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Noncovalent Interactions in Organometallic Compounds Formation of an Intramolecular MetalЦCarbon Ion Pair in Zirconium Borate Betaines.

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A. K. Beck. D.A. Plattner, F. N. M. Kuhnle, J. Org. Chem. 1995,60,17881799.
[8] D.Seebach. D.A. Plattner, A.K. Beck, Y. M. Yang, D. Hunziker, Hefv.
Chim. Acta 1992.75,2171-2209.
[9]Review: K. Mikami in Encyclopedia of Reagents for Organic Synthesis, Vol.
I (Ed.: L. A. Paquette), Wiley, Chichester, UK, 1995,p. 407;C. A. Martin,
Ph. D. Thesis Massachusetts Institute of Technology, Cambridge, MA,
USA. 1988:J. T. Wang, X. Fan, X. Feng, Y. M. Qian, Synthesis 1989,291292: G.E. Keck, K. H. Tarbet, L. S. Geraci, J. Am. Chem. Soc. 1993,115,
8467-8468: K. Mikami. S. Matsukawa, Tetrahedron: Asymmetry 1995, 6,
2571 -2574:J. W. Faller, D. W. Sams, X. Liu. J. Am. Chem. Soc. 1996,118,
1217-1218: S. Weigand, R. Brtickner, Chenr. EUKJ. 1996, 2,1077-1084.
[lo] K. Mikami, S. Matsukawa. Nature 1997,385,613-615;
M. Mori, H. Imma, N.
Takai, Tetrahedron Letr.1997, 38, 6229-6232.
[ll] See Ref. [lot and for a similar (R)-3,3’,5,S-tetrachloro-4.4,6,6-tetramethylbiphenol, see: E. J. Corey, M. A. Letavic. M. C. Noe, S. Sarshar, Tetrahedron
Lett. 1994.35,7553-1556.
[I21 Reviews on ene reactions: K. Mikami, M. Shimizu, Chem. Rev. 1992,92,
1021 - 1050.B. B. Snider in Comprehensive Organic Synrhesrs, Vol. 2 and 5B
(Eds.: M. Trost. 1. Fleming), Pergamon, London, 1991:H. M.R. Hoffmann,
AngeM:. Chrm. 1969,81, 591-618;Angew. Chem. Irzt. Ed. Engl. 1969, 8,
556-571.
[13]K Mlkami. M. Terada, T. Nakai. J. Am. Chem. SOC.1989,111,1940-1941;
ibid. 1990.112. 3949-3954.
[14]M. G. Finn. K. B. Sharpless in Asymmetric Synthesis, Vol. 5 (Ed.: J. D.
Morrison), Academic Press. New York, 1985, p. 247; M. G. Finn. K. B.
Sharpless, J. Am Chem. SOC.1991,113,113-126.
onset of polymerization upon treatment of these active
Ziegler catalysts with a-olefins seems to cleave these ion
pairs
We recently found that (butadiene)zirconocene complexes3isaI add B(C6F5)3 at the terminal CH,group of the
conjugated diene ligand to yield the metallocene borate
betaines 4.C61The resulting substituted x-ally1 moiety in 4 is Econfigurated. This geometrically prohibits intramolecular
Zr...CH,[B] ion pairing in 4 analogous to the favorable
Zr ... CH,[B] interaction in 2. Instead, 4 is stabilized by
1
L
FJQ
-F-F
F
F
4
Noncovalent Interactions in Organometallic
Compounds: Formation of an Intramolecular
Metal - Carbon Ion Pair in Zirconium Borate
Betaines”*
Jorn Karl, Gerhard Erker,* Roland Frohlich,
Frank Zippel, Friedrich Bickelhaupt, Marcel
Schreuder Goedheijt, Otto S. Akkerman, Paul Binger,
and Jorg Stannek
Noncovalent metal - ligand interactions and ion pairing will
probably be of increasing importance as structural elements
and latent functionalities in the organometallic chemistry of
transition metals.i’] It will become necessary to learn about the
factors that govern the formation of such bonding features.
