IPr# - highly hindered, broadly applicable N-heterocyclic carbenes

Article abstract of DOI:10.1039/d1sc02619d

IPr (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) represents the most important NHC (NHC = N-heterocyclic carbene) ligand throughout the field of homogeneous catalysis. Herein, we report the synthesis, catalytic activity, and full structural and electronic characterization of novel, sterically-bulky, easily-accessible NHC ligands based on the hash peralkylation concept, including IPr#, Np# and BIAN-IPr#. The new ligands have been commercialized in collaboration with Millipore Sigma: IPr#HCl, 915653; Np#HCl; 915912; BIAN-IPr#HCl, 916420, enabling broad access of the academic and industrial researchers to new ligands for reaction optimization and screening. In particular, the synthesis of IPr# hinges upon cost-effective, modular alkylation of aniline, an industrial chemical that is available in bulk. The generality of this approach in ligand design is demonstrated through facile synthesis of BIAN-IPr# and Np#, two ligands that differ in steric properties and N-wingtip arrangement. The broad activity in various cross-coupling reactions in an array of N-C, O-C, C-Cl, C-Br, C-S and C-H bond cross-couplings is demonstrated. The evaluation of steric, electron-donating and π-accepting properties as well as coordination chemistry to Au(i), Rh(i) and Pd(ii) is presented. Given the tremendous importance of NHC ligands in homogenous catalysis, we expect that this new class of NHCs will find rapid and widespread application.

Full text of DOI:10.1039/d1sc02619d

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IPr# – highly hindered, broadly applicable N-
heterocyclic carbenes†
Cite this: Chem. Sci., 2021, 12, 10583
a
Qun Zhao,‡a Guangrong Meng,‡a Guangchen Li,‡a Carol Flach,
All publication charges for this article
have been paid for by the Royal Society
of Chemistry
Richard Mendelsohn,a Roger Lalancette,a Roman Szostak b and Michal Szostak
a
*
IPr (IPr ¼ 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) represents the most important NHC (NHC ¼ N-
heterocyclic carbene) ligand throughout the field of homogeneous catalysis. Herein, we report the
synthesis, catalytic activity, and full structural and electronic characterization of novel, sterically-bulky,
easily-accessible NHC ligands based on the hash peralkylation concept, including IPr#, Np# and BIAN-
IPr#. The new ligands have been commercialized in collaboration with Millipore Sigma: IPr#HCl, 915653;
Np#HCl; 915912; BIAN-IPr#HCl, 916420, enabling broad access of the academic and industrial
researchers to new ligands for reaction optimization and screening. In particular, the synthesis of IPr#
hinges upon cost-effective, modular alkylation of aniline, an industrial chemical that is available in bulk.
The generality of this approach in ligand design is demonstrated through facile synthesis of BIAN-IPr#
and Np#, two ligands that differ in steric properties and N-wingtip arrangement. The broad activity in
various cross-coupling reactions in an array of N–C, O–C, C–Cl, C–Br, C–S and C–H bond cross-
couplings is demonstrated. The evaluation of steric, electron-donating and p-accepting properties as
well as coordination chemistry to Au(I), Rh(I) and Pd(II) is presented. Given the tremendous importance of
NHC ligands in homogenous catalysis, we expect that this new class of NHCs will find rapid and
widespread application.
