Synthesis and structure of [η4- tetrakis(arylethoxyphosphoryl)cyclobutadiene]-(η5- cyclopentadienyl)cobalt(I) complexes

Article abstract of DOI:10.1246/cl.2004.1004

[η⁴-Tetrakis(arylethoxyphosphoryl)cyclobutadiene] (η⁵-cyclopentadienyl)cobalt(I) complexes were synthesized by reaction of bis(arylethoxyphosphoryl)acetylenes with CpCo(CO)₂ and several diastereomers were isolated. Whole molecular structure of the tetraphosphorylcyclobutadiene complex was significantly affected by relative configuration of the phosphoryl groups.

Full text of DOI:10.1246/cl.2004.1004

1004
Chemistry Letters Vol.33, No.8 (2004)
Synthesis and Structure of [ꢀ4-Tetrakis(arylethoxyphosphoryl)cyclobutadiene]-
(ꢀ5-cyclopentadienyl)cobalt(I) Complexes
Shigeru Sasaki,ꢀ Kiyotoshi Kato, Yoshihiro Tanabe, and Masaaki Yoshifujiꢀ
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578
(Received April 26, 2004; CL-040475)
[ꢀ4-Tetrakis(arylethoxyphosphoryl)cyclobutadiene](ꢀ5-cy-
clopentadienyl)cobalt(I) complexes were synthesized by reac-
tion of bis(arylethoxyphosphoryl)acetylenes with CpCo(CO)2
and several diastereomers were isolated. Whole molecular struc-
ture of the tetraphosphorylcyclobutadiene complex was signifi-
cantly affected by relative configuration of the phosphoryl
groups.
31P NMR (ꢂ 8.6 (s)) and 13C NMR of acetylenic carbons (ꢂ 93.6
1
2
(dd, JPC ¼ 182:8 Hz, JPC ¼ 26:3 Hz)) appeared as single sig-
nals in spite of introduction of the (ꢁ)-menthoxy groups. Rela-
tive configuration of the phosphoryl groups of 1a was estimated
by comparison with the physical data of 1b.
Reaction of an isomeric mixture of 1a ((R*,S*)-1a: (R*,R*)-
1a = 1:1) with CpCo(CO)2 in refluxing xylenes resulted in for-
mation of an inseparable isomeric mixture of the cyclobutadiene
complex 2a. The ratio of the isomers was estimated to be
(R*,R*,R*,R*)-2a:(R*,S*,R*,S*)-2a:(R*,R*,S*,S*)-2a:(R*,R*,
R*,S*)-2a = 1:1:2:4 from 31P NMR and 1H NMR signals of cy-
clopentadienyl protons. On the other hand, the reaction of the
single diastereomer, (R*,R*)-1 and (R*,S*)-1, afforded a mixture
composed of two diastereomers, (R*,R*,S*,S*)-2 and (R*,R*,
R*,R*)-2 (1:1), and (R*,R*,S*,S*)-2 and (R*,S*,R*,S*)-2 (1:1),
respectively, and (R*,R*,R*,R*)-2a, (R*,S*,R*,S*)-2a, and
(R*,S*,R*,S*)-2b were isolated in a diastereomerically pure
form in 12, 21, and 9%, respectively.
Cyclic ꢁ-conjugated systems carrying adjacent phosphorus
functional groups have received considerable interest. There
have been several reports of five1 and six2 membered ꢁ-conju-
gated systems carrying phosphorus functional groups in array.
Recently, we reported synthesis, structure, and coordination
properties of [ꢀ4-tetrakis(diethoxyphosphoryl)cyclobutadiene]-
(ꢀ5-cyclopentadienyl)cobalt(I),3 which acted as a bisbidentate li-
gand for one dimensional coordination polymer. Tetraphosphor-
ylcyclobutadiene ligands carrying chiral phosphorus centers are
expected to have unique structure and properties due to intramo-
lecular interaction among adjacent phosphorus substituents as
well as asymmetric coordination or hydrogen bonding of the
phosphoryl groups. Herein, we report synthesis and structure
of the [ꢀ4-tetrakis(arylethoxyphosphoryl)cyclobutadiene](ꢀ5-
cyclopentadienyl)cobalt(I). Several diastereomers of different
relative configuration of the four phosphoryl groups were
isolated.
i) Mg
ii) ClP(OEt)2
Cl
Cl
Ar(EtO)(O)P
(R*,R*)-1: (R*,S*)-1 = 1 : 1
1a: Ar = Ph
P(O)(OEt)Ar
ArP(OEt)2
ArBr
1b: Ar = 4-(–)-menthoxymethylphenyl
Bis(arylethoxyphosphoryl)acetylene 1a4 was synthesized by
the reaction4 of aryldiethoxyphosphine with dichloroacetylene5
and was obtained as a 1:1 diastereomeric mixture. Acetylene
1b was similarly synthesized from 1-bromo-4-[(ꢁ)-menthoxy-
methyl]benzene.6 Purification of the mixture by silica gel col-
umn chromatography followed by GPC (1a) or recrystallization
(1b) gave diastereomeric pure forms.7
Figure 2. Molecular structures of (R*,R*,R*,R*)-2a. Hydrogen
atoms and solvents were omitted for clarity. (a) Side view,
(b) Top view.