We now found that for a class of metallocene borate betaines
geometric parameters of the allyl unit constitute the structural
element that determines whether the electron-deficient metal
center is stabilized by an intramolecular M ...CH,[B] ([B] =
B(C,F,),) ion pair[,] or by M ... F-C c~ordination.[~)
T. J. Marks et al. demonstrated that dimethylzirconocenes 1
(RCp=substituted cyclopentadienyl) are able to transfer a
methyl anion to the strong Lewis acid tris(pentafluor0pheny1)borane. The resulting products 2 favor structures with
a rather stable ion pair in the solid state as well as in solution
(Zr.-.CH,[B]-2.55 A, A G ~ i , - 1 6 - 1 8 kcalmol-I). Only the
[*] Prof.Dr.G. Erker, Dr. J. Karl, Dr. R. Frohlich, Dr. F. Zippel
[‘“I
Organisch-chemisches Institut der Universitat
Corrensstrasse 40,D-48149Miinster (Germany)
Fax: Int. code + (251)83-39772
e-mail : erker@uni-muenster.de
Prof. Dr.F. Bickelhaupt, Dr.M. Schreuder Goedheijt, Dr. 0. S. Akkerman
Fakulteit der Scheikunde, Vnje Universiteit Amsterdam (The Netherlands)
Prof. Dr.P Binger, Dr. J. Stannek
Max-Planck-Institut fur Kohlenforschung, Miilheim (Germany)
Financial support by the Fonds der Chemischen Industrie, the Deutsche
Forschungsgemeinschaft, and the Ministerium fur Wissenschaft und Forschung des Landes Nordrhein-Westfalen is gratefully acknowledged. G.E.
and F.B. thank the Alexander von Humboldt-Foundation for their support
of this work with the Max-Planck-Forschungspreis.
Angew Chem. In[. Ed. Engl. 1997.36.No. 24
coordination of an ortho-F atom of a C6F5 substituent on
boron to the electrophilic metal center. The strength of
this Z r . . . F interaction was determined to be about
8.5 kcal m0l-l.[~1Addition of a reactive a-olefin again removes
this “protecting group” from the catalytically active Zr+
center, and complexes 4 serve as active single-component
metallocene Ziegler catalysts.161
If the interpretation is correct that intramolecular
Zr...CH,[B] ion pairing in 4 is disfavored due to the
geometrically prohibitive E position of the CH2[B] substituent at the n-ally1 ligand, then the intramolecular Zr-C ion
pairs of the metallocene borate betaine system should be
observed again in cases where the isomeric 2-allyl-CH,[B]
arrangements are favored. We have synthesized two such
betaine systems, and characterized them stereochemically and
with regard to the intramolecular interaction between allylCH,[B] and Zr.
As a first substrate we employed (ortho-quin0dimethane)zirconocene (5).[5bIThis complex marks the metallacyclic
extreme of the (s-cis-diene)metallocene family of complexes:
the n interaction between Zr and carbon atoms C2 and C3 is
5
6
only marginally pronounced. Nevertheless, this complex, in
which the cisoid arrangement of the C1-C2 and C3-C4
vectors has become fixed by the anellated phenylene moiety,
exhibits a variety of chemical features typical of the (s-cis-1,3diene)zirconium complexes[5]
Complex 5 reacts instantaneously with one molar equivalent of B(C6F,), at room temperature in toluene to form the
1:l addition product 6. Adding a layer of pentane above the
solution of the product in toluene furnished single crystals of 6
within three days that were suited for an X-ray structure
analysis This confirmed that the B(C&& moiety had added to
the C4 atom. Compound 6 constitutes an internal ion pair that
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contains a [Cp,ZrR]+ cation and a [RB(C,F,),]- anion in a
single molecule (Figure 1).The Cp,Zr moiety of 6 exhibits the
usual structural parameters of Group 4 bent metallocenes.[*]
The Zr-C1 bond is very short (2.264(3) as opposed to 2.776(3)
for Zr-C2 and 2.898(3) A for Zr-C3). It is the coordination
Q
Already at 253K 14resonances are observed (two of the
ortho-F resonances are accidentally isochronous). These
spectra also clearly rule out the presence of any coordination
of F to the electrophilic Zr center in solution. The observed
characteristic splitting pattern originates from hindered
rotation of the B(C6F5), "propeller" on the NMR time scale,
which is similar to the situation in several other R-B(C6F5),
The formation of an internal ion pair in 6 is not unique, but
apparently in general present as soon as the metallocene
borate betaine features the sterically favorable Z-ally1
arrangement.[") Therefore, we treated the (y4-butadiene)
(y8-cyc1ooctatetraene)zirconium complex 7[121with B(C,F,), .
