Cyclometalation of thiobenzophenones with mononuclear methyliron and -cobalt complexes

Article abstract of DOI:10.1002/ejic.200800397

Under smooth conditions (-70°C) thiobenzophenone derivatives react with [Fe(CH₃)₂(PMe₃)₄] to form five-membered metallacycles 1 and 2 by C-H activation. These complexes show octahedral coordination geometry; wit

Full text of DOI:10.1002/ejic.200800397

SHORT COMMUNICATION
DOI: 10.1002/ejic.200800397
Cyclometalation of Thiobenzophenones with Mononuclear Methyliron and
-cobalt Complexes
Robert Beck,*[a,b] Hongjian Sun,*[b] Xiaoyan Li,[b] Sebnem Camadanli,[a] and
Hans-Friedrich Klein[a]
Keywords: C–H activation / Cyclometalation / Cobalt / Iron / Nickel / S ligands
Under smooth conditions (–70 °C) thiobenzophenone deriva- zerovalent η2-C=S complexes 5 and 6, possessing triangular-
tives react with [Fe(CH3)2(PMe3)4] to form five-membered
metallacycles 1 and 2 by C–H activation. These complexes
show octahedral coordination geometry; with [Co(CH3)-
(PMe3)4], complexes 3 and 4 with trigonal-bipyramidal coor-
dination are formed. Reaction with basic [Ni(CH3)2(PMe3)3]
causes reductive elimination (of ethane) with formation of
planar coordination. The structures of the complexes were
confirmed by X-ray diffraction, and their coordination geom-
etry is discussed.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Introduction
Results and Discussion
Stoichiometric and catalytic transformations involving
We describe here for the first time cyclometalation reac-
C–H activations are of special interest in synthetic chemis- tions, under mild conditions, of thiobenzophenones by C–
try, especially for an easy functionalization of specific H activation at mononuclear iron and cobalt centers.
bonds.
When combining the starting materials in diethyl ether
In comparison to 4d and 5d transition metals, the avail- (Scheme 1) at –70 °C, according to the procedure described
ability of cobalt and iron compounds provides a new and in the Experimental Section, an immediate change of color
low-cost route to metallation reactions initiated by C–H from red to green is observed, accompanied by gas evol-
bond activation. At this stage it is interesting that little is ution (CH4).
known about this type of reactive intermediates.
Cyclometalation reactions are known for almost all tran-
sition metals, and typically a pre-coordination of an an-
choring group which contains a donor atom N, P, O or S
(S-donating ones restricted to thioether and thiolato
groups) is assumed.[1–2]
Likewise, reactions and catalytic functionalizations of
benzophenones have been already studied.[3] However, for
Scheme 1. Reaction of thiobenzophenones with Fe(CH3)2(PMe3)4.
such homologous thiobenzophenones, there are until now
only few examples described in the literature.[4–6] Thioben-
Green hexagonal crystals are obtained from pentane
solutions at –27 °C with a yield of 78% (2: green, rhombic
zophenones with only one anchoring group form just an
end-on C=S coordination or bridge metal centers (Os),[7]
crystals, 81% yield).
allow an η2-coordination (Pt, V, Ti),[8] or lead to a hetero-
1
The H NMR spectroscopic data for 1 shows a charac-
lytic C=S bond breaking (Mo).[9]
teristic resonance of the FeCH3 group at δ = 0.54 ppm (3
H) split to a broad triplet (3JP,H = 11.8 Hz), whereas the
coupling with the cis-disposed trimethylphosphane ligand
collapses by reversible dissociation.
The carbon and C=S metallation is demonstrated by
characteristic chemical shifts observed in the 13C NMR
[a] Eduard-Zintl-Institut für Anorganische und Physikalische
Chemie der Technischen Universität Darmstadt,
spectra for C (1: δ = 195.4 ppm; 2: δ = 193.4 ppm) and for
Petersenstrasse 18, 64285 Darmstadt, Germany
the C=S function (1: δ = 163.9 ppm; 2: δ = 156.4 ppm).
