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Decaphenylferrocene and Decaphenylferrocenium Tetrafluoroborate.

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141 Foi- X-ray crystallographic studies of a human r-thrombin complex. biological
acti\ities. and t o t a l synthesis ofcyclotheonamide A, see: B. E. Maryanoff. X.
Q i u . K . P. Padmanabhan. A. Tulinsky. H. R. Almond, Jr.. P. Andrade-Gordon. M. N . Greco. J. A . Kauffman, K. C. Nicolaou. A. Liu. P. H. Brungs. N.
Fusetani. P r o < . N u / / . Acorl. Scr. USA 1993. YO. X04X.
[5] For the synthesis of fragments ofcyclotheonamides: a) P. Roth. R. Metternich.
E./r-u/ic.dr-oti
Lclr. 1992. 33. 3993; b) P. Wipf. H. Kim, Te/ruhrr/rof?Lrrr. 1992.
33. 4175. c) J. Deng. Y Hamada. T. Shioiri in Prptidcz Clieniisrrj f Y Y 2 (Proc.
2nd Jpn Symp. Peptide Chem.) (Ed.: N . Ymaihara), Escom. Leiden. 1993. 72.
[6] A. Y. Lee. M . Hagihara. R. Karmacharya. M. W. Albeis. S. L. Schreiber. J.
Clardy. J A n r . Chcwi. S o . 1993. 113. 12619.
[7] S. Tdkwna. Y. Hamdda. T. Shioiri. Chciii. P/?urtn. Bid/. 1982, 30, 3147. and
references therein.
[8] S. ('hen, J. Xu. Iefro/ic&on Le/r. 1991. 32. 6711: J. Dudash. Jr.. J. Jiang. S. C .
Mtiyer. M. M. Joullie. Sj,nrh. Co!n/nun. 1993. 23. 349.
[9] For aryl groups as the synthetic equivalent of carboxyl groups. see: F. Matsuu ~ i Y.
. Hamadn. T. Shioiri. ZJ?.rr.uhrdr-on.
1994.50. 265: Te.rrulwdron Lett. 1994,
35. 733. and references therein.
[lo] The configurations of 5 were determined by the ' H N M R spectra of the corresponding oxazolinones A : major isomer (.rw):
HN NHMtr
6(5-H) = 5.5X ( J = X.25 Hz): minor isomer (unri):
6(5-H) = 5.09 ( J = 6.59 HL): M. A. Poss. J. A. Reid,
7i.rrrrhrdroii LCVI.
1992, 33. 141 1
HN
0
[ l l ] P. H. J. Carlsen. T. K;rtsuki, V. S. Martin. K . B. Sharpless, J. Or:. Chew. 1981, 46, 3936: M . T. Nu5ez. V. S.
Martin, ihrd. 1990. 55. 192X.
[I21 The corresponding vinylogous (R)-tyrosine ester was obtained analogously in
X9",. yield ( E : Z= 95:5). See also ref.[5c].
[13] Y. Hnmada. M. Shibata. T. Sugiura. S. Kato. T. Shioiri. J: Org. Chrfn. 1987, 52,
1252.
[14] M Waki, Y, Kitajima. N. Izumiya. Sjxrhr~.s;s1981, 266.
[15] 15a. m.p. 87-88°C. [.I:'
= -43.4 ( L =1.06 in CHCI,); 15b: m.p. 105106 <', [z]:~' = 19.0 ((, = 1.09 in CHCI,). The configurations of the hydroxyl
I'unctiona in 15a and 15b were deduced from those of their precursors 5 ; see
'1lSO ref [lo]
[16] D. U . Dess. J. C. Martin. .
I
Ail?. Chcm. Soc. 1991. 113. 7277.
[17] The
values for our synthetic cyclotheonamide B (2a) against thrombin
and trypsin are 7.2 and 17 ngmL-'. respectively, while those for natural cyclotheonamide A (1) are 7.2 and 10 n g m L - ' under the same conditions. Since
cyclotheonamide B was not available. the comparative study of the enzyme
inhibition was not possible.
