Synthesis, structures and catalytic activity of cyclometalated rhenium complexes

Article abstract of DOI:10.1039/c6ra28263f

Thermal reactions of aryl-substituted phosphines or phosphinites with Re₂(CO)₁₀ in chlorobenzene resulted in the corresponding five-membered cyclometalated rhenium complexes (1-5) via an intramolecular activation of the C(sp²)-H or C(sp³)-H bond. The only exception occurred in the case of (1-naphthyl)diisopropylphosphinite, which gave a diphosphinite-substituted dinuclear rhenium complex 6. Competition reaction indicated that the aromatic C(sp²)-H bond is more likely to be activated than the C(sp³)-H bond under the same conditions. Photolysis of 1 or 2 in CHX₃ led to the cleavage of the Re-C σ bond to yield corresponding phosphine-substituted tetracarbonyl rhenium halides 7-10. Complex 1 reacted with CF₃COOH in CH₂Cl₂ to give addition product 11. Photolysis of cyclorhenated complexes 1-3 with a series of aryl halides in benzene resulted in the stoichiometric formation of biphenyl, together with corresponding phosphine-substituted tetracarbonyl rhenium halides (7, 9, 10, 12, and 13). When base was introduced into the above reaction, a catalytic system was established. Under optimized conditions, complex 1 provided moderate yield of biphenyl in a couple of hours at a [Re] : substrate ratio of 1 : 200. Molecular structures of complexes 1, 6, 9, and 11 were determined by X-ray diffraction.

Full text of DOI:10.1039/c6ra28263f

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Synthesis, structures and catalytic activity of
cyclometalated rhenium complexes†
Cite this: RSC Adv., 2017, 7, 17063
*
Ruichen Sun, Tian Wang, Shaowei Zhang, Xiaodan Chu and Bolin Zhu
Thermal reactions of aryl-substituted phosphines or phosphinites with Re2(CO)10 in chlorobenzene resulted
in the corresponding five-membered cyclometalated rhenium complexes (1–5) via an intramolecular
activation of the C(sp2)–H or C(sp3)–H bond. The only exception occurred in the case of (1-naphthyl)
diisopropylphosphinite, which gave
a diphosphinite-substituted dinuclear rhenium complex 6.
Competition reaction indicated that the aromatic C(sp2)–H bond is more likely to be activated than the
C(sp3)–H bond under the same conditions. Photolysis of 1 or 2 in CHX3 led to the cleavage of the Re–C
s bond to yield corresponding phosphine-substituted tetracarbonyl rhenium halides 7–10. Complex 1
reacted with CF3COOH in CH2Cl2 to give addition product 11. Photolysis of cyclorhenated complexes 1–
3 with a series of aryl halides in benzene resulted in the stoichiometric formation of biphenyl, together
with corresponding phosphine-substituted tetracarbonyl rhenium halides (7, 9, 10, 12, and 13). When
base was introduced into the above reaction, a catalytic system was established. Under optimized
conditions, complex 1 provided moderate yield of biphenyl in a couple of hours at a [Re] : substrate ratio
of 1 : 200. Molecular structures of complexes 1, 6, 9, and 11 were determined by X-ray diffraction.
Received 15th December 2016
Accepted 14th March 2017
DOI: 10.1039/c6ra28263f
rsc.li/rsc-advances
or a mixture thereof). In this paper, we report the synthesis of
a series of cyclometalated rhenium complexes starting from the
Introduction
precursor Re2(CO)10, as well as their catalytic activity in direct
arylation of arenes with aryl halides.
Cyclometalation has always been one of the most widely
investigated reactions in the eld of organometallic chemistry
since it was rst discovered in the early 1960s.1 The reason that
cyclometalation has received such considerable attention is
mainly due to the following three aspects: (i) it represents
probably the mildest route for the intramolecular activation of
C–H bonds, and forms a cyclometalated complex containing
a new M–C s bond. (ii) Cyclometalated complexes have wide
applications in many elds, such as photosensitizers for solar
cells2 and OLED materials.3 (iii) As catalysts for a wide range of
reactions, including metathesis reactions,4 cross-coupling
reactions,5 and transfer hydrogenation reactions.6 Of all tran-
sition metals, cyclometalated rhenium complexes have recently
attracted more and more attention due to their luminescent
properties, which may have potential as liquid crystals,7 and in
particular, their indispensable role in many catalytic cycles,
including the rhenium-catalyzed annulation reaction of
aromatic imines with alkynes,8 alkenes,9 or aldehyde,10 and
alkylation of 2-phenyl, or alkenyl-substituted pyridine.11
Generally, the most widely used precursors for cyclorhenation
are Re(X)(CO)5 (X ¼ H, Me, Cl, or Br) and Re(Cp)L3 (L ¼ CO, PR3,
Results and discussion
Reaction of Re2(CO)10 with (1-naphthyl)diphenyl phosphine
or diisopropyl(1-naphthyl) phosphine
A solution of Re2(CO)10 and 2 equiv. of (1-naphthyl)diphenyl
phosphine or diisopropyl(1-naphthyl) phosphine in chloro-
benzene was reuxed overnight to result in corresponding ve-
membered cyclorhenated complex 1 or 2 in good yields (Scheme
1). Obviously, the formation of complexes 1 and 2 goes through
an intramolecular activation of C(sp2)–H bond on the adjacent
a position of naphthyl ring. The 1H NMR spectrum of 1 showed
six peaks centered at d 8.21 (1H), 7.95 (1H), 7.68 (1H), 7.60 (1H),
7.55–7.49 (1H, overlapping with peaks for protons on two
phenyl rings), 7.35 (1H) corresponding to six protons of the
metalated naphthyl group. More distinctly, the 1H NMR
Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Key
Laboratory of Inorganic–Organic Hybrid Functional Material Chemistry, Ministry of
Education, College of Chemistry, Tianjin Normal University, Tianjin 300387, PR
China. E-mail: hxxyzbl@gmail.com; Fax: +86-22-23766532; Tel: +86-22-23766515
† CCDC 1520723–1520726. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c6ra28263f
Scheme
Re2(CO)10
1
.
