Platinum complexes of alkynyl-substituted dimethyldihydropyrenes

Article abstract of DOI:10.1021/om3007008

A series of photochromic dimethyldihydropyrenes (DHP) bearing ethyne substituents in the 4-position (^RDHP-C≡CH; R = H (4), acetyl (5), benzoyl (6), 1-naphthoyl (7), benzo[e] (8)) were prepared for use as precursors to ethynyl ligands. Dehydroha

Full text of DOI:10.1021/om3007008

Article
pubs.acs.org/Organometallics
Platinum Complexes of Alkynyl-Substituted
Dimethyldihydropyrenes
Pengrong Zhang, David J. Berg,* Reginald H. Mitchell,* Allen Oliver,† and Brian Patrick‡
Department of Chemistry, University of Victoria, P.O. Box 3065, Victoria, British Columbia, Canada V8W 3V6
S
* Supporting Information
ABSTRACT: A series of photochromic dimethyldihydropyr-
enes (DHP) bearing ethyne substituents in the 4-position
(RDHP-CCH; R = H (4), acetyl (5), benzoyl (6), 1-
naphthoyl (7), benzo[e] (8)) were prepared for use as
precursors to ethynyl ligands. Dehydrohalogenation of the
adduct of these ethynes with various PtCl2(L)2 complexes
afforded a series of cis and trans square-planar bis(DHP-
ethynyl) platinum complexes, (RDHP-CC)2Pt(L)2 (cis, R =
H, L2 = PEt3 (9), acetyl, PEt3 (10), benzoyl, PEt3 (11), 1-naphthoyl, PEt3 (12), benzo[e], PEt3 (13), benzoyl, PPh3 (14),
benzo[e], PPh3 (15); trans, R = H, L2 = dppe (16), benzo[e], dppe (17), acetyl, bipy (18), 1-naphthoyl, bipy (19), H, phen
(20)). The DHP-ethynes bearing acyl and benzo[e] substituents on the DHP (5−8) and their platinum complexes (10−19) are
photochromic and undergo ring opening to the related cyclophanediene (CPD) isomer on irradiation with visible light (λ >550
nm). In the case of the benzo[e]DHP 8, adding a 4-ethynyl substituent increases the rate of photo-opening 4-fold; however, in
the acylDHP series 5−7, addition of a 4-ethynyl group slows the rate of photo-opening by a factor of about 4. The platinum
complexes generally open more slowly than the corresponding alkyne precursors, again by a factor of about 4. The rate of photo-
opening does not appear to be affected significantly by the nature of the ancillary ligands or the metal geometry, suggesting that
there is poor electronic communication between the platinum center and the DHP π system. The thermal back-reaction from the
open CPD to closed DHP form is about 50% faster for the metal complexes than for the DHP-ethyne precursor. The platinum
complexes and the DHP-ethynes were characterized by NMR and IR spectroscopy and MS and by X-ray crystallography for
metal complexes 10, 11, 14, 15, and 17.
INTRODUCTION
■
Photochromic molecules have been intensively studied due to
their potential applications in optical switches and storage
devices.1 The diarylethene class of photochromes has been
studied by Irie, Branda, and others.2 For many years, we have
focused our attention on the dimethyldihydropyrene (DHP)−
dimethylmetacyclophanediene (CPD) system, 1c/1o (c =
closed; o = open).3−8 Molecules of type 1c exhibit negative
photochromism in that the thermally more stable and colored
form bleaches to the colorless form 1o on irradiation with
orange or red light (λ >550 nm). Irradiation with UV light
rapidly converts 1o back to 1c, but the thermal (dark) back-
reaction also occurs at room temperature. Introduction of
organic or organometallic groups on the DHP periphery, or at
the internal methyl positions, can dramatically alter the
photochromic behavior.3,9,10 In general, introduction of acyl
metal fragment connected to the DHP framework by σ bonds
have been reported. DHP-alkynyl complexes of a group 10
metal such as Pt are particularly interesting for a number of
reasons. Marder has shown that electronic communication
through a −CC−Pt−CC− linkage is only slightly smaller
than that through a phenylene −CC−C6H4−CC−
groups or annelation increases the quantum yield of the photo-
opening reaction and slows down the thermal back-
reaction.5−7,9,11 One of the better photochromes in this family,
the benzo[e] derivative 2c(BDHP)/2o(BCPD), shows 100%
conversion between the two photostates. However, even in this
case the thermal back-reaction is not fully suppressed.
Although a number of organometallic π complexes of DHP
Received: July 25, 2012
Published: November 8, 2012
derivatives have been prepared,10 no complexes containing a
© 2012 American Chemical Society
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bridge.12 Metal-connected polyynes have attracted considerable
attention as fundamental building blocks in macromolecular
wires;13 therefore, the potential to use a DHP-photochrome as
an optical switch where the open (CPD) form breaks
conjugation and changes the wire conductivity is intriguing.
Additionally, metal−alkynyl σ complexes show interesting
properties in their own right and have been used in nonlinear
optical, light-emitting diode, and luminescent materials.14 The
potential to alter these properties by changing the state of the
DHP photochrome also exists.
We are also interested in possible cooperative behavior
between DHP-photochromes in complexes containing two (or
more) photochromic units. Platinum complexes containing two
DHP-alkynyl ligands provide a good opportunity to observe
cooperative behavior. The original hypothesis was that energy
transfer between photochromic units through a spacer would
accelerate photo-opening. Earlier work on bis(DHP) systems
with homoconjugation (−CO− linker), no conjugation
(−CH2− linker), and fused conjugation (arene bridge) showed
that the DHP units opened and closed independently and
multiple states were observed, although no photo-opening rate
enhancement was achieved.15 Bandyopadhyay previously
synthesized a bis-photochrome having two benzo[e]DHP
photochromic units joined by a butadiyne spacer, 3.16
Unfortunately, difficulties in distinguishing the fully closed
(3cc) and partially open (3co) states made it impossible to
evaluate cooperative effects during the photo-opening process.
Insertion of a Pt center between the butadiyne alkynes is
expected to provide similar electronic communication to the
butadiyne system 3 but also allow tuning of the electronic
properties of the Pt spacer by changing the ancillary ligands on
the metal.
yield (Φo = 0.0015).6 Therefore, to explore the photo-opening
reactions in metal complexes, enhancement of the photo-
opening quantum yield is critical. Adding one alkyne at the 4-
position or two alkynes at the 4- and 9-positions of DHP has
been shown to decrease the quantum yield relative to 1 by
factors of 2.7 and 2.9 times, respectively.6 However, we have
previously shown that adding a ketone or aldehyde group at the
2- or 4-position of DHP 1 increases the photo-opening rate and
the thermal back-reaction from CPD to DHP (1o → 1c).11b
For example, adding a benzoyl group at the 4-position of 1
increased the photo-opening quantum yield by 2.5 times, while
increasing the thermal return rate by 1.5 times.6 The fused
benzo group in BDHP 2 dramatically increases the quantum
yield (Φo = 0.04), and addition of an ethynyl group at the 4-
position of 2 further enhances the photo-opening quantum
yields by a factor of ca. 2.7 Given the noted unpredictability of
the photochemical properties of DHP-alkynes, we elected to
investigate the platinum complexes of several 4-acylDHP-
ethynes (5−7), as well as BDHP-ethyne (8) and the simple
DHP-ethyne prototype (4). The various DHP-ethynes used in
this work are shown in Chart 1, and the synthetic route to the
new 4-acylDHP-ethynes is shown in Scheme 1.
Chart 1
The synthesis of the 4-acylDHP-ethynes 5−7 is relatively
straightforward starting from the parent DHP 1. Friedel−Crafts
a
Scheme 1. Synthesis of 4-acylDHP-10-ethynes
a
Conditions and yields: (a) RC(O)Cl, AlCl3, CH2Cl2, room
temperature, yields 36 (CH3), 40 (Ph), 42% (Np); (b) I2,
RESULTS AND DISCUSSION
−
Ag(collidine)+PF6 , CH2Cl2, room temperature, 12 h, yields 75
■
In order to prepare DHP-alkynyl complexes of Pt2+, we first
had to synthesize DHP-alkynes having suitable photochemical
properties. The DHP 1 does not open photochemically using
low-intensity light sources, due to its intrinsically low quantum
(CH3), 75 (Ph), 90% (Np); (c) TMS-CCH, Pd(PPh3)2Cl2, CuI, NEt3,
room temperature, yields 98 (CH3), 95 (Ph), 95% (Np); (d) K2CO3,
THF/CH3OH, yields 100 (CH3), 94 (Ph), 100 (Np). Minor amounts
(5−15%) of the 4-acyl-9-ethynyl isomer were isolated in all cases.
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acylation occurs readily at the 4-position of the very electron
rich DHP, but care must be taken to avoid excess acid chloride
or long reaction times, since this can result in significant double
acylation and, in the case of acetyl chloride, replacement of one
tert-butyl group by an acetyl function.6,17 Iodination of the 4-
complexes were purified by recrystallization from hexane and
dichloromethane; the major and minor isomers were separated
1
in some cases. The complexes were characterized by H, 13C,
31P, and 195Pt NMR spectroscopy (solubility permitting) as well
as by electrospray mass spectrometry, elemental analysis, IR
and UV/vis spectroscopy. Significant spectroscopic data for Pt
complexes 9−20 as well as for the free parent DHP-alkynes 4−
8 are given in Table 1. In cases where the 10-isomers could not
be obtained free from the 9-isomer, the 9:1 isomer ratio
allowed easy extraction of data for the 10-isomer; see the
Experimental Section for full details.
acylDHPs with iodine and Ag(collidine)+PF6 afforded the
−
major 4,10-isomer shown in Figure 1 in 50−75% yield, but
about 10−15% of the minor 4,9-isomer was also formed.6 The
structures of the major and minor isomers were established by
2D NMR spectroscopy, and although they were chromato-
graphically separable with some difficulty, we elected to carry
the isomeric mixture forward. Sonogashira coupling of the
acylDHP iodides with (trimethylsilyl)acetylene followed by
removal of the TMS group afforded the desired terminal
alkynes 5−7. Only the 10-isomers of 5−7 are shown, but small
amounts (5−15%) of the 9-isomers were also obtained (see the
Experimental Section for details).
Platinum complexes 9−15 containing monodentate phos-
phine ligands, PEt3 or PPh3, adopt a trans square-planar
geometry, as shown by the triplet (2JPC = 14−29 Hz (cis-P)) for
the alkynide α-C in the 13C NMR spectrum. In contrast,
complexes 16 and 17, which contain the bidentate dppe ligand,
must adopt a cis geometry and show a doublet of doublets
pattern for this carbon in the 13C NMR (2JPC = 150 Hz (trans-
P), 14−15 Hz (cis-P)). These geometries were confirmed by X-
ray crystallography for 10, 11, 14, 15, and 17 (vide infra).
Complexes 18−20, containing the chelating amines bipy and
phen, can be assumed to adopt a cis geometry due to the
constraints of the chelate. Complexes of the type trans-Pt(C
CR)2(L)2 are more common in the literature than their cis
isomers,18 although Sonogashira has shown that the cis
complexes can be isolated if the reactions are carried out at
low temperature.19 Similarly, Tykwinski has shown that
conversion of the trans to cis isomers occurs readily when a
monodentate phosphine such as PPh3 is replaced by a bidentate
phosphine such as dppe.20
Platinum Complexes. The platinum alkynide complexes
were prepared by dehydrohalogenation of the adduct between
the parent alkyne 4−8 and the appropriate PtCl2(L)2 precursor
with diethylamine using CuI as a catalyst (Scheme 2). The
a
Scheme 2
The IR stretching frequencies of the carbonyl groups in
complexes containing the acylDHP unit do not change
substantially from the free alkyne to the platinum alkynide
complex. The CC stretching frequency of the alkyne itself
shows a small decrease in the PEt3 complexes 9−13 ranging
a
Conditions: (a) CuI, HNEt2, 50 °C.
