3300 J. Am. Chem. Soc., Vol. 119, No. 14, 1997
Karakaya et al.
mmol) and chloroformic acid ethyl ester (0.29 mL, 3.0 mmol). This
mixture is stirred for 1 h at 0 °C before an aqueous solution of sodium
azide (1.24 g, 20 mmol) is added. The resulting suspension is stirred
for 10 h, ice-water is added, and the mixture is extracted (3×) with
dichloromethane. The combined organic layers are dried over MgSO4,
the solvent is removed at 0 °C in vacuum, and the residue is
chromatographed through basic alumoxide (eluent hexane/acidic acid
ethyl ester ) 4:1). The product is freeze-dried (benzene) to give 3e as
Conclusion
Dendronized PPPs can be obtained either by dendronizing
already existing PPP backbones or by employing dendronized
monomers in Suzuki cross-couplings. In the first approach, the
best results are obtained when the attachment of the dendrons
is done through urethane formation. This way even a third
generation dendron can be attached to a PPP derivative with a
number average degree of polymerization Pn ) 82. The second
approach is also successful despite the steric crowding of the
macromonomers coupling site. The molecular weights achieved
are at least as high as the ones of the first approach. This puts
the most important advantage of the second approach nicely
into the center of consideration, which is the fact that the degree
of coverage is here inherently 100%. Thus, if the described
hybrids of dendrimers and rigid-rod polymers actually attain
cylindrical shape in solution (which still needs to be proved),
their shape should undoubtlessly be perfect.
1
white powder: yield 2.40 g (65%); H-NMR (270 MHz, CDCl3) δ
5.05 (m, 28 H), 6.65 (s, 8 H), 6.24 (m, 12 H), 6.90 (s, 1 H), 7.28-7.6
(m, 40 H); 13C-NMR (68 MHz, CDCl3) δ 70.0, 101.5, 101.6, 106.3,
108.1, 108.3, 127.9, 128.5, 132.4, 136.7, 138.6, 139.1, 159.1, 160.1,
172. Anal. Calcd. for C105H89N3O15 (1632.869): C, 77.24.13; H, 5.49;
N, 2.57. Found: C, 77.15; H, 5.60; N, 2.22.
Poly{2,5-dihexyl-1′-methyl-2′-[((([3,5-bis(3,5-bis(3,5-bis(benzyloxy)-
benzyloxy)benzyloxy)]amino)carbonyl)oxy)ethyl]biphen-4,4′-diyl}
(5d). To a refluxing solution of polymer 5b (100 mg, 0.26 mmol) in
dry toluene is added a solution of 3e (1.38 g, 1.43 mmol) in dry toluene
(20 mL), and refluxing is continued for 12 h when the reaction is
quenched with water. The aqueous layer is washed with toluene (50
mL), and the combined organic layers are dried over MgSO4. After
removal of the solvent, the residue is separated into low molecular
weight side products and the polymer by preparative GPC using THF
as eluent. Polymer 5d is then precipitated into ethanol and freeze-
dried (benzene) to give a colorless material: yield 310 mg (59%); 1H-
NMR (500 MHz, CDCl3) δ 0.84 (s, 6 H), 1.20 (s, 12 H), 1.46 (s, 4 H),
2.20 (s, 2 H), 1.47 (s, 4 H), 2.17 (s, 3 H), 2.46 (s, 4 H), 4.19 (s, 2 H),
4.92 (m, 28 H), 6.25 (m, 1 H), 6.57 (m, 21 H), 7.31 (m, 44 H); 13C-
NMR (63 MHz, CDCl3) δ 14.0, 19.7, 22.5, 29.0, 31.0, 31.5, 32.9, 65.4,
70.0, 97.9, 101.6, 106.4, 127.5, 127.9, 128.5, 130.2, 133.9, 136.8, 137.6,
Experimental Section
General Methods. Compounds 1,4 2a-c,4 2d,12 3a-c,4 4,3a 5,12
and 714 were prepared according to literature procedures. 4-Methyl-
benzyl alcohol and trimethylsilyl iodide were purchased from Aldrich
and used without further purification. Solvents were dried according
to standard procedures. All reactions were carried out under nitrogen.