The molecular structure of 1 (Figure 1) shows an octahe-
drally coordinated iron center with three meridionally dis-
posed P-donors. The other three ligand positions are occu-
E-mail: metallacycle@gmail.com
[b] School of Chemistry and Chemical Engineering, Shandong,
University,
Shanda Nanlu 27, 250100 Jinan, P. R. China
E-mail: hjsun@sdu.edu.cn
Eur. J. Inorg. Chem. 2008, 3253–3257
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3253

R. Beck, H. Sun, X. Li, S. Camadanli, H.-F. Klein
SHORT COMMUNICATION
pied by the metallated C-atom, the S-donor atom and the [C1–Co1–P3 169.50(9)°] with three phosphorus nuclei in
methyl group (C1) trans to the sulfur atom. The bond equatorial and axial positions. The coordination sphere is
lengths of the iron atoms to the two trans-oriented P-atoms completed by the metalated carbon atom C1 (axial) and the
are 2.242 and 2.246 Å; they are almost identical, and only S-donor (equatorial) which attacks the cobalt center with a
in the Fe1–P2 distance (2.269 Å) is the trans influence of bite angle of [C1–Co1–S1 84.53(9)°]. The measured C=S
the metallated carbon atom C2 noticed. The significantly bond length of 1.688(3) Å is similar to that of 1.
different Fe–C bond lengths [Fe1–C1 2.106 Å, Fe1–C2
2.022(4) Å] are attributed to the different carbon hybridiza-
tions (sp3-C and sp2-C).[10] The C8–S1 bond of 1.675(4) Å
is slightly shorter than that found in free thiobenzophenone
(1.635 Å)[11] and confirms the double-bond character of the
C=S bond. In contrast, thiolato complexes of cobalt exhibit
typical bond lengths in a range between 1.80–1.85 Å for the
C–S single bond.[12]
Figure 2. Molecular structure of 4; selected distances [Å] and
angles [°]: Co1–C1 1.965(3), Co1–S1 2.1510(9), Co1–P1 2.1940(10),
Co1–P2 2.2196(10), Co1–P3 2.2203(10), C7–S1 1.688(3); C1–Co1–
S1 84.53(9), C1–Co1–P3 169.50(9), C1–Co1–P1 87.11(9), S1–Co1–
P1 112.86(4), C1–Co1–P2 92.12(9), S1–Co1–P2 132.87(4), P1–
Co1–P2 113.89(4).
Figure 1. Molecular structure of 1; selected distances [Å] and
When basic Ni(CH3)2(PMe3)3 is used under analogous
experimental conditions, the reductive elimination prevails
against the C–H activation (Scheme 3).
angles [°]: Fe1–C1 2.106(5), Fe1–C2 2.022(4), Fe1–S1 2.168(37),
Fe1–P1 2.246(19), Fe1–P2 2.269(22), Fe1–P3 2.242(18), C8–S1
1.675(4); C2–Fe1–S1 83.87(12), C1–Fe1–S1 175.37(15), P3–Fe1–P1
158.34(5), C2–Fe1–P2 168.54(12), C1–Fe1–P2 91.69(15), P3–Fe1–
P2 100.06(5), P1–Fe1–P2 95.29(5).
Under analogous experimental conditions with the meth-
ylcobalt compound (Scheme 2), the cyclometalation of
thiobenzophenones occurs with similar reaction rates
(120 min), without a significant effect caused by the substit-
uent [R = H, N(CH3)2].
Scheme 3. Reaction of thiobenzophenones with Ni(CH3)2(PMe3)3.
The orange-brown crystals of 6 obtained from a pentane
solution at –27 °C are extremely air-sensitive and melt at
92 °C with decomposition (5: yellow powder, dec. Ͼ 97–
99 °C).
Scheme 2. Reaction of thiobenzophenones with Co(CH3)(PMe3)4.
In comparison with free thiobenzophenone, presenting a
The loss of both nickel-bound methyl substituents can
chemical shift at δ =230.0 ppm in 13C NMR spectrum, the be confirmed by the NMR spectra of 5 and 6, and the mul-
C=S function of the newly coordinated complex exhibits an tiplicities of the signals reveal the high symmetry of the
intense high-field shift of approx. 60 ppm (3:
167.6 ppm; 4: δ = 171.1 ppm).
