Enhanced dual visible light fluorescence from the 2,2′-dipyridyl tungsten alkylidyne complex [W(=CC6H4NMe 2-4)(O2CCF3)(CO)2{K 2-2,2′-(NC5H4)2}]: An organometallic twisted intramolecular charge transfer state

Article abstract of DOI:10.1021/om0493006

The N,N-dimethylanilino tungsten alkylidyne complex [W(≡CC ₆H₄NMe_2-4)CO₂CCF₃(CO) _2- (NC₅H₄Me-₄₎₂] has been synthesized, characterized, and employed as a precursor to neutral and cationic 2,2′-dipyridyl and TMEDA (N,N,N,N-tetramethylethylenediamine) complexes, which display dual blue and yellow fluorescences in CH₂Cl₂ solutions at ambient temperatures with surprisingly high quantum yields for this class of organometallic complex. The efficiencies of the radiative emissions from the 2,2′-dipyridyl complex [W(≡CC₆H ₄NMe_2- 4)(O₂CCF₃)(CO) ₂{k²-2,2′-(NC₅H₄₎₂}] are particularly impressive. The dual nature of the emissions (λ_em ≈ 450 and 540-580 nm) is attributed to independent, short-lived (ns) twisted intramolecular charge transfer (¹TICT) and ¹dw-π*_w-π*_w=≡CAr states, respectively, the former being well understood in organic aromatic systems, but yet to be described for organometallic complexes.

Full text of DOI:10.1021/om0493006

Organometallics 2005, 24, 707-714
707
Enhanced Dual Visible Light Fluorescence from the
2,2′-Dipyridyl Tungsten Alkylidyne Complex
[W(tCC6H4NMe2-4)(O2CCF3)(CO)2{K2-2,2′-(NC5H4)2}]: An
Organometallic Twisted Intramolecular Charge Transfer
State
Paul A. Jelliss* and Keith M. Wampler
Department of Chemistry, Saint Louis University, St. Louis, Missouri 63103
Aleksander Siemiarczuk
Fast Kinetics Application Laboratory, Photon Technology International (Canada) Inc.,
347 Consortium Court, London, Ontario, Canada N6E 2S
Received September 8, 2004
The N,N-dimethylanilino tungsten alkylidyne complex [W(tCC6H4NMe2-4)(O2CCF3)(CO)2-
(NC5H4Me-4)2] has been synthesized, characterized, and employed as a precursor to neutral
and cationic 2,2′-dipyridyl and TMEDA (N,N,N′,N′-tetramethylethylenediamine) complexes,
which display dual blue and yellow fluorescences in CH2Cl2 solutions at ambient temper-
atures with surprisingly high quantum yields for this class of organometallic complex. The
efficiencies of the radiative emissions from the 2,2′-dipyridyl complex [W(tCC6H4NMe2-
4)(O2CCF3)(CO)2{κ2-2,2′-(NC5H4)2}] are particularly impressive. The dual nature of the
emissions (λem ≈ 450 and 540-580 nm) is attributed to independent, short-lived (ns) “twisted
1
intramolecular charge transfer” (1TICT) and dW-π*WtCAr states, respectively, the former
being well understood in organic aromatic systems, but yet to be described for organometallic
complexes.
Introduction
process,4 or in the case of Fischer alkylidynes, to be
activated to further reactivity resulting in ligand-based
transformations or metal-centered radical reactions.3e,5,6
Photoluminescence from metal alkylidyne complexes
has been specifically reviewed by Hopkins.7 Low quan-
The emission of visible light from polypyridyl tungsten-
(0) d6 complexes is well established,1 while the photo-
physics of group 6 metal Fischer alkylidyne complexes,
though somewhat less studied,2 is nevertheless of topical
relevance to the quest for the development of light-
emitting metal complexes for applications in molecular
electronic control, communication, and sensing.3 Photo-
luminescence from low-valent organometallic species is
unusual, given the propensity for such complexes to
undergo ligand dissociation as the primary photo-
tum yield emission of red light (λem ≈ 750 nm, Φem
e
6.9 × 10-4) has been observed with the complexes
[M(tCAr)(CO){P(OMe)3}(η5-C5H5)] (1, M ) W, Mo;
Ar ) Ph, C6H4Me-2, C10H7-2) and attributed to a
3dM-π*MtCAr triplet state.8 Of particular note are the
complexes [W(tCR)Cl(CO)2(κ2-L2)] (2a, R ) Ph, L2 )
TMEDA; 2b, R ) But, L2 ) TMEDA; 2c, R ) Ph, L2 )
2,2′-dipyridyl) (Chart 1).9 Mayr et al. have observed
orange emission (λem ) 640 nm) from complex 2a,
* To whom correspondence should be addressed. E-mail:
jellissp@slu.edu.
(1) (a) Lees, A. J. Coord. Chem. Rev. 1998, 177, 3. (b) Stufkens, D.
J. Coord. Chem. Rev. 1990, 104, 39. (c) Rawlins, K. A.; Lees, A. J. Inorg.
Chem. 1989, 28, 2154. (d) Manuta, D. M.; Lees, A. J. Inorg. Chem.
1986, 25, 1354. (e) Manuta, D. M.; Lees, A. J. Inorg. Chem. 1986, 25,
3212. (f) Servaas, P. C.; van Dijk, H. K.; Snoeck, T. L.; Stufkens, D. J.;
Oskam, A. Inorg. Chem. 1985, 24, 4494. (g) Manuta, D. M.; Lees, A. J.
Inorg. Chem. 1983, 22, 3825. (h) Balk, R. W.; Stufkens, D. J.; Oskam,
A. Inorg. Chem. 1980, 19, 3015. (i) Balk, R. W.; Stufkens, D. J.; Oskam,
A. Inorg. Chim. Acta 1978, 28, 133. (j) Wrighton, M. S.; Morse, D. L.
J. Organomet. Chem. 1975, 97, 405.
(2) (a) Trammell, S.; Sullivan, B. P.; Hodges, L. M.; Harmon, W. D.;
Smith, S. R.; Thorp, H. H. Inorg. Chem. 1995, 34, 2791. (b) Carter, J.
D.; Kingsbury, K. B.; Wilde, A.; Schoch, T. K.; Leep, C. J.; Pham, E.
K.; McElwee-White, L. J. Am. Chem. Soc. 1991, 113, 2947.
(3) (a) Long, N. J.; Kershaw, S. V. In Optoelectronic Properties of
Inorganic Compounds; Roundhill, D. M., Fackler, J. P., Jr., Eds.;
Plenum Press: New York, 1999; pp 107-159, 349-403. (b) Yam, V.
W.-W.; Kam-Wing Lo, K.; Man-Chung Wong, K. J. Organomet. Chem.