At ambient temperature the Lewis acidic borane adds instantaneously and with complete regioselectivity to the C4 atom of
the butadiene ligand to form 8. Again we obtained single
I
Figure 1. Molecular structure of betalne 6. The ion-pair interaction between Zr
and C4 is indicated by a dashed line. Selected bond lengths
and angles ["I:
Zr-C1 2.264(3), Zr-C4 2.595(3), Zr-C,, (av) 2.508(4), C1-C2 1.472(5), a - C 3
1.414(4), C2-C.5 1.406(5), C-C6 1.358(5), C6-C7 1.395(5), C7-C8 1.370(5),
C3pC8 1.401(4), C3FC4 1.517(4), C4-B 1.682(3), B-21 1.655(4), BpC31 1.663(5),
B-C41 1.646(5); Cl-C2-C5 119.713). C2-C5-C6 122.3(3), C 5 X 6 - 0 119.5(4), C6C7-C8 119.9(4), C7-C8-C3121.6(3), C8-C3-C4 119.8(3), C3-C4-B 119.1(3), C4-BC21 117.4(2), C4-B-C31 108.1(3), C4-B-C41 103.3(2), C21-B-C31 102.3(2), (21B-C41 112.1(3), C31-B-C41 114.0(2); see text for additional values.
[A]
pattern of the sp3-hybridized carbon atom C4, which bears the
B(C6F5), substituent, that makes 6 structurally noteworthy.
Atom C4 exhibits a rather short distance to the zirconium
atom (2.595(3) A), and the Zr-C4-B angle is 155.3(2)". The
C4-Zr vector points in a direction opposite to the C4-B
vector. We regard the Zr-C4 bond as an electrostatic ion pair.
Consequently, both C-H bonds at C4 are oriented toward the
transition metal (C3-C4-B 119.1(3)"), which is different from
the situation at the distorted-tetrahedrally tetracoordinated
C1. The resulting "ion-paired five-membered metallacycle" is
nonplanar and structurally resembles the "envelope" geometry of the starting material 5; its folding angle (i. e., the angle
between the Zr/Cl/C4 and C2/C3/C5- C8 planes in 6 ) amounts
to 68.6".L91Some of the bond angles inside the five-membered
ring are quite different than normal (Cl-Zr-C4 75.41(11),
Zr-Cl-C2 93.5(2), Zr-C4-C3 85.4(2), Cl-C2-C3 121.7(3),
C2-C3-C4 121.6(3)"). The heavy atoms at C4 (Zr, C3, B) are
almost coplanar (sum of angles 359.8'). Thus, the C4-B vector
attains an almost gauche orientation to its neighboring aromatic
ring (dihedral angles C8-C3-C4-B - 47.9(4), C2-C3-C4-B
135.0(3)"). The internal ion pair formed between Zr and C4
apparently leads to an optimal situation with regard to steric
interaction and electrostatic stabilization of 6.
In solution at 253 K 6 exhibits NMR signals for a pair of
diastereotopic Cp ligands (d('H/13C)= 5.4M12.0, 4.48/111.1
at 600/150MHz) as well as C1 (S('H)=2.17, 1.80) and C4
protons (6('H) = 0.89, 0.30).[91The I3CNMR resonance for C1
appears at 6 = 57.6; the signal for C4 is probably very broad
due to the adjacent boron nucleus and could not be located.
Complex 6 exhibits temperature-dependent I9FNMR spectra.
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8
crystals from a solution in toluene within three days after
cautiously adding a layer of pentane. The X-ray structure
analysis of 8 shows the presence of a y8-cot ligand (Zr-C(cot)
2.371(5) - 2.433(5) A) and a Z-configured CH,[B]-substituted allyl ligand at zirconium (Figure 2). The coordination of
[A]
Figure 2. Molecular geometry of 8. Selected bond lengths
and angles ["I:
Zr-C,,, (av) 2.403(3), B-C11 1.656(5), B-C21 1.645(5), B-C31 1.656(6); C1-ZrC2 31.1(2), CI-Zr-C3 59.7(2), Cl-Zr-C4 69.8(2), c2-Zr-C3 34.4(2), C2-Zr-C4
60.1(1), C3-Zr-C4 34.7(1), Zr-CI-C2 68.8(3), Zr-CZ-Cl S0.0(3). Zr-C2-C3 65.6(2).
