Synthesis and molecular structure of tetranuclear Cu4P4 complexes with R2P-O-PR2 ligands

Article abstract of DOI:10.1016/j.ica.2014.07.060

The reaction of secondary phosphine oxides R₂P(O)H 1 with Cu(OAc)₂ under nitrogen atmosphere produced complexes [(R₂P)₂O(CuOAc)₂]₂ 2. A rapid ligand exchange took place when treating complexes 2 with NH₄Cl to generate [(R₂P)₂O(CuCl)₂]₂ 3 in good yields. The structures of 3 were determined by X-ray crystallography, showing that the geometries of these tetranuclear copper complexes vary with the R group of the phosphorus units. Compared to complexes 2 which are air sensitive, complexes 3 are stable under air.

Full text of DOI:10.1016/j.ica.2014.07.060

Inorganica Chimica Acta 422 (2014) 36–39
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Synthesis and molecular structure of tetranuclear Cu P complexes with
4
4
R P–O–PR ligands
2
2
a
a,
⇑
a
a
b,
⇑
Yalei Zhao , Yongbo Zhou , Tieqiao Chen , Shuang-Feng Yin , Li-Biao Han
a
State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, China
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8565, Japan
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 May 2014
Received in revised form 30 July 2014
Accepted 31 July 2014
Available online 7 August 2014
The reaction of secondary phosphine oxides R P(O)H 1 with Cu(OAc)2 under nitrogen atmosphere pro-
2
duced complexes [(R
2
P)
2
O(CuOAc)
2
]
2
2. A rapid ligand exchange took place when treating complexes 2
3 in good yields. The structures of 3 were determined by X-
with NH Cl to generate [(R
4
2
P) O(CuCl) ]
2
2 2
ray crystallography, showing that the geometries of these tetranuclear copper complexes vary with the
R group of the phosphorus units. Compared to complexes 2 which are air sensitive, complexes 3 are stable
under air.
Dedicated to Professor Don Tilley on the
occasion of his 60th birthday.
Ó 2014 Elsevier B.V. All rights reserved.
Keywords:
Secondary phosphine oxides
Ligand exchange
P–O–P ligand
Tetranuclear copper(I) complex
0
1
. Introduction
complexes with R
well known.
2
2
P–(CH )
n
–PR
2
[4–7] and R
2
P–NR –PR
2
[8] are
2
Secondary phosphine oxides R P(O)H 1 have increasingly
attracted attentions as robust preligands for transition metal catal-
ysis [1]. These compounds show unique tautomerism between the
R
2
PðOÞH
4
NH Cl
CuðOAÞ2 ꢀ! ½ðR
2
PÞ OðCuOAcÞ ꢁ ꢀ! ½ðR
2
PÞ OðCuClÞ ꢁ
ð1Þ
2
2
2
2
2
2
2 2
pentavalent R P(O)H and the trivalent R P(OH) tautomers which,
likes other trivalent organophosphorus compounds, can ligate to
transition metals. During a study on the possible coordination of
2. Experimental
R
2
P(O)H with copper salts, we found that a reaction of Cu(OAc)
with R P(O)H 1b (R = Ph(CH ) could produce a unique tetranu-
clear [(R P) O(CuOAc) complex 2b [2] in which R P–O–PR for-
2
1H, 13C and 31P NMR spectra were recorded on a JEOL LA-400
1
13
31
2
2
)
4
instrument (400 MHz for H, 100 MHz for C, and 162 MHz for
NMR spectroscopy). CDCl was used as the solvent. Chemical shift
values for H and C were referred to internal Me Si (0 ppm), and
O, 0 ppm). Melt-
ing point was recorded on an OptiMelt instrument (90-264 VAC).
Saturated NH Cl aqueous solution was not degassed.
P
2
2
2
]
2
2
2
3
1
13
mally derived in situ from the dehydration of two secondary
phosphine oxides. However, this complex is difficult to handle
because it is extremely air sensitive and decomposes readily in air.
