Synthesis and reactivity of cobalt complexes with pendant nitrogen functional groups

Article abstract of DOI:10.1002/ejic.200700447

Several derivatives of cyclopentadienylcobalt complexes having a pendant amino-functionalised side chain (Cp′) are described, the cyclopentadienyl ligands being (2-amino-ethyl)cyclopentadienyl, (2-piperidinoethyl) cyclopentadienyl, 1-(2-piperidinoethyl)-2,3,4,5-tetraisopropylcyclopentadienyl and 2-picolylcyclopentadienyl. Chelation by the amino-functionalised side chain occurred when the Cp*-cobalt(I) dicarbonyl complexes 5, 6, 7 and 8 were oxidised by iodine, thereby forming the corresponding Cp*-cobalt(III) chelates 9, 10, 11 and 12, respectively, through the diiodocarbonyl intermediates 5′, 6′, 7′ and 8′, respectively. The stabilities of the intermediates differ greatly due to the different amino functions in the pendant side chain. Structural studies of 9, 10 and 12 were carried out and the correlation of the I-Co-I angles and the repulsive forces from the amino-functionalised groups with the stabilities of the intermediates is discussed. The diiodocarbonyl-η⁵-(2-piperidinylethyl) cyclopentadienylcobalt(III) intermediate 6′ becomes reduced to 6 by the CO released upon chelation of the former when the concentration of CO reaches about 0.088 mol L^-1. The chelated piperidine group in 10 could be easily replaced by triphenylphosphane to form the diiodotriphenylphosphanyl- η⁵-(2-piperidinioethyl)cyclopentadienylcobalt(III) iodide dichloromethane solvate 13 in the presence of hydrogen iodide. A strong N-H...1 hydrogen bond with an N...I distance of 3.414(14) A and a D-H...A angle of 164.1° were found in 13. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700447

FULL PAPER
DOI: 10.1002/ejic.200700447
Synthesis and Reactivity of Cobalt Complexes with Pendant Nitrogen
Functional Groups
Longjin Li,[a] Shuang Han,[b] Qiang Li,[a] Zhenxia Chen,[a] and Zhen Pang*[a]
Keywords: Cyclopentadienylcobalt complexes / Carbonylcobalt complexes
Several derivatives of cyclopentadienylcobalt complexes
having a pendant amino-functionalised side chain (CpЈ) are
described, the cyclopentadienyl ligands being (2-amino-
ethyl)cyclopentadienyl, (2-piperidinoethyl)cyclopentadienyl,
angles and the repulsive forces from the amino-function-
alised groups with the stabilities of the intermediates is dis-
cussed. The diiodocarbonyl-η5-(2-piperidinylethyl)cyclopen-
tadienylcobalt(III) intermediate 6Ј becomes reduced to 6 by
1-(2-piperidinoethyl)-2,3,4,5-tetraisopropylcyclopentadienyl the CO released upon chelation of the former when the con-
and 2-picolylcyclopentadienyl. Chelation by the amino-func-
tionalised side chain occurred when the Cp*-cobalt(I) dicar-
bonyl complexes 5, 6, 7 and 8 were oxidised by iodine,
thereby forming the corresponding Cp*-cobalt(III) chelates
9, 10, 11 and 12, respectively, through the diiodocarbonyl in-
termediates 5Ј, 6Ј, 7Ј and 8Ј, respectively. The stabilities of
the intermediates differ greatly due to the different amino
functions in the pendant side chain. Structural studies of 9,
10 and 12 were carried out and the correlation of the I–Co–I
centration of CO reaches about 0.088 molLϪ1. The chelated
piperidine group in 10 could be easily replaced by tri-
phenylphosphane to form the diiodotriphenylphosphanyl-η5-
(2-piperidinioethyl)cyclopentadienylcobalt(III) iodide dichlo-
romethane solvate 13 in the presence of hydrogen iodide. A
strong N–H···I hydrogen bond with an N···I distance of
3.414(14) Å and a D–H···A angle of 164.1° were found in 13.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
these complexes can be easily broken under mild condition
thereby creating a vacant site on the metal and such com-
plexes therefore have applications in catalysis. The reactivity
of the active intermediate is strongly influenced by the
changes in the electronic density on the metal centre and
the steric nature of the chelating donor moiety. Thus, an
improved understanding of the factors governing the chela-
tion of the tethered functional group should lead to more
control over the design of more efficient catalytic processes.
Many complexes with a chelating pendant Lewis base teth-
ered to a Cp ligand have be synthesised and studied.[9–22]
We are interested in the chemistry of the half-sandwich type
complexes with a pendant chelating functional group, espe-
cially those containing nitrogen atoms in the pendant side
chain and in the factors which can influence the ability of
the pendant group to chelate to the metal. In this paper we
report the synthesis and reactivity of several cobalt com-
plexes with nitrogen functionalised pendant side chain cy-
clopentadienyl ligands.
Introduction
The cyclopentadienyl group is one of the most important
ligands in organometallic chemistry.[1] Its derivatives with
Lewis bases in a pendant side chain that are capable of
binding to hard and soft centres in a hemilabile manner
promise a rich coordination chemistry and unusual reac-
tions at the metal centre.[2] The Lewis bases may included
alkenes,[3] phosphorus atoms,[4] thioethers, ethers and ester
groups.[5] N-Based Lewis bases tethered to the Cp ligand
have been frequently used as hemilabile ligands. Such li-
gands can only weakly coordinate to late transition metal
centres forming a chelate bond which can also be easily
broken under mild conditions. Since the binding strength
between the metal and the donor ligand can be controlled
sterically or electronically, structural modification to such a
pendant side chain can greatly influence the physical and
chemical properties of these complexes[6] and some molecu-
lar switches, which have been designed, are based on this
concept.[7,8] Furthermore, the weak coordinate bond in
Results and Discussion
[a] Department of Chemistry, Shanghai Key Laboratory of Molec-
ular Catalysis and Innovative Materials,
Four
compounds
C5H5CH2CH2NH2
(1),
C5H5CH2CH2NC5H10 (2), C5(C3H7)4HCH2CH2NC5H10 (3)
and C5H5CH2NC5H4 (4) with a space of two carbon atoms
between the nitrogen atom and cyclopentadienyl ring were
all synthesized using a similar strategy, i.e. treatment of so-
Fudan University, Shanghai 200433, P. R. China
E-mail: zpang@fudan.edu.cn
[b] Department of Chemistry, Yuncheng College of Shanxi Prov-
ince,
Yuncheng City, Shanxi Province 044000, P. R. China
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L. Li, S. Han, Q. Li, Z. Chen, Z. Pang
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Scheme 1.
dium cyclopentadienide with a suitable halogenated alk- with the literature report because they show evidence of the
ylamine followed by standard aqueous workup. Because of appearance of a strong carbonyl absorption band at higher
the good solubility of 1 in aqueous solution, strong acidic frequencies for the solutions which is in contrast to the two
(pH Ͻ 1) and basic (pH Ͼ 14) conditions must be kept carbonyl stretching frequencies observed for the precursors.
during the aqueous workup in order to increase the yield. This carbonyl absorption must come from the reaction in-
The reaction of compounds 1–4 with Co2(CO)8 in dichloro- termediates 5Ј–8Ј as listed in Table 1. However, in all cases,
methane in the presence of a sacrificial olefin 3,3-dimethyl- the black purple precipitate appeared immediately after the
1-butene gave the substituted dicarbonylcyclopentadienyl- addition of iodine and the isolated precipitates also showed
1
cobalt(I) complexes 5–8 in moderate yields, Scheme 1.[23] If one carbonyl absorption band. Elemental analyses and H
the syntheses were to be done in a higher boiling point sol- NMR spectroscopy indicated that the isolated products
vent, the yields should increase.
