Functionalised 2,2′-bipyridine ligands for the preparation of metallostars; X-ray structures of free ligands and preparation of copper(I) and silver(I) complexes

Article abstract of DOI:10.1016/S0277-5387(02)01310-4

2,2-Bipyridine ligands bearing functionalised aryl substituents have been prepared with the aim of subsequent functionalisation and the preparation of multinuclear metallostars. The key intermediates are compounds containing 4-methoxyphenyl substituents w

Full text of DOI:10.1016/S0277-5387(02)01310-4

Polyhedron 22 (2003) 93ꢁ108
/
www.elsevier.com/locate/poly
Functionalised 2,2?-bipyridine ligands for the preparation of
metallostars; X-ray structures of free ligands and preparation of
copper(I) and silver(I) complexes
Edwin C. Constable ꢀ, Catherine E. Housecroft ꢀ, Markus Neuburger, Ingo Poleschak,
Margareta Zehnder
Department of Chemistry, University of Basel, Spitalstrasse 51, CH 4056 Basel, Switzerland
Received 11 July 2002; accepted 14 August 2002
Abstract
2,2-Bipyridine ligands bearing functionalised aryl substituents have been prepared with the aim of subsequent functionalisation
and the preparation of multinuclear metallostars. The key intermediates are compounds containing 4-methoxyphenyl substituents
which may be converted to 4-hydroxyphenyl substituted ligands. Copper(I) and silver(I) complexes of 4,4?-di(methoxyphenyl)-6,6?-
dimethyl-2,2?-bipyridine have been prepared and structurally characterised as have the ligands 4,4?-di(methoxyphenyl)-6,6?-
dimethyl-2,2?-bipyridine and 4,4?-di(methoxyphenyl)-2,2?-bipyridine.
# 2002 Published by Elsevier Science Ltd.
Keywords: Copper; Silver; Ruthenium; 2,2?-Bipyridine; Metallostar; X-ray
1. Introduction
which, particularly in the case of ruthenium(II) com-
plexes, have near optimal photophysical properties (long
excited state lifetimes, absorption maxima near the
energy maximum of the solar energy spectrum, suitable
redox properties) [11]. However, the {M(bpy)3} motif is
chiral and can exist as D or L configurations [12,13]. In
general, synthetic procedures for the preparation of
metallodendrimers are regiospecific but not diastereos-
pecific and compounds with multiple {M(bpy)3} motifs
will be formed as ill-defined mixtures of diastereoi-
somers [13]. As the precise spatial control of the
photoactive subunits is of prime importance in the
design of photoconversion devices, we and others
adopted the achiral {M(tpy)2} motif in preference
[14,15] and have recently addressed the poor photo-
physical properties of {Ru(tpy)2} domains through
Many contemporary approaches to the construction
of photoconversion devices are based upon multinuclear
complexes which act either as photocollecting arrays or
as multifunctional devices, which both collect light
energy and transform it into stored chemical energy
[1ꢁ4]. Increasing knowledge of the molecular detail of
/
the biological photoconversion systems has served to
emphasise that a key feature in the successful design of
artificial photoconversion devices will be the precise
control of the spatial arrangement of the individual
functional elements [5]. These constraints on the spatial
arrangement of components in photoactive assemblies
have led us and others to develop strategies for the
synthesis of metallodendrimers incorporating, in parti-
cular, ruthenium(II), osmium(II), rhodium(III) and
ligand design [16ꢁ18]. Constraints upon the growth of
/
dendrimers as they approach the de Gennes generation
limit [19], have led us to propose the use of metallostars
rather than metallodendrimers. In a metallostar, the
primary branching occurs in the core zeroth generation
and subsequent growth is linear [20]. By definition, first
generation metallostars and metallodendrimers are sy-
nonymous. In this paper, we further develop the
iridium(III) centres [6ꢁ
drimers are based upon multiple {M(bpy)3} motifs
/
10]. Many of these metalloden-
ꢀ Corresponding authors. Tel.: ꢂ
1015
/
41-61-267-1001; fax: ꢂ41-61-267-
/
E-mail address: edwin.constable@unibas.ch (E.C. Constable).
0277-5387/02/$ - see front matter # 2002 Published by Elsevier Science Ltd.
PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 3 1 0 - 4

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E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ108
/
synthesis of heptanuclear first generation metallostars in
which the core motif is a single {M(bpy)3} domain and
in which the pendant metal centres are found in
{M(tpy)2} substructures. A characteristic feature of the
design of these new metallostars is the replacement of
some of the ether linkages present in our prototype
measurements were performed using a Perkin Elmer
Lambda 19 spectrophotometer and were recorded in
acetonitrile at a concentration of 5ꢃ
10ꢄ5 M. FAB and
/
EI mass spectra were recorded on a Kratos MS50
instrument. Time of flight (MALDI) spectra were
recorded using a PerSeptive Biosystems Voyager-RP
Biospectrometry Workstation. Electrochemical mea-
systems by stable, conjugated Cꢀ
/
C bonds [21ꢁ26].
/
2. Experimental
surements were performed with an Amel model 553
potentiostat connected to an Amel model 567 function
generator and an Amel model 560/A interface or an Eco
Chemie Autolab PGSTAT 20 system using platinum
bead working and auxiliary electrodes with an Ag/AgCl
electrode as reference. The experiments were conducted
using purified acetonitrile as solvent and 0.1 M
[Bun4N][BF4] as supporting electrolyte; ferrocene was
2.1. General procedures
Infrared spectra were recorded on a Mattson Genesis
Fourier-transform spectrophotometer with samples in
1
compressed KBr discs. H NMR spectra were recorded
on Bruker AM 250 or 400 MHz spectrometers. UVꢁVis
/

