η5-cyclopentadienyl)(η4-di- and tetra-phosphorylcyclobutadiene)cobalt(I): Synthesis, structure, and formation of 1-D coordination polymer

Article abstract of DOI:10.1039/b204779a

η⁵-Cyclopentadienyl)(η⁴-di- and tetra-phosphorylcyclobutadiene)cobalt(I) complexes were synthesized by the reaction of mono- and diphosphorylacetylenes with (CpCo(CO)₂, respectively. The tetraphosphoryl derivative has prov

Full text of DOI:10.1039/b204779a

(h5-Cyclopentadienyl)(h4-di- and
tetra-phosphorylcyclobutadiene)cobalt( ): Synthesis, structure, and
I
formation of 1-D coordination polymer†
Shigeru Sasaki,* Yoshihiro Tanabe and Masaaki Yoshifuji*
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan.
E-mail: yoshifj@mail.cc.tohoku.ac.jp; Fax: +81 22 217 6562; Tel: +81 22 217 6558
Received (in Cambridge, UK) 17th May 2002, Accepted 11th July 2002
First published as an Advance Article on the web 25th July 2002
5
(h5-Cyclopentadienyl)(h4-di- and tetra-phosphorylcyclobu-
tadiene)cobalt( ) complexes were synthesized by the reaction
of mono- and diphosphorylacetylenes with CpCo(CO)2,
respectively. The tetraphosphoryl derivative has proved to
work as a bis-bidentate ligand affording a one-dimensional
coordination polymer with Ce(III).
ne)(h -cyclopentadienyl)cobalt(
I
) type reported by Baxter et
I
al.,11 obtained by the reaction of dimethyl 1-propynylphospho-
nate with CpCo(CO)2 under very similar conditions to ours, was
not obtained. Products of the reaction seemed to depend
significantly on the substituent. Complexes 3a, 3b, and 4 were
purified by column chromatography on SiO2.
The structures of complexes 3a, 3b, and 4 were characterized
by 1H, 13C, and 31P NMR, MS, IR, and UV-Vis spectra.
Formation of the cyclobutadiene ring and the position of the
substituents were clearly characterized by 13C NMR signals.
Cyclic p-conjugated systems fully substituted by heteroatoms
have attracted considerable attention, since they are expected to
have a unique structure due to intramolecular interaction
between the adjacent functional groups, unique physical
properties due to intermolecular interaction between p-conju-
gated systems and the functional groups, and ability for
coordination or hydrogen bonding to form a novel molecular
assembly. However, the number of cyclic p-conjugated systems
carrying neighbouring phosphorus functional groups is still
The cyclobutadiene carbons of 3a and 3b attached to the
1
phosphoryl substituent appeared as dd (3a: d 57.0 (dd, JPC
=
=
3
1
3
211.0, JPC = 19.6 Hz), 3b: d 66.1 (dd, JPC = 99.8, JPC
15.8 Hz)), while the other cyclobutadiene carbons were
observed at lower field as a triplet (3a: d 83.6 (t, 2JPC = 7.5 Hz),
2
3b: d 87.7 (t, JPC = 4.9 Hz)). The magnitude and pattern of
limited.
Pentaphosphinocyclopentadienyl
complex,1
13C–31P coupling strongly suggested formation of head-to-tail
cyclobutadiene complexes as observed in the previous re-
ports.12 The cyclobutadiene carbon of 4 was interpreted by
1,2,3,4-tetraphosphinobenzene,2
tetraphosphorylbenzoqui-
none3 have been reported so far. Oligomerization of acetylenes
5
1
2
3
by (h -cyclopentadienyl)cobalt(
I
) complexes4 is a general
assigning the JPC, JPC and JPC values similar to those of 3a
4
1
2
3
method to prepare p-conjugated systems such as benzenes, (h -
(4: d 66.0 (ddt, JPC = 216.0, JPC = 8.2, JPC = 16.7 Hz)).
