Inorganic Chemistry
Article
Synthesis of Dirhodium(II,II) Complexes. The acetate com-
plexes (C1, C2) were synthesized through modified reported
procedures.24,25 Formamidinate complexes C3−C6 were obtained
through a modified literature method26 and improved upon as
follows. First, a Schlenk tube equipped with a magnetic stirrer bar was
charged with ligand (3.04 mmol, 10 equiv) (C3, C5, C6) or (7.48
mmol, 25 equiv) (C4), whereafter the tube was evacuated and filled
with N2 in 3 cycles to create an inert atmosphere. The ligand was
heated to 155 °C, forming a melt to which C2 (0.304 mmol, 1.00
equiv) was added. The reaction mixture was stirred at the same
temperature for an additional 18 h (C3, C5, C6) and under static
vacuum at the same temperature (C4). The reaction mixture was
cooled to ambient temperature before methanol (30 mL) was added,
forming a suspension which was subsequently heated to 40 °C (C3,
C5, C6) or 60 °C (C4) for 15 min. The mixture was filtered under
vacuum while hot and washed with pentane (2 × 10 mL) followed by
cold methanol (2 × 20 mL). The resulting solid was filtered under
vacuum and washed with methanol (2 × 10 mL) (C3, C5, C6) or
recrystallized from acetone (20 mL) (C4). The resulting solids were
dried under vacuum at 100 °C for 6 h to afford green (C3, C6) or
brown (C4, C5) microcrystals. Crystals suitable for analyses by single-
crystal X-ray diffraction were grown via slow diffusion of hexane into
concentrated solutions of either C3 or C5 in dichloromethane.
Dirhodium(II,II) Tetraacetate (C1).24 RhCl3·3H2O (0.504 g, 1.92
mmol) and NaOAc·3H2O (0.787 g, 5.78 mmol) were reacted in the
presence of absolute ethanol (15 mL), and glacial acetic acid (15 mL)
was added under N2 atmosphere to afford a green powder.
Yield: 0.125 g, 70%. Melting point: 324.1−343.8 °C. IR (ATR): ν
(cm−1) = 1588 (sharp, strong, CN) and 1241 (sharp, medium, C
1
F). H NMR (300 MHz, CDCl3) δppm = 7.89 (s, 4H, CHformamidine),
6.89−6.82 (m, 32H, CHAr). 13C{1H} NMR (101 MHz, CDCl3) δppm
= 166.5 (s, CHformamidine), 156.7 (d, 1J = 246.1 Hz, CAr), 138.1 (d, 4J =
4.7 Hz, CHAr), 126.2 (s, CHAr), 123.9 (d, 2J = 13.8 Hz, CHAr), 115.7
3
(s, CAr), 115.5 (d, J = 6.4 Hz CHAr). 19F NMR (377 MHz, CDCl3)
δppm = −129.9 (s). HR-ESI-MS (m/z): 1131.1124 (100%, [M + H]+,
requires 1131.1125).
Dirhodium(II,II) Tetrakis(bis(4-fluorophenyl)formamidinate)
(C6). Ligand L3 (0.351 g, 1.56 mmol) was reacted with complex
C2 (0.100 g, 0.152 mmol), affording green microcrystals.
Yield: 0.157 g, 91%. Melting point: 381.1−384.9 °C (decom-
position without melting). IR (ATR, cm−1): ν = 1583 (sharp, strong,
CN), 1209 (sharp, medium, CF). 1H NMR (400 MHz, CDCl3)
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δppm = 7.69 (t, J = 3.1 Hz, 4H, CHformamidine), 6.81 (t, J = 8.2 Hz,
16H, CHAr), 6.55−6.51 (m, 16H, CHAr). 13C{1H} NMR (101 MHz,
CDCl3) δppm = 162.7 (s, CHformamidine), 160.3 (d, 1J = 243.5 Hz, CAr),
146.6 (d, 4J = 2.5 Hz, CAr), 125.3 (d, 3J = 7.9 Hz, CHAr), 115.9 (d, 2J
= 22.3 Hz CHAr). 19F NMR (377 MHz, CDCl3) δppm = −120.3 (s).
HR-ESI-MS (m/z): 1131.1107 (100%, [M + H]+, requires
1131.1125).
Single-Crystal X-ray Diffraction. Single-crystal X-ray diffraction
data (C3 and C5) were collected using a Bruker Kappa APEX II
DUO diffractometer equipped with graphite-monochromated Mo−
Kα radiation (λ = 0.71073 Å). The temperature was controlled by an
Oxford Cryostream cooling system (Oxford Cryostat). Cell refine-
ment and data reduction were achieved using the program SAINT.27
The data were scaled and absorption correction was accomplished
using SADABS.28 The structure was solved by direct methods by
using SHELXS-97 and refined by full-matrix least-squares methods
based on F2 using SHELXL-2018.29 Refinement of non-hydrogen
atoms was carried out anisotropically. All hydrogen atoms were placed
in idealized positions and refined in riding models with a Uiso assigned
1.2 or 1.5 times the Ueq of their parent atoms, and the bond distances
were constrained from 0.95 to 0.99 Å. The methyl−phenyl moieties
(C3) were disordered over two positions, and site occupancies were
refined to 0.47(2) versus 0.53(2) and to 0.45(2) versus 0.55(2). The
fluorine atom F4 (C5) was disordered over two positions assigned as
F4A and F4B, with refined site occupancy factors of 0.773(3) and
0.227(3). The programs X-Seed, Mercury, and POV-Ray were used to
produce ORTEP images of compounds C3 and C5.29,30 Selected
crystallographic data and structure refinement properties are reported
General Method for Hydroformylation Reactions. Hydro-
formylation reactions were carried out in a 90 mL stainless steel pipe
reactor equipped with a Teflon-coated magnetic stirrer bar. The
reactor was charged with toluene (5 mL), substrate (1-octene, 7.175
mmol), internal standard n-decane (1.26 mmol), and catalytic
precursor (2.87 × 10−3 mmol), calculated per dirhodium core unit,
equivalent to a rhodium metal loading of 5.74 × 10−3 mmol. The pipe
reactor was purged with nitrogen three times, followed by purging
with syngas (1:1, CO/H2) three times. The reactor was pressurized to
the desired pressure and consequently heated to the desired
temperature. Samples were collected at the beginning and end of
each reaction. All reactions were performed in triplicate and are
recorded as an average of three identical experiments.