Herein, we report the synthesis and structural characterization
4
3
1
3 4 2
thatfor P wasreferredtoH PO (85%solutioninD
4
of similar tetranuclear copper complexes [(R
simply mixing R P(O)H with Cu(OAc) and treating the resulted
mixture with an aqueous NH Cl solution (Eq. (1)). Contrary to [(R2-
P) O(CuOAc) , these [(R P) O(CuCl) complexes can be handled
under air. It was noted that such R P–O–PR ligated-complexes are
rarely reported in coordination chemistry [3], although similar
2 2 2 2
P) O(CuCl) ] 3, by
2
2
2
2 2 2 2
.1. Synthesis of [(n-Bu P) O(CuCl) ] 3a
4
2
2
]
2
2
2
2
]
2
To a flask were added dibutyl secondary phosphine oxide (n-
P(O)H, 3 mmol), anhydrous Cu(OAc) (2 mmol) and THF
2
2
Bu
2
2
(
5 mL) under nitrogen atmosphere. The mixture was stirred at
room temperature for 2 h, and then 15 mL chilled saturated NH Cl
aqueous solution was added. The crude product was extracted
with CHCl and dried over MgSO . The volatiles were removed
under vacuum and the product 3a was isolated using a preparative
GPC using CHCl as eluent. Yield: 393 mg, 52%.
4
⇑
Corresponding authors.
E-mail addresses: zhouyb@hnu.edu.cn (Y. Zhou), libiao-han@aist.go.jp
3
4
(
L.-B. Han).
3
http://dx.doi.org/10.1016/j.ica.2014.07.060
020-1693/Ó 2014 Elsevier B.V. All rights reserved.
0

Y. Zhao et al. / Inorganica Chimica Acta 422 (2014) 36–39
37
The complex 3a was dissolved in a mixed solvent of THF (2 mL)
and Et O (2 mL), and then hexane (10 mL) was added. The solution
nitrogen gave two new signals at 55.7 ppm and 122.6 ppm [2],
which were assigned to n-Bu P(O)OH and [(n-Bu P) O(CuOAc)
2a, respectively. Complex 2a was air sensitive that collapsed
rapidly to n-Bu P(O)OH when exposed to air. Surprisingly,
however, by pouring the above reaction mixture into a chilled
saturated aqueous NH Cl solution, a complex [(n-Bu P) O(CuCl)
3a was obtained via ligand exchange of the acetate group in 2a
with the chloro anion of NH Cl. Contrary to complex 2a, complex
2
2
2
2
2 2
]
was slowly cooled down to ꢀ30 °C to give colorless crystals suit-
able for X-ray analysis.
2
1
H NMR (CDCl
3
, 400 MHz): d 1.87–1.76 (m, 16H, CH
2
), 1.62–
), 0.93 (t, 24 H, J = 7.0,
),
), P NMR
1
CH
2
.52 (m, 16H, CH
2
), 1.48–1.39 (m, 16H, CH
2
4
2
2
2 2
]
1
3
3
). C NMR (CDCl
3
, 100 MHz): d 31.5 (d, JCP = 11.1 Hz, CH
2
3
1
4.9 (s, br, CH
2
), 24.1 (d, JCP = 6.5 Hz, CH
2
), 13.6(s, CH
2
4
(
2
1
CDCl
3
, 162 MHz): d 123.1. M.P.: 76.1–77.3 °C; decomposed at
10.0 °C. Anal. Calc. for C32 Cu : C, 38.10; H, 7.19; Cl,
3a could be handled in air without decomposition.
H72Cl
4
4 2 4
O P
4.06. Found: C, 38.35; H, 7.16; Cl, 13.84% (see Scheme 1).
If the reaction mixture was exposed to air (<10 min) before the
addition of NH
not be obtained at all but n-Bu
4
Cl aqueous solution, [(n-Bu
P(O)OH was obtained in 92% yield
as a white solid: H NMR (CDCl3, 400 MHz): d 9.00 (s, 1H, OH),
.71–1.62 (m, 4H, CH ), 1.61–1.53 (m, 4H, CH ), 1.45–1.36 (m, 4H,
CH ), 0.92 (t, 6H, J = 6.86 Hz, CH ). C NMR (CDCl3, 100 MHz): d
8.7 (d, JCP = 92.0 Hz, CH ), 23.9 (d, JCP = 15.5 Hz, CH ), 23.6 (d,
CP = 4.0 Hz, CH
), 13.6. 31P NMR (CDCl3, 201.95 MHz): d 59.6.
