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Coordination of CO to the Alkaline Earth Metallocene [(Me5C5)2Ca].

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[lo] X-ray structure analysis of 6 : colorless crystals froin CHCI,, C,2HILN4,
M , = 472.63, monoclinic, space group C:,,,crystal size 0.25 x 0.50 x 0.70 mm,
u = 22.86(3), h = 6.893(7). c =17.37(1) A. {i =355.39(5) , V = 2472.7
F(O00) = 1008, Z = 4, pralCd
= 1.27 g ~ m - 11
~ =. 0.07 mni- I , Mo,, radiation.
E. = 0.7107 A. Intensity data were collected on a SYNTEX R3 diffractometer.
2740 measured reflections, 1402 independent reflections within / > 2.%(/).
number of reflections within I > 2.041) not defined. The atructure was solved
with Patterson-Fourier methods carried out with SHELXTL PLUS.
R = 0.061. R, = 0.051 Further details of the crystal structure investigation
may be obtained from the Fachinformationszentrum Karlaruhe, D-76344 Eggenstein-Leopoldshafen (Germany) on quoting the depository number CSD58 843.
[11] Analogous compounds with piperarine instead of I g. i n which the chair conI
C ~ L VSuc,.
formation is favored: K. Rissanen, J. Breitenbach, J. Huiiskonrn. .
Chenl. Comnirin. 1994. 1265.
[12] Piperarine macrocycles with chair conformation. which changes to boat conformation after metal complexation: P. W. Wade. R D. Hancock. J. C. A.
Boeyens. S M. Dobson, J Cl7rni. S i r . . Ddrun firm.%.1990. 483.
[13] R. W. Alder. A w . Cli07i. Re\. 1983. 16. 321
Fig. 7 . Cryatid structure of the mer[r-cyclophane 6 [lo]
Coordination of CO to the Alkaline Earth
Metallocene [ (Me5C&Ca]**
Peter Selg, Hans H. Brintzinger,*
Richard A. Andersen," and Istvlin T. Horvlith*
Dedicated to Professor Richard R . Schmidt
on the occasion of his 60th hirlhduy
Scheme 3. Pos\ible equilibrium between the "outside" (6a) and "inside" isomer
(6b) o f 6 by nitrogen inversion and rotation of the benzylic methylene groups.
trum. Corresponding complexation reactions of 6 with Ag+
ions have not been successful.
In light of the structures of the bicyclic triyne 3 and the cyclophane 6 we propose the name ''K boat" cages for the bridged
diazacy clodecadi y nes.
Received: October 5 , 1994
Revised version: December 29. 1994 [Z 7379 IE]
1995, 107, 867
German version: A n g e ~ Cheni.
Keywords: alkynes . cage compounds . phanes
C. J Pedei-son. J. Ani. Chern. Sue 1967,XY. 2495; b) C. J. Pederson. Aiigeh
1988. 100. 1053: AnRPli. CheiJl. In/. Ed. €fig/. 1988. 100. 1021; c ) J.-M.
Lehn. fhid. 1988. 1110. 91 and 1988. 100, 89: d ) F. Vogtle, Supramo/eku/ure
U i e i i f w . Teuhner, Stuttgart, 1992; e) Croiiw Curi?puiind~,
Tuirurd~Firrrrre Applt~ u / t w i . %(Ed..
S. R. Cooper). VCH. Weinheim, 1992; f ) B. Dietrich. P. Viout,
S ~ ~ TWeinheim,
Lehn. Mot r o q d i [ C I I P I J I ~ SVCH,
[2] F P. Schmidtcheii. A. Gleich. A. Schuinmer. Pure Appl. C/~enr.1989. 61,
[ 3 ] 1). O'Krongly. S. R. Denmeade. M . Y Chiang. R Breslow. J. A m . Chcrii. Soc.
