Synthesis and reactivity of boron-functionalized C2B 5-closo-carboranes

Article abstract of DOI:10.1515/znb-2005-0602

Treatment of the nido-2,3-Et₂C₂B₄H ₄^2- dianion (1) with monoboron reagents led to closo-C₂B₅ carborane derivatives with functional substituents at the inserted apical boron atom. The reactions of 1 with BX ₃ (X = Br, I) afforded the corresponding closo-1-X-2,3-Et ₂C₂B₅H₄ (2a,b), and with PhC≡CBcat (cat = O₂C₆H₄) produced the alkynyl-substituted closo-1-C≡CPh-2,3-Et₂C₂B ₅H₄ (2c). Pd-catalyzed Negishi-type cross-coupling reactions of 2b with RC≡CZnCl at room temperature gave the corresponding closo-1-C≡CR-2,3-Et₂C₂B₅H₄ derivatives 2d-f, R = SiMe₃, Me, and tBu, respectively. Compound 3 with two C₂B₅ moieties linked via a C=C unit was obtained by a similar boron incorporation reaction with cis-Cl₂B(Et)C=C(Et) BCl₂. The reactions of 2c,d with Co₂(CO)₈ afforded the dicobaltatetrahedrane-substituted carboranes 4c and d, in which the clusters C₂B₅ and Co₂C₂ are connected by a B-C bond. Compounds 4c,d lost the apical boron on wet silica gel or sand to give the nido-C₂B₄-C₂Co₂ compounds 5c,d. Formation of the carboranyl-substituted (η⁵- C₅H₅)Co(cyclobutadiene) complex 6c was observed in the reaction of 2c with (η⁵-C₅H₅)Co(C ₂H₄)₂. The composition of the products follows from NMR and MS data.

Full text of DOI:10.1515/znb-2005-0602

Synthesis and Reactivity of Boron-Functionalized C2B5-closo-Carboranes
Yong Nie, Avijit Goswami, and Walter Siebert
Anorganisch-Chemisches Institut der Universita¨t Heidelberg,
Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany
Reprint requests to Prof. Dr. W. Siebert. Fax: + 49-(0)6221/545609.
E-mail: walter.siebert@urz.uni-heidelberg.de
Z. Naturforsch. 60b, 597 – 602 (2005); received March 14, 2005
Dedicated to Dr. Karlheinz Schmidt on the occasion of his 60th birthday
Treatment of the nido-2,3-Et2C2B4H42−dianion (1) with monoboron reagents led to closo-C2B5
carborane derivatives with functional substituents at the inserted apical boron atom. The reactions
of 1 with BX3 (X = Br, I) afforded the corresponding closo-1-X-2,3-Et2C2B5H4 (2a,b), and with
PhC≡CBcat (cat = O2C6H4) produced the alkynyl-substituted closo-1-C≡CPh-2,3-Et2C2B5H4 (2c).
Pd-catalyzed Negishi-type cross-coupling reactions of 2b with RC≡CZnCl at room temperature gave
the corresponding closo-1-C≡CR-2,3-Et2C2B5H4 derivatives 2d-f, R = SiMe3, Me, and tBu, re-
spectively. Compound 3 with two C2B5 moieties linked via a C=C unit was obtained by a similar
boron incorporation reaction with cis-Cl2B(Et)C=C(Et)BCl2. The reactions of 2c,d with Co2(CO)8
afforded the dicobaltatetrahedrane-substituted carboranes 4c and d, in which the clusters C2B5 and
Co2C2 are connected by a B-C bond. Compounds 4c,d lost the apical boron on wet silica gel or
sand to give the nido-C2B4-C2Co2 compounds 5c,d. Formation of the carboranyl-substituted (η5-
C5H5)Co(cyclobutadiene) complex 6c was observed in the reaction of 2c with (η5-C5H5)Co(C2H4)2.
The composition of the products follows from NMR and MS data.
Key words: Boron, Carborane, Cross Coupling, Cobalt, Cluster Linkage
Introduction
erate yields [7]. The parent closo-2,3-C2B5H7 [10]
has been isolated in ca. 65% yield by vacuum ther-
molysis of nido-4,5-C2B6H10. More recently Grimes,
Siebert et al. [11] reported the benzene-centered 1,3,5-
(closo-Et2C2B5H4)3C6H3 by reacting the nido-2,3-
Of the four possible isomers of the closo-C2B5H7
carborane (1,2-, 1,7-, 2,3- and 2,4-), the 2,3- and 2,4-
isomers are known, and studies of their chemistry
have focused on the 2,4- compounds [1 – 3]. The much
lower interest in the 2,3-isomer, which is predicted
by calculations [4] to be 15– 25 kcal/mol less sta-
ble than the 2,4-isomer, may be due to its difficult
accessibility. The first C-alkyl derivative closo-2,3-
Me2C2B5H5 was obtained in low yield by Schaeffer
et al. [5] in the gas phase reaction of octaborane(12)
with 2-butyne. Sneddon et al. [6] found a better way
to closo-2,3-Et2C2B5H5 by a capping reaction (boron
insertion) of nido-2,3-Et2C2B4H6 with Et3N·BH3 at
2−
Et2C2B4H4 dianion with tris(diiodoboryl)benzene,
which gave the corresponding 1,3,5-tris-nido-C2B4
carborane on silica. We have described the formation
of closo-2,3-Et2C2B5I5 [12] from the reaction of 3-
hexyne, BI3, and a NaK2.8 alloy at room temperature.