Received 12th May 2021
Accepted 28th June 2021
DOI: 10.1039/d1sc02619d
rsc.li/chemical-science
severely limited by challenges in controlling the alkylation
selectivity, and the most common industrial route exploits
lengthy and inexible route through phenol alkylation.8
Taking inspiration from elegant studies in NHC design by
Nolan,9 Glorius,10 Bertrand,11 Marko12 and others13 (Fig. 1), as
Introduction
N-Heterocyclic carbenes (NHCs) have emerged as tremendously
valuable ligands in homogeneous catalysis.1,2 The broad appli-
cation of NHC ligands is a consequence of strong s-donation of
the carbene center3 and variable steric bulk of wingtip groups4
that are oen not easily attainable using other classes of
ligands, including phosphines. Furthermore, through exploit-
ing the exible steric bulk of the wingtips, NHC ligands allow
for kinetic stabilization of metals and intermediates at unusual
oxidation states,5 while their well-dened topology has found
widespread application in ne-tuning of reactivity at the metal
center.6
In this context, by far the most important NHC ligand in the
eld of homogeneous catalysis is bulky IPr (Fig. 1, 1) reported by
Nolan and Arduengo in 1999.1,2 While its synthesis from Dipp
(Dipp ¼ 2,6-diisopropylaniline) is facile,7 the problem lies in the
preparation of Dipp precursor. The preparation of Dipp is
aDepartment of Chemistry, Rutgers University, 73 Warren Street, Newark, NJ 07102,
USA. E-mail: michal.szostak@rutgers.edu
bDepartment of Chemistry, Wroclaw University, F. Joliot-Curie 14, Wroclaw 50-383,
Poland
Fig. 1 State-of-the-art of sterically-demanding N-heterocyclic car-
benes in catalysis. Note that IPr-hash ligands are commercially avail-
able from Millipore Sigma (IPr#HCl, 915653; Np#HCl; 915912; BIAN-
IPr#HCl, 916420).
† Electronic supplementary information (ESI) available: Experimental details and
computational data. CCDC 2077050 and 2077053. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/d1sc02619d
‡ These authors contributed equally.
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well as following our interest in NHC catalysis14 and the paraformaldehyde (1.1 equiv.) to TMSCl (1.1 equiv.) in EtOAc at
synthesis of N-containing molecules,15 we sought to expand the 70 ꢀC (25 g, 40 mmol scale).18 We found that this procedure
concept of sterically-hindered, easily accessible NHC ligands. allows for much milder cyclization to 5 than the HCl/ZnCl2
We considered that a bulky version of IPr, wherein the amine is combination,12 which again proved problematic for large-scale
prepared directly via modular alkylation of aniline, an indus- runs and was riddled with retro-Friedel–Cras products. The
trial chemical that is available in bulk16 in a cost-effective TMSCl procedure could be conveniently followed by color
manner should be accessible. Further, we hoped to demon- change from yellow to light grey, indicating completion of the
strate the generality of this approach through facile synthesis of reaction.
NHC analogues with varying steric and electronic properties of
Crucially, the entire sequence 6 / 5 is highly practical: (1)
the NHC topology as well as generality of the ligand design in the three steps do not require purication of the intermediates,
cross-couplings by numerous bond breaking events.
(2) the nal product is obtained aer facile work-up (ltration),
(3) the procedure uses industrial chemicals available in bulk, (4)
the sequence is routinely performed within two days.
Results and discussion
With multigram access to IPr# secured, we next compre-
hensively evaluated steric and electronic properties of this novel
NHC ligand. As shown in Scheme 2, the gold complex [Au(IPr#)
Cl] (9) was prepared using the general method,19 while Rh(I)
complexes, [Rh(IPr#)(CO)2Cl] (10) and [Rh(IPr#)(acac)CO] (11)
were prepared aer generating the free carbene in situ by
deprotonation of IPr#HCl with a slight excess of either KHMDS
or KOtBu. The Rh(I) complex (10) could be prepared either
directly by using rhodium dicarbonyl chloro dimer [{Rh(CO)2(m-
Cl)}2] (path b) or in a mild two-step procedure via [Rh(IPr#)(cod)
Cl]20 and the reaction with carbon monoxide (path c). We have
also generated the selenium adduct [Se(IPr#)] (12) by adding the
free carbene generated in situ to excess of selenium.21 The Pd(II)
complex [Pd(IPr#)(cin)Cl] (13) was prepared by generating the
free carbene in situ and coordinating to the palladium cinnamyl
dimer [{Pd(cin)(m-Cl)}2].22 Importantly, all complexes were
found to be stable to air and moisture. Complexes 9 and 13 were
fully characterized by X-ray crystallography (Fig. 2 and 3, vide
infra).23
The synthesis of IPr# (Scheme 1, 5) was selected as our starting
point. It should be noted that the direct three-fold peralkylation
of aniline is signicantly more challenging than the alkylation
of para-blocked toluidine as a consequence of N-/C-alkyl
migration.17 Aer experimentation, we were pleased to nd
that 2,4,6-tribenzhydrylaniline 7 could be prepared in 79% yield
(93 g, 200 mmol scale) by adding HCl (1.0 equiv.) to a solution of
aniline (1.0 equiv.ꢀ), diphenylmethanol (3.5 equiv.) and ZnCl2
(0.5 equiv.) at 160 C.
