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Dynamic Motion in [HFe(CO)4] Ions as Observed by Mssbauer SpectroscopyЧEvidence for Hydride УTunnelingФ.

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(VMS)[17]), full-matrix least-squares refinement. Hydrogen atoms: riding
model, isotropic U . Weightingscheme: w-' = G'(F/ + 0.0006F2;345 parameters refined; final R indices (observed and all data): 0.00675 (R, = 0.00820),
G o f 2.38. largest and smallest difference peak (residual electron density primarily around the CH,CI, molecules): 0.63 and -0.94 ek'.[lX].
4 a : A suspension of 3 a (300 my, 0.666 mmol) in ethyl acetate (15 mL) was
hydrogenated over 10% PdjC (100 mg) for 5 days at 65 'C. Acetic anhydride
(0.5 mL) was added, and the mixture filtered after 15 min. Chromatography on
basic alumina gave the diacetate 4 a (202 mg, 0.454 mmol, 68 Yo);m.p. 290295"C(decomp.); 'HNMR(CDCI,,300 MHz): S =1.00-1.28(m,8H), 1.331.58(m,XH).1.67(br.s.4H),1.93(s,6H),3.01(m,4H),3.66(centeredm,4H),
3.74 (br. s, 2H), 4.02 (br. s, 4H), "C NMR (CDCI,, 75.5 MHz): 6 = 21.46,
24.21, 25.10, 25.49, 25.94 (double intensity), 27.76, 27.80, 43.69. 50.97, 51.05,
105.02, 114.94, 138.55, 142.95, 173.55. -X-ray analysis: Colorless prisms were
grown from CH,Cl,/light petroleum by the vapor diffusion technique, and a
crystal of 0.15 x 0.20 x 0.25 mm was selected. Slow evaporation of the cosolvating dichloromethane was observed. C,,H,,N,O,
CH,CI, (529.6); triclinic,
Pi. =10.82(1), b = I O . Y ~ ( I ) , =13.21(1)A; = 94.6(7), p =103.28(7), =
105.10(7)", 2 = 2; e,.d,.d,=1.21 gem-! Absorption coefficient = 0.25 mm-l.
F(OO0) = 568. Diffractometer: Syntex R3, Mo,,, 2 5 ° C 20 range: 3.0-43.0",
scan type: (0. 3403 reflections collected; 1750 with F > 2.50(F/; empirical
absorption correction ( 5 reflections 9.5 < 2 0 < 38.5", transmission min. 0.79,
max. 1.00). Solution by direct methods (Siemens SHELXTL PLUS (VMS)
[17]), full-matrix least-squares refinement. Hydrogen atoms: riding model,
isotropic U . 354parameters refined; R indices (observed data): 0.095 ( R , =
0.082), Gof: 3.44, largest and smallest difference peak: 0.38 and -0.29 e k ' .
The crystal decomposed slightly during the measurement. [IX].
Received: February 25, 1992 [Z 5209 lE]
German version: Angew. Chem. 1992,104, 899
CAS Registry numbers:
2a, 141510-04-5; 3a, 141510-05-6; 4a, 141510-06-7; H,N(CH,),NH,,
24-2.
646-
[l] P. M. Keehn, S . M. Rosenfeld, Cydophanes, Academic Press. New York,
1983; Top. Curr. Chem. 1983, 113; ibid. 1983, 115; F. Vogtle, Cyclophanchemie, Teubner, Stuttgart, 1990; F. Bickelhaupt, Pure Appl. Chem. 1990,
62,373; L. W. Jenneskens, H. J. R. DeBoer, W H. Wolf, F. Bickelhaupt, J.
Am. Chem. Soc. 1990, 112, 8941 and references cited therein. For the
synthesis of pyridino-metacyclophanes by coupling reactions with di-Grignard reactions, see: K. Tamao, S. Kodama, T. Nakatsuka, Y. Kiso, M,
Kumada, ibid. 1975, 97, 4405.
[2] a) J. J. Wolff, S. F. Nelsen, D. R. Powell, J. Org. Chem. 1991, 56, 5908;
J. Wolff, S. F. Nelsen, P. A. Petillo, D. R. Powell, Chem. Ber. 1991,
b) .I.