2 2 2 2
P) O(CuCl) ] 3a could
2
1
1
2
2
13
2
3
2
J
2
2
2
2 4 2 2 2 2
2.2. Synthesis of [((Ph(CH ) ) P) O(CuCl) ] 3b
[
((Ph(CH
CHCl was added to 20 mL chilled saturated NH
tion and stirred vigorously for 10 min. The product was then
extracted with CHCl and dried over MgSO . The product was iso-
lated using a preparative GPC using CHCl as eluent. Yield: 278 mg,
6%. The product was dissolved in THF (2 mL) and Et O (2 mL).
2
)
4
)
2
P)
2
O(CuOAc)
2
]
2
2b [2] (343 mg, 0.2 mmol) in 5 mL
3
4
Cl aqueous solu-
3
4
3
8
2
Hexane (8 mL) was then added. The solution was slowly cooled
to ꢀ30 °C to give colorless crystals suitable for X-ray analysis.
1
White solid: H NMR (CDCl3, 400 MHz): d 7.20–7.16 (m, 16H),
7
4
1
2
.10–7.05 (m, 24H), 2.54 (t, J = 7.4 Hz, 16H, CH
2
), 1.71–1.52 (m,
). C NMR (CDCl3, 100 MHz): d 142.0, 128.4, 128.3,
25.7, 35.4, 32.6 (t, JCP = 6.6 Hz, CH ), 31.7 (d, JCP = 10.7 Hz, CH ),
2.6. P NMR (CDCl3, 161.84 MHz): d 123.0. Anal. Calc. for C80
Cu : C, 59.40; H, 6.48. Found: C, 60.11; H, 6.41%. M.P.: 84.6–
1
3
8H, CH
2
2
2
3
1
H
104-
Cl
4
4 2 4
O P
8
5.5 °C; decomposed at 270 °C (see Scheme 2).
3
. Results and discussion
3.1. Synthesis of [(R
2 2 2 2
P) O(CuCl) ] 3 complexes
As indicated by 31P NMR spectroscopy, the reaction of
Fig. 1. Molecular structure of 3a. Hydrogen atoms are omitted for clarity. Bottom:
Core structure of 3a (only Cu, P, O and Cl are shown).
n-Bu P(O)H with Cu(OAc) in THF-d at room temperature under
2
2
8
n-Bu
n-Bu
P
O
n-Bu
Cl Cu
n-Bu
2
P(O)H
Cl
(
(
1)THF, rt, N
2
(1) THF, rt, N2
(2) NH Cl aq, CHCl
3
n-Bu
n-Bu
n-Bu
P
P
n-Bu
2
PO
2
H
Cu
Cu
O
2) air, H
2
O
Cu( OAc)
4
2
Cu
P
n-Bu
n-Bu
Cl Cl
3
a
Scheme 1. Synthesis of [(n-Bu
2
P)
2
O(CuCl)
2
]
2
3a.
R
Cl
Cl
R
P
O
O
R
R
O
P
O
O
O
Cu
Cu
R
P
P
Cu
Cu( OAc)2
THF, rt, N2
O
Cu
R
R
CHCl3
R
P-H
R
Cu
Cu
P
R
R
Cu
O
R
R
P
Cu
O
O
NH Cl aq.
4
Cl
Cl
R = Ph(CH2)4 3b
P
R
P
R
O
R
O
O
R
R
2b
2 4 2 2 2 2
Scheme 2. Synthesis of [((Ph(CH ) ) P) O(CuCl) ] 3b.

3
8
Y. Zhao et al. / Inorganica Chimica Acta 422 (2014) 36–39
Table 1
Table 2
Selected bond lengths and bond angles for complex 3a.
Selected bond lengths and bond angles for complex 3b.