δ
=
molecule, which is confirmed by an X-ray structure analysis
of 6.
The molecular configuration of 3 is confirmed by X-ray
The molecular structure of 6 (Figure 3) shows a triangu-
crystal structure determination (Figure 2). The coordina- lar-planar coordination geometry with two P-ligand atoms
tion geometry can be described as trigonal-bipyramidal and the midpoint of the η2-C=S coordination [Ni–
3254
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3253–3257

Mononuclear Methyl-Iron and -Cobalt Complexes
ing with ice-cold pentane and drying in vacuo afforded analytically
pure substances 1–6.
S 2.1289 Å and Ni C 2.020(2) Å] in-plane attached to the
zerovalent nickel atom. The C=S bond is with 1.769(2) Å,
as expected, longer than in 1 and 4, which corresponds to
the aforementioned η2-C=S platinum complex.[8]
1: Yield 865 mg (78%), m.p. 112–114 °C. IR (Nujol): ν = 1601 (m,
˜
νC=C), 1570 (m, νC=C), 1513 (m, νFeC=C), 943 (vs, ρ1PCH3)
3
cm–1. 1H NMR (500 MHz, [D8]thf, 300 K): δ = 0.54 (t, JP,H
=
11.8 Hz, 3 H, FeCH3), 0.60 (s, 18 H, PCH3), 1.51 (s, 9 H, PCH3),
3
3
6.76 (t, JH,H = 6.8 Hz, 1 H, CH), 7.22 (t, JH,H = 7.0 Hz, 1 H,
3
CH), 7.22 (t, JH,H = 7.0 Hz, 1 H, CH), 7.29–7.33 (m, 3 H, Ar-H),
4
3
7.68 (d, JP,H = 4.6 Hz, 1 H, CH), 7.75 (d, JH,H = 7.9 Hz, 2 H,
CH), 7.89 (d, 3JH,H = 7.5 Hz, 1 H, CH) ppm. 13C NMR (125 MHz,
[D8]thf, 300 K): δ = –7.6 (m, FeCH3), 17.1 (tЈ, |1JP,C
+
3JP,C| =
10.8 Hz, PCH3), 20.0 (d, 1JP,C = 6.6 Hz, CH2), 119.9 (s, CH), 122.3
(s, CH), 123.9 (s, CH), 125.5 (s, CH), 128.1 (s, CH), 147.0 (s, CH),
147.7 (s, C), 158.7 (s, C), 163.9 (s, C=S), 195.4 (s, FeC) ppm. 31P
NMR (202 MHz, [D8]thf, 296 K): δ = 10.2 (br. s, 2 P, PCH3), –63.4
(br. m, 1 P, PCH3) ppm. C26H38FeNP3 (513.3): calcd. C 60.83, H
7.46, N 2.73, P 18.10; found C 60.62, H 7.15, N 2.78, P 18.21.
2: Yield 803 mg (81%), m.p. (dec.) 106–108 °C. IR (Nujol): ν =
˜
1602 (m, νC=C), 1573 (m, νC=C), 1517 (m, νFeC=C), 943 (vs,
ρ1PCH3) cm–1. 1H NMR (300 MHz, [D8]thf, 300 K): δ = 0.06 (t,
3JP,H = 9.3 Hz, 3 H, FeCH3), 0.71 (s, 18 H, PCH3), 1.25 (s, 9 H,
3
PCH3), 2.35 (s, 6 H, NCH3), 2.56 (s, 6 H, NCH3), 6.46 (d, JH,H
=
8.5 Hz, 1 H, CH), 6.51 (d, 3JH,H = 8.7 Hz, 2 H, CH), 7.53 (d, 4JH,H
3
= 2.7 Hz, 1 H, CH), 7.75 (d, JH,H = 8.7 Hz, 2 H, CH), 8.06 (d,
Figure 3. Molecular structure of 6; selected distances [Å] and
angles [°]: Ni1–C17 2.020(2), Ni1–S1 2.1289(8), Ni1–P1 2.1510(9),
Ni1–P2 2.1817(8), C17–S1 1.769(2); P1–Ni1–P2 105.66(3), C17–
S1–Ni1 61.60(7), C17–Ni1–P1 102.01(6), S1–Ni1–P1 152.35(2),
C17–Ni1–P2 152.30(6).
