Nickel-catalyzed manipulation of tertiary phosphines via highly selective C-P bond cleavage

Article abstract of DOI:10.1039/c3cc43640c

A catalytic cycle involving oxidative addition of nickel(0) with a carbon-carbon single bond in the three-membered ring of diarylmethylenecyclopropa[b]naphthalenes, highly selective cleavage of the C-P bond, and migration of the aryl group of phosphine consequently provides a new type of bulky phosphine in excellent yields.

Full text of DOI:10.1039/c3cc43640c

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Nickel-catalyzed manipulation of tertiary phosphines
via highly selective C–P bond cleavage†
Cite this: Chem. Commun., 2013,
49, 7747
ab
Jian Cao,a Xian Huangz and Luling Wu*a
Received 15th May 2013,
Accepted 1st July 2013
DOI: 10.1039/c3cc43640c
www.rsc.org/chemcomm
A catalytic cycle involving oxidative addition of nickel(0) with a carbon–
In many transition-metal-catalyzed reactions, bulky phosphines
carbon single bond in the three-membered ring of diarylmethylene- show better reactivity than ordinary phosphines.4 Thus, much attention
cyclopropa[b]naphthalenes, highly selective cleavage of the C–P bond, has been focused on the synthesis of bulky phosphines in recent years.
and migration of the aryl group of phosphine consequently provides a However, the methods are mostly limited to the reaction of a chloro-
new type of bulky phosphine in excellent yields.
phosphine with bulky organometallic reagents5 and the transition-
metal-catalyzed phosphination or phosphinylation of a bulky aryl
As a challenging topic, the cleavage of C–P bonds has attracted much halide.6 We envisioned that selective cleavage of a C–P bond may
attention in the past few decades.1 Particularly, the C–P bond cleavage provide a potential efficient synthesis of bulky phosphines. In this
of tertiary phosphines has attracted much attention because many communication we wish to disclose an unprecedented nickel-catalyzed
tertiary phosphines act as important ligands for transition metals atom-economical and highly selective C–P bond cleavage of phosphines
and as versatile intermediates in organic synthesis.2 Reports on C–P 1 coupled with a ring-opening reaction of diarylmethylenecyclopropa[b]-
bond activation of tertiary phosphines with transition metals have naphthalenes 2,7 leading to an efficient synthesis of a new type of bulky
been disclosed in the past years.3 Most of these reports show C–P phosphine (Scheme 1, eqn (2)).
bond activation of tertiary phosphines with a stoichiometric amount
During our studies on the synthetic utility of diarylmethyl-
of transition metal to provide stable metal compounds (Scheme 1, enecyclopropa[b]naphthalenes 2, we recently reported a highly
eqn (1)).3a–f However, very few examples of C–P activation of tertiary regioselective Pd(0)-catalyzed [3+2] cycloaddition reaction of
phosphines with a catalytic amount of transition metal have been diarylmethylenecyclopropa[b]naphthalenes with alkenes, alkynes
reported. For example, Chan and coworkers have reported a catalytic or arynes to produce 1(3)-alkylidene-2,3-dihydro-1H-cyclopenta[b]-
user-friendly phosphination of aryltriflates and triarylphosphines pro- naphthalene, 1-alkylidene-1H-cyclo-penta[b]naphthalene and 11-diaryl-
viding a variety of substituted phosphines via C–P bond cleavage.3g,h
methylene-11H-benzo[b]fluorine derivatives, respectively.8 We proposed
a mechanism in which the reaction is initiated by the oxidative addition
of a Pd(0) species to the three-membered ring of compound 2. As a
further exploration of the reaction mechanism, we recently tried
to prepare the nickelacyclobutene A. We envisaged that the reaction
of 1-(diphenylmethylene)-1H-cyclopropa[b]naphthalene (2a) with
Ni(PPh3)2 generated in situ from Ni(PPh3)2Cl2 and Zn would give
A via oxidative addition. However, the expected nickelacyclobutene
A was not isolated and a new product 3a was obtained instead
(Scheme 2). Through spectroscopic (1H, 13C, 31P NMR, MS) and
X-ray diffraction analysis,9 we identified the structure of this new
product, which is shown in Fig. S1 (ESI†). Obviously, the reaction
showed an unexpected Ni-mediated ring-opening coupling of 2a
Scheme 1 C–P cleavage reactions reported previously and in this report.
a Department of Chemistry, Zhejiang University, Hangzhou 310028, P. R. China.