were mixtures of the CO-free chelates 9–12 and their corre-
All the dicarbonylcobalt(I) complexes show two charac- sponding diiodocarbonyl complexes 5ЈϪ8Ј. For example,
teristic absorption bands in their IR spectra indicating that the 1H NMR spectrum of the precipitate obtained from the
two terminal carbonyl groups are present and that the ni- solution of iodine and 5 shows three peaks at δ = 4.22, 3.60
trogen atoms in the side chains do not coordinate to the and 2.42 ppm. The first and third peaks result from the
cobalt atoms. No chelation was observed between the co- methylene groups between the cyclopentadienyl and amino
balt(I) and the nitrogen functional group except under irra- groups in chelate 9. The peak of 3.60 ppm could also come
diation of light.[24] The characteristic ν(CO) data are listed from the dimethylene group but it is shifted 0.12 ppm
in Table 1.
downfield compared with the similar resonance in 5, indi-
cating a free side chain in the CoIII product 5Ј. A carbonyl
stretching frequency at 2068 cm–1 was found for the solid
but its intensity diminished at room temperature after one
weak indicating the existence of the unstable 5Ј and, hence,
the isolated solid was initially a mixture of 5Ј and 9. The
carbonyl stretching frequency of the solid product isolated
from a solution of iodine and 6 or 7 was found at 2060 or
2046 cm–1, respectively, but the signal disappeared at room
temperature after about one day indicating the isolated
products to be mixtures of 6Ј and 10 or 7Ј and 11, respec-
tively. Only the precipitate isolated form a solution of iodine
and 8 gave the pure chelated product 12. The stability of
the reaction intermediates is therefore of the order 5Ј Ͼ
6Ј:7Ј Ͼ 8Ј. The oxidising process is illustrated in Scheme 2.
The crystal structures of the chelates 9, 10 and 12 were
Table 1. Characteristic CO stretching frequencies of dicarbonyl-
cobalt(I) complex and their corresponding diiodo-monocarbonyl-
cobalt(III) intermediates.
CpЈ(CO)2Co ν(CO) [cm–1][a] Monocarbonyl ν(CO) [cm–1]
5
6
7
8
2017, 1951
2019, 1954
2003, 1943
2016, 1948
5Ј
6Ј
7Ј
8Ј
2068[b], 2074[c]
2060[b], 2066[c]
2050[a], 2046[b]
2077[c]
[a] Neat sample. [b] KBr pellets. [c] Dichloromethane solution.
Complexes 5–8 can be easily oxidised by iodine to yield
the corresponding cobalt(III) complexes.[25] It has been re-
ported that when iodine is added to an ether solution of
carbonyl cyclopentadienylcobalt(I) complexes with an N-
donor function in the side chain, the corresponding che- determined and all of them show that the tethered amino
lated diiodo-cobalt(III) complexes precipitate spontane- group is intramolecularly coordinated to the cobalt atom.
ously from the reaction mixture as black microcrystals.[24a] The ORTEP diagrams and the selected structural param-
It is believed that the chelate is formed via the diiodocar- eters of 9, 10 and 12 are given in Figure 1, Figure 2 and
bonyl complex (vide infra) since, when the CO-free chelate Figure 3. The Co–N bond lengths in 9, 10 and 12 were
precipitates, the solution is still dark purple in colour indi- found to be 1.979(8), 2.097(3) and 1.956(6) Å, respectively.
cating the presence of the monocarbonyl species and this is All of these bond lengths are slightly shorter than those in
1
supported by H NMR spectroscopic observations. In our related tetramethyl-substituted diiodocyclopentadienylco-
experiment, the observations made upon the addition of io- balt(III) complexes, e.g. 2.115(6) Å in diiodo-η5:η1-[l-(2-
dine to the dichloromethane solutions of 5–8 are consistent N,N-dimethylaminoethyl)-2,3,4,5-tetramethyl cyclopenta-
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Co Complexes with Pendant Nitrogen Functional Groups
above structural data indicates that a large repulsive force
might exist in 10 between the iodine ligands and the methyl-
ene groups in the piperidine ring adjacent to the nitrogen
atom which pushes the iodine ligands away from the piperi-
dine moiety and leads to the smallest I–Co–I angle as well
as the longest Co–N bond length among the three chelates.
Scheme 2.
dienyl] cobalt(III) (“aminoethyl”)[24a] and 2.205(2) Å in di-
iodo-η5:η1-[l-[2-(dimethylamino)phenyl]-2,3,4,5-tetramethyl-
cyclopentadienyl]cobalt(III) (“aminophenyl”).[18] Consider-
ing that the alkyl ring of piperidine is an electron-releasing
substituent, the nitrogen atom in the tethered side chain in
10 should be a stronger σ donor compared with that in 9
and 12 and the chelate bond in 10 would be expected to be
the strongest one among the three analogues. However, the
Figure 2. ORTEP diagram of 10 with the probability ellipsoids
drawn at the 50% level. Hydrogen atoms have been omitted for
clarity. Selected bond lengths [Å] and angles [°]: Average Co–
C(ring) 2.055(6), Co(1)–N(1) 2.097(3), Co(1)–I(1) 2.6015(7), Co(1)–
I(2) 2.5714(8), average C–C(ring) 1.4084(6), I(1)–Co(1)–I(2)
92.70(2), I(1)–Co(1)–N(1) 100.32(8), I(2)–Co(1)–N(1) 96.34(9),
chelate bond in 10 was found to be the longest. For easy Co(1)–N(1)–C(7) 104.1(2).
comparison between these analogues, some structural pa-
rameters are listed in Table 2. The average lengths of the
Co–I bonds in 9, 10 and 12 are 2.5979(10), 2.5865(3) and
2.5788(16) Å, respectively Ϫ all slightly shorter than
2.622(2) Å found in “aminoethyl” and 2.604(1) Å found in
“aminophenyl”. The average cobalt–carbon(ring) bond
lengths show the same trend but all are still in the expected
range. The I–Co–I bond angles are 96.50(5), 92.70(2) and
96.68(4) degrees in 9, 10 and 12, respectively. The corre-
sponding values reported for “aminoethyl” and “ami-
nophenyl” are 94.5(1) and 91.302(12)°, respectively. The-
I–Co–N bond angles found in 9, 10 and 12 are 92.07(16),
100.32(8) and 95.12(18)°, respectively. A comparison of the
Figure 3. ORTEP diagram of 12 with the probability ellipsoids
drawn at the 50% level. Hydrogen atoms have been omitted for
clarity. Selected bond lengths [Å] and angles [°]: Average Co–
C(ring) 2.039(8), Co(1)–N(1) 1.956(6), Co(1)–I(1) 2.5779(16),
Co(1)–I(2) 2.5796(16), average C–C(ring) 1.403(14), N(1)–C(7)
1.351(10), N(1)–C(11) 1.327(10), C(7)–C(8) 1.392(12), C(8)–C(9)
1.360(14), C(9)–C(10) 1.370(14), C(10)–C(11) 1.365(12), I(1)–
Co(1)–I(2) 96.68(4), I(1)–Co(1)–N(1) 95.12(18), I(2)–Co(1)–N(1)
95.12(19), Co(1)–N(1)–C(7) 116.9(5).
