Nanometric dendritic macromolecules: Stepwise assembly by double (2,2′: 6′,2″-terpyridine)ruthenium(I) connectivity

Article abstract of DOI:10.1039/a700127d

The construction of nanometric, dendritic macromolecules by bis(2,2′: 6′,2″-terpyridine)ruthenium(II) connectivity is investigated. The assembly methodology, which incorporates both the control of metal complexation sites and degree of flexibility within the linkages, has been demonstrated.

Full text of DOI:10.1039/a700127d

Nanometric dendritic macromolecules: stepwise assembly by double
(
2,2∞56∞,2◊-terpyridine)ruthenium(
I
) connectivity
George R. Newkome* and Enfei He
Center for Molecular Design and Recognition, University of South Florida, T ampa, Florida 33620, USA
The construction of nanometric, dendritic macromolecules by bis(2,2∞56∞,2◊-terpyridine)ruthenium() connectivity is investigated.
The assembly methodology, which incorporates both the control of metal complexation sites and degree of flexibility within the
linkages, has been demonstrated.
Interest in specifically assembled, dendritic nanostructures has
continued to escalate over the past decade1 and will continue
to do so due to the anticipation of their novel properties.
Dendritic systems which incorporate metal centres are either
of a random nature by simple molecular inclusion within the
macrostructure,2 or at a specific predetermined binding locus3
either within the assembly or on its surface. Such metallo-
macroassemblies aÂord entrance to materials capable of novel
magnetic, electronic, photooptical or catalytic properties. As a
prelude to the construction process, we previously reported4–6
the use of bis(2,2∞56∞,2◊-terpyridine)ruthenium() (herein
denoted by [—<Ru>—]), as the mode of connectivity, in
order to combine preconstructed, pseudo-spherical dendritic
fragments in a predetermined way. Such connectivity permitted
the analysis of the final product by the easy quantification of
the metal centre(s) by simple electrochemical procedures. This
type of connectivity (i.e., incorporation of multiple centres)
gave rise to the dodecaruthenium complex4 1 and the single
metal centre aÂorded the bisdendrimer5 2 (Fig. 1); these rep-
resent our initial approaches to the specific assembly of discrete
dendritic networks by the connection of established constructs.
We herein describe the use of two metal centres per appendage
saturated aqueous NaHCO solution was carefully added, then
3
the solvent was removed in vacuo to aÂord a white solid, which
was extracted with absolute EtOH (3×100 cm3). The extract
was concentrated in vacuo to give tetraol 4, as a colourless oil.
(8.26 g, 95%) (Found: C, 55.69; H, 9.61. C H O requires C,
1
7 36 8
55.42; H, 9.85%); 1H NMR (MeOD), d 1.78 (m, 2H,
CH CH OH), 3.38 (s, 2H, CH O), 3.55 (t, J 5.0 Hz, 2H,
2
2
2
OCH ), 3.69 (t, J 5.1 Hz, 2H, CH OH); 13C NMR (MeOD),
2
2
d 31.8 (CH CH OH), 44.9 (Cquat), 60.5 (CH OH), 69.7 (OCH ),
2
2
2
2
70.7 (CH O); IR (neat), 3364, 2948, 2879, 1493, 1424, 1363,
2
1109 cm−1.
Tetrakis{5-[4∞-oxa-(2,2∞56∞,2◊-terpyridinyl)]-2-
oxapentyl}methane 5
To a suspension of powdered KOH (1.10 g) in dry Me SO
2
(
4
15 cm3), was added tetraol 4 (600 mg, 1.63 mmol) in Me SO
2
(
5 cm3). The suspension was heated to 60 °C for 30 min, then
∞-chloro-2,2∞56∞,2◊-terpyridine9 (4∞-Cl-tpy; 1.92 g, 4.4 equiv.)
was added. After 24 h at 60 °C, the mixture was cooled and
poured into cold water (300 cm3). The resultant white solid
was filtered, washed with water, and dried in vacuo to give a
oÂ-white solid, which was column chromatographed eluting
[—<Ru>—(×)—<Ru>—] for attachment to a four-direc-
with 15% EtOAc in CH Cl to aÂord 5, as a white solid
tional core; this assembly methodology incorporates (i) pos-
itional control over the metal complexation sites and (ii) a
variable flexibility within the linkages (×) between those con-
nectivity sites.
