Phenanthridine-Containing Pincer-like Amido Complexes of Nickel, Palladium, and Platinum

Article abstract of DOI:10.1021/acs.inorgchem.7b00075

Proligands based on bis(8-quinolinyl)amine (L1) were prepared containing one (L2) and two (L3) benzo-fused N-heterocyclic phenanthridinyl (3,4-benzoquinolinyl) units. Taken as a series, L1-L3 provides a ligand template for exploring systematic π-extension

Full text of DOI:10.1021/acs.inorgchem.7b00075

Article
pubs.acs.org/IC
Phenanthridine-Containing Pincer-like Amido Complexes of Nickel,
Palladium, and Platinum
Pavan Mandapati, Patrick K. Giesbrecht, Rebecca L. Davis, and David E. Herbert*
Department of Chemistry and the Manitoba Institute for Materials, University of Manitoba, 144 Dysart Rd, Winnipeg, MB R3T 2N2,
Canada
S
* Supporting Information
ABSTRACT: Proligands based on bis(8-quinolinyl)amine (L1) were
prepared containing one (L2) and two (L3) benzo-fused N-
heterocyclic phenanthridinyl (3,4-benzoquinolinyl) units. Taken as a
series, L1−L3 provides a ligand template for exploring systematic π-
extension in the context of tridentate pincer-like amido complexes of
group 10 metals (1-M, 2-M, and 3-M; M = Ni, Pd, Pt). Inclusion of
phenanthridinyl units was enabled by development of a cross-coupling/
condensation route to 6-unsubstituted, 4-substituted phenanthridines
(4-Br, 4-NO2, 4-NH2) suitable for elaboration into the target ligand
frameworks. Complexes 1-M, 2-M, and 3-M are redox-active;
electrochemistry and UV−vis absorption spectroscopy were used to
investigate the impact of π-extension on the electronic properties of the
metal complexes. Unlike what is typically observed for benzannulated ligand−metal complexes, extending the π-system in metal
complexes 1-M to 2-M to 3-M led to only a moderate red shift in the relative highest occupied molecular orbital (HOMO)−
lowest unoccupied molecular orbital (LUMO) gap as estimated by electrochemistry and similarly subtle changes to the onset of
the lowest-energy absorption observed by UV−vis spectroscopy. Time-dependent density functional theory calculations revealed
that benzannulation significantly impacts the atomic contributions to the LUMO and LUMO+1 orbitals, altering the orbital
contributions to the lowest-energy transition but leaving the energy of this transition essentially unchanged.
and as a cocatalyst in hydrogenation reactions.9 To our
knowledge, only a handful of multidentate ligands that bring
INTRODUCTION
■
Extending the π-system of conjugated ligands is widely used to
phenanthridinyl units into the coordination sphere of metals
tune electronic transitions in transition metal1 and main-group2
are known. Emissive tris(4-phenanthridinolato)lithium and
complexes without significantly altering the parent ligand
framework. This can provide important flexibility in the design
of new emissive molecules and photosensitizers, as photo-
aluminum complexes have been used in electroluminescent
devices.10 (R)- and (S)-6-(2′-diphenylphosphino-l′-naphthyl)-
phenanthridines were applied as atropisomeric ligands in Pd-
physical properties can be adjusted without wholesale changes
catalyzed allylic alkylations.11 fac-Binding, tridentate bis-
to the core molecular shape. Furthermore, as exemplified by a
(phenanthridinylmethyl)amines bound to Re(I) carbonyls
published series of (BPI)PtCl (BPI = bis(2-pyridylimino)-
isoindolate) complexes, red or blue shifts are both possible with
have been used for live-cell fluorescence imaging.12 Chelate-
assisted C−H activation of substituted 6-arylphenanthridines
increasing π-extension. The direction of the shift was
has been used to generate luminescent C,N-cyclometalated
rationalized by establishing how the site of benzannulation
phenanthridine-containing platinum(II)13 and deep-red-emit-
impacts the energies of the frontier orbitals (HOMO/
ting iridium(III) complexes.14 We have reported the prepara-
tion of (4-diphenylphosphino)phenanthridine analogs of (8-
diphenylphosphino)quinolines that can be used to form
luminescent Cu and Zn coordination compounds.15
LUMO).1d
In this context, tridentate pincer-type ligands containing
benzannulated aromatic N-heterocycles offer the potential to
form robust complexes bearing an electronically accessible
extended π-system.3 The benzannulated aromatic N-hetero-
cycle phenanthridine (3,4-benzoquinoline) is much less well-
known as a ligand than its more symmetric isomer acridine
(2,3-benzoquinoline),4 the readily cyclometalated benzo[h]-
quinoline (7,8-benzoquinoline)5 and quinoline itself (2,3-
benzopyridine). This is despite phenanthridine’s utility in
fluorescent DNA intercalators such as ethidium bromide6 and
related emissive organic materials,7 in platin drug candidates
(phenathriplatin: cis-[Pt(NH3)2(phenanthridine)Cl]NO3),8
In this work, we present a synthetic route to tridentate
phenanthridine-containing ligand frameworks based on bis(8-
quinolinyl)amine (L1; Figure 1).16 Once deprotonated, these
compounds (L2, L3) are capable of binding as monoanionic
{NNN}− amido ligands,17 and therefore present an opportunity
to investigate the coordination chemistry of phenanthridine-
Received: January 16, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b00075
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 1. Proligands bis(8-quinolinyl)amine (L1), (4-
methylphenanthridinyl)(8-quinolinyl)amine (L2), bis(4-
methylphenanthridinyl)amine (L3), and group 10 metal complexes
(1-M, 2-M, and 3-M; M = Ni, Pd, Pt) discussed in this work.
Figure 2. (a) One-pot Pd-catalyzed coupling/condensation route to 4-
substituted phenanthridines (4-Br/4-NO2); (b) reduction of 4-NO2
to 4-NH2; (c) synthesis of π-extended pincer-type proligand L2 and
metal complexes 2-M; (d) synthesis of L3 and metal complexes 3-M
(LnMCl2 = NiCl2(H2O)6, (1,5-COD)PdCl2 or (1,5-COD)PtCl2).
containing “pincer-type” ligands with divalent group 10 metal
ions. The resultant complexes allowed us to evaluate the impact
of sequential quinoline-to-phenanthridine π-extension on their
electronic properties, which we reasoned would be substantial
given that benzannulation site-dependent red shifts of 10 nm
and blue shifts of nearly 50 nm of the lowest energy absorption
were observed in related series of π-extended ligand−metal
complexes.1d Contrary to our initial hypothesis, while
significant shifts are observed in the absorption spectra of L1,
L2, and L3, the impact of π-system extension proved to be
much more subtle in the group 10 metal complexes 1-M, 2-M,
3-M (M = Ni, Pd, Pt).
conditions [150 °C, 72 h; 5 mol % Pd(OAc)2, (1,1′-
diphenylphosphino)ferrocene (dppf); sodium-tert-pentoxide]
gave high isolated yields (>90%) of both the asymmetric (2-
methylphenanthridinyl)(8-quinolinyl)amine (L2; Figure 2c),
and the symmetric bis(2-methylphenanthridinyl)amine (L3;
Figure 2d).
Both L2 and L3 show spectroscopic features diagnostic of
phenanthridine groups (Table 1). The downfield shift of the 1H
and 13C NMR resonances attributed to the [CH] unit in the 6-
position adjacent to the nitrogen in the phenanthridinyl ring
system is consistent with a dominant “imine-bridged, biphenyl”
resonance contributor, which maximizes the number of
aromatic subunits in accordance with Clar’s postulate.20
Accordingly, the solid-state X-ray structures of L2 and L3
show one short CN distance in each phenanthridine unit
[L2: N(1)−C(1) 1.298(2); L3: N(1)−C(1) 1.305(4), N(3)−
C(15) 1.307(3) Å; Figure 3].
RESULTS AND DISCUSSION
■
Bis(8-quinolinyl)amine (L1) provides two equivalent con-
ceptual sites for π-extension to phenanthridinyl analogues
(Figure 1). We decided to adapt Peters’ cross-coupling
methodology16c for the synthesis of L2−L3 and so first
established a general preparative route to 4-substituted halo-
and aminophenanthridines by combining C−C and C−N bond
formation in a one-pot, Pd-catalyzed cross-coupling/condensa-
tion of substituted anilines with 2-formylphenylboronic acid
(Figure 2a, Table S1).18 Phenanthridines lacking substituents in
the 6-position are less common than 6-subsituted analogues,
due to the electrophilic reactivity of the carbon at this
position.19 Using para-substituted 2-bromo-6-iodo-4-methylani-
line, we achieved higher isolated yields (>90%) of 4-bromo-2-
methylphenanthridine (4-Br) compared with the analogous
preparation of 4-bromophenanthridine from 2,6-dibromoani-
line (isolated yields of ∼35%),15 as the iodoarene can be easily
prepared and is more active in cross-coupling. Direct coupling
of 2-formylphenyl boronic acid with 1,2-diamino-6-iodo-
toluene gave only moderate conversions (∼50% by NMR) to
4-NH2, likely due to coordination of the aminophenanthridine
to Pd. However, 2-methyl-4-nitrophenanthridine (4-NO2) was
readily obtained from 2-bromo-6-nitro-4-methylaniline, and
reduction of 4-NO2 with Zn/NH2−NH2 and formic acid
allowed isolation of 4-NH2 in good yield (>85%, Figure 2b).
With the 4-substituted phenanthridines in hand, forcing
1
No significant changes to the pseudo C2v symmetric H
NMR spectrum of L3 in CD2Cl2 were observed on cooling
from 25 to −90 °C, implying that there is no significant barrier
to the compound adopting a planar configuration, though in
the solid state L3 adopts a nonplanar structure (dihedral angle
between the two phenanthridinyl units = 31.1°). In
comparison, the dihedral angle between phenanthridinyl and
quinolinyl units observed in the solid-state structure of L2 is
considerably smaller (3.4°; Figure 3).
L2 and L3 bear two sp2-hybridized, hard N donors and, on
deprotonation, a diarylamido Lewis basic site. L1 has a similar
donor set and, as might be expected from this rigid donor core,
binds to group 8,22 group 9,16d divalent group 10,16c Cu(II),16b
and Zn(II)16d ions in a planar, meridional fashion. Facial
binding, however, was also shown to be possible in an
octahedral Pt(IV) complex.23 L2 and L3 provide an
opportunity to assess the impact of benzannulation on the
donor strength of the N-heterocyclic arms. The donor ability of
pyridine toward the Lewis acid BCl3 is between that of
quinoline and acridine,24 consistent with the order of their pKa
values (quinoline < pyridine < acridine). Phenanthridine has a
B
DOI: 10.1021/acs.inorgchem.7b00075
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Table 1. Selected Solution NMR Data for L1-L3 and 1-M/2-M/3-M
Article
a
b
L1
L2
L3
1-Ni
1-Pd
1-Pt
9.14
148.8
2-Ni
2-Pd
2-Pt
9.49
151.1
3-Ni
3-Pd
3-Pt
δ(1H) C6-H /ppm
δ(13C) C6-H/ppm
8.97
9.27
9.29
8.66
8.95
9.05
9.27
9.10
9.38
9.58
148.1
150.1
150.1
150.6
149.5
154.1
151.8
154.0
151.8
151.0
a
b
Diagnostic [CH] resonances; Figure 2. From ref 16c and this work.
