Halogen exchange at boron in nido-C4B2 carboranes

Article abstract of DOI:10.1016/j.jorganchem.2005.05.037

The Pd(PPh₃)₄-catalyzed reaction of 1-iodo-6-phenylethynyl-2,3,4,5-tetraethyl-2,3,4,5-tetracarba-nido-hexaborane(6) (1a) with in situ generated arylzinc reagents (from arylbromides) leads to 1-bromo-6-phenylethynyl-2,3,4,5-tetraethyl-2,3,4,5-tetracarba-nido-hexaborane(6) (2a) and a trace amount of nido-(EtC)₄(BCCPh)₂ (3a). 3a is separately synthesized by a Pd-catalyzed Negishi-type coupling reaction of 1a with phenylethynyl-zincchloride. This is confirmed by the Pd-catalyzed reactions of 1-iodo-6-tert-butyl-ethynyl-2,3,4,5-tetraethyl-2,3,4,5-tetracarba- nido-hexaborane(6) (1b) with n-BuBr and PhZnCl, respectively, which produce the brominated carborane 2b and nido-(EtC)₄(BCCtBu)₂ (3b). With a dialkynylzinc reagent, a similar reaction of 1-iodo-6-p-tolylethynyl-2,3, 4,5-tetraethyl-2,3,4,5-tetracarba-nido-hexaborane(6) (1c) gives the linked compound 4, and a very small amount of ZnI₂(OPPh₃) ₂ is formed. The selective basal halogen exchange of 1,6-diiodo-2,3,4,5-tetraethyl-2,3,4,5-tetracarba-nido-hexaborane(6) (5) with an excess of AgF leads to 1-iodo-6-fluoro-2,3,4,5-tetraethyl-2,3,4,5-tetracarba- nido-hexa-borane(6) (6). The composition of the products follows from NMR and MS data and a single crystal X-ray analysis of 2a. The X-ray structure of ZnI ₂(OPPh₃)₂ is reported.

Full text of DOI:10.1016/j.jorganchem.2005.05.037

Journal of Organometallic Chemistry 690 (2005) 4531–4536
www.elsevier.com/locate/jorganchem
Halogen exchange at boron in nido-C4B2 carboranes
*
Yong Nie, Hans Pritzkow, Hubert Wadepohl, Walter Siebert
Anorganisch-Chemisches Institut der Universita¨t Heidelberg, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany
Received 20 April 2005; received in revised form 13 May 2005; accepted 26 May 2005
Available online 12 September 2005
Dedicated to Prof. Sheldon G. Shore on the occasion of his 75th birthday
Abstract
The Pd(PPh3)4-catalyzed reaction of 1-iodo-6-phenylethynyl-2,3,4,5-tetraethyl-2,3,4,5-tetracarba-nido-hexaborane(6) (1a) with in
situ generated arylzinc reagents (from arylbromides) leads to 1-bromo-6-phenylethynyl-2,3,4,5-tetraethyl-2,3,4,5-tetracarba-nido-
hexaborane(6) (2a) and a trace amount of nido-(EtC)4(BC„CPh)2 (3a). 3a is separately synthesized by a Pd-catalyzed Negishi-type
coupling reaction of 1a with phenylethynyl-zincchloride. This is confirmed by the Pd-catalyzed reactions of 1-iodo-6-tert-butyl-
ethynyl-2,3,4,5-tetraethyl-2,3,4,5-tetracarba-nido-hexaborane(6) (1b) with n-BuBr and PhZnCl, respectively, which produce the
brominated carborane 2b and nido-(EtC)4(BC„CtBu)2 (3b). With a dialkynylzinc reagent, a similar reaction of 1-iodo-6-p-
tolylethynyl-2,3,4,5-tetraethyl-2,3,4,5-tetracarba-nido-hexaborane(6) (1c) gives the linked compound 4, and a very small amount
of ZnI2(OPPh3)2 is formed. The selective basal halogen exchange of 1,6-diiodo-2,3,4,5-tetraethyl-2,3,4,5-tetracarba-nido-hexabo-
rane(6) (5) with an excess of AgF leads to 1-iodo-6-fluoro-2,3,4,5-tetraethyl-2,3,4,5-tetracarba-nido-hexa-borane(6) (6). The compo-
sition of the products follows from NMR and MS data and a single crystal X-ray analysis of 2a. The X-ray structure of
ZnI2(OPPh3)2 is reported.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Boron; Carborane; Halogen exchange; Palladium catalysis
1. Introduction
Onak et al. [3] studied the halide exchange reactions
involving B-halogenated closo-2,4-C2B5 carborane deri-
vatives, leading to carborane products with lighter halo-
gen atom(s) than the leaving halogen atom(s). Stanko
et al. [4] described that 2-iodo-p-carborane was trans-
formed to 2-chloro-p-carborane by treatment with CuCl;
the exchange with Na131I in 10-iodo-o-carborane, 9-iodo-
m-carborane and 2-iodo-p-carborane, respectively, was
observed [4b]. The Pd-catalyzed exchange reactions [5]
afforded a series of 125I-labelled o,m,p-carboranes.
