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ESCA Investigations of Bis(arene)chromium Complexes.

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Table 1 Ethyl 2-alkylthio-2-oxazoline-4-carboxylates( 2 ) and ethyl cc-(N-alky1thiocarbonylamlno)acrylates( 5 )
synthesized
15)
(2)
R'
R'
(c)
CH,
CH,
CH,
CH,
-(CHJ4-
(d)
-(CH,),-
iu)
(h)
(e)
[a]
[b]
[c]
[d]
[el
[fl
H
H
ChH,
C,H,
R3
CH,
CH2ChH5
CH2CH=CH2
CH2C6H,
CH,
CH,
X
Yield
"701
I
Br
65 [a. CJ
77 [b, c]
71 [a, c]
78 [d, e]
98 [ a , q
56 [el
Br
Br
I
I
B.p. ["C/torr]
Yield
M p.["C]
(&/trans)
["/.I
(EIZ)
47 [d]
80 [d]
47 [dJ
70 [el
82 [d]
98 [f]
77-77.5
91.0 -91.5
61
76.5- 77.0
( I :3.0)
( I : 3.3)
83-86/05
130-1 3510.05
120-125/0.1
-
(1:23)
(<5:100)
With potassium rert-butoxide.
With sodium hydride.
After purification by distillation.
After purification by recrystallization.
After purification by chromatography
Crude product.
Ethyl 2-( N-benzylthiocurbonylamino)-P,P-dimethy[acrylut~
(5b):
( 2 b ) (5.8g, 20mmol) was added dropwise to potassium
terr-butoxide (3.4 g, 30mmol) in anhydrous tetrahydrofuran (30ml) under nitrogen with stirring at -60°C. After
30min acetic anhydride was squirted in and the cooling
bath removed. The product was worked up as for ( 2 b )
but with diethyl ether (l00ml) as solvent to give 5.4g
(93Yo)ofcrude ( 5 b ) (white needles). Recrystallization from
light petroleum (%60T)/ether
(2 : 1) furnished 4.6g
(80%) of (Sb).-IR
(KBr): 3230 (NH), 1720 and 1630
(C=O), 1500 (amide II), and 1640 cm- (C=C).-'HNMR (CDC13): r=3.2 (s, NH), 7.85 and 8.15 (both s,
CH3).
( / a ) , counter ion [B(C61&J4]( / h ) , counter ion [PF6]-
( h i , counter ion [f3(c6H5)4](?h), counter ion [PF&
G
P
'
Cr
Cf
Cr
Received: May 7, 1973 [Z X37b IE]
German version' Angew. Chem. XS. 660 (1973)
[ I ] D. H o p p e , Angew. Chem. 84, 956 (1972): Angew. Chem. internat.
Edit. 11, 933 (1972).
[2] D. H n p p r , Angew. Chern. 85, 659 (1973); Angew. Chem. internat.
Edit. 12,656 (1973).
[3] To be regarded as electrocyclic ring cleavage of a "cyclopentenyl
anion" to give a "pentddienyl anion": see U . Schellkopf, F . G i d u r t ,
R . Schriidrr, and D. H o p p r , Liebigs Ann. Chem. 766, 116 (1972).
[4] For a review see E . Schrdder and K . Liibkr- The Peptides. Academic
Press, New York 1965, Vol. 1. p. 41
ESCA Investigations of Bis(arene)chromium
Complexes
By Herbert Binder and Ch. Elschenbr~ich[*~
He(1) photoelectron spectra have been reported for symmetrical and unsymmetrical bis(arene)chromiumcomplexes['],
but there have been no previous measurements of the
corresponding X-ray photoelectron (ESCA) spectra[']
which could provide valuable information about the intramolecular charge distribution. We now report ESCA investigations [measurements were performed on an A.E.I. ES100 photoelectron spectrometer, Al-Kxl .2 radiation ( 1486.6
eV)] for the n-complexes ( 1 )-(5).
