An experimental and computational comparison of phosphorus-and selenium-based ligands for catalysis

Article abstract of DOI:10.1139/cjc-2015-0417

To compare and contrast the bonding and reactivity of organoselenium ligands with organophosphines in coordination complexes, a new palladium(II) complex of the Se,N-chelating ligand o-(NH₂)(X)C₆H₄ (X = SePh, 2) was prepared. Its characterization by NMR spectroscopy, single-crystal X-ray diffraction, and density functional theory calculations is contrasted with the Pd^II complex of the related P,N-chelating ligand (X = PPh₂, 1). These techniques indicate that the phenylseleno moiety is a weaker σ donor to the PdCl₂ fragment than the diphenylphosphino group. Both complexes were suitable to catalyze the Suzuki-Miyaura coupling of p-tolylboronic acid and 4-bromobenzaldehyde.

Full text of DOI:10.1139/cjc-2015-0417

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1
ARTICLE
An experimental and computational comparison of
phosphorus- and selenium-based ligands for catalysis
Jamie S. Ritch and Bronte J. Charette
Abstract: To compare and contrast the bonding and reactivity of organoselenium ligands with organophosphines in coordina-
tion complexes, a new palladium(II) complex of the Se,N-chelating ligand o-(NH2)(X)C6H4 (X = SePh, 2) was prepared. Its charac-
terization by NMR spectroscopy, single-crystal X-ray diffraction, and density functional theory calculations is contrasted with the
PdII complex of the related P,N- chelating ligand (X = PPh2, 1). These techniques indicate that the phenylseleno moiety is a weaker
␴ donor to the PdCl2 fragment than the diphenylphosphino group. Both complexes were suitable to catalyze the Suzuki–Miyaura
coupling of p-tolylboronic acid and 4-bromobenzaldehyde.
Key words: organoselenium compounds, coordination chemistry, X-ray crystallography, density functional theory, Suzuki–
Miyaura coupling.
Résumé : En vue d’effectuer une comparaison différentielle de ligands organoséléniés et d’organophosphines sur le plan de
leurs propriétés de liaison et de leur réactivité dans des complexes de coordination, nous avons synthétisé un nouveau complexe
de palladium(II) et du ligand chélateur a` base de sélénium et d’azote o-(NH2)(X)C6H4 (X = SePh, 2). Nous avons caractérisé ce
complexe par spectroscopie RMN, diffraction des rayons X sur cristal unique et calculs de la théorie de la fonctionnelle de la
densité pour le comparer au complexe de PdII et du ligand chélateur analogue a` base de phosphore et d’azote (X = PPh2, 1). Ces
techniques indiquent que le groupement phénylseleno est un donneur ␴ plus faible envers le fragment PdCl2 que le groupement
diphénylphosphino. Par ailleurs, les deux complexes se sont révélés capables de catalyser le couplage de Suzuki–Miyaura entre
l’acide p-tolylboronique et le 4-bromobenzaldéhyde. [Traduit par la Rédaction]
Mots-clés : composés organoséléniés, chimie de coordination, radiocristallographie, théorie de la fonctionnelle de la densité,
couplage de Suzuki–Miyaura.
with activities surpassing even state-of-the-art phosphine-based
systems have emerged.5
Introduction
Rational ligand design is an essential tool for homogeneous
catalysis research. Amongst the many reported ligand scaffolds, a
common element for palladium-based catalysts is the incorpora-
tion of organophosphorus donors. Phosphines are valued for their
strong ␴ donor ability in conjunction with the ability to act as a
␲-acid. Over the last several decades, there has been a growing
interest in the use of selenoether-type ligands as alternatives to
phosphines. Organoselenium ligands and their complexes to met-
als such as nickel, palladium, and rhodium are often air- and
moisture-stable and have shown catalytic activity in a number of
transformations including carbon–carbon coupling reactions.1 Li-
gand synthesis often involves the use of an organic diselenide
such as Ph2Se2 with NaBH4 to effect convenient selenylation of
organic halides via a PhSe− equivalent.
