Piano-Stool Iron Complexes as Precatalysts for gem-Specific Dimerization of Terminal Alkynes

Article abstract of DOI:10.1021/acs.organomet.0c00271

A series of piano-stool Fe-NHC complexes have been prepared and characterized. The NHC ligands used herein possess a benzyl and a mesityl wingtip groups and have different electronic structures within the NHC rings. The catalytic activities of these Fe co

Full text of DOI:10.1021/acs.organomet.0c00271

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Article
Piano-Stool Iron Complexes as Precatalysts for gem-Specific
Dimerization of Terminal Alkynes
Qiuming Liang, Kasumi Hayashi, Karolina Rabeda, Jose L. Jimenez-Santiago, and Datong Song*
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ABSTRACT: A series of piano-stool Fe−NHC complexes have
been prepared and characterized. The NHC ligands used herein
possess a benzyl and a mesityl wingtip groups and have different
electronic structures within the NHC rings. The catalytic activities
of these Fe complexes have been examined for the homodimeriza-
tion of terminal alkynes.
complexes toward organic transformations, especially when
ligand-based reactivity is involved.39,40,57−61 We have devel-
oped a piano-stool iron catalyst featuring Cp* and picolyl−
NHC ligands toward the geminal specific dimerization of
terminal alkynes (I in Chart 1).39 Both aryl and aliphatic
alkynes are compatible, and a broad range of functional groups
can be tolerated, including NH and OH groups. Experimental
and computational studies show that the bulky mesityl group
on the NHC ligand is crucial for both the alkyne C−H
activation and geminal specificity and that the pyridine group
of the ligand retards the catalytic activity by coordinating to
the metal center to generate stable off-cycle 18e species. These
results have led to rational catalyst designs, replacing the
picolyl wingtip group of the NHC ligand with noncoordinating
substituents of various sizes. Among the series of complexes
examined, [FeClCp*(IMesBn)] (where IMesBn is the NHC
with mesityl and benzyl wingtip groups) shows the highest
catalytic performance (II in Chart 1).40 With the optimal
wingtip groups determined, we set out to compare the catalytic
activity of piano-stool iron complexes of NHCs bearing the
optimal wingtip groups and various electronic properties.
Herein we report the syntheses, characterizations, and catalytic
activities of a new series of [FeClCp*(NHC)] complexes 1−5,
where the NHC ligands are 4,5-dimethylimidazolylidene (L1),
benzimidazolylidene (L2), 4,5-dihydro-imidazolylidene (L3),
INTRODUCTION
■
The catalytic dimerization of terminal alkynes is an effective
synthetic route for conjugated enynes, owing to its unity atom
economy and the availability of various alkyne precursors.1−5
The main challenge is to control the regio- and stereo-
selectivity. The homodimerization of a terminal alkyne may
yield up to three isomeric enyne products,1−3 whereas the
cross-dimerization of two different terminal alkynes may result
in an even more complicated mixture of products.1−3
Moreover, the formations of cumulenes, higher oligomers,
and polymers may further complicate the reaction outcome.1−3
A large number of catalysts, mostly precious-metal catalysts
and f-block elements, have been extensively investi-
gated.1−3,6−22 Meanwhile, there have been increasing research
endeavors toward the development of sustainable and
environmentally benign alternatives to noble-metal catalysts
for alkyne dimerization.23−40 Such an effort is evidenced by the
rapid development of iron-based catalysts. For example, a few
iron-hydride complexes of P,N,P-pincer ligands have proven
effective toward the Z-selective dimerization of arylacetylenes
at room temperature without any additive.34−36 The iron
complex of a cyclic (alkyl)aminocarbene ligand has been
reported as an E-selective catalyst toward the dimerization of
arylacetylenes in the presence of a large excess of KOtBu at
high temperatures.37 The cation-dependent E/Z selectivity has
been demonstrated in the dimerization of arylacetylenes
catalyzed by the iron(II) complex of an N,N,N-tridentate
ligand.38
Received: April 21, 2020
N-heterocyclic carbenes (NHCs) are widely used ligands in
coordination chemistry and homogeneous catalysis due to
their strong σ-donating and weak π-accepting nature along
with their easily accessible and tunable structures.41−56 Our
group has been interested in the chemistry of iron−NHC
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Chart 1. Piano-Stool Fe-NHC Precatalysts toward the
Dimerization of Terminal Alkynes
Scheme 1. Syntheses of Complexes 1−5
1,2,3-triazolylidene (L4), and 1,2,4-triazolylidene (L5),
respectively (Chart 1).
