Communications
Table 1: Comparison between selected parameters (bond lengths in pm,
Experimental Section
bond angles in degrees) for 3b with calculated parameters for [{HB(m-
The reactions were carried out under an Ar atmosphere using
standard Schlenk techniques. All solvents were rigorously dried by
applying standard procedures prior to their use. The synthesis of
[HB(m-hpp)]2 (1) was accomplished as reported previously in
reference [5].
hpp)]2BH2]+.
exp.
RI-MP2/
def2-
B3LYP/
6-311
TZVPP
+ +G(d,p)
2a: 9-BBN dimer (67 mg, 0.55 mmol of the monomer) and
bis(trifluoromethanesulfonyl)imide (140 mg, 0.50 mmol) were dis-
solved in toluene (1 mL) and refluxed for 1 h. The solution was used
without further purification.
2b: 9-BBN dimer (134 mg, 1.10 mmol of the monomer) and
trifluoromethanesulfonic acid (89 mL, 1.00 mmol) were dissolved in
toluene (1.5 mL) and refluxed for 1 h. The solution was used without
further purification.
B1-B2/B4-B5
B1-B3/B4-B6
B2-B3/B5-B6
B3-C15/B6-C65
B3-C19/B6-C69
B–N (av)
B1-H1/B4-H4
B2-H2/B5-H5
B3···H1/B6···H4
B3···H2/B6···H5
B1-B2-B3/B4-B5-B6
B2-B3-B1/B5-B6-B4
B3-B1-B2/B6-B4-B5
184.9(5)/184.2(5)
181.9(5)/178.0(5)
178.4(5)/184.1(5)
158.4(5)/159.1(5)
158.8(5)/158.4(5)
151.4
115(3)/119(4)
116(4)/108(4)
166(4)/153(4)
164(4)/171(4)
181.8
178.1
178.0
–
183.3
175.9
182.6
–
–
–
151.5/151.7 152.8
124.2
124.3
156.4
156.0
59.3
61.4
59.3
118.3
122.5
125.9
172.1
148.0
57.5
61.5
61.1
116.9
122.7
3a: The solution of 2a was slowly added to a suspension of 1
(150 mg, 0.50 mmol) in toluene (10 mL). After the mixture had been
stirred at room temperature for 2 h, it was filtered, concentrated, and
stored at 38C. After a few days pure 3a crystallized in 31% yield
(107 mg, 0.15 mmol). C,H,N analysis (%) for C24H40B3F6N7O4S2
(701.17 gmolÀ1): calcd: C 41.11, H 5.75, N 13.98; found: C 39.93, H
5.59, N 13.25; 1H NMR (C6D6, 600 MHz): d = 3.20–3.10 (m, 8H, CH2-
N), 2.64–2.60 (m, 4H, CH2-N), 2.31 (bs, 2H, B-H), 2.28–2.24 (m, 4H,
CH2-N), 2.07–1.98 (m, 6H, CH2 9-BBN), 1.72–1.60 (m, 6H, CH2 9-BBN),
1.55–1.52 (m, 4H, CH2 hpp), 1.27–1.20 (m, 4H, CH2 hpp), 0.90 ppm (bs,
2H, CH-B); 13C{1H} NMR (100 MHz, C6D6): d = 156.5 (Cquart), 121.2
60.08(19)/57.8(2)
61.74(19)/61.1(2)
58.18(18)/61.1(2)
B1-B2-H2/B4-B5-H5 124.3(18)/124(2)
B2-B1-H1/B5-B4-H4 121.6(18)/119.3(17) 118.4
The topology of the electron-density distribution in
[{HB(m-hpp)}2BH2]+ is shown in Figure 4. The bond critical
points are highlighted. Four bond critical points are located in
the B3 plane, two along the B1/B2 H bonds, one between B1
and B2, and another one in the center of the B3 ring. The B1
B2 bonding path is significantly bent towards B3, indicating 3-
center-2-electron bonding. The presence of closed B-B-B
three-center bonding is in accordance with s-aromatic
character. The bonding is therefore comparable to that in
the B3H8À ion.[11,12]
1
(q, J(C,F) = 322 Hz, CF3), 54.8 (CH2-N), 43.3 (CH2-N), 35.7 (CH2 9-
BBN), 24.9 (CH2 9-BBN), 22.5 (bs, CH-B), 21.5 ppm (CH2 hpp); 11B NMR
(128 MHz, C6D6): d = 38.98 (bs, half line width ca. 5.4 ppm, B9-BBN),
1
À1.87 ppm (d, J(B,H) = 79.9 Hz, Bhpp); 19F NMR (375 MHz, C6D6):
À
À
~
d = À80.34 ppm (CF3); IR (KBr): n = 2979 (m; C-H val.), 2947 (s; C-
H val.), 2915 (s; C-H val.), 2886 (s; C-H val.), 2689 (w), 2655 (w), 2290
=
(w), 1614 (s) (B-H-B), 1565 (s; C N val.), 1486 (w), 1444 (m), 1400
(m), 1359 (s), 1352 (s), 1323 (s), 1296 (w), 1280 (m), 1225 (s), 1198 (s),
1140 (s), 1054 (s) cmÀ1; MS (ESI+): m/z (%): 421.2 (67) [MÀNTf2]+,
299.4 (100) [1ÀH]+.