2 2
(
1.65 g, 78%), mp 161–164 °C (Found: C, 71.70; H, 5.57; N,
1
2.78; C H N O requires C, 71.50; H, 5.61; N, 12.99%); 1H
7
7 72 12 8
NMR, d 1.98 (m, 8H, J 5.6 Hz, OCH CH ), 3.42 (s, 8H, CH O),
2
2
2
3
.52 (t, 8H, J 5.6 Hz, OCH ), 4.18 (t, 8H, J 5.6 Hz,
2
OCH CH CH ), 7.24 (t, 8H, J 5.2 Hz, H5,5◊), 7.74 (t, 8H,
2
2
2
Experimental
J 7.6 Hz, H4,4◊), 7.94 (s, 8H, H3∞,5∞), 8.54 (d, 8H, J 7.9 Hz,
H3,3◊), 8.62 (d, 8H, J 4.7 Hz, H6,6◊); 13C NMR, d 29.4
Equipment and materials
(
OCH CH ), 45.6 (Cquat), 65.2 (OCH CH CH ), 67.6 (OCH ),
2
2
2
2
2
2
Melting points are uncorrected and were measured on a Mel-
Temp apparatus. All reactions were conducted under a nitrogen
atmosphere. 1H and 13C NMR spectra were recorded on a
69.9 (CH O), 107.5 (C5,5◊), 121.3 (C4,4◊), 123.8 (C3,3◊), 136.7
2
(C3∞,5∞), 149.1 (C6,6◊), 156.2 (C2,2◊), 157.0 (C2∞,6∞), 167.2 (C4∞); IR
(KBr), 3063, 2933, 2876, 1609, 1593, 1570, 1493, 1440, 1416,
Bruker AC250 MHz spectrometer using CDCl as solvent,
1362, 1209, 1093, 801 cm−1.
3
unless otherwise indicated, with Me Si as the internal standard
4
(
d=0). IR spectra were recorded on a Perkin-Elmer 621 grating
4-[4∞-Oxa-(2,2∞56∞,2◊-terpyridinyl )]butanoic acid 6
IR spectrometer. UV–VIS spectra were recorded on
a
To a solution of 4-hydroxybutanoic acid (942 mg, 7.47 mmol)
HP8452A diode array spectrophotometer. Elemental analyses
were performed by M-H-W Laboratories, Phoenix, AZ.
All reagents were purchased from Aldrich. Column chroma-
tography was performed using activated basic aluminium oxide
and KOH (3 g) in dry Me SO (30 cm3) at 60 °C, was added
2
4
∞-Cl-tpy (2.00 g, 7.47 mmol). The mixture was maintained for
3
6 h, then cooled to 25 °C and poured into water (600 cm3)
aÂording a yellow transparent solution. The pH was adjusted
to neutral by the addition of 10% aqueous HCl resulting in
the formation of a white precipitate, which after standing for
at least 2 h, was filtered, washed with water, dried in vacuo to
give the acid 6, as a white solid (2.15 g, 86%); mp 173–175 °C
(Found: C, 68.29; H, 5.29; N, 12.30. C H N O requires C,
(
150 mesh, Brockmann I; Aldrich).
