Polydentate coordination of the thallium atom in complexes with chiral amidinylcyclopentadienyl ligands

Article abstract of DOI:10.1023/A:1011323629390

The chiral thallium amidinium cyclopentadiene-N-ylide complexes [C₅(CO₂Me)₄(ArNC(Ar′)NAr]T1 were synthesized and structurally characterized by X-ray diffraction analysis and NMR spectroscopy. In these complexes, an unusual

Full text of DOI:10.1023/A:1011323629390

890
Russian Chemical Bulletin, International Edition, Vol. 50, No. 5, pp. 890—894, May, 2001
Organometallic Chemistry
Polydentate coordination of the thallium atom in complexes with chiral
amidinylcyclopentadienyl ligands
G. A. Dushenko,a« I. E. Mikhailov,a G. Reck,b B. Schulz,b A. Zschunke,b and V. I. Minkin a
aInstitute of Physical and Organic Chemistry, Rostov State University,
194/2 prosp. Stachki, 344038 Rostov-on-Don, Russian Federation.
Fax: +7 (863 2) 28 5667. E-mail: mikhail@ipoc.rnd.runnet.ru
bFederal Institute of Materials Science, 12489 Berlin, Germany.*
Fax: (030) 8104 5972. E-mail: adolf.zschunke@bam.de
The
chiral
thallium
amidinium
cyclopentadiene-N-ylide
complexes
[C5(CO2Me)4{ArNC(Ar´)NAr}]Tl were synthesized and structurally characterized by X-ray
diffraction analysis and NMR spectroscopy. In these complexes, an unusual mode of
coordination of the thallium atom was found, viz., the thallium atom is coordinated by both
the side-chain nitrogen atom (N—Tl, 2.833(6) Å) and the π system of the cyclopentadienyl
ring (Tl—Cp, 2.887(4) Å; η5-bonding).
Key words: thallium complexes, cyclopentadienyl ligands with a donor side chain,
amidines, chirality, X-ray diffraction analysis.
The aim of the present study was to synthesize stable
Cyclopentadienylthallium complexes are important
precursors of organic and organometallic compounds.
Recently,1,2 we have prepared the first chiral
N-amidine-functionalized cyclopentadienyl ligands
[C5(CO2Me)4{ArNC(Ar´)NAr}]H and their gold(I)- and
mercury(II)-containing complexes characterized by
bidentate coordination of the metal (hydrogen) atom by
both the cyclopentadienyl fragment and the side-chain
nitrogen atom. Such chiral N-functionalized cyclo-
pentadienyl complexes with additional intramolecular
coordination of the metal atom by the side-chain nitro-
gen atom are attractive as catalysts for asymmetric
syntheses.3—5
chiral cyclopentadienylthallium(I) complexes containing
the amidinyl substituents in the five-membered ring,
viz., N,N´-diaryl-N-thallium-benz(α-naphth)amidi-
nium-N´-[2,3,4,5-tetra(methoxycarbonyl)cyclopenta-
dien-1-yl]ides, and to study their structures in the solid
state and in solutions by X-ray diffraction analysis and
NMR spectroscopy.
Results and Discussion
Treatment of N,N´-diaryl-N-methoxycarbonyl-
benz(α-naphth)amidinium-N´-[2,3,4,5-tetra(methoxy-
carbonyl)cyclopentadien-1-yl]ides (1) with a methanolic
solution of TlOH afforded N,N´-diaryl-N-thallium-
benz(α-naphth)amidinium-N´-[2,3,4,5-tetra(methoxy-
* Bundesanstalt für Materialforschung und -prüfung (BAM),
Richard-Willstätter Strasse 11, 12489 Berlin, Deutschland.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 852—856, May, 2001.
1066-5285/01/5005-890 $25.00 © 2001 Plenum Publishing Corporation

Chiral amidinylcyclopentadienylthallium
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 5, May, 2001
891
carbonyl)cyclopentadien-1-yl]ides (2) in 85—87% yields.
The reactions were accompanied by elimination of the
N-methoxycarbonyl group (Scheme 1).
C(18)
C(19)
C(13)
C(17)
C(20)
Scheme 1
C(16)
C(9)
Cl
C(8)
C(161)
Ar´
Ar´
C(24)
C(25)
C(10)
C(11)
C(15)
C(23)
Ar
R
Ar
Ar
C(7)
C(14)
N(6)
N
–
N
N
–
N
+
+
C(22)
Ar
Tl
C(28)
C(12)
R
R
R
TlOH
R
C(26)
O(30)
–MeOCOOH
C(27)
O(42)
C(21)
C(5)
C(1)
C(29)
C(32)
R
R
R
R
C(41)
1
2
C(44)
R = CO2Me; Ar = 4-MeC6H4; Ar´ = 1-C10H7 (a), 2-ClC6H4 (b),
2-Cl-6-MeC6H3 (c)
C(2)
C(3)
O(31)
O(43)
Tl
C(4)
Complexes 2 exist as yellow crystals resistant to oxida-
tion with atmospheric oxygen and moisture and are
readily soluble in most organic solvents.