Bond lengths (Å)
Bond angels (°)
Bond lengths (Å)
Bond angels (°)
Cu1–P1
Cu1–Cl1
Cu1–Cl
O1–P1
Cu1–Cu1
2.1796(7)
2.2742(7)
2.2907(7)
1.6428(15)
2.9570(6)
3.2883(4)
P1–Cu1–Cl1
P1–Cu1–Cl1
Cl1–Cu1–Cl1
P1–Cu1–Cu1
128.29(3)
124.47(3)
107.103(17)
83.46(2)
Cu1–P2
Cu1–Cl1
Cu1–Cl2
Cu1–Cu2
2.1727(6)
2.2863(6)
2.3047(6)
2.8409(5)
3.0697(5)
2.1716(6)
2.2684(6)
2.3244(6)
1.6389(13)
1.6518(13)
P1–O1–P2
P1–Cu2–Cu1
P2–Cu1–Cu2
Cu2–Cl2–Cu1
Cu1–Cl1–Cu2
Cu1–Cu2–Cl2
Cu2–Cu1–Cl2
Cu1–Cu2–Cu1
Cu2–Cu1–Cu2
123.58(8)
91.59(2)
87.75(2)
84.321(19)
76.067(16)
130.418(17)
144.260(16)
82.51(1)
0
0
0
0
0
Cl1–Cu1–Cu1
85.62(2)
Cu1–Cu2
0
0
0
Cu1–Cu1
Cl1 –Cu1–Cu1
106.58(2)
120.45(17)
92.16(3)
63.28(1)
53.440(9)
Cu2–P1
Cu2–Cl2
Cu2–Cl1
O1–P1
P1–O1–P1
Cu1–Cl1–Cu1
0
0
0
0
Cu1–Cu1–Cu1
97.490(11)
0
Cu1–Cu1 –Cu1
O1–P2
Cu(I) atoms with classic Cu–Cl–Cu angles (92.16(3)°) and Cu–Cl
bond lengths (2.2742(8)–2.2907(7) Å) [11].
2 4 2 2 2 2
3.3. Crystal structure of [((Ph(CH ) ) P) O(CuCl) ] (3b)
The complex consists of a six-membered ring of four copper(I)
atoms and two chloride atoms, with the four copper atoms in the
plane (Fig. 2, Table 2). Pairs of copper atoms on each edge around
the plane are both bridged further by a chloride and a [[Ph(CH
2 4 2-
) ]
P] O ligand, which form two five-membered rings (P–O–P–Cu–Cu)
2
and two three-membered rings (Cu–Cl–Cu), respectively. The Cu–
0
Cu distances of Cu1–Cu2 and Cu1–Cu2 are of 2.8409(5) and
3
.0697(5) Å, respectively, the former is close to the sum of their
van der Waals radii (2.80 Å). The Cu–Cu distances of 3b are slight
shorter than those of 3a, whereas the Cu–Cu distance
(
2.8409(5) Å) of 3b is longer than that of the air sensitive complex
b (2.6809(6) Å). The Cu–Cl distances vary from 2.27 to 2.32 Å. It is
interesting to compare with the structure of complex 3a. Thus, a
slight difference in the alkyl group R of R P(O)H can give a different
geometry of the resulted complex 3, i.e. tetrahedron geometry for
2
2
3
a, but parallelogram for 3b.
4
. Conclusions
We have prepared unique tetranuclear copper complexes [(R2-
P)
2
O(CuCl)
P(O)H with copper acetate followed by ligand exchange with
NH Cl. The core structures of [(R P) O(CuCl) vary with the R
2 2
] through the reaction of secondary phosphine oxide
R
2
4
2
2
2 2
]
group.
Fig. 2. Molecular structure of 3b. Hydrogen atoms are omitted for clarity. Bottom:
Core structure of 3b (only Cu, P, O and Cl are shown).
Acknowledgments
Partial supports from NSFC (21172062, 21273066), the Doctoral
Fund of Chinese Ministry of Education (No. 20110161120008), and
the Fundamental Research Funds for the Central Universities
Similarly, complex [((Ph(CH
by treating complex [((Ph(CH
ous NH
with the chloro atom.
2
)
4
)
2
P)
2
O(CuCl)
2
]
]
2
3b was obtained
2b with an aque-
) ) P) O(CuOAc)
2 4 2 2
Cl solution through ligand-exchange of the acetate group
2
2
4
(
Hunan University) are acknowledged.
Appendix A. Supplementary material
3
.2. Crystal structure of [(Bu
2 2 2 2
P) O(CuCl) ] (3a)
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ica.2014.07.060.
X-ray analysis shows that complex 3a consists of a Cu
4 4 4
P Cl
unit (Fig. 1, Table 1), where each P–O–P group coordinates to
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