RESULTS AND DISCUSSION
■
Syntheses and Characterizations of Precatalysts.
Complexes 1−4 were synthesized from the reaction of
[FeClCp*(TMEDA)]62 with the in situ generated carbene
ligands L1−L4, respectively, and isolated in 70−83% yields
(Scheme 1). Complex 5 was prepared from the reaction of
[HL5]Cl with the in situ generated [FeCp*(HMDS)]63
spin ferrous centers.40,65 The quality of the crystallographic
data for 2 (1.954(8) and 1.923(9) Å) makes it difficult to make
a meaningful comparison. The Fe−Cp*cent distance and Fe−Cl
bond length in 4 are also longer than those in 1−3 and 5,
respectively. Consequently, 4 is much more unstable in
comparison to 1−3 and 5. For example, 1−3 and 5 slowly
decompose into [FeCl2(NHC)2] and FeCp*2 in both solution
and the solid state at room temperature but can be stored at
−35 °C for months without significant decomposition, similar
to complex II; in contrast, 4 slowly decomposes even at −35
°C in both solution and the solid state.
Catalytic Dimerization of Phenylacetylene. On the
basis of the established catalytic conditions used for the piano-
stool iron−NHC complex II (Chart 1), the iron complexes 1−
5 were evaluated toward the catalytic dimerization of
phenylacetylene using a 3 mol % loading of the [Fe]
precatalyst and LiHMDS in toluene at room temperature.
Complex 1 featuring the 4,5-dimethylimidazolidene ligand
gives an 81% conversion of phenylacetylene to the geminal
dimer within 3 h (Table 2, entry 1). Complex 2 with the
benzimidazolylidene ligand gives a 97% conversion in 1 h and
full conversion within 3 h (Table 2, entry 2). Complex 3 with
the 4,5-dihydroimidazolidene ligand gives an 89% conversion
in 1 h (i.e., slightly less active than complex 2) and full
1
(HMDS = hexamethyldisilazide). The H NMR spectra of
1−5 in C6D6 at room temperature show broadened and
paramagnetically shifted resonances spanning the range of −95
to +146 ppm. One of the methyl groups in 2, 4, and 5 could
1
not be observed in the H NMR spectra, presumably due to
the close interaction with the iron center (i.e., one of the o-
methyl groups of the mesityl group). The solution magnetic
moments of 1−5 at room temperature (measured by the Evans
method)64 were determined to be 3.4−3.7 μB, consistent with
intermediate-spin Fe(II) centers (S = 1).40,65 The solid-state
structures of 1−5 feature the two-legged piano-stool geometry
(Figure 1). To the best of our knowledge, complex 5
represents the first crystallographically characterized 1,2,4-
triazolylidene complex of iron. The Fe−Ccarbene bond lengths in
1 (1.981(5) and 1.982(5) Å) (Table 1) are comparable to that
found in II (1.980(4) Å).40 The Fe−Ccarbene bond length in 5
(1.962(2) Å) is statistically similar to those in 1 and II. The
Fe−Ccarbene bond length in 3 (1.942(2) Å) is shorter than
those in 1 and II, while the Fe−Ccarbene bond length in 4
(2.033(7) Å) is longer. The Fe−Cp*cent distances in complexes
1−5 are within the range of 1.784(1)−1.896(4) Å, similar to
those of the related piano-stool complexes with intermediate-
B
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Figure 1. X-ray structures of 1 (top left), 2 (top middle), 3 (top right), 4 (bottom left), and 5 (bottom right). The thermal ellipsoids are shown at
30% probability. Hydrogen atoms are omitted, and only one component of the disordered portions is shown for clarity.