C(33)
O(35)
O(34)
C(37)
O(38)
The crystal structure of thallium derivative 2c was
established by X-ray diffraction analysis (Fig. 1). This
compound exists as a zwitterion as evidenced by the
close values of the C—C bond lengths in the cyclo-
pentadienyl ring and the N—C(14) bond lengths in the
amidine fragment (Table 1).
O(39)
C(40)
O(36)
Fig. 1. Molecular structure of compound 2c.
The structure of ylide 2c is characterized by the Z
configuration of the amidine fragment, the coordination
of the Tl atom by the nitrogen atom of the amidine
fragment (N(21)—Tl 2.833(6) Å), and short distances
between the Tl atom and the C atoms of the cyclo-
pentadienyl ring. The plane of the amidine fragment is
almost perpendicular to the plane of the cyclopentadienyl
ring (the C(5)—C(1)—N(6)—C(14) torsion angle is
76.7°) due to which the distances between the Tl atom
and the C atoms of the five-membered ring are rather
short (Fig. 2):
Bond Tl—C(1) Tl—C(2) Tl—C(3) Tl—C(4) Tl—C(5)
d/Å
3.18
3.15
3.10
3.08
3.13
These short distances are indicative of strong attractive
interaction due to π-bonding of the η5 type between the
Table 1. Selected bond lengths (d) and bond angles (ω) in the structure of ylide 2c
Bond
d/Å
Angle
ω/deg
Angle
ω/deg
Tl—N(21)
Cl—C(20)
2.833(6)
C(14)-N(6)—C(7)
C(14)—N(6)—C(1)
C(7)—N(6)—C(1)
C(14)—N(21)—C(22)
C(14)—N(21)—Tl
C(22)—N(21)—Tl
C(5)—C(1)—C(2)
C(5)—C(1)—N(6)
C(2)—C(1)—N(6)
C(3)—C(2)—C(1)
C(3)—C(2)—C(29)
C(1)—C(2)—C(29)
C(4)—C(3)—C(2)
C(4)—C(3)—C(33)
C(2)—C(3)—C(33)
C(3)—C(4)—C(5)
C(3)—C(4)—C(37)
C(5)—C(4)—C(37)
123.9(6)
119.1(6)
116.7(6)
122.3(6)
132.3(5)
105.4(5)
109.0(6)
126.6(7)
124.4(7)
106.1(6)
127.9(7)
126.0(7)
110.3(7)
126.8(7)
122.8(7)
107.9(7)
126.0(8)
126.1(8)
C(1)—C(5)—C(4)
106.6(6)
121.4(7)
131.9(8)
119.3(8)
121.3(8)
119.8(7)
124.1(7)
116.0(7)
123.4(8)
119.5(8)
1.714(11)
1.374(10)
1.431(10)
1.431(10)
1.283(10)
1.413(10)
1.402(11)
1.422(10)
1.400(10)
1.478(11)
1.373(11)
1.506(11)
1.431(11)
1.474(11)
1.492(12)
1.502(10)
2.788(6)
C(1)—C(5)—C(41)
C(4)—C(5)—C(41)
C(12)—C(7)—N(6)
C(8)—C(7)—N(6)
N(21)—C(14)—N(6)
N(21)—C(14)—C(15)
N(6)—C(14)—C(15)
C(20)—C(15)—C(14)
C(16)—C(15)—C(14)
N(6)—C(14)
N(6)—C(7)
N(6)—C(1)
N(21)—C(14)
N(21)—C(22)
C(1)—C(5)
C(1)—C(2)
C(2)—C(3)
C(2)—C(29)
C(3)—C(4)
C(3)—C(33)
C(4)—C(5)
C(4)—C(37)
C(5)—C(41)
C(14)—C(15)
Tl—O(34)a
C(15)—C(16)—C(161) 130.3(10)
C(17)—C(16)—C(161) 107.5(11)
C(15)—C(20)—Cl
C(19)—C(20)—Cl
C(27)—C(22)—N(21)
N(21)—C(22)—C(23)
O(34)b—Tl—N(21)
C(33)—O(34)—Tla
122.2(7)
115.4(9)
119.3(8)
122.6(8)
99.0(2)
144.7(6)
a The symmetry transformation x + 1/2, –y + 1/2, –z + 1.
b The symmetry transformation x – 1/2, –y + 1/2, –z + 1.