Relative configuration of phosphoryl groups of (R*,S*)-1b
was determined by X-ray crystallography from the comparison
with an internal standard, the (ꢁ)-menthoxy groups (Figure 1).8
Figure 3. Molecular structures of (R*,S*,R*,S*)-2a. Hydrogen
atoms and solvents were omitted for clarity. (a) Side view,
(b) top view.
Figure 1. Molecular structure of (R*,S*)-1b. Hydrogen atoms
were omitted for clarity.
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.8 (2004)
1005
References and Notes
1
Tetrakis(arylethoxyphosphoryl)cyclobutadiene complexes 2
1
K. Sunkel, C. Stramm, and S. Soheili, J. Chem. Soc., Dalton
¨
Trans., 1999, 4299.
were characterized by H, 13C, and 31P NMR spectra7 and the
structures of complexes (R*,R*,R*,R*)-2a and (R*,S*,R*,S*)-
2a were further investigated by X-ray crystallography
(Figures 2 and 3),8 where difference of the relative configuration
of the phosphoryl groups resulted in clear contrast of the whole
molecular structure. The cyclobutadiene complex (R*,R*,R*,
R*)-2a crystallized as racemic crystals with one water molecule.
According to (R*,R*,R*,R*) configuration of the phosphoryl
groups, four phenyl groups situated opposite to the CoCp moi-
ety, and the phosphoryl oxygens (P(O)) located below the cyclo-
butadiene plane pointing in the same direction along the cyclo-
butadiene square. Molecular structure of (R*,S*,R*,S*)-2a
obtained from X-ray crystallography of a single crystal, which
included two water molecules being hydrogen bonded to the
phosphoryl oxygens, showed marked difference from the
(R*,R*,R*,R*)-2a. Four phenyl groups aligned alternately above
and below the cyclobutadiene plane and four phosphoryl oxy-
gens also alternately located below and above the cyclobuta-
diene plane, pointing in the same direction. Two phosphorus
atoms of (R*,S*,R*,S*)-2a possessing phenyl groups in the
CoCp side considerably deviated from the cyclobutadiene plane
2
H. C. E. McFarlane and W. McFarlane, Polyhedron, 7, 1875
(1988); T. Reetz, U.S. Patent 2935518 (1960); M. A. Fox,
D. A. Chandler, Adv. Mater., 3, 381 (1991).
S. Sasaki, Y. Tanabe, and M. Yoshifuji, Chem. Commun., 2002,
1876.
E. P. Kyba, S. P. Rines, P. W. Owens, and S. P. Chou, Tetrahedron
Lett., 22, 1875 (1981).
J. N. Denis, A. Moyano, and A. E. Greene, J. Org. Chem., 52, 3461
(1987).
3
4
5
6
7
H. Brunner, J. Furst, and J. Ziegler, J. Organomet. Chem., 454, 87
(1993).
¨
1
Selected H (400 MHz, CDCl3) and 31P NMR (162 MHz, CDCl3)
data: (R*,R*)-1a: 1H NMR ꢂ 7.82 (m, 4H), 7.60 (m, 2H), 7.48 (m,
4H), 4.30 (m, 4H), 1.42 (t, JHH ¼ 7:06 Hz, 6H); 31P NMR ꢂ 8.7 (s).
(R*,S*)-1a: 1H NMR ꢂ 7.86 (m, 4H), 7.62 (m, 2H), 7.51 (m, 4H),
4.23 (m, 4H), 1.36 (t, JHH ¼ 7:06 Hz, 6H); 31P NMR ꢂ 8.6 (s).
(R*,R*)-1b: 1H NMR ꢂ 7.77 (m, 4H), 7.44 (m, 4H), 4.29–4.21
(m, 4H), 1.39 (t, JHH ¼ 7:06 Hz, 6H); 31P NMR ꢂ 8.7 (s).