E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ
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95
added at the end of each experiment as an internal
reference. The compounds 1-pyridiniopropanone bro-
mide [27], [Pd(PPh3)4] [28], [Ru(tpy)(Cltpy)][PF6]2 [29]
and [Cu(MeCN)4][PF6] [30] were prepared by the
literature methods; all other compounds were used as
supplied commercially.
needles of 4,4?-di(4-chlorophenyl)-6,6?-dimethyl-2,2?-bi-
pyridine (2) (0.200 g, 50%), m.p. 230-234 8C (Anal.
Found: C, 70.6; H, 4.8; N 6.8. C24H18N2Cl2 requires C,
71.1; H, 4.5; N, 6.9%); dH (CDCl3) 8.47 (2H, d, J3A,5A
1.4 Hz, H3A), 7.71 (4H, d, J2B,3B 8.8 Hz, H2B), 7.48 (4H,
d, J2B,3B 8.8 Hz, H3B), 7.37 (2H, d, J3A,5A 1.4 Hz, H5A),
2.78 (6H, s, CH3); dC (CDCl3) 159.0, 156.9, 148.7,
2.2. Synthesis of 4,4?-di(4-methoxyphenyl)-6,6?-
dimethyl-2,2?-bipyridine (1)
137.7, 135.4, 129.6, 128.9, 121.3, 116.8, 25.2; n¯max (cmꢄ1
1600s, 1547s, 1492 s, 1382m, 1093s, 1013m, 829s, 757m,
)
478m (KBr); m/z 404/406/408 (Mꢂ), 369/371 (Mꢀ
/
Cl),
202 (M2ꢂ) (EI); lmax, nm, (CHCl3) 254 (o, Mꢄ1 cmꢄ1
,
51 900), 303 (17 000).
A mixture of 4-methoxybenzaldehyde (13.6 g, 100
mmol), butane-2,3-dione (4.3 g, 50 mmol), EtOH (50
cm3) and piperidine (0.5 cm3) were heated to reflux for 2
h and then the solution allowed to cool. After 24 h in the
2.4. Synthesis of 4,4?-di(4-hydroxyphenyl)-6,6?-dimethyl
-2,2?-bipyridine (3)
refrigerator, orangeꢁyellow crystals of 1,6-di(4-methox-
/
yphenyl)hexa-1,5-diene-3,4-dione were collected by fil-
tration and washed with a little cold MeOH. This dione
(0.322 g, 1.0 mmol), 1-pyridiniopropanone bromide
(0.432 g, 2.0 mmol) and NH4OAc (2 g) in EtOH (10
cm3) were heated to reflux for 4 h. On cooling, 4,4?-di(4-
methoxyphenyl)-6,6?-dimethyl-2,2?-bipyridine (1) crys-
tallised and was collected by filtration. The product
was washed with MeOH, dried under reduced pressure
and recrystallised from EtOH/pentane to give colourless
needles of 4,4?-di(4-methoxyphenyl)-6,6?-dimethyl-2,2?-
Concentrated hydrochloric acid (5.5 cm3) was added
with vigorous stirring to pyridine (6.0 cm3) cooled to
0 8C. After the addition was complete, the mixture was
heated and water distilled off until the internal tempera-
ture reached 200 8C (ꢀ
3 cm3 volume). The resultant
/
pyridinium chloride was cooled to 140 8C and 1 (0.200
g, 0.50 mmol) was added in one portion. An immediate
colour change to green occurred and heating to reflux
was resumed for 4 h. The mixture was then allowed to
cool to 100 8C, when water (100 cm3) was added and
the mixture stirred for 12 h at room temperature. The
green precipitate that resulted was collected by filtra-
tion, washed well with water and chloroform and dried
under vacuum to give 3 as a green powder (0.180 g, 97%)
bipyridine (1) (0.130 g, 35%), m.p. 250ꢁ
Found: C, 76.6; H, 6.1; N 6.75. C26H24N2O2×
/
252 8C (Anal.
2/3H2O
/
requires C, 76.5; H, 6.25; N, 6.86%); dH (CDCl3) 8.82
(2H, d, J3A,5A 1.4 Hz, H3A), 7.78 (4H, d, J2B,3B 8.8 Hz,
H2B), 7.42 (2H, d, J3A,5A 1.4 Hz, H5A), 7.03 (4H, d,
J2B,3B 8.8 Hz, H3B), 3.88 (6H, s, OCH3), 2.75 (6H, s,
CH3); dC (CDCl3) 160.6, 158.1, 155.4, 149.6, 130.6,
m.p. ꢁ270 8C (Anal. Found: C, 77.9; H, 5.8; N, 7.3.
/
C24H20N2O2 requires C, 78.2; H, 5.5; N, 7.6%); dH
(CD3SOCD3) 8.67 (2H, d, J3A,5A 1.4 Hz, H3A), 8.03 (2H,
d, J3A,5A 1.4 Hz, H5A), 7.78 (4H, d, J2B,3B 8.8 Hz, H2B),
6.98 (4H, d, J2B,3B 8.8 Hz, H3B), 2.78 (6H, s, CH3); dC
(CD3SOCD3) 161.7, 152.5, 148.0, 146.3, 129.5, 127.1,
122.9, 120.0, 114.8, 55.5; n¯max (cmꢄ1) 3145br, 1630m,
1587s, 1519s, 1477m, 1406m, 1278s, 1210s, 1184s,
1111w, 994w, 825s, 570m (KBr); m/z 369/371 (MHꢂ)
128.5, 120. 9, 116.8, 114.4, 55.4, 24.4; n¯max (cmꢄ1
)
2961w, 2919w, 2838w, 1609s, 1534s, 1548m, 1513s,
1460m, 1438m, 1383m, 1365w, 1291m, 1241s, 1208w,
1175s, 1112w, 1073w, 1029s, 832s, 795w, 576m, 526w,
510w (KBr); m/z 396 (Mꢂ) (EI); lmax, nm, (CHCl3) 243
(o, Mꢄ1 cmꢄ1, 17 700 ), 269 (34 300), 291 (32 800).
2.3. Synthesis of 4,4?-di(4-chlorophenyl)-6,6?-dimethyl-
2,2?-bipyridine (2)
(EI); lmax, nm, (CD3SOCD3) 272 (o, Mꢄ1 cmꢄ1
,
26 500), 291 (26 700).
A mixture of 4-chlorobenzaldehyde (14.0 g, 100
mmol), butane-2,3-dione (4.3 g, 50 mmol), EtOH (50
cm3) and piperidine (0.5 cm3) were heated to reflux for 2
h and then the solution was allowed to cool. After 24 h
2.5. Synthesis of 4-methoxyphenylboronic acid
Magnesium turnings (1.20 g, 50 mmol) and a few
grains of iodine were heated under argon with a heat
gun until violet fumes were evolved. Diethyl ether (5
cm3) was then added to the cooled flask and 9.6 cm3 of a
solution of freshly distilled 4-bromoanisole (9.40 g, 50
mmol) in diethyl ether (10 cm3) was added. The reaction
was initiated by warming gently, after which the
remaining 4-bromoanisole solution was added dropwise
at such a rate that gentle reflux was maintained. Finally,
the mixture was warmed to 40 8C for 30 min after
which the solution was transferred dropwise into a
solution of (iPrO)3B (7.70 g, 55 mmol, 8.3 cm3) in THF
in the refrigerator, orangeꢁyellow crystals of 1,6-di(4-
/
chlorophenyl)hexa-1,5-diene-3,4-dione were collected by
filtration and washed with a little cold MeOH. This
dione (0.330 g, 1.0 mmol), 1-pyridiniopropanone bro-
mide (0.432 g, 2.0 mmol) and NH4OAc (2 g) in EtOH
(10 cm3) were heated to reflux for 4 h. On cooling, 4,4?-
di(4-chlorophenyl)-6,6?-dimethyl-2,2?-bipyridine
(2)
crystallised and was collected by filtration. The product
was washed with MeOH, dried under reduced pressure
and recrystallised from CHCl3/ether to give colourless