Tetrakis(5-hydroxy-2-oxapentyl)methane 4
To a solution of 6,6-bis(carboxy-2-oxabutyl)-4,8-dioxaunde-
cane-1,11-dicarboxylic acid7 3 (10 g, 23.6 mmol) in dry THF
1
9 17 3 3
(
50 cm3) at 0 °C, was added dropwise a BH ·THF8 solution
68.05; H, 5.11; N, 12.53%); 1H NMR, d 2.21 (m, 2H, J 6.0 Hz,
3
(
104 cm3, 4.4 equiv.) over 30 min. The solution was stirred for
OCH CH CH ), 2.57 (t, 2H, J 7.1 Hz, CH CO H), 4.31 (t, 2H,
2
2
2
2
2
1
h, then warmed to 25 °C and stirred for 3 h. Excess of a
J 6.0 Hz, OCH ), 7.38 (td, 2H, J 4.9, 1.0 Hz, H5,5◊), 7.88 (td,
2
J. Mater. Chem., 1997, 7(7), 1237–1244
1237

Fig. 1 Dendritic architectures incorporating (—<Ru>—) units
2
H, J 7.8, 1.8 Hz, H4,4◊), 7.92 (s, 2H, H3∞,5∞), 8.61 (d, 2H,
tert-butyl 4-[(2-tert-butoxycarbonyl)ethyl]-4-aminoheptane-
dicarboxylate 710 (2.48 g, 5.97 mmol) was added. The reaction
mixture was stirred for 36 h, after which the white precipitate
was filtered oÂ. The filtrate was concentrated in vacuo aÂording
J 7.9 Hz, H3,3◊), 8.67 (d, 2H, J 4.3 Hz, H6,6◊); 13C NMR, d 24.6
(
OCH CH CH ), 30.7 (CH CO H), 67.4 (OCH ), 107.6 (C5,5◊),
2
2
2
2
2
2
1
21.9 (C4,4◊), 124.1 (C3,3◊), 137.3 (C3∞,5∞), 148.9 (C6,6◊), 156.1
(
C2,2◊), 157.0 (C2∞,6∞), 167.2 (C4∞), 175.7 (CO H); IR (KBr), 3063,
a crude oil, which was dissolved in Et O (200 cm3), washed
2
2
2
956, 2918, 2879, 1709, 1593, 1570, 1478, 1450, 1416, 1370,
with 10% aqueous Na CO (2×100 cm3), brine (2×100 cm3),
2
3
1
262, 1209, 1040, 801, 747 cm−1.
dried (MgSO ), and concentrated in vacuo to aÂord a solid,
4
which was recrystallized from cyclohexane (3.15 g, 72%); mp
1
46–149 °C (Found: C, 67.36; H, 7.51; N, 7.85. C H N O
N-{Tris[(2-tert-butoxycarbony)ethyl]methyl}[4∞-oxa-
4
1 56 4 8
requires C, 67.19; H, 7.70; N, 7.64%); 1H NMR, d 1.42 (s, 27H,
(
2,2∞56∞,2◊-terpyridinyl)]butamide 8
CH ), 2.01 (t, 6H, J 8.2 Hz, CH CO ), 2.23 (m, 8H,
3
2
2
To a solution of acid 6 (2.0 g, 5.97 mmol) in dry DMF (30 cm3),
CH CH CONH, CH CH CO ), 2.36 (t, 2H,
J
7.1 Hz,
2
2
2
2
2
were added dicyclohexylcarbodiimide (DCC; 1.23 g,
CH CONH), 4.28 (t, 2H, J 5.9 Hz, OCH ), 6.03 (s, 1H, NH),
2
2
5