124, 1719; c) J. J. Wolff, S. F. Nelsen. D. R. Powell, J. M. Desper, ibid.
1991, 124, 1727.
[3] J. M. Chance, B. Kahr, A. B. Buda, J. S. Siegel, J. Am. Chem. Soc. 1989,
i f f , 5940.
[4] See for example: D. A. Dixon, J. C. Calabrese, R. L. Harlow, J. S. Miller,
Angew. Chem. 1989,101.81; Angew. Chem. l n t . Ed. Engl. 1989,28,92 and
references cited therein.
[5] J. M. Chance, B. Kahr, A. B. Buda, J. P. Toscano, K. Mislow, J. Org.
Chem. 1988, 53, 3226.
[6] Monoalkylamines, e.g., 2,2-dimethylpropyl-, iso-propyl-, and terr-butylamine. have also been used successfully for the synthesis of 2 and 3 in
comparable yields (J. J. Wolff, I. Bolocan, unpublished results).
[7] An ideal boat form requires two internal torsional angles of ci, two of -%,
and two of 0".
[XI Instead of calculating angles between planes defined by ring carbon atoms
(see, e.g.. G. Maas. J. Fink, H. Wingert, K. Btatter, M. Regitz, Chem. Ber.
1987, 120. 819) we have used the sum of absolute torsional angles as a
single parameter to characterize the amount of ring distortion [2a]. An
exponential correlation exists [2c] between the averaged C-C bond length
within the ring and the sum of the dihedral angles. which also holds in the
case of 3a.
[9] T. S. Choi, J. E. Abel, Acta Crystallogr. Sect. B 1972, 28, 193.
[lo] The protons for the methylene groups next to all amino nitrogen atoms are
diastereotopic.
[ l l ] S. Dahne, F. Moldenhauer. Prog. Phys. Org. Chem. 1985, 15, 1 and literature cited therein.
[12] See, for example: K. Elbl, C. Krieger, H. A. Staab, Angew. Chem. 1986,98,
1024; Angew. Chem. l n t . Ed. Engl. 1986, 25, 1023; J. S. Miller, D. A.
Dixon, J. C. Calabrese, C. Vazquez. P. J. Krusic, M. D. Ward, E. Wasserman, R. L. Harlow, J. Am. Chem. Sor. 1990, f t 2 , 381; H. A. Staab, J.
Hofmeister, C. Krieger, Angew. Chem. 1991.103,1003; Angew. Chem. l n t .
Ed, EngL 1991,30,1030; H. Bock, K. Ruppert, C. Nather, Z. Havlas, ibid.
1991, 103, 1194 and 1991, 30, 1180. The first experimental evidence for
cyanine structures in charged polyamino benzene derivatives is found in H.
Kahler, G. Scheibe, Z . Anorg. A/%. Chem. 1956, 285, 221.
[13] Investigations on the electronic situation in 1 and 3 by computational
methods will be pusblished elsewhere.
884
6
VCH Verlagsge.cellschaft mbH, W-6940 Weinhem?, I992
[I41 The I3C NMR spectrum shows that all carbon atoms of the pipridine ring
are nonequivalent, whereas the benzene ring has C, symmetry (four signals). Hence, the piperidine ring undergoes fast ring inversion, but the flip
of the cyclophane bridge and the rotation of the piperidine ring around the
C-N bond is slow.
[15] For cosolvates, see M. C. Etter, S. M. Reutzel, J. Am. Chem. Soc. 1991,
113, 2586 and references cited therein; E. Weber, S. Finge, I. Csoregh, J.
Org. Chem. 1991, 56, 7281; Top. Curr. Chem. 1987, 140; ibid. 1988, 149.
[16] P. Engelbertr (Chemische Fabrik Griesheim), D.R.P. 767510,1936; Chem.
Ahsrr. 1955,49,14X03d; M. E. Hill. F. Taylor, Jr., .
I
Org. Chem. 1960,25,
1037.
