Insertion of CO2 and COS into Bi-C bonds: Reactivity of a bismuth NCN pincer complex of an oxyaryl dianionic ligand, [2,6-(Me 2NCH2)2C6H3]Bi(C 6H2tBu2O)

Article abstract of DOI:10.1021/ja403133f

The reactivity of the unusual oxyaryl dianionic ligand, (C ₆H₂^tBu₂-3,5-O-4)^2-, in the Bi³⁺ NCN pincer complex Ar′Bi(C₆H ₂^tBu₂-3,5-O-4), 1, [Ar′ = 2,6-(Me ₂NCH₂)₂C₆H₃] has been explored with small molecule substrates and electrophiles. The first insertion reactions of CO₂ and COS into Bi-C bonds are observed with this oxyaryl dianionic ligand complex. These reactions generate new dianions that have quinoidal character similar to the oxyaryl dianionic ligand in 1. The oxyarylcarboxy and oxyarylthiocarboxy dianionic ligands were identified by X-ray crystallography in Ar′Bi[O₂C(C₆H₂ ^tBu₂-3-5-O-4)-κ²O,O′], 2, and Ar′Bi[OSC(C₆H₂^tBu₂-3-5-O-4)- κ²O,S], 3, respectively. Silyl halides and pseudohalides, R₃SiX (X = Cl, CN, N₃; R = Me, Ph), react with 1 by attaching X to bismuth and R₃Si to the oxyaryl oxygen to form Ar′Bi(X)(C₆H₂^tBu₂-3,5- OSiR₃-4) complexes, a formal addition across five bonds. These react with additional R₃SiX to generate Ar′BiX₂ complexes and R₃SiOC₆H₃^tBu₂-2,6. The reaction of 1 with I₂ forms Ar′BiI₂ and the coupled quinone, 3,3′,5,5′-tetra-tert-butyl-4,4′- diphenoquinone, by oxidative coupling.

Full text of DOI:10.1021/ja403133f

Article
pubs.acs.org/JACS
Insertion of CO2 and COS into Bi−C Bonds: Reactivity of a Bismuth
NCN Pincer Complex of an Oxyaryl Dianionic Ligand, [2,6-
t
(Me2NCH2)2C6H3]Bi(C6H2 Bu2O)
Douglas R. Kindra, Ian J. Casely, Megan E. Fieser, Joseph W. Ziller, Filipp Furche, and William J. Evans*
Department of Chemistry, University of California, Irvine, California 92697-2025, United States
S
* Supporting Information
ABSTRACT: The reactivity of the unusual oxyaryl dianionic
ligand, (C6H2 Bu2-3,5-O-4)2−, in the Bi3+ NCN pincer complex
t
t
Ar′Bi(C6H2 Bu2-3,5-O-4), 1, [Ar′ = 2,6-(Me2NCH2)2C6H3]
has been explored with small molecule substrates and
electrophiles. The first insertion reactions of CO2 and COS
into Bi−C bonds are observed with this oxyaryl dianionic
ligand complex. These reactions generate new dianions that
have quinoidal character similar to the oxyaryl dianionic ligand in 1. The oxyarylcarboxy and oxyarylthiocarboxy dianionic ligands
were identified by X-ray crystallography in Ar′Bi[O2C(C6H2 Bu2-3-5-O-4)-κ2O,O′], 2, and Ar′Bi[OSC(C6H2 Bu2-3-5-O-4)-
t
t
κ2O,S], 3, respectively. Silyl halides and pseudohalides, R3SiX (X = Cl, CN, N3; R = Me, Ph), react with 1 by attaching X to
t
bismuth and R3Si to the oxyaryl oxygen to form Ar′Bi(X)(C6H2 Bu2-3,5-OSiR3-4) complexes, a formal addition across five bonds.
t
These react with additional R3SiX to generate Ar′BiX2 complexes and R3SiOC6H3 Bu2-2,6. The reaction of 1 with I2 forms
Ar′BiI2 and the coupled quinone, 3,3′,5,5′-tetra-tert-butyl-4,4′-diphenoquinone, by oxidative coupling.
Scheme 1. Possible Bonding Arrangements for 1, the
Bismuth NCN Pincer Complex of the Oxyaryl Dianionic
INTRODUCTION
■
Recent studies of the chemistry of bismuth stabilized by the
NCN phenyl pincer ligand, 2,6-(Me2NCH2)2C6H3, Ar′,1−7
have revealed that a new type of ligand, a dianionic oxyaryl
Ligand (C6H2 Bu2-3,5-O-4)2−
t
species, (C6H2 Bu2-3,5-O-4)2−, can be created when sterically
t
bulky aryloxide ligands react with Ar′BiCl2, eq 1.8 In contrast to
small molecule substrates into a Bi−C bond. These reactions
generate two new dianionic ligands with quinoidal character-
istics. Reactions of silyl halides and pseudohalides are also
reported in which Me3Si−X formally adds over five bonds to
the bismuth and oxygen components of complex 1.
reactions with smaller aryloxide anions that make the three-
EXPERIMENTAL DETAILS
i
■
ligand complexes Ar′Bi(OC6H3R2)2 (R = Me, Pr), Ar′BiCl2
t
All manipulations and syntheses described below were conducted with
the rigorous exclusion of air and water using standard Schlenk line and
glovebox techniques under an argon or dinitrogen atmosphere.
Solvents were sparged with UHP argon and dried by passage through
columns containing Q-5 and molecular sieves prior to use. Deuterated
NMR solvents were dried over NaK alloy, degassed by three freeze−
pump−thaw cycles, and vacuum transferred before use. 1H NMR
spectra were recorded on Bruker DR400, GN500, or CRYO500 MHz
spectrometers (13C NMR spectra on the 500 MHz spectrometer
operating at 125 MHz, 19F NMR spectra on the DR400 spectrometer
operating at 375 MHz) at 298 K unless otherwise stated and
referenced internally to residual protio-solvent resonances. GC−MS
reacts with KOC6H2 Bu2-2,6 to form a product with only two
t
ligands, Ar′Bi(C6H2 Bu2-3,5-O-4), 1. This reaction involves
t
C−H bond activation and formation of HOC6H3 Bu2-2,6 as a
byproduct.
NMR and IR spectroscopy, crystallographic studies, and
DFT calculations indicate that complex 1 is a Bi3+ complex with
an oxyaryl dianionic ligand that has ring C−C and C−O
distances consistent with considerable quinoidal character.8
This complex is best described by structure A, Scheme 1, rather
than as a Bi2+ complex of a radical, structure B, or a complex
with a BiC(aryl) double bond, structure C.
We describe here the reaction chemistry of this unusual
oxyaryl dianionic ligand complex. Complex 1 reacts with CO2
and COS to provide the first examples of insertion of these
Received: March 28, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/ja403133f | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
t
spectra were collected on a ThermoTrace MS and GC−MS
[2,6-(Me2NCH2)2C6H3]Bi[O213C(C6H2 Bu2-3-5-O-4)-κ2O,O′],
2-13C. The 13C analogue of 2 was prepared analogously from 13CO2
(90 mg, 73%). 13C NMR (125 MHz, acetonitrile-d3): δ 175.8
instrument. Elemental analyses were conducted on a Perkin-Elmer
t
2400 Series II CHNS elemental analyzer. KOC6H3 Bu2-2,6 and
[O213C(C6H2 Bu2O)] 130.6, 129.1, 127.8, and, 126.2 [m- and p-
(Me2NCH2)2C6H3 and O2C(C6H2 Bu2O)], 68.7 [(Me2NCH2)2C6H3],
t
t
KOC6H2 Bu2-2,6-Me-4 were synthesized via an adaptation of a
t
literature procedure by treatment of the parent phenol with 1 equiv
of KN(SiMe3)2 in toluene, followed by filtration of the resulting white
solid, and washing with hexane.9 [Et3NH][BPh4] was synthesized by
treatment of [Et3NH][Cl] with NaBPh4 in water, followed by filtration
and drying under a high vacuum (10−5 Torr) for 48 h.8 CO2 (99.98%),
13CO2 (99%), and COS (96+ %) were purchased from Airgas,
Cambridge Isotope Laboratories, and Matheson, respectively. Phenol
reagents were sublimed prior to use. Me3SiN3 and Me3SiCN (Sigma-
Aldrich) were distilled under argon before use. Me3SiCl (Alfa Aesar,
98+%) and Ph3SiCl (Sigma-Aldrich, 97%) were received packed under
argon and used without further purification. Ar′Bi(OC6H3Me2-2,6)2
was prepared according to the literature.8
46.3 [(Me2NCH2)2C6H3], 35.6 [q-O2C(C6H2(CMe3)2O)], 30.7
[O2C(C6H2(CMe3)2O)]. IR: 3631w, 2951s, 2794w, 1665w, 1591s,
1523m (calcd 1512), 1468s, 1424s, 1305s (calcd 1293), 1010m, 841s,
694m cm−1.
