Organometallics
Article
reciprocal centimeters. Accurate mass (HRMS) measurements were
performed on a Waters Xevo G2-XS QTOF mass spectrometer
equipped with a LockSpray source and Atmospheric pressure Solids
Analysis Probe (ASAP). The solid sample was swabbed with the probe,
which was then inserted into the source with a source gas (nitrogen)
temperature of 600 °C. The probe remained in the source for 1 min or
until sample peaks were no longer observed, after which the probe was
removed. The APCI+ corona pin current was set to 0.8 μA. The
calculation of the percent buried volumes (%Vbur) and the steric maps
sphere of radius 3.5 Å about the metal center and Bondi van der Waals
radii scaled by a factor of 1.17.
X-ray Structure Determinations. X-ray diffraction data were
collected on a Bruker Apex II diffractometer. The structures were solved
by using direct methods and standard difference map techniques and
were refined by full-matrix least-squares procedures on F2 with
SHELXTL (Version 2014/7).166 Crystallographic data have been
deposited with the Cambridge Crystallographic Data Centre (CCDC
1602 (m), 1586 (m), 1546 (m), 1494 (m), 1455 (w), 1211 (w), 984
(w), 748 (s), 688 (s), 501 (m). IR, CH2Cl2 (cm−1): 2072, 1992.
Synthesis of (NitronNHC)Ir(PPh3)(CO)Cl. A solution of
(NitronNHC)Ir(COD)Cl (11 mg, 0.017 mmol) in C6D6 (0.7 mL) was
treated with PPh3 (5 mg, 0.019 mmol) and transferred to an NMR tube
equipped with a J. Young valve, which was degassed via a freeze−
pump−thaw cycle and then exposed to CO (1 atm). The solution
immediately turned a paler yellow color and was shaken for 5 min. After
this time, the volatile components were removed via lyophilization to
afford a pale yellow powder, which was washed with pentane (1 × 2
mL) and dried in vacuo to afford (NitronNHC)Ir(PPh3)(CO)Cl (4 mg,
28%). Crystals suitable for X-ray diffraction were obtained via slow
evaporation of a benzene solution. 1H NMR (C6D6): 5.60 [br, 1H of
NitronNHC N−H], 6.83−7.54 [22 H of NitronNHC and PPh3], 7.78 [m,
6H of PPh3], 8.99 [d, 2H of NitronNHC, 3JH−H = 8 Hz]. 31P{1H} NMR
(CD3CN): 24.1 [s, PPh3]. IR (cm−1): 3053 (w), 1947 (s, [ν(CO)]),
1617 (m), 1601 (m), 1585 (m), 1543 (m), 1495 (m), 1435 (m), 1095
(w), 747 (m), 689 (s), 530 (m), 511 (m). Mass spectrum: m/z
843.0511 (M + 1).
Synthesis of (NitronNHC)2NiBr2. A mixture of NiBr2 (11 mg, 0.050
mmol) and Nitron (34 mg, 0.109 mmol) in acetonitrile (1 mL) was
heated at 80 °C for 1 day, thereby resulting in the formation of a pale
red-pink precipitate, which was isolated via decantation, washed with
diethyl ether (1 × 2 mL), and dried in vacuo to afford
(NitronNHC)2NiBr2 (15 mg, 36%). Red crystals suitable for X-ray
diffraction were obtained directly from a less concentrated reaction
mixture comprising NiBr2 (2 mg), Nitron (5 mg), and acetonitrile (1
mL). 1H NMR (CD3CN): 6.75 [t, 1H of Nitron, 3JH−H = 7 Hz], 7.19 [t,
2H of Nitron, 3JH−H = 8 Hz], 7.42−7.64 [m, 8H of Nitron], 7.84 [d, 2H
of Nitron, 3JH−H = 8 Hz], 7.91 [d, 2H of Nitron, 3JH−H = 8 Hz], 9.36
[broad s, 1H of Nitron N−H] (due to low solubility, the NMR
spectrum was obtained by performing the reaction in CD3CN). IR
(cm−1): 3331 (m), 3063 (w), 2353 (w), 2320 (w) 1615 (s), 1598 (s),
1584 (s), 1542 (s), 1494 (s), 1452 (m), 1435 (m), 1374 (m), 1318 (m),
1300 (m), 1284 (m), 1257 (m), 1234 (m), 1208 (m), 1028 (m), 976
(m), 893 (m), 747 (s), 686 (s), 457 (m), 427 (m). Mass spectrum: m/z
831.1625 (M + 1).
