Metal π complexes of benzene derivatives. Germanium in the periphery of bis (benzene) vanadium and bis(benzene)chromium. Synthesis and structure of new heterametallocyclophanes

Article abstract of DOI:10.1021/om970249y

Mono- and digerma[n]metallocyclophanes (n = 1, 2) [(η⁶,η⁶-dimethyldiphenylgermane)M] (M = Cr, 17; V, 18^?), [(η⁶,η^6′-tetraphenylgermane)M] (M = Cr, 20; V, 21^?), and [(1,1,2,2-tetramethyl-1,2-di-η⁶,η ^6′-phenyldigermane)Cr] (24) were synthesized by means of lithiation and subsequent reaction with dichlorodimethylgermane or dichlorodiphenylgermane. Metal - ligand cocondensation of bromodimethylphenylgermane with chromium atoms followed by reductive coupling with lithium naphthalide gave the digermane complex 24. Additionally, the nonbridged derivatives [bis(trimethylgermyl-η⁶-benzene)M] (M = Cr, 10d; V, 11^?), [(trimethylgermyl-η⁶-benzene)(η⁶-benzene)Cr] (10m), and [bis(triphenylgermyl-η⁶-benzene)M] (M = Cr, 14; V, 15^?) were prepared and characterized by ¹H- and ¹³C-NMR (10m, 10d, 14, 17, 20), cyclic voltammetry (CV) (10d, 11^?14, 15^?, 18 ^?, 21^?, 24), and EPR spectroscopy (10d^?+, 11^?, 14^?+, 15^?, 18^?, 21^?, 24^?+). Crystals of 20 were subjected to a structure determination by X-ray diffraction, which disclosed a bending of the sandwich axis from linearity by 14.4°. The strain exerted on the coordinated benzene ring forces a pyramidal structure on the ipso-C leading to a markedly shielded ¹³C-NMR resonance. An EPR spectroscopic investigation of the vanadium derivatives reveals an increasing metal to ligand spin delocalization and the appearance of orthorhombic g and A tensors on bending the sandwich axis. While the redox potentials are virtually unaffected, when passing from the unstrained vanadium complexes 11^? and 15^? to the germa[1]vanadocyclophanes 18^? and 21^?, the transient monocationic species of the latter are destabilized dramatically. No evidence of ring-opening polymerization was observed on heating 18^? to 165°C. Instead, metal-ligand cleavage occurs.

Full text of DOI:10.1021/om970249y

Organometallics 1997, 16, 4589-4596
4589
Meta l π Com p lexes of Ben zen e Der iva tives. Ger m a n iu m
in th e P er ip h er y of Bis(ben zen e)va n a d iu m a n d
Bis(ben zen e)ch r om iu m . Syn th esis a n d Str u ctu r e of New
Heter a m eta llocyclop h a n es†,1
Christoph Elschenbroich,* Eckhardt Schmidt, Rolf Gondrum, Bernhard Metz,
Olaf Burghaus, Werner Massa, and S. Wocadlo
Fachbereich Chemie der Philipps-Universita¨t, D-35032 Marburg, Germany
Received March 24, 1997X
Mono- and digerma[n]metallocyclophanes (n ) 1, 2) [(η6,η6′-dimethyldiphenylgermane)M]
(M ) Cr, 17; V, 18•), [(η6,η6′-tetraphenylgermane)M] (M ) Cr, 20; V, 21•), and [(1,1,2,2-
tetramethyl-1,2-di-η6,η6′-phenyldigermane)Cr] (24) were synthesized by means of lithiation
and subsequent reaction with dichlorodimethylgermane or dichlorodiphenylgermane. Metal-
ligand cocondensation of bromodimethylphenylgermane with chromium atoms followed by
reductive coupling with lithium naphthalide gave the digermane complex 24. Additionally,
the nonbridged derivatives [bis(trimethylgermyl-η6-benzene)M] (M ) Cr, 10d ; V, 11•),
[(trimethylgermyl-η6-benzene)(η6-benzene)Cr] (10m ), and [bis(triphenylgermyl-η6-benzene)M]
1
(M ) Cr, 14; V, 15•) were prepared and characterized by H- and 13C-NMR (10m , 10d , 14,
17, 20), cyclic voltammetry (CV) (10d , 11•, 14, 15•, 18•, 21•, 24), and EPR spectroscopy (10d •+
,
11•, 14•+, 15•, 18•, 21•, 24•+). Crystals of 20 were subjected to a structure determination by
X-ray diffraction, which disclosed a bending of the sandwich axis from linearity by 14.4°.
The strain exerted on the coordinated benzene ring forces a pyramidal structure on the ipso-C
leading to a markedly shielded 13C-NMR resonance. An EPR spectroscopic investigation of
the vanadium derivatives reveals an increasing metal to ligand spin delocalization and the
appearance of orthorhombic g and A tensors on bending the sandwich axis. While the redox
potentials are virtually unaffected, when passing from the unstrained vanadium complexes
11• and 15• to the germa[1]vanadocyclophanes 18• and 21•, the transient monocationic species
of the latter are destabilized dramatically. No evidence of ring-opening polymerization was
observed on heating 18• to 165 °C. Instead, metal-ligand cleavage occurs.
In tr od u ction
Attachment of short interannular bridges to bis(η6-
arene)metal units leads to heterametallocyclophanes, a
class of molecules which lends itself to the study of the
influence exerted by distortion of the sandwich unit on
chemical and spectroscopic properties. Whereas ex-
amples featuring one-atom carbon bridges have not as
yet been forthcoming, the larger covalent radii of Si and
Zr allowed the synthesis of the hetera[1]metallo-
prepared a variety of derivatives of bis(benzene)chro-
mium (7) and bis(benzene)vanadium (8•) which bear
substituents bonded to the η6-arene via a group 14
element (C, Si, Ge, Sn, Pb).6 Here we report on new
organogermyl arene complexes of V and Cr and compare
their properties with those of the silicon analogues.
