Replacing sulfonate by carboxylate: Application of pyridyliminocarboxylato copper(II) complexes in rac-lactide polymerization and Chan-Evans-Lam coupling

Article abstract of DOI:10.1139/cjc-2018-0402

Copper(II) complexes carrying pyridylmethyleneaminobenzoate or-propanoate ligands, LCuX, were prepared in one-pot reactions from pyridinecarboxaldehyde, aminobenzoic acid or β-alanine, and CuX₂ (X = Cl, NO₃, OAc, or OTf). All complexes were characterized by single-crystal X-ray diffraction studies and formed either dimers, tetramers, or coordination polymers. Attempted preparation of the respective alkoxide complexes, LCu(OR), was unsuccessful, but use of LCuX/NaOMe mixtures in rac-lactide polymerization indicated under some conditions coordination-insertion polymerization via a copper alkoxide as the mechanism. The complexes performed poorly in rac-lactide polymerization, showing low activities (12 h to completion at 140 °C), low to moderate heterotacticity (P_r = 0.6-0.8), and poor polymer molecular weight control (intramolecular transesterification). They were competent catalysts for Chan-Evans-Lam couplings with phenylboronic acid, without any indication of side reactions such as deboration or aryl homocoupling. The complexes were active in undried methanol, without addition of base, ligand, or molecular sieves. Aniline, n-octylamine, and cyclohexylamine were coupled quantitatively under identical reaction conditions. There is only little influence of the anion on activities (less than a factor of 2) but a strong influence on induction periods. The complexes were not active in CEL coupling with alcohols, phenols, or alkylboronic acids.

Full text of DOI:10.1139/cjc-2018-0402

Page 1 of 38
Replacing sulfonate by carboxylate: Application of
pyridyliminocarboxylato copper(II) complexes in rac-
lactide polymerization and Chan-Evans-Lam coupling.
Valérie Hardouin Duparc, Clémentine Dimeck, Frank Schaper*
Centre in Green Chemistry and Catalysis, Département de chimie, Université de Montréal, 2900
Boul. E.-Montpetit, Montréal, QC, H3T 1J4, Canada
* Frank.Schaper@umontreal.ca
Author email adresses :
Valérie Hardouin Duparc : valerie.hardouin.duparc@gmail.com
Clémentine Dimeck : clementine.dim@outlook.fr
Frank Schaper : Frank.Schaper@umontreal.ca
1

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Abstract
Copper(II) complexes carrying pyridylmethyleneaminobenzoate or –propanoate ligands,
LCuX, were prepared in one-pot reactions from pyridinecarboxaldehyde, aminobenzoic acid
or -alanine, and CuX2 (X = Cl, NO3, OAc or OTf). All complexes were characterized by single-
crystal X-ray diffraction studies and formed either dimers, tetramers or coordination
polymers. Attempted preparation of the respective alkoxide complexes, LCu(OR), was
unsuccessful, but use of LCuX/NaOMe mixtures in rac-lactide polymerization indicated
under some conditions coordination-insertion polymerization via a copper alkoxide as the
mechanism. The complexes performed poorly in rac-lactide polymerization, showing low
activities (12 h to completion at 140 °C), low to moderate heterotacticity (Pr = 0.6-0.8) and
poor polymer molecular weight control (intramolecular transesterification). They were
competent catalysts for Chan-Evans-Lam couplings with phenylboronic acid, without any
indication of side reactions such as deboration or aryl homocoupling. The complexes were
active in undried methanol, without addition of base, ligand or molecular sieves. Aniline, n-
octylamine and cyclohexylamine were coupled quantitatively under identical reaction
conditions. There is only little influence of the anion on activities (less than a factor of 2), but
a strong influence on induction periods. The complexes were not active in CEL coupling with
alcohols, phenols, or alkylboronic acids.
Copper complexes, homogenous catalysis, Chan-Evans-Lam coupling, lactide polymerization,
mechanism
2

