universiteit
De Boelelaan 1083. NL-1081 HV Amsterdam (The Netherlands)
Fax: Int. code +(20)4447488
mbH. 0-69451 Wemherm, 1996
S 15.00f 2 5 0
6(31P)= 24.1, 1 : l : l : l quartet, 2J(7Li,31P)=7.5 HzL9])clearly
indicated coordination of four HMPA molecules to the lithium
ion of 5. Since a single "Si NMR signal at -116.2 persisted
from - 120 to 20 "C, 5-L, (L = HMPA) must be more stable
than 2 plus methyllithium throughout the temperature range
studied. A single methyl signal and a single set of six phenylene
carbon signals in the 13CNMR spectra indicate that stereoisomers of 5-L, (L = HMPA) interconvert rapidly on the I3C
NMR time scale, even at - 120 "C.
The reaction of butyllithium (1 equiv) with 2 in T H F is
analogous to that of methyllithium. At -80 "C the "Si NMR
signal of the Stbutyldimethyl analogue of 5 is found at
6 = - 113.6.['01 By contrast, in ether at - 80 "C as well as at
higher temperatures, neither the methyllithium/2 system nor the
butyllithium/2 system exhibits a 29SiNMR signal of pentacoordinated silicon. Above - 14 "C formation of 9-butyl-9-methyl9H,9-~ilafluorene[~"]
is evident, strongly suggesting, as Kumada
and c o - w o r k e r ~ [had
~ ~ ] already proposed for the present reaction and for related ones, that 5 and analogues are accessible
kinetically also in ether.["] However, in this solvent, the thermodynamic stability of 5 and its analogues relative to that of 2
plus methyllithium or butyllithium is so low that they cannot be
detected. It appears that the stabilities of ate complexes of
Group 4 elements depend to a large degree on the strength of
complexation of their countercations by the solvent or other
Lewis bases. Thus, organofluorosilicates are most stable as the
[l 81crown-6 potassium salts.["] The present order of propensity
for complexation of the lithium ions and, thereby, stabilization
of 5 and analogues, HMPA > T H F > ether, applies also to
lithium pentaorganostannates.[' 31 The fact that 5 is present in
T H F in substantial concentrations suggests to us optimum complexation of the lithium ion, that is the existence of 5-L,
(L = THF). This is in accord with known structures of THFcomplexed lithium salts['41 and is supported by the value of the
reaction entropy in T H E The ratios of the integrals of the NMR
signals of the methyl protons of methyllithium, 5, and 2, in T H F
at eleven temperatures (- 54 to - 9 "C) were used to determine
the equilibrium constant K for the reaction 1/4Me,Li, + 2 = 5,
whenceAH=-55&2kJmol-',AS= -225f6JK-'mol-'
were obtained. The value of A S indicates a strong decrease of
the number of particles, as one would expect for the formation
of a tetrasolvate,[15] suggesting that actually reaction (a) is occurring.
1/4Me,Li4.4THF f 3 T H F f 2
e 5-L,
= THF)
Any interpretation of the value of AH in terms of silicate
formation from tetraorganosilanes and carbanionsrt61is precluded by the unknown energy contributions associated with the
deaggregation of Me4Li;4THF as well as with the separation
of ions and the complexation of the lithium ion by T H F in 5-L,
(L = THF).
Chemical shifts of the 29Si NMR signals arising upon treatment of 2 with phenyllithium and teur-butyllithium let us conclude that lithium silicates are also formed in these systems,
presumably Li[SiC,,H8Me,Ph].4THF,
-8OOC) =
-112.7, and Li[SiCt,H8Me2tBu].4THF, 6("Si, -SOT) =
- 102.5, respectively. A similar high-field resonance (6("Si,
- 80 "C) = - 102.3) in the system tetraphenylsilane/phenyllithium/THF-HMPA proves that lithium pentaorganosilicates
(here Li[SiPh,].4 HMPA) are also formed from tetraphenylsilane.
In summary: In T H F equilibria are established between various o-organolithiums and either 9,9-dimethyl-9H,9-silafluorene
(2) or tetraphenylsilane, and the corresponding lithium silicates.
VerlagsgesellschufrmbH, 0-69451 Wernheim, 1996
The latter can be monitored by NMR spectroscopy at low temperatures and their stability is increased by coordination of
HMPA to lithium. To our knowledge these are the first pentaorganosilicates described. Present studies aim at the preparation of lithium pentaorganosilicates from other tetraorganosilanes.