Computational Details. Calculations were carried out using DFT
as implemented in the Jaguar 8.9 (release 15) suite of ab initio quantum
chemistry programs.167 Geometry optimizations were performed with
the B3LYP density functional using the LACVP** basis sets, and
Synthesis of (NitronNHC)Ir(COD)Cl. A suspension of [Ir(COD)-
Cl]2 (245 mg, 365 mmol) in acetonitrile (10 mL) was treated with
Nitron (228 mg, 730 mmol) and stirred for 21 h, resulting in the
formation of a yellow precipitate in a dark brown solution. The
precipitate was isolated via centrifugation, washed with diethyl ether (1
× 2 mL), and dried in vacuo to afford (NitronNHC)Ir(COD)Cl as a
yellow powder (302 mg, 64%). Yellow crystals suitable for X-ray
diffraction were obtained via slow evaporation of an acetonitrile
1
solution. H NMR (C6D6): 1.25 [m, 1H of COD], 1.45 [m, 4H of
COD], 1.63 [m, 1H of COD], 1.90 [m, 1H of COD], 2.04 [m, 1H of
COD], 2.45 [m, 1H of COD], 2.84 [m, 1H of COD], 4.97 [m, 1H of
COD], 5.05 [m, 1H of COD], 5.82 [s, 1H of NitronNHC N−H], 6.84 [t,
1H of NitronNHC, 3JH−H = 7 Hz], 7.09 [m, 6H of NitronNHC], 7.17 [t,
2H of NitronNHC, 3JH−H = 8 Hz], 7.24 [t, 2H of NitronNHC, 3JH−H = 8
Synthesis of (NitronNHC)2PdCl2. A mixture of PdCl2 (5 mg, 0.028
mmol) and Nitron (18 mg, 0.058 mmol) was dissolved in CD3CN (1
mL), transferred to an NMR tube equipped with a J. Young valve, and
heated at 80 °C for 24 h. After this time, a dark green solution had
formed along with the formation of green crystals suitable for X-ray
diffraction. The crystals were isolated by decantation, washed with
diethyl ether (1 × 2 mL), and dried in vacuo to afford
(NitronNHC)2PdCl2 (7 mg, 31%). The green crystals obtained from
the reaction were suitable for X-ray diffraction. Anal. Calcd for
(NitronNHC)2PdCl2: C, 59.9; H, 4.0; N, 14.0. Found: C, 59.4; H, 3.6; N,
14.0. IR (cm−1): 3416 (w), 3288 (m), 3134 (w), 3058 (m), 2064 (w),
1614 (s), 1597 (s), 1583 (s), 1543 (s), 1494 (s), 1468 (s), 1441 (s),
1379 (m), 1322 (m), 1236 (m), 1214 (m), 1072 (m), 1029 (m), 975
(m), 878 (w), 748 (s), 686 (s), 526 (s), 475 (s).
Hz], 7.63 [br, 2H of NitronNHC
,
3JH−H = 8 Hz], 8.93 [d, 2H of
NitronNHC, JH−H = 8 Hz]. 13C{1H} NMR (C6D6): 29.2 [s, CH2 of
COD], 30.3 [s, CH2 of COD], 32.7 [s, CH2 of COD], 34.3 [s, CH2 of
COD], 52.2 [s, CH of COD]. 52.8 [s, CH of COD], 84.5 [s, CH of
COD], 86.2 [s, CH of COD], 118.0 [NitronNHC], 123.0 [NitronNHC],
123.8 [NitronNHC], 128.9 [NitronNHC], 129.2 [NitronNHC], 129.5
[NitronNHC], 129.9 [NitronNHC], 134.8 [NitronNHC], 138.6 [Ni-
tronNHC], 140.5 [NitronNHC], 149.7 [NitronNHC], 182.3 [s, CN2 of
NitronNHC]. Anal. Calcd for (NitronNHC)Ir(COD)Cl: C, 51.9; H, 4.4;
N, 8.6. Found: C, 52.3; H, 4.1; N, 8.4. IR (cm−1): 3289 (w), 2882 (w),
2833 (w), 1630 (m), 1596 (m), 1489 (m), 1452 (w), 1369 (m), 1320
(w), 1233 (w), 1170 (w), 971 (m), 751 (s), 693 (s), 506 (m).