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Introduction
Copper has found widespread use in catalytic transformations,1-2 but its application in
polymerization catalysis caused some controversy. It has been widely employed in radical
polymerizations involving a Cu(I)/Cu(II) redox couple,3-4 but much less in homogenous, 2-
electron processes. Copper(II) diimine complexes have been reported to copolymerize
ethylene and methacrylate by a coordination-insertion mechanism.5-7 However, the very low
activity of the system and the lack of a convincing mechanism make it doubtful that copper(II)
does indeed polymerize ethylene. Radical mechanisms, involving copper(I) or ligand transfer
to a catalytically active Al-species have been proposed as potential alternative reaction
pathways.8-9 Cu(II) complexes have also been claimed to polymerize acrylonitrile via a
coordination-insertion mechanism,10 but again this was doubted later and a different
mechanism, not involving Cu(II), was proposed to be responsible for the observed results.11
There is no doubt, however, that Cu(II) complexes are active in the ring-opening
polymerization of lactide to polylactic acid (PLA).
There is currently significant interest in the controlled polymerization of lactide,12-31 but
efforts have been concentrated for the most part on catalysts based on groups 1-4 and 12-14.
In the limited number of copper-catalyzed reactions, polymerizations proceeded either via
Lewis-acid activation of the monomer,32-41 or via insertion into a copper-alkoxide bond.42-53
We have previously reported that diketiminate copper alkoxides provide highly active, but
controlled polymerization catalysts.51-53 They are, however, very sensitive to air and moisture,
which severely limits their applicability. To provide copper(II) polymerization catalysts with
a ligand framework less susceptible to oxidation and hydrolysis, we recently investigated
copper complexes with sulfonate-based ligands (Scheme 1, A - C). The sulfonate complexes
proved to be unsuitable for lactide polymerization: the respective alkoxide complexes could
not be isolated or – based on polymerization results – not even be prepared in situ.54-55 They
proved to be, however, highly competent catalysts for Chan-Evans-Lam couplings of N-
nucleophiles.54-57 Chan-Evans-Lam couplings are oxidative, copper-catalyzed couplings
between a boronic acid and a second nucleophile, with copper(II) acetate being the most
widely employed catalyst.58-60 Compared to the Ullmann-Goldberg reaction or Buchwald-
Hartwig aminations catalyzed by palladium or copper, CEL couplings proceed under much
milder conditions, often at room temperature, and are thus more attractive for complicated
and sensitive substrates.61-72 Complexes A-C, but in particular B, showed quantitative
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conversion of amines, anilines and N-heterocycles using an identical reaction protocol and
requiring a minimum of optimization of reaction conditions.54-57
Based on the assumption that one reason for the instability of (Lsulfonate)Cu(OR) in lactide
polymerization is related to desulfonation, we investigated analogs to B and C, replacing the
sulfonate group with carboxylate (D and E, Scheme 1), as catalysts in lactide polymerization.
In Chan-Evans-Lam (CEL) couplings, the sulfonate group of A-C was proposed to bridge to
boron in an intermediate dinuclear complex prior to transmetallation. Complexes D and E
were thus also investigated for CEL couplings to test whether the carboxylate group is
capable of providing the same functionality. Complexes (L1)CuX, D, have been previously
prepared by Mitra and coworkers with oxalate, nitrate/azide and fluoroacetate anions.73-75
[(L2)Cu]X, E, has been reported with X = oxalate, azide or nitrate.76-79 To allow comparisons
with the respective sulfonate complexes, we targeted complexes with chloride, nitrate,
acetate and triflate counteranions.
Results and Discussion
Ligand syntheses. Our attempts to prepare L1H following literature protocols75 did not afford
a clean product.80 Best results in optimizing ligand synthesis were obtained by using a Dean-
Stark apparatus to eliminate water or microwave reactions in the presence of molecular
sieves, both of which afforded 80% conversion. Despite numerous attempts, conversion could
not improved any further. Attempts to purify the ligand were not successful and at best 95%
purity according to NMR could be obtained. Preparation of -alanine-based ligand L2H has
not been reported and attempts similar to the synthesis of L1H failed. While we cannot
exclude a simple experimental problem on our side, the analogous sulfonate-based ligands
were reported to be highly sensitive to hydrolysis.79 On the other hand, they assemble readily
to the ligand in the presence of a metal center to provide the respective metal complex.81 L1H
(95% purity) was thus employed for the attempted preparation of alkoxide complexes, while
copper complexes with L1 or L2 ligands and other anions were obtained by direct
condensation of the ligand on the metal center (Scheme 2).
Complex syntheses. Reaction of anthranilic acid with pyridinecarbaldehyde and copper(II)
chloride in methanol cleanly provided (L1)CuCl·H2O, 1, which crystallized as the dinuclear
chloride bridged complex (Scheme 3, Table 1, Fig. 1). The coordination geometry around
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copper is square-pyramidal ( = 0.0) with L1 and chloride in the equatorial plane and the
bridging chloride in the apical position with an elongated (d = 0.4 Å) bond to copper. The
structure of carboxylate complex 1 is very similar to the respective sulfonate complex B (Table
1). The only difference is the twisting of 30° between the aryl and the pyridyl rings in B,
required by the tetrahedral geometry of the sulfonate group, (only 5° in 1) and a very slightly
shorter Cu-O distance (d = 0.06 Å) for carboxylate vs. sulfonate coordination. Since the
presence of co-crystallized water might prevent preparation of alkoxide complexes, 1 was
recrystallized in dry methanol to provide (L1)CuCl·MeOH, 2, which is isostructural with
water replaced by methanol (Scheme 3, Fig. 1, Table 1).
Table 1. Selected geometric data of X-ray structures of 1-5
B a
1
2
3
4
5
Cu-O2C
1.964(2) 1.891(1),
1.905(1)
1.892(6),
1.900(6)
1.942(4) –
1.954(4)
1.894(1)
1.926(3)
Cu-N(=C)
2.068(2) 2.020(2),
2.003(2)
2.020(7),
2.015(7)
1.968(5) –
1.980(5)
1.996(2)
1.988(2)
1.998(3)
Cu-Npyridine 2.002(2) 2.002(2),
2.003(2)
2.020(7),
1.998(7)
2.008(5) –
2.025(5)
1.983(4)
2.200(4)
Cu-OH2
2.153(5) –
2.168(5)
Cu-X b
Cu-L b

2.276(1) 2.287(2),
2.305(2)
2.305(3),
2.306(2)
1.973(1)
2.295(2)
0.1
2.679(1) 2.720(2),
2.660(2)
2.676(3),
2.656(2)
1.935(4) –
1.941(4)
1.950(3)
0.0
0.0
0.1, 0.1
0.1, 0.1
0.5
a
82 b
Data taken from ref.
L=µ-O2CR
B, 1, 2: X=µ-Clshort, L=µ-Cllong. 3: L=µ-CO2. 4: X=µ-OAcshort, L=µ-OAclong. 5:
Reactions in the presence of copper nitrate or copper acetate yielded the respective complexes
[(L1)Cu(OH2)][NO3]·H2O, and (L1)Cu(OAc)·2H2O, 4, both with co-
3,75
crystallized/coordinated water (Scheme 3, Table 1, Fig. 1). Recrystallization in dry methanol
to remove water failed in these cases. Complex 3 crystallizes as a tetramer in the structure
described previously.75, 83 Acetate complex 4 crystallizes as a dimeric complex with bridging
acetate ligands. Surprisingly, the acetate shows a monodentate coordination to the copper
centres instead of the more common bidentate bridging mode and is structurally very similar
to the chloride-bridged complex 1 or 2. The triflate complex [(L1)Cu(OH2)][OTf], 5, can be
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obtained by either anion exchange from 1 with AgOTf or by direct reaction of copper(II)
triflate with the ligand precursors (Scheme 3). In both cases, the complex crystallizes as a 1D
coordination polymer (Fig. 1). A bridging carboxylate replaced the triflate anion in the metal
coordination sphere. Water occupies the apical position and completes the square-pyramidal
coordination geometry. Again, metrical data are highly similar to the respective sulfonate
complex (Table 1).
Initial reactions with -alanine instead of anthranilic acid following the same protocol did
not provide the desired complex (L2)CuCl, but (L2H)CuCl2 in appr. 50% yield (Scheme 4, Fig.
S1 and S2). Clearly, formal HX elimination is more difficult with alanine. After addition of
additional potassium hydroxide base, the reaction cleanly provided (L2)CuCl, 6 (Scheme 4).
Complex 6 formed a coordination polymer in the solid state, with square-pyramidal
coordination around copper and bridging carboxylate in the apical position (Fig. 2, Table 2).
Reactions with copper acetate or copper nitrate did not yield the desired products with or
without potassium hydroxide. During one attempt, the acetate complex (L2)Cu(OAc) was
formed, but it crystallized unfortunately as an adduct with copper acetate,
(L2)Cu(OAc)·Cu(OAc)2 (Scheme 4). (L2)Cu(OAc) formed an acetate-bridged coordination
polymer, the chains of which were crosslinked by carboxylate coordination to the apical
position of the copper acetate paddlewheel complex (Fig. S3). The triflate complex
(L2)Cu(OTf), 7, was prepared by anion exchange of the chloride complex (Scheme 4). As the
nitrate complex 3, triflate complex 7 crystallizes as a tetramer with bridging coordination of
the carboxylate group. The triflate anion remains coordinated to copper. The higher flexibility
of the aliphatic backbone permitted a weak interaction of the copper centre with the bridging
carboxylate oxygen (2.7 Å), resulting in a distorted octahedral coordination geometry (Table
2, Fig. 2).
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Table 2. Geometrical details of the X-ray structures of 6, (L2H)CuCl2, (L2)Cu(OAc)·Cu(OAc)2 and 7
(L2H)CuCl2
6
(L2)Cu(OAc)·Cu(OAc)2
1.953(3)
7
Cu-O2CO
Cu-N(=C)
1.948(1)
1.983(1)
2.038(1)
1.948(9), 1.955(9)
1.956(12), 1.974(12)
1.993(10), 2.019(10)
2.268(10), 2.321(10)
2.035(2)
1.996(4)
Cu-Npyridine 2.031(2)
1.018(4)
Cu-X a
Cu-L a
2.265(1), 2.274(1) 2.263(1)
2.952(1), 2.570(1) 2.285(1)
1.963(3)
2.197(4), 2.616(4)
1.944(9), 1.957(9),
2.672(7), 2.710(10)
0.1
0.1