However, the reasons for such differences in activity are not
well understood. The strong electron donor ability of selenium
has been cited as an advantage of selenium-containing ligands;
however, detailed electronic structure studies or direct compari-
sons between phosphine and selenoether ligands to this end re-
main rare. Additionally, the identity of the active catalyst is at
times uncertain. In some systems, the PdII coordination complex
serves as a precatalyst that forms palladium selenide nanopar-
ticles under thermal conditions, and these have been implicated
as the source of Pd(0) particles (the “true catalyst”) for Heck trans-
formations.9 This does not, however, preclude single-site catalysis
in other processes and mechanistic details are scant for many
reported selenium-containing catalyst systems.
A variety of scaffolds have been explored; some examples of
multidentate hard–soft selenoether-containing ligands are illus-
trated in Chart 1. Palladium(II) complexes of the ligands A2 and B3
are effective Suzuki–Miyaura catalysts, while ligands C,4 D,5 and
E6 have been used to catalyze the Heck reaction. Ligand D is commer-
cially available from Sigma-Aldrich and [{(2,6-PhSeCH2)2C6H3}PdX] can
also catalyze, for example, the boronation of allylic alcohols (X =
Cl),7 and the allylation of aldehydes with organotin reagents (X =
OAc).8 As further examples are reported, selenium-based catalysts
This contribution examines two [Pd(L)Cl2] complexes where L is
either a chelating phosphine or selenoether ligand, both of which
contain the same ortho-subtituted aniline framework and differ
only by the second heteroatom donor (–SePh or –PPh2). It is there-
fore possible to make a direct comparison of their structures,
NMR properties, and ␴ donor ability. Additionally, their effective-
ness as catalysts in a Suzuki–Miyaura coupling reaction is evalu-
ated.
Received 25 August 2015. Accepted 3 November 2015.
J.S. Ritch and B.J. Charette. Department of Chemistry, The University of Winnipeg, 515 Portage Avenue, Winnipeg, MB R3B 2E9, Canada; Department
of Chemistry, 360 Parker Building, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.
Corresponding author: Jamie S. Ritch (email: j.ritch@uwinnipeg.ca).
This article is part of a Special Issue dedicated to celebrating the 50th Anniversary of the Department of Chemistry at the University of Calgary and to highlighting the chemical
research being performed by faculty and alumni.
Can. J. Chem. 94: 1–6 (2016) dx.doi.org/10.1139/cjc-2015-0417
Published at www.nrcresearchpress.com/cjc on 10 November 2015.

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Can. J. Chem. Vol. 94, 2016
Chart 1.
petes with 2 for coordination to palladium rather than contami-
nation by unreacted 2. All resonances of the product spectrum
become broadened at higher temperature, which seems to sup-
port this hypothesis. Additionally, in CD3CN, no signals for the
free ligand are visible.
X-ray crystallography
As the solid-state structure of 3 has not been previously re-
ported and 4 is a new compound, we pursued X-ray quality single
crystals of these complexes for diffraction studies. Suitable crys-
tals of 3·2DMSO and 4·MeCN were grown in their respective sol-
vents. Thermal ellipsoid plots are shown in Figs. 1 and 2; selected
metrical parameters are presented in Table 1. The two structures
are overall consistent with the solution-state NMR data, indicating
square-planar palladium(II) chloride complexes of the cis-chelating
ligands 1 and 2 (sum of angles around palladium: 360.1° and
360.2°, respectively). With the exception of the phenyl groups
and amino protons, all atoms in complexes 3 and 4 are nearly
coplanar — the largest deviations from planarity involve chlorine
atoms. The PdCl2 moiety is slightly twisted out of the mean plane
in 3 (displacements of chlorine atoms +0.099 and −0.078 Å) and
one chlorine atom in 4 is 0.095 Å from the mean plane. The
selenium atom in complex 4 is chiral — the centrosymmetric
structure contains a 1:1 mixture of enantiomers.