Received: December 13, 1995
Revised version: February 8, 1996 128641IE]
German version: Angew. Chem. 1996, fO8,1183-1184
Keywords: lithium compounds
compounds - substitutions
NMR spectroscopy
- silicon
[l] Overview: C. Chuit, R. J. P. Corriu, C. Reye, J. C. Young, Chem. Rev. 1993,93.
121 S. A. Sullivan, C. H. DePuy, R. Damrauer, J Am. Chem. Soc. 1981, f03,480.
[3] a) M. Ishikawa, T. Tabohashi, H. Sugisawa, K. Nishimura, M. Kumada, J.
Organomet. Chem. 1983,250,109; b) N. Tokitoh, T. Matsumoto, H. Suzuki, R.
Okazaki. Tetrahedron Letf. 1991, 32, 2049; c) V. Gevorgyan, L. Borisova, E.
Lukevics, J. Organomet. Chem 1992, 441, 381.
141 Prepared by monolithiation of 2,2'-dibromobiphenyl and subsequent reaction
with chlorotrimethylsilane. We thank Drs. G. P. M. van Klink for a sample of
this compound.
[ 5 ] B.J. Helmer, R. West, R. J. P. Corriu, M. Poirier, G. Royo, A. De Saxce, J.
Organomet. Chem. 1983, 251, 295.
[6] 13C NMR (100.63 MHz, [DJTHF, -80°C): 6 =166.92 (C-2, satellites:
'J(29Si,13C)= 46.8 Hz), 145.80 (C-1). 136.05, 125.14, 124.90, 118.40 (C-3 to
C-6). 12.37 (CH,, satellites: 'J(29Si,13C)= 46.9 Hz).
[7] 'H N M R (400.13 MHz, [DJTHF, -SOT): b =7.58 (dd, 'J(H,H) =7.5,
4J(H,H) =l.OHz, 2H, Ar), 7.56 (dd, 'J(H,H) =7.0, 4J(H,H) =1.4 Hz, 2H,
Ar).6.93(ddd,'J(H,H) =7.5,3J(H,H)=7.1,4J(H,H)=1.4Hz,2H,Ar),6.88
(ddd. 3J(H,H) =7.0, ,J(H,H) =7.1, ,J(H,H) =l.OHz, 2H, Ar), 0.03 (s, 9H,
181 External standard: 0.3 M LiCl in methanol.
[9] H. J. Reich, J. P. Borst, R. R. Dykstra, D. P. Green, J. Am. Chem. SOC.1993,
lf5, 8728.
[lo] After warming to room temperature, 9-butyl-9-methyl-9H,9-silafluorene
isolated [3a].
1111 Calculations indicate that one-step substitution on silicon is always less favorable than reaction via pentacoordinated intermediates (Y Apeloig, The Chemistry oforgunic Silicon Compounds (Eds.: S . Patai, Z. Rappoport), 1989, Wiley, New York, p. 57).
[12] R. Damrauer, S. E. Danahey, Organomeralfics1986, 5 , 1490.
[13] H. J. Reich, N. H. Phillips, J. Am. Citem. Soc. 1986, f08,2102.
[14] See W. N. Setzer, P. von Raguk Schleyer, Adv. Organomet. Chem. 1985,24,353.
[15] Strikingly. AS= - l l O f 2 9 J K - 'm o l - '
was found for the reaction Bu,.
Li4-4THF+4 TH F e 2Bu2Li,-4THF, in which the tetra(THF) solvate of
butyllithium tetramer reacts with four molecules of THF to give two molecules
of a new tetra(THF) solvate (J. Heinzer, J. F. M. Oth, D. Seebach, Helv. Chim.
Actu 1985, 68, 1848). This is practically half of the decrease in entropy found
in the present study where we postulate formation of a single molecule of
tetra(THF) solvate from (formally) 0.25 molecules of the tetra(THF) solvate
of methyllithium tetramer, three molecules of THF, and one molecule of 2.
[16] According to calculations, formation of organosilicates from silanes and
carbanions is strongly exothermic: M. S . Gordon, L. P. Davis, L. W. Burggraf.
R. Damrauer, J Am. Chem. SOC.1986, 108, 7889.
0570-0833j96j3510-1128S 15 00+.25/0
Angew>.Chem. I n t . Ed. Engl. 1996, 35,N o . 10
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first, observations, biphenyldiyltrimethylsilicate, pentaorganosilicates, lithium
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