Table 1. Bond Lengths (Å) and Angles (deg) for 1−5
a
a
1
2
3
4
5
Fe−Ccarbene
Fe−Cl
1.981(5)
1.982(5)
2.252(2)
2.250(2)
92.1(1)
92.1(2)
1.803(3)
1.832(7), 1.787(7)
1.954(8)
1.923(9)
2.249(3), 2.21(3)
2.256(3), 2.21(2)
90.9(2)
91.2(3)
1.843(4), 1.819(4)
1.785(4)
1.942(2)
2.033(7)
1.962(2)
b
b
2.2518(7)
94.17(5)
1.788(1)
2.290(2)
99.2(2)
2.234(1)
91.19(7)
1.784(1)
Ccarbene−Fe−Cl
Fe−Cp*cent
b
1.896(4)
b
a
b
Two crystallographically independent molecules are found in the asymmetric unit. Disordered component.
conversion within 3 h (Table 2, entry 3). Complex 4
possessing a 1,2,3-triazolylidene ligand displays reactivity
(Table 2, entry 5) similar to that of complex 2. Complex 5,
possessing a 1,2,4-triazolylidene ligand, shows poor reactivity,
giving only 30% conversion in 3 h (Table 2, entry 4); the
NMR yield of the enyne product is even lower, which is not yet
fully understood. We also examined the robustness of catalysts
1−4 by lowering the catalyst loadings. With a 1 mol % loading
of [Fe] precatalyst and LiHMDS, only 2 gives full conversion
in 6 h (Table 2, entries 6−9). No other product was observed
in the 1H NMR spectra in all cases. In comparison, the
previously reported complex II (Chart 1)40 gives full
conversion at a 3 mol % catalyst loading within 0.5 h at
room temperature and poor conversions at a 1 mol % catalyst
loading due to catalyst decomposition.
Catalytic Dimerization of Terminal Alkynes. Having
identified complex 2 as the most active and robust precatalyst
among 1−5, next we explored the substrate scope using 2.
Phenylacetylene and p-Me-, p-F-, p-NMe2-, and m-NH2-
substituted phenylacetylenes can be fully converted into the
corresponding geminal enyne products within 3 h at room
temperature (Table 3, entries 1−5). The dimerization of p-
NH2-substituted phenylacetylene is slightly slower and lower
yielding (Table 3, entry 6). Ferrocenylacetylene can also be
fully converted into the corresponding geminal enyne product
in 3 h with a good yield under the standard conditions (Table
3, entry 7). The dimerization of 1-hexyne retains the high yield
and geminal specificity (Table 3, entry 8), although the
reaction is slightly slower than the dimerization of phenyl-
acetylene. The functionalized aliphatic alkynes N-methyl-N-
propargylbenzylamine and 5-chloro-1-pentyne can also be fully
converted in 3 h under the standard conditions (Table 3,
entries 9 and 10). With N,N-dimethylpropargylamine and 3,3-
diethoxypropyne substrates, the reactions could only give
moderate conversions and low yields (Table 3, entries 11 and
12). The unprotected propargyl alcohol shows no conversion
(Table 3, entry 13).
CONCLUSION
■
A series of piano-stool [FeClCp*(NHC)] complexes 1−5
were prepared and characterized. The NHC ligands L1−L5
have the same wingtip groups (mesityl and benzyl) but differ
from one another electronically within the five-membered
NHC rings. The thermal stabilities of 1−3 and 5 are similar to
that of II, whereas 4 is the least stable: i.e., it decomposes even
at −35 °C in both the solid state and in solution. The catalytic
activities of 1−5 toward the homodimerization of terminal
alkynes have been examined in the presence of an equimolar
amount of LiHMDS. With a 3 mol % catalyst loading at room
temperature, complexes 1−5 can give the corresponding gem-
1,3-enynes exclusively with poor to excellent yields. Among the
five new complexes reported herein, complex 2 with a
benzimidazolylidene ligand shows the highest catalytic activity
and robustness under ambient conditions at low catalyst
C
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a
Table 2. Catalytic Activities of Complexes 1−5 toward the
Table 3. Substrate Scope
a
gem-Specific Dimerization of Phenylacetylene
entry
1
[Fe]
1
x (mol %)
t (h)
conversn (%)
yield (%)
3
1
3
1
3
1
3
1
3
1
3
6
6
6
6
37
81
97
>99
89
>99
>99
>99
20
30
46
>99
67
49
22
64
96
98
86
98
90
98
6
2
3
4
5
2
3
4
5
3
3
3
3
8
6
7
8
9
1
2
3
4
1
1
1
1
36
98
28
30
a
General conditions: phenylacetylene (0.2 mmol), mesitylene (28 μL,
0.2 mmol, internal standard), precatalyst solution in toluene (0.5 mL,
1.2 × 10−2 M, 6 μmol, 3 mol %), LiHMDS solution in toluene (0.5
mL, 1.2 × 10−2 M, 6 μmol, 3 mol %), room temperature. The
conversions (of phenylacetylene) and yields (of the geminal product)
are based on the 1H NMR integrations using mesitylene as the
internal standard.