Table 1. Select Spectroscopic Data for DHP-alkynes and the Corresponding DHP-alkynide Complexes of Platinum, (DHP-C
a
C)2Pt(L)2
no.
alkyne/alkynide
L
geom
δint
δα
δβ
δPt
1JPt−P
2JP−C
νCC
νCO
4
DHP
−3.64
−3.81
−3.72
−3.70
−1.19
−3.85
−3.74
−3.63
−3.62
−1.03
−3.87
−1.25
−3.41
82.5
82.4
84.7
84.1
2085
2091
2091
2093
2090
2082
2081
2077
2080
2071
2092
2099
2093
5
CH3C(O)DHP
PhC(O)DHP
NpC(O)DHP
BDHP
1665
1639
1631
6
82.4
84.1
7
82.4
84.0
8
82.6
84.3
9
DHP
PEt3
PEt3
PEt3
PEt3
PEt3
PPh3
PPh3
dppe
trans
trans
trans
trans
trans
trans
trans
cis
115.1
115.1
n.o.
111.0
110.5
110.9
110.4
111.0
115.3
115.8
113.3
2383
2384
2383
2385
2398
2651
2677
2277
29
29
10
11
12
13
14
15
16
CH3C(O)DHP
PhC(O)DHP
NpC(O)DHP
BDHP
−252
1666
1640
1641
n.o.
n.o.
15
n.o.
n.o.
115.1
n.o.
−220
−252
−254
−382
PhC(O)DHP
BDHP
1650
118.6
114.2
15
b
DHP
150
c
15
b
17
BDHP
dppe
cis
−1.07
113.4
112.5
−379
2246
150
14
2093
2094
2096
c
18
19
20
CH3C(O)DHP
NpC(O)DHP
DHP
bipy
bipy
phen
cis
cis
cis
−3.70
−3.58
−3.78
92.3
94.1
n.o.
102.8
102.5
103.8
1663
a
δint, δα, δβ, and δPt refer to the chemical shifts of the internal methyl protons (average value), terminal alkyne carbon (α), internal alkyne carbon (β),
and 195Pt resonances in C6D6, respectively. n.o. indicates the experiment was performed but the resonance was not observed. δ values are given in
b
c
ppm, J values are given in Hz, and ν values are given in cm−1. Coupling to the trans-P. Coupling to the cis-P.
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Table 2. Selected Bond Lengths (Å) and Angles (deg) for trans-(RDHP-CC)2Pt(PR′3)2 (10, R = CH3C(O), R′ = Et; 11, R =
a
PhC(O), R′ = Et; 14, R = PhC(O), R′ = Ph; 15, R = C6H4, R′ = Ph) and cis-(RDHP-CC)2Pt(dppe) (17, R = C6H4)
10
11
14
15
17
Pt(1)−C(1)
Pt(1)−P(1)
C(1)−C(2)
C(2)−C(3)
2.009(6)
2.295(2)
1.196(9)
1.450(8)
1.398
2.009(7)
2.296(3)
1.191(9)
1.430(9)
1.393
1.995(4)
2.3064(9)
1.208(6)
1.431(6)
1.400
1.996(3)
2.297(8)
1.214(4)
1.429(4)
1.405
1.995(8)
2.261(2)
1.191(11)
1.450(12)
1.398
DHP C−Cav
b
sum DHP C−C alternation
C(1)−Pt(1)−C(1)′
P(1)−Pt(1)−P(1)′
P(1)−Pt(1)−C(1)
P(1)−Pt(1)−C(1)′
Pt(1)−C(1)−C(2)
C(1)−C(2)−C(3)
0.19(3)
180(2)
180
0.15(4)
180
0.19(3)
180
0.49(2)
180.0(1)
180
0.63(4)
89.1(4)
87.01(10)
92.0(2)
177.1(3)
175.9(8)
175.9(10)
32.7
180
180.00(6)
93.23(11)
86.77(11)
174.6(3)
173.1(4)
65.6
90.7(2)
89.3(2)
176.3(5)
173.4(6)
26.4
94.7(2)
85.3(2)
173.3(7)
176.2(7)
6.7
92.93(9)
87.07(9)
173.6(3)
173.4(4)
70.3
c
DHP-SqP dihedral
d
DHP-(PhCO) dihedral
61.1
56.7
a
b
C6H4 = benzo[e]DHP. ∑(|bond length − average bond length|) for the 14 DHP edge bonds; esd values are derived from the individual bond
c
d
length esd values. Dihedral angle between the PtC2P2 square plane and the mean DHP plane. Dihedral angle between the mean C6 plane of the
PhCO substituent and the mean DHP plane.
from 3 to 19 cm−1. However, the CC stretching frequency
shows a very slight increase in trans complexes with PPh3 (14
and 15) and the cis complexes (16−20). These observations
would seem to imply that there is relatively little π electronic
interaction between the metal and the alkynide or DHP
fragments. It has been reported in the literature that changing
the donor properties of the phosphine causes changes in the
CC stretching frequency in trans-Pt(CCR)2(L)2 (L =
PCy3, P(OPh)3) complexes, although the effect appears to be
small.21
crystallography; selected bond distances and angles are given in
Table 2. Disorder of the internal methyl groups of the DHP
unit is virtually always observed in DHP structures, and that
was the case here as well. In addition, the tert-butyl substituents
show the typical rotational disorder and further disorder was
also observed for the acyl groups in complexes 10, 11, and 14.
ORTEP325 plots of complexes 10, 14, and 17 are shown in
Figures 1−3, respectively. ORTEP3 plots of 11 and 15 are
The internal methyl groups of DHP lie within the strong
shielding region of the DHP ring current, and their chemical
shifts have been shown by us to be extremely sensitive probes
of this ring current.4,10c,22 In the trans complexes containing
PEt3 (10−13) and the cis complexes bearing dppe (16 and 17)
and bipy (18 and 19) ancillary ligands, the internal methyl
groups show a small downfield chemical shift change relative to
the free DHP-ethynes ranging from Δδ = +0.06 to +0.30 ppm
with a median Δδ = +0.12 ppm. A downfield shift indicates a
small reduction in DHP ring current. On the other hand, the
trans-PEt3 (9) and trans-PPh3 complexes (14 and 15) and the
cis-phen complex (20) show small upfield shifts for the internal
methyl groups of Δδ = −0.06 to −0.21 ppm, suggesting a small
increase in ring current. However, the magnitude of these shifts
are small; therefore, other factors such as shielding or
deshielding caused by nearby phenyl groups in complexes
containing PPh3 or dppe ligands might be as important as
minor changes in ring current. Overall it appears that the effect
of the platinum center on the DHP π system is small, consistent
with the conclusion drawn from the IR spectra.
Figure 1. ORTEP325 plot of trans-(CH3C(O)DHP-CC)2Pt(PEt3)2
(10; 50% probability ellipsoids). The dichloromethane of solvation has
been omitted for clarity, and only one component for the disordered
internal methyl groups and acetyl group is shown.
1
The average JPt−P coupling constant in the cis-dppe
complexes 16 and 17 is 2262 Hz, about 300 Hz smaller than
might be expected from the trans complexes based on the
groups attached to the phosphorus.23,24 The smaller coupling
constant clearly indicates that the DHP-alkynide ligand has a
greater trans influence than a phosphine, consistent with its
greater σ donor character. The stronger trans influence of
alkynides compared to that of phosphines has been commented
on before in the case of cis- and trans-Pt(CCH)2(PEt3)2.23a
Structural Studies. The solid-state structures of five
Pt(CC-DHP)2(L)2 complexes were determined by X-ray
included in the Supporting Information but are generally
similar to the plots of 10 and 14, respectively. There are many
examples of structurally characterized Pt(CCAr)2(L)2
complexes (Ar = aryl; L = PR3, PAr3 or L2 = dppe), and the
bond lengths within these complexes show a Gaussian
distribution with narrow standard deviations, as summarized
for comparison in Table 3. The mean CC triple-bond length
is essentially insensitive to changes in the phosphines, alkyne
substituents, or geometry, and the DHP-alkynide CC
distance in the complexes investigated here fall very close to
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1
to the conclusion drawn from JPt−P coupling constants above.
The coupling constant data is almost certainly a more reliable
predictor of trans influence, as the percentage variation in the J
values is far greater across a broad range of complexes than is
the bond length. Nevertheless, the fact that these indicators are
in opposition suggests that the trans influences of the alkynide
and phosphine are similar.
The C−C bond lengths around the periphery of the 14-
annulene DHP ring in 1c, like those in benzene, are very nearly
equal and no significant bond length alternation is observed.
Substituents such as the acyl and ethynyl groups in 4−7 are
expected to cause some bond length alternation, because the C
π orbitals are no longer equal in energy but the effect is
relatively small. This alternation is best quantified by taking the
sum of the bond length differences between all adjacent C−C
bonds. The sums of the bond length alternation for the
platinum complexes containing acyl-DHP alkynides range from
0.15(4) to 0.19(3) Å. In contrast, fusing a benzene ring at the
[e]-position causes much greater bond length alternation
because this ring prefers to remain a 6π aromatic unit rather
than participate in a larger π system.4,22b As a result, this causes
bond fixation in the 14-annulene periphery and strong bond
alternation is observed for 2c. The sums of the bond length
alternation for the platinum complexes containing benzo-fused
DHP alkynides 15 and 17 are 0.49(2) and 0.63(4) Å,
respectively. By comparison, the sum of the bond alternation
in 2c is 0.54(2) Å. The sum of the C−C bond length
alternation is a measure of ring current, with greater bond
length alternation implying a reduced ring current. As discussed
above, the chemical shift of the internal methyl groups is a
sensitive measure of ring current; thus, as expected, the internal
methyls of 2c are not as far upfield as those in 1c (−1.58 vs
−4.06 ppm). Interestingly, the bond alternation data for 15 and
17 suggest that there is greater bond fixation in 17 and
therefore a lower ring current, which agrees well with the
observed internal methyl chemical shifts (δint −1.25 (15),
−1.07 (17)).
The DHP ring plane is only twisted out of the square plane
by 26 and 6° for the PEt3 complexes 10 and 11, respectively. In
contrast, the DHP plane is twisted by 66 and 70°, respectively,
relative to the square plane in PPh3 complexes 14 and 15; the
cis-dppe complex 17 is intermediate with a planar dihedral
angle of 33°. Presumably the greater twist observed in the PPh3
complexes is a function of steric crowding caused by the larger
phosphine ligands. It is tempting to assert that the near- planar
arrangement in 11 represents an electronic preference, but
packing effects in the solid state may also be responsible for this
orientation.
Photochemical Studies. As mentioned earlier, features
such as photo-opening rates and thermal closing rates,
associated with photoswitchable molecules, are particularly
important to their applications. Some of the complexes were
selected to investigate the effects caused by changing the
ligands and substituents on their photochemical properties.