[2,6-(Me2NCH2)2C6H3]Bi[OSC(C6H2 Bu2-3-5-O-4)-κ2O,S], 3. A
t
100 mL sealable side arm Schlenk flask was charged with bright
orange 1 (150 mg, 0.25 mmol). Addition of acetonitrile (15 mL)
formed a red solution. The flask was placed on a high vacuum line,
degassed, and charged with 1 atm of carbonyl sulfide (COS) gas. After
stirring at room temperature for 1 h, an orange precipitate formed.
The flask was degassed with three freeze−pump−thaw cycles and
moved into a nitrogen-filled glovebox. The solids were collected via
centrifugation, washed with hexane, and dried under a vacuum giving 3
as an orange powder (108 mg, 65%). X-ray quality crystals were grown
from a saturated acetonitrile solution at −30 °C. 1H NMR (500 MHz,
t
[2,6-(Me2NCH2)2C6H3]Bi(C6H2 Bu2-3,5-O-4), 1. This procedure is
an improved route to 1 compared to that in the literature.8 A white
t
opaque suspension of KOC6H3 Bu2-2,6 (1.16 g, 4.74 mmol) in THF
(15 mL) was slowly added by pipet into a stirred solution of Ar′BiCl2
(1.00 g, 2.31 mmol) in THF (70 mL). The cloudy white mixture
turned yellow, then orange, and finally a dark red color after mixing.
After 4 h of stirring, the reaction solution was centrifuged and filtered
to remove insoluble material. Addition of hexane (300 mL) to the
stirred filtrate generated an orange insoluble material that was filtered,
washed with additional hexane, and dried under a vacuum. This crude
product was dissolved in THF and allowed to precipitate with the
2
acetonitrile-d3): δ 7.70 [d, JHH = 7.34 Hz, 2H, (Me2NCH2)2C6H3],
7.54 [t, JHH = 14.8 Hz, 1H, (Me2NCH2)2C6H3], 7.48 [s, 2H,
3
t
OSC(C6H2 Bu2O)], 4.29 [s, 4H, (Me2NCH2)2C6H3], 2.67 [br s, 12H,
(Me2NCH2)2C6H3], 1.28 [s, 18H, OSC(C6H2 Bu2O)]. 13C NMR (125
t
MHz, acetonitrile-d3): δ 130.8, 129.6, 127.4, and 126.3 [m- and p-
(Me2NCH2)2C6H3 and OSC(C6H2 Bu2O)], 69.8 [(Me2NCH2)2C6H3],
t
48.0 [br s, (Me2NCH2)2C6H3], 36.5 [q-OSC(C6H2(CMe3)2O)], 30.3
[OSC(C6H2(CMe3)2O)]. IR: 2957s, 2816s, 2780s, 1735s, 1597m,
1448s, 1362m, 1296w, 1227s, 1185s, 1097s, 1019s, 843s, 792m, 758s,
713w, 618w cm−1. Anal. Calcd for C27H39BiN2O2S·CH3CN: C, 49.34;
H, 6.00; N, 5.96. Found: C, 49.30; H, 5.89; N, 5.47. UV−Vis
(MeCN): λmax (nm), ε (M−1 cm−1) 396, 38300; 270, 14400.
t
addition of hexane. This reduced the amount of HOC6H3 Bu2-2,6
byproduct and caused the color to become bright orange. This process
was repeated 3 times to give analytically pure bright orange 1 (850 mg,
61%). 1H NMR (500 MHz, acetonitrile-d32): δ 7.51 [m, 5H,
t
(Me2NCH2)2C6H3 and C6H2 Bu2O], 3.88 [d, JHH = 14.7 Hz, 2H,
t
{[2,6-(Me2NCH2)2C6H3]Bi[O2C(C6H2 Bu2-3-5-OH-4)-κ2O,O′]}-
2
(Me2NCH2)2C6H3], 3.76 [d, JHH = 14.7, 2H, (Me2NCH2)2C6H3],
[BPh4], 5. A colorless solution of [Et3NH][BPh4] (130 mg, 0.31
mmol) in THF (12 mL) was slowly added to a stirred yellow
suspension of 2 (190 mg, 0.29 mmol) in THF (5 mL). The reaction
mixture quickly became a very pale yellow solution. After stirring at
room temperature for 1 h, the solvent was removed under a vacuum
yielding a fluffy off-white powder. The crude product was further
purified by recrystallization in acetonitrile at −30 °C yielding white
2.67 [s, 6H, (Me2NCH2)2C6H3], 2.26 [s, 6H, (Me2NCH2)2C6H3], 1.24
t
[s, 18H, C6H2 Bu2O]. 13C NMR (125 MHz, acetonitrile-d3): δ 182.7
t
[i-(Me2NCH2)2C6H3], 174.5 [i-C6H2 Bu2O], 159.0 and 139.6
t
[C6H2 Bu2O], 149.7 [o-(Me2NCH2)2C6H3], 134.5, 129.0, and 127.7
[m- and p-(Me2 NCH2 )2 C6 H3 and C6 H2 t Bu2 O], 67.2
[(Me2 NCH2 )2 C6 H3 ], 46.5 [(Me2 NCH2 )2 C6 H3 ], 46.4
[(Me2 NCH2 )2 C6 H3 ], 34.9 [q-C6 H2 (CMe3 )2 O], 29.1
[C6H2(CMe3)2O]. IR: 3045w, 2991w, 2943m, 2894m, 2840w,
2797w, 1554s, 1477s, 1432s, 1374m, 1354m, 1333m, 1300w, 1254m,
1202w, 1173w, 1127w, 1091s, 1034w, 1005m, 885w, 840s, 803w,
775w, 709w, 530w, 444m cm−1. Anal. Calcd for C26H39N2OBi: C,
51.64; H, 6.51; N, 4.63. Found: C, 52.07; H, 6.99; N, 4.35.
1
needle-shaped crystals of 5 (254 mg, 88%). H NMR (500 MHz,
acetonitrile-d3): δ 7.88 [d, JHH = 7.50 Hz, 2H, (Me2NCH2)2C6H3],
7.78 [s, 2H, O2C(C6H2 Bu2OH)], 7.65 [t, JHH = 15.0 Hz, 1H,
(Me2NCH2)2C6H3], 7.29 [m, 8H, m-BPh4], 7.01 [m, 8H, o-BPh4],
6.84 [m, 4H, p-BPh4], 6.13 [s, 1H, O2C(C6H2 Bu2OH)], 4.46 [s, 4H,
2
t
3
t
(Me2NCH2)2C6H3], 2.76 [s, 12H, (Me2NCH2)2C6H3], 1.39 [s, 18H,
t
[2,6-(Me2NCH2)2C6H3]Bi[O2C(C6H2 Bu2-3-5-O-4)-κ2O,O′], 2. A
t
O2C(C6H2 Bu2OH)]. 13C NMR (125 MHz, acetonitrile-d3): δ 163.8
t
100 mL sealable side arm Schlenk flask was charged with bright orange
1 (130 mg, 0.22 mmol). Addition of acetonitrile (10 mL) formed a red
solution. The flask was placed on a high vacuum line, degassed, and
charged with 1 atm of carbon dioxide. After stirring at room
temperature for 1 h, a yellow precipitate formed. The flask was
degassed with three freeze−pump−thaw cycles and transferred to an
argon-filled glovebox. The reaction mixture was concentrated under a
vacuum, and the solids were collected via centrifugation, washed with
hexane, and dried under a vacuum giving 2 as a yellow powder (102
mg, 73%). X-ray quality crystals were grown from a saturated
[BPh4] 155.4 [O2C(C6H2 Bu2OH)], 137.7 [BPh4], 131.9, 129.5, 128.4,
and 126.6 [m- and p- (Me2NCH2)2C6H3 and O2C(C6H2 Bu2OH)],
t
122.8 [BPh4], 69.1 [(Me2NCH2)2C6H3], 47.1 [(Me2NCH2)2C6H3],
35.2 [q-O2C(C6H2(CMe3)2OH)], 30.2 [O2C(C6H2(CMe3)2OH)]. IR:
3620s, 3414br, 3057s, 2958s, 2872s, 2798m, 1948w, 1887w, 1817w,
1598s, 1562s, 1476s, 1388s, 1239s, 1117s, 1004s, 889m, 836s, 733s,
707s, 612s cm−1. Anal. Calcd for C50H58BN2O3Bi: C, 62.90; H, 6.12;
N, 2.93. Found: C, 63.19; H, 5.99; N, 2.91.
t
[2,6-(Me2NCH2)2C6H3]Bi(Cl)(C6H2 Bu2-3,5-OSiMe3-4), 6. A scin-
tillation vial was charged with bright orange 1 (100 mg, 0.17 mmol).
