9,10-dihydroplatinaanthracenes with aromatic diimine ligands: Syntheses and spectroscopic and computational studies of new luminescent materials

Article abstract of DOI:10.1021/om700997v

9,10-Dihydroplatinaanthracenes with aromatic nitrogen ligands were synthesized, derived from 2,2′-bipyridine, 4,4′-dichloro-2,2′- bipyridine, 4,4′-dimethoxy-2,2′-bipyridine, 4,4′- bis(dimethylamino)-2,2′-bipyridine, 4,4′-di-tert-butyl-2,2′- bipyridine, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline, and 2,2′-biquinoline. For comparison purposes, the N,N,N′,N′-tetramethylethylenediamine- derived compound was also obtained. A single-crystal X-ray structure determination was carried out on [H₂C(C₆H ₄)₂]Pt(2,9-dimethyl-1,10-phenanthroline), revealing a pronounced boat conformation of the metallacyclic ring. The diimine-derived compounds are highly luminescent in the solid state at room temperature, as well as in frozen solution. The luminescent complexes are easily prepared by ligand substitution from the new organometallic platinum precursor {[H ₂C-(C₆H₄)₂]Pt(SEt₂)} _n (n = 2, 3). Spectroscopic data are provided on absorbance and emission in the UV-visible range. In order to obtain insight into orbital energies and the tunability of the optical properties, electrochemical data, as well as DFT and TD-DFT data, were obtained. The lowest-energy absorbances are due to charge transfer from orbitals located largely on the electron-rich metallacyclic ligand with some coefficient on Pt into π* orbitals of the diimine. Computations suggest that the low-energy bands mostly originate from charge transfer from the HOMO-2, HOMO-1, and HOMO to the LUMO (rarely LUMO+1 and LUMO+2) molecular orbitals. Emission maxima range from 536 to 690 nm.

Full text of DOI:10.1021/om700997v

Organometallics 2008, 27, 1765–1779
1765
9,10-Dihydroplatinaanthracenes with Aromatic Diimine Ligands:
Syntheses and Spectroscopic and Computational Studies of New
Luminescent Materials
Antonio G. De Crisci,† Alan J. Lough,‡ Kanwarpal Multani,† and Ulrich Fekl*,†
Department of Chemical and Physical Sciences, UniVersity of Toronto Mississauga, 3359 Mississauga
Road N, Mississauga, Ontario, Canada L5L 1C6, and X-ray Crystallography Lab, UniVersity of Toronto
St. George, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6
ReceiVed October 5, 2007
9,10-Dihydroplatinaanthracenes with aromatic nitrogen ligands were synthesized, derived from 2,2′-
bipyridine, 4,4′-dichloro-2,2′-bipyridine, 4,4′-dimethoxy-2,2′-bipyridine, 4,4′-bis(dimethylamino)-2,2′-
bipyridine, 4,4′-di-tert-butyl-2,2′-bipyridine, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline,
3,4,7,8-tetramethyl-1,10-phenanthroline, and 2,2′-biquinoline. For comparison purposes, the N,N,N′,N′-
tetramethylethylenediamine-derived compound was also obtained. A single-crystal X-ray structure
determination was carried out on [H2C(C6H4)2]Pt(2,9-dimethyl-1,10-phenanthroline), revealing a pro-
nounced boat conformation of the metallacyclic ring. The diimine-derived compounds are highly
luminescent in the solid state at room temperature, as well as in frozen solution. The luminescent complexes
are easily prepared by ligand substitution from the new organometallic platinum precursor {[H2C-
(C6H4)2]Pt(SEt2)}n (n ) 2, 3). Spectroscopic data are provided on absorbance and emission in the
UV–visible range. In order to obtain insight into orbital energies and the tunability of the optical properties,
electrochemical data, as well as DFT and TD-DFT data, were obtained. The lowest-energy absorbances
are due to charge transfer from orbitals located largely on the electron-rich metallacyclic ligand with
some coefficient on Pt into π* orbitals of the diimine. Computations suggest that the low-energy bands
mostly originate from charge transfer from the HOMO-2, HOMO-1, and HOMO to the LUMO (rarely
LUMO+1 and LUMO+2) molecular orbitals. Emission maxima range from 536 to 690 nm.
field since the seminal 1990 paper.5 Co-ligands reported, in
addition to the chelating hydrocarbon forming part of the
metallacyclic ring, have been alkenes (cyclooctadiene), phos-
phines, and, for Pt(IV) compounds, additional halides.4 Surpris-
ingly, no reports are available on nitrogen-based ligands
coordinated to 9,10-dihydroplatinaanthracenes. Attaching nitrogen-
based aromatic ligands, such as substituted 2,2′-bipyridines or
1,10-phenanthrolines, to a 9,10-dihydroplatinaanthracene prom-
ises to provide highly luminescent materials, as might be inferred
from the fact that platinum(II) complexes featuring an N2C2
coordination sphere have often been found to be luminescent,
in particular if the nitrogen donors are part of a π-system.
Examples of such luminescent N2C2Pt systems are platinum(II)
centers bis-chelated by ortho-deprotonated phenylpyridine,6
platinum(II) bisacetylides having aromatic diimines,7 monoacetyl-
ides containing a cyclometalated 6-phenyl-2,2′-bipyridine,8 and
also diarylplatinum(II) complexes containing as nitrogen donors
Introduction
Metallacycles are important organometallic compounds, and
a metallacycle may be defined as “a carbocyclic system with
one or more carbons replaced by a transition metal”.1
Four-membered and five-membered metallacycles are relevant
for a host of catalytic cycles leading to C-C bond formation,
and while such metallacycles have been studied in much detail
in the past, six-membered metallacycles have been studied much
less, until, it seems, rather recently.2 However, an increased
amount of research has been directed toward six-membered
metallacycles in the last several years, due to the comparably
young field of metallabenzenes.3 A significant part of our
research activity aims at synthetically extending the field of six-
membered metallacycles involving platinum (platinacycles), and
we found the field related to the 9,10-dihydroplatinaanthracenes
highly attractive. The first 9,10-dihydroplatinaanthracenes were
developed in the pioneering work by Alcock, Bryars, and
Pringle,4 and there exists essentially no published work in this
(5) However, for a bucky-bowl complex that contains a substructure
resembling a platinaanthracene: Shaltout, R. M.; Sygula, R.; Sygula, A.;
Fronczek, F. R.; Stanley, G. G.; Rabideau, P. W. J. Am. Chem. Soc. 1998,
120, 835.
* Corresponding author. E-mail: ulrich.fekl@utoronto.ca.
† Department of Chemical and Physical Sciences.
(6) Maestri, M.; Sandrini, D.; Balzani, V.; Chassot, L.; Jolliet, P.; von
Zelewsky, A. Chem. Phys. Lett. 1985, 122, 375.
‡ X-ray Crystallography Lab.
(1) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry, 2nd ed.; University
Science Books: Mill Valley, CA, 1987.
(7) (a) Hissler, M.; McGarrah, J. E.; Connick, W. B.; Geiger, D. K.;
Cummings, S. D.; Eisenberg, R. Coord. Chem. ReV. 2000, 208, 115. (b)
Whittle, C. E.; Weinstein, J. A.; George, M. W.; Schanze, K. S. Inorg.
Chem. 2001, 40, 4053. (c) Kang, Y.; Lee, J.; Song, D.; Wang, S. Dalton
Trans. 2003, 3493. (d) Wadas, T. J.; Lachicotte, R. J.; Eisenberg, R. Inorg.
Chem. 2003, 42, 3772.
(2) (a) Puddephatt, R. J. Coord. Chem. ReV. 1980, 33, 149. (b) Dyker,
G. Chem. Ber. 1997, 130, 1567. (c) Cámpora, J.; Palma, P.; Carmona, E.
Coord. Chem. ReV. 1999, 193–195, 207.
(3) (a) Bleeke, J. R. Chem. ReV 2001, 101, 1205. (b) Landorf, C. W.;
Haley, M. M. Angew Chem., Int. Ed. 2006, 45, 3914.
(4) Alcock, N. W.; Bryars, K. H.; Pringle, P. G. J. Chem. Soc., Dalton
Trans. 1990, 1433.
(8) (a) Experimental work: Lu, W.; Mi, B.-X.; Chan, M. C. W.; Hui,
Z.; Zhu, N.; Lee, S.-T.; Che, C.-M. Chem. Commun. 2002, 206. (b) DFT
and TD-DFT Computations: Zhou, X.; Pan, Q.-J.; Xia, B.-H.; Li, M.-X.;
Zhang, H.-X.; Tung, A.-C J. Phys. Chem. A 2007, 111, 5465.
10.1021/om700997v CCC: $40.75
2008 American Chemical Society
Publication on Web 03/15/2008

1766 Organometallics, Vol. 27, No. 8, 2008
De Crisci et al.
Scheme 1
Scheme 2
either 1,4-diaza-1,3-butadienes,9 aromatic diimines10 (such as
2,2′-bipyridines or 1,10-phenanthrolines), substituted pyridyl-
benzimidazoles,11 or substituted dipyridylamines.12 While this
list is not exhaustive, it is interesting that six-membered
metallacycles are underutilized, and the promising luminophores
that could be obtained with nitrogen-chelated 9,10-dihydro-
platinaanthracenes have not been synthesized so far. Platinum-
based luminescent materials are of great interest as efficient
emitting layers in organic light-emitting diodes (OLEDs).13
Here, we report the syntheses of the first 9,10-dihydroplati-
naanthracenes containing nitrogen-based ligands. Most of the
new compounds show intense luminescence, and varying the
nitrogen ligand allows facile tuning of the emission frequency
from green to red. We are complementing the synthetic and
spectroscopic data with electrochemical data and MO computa-
tions, in order to gain insight into how changing the ligand
affects orbital energies.
suggested by Pringle.14 Sodium-enriched lithium (3) proved
essential for the synthesis of 2,2′-dilithiodiphenylmethane (4).
Compound 4 has to be carefully prepared to control the amount
of basic impurities (see Experimental Section), which then
allows smooth reaction of an ether solution of 4 with cis-
PtCl2(SEt2)2 (5, Scheme 2) to produce metallacyclic 6 (Experi-
mental Section). The oligomer 6 is obtained as a mixture of a
major (78%, per Pt) and a minor (22%) species, which both
have the composition “[H2C(C6H4)2]Pt(SEt2)” and appear to
differ only by the degree of oligomerization (cyclic dimer vs.
cyclic trimer). From a synthetic point of view, the mixture is
an excellent reagent for the synthon “[H2C(C6H4)2]Pt”. Adding
an excess of free diethyl sulfide quantitatively yields a mono-
nuclear complex containing two SEt2 molecules per Pt, namely,
[H2C(C6H4)2]Pt(SEt2), 6b. We note that 6, {[H2C(C6H4)2]-
Pt(SEt2)}n (n ) 2, 3), is reasonably stable to air and water, and
it appears as an off-white solid that is sparingly soluble in most
organic solvents. 1H NMR spectroscopy demonstrates for 6 that
the two methylene hydrogens (exhibiting platinum satellites)
are chemically inequivalent, as previously observed4 for the
phosphine-ligated platinum(II) complexes. A very similar
observation is made for 6b, [H2C(C6H4)2]Pt(SEt2)2, shown in
Figure 1.
NOESY experiments (at 0 °C in dichloromethane-d2) confirm
that the axial proton (proton spatially closer to the Pt atom)
gives rise to the largest platinum coupling for the peak which
is located further downfield in the 1H NMR spectrum. Somewhat
related close spatial proximities have been reported for a system
where a chelating bis(N-7-azaindolyl)methane, having a central
CH2 moiety, was used.15 It was reported that the seven-
membered ring was severely puckered and that the CH2 moiety
was rather close to Pt, with the shorter Pt-H distance being
2.44 Å from the platinum center. For the compounds we report
here, the six-membered ring of the [H2C(C6H4)2]Pt unit should
provide for a larger Pt-H distance, and in fact we observe for
a [H2C(C6H4)2]Pt unit chelated by 2,9-dimethylphenanthroline
(see below) that the closest Pt-H distance involving a metal-
lacyclic methylene hydrogen is 3.07 Å. It is likely that the larger
4JPtH coupling for the proton closer to the platinum center is
due to some “through-space” coupling component.
Results and Discussion
Syntheses. All luminescent complexes in this work were
synthesized using a dialkylsulfide-bridged oligomer, {[H2C-
(C6H4)2]Pt(SEt2)}n (n ) 2, 3), as the precursor providing the
metallacyclic units. The oligomer was prepared in four steps
by modification of published procedures, using commercially
available compounds (Schemes 1 and 2). The Grignard reagent
derived from 1-bromo-2-chlorobenzene was coupled with
2-chlorobenzaldehyde to yield 2,2′-dichlorodiphenylmethanol
(Scheme 1, compound 1). Reduction provided 2,2′-dichlo-
rodiphenylmethane (2) in excellent yield. Crucial for the
assembly of the metallacyclic unit is the use of lithium
containing a very well-defined amount of sodium (2.5%), as
(9) (a) Kaim, W.; Klein, A.; Hasenzahl, S.; Stoll, H.; Záliš, S.; Fiedler,
J. Organometallics 1998, 17, 237. (b) Klein, A.; van Slageren, J.; Záliš, S.
Inorg. Chem. 2002, 41, 5216.
(10) (a) Klein, A.; Kaim, W. Organometallics 1995, 14, 1176. (b)
Dungey, K. E.; Thompson, B. D.; Kane-Maguire, N. A. P.; Wright, L. L.
Inorg. Chem. 2000, 39, 5192. (c) Klein, A.; van Slageren, J.; Záliš, S. Eur.
J. Inorg. Chem. 2003, 1917.
(11) Liu, Q.-D.; Jia, W.-L.; Wang, S. Inorg. Chem. 2005, 44, 1332.
(12) Liu, Q.-D.; Jia, W.-L.; Gang, W.; Wang, S. Organometallics 2003,
22, 3781.
With precursor 6 in hand, synthesis of the nitrogen-chelated
complexes proved straightforward. All chelate ligands used were
commercially available, with the exception of 4,4′-bis(dimethyl-
(13) (a) Baldo, M. A.; O’Brien, D. F.; You, Y.; Shoustikov, A.; Sibley,
S.; Thompson, M. E.; Forrest, S. R. Nature 1998, 395, 151. (b) Wong,
W.-Y.; He, Z.; So, S.-K.; Tong, K.-L.; Lin, Z. Organometallics 2005, 24,
4079. (c) He, Z.; Wong, W.-Y.; Yu, X.; Kwok, H.-S.; Lin, Z. Inorg. Chem.
2006, 45, 10922. (d) Evans, R. C.; Douglas, P.; Winscom, C. J. Coord.
Chem. ReV. 2006, 250, 2093. (e) Zhou, G.-J.; Wang, X.-Z.; Wong, W.-Y.;
Yu, X.-M.; Kwok, H.-S.; Lin, Z. J. Organomet. Chem. 2007, 692, 3461.
(14) Pringle, P. G. (University of Bristol), personal communication.
(15) Song, D.; Wang, S. Organometallics 2003, 22, 2187.

