Selective and mild synthesis of mono- and diarylated group 13-15 halides using [CuMes]n, a readily available, thermally stable organocopper(I) reagent

Article abstract of DOI:10.1021/om9901224

The use of mesitylcopper, a soluble, thermally stable arylcopper compound, was investigated as an alternative to less selective organolithium and Grignard reagents or toxic mercury, tin, and organozinc compounds. [CuMe]₅·toluene (1) was found to readily react with various main group metal halides MX_n and RMX_n (M = B, Sn; X = Cl, Br; R = nBu, Ph, 1,1′-fc) to give, depending on the stoichiometry of the reactions, monoarylated, diarylated, or mixed substituted species MesMX_n-1, Mes₂MX_n-2, and MesRMX_n-1 (2-5) in high yields.

Full text of DOI:10.1021/om9901224

2628
Organometallics 1999, 18, 2628-2632
Selective a n d Mild Syn th esis of Mon o- a n d Dia r yla ted
Gr ou p 13-15 Ha lid es Usin g [Cu Mes]n , a Rea d ily
Ava ila ble, Th er m a lly Sta ble Or ga n ocop p er (I) Rea gen t
Frieder J a¨kle and Ian Manners*
Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S
3H6 Canada
Received February 22, 1999
The use of mesitylcopper, a soluble, thermally stable arylcopper compound, was investi-
gated as an alternative to less selective organolithium and Grignard reagents or toxic
mercury, tin, and organozinc compounds. [CuMes]5‚toluene (1) was found to readily react
with various main group metal halides MXn and RMXn (M ) B, Sn; X ) Cl, Br; R ) nBu,
Ph, 1,1′-fc) to give, depending on the stoichiometry of the reactions, monoarylated, diarylated,
or mixed substituted species MesMXn-1, Mes2MXn-2, and MesRMXn-1 (2-5) in high yields.
In tr od u ction
molecules, respectively.12,22-26 Even mononuclear spe-
cies have been isolated when stabilized with phosphine,
sulfide, and alkyne donors.4,22,27-29 Despite extensive
studies on structural aspects, the unique bonding situ-
ation in organocopper compounds, and their use in
organic synthesis for C-C bond formation via organo-
copper intermediates, the use of copper reagents as alkyl
or aryl transfer reagents in organometallic synthesis has
been reported only for very few specific cases.30
Organocopper compounds have attracted considerable
attention during the past 20 years as a result of their
important role in carbon-carbon bond forming reactions
in organic syntheses.1,2 In most cases the organocopper
reagents have been reacted in situ without isolation of
the active copper species. This is not surprising in view
of the air and moisture sensitivity and the thermal
lability of many alkylcopper compounds. Arylcopper
compounds on the other hand show much higher
thermal stability, being perfectly stable at ambient
temperature under an inert atmosphere.3 Their thermal
stability strongly depends on the substitution pattern
at the aryl group. It has been shown in many cases that
in particular bulky substituents and heteroatom donors
in ortho position such as ethers, amines, or phosphines
lead to increased stability. As a consequence, a large
variety of thermally stable, well-defined aryl- and even
alkylcopper compounds have recently been synthesized
and structurally characterized.3-5 These studies have
shown that organocopper compounds either assemble
to small, soluble aggregates or form (insoluble) poly-
meric species. The formation of smaller aggregates is
favored by bulky substituents,5-13 chelating donor
substituents,14-21 and the presence of external donor
The most commonly used reagents for the introduc-
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Oxford, 1995; Vol. 12, Chapter 3.2.
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Comprehensive Organometallic Chemistry; Abel, E. W., Stone, F. G.
A., Wilkinson, G., Eds.; Pergamon Press: Oxford, 1995; Vol. 3, Chapter
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10.1021/om9901224 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 06/18/1999

Synthesis of Group 15 Halides Using [CuMes]n
Organometallics, Vol. 18, No. 14, 1999 2629
separated by filtration through a fritted glass disk and washed
with toluene. All volatile material was removed under high
vacuum, and the resulting crude product was analyzed by H
NMR spectroscopy. The ortho-methyl groups of the mesityl
moiety are very sensitive to the substitution pattern and allow
for facile distinction between mono-, di-, or trisubstituted
species.