96
E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ108
/
(30 cm3) at ꢄ
/
78 8C. After stirring for 30 min a white
over MgSO4 and the solvent removed in vacuo. The
residue was recrystallised from EtOH/CHCl3 to give a
first crop of 4 as colourless needles (0.34 g). The mother
liquor was chromatographed (SiO2, hexanes:CHCl3:-
MeOH saturated with ammonia, 10:5:1 Rf 0.51) to give
precipitate formed. The mixture was then stirred over-
night and allowed to warm to room temperature after
which hydrochloric acid (4 M, 20 cm3) was added and
the clear solution stirred for 1 h. The phases were
separated and the organic phase extracted twice with 4:1
NH4Cl (saturated aqueous solution): 4 M NaOH. The
combined aqueous phases were acidified with hydro-
chloric acid (4 M) and extracted three times with
EtOAc. The combined organic phases were then dried
over MgSO4 and the solvent was evaporated. The crude
4-methoxyphenylboronic acid was obtained as a light
brown solid and was used without further purification
another 0.21 g of 5 (0.550 g, 75%) m.p. 206ꢁ
/
208 8C
(Anal. Found: C, 77.25; H, 5.7; N, 7.5. C24H40N2O2×
/1/
4H2O requires C, 77.3; H, 5.5; N, 7.5%); dH (CDCl3)
8.71 (d, J 5.2 Hz, 2H, H6A), 8.69 (d, J 1.8 Hz, 2H, H3A),
7.76 (d, J 8.9 Hz, 4H, H2B), 7.53 (dd, J 5.2, 1.8 Hz, 2H,
H5A), 7.03 (d, J 8.9 Hz, 4H, H3B), 3.89 (s, 6H, CH3); dC
(CDCl3) 160.6, 156.7, 149.6, 148.8, 130.6, 128.4, 121.1,
118.5, 114.5, 55.4; m/z 369.4 (Mꢂ) (ESMS); lmax, nm,
(CHCl3) 237 (o, Mꢄ1 cmꢄ1, 33 000), 264 (62 900), 284
(59 700); lemission, nm, (lirrad 284 nm, CHCl3, 298 K)
365, 692; n¯max (cmꢄ1) 1608m, 1592s, 1542m, 1515s,
1458s, 1446m, 1301m, 1285m, 1253s, 1186s, 1040m,
1019m, 826m, 574m (KBr).
(1.50 g, 20%) m.p. 106ꢁ108 8C (dec.); dH (CD3OD)
/
8.17 (d, J 8.4 Hz, 2H, H2A), 7.02 (d, J 8.4, 2H, H3A),
3.88 (s, 3H, Me).
2.6. Synthesis of 4,4?-di(4-methoxyphenyl)-2,2?-
bipyridine (4)
2.6.1. By Stille coupling
4-Bromoanisole (1.60 g, 8.5 mmol, 2.4 cm3) was
dissolved in THF (100 cm3) and the solution cooled to
2.7. Synthesis of 4,4?-di(4-hydroxyphenyl)-2,2?-
bipyridine (5)
ꢄ
90 8C after which n-BuLi (5.5 cm3, 8.8 mmol, 1.6 M
in hexanes) was added dropwise and the mixture stirred
at this temperature for 30 min. The solution was then
/
2.7.1. Method 1
Concentrated hydrochloric acid (5.5 cm3) was added
cautiously to vigorously stirred pyridine (6.0 cm3) after
which the mixture was heated until the internal tem-
perature had reached 200 8C. The resultant pyridinium
chloride was then cooled to 140 8C, 4 (0.180 g, 0.49
mmol) added and the temperature raised to 200 8C for
4 h, after which the reaction mixture was cooled to
100 8C and treated with H2O (100 cm3). After stirring
overnight, the green solid precipitate was filtered off,
washed well with water and dried in vacuo to give 5.
HCl (0.161 g, 97%) (Found: C, 67.1; H, 4.9; N, 7.5.
allowed to warm to ꢄ
nane (2.80 g, 8.5 mmol) in THF (20 cm3) was added.
The solution was then raised in temperature to ꢄ50 8C
/
70 8C and tri-n-butylchlorostan-
/
and stirred for 1 h after which it was allowed to warm to
room temperature overnight. The solvent was then
evaporated in vacuo and DMF (75 cm3) added to the
yellow oil containing 4-tri-n-butylstannylanisole; finally,
4,4?-dibromo-2,2?-bipyridine (1.30 g, 4.0 mmol) and
[Pd(PPh3)4] (0.30 g, 3 mol%) were added and the mixture
stirred at 120 8C for 2 d. The solvent was then removed
under high vacuum, the residue treated with
H2O:MeOH (1:1, 30 cm3) and the off-white precipitate
collected by filtration, washed with a small amount of
cold MeOH and recrystallised from EtOH/CHCl3 to
C22H17N2O2Cl×/H2O requires C, 66.9; H, 4.85; N, 7.1%).
2.7.2. Method 2
give white needles of 4 (0.270 g, 18%) m.p. 205ꢁ
/
207 8C.
A solution of 4 (0.400 g, 1.1 mmol) in CHCl3 (30 cm3)
was cooled to 0 8C and treated with BBr3 (1.2 cm3, 1.0
M solution in CH2Cl2). The reaction mixture was then
stirred overnight and allowed to warm to room tem-
perature, after which H2O (10 cm3) was added and the
precipitate filtered off, washed well with CHCl3, H2O,
MeOH and dried in vacuo to give 5 (0.356 g, 96%) m.p.
2.6.2. By Suzuki coupling
4,4?-Dibromo-2,2?-bipyridine (0.60 g, 2.0 mmol) was
dissolved in toluene (40 cm3) and aqueous Na2CO3
solution (2 M, 25 cm3) added. The biphasic mixture was
purged with Ar and [Pd(PPh3)4] (0.11 g, 5.0 mol%) was
added under argon. Finally an Ar-purged solution of 4-
methoxyphenylboronic acid (0.76 g, 5.0 mmol) in EtOH
(20 cm3) was added slowly and the mixture refluxed at
110 8C for 2 d. The resulting dark solution was diluted
with water (30 cm3) and toluene (30 cm3); EtOH was
removed in vacuo and the phases were separated. The
aqueous phase was extracted twice with CHCl3 (30 cm3).
The combined organic phases were washed with satu-
rated aqueous sodium chloride solution twice, dried
ꢁ
270 8C. m/z 341 (Mꢂ) (ESMS); n¯max (cmꢄ1) 3144br,
/
3063w, 1631m, 1606s, 1586s, 1518m, 1476m, 1454w,
1404w, 1332w, 1276s, 1209s, 1185s, 823s, 662m, 502w
(KBr); dH (CD3SOCD3) 10.40 (br s, 2H, OH), 8.97 (s,
2H, H3A), 8.78 (d, J 6.0 Hz, 2H, H6A), 8.08 (d, J 6.0 Hz,
2H, H5A), 8.00 (d, J 8.4 Hz, 4H, H2B), 7.01 (d, J 8.4 Hz,
4H, H3B); dC (CD3SOCD3) 160.5, 152.3, 148.8, 146.6,
129.4, 125.6, 122.2, 119.3, 116.3; lmax, nm, (CH3SOCH3)
254 (o, Mꢄ1 cmꢄ1, 21 900), 272 (29 400), 294 (32 100).

