Pentamethylcyclopentadienylgallium (Cp*Ga): Alternative synthesis and application as a terminal and bridging ligand in the chemistry of chromium, iron, cobalt, and nickel

Article abstract of DOI:10.1021/om970913a

An alternative synthetic route to η⁵-pentamethylcyclopentadienylgallium (Me₅C₅Ga, Cp*Ga, 1) via reductive dehalogenation of (pentamethylcyclopentadienyl)diiodogallane (Cp*GaI₂, 2) is reported. In addition, the behavior of compound 1 as a ligand in transition metal chemistry is examined. In the reaction of 1 with Cr(CO)₅(C₈Hi₁₄) (C₈H₁₄ = ciscyclooctene), Fe₂(CO)₉, Fe(CO)₃CHT (CHT = cycloheptatriene), Co₂(CO)₈, and Ni(CO)₄ the new complexes Cr(Cp*Ga)(CO)₅ (3), Fe(CP*Ga)(CO)₄ (4), Fe₂(μ-Cp*Ga)₃(CO)₆ (5), Co₂(μ-Cp*Ga)₂(CO)₆ (6), and Ni₄(μ-Cp*Ga)₄(CO)₆ (8), respectively, were obtained. They were characterized by analytical and spectroscopic methods; solid-state structures were determined by X-ray diffraction analysis. In the reaction of 1 with Ni(CO)₄, the complex Ni(Cp*Ga)-(CO)₃ (7) is an intermediate, which was characterized by IR and NMR data. The η⁵-bonding mode within the Cp*Ga ligand is maintained, apart from one Cp*Ga unit in 5 which exhibits η³/η¹-bonding. The cone angle of η⁵-Cp*Ga is 112°, as determined on the basis of structural data of 3 and 4. Concerning the σ-donor/π-acceptor properties, 1 is classified as a predominant electron donor.

Full text of DOI:10.1021/om970913a

Organometallics 1998, 17, 1305-1314
1305
P en ta m eth ylcyclop en ta d ien ylga lliu m (Cp *Ga ):
Alter n a tive Syn th esis a n d Ap p lica tion a s a Ter m in a l a n d
Br id gin g Liga n d in th e Ch em istr y of Ch r om iu m , Ir on ,
†
Coba lt, a n d Nick el
Peter J utzi,* Beate Neumann, Guido Reumann, and Hans-Georg Stammler
Fakult a¨ t f u¨ r Chemie, Universit a¨ t Bielefeld, Bielefeld, Germany
Received October 20, 1997
5
An alternative synthetic route to η -pentamethylcyclopentadienylgallium (Me
5
C
5
Ga,
Cp*Ga, 1) via reductive dehalogenation of (pentamethylcyclopentadienyl)diiodogallane
Cp*GaI , 2) is reported. In addition, the behavior of compound 1 as a ligand in transition
metal chemistry is examined. In the reaction of 1 with Cr(CO) (C 14 ) cis-
cyclooctene), Fe (CO) , Fe(CO) CHT (CHT ) cycloheptatriene), Co (CO) , and Ni(CO) the
new complexes Cr(Cp*Ga)(CO) (3), Fe(Cp*Ga)(CO) (4), Fe (µ-Cp*Ga) (CO) (5), Co (µ-
Cp*Ga) (CO) (6), and Ni (µ-Cp*Ga) (CO) (8), respectively, were obtained. They were
characterized by analytical and spectroscopic methods; solid-state structures were determined
by X-ray diffraction analysis. In the reaction of 1 with Ni(CO) , the complex Ni(Cp*Ga)-
CO) (7) is an intermediate, which was characterized by IR and NMR data. The η -bonding
mode within the Cp*Ga ligand is maintained, apart from one Cp*Ga unit in 5 which exhibits
(
2
5
8 8
H14) (C H
2
9
3
2
8
4
5
4
2
3
6
2
2
6
4
4
6
4
5
(
3
3
1
5
η /η -bonding. The cone angle of η -Cp*Ga is 112°, as determined on the basis of structural
data of 3 and 4. Concerning the σ-donor/π-acceptor properties, 1 is classified as a
predominant electron donor.
In tr od u ction
Si) can be obtained in good yield by reduction of Cp*2-
SiCl2 with alkali metal naphthalenides. As an example
5
In the last few years, the inorganic and organo-
metallic chemistry of monovalent gallium has attracted
much attention; several compounds have been synthe-
from group 13 chemistry, the cluster compound (Cp*Al)4,
which was first synthesized by Schn o¨ ckel et al., can
6
also be obtained by reduction of Cp*AlCl2 with potas-
1
,2
sized and characterized only recently.
Pentamethyl-
7
sium in 20% yield. We report here a procedure to
cyclopentadienylgallium (Me5C5Ga, Cp*Ga, 1) was first
prepared by Schn o¨ ckel et al. using metastable solutions
of Ga(I)Cl, which are difficult to prepare.1c These
solutions react with Cp*2Mg or Cp*Li to give Cp*Ga in
unspecified yields.2b The fundamental properties of
Cp*Ga have been described by Schn o¨ ckel et al. Inter-
estingly, Cp*Ga is a monomer in the gas phase and in
prepare Cp*Ga in good yield via reductive dehalogena-
tion of Cp*GaI2 with potassium using ultrasonic metal
activation.
Due to the metal-centered lone pair, monovalent
group 13 compounds principally act as donor ligands in
transition metal chemistry, as exemplified by species
8
9
such as Me5C5Al (Cp*Al) and InC(SiMe3)3. As part of
our studies concerning the reactivity of Cp*Ga, we
report the synthesis and structural characterization of
the coordination compounds Cr(Cp*Ga)(CO)5, 3,
Fe(Cp*Ga)(CO)4, 4, Fe2(Cp*Ga)3(CO)6, 5, Co2((Cp*Ga)2-
3
,4
solution but forms a hexamer in the solid state.
A common synthetic route to sandwich or half-
sandwich complexes of subvalent main group elements
is the reductive dehalogenation of Cp*nMXm compounds.
As an impressive example, decamethylsilicocene (Cp*2-
(CO)6, 6, and Ni4(Cp*Ga)4(CO)6, 8, in which Cp*Ga for
the first time acts as a donor ligand in transition metal
chemistry.
*
Prof. Dr. Peter J utzi, Fakult a¨ t f u¨ r Chemie, Universit a¨ t Bielefeld,
Universit a¨ tsstrasse, 33615 Bielefeld.
†
Dedicated to Prof. Achim M u¨ ller on the occasion of his 60th
(5) J utzi, P.; Kanne, D.; Kr u¨ ger, C. Angew. Chem. 1986, 98, 163;
Angew. Chem. Int. Ed. Engl. 1986, 25, 164.
Ed.Engl. 1985, 24, 893. (b) Dohmeier, C.; Loos, D.; Schn o¨ ckel, H.
Angew. Chem. 1996, 108, 141; Angew. Chem., Int. Ed. Engl. 1996, 35,
(6) Dohmeier, C.; Robl, C.; Tacke, M.; Schn o¨ ckel, H. Angew. Chem.
1991, 103, 594; Angew. Chem., Int. Ed. Engl. 1991, 30, 564.
(7) Schulz, S.; Roesky, H. W.; Koch, H. J .; Sheldrick, G. M.; Stalke,
D.; Kuhn, A. Angew. Chem. 1993, 105, 1828; Angew. Chem., Int. Ed.
Engl. 1993, 32, 1729.
1
1
29. (c) Tacke, M.; Plaggenborg, L.; Schn o¨ ckel, H. Z. Anorg. Allg. Chem.
991, 604, 35.
(2) Kuchta, M. C.; Bonanno, J . B.; Parkin, G. J . Am. Chem. Soc.
1
1
996, 118, 10914. (b) Loos, D.; Schn o¨ ckel, H. J . Organomet. Chem.
993, 463, 37. (c) Uhl, W.; Hiller, W.; Layh, M.; Schwarz, W. Angew.
(8) Dohmeier, C.; Krautscheid, H.; Schn o¨ ckel, H. Angew. Chem.