9,10-Dihydroplatinaanthracenes with Aromatic Diimine Ligands
Organometallics, Vol. 27, No. 8, 2008 1767
Figure 3. 1,10-Phenanthroline series: compounds 13–15.
Figure 1. Room-temperature 200 MHz 1H NMR spectrum, in C6D6,
of the methylene region of 6b, [H2C(C6H4)2]Pt(SEt2)2, obtained from
cyclic oligomer 6 using an excess of SEt2. Peaks appear at 3.74
4
(1Ha, d, C-H, JPtH ) 9.6 Hz, JHH ) 13.0 Hz) and 4.51 (1Hb, d,
C-H, 4JPtH ) 18.8 Hz, JHH ) 13.2 Hz). Assignment was confirmed
by NOESY (Experimental Section).
Figure 4. Compounds derived from 2,2′-biquinoline (16) and tmeda
(17).
spectroscopic observation is made that the two methylene
protons on every metallacyclic compound (8–17) are not
equivalent, such that the relative rigidity, on the time scale given
by the magnetic field strength and the peak-to-peak separation,
that was seen for 6 and 6b (see above) is also present in the
luminescent materials 8-16 and compound 17. Also, Pt satellites
are clearly seen for each of the two methylene protons (best
observed at low field strength).
Structure of [H2C(C6H4)2]Pt(2,9-dimethyl-1,10-phenan-
throline) (14). Crystals suitable for X-ray diffraction were
obtained for (CH2(C6H4)2)Pt(2,9-dimethyl-1,10-phenanthroline),
compound 14. A single-crystal X-ray structure determination
(details in the Experimental Section, molecular structure in
Figure 5) confirmed that the desired product has been made
and provides relevant data on the geometry of the nitrogen ligand
and the metallacyclic moiety.
The platinum environment can be described as approximately
square-planar, but distortions from planarity, likely caused by
steric repulsion (methyl groups on the phenanthroline ligand),
are significant: Pt1 is dislocated by 0.1023(3) Å from the plane
formed by the donor atoms (N1, N1′, C1, C1′). The platinacycle
adopts a very pronounced boat conformation (see Figure 5),
similar to the boat conformation of [H2C(C6H4)2]Pt(PEt3)2.4,16
The 2,9-dimethyl-1,10-phenanthroline ligand is not planar, and
best planes through the outer aromatic rings of this nitrogen
ligand form a dihedral angle of 18.9(3)°. The phenanthroline
ligand plane (defined by N1, C13, C13′, N1′) forms a dihedral
angle of 30.8(3)° with the PtN2 plane (Pt1, N1, N1′), demon-
strating the pucker in the five-membered chelate ring involving
the nitrogen ligand. It is relevant here that π-stacking interactions
and Pt-Pt close contacts can occur in solid-state structures of
platinum compounds, and it is known that such interactions can
influence the emissive properties of platinum(II) luminophores.
Figure 2. 2,2′-Bipyridine series: compounds 8–12.
amino)-2,2′-bipyridine (7), which was prepared according to a
modified literature procedure (see Experimental Section). Syn-
thesis of the monomeric nitrogen-chelated metallacyclic com-
pounds 8–17 was achieved by adding 1 equiv of the nitrogen
donor ligand per one Pt of 6, followed by gentle reflux in
benzene. The bipyridine-derived compounds (8-12) are shown
in Figure 2, whereas the phenanthroline-derived compounds
(13-15) are shown in Figure 3. The compounds derived from
2,2′-biquinoline (16) and N,N,N′,N′-tetramethylethylenediamine
(tmeda) (17) are shown in Figure 4. All new nitrogen chelates
8-17 were unambiguously characterized, including elemental
analysis, as described in the Experimental Section. For the
1
majority of complexes, both H and 13C NMR spectroscopic
data were obtained. For the few examples where solubility was
1
very low, only H NMR spectroscopy was performed, and it
was then performed at elevated temperature. UV–visible
spectroscopy was performed on all compounds 8–17, discussed
in detail below. The metallacyclic compounds are air- and water-
stable as solids, but mildly hygroscopic. The important NMR
(16) DFT computations using RB3LYP and the SDD basis set also
predict a boat-shape conformation of all platinacycles. Compound 13 is
shown in the Supporting Information.

1768 Organometallics, Vol. 27, No. 8, 2008
De Crisci et al.
The lowest-energy bands (in acetonitrile) for the 2,2′-bipyridine
series, the 1,10-phenanthroline series, and the set having the
two remaining compounds (biquinoline and tmeda) are shown
in Figures 6, 7, and 8, respectively (see Supporting Information
for complete UV–vis spectra). The position of the lowest-energy
absorption maximum strongly depends on the nature of the
nitrogen chelate. For compounds containing substituted 2,2′-
bipyridines (8–12, Figure 6) and 1,10-phenanthrolines (13–15,
Figure 7), the positions of the maxima are in the range between
395 and 455 nm, where the 395 nm value refers to the highly
electron-rich 4,4′-bis(dimethylamino)-2,2′-bipyridine complex
11 and the 455 nm value to the electron-deficient 4,4′-dichloro-
2,2′-bipyridine complex 9. This dependence suggests that the
lowest-energy transition is a transition from an orbital that is
largely unaffected by substituents on the nitrogen chelate (likely
located on the metallacyclic ring and/or Pt) into an empty π*
orbital on the nitrogen chelate, a situation that is frequently
encountered when the Pt(II) is in a strong-field environment,
such as provided by two aryls. DFT computations (below) will
show that these excitations indeed occur from an orbital that is
located at the metallacycle and Pt (the HOMO or an energeti-
cally very close filled orbital) into normally the LUMO, which
is essentially a purely diimine-based π* orbital. Such transitions
would be called “ligand-to-ligand charge transfer” (LLCT, from
metallacyclic ligand to diimine) if the fact is ignored that the
donor orbital has a small but not completely negligible coef-
ficient involving a platinum d orbital. However, since the donor
orbital has mixed ligand/metal character, a more accurate term
is “mixed-metal/ligand-to-ligand” charge transfer (MMLLCT).7
Similar MMLLCT transitions have been reported for the five-
ring metallacycle systems Pt(biphenyl-diyl)(diimine).19 The
slightly more general term “charge-transfer-to-diimine” is
equally applicable. Expectedly, the lowest-energy transition20
occurs at very high energy (281 nm) when a π-system on the
nitrogen chelate is missing, such as in 17, and occurs at very
low energy for an extended π-system, such as in 16, at 523
nm.
Compound 16 has an extended π-system which shows a four-
band structure spectrum. We tentatively assign the 250 nm peak
to a π to π* intraligand transition (ILT) of the C^C part of the
molecule, while a broadened peak in the 280–380 nm region may
be attributed to a π to π* intraligand transition (ILT) of the extended
N^N part of the molecule. The lowest-energy transition occurs at
523nm, assigned as a charge-transfer-to-diimine.
Electrochemistry. Cyclic voltammetry was used to determine
the ground-state redox potentials for complexes 8-17. The
redox potentials, where reversibility or lack thereof is indicated,
are included in Table 1. Typically, the complexes each display
two diimine-based reduction potentials (no reduction for the
tmeda-chelated complex 17) and, possibly due to the restrictions
imposed by solvent oxidation at very positive potentials, only
one oxidation potential. The first reduction process is for the
most part reversible, while the second one is mostly quasi-
reversible or irreversible. The oxidation waves are irreversible
(even fast sweep rates and small solvent windows) with the
exception of the tmeda complex 17, which exhibits a quasi-
reversible wave. This might be due to steric stabilization of the
Pt(III) intermediate, via the added steric bulk.21 The reduction
Figure 5. Molecular structure of [H2C(C6H4)2]Pt(2,9-dimethyl-1,10-
phenanthroline) (14). In addition to a thermal ellipsoid plot (top,
30% probability; hydrogens as spheres of arbitrary radius), a ball-
and-stick plot (bottom, hydrogens omitted for clarity) is shown in
order to highlight the geometry of the six-membered chelate ring.
The molecule has crystallographic mirror symmetry (mirror plane
through C7, Pt1, and the center between N1 and N1′). Selected
distances and angles (Å, deg): Pt1-C1, 1.999(5); Pt1-N1, 2.130(5);
C1-Pt1-C1′, 83.9(3); N1-Pt1-N1′, 78.1(2); C1-Pt1-N1′, 98.7(2);
C1-Pt1-N1, 173.6(2); arenes in the metallacyclic ring are not
coplanar: dihedral angle between best plane through C1-C2-C3-
C4-C5-C6 and best plane through C1′-C2′-C3′-C4′-C5′-C6′,
67.6(3); boat conformation of the metallacyclic ring: dihedral angle
between plane through C1-Pt1-C1′ and plane through C6-C7-C6′,
86.0(6).
In a study by Lu et al.,17 where such effects were seen, π-π
contacts were crystallography determined to be in the 3.12 to
3.40 Å range. Pt-Pt distances in complexes where the Pt-Pt
interaction has a significant impact on luminescent properties
are typically around 3.5 Å.18 In the crystal structure of
compound 14, however, the closest Pt-Pt distance is 5.331(3)
Å, the closest ring centroid separation is 4.577(3) Å, and this
is outside the range for significant π-π stacking interactions.
No close, parallel packing of π-ligands is observed in the solid-
state structure. Apparently, the pronounced pucker of the six-
membered metallacyclic ring prevents packing involving sig-
nificant π-stacking. A similar puckered structure also exists for
the remaining compounds, as judged from the fact that all
compounds show nonequivalent methylene hydrogens in the 1H
NMR spectrum. All emissions are in the visible range, and
visually, emissions have the same color for microcrystalline
powder and frozen, glassy, dilute solutions (benzene, dimeth-
ylsulfoxide, tetrahydrofuran, dichloromethane, and hexanes),
demonstrating that the emissive properties are due to electronic
effects within the molecule and are not significantly influenced
by stacking effects.
(18) Miskowski, V. M.; Houlding, V. H.; Che, C.-M.; Wang, Y. Inorg.
Chem. 1993, 32, 2518.
UV/Vis Absorption. UV–vis spectra were obtained for
compounds 8 to 17, and the data are summarized in Table 1.
(19) Blanton, C. B.; Murtaza, Z.; Shaver, R. J.; Rillema, D. P. Inorg.
Chem. 1992, 31, 3230.
(20) For a discussion of what will be the lowest-energy transition in
which metal complex: Roundhill, D. M. Photochemistry and Photophysics
of Metal Complexes; Plenum Press: New York, 1994; p 81.
(17) Lu, M.; Chan, M. C. W.; Cheung, K.-K.; Che, C.-M. Organome-
tallics 2001, 20, 2477.

