RuCp* complexes of ambidentate 4,5-diazafluorene derivatives: From linkage isomers to coordination-driven self-assembly

Article abstract of DOI:10.1021/om400846f

The coordination chemistry of the {RuCp}⁺ fragment was studied toward several 4,5-diazafluorene derivatives. The ambidentate nature of these 4,5-diazafluorene derivatives with multiple coordination sites allowed for the syntheses of different linkage isomers and self-assembled macrocycles. Both a tetramer (2) and a monomer (3) of [RuCpL] (where L^- = 4,5-diazafluorenide) were prepared with the L^- ligand. The dimeric head-to-tail macrocycles [CpRu(L_pH)]₂Cl₂ (4) and [CpRuL_p]₂ (5) were obtained with the ditopic L _pH and L_p^- ligands (where L_pH = 9-(2-(diphenylphosphino)ethyl)-4,5-diazafluorene and L_p^- = 9-(2-(diphenylphosphino)ethyl)-4,5-diazafluorenide). The bulky arene-substituted L_MesH ligand (where L_MesH = 3,6-dimesityl-4,5-diazafluorene) was prepared, and its coordination to {RuCp}⁺ gave [CpRu(L_MesH)]Cl (13). The selective syntheses of different linkage isomers of [RuCp(L_Mes)] (14 and 15) (where L_Mes^- = 3,6-dimesityl-4,5-diazafluorenide) were also demonstrated.

Full text of DOI:10.1021/om400846f

Article
pubs.acs.org/Organometallics
RuCp* Complexes of Ambidentate 4,5-Diazafluorene Derivatives:
From Linkage Isomers to Coordination-Driven Self-Assembly
Vincent T. Annibale, Rhys Batcup, Tao Bai, Sarah J. Hughes, and Datong Song*
Davenport Chemical Research Laboratories, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto,
Ontario, Canada M5S 3H6.
*
S Supporting Information
ABSTRACT: The coordination chemistry of the {RuCp*}+
fragment was studied toward several 4,5-diazafluorene derivatives.
The ambidentate nature of these 4,5-diazafluorene derivatives with
multiple coordination sites allowed for the syntheses of different
linkage isomers and self-assembled macrocycles. Both a tetramer
−
(
2) and a monomer (3) of [RuCp*L] (where L = 4,5-
−
diazafluorenide) were prepared with the L ligand. The dimeric
head-to-tail macrocycles [Cp*Ru(L H)] Cl (4) and [Cp*RuL ]
p 2
p
2
2
−
(
5) were obtained with the ditopic L H and Lp ligands (wher−e
p
LpH = 9-(2-(diphenylphosphino)ethyl)-4,5-diazafluorene and Lp
9-(2-(diphenylphosphino)ethyl)-4,5-diazafluorenide). The bulky
=
arene-substituted LMesH ligand (where LMesH = 3,6-dimesityl-4,5-
+
diazafluorene) was prepared, and its coordination to {RuCp*} gave [Cp*Ru(LMesH)]Cl (13). The selective syntheses of
different linkage isomers of [RuCp*(LMes)] (14 and 15) (where LMes− = 3,6-dimesityl-4,5-diazafluorenide) were also
demonstrated.
INTRODUCTION
exception where both coordination sites of the ligand are used
■
13
−
is [Pd(L)(PPh )Cl] , where L was bound to Pd(II) through
Ambidentate ligands, which feature several potential coordina-
tion sites, provide an opportunity to form linkage isomers or
potentially serve as building blocks for coordination-driven self-
3
2
both one of the N-donors and the anionic C-donor of the
1
ligand backbone in an η (σ)-fashion.
1
−6
Recently we have demonstrated that in the heterodinuclear
assembly.
Organometallic Ru fragments have been used in
complex [(IPr)Cu(L)Pt(Ph) ] the Cu(I) center is bound to
the self-assembly of a variety of supramolecular complexes and
macrocycles, where several display intriguing photophysical,
molecular recognition, and anticancer properties.
2
1
the carbon site of diazafluorenide in an η (π)-fashion and the
Pt(II) center is coordinated to the N,N-chelate site.
6
−12
19
Our group has been actively exploring the chemistry and
We later installed a phosphine arm at the 9-position of
reactivity of the 4,5-diazafluorene (LH) and 4,5-diazafluorenide
diazafluorene to give the L H ligand, which can also be
p
−
13−18
−
18
ligands (L ) (Chart 1).
Diazafluorene is a bipyridyl ligand
deprotonated to form the Lp ligand (Chart 1). We
demonstrated ligand transfer of Lp− from Cu(I) to either
18
Chart 1. Ambidentate Ligands Used in This Study
Rh(I) or Au(I), resulting in macrocyclic complexes. LpH and
Lp are also ambidentate ligands with phosphine and N-donor
coordination sites. In addition, Lp can also anchor a metal in
−
−
the P,C-coordination site. Recently we have demonstrated that
in the heterodinuclear complex [(IPr)Cu(L )Pt(Ph) ] the
p
2
tethered phosphine of Lp− helps anchor the Pt(II) center onto
the carbon site of the diazafluorenide, and the Cu(I) center is
19
bound to the N,N-chelate site.
The installation of aryl groups ortho to the N-donors of the
diazafluorenide framework can provide steric protection and
allow access to reactive low-coordinate N-bound metal centers
−
(
L H and L ; see Chart 1). As a monoanionic α-diimine
Ar
Ar
with a methylene linker that can be deprotonated to form the
−
ligand, LAr is analogous to the β-diketiminate ligand (also
known as nacnac), e.g., overall −1 charge, N-donor set, and
monoanionic diazafluorenide ligand. An interesting feature of
20
−
the ambidentate L ligand is that it potentially has two metal-
binding sites: the N-donors and the C-donors of the central
Cp -like ring. However in most examples L binds metals with
its nitrogen donors, without utilizing the C-donors. One
−
−
Received: August 22, 2013
Published: October 8, 2013
©
2013 American Chemical Society
6511
dx.doi.org/10.1021/om400846f | Organometallics 2013, 32, 6511−6521

Organometallics
Article
noninnocent carbon backbone. 7,21−27 These bulkier diaza-
1
precipitate. After 2 h with no agitation the dark purple microcrystalline
precipitate of 1 was collected by filtration and washed with a minimal
amount of THF and hexanes (295 mg, 75% yield). Crystals of X-ray
diffraction quality were grown from vapor diffusion of hexanes into a
−
fluorenide derivatives are also ambidentate: LAr has a N,N-
chelate site and the C-donors of the central Cp moiety; in
−
addition, there is also the possibility of the aryl substituent
participating in bonding. Similar to 4,5-diazafluorenide
derivatives, ambidentate bis-imine-functionalized pentafulvenes
1
THF solution of 1. H NMR (600 MHz, CD Cl , δ): 8.93 (d, J = 5.3
2
2
Hz, 2H), 7.80 (d, J = 7.5 Hz, 2H), 7.45 (dd, J = 7.6, 5.2 Hz, 2H), 4.13
13
(
1
s, 2H), 1.74 (s, 15H). C NMR (151 MHz, CD Cl , δ): 162.23,
28−30
2 2
−
2
also have a Cp moiety and a κ -[N,N] chelate.
1
48.89, 135.45, 131.60, 125.40, 75.61, 36.71, 10.37. H NMR (600
, δ) 8.89 (d, J = 5.2 Hz, 2H), 7.72 (d, J = 7.5 Hz, 2H),
7.37 (dd, J = 7.5, 5.3 Hz, 2H), 4.05 (s, 1H), 4.04 (s, 1H), 1.71 (s,
15H). 13C NMR (151 MHz, CDCl
, δ): 162.14, 148.73, 134.83,
31.18, 124.86, 75.18, 36.41, 10.43. Anal. Calcd for C H N RuCl: C,
−
The Cp* (C Me ) ligand has been used extensively in
organometallic chemistry as a sterically demanding, electron-
donating ligand to stabilize reactive or coordinatively
5
5
MHz, CDCl
3
3
3
1−39
40−45
46−50
1
unsaturated complexes.
Tilley
and Caulton
21 23
2
+
57.33; H, 5.27; N, 6.37. Found: C, 57.25; H, 5.21; N, 6.28.
have demonstrated the use of the {RuCp*} fragment in
reactive, π-stabilized unsaturated species including two-legged
piano-stool complexes. Stradiotto and co-workers have also
examined the chemistry of coordinatively unsaturated zwitter-
ionic RuCp* complexes and cases of linkage isomerism and
Synthesis of [Ru(Cp*)(L)] (2). Method A. In the glovebox, 15 mg
4
(
89.12 μmol) of LH and 10 mg (89.12 μmol) of KOtBu were
dissolved in 3 mL of THF and stirred for 2 h, resulting in a purple
solution of KL. Addition of the KL solution to 24.2 mg (22.30 μmol)
3
of [RuCp*(μ -Cl)] dissolved in 8 mL of THF yielded purple X-ray
4
51−57
small-molecule activation.