3
Synthesis of (NitronNHC)Ir(CO)2Cl. A solution of (NitronNHC)Ir-
(COD)Cl (20 mg, 0.031 mmol) in C6D6 (0.7 mL) in an NMR tube
equipped with a J. Young valve was degassed via a freeze−pump−thaw
cycle and then exposed to CO (1 atm). The solution immediately
turned a paler yellow color and was occasionally shaken for 1 h. The
volatile components were then removed via lyophilization to afford a
pale yellow powder, which was washed with pentane (1 × 2 mL) and
dried in vacuo to afford (NitronNHC)Ir(CO)2Cl (13 mg, 70%). Crystals
suitable for X-ray diffraction were obtained via slow evaporation of a
benzene solution. 1H NMR (C6D6, 500 MHz): 5.46 [s, 1H of
NitronNHC N−H], 6.84 [t, 1H of NitronNHC, 3JH−H = 8 Hz], 6.95−7.25
Catalytic Decarboxylation of Formic Acid by (NitronNHC)Ir-
(CO)2Cl. (a) A solution of (NitronNHC)Ir(CO)2Cl (2.1 mg, 0.0035
mmol) in C6D6 (0.7 mL) in an NMR tube equipped with a J. Young
valve was treated with formic acid (19.4 mg, 0.41 mmol) and heated at
80 °C. The reaction was monitored via 1H NMR spectroscopy, thereby
demonstrating the disappearance of formic acid and the formation of
H2 (TOF = 78 day−1). The vessel can be recharged with formic acid
several times and still maintain activity.
(b) A solution of (NitronNHC)Ir(CO)2Cl (2.1 mg, 0.0035 mmol) in
C6D6 (0.7 mL) in an NMR tube equipped with a J. Young valve was
treated with H13CO2H (6 mg, 0.128 mmol) and heated at 80 °C. The
reaction was monitored via NMR spectroscopy for 45 h, thereby
[m, 12H of NitronNHC], 8.44 [d, 2H of NitronNHC, 3JH−H = 8 Hz]. 13
C
NMR (C6D6): 118.0 [NitronNHC], 123.5 [NitronNHC], 125.0
[NitronNHC], 129.3 [NitronNHC], 129.4 [NitronNHC], 130.3 [Ni-
tronNHC], 130.9 [NitronNHC], 133.4 [NitronNHC], 137.9 [NitronNHC],
139.9 [NitronNHC], 150.4 [NitronNHC], 168.6 [CO], 174.8 [CO], 180.8
[CN2 of NitronNHC]. Anal. Calcd for (NitronNHC)Ir(CO)2Cl: C, 44.3;
H, 2.7; N, 9.4. Found: C, 45.8; H, 2.8; N, 9.2. IR, solid (cm−1): 3306
(w), 3067 (w), 2066 (vs) [ν(CO)], 1980 (vs) [ν(CO)], 1622 (m),
1
demonstrating the formation of H2 and 13CO2, as determined by H
and 13C NMR spectroscopy.
Catalytic Hydrosilylation of Benzaldehyde by PhSiH3 Using
(NitronNHC)Ir(CO)2Cl. A solution of (NitronNHC)Ir(CO)2Cl (5.6 mg,
0.009 mmol), benzaldehyde (65 mg, 0.612 mmol), and PhSiH3 (17.3
mg, 0.160 mmol) in C6D6 (0.7 mL) in an NMR tube equipped with a J.
Young valve was heated at 60 °C. The reaction was monitored by 1H
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Organometallics 2021, 40, 166−183