Since the redox potentials E1/2 and hyperfine coupling
constants a(51V) are highly sensitive to changes in the
ligand periphery, even small differences in the covalent
radii (Si 1.17, Ge 1.22 Å) and the attendant changes in
C-E bond lengths and angles of tilt may trigger
measurable responses. Furthermore, the decrease in
bond strength (C-Si 301, C-Ge 237 kJ mol-1) may have
the effect that rupture of the interannular link occurs
at lower temperatures for >GeR2, compared to >SiR2
bridges. This could possibly lead to thermal ring-
cyclophanes 1• ,2 2•,3 3,3,4 4,3 5•,5 and 6.5
Conspicuous features of these strained sandwich
complexes include the ease of protodesilylation and,
compared to the unsubstituted parent molecules, the
anodic shifts of the redox potentials as well as the
increase in metal f ligand spin delocalization effected
by bending of the bis(arene)metal unit.3 We have
† Dedicated to Professor Gottfried Huttner on the occasion of his
60th birthday.
X Abstract published in Advance ACS Abstracts, September 1, 1997.
(1) Metal π Complexes of Benzene Derivatives. 51. Part 50: Elschen-
broich, Ch.; Ku¨hlkamp, P.; Koch, J .; Behrendt, A. Chem. Ber. 1996,
129, 871.
(2) Hurley, J . Ph.D. Thesis, Philipps-Universita¨t, Marburg, Ger-
many, 1989.
(3) Elschenbroich, Ch.; Hurley, J .; Metz, B.; Massa, W.; Baum, G.
Organometallics 1990, 9, 889.
(4) Hultzsch, K. C.; Nelson, J . M.; Lough, A. J .; Manners, I.
Organometallics 1995, 14, 5496.
(5) Elschenbroich, Ch.; Schmidt, E.; Metz, B.; Harms, K. Organo-
metallics 1995, 14, 4043.
(6) Schmidt, E. Diplomarbeit, Philipps-Universita¨t, Marburg, Ger-
many, 1988; Doktorarbeit, Philipps-Universita¨t, Marburg, Germany,
1991.
S0276-7333(97)00249-5 CCC: $14.00 © 1997 American Chemical Society

4590 Organometallics, Vol. 16, No. 21, 1997
Elschenbroich et al.
Sch em e 1
opening polymerization for the >GeR2 derivatives,7 a
process which failed for the >SiR2 analogues 3 and 4.4
In order to test whether the new germa[1]metallo-
cyclophanes can be converted into bis(arene)metal
backbone polymers, the thermal behavior of 18• was
checked. Whereas the ferrocene analogue [(η5-C5H4)2-
GeMe2]Fe was reported to undergo rapid thermal ring-
opening polymerization when heated in the melt7, [(η6-
C6H5)2GeMe2]V (18•) decomposes at 160-165 °C prior
to melting. If the thermolysis is carried out in an
evacuated tube, a black solid residue and a metallic
mirror form at the bottom of the tube; droplets of a pale
yellow liquid collect at cooler, upper sections. The
condensate contains the free ligand Ph2GeMe2, identi-
fied by means of mass spectrometry.
Resu lts a n d Discu ssion
The new organogermyl derivatives 10, 11•, 14, 15•,
17, 18•, 20, 21•, 23, and 24 were prepared as shown in
Scheme 1. They are air- and moisture-sensitive, the
maximum of sensitivity being displayed by compounds
17 and 18•. However, in the unstrained species pro-
tolytic cleavage of the C(η-arene)-Ge bonds occurs less
readily than in the corresponding organosilyl deriva-
tives: the organogermyl complexes 10 and 14 can be
subjected to the purification cycle: (complex)0 (+O2) f
(complex)+ (+Na2S2O4/NaOH) f (complex)0. Under
these conditions quantitative desilylation would take
place.
Crystals suitable for an X-ray structural analysis
were obtained for complex 20. In view of the importance
of the structural data for further discussion, they will
be presented first.
Molecu la r Geom etr y of [(C6H5)2Ge(η6-C6H5)2]Cr
(20). An ORTEP drawing of the structure of 20 in the
(7) Foucher, D. A.; Edwards, M.; Burrow, R. A.; Lough, A. J .;
Manners, I., Organometallics 1994, 13, 4959.
(8) Elschenbroich, Ch. J . Organomet. Chem. 1970, 22, 677.

Metal π Complexes of Benzene Derivatives
Organometallics, Vol. 16, No. 21, 1997 4591
This is a consequence of the larger inter-arene distance
in bis(benzene)vanadium (3.32 Å10 ) compared to that
in bis(benzene)chromium (3.22 Å11). Marked differences
are, however, observed in the geometry of the bridges
>EPh2 (E ) Si, Ge): the angle C1-E-C1′ is more acute
for E ) Ge (91.8(2)°) than for E ) Si (96.0(2)° 3). A
similar gradation has been observed for the couple
[Me2E(η6-C5H4)2]Fe, E ) Si, Ge.7
In concordance with equal tilting angles for 20 and
4, the angle between the E-C1 (or F-C1′) bond axis
and the respective η6-arene decreases by 2.1° upon the
change from E ) Si (40.8(2)°) to E ) Ge (38.7(2)°). The
distance Cr‚‚‚E between the central metal atom and the
group 14 element in the interannular bridge slightly
increases from 2.842(2) Å (E ) Si, 43) to 2.958(1) Å (E
) Ge, 20).
Nu clea r Ma gn etic Reson a n ce. The NMR data for
the new organogermylarene complexes reported here
closely resemble those for the organosilyl analogues3 and
therefore do not need extensive discussion. Attention
should, however, be drawn to the most characteristic
feature, which consists in the extremely large coordina-
tion shift ∆δ(13C) experienced by the ipso-C resonance
in the germa[1]chromocyclophane 20. As depicted in
Scheme 2, the upfield shift caused by the bending
distortion at the carbon atoms which are involved in the
interannular bridge is comparable in magnitude to the
shift brought about by metal coordination. This phe-
nomenon has been traced to a change in carbon hybrid-
ization from sp2 toward sp3.3,7,12
F igu r e 1. Molecular structure of compound 20 in the
crystal. Ellipsoids are drawn at the 50% level.