1999, 578, 3. (c) McElwee-White, L.; Kingsbury. K. B.; Carter, J. D. In
Photosensitive Metal-Organic Systems. Mechanistic Principles and
Applications; Kutal, C., Serpone, N., Eds.; Advances in Chemistry 238;
American Chemical Society: Washington, DC, 1993; pp 335-349.
(4) Geoffroy, G. L.; Wrighton, M. S. Organometallic Photochemistry;
Academic Press: New York, 1976.
(5) (a) Beevor, R. G.; Freeman, M. J.; Green, M.; Morton, C. E.;
Orpen, A. G. J. Chem. Soc., Dalton Trans. 1991, 3021. (b) Sheridan,
J. B.; Pourreau, D. B.; Geoffroy, G. L.; Rheingold, A. L. Organometallics
1988, 7, 289. (c) Mayr, A.; Asaro, M. F.; Glines, T. J. J. Am. Chem.
Soc. 1987, 109, 2215. (d) Green, M. J. Organomet. Chem. 1986, 300,
93.
(6) (a) Schoch, T. K.; Orth, S. D.; Zerner, M. C.; Jørgensen, K. A.;
McElwee-White, L. J. Am. Chem. Soc. 1995, 117, 6475. (b) McElwee-
White, L.; Kingsbury. K. B.; Carter, J. D. J. Photochem. Photobiol. A:
Chem. 1994, 80, 265. (c) Mortimer, M. D.; Carter, J. D.; McElwee-
White, L. Organometallics 1993, 12, 4493. (d) Kingsbury, K. B.; Carter,
J. D.; Wilde, A.; Park, H.; Takusagawa, F.; McElwee-White, L. J. Am.
Chem. Soc. 1993, 115, 10056. (e) Carter, J. D.; Schoch, T. K.; McElwee-
White, L. Organometallics 1992, 11, 3571.
(7) Da Re, R. E.; Hopkins, M. D. Coord. Chem. Rev. 2005, submitted.
(8) Schoch, T. K.; Main, A. D.; Burton, R. D.; Lucia, L. A.; Robinson,
E. A.; Schanze, K. S.; McElwee-White, L. Inorg. Chem. 1996, 35, 7769.
(9) Bocarsly, A. B.; Cameron, R. E.; Rubin, H. D.; McDermott, G.
A.; Wolff, C. R.; Mayr, A. Inorg. Chem. 1985, 24, 3976.
10.1021/om0493006 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 01/19/2005

708 Organometallics, Vol. 24, No. 4, 2005
Jelliss et al.
their diagnostic9-11 singlet resonances at δ 277.0 and
221.4 in the 13C{1H} NMR spectrum were the alkyli-
dyne, WtC, and carbonyl, WCO carbons, respectively,
also attesting to a Cs structure, at least in solution. The
νmax(CO) resonances (1976, 1886 cm-1) compare well
with those of the related complex [W(tCC6H4NH2-4)-
Cl(CO)2(NC5H4Me-4)2] (1979, 1890 cm-1), which pos-
sesses a para-donor amino group, NH2, on the alkyli-
dyne.12 Substitution of the 4-methylpyridine ligands by
a chelating 2,2′-dipyridyl in CH2Cl2 resulted in the
quantitative formation of the complex [W(tCC6H4-
NMe2-4)(O2CCF3)(CO)2{κ2-2,2′-(NC5H4)2}] (4a) (Tables
1 and 2). Standard spectroscopic methods have been
used to characterize complex 4a. The IR spectrum is
comparable with that of complex 2c with νmax(CO)
resonances at 1973 and 1888 cm-1 (4a) versus 1986 and
1899 cm-1 (2c) and relatively unchanged with respect
to the precursor complex 3. These resonances appear
to be relatively solvent independent, with no indication
of any chemical transformation in a more polar coordi-
Chart 1
Chart 2
1
nating solvent such as MeCN. From H and 13C{1H}
NMR spectra, the NMe2 (δ 2.84 (1H) and 40.3 (13C)),
WtC (δ 281.3), and WCO (δ 225.0) resonances are
barely adjusted with respect to the precursor 3. Both
complexes 3 and 4a were isolated and studied as the
trifluoracetato complexes rather than the more ubiqui-
tous halo complexes, because of their greatly improved
tractability on the open benchtop. Unlike the halo
complexes, the trifluoroacetato complexes, which are
thermodynamically stable, are not hygroscopic,
rendering handling of the solid in air much easier.
The complex [W(tCC6H4NMe2-4)(NCMe)(CO)2{κ2-2,2′-
(NC5H4)2}][PF6] (5a) has been synthesized in good yield
by displacement of the CF3CO2- ligand by MeCN in the
presence of TlPF6. The νmax(CN) resonance due to the
coordinated MeCN molecule was readily identified at
2254 cm-1 in the IR spectrum, while the νmax(CO) peaks
were, as expected, shifted to higher energy (1981 and
1900 cm-1) versus those of the parent neutral complex
4a. The absence of νmax(CO) resonances due to the
providing that the aromatic phenyl and aliphatic TME-
DA are both present. The complexes became nonemis-
sive if the aromatic group was substituted for But, as
in 2b, or the TMEDA for 2,2′-dipyridyl as in 2c. The
latter was attributed to internal quenching of 3dM-π*Mt
emission by the 2,2′-dipyridyl ligand. This would
CPh
seem to suggest that such polypyridyl-alkylidyne ligand
combinations do not represent a logical avenue of
pursuit, but we report herein enhanced dual blue-yellow
emission of light from just such a complex molecule and
single blue emission from its derivative cationic MeCN
adduct. The blue fluorescence, attributed to a twisted
intramolecular charge transfer (TICT) state, is the first
such photophysical response to be reported for an
organometallic complex.
-
CF3CO2 ligand confirmed its complete displacement.
1
The MeCN resonances were also identified in the H
and 13C{1H} NMR spectra (δ 2.11 (1H) and 1.5, 114.3
(13C)), while the NMe2 resonances were relatively unaf-
fected by the change in charge of the complex (δ 2.91
(1H) and 40.2 (13C)).
To provide an aliphatic comparison to the 2,2′-
dipyridyl complex 4a, complex 3 was treated with
N,N,N′,N′-tetramethylethylenediamine (TMEDA) to
Results and Discussion
yield
[W(tCC6H4NMe2-4)(O2CCF3)(CO)2{κ2-Me2N-
Synthesis and Characterization. The complex
[W(tCC6H4NMe2-4)(O2CCF3)(CO)2(NC5H4Me-4)2] (3)
(Chart 2) has been synthesized by the method of
Mayr,9,10 isolated following column chromatography and
fully characterized by IR spectroscopy, microanalysis
(Table 1), and NMR spectroscopy (Table 2). Of particular
note in this complex is the presence of the strongly
electron donating NMe2 group, the methyl groups of
(CH2)2NMe2}] (4b), by analogy with the formation of the
Mayr complex 2a. The νmax(CO) resonances (1974, 1882
cm-1) are close in value to both complexes 3 and 4a,
1
while H and 13C{1H} NMR data clearly indicate the
displacement of the 4-methylpyridine molecules by the
chelating TMEDA ligand with resonances for the dias-
tereotopic NMe groups at δ 2.87 and 3.16 (1H) and at δ
58.4 and 61.5 (13C). The alkylidyne aryl system is again
virtually unchanged from the parent complex 3 with the
alkylidyne carbon resonating at δ 279.1 and the equiva-
1
which were readily identified in H and 13C{1H} NMR
spectra at δ 3.00 (1H) and 40.3 (13C). Also identified by
(10) (a) McDermott, G. A.; Dorries, A. M.; Mayr, A. Organometallics
1987, 6, 925. (b) Mayr, A.; McDermott, G. A.; Dorries, A. M. Organo-
metallics 1985, 4, 608. (c) Hart, I. J.; Hill, A. F.; Stone, F. G. A. J.
