Diverse Functionalization of Ruthenium-Chelated 2-Picolylamines: Oxygenation, Dehydrogenation, Cyclization, and N-Dealkylation

Article abstract of DOI:10.1021/acs.inorgchem.9b03065

Chemical noninnocence of metal-coordinated 2-picolylamine (PA) derivatives has been introduced upon its reaction with the metal precursor [Ru^II(Cl)(H)(CO)(PPh₃)₃] under basic conditions. This in effect leads to the facile formation of metalated amide, imine, ring-cyclized pyrrole, and an N-dealkylated congener based on the fine-tuning of an amine nitrogen (N_amine) and a methylene center (C_α) at the PA backbone. It develops oxygenated L1′ in 1 and cyclized L4′ in 4 upon switching of the N_amine substituent of PA from aryl to an electrophilic pent-3-en-2-one moiety. On the other hand, imposing the substituent at the C_α position of PA modifies its reactivity profile, leading to a dehydrogenation (2/3) or N-dealkylation (6) process. The divergent reactivity profile of metalated PA is considered to proceed through a common dianionic intermediate. Further, a competitive scenario of C-H bond functionalization of coordinated PA versus the ligand-exchange process has been exemplified in the presence of external electrophile such as benzyl bromide or methylene iodide. Authentication of the product formation as well as elucidation of the reaction pathway has been addressed by their crystal structures and spectroscopic features in conjunction with the transition-state (TS) theory.

Full text of DOI:10.1021/acs.inorgchem.9b03065

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Diverse Functionalization of Ruthenium-Chelated 2‑Picolylamines:
Oxygenation, Dehydrogenation, Cyclization, and N‑Dealkylation
Sanjib Panda,* Arijit Singha Hazari, Manish Gogia, and Goutam Kumar Lahiri*
Department of Chemistry, Indian Institute of Technology (IIT) Bombay, Powai, Mumbai 400076, India
S
* Supporting Information
ABSTRACT: “Chemical noninnocence” of metal-coordinated 2-picolylamine (PA)
derivatives has been introduced upon its reaction with the metal precursor [RuII(Cl)-
(H)(CO)(PPh3)3] under basic conditions. This in effect leads to the facile formation of
metalated amide, imine, ring-cyclized pyrrole, and an N-dealkylated congener based on the
fine-tuning of an amine nitrogen (Namine) and a methylene center (Cα) at the PA
backbone. It develops oxygenated L1′ in 1 and cyclized L4′ in 4 upon switching of the
N
amine substituent of PA from aryl to an electrophilic pent-3-en-2-one moiety. On the other
hand, imposing the substituent at the Cα position of PA modifies its reactivity profile,
leading to a dehydrogenation (2/3) or N-dealkylation (6) process. The divergent reactivity
profile of metalated PA is considered to proceed through a common dianionic
intermediate. Further, a competitive scenario of C−H bond functionalization of
coordinated PA versus the ligand-exchange process has been exemplified in the presence
of external electrophile such as benzyl bromide or methylene iodide. Authentication of the
product formation as well as elucidation of the reaction pathway has been addressed by their crystal structures and
spectroscopic features in conjunction with the transition-state (TS) theory.
Scheme 1. Ruthenium-Chelation-Assisted Varying
Functionalization of PA
INTRODUCTION
■
a
Nitrogenous heterocycles, the skeletal moieties in numerous
biologically active species and natural products, have received
continuing research interest from the broader perspectives of
its utility in synthetic chemistry.1 Variegated strategies are
therefore employed in procuring such diversified products.
Among them, functionalization via the assistance of a metal ion
is considered to be one of the facile synthetic protocols to
introduce structural miscellany onto these substrate back-
bones.2 In this regard, diversification of 2-picolylamine (PA)-
derived molecular frameworks has gained profound attention
because these are the important scaffolds of many natural
products, synthetic drugs, and building blocks.3 Besides, they
have found widespread application in coordination chemistry
because of their enriched donor ability and robust nature.4
However, a few reports relating to the “non-spectator” feature
(oxygenation and oxidative dehydrogenation) of the coordi-
nated picolyl fragment in PA and its allied backbones are
accounted for under special circumstances,5 but the activation
of PA toward cyclization still remains elusive.
In this context, the present paper demonstrates poorly
explored multifarious reactivity strategies of ruthenium-
coordinated PA and its structural analogues under basic
conditions. It includes systematic alteration of the reactivity at
the methylene center (Cα) of PA as a function of metal
chelation as well as modulation of the substrate backbone
(Scheme 1). This, in turn, leads to (i) aerial oxygenation (CH2
→ CO) of N-aryl-substituted PA to amide, (ii) formation of
imine (−CH−NH → −CN) upon selective substitution at
Cα of PA, and (iii) ring-closing scenario by integrating an
a
E+ stands for an external electrophile.
electrophilic counterpart in its backbone, which, however,
results in N-dealkylation upon affixing alkyl/aryl substitution at
Cα. On the other hand, PA fails to react with the external
electrophiles (E+) and instead undergoes a ligand-exchange
process. Structural and mechanistic details along with
correlation of the reactivity have been authenticated by
spectroscopic and theoretical details.
RESULTS AND DISCUSSION
■
Synthetic, Structural, and Spectroscopic Aspects.
Complexes with the general formula [RuII(H/Cl)(L′)(CO)-
Received: October 19, 2019
© XXXX American Chemical Society
A
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(PPh3)2](ClO4)n (n = 0 for 1 and 4 and n = 1 for 2 and 3)
involving functionalized ligand moieties (L′ in Scheme 2) are
used to balance the charge of the complexes. However, the
same reaction in the absence of a base under a N2 atmosphere
fails to extend the desired dehydrogenation process, which, in
turn, suggests base-induced oxidative dehydrogenation in 2/3.6
Remarkably, complexation of the PA derivative with a suitably
placed electrophilic moiety in its backbone such as 4-[(pyridin-
2-ylmethyl)amino]pent-3-en-2-one (HL4) under similar re-
action conditions leads to intramolecular 5-exo-trig ring
cyclization to yield a pyridylpyrrole (L4′) derivative in
[RuII(H)(L4′)(CO)(PPh3)2] (4). The influence of π-accept-
ing CO/PPh3 facilitates stabilization of the RuII state in 1−4
(Scheme 2).
a
Scheme 2. Synthetic Outline for 1−6
Replacement of the electron-withdrawing pyridine ring of
PA in HL4 by the electron-donating thiophene ring in
[(thiophen-2-ylmethyl)amino]pent-3-en-2-one (HL5) yields
ruthenium-coordinated L5− in [RuII(H)(L5)(CO)(PPh3)2]
(5) instead of the otherwise expected five-membered metal-
laheterocycle as in 4 (Scheme 2). It indeed signifies the pivotal
role of the pyridinyl moiety and Lewis acidity of the transition
metal in the ring-closing process.
In contrast, the introduction of a bulkier “Ph” group at the
Cα position (HL6) inhibits the aforestated ring formation on
the [Ru(Cl)(H)(CO)(PPh3)3] platform (Scheme 2) because
of the improper orientation of the linking atoms to achieve the
optimal trajectory, as has also been revealed from its crystal
structure (Figure 1). It, however, affords metal acetylacetonate
(6) and phenyl(pyridin-2-yl)methanimine along with ill-
defined side products as a consequence of the N-dealkylation
process. A similar phenomenon has also been observed for the
analogous HL7 bearing methyl substitution at Cα. The
formation of a phenyl(pyridin-2-yl)methanimine or (pyridin-
2-yl)ethanimine byproduct during the reaction of [Ru(Cl)-
(H)(CO)(PPh3)3] and HL6 or HL7, respectively, is supported
by the respective gas chromatography (GC)−mass spectrom-
etry (MS) spectra.
The impact of an electron-poor {RuII(H)(CO)(PPh3)2}
metal fragment toward the ring cyclization process in 4 has
been further verified by considering an alternate metal
precursor, {RuII(pap)2}, encompassing strongly π-accepting
pap = 2-phenylazopyridine7 (Scheme 3). As anticipated, the
reaction proceeds through the same ring-closing process to
yield {RuII(pap)2}-chelated pyridylpyrrole (L4′) in 4A,
supported by its mass/NMR (Figures S1 and S12).
