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First Structure of a Mixed OrganosodiumLithium Alkoxide Compound Model for a Superbase.

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Fig. 2 . Crystal structure of 3 b (ORTEP). Ring bond angles: [ 1: CI1-Bl-Cl
117.3(2), Cl-B1-Cl a 124.9(3), Bl-Cl-C2 128.512). Cl-C2-C3 129.4(2). C2-C3C3a 129.6(2).
C-Mo distances, and the boron atom is displaced out of the
ring plane away from Mo by 0.05 A. Thus, complexation
causes this distortion of the planar free ligand. Similar distortions are found in the structures of 3c and 4 and indeed
in most other complexed boron heterocycles." 6 , 'I
In addition, the formal double bonds (C1 -C2, C3-C3a)
lengthen on complexation, while the formal single bonds
(BI -C1, C2ZC3) remain unchanged. This suggests that the
Mo atom removes electron density primarily from the electron-rich regions of the borepin ring which are trans to the
CO ligands. The B-C1 unit is thereby eclipsed by one CO
ligand. The conformational preferences of similar complexes
have been discussed in detail by using an EH-MO model.["]
The effect of complexation is to reduce the C-C bond alternation from 0.058 8, in 1 b to 0.023 8, in 3 b. Therefore
the delocalized n bonding is enhanced in 3 b.
Experimental Procedure
3 b : A solution of I b (140mg. 1.1 mmol) in pentane ( 2 m L ) was added to a
suspension of [(C,H,N),Mo(CO),] (480 mg, 1.1 mmol) in ether (20 mL) at
25 'T Then BF, . OEt, (0.84 mL. 6.8 mmol) was added dropwise with stirring
over 2 mins. After 3 h the solvent was removed under vacuum, and the residue
was extracted with hexane. Crystallization at - 2 0 ' C afforded 220 mg
(0.7 mmol) of crude crystals. Recrystallization from hexane gave orange cubes,
M.p. 132-135'C. High-resolution EI-MS- calcd. for C,H,"B35C198Mo0,:
305.9153; found: 305.9146. IK (hexane): i. = 2024, 1974, 1947cm-' (vs, C 0 ) :
' H NMR (360 MHz, C,D,): 6 = 4.84 (br d, H#), 4.45 (d, 3," = 11.4 Hz, H,).
4.26 (m, Jo;=7.8 Hz, HJ; IlB N M R (115.5 MHz. C,D,): 6 = 30.5 (br);
N M R (90.6 MHz, C,D,): 6 = 213.9 (CO), 109.4 (C,,), 95.9 (C,), 92.0 (br, C,).
3 a : To a solution of 3 b (40 mg, 0.1 mmol) in toluene (6 mL) at -60°C was
added with stirring 0.32 mL of a 1.0 M solution of Li[BEt,H] in THF. After the
solution had been warmed to 25 C, the solvent was removed under vifcuum. A
brown residue remained which was extracted with hexane. Removal of the
solvent under vacuum left an orange oil which crystallized a t 2 5 ' C . Recrystallization from hexane gave bright orange crystals, M.p. 165 -C (decamp). Highresolution EI-MS: calcd. for C,H,'1B98Mo0,: 271.9542; found: 271.9546. IR
(hexane): i = 2018, 1966, 1943 (vs, CO), 2512cm-' (w, BH); ' H N M R
( 3 6 0 M H z , C 6 D 6 ) : 6 = 5.16(brd,H,,),4.62(dd,Jav=11.4,3J, , , = 6 H z , H , ) ,
4.42 (m, J,,, =7.8 Hz. Hs), BH (not observed); "B NMR (1 15.5 MHz, C,D,,):
is = 23.1 (br d , JRH= 94 Hz); " C NMR (90.6 MHz, C,D,): 6 = 214.0 (CO),
112.8 (C&, 97.4 (C,,)C, (not observed)
Received: January 27, 1993 [Z 5834 IE]
German version: Angew. Chein. 1993, 10s. 1112
111 E. E. van Tamelen. G. Brieger. K. G. Untch, 7i,truhedron Leir. 1960, K. 14.
121 a) A. J. Leusink, W Drenth, J. G. Noltes, G. J. M. van der Kerk, Tetrahedron Leu. 1967, 1263; b) G. Axelrad, D. Halpern, J. Chem. SOL..D. 1971,
291; c) A. J. Ashe, Ill, J. W. Kampf, C. M. Kausch, H. Konishi, M. 0.
