A R T I C L E S
Zheng et al.
σ-dimer 12b chelated with the copper(II) center. Complexation
with transition metals having only axial coordination positions
17
available could prevent this dimerization reaction. Further work
on the synthesis of a series of parent and substituted 2-aza-,
2
,5-diaza-, and 2,5,8-triazaphenalenyl radicals, as well as their
complexation with transition metal ions, is currently under way.
Experimental Section
General Remarks. All reactions were performed under argon, and
ESR spectra were recorded on a Bruker ESP380E spectrometer.
2
,3-Dihydro-(2-phenylmethyl)-1H-benz[de]isoquinoline (5). An-
hydrous aluminum chloride (0.53 g, 4.0 mmol) and LiAlH (0.15 g,
.0 mmol) were added to 15 mL of cold, dry THF (ice bath) with
4
4
stirring. After removal of the ice bath, N-benzylnaphthalimide (0.287
g, 1.0 mmol) was added in small portions. The mixture was stirred at
4
0 °C for 5.5 h, and then at room temperature for 10 h. The resulting
mixture was poured into 100 mL of cold 0.3 N HCl and stirred for 1
h. After filtration, the filtrate was basified with 20% KOH up to pH )
Figure 6. X-ray structure of Cu(hfac)2(1,1′-bi-1H-2-azaphenalene) (11).
1
4, and then the amine was extracted with diethyl ether (3 × 100 mL).
The organic layer was dried with magnesium sulfate and purified by
chromatographic filtration through a pad of silica gel (CH Cl /EtOAc
:1) to give compound 5 as a yellow solid (0.23 g, 89%), mp 68-70
2
toward σ-dimerization are so because of bulky substituents. It
2
2
is likely that the lowered SOMO energy of the 2-azaphenalenyl
radical 2 (Table 2) as compared to that of the phenalenyl radical
4
°
1
C. H NMR (500 MHz, CDCl
J ) 6.9 Hz, 2H), 7.35-7.5 (m, 7H), 7.74 (d, J ) 6.9 Hz, 2H).
NMR (100 MHz, CDCl ): δ 56.4, 61.9, 122.0, 125.6, 126.0, 127.3,
128.2, 128.3, 129.2, 133.1, 133.1, 137.9. IR (KBr): 3030, 2932, 2800,
3
): δ 3.86 (s, 2H), 4.04 (s, 4H), 7.21 (d,
1
3
1
stabilizes it toward dimerization by a few kcal/mol. It is also
C
foreseeable that this stabilization is even larger for the 2,5-diaza-
and 2,5,8-triazaphenalenyl radicals 3 and 4, which would be
an important asset for use of these parent radicals for metal
complexation to form two- and three-dimensional networks.
Complexation of the 2-Azaphenalenyl Radical 2. Upon
attempted complexation of radical 2, generated in situ by air
oxidation of the intermediate 2-azaphenalene 8b, with Cu(hfac)2
3
-
1
1
(
600, 1496, 817, 796, 752, 698 cm . HRMS (EI) calcd for C19
16
H N
+
[M - H] ), 258.1283; found, 258.1286.
2
,3-Dihydro-1H-benz[de]isoquinoline (6). To a solution of com-
pound 5 (4.1 g, 16 mmol) in 50 mL of dry dichloromethane was added
ethyl chloroformate (2.0 mL, 21 mmol), and the mixture was refluxed
for 8 h. The solvent was then removed under reduced pressure, and to
the residue was added 120 mL of an ethylene glycol solution of KOH
(hfac ) hexafluoroacetylacetonate), the coordinated complex
11 was formed instead in 50% yield and characterized by X-ray
(23 g, 424 mmol) and hydrazine monohydrate (4.0 g, 80 mmol). The
diffraction (Figure 6). Significantly, complex 11 is the first
structurally characterized σ-dimer of a phenalenyl radical
derivative, evidently due to the inherently labile nature of these
compounds. The copper(II) center adopts a distorted octahedral
coordination geometry with the two ligated nitrogen atoms of
the ligand in cis-relationship. The C-C single bond connecting
the two phenalene units of 2 has a length of 1.583 Å, slightly
longer than a normal C-C single bond (1.54 Å). This, on the
other hand, is consistent with a weak bond dissociation enthalpy
for dimer 12b even in this complexed state. It is likely that the
dimerization of the 2-azaphenalenyl radical 2 in this situation
is promoted by stabilization of the product through chelate
formation,1 helped in part by the known propensity for the
mixture was heated under reflux for 4 h, and then poured into water
and extracted with diethyl ether. The organic layer was dried with
magnesium sulfate. Column chromatography (EtOAc, then MeOH) gave
1
compound 6 as a light yellow solid (2.4 g, 89%), mp 58-60 °C. H
NMR (400 MHz, CDCl
3
): δ 2.23 (br s, 1H), 4.28 (s, 4H), 7.15 (d, J
) 8.3, J ) 7.0 Hz, 2H), 7.71 (d, J ) 8.3
Hz, 2H). C NMR (100 MHz, CDCl ): δ 49.8, 121.2, 125.6, 126.3,
28.3, 133.5, 134.4. IR (KBr): 3253, 2936, 2847, 1598, 1508, 1052,
)
7.0 Hz, 2H), 7.40 (dd, J
1
2
13
3
1
9
1
-
1
+
10, 820, 794, 772 cm . HRMS (EI) calcd for C12
68.0813; found, 168.0808.