Rea ction of Sn Cl4 w ith 1: Syn th esis of MesSn Cl3 (2a ).
Compound 2a was obtained from 1 (1.00 g, 4.97 mmol CuMes)
in toluene (30 mL) and SnCl4 (1.36 g, 5.22 mmol) in toluene
(10 mL) as a white solid in ca. 97% purity according to 1H NMR
spectroscopy. Recrystallization from hexanes at -55 °C gave
colorless needles of spectroscopically pure 2a (1.57 g, 92%).
Spectroscopic data for 2a are given in the literature.36,37
Rea ction of Sn Cl4 w ith 2 equ iv of 1: Syn th esis of
Mes2Sn Cl2 (2b). Compound 2b was obtained from 1 (10.08 g,
50.1 mmol CuMes) in toluene (200 mL) and SnCl4 (6.51 g, 25.0
mmol) in toluene (50 mL) as a white solid in greater than 97%
purity according to 1H NMR spectroscopy. Recrystallization
from hot toluene gave colorless needles of spectroscopically
pure 2b (9.30 g, 87%). Spectroscopic data for 2b are given in
the literature.36,37
nolithium and Grignard reagents. However, these highly
reactive species are often not selective enough to
exclusively produce mono- and disubstituted metal
complexes, respectively. Furthermore, their preparation
in ether solvents can lead to side reactions of the metal
halide with the solvent, particularly in the case of group
13 halides. Organomercury, zinc, or tin reagents on the
other hand are generally less reactive and more selective
and are therefore widely used. However, in view of their
toxicity alternative alkyl and aryl group transfer re-
agents are highly desirable. As part of our ongoing
interest in alkyl- and aryl-substituted main group
halides as precursors for the synthesis of [1]ferroceno-
phanes,31-33 we report in this paper on the general
applicability of thermally stable, isolable arylcopper
reagents for metathesis reactions with various main
group metal halides. To demonstrate the scope of
organocopper compounds as very selective and mild
arylating reagents, we have chosen mesitylcopper,
which can be prepared easily and on a large scale from
the respective Grignard species.12,23,24,34
1
Rea ction of n Bu Sn Cl3 w ith 1: Syn th esis of Mesn -
Bu Sn Cl2 (3a ). Compound 3a was obtained from 1 (0.81 g, 4.03
mmol CuMes) in toluene (30 mL) and nBuSnCl3 (1.20 g, 4.25
mmol) in toluene (10 mL) as a white solid in ca. 97% purity
according to 1H NMR spectroscopy. Recrystallization from hot
hexanes gave colorless needles of analytically pure 3a (1.31
g, 89%). For 3a : 1H NMR (300 MHz, CDCl3, 20 °C) δ ) 6.95
(s/d, J (117/119Sn, H) ) 34 Hz, 2 H, meta-Mes), 2.56 (s/d,
J (117/119Sn, H) ) 9 Hz, 6 H, ortho-Me), 2.30 (s/d, J (117/119Sn, H)
) 5 Hz, 3 H, para-Me), 2.0-1.8, 1.51 (m, m, 4 H, 2H, CH2-
CH2CH2), 0.98 (t, J (H, H) ) 7.1 Hz, 3 H, Me); 13C NMR (75.5
MHz, CDCl3, 20 °C) δ ) 143.7 (s/d, J (117/119Sn, 13C) ) 59, 62
Hz, ortho-Mes), 141.8 (s/d, J (117/119Sn, 13C) ) 14 Hz, para-Mes),
137.1 (ipso-Mes), 129.2 (s/d, J (117/119Sn, 13C) ) 70, 73 Hz, meta-
Mes), 30.4 (s/d, J (117/119Sn, 13C) ) 469, 491 Hz, Sn-CH2), 26.7
(s/d, J (117/119Sn, 13C) ) 42 Hz, CH2), 26.0 (s/d, J (117/119Sn, 13C)
) 102, 107 Hz, CH2), 24.8 (s/d, J (117/119Sn, 13C) ) 45 Hz, ortho-
Me), 21.1 (para-Me), 13.5 (s, CH3); 119Sn NMR (111.8 MHz,
CDCl3, 20 °C) δ ) 38.3; m/z (%) 331 (65) [M+ - Cl], 309 (100)
[M+ - nBu], 274/273 (33) [MesSnCl+/MesSnCl+ - H], 239/238
(34) [MesSn+/MesSn+ - H]; C13H20Cl2Sn (365.92) calcd C 42.67,
H 5.51; found C 42.74, H 5.51.