.97 mmol) and 1-hydroxybenzotriazole (1-HOBT; 806 mg,
7.32 (td, 2H, J 4.8, 1.8 Hz, H5,5◊), 7.84 (td, 2H, J 7.8, 1.7 Hz,
5
.97 mmol) at 25 °C. This mixture was stirred for 1 h, then di-
H4,4◊), 8.01 (s, 2H, H3∞,5∞), 8.60 (d, 2H, J 8.0 Hz, H3,3◊), 8.68 (d,
1
238
J. Mater. Chem., 1997, 7(7), 1237–1244

Scheme 1 Reagents and conditions: i, BH ·THF, 1 h, 0°C, then 3 h, 25 °C; ii, 4∞-Cl-tpy, KOH, Me SO, 24 h, 60 °C
3
2
Scheme 2 Reagents and conditions: i, 4∞-Cl-tpy, KOH, Me SO, 36 h, 60 °C; ii, DCC, 1-HOBT, DMF, 36 h, 25 °C; iii, RuCl Ω3H O, MeOH, 3 h, reflux
2
3
2
J. Mater. Chem., 1997, 7(7), 1237–1244
1239

Scheme 3 Reagents and conditions: i, 4∞-Cl-tpy, KOH, Me SO, 36 h, 60°C; ii, 4-ethylmorpholine, MeOH, 2 h, reflux
2
Scheme 4 Reagents and conditions: i, DCC, 1-HOBT, DMF, 48 h, 25 °C; ii, RuCl ·3H O, MeOH, 6 h, reflux
3
2
1
240
J. Mater. Chem., 1997, 7(7), 1237–1244

Scheme 5 Reagents and conditions: i, 4-ethylmorpholine, MeOH–CHCl , 4 h, reflux
3
2
H, J 4.3 Hz, H6,6◊); 13C NMR, d 25.2 (CH CH CON), 28.2
(2×10 cm3) then dried in vacuo, yielding 9, as a yellow–brown
solid (1.94 g, 76%); mp>202°C (decomp.); (Found C, 52.17;
H, 5.95; N, 6.06. C H Cl N O Ru requires C, 52.37; H, 6.00;
2
2
(
CH ), 29.9 (CH CO ), 30.2 (CH CH CO ), 33.6 (CH CON),
3
2
2
2
2
2
2
5
7.6 (NHC), 67.4 (OCH ), 80.8 [C(CH ) ], 107.5 (C5,5◊), 121.4
2
3 3
41 56 3 4 8
(
C4,4◊), 123.9 (C3,3◊), 136.9 (C3∞,5∞), 149.1 (C6,6◊), 156.2 (C2,2◊),
N, 5.96%); IR (KBr), 3340, 3071, 2987, 2940, 1732, 1670, 1609,
1
57.2 (C2∞,6∞), 167.2 (C4∞), 171.6 (CONH), 173.0 (CO ); IR
1555, 1471, 1370, 1224, 1160, 1047, 801 cm−1; UV–VIS, l
=
2
max
(
KBr), 3341, 3063, 3010, 2987, 2933, 1732, 1671, 1586, 1563,
232 (e=3.27×104), 278 (2.91×104), 312 (1.63×104), 402
1
478, 1452, 1362, 1155, 793 cm−1.
(9.32×103), 466 nm (3.73×103 dm3 mol−1 cm−1).
Ruthenium(III ) complex of N-{tris[(2-tert-
butoxycarbony)ethyl]methyl}[4∞-oxa-(2,2∞56∞,2◊-
terpyridinyl )]butamide 9
5-Aminopentyl 4∞-(2,2∞56∞,2◊-terpyridinyl ) ether 10
To a suspension of powdered KOH (2.0 g) in dry Me SO
2
(
30 cm3), was added 5-aminopentan-1-ol (770 mg, 7.47 mmol).