The Pd–Se distance in 4 is approximately 7% elongated com-
pared to the Pd–P distance in 3, consistent with the larger covalent
radius of selenium. The lower s-character of the selenium-centred
bonding orbitals is also borne out in the metrical data: the bond
angles around selenium are noticeably smaller than those for
phosphorus, e.g., the Pd–X–Cphenyl angles for 3 and 4 are 101.31(6)°
and 115.56(3)–118.94(10)°, respectively. Another notable feature of
the X-ray data are the Pd–Cl distances: those distances trans to the
NH2 group in each complex are not significantly different (3:
2.3001(9) Å; 4: 2.3017(5) Å), while those trans to phosphorus and
selenium differ by approximately 0.03 Å (3: 2.3607(8) Å; 4:
2.3352(5) Å). In the context of the thermodynamic trans-effect,13
the Ph2P group is therefore observed to be a stronger ␴ donor than
the PhSe group in the presently studied system. This is consistent
with other findings that heavy chalcogenoethers are modest ␴
donors compared to organophosphines.14,15
Results and discussion
Synthesis and NMR characterization of metal complexes
The ligands o-(NH2)(X)C6H4 (1) (X = PPh2)10 and 2 (X = SePh)11 were
prepared according to the reported procedures, from 2-fluoroaniline
and 2-chloronitrobenzene, respectively. Palladium(II) complexes
of the ligands were targeted to furnish diamagnetic complexes
amenable to NMR studies and with a square-planar geometry for
evaluation of the relative thermodynamic trans-effect of phos-
phorus and selenium donor sites. The chelating ligands were sep-
arately reacted with [PdCl2(COD)] (COD = 1,5-cyclooctadiene) in
CH2Cl2 at room temperature (eq. 1). The resultant complexes
[PdCl2(o-(NH2)(X)C6H4)] (3) (X = PPh2) and 4 (X = SePh) precipitated
from the reaction mixtures in high yields (83%–100%). The phos-
phine complex 3 has been previously prepared using another
method and investigated as an anti-cancer agent,12 while the se-
lenoether complex 4 has not been reported. Complex 3 is a yellow
solid, with no appreciable solubility in hydrocarbons, THF, Et2O,
or CH2Cl2; it is sparingly soluble in hot MeCN and soluble in
DMSO. Complex 4 is an orange solid that is similarly insoluble in
common organic solvents, slightly more soluble than 3 in MeCN,
and very soluble in DMSO.
Both crystal structures feature well-ordered lattice solvent mol-
ecules. In the (P,N) complex 3, the NH2 protons are each hydrogen
bonded to one crystallographically unique DMSO molecule with
N–H···O distances of 2.823(4) and 2.821(4) Å. This secondary bonding
motif has been observed for related metal complexes, including
the octahedral ruthenium(II) complex [RuCl2(1)(CO)2]·4DMSO16
and the square-planar palladium(II) complex [PdCl2(4,5-dax)]·2DMSO
(4,5-dax = 4,5-diaminoxylene).17 The crystal structure of (Se,N) com-
plex 4 features a lattice acetonitrile molecule, but it does not
engage in any significant secondary bonding interactions. The
closest intermolecular contacts to the NH2 protons in 4 are two
N–H···Cl interactions (3.295(2) and 3.331(2) Å) generating a
staircase-type packing arrangement (Fig. 3). With H···Cl distances
of 2.53(3) and 2.54(3) Å, these contacts are in the range of
“medium”-length hydrogen bonds involving metal-bound chlo-
rine atoms.18 No intermolecular Pd···Se interactions are detected.
(1)
Evidence of X,N-coordination in both cases was clearly observed
by NMR spectroscopy. The 31P NMR spectrum of 3 (d6-DMSO) indi-
cates a singlet resonance shifted by +66.6 ppm compared to the
free ligand 1, and the NH2 singlet resonance in the 1H NMR spec-
trum is similarly shifted by +2.75 ppm. For the Se,N-complex 4, the
77Se NMR signal appears 178 ppm downfield of the signal for 2. The
NH2 group, in addition to being significantly shifted by +2.40 ppm
in the 1H NMR spectrum compared to free ligand, also manifests
as two closely spaced broad singlets with a separation of 13 Hz.