Addition of THF (10 mL) formed a dark red solution. When a
colorless solution of Me3SiCl (22 μL, 0.17 mmol) in THF (10 mL)
was added to the reaction vessel, the mixture instantly turned clear and
colorless. After 3 h, the mixture was an off-white suspension and was
stored overnight at −30 °C to precipitate further product. The
supernatant was decanted, and the white solids were washed with cold
THF and collected by centrifugation. The white powder was dried
1
acetonitrile solution at −30 °C. H NMR (500 MHz, acetonitrile-d3):
2
δ 7.70 [d, JHH = 6.99 Hz, 2H, (Me2NCH2)2C6H3], 7.64 [s, 2H,
t
3
O2C(C6H2 Bu2O)], 7.52 [t, 1H, JHH = 14.8 Hz, (Me2NCH2)2C6H3],
4.29 [s, 4H, (Me2NCH2)2C6H3], 2.68 [s, 12H, (Me2NCH2)2C6H3],
t
1.36 [s, 18H, O2C(C6H2 Bu2O)]. 13C NMR (125 MHz, acetonitrile-
d3): δ 130.6, 129.1, 127.8, and, 126.2 [m- and p- (Me2NCH2)2C6H3
t
and O2C(C6H2 Bu2O)], 68.7 [(Me2NCH2)2C6H3], 46.3
1
[(Me2NCH2)2C6H3], 35.6 [q-O2C(C6H2(CMe3)2O)], 30.7 [O2C-
(C6H2(CMe3)2O)]. IR: 3631w, 2951s, 2794w, 1665w, 1591s,
1546m, 1468s, 1424s, 1322s, 1010m, 841s, 694m cm−1. Anal. Calcd
for C27H39N2O3Bi: C, 50.00; H, 6.06; N, 4.32. Found: C, 49.70; H,
5.93; N, 4.23. UV−Vis (MeCN): λmax (nm), ε (M−1 cm−1) 357,
15600; 249, 18600.
under a vacuum to yield analytically pure 6 (101 mg, 86%). H NMR
(500 MHz, acetonitrile-d3): δ 8.02 [s, 2H, C6H2 Bu2OSiMe3], 7.59 [s,
t
2
3H, m- and p- (Me2NCH2)2C6H3], 4.13 [d, JHH = 14.8 Hz, 2H,
(Me2NCH2)2C6H3], 3.72 [d, 2JHH = 14.8 Hz, 2H, (Me2NCH2)2C6H3],
t
2.52 [br s, 12H, (Me2NCH2)2C6H3], 1.28 [s, 18H, C6H2 Bu2OSiMe3],
t
0.32 [s, 9H, C6H2 Bu2OSiMe3]. 13C NMR (125 MHz, acetonitrile-d3):
B
dx.doi.org/10.1021/ja403133f | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

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δ 188.4 [i-(Me2NCH2)2C6H3], 176.5 [i-C6H2 Bu2OSiMe3], 154.0 and
mixture of 1, 9, and [2,6-(Me2NCH2)2C6H3]Bi(CN)2, 10. A small
amount of colorless X-ray quality crystals of 9 grew at −30 °C from a
saturated acetonitrile solution of this crude solid. 1H NMR (500 MHz,
t
143.9 [C6H2 Bu2OSiMe3], 150.6 [o-(Me2NCH2)2C6H3], 136.4
[C6H2 Bu2OSiMe3], 129.3 [p-(Me2NCH2)2C6H3], 127.8 [m-
(Me2 NCH2 )2 C6 H3 ], 67.8 [(Me2 NCH2 )2 C6 H3 ], 47.0
[(Me2NCH2)2C6H3], 35.3 [q-C6H2(CMe3)2OSiMe3], 30.8
[C6H2(CMe3)2OSiMe3], 2.53 [C6H2 Bu2OSiMe3]. IR: 3037w,
2956m, 2903m, 2869m, 2835w, 2793w, 2711w, 1579w, 1551w,
1469m, 1451m, 1417m, 1392m, 1361m, 1256m, 1231m, 1202m,
1176w, 1150w, 1131m, 1070w, 1034w, 1003m, 910m, 843s, 770m,
710w, 676w, 637w, 562w, 528w, 481w, 451w, 412w cm−1. Anal. Calcd
for C29H48BiClN2OSi: C, 48.83; H, 6.80; N, 3.93. Found: C, 48.93; H,
6.77; N, 3.84.
t
t
acetonitrile-d3): δ 8.01 [s, 2H, C6H2 Bu2OSiMe3], 7.38 [s, 3H, m- and
p-(Me2NCH2)2C6H3], 3.85 [br s, 2H, (Me2NCH2)2C6H3], 3.35 [br s,
2H, (Me2NCH2)2C6H3], 2.19 [s, 12H, (Me2NCH2)2C6H3], 1.31 [s,
t
t
t
18H, C6H2 Bu2OSiMe3], 0.36 [s, 9H, C6H2 Bu2OSiMe3]. 13C NMR
t
(125 MHz, acetonitrile-d3): δ 174.1 [i-C6H2 Bu2OSiMe3], 165.9 [CN],
152.6 and 142.7 [C6H2 Bu2OSiMe3], 150.0 [o-(Me2NCH2)2C6H3],
136.4 [C6H2 Bu2OSiMe3], 128.51 [p-(Me2NCH2)2C6H3], 128.19 [m-
t
t
(Me2 NCH2 )2 C6 H3 ], 67.0 [(Me2 NCH2 )2 C6 H3 ], 44.1
[(Me2NCH2)2C6H3], 35.1 [q-C6H2(CMe3)2OSiMe3], 30.8
t
t
[2,6-(Me2NCH2)2C6H3]Bi(Cl)(C6H2 Bu2-3,5-OSiPh3-4), 7. A scin-
[C6H2(CMe3)2OSiMe3], 2.70 [C6H2 Bu2OSiMe3].
tillation vial was charged with bright orange 1 (100 mg, 0.17 mmol).