Recently, Grushin et al. [6] reported that, in the presence
of n-Bu4NBr, 9-I-m-carborane underwent halogen ex-
change to give 9-Br-m-carborane in the presence of a Pd
catalyst. In the case of the nido-C4B2 cluster, it has been
observed that a 6-bromo-peralkylated nido-C4 B2 carbo-
rane reacts with AgF to give the 6-F-carborane derivative
when a catalytic amount of Et3N was present [7].
B-halogenated polyhedral borane and carborane
clusters are useful precursors for organyl-substituted
products via direct or transition metal-catalyzed trans-
formations, and for labeled derivatives via isotopic
exchange in biomedical studies. Halogenated com-
pounds can be obtained by (selective) halogenation of
the B–H groups of boranes and carboranes. Although
halogen exchange is a conventional way to functional-
ized organoboron compounds [1], it is rare in polyhedral
borane and carborane chemistry [2].
*
Corresponding author. Tel.: +49 6221 548485; fax: +49 6221
545609.
E-mail address: walter.siebert@urz.uni-heidelberg.de (W. Siebert).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.05.037

4532
Y. Nie et al. / Journal of Organometallic Chemistry 690 (2005) 4531–4536
R
B
Recently, we have developed a one-pot synthesis of
1,6-diiodo-2,3,4,5-tetraalkyl-2,3,4,5-tetracarba-nido-hexa-
boranes(6) [8a], involving disubstituted alkynes, BI3 and
NaK2.8. While the basal B–I bond is easily cleaved by a
variety of nucleophiles, the apical B–I group remains
largely inert, its substitution has been achieved by a
Pd(0)-catalyzed Negishi-type cross-coupling reaction
with an alkynylzinc reagent [8b] (Scheme 1). In order
to study the scope and limitations of the apical function-
alization, we have carried out similar reactions involving
in situ generated arylzinc reagents (from arylbromides),
however, the apical brominated species is observed in-
stead of the expected products. Herein, we report on
the apical halogen substitution as well as an example
of selective basal halogen exchange.
Et
1) 2 or 3 equiv. n-BuLi
2) 2 or 3 equiv. ZnCl2
Et
Et
4,4'-(C6H4)2Br2
or
B
Ph
3a R = C2Ph
3) 1a, Pd(PPh3)4 (cat.)
1,3,5-C6H3Br3
Et
2a R = Br
Scheme 2.
Br1
B1
C5
C6
C3
C4
B2
C1
C2
C15
2. Results and discussion
As outlined in Scheme 2, the reactions of 1a with aryl
zinc reagents (generated in situ from 4,40-dibromobiphe-
nyl and 1,3,5-tribromobenzene, respectively, with the
appropriate amounts of n-BuLi and ZnCl2) in the pres-
ence of a catalytic amount of Pd(PPh3)4, did not give the
apically linked clusters, but the brominated product 2a.