A solution of RuCl ·3H O (709 mg, 2.71 mmol) and 8 (2.0 g,
The suspension was stirred at 60 °C for 30 min, then 4∞-Cl-tpy
(2.00g, 7.47 mmol) was added. The whole mixture was stirred
at 60 °C for an additional 36 h. After cooling to 25 °C, the
mixture was poured into water (600 cm3), stirred, then allowed
3
2
2
.71 mmol) in MeOH (50 cm3) was refluxed for 3 h. After
cooling, the yellow–brown precipitate was filtered, washed
sequentially with MeOH (5 cm3), water (2×20 cm3) and Et O
2
J. Mater. Chem., 1997, 7(7), 1237–1244
1241

to set for 3 h. The precipitate was filtered, washed with water,
and dried in vacuo to give a crude product, which was column
chromatographed eluting with 10% MeOH in CH Cl to yield
(CONHCH ), 57.4 (CONHC), 67.4 (free tpy-OCH ,), 69.3
2
2
(OCH ), 71.0 (CH O), 107.2 (free tpy C5,5◊), 111.1 (C5,5◊), 121.2
2
2
(free tpy C4,4◊), 123.9 (free tpy C3,3◊), 124.5 (C4,4◊), 127.8 (C3,3◊
), 136.9 (free tpy C3∞,5∞), 137.7 (C3∞,5∞), 148.9 (free tpy C6,6◊),
152.0 (C6,6◊), 153.7 (C2,2◊), 156.7, 156.8 (C2∞,6∞, free tpy C2,2◊),
2
2
1
0, as a light yellow solid (1.78 g, 71%); mp 104–106 °C
(
Found: C, 72.04; H, 6.46; N, 16.60. C H N O requires C,
2
0 22 4
7
1.83; H, 6.63; N, 16.75%); 1H NMR, d 1.49–1.55 (m, 6H,
158.0 (free tpy C2∞,6∞), 162.5 (CONHCH ), 165.9, 166.2, 166.8
2
(C4∞, free tpy C4∞), 172.1 (CONHC), 172.9 (CO ); IR (KBr),
2
NH , NCH CH CH ), 1.82 (m, 2H, CH CH O), 2.67 (t, 2H,
2
2
2
2
2
2
J 6.1 Hz, NCH ), 4.17 (t, 2H, J 6.2 Hz, CH O), 7.29 (td, 2H,
3418, 3333, 3071, 2980, 2940, 2851, 1724, 1678, 1616, 1563,
2
2
J 4.9, 1.6 Hz, H5,5◊), 7.78 (td, 2H, J 7.2, 1.4 Hz, H4,4◊), 8.01 (s,
1470, 1393, 1370, 1216, 1162, 847, 790, 754 cm−1; UV–VIS,
2
H, H3∞,5∞), 8.59 (d, 2H, J 7.9Hz, H3,3◊), 8.65 (d, 2H, J 4.4 Hz,
l
=244 (e=6.86×104), 270 (7.13×104), 304 (7.19×104),
max
H6,6◊); 13C NMR, d 23.2 (NCH CH CH ), 28.8 (CH CH O),
488 nm (1.99×104 dm3 mol−1 cm−1).
2
2
2
2
2
3
3.3 (NCH CH ), 42.0 (NCH ), 67.9 (CH O), 107.3 (C5,5◊),
2
2
2
2
1
21.2 (C4,4◊), 123.7 (C3,3◊), 136.6 (C3∞,5∞), 148.9 (C6,6◊), 156.0
Ruthenium(II ) ruthenium(III ) complex 13
(
C2,2◊), 156.9 (C2∞,6∞), 167.1 (C4∞); IR (KBr), 3359, 3299, 3059,
3
014, 2947, 2865, 1598, 1583, 1576, 1470, 1448, 1410, 1358,
A solution of RuCl ·3H O (80 mg, 306 mmol) and 12 (542 mg,
3
2
1
208, 1043, 803 cm−1.
306 mmol) in MeOH (20 cm3) was refluxed for 6 h. After
cooling to 25 °C, the red precipitate was filtered, washed with
cold MeOH (2 cm3), water (2×10 cm3), and dried in vacuo to
yield crude product 13, as a dark-red solid (206 mg, 34% crude
yield); mp>152°C (decomp.); IR (KBr), 3425, 3071, 2980,
Amino-ruthenium(II ) complex 11
To a suspension of complex 9 (300 mg, 318 mmol) in MeOH
(
20 cm3) were added amine 10 (106 mg, 318 mmol) and 4-
2
940, 1724, 1655, 1617, 1547, 1470, 1371, 1163, 847, 793 cm−1;
ethylmorpholine (73 mg). The mixture was refluxed for 2 h
until it turned into a clear red solution. After cooling to 25 °C,
saturated NH PF in MeOH (10 cm3) was added, then the
UV–VIS, l
=232 (e=7.25×104), 270 (7.53×104), 304
max
(
7.49×104), 488 nm (2.06×104 dm3 mol−1 cm−1). This prod-
4
6
uct was not purified but carried on to the next reaction.