Addition of THF (10 mL) formed a dark red solution. Addition of
Ph3SiCl (49 mg, 0.17 mmol) in THF (12 mL) caused no immediate
change in appearance. After stirring overnight, the reaction mixture
became a yellow suspension. The solids were collected by
centrifugation and washed three times with THF to afford 7 as a
white solid (99 mg, 67%). 1H NMR (500 MHz, acetonitrile-d3): δ 7.85
Reaction of 1 with Excess Me3SiCl. Me3SiCl (32 μL, 0.25
mmol) was added by microsyringe to a stirred dark red solution of 1
(50 mg, 0.08 mmol) in THF (5 mL). The reaction mixture
immediately became colorless and was stirred for 12 h. After solvent
removal, the resulting white solid (52 mg) was stirred in hexane (5
mL) for 30 min, and the insoluble material was collected by
centrifugation to yield an off white solid (20 mg) that was determined
1
t
to be the known dichloride Ar′BiCl2 by 1H and 13C NMR
[s, 2H, C6H2 Bu2OSiPh3], 7.61 [s, 3H, (Me2NCH2)2C6H3], 7.53 [t,
t
3JHH = 8.03 Hz, 6H, o-C6H2 Bu2OSiPh3], 7.45 [m, 3H, p-
spectroscopy. Solvent was removed from the mother liquor under
t
3
t
reduced pressure affording a white solid determined to be
C6H2 Bu2OSiPh3), 7.33 [t, JHH = 15.3 Hz, 6H, m-C6H2 Bu2OSiPh3],
4.14 [d, 2JHH = 15.0 Hz, 2H, (Me2NCH2)2C6H3], 3.82 [d, 2JHH = 15.0
Hz, 2H, (Me2NCH2)2C6H3], 2.60 [br s, 12H, (Me2NCH2)2C6H3],
10
t
1
Me3SiOC6H3 Bu2-2,6 (7 mg) by H NMR spectroscopy and GC−
MS.
t
t
0.91 [s, 18H, C6H2 Bu2OSiPh3]. 13C NMR (125 MHz, acetonitrile-d3):
δ 187.3 [i-(Me2NCH2)2C6H3], 176.5 [i-C6H2 Bu2OSiPh3], 154.7 and
Reaction of 6 with KOC6H3 Bu2-2,6. A cloudy white mixture of 6
t
(90 mg, 0.13 mmol) in THF (8 mL) immediately turned dark red
t
t
upon the addition of KOC6H2 Bu2-2,6 (32 mg, 0.13 mmol). After
145.8 [C6H2 Bu2OSiPh3], 151.7 [o-(Me2NCH2)2C6H3], 137.9
[C6 H2 t Bu2 OSiPh3 ], 137.4 [o-C6 H2 t Bu2 OSiPh3 ], 135.4
stirring overnight, the solvent was removed under reduced pressure,
and the crude orange solid was stirred in hexane (8 mL) for 2 h. The
mixture was centrifuged to recover orange solids (75 mg) that were
t
t
[C6H2 Bu2OSiPh3], 131.5 [m-C6H2 Bu2OSiPh3], 131.0 [p-
C6H2 Bu2OSiPh3], 129.4 [p-(Me2NCH2)2C6H3], 129.1[m-
t
1
identified as 1 by H NMR spectroscopy. Hexane was removed from
(Me2 NCH2 )2 C6 H3 ] 69. 0 [(Me2 NCH2 )2 C6 H3 ], 48. 4
[(Me2NCH2)2C6H3], 37.2 [q-C6H2(CMe3)2OSiPh3], 32.8
the supernatant under a vacuum to yield an off-white solid that was
identified by 1H NMR spectroscopy and GC−MS as (2,6-di-tert-
butylphenoxy)trimethylsilane10 (35 mg, 97%).
t
[C6H2 (CMe3)2OSiPh3]. IR: 2955m, 2866m, 1589w, 1468m, 1415s,
1223s, 1114s, 1002m, 907m, 842s, 774m, 742m, 701s, 573w, 510s,
453w cm−1. Anal. Calcd for C44H54BiClN2OSi: C, 58.76; H, 6.05; N,
3.11. Found: C, 57.65; H, 6.41; N, 3.11.
t
Reaction of 6 with KOC6H3 Bu2-2,6-Me-4. A cloudy white
mixture of 6 (60 mg, 0.08 mmol) in THF (8 mL) immediately turned
t
t
dark red upon the addition of KOC6H2 Bu2-2,6-Me-4 (22 mg, 0.08
{[2,6-(Me2NCH2)2C6H3]Bi(C6H2 Bu2-3,5-OSiMe3-4)}{CF3SO3}, 8.
mmol) in THF (3 mL). After stirring for 3 h, the solvent was removed
under reduced pressure, and the crude orange solid was stirred in
hexane (10 mL) for 15 min. The mixture was then centrifuged to
A stirred white mixture of 6 (81 mg, 0.11 mmol) in THF (8 mL)
rapidly turned clear and colorless upon the addition of AgOTf (31 mg,
0.12 mmol) in THF (3 mL). Subsequently, slow formation of a white
precipitate occurred. After stirring overnight, the reaction mixture was
centrifuged to remove off-white insoluble material consistent with
silver chloride. The solvent was removed from the colorless
supernatant under a vacuum to give 8 as a white powder (84 mg,
89%). X-ray quality crystals were grown from a saturated acetonitrile
1
recover orange solids (35 mg) that were identified as 1 by H NMR
spectroscopy. The hexane was removed from the supernatant under a
1
vacuum to yield a white solid that was identified by H NMR and
GC−MS as (2,6-di-tert-butyl-4-methylphenoxy)trimethylsilane11 (22
mg, 94%).
1
[2,6-(Me2NCH2)2C6H3]Bi(CN)2, 10. Neat Me3SiCN (24 μL, 0.19
mmol) was added via microsyringe to a stirred yellow solution of
Ar′Bi(OC6H3Me2-2,6)2 (50 mg, 0.08 mmol) in THF (5 mL). The
yellow color faded, and a white precipitate began to form over 5 min.
Stirring was continued for 1 h, and hexane (5 mL) was added. The
mixture was filtered, and the filtrate was washed with a 1:1 THF/
hexane (5 mL) mixture and dried under reduced pressure to afford 10
as a white solid (29 mg, 82%). Single crystals were grown from a
concentrated MeCN solution stored at −30 °C overnight. 1H NMR at
solution at −30 °C. H NMR (500 MHz, acetonitrile-d3): δ 7.91 [s,
t
2H, C6H2 Bu2OSiMe3], 7.64 [s, 3H, (Me2NCH2)2C6H3], 4.06 [d, 2JHH
2
= 15.0 Hz, 2H, (Me2NCH2)2C6H3], 3.77 [d, JHH = 15.0 Hz, 2H,
(Me2NCH2)2C6H3], 2.75 [s, 6H, (Me2NCH2)2C6H3], 2.25 [s, 6H,
t
(Me2NCH2)2C6H3], 1.29 [s, 18H, C6H2 Bu2OSiMe3], 0.33 [s, 9H,
t
C6H2 Bu2OSiMe3]. 13C NMR (125 MHz, acetonitrile-d3): δ 186.5 [i-
(Me2 NCH2 )2 C6 H3 ], 174.2 [i-C6 H2 t Bu2 OSiMe3 ], 155.8
t
[C6H2 Bu2OSiMe3], 151.7 [o-(Me2NCH2)2C6H3], 145.5
[C6 H2 t Bu2 OSiMe3 ], 137.3 [C6 H2 t Bu2 OSiMe3 ], 131.1
[(Me2 NCH2 )2 C6 H3 ], 129.5 [(Me2 NCH2 )2 C6 H3 ], 68.7
[(Me2NCH2)2C6H3], 48.3 [(Me2NCH2)2C6H3], 36.6 [q-
C6H2(CMe3)2OSiMe3], 32.0 [C6H2(CMe3)2OSiMe3], 3.6
2
298 K (500 MHz, acetonitrile-d3): δ 7.60 [d, JHH = 7.5 Hz, 2H, m-
(Me2NCH2)2C6H3], 7.49 [t, 3JHH = 7.5 Hz, 1H, p-(Me2NCH2)2C6H3],
4.41 [br
s 2H, (Me2NCH2)2C6H3], 4.04 [br s, 2H,
t
[C6H2 Bu2OSiMe3]. 19F NMR (375 MHz, acetonitrile-d3): δ −79.36
(Me2NCH2)2C6H3], 2.81 [br s, 6H, (Me2NCH2)2C6H3], 2.00 [br s,
6H, (Me2NCH2)2C6H3]. 13C NMR (125 MHz, acetonitrile-d3): δ
152.1 [o-(Me2NCH2)2C6H3], 129.7 [p-(Me2NCH2)2C6H3], 128.7 [m-
(Me2NCH2)2C6H3], 67.6 [(Me2NCH2)2C6H3], 45.5 [br s,
(Me2NCH2)2C6H3], 41.4 [br s, (Me2NCH2)2C6H3]. IR: 3046w,
2988w, 2967w, 2871m, 2834m, 2802m, 2782w, 2133m, 1579w,
1474m, 1454m, 1401w, 1359w, 1275w, 1253m, 1230w, 1212w, 1174w,
1147w, 1098w, 1036m, 1010s, 970w, 894w, 842s, 794m, 765m, 708w,
526w, 467w, 437w cm−1. Anal. Calcd for C14H19BiN4: C, 37.17; H,
4.24; N, 12.38. Found: C, 37.28; H, 4.08; N, 12.22.