9,10-Dihydroplatinaanthracenes with Aromatic Diimine Ligands
Organometallics, Vol. 27, No. 8, 2008 1769
Table 1. Absorption Spectral and Electrochemical Data for Compounds 8 to 17 at Room Temperature
E1/2ox/V
(vs Fc+/Fc)a
E1/2red/V
complex
λ
abs/nm (ꢀ/104 M-1 cm-1 a
)
(vs Fc+/Fc)a
Pt(CH2(C6H4)2)(2,2′-bipyridine), 8
188 (2.98), 207 (2.64), 240sh (0.930), 290 (0.709),
429 (0.190)
192 (3.98), 203 (4.10), 249sh (0.641), 296 (0.512),
455 (0.130)
199 (17.22), 210 (17.76), 231sh (7.43), 275 (4.54),
289sh (3.63), 411 (0.721)
0.612d
0.671d
0.551d
0.42b,d,e
0.597d
0.53d,e
0.648d
-1.91, -2.57c
-1.66, -2.33d,e
-2.02c, -2.69c
-2.33b,c -3.05b,d
-2.01, -2.64c
-1.93, -2.55c,e
-2.09c, -2.81c,e
Pt(CH2(C6H4)2)(4,4′-dichloro-2,2′-bipyridine), 9
Pt(CH2(C6H4)2)(4,4′-dimethoxy-2,2′-bipyridine), 10
Pt(CH2(C6H4)2)(4,4′-bis(dimethylamino)-2,2′-bipyridine), 11 191 (6.06), 207 (7.44), 268 (4.76), 294sh (2.86),
309sh (2.57), 395 (0.80)
192 (5.22), 203 (5.39), 246sh (1.09), 296 (1.10),
421 (0.265)
192 (4.97), 203 (5.71), 225sh (1.85), 267 (1.17),
296sh (0.39), 347sh (0.102), 379sh (0.12), 430 (0.17)
192 (4.42), 203 (4.54), 232 (2.88), 271 (1.65), 293sh (0.988),
361 (0.23), 423 (0.23)
Pt(CH2(C6H4)2)(4,4′-di-tert-butyl)-2,2′-bipyridine), 12
Pt(CH2(C6H4)2)(1,10-phenanthroline), 13
Pt(CH2(C6H4)2)(2,9-dimethyl-1,10-phenanthroline), 14
Pt(CH2(C6H4)2)(3,4,7,8-tetramethyl-1,10-phenanthroline), 15 192 (5.51)f, 210 (6.76)f, 231sh (3.89)f, 272 (3.53)f,
0.45d,e
0.59b,d,e
0.785d
-2.21c, -2.91c
-2.10b,c, -2.48b,c
-2.05c, -2.40d,e
306sh (1.39)f, 405 (0.55)f
Pt(CH2(C6H4)2)(2,2′-biquinoline), 16
191sh (2.97), 207 (3.51), 259 (2.51), 275sh (1.37), 309sh (0.81),
328 (0.79), 340sh (0.68), 374 (0.17), 523 (0.07)
194 (9.08), 209sh (7.67), 265 (1.33), 281 (1.31),
287sh (1.18)
Pt(CH2(C6H4)2)(N,N,N′N′-tetramethylethylenediamine), 17
0.513c
no reductions visible
a UV–vis spectra and electrochemical data were measured in anhydrous deoxygenated CH3CN using a quartz cuvette unless otherwise noted.
b Electrochemical measurement was performed in anhydrous, degassed DMF. c Quasireversible process. d Irreversible process. e Broad. f Larger error
associated in the determination of ꢀ (up to (30%) due to very low solubility. See Supporting Information for UV/vis spectra and CV diagrams.
Figure 6. Charge-transfer-to-diimine absorption bands (normalized, in acetonitrile at room temperature) for 2,2′-bipyridine-derived Pt-
metallacycle series, having the following ligands: 2,2′-bipyridine (for 8), 4,4′-dichloro-2,2′-bipyridine (for 9), 4,4′-dimethoxy-2,2′-bipyridine
(for 10), 4,4′-bis(dimethylamino)-2,2′-bipyridine (for 11), 4,4′-di-tert-butyl-2,2′-bipyridine (for 12).
values correlate well with the donating ability of the N^N
chelate. The more donating the ligand is, the more negative the
first reduction potential becomes. For the electron-rich com-
pound 11, chelated by 4,4′-bis(dimethylamino)-2,2′-bipyridine,
the first (reversible) reduction occurs at -2.33 V, whereas the
system involving the least electron-rich ligand, namely, com-
pound 9 (having 4,4′-dichloro-2,2′-bipyridine), is reduced at
-1.66 V. The order of decreasing ease of reduction follows 9,
8, 12, 10, and 11 for the 2,2′-bipyridine series and 13, 14, and
15 for the 1,10-phenanthroline series. A representative example
is shown in Figure 9, the cyclic voltammogram (CV) of 4,4′-
di-tert-butyl-2,2′-bipyridine, 12. One reversible reduction occurs
at -2.01 V, a quasi-reversible reduction occurs at -2.64 V,
and an irreversible oxidation occurs at 0.597 V relative to the
internal ferrocene/ferrocenium (Fc/Fc+) reference couple.
The substituted 1,10-phenanthroline series shows a similar
trend, with the most electron-rich diimine, 3,4,7,8-tetramethyl-
1,10-phenanthroline, giving rise to the most negative first
reduction potential, namely, -2.21 V, whereas -1.93 V is
observed for the system having the less electron-rich ligand 1,10-
phenanthroline. Correlations between electrochemical and spec-
troscopic data are well-known.22–24 In the particular case of a
charge-transfer-to-diimine as the lowest-energy optical transition,
the transition can be viewed as ejection of an electron out of
one of the highest occupied molecular orbitals (metallacycle-
Pt based, orbital energy probed by the redox potential for
oxidation) and injection of an electron into the diimine-based
LUMO (orbital energy probed by the first reduction potential).
The correlation is very good for the new metallacyclic systems,
and Figure 10 shows a plot of the photon energy for absorption
versus “empirical HOMO–LUMO gap”, as defined by the
difference between potential for first oxidation and potential for
first reduction. The data show a good linear agreement, and a
small intercept (0.41) combined with a slope of very close to
(21) Johansson, L.; Ryan, O. B.; Rømming, C.; Tilset, M. Organome-
tallics 1998, 17, 3957.
(22) Cummings, S. D.; Eisenberg, R. J. Am. Chem. Soc. 1996, 118, 1949.
(23) Lever, A. B. P.; Pickens, S. R.; Minor, P. C.; Licoccia, S.;
Ramaswamy, B. S.; Magnell, K. J. Am. Chem. Soc. 1981, 103, 6800.
(24) Rezvani, A. R.; Crutchley, R. Inorg. Chem. 1994, 33, 170.

1770 Organometallics, Vol. 27, No. 8, 2008
De Crisci et al.
Figure 7. Charge-transfer-to-diimine absorption bands (normalized, in acetonitrile at room temperature) for 1,10-phenanthroline-derived
Pt-metallacycle series, using the following ligands: 1,10-phenanthroline (for 13), 2,9-dimethyl-1,10-phenanthroline (for 14), 3,4,7,8-tetramethyl-
1,10-phenanthroline (for 15).
Figure 8. UV–vis spectra showing molar absorptivities for the complexes of 2,2′-biquinoline (for 16) and N,N,N′N′-tetramethylethylenediamine
(for 17), in acetonitrile at room temperature.
unity (0.99) demonstrates that the “empirical HOMO–LUMO
gap”, as measured by electrochemistry, is indeed a very
reasonable predictor of the lowest-energy optical absorbance.
Computations are complementing our experimental data, and
we will discuss computed (DFT) HOMO–LUMO gaps below.
It can be mentioned here that a good correlation also exists for
the DFT-calculated HOMO–LUMO gap vs the difference
between the ground-state oxidation and reduction potentials (see
Supporting Information for plot).
M). Interaction with solvent or self-quenching25 might be
responsible for the apparent lack of emission in room-temper-
ature solution, which contrasts with intense emission from the
solid state. In our quest to tune the emission wavelengths such
that a large part of the visible spectrum is covered, we found
that the emission wavelength is straightforwardly influenced for
the substituted 2,2′-bipyridine series. With the exception of 4,4′-
bis(dimethylamino)-2,2′-bipyridine (11), the more donating the
ligand is, the higher the energy of emission becomes, where
4,4′-dimethoxy-2,2′-bipyridine (10) as a ligand effects a broad
emission in the green region, at 536 nm. The most electron-
deficient substituted 2,2′-bipyridine, 4,4′-dichloro-2,2′-bipyridine
(9), lead to a red-shifted emission in the orange region, at 595
nm (Figure 12).
Luminescence. When excited with UV light (365 nm), all
solid, microcrystalline samples of compounds 8-16, that is, all
nitrogen-chelated Pt compounds described here except the
tmeda-chelated 17, show bright emission at room temperature,
ranging from green, yellow, orange to red. Pictures of lumi-
nescent powders are shown in Figure 11, emission spectra for
8-12 are shown in Figure 12, and peaks are tabulated in Table
2. Very similar emissions are obtained from frozen solutions at
liquid nitrogen temperature, but no emission is detected at room
temperature in benzene, hexanes, dimethylsulfoxide, tetrahy-
drofuran, and dichloromethane solution (concentration ∼0.0001
However, no such clear trend is visible for the emission maxima
belonging to the small series (three members) containing 1,10-
phenanthroline (structures in Figure 3, emission spectra in the
(25) (a) Connick, W. B.; Geiger, D.; Eisenberg, R. Inorg. Chem. 1999,
38, 3264. (b) Fleeman, W. L.; Connick, W. B. Comments Inorg Chem.
2002, 23, 205.