[I71 G. M. Sheldrick. SHELXTL PLUS, Versions 4.2 (3a) and 3.4 (4a);
Siemens Analytical X-ray Instruments, Madison, WI, 1990, and Nicolet
Instrument Corporation, 1988, respectively.
[I81 Further details of the crystal structure determinations are available on
request from the Fachinformationszentrum Karlsruhe, Gesellschaft fur
wissenschaftlich-technische Information mbH. D-W-7514 EggensteinLeopoldshafen 2, on quoting the depository number CSD-56231, the
names of the authors, and the journal citation.
Dynamic Motion in [HFe(CO),] - Ions as
Observed by Mossbauer SpectroscopyEvidence for Hydride "Tunneling"**
By Gary J. Long,* Fernande Grandjean,
and Kenton H. Whitmire
Solution['-31 and s o l i d - ~ t a t e [ ~MAS
- ~ ] 13C NMR spectroscopy (MAS = Magic Angle Spinning) as well as
Mossbauer spectros~opy,[~-'
'I have proven useful methods
in revealing molecular dynamics in organometallic compounds and clusters. Herein, we report the first study of the
dynamic motion of the iron atom in several salts containing
the [HFe(CO),]- anion by Mossbauer spectroscopy. Hanson and WhitmireL8]have found that MAS I3C NMR spectra
of 1 and 2 show dynamic exchange of the axial and equato-
rial carbonyl ligands in [HFe(CO),]-. This exchange may
result from either a Berry pseudorotation"'] or, perhaps
more likely, from "tunneling" of the hydrido ligands within
the anion ("tunneling" here refers to a change of position not
to the tunnel effect in quantum chemistry). These authors
reported an activation energy of 29 f 3 kJmol-' for the
axial-equatorial exchange in 2. The displacement of the iron
atom as determined by Mossbauer spectroscopy provides
strong support for the existence of hydride tunneling in the
anion.
The Mossbauer spectra at 78K1'31 of 1, 2, and the
[Me,N]+ salt 3 are all very similar and show a single quadrupole doublet. In contrast the Mossbauer spectra at 295K[14]
[*] Prof. G . J. Long
Department of Chemistry
University of Missouri-Rolla
Rolla, MO 65401 (USA)
Prof. F. Grdndjean
Institut de Physique, BS, Universite de Liege (Belgium)
Prof. K. H. Whitmire
Rice University, Texas (USA)
[**I This work was supported by the Petroleum Research Fund, administered
by the American Chemical Society, and a NATO Cooperative Scientific
Research Grant (No. 861685).
0S70-0833/9210707-0884.$'3.50+.25/0
Angew. Chem Int. Ed. Engl. 1992, 31. N o 7
are quite different; 1 exhibits a quadrupole doublet, 2 exhibits a highly broadened absorption profile, and 3 gives no
observable absorption spectrum at this temperature. The
logarithm of the area beneath the absorption bands plotted
against temperature (Fig. 1) reveals a departure from the
expected linear behavior of the Debye model['01 above ca.
240 K for 1, above ca. 220 K for 2, and above ca. 180K for
3. The very small areas under the absorption bands, and
hence recoil-free fractions, observed at higher temperatures,
result from a motion of the iron atom. In the case of 2, the
temperature at which the onset of this motion occurs is coincident with the coalescence temperature for the signals of the
equatorial and axial carbonyl ligands in the MAS '3CNMR
Unfortunately, the solid-state structures of 218'
and 3 are unknown, but the structure determination[151of 1
at room temperature reveals that the [HFe(CO),]- ion has a
structure which is intermediate between a hydride facecapped tetrahedron and a trigonal bipyramid in which the
hydride occupies an axial position.
(see Fig. l), between 85 and 240 K for I, 85 and 220 K for 2,
and 85 and 180 K for 3, yields the Debye temperatures, OD,
given in Table 1. This table also includes the effective recoil
mass M,,,, which may be obtained from the temperature
dependence of the isomer shift, and the resulting Mossbauer
temperature.["' The observed values of these parameters are
Table 1. Lattice properties of [HFe(CO)J
bauer spectra.