This is consistent with two diastereotopic protons that are not
rapidly exchanged on the NMR timescale, as would be expected
for a square-planar complex featuring two stereochemically dis-
tinct faces. Here, the steric differentiation is provided by the SePh
donor group, with a phenyl substituent projecting out of one side
of the molecular plane and a lone pair out of the other. An inter-
Computational studies
To probe the electronic structure of the related complexes 3 and
4, DFT calculations were conducted on these structures using the
M06 functional, which is corrected for dispersion and has been
found to give more accurate bond lengths for transition metal
complexes compared to nondispersion corrected functionals, e.g.,
B3LYP.19 First to third row atoms were modeled using the
6-31G(d,p) basis set, whereas the cc-pVTZ basis set with SDB rela-
tivistic effective core potentials was used for palladium and sele-
nium.
1
esting feature of the H NMR spectrum of 4 is the visibility of
low-intensity signals corresponding to the free ligand (those not
overlapping with product signals). These resonances are observed
even in recrystallized samples, suggesting a solution equilibrium
in d6-DMSO (in the slow-exchange regime) where the solvent com-
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Ritch and Charette
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Fig. 1. Thermal ellipsoid plot (50% probability) of 3·2DMSO; carbon-
Fig. 3. Packing diagram for complex 4 showing N–H···Cl hydrogen bonds.
bound hydrogen atoms are omitted for clarity.
Fig. 2. Thermal ellipsoid plot (50% probability) of one enantiomer of
complex 4·MeCN; carbon-bound hydrogen atoms and the lattice
solvent molecule are omitted for clarity.
The optimized structures featured metrical parameters very
similar to the crystal data, mainly differing by rotation of phenyl
rings in the absence of crystal packing forces. Notably, the larger
elongation of the Pd–Cl bond trans to phosphorus versus that trans
to selenium is preserved in these gas-phase calculations (2.3450
versus 2.3177 Å), suggesting that the difference is unlikely due to a
packing or hydrogen bonding effect. Analysis of the frontier or-
bitals (Fig. 4) indicated the HOMO compositions as mostly Cl(p),
P(p), or Se(p) and Pd(d) orbital combinations, while the LUMOs also
have larger contributions from N(p) and are ␴-antibonding with
respect to the PdL4 square planes. HOMO–LUMO gaps of 4.28 eV
for 3 and 4.07 eV for 4 are observed. The first ionization energies,
estimated using Koopman’s theorem, of 6.31 eV (3) and 6.43 eV (4)
indicate that the phosphine complex is more susceptible to oxi-
dation, as would be expected.20
Qualitative values of ⌬Gor×n for eq. 1 were estimated computa-
tionally in the gas phase (−62.5 kJ mol−1 for 3 and +0.5 kJ mol−1 for
4). The formation of the phosphine complex 3 is predicted to be
more favourable than that of the selenoether complex 4 and
hence ligand 1 is a stronger chelate ligand towards PdCl2 relative
to COD than 2. This is consistent with the higher trans influence of
1 versus 2 observed in the X-ray data as well as the experimental
NMR spectral data for 4, which suggested dynamic behaviour in-
volving some degree of dissociation of 2 in d6-DMSO solution.
Table 1. Selected bond lengths (Å) and angles (°)
for complexes [(o-(NH2)(X)C6H4)PdCl2].
X = PPh2 (3)
X = SePh (4)
Pd1−N1
Pd1−X1
Pd1−Cl1
Pd1−Cl2
X1−C1
N1−C2
Cl1−Pd1−Cl2
Pd1−X1−C7
Pd1−X1−C13
X1−Pd1−N1
X1−C1−C2−N1
2.048(3)
2.2050(8)
2.3001(9)
2.3607(8)
1.806(3)
1.458(4)
94.51(3)
118.94(10)
115.56(10)
85.61(8)
3.3(4)
2.0456(18)
2.3575(3)
2.3017(5)
2.3352(5)
1.933(2)
1.459(3)
94.18(2)
101.31(6)
Catalysis experiments
To test the relative catalytic competencies of complexes 3 and 4,
they were employed in the Suzuki–Miyaura coupling reaction of
p-tolylboronic acid with 4-bromobenzaldehyde, utilizing condi-
tions similar to those reported for the CuI-catalyzed coupling of
arylboronate esters with aryl iodides using the P,N-chelating li-
gand 1-tBu2P-2-NMe2C6H4.21 Conversion as measured by GC–MS
was investigated for the two complexes, in addition to [PdCl2(COD)],
under several reaction conditions (Table 2). DMF was used as the
reaction solvent to ensure solubility of the catalyst.