3JH,H = 9.3 Hz, 1 H, CH) ppm. 13C NMR (125 MHz, [D8]thf,
300 K): δ = –5.8 (t, JP,C = 24.7 Hz FeCH3), 15.5 (tЈ, |1JP,C + JP,C
|
2
3
= 13.5 Hz, PCH3), 17.9 (m, PCH3), 39.8 (s, NCH3), 40.0 (s, NCH3),
107.2 (s, CH), 112.1 (s, CH), 121.9 (s, CH), 125.8 (s, CH), 129.0 (s,
CH), 130.3 (s, 1 C), 135.1 (s, 1 C), 146.4 (s, 1 C), 151.3 (s, 1 C),
156.4 (s, C=S), 193.4 (s, FeC) ppm. 31P NMR (121.5 MHz, [D8]thf,
296 K): δ = 17.8 (br. s, 1 P, PCH3), 14.8 (br. s, 2 P, PCH3) ppm.
C27H49FeN2P3S (582.5): calcd. C 55.67, H 8.40, N 4.81, S 5.50;
found C 56.43, H 9.63, N 4.52, S 5.54.
Conclusions
We have shown that, under mild conditions, the cyclo-
metalation of thiobenzophenones by C–H activation of 3d
transition metals was realized by using iron and cobalt cen-
ters. The rate of cyclometalation appears to be independent
of the para substituent [R = H or N(CH3)2] and the metal
(Fe, Co).
The synthesized complexes are model compounds which
are related with suggested ruthenium intermediates of the
first step in the catalytic cycle for the C–C coupling of
benzophenones. Furthermore, as the iron and cobalt cen-
ters retain their low oxidation states with similar effect of
donor atoms after the reaction, it should be possible to per-
form a second C–H activation. A subsequent elimination
step accompanied with a C–C coupling would facilitate a
catalytic reaction sequence. Experiments with this aim are
the subject of current investigations.
3: Yield 540 mg (67%), m.p. 106–108 °C. IR (Nujol): ν = 1599 (m,
˜
νC=C), 1580 (m, νC=C), 1519 (m, νCoC=C), 945 (vs, ρ1PCH3)
1
cm–1. H NMR (300 MHz, [D8]thf, 300 K): δ = 1.28 (br. s, 27 H,
PCH3), 6.75 (br. s, 1 H, CH), 7.14 (br. s, 2 H, CH), 7.34 (br. s, 2
H, CH), 7.84 (br. s, 2 H, CH), 8.06 (br. s, 1 H, CH), 8.45 (br. s, 1
H, CH) ppm. 13C NMR (125 MHz, [D8]thf, 300 K): δ = 20.4 (d,
5
1JP,C = 18.5 Hz, PCH3), 114.9 (d, JP,C = 4.3 Hz, CH), 119.1 (s,
CH), 120.2 (s, CH), 122.2 (s, CH), 123.0 (s, CH), 127.3 (s, CH),
148.8 (d, 4JP,C = 6.1 Hz, 1 C), 157.6 (s, 1 C), 167.6 (m, C=S), 175.3
(m, CoC) ppm. 31P NMR (202 MHz, [D8]thf, 296 K): δ = 22.3 (br.
s, 3 P, PCH3) ppm. C22H36CoP3S (484.4): calcd. C 54.55, H 7.49,
P 19.18; found C 53.45, H 7.53, P 18.33.