(R*,S*)-1b: 1H NMR ꢂ 7.82 (m, 4H), 7.48 (m, 4H), 4.23–4.18
(m, 4H), 1.35 (t, JHH ¼ 7:08 Hz, 6H); 31P NMR ꢂ 8.6 (s). (R*,R*,
R*,R*)-2a: 1H NMR ꢂ 7.40 (brt, 4H), 7.07 (brt, 8H), 6.73 (brs,
8H), 5.81 (s, 5H), 4.23 (m, 4H), 4.02 (m, 4H), 1.32 (t, JHH
¼
7:00 Hz, 12H); 31P NMR ꢂ 26.9 (s). (R*,R*,S*,S*)-2a: 1H NMR
ꢂ 7.77 (m, 4H), 7.52 (m, 3H), 7.37 (brm, 9H), 7.19 (m, 4H),
5.11 (s, 5H), 4.16–3.80 (m, 8H), 1.34 (t, JHH ¼ 7:04 Hz, 6H),
1.16 (t, JHH ¼ 7:03 Hz, 6H); 31P NMR ꢂ 29.5 (d, JPP ¼ 17:8 Hz),
29.1(d, JPP ¼ 17:8 Hz). (R*,S*,R*,S*)-2a: 1H NMR ꢂ 8.22 (brq,
8H), 7.52 (brm, 12H), 4.49 (s, 5H), 3.84 (brm, 8H), 1.20 (t,
JHH ¼ 7:02 Hz, 12H); 31P NMR ꢂ 29.7 (s). (R*,R*,R*,S*)-2a:
1H NMR ꢂ 5.32 (s, 5H, Cp); 31P NMR ꢂ 30.3–27.1. (R*,S*,R*,
ꢀ
(0.47(2) (P2) and 0.48(2) (P4) A above the plane), on the other
ꢀ
hand, deviation more than 0.2 A was not observed for the re-
maining phpsphorus atoms of (R*,S*,R*,S*)-2a as well as the
four phosphorus atoms of (R*,R*,R*,R*)-2a.
Structural difference of the isomers was clearly reflected on
1H, 13C, and 31P NMR spectra. 31P NMR of (R*,R*,R*,R*)-2a (ꢂ
26.9) and (R*,S*,R*,S*)-2a (ꢂ 29.7) appeared as a singlet peak,
whereas that of (R*,R*,S*,S*)-2a was observed as an AB pattern
with a significant magnitude of coupling (ꢂ 29.5, 29.1, J ¼ 17:8
Hz) which suggested strongly interacting inequivalent phospho-
rus atoms, and (R*,R*,R*,S*)-2a showed several signals in ꢂ 27–
S*)-2b: 1H NMR ꢂ 8.29 (m, 8H), 7.49 (m, 8H), 4.71 (d, JHH
12:18 Hz, 2H), 4.70 (d, JHH ¼ 11:95 Hz, 2H), 4.47 (d, JHH
¼
¼
12:18 Hz, 2H), 4.45 (d, JHH ¼ 11:95 Hz, 2H), 4.37 (s, 5H), 3.85–
3.74 (brm, 8H), 3.22–3.13 (m, 4H), 2.33–2.25 (m, 4H), 2.21–
2.15 (brm, 4H), 1.69–1.64 (brm, 4H), 1.65–1.59 (brm, 4H), 1.40–
1.33 (brm, 4H), 1.29–1.25 (m, 4H), 1.19–1.15 (m, 12H), 0.97–0.92
(brm, 4H), 0.92 (d, JHH ¼ 6:55 Hz, 12H), 0.91–0.88 (brm, 4H),
0.89 (d, JHH ¼ 7:21 Hz, 12H), 0.83–0.80 (brm, 4H), 0.71 (d,
JHH ¼ 6:92 Hz, 12H); 31P NMR ꢂ 29.7 (s), 29.5 (s). (R*,R*,S*,
1
31. H NMR spectra of (R*,R*,R*,R*)-2a showed the most de-
shielded Cp (ꢂ 5.81) and the most shielded phenyl protons. On
the other hand, opposite tendency was observed for (R*,S*,
R*,S*)-2a (ꢂ 4.41). (R*,R*,S*,S*)-2a showed two inequivalent
aryl and ethoxy groups consistent with 31P NMR, and the Cp
and Ph groups were observed in the intermediate region between
(R*,R*,R*,S*)-2a and (R*,S*,R*,S*)-2a. 13C NMR of cyclobuta-
S*)-2b: 31P NMR ꢂ 29.7 (d, JPP ¼ 18:9 Hz), 29.1(d, JPP
18:9 Hz). (R*,R*,R*,R*)-2b: 31P NMR ꢂ 27.9 (s), 26.9 (s).