Reactions of 1-naphthyl-substituted phosphines with
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spectrum of 2 exhibited ve well-separated multiplets at d 8.16
(1H), 7.85 (1H), 7.58 (2H), 7.43 (1H), 7.28 (1H) for resonance of
six protons on the metalated naphthyl group. The IR spectra of 1
and 2 (KBr lm) indicated the expected strong n(CO) absorp-
tions in the range 2084–1925 cmꢀ1 for terminal carbonyls. The
structure of 1 was further conrmed by single-crystal diffraction
analysis, which is shown in Fig. 1, with selected bond lengths
and angles. It reveals an octahedral geometry with the rhe-
nium(I) center coordinated by four carbonyl groups, one phos-
phorus atom P(1), and one metalated carbon atom C(3), in
which P(1) and C(3) are mutually adjacent. Re–P bond length is
Scheme 2 Reaction of diisopropyl(o-methylphenyl) phosphine with
Re2(CO)10
.
CH2. These resonances conrm the expected C(sp3)–H bond
activation.
˚
˚
2.4413(9) A, a litter longer than that (2.428(3) A) in four-
membered cyclorhenated analogue Re(CO)4(PPh2CH2CH2).12
Reactions of Re2(CO)10 with diisopropyl(2-methylnaphthyl)
phosphine
Since both C(sp2)–H bond and C(sp3)–H bond could be activated
in cyclometalation of Re2(CO)10 with phosphines, we were
curious about the relative activity between them. Therefore,
diisopropyl(2-methylnaphthyl) phosphine was chosen as the
ligand, which provides both C(sp2)–H and C(sp3)–H bonds at the
appropriate positions, to test the competition reaction. There-
fore, reaction of Re2(CO)10 with diisopropyl(2-methylnaphthyl)
phosphine under the above-mentioned conditions was per-
Reaction of Re2(CO)10 with diisopropyl(o-methylphenyl)
phosphine
Having demonstrated that phosphine ligand could be employed
as a donor group for metalation of a naphthyl C(sp2)–H bond in
complexes 1 and 2, we decided to test whether it could also
promote activation of a C(sp3)–H bond. The corresponding
reaction of Re2(CO)10 with diisopropyl(o-methylphenyl) phos-
phine was carried out, which afforded a product 3 in 50% yield
(Scheme 2). The 1H NMR spectrum of 3 showed three multiplets
at d 7.38 (1H), 7.24 (2H), 7.04 (1H) duo to four protons on the
phenyl ring, one multiplet at d 2.49 (2H) for methenyl signal,
and two doublets of doublets at d 1.20 (6H) and 1.05 (6H) for
signals of four methyls on two isopropyl groups. However, there
was no signal for the methyl on the phenyl ring; instead one
multiple at d 2.50, integrating to 2H, assigned to a metal-bound
1
formed, which gave a product 4 (Scheme 3). The H NMR spec-
trum of 4 showed four multiplets in the aromatic region, all
integrating to 5H due to the naphthyl ring, and a doublet at
d 2.71, assigned to signal for the methyl on the naphthyl ring.
These resonances indicated that the aromatic C(sp2)–H bond is
selectively activated in the reaction to form the ve-membered
cyclometalated complex 4. The reason that the aromatic C(sp2)–
H bond activation is favored over C(sp3)–H bond activation is
probably owing to the higher thermal stability of aryl hydrogen
activated product when compared to alkyl hydrogen activated
product.
Reactions of Re2(CO)10 with phosphinites
In order to explore applicable scope of this type of cyclo-
metalation, ligand was extended to phosphinite. Therefore
reaction of Re2(CO)10 with o-methylphenyl diisopropylphos-
phinite was examined, which produced the corresponding ve-
membered cyclometalated complex 5 (Scheme 4). The 1H NMR
spectrum of 5 showed three multiplets (d 7.55, 6.84, and 6.71) in
the aromatic region, each integrating to 1H due to the phenyl
ring, and a singlet at d 2.25, assigned to signal for the methyl on
1
the phenyl ring. These H NMR information conrms an ortho
aromatic C(sp2)–H bond activation.
However, when Re2(CO)10 reacted with another phosphinite,
1-naphthyl diisopropylphosphinite under the above-mentioned
conditions, the reaction did not produce the similar ve-
Fig. 1 Thermal ellipsoid drawing of 1 showing the labeling scheme
and 50% probability ellipsoids; hydrogens are omitted for clarity.