1994, 106, 2570; Angew. Chem., Int. Ed. Engl. 1994, 33, 2482. (b)
Weiss, J .; Stetzkamp, D.; Nuber, B.; Fischer, R. A.; Boehme, C.;
Frenking, G. Angew. Chem. 1997, 109, 95; Angew. Chem., Int. Ed. Engl.
1997, 36, 70.
(9) Uhl, W.; Pohlmann, M. Organometallics 1997, 16, 2478. (b) Uhl,
W.; S. U. Keimling, Hiller, W.; Neumayer, M. Chem. Ber. 1996, 129,
397. (c) Uhl, W.; Keimling, S. U.; Hiller, W.; Neumayer, M. Chem. Ber.
1995, 128, 1137.
Chem. 1992, 104, 1378; Angew. Chem., Int. Ed. Engl. 1992, 31, 1364.
d) Linti, G. J . Organomet. Chem. 1996, 520, 107. (e) Beachley, O. T.,
J r.; Patzik, J .; Noble, M. J . Organometallics 1994, 13, 2885.
3) Loos, D.; Baum, E.; Ecker, A.; Schn o¨ ckel, H.; Downs, A. J . Angew.
Chem. 1997, 109, 894; Angew. Chem., Int. Ed. Engl. 1997, 36, 860.
4) Haaland, A.; Martinsen, K. G.; Volden, H. V.; Loos, D.; Schn o¨ ckel,
H. Acta Chem. Scand. 1994, 48, 172.
(
(
(
S0276-7333(97)00913-8 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 02/28/1998

1
306 Organometallics, Vol. 17, No. 7, 1998
J utzi et al.
Sch em e 1
The exceptional thermal stability of 1 is worth men-
tioning. Fractional distillation at 80 °C could be per-
formed without any decomposition. Furthermore, under
MOMBE (metal organic molecular beam epitaxy) condi-
tions, 1 turned out to be stable toward fragmentation
up to temperatures of approximately 600 °C.13
Recent investigations show that 1 can also be pre-
pared starting from the dichloro (Cp*GaCl2) or the
dibromo (Cp*GaBr2) compound, but in somewhat lower
yields. In the reaction with Cp*GaCl2, the compound
K[Cp*GaCl3] is an intermediate; it forms a tetrameric
1
4
aggregate in the solid state.
2
F igu r e 1. Molecular structure of Cp*GaI , 2.
Due to the fact that 1 possesses a nonbonding electron
pair (lone pair), Lewis-base activity can be anticipated.
Thus, 1 should act as a σ-donor ligand in transition
metal chemistry. Keeping in mind the easy haptotropic
Sch em e 2
1
5
shift in main group cyclopentadienyl compounds, an
5
3
1
η f η f η rearrangement in 1 might create vacant
coordination sites at the gallium center. As a result, 1
might act also as a π-acceptor ligand. In this context,
the application of 1 as a ligand in transition metal
complexes is of special interest. We started our inves-
tigations with examples from the chemistry of chro-
mium, iron, cobalt, and nickel.
Resu lts a n d Discu ssion
Pentamethylcyclopentadienylgallium dihalides can be
regarded as useful starting materials for the synthesis
of Cp*Ga (1) by reductive dehalogenation. Keeping in
mind the leaving group character of cyclopentadienyl
ligands and the competition in elimination reactions,
the diiodo compound Cp*GaI2 (2) seems to be the most
suitable for a successful reduction process.
When a solution of Cr(CO)5(C8H14) (C8H14 ) cis-
1
6
cyclooctene) and 1 in n-hexane was heated under
reflux, the cyclooctene ligand was replaced by 1 and the
complex Cr(Cp*Ga)(CO)5, 3, was formed (see Scheme
1
0
2
). Removal of all volatile components in vacuo led to
Compound 2 was prepared by the reaction of
an air-sensitive yellow powder which was recrystallized
from hot n-hexane for further purification. Compound
Cp*SiMe311 with GaI3 in refluxing n-hexane (see Scheme
1
). After evaporation the solvent and of Me3SiI, 2 could
3
exhibits a sharp melting point at 156 °C and decom-
be obtained in very high yield following crystallization
from a n-hexane/toluene mixture as an orange air- and
moisture-sensitive compound. As shown by an X-ray
structure analysis, 2 exists as an iodo-bridged dimer
with σ-bonded Cp* ligands. There are no extraordinary
structural features compared to the corresponding
chloro compound Cp*GaCl2,1 so the structure is not
discussed in detail here. The molecular structure of 1
is shown in Figure 1. Crystallographic data are given
in Table 1, and selected bond lengths and angles are
collected in Table 2.
poses at approximately 240 °C. The complex dissolves
easily in aprotic organic solvents. Crystals suitable for
an X-ray structure analysis were obtained from a
n-hexane solution. The molecular structure of 3 is
shown in Figure 2. Crystallographic data are given in
Table 1, and selected bond lengths and angles are
collected in Table 3.
2
In compound 3, the chromium atom is positioned in
an octahedral coordination sphere. Cp*Ga is a terminal
ligand with a Cr-Ga distance of 2.4046(7) Å. The small
deviation of the Cp(centroid)-Ga-Cr vector from lin-
earity presumably is caused by packing effects. Within
For the synthesis of 1, a solution of 2 in toluene was
treated with a small excess of potassium under ultra-
sonic activation at 70 °C (see Scheme 2). After filtration
and evaporation of the solvent, compound 1 was ob-
tained in good yield by distillation in vacuo as a slightly
yellow, air-sensitive liquid, which solidified after several
5
the Cp*Ga fragment, the η -bonding mode of the Cp*
ring is maintained; the Ga-C distances are quite
similar, with an average value of 2.260(3) Å. Compound
3
exhibits Cr-C(CO) distances in the normal range
observed for Cr(CO)5L complexes. Thus, all equatorial
1
days during storage at 4 °C. The spectroscopic data ( H
Cr-C(CO) distances are equal within experimental
1
3
and C NMR) agree well with those reported by
Schn o¨ ckel et al.2b
(13) Aschentrup, A.; Moltchanov, A.; Tappe, T.; Schmiedeskamp, B.;
Reumann, G.; J utzi, P. Manuscript in preparation.
(14) J utzi, P.; Reumann, G. Manuscript in preparation.
(15) Fisher, J . D.; Budzelaar, P. H. M.; Shapiro, P. J .; Staples, R.
J .; Yap, G. P. A.; Rheingold, A. L. Organometallics 1997, 16, 871.
(16) Grevels, F. W.; Skibbe, V. J . Chem. Soc., Chem. Commun. 1984,
681.
(
10) J utzi, P.; Comm. Inorg. Chem. 1987, 6, 123.
(11) Llinas, G. H.; Mena, M.; Palacios, F.; Royo, P.; Serrano, R. J .
Organomet. Chem. 1988, 340, 37.
12) Beachley, O. T.; Hallock, R. B.; Zhang, H. M.; Atwood, J . L.
Organometallics 1985, 4, 1675.
(

Pentamethylcyclopentadienylgallium
Organometallics, Vol. 17, No. 7, 1998 1307

1
308 Organometallics, Vol. 17, No. 7, 1998
J utzi et al.
F igu r e 2. Molecular structure of Cr(Cp*Ga)(CO)
5
, 3.