Structurally the Cp* ligand also
diffraction quality crystals of 2 after 5 days. The supernatant containing
KCl and other impurities was decanted from the crystals, and the
crystals were washed with 5 mL of THF and dried under vacuum (11
mg, 31% yield).
7
blocks three fac-coordination sites of Ru(II), allowing for the
self-assembly of molecular architectures with RuCp* half-
sandwich vertices. Here we report the syntheses of RuCp*
complexes of 4,5-diazafluorene derivatives. The ambidentate,
multifunctional ligands utilized enabled the isolation of linkage
isomers and self-assembled macrocycles. We also present the
syntheses of diazafluorene ligands with aryl substituents ortho
to the N-donors.
Method B. In the glovebox, 115 mg (0.26 mmol) of 1 was partially
dissolved in 5 mL of THF, and 520 μL of 0.5 M K[HBEt ] in THF
3
was added, giving a dark red-brown solution and H evolution. The
2
reaction mixture was stirred at RT for 1 h; then the solvent was
removed under vacuum, and the residue was extracted into benzene,
filtered, and left to stand. After 3 days dark purple, large, X-ray
diffraction quality crystals of 2·2(C H ) had formed. The supernatant
6
6
EXPERIMENTAL SECTION
was pipetted off, and the crystals were washed with pentane and dried
under vacuum (24 mg, 22% yield based on 2·(C H )). The poor
■
General Information. All air- or moisture-sensitive operations
were performed using Schlenk/vacuum-line techniques under
dinitrogen or in a dinitrogen atmosphere glovebox from MBraun.
Workups for organic reactions were done in air. High-temperature and
6
6
solubility of complex 2 in all common NMR solvents hindered
solution-based NMR characterization. Anal. Calcd for (C H N Ru )·
84 88
8
4
(
C H ): C, 63.89; H, 5.60; N, 6.62. Found: C, 63.52; H, 5.48; N, 6.44.
Synthesis of [RuCp*(L)] (3). In the glovebox, 67 mg (0.398
6 6
-
pressure reactions were done in stainless steel Parr acid digestion
vessels and heated with a Parr 5000 multireactor heater-stirrer system.
mmol) of LH was dissolved in 4 mL of THF and added dropwise to a
5
8,59
18
3
60
4,5-Diazafluorene (LH),
LpH, and [RuCp*(μ -Cl)]4 were
stirring suspension of 35 mg (1.46 mmol) of pentane-washed NaH
synthesized from literature procedures. Compound 6 was synthesized
suspended in 4 mL of THF. Upon the addition of LH, H evolution
2
6
1,62
by a modified literature procedure using toluene as the solvent.
Compound 7 was synthesized using a literature procedure from Guo
and co-workers, with the following modifications to the workup.
After the reaction the HOtBu solvent was removed by rotary
evaporation, the crude was extracted with CHCl , and the organic
layer was washed with H O. To the CHCl extract was added 5% by
volume of methanol along with MgSO , and the mixture was filtered
through a silica gel plug. Removal of the solvent yields H NMR pure
compound 7 in 83% yield. Compounds 8
synthesized directly from literature procedures. Thin-layer chromatog-
raphy was performed with silica gel 60 F254 Al-backed TLC plates,
spots were visualized under UV, and column chromatography was
performed using SiliaFlash P60 silica gel from Silicycle. Glassware was
dried overnight in a 180 °C oven prior to use except for NMR tubes,
which were dried overnight in a 60 °C oven. THF, toluene, DME,
pentane, hexanes, diethyl ether, benzene, and benzene-d were dried
over Na/benzophenone and either distilled under nitrogen or vacuum-
transferred before use. DMSO-d was dried over CaH at 80 °C
overnight and vacuum distilled prior to use. CD Cl and CDCl were
was observed, and the reaction mixture was stirred at RT for 30 min,
giving a purple-pink solution along with excess NaH. The NaL
62
solution was simultaneously filtered and added dropwise to a stirred
3
solution−suspension of 98 mg (0.09 mmol) of [RuCp*(μ -Cl)]
in 6
4
mL of THF over the course of 15 min. After the addition of NaL is
complete the solution−suspension appeared brown, and the reaction
mixture was stirred at RT for 2 h. The solvent and volatiles were
removed under vacuum, and the brown residue was extracted into
toluene and filtered to remove a dark precipitate and KCl. The solvent
from the orange filtrate was removed under vacuum, and the product
was triturated with pentane (63 mg, 43% yield). X-ray diffraction
3
2
3
4
1
6
1,62
61
and 9 were
quality crystals of 3 were grown by vapor diffusion of hexanes into a
1
benzene solution. H NMR (600 MHz, CDCl
, δ): 8.71 (dd, J = 3.8,
3
1.6 Hz, 2H), 7.66 (dd, J = 8.7, 1.6 Hz, 2H), 6.86 (dd, J = 8.7, 3.8 Hz,
2H), 5.12 (s, 1H), 1.31 (s, 15H). 13C NMR (151 MHz, CDCl
149.17, 135.18, 117.74, 107.07, 89.27, 81.21, 56.80, 9.47. H NMR
, δ):
3
1
6
(600 MHz, C
2H), 6.41 (dd, J = 8.7, 3.8 Hz, 2H), 4.81 (s, 1H), 1.25 (s, 15H).
NMR (151 MHz, C , δ): 149.18, 134.59, 117.79, 107.88, 89.53,
81.02, 56.92, 9.46. Anal. Calcd for C21 Ru: C, 62.51; H, 5.50; N,
6.94. Found: C, 62.86; H, 5.66; N, 7.11.
Synthesis of [RuCp*(L H)] Cl (4). In the glovebox, 10 mg (9.2
was dissolved in 12 mL of THF, and 14
H was dissolved in 8 mL of THF. The L H
p
D ): δ 8.74−8.61 (m, 2H), 7.21 (dd, J = 8.7, 1.5 Hz,
6 6
13
C
6
2
D
6 6
2
2
3
1
31
13
dried over CaH and vacuum transferred prior to use. H, P, and
C
H N
22 2
2
NMR spectra were recorded on a Varian 300 MHz, Varian 400 MHz,
Bruker Avance III 400 MHz, or Agilent DD2-600 MHz NMR
spectrometer. All chemical shifts are reported in ppm relative to
residual protio-solvent peaks, and 31P NMR are referenced externally
using 85% H PO in a flame-sealed capillary. GC-MS analyses were
p
2
2
3
μmol) of [RuCp*(μ -Cl)]
mg (36.8 μmol) of L
4
p
3
solution was carefully layered on top of the [RuCp*(μ -Cl)] solution,
3
4
4
carried out on an Agilent 7980A GC system (equipped with an HP-5
column) connected with a 5975C inert XL MSD using hydrogen as
the carrier gas. Elemental analyses were performed by ANALEST at
the University of Toronto.
resulting in a purple solution. Slow evaporation of the THF solvent
yielded orange crystals of 4 suitable for X-ray crystallographic analysis.
