A comparative study of base-free arylcopper reagents for the transfer of aryl groups to boron halides

Article abstract of DOI:10.1016/S0022-328X(03)00588-6

A comparative study on the reactivity and selectivity of arylcopper species in reactions with boron halides was performed. Mesitylcopper reacts with BX₃ (X=Cl, Br) in toluene at low temperature under highly selective formation of the monosubstituted boranes MesBX₂. The dimesitylboranes Mes₂BX are gradually formed with a twofold excess of the organocopper reagent at elevated temperature. In contrast, pentafluorophenylcopper shows a tendency for formation of B(C₆F₅) ₃ in reactions with BX₃ irrespective of the stoichiometry used, suggesting a strong impact of electronic factors on the selectivity of the aryl transfer reaction. New procedures for the synthesis of the pentafluorophenylboron halides C₆ F₅BX₂ (X=Cl: 57%; X=Br: 62%) and of tris(pentafluorophenyl)borane (80%) and related mixed-substituted triarylboranes from the base-free isolable pentafluorophenylcopper precursor have been developed.

Full text of DOI:10.1016/S0022-328X(03)00588-6

Journal of Organometallic Chemistry 681 (2003) 134ꢁ142
/
www.elsevier.com/locate/jorganchem
A comparative study of base-free arylcopper reagents for the transfer
of aryl groups to boron halides
Anand Sundararaman, Frieder Jakle *
¨
Department of Chemistry, Rutgers University-Newark, 73 Warren Street, Newark, NJ 07102, USA
Received 18 March 2003; received in revised form 13 June 2003; accepted 17 June 2003
Abstract
A comparative study on the reactivity and selectivity of arylcopper species in reactions with boron halides was performed.
Mesitylcopper reacts with BX3 (XꢀCl, Br) in toluene at low temperature under highly selective formation of the monosubstituted
/
boranes MesBX2. The dimesitylboranes Mes2BX are gradually formed with a twofold excess of the organocopper reagent at
elevated temperature. In contrast, pentafluorophenylcopper shows a tendency for formation of B(C6F5)3 in reactions with BX3
irrespective of the stoichiometry used, suggesting a strong impact of electronic factors on the selectivity of the aryl transfer reaction.
New procedures for the synthesis of the pentafluorophenylboron halides C6F5BX2 (Xꢀ
/
Cl: 57%; XꢀBr: 62%) and of
/
tris(pentafluorophenyl)borane (80%) and related mixed-substituted triarylboranes from the base-free isolable pentafluorophenyl-
copper precursor have been developed.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Boron; Copper; Organoborane; Organocopper reagent; Arylation; Lewis acid
1. Introduction
limited to very strong electrophiles such as boron
tribromide or boron trichloride [3]. Furthermore, the
The most commonly used reagents for the introduc-
tion of aryl substituents to main group metal halides are
organolithium and Grignard reagents. However, these
highly reactive species are often not selective enough to
exclusively produce partially arylated mixed-substituted
metal complexes. In addition, their preparation in ether
solvents can lead to side reactions of the metal halide
with the solvent. This problem is frequently encountered
in reactions involving Group 13 halides [1]. Less reactive
and more selective reagents such as organomercury,
organozinc, organotin, or organosilicon species have
therefore been developed and are now being widely used
[1]. However certain limitations also restrict the general
applicability of these reagents as, for example, mercury
boron or zinc boron exchange reactions often require
use of siliconꢁ
can in certain cases be hampered by preferred transfer of
the alkyl substituents in ArSiMe3 or ArSnMe3 over the
/
boron and tinꢁboron exchange reactions
/
desired reaction of the siliconÃ
/
aryl bond [4]. We are
currently exploring the application of arylcopper re-
agents for the selective transfer of aryl groups to Group
13 halides as part of our studies aimed at the develop-
ment of new multifunctional and polymeric Lewis acids
[4d,5]. The use of organocopper reagents may provide
an interesting option in this chemistry especially in view
of the high toxicity of organomercury and organotin
species.
Despite extensive studies on structural aspects, the
unique bonding situation in organocopper compounds,
and their widespread applications in organic synthesis
high temperatures [2] and siliconꢁboron exchange is
/
for carbonÃ/carbon bond formation via organocopper
intermediates [6], the use of organocopper reagents as
alkyl or aryl transfer reagents in organometallic synth-
esis has been studied only in very few specific cases.
Most notably, van Koten and coworkers have intro-
* Corresponding author. Tel.: ꢂ
1264.
/
1-973-353-5064; fax: ꢂ1-973-353-
/
E-mail address: fjaekle@andromeda.rutgers.edu (F. Jakle).
¨
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00588-6

A. Sundararaman, F. Jakle / Journal of Organometallic Chemistry 681 (2003) 134ꢁ
/
142
135
¨
duced organocopper reagents [ArCu]n (Arꢀ
/
2-
2.1. Reactivity of mesitylcopper toward boron halides
[15,16]
Me2NCH(Me)C6H4) with donor substituents in ortho-
position for the preparation of hypercoordinate orga-
notin compounds ArRSnX2 and Ar2SnX2 [7] including
chiral species ArRR?SnX [8]. Furthermore, formation of
the trisubstituted tin halides Ph3SnX and Me2PhSnX
from phenylcopper was found to proceed with high
selectivity [7a]. Even monosubstituted organotin halides
ArSnCl3 are accessible in very high yield when the
bulkier mesityl group is used [9]. However, few studies
on the reactivity of organocopper species toward Group
13 halides have been undertaken [10,11].
A number of different routes for the synthesis of
mesityldichloroborane (3a) and mesityldibromoborane
(3b) in moderate to high yields have been previously
described. These include reactions of mesitylboroxin
(22%) [17], mesitylmercuric bromide (49%) [18], or
mesityltrimethylsilane (75ꢁ84%) [3b,3c] with BCl3 or
/
BBr3. However, in the series of dimesitylboron halides,
the only thoroughly studied compound is dimesityl-
boron fluoride, which is obtained through reaction of
We report in this paper on the influence of electronic
characteristics of organocopper reagents on the reactiv-
ity and selectivity in metathesis reactions with boron
halides. In order to account for electronic effects, we
undertook a detailed comparative study of two arylcop-
per species, mesitylcopper [12] and pentafluorophenyl-
copper [13], which feature similar steric yet very
different electronic properties. An impact of the electro-
nic characteristics on the reactivity may be expected as,
for example, structural aspects of organocopper species
are known to strongly depend on the nature of the
organic substituents [6]. Indeed, we have recently
discovered that pentafluorophenylcopper displays a
tetrameric structure with unique p-coordination of
toluene in the solid state [14], whereas Ha˚kansson and
coworker have shown that mesitylcopper crystallizes as
a pentamer from toluene without any interactions
between copper and cocrystallized toluene molecules
[12d].
mesityllithium or the Grignard reagent with BF3×
We found that when 1 was treated with a slight excess
(1.05 equivalents) of BCl3 or BBr3 in toluene at ꢃ78 8C
/
Et2O.