9,10-Dihydroplatinaanthracenes with Aromatic Diimine Ligands
Organometallics, Vol. 27, No. 8, 2008 1771
Figure 9. Cyclic voltammogram (CV) of 12, measured in acetonitrile at 28 °C. Potentials are referenced relative to internal Fc/Fc+ (defined
as 0 V). Scan rate is 1000 mV/s. TBAHFP (0.1 M) was used as the supporting electrolyte.
Figure 10. Plot of experimental (UV–vis, acetonitrile) transition energy for absorbance, Eabs, vs the difference between the ground-state
oxidation and reduction potentials, for complexes 8 to 12. Linear regression analysis yields R2 ) 0.9338, and equation of line is y )
0.9929x + 0.41. Circled datum denotes electrochemical data obtained in DMF solvent.
Supporting Information), and this might be related to the broad
and complex nature of the emission bands for the 1,10-phenan-
throline-derived compounds. Furthermore, the 2,2′-biquinoline
complex 16 yields deep red luminescence at 690 nm, whereas the
tmeda complex 17 yields no significant emission.
DFT Calculations. Molecular orbital calculations (Gaussian
03) using Becke’s hybrid three-parameter functional with Lee,
Yang, and Parr correlation functional (B3LYP),26,27 a variant
of density functional theory (DFT), were performed on the
ground states (singlet) of the new diimine compounds 8-16
and the tmeda compound 17, in order to determine the energies
of the high-lying filled and the low-lying unoccupied orbitals
and to test the hypothesis that the former ones are localized
largely on the metallacycle and the latter ones, for diimine
compounds, largely on the diimine. As can be seen from Figures
13,14,15, for all compounds (see Supporting Information as
well), the HOMO is mainly metallacycle-based with some
d-orbital contribution from Pt. For all diimine-based compounds,
the LUMO is almost entirely based on the diimine ligand.
Consequently, substituents on the diimine influence the HOMO
very little but have a pronounced effect on the LUMO. It results
that the HOMO–LUMO gap is strongly influenced by substit-
uents on the diimine, and the HOMO–LUMO gaps range from
as low as 53.34 kcal/mol to as high as 62.75 kcal/mol. This
9.41 kcal/mol range (gas phase) is responsible for the fact that
the position of the low-energy absorbance maximum is easily
tuned by attaching electron-donating or electron-withdrawing
substituents to the metallacycle. Similarly, the emission proper-
ties are tuned. While the emission maxima are, naturally, shifted
to higher wavelength compared to the charge-transfer-to-diimine
absorbances (data in Table 2), a change in the electron density
(26) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(27) Stephens, P. J.; Devlin, F. J.; Cabalowski, C. F.; Frisch, M. J. J.
Phys. Chem. 1994, 98, 11623.

1772 Organometallics, Vol. 27, No. 8, 2008
De Crisci et al.
effects on electronic structure.31 Despite the fact that the TD-
DFT calculations were carried out using PCM, there is still only
semiquantitative agreement between the calculated and the
observed lowest-energy absorbance maxima. The trends ob-
served are reproduced well by the computations, but the
transition energies for the charge-transfer-to-diimine are con-
sistently underestimated by between 9 and 70 nm. This level
of disagreement between TD-DFT calculations and experiments
is commonly observed, and the extent of disagreement may
depend on the strength of the solvatochromism of the
molecule.9b Factors that likely account for the less-than-perfect
agreement between TD-DFT predictions and experimental data
are probably relativistic effects (only partially included in the
effective core potentials used) and spin–orbit coupling,31 as well
as solute–solvent interactions that go beyond purely electrostatic
interactions.
Figure 11. Room-temperature luminescence, caused by 365 nm
excitation, from powder samples (thin layer) of compounds 8-17.
Regarding apparent relative intensities: layer thickness was not
uniform and the brightness/contrast of the relatively weakly emitting
(very thin layer) sample 8 was enhanced relative to 9-15. Blue
specks due to luminescence of the edges of the supporting glass
slides were removed from the picture. The photograph of samples
16 and 17, shown in the inset, was taken with the UV lamp very
close (violet strip caused by excitation light).
Summary and Conclusion
In summary, the first nitrogen-chelated 9,10-dihydroplati-
naanthracenes have been reported, and interesting optical
properties are displayed by those compounds that contain
aromatic diimine ligands. The lowest-energy optical absorbances
are assigned as charge-transfer-to-diimine transitions, as con-
firmed by DFT and TD-DFT computations. The absorbance
maxima are straightforwardly tuned, particularly for the bipy-
ridine-derived systems, using electron-deficient or electron-
donating substituents on the diimine, consistent with the
proposed nature of these transitions (electron-deficient diimines
lead to lower-energy transitions). The diimine-derived systems
are strongly luminescent in the solid state at room temperature,
and for the most part, different substituents on the diimine shift
the emission maxima in the same direction in which they shift
absorbance maxima. We have realized emission colors ranging
from red to green, and an even wider range can probably be
realized. For future applications it may become significant that
the arenes in the puckered metallacyclic ring are unable to rotate
freely or to easily convert into a planar geometry. It may become
important, regarding luminescence quenching mechanisms, that
rotation of the arenes is hindered. Also, the “fixed” nonzero
angle between the metallacyclic arenes and the diimine unit most
certainly makes electronic transitions different from those
observed in completely planar systems. Investigations into the
details of these effects (such as emission lifetimes) will be the
topic of further studies in our group.
of the diimine influences the wavelength of the emission in a
similar way to how it influences the wavelength of the lowest-
energy absorbance. The tmeda complex 17 is computed to have
a larger HOMO–LUMO gap of 107.93 kcal/mol, consistent with
the experimental observation that it has no charge transfer in
the visible region. According to molecular orbital diagrams, the
LUMO is diamine-based for complex 17. In the absence of a
π-system on tmeda, the LUMO is based on the saturated
backbone and has essentially C-H σ* character (Supporting
Information). In solution phase, using the PCM model (see TD-
DFT section, below), the trends are the same, but the HO-
MO–LUMO gaps are larger (Table 3).
Time-Dependent Density Functional Theory (TD-DFT).
Time-dependent density functional theory (TD-DFT) computa-
tions were performed in order to more thoroughly probe the
nature of the lowest-energy excitations. The most appealing
characteristic of TD-DFT is the ability of the computation to
predict λmax, which corresponds to vertical electronic transitions
computed on the ground-state geometries, especially when
solvent effects are accounted for.28 Solvent effects (solvato-
chromic shifts) have been previously discussed, using MO
calculations, for platinum diimine dithiolate systems that show
similar MMLLCT transitions.29 We performed the computations
on the diimine-containing compounds 8 to 1630 using RB3LYP
with the SDD basis set and acetonitrile solvent (see Experimental
Section). It is predicted that the lowest-energy transitions do
occur mostly from HOMO-2, HOMO-1, and HOMO to the
π* LUMO of the diimine ligand with the exception of
compound 11, where the MMLLCT is mainly centered in the
HOMO–LUMO. Table 4 summarizes the computed three
lowest-energy optical transitions for the highly colored diimine-
containing compounds 8 to 16.
Experimental Section
General Information. All manipulations involving organome-
tallic compounds were carried out with the use of a vacuum line
and a dry glovebox using oven-dried glassware and J. Young NMR
tubes. 1H and 13C{1H} NMR spectra were obtained on Varian
Gemini 200 MHz or Unity/Inova Varian 500 MHz spectrometers.
All NMR spectra were taken at 20 °C unless otherwise noted.
The polarizible continuum model (PCM), which we used, is
one of the most widely used methods for modeling solvent
1
Residual proton and carbon peaks were used as reference: H (δ,
ppm, chloroform-d, 7.24; dichloromethane-d2, 5.32, benzene-d6,
7.16, dimethylsulfoxide-d6, 2.49), 13C (δ, ppm, chloroform-d, 77.3;
dimethylsulfoxide-d6, 39.49; dichloromethane-d2, 53.8). The chemi-
cal shifts are reported in parts per million (δ), and the multiplicities
are reported as s (singlet), d (doublet), (triplet), q (quartet), m
(multiplet), and br (broad). CD2Cl2 and CDCl3 were obtained from
Cambridge Isotopes and were dried over CaH2 and vacuum-
transferred before use. (CD3)2SO and C6D6, were purchased from
(28) Jacquemin, D.; Perpète, E. A.; Scalmani, G.; Frisch, M. J.; Ciofini,
I.; Adamo, C. Chem. Phys. Lett. 2006, 421, 272.
(29) (a) Paw, W.; Cummings, S. D.; Mansour, M. A.; Connick, W. B.;
Geiger, D. K.; Eisenberg, R. Coord. Chem. ReV. 1998, 171, 125. (b) Zuleta,
J. A.; Bevilacqua, J. M.; Proserpio, D. M.; Harvey, P. D.; Eisenberg, R.
Inorg. Chem. 1992, 31, 2396.
(30) For tmeda-based compound 17, a lowest-energy transition of 277.9
nm is predicted (experimental: 281 nm), where the transition involves not
only the LUMO but also the LUMO+1. However, the LUMO+1 is
computed to have a positiVe orbital energy, which indicates that the DFT
method employed may not be perfectly applicable to systems where the
empty orbitals are very high in energy.
(31) Preat, J.; Loos, P.-F.; Assfeld, X.; Jacquemin, D.; Perpète, E. A.
Int. J. Quantum Chem. 2007, 107, 574.

9,10-Dihydroplatinaanthracenes with Aromatic Diimine Ligands
Organometallics, Vol. 27, No. 8, 2008 1773
Figure 12. Lowest-energy emission bands for substituted 2,2′-bipyridine series, involving 2,2′-bipyridine (8), 4,4′-dichloro-2,2′-bipyridine
(9), 4,4′-dimethoxy-2,2′-bipyridine (10), 4,4′-bis(dimethylamino)-2,2′-bipyridine (11), and 4,4′-di-tert-butyl-2,2′-bipyridine (12), all measured
at room temperature in the solid state. Emission intensities have been normalized. λexc ) 425 nm. Emission spectra for the 1,10-phenanthroline
series (13-15) and 2,2′-biquinoline-derived 16 can be found in the Supporting Information.
Table 2. Room-Temperature, Lowest-Energy Absorption Max in
Acetonitrile Solution and Solid Emission Max for Compounds
8 to 17
absorption
max/nm
(nm)c
emission
max/nm
(nm)
metallacycle compound
2,2′-bipyridine, 8
4,4′-dichloro-2,2′-bipyridine, 9
4,4′-dimethoxy-2,2′-bipyridine, 10
4,4′-bis(dimethylamino)-2,2′-bipyridine, 11
4,4′-di-tert-butyl-2,2′-bipyridine, 12
1,10-phenanthroline, 13
429
455
411
395
421
430
423
405
523
281
556a
595a
536a
542a
548a
557a
565a
590a
690b
2,9-dimethyl-1,10-phenanthroline, 14
3,4,7,8-tetramethyl-1,10-phenanthroline, 15
2,2′-biquinoline, 16
N,N,N’N′-tetramethylethylenediamine, 17
b
a λexc ) 425 nm. λexc ) 525 nm. c Measured in acetonitrile solution.
Cambridge Isotopes. Diethyl ether, tetrahydrofuran, hexanes, and
benzene (protio and deuterated) were dried over sodium-benzophe-
none and vacuum-transferred before use. Elemental analyses were
conducted at Guelph Laboratories, Guelph, ON, Canada, and
Analytical Laboratory for Environmental Science and Research
Training (ANALEST), Toronto, ON, Canada. Mass spectrometry
(MALDI) was conducted at Advanced Instrumentation for Molec-
ular Structure (AIMS), Toronto, ON, Canada.
Chemicals. The diimines, 2,2′-bipyridine (g99%), 4,4′-di-tert-
butyl-2,2′-bipyridine (98%), 4,4′-dimethoxy-2,2′-bipyridine (97%),
3,4,7,8-tetramethyl-1,10-phenanthroline (g99%), 2,9-dimethyl-1,10-
phenanthroline (crystalline), 2,2′-biquinoline (98%), and N,N,N′,N′-
tetramethylethyelenediamine (g99%) were dried and/or degassed
under vacuum (0.006 Torr) and used as received from Aldrich.
Anhydrous 1,10-phenanthroline (99%) was purchased from Alfa-
Aesar. 4,4′-Dichloro-2,2′-bipyridine (99.9%) was purchased from
Carbosynth Limited of the United Kingdom. 4,4′-Bis(dimethyl-
amino)-2,2′-bipyridine was prepared by a modified literature
method.32,33 K2PtCl4 (99.9%) was purchased from Strem Chemicals.
2-Bromochlorobenzene (99%), 2-chlorobenzaldehyde (g99%), Mg,
small turnings (99.98%), diethylsulfide (98%), glacial acetic acid
(99.7%), iodine chips (99%), hypophosphorous acid (50% aqueous
Figure 13. Shapes of relevant orbitals and their energies (eV) for
the prototypical 2,2′-bipyridine complex 8, calculated using G03/
RB3LYP using the SDD basis set for singlet ground state (see
Supporting Information for compounds 9–12).
solution), lithium chips (0.5% sodium), 1,2-dibromoethane (g99%),
sodium in kerosene (99%), benzophenone (99%), calcium hydride
(g97%), anhydrous magnesium sulfate (99%), ammonium chloride
(g99.5%), sodium sulfate (g99.0%), sodium bicarbonate (g99.5)%,
phenolphthalein (pH indicator), and ferrocene (g98.0%) were
purchased from Sigma-Aldrich. 0.02000 N +/-0.00002 hydro-
chloric acid solution was purchased from VWR International (Ricca
Chemicals). Solvents such as anhydrous 1,2,3,4-tetrahydronaph-
thalene (99%), pentane (99%), acetonitrile (99%), and dimethyl-
formamide (99.8%) were used without any further modification and
purchased from Sigma. Electrochemical grade silver nitrate and
tetrabutylammoniunhexafluorophosphate (TBAHFP) were also pur-
chased from Sigma. 2,2′-Dichlorodiphenylmethanol was prepared
from the following literature method.34
(32) Heindel, N. D.; Kennewell, P. D. J. Chem. Soc. D., Chem. Commun.
1969, 38.
(33) Wehman, P.; Dol, G. C.; Moorman, E. R.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M.; Fraanje, J.; Goubitz, K. Organometallics 1994, 13,
4856.