[s, 3F, CF3SO3]. IR: 2959m, 2918m, 2874m, 1470m, 1416m, 1393m,
1266s, 1236s, 1156m, 1031s, 913m, 844s, 780w, 637s cm−1. Anal.
Calcd. for C30H48BiF3N2O4SSi: C, 43.58; H, 5.85; N, 3.39. Found: C,
43.15; H, 5.74; N, 3.85.
t
[2,6-(Me2NCH2)2C6H3]Bi(CN)(C6H2 Bu2-3,5-OSiMe3-4), 9.
Me3SiCN (10 μL, 0.08 mmol) dissolved in THF (2 mL) was added
to a dark red solution of 1 (50 mg, 0.08 mmol) in THF (8 mL). The
reaction mixture turned light yellow within 2 min of addition. After
stirring for 30 min at ambient temperature, the reaction mixture was
filtered, and the solvent was removed under a vacuum leaving orange-
yellow solids (48 mg). 1H NMR spectroscopy showed a complex
The mother liquors isolated from the syntheses of Ar′Bi(CN)2, 10,
and Ar′Bi(N3)2, 11, via this Ar′Bi(OC6H3Me2-2,6)2-based route were
C
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Table 1. X-ray Data Collection Parameters for [2,6-(Me2NCH2)2C6H3]Bi[O2C(C6H2 Bu2-3-5-O-4)-κ2O,O′], 2, [2,6-
t
t
t
(Me2NCH2)2C6H3]Bi[OSC(C6H2 Bu2-3-5-O-4)-κ2O,S], 3, {[2,6-(Me2NCH2)2C6H3]Bi(C6H2 Bu2-3,5-OSiMe3-4)}{CF3SO3}, 8,
t
[2,6-(Me2NCH2)2C6H3]Bi(CN)(C6H2 Bu2-3,5-OSiMe3-4), 9, and [2,6-(Me2NCH2)2C6H3]Bi(N3)2, 11
2
3
8
9
11
empirical formula
formula weight
T (K)
C27H39BiN2O3·CH3CN
689.64
C27H39BiN2O2S
664.64
C30H48BiF3N2O4SSi·CH3CN
C30H48BiN3OSi
703.78
C12H19BiN8·CH3CN
525.39
867.88
143(2) K
orthorhombic
Pbca
88(2)
88(2)
93(2)
88(2)
crystal system
space group
a (Å)
monoclinic
P21/c
monoclinic
P21/n
triclinic
triclinic
P1
P1
̅
̅
12.7738(6)
13.9744(7)
17.9010(8)
90
13.2358(5)
17.3249(7)
13.3003(5)
90
12.0702(7)
16.4669(9)
37.181(2)
90
12.9129(7)
14.9962(8)
17.9034(10)
101.3228(6)
101.2366(6)
98.9213(6)
3266.2(3)
4
8.2299(5)
9.5398(6)
12.9942(9)
108.9940(6)
101.4449(6)
102.6115(6)
900.33(10)
2
b (Å)
c (Å)
α (deg)
β (deg)
106.3798(5)
90
116.1287(4)
90
90
γ (deg)
volume Å3
90
3065.7(3)
4
2738.20(18)
4
7390.0(7)
8
Z
ρcalcd (Mg/m3)
1.494
1.612
1.560
1.431
1.938
μ (mm−1
)
5.782
6.540
4.913
5.459
9.808
a
R1 [I > 2.0σ(I)]
0.0220
0.0163
0.0177
0.0167
0.0123
a
wR2 (all data)
0.0503
0.0380
0.0401
0.0385
0.0296
a
2
2
Definitions: Rl = Σ(||Fo| − |Fc||)/Σ|Fo|, wR2 = [Σ[w(Fo − Fc2)2]/Σ[w(Fo )2]]1/2
.
dried to yield off white solids identified as (2,6-dimethylphenoxy)-
trimethylsilane.12
X-ray Crystallographic Data. Crystallographic information for
complexes 2, 3, 8, 9, and 11 is summarized in Table 1 and in the
Supporting Information.
[2,6-(Me2NCH2)2C6H3]Bi(N3)2, 11, from 1. Neat Me3SiN3 (28 μL,
0.21 mmol) was added via microsyringe to a stirred dark red solution
of 1 (55 mg, 0.09 mmol) in THF (5 mL). The red color faded, and a
white precipitate began to form over 5 min. Stirring was continued for
1 h, and hexane (5 mL) was added. The solids were collected by
filtration, washed with a 1:1 THF/hexane mixture (5 mL), and dried
under reduced pressure to afford 11 as a white solid (40 mg, 96%). 1H
RESULTS
■
CO2 and COS Insertion Reactivity of 1. The red oxyaryl
t
complex, Ar′Bi(C6H2 Bu2-3,5-O-4), 1, reacts within 1 h with
carbon dioxide in acetonitrile to form a yellow product that can
be recrystallized from acetonitrile and identified by X-ray
crystallography as the oxyarylcarboxy complex Ar′Bi[O2C-
2
NMR (500 MHz, acetonitrile-d3): δ 7.79 [d, JHH = 7.5 Hz, 2H, m-
(Me2NCH2)2C6H3], 7.60 [t, 3JHH = 7.5 Hz, 1H, p-(Me2NCH2)2C6H3],
4.31 [s, 4H, (Me2NCH2)2C6H3], 2.82 [s, 12H, (Me2NCH2)2C6H3].
13C NMR (125 MHz, acetonitrile-d3): δ 151.9 [o-(Me2NCH2)2C6H3],
129.5 [p-(Me2NCH2)2C6H3], 128.4 [m-(Me2NCH2)2C6H3], 67.8
[(Me2NCH2)2C6H3], 45.5 [(Me2NCH2)2C6H3]. IR: 3046w, 2998w,
2965w, 2889w, 2864w, 2829w, 2786w, 2033vs, 2012vs, 1578w, 1453m,
1423m, 1401w, 1352w, 1312m, 1263m, 1227w, 1211w, 1172w, 1158w,
1088w, 1029m, 999m, 986m, 955w, 911w, 841s, 782m, 708w, 638w,
613w, 480w, 454m cm−1. Anal. Calcd for C12H19BiN8: C, 29.75; H,
3.96; N, 23.14. Found: C, 30.14; H, 3.97; N, 23.08.
t
(C6H2 Bu2-3-5-O-4)-κ2O,O′], 2, Figure 1, eq 2. Complex 1
[2,6-(Me2NCH2)2C6H3]Bi(N3)2, 11, from Ar′Bi(OC6H3Me2-2,6)2.
Me3SiN3 (28 μL, 0.21 mmol) by microsyringe was added to a stirred
yellow solution of Ar′Bi(OC6H3Me2-2,6)2 (55 mg, 0.09 mmol) in
THF (5 mL). The yellow color faded and a white precipitate formed
over 3 min. Stirring was continued for 1 h and hexane (5 mL) was
added. The solid was collected via centrifugation and dried under a
reacts similarly with carbonyl sulfide (COS) to form the
t
oxyarylthiocarboxy complex Ar′Bi[OSC(C6H2 Bu2-3-5-O-4)-
κ2O,S], 3, Figure 2. Complexes 2 and 3 were also characterized
by NMR and IR spectroscopy and elemental analysis. To the
best of our knowledge, the reactions in eq 2 are the first
examples of insertion of CO2 and COS into Bi−C bonds.
To examine the generality of the insertion reactivity in eq 2,
analogous CO2 reactions were examined with BiPh3 and
1
vacuum to afford 11 as a white solid (40 mg, 96%) identified by H
and 13C NMR spectroscopy. (2,6-Dimethylphenoxy)trimethylsilane12
was isolated and identified as described above in the synthesis of 10.
Reaction of 1 with Iodine. Addition of a THF (2 mL) solution of
iodine (31 mg, 0.12 mmol) to a stirred dark red solution of 1 (74 mg,
0.12 mmol) in THF (8 mL) caused the reaction mixture immediately
to become pale yellow in color. Stirring was continued for 1 h, the
mixture was filtered, and the solvent was removed from the filtrate.