Kristen, J. Kroker, OrgunomeruNics 1990, 9, 2944.
131 A. T. Jeffries, 111, S. Gronowitz, Chem. Scr. 1973. 4, 183.
R g VCH Verlugsgesell.scha/r m6H, 0-69451 WeinheBn, 1993
a) J. J. Eisch, J. E. Galle. J. Am. Chem. Soc. 1975.97.4436; b) See also: A.
Geisberger. dissertation. Universltit, Giessen, 1990.
W. Schacht, D. Kaufmann, Angeir. Chem. 1987.99.682; A n p i s . Cliiw~Inr.
Ed. EngI. 1987. 26, 665.
a)A. J. Ashe. Ill, F. J. Drone, J. Am. Cl7em. Soc. 1987,109,1879; rhd. 1988,
110. 6599; b) A. J. Ashe, 111. F. J. Drone, C. M. Kausch. J. Kroker, S. M.
Al-Taweel, Pure Appl. Chem. 1990, 513.
Y. Sugihara. T. Yagi, I. Murata. A. Imamura. J. Am. Chem. Soc. 1992,114,
Y. Nakadaira, R. Sato, H. Sakurai, C h m . Lrrf. 1987, 1451.
A. J. Ashe, 111. J. W. Kampf. Y. Nakadaira, J. M. Pace, Angew. Chem. 1992,
f04, 1267. Angen. Chem. Inr. Ed. Engl. 1992, 31. 1255.
a) J. M . Schulman, K. L. Disch, M. L. Sabio, J. A m . Chem. Soc. 1982,104,
3785, ;hid. 1984. fO6. 7696; b) Terruhedron Left. 1983. 24, 1863; c) J. M.
Schulman, R. L. Disch, Organomerullics 1989, 8, 733.
1 b: Monoclinic space group CZ/c (no. 15) with (I =11.338(6), 6 =
8.597(5), c =7.493(4) A. /{ =121.61(4)"; V = 622 l(6) A'; Z = 4 (p,,,,, =
1.328gcm-3);p(Mo,,) = 4 . 8 8 c m - ' : 1133 uniquereflections; 1094 wlth
F;, 2 0.6a(F) were used in refinement; R = 0.0365. R, = 0.0662; G O F =
1.20. 3b: Orthorhombic space group Pnmu (no. 62) with u = 8.057(1),
h=10.623(2).( = 1 2 . 7 1 8 ( 3 ) & 2 = 4 ( ~ , = 1 . 8 5 5 g ~ m ~ ~ ) : p ( M o , , ) =
14.02 c m - ' : 1329 unique reflections; 1314 with Fo 2 2~ ( F ) were used in
refinement; R = 0.0260, R, = 0.0457; G O F = 2.56. Further details of the
crystal structure investigations are available on request from the Director
of the Cambridge Crystallographic Data Centre. 12 Union Road. GBCambridge CB21EZ (UK), on quoting the full journal citation.
[12] BMe, (1.58 A): L. S. Bartell, B. L. Caroll, J. Chem. Phys. 1965, 42, 3076.
[13] M. Traetteberg. J. Am. Chem. Soc. 1964.86.426s; S . S. Butcher, J. Chem.
P h n . 1965.42, 1833: K. E. Davis. A. Tu1insky.J. A m . Chem. Soc. 1966.88.
[14] D. W. J. Cruicksank. R. A. Sparks. Proc. R. Soc. London, Ser. A 1960.2S8,
1151 a) Gaussian 90. Revision I: M. J. Frisch, M. Head-Gordon; G. W. Tucks,
J. B. Foresman. H. B. Schlegel, K. Raghavachari, M. Kobb, J. S. Binkley,
C. Gonzdlez, D. J. Fox, R. A. Whiteside. K. Seager. C. F. Melius, J. Baker,
R. L. Martin, L. R. Kahn. S. Topiol. J. A. Pople. Gausran Inc. Pittsburgh,
PA. USA 1990; b) 6-31G* basis set: P. C. Hariharar, J. A. Pople, Theor.