4: Yield 427 mg (45%), m.p. (dec.) 120–122 °C. IR (Nujol): ν =
˜
1601 (m, νC=C), 1570 (m, νC=C), 1515 (m, νCoC=C), 941 (vs,
1
ρ1PCH3) cm–1. H NMR (500 MHz, [D8]thf, 296 K): δ = 1.17 (br.
s, 27 H, PCH3), 2.37 (s, 6 H, NCH3), 2.61 (s, 6 H, NCH3), 6.42 (d,
3
3JH,H = 8.2 Hz, 1 H, CH), 6.55 (d, JH,H = 8.5 Hz, 2 H, CH), 7.45
4
3
(d, JH,H = 2.5 Hz, 1 H, CH), 7.66 (d, JH,H = 8.5 Hz, 2 H, CH),
8.01 (d, JH,H = 8.5 Hz, 1 H, CH) ppm. 13C NMR (121.5 MHz,
3
1
3
Experimental Section
[D8]thf, 296 K): δ = 20.4 (td, JP,C = 22.5, JP,C = 3.7 Hz PCH3),
40.4 (s, NCH3), 41.1 (s, NCH3), 110.9 (s, CH), 113.7 (s, CH), 123.6
(s, CH), 126.3 (s, CH), 130.7 (s, CH), 132.4 (s, 1 C), 133.3 (s, 1 C),
141.7 (s, 1 C), 151.8 (s, 1 C), 171.1 (s, C=S), 175.3 (s, CoC) ppm.
31P NMR (202 MHz, [D8]thf, 296 K): δ = 17.1 (br. s, 3 P, PCH3)
ppm. C26H46CoN2P3S (570.58): calcd. C 54.73, H 8.13, N 4.91, S
5.62; found C 54.23, H 8.55, N 4.77, S 5.67.
General
Procedure:
Solutions
of
[Fe(CH3)2(PMe3)4],[13]
[CoCH3(PMe3)4],[14] or [Ni(CH3)2(PMe3)3][15] in diethyl ether
(50 mL) on a scale of about 1–2 mmol were combined with equi-
molar amounts of the thiobenzophenones in the same solvent
(50 mL) and the mixtures stirred at –70 °C. The reaction mixture
was warmed up to 20 °C and stirred for another 120 min (maxi-
mum). The volatiles were removed in vacuo, and the residue was
extracted with pentane through a glass-sinter disc (G3). Crystals
formed upon cooling of the solution to –27 °C. Decantation, wash-
5: Yield 493 mg (71%), m.p. (dec.) 92–94 °C. IR (Nujol): ν = 1575
˜
1
(m, νC=C), 923 (vs, ρ1PCH3) cm–1. H NMR (300 MHz, [D8]thf,
3
296 K): δ = 0.90 (br. s, 18 H, PCH3), 6.65 (d, JH,H = 8.7 Hz, 4 H,
Eur. J. Inorg. Chem. 2008, 3253–3257
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3255

R. Beck, H. Sun, X. Li, S. Camadanli, H.-F. Klein
SHORT COMMUNICATION
Table 1. Crystal data for 1, 4 and 6.