1985. 1U7. 5544: A. Bencini. V. Fusi, M. Micheloni. B. Valtancoli, J. Chcitf.Sue.
c/7<'ili~ ' i J i 7 1 i J 1 1 l f f1994.
[4] B. J. Whitlock. H. W. Whitlock. J. An?. Clrrm. Sue. 1994. 116, 2201; review: F.
Diederich. C'r(/up/iune.\, Monographs in Supramolecular Chemistry 2 ; The
Royal Society of Chemistry. London, 1991.
[5] A. Nakiino. Y. Li. P. Geoffroy, M. Kim. J. L. Atuood, S. Bott. H. Zhang. L.
Echegoycn. G. W. Gokel. E~ra/7rdmtLair. 1989. 30. 5099.
.I A m . C h i ? .Soc. 1985. 107. 6108.
[7] R. Gkitrr. J Ritter. H . Irngartinger, J. Lichtenthiler. Teirahedrun L e / / . 1991.
32, 2883: i b d 1991. 32. 2887.
[XI .I. Riltci-. H. Irngxtinger. R. Gleiter. unpublished.
J. 8 . Lambert. Y.
191 J.-J. Dclpuech in Ci,c,/icOrganonitriijirn S f r v e o d ~ n a m i [(Eds.:
l.'ikcuchi). VCH. Weinheim. 1992.
Compared to the countless transition metal carbonyl complexes, in which CO acts as a K acceptor for d electrons on the metal
center, CO coordination to main group compounds has been
observed in a few instances only. A gas-phase species HCO' has
been found to have its v(C0) absorption at 2184 cm"."] Diborane reacts with CO to give a volatile complex [H,B-CO] with
v(C0) = 21 65 cm- t.[21 Microwave spectroscopy yields a dipole
moment of 1.8 D for this molecule,[31consistent with the charge
distribution (H3B--C=O+].L41
Me,AI was found to form a complex [Me3A1-CO] with v(C0) = 2185 cm-' in a CO matrix at
15-35 K.[51The increase of v(C0) above that of free CO
(2143 cm-1)[61in all of these complexes indicates that CO is
acting solely as a o-donor ligand here. In [Me$-CO] and
[(Me,C,),Si-CO],['~ 1' on the other hand, v(C0) is decreased to
1962 and 2065 cm- I , respectively, consistent with a x-donor
action of these divalent silicon species. Apart from low-temperature matrix studies,['] CO coordination to alkaline earth compounds has not been reported so far. Here, we describe evidence
Prof. Dr. H. H. Brintzinger. Dipl.-Chem. P. Selg
Fakultit fur Chemie der Universitit
D-78434 Konstanz (Germany)
Telefax: Int. code (7531)883137
Prof. Dr. R. A. Andersen
Department of Chemistry and
Chemical Science Division of Lawrence Berkeley Laboratory
University of California
Berkeley, CA 94720 (USA)
Telefax: Int. code (510)642-8369
Dr. I. T. Horvrith
Corporate Research Science Laboratories
Exxon Research and Engineering Company
Annandale, NJ 08801 (USA)
Telefax: Inl. code +(908)730-3042
This work was supported by the Deutsche Forschungsgemeinschaft. by the
Fonds der ChemiscIie Industrie, and by the Director. Office of Energy Research. Office of Basic Energy Sciences, Chemical Sciences Division of the
U. S. Department of Energy, under contract DE-AC03-76SF00098. R. A. A
thanks the Alexander-von-Humboldt Foundation for a Senior Scientist
for the formation of the first carbonyl complex of an organo
alkaline earth molecular compound, [(Me,C,),Ca-CO].
When a solution of [(Me,C,),Ca]["] in toluene is exposed to
CO pressures of 2.5-70 bar in an elevated-pressure IR
a new v(C0) absorption appears at 2158 cm-'. The appearance
of this band, as well as its loss in intensity upon release of CO
pressure, is practically instantaneous; repeated measurements at
any given pressure show that these changes are reversible. Figure
1 shows the IR spectrum as a function of CO pressure at 10 "C.
