Nitrogen-functionalized cyclopentadienyl ligands with a rigid framework: Complexation behavior and properties of Cobalt(I), -(II), and -(III) half-sandwich complexes

Article abstract of DOI:10.1021/om0007163

Reaction of 2-lithio-N,N-dimethylaniline with 2,3,4,5-tetramethylcyclopentenone yields 1-[2-(N,N-dimethylaminophenyl)]-2,3,4,5-tetramethylcyclopentadiene (2). As in 1-(8-quinolyl)-2,3,4,5-tetramethylcyclopentadiene (1), the N-donor is connected to the Cp ring by a rigid C₂ spacer. Co₂(CO)₈ reacts with 1 or 2 to give the Co^I-dicarbonyl half-sandwich complexes 7 and 3, respectively. Irradiation leads to the binuclear complexes 4 and 8 with a Co-Co double bond. Oxidation of 3 or 7a is possible with iodine. Whereas 7a directly forms the Co^III complex 9 with coordination of the quinoline to the metal, 3 yields the monocarbonyldiiodo complex 5. Upon gentle heating in dichloromethane, 5 loses carbon monoxide to give the cobalt complex 6, displaying intramolecular nitrogen coordination. Reaction of the dimethylaniline-substituted cyclopentadienide 10 with CoCl₂ yields the Co^II complex 11. The Co^III complex 6 and the Co^II complex 11 were treated with methylaluminoxane (MAO) and gave low-activity catalysts for the polymerization of ethylene.

Full text of DOI:10.1021/om0007163

Organometallics 2001, 20, 827-833
827
Nitr ogen -F u n ction a lized Cyclop en ta d ien yl Liga n d s w ith
a Rigid F r a m ew or k : Com p lexa tion Beh a vior a n d
P r op er ties of Coba lt(I), -(II), a n d -(III) Ha lf-Sa n d w ich
Com p lexes
Markus Enders,* Gunter Ludwig, and Hans Pritzkow
Anorganisch-Chemisches Institut, Universita¨t Heidelberg, Im Neuenheimer Feld 270,
D-69120 Heidelberg, Germany
Received August 15, 2000
Reaction of 2-lithio-N,N-dimethylaniline with 2,3,4,5-tetramethylcyclopentenone yields
1-[2-(N,N-dimethylaminophenyl)-2,3,4,5-tetramethylcyclopentadiene (2). As in 1-(8-quinolyl)-
2,3,4,5-tetramethylcyclopentadiene (1), the N-donor is connected to the Cp ring by a rigid
C2 spacer. Co2(CO)8 reacts with 1 or 2 to give the CoI-dicarbonyl half-sandwich complexes 7
and 3, respectively. Irradiation leads to the binuclear complexes 4 and 8 with a Co-Co double
bond. Oxidation of 3 or 7a is possible with iodine. Whereas 7a directly forms the CoIII complex
9 with coordination of the quinoline to the metal, 3 yields the monocarbonyldiiodo complex
5. Upon gentle heating in dichloromethane, 5 loses carbon monoxide to give the cobalt
complex 6, displaying intramolecular nitrogen coordination. Reaction of the dimethylaniline-
substituted cyclopentadienide 10 with CoCl2 yields the CoII complex 11. The CoIII complex
6 and the CoII complex 11 were treated with methylaluminoxane (MAO) and gave low-activity
catalysts for the polymerization of ethylene.
In tr od u ction
Here we report the synthesis of the cyclopentadiene
2, which is functionalized with an N,N-dimethylaniline,
and the use of 1 and 2 for the preparation of cobalt(I),
-(II), and -(III) half-sandwich complexes. In both systems
the spacer group between the nitrogen atoms and the
cyclopentadiene is a rigid C2 chain.
During the past decade cyclopentadienyl ligands
bearing a sidearm with a donor moiety have attracted
a lot of attention in organometallic chemistry.1 In these
hemilabile ligands, the association character and place-
holder function of the donor group could steer catalytic
processes.2 Half-sandwich complexes of cobalt with
intramolecular phosphorus coordination are known for
the cobalt atom in oxidation states +I and +II.1e
However, the corresponding complexes with pendant
nitrogen ligands have only been prepared with CoIII
centers.3 Nitrogen donors such as amines or pyridines
prefer bonding to transition metals in high oxidation
states. Due to their poor acceptor quality, they coordi-
nate only weakly to electron-rich transition metals and
labile complexes are built. In contrast, the Cp ligand
(Cp ) C5R5, R ) H, alkyl, aryl) is known to form strong
bonds to many transition metals. Therefore a chelating
ligand in which Cp is combined with an amine becomes
hemilabile with late transition metals.
Resu lts
Liga n d Syn th esis. The synthesis of the new cyclo-
pentadiene 2 follows the route for the preparation of 1.4
We treated orthometalated N,N-dimethylaniline5 with
tetramethylcyclopentenone. After acidic workup and
treatment with ammonia, 2 was purified by distillation
and a yellow viscous liquid was obtained. The NMR
spectra show that a mixture of the three isomers 2a ,
2b, and 2c is present. However, the ratio of the isomers
changes when the mixture is stored at room tempera-
ture. After several weeks, the isomer 2b becomes the
main product and separates as light yellow crystals.
We have synthesized the functionalized cyclopenta-
diene 1, where the nitrogen donor atom is incorporated
into a rigid aromatic framework.4 Deprotonation of 1
leads to a chelating ligand which forms stable, crystal-
line half-sandwich compounds with early transition
metals.
(1) Review articles: (a) Okuda, J . Comm. Inorg. Chem. 1994, 16,
185. (b) J utzi, P.; Siemeling, U. J . Organomet. Chem. 1995, 500, 175.
(c) J utzi, P.; Redeker, T. Eur. J . Inorg. Chem. 1998, 6, 663. (d) Mu¨ller,
C. Vos, D. J utzi, P. J . Organomet. Chem. 2000, 600, 127. (e) Buten-
scho¨n, H. Chem. Rev. 2000, 100, 1527. (f) Siemeling, U. Chem. Rev.