F igu r e 3. Molecular structure of Fe(Cp*Ga)(CO)4, 4.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(
d eg) for 2
Sch em e 3
Ga(1)-C(1)
Ga(1)-I(1)
Ga(1)-I(2)
Ga(1)-I(2a)
2.008(6)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(1)
1.475(9)
1.370(9)
1.451(10)
1.352(10)
1.491(9)
2.4895(11)
2.7150(11)
2.7131(10)
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 4
C(1)-Ga(1)-I(1)
C(1)-Ga(1)-I(2)
C(1)-Ga(1)-I(2a)
I(2)-Ga(1)-I(2a)
123.6(2)
111.5(2)
110.8(2)
92.78(2)
Ga(1)-C(1)-C(2)
Ga(1)-C(1)-C(5)
Ga(1)-C(1)-C(6)
C(2)-C(1)-C(5)
96.5(4)
95.7(4)
112.8(5)
104.9(5)
Ga(1)-C(1)
Ga(1)-C(2)
Ga(1)-C(3)
Ga(1)-Fe(1)
2.193(2)
Fe(1)-C(7)
Fe(1)-C(8)
Fe(1)-C(9)
O(1)-C(7)
O(2)-C(8)
O(3)-C(9)
1.789(3)
1.7885(17)
1.781(2)
1.142(3)
1.147(2)
1.143(3)
2.2110(14)
2.2576(15)
2.2731(4)
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
d eg) for 3
(
Ga(1)-C(1)
Ga(1)-C(2)
Ga(1)-C(3)
Ga(1)-C(4)
Ga(1)-C(5)
Ga(1)-Cr(1)
2.277(3)
2.246(3)
2.236(3)
2.260(3)
2.282(4)
2.4046(7)
Cr(1)-C(11)
Cr(1)-C(12)
Cr(1)-C(13)
Cr(1)-C(14)
Cr(1)-C(15)
O(1)-C(11)
O(2)-C(12)
O(3)-C(13)
O(4)-C(14)
O(5)-C(15)
1.896(4)
1.900(4)
1.904(4)
1.899(4)
1.858(4)
1.143(5)
1.149(5)
1.142(4)
1.141(4)
1.146(4)
C(7)-Fe(1)-C(8)
C(7)-Fe(1)-Ga(1)
118.15(5) C(8)-Fe(1)-Ga(1)
84.01(5)
90.40(9) C(9)-Fe(1)-Ga(1) 174.34(7)
carbonyl region (2052, 1982, 1918, and 1902 cm-1) are
expected on the basis of a local C4v symmetry; the
-1
usually IR-forbidden B1 mode at 1982.3 cm is present
due to the symmetry reduction caused by the C5
symmetry of the Cp* ring. Owing to its thermal
stability, compound 3 could be characterized with
standard EI-MS techniques. The molecular ion is
observed at 396 amu with the correct isotopic pattern;
the loss of five CO molecules leads to the Cp*GaCr
fragment at 256 amu with the highest observed inten-
sity.
A comparable iron complex with a terminal Cp*Ga
ligand was prepared using Fe2(CO)9 as the staring
material. Thus, reaction of Fe2(CO)9 with 1 in n-hexane
furnished the complex Fe(Cp*Ga)(CO)4, 4, in moderate
yield (see Scheme 3).
Compound 4 could be isolated in pure form only by
repeated recrystallization from n-hexane. It is an air-
sensitive, yellow solid, which melts at 112 °C with
decomposition accompanied by gas evolution and a color
change to deep red. Dissolved in organic media, 4
decomposes very readily and, thus, must be handled
with great care. Crystals suitable for an X-ray structure
analysis were obtained from a n-hexane solution. The
molecular structure of compound 4 is depicted in Figure
3. Crystal structure parameters are given in Table 1,
and selected bond lengths and angles are collected in
Table 4.
C(14)-Cr(1)-C(12) 176.62(15) C(15)-Cr(1)-Ga(1) 179.81(12)
C(11)-Cr(1)-C(13) 178.53(15)
error (average value 1.900(4) Å). This value is almost
1
7
+
the same as that observed in Cr(CO)6 (1.909(3) Å) or
in related phoshane Cr(CO)5L complexes (e.g., 1.893 Å
for L ) PMe3,18 1.880 Å for L ) PPh3 ). In contrast to
the equatorial CO ligands, the axial one is more effected
by the trans-orientated Cp*Ga ligand. Thus, a signifi-
cantly shorter Cr-CO (trans) distance (1.858(4) Å) than
in Cr(CO)6 (1.909(3) Å) is observed, indicating a more
effective electron donation from the chromium atom.
The Cr-CO (trans) distance in 3 is comparable to those
in Cr(CO)5L complexes with L ) PMe3 (1.850(2) Å) and
PPh3 (1.845(4) Å),19 indicating similar σ-donor proper-
ties of the ligands L.
The solution-NMR data of compound 3 are in accord
with the solid-state structure and with a η -bonded Cp*
19
1
8
5
ring. Thus, only one singlet at 1.64 ppm is observed in
1
13
the H NMR spectrum. Correspondingly, the C NMR
spectrum shows two resonances for the Cp* ring carbon
atoms (8.84 (Cp*-Me), 115.20 ppm (Cp*-ring)) and, in
addition, two signals for the five carbonyl C atoms
(
219.01 (equatorial CO), 224.26 ppm (axial CO)). In the
IR spectrum of 3, the four absorptions observed in the
In compound 4, the iron atom is surrounded by four
CO ligands and one Cp*Ga ligand in a trigonal-bipyra-
midal geometry. The Cp*Ga ligand is fixed terminally
in an axial position with an Fe-Ga distance of
2.2731(4) Å. The small deviation of the Cp*(centroid)-
(
(
(
17) Whitaker, A.; J effery, J . W. Acta Crystallogr. 1967, 23, 977.
18) Lee, K. J .; Brown, T. L. Inorg. Chem. 1992, 31, 289.
19) Plastas, H. J .; Stewart, J . M.; Grim, S. O. Inorg. Chem. 1973,
1
2, 265.

Pentamethylcyclopentadienylgallium
Organometallics, Vol. 17, No. 7, 1998 1309
Sch em e 4
Ga-Fe-C(9) vector from liniarity is presumably caused
by packing effects. The molecule is located on a crystal-
lographic mirror plane which is identical with the Fe-
5
Ga-C(7) plane. Within the Cp*Ga fragment, the η -
bonding mode of the Cp* ring is maintained; the Ga-C
distances are quite similar with an average value of
2
.226(2) Å. The geometry around the iron center does
not exactly correspond to a trigonal bipyramid. Thus,
small deviations from the ideal angles are observed (see
Table 4). All equatorial Fe-C (CO) distances are equal
within the experimental error (average value 1.789(3)
Å). This value is slightly smaller than that observed
in Fe(CO)5 (1.803(2) Å)20 and comparable to those in
related phoshane Fe(CO)4L complexes (e.g., mean value
t
21
22
for L ) P Bu3 is 1.792 Å, for L ) PPh3 is 1.795 Å ).
In contrast to the equatorial CO ligands, the axial one
is more effected by the trans-orientated Cp*Ga ligand.
Thus, a significantly shorter axial Fe-CO distance
(
1.781(2) Å) than in Fe(CO)5 (1.811(2) Å)20 is observed,
indicating a more effective electron donation from the
5
F igu r e 4. Molecular structure of (CO)
µ -(η -Cp*Ga)]Fe(CO) , 5.
2 3
3
Fe[µ
2
-(η -Cp*Ga)
2
iron atom. The axial Fe-CO distance in 3 is compa-
3
t
rable to those in Fe(CO)4L complexes with P Bu3
2
1
22
(
1.768(4) Å) and L ) PPh3 (1.795(4) Å), indicating
Ta ble 5. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5
similar σ-donor properties of the ligands L.
The η -bonded Cp* ring present in the solid state is
5
Ga(1)-C(1)
Ga(1)-C(2)
Ga(1)-C(3)
Ga(1)-C(4)
Ga(1)-C(5)
Ga(1)-Fe(1)
Ga(1)-Fe(2)
Ga(2)-Fe(1)
Ga(2)-Fe(2)
Fe(1)-Fe(2)
O(1)-C(17)
O(2)-C(18)
O(3)-C(19)
O(4)-C(20)
2.482(6)
2.286(5)
2.209(5)
2.334(5)
2.513(5)
2.454(3)
2.401(3)
2.354(4)
2.436(5)
2.908(6)
1.159(8)
1.152(6)
1.146(8)
1.161(5)
C(1)-C(5)
1.405(7)
1.420(7)
1.439(7)
1.442(6)
1.423(7)
2.087(7)
2.383(5)
2.811(5)
1.448(5)
1.406(6)
1.407(9)
1.772(7)
1.780(6)
1.780(7)
1.777(5)
also found in solution. Thus, only one singlet at 1.60
C(1)-C(2)
1
ppm is observed in the H NMR spectrum. Correspond-
C(2)-C(3)
ingly, the 13C NMR spectrum shows two resonances for
C(3)-C(4)
C(4)-C(5)
the Cp* ring (8.77 (Cp*-Me), 115.43 ppm (Cp*-ring)).
