Rhodium-catalyzed phenylation of N-arylsulfonyl aldimines with sodium tetraphenylborate or trimethyl(phenyl)stannane

Article abstract of DOI:10.1016/S0022-328X(99)00562-8

The rhodium-catalyzed addition reactions of trimethyl(phenyl)stannane and sodium tetraphenylborate to N-phenylsulfonyl aldimines RCH=NSO₂Ph (R=alkyl and aryl) provided R(Ph)CHNHSO₂Ph in high yields. A cationic and free phosphine complex [Rh(cod)(MeCN)₂]BF₄ was found to be an efficient catalyst for the addition of PhSnMe₃, whereas [Rh(cod)(MeCN)₂]BF₄/dppb catalyzed the addition of Ph₄BNa to various N-sulfonyl aldimines in dioxane at 90°C. The scope and limitations of the reactions, as well as the effect of varying the reaction conditions, are discussed.

Full text of DOI:10.1016/S0022-328X(99)00562-8

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 595 (2000) 31–35
Rhodium-catalyzed phenylation of N-arylsulfonyl aldimines with
sodium tetraphenylborate or trimethyl(phenyl)stannane
Masato Ueda, Norio Miyaura *
Di6ision of Molecular Chemistry, Graduate School of Engineering, Hokkaido Uni6ersity, Sapporo 060-8628, Japan
Received 12 August 1999; accepted 10 September 1999
Abstract
The rhodium-catalyzed addition reactions of trimethyl(phenyl)stannane and sodium tetraphenylborate to N-phenylsulfonyl
aldimines RCHꢀNSO2Ph (R=alkyl and aryl) provided R(Ph)CHNHSO2Ph in high yields. A cationic and free phosphine complex
[Rh(cod)(MeCN)2]BF4 was found to be an efficient catalyst for the addition of PhSnMe3, whereas [Rh(cod)(MeCN)2]BF4/dppb
catalyzed the addition of Ph4BNa to various N-sulfonyl aldimines in dioxane at 90°C. The scope and limitations of the reactions,
as well as the effect of varying the reaction conditions, are discussed. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Rhodium-catalyzed phenylation; N-arylsulfonyl aldimines; Sodium tetraphenylborate; Trimethyl(phenyl)stannane
catalyzed carbon–carbon bond forming reactions. For
example, the cross-coupling reaction of organoboron
compounds involving the transmetalation to palladium-
(II) halides has proved to be a general technique for a
wide range of selective carbon–carbon bond-forma-
tions [9]. Although the metal-catalyzed addition reac-
tion of organoboron compounds has not yet been well
developed, the conjugate 1,4-addition of aryl- and 1-
alkenylboronic acids to a,b-unsaturated ketones [10,11]
and 1,2-addition to aldehydes [12] were recently found
to be efficiently catalyzed by a rhodium(I) complex
having a bidentate phosphine ligand with a large bite
angle (Eqs. (1) and (2)).
1. Introduction
The addition of the metal–carbon bond to the car-
bon–heteroatom double bond is a very popular reac-
tion in main metal reagents of lithium and magnesium
[1], but not much attention has been focused on the
corresponding reaction of transition-metal compounds.
However, the metal-catalyzed reactions, involving an
insertion of the carbon–heteroatom bond to the car-
bon–transition metal bond, were recently extensively
studied because the reactions are of interest due to their
potential application to asymmetric synthesis. The addi-
tions of arylstannanes [2,3] and arylsilanes [4] to alde-
hydes, ketones or imines are catalyzed by a rhodium
complex, Ni(acac)2/PPh3 catalyzes the methylation of
aldehydes with trimethylaluminum [5], and allylstan-
nanes [6,7] and allylsilanes [8] add to aldehydes and
imines in the presence of PdCl2(PPh3)2 or PtCl2(PPh3)2.