E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ
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97
2.8. Synthesis of the bisruthenated ligand 6 [PF6]4
7.14 (d, J 8.9, 8H, H3B), 3.90 (s, 12H, OCH3), 2.12 (s,
PF6), 397 (I) (ESMS); lmax
nm, (MeCN) 210 (o, Mꢄ1 cmꢄ1, 61 800), 280 (90 700),
482 (9600); lemission, nm, (lirrad 482 nm, MeCN, 298 K)
619; n¯max (cmꢄ1) 1603 s, 1580w, 1544m, 1519s, 1460w,
1439w, 1394w, 1254s, 1293m, 1182s, 1030m, 844w, 829s,
584w, 557m (KBr).
12H, CH3); m/z 855 (Mꢁ
/
,
The complex [Ru(tpy)(Cltpy)][PF6]2 (0.065 g, 0.073
mmol) was dissolved in MeCN (40 cm3) and K2CO3
(0.400 g) and several crystals of NaI were added. The
suspension was heated to 60 8C and a solution of 3
(0.013 g, 0.035 mmol) in CD3SOCD3 (4 cm3) was added
dropwise. After the addition was complete, the suspen-
sion was stirred at 80 8C for 24 h and the progress of
the reaction monitored by TLC. The reaction mixture
was then cooled and poured into water (100 cm3) and
[NH4][PF6] added until there was no further precipita-
tion. The crude red product was collected over Celite,
washed well with water and dissolved in aqueous MeCN
(MeCN:H2O; 9:1). After evaporation of the solvent, the
complex was purified by chromatography (SiO2,
2.10. Synthesis of [Ag(1)2][PF6]
A solution of Ag[BF4] (0.010 g, 0.05 mmol) in EtOH
(10 cm3) was added dropwise to a solution of I (0.040 g,
0.10 mmol) in EtOH (40 cm3) and the mixture stirred for
2 h at room temperature after which H2O (50 cm3) and
ammonium hexafluorophosphate were added and the
organic solvent removed in vacuo. The precipitate was
collected over Celite, washed with water and redissolved
in acetone and purified by recrystallisation from ace-
tone/ether to give orange yellow cubes of [Ag(1)2][PF6]
(0.0393 g, 75%) (Anal. Found: C, 59.2; H, 4.8; N 5.3.
C52H48N4O4AgPF6 1/2H2O requires C, 59.2; H, 4.7; N,
5.3%); dH (CD3CN) 8.42 (s, 4H, H3A), 7.84 (d, J 8.9,
8H, H2B), 7.69 (s, 4H, H5A), 7.07 (d, J 8.9, 8H, H3B),
MeCNꢁ
/
saturated aqueous KNO3ꢁ/H2O 20:0.5:1). The
product was collected as a band with Rfꢅ
/0.23 and
treated with water (20 cm3) and a small amount of
[NH4][PF6]. The MeCN was removed in vacuo and the
red solid product was collected over Celite. After
washing with water the complex was redissolved in
aqueous MeCN (MeCN:H2O; 9:1), filtered and the
solvent removed in vacuo to give a red solid that was
dried under high vacuum (0.029 g, 40%) (Anal. Found:
3.85 (s, 12H, OCH3), 2.55 (s, 12H, CH3); m/z 901 (Mꢁ
/
PF6); lmax, nm, (MeCN) 268 (o, Mꢄ1 cmꢄ1, 85 100),
283 (83 100); lemission, nm, (lirrad 283 nm, MeCN, 298 K)
381; n¯max (cmꢄ1) 2956w, 2934w, 2911w, 2838w, 1600s,
1548s, 1515s, 1461s, 1439w, 1395w, 1292s, 1252s,
1220m, 1181s, 1031s, 840s, 578m, 558m (KBr).
C 47.36, H 3.2, N 9.4. C84H60N14O2Ru2P4F24×
requires C, 47.7; H, 3.1; N, 9.3%); m/z 894.3 (Mꢁ
2PF6)2ꢂ 3PF6)3ꢂ 4PF6)4ꢂ
548.4 (Mꢁ 372.7 (Mꢁ
/2H2O
/
,
/
,
/
(ESMS); dH (CD3CN) 8.75 (d, J 8.1 Hz, 4H, H3F),
8.64 (d, J 1.2 Hz, 2H, H5A), 8.50 (d, J 8.0 Hz, 4H, H3E),
8.42 (s, 4H, H3C), 8.40 (d, J 8.2 Hz, 4H, H3D), 8.38 (t, J
8.1 Hz, 2H, H4F), 8.13 (d, J 8.8 Hz, 4H, H2B), 7.92 (ddd,
J 15.7, 7.8, 1.5 Hz, 4H, H4E), 7.86 (ddd, J 15.7, 7.8, 1.5
Hz, 4H, H4D), 7.74 (d, J 1.2 Hz, 2H, H3A), 7.65 (d, J 8.8
Hz, 4H, H3B), 7.47 (d, J 4.9 Hz, 4H, H6E), 7.32 (d, J 4.9
Hz, 4H, H6D), 7.21 (ddd, J13.2, 5.6, 1.3 Hz, 4H, H5E),
7.13 (ddd, J 13.2, 5.6, 1.3 Hz, 4H, H5D), 2.83 (s, 6H,
CH3); lmax, nm, (MeCN) 272 (o, Mꢄ1 cmꢄ1, 69 900),
305 (85 300), 480 (20 000); n¯max; cmꢄ1, 1600m, 1508w,
1465w, 1449w, 1434w, 1405m, 1384s, 1286w, 1227m,
1189w, 841s, 788w, 767w, 588m (KBr).
2.11. Synthesis of [Ru(bpy)2(L)][PF6]2 (Lꢅ
/
1,2 or 3)
2.11.1. Method 1, thermal
A suspension of [Ru(bpy)2Cl2] (0.048 g, 0.10 mmol)
and the appropriate ligand (0.10 mmol) in 1,2-ethane-
diol (40 cm3) was treated with N-ethylmorpholine (1
drop) and the mixture stirred at 110 8C for 24 h, after
which the red solution was treated with water (120 cm3).
The solution was then filtered to remove any particulate
matter and then treated with ammonium hexafluoro-
phosphate to give a red precipitate. This precipitate was
collected over Celite, washed well with water and then
dissolved in acetonitrile and purified by chromatogra-
2.9. Synthesis of [Cu(1)2][PF6]
phy over silica gel using MeCNꢁ/saturated aqueous
A solution of [Cu(MeCN)4][PF6] (0.019 g, 0.05 mmol)
in EtOH (10 cm3) was added dropwise to a solution of 1
(0.040 g, 0.10 mmol) in EtOH (40 cm3) and the mixture
stirred for 2 h at room temperature after which H2O (50
cm3) was added and the organic solvent removed in
vacuo. The precipitate was collected over Celite, washed
with water and redissolved in MeCN and purified by
recrystallisation from acetone/ether to give dark red
crystals of [Cu(1)2][PF6] (0.0342 g, 66%) (Anal. Found:
KNO3 solutionꢁwater 20:0.5:1 as the mobile phase. In
/
each case, the major red fraction was collected and the
product precipitated with ammonium hexafluoropho-
sphate. Recrystallisation from acetonitrile or acetoni-
trile-diethyl ether yielded the desired compounds as
analytically pure red solids.
2.11.2. Method 2, microwave
A suspension of [Ru(bpy)2Cl2] (0.048 g, 0.10 mmol)
and the appropriate ligand heated to reflux for 6 min in
a modified domestic microwave oven. After this period,
the reaction mixture was worked up as described above.
C, 61.85; H, 3.2; N 9.4. C52H48N4O4CuPF6×
/1/2H2O
requires C, 61.8; H, 4.9; N, 5.5%); dH (CD3CN) 8.64 (s,
4H, H3A), 7.95 (d, J 8.9, 8H, H2B), 7.78 (s, 4H, H5A),