Exp er im en ta l Section
The compounds Me3SnCl, Me2SnCl2, nBuSnCl3, PhSnCl3,
SnCl4, BCl3, and PCl3 were purchased from Aldrich and were
used without further purification. 1,1′-fc(BBr2)2 was synthe-
sized from ferrocene and BBr3 in hexanes according to a
literature procedure.35 [CuMes]5‚toluene (1) was synthesized
from MesMgBr and CuCl in THF and recrystallized from
toluene according to a literature procedure.12 Compound 1 is
also commercially available from Alfa AESAR. All reactions
and manipulations were carried out under an atmosphere of
prepurified nitrogen using either Schlenk techniques or an
inert-atmosphere glovebox (Vacuum Atmospheres). Solvents
were dried over sodium/benzophenone and freshly distilled
prior to use. 1H NMR spectra of 200, 300, or 400 MHz and
50.3, 75.5, or 100.5 MHz 13C NMR spectra were recorded on
either a Varian XL200, a Varian XL300, or a Unity 400
spectrometer, respectively. 119Sn (111.8 MHz) and 11B (160.4
MHz) NMR spectra were recorded on a Varian XL 300 and a
Unity 500 spectrometer, respectively. All solution 1H and 13C
NMR spectra were referenced externally to TMS. 119Sn and
11B NMR spectra were referenced externally to SnMe4 and to
BF3‚Et2O, respectively. Mass spectra were obtained with the
use of a VG 70-250S mass spectrometer operating in an
electron impact (EI) mode. Elemental analyses were performed
by Quantitative Technologies Inc., Whitehouse, NJ .
Rea ction of P h Sn Cl3 w ith 1: Syn th esis of MesP h Sn Cl2
(3b). Compound 3b was obtained from 1 (1.00 g, 4.97 mmol
CuMes) in toluene (30 mL) and PhSnCl3 (1.58 g, 5.22 mmol)
in toluene (10 mL) as a colorless oil in ca. 95% purity according
1
to H NMR spectroscopy. Recrystallization from hot hexanes
gave large colorless needles of analytically pure 3b (1.63 g,
85%). For 3b: 1H NMR (400 MHz, CDCl3, 20 °C) δ ) 7.76 (m,
2 H, ortho-Ph), 7.51 (m, 3 H, meta-Ph, para-Ph), 6.95 (s/d,
J (117/119Sn, H) ) 28 Hz, 2 H, meta-Mes), 2.52 (s/d, J (117/119Sn,
H) ) 10 Hz, 6 H, ortho-Me), 2.29 (s, 3 H, para-Me); 13C NMR
(75.5 MHz, CDCl3, 20 °C) δ ) 144.2 (s/d, J (117/119Sn, 13C) ) 60,
62 Hz, ortho-Mes), 142.6 (ipso-Mes), 142.1 (s/d, J (117/119Sn, 13C)
) 15 Hz, para-Mes), 135.2 (ipso-Ph), 134.3 (s/d, J (117/119Sn, 13C)
) 62, 64 Hz, ortho-Ph), 131.1 (s/d, J (117/119Sn, 13C) ) 17 Hz,
para-Ph), 129.6 (s/d, J (117/119Sn, 13C) ) 81, 84 Hz, meta-Ph),
129.4 (s/d, J (117/119Sn, 13C) ) 79, 82 Hz, meta-Mes), 25.3 (s/d,
J (117/119Sn, 13C) ) 48 Hz, ortho-Me), 21.1 (s/d, J (117/119Sn, 13C)
) 9 Hz, para-Me); 119Sn NMR (111.8 MHz, C6D6, 20 °C) δ )
-40.9; m/z (%) 386 (20) [M+], 351 (36) [M+ - Cl], 308 (100)
[M+ - Ph - H]; C15H16Cl2Sn (385.91) calcd C 46.69, H 4.18;
found C 46.86, H 4.16.