Fe displacement [A] [a]
AE,,, [kJ mol-'1
dlnA/dT[K-'] [c]
8, [KI
d&/dT[mms-' K-'1
Mcf,[g mol-'l
ern [KI
salts 1-3 derived from the Moss-
0.34
0.1 1
0.26
9.1
[bl
29.2
- 7 . 4 0 ~lo-'
-1.10~
- 8 . 2 0 ~lo-'
129
135
111
-3.98~10-~ -3.79~10-~ -3.84~10-~
108
125
112
81
109
83
[a] Determined at 280K. [b] Too few data points were available to obtain a
reliable value. [c] A = area under the absorption bands (Fig. 1).
jr
-2
--31 1
0
,
,
100
,
,
200
T IKI
,
300
-
,
400
Figure 1. The temperature dependence of the logarithm of the area under the
absorption band for 1 (o), 2 (o), and 3 (D). The logarithmic scale has not been
normalized and hence the relative values for the different compounds are arbitrary.
The dynamics of the iron motion, as reflected in the temperature dependence of the logarithm of the area under the
absorption bands in the Mossbauer spectrum, may be treated in a fashion similar to that used to understand hydride
diffusion in niobium.['61 The temperature dependence of the
recoil-free fraction, which is proportional to the area under
the absorption band, may be written as Equation (I), where
Lib(T ) is the normal recoil-free fraction arising from lattice
vibrations andf,,,(T) accounts for the loss of the area under
the absorption band due to the local displacement of the iron
center during the dynamic process. The magnitude of the
dynamic displacements expected for the iron atom, f,,, , is
given by Equation (2), where k is the wavenumber of the
A,, = exp (- k Z (u2>,,,/3)
(2)
14.4 keV pray and ( u ' ) ~ , ,is the mean-square displacement
of the iron atom. The linear behavior of the Debye model
Angew. Chem. h i . Ed. Engl. 1992, 313No. 7
0
characteristic of organoiron compounds.[' At higher temperatures fvib(T)can be calculated from the straight lines in
~ be obtained
Figure 1. The values off,,,( T ) and (u ' ) ~ ,may
from Equations ( 3 ) and (2), in conjunction with the measured area under the absorption band and the calculated
fvib( T ) . The resulting root-mean-square iron displacements
the Fe-Ccarbony,
disat 280K are given in Table 1. In
tance is approximately 1.7 to 1.8 A, and hence the displacement of the iron atom observed at 280K represents about
15% of the bond length. If we assume similar Fe-Ccarbony,
lengths in 1 and 3, a very reasonable assumption, then the
corresponding values would be 6 and 20%, respectively. The
displacements of the iron atoms observed in 2 and 3 are far
larger than would be expected for a Berry pseudorotation
and strongly support the hypothesis of tunneling of the hydride ion between the faces of the tetrahedral or pseudotetrahedral [Fe(CO),] moiety. This was proposed earlier by Hanson and Whitmire[*] on the basis of their MAS 13C NMR
results. A similar "tetrahedral tunneling" mechanism was
proposed for the non-quantum mechanical tunneling of hydrido ligands without motion of the other ligands in several
octahedral dihydridoiron complexes with phosphorus ligands.["]
If we assume that the displacement of the iron atom is
induced by the hydride tunneling, the change of ( u ' ) ~ , ,with
temperature['81 is proportional to exp( - AEac,/kBT),
where
AE,,, is the activation energy for the displacement of the iron
atom and hence for the tunneling. The corresponding activation energies for 2 and 3, which were obtained from Figure 2,
are given in Table 1. The activation energy of 29.2 kJmol-'
for 2 is identical to the value determined from "C NMR
spectroscopy,[81but substantially smaller than those reported for the octahedral dihydroiron complexes.['71 The very
large observed displacement of the iron atom strongly supports a hydride tunneling in preference to the alternate Berry
pseudorotation"'] as the mechanism which exchanges the
axial and equatorial carbonyl ligands in the solid state. We
propose that, simultaneously with the tunneling of the hydrido ligand, the iron atom moves to one of the four apexes of
a smaller, perhaps distorted, tetrahedron imbedded within
the pseudotetrahedral environment of the carbonyl ligand.