The COSY spectrum of 10 reveals that the methylene
protons in the piperidine ring adjacent to nitrogen atom
suffer large steric hindrance and retain their configuration
in solution at room temperature (Figure 4). The methylene
protons on the α carbon in the piperidine ring are split into
two sets of signals. The signals of the protons in the e posi-
tion at δ = 3.52 show a strong correlation with the methyl-
ene protons on the β carbon in the piperidine ring (δ =
1.72 ppm) and the signals of the protons in the a position
at δ = 2.93 show a strong correlation with the methylene
Figure 1. ORTEP diagram of 9 with the probability ellipsoids
drawn at the 50% level. Hydrogen atoms have been omitted for
clarity. Selected bond lengths [Å] and angles [°]: Average Co–
C(ring) 2.045(1), Co(1)–N(1) 1.979(8), Co(1)–I(1) 2.5979(10),
Average C–C(ring) 1.4054(4), I(1)–Co(1)–I(1A) 1 96.50(5), I(1)–
Co(1)–N(1) 92.07(16), I(1A)–Co(1)–N(1) 92.07(16), Co(1)–N(1)–
C(5) 110.3(7).
Eur. J. Inorg. Chem. 2007, 5127–5137
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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L. Li, S. Han, Q. Li, Z. Chen, Z. Pang
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Table 2. List of the structural parameters of the cyclopentadienylcobalt complexes with a nitrogen functional group in the pendant side
chain.
Chelates
I–CoϪI [°]
Co–N [Å]
Co–Iav [Å]
Co–C(ring)av [Å]
9
96.50(5)
92.70(2)
96.68(4)
95.40(8)
94.5(1)
1.979(8)
2.097(3)
1.956(6)
2.239(5) (Co–P)
2.115(6)
2.5979(10)
2.5865(3)
2.5788(16)
2.580(3)
2.622(2)
2.604(1)
2.044(7)
2.055(4)
2.039(8)
2.094(17)
2.095(5)
2.080(3)
10
12
13
Aminoethyl[24a]
Aminophenyl[15]
91.302(12)
2.205(2)
protons on the ω carbon in the piperidine ring (δ = have an available d orbital, the π system of pyridine makes
1.22 ppm). The methylene protons on the β carbon in the the donor nitrogen atom in the tethered side chain of 12
piperidine are in a free-flipping motion and give rise to a undergo a stronger interaction with the metal compared
broadened multiplet. We can deduce that the flipping of the with an S or P atom. Thus we may assert that there is a
methylene protons on the α carbon in the piperidine ring in partial double bond in existence in 12 which leads to a
10 is prevented by steric hindrance in the chelated form. shorter Co–N bond.
This steric hindrance results from the repulsive force of the
iodine ligands which keeps the σ orbitals between cobalt
and the amino nitrogen from fully overlapping and thus a
longer chelate Co–N bond results. The side chains in 9 and
10 are coordinated to the cobalt in a zigzag fashion and,
consequently, the latter can be expected to exist as chiral
molecules. However, the very fast flip of the side chain
makes the two enantiomers show only one set of signals in
1
their H NMR spectra. Similar situations have also been
found in “aminoethyl” and “aminophenyl” and by Wang et
al. in the molybdenum complex [C5H4CH2CH2NMe2]-
Mo(CO)2I.[26] In the crystal structure of 12, an idealised
mirror plane of the Cp*CoI2 fragment was found which
almost coincides with the plane of the pyridine ring. The
observed orientation allows the maximum overlap between
the π system in pyridine and one of the two suitable d-type
donor orbitals at the cobalt centre.[27] Pyridine is considered
a moderate π acceptor because its LUMO is not as low in
energy as, for example, that of pyrazine which is known as
a good π acceptor.[28] Thus, besides the normal σ interac-
tion, a weak π interaction between the metal and donor
nitrogen is also possible. This binding pattern between the
nitrogen and cobalt results in the shortest Co–N bond
among the three. In the indenyl-nickel analogues reported
by L. E. Groux and D. Zargarian,[30] N–C bond lengths
Figure 4. COSY spectrum of diiodo-η5:η1-(2-piperidinoethyl)cyclo-
pentadienylcobalt(III) (C5H4C2H4N5H10CoI2) (10) in CDCl3 at
25 °C.
Since the metal–CO bond is weaker[25] for the cobalt(III)
and C–C bond lengths in the tethered pyridine moiety were complex compared with that in the cobalt(I) complex, the
found to be longer in the chelated form [average 1.354(3) Å amino nitrogen as a σ donor in the pendant side chain can
and 1.376(3) Å, respectively] than in the non-chelated form replace the CO group in the oxidised diiodocarbonyl inter-
[average 1.335(5) Å and 1.360(6) Å, respectively]. Thus a de- mediates. Although there is greater steric hindrance around
localisation of electron density from nickel to the pyridine the donor atom in the piperidine moiety compared with the
π system could be assumed. The corresponding N–C bond amino moiety, the formation of 10 was still found to be
lengths [average 1.339(10) Å] and the C–C bond lengths much faster than that of 9. This phenomenon suggests that
[average 1.372(13) Å] found in 12 are comparable with those the rate of chelation might be determined by the strength
of the chelated forms of the indenyl-nickel complexes. Com- of the Lewis basicity of the nitrogen atom in the donor
paring the slightly shorter C–C bond lengths in the Cp ring function. However, by oxidation of 8 with iodine, pure 12
[average 1.403(14) Å] found in 12 with the corresponding was obtained directly and we did not find a carbonyl ad-
data for 9 and 10 [average 1.4054(4) and 1.4084(6) Å, sorption band in the precipitate thus indicating the chela-
respectively], a possible delocalisation of electron density tion here is the fastest among the four dicarbonyl reaction
from cobalt to the pyridine π system is likely. The σ, π inter- precursors. If the σ donor ability of the lone pair on the
action between a donor atom possessing d orbitals (such as nitrogen atom in the pendant side chain were only deter-
S and P from the ligand) and the metal in half-sandwich mined by the hybridisation of the orbital, the rate of chela-
complexes is also known.[31,32] Although nitrogen does not tion in 8 should be slower than was observed in 6 or 7. The
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Co Complexes with Pendant Nitrogen Functional Groups
driving force for the faster rate of chelation can be attrib- tration of the intermediate and time can be deduced. We
uted to the formation of a partial double bond between estimated the initial absorbance (t = 0) of the diiodocarbon-
cobalt and nitrogen. The π interaction between cobalt(III) ylcobalt(III) intermediate from the interception of the line
and nitrogen as well as the less steric hindrance and the low with the ordinate by extrapolation. The carbonyl ab-
degree of freedom in the functionalised arm in 8 are more sorbance of 6 in dichloromethane was found obey the Lam-
than enough to compensate for the lower σ donor ability bert–Beer law quiet well within our experimental range. The
of the N-based pendant function. Thus, the shortest lifetime concentration of each species at anytime can thus be calcu-
of the diiodocarbonyl intermediate 8Ј and the fastest rate lated and such data are listed in Table 3. The reaction oc-
of chelation observed during the oxidation process of 8 can curring in the IR cell can be described as shown in
be understood.
Scheme 3.
