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Diastereoselective Addition of n-Butyllithium to 2-Phenylpropanal A Reassessment of the Solvent and Temperature Effects.

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strain in controlling the regiochemistry observed here (Table I ,
entry 4).
The reaction of 1 with secondary or tertiary propargylic carbonates has been shown to provide allenyItitanium compounds
which, in turn, react with aldehydes to give homopropargyl
alcohols.[’ * I However. the results obtained by the reaction of 1
with 6 strongly suggested that the reaction with carbonate
would afford the
derivatives 13 of 1-alkynylcyclopropanols[61
propargyltitaniutn compounds 14 rather than the more strained
allenyltitaniums 15 as shown in Scheme 3.”*] Thus, the subse-
OC(0)OEt
13
i i p i Pr),
I
A1
15
14
i
1. R ~ C H O
2. HzO
OC(0)OEt
1. R%HO
2. H20
OH
R~*OH
17
16
Scheme 3. Synthesis of 16 and 17.
Keywords: cyclopropanes
compounds
-
propargyl compounds
*
titanium
A. Kasatkin, T. Nakagawa, S. Okamoto, F. Sato, J Am. Cheni. Suc 1995. 117,
3881.
M. T. Reetz. Top. Curr. Chenz. 1982, 106, 1; D. Seebach. B. Weidmann, L.
Widler, Modern Syntheric Methods. Transition Metals in Orgum(.Synthesis (Ed.
R. Scheffald), Otto Salle Verlag, Frankfurt, 1983, pp. 217--354: M. T. Reetz,
Organotiraniuni Reagent.\ in Organic S~nr17esi.r.Springer, Heidel berg, 1986.
R. W Hoffmann. Angen. Cheni. 1982, 94, 569: Angew Chem I n t Ed. Engl
1982. 21. 555: Y Yamamoto, Acc. Chem. Rrs. 1987. 20, 243.
R. Hanko, D. Hoppe, Angeir. Chem. 1982, 94, 378; Angeii. Chm7. Int. Ed.
Engl. 1982.21.372; B. Weidmann. D. Seebach, ;bid 1983.95. 12 and 1983.22,
31.
P. K Zubaidha. A. Kasatkin, F. Sato, J Chem. Soc. Cheni. Conimun. 1996,197.
1-Vinyl- and I-alkynylcyclopropanols were prepared by the reaction of 1ethoxycyclopropanol with two equivalents of vinyl- and aikynytmagneslum
bromides, respectively (see ref. 171); the successive treatment of the tertiary
alcohols with 1.1 equiv EtMgBr (Et,O, O’C. 5 min) and 1.2 equiv EtOC(0)CI
(20-C. 4 h) gave the carbonates 6 and 13 in 80-90% yield
J. R. Y. Salaun. Top. Curr. Chem. 1988, /44. 1.
The ring strain of methy~enecyciopropdneis 14 kcalmol-’ higher than that of
methylcyclopropane: A. Krief. Top. Cuvr Chem. 1987. 135. 35.
P. Binger. H. M. Buch. Top. Curr. Chum. 1987, 135, 77; T. Ohta. H. Takaya,
Comprehensive Organic Sinrhesis, Vol. 5 (Eds.. B. M. Trost, 1. Fleming),
Pergamon. Oxford, 1991, p- 1188. See also: S. Brise, S. Schomenauer, G.
McGaffin. A. Stolle, A. de Meijere, Chenz. Eur. J 1996, 2. 545. and references
therein
The related lithium derivatives prepared by the treatment of I-alkenyl-lmethylseleno-cyclopropanes with BuLi exhibited low regioselectivity in the
reaction with aldehydes. S. Halazy, A. Krief, Tetrahedron Lrrt. 1981. 22,4341.
T. Nakagawa. A. Kasatkin, F. Sato, Terrahedroii Lert. 1995,36. 3207. See also.
K. Furuta. M. Ishiguro. R. Haruta. N. Ikeda, H. Yamamoto. Bull. Chenz. Soc
Jpn 1984, 57. 2768.