2000, 100, 1495.
(2) (a) Lindner, E. Coord. Chem. Rev. 1991, 91, 27. (b) Cornils, B.;
Herrmann, W. A.; Schlo¨gl, R.; Wong, C. Catalysis from A to Z; Wiley-
VCH: Weinheim, 2000.
The X-ray structure analysis of 2b shows that the
mainly planar cyclopentadiene forms an angle of 50.7°
to the aniline moiety. Because of the conjugation
(3) J utzi, P.; Kirsten, M. O.; Dahlhaus, J .; Neumann, B.; Stammler,
H. G. Organometallics 1993, 12, 2980.
(4) Enders, M.; Rudolph, R.; Pritzkow, H. Chem. Ber. 1996, 129, 459.
(5) Lepley, A.; Khan, W. A.; Gumanini, A. B. J . Org. Chem. 1966,
31, 2047.
10.1021/om0007163 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 02/02/2001

828 Organometallics, Vol. 20, No. 5, 2001
Enders et al.
Sch em e 1. P r ep a r a tion of CoI a n d CoIII
Com p lexes Sta r tin g w ith th e
Dim eth yla n ilin e-Su bstitu ted Cyclop en ta d ien e 2
respectively. Therefore there is no strong interaction
between the two π-systems of the ligand. The lone pair
of the noncoordinating nitrogen atom points above the
plane of the Cp ring opposite the metal center.
Nitrogen donors are weak ligands for low-valent late
transition metals. Therefore the aniline group in 3
cannot displace a CO ligand. To create a vacant coor-
dination site, we eliminated one carbon monoxide by
irradiation of 3 in hexane. The red-brown solution turns
green after a few hours of irradiation with a mercury
high-pressure lamp. IR spectroscopy shows that the two
absorptions from the terminal carbonyl ligands of 3
become less intense and that a new product is formed
(4) with a bridging carbonyl group giving a band in the
IR at 1770 cm-1. After 4 days the reaction is complete.
The NMR spectrum of 4 is very similar to that of the
starting compound 3. The mass spectrum indicates that
a dimeric complex was formed. This was not unexpected
because it is known that C5H5Co(CO)2 and C5(CH3)5-
Co(CO)2 also form dimers upon irradiation.9 Complex
4 was analyzed by X-ray crystallography (Figure 3). The
solid-state structure shows a bimetallic molecule with
bridging CO ligands and pendant N,N-dimethylaniline
groups. Therefore, the loss of one CO ligand in 3 was
not compensated by coordination of the free nitrogen
donor but by dimerization of the resulting 16-VE frag-
ment. The metal centers in 4 obey the 18-electron rule
by interacting via a Co-Co double bond. The distance
between the two Co atoms (2.346 Å) lies in the expected
range for such molecules.9
between the double bonds in the five-membered ring
and the adjacent aniline, isomer 2b is thermodynami-
cally favored over 2a . An additional stabilization comes
from the interaction of the acidic H atom of the Cp ring
and the nitrogen atom. The two ring systems are
oriented in a way that the nitrogen lone pair points
toward the acidic H atom of the Cp ring. The distance
N1-H10 (2.55 Å) is shorter than the sum of the van
der Waals radii (2.75 Å), so that the interaction can be
described as a C-H‚‚‚N hydrogen bond.6 We were also
able to obtain crystals from the quinolyl-substituted
cyclopentadiene 1. Similar to 2b, the orientation of the
Cp ring and the quinoline moiety allows interaction of
the proton H14 with the nitrogen lone pair, and a H14-
N1 distance of 2.59 Å results. The proximity of the
heterocyclic system to H14 is also observable in solu-
The donor properties of the chelating nitrogen ligands
for cobalt in oxidation state +III have also been inves-
tigated. The half-sandwich complex 3 reacts with iodine
at room temperature, and dark brown crystals of 5 are
formed. The IR spectrum proves that there is still one
terminal CO ligand present (2056.7 cm-1). However, the
EI mass spectrum shows only an ion without carbon
monoxide and with one iodine atom. J utzi et al. have
already demonstrated that oxidation of amino-function-
alized Cp-cobaltdicarbonyl complexes with halogens
leads to CoIII compounds in which one CO ligand
remains in the molecule and the nitrogen function does
not interact with the metal center.3 In our case we
observed exactly the same behavior. In addition we
confirmed the structure of 5 by X-ray crystallography.10
Gentle heating of 5 in dichloromethane is sufficient
to replace the CO ligand by intramolecular coordina-
tion of the dimethylamino group to give green, crystal-
line 6.
1
tion: the chemical shift of the H14 atom in the H NMR
spectrum of 1 (δ(H10) ) 4.24) is clearly shifted downfield
compared to that of C5(CH3)5H.7
Coba lt Com p lexes Sta r tin g fr om 2. It is well
known that substituted cyclopentadienes react with Co2-
(CO)8 under elimination of hydrogen and formation of
dicarbonyl cobalt half-sandwich compounds.3,8 We treated
dicobaltoctacarbonyl with cyclopentadiene 2 in refluxing
tetrahydrofuran. After purification by chromatography,
the dicarbonyl complex 3 was obtained as red-brown,
air-sensitive crystals in good yield (Scheme 1).
The IR spectrum of 3 shows two intense absorptions
(1950.7 and 2009.6 cm-1), proving that two CO ligands
are present, and therefore no coordination of the nitro-
gen donor to the saturated cobalt(I) center can occur.
In addition we analyzed the solid-state structure of 3
(Figure 2). Two independent molecules are present in
the unit cell, and each shows the expected half-sandwich
arrangement. The planes of the Cp ring and the
aromatic substituent form angles of 69.0° and 69.7°,
1
The H and 13C NMR signals of the dimethylamino
group in 6 are shifted to lower field compared to those
of compound 5 (∆δ ) 0.5 in 1H NMR, ∆δ ) 19 in 13C
NMR). The crystal structure analysis of 6 (Figure 4)
demonstrates the suitable geometry of the new ligand
for chelate complexes.