1
The H-NMR spectra of dendronized polymers were recorded with a
repetition rate of 13 s and a sweep width of 20 ppm on a Bruker 500
MHz spectrometer in order to obtain reliable integrations. Signals that
appeared because of traces of dirt in the probe head were automatically
substracted before integration. The molecular weight determinations
were done using a Thermo Separation Products set-up with three DVB-
mixed (DVB ) divinylbenzene) bead columns, a H502B viscosimeter
detector, and a Wyatt Dawn DSP laser photometer, coupled with an
Optilab 903 interferometric refractometer. Complex molecular ion
peaks in the mass spectra match perfectly with the calculated isotope
pattern. Only the two most intense peaks are given (relative intensities).
1-Methyl-4-(bromomethylene)-2,5-dibromobenzene (6a). To a
darkened solution of 4-methylbenzyl alcohol (24.4 g, 0.20 mol) in
dichloromethane (20 mL) is dropped a solution of bromine (80 g, 0.50
mol) in the same solvent (10 mL) containing a few crystals of iodine.
The resulting solution is refluxed for 1 d, another portion of bromine
is added (20 g, 0.125 mol), and refluxing is continued for another 10
h. This solution is then poured into aqueous KOH (20%, 100 mL),
and the phases are separated. The aqueous one is washed with
methylene chloride (2×, 50 mL each), and the combined organic layers
are dried over MgSO4. After removal of the solvent, the residue is
recrystallized from ethanol to give 6a as colorless crystals. For 6a:
139.2, 139.8, 153.1, 160.0. Anal. Calcd. for
C132H127N1O16
(1983.48): C 79.93; H 6.45. Found: C 80.23; H 6.50.
Poly[2,5-dihexyl-2′-(methoxymethyl)-5′-methylbiphen-4,4′-diyl]
(8a). To the two-phase system of 1 M Na2CO3 (100 mL) and toluene
(30 mL) are added the monomers 6b (524 mg, 1.8 mmol) und 7 (609
mg, 1.82 mmol). After careful degassing tris[tri(p-tolyl)phosphine]-
palladium(0) (24 mg, 1.3 mol %) is added to this mixture which is
then refluxed for 48 h. Sometimes the precipitation of metallic Pd is
observed. The aqueous phase is washed with toluene (50 mL), and
the combined organic layers are dried over MgSO4. The organic layer
is reduced to approximately 10 mL and then poured into MeOH (300
mL). The precipitate formed is recovered by centrifugation, and the
procedure is repeated. Freeze-drying (benzene) affords polymer 8a as
fibrous material: yield 640 mg (94%); 1H-NMR (270 MHz, CDCl3) δ
0.82 (s, 6 H), 1.22 (s, 12 H), 1.46 (s, 4 H), 2.21 (s, 3 H), 2.43 (s, 4 H),
3.30 (s, 3 H), 4.28 (s, 2 H), 6.8-7.8 (m, 4 H); 13C-NMR (63 MHz,
CDCl3) δ 14.1, 20.0, 22.6, 29.2, 30.9, 31.6, 32.9, 35.5, 129.0, 130.1,
131.8, 133.8, 135.7, 137.7, 138.6, 139.6, 141.1. Anal. Calcd. for
C27H38O (378.603): C, 85.66; H, 10.12. Found: C, 84.73; H, 9.75.
For molecular weights, see text.
1
yield 46 g (78%); mp 72 °C; H-NMR (270 MHz, CDCl3) δ 2.34 (s,
3 H), 4.49 (s, 2 H), 7.40 (s, 1 H), 7.60 (s, 1 H); 13C-NMR (68 MHz,
CDCl3) δ 22.4, 32.1, 122.7, 123.8, 134.3, 134.8, 136.0, 140.2; MS (EI)
m/z 342 (12.5), 344 (12.3). Anal. Calcd. for C9H10Br2O (342.855):
C, 28.03; H, 2.06. Found: C, 28.03; H, 2.06.