Chiin. Actu 1973, 28. 213; M. M. Francil, W. J. Pietro, W. J. Hehre, J. S.
Brinkley, M. S. Gordon, D, J. DiFries, J. A. Pop1e.J. Chem. Phys. 1982, 77,
[16] For a discussion of complexes of other boron heterocycles see: G. E. Herberich, in Comprehensive Or-gunometullie Chemisrry, Vol. f (Eds. : G.
Wilkinson, F. G. A. Stone, E. W Abel), Pergamon, Oxford, 1982, p. 381.
11 71 a) G. E. Herberich. W. Boveleth, B. Hessner, D. P. J. Koffer, M. Negele, R.
Saive. J . Orgunomer. Chem. 1986,308, 153; b) W. Siebert, M. Bochmann,
J. Edwin, C . Kruger. Y.-H. R a y , Z. Narurforsch. B 1978.33, 1410; c) G.
Huttner. W. Gartzke. Chem. 5er. 1974, 107, 3786; d ) G. E. Herberich, B.
Hessner. S. Beswetherick, J. A. K. Howard, P. Woodward, J Orgunomer.
Chem. 1980. 192,421 ; e) G. E. Herberich, B. Hessner, M. Negele, J. A. K.
Howard. ibid. 1987. 336, 29.
a ) T. A. Albright. P. Hofmann. K. Hoffmann, J. Am. Chem. Soc. 1977.99,
7546; b) T. A. Albright, R. Hoffmann. Chem. Brr. 1978, f f i , 1578; c) T. A.
Albright, Ace. Chem. Res. 1982, 15, 149.
First Structure of a Mixed Organosodium/Lithium
Alkoxide Compound : Model for a Superbase""
By Sjoerd Hardw and Andrew Streitwieser*
Mixtures of organolithium compounds and alkali metal
alkoxides ROM (M = Na, K, Rb, Cs), such as BuLilKOtBu,
are known as "superbases" and widely used in modern organic synthesis."' The development and application of these
superbase systems have been subjects of chemical research
for nearly three decades, yet the molecular structures of such
systems are still a matter of controversy. The topic has been
reviewed recently.[*] It is generally believed that the high
reactivity of RLi/R'OM (M = Na, K, Rb, Cs) mixtures is
[*] Prof. Dr. A. Streitwieser, Dr. S. Harder
Department of Chemistry, University of California
Berkeley, CA 94720 (USA)
Telefax: Int. code +(510)642-8369
S. H. thanks the NWO for a fellowship. This research was supported in
part by the National Science Foundation (grant no. CHE87-21134).
OS7O-O833/9310707-1066$ 10.00+ .2S:0
Angew. Chem. Inr. Ed. Engl. 1993. 32, No. 7
caused by metal exchange, forming RM/R'OLi. The interaction of the smaller Li cation with the smaller 0 anion is
favored ele~trostatically.[~~
Organoalkali metal species, however, are commonly aggregated in the solid state and in solution.14]The superbase mixture may well exist as mixed aggregates of RM and R'OLi monomers (1) or may be present as
separate aggregates of RM and ROLi (2).
2-sodiomethylphenoxide (6).['' Single-crystal X-ray structure analysis[81of 6 . tmeda (tmeda = tetramethylethylenediamine) reveals a tetrameric aggregate with approximate,
noncrystallographic S, symmetry (Fig. 1).
Ab initio calculations on Li/Na dimer systems151have
shown the importance of Li-0 bond formation in the metalexchange reaction [Eq. (a)]. The number of 0-Li bonds is
(MeLi)? + (NaOH),
+ (LiOH),
AE = - 8.2 kcalmol-' (a)
maximized in this reaction. There is, however, only a small
energy difference between the separate MeNa and LiOH
dimers and a mixed aggregate [Eq. (b)].