Zr-C3-C2 80.0(2), Zr-C3-C4 85.5(2), Zr-C4-C3 59.8(2), CI-C2-C3 123.2(4), C2C3-C4 122.2(4), C3-C4-B 114.7(3); see text for additional values.
the allyl ligand to zirconium is rathtr unsymmetrical. The
Zr-C3 bond is the shortest (2.266(4) A), whereas the Zr-C2
and Zr-C1 bonds are markedly longer (2.450(4) and
2.588(5) A, respectively). Accordingly, there is a short - long
sequence of the C-C bond lengths in the allyl unit (Cl-C2
1.359(8), C2-C3 1.407(6) A). The C3-C4 bond length is
1.493(5) A. Atom C4 again has distorted trigonal-bipyramidal
coordination (C4-B 1.665(5), C4-Zr 2.614(4) A; Zr-C4-B
148.8(3)"). The dihedral angle C2-C3-C4-B amounts to
- 139.6(4)". The hydrogen atoms at C4 are apparently
oriented in the direction of the metal atom. We conclude
that 8 also forms an internal ion pair to give rise to a fivemembered metallacycle. The essential structural features of
the complexes 8 and 6 are closely related in this respect.
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In solution 8 shows 'H and 13CNMR resonances for the v8cot ligand at 6 = 5.94 and 96.9, respectively ('JCH
= 169 Hz).
The I3C NMR signals for the carbon atoms of the allyl ligand
appear at 6 = 79.9 ('JcH
= 166, 158 Hz), 127.1 (154 Hz), and
103.1 (172 Hz); the corresponding 'H NMR resonances are at
6 = 2.80, 2.05 (syn,anti-1-H), 4.75 ("meso"-2-H), and 2.08
(~yn-3-H).['~]
The gauche orientation of the B(C6F& substituent at C4 (see above) together with the Zr-C4 ion pair make
the hydrogen atoms 4-H and 4-H' diastereotopic. Consequently two 'H NMR resonances are found at 6 = 0.07 and
- 1.00. The I3CNMR signal for C4 appears at 6 = 14.1 (*JCB
=
37 Hz); this is typical for a CH,[B] carbon atom that has a
direct contact to zirconium. The I9F NMR spectrum of 8
shows three sharp resonances for the ortho-, meta-, and para-F
atoms of the B(C,F,), substituent down to 193 K. There is no
indication of C-F coordination in solution.
The results described here show that the intramolecular
stabilization of Group 4 metallocene borate betaines is
controlled by the geometrical features of their CH,[B]substituted allyl moiety. The E configuration leads to favored
coordination of an ortho-C-F moiety to the zirconium center,
whereas the respective Z orientation results in the formation
of a stable ion pair interaction between the transition metal
and the CH,[B]
R =0.038, wR2= 0.084, max./min. residual electron density 0.691- 0.37 e,&3.
Hydrogen atoms were calculated and refined as riding atoms.
X-ray crystal structure analysis of 8: 0.60 x 0.50 x 0.40 m m , a = 11.365(1), b =
17.676(1), c = 14.047(3) A, /l=99.10(1), V=2786.4(7) A3, pc.,lcd
= 1.815 gem-),
p = 5.17 cm-', empirical absorption correction with rp-scan data (0.878 5 C 5
0.998), Z = 4 , monoclinic, space group PZJn (no. 14). 1= 6.71073 A,T=223 K,
5661
a128 scans, 5889 measured reflections (ih, - k, + I ) , [ (sin8)11] = 0.62 k',
independent and 4003 observed reflections [ I 2 2o(I)], 424 refined parameter,
R =0.046, wR2=0.122, max.1min. residual electron density 0.831 - 0.77 e A-,.
Hydrogen atoms were calculated and refined as riding atoms.
Both data sets were measured on an Enraf Nonius MACH3-diffractometer. The
following computer programs were used: MolEN for data reduction, SHELXS86 for structure solution, SHELXL-93 for structure refinement, SCHAKAL-92
for graphics. 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-100478.Copies of the data
can be obtained free of charge o n application to The Director, CCDC, 12 Union
Road, Cambridge CB21E2, UK (fax: int. code + (1223)336-033; e-mail:
deposit@chemcrys.cam.ac.uk).