methanol was removed in vacuo, the resulting red solid was
dissolved in CHCl (4 cm3), which was then slowly added to
3
Et O (100 cm3) with stirring, to yield a red precipitate, which
Dendritic complex 14
2
was filtered, and dried in vacuo to give complex 11, as a red
To a suspension of complex 13 (429 mg, 216 mmol, 4.4 equiv.)
in MeOH (30 cm3) were added tetrakisterpyridine core 5
(63.5 mg, 49 mmol) and 4-ethylmorpholine (45 mg) in MeOH–
solid (336 mg, 72%); mp >152 °C (decomp.); (Found: C, 49.92;
H, 5.29; N, 7.28. C H F N O P Ru requires C, 50.24; H,
6
1 78 12 8 9 2
5
.39; N, 7.68%); 1H NMR (CD CN), d 1.11–1.45 (m, 31H,
3
CHCl (251, v/v, 5 cm3). The mixture was refluxed for 4 h
NCH CH CH , CH ), 1.8–2.0 (m, 10H, CH CH O,
3
2
2
2
3
2
2
until it turned into a clear red solution. After cooling to 25 °C,
OCH CH , CH CH CO ), 2.22 (m, 6H, CH CO ), 2.45 (t, 2H,
2
2
2
2
2
2
2
an excess of NH PF was directly added to the solution to
J 7.0 Hz, CH CON), 3.00 (br s, 2H, H NCH ), 4.52 (m, 4H,
4
6
2
2
2
2
form a red precipitate, which was filtered, washed sequentially
CH O, OCH ), 6.67 (s, CONH), 7.16 (m, 4H, H5,5◊), 7.42 (m,
2
with cold MeOH (2×5 cm3), water (2×15 cm3), Et O
4
H, H6,6◊), 7.88 (m, 4H, H4,4◊), 8.35–8.60 (m, 8H, H3,3◊, H3∞,5∞);
2
(
2×5 cm3), and dried in vacuo to yield 14, as a red solid
1
3C NMR (CD CN),
d
23.8 (NCH CH CH ), 25.0
3
2
2
2
(416 mg, 85%); mp 219–221 °C (Found: C, 47.66; H, 4.32; N,
(
CH CH CON), 28.4 (d, CH , CH CH O), 29.7 (d,
2
2
2
2
3
2
2
7.95. C
H
F N O P Ru requires C, 47.87; H, 4.49; N,
CH CH CO ),
32.7
(d,
CH CON,
H NCH CH ),
397 444 96 56 52 16
8
2
2
2
2
2
2
7.88%); 1H NMR (CD CN), d 1.30–3.90 (br m, 236H, CH ,
4
1.7(H NCH ), 58.6 (NHC), 70.3 (OCH ), 71.1 (CH O), 112.2
3
2
2
2
2
CH ), 4.53 (m, 40H, OCH , CH O), 6.47 (s, 4H, CONH), 7.15
(
C5,5◊), 125.4 (C4,4◊), 128.5 (C3,3◊), 138.7 (C3∞,5∞), 153.5 (C6,6◊),
3
2
2
(
m, 32H, H5,5◊), 7.40 (m, 32H, H6,6◊), 7.86 (m, 32H, H4,4◊),
1
57.5 (C2,2◊), 159.4 (C2∞,6∞), 167.0 (d, C4∞), 172.9 (CONH), 173.7
8
.35–8.60 (m, 64H, H3,3◊, H3∞,5∞); 13C NMR (CD CN), d 23.1,
(
CO ); IR (KBr), 3417, 3295, 3086, 2980, 2940, 1719, 1614,
3
2
25.0, 25.9, 28.4 (CH ), 29.8, 29.9, 30.5, 30.6, 32.7, 32.8, 40.0
1
470, 1394, 1370, 1213, 1162, 1040, 840, 788, 754 cm−1;
3
(
CONHCH ), 58.0 (CONHC), 68.0–70.0 (m, all CH O,
UV–VIS, l
=244 (e=4.76×104), 270 (5.17×104), 304
2
2
max
OCH ), 81.3 (CO C), 112.1 (d, C5,5◊), 125.5 (d, C4,4◊), 128.5
(
6.08×104), 488 nm (1.81×104 dm3 mol−1 cm−1).