/
and allowed to slowly warm to ambient temperature, the
spectroscopically pure monoarylated boranes 3a and 3b
were obtained in very high yields. NMR spectroscopy
did not reveal formation of any diarylated by-product.
The isolated yields for 3a and 3b after high-vacuum
distillation (Scheme 1; Table 1) were 88 and 91%,
respectively. Even when a twofold excess of 1 was
treated with BCl3 or BBr3 under similar conditions,
further reaction did not take place, but the monoary-
lated species 3a and 3b were observed as the major
product in addition to unreacted 1. Only after prolonged
heating of the mixture to 100 8C was a second aryl group
transferred to the boron center to give the dimesityl-
boron halides 4a and 4b in ca. 60 and 95% spectroscopic
yield, respectively (Scheme 1). Alternatively, the isolated
species MesBX2 (XꢀCl, Br) may be treated with one
/
equivalent 1 at ambient temperature and subsequently
heated to 100 8C for 12 h to give 4a and 4b in slightly
higher spectroscopic yields of 80 and 97%, respectively.
The comparatively lower yield of 4a was traced back to
formation of significant amounts of the coupled by-
product dimesitylene, which was identified by compar-
2. Results and discussion
The toluene solvate of mesitylcopper was synthesized
as described by Ha˚kansson and coworker [12d] and
pentafluorophenylcopper can be prepared conveniently
and in large quantities from the Grignard reagent and
CuCl in diethyl ether according to a procedure reported
by Cairncross and Sheppard [13]. Colorless crystals of
1
ison of the H-NMR signals with data reported in the
literature [19,20]. Compounds 4a and 4b were purified
by recrystallization from hexanes at ꢃ37 8C and iso-
/
lated in 34 and 74% yield, respectively. Even though a
slight excess of the organocopper reagent was employed,
the trisubstituted product, trimesitylborane (5), was not
[CuMes]5×
/
toluene (1) and [Cu(C6F5)]4(h2-toluene)2 (2)
/
were obtained by recrystallization from toluene at ꢃ
37 8C. Freshly prepared solutions of 1 and 2 were
reacted in toluene with the chosen boron halide in a
1:1, 2:1, or 3:1 ratio, respectively. The crude reaction
1
mixtures were filtered, analyzed by H-NMR spectro-
scopy, and the products were subsequently isolated by
recrystallization or distillation. Results for reactions of 1
and 2 with selected boron halides in toluene solution are
summarized in Tables 1 and 2. Both yields as deter-
mined by 1H-NMR spectroscopy and isolated yields
after recrystallization or distillation of the product are
given based on the limiting reagent.
Scheme 1. Reactions of 1 with boron halides; XꢀCl, Br.
/

136
A. Sundararaman, F. Jakle / Journal of Organometallic Chemistry 681 (2003) 134ꢁ
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142
¨
Table 1
NMR spectroscopic and isolated yields for reactions of 1 with boron halides
CuAr
Borane (equivalent)
Conditions
NMR (%yield) a
ArBX2 Ar2BX
Isolated species (%yield)
Ar3B
1
1
1
1
1
1
1
1
BCl3 (1.05)
BBr3 (1.05)
ꢃ
/
78 8C to r.t.
ꢀ
ꢀ/
/
97
97
15
0
0
0
0
0
0
0
0
0
0
0
3a (88)
3b (91)
b,c,d
ꢃ
/
78 8C to r.t.
BCl3 (0.48)
BBr3 (0.48)
ꢃ
/
78 to 100 8C; 24 h
78 to 100 8C; 12 h
78 to 60 8C; 2 h
60
95
95
50
80
97
ꢃ
/
4b (72) d
6 (84) e
b,c
PhBCl2 (1.05)
PhBCl2 (0.48)
MesBCl2 (1.0)
MesBBr2 (1.0)
ꢃ/
ꢁ/
ꢁ/
r.t. to 100 8C; 12 h
r.t. to 100 8C; 12 h
r.t. to 100 8C; 12 h
15
4a (34) c
4b (74)
ꢁ/
a
Estimated yield from 1H-NMR spectroscopy.
The product was not isolated.
b
c
The coupling product dimesitylene was observed as a major by-product.
The diarylated species was not formed at room temperature.
The reaction started below room temperature.
d
e
formed. Indeed, we did not observe formation of species
5 even when a larger excess of 1 (above three equiva-
lents) was used under forcing reaction conditions (36 h
at 100 8C) [21].
curic bromide, which gives dibromo(pentafluorophe-
nyl)borane and bromobis(pentafluorophenyl)borane in
80 and 35% yield, respectively. Similarly, Frohn et al.
[2f] have synthesized C6F5BBr2 from C6F5HgEt and
BBr3 in 82% yield. Moreover, Piers and coworkers have
recently investigated bis(pentafluorophenyl)zinc as a
potential reagent [2g]. Although reaction of the organo-
zinc reagent with boron halides does not lead to selective
formation of the mono- or diarylated products, the
arylzinc reagent has proven highly useful for the
synthesis of triarylated boranes [2g]. Given the success-
ful use of mesitylcopper in reactions with boron halides,
we anticipated that pentafluorophenylcopper (2) may
also serve as a selective reagent for the introduction of
pentafluorophenyl groups at boron.
We anticipated that steric factors may be dominating
the reactivity of the tetrameric species 1 and therefore
decided to study the reactivity of dichlorophenylborane.
Indeed, 1 slowly reacts with PhBCl2 even below room
temperature to give mesitylphenylchloroborane (6) in
95% spectroscopic yield. However, the reduction in
steric bulk did not lead to placement of three aryl
groups at boron. Reaction of PhBCl2 with two equiva-
lents of 1 did not give the expected dimesitylphenylbor-
ane (7), but resulted in formation of the coupling
product dimesitylene in addition to monosubstituted 6.
In a similar reaction between the isolated species 6 and 1
no reaction was observed even after 36 h at 100 8C.
Pentafluorophenylcopper (2) was treated with boron
trichloride or boron tribromide, respectively, in toluene
at ꢃ78 8C; the reaction mixture was allowed to warm up
/
to ambient temperature, and the product distribution
was studied by 19F-NMR spectroscopy. The predomi-
nant species observed by NMR in equimolar reactions
with either BCl3 or BBr3 are the monosubstituted
compounds C6F5BCl2 (8a) and C6F5BBr2 (8b). How-
ever, the desired products are accompanied by small
amounts of the diarylated boranes (C6F5)2BX (9a, 9b)
and the triarylated tris(pentafluorophenyl)borane (10)
(Table 2; Scheme 2. In order to maximize the yield of the
aryldichloroboranes 8a and 8b, we decided to add the
organocopper species to an excess of boron halide at low
temperature. Such a reverse addition protocol indeed
improves the spectroscopic yields, but does not com-
pletely eliminate formation of 9 or 10 (Table 2).