Gen er a l Syn th etic P r oced u r e. A solution of the chosen
element halide in toluene was added slowly to a freshly
prepared solution of 1 in toluene at -30 °C (tin halides) and
-78 °C (boron halides), respectively. The reaction mixture was
slowly warmed to room temperature, stirred for 12 h, and
heated to 50 °C for 1 h. An amber-orange precipitate formed
initially, which gradually turned white (exception: in the
reaction of 1 with PCl3 an orange solid was not observed, but
a white precipitate formed slowly). The copper halide was
(30) van Koten, G.; Noltes, J . G. In Comprehensive Organometallic
Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon
Press: Oxford, 1982; Vol. 2, Chapter 14.
(31) Braunschweig, H.; Dirk, R.; Mu¨ller, M.; Nguyen, P.; Resendes,
R.; Gates, D. P.; Manners, I. Angew. Chem., Int. Ed. Engl. 1997, 36,
2338.
(32) Rulkens, R.; Lough, A. J .; Manners, I. Angew. Chem., Int. Ed.
Engl. 1996, 35, 1805.
(33) J a¨kle, F.; Rulkens, R.; Zech, G.; Foucher, D. A.; Lough, A. J .;
Manners, I. Chem. Eur. J . 1998, 4, 2117.
Rea ction of BCl3 w ith 1: Syn th esis of MesBCl2 (4).
Compound 4 was obtained from 1 (1.00 g, 4.97 mmol CuMes)
(34) Tsuda, T.; Yazawa, T.; Watanabe, K.; Fujii, T.; Saegusa, T. J .
Org. Chem. 1981, 46, 192.
(35) Ruf, W.; Renk, T.; Siebert, W. Z. Naturforsch. 1976, 31b, 1028.
(36) Berwe, H.; Haas, A. Chem. Ber. 1987, 120, 1175.
(37) Brown, P.; Mahon, M. F.; Molloy, K. C. J . Organomet. Chem.
1992, 435, 265.

2630 Organometallics, Vol. 18, No. 14, 1999
J a¨kle and Manners
Ta ble 1. NMR Sp ectr oscop ic a n d Isola ted Yield s
for Rea ction s of 1 w ith Ma in Gr ou p Elem en t
Ha lid es MXn
in toluene (30 mL) and BCl3 (1 M in hexane, 5.2 mL, 5.2 mmol)
as a colorless liquid in greater than 97% purity according to
1H NMR spectroscopy. Distillation under reduced pressure
gave 4 (0.88 g, 88%). For 4: C9H11BCl2 (200.90) calcd C 53.81,
H 5.51; found C 54.54, H 5.70; spectroscopic data for 4 are
given in the literature.38
isolated
MXn (equiv)
SnCl4 (1.05)
product
yield (%)a yield (%)
MesSnCl3 (2a )
Mes2SnCl2 (2b)
MesnBuSnCl2 (3a )
MesPhSnCl2 (3b)
MesBCl2 (4)
97
>97
97
92
87
89
85
88
72
Rea ction of 1,1′-fc(BBr 2)2 w ith 2 equ iv of 1: Syn th esis
of 1,1′-fc(BBr Mes)2 (5). Compound 5 was obtained from 1
(1.53 g, 7.62 mmol CuMes) in toluene (50 mL) and 1,1′-fc-
(BBr2)2 (2.00 g, 3.81 mmol) in toluene (50 mL) as a red oil in
ca. 97% purity according to 1H NMR spectroscopy. Recrystal-
lization from hexanes gave red crystals of analytically pure 5
(1.66 g, 72%). For 5: 1H NMR (400 MHz, C6D6, 20 °C) δ )
6.68 (s, 4 H, meta-Mes), 4.53 (m, 8 H, Cp), 2.25 (s, 12 H, ortho-
Me), 2.13 (s, 6 H, para-Me); 13C NMR (100.5 MHz, C6D6, 20
°C) δ ) 138.9 (para-Mes), 138.4 (ortho-Mes), 128.4 (meta-Mes),
77.9, 77.5 (Cp), 23.0 (ortho-Me), 21.2 (para-Me), not observed
(ipso-Me, ipso-Cp); 11B NMR (160.4 MHz, C6D6, 20 °C) δ ) 68.0
(h1/2 ) 1000 Hz); m/z (%) 604 (100) [M+]; C28H30B2Br2Fe
(603.82) calcd C 55.70, H 5.01; found C 55.15, H 4.96.