Herein we report on the synthesis of apically func-
tionalized closo-C2B5 carboranes, and the reactions of
some of the alkynyl- substituted derivatives with cobalt
complexes.
◦
140 C in 50 – 60% yield. Alternatively, closo-2,3-
Results and Discussion
Et2C2B5H5 is formed in the reaction of nido-2,3-
Et2C2B4H5−Na+ and Me2S·BH3 (44% yield), or from
the nido-2,3-Et2C2B4H42−Na+Li+ and Me2S·BHBr2
(49% yield) [6 – 9]. Sneddon and Beck also studied
the reaction of nido-2,3-Et2C2B4H42−Na+Li+ with
PhBCl2 and MeBBr2, respectively, and obtained closo-
1-R-2,3-Et2C2B5H4 (R = Ph, Me) derivatives in mod-
Boron insertion or capping reactions [13] are a
convenient pathway to functionalized carborane prod-
ucts. To achieve apically B-halogenated closo-2,3-
C2B5 carborane derivatives, we carried out reactions
2−
of the nido-2,3-Et2C2B4H4 dianion (1, formed by
deprotonation of nido-2,3-Et2C2B4H6 with 2 equiv. n-
c
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598
Y. Nie et al. · Synthesis and Reactivity of Boron-Functionalized C2B5-closo-Carboranes
Scheme 1.
Scheme 3.
BuLi in diethylether, Scheme 1) and BX3 (X = Br, I)
in toluene, which led to 2a,b as yellow oils, respec-
tively. Their 11B NMR spectra exhibit signals at 6.3
(B4,6), 1.2 (B5), −17.4 (B7), and −23.6 (B1) (2a), and
6.7 (B4,6), 1.9 (B5), −18.3 (B7), and −31.9 (B1) ppm
(2b), in a ratio of 2:1:1:1, respectively. The mass spec-
tra of 2a,b give the corresponding molecular ion peaks
with correct isotopic patterns.
the yellow solution of 2b in THF turned to red
upon addition of a catalytic amount of Pd(PPh3)4,
and again gradually to yellow after the correspond-
ing zinc reagents were added. It is noteworthy that the
Pd-catalyzed cross coupling in the present work was
achieved at ambient temperature (48– 72 h), whereas
in most of the reported Pd-catalyzed coupling reactions
involving halogenated borane or other carborane clus-
ters, either heating or longer reaction time or both are
needed [16– 22]. The initial attempt to obtain 2d by
heating the THF solution at reflux led only to a mixture
of 2d and unidentified carborane species. The effort
to obtain the proposed oxidative addition intermediate
2,3-Et2C2B5-Pd(PPh3)2I by reacting 2b and Pd(PPh3)4
in THF at room temperature was not successful, in-
stead red crystals of trans-Pd(PPh3)2I2 [23] were ob-
served, which was also formed in a trace amount in the
preparation of 2d. The desilylation reaction of 2d with
n-Bu4NF in THF did not lead to a terminal carborany-
lacetylene, only degradation of the cluster occurred.
A similar reaction of 1 with cis-Cl2B(Et)C=C(Et)-
BCl2 produced compound 3 (Scheme 3), in which two
closo-2,3-C2B5 clusters are linked via a C=C double
bond unit. Its 11B NMR spectrum exhibits broad sig-
nals at 6.2 (B4,6), 2.9 (B5), −4.7 (B1), and −21.5
(B7) ppm. The mass spectrum shows the molecular ion
peak with correct isotopic envelope.
The formation of 2a,b is of interest, as the bromin-
ation of closo-2,3-Et2C2B5H5 with Br2 or Br2/AlBr3
occurs selectively at the B5 position, affording closo-
5-Br-2,3-Et2C2B5H4 as the single product in moder-
ate yield [7]. Wrackmeyer et al. [14] studied the reac-
tion of nido-[2,4-(EtC)2(BEt)4H]− Na+ with BBr3 to
give closo-1-Br-2,4-(EtC)2(BEt)4B as a side product,
the major product being closo-2,4-(EtC)2(BEt)4BH.