The aniline ring and the planar Cp ligand are nearly
orthogonal (92.9°). This brings the nitrogen donor into
an ideal position to coordinate to the metal center with
(6) (a) Bondi, A. J . Phys. Chem. 1964, 68, 441. (b) Mascal, M. Chem.
Commun. 1998, 303. (c) Taylor, R. Kennard, O. J . Am. Chem. Soc.
1982, 104, 5063.
(7) Burger, W.; Delay, A.; Mazenod, F. Helv. Chim. Acta 1974, 57,
2106.
(8) (a) Okuda, J .; Zimmermann, K. H. Chem. Ber. 1989, 122, 1645.
(b) Cirjak, L. M.; Ginsburg, G. E.; Dahl, F. Inorg. Chem. 1982, 21, 940.
(9) Baldwin, J . C.; Kaska, W. C. J . Organomet. Chem. 1979, 165,
373.
(10) The quality of the structure analysis of 5 is poor. In the crystals
of compound 5 one I2 molecule in the bridge interacts with two metal
complexes forming an I4 bridge. A similar arrangement has been found
in compound 9 (see Figure 5). Such iodine bridges are known (see ref
11).

N-Functionalized Cyclopentadienyl Ligands
Organometallics, Vol. 20, No. 5, 2001 829
F igu r e 1. Solid-state structures of 1 (left) and 2b (right). Selected bond lengths [Å] and angles [deg]: 1: C1-C10 1.480-
(4), C10-C11 1.360(4), C11-C12 1.472(4), C12-C13 1.341(4), C13-C14 1.518(4), C10-C14 1.508(4), C14-N1 3.113(5),
H14-N1 2.59(3), C14-C10-C1-C2 52.5(4); 2b: C1-C9 1.482(2), C9-C10 1.513(2), C10-C11 1.509(2), C11-C12 1.342-
(2), C12-C13 1.478(2), C13-C9 1.355(2), C10-H10 0.98(2), C10-N1 3.120(2), H10-N1 2.55(2), C2-N1-C8 116.78(11),
C2-N1-C7 114.37(11), C10-C9-C1-C2 51.1(2).
F igu r e 4. Solid-state structure of 6. Selected bond lengths
[Å] and angles [deg]: Co-C9 2.014(3), Co-C10 2.071(3),
Co-C11 2.124(3), Co-C12 2.136(3), Co-C13 2.055(3), Co-
I1 2.612(1), Co-I2 2.595(1), Co-N 2.205(2), planeCp
-
F igu r e 2. Solid-state structure of 3, showing one of the
two independent molecules in the unit cell. Selected bond
lengths [Å] and angles [deg] of the molecule shown: Co-
planeaniline 92.9, C2-N-Co 108.8(2), C2-N-C7 107.67(22),
C7-N-C8 107.3(3).
C
Cp 2.065-2.097; Co-CCO 1.732-1.740, C-O 1.147-1.151,
C2-N1 1.421(1); C7-N1 1.456(2); C2-N1-C7 114.62(12);
tance is 0.12 Å shorter than the average distance from
the metal center to C11 and C12. Similar shifts are
observed for other donor-functionalized Cp cobalt com-
plexes such as 9 and 11 or examples from the litera-
ture.3
C2-N1-C8 115.87(12); C7-N1-C8 110.67(14); planeCp
planedimethylaniline 69.7.
-
Coba lt Com p lexes Sta r tin g fr om 1. We compared
the ligand properties of 2 with those of the quinoline-
substituted cyclopentadiene 1. The donor properties of
the nitrogen atoms in 1 and 2 are slightly different.
Whereas 2 has an sp3-nitrogen atom without any
acceptor properties, the sp2-nitrogen atom of the quino-
line group in 1 is also able to accept electron density
because empty π*-orbitals are available.
1 reacts with Co2(CO)8 to give the cobalt complex 7a .
In addition we isolated a second complex (7b) as a
byproduct in up to 5% yield. In 7b the quinoline is
hydrogenated in the heterocyclic moiety. As was the case
with 3, 7a is transformed to a bimetallic complex (8)
with bridging CO ligands. However, complex 7a shows
different behavior upon oxidation. Both CO ligands are
eliminated by reaction of the red-brown solution in
hexane with iodine, leading directly to compound 9. The
observed reactivity shows that the sp2-nitrogen atom of
the quinolyl substituent is able to displace carbon
F igu r e 3. Solid-state structure of 4. Selected bond lengths
[Å] and angles [deg]: Co-CCp 2.084-2.117; Co1-C18
1.860(2); C-O 1.184(3), Co-Co 2.346(1), C7-N1 1.467(3);
C8-N1 1.457(3); C2-N1-C8 113.4(2); C8-N1-C7 110.6-
(2); C2-N1-C7 115.4(2); planeCp-planedimethylaniline 67.30.
a distance of 2.205 Å. The angles at the nitrogen atom
(107-109°) are very close to the ideal value for a
tetrahedral arrangement. The cobalt atom is not cen-
tered below the Cp ring, but shifted toward the N,N-
dimethylaniline substituent. Therefore the Co-C9 dis-

830 Organometallics, Vol. 20, No. 5, 2001
Enders et al.
Sch em e 2. P r ep a r a tion of CoI a n d CoIII
Com p lexes Sta r tin g w ith th e
Qu in olin e-Su bstitu ted Cyclop en ta d ien e 1
F igu r e 5. Solid-state structure of 9 with coordinated I2.
Selected bond lengths [Å] and angles [deg]: Co1-C10
2.016(3), Co1-C11 2.082(2), Co1-C12 2.121(3), Co1-C13
2.135(3), Co1-C14 2.047(3), Co-I1 2.608(1), Co-I3 2.595-
(1), Co-N 1.981(2), I1-I2 3.3625(2), planeCp-planequinoline
63.0, C10-C1-C9 126.99(24), C10-C1-C2 113.65(21),
Co1-I1-I2 97.29(1), I1-I2-I2′ 178.13(1).