Ta ble 1. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) in [(C6H5)2Ge(η6-C6H5)2]Cr (20)
Cr-C1
2.130(3)
2.160(3)
2.163(4)
2.122(3)
2.159(4)
2.156(4)
1.974(3)
1.968(3)
1.432(5)
1.407(5)
1.406(5)
1.388(5)
1.374(5)
1.375(5)
1.420(5)
1.416(5)
1.404(5)
1.393(5)
1.385(5)
1.370(5)
Cr-C2
2.126(3)
2.179(4)
2.127(4)
2.126(3)
2.167(4)
2.127(3)
1.941(3)
1.944(3)
1.418(5)
1.398(5)
1.419(5)
1.401(5)
1.380(5)
1.381(5)
1.427(5)
1.389(5)
1.410(5)
1.376(5)
1.371(5)
1.376(5)
Cr-C3
Cr-C4
Cr-C5
Cr-C6
Cr-C1′
Cr-C3′
Cr-C5′
Ge-C1
Cr-C2′
Cr-C4′
Cr-C6′
Ge-C7
Ge-C1′
C1-C2
C2-C3
C4-C5
C7-C12
C8-C9
C10-C11
C1′-C2′
C2′-C3′
C4′-C5′
C7′-C12′
C8′-C9′
C10′-C11′
Ge-C7′
C1-C6
C3-C4
C5-C6
C7-C8
C9-C10
C11-C12
C1′-C6′
C3′-C4′
C5′-C6′
C7′-C8′
C9′-C10′
C11′-C12′
Electr on P a r a m a gn etic Reson a n ce. The influ-
ence tilting exerts on the EPR properties of bis(arene)-
metal radicals has concerned us before3,13 because an
analysis of the g tensor may help to describe the
structure of paramagnetic sandwich complexes in cases
where NMR and X-ray diffraction data are unavailable.
Furthermore, it furnishes information on the extent of
metal-ligand spin delocalization thereby providing
hints at the electronic structure. EPR spectra of the
vanadium complexes are depicted in Figure 2 (11•, 18•),
and the EPR parameters for these neutral species,
together with those for the chromium-containing radical
cations 10d •+, 14•+, and 24•+, are collected in Table 2.
The interannularly bridged radical cations 17•+ and 20•+
are inaccessible (vide infra). Inspection of the data
reveals that, as in the case of peripheral substitution
C1-Ge-C1′
C1-Ge-C7′
C1′-Ge-C7′
Ge-C1-C2
Ge-C1-C6
C2-C1-C6
C1-C2-C3
C2-C3-C4
C3-C4-C5
C4-C5-C6
C1-C6-C5
Ge-C7-C8
Ge-C7-C12
C8-C7-C12
C7-C8-C9
C8-C9-C10
C10-C11-C12
C7-C12-C11
91.79(14)
113.3(2)
114.86(14)
113.7(2)
115.1(2)
116.8(3)
121.2(3)
120.9(3)
119.2(3)
120.2(3)
121.5(3)
121.0(3)
121.3(3)
117.7(3)
120.9(3)
120.2(3)
119.9(3)
121.3(3)
C1-Ge-C7
112.75(14)
111.3(2)
111.48(14)
114.6(2)
115.1(2)
116.7(3)
121.5(3)
120.4(3)
119.7(4)
120.2(3)
121.4(3)
121.8(3)
120.5(3)
117.6(3)
121.1(3)
120.0(4)
119.6(4)
121.6(3)
C1′-Ge-C7
C7-Ge-C7′
Ge-C1′-C2′
Ge-C1′-C6′
C2′-C1′-C6′
C1′-C2′-C3′
C2′-C3′-C4′
C3′-C4′-C5′
C4′-C5′-C6′
C1′-C6′-C5′
Ge-C7′-C8′
Ge-G7′-C12′
C8′-C7′-C12′
C7′-C8′-C9′
C8′-C9′-C10′
C10′-C11′-C12′
C7′-C12′-C11′
by R3Si groups,3 for the unstrained species 10d •+, 14•+
,
(9) Elschenbroich, Ch.; Bretschneider-Hurley, A.; Hurley, J .; Be-
hrendt, A.; Massa, W.; Wocadlo, S.; Reijerse, E. Inorg. Chem. 1995,
34, 743.
crystal is shown in Figure 1, and bond lengths and bond
angles are collected in Table 1. As expected, the
structure of 20 mimics that of the silicon analogue 4.
Yet, it is interesting to explore to what extent the
increase in covalent radius from Si to Ge translates into
structural parameters of the complexes. Slippage is
virtually absent in 20 since the perpendicular projection
of the chromium atom on the ring least-squares planes
deviates from the ring centers by less than 0.05 Å.
Surprisingly, the tilting of the η6-arene ligands is
unaffected by exchanging Si for Ge in the interannular
bridge in that, for both complexes 43 and 20, the
sandwich axis is bent by 14.4(2)°. This contrasts with
the increase in tilting angle from 14.4(2)° to 19.9(1)° 9
upon change of the central metal atom from chromium
to vanadium, retaining the heteroatom Si in the bridge.
(10) Fischer, E. O.; Fritz, H. P.; Manchot, J .; Priebe, E.; Schneider,
R. Chem. Ber. 1963, 96, 1418.
(11) Haaland, A. Acta Chem. Scand. 1965, 19, 41. Keulen, E.;
J ellinek, F. J . Organomet. Chem. 1966, 5, 490.
(12) Osborne, A. G.; Whiteley, R. H.; Meads, R. A. J . Organomet.
Chem. 1980, 193, 345.
(13) Elschenbroich, Ch.; Schneider, J .; Prinzbach, H.; Fessner, W.
D. Organometallics 1986, 5, 2091.
(14) The presence of an interannular bridge in 24+ cannot be
inferred with confidence from g and hyperfine data since they do not
differ sufficiently. It is, however, proven by the different extents to
which the lines in the high-field 53Cr satellite spectra are broadened,
relative to those at low field. Since this mI(53Cr) dependent broadening
correlates with the rate of tumbling in solution and thereby the
effective molecular volume, the fact that the low-field/high-field ratio
of spectral amplitudes equals 2.26 for 24•+ and 2.61 for the “open”
complex 10•+ attests to the presence of an interannular link in 24•+
(15) Elschenbroich, Ch.; Bilger, E.; Metz, B. Organometallics 1991,
10, 2823.
.
(16) Lepeska, B.; Chvalovsky, V. Collect. Czech. Chem. Commun.
1970, 35, 261.

4592 Organometallics, Vol. 16, No. 21, 1997
Elschenbroich et al.