(MeNa)>+ (LiOH),
2(MeNa/LiOH) A E
f 1 . 3 kcalrnol-'
This result suggests equilibria between 1 and 2 or at least
the possible existence of short-lived mixed aggregates.
Because of the extreme reactivity of the superbase metalating reagents, the only report on the molecular structure of
these compounds has been an NMR study of the model
system cesium triphenylmethane/lithium 3-ethyl-3-heptoxide.L31 The authors could not detect mixed aggregates in this
All efforts so far to make crystals of superbase mixtures
for X-ray diffraction studies have failed. The mixing of several organolithium compounds with several sodium or
potassium alkoxides has resulted in microcrystalline precipitates of the pure organosodium or -potassium compounds.[61
This observation does not rule out the existence of mixed
aggregates in solution since the precipitate only represents
the least soluble species.
An alternative approach to the study of the structural
properties of RM/R'OLi mixtures (M = Na, K, Rb, Cs) is
the synthesis, crystallization, and X-ray diffraction analysis
of compounds that contain both functionalities (C-M and
0-Li) in one molecule. This approach in one sense circumvents the problem but could provide information on bonding
and coordination patterns in mixed aggregates. For example, such compounds may form structures in which Li
and M are doubly bridging between the anionic centers (3),
a structure type common for dilithiated species,[4a1or they
may form polymeric structures in which distinct C-M and
0-Li interactions can be recognized (4).
A compound with both functionalities (C-M and 0-Li)
was obtained by treating sodium 2,4,6-trimethylphenoxide
( 5 ) with butyllithium in hexane to yield lithium 4,6-dimethylAnxrw. Cliem. I I I I .Ed. Ennl. 1993, 32, No. 7
Fig. 1. Crystal structure of 6 tmeda (hydrogen atoms omitted). The tetrameric aggregate has approximate S , symmetry. Average bond lengths [A] and
angles I"]: C-Li 2.17(2), 0-Li 1.97(2), C-Na 2.671(9), 0 - N a 2.410(6), N-Na
2.496(9); Li-0-Li 82.0(7), 0-Li-0 97.4(8), N-Na-N 72.6(3).
The core of the structure is a distorted cube made up of 0
and Li atoms, whose edges are formed by eight 0-Li bonds
1.97(2)-2.06(2) 8,in length and four significantly shorter 0Li bonds 1.88(2t1.91(2) 8, in length. The four shorter bonds
are nearly colinear with the four Car,,-0 bonds (C-0-Li
angles vary from 165.1(7)@to 171.3(7)").The Li-0 distances
are similar to those in a tetrameric Li alkoxide (0-lithio-Nmethylpseudoephedrin, 1.87- 1.99 8,)['I and a tetrameric
lithium ester enolate (1.90-2.04 8,).[lo1
Each of the Li bridges between the anionic carbon and
oxygen centers is part of a puckered five-membered Li-C-CC-0 ring. This type of benzyl-Li interaction is novel for
benzyl alkali metal compounds in which the metal atom is
usually bonded to an sc-benzyl carbon atom and approximately perpendicular to the benzyl plane. The C-Li distances range from 2.14(2) to 2.21(2) 8, and are somewhat
shorter than those in benzyllithium which range from
2.189(8) to 2.229(8) A).['']
The Na atoms are coordinated perpendicular to the plane
of the benzyl group with an average distance of 2.671(9) 8,
to the carbanion center; this is comparable to the average
CH,-Na distance of 2.68 8, in tetrameric benzylsodium . tmeda.[l2]Short distances to atoms in the ring system
are shown in Figure 2. The Na-0 contact (3.75 8,) is quite
long, but there is a shorter contact of 2.410(6) 8,between the
Na atom and another 0 atom in the LiO cube. This is somewhat longer than the Na-0 distances in dimeric sodium
2,4,6-tris(trifluoromethyl)phenoxide, which range from
2.231 to 2.313
The coordination sphere around Na in
6 is completed by chelation to tmeda; the Na-N distances are
in the normal range of 2.445(8)-2.528(9) 8,. The coordina-
; VCH VerluRsResell.s~hu~
mhH, 0.69451 Wcmhuim, 1993
$ 10.00+ 2510
161 a) L. Lochmann, D. Lim, J. Organomet. Chem. 1971,28, 153; b) R. Pi, W.
