New ligands in the 2,2′-dipyridylamine series and their Re(I) complexes; synthesis, structures and luminescence properties

Article abstract of DOI:10.1039/b312647a

A series of new derivatives of the di(2-pyridyl)amine ligand has been prepared, having the general formula (py)₂NR, where R is one of a wide range of groups including naphthyl, pyrenyl, benzo-18-crown-6, pyrenyl, oxazolyl and bromo-biphenyl. All ligands are luminescent, with emission maxima between 370 and 520 nm, and with quantum yields in fluid solution of up to 0.74. Reaction of these ligands with Re(CO)₅Cl afforded complexes of the type [Re(CO)₃ClL] in which the di(2-pyridyl)amine ligand binds as an N,N-bidentate chelate via the two pyridyl units; five such complexes have been structurally characterised. With one exception the complexes are essentially non-luminescent, which we ascribe to the energetic availability of metal-based d-d excited states which can quench any MLCT or ligand-centred excited states. The exception is [Re(CO)₃Cl(tppd)] [where tppd = N,N,N′, N′-tetrakis(2-pyridyl)-p-phenylenediamine] in which one di(2-pyridyl) amine site is occupied by a {Re(CO)₃Cl} unit but the other is vacant; this luminesces in fluid solution at 516 nm (φ = 0.04, τ = 42 ns).

Full text of DOI:10.1039/b312647a

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P A P E R
New ligands in the 2,20-dipyridylamine series and their Re(I)
complexes; synthesis, structures and luminescence properties
a
b
a
ac
¨
Nail M. Shavaleev, Andrea Barbieri, Zoe R. Bell, Michael D. Ward* and
Francesco Barigelletti*b
a
School of Chemistry, University of Bristol, Cantock’s Close, Bristol UK BS8 1TS
Istituto ISOF-CNR, Via P. Gobetti 101, 40129, Bologna, Italy. E-mail: franz@isof.cnr.it
Department of Chemistry, University of Sheffield, Brook Hill, Sheffield UK S3 7HF.
E-mail: m.d.ward@sheffield.ac.uk; Fax: 0114 2229346
b
c
Received (in Durham, UK) 9th October 2003, Accepted 13th January 2004
First published as an Advance Article on the web 12th February 2004
A series of new derivatives of the di(2-pyridyl)amine ligand has been prepared, having the general formula
(py)2NR, where R is one of a wide range of groups including naphthyl, pyrenyl, benzo-18-crown-6, pyrenyl,
oxazolyl and bromo-biphenyl. All ligands are luminescent, with emission maxima between 370 and 520 nm, and
with quantum yields in fluid solution of up to 0.74. Reaction of these ligands with Re(CO)5Cl afforded
complexes of the type [Re(CO)3ClL] in which the di(2-pyridyl)amine ligand binds as an N,N-bidentate chelate
via the two pyridyl units; five such complexes have been structurally characterised. With one exception the
complexes are essentially non-luminescent, which we ascribe to the energetic availability of metal-based d-d
excited states which can quench any MLCT or ligand-centred excited states. The exception is [Re(CO)3Cl(tppd)]
[where tppd ¼ N,N,N0,N0-tetrakis(2-pyridyl)-p-phenylenediamine] in which one di(2-pyridyl)amine site is
occupied by a {Re(CO)3Cl} unit but the other is vacant; this luminesces in fluid solution at 516 nm (f ¼ 0.04,
t ¼ 42 ns).
dpa derivatives of dpa with a variety of substituents attached
Introduction
to the amine N atom. These substituents include strongly
fluorescent aromatic chromophores such as naphthlane or pyr-
ene, and in one case an 18-crown-6 macrocyclic unit which
could be used for additional metal-ion binding. Complexes
of these ligands with {Re(CO)3Cl} units are also described in
this paper, including their structures and luminescence proper-
ties. Such rhenium(I) carbonyl complexes with diimine-type
ligands often show visible luminescence originating from a
metal-to-ligand charge-transfer excited state,13–15 which has
been exploited for development of sensors and luminescent
labels,16 and in electroluminescent materials.17 It was reported
recently that Re(CO)5Cl does not react with dpa in solution or
in a melt, and that a reaction takes place only in the presence
of PPh3 to give the complex [Re(CO)2(PPh3)(dpa)Cl].7 How-
ever we have found that dpa derivatives easily react with
Re(CO)5Cl to give the expected [Re(CO)3Cl(NN)] adducts
described here. It should be noted that some rhenium(III) and
rhenium(VII) complexes of the related ligand tris(2-pyridyl)-
amine have also been studied.8a
Many coordination complexes of 2,20-dipyridylamine (dpa)1–7
and its substituted derivatives8–11 have been prepared and
structurally characterised, partly because the different coordi-
nation modes available to the ligand result in unusual structural
chemistry, and partly because of the luminescence properties of
some of the complexes. 2,20-Dipyridylamine on its own is
weakly luminescent,12 and this is retained in some of its com-
plexes; for example, ligand-based blue fluorescence has been
reported for zinc(II)2 and cadmium(II)3 complexes of dpa, and
also for organoaluminium complexes with deprotonated
dpa.4 Emission from ligand-based or charge-transfer excited
states has been observed for complexes of iridium(III),5 rhodi-
um(III)5 and ruthenium(II)6 with neutral or deprotonated dpa.