It has been demonstrated by Jutzi et al. that performing
the reduction of diiodo cobalt(III) chelates with sodium
amalgam under an atmosphere of carbon monoxide leads
to the formation of dicarbonylcobalt(I) species. Without the
presence of sodium amalgam, only diiodocarbonylco-
balt(III) was formed in an equilibrium with the correspond-
ing diiodo cobalt(III) chelate.[24,29] Irreversible displace-
ment of the intramolecular coordinated ligand was only
achieved under very drastic conditions. In our experiments,
we found that carbon monoxide not only replaced the intra-
molecularly coordinated ligand but also reduced the co-
balt(III) complex to a cobalt(I) complex. In a airtight reac-
tion vessel, we observed that the reaction intermediate di-
iodocarbonyl-η5-(2-piperidinylethyl)cyclopentadienylcobal-
t(III) 6Ј was reduced to its corresponding dicarbonylco-
balt(I) 6 by the CO released during the chelation of the
tethered piperidinyl ligand as shown by the IR spectrum
depicted in Figure 5. Since the decay of the adsorption of
the metal–carbonyl bond at 2066 cm–1 clearly shows the
Figure 5. Reduction of diiodocarbonyl-η5-(2-piperidinylethyl)cy-
clopentadienylcobalt(III) by carbon monoxide released via its own
chelation. The inset IR spectra show the reducing ν(CO) of 6Ј at
2066 cm–1 and the increasing ν(CO) of 6 at 2017 and 1953 cm–1,
pattern of a first-order reaction and the plot of logA(νCO
)
vs. t has a good linear relationship (R2 Ͼ 0.999) after an
882 s inducing period, the relationship between the concen- respectively.
Table 3. Changes of the carbonyl absorbance during the chelation of 6 after being oxidised by iodine in dichloromethane solution.
2066 cm–1
A
2017 cm–1
A
1953 cm–1
A
CO released
CO consumed
free CO
[molLϪ1
]
t / s
[molLϪ1
]
[molLϪ1
]
0
0.468
0.439
0.391
0.346
0.309
0.283
0.255
0.235
0.009
0.019
0.046
0.086
0.119
0.142
0.166
0.183
0.012
0.018
0.042
0.076
0.107
0.128
0.149
0.165
161
304
451
571
651
742
808
0.174
0.188
0.202
0.214
0.222
0.23
0.0002
0.0021
0.0073
0.0149
0.0213
0.0256
0.0302
0.1674
0.1659
0.1574
0.1502
0.1448
0.1396
0.136
0.236
882
972
0.214
0.19
0.202
0.225
0.24
0.257
0.271
0.29
0.302
0.313
0.318
0.33
0.335
0.342
0.344
0.351
0.359
0.181
0.203
0.217
0.233
0.249
0.264
0.276
0.287
0.295
0.301
0.308
0.313
0.317
0.324
0.331
0.199
0.212
0.222
0.232
0.24
0.0335
0.0371
0.0415
0.0444
0.0476
0.0503
0.0539
0.0562
0.0583
0.0593
0.0616
0.0625
0.0639
0.0643
0.0656
0.0878
0.0877
0.0892
0.0891
0.0893
0.088
0.0873
0.0873
0.0887
0.0863
0.0868
0.0855
0.087
1050
1133
1213
1319
1397
1487
1554
1634
1699
1757
1817
1927
2052
0.171
0.152
0.135
0.116
0.104
0.09
0.081
0.071
0.065
0.06
0.25
0.256
0.262
0.267
0.271
0.274
0.277
0.28
0.054
0.046
0.04
0.284
0.288
0.0872
0.0867
Average:
0.0876
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L. Li, S. Han, Q. Li, Z. Chen, Z. Pang
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Scheme 3.
According to Scheme 3, each molecule of the diiodocar- formed diiodotriphenylphosphanyl-η5-(2-piperidinoethyl)-
bonyl intermediate 6Ј can provide one molecule of carbon cyclopentadienylcobalt(III) was thus protonated by hydro-
monoxide after chelation. To produce each molecule of di- gen iodide to give the corresponding piperidinium salt 13,
carbonylcobalt(I) 6 requires three molecules of carbon crystals of which could be easily grown. From a crystal of
monoxide. The difference between the consumed molecules suitable size we were able to determine the structure of 13.
of diiodocarbonyl intermediate 6Ј and the formed mole- The ORTEP diagram of 13 is given in Figure 6. It is inter-
cules of 6 is the free carbon monoxide that dissolves in solu- esting to find that the I–Co–I angle in 13 is 95.40(8)° and
tion as listed in Table 3. Based on these data, our calcula- the I–Co–P angles are 91.57(14) and 92.79(14)°. Comparing
tions reveal that after the first 882 s induction period, the the corresponding value of 92.70(2)° found in 10 suggests
difference in the concentration of the cobalt(III) and (I) that the triphenylphosphane ligand experiences a smaller
species determined by IR measurements at the same time repulsive effect compared with the tethered intramolecular
remains a constant 0.088 molLϪ1. Since the solubility of coordinated piperidine group. Triphenylphosphane is
carbon monoxide in organic solvents cannot reach such a known as a ligand with a large stereochemical effect and
high lever under normal conditions, bubbling carbon mon- has a cone angle of 143°.[33] However, as a strong σ donor
oxide through a solution of a cobalt(III) chelate cannot ligand, triphenylphosphane still shows a larger trans effect
produce an oxidation state +1. We did not observe such than piperidine. The Co–C(5) bond trans to Co–P of
self-reduction in similar experiments with 5 and 8. This can 2.141(16) Å is 0.085 Å longer than the cis Co–C(3) bond
be attributed to the rate of chelation in 9 being too slow to which is 2.056(16) Å. For comparison, the Co–C(2) bond
allow a sufficiently high concentration of carbon monoxide in 10 trans to Co–N is 2.086(4) Å, i.e. only 0.053 Å longer
to form in the reaction vessel and also because a small leak- than the cis Co–C(5) bond which is 2.033(4) Å. There is one
age of CO from the IR cell cannot be entirely prevented. iodide counterion hydrogen bonded to the cation through
On the other hand, the rate of chelation in 12 is too fast N–H···I interactions with an N···I distance of 3.414(14) Å
and the carbon monoxide had already escaped form the (Figure 7). This is an almost linear hydrogen bond with
reaction solution after the iodine had been added.
d(D–H) = 0.91 Å, d(H···A) = 2.53 Å and ϽD–H···A =
It is interesting to compare the properties of the tethered 164.1°. A short contact between the iodide counterions and
functional side chains in “aminoethyl”, 10 and “ami- the hydrogen atom at C(12) adjacent to the nitrogen atom
nophenyl” since the stereochemical environments around also exists and this should help the molecules pack in the
the Co–N bonds are similar. The diiodomonocarbonyl pre- crystal. To the best of our knowledge, this is one of the
cursor of “aminoethyl” reported could only exist in solution
under an atmosphere of carbon monoxide whereas the di-
iodomonocarbonyl analogue of 10 could be isolated in the
solid-state but could not be fully characterised because of
its instability; completion of the chelation was observed af-
ter only about one day. The diiodomonocarbonyl analogue
of “aminophenyl” was isolated from a solution after 16 h
stirring at room temperature under N2 and in a yield of
58%. The big difference in chelating ability is consistent
with the repulsive force between the iodine ligands and the
methyl (methylene) groups adjacent to the nitrogen atom. A
comparison of the structural parameters of these analogues
using the values of I–Co–I bond angles and the Co–N bond
lengths found the largest in “aminoethyl” and the smallest
in “aminophenyl”.
Figure 6. ORTEP diagram of 13 with the probability ellipsoids
drawn at the 50% level. Hydrogen atoms, dichloromethane solvate
Triphenylphosphane is known to be a better ligand for
late transition metal complexes than amines. At room tem-
perature, triphenylphosphane can replace the intramolecu-
larly coordinated piperidine group in 10. Since tri-
phenylphosphane is easily oxidised by iodine to form
I2PPh3 which is itself readily hydrolysed by moisture to gen-
molecule and iodide anion have been omitted for clarity. Selected
bond lengths [Å] and angles [°]: Average Co–C(ring) 2.094(11),
Co(1)–P(1) 2.239(5), Co(1)–I(1) 2.592(3), Co(1)–I(2) 2.568(2),
average C–C(ring) 1.40(2), N(1)–C(7) 1.488(19), N(1)–C(12)
1.46(2), I(1)–Co(1)–I(2) 95.40(8), I(1)–Co(1)–P(1) 92.79(14), I(2)–
Co(1)–P(1) 91.57(14), Co(1)–P(1)–C(13) 118.0(5), Co(1)–P(1)–
erate hydrogen iodide and triphenylphosphane oxide, the C(19) 112.7(7), Co(1)–P(1)–C(25) 115.2(5).