Routinely, 70–75% yields were obtained on 10–20 mmol
scale. This represents a signicant improvement over the
previous Friedel–Cras method involving addition of a mixture
of ZnCl2 and HCl at 160 ꢀC,12 which led to irreproducible results.
We note that alkylation of aniline at para position occurs last;
the N-alkylation products were not observed. The synthesis of
diimine 8 was smoothly effected by reacting glyoxal (1.0 equiv.)
with amine 7 (2.0 equiv.) and MgSO4 (2.5 equiv.) (70 g,
160 mmol scale). We found that the reaction was slower than in
the synthesis of IPr*,12 suggesting more pronounced steric
character. The optimum results were obtained by monitoring
Extensive studies by Cavallo et al. demonstrated the %
buried volume (%Vbur) and steric maps of model [Au(NHC)Cl]
complexes as the best indication of quantifying the steric
impact of NHC ligands.4,24 In our case, [Au(IPr#)Cl] is linear (C–
1
the reaction progress by H NMR, and driving the reaction to
completion by slightly elevating the temperature (40 ꢀC) or
adding slight excess of glyoxal, if needed. The diimine was
formed as exclusively the s-trans isomer. The cyclization step
occurred smoothly upon exposing the diimine (1.0 equiv.) and
ꢀ
ꢀ
Au–Cl, 180.0 ; C–Au, 1.972 A), making it a good model for
evaluating %Vbur. Thus, with the (%Vbur) of 54.4%, [Au(IPr#)Cl]
represents one of the bulkiest NHC ligands prepared to date
Scheme 2 Synthesis of IPr# complexes. Conditions: (a) AuCl$Me2S
(1.0 equiv.), K2CO3 (6.0 equiv.), acetone, 60 ꢀC, 2 h, 90%. (b) KHMDS
(1.8 equiv.), [Rh(CO)2Cl]2 (0.5 equiv.), toluene, 23 ꢀC, 15 h, 88%. (c)
Scheme 1 Synthesis of IPr# and the Diimine Precursors. Conditions: [Rh(cod)Cl]2 (0.5 equiv.), K2CO3 (2.0 equiv.), acetone, 60 ꢀC, 8 h, 71%,
(a) 6 (1.0 equiv.), Ph2CHOH (3.5 equiv.), ZnCl2 (0.5 equiv.), HCl (36%, aq, then CO, CH2Cl2, 23 ꢀC, 15 h, 90%. (d) KOtBu (2.0 equiv.),
1.0 equiv.), 160 ꢀC. (b) 7 (1.0 equiv.), (CHO)2 (40%, aq, 0.5 equiv.), [Rh(acac)(CO)2] (1.0 equiv.), THF, 23 ꢀC, 15 h, 93%. (e) Se (3.0 equiv.),
MgSO4 (2.5 equiv.), 23 ꢀC. (c) 8 (1.0 equiv.), (CH2O)n (1.1 equiv.), TMSCl NaHMDS (1.2 equiv.), THF, ꢁ78 to 23 ꢀC, 15 h, 95%. (f) KOtBu (1.1 equiv.),
(1.1 equiv.), EtOH, 70 ꢀC.
