Synthesis and luminescence behaviour of rhenium(I) diynyl complexes. X-Ray crystal structures of [Re(CO)3(tBu2bpy)(C≡C-C≡CH)] and [Re(CO)3(tBu2bpy)(C≡C-C≡CPh)]

Article abstract of DOI:10.1039/a804775h

Luminescent rhenium(I) diynyl complexes [Re(CO)₃(^tBu₂-bpy)(C≡C-C≡CH)] and [Re(CO)₃(^tBu₂bpy)(C≡C-C≡CPh)] were synthesized and their photophysical properties studied; the crystal structures h

Full text of DOI:10.1039/a804775h

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Synthesis and luminescence behaviour of rhenium( ) diynyl complexes. X-Ray
I
crystal structures of [Re(CO)3(tBu2bpy)(C°C–C°CH)] and
[Re(CO)3(tBu2bpy)(C°C–C°CPh)]
Vivian Wing-Wah Yam,* Samuel Hung-Fai Chong and Kung-Kai Cheung
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, People’s Republic of China.
E-mail: wwyam@hkucc.hku.hk
Luminescent rhenium(
I
) diynyl complexes [Re(CO)3(tBu2-
and
[Re(CO)3(tBu2bpy)(C°C–
than 1 is consistent with the better s- and p-donating abilities of
PhC°C–C°C than HC°C–C°C,1j,8,9 which render the Re(
)
bpy)(C°C–C°CH)]
I
C°CPh)] were synthesized and their photophysical proper-
ties studied; the crystal structures have also been deter-
mined.
centre more electron rich, and raise the Re dp orbital energy.
Similar trends have been observed in the related alkynyl system
[Re(CO)3(tBu2bpy)X],3 in which the MLCT absorption band
occurs at higher energy for X = HC°C than when X =
PhC°C.
There has been a rapidly growing interest in the chemical and
physical properties of Cn-bridged metal-containing materials,1
in view of their potential applications as nonlinear optical
materials, molecular wires, and molecular electronics. With the
recent reports on the successful isolation of acetylide-bridged
Excitation of 1 and 2 both in the solid state and in fluid
solutions at room temperature at l > 400 nm resulted in strong
3
orange luminescence, attributed to the MLCT phosphores-
cence. The excitation spectra of 1 and 2 in THF show excitation
bands at ca. 400 nm and 410 nm, respectively, which closely
resemble those of the MLCT absorption maxima. The photo-
physical data are summarized in Table 1. The slightly lower
MLCT emission energy of 2 than 1 in THF is in line with the
stronger s- and p-donating abilities of the phenyldiynyl unit
than the butadiynyl ligand, i.e. PhC°C–C°C (625 nm) <
HC°C–C°C (620 nm). Similar trends have been observed in
the monoacetylide analogues [PhC°C (688 nm) < HC°C (670
nm)].3 It is interesting to note that both 1 and 2 emit at higher
energies than their respective monoacetylide counterparts, i.e.
in the [Re(CO)3(tBu2bpy)X] system, the emission energies in
THF follow the order: HC°C–C°C (620 nm) > HC°C (670
nm); PhC°C–C°C (625 nm) > PhC°C (688 nm). The
observation of a blue shift in emission energies upon increasing
rhenium(
incorporating metal-to-ligand charge transfer (MLCT) excited
I
) organometallics1a–g,2 and our recent efforts in