3b: The solution of 2b was slowly added to a suspension of 1
(300 mg, 1.00 mmol) in toluene (12 mL). After the mixture had been
stirred at room temperature for 2 h, it was filtered and concentrated.
The product was precipitated by addition of petroleum ether (40/60).
After filtration and drying in vacuo, colorless solid 3b was obtained in
30% yield (170 mg, 0.30 mmol). Crystals suitable for X-ray crystal-
lography were grown by overlayering a toluene solution with
petroleum ether (40/60) at 38C. C,H,N analysis (%) for
C23H40B3F3N6O3S (570.10 gmolÀ1): calcd: C 48.46, H 7.07, N 14.74;
found: C 47.24, H 6.88, N 14.44; 1H NMR (600 MHz, C6D6): d = 3.42–
3.37 (m, 8H, CH2-N), 2.65–2.62 (m, 4H, CH2-N), 2.38 (bs, 2H, B-H),
2.30–2.26 (m, 4H, CH2-N), 2.09–2.01 (m, 6H, CH2 9-BBN), 1.75–1.68 (m,
6H, CH2 9-BBN), 1.58–1.53 (m, 4H, CH2 hpp), 1.33–1.26 (m, 4H, CH2 hpp),
1.04 ppm (bs, 2H, CH-B); 13C{1H} NMR (150 MHz, C6D6): d = 157.7
(Cquart), 45.9 (CH2-N), 43.3 (CH2-N), 35.7 (CH2 9-BBN), 25.1 (CH2 9-BBN),
22.5 (bs, CH-B), 21.7 (CH2 hpp); 11B NMR (128 MHz, C6D6): d = 39.05
Finally, we calculated the electron affinity of the model
cation [{HB(m-hpp)}2BH2]+. Using B3LYP/6-311 ++ G(d,p) a
DH0 value of À2.3 eV was obtained for the addition of one
electron to give the neutral radical. The DH0 value for
addition of a second electron to yield the monoanion was
close to zero.
These results are indicative of interesting chemical
+
reactivity of the synthesized B3H6 analogue, which will be
the subject of future work.
1
(bs, half line width ca. 5.4 ppm, B9-BBN), À1.73 (d, J(B,H) = 80.6 Hz,
Bhpp); 19F NMR: d = À77.80 ppm (s, CF3); IR (KBr): n = 2940 (m) (C-
~
H val.), 2918 (m) (C-H val.), 2880 (s) (C-H val.), 2840 (s) (C-H val.),
2686 (w), 2657 (w), 2293 (w) (B-H val.), 1626 (s), 1610 (s) (B-H-B),
=
1574 (s) (C N val.), 1476 (w), 1453 (w), 1401 (m), 1374 (m), 1356 (w),
1323 (s), 1270 (s), 1222 (m), 1236 (m), 1222 (s), 1146 (6), 1109 (w),
1068 (m), 1051 (m), 1031 (s) cmÀ1; MS (ESI+): m/z (%): 421.2 (54)
[MÀOTf]+, 301.4 (100) [1+H]+.
Crystal data for 3b: C23H40B3F3N6O3S, Mr = 570.10, 0.40 ꢀ 0.25 ꢀ
0.10 mm3, monoclinic, space group P21/n, a = 13.206(9), b = 28.39(2),
Figure 4. Topology of the electron-density distribution of [{HB(m-
hpp)}2BH2]+ (RI-MP2/def2-TZVPP) and bond paths in the plane
defined by the three B atoms. Electron density (av, in eꢂÀ3) at the
(3,À1) bond critical points (triangles): 0.152 (B–H), 0.128 (B1–B2),
0.118 (B1-B2-B3). Lines were drawn at 0.004, 0.008, 0.02, 0.04, 0.08,
c = 14.501(10) ꢁ, b = 91.84(1)8, V= 5434(6) ꢁ3, Z = 8, 1calcd
=
1.394 MgmÀ3
,
MoKa radiation (graphite-monochromated, l =
0.71073 ꢁ), T= 100 K, q range 2.0 to 27.98. Reflections measured
110786, independent 22952, Rint = 0.0571. Final R indices [I > 2s(I)]:
R1 = 0.0610, wR2 = 0.1624. H-atoms on B refined.
0.11, 0.13, 0.2, 0.4, 0.8, 2, 4, 8, 20, 40, 80, 200, 400, 800 eꢂÀ3
.
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 10444 –10447