a
(L2H)CuCl2: L=µ-Cllong, µ-O2CR. 6: X=Cl, L=µ-O2CR. (L2)Cu(OAc)·Cu(OAc)2: X=OAc, L=µ-OAc,µ-
OAc. 7: X=OTf, L=µ-O2CR, µ-O2CR.
Reactions of -alanine with thiophene aldehyde, pyrrole aldehyde or benzaldehyde in the
presence of copper(II) chloride did not provide crystalline material. If -alanine instead of -
alanine was employed, condensation with pyridinecarboxaldehyde in the presence of copper
nitrate provided complex 8, containing a tridentate ligand consisting of one -alanine and
two pyridinecarboxaldehyde moieties (Scheme 5; for its crystal structure, see Fig. S4).
Formation of 8 was not investigated in detail, but can be envisioned to proceed via formation
of (L)Cu(NO3), attack of the C=N double bond on a coordinated pyridinecarboxaldehyde,
formal hydrogen shift from methine to N and quarternisation of pyridine by the carbocation.
While only a single diastereomer was isolated in 50% of the theoretical yield, the chiral center
of alanine reacted under racemization, not inversion. The hydrogen shift from methine to N
is thus more likely to proceed via deprotonation-protonation than via a direct 1,2-H shift.
UV/vis-spectra. Complexes 1-7 show a d-d transition around 750 nm and an interligand or
LMCT transition around 340 nm for 1-5 and around 288 nm for 6 and 7 (Fig. 3). The higher-
energy transition is practically invariant with the nature of the anion. The more
bathochromic shift in 1-5 can be assigned to the extended -system of the ligand. The same
qualitative trend is observed in iminopyridines with N-aryl and N-alkyl substituents.84-85
Only in the acetate complex 4 a somewhat different shape of this transition is observed. A
similar trend for the respective sulfonate complexes was explained with persisting bridging
coordination of the acetate in solution to form dinuclear (or polynuclear) complexes.55
In contrast to the higher-energy transition, the d-d transition shows a clear effect of the anion
–
with max increasing in the order AcO– < TfO– < Cl– = NO3 for 1-5, as well as for 6, 7 and
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(L2)Cu(OAc)·Cu(OAc)2. This correlates qualitatively with expectations about the
coordinating ability of the anion and is consistent with the anion-displacement equilibria in
solution claimed to be present in the sulfonate analogs B.57
rac-Lactide polymerization. Preparation of copper alkoxide complexes (L1)Cu(OR) was
attempted by reaction of Cu(OMe)2 or Cu(OiPr)2 with L1H in the best purity available.
Reaction in either THF or acetonitrile provided strongly colored solutions, but no crystalline
product could be obtained. Alternatively, 2-5 were reacted with NaOMe, NaOEt or KOtBu in
various solvents. Again, strong coloration of reaction solutions indicated reactivity, but no
product could be isolated. The copper alkoxide complexes required for coordination-insertion
polymerization were thus prepared in situ by addition of one equiv sodium methoxide to
lactide polymerizations with 2-6. Alternatively, polymerization via an activated-monomer
mechanism was investigated with one equiv benzyl alcohol as co-initiator. In this mechanism,
ring-opening of metal-coordinated lactide is not achieved by intramolecular insertion into a
metal-alkoxide bond, but by intermolecular attack of free alcohol to form – after proton
transfer – a new, free polymeryl alcohol.
Activities of 2-6 in lactide polymerization are summarized in table 3; full data on all
polymerizations can be found in table S1. For ease of comparison, all reactions were quenched
after 12 h. Activities determined after 2 h reaction time (Table S1), are in rough agreement
with conversions after 12 h, indicating that lack of full conversion is not due to catalyst
decomposition. It is important to note that 3-5 contained water in their crystal structures,
but that 2 and 6 did not. At room temperature in dichloromethane solution all complexes
were inactive towards polymerization either in the absence or presence of either sodium
methoxide or benzyl alcohol. Complexes 2, 3, 5 and 6 were likewise inactive in toluene at 90
°C, but acetate complex 4 showed a moderate conversion of 40% after 12 h, with a very slight
heterotactic preference (Pr = 0.60) (Table 3, S1). In the presence of 1 equiv benzyl alcohol,
reactivities were identical : 4 produced PLA in 44% conversion after 12 h (Pr = 0.63), the
others were inactive. With sodium methoxide as co-initiator, 2, 3 and 5 became active and
achieved conversions of 60-95% after 12 h. 6 was not active and, curiously, acetate complex 4
became less active upon addition of sodium methoxide. In melt polymerizations at 140 °C
without co-initiator, complexes 2-4 were active (71-96% conversion after 12 h, Pr = 0.69-0.84),
while 5-7 were not (<25% after 12 h). In the presence of 1 equiv of benzyl alcohol, in general
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the same observations were made, although the activity of 4 was reduced and 7 showed 74%
conversion. Stereocontrol was similar to reactions without initiator (Pr = 0.62-0.85). In the
presence of sodium methoxide, melt polymerizations presented a very different picture: All
complexes 2-7 were now active with 75-93% conversion after 12 h and the obtained polymers
showed notably reduced heterotacticity (Pr = 0.52-0.61). Polydispersities ranged from 1.1 to
1.6 (Table S1), without any obvious correlation to reaction conditions or catalyst. All
polymerization showed drastically lower than expected polymer molecular weights. The only
exception being melt polymerizations in the presence of NaOMe, where polymer molecular
weights were notably larger, even if still lower than expected (Table S1).
Table 3. Activities of 2-7 in rac-lactide polymerization under different conditions. a
Conditions
2 (Cl)
n. r.
n. r.
n. r.
n. r.
n. r.
95%
20%
96%
100%
85%
3 (NO3) 4 (OAc) 5 (OTf)
6 (Cl)
n. r.
n. r.
n. r.
n. r.
n. r.
n. r.
n. r.
22%
28%
76%
7 (OTf)
RT, CH2Cl2
n. r.
n. r.
n. r.
n. r.
n. r.
60%
12%
80%
90%
76%
n. r.
n. r.
n. r.
40%
44%
16%
10%
71%
39%
93%
n. r.
n. r.
n. r.
n. r.
n. r.
91%
15%
17%
16%
74%
RT, CH2Cl2, 1 equiv BnOH
RT, CH2Cl2, 1 equiv NaOMe
90 °C, toluene
90 °C, toluene, 1 equiv BnOH
90 °C, toluene, 1 equiv NaOMe
90 °C, toluene, 1 equiv NaOMe + BnOH
140 °C, no solvent
17%
74%
75%
140 °C, no solvent, 1 equiv BnOH
140 °C, no solvent, 1 equiv NaOMe
a All reactions were quenched after 12 h. For conversions after 2 h, see table S1. n.r. = no reaction
The ensemble of polymerization results is difficult to interpret mechanistically.
Polymerizations at 90 °C agree with a coordination-insertion polymerization catalyzed by
copper complexes: In the absence of co-initiator only acetate complex 4 is active, bearing the
only anion which could reasonably be expected to initiate polymerization. That activity is
unaffected by addition of benzyl alcohol, but increased upon addition of sodium methoxide,
likewise supports a coordination-insertion mechanism. One would have expected that water-
containing and water-free complexes react differently upon addition of sodium methoxide,
but, considering the activity of the acetate complex, catalysts may be able to recover from
hydrolysis if the copper hydroxides formed react with lactide to form copper carboxylate salts.
Sodium methoxide itself is active under these conditions (Table S1), but unlikely to be the
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active species: (a) The microstructure of PLA produced with 2, 3 and 5 was slightly
heterotactic (Pr = 0.66 – 0.71), while anionic polymerization with sodium methoxide produces
atactic PLA (Table S1). (b) In the presence of 6, which does not contain water in its crystal
structure, no polymer was obtained, indicating that sodium methoxide was not available for
polymerization in this case.
The activity of 2-4 in melt polymerizations without co-initiator is puzzling: For an activated-
monomer mechanism, water would be the most likely initiator, but water-free 2 was active,
while 5, containing coordinated water, was not. Also, polymerizations in the presence of
benzyl alcohol did not show the rate increase which would be expected if initiation by protic
impurities is replaced by an added alcohol. In fact, the activity of 4 was reduced by the
addition of benzyl alcohol: activities decreased in the order 71%, 62%, and 39% in the
presence of 0, 0.2, and 1 equiv of benzyl alcohol, respectively. The effect is not limited to
benzyl alcohol: addition of 1 equiv of isopropanol or phenol to polymerizations with 4 likewise
reduced activity from 71% to 44% and 40%, respectively (Table S1). Intrigued by this, we
repeated polymerizations with 2, 3 and 5 at 90 °C in the presence of sodium methoxide, but
now with an additional equivalent of benzyl alcohol. Activities were again suppressed from
60-95% to 12-20% (Table 3). The fact that suppression of activity occurred with different
alcohols and was dependent on the amount of alcohol used, argues against contaminations
or decomposition reactions as explanation for the reduced activity. We do not have a
mechanistic explanation for the negative impact of additional alcohol on reactivity, but it is
clearly incompatible with an activated-monomer mechanism.
While the acetate anion in 4 could be considered a potential initiating group, chloride and
nitrate anions are not expected to initiate polymerization by a coordination-insertion
mechanism, even at 140 °C. Considering the activity of acetate complex 4 at 90 °C, the ligand
carboxylate group is most likely responsible for activity at 140 °C, either by direct insertion
into Cu-acyl or by deprotonation of protic impurities. The latter is unlikely, since activity of
2 was unaffected by addition of either water or lactic acid (Table S1), and insertion into the
carboxylate group is thus the most likely mechanism (Scheme 6). MALDI-analyses of
polymers obtained with 2 and 4 in the presence and absence of benzyl alcohol all show the
presence of a series with m/z = 72·n + M(Na), indicative of cyclic oligomers produced by
intramolecular transesterification. A second series of m/z = 72·n + 18 + M(Na) indicates
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Page 11 of 38
hydroxyl-terminated linear chains for 4, as well as for water-free 2. The latter probably result
from opening of cyclic oligomers by water under MS conditions. For PLA obtained in the
presence of benzyl alcohol, a series of benzyl-terminated chains is likewise obtained, which
might arise either from benzyl alcohol acting as chain-transfer reagent or from opening of
cyclic oligomers by reaction with benzyl alcohol under MS conditions. It is tempting to assign
the high amount of intramolecular transesterification to the formation of a reactive carbonate
group at the chain end, close to the metal alkoxide (Scheme 6). The latter would encourage
formation of cyclic oligomers, in a mechanism similar to that proposed for NHC-catalyzed
polymerization of lactide.86 However, the low polymer molecular weights were also observed
for polymerizations at 90 °C, in complexes which were active only in the presence of sodium
methoxide.
For melt polymerization in the presence of sodium methoxide, similar activities of all
catalysts, reduced heterotacticity of the polymer and increased polymer molecular weights,
all indicate that sodium methoxide does not react (completely) with LCuX under these
conditions and is at least partly responsible for the formation of polymer produced at 140 °C.
Complexes 6 and 7 with an aliphatic backbone display – on average – lower activities (Table
3, S1). Taken aside the activity of the acetate complex at 90 °C, there is no clear correlation
of activity with the nature of the anion. Pr values vary strongly under similar conditions
without any correlation to the nature of the anion, indicative that 2-7 do not reliably form a
single active species under these conditions.
Chan-Evans-Lam couplings. A drawback of typical CEL couplings with simple copper salts
is the high substrate dependence on reaction conditions, which in most cases require the
optimization of reaction conditions even for closely related substrates, such as aniline and
amine.87-88 Complexes B were shown to be not just highly reactive in CEL couplings, but also
to function with a simple and general reaction protocol (various solvents tolerated, water
tolerated, no base or ligand additive required, and applicable for aniline, amines as well as
other N-nucleophiles under identical conditions).55-57 This was rationalized by the fact that
the ligand is responsible for solubilisation of the complex and – via the sulfonate group in B
– coordinates to boron to form a dinuclear complex, proposed as an intermediate prior to
transmetallation.89-91 In CEL couplings with simple copper salts, the anion typically acts as
the bridging ligand. Consequently, CEL couplings with CuX2 salts normally show a strong
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dependence of activity on the counteranion, while couplings with B did not. Complexes 1-7
were investigated in CEL couplings to see if these characteristics can be transferred to a
carboxylate-based ligand or if the sulfonate group is essential. Complexes 1-7 were active in
CEL couplings under the exact same reaction conditions employed for B, i. e. room
temperature, methanol solution, 1.5 equiv PhB(OH)2, 2.5 mol% catalyst, no base or further
ligand added (Scheme 7).
As for B, neither deboration, nor coupling to solvent, nor aryl homocoupling was observed.
An excess phenylboronic acid is thus not necessary to for the reactions to reach completion,
but was employed to allow comparison with data for B. Full conversion was reached for the
coupling of the more nucleophilic cyclohexylamine and n-octylamine with phenylboronic acid
using 1-5 (Table 4). For aniline as nucleophile, however, using chloride and triflate complexes
1 and 5 did not lead to full conversion (Table 4). The reason for this is unclear and does not
correlate with qualitative coordination strength of the anions to copper. Reactions with
cyclohexylamine were investigated in detail to address the dependence of reactivity on the
counteranion. In the mechanism proposed for B, the reactive species is proposed to be cationic
and the anion involvement is limited to its influence on the dissociation equilibrium.
Consequently, only a small influence of the anion on reactivity was observed for complexes
B.55 The same was observed for 1-5: apparent first-order rate constants varied by less than a
factor of two between the most and the least active complex (Fig. 4, Table 4). The anion has,
however a remarkable influence on the length of the induction period, which differed between
5 – 70 min. As expected, the more nucleophilic substrates cyclohexylamine and n-octylamine
show 4-5 times higher reactivity than aniline (Table 4).
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Table 4. Chan-Evans-Lam coupling with phenylboronic acid
Catalyst
Anion
Aniline
Conversion a
25%
n-Octylamine
Conversion b
100%
Cyclohexylamine
Conversion a
kobs
t0
1
Cl–
95%
100%
100%
96%
0.39(1) h–1
0.34(2) h–1
0.67(1) h–1
0.48(5) h–1
> 0.3 h–1
5 min
–
3
4
5
6
7
8
NO3
100%
100% c
26%
100%
70 min
20 min
45 min
>210 min
330 min
120 min
AcO–
TfO–
Cl–
100% d
100%
23%
100%
48%
TfO–
0%
100%
80%
> 0.09 h–1
0.19(4) h–1
–
NO3
0%
100%
100%
a after 12 h. b after 4.5 h. c kobs = 0.13(4) h–1 d kobs = 0.51(4) h–1
While still highly competent in CEL couplings, replacing the sulfonate group with a
carboxylate in 1-5 resulted in an overall drop of activity compared to complexes of type B
(Scheme 1). Coupling with aniline was appr. 4-5 times faster with B and reactions with
octylamine which require several hours with 1-5 reach completion in 10 min with B. The
lower reactivity might be associated with the geometry of the carboxylate vs. the sulfonate
group: Coordination of boron to the rigid carboxylate group places the phenylboronic acid by
necessity farther away from the copper center than coordination to the tetrahedral and more
flexible sulfonate group (Scheme 8).
Couplings with 6 and 7, having an alkyl backbone in the ligand, show smaller rate constants
and significantly longer induction periods. As for B, dissociation of the anionic ligand from
copper thus seems not to be required in the catalytic cycle. Complex 8 shows, despite the
complex nature of the ligand backbone, the same general characteristics as 1-7, i. e. a
tridentate, mono-anionic ligand with a coordinated carboxylate. As such, it was likewise
tested in CEL couplings and proved to be a competent catalyst under the same mild reaction
conditions for amines, but not for aniline (Table 4).
Substrate scope in comparison to sulfonate complexes B. Complexes of type B were not
reactive toward weaker nucleophiles, such as alcohols or phenols. They also did not show any
reactivity with alkylboronic acids. Complexes 1-5 unfortunately showed the same lack of
reactivity. Neither coupling of phenol or alcohol with phenylboronic acid, nor coupling of
octylamine or aniline with sec-butylboronic acid or cyclohexylboronic acid was observed
under a variety of reaction conditions and up to temperatures of 120 °C.
13