The resulting yellow solid was stirred in hexane (5 mL) for 1 h to
extract the organic byproduct. The yellow insoluble material was
separated by centrifugation (62 mg) and determined by X-ray
crystallography to be Ar′BiI2.1 The hexane solution was evaporated
under reduced pressure to yield a yellow solid (22 mg) identified by
1H and 13C NMR spectroscopy and GC−MS as the coupled product
(3,3′,5,5′-tetra-tert-butyl-4,4′-diphenoquinone).13,14
8
t
[Ar′Bi(C6H2 Bu2-3,5-OH-4)][BPh4], 4, a molecule that is
closely related to 1 in composition and structure, but contains a
conventional aryl monoanionic ligand instead of an oxyaryl
dianionic ligand. Complex 4 has the same atom connectivity as
1 except that the oxo ligand is protonated and the bond
distances are normal for the aryl rings rather than quinoidal
(see Figure 3). Neither BiPh3 nor 4 react with CO2 under the
conditions of eq 2.
Structural Analysis of the Oxyarylcarboxy and Oxy-
arylthiocarboxy Complexes. X-ray crystallography revealed
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Figure 1. ORTEP15 representation of Ar′Bi[O2C(C6H2 Bu2-3-5-O-4)-κ2O,O′], 2, from two perspectives, with thermal ellipsoids drawn at the 50%
t
probability level. Hydrogen atoms are omitted for clarity.
t
Figure 2. ORTEP representation of Ar′Bi[OSC(C6H2 Bu2-3-5-O-4)-κ2O,S], 3, from two perspectives, with thermal ellipsoids drawn at the 50%
probability level. Hydrogen atoms are omitted for clarity.
Figure 3. Bond distances in the oxyaryl, oxyarylcarboxy, and oxyarylthiocarboxy dianionic ligands of compounds 1, 2, and 3 and the normal bond
lengths of the closely related monoanionic hydroxyaryl ligand in 4.
that 2 and 3 have structures similar to that of 1. As seen in
Figures 1 and 2, complexes 2 and 3 each have their two
polydentate ligands oriented at right angles. This provides a
large amount of space around the metal as is typical for
bismuth.1−8,16−19 Complex 1 also has its two ligand planes at
90°, but the orientation differs from that in 2 and 3. If the Ar′
ligand is in the yz plane in all three compounds, the dianionic
ligands of 2 and 3 are in the xy plane, whereas the dianionic
ligand in 1 is in the xz plane. The difference occurs presumably
to minimize steric interactions between the oxyaryl ring and Ar′
since the oxyaryl ring is closer to bismuth in 1. In 2, the
178.5(2)° Bi1−C13−C14 angle leads to a 92.4(1)° angle
between the Ar′ aryl ring and the aryl ring in the dianionic
ligand. The analogous angles in 1 are 176.3(2)° and 96.1(1)°.
These angles differ in 3, which has a 167.9(2)° Bi1−C13−C14
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angle and a 95.71(6)° angle between the C6 rings of the two
ligands.
The Ar′−Bi moieties of 2 and 3 are conventional like those
in 1 and its precursor, Ar′BiCl2,1 Table 2. However, the
Table 2. Comparison of Bi−C and Bi−N Distances
Involving the Ar′ Ancillary Ligand
Bi−C(Ar′) (Å)
Bi−N(Ar′) (Å)
of the crystal did not allow detailed discussion of metrical
parameters.
1
2.208(3)
2.215(3)
2.211(2)
2.202(3)
2.224(4)1
2.268(8)33
2.517(3), 2.568(3)
2.542(3), 2.549(3)
2.544(2), 2.619(2)
2.512(2), 2.547(2)
2.571, 2.5611
2
Density Functional Theory Analysis of the Oxy-
arylcarboxy and Oxyarylthiocarboxy Dianionic Ligands.
Density functional theory calculations on 2, 4, and 5 reveal
structural minima that agree very well with the crystallographic
data. In the case of 3, however, the converged calculated
structure (Figure S1 in Supporting Information) did not show
the upward bend seen in Figure 2. This structural variation may
be due to crystal packing. In both 2 and 3, the new dianionic
ligands were found to have delocalized bonding with quinoidal
character that was not present in the protonated version of 2,
namely, 5. An analogous difference was observed in the
calculations on 1 and 4.8
3
4
Ar′BiCl2
BiPh3
dianionic ligands in 2 and 3 have unusual delocalized bonding
as in 1 and in contrast to 4 as shown in Figure 3. For example,
the 1.278(2) Å C(17)−O(3) and 1.258(2) Å C(17)−O(2) C−
O(oxyaryl) bond distances of 2 and 3, respectively, are
intermediate between single and double bonds (phenol C−O
1.364 Å, quinone CO 1.220(2) Å20) like the 1.265(4) Å
analogue in 1. The 1.435(4) and 1.407(3) Å C(13)−C(14)
distances connecting the aryl ring to the CO2 and COS carbon
atoms in 2 and 3, respectively, are also both intermediate
between single and double bonds. Since the C(15)−C(16) and
C(18)−C(19) distances in 2 and 3 are the shortest in the aryl
ring like the analogues in 1, both 2 and 3 have bond distance
patterns consistent with quinoidal character. Hence, the
structural parameters of the dianionic ligand in 1 are
maintained after insertion of CO2 and COS.
The highest occupied molecular orbitals (HOMOs) of 2 and
3 are compared with that of 1 in Figure 4. All three HOMOs
Complexes 2 and 3 are diamagnetic like 1. However the
1
characteristic splitting of the Ar′ protons in the H NMR
spectrum of 1, caused by the asymmetric geometry of the
twisted pincer arms, was not observed: only a single set of
resonance was observed for the Ar′ protons in each case. A
resonance for the inserted carboxy carbon atom of 2 was
located at 175.8 ppm in the 13C NMR spectrum of a 13C
enriched version of 2. IR spectroscopy of 2 shows absorptions
at 1545 and 1322 cm−1 that fall in the range characteristic of
asymmetric and symmetric stretching vibrations for carboxylate
ligands.21,22 These absorptions shift to 1523 and 1305 cm−1
(Hooke’s law calculation: 1512 and 1293 cm−1) in the 13C
enriched analogue. The IR spectrum of 3 contains absorptions
at 1735 and 1597 cm−1, attributable to C−O stretching
vibrations that are similar to the 1710−1718 and 1559 cm−1
absorptions of free carbonyl sulfide.23 An IR absorption at 1019
cm−1 in 3 is in the 934−1043 cm−1 C−S stretching region
found in other metal-bound thiocarboxylate ligands.24−26
Protonation of 2 to Form a Carboxyphenol Complex.
The structural uniqueness of the dianionic oxyaryl ligand of 1
was originally defined in part by examining its protonated
Figure 4. From left to right, HOMO of compounds 1, 2 and 3. All
orbitals are drawn with a contour value of 0.05.
are similar in the oxy parts of the ligands shown at the top of
the figure. The HOMOs of 2 and 3 differ from 1 in the bottom
part of the figure. In both 2 and 3, the HOMO has considerable
CC character between the ipso carbon and the carboxyl or
thiocarboxyl carbon. This extends the quinoidal character of the
ligands as seen in Scheme 2.
Scheme 2. Quinoidal Resonance Structures of the Dianionic
Ligands of Compounds 2 and 3, Respectively, Showing
Double Bond Character
t
analogue, [Ar′Bi(C6H2 Bu2-3,5-OH-4)][BPh4], 4, which has
normal bond distances in the aryl ring.8 A similar comparison
was sought for 2. Addition of [Et3NH][BPh4] to 2 yielded a
t
white solid in >85% yield identified as {Ar′Bi[O2C(C6H2 Bu2-3-
5-OH-4)-κ2O,O′]}[BPh4], 5, by elemental, spectroscopic, and
This multiple bonding with the ipso carbon is not found in
the HOMO of 1 nor in any other orbitals of 1: there is only a
small interaction between the ipso carbon and bismuth. Hence
there is a higher negative charge on the ipso carbon in 1 that
correlates with its reactivity with CO2 and COS.