&
-
dered. A propeller-like structure, analogous to that observed for
decaphenyl~tannocene.[~]
is adopted. It is argued that the short
Fe-Cp, distance of 170 pm (Cp, = center of cyclopentadienyl
ligand),[41which has been shown to be necessary for additional
n-bond stabilization of ligand-iron bonding in symmetric sandwich compounds, can no longer be achieved. However. in octaphenylferro~ene,[~]
which has only two fewer phenyl groups,
an Fe-Cp7 distance well within that required for stabilization is
observed. The same holds for the recently described pentaphenylferrocenethland for decabenzylferrocene.['. s] in which
all the benzyl groups point away from the metal. in contrast to
all other previously known pentabenzylcyclopentadienyl compIexes.[']
At first our investigations confirmed the argument based on
bond-length criterion presented above. Thus, reaction of
[ (C,Ph,)Fe(CO),Br][tol in xylene at 80 "C yielded, after hydrolysis with conc. HCI. only the orange-red salt 2. In the complex
cation of 2, a sterically less demanding xylene molecule was
found to replace the second C,Ph, ligand.["] Also, the metathesis and metal-vapor methods successfully employed in
the synthesis of decaphenylstannocene could not be applied to
decaphenylferrocene. However, when [(C,Ph,)Fe(CO),Br] was
heated for two days in boiling xylene [Eq. (a)], 1 was isolated in
3 0 % yield as a pink, microcrystalline powder, insoluble in all
common solvents. Complex 1. which is inert to 0.1 N HCI and is
stable up to 400"C, was also formed when 2 was heated to
350 T [Eq. (b)].
Z[(C,Ph,)Fe(CO),Br]
imoc
[Fe(C,Ph,),]
+ FeBrz + 4 CO
(a)
I
The single crystal X-ray structure analysis of I (Fig. I)['*'
performed on the microcrystals obtained could only be refined
to R = 0.1 59. An in-depth discussion of the bonding in 1 is there-
Decaphenylferrocene and Decaphenylferrocenium
Tetrafluoroborate""
H e r b e r t S c h u m a n n , * Alexander Lentz,
Roman Weimann, and Joachim P i c k a r d t
In tneniov?, oj'J J Zuckerman
fore not possible. However, like the 13C solid-state NMR. IR.
and Raman spectra,[131the structure analysis also confirms the
presence of a symmetric sandwich complex, isostructural with
decaphenyl~tannocene.['~~
Oxidation of 1 with NOBF, yielded
Although decaphenylferrocene (1) was first described in 1983
by Slocum et al.,"] a symmetrical sandwich structure has not to
date been established for this metallocene. The N M R spectra of
I , obtained from [Fe(CO),] and C,Ph,Br, were interpreted by
Masters et al. in terms of a zwitterionic complex [($-C,Ph,)Fe]+
[($-ChH5-C5Ph4]-.[21The proposed structure could not however be confirmed by X-ray structure analysis. One argument in
favor of this zwitterionic structure arises from the considerable
spatial requirements of the five phenyl groups, whose coplanar
arrangement about the cyclopentadienyl anion is therefore hin[*I
Protl Dr. H. Schumann. Dr. A. Lentr. Dr. R. Weimann. Prof. Dr. J. Pickardt
Inhtitut fur Anorganische und
Analytische Chemie der Technischen Uuiversitlt
S t r a s e des 17. Juni 135. D-10623 Berlin (FRG)
Telet'ax: Int. code + (30)314-22168
[**I
This work w a s supported by the Deutsche Forschungsgemeinschaft(SFB "Anisotropic Fluids") and the Bundesministerium fur Bildung und Wissenschaft
through the Graduiertcnkolleg "Synthese und Strukturaufklirnng niederrnolek iilarer Verbindungen".
Fig. 1. ORTEP diagram of a molecule of I (ellipsoids at the 50% probability level)
The average distance between the Fe atom and the C atoms of the C p ligand is
211 pm.
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decaphenylferrocenium tetrafluoroborate 3 [Eq. (c)] in 81 YO
yield as dark. reddish brown crystals, which were extremely
soluble in polar solvents.