F igu r e 2. EPR spectra of the methylgermyl derivatives 11• and 18• in toluene. A: Fluid solution, 295 K. B: Rigid solution,
140 K. C: Simulation.
Sch em e 2
11•, and 15• an electronic effect of R3Ge groups on the
EPR spectra is hardly noticeable. However, the intro-
duction of an interannular bridge >GeR2 results in a
change of the g and A(51V) tensors from effectively axial
to rhombic. The differences between the parameters for
the perpendicular orientation (indexes 1 and 2 in Table
2) are larger for Ge, as compared to Si as a member of
the interannular link. In fact, in the case of 2• these
differences were too small to be resolved. Since the tilt
of the sandwich units is virtually unaffected by a
substitution of Si by Ge and the distance between the
central atom and the heteroatom in the bridge actually
increases (compare the structural data for 4 and 20),
one is forced to conclude that it is the nature of the
bridging atom which governs the magnitude of the
perturbation, reflected in the rhombicity of g and A
(51V). While the distances M‚‚‚E (M ) Cr, V; E ) Si,
Ge) in the tilted complexes under investigation certainly
exceed those appropriate for regular covalent bonds, a
value of 2.45 Å being derived from atomic radii, weak
dative interactions may still be operative. Interactions
of this kind have been postulated for the related series
of [1]germaferrocenophanes based on Mo¨ssbauer spec-
troscopic results.7 In the case of the radicals 18• and
21• the differentiation between the two equatorial
components may be traced to a small contribution by
the heteroatom E which raises the degeneracy in the x,
y plane. This effect should be more pronounced for E
) Ge than for E ) Si, bearing in mind that the spin-
orbit coupling constant λ(Ge) exceeds the value λ(Si) by

Metal π Complexes of Benzene Derivatives
Organometallics, Vol. 16, No. 21, 1997 4593
Ta ble 2. EP R Da ta for th e Com p lexes 2•, 7•+, 8•, 10d •+, 11•, 14•+, 15•, 18•, 21•, 24•+, a n d 25•
8• a,c
11• a,f
18• a,f
15• a,f
21• a,f
25•
2•
7•+ b,c
10d •+ b
24•+ b
14•+ b
giso
g1
g2[g ]
g3[g|]
1.9860c
1.9853
1.9872
1.9780
1.9821
2.0014
1.9872
5.611
1.9858
1.9859
1.9765
1.9806
2.0000
1.9857
5.636
1.9864
1.9866
1.9867
1.9861
1.9881
1.9866
1.978
2.001
1.9739
1.9988
1.9835
6.330
1.9754
1.9979
1.9829
6.461
1.980
1.999
1.979
2.002
1.979
2.002
1.9799
2.0000
g (calcd)
a(53Cr,51V)d
a(1H)d
6.38
0.40
6.34
0.40
5.63
1.81
0.338
1.80
0.331
1.77
0.301
1.80
0.302
A1(53Cr,51V)d
A2(53Cr,51V)[A ]d
A3(53Cr,51V)[A|]d
9.032
7.998
-0.149
5.627
8.979
8.063
-0.128
5.638
9.25
0.64
9.245
0.489
6.330
9.171
1.037
6.460
9.31
0.40
8.50
0
2.69
0.05
A(53Cr,51V)
d
a
b
d
g
In toluene. In 1:1 CHCl3/DMF. c Reference 3. In mT. f Data obtained through fit routine program CWSIM, ref 18. Anisotropy
incompletely resolved.
a factor of 5.17 Axial g and A(51V)-hyperfine tensors
wereobserved, however, for the complex 5•, which con-
tains zirconium in the one-atom interannular link.5 This
zircona[1]vanadocyclophane is only minimally distorted
from axiality (tilt angle 3.7°), and the considerably
larger distance V‚‚‚Zr of 3.25(2) Å (sum of covalent radii
) 2.76 Å) should preclude the type of dative interaction
which was postulated for the germanium-linked com-
plexes 18• and 21• to account for the EPR features. As
has been demonstrated before,5 tilting of the bis(η6-
arene)vanadium unit also modifies the isotropic hyper-
fine coupling constant a(51V); in concordance with the
similar tilt angle for the complexes 2• and 21•, a
considerably decreased value a(51V) ) 5.63 mT is
observed for both [1]vanadocyclophanes whereas the
nonbridged, untilted complexes possess a(51V) param-
eters of 6.34 ((Ph3Si-η6-C6H5)2V) (25•), 6.33 (11•), and
6.46 mT (15•), respectively. This effect has been inter-
preted in terms of more extensive metal-ligand orbital
mixing which accompanies the deviation from axial
symmetry. A less than 2% decrease in the coupling
constant a(53Cr) is observed upon proceeding from [(Me3-
Ge-η6-C6H5)2Cr]•+ (10•+) to the 1,2-digerma[2]chromo-
cyclophane 24•+
.
Due to the larger bridge, Me2-
GeGeMe2, 24 is unstrained and the two η6-arenes should
maintain their parallel disposition. Therefore, as in the
case of the zircona[1]vanadocyclophane 5• 5 (tilting angle
3.7°) spin distribution is not markedly changed. Pre-
sumably it is the lack of strain to which the radical
cation 24•+ owes its existence.14
Cyclic Volta m m etr y. The redox behavior of the
organogermanyl derivatives of bis(benzene)vanadium
and bis(benzene)chromium is represented by cyclic
voltammetric traces (Figure 3) and by the pertaining
parameters, which are collected in Table 3. Reversible
or at least partly reversible reductions are only observed
for the vanadium species where electron transfer leads
to an 18 valence electron configuration at the central
metal atom. Anions which are stable on the time scale
of the CV experiment are also obtained for the deriva-
tives 18• and 21•, which contain the one-atom inter-
annular bridges >GeMe2 and >GePh2, respectively. For
the vanadium complexes, electrochemical oxidation is
reversible if the two rings carry individual R3Ge groups
F igu r e 3. Cyclic voltammetric traces for the complexes
15•, 18•, 11•, and 21• at -50 °C in 1,2-dimethoxyethane/
0.1 M tetrabutylammonium perchlorate: working elec-
trode, glassy carbon; reference electrode, SCE.
but irreversible if a one-membered interannular link
>R2Ge is present.