states into rhenium( ) acetylide units to make luminescent rigid-
I
rod materials,3 we have extended our work to employ the diynyl
unit as the ligand to extend the carbon chain. Herein are reported
the synthesis, structure and luminescence behaviour of two
rhenium(
I
)
diynyl complexes, [Re(CO)3(tBu2bpy)(C°C–
C°CH)] 1 and [Re(CO)3(tBu2bpy)(C°C–C°CPh)] 2.
Reaction of a mixture of [Re(CO)3(tBu2bpy)Cl],4 KF, AgOTf
and Me3SiC°C–C°CSiMe3 in a 1 : 1 : 1 : 3 ratio in MeOH
under reflux conditions in an inert atmosphere of nitrogen for 24
h afforded [Re(CO)3(tBu2bpy)(C°C–C°CH)], which was
isolated as orange crystals after purification by column
chromatography on silica gel using dichloromethane as eluent,
followed by recrystallization from dichloromethane–diethyl
ether. On the other hand, reaction of a mixture of
[Re(CO)3(tBu2bpy)Cl], AgOTf, NEt3 and PhC°C–C°CH5 in
a 1 : 1 : 2 : 1.5 ratio in refluxing THF under nitrogen for 24 h
afforded [Re(CO)3(tBu2bpy)(C°C–C°CPh)]. Purification by
column chromatography on silica gel using dichloromethane–
light petroleum (1 : 1 v/v) as eluent, followed by subsequent
recrystallization from dichloromethane–light petroleum yielded
[Re(CO)3(tBu2bpy)(C°C–C°CPh)] as yellow crystals. The
identities of both complexes 1 and 2 have been confirmed by
1
satisfactory elemental analyses, H NMR spectroscopy, FAB-
MS,† and X-ray crystallography.‡
Fig. 1 and 2 depict the perspective drawings of complexes 1
and 2 with atomic numbering, respectively. Both structures
show a slightly distorted octahedral geometry about Re with the
three carbonyl ligands arranged in a facial fashion. The N–Re–
N bond angles of 74.6(2) and 73.9(1)° for 1 and 2, respectively,
are less than 90°, as required by the bite distance exerted by the
steric demand of the chelating bipyridine ligand. The two C°C
bond lengths are 1.199(10) and 1.19(1) Å for 1 and 1.198(7) and
1.189(7) Å for 2, which are comparable to those found for
diynyl systems.1d,6 The Re–C°C–C°C units are essentially
linear with bond angles of 175.2(6)–179.8(10) and
175.7(5)–178.6(6)° for 1 and 2, respectively.
Fig. 1 Perspective drawing of complex 1 with atomic numbering. Hydrogen
atoms have been omitted for clarity. Thermal ellipsoids are shown at the
50% probability level. Selected bond distances (Å) and bond angles (°):
Re(1)–C(1) 1.946(9), Re(1)–N(1) 2.168(5), Re(1)–N(2) 2.183(4), Re(1)–
C(4) 2.114(8), C(4)–C(5) 1.199(10), C(6)–C(7) 1.19(1), N(1)–Re(1)–N(2)
74.6(2), N(1)–Re(1)–C(2) 171.1(2), C(1)–Re(1)–C(4) 174.4(3),
C(4)–C(5)–C(6) 178.3(8), C(5)–C(6)–C(7) 179.8(10).
The electronic absorption spectra of 1 and 2 show intense
absorption bands at ca. 404 and 416 nm, respectively, in
tetrahydrofuran. With reference to previous spectroscopic work
on rhenium(
) diimine systems,3,4,7 the intense low energy
I
absorption is tentatively assigned as the dp(Re) ? p*(tBu2bpy)
MLCT transition. The lower MLCT absorption energy for 2
Chem. Commun., 1998
2121