Coupling constants between the phosphorus atoms (3JPP and
4JPP), which are generally small (ca. 10 Hz)13 between the
phosphoryl phosphorus nuclei, seemed to have little influence
on the spin–spin coupling system. 31P NMR (81 MHz, CDCl3)
signals of 3a, 3b, and 4 were observed in the typical region of
the phosphoryl groups (3a: d 20.6, 3b: d 26.5, 4: d 16.0).
Significant intramolecular interaction among neighboring phos-
phoryl groups in 4 was ruled out from the small difference in
chemical shift between 3a and 4. The effect of the phosphoryl
group was not significant in the UV-Vis spectra, which were
similar to those of an unsubstituted derivative.14 The structure
and alignment of substituents in 3b were finally confirmed by
X-ray crystallography of 3b·EtOH (Fig. 1).‡
5
cyclobutadiene)(h -cyclopentadienyl)cobalt( ), and cobaltacy-
I
clopentadienes, depending on the substrates and conditions. In
fact, hexaborylbenzene was synthesized by the reaction of
diborylacetylene with CpCo(CO)2.5 Herein, we report synthesis
5
4
of (h -cyclopentadienyl)(h -di- and tetra-phosphorylcyclobuta-
diene)cobalt( ) complexes by the reaction of phosphorylacety-
I
lenes with CpCo(CO)2, and their structures, together with redox
properties and unique transition metal complex formation.
Acetylene 1a6 was allowed to react with CpCo(CO)2 in
refluxing xylene and the reaction was monitored by 31P NMR
spectroscopy (Scheme 1). Formation of the cyclobutadiene
complex 3a as a single isomer without significant side reactions
was confirmed by disappearance of the signal of alkynylphos-
phoryl group of 1a (dP = 25.3) and growing signals due to the
phosphoryl group of 3a (dP = 20.6) attached to the cyclobuta-
diene. Acetylene 1b7 afforded complex 3b as a main product
similarly to 1a except for the formation of a significant amount
of a side product.8 Diphosphorylacetylene 29 was also con-
verted to complex 4 in moderate yield. Irradiation10 with a 500
W Xe-lamp slightly improved the yield in some cases and
addition of a catalytic amount of CpCo(CO)2 afforded only a
trace amount of the cyclobutadiene complex with recovery of
Structural parameters of 3b were within the range of the
4
5
reported (h -cyclobutadiene)(h -cyclopentadienyl)cobalt(
).15
I
One of the oxygens of the phosphoryl groups (O2) was weakly
hydrogen-bonded to ethanol, and that was in agreement with
nOH = 3372 cm21 observed in IR spectrum (KBr). Such
hydrogen bond formation by phosphoryl compounds in the
crystals is well known.16
4
the starting material. A compound of the (h -cyclopentadieno-
Fig. 1 ORTEP drawing of 3b with thermal ellipsoid of 50% probability.
Selected bond lengths (Å) and angles (°): P1–C6 1.783(4), P1–O1 1.487(3),
P2–C8 1.782(4), P2–O2 1.499(3), C6–C7 1.467(6), C7–C8 1.466(6), C8–
C9 1.461(5), C6–C9 1.462(6), C6–C7–C8 90.1(3), C7–C8–C9 89.8(3), C6–
C9–C8 90.5(3), C7–C6–C9 89.7(3). The hydrogen bond is shown by the
dotted line.
Scheme 1
† Electronic supplementary information available: Synthetic procedure,
physical data, and crystallographic data. See http://www.rsc.org/suppdata/
cc/b2/b204779a/
1876
CHEM. COMMUN., 2002, 1876–1877
This journal is © The Royal Society of Chemistry 2002

4
5
(h -Cyclobutadiene)(h -cyclopentadienyl)cobalt(
I
)
com-
structure of 5 became a one-dimensional polymeric chain with
the alternate distances of Co( ) and Ce(III) as 5.28 and 5.42 Å.
The high oxidation potential and molecular structure of 4
suitable for a bis-bidentate ligand would be responsible for the
formation of the one-dimensional coordination polymer. The
Ce(IV) ions were presumably reduced to Ce(III) during the work-
up procedure.