After 8 days, the supernatant was decanted; the crystals were washed
1
with cold THF and dried under vacuum (10.8 mg, 45% yield). H
3
Synthesis of [RuCp*(LH)Cl] (1). In the glovebox 230 mg (0.21
NMR (DMSO-d , 400 MHz, δ): 8.75 (d, J = 5.47 Hz, 2H), 7.70−7.59
6
3
3
3
3
mmol) of [RuCp*(μ -Cl)] was dissolved in 7 mL of THF, and 150
(m, 10H), 7.50 (dd, J = 7.55 Hz, J = 5.44 Hz, 2H), 7.40 (d, J = 7.59
4
3
4
mg (0.89 mmol) of LH was added, resulting in a dark purple
Hz, 2H), 4.16 (t, J = 7.40 Hz, 1H), 1.86−1.80 (m, 2H), 1.11 (d, J
H−P
dx.doi.org/10.1021/om400846f | Organometallics 2013, 32, 6511−6521
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512

Organometallics
Article
1
3
1
=
1.23 Hz, 15H), 0.18−0.14 (m, 2H). C{ H} NMR (DMSO-d , 100
chromatography first eluting with hexanes and gradually increasing the
amount of EtOAc until a final elution solvent of hexanes−EtOAc
(8:1). After chromatography the solvent was removed by rotary
evaporation, followed by drying the product under high vacuum, giving
6
MHz, δ): 160.2, 151.8, 137.9, 133.4, 133.1, 132.7 (d, J
= 11.8 Hz),
C−P
1
8
32.5, 130.3, 128.8 (d, J
= 9.6 Hz), 126.6, 84.0 (d, JC−P = 1.8 Hz),
C−P
.6. 31P{ H} NMR (DMSO-d , 162 MHz, δ): 37.7. Anal. Calcd for
1
6
C H N P Ru Cl : C, 64.46; H, 5.56; N, 4.30. Found: C, 64.07; H,
11 as a bright yellow solid with yellow luminescence under 365 nm
70
72
4
2
2
2
1
5
.72; N, 4.06.
irradiation (3.137 g, 95% yield). R = 0.73 (hexanes−EtOAc, 2:1). H
f
Synthesis of [RuC *(L )] (5). Method A. In the glovebox, 50 mg
NMR (400 MHz, CDCl , δ): 8.06 (d, J = 7.7 Hz, 2H), 7.26 (d, J = 7.6
p
p
2
3
1
3
(
131.4 μmol) of L H and 14.7 mg (131.4 μmol) of KOtBu were
Hz, 2H), 6.89 (s, 4H), 2.30 (s, 6H), 2.07 (s, 12H). C NMR (100
MHz, CDCl3, δ): 189.85, 166.90, 164.05, 137.99, 137.19, 135.61,
131.57, 128.30, 128.01, 125.97, 21.23, 20.41.
p
dissolved in 2 mL of THF and stirred for 2 h, resulting in a purple
solution of KL . To the solution of KL was added 35.7 mg (32.9
p
p
3
μmol) of solid [RuCp*(μ -Cl)] , and the mixture was stirred for 2 h.
Synthesis of 3,6-Dimesityl-4,5-diazafluorene (L H) and
4
Mes
The solvent was removed under vacuum, leaving a brown residue,
which was extracted into 10 mL of toluene and filtered. The brown
toluene solution was heated at 100 °C overnight, resulting in a bright
green solution. The green solution was filtered, and the solvent was
removed under vacuum to give complex 5 (60 mg, 74% yield). X-ray
diffraction quality crystals can be grown by either vapor diffusion of
hexanes into a benzene solution (5) or vapor diffusion of pentane into
a DME solution (5·(pentane)).
9,9′-Bi-3,6-dimesityl-4,5-diazafluorenyl (12). In parallel, two
Parr acid digestion vessels were each charged with 570 mg (total of
1.140 g, 2.72 mmol) of 11 and 12 mL of hydrazine hydrate, sealed, and
heated for 7.5 h at 180 °C. After cooling to RT overnight the reaction
mixtures from the two bombs were combined and extracted with 3 ×
25 mL of DCM. The DCM extracts were dried over MgSO and
4
filtered, and the solvent was removed by rotary evaporation. The TLC
plate revealed two main products, which both fluoresce bright blue
under 364 nm irradiation: LMesH with R = 0.5 and 12 with R = 0.2
Method B. To 18.6 mg (14.25 μmol) of 4 was added 1 mL of a 29.7
μmol/mL solution of KOtBu, and the mixture was left to sit overnight
at RT to yield a green solution. The solvent and volatiles were
removed under vacuum, and the residue was extracted into toluene,
filtered, and dried under vacuum to give complex 5 (16.2 mg, 92%
f
f
(hexanes−EtOAc, 3:1). Silica gel column chromatography was
performed eluting with hexanes, initially gradually increasing the
amount of EtOAc until a final hexanes−EtOAc (3:1) until all of the
3,6-dimesityl-4,5-diazafluorene had eluted off the column. The solvent
was removed by rotary evaporation, and the product was dried under
high vacuum to give 836 mg (75% yield) of LMesH as a white solid. X-
ray diffraction quality crystals were grown by diffusion of hexanes into
a toluene solution of 3,6-dimesityl-4,5-diazafluorene and placing the
mixture in a −30 °C freezer. The silica gel column was flushed with
EtOAc−MeOH (100:1) elution solvent until all of the 12 had eluted
off the column. The solvent was removed by rotary evaporation, and
the product was dried under high vacuum to give 130 mg (12% yield)
of 12 as a white solid. X-ray diffraction quality crystals were grown by
1
3
yield). H NMR (C D , 300 MHz): δ 7.85 (d, J = 4.72 Hz, 2H),
6
6
3
4
7
1
.71−7.65 (m, 4H), 7.35−7.26 (m, 6H), 7.23 (dd, J = 7.22 Hz, J =
3 3
.39 Hz, 2H), 6.95 (dd, J = 7.76 Hz, J = 4.71 Hz, 2H), 2.54−2.44
4
(
m, 2H), 1.37 (d, J
= 1.37 Hz, 15H), −0.55 to −0.66 (m, 2H).
H−P
1
3
1
C{ H} NMR (C D , 100 MHz): δ 142.5, 135.2, 134.9, 134.6, 133.5
6
6
(
9
d, JC−P = 10.59 Hz), 129.1 (d, JC−P = 1.74), 126.5, 124.3, 121.8, 116.8,
5.1 (d, JC−P = 9.89 Hz), 82.4 (d, JC−P = 2.18 Hz), 9.9. 3 P{ H} NMR
1
1
(
C D , 121.5 MHz): δ 38.0. Anal. Calcd for C H N P Ru ·
6 6 70 70 4 2 2
(
C H O ): C, 67.25; H, 6.10; N, 4.24. Found: C, 66.79; H, 5.90;
4
10
2
N, 4.31.
1
Synthesis of 3,6-Dichloro-4,5-diazafluoren-9-one (10). In air
.533 g (16.2 mmol) of freshly powdered yellow 2,9-dichloro-1,10-
4
phenanthroline-5,6-dione (9) and 2.164 g (38.6 mmol) of KOH were
dissolved/suspended in 220 mL of H O and heated to reflux with
160.14, 159.35, 138.23, 137.08, 136.04, 135.66, 132.96, 127.97, 123.74,
32.07, 21.19, 20.48. Anal. Calcd for C H N : C, 86.10; H, 6.98; N,
2
vigorous stirring. After 10 min of reflux a dark brown reaction mixture
resulted. An aqueous solution consisting of 1.951 g (12.3 mmol) of
KMnO dissolved in 220 mL of H O was heated to 60 °C, and the
29
28
2
6.92. Found: C, 85.92; H, 6.97; N, 6.95.
1
Characterization of 12. H NMR (500 MHz, CD Cl , δ): 7.48 (br
4
2
2
2
warm KMnO solution was added dropwise to the vigorously stirred,
s, 4H), 7.06 (br d, J = 8.0 Hz, 4H), 6.89 (s, 8H), 5.11 (s, 2H), 2.29 (s,
4
12H), 1.96 (br s, 24H). 13C NMR (126 MHz, CDCl , δ): 161.08,
refluxing, brown reaction mixture over the course of 3.5 h. After the
addition of the KMnO4 solution was complete the dark reaction
mixture was left to reflux overnight. The reaction mixture was cooled
to RT and extracted with 3 × 300 mL of DCM, the combined DCM
3
159.25, 137.68, 137.18, 136.59, 135.63, 131.93, 127.89, 123.57, 44.85,
21.06, 20.22. Anal. Calcd for C H N ·0.27(CHCl )·0.49(O(C H ) )
5
8
54
4
3
2
5 2
1
(ratio of 12 to CHCl and Et O determined by integration of H
3
2
extracts were dried over MgSO and filtered, and the solvent was
NMR spectrum): C, 82.62; H, 6.79; N, 6.39. Found: C, 83.16; H, 6.94;
4
removed by rotary evaporation. The crude product was purified by
silica gel column chromatography eluting initially with DCM, gradually
increasing the amount of EtOAc in the elution solvent until a final
elution solvent of DCM−EtOAc (10:1). After chromatography the
solvent was removed by rotary evaporation, and the product was dried
under high vacuum to give 10 as a pale yellow microcrystalline solid
N, 6.43.
Selective Synthesis of 3,6-Dimesityl-4,5-diazafluorene
(LMesH). LMesH can be synthesized more selectively (without
formation of the 12 byproduct) and with a higher yield using a
procedure analogous to that above. The only differences in procedures
were the quantity of 11 per reaction bomb and the reaction time. In
parallel, 10 Parr acid digestion vessels were each charged with 360 mg
(total of 3.6 g, 8.6 mmol) of 11 and 12 mL of hydrazine hydrate,
sealed, and heated at 180 °C for 24 h. Workup was performed similar
to what was mentioned above (3.198 g, 92% yield).