Chem. Soc., Dalton Trans. 1989, 2261. (d) Dossett, S. J.; Hill, A. F.;
Jeffery, J. C.; Marken, F.; Sherwood, P.; Stone, F. G. A. J. Chem. Soc.,
Dalton Trans. 1988, 2453.
(11) (a) Hoffmeister, H.; Mayr, A. Adv. Organomet. Chem. 1991, 32,
227. (b) Gallop, M. A.; Roper, W. R. Adv. Organomet. Chem. 1986, 25,
121.
(12) Yu, M. P. Y.; Mayr, A.; Cheung, K.-K. J. Chem. Soc., Dalton
Trans. 1998, 475.

Dual Fluorescence in Tungsten Alkylidynes
Organometallics, Vol. 24, No. 4, 2005 709
Table 1. Analytical and Physical Data
analysisb/%
H
compound
color
yield/%
34
νmax(CO)a/cm-1
1976vs,c 1886vs,c 1688vs,d 1596vsd
C
N
[W(tCC6H4NMe2-4)(O2CCF3)(CO)2-
(NC5H4Me-4)2], 3
yellow
44.8 (44.7)
4.1 (3.6)
6.5 (6.3)
[W(tCC6H4NMe2-4)(O2CCF3)(CO)2{κ2-
2,2′-(NC5H4)2}], 4ae
red
98
97
96
97
1973vs,c 1888vs,c 1689vs,d 1595vsd
1974vs,c 1882vs,c 1711vs,d 1605vsd
1981vs,c 1900vsc,f
43.6 (43.1)
37.5 (37.9)
39.0 (38.7)
34.0 (33.8)
3.0 (2.8)
4.8 (4.4)
2.9 (3.0)
4.9 (4.3)
6.2 (6.6)
6.8 (7.0)
7.2 (7.8)
8.6 (8.3)
[W(tCC6H4NMe2-4)(O2CCF3)(CO)2{κ2-
Me2N(CH2)2NMe2}], 4b
yellow
red
[W(tCC6H4NMe2-4)(NCMe)(CO)2{κ2-
2,2′-(NC5H4)2}][PF6], 5a
[W(tCC6H4NMe2-4)(NCMe)(CO)2{κ2-
Me2N(CH2)2NMe2}][PF6], 5b
yellow
1984vs,c 1892vsc,g
a Measured in CH2Cl2 at 298 K. b Calculated values are given in parentheses. c CO ligand. d CF3CO2- ligand. e Full IR spectrum (THF,
f
1300-2000 cm-1) given in Supporting Information. νmax(CN) 2254 cm-1
.
g νmax(CN) 2252 cm-1
.
Table 2. 1H and 13C NMR Dataa
compd
1H/δ
13C/δb
3c
8.66 (d, 4H, NC5H4Me, J ) 6), 7.29 (d, 2H, C6H4NMe2,
J ) 9), 7.11 (d, 4H, NC5H4Me, J ) 6), 6.54 (d, 2H,
C6H4NMe2, J ) 9), 3.00 (s, 6H, C6H4NMe2), 2.35 (s, 6H,
NC5H4Me)
9.26 (d, 2H, N2C10H8, J ) 5), 8.15 (d, 2H, N2C10H8, J )
8), 8.08 (t, 2H, N2C10H8, J ) 8), 7.51 (t, 2H, N2C10H8, J )
7), 7.05 (d, 2H, C6H4NMe2, J ) 9), 6.36 (d, 2H, C6H4NMe2,
J ) 9), 2.84 (s, 6H, C6H4NMe2)
277.0d (WtC), 221.4d (CO), 167.7 (CF3CO2), 151.3,
149.4, 124.8 (NC5H4Me), 150.4, 132.6, 128.9, 126.0
(C6H4NMe2) 111.2 (CF3CO2), 40.3 (C6H4NMe2),
21.3 (NC5H4Me)
4ae
4bf
5ae
5bf
281.3d (WtC), 225.0d (CO), 162.3 (CF3CO2),
156.9, 150.9, 140.8, 123.9, 119.5 (N2C10H8)
155.5, 134.2, 131.8, 127.5 (C6H4NMe2), 111.5
(CF3CO2) 40.3 (C6H4NMe2)
7.17 (d, 2H, C6H4NMe2, J ) 9), 6.54 (d, 2H, C6H4NMe2,
J ) 9), 3.16 (s, 6H, CH2NMe), 2.95 (s, 6H, C6H4NMe2),
2.87 (s, 6H, CH2NMe), 2.86-2.80 (m br, 4H, CH2NMe)
279.1d (WtC), 222.5d (CO), 168.8 (CF3CO2),
151.9, 139.6, 131.2, 114.4 (C6H4NMe2), 111.5
(CF3CO2), 61.5, 58.4, 52.2 (CH2NMe), 40.5
(C6H4NMe2)
9.35 (d, 2H, N2C10H8, J ) 5), 8.78 (d, 2H, N2C10H8, J )
8), 8.22 (t, 2H, N2C10H8, J ) 8), 7.66 (t, 2H, N2C10H8, J )
7), 7.05 (d, 2H, C6H4NMe2, J ) 9), 6.46 (d, 2H, C6H4NMe2,
J ) 9), 2.91 (s, 6H, C6H4NMe2), 2.11 (s, 3H, MeCN)
7.19 (d, 2H, C6H4NMe2, J ) 9), 6.54 (d, 2H, C6H4NMe2, J )
9), 3.21 (s, 6H, CH2NMe), 2.97 (s, 6H, C6H4NMe2), 2.94 (s,
6H, CH2NMe), 2.87-2.78 (m br, 4H, CH2NMe), 2.30 (s, 3H,
MeCN)
282.1d (WtC), 224.9d (CO), 156.9, 151.7, 140.3,
129.4, 118.6 (N2C10H8), 155.5, 131.8, 130.9, 127.6
(C6H4NMe2), 114.3 (MeCN), 40.2 (C6H4NMe2), 1.5
(MeCN)
279.5d (WtC), 221.6d (CO), 147.4, 142.1, 131.1,
118.7 (C6H4NMe2), 113.2 (MeCN), 61.2, 58.3, 52.3
(CH2NMe), 40.5 (C6H4NMe2), 1.4 (MeCN)
a Chemical shifts (δ) in ppm, coupling constants (J) in Hz, measurements at 298 K. b 1H-decoupled, chemical shifts are positive to high
frequency of SiMe4. c Measured in CD2Cl2. d 183W satellite peaks too weak to be observed, even at -50 °C. e Measured in d8-THF. f Measured
in CDCl3.