Benzannulation decreases solubility, which was found to be
generally poor in organic solvents for all complexes despite
introduction of methyl groups to the N-heterocyclic arms in L2
and L3, with metal complexes of L2−L3 precipitating from
solution over the course of the reaction. Coordination of the
proligands was followed by the shift of the diagnostic NMR
spectroscopic resonances of the [CH] unit in the 6-position of
the phenanthridinyl arms of L2 and L3 (Table 1).
Coordination of L2 in 2-Ni results in shifts of the signals for
the [C6−H] unit to 9.05 (1H, CDCl3) and 154.1 ppm
(13C{1H}), with the equivalent resonances in 2-Pt observed at
9.49 and 151.1 ppm. In comparison, the same signals in 2-Pd
are only slightly different from those of the free amine (9.27
1
and 151.8 ppm; cf. 1-Ni: H 8.66, 13C{1H} 150.6 ppm; 1-Pd:
1
1H 8.95, 13C{1H} 149.5 ppm; 1-Pt: H 9.14, 13C{1H} 148.8
ppm).16c For 3-M, the same trend is observed, with increasing
1
deshielding of the diagnostic H NMR resonance going down
the group; the C6-H proton signal resonates at 9.10 (3-Ni),
9.38 (3-Pd), and 9.58 ppm (3-Pt). No exchange is seen with
free ligand in solution. The diagnostic spectroscopic signatures
confirm stable complexation.
Slow diffusion of diethyl ether into chloroform solutions of
2-M or 3-M (M = Ni, Pd, Pt) afforded single crystals suitable
for X-ray diffraction. In each case, high-quality single crystals
with long-range order were obtained as a CHCl3 solvate. The
metal complexes of L2 (2-M) and L3 (3-M) are isostructural
with previously reported structures of 1-Ni, 1-Pd, and 1-Pt
(Figure 4).16c In each structure, the three nitrogen donor atoms
of the ligands are coplanar with the coordinated metal atom,
with M−Cl distances increasing with the size of the divalent
metal ion (Table 2). The trans influence of the amido N donor
in L1 was previously suggested to be minimal, as the amido N
was found to bind selectively trans-disposed to strong trans
influence alkyls/hydrides when a cis disposition was possible.22
Direct comparison of trans influence of the amido N in 2-M/3-
M to 1-M through solid-state M−Cl bond distances is
complicated by the presence of close contacts between
CHCl3 and the chloride ligand in the crystal lattice of 2-M
and 3-M. Complexes of the two phenanthridine-containing
ligands (2-M, 3-M) show statistically indistinguishable M−Cl
bond distances, consistent with similar trans influences of the
amido N in L2 and L3.
Figure 3. ORTEPs21 of L2 and L3, with thermal ellipsoids shown at
30% (L2) and 50% (L3) probability levels. For each structure, two
views are shown. Selected bond distances (Å) for L2: C(1)−N(1)
1.298(2), C(9)−N(1) 1.3811(17), C(9)−C(8) 1.4068(19), C(8)−
C(7) 1.4444(19), C(2)−C(1) 1.426(2), C(2)−C(7) 1.4127(18),
C(15)−N(3) 1.319(2); and L3: C(1)−N(1) 1.305(4), C(9)−N(1)
1.382(3), C(1)−C(2) 1.432(4), C(2)−C(7) 1.410(3), C(7)−C(8)
1.448(4), C(8)−C(9) 1.410(3), C(15)−N(3) 1.307(3), C(23)−N(3)
1.385(3), C(15)−C(16) 1.428(4), C(16)−C(21) 1.413(4), C(21)−
C(22) 1.447(3), C(22)−C(23) 1.412(3).
The trans influence of phenanthridine as a ligand can be
thought of as similar to that of pyridine; statistically
indistinguishable Pt−N bond distances were reported trans to
the N-heterocyclic donor in cis-[Pt(NH3)2(phenanthridine)-
Cl][OSO2CF3] and cis-[Pt(NH3)2(pyridine)Cl][OSO2CF3].25
In all 2-M complexes, the phenanthridinyl N(1)−M distances
are shorter than the quinolinyl N(3)−M distance trans to them
and also shorter than the corresponding phenanthridinyl
N(3)−M bond distance in 3-M (which is trans to a
phenanthridinyl donor); however, the values are not distin-
guishable outside of the 3σ statistical limit (Table 2). The
comparable bond distances suggest similar donor strengths for
the phenanthridinyl and quinolinyl arms as well; however, they
similar pKa to that of acridine (5.58), implying a similar “donor
strength” toward H+. With larger Lewis acids, phenanthridine
(3,4-benzoquinoline) should be less sterically encumbered than
acridine (2,3-benzoquinoline), due to the asymmetry of
benzannulation. To compare the coordination chemistry of
our phenanthridine-containing ligands L2 and L3 with that of
L1, we targeted halide complexes of the group 10 triad, as the
analogous complexes of L1 (1-M) are known.16c
Divalent nickel, palladium, and platinum complexes of L1−
L3 were prepared in 65−89% yields from reaction with the
appropriate metal chloride salt in the presence of a base
(NaOtBu) in hot tetrahydrofuran (THF) or CH2Cl2.
C
DOI: 10.1021/acs.inorgchem.7b00075
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 4. ORTEPs21 with thermal ellipsoids shown at 50% (2-Pd, 3-Ni, 3-Pd) and 30% (2-Ni) probability levels, and hydrogens omitted for clarity.
For each structure, a top view perpendicular to the metal square plane and a bottom view along the Cl−M−N(2) axis are shown. Selected bond
angles (deg) for 2-Ni: N(1)−Ni(1)−N(3) 169.31(12), Cl(1)−Ni(1)−N(2) 178.67(10), N(1)−Ni(1)−N(2) 84.72(12), N(3)−Ni(1)−N(2)
84.60(13), N(1)−Ni(1)−Cl(1) 95.33(9), N(3)−Ni(1)−Cl(1) 95.34(10). 2-Pd: N(1)−Pd(1)−N(3) 165.94(8), Cl(1)−Pd(1)−N(2) 179.66(6),
N(1)−Pd(1)−N(2) 83.05(8), N(3)−Pd(1)−N(2) 82.89(8), N(1)−Pd(1)−Cl(1) 97.28(6), N(3)−Pd(1)−Cl(1) 96.78(6). 2-Pt: N(1)−Pt(1)−
N(3) 166.16(9), Cl(1)−Pt(1)−N(2) 179.20(7), N(1)−Pt(1)−N(2) 83.29(9), N(3)−Pt(1)−N(2) 82.88(9), N(1)−Pt(1)−Cl(1) 97.24(7), N(3)−
Pt(1)−Cl(1) 96.60(7). 3-Ni: N(1)−Ni(1)−N(3) 169.48(9), Cl(1)−Ni(1)−N(2) 176.71(7), N(1)−Ni(1)−N(2) 84.84(9), N(3)−Ni(1)−N(2)
84.68(9), N(1)−Ni(1)−Cl(1) 95.20(6), N(3)−Ni(1)−Cl(1) 95.31(7). 3-Pd: N(1)−Pd(1)−N(3) 166.04(12), Cl(1)−Pd(1)−N(2) 177.52(9),
N(1)−Pd(1)−N(2) 82.89(13), N(3)−Pd(1)−N(2) 83.17(12), N(1)−Pd(1)−Cl(1) 97.22(9), N(3)−Pd(1)−Cl(1) 96.74(9). 3-Pt: N(1)−Pt(1)−
N(3) 166.12(7), Cl(1)−Pt(1)−N(2) 178.56(6), N(1)−Pt(1)−N(2) 83.16(8), N(3)−Pt(1)−N(2) 82.98(8), N(1)−Pt(1)−Cl(1) 96.84(6), N(3)−
Pt(1)−Cl(1) 97.04(6).
Table 2. Selected Bond Distances for 1-M (from ref 16c) and 2-M/3-M (this work)
a
b
c
d
distance (Å)
M-N(1)
M-N(3)
M-N(2)
M-Cl(1)
N(1)−C(1)
N(3)−C(15)
1-Ni
2-Ni
3-Ni
1-Pd
2-Pd
3-Pd
1-Pt
2-Pt
3-Pt
1.8973(16)
1.899(3)
1.900(2)
2.0114(19)
1.997(2)
2.001(3)
1.994(3)
1.993(2)
1.995(2)
1.8973(16)
1.906(3)
1.900(2)
2.0017(19)
2.001(2)
2.001(3)
1.999(3)
1.999(2)
1.991(2)
1.8586(14)
1.858(3)
1.858(2)
1.962(2)
1.9620(19)
1.959(3)
1.966(3)
1.969(2)
1.9779(18)
2.1779(5)
2.2067(11)
2.2080(7)
2.3298(7)
2.3406(6)
2.3387(10)
2.3175(11)
2.3427(7)
2.3449(6)
1.323(2)
1.316(4)
1.312(3)
1.331(3)
1.301(3)
1.308(5)
1.338(5)
1.302(4)
1.326(2)
1.331(5)
1.311(3)
1.329(3)
1.331(3)
1.301(5)
1.318(5)
1.331(3)
1.315(3)
1.312(3)
a
b
c
Quinolinyl-N in 1-M; phenanthridinyl-N in 2-M/3-M. Quinolinyl-N in 1-M/2-M; phenanthridinyl-N in 3-M. Cl(1) shows close contact to
d
CHCl3 in lattice of 2-M/3-M. Labeled C(10) in ref 16c.
may also be a consequence of the rigid tridentate ligand
scaffold.
of phenanthridine itself is found at 343 nm (hexanes, π−π*),
shifting slightly to 346 nm in methanol,26 while the analogous
peak for quinoline is at 311 nm (ethanol).27 Consistent with
the deep red color of all nine metal complexes, spectra collected
for 1-M, 2-M, and 3-M contained a broad absorption with a
maximum at ∼500 nm (Figures 5b−d, Table 3). The significant
red shift of the lowest-energy peak for L1−L3 upon
coordination to a metal is consistent with metal participation
in the transition (i.e., M-π* metal-to-ligand charge transfer
(MLCT) character) in addition to ligand-centered π−π*
character.16d,22 The large extinction coefficients support the
contribution of charge transfer to this transition.
