6042 Organometallics, Vol. 28, No. 20, 2009
Dachs et al.
the half-reaction times tA1/2 and tB1/2 of steps A and B,
respectively, it was found that step A (coordination of the
two CtC bonds of 1a, followed by oxidative coupling) was
rate-determining for the reaction of the bulky 1a. In contrast,
step B, reaction of 2b (generated from the nonprotected and
thus less bulky diyne 1b) with the monoalkyne 3 with
subsequent recovery of the Wilkinson catalyst, was rate-
determining. We conclude that the first or second step may
be rate-determining according to the structure of the starting
reagents.
temperature for 5 h. Then, degassed diethyl ether (6 mL) was
added to the reaction mixture and a solid was precipitated. The
solvents were evaporated to afford 2b (0.048 g, 87%) as a red
solid: mp 96-99 °C; 1H NMR (200 MHz, CDCl3) δ 1.00 (d, J =
6.7 Hz, 18H), 1.10-1.28 (m, 36H), 2.81 (sept, J = 6.7 Hz, 4H),
3.00-3.04 (m, 4H), 3.30 (br s, 4H), 3.40-3.65 (m, 4H),
3.90-4.20 (m, 3H), 6.80-7.70 (m, 36H); 13C NMR (50 MHz,
CDCl3) δ 24.2, 25.7, 25.8, 30.2, 30.6, 34.8, 46.5, 48.6, 124.2,
124.7, 127.7, 128.8, 128.9, 129.0, 129.1, 130.3, 130.8, 131.2,
131.7, 133.1, 134.9, 135.0, 135.1, 149.0, 150.7, 151.6, 152.8,
153.4; 31P NMR (101 MHz, CD2Cl2) δ 19.6 (d, J = 119 Hz);
ESI-MS (m/z) 1314 [M - Cl - PPh3]þ; HRMS calcd. for
[C71H94N3O6PRhS3]þ 1314.5092, found 1314.5119. Conductiv-
ity measurements were done on a solution of 2b in CH2Cl2 or
DMF (5 mL) to determine whether the complex was cationic or
neutral. At 20 °C, in CH2Cl2, the conductivity increased from
9.3 μS cm-1 (residual conductivity of CH2Cl2) to 13.3 μS cm-1
after addition of 2b (17 mg, 0.01 mmol, 2 mM) and to 17 μS cm-1
for 2b (4 mM). In DMF, a strongly more dissociative solvent
than CH2Cl2, the conductivity increased from 2.6 μS cm-1
(residual conductivity of DMF) to 23.3 μS cm-1 after addition
of 2b (17 mg, 0.01 mmol, 2 mM). From these low values of
conductivities, we assume that complex 2b was not significantly
dissociated to the cationic complex and chloride anion.16,17
Spectroscopic data for 2c: 1H NMR (200 MHz, CDCl3) δ 2.45
(s, 6H), 2.54 (s, 3H), 3.00-3.34 (m, 4H þ 4H þ 2H), 7.16-7.67
(m, 42 H); 13C NMR (50 MHz, CDCl3) δ 22.3, 46.9, 48.9, 127.7,
128.6, 128.8, 128.9, 129.0, 130.0, 130.2, 130.3, 130.5, 130.9,
131.4, 134.6, 134.7, 134.9, 134.9, 136.8, 143.9, 144.1, 149.6,
149.7, 152.9, 153.6; 31P NMR (101 MHz, CD2Cl2) δ 22.9 (d,
J = 119 Hz); ESI-MS (m/z) 1240 [M - Cl]þ, 978 [M - Cl -
PPh3]þ; HRMS calcd for [C47H46N3O6PRhS3]þ 978.1336,
found 978.1377.
Experimental Part
All experiments were performed under an argon atmosphere.
31P NMR spectra were recorded on a Bruker spectrometer (101
MHz) with H3PO4 as an external reference. 1H and 13C NMR
spectra were recorded on Bruker spectrometers (200 and
400 MHz) with TMS as an internal reference. Cyclic voltam-
metry and chronoamperometry were performed at a gold disk
electrode (d = 2 mm) with a homemade potentiostat and a
waveform generator EGG model 175. Voltammograms were
recorded on a Nicolet 301 oscilloscope. Conductivity measure-
ments were performed on a Tacussel CDM210 conductivity
meter (cell constant = 1 cm-1).
Chemicals. Dichloromethane was distilled from calcium hy-
dride and kept under argon. The monoalkyne 3 and the Wilkinson
catalyst RhCl(PPh3)3 were commercially available. The diynes 1a,
1b, and 1c were prepared as previously described by us.2a,b
General Procedure for the [2þ2þ2] Cycloadditions of Diynes 1
and Monoalkyne 3. A degassed solution of diyne 1b (0.10 g, 0.10
mmol), 2-butyn-1,4-diol, 3 (0.011 g, 0.13 mmol), and chlorotris-
(triphenylphosphine)rhodium(I) (0.0046 g, 0.005 mmol, 5%
molar) in anhydrous toluene (15 mL) was heated at 65 °C for
7 h (TLC monitoring). The solvent was then evaporated and the
residue was chromatographed through silica gel with hexanes/
ethyl acetate (polarity from 7:3 to 6:4) to afford 4b (0.047 g,
43%) as a colorless solid. A sample specially purified for
elemental analysis was obtain by digestion from diethyl ether:
mp 210-212 °C (dec); IR (ATR) 3288, 2958, 2928, 2868, 2163,
1319, 1149 cm-1; 1H NMR (200 MHz, CDCl3) δ 1.17-1.30 (m,
54H), 2.91 (sept, J = 6.8 Hz, 3H), 3.37 (br s, 2H), 3.98-4.22 (m,
10H), 4.60 (s, 4H), 4.78 (s, 4H), 5.40-5.45 (m, 2H), 7.16 (s, 4H),
7.17 (s, 2H); 13C NMR (50 MHz, CDCl3) δ 24.2, 25.5, 25.6, 30.2,
30.4, 34.8, 42.4, 52.7, 59.0, 124.6, 124.7, 131.5, 131.8, 132.5,
137.8, 140.4, 151.1, 152.1, 153.8, 154.0; ESI-MS (m/z) 1036 [M þ
H]þ, 1053 [M þ NH4]þ, 1058 [M þ Na]þ; HRMS calcd. for
[C57H86N3O8S3]þ 1036.5572, found 1036.5546. Anal. Calcd for
Spectroscopic data for 2a: 31P NMR (101 MHz, CD2Cl2) δ
38.8 (d, J = 185 Hz); ESI-MS (m/z) 1514 [M - Cl - PPh3]þ.