5132 Eur. J. Inorg. Chem. 2007, 5127–5137
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Co Complexes with Pendant Nitrogen Functional Groups
strongest N–H···I hydrogen bonds found in the literature.
A similar N–H···I hydrogen bond was found in crystals of
Me3N·HI and it was probably found to be linear with an
N···I distance of 3.46(4) Å.[34] A further example can be
seen in the crystal structure of the hexakis(S,S-diphenylsulf-
imide)cobalt(II) diiodide S,S-diphenylsulfimide acetonitrile
solvate, [Co(C12H11NS)6]I2·C12H11NS·2C2H3N, in which
two iodide counterions are hydrogen-bonded to the cation
through N–H···I interactions, with N···I distances in the
range of 3.7302(19)–3.8461(19) Å and D–H···A angles in
the range of 156–172°.[35]
Experimental Section
General: All manipulations were carried out under an atmosphere
of purified nitrogen using standard Schlenk techniques except
where mentioned. All reagents were purchased from commercial
sources (Acros Organics or Lancaster Synthesis Ltd) in the highest
available purity and used as received. Solvents were purified by
standard methods and distilled under nitrogen before use. Glass-
ware was heated under vacuum and then flushed with N2 prior to
use. Alumina was heated at 300 °C under vacuum and then deacti-
vated by addition of about 6 wt.-% of deoxygenated water before
use.
Elemental analyses were performed on a Vario EL III Elemental
Analyaer (Analysensysteme GmbH, Germany). IR spectra were re-
corded on a Nicolet Avatar-360 FTIR spectrometer in KBr pellets.
A 0.2 mm NaCl IR cell was used to record the spectrum of solution
samples. 1H NMR spectra were recorded on a Bruker Avance-
DMX 500 NMR spectrometer or a JEOL ECA400 NMR spec-
trometer. The chemical shifts are reported in ppm relative to tet-
ramethylsilane. Mass spectra were recorded on a Hewlett–Packard
(USA) 6890/5073 gas chromatography–mass spectrometer. High
resolution matrix assisted laser desorption ionisation mass spectra
were recorded on an IonSpec 4.7 Tesla FTMS spectrometer at the
Shanghai Institute of Organic Chemistry, Chinese Academy of Sci-
ences, with 2,5-dihydroxybenzoic acid (DHB) serving as the ab-
sorbing matrix.
The crystal data were determined on a Bruker Smart-Apex CCD
X-ray diffractometer equipped with a graphite monochromator.
Data collection was performed with Mo-Kα radiation (λ
=
Figure 7. N–H···I hydrogen bonding in the unit cell of complex 13.
0.71073 Å) using the ω-2θ scan technique to a maximum 2θ value
of 26° at room temperature. The intensities were corrected for Lo-
rentz polarisation effects and empirical absorption with the SAD-
ABS program.[36] Structures of the crystals were solved by direct
methods and expanded using Fourier techniques. The non-hydro-
gen atoms were refined anisotropically with full-matrix least-
squares methods. Hydrogen atoms were not included in the refine-
ments. The final agreement factors are described with R1 and wR2
values for observed reflections. All calculations were performed on
a PC computer using SHELX-97[37] the Bruker Smart program.
Crystal data and experimental details for 9, 10, 12 and 13 are listed
Conclusions
This paper reports the synthesis and reactivity of several
cyclopentadienylcobalt complexes having a pendant amino-
functionalised side chain. Intramolecular coordination by
the pendant amino-functionalised side chain occurs when
the oxidation state of the cobalt changes from +I to +III
via a diiodocarbonyl intermediate. The stabilities of the in- in Table 4 and selected bond lengths and angles are listed under
the respective ORTEP diagrams.
termediates differ greatly due to the different amino func-
tions in the pendant side chains. Structural studies of che-
lates 9, 10 and 12 have been carried out and these show
that the Co–N bond length does not correlate with the sta-
bility of the diiodocarbonyl intermediate precursors but
that there exists a correlation between the I–Co–I angles
with the repulsive force from the methyl or methylene
groups adjacent to the nitrogen atom. The intermediate di-
iodocarbonyl-η5-(2-piperidinylethyl)cyclopentadienylco-
Synthesis of Compounds and Complexes
2-Aminoethylcyclopentadiene (1): Freshly distilled THF (50 mL)
was added to a 250 mL Schlenk tube containing sodium sand
(1.7835 g, 77.58 mmol) and the mixture was cooled in an ice-water
bath. Freshly distilled cyclopentadiene (9 mL) was added dropwise
and H2 gas started to bubble out. After 30 min the bubbling
stopped and the sodium sand had disappeared. The resultant pink
solution was added by cannula to another 150 mL of Schlenk tube
balt(III) 6Ј can be reduced to dicarbonylcyclopentadienyl- containing BrCH2CH2NH2·HBr (4.1 g, 20.21 mmol) in THF
(50 mL) which had already been cooled in an ice-water bath. The
reaction mixture was then stirred at room temperature for 48 h dur-
ing which time a white solid precipitated out from the solution.
Water (50 mL) was added by cannula to the reaction mixture to
dissolve the white precipitate. The organic layer was then separated.
The aqueous phase was extracted with hexane (3ϫ20 mL). The
extract and the organic phase were combined and the volume was
reduced to about 15 mL, cooled in an ice-water bath and acidified
with aqueous HCl (concentrated HCl/water, 1:4). The separated
aqueous phase was added directly to an ice-cold solution made
from hexane (20 mL) and aqueous NaOH solution. The basic
cobalt(I) 6 by the CO released due chelation of the former
at a CO concentration of about 0.088 molLϪ1. The chelated
piperidinyl group in 10 can easily be replaced by tri-
phenylphosphane to form the diiodotriphenylphosphanyl-
η5-(2-piperidinioethyl)cyclopentadienylcobalt(III)
iodide
dichloromethane solvate 13 in the presence of hydrogen io-
dide. A strong N–H···I hydrogen bond with a N···I distance
of 3.414(14) Å and a D–H···A angle of 164.1° was observed
in 13. It is one of the strongest N–H···I hydrogen bonds
reported up to now.
Eur. J. Inorg. Chem. 2007, 5127–5137
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5133

L. Li, S. Han, Q. Li, Z. Chen, Z. Pang
FULL PAPER
product was identified as a 1:1 mixture of isomers. 1H NMR
(CDCl3): δ = 6.44 (d, J = 1.17 Hz, 1.5 H, =CH), 6.29 (d, J =
4.25 Hz, 0.5 H, =CH), 6.23 (s, 0.5 H, =CH), 6.09 (s, 0.5 H, =CH),
2.98 (s, 1 H, =CHCHϪ), 2.87–2.91 (m, 3 H, ϪCH), 2.56 (t, J =
6.7 Hz, 1 H, ϪCH2), 2.51 (t, J = 6.7 Hz, 1 H, ϪCH2) ppm. GCMS:
m/z (%) = 109 (45) [M]+, 80 (100) MH – CH2NH2]+; retention
times: 8.247, 8.327 min.
Table 4. Crystal data and structure refinement details for 9, 10, 12
and 13.