UV−Visible Absorption Spectroscopy. The electronic
absorption spectra of proligands L1−L3 and metal complexes
1-M, 2-M, and 3-M were measured in both CH2Cl2 and N,N-
dimethylformamide. The absorption observed for 1-M/2-M/3-
M obeys Beers’ Law only over a limited low concentration
range (<5 × 10−5 M), suggesting ground-state aggregation may
occur at higher concentrations. The UV−vis absorption spectra
of L1, L2, and L3 are marked by a broad peak at low energy,
whose maximum shifts to shorter wavelength (L1: 400 nm; L2:
392 nm; L3: 382 nm; Figure 5a) with increasing conjugation.
However, this low energy peak also broadens, and the onset of
absorption is observed at higher wavelengths (i.e., λonset L3 >
L2 > L1). For comparison, the first absorption band maximum
In contrast to the free amines, there is no significant shift in
the maximum of this broad absorption band when changing
from L1 to L2 to L3 for any of the three series of metal
D
DOI: 10.1021/acs.inorgchem.7b00075
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 5. UV−vis absorption spectra (CH2Cl2, 22 °C) for (a) L1−L3, (b) 1-Ni/2-Ni/3-Ni, (c) 1-Pd/2-Pd/3-Pd, (d) 1-Pt/2-Pt/3-Pt.
Table 3. Electrochemical Potentials and UV−Vis Absorption Parameters for Complexes 1−3 (Ni, Pd, Pt)
a
a
b
c
d
Epeak, red
,
V
Epeak, ox
,
V
ΔEox1‑red
,
V
λ, nm (ε, M−1 cm‑1 × 1 × 10−3
)
fwhm λmax, nm
1-Ni
2-Ni
3-Ni
1-Pd
2-Pd
3-Pd
1-Pt
2-Pt
3-Pt
−2.28
−2.25
−2.20
−2.08
−2.06
−2.05
−2.09, −1.37
−2.10, −1.40
−2.15, −1.45
0.26
0.20
2.54
2.45
301 (31.2), 337 (5.2), 371 (sh), 499 (8.0)
86
89
284 (25.6), 313 (24.1), 339 (15.1), 356 (sh), 395 (4.0), 498 (8.7)
319 (27.4), 336 (22.9), 354 (15.5), 402 (6.7), 496 (7.8)
291 (29.8), 372 (2.5), 489 (8.8)
e
e
0.16
2.36
2.34
2.33
2.23
2.34
2.25
2.20
91
0.26
0.27
87
278 (22.1), 306 (17.5), 338 (sh), 392 (3.3), 492 (6.9)
308 (sh), 318 (12.8), 334 (8.3), 398 (3.1), 489 (4.2)
300 (33.6), 339 (7.7), 356 (6.6), 383 (3.1), 503 (9.8)
314(24.3), 337 (17.2), 353 (sh), 405 (4.2), 503 (9.4)
322 (32.4), 336 (27.4), 354 (20.1), 406 (5.6), 503 (10.7)
98
0.18, 0.30
0.25
104
87
f
f
f
0.15, 0.31
91
0.05, 0.20
88
a
Measured for CH2Cl2 solutions with 0.1 M [nBu4N][PF6] as the supporting electrolyte, via DPV with potentials reported referenced to the Fc0/+
b
c
d
redox couple. ΔEp = Eox − Ered. Ambient temperature, CH2Cl2. Maximum of broad peak observed at lowest energy in spectrum in CH2Cl2.
1/2
e
f
Value represents middle of two unresolved peaks. Surface-based deposition observable only at slow scan rates and/or DPV.
complexes. This was surprising, given we intuitively expected
extending ligand conjugation to have some impact on the
frontier orbital energies. Modest broadening of the low-energy
absorption can be seen for 1-Ni/2-Ni/3-Ni and 1-Pd/2-Pd/3-
Pd, with the full width at half max (fwhm) increasing on
average by 7 nm and up to 17 nm, when the fwhm for the
broad absorption of 1-Pd is compared with 3-Pd. As with L1−
L3, the onset of absorption is observed at higher wavelengths as
well (i.e., λonset 3-M > 2-M > 1-M; M = Ni, Pd). The low-
energy absorptions for 1-Pt/2-Pt/3-Pt are essentially un-
changed by the alterations to the ligand structure. The major
difference to the absorption spectrum for each of the three
series of metal complexes is the appearance of up to four
additional peaks at higher energy (300−430 nm) that grow in
intensity when comparing complexes of L2 and L3 and,
therefore, result from the phenanthridinyl arms.
observed for each set of metal complexes led us to expect that
the optical highest occupied molecular orbital (HOMO)−
lowest unoccupied molecular orbital (LUMO) gap is mostly
unaffected by increasing conjugation from 1-M to 2-M to 3-M,
apart from a slight red shift indicated by the shift in the long-
wavelength edge of the absorption spectra. Electrochemistry
has been used to evaluate trends in the relative energies of the
frontier orbitals within series of similar compounds.28
The electrochemical properties of 1-M, 2-M, and 3-M were
examined in solution using cyclic voltammetry (CV) and
differential pulse voltammetry (DPV; Figure 6, Table 3). All
complexes show irreversible reduction waves at ca. −2 V (vs
Fc0/+; Fc = ferrocene), with no return wave apparent at any of
the tested scan rates (50−800 mV·s−1). The low solubility of
the compounds results in the appearance of a prepeak feature
observed in the cathodic scans not observed at faster scan rates,
attributed to adsorption of dissolved complex onto the
electrode surface.29 This is particularly pronounced for the Pt
Electrochemistry of 1-M, 2-M, and 3-M. The invariant
position of the maximum of the lowest-energy absorption band
E
DOI: 10.1021/acs.inorgchem.7b00075
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
complexes (the maximum solution concentration achieved with
3-Pt was 0.72 mM). Comparing these reductive events for 1-
M/2-M/3-M (M = Ni, Pd), a slight anodic shift is observed
with extended conjugation (1-M → 2-M → 3-M). This trend is
in keeping with the conventional expectation that a larger π-
system would stabilize the negative charge to a greater extent;
however, we are cautious in overinterpreting this observation
due to the issues with low complex solubility. In contrast, a
slight cathodic shift is observed for the Pt series, with
Epeak,cathodic (3-Pt) < Epeak,cathodic (2-Pt) < Epeak,cathodic (1-Pt).
Quasi-reversible, broad oxidation events were also observed
for all nine complexes at ∼0.2 V versus Fc0/+. The addition of a
second fused ring in 3-M leads to the appearance of a second
broad feature at less anodic potentials. While we cannot rule
out whether this feature is due to aggregate formation, no
visible deposition was observed on the electrodes following
these scans; so far we have been unable to isolate a soluble
chemically oxidized cationic species. In comparison, Pt
complexes of π-extended derivatives of 1,3-bis(2-
pyridiylimino)pyrrole/pyrrolate/isoindolate exhibited reversi-
ble reductions and irreversible oxidations.1d The reduction and
oxidation events, respectively, observed for all nine group 10
metal complexes of L1−L3 are within a relatively narrow
potential window. This is consistent with largely ligand-based
redox events influenced by coordination to a metal;30 the redox
chemistry of organic N-heterocycle fused phenanthridines has
been reported in a similar range (0.38−1.5 V vs Fc0/+).31
Taking the difference between the first observed oxidation
event and the reduction peak observed by DPV (ΔEox1‑red), the
relative HOMO−LUMO gap for the series of complexes can be
estimated. The irreversibility of the peaks and presence of an
absorption prefeature makes it problematic to precisely quantify
the HOMO−LUMO separation using electrochemical data, but
the relative trend for all three metals is that ΔEox1‑red decreases
with increasing conjugation (1-M → 2-M → 3-M).32
ELECTRONIC STRUCTURE CALCULATIONS
■
We performed density functional theory (DFT) calculations,
incorporating a polarizable continuum model (DFT-PCM) to
model solvent effects, and time-dependent DFT-PCM
(TDDFT-PCM) calculations to probe the impact of
benzannulation on the electronic structure of 1-M/2-M/3-M
and explain the experimental UV−vis absorption spectra. As the
trends for the Ni and Pd systems were found to be similar, only
the Ni complexes are presented. The Pt complexes were not
analyzed for this work. All structures were optimized with
(SMD-M06/6-31+G(d,p)), and optimized geometries are in
good agreement with the experimental X-ray crystallography
data (see Supporting Information for details).33
Figure 6. Cyclic voltammograms () and corresponding differential
pulse voltammograms (---) of 1-M, 2-M, and 3-M (1.5 mg/15 mL) in
CH2Cl2 with 0.1 M [nBu4N][PF6] as the supporting electrolyte; (a) M
= Ni, (b) M = Pd, (c) M = Pt. CV scan rates were 100 mV/s. Data in
the high and low potential regions were collected in separate scans.
Table 4. TDDFT Vertical Excitation Energies and HOMO, LUMO, and LUMO+1 Energies for Complexes 1-Ni/2-Ni/3-Ni
HOMO (eV)
LUMO (eV)
LUMO+1 (eV)
λcalc (nm)
assignment
oscillator strength
coefficient
% contribution
1-Ni
2-Ni
−5.35
−1.90
−1.85
494.34
483.13
490.66
HOMO→LUMO
HOMO→LUMO+1
HOMO→LUMO
HOMO→LUMO+1
HOMO→LUMO
HOMO→LUMO+1
HOMO→LUMO
HOMO→LUMO+1
0.3698
0.0078
0.2131
0.701 42
0.703 19
0.537 12
0.452 06
−0.452 15
0.535 81
0.701 83
0.697 07
98.4
98.9
57.7
40.9
40.9
57.4
98.5
97.2
−5.32
−5.28
−1.88
−1.90
−1.84
−1.79
483.83
0.1722
3-Ni
496.51
485.04
0.0221
0.3536
F
DOI: 10.1021/acs.inorgchem.7b00075
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 7. Orbital diagrams of the HOMO, LUMO, and LUMO+1 for 1-Ni, 2-Ni, and 3-Ni.
The trends in calculated energies shown in Table 4
correspond well with those observed in the experimental
electrochemistry. The calculated HOMO energy levels increase
with extended conjugation of the ligand (1-M → 2-M → 3-M),
consistent with the observed cathodic shift in oxidation
potential. The observed trend in the onset of reduction
potentials is not reproduced; however, as noted above, the
irreversibility of the cathodic electrochemical events and
presence of absorption prefeatures complicate precise analysis
of the peak positions.
Using the optimized structures, vertical excitation energies
were determined using TDDFT. The lowest-energy vertical
transitions for solution (universal solvation model (SMD))
calculations are in good qualitative agreement with the
experimental absorption trends (Table 3). Consistent with
the observed experimental spectra, the increase in conjugation
in the ligands has little effect on the position of the low-energy
absorption of the metal complexes. However, benzannulation
does impact the nature of the absorption, as can be seen
through analysis of atomic contributions to the computed
molecular orbitals.