Selected bond lengths [A˚] and angles [ꢁ] are Re(1)–P(1) 2.4413(9), P(1)–
C(1) 1.812(3), Re(1)–C(23) 1.987(4), Re(1)–C(24) 1.960(4), Re(1)–C(25)
1.969(4), Re(1)–C(26) 2.003(4), :C(3)–Re(1)–C(25) 173.87(14),
:C(24)–Re(1)–P(1) 170.15(12), :C(23)–Re(1)–C(26) 171.80(16), Scheme 3 Reaction of diisopropyl(2-methylnaphthyl) phosphine with
:C(3)–Re(1)–P(1) 79.05(9), :Re(1)–P(1)–C(1) 103.52(12).
Re2(CO)10.
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Scheme 4 Reaction of o-methylphenyl diisopropylphosphinite with
Re2(CO)10
.
Scheme 6 Photolysis of 1 or 2 in CHX3 (X ¼ Cl, Br).
reactivity, we similarly treated the P-contained cyclorhenated
complex 1 with excess I2 in CH2Cl2 at room temperature for 24 h,
however, no reaction occurred. This result may indicate the
higher stability of 1 when compared with N-contained analogues.
Therefore we decided to try the decyclometalation of 1 or 2 under
UV light conditions. A solution of complex 1 or 2 in CHCl3 or
CHBr3 was irradiated by UV lamp to give corresponding
phosphine-substituted tetracarbonyl rhenium halide 7–10
(Scheme 6). Obviously, the Re–C bond of the ve-membered ring
in 1 or 2 is cleavaged readily during the photolysis. Complexes 7–
10 were fully characterized by spectroscopic analysis, as well as
crystallographic analysis for 9. The molecular structure of 9 was
shown in Fig. 3, with selected bond lengths and angles. Pseu-
dooctahedral geometry is observed around the Re atom. The
bromine and the (1-naphthyl)diphenyl phosphine groups are cis
Scheme
Re2(CO)10
5 Reaction of 1-naphthyl diisopropylphosphinite with
.
membered cyclometalated complex, instead
a dinuclear
complex 6 was obtained (Scheme 5). The 1H NMR spectrum of 6
showed six multiplets in the aromatic region, all integrating to
7H corresponding to protons of the naphthyl ring. These reso-
nances indicate the absence of aromatic C(sp2)–H bond acti-
vation. The structure of 6 was further conrmed by single-
crystal diffraction analysis, which is shown in Fig. 2, with
selected bond lengths and angles. It consists of a pair of square
pyramidal Re(CO)4(P) units linked by a Re–Re bond. Each
phosphinite ligand is located at the top of the pyramid. Two sets
of carbonyl groups bounded to two rhenium atoms occur as the
˚
to each other. The Re(1)–P(1) bond length is 2.5016(12) A, longer
˚
than that (2.4413(9) A) in ve-membered cyclorhenated structure
of 1, which could be attributed to nonbonding interactions
between the phosphine and Re(CO)4Br units.
Besides, for further comparison of reactivity, we also per-
formed the photolysis of 1 with CF3COOH. Aer a solution of 1
˚
staggered conformation. Re–Re bond length is 3.0606(5) A,
a litter longer than that (3.04 A) in Re2(CO)10.
13
˚
Cleavage of the cyclometalated Re–C bond of 1 or 2
Lu has reported the chemical behavior of the similar N-contained
cyclorhenated complexes, including the electrophilic addition
reactions of cyclorhenated complexes with HBr, RCO2H, or I2,
which caused the opening of the metallacyclic ring to generate
the corresponding rhenium products.14 For comparison of
Fig. 2 Thermal ellipsoid drawing of 6 showing the labeling scheme Fig. 3 Thermal ellipsoid drawing of 9 showing the labeling scheme
and 50% probability ellipsoids; hydrogens are omitted for clarity. and 50% probability ellipsoids; hydrogens are omitted for clarity.
Selected bond lengths [A˚] and angles [ꢁ] are Re(1)–Re(1A) 3.0606(5), Selected bond lengths [A˚] and angles [ꢁ] are Re(1)–P(1) 2.5016(12),
Re(1)–P(1) 2.3419(15), Re(1)–C(1) 1.982(10), Re(1)–C(2) 1.977(7), Re(1)– Re(1)–Br(1) 2.620(2), Re(1)–C(23) 2.016(6), Re(1)–C(24) 1.968(5), Re(1)–
C(3) 1.977(10), Re(1)–C(4) 1.958(8), :P(1)–Re(1)–Re(1A) 177.56(4), C(25) 1.997(6), Re(1)–C(27) 1.952(8), :P(1)–Re(1)–C(24) 176.40(16),
:C(1)–Re(1)–C(3) 173.0(3), :C(2)–Re(1)–C(4) 168.1(3).
:C(23)–Re(1)–C(25) 178.0(2), :Br(1)–Re(1)–C(27) 169.1(6).