Similarly, the reaction of 1 with PhC≡CBcat (cat =
O2C6H4) produced the apically alkynyl-substituted
closo-1-C≡CPh-2,3-Et2C2B5H4 (2c) (Scheme 2) as a
yellow oil. A more efficient way to 2d-f was found
by the Pd-catalyzed Negishi-type cross-coupling reac-
tions of 2b (Scheme 2). The 11B NMR spectrum of
2c shows signals at 6.4 (B4,6), 1.8 (B5), −16.1 (B1),
and −18.7 (B7) ppm in a ratio of 2:1:1:1, and sim-
ilar shifts are observed for 2d-f. There is no signifi-
cant “anti-podal” effect [15] of the halogen atoms (in
2a,b), or RC2 groups (in 2c-f) at B1 upon B7, as the
11B NMR shifts for B7 in 2a-f (−17.4 to −20.3 ppm
in CDCl3) are comparable to that of closo-2,3-C2B5H7
(B7: −17.9 ppm) [10]. By contrast, the chemical shift
for closo-1-butenyl-2,3-C2B5H6 (B7: −25.0 ppm) dif-
fers considerably from that of closo-2,3-C2B5H7 [10].
The Pd-catalyzed reactions could be easily moni-
tored by the stepwise color change and by 11B NMR:
The reactions of 2c,d with Co2(CO)8 afforded
the dicobaltatetrahedrane derivatives 4c,d as brown
oils, each having the C2B5 and Co2C2 clus-
ters connected by a B-C bond. As observed for
the benzene-centered triscarboranyl compound 1,3,5-
(closo-Et2C2B5H4)3C6H3 [11], our attempt to purify
Scheme 2.
Scheme 4.
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Y. Nie et al. · Synthesis and Reactivity of Boron-Functionalized C2B5-closo-Carboranes
599
cis-Cl2B(Et)C=C(Et)BCl2. The reactions of carbor-
anylacetylenes 2c,d with Co2(CO)8 afforded 4c,d, in
which a closo-C2B5 and a nido-Co2C2 cluster are
connected by a B-C bond. Compounds 4c,d lost
the apical boron atom on silica gel to give nido-
C2B4-Co2C2 5c,d. The formation of the carboranyl-
substituted CpCo(cyclobutadiene) complex 6c was ob-
served in the reaction of 2c with CpCo(C2H4)2.
Scheme 5.
compounds 4c,d by column chromatography on silica
gel or sand led to mixtures of 4c,d and the nido-C2B4-
clusters 5c,d, respectively, formed by elimination of a
BH group [as B(OH)3 in a “decapitation” reaction [24]
of 4c,d with H2O and protonation to give 5c,d].
Experimental Section
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 specta were recorded on a Bruker DRX
200 spectrometer (1H: 200.13 MHz, 11B: 64.21 MHz, 13C:
50.32 MHz) in CDCl3 and C6D6 as solvents. Et2O•BF3
was used as the external standard for 11B NMR. As in-
ternal references for 1H and 13C NMR, the signals of the
deuterated solvents were used and the shifts calculated rel-
ative to TMS. MS: ZAB-2F VH Micromass CTD spectro-
meter, and a JEOL MS Station JMS 700 spectrometer. nido-
2,3-Et2C2B4H6 was kindly provided by Prof. R. N. Grimes
(Charlottesville, USA).
The 11B NMR spectrum of 4c (in hexane, before
column chromatography)exhibits signals at 7.2 (B4,6),
2.9 (B5), −5.6 (B7), and −20.5 (B1) ppm in a ratio of
2:1:1:1. After chromatography new signals appeared
at −2.8 and −35.6 ppm, indicating the formation of
5c. Additionally, the mass spectra of 4c/5c exhibit the
molecular ion peaks at m/z = 527 and m/z = 517, re-
spectively, and the characteristic fragments of sequen-
tial loss of the six carbonyl ligands. The 11B NMR and
MS spectra of 4d/5d provide similar information.
No reaction was observed between 2c and CpCo-
(CO)2 (Cp = η5-C5H5) in refluxing toluene (1 week)
as monitored by 11B NMR. However, adding [CpCo-
(C2H4)2] to this mixture and refluxing for addi-
1-Bromo-2,3-diethyl-2,3-dicarbaheptaborane(7) (2a)
2,3-Et2C2B4H6 (250 mg, 1.91 mmol) in diethyl ether
tional 6 days led to a brown mixture (after filtration (30 ml) was treated with n-BuLi (2.5 M in hexane, 1.55 ml,
3.8 mmol) at −65 ◦C. The solution was stirred for 4 h
through a pad of sand), in which the C2B5-substi-
at r.t., then the solvent removed in vacuo, the residue dis-
tuted CpCo(cyclobutadiene) complex 6c, the C2B4-
substituted analog 6d (from partial decapitation of
6c), and the partial degradation (of 2c) product 7c
(Scheme 5) were detected, with the latter two being the
minor species (11B NMR: δ = 6.3, 2.2, −4.0, −16.6,
−19.6, −45.1 ppm; EI-MS: m/z = 606 for 6c, 597 for
6d, and 232 for 7c, respectively). Compounds 6d and
7c may be formed in a way similar to 5c,d. No evi-
dence was found for cyclotrimerization in this case.