The formation of 2a was first deduced from its 11B
NMR spectrum (d = 10.6, ꢀ40.2 ppm), the signal for
the basal boron (10.6 ppm) is unchanged compared to
that of 1a (10.3 ppm), but that of the apical boron is
downfield shifted (ꢀ40.2 ppm) relative to that of 1a
(ꢀ52.6 ppm). The mass spectrum exhibits a base peak
at m/z = 366/368 with the correct isotopic pattern for
(EtC)4(BC2Ph)(BBr). In addition, a very weak peak at
m/z = 388 in the mass spectrum is assigned to be nido-
(EtC)4(BC2Ph)2 (3a). It is available from the separate
reaction of 1a with PhC„CZnCl in the presence of
the catalyst Pd(PPh3)4, similar to the formation of
(EtC)4(BC2Ph)(BC2SiMe3) (Scheme 1) [8b]. The yellow
product 3a was obtained by heating the reaction mix-
tures for 7 days. Interestingly, the 11B NMR signal of
the substituted apical boron is only slightly downfield
shifted (d = ꢀ49.8 ppm) compared to that of 1a.
Fig. 1. Molecular structure of 2a. Hydrogen atoms omitted for clarity.
˚
Selected bond lengths (A) and angles (ꢁ): Br(1)–B(1) 1.906(3), B(1)–
C(3) 1.712(3), B(1)–C(4) 1.720(4), B(1)–C(5) 1.717(3), B(1)–C(6)
1.711(4), B(1)–B(2) 1.820(4), B(2)–C(3) 1.523(3), B(2)–C(6) 1.529(3),
B(2)–C(1) 1.531(3), C(3)–C(4) 1.456(3), C(4)–C(5) 1.442(4), C(5)–C(6)
1.451(3), C(1)–C(2) 1.208(3), C(2)–C(15) 1.434(3); B(2)–B(1)–Br(1)
138.76(17), C(1)–B(2)–B(1) 132.12(19), C(2)–C(1)–B(2) 174.0(2), C(1)–
C(2)–C(15) 174.9(3).
174.0(2)ꢁ [cf. those in 1a 177.0ꢁ, and in (EtC)4(BC2Ph)-
(BC2SiMe3) 173.2ꢁ]. The apical B–Br group [bond
length: 1.906(3) A] is bent away from the Bbasal [B2–
˚
B1–Br1 138.76(17)ꢁ], comparable to those in 1a and
(EtC)4(BC2Ph)(BC2SiMe3) [143.3(3)ꢁ and 141.3(3)ꢁ,
respectively].
The formation of 2a implies that the apically bromi-
nated nido-C4B2 carborane derivative is not suitable for
the Pd-catalyzed Negishi-type cross coupling with zinc
reagents. Obviously the bromine sources for the forma-
tion of 2a are 4,40-dibromodiphenyl and 1,3,5-tribromo-
benzene. They react with n-BuLi to generate n-BuBr
along with the aryllithium reagents, which in turn yield
with ZnCl2 the corresponding zinc reagents.
Two control reactions were therefore carried out
(Scheme 3). The reaction of 1b with n-BuBr and a cata-
lytic amount of Pd(PPh3)4 produced the brominated 2b,
whereas the similar reaction of 1b with PhZnCl did not
The structure of 2a (Fig. 1) has been established by a
single crystal X-ray diffraction analysis, which is very
similar to that of 1a [8b]. The alkynyl B2–C1–C2 moiety
is almost linear, the corresponding B–C–C angle is
C2SiMe3
I
B
B
Me3SiC2ZnCl
Et
Et
Et
Et
Et
Et
Pd(PPh3)4
(cat.)
B
Ph
THF
B
Ph
Et
Et
1a
Scheme 1.

Y. Nie et al. / Journal of Organometallic Chemistry 690 (2005) 4531–4536
4533
C2tBu
Ph
B
B
Et
Et
Et
Et
Et
Et
B
tBu
B
tBu
Et
Et
3b
[tBuC2ZnCl]
PhZnCl
Pd(PPh3)4 (cat.)
