Chiral organotin complexes stabilized by C,N-chelating oxazolinyl-o-carboranes

Article abstract of DOI:10.1016/j.jorganchem.2009.10.030

A series of chiral organotin halides containing 2-(4-R)-oxazolinyl-o-carboranes (R = i-propyl 1, t-butyl 2; Cab^Oxa) was prepared from o-carborane with a chiral oxazoline auxiliary. X-ray structural analysis of the representative chiral organotin halide, [2-(4-i-propyl)-oxazolinyl-o-carboranyl]SnMe₂Br (4), revealed the formation of a stable penta-coordinated tin center due to a N → Sn interaction. Similar O → Sn assisted intramolecular penta-coordinated tin complexes (9 and 10) were prepared from methoxy-o-carborane ligands, MeOCH(Z)-o-carborane (Z = H 7, Ph 8; Cab^OMe), respectively, and a rigid o-carboranyl backbone provided the basic skeleton for the facile formation of organotin complexes.

Full text of DOI:10.1016/j.jorganchem.2009.10.030

Journal of Organometallic Chemistry 695 (2010) 463–468
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Note
Chiral organotin complexes stabilized by C,N-chelating oxazolinyl-o-carboranes
a
b
b,
Jong-Dae Lee a, , Hyo-Suk Kim , Won-Sik Han , Sang Ook Kang
*
*
a Department of Chemistry, Chosun University, Gwangju 501-759, Republic of Korea
b Department of Advanced Material Chemistry, Korea University, Sejong, Chungnam 339-700, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 August 2009
Received in revised form 17 October 2009
Accepted 23 October 2009
Available online 27 October 2009
A series of chiral organotin halides containing 2-(4-R)-oxazolinyl-o-carboranes (R = i-propyl 1, t-butyl 2;
CabOxa) was prepared from o-carborane with a chiral oxazoline auxiliary. X-ray structural analysis of the
representative chiral organotin halide, [2-(4-i-propyl)-oxazolinyl-o-carboranyl]SnMe2Br (4), revealed the
formation of a stable penta-coordinated tin center due to a N ? Sn interaction. Similar O ? Sn assisted
intramolecular penta-coordinated tin complexes (9 and 10) were prepared from methoxy-o-carborane
ligands, MeOCH(Z)-o-carborane (Z = H 7, Ph 8; CabOMe), respectively, and a rigid o-carboranyl backbone
provided the basic skeleton for the facile formation of organotin complexes.
Keywords:
Organotin complexes
Chiral oxazoline
Ó 2009 Elsevier B.V. All rights reserved.
o-Carborane backbone
Intramolecular coordination
1. Introduction
2. Results and discussion
Chiral organotin complexes have been developed as efficient re-
agents for a wide variety of organic transformations in stereospe-
cific reactions [1–3]. The most important work involves the chiral
induction of organotin complexes, one of the notable accomplish-
ments being free-radical enantioselective reductions [4–6]. In such
cases, a penta-coordinated tin center was completed with intramo-
lecularly coordinated nitrogen atoms [7–12]. It has been reported
that chiral oxazoline rings induce stereospecific reactions
[13–16] due to the closer proximity of the stereogenic motif to
the metal center. Such a superior chiral auxiliary can be more effi-
cient when a suitable ligand backbone is provided. In this study, a
rigid and sterically demanding o-carborane backbone was used to
assist the proceeding stereospecific reactions [17].
The ligand systems, chiral [2-(4-R)-oxazolinyl]-o-carborane (R =
i-propyl 1, t-butyl 2), consisted of two dissimilar coordination
modes of carbon in carborane. The imine functionalities of the
oxazoline unit were produced using a standard procedure [17] by
reacting lithio-o-carborane with 2-bromo-(4-R)-oxazoline in a
THF solution. Treatment of compounds 1 and 2 with a 1.1 equiv
of n-BuLi and 1 equiv of Me2SnX2 (X = Cl, Br) in diethyl ether at
ꢀ10 °C for 10 min gave the chiral oxazoline substituted o-carbor-
anylorganotin halides with the general formula [2-(4-R)-oxazoli-
nyl-o-carboranyl]SnMe2X (R = i-propyl, X = Cl 3, Br 4; R = t-butyl,
X = Cl 5, Br 6) in good yield (3: 77%, 4: 84%, 5: 75%, 6: 81%, Scheme
1).
All new compounds were characterized by Fourier transform
infrared (IR), 1H, 11B, 13C and 119Sn nuclear magnetic resonance
(NMR) spectroscopy, elemental analysis, high-resolution mass
spectroscopy, and single-crystal X-ray crystallography. Compounds
3–6 were moderately stable in air and decomposed only slowly
when in contact with moisture. The kinetic stability of compounds
3–6 is due to the formation of a five-membered chelate ring, which
protects the Sn atom from external nucleophilic attack. The 1H NMR
signals for both NCH and OCH2 of the oxazoline ring in compounds
3–6 were observed downfield from those found in the free ligands.