Organoboron compounds are highly electrophilic,
but the organic groups on boron are weakly nucleo-
philic, thus limiting the use of organoboron reagents
for the ionic reactions. However, organoboron com-
pounds, even organoboronic acids and esters, readily
transmetalate to other metals, thus allowing the metal-
(1)
(2)
The reaction proceeds in protic media or even in an
aqueous solution because both the B–C and the Rh–C
bonds are stable to water and alcohols. The asymmetric
1,4-additions using a chiral phosphine/rhodium com-
plex were also demonstrated [11]. Here we report our
first attempts to extend the protocol to the addition of
* Corresponding author. Fax: +81-11-706-6561.
E-mail address: miyaura@org-mc.eng.hokudai.ac.jp (N. Miyaura)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00562-8

32
M. Ueda, N. Miyaura / Journal of Organometallic Chemistry 595 (2000) 31–35
sodium tetraphenylborate and trimethyl(phenyl)stan-
nane to aldimines [13] (Eq. (3)).
2. Results and discussion
2.1. Addition of PhSnMe3 to aldimines
Various organometallic reagents which can trans-
metalate to rhodium(I) complexes will undergo the
1,2-addition to the C–N double bond. Among the
reagents examined, trimethyl(phenyl)stannane (2a) was
found to be an excellent reagent for phenylation of the
N-sulfonyl aldimine in the presence of a cationic
rhodium complex [Rh(cod)(MeCN)2]BF4 (3), but the
reaction was very slow with neutral rhodium complexes
such as Rh(acac)(CO)2 and Rh(acac)(CH2ꢀCH2)2, or
their combination with phosphine ligands. The addi-
tions of 2a to aldimines are summarized in Table 1.
The reaction readily proceeded in THF at 60°C in the
presence of 3 (3 mol%), but the addition of a phosphine
ligand slowed down the reaction significantly (entries
2–6). Higher yields were easily realized for N-sulfonyl
aldimines, but N-phenyl aldimine gave 58% of the
addition product (entry 9), the results of which were in
contrast to the similar reaction of Ph4BNa discussed
below (Table 3). The reaction has broad applicability
for various aldimines under aprotic conditions, but the
formation of toxic by-products may limit the use of
organostannanes for organic synthesis.
(3)
Table 1
Addition of trimethyl(phenyl)stannane (2a) to aldimines a
Entry
Imine
Catalyst
Yield
(%) b
1
2
3
4
5
6
7
8
9
PhCHꢀNSO2Ph
3
71
50
64
42
44
3/2PPh3
3/dppp c
3/dppb d
3/dppf e
3/(S)-binap f
57
4-MeOC6H4CHꢀNSO2Ph
4-FC6H4CHꢀNSO2Ph
PhCHꢀNPh
3
3
3
(72)
(89)
(56)
a A mixture of imine (1 mmol), PhSnMe2 (1.3 mmol), and catalyst
(0.03 mmol, 3 mol %) in THF was stirred for 16 h at 60°C.
b GC yields and isolated yields are in parentheses.
c 1,3-bis(diphenylphosphino)propane.
2.2. Addition of Ph4BNa to N-sulfonyl aldimines
The 1,2-addition of organoboronic acids to aldehydes
[12] and the 1,4-addition to a,b-unsaturated ketones
[10] afforded good results in an aqueous solvent (Eqs.
(1) and (2)). However, a similar addition reaction of
phenylboronic acid to N-sulfonyl aldimine 1 (R1=Ph,
R2=SO2Ph) at 80°C in DME/H2O (6/1) resulted in the
formation of diphenylmethanol (45%) through a se-
quence of hydrolysis of 1 with water and phenylation of
resulting benzaldehyde (Eq. (1)). Thus, sodium te-
traphenylborate 2b was chosen as the arylation reagent
of imines to carry out the reaction under anhydrous
conditions.
d 1,4-bis(diphenylphosphino)butane.
e 1,1%-bis(diphenylphosphino)ferrocene.
f (S)-2,2%-bis(diphenylphosphino)-1,1%-binaphthyl.