However, careful fractional vacuum distillation allowed
us to obtain compounds 8a and 8b with isolated yields of
57 and 62%, respectively.
2.2. Reactivity of pentafluorophenylcopper toward boron
halides [22,23]
Due to the strongly electron-withdrawing nature of
the aryl group, pentafluorophenyltrimethylsilane and
pentafluorophenyltrimethylstannane cannot readily be
applied to the synthesis of (perfluoroaryl)boranes
through silicon or tinꢁboron exchange reactions [24].
/
In contrast to the typically observed reactivity pattern,
transfer of a methyl group occurs more readily than that
of the aryl group. The pentafluorophenyl group is
therefore transferred only under forcing conditions
with an excess of borane [25]. The currently most widely
used reagent is bis(pentafluorophenyl)dimethyltin,
which has first been described by Chambers and Chivers
[26] in 1963. A number of studies have since been
undertaken aimed at the development of a new alter-
native methodology. Most notably, Bochmann and
coworkers [2e] have introduced pentafluorophenylmer-
Low-temperature reaction of BBr3 with three equiva-
lents of 2 gave the triarylated species tris(pentafluor-

A. Sundararaman, F. Jakle / Journal of Organometallic Chemistry 681 (2003) 134ꢁ
/
142
137
¨
Table 2
NMR spectroscopic and isolated yields for reactions of 2 with boron halides
CuAr
Borane (equivalent)
Conditions
NMR (%yield) a
Isolated species (%yield)
ArBX2
Ar2BX
Ar3B
b
b
b
b
2
2
2
2
2
2
2
2
BCl3 (1.00)
BCl3 (0.50)
BBr3 (1.00)
BBr3 (0.50)
BBr3 (0.33)
PhBCl2 (0.5)
BCl3 (3)
ꢃ
/
78 8C to r.t.
78 8C to r.t.
78 8C to r.t.
78 8C to r.t.
78 8C to r.t.
78 8C to r.t.
78 8C to r.t. c
78 8C to r.t. c
56
28
74
34
0
30
35
16
23
0
14
37
10
43
ꢃ
/
ꢃ
/
ꢃ
/
ꢃ
/
ꢀ
/
97
95
8
10 (80)
11 (56)
8a (57)
8b (62)
ꢃ
/
ꢁ/
65
87
5
ꢃ
/
27
10
BBr3 (3)
ꢃ/
3
a
Estimated yield from 19F-NMR spectroscopy.
Separation of the individual boranes was not attempted.
A solution of the organocopper reagent in CH2Cl2 was slowly added to the borane solution.
b
c
are highly useful intermediates in the development of
powerful multifunctional Lewis acid catalysts and of
advanced molecular and polymeric luminescent materi-
als [15,16,22,23].
We found that mesitylcopper reacts with boron
halides BX3 (XꢀCl, Br) under highly selective forma-
/
tion of the monosubstituted borane MesBX2 or the
disubstituted Mes2BX depending on the molar ratio of
the reagents and the temperature. To our knowledge,
the unusually high selectivity for the species MesBX2
surpasses that of any other currently available method
such as the use of mercury reagents or arylsilanes.
Although a preference for formation of (C6F5)BX2 at
low temperature was observed, overall the selectivity for
monoarylated or diarylated species was considerably
lower with pentafluorophenylcopper. However, use of
an excess of borane BX3 in a reverse addition protocol
followed by high-vacuum fractionation gives the mono-
arylated boranes C6F5BX2 in moderate to good yields.
Moreover, pentafluorophenylcopper serves as a conve-
nient base-free reagent for the high-yield synthesis of
tris(pentafluorophenyl)borane and related mixed-substi-
tuted species such as phenylbis(pentafluorophenyl)bor-
ane.
Our observations indicate that both the steric and
electronic nature of the mono- and diarylated inter-
mediates critically effect the overall selectivity. Highly
selective formation of MesBX2 can be traced back to the
lower Lewis acidity and increased steric bulk of MesBX2
relative to BX3. Use of the less sterically encumbered
phenyldichloroborane leads to faster but still very
selective formation of MesPhBCl. In contrast to the
strongly reduced Lewis acidity of MesBX2, C6F5BX2
represents an organoboron halide of only slightly lower
Lewis acidity than that of the boron halides BX3
themselves [30]. Consequently, a lower selectivity is
observed and steric effects rather than electronic factors
are likely responsible for the preference for formation of
Scheme 2. Reactions of 2 with boron halides; XꢀCl, Br.
/
ophenyl)borane (10) [27] selectively and in high yield
(80% after sublimation). Similarly, mixed triarylated
boranes are readily accessible from arylboron halides
through reaction with 2 in non-coordinating solvents.
For example, the reaction of phenyldichloroborane with
2 yields PhB(C6F5)2 (11) in ca. 95% spectroscopic yield
[28,29]. Especially noteworthy is that these reactions are
conveniently performed in aromatic or chlorinated
solvents, in which both the organocopper species and
the boron halide are highly soluble and perfectly stable.
Moreover, the products are obtained in ꢀ95% purity
/
according to 1H- and 19F-NMR analyses and are readily
isolated by filtration from the insoluble copper halides.
3. Summary and conclusions
We have performed a comparative study on the
reactivity and selectivity of arylcopper species in reac-
tions with boron halides. The reagents [CuMes]5×
/
toluene
and [(C6F5)Cu]4(h2-toluene)2 were chosen because of
their similar steric, yet very different electronic proper-
ties. Furthermore, the mesityl- and pentafluorophenyl-
boranes obtained through reaction with boron halides

138
A. Sundararaman, F. Jakle / Journal of Organometallic Chemistry 681 (2003) 134ꢁ
/
142
¨
the monoarylated species (C6F5)BX2 at low tempera-
ture.
Fluorinated grease was used for ground glass joints in
reactions involving boron trihalides.
In comparison to other organometallic reagents, aryl
copper species show on one hand higher reactivity than
arylsilanes or arylmercury species and on the other hand
improved selectivity compared to highly reactive orga-
nolithium species or Grignard reagents. The ease of
isolation and purification of the arylcopper compounds
and their suitability for reactions in inert solvents such
as hexanes, toluene, and even chlorinated solvents
provide additional advantages. Organocopper reagents
therefore represent an interesting alternative to currently
used highly toxic organotin and organomercury species.