2
2
(
C3,3◊), 138.8 (C3∞,5∞), 153.5 (C6,6◊), 157.4 (C2,2◊), 159.4 (C2∞,6∞),
1
67.1 (d, C4∞), 172.4 (CONHC), 174.0 (CO ); IR (KBr), 3425,
Complex 12
2
3
118, 3079, 2979, 2941, 1724, 1671, 1617, 1547, 1470, 1425,
To a solution of 4-[4∞-oxa-(2,2∞56∞,2◊-terpyridinyl)]butanoic
acid 6 (207 mg, 618 mmol) in dry DMF (15 cm3) were added
DCC (128 mg, 618 mmol) and 1-HOBT (83.5 mg, 618 mmol) at
1217, 848, 786 cm−1; UV–VIS, l
=244 (e=3.68×105), 270
max
(3.99×105), 304 (4.77×105), 488 nm (1.41×105 dm3
mol−1 cm−1).
2
5 °C. The mixture was stirred for 1 h, then amine 11 (901 mg,
6
18 mmol) was added. The whole mixture was stirred for 48 h,
after which the white precipitate was filtered. The red filtrate
Results and Discussion
was concentrated in vacuo to aÂord a crude residue, which
Synthesis of the tetrakisterpyridine core 5
was dissolved in CHCl (200 cm3), washed with saturated
3
aqueous NaHCO (2×50 cm3), then brine (2×100 cm3), dried
The synthesis of tetrakisterpyridine core 5 was initiated from
the readily available tetracarboxylic acid 3, which has been
demonstrated to be an ideal core for the construction of a
four-directional dendritic materials.7 Acid 3, prepared10 in high
yield and purity from pentaerythritol and acrylonitrile, fol-
3
(
MgSO ), and concentrated in vacuo. The crude residue was
4
column chromatographed eluting with 10% MeOH in CH Cl
2
2
to yield 12, as a red solid (465 mg, 42%); mp 90–94 °C (Found:
C, 53.95; H, 5.50; N, 9.47. C H F N O P Ru requires C,
80 93 12 11 11 2
5
4.11; H, 5.28; N, 8.68%); 1H NMR, d 1.11–1.45 (m, 31H,
lowed by hydrolysis, was reacted8 with BH in THF at 0 °C
3
NCH CH CH , CH ), 1.8–2.0 (m, 12H, OCH CH ,
to aÂord tetraol 4, which was then treated with at least 4
2
2
2
3
2
2
CH CH O, OCH CH , CH CH CO ), 2.22 (m, 6H, CH CO ),
equivalents of 4∞-chloro-2,2∞56∞,2◊-terpyridine9 (4∞-Cl-tpy) in the
2
2
2
2
2
2
2
2
2
2
.40–2.46 (m, 4H, CH CONH, CH CONH), 3.10 (m, 2H,
presence of powered KOH in anhydrous Me SO at 60 °C to
2
2
2
CONHCH ), 4.52 (m, 6H, OCH , CH O, OCH ), 6.56 (s,
give the desired tetrakisterpyridine core 5 in 74% yield after
2
2
2
2
CONHC), 7.16–8.70 (m, tpy H); 13C NMR,
d
23.1
purification, Scheme 1. The structure of core 5 was confirmed
(1H NMR) by the definitive upfield shift (Dd=−0.52 ppm) for
the singlet for the 3∞,5∞-terpy H upon the 4∞-terpy Cl to 4∞-terpy
OR conversion. In 13C NMR, the peak shifts for the C5,5◊ from
(
NCH CH CH ), 25.0 (d, CH CH CONH, CH CH CONH),
2
2
2
2
2
2
2
2
2
8.0 (d, CH , CH CH O), 29.8 (d, CH CH CO ), 31.7, 32.3,
3
2
2
2
2
2
3
2.7 (CH CONH, H NCH CH ,
CH CONH), 39.2
2
2
2
2
1
242
J. Mater. Chem., 1997, 7(7), 1237–1244

d 121.1 to 107.3 and for C4∞ from d 146.5 to 167.1 further
complex heteroaryl H region supports the presence of structur-
ally dissimilar terpyridine environments. Whereas in its 13C
NMR spectrum, the two pairs of diÂerent terpyridines aÂorded
complex patterns with peaks for each carbon atom due to the
small diÂerence caused by the two layers of ruthenium()
terpyridines centres connected by the slightly diÂerent organic
linkages. All signals (13C NMR) were, however, resolved to
show each moiety of the dendritic complex, with the exception
of the quaternary core carbon, which should have appeared at
d 45.6; the absence of this signal is reasonable since it is the
only unique atom in the dendritic assembly.