88.07(5)
2.6(3)
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Can. J. Chem. Vol. 94, 2016
Fig. 4. Frontier orbitals of complexes 3 and 4.
Table 2. Comparative use of 3, 4, and [PdCl2(COD)] for a Suzuki−Miyaura
coupling reaction.
Experimental section
General considerations
All manipulations were conducted under an inert atmosphere
of argon using standard glovebox or Schlenk/vacuum line tech-
niques, except where noted. The solvents dichloromethane, diethyl
ether, and toluene (ACS grade) were sparged with argon and dried
by passage through two columns of activated alumina before stor-
age in PTFE-sealed glass vessels; diethyl ether was stored over
sodium/benzophenone. Solvents were transferred by vacuum dis-
tillation into PTFE-sealed storage flasks over activated 4 Å molec-
ular sieves for Schlenk manipulations. Acetonitrile was dried by
stirring over CaH2 overnight and then distilled onto activated 3 Å
molecular sieves. d6-DMSO was dried over activated 4 Å molecular
sieves and degassed using at least three freeze–pump–thaw cycles.
The reagents [PdCl2(COD)]22 and o-(NH2)(X)C6H4 (X = PPh2,10
SePh11) were prepared according to the literature procedures.
DMSO (anhydrous), p-tolylboronic acid, 4-bromobenzaldehyde, ce-
sium fluoride, and 4-nitrobenzaldehyde were purchased from
commercial sources and used as received. Melting points were
recorded from samples sealed under argon in capillary tubes.
Entry
Catalyst
Temperature (°C)
Time (h)
Yield (%)
1
None
[PdCl2(COD)]
3
4
[PdCl2(COD)]
3
4
[PdCl2(COD)]
3
4
120
120
120
120
50
50
50
23
23
14
14
14
14
14
14
14
14
14
14
9a
2
3
4
5
6
7
8
9
10
>95%
>95%
>95%
35a
20a
36a
24a
13a
23
13a
Note: Conditions: boronic acid (0.1 mmol), aryl bromide (0.1 mmol), DMF (0.5 mL),
catalyst (5 mol%), CsF (0.15 mmol).
aYields measured by GC−MS versus the internal standard 4-nitrobenzaldehyde.
Instrumentation
NMR spectra were collected on a Bruker 400 MHz Avance III
spectrometer. Chemical shifts are reported in parts per million
(ppm). 1H and 13C resonances are referenced to residual protons or
carbon atoms in the deuterated solvent. For other nuclei, the
external standards Ph2Se2 in CDCl3 (77Se) and H3PO4(aq) (31P) were
utilized. Elemental analyses were performed by Canadian Micro-
analytical Ltd. (Delta, British Columbia, Canada). GC–MS analysis
was conducted using an Agilent 5975C system. High-resolution
mass spectra (HRMS) were obtained using a quadrupole ion trap
mass spectrometer with electrospray ionization (ESI).
In the absence of a palladium complex, <10% conversion was
observed at 120 °C, while 5 mol% of [PdCl2(COD)], 3, or 4 affords
quantitative conversion. At 50 °C, the selenium-containing com-
plex 4 shows higher conversion than the phosphine complex 3
but does not outperform [PdCl2(COD)] and all complexes
yield <50% conversion. Finally, at room temperature, no catalyst
exceeds 25% conversion, and the COD complex reaches higher
yields than both 3 and 4, which are equal at 13%.
Conclusions
Synthesis of 3
The new palladium(II) complex (4) of a chelating organosele-
nium ligand has been prepared and characterized by a number of
methods to contrast its properties with the phosphine-ligated an-
alogue 3. Experimental evidence from 1H NMR spectra and X-ray
structural analysis indicates that the phenylselenyl substituent
has a lower ␴ donor ability towards PdII and ligand 2 is general is
more weakly bound, which was corroborated computationally by
DFT, including free energy calculations. Both complexes 3 and
4 are active catalysts in the Suzuki–Miyaura coupling of an
arylboronic acid with an aryl bromide, albeit with activities not
significantly higher than the simple COD complex of PdCl2.