Page 14 of 38
Conclusions
Pyridylimino carboxylate copper(II) complexes based on anthranilic acid or -alanine with
different anions are readily available from simple starting materials in a one-pot reaction.
While copper(II) alkoxide complexes could not be isolated, rac-lactide polymerization data
supports a coordination-insertion mechanism by copper alkoxide complexes under some
conditions. This is in contrast to polymerization with their sulfonate analogs and replacement
of sulfonate by carboxylate thus indeed increased the accessibility of copper(II) alkoxide
complexes. Several mechanisms seem to be in play, however, and at 140 °C sodium methoxide
seems to initiate polymerization on its own instead of reacting with the copper complexes.
Although a step up from the performance of their sulfonate analogs, catalyst performance
remains highly unsatisfactory with low and irregular activities, moderate heterotacticities,
and severe lack of polymer molecular weight control. Compared to our previous work which
showed excellent stereocontrol with Cu(II) complexes, the lack of steric bulk towards the
apical positions of the copper complex might be responsible for the lack of polymer molecular
weight control.
In CEL couplings, in particular anthranilic acid-based complexes 1-5 were competent
catalysts. There is no evidence of typically observed side reactions, such as deboration or aryl
homocoupling, and they are active for amines as well as anilines under the same,
unoptimized reaction conditions. While they still outperform the simple copper salts typically
employed, their performance is somewhat lower than that of the corresponding sulfonate
complexes recently reported by our group. This can gratifyingly be explained by the structure
of the carboxylate- or sulfonate-bridged dinuclear copper-boron species proposed in the
mechanism for these complexes. Catalyst design for CEL couplings should thus include
groups able to coordinate to boron which either place the boronic acid in close contact to the
metal center or contain sufficient intermolecular flexibility to allow it to approach the copper
center in the transmetallation step.
Experimental section
General. Phenylboronic acid was purified by washing with dichloromethane until the filtrate stayed colorless. rac-
Lactide (98%) was purchased from Sigma–Aldrich, purified by 3 recrystallizations from dry ethyl acetate and kept
◦
at –30 C. All other chemicals were purchased from common commercial suppliers and used without further
purification. Elemental analyses were performed by the Laboratoire d’analyse élémentaire (Université de
14