The ligands and complexes have been characterized by their
crystal structures, electrospray ionization mass spectrometry
(ESI-MS)/GC−MS, and spectroscopic (1H/13C/31P NMR,
UV−vis, and IR) signatures (Figure 1, Table 1, and Figures
S1−S16 and Tables S1−S7). N,N and O,O donors of the
functionalized PA (i.e., L′) form five- and six-membered
chelates with the metal ions in 1−4 and 6, respectively (Figure
1). The anionic N2 donor of L1′ (1) or L4′ (4) is in a trans
orientation with respect to the M−CO bond because of the
trans effect of CO. A comparison of the Ru1−C1(CO) and
C1−O1 bonds in 1 and 4 suggests a lesser synergistic back-
bonding effect [(dπ)RuII → (π*)CO; MCO ↔ MC
O] in the latter8 because of electron delocalization from the
pyrrolide moiety to the pyridyl backbone in L4′, as has also
been reflected in its remarkably shorter C6−C7 bond length
[1.411(8) Å]. Consequently, the amidate function of the
carboxamido ligand (L1′) in 1 is perturbed to some extent, as
supported by its partially biased C7O2 [1.26(1) Å] and
C7−N2 [1.35(1) Å] distances.9 In contrast, CO remains trans
to the pyridyl or isoquinolyl N1 in 2 or 3 incorporating two
a
NaClO4 is required only for the synthesis of 2 and 3.
obtained from the reactions of a 1:1 mixture of [RuII(Cl)(H)-
(CO)(PPh3)3] and the respective PA-derived ligand precursors
(HL) in refluxing tert-butyl alcohol (tBuOH) in the presence
t
of BuOK base under aerobic conditions. The use of N-
(pyridin-2-ylmethyl)aniline (HL1 in Scheme 2) results in
coordinated phenyl(picolinoyl)amide (L1′) in [RuII(H)(L1′)-
(CO)(PPh3)2] (1) via aerobic oxygenation at Cα in an
intermolecular fashion. Involvement of aerial oxygen in the
conversion sequence has been confirmed by an 18O2-isotope-
labeling experiment (Figure S2). In contrast, the reaction of
[RuII(Cl)(H)(CO)(PPh3)3] with Cα-substituted PA in phenyl-
(pyridin-2-yl)methanamine (HL2) and tetrahydro-1,1′-bis-
(isoquinoline) (HL3, a mimicked PA) leads to the
corresponding imine counterparts L2′ and L3′ in isolated
[RuII(Cl)(L2′)(CO)(PPh3)2]ClO4 (2) and [RuII(H)(L3′)-
(CO)(PPh3)2]ClO4 (3), respectively, where excess NaClO4 is
B
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Figure 1. ORTEP diagrams. H atoms (except the selective one), solvent molecules, and counteranions are omitted for clarity. Thermal ellipsoids
are at 40% probability.
NMR. Each complex molecule displays one 31P NMR signal
Scheme 3. Impact of the Ancillary Ligand on Cyclization
corresponding to two trans-positioned PPh3 groups and a
triplet pattern for Ru−H of 1, 3, and 4 in 31P NMR due to its
coupling with two PPh3 (ΣI = 1) groups.10
Effect of External Electrophiles. In order to understand
the role of external electrophiles, the reaction of HL1 and
[Ru(Cl)(H)(CO)(PPh3)3] is carried out in the presence of
t
benzyl bromide (an external electrophile) and BuOK base in
dry toluene under an inert atmosphere. It yields metal-
coordinated imine in [Ru(L1″)(Br)2(CO)PPh3] (1A) instead
of the insertion of an electrophile (−CH2Ph) at the Cα
position of PA (Figures 2a and S13). Excess benzyl bromide
in the reaction has possibly played the dual role of substrate
and oxidant. Moreover, the formation of 1A is associated with
the additional ligand-exchange processes, i.e., initial labilization
of bulky PPh3 by a bromide ion followed by the consequent
substitution of other anionic ligands. Further, the base-induced
rapid dehydrogenation process of PA under an inert
atmosphere did not allow intermolecular reaction between
the external electrophile and nucleophilic methylene center of
PA.
The analogous reaction of [Ru(Cl)(H)(CO)(PPh3)3] and
HL2 in the presence of methylene iodide in lieu of benzyl
bromide as an external electrophile results in 2 (imine product,
major) along with a metal-coordinated amine product in
[Ru(I)2(CO)(L2)(PPh3)2] (2A, minor; Figure 2b). The
decrease in the Lewis acidity of the metal ion in the presence
Table 1. Selected Crystallographic Bond Lengths (Å)
1
2
3
4
Ru1−C1
C1−O1
C7−N2
C6−C7
C6−N1
1.822(7)
1.185(9)
1.35(1)
1.51(1)
1.353(9)
1.86(1)
1.11(2)
1.29(1)
1.48(2)
1.39(1)
1.847(9)
1.16(1)
1.31(1)
1.48(1)
1.329(9)
1.860(5)
1.136(6)
1.373(8)
1.411(8)
1.379(6)
neutral N donors, respectively. This causes a lesser extent of
Ru1−C1 or C1−O1 bond perturbation. The appearance of a
new C7O2 bond in L1′ of 1 and the disappearance of the
CO bond of the β-ketoiminate (acnac) fragment in L4′ of 4
are attributed to functionalization of the picolyl (C7) center, as
has also been supported by their NMR resonances. On the
other hand, dehydrogenation of amine → imine in 2/3 is
evident from the shorter C7−N2 bond length in L2′/L3′ as
1
well as by the absence of the picolyl proton (Cα−H) in H
C
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extended additional stability to the system via conjugation of
Cα− (DA2) into the phenyl ring along with the pyridyl moiety.
Therefore, a common dianionic intermediate (DA),
generated via activation of the acidic methylene group of PA
upon coordination to electrophilic {Ru(H/Cl)(CO)(PPh3)2}
or {Ru(pap)2}, is considered to correlate the reactivity
patterns.11,5a The reactive Cα center of DA1 (no longer
“spectator”) reacts with the molecular oxygen in an
intermolecular fashion to yield 1. However, the presence of
an electrophilic substituent at DA4 facilitates the intra-
molecular reaction between the carbonyl center and reactive
Cα, leading to the formation of a cyclized product in 4. On the
contrary, substitution at Cα results in imine (2 or 3) via two-
electron oxidation of DA2/3. Similarly, the formation of imine
in 1A (Figure 2a) can be attributed to two-electron oxidation
of in situ generated DA1 (Figure 4) under anoxic conditions.
The apparently unfavorable formation of DA encompassing
two adjacent negative charges (Figure 4) could possibly be
stabilized to some extent by π-back-donation from RuII(t2g6) to
CO/PPh3 as well as via the delocalization of negative charge
into the pyridine moiety to form a dearomatized structure, as
depicted in Figure 4.8,12 Thus, the cooperative interplay of
metal chelation and suitable substituents in the PA frameworks
is decisive for the substrate activation processes. Further, in the
present scenario, PA with a suitably positioned electrophilic
function (as in HL4, Scheme 2) follows the faster intra-
molecular cyclization path (4 in Scheme 2) instead of the
intermolecular oxygenation route.
Figure 2. Reaction with external electrophiles. Reaction conditions:
(i) tBuOH/tBuOK, N2 atmosphere, 100 °C, 12 h. (a) Imine
formation under an inert atmosphere. ORTEP of 1A. Bond lengths
(Å): C7−N2 1.287(8); C6−C7, 1.459(8); C6−N1, 1.341(6). (b)
Ligand-exchange reaction. ORTEP of 2A. Bond lengths (Å): C7−N2,
1.499(7); C6−C7, 1.603(8); C6−N1, 1.336(5).
The proposed pathway in Figure 4 has further been
evaluated computationally by using the B3LYP/6-31G**/
LANL2DZ level of theory (Figures 5 and S17−S19 and Table
S8).13 The outline of the oxygenation process in Figure 4 is
derived primarily based on the earlier reports by de Bruin and
co-workers for the analogous system.5a,14 The first step for the
oxygenation process through the anionic pathway involves the
formation of a short-lived peroxide intermediate (I11a in Figure
5; O−O = 1.465 Å), which undergoes subsequent proton
shuttling (TS1a) followed by heterolytic cleavage of the O−O
bond to generate thermodynamically stable 1. The formation
of a peroxide intermediate has been considered to follow via
either (i) one-electron oxidation of DA1 ({RuII-L12−}−, S = 0)
of a weak-field iodide ligand possibly facilitates stabilization of
the metalated amine in 2A. The simultaneous formation of 2
and 2A rationalizes a competitive scenario, C−H activation
versus ligand-exchange phenomenon at the metal center in
inhibiting the desired functionalization.