Chemical shifts F EBcan be determined from the measured
electron-binding energies EB and from the former it is
[*] Dr. H. Binder
Institut fur Anorganische Chemie der Universitat
7 Stuttgart 80, Pfaffenwaldring 55 (Germany)
Dr. Ch. Elschenbroich
Physikalisch-chemisches lnstitut der Universitiit
CH-4056 Basel, Klingelbergstrasse 80 (Switzerland)
Angrw. Chrm. inrrrnur. Edit. 1 Vo1. I2 ( 1 9 7 3 ) 1 No. X
possible in principle to describe the electronic environments of atoms in the molecules. We were especially interested in the charge distribution between the central metal
and aromatic ligands as a function of ring size. The complexes ( 1 ) - ( S ) , however, yield only one, unstructured
line(line width 1.7eV)for the CIS 1evel.Clearly the n-bonded
ligands C,H, ( n= 5, 6, or 7) differ in 6 E, by an amount
less than 0.5 eV, from which the limit for the difference
inchargeson theligandsC5H5and C 7 H 7can be estimated:
since a whole positive charge localized on a C atom leads
to a shift 6EB of L'U. 5 eV for the CIS level1"I, complete
charge separation (C5H5)*-Cr(C7H7)6+
(6= I ) would, it
is to be expected, lead to a difference of about 1.7 eV
between the CIS binding energies for the ligands cyclopentadienyl (6 E , (C1s)= - 5/5 = - 1.O eV) and cycloheptatrienyl(6 ER= 5/7 = 0.7 eV). The fact that for ( 5 ) these
C1 s binding energies differ by < 0.5 eV indicates that 6 < 1/3.
Thus the charge distribution between the ligands in unsymmetrical sandwich complexes of chromium is largely equalized, which accords with the low dipole moment of 0.8
DI5] and with 'H-NMR results161.
Table 1 contains the EB values for the CrZpl J 3 2 p 3
(spin orbit doublet) and for the Cr3p and Cr3s levels
as well as the line widths for Cr2p3,2 and the observed
Cr3s multiplet ~ p l i t t i n g s [ ~Since
. ~ ! theC Is binding energies
for the complexes ( 1 )-( 5 ) are equal within experimental
error, the total charges on the complexes show the Cr
binding energies to be divisible into two groups ( I )-( 2 )
and (3)-(5). This confirms previous ESR findings[']
according to which one electron is removed from an M O
+
+
659
with predominant Cr3d character in the transition
(arene)*Cro+[(arene)zCr’] f
Table 1. Electron binding energies EB [a] for the complexes 1 l ) - ( S )
unpaired electrons of ( 1 )-(3) (which have predominant
Cr3d,2 characterC91)depends on the size of the exchange
integral between 3d,2 and 3s, since the spin density of
a d orbital can be transferred to the Cr nuclear position
only by polarization of the inner s shells.
Received: April 13, 1973 [ Z 845 IE]
German version: Angew. Chem. 85, 665 (1973)
Linewidth
586.7
586.2
511.1
577.1
2.5
1.7
19.0
76.8
46.6
2.2
46.5
19.5
2.3
11.2
586.8
585.5
584.8
585.3
511.3
516.3
575.1
576.0
1.8
1.7
1.5
-
-
-
16.9
16.1
77.1
-
1
.-
-
45.4
45.4
45.7
44.8 [lo]
[a] Referred to E,(Cls)= 286.6 eV [ 3 ] .
[b] Decomposition during measurement (binding energies and multiplet
splitting identical with those for CrF, [S]).
[l] S. Evans, 3. C . Green, and S. E . Jackson, J. C. S. Faraday I1 1972,
249.
[ 2 ] C . Nordling, Angew. Chem. 84, 144 (1972); Angew. Chem. internat.
Edit. I I . 83 (1972).
[31 R. Gkiter, R . Seeger, H . Binder, E. Fluck, and M . Cais, Angew.
Chem. 84, 1107 (1972); Angew. Chem. internat. Edit. 1 1 , 1028 (1972).
[4] G . A . Oloh, G . D. Mateescu, L. A. Wilson, and M . H. Gross, J.
Amer. Chem. SOC.92, 7231 (1970).
[5] E . 0. Fischer and S. Brritschafi, Angew. Chem. 75,94 (1963): Angew.
Chem. internat. Edit. 2, 44 (1963).
[6] R. D. Fischer, 2. Naturforsch. IBu, 1373 (1963).
[7] C . S. Fadley in D. A . Shirley. Electron Spectroscopy. North Holland,
Amsterdam 1972, p. 781.
[S] J . C . Carcrr, G . K . Schwritzer, and 7: A. Carlson, J. Chem. Phys.