Page 15 of 38
Montreal). UV/vis spectra were recorded on a Cary Series UV-Vis-NIR spectrophotometer from Agilent
Technology. GC-MS spectra were recorded on an Agilent Technology GC/MS.
O
OH
Toluen
CO2H
NH2
Dean-Stark
O
N
+
N
N
reflux, 12 h
2-((Pyridin-2-ylmethylene)amino)benzoic acid, L1H. 2-Pyridinecarboxaldehyde (95 µL, 1.0 mmol) and aniline-2-
carboxylic acid (anthranilic acid, 137 mg, 1.0 mmol) were dissolved in anhydrous toluene (15 mL). The mixture
was refluxed overnight, cooled to room temperature and filtered. After evaporation of the solvent, the residue was
analyzed by 1H NMR to show 80% conversion to product. Purification by column chromatography with a gradient
of solvent from 8/2 : hexane/ethyl acetate to 2/8 : hexane/ethylacetate yielded the product in 95% purity according
to NMR (147 mg, 65%).
1H NMR (DMSO-d6, 400 MHz) δH: 8.66 (d, J = 4, 1H, py), 8.00 (s, 1H, PyCH(=N)), 7.74 (t, J = 8, 1H, Py), 7.5 (m,
2H), 7.2 (m, 2H), 7.05 (d, J = 8, 1H), 6.90 (t, J = 8, 1H), 6.31 (s, 1H CO2H). Anal. Calcd. for C13H10N2O2 : C, 69.02;
H, 4.46; N, 12.38. Found: C, 69.43; H, 4.78; N, 12.02. HRMS(ESI), m/z (M+H+, 100), Calcd. for C13H11N2O2
: 227.0826, Found: 227.0815.
N
O
N
1. H2O, MeOH
60 °C, 1 h
N
O
CO2H
NH2
Cu
O
Cl
Cl
O
·2 H2O
+
N
O
Cu
2. CuCl2·2 H2O
rt, 1 h
N
(L1)2Cu2(µ-Cl)2·2 H2O, 1. 2-Pyridinecarboxaldehyde (95 µL, 1.0 mmol) was added to a hot solution (60 °C) of
aniline-2-carboxylic acid (anthranilic acid, 137 mg, 1.0 mmol) in water/methanol (5/10 mL). The mixture was
stirred for one hour at 60 °C. CuCl2·2 H2O (187 mg, 1.1 mmol) was added, heating was stopped and the green
solution was stirred another hour. After filtration, slow evaporation of the solvent afforded green, X-ray quality
crystals (256 mg, 75%).
UV-vis (DMSO, 4.0∙10–3 M or 6.17∙10–5 M) [max, nm (, M–1∙cm–1)] : 338 (9132), 719 (40). Anal. Calcd. for
C13H9ClCuN2O2·1 H2O : C, 45.62; H, 3.24; N, 8.19. Found: C, 45.35; H, 3.15; N, 8.00.
{(L1)Cu(µ-Cl)}2·2 MeOH, 2. Recrystallisation of 1 (100 mg, 0.29 mmol) in anhydrous MeOH (2 mL) led to copper
complexes with a co-crystallized methanol (35 mg, 34%). UV-vis (DMSO, 4.8∙10–3 M or 6.2∙10–5 M) [max, nm (, M–
1∙cm–1)] : 338 (9196), 719 (51). Anal. Calcd. for C13H9ClCuN2O2·MeOH : C, 47.20; H, 3.68; N, 7.86. Found: C, 46.88;
H, 3.34; N, 7.49.
15