It is apparent that the change in absorbance at 2158 cm-',
AE(2158), is a suitable measure for the extent of complex formation. A linear Hildebrand-Benesi plot['31of AE(2158)-' against
Table 1. Temperature dependence of equilibrium constants K for reaction (a) and
K for reaction (b) in toluene, as determined by IR spectroscopy (with e.s.d.).
T/ "C
These data are confirmed by a 13C NMR study at elevated
CO pressures." 'I Solutions of [(Me,C,),Ca] in [DJtoluene under CO pressures up to 80 bar give only one I3C NMR signal
each for their C,-ring, CH,, and CO carbon atoms in the temperature range between + 30 and -70 0C,['81indicating that the
exchange of CO is rapid on the NMR time scale. The chemical
shifts of these signals change with increasing CO pressure as
indicated in Table 2. As changes in chemical shifts, A6. are a
Table 2 . "C NMR data for [(Me,C,),Ca]
neat T = 31.5 C [a].
+ CO s[(Me,C,),Ca-CO] in [D,]tolue-
lO.YO(1) [b]
113.19(4) [b]
184.7 [b]
180.4 [b]
[a] Measured with a JEOL JMN GX 400 spectrometer operated at 96.4 MHr.
chemical shifts relative to 6(C,D,CD,) = 20.4. [b] Obtained by least- square analysis from the values observed at p(C0) = 15-80 bar.
linear function of the mole fractions of free and complexed
species, the equilibrium constant K, as well as the limiting values
of A6 for complete complex formation, can be obtained by a
-0.05 I
least-squares analysis of the essentially linear plots of Ah-'
2250 2200 2150 2100 2050 2000
against p ( C 0 ) - ' . A value of K = 0.024 bar-' at 31.5 "C, obt
tained in this manner, is in agreement with that derived from the
Fig. 1. IR spectra of a 4 x ~ O - ' M solution of [(Me,C,),Ca] in toluene at 10°C at
IR data discussed above. A chemical shift of 6 = 180.4, deterCO pressures of 5. 10,20.40, and 60 bar; top: Base-line corrected spectra, bottom:
mined for CO in [(Me,C,),Ca-CO], places this CO resonance at
Spectra corrected for the absorption of solvent and free CO in solution.
higher fields than that of free CO in toluene solution (6 = 184.7).
[ (Me,C,),Ca-CO] differs in this regard from transition metal
carbonyl complexes with partly filled nd subshells; in these, the
p(CO)-' indicates a stoichiometry [(Me,C,),Ca-C0]['4] and an
CO ligands have their I3C NMR signals at substantially lower
equilibrium constant K = 0.036 bar-' for the reaction between
fields than the signal of free C0.[19,20]
solvated decamethyl calcocene and gaseous CO [Eq. (a)]. Since
With regard to both the I3C chemical shift of its CO ligand to
higher fields and the shift of v(C0) to higher frequencies, compared to the respective values of free CO, [(Me,C,),Ca-CO]
[(Me,C,),Ca](tol) + CO(gas)
resembles a number of recently reported noble metal CO comthe concentration of dissolved CO is proportional to CO presplexes, mostly with nd" electron config~ration."~l
Our results
sure, c(C0) =p(CO) x 7.1 x 1 0 - 3 ~bar-', throughout the
show that d electrons are not essential for exothermic CO coortemperature and pressure range considered here,[121a value of
dination. [(Me,C,),Ca] appears to make up for its lack of d
electrons by an unusual Lewis acidity, which is probably related
K = 5.1 M - ' is obtained for the corresponding reaction involving
dissolved CO [Eq. (b)]. IR spectroscopic measurements in the
to its bent structure.[213 Metal-ligand bond formation can
thus presumably occur with expenditures of reorganization energy much smaller than those required to bend typical transition
[(Me,C,),Ca](tol) + CO(tol) <[(Me,C,)lCa-CO](tol)
metal sandwich compound^.[^^.^^^ In accord with this notion,
temperature range of -27 to 32°C give values for the equino carbonyl complex formation is observed, up to CO pressures
of 50 bar, in solutions of [(Me,C,),Mg] in toluene, for which a
librium constants as summarized in Table 1; [ l 6 I from these, thermodynamic values of AH," = - 25 f5 kJ mol- and ASa' =
strictly linear geometry has been established.[' 'I Preliminary
experiments with the bent alkaline earth metallocene
10 Jmol-'K-' are obtained for complex formation
[(Me,C,),Sr] 12z. 241 indicate the formation of a carbonyl comaccording to Equation (a), while values of AH: =
plex with v(C0) = 2159 cm-', similar to that observed for
- 2 5 f 5 kJmol-'
and AS: = -70+10 Jmol-'K-' are ob[(Me,C,),Ca-CO].