9
10
Empirical formula
Fw
C7H10CoI2N
420.82
C12H18CoI2N
489.00
T [K]
λ [Å]
Crystal system
Space group
293(2)
0.71073
orthorhombic
Pnma
293(2)
0.71073
monoclinic
P21/c
(2-Piperidinoethyl)cyclopentadiene (2): The compound was synthe-
sised according to the reported procedure with little modifica-
tion.[14] The product was purified on an alumina column. The re-
sultant oily product was identified as a 1:1 mixture of isomers and
a yield of 40% was redorded. 1H NMR (CDCl3): δ = 6.45 (s, =CH),
6.42 (s, =CH), 6.27 (s, =CH), 6.19 (s, =CH), 6.05 (s, =CH), 3.59
(t, J = 7.34 Hz, 2 H, ϪCH2Ϫ), 2.93 (d, J = 16.03 Hz, 1 H, ϪCHϪ),
2.69 (t, J = 7.35 Hz, 2 H, ϪCH2N), 2.45 (m, 4 H, ϪNCH2Ϫ), 1.60
Unit cell dimensions
a [Å]
b [Å]
c [Å]
α [°]
β [°]
γ [°]
7.393(2)
11.708(3)
11.822(3)
90
90
90
1023.2(5)
4
2.732
14.934(4)
11.805(3)
16.153(4)
90
91.384(4)
90
2846.9(12)
8
2.282
V [Å3]
Z
1
(m, 4 H, ϪCH2Ϫ), 1.46 (m, 2 H, ϪCH2Ϫ) ppm. H NMR ([D6]-
acetone): δ = 6.42 (s, =CH), 6.21 (s, =CH), 6.03 (s, =CH), 5.94 (s,
=CH), 5.47 (s, =CH), 5.11 (d, J = 14.41 Hz, 2 H, ϪCH2Ϫ), 2.91
(d, J = 7.10 Hz, 1 H, ϪCHϪ), 2.50 (m, 2 H, ϪCH2N), 2.42 (m, 4
H, ϪCH2N), 2.12 (m, 2 H, ϪNCH2Ϫ), 1.44 (m, 4 H, ϪCH2Ϫ),
1.24 (m, 2 H, ϪCH2Ϫ) ppm. 13C NMR ([D6]acetone): δ = 146.58,
144.12, 133.74, 132.59, 131.37, 129.65, 125.82, 125.43, 123.92
(=CH), 58.52, 57.85, 56.79 (CpCH2CH2NϪ), 53.63 (α-NCH2Ϫ),
ρcalcd. [mgmϪ3
]
Limiting indices
–9 Յ h Յ 8
–13 Յ k Յ 14
–14 Յ l Յ 12
4402/1062
0.0260
1.159
7.653
–18 Յ h Յ 14
–12 Յ k Յ 14
–16 Յ l Յ 19
12945/5599
0.0292
0.791
5.519
Reflections coll./unique
Rint
Goodness-of-fit on F2
Abs. coeff. [mm–1
Crystal size [mm]
]
42.48,
40.25,
33.29
(ϪCH2Ϫ),
27.32,
26.79,
26.57
0.15ϫ0.10ϫ0.10 0.15ϫ0.10ϫ0.08
(CpCH2CH2NϪ), 25.02, 23.46 (ϪCH2Ϫ) ppm. GCMS: m/z (%) =
177 (25) [M]+, 98 (100) [M – C5H5CH2]+, 80 (10) [MH –
CH2NC5H10]+; retention times: 10.03, 10.15 min.
θ range for data collection [°] 2.45 to 26.00
1.36 to 26.01
R1 = 0.0275
wR2 = 0.0427
R1 = 0.0453
wR2 = 0.0452
0.829/–0.738
R indices
R1 = 0.0365
wR2 = 0.0927
R1 = 0.0402
wR2 = 0.0949
1.101/–1.208
I Ͼ 2σ(I)
R indices
for all data[a]
Largest diff. peak/hole [eA–3
1-(2-Piperidinoethyl)-2,3,4,5-tetraisopropylcyclopentadiene
(3):
C5H10NC2H4Cl·HCl (5.174 g, 28.26 mmol) was added to an ice-
cold mixture of hexane (30 mL) and aqueous KOH solution. The
organic layer containing free C5H10NC2H4Cl was separated and
dried with MgSO4. The volume was reduced to about 10 mL and
THF (15 mL) was then added. The mixed solution was added by
cannula to another 150 mL capacity Schlenk tube containing po-
tassium tetraisopropylcyclopentadienide[19] (7.07 g, 25.8 mmol) and
THF (60 mL). The resultant reaction mixture was heated to reflux
for 24 h. The reaction was then quenched with water, extracted with
hexane and eluted on an alumina column. A yellowish oil was ob-
]
12
13
Empirical formula
Fw
C11H10CoI2N
468.93
C31H36Cl2CoI3NP
964.11
T [K]
λ [Å]
Crystal system
Space group
293(2)
293(2)
0.71073
monoclinic
P2(1)
0.71073
triclinic
¯
P1
Unit cell dimensions
a [Å]
b [Å]
c [Å]
α [°]
β [°]
γ [°]
7.188(3)
8.157(4)
11.798(5)
92.976(6)
91.282(6)
115.947(4)
620.4(5)
2
11.674(4)
7.993(3)
18.581(7)
90
92.043(6)
90
1732.7(11)
2
1.848
1
tained (3.5 g, 10.1 mmol) in a yield of 35.9%. H NMR (CDCl3):
δ = 3.16 (m, ϪCHCϪ), 2.74 (m, ϪCHCϪ), 2.46 (b, ϪCH2N), 2.29
(b, ϪNCH2), 1.87 (m, ϪCHMe2), 1.62 (b, ϪCH2Ϫ), 1.54 (b,
ϪCH2Ϫ), 1.39 (m, ϪCHMe2), 1.19 (m, ϪCHMe2), 1.12 (m,
ϪCHMe2), 1.01 (m, ϪCHMe2) ppm. GCMS: m/z (%) = 345 (15)
[M]+.
V [Å3]
Z
ρcalcd. [mgmϪ3
]
2.510
2-Picolylcyclopentadiene (4): This compound was synthesised ac-
cording to the reported procedure.[22] The product was separated
on an alumina column. The resultant oily product was identified
as 1:1 mixture of isomers. 1H NMR (CDCl3): δ = 8.54 (t, J =
4.80 Hz, 1 H, =CH), 7.59 (m, 1 H, =CH), 7.17 (t, J = 6.88 Hz, 1
H, =CH), 7.11 (t, J = 4.60 Hz, 1 H, =CH), 6.44 (m, =CH), 6.29
(m, =CH), 6.23 (m, =CH), 6.10 (m, =CH), 3.94 (s, ϪCH2Ϫ), 3.91
(s, ϪCH2Ϫ), 3.00 (s, ϪCHϪ), 2.92 (t, ϪCH2Ϫ) ppm.