1774 Organometallics, Vol. 27, No. 8, 2008
De Crisci et al.
Figure 14. Shapes of relevant orbitals and their energies (eV) for the prototypical 1,10-phenanthroline complex 13, calculated using G03/
RB3LYP using the SDD basis set for singlet ground state (see Supporting Information for compounds 14 and 15).
45 min, while the solution was stirred under reflux. The reaction
was then refluxed for an additional 1.5 h or until most of the
Mg turnings were in solution. A dry diethyl ether solution (12
mL) containing degassed 2-chlorobenzaldehyde (5.14 g, 4.12
mL, 0.0366 mol) was added dropwise, but rapidly (not stream-
ing). The reaction mixture was refluxed for another 2 h and
allowed to stir at room temperature overnight. Stirring may be
difficult because of the salt formation. The slurry was treated
with 150 mL of 25% NH4Cl and 25 mL of 3 N HCl. The phases
were separated and the aqueous phase was extracted four times
with 50 mL of diethyl ether. The combined diethyl ether extracts
were washed with 150 mL of distilled water, 125 mL of 10%
Na2SO3, and 150 mL of distilled water. The diethyl ether solution
was dried with MgSO4, filtered, and evaporated in vacuo,
yielding a crude yellow oil. This oil was vacuum-distilled, giving
the carbinol as a white solid with slightly greenish tinge: bp
128 °C at 0.027 kPa, 46% yield (4.25 g). Carbinol peak
confirmed by D2O exchange in CDCl3. 1H NMR (200 MHz,
CDCl3): δ 7.15-7.45 (8H, m, Ar-H), 6.52 (1H, d, C-H, J ) 3.6
Hz), 2.57 (1H, d, OH, J ) 4.0 Hz). 13C NMR (125 MHz, CDCl3):
δ 139.49, 133.47, 129.77, 129.25, 128.49, 127.13, 69.84.
Synthesis of 2,2′-Dichlorodiphenylmethane, 2. Iodine (4.71 g,
0.0186 mol), 2,2′-dichlorodiphenylmethanol (4.71 g, 0.0186 mol),
and glacial acetic acid (110 mL) were stirred under nitrogen in a
250 mL round-bottomed flask with a condenser for about 15 min.
Figure 15. Shapes of relevant orbitals and their energies (eV) for
2,2′-biquinoline compound 16, calculated using G03/RB3LYP using
Hypophosphorous acid, H3PO2 (50% aqueous, 9.5 mL, 0.092 mol),
was added by syringe, and the mixture was heated to 60 °C. The
mixture was stirred for 20 h under nitrogen and then diluted with
55 mL of water. The milky white aqueous phase was extracted
with two 50 mL portions of hexanes, and the volume was reduced
in vacuo. The organic layer was dried over MgSO4 for 24 h and
filtered, and solvent was removed under vacuum.35 If the oil is
purple in color, this can be removed by vacuum or washing with
solution of aqueous bisulfite (the color is from iodine).36 A vacuum
distillation of the oily product gives a clear oil in 96% yield (4.23
the SDD basis set for singlet ground state (see Supporting
Information for compound 17).
Synthesis of Precursors for Luminescent Platinum Com-
plexes. Synthesis of 2,2′-Dichlorodiphenylmethanol, 1. This is
a slightly modified literature procedure:34 a 100 mL three-necked
round-bottom flask equipped with a stir bar, an addition funnel,
and a condenser was charged with Mg turnings (0.924 g, 0.0380
mol), which were activated with a 400 °C heat gun under vacuum
for 1 h. To the activated Mg turnings was added dry diethyl
ether (25 mL), and a solution containing degassed 1-bromo-2-
chlorobenzene (7.00 g, 4.27 mL, 0.0365 mol) in dry ether (15
mL) was added via the addition funnel over a period of 30 to
1
g); impurities remain below 130 °C at 0.020 kPa. H NMR (200
MHz, CDCl3): δ 6.98-7.41 (8H, m, Ar-H), 4.19 (2H, s, CH2). 13
C
(34) Kepler, J. A.; Sparacino, C. M.; Howe, C. R.; Austin, R. D.
J. Labelled Compds Radiopharm. 1982, 19, 271.
(35) Gordon, P. E.; Fry, A. J. Tetrahedron Lett. 2001, 42, 831.
(36) Fry, A. J. (Wesleyan University) personal communication.

9,10-Dihydroplatinaanthracenes with Aromatic Diimine Ligands
Organometallics, Vol. 27, No. 8, 2008 1775
Table 3. Calculated HOMO–LUMO Gap Using G03 at the RB3LYP Level with SDD Atomic Basis Set
gas phase HOMO–LUMO gap,
solution phase HOMO–LUMO gap,
hartrees (kcal/mol)b
metallacycle compound
2,2′-bipyridine, 8
4,4′-dichloro-2,2′-bipyridine, 9
hartrees (kcal/mol)a
0.092 (57.73)
0.085 (53.34)
0.091
0.118 (74.04)
0.109 (68.40)
0.116
4,4′-dimethoxy-2,2′-bipyridine, 10
(57.10)
(72.79)
4,4′-bis(dimethylamino)-2,2′-bipyridine, 11
4,4′-di-tert-butyl-2,2′-bipyridine, 12
1,10-phenanthroline, 13
0.100 (62.75)
0.098 (61.50)
0.094
0.126 (79.07)
0.121 (75.93)
0.120
(58.99)
(75.30)
2,9-dimethyl-1,10-phenanthroline, 14
3,4,7,8-tetramethyl-1,10-phenanthroline, 15
0.098 (61.50)
0.097
0.121 (75.93)
0.125
(60.86)
(78.44)
2,2′-biquinoline, 16
0.085
(53.34)
0.101
(63.38)
N,N,N’N′-tetramethylethylenediamine, 17
0.172
(107.93)
0.193
(121.11)
a Using singlet ground-state DFT at RB3LYP correlation and SDD basis set. b Using singlet ground-state TD-DFT at RB3LYP correlation and SDD
basis set with PCM solvent model with acetonitrile (see DFT notes in Experimental Section).
Table 4. Analysis of absorbances for compounds 8–16. Experimental values are listed for comparison with computed (TD-DFT, singlet
excitations, G03/RB3LYP, SDD basis set) absorbance data. The three lowest-energy transitions are shown for the TD-DFT computations.
main character
MO# f MO#
transition
energy/eV (nm)
oscillator
strength (f)
experimental
compound
8
(1 ) lowest)
assignmentd
λ
abs/nm (ꢀ /M-1 cm-1 a
)
1
2
3
95% S1 94 f 95b
97% S1 92 f 95
94% S1 93 f 95
2.52 (491.5)
2.59 (478.3)
2.63 (471.2)
0.0108
0.0014
0.0920
MMLLCT/LLCT
MLCT
MMLLCT
429 (1900)
9
1
2
3
95% S1 110 f 111b
97% S1 108 f 111
94% S1 109 f 111
95% S1 110 f 111b
96% S1 108 f 111
94% S1 109 f 111
2.29 (540.5)
2.37 (524.2)
2.40 (515.8)
0.0118
0.0018
0.0932
MMLLCT/LLCT
MLCT
MMLLCT
455 (1330)
411 (7210)
395 (8000)
421 (2650)
430 (1733)
10
11
12
13
1
2
3
2.48 (499.3)
2.56 (484.6)
2.57 (481.6)
0.0072
0.0032
0.0977
MMLLCT/LLCT
MLCT
MMLLCT
1
2
3
96% S1 117 f 119
95% S1 118 f 119b
98% S1 116 f 119
95% S1 126 f 127b
96% S1 124 f 127
94% S1 125 f 127
95% S1 100 f 101b
90% S1 98 f 101
7% S1 99 f 101
83% S1 99 f 101
7% S1 98 f 101
6% S1 100 f 102
2.78 (446.1)
2.83 (438.1)
2.90 (427.5)
0.0101
0.1389
0.0017
MMLLCT/LLCT
MMLLCT/LLCT
MLCT
1
2
3
2.62 (473.6)
2.69 (461.7)
2.71 (457.9)
0.0121
0.0017
0.1031
MMLLCT/LLCT
MLCT
MMLLCT
1
2
2.56 (483.8)
2.63 (471.9)
2.63 (471.9)
2.66 (466.9)
2.66 (466.9)
2.66 (466.9)
0.0084
0.0050
0.0050
0.0799
0.0799
0.0799
MMLLCT/LLCT
MLCT
MMLLCT
MMLLCT
MLCT
3
MMLLCT/LLCT
14
15
1
2
3
95% S1 108 f 109b
98% S1 106 f 109
89% S1 107 f 109
7% S1 108 f 110
2.61 (475.3)
2.64 (469.3)
2.69 (461.3)
2.69 (461.3)
0.0064
0.0036
0.0835
0.0835
MMLLCT/LLCT
MLCT
MMLLCT
423 (2300)
405 (5500)c
MMLLCT/LLCT
1
2
93% S1 116 f 118
56% S1 115 f 118
33% S1 116 f 117b
8% S1 114 f 118
89% S1 114 f 118
5% S1 116 f 117b
2.72(455.1)
2.78 (446.6)
2.78 (446.6)
2.78 (446.6)
2.80 (442.6)
2.80 (442.6)
0.0050
0.0311
0.0311
0.0311
0.0047
0.0047
MMLLCT/LLCT
MMLLCT
MMLLCT/LLCT
MLCT
MLCT
MMLLCT/LLCT
3
16
1
2
3
95% S1 120 f 121b
95% S1 118 f 121
88% S1 119 f 121
2.08 (595.9)
2.17 (572.4)
2.27 (545.4)
0.0064
0.0042
0.1487
MMLLCT/LLCT
MLCT
MMLLCT
523 (700)
a UV–vis spectra data were measured in anhydrous deoxygenated CH3CN using a quartz cuvette. b HOMO–LUMO. c Larger error associated in the
determination of ꢀ (up to (30%) due to very low solubility. d MLCT, metal-to-ligand charge transfer; LLCT, ligand-to-ligand charge transfer;
MMLLCT, mixed-metal-ligand-to-ligand charge transfer.
NMR (125 MHz, CDCl3): δ 137.32, 134.63, 130.92, 129.74, 128.10,
127.12, 36.97.
and the temperature was maintained at this level for 15 min. Then
the heat was turned off. The contents were allowed to slowly cool
to room temperature under vigorous stirring. Under an atmosphere
of argon, the tetralin was carefully covered with a layer of pentane;
the light lithium rose to the top of the pentane layer. Using a pipet,
most of the brownish tetralin solution beneath the pentane was
removed. The very small lithium pellets were washed several times
with anhydrous pentane and dried under vacuum.37
Synthesis of Lithium Pellets Containing 2.5% Sodium,
Alloy, 3. In an oven-dried 500 mL flat-bottomed flask fitted with
a large stir bar and argon inlet/outlet, lithium chips (1–3 g)
containing 0.5% sodium and additional sodium metal (2% w/w)
were heated to a boil in anhydrous tetralin (bp 207 °C, 50 mL).
The contents were stirred vigorously until all metal had melted,