Page 16 of 38
O
N
+
1. H2O, MeOH
60 °C, 1 h
O
CO2H
NH2
[NO3]–
OH2
O
Cu
·H2O
+
N
2. Cu(NO3)2·2.5 H2O
rt, 1 h
N
4
[(L1)Cu(OH2)]4[NO3]4, 3. Equivalent to 1, from Cu(NO3)2·2.5 H2O (255 mg, 1.1 mmol). Slow evaporation of the
solvent provided green, X-ray quality crystals (306 mg, 83%).
UV-vis (DMSO, 4.5∙10–3 M or 5.6∙10–5 M) [max, nm (, M–1∙cm–1)] : 338 (8041), 717 (47). Anal. Calcd. for
C13H9CuN3O5·1¼H2O : C, 41.83; H, 3.10; N, 11.26. Found: C, 42.01; H. 3.18; N, 11.11.
O
1. H2O, MeOH
N
Ac
CO2H
NH2
60 °C, 1 h
O
O
O
N
O
Cu
+
N
Cu
·4 H2O
2. Cu(OAc)2·H2O
rt, 1 h
N
O
O
Ac
N
(L1)2Cu2(µ-OAc)2·4 H2O, 4. Equivalent to 1, from Cu(OAc)2·H2O (219 mg, 1.1 mmol). Slow evaporation of the
solvent yielded green, X-ray quality crystals (222 mg, 58%).
UV-vis (DMSO, 4.6∙10–3 M or 4.0∙10–5 M) [max, nm (, M–1∙cm–1)] : 327 (6871), 690 (86). Anal. Calcd. for
C15H12CuN2O4·2 H2O : C, 46.94; H, 4.20; N, 7.30. Found: C, 46.36; H, 4.33; N, 7.64.
O
N
+
O
1. H2O, MeOH
60 °C, 1 h
OH2
[OTf] -
CO2H
NH2
Cu
O
+
N
N
2. Cu(OTf)2
rt, 1 h
{[(L1)Cu(OH2)]}n[OTf], 5. Method 1 : Equivalent to 1, from Cu(OTf)2 (398 mg, 1.1 mmol). Slow evaporation of the
solvent provided green, X-ray quality crystals (332 mg, 73%).
UV-vis (DMSO, 3.9∙10–3 M or 4.9∙10–5 M) [max, nm (, M–1∙cm–1)] : 338 (8470), 697 (65). Anal. Calcd. for
C14H9CuF3N2O5S1·1.5 H2O: C, 36.17; H, 2.60; N, 6.03; S, 6.90. Found: C, 36.26; H, 2.77; N, 6.37; S, 7.23.
Method 2 : Silver triflate (75 mg, 0.40 mmol) was added to a suspension of 1 (100 mg, 0.29 mmol) in dry THF (10
mL) under nitrogen. After one hour of stirring at ambient temperature, a precipitate appeared and the color of
the solution intensified. After filtration, slow evaporation of the green solution (under N2), afforded green crystals
(83 mg, 63%). The compound shows the same crystal structure and an identical UV/vis spectrum to the one
prepared above.
16

Page 17 of 38
HO2C
O
Cl
1. H2O, MeOH
60 °C, 1 h
Cu Cl
N
O
OH
·1 H2O
+
N
N
2. CuCl2·2 H2O
rt, 1 h
NH2
(L2H)CuCl2·H2O. Equivalent to 1, from -alanine (89 mg, 1.0 mmol), 2-pyridinecarboxaldehyde (95 µL, 1.0 mmol)
and CuCl2·2 H2O (187 mg, 1.1 mmol). Slow evaporation of the solvent yielded green, X-ray quality crystals (171
mg, 49%).
UV-vis (DMSO, 5.1∙10–3 M or 6.4∙10–5 M) [max, nm (, M–1∙cm–1)] : 288 (7442), 741 (95). Anal. Calcd. for
C9H10CuN2O2Cl2·1 H2O : C, 32.69; H, 3.66; N, 8.47. Found: C, 32.34; H, 3.68; N, 8.11.
O
1. KOH
H2O, MeOH
60 °C, 1 h
O
O
Cu Cl
N
O
OH
N
+
N
2. CuCl2·2 H2O
rt, 1 h
NH2
(L2)2Cu2(µ-Cl)2, 6. 2-Pyridinecarboxaldehyde (95 µL, 1.0 mmol) and potassium hydroxide (56 mg, 1.0 mmol) were
added to a hot solution (60 °C) of 3-propanoic acid (-alanine, 89 mg, 1.0 mmol) in water/methanol (5/10 mL). The
mixture was stirred for one hour at 60 °C. CuCl2·2 H2O (187 mg, 1.1 mmol) was added, heating was stopped and
the solution was stirred another hour. After filtration, slow evaporation of the solvent afforded blue-green, X-ray
quality crystals (214 mg, 78%).
UV-vis (DMSO, 6.1∙10–3 M or 7.6∙10–5 M) [max, nm (, M–1∙cm–1)] : 288 (5794), 786 (62). Anal. Calcd. for
C9H9ClCuN2O2 : C, 39.14 H, 3.28; N, 10.14. Found: C, 38.80 H, 3.53; N, 9.78.
O
O
O
1. H2O, MeOH
60 °C, 1 h
Cu OAc
N
O
·Cu(OAc)2
OH
NH2
N
+
N
2. Cu(OAc)2·H2O
rt, 1 h
(L2)Cu(OAc)·Cu(OAc)2. Equivalent to 1, from 3-aminopropanoic acid (-alanine, 89 mg, 1.0 mmol), 2-
pyidinecarboxaldehyde (95 µL, 1.0 mmol), and Cu(OAc)2·H2O (219 mg, 1.1 mmol). Slow evaporation of the solvent
yielded blue-green, X-ray quality crystals (216 mg, 45%).
UV-vis (DMSO, 0.6∙10–2 M or 33∙10–4 M) [max, nm (, M–1∙cm–1)] : 305 (2500), 716 (115). Anal. Calcd. for
C11H12CuN2O4∙Cu(OAc)2 : C, 37.42; H, 3.77; N, 5.82. Found: C, 37.76; H, 4.01; N, 6.49.
O
N
O
N
O
O
1.1 eq AgOTf
Cu OTf
Cu Cl
N
N
THF
rt, N2
(L2)CuOTf, 6. Silver triflate (104 mg, 0.40 mmol) was added to a suspension of 1 (100 mg, 0.37 mmol) in dry THF
(10 mL) under nitrogen atmosphere. After one hour of reaction at ambient temperature, a precipitate appeared
17