tained for Equation (b).
VCH Verlugsgesell.~cIiulrmbH, 0-69451 Weinheirn, 1995
0570-0833/95/0707-07923 10.00+ .25/0
Angew. Cliem. I n [ . Ed. Engl. 1995, 34, No. 7
This is the first example of CO binding to a molecular alkaline
earth metal compound. Previously described [(Me,C,),Ca]
complexes, such as [(Me,C,),Ca(PEt,)],[251 [(Me,C,),Ca(MeC=C[(Me,C,),Ca(Me,Si-CrC-CEC-SiMe,)],1271
and [(Me,C,)ZCa(CN-2,6-xylyl),l 12'] show that one o r two ligands can be coordinated at the Ca center. In the case of the
carbonyl complex reported here, only one CO ligand appears to
be taken up in the pressure range studied. The binding of CO to
the Ca center is weaker than that of the diethyl ether hgand in
[(Me,C,),Ca(OEt,)]. as OEt, is not displaced by C O at pressures up to 120 bar. This observation and the similarity of i(C0)
frequencies in [H,B-CO] and [(Me,C,),Ca-CO] are consistent
with the view that CO acts solely as a 0-donor ligand towards
[(Me,C,)zCn] and that dipolar interactions are important for
the Ca--CO bond.
1201 A
N M R signal at 6 = I 5 8 is observed for [H,B-c'O]' L. W. Hall. D. W.
Lownian. P. D. Ellis. J. D. Odom, fnor.,q. Chrrii. 1975. 14. 580.
[ Z l ] R. A. Williams. T. P. Hanuaa. J. C. Huffman, O,:q~riion?ci~il/il~.\
1990. Y. 1128.
1221 The energy required to change the centroid-cnlcium-centrold angle in the range
o f 180 to 150' has been estimated to be very s m a l l : R. Bloin. K. Faegri, Jr..
Y 1990. 9 . 372: M. Kaupp. P. \ o n R. Schleyer. M.
H. V Volden. Or,~iiri[~fii[,ru//i[
Dolg, H . Stoll. J A m . Chcr?i.Sot. 1992. 114. 8202. T. K. Hollis. J. K. Burdett.
8. Bornich. Org~~iioiii1,ri~ll;t.~
IY93. 12. 3385.
[23] H. H. Brintzinger. L. L. Lohr, Jr., K. L. Tang Wong. J A f i i C / i c w i . Soc. 1975,
97. 5146: K. M. Simpson. M. E Rettig. R. M. Wing. O ~ x ~ f ~ r ( ~ i i 1992.
i ~ , ~ 11.
[24] R. A. Andersen. R. Blom. C. J. Burns. H . V Volden. J. C'hmn. S o r . C/ierii.
Coiiiiifiiii. 1987, 768.
[25] C. J. Burns. R. A. Andersen. J Orpfioi?irr.C'hcrff. 1987. 32.5. 31
[26] C. J. Burns. PhD Thesis. University of California Berkele). 1987.