1776 Organometallics, Vol. 27, No. 8, 2008
De Crisci et al.
Synthesis of 2,2′-Dilithiodiphenylmethane Solution, 4. The
freshly made (as per the method above) Na-enriched Li (0.180 g,
0.025 mol) was cut into pieces using scissors and flattened with a
glass bottle (used as a roller) into thin sheets (0.5 cm by 3 cm) of
lustrous metal foil, which were then placed in diethyl ether (5 mL)
in a one-neck, 100 mL round-bottomed flask (oven-dried) under
Ar atmosphere. The flask was fitted with a stir bar and addition
funnel and cooled to 0 °C on ice. A solution of 2,2′-dichlorodiphe-
nylmethane (0.5 g, 0.00215 mol) in diethyl ether (9 mL) was added
dropwise over a period of 45 min with vigorous stirring under
dynamic argon atmosphere. The resulting orange solution was then
glass stoppered (under static argon), transferred to a 2 °C refrigerator
with power outlets and stir plate, and left to stir vigorously for 20
to 22 h. Under argon atmosphere, at room temperature, the reaction
mixture was filtered of excess lithium metal using a 0.2 µm
Whatman disk filter and 30 mL glass syringe. The remaining excess
Li chips and flask were washed two times with 2 mL of dry ether,
the washings were combined, and the 18 mL organolithium solution
was stored in a -35 °C freezer (although it is recommended to use
organolithium solution as quickly as possible). LiCl salt was isolated
and tested via flame test to give a red combustion flame. The
concentration of the dilithio compound was determined by a Gilman
double titration where separate aliquots (0.5 mL each) were
quenched with water and 1,2-dibromoethane and titrated against
0.020000 ( 0.00002 N HCl using phenolphthalein indicator for
the neutralization. Yield was calculated to be 80% to 93%
organolithium (not necessarily dilithium reagent, as monolithiated
reagent can also give a false positive) for this 0.5 g scale. The
solution is dark orange and should be stored under argon at -35
°C. Organolithium solutions containing more then 15% basic
impurities were rejected.4,14,38–41
Synthesis of cis-PtCl2(SEt2)2, 5. K2PtCl4 (4.15 g, 0.0100 mol)
was dissolved in 50 mL of water and stirred vigorously in a 100
mL round-bottomed flask to give a deep red solution. Diethyl sulfide
(3.61 g, 4.31 mL, 0.0400 mol) was added, and the flask was
stoppered. The originally deep red supernatant solution became
colorless while a yellow precipitate formed (within 20 min). The
mixture was then stirred for an additional 24 h or until the yellow
precipitate (trans-isomer), initially formed, dissolves completely.
The resulting clear yellow solution is then reduced to dryness, by
applying vacuum at 25 °C, to yield a yellow-white precipitate. The
isomeric mixture is extracted from the residue, by treatment with
a minimum amount of hot benzene (40 mL). The hot solution is
filtered on a hot funnel to remove KCl. After filtration, the benzene
solution is evaporated to half-volume and cooled in an ice bath,
whereupon fine, yellow crystals of the cis-isomer form. The crystals
are separated by suction filtration and washed with several 5 mL
portions of hexanes to remove any trans-isomer. Yield: 83% (3.71
g). 1H NMR (200 MHz, CDCl3, diastereotopic methylene hydrogens
denoted as Ha/Hb): δ 3.10–3.43 (4H, m, S-Ha), 2.43–2.94 (4H, m,
S-Hb), 1.40 (12H, t, CH3, J ) 7.4 Hz). 13C NMR (125 MHz,
CDCl3): δ 32.36, 13.26.42
100 mL of H2O at 25 °C43) was added to quench the solution, and
the volatiles were evaporated under vacuum to give a brown sludge
in water. The mixture was then extracted with 3 × 45 mL of
dichloromethane, and the volume was reduced under vacuum and
dried over MgSO4 overnight. (If the organolithium solution is of
high quality, i.e., less than 15% basic impurity, upon the first
extraction of the aqueous phase, a white insoluble powder can be
seen dropping to the bottom of the extraction funnel. This is the
desired product, and use of MgSO4 should be skipped, as this
insoluble product will be lost during the filtration of MgSO4.) The
light brown solution was then filtered, and MgSO4 residue was
washed with two 45 mL portions of dichloromethane, as the
oligomer is appreciably soluble in dichloromethane. The washings
were combined and dried in vacuo to yield a dark brown oil. Then
2 mL of acetone was added to reveal a white powder. The solid
was isolated by centrifugation and washed with a minimal amount
(∼1 mL) of cold acetone. The white solid was dried in vacuo and
placed in a -35 °C freezer. The product was obtained in 52% (162
mg) yield. Yield and overall procedure are similar to what has been
reported for other dialkylsulfide-bridged oligomers of diarylplatinum
complexes.44–46 NMR spectroscopy showed that 6 was present in
two forms, 6(major) and 6(minor), in a ratio of 78:22 (per Pt). The two
distinct species are assigned as cyclic oligomers with n ) 2 or 3.
A mixture of cyclic dimer and trimer has been reported for the
similar [PtPh2(S(CH3)2)]n (n ) 2, 3), where both the dimer and the
trimer have been crystallographically characterized.47 No attempt
has been made here to assign the individual nuclearity of the major
and the minor species of 6.
1
6
(major). H NMR (500 MHz, C6D6): δ 6.93-7.32 (m, aromatic
region overlap with aromatic region of 6(minor)), 4.46 (1 H, d, CH2,
J) 14.0 Hz), 3.68 (1 H, d, CH2, J) 14.0 Hz), 2.60 (2 H, m,
S-CH2CH3), 2.28 (2 H, m, S-CH2CH3), 1.31 (6 H, t, S-CH2CH3,
J) 7.5 Hz). 6(minor) 1H NMR (500 MHz, C6D6): δ 6.93-7.32 (m,
aromatic region over lap with aromatic region of 6(major)), 4.38 (1
H, d, CH2, J ) 13.5 Hz), 3.62 (1 H, d, CH2, J ) 14.0 Hz), 2.92 (2
H, m, S-CH2CH3), 2.09 (2 H, m, S-CH2CH3), 1.58 (3 H, t,
S-CH2CH3, J ) 7.0 Hz), 1.02 (3H, t, S-CH2CH3, J ) 7.0 Hz). 13
C
NMR (125 MHz, CDCl3) of 6(major) only: δ 146.07, 143.21, 133.86,
126.08, 124.74, 123.75, 50.28, 31.19, 12.63. m/z [MALDI-TOF-
MS]: 451.3; predicted for monomeric (gas-phase ion) C17H20Pt1S1,
451.1. The isotope pattern (450.3, 82%; 451.3, 100%; 452.3, 85%;
453.3, 19%; 454.3, 23%; 455.3, 4%) is in perfect agreement with
the pattern predicted for C17H20Pt1S1 (see Supporting Information,
Figures S13 and S14).
Solution Data for 6b and NOE Assignment of Nonequiva-
lent Methylene (CH2) Protons. An excess (approximately 5 to 10
equiv) of SEt2 was added to a stirred/shaken suspension of
compound 6 in approximately 480 µL of CD2Cl2 to give the highly
soluble, monomeric Pt(SEt2)2(CH2(C6H4)2), 6b, after gentle reflux
1
for 4 min. H NMR (500 MHz, CD2Cl2): δ 7.38 (2H, m, Ar-H,
3JPtH ) 73 Hz), 7.01 (2H, m, Ar-H, 3JPtH ) unresolved broad base),
6.69–6.87 (4H, m, Ar-H), 4.08 (1H, d, C-H, 4JPtH ) 16.0 Hz, J )
4
Synthesis of {[H2C(C6H4)2]Pt(SEt2)}n (n ) 2, 3), 6. Solid
PtCl2(SEt2)2 (5) (0.307 g, 0.688 mmol) was added to a dark orange
solution of 0.130 M 2,2′-dilithiodiphenylmethane (5.60 mL, 0.728
mmol) in diethyl ether at room temperature. The mixture was stirred
for 4 h at ambient temperature under static argon to give a light
brown precipitate. Then 7.00 mL of water (solubility of LiCl 84.5g/
13.5 Hz), 3.37 (1H, d, C-H, JPtH ) unresolved, broad base, J )
13.5 Hz), 2.78–2.85 (4H, m, coordinated S-CH2CH3), 2.63–2.71
(4H, m, coordinated S-CH2CH3), 2.53 (18H excess, free S-CH2CH3,
q, J ) 7.4 Hz), 1.28 (12H, t, coordinated S-CH2CH3, J ) 8.0 Hz),
1.24 (27 H excess, free S-CH2CH3, t, J ) 8.0 Hz). 13C NMR (125
MHz, CD2Cl2) δ 149.12, 145.56, 136.32, 125.57, 124.42, 122.67,
51.20, 28.91 (S-CH2CH3 of coordinated SEt2), 25.37 (S-CH2CH3
of free SEt2), 14.93 (S-CH2CH3 of coordinated SEt2), 13.35 (S-
(37) Keese, R.; Brändle, M. P.; Trevor, P. T. Practical Organic
Chemistry: A Students Guide, Chichester; Hoboken, NJ.: Wiley, 2006, P.
135.
(38) Gilman, H.; Haubein, A. H. J. Am Chem. Soc., 1944, 66, 1515.
(39) Wakefield, B. J. Organolithium Methods, Academic Press; London,
1988.
(40) Wakefield, B. J. The Chemistry of Organolithium Compounds.
Pergamon Press; New York, 1972.
(41) Shriver, D. F. The Manipulation of Air-SensitiVe Compounds.
Wiley-Interscience Publication; New York, 1986.
(42) Kauffman, G. B.; Cowan, D. O. Inorg. Synth., 1966, 6, 211.
(43) CRC Handbook of Chemistry and Physics, 87th Edition. 2006-
2007. http://www.hbcpnetbase.com/ Accessed September 2007.
(44) Lacabra, M. A. C.; Canty, A. J.; Lutz, M.; Patel, J.; Spek, A. L.;
Sun, H.; van Koten, G. Inorg. Chim. Acta, 2002, 327, 15.
(45) Plutino, M. R.; Monsù Scolaro, L.; Albinati, A.; Romeo, R. J. Am.
Chem. Soc., 2004, 126, 6470.
(46) Steele, B. R.; Vrieze, K. Transition Met. Chem., 1977, 2, 140.
(47) Song, D.; Wang, S. J. Organomet. Chem. 2002, 648, 302.