New materials with improved photophysical properties
based on dpa have been prepared by substitution of the amine
hydrogen atom with an organic group.9–11 Using a polyfunc-
tional organic group as a spacer between two or more dpa ter-
mini has allowed access to new linear or star-shaped bridging
ligands. A variety of such bridging ligands and their mono-
and polynuclear complexes with zinc(II), silver(I), platinum(II)
and lanthanide(III) ions have recently been synthesized and
structurally characterised, and many of these—like the com-
plexes of the parent ligand—show strong blue lumines-
cence.9–11 Organoboron and organosilicon derivatives, and
some zinc(II) and silver(I) complexes of dpa derivatives, show
efficient blue luminescence as solids and in solution, while their
lanthanide(III) tris-b-diketonate complexes show sensitized
lanthanide(III) emission in the solid state. 2,20-Dipyridylamine
derivatives have been used as blue emitters in electrolumines-
cent devices,10 and a luminescent sensor for benzene based
on the zinc(II) complex of 1,3,5-tris[p-(2,20-dipyridylamino)-
phenyl]benzene has been reported.11
Experimental
General details
2,20-Dipyridylamine, other organic reagents, and Re(CO)5Cl
were obtained from Aldrich or Lancaster Synthesis and used
without further purification. The following instrumentation
was used for routine spectroscopic characterisation: UV/Vis
spectra, a Perkin-Elmer Lambda 2 spectrophotometer; 1H
NMR spectra, a Jeol GX-270 spectrometer at 270 MHz; EI
and FAB mass spectra, a VG-Autospec spectrometer.
Syntheses of 2,20-dipyridylamine derivatives9,10
In this paper we report the syntheses, characterisation, crys-
tal structures and luminescence properties of a series of new
Method 1. A solid mixture of dpa, the appropriate bromo-
aromatic derivative, KOH (excess, 1.5 equiv, compared to of
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
398
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 3 9 8 – 4 0 5

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dpa) and CuSO4ꢀ5H2O (catalytic amount) under N2 was
heated at 180 ꢁC for 6 h during which time it melted and then
re-solidified. Specific quantities for each reaction are given
below; one of the two components (the dpa or the bromo-aro-
matic) was used in excess according to which was more soluble
in EtOH; the residue of that component was easily removed at
the end of the reaction during recrystallisation from EtOH.
The reaction mixture was cooled and partitioned between
water and dichloromethane, with the final pH of the aqueous
phase adjusted to 6.5–7 using acetic acid or NaHCO3 . The
organic phase was separated, dried with MgSO4 , and the sol-
vent removed under reduced pressure. The crude product was
purified by column chromatography on alumina on a short
column eluting with CH2Cl2 , or acetone/CH2Cl2 . The chro-
matography was followed with the use of a hand-held UV
lamp (365 nm); the main fraction showing blue luminescence
was collected, evaporated to dryness, and recrystallized twice
from a small amount of boiling ethanol. The solid was washed
with cold ethanol and hexane and dried under vacuum. This
procedure usually gave analytically pure product, however in
some cases additional column chromatography was required
which was carried out on alumina eluting with CH2Cl2 , or
acetone/CH2Cl2 .
washing the product on filter each time with cold ethanol
and hexane. Anal. calc. for C18H18N4 : C, 74.5; H, 6.3; N,
19.3. Found: C, 74.7; H, 6.6; N, 19.4%. EI MS: m/z 290
(100%, Mþ). 1H NMR (CDCl3): d 8.30 (2H, d; pyridyl H6),
7.49 (2H, td; pyridyl H4), 7.10 (2H, d; phenyl), 6.96 (2H, d;
pyridyl H3), 6.85 (2H, ddd; pyridyl H5), 6.75 (2H, d; phenyl),
2.97 (6H, s; NMe2).
DP18C6. This was prepared from dpa (1.97 g, 11.5 mmol),
40-bromobenzo-18-crown-6 (3.0 g, 7.7 mmol), K2CO3 (1.59
g) and CuSO4ꢀ5H2O (0.20 g) by method 2, which gave 2.18 g
(59%) of the product. Anal. calc. for C26H31N3O6 : C, 64.9;
H, 6.5; N, 8.7. Found: C, 65.1; H, 6.7; N, 8.8%. EI MS: m/z
481 (100%, Mþ). 1H NMR (CDCl3): d 8.30 (2H, d; pyridyl
H6), 7.52 (2H, td; pyridyl H4), 6.96 (2H, d; pyridyl H3), 6.88
(3H, m; pyridyl H5 and one phenyl H), 6.75 (2H, m; phenyl),
4.17 (2H, t; CH2), 4.06 (2H, t; CH2), 3.93 (2H, t; CH2), 3.87
(2H, t; CH2), 3.68–3.82 (12H, m; 6 CH2 groups).
2NDPA. This was prepared from dpa (3.60 g, 21.0 mmol),
2,8-dibromonaphthalene (1.00 g 3.5 mmol), K2CO3 (2.42 g)
and CuSO4ꢀ5H2O (0.1 g) by method 2, which gave 0.43 g
(27%) of the product. Anal. calc. for C30H22N6 : C, 77.2; H,
4.8; N, 18.0. Found: C, 76.6; H, 5.0; N, 17.9%. EIMS: m/z
466 (100%, Mþ). 1H NMR (CDCl3): d 8.34 (4H, d; pyridyl
H6), 7.70 (2H, d; naphthyl), 7.57 (6H, m; pyridyl H4 and two
naphthyl H), 7.29 (2H, dd; naphthyl), 7.03 (4H, d; pyridyl
H3), 6.94 (4H, ddd; pyridyl H5).
Method 2. A solution of dpa and the appropriate bromo-
aromatic derivative in CH2Cl2 (10 cm3; see below for quanti-
ties of reagents) was mixed with a solution of K2CO3 (1 equiv.
with respect to dpa) and CuSO4ꢀ5H2O (catalytic amount) in
water (10 cm3). The resulting biphasic mixture was evaporated
to dryness and further dried under vacuum; this procedure
ensures thorough mixing of components. The resulting solid
mixture was heated under N2 at 180 ꢁC for 6 h, and worked
up as described in method 1 above.