Future studies will examine the donor ability of a wider range of
selenium (and tellurium) donor ligands as compared to other het-
eroatoms such as nitrogen and phosphorus. The coordination
chemistry of 2 towards other transition metals such as nickel and
copper will be investigated to study their structures and reactiv-
ity, with the possibility of improving solubility of complexes
through variation of the substitution patterns on the aromatic
ring and selenium centre. Additionally, the mechanism of cata-
lytic processes involving heavy chalcogenoethers will be probed
computationally and experimentally.
To a mixture of ligand 1 (168 mg, 0.61 mmol) and [PdCl2(COD)]
(157 mg, 0.55 mmol) was added CH2Cl2 (25 mL). The yellow solu-
tion was stirred for 1 h at room temperature, during which time a
yellow precipitate formed. The volatiles were removed in vacuo,
and the resultant solid was washed with Et2O (3 × 5 mL). After
drying in vacuo, 3 was obtained as a yellow powder in quantitative
yield. Solution 1H and 31P NMR spectral data in d6-DMSO matched
that reported in the literature.12 Anal. calcd. (%): C 47.55, H 3.55, N
3.08; found: C 47.38, H 3.41, N 3.09. An X-ray quality single crystal
of 3·2DMSO was grown from a layered DMSO–toluene solution at
room temperature.
Synthesis of 4
Complex 4 was prepared in a method analogous to that used for
complex 3 using ligand 2 (162 mg, 0.65 mmol) and [PdCl2(COD)]
(171 mg, 0.60 mmol) and isolated as an orange powder (211 mg,
83%, mp > 240 °C (dec.)). 1H NMR (d6-DMSO) ␦: 7.88–7.68 (overlap-
ping m and d, JHH(d) = 13 Hz, 4H, aromatic CH (m) and NH2 (d)),
7.61–7.37 (m, 7H, aromatic CH); low-intensity resonances corre-
sponding to approximately 12% free ligand 2 were observed at ␦
7.27–7.13 (m, aromatic CH), 6.82 (d, JHH = 8 Hz, aromatic CH), 6.54
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Ritch and Charette
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Table 3. Crystallographic Data for 3·2DMSO and 4·MeCN.
Compound
3·2(C2H6OS)
4·C2H3N
Empirical formula
C22H28Cl2NO2PPdS2
C14H14N2Cl2SePd
Formula weight
610.84
466.53
Temperature (K)
193(2)
193(2)
Crystal system
Monoclinic
Monoclinic
Space group
a (Å)
P21/n
10.9748(6)
P21/c
10.7926(6)
b (Å)
18.4224(10)
7.3379(4)
c (Å)
13.0833(7)
20.5576(12)
␣ (°)
90
90
␤ (°)
105.6894(7)
99.4615(7)
␥ (°)
90
2546.7(2)
4
1.593
1.185
1240
90
Volume (Å3)
Z
1605.91(16)
4
1.93
3.745
D
calcd. (g cm−3
)
␮ (mm−1
F(000)
)
904
Crystal size (mm3)
0.335×0.082×0.041
MoK␣ (␭ = 0.71073 Å)
1.959−27.6
−14 ≤ h ≤ 14, −23 ≤ k ≤ 23, −16 ≤ l ≤ 16
21623
5876 (Rint = 0.0434)
5876/2/292
1.04
0.446×0.192×0.09
MoK␣ (␭ = 0.71073 Å)
1.913−28.25
−14 ≤ h ≤ 12, −9 ≤ k ≤ 9, −27 ≤ l ≤ 27
11808
3864 (Rint = 0.0202)
3864/0/190
1.04
Radiation
␪ range for data collection (°)
Index ranges
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indexes (I > 2␴(I))
Final R indexes (all data)
R1 = 0.0364, wR2 = 0.0875
R1 = 0.0498, wR2 = 0.0959
1.18/−0.59
R1 = 0.0210, wR2 = 0.0518
R1 = 0.0245, wR2 = 0.0534
0.57/−0.45
Largest diff. peak/hole (e Å−3
)
(t, JHH = 8 Hz, aromatic CH), and 5.32 (br s, NH2). 13C{1H} NMR
(d6-DMSO) ␦: 147.3 (s), 137.9* (s), 133.5 (s), 131.6* (s), 131.2 (s), 130.7 (s),
130.2 (s), 129.4* (s), 128.8 (s), 128.1 (s), 126.3* (s), 125.7 (s); resonances
marked with an asterisk match 13C chemical shifts for the free
ligand 2. Of these four resonances (of 12 total), two are likely
overlapping signals from 2 and 4 and two are from 2.