Yield: 0.289 g, 67%. Melting point: 310.9−315.3 °C (decom-
position without melting). IR (ATR): ν (cm−1) = 1572 (sharp, strong,
1
CO) and 1409 (sharp, medium, CO). H NMR (400 MHz,
DMSO-d6) δppm = 1.79 (s, 12H, CH3). 13C{1H} NMR (101 MHz,
DMSO-d6) δppm = 190.6(s, Ccarbonyl), 23.5 (s, CH3). HR- ESI-MS (m/
z): 460.8655 (100%, [M + H2O + H]+, requires 460.8452).
Dirhodium(II,II) Tetrakis(trifluoromethyl acetate)(diacetic acid)
(C2).25 Compound C1 (0.107g, 0.231 mmol) was reacted with
trifluoroacetic acid (35 mL, 457 mmol), affording a green solid.
Yield: 0.138 g, 92%. Melting point: 330.7−334.1 °C (decom-
position without melting). IR (ATR): ν (cm−1) = 1655 (sharp, strong,
CO), 1226 (sharp, medium, CO), and 1160 (sharp, strong, C
1
F). H NMR (400 MHz, DMSO-d6) δppm = 2.08 (s, CH3 (AcOH)).
13C{1H} NMR (101 MHz, DMSO-d6) δppm = 199.5 (s, Ccarbonyl),
30.12 (s, CH3). 19F NMR (377 MHz, DMSO-d6) δppm = −73.8 (m).
HR- ESI-MS (m/z): 777.7986 (100%, [M]+, requires 777.7792).
Dirhodium(II,II) Tetrakis(di-p-tolylformamidinate) (C3).26 Ligand
L1 (0.340 g,1.52 mmol) was reacted with complex C2 (0.100 g, 0.152
mmol), affording green microcrystals.
Yield: 0.137 g, 82%. Melting point: 376.7−379.2 °C (decom-
position without melting). IR (ATR): ν (cm−1) = 1587 (sharp, strong,
CN). 1H NMR (300 MHz, CDCl3) δppm = 7.70 (s, 4H,
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CHformamidine), 6.89 (d, J = 8.2 Hz, 16H, CHAr), 6.60 (d, J = 8.2
Hz, 16H, CHAr), 2.25 (s, 24H, CH3). 13C{1H} NMR (100 MHz,
CDCl3) δppm = 162.2 (s, CHformamidine), 148.7 (s, CAr), 132.4 (s,
CHAr), 129.3 (s, CHAr), 124.2 (s, CAr), 20.8 (s, CH3). HR-ESI-MS
(m/z): 1098.3077 (100%, [M]+, requires 1098.3051).
Dirhodium(II,II) Tetrakis(di-o-tolylformamidinate) (C4). Ligand
L2 (1.68 g, 7.48 mmol) was reacted with C2 (0.200 g, 0.304 mmol),
affording brown microcrystals.
Yield: 0.0971 g, 34%. Melting point: 364.9−367.1 °C (decom-
position without melting). IR (ATR): ν (cm−1) = 1586 (sharp, strong,
CN). 1H NMR (600 MHz, CDCl3) δppm = 7.72 (s, 4H,
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3
CHformamidine), 6.97 (d, 8H, J = 7.3 Hz, CHAr), 6.91 (t, 8H, J =
7.6 Hz, CHAr), 6.87 (t, 8H, 3J = 7.3 Hz, CHAr), 6.73 (br s, 8H, CHAr),
1.98 (s, 24H, CH3). 13C{1H} NMR (100 MHz, CDCl3) δppm = 168.4
(s, CHformamidine), 151.1 (s, CAr), 132.2 (s, CAr), 131.1 (s, CHAr), 130.9
(s, CHAr), 126.3 (br s, CHAr), 123.7 (s, CHAr), 19.27 (s, CH3). HR-
ESI-MS (m/z): 1098.3041 (96%, [M]+, requires 1098.3051);
1084.2808 (100%, [M − CH3 + H]+, requires 1084.2850).
Mercury Poisoning Studies. The hydroformylation reactions
were carried out in a 90 mL stainless steel pipe reactor equipped with
a Teflon-coated magnetic stirrer bar. The reactor was charged with
toluene (5 mL), 1-octene (7.175 mmol), internal standard n-decane
(1.26 mmol), a drop of mercury, and compound C1 (2.87 × 10−3
mmol). The pipe reactor was flushed with nitrogen three times,
followed by purging with syngas (1:1, CO/H2) three times. The
reactor was pressurized to 50 bar and heated to 95 °C for 4 h.
Dirhodium(II,II) Tetrakis(bis(2-fluorophenyl)formamidinate)
(C5). Ligand L4 (0.353 g, 1.57 mmol) was reacted with complex
C2 (0.100 g, 0.152 mmol), affording brown microcrystals.
C
Inorg. Chem. XXXX, XXX, XXX−XXX