DPAPYR. This was prepared from dpa (1.83 g, 10.7 mmol),
1-bromopyrene (1.0 g, 3.6 mmol), K2CO3 (2.5 g) and
CuSO4ꢀ5H2O (0.1 g) by method 2, which gave 0.27 g (21%)
of the product. Anal. calc. for C26H17N3 : C, 84.1; H, 4.6; N,
11.3. Found: C, 83.9; H, 4.6; N, 11.4%. EIMS: m/z 371
(100%, Mþ). 1H NMR (CDCl3): d 8.31 (2H, d; pyridyl H6),
7.9–8.3 (9H, m; pyrene); 7.49 (2H, td; pyridyl H4), 6.95 (2H,
d; pyridyl H3), 6.88 (2H, m; pyridyl H5).
All new dpa derivatives were obtained as air- and moisture-
stable white or pale yellow solids which were soluble in chlori-
nated solvents, arenes, and boiling ethanol, but insoluble in
hexane and cold ethanol.
TPPD,9b 2-TPA8a and 3-TPA were synthesized according to
the literature methods.
X1P. This was prepared from dpa (1.71 g, 10.0 mmol), 2-(4-
bromophenyl)-5-phenyl-1,3,4-oxadiazole (1.0 g, 3.3 mmol),
K2CO3 (2.3 g) and CuSO4ꢀ5H2O (0.1 g) by method 2, which
BPBr. This ligand was obtained as a by-product in the
synthesis of N,N,N0,N0-tetra(2-pyridyl)biphenyl-4,40-diamine
according to the literature method.9b Anal. calc. for
C22H16BrN3 : C, 65.7; H, 4.0; N, 10.5. Found: C, 66.1; H,
4.3; N, 9.9%. EI MS: m/z 402 (100%, Mþ). 1H NMR (CDCl3):
d 8.35 (2H, d; pyridyl H6), 7.5–7.6 (6H, m; pyridyl H4 and two
pairs of phenyl H), 7.45 (2H, d; phenyl), 7.24 (2H, d; phenyl),
7.05 (2H, d; pyridyl H3), 6.95 (2H, ddd; pyridyl H5).
gave 0.79
g (60%) of the product. Anal. calc. for
C24H17N5O: C,73.5; H, 4.4; N, 17.9. Found: C, 74.1; H, 4.2;
1
N, 18.0%. EIMS: m/z 390 (100%, Mþ). H NMR (CDCl3): d
8.38 (2H, d; pyridyl H6), 8.06–8.18 (4H, m; phenyl); 7.64
(2H, td; pyridyl H4), 7.53 (3H, m; phenyl), 7.29 (2H, d; phe-
nyl), 7.07 (2H, d; pyridyl H3); 7.02 (2H, ddd; pyridyl H5)
X1N. This was prepared from dpa (2.50 g, 14.6 mmol), 2-(4-
bromophenyl)-5-(1-naphthyl)-1,3,4-oxadiazole (2.0 g, 5.7
mmol), K2CO3 (2.5 g) and CuSO4ꢀ5H2O (0.1 g) by method
2, which gave 2.22 g (88%) of the product. Anal. calc. for
C28H19N5O: C, 76.2; H, 4.3; N, 15.9. Found: C, 76.4; H, 4.6;
NAP. This was prepared from dpa (3.03 g, 17.7 mmol), 2-
bromonaphthalene (3.94 g, 19.0 mmol), KOH (1.40 g) and
CuSO4ꢀ5H2O (0.075 g) by method 1, which gave 1.24 g
(23%) of the product. Anal. calc. for C20H15N3 : C, 80.8; H,
5.1; N, 14.1. Found: C, 81.7; H, 5.4; N, 14.2%. EI MS: m/z
296 (100%, Mþ). 1H NMR (CDCl3): d 8.34 (2H, d; pyridyl
H6), 7.8–7.9 (2H, m; naphthyl), 7.69 (1H, m; naphthyl),
7.52–7.62 (3H, m; pyridyl H4 and one naphthyl H), 7.42
(2H, m; naphthyl), 7.33 (1H, dd; naphthyl), 7.05 (2H, d; pyri-
dyl H3), 6.95 (2H, ddd; pyridyl H5).
1
N, 16.1%. EIMS: m/z 440 (100%, Mþ). H NMR (CDCl3): d
9.28 (1H, d; naphthyl), 8.39 (2H, d; pyridyl H6), 8.27 (1H, d;
naphthyl), 8.16 (2H, d; phenyl), 8.05 (1H, d; naphthyl), 7.95
(1H, d; naphthyl), 7.58–7.75 (5H, m; pyridyl H4 and three
naphthyl H), 7.32 (2H, d; phenyl), 7.08 (2H, d; pyridyl H3);
7.03 (2H, ddd; pyridyl H5).
Synthesis of rhenium(I) complexes with 2,20-dipyridylamine
derivatives
NMe. This was prepared from dpa (3.03 g, 17.7 mmol), 4-
bromo-N,N-dimethylaniline (3.80 g, 19.0 mmol), KOH (1.40
g) and CuSO4ꢀ5H2O (0.075 g) by method 1, which gave
1.055 g (21%) of the product. The green-blue oil obtained after
column chromatography was sonicated with hexane to give a
dark red solution and a pale-green solid: the solid was filtered
off and recrystallized twice from a small amount of ethanol
The complexes were prepared by refluxing Re(CO)5Cl and
the appropriate ligand, in a 1:1 molar ratio (or, in some cases,
using excess of ligand) in degassed toluene (30 cm3) for 24 h
under N2 . In the course of the reaction the solution changed
its colour to pale yellow and a white/yellow precipitate
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 3 9 8 – 4 0 5
399

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formed. The reaction mixture was evaporated to dryness;
the residue was purified by column chromatography on
alumina eluting with CH2Cl2 , unless stated otherwise. The
chromatography was followed with the use of a hand-held
UV lamp (365 nm). The fraction containing the product
(non-luminescent, unless stated otherwise) was collected,
reduced in volume and the complex precipitated by addition
of hexane; the product was filtered off, washed with hexane
and ether, and finally dried under vacuum. All new complexes
are air- and moisture-stable white solids which are soluble in
acetone, chlorinated solvents and tetrahydrofuran, but insolu-
ble in hexane and ether.
for C25H16BrClN3O3Re: C, 42.4; H, 2.3; N, 5.9. Found: C,
42.4; H, 2.2; N, 5.5%. IR (CH2Cl2 , cmꢂ1): 2023, 1917, 1889.