[Fe(C,Ph,)J
1
+ [NO]' [BFJ
-
[Fe(C,Ph,)21-[BF,I~ + NO
3
(C)
Cyclic voltammetric investigations (Fig. 2) show that 3 is reversibly reduced to 1 in CH,CN. Precipitation of 1. which is
+ 828
t
A
ions are located within the unit cell. The positions occupied by
the Fe atoms are related by a crystallographic center of inversion. One of the two cations is shown in Figure 3. The sandwich
structure of the symmetrically disposed cyclopentadienyl ligands can be clearly seen. The cyclopentadienyl ligands are separated by distances of 358.6 (Fel) and 358.0 pin (Fe2). The Fe"
ions are shifted by 6.7 (Fel) and4.7 pm (Fe2) from the Cp,-Cp,
line. The phenyl substituents bound to the planar cyclopentadienyl ligands are not only twisted out of the plane of the cyclopentadienyl ligands in a propeller-like arrangement. but also
point away from the metal center. The two cyclopentadienyl
ligands are therefore able to approach the Fe3+ ion more easily.
Although the interplanar distance is 27 pin greater than that
observed for decabenzylferrocene (331.3 pml']). it is, nonetheless, clearly shorter than that for decaphenylstannocene
(480.2 prnL3]). In the latter, molecular stabilization through TI
interactions between the central tin atom and the cyclopentadienyl ligands is not possible. but also not necessary.
Espcriinentril Proc,r~lirrr
+
+ 657
I
-
son
I
n
I
-1-
501)
I
-k 1000
3
E[mVl
I : A blue solution of[(C,Ph,)Fe(CO)lBr] (2.5 g. 3.9 mmol) in xylenc (100 m L ) was
heated under i-efluw foi- 48 h The mixture was acidified to pH 1 with conc HCI a n d
ice wLitrr A i-eddisli b r o u n pi-ecipitate was collectcd a n d combined w i t h the organic
phasc from the filtrate. The mixture w a n conccntrated and the solid obtained extracted (01-24 h \ + i l l i toluene. 2 d with T H E and then 5 h with CH,CI,. The product
1 \+:IS obtained from the residue and dried at l o - ' Toorr. Correct C.H analqsis. M S
(70 cV. .:70 Cj: 111.1: ("c):94X (32) [W + HI. 947 ( 5 6 ) [.if' I . 946 (100) [W - HI.
501 ( 2 3 ) [.Ift
- C,Ph,]. 446 ( 2 ) [C,Ph, ' 1 .
~
Fig. 2. Cyclic voltammogram of[Fe(C,Ph,j,] [Fe(C,Ph,j,] ' [BFJ [4.4
mg o f 3
per i n 1 of C H , C N solvent: rupporting electrolyte Bu4NBFA(0 1 M): Pt'Pt elcctiode\ (0.56 cin'): Ag'AgCI reference electi-ode(Metrohni): salt bridge agar- ;ig;ir'
h a t . KCI solution, potential scanned .it 200 mVsC': room temperalure: f;(, =
+743 m V (Ag.AgCI)].We thank Dr. Miklnutr. Scliei-inp AG. Bei-lin, for llic cyclic
\olt~inmetricmeasurements.
I
only sparingly soluble in CH,CN. is observed. The redox potential [mV] for the one-electron oxidation of 1 is 743 (AgAgCI)
and is therefore of the same order of magnitude as the values
obtained for the parent compound ferrocene ( + 493[Is1 and
+ 433[l6] in CH,CN. + 593 in THF[I6]), decabenzylferrocene
( + 333 in CH,CN, + 563 in THF).""] pentabenzylferrocene
( + 443 in CH,C12),11h1 and benzylferrocene ( + 403 in
CH,CN)["] (all vs. AglAgCI).
The salt 3 crystallizes from CH2C12 with two molecules of
solvent in the crystal lattice.[181
Two independent [Fe(C,Ph,),]+
+
3 : To :i wspcnsion of I (0.61) g. 0.63 mmol) i n CH
(20 m L ) was added rapidly
NOBF4 (0.
I ? 8, 1.00 minol). After i t had heen Ltirr
r 12 h iit irooin tempet-atiirc.
the mixture \\as filtered. l'hc solution was tre'ited with ether (20 inL) a n d cooled to
--30 C. Reddish brown ci I d s of 3 were obtained (0.53 g. 8 1 % ) . M.p. 315 C
(dec.): correct C.H anal>si ' H N M R (770 MHr. CD2CI,. TMS) 0 = 5.9-6.6
H].947(33)[.1.1+].946(34)
(p11-H): MSi70eV. 360 C):III :io6):94Xi15j[:Lft
[ S l ' . fl]. 502 (13) 111' - C,Ph, + HI. 501 (25) [Mi - C5Ph5], 446 (13)
[C.Ph, '1.