(
2.558 g, 63% yield). X-ray diffraction quality crystals were obtained by
vapor diffusion of pentane into a CHCl solution of 10. R = 0.48
3
f
1
(
7
1
DCM). H NMR (400 MHz, CDCl , δ): 7.95 (d, J = 7.9 Hz, 2H),
3
.43 (d, J = 7.9 Hz, 2H). 13C NMR (101 MHz, CDCl , δ): δ 187.02,
3
63.11, 158.42, 133.85, 128.20, 126.07.
Synthesis of [RuCp*(LMesH)]Cl (13). In the glovebox, 145 mg
(0.13 mmol) of [RuCp*(μ -Cl)]
3
Synthesis of 3,6-Dimesityl-4,5-diazafluoren-9-one (11). In a
4
and 214 mg (0.52 mmol) of LMes
H
Schlenk flask under a dinitrogen atmosphere 1.990 g (7.9 mmol) of 10
and 3.884 g (23.68 mmol) of 2,4,6-trimethylphenylboronic acid were
dissolved in 200 mL of toluene, and 100 mL of 1.7 M Na CO was
were dissolved in 15 mL of THF and left to sit at RT for 7 days (no
stirring). After 7 days colorless X-ray diffraction quality crystals of 13·
(THF) had formed, and the crystals were collected by filtration,
2
3
added. The mixture was thoroughly degassed; then 778 mg (0.67
washed with THF and hexanes, and dried under vacuum (242 mg,
1
mmol) of Pd(PPh ) was quickly added. The yellow biphasic reaction
67% yield). H NMR (600 MHz, DMSO-d , δ): 8.23 (d, J = 7.8 Hz,
3
4
6
mixture was vigorously stirred and heated in a 115 °C oil bath
overnight. After the reaction mixture cooled to RT the toluene and
aqueous phases were separated, and the aqueous phase was extracted
with 3 × 100 mL of DCM. The combined organic extracts were dried
1H), 8.19 (d, J = 7.8 Hz, 1H), 7.56 (d, J = 7.8 Hz, 1H), 7.37 (d, J = 7.8
Hz, 1H), 6.95 (s, 2H), 5.89 (s, 2H), 4.14 (s, 2H), 2.28 (s, 3H), 2.16 (s,
3H), 2.04 (s, 6H), 1.89 (s, 6H), 1.87 (s, 15H). 13C NMR (151 MHz,
DMSO-d , δ): 158.62, 158.49, 157.65, 151.73, 138.08, 137.79, 136.58,
6
over MgSO and filtered, and the solvent was removed by rotary
136.42, 135.04, 134.18, 133.75, 128.03, 124.30, 124.14, 105.31, 99.79,
4
evaporation. The crude product was purified by silica gel column
98.38, 94.88, 88.55, 31.86, 20.66, 20.00, 17.28, 16.91, 9.46. Anal. Calcd
6
513
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for (C H N RuCl)·1.5(OC H ) (ratio of complex 13 to THF
determined by integration of H NMR spectrum): C, 68.90; H, 7.07;
N, 3.57. Found: C, 68.43; H, 7.14; N, 3.69.
line complex 1 (Scheme 1). Complex 1 is soluble in DCM or
chloroform, slightly soluble in THF, DME, benzene, and
39
43
2
4
8
1
Synthesis of Arene Isomer [RuCp*(LMes)] (14). In the glovebox,
8 mg (0.14 mmol) of 13 was suspended in 10 mL of THF, and 16 mg
Scheme 1. Syntheses of Complexes 1, 2, and 3
9
(
0.14 mmol) of KOtBu dissolved in 10 mL of THF was added,
yielding a red solution, which was stirred at RT overnight. After
overnight the red reaction mixture was filtered, and toluene was
layered carefully on top, yielding red X-ray diffraction quality crystals,
which were collected by filtration and dried under vacuum (55 mg,
1
5
1
6
9% yield). H NMR (600 MHz, DMSO-d , δ): 7.75 (d, J = 8.3 Hz,
6
H), 7.71 (d, J = 8.4 Hz, 1H), 6.88 (s, 2H), 6.87 (d, J = 8.4 Hz, 1H),
.82 (d, J = 8.3 Hz, 1H), 5.93 (s, 1H), 5.75 (s, 2H), 2.27 (s, 3H), 2.13
(
s, 3H), 2.12 (s, 6H), 1.98 (s, 6H), 1.92 (s, 15H). 13C NMR (151
MHz, DMSO-d , δ): 138.12, 135.82, 134.32, 132.46, 127.80, 127.50,
6
1
2
0
22.06, 117.63, 116.21, 108.92, 98.95, 94.17, 88.73, 78.40, 20.68,
0.67, 17.60, 17.36, 9.62. Anal. Calcd for (C H N Ru)·(C H )·
39
42
2
7
8
.5(OC H ) (ratio of 14 to toluene and THF solvents determined
4
8
1
from integration of H NMR spectrum of EA sample): C, 75.06; H,
7
.09; N, 3.65. Found: C, 74.76; H, 6.67; N, 3.41.
Synthesis of Sandwich Isomer [RuCp*(LMes)] (15). In the
glovebox, 214 mg (0.53 mmol) of LMesH and 66 mg (0.59 mmol) of
KOtBu were dissolved in 3 mL of THF, giving a deep red solution of
KLMes, which was left at RT for 30 min. The solution of KLMes was
3
then added to 143 mg (0.13 mmol) of [RuCp*(μ -Cl)] dissolved in 4
4
mL of THF, resulting in an orange solution of 15. After 1 h the
volatiles were removed under vacuum, the orange residue was
extracted into toluene and filtered, and the solvent was removed
under vacuum, giving an orange microcrystalline sample of 15 (300
mg, 88% yield). X-ray diffraction quality crystals can be grown by
either vapor diffusion of Et O into a THF solution (15·Et O) or vapor
2
2
1
diffusion of hexanes into a benzene solution (15·C H ). H NMR
600 MHz, CDCl , δ): 7.73 (d, J = 8.8 Hz, 2H), 6.90 (d, J = 8.8 Hz,
6
6
(
3
2
1
1
2
H), 6.88 (s, 4H), 5.12 (s, 1H), 2.30 (s, 6H), 2.18 (br s, 12H), 1.59 (s,
5H). 13C NMR (151 MHz, CDCl , δ): 159.79, 138.92, 136.95,
3
34.96, 129.18, 128.37, 121.00, 108.27, 87.18, 82.34, 56.88, 21.22,
toluene, and insoluble in diethyl ether, pentane, and hexanes.
0.97, 11.03. Anal. Calcd for (C H N Ru)·0.6(C H ) (ratio of 15 to
When complex 1 was dissolved in DMSO-d , the deep purple
39
42
2
7
8
6
1
toluene determined from integration of H NMR spectrum of EA
sample): C, 74.64; H, 6.79; N, 4.03. Found: C, 74.98; H, 7.03; N, 3.88.
X-ray Crystallography. The X-ray diffraction data were collected
on a Bruker Kappa Apex II diffractometer and processed with the
Bruker Apex 2 software package. Data were collected with graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å) at 150 K
controlled by an Oxford Cryostream 700 series low-temperature
system. The structures were solved by the direct methods or Patterson
solution formed initially turned bright orange within a few
1
seconds; the H NMR spectrum showed signals of free LH and
a singlet belonging to Cp*, likely indicating ligand substitution
with DMSO-d had occurred. Compound 1 is air-sensitive in
63
6
solution. When a CDCl solution of 1 was exposed to air,
3
1
uncoordinated 4,5-diazafluoren-9-one was observed by
H
NMR. Previously we had reported the selective oxidation of
the CH moiety of the LH ligand by air in the complex
64
method and refined using SHELX-2013. The residual electron
density from disordered solvent molecules in the lattices of 2, 4, 5·
2
15
[RuCl (LH)(PPh ) ], giving a Ru-diazafluorenone complex.
2
3 2
3
(
pentane), and 13·(THF) was removed with the SQUEEZE function
Free LH with typically unreactive C(sp )−H bonds is air-stable,
65
1
of PLATON, and their contributions were excluded in the formula.