lent carbonyl carbons at δ 222.5 in the 13C{1H} NMR
spectrum. In the same spectrum, the alkylidyne NMe2
group has a resonance at δ 40.5. The invariance of these
data from complexes 3 through 4b would seem to
suggest similar electron density distributions along the
metal-alkylidyne-aryl-donor group assembly. Finally,
the cationic acetonitrile adduct, [W(tCC6H4NMe2-4)-
(NCMe)(CO)2{κ2-Me2N(CH2)2NMe2}][PF6] (5b), analo-
gous to the complex salt 5a, has been synthesized in a
similar manner, by treatment of complex 4b with TlPF6
in MeCN/THF. Once again, the νmax(CN) absorption
arising from the complex is observed at 2252 cm-1 and
acquisition of the cationic charge at the metal center is
offset by the substitution with a somewhat stronger
donor MeCN ligand, despite the latter’s improved
-
π-acidity over the CF3CO2 ligand. Indeed, the very
slight increase in νmax(CO) values (ca. 10 cm-1) observed
upon formation of 4,5b from 4,5a bears this out, in
addition to the above-discussed NMR characteristics.
Photoluminescence. In contrast to the previously
mentioned complexes 2b and 2c, solutions of all five
complexes 3-5b are emissive in the visible region in
CH2Cl2 at ambient temperatures upon UV photoexcita-
tion. Photoabsorption and -emission data for the five
complexes are presented in Table 3. Representative
excitation/emission spectra are given in Figure 1 for
complex 4a. Structureless blue emission (ca. 450 nm)
is common to all five complexes, with excitation and
emission wavelengths being all but invariant. The
presence of the 2,2′-dipyridyl ligand clearly enhances
this emission with significant quantum yields for com-
plexes 4a (Φ451 ) 1.04 × 10-2) and 5a (Φ450 ) 1.26 ×
10-2) versus Φ448 ) 1.25 × 10-3 for complex 3. This
would seem to indicate that the emissive absorption is
primarily confined to the WtCC6H4NMe2-4 π-π* sys-
tem, with the presence of the 2,2′-dipyridyl ligand
stimulating radiative emission without directly impact-
ing the electronic transitions.
νmax(CO) resonances appear at 1984 and 1892 cm-1
,
shifted to higher energy as expected with the formation
of a cationic adduct from its neutral parent complex 4b.
There also appears to be little impact on the character-
istic NMR resonances for compound 5b versus those of
complex 4b, with the exception of the appearance of
1
signals at δ 2.30 and 1.4 in the H and 13C{1H} NMR,
respectively, for the MeCN methyl group and at δ 113.2
for the nitrilo carbon in the latter spectrum. The
alkylidyne aryl system is invariant with respect to the
parent complex 4b, with the alkylidyne WtC carbon
resonating at δ 279.5 and the equivalent carbonyl
carbons at δ 221.6 in the 13C{1H} NMR spectrum. The
remaining resonances in both the 1H and 13C{1H} NMR
spectra are also very similar to those of complex 4b. In
terms of the level of electron density, it thus seems that
The electronic absorption spectrum of complex 4a
(Figure 2) indicates that a shoulder at ca. 315 nm

710 Organometallics, Vol. 24, No. 4, 2005
Jelliss et al.
Table 3. UV-Vis Absorption and
Photoluminescence Dataa
compd λmax/nm (ꢀ × 10-3/M-1 cm-1
)
λex, λem/nmb Φem × 103 c
3
290 (14.50), 372 (18.07), 468
317, 448
472, 540
317, 451
470, 580
317, 453
458, 554
317, 450
1.25
0.970
10.4d
6.37e
2.03
0.700
12.6
(2.93)
4a
4b
5a
5b
300 (18.60), 315 (sh), 371
(18.60), 470 (3.34)
286 (12.10), 364 (17.00),
449 (1.70)
249 (17.50), 308 (16.90), 380
(9.00), 472 (6.50)
289 (11.90), 363 (19.70), 449
(1.65)
316, 451
410, 536
2.14
0.121
a Measured in CH2Cl2 (25 µM) at 298 K. λex ) excitation
maximum, λem ) emission maximum. All spectra are excitation
and emission corrected. c Emission quantum yield, Φem, relative
to 9-cyanoanthracene (Φem ) 1.00), (10%, corrected for self-
absorption. d Lifetime, τ451 ) 4.4 ns. e Lifetime, τ580 ) 1.1 ns (82%)
and 5.3 ns (18%).
b
Figure 3. Electronic absorption spectrum (s) for a 250
µM solution of complex 4a and photoexcitation spectra for
a 2 µM solution of the same complex at λem ) 451 nm (- - -)
and λem ) 580 nm ()) at ca. 4 × slit width.
3 absorbs in this vicinity, it is much weaker than for
complex 4a. Further analysis shows that absorption at
ca. 370 nm is common to both complexes 3 and 4a, is
not solvatochromic, and is nonemissive. This might be
suggestive of a “pure” πWtCAr-π*WtCAr transition, while
that at ca. 315 nm, which is responsible for radiative
emission, is “contaminated” by possible LMCT charac-
ter, namely, nNMe -π*WtCAr. This absorption would not
2
necessarily be classed as a charge transfer band, thanks
to significant lone-pair-ligand-metal mixing in the
ground state, which is in turn due to the expected
planarity and parallel orientation of the NMe2 group
with respect to the aryl-alkylidyne π framework. Sup-
porting this notion is the absence of emission for the
complex 2c, which possesses no such donor group on
the alkylidyne moiety. Our own measurements on CH2-
Cl2 solutions of the para-toluidyne complex [W(tCC6H4-
Me-4)(O2CCF3)(CO)2(NC5H4Me-4)2] also show a com-
plete absence of blue fluorescence.
Figure 1. Photoexcitation and -emission spectra for a 25
µM solution of complex 4a in CH2Cl2: ()) λex ) 317, λem
)
451 nm (left ordinate); (s) λex ) 470, λem ) 580 nm (right
ordinate).
The band-shape asymmetry between excitation and
emission spectra noted in Figure 1, common to mea-
surements of this higher energy emission in all the
complexes, is symptomatic of some nuclear rearrange-
ment. Furthermore, these features are independent of
the presence of triplet sensitizers (e.g., O2), implying
that a distorted singlet excited state with substantial
metal d character is responsible for this blue emission.