It has been recently shown by using “C NMR spectroscopy that Iithiated
dicyclopropylacetylene exists exclusively as a propargyllithium (but not allenyllithium) compound. H. J. Reich, J. E.Holladay, J Am. Chem. Soc. 1995,
117, 8470.
To our knowledge, no general approach to compounds containing an 1alkenylidenecyclopropdne fragment has been developed so f‘ar. For a few examples of this type of compound prepared by using other methods. see: T.
Liese, A. de Meijere, Chem. Eer. 1986, ff9,2995: J. Al-Dula)ymi, M. S. Baird,
Tetrahedron Lett. 1988.29,6147. K. Tanaka, K. Otsubo, K. Fuji. Sjnlett 1995,
933.
It is noteworthy that lithiated 1-ethoxy-2-(trimethylsilylethynyl)cycIopropane
showed the opposite regioselectivity to afford only acetylenic addition products in the reaction with carbonyl compounds: H. C. Militzer. S. Schoemenauer, C. Otte. C. Puls. J. Hain, S. Braese, A. de Meijere, Svirhesis 1993, 998.
quent treatment with aldehydes would give the allenic cyclopropanes 16, which are of synthetic interest but are not readily
available by other
As expected, the reaction of 1
with the ethyl carbonate derivative 13a of I-(phenylethyny1)cyclopropanol followed by addition of PhCHO led primarily to the allenic cyclopropane 16a with only 7 YOyield of the
corresponding regioisomeric alkynylcyclopropane 17a (Table 1,
entry 5). Similarly, the treatment of the titanium reagents generated from the carbonates 13a-c with EtCHO and/or CH,O
afforded 16 exclusively (entries 6- 8) or predominantly (entry 9) .[I4]
Diastereoselective Addition of n-Butyllithium
to 2-Phenylpropanal: A Reassessment of the
Solvent and Temperature Effects**
Experimental Procedure
Gianfranco Cainelli,* Daria Giacomini,* P. Galletti,
and A. Marini
The following procedure for preparation of 9a and 10a (entry 1 in Table 1) is representative To a solution of [Ti(OiF’r),] (284mg. l.00mmol) and 6 (156mg,
0.50 mmol) in EtzO (7.5 mL) was added dropwise iPrMgCl (1.35 mL, 1.48 M in
Et,O, 2.00 mmo1)at -50 C. Thereactionmixturewasstirredat -4510 -40’Cfor
1 h, then EtCHO (58 mg. 1.00 mmol) was added. The reaction mixture was stirred
for 1 h at -45 to -40 ’C then hydrolyzed with a solution of water (1.2 mL) in T H F
(3.0 mL). warmed up to 20 C, and stirred for 30 min. The organic layer was decanted and the white solid was washed thoroughly with ether. The combined organic
layers were dried over MgSO, and concentrated under reduced pressure. After
separation by column chromatography (silica gel, hexane:EtOAc = 5 : I), a mixture
of 9a and 10a (4X mg. 76% total yield) was isolated as a colorless oil. ‘H N M R
(300 MHz, CDCI,): 9a: d = 0.97 (t. J = 6.3 Hz, 3 H ) , 1 09 (m. 2H). 1.43-1.70 (m,
10a:6=0.62(m,2H).2.95
4H).2.22- 2.48(m,ZH),3.67(m,lH),5.8O(m,lH);
(m, 1 H). 4.96 -5.03(m,2H),6.13 ( d d , J =16.8,10.2 Hz, 1 H). I 3 C N M R (75 MHz.
CDC13):9a:6=1 93.2.67.9.91,29.55,39.31,72.65,114.25,124.89;10a:~=11.02,
12.29. 27.90. 79.40, 113.57.