Received' behruaiy X. 1994
R e v i d veriion: April 21. 1 Y Y 3 [Zh677IE]
German vcrsion: d i y c i i - . C / i m 1994. 1b6. 1827
+
[ I ] D. h! Slocuni. S. Johnson. 41. Matusz. S.Dur;ij. 1. L. Cmsrik, ti. M . Simpson.
D A. Owen. P o h n i . A l a r w . .Si,i. Oip. 1983. 49, 353-357. D W. Slocum. S.
DUIXJ.M . Matus/. I. L. Cmai-ik. K M . Simpson. D A. O n e n in :Metii/ Cm/ ~ i i i i i i iP~ o / y r r i < . S i\/ciii.\ (Ed\ ' J E Slieata. C , E. C'arr,iher. ( ' U . Pittmiinn).
Plenum. N e u York, 1985. p. 59.
[2] K . N. Brown. L D Field. P. A. Lay. C. M Lindall. A . F. Masters. J. C/WJI.
.slj(. c/ii~lll.
~ ( j i l l i i i i l i i . iwn. 408-410.
[3] M . J. Heeg. C. Janiak. J J. Zuckrrman. J. , 4 i n . Chriii. S o r 1984. 106. 425')
4261.
141 0. Scilci. J. D. Dunttz, .Acrci C'ij.strr//ogi..'i?ci. B 1979. 35. 1068 1074: Yti. T
Srruchkov. V. G . Andrionov. T. N . Salnikov,i. 1. R . Lgatifov. R . B. Materiko\ a . J 0 r : i r i i o i i r i ~ r U w i j i . 1978, 145. 213 -223. D. P. Freyberg, J 1.Robbini.
K . N. Raymond. J C'. Smart. J. A i i i C / i ~ i ?,So<.
7.
1979. 101. 897 X97. J. Okuda.
E Herdtweck. C / x w . 8 e r . 1988. 121. 1899-1905.
[ S ] M. P. Castellani. .I.
M . K'ripht. S 1. Gcih. A. L . Rheingold. hi C. Tropler,
~ ~ i ~ ~ ~ i i ~ ~ 1986.
~ i i r 5.
~ ~1 IrI6
~ i 1l 122.
li~~.~
[6] M J. Aroney. I. E. Buy\. G. D. Dennis. L 0 . Field. T. W. Hamhley. P. A. Lay.
A. F. Masters. Po,/i./ic~/ion1993. 13. 2051 2056.
171 H . Schumann. C. Jani,th. R D. tiohn. J. Loebel. A. Dietrich. .I O r p r i i o i i i o
Clioii 1989. 365. 137- 150.
[XI M D Rausch. Xi'. M Tsni. .I.\\'. Ch,imher~. R . D . Roger?. H G. All.
~ i ~ ~ ~ i l l l ~ l l l \~ ~19x9.
t i l / / x.
; l 816-821
191 c'. Saniok, H. Schumanii. .lift.. Oi,eoiioiirci. U i ~ i i i 1992.
.
33. 291 393
[I01 S . McVeq. P. L. Pauwn. J. C/ii,iii. .So<.. 1965. 4312 4318.
[1 I] A . Lent/. Dissertation. Technische Univcrsitiit Berlin. 1993.
[I21 C-,,H,,,Fe ( I ) . ,M = 947.01, cryyt I dimensions 0.03 x 0.03 x 0.23 iimi', monoc l i n i c . P 2 , l i (110. 14). l i = 211 71x1. h = I313.9(Xj, c = 941.4(8) pm. /j =
1 14.??(6) . I = 2iX6(3) x I o P " ~
Z=
' .2. pr,,,rii =1.32gcin-'. / I = 6.03cm-'.
Eiir~if-Noniii~
CAD4 dill'i-;ictoineter. Cu,, radiation. i =71 ,069 pni. graphitc
i i i i i i i ~ ~ h r o m a t o rI. = 210 ti. 1 < 211 5 48 . i Y 9 2 ine;isured ieflectioiis. o f
w h i c h 17Y4 wcre indepeiident (R,,,,= 0.0447).1231 ohserbed rellections with
(c,j >_ 4n(I.,). wliictoii by direct methods and structure refinement with
SHELX76. ahsorption correction (DIFABS. nun. 0.785. max. 1.265).