9,10-Dihydroplatinaanthracenes with Aromatic Diimine Ligands
Organometallics, Vol. 27, No. 8, 2008 1777
CH2CH3 of free SEt2). NOESY Spectra taken at 0 °C. Irradiation
of the methylene peak at 3.37 ppm leads to an NOE observation at
4.08 and 7.01 ppm. Irradiation of the methylene peak at 4.08 ppm
leads to an NOE observation at 3.37 ppm. Irradiation of the aromatic
peak at 7.01 ppm leads to an NOE observation at 3.37 ppm.
Synthesis of 4,4′-Bis(dimethylamino)-2,2′-bipyridine (7). This
ligand has been previously synthesized and fully characterized, but
the synthesis was low-yielding (23%).33 We obtained it in improved
yield by using a modification of a literature procedure for substituted
pyridines.32 4,4′-Dichloro-2,2′-bipyridine (0.250 g, 0.0011 mol) was
refluxed with stirring in dimethylformamide (4.00 mL, 3.78 g, 0.052
mol) at 165 °C for 18 h in a 25 mL Pyrex reaction vessel. Removal
of excess DMF was accomplished by evacuation. Dissolution of
the hydrochloride salt was done by adding a saturated sodium
bicarbonate solution to the precipitate and shaking vigorously in
an extraction funnel to yield an insoluble product. The insoluble
product was triturated, filtered, washed with copious amounts of
distilled water, and dried in vacuo to yield a light beige powder in
58% yield (156 mg). 1H NMR (200 MHz, (CD3)2SO): in excellent
agreement with literature,33 δ 8.19 (2H, d, Ar-H, J ) 5.8 Hz), 7.66
(2H, d, Ar-H, J ) 2.4 Hz), 6.63 (2H, dd, Ar-H, J ) 2.6, 6.0 Hz),
3.01 (12H, s, ArN-CH3). 13C NMR (125 MHz, (CD3)2SO): δ
155.89, 154.78, 148.79, 106.74, 103.04, 38.90 (sh on DMSO peak).
) 7.0 Hz), 3.96 (1H, d, CH2, J ) 13.0 Hz), 3.32 (1H, d, CH2, J )
unresolved). 13C NMR (125 MHz, (CD3)2SO): δ 156.40, 150.10,
147.33, 145.10, 144.98, 137.12, 127.79, 127.75, 124.67, 124.19,
121.78, 50.40. Anal. Calcd for PtC23H16N2Cl2: C, 47.11; H, 2.75;
N, 4.78. Found: C, 47.03; H, 2.95; N, 5.17.
Synthesis of Pt(CH2(C6H4)2)(4,4′-dimethoxy-2,2′-bipyridine),
10. This complex was prepared using the method described for
Pt(CH2(C6H4)2)(2,2′-bipyridine) (8) to give a yellow-green precipi-
tate in quantitative yield. Analytically pure samples can be achieved
by washing insoluble products in copious amounts of benzene and
1
hexanes. H NMR (500 MHz, (CD3)2SO): δ 8.66 (2H, d, ArN-H,
J ) 6.5 Hz), 8.26 (2H, s, ArN-H), 7.37 (2H, dd, ArN-H, J ) 1.5,
5.70 Hz), 7.26 (2H, d, Ar-H, 3JPtH ) broad base (unresolved), J )
7.0 Hz), 6.95 (2H, d, Ar-H, J ) 7.0 Hz), 6.80 (2H, t, Ar-H, J )
7.0 Hz), 6.73 (2H, t, Ar-H, J ) 7.0 Hz), 4.01 (6H, s, OCH3), 3.95
(1H, d, CH2, J ) 13.0 Hz), 3.30 (1H, d, CH2, J ) unresolved). 13
C
NMR (125 MHz, (CD3)2SO): δ 166.78, 157.30, 150.29, 147.41,
146.02, 137.26, 127.75, 123.94, 121.24, 112.50, 110.39, 56.70,
37(sh on DMSO solv peak). Anal. Calcd for PtC25H22N2O2 · ½H2O:
C, 51.19; H, 3.95; N, 4.78. Found: C, 51.24; H, 3.92; N, 4.22.
Synthesis of Pt(CH2(C6H4)2)(4,4′-bis(dimethylamino)-2,2′-bi-
pyridine), 11. This complex was prepared using the method
described for Pt(CH2(C6H4)2)(2,2′-bipyridine) (8) to give a greenish-
yellow precipitate in quantitative yield. Analytically pure samples
can be achieved by washing insoluble products in copious amounts
Synthesis of Monomeric Luminescent Platinum Complexes.
Synthesis of Pt(CH2(C6H4)2)(diimine) 8–17. The Pt(CH2(C6H4)2)-
(diimine) complexes were prepared by displacement of the dieth-
ylsulfide ligands to give the monomeric metallacyclic diimine
complexes. The reactions were performed on NMR scales (8 to 26
1
of benzene and hexanes. H NMR (500 MHz, (CD3)2SO): δ 8.31
(2H, d, ArN-H, J ) 6.5 Hz), 7.59 (2H, d, ArN-H, J ) 2.5 Hz),
7.24 (2H, d, Ar-H, J ) 7.0 Hz), 6.90 (2H, d, Ar-H, J ) 7.0 Hz),
6.86 (2H, dd, ArN-H, J ) 3.0, 6.75 Hz), 6.75 (2H, t, Ar-H, J )
6.0 Hz), 6.69 (2H, t, Ar-H, J ) 7.5 Hz), 3.91 (1H, d, CH2, J )
13.0 Hz), 3.27 (1H, d, CH2, J ) 13.5 Hz), 3.15 (12H, s, CH3). Too
insoluble to obtain 13C. Anal. Calcd for PtC27H28N4 · 2H2O: C,
50.70; H, 5.04; N, 8.76. Found: C, 50.74; H, 4.81; N, 8.34.
1
mg), and conversion was quantitative by 500 MHz H NMR, but
isolated yields varied from 88 to 96%.
Synthesis of Pt(CH2(C6H4)2)(2,2′-bipyridine), 8. To a suspen-
sion of {[H2C(C6H4)2]Pt(SEt2)}n (n ) 2), 6 (8.00 mg, 0.00887
mmol), in 560 uL of C6D6 in a J. Yonge NMR tube was added
2,2-bipyridine (2.77 mg, 0.0177 mmol). The solution was sonicated
for 1 min and heated to reflux for 5 min while a color change
occurred. The highly colored product was initially (at elevated
temperature) dissolved and then slowly crystallized upon cooling.
Synthesis of Pt(CH2(C6H4)2)(4,4′-di-tert-butyl)-2,2′-bipyri-
dine), 12. This complex was prepared using the method described
for Pt(CH2(C6H4)2)(2,2′-bipyridine) (8) to give a green-yellow
precipitate in quantitative yield. Analytically pure samples can be
achieved by washing insoluble products in copious amounts of
benzene and hexanes. 1H NMR (500 MHz, (CD3)2SO): δ 8.80 (2H,
d, ArN-H, J ) 6.0 Hz), 8.65 (2H, d, ArN-H, J ) 1.5 Hz), 7.77
(2H, dd, ArN-H, J ) 2.0, 6.0 Hz), 7.27 (2H, d, Ar-H, J ) 7.5 Hz),
6.96 (2H, d, Ar-H, J ) 6.5 Hz), 6.83 (2H, t, Ar-H, J ) 7.5 Hz),
6.75 (2H, t, Ar-H, J ) 7.5 Hz), 3.95 (1H, d, CH2, J ) 13.0 Hz),
3.31 (1H, d, CH2, J ) unresolved), 1.42 (18H, s, CH3). 13C NMR
(125 MHz, (CD3)2SO): δ 162.64, 155.49, 148.91, 147.42, 146.12,
137.39, 124.03, 123.97, 123.86, 121.42, 120.86, 50.61, 35.75, 29.91.
Anal. Calcd for PtC31H34N2 · ½H2O: C, 58.29; H, 5.52; N, 4.39.
Found: C, 58.46; H, 5.89; N, 4.36.
Synthesis of Pt(CH2(C6H4)2)(1,10-phenanthroline), 13. This
complex was prepared using the method described for Pt(CH2-
(C6H4)2)(2,2′-bipyridine) (8) to give a yellow precipitate in quantita-
tive yield. Analytically pure samples can be achieved by washing
insoluble products in copious amounts of benzene and hexanes and
precipitation of slowly cooled, supersaturated acetonitrile solutions.
1H NMR taken at 30 °C (500 MHz, (CD3)2SO): δ 9.30 (2H, dd,
ArN-H, J ) 1.0, 5.25 Hz), 8.99 (2H, dd, ArN-H, J) 1.0, 8.0 Hz),
8.29 (2H, s, ArN-H), 8.15 (2H, dd, ArN-H, J ) 5.0, 8.0 Hz), 7.46
(2H, d, Ar-H, J ) 7.5 Hz), 7.03 (2H, d, Ar-H, J ) 8.0 Hz), 6.92
(2H, t, Ar-H, J ) 7.0 Hz), 6.81 (2H, t, Ar-H, J ) 7.5 Hz), 4.04
(1H, d, CH2, J ) 13.5 Hz), 3.39 (1H, d, J ) 13.5 Hz). Too insoluble
to obtain 13C. Anal. Calcd for PtC25H18N2 · ½H2O: C, 54.54; H,
3.48; N, 5.09. Found: C, 54.56; H, 3.48; N, 5.15.
1
The reaction was monitored to completion by H NMR using the
3
appearance of free diethylsulfide peaks at 2.26 ppm (4H, q, J )
3
7.0 Hz) and 1.05 ppm (6H, t, J ) 7.5 Hz) and the disappearance
of coordinated diethylsulfide peaks as indicative of reaction
progress. The solution was dried under reduced pressure to remove
free SEt2 and solvent to reveal a yellow product in quantitative
yield. Product is mostly insoluble in organic solvents. Analytically
pure samples can be achieved by washing the insoluble product in
copious amounts of benzene and hexanes. 1H NMR (500 MHz,
(CD3)2SO): δ 8.92 (2H, d, ArN-H, J ) 5.5 Hz), 8.70 (2H, d, ArN-
H, J ) 8.0 Hz), 8.37 (2H, t, ArN-H, J ) 8.0 Hz), 7.79 (2H, t,
3
ArN-H, J ) 7.0 Hz), 7.30 (2H, d, Ar-H, JPtH ) broad base
(unresolved), J ) 7.5 Hz), 6.98 (2H, d, Ar-H, J ) 7.0 Hz), 6.86
(2H, t, Ar-H, J ) 7.0 Hz), 6.77 (2H, t, Ar-H, J ) 7.5 Hz), 3.98
(2H, d, CH2, J ) 13.0 Hz), 3.36 (1H, d, CH2, J ) unresolved). 13
C
NMR (125 MHz, (CD3)2SO): δ 155.55, 149.17, 147.48, 145.72,
144.13, 138.76, 137.37, 127.23, 124.10, 123.72, 121.59, 50.56.
Anal. Calcd for PtC23H18N2 · ½H2O: C, 52.47; H, 3.64; N, 5.32.
Found: C, 52.80; H, 3.43; N, 4.86.
Synthesis of Pt(CH2(C6H4)2)(4,4′-dichloro-2,2′-bipyridine),
9. This complex was prepared using the method described for
Pt(CH2(C6H4)2)(2,2′-bipyridine) (8) to give an orange precipitate
in quantitative yield. Analytically pure samples can be achieved
by washing the moderately soluble product in copious amounts of
benzene and hexanes and precipitation from a slowly cooled,
supersaturated acetonitrile solution. 1H NMR (500 MHz,
(CD3)2SO): δ 8.98 (2H, s, ArN-H), 8.83 (2H, d, ArN-H, J ) 6.0
Hz), 7.95 (2H, dd, ArN-H, J ) 1.75, 5.15 Hz), 7.27 (2H, d, Ar-H,
3JPtH ) broad base (unresolved), J ) 7.0 Hz), 6.98 (2H, d, Ar-H,
J ) 7.0 Hz), 6.85 (2H, t, Ar-H, J ) 7.0 Hz), 6.77 (2H, t, Ar-H, J
Synthesis of Pt(CH2(C6H4)2)(2,9-dimethyl-1,10-phenanthro-
line), 14. This complex was prepared using the method described
for Pt(CH2(C6H4)2)(2,2′-bipyridine) (8) to give a yellow precipitate
in quantitative yield. Analytically pure samples can be achieved
by washing insoluble products in copious amounts of benzene and

