Diruthenium complexes with a 1,8-Naphthyridine-based Bis(silyl) supporting ligand: Synthesis and structures of complexes containing RuII2(μ-H)2 and RuI2 cores

Article abstract of DOI:10.1246/cl.171099

We designed a novel naphthyridine-based supporting ligand involving two silyl coordinating moieties at 2,7-positions, t^-BuNBSi, for the synthesis of dinuclear metal complexes. Reaction of a ligand precursor ^t-BuNBSi(H)₂ (1) with Ru₃(CO)₁₂ gave a di-μ-hydridodiruthenium(II,II) complex (^t-BuNBSi)Ru₂(μ-H)₂(CO)₄ (2). Photoirradiation to 2 resulted in the formation of a diruthenium(I,I) complex (^t-BuNBSi)Ru₂(CO)₆ (3). The SiRuRuSi linkage of 2 takes a zigzag arrangement, whereas that of 3 adopts a roughly linear one.

Full text of DOI:10.1246/cl.171099

Advance Publication Cover Page
Diruthenium Complexes with a 1,8-Naphthyridine-Based Bis(silyl) Supporting Ligand:
Synthesis and Structures of Complexes Containing RuII
(µ-H)
and RuI
Cores
2
2
2
Indra Kusuma, Takashi Komuro, and Hiromi Tobita*
Advance Publication on the web January 13, 2018
doi:10.1246/cl.171099
©
2018 The Chemical Society of Japan
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1
Diruthenium Complexes with a 1,8-Naphthyridine-Based Bis(silyl) Supporting Ligand:
II
I
2
Synthesis and Structures of Complexes Containing Ru (µ-H) and Ru Cores
2
2
Indra Kusuma, Takashi Komuro, and Hiromi Tobita*
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
E-mail: tobita@m.tohoku.ac.jp
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We designed a novel naphthyridine-based supporting
ligand involving two silyl coordinating moieties at 2,7-
4
2 development of an unprecedented napy-based ligand having
t-Bu
43 two silyl ligand moieties in the substituents at 2,7-positions
44 for the synthesis of dimetal complexes. We have previously
45 synthesized a mononuclear ruthenium–carbonyl comple5xa
46 bearing an SiNSi-type bis(silyl)–pyridine pincer ligand.
positions,
NBSi, for the synthesis of dinuclear metal
t-Bu
complexes. Reaction of a ligand precursor NBSi(H) (1)
2
with Ru (CO)
gave
a di-µ-hydridodiruthenium(II,II)
3
12
t-Bu
complex ( NBSi)Ru (µ-H) (CO) (2). Photoirradiation to
2
2
4
t-
B2 u resulted in formation of a diruthenium(I,I) complex (
NBSi)Ru (CO) (3). The Si–Ru–Ru–Si linkage of 2 takes
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Along this line, we developed 2,7-bis[(di-tert-
2
6
butylsilyl)methyl]-1,8-naphthyridine as an St-BiNu NSi-type
a zigzag arrangement, whereas that of 3 adopts a roughly
linear one.
tetradentate ligand precursor, abbreviated as
NBSi(H)2
1
(Chart 1), and examined the synthesis of diruthenium–
carbonyl complexes. Since silyl ligands possess not only
1
1
1
2
Keywords: 2,7-Disubstituted
Diruthenium complex | Silyl ligand
1,8-naphthyridine
|
strong σ-donating ability but also strong trans influence, the
t-Bu
dimetal center bearing
NBSi is expected to show some
specific structural and electronic features caused by
weakening of a metal–metal or metal–element bond(s)
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Development of supporting ligands for dinuclear
complexes is an important subject in coordination chemistry.
This is because dinuclear complexes display greater
structural variety than mononuclear ones and also show
specific reactivity arising from cooperative effect of plural
metal centers for accommodation2 and activation of
6
located trans to silyl silicon atoms.