Received: June 11. 1997 [Z10534IE]
German version: Angew. Chem. 1997,109,2914-2917
-
Keywords: betaines
ion pairs
Ziegler catalysts zirconium
-
-
sandwich complexes
-
[l] Electrostatically dominated bonding features are rather the rule with
organometallic compounds of the electropositive main group metals; see for
example A. M. Sapse, l? von R. Schleyer, Lifhrum Chemistry, Wiley, New
York, 1995. and references therein; Comprehensive Organometallic Chemistry 11, Vol. 1 (Eds.: E. W. Abel, F. G. A. Stone, G. Wilkinson), Pergamon,
1995. and references therein.
Experimentai Section
[2] J. J. Eisch, K. R. Caldwell, S. Werner, C. Kriiger, Organometallics 1991.10,
3417; A. D. Horton, J. H. G. Frijns, Angew. Chem. 1991,103, 1181; Angew.
All reactions were carried out under argon.
Chem. In[. Ed. Engl. 1991,30,1152; X. Yang, C. L. Stem. T. J. Marks, J. Am.
Chem. SOC.1991,113,3623;C. Sishta, R. M. Hathorn. T. J. Marks, ibid. 1992,
6: Complex 5 [ 5 ] (326 mg, 1.00 mmol) and B(C,F,), (520 mg, 1.01 mmol) were
114,1112; M. Bochmann, Angew. Chem. 1992,104,1206; Angew. Chem. Int.
suspended in toluene (2 mL), and a layer of pentane was carefully added. After
Ed. Engl. 1992, 31, 1181; M. Bochmann, S. J. Lancaster. M. B. Hursthouse,
three days the betaine was isolated as red crystals; yield 585 mg (70%); m.p.
K. M. A. Malik, Organometallics 1994,13,2235; M. Bochmann, S. J. Lancaster,
104°C (decomp). 'H NMR (599.9 MHz, 253 K, [D,]toluene): 6=7.59 (d,
Angew. Chem. 1994,106,1715; Angew. Chem. Int. Ed Engl. 1994.33.1634;
'J(H.H) = 8.1 Hz, 1H, 5-H), 6.78 (pseudo t, 1H, 7-H), 6.73 (pseudo t, I H, 6P. A. Deck, T. J. Marks, J. Am. Chem. SOC.1995,117.6128:M. A. Giardello,
H),6.26(d,?I(H,H)=8.1 Hz,lH.8-H),5.41,4.48(eachs,eachSH,Cp),2.17(d,
M. S . Eisen, C. L. Stern, T. J. Marks, ibid. 1995, 117, 12114; J. Organomet.
'J(H.H)=12.7Hz,1H,l-H),1.80(d,2J(H,H)=12.7Hz,1H,l-H),0.89(br,1H,
Chem. 1995,497. 5 5 ; A. Cano, T. Cuenca, P. Gomez-Sal, A. Manzanero, P.
4-H'), 0.30 (br. 1 H, 4-H); "C NMR (150.8 MHz, 253 K, [D,]toluene): 6 = 148.3
Royo, ibrd. 1996,524,227;A. D. Horton, Organometallrcs1996.15.2675; Y.(d, 'J(C,F) = 250 Hz. o-B(C,F,),), 140.6, 140.3 (each C, C-2, C-3). 139.4 (d,
X. Chen, C. L. Stern, S. Yang, T. J. Marks, J. Am. Chem. SOC. 1996, 118,
'J(C.F) =250 Hz. pB(CbFJj). 137.5 (d, 'J(C,F) = 250 Hz, m-B(C,F,),), 131.0
12451; see also B. Temme, J. Karl, G. Erker, Chem. Eur. .I. 1996.2, 919; J.
(CH, C-5). 130.6 (CH. C-7). 129.8 (CH, C-8), 126.3 (CH, C-6), 112.0,lll.l (each
Karl, G. Erker, J. Mol. Catal.. in press; Chem. Ber. 1997, /.?U, 1261.
CH, Cp). 57.6 (CH,. C-1), signals for the ipso-C of C,F, and C4 were not detected
[3] a) A. D. Horton, A. G. Orpen, Organometallics 1991, 10. 3910; X. Yang,
at 253 K (assignments were supported by the results of GCOSY, GHSQC, and
C. L. Stern, T. J. Marks, ibid. 1991, 10. 840; Angew. Chem. 1992,104, 1406;
GHMBC experiments [16]); IYFNMR (564.3 MHz, 253 K, [D,]toluene): 6 = Angew. Chem. Int. Ed. Engl. 1992.31.1375; J. Ruwwe, G. Erker, R. Frohlich,
167.3. -166.1 ( 2 x ) , -165.3, -164.7, -162.0 (br, 6F. m-F), -160.5, -159.6,
ibid. 1996,108,108; bm. 1996,35,80; b) A. R. Siedle. R. A. Newmark, W. M.