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Photolysis of 1–3 with 5 equiv. of bromobenzene in benzene
under N2 for 1–4.5 h produced a yellow solution. Aer removal
of the solvent under vacuum, the residue was carefully sepa-
rated in air by column chromatography on silica gel, and
afforded the corresponding phosphine-substituted tetra-
carbonyl rhenium bromides 9, 10, and 12 (Scheme 8). Besides,
the reactions also stoichiometrically produced biphenyl (92–
98%, entries 1–3 in Table 1). Further activation of C–I bond and
the relatively inert C–Cl bond by 1 was also conducted by
photolysis of 1 with iodobenzene and chlorobenzene in
benzene, which similarly provided the corresponding
phosphine-substituted tetracarbonyl rhenium iodide (13) and
chloride (7), as well as the biphenyl (Scheme 8) (entries 4–5,
Table 1). To expand the scope of the substrates, photolysis of
several para-substituted aryl halides with 1 were examined, and
the reactions gave similarly the rhenium halides 7 or 9, and the
para-substituted biphenyl, no matter when the substituent is an
electron-donating (MeO) or electron-withdrawing (CF3, CH3CO)
group (entries 6–10, Table 1). Next, the source of the biphenyl
was investigated. Photolysis of 1 with p-bromoanisole in
benzene-d6 generated the 4-methoxybiphenyl-d5 (p-CH3O–
C6H4–C6D5), completely no biphenyl or 4,40-dimethoxybiphenyl
were observed. It is revealed that the p-CH3O–C6H4 and C6D5
moieties in the resulting substituted biphenyl come from p-
bromoanisole and solvent benzene-d6, respectively.
Scheme 7 Photolysis of 1 with CF3COOH in CH2Cl2.
with CF3COOH in CH2Cl2 was irradiated for 8 h, a white product
11 was obtained in moderate yield (Scheme 7). Complexes 11
was fully characterized by spectroscopic and crystallographic
analysis. The molecular structure of 11 was shown in Fig. 4.
Similarly to 9, the pseudooctahedral geometry is observed
around the Re atom. The carboxylate (CF3CO2) and the (1-
naphthyl)diphenyl phosphine groups are cis to each other. The
˚
˚
Re(1)–P(1) bond length is 2.494(2) A, close to (2.5016(12) A) that
˚
in 9, but also longer than that (2.4413(9) A) in ve-membered
ring structure of 1. The formation of 11 indicates that the
reactivity of 1 is similar to that of N-contained analogues when
reacted with CF3CO2H.14
Photochemical reactions of 1–3 with aryl halides in benzene
We have reported the photochemical reactions of cyclo-
pentadienylrheniumtricarbonyls [(h5-C5R5)Re(CO)3] (R ¼ Me or
H), or doubly-bridged biscyclopentadienyl dirhenium carbonyls
with aryl halides in benzene, which generate biphenyl almost
stoichiometrically, as well as the corresponding rhenium
dicarbonyl products.15 In order to expand the reaction scope of
this type, we used cyclometalated rhenium complexes 1–3 as
starting materials and tried the similar photochemical reac-
tions with aryl halides in benzene.
Rhenium-catalyzed direct arylation of arenes with aryl halides
On the basis of the photochemical reactions described above,
we considered if the products, the phosphine-substituted tet-
racarbonyl rhenium halides, could revert to the original cyclo-
metalated rhenium complexes 1–3, then a catalytic cycle would
be created. Generally, cyclometalation of the ligand-substituted
rhenium halides could be realized in the presence of base. Lu
has reported
a cyclometalation reaction of ReBr(CO)4[-
C(NHR)(NHPh)] (R ¼ iPr, or Pr) with Et2NH in CH2Cl2 to give
Re(CO)4[h2-C(NHR)(NHPh)].14 For optimization of reaction
conditions, the cross-coupling of 4-bromoanisole with benzene
was selected as the model reaction. The reactions were carried
out with 0.5 mol% of cyclometalated rhenium complex 1 in
benzene and different bases were used. Only NaOH as the base
afforded the biphenyl product in moderate yield (59%, entry 1 of
Table 2), whereas other tested bases such as K2CO3, KOAc,
tBuOK, and pyrrolidine gave rise to lower yields (26–50%,
entries 2–5). Other two cyclometalated rhenium complexes 2
and 3 as catalysts were also screened under the optimized
conditions, complex 2 afforded slightly higher yield (68%, entry
6) than 1, while complex 3 gave much lower yield (26%, entry 7).
To expand the scope of the substrates, other aryl bromides,
Fig. 4 Thermal ellipsoid drawing of 11 showing the labeling scheme
and 50% probability ellipsoids; hydrogens are omitted for clarity.
Selected bond lengths [A˚] and angles [ꢁ] are Re(1)–P(1) 2.494(2), Re(1)–
O(1) 2.145(5), Re(1)–C(23) 1.971(9), Re(1)–C(24) 2.007(8), Re(1)–C(25)
1.915(8), Re(1)–C(26) 2.003(8), :P(1)–Re(1)–C(23) 174.4(2), :C(24)– Scheme
8
Photochemical reactions of 1–3 with aryl halides in
Re(1)–C(26) 176.4(3), :O(1)–Re(1)–C(25) 176.0(3).
benzene.
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Table 1 Photochemical reactions of 1–3 with aryl halides in benzenea
Entry
Re
R0
X
t [h]
Productb
Yieldc [%]
Re prod.