Received: June 10. 1996
Revised version: July 29, 1996 F29206JEJ
German version: Angew. Chem. 1996, 108, 3024-3025
Angew Chem. In!. Ed. Enyl. 1996. 35, No. 23/24
The mechanism of asymmetric induction in reactions ofa-chiral aldehydes and ketones has been a subject of continued speculation since Cram and Kopecky’s seminal work.[’] Among several factors that have been recognized to influence the n-facial
diastereoselectivity, the role of the solvent has hitherto been
underestimated.
[‘I Prof. Dr. G. Cainelli, Dr. D. Giacomini, P. Galletti. A. Marini
Dipartimento di Chimica “G: Ciamician”
Via Selmi 2, 1.40126 Bologna (Italy)
Fax: Int. code +(51)25-9456
e-mail: cainelli(2 ciamOl ciam.unibo.it
(**I This work was supported by Minister0 dell’ Universitl e dclla Ricerca Scientifica e Tecnologica (MURST) (fond; 60%) and the University of Bologna (fund
for selected topics). We thank Micaela Fabbri for performing the HPLC
analysis.
,c VCH Verlugsgesellsckafi mhH, 0.69451
Weinheim, 1996
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Recently we demonstrated that in nucleophilic addition reactions to 0-protected (2S)-lactal['] and to its corresponding N(trimethyl~ilyl)irnine,~~]
the diastereoselection was highly dependent on the nature of the solvent and on the temperature. In
these a-oxy substrates, chelation was often invoked to account
for the stereochemical outcome of the reactions with
organometallic reagents; thus, the diastereoselection was often
discussed in terms of a chelation versus a nonchelation mechanism.f41
In the present investigation, in which we use racemic 2phenylpropanal lr5]as the model aldehyde, we focus on the
influence of the solvent and temperature on the x-facial
diastereoselectivity. Compound 1 has been studied previously
by Reetz et a1.,[61who highlighted the high Cram-selectivity of
this substrate (90-94%) in reaction with nBuLi under standard
conditions (THF, -78"C), while a lower selectivity was observed when the reaction was carried out using n-pentane as
solvent. We report here on a systematic study of the diastereofacia1 selectivity of 1 in reactions with nBuLi using hydrocarbons
and ethers as solvents.
The addition reaction was performed by adding a stoichiometric amount of nBuLi (1.6 M solution in hexane) to 1 in different dry solvents. The reaction temperature was varied over a
range between the melting and boiling point of the respective
solvents (Scheme 1). The diastereomeric excess (de)of products
4 solvent
+ nBuLi
0
1
& + &
OH
temperature
anti (Cram product)
2
OH
syn ( anticram product)
3
Table 1. Influence of temperature and solvent on the diastereoselectivity of the
nucleophilic addition of n-butyllithiurn to 2-phenylpropanal. The de values were
determined by HPLC analysis.
Solvent
T I"C1
de [YO]
antilsyn
Yield
THF
THF
THF
THF
THF
THF
THF
THF
tBuOMe
rBuOMe
tBuOMe
rBuOMe
tBuOMe
tBuOMe
tBuOMe
tBuOMe
rBuOMe
1 .Cdioxane
1,Cdioxane
1.Cdioxane
1.4-dioxane
1.4-dioxane
n-hexane
n-hexane
n-hexane
n-hexane
n-hexane
n-hexane
n-hexane
n-hexane
n-hexane
n-hexane
n-hexane
-91
- 79
- 60
- 50
- 40
- 30
- 14
86
78
78
74
64
66
60
46
82
82
74
70
70
66
62
56
50
52
48
44
42
38
66
66
64
64
64
60
56
56
54
46
42
93: 7
89: 11
89: 11
87:13
82: 18
83:17
80 :20
73:27
91.9
91.9
87:13
85:15
85:15
83:17
81:19
78 :22
75:25
76~24
74:26
72:28
71 :29
69:31
83:17
83:17
82:18
82:18
82:18
80:20
78:22
78:22
77:23
73~27
71:29
76
73
75
83
83
81
65
80
78
60
76
73
60
96
83
78
7
- 86
- 69
- 60
- 40
- 31
- 15
7
23
54
15
34
54
69
79
- 93
- 80
- 69
- 60
- 50
- 32
-17
- 9
4
31
54
pi]
52
68
75
78
68
65
86
96
76
96
78
86
70
81
81
78
76
Scheme 1. Syntheses of 2 and 3. Solvents: THF, tBuOMe, 1.4-dioxane, propane,
n-pentane, n-hexane, n-octane, n-decane, n-dodecane. cyclohexdne, cyclopentane.