- 159.4 (br. 3F, p-F), - 141.7, - 137.3, - 134.3, - 130.6, - 129.5, - 128.8 (br, 6F, oLamanna, J. C. Huffman, Organometallics 1993, 12. 1491. c) R. Uson, J.
F); IR (KBr): i.=311Y. 2963, 2921, 1642, 1513, 1458, 1382, 1281, 1085, 981,
ForniCs, M. Tomas, F. A. Cotton, L. R. Falvello, J. Am. Chem. SOC.1984,106,
825 cm-'; elemental analysis calcd for C,,H,,BF,Jr
(837.5): C 51.63, H 2.17;
2482; R. M. Catala, D. Cruz-Garritz, A. Hills, D. L. Hughes, R. L. Richards,
found: C 50.93, H 2.75.
l? Sosa, H. Torrens, J. Chem. SOC. Chem. Commun. 1987, 261; H. Plenio, R.
8: Complex 7 1121 (250 mg, 1.00 mmol) and B(CbF5), (520 mg, 1.02 mmol) were
Diodone, Chem. Ber. 19%. 129,1211;J. Am. Chem. SOC. 19%. 118,356; H.
allowed to react in toluene (2 mL). The color of the solution changed from bluePlenio, R. Diodone, D. Badura.Angew. Chem. 1997.109.130; Angew. Chem.
green to red-brown. A layer of pentane (6 mL) was carefully added. After three
Int. Ed. Engl. 1W,36,156; Reviews: R. J. Kulawiec, R. H. Crabtree, Coord.
days at ambient temperature the product was obtained as red crystals; yield
Chem. Rev. 1990, 99. 89; S. H. Strauss. Chem. Rev. 1993, 93, 927; J. L.
530 mg (70%); m.p. 54'C (decomp). 'H NMR (599.9 MHz, 298 K, [D,]toluene):
Kiplinger. T. G. Richmond, C. E. Osterberg, ibid. 1994. 94, 373; R. J.
6=5.94(s.8H,cot).4.75(m,1H,2-H),2.80(dd,2'3J(H.H)=9.8,2.0Hz,lH,1- Kulawiec. E. M. Holt, M. Lavin, R. H. Crabtree, Inorg. Chem. 1987.26.2559.
H ) , 2.08 (m. 1 H. 3-H). 2.05 (d. 'J(H,H) = 9.8 Hz, 1 H, 1-H), 0.07 (br, 1H, 4-H).
[4] X. Yang. C. L. Stern, T. J. Marks.J. Am. Chem. Soc. 1994.116,10015; L. Jia,
- 1.00 (br. 1 H, 4-H); "C NMR (150.8 MHz, 298 K, [D,]toluene): 6 = 148.4 (d,
X. Yang. A. Ishihara, T. J. Marks, OrganometaIIics1995, /4. 3135. B(C,F,),:
'J(C.F) = 240 Hz. o-B(C,Fj),), 139.0 (d, 'J(C,F) = 240 Hz, p-B(CP,),). 137.3 (d,
A. G. Massey. A. J. Park, F. G. A. Stone, Proceedings Chem. SOC.1963.212;
'J(C,F) =240 Hz, m-B(C,F,),), 127.1 (CH, 'J(C,H) = 154 Hz, C-2). 103.1 (CH,
A. G. Massey, A. J. Park, J. Organomet. Chem 1964,2, 245.
'J(C.H) = 172 Hz, C-3). 96.9 (CH, 'J(C,H) = 169 Hz, COT), 79.9 (CH,,
[5] a) G. Erker, C. Kruger. G. Miiller, Adv. Organomet. Chem. 1985,24,1. and
'J(C.H)= 166. 158 Hz, ?I(C,H) = 9 Hz. C-l), 14.1 (CH,, 'J(C.B)=37 Hz. C-4),
references therein. b) G. S. Bristow, M.F. Lappert, T. R. Martin, J.L.
the signal for the @so-C of C,F5 was not observed (the assignments were
Atwood, W. E. Hunter, J. Chem. Soc. Dalton Trans. 1984.399.
supported by GCOSY and GHSQC experiments [16]); IyF NMR (564.3 MHz,
[6] B. Temme, G. Erker, J. Karl, H. Luftmann, R. Frohlich. S. Kotila, Angew.