892
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 5, May, 2001
Dushenko et al.
dienylthallium, the Tl atom has the coordination num-
ber of 5 and is coordinated to two vicinal carbonyl O
atoms of one anion and three O atoms of other anions.
In the crystal, the carbonyl O atoms of each anion are
coordinated to four different metal atoms (see Fig. 3).6
Molecule 2c is sterically overcrowded, and two
methoxycarbonyl groups are rotated with respect to the
plane of the cyclopentadienyl ring. The torsion angles in
the structure are as follows.
C(15)
C(7)
C(14)
N(6)
C(22)
N(21)
C(29)
C(2)
C(1)
Angle
α/deg
O(34)**
C(1)—C(2)—C(29)—O(30)
C(2)—C(3)—C(33)—O(35)
C(3)—C(4)—C(37)—O(39)
C(1)—C(5)—C(41)—O(42)
22.9
72.7
15.2
45.6
Tl
C(5)
C(41)
C(3)
C(4)
O(38)*
The Cl atom and the o-Me group in the aryl substituent
at the C(14) atom are bent upward. The bond angles
have the following values:
C(33)
C(37)
Angle
ω/deg
Angle
ω/deg
Fig. 2. Projection of molecule 2c illustrating η5-coordination of
the Tl atom by the cyclopentadienyl ring. O* and O** are the
carbonyl oxygen atoms of two adjacent molecules. The dis-
tances/Å: Tl—center of Cp is 2.887(4), Tl—O(38)* is 3.092(8),
and Tl—O(34)** is 2.788(6).
C(15)—C(20)—Cl 122.2 C(15)—C(16)—C(161) 130.3
C(19)—C(20)—Cl 115.4 C(17)—C(16)—C(161) 107.5
In the Z-amidine fragment, both tolyl groups are
rotated with respect to the plane of the
amidine moiety (the C(14)—N(6)—C(7)—C(8) and
C(14)—N(21)—C(22)—C(23) torsion angles are 50.9°
and 53.5°, respectively). In spite of this conformation
of the N-tolyl fragments, the bulky 2,6-substituted
aryl group at the C(14) atom cannot be located in
the plane of the amidine fragment and deviates
from this plane because of steric hindrances (the
N(6)—C(14)—C(15)—C(16) torsion angle is 63.3°) re-
sulting in the chirality of the structure of ylide 2c.
According to the data of X-ray diffraction analysis,
1H and 13C NMR spectroscopy, and IR spectroscopy,
complexes 2a—c exist as zwitterions both in the solid
state and in solutions.
The IR spectra of compounds 2a—c have no absorp-
tion bands corresponding to the C=N bonds and the
C=C bonds of the cyclopentadienyl ring. The carbonyl
groups are manifested as four absorption bands because
the the methoxycarbonyl substituents are located at
different angles with respect to the plane of the
cyclopentadienyl ring and, hence, are nonequivalent
(Table 2).
In the 13C NMR spectra of complexes 2a—c (see the
Experimental section), all signals for the C atoms of the
cyclopentadienyl ring are observed at δ 105—123. The
negative charge is localized on the Cp ring, which is
confirmed by the fact that the above-mentioned signals
are shifted upfield compared to the signals for the
sp2-hybridized carbon atoms of the Cp ring in 5-me-
thyl-1,2,3,4,5-pentamethoxycarbonylcyclopentadiene7
(δ 140.62 and 145.46). The signals for the C atoms of
the amidine NCN groups are observed at δ 159—161,
which is characteristic of the positively charged C at-
oms. These data agree with the ylide structure of com-
pound 2 in solution. The coordination of the Tl atom by
thallium atom and the negatively charged cyclopenta-
dienyl ring (the distance between the Tl atom and the
center of the Cp ring is 2.887(4) Å).
In the crystal structure, the Tl atom is additionally
coordinated by the carbonyl oxygen atoms of two adja-
cent molecules (the Tl—O(38)* and Tl—O(34)** bond
lengths are 3.092(8) and 2.788(6) Å, respectively)
(see Fig. 2).