I
Br
B
B
Et
Et
Et
Et
Et
Et
n-BuBr
B
B
tBu
tBu
Pd(PPh3)4 (cat.)
THF
Et
Et
1b
2b
Scheme 3.
give any apically phenylated product, but the apically
alkynylated species 3b, as indicated by its 11B NMR
spectrum (d = 8.9, ꢀ52.6 ppm, comparable to that of
3a) and mass spectrum (m/z = 348). The formation of
3b may originate from an intermolecular reaction: the
basal B–Calkynyl group of 1b is cleaved thereby forming
the alkynylzinc reagent tBuC„CZnCl, which reacts
with the apical B–I group of another molecule of 1b to
form 3b under Pd catalysis.
I2
Zn1
P1
P2
O2
O1
I1
While 1c did not react with LiC„C(CH2)4C„CLi,
its reaction with the corresponding zinc reagent
ClZnC„C(CH2)4C„CZnCl produced the apically
linked cluster 4 (Scheme 4) in the presence of a Pd cat-
alyst. The yellow oil exhibits in the 11B NMR spectrum
two signals at d = 10.2 and ꢀ49.4 ppm. The mass spec-
trum of 4 shows the molecule ion peak with the correct
isotopic pattern. After workup colorless crystals (a very
small amount) were unexpectedly obtained and found to
be ZnI2(OPPh3)2 by an X-ray structure analysis. The
zinc center (Fig. 2) adopts a slightly distorted tetrahe-
dral geometry. The formation of the long known
ZnI2(OPPh3)2 [9] results obviously from ZnI2 and
OPPh3 (formed by contact of air with PPh3 from
Pd(PPh3)4).
Fig. 2. Molecular structure of ZnI2(OPPh3)2. Hydrogen atoms omit-
˚
ted for clarity. Selected bond lengths (A) and angles (ꢁ): I(1)–Zn(1)
2.5550(4), I(2)–Zn(1) 2.5439(4), Zn(1)–O(1) 1.977(2), Zn(1)–O(2)
1.967(2), O(1)–P(1) 1.506(2), O(2)–P(2) 1.503(2); O(2)–Zn(1)–O(1)
101.06(9), O(2)–Zn(1)–I(2) 110.59(6), O(1)–Zn(1)–I(2) 112.11(6), O(2)–
Zn(1)–I(1) 111.32(6), O(1)–Zn(1)–I(1) 104.29(6), I(2)–Zn(1)–I(1)
116.275(12).
the difluoro-nido-C4B2 intermediate 7, which, as has
been demonstrated by Timms [10], would rearrange to
give the classic structure 8. While no reaction was ob-
served between 5 and SbF3 in hexane at room tempera-
ture, the reaction with AgF (without catalyst) led only to
the basal-substituted monofluoro derivative 6, charac-
terized by its 11B NMR spectrum [d = 21.8, ꢀ53.1 ppm,
cf. that of 5: d = 5.5 (Bbasal) and ꢀ52.5 (Bapical) ppm].
The mass spectrum exhibits the molecule ion peak at
m/z = 332 with the correct isotopic distribution.
The reactions of 5 [8a] with an excess of AgF and
SbF3, respectively, were carried out (Scheme 5) to obtain
Et
Et
B
C2-p-tolyl
Et
I
Et
B
B
R
B
Et
Et
Et
3. Conclusion
[(CH2)4C2ZnCl]2
Pd(PPh3)4
B
(cat.)
p-tolyl
We have shown that the halogen exchange occurs at
both the basal and the apical boron atoms of the nido-
C4B2 carboranes. In accord with Onak [3], such halogen
exchange reactions depend on the strength of the B–X
(X = F, Cl, Br, I) bonds, which is possible only with hea-
vier halogens as leaving atoms.
Et
Et
Et
1c
B
C2-p-tolyl
Et
Et
R = C2(CH2)4C2
4
Scheme 4.

4534
Y. Nie et al. / Journal of Organometallic Chemistry 690 (2005) 4531–4536
F
F
B
Et
F
Et
Et
Et
Et
B
Et
Et
xs. AgF
or SbF3
I
B
B
B
B
Et
F
8
Et
Et
Et
I
7
B
I
B
Et
F
Et
Et
Et
xs. AgF
- AgI
5
Et
6
Scheme 5.
