Formation and crystal structure of stable five-coordinate diorgano cobalt(III) complexes

Article abstract of DOI:10.1002/zaac.200500182

The mer-octahedral complexes(2-carbonyl)(4-Me)(6-tBu)-phenolato[C,O] hydridotris(trimethylphosphine)cobalt(III) (1) or (1-carbonyl)(2-oxo)(1,2- diphenylethene)[C,O]hydridotris(trimethylphosphine)cobalt(III) (2) via formal insertion of propynoic acid ethyl ester into Co-H functions afford pentacoordinate vinylcobalt(III) 3 and 4, respectively, that are diamagnetic and attain a square pyramidal structure as exemplified by an X-ray diffraction analysis of 3.

Full text of DOI:10.1002/zaac.200500182

Formation and Crystal Structure of Stable Five-coordinate Diorgano Cobalt(III)
Complexes
Xiaoyan Li*,a, Hongjian Suna, Hans-Friedrich Kleinb, and Ulrich Flörkec
a Jinan / P.R. China, School of Chemistry and Chemical Engineering, Shandong University
b Darmstadt / Germany, Eduard-Zintl-Institut für Anorganische und Physikalische Chemie der Technischen Universität Darmstadt
c Paderborn / Germany, Anorganische und Analytische Chemie der Universität Paderborn
Received March 29th, 2005.
Abstract. The mer-octahedral complexes(2-carbonyl)(4-Me)(6-tBu)-
phenolato[C,O]hydridotris(trimethylphosphine)cobalt(III) (1) or
(1-carbonyl)(2-oxo)(1,2-diphenylethene)[C,O]hydridotris(trimethyl-
phosphine)cobalt(III) (2) via formal insertion of propynoic acid
ethyl ester into Co-H functions afford pentacoordinate vinylcobal-
t(III) 3 and 4, respectively, that are diamagnetic and attain a square
pyramidal structure as exemplified by an X-ray diffraction analysis
of 3.
Keywords: Cobalt; Acyl(vinyl)cobalt; Penta-coordination; Phos-
phorus ligands; Crystal structure
Introduction
The majority of these complexes that have been structur-
ally characterized are of the square pyramidal type
[CoL4LЈ][4, 6], where L4 is a square-planar system such as
porphyrin, salen or other chelating ligands, and LЈ is an
organo or a halide group [4, 6, 7]. Most of them are low-
spin and diamagnetic. There have been few examples with
structures of trigonal-bipyramidal coordination geometry.
These high-spin cobalt(III) complexes can be spectroscopi-
cally studied with EXAFS to yield structural information
[8]. Their paramagnetic properties can be easily investigated
through solid or solution magnetic moments.
Cobalt(III) with its low-spin d6 configuration tends to form
six-coordinate complexes in octahedral coordination ge-
ometry attaining 18 valence electrons. Cobalt(III) com-
plexes with five-coordinate CoIII as stable species under am-
bient conditions are known in rare examples [1].Usually
they are considered as reactive intermediates in ligand-ex-
change reactions [2].The understanding that the active site
of vitamin B12 contains
a
readily homolyzable
CoIIIϪcarbon bond and a five-coordinate square pyramidal
geometry has fuelled research into preparation and reactiv-
ity of cobalt complexes, in particular those compounds that
serve as models for bioinorganic systems [3]. Examples of
five-coordinate alkyl cobalt(III) complexes usually are mac-
rocycle compounds because most of them were synthesized
as model compounds for vitamin B12 as well as for cobala-
mins [4, 5]. Quite generally, complexes with five-coordinate
cobalt(III) as coordinatively unsaturated compounds may
have a potential in homogeneous catalysis.
We have recently reported some insertion reactions of tri-
methylphosphine-supported
hydrido(acyl)enolatocobal-
t(III) complexes with phenylethine, trimethylsilylethine and
bis(trimethylsilyl)butadiyne [9]. Products of these reactions
are complexes with five-coordinate cobalt(III), which were
characterized by routine spectroscopy (NMR, IR) and el-
emental analysis, whereas the configuration of these low-
spin diamagnetic complexes has not been structurally con-
firmed. Here we present some new insertion reactions of
the Co-H bond with propynoic acid ethyl ester.
* Xiaoyan Li
School of Chemistry and Chemical Engineering
Shandong University
Shanda Nanlu 27
Results and Discussion
250100 Jinan / PR China
Complexes with two five-coordinate cobalt(III) atoms (3, 4)
were obtained through the insertion reaction of acyl(hydri-
do)cobalt(III) complexes (1, 2) and propynoic ethyl ester
[Equations (1), (2)].