1
2
3
4
5
6
7
8
9
1
2
3
1
1
1
1
1
1
1
H
H
H
H
Br
Br
Br
Cl
I
Br
Br
Br
Cl
Cl
1
1
1
4
1
4
1
1
Biphenyl
Biphenyl
Biphenyl
Biphenyl
>98
95
92
85
92
98
97
80
90
87
9
10
12
7
13
9
9
9
7
7
H
Biphenyl
p-MeO
p-CF3
p-CH3CO
p-MeO
p-CF3
p-MeO–biphenyl
p-CF3–biphenyl
p-CH3CO–biphenyl
p-MeO–biphenyl
p-CF3–biphenyl
4.5
1.5
10
a
Reaction conditions: irradiation of 1–3 (0.10 mmol) and Ar–X (0.50 mmol) in 10 mL benzene solvent with a 500 W high-pressure Hg lamp (lmax
¼
365 nm) in the ice-water bath. b Biphenyl products were isolated by routine silica gel column chromatography, and identied by comparing their
respective 1H NMR spectra with authentic samples. Isolated yield (based on unrecovered 1–3).
c
Table
2 Rhenium-catalyzed direct arylation of arenes with aryl
partially under UV irradiation, which may explain the
moderate catalytic performance of 1. Based on the results
described above, a plausible catalytic mechanism is tenta-
tively proposed: rst, a CO is dissociated from cyclometalated
rhodium complexes 1–3 under UV irradiation to give a 16eꢀ
unsaturated species; this is followed by oxidative addition of
a C–X bond on aryl halides (Ph–X) to form the Re(III) inter-
mediate. In the next step, a radical aromatic substitution that
involves the aromatic radical with the solvent benzene might
occur to give biphenyl and the corresponding cyclometalated
rhenium hydride halide complexes, which undergo reductive
elimination and recoordination of CO to afford the ring-
opening complexes (7, 9, 10, 12, and 13). In the nal step,
cyclometalation of ring-opening complexes is achieved in the
presence of base to generate the catalytic cycle. When we
tried to synthesize the Re(III) intermediate to support the
mechanism, unfortunately, we did not obtained the expected
product either from photolysis of 1–3 in pure Ph–X or
photolysis of 1–3 and Ph–X in cyclohexane.
halidesa
t
Yieldb,c
[%]
Entry Cat Base
R0
X
[h] Productb
1
2
3
4
5
6
7
8
1
1
1
1
1
2
3
1
1
1
1
NaOH
K2CO3
KOAc
p-MeO Br
p-MeO Br
p-MeO Br
p-MeO Br
4
4
4
4
6
5
5
4
3
8
8
p-MeO–biphenyl 59
p-MeO–biphenyl 30
p-MeO–biphenyl 26
p-MeO–biphenyl 50
p-MeO–biphenyl 29
p-MeO–biphenyl 68
p-MeO–biphenyl 26
tBuOK
Pyrrolidine p-MeO Br
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
p-MeO Br
p-MeO Br
H
p-CF3
H
Br
Br
Cl
I
Biphenyl
p-CF3–biphenyl
Biphenyl
65
60
26
35
9
10
11
H
Biphenyl
a
Reaction conditions: irradiation of 1–3 (0.01 mmol), Ar–X (2.0 mmol),
and base (2.0 mmol) in 20 mL benzene solvent with a 500 W high-
b
pressure Hg lamp (lmax ¼ 365 nm) in the ice-water bath. Biphenyl
Summary
products were isolated by routine silica gel column chromatography,
and identied by comparing their respective 1H NMR spectra with
authentic samples. c Isolated yield (based on unrecovered 1–3).
A series of ve-membered cyclometalated rhenium complexes
(1–5) were synthesized by thermal treatment of aryl-substituted
phosphines or phosphinites with Re2(CO)10 in chlorobenzene.
The formation of cyclorhenated complexes went through an
intramolecular activation of C(sp2)–H or C(sp3)–H bond.
Competition reaction indicated that the aromatic C(sp2)–H
bond is more likely to be activated than C(sp3)–H bond under
the same conditions. The chemical behavior of the cyclo-
rhenated complexes 1, 2 or 3 has been investigated, including
photolysis of 1 or 2 in CHX3, reaction of 1 with CF3COOH, and
photolysis of 1–3 with aryl halides in benzene, all of them
caused the cleavage of Re–C s bond and then the opening of
metallacycle. Some reaction indicated the lower reactivity of the
cyclometalated rhenium complexes in this work than that of N-
contained cyclorhenated complexes. Besides, complexes 1–3
exhibited moderate catalytic activity on direct arylation
of arenes with aryl halides under UV irradiation at
a [Re] : substrate ratio of 1 : 200.
including bromobenzene, and 4-bromobenzotriuoride were
examined, and the reactions afforded the corresponding
biphenyl in yields of 65% and 60% (entries 8 and 9). Besides,
the substrates chlorobenzene and iodobenzene were also tested
using the catalyst 1, which resulted in lower yields (26% and
35%, entries 10 and 11).
Unfortunately, rhenium catalysts 1–3 did not show higher
activity to direct arylation of arenes with aryl halide under
our current conditions. When we performed the photolysis of
phosphine-substituted tetracarbonyl rhenium bromide 9 in
benzene in the presence of NaOH, the expected cyclo-
metalated rhenium complex 1 was observed, at the same
time, we also obtained some free ligand, (1-naphthyl)
diphenyl phosphine. Obviously, complex 9 was decomposed
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6H, CH3), 0.83 (dd, 6H, CH3). 31P{1H} NMR: d 64.0. IR (nCO): 2074
(s), 1980 (s), 1927 (s) cmꢀ1. Anal. calcd for C21H22O4PRe: C,
45.40; H, 3.99. Found: C, 45.27; H, 3.83.