Limiting indices
–8 Յ h Յ 8
–8 Յ k Յ 9
–13 Յ l Յ 14
2615/2164
0.0252
0.991
6.326
–13 Յ h Յ 13
–9 Յ k Յ 9
–19 Յ l Յ 22
7306/5608
0.0482
0.927
3.389
Reflections coll./unique
Rint
Goodness-of-fit on F2
Abs. coeff. [mm–1
Crystal size [mm]
]
0.15ϫ0.08ϫ0.05 0.15ϫ0.10ϫ0.08
θ range for data collection [°] 1.73 to 25.01
R indices
1.10 to 25.01
R1 = 0.0641
wR2 = 0.1493
R1 = 0.0974
wR2 = 0.1719
2.055/–1.536
R1 = 0.0456
wR2 = 0.1126
R1 = 0.0570
wR2 = 0.1182
1.735/–1.392
Dicarbonyl-η5-(2-aminoethyl)cyclopentadienylcobalt(I)
(5):
1
I Ͼ 2σ(I)
R indices
(0.612 g, 5.61 mmol) was dissolved in CH2Cl2 (20 mL) containing
3,3-dimethyl-l-butene (5 mL) and the solution added by cannula to
for all data[a]
Largest diff. peak/hole [eA–3
a
CH2Cl2 solution (30 mL) containing Co2(CO)8 (0.6259 g,
]
1.83 mmol) at 0 °C. The deep red reaction mixture was stirred at
ambient temperature and was inspected by observing the two char-
acteristic νCO bands (2017, 1951 cm–1) in the IR spectrum until
their intensities became constant. This took about 24 h. The vol-
ume of the reaction mixture was reduced to about 2 mL under
vacuum and the resultant solution was loaded on an alumina col-
aqueous phase (pH Ͼ 14) was extracted with hexane (3ϫ20 mL).
The organic phase and extract were combined, dried with anhy-
drous MgSO4 and the solvents evaporated to give the product as
an oily liquid (0.487 g, 4.46 mmol). Yield: 22.1%. The resultant oily
5134
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 5127–5137

Co Complexes with Pendant Nitrogen Functional Groups
umn and rinsed with 1:1 solvent mixture of THF and hexane. A
deep red band was collected and the solvent was evaporated in
vacuo. A deep red oily product was obtained (0.34 g). Yield 42.0%.
Diiodo-η5:η1-(2-piperidinoethyl)cyclopentadienylcobalt(III) (10): A
similar synthetic procedure was used as described for complex 9.
Thus 6 (0.226 g, 0.776 mmol) in ether (15 mL) was added to iodine
1H NMR (CDCl3): δ = 5.02 (s, 2 H, =CH), 4.92 (s, 2 H, =CH), (0.1985 g, 0.782 mmol) in ether (15 mL) and the solution stirred
3.48 (m, 4 H, ϪCH CH Ϫ) ppm. IR (neat): ν = 3365, 2960, overnight. The resultant green-black precipitate was washed with
˜
max
2
2
2016 (C=O), 1951 (C=O), 1598, 1439, 1366, 1261, 1090, 1023, 898,
hexane until the washings became colourless. The solid showed a
medium strong νCO band at 2059 cm–1 which disappeared after
about 12 h. The solid was dissolved in dichloromethane and filtered
through a pad of celite and the solvent was then evaporated. A
green-black solid was obtained (0.204 g). Yield 53.8%. Crystals
suitable for X-ray crystallographic analysis were obtained from a
sample dissolved in dichloromethane and layered with hexane.
C12H18CoI2N (489.02): calcd. H 3.71, C 29.47, N 2.86; found H
802 cm–1.
Dicarbonyl-η5-(2-Piperidinoethyl)cyclopentadienylcobalt(I) (6):
A
similar synthetic procedure was used as described for complex 5.
Thus Co2(CO)8 (0.976 g, 2.84 mmol) and 2 (1.43 g, 8.07 mmol)
were stirred together for 20 h and the resultant mixture passed
down an alumina column to produce a deep red oily product
(0.226 g). Yield 13.7%. 1H NMR (CDCl3): δ = 5.04 (s, 2 H, =CH),
4.90 (s, 2 H, =CH), 2.49 (2 H, ϪCH2NϪ), 2.43 (4 H, ϪNCH2Ϫ),
2.18 (2 H, ϪCH2Ϫ), 1.60 (4 H, ϪCH2Ϫ), 1.45 (2 H, ϪCH2Ϫ) ppm.
1
3.61, C 29.58, N 2.71. H NMR (CDCl3): δ = 5.46 (s, 2 H, =CH),
5.19 (s, 2 H, =CH), 4.41 (t, J = 6.40 Hz, 2 H, ϪCH2NϪ), 3.52
(d, J = 13.7 Hz, 2 H, ϪNCHeHaϪ), 2.93 (t, J = 13.7 Hz, 2 H,
ϪNCHeHaϪ), 2.51 (t, J = 6.40 Hz, 2 H, ϪCH2Ϫ), 1.72 (m, 4 H,
IR (neat): ν
= 3401, 2935, 2854, 2800, 2766, 2019 (C=O), 1954
˜
max
(C=O), 1603, 1445, 1373, 1352, 1262, 1155, 1114, 1039, 862,
1
ϪCH2Ϫ), 1.22 (m, 2 H, ϪCH2Ϫ) ppm. H NMR ([D6]acetone): δ
802 cm–1.
= 5.69 (s, 2 H, =CH), 5.11 (s, 2 H, =CH), 4.49 (t, J = 6.40 Hz, 2
H, ϪCH2NϪ), 3.61 (d, J = 13.3 Hz, 2 H, ϪNCHeHaϪ), 2.81 (t, J
= 13.3 Hz, 2 H, ϪNCHeHaϪ), 2.68 (t, J = 6.40 Hz, 2 H, ϪCH2Ϫ),
1.90 (m, 4 H, ϪCH2Ϫ), 1.13 (m, 2 H, ϪCH2Ϫ) ppm. 13C NMR
([D6]acetone): δ = 112.93 (CpCH2Ϫ), 83.49 (Cp), 81.38 (Cp), 65.50
(ϪCH2CH2NϪ), 61.10 (ortho-NCH2Ϫ), 25.39 (CpCH2CH2NϪ),
24.32, 22.30 (ϪCH2Ϫ) ppm. MS (HiRMALDI): m/z (%): 514.9
(12.5) [M + DHB – I – H]+, 422.9 (4.0) [M + H2O – NC5H10]+,
379.1 (23) [M + H2O – I – H]+, 362.0 (10) [M – I]+. IR (KBr pellet):
Dicarbonyl-η5-1-(2-piperidinoethyl)-2,3,4,5-tetraisopropylcyclopenta-
dienylcobalt(I) (7): A similar synthetic procedure was used as de-
scribed for complex 5. Thus Co2(CO)8 (0.4944 g, 1.45 mmol) and
3 (1.00 g, 2.90 mmol) were stirred under reflux for 24 h and the
resultant mixture passed down an alumina column to produce a
deep red oily product (0.785 g). Yield 59.0%. 1H NMR (CDCl3): δ
= 2.44 (s, 2 H, ϪCH2N), 2.29 (b, 4 H, ϪNCH2), 1.91 (m, 4 H,
ϪCHMe2), 1.87 (s, 2 H, ϪCH2Ϫ), 1.54 (b, 6 H, ϪCH2Ϫ), 1.26 (m,
6 H, ϪCHMe2), 1.16 (m, 12 H, ϪCHMe2), 1.11 (m, 6 H,
νmax = 3076, 2932, 2856, 2801, 1726, 1603, 1468, 1443, 1393, 1353,
˜
1309, 1261, 1101, 1025, 802 cm–1. UV/Vis (CH3CN): λmax (ε) = 248
(1.01ϫ104), 286 (7.06ϫ103), 587 (5.79ϫ102) nm.
ϪCHMe ) ppm. IR (neat): ν
= 3389, 2960, 2932, 2871, 2003
˜
2
max
(C=O), 1942 (C=O), 1466, 1381, 1367, 1261, 1155, 1108, 1041, 861,
806 cm–1.