Complexes 3 and 4 were obtained as red solids that are
soluble in pentane or diethylether. The solids can be
handled in air for several days without any sign of de-
composition, while thermal degradation under argon begins
above 145 °C and 140 °C, respectively.
In the infrared spectra typical bands for ν(CoϪH) or
ν(CϵC) vibrations are absent. The ν(CϭO) vibrations of
the chelating ligand in complexes 3 and 4 experience a ba-
thochromic shift of about 30Ϫ50 cmϪ1 with respect to 1
and 2.
* Prof. Dr. H.-F. Klein
Eduard-Zintl-Institut für Anorg. und Physik. Chemie
der Technischen Universität Darmstadt
Petersenstraße 18,
D-64285 Darmstadt, Germany
E-mail: hfklein@hrz2.hrz.tu-darmstadt.de
* Dr. U. Flörke
Anorg. und Analyt. Chemie
der Universität Paderborn
Warburger Straße
D-33098 Paderborn, Germany
E-mail: ulrich.floerke@uni-paderborn.de
Supporting information for this article is available on the
WWW under http://www.wiley-vch.de/home/zaac or from the
author
Z. Anorg. Allg. Chem. 2005, 631, 1929Ϫ1931
DOI: 10.1002/zaac.200500182
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
1929

X. Li, H. Sun, H-F. Klein, U. Flörke
˚
Figure 1 Molecular structure of 3; selected bond distances/A and
angles/deg:
Co1ϪC1, 1.8651(18), Co1ϪC13 1.9129(19), Co1ϪO2 1.9501(12),
Co1ϪP1 2.2141(6), Co1ϪP2 2.2220(6), C13ϪC14 1.324(3),
O1ϪC1 1.217(2), O3ϪC15 1.226(2), C1ϪCo1ϪC13 103.90(8),
O2ϪCo1ϪP2 93.15(4), C1ϪCo1ϪO2 87.43(7), C13ϪCo1ϪO2
168.67(6), C1ϪCo1ϪP1 89.44(6), C13ϪCo1ϪP1 87.82(6),
O2ϪCo1ϪP1 92.55(4), C1ϪCo1ϪP2 89.00(6), C13ϪCo1ϪP2
86.96(6), P1ϪCo1ϪP2 174.02(2), C14ϪC13ϪC15 122.39(19),
C14ϪC13ϪCo1 139.26(17), C15ϪC13ϪCo1 98.35(12).
1
From H NMR data we assign a pseudo-triplett (0.9 Ϫ
1.1 ppm) with strong coupling (Η2JP,H ϩ JP,HΗ ϭ 8.1 Hz) to
the trans-PMe3 ligands. Signals of two geminal protons in
the alkenyl group are found in the range expected of alk-
enyl-CH groups with coupling constants J ϭ 3 Hz, which
4
2
are typical for geminal alkenyl protons in a compound with
five-coordinate cobalt(III). In the 31P NMR spectra at
Ϫ30 °C both compounds show singlets for the trans-PMe3
groups. The diamagnetic properties of these compounds are
compatible with a square pyramidal configuration. The acyl
group occupies the axial position where its trans-effect and
spacial distribution are accommodated more easily than in
the presence of trimethylphosphine as sixth ligand. This as-
signment is verified through a single crystal X-ray diffrac-
tion study. From pentane crystals of 3 suitable for X-ray
diffraction were obtained.
glyoxime model systems and cobalamines [12]. In case of
complex 3 and 4, the coordination system with two phos-
phine ligands, one acyl group, one vinyl group and one
phenoxy group certainly rates among the more electron-rich
compounds. However, five-coordinate cobalt(III) species
can be more stable thermally than their six-coordinate
counterparts, which can be inferred from the equilibrium
of compounds with five and six-coordinate cobalt(III) as
observed in our earlier work [10].
To our knowledge, this presentation is the first example
of a structurally characterized five-coordinate diorganocob-
alt(III) complex.
The molecular structure of compound 3 is shown in Fig-
ure 1. The cobalt atom is located above the basis of a square
pyramid and attains penta-coordination with two equa-
torial phosphorus atoms of trans-trimethylphosphine li-
gands, a carbon atom of the vinyl group, and an oxygen
atom of the phenoxy group. The carbon atom of the acyl
group is located in the apex above the square pyramid.
Experimental Part
General procedures and materials: Standard vacuum techniques
were used in manipulations of volatile and air-sensitive material.
Solvents were dried by known procedures and used freshly distilled.