Photochemists have traditionally used quantum yields to
compare photoefficiencies. Thus, for the reaction DHP 1c →
CPD 1o, Φ was found to be 0.0015, in comparison to 0.006 for
the parent 14-annulene without the tert-butyl groups.6 On the
other hand, fusing a benzo group in the [e]-position increases
Φ by about 7-fold to 0.042 for BDHP 2. However, absolute
quantum yields are time consuming to measure and we have
found that reliable comparisons can be made by measuring the
relative rates of opening for two samples side by side under the
Figure 2. ORTEP325 plot of trans-(PhC(O)DHP-CC)2Pt(PPh3)2
(14; 30% probability ellipsoids). The dichloromethane of solvation has
been omitted for clarity, and only one component for the disordered
internal methyl groups and benzoyl group is shown.
Figure 3. ORTEP325 plot of cis-(BDHP-CC)2Pt(dppe) (17; 30%
probability ellipsoids). Only one component of the disordered internal
methyl groups is shown.
Table 3. Summary of Bond Length Data for Various (ArC
a
C)2Pt(L)2 Complexes
distance
ligand (L) bond length (Å) mean length (Å) std dev
Pt−C
PR3
1.981−2.047
1.981−2.027
1.997−2.031
2.281−2.316
2.286−2.325
2.258−2.289
1.128−1.239
1.152−1.217
1.176−1.211
1.414−1.487
1.434−1.461
1.411−1.452
2.003
2.008
2.018
2.299
2.309
2.270
1.198
1.197
1.190
1.443
1.445
1.437
0.015
0.014
0.012
0.007
0.013
0.003
0.026
0.019
0.012
0.018
0.007
0.012
PAr3
dppe
PR3
Pt−P
PAr3
dppe
PR3
C1C2
C2−C3
PAr3
dppe
PR3
PAr3
dppe
a
The numbers of reported structures in the Cambridge Structural
Database containing PR3, PAr3, and dppe are 29, 13, and 11,
respectively, at the time of submission.
the mean values. The Pt−P and Pt−C distances for the DHP-
alkynide complexes are also similar to those reported, although
the Pt−C distance in the cis-dppe complex 17 is at 1.995(8) Å
slightly shorter than that in any other cis-Pt(CCAr)2(dppe)
complex.
One interesting observation from the bond length data in
Table 2 is that the Pt−P distance is significantly shorter in the
cis-dppe complex 17 than in the trans-alkynide complexes 10,
11, 14, and 15. A shorter Pt−P bond when the phosphine is
trans to an alkynide in comparison to when it is trans to a
phosphine (cf. 17 vs 15) implies that the trans influence of the
alkynide is weaker than that of the phosphine. This is contrary
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same conditions of temperature, light source, and solvent. The
absolute rates measured are not meaningful, but the rate
relative to the standard can be used for comparison. We have
made much use of BDHP as a standard previously and,
provided that the two samples measured have absorptions in
the same region, good comparative results are consistently
observed.26
sample of the same concentration. A plot of mole fraction
remaining of the closed form versus time gives good linear
behavior over the first few minutes of irradiation in all cases,
confirming that, by the NMR method, zero-order kinetics are
obtained (Figure 5). The relative rates of photo-opening,
The visible openings were performed using a 500 W tungsten
light source fitted with a 550 nm cutoff filter. The photo-
chemical reactions were followed by either UV−vis spectros-
copy or NMR spectroscopy. The photochemical reaction rate
depends directly on the number of photons and the
concentration of the photochrome. When excess photons are
provided, the photochemical reaction rate only depends on the
concentration of the photochrome, and pseudo-first-order
kinetics are observed. In practice, Robinson and Mitchell
found that NMR samples follow a pseudo-zero-order rate law,
while UV−vis samples follow pseudo-first-order kinetics in the
photo-opening process.27 The difference in rate law is due to
the different concentrations involved in the two methods and
the efficiency of light penetrating through the sample
solutions.27 At the much higher photochrome concentrations
of the NMR experiment, only photochrome molecules very
near the surface of the sample are irradiated by light, and this
effectively leads to a condition where the concentration of
photochrome is constant while the number of photons is in
large excess. However, this is only strictly true at the beginning
of the opening processes and, since the open CPD isomer is
colorless, light penetrates further into the sample with time,
causing a change in rate law toward first order. Initial rates,
usually obtained over the first 5−10 min depending on the
sample (vide infra), can therefore be accurately obtained using
a zero-order treatment.
■
Figure 5. Zero-order plot for the photo-opening of BDHP 2 ( ),
●
○
▲
BDHP-CCH 8 ( ), and the platinum complexes 13 ( ), 15 ( ), and
17 ( ) followed by H NMR spectroscopy: mole fraction of the closed
1
⧫
isomer versus time for samples irradiated at >550 nm.
Table 4. Relative Photo-Opening Rates of DHP-alkynes,
Their Precursors, and Platinum Alkynide Complexes
a
compd
BDHP 2
krel
When irradiation is carried out on NMR samples, the
platinum complexes open completely. The NMR sample shows
a downfield shift of the internal methyl resonances from −1.02
and −1.04 ppm in the fully conjugated closed (DHP) form to
1.52 and 1.53 ppm in the “open” CPD isomer. Gradual
reduction of the long-wavelength absorptions in the UV−vis
spectrum of 13 can be seen in Figure 4.
The photo-opening of the BDHP-ethyne 8 and its platinum
complexes 13, 15, and 17 was most conveniently carried out by
irradiating NMR samples in d6-benzene alongside a BDHP 2
1
BDHP-CCH 8
4
13
1
15
1
17
1
CH3C(O)DHP
CH3C(O)DHP-CCH 5
10
1
0.4
0.1
1
NpC(O)DHP
NpC(O)DHP-CCH 7
12
0.25
0.06
a
Relative to the parent DHP: BDHP 2, CH3C(O)DHP, or
NpC(O)DHP, respectively
summarized in Table 4, show that BDHP-ethyne 8 opens about
4 times faster than BDHP 2. However, the platinum complexes
13, 15, and 17 all open at about the same rate as BDHP 2,
meaning that conversion to the alkynide slows the rate of
opening by a factor of about 4. The geometry of the platinum
complex and the identity of the ancillary phosphines have no
discernible effect on the rate of photo-opening.
The photo-opening of the acylDHP-ethynes 5 (acyl =
CH3C(O)) and 7 (acyl = NpC(O)) and their respective trans-
(acylDHP-CC)Pt(PEt3)2 complexes 10 and 12 was followed
by UV−vis spectroscopy and showed good first-order kinetics
(the plot for 12 and NpC(O)DHP is shown in Figure 6). In
this case, the platinum complexes opened between 10 and 17
times slower for 10 and 12, respectively, than for the parent
acylDHP and about 4 times slower than for the acylDHP-
Figure 4. Photo-opening of 13 on irradiation at >550 nm: (a) 0 min;
(b) 30 min; (c) 60 min; (d) 210 min.
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closing of BDHP-ethyne 8 and its platinum complexes 13, 15,
and 17 by 1H NMR spectroscopy. The thermal closing process
follows first-order kinetics; the half-life, τ1/2, as well as the
enthalpy (ΔH⧧) and entropy (ΔS⧧) of activation obtained from
an Eyring plot (not shown) are collected in Table 5. Although
Table 5. Thermal Closing Rates of DHP-alkynes, Their
Precursors, and Platinum Alkynide Complexes
a
b
ce
,
de
,
compd
BDHP 2
τ1/2
krel
ΔH⧧
ΔS⧧
87
67
62
62
42
38
33
1
100
102
97
+16
CH3C(O)DHP
1.3
1.4
1.4
2.1
2.3
2.6
−7
−13
+15
−13
−15
−22
5
8
109
99
13
15
99
17
96
a
b
c
d
e
In h. Relative to BDHP 2. In kJ mol−1, In J mol−1 K−1 Typical
errors in ΔH⧧ and ΔS⧧ are ca. 3 kJ mol−1 and 10 J mol−1 K−1,
●
Figure 6. First-order plot for the photo-opening of NpC(O)DHP ( )
■
and trans-[NpC(O)DHP]2Pt[PEt3]2 (12; ) followed by UV−vis
spectroscopy: ln[Aclosed/Atotal] versus time for samples irradiated at
respectively.
>550 nm.
the platinum complexes were not investigated, the acetylDHP-
ethyne 5 and the related 4-acetylDHP are included for
comparison. In both the BDHP and 4-acetylDHP series,
adding an ethynyl group resulted in slightly faster thermal
closure as the half-life decreased from 87 to 62 h on going from
2 to 8 and from 67 to 62 h on going from 4-acetylDHP to 5. In
comparison, the half-life decreased ca. 33−50% on going from
the free alkyne 8 (62 h) to platinum complexes 13 (42 h), 15
(38 h), and 17 (33 h). The half-life for the ring-closing reaction
has previously been shown to decrease significantly on
introduction of electron-withdrawing groups such as trifluor-
oacetyl. It has been suggested that this is due to stabilization of
a diradical transition state by electron-withdrawing substitu-
ents.7,8,17,28 It is interesting to note therefore that the most
electron-rich platinum center is found in complex 13, bearing
PEt3 ancillary ligands, and this complex does in fact have the
longest half-life. Although the effect is not large, it does suggest
that there is a small effect of the metal electronic environment
on the thermal closing reaction. As might be anticipated for a
reaction involving rigid products and reactants and presumably
minor changes in solvation, the entropy of activation is near
zero when the large error is taken into account.
ethynes (Table 4). Thus, in this case, adding an ethynyl group
to an acyl-DHP slows the photo-opening by between ca. 2.5
and 4 times, whereas in the case of the BDHP unit, adding an
ethynyl group increased the photo-opening rate 4-fold. In both
the BDHP and acylDHP cases, deprotonation to an alkynide
and formation of a σ complex with platinum slows the photo-
opening by a factor of 4.
The open CPD isomer normally undergoes rapid and
complete ring closure to the DHP form on exposure to UV
light (254 nm), as illustrated for BDHP 2 in Figure 7. Past
Concluding Remarks. The introduction of ethynyl groups
onto the DHP periphery resulted in a 4-fold decrease in the
photo-opening rate for the acyl-substituted compounds 5 and 7
but a 4-fold increase in photo-opening rate for the benzo-fused
DHP-ethyne 8. However, in both series, the deprotonation of
the DHP-ethyne and formation of the bis(DHP-ethynyl)
platinum complexes resulted in another 4-fold decrease in the
rate of photo-opening. Crystallographic, IR, and NMR
spectroscopic studies suggest that the extent of electronic
communication between the DHP π system and the platinum
center is quite small. This is reflected in the fact that changes in
the ancillary ligands and geometry cause no difference in the
rate of photo-opening among 13, 15, and 17. The thermal
closing rate from CPD back to the DHP isomer increases by
about 40% on introduction of an ethynyl group in 8 relative to
BCPD 2o. A further increase in the rate of thermal closing
occurs on formation of the platinum complexes 13, 15, and 17.
No evidence for cooperative effects during either photo-
opening or thermal closing was observed.
Figure 7. Photochemical conversion of 2o → 2c on UV irradiation at
254 nm.
experience has shown that the rate of closing with UV light is
almost invariant to the substituents on the DHP, but we
nevertheless decided to check whether this was true for one of
the platinum complexes. Irradiation of 13o (the CPD form of
13) with a small UV light source resulted in the same closing
rate as for 2 within experimental error, verifying that the UV
closure rate is insensitive to the DHP substituents.
In contrast to the UV photochemical closing, thermal closing
of the open CPD isomer is generally very sensitive to the
substituents on the ring system. We followed the thermal
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A small amount of the 9-acetyl isomer was also present, but it was not
separated and fully characterized.