It should be noted that the H and Au atoms in the
[C5(CO2Me)4{ArNC(Ar´)NAr}]H ligands and their com-
plexes with AuPPh3, respectively, are covalently bound
to the amidine N atom and are additionally η1- and
η2-coordinated by the π system of the Cp ring (the
H—C(1), Au—C(1), and Au—C(5) bond lengths are
2.46(8), 2.938, and 3.116 Å, respectively).1,2 In com-
plex 2c, the Tl atom is η5-bound to the π system of the
Cp ring resulting in weakening of the Tl—N bond
compared to the H—N and Au—N bonds in the
[C5(CO2Me)4{ArNC(Ar´)NAr}]H ligand and in its AuI
complex, respectively. This weakening is manifested in
a lesser degree of equalization of the bond lengths in the
amidine fragment of ylide 2c (the N(6)—C(14) and
N(21)—C(14) bond lengths are 1.374 and 1.283 Å,
respectively), whereas these distances in the initial ligand
1
are virtually equal (1.320 and 1.315 Å ).
The cyclopentadienylthallium derivatives containing
N-functionalized side chains, which have been described
previously,4,5 viz., C5R4(CH2CH2NMe2)Tl (R = H or
Me) and C5H4[CH(Ph)CH(Me)NMe2]Tl, differ from
compound 2 in that the Tl atom in the former deriva-
tives is coordinated only by the π system of the
cyclopentadienyl ring and does not form a bond with
the N atom. In pentamethoxycarbonylcyclopenta-

Chiral amidinylcyclopentadienylthallium
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 5, May, 2001
893
Table 2. Characteristics of complexes 2a—c
Com-
pound
Found
Calculated
Molecular
formula
IR,
Nujol mulls,
1H NMR at 298 K
(CD3CN), δ
(%)
N
–1
ν/cm
C
H
Cl
—
Tl
Me (s)
OMe (s, 3 H) Ar (m)
2a
53.61 3.99
53.69 3.91
3.23 23.99 C38H33N2O8Tl
3.30 24.04
1730, 1700, 1695,
1690, 1580, 1520,
1480, 1200, 1180
1.91 (3 H),
1.96 (3 H)*
1.98 (3 H),
2.02 (3 H)
3.64, 3.75,
3.83, 3.84*
3.71, 3.73,
3.76, 3.87
3.66, 3.67,
3.74, 3.80
6.34—8.10
(15 H)*
6.48—8.27
(15 H)
6.55—7.60
(12 H)
2b
2c
48.88 3.70
48.94 3.62
4.19
4.25
3.29 24.55 C34H30ClN2O8Tl 1740, 1730, 1710, 1700, 2.15 (6 H)
3.36 24.49
1600, 1520, 1500,
1410, 1220, 1180
49.49 3.75
49.54 3.80
4.23
4.18
3.36 24.15 C35H32ClN2O8Tl 1750, 1740, 1705, 1700, 2.14 (6 H),
3.65, 3.67,
3.73, 3.79
6.50—7.65
(11 H)
3.30 24.09
1590, 1520, 1510, 1410, 2.20 (3 H)
1220, 1200, 1190
* CDCl3 as the solvent.
the cyclopentadienyl moiety is manifested in the
downfield shifts of the signals for the C atoms of the
five-membered ring compared to the corresponding sig-
nals of the 1-(N,N´-di(p-tolyl)-α-naphthamidinyl)-
2,3,4,5-tetra(methoxycarbonyl)cyclopentadienide anion.2
Previously, an analogous criterion has been used as a
proof that the π system of the Cp ring is involved in
coordination (see Refs. 3—5 and references cited therein).
(see Table 2). Analogously, the C(2)—C(5) atoms of the
cyclopentadienyl ring give four different signals in the
13C NMR spectra. These facts are indicative of the
absence of the symmetry plane in molecules 2a—c and,
hence, of their chiral structures. Unlike compounds
2a—c, the ylides [C5(CO2Me)4{ArNC(Ph)NAr}]H and
their analogs containing the phenyl substituent at the
carbon atom of the amidine group1,2 possess the Cs
symmetry.
1
According to the H and 13C NMR spectral data,
both the protons and the C atoms of the methoxycar-
bonyl groups in complexes 2a—c containing the bulky
α-naphthyl or o-substituted aryl fragments at the C atom
of the amidine moiety are magnetically nonequivalent
No changes were found in the NMR spectra of
compounds 2a—c upon heating of their solutions in
acetonitrile-d3 to 80 °C, which is evidence for their
rather high stability.
Layer 1
Layer 2
Fig. 3. Unit cell of the crystal structure of compound 2c.