loadings. In addition, complex 2 is compatible with both
alkylacetylenes and arylacetylenes bearing various functional
groups, maintaining its gem specificity. Such an overall catalytic
performance places complex 2 among the best gem-selective
catalysts to date.3,9,11,13,23,67−70
Among all the NHC ligands in the series of Fe complexes
compared herein, L2 is the least electron donating one. Such
an electronic property of L2 may contribute to the best
thermal stability of the corresponding complex 2 because the
relatively weak trans influence of L2 makes the Cp* in complex
2 less labile in comparison to those in the other complexes.
With such a ligand effect in mind, the use of a weaker donor,
such as simple tertiary phosphines, in lieu of NHCs might
result in more robust catalysts. However, monodentate ligands
with weaker donors (including simple phosphines) are usually
quite labile when they are bound to open-shell iron centers,
which would likely cause more instability in the complexes. To
improve the stability of the two-legged piano-stool iron
(pre)catalysts, tethering the NHC and Cp* ligands together
is likely an effective strategy, taking advantage of the chelate
effect. Such an effort is underway in our laboratory.
a
General conditions: phenylacetylene (0.2 mmol), mesitylene (28 μL,
0.2 mmol, internal standard), toluene solution of 2 (0.5 mL, 1.2 ×
10−2 M, 6 μmol, 3 mol %), LiHMDS solution in toluene (0.5 mL, 1.2
× 10−2 M, 6 μmol, 3 mol %), room temperature. The conversions (of
the alkyne starting materials) and yields (of the geminal products) are
1
based on the H NMR integrations using mesitylene as the internal
standard.
solvent signals. Solution magnetic moments were measured at 25 °C
using the method originally described by Evans with stock and
experimental solutions containing a known amount of a cyclohexane
standard.64 Elemental analyses were carried out at the ANALEST at
the University of Toronto. Due to the poor thermal stability of
complexes 1−5, we were unable to obtain satisfactory elemental
analysis results. The best elemental analysis results obtained so far are
provided below. Unless otherwise noted, all chemicals were purchased
from commercial sources and used as received.
Syntheses of 1−3. To a solid mixture of the ligand precursor (0.5
mmol) and KHMDS (99.7 mg, 0.5 mmol) was added 5 mL of diethyl
ether. The reaction mixture was stirred for 1 h and then filtered
through Celite. The filtrate was cooled to −80 °C and then slowly
added into a cold (−80 °C) stirred suspension of FeClCp*-
EXPERIMENTAL SECTION
■
All reactions were carried out in a dinitrogen-filled glovebox or using
the standard Schlenk techniques under dinitrogen. Glassware was
dried in a 180 °C oven overnight. Diethyl ether, hexanes, pentane, and
toluene solvents were dried by refluxing and distilling over sodium
under dinitrogen. THF solvent was dried by refluxing and distilling
over sodium benzophenone ketyl under dinitrogen. C6D6, and CDCl3
were degassed through three consecutive freeze−pump−thaw cycles.
All solvents were stored over 3 Å molecular sieves prior to use. Unless
otherwise noted, all NMR spectra were recorded on an Agilent DD2
600 MHz spectrometer at 25 °C. Chemical shifts are referenced to the
D
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(TMEDA)62 (171.4 mg, 0.5 mmol) in 2 mL of THF. The resulting
mixture was warmed to room temperature slowly with stirring over 1
h. All volatiles were removed under vacuum. The residue was
dissolved in diethyl ether (5 mL) and filtered through Celite. The
filtrate was concentrated under reduced pressure to ∼2 mL and
cooled to −35 °C to yield a crystalline solid of product. The
supernatant was decanted off, and the crystals were washed with cold
diethyl ether (1 mL) and pentane (3 × 1 mL) and dried under
vacuum. X-ray-quality crystals were obtained by cooling a
concentrated diethyl ether solution at −35 °C. The preparation
protocols of precursors of L1, L2, L4, and L5 are detailed in the
Supporting Information, while the precursor of L3 was prepared using
a literature procedure.66
(3H), −8.68 (2H), −19.89 (3H). One of the methyl groups (3H) was
not observed in the range of +200 to −200 ppm. μeff (Evans): 3.7 μB.