This can be explained by the trigonal-bipyramidal geometry with
the nitrogen atom of the oxazoline unit and the halogen atom in
the axial positions as well as by evidence of Sn–N coordination in
solution. Information on the ligand geometry in solution at tin in
compounds 3–6 was obtained from the 119Sn chemical shifts and
2J(119SnꢀC1H3) values. These depend on the coordination number
Chiral oxazolinyl-o-carborane (CabOxa) ligands have a nitrogen
donor atom adjacent to the stereogenic carbon center at the oxaz-
oline ring. When these ligands coordinate to the metal center, the
stereogenic carbon atom will induce chiral recognition most effec-
tively. This paper reports the synthesis and characterization of chi-
ral organotin complexes (3–6) with bidentate chiral oxazoline
ligands containing o-carbaborane as the rigid backbone. In addi-
tion, comparative studies using C,O-chelating ligands, CabOMe, have
assisted in determining the relationship between the tin com-
plexes (9 and 10) with respect to the structures and electronic ef-
fects of each ligand series.
* Corresponding authors. Tel.: +82 41 860 1334; fax: +82 41 867 5396 (S.O. Kang).
E-mail address: sangok@korea.ac.kr (S.O. Kang).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.10.030

464
J.-D. Lee et al. / Journal of Organometallic Chemistry 695 (2010) 463–468
provided by the observed absolute 119Sn NMR chemical shifts val-
R
*
R
H
H
ues. As reported in the literature [23], d(119Sn) values in the range
ꢀ210 to ꢀ400, ꢀ90 to ꢀ190, and 200 to ꢀ60 ppm are associated
with six-, five-, and four-coordinate tin centers, respectively. Com-
pounds 9 and 10 exhibited chemical shifts of (d(119Sn) ꢀ108.2 (9)
and ꢀ110.3 (10) ppm) with respect to Ph2BrSn(CH2-16-crown-5)
[24] (d(119Sn) ꢀ96 ppm). Overall, these results favor the existence
of an intramolecular Sn–O interaction in compounds 9 and 10,
which leads to the trigonal-bipyramidal coordination of the Sn
atom. The spectroscopic data indicates that complexes 9 and 10
have a related structure. It is believed that the o-carboranyl carbon
atom and two alkyl ligands are at the equatorial sites, while the
more electronegative oxygen atom of methoxymethyl-o-carborane
and the bromide atom reside at the axial positions.
*
N
N
1. n-BuLi
2.
1. n-BuLi
Sn
H
O
O
X
O
2. Me2SnX2
Br
*
N
R
: C
R = iPr, X = Cl 3, Br 4
R = tBu, X = Cl 5, Br 6
R = iPr 1, tBu 2
unmarked vertices: BH
of icosahedra
Scheme 1. Synthesis of [2-(4-R)-oxazolinyl-o-carboranyl]SnMe2X (R = iPr, X = Cl 3,
Br 4; tBu, X = Cl 5, Br 6).
of tin [18–20] and were compared with those of the penta-coordi-
nated methyl-substituted organotin halides. The observed d(119Sn)
and 2J(119SnꢀC1H3) values suggested penta-coordinate geometry at
tin for compounds 3–6. Indeed, there was close agreement of the
NMR spectroscopic data between compounds 3–6 and (ArOxa)-
Me2SnBr [21], particularly the 2J(119SnꢀC1H3) coupling constants
(77.2 Hz in (CabOxa)Me2SnBr (4) and 75 Hz in (ArOxa)Me2SnBr).
The spectroscopic data suggests that complexes 3–6 have a related
structure. A trigonal-bipyramidal structure for compounds 3–6 in
solution was proposed based on the 1H, 13C, and 119Sn NMR
spectroscopy. This was expected because the tin atom in organotin
halides containing a C,N-chelating ligand normally has trigonal-
bipyramidal coordination geometry due to intramolecular coordi-
nation. It is believed that the o-carboranyl carbon atom and two
alkyl ligands are at the equatorial sites, while the more electroneg-
ative nitrogen atom of oxazolinyl-o-carborane and halide atom
reside at the axial positions.
New types of C,O-chelated organotin bromides with Sn–O intra-
molecular interactions were attempted as a variation of the gener-
ation of organotin compounds stabilized by o-carboranyl ligands.
Accordingly, the synthesis and single-crystal X-ray crystallo-
graphic studies of organotin bromides containing new types of
methoxy-o-carborane ligands, MeOCH(Z)-o-carborane (Z = H 7, Ph
8), were carried out. C,O-chelating ligands, 7 and 8, were prepared
by reacting o-carboranyl- or o-carboranyl(phenyl)methanol [22]
with CH3I in the presence of 3 equiv of NaH in THF at 0 °C (Scheme
2). After ligand deprotonation of compounds 7 and 8 by n-BuLi at
ꢀ10 °C in diethyl ether for 10 min, methathesis reactions with
Me2SnBr2 were carried out to produce the desired intramolecularly
stabilized C,O-chelated organotin complexes, 9 and 10, in good
yield (9: 84%; 10: 83%, Scheme 2).