In addition, only one resonance for the four carbonyl
ligands is observed at 214.21 ppm, indicating pseudoro-
tation in solution. The IR spectrum of compound 4
shows three absorptions in the carbonyl region, as
expected on the basis of local C3v symmetry (2037, 1966,
Ga(2)-C(11)
Ga(2)-C(12)
Ga(2)‚‚‚C(13)
C(11)-C(12)
C(12)-C(13)
C(13)-C(13a)
Fe(1)-C(17)
Fe(1)-C(18)
Fe(2)-C(19)
Fe(2)-C(20)
-
1
1
942 cm ). Compound 4 could be characterized with
standard EI-MS techniques. The molecular ion is
observed at 372 amu with the correct isotopic pattern.
The successive loss of the four CO ligands leads to the
Fe(2)-Ga(1)-Fe(1) 73.57(13) C(20a)-Fe(2)-C(20)
99.7(3)
98.8(2)
98.5(2)
119.8(2)
116.5(2)
113.7(2)
+
Cp*GaFe fragment at 260 amu with the highest
Fe(1)-Ga(2)-Fe(2) 74.7(2)
Ga(1)-Fe(2)-Fe(1) 54.05(9)
C(20)-Fe(2)-C(19)
C(17)-Fe(1)-C(18)
observed intensity.
Ga(2)-Fe(1)-Fe(2) 53.91(13) C(17)-Fe(1)-Fe(2)
Refluxing a solution of 1 and Fe(CO)3CHT (CHT )
cycloheptatriene) in toluene led to the formation of the
Ga(1)-Fe(1)-Fe(2) 52.38(9)
C(18)-Fe(1)-Fe(2)
C(20)-Fe(2)-Fe(1)
5
dinuclear iron complex (CO)3Fe{[µ-Ga(η -Cp*)]2[µ-Ga-
3
(
η -Cp*)]}Fe(CO)3 (5) (see Scheme 4), which could be
bridging carbonyl ligands are replaced by bridging
Cp*Ga units resulting in D3h symmetry for the (CO)6-
Fe2Ga3 framework. The central part of the molecule can
also be viewed as an Fe2Ga3 cluster of trigonal-bipyra-
midal symmetry with the iron atoms in axial and the
gallium atoms in equatorial positions. The remaining
six terminal carbonyl ligands are orientated in an
eclipsed conformation in relation to the iron-iron vector.
The Fe-Fe distance in 5 (2.908(6) Å) is elongated in
obtained as an air-sensitive red powder after removing
all volatiles in vacuo. Compound 5 dissolves easily in
aprotic aromatic solvents such as toluene or benzene.
In the solid-state, the complex decomposes at 270 °C.
Crystals suitable for an X-ray crystal structure analysis
were obtained by crystallization from hot benzene. The
molecular stucture of 5 is shown in Figure 4. Crystal-
lographic data are given in Table 1, and selected bond
lengths and angles are collected in Table 5.
2
3
comparison to Fe2(CO)9 (2.522(1) Å) but shortened
compared to the distance in (CO)3Fe[µ-InC(SiMe3)3]3-
Fe(CO)3 (2.992(2) Å). The effect of different bridging
Compound 5 can be regarded as a derivative of the
dinuclear iron carbonyl complex Fe2(CO)9, in which the
9
a
(
20) Braga, D.; Grepioni, F.; Orpen, A. G. Organometallics 1993,
units X in Fe2(CO)6(µ-X)3 complexes on the respective
1
2, 1481.
(
21) Pickardt, J .; R o¨ sch, L.; Schumann, H. J . Organomet. Chem.
1
976, 107, 241.
(23) Cotton, F. A.; Troup, J . M. J . Chem. Soc., Dalton Trans. 1974,
(22) Riley, P. E.; Davis, R. E. Inorg. Chem. 1980, 19, 159.
800.

1
310 Organometallics, Vol. 17, No. 7, 1998
J utzi et al.
Sch em e 5
Fe-Fe distances has been discussed in more detail by
Uhl et al.9
a
The structure-determining space requirement of the
three gallium-bonded Cp* ligands prohibits a molecular
C3v symmetry with a C3 axis along the Fe-Fe vector.
5
Thus, deviations from the ideal η -bonding within the
Cp*-Ga units and from symmetrical µ2-coordination
(equal Ga-Fe bonds) finally lead to only molecular
mirror symmetry. In fact, the molecule is located on a
crystallographic mirror plane. The most obvious devia-
5
tion from η -coordination is observed for the Cp* ligand
at Ga(2). From the bond lengths and angles given in
3
1
Table 5, one can conclude an η /η coordination mode.
Thus, the Ga(2)-C(11) bond length (2.087(7) Å) is in
the range of Ga-C(Cp*) σ-bonds. For comparison, in
Cp*GaX2 compounds, the (Cp*)C-Ga distance is
5
F igu r e 5. Molecular structure of (CO) Co[µ -(η -Cp*Ga)] -
3
2
2
1
2
2
.008(6) Å for X ) I and 1.97(1) Å for X ) Cl.
3
Co(CO) , 6.
Furthermore, the C(14) methyl group is bent away from
the Cp ring plane by 17.7°, indicating a tendency for
Ta ble 6. Selected Bon d Len gth s (Å) a n d An gles
(
d eg) for 6
3
sp -hybridization at carbon atom C(11). Much smaller
5
Ga(1)-C(1)
Ga(1)-C(2)
Ga(1)-C(3)
Ga(1)-C(4)
Ga(1)-C(5)
Ga(1)-Co(1)
Ga(1)-Co(2)
Ga(2)-Co(1)
Ga(2)-Co(2)
O(1)-C(21)
O(2)-C(22)
O(3)-C(23)
O(4)-C(24)
O(5)-C(25)
O(6)-C(26)
2.241(3)
2.275(3)
2.315(3)
2.338(3)
2.289(3)
2.3926(5)
2.3784(5)
2.3959(5)
2.3884(5)
1.146(4)
1.145(4)
1.146(4)
1.141(4)
1.146(4)
1.139(4)
Ga(2)-C(11)
Ga(2)-C(12)
Ga(2)-C(13)
Ga(2)-C(14)
Ga(2)-C(15)
Co(1)-Co(2)
Co(2)-C(21)
Co(2)-C(22)
Co(2)-C(23)
Co(1)-C(24)
Co(1)-C(25)
Co(1)-C(26)
2.289(3)
2.261(3)
2.264(3)
2.303(3)
2.295(3)
2.8278(6)
1.778(4)
1.771(4)
1.777(3)
1.780(4)
1.769(4)
1.779(4)
deviations from ideal η -coordination are observed for
the remaining two Cp*Ga units (Ga(1)-Cp*; Ga(1a)-
Cp*; see Table 5). The described deviations from ideal
5
η -Cp* - Ga bonding correspond to the observed asym-
metry in the µ2-GaCp* bridging situations. As seen
from Table 5, the Ga-Fe bond lengths vary between
2
.354(4) and 2.454(3) Å.