Bauer, P. von R. Schleyer, ibid. 1986, 306, C1; c) S. Harder, unpublished
Fig. 2. Metal coordination around each aryl ring in 6 with average distances
tion sphere of the oxygen atom in this aggregate deviates
from the commonly observed trigonal (in ROLi dimers) and
tetrahedral (ROLi tetramers/hexamers), and can be described best as tetragonal-pyramidal.
The structure of 6 .tmeda is the first of a "mixed"
organosodium/lithium alkoxide aggregate. The structure is
dictated by 0-Li bonding. The observed cube structure results from the formation of the maximum number of 0-Li
bonds; Na-0 coordination is of minor importance in the
coordination sphere of the five-coordinate oxygen atom. The
structure of 6 indicates that lithium alkoxides also have a
dominating role in superbases in solution and suggests that
analogous interactions occur between RM (M = Na, K, Rb,
Cs) and R'OLi aggregates. That is, lithium alkoxide dimers
or tetramers can be distorted to extend the coordination
sphere around the 0 atom for interaction with the alkali
metal (7). The resulting reduced coordination of the carban-
ion then effectively increases its basicity; such structural effects thereby contribute to the superbasicity of such mixtures. For comparison, the solid-state structure of (nBuLi . LiOtBu), may be viewed as a distorted cube made up of
a LiOtBu tetramer which is opened on two sides to interact
with two BuLi dimers
Received: January 26, 1993 [Z 5828 IE]
German version: Angew. Chem. 1993, 105. 1108
[I] a) L. Lochmann, J. Pospisil, D. Lim, Tetrahedron Left. 1966, 257; b) M.
Schlosser, J. Orgunomet. Chem. 1967,8,9; c) L. Brandsma, H. D. Verkruijsse, Preparative Polar Organometallic Chemistry, Vol. I, Springer, Berlin,
1987; d) L. Brandsma, Preparative Polar Organometallic Chemistrj,
Vol. 2, Springer, Berlin, 1990.
[2] W. Bauer, L. Lochmann, J. Am. Chem. Soc. 1992, 114, 7482.
[3] This preference for Li-0 bonding is shown clearly by replacing anionic
and cationic centers in these highly ionic compounds by simple unit negative and positive point charges, and calculating the potential energies. If R
is the covalent radius of a nucleus, and R, > R,: and R, > R,, then
l/(Rc RM) I/(R,,
R,) is always larger than l/(Rc + RJ +
l/(R, + R,,), no matter what the exact values of R are.
[4] a) W. Setzer, P. von R. Schleyer, Adv. Organomet. Chem. 1985, 24, 353;
b) C. Schade, P. von R. Schleyer, ibid. 1988. 27, 169; c) W. Bauer, D.
Seebach, Helv. Chim. Actu 1984. 67, 1972.
[5] MP4SDTQ/6-31 G*//6-31 G*(+ ZPE) Calculations: S. Harder, T.
Kremer, P. von R. Schleyer. J. Organornet. Chem., submitted.
[7] Compound 6 was synthesized by treating a white suspension of 5 (1.0 g,
6.3 mmol) in 10 mL of hexane with BuLiihexane (2.0 M, 6.6 mmol) under
nitrogen at reflux. The resulting yellow powder (quantitative yield) underwent complete monodeuteration at the benzylic carbon when treated with
[8] Crystal structure data of 6 . tmeda, orthorhombic, a = 19.220(3),
h = 18.032(4), c = 39.806(8) A, V = 13796(5) A3, space group Pbca, formula {(C,H,,OLiNa). (C6H,6N2)]4, M = 1121.26, 2 = 8, pca,cd
1.080 g ~ m - ~(Mo,,)
= 0.8 c m - ' ; 9837 unique reflections were measured on a Enrdf-Nonius CAD4 diffractometer (Mo,, radiation, graphite
monochromator, T = - 95 'C) and 3704 reflections with F 2 > 2.5u(F2)
were considered observed. Solution by direct methods with SHELXS-86
1151, refinement by minimalization of Xw(F0-F,)' to R = 0.077 and
WR= 0.069 with M' = 1/u2(F,), non-hydrogen atoms anisotropic; H atoms
were assigned idealized locations and isotropic thermal parameters approximately 1.3 times that of the atoms to which they are attached. Two
of the four tmeda molecules show disordering which IS common for tmeda
and well described in literature [16]. Disorder in the structure o f 6 . tmeda
was described best with large anisotropic parameters on the disordered
atoms. Unfortunately, benzylic hydrogen atoms could not be detected in
the difference Fourier map, and the hybridization at the benzylic carbon
atom remains unknown. Plots were made with the EUCLID package [17].