For 2, the shape of the absorption bands gradually changes
from a narrow symmetric quadrupole doublet (85 K)[13]to a
broad absorption band (295 K),[l4I a broadening which can
VCH Verlagsgese1l.whufi mhH, W-6940 Weinheim, 1992
OS70-0833/92/0707-0885 S 3.50+ ,2510
885
-1
[I31 At 78K. the isomer shifts are -0.169, -0.365, and -0.165 m m s - ' , the
quadrupole splittings are 1.33, 1.38, and 1.33 mm s - ' , and the linewidths
are 0.24. 0.26, and 0.27 mm s - for 1, 2, and 3, respectively.
(141 At 295K. the isomer shifts are -0.256 and -0.240mms-', the quadrupole splittings are 1.14 and 0.72 mms-', and the linewidths are 0.27 and
1.3mms-' for 1 and 2. respectively. At 280K, the isomer shift is
-0.235 mms-', the quadrupole splitting is 0.74 mms-', and the
linewidth is 0.32 mms-' for 3.
[I51 M. B. Smith, R. Bau, .
I
A m . Chem. Soc. 1973, 95, 2388.
[16] R. Wordel, F. E. Wagner, J Less-Common Mer. 1987, 129, 27.
[17] P. Meakin, E. L. Muetterties, 5. P. Jesson, J. Am. Chem. SOC.1973, 95, 7 5 .
[I81 P. Raj, A. Sathyamoorthy, J. Less-Common Met. 1987, 129, 251.
(191 J. A. Tjon, M. Blume, Phy.7. Rev. 1968, 163, 456.
I201 R. B. King, Organometallic Syntheses, Vol. I, Academic Press, New York,
1965, p. 96.
-2
I
-3
In < u * = - ~ , ,
-4
-5
-6
-1
3
4
5
T-' [lo3x K-'l
-
6
Figure 2. The logarithm of the mean square displacement of the iron atoms
versus the reciprocal of the temperature for 3 (m) and 2 (0).
be attributed to the previously discussed dynamic process.
This behavior corresponds to a distinct increase in the symmetry of the electronic arrangement about the iron center,
presumably because the hydride tunneling averages the electric field gradient at the iron center to zero. Thus it is possible
to use the T j o n - B l ~ m e ~model
' ~ l to fit the observed broadening of the absorption bands in the Mossbauer spectrum. The
logarithm of the resulting rate of the dynamic process, versus
the inverse temperature, gives an activation energy of
27 +_ 3 kJmol-' for 2. This value agrees rather well with the
29 kJ mol- ' obtained above, especially when one considers
that the values are obtained in a completely different fashion. We are currently studying other salts of [HFe(CO),]- in
an effort to understand the way in which different cations
influence the tunneling process. Furthermore inelastic neutron scattering experiments with deuterated [HFe(CO),]are planned.
Experimental Procedure
Compounds 1, 2, and 3 have been prepared by modifications of previously
published procedures. [S, 201 The Mossbauer spectra were recorded as described earlier and the isomer shifts are reported relative to a-iron foil at room
temperature. [Ill
Received: January 14, 1992 [Z 5118 IE]
German version: Angew. Chem. 1992, 104, 891
CAS Registry numbers:
1, 56791-54-9; 2, 25879-01-0; 3, 63814-56-2; [HFe(CO),]-, 18716-80-8
(11 P. Meakin, E. L. Muetterties, J. P. Jesson. J. A m . Chem. SOC.1972, 94,
5271.
[2] P. Meakin, J. P. Jesson, E N. Tebbe, E. L. Muetterties, 1 Am. Chem. Sot.
1971, 93, 1797.
[3] J. P. Jesson, P. Meakin, J. Am. Chem. Soc. 1973, 95, 1344.
[4] S. Aime in The Time Domain in Sucface and Structural Dynamics (Eds.:
G. J. Long, F. Grandjean), Kluwer, Dordrecht, 1988, pp. 65-80.
[S] H. W. Spiess, R. Grosescu, U. Haeberlen. Chem. Phys. 1974, 6 , 226.