Anal. Calcd for C28H34N3FeCl: C, 66.74; H, 6.80; N, 8.34. Found: C,
65.16; H, 6.26; N, 8.49.
General Procedure for the Catalytic Dimerization of
Alkynes. A 2-dram vial was charged with LiHMDS solution in
toluene (0.5 mL, 1.2 × 10−2 M, 6 μmol, 3 mol %), mesitylene (28 μL,
0.2 mmol, internal standard), alkyne substrate (0.2 mmol), and the
Fe-catalyst solution in toluene (0.5 mL, 1.2 × 10−2 M, 6 μmol, 3 mol
%) in that sequence. The reaction mixture was stirred for the
indicated time. An NMR sample was prepared using 0.1 mL of the
reaction mixture in 0.4 mL of CDCl3 and filtered. The conversion and
yield of the reaction were calculated on the basis of the integrations of
the 1H NMR signals of the starting material and product, respectively,
relative to that of the internal standard (600 MHz, 16 scans, 25 s
relaxation delay, 90° pulse).
Complex 1. By the general procedure using [HL1]Cl (170.5 mg,
0.5 mmol), 1 was obtained as a yellow crystalline solid (202.3 mg,
1
76%). H NMR (600 MHz, C6D6): δ 114.90 (15H), 46.01 (3H),
27.94 (3H), 22.71 (3H), −1.81 (1H), −2.74 (2H), −8.28 (3H),
−12.56 (2H), −17.58 (2H), −26.67 (2H). One of the methyl groups
(3H) was not observed in the range of +200 to −200 ppm. μeff
(Evans): 3.5 μB. Anal. Calcd for C31H39N2FeCl: C, 70.13; H, 7.40; N,
5.28. Found: C, 69.49; H, 6.90; N, 5.31.
Complex 2. By the general procedure using [HL2]Br (203.7 mg,
0.5 mmol), 2 was obtained as red-orange crystals (229.6 mg, 83%).
1H NMR (600 MHz, C6D6): δ 34.06 (3H), 33.17 (15H), 23.18 (1H),
15.50 (d, J = 6.8 Hz, 1H), 14.52 (1H), 14.19 (d, J = 6.8 Hz, 1H), 3.91
(1H), 1.21 (d, J = 6.9 Hz, 2H), 0.38 (t, J = 6.8 Hz, 1H), −4.76 (s, 1H,
3H), −7.30 (1H), −8.64 (2H), −10.46 (1H), −21.00 (3H), −88.35
(1H). μeff (Evans): 3.7 μB. Anal. Calcd for C33H37N2FeCl: C, 71.68;
H, 6.74; N, 5.07. Found: C, 71.16; H, 6.98; N, 4.95.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00271.
■
sı
Experimental procedures, selected crystallographic data
tables, and NMR spectra (PDF)
Accession Codes
CCDC 1998142−1998147 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Complex 3. By the general procedure using [HL3]Cl (157.5 mg,
1
0.5 mmol), 3 was obtained as yellow crystals (182.0 mg, 72%). H
NMR (600 MHz, C6D6): δ 41.30 (3H), 34.90 (15H), 24.72 (1H),
18.03 (1H), 9.03 (1H), 7.02 (2H), 5.29 (2H), 4.07 (1H), −4.88
(3H), −6.30 (1H), −7.84 (1H), −10.10 (1H), −21.02 (3H), −44.89
(1H), −95.15 (1H). μeff (Evans): 3.4 μB. Anal. Calcd for
C29H37N2FeCl: C, 68.98; H, 7.39; N, 5.55. Found: C, 68.91; H,
7.23; N, 5.10.