Mechanistic Outline. To gain insights into the aforesaid
transformation processes, a controlled reaction involving HL2
with a phenyl substituent at its Cα and [Ru(Cl)(H)(CO)-
(PPh3)3] has been followed in refluxing dry toluene in the
t
presence of BuOK under anoxic conditions. The resultant
green solution, however, quickly changes to 2 (yellow) under
oxic conditions. The transformation of green to yellow (2) is
monitored spectrophotometrically in deaerated tetrahydrofur-
●
by molecular oxygen (3O2, S = 1) to produce DA1 ({RuII-
●−
L1●−}, S = 1/2) and O2
(S = 1/2), followed by their
1
intermolecular interaction, or (ii) interaction of DA1 (S = 0)
an (THF) at 313 K (Figure 3). H NMR of the in situ
with 1O2 (S = 0). The necessary change in the multiplicities for
generated green solution in benzene-d6 fails to display the
characteristic resonance of Cα−H around 3−5.5 ppm (Figure
S5f), possibly implying involvement of the dianionic
intermediate (DA, Figure 4) in the conversion sequence.11,5a
DA2 (Figure 4) was selectively chosen to follow because
phenyl substitution at the methine carbon of HL2 has
3
1
the activation of O2(3Σg−) to O2(1Δg) in pathway ii may be
assisted by its interaction with the complex under a strong
crystal field.15,16 The density functional theory (DFT)
calculations, however, prefer pathway i over pathway ii
[ΔE(path ii−path i) = ∼33 kcal mol−1]. Nevertheless, the
presence of K+ provides further stability to the system (Figure
S18). The selective interaction of a πg* singly occupied
molecular orbital of superoxide with the methine center of
●
DA1 in pathway i has also been supported by the L1-
●
dominated spin in DA1 (L1, 0.99; {Ru(H)(CO)(PPh3)2},
0.01; Figure S19).
The alternate radical pathway (Figure 4) involving the
interaction of in situ generated one-electron-oxidized DA1● (S
1
3
= /2) with ground-state O2 (diradical, S = 1) is also equally
probable.5a,14 This gives rise to the oxygenated L1′ in 1 via a
17
1
possible superoxide intermediate (S = /2). Electron release
and uptake processes are, however, balanced in the reaction
sequence.
Figure 3. Change in the spectral profile for DA → 2 in THF at 313 K.
D
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Figure 4. Proposed pathway for correlation of the reactivities. Charge on the amide nitrogen (N−) is not shown for clarity. a stands for the anionic
pathway, and r stands for the radical pathway.
at the final stage directs the formation of 4. Elongation of a
newly formed C−C bond in I14 (>1.6 Å) and a C−O distance
in I24 (1.493 Å) is a reflection of electronic consequence due
to molecular strain.19 Moreover, cyclization in the presence of
an acnac substituent in PA also reveals the ambiphilic feature
of acnac.20 Finally, the greater thermodynamic stability of the
products (ΔG highly negative) with respect to their metastable
dianionic counterpart favors the overall transformation
processes.
CONCLUSION
■
Although PA-derived ligands have widely been applied as
“spectator” ligands, the present paper highlights a diverse
reactivity profile (aerobic oxygenation, dehydrogenation, ring
formation, and N-dealkylation) of suitably designed PA
derivatives (i.e., their “chemical noninnocence”) on selective
Figure 5. Gibbs free energy (ΔG, 298 K) profile (not to scale) for the
formation of 1 (anionic pathway, red) and 4 (blue) at the B3LYP
level in 2-butanol.13 The associated ΔG/ΔH are shown in each state.
ΔG of the starting substrates is taken as zero. Only the core structures
are shown here.
ruthenium platforms. Correlation of the reactivity suggests that
simple tuning of the PA backbone at the amine nitrogen results
in its varying functionalization modes including intermolecular
(oxygenation) to intramolecular (cyclization) transformations.
On the other hand, insertion of an alkyl or aryl sustituent at the
Cα of PA inhibits the aforestated conversions and instead
facilitates the dehydrogenation or N-dealkylation process. The
present deliberation is therefore expected to introduce a new
avenue in the specific direction of metal-assisted C−H
functionalization to achieve biologically relevant heterocyclic
ring congeners via fine tuning of the ligand environment.
The reaction pathway for 4 includes a 5-exo-trig cyclization
between anionic Cα and electrophilic CO counterparts of
the acnac moiety. The approach of in situ generated Cα− to the
2
carbonyl moiety (SN path) at an angle of 112° (close to the
Burgi−Dunitz angle, TS4 in Figure 5) extends the optimum
trajectory for n(Cα ) → π*(CO) interaction.18 This leads to
−
EXPERIMENTAL SECTION
transient I14, which then rearranges to I24. The lowering in
energy of I24 may be a consequence of the negative charge
delocalization onto the pyridyl backbone. Elimination of KOH
■
Materials. The precursor complexes [Ru(Cl)(H)(CO)(PPh3)3]21
and ctc-[Ru(pap)2(EtOH)2]22 and the ligands HL1−HL423−26 were
E
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prepared by following the literature procedures. Newly designed
HL5−HL7 were synthesized by following a procedure similar to that
for HL4.26 Other chemicals and solvents were of reagent grade and
were used as received. For spectroscopic studies, HPLC-grade
solvents were used. 18O2 was procured from ICON Isotope.
Physical Measurements. The electrical conductivity was
checked using an autoranging conductivity meter (Toshcon
Industries, India). 1H/13C/DEPT-135/31P NMR spectra were
recorded on a Bruker Avance III 400 or 500 MHz spectrometer.
Elemental analyses were recorded on a Thermoquest (EA 1112)
microanalyzer or a Thermo Finnigan (FLASH EA 1112) instrument.
The ESI-MS was checked on a Bruker Maxis Impact (282001.00081)
spectrometer. GC−MS experiments were performed on an Agilent
5975C spectrometer. IR spectra of the complexes were recorded on a
Nicolet spectrophotometer. Electronic spectral studies were per-
formed on a PerkinElmer Lambda 1050 spectrophotometer.
Crystallography. X-ray diffraction data were collected using a
Rigaku Saturn-724+ CCD single-crystal X-ray diffractometer using a
Mo Kα or Cu Kα source. Data collection was evaluated by using the
Crystal Clear-SM Expert software. The data were collected by the
standard ω-scan technique. The structures were solved by direct
methods using SHELXS-97 and refined on F2 by full matrix least
squares with SHELXL-2014/2016/2018.27 All data were corrected for
Lorentz and polarization effects, and all non-H atoms were refined
anisotropically. The remaining H atoms were placed in geometrically
constrained positions and refined with isotropic temperature factors,
generally 1.2Ueq of their parent atoms. H atoms were included in the
refinement process as per the riding model. CCDC 1951286 (1),
1951287 (2), 1951288 (3), 1951290 (4), 1951289 (6), 1951291
(1A), 1951292 (2A), and 1951293 (HL6) contain the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Computational Studies. Full geometry optimization was
performed by using the DFT method at the B3LYP level.28 Except
ruthenium, all other elements were assigned the 6-31G** basis set.
The LANL2DZ basis set with an effective core potential was
employed for the Ru atom.29 All calculations were performed with the
Gaussian 09 program package.30 Calculated structures were visualized
with ChemCraft.31
Transition-state calculations were performed at the B3LYP level of
theory starting from infinitely separated substrates. Single imaginary
frequencies for the transition states (TSs) and real frequencies for the
local minima were obtained. The connectivity of each TS was
validated through a relaxed potential energy surface scan for the
corresponding reaction coordinate and found to be the highest-energy
point that connected the relevant reactant and product. The zero-
point vibrational energies and thermal corrections were obtained from
the harmonic frequency calculations at the B3LYP level of theory in 2-
butanol.
tone (2.7 mL, 27.1 mmol) were used. Yield: 5.6 g (78%). Single
crystals of HL6 were obtained from a 2:1 dichloromethane/methanol
1
solution. H NMR (400 MHz, CDCl3): δ 8.51 (d, J = 4.1 Hz, 1H),
7.52 (td, J = 7.7 and 1.6 Hz, 1H), 7.33 (d, J = 7.5 Hz, 2H), 7.24 (t, J =
7.7 Hz, 3H), 7.15 (t, J = 7.3 Hz, 1H), 7.07−7.01 (m, 1H), 5.79 (d, J =
7.9 Hz, 1H), 5.01 (s, 1H), 1.99 (s, 3H), 1.81 (s, 3H). 13C NMR (101
MHz, CDCl3): δ 195.63, 161.86, 160.29, 149.49, 141.22, 137.12,
128.95, 127.70, 126.77, 122.45, 121.12, 96.65, 62.99, 28.96, 19.41.