The asymmetry observed for 5 in the solid state is
not maintained in solution, where NMR spectroscopic
data indicate dynamic processes, which finally lead to
an averaged information on the basis of a molecular C3v
1
symmetry. Thus, the H NMR spectrum of 5 shows only
one sharp singlet at δ ) 2.05 ppm for the Cp* methyl
groups, indicating only one type of Cp*Ga ligand. In
agreement with this result, the 13C NMR spectrum
shows one resonance for the Cp* methyl groups (δ 10.85
ppm) and one resonance for the Cp* ring carbon atoms
Co(2)-Ga(1)-Co(1) 72.696(17) C(25)-Co(1)-C(26) 109.15(16)
Co(2)-Ga(2)-Co(1) 72.461(17) C(25)-Co(1)-C(24) 107.82(16)
Ga(1)-Co(1)-Co(2) 53.420(15) C(26)-Co(1)-C(24) 99.74(15)
Ga(1)-Co(2)-Co(1) 53.883(14) C(22)-Co(2)-C(21) 110.25(15)
Ga(2)-Co(2)-Co(1) 53.892(15) C(22)-Co(2)-C(23) 108.01(15)
Ga(2)-Co(1)-Co(2) 53.647(14) C(23)-Co(2)-C(21) 99.04(15)
(δ 119.21 ppm). Furthermore, one resonance for the six
O(1)-C(21)-Co(2) 178.1(3)
O(2)-C(22)-Co(2) 174.8(3)
O(3)-C(23)-Co(2) 176.5(3)
O(4)-C(24)-Co(1) 176.6(3)
O(5)-C(25)-Co(1) 172.4(3)
O(6)-C(26)-Co(1) 177.5(3)
C(21)-Co(2)-Co(1) 97.96(11)
C(22)-Co(2)-Co(1) 135.14(11)
C(23)-Co(2)-Co(1) 100.82(11)
C(24)-Co(1)-Co(2) 100.29(12)
C(25)-Co(1)-Co(2) 136.18(11)
C(26)-Co(1)-Co(2) 98.11(12)
carbonyl carbon atoms is observed (δ 216.73 ppm). In
the νCO region of the IR spectrum, only these absorptions
are observed, which are in the typical range for terminal
CO ligands (1951 and 1923 cm-1). Due to its thermal
stability, compound 5 can be characterized by standard
EI-MS techniques. At a sample temperature of ap-
proximately 400 °C, a strong signal for the molecular
ion is detected at 894 amu with the correct isotopic
pattern. Successive loss of Cp*Ga and CO units is
observed. The loss of one Cp*Ga and three CO ligands
leads to a fragment at 606 amu with the highest
intensity.
230 °C. Compound 6 could be crystallized from hot
toluene as red needles suitable for an X-ray structure
analysis.
The molecular structure of 6 is shown in Figure 5.
Crystallographic data are collected in Table 1, and
selected bond lengths and angles are collected in Table
6.
When Cp*Ga (1) was reacted with Co2(CO)8 in a
n-hexane solution, rapid gas evolution occurred already
at room-temperature, indicating substitution of carbon
monoxide. Heating of the reaction mixture completed
Compound 6 can be described as a derivative of the
dinuclear cobalt carbonyl complex Co2(CO)8 in its solid-
state structure, in which the bridging carbonyl ligands
are replaced by bridging Cp*Ga units. The six terminal
carbonyl ligands are orientated in an eclipsed conforma-
tion in relation to the cobalt-cobalt vector. Due to the
pseudo C2v symmetry, the CO-Co-Co-CO plane rep-
resents a mirror plane of the molecule; a C2 axis bisects
the Co-Co vector. The Co-Co distance in 6 (2.8278(6)
5
the formation of the compound (CO)3Co[µ2-Ga(η -
Cp*)]3Co(CO)3 (6), which precipitated as an air-sensitive
orange-red powder in good yield (see Scheme 5). Com-
pound 6 is only poorly soluble in aprotic organic
solvents. In the solid state, the complex decomposes at

Pentamethylcyclopentadienylgallium
Organometallics, Vol. 17, No. 7, 1998 1311
Sch em e 6
Å) is elongated in comparison to Co2(CO)8 (2.5301(8) and
2
4
2
(
.5278(8) Å) and also to (CO)3Co[µ-InC(SiMe3)3]2Co-
CO)3 (2.8014(6) Å).9b In both Cp*Ga units, the η -
5
bonding mode is maintained. The gallium atoms are
located in approximately the central position above the
Cp* ring systems; the respective Ga-C(Cp*) distances
only vary between 2.241(3) and 2.338(4) Å (see Table
6
) with an average value of 2.287(3) Å. Furthermore,
all methyl groups are located within the corresponding
C5-ring planes.
Despite its poor solubility even in benzene-d6, 6 could
1
13
be characterized by NMR techniques. The H and
C
NMR spectra confirm the solid-state structure to be
5
present also in solution. As expected for η -Cp* units,
only one type of methyl group and ring carbon atom is
1
13
found in the H NMR (δ 1.93 ppm) and C NMR
spectrum (δ 9.94 and 116.75 ppm). The resonance for
the six carbonyl carbon atoms can be detected only after
a 12 h aquisition time as a very small and broad signal
F igu r e 6. Molecular structure of Ni
4 4 6
(Cp*Ga) (CO) , 8.
Ta ble 7. Selected Bon d Len gth s (Å) a n d An gles
(
d eg) for 8
(δ 206.00 ppm). In the νCO region, the IR spectrum of 6
Ga(1)-Ni(1)
Ga(1)-Ni(2)
Ga(1)-Ni(4)
Ga(2)-Ni(1)
Ga(2)-Ni(2)
Ga(2)-Ni(3)
Ga(3)-Ni(2)
Ga(3)-Ni(3)
Ga(4)-Ni(3)
Ga(4)-Ni(4)
Ni(1)-Ni(2)
Ni(1)-Ni(3)
Ni(1)-Ni(4)
Ni(2)-Ni(3)
Ni(2)-Ni(4)
Ni(3)-Ni(4)
2.4599(13)
2.3166(11)
2.5824(12)
2.4256(12)
2.3173(13)
2.8321(13)
2.2933(11)
2.4399(12)
2.4452(12)
2.4358(12)
2.5080(12)
2.4273(12)
2.621(2)
Ni(1)-C(43)
Ni(1)-C(41)
Ni(2)-C(42)
Ni(3)-C(43)
Ni(3)-C(44)
Ni(4)-C(45)
Ni(4)-C(46)
O(1)-C(41)
O(2)-C(42)
O(3)-C(43)
O(4)-C(44)
O(5)-C(45)
O(6)-C(46)
1.885(6)
1.729(6)
1.735(6)
1.942(6)
1.748(6)
1.754(6)
1.770(7)
1.153(7)
1.145(7)
1.161(7)
1.139(7)
1.142(7)
1.153(8)
shows absorptions in the typical range for terminal CO
-
1
ligands (between 2023 and 1948 cm ). In the EI mass
spectrum of 6, the molecular ion and the fragments
formed by successive loss of carbon monoxide are
detected with very small intensities; the spectrum is
dominated by the loss of CO and Cp*Ga.
When a solution of Cp*Ga in n-hexane was added
dropwise to an excess of Ni(CO)4, immediate gas evolu-
tion indicated CO substitution and a highly unstable
colorless intermediate (7) was formed. Further stirring
or gentle heating caused further gas evolution and a
color change to red, which intensified after removing
all volatile components in vacuo. The remaining red
crystalline solid was characterized as the cluster com-
pound Ni4(Cp*Ga)4(CO)6 (8) (see Scheme 6). In the solid
state, 8 decomposes at 180 °C. The air-sensitive com-
plex readily dissolves in the usual organic solvents.
Recrystallization from n-hexane/toluene at 4 °C gave red
plates of 8 suitable for an X-ray structure analysis.
The unstable intermediate is presumably the mono-
substitution product Ni(Cp*Ga)(CO)3 (7), as indicated
in an independent experiment. Thus, equimolar quan-
tities of the starting materials were reacted in benzene-
d6 solution and investigated spectroscopically. Only a
2.5926(13)
2.6586(13)
2.6579(13)
Ni(1)-Ni(3)-Ni(2)
Ni(1)-Ni(4)-Ni(2)
Ni(1)-Ni(4)-Ni(3)
Ni(1)-Ni(2)-Ni(4)
Ni(2)-Ni(3)-Ni(4)
59.84(3)
56.72(3)
54.74(3)
60.89(4)
60.83(4)
Ni(2)-Ni(1)-Ni(4)
Ni(3)-Ni(1)-Ni(4)
Ni(3)-Ni(2)-Ni(4)
Ni(3)-Ni(4)-Ni(2)
62.40(4)
63.40(4)
60.80(4)
58.37(4)
given in Table 1, and selected bond lengths and angles
are collected in Table 7.