Financial support by Tokuyama Science Foundation, The
Japan Securities Scholarship Foundation, and Grants-in-Aid for
Scientific Research from the Ministry of Education, Culture,
Sports, Science and Technology (Nos. 12740335, 08454193
and 09239101) is gratefully acknowledged. The authors also
thank the Instrumental Analysis Center for Chemistry, Graduate
School of Science, Tohoku University, for measurement of 600
MHz NMR, mass spectra, and elemental analysis.
plexes are generally oxidized at moderate potential.17 Redox
potentials of 3a, 3b, and 4 obtained by cyclic voltammetry are
summarized in Table 1. The cyclic voltammograms of 3a, 3b,
and 4 consisted of irreversible oxidation and reversible
reduction waves. Effect of the phosphoryl groups as electron-
withdrawing substituents appeared clearly in the redox poten-
tials, where substitution of the phosphoryl group raised and
lowered the oxidation and reduction potentials, respectively.
Thus, 4 has a higher oxidation potential by 0.61 V and a lower
reduction potential by 0.19 V, respectively, than 3a.
I
Table 1 Redox potentials of 3a, 3b, and 4a
Complex
Solvent
Eox/Vb
Ered/Vc
3a
3b
4
Dichloromethane
DMF
Dichloromethane
DMF
Dichloromethane
DMF
0.97
0.71
1.11
0.81
1.58
22.27
22.26
22.08
Notes and references
¯
‡
Crystal data for 3b·EtOH: C47H41CoO3P2, M = 774.72, triclinic, P1
(#2), a = 12.41(2), b = 16.793(4), c = 9.731(2) Å, a = 105.17(2), b =
97.21(1), g = 97.70(4)°, V = 1912(2) Å3, Z = 2, Dc = 1.345 g cm23
F(000) = 808.00, m(Mo-Ka) = 0.575 mm21, Rigaku RAXIS-IV Imaging
Plate, T = 120 K, Reflection collected/unique = 10597/6242 (2qmax
50.1°, Rint = 0.032), R/Rw = 0.063/0.091(all data), GOF = 1.75, max./min.
residual electron density 0.57/–0.57 e Å23
,
a Solvent: dichloromethane or DMF with 0.10 mol L21. n-Bu4NClO4 as a
supporting electrolyte, working electrode: glassy carbon, counter electrode:
Pt wire, reference electrode: 0.01 mol L21 AgNO3 in acetonitrile with 0.10
mol L21 n-Bu4NClO4/Ag, ferrocene/ferrocenium = 0.18 V for dichloro-
methane and 0.04 V for DMF, scan rate: 30 mV s21
potential. c Half wave potential.
=
.
Crystal data for 5: C50H90N6O42P8Co2Ce2, M = 2093.17, monoclinic,
P21/c (#14), a = 18.845(3), b = 20.469(4), c = 21.270(8) Å, b =
106.65(2)°, V = 7860(3) Å3, Z = 4, Dc = 1.769 g cm23, F(000) =
4232.00, m(Mo-Ka) = 1.812 mm21, Rigaku RAXIS-IV Imaging Plate, T =
120 K, Reflection collected/unique = 14426/14038 (2qmax = 51.1°, Rint
0.034), R/Rw = 0.066/0.055(all data), GOF = 1.14, max./min. residual
electron density 1.35/–1.14 e Å23
CCDC reference numbers 183873 and 183874. See http://www.rsc.org/
suppdata/cc/b2/b204779a/ for crystallographic data in .cif or other elec-
tronic format.
.
b Irreversible, peak
=
To remove the CpCo moiety from the cyclobutadiene
ligand,18 complex
was allowed to react with
4
.
(NH4)2[Ce(NO3)6] in acetone. Contrary to expectation, no
products originated from decomplexation were obtained, but
yellow crystals 5 with the composition of 4·[Ce(NO3)3] were
isolated in 48% yield after recrystallization from DMF–ethanol
(Scheme 2). The complex 5 was sparingly soluble in most
organic solvents. The H, 13C, and 31P NMR spectra of 5
1
1 K. Sünkel, C. Stramm and S. Soheili, J. Chem. Soc., Dalton Trans.,
1999, 4299.