4. Experimental
125.7, 131.7 (Ph), alkynyl carbon atoms n.o. EI-MS:
m/z (%) = 366 (100) [M+], 388 (3) [3a+]. HR-MS (EI):
12
4.1. General
m/z = 366.1330 [M+]; Calc. for
C
1H2511B2 79Br
20
366.1326 (Dm = 0.4 mmu); m/z = 388.2556 [3a+]; Calcd.
for
12
All reactions and manipulations were performed in
dry glassware under argon or nitrogen using standard
Schlenk techniques. Solvents were dried, distilled and
saturated with nitrogen. NMR spectra were recorded
on a Bruker DRX 200 spectrometer (1H: 200.13 MHz,
11B: 64.21 MHz, 13C: 50.32 MHz ) in CDCl3, CD2Cl2
and C6D6 as solvents. Et2OBF3 was used as external
C
1H30 11B2 388.2533 (Dm = 2.3 mmu).
28
4.3. 1-Bromo-6-tert-butylethynyl-2,3,4,5-tetraethyl-
2,3,4,5-tetracarba-nido-hexaborane(6) (2b)
A portion of nBuBr (130 mg, 0.95 mmol) was added
to a mixture of 1b (180 mg, 0.46 mmol) and Pd(PPh3)4
(30 mg, 0.026 mmol) in THF (15 mL) at r.t. The yellow
mixture was stirred overnight and heated at reflux for 5
days. After removing the solvent the yellow brown resi-
due was extracted with hexane (2 · 20 mL) and filtered.
The filtrate was dried in vacuo to give 2b (136 mg, 85%)
standard for 11B NMR. As internal references for H
1
and 13C NMR, the signals of the deuterated solvents
were used, the shifts were calculated relative to TMS
and given in ppm. MS: ZAB-2F VH Micromass CTD
spectrometer, and a JEOL MS Station JMS 700
spectrometer.
1
as a red-orange oil. H NMR (C6D6): d = 1.0 (br, 6H,
CH3), 1.27 (s, 9H, tBu-H), 1.3 (br, 6H, CH3), 2.0–2.3
(m, 8H, CH2). 11B NMR (C6D6): d = 11.1 (s, Bbasal),
ꢀ40.0 (s, Bapical). 13C NMR (C6D6): d = 13.0, 14.0
(CH3), 17.6, 19.3 (CH2), 29.8 (C(CH3)3), 31.1
(C(CH3)3), 103 (br, CBbasal), 112.7 (CEt), alkynyl
carbon atoms n.o. EI-MS: m/z (%) = 348 (100) [M+].
4.2. 1-Bromo-6-phenylethynyl-2,3,4,5-tetraethyl-2,3,4,5-
tetracarba-nido-hex-borane(6) (2a)
A portion of nBuLi (2.5 M in hexanes, 1.2 ml,
3 mmol) was added into a solution of 1,3,5-tribromo-
benzene (254 mg, 0.8 mmol) in THF (15 mL) at
ꢀ60 ꢁC, and slowly warmed to r.t.. To this solution
ZnCl2 (340 mg, 2.5 mmol) was added and stirred for
3 h. The resulting light yellow solution was then added
to a mixture of 1a (240 mg, 0.56 mmol) and Pd(PPh3)4
(80 mg, 0.07 mmol), and the mixture was heated at
reflux for 7 days. All volatiles were removed, the black
oily residue was extracted with hexane (30 mL) and fil-
tered. The light yellow filtrate was dried in vacuo to give
2a (201 mg, 94%) as a yellow oil. 3a was identified only
by MS. Suitable crystals for X-ray analysis were
HR-MS (EI): m/z = 348.1644 [M+]; Calcd. for
12
C
1H2911B279Br 348.1638 (Dm = 0.6 mmu).