[Pd(cin)Cl]2 (0.45 equiv.), THF, 23 ꢀC, 15 h, 89%.
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Fig. 2 X-ray crystal structure of complex 9. Two views: front (top);
side (bottom). Hydrogen atoms have been omitted for clarity. Selected
ꢀ
ꢀ
bond lengths [A] and angles [ ]: Au–C1, 1.972; Au–Cl, 2.2768; C1–N1,
1.356; C3–N1, 1.442(2); C1–Au–Cl, 180.0; N1–C1–N1, 104.9; C3–N1–
C1, 122.7; N1–C1–Au, 127.5. Note the symmetry across the Cl–Au–C1
axis in 9. CCDC 2077050.†
Fig. 3 X-ray crystal structure of complex 13. Two views: front (top);
side (bottom). Hydrogen atoms have been omitted for clarity. Selected
ꢀ
ꢀ
bond lengths [A] and angles [ ]: Pd–C1, 2.044(4); Pd–Cl, 2.374(1); Pd–
C49, 2.121(4); Pd–C50, 2.130(6); Pd–C51, 2.210(7); C1–N1, 1.364(5);
C1–N2, 1.368(4); C4–N1, 1.452(4); C58–N2, 1.440(5); C1–Pd–C49,
103.2(2); C1–Pd–C50, 138.5(2); C1–Pd–C51, 169.4(2); C49–Pd–C51,
67.0(2); C1–Pd–Cl, 93.7(1); N1–C1–N2, 103.3(3); C4–N1–C1, 124.9(3);
C58–N2–C1, 124.7(3). CCDC 2077053.†
(Table 1).1,2,4 This value compares well with the (%Vbur) of 50.4%
ꢀ
19
ꢀ
determined for [Au(IPr*)Cl] (C–Au–Cl, 178.3 ; C–Au, 1.987 A),
indicating a subtle but important effect of the para-diphe-
nylmethyl substitution on the steric properties of the ligand.
A graphical representation of the steric mapping of the metal
center in [Au(IPr#)Cl] is shown in Fig. 4A (vide infra).
The Tolman electronic parameter (TEP) allows to evaluate
electronic properties of NHC ligands.3 Thus, the CO stretching
frequencies of [Rh(IPr#)(CO)2Cl] are nsym ¼ 2079.5 cmꢁ1 and
nasym ¼ 1999.5 cmꢁ1 (CH2Cl2, 0.20 M),25 respectively, which
corresponds to a TEP of 2051.8 cmꢁ1 as a combined measure of
the electronic properties of the ligand. These values match well
with the IPr ligand (TEP of 2051.5 cmꢁ1), IPr* (TEP of
2052.7 cmꢁ1) and CAACCy (TEP of 2048.6 cmꢁ1) and indicate
one of the most donating 5-membered NHCs prepared to date.
Likewise, the use of selenourea adducts permits to evaluate
The synthesis of [Rh(IPr#)(acac)CO] demonstrates that the
extremely bulky IPr# is able to accommodate asymmetrical, k2-
O,O-bound ligands like acac to the metal center. Presumably,
this leads to steric adjustment of the ligand topology to t the
Rh coordination plane.
This property is conrmed through the synthesis and full
crystallographic characterization of [Pd(IPr#)(cin)Cl] (Fig. 3).
Following the earlier reports,9,13a Pd(II) allyl-type complex (13)
was selected as a model well-dened, air- and moisture-stable
Pd(II)–NHC precatalyst to evaluate the performance of IPr# in
cross-coupling reactions. The X-ray crystallographic analysis
revealed the (%Vbur) of 44.7% with 63.7%, 29.9%, 58.2%, 26.9%
77
p-backbonding from the Se NMR spectra.21 The dSe value of
108.11 ppm for [Se(IPr#)] (CDCl3) suggests that the expanded
substitution leads to slightly higher p-accepting properties than
IPr (dSe ¼ 90 ppm), and IPr* (dSe ¼ 106 ppm) and much lower
than CAACMe2 (dSe ¼ 492 ppm), as expected from the C-
substitution.