Our calculations on the complex with the smallest π-system
(1-Ni) predict that the HOMO → LUMO transition defines
the lowest-energy excitation at 494 nm (98% calculated
contribution). The HOMO of this complex consists largely of
contributions from the π system of the C6-benzo rings and
amido lone pair, with small contributions from the d- and p-
orbitals of the nickel and chloride, respectively, and the C−N π
bond of the quinolinyl rings (Figure 7). The LUMO of this
system has a small contribution from the Ni but is otherwise
largely delocalized across the π system of the ligand.
The extended π system of 2-Ni produces two low-energy
excitations at 491 and 484 nm with nearly equal oscillator
strengths (Table 4). The excitation at 491 nm is dominated by
the HOMO → LUMO transition (58% calculated contribu-
tion) but contains significant HOMO → LUMO+1 character
(41% calculated contribution). The excitation at 484 nm is
dominated by the HOMO → LUMO+1 transition (57%) but
contains significant HOMO → LUMO character (41%). The
HOMO of this system is similar to that of 1-Ni in that it
consists largely of contributions from the π system of the benzo
moieties, the central amido lone pair, and, to a smaller extent,
the CN π-bond. The LUMO of 2-Ni consists of
contributions from both ligand arms and Ni. Qualitatively,
the structure of the LUMO+1 in the calculated structure of 2-
Ni more closely resembles the orbital configuration of the
LUMO of 1-Ni and is delocalized across the π system of the
ligand (Figure 7). Further expansion of the π system of the
ligand in 3-Ni produces an excitation at 490 nm that is defined
by the HOMO → LUMO+1 transition (97%). The orbital
contributions of the HOMO, LUMO, and LUMO+1 of the 3-
Ni complex closely resemble those of the 2-Ni complex, with
the LUMO/LUMO+1 character inverted compared to 1-Ni
(Figure 7). The main impact of benzannulation in the series 1-
Ni → 2-Ni → 3-Ni therefore appears to be to cause the energy
of the LUMO of 1-Ni to rise, while at the same time lowering
the energy of the LUMO+1 (which becomes the LUMO of 2-
Ni and 3-Ni). The orbital contributions to the HOMO, in
comparison, remain largely unchanged from 1-Ni → 2-Ni → 3-
Ni, while the energy of this orbital is calculated to rise slightly,
in keeping with conventional expectations of extended
conjugation and consistent with the trends in the experimental
anodic electrochemistry. Interestingly, in both pseudo-C2v
symmetric complexes (1-Ni and 3-Ni), only one low-energy
transition has significant calculated oscillator strength, and the
atomic contributions to the orbitals involved in this transition
are very similar. In the Cs symmetric 2-Ni, both the HOMO →
LUMO and HOMO → LUMO+1 transitions contribute to the
low-energy absorptions.
This is qualitatively consistent with Gordon and Thompson’s
model1d for understanding shifts in frontier orbital energies
following benzannulation: there is minimal HOMO density at
G
DOI: 10.1021/acs.inorgchem.7b00075
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
the site of benzannulation in 1-Ni by a conceptual cis-1,3-
butadiene fragment. No orbital mixing or significant change to
the HOMO energy/character would therefore be expected. In
contrast, there is a bisecting nodal plane in the LUMO of 1-Ni
at the site of benzannulation. There is therefore a symmetry
match with the HOMO of a cis-1,3-butadiene fragment (a2, C2v
point group), which can therefore act as an effective electron-
donating group to the LUMO of 1-Ni, leading to its
destabilization.
In a relevant literature example, similarly extending ligand
conjugation for a series of annulated meso-tetraphenylmetallo-
porphyrins was found not to significantly impact the energy of
the HOMO and LUMO with respect to the parent porphyrin
but did lead to significant destabilization of the HOMO−1.34 In
this case, destabilization of the HOMO−1 led to this orbital
rising above the parent HOMO in energy (and become the
new HOMO in the benzannulated complexes), thus leading to
a red shift in the absorption and emission spectra. A similar
effect occurs in the series 1-Ni → 2-Ni → 3-Ni, where the
orbitals comprising the LUMO and LUMO+1 in the parent
complex (1-Ni) formally change positions upon benzannula-
tion (2-Ni/3-Ni). In our series, however, the slight rise in the
energy of the HOMO upon benzannulation is matched by a
similar rise in the energy of the LUMO+1. The shift in the
character of the lowest-energy transition from HOMO →
LUMO (1-Ni) to HOMO → LUMO/HOMO → LUMO+1
(2-Ni) to strictly HOMO → LUMO+1 (3-Ni) then results in
similar energies for these transitions calculated by theory and
observed experimentally.
EXPERIMENTAL SECTION
■
Unless otherwise specified, all-air sensitive manipulations were
performed either in a N2-filled glovebox or using standard Schlenk
techniques under Ar. 2-Formylphenylboronic acid (AK Scientific), N-
iodosuccinimide (AK Scientific), N-bromosuccinimide (Alpha Aesar),
Pd(PPh3)4 (Sigma-Aldrich), Pd(OAc)2 (Sigma-Aldrich), 1,1′-bis-
(diphenylphosphino)ferrocene (dppf, Sigma-Aldrich), Na2CO3
(Alpha Aesar), trifluoroacetic acid (Sigma-Aldrich), sodium tert-
pentoxide (NaOtPen, Sigma-Aldrich), sodium tert-butoxide (NaOtBu,
Sigma-Aldrich), zinc (Alpha Aesar), hydrazine hydrate (Sigma-
Aldrich), formic acid (Alpha Aesar), and NiCl2·6H2O (Alpha Aesar)
were purchased and used without any further purification. 2-Bromo-4-
methylaniline,35 Pd(1,5-cyclooctadiene)Cl2,36 Pt(1,5-cyclooctadiene)-
Cl2, L1, 1-NiCl, 1-PdCl, and 1-PtCl16c were synthesized according to
published procedures. Organic solvents were dried and distilled using
appropriate drying agents prior to use. Distilled water was degassed
prior to use. One- and two-dimensional NMR spectra were recorded
on Bruker Avance 300 MHz or Bruker Avance-III 500 MHz
spectrometers. 1H and 13C{1H} NMR spectra were referenced to
residual solvent peaks.37 Elemental analyses were performed by
Microanalytical Service Ltd., Delta, BC (Canada).
For electrochemical analysis, 1−2 mg of each compound was
dissolved in 15 mL of CH2Cl2 containing 0.1 M (nBu4N)PF6, and
purged with Ar for 20 min before analysis. All electrochemical
experiments were conducted under inert (Ar) atmosphere using a CHI
760c bipotentiostat, a freshly polished (0.03 μm alumina paste) 3 mm
diameter glassy carbon working electrode (BASi), a Ag/Ag+ quasi-
nonaqueous reference electrode separated by a Vycor tip, and a Pt wire
counter electrode. Cyclic voltammetric (CV) experiments were
conducted using scan rates of 50−800 mV/s. Differential pulse
voltammetry (DPV) experiments were conducted using a 5 mV
increment, 50 mV amplitude, 0.1 s pulse width, 0.0167 s sample width,
and 0.5 s pulse period. Upon completion of all CV and DPV analyses,
ferrocene (Fc) was added to the solution as an internal standard, with
all potentials reported versus the Fc0/+ redox couple.38
Preparation of 2-Bromo-6-iodo-p-toluidine. Trifluoroacetic
acid (30 mol %, 1.23 mL) was added to a stirred acetonitrile solution
(300 mL) of 2-bromo-4-methylaniline (10.1 g, 53.7 mmol) at 0 °C,
followed by addition of N-iodosuccinimide (12.7 g, 56.4 mmol) in
small portions over 1.5 h. The mixture was stirred for 0.5 h at this
temperature, after which the ice bath was removed, and stirring
continued for 2 h. The solvent was then removed in vacuo, the residue
taken up in CH2Cl2 and washed with brine (3 × 100 mL). The organic
layer was dried over Na2SO4, and volatiles were removed to leave a
gray solid, which was used without further purification. Isolated yield =
16.0 g (95%). The 1H NMR spectrum was consistent with that
previously reported.39
Preparation of 2-Iodo-6-nitro-p-toluidine. An identical proce-
dure to the synthesis of 2-bromo-6-iodo-p-toluidine was employed,
using 2-nitro-p-toluidine (5.01 g, 32.9 mmol) and N-iodosuccinimide
(12.7 g, 34.5 mmol). Isolated yield of orange solid = 7.60 g (96%).
The 1H NMR spectrum was consistent with previously reported
values.40
CONCLUSION
■
A synthetic methodology has been established allowing the
preparation of a series of tridentate proligands templated on
bis(8-quinolinyl)amine (L1), bearing one (L2) or two
phenanthridinyl (L3) units. Compounds L2 and L3 bind as
tridentate, mer-bound pincer-like amido ligands to divalent
group 10 metal ions (Ni, Pd, and Pt). In contrast to the
differences observed in the low-energy absorption transitions of
L1−L3, the maxima observed for the lowest-energy absorptions
of 1-M to 2-M to 3-M (M = Ni, Pd, Pt) do not shift
appreciably, though the onset of absorption edges to higher
wavelengths, consistent with the trend of slight red shift in the
HOMO−LUMO gap estimated from electrochemistry. DFT
calculations reveal that, more so than simply impacting the
frontier orbital energies, benzannulation strongly affects the
atomic contributions to the LUMO and LUMO+1, with the
orbital character of these MOs in 2-M and 3-M switched
compared with those of 1-M. In addition, while the lowest-
energy absorption in the bis(quinolinyl) 1-M is dominated by
the HOMO → LUMO excitation, the analogous absorption in
the bis(phenanthridinyl) 3-M is dominated by the HOMO →
LUMO+1 excitation; the mixed quinolinyl/phenanthridinyl 2-
M has both HOMO → LUMO and HOMO → LUMO+1
character. This suggests that complexes of ligands L1−L3 with
heavier metals such as 1-Pt, 2-Pt, and 3-Pt may present
interesting trends in their emission spectra, where a
straightforward correlation with the extent of π-conjugation
may not exist and the orbital structure of the frontier orbitals
may influence other parameters such as radiative rate constants
and zero-field splittings.32 Investigations to this extent are
currently underway in our laboratories.