4.2. Reaction of 1 with one equivalent BCl3: synthesis of
3a [17]
A solution of BCl3 (5.2 ml, 1 M in hexanes, 5.2 mmol)
was added dropwise to a suspension of 1 (1.00 g, 4.97
mmol) in toluene (25 ml) at ꢃ
immediately turned orange-red upon addition of the
borane. The mixture was stirred at ꢃ78 8C for 2 h and
/
78 8C. The suspension
/
then allowed to slowly warm to room temperature (r.t.)
overnight yielding a white precipitate in a colorless
solution. After filtration from the insoluble material all
volatile components were removed under high vacuum.
1
4. Experimental
The spectroscopic yield of 3a was determined by H-
NMR to be ꢀ97%. The crude product was purified by
/
4.1. Materials and general methods
distillation under reduced pressure to give 0.88 g (88%)
1
analytically pure 3a as a colorless liquid. For 3a: H-
The compounds 2-bromomesitylene, CuCl (prepuri-
fied grade), CuBr, and BCl3 (1 M in hexanes) were
purchased from Acros; PhBCl2, BCl3 (1 M in CH2Cl2)
and BBr3 were purchased from Aldrich and C6F5Br was
purchased from Fluorochem. The compounds PhBCl2,
BBr3, and C6F5Br were distilled under vacuum prior to
use, and CuBr was purified according to a literature
procedure [31]. Mesitylcopper [12] and pentafluorophe-
nylcopper [13] were prepared according to literature
procedures and recrystallized from toluene. All reactions
and manipulations were carried out under an atmo-
sphere of prepurified nitrogen using either Schlenk
techniques or an inert-atmosphere glove box (Innovative
Technologies). Ether solvents were distilled from Na/
benzophenone prior to use. Hydrocarbon and chlori-
nated solvents were purified using a solvent purification
system (Innovative Technologies); chlorinated solvents
were subsequently degassed via several freeze pump
thaw cycles. All 500 MHz 1H-NMR spectra, 125.7 MHz
13C-NMR spectra, and 470.2 MHz 19F-NMR spectra
were recorded on a Varian INOVA NMR spectrometer
operating at 499.91 MHz. The 400 MHz 1H-NMR
spectra, 100.5 MHz 13C-NMR spectra, 376.2 MHz 19F-
NMR spectra, and 128.3 MHz 11B-NMR spectra were
recorded on a Varian VXR-S spectrometer. All solu-
tion’s 1H- and 13C-NMR spectra were referenced
internally to the solvent signals. 11B-NMR spectra
NMR (C6D6, 400 MHz): dꢀ
(s, 6H, ortho-Me), 2.01 (s, 3H, para-H); 13C-NMR
(C6D6, 125.7 MHz): dꢀ140.0 (para-Mes), 137.7 (ortho-
Mes), 136 (br, ipso-Mes), 128.1 (meta-Mes), 21.9 (ortho-
Me), 21.1 (para-Me); 11B-NMR (C6D6, 128.3 MHz):
/
6.54 (s, 2H, meta-Ph), 2.14
/
dꢀ
/
60.3 (h1/2
53.81; H, 5.51. Found: C, 54.54; H, 5.70%.
ꢀ
/
250 Hz); C9H11BCl2 (200.90)*Calc.: C,
/
4.3. Reaction of 1 with one equivalent BBr3: synthesis of
3b [3b,3c,18]
A solution of BBr3 (2.63 g, 10.5 mmol) in toluene (5
ml) was added dropwise at ꢃ78 8C to a suspension of 1
/
(2.01 g, 10.0 mmol) in toluene (25 ml). The suspension
immediately turned orange-red upon addition of the
borane. The mixture was stirred at ꢃ78 8C for 2 h and
/
then allowed to slowly warm to r.t. overnight yielding a
white precipitate in a colorless solution. After filtration
from the insoluble material all volatile components were
removed under high vacuum. The spectroscopic yield of
3b was determined by 1H-NMR to be ꢀ
97%. The crude
/
product was purified by distillation under reduced
pressure to give 2.64 g (91%) analytically pure 3b as a
1
colorless liquid. For 3b: H-NMR (C6D6, 500 MHz):
dꢀ
/
6.52 (s, 2H, meta-Ph), 2.14 (s, 6H, ortho-Me), 2.02
(s, 3H, para-Me); 13C-NMR (C6D6, 100.5 MHz): dꢀ
/
141.0 (br, ipso-Mes), 139.9 (para-Mes), 136.0 (ortho-
Mes), 128.2 (meta-Mes), 21.7 (ortho-Me), 21.0 (para-
were referenced externally to BF3×
19F-NMR spectra were referenced to a,a?,a??-trifluoro-
toluene (0.05% in C6D6; dꢀ 63.73). All NMR spectra
/
Et2O (dꢀ/0) and
Me); 11B-NMR (C6D6, 128.3 MHz): dꢀ
/62.1 (h1/2
ꢀ230
/
/
ꢃ
/
Hz); C9H11BBr2 (289.80)*
/
Calc.: C, 37.30; H, 3.83.
were recorded at ambient temperature. The abbrevia-
tions Mes and Pf are used for 2,4,6-trimethylphenyl and
for pentafluorophenyl, respectively. Elemental analyses
were performed by Quantitative Technologies, Inc.,
Whitehouse, NJ.
Found: C, 38.05; H, 3.88%.
4.4. Reaction of 1 with 0.5 equivalent BCl3: attempted
synthesis of 4a
Caution! BBr3 and BCl3 are toxic and highly corrosive
and should be handled appropriately with great care.
A solution of BCl3 (4.8 ml, 1 M in xylene, 4.8 mmol)
was added dropwise to a suspension of 1 (2.01 g, 10.0

A. Sundararaman, F. Jakle / Journal of Organometallic Chemistry 681 (2003) 134ꢁ
/
142
139
¨
mmol) in toluene (30 ml) at ꢃ
mixture immediately turned orange-red and was stirred
/
78 8C. The reaction
high vacuum. The spectroscopic yield of 4b was
determined by 1H-NMR to 95%. The crude product
was purified by recrystallization from hexanes at
at ꢃ78 8C for 4 h. The mixture was then allowed to
/
warm to r.t. and stirred for an additional 12 h. During
this period the precipitate turned light orange. 1H-NMR
spectroscopy of the light yellow solution showed the
formation of 3a and an unidentified species that gives
ꢃ37 8C to give 1.04 g (72%) analytically pure 4b as a
/
1
colorless crystalline solid. H-NMR (C6D6, 500 MHz):
dꢀ6.64 (s, 4H, meta-Ph), 2.34 (s, 12H, ortho-Me), 2.05
(s, 6H, para-Me); 13C-NMR (C6D6, 100.5 MHz): dꢀ
/
/
rise to a set of broad peaks (d (C6D6)ꢀ6.66 (br s, 2H),
/
141.0 (br, ipso-Mes), 140.4 (para-Mes), 140.3 (ortho-
2.73 (br s, 6H), 1.98 (br s, 3H)) in addition to residual
starting material 1. The mixture was then slowly heated
to 100 8C and kept stirring for 12 h. The precipitate
turned purple and a colorless solution was obtained.