10-Benzoyl-2,7-di-tert-butyl-10c,10d-dimethyl-4-ethynyl-
trans-10c,10d-dihydropyrene (6a) and the 9-Benzoyl Isomer
EXPERIMENTAL SECTION
■
All solvents and reagents were purchased from Sigma-Aldrich and used
without further purification unless otherwise stated. Acetonitrile and
CH2Cl2 were distilled from calcium hydride prior to use. Diethyl ether,
benzene, toluene, hexane, and THF-d8 were dried by distillation from
sodium and benzophenone. Sodium iodide was dried in an oven at 110
°C for 12 h. Silica gel (Merck, 60−200 mesh) and alumina (Aldrich,
activated, neutral, Brockmann I, standard grade, ∼150 mesh) used for
chromatography were deactivated with 5% (w/w) of water.
The synthesis of BDHP (2),5 4-ethynyl-DHP (4),7 and 4-ethynyl-
benzo[e]DHP (8, 4-ethynyl-BDHP)7 were carried out according to
previously published procedures. The 10-acyl-4-ethynyl-DHP com-
pounds 3 (acyl = CH3CO), 4 (acyl = PhCO), and 5 (acyl = β-
NaphCO) were prepared by Friedel−Crafts acylation of the parent
DHP followed by electrophilic iodination,6,11b introduction of the
alkyne functionality by Sonogashira coupling with (trimethylsilyl)-
acetylene, and subsequent TMS deprotection with K2CO3 in a
MeOH−THF mixture (Scheme 1). Full experimental and character-
ization details for all intermediates and byproducts are given in the
Supporting Information. Spectroscopic details for the new alkynes 5−
7 themselves are given below.
(6b). 6a (10-benzoyl isomer): 1H NMR (500 MHz, CDCl3) δ 9.04 (d,
J = 1.2 Hz, 1H, H-1), 8.91 (d, J = 1.2 Hz, 1H, H-3), 8.68 (s, 1H, H-5),
8.62 (s, 1H, H-9), 8.57 (s, 1H, H-8), 8.56 (s, 1H, H-6), 7.90−7.88 (m,
2H, H-2′), 7.61 (tt, J = 7.4, 1.3 Hz, 1H, H-4′), 7.51−7.47 (m, 2H, H-
3′), 3.73 (s, 1H, CCH), 1.64 (s, 9H, 7-C(CH3)3), 1.57 (s, 9H, 2-
C(CH3)3), −3.71 (s, 3H, 10b/10c-CH3), −3.72 (s, 3H, 10b/10c-
CH3); 13C{1H} NMR (125 MHz, CDCl3) δ 199.19 (PhCO), 150.38
(C-2), 147.13 (C-7), 140.65 (C-1′), 139.72 (C-3a), 136.99 (C-10a),
135.66 (C-5a/10d), 134.88 (C-5a/10d), 132.73 (C-4′), 130.55 (C-2′),
130.40 (C-10), 128.57 (C-3′), 128.13 (C-5), 125.95 (C-9), 124.69 (C-
8), 123.46 (C-6), 121.09 (C-1), 120.39 (C-3), 114.01 (C-4), 84.10
(CCH), 82.41 (CCH), 36.80 (2-C(CH3)3), 36.17 (7-C(CH3)3),
32.00 (7-C(CH3)3), 31.87 (2-C(CH3)3), 31.33 (C-10b), 29.34 (C-
10c), 15.31 (10b/10c-CH3), 15.07 (10b/10c-CH3). 6b (9-benzoyl
1H NMR spectra were recorded on Bruker Avance 500 or 360 MHz
spectrometers; 13C NMR spectra were recorded on these instruments
1
at 125.8 or 90.6 MHz, respectively. H and 13C NMR spectra were
referenced to residual solvent resonances, while 195Pt and 31P were
1
referenced to external K2PtCl4 and 85% H3PO4, respectively. In H
NMR assignments, H-1,2 indicates H-1 and H-2 while H-1/2 denotes
H-1 or H-2. Infrared spectra were recorded on a Bruker IFS25 FT-IR
spectrometer, and only the major peaks are reported. All samples were
prepared as potassium bromide disks unless otherwise specified. UV−
vis spectra were recorded on a Cary 5 UV−vis−near-IR spectrometer
in suitable solvents. Melting points were determined on a Reichert
7905 melting point apparatus with an Omega Engineering Model 199
chromel alumel thermocouple and are not corrected. Elemental
analyses were performed by Canadian Microanalytical Services Ltd.,
Vancouver, B.C., Canada or the Chemistry Department of the
University of British Columbia, Vancouver, BC, Canada. Mass
spectrometric analyses were carried out at the Department of
Chemistry at the University of British Columbia.
1
isomer): H NMR (500 MHz, CDCl3) δ 9.07, 8.89, 8.64, 8.60, 8.58,
8.52, 3.75, 1.68, 1.54, −3.71, −3.73 (select resonances listed). Mixed
isomers 6a and 6b: mp 155−157 °C; IR (KBr) ν 3293, 3245, 2964,
2924, 2905, 2865, 2091, 1639, 1596, 1476, 1447, 1385, 1362, 1347,
1324, 1267, 1247, 1233, 1210, 1196, 1173, 1023, 941, 901, 872, 804,
729, 697, 681, 669 cm−1; UV−vis (toluene) λmax (εmax, L mol−1 cm−1)
355 (52 700), 406 (26 200), 497 (7500), 671 (2400) nm; EI MS m/z
472 (M+); HRMS calcd for C35H36O 472.2766, found 472.2766.
2,7-Di-tert-butyl-10b,10c-dimethyl-4-ethynyl-10-(1′-naph-
thoyl)-trans-10b,10c-dihydropyrene (7a) and the 9-naphthoyl
10-Acetyl-2,7-di-tert-butyl-10b,10c-dimethyl-4-ethynyl-
1
trans-10b,10c-dihydropyrene (5): H NMR (500 MHz, CDCl3) δ
Isomer (7b). 7a (10-naphthoyl isomer): 1H NMR (500 MHz,
CDCl3) δ 9.34 (d, J = 0.9 Hz, 1H, H-1), 9.05 (d, J = 0.8 Hz, 1H, H-3),
8.68 (s, 1H, H-5), 8.62 (s, 1H, H-9), 8.54 (s, 1H, H-6), 8.47 (s, 1H, H-
8), 8.45 (d, J = 7.9 Hz, 1H, H-8′), 8.06 (d, J = 8.3 Hz, 1H, H-4′), 7.98
(d, J = 7.9 Hz, 1H, H-5′), 7.63−7.61 (m, 1H, H-2′), 7.56−7.54 (m,
1H, H-6′), 7.51−7.47 (m, 2H, H-3′,7′), 3.73 (s, 1H, CCH), 1.60 (s,
9H, 7-C(CH3)3), 1.56 (s, 9H, 2-C(CH3)3), −3.69 (s, 3H, 10b-CH3),
−3.70 (s, 3H, 10c-CH3); 13C{1H} NMR (125 MHz, CDCl3) δ 200.81
(NpCO), 151.71 (C-2), 146.99 (C-7), 140.48 (C-3a), 139.96 (C-1′),
137.72 (C-10a), 135.57 (C-5a/10d), 134.79 (C-5a/10d), 134.12 (C-
8′b), 131.71 (C-4′), 131.48 (C-8′), 130.74 (C-10), 129.15 (C-2′),
128.67 (C-5′), 128.55 (C-5), 127.67 (C-9), 127.53 (C-7′), 126.68 (C-
6′), 126.16 (C-8′), 125.46 (C-8), 124.81 (C-3′), 123.96 (C-6), 121.18
(C-1), 120.45 (C-3), 114.01 (C-4), 84.04 (CC−H), 82.44 (CC-
H), 36.92 (2-C(CH)3), 36.12 (7-C(CH)3), 31.95 (2/7-C(CH)3),
31.87 (2/7-C(CH)3), 31.66 (C-10b), 29.30 (C-10c), 15.28 (10b/10c-
CH3), 15.09 (10b/10c-CH3). Mixed isomers 7a and 7b: IR (KBr) ν
3304, 3252, 2962, 2923, 2866, 2093, 1631, 1588, 1462, 1383, 1345,
1277, 1258, 1229, 1198, 1121, 1091, 943, 894, 880, 783, 681, 668
cm−1; UV−vis (toluene) λmax (εmax, L mol−1 cm−1) 355 (41 007), 411
(46 473), 493 (6524), 620 (584), 678 (2499) nm; EI MS m/z 522
9.73 (d, J = 1.2 Hz, 1H, H-1), 9.04 (d, J = 1.1 Hz, 1H, H-3), 8.92 (s,
1H, H-9), 8.65 (s, 1H, H-5), 8.64 (s, 1H, H-8), 8.53 (s, 1H, H-6), 3.72
(s, 1H, CCH), 3.06 (s, 3H, COCH3), 1.70 (s, 9H, 2-C(CH3)3), 1.66
(s, 9H, 7-C(CH3)3), −3.80 (s, 3H, 10c-CH3), −3.81 (s, 3H, 10b-
CH3); 13C{1H} NMR (125 MHz, CDCl3) δ 202.27 (COCH3), 152.38
(C-2), 146.86 (C-7), 140.69 (C-3a), 136.63 (C-10a), 135.53 (C-5a/
10d), 135.22 (C-5a/10d), 128.49 (C-5), 125.99 (C-9), 125.21 (C-8),
123.90 (C-6), 121.64 (C-1), 120.44 (C-3), 113.99 (C-4), 84.05 (C
CH), 82.40 (CCH), 37.10 (2-C(CH3)3), 36.12 (7-C(CH3)3), 32.06
(2/7-C(CH3)3), 32.00 (2/7-C(CH3)3), 31.47 (C-10b), 31.04
(COCH3), 29.19 (C-10c), 15.21 (10b/10c-CH3), 15.16 (10b/10c-
CH3); IR (KBr) ν 3309, 3262, 2963, 2925, 2865, 2091, 1665, 1477,
1444, 1383, 1361, 1348, 1242, 1225, 1207, 1153, 928, 889, 679, 665
cm−1; UV−vis (toluene) λmax (εmax, L mol−1 cm−1) 372 (42 800), 405
(52 200), 493 (6500), 557 (552), 618 (571), 681 (2880) nm; EI MS
m/z 410 (M+); HRMS calcd for C30H34O 410.2610, found 410.2613.
Anal. Calcd for C30H34O: C, 87.76; H, 8.35. Found: C, 86.93; H, 8.48.
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1
(M+); HRMS calcd for C39H38O 522.2923, found 522.2921. Anal.