We synthesized the target ligand precursor 2,7-bis[(di-
t-Bu
tert-butylsilyl)methyl]-1,8-naphthyridine ( NBSi(H) ) (1)
2
by six step reactions as illustrated in Scheme 1. Known 2,7-
dimethyl-1,8-naphthyridine (E) as the precursor of 1 was
prepared by a newly-designed synthetic route from easily-
1
3,4
substrates. 1,8-Naphthyridine (napy) and its derivatives
have been widely utilized as such supporting ligands, since
the napy backbone has a rigid structure and can hold two
7,8
available 2-aminopyridine, which results in moderate to
high yields of intermediates A–E. In the final step, the
2
–4
metal centers in proximity. In particular, napy derivatives
t-Bu
ligand precursor
NBSi(H)2 (1) was obtained in 88%
4
with coordinating moieties at 2,7-positions (Chart 1) have
isolated yield by dilithiation of the methyl groups of E with
n-butyllithium (2.2 equiv.) at –78 °C followed by coupling
with di-tert-butylchlorosilane (Scheme 1, see the Supporting
Information for detail). Compound 1 is the first example of
recently been attracted considerable attention as supporting
4
a,c–h
ligands for dinuclear-complex catalysts,
where a dimetal
core is effectively stabilized by chelation to each metal
1
,4a,c–e
4f
center. For example, Uyeda et al.
and Bera et al.
a
1,8-naphthyridine-based ligand precursor bearing
developed dinickel- and diruthenium-complex catalysts,
respectively, bearing napy–diimine type tetradentate ligands.
In these catalysts, each dimetal core is considered to
facilitate transformation of organic molecules effectively by
the cooperative effect. However, to the best of our
knowledge, previous 2,7-disubstituted napy ligands used for
the synthesis of dinuclear complexes were limited only to
ones having nitrogen-, oxygen-, or carbon-donor
(hydrosilyl)methyl groups at the 2,7-positions.
O
(i)
O
(ii)
(iii)
N
NH2
N
NH2
N
NH
N
NH
H
H
O
O
B
C
A
(iv)
H
Si
H
Si
4
(vi)
(v)
N
N
N
N
coordinating moieties at the ends of 2,7-substituents.
N
N
E
D
1
7
1
t-Bu
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7
2
3
4
5
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Scheme 1. Synthesis of the ligand precursor NBSi(H)
2
(1) from 2-
N; (ii) (1) n-BuLi,
(2) DMF; (iii) 3 N HCl; (iv) (1) acetone, (2) saturated KOH in
7a
aminopyridine. Reactants: (i) pivaloyl chloride, Et
3
7
a
7a
7
b
7c
MeOH; (v) (1) MeLi, (2) KMnO
equiv.), (2) (t-Bu) SiHCl (2.5 equiv.).
4
in acetone; (vi) (1) n-BuLi (2.2
2
3
3
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1
Compound 1 was characterized by NMR, IR, and mass
1
Chart 1
spectroscopy (see the Supporting Information). The
H
NMR spectrum of 1 shows only two doublet signals for the
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1
As part of our continuous study on the design and
synthesis of transition-metal complexes bearing a silyl-
ring protons of 1,8-naphthyridine at 7.83 and 7.20 ppm. An
3
Si–H signal appears as a triplet at 3.63 ppm ( J = 3.6 Hz)
HH
5
containing multidentate ligand, this time, we focused on the

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due to the coupling with two methylene protons (2.73 ppm,
doublet). Observation of one strong singlet signal for tert-
butyl groups at 0.96 ppm shows that four tert-butyl groups
44 deviations. To gain a more insight into the detailed structure
45 of the Ru H core, the hydrido-ligand positions were also
2
2
46 investigated by the DFT calculation of a simplified model
2
9
1
Me
are equivalent. In the Si{ H} NMR spectrum of 1, a signal
appears at 14.6 ppm. These observations indicate that
compound 1 adopts a C -symmetric structure in solution.
47 complex ( NBSi)Ru (µ-H) (CO) (2´), which has two
2
2
4
48 methyl groups on each silicon atom instead of tert-butyl
49 groups, at the B3PW91 level using a mixed basis set, i.e.