1778 Organometallics, Vol. 27, No. 8, 2008
De Crisci et al.
1
hexanes. H NMR (500 MHz, (CD3)2SO): δ 8.76 (2H, d, ArN-H,
UV–vis spectrophotometer with OLIS Spectral Works software
version 4.3 with no digital filtering and lamp change occurring at
385 nm. Emission spectra were obtained on a Fluoromax-4
fluorescence spectrofluorometer equipped with 150 W xenon,
continuous output, ozone-free lamp and Hamamatsu R928P pho-
tomultiplier tube detector. Powders were suspended in a minimal
amount of dry hexanes and placed on glass slides during which
solvent evaporation furnished the self-adhesive samples to the glass
microscope slides. Room-temperature emissions of the solid sample
were collected with the glass slide at 45°, reflecting the original
light source opposite of the detector. The emission spectra were
corrected for the detector sensitivity in the region below 12500
cm-1 (800 nm) and calibrated with anthracene standard (emission).
Electrochemical Measurements. Cyclic voltammograms were
obtained using a BASi Epsilon electrochemical workstation. The
electrochemical cell consisted of a platinum wire auxiliary electrode,
nonaqueous Ag/Ag+ reference electrode, and platinum disk working
electrode. TBAHFP (0.1 M) in degassed, low-water (8.7 ppm)
acetonitrile was used as the electrolyte. Potentials reported are
referenced relative to the freshly sublimed internal standard,
ferrocene/ferrocenium (Fc/Fc+), the reversible redox potential for
which is referenced as zero. The nonaqueous electrode was filled
with 0.1 M TBAHFP and 0.01 M AgNO3 solution in acetonitrile.
Compound solutions were made as 0.001 M acetonitrile solutions
(DMF solution for insoluble species) and contained electrolyte
solution as well. This decreases the initial concentration of the
platinum solution slightly. Analysis was performed in a dry
glovebox (Ar atmosphere). The positive feedback iR compensation
circuitry of the potentiostat was employed; the reversible separation
of the anodic and cathodic peaks for the Cp2Fe oxidation was 58–71
mV in acetonitrile using BASi Episilon EC software version
1.60.70_XP, BASi ComServer Ver. 3.09, and Firmware Ver. 1.50.
J ) 8.0 Hz), 8.15 (2H, s, ArN-H), 7.91 (2H, d, ArN-H, J ) 8.5
Hz), 6.98 (2H, d, Ar-H, J ) 7.0 Hz), 6.76 (2H, d, Ar-H, J )
7.5 Hz), 6.65 (2H, t, Ar-H, J ) 7.0 Hz), 6.55 (2H, t, Ar-H, J ) 7.0
Hz), 4.35 (1H, d, CH2, J ) 13.0 Hz), 3.40 (1H, d, J ) 13.0 Hz),
2.35 (6H, s, CH3). 13C NMR (125 MHz, (CD3)2SO): δ 161.73,
147.12, 146.67, 138.28, 137.46, 137.28, 127.47, 125.95, 124.19,
122.60, 121.41, 119.98, 58.16, 28.25. Anal. Calcd for PtC27H22N2:
C, 56.94; H, 3.89; N, 4.92; S, 0. Found: C, 56.47; H, 3.81; N, 4.81;
S, <0.2. See Figure 5 and Supporting Information for details on
the crystal structure.
Synthesis of Pt(CH2(C6H4)2)(3,4,7,8-tetramethyl-1,10-phenan-
throline), 15. This complex was prepared using the method
described for Pt(CH2(C6H4)2)(2,2′-bipyridine) (8) to give a yellow
precipitate in quantitative yield. 1H NMR spectra were taken at 60
°C to aid dissolution. The resulting heat coalesces the inequivalent
methylene CH2 to broadened peaks, probably due to ring flipping
at elevated temperatures. Analytically pure samples can be achieved
by washing insoluble products in copious amounts of benzene and
hexanes and precipitation of slowly cooled, supersaturated aceto-
1
nitrile solutions. H NMR (500 MHz, (CD3)2SO): δ 9.03 (2H, s,
ArN-H), 8.40 (2H, s, ArN-H), 7.44 (2H, d, Ar-H, J ) 6.0 Hz),
7.01 (2H, d, Ar-H, J ) 8.5 Hz), 6.91 (2H, t, Ar-H, J ) 7.5 Hz),
6.80 (2H, t, Ar-H, J ) 7.0 Hz), 4.0 (1H, s br, CH2), 3.1 (1H, s br,
CH2), 2.75 (6H, s, ArN-CH3), 2.55 (6H, s, ArN-CH3). Too insoluble
to obtain 13C. Anal. Calcd for PtC29H26N2: C, 58.28; H, 4.39; N,
4.69. Found: C, 58.58; H, 4.38; N, 4.69.
Synthesis of Pt(CH2(C6H4)2)(2,2′-biquinoline), 16. This com-
plexwaspreparedusingthemethoddescribedforPt(CH2(C6H4)2)(2,2′-
bipyridine) (8) to give a purple precipitate in quantitative yield. It
required 40 min more for complete substitution to occur, with
respect to most other bipyridine substitutions. Using 3 equiv of
2,2′-biquinoline with respect to the oligomer ensures faster and more
complete substitution. Analytically pure samples can be achieved
by washing insoluble products in copious amounts of benzene and
hexanes and precipitation of slowly cooled, supersaturated aceto-
X-Ray Crystallography. Crystal Structure of Pt(CH2(C6H4)2)-
(2,9-dimethyl-1,10-phenanthroline), 14. A crystalline sample of
[H2C(C6H4)2]Pt(2,9-dimethyl-1,10-phenanthroline), compound 14,
was obtained from DMSO-d6 solvent, when a hot solution was
allowed to cool to room temperature. Crystals were obtained as
orange blocks. C27H22N2Pt, Mr ) 569.56, orthorhombic, space group
Pnma, a ) 19.8057(2) Å, b ) 18.9645(7) Å, c ) 5.3313(4) Å; V
) 2002.46(17) Å3, Z ) 4, Fcalc ) 1.889 Mg/m3, Mo KR radiation
(λ ) 0.71073 Å), crystal dimensions 0.10 × 0.06 × 0.03 mm3, A
total of 11 446 reflections were collected on a Nonius Kappa CCD
area detector at 150(2) K, of which 2349 were independent. The
structure was solved by direct methods and refined on F2 using
the SHELXTL (version 6.12) software package. Final residuals:
R1 ) 0.0357 (I > 2σ(I)), wR2 ) 0.0855 (all data). Further details
of the crystal structure investigations may be obtained from the
Cambridge Crystallographic Data Centre, on quoting the depository
number CCDC 658 451.
1
nitrile solutions. H NMR (500 MHz, (CD3)2SO): δ 9.07 (2H, d,
ArN-H, J ) 8.5 Hz), 8.96 (2H, d, ArN-H, J ) 8.5 Hz), 8.20 (2H,
d, ArN-H, J ) 7.5 Hz), 7.77 (2H, d, Ar-H, J ) 8.5 Hz), 7.67 (2H,
t, ArN-H, J ) 7.5 Hz), 7.37 (2H, t, ArN-H, J ) 7.0 Hz), 7.07 (2H,
d, Ar-H, J ) 7.0 Hz), 6.62 (2H, t, Ar-H, J ) 7.0 Hz), 6.23 (2H, t,
Ar-H, J ) 7.0 Hz), 6.10 (2H, d, ArN-H, J ) 7.0 Hz), 4.65 (1H, d,
CH2, J ) 12.5 Hz), 3.56 (1H, d, CH2, J ) 13.0 Hz). 13C NMR
(125 MHz, (CD3)2SO): δ 156.92, 155.29, 147.23, 146.57, 136.97,
136.64, 130.16, 129.38, 128.16, 128.04, 127.42, 125.30, 123.45,
123.34, 118.84, 50.25. Anal. Calcd for PtC31H22N2 · ½H2O: C,
59.42; H, 3.70; N, 4.47. Found: C, 59.64; H, 3.66; N, 4.56.
Synthesis of Pt(CH2(C6H4)2)(N,N,N′N′-tetramethylethylene-
diamine), 17. This complex was prepared using the method
described for Pt(CH2(C6H4)2)(2,2′-bipyridine) (8) to give a white
precipitate in quantitative yield. This complex is very soluble in
most organic solvents and was purified by recrystallization by slow
evaporation in benzene. 1H NMR (200 MHz, CDCl3): δ 7.37 (2H,
m, Ar-H, 3JPt-H ) 74.0 Hz), 6.98 (2H, m, Ar-H, 3JPtH ) unresolved
broad base), 6.75–6.67 (4H, m, Ar-H), 4.16 (1H, d, CH2, J ) 13.0
Density Functional Theory (DFT) and Time-Dependent
Density Functional Theory Calculations (TD-DFT). DFT cal-
culations were performed using Gaussian 03W48 using the restricted
(48) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A.; , Vreven, T., Jr.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, Nakai, O.; Klene, M.; Li, X.;
Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo,
J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.;
Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels,
A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,
B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03,
Revision D.01; Gaussian, Inc.: Wallingford, CT, 2004.
4
4
Hz, JPt-H ) 19.2 Hz), 3.35 (1H, d, CH2, J ) 13.0 Hz, JPt-H
)
3
11.2 Hz), 2.88 (6H, s, CH3, JPt-H ) 18.0 Hz), 2.59 (4H, s, CH2,
3JPt-H ) 11.6 Hz), 2.39 (6H, s, CH3, JPt-H ) 25.2 Hz). 13C NMR
3
(125 MHz, CDCl3): δ 147.82, 140.82, 135.79, 124.60, 123.66,
121.67, 61.94, 51.64, 50.85, 49.40. Anal. Calcd for
PtC19H26N2 · ½H2O: C, 46.91; H, 5.59; N, 5.76. Found: C, 46.95;
H, 5.96; N, 5.37.
Spectroscopic Characterization. UV–vis spectra were obtained
on an OLIS-14 (upgraded Cary-14) spectrophotometer with solution
concentrations in the 0.02 to 0.07 mM range (see Supporting
Information), using 1 cm path-length SUPRASIL QS-110 matching
quartz cuvettes. The Windows NT-based computer controlled the

9,10-Dihydroplatinaanthracenes with Aromatic Diimine Ligands
Organometallics, Vol. 27, No. 8, 2008 1779
B3LYP26 correlation and SDD atomic basis set with effective core
potentials (ECP)49 as implemented in the Gaussian 03 software.
The SDD basis set is the combination of the Huzinaga–Dunning
double-ꢀ basis set50 on lighter elements with the Stuttgart-Dresden
relativistic effective core potential (RECP) basis set combination51
on platinum. The HOMO (highest occupied molecular orbital) and
LUMO (lowest unoccupied molecular orbital) energies were
determined using minimized singlet geometries to approximate the
ground state. After minimization, vibrational analysis was performed
at the same level of calculation to determine if imaginary frequen-
cies were present. Compounds 8 to 17 showed no imaginary
frequencies. TD-DFT calculations were performed at minimized
singlet structures at the restricted B3LYP26 level using the SDD49–51
basis set in order to predict their low-energy absorptions. Consider-
ing the differences of the absorption behaviors in gas and solution,
the solvent effects of CH3CN were taken into account by means of
the polarizible continuum model (PCM),52 as implemented in the
Gaussian 03 software using default settings. TD-DFT data were
analyzed using SWizard software Ver. 4.4.53 Molecular orbital
visualizations were creating using Facio Version 10.9.9 using an
iso-value of 0.02 unless otherwise stated.54
Acknowledgment. Funding by the Natural Science and
Engineering Research Council (NSERC) of Canada, the
Canadian Foundation of Innovation, and the University of
Toronto (Connaught Foundation) is gratefully acknowledged.
We thank Dr. Gord Hamer and Dr. Peter Mitrakos for
assistance with NMR spectroscopy. We would like to
acknowledge valuable discussions with Professors Robert H.
Morris and Datong Song. We thank Mr. Baoxu Liu and
Professor Claudiu Gradinaru for the acquisition of the
emission spectra.
Supporting Information Available: X-ray crystallographic data
for 14 (CIF) and additional orbital pictures, geometry-optimized
structures, as well as additional crystallographic data, cyclic
voltammograms, spectroscopic information, and correlation graphs
(PDF). The CIF may be obtained, free of charge, from the
Cambridge Crystallographic Data Centre, on quoting the depository
number CCDC 658 451. Both the CIF and the PDF are available
free of charge via the Internet at http://pubs.acs.org.
(49) Hay, P. J.; Wadt, W. R. J. Chem. Phys., 1985, 82, 270.
(50) Dunning, T. H., Jr.; Hay, P. J. Modern Theoretical Chemistry;
Editor, Schaefer, H. F.; Plenum: New York, 1976; Vol. 3, p 1.
(51) Dolg, M. Effective Core Potentials. In Modern Methods and
Algorithms of Quantum Chemistry; John von Neumann Institute for
Computing: Jülich, 2000, Vol. 1, p 479.
(52) (a) Cossi, M.; Scalamni, G.; Regar, N.; Barone, V. J. Chem. Phys.
2002, 117, 43. (b) Barone, V.; Cossi, M. J. Chem. Phys. 1997, 107, 3210.
(53) Gorelsky, S. I. SWizard program, http://www.sg-chem.net, Uni-
versity of Ottawa, Canada, 2007.
OM700997V
(54) Suenaga,M.KyushuUniversity,Japan.http://www1.bbiq.jp/zzzfelis/Facio.html.