H10N ([M - H] ),
N-Chloro-2,3-dihydro-1H-benz[de]isoquinoline (7). To a solution
of compound 6 (50 mg, 0.3 mmol) in 20 mL of diethyl ether was added
a suspension of N-chlorosuccinimide (39 mg, 0.3 mmol) in 10 mL of
diethyl ether at 0 °C. The mixture was stirred for 30 min at 0 °C. After
filtration, the filtrate was concentrated and passed through a pad of
7
1
8
Cu(hfac)2 complex to distort to a cis-octahedral geometry.
silica gel (CH
8%), mp > 30 °C (dec). H NMR (500 MHz, CDCl
4H), 7.22 (d, J ) 7.1 Hz, 2H), 7.45 (dd, J ) 8.3, J ) 7.0 Hz, 2H),
.77 (d, J ) 8.3, 2H). 13C NMR (125 MHz, CDCl
): δ 64.2, 122.6,
25.8, 126.8, 126.9, 131.0, 132.8. IR (KBr): 2950, 1600, 1507, 1395,
2 2
Cl ) to give compound 7 as a light yellow solid (60 mg,
Conclusion
1
9
3
): δ 4.65 (s,
The 2-azaphenalenyl radical 2 has been synthesized and
characterized by ESR spectroscopy. Variable-temperature ESR
experiments with the phenalenyl (1) and 2-azaphenalenyl (2)
radicals find that substitution of a CH group by a nitrogen atom
appears to stabilize the radical toward dimerization. Attempts
to trap radical 2 by complexation with Cu(hfac)2 lead to the
1
2
7
1
1
3
-
1
368, 1337, 1262, 821, 798, 772, 722, 577 cm . HRMS (EI) calcd
+
for C12
H
10NCl (M ), 203.0502; found, 203.0508.
Generation of 3H-Benz[de]isoquinoline 8b for Characterization.
To a solution of compound 7 (5 mg, 0.025 mmol) in 1 mL of CD Cl
2
2
in a standard NMR tube was added triethylamine (0.05 mL, 0.36 mmol).
After the solution was left standing for 25 min, the H NMR spectrum
(
17) In an attempt to block the σ-dimerization of radical 2, complexation was
performed with the dinuclear complex Rh (CF COO) , which has only axial
1
2
3
4
coordination positions available. A green powder of a new complex
precipitated, which is ESR active. However, because radical 2 cannot be
obtained in pure form due to its reactivity with excess air (as found through
attempts at crystallization) or with silica gel upon attempted chromatog-
raphy, full characterization could not be performed. The solid likely is a
mixture of 1:1 and 1:2 rhodium complexes with radical 2 (IR).
was recorded, and then immediately thereafter the mass spectrum of
8b was taken (UCLA Mass Spectrometry facility). H NMR (500 MHz,
CD Cl ): δ 5.44 (br d, J ) 2.7 Hz, 2H), 7.29 (m, 2H), 7.45 (m, 2H),
2 2
1
7
.64 (d, J ) 8.2 Hz, 1H), 7.79 (d, J ) 8.7 Hz, 1H), 8.48 (t, J ) 2.7
+
(18) Pradilla-Sorzano, J.; Fackler, J. P., Jr. Inorg. Chem. 1973, 12, 1174-1182.
Hz, 1H). HRMS (EI) calcd for C12
H
9
N (M ), 167.0735; found,
5790 J. AM. CHEM. SOC.
9
VOL. 125, NO. 19, 2003