The solvolytic cleavage of the one-membered inter-
annular bridge in the corresponding chromium com-
plexes prevents a study of their electrochemical behav-
ior. However, a two-membered interannular link,
GeMe2GeMe2, confers reversibility on the oxidation of
24. It may therefore be concluded, that the cleavage of
the Carene-Ge bond is initiated by electrophilic attack
at the ipso carbon atom which in the case of the strained
tilted germa[1]metallocyclophanes 17 and 20 carries
high electron density, as implied by the NMR data.
(17) (a) Lu, C. C.; Carlson, T. A.; Malik, F. B.; Tucker, T. C.; Nestor,
C. W., J r. Atomic Data 1971, 3, 1. Carlson, T. A. Photoelectron and
Auger Spectroscopy; Plenum Press: New York, 1975; p 113 f. (b)
Klapo¨tke, T. M.; Schulz, A. Quantenmechanische Methoden in der
Hauptgruppenchemie; Spektrum Akademischer Verlag: Heidelberg,
1996; p 177.
(18) Burghaus, O. University of Marburg, unpublished data.

4594 Organometallics, Vol. 16, No. 21, 1997
Elschenbroich et al.
Ta ble 3. Cyclic Volta m m etr ic Da ta for th e Com p ou n d s 10d , 11•, 14, 15•, 18•, 21•, 24, 8•, a n d th e Sta n d a r d 7•
E1/2(0/-)/Vb
∆Ep/mVb
rb
E1/2(+/0)/Vb
∆Ep/mVb
rb
Epae/V
Epae/V
10d c
11d,g
14c
15d
18d
21d
24c
8f
-2.64e
-2.66
-0.65
-0.30
-0.54
-0.17
-0.31e
-0.19e
-0.69
-0.35
-0.73
76
61
62
73
1.0
1.0
1.0
1.0
0.99
0.35
1.08
0.66
75
∼0.5
0.57
-2.52
-2.62
-2.59
110
78
74
∼0.6
∼0.6
∼0.8
91
66
65
1.0
1.0
1.07
0.24
-2.71
<-3.1
74
0.93
0.46
7d,g
a
In 1,2-dimethoxyethane/0.1 M tetraethylammonium perchlorate at a glassy carbon electrode versus a saturated calomel electrode.
E1/2 ) /2(Epa + Epc), ∆Ep ) Epa - Epc, r ) Ip(fwd)/Ip(rev).
c At 20 °C. At -50 °C. e Peak potential of an irreversible wave. f At -35 °C, ref
b
1
d
15. Determined in a sample solution which was 4.65 × 10-3 M both in 11• and in 7. Identical peak heights for 11 and the reversible
standard 7 attest to the 1e nature of the redox processes. The current function Ip/ν1/2 proved to be independent of scan rate (50 < ν < 400
mV s-1).
g
2
We reported earlier that the substitution of a hydro-
gen atom by a SiPh3 group causes an anodic shift of
about 95 mV per SiPh3 group for the reduction potential
E1/2(0/-) of the bis(η6-arene)vanadium unit.3 The slightly
smaller value found for the GePh3 substituent (75 mV
per GePh3 group) reflects the small differences in
electronegativity between silicon and germanium. (Al-
lred-Rochow values: C 2.50, Si 1.74, Ge 2.02). The
reduction of 11•, the trimethylgermyl analogue of 15•,
is not fully reversible. This is probably due to interfer-
ence of the reduction of the coordinated ligand 9, which
gives rise to an irreversible wave in the chromium
complex [(Me3Ge-η6-C6H5)2Cr] (10d ) at -2.64 V. Thus,
in order to evaluate the electronic effect of the GeMe3
group, it is necessary to compare the reversible oxida-
tions of 15+/0 and 11+/0 with that of 8+/0. The differences
E1/2(15+/0) - E1/2(8+/0) ) 190 mV and E1/2(11+/0) -
E1/2(8+/0) ) 50 mV indicate that the anodic shift de-
creases on exchanging phenyl by methyl groups. This
gradation is expected in view of the larger acceptor
capability of phenyl vs methyl.
occupied orbital a1(V(3dz )) with molecular orbitals
whose degeneracies have been raised by the structural
distortion.
Exp er im en ta l Section
Chemical manipulations and physical measurements were
carried out using techniques and instruments specified previ-
ously.3
Cr ysta l Str u ctu r e Deter m in a tion of [(C6H5)2Ge(η6-
C6H5)2]Cr (20). A crystal of 20 was grown from a saturated
solution in toluene at 4 °C. Data were collected on a four circle
diffractometer (CAD4, Enraf-Nonius) at room temperature.
The structure was solved in the monoclinic space group P21/n
(a ) 7.695(2) Å, b ) 18.794(4) Å, c ) 12.729(3) Å, â ) 94.34-
(3)°) using Patterson methods and difference Fourier synthe-
ses. All atoms including the hydrogen atoms were localized.
The refinement, however, was performed with hydrogen atoms
in calculated positions (d(C-H) ) 0.96 Å) with common
isotropic temperature factors. The final residuals were wR2
) 0.072 for all 2223 independent reflections corresponding to
R1 ) 0.028 for the observed reflections (F0 > 4σ(F0)). Bond
lengths, angles, and the data collection and refinement
parameters are listed in Tables 1 and 4, respectively. Atomic
coordinates and displacement parameters have been deposited
with the Fachinformationszentrum Karlsruhe, Gesellschaft fu¨r
wissenschaftlich-technische Information mbH, D-76344 Egg-
enstein-Leopoldshafen, Germany; Depository No. CSD 405
982.
Assessing the effect exerted by bending of the sand-
wich axis on the redox potentials is hampered by the
unknown electronic influences the interannular bridge
inflicts on the energy of the redox orbital. As a rough
guess one may assume that the effect of substitution of
one hydrogen atom for a GePh3 group (75 mV) is
comparable to the exchange of two hydrogens by an
interannular GePh2 link. Under this assumption the
difference of the reduction potentials of [Ph2Ge(η6-
C6H5)2]V (21•) and the parent complex 8• (80 mV) should
be a superposition of substitutional (75 mV) and bending
(5 mV) effects. For the silicon analogue [Ph2Si(η6-
C6H5)2]V (2•) a small bending influence of 35 mV was
calculated using the same approach.3 Taking into
account that [Ph2Ge(η6-C6H5)2]Cr (20) and [Ph2Si(η6-
C6H5)2Cr] (4) have identical ring tilts, it may be con-
cluded that the effect exerted on the redox behavior by
bending of the sandwich structure is, at best, marginal.