◦
solved in toluene (15 ml) and cooled to −20 C. A solu-
tion of BBr3 (550 mg, 2.2 mmol) in toluene (15 ml) was
added dropwise. The reaction mixture was warmed to r.t.
and stirred overnight. All volatiles were removed, the white
residue was extracted with hexane (30 ml) and filtered to
give a slight yellow filtrate, which was dried in vacuo to
leave 2a as a yellow oil (298 mg, 71%). – 1H{11B} NMR
3
(CDCl3): δ = 1.36 (t, 6 H, JH,H = 7.6 Hz, CH3), 2.64 (q,
4 H, 3JH,H = 7.6 Hz, CH2), 3.4 (br., 1 H, B5-H), 4.2 (br., 2 H,
B4,6-H), signal for B7-H n.o. – 11B NMR (CDCl3): δ = 6.3
(d, JB,H = 170 Hz, B4,6), 1.2 (d, JB,H = 170 Hz, B5), −17.4
(s, B1), −23.6 (d, JB,H = 180 Hz, B7). – 13C NMR (CDCl3):
δ = 13.2 (CH3), 22.1 (CH2), 113.5 (br., Ccage). – EI-MS:
m/z (%) = 220 (100) [M+], 205 (36) [M+ −Me]. – HR-MS
Conclusion
Apically functionallized closo-1-R-2,3-Et2C2B5H4
compounds (R = Br, I, C2Ph) (2a-c) have been prepar-
2−
ed either by treatment of the nido-2,3-Et2C2B4H4
(EI): m/z = 220.0751 [M+]; calcd. for 12C6 H1411B579Br
1
dianion (1) with BX3 (X = Br, I) or PhC≡CBcat. A
more efficient pathway to apically alkynyl-substituted
derivatives was developed via Pd-catalyzed Negishi-
type cross-coupling reactions of 2b with R’C≡CZnCl
at room temperature to give closo-1-C≡CR’-2,3-Et2C2
B5H4 (2d-f, R’ = SiMe3, Me, tBu). Compound 3
with two C2B5 moieties linked via a C=C unit was
220.0744 (∆m = 0.7 mmu).
1-Iodo-2,3-diethyl-2,3-dicarbaheptaborane(7) (2b)
Similar procedure as described for 2a. 2,3-Et2C2B4H6
(165 mg, 1.26 mmol), n-BuLi (2.5 M in hexane, 1 ml,
2.5 mmol), BI3 (498 mg, 1.27 mmol). 2b was obtained as a
yellow oil (320 mg, 95%). – 1H NMR (CDCl3): δ = 1.38 (t,
3
3
obtained by a similar boron insertion reaction with 6 H, JH,H = 7.8 Hz, CH3), 2.61 (q, 4 H, JH,H = 7.8 Hz,
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600
Y. Nie et al. · Synthesis and Reactivity of Boron-Functionalized C2B5-closo-Carboranes
CH2). – 11B NMR (CDCl3): δ = 6.7 (d, JB,H = 173 Hz, 2 mmol), Pd(PPh3)4 (40 mg, 0.035 mmol). 2e was ob-
B4,6), 1.9 (d, JB,H = 173 Hz, B5), −18.3 (d, JB,H = 180 Hz, tained as a yellow oil (297 mg, 85%). – 1H{11B} NMR
3
B7), −31.9 (s, B1). – 13C NMR (CDCl3): δ = 13.3 (CH3), (CDCl3): δ = 1.37 (t, 6 H, JH,H = 7.7 Hz, CH3), 1.63 (s,
3
22.4 (CH2), 113.9 (br., Ccage). – EI-MS: m/z (%) = 267 (100) 3 H, Me), 2.70 (q, 2 H, JH,H = 7.7 Hz, CH2), 2.71 (q,
3
[M+], 112 (28) [M+ −I−C2H4].