50 LANL2DZ (for Ru) and 6-31G(d,p) (for the other atoms)
51 (see the Supporting Information). In the optimized structure
52 of 2´, two Ru atoms are asymmetrically bridged by a pair of
53 hydrido ligands where the Ru–H bonds trans to Si (1.909 Å
54 each) are longer than those trans to CO (1.765 Å each)
55 probably due to strong trans influence of the silyl ligand
56 moieties. According to the recent suggestion of bond
57 classification for bridging hydrido complexes with M–H–M
2
v
t-Bu
The ligand precursor NBSi(H) (1) reacted with 2/3
2
molar equiv. of Ru (CO) in toluene at 90 °C to give an air-
3
12
t-Bu
stable diruthenium(II,II) complex ( NBSi)Ru (µ-H) (CO)
4
2
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
(2) as an orange powder in 31% isolated yield via Si–H
oxidative addition as well as ligand substitution (Scheme
9
1
2). The H NMR spectrum of 2 in C D shows a singlet
6
6
signal for two hydrido hydrogens at –6.21 ppm. The two
methylene protons on the same carbon atom (SiCH H )
A
B
1
2
were observed as two inequivalent doublets at 2.72 and 2.66
58 3c-2e bonds by Green, Green, and Parkin, we can
59 represent the structure of 2 as depicted in Scheme 2 by
2
1
ppm ( J = 17.2 Hz), and the H signals for the tert-butyl
HH
1
groups on each silicon atom also appeared inequivalently as
60 application of the “half-arrow” method. Since the H and
2
9
1
29
two singlets at 1.41 and 0.99 ppm. The Si{ H} NMR
spectrum of 2 exhibits a single signal for the silyl ligand
moieties at 73.8 ppm. These NMR data support that
61
Si NMR spectra show that 2 has a pseudo C -symmetric
2
62 structure (vide supra), the zigzag Si–Ru–Ru–Si arrangement
63 of 2 is considered to be maintained in solution.
complex 2 adopts a C -symmetric structure in solution
2
where the C axis passes through the midpoint between the
2
two metal centers and the central carbon atoms of the
naphthyridine ring. The IR spectrum of 2 shows four
absorption bands for CO vibration at 2013, 1990, 1944, and
–
1
1927 cm in accordance with the structure of 2.
2
2
7
8
Scheme 2. Synthesis of diruthenium complexes 2 and 3.
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Single crystal X-ray structure analysis revealed that
complex 2 has two octahedrally-coordinated Ru centers
Figure 1. Crystal structure of 2: (a) side view and (b) top view.
t-Bu
bridged by two hydrido ligands and a NBSi ligand in a µ-
66 Thermal ellipsoids are drawn at the 50% probability level, and all the
67 hydrogen atoms except hydrido hydrogens are omitted for clarity.
2
2
10
κ (Si,N):κ (Si,N) coordination mode (Figure 1a). The Si–
Ru–Ru–Si linkage adopts a zigzag arrangement (Figure 1b)
possibly due to the presence of the two µ-hydrido ligands
that bridge the two octahedral Ru centers. The Ru–Ru
distance (2.6994(5) Å) is close to that of a di-µ-
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2
Selected bond distances (Å) and angles (°) and selected torsion angles
(°): Ru(1)–Ru(2) 2.6994(5), Ru(1)–Si(1) 2.3891(13), Ru(2)–Si(2)
2.3887(11), Ru(1)–N(1) 2.202(3), Ru(2)–N(2) 2.186(4), Ru(1)–H(1)
1.69(5), Ru(1)–H(2) 1.88(8), Ru(2)–H(1) 1.86(6), Ru(2)–H(2) 1.83(8);
Ru(2)–Ru(1)–Si(1) 134.17(3), Ru(1)–Ru(2)–Si(2) 130.81(3), Si(1)–
5
hydridodiruthenium complex [(η -C Me )Ru(µ-H)(CO)]
73 Ru(1)–N(1) 80.97(10), Si(2)–Ru(2)–N(2) 80.62(10), Si(1)–Ru(1)–H(2)
5
5
2
1
1
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4
5
6
175(2), Si(2)–Ru(2)–H(1) 167.7(17); N(1)–Ru(1)–Ru(2)–N(2)
–
(2.6920(3) Å) having the same electron count. Positions of
two bridging hydrido hydrogens were determined by a
differential Fourier map and refined, but the values of Ru–H
bond distances (Ru(1)–H(1) 1.69(5) Å, Ru(1)–H(2) 1.88(8)
Å, Ru(2)–H(1) 1.86(6) Å, and Ru(2)–H(2) 1.83(8) Å) could
not be compared with each other due to their large standard
15.81(14), C(2)–Ru(1)–Ru(2)–C(4) 6.6(2), Ru(1)–N(1)–C(18)–C(17)
170.0(3), Ru(2)–N(2)–C(18)–C(17) 168.5(3).
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7
8
9
Photoreaction of complex 2 in benzene at 7 °C for 20 h
under argon using a 450 W medium pressure mercury lampt-
gave an air stable (hexacarbonyl)diruthenium complex (

3
Bu
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NBSi)Ru (CO) (3) as a dark brown powder in 47%
60 dihedral angle of 24.10(7)° between the least-squares plane
61 defined by the Ru(1), Ru(2), Si(1), and Si(2) atoms and that
62 of the 1,8-naphthyridine ring.