Calcd for C39H38O: C, 89.61; H, 7.33. Found: C, 86.04; H, 7.39.
trans-Bis[2′-(2,7-di-tert-butyl-10b,10c-dimethyl-trans-
10b,10c-dihydropyren-4-yl)ethynyl]bis(triethylphosphino)-
10 (50 mg, 50% yield). 10a (major isomer, bis-10-acetyl): H NMR
(500 MHz, CD2Cl2) δ 9.70 (d, J = 1.0 Hz, 2H, H-1), 9.19 (d, J = 1.1
Hz, 2H, H-3), 8.80 (s, 2H, H-9), 8.57 (s, 2H, H-5), 8.54 (s, 2H, H-8),
8.42 (s, 2H, H-6), 3.05 (s, 6H, COCH3), 2.47−2.45 (m, 12H,
PCH2CH3), 1.71 (s, 18H, 7-C(CH3)3), 1.67 (s, 18H, 2-C(CH3)3),
1.37 (t, J = 7.6 Hz, 18H, PCH2CH3), −3.72 (s, 6H, 10c-CH3), −3.75
(s, 6H, 10b-CH3); 13C{1H} NMR (125 MHz, CD2Cl2) δ 202.55
(COCH3), 150.43 (C-7), 146.44 (C-2), 139.29 (C-3a), 136.64 (C-5a/
10d), 136.24 (C-10a), 135.29 (C-5a/10d), 128.90 (C-5), 128.25 (C-
10), 123.88 (C-9), 122.97 (C-8), 122.79 (C-4), 121.76 (C-6), 121.56
1
(C-3), 120.62 (C-1), 115.13 (d, JPt−C = 29.4 Hz, CC-Pt), 110.46
(CC−Pt), 36.93 (7-C(CH3)3), 36.07 (2-C(CH3)3), 32.21 (7-
C(CH3)3), 32.10 (2-C(CH3)3), 31.67 (C-10b), 31.13 (COCH3),
29.44 (C-10c), 17.04 (t, J = 17.4 Hz, PCH2CH3), 15.59 (10c-CH3),
15.32 (10b-CH3), 8.89 (PCH2CH3); 31P{1H} NMR (CDCl3, 202
MHz) δ 13.12 (1JPt−P = 2384 Hz); 195Pt NMR (CD2Cl2, 77 MHz) δ
−252.22 (1JP−Pt = 2655 Hz); Mixture of isomers 10a and 10b: mp
180−187 °C; IR (KBr) ν 2964, 2784, 2081, 1666, 1459, 1409, 1379,
1348, 1242, 1224, 1207, 1154, 1035, 890, 768, 733 cm−1; UV−vis
(cyclohexane) λmax (εmax, L mol−1 cm−1) 279 (7500), 387 (20 200),
429 (29 600), 494 (8000), 697 (3500) nm; ESI MS m/z 1249 (M+ +
H); HRMS calcd for C72H96O2P2Pt + H 1249.6591, found 1249.6556.
trans-Bis[2″-(9-benzoyl-2,7-di-tert-butyl-10b,10c-dimethyl-
t r a n s - 1 0 b , 1 0 c - d i h y d r o p y r e n - 4 - y l ) e t h y n y l ] b i s -
platinum(II) (9). DHP-ethyne 4 (84 mg, 0.23 mmol) and trans-
Pt(PEt3)2Cl2 (50 mg, 0.10 mmol) were mixed in degassed diethyl-
amine (20 mL) in a Schlenk tube at room temperature. CuI (1.0 mg,
0.0052 mmol) was added, and the reaction mixture was heated to a
mild reflux at 50 °C under argon for 12 h. The amine was removed
under reduced pressure and the crude residue purified on alumina
(deactivated with 5% water) using hexane and dichloromethane as
eluant. The DHP-ethyne 4 (5 mg, 69% recovery) was eluted first
(using hexane/CH2Cl2 10/1), and complex 9 (100 mg, 95% yield)
eluted second with 1/1 hexane/CH2Cl2. Complex 9 was recrystallized
from CH2Cl2 and methanol to afford dark green crystals: Mp 166−168
°C; 1H NMR (500 MHz, CD2Cl2) δ 9.130 (s, 1H, H-3), 9.128 (s, 1H,
H-3), 8.52 (s, 2H, H-5), 8.51 (s, 2H, H-1), 8.48 (s, 2H, H-8), 8.45 (s,
2H, H-6), 8.40 (AB, J = 7.8 Hz, 2H, H-9), 8.38 (AB, J = 7.8 Hz, 2H, H-
10), 2.56−2.50 (m, 12H, CH2CH3), 1.73 (s, 18H, 2-C(CH3)3), 1.70
(s, 18H, 7-C(CH3)3), 1.41 (dt, 2JP−H = 16.5 Hz, 3JH−H = 7.7 Hz, 18H,
−CH2CH3), −3.83 (s, 6H, 10c-CH3), −3.86 (s, 6H, 10b-CH3);
13C{1H} NMR (125 MHz, CD2Cl2) δ 146.50 (C-7), 145.75 (C-2),
137.61 (C-10a/10d), 137.58 (C-10a/10d), 137.11 (C-5a), 136.46 (C-
3a), 127.04 (C-5), 123.43 (C-9/10), 122.82 (C-9/10), 122.17 (C-4),
121.45 (C-1), 121.05 (C-3), 120.77 (C-8), 119.87 (C-6), 115.11 (1JPt−C
= 29 Hz, CCPt), 110.95 (CCPt), 36.57 (2-C(CH3)3), 36.38 (7-
C(CH3)3), 32.46 (2-C(CH3)3), 32.26 (7-C(CH3)3), 30.85 (C-10b),
(triethylphosphino)platinum(II) (11a) and the 9-Benzoyl 10-
Benzoyl Isomer (11b). Using the same procedure described for
making 9, an isomeric mixture of benzoylDHP-ethyne 6 (30 mg, 0.063
mmol), Pt(PEt3)2Cl2 (15 mg, 0.030 mmol), and CuI (1.0 mg, 5.3 ×
10−3 mmol) was reacted in Et2NH (6 mL) to afford pure 11 as dark
red crystals after recrystallization from a mixture of hexane, CH2Cl2,
and methanol. In this case, the major isomer was the bis-9-benzoyl
isomer, despite the fact that the major isomer of the alkyne was
confirmed to be the 10-benzoyl 4-ethynyl DHP. The identity of the
major isomer was established by 2D NMR studies. The most probable
reason for this difference is that repeated recrystallization of the
benzoylDHP-ethyne before reaction with platinum resulted in
enrichment of the crystals in the less soluble 9-benzoyl-4-ethynylDHP
(14 mg, 35% yield). 11a (major isomer, bis-9-benzoyl): 1H NMR (500
MHz, CDCl3) δ 9.19 (s, 1H, H-3), 8.91 (s, 1H, H-8), 8.55 (s, 1H, H-
10), 8.53 (s, 1H, H-5), 8.48 (s, 1H, H-1), 8.41 (s, 1H, H-6), 7.93−7.89
(m, 2H, H-2′), 7.60 (t, J = 7.5 Hz, 1H, H-4′), 7.52−7.47 (m, 2H, H-
3′), 2.54−2.43 (m, 6H, PCH2CH3), 1.68 (s, 9H, 2-C(CH3)3), 1.56 (s,
9H, 2-C(CH3)3), 1.44−1.35 (m, 9H, PCH2CH3), −3.60 (s, 3H, 10b-
CH3), −3.65 (s, 3H, 10c-CH3); 13C{1H} NMR (125 MHz, CDCl3) δ
199.36 (COPh), 149.35 (C-2), 145.77 (C-2), 141.24 (C-1′), 139.18
(C-5a), 136.66 (C-10a), 136.29 (C-3a), 134.84 (C-10d), 132.33 (C-
4′), 130.57 (C-2′), 128.45 (C-9), 127.39 (C-5), 125.23 (C-10), 124.08
(C-4), 123.44 (C-1), 123.02 (C-3), 119.90 (C-6,8), 110.86 (CCPt),
36.48 (7-C(CH3)3), 36.28 (2-C(CH3)3), 32.20 (2-C(CH3)3), 31.92 (2-
C(CH3)3), 31.17 (C-10c), 30.20 (C-10b), 17.05 (t, J = 14 Hz,
PCH2CH3), 16.10 (10b-CH3), 15.10 (10c-CH3), 8.91 (PCH2CH3);
31P{1H} NMR (CDCl3, 145 MHz) δ 12.81 (1JPt−P = 2383 Hz); 11b:
1
30.30 (C-10c), 17.36 (t, JP−C = 17 Hz, CH2CH3), 15.60 (C-10c),
14.81 (C-10b), 9.10 (CH2CH3); 31P{1H} NMR (202 MHz, CD2Cl2) δ
13.24 (1JPt−P = 2383 Hz); IR (KBr) ν 3034, 2963, 2904, 2872, 2082,
1457, 1379, 1357, 1343, 1254, 1231, 1034, 882, 768, 733, 664 cm−1;
UV−vis (cyclohexane) λmax (εmax, L mol−1 cm−1) 366 (97 300), 408
(136 000), 479 (30 200), 504 (32 700), 670 (5370) nm; ESI MS m/z
1164 (M+); HRMS calcd for C68H92P2Pt 1164.6301, found 1164.6389.
trans-Bis-[2′-(10-acetyl-2,7-di-tert-butyl-10b,10c-dimethyl-
t r a n s - 1 0 b , 1 0 c - d i h y d r o p y r e n - 4 - y l ) e t h y n y l ] b i s -
(triethylphosphino)platinum(II) (10a) and the 9-Acetyl 10-
Acetyl Isomer (10b). Using the same procedure as for 9, the ethyne
5 (70 mg, 0.17 mmol) and trans-Pt(PEt3)2Cl2 (43 mg, 0.086 mmol)
with CuI (2.0 mg, 0.011 mmol) in degassed Et2NH (15 mL) gave
complex 10. Chromatography on silica gel using 1/1 hexane/CH2Cl2
followed by recrystallization from CH2Cl2 and methanol afforded pure
1H NMR (500 MHz, CDCl3) δ 9.18 (s), 8.87 (s), 8.59 (s), 8.50 (s),
8.46 (s), 8.45 (s), 1.66 (s, C(CH3)3), 1.58 (s, C(CH3)3), −3.62 (s,
internal CH3), −3.64 (s, internal CH3) these are the only clearly
distinguishable resonances for the minor isomer. Mixture of isomers
8129
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Organometallics
Article
11a and 11b: mp 190−198 °C; IR (KBr) ν 2963, 2904, 2873, 2077,
1640, 1511, 1446, 1379, 1345, 1258, 1245, 1209, 1174, 1035, 1021,
892, 767, 733, 698 cm−1; UV−vis (toluene) λmax (εmax, L mol−1 cm−1)
370 (sh, 50 200), 427 (96 300), 523 (24 300), 621 (770), 681 (1990)
nm; ESI MS m/z 1373 (M+); HRMS calcd for C82H100O2P2Pt + H
1373.6904, found 1373.6871.