Sch em e 3. P r ep a r a tion of th e Coba lt(II)
Ha lf-Sa n d w ich Com p lex 11
presence of phosphines, or pyridine as external donors,
it is possible to isolate compounds of the type [CpCoL2]+
or CpCoLX (L ) phosphine, X ) halogen).12,13 We
deprotonated the functionalized cyclopentadiene 2 with
n-BuLi and obtained the lithium salt 10, which was
treated with CoCl2 in tetrahydrofuran at room temper-
ature (Scheme 3).
By this route we obtained the CoII complex 11 as a
blue powder in 76% yield. The EI mass spectrum shows
the molecular ion in 33% abundance. Blue needles that
were suitable for X-ray analysis precipitated from a
toluene solution (Figure 6).
F igu r e 6. Solid-state structure of 11. Selected bond
lengths [Å] and angles [deg]: Co-C7 1.977(3), Co-C8
2.081(2), Co-C9 2.099(2), Co-Cl 2.224(1), Co-N 2.025(3),
planeCp-planeaniline 90.0, C2-N-Co 108.8(2), C2-N-C10
110.0(2), C10-N-Co 109.2(2).
The molecule has a mirror plane going through the
aniline ring as well as the cobalt, chlorine, and one of
the carbon atoms of the Cp ring. The distance between
the metal center and the plane of the five-membered
ring is 1.667 Å and thus significantly shorter than those
in CoIII complexes 6 (1.684 Å) and 9 (1.683 Å). In
addition the Co-N bond in 11 (2.025(3) Å) is much
shorter than in 6 (2.205 Å). We conclude that due to
the lower coordination number of the cobalt atom, the
ligands are more strongly bound in 11 than in 6.
We recorded an EPR spectrum of 11 in frozen toluene
at 110 K (Figure 7). The resonance shows a rhombic
g-tensor with characteristic 59Co hyperfine structure.
Two g-values and the corresponding hyperfine coupling
constants were directly taken from the spectrum; the
values for the third octet in the middle of the spectrum
were determined by comparison with a simulated
spectrum (see Figure 7 for details).14
monoxide easily in cobalt(III) complexes, whereas the
dimethylaminoaniline ligand binds less strongly to the
metal.
The crystal structure analysis of a charge-transfer
adduct of two molecules of 9 with one iodine molecule
is shown in Figure 5. The CoIII center is coordinated by
the nitrogen donor, and the nearly planar quinoline
(max. deviation from planarity 0.017 Å) builds an
interplanar angle of 83° to the Cp ring. Two half-
sandwich complexes are linked by an I2 molecule,
forming a nearly linear I4 chain. Similar arrangements
of iodine chains are known.11
Coba lt(II) Com p lexes. Cyclopentadienyl half-sand-
wich complexes of cobalt(I) and cobalt(III) are common.
The reaction of CoII salts with cyclopentadienides leads
preferably to cobaltocene derivatives, because the in-
termediate half-sandwich complex is electronically un-
saturated (15 valence electrons). With the pentameth-
ylcyclopentadienyl ligand, half-sandwich complexes of
cobalt(II) have been isolated as dimers. However, in the
(12) (a) Pfeiffer, E.; Kokkes, M. W.; Vrieze, K. Transition Met. Chem.
1979, 4, 393. (b) McKinney, R. J . Inorg. Chem. 1982, 21, 2051. (c)
Broadley, K.; Connelly, G. N.; Geiger, W. E. J . Chem Soc., Dalton
Trans. 1983, 121.
(13) (a) Koelle, U.; Fuchs, B.; Khouzami, F. Angew. Chem., Int. Ed.
Engl. 1982, 21, 131; Angew. Chem. Suppl. 1982, 230. (b) Koelle, U.;
Fuchs, B.; Belting, M.; Raabe, E. Organometallics 1986, 5, 980. (c)
Raabe, E.; Koelle, U. J . Organomet. Chem. 1985, 279, C29.
(14) WINEPR SimFonia, Version 1.25; Bruker Analytische Messtech-
nik: Karlsruhe, 1996.
(11) (a) Gray, L. R.; Gulliver, D. J .; Levason, W.; Webster, M. Inorg.
Chem. 1983, 22, 2362. (b) Le Bras, J .; Amouri, H.; Vaissermann, J .
Inorg. Chem. 1998, 37, 5056.

N-Functionalized Cyclopentadienyl Ligands
Organometallics, Vol. 20, No. 5, 2001 831
The dimethylamino group as well as the 8-quinolyl
group is able to displace CO ligands in CoIII compounds,
but not in CoI compounds. The quinolyl substituent
shows a greater tendency to bind to the CoIII center
compared to the N,N-dimethylamino group. Crystal
structure determinations of the cobalt complexes with
intramolecular nitrogen coordination prove the tailored
fit of the new ligand for the formation of half-sandwich
compounds. The paramagnetic CoII complex 11 is stable
toward ligand dismutation with formation of a cobal-
tocene derivative. The EPR spectrum shows a rhombic
g-tensor and large 59Co electron coupling. In combina-
tion with methylaluminoxane complexes 6 and 11 show
low activity for the polymerization of ethylene.
F igu r e 7. Experimental X-band EPR spectrum of 11 in
frozen toluene solution at 110 K (top) and simulated
spectrum (bottom). Parameters used for simulation: A(x,x)
) 92.0 G, g(x) ) 2.265, line width ) 10 G; A(y,y) 18.0 G,
g(y) ) 2.090, line width ) 18 G; A(z,z) 41.0 G, g(z) ) 1.975,
line width ) 16 G.
Exp er im en ta l Section
All manipulations were carried out under a nitrogen atmo-
sphere with anhydrous solvents saturated with nitrogen.
Glassware was heated under vacuum prior to use. Compound
1 was synthesized according to the reported procedure.4 NMR
spectra were recorded on a Bruker AC200 spectrometer (200.1
To obtain chelated Co(I) complexes, 11 and 9 have
been reduced with Na/Hg in the presence of CO.
However, only the dicarbonyl complexes 3 and 7a ,
respectively, have been obtained. A similar reduction
experiment in the presence of ethylene did not lead to
isolable products.