2 H, JH,H = 7.7 Hz, CH2), 3.7 (br., 1 H, B5-H), 4.2 (br.,
2 H, B4,6-H), −1.5 (br., 1 H, B7-H). – 11B NMR (CDCl3):
δ = 6.3 (d, JB,H = 165 Hz, B4,6), 2.2 (d, JB,H = 170 Hz, B5),
−16.3 (s, B1), −20.3 (d, JB,H = 168 Hz, B7). – 13C NMR
(CDCl3): δ = 4.2 (Me), 13.5 (CH3), 22.3 (CH2), 102.4
(MeC ≡), 114.7 (br., Ccage), signal for B-C≡ n.o.. – EI-MS:
m/z (%) = 179 (100) [M+], 164 (82) [M+ −Me]. – HR-
1-Phenylethynyl-2,3-diethyl-2,3-dicarbaheptaborane(7) (2c)
Similar procedure as described for 2a. 2,3-Et2C2B4H6
(340 mg, 2.6 mmol), n-BuLi (2.5 M in hexane, 2.1 ml,
5.25 mmol), PhC≡CBcat (570 mg, 2.6 mmol). 2c was ob-
tained as an orange red oil (393 mg, 63%). – 1H NMR
1
MS (EI): m/z = 180.1801 [M+]; calcd. for 12C9 H1711B5
3
(CDCl3): δ = 1.48 (t, 6 H, JH,H = 7.6 Hz, CH3), 2.82 (q,
180.1796 (∆m = 0.5 mmu).
3
3
2 H, JH,H = 7.6 Hz, CH2), 2.82 (q, 2 H, JH,H = 7.4 Hz,
CH2), 7.37 (m, 5 H, Ph). – 11B NMR (CDCl3): δ = 6.4
(br., B4,6), 1.8 (br., B5), −16.1 (s, B1), −18.7 (br., B7). –
13C NMR (CDCl3): δ = 13.6 (CH3), 22.5 (CH2), 94.1
(PhC≡), 115.1 (br., Ccage), 122.5, 128.2, 128.7, 132.0 (Ph),
signal for B-C≡ n.o.. – EI-MS: m/z (%) = 241 (100) [M+],
1-tert-Butylethynyl-2,3-diethyl-2,3-dicarbaheptaborane(7)
(2f)
Similar procedure as described for 2d. tBuC≡CH
(175 mg, 2.1 mmol), nBuLi (2.5 M in hexane, 0.9 ml,
22 mmol), ZnCl2 (299 mg, 2.5 mmol), 2b (534 mg, 2 mmol),
Pd(PPh3)4 (75 mg, 0.065 mmol). 2f was obtained as a yel-
low oil (292 mg, 66%). – 1H{11B} NMR (CDCl3): δ = 1.05
226 (34) [M+ −Me]. – HR-MS (EI): m/z = 242.1986 [M+];
12
calcd. for
C
1H1911B5 242.1952 (∆m = 3.4 mmu).
14
3
(s, 9 H, tBu), 1.36 (t, 6 H, JH,H = 7.6 Hz, CH3), 2.71 (q,
1-Trimethylsilylethynyl-2,3-diethyl-2,3-dicarbahepta-
borane(7) (2d)
3
4 H, JH,H = 7.6 Hz, CH2), 3.74 (br., 1 H, B5-H), 4.22
(br., 2 H, B4,6-H), −1.5 (br., 1 H, B7-H). – 11B NMR
The zinc reagent was prepared by treatment of
Me3SiC≡CLi (preformed from Me3SiC≡CH and n-BuLi,
218 mg, 2.1 mmol) with a solution of ZnCl2 (286 mg,
2.1 mmol) in THF (6.5 ml) at −10 ◦C, and stirred at r. t. for
2 h. In another flask, a solution of 2b (534 mg, 2 mmol) in
THF (10 ml) was added to a solution of Pd(PPh3)4 (75 mg,
0.065 mmol) in THF (10 ml). To the resulting red solu-
tion the zinc reagent was added at r. t. The reaction mix-
ture became yellow during 1 h. After completion all volatiles
were removed in vacuo, the brown residue was extracted
with hexane (40 ml) and filtered. The yellow filtrate was
dried to give 2d as an orange red oil (340 mg, 72%). Af-
ter NMR measurement in CDCl3, pieces of red crystals were
formed, which were identified by X-ray analysis to be trans-
(CDCl3): δ = 6.4 (d, JB,H = 159 Hz, B4,6), 1.3 (d, JB,H
=
199 Hz, B5), −15.9 (s, B1), −20.2 (d, JB,H = 169 Hz, B7). –
13C NMR (CDCl3): δ = 13.3 (CH3), 22.3 (CH2), 29.7,
30.6 (tBu), 104.2 (tBuC ≡), 114.6 (br., Ccage), signal for B-
C≡ n. o.. – EI-MS: m/z (%) = 221 (39) [M+], 206 (100)
[M+ −Me]. – HR-MS (EI): m/z = 222.2273 [M+]; calcd.