DEPT-135 (101 MHz, CDCl3): δ 149.49, 137.12, 128.95, 127.70,
126.77, 122.44, 121.12, 96.65, 62.99, 28.96, 19.40. HRMS
(C17H18N2O; {HL6 + H}+). Calcd: m/z 267.1492. Found: m/z
267.1477. IR: 1603 cm−1 [ν(CO)].
4-[[1-(Pyridin-2-yl)ethyl]amino]pent-3-en-2-one (HL7). 1-(Pyri-
din-2-yl)ethan-1-amine (5.0 mL, 41.0 mmol) and acetylacetone (4.2
mL, 41.0 mmol) were used. Yield: 7.2 g (86%). 1H NMR (500 MHz,
CDCl3): δ 11.19 (d, J = 6.7 Hz, 1H), 8.48 (dt, J = 1.5 and 4.5 Hz,
1H), 7.61 (td, J = 7.7 and 1.8 Hz, 1H), 7.22 (d, J = 7.9 Hz, 1H), 7.11
(ddd, J = 7.5, 4.9, and 1.1 Hz, 1H), 4.95 (s, 1H), 4.77−4.69 (m, 1H),
1.97 (s, 3H), 1.75 (s, 3H), 1.51 (s, 3H). 13C NMR (126 MHz,
CDCl3): δ 195.48, 162.90, 162.35, 149.20, 137.24, 122.22, 119.52,
96.03, 54.72, 28.88, 23.05, 19.16. DEPT-135 (126 MHz, CDCl3): δ
149.20, 137.24, 122.21, 119.52, 96.03, 54.72, 28.88, 23.05, 19.16.
HRMS (C12H16N2O; {HL7 + H}+). Calcd: m/z 205.1335. Found: m/
z 205.1344. IR: 1610 cm−1 [ν(CO)].
Preparation of the Complexes. Synthesis of 1−5. Complexes
1−5 were prepared by following a general synthetic route using the
respective preformed HL ligands. To the pale-pink solution of
[Ru(Cl)(H)(CO)(PPh3)3] in tBuOH in an oven-dried round bottom
flask was added a yellow solution of the respective HL in tBuOH and
tBuOK. The solution was refluxed under an aerial atmosphere for ∼4
h. The solution gradually turned to yellow with progression of the
reaction. Evaporation of the solvent under vacuum afforded a yellow
solid, which was subjected to chromatographic purification by using a
neutral alumina column and varying the mixture of dichloromethane/
petroleum ether as the eluent. Removal of the solvent under vacuum
resulted in complexes 1−5. An aqueous solution of excess NaClO4
was added to precipitate the cationic complexes 2 and 3.
[RuII(H)(L1′)(CO)(PPh3)2] (1). [Ru(Cl)(H)(CO)(PPh3)3] (150 mg,
t
t
0.158 mmol), HL1 (29 mg, 0.158 mmol), BuOH (20 mL), BuOK
(53 mg, 0.473 mmol). Yield: 118 mg (88%). Slow evaporation of its
dichloromethane solution gave yellow crystals of 1. MS (ESI+,
1
CH3CN; {1}+). Calcd: m/z 851.16. Found: m/z 851.18. H NMR
(500 MHz, CDCl3): δ 7.92 (d, J = 5.1 Hz, 1H), 7.73 (d, J = 7.8 Hz,
1H), 7.71−7.63 (m, 2H), 7.60−7.52 (m, 2H), 7.46 (td, J = 7.5 and
2.6 Hz, 3H), 7.44−7.33 (m, 11H), 7.22 (t, J = 7.3 Hz, 6H), 7.15 (t, J
= 7.3 Hz, 10H), 6.96−6.88 (m, 2H), 6.63−6.57 (m, 2H), −10.43 to
−10.66 (t, 1H). 13C NMR (126 MHz, CDCl3): δ 206.30, 166.00,
158.15, 153.46, 150.82, 133.72, 133.66, 133.60, 129.28, 128.03,
127.99, 127.94, 127.25, 127.08, 126.16, 125.46, 124.08, 121.47. 31P
NMR (162 MHz, CDCl3): δ 43.43. Anal. Calcd for C49H40N2O2P2Ru:
C, 69.09; H, 4.73; N, 3.29. Found: C, 69.37; H, 4.57; N, 3.34. IR
(KBr, cm−1): 1919 [ν(CO)], 1664 [ν(CO)PA]. Molar
conductivity (CH3CN): ΛM = 6 Ω−1 cm2 M−1. UV−vis [λ, nm (ε,
M−1 cm−1)]: 338 (5200), 233 (38200).
General Procedure for the Synthesis of HL5−HL7. Acetylacetone
was added dropwise to a methanolic solution of the respective amines,
and the mixture was stirred overnight under refluxing conditions to
obtain a yellow solution. It was washed with n-pentane and dried
under vacuum. Purification by column chromatography (using a
neutral alumina column with a varying ratio of the dichloromethane/
acetonitrile mixture) led to the resulting yellow oily liquid of the
corresponding HL.
[RuII(Cl)(L2′)(CO)(PPh3)2]ClO4 (2). [Ru(Cl)(H)(CO)(PPh3)3]
(150 mg, 0.158 mmol), HL2 (29 mg, 0.158 mmol), NaClO4(190
t
t
mg, 1.58 mmol, 10 equiv), BuOH (20 mL), and BuOK (53 mg,
0.473 mmol) were used. Yield: 116 mg (76%). Slow evaporation of its
dichloromethane solution gave reddish-yellow crystals of 2. MS (ESI+,
4-[(Thiophen-2-ylmethyl)amino]pent-3-en-2-one (HL5). Thio-
phen-2-ylmethanamine (5.0 mL, 48.7 mmol) and acetylacetone (5.0
mL, 48.7 mmol) were used. Yield: 8.5 g (90%). 1H NMR (500 MHz,
CDCl3): δ 11.07 (s, 1H), 7.18 (dd, 1H), 6.91 (s, 1H), 5.01 (s, 1H),
4.55 (d, J = 6.1 Hz, 2H), 1.99 (s, 3H), 1.93 (s, 3H). 13C NMR (126
MHz, CDCl3): δ 195.51, 162.43, 141.21, 127.02, 125.05, 124.91,
96.21, 41.89, 28.91, 18.75. DEPT-135 (126 MHz, CDCl3): δ 127.02,
125.05, 124.91, 96.21, 41.90, 28.91, 18.76. HRMS (C10H13NOS;
{HL5 + H}+). Calcd: m/z 196.0791. Found: m/z 196.0786. IR: 1647
cm−1 [ν(CO)].
1
CH3CN; {2 − ClO4}+). Calcd: m/z 871.13. Found: m/z 871.17. H
NMR (400 MHz, CD3CN): δ 10.91 (s, 1H), 7.91 (t, J = 7.8 Hz, 1H),
7.83 (d, J = 5.1 Hz, 1H), 7.59 (d, J = 7.7 Hz, 1H), 7.51 (t, J = 7.6 Hz,
2H), 7.43 (dd, J = 11.4 and 5.0 Hz, 8H), 7.39−7.25 (m, 24H), 7.05−
7.00 (m, 1H), 6.34 (d, J = 7.2 Hz, 2H). 13C NMR (101 MHz,
CD3CN): δ 203.89, 177.25, 151.72, 151.13, 138.87, 133.86, 133.80,
133.75, 132.61, 131.48, 130.85, 129.85, 129.74, 129.51, 129.28,
128.82, 128.77, 128.72, 128.65, 127.44, 117.37. 31P NMR (162 MHz,
CDCl3): δ 37.43. Anal. Calcd for C49H40N2O5P2Cl2Ru: C, 60.62; H,
4.15; N, 2.89. Found: C, 60.95; H, 4.13; N, 2.63. IR (KBr, cm−1):
1977 [ν(CO)]. Molar conductivity (CH3CN): ΛM = 102 Ω−1 cm2
4-[[Phenyl(pyridin-2-yl)methyl]amino]pent-3-en-2-one (HL6).