98
E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ108
/
2.11.3. [Ru(bpy)2(1)][PF6]2
Yield: thermal, 0.020 g, 17%; microwave, 0.068 g 60%.
(ddd, J 8.0, 5.6, 1.4 Hz, 2H, H5LB), 1.71 (s, 6H, CH3);
lmax, nm, (MeCN) 252 (o, Mꢄ1 cmꢄ1, 85,300), 283
(97,100) 427 (12,300); n¯max (cmꢄ1) 1606w, 1468w,
(Anal. Found:
C46H40N6O2RuP2F12×
N, 7.4%); m/z 956 (Mꢁ
C
48.75,
2H2O requires C, 48.7; H, 3.9;
PF6)ꢂ (MALDI TOF); dH
H
4.1,
N
7.3.
/
1449m, 1428w, 840s, 763m, 731w, 558m (KBr); E1/2
1.05 (V versus ferrocene/ferrocenium, MeCN, cyclic
voltammetry), ꢄ2.08, ꢄ2.27, ꢄ2.69).
ꢂ
/
/
(CD3CN) 8.64 (d, J 1.2 Hz, 2H, H3A), 8.51 (dd, J 8.0,
1.4 Hz, 2H, H3LA), 8.43 (dd, J 8.0, 1.4 Hz, 2H, H3LB),
8.10 (dt, J 8.0, 1.4 Hz, 2H, H4LA), 8.05 (dd, J 5.6, 1.3
Hz, 2H, H6LA), 7.95 (dt, J 8.0, 1.4 Hz, 2H, H4LB), 7.93
(d, J 8.8 Hz, 4H, H2B), 7.65 (dd, J 5.6, 1.3 Hz, 2H,
H6LB), 7.58 (d, J 1.2 Hz, 2H, H5B), 7.49 (ddd, J 8.0, 5.6,
1.4 Hz, 2H, H5LA), 7.23 (ddd, J 8.0, 5.6, 1.4 Hz, 2H,
H5LB), 7.13 (d, J 8.8 Hz, 4H, H3B), 3.87 (s, 6H, OCH3),
/
/
/
2.11.5. [Ru(bpy)2(3)][PF6]2
Yield: thermal, 0.015 g, 14%; microwave, 0.047 g 44%.
(Anal. Found: 45.9, 4.0, 8.6.
C44H36N6O2RuP2F12×KNO3 requires C, 45.1; H, 3.1;
N, 8.3%); m/z 967 (Mꢁ
PF6)ꢂ (MALDI TOF); dH
C
H
N
/
/
(CD3CN) 8.59 (d, J 1.2 Hz, 2H, H3A), 8.51 (dd, J 8.0,
1.4 Hz, 2H, H3LA), 8.43 (dd, J 8.0, 1.4 Hz, 2H, H3LB),
8.08 (dt, J 8.0, 1.4 Hz, 2H, H4LA), 8.03 (dd, J 5.6, 1.3
Hz, 2H, H6LA), 7.94 (dt, J 8.0, 1.4 Hz, 2H, H4LB), 7.81
(d, J 8.8 Hz, 4H, H2B), 7.63 (d, J 8.8 Hz, 4H, H3B), 7.54
(d, J 1.2 Hz, 2H, H5B), 7.46 (ddd, J 8.0, 5.6, 1.4 Hz, 2H,
H5LA), 7.21 (ddd, J 8.0, 5.6, 1.4 Hz, 2H, H5LB), 6.98 (dd,
J 5.6, 1.3 Hz, 2H, H6LB), 1.67 (s, 6H, CH3); lmax, nm,
(MeCN) 256 (o, Mꢄ1 cmꢄ1, 29,600), 289 (56,400) 428
(8,000); n¯max (cmꢄ1) 3433 s br, 1608s, 1543w, 1520m,
1464w, 1446m, 1385m, 1277w, 1221w, 1180w, 842s,
1.71 (s, 6H, CH3); lmax, nm, (MeCN) 242 (o,
Mꢄ1 cmꢄ1, 29,300), 252 (25,600), 282 (85,000) 424
(13,900); n¯max (cmꢄ1) 1605m, 1517w, 1466w, 1447w,
1253w, 1227m, 1183w, 842s, 764m, 558m (KBr); E1/2
1.06 (V versus ferrocene/ferrocenium, MeCN, cyclic
voltammetry), ꢄ1.75, ꢄ1.96, ꢄ2.17).
ꢂ
/
/
/
/
2.11.4. [Ru(bpy)2(2)][PF6]2
Yield: thermal, 0.020 g, 18%; microwave, 0.060 g 52%.
(Anal. Found: 44.2, 3.4, 8.35.
C44H34N6Cl2RuP2F12×KNO3 requires C, 43.7; H, 2.8;
N, 8.10%); m/z 967 (Mꢁ
PF6)ꢂ (MALDI TOF); dH
C
H
N
764m, 733w, 558m (KBr); E1/2
cene/ferrocenium, MeCN, cyclic voltammetry), ꢄ
2.01, ꢄ2.26).
ꢂ
/
0.96 (V versus ferro-
/
/1.92,
/
(CD3CN) 8.66 (d, J 1.2 Hz, 2H, H3A), 8.52 (dd, J 8.0,
1.4 Hz, 2H, H3LA), 8.43 (dd, J 8.0, 1.4 Hz, 2H, H3LB),
8.11 (dt, J 8.0, 1.4 Hz, 2H, H4LA), 8.03 (dd, J 5.6, 1.3
Hz, 2H, H6LA), 7.97 (dt, J 8.0, 1.4 Hz, 2H, H4LB), 7.92
(d, J 8.8 Hz, 4H, H2B), 7.65 (dd, J 5.6, 1.3 Hz, 2H,
H6LB), 7.64 (d, J 1.2 Hz, 2H, H5B), 7.63 (d, J 8.8 Hz,
4H, H3B), 7.49 (ddd, J 8.0, 5.6, 1.4 Hz, 2H, H5LA), 7.25
ꢄ
/
/
2.12. Crystal structure determinations
The structures were solved and refined by direct
methods using standard techniques as indicated in Table
1 using the programmes CRYSTALS [31], SHELXS-86 [32],
Table 1
Crystal data for 1, 4, [Ag(1)2][PF6], [Ag(1)(MeCN)][BF4]×MeCN and [Ru(bpy)2(2)][PF6]2×3MeCN×0.5H2O
Compound
1
4
[Ag(1)2][PF6]
[Ag(1)(MeCN)][BF4]×MeCN [Ru(bpy)2(2)][PF6]2×3MeCN×0.5H2O
Formula
M (g molꢄ1
C26H24N2O2 C24H10N2O2 C52H48AgN4O4PF6 C60H60Ag2B2F8N8O4
C50H44RuN9Cl2P2F12O0.5
1240.88
monoclinic
P21/c
)
396.49
triclinic
¯
P1/
368.44
1045.81
monoclinic monoclinic
1346.52
monoclinic
P21/n
Crystal system
Space group
/
P21/c
0.64
P21/c
0.51
m (mmꢄ1
Final R (observed)
)
0.60
0.748
0.52
0.0944
0.0831
0.0491
0.0659
9.542(1)
10.401(1)
11.772(1)
98.451(8)
103.156(8)
109.633(8)
1039.3(2)
293
0.0494
0.0658
10.896(2)
5.382(1)
15.927(2)
90
0.0485
0.0446
17.118(4)
14.778(3)
19.621(6)
90
0.0429
0.1129
13.934(4)
7.9270(10)
27.179(8)
90
Final Rw (observed)
˚
a (A)
˚
20.9764(8)
12.3992(6)
21.939(1)
90
b (A)
˚
c (A)
a (8)
b (8)
g (8)
V (A
T (K)
19.18(1)
90
98.37(4)
90
102.60(3)
90
105.138(3)
90
3)
˚
922.1(3)
293
4911.0(9)
293
2929.8(13)
190(1)
2
5508.22
193(1)
Z
2
420
2
388
4
2144
4
2508
F(0 0 0)
No. reflections
No. independent reflections 3918
1368
14776
4176
1834
1661
9355
8938
209927
19579
11783
6178
5231
No. observed reflections
3506
I ꢁ3s(I)
1453
I ꢁ3s(I)
5431
I ꢁ3s(I)
I ꢁ2s(I)
I ꢁ2s(I)

E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ
/108
99
Fig. 1. Pentanuclear and heptanuclear metallostars based upon {M(bpy)2} and {M(bpy)3} core motifs.

100
E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ108
/
SHELXS-93 [33] and SHELXS-97 [34]. Diagrams and
supplementary material were prepared using the above
programmes together with ORTEP-3 for Windows [35],
PLATON [36], and CAMERON [37].
octahedral coordination geometry. The compounds
1,6-bis(4-methoxyphenyl)-hexa-1,5-diene-3,4-dione and
1,6-bis(4-chlorophenyl)-hexa-1,5-diene-3,4-dione were
prepared as orange solids from the reaction of butane-
2,3-dione with 4-methoxybenzaldehyde or 4-chloroben-
zaldehyde respectively in the presence of piperidine [38].
Subsequent Krohnke reaction [42] of these 1,6-diaryl-
hexa-1,5-diene-3,4-diones with 1-pyridiniopropan-2-one
bromide (acetonylpyridinium bromide prepared by the
reaction of bromoacetone with pyridine [27]) and
ammonium acetate in ethanol gave the desired ligands
4,4?-di(4-methoxyphenyl)-6,6?-dimethyl-2,2?-bipyridine
1 and 4,4?-di(4-chlorophenyl)-6,6?-dimethyl-2,2?-bipyri-
3. Results and discussion
3.1. Strategy
We have previously reported the preparation of a
series of 1,6-diarylhexa-1,5-diene-3,4-diones from the
condensation of butane-2,3-dione with 4-substituted
benzaldehydes and their subsequent conversion to
4?,4ƒ-diaryl-2,2?:6?,2ƒ:6ƒ,2?ƒ-quaterpyridines [38]. We
have now used these precursor compounds to prepare
4,4?-diaryl-2,2?-bipyridines in which the aryl substituents
bear substituents which can be used in subsequent
chemical manipulation. Specifically, we have prepared
compounds with 4-chlorophenyl and 4-hydroxyphenyl
substituents as representative electrophilic and nucleo-
philic substituents. Although fully aware that haloben-
zene derivatives are normally inactive as electrophiles in
reactions with simple nucleophiles, we hoped that the
inductive effects associated with the coordination of a
metal ion to the bpy domain would be transmitted to the
4-chlorophenyl substituents, leading to activation in the
same way that reactions of 4-halopyridines with nucleo-
philes are dramatically enhanced upon coordination
[39,40]. In the case of ligand 2, this hope has proved
unfounded and in no case have we observed any
activation towards nucleophilic attack upon coordina-
tion. The 4-hydroxyphenyl substituents provide an
alternative approach in which reaction with electro-
philes will allow subsequent structural development. In
either case, the aim was the synthesis of a bis(ruthe-
nated) ligands which could be used for the convergent
assembly of pentanuclear or heptanuclear metallostars
based upon {M(bpy)2} or {M(bpy)3} core motifs (Fig.
1). The bpy metal-binding domain can be optimised for
the formation of complexes with metal ions possessing
either tetrahedral or octahedral coordination prefer-
ences by the introduction of substituents at the 6 and 6?-
positions [41]. These metallostars would differ from our
prototype systems by the presence of a hydrolytically
dine 2 as colourless needles in 35ꢁ50% yield. The
/
compounds were fully characterised and exhibited the
expected spectroscopic properties (see Section 2). The
ligand 4,4?-di(4-hydroxyphenyl)-6,6?-dimethyl-2,2?-bi-
pyridine 3 was prepared as a green solid in near-
quantitative yield by the demethylation of 1 by heating
with molten pyridinium chloride at 140 8C [43,44].
Once again, the new ligand 3 was fully characterised.
The synthetic routes to ligands 1, 2 and 3 are sum-
marised in Scheme 1.
3.3. Ligand synthesis-4,4?-diaryl-2,2?-bipyridine metal-
binding domains
Building upon our preliminary studies with the 6,6?-
dimethyl substituted systems, we concentrated upon the
preparation of nucleophilic ligands bearing 4-hydroxy-
phenyl substituents. We investigated a number of routes
for the preparation of the nucleophilic ligand 5, all of
which involved the deprotection of the methoxy com-
pound 4 in the last reaction step. The bisenones are not
useful intermediates for the synthesis of 2,2?-bipyridines
with only hydrogen substituents at the 6- and 6?-
positions. Initially we attempted to prepare 4 by Stille
coupling which is a powerful method for the preparation
of heteroaryls [45] and we selected 4,4?-dibromo-2,2?-
bipyridine, which is readily prepared in a four-step
procedure from 2,2?-bipyridine [46], as the key synthetic
intermediate. Lithiation of 4-bromoanisole with n-BuLi
in THF followed by reaction with tri-n-butylchlorotin
gave a solution containing 4-tri-n-butylstannylanisole.
The solvent was removed and the crude stannyl
compound dissolved in DMF and reacted directly with
4,4?-dibromo-2,2?-bipyridine in the presence of
[Pd(PPh3)4]. After work-up, the desired ligand 4 was
obtained in 18% yield. The low yield was disappointing,
and quenching experiments indicated that the difficulty
arose from side-reactions involving the 4-lithioanisole
[47].
stable Cꢀ
/
C bond linking the aryl ring to the bpy
domain, in contrast to the benzyl ethers introduced in
our earlier work [23].
3.2. Ligand synthesis-6,6?-dimethyl-4,4?-diaryl-2,2?-
bipyridine metal-binding domains
The introduction of methyl substituents into the 6 and
6?-positions of a bpy ligand stabilises complexes with
tetrahedral centres such as copper(I) and silver(I) and
destabilises tris complexes with metals adopting an
We finally adopted a method for the synthesis of 4
based upon the Suzuki coupling [48] of 4-methoxyphe-
nylboronic acid with 4,4?-dibromo-2,2?-bipyridine.
Commercially available 4-bromoanisole was converted