SnCl4 (0.50)
nBuSnCl3 (1.05)
PhSnCl3 (1.05)
BCl3 (1.05)
95
>97
1,1′-fc(BBr2)2 (0.50) 1,1′-fc(BBrMes)2 (5)
97
PCl3 (1.05)
PCl3 (2.00)
MesPCl2 (6)
MesPCl2 (6)
60
95
82
a
Estimated yield from 1H NMR spectroscopy.
formation of 8b and the presence of unreacted 1 (mixture of
tetramer and pentamer) in equimolar amounts. One further
species was identified in the reaction mixture. This compound
showed broad signals in the 1H NMR spectum and did not
1
show a 119Sn NMR signal. H NMR (200 MHz, C6D6, 20 °C):
Rea ction of P Cl3 w ith 1: Syn th esis of MesP Cl2 (6). (i)
Equimolar reaction of 1 (1.00 g, 4.97 mmol CuMes) in toluene
(30 mL) and PCl3 (0.72 g, 5.24 mmol) in toluene (10 mL) gave
ca. 60% 6 and 40% Mes2PCl (7) according to 1H NMR
spectroscopy of the crude product. (ii) Reaction of 1 (1.00 g,
4.97 mmol CuMes) in toluene (30 mL) with 2 equiv of PCl3
(1.37 g, 9.98 mmol) in toluene (10 mL) gave 6 in ca. 95% yield
according to 1H NMR spectroscopy of the crude product.
Distillation under reduced pressure gave spectroscopically
pure 6 (0.90 g, 82%).39
δ ) 6.59 (br, 2 H, meta-Mes), 2.71 (br, 6 H, ortho-Me), 1.94
(br, 3 H, para-Me); 13C NMR (50.3 MHz, C6D6, 20 °C) δ ) 154.9
(br, ortho-Mes), 141.9 (br, para-Mes), 126.9 (br, meta-Mes), 29.1
(ortho-Me), 21.3 (para-Me), not observed (ipso-Mes).
(c) Rea ction of Me3Sn Cl w ith 1 equ iv of 1: Syn th esis
of Me3Sn Mes (8b). A solution of Me3SnCl (0.25 g, 1.25 mmol)
in toluene (10 mL) was added slowly to a solution of 1 (0.25 g,
1.24 mmol CuMes) in toluene (30 mL) at room temperature,
stirred for 12 h, and heated to 50 °C for 1 h. A gray-green
precipitate formed, which was separated from the colorless
solution by filtration and washed with toluene (2 × 10 mL).
The combined filtrates were passed through a column (neutral
alumina with toluene as eluent), and all volatile material was
removed under vacuum to give spectroscopically pure 8b as a
colorless oil (0.30 g, 86%). For 8b: 1H NMR (300 MHz, C6D6,
20 °C) δ ) 6.77 (s/d, J (117/119Sn, H) ) 16 Hz, 2 H, meta-Mes),
2.29 (s/d, J (117/119Sn, H) ) 6 Hz, 6 H, ortho-Me), 2.15 (s, 3 H,
para-Me), 0.31 (s/d, J (117/119Sn, H) ) 51, 53 Hz, 9 H, Sn-CH3);
13C NMR (50.3 MHz, C6D6, 20 °C) δ ) 144.8 (s/d, J (117/119Sn,
13C) ) 34 Hz, ortho-Mes), 138.1 (s/d, J (117/119Sn, 13C) ) 9 Hz,
para-Mes), 137.6 (ipso-Mes), 128.2 (s/d, J (117/119Sn, 13C) ) 43
Hz, meta-Mes), 25.7 (s/d, J (117/119Sn, 13C) ) 32 Hz, ortho-Me),
21.1 (para-Me), -5.2 (s/d, J (117/119Sn, 13C) ) 322, 337 Hz, Sn-
CH3); 119Sn NMR (111.8 MHz, C6D6, 20 °C) δ ) -52.3; m/z (%)
Attem p ts to Isola te a n In ter m ed ia te [Ar Cu ‚Cu X]n . (a )
R ea ct ion of Me2Sn Cl2 w it h 2 eq u iv of 1: Syn t h esis of
Me2Sn Mes2 (8a ). A solution of Me2SnCl2 (0.30 g, 1.37 mmol)
in toluene (10 mL) was added to a solution of 1 (0.55 g, 2.73
mmol CuMes) in toluene (30 mL) at -30 °C. The reaction
mixture was slowly warmed to room temperature and stirred
for 2 h. A slightly gray precipitate formed, which was sepa-