Melting points/decomposition temperatures: Sealed capillaries, un-
corrected values. Literature methods were applied in the prep-
aration of complexes 1 and 2 [12]. Propynoic acid ethyl ester was
used as purchased. IR: Nujol mulls between KBr discs, Bruker
spectrophotometer type FRA 106. 1H and 13C NMR spectra
(300 MHz, 500 MHz , 75 MHz and 125 MHz) were recorded with
Bruker ARX-300, ARX-500 spectrometer respectively, 31P NMR
spectra (81 MHz, 202 MHz) were recorded with Bruker AM-200
and ARX-500 spectrometer respectively, 13C and 31P NMR reson-
ances were obtained with broad-band proton decoupling. C, H
analyses were carried out in a german ELEMENTAR Vario
ELIII analyser.
˚
The distance Co-C1 (1.865(2) A) is shorter than that of
the six-coordinate halogeno acyl phenolato cobalt(III) com-
plexes where CoϪC separations ranges from 1.910 to
˚
1.942 A [10], which is in turn shorter than those of hydri-
do(acyl)phenolato cobalt(III) complexes with CoϪC dis-
˚
tances ranging from 1.925 to 1.952 A [11]. These findings
can be rationalized by a stronger CoϪC bonding interac-
tion of the acyl group with an empty trans-position, where
2
an additional donor would compete for the metal dz or-
bital.
Presently the stabilization of complexes with five-coordi-
nate cobalt(III) is not fully understood. It has been sug-
gested that this coordination number is favoured by elec-
tron-rich ligand systems. This hypothesis was supported by
a study in which axial base exchange rates for [CoR(sal-
oph)] compounds were compared to exchange rates for
Preparation of (3-tert-butyl-5-methyl-2-oxobenzoyl)(1-ethoxocar-
bonyl-1-vinyl)trans- bis(trimethylphosphine)cobalt(III) (3): A sample
of (3-tert-butyl-5-methyl-2-oxo-benzoyl)-hydridotris(trimethylpho-
sphine)cobalt(III) (1) (0.64 g, 1.34 mmol) was dissolved in 50 mL
1930
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
zaac.wiley-vch.de
Z. Anorg. Allg. Chem. 2005, 631, 1929Ϫ1931

Stable Five-coordinate Diorgano Cobalt(III) Complexes
˚
of THF and propynoic ethyl ester (0.28 g, 2.86 mmol) was added
dropwise with stirring at Ϫ80 °C. The reaction mixture was
warmed to 20 °C and stirred for 18 h. During this period the reac-
tion solution turned brown. After removal of the solvent at reduced
pressure the solid residue was extracted with pentane (80 mL). The
product precipitated as yellow crystalline material at at Ϫ27 °C.
Yield: 0.67 g (26.6 %), m. p. 140Ϫ141 °C (dec.). C23H39CoO4P2
(500.4): C 55.20 (calc. 55.59), H 7.86 (calc. 7.82) %.
13.8122(7) A, ϕ ϭ 111.661(1), β ϭ 97.003(1), γ ϭ 98.230(1),° V ϭ
3 Ϫ3
˚
1333.52(12) A , Dc ϭ 1.246 g cm for Z ϭ 2, F(000) ϭ 532, μ ϭ
0.787 mmϪ1, Bruker AXS SMART APEX diffractometer, λ ϭ
0.71073 A, T ϭ 293 K, ω-scans, 18543 reflections, Θmax ϭ 28.28°,
˚
6606 independent reflections [R (int) ϭ 0.0347], semi-empirical ab-
sorption correction, hydrogens calculated, 282 refined parameters,
R ϭ 0.0365 (observed data), wR2 ϭ 0.0893 (independent data).
Crystallographic data (excluding structure factors) for the structure
described in this publication have been deposited as supplementary
material with the Cambridge Crystallographic Data Centre. Depo-
sition number is CCDC-252876 for 3. Copies of the data can be
obtained free of charge on application to CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK [Fax:ϩ44-1223-336-033; E-mail:
deposit@ccdc.cam.ac.uk].
IR (Nujol): ν(CϭO) 1659 s, 1641 s; (CϭC) 1613 m, 1593 m,
1
1581 m, 1544 m cmϪ1. H NMR (500 MHz, [D8]THF, 297 K): δ ϭ
0.92 (tЈ, 18 H, Η2JP,H
ϩ
4JP,HΗ ϭ 8.1 Hz, PCH3), 1.22(t, 3H, 3J ϭ
7.1 Hz, OCH2CH3), 1.33 (s, C(CH3)3), 2.00 (s, CH3), 3.99 (q, 2H,
4
3J ϭ 7.1 Hz OCH2CH3), 5.90 (dt, 1 H, JP,H ϭ 4.8 Hz, 2J ϭ
3.0 Hz, ϭ CH2), 6.27 (dt, 1H, 4JP,H ϭ 6.4 Hz, 2J ϭ 3.0 Hz, ϭCH2),
6.59 (d, 1 H, 4J ϭ 2.0 Hz, CH), 6.74 (d, 1H, 4J ϭ 2.0 Hz, CH) ppm.