Preparation of 4-Bromo-2-methylphenanthridine. A 500 mL
Teflon-stoppered flask was charged with Pd(PPh3)4 (0.87 g, 0.75
mmol) and 50 mL of 1,2-dimethoxyethane (DME). After this was
stirred briefly to mix, 2-bromo-6-iodo-p-toluidine (7.80 g, 25.0 mmol),
2-formylphenylboronic acid (4.16 g, 27.8 mmol), and an additional 70
mL of DME were added, followed by Na2CO3 (8.0 g, 76 mmol)
dissolved in 100 mL of degassed water. The flask was then sealed, and
the mixture was stirred vigorously for 6 h in an oil bath (130 °C). The
flask was then allowed to cool, charged with 80 mL of 2 M HCl, and
refluxed for additional 2 h. The reaction mixture was cooled,
neutralized with NaOH, and pumped to dryness. The residue was
then taken up in CH2Cl2 (100 mL) and washed with brine (3 × 100
mL). The organic layer was separated and dried over Na2SO4, and
volatiles removed to leave a yellow-brown solid. Column chromatog-
raphy on basic alumina gave pale yellow solid 4-Br (Rf = 0.41; 1:5
1
EtOAc/hexane). Isolated yield = 6.3 g (91%). H NMR (CDCl3, 500
H
DOI: 10.1021/acs.inorgchem.7b00075
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
MHz, 22 °C): δ 9.29 (s, 1H, C6−H), 8.52 (d, 1H, JHH = 8.3 Hz, C10−
H), 8.26 (s, 1H, C3−H), 8.03 (d, 1H, JHH = 7.9 Hz, C7−H), 7.90−7.77
(overlapped m, 2H, C1−H, C9−H), 7.70 (app t, 1H, JHH = 7.5 Hz,
C8−H), 2.57 ppm (s, 3H, CH3). 13C{1H} NMR (CDCl3, 300 MHz, 22
°C): δ 153.5 (C6), 144.3 (CAr), 142.8 (CAr), 140.0 (CAr), 137.8 (CAr),
134.1 (C1), 132.1 (CAr), 131.3 (C9), 129.0 (C7), 128.1 (C8), 126.6
(CAr), 125.6 (CAr), 125.4 (CAr), 122.1 (C10), 121.7 (C3), 21.7 ppm
(CH3).
Preparation of 2-Methyl-4-nitrophenanthridine. An identical
procedure to the synthesis of 4-bromo-2-methylphenanthridine was
employed, using Pd(PPh3)4 (0.42 g, 0.36 mmol), 2-iodo-6-nitro-p-
toluidine (5.02 g, 18.0 mmol), and 2-formylphenylboronic acid (3.01
g, 20.0 mmol). Following column chromatography (Rf = 0.25; 1:5
EtOAc/hexane), isolated yield of 4-NO2 as a yellow-brown solid = 4.0
g (93%). 1H NMR (CDCl3, 300 MHz, 22 °C): δ 9.34 (s, 1H, C6−H),
8.61 (d, 1H, JHH = 8.3 Hz, C10−H), 8.54 (s, 1H, C3−H), 8.11 (d, 1H,
JHH = 7.9 Hz, C7−H), 7.99−7.89 (m, 1H, C9−H), 7.88−7.71
(overlapped m, 2H; C1−H, C8−H), 2.69 ppm (s, 3H, CH3). 13C{1H}
NMR (CDCl3, 300 MHz, 22 °C): δ 155.1 (C6), 149.3 (CAr), 136.8
(CAr), 134.3 (CAr), 132.0 (C8), 131.3 (CAr), 129.3 (C7), 128.9 (C9),
126.7 (CAr), 125.6 (CAr), 125.5 (C3), 123.8 (C1), 122.2 (C10), 21.9
ppm (CH3).
(dimethylformamide (DMF)): λ (ε) 267 (45 400), 308 (14 700),
392 nm (17 650 M−1 cm−1).
S y n t h e s i s o f M e ‑ P h e n N N ( H ) N P h e n ‑ M e B i s ( 2 -
methylphenanthridinyl)amine. A 500 mL Teflon-stoppered flask
was charged with Pd(OAc)2 (0.25 g, 1.10 mmol), dppf (0.96 g, 1.76
mmol), and 30 mL of toluene and stirred briefly. Next, 4-Br (6.02 g,
22.1 mmol), 4-NH2 (5.01 g, 24.0 mmol), and an additional 120 mL of
toluene were added, followed by NaOtPen (3.60 g, 32.6 mmol). The
flask was then sealed, and the mixture was stirred vigorously for 72 h in
an oil bath (150 °C) before drying in vacuo. Isolation and workup was
as for L2 (Rf = 0.5; 1:5 EtOAc/hexane). Isolated yield of L3 = 7.9 g
1
(90%). H NMR (CDCl3, 300 MHz, 22 °C): δ 10.63 (br s, 1H, N−
H), 9.29 (s, 2H, C6−H), 8.61 (d, 2H, JHH = 8.3 Hz, C10−H), 8.08 (app
d, 2H, JHH = 8.0 Hz, C7−H), 7.90−7.80 (overlapped m, 6H; C1−H,
C3−H, C9−H), 7.73−7.67 (app t, 2H, JHH = 7.5 Hz, C8−H), 2.67 ppm
(s, 6H, CH3). 13C{1H} NMR (CDCl3, 300 MHz, 22 °C): δ 150.1
Phen
(
(
(
(
C H), 139.7 (PhenCAr), 137.6 (PhenCAr), 133.9 (PhenCAr), 132.7
Ar
Phen
Phen
Phen
C ), 130.7 (PhenCArH), 128.8 (PhenCArH), 127.3 (PhenCArH), 127.0
Ar
C ), 124.9 (PhenCAr), 122.5 (PhenCArH), 112.7 (PhenCArH), 112.5
Ar
C H), 23.0 ppm (CH3). UV−vis (DMF): λ (ε) 266 (44 800),
Ar
297 (24 500), 307 (shoulder), 382 nm (17 050 M−1 cm−1).
Synthesis of (Me‑PhenNNNQuin)NiCl. NiCl·6H2O (0.14 g, 0.6
mmol) and NaOtBu (60 mg, 0.63 mmol) were added as solids to a
solution of L2 (0.2 g, 0.6 mmol) in CH2Cl2 (10 mL) and the mixture
stirred vigorously at 50 °C for 12 h. The resulting red suspension was
allowed to cool and the volatiles removed in vacuo. The residue was
then washed with diethyl ether (3 × 10 mL) and ethanol (3 × 10 mL).
While the solubility of 2-Ni is poor in general, it was observed to be
highest in CHCl3 compared with other common organic solvents.
Preparation of 4-Amino-2-methylphenanthridine. To a
stirred solution of 4-NO2 (5.02 g, 21.0 mmol) in methanol (100
mL), Zn dust (2.75 g, 42.0 mmol), and hydrazinium monoformate
solution (54 mL; prepared by slowly neutralizing equal molar amounts
of hydrazine hydrate (50 mL) with 85% formic acid (4 mL) in an ice−
water bath) were added and stirred vigorously at 60 °C. The resulting
green suspension was cooled and filtered using diatomaceous earth.
The filtrate was pumped dry; the residue dissolved in CH2Cl2 (100
mL) and washed with brine (3 × 60 mL). The organic layer was dried
over Na2SO4 and filtered, and the volatiles were removed to leave
green-brown solid 4-NH2, which was purified using column
chromatography (basic alumina, Rf = 0.25; 1:5 EtOAc/hexane).
Isolated yield = 3.74 g (86%). 1H NMR (CDCl3, 300 MHz, 22 °C): δ
9.07 (s, 1H, C6−H), 8.52 (d, 1H, JHH = 8.3 Hz, C10−H), 7.97 (d, 1H,
JHH = 7.9 Hz, C7−H), 7.86−7.74 (m, 1H, C9−H), 7.69−7.61
(overlapped m, 2H; C1−H, C8−H), 6.85 (s, 1H, C3−H), 4.96 (br s,
2H, N−H), 2.51 ppm (s, 3H, CH3). 13C{1H} NMR (CDCl3, 300
MHz, 22 °C): δ 149.4 (C6), 144.5 (CAr), 137.8 (CAr), 132.6 (CAr),
132.0 (CAr), 130.4 (CAr), 128.6 (CAr), 127.1 (CAr), 126.8 (CAr), 124.6
(CAr), 122.4 (CAr), 113.1 (CAr), 110.9 (C3), 22.4 ppm (CH3).
Synthesis of Me‑PhenNN(H)NQuin (2-Methylphenanthridinyl)(8-
quinolinyl)amine. A 500 mL Teflon-stoppered flask was charged
with Pd(OAc)2 (0.25 g, 1.10 mmol), (dppf; 0.96 g, 1.76 mmol), and
toluene (30 mL). After this was stirred briefly, 4-Br (6.01 g, 22.0
mmol), 8-aminoquinoline (3.33 g, 23 mmol), and an additional 120
mL of toluene were added, followed by (NaOtPen; 3.60 g, 33.0
mmol), and the mixture was stirred vigorously for 72 h in an oil bath
(150 °C). After the flask was cooled and the volatiles were removed,
the residue was taken up in CH2Cl2 (120 mL), and the resulting
suspension was filtered over diatomaceous earth and dried to leave a
red solid, which was purified using column chromatography (basic
alumina; 1:5 EtOAc/hexane; Rf = 0.5). Isolated yield of L2 = 6.8 g
1
Isolated yield of 2-Ni = 0.209 g (81%). H NMR (CDCl3, 300 MHz,
22 °C): δ 9.05 (s, 1H, CAr−H), 8.71 (d, 1H, JHH = 4.8 Hz, CAr−H),
8.43 (d, 1H, JHH = 8.3 Hz, CAr−H), 8.13 (d, 1H, JHH = 8.2 Hz, CAr−
H), 7.97 (d, JHH = 1H, 7.9 Hz, CAr−H), 7.85 (t, 1H, JHH = 7.6 Hz,
CAr−H), 7.64 (t, 1H, JHH = 7.5 Hz, CAr−H), 7.55 (d, 1H, JHH = 7.9
Hz, CAr−H), 7.50−7.32 (overlapped m, 3H, CAr−H), 7.29 (t, 1H, JHH
= 5.4 Hz, CAr−H), 6.93 (d, 1H, JHH = 8.0 Hz), 2.58 ppm (s, 3H, CH3).
13C{1H} NMR (CDCl3, 500 MHz, 22 °C): 154.1 (CArH), 150.5
(CArH), 148.4 (CAr), 148.3 (CAr), 147.7 (CAr), 140.8 (CAr), 139.9
(CArH), 138.6 (CArH), 133.0 (CAr), 132.6 (CArH), 130.0 (CArH),
129.8 (CAr), 129.5 (CArH), 127.8 (CArH), 126.3 (CAr), 125.5 (CAr),
122.4 (CArH), 121.1 (CArH), 22.8 ppm (CH3). UV−vis (DMF): λ (ε)
282 (25 750), 311 (21 800), 337 (13 200), 360 (sh), 400 (sh), 485 nm
(8400 M−1 cm−1). Anal. Calcd for C23H16N3NiCl: C, 64.46; H, 3.76.
Found: C, 64.30; H, 3.99%.