3 i
2 and 3 in the crude reaction mixture was determined by HPLC
analysis.['] Results obtained with THF, rBuOMe, p-dioxane,
and n-hexane are given in Table 1.
The temperature dependence of the de values was analyzed
according to the modified Eyring equation [Eq. (a)],[*] where
i
,r
In (anfilsyn)
InP= - ( A A H ' / R T ) + ( A A S * / R )
(1)
P = k(anti)/k'(syn)= III', k and k' are the overall rate constants, and I and I' are the chromatographic area [%] of 2 and
3, respectively. The results are summarized in Figure 1.
At low temperature, THF exhibited the best diastereoselectivity, while reactions in tBuOMe and 1,4-dioxane gave lower de
values. A continuous linear correlation between the In (anti/syn)
value and 1/Twas observed in all ethers; in contrast, in reactions
carried out in n-hexane we established an inversion temperature
(T,;,,).[91 A small amount (5%) of THF in n-hexane was sufficient to obtain results similar to those obtained in pure THF.
This could be attributed to a direct (primary shell) THF-lithium interaction, where the donor solvent acts as ligand to the
lithium coordination sphere." The evidence of an inversion
temperature for n-hexane prompted further investigation. The
Eyring plots for a series of linear and cyclic hydrocarbons is
shown in Figure 2. Each aldehyde-solvent combination
showed two linear regions, and a characteristic inversion temperature was observed in each case." 'I
Interestingly, for linear hydrocarbons and their cyclic counterparts, the inversion point
represents a cusp with an opposite orientation. The pattern is consistent with the chain length
2850
VCH t4rlagsgeseilschaft mhH. 0-69451 Wemherm, 1996
190
/ -% i
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dePh
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0.5 7
24
2.8 4
2.6 - -
+aa
2.4 - -
..84
::76
T
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0.8f
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Angew Chem. Inr Ed. End. 1996. 35. No. 23124
COMMUN[CATIONS
1.8
1.6
1.4
I
dePk
In contrast with our results with the N(trimethylsily1)imine of l a ~ t a l ,we
' ~ ~did not obtain an optimal value of the selectivity for the
aldehyde 1 at a reaction temperature near to 7;,
and moreover solvents with a Tntvalue close to
the 7; value, such as n-decane and n-dodecane,
produced a lower diastereoselectivity.
The inversion temperatures for all the linear
and cyclic hydrocarbon solvents examined
ranged between 205 and 317 K. noteworthy is
that the 7;,,vvalue for linear hydrocarbons increases as the chain length increases on going
from n-pentane to n-dodecane (Table 2) .1'21
Table 2 . Melting points [K] of several solwnts and inversion
temperatures
[KJ for the reaction of I to give 2 and 3 in
these solvents .
0.8
rnv
0.6
0.4
0.0028
0.0033
0.0038
0.0043
1IT I K
-
0.0048
'
d
0.0053
0.0058
Solvent
MP
T",
n-pentane
n-hexane
cyclopentane
17-octane
n-decane
n-dodecane
cyciohexane
143
178
179
216
243
261
279.5
205.3
227.8
225.1
287
271.7
309.6
317
Assuming that the inversion temperature is a
property of every substrate-solvent pair, all
efforts to correlate TnC.