Measurements in MeTHF (2-methyltetrahydrofuran) at
77 K revealed a more structured emission, although
essentially wavelength invariant (λem ) 450 nm) with
a vibronic progression, ∆νj0,1 ≈ 1350 cm-1 (Figure 4).
This closely matches a strong vibration at 1370 cm-1
in the IR spectrum (Supporting Information), which can
be assigned to the aromatic-C-N stretch for the
NMe2 group and is just outside the expected range
(1310-1360 cm-1) for such a vibrational excitation in
an organic tertiary aromatic amine.13 The excitation
peak (λex ) 290 nm) was slightly blue-shifted by some
2940 cm-1 and comparatively broader with some struc-
ture as well.
Figure 2. Electronic absorption spectra for 250 µM
solutions of complexes 3 and 4a: ()) 3 in CH2Cl2; (s) 4a
in CH2Cl2; (- - -) 4a in MeCN. Inset shows expansion of
absorbances for 4a in CH2Cl2 and MeCN between 280 and
330 nm.
appears to be the emissive absorption, which is very
slightly blue-shifted in MeCN solution, indicating little
change in polarity upon absorption, typical for signifi-
cant metal-ligand mixing in the ground state. A close
match between the absorption shoulder and the excita-
tion peak is noteworthy (Figure 3). Unfortunately this
absorption is obscured by the stronger, higher energy
absorption in the UV-vis spectra of the other complexes
4b, 5a, and 5b. Although the 4-methylpyridine complex
Lifetime measurements of CH2Cl2 solutions at 298 K
and MeTHF solutions at 77 K using a pulsed N2 laser
(λ ) 337 nm) indicate τ450 e 10 ns for all the new
complexes, further supporting exclusive singlet spin
(13) Mohan, J. Organic Spectroscopy-Principles and Applications;
CRC Press: New York, 2000; pp 60-61.

Dual Fluorescence in Tungsten Alkylidynes
Organometallics, Vol. 24, No. 4, 2005 711
Scheme 1. Implication of an Emissive Twisted
Intramolecular Charge Transfer (TICT) Complex
in the Blue Fluorescence of the Complexes 3-5a
Figure 4. Photoexcitation and -emission spectra for a 25
µM solution of complex 4a in MeTHF at 77 K: (s) λex
290 nm; ()) λem ) 450 nm.
)
a X- ) CF3CO2-, MeCN; NkN ) 2 × NC5H4Me-4, κ2-2,2′-
(NC5H4)2, κ2-Me2N(CH2)2NMe2. The symbols δx/δQ do not
represent overall charge distribution, but partial charge
dislocation resulting from the transition. Once twisted, full x/Q
charge separation must occur.
detectable long lifetime (which we take to imply as a
sub-10 ns time scale from the experimental parameters
given), as opposed to a coexisting nontwisted excited
state (planar intramolecular charge transfer, PICT),
which showed fluorescence at λem ) 439 nm (5 e τ e 25
ns) and an associated long-lived (τ ) 700 ms) π-π*
emission at λem ) 453 nm at 77 K. The mechanism of
the distortion involved a simple 90° twisting of the NMe2
group relative to the planar hyperconjugated architec-
ture of the diphenylhexatriene backbone. These photo-
physical experimental results have been supported by
a range of high-level computational calculations, includ-
ing time-dependent density functional theory studies,
on organic aromatic acceptor-donor chromophores,
4-ZC6H4NR2 (Z ) acceptor group, e.g., CN, NO2, R )
Figure 5. Fluorescence decay curves for λem ) 451 nm
(], τ ) 4.4 ns) and 580 nm (O, τ ) 1.1 ns (82%), 5.3 ns
(18%)) with their respective fits (-). Instrument response
measurements are indicated (- - -).
character in the excited state. Closer analysis of complex
4a at ambient temperatures using a faster pulsed
N2 laser revealed a single-exponential decay with τ451
) 4.4 ns (Figure 5). Such short lifetimes coupled with
high quantum yields for high-energy visible light emis-
sion, although expected from the Einstein A coefficient,14
are highly unusual for organometallic complexes given
the alternate photoreactive pathways usually available
following UV excitation.
However, these observations permit us to pinpoint the
nature of the distortion. It has been reported by Lin and
co-workers that twisted intramolecular charge transfer
(1TICT) rotamer formation in the molecule 4-Me2NC6H4-
(CHdCH)3C6H4NO2-4 is responsible for very short-lived
fluorescence at λem ) 525 nm in hexane.15 Similar
photophysical properties were concomitantly reported
by Whitten and co-workers for the related species 4-Me2-
NC6H4(CHdCH)nC6H4NO2-4 (n ) 1-3),16 and the phe-
nomenon has been extensively studied by Rettig17
following its discovery by Grabowski, Siemiarczuk, and
co-workers.18 Although Lin’s emission was weak to
moderate, even at 77 K, it was reported to have no
1
Me).19 We propose a similar TICT state for the com-
plexes 3-5 (Scheme 1), which is consistent with that of
the organic analogue 4-Me2NC6H4(CHdCH)3C6H4
NO2-4, although the organometallic tungsten complexes
clearly emit very strongly in solution at ambient tem-
peratures. A nondistorted triplet excited state is pre-
cluded, as one would expect such a metal-purturbed
system to have a much longer decay lifetime. Indeed
the long-lived undistorted phosphorescent state ob-
served in Lin’s organic system is absent in the tungsten
alkylidynes, possibly due to efficient singlet-singlet
crossover to a second metal-based rapidly relaxing
fluorescent state (vide infra). It is also noteworthy that
Rettig attributes sulfur d orbital participation in the
TICT emission from 4,4′-dimethylaminophenyl sulfone
to a diminished nonradiative singlet-to-triplet transi-
tion.20
It was also reported for 4-Me2NC6H4(CHdCH)3C6H4-
NO2-4 that, along with expected red-shifting of λem, a
decrease in 1TICT emission was observed as solvent
polarity increased and accredited to strong intermo-
lecular bonding, particularly in hydrogen-bonding sol-
(14) Hollas, J. M. Modern Spectroscopy, 3rd ed.; Wiley: New York,
1996; p 27.
(15) Lin, C. T.; Guan, H. W.; McCoy, R. K.; Spangler, C. W. J. Phys.
Chem. 1989, 93, 39.
(16) Shin, D. M.; Whitten, D. G. J. Phys. Chem. 1988, 92, 2945.
(17) Rettig, W. Angew. Chem., Int. Ed. Engl. 1986, 25, 971, and
references therein.
(19) (a) Jamorski Jo¨dicke, C.; Lu¨thi, H. P. J. Am. Chem. Soc. 2003,
125, 252. (b) Jamorski Jo¨dicke, C.; Lu¨thi, H. P. J. Chem. Phys. 2002,
117, 4146. (c) Jamorski Jo¨dicke, C.; Lu¨thi, H. P. J. Chem. Phys. 2002,
117, 4157.
