Copper(I)/S8 Reversible Reactions
A R T I C L E S
we purged argon for 10 s to ensure thorough mixing of sulfur solution
with the copper(I) solution. The resulting solution in cuvette was kept
at -80 °C, the color changed from yellow to purple, and complex 2
and the spectrum were recorded. Warming to RT caused the re-
formation of initial spectrum of copper(I) species of 1. Cooling to
-80 °C regenerated 2 completely. This cycle can be performed several
times under inert atmosphere (10 cycles were performed) without any
decrease in absorption intensity (Figure S4, Supporting Information).
Reaction of [{(TMPA′)CuII}2(µ-1,2-S22-)]2+ (2) with CO. A
deoxygenated 3.1 mL THF solution of 2 (0.0120 g, 0.005 mmol) at
-80 °C reacted with CO in a reversible fashion; bubbling with CO
gas caused an immediate bleaching of the purple color as seen by the
loss of all absorption features (Figure 6). This colorless solution was
independently determined as the copper(I) carbonyl adduct of TMPA′,
[(TMPA′)CuI(CO)]+ (8), as defined by its FTIR spectrum, which had
a distinct CO stretch at 2094 cm-1 (Figure S5, Supporting Information).
Bubbling this colorless solution with argon for 5 min at -80 °C led to
reformation of the solution’s purple color, which was concomitant with
a growth in the absorption features related to 2. This suggested that,
during CO reaction with 2, elemental sulfur formation occurred, because
no additional sulfur from outside was added. The colorless solutions
formed by CO bubbling of the purple solution of 2 described above
led to the isolation of 8 (0.0089 g, 75% yield) following precipitation
with 25 mL of pentane and recrystallization from CO-saturated solutions
of THF/pentane. Anal. Calcd for [(TMPA′)CuI(CO)]B(C6F5)4‚H2O;
C45H24BCuF20N4O3: C, 48.13; H, 2.15; N, 4.99; Found: C, 47.86; H,
1.99; N, 5.37. 1H NMR (DMSO): δ 3.33 (2H, H2O), 3.47 (s, 3H, CH3),
4.20 (6H, 3CH2), 4.76 (s, 2H, CH2O), 7.1-7.5 (br), 7.7-7.9 (br), 8.7
(d, 2H).
S6, Supporting Information. Additional bubbling did not change the
spectrum further. The purple product forms appeared to be [{(TMPA′)-
CuII}2(O2)]2+ (9), a µ-1,2-peroxodicopper(II) complex. Upon warming
to RT, the purple species 9 decomposed to a green species that cannot
be used to reform 9. Thus, with respect to temperature, the reactivity
of 1/O2 is irreversible.
Reaction of [{(TMPA′)CuII}2(µ-1,2-S22-)](B(C6F5)4)2 with PPh3.
Compound 1 (0.0485 g, 0.042 mmol) was dissolved in 4 mL of THF
under argon in a 10 mL Schlenk flask, elemental sulfur (0.0014 g,
0.043 mmol) was added, and the solution was stirred under argon. After
being cooled to -80 °C using an acetone/dry ice bath, 100 µL of a
THF solution prepared by dissolving PPh3 (0.220 g, 0.839 mmol) in
1 mL of THF was added anaerobically and the reaction was kept at
-80 °C for 8 h. A quantity of 200 µL of solution was taken from the
resulting solution for quantitative analysis by 31P NMR at room
temperature with P(Mes)3 as reference: (400 MHz); δ 43.37 (SdPPh3),
3.41 ([(TMPA′)CuI(PPh3)](B(C6F5)4); (11), -35.91 (P(Mes)3) ppm. On
the basis of integration, the ratio of SdPPh3/(11) (∼1:0.9) showed that
the reaction was 90% complete. The copper complex was then
precipitated from product solution by addition of 50 mL of pentane.
Analysis of the supernatant by GC and GC-MS (see below for
conditions) confirmed the formation of SdPPh3 (0.012 g, 95% yield);
authentic commercial SdPPh3 was also used for comparison. The
copper product, [(TMPA′)CuI(PPh3)]B(C6F5)4; (11)-B(C6F5)4
(0.0478 g, 85% yield), was isolated by redissolving the precipitate
obtained (above) in THF, adding pentane again and recrystallizing from
THF/pentane. The precipitate was dried in vacuo and analyzed by 31
P
NMR in THF with P(Mes)3 as reference: (400 MHz); δ 3.40 (11),
1
-35.91 (P(Mes)3) ppm. The H NMR (DMSO, RT): δ 3.37 (s, 3H,
Reaction of [{(TMPA′)CuII}2(µ-1,2-S22-)]2+ (2) with TMPA.
Complex 1 (0.0057 g, 0.005 mmol) was dissolved in 3.2 mL of THF
under argon in a UV-vis cuvette. This cuvette was cooled to -80 °C,
and an initial spectrum was recorded. Solid elemental sulfur
(0.0084 g) was dissolved in 5 mL of THF upon being stirred in a
10 mL Schlenk flask under argon. This sulfur solution was cooled at
-80 °C in an acetone/dry ice bath. Sulfur solution (100 µL, 0.005
mmol) was added to the copper(I) solution. With a long needle, argon
was purged for 10 s, and the resulting solution in cuvette was kept at
-80 °C. The color change occurred from yellow to purple complex 2.