After filtration from the insoluble material all volatile
components were removed under high vacuum. 1H-
NMR spectroscopy showed the formation of 4a (ca.
60%), 3a (ca. 15%), and the coupling product dimesity-
lene (ca. 15%). Isolation of 4a was not attempted.
Mes), 129.4 (meta-Mes), 23.5 (ortho-Me), 21.2 (para-
Me); 11B-NMR (C6D6, 128.3 MHz): dꢀ
Hz); C18H22BBr (329.09)*
Found: C, 65.20; H, 6.91%.
/
72.1 (h1/2
ꢀ600
/
/
Calc.: C, 65.70; H, 6.74.
4.7. Reaction of 1 with 3b: alternative synthesis of 4b
A solution of 3b (0.67 g, 2.31 mmol) in toluene (5 ml)
was added to a solution of 1 (0.50 g, 2.43 mmol) in
toluene (25 ml) at r.t. No reaction was observed at r.t.
Upon heating of the mixture to 100 8C for 3 h the
solution gradually turned colorless and a white pre-
cipitate formed. After filtration from the insoluble
material all volatile components were removed under
high vacuum. The spectroscopic yield of 4b was
4.5. Reaction of 1 with 3a: alternative synthesis of 4a
A solution of 3a (1.09 g, 5.43 mmol) in toluene (5 ml)
was added to a solution of 1 (1.09 g, 5.42 mmol) in
toluene (25 ml). At r.t. no reaction was observed. Upon
heating of the mixture to 100 8C for 36 h the solution
gradually turned colorless and a white precipitate
formed. After filtration from the insoluble material all
volatile components were removed under high vacuum.
1
determined by H-NMR to be 97%. The crude product
was purified by recrystallization from hexanes at
1
The spectroscopic yield of 4a was determined by H-
ꢃ37 8C to give 0.56 g (74%) of analytically pure 4b as
/
NMR to 80%. All volatile materials were removed first
at r.t. and then at 100 8C under high vacuum. The
residue was purified by recrystallization from hexanes at
a colorless crystalline solid.
ꢃ37 8C to give 0.53 g (34%) analytically pure 4a as a
/
1
colorless crystalline solid. For 4a: H-NMR (C6D6, 500
MHz): dꢀ6.66 (s, 4H, meta-Ph), 2.31 (s, 12H, ortho-
Me), 2.07 (s, 6H, para-Me); 13C-NMR (C6D6, 100.5
MHz): dꢀ140.9 (ortho-Mes), 140.4 (para-Mes), 139
(br, ipso-Mes), 129.3 (meta-Mes), 23.2 (ortho-Me), 21.2
(para-Me); 11B-NMR (C6D6, 128.3 MHz): dꢀ
69.5
(h1/2 650 Hz); C18H22BCl (284.64)*Calc.: C, 75.96;
H, 7.79. Found: C, 76.01; H, 7.91%.
4.8. Reaction of 1 with PhBCl2: synthesis of 6
/
A solution of PhBCl2 (1.36 ml, 10.5 mmol) in toluene
(5 ml) was added dropwise to a solution of 1 (2.01 g,
/
10.0 mmol) in toluene (25 ml) at ꢃ78 8C. The suspen-
/
/
sion gradually turned orange-red upon addition of the
borane. The reaction mixture was allowed to slowly
warm to r.t. and subsequently kept at 60 8C for 2 h. A
white precipitate formed in a colorless solution. After
filtration from the insoluble material all volatile com-
ponents were removed under high vacuum. The spectro-
scopic yield of 6 was determined by 1H-NMR to be 95%.
The crude product was purified by distillation to give
ꢀ
/
/
4.6. Reaction of 1 with 0.5 equivalent BBr3: synthesis of
4b
A solution of BBr3 (0.45 ml, 4.75 mmol) in toluene (5
ml) was added dropwise at ꢃ78 8C to a suspension of 1
/
2.17 g (84%) spectroscopically pure 6 as a colorless
(2.01 g, 10.0 mmol) in toluene (25 ml). The suspension
immediately turned orange-red upon addition of the
borane. The reaction mixture was allowed to slowly
warm to r.t., which resulted in an orange suspension.
1H-NMR spectroscopy of the light yellow solution
indicated the formation of 3b in addition to residual
starting material 1. Upon heating of the mixture to
100 8C for 12 h the solution turned colorless and a white
precipitate formed. After filtration from the insoluble
material all volatile components were removed under
1
liquid. H-NMR (C6D6, 500 MHz): dꢀ
/
8.03 (d, Jꢀ
8 Hz, 1H, para-Ph), 7.08
8 Hz, 2H, meta-Ph), 6.72 (s, 2H, meta-Mes),
2.18 (s, 3H, para-Me), 2.10 (s, 6H, ortho-Me); 13C-
NMR (C6D6, 125.7 MHz): dꢀ138.5 (para-Mes),
138.5ꢁ138.0 (br, ipso-Mes, ipso-Ph), 137.8 (ortho-
/
8
Hz, 2H, ortho-Ph), 7.18 (t, Jꢀ
/
(ps t, Jꢀ
/
/
/
Mes), 137.7 (ortho-Ph), 134.7 (para-Ph), 128.5, 127.9
(meta-Ph, meta-Mes), 22.2 (ortho-Me), 21.2 (para-Me);
11B-NMR (C6D6, 128.3 MHz): dꢀ
/
67.4 (h1/2
ꢀ550 Hz).
/

140
A. Sundararaman, F. Jakle / Journal of Organometallic Chemistry 681 (2003) 134ꢁ
/
142
¨
4.9. Reaction of 1 with 0.5 equivalent PhBCl2: attempted
synthesis of 7
ponents were slowly removed under high vacuum first at
ꢃ25 8C and subsequently over a period of 3 h at 0 8C.