(18) Grabowski, Z.; Rotkiewicz, K.; Siemiarczuk, A.; Cowley, D. J.;
Baumann, W. Nouv. J. Chim. 1979, 3, 443.
(20) Rettig, W.; Chandross, E. A. J. Am. Chem. Soc. 1985, 107, 5617.

712 Organometallics, Vol. 24, No. 4, 2005
Jelliss et al.
assignment. Closer analysis of the photoexcitation
spectrum measured back to 290 nm very informatively
revealed a further excitation peak at λex ) 319 nm,
again overlapping with the absorption that also pro-
duces the higher energy 1TICT emission (Figure 3). This
same excitation peak was still readily apparent at
emission wavelengths beyond 650 nm, where emission
from the 1TICT state has fallen close to zero. However,
the narrower Stokes shift (4035 cm-1 (4a) and range
2700-5700 cm-1 for all compounds) observed for the
photoluminescence in our complexes, resulting in gener-
ally yellow light emission rather than the lower energy
red light produced by the complexes 1, is highly sug-
gestive of strong 1dW-π*WtCAr singlet character as
opposed to emission from a triplet manifold. Insensitiv-
ity of the photoluminescence of complexes 3 and 4a to
the presence of triplet sensitizers (O2, 10 mM anth-
racene) once again supports this. Furthermore, time-
resolved fluorescence using a fast pulsed N2 laser again
yielded a very short lifetime, which was biexponential
with τ580 ) 1.1 ns (82%) and 5.3 ns (18%) at λem ) 580
nm (Figure 5). Both these values, which may result from
Figure 6. Photoexcitation and -emission spectra for 2 µM
solutions of complex 4a in CH2Cl2/MeCN mixtures in order
of decreasing intensity: 100:0 (neat CH2Cl2); 80:20; 50:50;
1
20:80; 0:100 (neat MeCN): (a) higher energy TICT emis-
1
sion; (b) lower energy dW-π*WtCAr emission.
vents. This made emissive relaxation back to a planar
ground state less likely, and the ratio of the intensities
of TICT/PICT emission thus decreased in the more polar
solvents. We too observe a dramatic reduction in emis-
sion intensity in MeCN (ca. 90%) versus that observed
in CH2Cl2 solutions, especially for complex 4a, which
also demonstrates substantial red-shifting of the emis-
sion maximum from λem ) 450 nm in CH2Cl2 to 535 nm
in MeCN (Figure 6a) for this complex, while λex remains
virtually unchanged. Static singlet quenching by MeCN
should not account for this, and intermolecular solvent-
solute interference with the ground state configuration,
as has been observed with 4-Me2NC6H4(CHdCH)3C6H4-
NO2-4, is a more likely explanation.15 An even steeper
decline (ca. 85%) in emission intensity was noted for the
same molarity of complex 4a in a solution of CH2Cl2/
EtOH (50:50).
Complexes 3 and 4a show a second broader structure-
less emission, both with similar excitation (λex ≈ 470
nm) and with complex 3 emitting at λem ) 580 and
complex 4a significantly blue shifted at λem ) 540 nm.
While the quantum yield for this emission in complex
3 (Φ540 ) 9.70 × 10-4) is modest, that in complex 4a
(Φ580 ) 6.37 × 10-3) is again noticeably enhanced by
the presence of the 2,2′-dipyridyl ligand. Curiously,
however, radiative emission in this second wavelength
regime is absent for cationic derivative complex 5a. Here
it seems that the intramolecular quenching by the 2,2′-
dipyridyl ligand, identified by Mayr in complex 1c,
might now be operating, especially in light of the optical
behavior of compound 5b, discussed below. This may
be due to a closer energy match between the 2,2′-
dipyridyl and WtCC6H4NMe2-4 π* orbitals. Band-shape
similarity between excitation and emission spectra, both
at 298 K in CH2Cl2 (Figure 1) and at 77 K in MeTHF,
suggests that these are the same parity-forbidden, spin-
allowed dW-π*WtCAr singlet-singlet transitions identi-
fied in complexes 1.8 Furthermore, the moderately low
molar absorbivity at these excitation wavelengths in the
electronic absorption spectra of the complex (Table 3,
Figure 2) supports the notion of substantial d character
in the π*WtCAr state, this feature also being identified
in the complexes 1. An excellent match between the
broad absorption peak and photoexcitation spectrum is
apparent (Figure 3). A distinct lack of rigidochromism
of the emission wavelength in the photoemission spectra
measured in MeTHF at 77 K is also supportive of this
1
closely energy-matched but not identical dW-π*WtCAr
states resulting from the low symmetry of the complex,
are considerably shorter than the accepted range for
phosphorescence from a 3dW-π*WtCAr state (10-500 ns)
in solution at ambient temperatures.7 As with the
higher energy emission of complex 4a, a significant
decrease in intensity of emission is noted in MeCN,
although there are two important differences: (i) the
intensity decreases by only ca. 65% from neat CH2Cl2
to neat MeCN, and (ii) there is a very slight blue shifting
in emission wavelength from λem ) 580 to 565 nm
(Figure 6b). Although it is very tempting to conclude a
singlet state is indeed responsible for this emission, a
very short-lived phosphorescent 3dW-π*WtCAr state
might account for the lack of intersystem crossing
between the two emissive states. On the other hand,
this is exceedingly unlikely with τ580 ) 1.1 ns, and the
absence of a singlet-singlet interaction in this case can
be accounted for, if one of the excited fluorescent states
is a very short-lived distorted species, while the other
is an undistorted metal-based singlet state with a
comparable or shorter lifetime, as has been found. Even
a triplet assignment to the τ580 ) 5.3 ns component
would be tenuous at best. Such short-lived phosphores-
cence would be very difficult if not impossible to detect
through energy transfer experiments and as such cannot
be ruled out.
Absence of the so-called “normal” fluorescence (at
1
even shorter wavelength) from a nondistorted nNMe
-
2
1
π*WtCAr state normally accompanying TICT emission
may be attributed to the efficient distribution of energy
1
to the lower energy dW-π*WtCAr state through inter-
system crossover (IS, Scheme 2) as well as to the 1TICT
state itself. Communication between the two non-
distorted singlet states of complex 4a is strongly sup-
ported by the observation of two photoexcitation peaks
at 319 and 470 nm (Figures 1 and 3) corresponding to
the yellow emission.
The TMEDA complexes 4b and 5b both show the
dual emission characteristics of complexes 3 and 4a (λem
) 453, 554 nm (4b) and 451, 536 nm (5b), Table 3),
although it should be noted that while the lower energy

Dual Fluorescence in Tungsten Alkylidynes
Organometallics, Vol. 24, No. 4, 2005 713
Scheme 2. Generalized Relative Energy Diagram
for Dual Fluorescence from Complex 4a (not
drawn to scale)a
short-lived singlet manifolds resulting from distinct
1TICT nNMe -π*WtCAr and 1dW-π*WtCAr transitions. The
2
latter has been previously reported for group 6 metal
alkylidynes, but as a lower energy triplet emission only.