2
6
isolated yield (Scheme 2). Since the number of CO ligands
increased from four in complex 2 to six in complex 3, we
next examined the photoreaction of 2 under a CO
atmosphere (1 atm). As was expected, the reaction time until
completion was dramatically shortened from 20 h to 1 h,
and the NMR yield of 3 was improved from 52% to 62%.
Although we have not characterized Ru-containing
byproducts formed in these photoreactions, the conversion
from 2 to 3 is considered to proceed via the following three
processes: (1) photo-induced CO dissociation, which is well
established for carbonyl complexes, from complex 2, (2)
photo-induced reductive elimination of two hydrido ligands
from 2 possibly as H2 together with the formation of
coordinatively unsaturated species,
of liberated CO to this species giving 3.
Unlike complex 2 whose Ru centers adopt the
oxidation number of +2, the Ru centers in complex 3 have
the oxidation number of +1, demonstrating that NBSi can
support the dinuclear ruthenium center with some different
oxidation states. The Si{ H} NMR spectrum of 3 shows a
signal for the silyl coordinating moieties at 102.3 ppm. This
signal is shifted downfield in comparison with that of 2 by
28.5 ppm. The IR spectrum of 3 exhibits six terminal CO
absorption bands at 2050, 2011, 1986, 1973, 1954, and 1927
cm . Complex 3 has a characteristic color of dark brown,
which is significantly different from that of 2 (orange). The
UV-vis spectrum of 3 (Figure S11) shows two weak
absorption maxima in a longer-wavelength region (> 450
nm), i.e. 480 and 717 nm, whereas that of 2 (Figure S7) did
not show any absorption maxima in this region. Thes7e
absorption maxima are presumably attributable to metal (d )
to ligand (napy) charge transfer in accordance with the
assignments in previous reports for related diruthenium(I,I)
1
1
1
1
1
1
1
1
1
1
2
2
2
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3,14
1a5nd (3) coordination
t-Bu
2
9
1
–
1
6
3
64 Figure 2. Crystal structure of 3: (a) side view and (b) top view.
65 Thermal ellipsoids are drawn at the 50% probability level, and all the
6
6
hydrogen atoms are omitted for clarity. Selected bond distances (Å) and
3
a,b
67 angles (°) and selected torsion angles (°): Ru(1)–Ru(2) 2.8579(3),
complexes having napy-based multidentate ligands.
6
8
Ru(1)–Si(1) 2.4411(6), Ru(2)–Si(2) 2.4377(7), Ru(1)–N(1) 2.1892(19),
The molecular structure of 3 was determined by single
crystal X-ray structure analysis, revealing that complex 3
has two octahedrally-coordinated ruthenium centers bridged
6
9 Ru(2)–N(2) 2.1980(19); Ru(2)–Ru(1)–Si(1) 160.807(18), Ru(1)–
70 Ru(2)–Si(2) 160.797(18); N(1)–Ru(1)–Ru(2)–N(2) 28.12(7), C(2)–
71 Ru(1)–Ru(2)–C(5) 31.50(11), Ru(1)–N(1)–C(20)–C(19) –160.03(16),
t-Bu
10
7
2
Ru(2)–N(2)–C(20)–C(19) –160.16(16).
by
NBSi (Figure 2a). In contrast to di-µ-hydrido
complex 2, the Si–Ru–Ru–Si linkage in 3 adopts a roughly
linear arrangement in which each of the silyl silicon atoms
is located trans to the Ru–Ru bond. The Ru–Ru bond
distance of 2.8579(3) Å is similar to that of a bis(silyl)
diruthenium(I,I)
Ru(CO) {Si(OSiMe ) } (2.909(1) Å). Nevertheless, this
1
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In the H NMR spectrum of 3 in C D at room
6
6
tt-eBmu perature, each of the methylene and tert-butyl protons of
NBSi showed one singlet signal at 2.80 ppm for CH and
2
1
1.14 ppm for t-Bu. Variable temperature H NMR spectra in
CD Cl (see Figure S12) demonstrated that both of the CH
2
complex
{(Me SiO) Si}(CO) Ru–
3 3 4
16
2
2
4
3 3
and t-Bu signals gradually broadened as the solution was
cooled from 300 K to 220 K. These observations prove the
fluxionality of 3 in solution that causes the exchange of two
protons in the methylene groups and of two tert-butyl
groups bound to each silicon atom. This fluxional behavior
probably occurs through flip of the Si–Ru–Ru–Si linkage
across the naphthyridine-ring plane.
distance is far longer than those of Ru(I)–Ru(I) complexes
with napy-based ligands (normally shorter than 2.7 Å).