Table 1 Summary of steric and electronic parameters
d(77Se)
Furthermore, one-bond CH J coupling constants obtained
1
from 13C satellites of the H NMR spectrum26 provide good
NHC
%Vbur [Au]
TEP [cmꢁ1
]
[ppm]
1JCH [Hz]
indication of s-donating properties of an NHC ligand. The value
of 224.50 Hz for IPr#HCl (CDCl3) is consistent with this ligand
being as strongly s-donating as IPr (1JCH ¼ 223.70 Hz), but at the
same time signicantly more sterically-demanding and exible.
The chemical shi of the iminium proton in IPr#HCl was found
at 12.6 ppm (CDCl3), which is signicantly downeld compared
with other imidazolium salts.27
IPr#
IPr
54.4
45.4
50.4
51.0a
2051.8
2051.5
2052.7
2048.6
108
90
224.50
223.70
224.99
188.53
IPr*
106
CAACCy
492b
a
b
Menthyl instead of cyclohexyl. Me2 instead of cyclohexyl.
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Fig. 4 Topographical steric maps of [Au(IPr#)Cl] (9) and [Pd(IPr#)(cin)
Cl] (13) showing %Vbur per quadrant.
for each quadrant (Fig. 4B). The values can be compared with
the (%Vbur) of 54.4% for the linear [Au(IPr#)Cl] with 65.9%,
43.0%, 65.9%, 43.0% for each quadrant (Fig. 4A). Thus, the IPr#
ligand is capable of both (1) adjusting the steric environment,
and (2) asymmetrical twisting around the metal center, which
furnishes important in catalysis differentiated quadrant distri-
bution arising from the very bulky yet exible ligand topology.
ꢀ
The C–Pd, Pd–Cl, and Pd–C(Ph) bond lengths of 2.044 A, 2.374
ꢀ
ꢀ
A, and 2.210 A in 13 are in the range for Pd(II)-allyl type
ꢀ
ꢀ
complexes ([Pd(IPr)(cin)Cl], C–Pd, 2.027 A; Pd–Cl, 2.357 A; Pd–
ꢀ
C(Ph), 2.245 A).
It is further worth noting that diphenylmethyl substituents
of the IPr# wingtips extend beyond the metal center in both 9
and 13, which might inuence both (1) substrate approach, and
(2) coordination of active intermediates formed during the
catalysis. We hypothesize that the addition of a para-substituent
has steric effect due to proximity to the metal center, while two
additional effects are increase of donation and inhibition of N-
wingtip rotation around the N–Ar axis.
The activity of IPr# was evaluated in various palladium-
catalyzed cross-couplings (Scheme 3). As stated above,
[Pd(IPr#)(cin)Cl] was selected due to the success of well-dened
Pd(II)–NHCs supported by allyl-type throw-away ligands and the
potential to tune the catalyst activity by allyl modications.9,13a
The results outlined in Scheme 3 indicate very high degree of
generality of IPr#. As such, amide N–C(O) Suzuki cross-coupling
(entry 1),14 ester C–O amidation (entry 2),28 amide N–C(O)
transamidation (entry 3),29 C–Cl Suzuki cross-coupling (entry
4),30 C–Cl Buchwald–Hartwig amination (entry 5),31 C–Br Fer-
inga coupling using both aryl- (entry 6)32 and challenging
alkyllithium possessing b-hydrogens (entry 7),33 C–Cl ketone a-
arylation (entry 8),34 C–S sulfur metathesis (entry 9)35 and C–H
activation (entry 10)36 all proceeded in good to excellent yields.