298 K. [DJbenzcne): 6 = - 165.7 (t, ,J(F,F) =21 Hz, 6F, m-F), - 161.1 (t.
Chem. 1995,107. 1867; Angew. Chem. Int. Ed. Engl. 1995,34, 1755.
'J(F.F) = 20 Hz, 3 F, p-F), - 135.0 (d, 'J(F,F) =21 Hz, 6F, o-F); IR (KBr): G=
[7] J. Karl, G. Erker, R. Frohlich, J. Am. Chem. SOC. 1997. 119, 11165; J. Karl,
3086. 2963. 2922. 1645, 1516, 1454. 1274, 1086, 976, 814, 757 cm-'; elemental
Dissertation, Universitat Miinster, 1997. The remotely related complex
analysis calcd for C,,,H,,BFI5Zr(761.4): C 47.32, H 1.85; found: C 47.11, H 2.12.
Cp?ZrOB(C,F,), also features an internal Zr ... F contact, whose bond
X-ray crystal structure analysis of 6: 0.60 x 0.50 x 0.08 mm, a = 27.026(2), b =
dissociation energy was estimated to be about 10 kcalmol-' from the
12.785(1). c=20.425(1) A. /3=117.54(1), V=6256.7(7) 2,p,,,,,=1.778g~m-~,
temperature-dependent "T NMR spectra (see ref. [3b])
p = 4.70 cm I, empirical absorption correction wirh 9-scan data (0.968 5 C 5
[S] Comprehensive Organometallic Chemistry, Vol. 4 (Eds.: E. Abel, F. G. A.
0.999). Z = 8 , monoclinic, space group C21c (no. 15), 1=0.71073 A,T=223 K,
Stone. G. Wilkinson), Pergamon, 1995; D. J. Cardin, M. F. Lappert, C. L.
w128 scans. 6543 measured reflections ( ih , - k, + I ) , [ (sinO)W] = 0.62 A-'.6357
Raston. Chemistry of Organo-Zirconium and -Hafnium Compounds, Wiley,
independent and 3905 observed reflections [I2 2o(f)], 478 refined parameters,
New York, 1986.
Angew. Chem. In!. Ed. Engl. 1997,36, No. 24
0 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1997
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Compound 5 is dynamic and shows a rapid flipping of the nonplanar
metallacyclic five-membered ring, thereby interconverting the isoenergetic
envelope conformations. The internal organometallic ion pair of 6 features
an analogous automerization reaction, albeit with a substantially increased
activation barrier (T,,,,,,,,, (Cp) = room temperature).
W. Ahlers, B. Temme, G. Erker, R. Frohlich, T. Fox, J. Organomet. Chem.
1997,527.191; W. Ahlers, G. Erker, R. Frohlich, F. Zippel, Chem. Ber., 1997,
130,1079.
W. J. Highcock, R. M. Mills, J. L. Spencer, P. Woodward, J. Chem. SOC.
Chem. Commun. 1982,128; D. J. Brauer, C. Kriiger, Organometallzcs 1982,
I, 204, 207.
a) G. Wilke, L. Stehling, unpublished results; b) G. Wilke in Fundam. Res.
Homogeneous Catal. (Ed.: M. Tsutsui), Plenum Press, New York 1979, 3,
p. 1; c) experimental procedure: J. Wicher. Dissertation, Universitat
Bochum, 1983; d) 'H NMR spectrum: R. Benn, G. Schroth, J. Organomet.
Chem. 1982,228.71.
E. G. Hoffmann, R. Kallweit, G. Schroth, K. Seevogel, W. Stempfle. G.
Wilke, J. Organomef.Chem. 1975, 97, 183; A. D. Horton, Organometallics
1992, 11, 3271.
The group in Amsterdam also added B(C,Fs), to 1,l-bis(cyclopentadieny1)zirconaindane [15] with opening of the Zr-C(spi) bond. According to NMR
spectroscopy we assume a specific product geometry that at the same time
conformationally favors the interaction of the zirconium atom with the
CH2[B] moiety (6(I3C)= 14.6) and one of the ortho-fluorine substituents
(6(I9F)=- 180.2), which are both located in the major plane of the bent
metallocene unit: M. Schreuder Goedheijt, dissertation, Vrije Universiteit
Amsterdam, 1996.