2.1. Structural study
The structures of compounds 4, 7, 8, and 9 were determined by
X-ray structural analysis. Selected interatomic distances and an-
gles are presented in the appropriate figure caption (Figs. 1–4). De-
tailed information on the structural determinations and structural
features of all four compounds are provided in the Supporting
Information. Figs. 1 and 4 show the penta-coordinated organotin
bromide structures tethered by chiral oxazolinyl- (4) and
methoxymethyl- (9) o-carborane, respectively. Figs. 2 and 3 show
the conformations of the ligands, consisting of methoxymethyl-
(7) and methoxy(phenyl)methyl-o-carborane (8), respectively. In
compounds 4 and 9, each central tin atom has a distorted trigo-
nal-bipyramid structure with the electronegative atoms (N, Br (4)
or O, Br (9)) in the axial positions and all carbon atoms in equato-
rial positions, which is in accordance with previously published
The C,O-chelating organotin complexes were stabilized by the
formation of a five-membered chelate ring. Compounds 9 and 10
were purified by low-temperature recrystallization in toluene. Sat-
isfactory elemental analyses were obtained for compounds 9 and
10, and the 1H, 13C, and 119Sn NMR spectral data was consistent
with the presence of methoxymethyl-o-carboranyl ligands. Down-
field shifts of the signals for both OCH3 and OCH2 were observed in
the 1H NMR spectra in compounds 9 and 10, which is in accord
with the presence of Sn–O bonds. 1H NMR suggested that com-
pounds 9 and 10 are penta-coordinated in solution. Additional evi-
dence for penta-coordinate tin centers in these compounds was
OMe
OH
O
Sn
H
H
Z
Z
1. n-BuLi
1. NaH
2. CH3I
Z
Br
2. Me2SnBr2
Fig. 1. ORTEP presentation at the 30% probability level of the molecular structure of
compound 4. The hydrogen atoms are omitted for clarity. Selected interaction
distances (Å) and angles (°): Sn(1)ꢀN(1) = 2.500(1), Sn(1)ꢀBr(1) = 2.614(2),
Sn(1)ꢀC(1) = 2.197(2), C(2)ꢀC(3) = 1.492(2), C(3)ꢀN(1) = 1.241(2); Br(1)ꢀSn(1)ꢀN(1) =
169.6(3), Br(1)ꢀSn(1)ꢀC(1) = 95.3(4), C(1)ꢀSn(1)ꢀN(1) = 74.7(5), Sn(1)ꢀN(1)ꢀC(3) =
114.5(1).
Z = H7, Ph8
Z = H9, Ph10
Scheme 2. Synthesis of [CH3OCH(Z)-o-carboranyl]SnMe2Br (Z = H 9, Ph 10).

J.-D. Lee et al. / Journal of Organometallic Chemistry 695 (2010) 463–468
465
Fig. 2. ORTEP presentation at the 30% probability level of the molecular structure of
compound 7. The hydrogen atoms are omitted for clarity. Selected interaction
distances (Å) and angles (°): O(1)ꢀC(3) = 1.327(4), O(1)ꢀC(4) = 1.425(4),
O(10)ꢀC(30) = 1.336(4), O(10)ꢀC(40) = 1.420(3); C(3)ꢀO(1)ꢀC(4) = 113.7(3), O(1)ꢀ
C(3)ꢀC(1) = 111.6(3), C(3’)ꢀO(10)ꢀC(40) = 112.2(3), O(1’)ꢀC(30)ꢀC(10) = 110.9(3).
Fig. 4. ORTEP presentation at the 30% probability level of the molecular structure of
compound 9. The hydrogen atoms are omitted for clarity. Selected interaction
distances (Å) and angles (°): Sn(1)ꢀO(1) = 2.579(4), Sn(1)ꢀBr(1) = 2.537(3),
Sn(1)ꢀC(1) = 2.193(2); Br(1)ꢀSn(1)ꢀO(1) = 169.8(3), Br(1)ꢀSn(1)ꢀC(1) = 98.4(5),
C(1)ꢀSn(1)ꢀO(1) = 71.4(6), Sn(1)ꢀO(1)ꢀC(3) = 121.1(1).
and co-workers [27] and Wade and co-workers [28]. As a conse-
quence of the Sn–N interaction, the Sn(1)–Br(1) distance
(2.614(2) Å) is longer than that observed in other hypervalent tri-
organotin bromides (2.599(4) Å) [29]. The structure shows that
the nitrogen atom of the oxazoline ring coordinates preferentially
to tin, even though Sn–O coordination would lead to a sterically
less crowded molecule. Furthermore, considerable distortions from
an idealized trigonal-bipyramid are evident in the solid state due
to the sp2 C(3) and N(1) of the oxazoline ring. Therefore, the angle
associated with axial ligand N(1)–Sn(1)–Br(1) deviates from linear-
ity (169.6(3)°) due to its proximity to the sterically incumbent
oxazolinyl unit.