Synthesis of (Me‑PhenNNNQuin)PdCl. To a stirred solution of L2
(0.22 g, 0.66 mmol) in 10 mL of THF, Pd(COD)Cl2 (0.17 g, 0.60
mmol) and NaOtBu (0.060 g, 0.63 mmol) were added, and the
mixture was stirred vigorously at 70 °C for 12 h. The resulting red
suspension was allowed to cool, and the volatiles were removed in
vacuo. The residue was then washed with diethyl ether (3 × 10 mL)
and ethanol (3 × 10 mL). Solubility is similar to that of 2-Ni. Isolated
yield of 2-Pd = 0.228 g (83%). 1H NMR (CDCl3, 500 MHz, 22 °C): δ
9.27 (s, 1H, CAr−H), 8.96 (br s, 1H, CAr−H), 8.43 (d, 1H, JHH = 8.6
Hz, CAr−H), 8.17 (d, 1H, JHH = 8.0 Hz, CAr−H), 8.00 (d, 1H, JHH
=
7.9 Hz, CAr−H), 7.86 (app t, 1H, JHH = 7.3 Hz, CAr−H), 7.67 (app t,
1H, JHH = 7.0 Hz, CAr−H), 7.54 (s, 1H, CAr−H), 7.48−7.43
(overlapped m, 2H, CAr−H), 7.40−7.31 (m, 1H, CAr−H), 7.0 (br s,
1H, CAr−H), 2.60 ppm (s, 3H, CH3). 13C{1H} NMR (CDCl3, 500
MHz, 22 °C): δ 151.8 (CArH), 149.9 (CAr), 149.8 (CAr), 148.9
(CArH), 148.3 (CAr), 141.4 (CAr), 140.1 (CArH), 138.7 (CArH), 132.8
(CAr), 132.7 (CArH), 131.3 (CAr), 129.9 (CArH), 129.6 (CArH), 128.1
(CArH), 126.9 (CAr), 126.2 (CArH), 122.6 (CArH), 121.2 (CArH),
114.8 (CArH), 114.2 (CAr), 112.5 (CAr), 110.7 (CAr), 22.8 ppm (CH3).
UV−vis (DMF): λ (ε) 266 (30 000), 277 (28 850), 307 (22 050), 336
(sh), 392 (4250), 489 nm (9950 M−1 cm−1). Anal. Calcd for
C23H16N3PdCl: C, 58.00; H, 3.39. Found: C, 57.54; H, 3.37%.
Synthesis of (Me‑PhenNNNQuin)PtCl. To a stirred solution of L2
(0.20 g, 0.60 mmol) in 10 mL of THF, Pt(COD)Cl2 (0.22g, 0.60
mmol) and NaOtBu (0.06 g, 0.63 mmol) were added, and the mixture
was stirred vigorously at 70 °C for 12 h. The resulting red suspension
1
(93%). H NMR (CDCl3, 500 MHz, 22 °C): δ 10.69 (br s, 1H, N−
H), 9.27 (s, 1H, C6−H), 8.99 (dd, 1H, JHH = 4.1, 1.7 Hz; QuinCAr−H),
Phen
8.57 (d, 1H, JHH = 8.3 Hz;
C −H), 8.14 (dd, 1H, JHH = 8.2, 1.6
Ar
Quin
Hz;
C −H), 8.04 (d, 1H, JHH = 7.7 Hz; PhenCAr−H), 7.94 (d, 1H,
Ar
Quin
Phen
JHH = 7.6 Hz;
C −H), 7.86 (s, 1H,
C −H), 7.85 (s, 1H,
Ar
Ar
Phen
Phen
C −H), 7.83−7.77 (m, 1H,
C −H), 7.67 (app t, 1H, JHH =
Ar
Ar
Phen
Quin
7.7 Hz;
C −H), 7.54 (app t, 1H, JHH = 7.9 Hz,
C −H), 7.45
Ar
Ar
Quin
(dd, 1H, JHH = 8.2, 4.2 Hz;
C −H), 7.32 (d, 1H, JHH = 8.1 Hz,
Ar
C −H), 2.65 ppm (s, 3H, CH3). 13C{1H} NMR (CDCl3, 500
Quin
Ar
MHz, 22 °C): δ 150.1 (PhenCArH), 148.1 (QuinCArH), 140.2 (CAr),
139.4 (CAr), 139.2 (CAr), 137.5 (CAr), 136.2 (QuinCArH), 133.8 (CAr),
132.6 (CAr), 130.6 (PhenCArH), 129.1 (CAr), 128.7 (PhenCArH), 127.3
Quin
(
(
C H), 127.2 (PhenCArH), 126.4 (CAr), 124.8 (CAr), 122.4
Ar
C H), 121.7 (QuinCArH), 117.7 (QuinCArH), 112.8 (PhenCArH),
Phen
Ar
112.6 (PhenCArH), 109.8 (QuinCArH), 22.9 ppm (CH3). UV−vis
I
DOI: 10.1021/acs.inorgchem.7b00075
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
was allowed to cool, and the volatiles were removed in vacuo. The
residue was then was washed with diethyl ether (3 × 10 mL) and
acetonitrile (3 × 10 mL). Solubility is similar to that of 2-Ni and 2-Pd.
Computational Details. All calculations were performed using the
Gaussian 09 program package.41 Initial geometries were taken from X-
ray crystallographic data and were optimized with M06/6-31+G(d,p)
method. Vibrational frequencies were computed at the same level to
identify structures as energy-minimum or transition-state structures
and to evaluate zero-point vibrational energies and thermal energies at
298 K. Solvation effects (CH2Cl2) were modeled using the SMD
approach. SMD-TDDFT calculations were conducted using M06/6-
31+G(d,p) with solvent equilibration. The first 50 states were
considered in all SMD-TDDFT calculations to cover UV and visible
range of the spectrum.
1
Isolated yield of 2-Pt = 0.239 g (71%). H NMR (CDCl3, 500 MHz,
22 °C): δ 9.49 (s, 1H, CAr−H), 9.17 (d, 1H, JHH = 4.7 Hz, CAr−H),
8.40 (d, 1H, JHH = 8.2 Hz, CAr−H), 8.22 (d, 1H, JHH = 8.1 Hz, CAr−
H), 8.02 (d, 1H, JHH = 7.8 Hz, CAr−H), 7.86 (app t, 1H, JHH = 7.5 Hz,
CAr−H), 7.67−7.65 (overlapped m, 2H, CAr−H), 7.53 (s, 1H, CAr−
H), 7.47−7.40 (overlapped m, 2H, CAr−H), 7.36 (dd, 1H, JHH = 7.9,
4.9 Hz; CAr−H), 6.97 (d, 1H, JHH = 7.7 CAr−H), 2.60 ppm (s, 3H,
CH3). 13C{1H} NMR (CDCl3, 500 MHz, 22 °C): δ 151.1 (CArH),
149.3 (CAr), 149.2 (CAr), 148.7 (CAr), 148.3 (CArH), 142.2 (CAr),
140.0 (CArH), 138.8 (CArH), 132.9 (CArH), 132.7 (CArH), 131.5
(CAr), 129.9 (CArH), 129.4 (CArH), 128.2 (CArH), 127.0 (CAr), 126.2
(CAr), 122.6 (CArH), 121.2 (CArH), 115.4 (CArH), 114.7 (CAr), 113.5
(CAr), 111.1 (CArH), 22.8 (CH3) ppm. Anal. Calcd for C23H16N3PtCl:
C, 48.90; H, 2.85. Found: C: 48.64; H: 2.87%.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b00075.
Synthesis of (Me‑PhenNNNPhen‑Me)NiCl. To a stirred solution of L3
(0.20 g, 0.50 mmol) in CH2Cl2 (10 mL), NiCl2·6H2O (0.12 g, 0.50
mmol) and NaOtBu (0.052 g, 0.53 mmol) were added, and then the
solution was stirred vigorously at 50 °C for 12 h. The resulting red
suspension was allowed to cool, and the volatiles were removed in
vacuo. The red residue was then washed with diethyl ether (3 × 10
mL) and ethanol (3 × 10 mL). Isolated yield of 3-Ni = 0.221 g (89%).
1H NMR (CDCl3, 500 MHz, 22 °C): δ 9.10 (s, 2H, CAr−H), 8.43 (d,
2H, JHH = 8.3 Hz, CAr−H), 8.00 (d, 2H, JHH = 8.1 Hz, CAr−H), 7.92−
7.81 (m, 2H, CAr−H), 7.65 (app t, 2H, JHH = 7.5 Hz, CAr−H), 7.48 (s,
2H, CAr−H), 7.36 (s, 2H, CAr−H), 2.60 ppm (s, 6H, CH3). 13C{1H}
NMR (CDCl3, 500 MHz, 22 °C): δ 154.0 (CArH), 139.9 (CArH),
133.0 (CAr), 132.6 (CArH), 130.0 (CArH), 127.8 (CArH), 126.3 (CAr),
125.6 (CArH), 122.4 (CArH), 116.24 (CAr), 113.3 (CAr), 109.2 (CArH),
107.1 (CArH), 23.0 ppm (CH3). UV−vis (DMF): λ (ε) 265 (22 300),
274 (sh), 319 (13 600), 339 (11 250), 358 (7500), 398 (sh), 498 nm
(4100 M−1 cm−1). Anal. Calcd for C28H20N3NiCl: C, 68.27; H, 4.09.
Found: C, 68.28; H, 4.11%.
Experimental details of optimization of cross-coupling
routes to 4-Br, 4-NO2, 4-NH2, L2, and L3; multinuclear
NMR spectra of all new compounds; details of X-ray
crystallography experiments; details of computational
methods (PDF)
X-ray crystallographic information (CIF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: david.herbert@umanitoba.ca.
■
ORCID
David E. Herbert: 0000-0001-8190-2468
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Synthesis of (Me‑PhenNNNPhen‑Me)PdCl. To a stirred solution of L3
(0.22 g, 0.55 mmol) in THF (10 mL), Pd(COD)Cl2 (0.14 g, 0.50
mmol) and NaOtBu (0.050 g, 0.53 mmol) were added, and the
mixture was stirred vigorously at 70 °C for 12 h. The resulting red
suspension was allowed to cool, and the volatiles were removed in
vacuo. The red residue was then washed with diethyl ether (3 × 10
mL) and ethanol (3 × 10 mL). Isolated yield of 3-Pd = 0.211 g (78%).
1H NMR (CDCl3, 500 MHz, 22 °C): δ 9.38 (s, 2H, CAr−H), 8.50 (d,
2H, JHH = 8.3 Hz, CAr−H), 8.08 (d, 2H, JHH = 7.9 Hz, CAr−H), 7.94−
7.87 (m, 2H, CAr−H), 7.72 (app t, 2H, JHH = 7.4 Hz, CAr−H), 7.67 (s,
2H, CAr−H), 7.53 (s, 2H, CAr−H), 2.66 ppm (s, 6H, CH3). 13C{1H}
NMR (CDCl3, 500 MHz, 22 °C): δ 151.8 (CArH), 132.8 (CArH),
130.0 (CArH), 128.2 (CArH), 122.7 (CArH), 22.9 ppm (CH3). The
poor solubility of 3-Pd precluded assignment of all peaks in the
13C{1H} NMR spectrum. UV−vis (DMF): λ (ε) 266 (31 350),
318(16 200), 335 (10 550), 397 (3800), 496 nm (5350 M−1 cm−1).