1
4
6
Empirical formula
Formula mass
C20H40FeP3S
461.34
C26H46CoN2P3S
570.55
C23H38N2NiP2S
495.26
Crystal size [mm]
Crystal system
Space group
0.12ϫ0.17ϫ0.5
triclinic
P1
0.10ϫ0.12ϫ0.28
orthorhombic
P212121
0.10ϫ0.35ϫ0.50
triclinic
P1
¯
¯
a [Å]
b [Å]
c [Å]
α [°]
9.113(12)
14.8030(13)
19.9730(12)
102.80(2)
98.04(2)
101.11(2)
2530.8(5)
4
10.7517(9)
16.4595(14)
17.2354(15)
90
90
90
3050.1(5)
4
1.242
8.2490(16)
11.846(2)
14.354(3)
99.24(3)
103.24(3)
107.51(3)
1261.7(4)
2
β [°]
γ [°]
V [Å3]
Z
Dcalcd. [g/cm3]
1.211
0.870
1.304
0.991
µ(Mo-Kα) [mm–1]
0.805
Temperature [K]
Data collection range [°]
h
k
293(2)
293(2)
293(2)
2.8 Յ 2θ Յ 54
–11 Յ h Յ 11
–18 Յ k Յ 18
–25 Յ l Յ 24
32783
10810 (Rint = 0.081)
793
3.4 Յ 2θ Յ 50
–12 Յ h Յ 12
–19 Յ k Յ 19
–20 Յ l Յ 14
16139
5403 (Rint = 0.027)
298
3.0 Յ 2θ Յ 54
–10 Յ h Յ 9
–15 Յ k Յ 10
–18 Յ l Յ 18
4447
3609 (Rint = 0.043)
304
l
Number of reflections measured
Number of unique data
Parameters
GoF on F2
1.162
1.021
0.970
R1 [I Ն 2σ(I)]
wR2 (all data)
0.0557
0.1311
0.0364
0.0964
0.0287
0.1081
CH), 8.06 (d, 3JH,H = 8.7 Hz, 4 H, CH) ppm. 13C NMR (125 MHz,
[D8]thf, 296 K): δ = 17.5 (m, PCH3), 18.3 (m, PCH3), 112.3 (s, CH),
130.4 (s, CH), 141.7 (s, 1 C), 147.9 (s, NC), 154.3 (s, C=S) ppm.
31P NMR (202 MHz, [D8]thf, 296 K): δ = 1.7 (br. s, 2 P, PCH3)
ppm. C19H28NiP2S (409.13): calcd. C 55.78, H 6.90, P 15.14; found
C 55.34, H 7.31, P 15.18.
Acknowledgments
Financial support of this work by the Fonds der Chemischen Indu-
strie is gratefully acknowledged. R. B. thanks the China Postdoc-
toral Science Foundation and the Shandong University Postdoc-
toral Science Foundation and Innovation.
6: Yield 310 mg (56%), m.p. (dec.) 97–99 °C. IR (Nujol): ν = 1581
˜
1
(m, νC=C), 925 (vs, ρ1PCH3) cm–1. H NMR (300 MHz, [D6]ben-
zene, 296 K): δ = 0.77 (br. s, 9 H, PCH3), 1.01 (br. s, 9 H, PCH3),
3
2.56 (s, 12 H, NCH3), 6.65 (d, JH,H = 8.7 Hz, 4 H, CH), 8.06 (d,
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3JH,H = 8.7 Hz, 4 H, CH) ppm. 13C NMR (125 MHz, [D6]benzene,
296 K): δ = 17.5 (m, PCH3), 18.3 (m, PCH3), 112.3 (s, CH), 130.4
(s, CH), 141.7 (s, 1 C), 147.9 (s, NC), 152.2 (s, C=S) ppm. 31P
NMR (202 MHz, [D6]benzene, 296 K): δ = –0.4 (br. s, 1 P, PCH3),
0.9 (br. s, 1 P, PCH3) ppm. C23H38N2NiP2S (495.3): calcd. C 55.78,
H 7.73, N 5.66, S 6.47; found C 55.53, H 8.41, N 5.77, S 5.73.
Crystal Structure Analysis: Crystal data are presented in Table 1.
Data collections were performed with a STOE IPDSII image-plate
detector using Mo-Kα radiation (λ = 0.71019 Å). Details of the
crystal structures are given in Table 1. Data collection: Stoe X-
AREA.[16] Cell refinement: Stoe X-AREA.[16] Data reduction: Stoe
X-RED.[16] The structure was solved by direct methods with
SHELXS-97,[17] and anisotropic displacement parameters were ap-
plied to non-hydrogen atoms in a full-matrix least-squares refine-
ment based on F2 using SHELXL-97.[17] In the title compounds,
the hydrogen atoms on C were placed at calculated positions (C–
H: 0.93 Å for CH groups and 0.96 Å for methyl groups) and were
allowed to ride on the parent atom [Uiso(H) = 1.2 U(C) for CH
groups and Uiso(H) = 1.5 U(C) for methyl groups]. CCDC-678969
for (for 1), -678970 (for 4) and -678971 (for 6) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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Received: April 18, 2008
Published Online: June 19, 2008
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