X-ray structural determinations of compound 9 authenticated
the expected trigonal-bipyramid geometries illustrated in Fig. 4.
The overall geometry was similar to that observed in compound
4. Therefore, the Sn atom has a distorted trigonal-bipyramid geom-
etry with the O(1) and Br(1) atoms in the axial positions and
o-carboranyl carbon atom and two alkyl ligands in the equatorial
plane. The angular distortions of the trigonal-bipyramid arise from
the geometric constraints associated with the bite angle of the
bidentate ligands [O(1)–Sn(1)–C(1)) angle of 71.4(6)°] in the pres-
ence of the O(1)–Sn(1)–Br(1) bond angle (169.8(3)°). Sn(1)–O(1)
and Sn(1)–Br(1) bond distances of 2.579(1) and 2.537(3) Å are sim-
ilar to the corresponding normal values for Sn–O (2.564(2) Å)
dative and Sn–Br (2.6088(4) Å) single bonds [24].
Fig. 3. ORTEP presentation at the 30% probability level of the molecular structure of
compound 8. The hydrogen atoms are omitted for clarity. Selected interaction
distances (Å) and angles (°): O(1)ꢀC(3) = 1.297(1), O(1)ꢀC(4) = 1.413(1);
C(3)ꢀO(1)ꢀC(4) = 116.8(9), O(1)ꢀC(3)ꢀC(1) = 109.4(7), C(1)ꢀC(3)ꢀC(5) = 112.4(7),
O(1)ꢀC(3)ꢀC(5) = 117.3(9).
results [25]. As expected, compound 4 is chiral, crystallizing in the
orthorhombic P212121 space group with the Flack parameter [26]
refining to 0.00, which confirms the presence of an enantiomeri-
cally pure compound. Unfortunately, the nine non-hydrogen atoms
of compound 4, C(1), C(2), C(3), B(3), B(4), B(6), B(7), B(9), and
B(10), were refined isotropically because of their non-positive tem-
perature factors that might occur due to systematic errors in the
observed amplitudes originating in possible merohedral twinning.
A strong Sn–N interaction was found in compound 4 with a dis-
tance of 2.500(1) Å, which lies in the normal range of Nsp2 ? Sn da-
tive bonding. A shorter Sn–N distance is expected because the
coordinating nitrogen atom is sp2-hybridized. Indeed, the Sn–N
distance in compound 4 is approximately 0.15 Å shorter than the
Sn–Nsp3 distances (2.648(6) Å) [25]. Recently, a similar strong
Nsp2 ? Sn interaction was reported in tin complexes by Zhang
3. Conclusion
In conclusion, chiral organotin compounds were synthesized
from chiral oxazolinyl auxillary containing o-carborane as a rigid
backbone and their structure was determined. NMR and single-
crystal X-ray crystallographic studies of compound 4 showed that
the chiral oxazolinyl-o-carborane ligands at the tin metal center
significantly affect both the stability of the starting compounds
and the electronic properties of the metal center due to the
strength of the Sn–N bond.

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J.-D. Lee et al. / Journal of Organometallic Chemistry 695 (2010) 463–468
4.4. General synthesis of the chiral organotin halides [2-(4-i-propyl)-
oxazolinyl-o-carboranyl]SnMe2Cl (3)
4. Experimental
4.1. General procedures
A 2.5 M n-BuLi solution (1.3 mL, 3.3 mmol) was added to a stir-
red solution of compound 1 (0.77 g, 3.0 mmol) in diethyl ether
(30 mL) at ꢀ10 °C through a syringe. The resulting solution was
stirred at ꢀ10 °C for 30 min. A solution of Me2SnCl2 (0.66 g,
3.0 mmol) in diethyl ether (10 mL) was added slowly to the
30 mL diethyl ether solution of compound 1ꢁLi at –10 °C. The reac-
tion temperature was maintained at –10 °C for 10 min. The reac-
tion mixture was filtered and the organic solvent was
evaporated. The crude product was dissolved in fresh distilled tol-
uene. The volume of the toluene solution was reduced and the
resulting concentrated solution allowed to stand at ꢀ10 °C for
2 days to allow crystallization. Compound 3 was obtained as color-
less crystals in 77% yield (1.01 g, 2.3 mmol). Mp: 168–170 °C (dec).