E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ
/108
101
Scheme 1.
to 4-methoxyphenylboronic acid by reaction with mag-
nesium to give a Grignard reagent followed by treat-
ment with tri(isopropyl)borate and subsequent
hydrolysis [49]. Initial attempts to conduct Suzuki
reactions of 4-methoxyphenylboronic acid with the
more readily available 4,4?-dichloro-2,2?-bipyridine
gave only very low yields of 4 and resulted in the
formation of significant amounts of the monofunctio-
nalised product 4-chloro-4?-(4-methoxyphenyl)-2,2?-bi-
pyridine. Accordingly, we returned to the more
activated compound 4,4?-dibromo-2,2?-bipyridine. The
reaction of 4,4?-dibromo-2,2?-bipyridine with 4-methox-
yphenylboronic acid proceeded smoothly in a biphasic
toluene-aqueous sodium carbonate medium in the pre-
sence of [Pd(PPh3)4] to give 4 as colourless needles in
75% overall yield. The compound was fully charac-
terised and its properties generally resembled those of 1,
although there is a blue-shifting of the maxima in the
derivatives to hydroxy analogs including that of 1 to 3
above and obtained 5 in 97% yield (Scheme 2). For
convenience, we later adopted a milder method of
deprotection involving treatment with BBr3 in CHCl3
[43,50] at 0 8C which gave 5 in 96% yield.
3.4. Solid state structures of 1 and 4
In order to obtain metrical data for subsequent use in
modelling and to quantify the effects of introducing the
methyl substituents into the 6,6?-positions, we have
determined the solid state structure of the ligands 1
and 4. The solid state structure of 1 is shown in Fig. 2.
The bpy domain adopts the expected trans conforma-
tion and is essentially planar with an angle of 1.158
between the least squares planes of the two rings. The 4-
methoxyphenyl substituents are crystallographically in-
dependent and are twisted with respect to the directly
bonded pyridine ring (least squares planes, 29.528,
38.818). The carbon and oxygen atoms of the methoxy
groups lie close to the plane of the directly bonded
electronic absorption spectra of :
/
6 nm between 1 and
4.
Two methods were investigated for the demethylation
of 4 to give 5. Initially, we used molten pyridinium
chloride, which has proved to be effective for the
conversion of a number of methoxy oligopyridine
phenyl ring (torsion angles 0.88ꢁ
domains are parallel and stacked with a shortest
˚
interplanar distance of 3.5 A.
/
1.88). Adjacent bpy
Scheme 2.

102
E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ108
/
˚
Fig. 2. Molecular structure of 1 showing the numbering scheme adopted. Selected bond lengths (A) and angles (8): N1ꢀ
N2ꢀC21 1.346(2); N2ꢀC25 1.341(2); C5ꢀC6 1.505(2); C25ꢀC26 1.503(2); C30ꢀO2 1.369(1); O2ꢀC33 1.414(2); C1ꢀN1ꢀ
117.6(1); C30ꢀO2ꢀC33 118.0(1); N1ꢀC5ꢀC6. 116.6(1); N2ꢀC25ꢀC26. 116.5(1).
/
C1 1.346(1); N1ꢀ
C5 117.4(1); C21ꢀ
/
C5 1.337(2);
/
/
/
/
/
/
/
/
/
N2ꢀC25
/
/
/
/
/
/
/
The molecular structure of 4 closely resembles that of
1 with the pyridine rings adopting a trans conformation.
The phenyl rings and the directly bonded pyridine ring
are near coplanar with an interplanar angle of 4.608 in
marked contrast to the significantly greater angles in 1.
The carbon and oxygen atoms of the methoxy groups lie
close to the plane of the directly bonded phenyl ring
about the interannular Cꢀ
/
C bond. The red copper(I)
complex exhibits an MLCT absorption at 482 nm with
an associated emission at 619 nm which are typical for
copper(I) bis(diimine) chromophores and lumophores
[51ꢁ55].
/
Good quality pale orange crystals of [Ag(1)2][PF6]
were obtained by the slow diffusion of diethyl ether
vapour into an acetone solution of the complex and the
X-ray solid state structure was determined. The struc-
ture of the [Ag(1)2]ꢂ cation present in [Ag(1)2][PF6] is
shown in Fig. 4. The silver is in a very irregular four
coordinate environment in which it is bonded to the four
nitrogen donors of the two ligands. The distortion from
a regular tetrahedral geometry is illustrated in Fig. 5.
with a torsion angle of 2.08. In the lattice, there are
˚
3.5 A distances between
stacking interactions with :
/
parallel planes (Fig. 3).
3.5. Coordination chemistry of 1 with copper(I) and
silver(I)
The four Agꢀ
/
N bonds vary considerably and lie in the
˚
2.372(4) A although the bite angles of
As mentioned in Section 3.2, ligand 1 is expected to
form stable 2:1 complexes with copper(I) and silver(I)
whereas 4 will form 3:1 complexes with octahedral metal
centres. The reaction of 1 with [Cu(MeCN)4][PF6] or
Ag[BF4] in ethanol gave solutions from which the 2:1
complexes [M(1)2][PF6] could be isolated by the addition
of ammonium hexafluorophosphate. The 1H NMR
spectra of CD3CN solutions of the complexes exhibited
four aromatic and two methyl resonances indicating
that on the NMR time-scale the two ligands are
equivalent and that the ligands remain symmetrical
range 2.259(3)ꢁ
/
71.8(1)8 and 71.3(1)8 are typical. The two ligands are not
orthogonal but make least squares planes angles of 78.88
with each other. The distortion from a tetrahedral
geometry is significant but is in accord with that
observed in other copper(I) and silver(I) bis(2,2?-bipyr-
idine) and bis(1,10-phenanthroline) complexes [56,57].
The only other close contact to the silver centre is the
oxygen atom of a methoxy group from an adjacent
˚
Ag contact of 4.114 A; this
cation which shows an O
/
Á Á Á
/
˚
Fig. 3. Molecular structure of 4 showing the numbering scheme adopted. Selected bond lengths (A) and angles (8): N1ꢀ
O1ꢀC16 1.365(2); O1ꢀC19 1.423(2); C2ꢀN1ꢀC6 116.5(1); C16ꢀO1ꢀC19 117.4(1).
/
C2 1.332(2); N1ꢀC6 1.339(2);
/
/
/
/
/
/
/