This lack of response is not unexpected if it is borne in
mind that the redox orbital is metal centered and
nonbonding. Therefore, variations in the ligand periph-
ery should influence the redox orbital only indirectly by
effecting a small change in the partial charge on the
central metal atom. By way of contrast, the 14.4(2)°
sandwich tilt is clearly reflected in the nonaxiality of
the g tensor for 18• and 21• (Table 2). This, again, is in
concordance with expectation since the deviations of gx
and gy from 2.0023 result from mixing of the singly
[Me3Ge-η6-C6H5]2Cr (10d ). Cocondensation route: In a 2
L reactor, chromium (0.5 g, 9.6 mmol) is evaporated from a
resistively heated tungsten spiral and cocondensed at 77 K
during 1.5 h with Me3GePh (13 g, 70 mmol). After warming
to room temperature the reddish brown product is dissolved
in 200 mL of toluene, the solution is filtered through Celite,
and the solvent is evaporated in vacuo. Yield of crude
material: 990 mg (24%). Sublimation at 80 °C/10-4 mbar
affords pure 10d as greenish black microcrystalline material
(350 mg, 8% yield). 1H NMR (benzene-d6): δ 4.24 (br, o-H),
4.13-4.18 (br, m-, p-H), 0.29 (s, CH3). 13C NMR (benzene-d6):
1
δ 81.1 (ipso-C), 78.3 (o-C, J (C,H) ) 170 Hz), 76.2 (m-C, 166
Hz), 74.8 (p-C, 167 Hz), -0.9 (CH3, 125 Hz). MS (EI, 70 eV):
m/ z (relative intensity) 442 (M+, 18.3), 248 (M+ - PhGeMe3,
21.2), 181 (PhGeMe2+, 100), 151 (PhGe+, 14.8), 52 (Cr+, 27.8).
Anal. Calcd for C18H28CrGe2: C, 48.95; H, 6.39. Found: C
49.19; H, 6.48.
[(Me3Ge-η6-C6H 5)(η6-C6H 6)]Cr (10m ) a n d [Me3Ge-η6-
C6H5]2Cr (10d ). Lithiation route: To a suspension of bis-
(benzene)chromium (7) (3.03 g, 14.6 mmol) in 200 mL of
cyclohexane is added at room temperature a 1.6 M solution of
n-butyllithium in hexane (22.7 mL, 36.4 mmol of n-BuLi) and
an equimolar amount of N,N,N′,N′-tetramethylethylenedi-
amine (5.6 mL, 36.4 mmol). The mixture is refluxed for 1 h
and cooled to 0 °C and a solution of trimethylchlorogermane
(12) (4.5 mL, 36.4 mmol) in 10 mL of cyclohexane is added

Metal π Complexes of Benzene Derivatives
Organometallics, Vol. 16, No. 21, 1997 4595
Ta ble 4. Cr ysta l Da ta , Da ta Collection , a n d
Refin em en t P a r a m eter s for [(C6H5)2Ge-
(η6-C6H5)2]Cr (20)
1,1′-dilithiated 7, is washed with three fractions of petroleum
ether (40/60) and suspended in 50 mL of diethyl ether. With
vigorous stirring at room temperature is added during 0.5 h
100 mL of a solution of triphenylchlorogermane (13) (1.6 g,
4.8 mmol) in diethyl ether. After stirring overnight and
filtration, the yellow solid is extracted with 100 mL of boiling
toluene. The extract is layered with an equal volume of
petroleum ether (40/60) and kept at -25 °C for 24 h. 14 is
obtained as a yellow microcrystalline material. Yield: 340 mg
(0.42 mmol, 18%). 1H NMR (benzene-d6): δ 4.40 (o-H), 4.23
(m-, p-H), 7.57 (o-H, GePh3), 7.04 (m-, p-H, GePh3). 13C NMR
(benzene-d6) δ 78.2 (ipso-C), 77.0 (o-C), 1J (C,H) ) 167 Hz), 80.4
(m-C, 165 Hz), 74.6 (p-C, 164 Hz), 137.9 (ipso-C, GePh3), 135.9
(o-C, GePh3), 128.6 (m-C, GePh3), 129.3 (p-C, GePh3). MS (EI,
70 eV): m/ z (relative intensity) 814 (M+, 19.0), 434 (M+ - Ph3-
Ge, 100), 305 (Ph3Ge+, 93.6), 228 (Ph2Ge+, 36.6), 151 (PhGe+,
19.5), 52 (Cr+, 22.7). Anal. Calcd for C48H40CrGe2: C, 70.82;
H, 4.95. Found: C, 70.87; H, 3.96.
formula
C24H20CrGe
fw
432.99
temp
293(2) K
wavelength
cryst syst
space group
unit cell dimens
0.710 73 Å
monoclinic
P21/n
a ) 7.695(2) Å
b ) 18.794(4) Å
c ) 12.729(3) Å
R ) 90°
â ) 94.34(3)°
γ ) 90°
vol
Z
1835.6(8) Å3
4
D(calcd)
abs coeff
F(000)
cryst size
θ range for data collctn
index range
no. of reflns collctd
no. of indep reflns
refinement
1.567 g cm-3
2.233 mm-1, ψ-scan correction
880
[P h 3Ge-η6-C6H5]2V (15•). The synthesis is performed as
described for 14. It affords 15 as a red, microcrystalline
material (yield 21%) which decomposes at 295 °C. EPR data:
see Table 2. MS (EI, 70 eV): m/ z (relative intensity) 813 (M+,
37.5), 433 (M+ - Ph3Ge, 100), 305 (Ph3Ge+, 84.6), 228 (Ph2-
Ge+, 57.0), 207 (C12H12V+, 61.0), 151 (PhGe+, 35.4), 51 (V+,
0.20 × 0.20 × 0.10 mm3
2.17-21.94°
-8 e h e 8, 0 e k e 19, 0 e l e 13
2341
2225 (Rint ) 0.0284)
full matrix least squares on
F2 (SHELXL-93a)
2223/0/236
42.2). Anal. Calcd for
Found: C, 71.00; H, 5.01.