[27] R A. Williams. T. P. Hanusa. J. C . Huffman. J. A m . Chwi. Sol.. 1990. 112.
Received: September 24. 1994
Revised version: December 23. 1994 [Z7350IE]
German version: AnpPw. Chrni. 1995, 107. 877
Keywords: alkaline earth metal compounds . carbonyl complexes . high-pressure chemistry . metallocenes
Benzopyranoisoxazolidines as Chiral Auxiliaries
for Asymmetric Synthesis**
Atsushi Abiko, Osamu Moriya, Sandra A. Filla,
[I]S. c'. Foster. A. R. W McKellar, T. J. Sears, J. Chcrii. Phys. 1984. 81. 578; P. B.
and Satoru Masamune"
Da\ies. P. A Hamilton. W J Rothwell. ihd. 1984, $1. 1598.
[Z] A. B. Burp. H. 1. Schlessinger. J. A m . Chem. Sot. 1937. 59. 780: A. B. Burg.
Highly stereoselective a-alkylation of cdrboxyk acid derivaf / ~ r i / . 1952. 74. 3482: G . W. Bethke. M. K. Wilson. J. Chefi?.Pliys. 1957. 26.
1 IIX; R. C . Taylor. !hid. 1957. 26. 1131.
tives (RCH,COX) can be performed with many known chiral
131 W. Gordy. H . Ring. A. B. Burg, P h n . R p r . 1950. 78. 512.
auxiliaries such as oxazolidinone,"] sultam heterocycles.['] and
[4] M. W. P. Strandberg. C . S. Pearsall. M. T. Weiss, J. Cli~iii.PIIKS.1949. 17. 429.
others.[31Here we report new chiral isoxazolidine auxiliaries ( l a
[5] R Sanche7. C . Arrington, C. A. Arrington. Jr.. J Am. Chon. Soc. 1989. (11,
and l b ) , which not only effect equally high asymmetric induc91 10. At room temperature no indication of coordination was obtained up to
ii c'0 pressure of 10 bar.
tion but also offer the following distinct advantages: 1 ) acyla[6] K. Nakanioto. Iir/r.irr~~l
S[)ecrru ( I / h r g u i i ; i imd Conrdiriuiiofi Cofiipoii~ids.
of the auxiliaries is achieved with an acid chloride and
2nd. edition. Wiley. New York. 1970. p. 78.
triethylamine, 2) alkylation with P-branched electrophiles can
[7] C . A. Arrington. J. T. Petty, S. E . Payne, W. C. K. Haskins, 1 Am. Chiwi. Sol.
be performed by using their triflates, and 3) alkylated products
1988. 110. 0240; M. Pearsall. R. West. ihrd 1988. 110. 7228.
181 M Tacke. C. Klein. D. J. Stufkens, A. Oskam. P. Jutzi. E. A. Bunte. 2. Anorz.
can be converted directly into the corresponding alcohols, alde.A//,q. C/iwi 1993. 619. 865.
hydes, and ketones in one step with recovery of the auxiliary (see
191 Coordination ufcarbon monoxide to thealkaline earth fluorides MgF?. CaF,.
SrF,. and BnF, as bell as to CaCI, in CO matrices at temperatures of about
10 K was deduced from the observation of one or several infrared absorption
b m d s hetween 2160 and 2205 cni-' [lOa] and from changes in the C a ~CI
stretching frequency [lOb].
[lo] a) R. H. Haupe. S. E. Gransden. J. L. Margrave. J Cheni. Sol. Dulron Truii.s.
1979. 745; h ) 1. R Beattie. P. J. Jones. N. A. Young. J A m Ch(w. So(. 1992.
114. 6146
[ l l ] R. A. Andersuii, J. M. Boncella. C . J. Burns, R. Blom. A. Haatand. H. V. Voldeii. J Urqmufiii,r. C'ireni. 1986. 312. C49; R . A. Andersen. R. Blom, J. M
Boncellit. C. .I Burns. H. V. Volden. Acru Cliem. Sciind Srr. A 1987. 41. 24.