E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ
/108
103
Fig. 4. Molecular structure of the [Ag(1)2]ꢂ cation present in [Ag(1)2][PF6] showing the numbering scheme adopted. Hydrogen atoms have been
˚
omitted for clarity. Selected bond lengths (A) and angles (8): Ag1ꢀ
/
N1 2.259(3); Ag1ꢀ
C11 1.351(5); N31ꢀC32 1.333(6); N31ꢀ
C23 1.369(7); O2ꢀC26 1.369(9); O31ꢀC46 1.374(6); O31ꢀ
N31 142.8(1); N2ꢀAg1ꢀN31 105.9(1); N1ꢀAg1ꢀN32 141.4(1); N2ꢀ
O2ꢀC26 119.5(6); C46ꢀO31ꢀC49 117.7(5); C53ꢀO32ꢀC56 117.2(5).
/
N2 2.372(4); Ag1ꢀ
C36 1.340(5); N32ꢀ
C49 1.405(8); O32ꢀ
Ag1ꢀN32 125.6(1); N31ꢀ
/
N31 2.321(3); Ag1ꢀ
C37 1.347(5); N32ꢀ
C53 1.376(5); O32ꢀ
Ag1ꢀ
/
N32 2.301(3); N1ꢀ
C41 1.336(6); O1ꢀ
C56 1.405(8);
N32 71.3(1);
/
C2
1.347(5); N1ꢀ
C16 1.372(4); O1ꢀ
N1ꢀAg1ꢀN2 71.8(1); N1ꢀ
C16ꢀO1ꢀC19 117.9(4); C23ꢀ
/
C6 1.349(5); N2ꢀ
C19 1.412(6); O2ꢀ
Ag1ꢀ
/
C7 1.341(4); N2ꢀ
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
has been discussed and paramaterised but in our case
the deviation from ideality is so great that the Dobson
angle is not a particularly useful parameter [58]. The
starting point for a description of the geometry is a
trigonal plane described by N1, N31 and N32 (sum of
the three Nꢀ
/
Agꢀ
/
N angles, 355.48) with the remaining
N2
distance of 2.372(4) A is the longest of the silverꢁ
N2 occupying an off-axis axial site. The Ag1ꢀ
/
˚
/
nitrogen distances. The bpy metal-binding domains are
approximately planar (torsion angles 2.578 and 3.138)
but each ligand shows a small torsion angle (11.948,
16.928) to one methoxyphenyl substituent and a larger
one (31.628, 33.878) to the other. The short Ag
/
Á Á Á
/
O
˚
distance of 4.114 A is to the methoxyphenyl substituents
with the greatest twisting with respect to the pyridine
ring. As with the free ligands, the carbon and oxygen
atoms of the methoxy groups lie within the plane of the
attached phenyl ring.
In the course of our studies on the silver complex, we
also prepared the tetrafluoroborate salt [Ag(1)2][BF4]
and slow recrystallisation from acetonitrile by the
diffusion of diethyl ether vapour into the solution gave
Fig. 5. A representation of the structure of the [Ag(1)2]ꢂ cation
showing the distortion from ideal D2d symmetry.
a new compound [Ag(1)(MeCN)][BF4]×
observed the displacement of bpy metal-binding do-
mains by acetonitrile in our earlier studies of silver(I)
/
MeCN. We have
methoxyphenyl group is stacked with one of the ligands
coordinated to the silver. The silver atom is effectively
encapsulated by the 6,6?-methyl substituents of the 1
ligands and although the coordination geometry is very
irregular, there is little opportunity for the silver to
increase its coordination number. The distortion from
ideal D2d symmetry in copper(I) bis(diimine) complexes
2,2?:6?,2ƒ-quaterpyridine complexes [59ꢁ62] and on the
basis of these we anticipated a three coordinate silver
/
complex. In order to confirm this proposal and to
investigate any silverꢁ/silver interactions we have also
determined the X-ray structure of [Ag(1)(MeCN)][BF4]×
/

104
E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ108
/
Fig. 6. Molecular structure of the [Ag(1)(MeCN)]ꢂ cation present in [Ag(1)(MeCN)][BF4] showing the numbering scheme adopted. Hydrogen atoms
˚
have been omitted for clarity. Selected bond lengths (A) and angles (8): Agꢀ
/
N3 2.121(2); Agꢀ
C6 1.349(3); N1ꢀC2 1.350(3); N2ꢀ
N1 72.49(8); C6ꢀN1ꢀC2 118.8(2); C16ꢀ
/
N2 2.259(2); Agꢀ
C16 1.341(4); N2ꢀ
N2ꢀC20 119.0(2); C24ꢀ
/
N1 2.296(2); C10ꢀ
C20 1.343(3); N3ꢀ
O2ꢀC27 118.1(2); N3ꢀ
/
O13 1.356(3);
O13ꢀ
N3ꢀAgꢀ
C28ꢀC29 179.7(4); C10ꢀ
/
C14 1.423(4); O2ꢀ
N2 150.64(9); N3ꢀ
O13ꢀ
/
C27 1.417(4); C24ꢀ
AgꢀN1 136.73(9); N2ꢀ
C14 117.0(2).
/
O2 1.365(3); N1ꢀ
/
/
/
/
/
C28 1.131(3);
/
/
/
/
/
Agꢀ
/
/
/
/
/
/
/
/
/
/
/
MeCN. The structure of the [Ag(1)(MeCN)]ꢂ cation is
presented in Fig. 6. The silver is three-coordinate and
bonded to the two nitrogen donors of 1 and the nitrogen
of an acetonitrile ligand. The remaining acetonitrile is
found as a solvent molecule in the lattice with no
destabilisation of octahedral complexes in which three
of these ligands are coordinated to the same centre.
An initial attempt to force three 1 ligands to
coordinate to a ruthenium centre was unsuccessful and
reaction of four equivalents of 1 with RuCl3×
/3H2O in
interaction with silver. The bite angle N1ꢀ
72.49(8)8 and the remaining angles in the coordination
sphere are 136.73(9)8 (N1ꢀAg1ꢀN3) and 150.64(9)8
(N2ꢀAg1ꢀN3); the sum of these three angles is
/
Ag1ꢀ/N2 is
1,2-ethanediol at 1208 or 1408 for period of up to 48 h
gave no evidence for the formation of [Ru(1)3]2ꢂ
species. On the basis of literature precedent [63,64], we
argued that it should be possible to coordinate at least
one of the sterically hindered ligands to a {Ru(bpy)2}
motif and accordingly prepared these compounds. Two
synthetic methods were investigated, both involving the
reaction of [Ru(bpy)2Cl2] with the appropriate ligand.
The compounds were obtained either by prolonged
thermal reaction (24 h at 110 8C) in 1,2-ethanediol or
by reaction for 6 min in 1,2-ethanediol in a modified
domestic microwave oven. In all cases, the yields were
significantly higher for the reactions under microwave
irradiation. After chromatographic purification, the
/
/
/
/
359.868 indicating that the compound is correctly
described as trigonal planar. The planes of the methox-
yphenyl substituents make torsions of 68 and 248 with
the directly bonded pyridine rings and the bpy domain
shows a small torsion of 28 between the two pyridine
rings. The silverꢁ
/
nitrogen distances are typical (Ag1ꢀ
/
˚
˚
N1 2.296(2) A, Ag1ꢀ
/
N2 2.259(2) A, Ag1ꢀ
Á Á ÁAg contact between adjacent
molecules is 4.876 A and so there are no significant
silverꢁsilver interactions.
/
N3 2.121(2)
˚
A. The shortest Ag
/
/
˚
/
three complexes [Ru(bpy)2(L)][PF6]2 (Lꢅ
were isolated as red solids.
The red colour arises from an MLCT absorption and
these have maxima:425 nm for the three complexes
/
1, 2 or 3)
3.6. Ruthenium(II) complexes of 6,6?-dimethyl
substituted ligands
/
[Ru(bpy)2(L)][PF6]2. The MLCT band is blue-shifted
with respect to [Ru(bpy)3]2ꢂ salts which typically have
an absorption maximum at 452 nm [65]. The origin of
this blue-shifting is not obvious, since related complexes
As discussed earlier, the presence of substituents in
the 6,6?-position of a diimine ligand (the cuproin motif)
allows the preparation of air-stable copper(I) complexes.
Conversely, their presence results in a very great steric