General Procedure for Cyclic Voltammetry. Experiments were
carried out in a three-electrode thermostated cell (25 °C) con-
nected to a Schlenk line. The reference was a saturated calomel
electrode separated from the solution by a bridge filled with
1.5 mL of CH2Cl2 containing nBu4NBF4 (0.3 M). The counter
electrode was a platinum wire of ca. 1 cm2 apparent surface area.
Eighteen milliliters of CH2Cl2 containing nBu4NBF4 (0.3 M)
were introduced into the cell followed by 25 mg (0.027 mmol) of
RhCl(PPh3)3. Cyclic voltammetry was performed at a steady
gold disk electrode (d = 2 mm) at the scan rate of 0.5 V s-1. Then
31 mg (0.027 mmol) of 1a was added to the cell. Cyclic
voltammetry was performed with time. Similar experiments
were performed from 26 mg (0.027 mmol) of 1b or 4.7 mg
(0.054 mmol) of the monoalkyne 3.
C57H85N3O8S3 Et2O (1110.631): C, 65.97; H, 8.62; N, 3.78; S,
3
In a second step, 2.3 mg (0.027 mmol) of the monoalkyne 3
was added to either 2a or 2b generated as reported just above.
The cyclic voltammetry was performed at fixed time intervals at
8.66. Found: C, 66.46 and 66.04; H, 8.75 and 8.86; N, 3.81 and
3.77; S, 8.26 and 8.20.
Spectroscopic data for 4a: mp 92-94 °C; IR (ATR) 3512,
2960, 2930, 2871, 1725, 1317, 1149, 1130 cm-1; 1H NMR (200
MHz, CDCl3) δ 1.12 (s, 18H), 1.18-1.45 (m, 54H), 2.92 (sept,
J = 7 Hz, 3H), 3.58 (br s, 2H), 3.89 (sept, J = 6.6 Hz, 4H), 4.29
(sept, J = 6.7 Hz, 2H), 4.85 (s, 4H), 4.85 (s, 4H), 5.02 (s, 4H),
7.15 (s, 4H), 7.16 (s, 2H); 13C NMR (50 MHz, CDCl3) δ 24.2,
25.5, 25.6, 28.3, 30.1, 34.8, 34.9, 45.2, 52.7, 58.9, 85.6, 124.2,
124.4, 131.1, 132.4, 134.5, 138.0, 140.7, 151.2, 151.4, 152.1,
153.4, 154.3; ESI-MS (m/z) 1236 [M þ H]þ, 1253 [M þ NH4]þ,
1258 [M þ Na]þ, 1274 [M þ K]þ. A sample specially purified for
elemental analysis was obtain by digestion from n-pentane:
HRMS calcd for [C67H101N3O12S3Na]þ 1258.6440, found
the scan rate of 0.5 V s-1
.
General Procedure for the Investigation of the Kinetics of the
Reaction of RhCl(PPh3)3 with 1a or 1b or 3 (step A in Scheme 3 or
4). Kinetic experiments were performed in the same cell as used
for cyclic voltammetry (vide supra). Eighteen milliliters of
CH2Cl2 containing nBu4NBF4 (0.3 M) was introduced into
the cell followed by 25 mg (0.027 mmol) of RhCl(PPh3)3.
The rotating gold disk electrode (Radiometer, EDI 65109,
d = 2 mm, angular velocity: ω = 105 rad s-1) was polarized
at þ1 V versus SCE. The decrease of the oxidation current of the
RhCl(PPh3)3 was recorded with time after addition of 31 mg
(0.027 mmol) of 1a until total conversion. Similar experiments
were done in the presence of 40 mg (0.054 mmol) of PPh3.
Similar experiments were done with 26 mg (0.027 mmol) of 1b
and 4.7 mg (0.054 mmol) of 3.
1258.6435. Anal. Calcd for C67H101N3O12S3 C5H12
3
(1308.882): C, 66.07; H, 8.70; N, 3.21; S, 7.35. Found: C, 65.80
and 65.83; H, 8.55 and 8.57; N, 3.25 and 3.27; S, 6.69 and 6.95.
General Procedure for the Synthesis of Rhodacyclopentadiene
RhIII, 2. A degassed solution of diyne 1b (0.040 g, 0.042 mmol)
and chlorotris(triphenylphosphine)rhodium(I) (0.039 g, 0.042
mmol) in degassed dichloromethane (4 mL) was stirred at room
General Procedure for the Investigation of the Kinetics of the
Reaction of 2a or 2b with the Monoalkyne 3 (step B in Scheme 3).
The kinetics of the reaction of 2.35 mg (0.027 mmol) of 3 with the