77Se{1H} NMR (d6-DMSO) ␦: 482. HRMS (ESI) m/z: [M + Na]+ calcd. for
C12H11Cl2NPdSeNa: 447.83608; found: 447.83519. Anal. calcd. (%):
C 33.87, H 2.61, N 3.29; found: C 33.21, H 2.43, N 3.25. An X-ray
quality single crystal of 4·MeCN was grown from a slowly cooled
concentrated solution of the complex in warm acetonitrile.
was added and the reaction mixture was diluted with ethyl acetate
(2 mL), filtered through a plug of silica gel in a Pasteur pipet, and
analyzed by EI GC–MS. Reaction conversion were determined by
integration of the total ion current and using the separately de-
termined relative response factors of the product and internal
standard.
DFT calculations
Starting from crystal structure coordinates, gas-phase closed-shell
geometry optimizations of complexes 3 and 4 were performed with
GAMESS29 using the M06 functional.30 The 6-31G(d,p) basis set was
used for carbon, hydrogen, nitrogen, and phosphorus, while relativ-
istic effective core potentials as implemented in SDB-cc-pVTZ were
applied to selenium and palladium.31 Molecular orbital plots were
generated at a contour level of 0.03 using wxMacMolPlt.32
X-ray crystallography
Data were collected for a suitable crystal of each complex with
a Bruker APEX-II CCD diffractometer at 193 K using APEX2.23 Cell
refinement and data reduction were carried out using SAINT,24
and numerical absorption correction was applied using SAD-
ABS.25 Using Olex2,26 the structure was solved with the SHELXS27
structure solution program using the Patterson method for 3 and
direct methods for 4. Least squares refinement of the structure
was carried out against F2 using SHELXL.28 The structures were
well ordered and no special considerations were needed for the
refinements. Carbon-bound hydrogen atoms were placed in cal-
culation positions and treated in a riding-model approximation,
while nitrogen-bound hydrogen atoms were located in the differ-
ence electron map and allowed to refine isotropically. The N–H
hydrogen atoms in 3 were restrained to a length of 0.89 Å. All
nonhydrogen atoms were modeled anisotropically. Selected crys-
tal data are given in Table 3.
Supplementary material
Supplementary material is available with the article through
the journal Web site at http://nrcresearchpress.com/doi/suppl/
10.1139/cjc-2015-0417. Further computational details, including
coordinates for optimized geometries, are tabulated in the
supplementary material. CCDC 1414987–1414988 contain the sup-
plementary crystallographic data for this paper. These data can be
obtained, free of charge, via www.ccdc.cam.ac.uk/conts/retrieving.
html (or from the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ, UK (Fax: 44-1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk)).
Acknowledgements
Financial support from the University of Winnipeg, an adjunct
appointment in the Department of Chemistry, University of Man-
itoba, and supercomputing resources from Compute Canada and
Westgrid are gratefully acknowledged. The authors thank Bob
McDonald (X-ray Crystallography Laboratory, Department of
Chemistry, University of Alberta) for single-crystal X-ray diffrac-
tion data collection and Dr. Jiaxi Wang (Mass Spectrometry Facil-
ity, Queen’s University) for ESI HRMS analysis. Dr. Joshua Hollett
General procedure for catalytic reactions
In a glovebox, boronic acid (0.1 mmol), aryl halide (0.1 mmol),
cesium fluoride (0.15 mmol), and catalyst (5 mol%) were weighed
into a vial equipped with a stir bar. Dimethylformamide was
added (0.5 mL) and the vial was sealed with a PTFE-lined screw
cap. The vial was heated to the reaction temperature for 14 h.
After cooling to room temperature, an internal standard
(4-nitrobenzeldehyde, 20 ␮L of a 0.5 mol L−1 solution in acetonitrile)
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(Department of Chemistry, The University of Winnipeg) is thanked
for useful discussions regarding DFT calculations.
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