More importantly, these results demonstrate that the IPr#
ligand is effective in an array of N–C, O–C, C–Cl, C–Br, C–S and
C–H bond cross-couplings with various organometallics (B, Li,
enolate, amine, sulde) across some of the most broadly
employed cross-couplings in industrial and academic setting-
s.1,2,6a–c In view of its general reactivity across numerous bonds,
IPr# might offer a signicant potential for catalytic reaction
development.
Scheme 3 Activity of [Pd(IPr#)(cin)Cl] 13 in cross-coupling reactions.
See ESI† for details.
selected the synthesis of BIAN-IPr# (14) and Np# (15) as two
representative examples to showcase the synthetic potential of
the “hash” NHC modular framework. Thus, BIAN (BIAN ¼
Generality and two further applications of the IPr# ligand
design peralkylation concept are presented in Scheme 4. We
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Fig. 5 HOMO and LUMO energy levels (eV) calculated at B3LYP 6-
311++g(d,p). See ESI† for details.
Scheme 4 Generalization of IPr# NHCs: (a) BIAN-IPr# and (b) Np#.
bis(imino)acenaphthalene) ligands have emerged as powerful
ligands in catalysis because of the structural rigidity of C–H
bonds bringing the wingtip substituents closer to the metal
center as well as redox-active properties, and strong s-donating
character of the carbene center.37 With the access to 2,4,6-tri-
benzhydrylaniline 7 in hand, the synthesis of BIAN-IPr# (14)
proceeded uneventfully readily furnishing 1.5 gram of 14 using
acenaphthoquinone (16) as the NHC precursor (see ESI†).
In the similar vein, the C2-symmetric imidazolin-2-ylidenes
bearing substituted naphthyl N-wingtips reported by Dorta
have emerged as the most active NHC ancillary ligands in Pd-
catalyzed cross-coupling and Ru-metathesis;38 however, the
synthesis of 2,7-substituted naphthyl wingtips has been a major
limitation. Applying the concept described herein, the synthesis
of Np# (15) exploiting the facile synthesis of 2,4,7-
tribenzhydrylnaphthalen-1-amine (17) by Friedel–Cras alkyl-
ation proceeded uneventfully and furnished 2.5 g of this
sterically-differentiated NHC ligand (see ESI†). Thus, the use of
“hash” concept permits a modular, rapid and cost-effective
ligand assembly that might be applicable to both (1) various
carbene classes (cf. BIAN-IPr#), and (2) diverse amines (cf. Np#).
It is further worth noting that BIAN-IPr# is the rst member of
the intriguing family of BIAN ligands2m that has been
commercialized (collaboration with Millipore Sigma, no.
916420, BIAN-IPr#HCl).39,40 Further applications of this concept
are underway in our laboratory.
To further assess the effect of substitution on electronic
properties of 5, HOMO and LUMO energy levels of IPr# and
other NHCs were determined at the B3LYP 6-311++g(d,p) level
(Table 2, Fig. 5 and ESI†).5a–c,11 Computation of HOMO and
LUMO provides the most accurate estimation of nucleophilicity
(more s-donating, higher HOMO) and electrophilicity (more p-
accepting, lower LUMO) of NHCs, however, the values for
comparison must be available at the same level of theory.
The HOMO of IPr# (ꢁ6.16 eV) is comparable with IPr (ꢁ6.01
eV), which is a routine model for s-donating NHCs. The more
hindered acenaphthene ring of BIAN-IPr# results in a similar
strongly nucleophilic (s-donating) (HOMOꢁ1, in-plane s-
orbital, ꢁ6.16 eV), and electrophilic (p-accepting) (LUMO+1 due
to required symmetry, ꢁ0.95 eV) ligand. Replacement of the N-
phenyl ring with N-naphthyl results in a C2-symmetric Np#
ligand similar to classic NHCs (HOMO+2, in-plane s-orbital,
ꢁ6.15 eV), with similar electrophilicity (LUMOꢁ2 due to
required symmetry, ꢁ0.97 eV). Thus, it is evident that the strong
s-donation in combination with the differentiated steric impact
renders the class of IPr# ligands well-suited for homogeneous
catalysis.