[6] H. Dorn, B. E. Hanson, E. Motell, Inorg. Chim. Acta 1981, 54; L71.
[7] B. E. Hanson, E. C. Lisic, J. T. Petty, G. A. Iannaconne, Inorg. Chem.
1986, 25,4062.
[XI B. E. Hanson, K. H. Whitmire, 1 Am. Chem. Sot. 1990, 112, 974.
191 E Grandjean in The Time Domain in Surface und Structurul Dynamics,
(Eds.: G. J. Long, F. Grandjean), Kluwer, Dordrecht, 1988, p. 287.
[lo] R. D. Ernst, D. R. Wilson, R. H. Herber, J. Am. Chem. SOC.1984, 106,
1646; R. H. Herber in Chemicul Mossbauer Spectroscopy (Ed.: R. H. Herber), Plenum, New York, 1984, pp. 199.
[I 11 F. Grandjean, G. J. Long, C. G. Benson, U. Russo. Inurg. Chem. 1988.27,
1524.
[I21 R. S. Berry, J. Chem. Phys. 1960, 32, 933.
886
8
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Molecular Modeling of the Class I Human
Histocompatibility Molecule HLA-A2 Presenting
an Allele-Specific Nonapeptide from Influenza
Matrix Protein**
By Norbert Zimmermann, Oiaf Rotzschke, Kirsten Falk,
Didier Rognan, Gerd Folkers, Hans-Georg Rammensee,
and Gunther Jung*
Dedicated to Professor Dietrich Brandenburg
on the occasion of his 60th birthday
MHC Class I proteins (Major Histocompatibility Complex) are found on the surface of most human cells. In the
immune system their function is to present fragments of
proteins of the inside of the cell in an antigen binding pocket
to the killer cell receptor. Fragments of endogenous proteins
(self peptides) are processed and presented when the cell is
healthy. If the cell is attacked by viruses, the cytotoxic Tlymphocytes (CTLs or killer cells) recognize the fragments of
foreign viral proteins (CTL epitopes) in the MHC antigen
binding pocket and destroy the affected cell. The X-ray crystal structure analysis of the human class I histocompatibility
antigen HLA-A2''] shows an antigen binding site composed
of two parallel a-helical domains a l and a 2 , which are connected with a central antiparallel P-sheet. This forms a deep
groove with six prominent pockets, the function of which is
thought to be the binding of amino acid side chains of antigenic peptides. Furthermore, the residual electron density
found in the peptide binding cleft IS assumed to be a mixture
of peptides cocrystallized with HLA-A2.
Recently, we found allele-specific oligopeptide motifs by
sequencing of self-peptides eluted from MHC I proteins.'']
Alignment of viral proteins with the dominant hydrophobic
anchor residues at positions 2, 6, and 9 of the HLA-A2
self-peptides suggested that the nonapeptide GILGFVFTL
(from influenza matrix protein) was a candidate for a naturally processed antigenic peptide (Table 1). This nonapeptide
was used to model a MHC peptide complex based on the
[*I Prof. Dr. G. Jung, Dip1.-Chem. N. Zimmermann
Institut fur Organische Chemie der Universitat
Auf der Morgenstelle 18, D-W-7400 Tiibingen (FRG)
0. Rotzschke, K. Falk, Priv.-Doz. Dr. H.-G. Rammensee
Max-Planck-Institut fur Biologie, Abteilung Immungenetik
Corrensstrasse 42, D-W-7400 Tiibingen (FRG)
Dr. D. Rognan, Prof. Dr. G. Folkers
Department Pharmazie der Eidgenossischen Technischen Hochschule,
ETH-Zentrum
Clausiusstrasse 25, CH-8092 Zurich (Switzerland)
[**I This work was supported by the Deutsche Forschungsgemeinschaft (SFB
323 and 120).
0570-0833J92/0707-0886 $3.50+.25/0
Angew. Chem. Ini. Ed. Engl. 1992, 31, N o . 7
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