AUTHOR INFORMATION
Corresponding Author
■
Datong Song − Davenport Chemical Research Laboratories,
Department of Chemistry, University of Toronto, Toronto,
Ontario M5S 3H6, Canada; orcid.org/0000-0001-6622-
5980; Email: d.song@utoronto.ca
Synthesis of 4. To a solid mixture of [HL4][BF4] (189.6 mg, 0.5
mmol) and KHMDS (99.7 mg, 0.5 mmol) was added 5 mL of diethyl
ether. The reaction mixture was stirred for 1 h and then filtered
through Celite. The filtrate was added to a suspension of
FeClCp*(TMEDA) (171.4 mg, 0.50 mmol) in 2 mL of THF. The
resulting mixture was stirred for 3 h at room temperature. All volatiles
were removed under vacuum. The residue was dissolved in diethyl
ether (5 mL) and filtered through Celite. The filtrate was
concentrated under reduced pressure to ∼2 mL and cooled to −35
°C to yield an orange crystalline solid of 4. The supernatant was
decanted off, and the crystals were washed with cold diethyl ether (1
mL) and pentane (3 × 1 mL) and dried under vacuum (180.3 mg,
70%). X-ray-quality crystals were obtained by cooling a concentrated
Authors
Qiuming Liang − Davenport Chemical Research Laboratories,
Department of Chemistry, University of Toronto, Toronto,
Ontario M5S 3H6, Canada
Kasumi Hayashi − Davenport Chemical Research Laboratories,
Department of Chemistry, University of Toronto, Toronto,
Ontario M5S 3H6, Canada
Karolina Rabeda − Davenport Chemical Research Laboratories,
Department of Chemistry, University of Toronto, Toronto,
Ontario M5S 3H6, Canada
Jose L. Jimenez-Santiago − Davenport Chemical Research
Laboratories, Department of Chemistry, University of Toronto,
Toronto, Ontario M5S 3H6, Canada
1
diethyl ether solution at −35 °C. H NMR (600 MHz, C6D6): δ
146.36 (15H), 10.18 (3H), 2.08 (1H), 1.97 (2H), −4.27 (2H), −5.47
(2H), −8.33 (3H), −12.67 (2H). One of the methyl groups (3H) was
not observed in the range of +200 to −200 ppm. μeff (Evans): 3.4 μB.
Anal. Calcd for C29H36N3FeCl: C, 67.25; H, 7.01; N, 8.11. Found: C,
66.23; H, 7.08; N, 7.98.
Synthesis of 5. To a stirred suspension of FeClCp*(TMEDA)
(171.4 mg, 0.50 mmol) in 2 mL of THF was added KHMDS (99.7
mg, 0.5 mmol) in 2 mL of THF. The mixture was stirred for 1 h and
slowly added to a suspension of [HL5]Cl in 2 mL of THF. The
mixture was stirred for 1 h at room temperature. All volatiles were
removed under vacuum. The residue was dissolved in diethyl ether (5
mL) and filtered through Celite. The filtrate was concentrated under
reduced pressure to ∼2 mL and cooled to −35 °C to yield a yellow
solid of 5. The supernatant was decanted off, and the crystals were
washed with cold diethyl ether (1 mL) and pentane (3 × 1 mL) and
dried under vacuum (164.7 mg, 65%). X-ray-quality crystals were
obtained by cooling a concentrated diethyl ether solution at −35 °C.
1H NMR (600 MHz, C6D6): δ 41.42 (15H), 37.86 (1H), 33.89 (2H),
3.83 (d, J = 7.6 Hz, 2H), 3.46 (t, J = 7.1 Hz, 1H), −0.92 (2H), −5.12
Complete contact information is available at:
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the Natural Sciences and Engineering Research
Council (NSERC) of Canada for funding. Q.L. thanks the
Ontario government for an Ontario Graduate Scholarship. K.R.
thanks the NSERC of Canada for an Undergraduate Summer
Research Award. JLJS thanks the Mexican National Council for
E
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Science and Technology (CONACyt) for a graduate fellow-
ship. We also acknowledge the Canadian Foundation for
Innovation Project #19119 and the Ontario Research Fund for
funding the CSICOMP NMR laboratory at the University of
Toronto, enabling the purchase of several new spectrometers.
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