18
4.4. 1,6-Bis(phenylethynyl)-2,3,4,5-tetraethyl-2,3,4,5-
tetracarba-nido-hexaborane(6) (3a)
To a solution of phenylacetylene (146 mg, 1.43 mmol)
in THF (10 mL) was added nBuLi (2.5 M in hexanes,
0.6 mL, 1.6 mmol) at ꢀ40 ꢁC. The mixture was stirred
for 30 min, ZnCl2 (218 mg, 1.6 mmol) in a solution of
THF (5 mL) was then added and the resulting yellow
solution was warmed up and stirred for 2 h. The solu-
tion was transferred to a mixture of 1a (436 mg,
1.1 mmol) and Pd(PPh3)4 (61 mg, 0.05 mmol) and the
resulting yellow mixture was heated at reflux for 7 days.
The solvent was removed, the yellow brown oily residue
was extracted with hexane (2 · 20 mL) and filtered. The
1
obtained by cooling a neat sample at 4 ꢁC. H NMR
3
(C6D6): 0.92 (t, 6H, JH,H = 7.6 Hz, CH3), 1.37 (t, 6H,
3JH,H = 7.6 Hz, CH3), 2.2–2.5 (m, 8H, CH2), 7.50 (m,
5H, Ph). 11B NMR (C6D6): d = 10.8 (s, Bbasal), ꢀ39.9
(s, Bapical). 13C NMR (C6D6): d = 13.8, 14.2 (CH3),
17.6, 19.4 (CH2), 105 (br, CBbasal), 112.8 (CEt), 124.9,

Y. Nie et al. / Journal of Organometallic Chemistry 690 (2005) 4531–4536
4535
yellow filtrate was dried in vacuo to give 3a (350 mg,
1
(%) = 706 (46) [M+]. HR-MS (EI): m/z = 706.5247
[M+]; Calcd. for 12C50 H6211B4 706.5224 (Dm = 2.3 mmu).
1
86%) as a yellow oil. H NMR (CDCl3): d = 1.28 (t,
3
6H,3JH,H = 7.5 Hz, CH3), 1.38 (t, 6H, JH,H = 7.5 Hz,
CH3), 2.3–2.5 (m, 8H, CH2), 7.2–7.6 (m, 5H, Ph). 11B
NMR (CDCl3): d = 9.9 (s, Bbasal), ꢀ49.8 (s, Bapical).
13C NMR (CDCl3): d = 13.8, 14.9 (CH3), 17.5, 19.3
(CH2), 104 (CBbasal), 112.7 (CEt), 127.5, 128.0, 131.8,
132.1 (Ph), alkynyl carbon atoms n.o. EI-MS: m/z (%)
4.7. 1-Iodo-6-fluoro-2,3,4,5-tetraethyl-2,3,4,5-tetracarba-
nido-hexaborane(6) (6)
(a) Reaction of 5 with SbF3: A solution of 5 (145 mg,
0.33 mmol) in hexane (3 mL) was added dropwise to a
suspension of SbF3 (600 mg, 3.4 mmol) in hexane
(2 mL) at r.t. The mixture was stirred for one week.
The starting compound 5 remained unreacted as
checked by 11B NMR (d = 6.5, ꢀ52.3 ppm).
= 388 (100) [M+]. HR-MS (EI): m/z = 388.2519 [M+];
12
Calcd. for
C
1H3011B2 388.2534 (Dm = ꢀ1.5 mmu).