12
for
C
1H2311B5 222.2265 (∆m = 0.8 mmu).
12
3,4-Bis[2’,3’-diethyl-2’,3’-dicarbaheptaboranyl(7)-1’]-3-
hexene (3)
Similar procedure as described for 2a. 2,3-Et2C2B4H6
(241 mg, 1.84 mmol), n-BuLi (2.5 M in hexane, 1.5 ml,
3.75 mmol), cis-3,4-bis(dichloroboryl)-3-hexene (227 mg,
0.92 mmol). 3 was obtained as a yellow oil (300 mg, 90%). –
1
Pd(PPh3)2I2. – H{11B} NMR (CDCl3): δ = 0.02 (s, 9 H,
3
1H NMR (CDCl3): δ = 0.61 (t, 6 H, JH,H = 7.5 Hz, Et-
3
SiMe3), 1.36 (t, 6 H, JH,H = 7.6 Hz, CH3), 2.71 (q, 4 H,
CH3), 1.23 (t, 6 H, 3JH,H = 7.5 Hz, cage-CH3), 1.47 (q, 4 H,
3JH,H = 7.6 Hz, CH2), 3.7 (br., 1 H, B5-H), 4.2 (br., 2
H, B4,6-H), −1.7 (br., 1 H, B7-H). – 11B NMR (CDCl3):
δ = 6.3 (br., B4,6), 1.5 (br., B5), −17.4 (s, B1), −19.1 (br.,
B7). – 13C NMR (CDCl3): δ = −0.39 (SiMe3), 13.4 (CH3),
22.4 (CH2), 102.4 (Me3SiC ≡), 114.8 (br., Ccage), signal
for B-C≡n.o. – 29Si NMR (CDCl3): δ = −19.4. – EI-MS:
3
3JH,H = 7.5 Hz, Et-CH2), 2.63 (q, 2 H, JH,H = 7.5 Hz,
3
cage-CH2), 2.67 (q, 2 H, JH,H = 7.6 Hz, cage-CH2). –
11B NMR (CDCl3): δ = 6.2 (br., B4,6), 2.9 (br., B5), −4.7
(s, B1), −21.5 (br., Hz, B7). – 13C NMR (CDCl3): δ = 13.9,
14.1 (CH3), 22.9, 26.5 (CH2), 114.6 (br., Ccage), 144 (br.,
C=C). – EI-MS: m/z (%) = 362 (100) [M+], 333 (680)
[M+ −Et]. – HR-MS (EI): m/z = 364.3893 [M+]; calcd. for
m/z (%) = 237 (16) [M+], 222 (100) [M+ −Me]. – HR-MS
(EI): m/z = 238.2050 [M+]; calcd. for
238.2035 (∆m = 1.5 mmu).
C
1H2311B528Si
11
12
12
11
C
1H38
B
364.3904 (∆m = −1.1 mmu).
18
10
Dicobaltatetrahedrane-substituted closo-C2B5 and nido-
C2B4 carboranes 4c, 5c
1-Methylethynyl-2,3-diethyl-2,3-dicarbaheptaborane(7) (2e)
Similar procedure as described for 2d. MeC≡CLi
A solution of 2c (196 mg, 0.81 mmol) in hexane (15 ml)
(115 mg, 2.5 mmol), ZnCl2 (240 mg, 2.5 mmol), 2b (534 mg, was added to a solution of Co2(CO)8 (276 mg, 0.81 mmol)
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Y. Nie et al. · Synthesis and Reactivity of Boron-Functionalized C2B5-closo-Carboranes
601
in hexane (15 ml) at −40 ◦C. The reaction mixture was (CH2), 115.5 (br., Ccage), 200.3 (CO). – 29Si NMR (C6D6):
warmed up to r.t. and stirred for 5 days to give a deep red δ = 38.3. – EI-MS: m/z (%) = 523 (2) [M+], 495 (12)
solution. The transformation was complete as monitored by [M+ −CO], 467 (6) [M+ −2CO], 439 (20) [M+ −3CO],
11B NMR. The solvent was removed, the dark brown residue 411 (51) [M+ −4CO], 383 (41) [M+ −5CO], 355 (46)
was taken up with CH2Cl2 (2 ml) and chromatographed [M+ −6CO]. – HR-MS (EI): m/z = 524.0362 [M+]; calcd.