with some classical solvent parameters, such as dielectric constant
and viscosity, failed. Interestingly, we found an
extrathermodynamic correlation between Tnu
and the melting points of the linear and cyclic
hydrocarbons; the resulting straight line has a
0.6 4
correlation coefficient ( r ) of 0.96 (Fig. 4). This
0.0026
0.0031
0.0036
0.0041
0.0046
0.0051
0.0056
suggests
a relationship between the inversion
l / T l K-'
temperature and the phase modification that
Fig. 2. E) ring plot, loi-the diastereomeric excess obtained in the nucleophilic addition of ti-butyilithium
happens on melting. This could be consistent
t o 1 at various temperature a) in propane (6
j. n-pentane ( 6 ) . rr-hexane ( 0 ) . n-octane (0)
. n-decane (A).
with the hypothesis that inversion points repren-dodecane ( 0 ) .and b) in cyclohexane (m). cyclopentane (0).
sent a transition between two "phases", which
in the case of solutions could be represented by two different solvation states (a more ordered one in
of the solvent: the longer the chain, the lower the diastereofacial
selectivity ; for example, the diastereofacial selectivity obtained
the low-temperature region) that have different k and k' values,
with propane is better than that with n-dodecane. It appears
and therefore different diastereoselectivi ty.
These results indicate the unexpected role the reaction solvent
that even though apolar aprotic solvents interact only slightly
plays in determining the inversion temperature and confirms its
with the solute (since only the nonspecific directional, inducpeculiar influence on the diastereofacial selectivity.
tion, and dispersion forces can operate) the diastereoselectivity
could be doubled by using a solvent with a short chain length.
To the best of o u r knowledge, this possibility has never been
Ti = 21 "C
raised in the discussion of diastereofacial selectivity. In both
temperature regions, the slopes of regression lines, which reflect
4000 -the enthalpic contribution, are not very different. On the other
,
hand, the differences in the intercepts ( A A S *) are significant.
Thus, the chain length effect might be ascribed to entropic
y - mx+48
control over the selectivity of this type of organometallic addir = 0.99
tion.
Considerable attention has been paid to the significance of
4
15
the difference 6AAH' = AAHF AAH: ( A A H : , T > Knvand
AAH:, T <
A plot of 6AAH* against the corresponding
&US*/ cal mol-' K-'
entropy term ciAAH' is linear for all the hydrocarbons mea-2000
-'Om
sured. From the slope of this plot (Fig. 3) we can determine the
Fig. 3. GAAH*.'BAAS* plot for the determination of the isoin~ersiontemperaisoinversion temperature 7; = 299 K (21 "C).
ture Tm,
""T
r,,,).
I
~
Annew. C'linrr. lnt Ed. Etrgl. 1996, 35. N o . 23,24
1;
VCH V e r l u ~ s ~ e s e l l . s cmhH.
h ~ ~ ~ 0.69451 Weinheim. IY96
4
0570-0~33!9613j23-2851P; 15.00+ .25 0
2851
COMMUNICATIONS
,t [F]
340
4
180
120
170
Synthesis and Structure of the Metalated Zintl
Ion [Ge,(p,,-Ge)Ni(PPh,)]2 Donna R. Gardner, James C. Fettinger, and
Bryan W. Eichhorn*
-
220
M.p.lU
270
Fig. 4. Correlation between melting points and inversion temperature for hydrocarbons.
'
Experimental Procedure
In a typical experiment. 1 (0.268 g, 2 mmol) was dissolved in anhydrous solvent
(20 mL) under inert atmosphere, and the solution cooled t o the desired temperature:
then n-butyllithium (2.2 mmol, 1.37 mL of a 1 . 6 solution
~
in n-hexane) was added.
After the starting aldehyde had disappeared (GC-monitoring), the reaction was
quenched at 0 ° C with a saturated aqueous solution of NH,CI, extracted with
CH,CI, (3 x 50 mL), and dried with MgSO, From HPLC analysis of the crude
product the anti?syn ratio and the de value were obtained. Chromatography of the
residue on a silica gel column gave the mixture of the two alcohols 2 and 3 so that
the chemical yield could be calculated.