Page 18 of 38
and the color of the solution intensified. After filtration, slow evaporation of the green solution (under N2), afforded
green crystals (95 mg, 66%).
UV-vis (DMSO, 2.7∙10–2 M or 1.3∙10–4 M) [max, nm (, M–1∙cm–1)] : 285 (4230), 703 (32). Anal. Calcd. for
C10H9CuF3N2O5S1 : C, 30.81; H, 2.33; N, 7.19 S, 8.22. Found: C, 30.49; H, 2.64; N, 6.85; S, 8.76.
O
+
O
1. H2O, MeOH
60 °C, 1 h
N
*
*
CO2H
OH2
Cu O3N [NO3]–
*N
O
*
H
+
NH2
H
N
2. Cu(NO3)2. 2.5 H2O
rt, 1 h
*
N
HO
H
[(L3)Cu(H2O)(NO3)][NO3], 8. Equivalent to 1, from (S)-2-aminopropanoic acid (L-alanine, 89 mg, 1.0 mmol), 2-
pyridinecarboxaldehyde (95 µL, 1.0 mmol) and Cu(NO3)2·2.5 H2O (255 mg, 1.1 mmol). Slow evaporation of the
solvent yielded green, X-ray quality crystals (50 mg, 25%).
UV-vis (DMSO, 1.0∙10–2 M or 1.0∙10–4 M) [max, nm (, M–1∙cm–1)] : 259 (8046), 826 (32).
rac-Lactide polymerization
At room temperature or 90 °C: Under nitrogen, the catalyst (0.01 mmol) was added to lactide (144 mg, 1.0 mmol)
in dry dichloromethane (1 mL) or dry toluene (1 mL). If desired, benzyl alcohol (5.0 × 10−2 M in CH2Cl2) and/or a
stock solution of sodium methoxide (5.0 × 10−2 M in CH2Cl2) was added to the reaction mixture. For reactions at
90 °C, the reactions vessel was sealed an placed in a pre-heated oil-bath. Reaction mixtures were quenched at the
desired polymerization time by addition of a dichloromethane solution of acetic acid (5 mM). Dry polymer samples
were stored at −80 °C.
At 140°C : In a pressure tube under nitrogen, the catalyst (0.010 mmol) was combined with lactide (144 mg, 1.0
mmol). If desired, benzyl alcohol (5.0 × 10−2 M in CH2Cl2) and/or a stock solution of sodium methoxide (5.0 × 10−2
M in CH2Cl2) was added to the reaction mixture. The tube was placed in a pre-heated oil bath outside the glovebox.
Reaction mixtures were quenched at the desired polymerization time by addition of a dichloromethane solution
of acetic acid (5 mM), rapidly cooled to RT and the solvent evaporated. Dry polymer samples were stored at −80
°C.
Characterization. Conversion was determined from 1H NMR by comparison to remaining lactide. Pr values were
determined from homodecoupled 1H NMR spectra and calculated from Pr = 2·I1/(I1+I2), with I1 = 5.15 – 5.21 ppm
(rmr, mmr/rmm), I2 = 5.21 – 5.25 ppm (mmr/rmm, mmm, mrm). The integration of the left multiplet and right
multiplet (I1 and I2) required only one, very reproducible dividing point of the integration, which was always taken
as the minimum between the two multiplets. Pr-values obtained this way were typically consistent to ±1% over
the course of one experiment and ±3% between different experiments under identical conditions. Molecular weight
analyses were performed on a Waters 1525 gel permeation chromatograph equipped with three Phenomenex
columns and a refractive index detector at 35 ◦C. THF was used as the eluent at a flow rate of 1.0 mL·min-1 and
18

Page 19 of 38
polystyrene standards (Sigma–Aldrich, 1.5 mg·mL-1, prepared and filtered (0.2 mm) directly prior to injection)
were used for calibration. Obtained molecular weights were corrected by a Mark-Houwink factor of 0.58.92
General procedure for Chan-Evans-Lam couplings. To a solution of amine (1.0 mmol) and phenylboronic acid (1.5
mmol) in methanol (1 mL)was added the desired catalyst (0.025 mmol). Trimethoxybenzene was added as internal
standard. The reaction was stirred open to air at ambient temperature. For kinetic experiments, 20 µL aliquots
were taken, diluted in ethyl acetate and analyzed by GC-MS. After the desired reaction time, the reaction was
quenched with 0.5 mL of a saturated aqueous solution of ammonium chloride. The organic layer was extracted
and filtered through a short silica plug to remove remaining copper complex. Products and side-products were
identified in the MS- and NMR-spectra from comparison to literature. Conversion was typically analysed by GC-
MS. Quantitative concentrations were determined by comparison to trimethoxybenzene standard. Calibration
factors between starting materials, products, side-products and trimethoxybenzene were determined from
simultaneous NMR and GC-MS analysis or by analysis of solutions prepared from isolated or commercially
available products.
X-ray diffraction studies. Crystal for X-ray diffraction were obtained from synthesis as described above.
Diffraction data were collected on a Bruker Venture METALJET diffractometer (Ga K radiation) or a Bruker
APEX II microsource (Cu K radiation).93 Data reduction was performed with SAINT,94 absorption corrections
with SADABS.95 Structures were solved by dual-space refinement (SHELXT).96 All non-hydrogen atoms were
refined anisotropic using full-matrix least-squares on F2 and hydrogen atoms refined with fixed isotropic U using
a riding model (SHELXL97).97 Complexes 2, 3, and 7 suffered from mediocre to bad crystal quality, but the
obtained structural data is sufficient to uphold the conclusions in the main text. Further experimental details can
be found in Table 5 and the supporting information (CIF).
19