FABMS: m/z 730 (10%, {M þ Na}þ), 707 (50%, Mþ), 679
(14%, {M ꢂ CO}þ), 672 (100%, {M ꢂ Cl}þ), 623 (24%,
{M ꢂ 3CO}þ).
[Re(CO)3Cl(NMe)]. Re(CO)5Cl (100 mg, 0.28 mmol) and
NMe (80 mg, 0.28 mmol) gave 117 mg (71%) of the product.
Anal. calc. for C21H18ClN4O3Re: C, 42.3; H, 3.0; N, 9.4.
Found: C, 42.5; H, 3.0; N, 9.5%. IR (CH2Cl2 , cmꢂ1): 2022,
1915, 1888. FABMS: m/z 619 (50%, {M þ Na}þ), 596 (13%,
{M}þ), 561 (95%, {M ꢂ Cl}þ).
[Re(CO)3Cl(TPPD)]. Re(CO)5Cl (105 mg, 0.29 mmol) and
TPPD (230 mg, 0.55 mmol) gave 120 mg (57%) of the product
which was eluted as a yellow-green luminescent fraction. Anal.
calc. for C29H20ClN6O3Re: C, 48.2; H, 2.8; N, 11.6. Found: C,
48.7; H, 2.5; N, 11.2%. IR (CH2Cl2 , cmꢂ1): 2023, 1917, 1889.
FAB MS: m/z 723 (55%, Mþ), 687 (35%, {M ꢂ Cl}þ).
[Re(CO)3Cl(DP18C6)]. Re(CO)5Cl (100 mg, 0.28 mmol) and
DP18C6 (133 mg, 0.28 mmol) gave 122 mg (56%) of the pro-
duct which was eluted with acetone/CH2Cl2 (starting with 0/
100 v/v and changing gradually to 50/50 v/v) as a yellow-
green-luminescent fraction. The product is only slightly soluble
in THF. Anal. calc. for C29H31ClN3O9Re: C, 44.2; H, 4.0; N,
5.3. Found: C, 44.6; H, 3.1; N, 4.8%. IR (CH2Cl2 , cmꢂ1):
2022, 1916, 1886. FABMS: m/z 810 (30%, {M þ Na}þ), 787
(25%, {M}þ), 752 (100%, {M ꢂ Cl}þ), 703 (15%,
{M ꢂ 3CO}þ).
[Re(CO)3Cl(2-TPA)]. Re(CO)5Cl (104 mg, 0.29 mmol) and
2-TPA (78 mg, 0.31 mmol) gave 125 mg (78%) of the product.
Anal. calc. for C18H12ClN4O3Re: C, 39.0; H, 2.2; N, 10.1.
Found: C, 38.9; H, 2.0; N, 9.7%. IR (CH2Cl2 , cmꢂ1): 2024,
1919, 1897. FABMS: m/z 577 (3%, {M þ Na}þ), 554 (18%,
Mþ), 526 (12%, {M ꢂ CO}þ), 519 (100%, {M ꢂ Cl}þ), 498
(22%, {M ꢂ 2CO}þ), 470 (10%, {M ꢂ 3CO}þ).
X-ray crystallography
X-Ray quality crystals were grown for [Re(CO)3Cl(2-TPA)]
a
and [Re(CO)3Cl(3-TPA)] by slow evaporation from
[Re(CO)3Cl(3-TPA)]. Re(CO)5Cl (100 mg, 0.28 mmol) and
3-TPA (73 mg, 0.29 mmol) gave 20 mg (14%) of the product
which was eluted with acetone/CH2Cl2 (starting with 0/100
v/v and changing gradually to 5/95 v/v). Anal. calc. for
C18H12ClN4O3Re: C, 39.0; H, 2.2; N, 10.1. Found: C, 39.5;
H, 2.3; N, 9.8%. IR (CH2Cl2 , cmꢂ1): 2024, 1920, 1894.
FABMS: m/z 577 (9%, {M þ Na}þ), 555 (7%, Mþ), 519
(12%, {M ꢂ Cl}þ).
CH2Cl2/hexane solution of each complex; for [Re(CO)3-
Cl(NMe)] and [Re(CO)3Cl(NAP)] by slow evaporation of a
THF/heptane solution; and for [Re(CO)3Cl(DP18C6)] by slow
cooling of a hot THF solution of the complex. For each com-
plex a suitable crystal was coated with hydrocarbon oil and
attached to the tip of a glass fibre, which was then transferred
to a Bruker-AXS SMART or APEX diffractometer under a
stream of cold N2 at 173 K (SMART instrument) or 100 K
(APEX instrument). Details of the crystal parameters, data
collection and refinement for each of the structures are col-
lected in Table 1. After data collection, in each case an empiri-
cal absorption correction (SADABS) was applied,18 and the
structures were then solved by conventional direct methods
and refined on all F2 data using the SHELX suite of pro-
grams.19 In all cases non-hydrogen atoms were refined with
anisotropic thermal parameters; hydrogen atoms were
included in calculated positions and refined with isotropic
thermal parameters which were ca. 1.2x (aromatic CH) or
1.5x (Me) the equivalent isotropic thermal parameters of their
parent carbon atoms. The refinements proceeded smoothly
[Re(CO)3Cl(NAP)]. Re(CO)5Cl (100 mg, 0.28 mmol) and
NAP (83 mg, 0.28 mmol) gave 80 mg (48%) of the product.