E-mail: wululing@zju.edu.cn
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, Shanghai 200032, P. R. China
† Electronic supplementary information (ESI) available: Experimental details and
1H, 13C NMR spectra of new compounds. CCDC 903816, 917493 and 917494. For
ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c3cc43640c
‡ Prof. Huang passed away on March 6, 2010. He had been fully in charge of this
project. At this moment, Prof. Luling Wu is helping in completing all his projects
with the help from Prof. Shengming Ma.
Scheme 2 Our proposal and our observation.
c
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with the ligand, i.e., triphenylphosphine, via a C–P bond cleavage
reaction with a unique regioselectivity, serving as a direct and
efficient synthesis of a new type of bulky tertiary phosphine.
We then focused our attention on realizing a catalytic reaction of
triphenylphosphine (1a) with 2a to produce 3a using just a catalytic
amount of NiCl2ꢀ6H2O and Zn. In a preliminary experiment, we
observed that treatment of triphenylphosphine (1a) with 1-(diphenyl-
methylene)-1H-cyclopropa[b]naphthalene (2a) in the presence of
NiCl2ꢀ6H2O (10 mol%) and Zn (30 mol%) in dioxane at 110 1C for
2 hours gave diphenyl[3-(1,2,2-triphenylvinyl)naphthalen-2-yl]phosphine
(3a) in 96% yield (entry 2, Table S1, ESI†). When we reduced the
Scheme 3 Nickel-catalyzed ring-opening coupling of 1a with 2k and 2l.
within 7 h and 18 h, respectively, because of the poor solublility of
amount of NiCl2ꢀ6H2O and Zn to 2 mol% and 6 mol%, respectively, the the substrates (entries 9 and 10, Table 1). The unsymmetrical
yield of 3a was still maintained at 96%, although 10 hours were substrate 2k, upon reacting with 1a, gave the desired compounds
required (entries 3 and 4, Table S1, ESI†). To shorten the reaction 3k and 3k0 that were easily separated via chromatography on a
time, the concentration was adjusted to 0.2 M and 0.4 M, with the best silica gel and isolated in yields of 49% and 22% (eqn (1), Scheme 3).
concentration being 0.2 M, which provided 96% of 3a within 0.5 h Similarly, the reaction of 1a and 2l produced 3l and 3l0 in isolated
(entries 5 and 6, Table S1, ESI†). Among the solvents examined, we yields of 46% and 17% (eqn (2), Scheme 3). The structures of 3k
found that dioxane was the best (entries 7–12, Table S1, ESI†). There- and 3l were confirmed by X-ray diffraction analysis (Fig. S1, ESI†).9
fore, a reaction in the presence of 2 mol% of NiCl2ꢀ6H2O and 6 mol%
Next, we investigated the reaction of a variety of phosphines with
of Zn in dioxane at 110 1C at a concentration of 0.2 M was established substrate 2a (Table 2). The reaction may be conducted with electron-
as standard conditions to explore the reaction scope (entry 5, Table S1, donating, electron-withdrawing group-substituted aryl phosphines,
ESI†). Here it should, of course, be noted that the reaction did not occur tri(b-naphthyl)phosphine and tri(furan-2-yl)phosphine (Table 2).
in the absence of the nickel catalyst (entry 1, Table S1, ESI†).
When Ar was the 2-methylphenyl group, no reaction was observed,
With the optimized conditions in hand, the scope of the reaction which might result from the steric hindrance of the methyl group
of 1a with a variety of 2 was examined. The results summarized in (entry 3, Table 2). The reaction gave a complex mixture when applying
Table 1 show that different products (3) could be obtained smoothly tri(n-butyl)phosphine 1k (entry 10, Table 2). Noteworthily, when
in high yields (entries 1–9, Table 1). (Diarylmethylene) cyclopropa[b]-
phosphines bearing only one phenyl, such as dibutyl(phenyl)-
naphthalenes with p-tolyl (2b), m-tolyl (2c) and o-tolyl (2d) as the aryl phosphine (1l) and dicyclohexyl(phenyl)phosphine (1m), were used,
groups gave their corresponding products in good yields in 1 hour, the corresponding products 3u and 3v were obtained in 92% and
3 hours and 48 hours, respectively (entries 2–4, Table 1). The prolonged 94%, respectively (eqn (1), Scheme 4), which showed that only the
reaction time for 3d might result from the steric hindrance of phenyl group migrated, exclusively.5c,d,10 Furthermore, even triphenyl-
the ortho-methyl groups. When (diarylmethylene) cyclopropa[b]- arsine could react with 2a to give its ring-opening coupling product 3w
naphthalenes bearing other electron-donating or electron- in 95% yield in the presence of 10 mol% of NiCl2ꢀ6H2O and 30 mol%
withdrawing aryl groups were employed, the reactions all gave of Zn in 36 hours (eqn (2), Scheme 4).11
the corresponding products 3 in good yields (entries 5–9, Table 1).