Page 20 of 38
Table 5. Details of X-ray Diffraction Studies
1
2
3
4
5
Formula
C26H20Cl2Cu2N4O5
666.44; 672
150; 1.34190
Triclinic
C52H46Cu4N12O25
1493.17; 6064
150; 1.34190
Monoclinic
P21/c
C15H16CuN2O6
383.84; 1576
150; 1.34190
Orthorhombic
Pbca
C14H11CuF3N2O6S
455.85; 3664
150; 1.34190
Orthorhombic
Fdd2
C27H22Cl2Cu2N4O5
680.46; 688
150; 1.34190
Triclinic
Mw (g/mol); F(000)
T (K); wavelength
Crystal System
Space Group
Unit Cell: a (Å)
b (Å)
P-1
P-1
7.0643(2)
9.7464(5)
11.4104(6)
13.1040(7)
107.274(2)
102.216(2)
102.993(3)
1293.84(12)
2; 1.747
21.2716(10)
21.2719(11)
27.1790(13)
90
8.5717(2)
18.0801(5)
20.4049(6)
90
22.214(3)
37.308(5)
7.8781(10)
90
12.7769(4)
13.9680(4)
79.5330(10)
88.2270(10)
80.2220(10)
1221.76(6)
2; 1.812
c (Å)
 (°)
107.558(3)
90
90
90
 (°)
90
90
 (°)
V (Å3)
11725.2(10)
8; 1.692
3162.29(15)
8; 1.612
6529.1(14)
16; 1.855
8.443; multi-scan
4.0-53.6; 0.99
20965; 0.049
3504; 0.059
3226; 0.039
0.092; 1.10
0.44
Z; dcalcd. (g/cm3)
 (mm–1); Abs. Corr.
 range (°); completeness
Collected reflections; R
Unique reflections; Rint
11.003; multi-scan 10.399; multi-scan 8.286; multi-scan
7.670; multi-scan
3.8-53.6; 1.00
31791; 0.024
3636; 0.046
3091; 0.075
0.080; 1.03
0.39
2.8-53.6; 1.00
47509; 0.021
5615; 0.042
3.2-52.3; 1.00
55375; 0.051
4614; 0.098
3491; 0.113
0.342; 1.43
2.43
2.6-53.6; 1.00
81161; 0.044
13461; 0.067
12030; 0.095
0.257; 1.07
3.25
Oberved Reflections; R1(F) 5502; 0.031
wR(F2) (all data); GoF(F2)
0.083; 1.08
0.67
Residual electron density
20

Page 21 of 38
Table 5. continued
6
7
8
(L1H)CuCl2
(L1)CuOAc·Cu(OAc)2
Formula
C9H9ClCuN2O2
276.17; 1916
100; 1.54178
Monoclinic
P21/c
C20H18Cu2F6N4O10S2 C15H17CuN5O10
C9H12Cl2CuN2O3
330.65; 668
100; 1.54178
Monoclinic
P21/n
C15H18Cu2N2O8
481.41; 956
150; 1.34190
Monoclinic
P21/c
Mw (g/mol); F(000)
T (K); wavelength
Crystal System
Space Group
Unit Cell: a (Å)
b (Å)
779.58; 3120
150; 1.34190
Monoclinic
P21/c
490.5; 2008
100; 1.54178
Monoclinic
P21/c
7.7942(2)
9.8050(3)
13.5262(4)
90
27.7325(18)
7.5286(5)
29.643(2)
90
12.4500(2)
9.6183(2)
30.7146(5)
90
8.8166(3)
14.6490(5)
10.1051(3)
90
8.5605(3)
26.0642(10)
8.4229(3)
90
c (Å)
 (°)
104.405(1)
90
114.689(4)
90
98.6150(10)
90
111.372(1)
90
97.167(2)
90
 (°)
 (°)
V (Å3)
1001.20(5)
4; 1.832
5623.3(7)
8; 1.842
3636.51(11)
8; 1.793
1215.37(7)
4; 1.807
1864.66(12)
4; 1.296
Z; dcalcd. (g/cm3)
 (mm–1); Abs. Corr.
 range (°); completeness
Collected reflections; R
Unique reflections; Rint
5.385; multi-scan 9.685; multi-scan
2.362; multi-scan 6.591; multi-sacn
12.606; multi-scan
3.0-60.8; 0.99
22025; 0.050
4260 0.072
3408; 0.059
0.172; 1.05
1.30
5.6-67.7; 0.99
25743; 0.0099
1937; 0.026
2.9-57.4; 0.99
22199; 0.167
5706; 0.160
3088; 0.159
0.422; 1.05
1.92
2.9-67.7; 1.00
36614; 0.012
3573; 0.026
3570; 0.035
0.089; 1.23
0.43
5.6-72.1; 0.99
29979; 0.012
2356; 0.028
2332; 0.024
0.062; 1.10
0.65
Oberved Reflections; R1(F) 1915; 0.024
wR(F2) (all data); GoF(F2)
0.065; 1.04
0.53
Residual electron density
21

Page 22 of 38
Supporting Information
Figures for crystal structures of (L2H)CuCl2, (L2)Cu(OAc)·Cu(OAc)2 and 8. Full listings of
polymerization experiments. Crystal structure data (CIF).
Acknowledgements
Funding was supplied by the NSERC discovery program (RGPIN-2016-04953) and the Centre
for Green Chemistry and Catalysis (FQRNT). We thank Dr. Thierry Maris for support with
X-ray diffraction, Elena Nadezhina for elemental analysis, and Prof. D. Zargarian for access
to GC/MS.
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Figure 1. X-ray structures (from left to right) of 1, 3, 4 and 5. Thermal ellipsoids are drawn at the 50% probability
level. Hydrogen atoms and co-crystallized water (1, 3, 4) and the nitrate anion (3) omitted for clarity. The inset
shows the 1D coordination polymer (5)n (see also Fig. S5)
Figure 2. Crystal structures of 6 and 7. Thermal ellipsoids are shown at 50% probability. Hydrogen atoms omitted
for clarity.
Figure 3. UV/vis spectra of 1 - 7 in DMSO
Figure 4. Concentration-time profiles for CEL couplings of cyclohexylamine with phenylboronic acid, catalyzed by
1-6. Conditions: 1.0 M cyclohexylamine, 1.5 M PhB(OH)2, 2.5 mol% catalyst, MeOH, RT, air. Conversion was
calculated from absolute concentrations of product and starting material, obtained by calibrated GC-MS analyses
vs. internal standard. The solid lines are theoretical conversions using the pseudo-first-order rate constants
determined by linear regression of the semilogarithmic plot.
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Scheme 1

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Scheme 2

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Scheme 3

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Scheme 4