Phenyl(pyridin-2-yl)methanamine (5.0 g, 27.1 mmol) and acetylace-
F
DOI: 10.1021/acs.inorgchem.9b03065
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
M−1. UV−vis [λ, nm (ε, M−1 cm−1)]: 440 (800), 281 (10400), 238
(10600).
and AgClO4 (117 mg, 0.56 mmol) were taken in EtOH (50 mL) and
refluxed for 2 h. The precipitated AgCl was filtered off through a
sintered-glass Gooch crucible. The filtrate was treated with HL4 (54
[RuII(H)(L3′)(CO)(PPh3)2]ClO4 (3). [Ru(Cl)(H)(CO)(PPh3)3] (150
mg, 0.158 mmol), HL3 (41 mg, 0.158 mmol), NaClO4(190 mg, 1.58
mmol, 10 equiv), tBuOH (20 mL), and tBuOK (53 mg, 0.473 mmol)
were used. Yield: 132 mg (83%). Slow evaporation of its 2:1
dichloromethane/hexane solution gave crystals of 3. MS (ESI+,
t
mg, 0.28 mmol) and BuOK (83 mg, 0.74 mmol), and the mixture
was heated to reflux for 8 h under atmospheric conditions. The
solvent was removed under reduced pressure. The residue was
moistened with a few drops of CH3CN. A saturated aqueous solution
of NaClO4 was added to the above concentrated solution and allowed
to cool at 273 K overnight. The precipitate thus obtained was filtered,
washed with chilled water to remove excess NaClO4, and dried in
vacuo over P4O10. The product was purified using a neutral alumina
column with 1:5 petroleum ether/CH2Cl2 as the eluent. Yield: 132
mg (64%). MS (ESI+, CH3CN; {4A − ClO4}+). Calcd: m/z 639.16.
Found: m/z 639.18. 1H NMR (400 MHz, CDCl3): δ 8.52 (d, J = 7.9
Hz, 1H), 8.46 (d, J = 8.0 Hz, 1H), 8.20 (dd, J = 7.0 and 5.7 Hz, 2H),
8.13 (dd, J = 7.8 and 1.1 Hz, 1H), 7.79−7.68 (m, 3H), 7.56 (t, J = 7.2
Hz, 1H), 7.50 (d, J = 8.2 Hz, 1H), 7.43 (d, J = 7.4 Hz, 1H), 7.39 (t, J
= 6.7 Hz, 1H), 7.28−7.11 (m, 5H), 7.01 (d, J = 8.1 Hz, 2H), 6.98 (d,
J = 8.2 Hz, 2H), 6.64 (t, J = 7.1 Hz, 1H), 5.78 (s, 1H), 2.42 (s, 3H),
1.54 (s, 3H). 13C NMR (101 MHz, CDCl3): δ 165.61, 156.46, 153.74,
149.72, 149.36, 148.87, 144.44, 139.47, 138.38, 138.03, 133.73,
133.27, 132.71, 129.43, 128.99, 128.39, 127.89, 127.76, 126.49,
123.04, 122.98, 118.47, 118.12, 116.12, 15.58, 14.15. Anal. Calcd for
C33H29N8O4Cl1Ru: C, 53.69; H, 3.96; N, 15.18. Found: C, 53.82; H,
3.62; N, 14.92. IR (KBr, cm−1): 1214 [ν(ClO4)]. Molar conductivity
(CH3CN): ΛM = 106 Ω−1 cm2 M−1. UV−vis [λ, nm (ε, M−1 cm−1)]:
546 (5200), 331 (20600), 225(sh).
1
CH3CN; {3 − ClO4}+). Calcd: m/z 913.21. Found: m/z 913.17. H
NMR (400 MHz, CDCl3): δ 8.79 (d, J = 5.9 Hz, 1H), 8.0−6.5 (m,
39H), 4.49 (d, J = 16.0 Hz, 1H), 2.95 (t, J = 16.2 Hz, 1H), 2.65 (d, J
= 17.6 Hz, 1H), 2.41−2.25 (m, 1H), −10.67 (t, J = 20.2 Hz, 1H). 13C
NMR (101 MHz, CDCl3): δ 204.01, 166.55, 154.16, 153.78, 152.31,
146.25, 146.17, 145.91, 137.06, 136.51, 136.01, 133.23, 133.17,
132.11, 132.06, 131.94, 130.67, 130.50, 130.34, 128.68, 128.64,
128.46, 128.41, 127.85, 127.57, 125.59, 124.75, 116.91, 56.39, 27.28.
DEPT-135 (13C NMR; 101 MHz, CDCl3): δ 145.91, 133.17, 133.04,
132.12, 130.67, 130.50, 130.34, 128.64, 128.29, 127.85, 127.57,
127.20, 126.38, 126.10, 125.60, 124.75, 56.32, 27.27. 31P NMR (202
MHz, CDCl3): δ 43.70. IR (KBr, cm−1): 1972 [ν(CO)]. Anal.
Calcd for C55H45N2O5P2Cl1Ru: C, 65.25; H, 4.48; N, 2.77. Found: C,
65.57; H, 4.73; N, 2.47. Molar conductivity (CH3CN): ΛM = 94 Ω−1
cm2 M−1. UV−vis [λ, nm (ε, M−1 cm−1)]: 496 (4880), 388 (15820).
[RuII(H)(L4′)(CO)(PPh3)2] (4). [Ru(Cl)(H)(CO)(PPh3)3] (150 mg,
t
0.158 mmol), HL4 (30 mg, 0.158 mmol), BuOH (20 mL), and
tBuOK (53 mg, 0.473 mmol) were used. Yield: 120 mg (93%). Slow
evaporation of its 2:1 dichloromethane/hexane solution gave crystals
of 4. MS (ESI+, CH3CN; {4 + H}+). Calcd: m/z 827.19. Found: m/z
827.20. 1H NMR (500 MHz, CDCl3): δ 7.40−7.32 (m, 12H), 7.30−
7.25 (t, J = 7.3 Hz, 7H), 7.24−7.16 (t, J = 7.5 Hz, 15H), 5.85 (s, 1H),
2.31 (s, 3H), 1.60 (s, 3H), −10.52 to −10.65 (t, J = 20.8 Hz, 1H). 13C
NMR (101 MHz, CDCl3): δ 156.51, 152.07, 141.33, 134.12, 133.99,
133.93, 133.87, 133.71, 133.60, 128.87, 127.60, 127.56, 127.51,
124.13, 115.37, 114.22, 114.06, 16.92, 14.90. 31P NMR (162 MHz,
CDCl3): δ 44.85. Anal. Calcd for C48H42N2OP2Ru: C, 69.81; H, 5.13;
N, 3.39. Found: C, 69.32; H, 5.36; N, 3.52. IR (KBr, cm−1): 1913
[ν(CO)]. Molar conductivity (CH3CN): ΛM= 2 Ω−1 cm2 M−1.
UV−vis [λ, nm (ε, M−1 cm−1)]: 408(sh), 354 (14600), 231 (48000).
[RuII(H)(L5)(CO)(PPh3)2] (5). [Ru(Cl)(H)(CO)(PPh3)3] (150 mg,
Caution! Perchlorate salts are generally explosive and should be
handled with care.
Synthesis of [Ru(Br)2(L1″)(CO)(PPh3)] (1A). To a pale-pink
solution of [Ru(Cl)(H)(CO)(PPh3)3] (150 mg, 0.158 mmol) in
degassed toluene (20 mL) in an oven-dried Schlenk tube were added
under a N2 atmosphere HL1 (29 mg, 0.158 mmol), followed by
tBuOK (53 mg, 0.473 mmol) and benzyl bromide (95 μL, 0.80 mmol;
approximately 5 equiv with respect to the ligand). The solution was
refluxed under an inert atmosphere overnight. The solution gradually
turned yellow with progression of the reaction. Evaporation of the
solvent under vacuum afforded a yellow solid, which was subjected to
chromatographic purification by using a neutral alumina column and
1:1 dichloromethane/petroleum ether as the eluent. Removal of the
solvent under vacuum resulted in 1A. Yield: 81 mg (70%). Slow
evaporation of its 2:1 dichloromethane/hexane solution gave orange
crystals of 1A. MS (ESI+, CH3CN; {1A + H}+). Calcd: m/z 734.92.