Received June 27. 1996 [Z9264IE]
German version: Angeir. Cllem. 1996, 108, 3016-3019
-
Keywords: aldehydes asymmetric synthesis . inversion temperature * nucleophilic additions . solvent effects
111 D. J. Cram, K. R. Kopecky. J. Am. Chem. Sac. 1952, 74. 5828.
[2] G. Cainelli, D. Giacomini. F. Perciaccante. TL.rraherlron Asymmetry 1994, 5 .
1913.
[3] G . Cainelli, D. Giacomini. M. Walzl, Angra. Chem 1995. /07, 2336; Angeir.
Cheni. Int. Ed. Eirgl. 1995, 34, 2150.
[4] M. T. Reetz, Anget<.Chem. 1984, 96. 542; Angew. Chem. In!. Ed. Engl. 1984.
23, 556.
IS] In testing diastereofacial selectivity, racemic aldehyde was employed. Only one
enantiomeric form is arbitrarily shown.
[6] M. T. Reetz. S. Stanchev. H. Haning, Tetrahedron 1992, 48. 6813.
[7] The diastereoselectivity of the product formation is ChdrdCteriZed by the de
value of the anti adduct, which was determined by HPLC analysis of the crude
product (column. Accubond OVS SV, 25 x 4.6 cm, T = 35 'C, flow =
1.5 mLmin-l, eluent H,O'CH,CN from 10 to 100% of H,O in 45 min).
[81 a) H. Eyring, J Phy.:. Chem. 1935, 3. 107; b) S. Glasstone. K . 1. Laidler, H.
Eyring, The Theory of Rate Processes. McGraw-Hill. New York. 1941, Chapter 4.
191 For a review see: H. Buschmaun, H.-D. Scharf. N. Hoffmann, P Esser, Angew.
Chem. 1991. 103,480; Angetr. Chem. Int. Ed. Engl. 1991.30.411. For recent
papers see- K. J. Hale. J. H. Ridd, J. Chem. Sac. Chem. Commun 1995.357; M.
Palucki, P. J. Pospisil, W. Zhang, E N. Jacobsen, J. Am. Chem. SOL.1994, 116.
9333; J. Brunne, N. Hoffmann, H.-D. Scharf, Tetrahedron 1994. 50. 6819; T.
Gobel, K. B. Sharpless, Angeir. Chem. 1993.105.1411; Angeir. Chem. In(. Ed.
Engl. 1993. 32. 1329; J. Muzart. E Hknin, J-P Pete, A M'boungou-M'Passi,
Tetrahedron Asymmetrr 1993, 4. 2531: 1. Toth. I. Guo. B. E. Hanson,
0rganometallic.s 1993. 12. 477.
[ 10) See for instance C. Reichardt. Solwn/s and Solvent Effrcts i n Organic. C h w islq, 2nd ed.. VCH, Weinheim, 1990.
[ l l ] In our opinion, this behavior is quite general for diastereoselective reactions in
solution. The absence of the inversion temperature was attributed either to a
results lie outside the observable range) or
limited temperature range (the
to the fact that the two slopes of the linear correlations differ too little to
appreciate the cusp.
[12] The plot of In (anti:.:w) against liT in propane did not reveal an inversion
temperature because in this reaction the inversion temperature could have a
lower value than the lowest reaction temperature we reached In fact. in this
solvent, at T I - 100 -C. the starting aldehyde was quite insoluble and the
conversion yield was very low.