Diiodo-η5:η1-1-(2-piperidinoethyl)-2,3,4,5-tetraisopropylcyclopenta-
dienylcobalt(III) (11): A similar synthetic procedure was used as
described for complex 9. Thus 7 (0.786 g, 1.71 mmol) in ether
(35 mL) was added to iodine (0.4456 g, 1.76 mmol) in ether
(10 mL) and the resultant mixture stirred overnight. A red-purple
solid precipitated which showed a medium-strong νCO band at
2046 cm–1. The solid was dissolved in dichloromethane and filtered
through a pad of celite and the solvent subsequently removed in
vacuo. A solid was obtained (0.165 g). Yield 15%. C24H42CoI2N
(657.35): calcd. H 6.44, C 43.85, N 2.13; found H 6.96, C 44.70, N
1.91. 1H NMR (CDCl3): δ = 1.72 (d, 6 H, ϪCH3), 1.70 (d, 6 H,
ϪCH3), 1.53 (d, ϪCH3), 1.50 (d, 6 H, ϪCH3), 2.05 (m, 4 H,
Me2CH), 3.83 (s, 2 H, ϪCH2NϪ), 3.65 (s, 4 H, ϪNCHeHaϪ), 3.32
(s, 2 H, ϪNCHeHaϪ), 3.18 (s, 4 H, ϪCH2Ϫ), 2.37 (m, 4 H,
ϪCH2Ϫ) ppm.
Dicarbonyl-η5-2-picolylcyclopentadienylcobalt(I) (8): A similar syn-
thetic procedure was used as described for complex 5. Thus
Co2(CO)8 (0.1755 g, 0.513 mmol) and 4 (0.1585 g, 1.01 mmol) were
stirred together for 13 h and the resultant mixture passed down an
alumina column to produce a deep red oily product (0.098 g). Yield
1
35.6%. H NMR (CDCl3): δ = 8.55 (s, 1 H, =CHϪN), 7.64 (t, 1
H, =CH), 7.26 (t, 1 H, =CH), 7.14 (t, 1 H, =CH), 5.09 (s, 2 H,
Cp), 4.93 (s, 2 H, Cp), 3.75 (s, 2 H, ϪCH Ϫ) ppm. IR (neat): ν
˜
2
max
= 3400, 3083, 3011, 2956, 2927, 2854, 2016 (C=O), 1948 (C=O),
1591 (C=N), 1570 (C=N), 1475, 1435, 1365, 1309, 1221, 1149,
1092, 1049, 995, 920, 820, 785, 749, 616 cm–1.
Diiodo-η5:η1-(2-aminoethyl)cyclopentadienylcobalt(III) (9): To
a
solution of 5 (0.087 g, 0.39 mmol) in ether (15 mL) was slowly
added a solution of iodine (1.00 g, 0.394 mmol) in ether with vigor-
ous stirring. A black-purple precipitate immediately appeared. The
reaction mixture was stirred for a further 1 h. The precipitate was
filtered and washed with hexane (2ϫ10 mL) and dried in vacuo. A
red-purple solid was obtained (0.171 g). Yield: 97.7%. The solid
showed a strong νCO band at 2068 cm–1 which disappeared after
about one week. The solid was dissolved in dichloromethane and
layered with hexane and a crystalline product was obtained
(0.148 g). Yield 90.2%. Crystals suitable for X-ray crystallographic
analysis were obtained from that crop. C7H10CoI2N (420.823):
Diiodo-η5:η1-2-picolylcyclopentadienylcobalt(III) (12): A similar
synthetic procedure was used as described for complex 9. Thus
complex 8 (0.098 g, 0.359 mmol) in hexane (10 mL) was added to
iodine (0.097 g, 0.382 mmol) in hexane (10 mL) and the mixture
stirred for 24 h. The resultant dark green precipitate was separated
and washed twice with hexane and dissolved in dichloromethane.
The solution was filtered and the solvent removed in vacuo. A dark
green solid was obtained (0.1615 g). Yield 96.0%. Crystals suitable
for X-ray crystallographic analysis were obtained from a sample
1
calcd. H 2.39, C 19.96, N 3.33; found H 2.44, C 19.86, N 3.41. H
NMR (CDCl3): δ = 5.51 (t, 2 H, =CH), 5.27 (t, 2 H, =CH), 4.22 dissolved in dichloromethane and crystallised by layering with hex-
(t, J = 5.48 Hz, 2 H, ϪCH2NϪ),2.42 (t, J = 6.42 Hz, 2 H,
ϪCH2NϪ) ppm. MS (HiRMALDI): m/z (%): 573.2 (3.0) [M +
ane. C11H10CoI2N (468.831): calcd. H 2.15, C 28.16, N 2.99; found
H 2.168, C 28.29, N 2.886. 1H NMR (CDCl3): δ = 7.97 (s, 1 H,
DHB – H]+, 545.2 (32) [M + DHB – CH2NH2]+, 438.2 (8.0) [M + =CHϪN), 7.70 (t, 1 H, =CH), 7.16 (d, 1 H, =CH), 7.00 (t, 1 H,
H O – H]+, 293.1 (26.0) [M – I – H]+. IR (KBr pellet): ν
=
=CH), 5.73 (s, 2 H, Cp), 5.38 (s, 2 H, Cp), 4.09 (s, 2 H,
˜
2
max
3192, 2961, 1571, 1459, 1310, 1263, 1120, 1035, 1013, 840, 734,
700.2 cm–1. UV/Vis (CH3CN): λmax (ε) = 247 (7.61ϫ103), 290
(1.04ϫ104), 360 (4.03ϫ103), 585 (4.53ϫ102) nm.
ϪCH2Ϫ) ppm. MS (HiRMALDI): m/z (%): 341.9 (10.0) [M – I]+.
IR (KBr pellet): νmax = 3090, 2960, 2924, 2858, 1605 (C=N), 1470,
˜
1439, 1417, 1391, 1262, 1151, 1102, 1048, 1021, 846, 764 cm–1. UV/
Eur. J. Inorg. Chem. 2007, 5127–5137
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5135

L. Li, S. Han, Q. Li, Z. Chen, Z. Pang
FULL PAPER
Vis (CH3CN): λmax (ε) = 246 (7.51ϫ 103), 286 (5.28ϫ 103), 405
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(6.32ϫ102), 593 (5.63ϫ102) nm.
Diiodotriphenylphosphanyl-η5-(2-piperidinioethyl)cyclopentadienyl-
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of crystallised product was separated by filtration. Crystals suitable
for X-ray crystallographic analysis were obtained. Structural analy-
sis demonstrates that a solvent molecule of dichloromethane is in-
corporated in the crystal lattice. The resultant product was thus
formulated as (C5H4C2H4NHC5H10CoI2PPh3)+ I– ·CH2Cl2. Based
on this composition, the yield was 47% 1H NMR (CDCl3): δ =
7.23–7.90 (m, 15 H, Ph), 5.45 (s, 2 H, =CH), 5.30 (s, 2 H, CH2Cl2),
4.08 (m, 2 H, ϪCH2NϪ), 3.97 (m, 2 H, ϪNCH2Ϫ), 3.93 (s, 2 H,
=CH), 3.82 (m, 2 H, ϪNCH2Ϫ), 3.00 (m, 2 H, ϪCH2Ϫ), 2.63 (s,
1 H, ϪNHϪ), 2.34 (m, 2 H, ϪCH2Ϫ), 1.97 (m, 4 H, ϪCH2Ϫ) ppm.
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˜
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Acknowledgments
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Support for this work was provided by the National Natural Sci-
ence Foundation of China, Grant No. 20471016. We also thank
Prof. Linhong Weng for her excellent work on the X-ray crystallo-
graphic analysis.
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5136
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 5127–5137

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Published Online: September 20, 2007
Eur. J. Inorg. Chem. 2007, 5127–5137
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5137