All manipulations were carried out under a dry, oxygen-free
nitrogen or argon atmosphere using standard Schlenk techniques
or in a Vacuum Atmosphere HE-493 drybox. Solvents were dried
by standard methods and distilled prior to use. The 1H, 11B, 13C
and 119Sn NMR spectra were recorded on a Varian Mercury 300
spectrometer operating at 300.1, 96.3, 75.4 and 111.9 MHz, respec-
tively. The chemical shifts are reported (d, ppm) in reference to tet-
ramethylsilane for 1H and 13C, boron trifluoride etherate for 11B, or
tetramethyltin for 119Sn spectroscopy. The IR spectra were re-
corded on a Biorad FTS-165 spectrophotometer. o-Carborane was
purchased from KatChem, and tetrabutylammonium fluoride,
paraformaldehyde, benzaldehyde, n-BuLi, dimethyltin dichloride
and dimethyltin dibromide were purchased from Aldrich chemi-
cals. The compounds were used without purification. 2-(4-R)-oxaz-
olinyl-o-carboranes (R = i-propyl, t-butyl)4 and methoxymethyl-
and methoxy(phenyl)methyl-o-carborane7 were prepared using
literature methods. Elemental analyses were performed using a
Carlo Erba Instruments CHNS-O EA1108 analyzer. The high-resolu-
tion mass spectra were measured at the Korea Basic Science Insti-
tute. All melting points were uncorrected.
12
11
HRMS: Calcd for
[ C B
1H26 35Cl14N16O119Sn]+ 441.1655.
10 10
Found: 441.1631. Anal. Calc. for C10H26B10ClNOSn: C, 27.38; H,
5.98; N, 3.19. Found: C, 27.40; H, 5.95; N, 3.21%. IR (KBr pellet,
cm–1 (C@N) 1690. 1H
) m(C–H) 3205, 3085, 2980, m(B–H) 2588, m
NMR (CDCl3) d 0.33 (s, 6H, Sn–CH3, 2J
= 75.3 Hz), 0.94 (d,
119SnꢀCH3
3H, CH(CH3)2, 3JCHꢀCH = 6.6 Hz), 1.11 (d, 3H, CH(CH3)2,
3
3JCHꢀCH = 6.9 Hz), 1.94 (m, 1H, CH(CH3)2), 4.23 (m, 1H, CHN), 4.22
3
(m, 1H, CH2O), 4.47 (m, 1H, CH2O). 13C NMR (75.4 MHz, CDCl3) d
4.21 (Sn–CH3); 13.6, 16.0 (CH(CH3)2); 28.8 (CH(CH3)2); 68.6
(Cab); 68.9, 70.5 (OCH2CHN); 70.3 (Cab); 166.3 (C@N). 11B NMR
(96.3 MHz, CDCl3) d –14.27 (2H), –11.59 (1H), –10.37 (1H), –9.16
(1H), –5.86 (3H), –3.37 (1H). 119Sn NMR (149.2 MHz, CDCl3) d –
124.4 (Sn–CH3).
4.2. Preparation of 2-(4-i-propyl)-oxazolinyl-o-carborane (1)
n-BuLi (2.0 mL, 5.0 mmol, 2.5 M solution in hexane) was added
dropwise to a solution of o-carborane (0.72 g, 5.0 mmol) in 50 mL
of dry THF at ꢀ78 °C with constant stirring. The mixture was al-
lowed to stir for 30 min at ꢀ78 °C at which time 2-bromo-4-i-pro-
pyl-oxazoline (1.06 g, 5.5 mmol) was added dropwise. The solution
was stirred for 1 h and then warmed to ambient temperature. The
reaction was quenched with water, extracted with ether, and dried
over anhydrous Na2SO4. The solvent was evaporated and the resi-
due was purified by silica gel column chromatography using hex-
ane as the eluent (Rf 0.4) to afford compound 1 as a pale yellow
oil in 74% yield (0.94 g, 3.7 mmol). Anal. Calc for C8H21B10NO: C,
37.63; H, 8.29; N, 5.48. Found: C, 37.60; H, 8.32; N, 5.44%. IR
4.5. Synthesis of organotin halide (4)
A procedure analogous to the preparation of compound 3 was
used but instead starting from compound 1 (0.77 g, 3.0 mmol) with