R
(Florisilꢀ, hexane). A brown fraction was obtained and dried for
C
17
1H2311B5Co2O628Si 524.0393 (∆m = −3.1 mmu);
12
to give a brown oil (302 mg), which was identified to be 5d: 11B NMR (C6D6): δ = 6.8 (br.), −2.9 (br.), −36.5
a mixture of 4c and 5c (ca. 4 : 1). 4c: 1H NMR (CDCl3): (apical boron). – 13C NMR (C6D6): δ = 13.9 (CH3), 21.9
δ = 1.31 (br., 6 H, CH3), 2.75 (br., 4 H, CH2), 7.33 (br., (CH2), signals for the other carbon atoms are weak. – EI-
5 H, Ph). – 11B{ H} NMR (hexane): δ = 7.2 (B4,6), 2.9 MS: m/z (%) = 514 (1) [M+], 486 (15) [M+ −CO], 458 (9)
1
(B5), −5.6 (B1), −20.5 (B7); – 11B NMR (CDCl3): δ = [M+ −2CO], 430 (16) [M+ −3CO], 402 (6) [M+ −4CO],
374 (13) [M+ −5CO], 346 (15) [M+ −6CO]. – HR-MS (EI):
6.7 (br., B4,6), 2.1 (br., B5), −6.3 (B1), −21.1 (d, JB,H
=
150 Hz, B7). – 13C NMR (CDCl3): δ = 14.0 (CH3), 22.2
(CH2), 115.5 (br., Ccage), 128.0, 128.8, 129.4, 137.7 (Ph),
199.2 (CO). – EI-MS: m/z (%) = 527 (2) [M+], 499 (5)
[M+ −CO], 471 (3) [M+ −2CO], 443 (12) [M+ −3CO],
415 (42) [M+ −4CO], 387 (28) [M+ −5CO], 359 (37)
1
m/z = 514.0335 [M+]; calcd. for 12C17 H2411B4Co2O628Si
514.0378 (∆m = −4.3 mmu).
(Cyclopentadienyl)[1,3-bisdicarbaheptaboranyl(7)-2,4-
diphenylcyclobutadiene] cobalt complex 6c
[M+ −6CO], 241 (100) [M+ −6CO−2Co]. – HR-MS (EI):
To a solution of 2c (195 mg, 0.81 mmol) in toluene (20 ml)
was added a portion of CpCo(CO)2 (81 mg, 0.45 mmol) at
r. t.. The deep red mixture was heated at reflux and moni-
tored by 11B NMR. After one week, CpCo(C2H4)2 (100 mg,
0.55 mmol) was added and the resulting mixture was again
heated at 70 ◦C (oil bath) for 6 days. After cooling the
brown mixture was dried to give a brown residue, which was
extracted with hexane and filtered through a pad of sand.
The filtrate was dried in vacuo, leaving a dark brown oil,
which was identified to be a mixture of 6c, 6d and 7c. –
11B NMR (toluene): δ = 6.3, 2.2, −4.0, −16.6, −19.6,
−45.1(w) ppm. – EI-MS: m/z (%) = 606 (10) [6c+], 597
(100) [6d+], 365 (27) [6c+ −2c], 232 (32) [7c+]. – HR-MS
m/z = 528.0262 [M+]; calcd. for
C
1H1911B5Co2O6
12
20
528.0311 (∆m = −4.9 mmu); 5c: 1H NMR (CDCl3): δ =
−1.22 (br., 2 H, BHB), 0.88 (br., 6 H, CH3), 2.40 (br., 4 H,
CH2), 7.42 (br., 5 H, Ph). – 11B NMR (CDCl3): δ = 6.7
(br.), −2.8 (br.), −35.6 (apical boron). – 13C NMR (CDCl3):
δ = 14.9 (CH3), 24.5 (CH2), signals for the other carbon
atoms are weak. – EI-MS: m/z (%) = 517 (2) [M+], 489 (5)
[M+ −CO], 461 (5) [M+ −2CO], 434 (12) [M+ −3CO],
406 (10) [M+ −4CO], 378 (15) [M+ −5CO], 350 (18)
[M+ −6CO], 231 (100) [M+ −6CO−2Co].
Dicobaltatetrahedrane-substituted closo-C2B5 and nido-
C2B4 carboranes 4d, 5d
11
(EI): m/z = 608.3672 [6c+]; calcd. for
C B Co
1H43
33 10
12
608.3627 (∆m = 4.5 mmu); m/z = 232.1932 [7c+]; calcd.
12
Similar procedures as described for 4c/5c. 2d (196 mg,
0.81 mmol), Co2(CO)8 (324 mg, 0.95 mmol). A brown oil
was obtained which was identified to be a mixture of 4d/5d
(ca. 7 : 1) (300 mg, ca. 57%) after the reaction mixture was
for
C
1H2011B4 232.1932 (∆m = −0.5 mmu).