/
The crude product was distilled under dynamic vacuum
at ca. 40 8C and condensed into a trap cooled with liquid
N2. Vacuum transfer of the crude product from the trap
into a Teflon-stoppered storage flask yielded spectro-
scopically pure 8a as a colorless liquid in a yield of 2.23 g
A solution of PhBCl2 (96 mg, 0.61 mmol) in toluene
was added dropwise to a suspension of 1 (0.25 g, 1.21
mmol) in toluene (50 ml) at ꢃ
/
78 8C. The reaction
mixture immediately turned orange-red and was stirred
1
at ꢃ
/
78 8C for 4 h. H-NMR spectroscopy of the light
(57%). 19F-NMR (C6D6, 470.2 MHz): dꢀ
2F, ortho-F), ꢃ146.6 (tr, J(F, F)ꢀ21 Hz, 1F, para-F),
162.4 (m, 2F, meta-F); 13C-NMR (C6D6, 125.7 MHz):
dꢀ146.5 (d, J(F, C)ꢀ256 Hz, ortho-F), 142.5 (d, J(F,
C)ꢀ261 Hz, para-Pf), 135.5 (d, J(F, C)ꢀ253 Hz,
meta-Pf), n.o. (ipso-Pf); 11B-NMR (C6D6, 128.3
MHz): dꢀ52.3 (h1/2 130 Hz).
/
ꢃ
/
129.9 (m,
yellow solution indicated the formation of 6 in addition
to starting material 1. The mixture was then slowly
heated to 100 8C and kept stirring for 12 h. The
precipitate turned purple and a clear solution was
obtained. After filtration from the insoluble material
all volatile components were removed under high
vacuum. 1H-NMR spectroscopy indicated the forma-
tion of 6 (ca. 50%) and dimesitylene (ca. 45%).
/
/
ꢃ
/
/
/
/
/
/
ꢀ
/
4.13. Reaction of 2 with excess of BBr3: synthesis of 8b
[2e,2f]
4.10. Reactions of 1 with 4a, 4b, and 6: attempted
synthesis of 5 and 7
Compound 2 was repeatedly extracted with hexanes
and subsequently dried under high vacuum at ambient
temperature for 12 h. A solution of toluene-free 2 (2.61
g, 11.3 mmol) in CH2Cl2 (20 ml) was added dropwise
over a period of 20 min to a solution of BBr3 (8.37 g,
A solution of the borane (1.0 mmol) in toluene (5 ml)
was added to a solution of 1 (0.21 g, 1.0 mmol) in
toluene (25 ml) at r.t. The mixture was heated to 100 8C
for 36 h. 1H-NMR spectroscopy showed in all cases the
presence of unreacted borane and 1.
34.0 mmol) in CH2Cl2 (30 ml) at ꢃ
addition a white precipitate formed. The reaction
mixture was stirred at ꢃ78 8C for 1 h and then slowly
/
78 8C. Upon
/
4.11. General procedure for reactions of 2 with BCl3 and
BBr3
warmed to r.t. and allowed to stir for 3 h. After filtration
from the insoluble material, all volatile components
were slowly removed at ꢃ20 8C under high vacuum.
/
A solution of BCl3 (1.0 ml, 1 M in hexanes, 1.0 mmol)
or BBr3 (0.25 g, 1.0 mmol) in toluene (3 ml) was added
to a solution of 2 (0.28 g, 1.0 mmol) in toluene (25 ml) at
The crude product was distilled under dynamic vacuum
at ca. 50 8C and condensed into a trap cooled with liquid
N2. The crude product was transferred under static
vacuum from the trap into a Teflon-stoppered storage
flask and was subsequently kept under dynamic vacuum
at 0 8C for 6 h in order to remove the excess boron
tribromide. Spectroscopically pure 8b was obtained as a
colorless liquid in a yield of 2.40 g (62%). 19F-NMR
ꢃ
/
78 8C. The reaction mixture was stirred at ꢃ78 8C for
/
1 h and then allowed to gradually warm to r.t. With
BBr3 initially a blue-colored precipitate formed, which
gradually turned off-white, whereas with BCl3 a white
precipitate is formed immediately. The product distribu-
tion in the colorless supernatant was estimated by 19F-
NMR spectroscopy (see Table 2). Preparative reactions
were performed as described with toluene-free 2 in
CH2Cl2 in order to facilitate work up of the products
(Scheme 2).
(C6D6, 470.2 MHz): dꢀ
147.4 (tr, J(F,F)ꢀ20 Hz, 1F, para-F), ꢃ
2F, meta-F); 13C-NMR (C6D6, 100.5 MHz): dꢀ
(d, J(F, C)ꢀ252 Hz, ortho-Pf), 143.7 (d, J(F, C)ꢀ
Hz, para-Pf), 137.4 (d, J(F, C)ꢀ253 Hz, meta-Pf), n.o.
(ipso-Pf); 11B-NMR (C6D6, 128.3 MHz): dꢀ
53.3
(h1/2 150 Hz).
/
ꢃ
/
130.3 (m, 2F, ortho-F),
161.9 (m,
146.2
254
ꢃ
/
/
/
/
/
/
/
4.12. Reaction of 2 with excess of BCl3: synthesis of 8a
[26b]
/
ꢀ
/
Compound 2 was repeatedly extracted with hexanes
and subsequently dried under high vacuum at ambient
temperature for 12 h. A solution of toluene-free 2 (3.60
g, 15.6 mmol) in CH2Cl2 (20 ml) was added dropwise
over a period of 20 min to a solution of BCl3 (41.4 ml,
4.14. Reaction of three equivalents of 2 with BBr3:
synthesis of B(C6F5)3 (10) [27]
A solution of BBr3 (0.48 g; 1.95 mmol) in CH2Cl2 (10
ml) was added dropwise to a solution of 2 (1.68 g, 6.06
1.13 M in CH2Cl2, 46.8 mmol) at ꢃ
addition a white precipitate formed. The reaction
mixture was stirred at ꢃ78 8C for 1 h and then allowed
/
78 8C. Upon
mmol) in CH2Cl2 (20 ml) at ꢃ
white precipitate formed. The reaction mixture was
stirred at ꢃ78 8C for 1 h, allowed to slowly warm to
r.t., and stirred for an additional 12 h. The reaction
/
78 8C. Upon addition a
/
/
to slowly warm to r.t. and allowed to stir for 3 h. After
filtration from the insoluble material, all volatile com-

A. Sundararaman, F. Jakle / Journal of Organometallic Chemistry 681 (2003) 134ꢁ
/
142
141
¨
(c) A. Pelter, K. Smith, H.C. Brown, Borane Reagents, Academic
Press, London, 1988.