Ca ta lytic Olefin P olym er iza tion . Several half-
sandwich complexes of transition metals, such as tita-
nium or chromium in oxidation states III or IV, with
functionalized Cp ligands show high activity as olefin
polymerization catalysts.15 It is also known that cationic
CoIII complexes of the type [C5Me5Co(H)L(C2H4)]+ (L )
PR3, P(OR)3) catalyze the polymerization of ethylene
with low activity.16 Highly active catalysts with late
transition metals have been developed with neutral
chelating nitrogen ligands.17
1
MHz for H; 50.3 MHz for 13C). EPR spectra were obtained on
a Bruker ESP300 instrument at 9.3 GHz equipped with a
frequency counter. Simulation of the anisotropic spectrum of
11 was carried out with the program SimFonia.14
1-(2-N,N-Dim eth yla m in op h en yl)-2,3,4,5,-tetr a m eth yl-
cyclop en ta d ien e (2). N,N-Dimethylaniline (30.0 g, 0.25 mol)
and 80.0 mL (0.20 mol) of 2.5 M n-BuLi in hexane were
refluxed for 52 h. At room temperature 27.1 g (0.20 mol) of
2,3,4,5-tetramethylcyclopent-2-enone was added, and the solu-
tion was heated to reflux for 48 h. After cooling to room
temperature 100 g of ice was added followed by 10 mL of
concentrated hydrochloric acid. The mixture was stirred for
30 min, extracted with diethyl ether, and dried over Mg2SO4.
Distillation at 125-135 °C/10-2 mbar gave 21.9 g of 2 (45%)
as a yellow oil. Storage of the isomeric mixture at room
temperature for several weeks led to the formation of the
crystalline isomer 2b. The spectroscopic data are given for 2b.
We tested the CoIII complex 6 as well as the CoII
complex 11 in catalytic olefin polymerization experi-
ments. Solutions of 6 or 11 in toluene were activated
with 1000 equiv of methylaluminoxane, and the mix-
tures were stirred under an atmosphere of ethylene at
room temperature for 1 h. The polymerization was
stopped by addition of a mixture of CH3OH/HCl. Filtra-
tion led to small amounts of solid polyethylene. The
activity of 6 as well as of 11 lies in the range between
3
1H NMR (CDCl3): δ ) 0.89 (d, 3 H, J (H,H) ) 4.0 Hz, CH3);
1.80 (s, 3 H, CH3); 1.88 (s, 6 H, CH3); 1.96 (s, 3 H, CH3); 2.64
3
(s, 6 H, N-CH3); 3.5 (q, 1 H, J (H,H) ) 4.0 Hz, CpH); 0.6.97-
7.05 (m, 2 H, CHAr); 7.02-7.35 (m, 2 H, CHAr). 13C NMR
(CDCl3): δ 11.1, 11.9, 12.5, 14.4 (Cp-CH3); 43.1 (N-CH3); 51.7
(CHCp); 117.0, 126.8, 127.4, 131.9 (CHAr); 121.2, 128.8, 130.0,
132.2, 134.1, 140.0 (Cq). EI MS: m/z (%) 241 (100, M+); 226
(34, M+ - CH3), 212 (42, M+ - 2CH3), 196 (30, M+ - 3CH3),
182 (20, M+ - 4CH3), 120 (10, M+ - Cp+), 77 (5, C6H5+). HR-
MS(EI): calcd for C17H23N 241.1830; found 241.1823.
3 and 8 (g(polymer) mmol-1
h-1 bar-1).
(catalyst)
Dica r bon yl-η5-[1-(2-N,N-d im eth yla m in oph en yl)-2,3,4,5-
tetr a m eth ylcyclop en ta d ien yl]coba lt(I) (3). A solution of
0.26 g (0.76 mmol) of Co2(CO)8 and 0.37 g (1.52 mmol) of 2 in
50 mL of THF was heated to reflux for 5 h. The solvent was
removed in a vacuum, and the red-brown oily residue was
extracted with 20 mL of hexane. The raw product was purified
by chromatography on Al2O3 (eluent toluene) to give 0.39 g of
3 (72%). 1H NMR (C6D6): δ 1.76 (s, 6 H, CH3), 1.62 (s, 6 H,
CH3); 2.87 (s, 6 H, CH3); 6.92-6.79 (m, 2 H, CHAr); 7.09-7.13
(m, 1 H, CHAr); 7.75 (d, 1 H, CHAr). 13C NMR (C6D6): δ 10.5,
10.9 (CH3); 43.1 (CH3); 56.3, 97.1, 97.5 (CCp); 108.5, 118.0,
121.8, 137.7, (CHAr); 126.4, 154.0 (CAr); 208.1 (CO). MS: (EI)
m/z (%) 355 (33, M+); 327 (18, M+ - CO); 297 (100, M+ - 2CO
- 2H); 241 (15, 2+). FT-IR: (hexane) ν (cm-1) 2009.6, 1950.7.
Anal. Calcd for C19H22NO2Co (355.3): C, 64.23; H, 6.24; N,
3.94. Found: C, 63.99; H, 6.32; N, 3.88.
Con clu sion
We have synthesized a hemilabile chelating ligand in
which an amino group is connected to a cyclopentadienyl
ring by a rigid C2 unit. The coordination properties of
the new ligand in comparison to the 8-quinolylcyclo-
pentadienyl ligand have been evaluated in terms of the
complexation chemistry of CoI, CoII, and CoIII centers.
(15) (a) Stevens, J . C.; Timmers, F. J .; Wilson, D. R.; Schmidt, G. F.
Nickias, P. N.; Rosen, R. K.; Knight, G. W. Lai, S. Y. (Dow Chemical
Co.), EP-B 0416815, 1990 [Chem. Abstr. 1991, 115, 93163m]. (b)
Emrich, R.; Heinemann, O.; J olly, P. W.; Kru¨ger, C.; Verhovnik, G. P.
J . Organometallics 1997, 16, 1511. (c) Theopold; K. H. Eur. J . Inorg.
Chem. 1998, 15. (d) Flores, J . C.; Chien, J . C. W.; Rausch, M. D.