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Notes and References
† 1: 1H NMR (300 MHz, acetone-d6, 298 K, relative to TMS): d 1.40 (s,
18H, tBu), 1.75 (s, 1H, C°CH), 7.70 (dd, 2H, 5- and 5A-pyridyl Hs), 8.60 (d,
2H, 3- and 3A-pyridyl Hs), 8.80 (d, 2H, 6- and 6A-pyridyl Hs). Positive FAB-
MS: ion clusters at m/z 588 {M}+, 560 {M 2 CO}+, 539 {M 2 [C°C–
C°CH]}+. UV–VIS [l/nm (e/dm3mol21cm21)]: THF, 248(16410),
284(17130), 404(3470); CH2Cl2, 310(6100), 396(2690). Elemental analy-
ses. Found: C 50.44, H 4.31, N 4.31. Calc. for 1·0.5H2O: C 50.29, H 4.36,
N 4.69%. 2: 1H NMR (300 MHz, acetone-d6, 298 K, relative to TMS): d
1.50 (s, 18H, tBu), 7.25 (s, 5H, Ph Hs), 7.80 (dd, 2H, 5- and 5A-pyridyl Hs),
8.70 (d, 2H, 3- and 3A-pyridyl Hs), 8.90 (d, 2H, 6- and 6A-pyridyl Hs).
Positive FAB-MS: ion clusters at m/z 665 {M}+, 636 {M 2 CO}+, 539 {M
2
[C°C–C°CPh]}+. UV–VIS [l/nm (e/dm3mol21cm21)]: THF,
298(48570), 340(14610), 416(3220).
‡ Crystal data for 1: [C25H25O3N2Re], M = 587.69, monoclinic, space
group P21/n (no. 14), a = 11.273(3), b = 12.748(1), c = 17.168(2) Å, b =
97.60(4)°, V = 2445.7(7) Å3, Z = 4, Dc = 1.596 g cm23, m(Mo-Ka) =
49.97 cm21, F(000) = 1152, T = 301 K. Convergence for 280 variable
parameters by least-squares refinement on F with w = 4Fo2/s2(Fo2), where
s2(Fo2) = [s2(I) + (0.025Fo2)2] for 2847 reflections with I > 3s(I) was
reached at R = 0.028 and wR = 0.034 with a goodness-of-fit of 1.22. For
2: [C31H29O3N2Re], M = 663.79, monoclinic, space group P21/c (no. 14),
a = 11.048(2), b = 11.795(2), c = 21.935(3) Å, b = 94.23(2)°, V =
2859.9(7) Å3, Z = 4, Dc = 1.542 g cm23, m(Mo-Ka) = 42.83 cm21
,
F(000) = 1312, T = 301 K. Convergence for 334 variable parameters by
least-squares refinement on F with w = 4Fo2/s2(Fo2), where s2(Fo2) =
[s2(I) + (0.030Fo2)2] for 3876 reflections with I > 3s(I) was reached at R
=
0.031 and wR
= 0.040 with a goodness-of-fit of 1.40. CCDC
Fig. 2 Perspective drawing of complex 2 with atomic numbering. Hydrogen
atoms have been omitted for clarity. Thermal ellipsoids were shown at the
50% probability level. Selected bond distances (Å) and bond angles (°):
Re(1)–C(1) 1.913(6), Re(1)–N(1) 2.188(4), Re(1)–N(2) 2.175(4), Re(1)–
C(4) 2.126(5), C(4)–C(5) 1.198(7), C(6)–C(7) 1.189(7), N(1)–Re(1)–N(2)
73.9(1), N(1)–Re(1)–C(1) 171.8(2), C(2)–Re(1)–C(4) 176.3(2),
C(4)–C(5)–C(6) 177.4(6), C(5)–C(6)–C(7) 178.6(6).
182/995.
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Table 1 Photophysical data for complexes 1 and 2
Emission,
Complex
Medium (T/K)
lem/nm (to/ms)
1
THF (298)
CH2Cl2 (298)
Solid (298)
620 ( < 0.1)
604 ( < 0.1)
565 ( < 0.1)
580
Solid (77)
EtOH–MeOH glass (4 : 1 v/v) (77)
THF (298)
Solid (298)
540
2
625 ( < 0.1)
570 ( < 0.1)
570
Solid (77)
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9199.
the C°C unit is in line with the assignment of a 3MLCT [dp(Re)
? p*(tBu2bpy)] origin and disfavours the assignment of a
3MLCT [dp(Re) ? p*(C°C–C°CR)] or a metal-perturbed 3IL
[p(C°C–C°CR) ? p*(C°C–C°CR)] origin. Given the
similar s-donating properties of the monoacetylide versus the
diynyl unit,9 the much better p-accepting ability of RC°C–
C°C than RC°C would become the dominating factor,
stabilizing the Re dp orbitals to a greater extent, and hence give
rise to a higher energy 3MLCT emission.
V. W.-W. Y. acknowledges financial support from the
Research Grants Council and The University of Hong Kong,
and S. H.-F. C. the receipt of a postgraduate studentship,
administered by The University of Hong Kong.
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3522; (b) D. L. Lichtenberger, S. K. Renshaw and R. M. Bullock, J. Am.
Chem. Soc., 1993, 115, 3276.
Received in Cambridge, UK, 23rd June 1998; 8/04775H
2122
Chem. Commun., 1998