The disordered Cp* ligand in complex 1 was modeled over three
positions. Non-hydrogen atoms were refined anisotropically except for
disordered portions, and hydrogen atoms were calculated using the
riding model. The selected crystallographic data are summarized in
Table S1.
but coordinated LH in complex 1 reacts with O in air. The H
2
NMR spectrum of complex 1 in dry and deoxygenated CDCl3
revealed two singlets at 4.05 and 4.04 ppm belonging to the
two inequivalent methylene protons of the coordinated LH
1
ligand. The H NMR in CD Cl revealed a singlet at 4.13 ppm
2
2
belonging to the methylene group of the coordinated LH
ligand. Crystals of complex 1 were obtained by vapor diffusion
of hexanes into a THF solution (Figure 1). Complex 1
crystallized in the monoclinic space group C2/c, where the cis-
N donors of LH and the chloride are coordinated to the RuCp*
half-sandwich. The bite angle of LH, N1−Ru1−N2, is 79.3(1)°.
It was thought that compound 1 might serve as an entry
point to bifunctional small-molecule activation and catalysis.
Upon deprotonation of coordinated LH in complex 1, a
coordinatively unsaturated “RuCp*(L)” hypothetically may
DFT Calculations. All calculations were performed using the
66
67,68
Gaussian 09 software package and B3LYP
method. Ruthenium
was treated with the SDD basis set with an effective core potential,
while other elements were treated with the 6-31G* basis set. The
geometry optimizations were performed with no symmetry constraint.
Vibrational frequency analyses were performed on all optimized
structures to obtain thermodynamic data.
RESULTS AND DISCUSSION
■
−
Coordination Chemistry of LH and L . We initially
explored the coordination chemistry of LH and ambidentate
engage in long-range metal−ligand cooperative activation of
−
3
69−73
L . The half-sandwich complex [RuCp*(μ -Cl)] first reported
small molecules.
Previously we showed that a metal−
4
by Fagan and co-workers proved to be a highly versatile RuCp*
dinitrogen complex [Ru(L)(PPh ) (H)(N )] forms upon
3 2 2
6
0
3
synthon. The addition of LH to 0.25 equiv of [RuCp*(μ -
deprotonation of coordinated LH, and [Ru(L)(PPh ) (H)-
3 2
16
−
Cl)] resulted in the precipitation of deep purple microcrystal-
(N )] reversibly splits H between the Ru(II) center and L .
2 2
4
6
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Figure 1. X-ray crystal structure of 1. Non-hydrogen atoms are shown
as 30% probability ellipsoids, and H atoms are shown as spheres of
arbitrary radius. Only one orientation of the disordered Cp* ligand is
shown for clarity. Selected distances (Å) and angles (deg): Ru1−N1,
2
.185(3); Ru1−N2, 2.197(3), Ru1−Cl1, 2.4683(9); Ru1−cent(C12−
C16), 1.7492(3); N1−Ru1−N2, 79.3(1); N1−Ru1−Cl1, 81.84(8);
N2−Ru1−Cl1, 87.94(8).
The addition of 1 equiv of K[HBEt ] to complex 1 followed by
3
extraction into benzene yielded dark purple X-ray quality
crystals of 2·2(C H ) after 3 days (Scheme 1). The benzene
6
6
extraction must be carried out soon after the reaction with
K[HBEt ] in order to obtain analytically pure crystals of 2·
3
Figure 2. X-ray crystal structure of 2. (A) Non-hydrogen atoms are
shown as 30% probability ellipsoids, and H atoms (except for H11 and
H22) are omitted for clarity. (B) Space-filling model of 2. Selected
distances (Å) and angles (deg): Ru1−N1, 2.1683(15); Ru1−N2,
2.1801(15); Ru1−C22, 2.2739(19); Ru1−cent(C23−C27),
2
(C H ) free of KCl and other impurities. Complex 2 is
6 6
insoluble in all common organic solvents after it has
crystallized, and thus solution-based NMR spectroscopy was
not possible. Compound 2·2(C H ) crystallizes in the triclinic
6
6
̅
space group P1, with a crystallographically imposed inversion
1
.7854(2); Ru2−N3, 2.1825(15); Ru2−N4, 2.1741(15); Ru2−C11,
center in the middle of the cavity formed by the tetramer.
Coordination-driven self-assembly of the tetraruthenamacro−-
cycle 2 occurs as a result of the ambidentate nature of the L
2.2626(18); Ru2−cent(C33−C37), 1.7826(2).
−
2
ligand. The four L ligands all engage in both κ -[N,N] and
1
η (σ) coordination modes, resulting in coordinatively saturated
Ru(II) centers. To estimate the size of the cavity formed by the
macrocycle, the distance of C11−C11′ is 3.361(5) Å, and the
distance of C22−C22′ is 10.372(3) Å. The cocrystallized
benzene solvent molecules do not form a host−guest complex
with 2, likely because the cavity is inaccessible, as seen in the
space-filling model (Figure 2). The protons bound to C11 and
C11′ are directed inward toward the cavity, while the protons
bound to C22 and C22′ point outward.
Complex 2 can also be synthesized by the salt metathesis of
Figure 3. X-ray crystal structure of 3. Non-hydrogen atoms are shown
as 30% probability ellipsoids, and H atoms are shown as spheres of
arbitrary radius. Selected distances (Å) and angles (deg): Ru1−
cent(C4−C5−C6−C7−C11), 1.85732(16); Ru1−cent(C12−C16),
3
KL and 0.25 equiv of [RuCp*(μ -Cl)] , where complex 2
4
crystallizes out of the reaction mixture with a different unit cell
in the monoclinic C2/m space group with a crystallographically
imposed inversion center and mirror plane (see Supporting
Information). Interestingly when NaL was used in the salt
metathesis instead of KL, a different product formed. After a
1
1
.78338(17); cent(C4−C5−C6−C7−C11)−Ru1−cent(C12−C16),
76.41(3).
−
1
2
solution of NaL was added dropwise to a solution containing
L binds to Ru(II) in either an η C,κ [N,N]-fashion, giving the
3
5
0
.25 equiv of [RuCp*(μ -Cl)] , an orange solution along with a
tetramer 2, or an η -fashion, giving the sandwich complex 3.
4
dark precipitate formed after 2 h at RT. The dark precipitate
likely complex 2, which may have also formed) and NaCl were
removed by filtration to give orange complex 3 in the filtrate
Scheme 1). Crystals of 3 were obtained by vapor diffusion of
DFT calculations show that 3 is more stable than 2. Heating a
suspension of complex 2 at 95 °C in C D for 1 week only
(
6
6
1
generates a small amount of complex 3 as determined by H
NMR spectroscopy, presumably due to the poor solubility of 2.
(
−
hexanes into a benzene solution (Figure 3). Complex 3
Coordination Chemistry of L H and L . The L H and
p
p
p
crystallizes in the orthorhombic space group P2 2 2 , where
Lp− ligands are multifunctional with a number of potential
1
1 1
−
5
both Cp* and the L ligands are coordinated in an η -fashion
to Ru(II). In the H NMR spectrum of 3, the proton at the 9-
position of the Ru-bound η -L resonates as a singlet at 5.12
and 4.81 ppm in CDCl and C D , respectively. Complexes 2
coordination sites. Previously we demonstrated that metals can
1
bind to L H through the N,N-chelate and the phosphine
p
5
−
−
moiety. In addition to these coordination modes L could also
p
1
8
19
bind Rh(I) or Pt(II) via the P,C-chelate site. The addition
3
6
6
3
and 3 may be viewed as linkage isomers of “RuCp*L”, where
of L H to 0.25 equiv of [RuCp*(μ -Cl)] in THF yields orange
p
4
6
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X-ray quality crystals of complex 4 after 8 days with slow
evaporation (Scheme 2 and Figure 4). Complex 4 is soluble in
P2 /c and is a head-to-tail macrocyclic dimer that possesses a
crystallographically imposed inversion center in the middle of
the cavity. Both the N,N-chelate and phosphine moieties of two
1
Scheme 2. Syntheses of Head-to-Tail Dimeric Macrocycles 4
and 5
separate L H ligands coordinatively saturate each of the two
p
+
pseudo-octahedral {RuCp*} vertices. The two diazafluorene
moieties are antiparallel, with an interplane separation distance
1
31
of ∼5.52 Å. The H and P NMR spectra are consistent with
the dimeric structure being retained in solution. In particular,
31
the P NMR spectrum in DMSO-d displays a singlet at 37.65
6
ppm, suggesting that the phosphine remains coordinated to
1
Ru(II). In the H NMR spectrum, the protons of the ethylene
linker appear as two multiplets at 1.84 and 0.16 ppm, while the
proton at the 9-position of the diazafluorene moiety appears as
a triplet at 4.16 ppm.