rated from a colorless solution by filtration and washed with
toluene (2 × 10 mL). The combined filtrates were analyzed by
1H NMR spectroscopy, indicating the exclusive formation of
disubstituted species 8a . Column chromatography of the crude
product (neutral alumina with toluene as eluent) followed by
removal of all volatile material under vacuum gave spectro-
scopically pure 8a as a colorless oil (0.40 g, 75%). For 8a : 1H
NMR (300 MHz, C6D6, 20 °C) δ ) 6.74 (s/d, J (117/119Sn, H) )
16 Hz, 4 H, meta-Mes), 2.32 (s/d, J (117/119Sn, H) ) 6 Hz, 12 H,
ortho-Me), 2.12 (s, 6 H, para-Me), 0.59 (s/d, J (117/119Sn, H) )
50, 53 Hz, 6 H, Sn-CH3); 13C NMR (75.5 MHz, C6D6, 20 °C) δ
) 144.4 (s/d, J (117/119Sn, 13C) ) 33 Hz, ortho-Mes), 139.9 (ipso-
Mes), 138.0 (para-Mes), 128.5 (s/d, J (117/119Sn, 13C) ) 42 Hz,
meta-Mes), 25.5 (s/d, J (117/119Sn, 13C) ) 32 Hz, ortho-Me), 21.1
(para-Me), -1.6 (s/d, J (117/119Sn, 13C) ) 324, 338 Hz, Sn-CH3);
119Sn NMR (111.8 MHz, C6D6, 20 °C) δ ) -100.6; m/z (%) 387
(2) [M+ - H], 373 (100) [M+ - Me], 269/268 (41) [M+ - Mes/
M+ - Mes - H], 274/273 (33) [MesSnCl+/MesSnCl+ - H], 239/
238 (34) [MesSn+/MesSn+ - H]; C20H28Sn (387.15) calcd C
62.05, H 7.29; found C 62.58, H 7.21.
284 (2) [M+], 269 (100) [M+ - Me], 239 (38) [MesSn+]; C12H20
Sn (283.00) calcd C 50.93, H 7.12; found C 50.92, H 7.35.
-
Resu lts a n d Discu ssion
In a general procedure, a freshly prepared solution
of [CuMes]5‚toluene (1) was reacted with the chosen
metal halide at -30 °C in toluene, and the reaction
mixture was stirred for 12 h at room temperature and
heated to 50 °C for 1 h. After filtration from the
insoluble copper halide all volatile material was re-
moved under vacuum. The crude product was analyzed
by 1H NMR spectroscopy prior to recrystallization or
distillation. Results for the reaction of 1 with selected
group 13-15 metal halides in toluene solution are
summarized in Table 1. Both the yields as determined
(b) Rea ction of Me3Sn Cl w ith 2 equ iv of 1. A solution
of Me3SnCl (0.25 g, 1.25 mmol) in toluene (10 mL) was added
to a solution of 1 (0.50 g, 2.49 mmol CuMes) in toluene (30
mL) at -30 °C, slowly warmed to room temperature, and
stirred for 2 days. An amber precipitate formed, which
gradually turned gray-green. The solid material (ca. 100 mg)
was separated from a yellow solution by filtration and was
washed with toluene (2 × 10 mL). The combined filtrates were
analyzed by 1H and 119Sn NMR spectroscopy, indicating the
1
by H NMR spectroscopy and the isolated yields after
recrystallization or distillation of the compounds are
given based on one unit of CuMes.
Alkyl or aryl groups are usually introduced to tin
halides through reaction with Grignard reagents or
lithium or aluminum organyls.40 However, selective
(38) Schacht, W.; Kaufmann, D. Chem. Ber. 1987, 120, 1331.
(39) 6 was previously synthesized from PCl3 and MesMgBr in ca.
80% yield; see: Xie, Z.-M.; Neilson, R. H. Organometallics 1983, 2,
921.