trans-Bis[2″-[10-(1-naphthoyl)-2,7-di-tert-butyl-10b,10c-di-
methyl-trans-10b,10c-dihydropyren-4-yl]ethynyl]bis-
C6D6) δ 144.94 (C-7), 144.02 (C-2), 138.40 (C-5a), 137.32 (C-3a),
136.26 (C-12e), 135.91 (C-12b), 130.65 (C-12a), 130.09 (C-12f),
126.89 (C-5), 126.63 (C-11), 126.37 (C-10), 125.46 (C-12) 125.42 (C-
9), 121.32 (C-4), 120.99 (C-3), 120.20 (C-6), 118.18 (C-1), 117.46
2
(C-8), 115.05 (t, JC−P = 15 Hz, CCPt), 111.00 (CCPt), 37.23
(C-12c), 36.44 (C-12d), 36.18 (2-C(CH3)3), 35.78 (7-C(CH3)3),
31.52 (2-C(CH31)3), 31.05 (7-C(CH3)3), 19.04 (12d-CH3), 18.67 (12c-
CH3), 17.47 (t, JC−P = 17.8 Hz, CH2CH3), 9.10 (CH2CH3); 31P{1H}
NMR (145 MHz, C6D6) δ 12.18 (1JPt−P = 2398 Hz); 195Pt NMR (77
MHz, C6D6) δ −219.79 (1JPt−P = 2400 Hz); IR (KBr) ν 2960, 2924,
2862, 2071, 1460, 1365, 1249, 1035, 870, 772, 749, 632 cm−1; UV−vis
(cyclohexane) λmax (εmax, L mol−1 cm−1) 341 (34 610), 355 (35 700),
399 (51 400), 418 (73 700), 502 (11 600), 525 (14 100), 553 (12
200), 641 (1050) nm; ESI MS m/z 1264 (M+); HRMS calcd for
C76H96P2Pt 1264.6614, found 1264.6599. NMR spectral data in
CDCl3: 1H NMR (500 MHz) δ internal methyl protons at −1.46 and
(triethylphosphino)platinum(II) (12a) and the 9-Naphthoyl 10-
Naphthoyl Isomer (12b). Using the same procedure described for 9,
1′-naphthoyl DHP-ethyne 7 (60 mg, 0.12 mmol), trans-Pt(PEt3)2Cl2
(30 mg, 0.060 mmol), and CuI (1.7 mg, 8.9 × 10−3 mmol) were
refluxed in degassed Et2NH (6 mL) for 12 h. Recrystallization of the
solid residue from benzene and pentane afforded dark orange crystals
1
of 12 (40 mg, 70% yield). 12a (major isomer, bis-10-naphthoyl): H
1
−1.49; 31P{1H} NMR (145 MHz) δ 12.2 (d, JPt−P = 2395 Hz); 195Pt
NMR (500 MHz, CDCl3) δ 9.31 (s, 2H, H-1), 9.20 (s, 2H, H-3), 8.60
(s, 2H, H-5), 8.50 (s, 2H, H-9), 8.46 (d, J = 8.4 Hz, 2H, H-8′), 8.43 (s,
2H, H-6), 8.37 (s, 2H, H-8), 8.05 (d, J = 8.3 Hz, 2H, H-4′), 7.98 (d, J =
8.0 Hz, 2H, H-5′), 7.64 (dd, J = 7.0, 1.0 Hz, 2H, H-2′), 7.57−7.52 (m,
2H, H-6′), 7.52−7.44 (m, 4H, H-3′,7′), 2.54−2.42 (m, 12H,
PCH2CH3), 1.61 (s, 9H, 7-C(CH3)3), 1.57 (s, 9H, 2-C(CH3)3),
1.43−1.34 (m, 18H, PCH2CH3), −3.62 (s, 6H, 10b,10c-CH3);
13C{1H} NMR (125 MHz, CDCl3) δ 201.07 (NpCO), 149.73 (C-
2), 146.54 (C-7), 140.39 (C-1′), 139.13 (C-3a), 137.26 (C-10a),
136.62 (C-5a/10d), 134.80 (C-5a/10d), 134.08 (C-8′b), 131.47 (C-
8′a), 131.36 (C-4′), 130.05 (C-10), 128.88 (C-5,2′), 128.57 (C-5′),
127.45 (C-7′), 126.54 (C-6′), 126.25 (C-8′), 125.51 (C-9), 124.83 (C-
3′), 123.29 (C-8), 121.82 (C-6), 121.48 (C-3), 120.27 (C-1), 119.96
(C-10), 110.43 (CCPt), 36.73 (2-C(CH3)3), 36.03 (7-C(CH3)3),
31.98 (2/7-C(CH3)3), 31.97 (2/7-C(CH3)3), 31.86 (C-10b), 29.53 (C-
10c), 17.00 (t, J = 17 Hz, PCH2CH3), 15.71 (10b-CH3), 15.16 (10b-
CH3), 8.85 (PCH2CH3); 31P{1H} NMR (CDCl3, 202 MHz) δ 12.89
NMR (77 MHz) δ −212.20 (1JPt−P = 2400 Hz).
trans-Bis[2″-(10-benzoyl-2,7-di-tert-butyl-10b,10c-dimethyl-
t r a n s - 1 0 b , 1 0 c - d i h y d r o p y r e n - 4 - y l ) e t h y n y l ] b i s -
(1JPt−P = 2383 Hz); 195Pt NMR (CDCl3, 77 MHz) δ −214.77 (1JP−Pt
=
1
2385 Hz). 12b (minor 9-naphthoyl 10-naphthoyl isomer): H NMR
(500 MHz, CDCl3) δ 9.37, 9.18, 8.54, 8.52, 8.42, 8.40 (d, J = 8.6 Hz),
only the clearly discernible resonances for 12b are listed. Mixture of
isomers 12a and 12b: mp 207−212 °C; IR (KBr) ν 2963, 2905, 2873,
2080, 1641, 1588, 1508, 1477, 1459, 1381, 1345, 1273, 1243, 1196,
1035, 891, 783, 768 cm−1; UV−vis (toluene) λmax (εmax, L mol−1 cm−1)
371 (70 200), 437 (109 000), 495 (25 600), 633 (2100), 694 (7500)
nm; ESI MS m/z 1473 (M+); HRMS calcd for C90H104O2P2Pt + H
1473.7217, found 1473.7190.
(triphenylphosphino)platinum(II) (14a) and the 9-Benzoyl 10-
Benzoyl Isomer (14b). Complex 14 was prepared using a procedure
similar to that for 9, by mixing benzoylDHP-ethyne 6 (70 mg, 0.15
mmol), trans-Pt(PPh3)2Cl2 (50 mg, 0.063 mmol), and CuI (1.0 mg,
0.0053 mmol) in Et2NH (10 mL). In this case, the product
precipitated from the mixture and after washing with methanol
afforded 30 mg of 14 as dark red crystals (30% yield). 14a (major
isomer, bis-10-benzoyl): 1H NMR (500 MHz, CD2Cl2) δ 8.71 (s, 2H,
H-1), 8.61 (s, 2H, H-3), 8.44 (s, 2H, H-8), 8.41 (s, 2H, H-9), 8.26 (s,
2H, H-6), 8.07−8.03 (m, 12H, H-2″,6″), 7.86 (d, J = 7.2 Hz, 4H, H-
2′), 7.64−7.60 (m, 4H, H-9,4′), 7.49 (t, J = 7.7 Hz, 4H, H-3′), 7.24−
7.17 (m, 18H, H-3″,4″,5″), 1.65 (s, 18H, 7-C(CH3)3), 1.34 (s, 18H, 2-
C(CH3)3), −3.87 (s, 6H, 10c-CH3), −3.88 (s, 6H, 10b-CH3); 13C{1H}
NMR (125 MHz, CD2Cl2) δ 199.50 (COPh), 148.49 (C-7), 146.89
(C-2), 141.49 (C-1′), 137.94 (C-3a), 136.63 (C-5a/10d), 136.34 (C-
10a), 135.92 (t, J = 5.6 Hz, C-2″,6″), 135.18 (C-5a/10d), 132.78 (C-
4′), 132.36 (t, J = 29.2 Hz, C-1”), 130.91 (C-4″), 130.77 (C-2′), 130.18
(C-10), 128.83 (C-3′), 128.49 (C-9/C-3″,5″), 128.44 (C-9/C-3″,5″),
128.40 (C-5/C-3″,5″), 124.11 (C-9), 123.16 (C-4), 122.72 (C-8),
121.57 (C-3,6), 120.42 (C-1), 115.29 (CCPt), 36.70 (7-C(CH3)3),
36.34 (2-C(CH3)3), 32.21 (2-C(CH3)3), 32.13 (7-C(CH3)3), 31.55
(C-10b), 29.85 (C-10c), 15.58 (10b-CH3), 15.33 (10c-CH3); 31P{1H}
trans-Bis[2′-(2,7-di-tert-butyl-12c,12d-dimethyl-trans-
12c, 12d-dihydrobenzo[e]pyren-4-yl)ethynyl]bis-
(triethylphosphino)platinum(II) (13). Complex 13 was prepared
using a procedure similar to that for 9, by refluxing ethyne 8 (40 mg,
0.096 mmol), Pt(PEt3)2Cl2 (23 mg, 0.046 mmol), and CuI (1.0 mg,
5.3 × 10−3 mmol) in Et2NH (6 mL) for 2 h. The product was
recrystallized from methanol to give dark red crystals of 13 (50 mg,
1
84% yield): mp 169−170 °C; H NMR (500 MHz, C6D6) δ 8.86−
8.83 (m, 2H, H-12), 8.80−8.78 (m, 2H, H-9), 8.58 (d, J = 1.3 Hz, 2H,
H-3), 8.49 (d, J = 1.3 Hz, 2H, H-1), 8.381 and 8.379 (s, 2H, H-8),
7.725 and 7.724. (s, 2H, H-5), 7.52 (s, 2H, H-6), 7.53−7.48 (m, 4H,
H-10,11), 2.34−2.21 (m, 12H, PCH2CH3), 1.60 (s, 18H, 2-C(CH3)3),
1.42 (s, 18H, 7-C(CH3)3), 1.28−1.18 (m, 18H, PCH2CH3), −1.02 (s,
6H, 12d-CH3), −1.04 (s, 3H, 12c-CH3); 13C{1H} NMR (125 MHz,
8130
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NMR (145 MHz, CD2Cl2) δ 18.28 (1JPt−P = 2651 Hz); 195Pt NMR
(77 MHz, CD2Cl2) δ −252.22 (JP−Pt = 2655 Hz). Mixture of isomers
14a and 14b: mp 172−180 °C; IR (film) ν 3056, 2963, 2092, 1650,
1595, 1480, 1435, 1246, 1098, 691 cm−1; UV−vis (toluene) λmax (εmax
,
L mol−1 cm−1) 373 (47 300), 433 (63 100), 493 (17 800), 684 (4600)
nm; ESI MS m/z 1661 (M+); HRMS calcd for C106H100O2P2Pt + H
1661.6904, found 1661.6877.
trans-Bis[2″-(2,7-di-tert-butyl-12c,12d-dimethyl-trans-
12c, 12d-dihydrobenzo[e]pyren-4-yl)ethynyl]bis-
−3.40 (s, 6H, H-10b), −3.41 (s, 6H, H-10c); 13C{1H} NMR (125
MHz, C6D6) δ 146.31 (C-2), 145.59 (C-7), 138.19 (C-10a/10e),
137.64 (C-3a), 137.04 (C-5a), 134.61−134.50 (meta-C), 131.49
(ortho-C, para-C), 129.35−129.24 (ortho-C, para-C), 128.5 (C-5
partially obscured by the solvent resonance), 123.59 (C-10), 123.18
(C-9), 122.81 (C-4), 122.70 (C-3), 121.80 (C-1), 120.84 (C-8), 120.39
2
2
(C-6), 114.16 (dd, JP(trans)‑C = 150 Hz, JP(cis)‑C = 15 Hz, CCPt),
113.28 (d, 2JP(trans)‑C = 35 Hz, CCPt), 36.50 (2-C(CH3)3), 36.26 (7-
C(CH3)3), 32.60 (2-C(CH3)3), 32.43 (2-C(CH3)3), 31.34 (C-10b),
30.89 (C-10c), 29.00−28.30 (m, PCH2CH2P), 15.98 (C-10b/10c),
(triphenylphosphino)platinum(II) (15). Complex 15 was prepared
using the same procedure as for 14, by mixing benzo[e]DHP-ethyne 8
(40 mg, 0.095 mmol), trans-Pt(PPh3)2Cl2 (35 mg, 0.045 mmol), and
CuI (1.0 mg, 0.0053 mmol) in Et2NH (10 mL). The red solid that
precipitated was recrystallized from toluene to give 15 (45 mg, 65%
15.60 (C-10b/10c); 31P{1H} NMR (202 MHz, CDCl3) δ 39.57 (1JPt−P
1
= 2277 Hz); 195Pt NMR (77 MHz, CDCl3) δ −381.53 (t, JPt−P
=
2278 Hz); IR (KBr) ν 2960, 2863, 2093, 1589, 1476, 1459, 1435,
1230, 1103, 881, 704, 690, 531 cm−1; UV−vis (toluene) λmax (εmax, L
mol−1 cm−1) 367 (55 200), 405 (54 600), 478 (12 100), 503 (12 100),
669 (2200) nm; ESI MS m/z 1327 (M+); HRMS calcd for C82H86P2Pt
+ H 1327.5910, found 1327.5889.