C48H40Ge2V: C, 70.91; H, 4.96.
data/restraints/params
goodness-of-fit on F2
1.087
[Me2Ge(η6-C6H5)2]Cr (17). Bis(benzene)chromium (2.5 g,
12 mmol) is lithiated as described above, and the mixture is
decanted. The solid is suspended in 150 mL of petroleum ether
(40/60), and during 45 min a solution of dimethyldichloroger-
mane (2.08 g, 12 mmol) in 40 mL of petroleum ether is added
at -20 °C. The solution is allowed to warm to room temper-
ature and is stirred for 2 h. Filtration through celite affords
a highly air-sensitive reddish-brown solution. Cooling to -25
°C causes precipitation of 17 as greenish brown crystals which
decompose at 178-182 °C. Yield: 750 mg (20%). 1H NMR
(benzene-d6): δ 3.81 (o-H), 4.66 (m-, p-H), 0.40 (CH3). 13C NMR
(benzene-d6): δ 37.5 (ipso-C), 76.5 (o-C, 1J (C,H) ) 168 Hz),
83.7 (m-C, 165 Hz), 79.1 (p-C, 166 Hz), -3.9 (CH3, 125 Hz).
final R indices [I > 2σ(I)]
R1 ) 0.0278; wR2 ) 0.0659
R1 ) 0.0403; wR2 ) 0.0718
0.485 and -0.371 e Å-3
R indices (all data)
largest diff peak and hole
a
Sheldrick, G. M. SHELXL-93, Program for the Refinement of
Crystal Structures; University of Go¨ttingen: Go¨ttingen, Germany,
1993.
during 1 h. The mixture is stirred for another 12 h and filtered
and the solvent is removed under reduced pressure. The
residue, a dark brown oil, is dissolved in petroleum ether/
diethyl ether (3:1) and chromatographed at a silica gel column
(20 × 4 cm). The first brown band which is eluted with
petroleum ether/diethyl ether contains a mixture of [(Me3Ge-
η6-C6H5)(η6-C6H6)]Cr (10m ) and [Me3Ge-η6-C6H5]2Cr (10d ),
which is separated by means of fractional sublimation at a
temperature gradient 70 > T > 25 °C. The upper section in
the tube contains the brown monosubstituted product 10m
(110 mg, 0.34 mmol, 2.3%) and the lower section the greenish-
brown disubstituted product 10d (820 mg, 1.86 mmol, 12.7%).
The second band on the column is eluted with toluene. It
contains unreacted bis(benzene)chromium (780 mg, 3.75 mmol,
26%). Higher, yellow bands which can only be eluted with
THF have not been analyzed.
Compound 10m : 1H NMR (THF-d8) δ 4.31 (o-H), 4.24 (m-,
p-H), 4.22 (η-C6H6), 0.29 (CH3); 13C{1H} NMR (THF-d8) δ 81.5
(ipso-C), 78.6 (o-C), 76.1 (m-C), 75.0 (p-C), 75.1 (C6H6), -1.1
(CH3). Anal. Calcd for C15H20CrGe: C, 55.45; H, 6.20.
Found: C, 55.56; H, 6.33. Compound 10d : 1H NMR (THF-
d8) δ 4.33 (o-H), 4.25-4.28 (m-, p-H), 0.33 (CH3); 13C{1H} NMR
(THF-d8) δ 81.5 (ipso-C), 78.6 (o-C), 76.6 (m-C), 75.1 (p-C),
-0.85 (CH3). Anal. Calcd for C18H28CrGe2: C, 48.95; H, 6.39.
Found: C, 48.75; H, 6.49.
MS (EI, 70 eV): m/ z (relative intensity) 310 (M+
, 79.4), 243
(Ph2GeMe+, 90.5), 208 (C12H12Cr+, 49.9), 181 (PhGeMe2+, 29.1),
151 (PhGe+, 36.9), 130 (C6H6Cr+, 67.7), 104 (GeMe+, 10.2), 52
(Cr+, 100). Anal. Calcd for C14H16CrGe: C, 54.44; H, 5.22.
Found: C, 53.84; H, 5.01.
[Me2Ge(η6-C6H5)2]V (18•). The preparation follows the
directions given for 17. Compound 18• is obtained as brown
crystals (yield 34%), which decompose without prior melting
at 160-165 °C. EPR data: see Table 2. MS (EI, 70 eV): m/ z
(relative intensity) 309 (M+, 90.5), 279 (M+ - 2CH3, 55.9), 243
(Ph2GeMe+, 100), 207 (C12H12V+, 18.0), 181 (PhGeMe2+, 38.1),
151 (PhGe+, 81.6), 129 (C6H6V+, 17.2), 51 (V+, 51.3). Anal.
Calcd for C14H16GeV: C, 54.63; H, 5.24. Found: C, 54.02; H,
5.35.
[P h 2Ge(η6-C6H5)2]Cr (20). The preparation follows the
directions given for 17, replacing Me2GeCl2 by Ph2GeCl2 (19).
The suspension is filtered, the residue is washed with two 50
mL portions of petroleum ether (40/60), and the solid is
dissolved in boiling toluene, concentrated in vacuo, and cooled
to -10 °C. 20 is obtained as small black crystals with a
metallic luster (yield 44%). 1H NMR (benzene-d6): δ 4.22 (o-
H), 4.66 (m-, p-H), 7.93-7.96 (o-H, GePh2), 7.29-7.32 (m-, p-H,
GePh2). 13C NMR (benzene-d6): δ 36.4 (ipso-C), 77.8 (o-C,
1J (C,H) ) 169 Hz), 83.9 (m-C, 165 Hz), 79.5 (p-C, 167 Hz),
136.5 (ipso-C, GePh2), 134.6 (o-C, GePh2, 159 Hz), 129.3 (m-
C, GePh2, 159 Hz), 129.9 (p-C, GePh2). MS (EI, 70 eV): m/ z
(relative intensity) 343 (M+, 57.3), 305 (Ph3Ge+, 100), 228 (Ph2-
Ge+, 82.7), 151 (PhGe+, 39.2), 52 (Cr+, 63.9). Anal. Calcd for
[Me3Ge-η6-C6H5]2V (11•) was prepared via lithiation and
subsequent reaction with Me3GeCl in analogy to the synthesis
of 10. The reaction and subsequent purification procedure
afforded brown needles. Yield :56%. EPR: see Table 2. MS
(EI, 70 eV): m/z (relative intensity) 441 (M+, 19.9), 181
(PhGeMe2+, 100), 151 (PhGe+, 20.5). Anal. Calcd for C18H28
VGe2: C, 49.07; H, 6.42. Found: C, 48.84; H, 6.43.