Experimental
General considerations
5, (45% yield). 1H NMR: d 7.55 (d, J ¼ 7.2 Hz, 1H), 6.84 (d, J ¼
7.2 Hz, 1H), 6.71 (t, J ¼ 7.2 Hz, 1H), 2.53 (m, 2H, CH), 2.25 (s, 3H,
CH3), 1.30 (dd, 6H, CH3), 1.21 (dd, 6H, CH3). 31P{1H} NMR:
d 158.3. IR (nCO): 2080 (s), 1982 (s), 1955 (s) cmꢀ1. Anal. calcd for
All reactions were carried out under nitrogen using standard
Schlenk and vacuum line techniques; however the workup was
carried out in air unless stated otherwise. All solvents were
distilled from appropriate drying agents under nitrogen prior to
1
use. H (400 MHz), 13C{1H} (100 MHz), and 31P{1H} (162 MHz)
C
17H20O5PRe: C, 39.15; H, 3.87. Found: C, 39.43; H, 3.81.
6, (66% yield). 1H NMR: d 8.20 (m, 2H), 7.80 (m, 2H), 7.58 (m,
NMR spectra were recorded on a Bruker AV400 instrument at
2H), 7.48 (m, 4H), 7.34 (m, 2H), 7.15 (m, 2H), 2.85 (m, 4H, CH),
1.43–1.31 (m, 24H, CH3). 13C{1H} NMR: d 200.2, 135.2, 128.0,
127.3, 126.6, 125.9, 125.4, 123.7, 122.2, 120.2, 115.8, 36.9, 32.8,
18.8, 18.5. 31P{1H} NMR: d 159.0. IR (nCO): 1965 (s), 1933 (s), 1897
(s) cmꢀ1. Anal. calcd for C40H42O10P2Re2: C, 43.01; H, 3.79.
Found: C, 42.85; H, 3.62.
room temperature with CDCl3 as solvent. Chemical shis were
1
recorded in ppm, referenced to residual H and 13C signals of
the non-deuterated CDCl3 (d 7.26 and 77.16) as internal stan-
dards or to the 31P signal of PPh3 (d ꢀ5.65) as an external
standard. Elemental analyses were performed on a Perkin-
Elmer 240C analyzer. IR spectra were recorded as KBr disks
on a Nicolet 560 ESP FTIR spectrometer. Re2(CO)10 was
purchased from Strem without further purication; the ligands
diisopropyl(1-naphthyl) phosphine,16 (1-naphthyl)diphenyl
General procedure for photolysis of 1 or 2 in CHX3 (X ¼ Cl, Br)
A solution of 1 or 2 (0.05 mmol) in CHX3 (5 mL) was irradiated
by UV light for 8 h, then the solvent was removed under vacuum,
the residue was chromatographed on a silica gel column with
a mixture of petrol ether/CH2Cl2 as the eluent. The products
were recrystallized from n-hexane/CH2Cl2 (1 : 1) at ꢀ10 ꢁC to
afford 7–10 as colorless crystals in yields of 54–81%.
phosphine,16
diisopropyl(o-methylphenyl)
phosphine,17
diisopropyl(2-methylnaphthyl) phosphine,17 o-methylphenyl
diisopropylphosphinite,18 and 1-naphthyl diisopropylphos-
phinite18 were prepared by literature methods.
1
7, (62% yield). H NMR: d 8.01 (m, 1H), 7.96 (m, 2H), 7.78–
General procedure for the reactions of Re2(CO)10 with
phosphines or phosphinites in chlorobenzene
7.73 (m, 4H), 7.54 (m, 1H), 7.50–7.39 (m, 8H), 7.36 (m, 1H). 31
P
{1H} NMR: d 3.1. IR (nCO): 2105 (m), 1997 (s), 1943 (s), 1896 (m)
cmꢀ1. Anal. calcd for C26H17ClO4PRe: C, 48.34; H, 2.65. Found:
C, 48.57; H, 2.49.
A mixture of Re2(CO)10 (0.05 mmol) and phosphine or phos-
phinite (2.0 equiv.) in chlorobenzene (10 mL) was reuxed for
10 h and then concentrated under vacuum, the residue was
chromatographed on a silica gel column with a mixture of
petrol ether/CH2Cl2 as the eluent. The products were recrystal-
lized from n-hexane/CH2Cl2 (1 : 1) at ꢀ10 ꢁC to afford 1–6 as
colorless crystals in yields of 45–85%.
8, (54% yield). 1H NMR: d 8.42 (d, J ¼ 8.4 Hz, 1H), 7.94 (d, J ¼
8.0 Hz, 2H), 7.73 (m, qH), 7.65 (m, 1H), 7.60–7.52 (m, 2H), 3.39
(m, 2H, CH), 1.58 (dd, 6H, CH3), 1.38 (dd, 6H, CH3). 31P{1H}
NMR: d 12.4. IR (nCO): 2105 (m), 2011 (s), 1922 (s) cmꢀ1. Anal.
calcd for C20H21ClO4PRe: C, 41.56; H, 3.66. Found: C, 41.35; H,
3.71.