G. Erker, K. Kropp, J. Am. Chem. SOC.1979,101,3659.
S. Braun, H. Kalinowski, S. Berger, 100 and More Basic NMR Experiments,
VCH, Weinheim, 19%, and references therein.
A Cyclic Octadecairon(II1) Complex, the
Molecular 18-Wheeler**
Stephen P. Watton, Peter Fuhrmann, Laura E. Pence,
Andrea Caneschi, Andrea Cornia, Gian Luca Abbati,
and Stephen J. Lippard"
The development of strategies for the synthesis of highnuclearity metal clusters has provided substantial impetus to
in several different fields, including materials chemistry,"]
bioinorganic chemistryJ2] and solid-state physi~s.l~,~l
The
architecture of large transition metal clusters can often result
in novel chemical and physical properties. For example,
polyiron and polymanganese complexes of nanometer size
and with high-spin ground states afford single-domain magnetic particles, which may display hysteresis effects of purely
molecular
It is of interest to investigate the properties of increasingly larger assemblies of interacting metal ions,
because they are expected to evolve gradually towards those
of bulk materials." a,1c] Furthermore, large cyclic polyrnetallic
clusters are also valued for their ability to mimic the properties of linear coordination polymer~.[~I
Previously we described a cyclic decairon(m) complex
having the composition [Fe(OCH,),(O,CCH,CI)],,, referred
to as a molecular ferric wheel, the solid-state properties of
which were thoroughly inve~tigated.[~]
A number of related
circular clusters have been synthesized, the latest of which
contains seven linked ferrocene rings and has been called a
molecular scoop wheel.I6I In the present communication we
report the synthesis, solid-state structure, and magnetic
behavior of the compound 1 (where XDK is the dianion of
rn-xylylenediamine bis(Kemp's triacid imide)).c7I This complex, which we designate the "molecular 18-wheeler", is the
largest cyclic ferric cluster reported so far, containing 18
iron(rI1) atoms in a ring.[*]
The title compound was obtained in the presence of
tetraalkylammonium carboxylate salts from slightly alkaline
methanolic solutions of the diiron(II1) complex 2 (see Experimental Section). This material was previously employed in
[Fe,0(XDK)(CH,0H),(H20)](N0,), .4 H 2 0
our laboratories to prepare models of the carboxylate-bridged
diiron cores present in a variety of non-heme proteins.[9]The
composition of the crystalline compound, a double salt having
the formula 1.6Et4N(N0,).15CH,0H-6Et,0.24H20,
was
established by elemental analysis and a single-crystal X-ray
diffraction investigation. Figure 1 displays the structure of the
molecular 18-wheeler viewed perpendicular to the plane of
the ring.
[*] Prof. Dr. S. J. Lippard, Prof. Dr. S. P. Watton, Dr. P. Fuhrmann,
Prof. Dr. L. E. Pence
Department of Chemistry
Massachusetts Institute of Technology
Cambridge, MA 02139 (USA)
Fax: Int. code + (617)258-8150
e-mail: lippard@lippard.mit.edu
Dr. A. Caneschi
Dipartimento di Chimica, Universita degli Studi di Firenze (Italy)
Dr. A. Cornia, Dr. G. L. Abbati
Dipartimento di Chimica, Universiti degli Studi di Modena (Italy)
[**I
*+
@-v=-=b
This work was supported by grants from the National Science Foundation
and the National Institute of General Medical Sciences (S.J.L.) and by a
Coordinate Project of the Italian CNR (A.C.). L.E.P. thanks the National
Institutes of Health for a postdoctoral fellowship.
2774
0 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1997
2
Figure 1. Ball-and-stick representation of 1, viewed perpendicular to the plane of
the ring. Iron atoms are drawn in black, oxygen atoms are shaded, carbon and
nitrogen atoms are depicted as open circles, and hydrogen atoms are omitted for
clarity.
0570-083319713624-2774$ 17.50+.5010
Angew. Chem. Int. Ed. Engl. 1997.36, No. 24
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organometallic, interactions, ion, intramolecular, compounds, formation, borate, pairs, zirconium, noncovalent, metalцcarbonyl, betaine
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