Table 2
Reaction conditions in the addtion of Ph4BNa (2b) to
PhCHꢀNSO2Ph a
Entry 2b
(equivalents)
Catalyst
Time (h) Yield
(%) b
The reaction conditions for the addition of 2b to
aldimines are summarized in Table 2. The imines did
not react with 2b at 90°C in the absence of a catalyst.
Both Rh(acac)(CH2ꢀCH2)2/dppb and [Rh(cod)2]BF4/
1
2
3
4
5
6
7
8
9
1.3
[Rh(acac)(C2H4)2/dppb c 16
40
50
77
97
79
76
99 (89)
87
61
[Rh(cod)2]BF4/dppb
3
16
16
16
16
16
3
dppb were ineffective (entries
1
and 2), but
3/2PPh3
[Rh(acac)(MeCN)2]BF4 (3) or its combination with a
phosphine ligand efficiently catalyzed the addition (en-
tries 3–9). The reaction smoothly proceeded in toluene
(76%) and dioxane (99%), but it was very slow in a
donating solvent such as DMF (18%). The rhodium-
catalyzed addition of organoboronic acids to aldehydes
(Eq. (1)) exhibited a pronounced effect of the phos-
phine ligand preferring the large bite angle (ÚPꢁRhꢁP)
[12]. Although there was no large difference in yields
between the representative ligands having various bite
3/dppec
3/dppp
3/dppb
3/dppf
3/(S)-binap
3/dppb
16
16
16
10
0.25
85
a A mixture of PhCHꢀNSO2Ph (1 mmol), Ph4BNa (0.5–1.3 mmol),
and catalyst (0.03 mmol, 3 mol %) in dioxane was stirred at 90°C.
b GC yields and isolated yields are in parentheses.
c 1,2-bis(diphenylphosphino)ethane.

M. Ueda, N. Miyaura / Journal of Organometallic Chemistry 595 (2000) 31–35
33
Table 3
products (entries 4–13). The reaction was not signifi-
cantly affected by the electronic effect of the sub-
stituents because both electron-rich and -deficient
aldimines gave similarly good results (entries 8–10),
which is in sharp contrast to the high electronic effect
observed in the addition of arylboronic acids to aro-
matic aldehydes [12]. The ortho-substituents retarded
the reaction, but it achieved 90% on prolongation the
reaction time to 16 h (entry 12). The addition to
alkylimines resulted in relatively low yields, but they
were not improved on prolongation of reaction time
(entry 13).
Rhodium-catalyzed addition of Ph4BNa (2b) to aldiminesa
Entry
Imine
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
PhCHꢀNC4H9
PhCHꢀNCH2Ph
PhCHꢀNPh
PhCHꢀNCOPh
PhCHꢀNSO2(4-ClC6H4)
PhCHꢀNSO2Ph
PhCHꢀNSO2(4-MeC6H5)
4-MeOC6H4CHꢀNSO2Ph
4-FC6H4CHꢀNSO2Ph
4-CF3C6H4CHꢀNSO2Ph
1-naphthylCHꢀNSO2Ph
2-MeC6H4CHꢀNSO2Ph
cyclo-C6H11CHꢀNSO2Ph
16
16
16
16
16
3
16
3
3
16
3
16
3
Trace
Trace
8
75
95
89
89
94
91
92
68
90
60
2.3. Reaction mechanism
Many transition-metal complexes catalyze the addi-
tion reactions of main metal reagents, but their mecha-
nism has not yet been studied in detail. However, the
transmetalation between the main metal reagents and
transition-metal complexes has been proposed as a key
step of the catalytic cycle [2–12]. Arylstannanes [14]
and sodium tetraarylborate [15,16] have been used for
the cross-coupling reaction with organic electrophiles
since they readily transmetalate to various transition-
metal halides such as palladium, platinum, and
rhodium. Thus, the present addition reaction to imines
should involve the transmetalation to the rhodium(I)
complex, which can be explained as follows: (i) the
transfer of the phenyl group of 2 to 3 produces phenyl-
rhodium(I) species 5, (ii) the insertion of the imine
double bond into the carbon–rhodium bond yields a
rhodium(I) amide 6, and finally, (iii) the transmetala-
tion between 2 and 6 produces 5 again (Fig. 1).
a A mixture of an imine (1 mmol), Ph4BNa (1.3 mmol), 3 and dppb
(0.03 mmol, 3 mol %) in dioxane was stirred at 90°C.
b Isolated yields based on the imines.