mixture was filtered through a fritted glass disk and
washed twice with CH2Cl2 (10 ml). All volatile materials
were removed under vacuum and the crude product was
purified by high-vacuum sublimation at 80 8C. Spectro-
scopically pure B(C6F5)3 (10) was obtained as a white
microcrystalline solid in a yield of 0.83 g (80%). 19F-
[2] (a) See for example: W. Gerrard, M. Howarth, E.F. Mooney,
D.E. Pratt, J. Chem. Soc. (1963) 1582;
(b) H. Gilman, L.O. Moore, J. Am. Chem. Soc. 80 (1958) 3609;
(c) B.E. Carpenter, W.E. Piers, R. McDonald, Can. J. Chem. 79
(2001) 291;
(d) D.A. Walker, T.J. Woodman, D.L. Hughes, M. Bochmann,
Organometallics 20 (2001) 3772;
NMR (C6D6, 470.2 MHz): dꢀ
F), ꢃ143.0 (m, 3F, para-F), ꢃ161.4 (m, 6F, meta-F);
13C-NMR (C6D6, 100.5 MHz): dꢀ
148.3 (d, J(F, C)
251 Hz, ortho-Pf), 145.2 (d, J(F, C)ꢀ262 Hz, para-
Pf), 137.6 (d, J(F, C)ꢀ254 Hz, meta-Pf), n.o. (ipso-Pf);
11B-NMR (C6D6, 162.3 MHz): dꢀ
59.4.
/
ꢃ
/
130.1 (m, 6F, ortho-
/
/
(e) R. Duchateau, S.J. Lancaster, M. Thornton-Pett, M. Boch-
mann, Organometallics 16 (1997) 4995;
/
(f) H.-J. Frohn, H. Franke, P. Fritzen, V.V. Bardin, J. Organo-
met. Chem. 598 (2000) 127;
ꢀ
/
/
/
(g) V.C. Williams, W.E. Piers, W. Clegg, M.R.J. Elsegood, S.
Collins, T.B. Marder, J. Am. Chem. Soc. 121 (1999) 3244.
[3] (a) C. Eaborn, J. Organomet. Chem. 100 (1975) 43;
(b) W. Haubold, J. Herdtle, W. Gollinger, W. Einholz, J.
Organomet. Chem. 315 (1986) 1;
/
4.15. Reaction of two equivalents of 2 with PhBCl2:
synthesis of PhB(C6F5)2 (11) [28]
(c) D. Kaufmann, Chem. Ber. 120 (1987) 853.
[4] (a) P.A. Deck, T.S. Fisher, J.S. Downey, Organometallics 16
(1997) 1193;
A solution of PhBCl2 (0.40 g, 2.52 mmol) in toluene (5
ml) was added dropwise to a solution of 2 (1.39 g, 5.02
(b) J.J. Eisch, B.W. Kotowicz, Eur. J. Inorg. Chem. (1998) 761;
(c) M. Schulte, F.P. Gabbaı, Can. J. Chem. 80 (2002) 1308;
¨
(d) J.A. Gamboa, A. Sundararaman, L. Kakalis, A.J. Lough, F.
mmol) in toluene (30 ml) at ꢃ
white precipitate formed. The reaction mixture was
stirred at ꢃ78 8C for 1 h, allowed to slowly warm to
/
78 8C. Upon addition a
Jakle, Organometallics 21 (2002) 4169.
¨
[5] Y. Qin, G. Cheng, A. Sundararaman, F. Jakle, J. Am. Chem. Soc.
¨
/
124 (2002) 12672.
r.t., and stirred for an additional 12 h. The reaction
mixture was filtered through a fritted glass disk and
washed twice with toluene (10 ml). All volatile materials
were removed under vacuum and the crude product was
[6] (a) G. van Koten, S.L. James, J.T.B.H. Jastrzebski, in: E.W. Abel,
F.G.A. Stone, G. Wilkinson (Eds.), Comprehensive Organome-
tallic Chemistry, vol. 3, Pergamon Press, Oxford, 1995;
(b) N. Krause, Modern Organocopper Chemistry, Wiley/VCH,
Weinheim, 2002;
purified by crystallization from hexanes at ꢃ37 8C.
/
Spectroscopically pure PhB(C6F5)2 (11) was obtained as
a colorless crystalline solid in a yield of 0.59 g (56%). 1H-
(c) E. Nakamura, S. Mori, Angew. Chem. Int. Ed. 39 (2000) 3750.
[7] (a) G. van Koten, C.A. Schaap, J.G. Noltes, J. Organomet. Chem.
99 (1975) 157;
NMR (C6D6, 500 MHz): dꢀ
/
7.53 (d, Jꢀ8 Hz, 2H,
/
(b) G. van Koten, J.T.B.H. Jastrzebski, J.G. Noltes, J. Organo-
met. Chem. 177 (1979) 283.
ortho-Ph), 7.25 (t, Jꢀ
Jꢀ
dꢀ
C)ꢀ
C)ꢀ
/
8 Hz, 1H, para-Ph), 7.11 (ps t,
/
8 Hz, 2H, meta-Ph); 13C-NMR (C6D6, 125.7 MHz):
[8] (a) G. van Koten, J.G. Noltes, J. Am. Chem. Soc. 98 (1976) 5393;
(b) G. van Koten, J.T.B.H. Jastrzebski, J.G. Noltes, W.M.G.F.
Pontenagel, J. Kroon, A.L. Spek, J. Am. Chem. Soc. 100 (1978)
5021.
/
146.6 (d, J(F, C)ꢀ
/
246 Hz, ortho-Pf), 143.1 (d, J(F,
/
258 Hz, para-Pf), 139.6 (ortho-Ph), 137.6 (d, J(F,
/
253 Hz, meta-Pf), 136.8 (para-Ph), 128.6 (meta-
Ph), 113.8 (ipso-Pf), n.o. (ipso-Ph); 19F-NMR (C6D6,
[9] F. Jakle, I. Manners, Organometallics 18 (1999) 2628.
¨
[10] For studies on the reactivity of organocopper species toward
triorganoboranes, see: (a) G. Costa, A. Camus, N. Marsich, L.
Gatti, J. Organomet. Chem. 8 (1967) 339;
376.2 MHz): dꢀ
2F, para-F), ꢃ
162.1 (m, 4F, meta-F); 11B-NMR (C6D6,
128.3 MHz): dꢀ60.6 (h1/2 750 Hz).
/
ꢃ
/
130.9 (m, 4F, ortho-F), ꢃ
/
149.5 (m,
/
/
ꢀ
/
(b) E. Kalbarczyk, S. Pasynkiewicz, J. Organomet. Chem. 290
(1985) 257.
[11] Organocopper species in combination with boranes BX3 (XꢀF,
/
alkyl), the so-called Yamamoto reagents, play a major role in
organic synthesis. See for example: (a) Y. Yamamoto, Angew.
Chem. Int. Ed. Engl. 25 (1986) 947;
Acknowledgements
(b) B.H. Lipshutz, E.L. Ellsworth, S.H. Dimock, J. Am. Chem.