The coordination chemistry of the Lp− ligand was
investigated. A THF solution of KLp and 0.25 equiv of
3
[
RuCp*(μ -Cl)] were allowed to react at RT overnight, giving
4
a brown reaction mixture. The reaction progress was monitored
by NMR in C D , where the P NMR spectrum showed a
31
6
6
major peak at 38.02 ppm and minor peaks at ∼82, 42.77, and
3
9.95 ppm. Heating the THF solution at reflux for 9 h did not
3
1
fully convert the mixture into one species by P NMR.
Removal of the THF solvent and refluxing the crude mixture in
toluene overnight yielded a bright green solution, which has
only one singlet at 38.03 ppm, belonging to complex 5
(
Scheme 2). Note that the reaction was commenced in THF
and there is a switch to toluene; this is because KL is insoluble
p
in toluene, and the reaction does not proceed to completion in
THF alone. The 31P NMR chemical shift suggests that the
1
phosphine remains coordinated to Ru(II) in solution. In the H
NMR spectrum, the ethylene protons appear as two multiplets
at 2.48 and −0.61 ppm. Complex 5 is soluble in THF, DME,
toluene, and benzene, but insoluble in hexanes and pentane. X-
ray diffraction quality crystals of 5 were grown from vapor
diffusion of hexanes into a benzene solution (Figure 5), or
crystals of 5·(pentane) were grown from vapor diffusion of
pentane into a DME solution (see Supporting Information).
Crystals of 5 grown from benzene−hexanes crystallized in the
monoclinic space group P2 /n; molecules of 5 do not possess a
1
crystallographically imposed inversion center, and the dihedral
angle between the two diazafluorenyl moieties is ∼13° within
Figure 4. X-ray crystal structure of 4. (A) Non-hydrogen atoms are
shown as 30% probability ellipsoids, and H atoms bound to C11 and
C11′ are shown as spheres of arbitrary radius. Chloride counterions
are omitted for clarity. (B) Space-filling model of dicationic portion of
Figure 5. X-ray crystal structure of 5. (A) Non-hydrogen atoms are
shown as 30% probability ellipsoids, and H atoms are omitted for
clarity. Selected distances (Å) and angles (deg): Ru1−N1, 2.171(3);
Ru1−N2, 2.197(3); Ru1−P2, 2.3302(9); Ru1−cent(C26−C30),
4
. Selected distances (Å) and angles (deg): Ru1−N1, 2.169(2); Ru1−
N2, 2.174(2); Ru1−P1, 2.3151(8); Ru1−cent(C26−C30), 1.8209(2);
N1−Ru1−N2, 79.73(9); N1−Ru1−P1, 89.95(7); N2−Ru1−P1,
92.11(6).
1
2
.8155(3); Ru2−N3, 2.178(3); Ru2−N4, 2.180(3); Ru2−P1,
.3260(9); Ru2−cent(C61−C65), 1.8103(3); N1−Ru1−N2,
DMSO and insoluble in THF, benzene, toluene, hexanes, and
pentane. Complex 4 crystallizes in the monoclinic space group
80.18(10); N1−Ru1−P2, 86.81(7); N2−Ru1−P2, 88.85(7); N3−
Ru2−N4, 80.46(10); N3−Ru2−P1, 90.44(7); N4−Ru2−P1, 85.36(7).
6
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one molecule of 5. Crystals of 5·(pentane) crystallize in the
recently reported that the oxidation of 6 could be carried out
62
triclinic space group P1
̅
with excess KOtBu in HOtBu in air. We found that Guo’s
reaction is higher yielding, less time-consuming, and highly
scalable; 216 g of the oxidation product 7 could be isolated in
83% yield in one batch. The reaction of compound 7 with PCl5
inversion center in the middle of the molecule, and therefore,
the diazafluorenyl moieties within one molecule are antiparallel.
The intramolecular separation distances between the diaza-
fluorenyl moieties are ∼4.80 and 4.69 Å for the two
independent molecules of 5, respectively. Complex 5 can also
be prepared by the deprotonation of complex 4 with KOtBu
and POCl gave 2,9-dichloro-1,10-phenanthroline (8) in 88%
3
61,62
yield, comparable to the literature.
It is worth noting that LH is prepared in two steps from 1,10-
(
Scheme 2). The advantage of this route is that it does not
phenanthroline: an oxidative ring contraction with KOH and
require a change of solvent during the preparation.
KMnO and a subsequent Wolff−Kishner reduction of the
4
LpH and Lp− both possess an N,N-chelate site and a
phosphine moiety at the opposite end of the ligand framework.
Similar to what has been reported previously in the literature of
coordination-driven self-assembly with ditopic ambidentate
resulting 4,5-diazafluoren-9-one.
58,59
The oxidative ring con-
traction of 8 with analogous reaction conditions was
unsuccessful; only a trace of the desired 3,6-dichloro-4,5-
diazafluoren-9-one (10) could be observed by NMR, likely due
to the limited solubility of 8 in water. The oxidative ring
contraction of 1,10-phenanthroline likely proceeds via a
1
,5,6
ligands,
despite the possible formation of constitutional
isomers and oligomers, a single head-to-tail isomer of 4 or 5
forms cleanly. A head-to-head isomer does not seem to be
thermodynamically favored.
5
8,74
phenanthrolinequinone intermediate.
Therefore, we deci-
ded to explore whether a ring contraction of 2,9-dichloro-1,10-
phenanthroline-5,6-dione (9) would give the desired com-
pound 10. The oxidation of compound 8 was carried out with
Synthesis of LMesH. We envisioned that aryl groups could
be installed onto the 4,5-diazafluorene framework at the 3- and
6
4
-positions via Suzuki coupling. The synthesis of 3,6-dimesityl-
,5-diazafluorene (LMesH) from 1,10-phenanthroline is shown
KBr and HNO in concentrated sulfuric acid; after workup a
71% yield of dione 9 was obtained, similar to the literature.
The rapid benzilic acid rearrangement and decarboxylation of
3
61
in Scheme 3. 1,10-Phenanthroline is first protected with excess
9
can be carried out by reacting 9 with KOH in refluxing H O.
2
a
Scheme 3
The subsequent oxidation by a slow addition of a dilute and
warm solution of KMnO gives the desired product 10 in 63%
4
1
yield. The H NMR spectrum of 10 in CDCl has two doublets
3
at 7.95 and 7.43 ppm, similar to the starting material 9, which
shows two doublets at 8.44 and 7.62 ppm. X-ray quality crystals
of 10 were obtained from vapor diffusion of pentane into a
CHCl solution, and crystallography revealed that indeed the
3
ring contraction had occurred, corroborating the GC-MS
information (Figure 6). Compound 10 crystallizes in the
a
Conditions: (a) Excess 1,3-dibromopropane, toluene, 110 °C, 4 h
Figure 6. X-ray crystal structure of 10. Non-hydrogen atoms are
shown as 30% probability ellipsoids, and H atoms are shown as
spheres of arbitrary radius.
6
1,62
62
(
90% yield);
(b) excess KOtBu, HOtBu, 45 °C (83% yield); (c)
61,62
POCl , PCl , 110 °C, 8 h (88% yield);
to 80 °C, 3 h (71% yield); (e) step 1: 2.38 equiv KOH, 100 °C, 10
(d) H SO , HNO , KBr, 0
3
5
2
4
3
61
min; step 2: 0.75 equiv KMnO4(aq) slow addition, 100 °C overnight
monoclinic space group P2 /c as a planar molecule. In the solid
(
63% yield); (f) 3 equiv 2,4,6-trimethylphenylboronic acid, 21.5 equiv
1
state compound 10 engages in dihalogen bonding, where the
short contact distance between Cl1 and Cl1′ of an adjacent
molecule is ∼3.38 Å. The Suzuki coupling reaction of
compound 10 with 2,4,6-trimethylphenylboronic acid in
toluene in the presence of aqueous Na CO and Pd(PPh )
(8.4 mol % vs compound 10) proceeded straightforwardly,
where compound 11 was obtained in 95% yield after column
chromatography. Compound 11 exhibits bright yellow
luminescence in the solid state and in solution when irradiated
with 365 nm UV light.
Na CO , 8.4 mol % Pd(PPh ) , toluene−H O (2:1), 115 °C,
2
3
3
4
2
overnight (95% yield); (g) hydrazine hydrate, 180 °C, 7.5 h (75%
yield of LMesH, 12% yield of 12) or overnight (92% yield of LMesH).