894
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 5, May, 2001
Dushenko et al.
c = 34.8492(12) Å, α = 90.0°, β = 90.0°, γ = 90.0°,
V = 6802.0(4) Å3, Z = 8, dcalc = 1.657 g cm–3. The X-ray
diffraction data were collected on a Bruker SMART diffracto-
meter equipped with a CCD detector (T = 293(2) K, graphite
monochromator, Mo-Kα radiation, λ = 0.71073 Å). The absorp-
tion coefficient was 4.881 mm–1; F(000) 3344; θ 2.20—29.03°;
the limiting indices –14 ≤ h ≤ 13, –15 ≤ k ≤ 23, –47 ≤ l ≤ 45;
36579 measured reflections; 8320 independent reflections
(Rint 0.0549); semiempirical absorption correction from ψ scans;
maximum and minimum transmissions were 0.284 and 0.202,
respectively. The refinement was performed by the least-squares
method using 8221 reflections; 0 restraints, 425 parameters
refined, GOOF based on F 2 was 1.268; the final R factors using
reflections with I > 2σ(I) were R1 = 0.0853, wR2 = 0.1655; the
R factors based on all data were R1 = 0.0937, wR2 = 0.1705,
∆fmax = 2.225, –1.369 e/Å3. The hydrogen atoms were placed
in geometrically calculated positions and refined using the
riding model. The selected lengths and bond angles in the
structure of 2c are given in Table 1. The atomic coordinates,
bond lengths, bond angles, and thermal parameters were depos-
ited with the Cambridge Structural Database.
To summarize, the Tl atom in complexes 2 is coor-
dinated in a polydentate fashion by the "hard" donor,
viz., by the side-chain N atom of the amidine moiety,
and by the "soft" donor, viz., by the π system of the Cp
ring (η5-bonding). This mode of coordination of the
thallium atom has not been observed previously in
related compounds. Such an unusual coordination is
favored by the fact that the plane of the amidine frag-
ment adopting the Z configuration is perpendicular to
the plane of the Cp ring due to the presence of the
bulky methoxycarbonyl and aryl substituents. The high
energy barrier hinders rotation of the α-naphthyl or
o-substituted aryl groups about the C—C bond of the
amidine moiety. All these factors are responsible for the
stability of the chiral structures of thallium derivatives 2.
Experimental
The 1H NMR spectra of solutions of the complexes
(0.05 mol L–1) were recorded on a Bruker AM spectrometer
operating at 300 MHz. The 13C NMR spectra of solutions of
the complexes (0.5 mol L–1) were measured on a Âruker AM
spectrometer operating at 75.47 MHz with Me4Si as the inter-
nal standard. The IR spectra were recorded on a Specord IR-75
instrument in Nujol mulls. The mass spectra were measured on
an HP 5995 A spectrometer (direct inlet of the sample,
EI, 70 eV, 60 °C). Methanol and benzene were purified accord-
ing to standard procedures.8
N,N´-diaryl-N-thallium-benz(α-naphth)amidinium-
N´-[2,3,4,5-tetra(methoxycarbonyl)cyclopentadien-1-yl]ides
(2a—c) (general procedure). Ylide 1 (5 mmol), which was
obtained according to a procedure reported previously,9 was
added to a solution of freshly prepared TlOH 10 (5 mmol) in
MeOH (80 mL). The reaction mixture was stirred at 40 °C for
1 h. Then the solvent was removed in vacuo and the residue was
crystallized by hot filtration from benzene (2a) or MeOH (2b
and 2c). The yields were 85—87%. Yellow crystals, m.p.
208—209 °C (2a), 186—187 °C (2b), and 237—238 °C (2c).
13C NMR (CDCl3), δ. 2a: 20.1, 20.4 (Me); 51.1, 51.4,
51.5, 51.9 (OMe); 106.1, 112.7, 114.8, 121.8 (C(1)—C(5),
Cpring.); 122.3, 124.4, 125.6, 125.6, 125.8, 126.4, 128.0, 128.2,
128.8, 129.1, 129.3, 130.0, 131.4, 131.9, 132.4, 134.8, 140.9,
143.5 (Ar); 161.4 (NCN); 164.5, 165.6, 166.3, 167.9 (C=O).
2b: 20.4, 20.6 (Me); 51.0, 51.4, 51.5, 51.9 (OMe); 105.5, 113.4,
114.2, 122.6 (C(1)—C(5), Cpring.); 122.6, 125.8, 125.9, 128.2,
128.4, 128.8, 129.1, 129.9, 131.7, 132.1, 132.3, 133.3,
135.0, 140.7, 142.8 (Ar); 159.4 (NCN); 164.3, 165.3, 166.1,
168.0 (C=O).
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos. 98-03-
33062, 99-03-33505, and 00-15-97320).
References
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X-ray diffraction analysis of complex 2c. Crystals of 2c
(C35H32ClN2O8Tl) are orthorhombic, M = 848.45, space
group Pbca, at 20 °C a = 10.9598(4), b = 17.8091(6),
Received February 15, 2001