R = 0 159. Kw = 0.166 (11 =l,n'((,)). nnisotropic refinement o r h c a \ y atom.
i\oti-opic rcfinciiicnt of lill other non-h>dropeii atoms. the positions of the H
iitoim wcrc cnlcul:itctd jl8hl
~
Fig. 3. O R T E P diagram of one of the two cations of 3 (ellipsoid? a t the SOY4
probability le\,elj. Selected hoiid lengths. debititions [pm] ;und interplanar anglcs [ 1.
Fe-Cl 717(1). Fe-C2 215(1). Fe-C3 213(1j. Fe-C4 216(1). Fe-C5 221(1). Cp-CII
1U6j. Cp-C21 34(6). Cp-C31 23(6). Cp-C41 19(6),Cp-CSI 1 4 ( 6 ) .Cp-Phl 43 7(7)
Cp-Ph2 57.616) . Cp-Ph3 47.217) . Cp-Ph4 50.9(7) . Cp-Ph? 4X.X(7)
.
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[I31 In the IR and Raman spectra. apart from the typical bands for C,Ph, ligands.
only three additional bands are observed: v,.(FeCp,)425 c m - ' (IR). v,(FeCp,)
2 9 0 c n - ' (IR). h(FeCp,j 170cm-' (Raman) [ I l l .
1141 M. _I. Heeg. R. H. Herber. C. Janiak. J. 1. Zuckerman. H. Schumann. W. F.
Manders. J Orgunomel. C'iienr. 1988. 346. 321 -337.
[15] S. P. Gubin. S. A. Smirnova. L. I Denisovich, A . A. Lubovich, J. Organomei.
CIwnf 1971. 30, 243 -255.
[16] P. Zanello. A. Cinquantini. S. Mangani. G. Opromolla. L. Pardi, C. Janiak.
M. D. Rauscli. J O r g m ~ n n i 'Clwni..
~.
in press: C. Janiak. personal communtcation
[I71 Ci. L . K. Hoh. W. E. McEwen. J. Kleinberg. J. Atn. Chiw. Soc. 1961, 83. 3949.
[I81 a ) C -,,HI,,BF,Fe.C,H,CI, (3): !b/ = 1203.68. crystal dimensions 0.23 x 0.10 x
0.10 mm'. tricltnic. Pi (no. 2). u =1346.7(7). h =1732.2(5). c = 1322.1(3) pm,
x =107.00(2). /I =100.80(3), 7 =74.00(4) V = 2815(2) x 10-3"m3, Z = 2,
( J ~ , , , ' ~= 1.32
1' = 4.51 c m - ' . Enraf-Nonius CAD4 diffractometer,
C u h X rxliatioii. .; =?1.069 pm. graphite monochromator. T = 190 K. 1 I
7 0 s 35 7681 measured reflections. of which 6131 were independent
(R,,,,= 0.02X0), 3756 observed reflections with ( F , ) 2 4u(.5,). solution bq direct
methods and structure refinement with SHELX76. absorption correction
(DIkABS. inin. 0.733, max. 1.369). R = 0.086. Rw = 0.094 (a. =l;u2(Fo)).refinement of all non-hydrogen atoms mostly anisotropic. otherwise isotropic,
the positions of the H atoms were calculated [18]. Rotational disorder of the F
atoms F2. F3. and F4 in the BF, anion could be established by refinement of
thc population factors F?. F3. F4 and F2a, F3a. F4a with approximately
0.4') 0.51, b ) Further details of the crystal structure investigation may he obtaiiicd from the Fachinformationszentrum Karlsruhe. D-76344 EggensteinLeopoldshafen ( F R G ) on quoting the depository number CSD-58235.
Thus, treatment of the bis(ethyltetramethylcyclopentadieny1)ytterbium complex 1 with the imidazol-2-ylidenes 2 leads to
the corresponding organolanthanoid-carbene adducts 3 in
good yields. Compounds 3 are thermally very stable (decomposition temperature at 0.1 mbar for 3 a is 229°C and 155 'C for
3b) and can be isolated as black crystals. They are soluble in
relatively polar and aromatic solvents such as tetrahydrofuran,
diethyl ether, toluene, and benzene. In contrast. they are only
sparingly soluble in hexane or pentane. Both products 3 are
considerably more stable to air and moisture than 1 .
.
.