Found: m/z 734.90. 1H NMR (500 MHz, DMSO-d6): δ 8.79 (d, 1H),
8.78 (s, 1H), 7.24−7.18 (m, 6H), 7.18−7.10 (m, 10H), 7.07−7.02
(m, 7H). 13C NMR (126 MHz, DMSO-d6): δ 169.31, 154.23, 152.37,
151.11, 138.96, 133.25, 133.18, 132.57, 132.18, 130.28, 129.35,
129.06, 128.76, 128.55, 128.47, 123.30. 31P NMR (162 MHz, DMSO-
d6): δ 48.71. Anal. Calcd for C31H25Br2N2OPRu: C, 50.77; H, 3.44;
N, 3.82. Found: C, 50.39; H, 3.29; N, 3.67. IR (KBr, cm−1): 1969
[ν(CO)]. Molar conductivity (CH3CN): ΛM = 4 Ω−1 cm2 M−1.
UV−vis [λ, nm (ε, M−1 cm−1)]: 495 (600), 310 (9400), 237 (18200).
Synthesis of [Ru(I)2(HL2)(CO)(PPh3)] (2A). To a pale-pink solution
of [Ru(Cl)(H)(CO)(PPh3)3] (150 mg, 0.158 mmol) in degassed
toluene (20 mL) was added under a N2 atmosphere in an oven-dried
Schlenk tube HL2 (29 mg, 0.158 mmol), followed by tBuOK (53 mg,
0.473 mmol) and CH2I2 (64 μL, 0.79 mmol, 5 equiv). The solution
was refluxed under an inert atmosphere overnight. The solution
gradually turned yellow with progression of the reaction. Evaporation
of the solvent under vacuum afforded a yellow solid, which was
subjected to chromatographic purification using a neutral alumina
column and 1:1 dichloromethane/petroleum ether as the eluent.
Removal of the solvent under vacuum resulted in complexes 2 (85
mg, 55%) and 2A (40 mg, 30%). Slow evaporation of its 2:1
dichloromethane/hexane solution gave yellow crystals of 2A. MS
(ESI+, CH3CN; {2A + H}+). Calcd: m/z 829.89. Found: m/z 829.94.
1H NMR (500 MHz, CDCl3): δ 9.28 (d, J = 4.9 Hz, 1H), 7.98−7.79
(m, 6H), 7.51 (t, J = 7.6 Hz, 1H), 7.34 (dd, J = 20.9 and 6.4 Hz,
13H), 7.21 (d, J = 3.3 Hz, 2H), 6.57 (d, J = 7.9 Hz, 1H), 5.58 (t, 1H),
3.63 (t, J = 10.5 Hz, 1H), 2.48 (dd, 1H). 13C NMR (126 MHz,
t
0.158 mmol), HL5 (31 mg, 0.158 mmol), BuOH (20 mL), and
tBuOK (53 mg, 0.473 mmol) were used. Yield: 13 mg (10%). The
poor yield and unstable feature of 5 (possibly due to a weakly
coordinating thiophenyl S donor) kept us from performing a detailed
characterization except MS identification. MS (ESI+, CH3CN; {5 −
Cl}+). Calcd: m/z 848.18. Found: m/z 848.17.
Synthesis of [Ru(acac)(Cl)(CO)(PPh3)2] (6; acac = Acetylaceto-
nate). To a pale-pink solution of [Ru(Cl)(H)(CO)(PPh3)3] (150
t
mg, 0.158 mmol) in BuOH (20 mL) in an oven-dried clean round-
bottom flask were added a yellow solution of HL6 (42 mg, 0.158
t
t
mmol) or HL7 (32 mg, 0.158 mmol) in BuOH and BuOK (53 mg,
0.473 mmol). The solution was refluxed under an aerial atmosphere
for ∼4 h. The solution gradually turned to yellow with progression of
the reaction. Evaporation of the solvent under vacuum afforded a
yellow solid, which was subjected to chromatographic purification by
using a neutral alumina column and 1:3 dichloromethane/petroleum
ether as the eluent. Removal of the solvent under vacuum resulted in
complex 6. Yield: ∼70 mg (∼55%). Slow evaporation of its 3:1
dichloromethane/methanol solution gave colorless crystals of 6. MS
1
(ESI+, CH3CN; {6}+). Calcd: m/z 789.11. Found: m/z 789.15. H
NMR (400 MHz, CDCl3): δ 7.79 (t, J = 6.2 Hz, 3H), 7.73−7.63 (m,
21H), 7.44−7.28 (m, 10H), 1.63 (s, 3H). 13C NMR (101 MHz,
CDCl3): δ 193.93, 155.08, 148.59, 137.12, 136.29, 134.67, 134.61,
134.39, 133.90, 133.65, 132.97, 131.01, 129.59, 128.75, 128.49,
128.29, 128.20, 127.90, 126.24, 124.65, 94.53, 29.72, 27.15. 31P NMR
(162 MHz, CDCl3): δ 50.94. Anal. Calcd for C42H37ClO3P2Ru: C,
64.00; H, 4.73. Found: C, 63.83; H, 4.93. IR (KBr, cm−1): 1937
[ν(CO)], 1589 [ν(CO)acac]. Molar conductivity (CH3CN): ΛM
= 6 Ω−1 cm2 M−1. UV−vis [λ, nm (ε, M−1 cm−1)]: 313 (6600), 241
(20000).
Synthesis of [Ru(L4′)(pap)2]ClO4 (4A; pap = 2-Phenylazopyr-
idine). The starting complex ctc-[Ru(pap)2Cl2] (150 mg, 0.28 mmol)
G
DOI: 10.1021/acs.inorgchem.9b03065
Inorg. Chem. XXXX, XXX, XXX−XXX

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CDCl3): δ 206.38, 163.71, 153.57, 140.31, 137.10, 135.27, 134.88,
133.86, 133.79, 129.90, 129.89, 129.68, 129.14, 128.31, 128.23,
128.15, 124.37, 124.35, 124.11, 124.09, 64.90. DEPT-135 (13C NMR;
126 MHz, CDCl3): δ 153.57, 137.10, 133.86, 133.79, 129.91, 129.89,
129.69, 129.14, 128.31, 128.23, 128.15, 124.37, 124.35, 124.11,
124.09, 64.90, 64.88. 31P NMR (202 MHz, CDCl3): δ 54.17. Anal.
Calcd for C31H27N2O1P1I2Ru: C, 44.89; H, 3.28; N, 3.38. Found: C,
44.76; H, 3.25; N, 3.14. IR (KBr, cm−1): 1942 [ν(CO)]. Molar
conductivity (CH3CN): ΛM = 6 Ω−1 cm2 M−1. UV−vis [λ, nm (ε,
M−1 cm−1)]: 351 (3600), 307 (17600), 241 (21200).
Isonitriles as Radical Acceptors. Chem. Soc. Rev. 2015, 44, 3505−
3521. (b) Ray, R.; Chandra, S.; Yadav, V.; Mondal, P.; Maiti, D.;
Lahiri, G. K. Ligand Controlled Switchable Selectivity in Ruthenium
Catalyzed Aerobic Oxidation of Primary Amines. Chem. Commun.
2017, 53, 4006−4009. (c) Kim, S.; Ginsbach, J. W.; Lee, J. Y.;
Peterson, R. L.; Liu, J. J.; Siegler, M. A.; Sarjeant, A. A.; Solomon, E.
I.; Karlin, K. D. Amine Oxidative N-Dealkylation via Cupric
Hydroperoxide Cu-OOH Homolytic Cleavage Followed by Site-
Specific Fenton Chemistry. J. Am. Chem. Soc. 2015, 137, 2867−2874.
(3) (a) Engin, M. S.; Demir, S.; Direkel, S.; Eymur, S.; Cay, S.;
Generation of Dianion (DA). To a pale-pink solution of
[Ru(Cl)(H)(CO)(PPh3)3] (150 mg, 0.158 mmol) in degassed
toluene (20 mL) in an oven-dried Schlenk tube was added under a
Guder, A. Synthesis, Characterization, Biological Activity, and DFT-
̈
Reactivity Assessment of Mn(II), Co(II), and Cu(II) Complexes of a
New N2O Tridentate Schiff Base. Russ. J. Gen. Chem. 2016, 86, 2855−
2861. (b) Xue, L.; Wang, H.-H.; Wang, X.-J.; Jiang, H. Modulating
Affinities of Di-2-picolylamine (DPA)-Substituted Quinoline Sensors
for Zinc Ions by Varying Pendant Ligands. Inorg. Chem. 2008, 47,
4310−4318.
t
N2 atmosphere HL2 (29 mg, 0.158 mmol), followed by BuOK (53
mg, 0.473 mmol). The solution was refluxed under an inert
atmosphere for 4 h. The solution gradually turned green with
progression of the reaction. Evaporation of the solvent under an inert
atmosphere led to a green solid. This was further subjected to UV−vis
(4) (a) Mirica, L. M.; Ottenwaelder, X.; Stack, T. D. P. Structure and
Spectroscopy of Copper-Dioxygen Complexes. Chem. Rev. 2004, 104,
1013−104. (b) Peterson, R. L.; Himes, R. A.; Kotani, H.; Suenobu,
T.; Tian, L.; Siegler, M. A.; Solomon, E. I.; Fukuzumi, S.; Karlin, K. D.