1
yield). 15: mp 180 °C dec; H NMR (500 MHz, C6D6) δ 8.83−8.79
(m, 4H, H-9,12), 8.39 (s, 2H, H-1), 8.37 (d, J = 1.1 Hz, 2H, H-8), 8.19
(m, 12H, H-2′), 7.83 (t, J = 1.1 Hz, 2H, H-3), 7.52−7.47 (m, 4H, H-
10,11), 7.26 (d, J = 1.0 Hz, 2H, H-6), 7.04 (t, J = 7.4 Hz, 12H, H-3′),
6.93 (t, J = 7.0 Hz, 6H, H-4′), 6.62 (dd, J = 3.9, 0.8 Hz, 2H, H-5), 1.46
(s, 2H, 7-C(CH3)3), 1.35 (s, 2H, 2-C(CH3)3), −1.22 (d, J = 3.3 Hz,
2H, 12d-CH3), −1.27 (d, J = 4.2 Hz, 2H, 12c-CH3); 13C{1H} NMR
(125 MHz, C6D6) δ 143.99 (C-7), 143.23 (C-2), 136.96 (C-5a),
cis-Bis[2″-(2,7-di-tert-butyl-12c,12d-dimethyl-trans-12c,12d-
dihydrobenzo[e]pyren-4-yl)ethynyl][bis(diphenylphosphino)-
2
136.86 (C-3a), 136.15 (t, JC−P = 6 Hz, C-2′), 135.87 (C-12e), 135.43
1
(C-12b), 132.63 (t, JC−P = 29.2 Hz, C-1′), 130.78 (C-4′), 130.61 (C-
3
12a), 129.99 (C-12f), 128.44 (t, JC−P = 5.5 Hz, C-3′), 127.28 (C-5),
126.16 (C-10,11), 125.41 (C-9 or 12), 125.34 (C-9 or 12), 121.24 (C-
2
4), 121.13 (C-3), 120.23 (C-6), 118.60 (t, JC−P = 15.1 Hz, CCPt),
118.04 (C-1), 117.29 (C-8), 115.77 (CCPt), 36.77 (C-12c), 36.05
(C-12d), 35.88 (2-C(CH3)3), 35.71 (7-C(CH3)3), 31.38 (2-C(CH3)3),
31.11 (7-C(CH3)3), 18.74 (12c-CH3), 18.65 (12d-CH3); 31P{1H}
NMR (202 MHz, C6D6) δ 19.02 (1JPt−P = 2677 Hz); 195Pt NMR (77
MHz, C6D6) δ −253.77 (t, 1JPt−P = 2695 Hz); IR (KBr) ν 3057, 2960,
2922, 2864, 2099, 1476, 1434, 1365, 1254, 1096, 743, 692, 521, 513
cm−1; UV−vis (toluene) λmax (εmax, L mol−1 cm−1) 342 (35 200), 359
(37 000), 423 (78 900), 529 (13 600) nm; ESI MS m/z 1553 (M+ +
H); HRMS calcd for C100H96P2Pt + H 1553.6692, found 1553.6676.
ethane-P,P′]platinum(II) (17). Using the procedure for complex 9,
DHP-ethyne 8 (40 mg, 0.095 mmol), Pt(dppe)Cl2 (30 mg, 0.046
mmol), and CuI (2.6 mg, 0.013 mmol) in Et2NH (7 mL) gave a red
solid. This was chromatographed on alumina with hexanes/CH2Cl2
(1/2) as eluent. The dialkyne dimer (5 mg, 12% yield) eluted first,
followed by 17 as a red solid after removal of solvent (16 mg, 25%
1
Open form, 15o: H NMR (500 MHz, C6D6) δ 8.17−8.11 (m, 2H),
8.11−8.04 (m, 10H), 7.76−7.69 (m, 4H), 7.22−7.18 (m, 4H), 7.08−
6.96 (m, 24H), 6.77−6.74 (m, 2H), 6.00 (s, 1H), 5.97 (s, 1H), 1.43 (s,
3H), 1.42 (s, 3H), 1.39 (s, 6H), 1.278 (s, 9H), 1.276 (s, 9H), 1.137 (s,
9H), 1.134 (s, 9H).
1
yield). 17: mp 200 °C dec; H NMR (500 MHz, C6D6) δ 8.86 and
cis-Bis[2″-(2,7-di-tert-butyl-10b,10c-dimethyl-trans-10b,10c-
dihydropyren-4-yl)ethynyl][bis(diphenylphosphino)ethane-
P,P′]platinum(II) (16). Complex 16 was prepared using a similar
procedure as for 14, by mixing DHP-ethyne 4 (50 mg, 0.135 mmol),
Pt(dppe)Cl2 (44 mg, 0.066 mmol), and CuI (1.6 mg, 0.0084 mmol) in
Et2NH (10 mL). The brown precipitate was chromatographed on
alumina with hexanes/CH2Cl2 (3/10) as eluent. The dialkyne dimer
eluted first (6 mg, 12% yield), followed by 16 as an orange solid after
removal of solvent. Washing with methanol afforded pure 16 as orange
microcrystals (22 mg, 25% yield). 16: mp 180 °C dec; 1H NMR (500
MHz, C6D6) δ 9.88 and 9.87 (s, 2H, H-3), 8.76 (s, 2H, H-5), 8.57 and
8.56 (s, 2H, H-1), 8.54 (s, 2H, H-8), 8.44 (AB, J = 8.9 Hz, 4H, H-
9,10), 8.38 (s, 2H, H-6), 8.26−8.16 (m, 4H, meta-H), 7.06−6.92 (m,
6H, ortho- and para-H), 2.08−1.91 (m, 4H, PCH2CH2P), 1.609 and
1.607 (s, 18H, 7-C(CH3)3), 1.435 and 1.424 (s, 18H, 2-C(CH3)3),
8.84 (s, 2H, H-3), 8.82−8.77 (m, 4H, H-9,12), 8.43 (s, 2H, H-1), 8.37
(s, 2H, H-8), 8.14−8.07 (m, 8H, meta-H), 7.50−7.44 (m, 4H, H-
10,11), 7.41 (s, 2H, H-5), 7.29 (s, 2H, H-6), 7.09−6.94 (m, 12H,
ortho- and para-H),1.98−1.81 (m, 4H, PCH2CH2P), 1.42 (s, 18H, 7-
C(CH3)3), 1.33 (s, 18H, 2-C(CH3)3), −1.06, −1.07, and −1.08
(12c,12d-CH3); 13C{1H} NMR (125 MHz, C6D6) δ 144.56 and
144.52 (C-2), 143.93 (C-7), 138.93 (C-3a), 137.45 and 137.43 (C-5a),
135.95 (C-12b/12e), 135.85 (C-12b/12e), 134.56 and 134.46 and
134.38 (meta-C), 131.46 (para-C), 130.66 (C-12a), 130.09 (C-12f),
129.29 and 129.26 and 129.20 (ortho-C), 127.59 and 127.55 (C-5),
126.37 and 126.10 (C-10,11), 125.50 and 125.32 (C-9,12), 122.09 (C-
3), 120.80 (C-4), 120.52 (C-6), 118.37 (C-1), 117.33 (C-8), 113.42
2
2
(dd, JP(trans)‑C = 150 Hz, JP(cis)‑C = 14 Hz, CCPt), 112.5 (dd,
2JP(trans)‑C = 36 Hz, 2JP(cis)‑C = 6 Hz, CCPt), 37.08 (C-12c), 36.33 (C-
8131
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12d), 36.09 (2-C(CH3)3), 35.72 (7-C(CH3)3), 31.36 (2-C(CH3)3),
31.13 (7-C(CH3)3), 28.76−28.36 (m, PCH2CH2P), 18.86 and 18.83
and 18.77 and 18.74 (12c,12d-CH3); 31P{1H} NMR (202 MHz, C6D6)
δ 40.24 (1JPt−P = 2246 Hz); 195Pt NMR (77 MHz, CD2Cl2) δ −378.8
(1JPt−P = 2268 Hz); IR (KBr) ν 3054, 2961, 2921, 2865, 2093, 1475,
1435, 1366, 1253, 1104, 873, 753, 712, 703, 690, 530; UV−vis
(cyclohexane) λmax (εmax, L mol−1 cm−1) 339 (63 600), 356 (70 700),
416 (130 000), 527 (12 200) nm; ESI MS m/z 1427 (M+), MS calcd
for C90H90P2Pt + H 1427.6223, found 1427.6248. NMR spectral data
1
in CD2Cl2: H NMR (360 MHz) δ 8.75−8.72 (m, 4H), 8.24, 8.23,
8.17−8.09 (m, 4H), 8.07 (t), 7.59−7.55 (m), 7.46−7.41 (m), 7.20, (s),
6.95 (s), 2.57−2.43 (m broad,) 1.47, (s, 18H), 1.269 (s, 9H), 1.266 (s,
9H), −1.539 (12c/12d-CH3), −1.542 (12c/12d-CH3); 31P{1H} NMR
(146 MHz) δ 41.41 (1JPt−P= 2268 Hz). Open form 17o: 1H NMR (500
MHz, C6D6) δ 8.03−7.85 (m, 8H), 7.75−7.68 (m, 6H), 7.21−7.17 (m,
4H), 7.07−6.92 (m, 16H), 6.91 (s, 1H), 6.89 (s, 1H), 6.80 (d, J = 2.1
Hz, 1H), 6.78 (d, J = 1.9 Hz, 1H), 2.00−1.64 (m, 8H),); 13C{1H}
NMR (125 MHz, C6D6) δ 150.74, 150.04, 145.38, 145.35, 140.77,
140.44, 140.16, 139.91, 139.21, 139.04, 135.25, 135.08, 134.32, 134.14,
131.55, 124.85, 124.80, 123.89, 34.62, 34.48, 31.93, 31.88, 31.43,
31.11, 19.95, 19.42; 31P{1H} NMR (202 MHz, C6D6) δ 40.34 and
40.31 (1JPt−P = 2242 Hz).