Conclusions
In summary, we have developed a new class of extremely
sterically-bulky, easily prepared NHC ligands by peralkylation
concept. The parent ligand, IPr#, is readily accessible in three
simple synthetic steps, exploiting the cost-effective, modular
peralkylation of aniline, an industrial chemical that is available
in bulk. Evaluation of structural and electronic properties has
provided insight into the steric impact, s-donation and p-
accepting properties. The parent IPr# is one of the largest yet
exible NHC ligands developed to date, while at the same time
one of the strongest s-donors. Crucially, the potential to utilize
the IPr# ligand in various Pd-catalyzed cross-coupling reactions
by numerous bond breaking events has been demonstrated.
The facile preparation of sterically-differentiated analogues
BIAN-IPr# and Np# has been described, and highlights the
capacity of this peralkylation design platform. The modularity
of this approach makes is attractive for future development of
Table 2 HOMO and LUMO energy levels (eV) of IPr# calculated at the
B3LYP 6-311++g(d,p) levela
NHC
HOMO [eV]
LUMO [eV]
IPr#
BIAN-IPr#
Np#
IPr*
IPr
ꢁ6.16
ꢁ6.16
ꢁ6.15b
ꢁ6.12
ꢁ6.01
ꢁ5.90
ꢁ0.96
ꢁ0.95
ꢁ0.97b
ꢁ0.90
ꢁ0.48
ꢁ0.33
IMes
a
b
See ESI for details.
rac-Np# (C2-symmetric), meso-Np# (CS-
symmetric), ꢁ6.13 eV and ꢁ0.94 eV. rac-Np# is more stable than meso-
Np# by 0.56 kcal molꢁ1 calculated at the B3LYP 6-311++g(d,p) level.
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NHC ligands. Given the tremendous importance of NHC
ligands and the commercial availability of the developed
ligands Millipore Sigma (IPr#HCl, 915653; Np#HCl; 915912;
BIAN-IPr#HCl, 916420), we expect that this new class of NHCs
will nd rapid and widespread application.39,40
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Data availability
The datasets supporting this article have been uploaded as part
of the supplementary material. Crystallographic data for 9 and
13 have been deposited at the CCDC under 2077050 and
2077053 and can be obtained from https://www.ccdc.cam.ac.uk/
structures/.
Author contributions
Q. Z., G. M., G. L. and M. S. conceived the work. Q. Z., G. M., G.
Z. performed the synthetic and characterization experiments
and analyzed the data. C. F. and R. M. contributed to the IR
studies. R. L. performed crystallographic studies. R. S. per-
formed computational studies. M. S. supervised the project and
wrote the manuscript.
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The authors declare the following competing nancial inter-
est(s): Rutgers University has led patent(s) on ligands and
precatalysts described in this manuscript (US 62/958565, Jan 8,
2020).
5 (a) D. Martin, M. Melaimi, M. Soleilhavoup and G. Bertrand,
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Acknowledgements
We gratefully acknowledge Rutgers University (MS), the NIH
(1R35GM133326, MS), the NSF (CAREER CHE-1650766, MS) and
the ACS PRF (DNI-55549) for generous nancial support. The
Bruker 500 MHz spectrometer used in this study was supported
by the NSF-MRI grant (CHE-1229030). Additional support was
provided by the Rutgers Graduate School in the form of Dean's
Dissertation Fellowship (GM). Supplement funding for this
project was provided by the Rutgers University Newark Chan-
cellor's Research Office. We thank the Wroclaw Center for
Networking and Supercomputing (grant number WCSS159).
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© 2021 The Author(s). Published by the Royal Society of Chemistry
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