1, (82% yield). 1H NMR: d 8.21 (d, J ¼ 6.0 Hz, 1H), 7.95 (d, J ¼
8.0 Hz, 1H), 7.68 (d, J ¼ 8.4 Hz, 1H), 7.60 (m, 1H), 7.55–7.49 (m,
5H), 7.44 (m, 6H), 7.35 (m, 1H). 13C{1H} NMR: d 189.1, 189.0,
152.4, 149.7, 144.3, 138.2, 134.7, 134.3, 132.8, 132.6, 132.5,
131.6, 130.8, 129.0, 128.9, 127.9, 124.6, 123.9. 31P{1H} NMR:
d 26.4. IR (nCO): 2084 (m), 1998 (s), 1976 (s), 1955 (s), 1929 (s)
cmꢀ1. Anal. calcd for C26H16O4PRe: C, 51.23; H, 2.65. Found: C,
51.37; H, 2.42.
9, (81% yield). 1H NMR: d 8.00 (m, 1H), 7.95 (m, 2H), 7.76 (m,
4H), 7.53 (m, 1H), 7.48–7.38 (m, 8H), 7.35 (m, 1H). 31P{1H} NMR:
d ꢀ0.3. IR (nCO): 2105 (s), 2012 (s), 1947 (s), 1921 (s) cmꢀ1. Anal.
calcd for C26H17BrO4PRe: C, 45.23; H, 2.48. Found: C, 45.18; H,
2.36.
1
10, (78% yield). H NMR: d 8.38 (m, 1H), 7.94 (m, 2H), 7.73
(m, 1H), 7.65 (m, 1H), 7.60–7.53 (m, 2H), 3.44 (m, 2H, CH), 1.58
(dd, 6H, CH3), 1.38 (dd, 6H, CH3). 31P{1H} NMR: d 7.3. IR (nCO):
2106 (s), 2010 (s), 1919 (s) cmꢀ1. Anal. calcd for C20H21BrO4PRe:
C, 38.59; H, 3.40. Found: C, 38.43; H, 3.42.
2, (85% yield). 1H NMR: d 8.16 (m, 1H), 7.85 (m, 1H), 7.58 (m,
2H), 7.43 (m, 1H), 7.28 (m, 1H), 2.58 (m, 2H, CH), 1.33 (dd, 6H,
CH3), 1.04 (dd, 6H, CH3). 13C{1H} NMR: d 190.2, 189.8, 189.7,
189.4, 152.5, 149.7, 143.9, 138.8, 134.5, 132.2, 128.1, 127.5,
124.1, 123.8, 29.7, 29.5, 20.3, 20.1. 31P{1H} NMR: d 49.2. IR (nCO):
2076 (w), 1970 (s), 1925 (s) cmꢀ1. Anal. calcd for C20H20O4PRe:
Reaction of 1 with CF3COOH
C, 44.36; H, 3.72. Found: C, 44.49; H, 3.48.
A solution of 1 (0.05 mmol) in CH2Cl2 (5 mL) was treated with
1
3, (56% yield). H NMR: d 7.38 (m, 1H), 7.27–7.21 (m, 2H), excess CF3COOH (0.3 mmol). The mixture was stirred for 24 h at
7.04 (m, 1H), 2.50 (m, 2H, CH2), 2.49 (m, 2H, CH), 1.20 (dd, 6H, room temperature. The solvent was removed under vacuum,
CH3), 1.05 (dd, 6H, CH3). 13C{1H} NMR: d 191.1, 190.3, 189.2, and the residue was chromatographed on a silica gel column
162.8, 134.3, 131.4, 130.2, 129.5, 123.9, 77.4, 28.1, 27.8, 19.3, with a mixture of petrol ether/CH2Cl2 as the eluent. The product
18.9. 31P{1H} NMR: d 48.8. IR (nCO): 2073 (s), 1986 (s), 1931 (s) was recrystallized from n-hexane/CH2Cl2 (1 : 1) at ꢀ10 ꢁC to
cmꢀ1. Anal. calcd for C17H20O4PRe: C, 40.39; H, 3.99. Found: C, afford 11 as colorless crystals in 48% yield.
40.74; H, 3.75.