1
,3-dibromopropane in refluxing toluene. Toluene was used as
2
3
3 4
the solvent for this reaction as opposed to the higher boiling
and more toxic nitrobenzene, or chlorobenzene, used in the
61
62
literature, and the N,N-protected product 6 could be isolated in
90% yield. The oxidation of 6 initially proved to be the
bottleneck in the earlier steps of the synthetic route. Previously
we performed this oxidation using [K Fe(CN) ] in basic
The Wolff−Kishner reduction of compound 11 was
accomplished with hydrazine hydrate at 180 °C in a sealed
stainless steel bomb. However a difference in the yields and
selectivity of the reaction was observed depending on the
amount of compound 11 per volume of hydrazine hydrate and
the reaction time at 180 °C. When a larger amount of 11 was
3
6
61
aqueous solution. Even with an optimized workup involving
neutralization with HBr and liquid−liquid extraction (that
forgoes a tedious Soxhlet extraction) the best yield obtained
was 45%, and the largest manageable scale in our hands only
produced ∼15 g of desired product 7. Guo and co-workers have
6
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reacted for a shorter period of time (570 mg of 11 with 12 mL
of hydrazine hydrate for 7.5 h), two spots exhibiting bright blue
luminescence under 365 nm UV irradiation were observed on
the TLC plate. The desired 3,6-dimesityl-4,5-diazafluorene
Scheme 4. Syntheses of Linkage Isomers 14 and 15
(
LMesH) with a higher R was isolated in 75% yield, while 9,9′-
f
bi-3,6-dimesityl-4,5-diazafluorenyl (12) with a lower R was
f
isolated in 12% yield. When a smaller amount of 11 was reacted
for a longer time (360 mg of 11 with 12 mL of hydrazine
hydrate overnight), LMesH could be isolated in 92% yield
without the formation of the 12 byproduct. Several peaks of the
1
H NMR spectrum of 12 are broad including those belonging
to the two ortho methyl groups of each of the mesityl
substituents and the pyridyl protons.
Crystals of LMesH were obtained by diffusion of hexanes into
a toluene solution (Figure 7), and crystals of 12 were obtained
Figure 7. X-ray crystal structure of LMesH. Non-hydrogen atoms are
shown as 30% probability ellipsoids, and H atoms are shown as
spheres of arbitrary radius.
Figure 9. X-ray crystal structure of 13. Non-hydrogen atoms are
shown as 30% probability ellipsoids, and H-atoms are shown as
spheres of arbitrary radius. The cocrystallized THF solvent molecule is
omitted for clarity. Selected distances (Å) and angles (deg): C4−C11,
1
.505(3); C7−C11, 1.509(3); Ru1−cent(C21−C26), 1.70914(18);
Ru1−cent(C30−C34), 1.81304(19); C4−C11−C7, 102.30(17); cent-
C21−C26)−Ru1−cent(C30−C34), 178.607(10).
(
soluble in DMSO, slightly soluble in THF, DME, benzene,
toluene, and diethyl ether, and insoluble in hexanes and
pentane. Complex 13 crystallizes in the triclinic space group P1,
̅
+
where one of the mesityl rings coordinates to the {RuCp*}
6
Figure 8. X-ray crystal structure of 12. Non-hydrogen atoms are
shown as 30% probability ellipsoids, and H atoms bound to C11 and
C40 are shown as spheres of arbitrary radius.
fragment in an η -fashion. The chloride is no longer bound to
the Ru center, and the N,N-chelate site of LMesH remains
unoccupied. The steric bulk of the LMesH and Cp* ligands,
+
along with the known affinity of the {RuCp*} fragment for π-
60
2
by diffusion of Et O into a CHCl solution (Figure 8). LMesH
aromatic ligands, likely prevented κ -[N,N] coordination in
complex 13, as opposed to what is observed in complex 1, with
a less sterically demanding LH ligand. The dihedral angle
between the diazafluorene and the uncoordinated mesityl
substituent planes is ∼52°, while the dihedral angle between the
diazafluorene and the coordinated mesityl planes is ∼60°. It is
2
3
crystallizes in in the orthorhombic space group Pbcn with
crystallographically imposed C2 symmetry bisecting the
molecule. The angle between the plane defined by the
diazafluorene moiety and the plane defined by the mesityl
moiety is ∼57°. Compound 12 crystallizes in the trigonal space
+
group P3 and adopts a gauche conformation about the bond
also worth noting that the {RuCp*} moiety points inward
toward the nitrogen chelate, rather than outward, which would
minimize steric repulsion from the Cp*. The H NMR
spectrum in DMSO-d revealed an unsymmetrical structure in
2
linking the two 3,6-dimesityl-4,5-diazafluorenyl moieties. The
H11−C11−C40−H40 torsion angle in 12 is 59.10(5)°, and the
length of the C11−C40 bond is 1.565(9) Å, similar to 9,9′-bi-
1
6
4
,5-diazafluorenyl, where a gauche conformation has also been
solution: four sets of pyridyl C-H peaks and two inequivalent
mesityl substituents. The two aromatic protons on the Ru(II)-
bound mesityl substituent are significantly upfield shifted to
5.89 ppm, compared to the protons on the dangling mesityl
substituent at 6.95 ppm. The methylene protons at the 9-
position of the diazafluorene moiety resonate as a singlet at
4.14 ppm.
7
5
established by X-ray crystallography.
Coordination Chemistry of LMesH and LMes−. With the
LMesH ligand in hand we decided to probe its coordination
chemistry. The addition of LMesH to 0.25 equiv of [RuCp*(μ -
Cl)] in THF gradually yielded colorless X-ray quality crystals
3
4
of 13 over one week (Scheme 4 and Figure 9). Complex 13 is
6
518
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Organometallics
Article
Complex 13 can be deprotonated with KOtBu to give the red
zwitterionic complex 14. Complex 14 is soluble in DMSO and
THF, but insoluble in toluene, benzene, DME, hexanes, and
pentane. Layering a THF solution of complex 14 with toluene
resulted in the formation of X-ray quality crystals (Figure 10).
Figure 11. X-ray crystal structure of 15·(C H ). Non-hydrogen atoms
6
6
are shown as 30% probability ellipsoids, and H atoms are shown as
spheres of arbitrary radius. The cocrystallized benzene solvent
molecule is omitted for clarity. Selected distances (Å) and angles
(
(
(
deg): Ru1-cent(C4−C5−C6−C7−C11), 1.86492(18); Ru1−cent-
C30−C34), 1.78074(18); cent(C4−C5−C6−C7−C11)−Ru1− cent-
C30−C34), 176.641(12).
Figure 10. X-ray crystal structure of 14. Non-hydrogen atoms are
shown as 30% probability ellipsoids, and H atoms are shown as
spheres of arbitrary radius. Selected distances (Å) and angles (deg):
C4−C11, 1.404(5); C7−C11, 1.403(5); Ru1−cent(C12−C17),
bent, with the centroid(C -ring of Cp*)−Ru−centroid(C -ring
5
5
of diazafluorenyl) angle of ∼177°. Analogously, complex 15
1
.7084(3); Ru1−cent(C30−C34), 1.8111(3); C4−C11−C7,
07.2(3); cent(C12−C17)−Ru1−cent(C30−C34), 179.08(2).
crystallizes in the monoclinic space group P2 /n as its diethyl
1
1
1
ether solvate. The H NMR spectrum in CDCl revealed a
3
symmetrical structure in solution, where the 2,6-methyl groups
on the mesityl substituents appear as a broad singlet at 2.18
ppm, indicating that the mesityl groups can slowly rotate at RT
and are not locked. The chemical shift of the backbone proton
Complex 14 crystallizes in the monoclinic space group P2 /c,
1
where complex 14 is structurally analogous to the complex
cation of 13. The Ru(II) center remains coordinated to the
arene. The 9-position of the diazafluorene moiety had been
deprotonated, as evidenced by the bond lengths and angles
about the backbone carbon and absence of chloride counterion.
The C4−C11−C7 angle in complex 13 is 102.30(17)°, while
after deprotonation the C4−C11−C7 angle in complex 14 is
−
at the 9-position of the LMes ligand appears at 5.12 ppm. A
related sandwich-type complex of CoCp* with 4,5-diazafluor-
76
enone has been reported. The selectivity of this reaction for
5
2
the η - over the κ -[N,N] coordination mode is likely governed
−
by sterics. While the less bulky L can coordinate through both
the N- and C-donors, the steric bulk of LMes precludes the κ -
N,N] coordination mode. In contrast β-diiminate ligands
monoanionic N-chelate ligands analogous to LAr ) coordinate
to Ru half-sandwich fragments through the κ -[N,N]
−
2
1
07.2(3)°. The dihedral angle between the diazafluorenyl and
[
(
the uncoordinated mesityl planes is ∼63°, while the dihedral
angle between the diazafluorenyl and the coordinated mesityl
planes is ∼86°. Similar to complex 13, the H NMR spectrum
of complex 14 in DMSO-d is also unsymmetrical, where most
−
1
2
2
4,77−79
coordination mode.