Me2SnBr2 (0.93 g, 3.0 mmol). Compound 4 was obtained as color-
less crystals (1.22 g, 2.5 mmol, 84%). Mp: 183–185 °C (dec). HRMS:
Calcd for
485.1160. Anal. Calc. for C10H26B10BrNOSn: C, 24.86; H, 5.43; N,
2.90. Found: C, 24.84; H, 5.41; N, 2.93%. IR (KBr pellet, cm–1
(C–H) 3207, 3085, 2982, (B–H) 2586,
(C@N) 1688. 1H NMR
= 77.2 Hz), 0.94 (d, 3H,
[ C B
1H26 80Br14N16O119Sn]+ 485.1150. Found:
12
11
10 10
)
m
m
m
(KBr pellet, cm–1
) m(C–H) 3014, 2990, 2982, m(B–H) 2604, m(C@N)
(CDCl3) d 0.31 (s, 6H, Sn–CH3, 2J
119SnꢀCH3
3
1700. 1H NMR (CDCl3) d 0.92 (d, 3H, CH(CH3)2, JCHꢀCH = 6.6 Hz),
3JCHꢀCH = 6.6 Hz),
1.11
(d,
3H,
CH(CH3)2,
3
CH(CH3)2,
3
3
0.99 (d, 3H, CH(CH3)2, JCHꢀCH = 6.9 Hz), 1.92 (m, 1H, CH(CH3)2),
3JCHꢀCH = 6.9 Hz), 1.94 (m, 1H, CH(CH3)2), 4.25 (m, 1H, CHN), 4.28
3
2
3
3.85 (brs, 1H, Cab-H), 4.16 (m, 1H, CHN), 4.19 (dd, 1H, CH2O, JC–
(m, 1H, CH2O), 4.48 (m, 1H, CH2O). 13C NMR (75.4 MHz, CDCl3) d
4.18 (Sn–CH3); 13.7, 16.4 (CH(CH3)2); 28.5 (CH(CH3)2); 68.6
(Cab); 68.7, 70.3 (OCH2CHN); 70.1 (Cab); 166.2 (C@N). 11B NMR
(96.3 MHz, CDCl3) d –15.88 (2H), –12.39 (3H), –9.88 (2H), –6.67
(3H). 119Sn NMR (149.2 MHz, CDCl3) d –120.1 (Sn–CH3).
H = 8.4 Hz), 4.45 (dd, 1H, CH2O, JC–H = 8.1 Hz). 13C NMR
2
(75.4 MHz, CDCl3) d 14.2, 18.6 (CH(CH3)2); 30.5 (CH(CH3)2); 68.4
(Cab), 70.5, 71.2 (OCH2CHN); 73.8 (Cab); 168.5 (C@N). 11B NMR
(96.3 MHz, CDCl3) d–14.05 (2H), –12.51 (3H), –8.93 (2H), –5.74
(3H).
4.6. Synthesis of organotin halide (5)
4.3. Preparation of 2-(4-t-butyl-)oxazolinyl-o-carborane (2)
A procedure analogous to the preparation of compound 3 was
used but instead starting from compound 2 (0.81 g, 3.0 mmol) with
Me2SnCl2 (0.66 g, 3.0 mmol). Compound 5 was obtained as color-
less crystals (1.02 g, 2.3 mmol, 75%). Mp: 176–178 °C (dec). HRMS:
A procedure analogous to the preparation of compound 1 was
used but instead starting from o-carborane (0.72 g, 5.0 mmol) with
2-brome-4-t-butyl-oxazoline (1.33 g, 5.5 mmol). Compound 2 was
obtained as a pale yellow oil by silica gel column chromatography
using hexane as the eluent (Rf 0.36) (0.93 g, 3.5 mmol, 69%). Anal.
Calc. for C9H23B10NO: C, 40.13; H, 8.61; N, 5.20. Found: C, 40.10;
1H28 35Cl14N16O119Sn]+ 455.1812. Found:
12
11
Calcd for
455.1804. Anal. Calc. for C11H28B10ClNOSn: C, 29.19; H, 6.24; N,
3.09. Found: C, 29.22; H, 6.26; N, 3.11%. IR (KBr pellet, cm–1
(C–H) 3002, 2985, (B–H) 2582,
(C@N) 1685. 1H NMR (CDCl3)
d 0.33 (s, 6H, Sn–CH3, 2J
= 75.7 Hz), 0.98 (s, 9H, C(CH3)3),
[ C B
11 10
)
H, 8.29; N, 5.17%. IR (KBr pellet, cm–1
(B–H) 2599,
(C@N) 1692. 1H NMR (CDCl3) d 0.96 (s, 9H,
)
m(C–H) 3007, 2989, 2984,
m
m
m
m
m
119SnꢀCH3
2
C(CH3)3), 3.84 (brs, 1H, Cab-H), 4.18 (t, 1H, CHN), 4.21 (dd, 1H,
4.27 (m, 1H, CHN), 4.30 (dd, 1H, CH2O, JC–H = 7.8 Hz), 4.44 (dd,
CH2O, JC–H = 8.1 Hz), 4.40 (dd, 1H, CH2O, JC–H = 8.2 Hz). 13C NMR
(75.4 MHz, CDCl3) d 22.4 (C(CH3)3); 33.8 (C(CH3)3); 68.1 (Cab),
70.9, 72.1 (OCH2CHN); 72.6 (Cab); 168.7 (C@N). 11B NMR
(96.3 MHz, CDCl3) d –19.62 (4H), –16.33 (2H), –12.72 (2H), –4.68
(2H).