On the basis of the above observations, we propose a plausible
The reaction of 2i and 2j needed longer times and were completed mechanism for this reaction (Scheme 5). Firstly, the reduction
reaction of Ni(PPh3)2Cl2 with Zn affords Ni0(PPh3)2. Subsequently,
oxidative addition of Ni0(PPh3)2 with the cyclopropane C–C bond of
Table 1 Nickel-catalyzed ring-opening coupling of triphenylphosphine (1a)
with diarylmethylenecyclopropa[b]naphthalenes (2)a
Table
2
Nickel-catalyzed ring-opening coupling of phosphines (1a) with
1-(diphenylmethylene)-1H-cyclopropa[b]naphthalene (2a)a
Entry
Ar
Time (h)
Isolated yield (%)
1
2
3
4
5
6
7
8
9
Ph (2a)
0.5
1
3
48
0.5
0.5
0.5
1
96 (3a)
96 (3b)
85 (3c)
86 (3d)
98 (3e)
95 (3f)
91 (3g)
98 (3h)
95 (3i)
Entry
Ar
Time (h)
Isolated yield (%)
4-MeC6H4 (2b)
3-MeC6H4 (2c)
2-MeC6H4 (2d)
4-MeOC6H4 (2e)
3,5-MeO-C6H3 (2f)
4-FC6H4 (2g)
4-ClC6H4 (2h)
4-BrC6H4 (2i)
1
2
3
4
5
6
7
8
9
3-MeC6H4 (1b)
4-MeC6H4 (1c)
2-MeC6H4 (1d)
4-MeOC6H4 (1e)
4-FC6H4 (1f)
4-ClC6H4 (1g)
4-BrC6H4 (1h)
2-Naphthyl (1i)
2-Furayl (1j)
4
4
24
5
0.5
1
1
0.5
12
24
92 (3m)
98 (3n)
NR
94 (3o)
98 (3p)
95 (3q)
96 (3r)
96 (3s)
94 (3t)
Complex
7
10
18
87 (3j)
10
n-Bu (1k)
a
a
The reaction was conducted with 0.24 mmol of 1a, 0.2 mmol of 2,
The reaction was conducted with 0.24 mmol of 1, 0.2 mmol of 2a,
0.004 mmol of NiCl2ꢀ6H2O, 0.012 mmol of Zn and 1 mL of solvent at 110 1C. 0.004 mmol of NiCl2ꢀ6H2O, 0.012 mmol of Zn and 1 mL of solvent at 110 1C.
c
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migrates from phosphorus to nickel and the phosphorus migrates
to the naphthyl ring to produce C via a four-membered transition
structure B (path a).3f After that, intermediate C undergoes reductive
elimination affording 3a while accepting another equivalent of
phosphine 1a to regenerate the catalytically active Ni0 catalyst. In
principle, the formation of 3a0 via the intermediate C0 is possible
(path b). Interestingly, the formation of 3a0 was not observed, which
is probably due to the steric hindrance in intermediate B0.
In conclusion, we have developed a nickel-catalyzed highly
selective C–P bond cleavage of tertiary phosphines involving a
ring-opening coupling reaction of diarylmethylenecyclopropa[b]-
naphthalenes to atom-economically provide differently substituted
bulky phosphines in excellent yields. The reactions are applicable to
a wide range of both phosphines and diarylmethylenecyclo-
propa[b]naphthalenes with different functionalities. Further studies
on the scope, mechanism, and synthetic applications of this trans-
formation are being carried out in our laboratory.
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We are grateful to the National Natural Science Foundation
of China (Project No. 20872127, 20732005 and J0830431), and
National Basic Research Program of China (2009CB825300),
and CAS Academician Foundation of Zhejiang Province, and
the Fundamental Research Funds for the Central Universities
for financial support.
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c
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Chem. Commun., 2013, 49, 7747--7749 7749