2 H. C. E. McFarlane and W. McFarlane, Polyhedron, 1988, 7, 1875.
3 F. Ramirez, E. H. Chen and S. Dershowitz, J. Am. Chem. Soc., 1959, 81,
4338.
dissolved in DMSO-d6 as well as the UV-Vis spectrum in DMF
suggested dissociation of the free 4 from the complex.
4 M. D. Rausch and R. A. Genetti, J. Org. Chem., 1970, 35, 3888; B. C.
Berris, Y.-H. Lai and K. P. C. Vollhardt, J. Chem. Soc., Chem.
Commun., 1982, 953; E. R. F. Gesing, J. Org. Chem., 1982, 47, 3192;
V. Bakthavachalam, M. d’Alarcao and N. J. Leonard, J. Org. Chem.,
1984, 49, 289; K. P. C. Vollhardt, Angew. Chem., Int. Ed. Engl., 1984,
23, 539.
5 A. Maderna, H. Pritzkow and W. Siebert, Angew. Chem., Int. Ed. Engl.,
1996, 35, 1501.
6 M. S. Chattha and A. M. Aguiar, J. Org. Chem., 1971, 36, 2719; E.
Fluck and N. Z. Seng, Anorg. Allg. Chem., 1972, 393, 126.
7 C. Charrier, W. Chodkiewicz and P. Cadiot, Bull. Soc. Chim. Fr., 1966,
3, 1002.
Scheme 2
The structure of 5 was finally determined by X-ray
crystallography (Fig. 2).‡ Three nitrates and two pairs of
adjacent phosphoryl groups of 4 coordinated as bidentate
ligands to the Ce(III) ion of coordination number 10. Inter-
estingly, 4 acted as a bis-bidentate ligand and the whole
8 Tentatively assigned to 1,3-diphenyl-2,4-bis(diphenylphosphoryl)buta-
diene according to 31P NMR (dP 31.3 (d, JPP = 9.6 Hz), 28.8 (d, JPP
9.6 Hz)) and MS (m/z 606) data.
=
9 E. P. Kyba, S. P. Rines, P. W. Owens and S.-S. P. Chou, Tetrahedron
Lett., 1981, 22, 1875.
10 C. Eickmeier, H. Junga, A. J. Matzger, F. Scherhag, M. Shim and K. P.
C. Vollhardt, Angew. Chem., Int. Ed. Engl., 1997, 36, 2103.
11 R. J. Baxter, G. R. Knox, M. McLaughlin, P. L. Pauson and M. D.
Spicer, J. Organomet. Chem., 1999, 579, 83.
12 Y. Wakatsuki, O. Nomura, K. Kitaura, K. Morokuma and H. Yamazaki,
J. Am. Chem. Soc., 1983, 105, 1907.
13 H. C. E. McFarlane and W. McFarlane, Polyhedron, 1999, 18, 2117.
14 M. Rosenblum, B. North, D. Wells and W. P. Giering, J. Am. Chem.
Soc., 1972, 94, 1239.
15 M. D. Rausch, G. F. Westover, E. Mintz, G. M. Reisner, I. Bernal, A.
Clearfield and J. M. Troup, Inorg. Chem., 1979, 18, 2605.
16 M. C. Etter, R. D. Gillard, W. B. Gleason, J. K. Rasmussen, R. W.
Duerst and R. B. Johnson, J. Org. Chem., 1986, 51, 5405; C. Lariucci,
R. H. de A. Santos and J. R. Lechat, Acta. Crystallogr., Sect. C, 1986,
C42, 1825; M. C. Etter and P. W. Baures, J. Am. Chem. Soc., 1988, 110,
639.
Fig. 2 (a) ORTEP drawing of unit structure of 5 with thermal ellipsoid of
50% probability. (b) One-dimensional polymeric structure of 5 running
parallel to the b axis, ethoxy groups are ommited for clarity.
17 U. Koelle, Inorg. Chim. Acta, 1981, 47, 13.
18 R. Gleiter, R. Merger and B. Nuber, J. Am. Chem. Soc., 1992, 114,
8921.
CHEM. COMMUN., 2002, 1876–1877
1877