The spectrum of 2 was recorded. Under argon atmosphere, 0.0316 g
of TMPA was dissolved in 1 mL of THF. Anaerobically, 50 µL of
THF solution of TMPA (0.005 mmol) was added to this purple solution,
and immediate color change occurred from purple to deep blue. Another
50 µL of THF solution of TMPA was added, and the spectrum was
recorded. Further addition of sulfur solution was performed, and no
change in spectrum was observed. Thus, the addition of TMPA caused
generation of species with absorption features at 568, 649, and 847
nm, which was identical to that observed for solutions from [(TMPA)-
CuI(CH3CN)]+ (3)/S8 reactivity (Figure 3A).
Reaction of [{(TMPA′)CuII}2(µ-1,2-S22-)](B(C6F5)4)2 with O2. A
3.9 mL 2-methyltetrahydrofuran (MeTHF) solution of 1 (0.0057 g,
0.005 mmol) was taken in a UV-vis cuvette under argon and 100 µL
of a MeTHF solution, which was 0.005 mM (prepared by adding
0.0167 g of S8 in 10 mL of MeTHF). The cuvette was cooled to
-124 °C, and an initial spectrum of 2 was recorded {λmax ) 540 nm
(ꢀ, 4600 M-1 cm-1)}. Dry dioxygen was bubbled for 30 s through the
solution using a long syringe needle, and the spectrum recorded is
shown in Figure 7. Additional bubbling did not change the spectrum
further. As described below, the product forms appeared to be
[{(TMPA′)CuII}2(O2)]2+ (9), a µ-1,2-peroxodicopper(II) complex {λmax
) 540 nm (ꢀ, 9550 M-1cm-1) and 610 nm, sh (ꢀ, 6500 M-1 cm-1)}.
Reaction of [(TMPA′)CuI]+ (1) with O2. A 3.8 mL THF solution
of 1 (0.0049 g, 0.004 mmol) was taken in a UV-vis cuvette under
argon. The cuvette was cooled to -80 °C, and an initial spectrum was
recorded. Dry dioxygen was bubbled for 30 s through the solution using
a long syringe needle, and the spectrum recorded is shown in Figure
CH3), 4.10 (6H, 3CH2), 4.42 (s, 2H, CH2O), 7.1-7.5 (m), 7.6-7.9
(m), 8.6 (d, 2H). Anal. Calcd for 11; C62H37BCuF20N4OP: C, 55.60;
H, 2.78; N, 4.18. Found: C, 55.30; H, 2.78; N, 4.21.
In a similar approach, compound 1 (0.162 g, 0.14 mmol) was
dissolved in 3 mL of THF under argon in a 10 mL Schlenk flask,
elemental sulfur (0.0045 g, 0.14 mmol) was added, and the solution
was stirred under argon. After being cooled to -80 °C using an acetone/
dry ice bath, 100 µL of a THF solution (0.036 g, 0.14 mmol) prepared
by dissolving PPh3 (0.36 g) in 1 mL of THF was added anaerobically,
and the reaction was kept at -80 °C for 8 h. 31P NMR was recorded
at room temperature with P(Mes)3 as reference: (400 MHz); δ 43.37-
(SdPPh3), 3.41 ([(TMPA′)CuI(PPh3)](B(C6F5)4); (11), -35.91(P(Mes)3)
ppm which shows near 1:0.85 integration of SdPPh3 and 11.
Reaction of [{(TMPA′)CuII}2(µ-1,2-S22-)](B(C6F5)4)2 with ArNC.
Compound 1 (0.0501 g, 0.043 mmol) was dissolved in 3.5 mL of THF
under argon in a 10 mL Schlenk flask, elemental sulfur (0.0014 g, 0.043
mmol) was added, and the solution was stirred under argon. After being
cooled to -80 °C using an acetone/dry ice bath, 100 µL of a THF
solution prepared by dissolving 2,6-dimethylphenyl isocyanide (ArNC)
(0.114 g, 0.870 mmol) in 1 mL of THF was added anaerobically, and
the reaction was kept cold at -80 °C for 1 h. The copper complex was
then precipitated from product solution by addition of 40 mL of pentane.
Analysis of the supernatant by GC and GC-MS (see below for
conditions) confirmed the formation of 2,6-dimethylphenyl isothiocy-
anate (ArNCS) in ∼85% yield; authentic commercial ArNCS was also
used for comparison. The copper product, [(TMPA′)CuI(CNAr)]+ (12),
was isolated by redissolving the precipitate obtained (above) in THF
and recrystallizing from THF/pentane. The intraligand cyanate stretching
ν(NtC) in 12 (in acetone) occurred at 2140 cm-1. The precipitate was
dried under vacuum and analyzed by 1H NMR (CDCl3): δ 1.6 (2.8H,
H2O), 2.6 (s, CH3, ArNC), 3.4 (s, 3H, CH3), 4.1 (s, 4H, 2CH2), 4.2 (s,
2H, CH2), 4.7 (s, 2H, CH2O), 7.1-7.4 (m), 7.6-7.8 (m), 8.6 (d, 2H).
Anal. Calcd. For [(TMPA′)CuI(CNAr)]B(C6F5)4‚(H2O)1.4; C53H33.8
-
BCuF20N5O2.4: C, 51.61; H, 2.76; N, 5.68. Found: C, 51.54; H, 2.50;
N, 5.57.
Reaction of [{(TMPA′)CuII}2(µ-1,2-S22-)](B(C6F5)4)2 (2) with
PhCH2Br. Compound 1 (0.0486 g, 0.043 mmol) was dissolved in 4
9
J. AM. CHEM. SOC. VOL. 129, NO. 28, 2007 8885
Maiti, Debabrata