Another example of linkage isomers
6
of the aromatic protons are downfield shifted compared to the
corresponding protons in complex 13. The proton at the 9-
from the literature with a ligand that possesses both a
cyclopentadienyl moiety and an aryl ring was reported by
8
0
−
position of the anionic LMes ligand in complex 14 appears as a
Masters and co-workers. The bulky cyclopentadienyl
−
singlet at 5.93 ppm, suggesting the aromaticity of the central
derivative (C
5 5
Ph ) forms two linkage isomers with Fe(II):
5
C -ring.
the conventional metallocene [Fe(η -C
5
Ph
5
)
2
] and the linkage
)}]. The crystal
4
5
5
5/6
Different linkage isomers of [RuCp*LMes] can be produced
depending on the reaction sequence. If the Ru-bound neutral
LMesH ligand was deprotonated, the Ru(II) center is
isomers [Fe(η -C
5
Ph
5
5
){(η -C
6
H
5
)(C
5
Ph
5
5/6
structure of [Fe(η -C
Ph ){(η -C H )(C Ph )}] revealed a
5 6 5 5 4
mixture of two similar yet independent molecules in the unit
−
5
coordinated to the arene; however, if LMes is added to Ru(II)
cell, where one of the phenyl rings is bound in either an η - or
8
0
+
6
directly, then the {RuCp*} unit is coordinated to the central
an η -fashion to the iron center. Thermodynamically 15 is 9.1
kcal·mol− more stable than 14, as determined by DFT.
1
C -ring. LMesH can be deprotonated with KOtBu in THF to
5
give a deep red solution of KLMes. When KLMes was reacted
Heating 14 at 110 °C in DMSO-d overnight does not result in
6
1
3
with 0.25 equiv of [RuCp*(μ -Cl)] , a bright orange metal-
any conversion to complex 15 by H NMR spectroscopy.
4
locene complex 15 was isolated (Scheme 4). Complex 15 is
CONCLUSIONS
In summary, we have shown the utility of diazafluorene
derivatives as ligands in the assembly of linkage isomers and
soluble in THF, DME, toluene, benzene, DCM, and chloro-
■
form, slightly soluble in DMSO, and insoluble in Et O, hexanes,
2
and pentane. Crystals of 15·(C H ) were obtained by vapor
6
6
+
diffusion of hexanes into a benzene solution (Figure 11);
macrocycles. The rich coordination chemistry of the {RuCp*}
−
−
analogously crystals of 15·(Et O) were grown by vapor
fragment was extended to the ambidentate LH/L , L H/L ,
2
p p
−
diffusion of diethyl ether into a THF solution (see Supporting
Information). Complex 15 crystallizes in the monoclinic space
and LMesH/LMes− ligand families. The L ligand can coordinate
through both the N-donors and the C-donor simultaneously to
form the tetrameric macrocyclic complex 2; it also can
−
group P2 /c as a benzene solvate, where both Cp* and L
1
Mes
5
5
ligands are coordinated in an η -fashion to Ru(II). The dihedral
angles between the diazafluorenyl plane and each mesityl ring
are 66.39° and 55.03°, respectively. The metallocene is slightly
coordinate in an η -fashion exclusively to form the sandwich
complex 3. The head-to-tail macrocyclic dimers were formed
−
with either L H or Lp ligands, giving complexes 4 and 5,
p
6
519
dx.doi.org/10.1021/om400846f | Organometallics 2013, 32, 6511−6521

Organometallics
Article
respectively. The synthesis of the LMesH ligand with mesityl
groups installed ortho to the N-donors was achieved in a
scalable manner. These newly installed mesityl groups within
the LMesH ligand framework provided an additional arene
coordination site. The sterically bulky LMesH ligand coordi-
(12) Vajpayee, V.; Song, Y. H.; Yang, Y. J.; Kang, S. C.; Cook, T. R.;
Kim, D. W.; Lah, M. S.; Kim, I. S.; Wang, M.; Stang, P. J.; Chi, K.
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13) Jiang, H.; Song, D. Organometallics 2008, 27, 3587−3592.
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nated to the {RuCp*} fragment through the arene
(
5
(
5
(
5
coordination site, furnishing complex 13, which can be
deprotonated to form the zwitterionic complex 14. When the
reaction sequence was changed, the linkage isomer, sandwich
complex 15, formed. Current efforts are focused on utilizing the
monomeric RuCp* complexes as redox-active metalloligands to
generate bimetallic complexes for small-molecule activation and
catalysis, as well as extending the β-diiminate analogy of LAr− to
include bulkier aryl groups and other metals.
2012, 31, 2184−2192.
(19) Batcup, R.; Chiu, F. S. N.; Annibale, V. T.; Huh, J.-E. U.; Tan,
R.; Song, D. Dalton Trans. 2013, DOI: 10.1039/C3DT52135D.
(
20) For reviews on β-diiminate chemistry see: (a) Bourget-Merle,
ASSOCIATED CONTENT
■
L.; Lappert, M. F.; Severn, J. Chem. Rev. 2002, 102, 3031. (b) Mindiola,
D. J. Angew. Chem., Int. Ed. 2009, 48, 6198. (c) Holland, P. L. Acc.
Chem. Res. 2008, 41, 905. (d) Roesky, H. W.; Singh, S.; Jancik, V.;
Chandrasekhar, V. Acc. Chem. Res. 2004, 37, 969. (e) Piers, W. E.;
Emslie, D. J. H. Coord. Chem. Rev. 2002, 131, 233−234. (f) Zhu, D.;
Budzelaar, P. H. M. Dalton Trans. 2013, 42, 11343−11354.
*
S
Supporting Information
NMR spectra, GC chromatograms, and MS spectra, DFT-
optimized geometry coordinates of 2, 3, 14, and 15;
crystallographic data tables and CIF files for 1, 2, 2·2(C H ),
6
6
3
, 4, 5, 5·(pentane), 10, LMesH, 12, 13·(THF), 14, 15·(C H ),
6 6
and 15·(Et O). This material is available free of charge via the
(21) Annibale, V. T.; Lund, L. M.; Song, D. Chem. Commun. 2010,
2
4
6, 8261−8263.
22) Annibale, V. T.; Tan, R.; Janetzko, J.; Lund, L. M.; Song, D.
Inorg. Chim. Acta 2012, 380, 308−321.
23) Ferro, L.; Coles, M. P.; Day, I. J.; Fulton, J. R. Organometallics
Internet at http://pubs.acs.org.
(
AUTHOR INFORMATION
■
*
(
Corresponding Author
E-mail: dsong@chem.utoronto.ca.
2010, 29, 2911−2915.
(24) Phillips, A. D.; Laurenczy, G.; Scopelliti, R.; Dyson, P. J.
Organometallics 2007, 26, 1120−1122.
Notes
(25) Hadzovic, A.; Song, D. Organometallics 2008, 27, 1290−1298.
(26) Scheuermann, M. L.; Fekl, U.; Kaminsky, W.; Goldberg, K. I.
The authors declare no competing financial interest.
Organometallics 2010, 29, 4749−4751.
27) Scheuermann, M. L.; Luedtke, A. T.; Hanson, S. K.; Fekl, U.;
Kaminsky, W.; Goldberg, K. I. Organometallics 2013, 32, 4752−4758.
28) Bailey, P. J.; Melchionna, M.; Parsons, S. Organometallics 2007,
6, 128−135.
29) Enk, B.; Eisenstecken, D.; Kopacka, L.; Wurst, K.; Mueller, T.;
Pevny, F.; Winter, R. F.; Bildstein, B. Organometallics 2010, 29, 3169−
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30) Bailey, P. J.; Rahman, M.; Parsons, S.; Azhar, M. R.; White, F. J.
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ACKNOWLEDGMENTS
(
■
We thank the Natural Science and Engineering Research
Council of Canada (NSERC) for funding. V.T.A. gratefully
thanks the NSERC for a postgraduate scholarship (PGS D2)
and the government of Ontario for an Ontario Graduate
Scholarship (OGS). The authors also wish to acknowledge the
Canadian Foundation for Innovation Project no. 19119 and the
Ontario Research Fund for funding the CSICOMP NMR lab at
the University of Toronto, enabling the purchase of several new
spectrometers.
(
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