The arylrhodium(I) complexes are unstable such as
to preclude isolation in pure form [17], but they appar-
ently are involved in various coupling reactions with
organic halides [18] and the addition to alkenes and
alkynes [19] since they are stable to some extent in
solution. The insertion of imine into the carbon–
rhodium bond and the subsequent transmetalation be-
tween arylboron compounds and the rhodium amide 6
have not yet been previously studied, but the assumed
pathway may be consistent with other related addition
reactions of organostannanes and organosilanes [2–8].
The cationic rhodium complex 3 exhibited high catalyst
efficiency over the neutral complexes, probably due to
its high reactivity on the transmetalation with 2 or by
high Lewis acidity on the coordination of imine to the
rhodium metal center.
Fig. 1. Catalytic cycle.
angles, a combination of 3 and dppb achieved a quanti-
tative yield within 3 h (entry 7). The ligand-accelerated
reactions are of interest due to their potential applica-
tion to asymmetric synthesis (entry 9). Although the
reaction was studied in the presence of a stoichiometric
amount of 2b, all four phenyl groups in 2b can partici-
pate in the catalytic cycle because the addition of 0.25
equivalents of 2b achieved a comparable yield (entry
10).
The additions of 2b to the representative aldimines in
the presence of 3/dppb (3 mol %) are summarized in
Table 3. The insertion of imines into the carbon–
rhodium bond may involve the nucleophilic attack of
the aryl group to the CꢁN double bond. Thus, the
reaction was markedly slow for the N-butyl, N-benzyl
and N-phenylimine derivatives (entries 1–3), whereas
the addition to activated aldimines with N-sulfonyl and
N-benzoyl groups afforded high yields of the addition
3. Experimental
All the experiments were carried out under argon
1
atmosphere. H-NMR spectra were recorded in CDCl3
by a Jeol JNM-A400II (400 MHz) spectrometer using

34
M. Ueda, N. Miyaura / Journal of Organometallic Chemistry 595 (2000) 31–35
Me4Si as an internal standard. Mass spectra were ob-
tained with a Finnigan ITD 800 for the GC–MS
analyses and Jeol FABmate and Jeol HX110 for the
high-resolution analyses. GC analyses were performed
using a Hitachi G-5000 equipped with a glass column
(OV-17 on Uniport B, 2 m).
3.3.3. N-Benzoyldiphenylmethylamine
IR (Nujol): 3320, 2350, 1638, 1515, 1473 cm−1
.
1H-NMR (400 MHz, CDCl3): l 6.46 (d, J=7.8 Hz,
1H), 6.65 (d, J=7.8Hz, 1H), 7.27–7.37 (m, 10H), 7.44
(t, J=7.8 Hz, 2H), 6.51 (t, J=7.8 Hz, 1H), 7.82 (d,
J=7.8 Hz, 2H). Calc. for C20H17NO 288.1388, found
288.1376.
3.1. Materials and reagents
3.3.4. N-p-Chlorophenylsulfonyldiphenylmethylamine
IR (Nujol): 3240, 2345, 1308, 1166, 1162 cm−1
.
N-Arylsulfonyl aldimines [20,21] and N-(phenyl-
methylene)benzamide [22,23] were prepared by the liter-
ture procedures. Ph4BNa was dried in vacuo for 24 h at
110°C. The literature procedure gave [Rh(cod)(Me-
CN)2]BF4 [24].