Cupric Superoxo-Mediated Intermolecular C-H Activation Chem-
istry. J. Am. Chem. Soc. 2011, 133, 1702−1705. (c) Lewis, E. A.;
Tolman, W. B. Reactivity of Dioxygen-Copper Systems. Chem. Rev.
2004, 104, 1047−1076.
1
(in degassed THF) and H NMR (benzene-d6) studies.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.9b03065.
■
S
MS spectra, crystal structures, NMR, GC−MS, crystallo-
graphic bond parameters, DFT-optimized structures,
Gibbs free energy plot, and Cartesian coordinates (PDF)
́
(5) (a) Tejel, C.; del Rıo, M. P.; Ciriano, M. A.; Reijerse, E. J.; Hartl,
F.; Zalis, S.; Hetterscheid, D. G. H.; Tsichlis i Spithas, N.; de Bruin, B.
Ligand-Centred Reactivity of Bis(picolyl)amine Iridium: Sequential
Deprotonation, Oxidation and Oxygenation of a “Non-Innocent”
Ligand. Chem. - Eur. J. 2009, 15, 11878−11889. (b) Padhi, S. K.;
Manivannan, V. Cu(NO3)2·3H2O-Mediated Synthesis of 4′-(2-
Pyridyl)-2,2′:6′,2″-terpyridine (L2) from N-(2-Pyridylmethyl)-
pyridine-2-methylketimine (L1). A C-C Bond-Forming Reaction
and the Structure of {[Cu(L2)(OH)(NO3)][Cu(L2)(NO3)2]}·2H2O.
Inorg. Chem. 2006, 45, 7994−7996. (c) Gomez, J.; Garcıa-Herbosa,
G.; Cuevas, J. V.; Arnaiz, A.; Carbayo, A.; Munoz, A.; Falvello, L.;
Fanwick, P. E. Diastereospecific and Diastereoselective Syntheses of
Ruthenium(II) Complexes Using N,N′ Bidentate Ligands Aryl-
pyridin-2-ylmethyl-amine ArNH-CH2-2-C5H4N and Their Oxidation
to Imine Ligands. Inorg. Chem. 2006, 45, 2483−2493. (d) Rowland, J.
M.; Olmstead, M. M.; Mascharak, P. K. Unusual Reactivity of
Methylene Group Adjacent to Pyridine-2-Carboxamido Moiety in
Iron(III) and Cobalt(III) Complexes. Inorg. Chem. 2002, 41, 2754−
2760. (e) Klappa, J. J.; Rich, A. E.; McNeill, K. One-Step Synthesis of
3,5-Disubstituted-2-pyridylpyrroles from the Condensation of 1,3-
Diones and 2-(Aminomethyl)pyridine. Org. Lett. 2002, 4, 435−437.
(f) Anjana, S.; Donring, S.; Sanjib, P.; Varghese, B.; Murthy, N. N.
Controlling the Oxidation of Bis-tridentate Cobalt(II) Complexes
having Bis(2-pyridylalkyl)amines: Ligand vs. Metal Oxidation. Dalton
Trans. 2017, 46, 10830−10836.
Accession Codes
CCDC 1951286−1951293 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
*Email: sanjibp@iitb.ac.in (S.P.).
*Email: lahiri@chem.iitb.ac.in (G.K.L.).
■
ORCID
Goutam Kumar Lahiri: 0000-0002-0199-6132
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support received from the Science and Engineering
Research Board (SERB, DST), J. C. Bose Fellowship (to
G.K.L., SERB), CSIR (fellowship to S.P.), and UGC
(fellowship to A.S.H.), New Delhi, India, is gratefully
acknowledged. We are thankful to Prof. G. Rajaraman, Raju
Saravanan, and Dipanjan Mandal (Department of Chemistry,
IIT Bombay) for their help. We also gratefully acknowledge
the valuable suggestions extended by the reviewers. Dedicated
to Professor Sourav Pal, IISER-Kolkata on the occasion of his
65th birthday.
(6) Campbell, A. N.; Stahl, S. S. Overcoming the “Oxidant
Problem”: Strategies to Use O2 as the Oxidant in Organometallic
C−H Oxidation Reactions Catalyzed by Pd (and Cu). Acc. Chem. Res.
2012, 45, 851−863.
(7) (a) Mandal, A.; Schwederski, B.; Fiedler, J.; Kaim, W.; Lahiri, G.
K. Evidence for Bidirectional Noninnocent Behavior of a Formazanate
Ligand in Ruthenium Complexes. Inorg. Chem. 2015, 54, 8126−8135.
(b) Panda, S.; Bera, S.; Lahiri, G. K. Electronic Impact of Ancillary
Ligand on the Oxygenation Profile of Ruthenium Coordinated β-
Diketiminate. Polyhedron 2019, 172, 45−57. (c) Panda, S.; Ansari, M.
A.; Mandal, A.; Lahiri, G. K. Near-IR Absorbing Ruthenium
Complexes of Non-Innocent 6,12-Di(pyridin-2-yl)indolo[3,2-b]-
carbazole: Variation as a Function of Co-Ligands. Chem. - Asian J.
2019, 14, 4631.
REFERENCES
■
(1) (a) Karlin, K. D. Model Offers Intermediate Insight. Nature
2010, 463, 168−169. (b) Gibson, S.; McGuire, R.; Rees, D. C.
Principal Components Describing Biological Activities and Molecular
Diversity of Heterocyclic Aromatic Ring Fragments. J. Med. Chem.
1996, 39, 4065−4072.
(8) (a) Rusanova, J.; Rusanov, E.; Gorelsky, S. I.; Christendat, D.;
Popescu, R.; Farah, A. A.; Beaulac, R.; Reber, C.; Lever, A. B. P. The
Very Covalent Diammino(o-benzoquinonediimine)
Dichlororuthenium(II). An Example of Very Strong π-Back Donation.
Inorg. Chem. 2006, 45, 6246−6262. (b) Rigo, M.; Hettmanczyk, L.;
(2) (a) Zhang, B.; Studer, A. Recent Advances in the Synthesis of
Nitrogen Heterocycles via Radical Cascade Reactions Using
H
DOI: 10.1021/acs.inorgchem.9b03065
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Heutz, F. J. L.; Hohloch, S.; Lutz, M.; Sarkar, B.; Mu
̈
ller, C.
477, 308−311. (c) Gunbas, G.; Hafezi, N.; Sheppard, W. L.;
Olmstead, M. M.; Stoyanova, I. V.; Tham, F. S.; Meyer, M. P.; Mascal,
M. Extreme oxatriquinanes and a record C−O bond length. Nat.
Chem. 2012, 4, 1018−1023.
Phosphinines versus Mesoionic Carbenes: A Comparison of
Structurally Related Ligands in Au(I)-Catalysis. Dalton Trans. 2017,
46, 86−95.
(20) Bera, S. K.; Panda, S.; Dey Baksi, S.; Lahiri, G. K. Diverse
Modes of Functionalisation of Ruthenium Coordinated β-Ketoimi-
nate Analogues. Dalton Trans. 2018, 47, 15897−15906.
(9) Nag, S.; Butcher, R. J.; Bhattacharya, S. N-(Aryl)picolinamide
Complexes of Ruthenium: Usual Coordination and Strategic
Cyclometalation. Eur. J. Inorg. Chem. 2007, 2007, 1251−1260.
(10) (a) Małecki, J. G.; Maron, A. A Ruthenium(II) Hydride
Carbonyl Complex with 4-Phenylpyrimidine as Co-ligand. Transition
Met. Chem. 2012, 37, 727−734. (b) Ghosh, P.; Panda, S.; Banerjee, S.;
Lahiri, G. K. Ruthenium-Hydride Mediated Unsymmetrical Cleavage
of Benzofuroxan to 2-Nitroanilido with Varying Coordination Mode.