1H, CH2O, JC–H = 7.9 Hz). 13C NMR (75.4 MHz, CDCl3) d 4.06 (Sn–
2
2
2
CH3); 20.7 (C(CH3)3); 32.1 (C(CH3)3); 68.6 (Cab); 68.9, 71.2
(OCH2CHN); 70.3 (Cab); 166.7 (C@N). 11B NMR (96.3 MHz, CDCl3)
d –17.38 (3H), –14.59 (2H), –10.76 (2H), –7.64 (1H), –6.79 (1H),
–3.18 (1H). 119Sn NMR (149.2 MHz, CDCl3) d –119.6 (Sn–CH3).

J.-D. Lee et al. / Journal of Organometallic Chemistry 695 (2010) 463–468
467
4.7. Synthesis of organotin halide (6)
Found: C, 17.29; H, 5.11%. IR (KBr pellet, cm–1
)
m
(C–H) 3178,
2888,
119SnꢀCH3
m
(B–H) 2581. 1H NMR (CDCl3) d 1.11 (s, 6H, Sn–CH3,
2
A procedure analogous to the preparation of compound 3 was
used but instead starting from compound 2 (0.81 g, 3.0 mmol) with
Me2SnBr2 (0.93 g, 3.0 mmol). Compound 6 was obtained as color-
less crystals (1.21 g, 2.4 mmol, 81%). Mp: 180–182 °C (dec). HRMS:
2J
= 69.8 Hz), 3.50 (s, 3H, OCH3), 4.19 (d, 1H, CH2, JC–
2
H = 6.4 Hz), 4.25 (d, 1H, CH2, JC–H = 6.5 Hz). 13C NMR (CDCl3) d
4.97 (Sn–CH3); 50.2 (OCH3); 67.8, 76.0 (Cab); 79.6 (CH2). 11B NMR
(CDCl3) d –18.47 (4B), –14.85 (1B), –10.57 (4B), –6.48 (1B). 119Sn
NMR (149.2 MHz, CDCl3) d –108.2 (Sn–CH3).
Calcd for
499.1300. Anal. Calc. for C10H26B10BrNOSn: C, 26.58; H, 5.68; N,
2.82. Found: C, 26.61; H, 5.65; N, 2.80%. IR (KBr pellet, cm–1
(C–H) 2988, 2881, (B–H) 2586,
(C@N) 1687. 1H NMR (CDCl3) d
0.31 (s, 6H, Sn–CH3, 2J
= 76.1 Hz), 0.97 (s, 9H, C(CH3)3),
[ C B
1H28 80Br14N16O119Sn]+ 499.1307. Found:
12
11
11 10
)
4.11. Synthesis of organotin halide (10)
m
m
m
A procedure analogous to the preparation of 9 was used but in-
stead starting from compound 8 (0.79 g, 3.0 mmol). Compound 10
was obtained as colorless crystals (1.23 g, 2.5 mmol, 83%). Mp:
119SnꢀCH3
2
4.25 (m, 1H, CHN), 4.30 (dd, 1H, CH2O, JC–H = 8.0 Hz), 4.44 (dd,
2
1H, CH2O, JC–H = 8.1 Hz). 13C NMR (75.4 MHz, CDCl3) d 4.01 (Sn–
1H25 80Br16O119Sn]+
12
11
CH3); 20.5 (C(CH3)3); 31.8 (C(CH3)3); 68.6 (Cab); 68.6, 71.0
(OCH2CHN); 70.3 (Cab); 166.4 (C@N). 11B NMR (96.3 MHz, CDCl3)
d –18.44 (3H), –10.24 (3H), –8.52 (2H), –6.44 (1H), –4.21 (1H).
119Sn NMR (149.2 MHz, CDCl3) d –117.8 (Sn–CH3).
140–141 °C. HRMS: Calcd for
494.1041. Found: 494.1078. Anal. Calc. for C12H25B10BrOSn: C,
29.29; H, 5.12. Found: C, 29.41; H, 5.16%. IR (KBr pellet, cm–1
[ C B
12 10
)
m
(C–H) 3046, 2872,
m
(B–H) 2580. 1H NMR (CDCl3) d 1.00 (s, 6H,
= 68.3 Hz), 3.50 (s, 3H, OCH3), 4.27 (s, 1H, PhCH),
Sn–CH3, 2J
119SnꢀCH3
4.8. Preparation of methoxymethyl-o-carborane (7)
7.11–7.30 (m, 5H, Ph). 13C NMR (CDCl3) d 3.26 (Sn–CH3); 54.2
(OCH3); 66.8, 70.4 (Cab); 81.2 (PhCH); 124.5, 127.1, 127.8, 130.4
(Ph). 11B NMR (CDCl3) d –19.51 (3B), –16.48 (1B), –14.47 (4B),
–6.81 (2B). 119Sn NMR (149.2 MHz, CDCl3) d –110.3 (Sn–CH3).