Organometallics 1994, 13, 4140.
(16) (a) Cracknell, R. B.; Orpen, A. G.; Spencer, J . L. J . Chem. Soc.,
Chem Commun. 1984, 326. (b) Schmidt, G. F.; Brookhart, M. J . Am.
Chem. Soc. 1985, 107, 1443.
Bis{ca r b on yl-η5-[1-(2-N ,N -d im e t h yla m in op h e n yl)-
2,3,4,5,-tetr am eth ylcyclopen tadien yl]cobalt(I)} (4). A Pyr-
ex Schlenk tube with a solution of 0.43 g (1.21 mmol) of 3 in
50 mL of hexane was irradiated with a 150 W mercury lamp
for 24 h. The color of the solution changed from red-brown to
(17) (a) Ittel, S. D.; J ohnson, L. K.; Brookhart, M. Chem. Rev. 2000,
100, 1169. (b) Britovsek, G. J . P.; Gibson, V. C.; Waas, D. F. Angew.
Chem., Int. Ed. 1999, 38, 428.

832 Organometallics, Vol. 20, No. 5, 2001
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t Deta ils for 1-4, 6, 7a , 9, a n d 11
Enders et al.
1
2b
3
4
empirical formula
fw
C
18H19
N
C17H23
241.36
N
C19H22CoNO2
355.31
C36H44Co2N2O2
654.60
249.34
cryst syst
triclinic
P1h
triclinic
P1h
triclinic
P1h
triclinic
P1h
space group
unit cell dimens: a, Å
b, Å
7.100(5)
7.2223(7)
8.4292(1)
14.9784(2)
15.0976(2)
107.392(1)
100.742(1)
92.757(1)
1776.15(4)
4
8.608(4)
9.012(4)
11.470(6)
78.02(3)
68.63(3)
76.88(3)
799.3(7)
1
9.170(10)
11.210(10)
93.36(5)
102.01(5)
93.27(5)
710.9(11)
2
1.165
0.067
268
10.3578(10)
10.9185(10)
67.116(2)
72.827(2)
88.440(2)
715.38(12)
2
1.121
0.064
264
c, Å
R, deg
â deg
γ, deg
volume, Å3
Z
density (calcd), Mg/m3
abs coeff, mm-1
F(000)
1.329
0.974
744
1.360
1.072
344
cryst size, mm3
θ range for data
collection, deg
index ranges
0.35 × 0.25 × 0.10
0.42 × 0.28 × 0.20
0.56 × 0.44 × 0.44
0.8 × 0.6 × 0.15
1.86 to 25.03
2.13 to 28.25
1.43 to 28.28
1.92 to 25.00
-8 e h e 8,
-10 e k e 10,
0 e l e 13
2503
2497
1402
-9 e h e 9,
-12 e k e 13,
0 e l e 14
-11 e h e 10,
-19 e k e 18,
0 e l e 20
23480
8588 [R(int) ) 0.031]
7358
-9 e h e 10,
-10 e k e 10,
0 e l e 13
2809
2809
2577
no. of reflns collected
no. of ind reflns
no. of reflns with I > 2σ(I)
completeness to θmax
abs corr
4903
3343 [R(int) ) 0.010]
2388
94.2%
semiemp. from
equivalents
0.928 and 0.851
3343/0/255
99.3%
ψ-scan
97.4%
99.9%
ψ-scan
semiemp. from
equivalents
0.831 and 0.639
8588/0/591
max. and min. transmn
no. of data/restraints/params
goodness-of-fit on F2
0.999 and 0.875
2497/0/248
0.985
1.000 and 0.702
2809/0/278
1.044
0.967
1.018
final R indices [I > 2σ(I)]
R1 ) 0.0569,
wR2 ) 0.1242
R1 ) 0.1303,
wR2 ) 0.1502
0.170 and -0.202
R1 ) 0.0457,
wR2 ) 0.1133
R1 ) 0.0672,
wR2 ) 0.1230
0.280 and -0.195
R1 ) 0.0283,
wR2 ) 0.0762
R1 ) 0.0345,
wR2 ) 0.0792
0.469 and -0.242
R1 ) 0.0274,
wR2 ) 0.0700
R1 ) 0.0317,
wR2 ) 0.0725
0.252 and -0.294
R indices (all data)
largest diff peak and
hole, e Å-3
6
7a
9 with I2
11
empirical formula
fw
cryst syst
space group
unit cell dimens a, Å
b, Å
C17 H22 Co I2
N
C20 H18 Co N O2
363.28
triclinic
P1h
8.362(5)
9.119(5)
12.310(7)
98.35(4)
104.25(4)
105.97(4)
851.5(8)
2
C18 H18 Co I3
687.96
N
C17 H22 Cl Co N
334.74
553.09
monoclinic
P2(1)/c
8.7194(4)
25.4550(12)
8.2347(4)
90
97.028(1)
90
1813.98(15)
4
monoclinic
P2(1)/c
13.2848(2)
7.6319(1)
19.7849(3)
90
101.783(1)
90
1963.69(5)
4
monoclinic
P2(1)/m
7.469(4)
10.662(5)
10.804(5)
90
109.97(2)
90
808.6(7)
2
c, Å
R, deg
â, deg
γ, deg
volume, Å3
Z
density (calcd), Mg/m3
abs coeff, mm-1
F(000)
2.025
4.344
1056
1.417
1.018
376
2.327
5.589
1276
1.375
1.216
350
cryst size, mm3
θ range for data
collection
0.32 × 0.20 × 0.11
0.80 × 0.50 × 0.40
0.40 × 0.18 × 0.15
0.45 × 0.45 × 0.15
1.60 to 28.29
1.75 to 24.98
1.57 to 28.26
2.01 to 27.99
index ranges
-11 e h e 11,
0 e k e 33,
0 e l e 10
12 363
4396 [R(int) ) 0.023]
4011
-9 e h e 9,
-10 e k e 10,
0 e l e 14
2994
2994
2917
-17 e h e 17,
0 e k e 10,
0 e l e 26
23452
4806 [R(int) ) 0.036]
4373
-9 e h e 9,
0 e k e 14,
0 e l e 14
2050
2050
1534
no. of reflns collected
no. of ind reflns
no. of reflections
with I > 2σ(I)
completeness to θmax
abs corr
97.8%
99.8%
ψ-scan
98.7%
multiscan
100.0%
ψ-scan
semiemp. from
equivalents
0.831 and 0.531
4396/0/278
max. and min. transmn
no. of data/restraints/
params
1.000 and 0.915
2994/0/247
0.831 and 0.568
4806/0/281
1.000 and 0.746
2050/0/154
goodness-of-fit on F2
final R indices
1.064
1.046
1.051
1.030
R1 ) 0.0246,
wR2 ) 0.0619
R1 ) 0.0279,
wR2 ) 0.0635
1.577 and -0.876
R1 ) 0.0245,
wR2 ) 0.0688
R1 ) 0.0252,
wR2 ) 0.0694
0.308 and -0.211
R1 ) 0.0196,
wR2 ) 0.0484
R1 ) 0.0231,
wR2 ) 0.0495
0.865 and -0.596
R1 ) 0.0374,
wR2 ) 0.0788
R1 ) 0.0657,
wR2 ) 0.0871
0.270 and -0.408
[I > 2σ(I)]
R indices (all data)
largest diff peak and
hole, e Å-3

N-Functionalized Cyclopentadienyl Ligands
Organometallics, Vol. 20, No. 5, 2001 833
green. The reaction mixture was concentrated in a vacuum,
and at - 30 °C green needles of 4 precipitated (0.31 g, 78%).