Poly[2,5-dihexyl-3′-(iodomethyl)-6′-methylbiphen-4,4′-diyl] (8b).
To a solution of polymer 8a (0.60 g, 1.6 mmol) in dry chloroform (50
mL) is added a solution of trimethylsilyl iodide (TMSI) (1.6 g, 8.0
mmol), and the mixture is refluxed for 24 h. The solvent (50 mL) is
then removed, and refluxing is continued for another 24 h. The polymer
is precipitated by pouring the cooled solution into MeOH (300 mL).
Repetition of this procedure and freeze-drying (benzene) affords
1-Methyl-4-(methoxymethylene)-2,5-dibromobenzene (6b). To a
suspension of NaH (8.8 g, 0.35 mol) in dry THF (200 mL) is dropped
methanol (10 g, 0.33 mol), the resulting mixture is stirred for 2 h at 20
°C before it is cooled to 0 °C and a solution of 6a (17.1 g, 0.05 mol)
in dry THF is added. After 12 h, the reaction is quenched with water
and the layers are separated. The aqueous layer is washed with diethyl
ether (2×), and the combined organic layers are dried over MgSO4.
After removal of the solvent, the oily residue is distilled through a 10
cm Vigreux column in high vacuum to give 6b as a colorless liquid:
yield 13.2 g (90%); bp 85 °C (0.001 mbar); 1H-NMR (270 MHz, CDCl3)
δ 2.31 (s, 3H), 3.42 (s, 2H), 4.42 (s, 2H), 7.35 (s, 1H), 7.57 (s, 1H);
13C-NMR (68 MHz, CDCl3) δ 22.2, 58.5, 72.9, 120.6, 123.8, 132.1,
133.9, 136.4, 138.5; HRMS calcd for C9H10Br2O, m/z 291.9099, found
291.9093. Anal. Calcd. for C9H10Br2O (293.985): C, 36.77; H, 3.43.
Found: C, 36.40; H, 3.25.
1
polymer 8b as a colorless fibrous material: yield 648 mg (85%); H-
NMR (270 MHz, CDCl3) δ 0.82 (s, 6 H), 1.23 (s, 12 H), 1.52 (s, 4 H),
2.20 (s, 3 H), 2.46 (s, 4 H), 4.00-4.80 (s, 2 H), 7.00-7.80 (m, 4 H);
13C-NMR (68 MHz, CDCl3) δ 5.4, 19.8, 22.5, 29.1, 30.8, 31.6, 32.9,
35.5, 58.2, 72.2, 129.4, 130.1, 131.2, 133.1, 134.7, 137.5, 138.7, 139.6,
140.5. Anal. Calcd. for C26H35I (474.474): C, 65.82; H, 7.44.
Found: C, 65.56; H, 7.32.
General Procedure for the Dendronization of Polymer 8b with
Dendrons 1b, 2b, and 3b. To a suspension of NaH (for 1b and 2b
48 mg, 1.92 mmol; for 3b 0.131 mg, 5.25 mmol) in THF (100 mL) is
added the respective dendron (1b 0.20 g, 0.64 mmol; 2b 0.47 g, 0.64;
3b 1.67 g, 1.05 mmol), and after 12 h at 20 °C, the solution is decanted.
A solution of polymer 8b (100 mg, 0.21 mmol) in dry THF (15 mL)
is then added dropwise. The mixture is stirred at 20 °C until it turns
opaque and then refluxed for 24 h. After the reaction is quenched
[3,5-Bis(3,5-bis(3,5-bis(benzyloxy)benzyloxy)benzyloxy)]-
benzoyl azide (3e). To a cooled suspension of 3 (X ) CO2H) (3.6 g,
2.2 mmol) in acetone (150 mL) is added triethylamine (0.42 mL, 3.0