There is to our knowledge no precedence for either
singlet fluorescence in group 6 metal alkylidyne com-
plexes nor TICT emission in organometallic complexes
in general, let alone with the intensity and efficiency
described above. The anomalously high quantum yields
for complexes 4a and 5a, in particular, may be at-
tributed to short lifetimes for both emissions, as well
as the impact of the stereorigid 2,2′-dipyridyl ligand.
Other current work is revealing interesting electro-
chemical behavior for these complexes in solution,
especially the cationic complex 5a, which displays
electrodeposition characteristics upon reduction. These
results will be reported in due course.
a It is assumed that both radiative emissions are ac-
companied by nonradiative relaxation.
yellow emission of 5a is completely quenched, that in
5b is detectable, though more than an order of magni-
tude weaker than observed for the strongest emission
by 4a at λem ) 580 nm. These observations verify that
the orthogonal 2,2′-dipyridyl ligand is itself not so
intimately involved in the emission processes, at least
in terms of orbital contribution; that is, luminescence
characteristics are confined mainly to the WtCC6H4-
NMe2-4 backbone and again serve to emphasize the fact
that, with the exception of the second, lower energy
emission of complex 5a (or rather lack thereof), the 2,2′-
dipyridyl ligand not only does not quench emission but
actually enhances it. The reason for this enhancement
is most likely due to the increased stereochemical
rigidity afforded by the 2,2′-dipyridyl chelating moiety.
Compounds 3, 4b, and 5b, with their more flexible bis-
(4-methylpyridine) and TMEDA ligands, possess in-
creased internal rotational degrees of freedom, which
may serve to increase the efficiency of nonradiative
decay relative to compounds 4a and 5a.
At this time, further work is in process to elucidate
the precise impact of polypyridyl ligands on the nature
of the photoluminescence in tungsten alkylidyne com-
plexes, by synthesizing complexes with modified 2,2′-
dipyridyl rings. Further work is also under way to
extend the hyperconjugated tungsten-alkylidyne back-
bone, using Sonogoshira coupling processes, which have
been successfully investigated by Mayr and co-work-
ers,21 to couple the WtC unit with acetylenic dimethy-
lanilino molecules, for example. Such variations may
lead to a more comprehensive tuning of the fluorescent
output. Most importantly, increased stereochemical
rigidity of the bidentate and potentially tridentate
ligands will be targeted in an attempt to increase the
efficiencies of emission, especially the blue TICT photo-
luminescence.
Experimental Section
All synthetic procedures were conducted under an atmo-
sphere of dry nitrogen or argon using Schlenk-line and
glovebox techniques. Solvents were freshly distilled under
argon from appropriate drying agents before use. Celite pads
used for filtration were 3 × 5 cm, and alumina (Brockmann
III) columns were 2 × 10 cm. Tungsten hexacarbonyl and
thallium(I) hexafluorophosphate were used as purchased from
Strem Chemicals. The reagents 4-bromo-N,N-dimethylaniline,
trifluoroacetic anhydride, 4-methylpyridine, 2,2′-dipyridyl, and
N,N,N′,N′-tetramethylethylenediamine were used as pur-
chased from Aldrich. The molarities of solutions of n-butyl-
lithium (1.6 M in hexane), purchased from Aldrich, were
checked by titration prior to use.
Spectroscopic Measurements. All solution measure-
ments were made at 298 K. IR measurements were made using
solution cells in a Perkin-Elmer RX-I FT-IR spectrometer.
UV-vis measurements were made between 220 and 800 nm
with a Shimadzu 2530 UV-visible absorption spectrophoto-
meter. NMR measurements were recorded using a Varian
Gemini 300 MHz spectrometer: 1H (300.0 MHz) and 13C
(75.4 MHz).
Fluorometry Measurements. Photoluminescence mea-
surements were made with a PTI QM4 fluorescence spectro-
photometer with a Xe arc lamp light source and digital PMT
detector. Emission and reference source gain excitation cor-
rections were applied to all steady state data. Slit widths were
set at 2-5 nm. Appropriate cutoff filters were used to eliminate
peaks due to solvent Raman-shifted bands and excitation
harmonics. Solution samples (2-25 µM) at ambient temper-
atures were measured in a quartz sample cuvette with Schlenk
attachment to deoxygenate samples. Samples measured at
77 K were degassed and analyzed in a quartz NMR tube with
Schlenk attachment and set in a quartz-bottomed Dewar flask
in an argon-filled sample chamber.
Quantum yields were assessed by comparison of integrated
peak intensities between those of the complexes at each of their
emission wavelengths and the singlet emission from deoxy-
genated 9-cyanoanthracene in hexane, which has Φem ) 1.00.
Concentrations of the complex solutions were adjusted to give
accurately measured absorbances of ca. 0.1 A at λex. A standard
solution of 9-cyanoanthracene was similarly created (λex
) 399 nm), and its integrated emission intensity measured
using an optical density (OD1) filter at the emission mono-
chromator entrance at consistently fixed slit widths for all
measurements. Quantum yields were then calculated accord-
ing to
Conclusions. We have isolated several tungsten
alkylidyne complexes using established synthetic tech-
niques and workup procedures, yielding highly pure
materials for photophysical analysis. With the exception
of one compound, 5a, which displays a single blue
fluorescence band, all the complexes display strong dual
blue-yellow fluorescence, with almost no variation of the
higher energy blue emission wavelength (λem ) 450 nm)
from one complex to the other. The mechanisms involve
Iint,x/fx
Φem
)
(21) Yu, M. P. Y.; Cheung, K.-K.; Mayr, A. J. Chem. Soc., Dalton
Trans. 1998, 2373.
(Iint,c/fc) × 100

714 Organometallics, Vol. 24, No. 4, 2005
Jelliss et al.
where Iint ) integrated intensity and f ) fraction of light
absorbed for solutions of the complexes (x) and of 9-cyanoan-
thracene (c). Emission quantum yields, Iint, were corrected for
self-absorption using transmission data parameters from the
UV-vis absorption spectra over the width of the emission
band.
the solution dropwise, forming a deep violet solution with the
evolution of CO gas. The solution was allowed to warm to
-35 °C, and then 4-methylpyridine (5.53 mL, 56.8 mmol) was
added to the solution dropwise, affording a change in color from
violet to green with further evolution of CO. The reaction
mixture was then allowed to warm to room temperature and
stirred for 48 h. After this time the solvent was removed in
vacuo and the solution was washed with hexanes (5 × 50 mL)
to remove excess 4-methylpyridine. The residue was dissolved
in the minimum volume of CH2Cl2-hexanes (20 mL, 4:1) and
chromatographed using the same solvent mixture. A first
yellow fraction containing 4-methylpyridine was eluted and
discarded, then followed by an intense yellow band, which was
collected. Removal of the solvent in vacuo and recrystallization
from CH2Cl2-hexanes (20 mL, 1:1) at -78 °C, washing with
hexanes (3 × 50 mL), and drying in vacuo afforded yellow
microcrystals of [W(tCC6H4NMe2-4)(O2CCF3)(CO)2(NC5H4Me-
4)2], 3 (3.19 g).