Compound 8 possesses a Ni4 tetrahedron as its central
framework. The Ni4 tetrahedron is strongly distorted,
and the Ni-Ni distances vary from 2.4273(12) to
2
.6586(13) Å. Each Ni atom is coordinated by a termi-
1
13
nal CO ligand. Additionally, one of the remaining CO
ligands coordinates terminally to a Ni atom (Ni(4)) while
the other is in a bridging position (between Ni(1) and
Ni(3)). All C-O and Ni-C distances are in the expected
range. Interestingly, the four Cp*Ga ligands coordinate
to the Ni core in a different manner. This is illustrated
in Figure 7, which shows the orientation of the four
gallium centers with respect to the Ni4 tetrahedron. The
coordination changes from a rather symmetrical µ3 mode
complexed Cp*Ga unit was detected in the H and
C
1
13
NMR spectrum ( H NMR 1.79 ppm (Cp*-Me); C NMR
1
3
9
.94 (Cp*-CH3), 114.12 ppm (ring C)). The C NMR
spectrum showed an additional resonance at 196.81 ppm
(
CO). The IR spectrum in the carbonyl region showed
-
1
two absorptions at 2066 (A1) and 1996 cm
(E), as
expected for a Ni(CO)3L complex with a local C3v
symmetry. Compound 7 could not be isolated and
turned out to be unstable under ordinary conditions
(
gallium atom Ga(1)) to a µ2 situation (gallium atom
(easy loss of CO and formation of 8, see Scheme 6).
Ga(4)). The gallium atoms Ga(2) and Ga(3) coordinate
to the Ni core in modes between symmetrical µ2 or µ3
situations. A terminal µ1 coordination is not observed.
As a consequence of the described bonding situation, the
gallium-nickel distances are quite different, varying
Compound 8 crystallizes with two molecules of tolu-
ene per formula unit. The molecular structure of 8 is
depicted in Figure 6. Crystal structure parameters are
(24) Leung, P. C.; Coppens, P. Acta Crystallogr. 1983, B39, 535.

1
312 Organometallics, Vol. 17, No. 7, 1998
J utzi et al.
F igu r e 8. Determination of the cone angle of Cp*Ga in
complexes. θ can be calculated by the following equation:
2
2
2
2
2
tan θ/2 ) (d×rCp* + rvdw d + r
- r
/d - rvdw
,
x
Cp*
vdw
where rvdw ) van der Waals radius of a methyl group; rCp*
)
(Cp*)centroid - C(methyl) distance; d ) (Cp*)centroid
F igu r e 7. Coordination modes of Cp*Ga units in 8.
from 2.2933(11) to 2.8321(13) Å; the Ga(2)-Ni(3) bond
is by far the longest (2.8321(13) Å); the average Ga-Ni
distance is 2.455(1) Å. In all four Cp*Ga ligands, the
η coordination mode of the Cp* unit is maintained.
Thus, the gallium atoms are located in approximately
a central position above the Cp* ring planes; the average
- M distance.
reductive dehalogenation of (pentamethylcyclopenta-
dienyl)diiodogallane, Cp*GaI2, leads to 1 in high yield,
making it available in large-scale quantities. The
exceptional thermal stability of 1 is noteworthy.
5
Due to the gallium-centered lone pair, 1 can act as a
ligand in transition metal chemistry, replacing, for
example, carbon monoxide or other weakly bound
ligands. The first examples with 1 as a ligand are
presented from the chemistry of chromium, iron, cobalt,
and nickel. They show that 1 can bind in terminal as
well as in bridging positions. Connection to two (µ2) or
even three (µ3) metal centers in a more or less sym-
metrical arrangement as in 5, 6, and 8 characterizes
the bridging situation. A terminal position is restricted
to mononuclear complexes such as 3, 4, and 7.
(Cp*)C-Ga distance is 2.322(6) Å. In addition, all
methyl groups are in a plane with the corresponding
C5-ring perimeter. As a consequence of its molecular
asymmetry, compound 8 crystallizes in space group P1h
in the form of enantiomers.
Lack of symmetry is also evident from the complexity
of the band pattern in the IR spectrum. In the νCO
region, four absorptions are observed both in the solid
state and in solution. An absorption at 1830 cm-
1
indicates the presence of bridging CO groups, whereas
the other three absorptions at 2000, 1972, and 1950
It is interesting to note that π-bonding between the
Cp* unit and the gallium atom is preserved in all
-
1
cm are typical for terminal CO ligands. In contrast,
5
1
13
transition metal complexes synthesized so far. An η -
the H and C NMR measurements in solution indicate
coordination is generally observed; but steric congestion
a highly fluxional structure of 8 on the NMR time scale.
3
1
1
can lead to an η /η bonding mode, as documented in
one of the three Cp*Ga ligands in the solid-state
structure of complex 5. Remember that haptotropic
shifts can easily occur in Cp compounds of the main
The H NMR spectrum shows only one singlet at 2.02
ppm for the Cp* methyl groups. Correspondingly, the
1
3
C NMR spectrum shows one resonance for the Cp*
methyl groups (10.18 ppm) and one resonance for the
Cp* ring carbon atoms (115.38 ppm). In addition, only
one resonance for the six carbonyl C atoms is observed
at 208.58 ppm. Compound 8 decomposes at 180 °C. In
EI-MS experiments, no nickel-containing fragments
were observed; only the loss of Cp*Ga and CO was
detected during heating, indicating decomposition under
these conditions also.
1
0
5
group elements. The spacial requirements of an η -
Cp*Ga ligand is documented by its cone angle, θ,27
which can be determined using simple trigonometric
calculations. Thus, with the van der Waals radius of a
2
8
methyl group (2.00 Å), with the average (Cp*)centroid-
C(Me) distance (2.717 Å) and with an averaged (Cp*)-
centroid-M distance (4.226 Å, taken from the structural
data of 3 and 4, one can calculate a cone angle of 112°,
as shown in Figure 8. For comparison, the cone angle
of PF3, PH2Et, PMe3, PEt3, and PPh3 is 104°, 111°, 118°,
Isoelectronic compounds of the type Ni4(CO)6L4 with
L ) PMe3,25 P Bu3, and P(C2H4CN)3 are already
n
25
26
known in the literature. In these compounds, the
ligands L are in terminal and the CO ligands in bridging
positions, leading to a skeletal Td symmetry. A quite
different situation is found in 8, in which the ligands L
2
9
1
32°, and 145°, respectively.
In transition metal chemistry, common ligands are
characterized with respect to their σ-donor/π-acceptor
properties. A corresponding classification of the Cp*Ga
ligand can be performed on the basis of X-ray crystal
stuctural data (Cp*-Ga and M-CO distances) and on
the basis of IR data (νCO region, trans effect). Crystal
structure data of 3 and 4 show that the (Cp*)C-Ga
bonds are shortened by approximately 7% in comparison
(Cp*Ga) occupy bridging positions and the CO ligands
are in terminal as well as in bridging positions.
Con clu sion s
A new method for the synthesis of pentamethylcyclo-
pentadienylgallium, Cp*Ga (1), has been developed. The
(
25) Bochmann, M.; Hawkins, I.; Yellowless, L. J .; Hursthouse, M.
B.; Short, R. L. Polyhedron 1989, 8, 1351.
26) Bennett, M. J .; Cotton, F. A.; Winquist, B. H. C. J . Am. Chem.
Soc. 1967, 89, 5366.
(27) Tolman, C. A. Chem. Rev. (Washington, D.C.) 1977, 77, 313.
(28) Pauling, L. Die Natur der chemischen Bindung, zweite Aufl.;
Verlag Chemie: Weinheim, 1964; p 245.
(
(29) White, D.; Coville, N. J . Adv. Organomet. Chem. 1994, 36, 95.

Pentamethylcyclopentadienylgallium
Organometallics, Vol. 17, No. 7, 1998 1313
this novel ligand. Interesting chemical properties of the
new complexes can be envisaged due to the flexibility
5
3
1
in Cp* bonding (η -η -η ) and due to the leaving-group
character of the Cp* unit.
Exp er im en ta l Section
Gen er a l Da ta . All manipulations were carried out under
a purified argon atmosphere using standard vacuum tech-
niques. The solvents were commercially available, purified by
conventional means, and distilled immediately prior to use.
The ultrasonic metal activation was performed using a Biob-
F igu r e 9. Resonance structures of Cp*GaML
n
complexes.
3
4
to those of Cp*Ga in the solid state or in the gas phase.