Anal. calc. for C23H15ClN3O3Re: C, 45.8; H, 2.5; N, 7.0.
Found: C, 45.4; H, 2.4; N, 6.9%. IR (CH2Cl2 , cmꢂ1): 2023,
1917, 1889. FABMS: m/z 626 (12%, {M þ Na}þ), 603 (50%,
Mþ), 576 (12%, {M ꢂ CO}þ), 569 (100%, {M ꢂ Cl}þ), 519
(20%, {M ꢂ 3CO}þ).
[Re(CO)3Cl(BPBr)]. Re(CO)5Cl (0.28 mmol) and BPBr (111
mg, 0.28 mmol) gave 144 mg (74%) of the product. Anal. calc.
Table 1 Crystallographic data.a
Compound
[Re(CO)3Cl(2-TPA)] [Re(CO)3Cl(3-TPA)] [Re(CO)3Cl(NMe)] [Re(CO)3Cl(DP18C6)]ꢀC4H8O [Re(CO)3Cl(NAP)]
Empirical formula
Formula weight
System, space group
T, K
C18H12ClN4O3Re
553.97
¯
triclinic, P1
100(2)
10.975(2)
13.661(2)
14.578(3)
107.544(15)
111.036(13)
102.713(17)
1808.1(6)
4
C18H12ClN4O3Re
553.97
¯
triclinic, P1
100(2)
11.125(4)
14.259(4)
14.454(6)
98.149(15)
111.39(2)
112.669(15)
1860.5(11)
4
C21H18ClN4O3Re
596.05
monoclinic, P21/n
173(2)
9.1998(15)
21.486(4)
21.451(4)
90
93.700(4)
90
4231.3(12)
8
1.871
9673, 0, 545
5.900
0.0274, 0.0534
C33H39ClN3O10Re
859.32
¯
triclinic, P1
100(2)
11.170(4)
11.937(4)
16.536(5)
74.20(3)
80.21(4)
62.56(2)
1880.3(11)
2
C23H15ClN3O3Re
603.03
¯
triclinic, P1
100(2)
12.1864(13)
13.9338(15)
14.076(2)
61.504(12)
85.830(8)
79.965(9)
2068.3(5)
4
˚
a, A
˚
b, A
˚
c, A
a, deg
b, deg
g, deg
3
˚
V, A
Z
Calcd density, Mg mꢂ3
2.035
Data/restraints/parameters 8268, 0, 487
1.978
1.518
1.937
8189, 0, 481
6.701
0.0481, 0.1146
8612, 0, 433
3.357
0.0371, 0.0743
9457, 0, 559
6.036
0.0259, 0.0561
m(mmꢂ1
)
6.895
0.0322, 0.0650
R1, wR2 [I > 2s(I)]b
a
b
˚
Data in common: l ¼ 0.71073 A. The value of R1 is based on selected data with I > 2s(I); the value of wR2 is based on all data.
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 3 9 8 – 4 0 5
400
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4

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ꢁ
˚
Table 2 Selected bond distances (A) and angles ( ) for the new
structures
[Re(CO)3Cl(NMe)] and [Re(CO)3Cl(NAP)] there are two
crystallographically independent molecules in the asymmetric
unit in each case.
[Re(CO)3Cl(2-TPA)]
Re(1)–C(51)
1.897(5)
1.922(5)
1.925(5)
2.194(4)
2.210(4)
2.4706(13)
80.26(14)
118.2(4)
118.0(4)
123.7(4)
58.0
Re(2)–C(161)
Re(2)–C(141)
1.904(5)
1.909(5)
1.912(5)
2.195(4)
2.198(4)
2.4759(15)
81.79(14)
117.8(4)
123.6(4)
117.6(4)
58.7
Re(1)–C(61)
Re(1)–C(41)
Re(1)–N(11)
Optical spectroscopy
Re(2)–C(151)
Re(2)–N(121)
Samples of the investigated compounds were purified by col-
umn chromatography on alumina eluting with CH2Cl2 or acet-
one/CH2Cl2 before proceeding with optical studies, so to
remove trace luminescent impurities. Absorption spectra of
dilute dichloromethane solutions (2 ꢃ 10ꢂ5 M) were obtained
with a Perkin-Elmer Lambda 5 spectrophotometer. Lumines-
cence spectra were obtained with a Spex Fluorolog II spectro-
fluorimeter, equipped with a Hamamatsu R928 phototube.