Further details of the crystal structure investigation are available from the
Director of the Cambridge Crystallographic Data Centre, 12 Union Road,
GB-Cambridge CB2 1EZ (UK), on quoting the full journal citation.
[9] E. M. Arnett, M. A. Nichols, A. T. McPhail, J. Am. Chem. SOC.1990. 112,
[lo] D. Seebach, R. Amstutz. T. Laube, W. B. Schweizer, J. D. Dunitz, J. Am.
Chem. Soc. 1985, 107, 5403.
[ I l l a) S. P. Patterman, I. L. Karle, G. D. Stucky, J. Am. Chem. Soc. 1970, 92.
1150; b) M. A. Beno, H. Hope, M. M. Olmstead, P. P. Power,
Organometullics 1985, 4, 2117; c) W. Zarges, M. Marsch, K. Harms, G.
Boche, Chem. Ber. 1989, 122, 2303.
[I21 C. Schade, P. von R. Schleyer. H. Dietrich, W. Mahdi, J. Am. Chem. Soc.
1986, 108, 2484.
[13] S. Brooker, F. T. Edelmann, T. Kottke, H. W. Roesky, G. M. Sheldrick, D.
Chem. Commun. 1991, 144.
Stalke, K. H. Whitmire, J. Chem. SOC.
[14] M. Marsch, K. Harms, L. Lochmann, G. Boche, Angew. Chem. 1990, fU2,
334; Angew. Chem. Inr. Ed. Engl. 1990, 29, 308.
[15] G. M. Sheldrick, SHELXS-86, Program for Crystal Structure Solution,
Gottingen, 1986.
[I61 a) R. Amstutz, T. Laube, W. B. Schweizer, D. Seebach, J. D. Dunitz, Helv.
Chim. A m 1984, 67, 224; b) S. Harder, Dissertation, University of
Utrecht, 1990. p. 60.
[17] A. L. Spek, The EUCLID package in Compuiational Crystallography
(Ed.: D. Sayre). Clarendon Press, Oxford, 1982, p. 528.
VCH Yerlagsgesellschuft mbH, 0-69451 Weinheim. 1993
Rapid Carboalumination of Alkynes in the
Presence of Water**
By Peter Wipp and Sungtaek Lim
The carboalumination of alkynes is one of the most versatile routes for the preparation of olefins with defined configurations."] Recent applications of this methodology in
natural products synthesis include the preparation of segments for lophotoxin,'21 m a ~ b e c i n ,and
~ ~ ]FK-506.14]Whereas the uncatalyzed carboalumination of nonfunctionalized
alkynes is slow even at elevated temperatures, the zirconiumcatalyzed variantr5]occurs under mild conditions. Methylalumination of I-octyne (1) in the presence of 1 equiv of
[Cp,ZrCI,], for example, yields 2-methyl-I-octene (2) and
2-nonene (3) in a 95 : 5 ratio after 3 h at 22 oC.'61
[*] Prof. Dr. P. Wipf, S. Lim
Department of Chemistry, University of Pittsburgh
Pittsburgh, PA 15260 (USA)
Telefax: Int. code + (412) 624-8552
[**I This work was supported by the University of Pittsburgh. We thank Prof.
H. Yamamoto for stimulating discussions.
0570-U833193/U707-IU~8b" 10.00+.2S/O
Angew. Chem. Int. Ed. Engl 1993, 32, No. 7
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superbase, structure, mode, compounds, first, organosodiumlithium, alkoxide, mixed
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