Natural population analyses (NPA) on 2 and 3 were
compared with that of 1 and indicate that insertion of CO2 and
1
crystallographic analysis, eq 3. The H NMR spectrum of 5
showed resonances typical for Ar′ and (BPh4)1−, as well as a
resonance at 6.13 ppm that is consistent with an OH proton. A
broad absorption at 3414 cm−1 consistent with an OH group
was observed by IR spectroscopy. X-ray crystallography
confirmed the atomic connectivity in 5, but the low quality
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COS does not significantly affect the electron density on the
formally dianionic ligands. In 1, the oxyaryl ligand has an NPA
value of 0.7 electrons, and the analogous numbers for 2 and 3
are 1.0 and 0.8 electrons, respectively. NPA calculations on the
ipso carbon of the dianionic ligand showed 4.515 electrons on
C13 of 1 compared to 4.224 and 4.183 electrons for C14 of the
oxyarylcarboxy and oxyarylthiocarboxy dianionic ligands of 2
and 3, respectively. The higher electron density on C13 in 1 is
spread out to the carboxyl and thiocarboxyl groups in 2 and 3
so that C14 in those compounds has lower electron density.
The electron density on C13 in 1 is also higher than the 4.435
and 4.347 values on the analogous carbons in the protonated
conventional aryl complex, 4, and BiPh3, respectively. This
difference can be used to rationalize the CO2 and COS
insertion reactivity observed for 1 and not for 4 and BiPh3.
Reactions of 1 with Silyl Halides and Pseudohalides.
Complex 1 reacts with 1 equiv of trimethylsilyl chloride to form
t
Ar′BiCl(C6H2 Bu2-3,5-OSiMe3-4), 6, in over 85% yield as
t
shown in eq 4. Ph3SiCl reacts similarly to form Ar′BiCl-
Figure 5. ORTEP representation of [Ar′Bi(C6H2 Bu2-3,5-OSiMe3-
4)][CF3SO3], 8, with thermal ellipsoids drawn at the 50% probability
level. Hydrogen atoms are omitted for clarity.
t
(C6H2 Bu2-3,5-OSiPh3-4), 7, in over 65% yield. These reactions
constitute formal addition of R3SiCl over five bonds. NMR
spectroscopy and elemental analytical data are consistent with
the compounds as formulated, but crystallographic confirma-
tion of these compounds has been elusive.
In order to further explore the nature of these silylated
products and in an attempt to derivatize 6 to crystallo-
graphically characterize an example of a Ar′Bi(monoanion)-
t
(C6H2 Bu2-3,5-OSiR3-4) complex, 6 was treated with 1 equiv of
−
AgOTf (OTf = CF3SO3 ). A precipitate consistent with AgCl
t
Figure 6. ORTEP representation of Ar′Bi(CN)(C6H2 Bu2-3,5-
formed, and the desired triflate derivative was isolated, eq 5.
OSiMe3-4), 9, with thermal ellipsoids drawn at the 50% probability
level. Hydrogen atoms are omitted for clarity.
provided a desired structural example, it was not the main
product of the Me3SiCN reaction. The predominant and most
commonly obtained product of the reaction was the dicyanide
complex, Ar′Bi(CN)2, 10, eq 6. Single crystals of 10 were
analyzed by X-ray crystallography, but a structure solution was
not obtainable, possibly because of disorder.
Although chloride in 6 was replaced by the triflate, X-ray
crystallography showed that the complex crystallized as an
t
outer sphere triflate complex, i.e. [Ar′Bi(C6H2 Bu2-3,5-OSiMe3-
4)][CF3SO3], 8, Figure 5. The 1H NMR spectrum of
compound 6 shows a single broad peak for the NMe2 protons
of Ar′, while compound 8 has two singlets similar to that seen
for 1. This difference may arise because the triflate ligand in 8 is
outer sphere, while 6 may have the chloride ligand coordinated
to the metal center.
t
Structural evidence for the Ar′Bi(X)(C6H2 Bu2-3,5-OSiR3-4)
products in eq 4 in which X was coordinated to bismuth was
obtainable by examining the reaction of 1 with the trimethylsilyl
pseudohalide, Me3SiCN. The reaction of 1 with Me3SiCN in
one case formed single crystals of the 1,5-addition product,
The formation of Ar′BiX2 products from R3SiX reactions
with 1 as observed for 9 and 10 in eq 6 appears to be general.
With Me3SiN3, NMR evidence for the initial 1,5-addition
t
product, Ar′Bi(N3)(C6H2 Bu2-3,5-OSiMe3-4) is observed, but
t
namely, Ar′Bi(CN)(C6H2 Bu2-3,5-OSiMe3-4), 9, that could be
the main product is Ar′Bi(N3)2, 11. In contrast to 10, this
characterized by X-ray crystallography, Figure 6. Although 9
complex can be crystallographically characterized as shown in
G
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Article
Figure 7. Metrical parameters on 8, 9, and 11 are presented in
the Supporting Information.
Regeneration of the Dianionic Oxyaryl Ligand from
t
Ar′BiCl(C6H2 Bu2-3,5-OSiMe3-4), 6. The reaction of 6 with 1
t
equiv of KOC6H3 Bu2-2,6 does not lead to a simple substitution
of chloride in a reaction analogous to that observed with
AgOTf in eq 5. Instead, the aryloxide reaction regenerates the
t
dianionic oxyaryl ligand, (C6H2 Bu2-3,5-O-4)2−, and compound
t
1 with formation of the silyl ether Me3SiOC6H3 Bu2-2,6 and
KCl, eq 8.
Figure 7. ORTEP representation of Ar′Bi(N3)2, 11, with thermal
ellipsoids drawn at the 50% probability level. Hydrogen atoms are
omitted for clarity.
Ar′BiX2 products are also obtainable from R3SiX reactions
with 1 when X = Cl. When 1 is reacted with an excess of
Me3SiCl, the known dichloride, Ar′BiCl2,1 is formed
The reaction pathway initially considered for eq 8 was a
t
t
radical process involving an Ar′Bi[OC6H3 Bu2-2,6](C6H2 Bu2-
3,5-OSiMe3-4) intermediate that would undergo Bi−O
homolysis as proposed for the synthesis of 1.8 This possibility
was tested with the analogous reaction of 6 with a para-methyl-
t
quantitatively along with the silyl ether Me3SiOC6H3 Bu2-
2,6,10 which was identified by 1H NMR spectroscopy and GC−
MS, Scheme 3. This reaction can also be done stepwise:
addition of Me3SiCl to the initial reaction product, 6, also
t
substituted aryloxide, KOC6H2 Bu2-2,6-Me-4. With the para
t
generates Ar′BiCl2 and Me3SiOC6H3 Bu2-2,6. The isolation of
position substituted, this phenolate cannot form the aryl radical
this silyl ether indicates that the [(C6H2 Bu2-3,5-OSiMe3-4)]1−
necessary in the radical pathway.8 However, the reaction of 6
t
t
unit in 6 has added hydrogen. When the reaction of 1 with
with KOC6H2 Bu2-2,6-Me-4 also immediately gives the
2
excess Me3SiCl was performed in CD3CN, H NMR spectros-
characteristic color change to dark red for the formation of 1.
Complex 1 is indeed formed in this reaction and the byproduct
silyl ether was identified as (2,6-di-tert-butyl-4-methylphenoxy)-
copy and GC−MS indicated that the ether product contained
deuterium on the carbon atom previously attached to bismuth,
i.e., Me3SiOC6H2 Bu2-2,6-D-4. Hence, solvent can be the
trimethylsilane11 by H NMR spectroscopy and GC−MS. It is
t
1
source of hydrogen or deuterium.
therefore more likely that the reaction of 6 with a phenolate
follows a less complex mechanism, Scheme 4, in which the
nucleophilic phenolate abstracts the Me3Si group with
concomitant KCl formation. This mechanism is consistent
with the experimental observations.