(40) Davies, A. G., Ed. Organotin Chemistry; VCH: Weinheim, New
York, Basel, Cambridge, Tokyo, 1997.

Synthesis of Group 15 Halides Using [CuMes]n
Organometallics, Vol. 18, No. 14, 1999 2631
Sch em e 1: Rea ction of 1 w ith Sn Cl4 a n d
Or ga n otin tr ich lor id es RSn Cl3
Sch em e 2: Rea ction of 1 w ith MCl3 (M ) B, P ) a n d
1,1′-fc(BBr 2)2
We were interested to see whether the use of 1 would
also be advantageous for the introduction of mesityl
groups to group 13 and group 15 halides. Reaction of 1
with BCl3 gave 4 as the only NMR spectroscopically
detectable product, which was isolated in 88% yield after
distillation (Scheme 2).46,47 Compound 1 can also be used
for the synthesis of mixed diorganohaloboranes, as
shown for the reaction of 1,1′-fc(BBr2)2 (fc ) Fe(η-C5H4)2)
partial substitution is in most cases difficult to achieve.
An alternative route involves a two-step procedure of
arylation to the tetraorganostannane and subsequent
dearylation via selective cleavage of Sn-C bonds with
halogens X2, halogen acids HX, or tin halides (Kochesh-
kov disproportion reaction). Milder reagents with metals
such as mercury, zinc, or copper allow for the use of
functionalized substituents and provide more selective
substitution. Organocopper reagents [ArCu]n (Ar )
2-CHRNMe2Ph) with donor substituents in ortho-posi-
tion were introduced by van Koten and co-workers for
the preparation of pentacoordinate and hexacoordinate
organotin compounds ArRSnX2 and Ar2SnX2,41,42 in-
cluding chiral compounds ArRR′SnX.43,44 Furthermore,
formation of the trisubstituted stannanes Ph3SnX and
Me2PhSnX from phenylcopper was found to proceed
very selectively.41 Despite these encouraging initial
reports organocopper reagents were not further consid-
ered in the synthesis of organotin compounds.
1
with 2 equiv of the copper reagent. H NMR spectros-
copy revealed the formation of 1,1′-fc(BBrMes)2 (5) in
ca. 97% yield. However, the isolated yield after recrys-
tallization from hexanes (72%) was significantly lower
due to the high solubility of 5. Surprisingly, reaction of
1 with one equiv PCl3 did not proceed with similar
chemoselectively and gave substantial amounts of Mes2-
PCl (7; 40%) in addition to MesPCl2 (6; 60%) (Scheme
2). However, when an excess of PCl3 was used (2 equiv),
6 was formed almost exclusively and was isolated in
82% yield after distillation.39
Mesityltin trichloride (2a ) was previously synthesized
by two different synthetic pathways. Reaction of mesi-
tyllithium and tin tetrachloride gave 40% of 2a after
fractionational distillation.45 In another attempt 2a was
prepared via redistribution between dimesityltin dichlo-
ride (2b) and tin tetrachloride in 62% yield after
distillation.36 Compound 2b on the other hand was
synthesized from dimesitylmercury and tin(II) chloride
in 53% yield after recrystallization.36 Preparation of 2b
from mesityllithium and tin tetrachloride gave this
compound in only 21% yield.37 We found that if 1 is used
as the arylating agent, spectroscopically pure 2a and
2b are obtained in 92 and 87% yield, respectively, after
a single recrystallization step (Scheme 1, Table 1). The
same synthetic method can be applied to synthesize
diorganodichlorostannanes with two different substit-
uents (Scheme 1). Reaction of 1 with nBuSnCl3 and
PhSnCl3 gave 3a and 3b in 89 and 85% isolated yield,
respectively. A small excess of the tin species (1.05
equiv) avoids formation of any trisubstituted compound,
whereas the tin reagent can easily be removed in high
vacuum or by one recrystallization step from hexanes.
Van Koten and co-workers previously reported the
initial formation of a red precipitate for the reaction of
R2SnX2 (R ) Me, Ph; X ) Cl, Br) with donor-substituted
phenylcopper derivatives [ArCu]n.41 This precipitate was
found to be a 1/1 complex of the organocopper compound
with cuprous halide ([ArCu‚CuX]n).41,48 The high selec-
tivity in these arylation reactions was therefore ascribed
not only to the steric bulk of the aryl group but also to
the formation of such an aggregate lowering the reactiv-
ity of the Cu-C bond toward the Sn-X bonds.41 Reac-
tion of 1 with tin and boron halides initially led to the
formation of an orange-amber precipitate, which gradu-
ally turned white upon stirring at room temperature.