Reduced distances indicate stronger σ-bonding due to
the presence of a gallium atom in a comparatively
higher oxidation state and allow the Cp*Ga ligand to
be classified as a predominant σ-donor in a strongly
lock Scientific Vibra-Cell (72412) apparatus. GaI
pared from the elements and sublimed in vacuo. Fe
Co (CO) , and Ni(CO)
without further purification. Cr(CO)
3
was pre-
2
9
(CO) ,
2
8
4
were commercially available and used
1
6
38
δ+
δ-
5
(C
8
H
14), Fe(CO)
3
CHT,
polarized bond (Ga -M ). The converse effect (pre-
dominant π-acceptor) should result in longer (Cp*)C-
Ga distances and possibly in a change in hapticity from
1
1
and Cp*SiMe
3
can be prepared according to the literature.
The melting point determinations were performed using a
B u¨ chi 510 melting point apparatus. Elemental analyses were
performed by the Microanalytical Laboratory of the Univer-
sit a¨ t Bielefeld. The NMR spectra were recorded in benzene-
5
3
1
η to η or even η ; this phenomenon is not observed.
Predominant σ-donor behavior of the Cp*Ga ligand
should also result in a strengthening of the transoid
metal-carbon bond and in a weakening of the respective
carbon-oxygen bond (trans effect). As expected, shorter
trans M-CO bonds are observed in the structures of 3
and 4, compared to the situation in the binary carbonyl
complexes Cr(CO)6 and Fe(CO)5. Details have been
discussed earlier.
1
6
d using a Bruker Avance DRX 500 spectrometer ( H 500.1
1
3
1
MHz; C{ H} 125.8 MHz). Chemical shifts are reported in
ppm and are referenced to benzene as an internal standard.
IR data were collected using a Bruker Vektor 22-FT spectrom-
eter. The samples were measured as KBr pellets or in solution
between KBr windows. Absorption intensities are reported
with abbreviations w (weak), m (medium), s (strong), vs (very
strong), and sh (shoulder). Mass spectrometry was performed
using a VG Autospec spectrometer. Only characteristic frag-
ments and isotopes of the highest abundance are listed.
In compounds of the type LCr(CO)5, LFe(CO)4, and
LNi(CO)3, the νCO symmetric stretching band (A1(1) or
A1) strongly depends on the trans-positioned ligand L.
For comparison, complexes with L ) PR3 and Cp*Ga
are considered in more detail. Thus, in LCr(CO)5
complexes, the A1(1) mode is observed at 1943 (L )
P r ep a r a tion of Cp *Ga I
g, 12.0 mmol) in n-hexane (15 mL) was added dropwise to a
refluxing suspension of GaI (5.41 g, 12.0 mmol) in n-hexane
2 3
(2). A solution of Cp*SiMe (2.51
3
(35 mL). While the reaction mixture was heated at reflux for
1 h, the color changed to red. Apart from a small amount of
solid decomposition products, all components were soluble.
After separation of the solution, all volatile components were
removed in vacuo. The remaining solid was recrystallized from
a n-hexane (50 mL)/toluene (10 mL) mixture to give 4.91 g
PEt3),30 1942 (L ) PPh3) , and 1918 cm (L ) Cp*Ga);
31
-1
in LFe(CO)4 complexes, the A1(1) mode is found at 1966
L ) PEt3), 1977 (L ) PPh3), and 1966 cm (L )
Cp*Ga); finally, in LNi(CO)3 complexes, the A1 mode is
observed at 2061 (L ) PEt3), 2068 (L ) PPh3), and
066 cm (L ) Cp*Ga). An inspection of those data
3
2
33
-1
(
3
4
34
(
2
10.7 mmol) of Cp*GaI , 2 (89% yield).
-
1
2
Decomposition point: 122 °C. 1H NMR: δ ) 1.71 (s, 15 H,
without recourse to force constants shows that the
ligand Cp*Ga is similar in its electronic properties to
triorganophosphanes, which are regarded as strong
donors but poor acceptors.35
1
3
Cp* methyl). C NMR: δ ) 11.69 (Cp* methyl), 122.28 (Cp*
ring). MS (EI, 70 eV) [m/z (rel int.)]: 450 [GaI
+
3
(49)], 323
+
+
+
+
[GaI
2
(89)], 136 [Cp*H (50)], 127 [I (66)], 121 [Cp*H - CH
3
-1
2
(100)]. Anal. Calcd for C10H15GaI (M ) 458.76 g mol ): C,
In a valence-bond picture, the predominant σ-donor
ability of the Cp*Ga ligand is best represented by
resonance structure a in Figure 9. A comparable
bonding situation has been described for Fe(Cp*Al)(CO)4
on the basis of crystal structure and spectroscopic data
and DFT calculations for the parent complex, Fe(CpAl)-
26.18; H, 3.29. Found: C, 25.8; H, 3.26.
P r ep a r a tion of Cp *Ga (1). Potassium, 0.98 g (10.0 mmol),
was added to a solution of 4.59 g (10.0 mmol) of Cp*GaI (2)
in 40 mL of toluene. During sonification with 200 W for 10
min, the reaction mixture was allowed to warm to 70 °C to
melt the potassium metal. After filtration and extraction of
the remaining grayish solid with 20 mL of toluene, the solvent
was removed from the combined yellow solutions. The re-
maining oil was distilled at 80 °C (8 Torr) to give 1.43 g (7.0
mmol) of Cp*Ga (1) (70% yield) as a light yellow liquid, which
2
8
b
(CO)4, only recently by Fischer et al. In comparison
to the Cp*Ga ligand, the σ-donor properties of anionic
-
R2Ga and of donor-stabilized RGa ligands are even
3
6,37
more predominant, as also reported by Fischer et al.
solidified after several days during storage at 4 °C.
1H NMR: δ 1.92 (s, 15 H, Cp* methyl). 13C NMR: δ 10.06
(Cp* methyl), 113.51 (Cp* ring).
The easy availability of Cp*Ga should allow the
synthesis of further transition metal complexes with
P r epar ation of Cr (Cp*Ga)(CO)
5 8
(3). A solution of (C H14)-
(
30) Dalton, J .; Paul, I.; Smith, J . G.; Stone, F. G. A. J . Chem. Soc.
A 1968, 1195.
31) Delbeke, F. T.; van der Kelen, G. P. J . Organomet. Chem. 1974,
4, 239.
32) Inoue, H.; Nakagome, T.; Kuroiwa, T.; Shirai, T.; Fluck, E. Z.
Naturforsch. B 1987, 42, 573.
33) Darensbourg, D. J .; Nelson, H. H. III; Hyde, C. L. Inorg. Chem.
974, 13, 2135.
Cr(CO) (0.40 g, 1.32 mmol) and Cp*Ga (1) (0.29 g, 1.41 mmol)
5
in 12 mL of n-hexane was refluxed for 1 h. On cooling to room
temperature, the product precipitated as a yellow powder.
Subsequently, all volatile components were removed in vacuo
(
6
(
5
to yield 0.45 g (1.13 mmol; 86%) of Cr(Cp*Ga)(CO) (3).
(
1
(
(
34) Tolman, C. A. J . Am. Chem. Soc. 1970, 92, 2953.
35) Bochmann, M. Organometallics 1; Oxford University Press:
(37) Schulte, M. M.; Herdtweck, E.; Raudaschl-Sieber, G.; Fischer,
R. A. Angew. Chem. 1996, 108, 489; Angew. Chem., Int. Ed. Engl. 1996,
35, 424.
(38) Brauer, G. Handbuch der Pr a¨ parativen Anorganischen Chemie
i 3 Bd. Stuttgart Enke 1981; p 1891.
London, 1994; p 14.
36) Fischer, R. A.; Schulte, M. M.; Herdtweck, E.; Mattner, M. R.
Inorg. Chem. 1997, 36, 2010.
(

1
314 Organometallics, Vol. 17, No. 7, 1998
J utzi et al.