Sample solutions were excited at the indicated wavelength,
and dilution was adjusted to obtain absorbance values
ꢄ0.15. While uncorrected luminescence band maxima are used
throughout the text, corrected spectra were employed for the
determination of the luminescence quantum yields. The correc-
tion procedure is based on use of a software which takes care
of the wavelength dependent phototube response. From the
area of the corrected luminescence spectra on an energy scale
(cmꢂ1), we obtained luminescence quantum yields F for the
samples with reference to [Ru(bpy)3]Cl2 or quinine sulfate as
standards (r, Fr ¼ 0.028 in air-equilibrated water,20 and 0.546
in 1 N H2SO4 ,21 respectively), and by using eqn. (1):22
Re(1)–N(21)
Re(1)–Cl(1)
Re(2)–N(111)
Re(2)–Cl(2)
N(11)–Re(1)–N(21)
C(12)–N(1)–C(22)
C(12)–N(1)–C(32)
C(22)–N(1)–C(32)
Py1/py2a
N(121)–Re(2)–N(111)
C(132)–N(2)–C(122)
C(132)–N(2)–C(112)
C(122)–N(2)–C(112)
Py1/py2a
substituentb
10.4
substituentb
15.3
[Re(CO)3Cl(3-TPA)]
Re(1)–C(41)
Re(1)–C(61)
1.895(10)
1.907(9)
1.911(9)
2.194(6)
2.201(6)
2.479(2)
80.8(2)
121.0(6)
122.1(6)
116.0(6)
61.4
Re(2)–C(151)
Re(2)–C(161)
1.897(9)
1.910(10)
1.939(8)
2.188(7)
2.200(7)
2.466(2)
81.8(2)
126.3(7)
116.8(7)
116.0(7)
60.1
Re(1)–C(51)
Re(1)–N(11)
Re(2)–C(141)
Re(2)–N(111)
Re(1)–N(21)
Re(1)–Cl(1)
Re(2)–N(121)
Re(2)–Cl(2)
N(11)–Re(1)–N(21)
C(33)–N(1)–C(22)
C(33)–N(1)–C(12)
C(22)–N(1)–C(12)
Py1/py2a
N(111)–Re(2)–N(121)
C(133)–N(2)–C(122)
C(133)–N(2)–C(112)
C(122)–N(2)–C(112)
Py1/py2a
substituentb
7.4
substituentb
19.9
[Re(CO)3Cl(NMe)]
Re(1)–C(61)
Re(1)–C(71)
1.905(4)
1.906(4)
1.907(5)
2.178(3)
2.182(3)
2.4666(11)
79.89(12)
122.7(3)
117.4(3)
116.8(3)
41.6
Re(2)–C(161)
Re(2)–C(171)
1.912(4)
1.914(4)
1.932(4)
2.188(3)
2.191(3)
2.4765(10)
79.29(11)
124.3(3)
116.2(3)
117.4(3)
39.2
F
Absr n2ðareaÞ
Re(1)–C(51)
Re(1)–N(11)
Re(2)–C(151)
Re(2)–N(121)
¼
ð1Þ
Fr Abs n2r ðareaÞr
Re(1)–N(21)
Re(1)–Cl(1)
Re(2)–N(111)
Re(2)–Cl(2)
where Abs and n are absorbance value of the solution and the
refractive index of the solvent, respectively. Band maxima and
relative luminescence intensities were affected by an uncer-
tainty of 2 nm and 20%, respectively. Luminescence lifetimes
were obtained using an IBH single-photon counting spectro-
meter equipped with a nitrogen-filled thyratron gated lamp
(lexc 337 or 358 nm). The uncertainty in the lifetime values is
within 8%.
N(11)–Re(1)–N(21)
C(22)–N(31)–C(12)
C(22)–N(31)–C(31)
C(12)–N(31)–C(31)
Py1/py2a
N(121)–Re(2)–N(111)
C(112)–N(131)–C(122)
C(112)–N(131)–C(131)
C(122)–N(131)–C(131)
Py1/py2a
substituentb
89.5
substituentb
88.1
[Re(CO)3Cl(DP18C6)]ꢀC4H8O
Re(1)–C(31)
Re(1)–C(41)
1.911(4)
1.911(4)
1.950(5)
2.175(3)
2.179(3)
2.4575(16)
78.82(12)
123.7(3)
116.4(3)
115.3(3)
40.5
Re(1)–C(51)
Re(1)–N(21)
Results and discussion
Syntheses of 2,20-dipyridylamine derivatives and their
rhenium(I) carbonyl chloride complexes
Re(1)–N(11)
Re(1)–Cl(1)
N(21)–Re(1)–N(11)
C(12)–N(1)–C(22)
C(12)–N(1)–C(61)
C(22)–N(1)–C(61)
Py1/py2a
The new ligands (listed in Scheme 1) were prepared by the solid
state reaction of 2,20-dipyridylamine with the appropriate
bromo-substituted aromatic derivative in the presence of base
and a catalytic amount of Cu(II) following the routes described
in the literature.9,10 The use of K2CO3 instead of KOH, and
the efficient pre-mixing of reagents provided by method 2
(see Experimental section), gave better results than method 1.
The same conclusion was reached by Pang and co-workers.10
The 2,20-dipyridylamine derivatives are insoluble in cold
ethanol and usually could be easily separated from starting
materials by recrystallization from ethanol; they were
successfully characterised on the basis of their NMR and elec-
tron-impact mass spectra, as well as correct elemental analyses.
The new rhenium(I) carbonyl chloride complexes of some of
these ligands were prepared in generally good (40–80%) yield
by reacting Re(CO)5Cl with the appropriate ligand in toluene,
followed by column chromatography on alumina. The low
yield (14%) of [Re(CO)3Cl(3-TPA)] may, on the basis of mass
spectral evidence, be due to the formation of the complex
[Re(CO)3Cl(k1-3-TPA)2] in which Re(I) is coordinated to two
monodentate 3-TPA ligands, presumably through the nitrogen
atoms of the 3-pyridine ring. This material however could not
be isolated in pure form. All isolated Re(I) complexes gave cor-
rect elemental analyses and showed strong molecular ions in
their FAB mass spectra (along with predictable fragmentation
patters due to loss of chloride and CO ligands). Three strong
substituentb
94.5
[Re(CO)3Cl(NAP)]
Re(1)–C(31)
Re(1)–C(51)
1.901(4)
1.913(4)
1.918(4)
2.178(3)
2.180(3)
2.4774(9)
81.25(10)
124.7(3)
116.3(3)
116.4(3)
35.5
Re(2)–C(151)
Re(2)–C(141)
1.909(4)
1.910(4)
1.911(4)
2.193(3)
2.200(3)
2.4701(9)
80.83(11)
114.3(3)
120.3(3)
122.7(3)
65.8
Re(1)–C(41)
Re(1)–N(21)
Re(2)–C(131)
Re(2)–N(111)
Re(1)–N(11)
Re(1)–Cl(1)
Re(2)–N(121)
Re(2)–Cl(2)
N(21)–Re(1)–N(11)
C(12)–N(1)–C(22)
C(12)–N(1)–C(2)
C(22)–N(1)–C(2)
Py1/py2a
N(111)–Re(2)–N(121)
C(112)–N(2)–C(122)
C(112)–N(2)–C(102)
C(122)–N(2)–C(102)
Py1/py2a
substituentb
90.0
substituentb
26.0
a
Angle between the mean planes of the two coordinated pyridyl rings of the
di(2-pyridyl)amine unit b Angle between the mean planes of the pendant substi-
tuent on the di(2-pyridyl)amine unit, and the mean plane defined by the amine N
atom and the two pyridyl C2 atoms (e.g. for [Re(CO)3Cl(2-TPA)], the angle
between the pendant pyridyl ring and the N(1)/C(12)/N(22) plane).