28
4.5. 1,6-Bis(tert-butylethynyl)-2,3,4,5-tetraethyl-2,3,4,5-
tetracarba-nido-hexaborane(6) (3b)
(b) Reaction of 5 with AgF: A solution of 5 (145 mg,
0.33 mmol) in hexane (3 mL) was added dropwise to a
suspension of AgF (180 mg, 1.4 mmol) in hexane
(7 mL) at r.t. with exclusion of light. The mixture was
stirred overnight and a colorless solution was obtained
after filtration, which was dried to give 6 (60 mg, 56%)
The solvents of a solution of PhLi (1.8 M in cyclohex-
ane/ether, v/v = 70/30, 1.62 mmol) were removed. THF
(10 mL) and ZnCl2 (235 mg, 1.72 mmol) were added at
0 ꢁC and stirred for 3 h. To the resulting light yellow
solution 1b (180 mg, 0.46 mmol) and Pd(PPh3)4
(28 mg, 0.024 mmol) were added, and the yellow mixture
was heated at reflux for 7 days. The solvent was
removed, and the dark brown residue was extracted with
hexane (2 · 20 mL) and filtered. The filtrate was dried in
vacuo to give 3b (60 mg, 37.5% based on 1b) as a yellow
1
as a colorless oil. H NMR (CDCl3): d = 1.18 (br, 6H,
CH3), 1.26 (br, 6H, CH3), 2.08 (m), 2.33 (m) (8H,
CH2). 11B NMR: d = 21.9 (br, Bbasal), ꢀ53.1 (s, Bapical).
13C NMR: d = 13.3, 14.1 (CH3), 18.5, 20.1 (CH2), 106
(br, CBbasal), signals for the other skeletal carbon atoms
n.o. EI-MS: m/z (%) = 332 (100) [M+], 205 (67) [M+ ꢀ I].
1
oil. H NMR (CD2Cl2): 1.2 (br, 6H, CH3), 1.3 (br, 6H,
HR-MS (EI): m/z = 332.0782 [M+]; Calcd. for
12
CH3), 1.36 (s, 9H, tBu-H), 1.37 (s, 9H, tBu-H), 2.2–2.4
(m, 8H, CH2). 11B NMR (CD2Cl2): d = 8.9 (s, Bbasal),
ꢀ52.7 (s, Bapical). 13C NMR (CD2Cl2): d = 13.9, 14.4
(CH3), 17.3, 19.0 (CH2), 29.8 (C(CH3)3), 30.8, 31.1
(C(CH3)3), 103 (br, CBbasal), 111.9 (CEt). EI-MS: m/z
(%) = 348 (100) [M+]. HR-MS (EI): m/z = 348.3153
C
1H2019F11B2 127I 332.0780 (Dm = 0.2 mmu).
12
4.8. Crystal structure determination for 2a and
ZnI2(OPPh3)2
Diffraction data were collected on a Bruker-AXS
Smart 1000 CCD diffractometer (Mo Ka radiation,
1
[M+]; Calc. for 12C24 H3811B2 348.3160 (Dm = ꢀ0.7 mmu).
˚
k = 0.71073 A, graphite monochromator, x-scans). Crys-
4.6. Apically C2(CH2)4C2-linked clusters 4
tal data and details of the measurements are summarized
in Table 1. Data were corrected for Lorentz polarization
and absorption effects (semi-empirical, SADABS [11]). The
structures were solved by direct methods (SHELXS86 [12])
and refined by full-matrix least-squares methods
(SHELXL97 [12]) based on F2 with all reflections. Non-
hydrogen atoms were refined anisotropically, hydrogen
atoms were located in difference Fourier syntheses and re-
fined isotropically (compound 2a) or input in calculated
positions [ZnI2(OPPh3)2].
n-BuLi (2.5 M in hexanes, 0.32 mL, 0.8 mmol) was
added to a solution of 1,7-octadiyne (43 mg, 0.40 mmol)
in THF (15 mL) at ꢀ60 ꢁC, and stirred for 2 h. To the
resulting white suspension ZnCl2 (110 mg, 0.8 mmol)
was added in one portion. The mixture was stirred for
2 h and half of the white suspension added to a mixture
of 1c (231 mg, 0.54 mmol) and Pd(PPh3)4 (30 mg,
0.026 mmol) in 10 mL of THF. The resulting mixture
was heated at reflux for 7 days. After removing the sol-
vent, the dark brown residue was extracted with hexane
(2 · 25 mL) and filtered. The light yellow filtrate was
dried in vacuo to give 4 (95 mg, 67%) as a yellow oil.
On standing at r.t., a few colorless crystals were
obtained and found to be ZnI2(OPPh3)2. 1H NMR
5. Supplementary material
Crystallographic data (excluding structure factors)
for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data
Center: CCDC No. 268967 for ZnI2(OPPh3)2, No.