1H NMR (C6D6): δ 1.47 (s, 12 H, CH3); 2.15 (s, 12 H, CH3);
2.38 (s, 12 H, CH3); 6.06 (d, 2 H, CHAr); 6.46 (dd, 2H, CHAr);
6.66 (d, 2 H, CHAr); 6.96 (dd, 2 H, CHAr). 13C NMR (C6D6): δ
8.8, 9.2 (CH3); 43.1 (CH3); 99.5, 93.4 (CCp); 117.6, 121.0, 127.6,
136.1 (CHAr) (some of the quartenary 13C resonances were not
detected due to the low solubility of 4). MS: (EI) m/z (%) 653
(19, M+); 355 (20, 3+); 327 (23, 3+ - CO); 299 (100, 3+ - 2CO);
241 (4, 2+). FT-IR (hexane) ν (cm-1): 1770. Anal. Calcd for
8.70 (dd, 1 H). 13C NMR (CD2Cl2): δ 9.4, 9.9 (CH3); 87.6, 97.4,
108.1 (CCp); 123.8, 127.9, 128.6, 129.0, 137.8, 157.5, (CHAr);
129.0, 129.6, 156.6 (CAr); 182.4 (CO). MS: (EI) m/z (%) 670
(21, M+), 614 (5, M+ - 2 CO), 335 (64, 7+ - CO), 307 (100, 7+
- 2CO). FT-IR: (hexane) ν (cm-1) 1770. Anal. Calcd for
C
38H36N2O2Co2 (670.6): C, 68.06; H, 5.41; N, 4.18. Found: C,
67.83; H, 5.49; N, 4.13.
Diiod o-η5-[1-(8-ch in olyl-2,3,4,5-tetr a m eth ylcyclop en ta -
d ien yl]coba lt (III) (9). A solution of 0.18 g (0.71 mmol) of
iodine in 20 mL of diethyl ether was added dropwise to a
solution of 0.25 g (0.69 mmol) of 7 in 30 mL of diethyl ether at
-30 °C. The reaction mixture was stirred at room temperature
for 16 h, the solvent was removed in a vacuum, and the brown-
violet residue was washed with 20 mL of hexane to give 0.10
g (26%) of brown-violet 9. In the presence of excess iodine,
crystals were obtained from dichloromethane at -30 °C. 1H
NMR (CDCl3): δ 2.00, 2.09 (s, 12 H, CH3); 7.28 (dd, 1 H); 7.74-
7.85 (m, 2 H); 7.99 (dd, 1 H); 8.25-8.35 (m, 2 H). 13C NMR
(CDCl3): δ 10.5, 12.2 (CH3); 89.9, 93.7, 105.2 (CCp); 123.0,
126.6, 127.7, 128.2, 136.4, 161.9 (CHAr); 128.3, 128.4, 155.8
(q, CAr). MS (FAB+): m/z (%) 561 (5, M+); 434 (90, M+ - I);
307 (M+ - 2I).
C
36H44N2O2Co2 (654.6): C, 66.05; H, 6.77; N, 4.28. Found: C,
65.79; H, 6.58; N, 4.26.
Ca r b on yld iiod o-η5-[1-(2-N,N-d im et h yla m in op h en yl)-
2,3,4,5-tetr a m eth ylcyclop en ta d ien yl]coba lt(III) (5). A so-
lution of 0.30 g (1.18 mmol) of I2 in 30 mL of diethyl ether
was added dropwise to a solution of 0.41 g (1.15 mmol) of 3 in
30 mL of diethyl ether at -30 °C. The color of the reaction
mixture changed from red-brown to dark violet. After stirring
for 16 h at room temperature, the reaction mixture was
concentrated to give violet crystals at -30 °C. The crystals
were washed with 10 mL of n-hexane and dried in a vacuum
1
(yield 0.39 g, 58%). H NMR (CD2Cl2): δ 2.27, 2.43 (s, 12 H,
CH3); 2.52 (s, 6 H, CH3); 7.16-7.21 (m, 2 H, CHAr); 7.38-7.50
(m, 1 H, CHAr); 8.01-8.05 (m, 1 H, CHAr). 13C NMR (CD2Cl2):
δ 10.8, 11.9 (CH3); 42.7 (CH3); 100.5, 101.5, 103.4 (CCp); 118.3,
121.4, 129.8, 133.6 (CHAr); 120.4, 153.2 (CAr). MS: (EI) m/z
(%) 426 (52, M+ - CO - I); 241 (99, 2+); 28 (100, CO+). FT-IR
(CH2Cl2): ν (cm-1) 2056.7.