1H-NMR (400 MHz, CDCl3): l 5.13 (d, J=7.3 Hz,
1H), 5.62 (d, J=7.3 Hz, 1H), 7.09–7.11 (m, 4H),
7.21–7.23 (m, 6H), 7.27 (d, J=8.5 Hz, 2H), 7.55 (d,
J=8.5 Hz, 2H). Calc. for C19H16NO2SClNa 380.0488,
found 380.0469 (FAB, m-nitrobenzyl alcohol, added
NaI).
3.2. General procedure for the addition of PhSnMe3
(Table 1)
3.3.5. N-p-Methylphenylsulfonyl diphenylmethylamine
The flask was charged with [Rh(cod)(MeCN)2]-
BF4(0.015 mmol) and imine (0.5 mmol), and flushed
with argon. THF (2 ml) and PhSnMe3 (0.65 mmol)
were successively added to the flask. After being stirred
at 60°C for 16 h, the reaction was quenched by addition
of water (2 ml). The product was extracted with ben-
zene, washed with water, and finally dried over MgSO4.
Chromatography over silica gel gave the corresponding
amines.
1
IR (Nujol): 3240, 2350, 1306, 1161 cm−1. H-NMR
(400 MHz, CDCl3): l 2.38 (s, 3H), 5.02 (d, J=7.1 Hz,
1H), 5.56 (d, J=7.1 Hz, 1H), 7.09–7.11 (m, 4H), 7.14
(d, J=8.3 Hz, 2H), 7.20–7.23 (m, 6H), 7.56 (d, J=8.3
Hz, 2H). Calc. for C20H20NO2S 338.1215, found
338.1236.
3.3.6. N-Phenylsufonyl-p-methoxyphenyl(phenyl)-
methylamine
IR (Nujol): 3240, 2995, 2305, 1492, 1295, 1228, 1156,
3.3. General procedure for the addition of Ph4BNa
(Tables 2 and 3)
1
1127 cm−1. H-NMR (400 MHz, CDCl3): l 3.75 (s,
3H), 4.99 (d, J=7.1 Hz, 1H), 5.56 (d, J=7.1 Hz, 1H),
6.74 (d, J=8.8 Hz, 2H), 6.99 (d, J=8.8 Hz, 2H),
7.08–7.11 (m, 2H), 7.17–7.22 (m, 3H), 7.35 (dd, J=
7.2, 8.3 Hz, 2H), 7.48 (t, J=7.2 Hz, 1H), 7.67 (d,
J=8.3 Hz, 2H). Calc. for C20H19NO3S 353.1085, found
353.1090.
The flask charged with [Rh(cod)(MeCN)2]BF4 (0.015
mmol), ligand (2PPh3, dppf, dppe, dppb, or dppb)
(0.015 mmol), N-arylsolfonylaldomine (0.5 mmol), and
Ph4BNa (0.65 mmol) was flushed with argon. Dioxane
(3 ml) was then added. After being stirred for 16 h at
90°C, water (2 ml) was added at room temperature.
The product was extracted with benzene, washed with
water, and dried over MgSO4. Chromatography over
silicagel gave the following amines.
3.3.7. N-Phenylsulfonyl-p-fluorophenyl(phenyl-
)methylamine
IR (Nujol): 3275, 3240, 2340, 1305, 1230, 1160 cm−1
.
1H-NMR (400 MHz, CDCl3): l 5.11 (d, J=7.,1 Hz,
1H), 5.58 (d, J=7.1 Hz, 1H), 6.89 (t, J=8.5 Hz, 2H),
7.04 (m, 4H), 7.20–7.24 (m, 4H), 7.36 (dd, J=7.3,
7.9Hz, 2H), 7.49 (t, J=7.3 Hz, 1H), 7.67 (d, J=7.9Hz,
2H). Calc. for C19H16NO2SFNa 364.0784, found
364.0764 (FAB, m-nitrobenzyl alcohol, added NaI).