¼
8
(R*,S*)-1b: colorless block from ethanol, 0:50 ꢂ 0:15 ꢂ 0:10
mm3, C40H60O6P2, M ¼ 698:86, monoclinic, P21 (#4), a ¼
5:5511ð4Þ, b ¼ 34:136ð4Þ, c ¼ 10:501ð1Þ A, ꢃ ¼ 95:192ð7Þꢃ,
ꢀ
V ¼ 1982:2ð3Þ A , Z ¼ 2, Dcalcd. ¼ 1:171 gcmꢁ1
,
Fð000Þ ¼
ꢀ 3
1
diene carbons of (R*,R*,R*,R*)-2a (ꢂ 71.9, ddt, JCP ¼ 146:0,
756:00, ꢄðMo KꢅÞ ¼ 0:152 mmꢁ1, T ¼ 115 K, Reflection collect-
ed/unique = 5029/3028 (2ꢆmax ¼ 52:0ꢃ, Rint ¼ 0:049), R1=R=
Rw ¼ 0:060=0:067=0:089, GOF ¼ 1:07, max/min residual elec-
3
2JCP ¼ 7:6, JCP ¼ 14:9 Hz) and (R*,S*,R*,S*)-2a (ꢂ 72.1, ddt,
2
3
1JCP ¼ 150:0, JCP ¼ 6:8, JCP ¼ 15:1 Hz) were observed as
ddt patterns characteristic of tetraphosphorylcyclobutadiene
complexes.3 Contrary to (R*,S*)-1b, influence of (ꢁ)-menthoxy
ꢀ ꢁ3
.
tron density 0:30=ꢁ0:66 eA . (R*,R*,R*,R*)-2a H2O: yellow
block from ethyl acetate, 0:25 ꢂ 0:15 ꢂ 0:15 mm3, C41H47O9-
P4Co, M ¼ 866:65, monoclinic, P21=n (#14), ꢃ a ¼ 12:037ð2Þ,
1
groups was observed in the H, 13C, and 31P NMR spectra of
ꢀ
b ¼ 16:087ð3Þ, c ¼ 21:797ð5Þ A, ꢃ ¼ 104:41ð2Þ , V ¼ 4087ð1Þ
A , Z ¼ 4, Dcalcd. ¼ 1:408 gcmꢁ1
,
Fð000Þ ¼ 1808:00,
ꢀ 3
(R*,S*,R*,S*)-2b. The phosphorus signals (ꢂ 29.8, 29.5) as well
1
ꢄðMo KꢅÞ ¼ 0:630 mmꢁ1
,
T ¼ 120 K, Reflection collected/
as cyclobutadiene carbons (ꢂ 72.2 (brd, JCP ¼ 145:0 Hz) 71.6
unique
=
29162/7491 (2ꢆmax ¼ 51:1ꢃ, Rint ¼ 0:039), R1=R
1
(brd, JCP ¼ 152:0 Hz)), which were observed as single reso-
=Rw ¼ 0:049=0:060=0:069, GOF ¼ 1:47, max/min residual elec-
nances for (R*,S*,R*,S*)-2a, were no longer equivalent, proba-
bly due to more congested alignment of the phosphoryl groups
than (R*,S*)-1b.
ꢀ ꢁ3
.
tron density 0:55=ꢁ0:88 eA . (R*,S*,R*,S*)-2a 2H2O: yellow
plate from ethyl acetate, 0:40 ꢂ 0:25 ꢂ 0:05 mm3, C41H49
-
O
10P4Co, M ¼ 884:66, orthorhombic, Pna21=n (#33), a ¼
ꢀ
ꢀ 3
14:691ð2Þ, b ¼ 19:303ð4Þ, c ¼ 15:365ð2Þ A, V ¼ 4357ð1Þ A ,
Z ¼ 4, Dcalcd. ¼ 1:348 gcmꢁ1, Fð000Þ ¼ 1848:00, ꢄðMo KꢅÞ ¼
0:595 mmꢁ1, T ¼ 120 K, Reflection collected/unique = 4408/
4151 (2ꢆmax ¼ 51:1ꢃ, Rint ¼ 0:051), R1=R=Rw ¼ 0:030=0:035=
0:039, GOF ¼ 0:93, max/min residual electron density 0:39=
The authors thank Grant-in-Aid for Scientific Research from
the Ministry of Education, Culture, Sports, Science and Technol-
ogy (Nos. 15550025 and 1330409) for financial support and the
Instrumental Analysis Center for Chemistry, Graduate School of
Science, Tohoku University, for measurement of 600 MHz NMR
and mass spectra.
ꢀ ꢁ3
ꢁ0:38 eA . All data were collected on a Rigaku RAXIS-IV
Imaging Plate. CCDC-236745 ((R*,S*)-1b), -236746 ((R*,R*,
.
R*,R*)-2a H2O), -236747 ((R*,S*,R*,S*)-2a 2H2O).
.
Published on the web (Advance View) July 12, 2004; DOI 10.1246/cl.2004.1004