Soc. 112 (1990) 5869;
Acknowledgement is made to the donors of The
Petroleum Research Fund, administered by the Amer-
ican Chemical Society, and to the Rutgers University
Research Council for financial support of this research.
(c) E. Nakamura, M. Yamanaka, S. Mori, J. Am. Chem. Soc. 122
(2000) 1826.
[12] (a) T. Tsuda, T. Yazawa, K. Watanabe, T. Fujii, T. Saegusa, J.
Org. Chem. 46 (1981) 192;
(b) S. Gambarotta, C. Floriani, A. Chiesi-Villa, C. Guastini, J.
Chem. Soc. Chem. Commun. (1983) 1156;
References
(c) E.M. Meyer, S. Gambarotta, C. Floriani, A. Chiesi-Villa, C.
Guastini, Organometallics 8 (1989) 1067;
(d) H. Eriksson, M. Ha˚kansson, Organometallics 16 (1997) 4243.
[13] (a) A. Cairncross, W.A. Sheppard, J. Am. Chem. Soc. 90 (1968)
2186;
[1] See for example: (a) K. Niedenzu, Organomet. Chem. Rev. 1
(1966) 305;
(b) R. Koster, in: R. Koster (Ed.), Methods of Organic Chemistry
¨
¨
(b) A. Cairncross, W.A. Sheppard, E. Wonchoba, W.J. Guild-
ford, C.B. House, R.M. Coates, Org. Synth. 59 (1980) 122.
(Houben-Weyl), vol. 3a/13, G. Thieme, Stuttgart (New York),
1982;

142
A. Sundararaman, F. Jakle / Journal of Organometallic Chemistry 681 (2003) 134ꢁ
/
142
¨
[14] A. Sundararaman, R.A. Lalancette, L.N. Zakharov, A.L. Rhein-
gold, F. Jakle, Organometallics, ASAP.
¨
boranes. Moreover, mesitylcopper solutions in toluene are
thermally stable at 100 8C.
[15] The resulting mesitylboron halides are important synthetic
intermediates toward the isolation of low-valent boron species
and strained cyclic organoboranes and also play a major role in
[21] H.C. Brown, V.H. Dodson, J. Am. Chem. Soc. 79 (1957) 2302.
[22] For two recent reviews on perfluorophenylboron halides, see: (a)
T. Chivers, J. Fluorine Chem. 115 (2002) 1;
(b) V.V. Bardin, H.-J. Frohn, Main Group Met. Chem. 25 (2002)
589.
the stabilization of unusual boronꢁ
/
nitrogen and boronꢁphos-
/
phorous species with low degree of association; see for example:
(a) P. Paetzold, A. Richter, T. Thijssen, S. Wurtenberg, Chem.
¨
[23] The resulting perfluorophenylboron halides represent highly
Lewis acidic boranes that play an important role as intermediates
for the development of new Lewis acid catalysts and cocatalysts;
see for example: (a) W.E. Piers, T. Chivers, Chem. Soc. Rev. 26
(1997) 345;
Ber. 112 (1979) 3811;
(b) W. Schacht, D. Kaufmann, Chem. Ber. 120 (1987) 1331;
(c) C. Pues, G. Baum, W. Massa, A. Berndt, Z. Naturforsch. B 43
(1988) 275;
(d) H.V.R. Dias, P.P. Power, J. Am. Chem. Soc. 111 (1989) 144;
(e) J.J. Eisch, S. Babak, J.D. Odom, A.L. Rheingold, J. Am.
Chem. Soc. 112 (1990) 1847;
(b) W.E. Piers, G.J. Irvine, V.C. Williams, Eur. J. Inorg. Chem.
(2000) 2131;
(c) E.Y.-X. Chen, T.J. Marks, Chem. Rev. 100 (2000) 1391.
[24] H.-J. Frohn, A. Lewin, V.V. Bardin, J. Organomet. Chem. 570
(1998) 255.
(f) B. Kaufmann, R. Jetzfellner, E. Leissring, K. Issleib, H. Noth,
¨
M. Schmidt, Chem. Ber. 130 (1997) 1677;
(g) J.D. Hoefelmeyer, F.P. Gabbaı, Organometallics 21 (2002)
¨
982.
[25] M.V. Metz, D.J. Schwartz, C.L. Stem, P.N. Nickias, T.J. Marks,
Angew. Chem. Int. Ed. 39 (2000) 1312.
[16] More recently, organoboranes with bulky mesityl substituents
have been introduced into the field of materials chemistry, where
they are used as precursors to new photoluminescent materials;
see for example: (a) N. Matsumi, K. Naka, Y. Chujo, J. Am.
Chem. Soc. 120 (1998) 10776;
[26] (a) R.D. Chambers, T. Chivers, Proc. Chem. Soc. (London)
(1963) 208;
(b) R.D. Chambers, T. Chivers, J. Chem. Soc. (1965) 3933;
(c) J.L.W. Pohlmann, F.E. Brinckman, G. Tesi, R.E. Donadio, Z.
Naturforsch. B 20 (1965) 1;
(b) Y. Shirota, J. Mater. Chem. 10 (2000) 1;
(c) C.D. Entwistle, T.B. Marder, Angew. Chem. Int. Ed. 41 (2002)
2927.
(d) D.J. Parks, W.E. Piers, G.P.A. Yap, Organometallics 17
(1998) 5492.
[27] (a) A.G. Massey, A.J. Park, F.G.A. Stone, Proc. Chem. Soc.
(London) (1963) 212;
[17] W. Schacht, D. Kaufmann, Chem. Ber. 120 (1987) 1331.
[18] O. Exner, U. Folli, S. Marcaccioli, P. Vivarelli, J. Chem. Soc.
Perkin Trans. II (1983) 757.
(b) A.G. Massey, A.J. Park, J. Organomet. Chem. 2 (1964) 245.
[28] P.A. Deck, C.L. Beswick, T.J. Marks, J. Am. Chem. Soc. 120
(1998) 1772.
[19] C. Elschenbroich, J. Schneider, H. Burdorf, J. Organomet. Chem.
391 (1990) 195.
[29] D.A. Walker, T.J. Woodman, D.L. Hughes, M. Bochmann,
Organometallics 20 (2001) 3772.
[20] The coupling product dimesitylene was observed in all high-
temperature reactions of boron trichloride or aryldichloroboranes
with excess 1 and was typically accompanied by precipitation of
purple-colored solids. Formation of coupling products and
colored precipitates was not observed in reactions with bromo-
[30] R.F. Childs, D.L. Mulholland, A. Nixon, Can. J. Chem. 60 (1982)
801.
[31] G.M. Whitesides, J.S. Sadowski, J. Lilburn, J. Am. Chem. Soc. 96
(1974) 2829.