without any significant problems. For [Re(CO)3Cl(DP18C6)]ꢀ
C4H8O and [Re(CO)3Cl(NMe)] a diffuse solvent correction was
applied to eliminate areas of residual electron density which
could not successfully be modelled as solvent molecules. In
the structures of [Re(CO)3Cl(2-TPA)], [Re(CO)3Cl(3-TPA)],
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 3 9 8 – 4 0 5
401

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Fig. 1 Structure of [Re(CO)3Cl(2-TPA)] (only one of the two
independent molecules is shown).
Scheme 1 Ligands described in this paper.
carbonyl absorption bands were observed for rhenium(I) com-
plexes in the IR region. Complexes were prepared with six of
the ligands, as listed in the Experimental section, and the lumi-
nescence properties of these complexes are discussed below.
The remaining ligands yielded Re complexes which were
poorly soluble and could not be purified by crystallisation or
chromatography to an extent sufficient for luminescence stu-
dies, so in these cases only the luminescence properties of the
ligands are reported.
Fig. 2 Structure of [Re(CO)3Cl(3-TPA)] (only one of the two
independent molecules is shown).
is even more variable; in one of the independent molecules in
[Re(CO)3Cl(3-TPA)] the pendant 3-pyridyl ring [atoms N(31)
to C(36), Fig. 2)] is almost coplanar with the plane of atoms
N(1), C(12) and C(22), whereas in [Re(CO)3Cl(NMe)] the cor-
responding angle, between the pendant phenyl ring and the
C(12)/N(31)/C(22) plane is 89.5ꢁ. The variability of this para-
meter is particularly evident in the two crystallographically
independent molecules of [Re(CO)3Cl(NAP)], where in one
case the naphthyl ring is exactly perpendicular to the adjacent
NC2 plane but in the second case the angle is only 26ꢁ.
Structures of rhenium(I) carbonyl chloride complexes with
2,20-dipyridylamine derivatives
The crystal structures of the five complexes [Re(CO)3Cl(2-
TPA)], [Re(CO)3Cl(3-TPA)], [Re(CO)3Cl(NMe)], [Re(CO)3Cl-
(DP18C6)] and [Re(CO)3Cl(NAP)] are shown in Figs. 1 to 5
respectively. In every case except [Re(CO)3Cl(DP18C6)], there
are two crystallographically independent molecules in the
asymmetric unit of which only one is shown. Selected bond
distances and angles are in Table 2.
In all cases the dipyridylamine ligand is coordinated as a
bidentate chelate via the two 2-pyridyl groups, giving a 6-mem-
bered chelate ring. The bond distances and angles around the
pseudo-octahedral Re centres are similar between the com-
plexes and unremarkable. In every case the central (tertiary
amine) N atom of the dipyridylamine ligand is nearly planar,
as shown by the fact that the sum of the three C–N–C angles
is close to 360ꢁ. The angle between the mean planes of the
coordinated pyridyl rings varies between ca. 35ꢁ and 61ꢁ across
the series of complexes. The orientation of the third substituent
Fig. 3 Structure of [Re(CO)3Cl(NMe)] (only one of the two indepen-
dent molecules is shown).
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
402
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 3 9 8 – 4 0 5

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Fig. 4 Structure of [Re(CO)3Cl(DP18C6)]ꢀthf (solvent molecule not
shown).
Fig. 6 Ground state absorption and luminescence spectra of the indi-
cated ligands in dichloromethane (lexc ¼ 330 nm for the luminescence
spectra).
nm is probably due to (predominant) amine N-to ring CT
transitions, as expected for aromatic amines.12 Higher-lying
features in the 250–270 nm region are ascribable to pyri-
dine-based (LC) transitions. In some cases, the distinct profile
for an aryl residue is easily identified. For instance, the typical
well resolved pyrene-based absorption (250–300 nm)23 is
found in the spectrum of DPAPYR (not shown in Fig. 6).
The luminescence band maximum for the ligands is found to
vary from 374 to 512 nm, Table 3, which represents an inter-
esting outcome having in mind the possible utilisation of these
compounds in the OLED technology.9,10 The luminescence
profiles are broad and this might be traced back to the CT
character for the emitting level. The ligands exhibit good lumi-
nescence intensities and lifetimes on the nanosecond time scale,
as expected for this type of amines.9–12 The luminescence
quantum yield, F, is however a changeable figure in the series,
see Table 3. On one extreme, very high values for F (not far
from unity), are found for X1P, DPAPPYR, and X1N. On
the contrary, for NMe, the luminescence intensity is the poor-
est in the series. This may be due to a combination of at least
two factors: the presence of an aliphatic amine centre and the
energy gap law for radiationless transitions. For the former
issue, it is known that the aliphatic amine centres may act as
electron donors,23 provided some energetic requirements are
met, thus causing luminescence quenching of the interacting
excited unit. For the latter issue, one may notice that for
NMe the detected luminescent level is the lowest in energy
within the studied series. This is precisely the condition for
enhanced radiationless rate constants in accord with the
‘‘energy gap law’’.24
Fig. 5 Structure of [Re(CO)3Cl(NAP)] (only one of the two indepen-
dent molecules is shown).
Optical spectroscopy
In Table 3 are collected relevant absorption features, lumines-
cence band maxima, and luminescence quantum yields and
lifetimes for the investigated 2,20-dipyridylamine derivatives.