Mp: 156 °C. 1H NMR: δ 1.64 (s, 15 H, Cp* methyl). 13C
NMR: δ 8.86 (Cp* methyl), 115.20 (Cp* ring), 219.01 (COequa-
whereupon immediate gas evolution was observed. While the
solution was heated at reflux for 30 min, the product precipi-
tated as an orange powder. After removal of all volatile
components in vacuo, the brown-red residue was washed with
-
1
torial), 224.26 (COaxial). IR (cm , KBr): 2052 (s, νCO, A
s, νCO, B ), 1918 (vs, νCO, A (1)), 1902 (vs, νCO, E), 1390 (w),
75 (m), 654 (s), 473 (w). MS (EI, 70 eV) [m/z (rel int.)]: 396
1
(2)), 1982
(
6
[
4
(
C
1
1
2
10 mL of n-hexane to yield 0.76 g (1.04 mmol, 42%) of Co -
+
+
+
+
M
(9)], 340 [M - 2CO (3)], 312 [M - 3CO (5)], 284 [M
CO (5)], 256 [M - 5CO (100)], 204 [Cp*Ga (10)], 136 [Cp*
-
2 6
(Cp*Ga) (CO) .
+
+
+
Decomposition point: 230 °C. 1H NMR: δ 1.93 (s, 15 H,
+
13
19)], 119 [CpH - CH
3
(22)], 69 [Ga (29)]. Anal. Calcd for
CrGa (M ) 396.99 g mol ): C, 45.38; H, 3.81.
Cp* methyl).
C NMR: δ 9.94 (Cp* methyl), 116.75 (Cp*
-
1
-1
15
H
15
O
5
ring), 206.00 (wide, CO). IR (cm , KBr): 2920 (m, sh), 2863
(m), 2023 (s), 1989 (s), 1953 (vs), 1948 (vs, sh), 1640 (w), 1449
(w), 1416 (w), 1383 (m), 550 (m), 522 (m), 501 (w), 470 (w).
Found: C, 45.34; H, 3.80.
4 2
P r ep a r a tion of F e(Cp *Ga )(CO) (4). A suspension of Fe -
+
+
+
(
CO)
9
(1.82 g; 5.00 mmol) and Cp*Ga (1) (1.02 g; 5.00 mmol)
MS (EI, 70 eV) [m/z (rel int.)]: 696 [M (<0.1)], 668 [M
-
-
+
+
in 30 mL of n-hexane was stirred at room temperature with
exclusion of light for 48 h. Subsequently, all volatile compo-
nents were removed in vacuo from the black solution. The
residual black solid was extracted with 30 mL of hot n-hexane.
The solution was cooled to -60 °C to crystallize the crude
product. Recrystallization from n-hexane yielded 0.53 g (1.42
CO(1)], 640 [M - 2CO(1)], 584 [M - 4CO(1)], 556 [M
+
+
5CO(0.1)], 526 [overlapping of M - 6CO and M - 4CO-Co
+
+
+
(3)], 204 [Cp*Ga (95)], 135 [Cp* (11)], 119 [Cp* - CH
3
(32)],
+
69 [Ga (91)]. Anal. Calcd for C26
30 6 2 2
H O Co Ga (M ) 695.83
-
1
g mol ): C, 44.88; H, 4.35. Found: C, 44.89; H, 4.31.
P r ep a r a tion of Ni (Cp *Ga ) (CO) (8). Cp*Ga (1) (0.74
g, 3.61 mmol) in n-hexane (5 mL) was added dropwise with
stirring to an excess of neat Ni(CO) (10.00 g, 58.6 mmol).
4
4
6
mmol; 28%) of Fe(Cp*Ga)(CO)
Decomposition point: 112 °C. H NMR: δ ) 1.60 (s, 15 H,
4
(4) as a yellow solid.
1
4
1
3
Cp* methyl).
ring), 214.21 (CO). IR (cm , n-hexane; νCO): 2037 (s, νCO
(2)), 1966 (s, νCO, A
C NMR: δ 8.77 (Cp* methyl), 115.43 (Cp*
Immediate gas evolution was observed, and the solution
remained colorless. During stirring and gentle heating,
further gas evolution occurred, whereupon the color changed
to red. The color intensified when all volatile components were
removed in vacuo, giving 8 as a red crystalline solid (1.00 g,
0.82 mmol, 91% yield based on Cp*Ga).
-
1
,
A
[
2
[
1
1
(1)), 1942 (vs, νCO, E). MS (EI, 70 eV)
+
+
+
m/z (rel int.)]: 372 [M (7)], 344 [M - CO (11)], 316 [M
CO (24)], 288 [M - 3CO (11)], 260 [M - 4CO (100)], 204
Cp*Ga (28)], 134 [Cp* (7)], 119 [Cp* - CH
50)]. Anal. Calcd for C14
-
+
+
+
+
+
+
3
(20)], 69 [Ga
-
Decomposition point: 180 °C. 1H NMR: δ 2.02 (s, 15 H,
(
H
15
O
4
FeGa (M ) 372.84 g mol 1):
1
3
C, 45.10; H, 4.06. Found: C, 45.03; H, 4.06.
P r ep a r a tion of F e (Cp *Ga ) (CO) (5). A solution of
Cp*Ga (1) (0.73 g, 3.56 mmol) in toluene (2 mL) was added
dropwise to a solution of Fe(CO) CHT (0.55 g, 2.37 mmol) in
Cp* methyl). C NMR: δ 10.18 (Cp* methyl), 115.38 (Cp*
-
1
2
3
6
ring), 208.58 (CO). IR (cm , KBr): 2976 (w), 2912 (m), 2858
(m), 2000 (s), 1972 (vs), 1950 (vs), 1834 (m), 1444 (w), 1419
3
(w), 1377 (m); C
6 6
H solution (CO range): 2001 (s), 1973 (vs),
toluene (5 mL). While the reaction mixture was heated at
reflux for 1 h, the color of the solution changed to red. After
the mixture was cooled to room temperature, all volatile
1951 (vs), 1826 (m). MS (EI, 70 eV) [m/z (rel int.)]: 204
+
+
+
[Cp*Ga (24)], 136 [Cp*H (32)], 134 [Cp* - H (32)], 121
+
+
[Cp*H -CH
3
3
(60)], 119 [Cp* - H-CH (100)]. Anal. Calcd
4 4
-
1
components were removed in vacuo to yield 0.63 g of Fe
Cp*Ga) (CO) (0.70 mmol, 59%).
Decomposition point: 270 °C. 1H NMR: δ 2.05 (s, 15 H,
2
-
for C46 Ni Ga (M ) 1222.69 g mol ): C, 45.19; H, 4.95.
H
60
O
6
(
3
6
Found: C, 44.75; H, 4.68.
1
3
Cp* methyl). C NMR: δ 10.85 (Cp* methyl), 119.21 (Cp*
Ack n ow led gm en t. The support of this work by the
Deutsche Forschungsgemeinschaft, the Universit a¨ t
Bielefeld, and the Fond der Chemischen Industrie is
gratefully acknowledged. We thank T. Pott for excellent
preparative work.
-
1
ring), 216.73 (CO). IR (cm ; KBr): 2912 (m, sh), 2861 (m),
1
951 (vs, sh), 1923 (vs), 1447 (m), 1379 (m), 1028 (w), 585 (s).
+
+
MS (EI, 70 eV) [m/z (rel int.)]: 894 [M (21)], 782 [M - 4CO
+
+
(
3)], 606 [M - 3CO-Cp*Ga (100)], 494 [M - 5CO-Fe-
+
+
+
Cp*Ga (27)], 204 [Cp*Ga (19)], 135 [Cp* (6)], 119 [Cp*
-
+
CH
3
(16)], 69 [Ga (36)]. Anal. Calcd for C36
H
45
O
6
Fe
2
Ga
3
(M
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, positional and thermal parameters, and selected bond
lengths and angles (44 pages). Ordering information is given
on any current masthead page.
-
1
)
894.61 g mol ): C, 48.33; H, 5.07. Found: C, 48.08; H,
.09.
P r ep a r a tion of Co
g, 5.22 mmol) in n-hexane (5 mL) was added dropwise to a
solution of Co (CO) (0.89 g, 2.61 mmol) in n-hexane (15 mL),
5
2
2 6
(Cp *Ga ) (CO) (6). Cp*Ga (1) (1.07
2
8
OM970913A