3.3.1. N-Phenylsulfonyl diphenylmethylamine
1
IR (Nujol): 3230, 2340, 1350, 1160 cm−1. H-NMR
(400 MHz, CDCl3): l 5.01 (d, J=7.2 Hz, 1H), 5.61 (d,
J=7.2 Hz, 1H), 7.08–7.11 (m, 4H), 7.20–7.22 (m, 6H),
7.35 (t, J=7.8 Hz, 2H), 7.48 (t, J=7.8 Hz, 1H), 7.68
(d, J=7.8 Hz, 2H). Calc. for C19H17O2NS 323.0960,
found 323.0961.
3.3.8. N-Phenylsulfonyl-p-trifluoromethylphenyl-
(phenyl)methylamine
3.3.2. N-Phenyldiphenylmethylamine
IR (Nujol): 3250, 2340, 1320, 1158, 1130, 760 cm−1
.
IR (neat): 3400, 3060, 3030, 2450, 1700, 1605, 1503,
1H-NMR (400 MHz, CDCl3): l 5.30 (d, J=7.1 Hz,
1H), 5.63 (d, J=7.1 Hz, 1h), 7.02–7.04 (m, 2H), 7.21–
7.28 (m, 4H), 7.33–7.38 (m, 3H), 7.47 (t, J=8.0 Hz,
2H), 7.67 (d, J=8.0 Hz, 2H). Calc. for
C20H16F3NO2SNa 414.0752, found 414.0765 (FAB, m-
nitrobenzyl alcohol, added NaI).
1455, 1415, 1313, 1265, 1205 cm−1 1H-NMR (400
.
MHz, CDCl3): l 5.49 (s, 1H), 6.54 (d, J=8.5 Hz, 2H),
6.69 (t, J=7.3 Hz, 1H), 7.11 (dd, J=7.3 and 8.5 Hz,
2H), 7.24–7.27 (m, 4H), 7.30–7.37 (m, 6H). Calc. for
C19H17N 259.1361, found 259.1358.

M. Ueda, N. Miyaura / Journal of Organometallic Chemistry 595 (2000) 31–35
35
3.3.9. N-Phenylsulfonyl-1-napthylphenylmethylamine
References
1
IR (Nujol): 3245, 2340, 1308, 1155 cm−1. H-NMR
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7.3 Hz, 2H), 7.73 (d, J=8.1 Hz, 1H), 7.83 (d, J=9.0
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373.1134.
3.3.10. N-Phenylsufonyl-o-methylphenyl(phenyl)-
methylamine
IR (Nujol): 3250, 2340, 1318, 1302, 1147 cm−1
.
1H-NMR (400 MHz, CDCl3): l 2.17 (s, 3H), 4.99 (d,
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(m, 6H), 7.19–7.20 (m, 3H), 7.33 (t, J=7.8 Hz, 2H),
7.45 (t, J=7.8 Hz, 1H), 7.66 (d, J=7.8 Hz, 2H).
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3.3.11. N-Phenylsufonyl-cyclohexyl(phenyl)-
methylamine
IR (Nujol): 3270, 2375, 1320, 1160 cm−1. H-NMR
1
(400 MHz, CDCl3): l 1.05–1.17 (m, 3H), 1.28 (d,
J=12.7 Hz, 1H), 1.54–1.59 (m, 3H), 1.73 (d, J=
12.7 Hz, 1H), 1.95 (d, J=12.7 Hz, 1H), 4.06 (t, J=
8.1 Hz, 1H), 6.88–6.90 (m, 2H), 7.07–7.09 (m, 3H),
7.23 (d, J=7.6 Hz, 2H), 7.36 (dd, J=7.3, 7.6 Hz,
1H), 7.56 (d, J=7.3 Hz, 2H). Calc. for C19H23NO2S
329.1449, found 329.1469.
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Acknowledgements
We appreciate Professor M. Ochiai, University of
Tokushima, sending us the synthesis procedure for
N-sulfonyl imine derivatives.
.
.