Organolanthanoid-Carbene-Adducts" *
H e r b e r t Schumann*, Mario Glanz, Jorn Winterfeld,
Holger Hemling, N o r b e r t K u h n , * und Thomas Kratz
Dedicxileu' to Profbssor Ekkehardt Lindner
on the occurion o f his 60th bivtlzdaj,
Carbenes usually exhibit acceptor properties as ligands and
are most often dependent on classic backbonding for the formation of stable metal complexes. For this reason lanthanoid
metals with their 4f electrons, which lie deep in the inside of the
electron shell and thus hardly participate in bonding, are considered to be very poor coordination partners for carbenes. The
reports that have recently appeared on stable derivatives of imida~ol-7-ylidene['~
open up new possibilities due to the nucleophilic character of these compounds. The successful synthesis of
stable adducts with iodine,[2] tellurium,[31selenium,[41and, in
particular, the bond formation to electron-deficient centers such
as Ge12.['] AIH3,[61and BH3[?] gave the impression that it
should also be possible to prepare lanthanoid carbene complexes.[*] Particularly suitable for this should be oligomethylated
bis(cyclopentadienyl)samarium(~~),-europium(ri), and -ytterbium(n) derivatives. which can not only alter the oxidation
state,["- "1 but also have enough space for a sterically demanding third ligand because of their bent structure.
&
%-
R
Y b - 0 3
R
I
2a R = M e
3a R = M e
2b R = fPr
3b R
=
iPr
The chemical shifts in the ' H and I3C N M R spectra of 3 a and
3b are as expected and are not significantly different from the
data of complex 1 and those of the carbenes 2. These results and
the intense dark color of the isolated adducts clearly show that
quasi-coordinative Yb"-C bonds are present in 3 and that 3a
and 3b are not paramagnetic Yb"' compounds. The I3C NMR
spectrum also indicates a new quality of the metal carbene interactions, since in 3, in contrast to the ylidene complexes of I,, Se,
Te, GeI,, BH,, and AIH,.[2-71 the carbene carbon atom is
slightly shifted for the first time to higher field by about 8 ppm.
The electron impact (70 eV) mass spectra of 3a and 3b show
no peak for the molecular ion; only several peaks for metal -carbene fragments occur in addition to the expected signals for
[(C,Me,Et)Yb]+ and [(C,Me,Et),Yb] * .
In the crystal the ylidene forms a planar five-membered ring,
the plane of which to a good approximation also contains all the
atoms bound to the heterocycle (Fig. 1 ) . Alternating bond
lengths, which are also observed in other complexes, occur within the carbene ring; however, here they are not so pronounced.[71Whereas the C 13-N (1.387(5) A) distance indicates
C6
-Fi
ITc1
C15
Yb
[*I Prof Dr H. Schuniann. Dr. M. Glanz. Di-. J. Wintei-feld, Dr. H. Hemling
I n s t i t t i l fur Aiiorganische und
Analytische Chemie der Technischen UniversitZt
Strassz des 17 Juni 1.15. 0-10623 Berlin (FRG)
Teletix: I n t code + (30j314-22168
Prof. Or. K. Kuhn, Dipl.-Chem. T. Kratz
Iiislttut fur Aiiorganische Chemie der Universitit
A u t der Morgenstelle 18, D-72076 Tiibingen (FRG)
[**I
Or$anomet:illic Compounds of Lanthanoids. Part 86. Thi5 work was supported h> the Deutsche Forschungsgemeinschaft. the Fonds der Chemischen Induhtrie. and the Bundesministerium fur Bildung und Wissenschaft (Graduiertenkolleg ..Synthese und Strukturaufkliirung niederinolekularer Verbindungen"). Part 8 5 . H. Schumann. J. Winterfeld. M. Glanz. R. D. Kohn. H. Hemling. .I. O~~:un~irirc!.
C / ~ e m in
. . press.
Fig. 1 . Crystal structure of 3 a (ORTEP [IZ]. thermal ellipsoids d r a a n a t 50%
probability level (the atom positions produced by symmetry operations [- v, y.
1.5-:] are not shown). Selected distances
and angles [ ] (standard deviations are
given in parentheses) [13]: Y b - C l 2.669(4), Y b CZ 2.692(4). Y b - C 3 2 688(4),
Y b b C 4 2.6?1(4). Yb C 5 2.648(3). Yb-C1Z 2.552(4); Cp-Yb-Cp 144.0(4). CpYb-C 12 107.5(4).
[A]
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