znz
2852
0 VCH
Since the discovery", *I and subsequent investigation[, - 6 ]
of the Group 14 Zintl ions, only a few transition metal
derivatives of these unusual clusters have been detected. The
only structurally characterized examples, the tin and lead
[cf~so-E,Cr(CO),]~-ions[~~
and the [Sn,{ Cr(CO),),j2 - ion,["
were made by two vastly different synthetic methods. Teixidor et al. characterized two Pt-E, species (E = Sn, Pb) by
N M R spectroscopy:["I however, little is known about their
structures. Even though there are several structurally characterized naked germanide ions (Ge",, where n = 2, 3, or 4;
Gef:-),I1 - 14] complexes of the germanide Zintl anion with
transition metals have not previously been described. Herein
we report the synthesis and characterization of [K([2.2.2]cryptand)],[Ge,(plo-Ge)Ni(PPh,)].en (for [2.2.2]cryptand see
[17], en = ethylenediamine), the first metalated germanide anion and only the second example of the rare nido-10 (iv + iv)["]
structure type.
The reaction of [Ni(CO),(PPh,),],
K,Ge,,[I61 and
[2.2.2]~ryptand['~]in ethylenediamine gives [Ge,(p,,-Ge)Ni(PPh,)l2-(1) as the [K([2.2.2]cryptand)]+ salt in low yields.
The compound [K([2.2.2]cryptand)I2(l) .en decomposes upon
exposure to air and moisture. The dark brown crystals have
been characterized by single-crystal X-ray diffraction, energy
dispersive X-ray analysis (EDX), microanalysis, and ' P NMR.
A single crystal X-ray diffraction study"'.
revealed two
[K([2.2.2]cryptand)]+ cations, an en solvent molecule, and the
[Ge,(plo-Ge)Ni(PPh,)]2-(1)
anion. This anion displays no crystallographic symmetry, consists of nine surface G e atoms, one
interstitial G e atom Ge(i), and an [Ni(PPh,)] fragment (Fig. 1).
The [Ni(PPh,)] fragment has been incorporated into the anion
framework as a vertex of the cluster. The two [K([2.2.2]cryptand)]' cations are well separated from the anion and are
not disordered. The en solvent molecule is not fully resolved due
to local disorder. Two independent crystal studies were performed on crystals of independent syntheses and both studies
gave the same results within experimental error.
The Ge-Ge bond distances for the surface Ge atoms range
These distances are similar to
from 2.595(4) to 3.291(4)
those of Ge-Ge contacts in other polygermanide clusters such
as [K([2.2.2]cryptand)],[P(C6H,),Ge,], where bonding G e contacts vary from 2.53 8, to 3.27
The distances between
the nearest neighbor surface G e atoms and the Ni atom range
from 2.364(3) to 2.381(3)
a longer contact exists between
Ni(1) and Ge(2) of 3.307(3) A. Excluding the longer contact, the
Ni-Ge bond lengths are similar to other reported distances, for
example, 2.36 (av) in [Ni9(pc,-GeEt)6(CO),]. r 2 0 - 2 5 1 The contacts between the surface G e atoms and the interstitial atom
Ge(i) range from 2.355(3) A to 2.446(3) A (average 2.40
and
are slightly shorter than those in metallic germanium
(2.44 A).[261The Ni-Ge(i) distance in 1 of 2.361 8, is significantly shorter than the Ni-Ge(i) contacts in the interstitial
G e clusters [Nii,Ge(CO),,]2-(average 2.49 and 2.69
and
[Ni,,Ge(C0),o]2-(average 2.47 A).[*'] The shorter distance in 1
Verlugsgesellschafi mbH, 0-69451 Weinheinr. 1996
A
A.
A
A.["
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[*I
Prof B. W. Eichhorn. D. R. Gardner. Dr. J. C. Fettingei
Department of Chemistry
University of Maryland
College Park, M D 20742 (USA)
Fax: Int. code +(301)314-9121
e-mail. b. .eichhorn(u umail.umd.edu
0570-0833i96i3S23-2RSZ S 15.(10+ 2 9 0
Angew. Chem. I n ! Ed. Engl 1996 IS. Nu.23i24
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diastereoselective, effect, reassessments, temperature, additional, solvents, butyllithium, phenylpropanal
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