Acknowledgment. We gratefully acknowledge support by the Excel-
lent Young Teachers Program of MOE, the Scientific Research
Foundation for the Returned Overseas Chinese Scholars, SEM, and
the Deutsche Forschungsgemeinschaft.
13C NMR (75.4 MHz, [D8]THF , 297 K): δ ϭ 9.7 (tЈ, Η1JP,C
ϩ
3JP,CΗ ϭ 26.5 Hz, PCH3), 12.7 (s, CH2CH3), 18.7 (s, CH3), 28.1 (s,
C(CH3)3), 33.4 (s, C(CH3)3), 58.7 (s, OCH2), 129.7 (ϭ CH2), 116.8,
129.0 (CH), 118.5, 136.5, 170.5, 173.7 (C). 31P NMR (81.0 MHz,
[D8]THF, 213 K): δ ϭ 13.3 (s, PCH3).
Preparation of (1-Carbonyl-2-oxo-1,2-diphenyl-diyl)(1-ethoxocar-
bonyl-1-vinyl)trans-bis (trimethylphosphine)cobalt(III), (4):
A
References
sample of (1-carbonyl-2-oxo-1,2-diphenyldiyl) hydridotris(trime-
thylphosphine)cobalt(III) (2) (1.07 g, 2.10 mmol) was dissolved in
50 mL of THF and propynoic ethyl ester (0.42 g, 4.29 mmol) was
added dropwise with stirring at Ϫ80 °C. The reaction mixture was
warmed to 20 °C and stirred for 18 h. During this period the reac-
tion solution turned red. After removal of the solvent at reduced
pressure the solid residue was extracted with pentane (80 mL), and
subsequently with diethyl ether (40 mL). The product precipitated
as orange crystalline material at Ϫ27 °C. Yield: 0.37 g (33.0 %). m.
p. 145-146 °C (dec.). C26H35CoO4P2 (532.4): C 58.66 (calc. 58.83),
H 6.63 (calc. 6.62) %.
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IR (Nujol): ν(CϭO) 1621 s, 1615 s; ν(CϭC) 1578 s, 1561 s cmϪ1
.
1H NMR (500.1 MHz, [D8]THF, 300 K): δ ϭ 1.11 (tЈ, 18H, Η2JP,H
4
3
ϩ J P,HΗ ϭ 8.1 Hz, PCH3), 1.18 (t, 3H, J ϭ 7.1 Hz, OCH2CH3),
3.98 (q, 3H, 3J ϭ 7.1 Hz, OCH2CH3), 5.86 (dt, 1H, 4JP,H ϭ 4.7 Hz,
2J ϭ 3.0 Hz, ϭCH2), 6.23 (dt, 1H, JP,H ϭ 6.5 Hz, 2J ϭ 3.0 Hz,
4
ϭCH2), 6.80Ϫ7.20 (m, 10H, CH), 8.79 (s, 1H). 13C NMR
(125.8 MHz, [D8]THF, 300 K): δ ϭ 10.7 (tЈ, Η1JP,C
ϩ
3JP,CΗ ϭ
26.4 Hz, PCH3), 14.0 (s, CH3) , 59.8 (s, OCH2), 110.7 (s, CCO),
131.1(ϭ CH2), 124.0, 127.4, 128.2, 128.9, 130.5 (CH), 137.1, 139.3
(C), 171.8 (s, CCO), 183.9 (s, C-O). 31P NMR (202.4 MHz,
[D8]THF, 300 K): δ ϭ 3.7 (s, PCH3).
[9] H.-F. Klein, X. Li, U. Flörke, H.-J. Haupt, Z. Naturforsch.
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[12] M. F. Summers, L. G. Marzilli, N. Bresciani-Pahr, L. Randac-
cio, J. Am. Chem. Soc., 1984, 106, 4478.
Crystallographic data for 3
(C23H39CoO4P2, Mr ϭ 500.41): crystal size 0.40 ϫ 0.35 ϫ 0.12 mm,
triclinic, space group P-1, a ϭ 9.2791(5), b ϭ 11.5217(6), c ϭ
Z. Anorg. Allg. Chem. 2005, 631, 1929Ϫ1931
zaac.wiley-vch.de
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
1931