With SnCl4, BCl3, and 1,1′-fc(BBr2)2 formation of a
precipitate was observed at the addition temperature,
whereas with RSnCl3 precipitation occurred at higher
temperatures, but still below 25 °C. Complete conver-
sion as evidenced by a color change to white required
prolonged reaction times or even slight heating (50 °C).
These observations prompted us to elucidate the pos-
sible formation of an aggregate [MesCu‚CuX]n as reac-
tion intermediate in analogy with van Koten’s results.
(41) Van Koten, G.; Schaap, C. A.; Noltes, J . G. J . Organomet. Chem.
1975, 99, 157.
(42) Van Koten, G.; J astrzebski, J . T. B. H.; Noltes, J . G. J .
Organomet. Chem. 1979, 177, 283.
(43) van Koten, G.; Noltes, J . G. J . Am. Chem. Soc. 1976, 98, 5393.
(44) van Koten, G.; J astrzebski, J . T. B. H.; Noltes, J . G.; Pontenagel,
W. M. G. F.; Kroon, J .; Spek, A. L. J . Am. Chem. Soc. 1978, 100, 5021.
(45) Weidenbruch, M.; Scha¨fers, K.; Schlaefke, J .; Peters, K.; von
Schnering, H. G. J . Organomet. Chem. 1991, 415, 343.
(46) The synthesis of MesBCl2 was previously described from tris-
(2,4,6-trimethylphenyl)boroxin and BCl3 in 22% yield; see ref 38.
(47) Organomercury compounds are the most commonly used re-
agents for the selective arylation of boron halides; see: Niedenzu, K.
Organomet. Chem. Rev. 1966, 1, 305.
(48) van Koten, G.; Noltes, J . G. J . Organomet. Chem. 1975, 84, 419.

2632 Organometallics, Vol. 18, No. 14, 1999
J a¨kle and Manners
Sch em e 3: Rea ction of Me2Sn Cl2 a n d Me3Sn Cl
w ith 2 equ iv of 1
contained a 1/1 mixture of 8b and 1. We conclude that,
even though it may initially form, a complex [MesCu‚
CuCl]n is not a stable intermediate in the described
metathesis reactions.49 The presence of donor substit-
uents on the aryl group seems to be essential in order
to stabilize such an aggregate.41 The observed high
chemoselectivity of 1 in reactions with tin and boron
halides may therefore primarily be attributed to the
steric bulk of the mesityl substituent and to the high
degree of aggregation of 1 in solution (tetrameric and
pentameric structure).
When Me2SnCl2 was treated with 2 equiv of CuMes
under similar conditions as applied by van Koten and
co-workers,41 quantitative formation of Me2SnMes2 (8a )
was observed and a reaction intermediate could not be
isolated (Scheme 3). Treatment of Me3SnCl with 2 equiv
of CuMes resulted in the formation of Me3SnMes (8b)
Ack n ow led gm en t. We wish to thank the donors of
the Petroleum Research Fund (PRF), administered by
the American Chemical Society, for financial support
of this work. We also wish to acknowledge a Deutsche
Forschungsgemeinschaft (DFG) postdoctoral fellowship
for F.J ., and I.M. is grateful to the National Science and
Engineering Research Council of Canada (NSERC) for
an E. W. R. Steacie Fellowship (1997-1999) and the
University of Toronto for a McLean Fellowship (1997-
2003).
1
and a gray precipitate (Scheme 3). However, H NMR
spectroscopy indicated that only 1 equiv CuMes was
used, and the soluble part of the reaction mixture
(49) The observed orange color of the precipitate in reactions with
1 may possibly be due to the presence of trace amounts of oxygen
resulting in an orange-red cluster compound [Cu10O2(Mes)6]: Håkans-
son, M.; O¨ rtendahl, M.; J agner, S.; Sigalas, M. P.; Eisenstein, O. Inorg.
Chem. 1993, 32, 2018.
OM9901224