NaH (0.36 g, 15.0 mmol) was added dropwise to a solution of o-
carboranylmethanol (0.87 g, 5.0 mmol) in 50 mL of dry THF at 0 °C
with stirring. The mixture was allowed to stir for 30 min at 0 °C at
which time iodomethane (0.78 g, 5.5 mmol) was added dropwise.
The solution was stirred for 1 h and then warmed to ambient tem-
perature. The reaction was quenched with water, extracted with
ether, and dried over anhydrous MgSO4. The solvent was evapo-
rated and the residue was purified by recrystallization in hexane
to afford compound 7 as colorless crystals in 92% yield (0.87 g,
4.6 mmol). Mp: 68–70 °C. Anal. Calc. for C4H16B10O: C, 25.52; H,
4.12. Crystal structure determination
Crystals of compounds 4, 7, 8, and 9 were obtained from toluene
at –10 °C, sealed in glass capillaries under argon, and mounted on
the diffractometer. The preliminary examination and data collec-
tion were performed using a Bruker SMART CCD detector system in
a single-crystal X-ray diffractometer equipped with a sealed-tube
X-ray source (40 kV ꢂ 50 mA) using graphite-monochromated Mo
8.57. Found: C, 25.57; H, 8.62%. IR (KBr pellet, cm–1
) m(C–H)
3066, 2785,
m
(B–H) 2581. 1H NMR (CDCl3) d 3.41 (s, 3H, OCH3),
K
a
radiation (k = 0.71073 Å). The preliminary unit cell constants
were determined using a set of 45 narrow-frame scans (0.3°
in ). The double-pass method of scanning was employed to ex-
3.94 (brs, 1H, Cab–H), 4.14 (s, 2H, CH2). 13C NMR (CDCl3) d 54.2
(OCH3), 68.7 (Cab), 76.1 (Cab), 82.5 (CH2). 11B NMR (CDCl3) d –
19.54 (4B), –16.82 (2B), –12.76 (2B), –8.33 (2B).
x
clude noise. The collected frames were integrated using an orienta-
tion matrix determined from the narrow-frame scans. The SMART
software package was used for data collection, and SAINT was em-
ployed for frame integration [30]. The final cell constants were
determined using a global refinement of the xyz centroids of the
reflections harvested from the entire data set. The structure solu-
4.9. Preparation of methoxy(phenyl)methyl-o-carborane (8)
A procedure analogous to the preparation of compound 7 was
used but instead starting from o-carboranyl(phenyl)methanol
(1.25 g, 5.0 mmol). Compound 8 was obtained as colorless crystals
(1.19 g, 4.5 mmol, 90%). Mp: 74–75 °C. Anal. Calc. for C10H20B10O:
tion and refinement were carried out using the SHELXTL
package [31].
-PLUS software
C, 45.43; H, 7.63. Found: C, 45.33; H, 7.67%. IR (KBr pellet, cm–1
)
m
(C–H) 3070, 2781,
m
(B–H) 2593. 1H NMR (CDCl3) d 3.44 (s, 3H,
Acknowledgment
OCH3), 3.93 (brs, 1H, Cab–H), 4.11 (s, 1H, PhCH), 7.14–7.30 (m,
5H, Ph). 13C NMR (CDCl3) d 55.8 (OCH3), 67.1 (Cab), 71.5 (Cab),
83.4 (PhCH), 125.4, 129.2, 129.8, 134.6 (Ph). 11B NMR (CDCl3) d–
19.85 (4B), –17.32 (2B), –11.76 (2B), –7.45 (2B).
This study was supported by research funds from Chosun Uni-
versity, 2007.
Appendix A. Supplementary material
4.10. General synthesis of the organotin halides (CabC,O)Me2SnBr (9)
CCDC 742034, 742035, 742036, 742037 contains the supple-
mentary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Center via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.jorganchem.2009.10.030.
A 2.5 M n-BuLi solution (1.3 mL, 3.3 mmol) was added to a stir-
red solution of compound 7 (0.56 g, 3.0 mmol) in diethyl ether
(30 mL) at –10 °C through a syringe. The resulting solution was
stirred at –10 °C for 30 min. A solution of Me2SnBr2 (0.93 g,
3.0 mmol) in diethyl ether (10 mL) was then added slowly to the
30 mL diethyl ether solution of compound 7ꢁLi at ꢀ10 °C. The reac-
tion temperature was maintained at –10 °C for 10 min. The reac-
tion mixture was then filtered and the organic solvent was
evaporated. The crude product was dissolved in fresh distilled tol-
uene. The volume of the toluene solution was reduced, and the
resulting concentrated solution was allowed to stand at –10 °C
for 2 days to allow crystallization. Compound 9 was obtained as
colorless crystals in 84% yield (1.05 g, 2.5 mmol). Mp: 134–
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