Anal. Calcd for C28H20N3PdCl·(CHCl3): C, 52.80; H, 3.21. Found: C,
52.72; H, 3.01%.
Funding
The Natural Sciences and Engineering Research Council is
thanked for a Discovery Grant to D.E.H. (RGPIN-2013−
03551) and a Canada Graduate Scholarship (P.K.G.). Purchase
of an X-ray diffractometer was possible through support of the
Canada Foundation for Innovation and Research Manitoba
(No. 32146). The Univ. of Manitoba is gratefully acknowledged
for start-up funding (D.E.H.) and GETS support (P.M.,
P.K.G.).
Notes
The authors declare no competing financial interest.
CCDC Nos. 1526650−1526657 contain the supplementary
crystallographic data for this paper. The data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/structures.
Synthesis of (Me‑PhenNNNPhen‑Me)PtCl. To a stirred solution of L3
(0.22 g, 0.55 mmol) in THF (10 mL), Pt(COD)Cl2 (0.14 g, 0.5
mmol) and NaOtBu (0.050 g, 0.53 mmol) were added, and the
mixture was stirred vigorously at 70 °C for 12 h. The resulting red
suspension was allowed to cool, and the volatiles were removed in
vacuo. The red residue was washed with diethyl ether (3 × 10 mL)
and acetonitrile (3 × 10 mL). Solubility of 3-Pt was generally poor in
ACKNOWLEDGMENTS
■
We are grateful to Prof. M. Khajehpour for access to a UV−vis
spectrometer. M. Cooper and Prof. F. Hawthorne are gratefully
acknowledged for collection of crystal data for L2 and 2-Ni.
1
all organic solvents. Isolated yield of 3-Pt = 0.226 g (65%). H NMR
REFERENCES
(CDCl3, 300 MHz, 22 °C): δ 9.58 (s, 2H, CAr−H), 8.45 (d, 2H, JHH
=
■
(1) (a) Roznyatovskiy, V. V.; Lee, C.-H.; Sessler, J. L. π-Extended
Isomeric and Expanded Porphyrins. Chem. Soc. Rev. 2013, 42, 1921−
1933. (b) Flamigni, L.; Encinas, S.; Barigelletti, F.; MacDonnell, F. M.;
Kim, K.-J.; Puntoriero, F.; Campagna, S. Excited-State Interconversion
Between Emissive MLCT Levels in a Dinuclear Ru(II) Complex
Containing a Bridging Ligand with an Extended π System. Chem.
Commun. 2000, 1185−1186. (c) Hayashi, K.; Nakatani, M.; Hayashi,
A.; Takano, M.; Okazaki, M.; Toyota, K.; Yoshifuji, M.; Ozawa, F.
8.3 Hz, CAr−H), 8.07 (d, 2H, JHH = 7.9 Hz, CAr−H), 7.93−7.86 (m,
2H, CAr−H), 7.77−7.60 (overlapped m, 4H, CAr−H), 7.47 (s, 2H,
CAr−H), 2.65 ppm (s, 6H, CH3). 13C{1H} NMR (CDCl3, 500 MHz,
22 °C): δ 151.0 (CArH), 140.0 (CArH), 132.7 (CArH), 129.9 (CArH),
128.3 (CArH), 126.2 (CArH), 122.7 (CArH), 22.9 ppm (CH3). Six
aromatic carbon signals could not be assigned in the 13C NMR
spectrum due poor solubility. Anal. Calcd for C28H20N3PtCl: C, 53.47;
H, 3.20. Found: C, 52.83; H, 3.31%.
J
DOI: 10.1021/acs.inorgchem.7b00075
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Synthesis and Structures of Platinum(0) Alkyne Complexes with
Extended π-Conjugated Systems. Organometallics 2008, 27, 1970−
1972. (d) Hanson, K.; Roskop, L.; Djurovich, P. I.; Zahariev, F.;
Gordon, M. S.; Thompson, M. E. A Paradigm for Blue- or Red-Shifted
Absorption of Small Molecules Depending on the Site of π-Extension.
J. Am. Chem. Soc. 2010, 132, 16247−16255. (e) Hussain, M.; El-Shafei,
A.; Islam, A.; Han, L. Structure-Property Relationship of Extended π-
Conjugation of Ancillary Ligands with and without an Electron Donor
of Heteroleptic Ru(II) Bipyridyl Complexes for High Efficiency Dye-
Sensitized Solar Cells. Phys. Chem. Chem. Phys. 2013, 15, 8401−8408.
(f) Li, Z.; Sun, W. Synthesis, Photophysics, and Reverse Saturable
Absorption of Platinum Complexes Bearing Extended π-Conjugated
CNN Ligands. Dalton Trans. 2013, 42, 14021−14029. (g) He, M.; Ji,
Z.; Huang, Z.; Wu, Y. Molecular Orbital Engineering of a
Panchromatic Cyclometalated Ru(II) Dye for p-Type Dye-Sensitized
Solar Cells. J. Phys. Chem. C 2014, 118, 16518−16525. (h) Li, Z.; Cui,
P.; Wang, C.; Kilina, S.; Sun, W. Nonlinear Absorbing Cationic
Bipyridyl Iridium(III) Complexes Bearing Cyclometalating Ligands
with Different Degrees of π-Conjugation: Synthesis, Photophysics, and
Reverse Saturable Absorption. J. Phys. Chem. C 2014, 118, 28764−
28775. (i) Ozawa, H.; Fukushima, K.; Urayama, A.; Arakawa, H.
Efficient Ruthenium Sensitizer with an Extended π-Conjugated
Terpyridine Ligand for Dye-Sensitized Solar Cells. Inorg. Chem.
2015, 54, 8887−8889. (j) Kuramochi, Y.; Ishitani, O. Iridium(III) 1-
Phenylisoquinoline Complexes as a Photosensitizer for Photocatalytic
CO2 Reduction: A Mixed System with a Re(I) Catalyst and a
Supramolecular Photocatalyst. Inorg. Chem. 2016, 55, 5702−5709.
(k) Fuertes, S.; Chueca, A. J.; Peralvarez, M.; Borja, P.; Torrell, M.;
Carreras, J.; Sicilia, V. White Light Emission from Planar Remote
Phosphor Based on NHC Cycloplatinated Complexes. ACS Appl.
Mater. Interfaces 2016, 8, 16160−16169.
(2) (a) Kappaun, S.; Rentenberger, S.; Pogantsch, A.; Zojer, E.;
Mereiter, K.; Trimmel, G.; Saf, R.; Moeller, K. C.; Stelzer, F.; Slugovc,
C. Organoboron Quinolinolates with Extended Conjugated Chromo-
phores: Synthesis, Structure, and Electronic and Electroluminescent
Properties. Chem. Mater. 2006, 18, 3539−3547. (b) Kiprof, P.;
Carlson, J. C.; Anderson, D. R.; Nemykin, V. N. Systematic Color
Tuning of a Family of Luminescent Azole-Based Organoboron
Compounds Suitable for OLED Applications. Dalton Trans. 2013,
42, 15120−15132. (c) Barbon, S. M.; Staroverov, V. N.; Gilroy, J. B.
Effect of Extended π Conjugation on the Spectroscopic and
Electrochemical Properties of Boron Difluoride Formazanate Com-
plexes. J. Org. Chem. 2015, 80, 5226−5235. (d) Yamazawa, S.;
Nakashima, M.; Suda, Y.; Nishiyabu, R.; Kubo, Y. 2,3-Naphtho-Fused
BODIPYs as Near-Infrared Absorbing Dyes. J. Org. Chem. 2016, 81,
1310−1315.
(3) Chelucci, G.; Thummel, R. P. Chiral 2,2′-Bipyridines, 1,10-
Phenanthrolines, and 2,2′:6′,2″-Terpyridines: Syntheses and Applica-
tions in Asymmetric Homogeneous Catalysis. Chem. Rev. 2002, 102,
3129−3170.
(4) Gunanathan, C.; Gnanaprakasam, B.; Iron, M. A.; Shimon, L. J.
W.; Milstein, D. ″Long-Range″ Metal-Ligand Cooperation in H2
Activation and Ammonia-Promoted Hydride Transfer with a
Ruthenium-Acridine Pincer Complex. J. Am. Chem. Soc. 2010, 132,
14763−14765.
(5) Neufeldt, S. R.; Sanford, M. S. Controlling Site Selectivity in
Palladium-Catalyzed C-H Bond Functionalization. Acc. Chem. Res.
2012, 45, 936−946.
(6) Krichevsky, O.; Bonnet, G. Fluorescence Correlation Spectros-
copy: the Technique and its Applications. Rep. Prog. Phys. 2002, 65,
251−297.
(7) Tumir, L.-M.; Radic Stojkovic, M.; Piantanida, I. Come-back of
Phenanthridine and Phenanthridinium Derivatives in the 21st
Century. Beilstein J. Org. Chem. 2014, 10, 2930−2954.
(8) Park, G. Y.; Wilson, J. J.; Song, Y.; Lippard, S. J. Phenanthriplatin,
a Monofunctional DNA-Binding Platinum Anticancer Drug Candidate
with Unusual Potency and Cellular Activity Profile. Proc. Natl. Acad.
Sci. U. S. A. 2012, 109, 11987−11992.
(9) (a) Lu, L.-Q.; Li, Y.; Junge, K.; Beller, M. Iron-Catalyzed
Hydrogenation for the In Situ Regeneration of an NAD(P)H Model:
Biomimetic Reduction of α-Keto-/α-Iminoesters. Angew. Chem., Int.
Ed. 2013, 52, 8382−8386. (b) Chen, Q.-A.; Gao, K.; Duan, Y.; Ye, Z.-
S.; Shi, L.; Yang, Y.; Zhou, Y.-G. Dihydrophenanthridine: A New and
Easily Regenerable NAD(P)H Model for Biomimetic Asymmetric
Hydrogenation. J. Am. Chem. Soc. 2012, 134, 2442−2448.
(10) (a) Kido, J.; Endo, J. A Novel Electroluminescent Metal
Complex: Tris(4-phenanthridinolato)aluminum(III). Chem. Lett.
1997, 26, 593−594. (b) Fukase, A.; Kido, J. Organic Electro-
luminescent Devices Having Self-doped Cathode Interface Layer. Jpn.
J. Appl. Phys., Part 2 2002, 41, L334−L336.
(11) Valk, J.-M.; Claridge, T. D. W.; Brown, J. M.; Hibbs, D.;
Hursthouse, M. B. Synthesis and Chemistry of a New P-N Chelating
Ligand: (R)- and (S)-6-(2′-diphenylphosphino-1′-naphthyl)-
phenanthridine. Tetrahedron: Asymmetry 1995, 6, 2597−610.