Inorg. Chem. 2017, 56, 10735−10747. (c) Kundu, S.; Dutta, D.;
(21) Ahmad, N.; Levison, J. J.; Robinson, S. D.; Uttley, M. F.;
Wonchoba, E. R.; Parshall, G. W. Complexes of Ruthenium, Osmium,
Rhodium, and Iridium Containing Hydride Carbonyl, or Nitrosyl
Ligands. Inorg. Synth. 2007, 15, 45−64.
(22) Goswami, S.; Chakravarty, A. R.; Chakravorty, A. Chemistry of
Ruthenium. 2. Synthesis, Structure, and Redox Properties of 2-
(Arylazo)pyridine Complexes. Inorg. Chem. 1981, 20, 2246−2250.
(23) Wang, Y.; Liu, H.; Zhang, X.; Zhang, Z.; Huang, D.
Experimental and Mechanistic Insights into Copper(II)−dioxygen
Catalyzed Oxidative N-Dealkylation of N-(2-Pyridylmethyl) phenyl-
amine and Its Derivatives. Org. Biomol. Chem. 2017, 15, 9164−9168.
Maity, S.; Weyhermuller, T.; Ghosh, P. Proton-Coupled Oxidation of
̈
a Diarylamine: Amido and Aminyl Radical Complexes of Ruthenium-
(II). Inorg. Chem. 2018, 57, 11948−11960.
(11) (a) Tejel, C.; Ciriano, M. A.; del Rio, M. P.; Hetterscheid, D.
G. H.; Tsichlis i Spithas, N.; Smits, J. M. M.; de Bruin, B. Ligand
Oxidation of a Deprotonated Bis(picolyl)amine IrI(cod) Complex.
̈
(24) Olbert, D.; Gorls, H.; Conrad, D.; Westerhausen, M.
Coordination Behavior of the Diphenylphosphanyl)[α-(2-pyridyl)-
benzyl]amide Anion toward Lithium and Zinc Cations. Eur. J. Inorg.
Chem. 2010, 2010, 1791−1797.
̈
Chem. - Eur. J. 2008, 14, 10932−10936. (b) Olbert, D.; Gorls, H.;
Conrad, D.; Westerhausen, M. Coordination Behavior of the
(Diphenylphosphanyl)[α-(2-pyridyl)benzyl]amide Anion toward
Lithium and Zinc Cations. Eur. J. Inorg. Chem. 2010, 2010, 1791−
1797.
(25) Qi, G.; Ji, Y. Q.; Judeh, Z. M. A. Novel Chiral C1-1′,2′,3′,4′-
Tetrahydro-1,10-bisisoquinolines: Synthesis, Resolution, and Appli-
cations in Catalytic Enantioselective Reactions. Tetrahedron 2010, 66,
4195−4205.
(12) Kotani, H.; Sugiyama, T.; Ishizuka, T.; Shiota, Y.; Yoshizawa,
K.; Kojima, T. Redox-Noninnocent Behavior of Tris(2-
pyridylmethyl)amine Bound to a Lewis Acidic Rh(III) Ion Induced
by C-H Deprotonation. J. Am. Chem. Soc. 2015, 137, 11222−11225.
(13) For the sake of simplicity in calculation, the energy of K+ has
been deducted at the product formation step instead of considering its
involvement in each step. Further, because of the comparable
dielectric constants of tert-butyl alcohol and 2-butanol, a computa-
tional study has been performed in a 2-butanol medium.
(14) (a) Tejel, C.; Ciriano, M. A.; del Rio, M. P.; van den Bruele, F.
J.; Hetterscheid, D. G. H.; Tsichlis i Spithas, N.; de Bruin, B.
Deprotonation Induced Ligand-to-Metal Electron Transfer: Synthesis
of a Mixed-Valence Rh(-I,I) Dinuclear Compound and Its Reaction
with Dioxygen. J. Am. Chem. Soc. 2008, 130, 5844−5845. (b) Panda,
S.; Bera, S. K.; Goel, P.; Dutta, A. K.; Lahiri, G. K. Ruthenium-
Chelated Non-Innocent Bis(heterocyclo)methanides: A Mimicked β-
Diketiminate. Inorg. Chem. 2019, 58, 11458−11469.
(15) (a) Mikheikin, I. D.; Vorontsova, I. K.; Abronin, I. A. Reactivity
of Molecular Oxygen on the Surface of Ionic Crystals. Int. J. Quantum
Chem. 2002, 88, 489−495. (b) Moro-Oka, Y. Reactivities of Active
Oxygen Species and Their Roles in the Catalytic Oxidation of Inactive
Hydrocarbon. Catal. Today 1998, 45, 3−12.
(16) (a) Tang, J.; Gao, X. J.; Tang, H.; Zeng, X. Dioxygen Activation
with Stable N-Heterocyclic Carbenes. Chem. Commun. 2019, 55,
1584−1587. (b) Reddy, A. R.; Bendikov, M. Diels-Alder Reaction of
Acenes with Singlet and Triplet Oxygen-Theoretical Study of Two-
State Reactivity. Chem. Commun. 2006, 1179−1181. (c) Panda, S.;
Mandal, A.; Ghosh, P.; Lahiri, G. K. Ru-Complex Framework toward
Aerobic Oxidative Transformations of β-Diketiminate and α-
Ketodiimine. Inorg. Chem. 2017, 56, 14900−14911.
(17) Ginsbach, J. W.; Peterson, R. L.; Cowley, R. E.; Karlin, K. D.;
Solomon, E. I. Correlation of the Electronic and Geometric Structures
in Mononuclear Copper(II) Superoxide Complexes. Inorg. Chem.
2013, 52, 12872−12874.
(18) (a) Baldwin, J. E. Rules for ring closure. J. Chem. Soc., Chem.
Commun. 1976, 734−736. (b) Alabugin, I. V.; Gilmore, K.;
Manoharan, M. Rules for Anionic and Radical Ring Closure of
Alkynes. J. Am. Chem. Soc. 2011, 133, 12608−12623.
(19) (a) Ishigaki, Y.; Shimajiri, T.; Takeda, T.; Katoono, R.; Suzuki,
T. Longest C-C Single Bondamong Neutral Hydrocarbonswith a
Bond Length beyond 1.8 Å. CHEM 2018, 4, 795−806. (b) Schreiner,
P. R.; Chernish, L. V.; Gunchenko, P. A.; Tikhonchuk, E. Yu.;
Hausmann, H.; Serafin, M.; Schlecht, S.; Dahl, J. E. P.; Carlson, R. M.
K.; Fokin, A. A. Overcoming Lability of Extremely Long Alkane
Carbon-Carbon Bonds Through Dispersion Forces. Nature 2011,
(26) Lake, B. R. M.; Shaver, M. P. Iron(II) β-Ketiminate Complexes
as Mediators of Controlled Radical Polymerization. Dalton Trans.
2016, 45, 15840−15849.
(27) (a) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, A64, 112−122. (b) Sheldrick, G. M. Program for Crystal
Structure Solution and Refinement; University of Goettingen:
Goettingen, Germany, 1997. (c) Sheldrick, G. M. Crystal structure
refinement with SHELXL. Acta Crystallogr., Sect. C: Struct. Chem.
2015, 71, 3−8.
(28) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-
Salvetti Correlation-Energy Formula into a Functional of the Electron
Density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−
789.
(29) (a) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss,
H. Energy-adjusted ab initio Pseudo Potentials for the Second and
Third row Transition Elements. Theor. Chim. Acta 1990, 77, 123.
(b) Fuentealba, P.; Preuss, H.; Stoll, H.; von Szentpaly, L. Proper
Account of Core-Polarization with Pseudopotentials: Single Valence-
Electron Alkali Compounds. Chem. Phys. Lett. 1982, 89, 418.
(30) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, T.; Vreven, T.;
Montgomery, J. A., Jr; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi,
R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar,
S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox,
J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austrin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A.
̈
D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.
Gaussian 09, revision A.02; Gaussian, Inc.: Wallingford, CT, 2009.
(31) Zhurko, D. A.; Zhurko, G. A. ChemCraft 1.5; Plimus: San
Diego, CA. Available at http://www.chemcraftprog.com.
I
DOI: 10.1021/acs.inorgchem.9b03065
Inorg. Chem. XXXX, XXX, XXX−XXX