(-)-Za. R=H
4- Y=CH,OH
[12] E. IJ. b u n RXIIJ.C. D. Schmulbach, H. H. Brintzinger, J Orgrinomer. C/iriii. (+)-la: R=H
(+)-lb- R=Me
1987. 3 X . 275. Blank experiments in the same cell without [(Me,C,j,Ca] give
5: Y=CHO
rise only to the absorption of free CO at 21 34 cm- I.
6 : Y=COCH,
[ I 31 H. A. Benesi. J. H. Hildebrand. J. A i i i . Ch~rir.Soc. 1949, 7 1 , 2703.
1141 A stoichionierry of [(Me,CsjlCa(CO),] cannot beexcluded o n the basis of the
Scheme 1. a ) CH,CH,COCI, Et,N.'CH2CI,. b) R'X. KHMDS:THF. c) LiBH,.
observation of a single CO stretching absorption alone. since the symmetric
EtOH/Et,O or LiAIHJTHF for 4; DIBAL-H:THF for 5: CH,MgBr,'THF for 6.
and asymmetric stretching vibrations of such a dicarbonyl species could be
unresolved (ci: ref. (IS]): this stoichiornetry is unlikely. however. sincea plot of
AE(215X)- ' b s . p(CO)-' deviates significantly from linearity.
[15] n-HondedcarhonylcompIexesofPd2'.Ptzi. A g + . A u + H
. g L t . a n d HE;' : D.
Syntheses of l a and l b are very simple and readily applicable
Bclii Dell'Amico. F. Calderazzo. P. Robino. A. Segre. J. C/imi. So(,. Dalton
to a large-scale preparation (about 1 mol). The isoxazolidine
7i-om. 1991. 3017: J. 1. Rack, B. Moasser. J. D. Gargulak. W. L. Gladfelter.
skeleton was constructed by an intramolecular [3 21 cycloadH. D. Hochheimer. S. H. Straws, J. Clieni. S o ( . Chewi. Conirnuii. 1994.685: H.
dition involving a nitrone.['] Thus, heating a mixture of o-allylWillnei-. M. Hodenhinder. C . Wang, F. Aubke, i h d . 1994. 1189: H. Willner. J.
Schnebs. G HNang. F. Mistry. R. Jones, J. Trotter. F. Aubke. J. A m . Chem.
So(. 1992. 114. X977: L. Weber. Aii,yeir. Chon. 1994. 106. 1131 ; Aiigeir. C / i ~ w .
[*] Prof. S. Masamune. Dr. 0. Moriya. Dr. S. A. Filln
I n r . El/. EyqI 1994. 33. 1077.
Department of Chemistry
[I61 An cssentinlly unchanged valueof i,(CO) = 2159 c m - ' and similar absorbance
Massachusetts Institute of Technology
changes in dependence on pressure and temperature are observed in methylcyCambridge, M A 02139 (USA)
clohexane solution and indicate that solvent effects areofminor importance for
Telefax: Int. code (617)253-1340
this cquilihrium reaction.
Dr. A. Abiko
1171 I T. Horvith. J. M. Millar. Chmi. Rev. 1991. 91. 1339.
Institute for Fundamental Research. Kao Corporation
1181 At lower temperatures. the solubility of [(Me,C,j,Ca] is insufficient for ' T
Ichikai-machi. Haga-gun, Tochigi, 321-34 (Japan)
NMR measurements.
[19] B. E. Maim. B. F. Taylor. I3C N M R Duru ./or Orgunonierollrc Cornp~iimii.~.
[**I S. M. gratefully acknowledges the National Institutes of Health. U. S. A.
Aciidemic Press. New York 1981.
(CA48175) for financial support.
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coordination, metallocene, me5c5, alkaline, earth, 2ca
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