Fig. 6 displays absorption and luminescence spectra for six
of these compounds. Data for the Re(I) complexes of the latter
group of ligands is collected in Table 4. All results
were obtained at room temperature in air-equilibrated
dichloromethane. For the luminescence studies lexc was 330 nm
(steady state spectra) or 337 nm (lifetimes); no dependence
on excitation wavelength was observed. Within Tables 3 and 4,
we have arbitrarily listed the compounds by sorting out an
increasing value for the emission wavelength, lem
.
The ligand absorption profiles illustrated in Fig. 6 (and
described in Table 3) are characterized by two band maxima
(or one maximum and a shoulder) in the 270–370 nm portion
of the UV region. The lowest-energy band around 300–310
Absorption and luminescence properties of the Re(I) com-
plexes of some of the dipyridylamines studied are summarized
in Table 4; only those complexes that were sufficiently soluble
Table 3 Spectroscopic and photophysical parameters for the investi-
gated ligandsa
Emissionb
Absorption
abs/nm (e/Mꢂ1cmꢂ1
l
)
lem/nm
F
t/ns
Table 4 Spectroscopic and photophysical parameters for the investi-
gated Re(I) complexes.a
2-TPA
NAP
BPBr
269 (14 700), 297 (19 450)
273 (25 900), 307 (20 800)
275 (sh), 309 (27 700)
343 (30 300)
374
386
390
399
405
415
421
438
452
512
0.08
0.22
0.23
0.69
0.22
0.74
0.73
0.10
0.06
0.01
3.6
1.7
1.0
1.5
4.3
3.9
2.1
5.3
2.5
0.9
Emissionb
Absorption
abs/nm (e/Mꢂ1cmꢂ1
Complex
l
)
lem/nm
F
t/nsc
X1P
2NDPA
DPAPYR
X1N
315 (37 750)
354 (21 000)
349 (34 750)
[Re(CO)3Cl(NAP)] 255 (sh), 293 (18 900)
[Re(CO)3Cl(BPBr)] 263 (32 500), 295 (sh)
[Re(CO)3Cl(DP18C6)] 251 (19 600), 295 (17 400)
—
—
—
—
—
—
—
—
—
DP18C6
TPPD
NMe
279 (15 000), 293 (15 100)
280 (sh), 306 (33 400)
279 (21 200), 311 (sh)
[Re(CO)3Cl(2-TPA)]
[Re(CO)3Cl(TPPD)]
[Re(CO)3Cl(NMe)]
266 (13 900), 307 (16 000) 492
259 (22 000), 304 (22 600) 516
263 (30 000), 296 (21 000) 582
<10ꢂ5 nd
0.04 42
<10ꢂ5 nd
a
b
a
b
At room temperature, in dichloromethane solvent. Excitation performed at
At room temperature, in dichloromethane solvent. Excitation
performed at l ¼ 330 nm for steady-state spectra, and at 337 nm for
lifetime measurements.
l ¼ 330 nm for steady-state spectra, and at 337 nm for lifetime measurements.
c
nd ¼ not detected.
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 3 9 8 – 4 0 5
403

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to be re-purified by chromatography and recrystallisation were
analysed. In general terms, the intense absorption bands in the
UV region should be associated with LC and CT transitions
centred on the corresponding dipyridylamine unit. These
bands are likely to obscure the much weaker MLCT features,
which appear as an additional tail towards the visible
region.13–15 For illustration purposes, in Fig. 7 are compared
the absorption spectra for TPPD and [Re(CO)3Cl(TPPD)].
Regarding the luminescence properties of the Re(I) complexes,
we notice that [Re(CO)3Cl(TPPD)] is the only one showing a
moderate luminescence intensity, Fig. 7 and Table 4. Its lumi-
nescence quantum yield, band maximum, lifetime, and the
broad luminescence profile are all consistent with a Re-to-L
CT nature for the emission.13–15 The other complexes show
essentially no (or very weak) luminescence apart from what
can obviously be ascribed to very small (<0.1%) traces of the
luminescent free ligand. At any rate, for all cases but one,
the Re(I) complexes are practically not luminescent, in contrast to
the strong luminescence intensity of the incorporated dipyridyl-
amine ligand. In order to discuss possible reasons for this
behavior, we notice that (i) the Re ! L CT lowest-lying level
is always expected to be lower in energy than the (formerly
luminescent) level centred on the coordinated amine unit (see
Tables 3 and 4), and that (ii) coordination of the ligand at
the Re(I) centre takes place with formation of a 6-membered
chelate ring (see above), as opposed to a 5-membered one
for most luminescent Re(I)-polypyridine complexes.13–15 This
is likely to result in a lower ligand field strength for the present
cases. As a consequence, lower-lying, thermally accessible d–d
MC levels could provide an efficient non-radiative path for dis-
posal of the excitation energy in the Re(I) complexes reported
here. This behaviour is well known for derivatives of
[Ru(bipy)3]2þ in which the ligand field strength around the
metal is reduced by steric distortions,25 and has recently been
demonstrated for a range of Re(I)-tricarbonyl-diimine com-
plexes,26 although it should be noted that a range of other
non-radiative decay pathways are in principle available.15c,26
Acknowledgements
We thank the Royal Society/NATO for a post-doctoral
fellowship to N.M.S.
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In conclusion, we have prepared a new series of ligands based
on the dpa core, which show moderate to strong luminescence.
Several of their complexes with {Re(CO)3Cl} units have been
prepared and structurally characterised; with one exception
these are non-luminescent, the exception from [Re(CO)3-
Cl(tppd)] in which one di(2-pyridyl)amine site is occupied by
a {Re(CO)3Cl} unit but the other is vacant.
9
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Fig. 7 Ground state absorption spectrum and luminescence spec-
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methane.
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
404
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 3 9 8 – 4 0 5

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