To aid in NMR analysis of the complicated mixtures of
t
Ar′Bi(X)(C6H2 Bu2-3,5-OSiMe3-4) and Ar′BiX2 formed from
reactions of Me3SiX with 1, Ar′Bi(N3)2 and Ar′Bi(CN)2 were
independently synthesized by treatment of the previously
8
t
reported bis(aryloxide) Ar′Bi(OC6H3Me2-2,6)2 with excess
Interestingly, the addition of KOC6H3 Bu2-2,6 to the chloride
Me3SiX reagent (X = N3 and CN), eq 7. The byproduct from
these reactions is the expected silyl ether, Me3SiOC6H3Me2-
complex, 6, leads to regeneration of 1 in a cyclic process,
t
Scheme 5, that involves the net conversion of KOC6H3 Bu2-2,6
2,6,12 as confirmed by H NMR spectroscopy and GC−MS.
and Me3SiCl to Me3SiOC6H3 Bu2-2,6 and KCl. Although this
1
t
t
Scheme 3. Direct Synthesis of Ar′BiCl2 and Me3SiOC6H3 Bu2-2,6 by 1 and Excess Me3SiCl and Step-Wise Synthesis through
Compound 6
H
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Journal of the American Chemical Society
Scheme 4. Possible Mechanism for Me3Si Abstraction and the Reformation of 1 from 6 and KOC6H2 Bu2-2,6-Me-4
Article
t
reactions, but the mechanism of the transformation is
unknown.
Scheme 5. Cyclic Synthesis of the Silyl Ether (2,6-Di-tert-
butylphenyl)(trimethylsilyl)ether
DISCUSSION
■
Although CO2 insertion into metal−carbon bonds is a
characteristic organometallic reaction for most metals,21,29,30
it is not as common with main group metals.31 To our
knowledge, the reactions of CO2 and COS with the oxylaryl
t
complex Ar′Bi(C6H2 Bu2-3,5-O-4), 1, are the first examples of
insertion of these substrates into Bi−C bonds. The fact that
CO2 does not react with BiPh3 and the aryl monoanion
8
t
complex [Ar′Bi(C6H2 Bu2-3,5-OH-4)][BPh4], 4, that is closely
related to 1, indicates that this reactivity arises from the special
electronic nature of the dianionic oxyaryl ligand.
The enhanced reactivity of the oxyaryl ligand in 1 can be
rationalized with the resonance structures in Scheme 7.
Scheme 7. Two Resonance Structures for the Oxyaryl
Dianionic Ligand of Compound 1
particular transformation is not difficult to effect by other
means, the reactions in Scheme 5 show that bismuth and the
oxyaryl dianionic ligand can participate in cyclic reaction
chemistry.
Reaction of 1 with Iodine. The reaction of 1 with I2 in
THF affords Ar′BiI2,1 analogous to the Ar′BiX2 species formed
in eq 6 and Scheme 3, but the coproduct is 3,3′,5,5′-tetra-tert-
butyl-4,4′-diphenoquinone,13,14 Scheme 6. The diphenoqui-
Resonance form D matches that expected in conventional
Bi−C(aryl) complexes that do not insert CO2. However,
quinoidal resonance structure E has enhanced negative charge
at the para-carbon position that could lead to the observed
reactivity with CO2 and COS. Since the bond distances in 1 are
in between those expected for D and E, structure E can be a
significant contributor to reactivity. The higher charge at this
para-carbon is not significantly stabilized by bismuth, as shown
by the DFT calculations, Figure 4, and hence this carbon is thus
more reactive than those in typical organobismuth complexes.
Since the oxyaryl dianionic ligand is known only in 1,
comparisons of its reactivity attached to other metals cannot
be made.
Scheme 6. Reaction of 1 with I2 to Form the Coupled
Product 3,3′,5,5′-Tetra-tert-butyl-4,4′-diphenoquinone
Insertion of CO2 and COS into the Bi−C bond of 1
t
generates two new dianionic ligands, [O2C(C6H2 Bu2-3,5-O-4)-
κ2O,O′]2− and [OSC(C6H2 Bu2-3,5-O-4)-κ2O,S]2−, both of
t
t
which also show delocalized bonding as in the [C6H2 Bu2-3,5-
O-4]2− dianion in 1. In the quinoidal resonance forms of these
dianionic ligands, the −2 charge localized on the para-carbon in
1 (Structure E above) can be spread over three additional
atoms as shown in Scheme 8.
1
none, identified by H and 13C NMR spectroscopy and by
The reactivity of 1 with R3SiCl, eq 4, can be rationalized by
resonance structure D in Scheme 7. The anionic phenolate
oxygen in that resonance form could be sufficiently nucleophilic
to react with a trimethylsilyl group to form a strong Si−O
bond. This would create a transient cationic species, [Ar′Bi-
GC−MS, is a common byproduct in bismuth aryloxide
chemistry and has been isolated from reactions of BiCl3 and
t
3 equiv of LiOC6H3 Bu2-2,6 by Hanna and co-workers in a
process thought to involve Bi−O bond homolysis.27,28 The
reaction formally involves the two electron oxidation of the
oxyaryl dianionic ligand by iodine as shown by the half
t
(C6H2 Bu2-3,5-OSiR3-4)]+, with an outer sphere X− counter-
anion that could subsequently coordinate to bismuth to make 6
I
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Journal of the American Chemical Society
Article
t
that converts KOC6 H3 Bu2 -2,6 and Me3 SiCl to
Scheme 8. Possible Resonance Structures of the
Oxyarylcarboxy Dianionic Ligand of Compound 2
t
Me3SiOC6H3 Bu2-2,6 and KCl using the bismuth complex in
a cyclic fashion to facilitate the transformation.
ASSOCIATED CONTENT
* Supporting Information
■
S
Computational details, selected bond distances, converged
calculated structure for 3, and crystallographic data (CIF) for 2,
3, 8, 9, and 11. This material is available free of charge via the
Internet at http://pubs.acs.org. CCDC 931429 (8), 931430
(3), 931431 (9), 931432 (11), and 931433 (2) contains the
supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
or 7. The synthesis of the outer sphere triflate salt,
t
[Ar′Bi(C6H2 Bu2-3,5-OSiMe3-4)][CF3SO3], 8, shows that
such cations can exist with the appropriate counteranion.
These reactions are analogous to the protonation of 2 to make
{Ar′Bi[OC(C6H2 Bu2-3-5-OH-4)O-κ2O,O′]}[BPh4], 5, eq 4.
t
The net result of nucleophilic attack on Me3SiX reagents
followed by capture of X− by bismuth is formal addition of Si−
X over five bonds.
AUTHOR INFORMATION
Corresponding Author
wevans@uci.edu
■
The reaction of excess R3SiX with 1 to produce Ar′BiX2, e.g.,
Notes
t
eq 6, and the stepwise reaction of Ar′BiCl(C6H2 Bu2-3,5-
The authors declare no competing financial interest.
OSiMe3-4), 6, with Me3SiCl to make Ar′BiCl2, Scheme 3, are
consistent with the stability of Ar′BiX2 complexes as end
products. Ar′BiX2 complexes are commonly observed in
reactions involving the [Ar′Bi]2+ moiety.2,17−19 The formation
ACKNOWLEDGMENTS
■
We thank the Chemical Sciences, Geosciences, and Biosciences
Division of the Office of Basic Energy Sciences of the
Department of Energy (DE-FG03-86ER13514 to W.J.E.) and
the U.S. National Science Foundation (CHE-1213382 to F.F.)
for financial support of this work. We also thank Ryan A.
Zarkesh and Jordan F. Corbey for assistance with X-ray
crystallography.
t
of the silyl ether product of this reaction, R3SiOC6H3 Bu2-2,6, is
consistent with the hydrogen abstraction chemistry frequently
found in bismuth reactions.32 In CD3CN, the hydrogen
(deuterium) was found to originate from solvent.
Attempts to obtain structural data on the bismuth complexes
in this study reveal some unexpected irregularities in the ability
to obtain single crystals suitable for crystallography. For
1
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■
[OC6H3Me2-2,6]1−, [OC6H3 Pr2-2,6]1−, [OC6H2 Bu2-2,6-Me-
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CONCLUSION
■
The quinoidal character of the unusual oxyaryl dianionic ligand,
t
t
(C6H2 Bu2-3,5-O-4)2−, in the Bi3+ complex Ar′Bi(C6H2 Bu2-3,5-
O-4), 1, has led to the first insertion reactions of CO2 and COS
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ligands with quinoidal character, [O2C(C6H2 Bu2-3-5-O-4)-
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complexes. These react with additional Me3SiX to generate
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t
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t
(C6H2 Bu2-3,5-OSiMe3-4) regenerates 1 in a cyclic process
J
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