3
a–d,4g
This elongation is obviously caused by strong trans
influence of the silyl ligands at the axial positions leading to
large destabilization of the Ru–Ru σ-bonding orbital as
expected from the proposal by Bera et al. for related Ru(I)–
Ru(I) complexes having N- or O-coordinating axial donors
supported by two 2-substituted napy-based ligands. The
Ru(CO) –Ru(CO) fragment of 3 adopts a staggered
conformation in order to avoid steric repulsion between CO
ligands bound to two different metal centers; e.g. the C(2)–
Ru(1)–Ru(2)–C(5) torsion angle
3
a
In conclusion, we have successfully synthesized and
characterized the first 1,8-naphthyridine-based SiNNSi-type
3
3
t-Bu
chelate ligand precursor,
NBSi(H)2, and dinuclear
t-Bu
t-Bu
ruthenium- NBSi complexes 2 and 3. The NBSi ligand
was found to support two different kinds of diruthenium
cores, i.e. Ru(II)–Ru(II) in 2 and Ru(I)–Ru(I) in 3. The
Ru(II)–Ru(II) complex 2 has a zigzag arrangement of the
= 31.50(11)°. This
conformation renders the Si–Ru–Ru–Si linkage tilted
against the naphthyridine ring (Figure 2b) as reflected in the

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Alexander, M. L. Good, Inorg. Chem. 1976, 11, 2615. b) C. Vu,
D. Walker, J. Wells, S. Fox, J. Heterocycl. Chem. 2002, 39, 829.
c) C. J. Chandler, L. W. Deady, J. A. Reiss, V. Tzimos, J.
Heterocycl. Chem. 1982, 19, 1017. d) C. He, S. J. Lippard,
Tetrahedron 2000, 56, 8245. e) H. Asahara, K. Muto, N.
Nishiwaki, Tetrahedron 2014, 70, 6522.
1
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Si–Ru–Ru–Si linkage, whereas the Ru(I)–Ru(I) complex 3
takes a roughly linear Si–Ru–Ru–Si linkage with a long Ru–
Ru bond distance. Studies on the synthesis of other
t-Bu
dinuclear transition-metal complexes having
NBSi and
on the reactivity of complexes 2 and 3 toward organic
compounds are in progress.
9
During the reaction of 1 with Ru (CO)12, an insoluble black solid
3
3
4
5
6
of unidentified byproducts was also formed.
10
Crystallographic data reported in this manuscript have been
deposited with Cambridge Crystallographic Data Centre as
supplementary publication nos. CCDC-1812369 (for 2) and
CCDC-1812370 (for 3). Copies of the data can be obtained free
of charge via CCDC Website.
K. Geetharani, S. K. Bose, S. Sahoo, B. Varghese, S. M. Mobin,
S. Ghosh, Inorg. Chem. 2011, 50, 5824.
J. C. Green, M. L. H. Green, G. Parkin, Chem. Commun. 2012,
48, 11481.
This work was supported by JSPS KAKENHI Grant
Numbers JP25410058, JP15H03782, and JP16K05714 from
the Japan Society for the Promotion of Science (JSPS). We
also acknowledge the Research and Analytical Center for
Giant Molecules, Tohoku University, for mass
spectroscopic measurements and elemental analysis.
1
1
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Supporting
Information
is
available
on
83 13 a) R. N. Perutz, B. Procacci, Chem. Rev. 2016, 116, 8506. b) H.
84
http://dx.doi.org/10.1246/cl.******.
Suzuki, R. Shimogawa, Y. Muroi, T. Takao, M. Oshima, G.
Konishi, Angew. Chem., Int. Ed. 2013, 52, 1773.
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14
During monitoring of the photoreaction of 2 under CO, a singlet
1
signal of dihydrogen was observed at 4.46 ppm by H NMR
spectroscopy.
Elucidation of the formation mechanism of 3 by the
photoreaction of 2 is currently under investigation.
P. Braunstein, J. R. Galsworthy, W. Massa, J. Chem. Soc.,
Dalton Trans. 1997, 4677.