-
[P h 3Ge-η6-C6H5]2Cr (14). To a suspension of bis(benzene)-
chromium (7) (500 mg, 2.4 mmol) in 100 mL of cyclohexane
are added a 1.6 M solution of n-butyllithium in hexane (3.6
mL, 5.8 mmol) and N,N,N′,N′-tetramethylethylenediamine
(0.86 mL, 5.8 mmol). After refluxing for 1.5 h the mixture is
cooled to room temperature and decanted to remove mono-
lithiated 7, which is soluble. The precipitate, which contains
C
24H20CrGe: C, 66.57; H, 4.66. Found: C, 66.70; H, 4.76.
[P h 2Ge(η6-C6H5)2]V (21•). The synthesis was as described
for 20. Compound 21• forms an olive black microcrystalline
material which is only sparingly soluble in toluene (yield 29%).
EPR data: see Table 2. MS (EI, 70 eV): m/ z (relative

4596 Organometallics, Vol. 16, No. 21, 1997
Elschenbroich et al.
intensity): 433 (M+, 59.0), 305 (Ph3Ge+, 100), 228 (Ph2Ge+,
4.38 (m-, p-H), 0.53 (CH3). 13C NMR (benzene-d6): δ 88.2 (ipso-
C), 80.9 (d, o-C, 1J (C,H) ) 164 Hz), 75.0 (d, m-C, 166 Hz), 76.3
84.9), 151 (PhGe+, 68.8), 51 (V+, 14.6). Anal. Calcd for C24H20
GeV: C, 66.73; H, 4.67; Found: C, 66.48; H, 4.52.
-
(d, p-C, 167 Hz), 126.8 (q, CH3, 126 Hz). MS (EI, 70 eV): m/ z
+
(Me2Br Ge-η6-C6H5)2Cr (23). In a 2 L reactor, cooled with
liquid N2, during a period of 2 h phenyldimethylbromogermane
(22)16 (15.0 g, 58 mmol) is cocondensed with chromium vapor
(0.5 g, 9.6 mmol). The reddish-brown product is dissolved in
toluene at room temperature, the dark red solution is filtered
through Celite, and solvent and excessive free ligand are
removed in vacuo. The residue which appears green (thin
layer) or brown (thick layer) may be sublimed under reduced
pressure (125 °C, 10-4 mbar). Yield: 980 mg (18%). 1H NMR
(benzene-d6): δ 4.16 (br, o-, m-, p-H), 0.71 (CH3). 13C{1H} NMR
(benzene-d6): δ 80.0 (ipso-C), 78.4 (o-C), 76.8 (m-C), 75.2 (p-
C), 4.70 (CH3). MS (EI, 70 eV): m/ z (relative intensity): 572
(M+, 5.2), 312 (M+ - L, 52.6), 181 (PhGeMe2+, 100), 151
(PhGe+, 20.3), 52 (Cr+, 20.9). Anal. Calcd for C16H22Br2-
CrGe2: C, 33.63; H, 3.88. Found: C, 33.88; H, 4.13.
(relative intensity) 412 (M+, 46.4), 310 (C6H6CrPhGeMe2
,
18.3), 208 (C12H12Cr+, 36.4), 181 (PhGeMe2+, 14.6), 151 (PhGe+,
7.2), 130 (C6H6Cr+, 39.8), 52 (Cr+, 100). Anal. Calcd for
C
16H22CrGe2: C, 46.49; H, 5.39. Found: C, 46.82; H, 5.56.
Th er m olysis of 18•. About 20 mg of 18• is gradually heated
in an evacuated, sealed tube (5 × 80 mm) at a rate of ∼4 °C
min-1
.
At 135 °C, droplets of a colorless liquid start to
condense at cooler sections of the vessel with no apparent
change in appearance of solid 18•. At 160-165 °C, extensive
decomposition of 18• sets in, leaving a black solid as residue.
The colorless liquid was subjected to mass spectrometric
analysis. MS (EI, 70 eV): m/ z (relative intensity) 258 (Ph2-
GeMe2, 2.2), 243 (Ph2GeMe, 100), 228 (Ph2Ge - H, 6), 181
(PhGeMe2, 13), 151 (PhGe, 22). The masses given represent
the 74Ge isotopomers.
[Me4Ge2-1,2-(η6-C6H5)2]Cr (24). From freshly sublimed
naphthalene (0.75 g, 58 mmol) and sodium (124 mg, 5.4 mmol)
is prepared a solution of Na+C10H8- in dimethoxyethane, and
the solution is cleared by filtration. To this is added at -25
°C over the course of 2 h a solution of 23 (1 g, 1.8 mmol) in
175 mL of dimethoxyethane. The yellow-brown solution,
obtained after stirring overnight at room temperature, is
brought to dryness in vacuo, and naphthalene is removed by
sublimation (50 °C, 10-4 mbar). The residue is extracted into
petroleum ether (40/60), and the solution is reduced to a
volume of 4 mL and cooled to -10 °C. Within 1 week the
germachromocyclophane 24 is obtained as small black crystals
(yield: 90 mg, 4%). 1H NMR (benzene-d6): δ 4.83 (o-H), 4.30-
Ack n ow led gm en t. We thank the Deutsche Fors-
chungsgemeinschaft (E.S.: Graduiertenkolleg Metal-
lorganische Chemie) and the Fonds der Chemischen
Industrie for financial support of this work.
Su p p or tin g In for m a tion Ava ila ble: Tables listing de-
tails of crystal data and structure refinement, atomic coordi-
nates and displacement parameters, and bond lengths and
angles for 20 (9 pages). Ordering information is given on any
current masthead page.
OM970249Y