For all compounds the fluorescence decays were measured
using a digital storage oscilloscope-based instrument.22 Excita-
tion was provided by a small N2 laser operating at 20 Hz using
no dye (λex ) 337 nm) or 4 × 10-3 M coumarin-440 in EtOH
(λex ) 440 nm). A small fraction of the excitation beam was
reflected onto a Texas Optoelectronics TIED 56 photodiode,
which triggered the oscilloscope.23 Emission from the sample
was detected with a fast-wired Burle 931-A photomultiplier
tube24 after passing through a small monochromator with 2.2
nm resolution. Emission was monitored at 451 and 580 nm in
consecutive experiments. The PMT output was sent into a
Tektronix TDS-350 digital storage oscilloscope. For each laser
pulse the oscilloscope collected a complete fluorescence decay.
Results from 256 laser pulses were averaged for each fluores-
cence decay. At least five decays were averaged to produce each
lifetime. Accurate fluorescence decays from compound 4a were
measured with a PTI model TM-3/2005 lifetime fluorescence
spectrophotometer. The instrument employed a PTI GL-330
pulsed nitrogen laser pumping a PTI GL-302 tunable dye laser
as an excitation source and a proprietary stroboscopic detection
system with an R928 photomultiplier. The decays were
analyzed with a PTI FeliX32 advanced analysis package
utilizing a discrete multiexponential fitting function and
iterative reconvolution. An attempt was made to check for any
long-lived emission within the 600-700 nm range utilizing the
nitrogen/dye laser combo and a gated phosphorescence detector
with an R928 photomultiplier. No emission with a lifetime
longer than 500 ns (gated detector resolution limit) was
observed.
Synthesis of [W(tCC6H4NMe2-4)(O2CCF3)(CO)2(NC5-
H4Me-4)2], 3. The procedure follows the general method of
Mayr.9,10 The compound 4-bromo-N,N-dimethylaniline (2.84 g,
14.2 mmol) was dissolved in Et2O (30 mL). To this solution
was added dropwise LiBun (8.88 mL, 1.6 M in hexane,
14.2 mmol), and the resulting reaction mixture was stirred
for 1 h at room temperature. After this time, [W(CO)6] (5.00
g, 14.2 mmol) was suspended in Et2O (50 mL). The cloudy
yellow solution of Li[C6H4NMe2-4] was added slowly via
cannula transfer to the [W(CO)6] suspension in aliquots of ca.
1.5 mL, producing the characteristic brilliant red-orange
solution of the anionic tungsten acyl complex [W(CO)5{C(O)-
C6H4NMe2-4}]-. The solution was stirred for 2 h, and then
the solvent was removed in vacuo. The resulting orange-
brown residue was redissolved in CH2Cl2 (30 mL) and filtered
through Celite. The filtrate was then cooled to -78 °C, and
trifluroacetic anhydride (2.00 mL, 14.2 mmol) was added to
Synthesis of [W(tCC6H4NMe2-4)(O2CCF3)(CO)2{K2-2,2′-
(NC5H4)2}], 4a. Complex 3 (0.15 g, 0.22 mmol) and 2,2′-
dipyridyl (0.04 g, 0.25 mmol) were dissolved in CH2Cl2 (25 mL),
and the solution was stirred at room temperature for 24 h,
resulting in a brilliant red solution. Solvent was removed in
vacuo, and the residue was washed with hexanes (5 × 10 mL)
and then recrystallized from CH2Cl2-hexanes (10 mL, 1:1),
yielding red microcrystals of [W(tCC6H4NMe2-4)(O2CCF3)-
(CO)2{κ2-2,2′-(NC5H4)2}], 4a (0.15 g).
Synthesis of [W(tCC6H4NMe2-4)(O2CCF3)(CO)2{K2-Me2N-
(CH2)2NMe2}], 4b. Using a similar procedure, complex 3 (0.15
g, 0.22 mmol) and N,N,N′,N′-tetramethylethylenediamine
(38 µL, 0.25 mmol) afforded yellow microcrystals of
[W(tCC6H4NMe2-4)(O2CCF3)(CO)2{κ2-Me2N(CH2)2NMe2}], 4b
(0.13 g).
Synthesis of [W(tCC6H4NMe2-4)(NCMe)(CO)2{K2-2,2′-
(NC5H4)2}][PF6], 5a. Complex 4a (0.10 g, 0.16 mmol) was
combined with TlPF6 (0.06 g, 0.17 mmol). A mixture of THF
and MeCN (27 mL, 25:2) was then added and stirred for 48 h,
producing a cloudy red solution. Solvent was removed in vacuo,
and the residue was redissolved in CH2Cl2 and filtered through
Celite. Following removal of solvent in vacuo and recrystal-
lization from CH2Cl2-hexanes (10 mL, 1:1), red microcrystals
of [W(tCC6H4NMe2-4)(NCMe)(CO)2{κ2-2,2′-(NC5H4)2}][PF6],
5a (0.11 g), were formed.
Synthesis of [W(tCC6H4NMe2-4)(NCMe)(CO)2{K2-Me2N-
(CH2)2NMe2}][PF6], 5b. Using a similar procedure, complex
4b (0.11 g, 0.17 mmol) and TlPF6 (0.06 g, 0.17 mmol) afforded
yellow microcrystals of [W(tCC6H4NMe2-4)(NCMe)(CO)2{κ2-
Me2N(CH2)2NMe2}][PF6], 5b (0.11 g).
Acknowledgment. Financial support from the ACS
Petroleum Research Fund (Type G grant) and from the
Saint Louis University Beaumont Faculty Development
Fund is acknowledged. We thank Dr. Steven Buckner
(SLU) for helpful advice.
(22) (a) Basile, F.; Cardamone, A.; Grinstead, K. D.; Miller, K. J.;
Lytle, F. E.; Caprara, A.; Clark, C. D.; Heritier, J.-M. Appl. Spectrosc.
1993, 47, 207. (b) Buckner, S. W.; Forlines, R. A.; Gord, J. R. Appl.
Spectrosc. 1999, 53, 115.
(23) Harris, J. M.; Barnes, W. T.; Gustafson, T. L.; Bushaw, T. H.;
Lytle, F. E. Rev. Sci. Instrum. 1980, 51, 988.
(24) Harris, J. M.; Lytle, F. E.; McCain, T. C. Anal. Chem. 1976,
48, 2095.
Supporting Information Available: Full IR spectrum
of complex 4a measured in THF. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM0493006