E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ
/108
105
Fig. 7. Molecular structure of the L-[Ru(bpy)2(2)]2ꢂ cation present in [Ru(bpy)2(2)][PF6] showing the numbering scheme adopted. Both L and D
˚
enantiomers are present in the lattice. Hydrogen atoms have been omitted for clarity. Selected bond lengths (A) and angles (8):Ru1ꢀ
/
N1 2.116(3);
N3 84.3(1); N2ꢀ
N5 100.4(1); N3ꢀRu1ꢀN5
N6 96.8(1); N5ꢀRu1ꢀN6 78.9(1).
Ru1ꢀ
Ru1ꢀ
99.1(1); N4ꢀ
/
N2 2.139(3); Ru1ꢀ
N3 94.3(1); N1ꢀRu1ꢀ
Ru1ꢀN5 82.7(1); N1ꢀ
/
N3 2.082(3); Ru1ꢀ
N4 98.0(1); N2ꢀ
Ru1ꢀN6 97.7(1); N2ꢀ
/
N4 2.049(3); Ru1ꢀ
Ru1ꢀN4 172.5(1); N3ꢀ
Ru1ꢀN6 90.5(1); N3ꢀ
/
N5 2.055(3); Ru1ꢀ
Ru1ꢀN4 78.5(1); N1ꢀ
Ru1ꢀN6 175.1(1); N4ꢀ
/
N6 2.066(3); N1ꢀ
Ru1ꢀN5 176.6(1); N2ꢀ
Ru1ꢀ
/
Ru1ꢀ
/
N2 79.4(1); N1ꢀ
/
Ru1ꢀ
/
/
/
/
/
/
/
/
/
/
/
/
Ru1ꢀ
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
are reported as having maxima closer to 450 nm,
although in all cases the absorptions are broad and
We have determined the solid state structure of the
complex [Ru(bpy)2(2)][PF6]2 to provide model data for
the construction of molecular wires based upon this as a
central unit. Suitable crystals were obtained by the
diffusion of diethyl ether vapour into an acetonitrile
solution of the complex; the structure of one of the pair
of D and L enantiomers of the chiral trischelate cations
show a second feature at :
/
430 nm [66ꢁ69]. In contrast
/
to [Ru(bpy)3]2ꢂ salts, the three complexes show only
very weak or no emission upon excitation in the MLCT
absorption, as observed for other 6,6?-disubstituted bpy
complexes [70]. The 1H NMR spectra of these com-
plexes are of some interest. The two rings of each bpy
ligand are expected to be magnetically inequivalent
depending upon whether they are trans to another bpy
present in the crystal of [Ru(bpy)2(2)][PF6]2×
0.5H2O is presented in Fig. 7. The two bpy ligands are
typical and approximately planar (torsion angles 28ꢁ48)
/
3CH3CN×
/
/
1
˚
N distances in the range 2.049(3)ꢁ2.082(3) A
ligand or the ligand L. This is observed in the H NMR
with Ruꢀ
/
/
spectrum, which shows four subspectra in the aromatic
region, corresponding to the two different magnetically
inequivalent bpy rings, the pyridine of the ligand L and
the aryl substituent of the L ligand. To date, we have
been unable to distinguish between the two bpy rings on
the basis of NOESY spectra. The complexes are redox
active and all exhibit a ruthenium(II)/(III) process close
similar to those observed in other [Ru(bpy)3]2ꢂ salts
[71]. All three of the coordinated bpy domains exhibit
bite angles between 78.58 and 79.48, typical of a 2,2?-
bipyridine coordinated to a second or third row transi-
tion metal centre [72]. Potential interactions between the
6,6?-dimethyl substituents of 2 with the metal centre and
the other bpy ligands result in a lengthening of the Ruꢀ
/
˚
to ꢂ
/
1.0 V versus ferrocene/ferrocenium, indicating that
N bonds to this ligand (Ru1ꢀ
/
N1 2.116(3) A, Ru1ꢀ
/N2
˚
the remote substituent on the phenyl substituent has
little influence at the metal. The ligand reduction
processes are much more sensitive to these substituents.
2.139(3) A). The two pyridine rings of the bpy domain
of 2 are not coplanar but exhibit a torsion angle of 21.28,
the chlorophenyl substituents are also substantially

106
E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ
/108
Scheme 3.
twisted with respect to the pyridine rings and form
torsion angles of 258 and 398. The presence of the methyl
substituents results in a significant distortion of the
geometry from ideality, but there are no short contacts
between the cations and other lattice species.
All attempts to prepare 6[PF6]4 from 2 or [Ru(b-
py)2(2)][PF6]2 by reaction with HOtpy or [Ru(tpy)(HOt-
py)][PF6]2 (HOtpyꢅ2,2?:6?,2ƒ-terpyridin-4?(1?H)-one)
/
[29] under a variety of conditions were unsuccessful.
4. Conclusions
3.7. The bisruthenated metallostar precursor
We have prepared a series of ligands which can be
further structurally elucidated to give metallostars with
octahedral or tertrahedral metal centres. The most
useful of these is the hydroxy compound 3, which has
bee ruthenated at the periphery to give the immediate
precursor for the metallostars. The coordination beha-
viour of the new ligands has been studied and X-ray
crystallographic studies have confirmed the anticipated
coordination geometries in the metal complexes and
which will lead to the metallostars. In a future publica-
tion, we will describe the preparation of metallostars
from these ligand systems.
The bisphenolic ligands 3 and 5 are the key to the
preparation of metallostars and we have established that
it is possible to metallate 3 to give a diruthenated
species. The complex [Ru(tpy)(Cltpy)][PF6]2 (Cltpyꢅ4?-
/
chloro-2,2?:6?,2ƒ-terpyridine) [29] contains a Cltpy li-
gand that is activated towards nucleophilic attack by
coordination to the ruthenium(II) centre. The reaction
of 3 with [Ru(tpy)(Cltpy)][PF6]2 proceeded smoothly in
acetonitrile-dmso containing potassium carbonate and
sodium iodide to give a deep red solution from which
the compound 6[PF6]4 was isolated in 40% yield after
chromatographic purification (Scheme 3). The electro-
spray mass spectrum of the product exhibited clusters of
peaks corresponding to the isotopomers of the ions
5. Supplementary material
1
{6(PF6)2}2ꢂ, {6(PF6)}3ꢂ and {6}4ꢂ and the H NMR
All crystallographic data have been deposited with the
Cambridge Crystallographic Data Centre, CCDC Nos
185693 (1), 185692 (4), 185691 ([Ag(1)(MeCN)][BF4]),
185694 ([Ag(1)2][PF6]), 189355 ([Ru(bpy)2(2)][PF6]2).
Copies of this information may be obtained free of
charge from The Director, CCDC 12 Union Road,
spectrum provides confirmatory evidence for the for-
mulation of the product. The singlet assigned to H3C is
characteristic and precludes the possibility of mixtures
of the starting materials. The assignments presented in
Section 2 are on the basis of COSY and NOESY
spectroscopy. The red compound exhibits an MLCT
absorption with a maximum at 480 nm but like the
majority of {Ru(tpy)2} chromophores is virtually non-
luminescent in fluid solution. The complex shows a
Cambridge CB2 1EZ, UK (fax: ꢂ44-1223-366033;
/
e-mail: deposit@ccdc.cam.ac.uk or www: http://www/
ccdc.cam.ac.uk.
single two-electron ruthenium(II)/(III) process at ꢂ0.85
/
V versus ferrocene/ferrocenium and a series of ligand
reductions. The ruthenium(II)/(III) process is at a very
similar potential to the model compound [Ru(tpy)(E-
Acknowledgements
tOtpy)][PF6]2 (EtOtpyꢅ
[29].
/
4?-ethoxy-2,2?:6?,2ƒ-terpyridine)
We thank the Schweizerischer Nationalfonds zur
Forderung der wissenschaftlichen Forschung, the Uni-
¨

E.C. Constable et al. / Polyhedron 22 (2003) 93ꢁ
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