1
8
References and Notes
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a) I. G. Powers, C. Uyeda, ACS Catal. 2017, 7, 936. b) H. Suzuki,
Eur. J. Inorg. Chem. 2002, 1009.
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16
2
a) J. A. Cabeza, L. A. Oro, A. Tiripicchio, M. Tiripicchio-
Camellini, J. Chem. Soc., Dalton Trans. 1988, 1437. b) A.
Tiripicchio, M. T. Camellini, R. Usón, L. A. Oro, M. A. Ciriano,
F. Vigiuri, J. Chem. Soc., Dalton Trans. 1984, 125. c) T. Suzuki,
Inorg. Chim. Acta 2006, 359, 2431.
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4
a) S. K. Patra, N. Sadhukhan, J. K. Bera, Inorg. Chem. 2006, 45,
4007. b) S. K. Patra, J. K. Bera, Organometallics 2006, 25, 6054.
c) R. K. Das, B. Saha, S. M. W. Rahaman, J. K. Bera, Chem. Eur.
J. 2010, 16, 14459. d) B. Saha, T. Ghatak, A. Sinha, S. M. W.
Rahaman, J. K. Bera, Organometallics 2011, 30, 2051. e) M. S.
Ziegler, K. V. Lakshmi, T. D. Tilley, J. Am. Chem. Soc. 2017,
139, 5378.
For selected examples of 2,7-disubstituted 1,8-naphthyridine
ligands, see: a) C. Uyeda, T. J. Steiman, S. Pal, Synlett 2016, 27,
814 and references therein. b) M. J. Behlen, Y.-Y. Zhou, T. J.
Steiman, S. Pal, D. R. Hartline, M. Zeller, C. Uyeda, Dalton
Trans. 2017, 46, 5493. c) Y.-Y. Zhou, C. Uyeda, Angew. Chem.,
Int. Ed. 2016, 55, 3171. d) S. Pal, Y.-Y. Zhou, C. Uyeda, J. Am.
Chem. Soc. 2017, 139, 11686. e) D. R. Hartline, M. Zeller, C.
Uyeda, J. Am. Chem. Soc. 2017, 139, 13672. f) I. Dutta, A.
Sarbajna, P. Pandey, S. M. W. Rahaman, K. Singh, J. K. Bera,
Organometallics 2016, 35, 1505. g) B. Saha, S. M. W. Rahaman,
P. Daw, G. Sengupta, J. K. Bera, Chem. Eur. J. 2014, 20, 6542.
h) C.-H. Lee, C.-L. Wu, S.-A. Hua, Y.-H. Liu, S.-M. Peng, S.-T.
Liu, Eur. J. Inorg. Chem, 2015, 1417. i) J.-P. Collin, A. Jouaiti,
J.-P. Sauvage, W. C. Kaska, M. A. McLoughlin, N. L. Keder, W.
T. A. Harrison, G. D. Stucky, Inorg. Chem, 1990, 29, 2238. j) E.
Binamira-Soriaga, N. L. Keder, W. C. Kaska, Inorg. Chem, 1990,
29, 3167. k) C. He, S. J. Lippard, Inorg. Chem, 2000, 39, 5225. l)
B.-C. Tsai, Y.-H. Liu, S.-M. Peng, S.-T. Liu, Eur. J. Inorg. Chem,
2016, 2783.
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a) T. Komuro, H. Tobita, Chem. Commun. 2010, 46, 1136. b) T.
Komuro, T. Kitano, N. Yamahira, K. Ohta, S. Okawara, N.
Mager, M. Okazaki, H. Tobita, Organometallics 2016, 35, 1209
and references therein. c) T. Komuro, T. Arai, K. Kikuchi, H.
Tobita, Organometallics 2015, 34, 1211.
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M. C. MacInnis, R. McDonald, M. J. Ferguson, S. Tobisch, L.
Turculet, J. Am. Chem. Soc. 2011, 133, 13622.
a) J. A. Turner, J. Org. Chem. 1983, 48, 3401. b) T. Ghatak, M.
Sarkar, S. Dinda, I. Dutta, S. M. W. Rahaman, J. K. Bera, J. Am.
Chem. Soc. 2015, 137, 6168. c) G. R. Newkome, K. J. Theriot, V.
K. Majestic, P. A. Spruell, G. R. Baker, J. Org. Chem. 1990, 55,
2838.
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For conventional methods for the synthesis of 2,7-dimethyl-1,8-
naphthyridine (E), see: a) M. A. Cavanaugh, V. M. Cappo, C. J.