57, 973 (1972).
[9] R . Prrns and F. J . Reinders, Chem. Phys. Lett. 3, 45 (1969).
[lo] D. N . Hmdrickson, J . M . Hollander, and
If the Cr binding energies shown in Table 1 are compared
with the corresponding value for Cr metal (reduced)[’O]
and with the results of CarIson et d.[81
for a series of
Cr compounds, it is evident that the Cr atom carries
a partial positive charge in the z-complexes (1 )-(5).
Thus the central atom is the positive end of the bonding
dipole metal-aromatic ligand also in the neutral complexes
(3)-(5). The acceptor character (Cr3d+CnH,, x*) of
the ligands is greater than their donor character (Cr3d,
4s+C,H,, n). The same result is derived from recent
semiempirical” ‘1 and ab-inifid”l MO calculations. For
the two isoelectronic complexes ( 4 ) and ( 5 ) the larger
EB(Cr)value of ( 5 ) indicates more pronounced x*-acceptor
properties for the unsymmetrical ligand combination xC,H, I x-C,H, than for the symmetrical combination nC~H~JX-C~H~.
It can further be recognized from the Cr binding energies
( 2 ~ , , ~ , 3s, 3p) that (3) belongs unambiguously to
thegroup ofCro complexes in respect to the intramolecular
charge distribution although it can be formally described
as a Cr1(d5)complex.
Removing a 3s electron from a paramagnetic molecule
leads to conditions of various spin multiplicities which
differ in energy (multiplet splitting) according to the different values of the exchange integral.
Table 2. Comparison of ESR and ESCA data for the complexes /1/--131.
U(’TI)
[GI
AE(Cr3s-3d) [eV]
EdCr2p ,!d[eV]
(2)
(11
(31
19.0
2.3
586.8
18.1
2.2
586.7
14.7
<1
585.5
In Table 2 the ESR hyperfine coupling constants[’31a(53Cr)
and the binding energies &(Cr2plp) are compared with
the ESCA multiplet splittings AE(Cr3s-3d). Both the ESR
coupling constants and the ESCA multiplet splittings decrease with decreasing charge on the central atom, which
corresponds to increasing delocalization of the unpaired
Cr3d,z electron. A correlation of this type between
AE(Cr3s-3d) and u ( ~ ~ appears
C ~ ) reasonable, if one considers that the isotropic hyperfine interaction of the
660
W L. Joliy, Inorg. Chem.
9, 612 (1970).
[ I I] S. E. Anderson and R . S . Drago, Inorg. Chem. 1 1 , 1564 (1912).
“21 M . M . CoutiPre, J . Demuinrk, and A. Veillard, Theor. Chim. Acta
27, 281 (1972).
[13] Ch. Elsrhenhroich and F . Gerson, J. Organornetal. Chem. 49, 445
(1913).
Cycloadditions of Benzvalene
By Manfred Christl[*]
Olefins having a strained double bond display a
pronounced reactivity in numerous cycloadditions. The
Diels-Alder additions“. and 1,3-dipolar cycloaddition~[~]
of norbornene ( 1 ) may be cited as examples. Steric conditions similar to those in ( I ) prevail in benzvalene14],presumably with even greater strain. (2) should therefore exhibit
comparable dipolarophilic and dienophilic activity. The
question then arises: How does the bicyclobutane system
behave?
Dissolution of the stable 2,4,6-trimethylbenzonitrile
in an ethereal solution of (2) afforded 98% of
colorless ( 3 a ) , m.p. 101-103”C[6], after 15 h at room
temperature. Structural information was provided by the
‘H-NMR spectrum (Table 1) in which the absorptions
of the mesityl group are accompanied by the characteristic
signals of the protons in positions 1 and 6 of the 2-isoxazoline system[’] and a four-proton multiplet. The absence
of signals due to olefinic protons suggests that the bicyclobutane system remains intact.
Reaction of benzonitrile oxide with (2) by the in-situ
gave 88% of ( 3 b ) (m.p. 106-108°C; NMR,
see Table 1).
[*] Dr. M . Christ1
Institut fur Organische Chemie der Universitat
8 Munchen 2, Karlstrasse 23 (Germany)
Anqew. Chem. internat. Edit. 1 Vol. 12 (1973) ,! No. 8
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