(12) Raszeja, L.; Maghnouj, A.; Hahn, S.; Metzler-Nolte, N. A Novel
Organometallic ReI Complex with Favourable Properties for
Bioimaging and Applicability in Solid-Phase Peptide Synthesis.
ChemBioChem 2011, 12, 371−376.
(13) Sicilia, V.; Fuertes, S.; Martin, A.; Palacios, A. N-Assisted CPh-H
Activation in 3,8-Dinitro-6-phenylphenanthridine. New C,N-Cyclo-
metalated Compounds of Platinum(II): Synthesis, Structure, and
Luminescence Studies. Organometallics 2013, 32, 4092−4102.
(14) Jiang, B.; Gu, Y.; Qin, J.; Ning, X.; Gong, S.; Xie, G.; Yang, C.
Deep-Red Iridium(III) Complexes Cyclometalated by Phenanthridine
Derivatives for Highly Efficient Solution-Processed Organic Light-
Emitting Diodes. J. Mater. Chem. C 2016, 4, 3492−3498.
(15) Mondal, R.; Giesbrecht, P. K.; Herbert, D. E. Nickel(II),
Copper(I) and Zinc(II) Complexes Supported by a (4-
diphenylphosphino)phenanthridine Ligand. Polyhedron 2016, 108,
156−162.
(16) (a) Jensen, K. A.; Nielsen, P. H. Chelates with Heterocyclic
Ligands. I. Chelates Derived from N,N′-Bis(8-quinolyl)-
ethylenediamine and Analogous Compounds. Acta Chem. Scand.
1964, 18, 1−10. (b) Puzas, J. P.; Nakon, R.; Petersen, J. L. Direct
Evidence for an SN1CB Mechanism. 4. Crystal and Molecular
Structure of Chloro(bis(8-quinolinyl)amido-N1,N2,N3)copper(II), a
Metal Chelate Containing an sp2-Hybridized Deprotonated Amine.
Inorg. Chem. 1986, 25, 3837−40. (c) Peters, J. C.; Harkins, S. B.;
Brown, S. D.; Day, M. W. Pincer-like Amido Complexes of Platinum,
Palladium, and Nickel. Inorg. Chem. 2001, 40, 5083−5091. (d) Maiti,
D.; Paul, H.; Chanda, N.; Chakraborty, S.; Mondal, B.; Puranik, V. G.;
Kumar Lahiri, G. Synthesis, Structure, Spectral and Electron-Transfer
Properties of Octahedral-[CoIII(L)2]+/[ZnII(L)2] and Square Planar-
[CuII(L){OC(O)CH3}] Complexes Incorporating Anionic Form of
Tridentate Bis(8-quinolinyl)amine Ligand. Polyhedron 2004, 23, 831−
840.
(17) (a) Chase, P. A.; van Koten, G. Nitrogen-Based Pincers: A
Versatile Platform for Organometallic Chemistry. In The Chemistry of
Pincer Compounds; Jensen, C. M., Ed.; Elsevier Science B.V.:
Amsterdam, 2007; pp 181−233. (b) Gade, L. H.; Melen, R. L. New
Chemistry with Anionic NNN Pincer Ligands. In The Privileged Pincer-
Metal Platform: Coordination Chemistry & Applications; van Koten, G.,
Gossage, R. A., Eds. Springer International Publishing: New York,
2016; Vol. 54, pp 179−208.
(18) Ruiz-Castillo, P.; Buchwald, S. L. Applications of Palladium-
Catalyzed C−N Cross-Coupling Reactions. Chem. Rev. 2016, 116,
12564−12649.
(19) Tummatorn, J.; Krajangsri, S.; Norseeda, K.; Thongsornkleeb,
C.; Ruchirawat, S. A New Synthetic Approach to 6-Unsubstituted
Phenanthridine and Phenanthridine-like Compounds Under Mild and
Metal-Free Conditions. Org. Biomol. Chem. 2014, 12, 5077−5081.
́ ́
(20) Maksic, Z. B.; Baric, D.; Muller, T. Clar’s Sextet Rule Is a
̈
Consequence of the σ-Electron Framework. J. Phys. Chem. A 2006,
110, 10135−10147.
(21) Macrae, C. F.; Edgington, P. R.; McCabe, P.; Pidcock, E.;
Shields, G. P.; Taylor, R.; Towler, M.; van de Streek, J. Mercury:
K
DOI: 10.1021/acs.inorgchem.7b00075
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Visualization and Analysis of Crystal Structures. J. Appl. Crystallogr.
2006, 39, 453−457.
(35) Lee, C.-I.; Zhou, J.; Ozerov, O. V. Catalytic Dehydrogenative
Borylation of Terminal Alkynes by a SiNN Pincer Complex of Iridium.
J. Am. Chem. Soc. 2013, 135, 3560−3566.
(22) Betley, T. A.; Qian, B. A.; Peters, J. C. Group VIII Coordination
Chemistry of a Pincer-Type Bis(8-quinolinyl)amido Ligand. Inorg.
Chem. 2008, 47, 11570−11582.
(36) Tsuji, J. Palladium Reagents and Catalysts: New Perspectives for
the 21st Century; Wiley: Hoboken, NJ, 2004.
(37) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.;
Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I. NMR
Chemical Shifts of Trace Impurities: Common Laboratory Solvents,
Organics, and Gases in Deuterated Solvents Relevant to the
Organometallic Chemist. Organometallics 2010, 29, 2176−2179.
(38) Connelly, N. G.; Geiger, W. E. Chemical Redox Agents for
Organometallic Chemistry. Chem. Rev. 1996, 96, 877−910.
(39) Guthrie, D. B.; Curran, D. P. Asymmetric Radical and Anionic
Cyclizations of Axially Chiral Carbamates. Org. Lett. 2009, 11, 249−
251.
(40) Van Rossom, W.; Asby, D. J.; Tavassoli, A.; Gale, P. A.
Perenosins: A New Class of Anion Transporter with Anti-Cancer
Activity. Org. Biomol. Chem. 2016, 14, 2645−2650.
(41) 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. Gaussian 09, revision A. 2; Gaussian, Inc.:
Wallingford, CT, 2009 (see Supporting Information for full reference).
(23) Harkins, S. B.; Peters, J. C. Unexpected Photoisomerization of a
Pincer-type Amido Ligand Leads to Facial Coordination at Pt(IV).
Inorg. Chem. 2006, 45, 4316−4318.
(24) Testa, A. C. The N-B Vibrational Frequency in Complexes of
Aromatic Azines with BCl3. Spectrochim. Acta, Part A 1999, 55A, 299−
309.
(25) Johnstone, T. C.; Lippard, S. J. The Chiral Potential of
Phenanthriplatin and Its Influence on Guanine Binding. J. Am. Chem.
Soc. 2014, 136, 2126−2134.
(26) Norek, M.; Dresner, J.; Prochorow, J. Spectroscopy and
Photophysics of Monoazaphenanthrenes. I. Absorption and Fluo-
rescence Spectra of Phenanthridine and 7,8-Benzoquinoline. Acta Phys.
Pol., A 2003, 104, 425−439.
(27) Sutherland, D.; Compton, C. The Absorption Spectra of Some
Substituted Quinolines and Their Methiodides. J. Org. Chem. 1952, 17,
1257−1261.
(28) (a) Slattery, D. K.; Linkous, C. A.; Gruhn, N. E.; Baum, J. C.
Semiempirical MO and Voltammetric Estimation of Ionization
Potentials of Organic Pigments. Comparison to Gas Phase Ultraviolet
Photoelectron Spectroscopy. Dyes Pigm. 2001, 49, 21−27. (b) Dan-
drade, B. W.; Datta, S.; Forrest, S. R.; Djurovich, P.; Polikarpov, E.;
Thompson, M. E. Relationship Between the Ionization and Oxidation
Potentials of Molecular Organic Semiconductors. Org. Electron. 2005,
6, 11−20. (c) Djurovich, P. I.; Mayo, E. I.; Forrest, S. R.; Thompson,
M. E. Measurement of the Lowest Unoccupied Molecular Orbital
Energies of Molecular Organic Semiconductors. Org. Electron. 2009,
10, 515−520.
(29) Wopschall, R. H.; Shain, I. Effects of Adsorption of Electroactive
Species in Stationary Electrode Polarography. Anal. Chem. 1967, 39,
1514−1527.
(30) Davidson, J. J.; DeMott, J. C.; Douvris, C.; Fafard, C. M.;
Bhuvanesh, N.; Chen, C.-H.; Herbert, D. E.; Lee, C.-I.; McCulloch, B.
J.; Foxman, B. M.; Ozerov, O. V. Comparison of the Electronic
Properties of Diarylamido-Based PNZ Pincer Ligands: Redox Activity
at the Ligand and Donor Ability Toward the Metal. Inorg. Chem. 2015,
54, 2916−2935.
(31) Yan, L.; Zhao, D.; Lan, J.; Cheng, Y.; Guo, Q.; Li, X.; Wu, N.;
You, J. Palladium-Catalyzed Tandem N-H/C-H Arylation: Regiose-
lective Synthesis of N-Heterocycle-Fused Phenanthridines as Versatile
Blue-emitting Luminophores. Org. Biomol. Chem. 2013, 11, 7966−
7977.
(32) Bossi, A.; Rausch, A. F.; Leitl, M. J.; Czerwieniec, R.; Whited, M.
T.; Djurovich, P. I.; Yersin, H.; Thompson, M. E. Photophysical
Properties of Cyclometalated Pt(II) Complexes: Counterintuitive Blue
Shift in Emission with an Expanded Ligand π System. Inorg. Chem.
2013, 52, 12403−12415.
(33) (a) Zhao, Y.; Truhlar, D. G. The M06 Suite of Density
Functionals for Main Group Thermochemistry, Thermochemical
Kinetics, Noncovalent Interactions, Excited States, and Transition
Elements: Two New Functionals and Systematic Testing of Four
M06-Class Functionals and 12 Other Functionals. Theor. Chem. Acc.
2008, 120, 215−241. (b) 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. (c) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.;
Frisch, M. J. Ab Initio Calculation of Vibrational Absorption and
Circular Dichroism Spectra Using Density Functional Force Fields. J.
Phys. Chem. 1994, 98, 11623−11627.
(34) Rogers, J. E.; Nguyen, K. A.; Hufnagle, D. C.; McLean, D. G.;
Su, W.; Gossett, K. M.; Burke, A. R.; Vinogradov, S. A.; Pachter, R.;
Fleitz, P. A. Observation and Interpretation of Annulated Porphyrins:
Studies on the Photophysical Properties of meso-Tetraphenylmetallo-
porphyrins. J. Phys. Chem. A 2003, 107, 11331−11339.
L
DOI: 10.1021/acs.inorgchem.7b00075
Inorg. Chem. XXXX, XXX, XXX−XXX