268968 for 2a. Copies of the data can be obtained free
of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: int. code +44
(1223)336 033; e-mail deposit@ccde.cam.ac.uk or
http://www.ccdc.cam.ac.uk).
(C6D6): d = 1.0 (br, 12H, CH3), 1.2 (br, 12H, Ccage
-
CH2), 1.4 (br, 4H, CH2CH2), 2.0 (br, 4H, „CCH2),
2.2–2.5 (m, 16H, CH2). 11B NMR (C6D6): d = 10.4 (s,
2B, Bbasal), ꢀ50.0 (s, 2B, Bapical). 13C NMR (C6D6):
d = 13.6, 14.0 (CH3), 17.4, 19.5 (cage-bound CH2),
20.9 („CCH2), 27.3 (CH2CH2), 105 (br, CBbasal),
111.9 (CEt), alkynyl carbon atoms n.o. EI-MS: m/z

4536
Y. Nie et al. / Journal of Organometallic Chemistry 690 (2005) 4531–4536
Table 1
Crystal data and details of data collection and structure solution of 2a and ZnI2(OPPh3)2
Identification Code
2a
ZnI2(OPPh3)2
Empirical formula
Formula weight
Temperature (K)
Crystal system
C20H25B2Br
366.93
103(2)
C36H30I2O2P2Zn
875.71
100(2)
Monoclinic
P2(1)/c
Triclinic
P1
Space group
Unit cell dimensions
˚
a (A)
7.6106(4)
16.0975(9)
10.0138(5)
10.2701(5)
10.6702(5)
65.5770(10)
62.7660(10)
89.9560(10)
863.99(7)
1
˚
b (A)
˚
c (A)
16.1470(9)
90
a (ꢁ)
b (ꢁ)
c (ꢁ)
101.127(1)
90
1941.0(2)
3
˚
V (A )
Z
4
1.256
Calculated density (g/cm3)
Absorption coefficient (mmꢀ1
F(0 0 0)
1.683
2.620
)
2.114
760
428
0.30 · 0.13 · 0.08
32.01.
Crystal size (mm)
Maximum (ꢁ)
Index ranges
0.37 · 0.24 · 0.03
30.51
ꢀ10/10, 0/22, 0/23
24,618
ꢀ14/14, ꢀ14/15, ꢀ15/15
Reflections collected
Independent reflections
Data/restraints/parameters
Flack x-parameter
Goodness-of-fit on F2
Final R indices
15,004
5932 [Rint = 0.0427]
5932/0/308
–
9363 [Rint = 0.0238]
9363/3/388
0.011(8)
1.080
0.997
R1 [I > 2r(I)]
wR2 (all data)
˚
Largest difference peak/hole (e A
0.0487
0.1497
0.0253
0.0572
ꢀ3
)
0.689/ꢀ0.760
0.910/ꢀ0.479
(d) F.A. Gomez, T. Onak, J. Arias, C. Alfonso, Main Group
Metal Chem. 13 (1990) 237.
Acknowledgments
[4] (a) V.I. Stanko, Y.V. GolÕtyanin, Zhu. Obsh. Khim. 40 (1970)
127 [translated from Russ. J. Gen. Chem., 40 (1970) 115];
(b) V.I. Stanko, N.G. Iroshnikova, Zhu. Obsh. Khim. 40
(1970) 311 [translated from Russ. J. Gen. Chem., 40 (1970)
281].
Support of this work by the Deutsche Forschungs-
gemeinschaft (Schwerpunktprogramm Polyeder and
SFB 623) and the Fonds der Chemischen Industrie is
gratefully acknowledged.
[5] K.J. Winberg, G. Barbera, L. Eriksson, F. Texidor, V. Tolma-
chev, C. Vinas, S. Sjo¨berg, J. Organomet. Chem. 680 (2003) 188.
[6] W.J. Marshall, R.J. Young, Jr., V.V. Grushin, Organometallics
20 (2001) 523.
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