11 1H NMR: d 8.03 (d, J ¼ 8.4 Hz, 1H), 7.97 (d, J ¼ 8.0 Hz, 1H),
4, (63% yield). 1H NMR: d 8.18 (m, 1H), 7.74 (m, 1H), 7.54 (m, 7.92 (d, J ¼ 8.8 Hz, 1H), 7.56–7.41 (m, 12H), 7.38 (d, J ¼ 8.8 Hz,
1H), 7.21 (m, 2H), 2.91 (m, 2H, CH), 2.71 (d, 3H, CH3), 1.49 (dd, 1H), 7.34 (m, 1H). 31P{1H} NMR: d 9.8. IR (nCO): 2106 (s), 1998 (s),
17068 | RSC Adv., 2017, 7, 17063–17070
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Table 3 Crystal data and summary of X-ray data collection for 1, 6, 9, and 11
1
6
9
11
Formula
fw
C
26H16O4PRe
C20H21O5PRe
558.54
C26H17BrO4PRe
690.47
C28H17F3O6PRe
723.58
609.56
T (K)
173.00(10)
Triclinic
P1
296(2)
Orthorhombic
Fdd2
24.564(3)
42.547(5)
7.7934(8)
90
173.00(10)
Triclinic
P1
154.5(9)
Monoclinic
P21/c
24.3119(9)
11.3315(3)
19.6695(6)
90
98.995(3)
90
5352.1(3)
8
Cryst syst
Space group
ꢀ
ꢀ
ꢁ
a (A)
11.9989(3)
14.4984(3)
14.8134(4)
64.239(2)
84.8034(19)
74.8834(19)
2239.82(10)
4
9.9390(5)
11.0789(5)
11.2433(6)
94.119(4)
97.332(4)
99.066(4)
1207.22(10)
2
ꢁ
b (A)
ꢁ
c (A)
a (deg)
b (deg)
g (deg)
90
90
ꢁ3
V (A )
8145.1(15)
16
1.822
6.073
4336
Z
Dcalc (g cmꢀ3
)
1.808
11.544
1176.0
1.900
6.784
660.0
1.796
4.662
2800.0
m (mmꢀ1
F(000)
)
Cryst size (mm)
Max. 2q (deg)
0.20 ꢂ 0.18 ꢂ 0.15
0.22 ꢂ 0.21 ꢂ 0.20
0.25 ꢂ 0.15 ꢂ 0.14
0.25 ꢂ 0.24 ꢂ 0.2
148.728
53.414
50.018
50.02
No. of rens collected
No. of indep rens/Rint
No. of params
16 330
8839/0.0273
577
13 167
4177/0.0346
254
7610
4240/0.0407
320
45 685
9416/0.0564
703
Goodness-of-t on F2
R1, wR2 [I > 2s(I)]
R1, wR2 (all data)
1.061
1.001
0.958
1.087
0.0294, 0.0764
0.0313, 0.0780
1.88, ꢀ0.99
0.0245, 0.0435
0.0295, 0.0453
0.578, ꢀ0.298
0.0329, 0.0571
0.0394, 0.0608
1.16, ꢀ1.42
0.0487, 0.1086
0.0563, 0.1129
1.92, ꢀ1.43
ꢀ3
˚
Largest diff peak and hole (e A
)
1960 (s), 1691 (s) cmꢀ1. Anal. calcd for C28H17F3O6PRe: C, 46.48; 5 min. Aer irradiation for 3–8 h in the ice-water bath, the
H, 2.37. Found: C, 46.63; H, 2.45.
solvent was removed under the reduced pressure. The residue
was chromatographed in air on silica gel using petroleum ether
as eluent. The corresponding biphenyl products were obtained
as colorless solids in yields of 26–68%.
General procedure for photolysis of 1–3 with aryl halides in
C6H6
A solution of 1–3 (0.05 mmol) and aryl halides (0.25 mmol) in dry
benzene (10 mL) in nitrogen ushed quartz tube was additionally
degassed by bubbling nitrogen thru for 5 min. Aer irradiation
for 1–4.5 h in the ice-water bath, the solvent was removed under
the reduced pressure. The residue was chromatographed in air
on silica gel using petroleum ether–CH2Cl2 mixture as eluent.
The rst band (colorless) afforded the corresponding biphenyl as
white solids (80–98%). The second band (colorless) gave corre-
sponding phosphine-substituted tetracarbonyl rhenium halides
(7, 9, 10, 12, and 13).
Crystallography
Single crystals of complexes 1, 6, 9, and 11 (CCDC 1520723–
1520726) suitable for X-ray diffraction were obtained by crys-
tallization from n-hexane/CH2Cl2 (1 : 1). Data collection was
performed on
a
Bruker SMART 1000, using graphite-
˚
monochromated Mo Ka radiation (u–2q scans, l ¼ 0.71073 A).
Semiempirical absorption corrections were applied for all
complexes. The structures were solved by direct methods and
rened by full-matrix least squares. All calculations were using
the SHELXTL-97 program system. The crystal data and
summary of X-ray data collection are presented in Table 3.
1
12, (32% yield). H NMR: d 7.46 (m, 1H), 7.32 (m, 3H), 3.27
(m, 2H, CH), 2.60 (s, 3H, CH3), 1.58 (dd, 6H, CH3), 1.37 (dd, 6H,
CH3). 31P{1H} NMR: d 9.8. IR (nCO): 2102 (s), 2018 (s), 1980 (s),
1938 (s) cmꢀ1. Anal. calcd for C17H21BrO4PRe: C, 34.82; H, 3.61.
Found: C, 35.13; H, 3.55.
Acknowledgements
13, (53% yield). 1H NMR: d 8.01–7.92 (m, 3H), 7.79–7.74 (m,
4H), 7.53 (m, 1H), 7.49–7.34 (m, 9H). 31P{1H} NMR: d ꢀ6.2. IR
(nCO): 2099 (s), 1992 (br), 1942 (s) cmꢀ1. Anal. calcd for C26-
H17IO4PRe: C, 42.34; H, 2.32. Found: C, 42.47; H, 2.15.
This work was nancially supported by the National Natural
Science Foundation of China (No. 21002069 and 21572160), the
Natural Science Foundation of Tianjin (No. 14JCYBJC20300),
and the Program for Innovative Research Team in University of
Tianjin (TD12-5038).
General procedure for catalytic reactions of 1–3 with aryl
halides in C6H6
Notes and references
A solution of 1–3 (0.01 mmol), aryl halides (2.0 mmol) and base
(2.0 mmol) in dry benzene (20 mL) in nitrogen ushed quartz
tube was additionally degassed by bubbling nitrogen thru for
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