14
Acknowledgements
Support of this work by the Deutsche Forschungsgemein-
filtered on a pad of sand. 4d: 1H NMR (C6D6): δ = 0.2 (br., schaft (Schwerpunktprogramm Polyeder and SFB 623) and
SiMe3), 1.3 (br., CH3), 2.2−2.4 (br., CH2). – 11B{ H} NMR the Fonds der Chemischen Industrie is gratefully acknowl-
1
(hexane): δ = 7.2 (B4,6), 2.5 (B5), −6.4 (B1), −20.9 (B7); – edged. We like to thank Prof. Russell N. Grimes (Char-
11B NMR (C6D6): δ = 6.8 (br. d, JB,H = 135 Hz, B4,6), 1.2 lottesville, USA) for providing the nido-2,3-Et2C2B4H6,
(br., B5), −6.9 (B1), −21.4 (br. d, JB,H = 179 Hz, B7). – and Dr. Chunhua Hu (RWTH, Aachen) for identifying
13C NMR (C6D6): δ = −0.30 (SiMe3), 13.6 (CH3), 21.8 Pd(PPh3)2I2 from a sample of 2d.
[1] R. N. Grimes, catboranes, Academic Press, New York
(1970).
[5] R. R. Rietz, R. Schaeffer, J. Am. Chem. Soc. 93, 1263
(1971).
[2] B. Stibr, Chem. Rev. 92, 225 (1992).
[3] T. Onak, in E. W. Abel, F. G. A. Stone, G. Wilkin-
son (eds): Comprehensive Organometallic Chemistry,
Vol. 1, p. 217, Pergamon, Oxford (1995).
[4] M. L. McKee, J. Am. Chem. Soc. 110, 5317 (1988),
and references therein.
[6] J. S. Beck, A. P. Kahn, L. G. Sneddon, Organometallics
5, 2552 (1986).
[7] J. S. Beck, L. G. Sneddon, Inorg. Chem. 29, 295
(1990).
[8] J. S. Beck, W. Quintana, L. G. Sneddon, Organometal-
lics 7, 1015 (1988).
Unauthenticated
Download Date | 11/17/19 11:07 PM

602
Y. Nie et al. · Synthesis and Reactivity of Boron-Functionalized C2B5-closo-Carboranes
[9] K. Su, P. J. Fazen, P. J. Carrol, L. G. Sneddon, Organo-
metallics 11, 2715 (1992).
[17] T. Peymann, C. B. Knobler, M. F. Hawthorne, Inorg.
Chem. 37, 1544 (1998).
[10] J. W. Bausch, D. J. Matoka, P. J. Carrol, L. G. Sneddon,
J. Am. Chem. Soc. 118, 11423 (1996), and references
therein.
[18] L. Eriksson, I. P. Beletskaya, V. I. Bregadze, I. B.
Sivaev, S. Sjo¨berg, J. Organomet. Chem. 657, 267
(2002).
[11] M. Bluhm, H. Pritzkow, W. Siebert, R. N. Grimes,
Angew. Chem. 112, 4736 (2000); Angew. Chem. Int.
Ed. 39, 4562 (2000).
[12] Y. Nie, S. Schwiegk, H. Pritzkow, W. Siebert, Eur. J.
Inorg. Chem. 1630 (2004).
[19] H. Yao, M. Sabat, R. N. Grimes, P. Zanello, F. Fabrizi
de Biani, Organometallics 22, 2581 (2003).
[20] R. G. Kultyshev, S. Liu, H. T. Leung, J. Liu, S. G.
Shore, Inorg. Chem. 42, 3199 (2003).
[21] Y. Nie, H. Pritzkow, W. Siebert, Eur. J. Inorg. Chem.
2425 (2004).
[22] I. P. Beletskaya, V. I. Bregadze, V. A. Ivushkin, P. V.
Petrovskii, I. B. Sivaev, S. Sjo¨berg, G. G. Zhigareva,
J. Organomet. Chem. 689, 2920 (2004).
[23] M. Kubota, S. Ohba, Y. Saito, Acta Crystallogr. Sec-
tion C, 47, 1727 (1991).
[13] M. F. Hawthorne, P. A. Wegner, J. Am. Chem. Soc. 90,
896 (1968).
[14] B. Wrackmeyer, H.-J. Schanz, W. Milius, C. McCam-
mon, Coll. Czech. Chem. Commun. 64, 977 (1999).
[15] M. Bu¨hl, P. v. R. Schleyer, Z. Havlas, D. Hnyk, S. Her-
manek, Inorg. Chem. 30, 3107 (1991) and refs. therein.
[16] L. I. Zakharkin, V. A. Olshevskaya, Synth. React.
Inorg.-Org. Chem. 21, 1041 (1991).
[24] R. G. Swisher, E. Sinn, R. N. Grimes, Organometallics
4, 890 (1985).
Unauthenticated
Download Date | 11/17/19 11:07 PM