thoyl Isomer (19b). Complex 19 was prepared according to the same
procedure as 9 from 1′-naphthoylDHP-ethyne 7 (100 mg, 0.192
mmol), Pt(bipy)Cl2 (43 mg, 0.096 mmol), and CuI (6.0 mg, 0.032
mmol) in Et2NH (15 mL). The crude product was recrystallized in a
mixture of CH2Cl2 and methanol to afford dark red crystals of 19 (10
1
mg, 7% yield). 19a (major isomer, bis-10-naphthoyl): H NMR (500
cis-Bis[2″-(10-acetyl-2,7-di-tert-butyl-10b,10c-dimethyl-
MHz, CD2Cl2) δ 10.34 (d, J = 5.2 Hz, 2H, H-6′), 9.53 (s, 2H, H-3),
9.28 and 9.27 (two overlapping s, 2H, H-1), 8.88 (s, 2H, H-5), 8.54 (s,
4H, H-6,9), 8.45 (s, 2H, H-8), 8.40 (d, J = 8.5 Hz, 2H, H-8″), 8.31−
8.25 (m, 4H, H-3′,4′), 8.08 (d, J = 8.1 Hz, 2H, H-4″), 8.01 (d, J = 8.3
Hz, 2H, H-5″), 7.78 (t, J = 6.7 Hz, 2H, H-5′), 7.64 (d, J = 7.1 Hz, 2H,
H-2″), 7.59−7.45 (m, 6H, H-3″,6″,7″), 1.62 (s, 18H, 7-C(CH3)3), 1.46
(s, 9H, 2-C(CH3)3), 1.45 (s, 9H, 2-C(CH3)3), −3.57 (s, 6H, 10b-
CH3), −3.59 (s, 6H, 10c-CH3); 13C{1H} NMR (125 MHz, CD2Cl2) δ
200.99 (NpCO), 157.18 (C-2′), 152.28 (C-6′), 150.58 (C-2), 147.01
(C-7), 140.85 (C-1″), 140.36 (C-3a), 139.60 (C-4′), 137.63 (C-10a),
136.80 (C-5a/10d), 135.22 (C-5a/10d), 134.45 (C-8″b), 131.68 (C-
8″a), 131.55 (C-4″), 130.49 (C-10), 130.08 (C-5), 129.02 (C-2″),
128.93 (C-5″), 128.35 (C-5′), 127.66 (C-7″), 126.87 (C-6″), 126.56
(C-8″), 126.21 (C-9), 125.28 (C-3″), 124.02 (C-8), 123.31 (C-3′),
122.88 (C-6), 121.92 (C-3,4), 120.88 (C-1), 102.52 (CCPt), 94.13
(CCPt), 37.00 (2-C(CH3)3), 36.32 (7-C(CH3)3), 32.22 and 32.21
(2/7-C(CH3)3), 32.17 (C-10b), 32.09 (2/7-C(CH3)3), 29.97 (C-10c),
15.78 (C-10b/10c), 15.36 (C-10b/10c). Mixture of isomers 19a and
19b: mp 260−267 °C; UV−vis (toluene) λmax (εmax, L mol−1 cm−1)
370 (70 600), 430 (93 000), 694 (8600) nm; ESI MS m/z 1394
(M++H); HRMS calcd for C88H82N2O2Pt 1393.6081, found
1393.6063.
trans-10b,10c-dihydropyren-4-yl)ethynyl](2,2′-bipyridine-
N,N′)platinum(II) (18a) and the 9-Acetyl 10-Acetyl Isomer
(18b). Complex 18 was prepared according to the same procedure as
9, from acetylDHP-ethyne 5 (60 mg, 0.15 mmol), Pt(bipy)Cl2 (30 mg,
0.067 mmol), and CuI (2.0 mg, 10 × 10−3 mmol) in Et2NH (6 mL).
Recrystallization of the crude product from a mixture of hexane and
CH2Cl2 afforded 18 as dark orange crystals (33 mg, 40% yield). 18a
1
cis-Bis[2″-(2,7-di-tert-butyl-10b,10c-dimethyl-trans-10b,10c-
(major isomer, bis-10-acetyl): H NMR (500 MHz, CDCl3) δ 10.33
dihydropyren-4-yl)ethynyl](1′,10′-phenanthroline-N,N′)-
(d, J = 5.3 Hz, 2H, H-6′), 9.70 (d, J = 1.4 Hz, 2H, H-1), 9.58 (d, J = 1.3
Hz, 2H, H-3), 8.87 (s, 2H, H-5), 8.83 (s, 2H, H-9), 8.55 (s, 2H, H-8),
8.46 (s, 2H, H-6), 8.23 (d, J = 1.4 Hz, 2H, H-3′), 8.22 (td, J = 7.9, 1.4
Hz, 2H, H-4′), 7.68 (td, J = 6.0, 2.3 Hz, 1H, H-5′), 3.05 (s, 6H,
COCH3), 1.66 (s, 18H, 7-C(CH3)3), 1.60 (s, 9H, 2-C(CH3)3), 1.59 (s,
9H, 2-C(CH3)3), −3.69 (s, 6H, 10c-CH3), −3.714/-3.715 (s, 6H, 10b-
CH3); 13C{1H} NMR (125 MHz, CDCl3) δ 202.52 (COCH3), 156.67
(C-2′), 152.08 (C-6′), 151.07 (C-2), 146.27 (C-7), 140.39 (C-3a),
138.91 (C-4′), 136.63 (C-10a), 136.61 (C-10a minor isomer), 136.33
(C-5a/10d), 135.17 (C-5a/10d), 130.09 (C-5), 128.09 (C-10), 127.78
(C-5′), 124.29 (C-9), 123.35 (C-8), 122.91 (C-3′), 122.36 (C-6),
122.01 (C-3), 121.72 (C-4), 120.68 (C-1), 120.65 (C-1 minor isomer),
102.77 (CC−Pt), 92.30 (CC-Pt), 36.96 (2-C(CH3)3), 36.95 (2-
C(CH3)3), 36.07 (7-C(CH3)3), 32.33 (2-C(CH3)3), 32.09 (7-
C(CH3)3), 31.69 (C-10b), 31.11 (COCH3), 29.51 (C-10c), 15.48
(10b/10c-CH3). Mixture of isomers 18a and 18b: mp 182−190 °C; IR
(KBr) ν 2962, 2923, 2905, 2865, 2094, 1663, 1657, 1606, 1585, 1468,
1449, 1422, 1408, 1378, 1348, 1243, 1225, 1207, 1155, 1123, 934, 891,
764, 747, 681, 665 cm−1; UV−vis (toluene) λmax (εmax, L mol−1 cm−1)
390 (78 400), 424 (87 700), 492 (19 600), 695 (8500) nm; ESI MS
m/z 1170 (M+ + H); HRMS calcd for C70H74N2O2Pt 1169.5455,
found 1169.5481.
platinum(II) (20). Complex 20 was prepared according to the same
procedure as 9 from DHP-ethyne 4 (50 mg, 0.135 mmol),
Pt(phen)Cl2 (29 mg, 0.065 mmol), and CuI (1.5 mg, 0.0079 mmol)
in Et2NH (8 mL). Brown, microcrystalline 20 precipitated from the
reaction mixture (15 mg, 21% yield). The low solubility of 20
precluded the 2D experiments required to assign all of the 1H and 13
C
1
resonances; therefore, these are simply listed without assignment. H
NMR (500 MHz, CD2Cl2) δ 10.55 (m, 2H, H-2,9), 9.51 (s, 2H), 8.82
(s, 2H), 8.78 (m, 2H), 8.52 (d, J = Hz, 2H), 8.50 (s, 4H), 8.43 (d, J =
1.0 Hz, 2H), 8.40 (d, J = 7.4 Hz, 2H), 8.15 (s, 2H), 8.09 (m, 2H),
1.70, 1.64, 1.62, −3.77 (internal CH3), −3.78 (internal CH3); 13C{1H}
cis-Bis[2‴-[10-(1-naphthoyl)-2,7-di-tert-butyl-10b,10c-di-
methyl-trans-10b,10c-dihydropyren-4-yl]ethynyl](2,2′-bipyri-
dine-N,N′)platinum(II) (19a) and the 9-Naphthoyl 10-Naph-
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NMR (125 MHz, C6D6) δ 152.25, 148.69, 146.44, 146.38, 138.57,
138.12, 137.71, 137.54, 136.86, 131.35, 128.15, 127.92, 126.85, 123.33,
123.1, 121.50, 121.31, 121.06, 120.92, 120.45, 103.18, 54.44, 54.22,
54.00, 53.79, 53.57, 42.63, 36.62, 36.40, 32.54, 32.25, 30.91, 30.42,
15.53, 15.01; IR (KBr) ν 3035, 2963, 2867, 2096, 1608, 1520, 1460,
1381, 1358, 1343, 1231, 883 cm−1; ESI MS m/z 1109 (M+).
X-ray Crystallographic Studies. Crystals for analysis were grown
by slow cooling of saturated solutions in a mixed solvent:
dichloromethane/methanol (10, 14), dichloromethane/hexane (11,
17), or toluene/hexane (15). Suitable crystals were selected under a
microscope and attached to a glass fiber prior to data collection at low
temperature (90 K for 10, 11, 14, and 15; 173 K for 17) using a
Bruker/Siemens SMART APEX (10, 11, 14, 15) or a Bruker X8 APEX
II (17) instrument (Mo Kα radiation, λ = 0.710 73 Å). Data were
measured using ω scans of 0.3° per frame for 10 (11), 20 (15) or 30 s
(10, 14), and a full sphere of data was collected; for 17, ω scans of 0.5°
per frame for 30 s were collected. Data reduction and correction for
Lorentz−polarization and decay were performed using SAINTPlus
software.29 Absorption corrections were applied using SADABS.30 The
structures were solved by direct methods and refined using least
squares on F2 as implemented in the SHELXTL program package.31
All non-hydrogen atoms were refined anisotropically except as noted
below.
Disorder was observed in all five structures related to the
orientation of the central methyl groups. In the structures of 14 and
17, this disorder was modeled straightforwardly using a ratio of 75:25
between the two orientations. Similarly, the structure of 15 was
modeled using a ratio of 50:50 between the two orientations.
Complexes 14 contained one well-ordered CH2Cl2 of solvation per
asymmetric unit, while 15 contained a hexane at 50% occupancy.
Complex 17 was determined to contain one very badly disordered
toluene molecule per asymmetric unit by using the Platon/Squeeze
program32 to generate a “solvent-free” data set. The number of
electrons removed by the Squeeze program (53 electrons/asymmetric
unit) corresponds to one toluene molecule; therefore, the formula
reported includes this solvent, although it was not located or refined in
the final least-squares cycle.
The disorder models used in treating the structures of 10 and 11
were more complex. In the case of 10, the disorder of the central DHP
moiety and the acyl group was refined using a ratio of 83:17 for the
two fractions. In addition, a disordered CH2Cl2 of solvation was
located and refined with 20% occupancy. For the structure of 11,
separate disorder models were used to account for the disorder of
different groups: two orientations of the Et groups on PEt3 (ratio
75:25), two orientations of each t-Bu group (ratios 73:27 and 70:30),
and two orientations of the PhCO unit (ratio 56:44). No significant
decomposition was observed during data collection for any of these
complexes. A summary of the data collection and refinement
parameters is given in the Supporting Information.
Photochemical Studies. The visible openings were performed
using a 500 W tungsten light source and a 550 nm cutoff filter. The
processes were followed by either UV−vis spectroscopy or NMR
spectroscopy. For the NMR experiments, the samples were prepared
in an inert-atmosphere glovebox using dry, oxygen-free solvents. In the
UV−vis experiments, solutions were prepared in solvents that were
previously degassed with argon for 15 min. During irradiation, samples
were chilled using an ice bath or cold water recirculating flow system.
The photo-opening rates for the complexes were compared with the
ligand precursor or other DHP compounds with similar photo-
opening rates. UV photoclosing experiments were performed using a
small UV light; only preliminary tests were performed, because the
photoclosing rates were fast in all cases.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: djberg@uvic.ca (D.J.B.); regmitch@uvic.ca (R.H.M.).
Present Addresses
†Notre Dame University, Notre Dame, IN.
‡University of British Columbia, Vancouver, BC, Canada.
Notes
The authors declare no competing financial interest.
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ASSOCIATED CONTENT
■
S
* Supporting Information
Text, tables, figures, and CIF files giving additional synthetic
details, characterization data, and crystallographic data for the
crystal structure studies in this paper. This material is available
free of charge via the Internet at http://pubs.acs.org.
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