support the transformation.
Synthesis of ruthenium(II ) complex connectors
4
-[4∞-Oxa-(2,2∞56∞,2◊-terpyridinyl)]butanoic acid 6, was pre-
pared by the reaction of 4∞-Cl-tpy with 4-hydroxybutanoic acid
in the presence of solid KOH in anhydrous Me SO at 60 °C
2
in 86% yield. The structure of 6 can be supported (NMR) by
the shift of H3∞,5∞ at d 8.46 to 7.92 denoting the formation of
the 4∞-ethereal bond. By taking advantage of the peptide
coupling method11 (Scheme 2) using dicyclohexylcarbodiimide
Hydrolytic or thermal deprotection, followed by subsequent
formation of a larger ‘dendritic’ surface can be accomplished
at either the appendage stage (8 or 12) or the four-directional
dendrimer (14). The former oÂers solubility advantages as well
as the ability to conveniently attach these metallo-modules to
other macromolecular materials; applications of these metallo-
macromolecules are in progress and will be reported elsewhere.
(
DCC) and 1-hydroxybenzotriazole (1-HOBT) in DMF, acid
6
was reacted with ‘Behera’s amine’ 710 to aÂord terpyridine
amide 8 in 72% yield. The new peak (1H NMR) at d 6.03
denotes the formation of the amide bond. In 13C NMR, the
formation of the ethereal bond can be concluded based on the
significant shifts of C5,5◊ and C4∞; the successful amidation is
supported by the shift of the signal assigned to newly intro-
duced quaternary carbon moiety (CONHC) from d 52.8 to
5
7.6. The yellow–brown microcrystalline, paramagnetic
Conclusion
ruthenium() complex 9 was prepared by refluxing 1 equival-
The construction of this new type of double tiered metallodend-
rimer shows the importance of the stepwise construction by
means of controlled metal complexation. This modular
approach also provides a much more versatile methodology
for the synthesis of specifically assembled metallodendrimers
and related polymers by using a combination of divergent and
convergent approaches.
ent of 8 with RuCl Ω3H O in methanol to give 76% yield,
3
2
which was used without further purification.
Preferential O- vs. N-arylation was realized when 5-amino-
pentan-1-ol was reacted with 4∞-Cl-tpy in the presence of
powered KOH in dry Me SO to aÂord the free 5-aminopentyl
2
4
∞-(2,2∞56∞,2◊-terpyridinyl) ether 10 in 71% conversion,
Scheme 3. The structure of 10 was readily confirmed by the
lack of change for the signals of H NMCH in both 1H and
2
2
1
3C NMR spectra. The significant chemical shifts (1H NMR)
This work was supported, in part, by the National Science
Foundation (DMR-96–22609) and the Army Research OÃce
(DAAH04–93-G-0448).
for H3∞,5∞ and C5,5◊, as well as for C4∞ (13C NMR) confirmed
the free amino group and the preferential formation of the 4∞-
ethereal bond. The aminoterpyridine 10 was then reacted with
1
equivalent of the ruthenium() complex 9 in boiling meth-
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6
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994, 106, 2507; (e) J. M. J. Fr e´ chet, C. J. Hawker and K. L. Wooley,
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3
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1
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4
6
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4
5
1
H NMR spectrum of 14 demonstrated the absence of para-
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