Ch lor o-η5-[1-(2-N,N-d im eth yla m in op h en yl)-2,3,4,5,-tet-
r a m eth ylcyclop en ta d ien yl]coba lt(I) (11). A 0.40 g (1.66
mmol) sample of the substituted cyclopentadiene 2 in 30 mL
of THF was deprotonated with 0.66 mL (1.65 mmol) of n-BuLi
(2.5 M in hexane) at room temperature. After 30 min the
orange solution was added dropwise to a suspension of 0.21 g
(1.62 mmol) of CoCl2 in 20 mL of THF. The reaction mixture
was stirred for 16 h, and the solvent was removed in a vacuum.
The blue solid was dissolved in 20 mL of toluene and filtered
through a fritted column (G4) to give 0.42 g (77%) of blue 11.
Crystals were obtained from a concentrated solution in toluene
at -30 °C. MS (EI): m/z (%) 334 (19, M+); 296 (21, M+ - HCl
- 2H); 241 (100, 2+); 120 (20, C6H4NMe2+). HR-MS (EI): calcd
for C17H22NCoCl 334.0773, found 334.0751. EPR (110 K): g1
) 2.265, g2 ) 2.090, g3 ) 1.975; A1 ) 92.0 G, A2 ) 18.0, A3 )
41.0 G.
Diiod o-η5-[1-(2-N,N-d im eth yla m in op h en yl)-2,3,4,5-tet-
r a m eth ylcyclop en ta d ien yl]coba lt(III) (6). A solution of
0.20 g (0.34 mmol) of 5 in 30 mL of dichloromethane was
heated to reflux for 6 h. Removal of solvent and washing with
1
hexane yielded 0.16 g (85%) of green 6. H NMR (CD2Cl2): δ
1.71, 2.13 (CH3); 2.93 (CH3); 7.42-7.53 (m, 2 H, CHAr); 7.63-
8.00 (m, 2 H, CHAr). 13C NMR (CD2Cl2): δ 11.2, 14.1 (CH3);
61.7 (CH3); 88.4, 91.1, 99.1 (CCp); 147.5, 160.6 (CAr); 121.3,
126.2, 127.3, 130.2 (CHAr). MS (EI) m/z (%): 426 (5.7, M+
I); 241 (100, 2+); 127 (38, I+).
-
Dica r bon yl-η5-[1-(8-ch in olyl-2,3,4,5-tetr a m eth ylcyclo-
p en ta d ien yl]coba lt(I) (7a ). A solution of 0.44 g (1.29 mmol)
of Co2(CO)8 and 0.64 g (2.57 mmol) of 1 in 50 mL of tetrahy-
drofuran was heated to reflux for 16 h. The solvent was
removed in vaccum, and the red-brown residue was extracted
with 50 mL of n-hexane and purified by chromatography on
Al2O3 (eluent toluene/hexane, 1:1). Yield: 0.28 g (30%). (The
hydrogenated derivative 7b was isolated in up to 5% yield and
X-r a y Cr ysta l Str u ctu r e Deter m in a tion s of 1-4, 6, 7a ,
9, a n d 11. Crystal data for 2, 3, 6, and 9 were collected on a
Bruker AXS SMART 1000 diffractometer with a CCD area
detector (Mo KR radiation, graphite monochromator, λ )
0.71073 Å) at -100 °C, and for 1, 4, 7a , and 11 on a Siemens
STOE AED2 (Mo KR radiation, graphite monochromator, λ )
0.71073 Å) at -70 °C. The structures were solved by direct
methods and refined by full-matrix least squares against F2
with all reflections using the SHELXTL-programs.18 All non-
hydrogen atoms were refined anisotropically. All hydrogen
atoms were located in difference Fourier maps and refined
isotropically. Crystal data and experimental details are listed
in Table 1.
1
identified by mass and NMR spectroscopy.) H NMR (C6D6):
δ 1.73, 2.11 (s, 12 H, CH3); 7.45 (dd,1 H); 7.63 (dd, 1 H); 7.85
(dd, 1 H); 8.18-8.20 (m, 2 H); 8.97 (dd, 1 H). 13C NMR (C6D6):
δ 10.5, 11.1 (CH3); 97.5, 98.9, 106.6 (CCp); 121.0, 127.5, 128.2,
133.6, 135.9, 136.6, 148.5, 149.9 (CAr); 208.7 (CO). MS: (EI)
m/z (%) 363 (12, M+); 335 (20, M+ - CO); 307 (100, M+ - 2
CO). FT-IR: (hexane) ν (cm-1) 1948.4, 2007.2. Anal. Calcd for
Ack n ow led gm en t. The authors gratefully acknowl-
edge financial support from the Deutsche Forschungs-
gemeinschaft (Sonderforschungsbereich 247) and the
state Baden-Wu¨rttemberg.
C
20H18NO2Co (363.3): C, 66.12; H, 4.99; N, 3.86. Found: C,
66.06; H, 5.04; N, 3.79.
Bis{ca r b on yl-η5-[1(8-ch in olyl)-2,3,4,5-t et r a m et h ylcy-
clop en ta d ien yl]coba lt(I) (8). A Pyrex tube with a solution
of 0.20 g (0.55 mmol) of 7 in 50 mL of hexane was irradiated
with the light of a 150 W mercury lamp for 24 h. The color of
the solution changed from red-brown to green. After removal
of the solvent in a vacuum, the raw product was washed with
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
crystal structure data for 1-4, 6, 7a , 9, and 11. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM0007163
1
hexane to give 0.12 g (65%) of 8 as a green powder. H NMR
(C6D6): δ 1.48, 2.19 (s, 12 H, CH3); 6.72 (d, 1 H); 6.88 (dd, 1
H); 7.31-7.36 (m, 1 H); 7.57-7.60 (m, 1 H); 7.65 (dd, 1 H);
(18) Sheldrick, G. M. SHELXTL NT V5.1; Bruker AXS: Madison,
WI, 1999.