Reactivity differences of Pt0 phosphine complexes in C - C bond activation of asymmetric acetylenes

Article abstract of DOI:10.1021/om900413a

Carbon-carbon bond activation reactions of asymmetric acetylene derivatives of the type L₂Pt(PhC≡CR) were studied with 1, 2-bis(diisopropylphosphino)ethane (dippe), 1, 2-bis(di-tert-butyl-phosphino) ethane (dtbpe), and 1-diisopropylphosphino-2-

Full text of DOI:10.1021/om900413a

6524 Organometallics 2009, 28, 6524–6530
DOI: 10.1021/om900413a
Reactivity Differences of Pt0 Phosphine Complexes in C-C Bond
Activation of Asymmetric Acetylenes
€
Ahmet Gunay, Christian Muller, Rene J. Lachicotte, William W. Brennessel, and
William D. Jones*
Department of Chemistry, University of Rochester, Rochester, New York 14627
Received May 19, 2009
Carbon-carbon bond activation reactions of asymmetric acetylene derivatives of the type L2Pt-
(PhCtCR) were studied with 1,2-bis(diisopropylphosphino)ethane (dippe), 1,2-bis(di-tert-butyl-
phosphino)ethane (dtbpe), and 1-diisopropylphosphino-2-dimethylaminoethane (dippdmae) che-
lates. (dippe)Pt(η2-PhCtCCH3) (1a), (dippe)Pt(η2-PhCtCCF3) (1b), and (dippe)Pt(η2-PhCtCC-
(CH3)3) (1c) showed no thermal reactivity at 160 °C, but 1b showed evidence for C-C cleavage to
form (dippe)Pt(Ph)(CtCCF3) upon irradiation with UV light (>300 nm). In comparison, dtbpe
analogues of these metal complexes, (dtbpe)Pt(η2-PhCtCCH3) (2a), (dtbpe)Pt(η2-PhCtCCF3) (2b),
and (dtbpe)Pt(η2-PhCtCC(CH3)3) (2c), showed either C-H or C-C activation products upon
photolysis. 2b produced (dtbpe)Pt(Ph)(CtCCF3), but 2a or 2c showed the formation of
(dtbpe)Pt(D)(C6D5) (2D) by activation of the C6D6 solvent. Compounds 2a-c showed no thermal
reactivity at 160 °C. Two complexes with the hemilabile chelate dippdmae were synthesized and fully
characterized, (dippdmae)Pt(η2-PhCtCCF3) (3b) and (dippdmae)Pt(η2-PhCtCC(CH3)3) (3c).
C-C cleavage products of the type (L2)Pt(Ph)(CtCCF3) were observed only upon photolysis of
compounds 1b, 2b, and 3b.
Introduction
not take advantage of the known strategies of relief of ring
strain,7-13 attainment of aromaticity,14,15 or forcing the
targeted bond into close proximity to the transition metal
center.1,2,16,17 The new examples involve alkynes containing
sp-sp2 (i.e., CtC-aryl) bonds. Here we report attempts to
activate the sp-sp3 C-C bonds by photolysis of mixed
aryl-alkyl acetylene complexes. Also, a comparison is made
between the effects of dippe, dtbpe, and dippmae ligands on
the activation reaction.
Carbon-carbon bond activation with the aid of transition
metal complexes remains one of the most challenging fields
in organometallic chemistry.1-4 While C-H bond activa-
tions have found many successful applications in organic
synthesis and industrial chemistry, mild C-C bond activa-
tion is currently far from practical use.5 New routes for the
efficient cleavage of C-C bonds will help convert naturally
abundant traditionally unreactive molecules into useful raw
materials1 and could offer potential applications in organic
synthesis and petroleum research.
Results and Discussion
To further develop this field, factors influencing C-C
bond cleavage need to be understood, and new examples of
metal insertions need to be elucidated.2 Our group recently
reported a new method6 for C-C bond activation that does
Synthesis and Characterization of L2Pt(alkyne) Com-
plexes. To examine the possibility of sp-sp3 C-C bond
activation, several aryl-alkyl acetylene complexes of the
type (chelate)Pt(η2-PhCtCR) containing the phosphine ligands
dippe (Pri2PCH2CH2PPri2), dtbpe (But2PCH2CH2PBut2), or
dippdmae (Pri2PCH2CH2NMe2) were prepared as shown in
eq 1. The syntheses all involve reaction of a 1:1:1 mixture of
*Corresponding author. E-mail: jones@chem.rochester.edu.
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by Transition Metals. In Topics in Organometallic Chemistry; Murai, S.,
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pubs.acs.org/Organometallics
Published on Web 10/30/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 22, 2009 6525
chelate, Pt(COD)2, and PhCtCR in C6D6, and heating at
55-100 °C for several hours is necessary. The tert-butyl
acetylene derivatives (c) were more difficult to form. For-
mation of 1c required heating at 100 °C for 20 h to obtain
100% conversion. Formation of 2c required heating to
100 °C in the presence of 20 equiv of alkyne. The 31P{1H}
NMR spectra of compounds 1a-c and 2a-c typically show
diphenylacetylene is also indicative of back-bonding.20
Rosenthal has characterized a large number of related L2Ni-
(alkyne) complexes,21 and some Pd and Pt derivatives are
known.22
Reactivity of L2Pt(alkyne) Complexes. Complexes 1a-2c
were all found to be thermally very stable. Heating to 160 °C
for 1-3 days in C6D6 showed no evidence of reaction for 1a,
2a, 1b, 2b, 1c, or 2c. However, 3b and 3c proved to be more
thermally sensitive. Upon heating (dippdmae)Pt(η2-
PhCtCCF3) (3b) either alone or with 5 equiv of PhCtCCF3
at 75 °C, another complex was seen to grow in. This species
shows two resonances in the 31P{1H} NMR spectrum, a
two doublets with platinum satellites (JP-P ≈ 50 Hz; JP-Pt
≈
3000 Hz). The “b” series of compounds containing a CF3-
substituted acetylene showed one of the phosphorus reso-
nances as a doublet of quartets due to the additional P-F
coupling (JP-F=10-16 Hz).
multiplet at δ 30.7 (JP-Pt=3565 Hz) and a doublet (JP-P
=
18 Hz) at δ 32.7 (JP-Pt=3304 Hz). In earlier studies of the
diphenylacetylene complex (dippdmae)Pt(η2-PhCtCPh), it
was established that the bis-monodentate complex
(dippdmae)2Pt(η2-PhCtCPh) can form if an extra equiva-
lent of dippdmae is present.23 By analogy to the chemical
shift and the Pt-P coupling constants of (dippdmae)2Pt(η2-
PhCtCPh) (δ 32.2, JP-Pt =3336 Hz), the new resonances
seen in the 31P NMR spectrum were assigned to
(dippdmae)2Pt(η2-PhCtCCF3) (Scheme 1). The high value
of the Pt-P coupling constant and the fact that one of the
phosphorus resonances was a multiplet while the other was a
doublet support this assignment. The fate of the residual Pt0
was not determined, and heating 3b at 100 °C for 1 day
caused decomposition.
Complexes 3b-c have the potential to form two regioi-
somers. Heating a 1:1:1 ratio of dippdmae, Pt(COD)2, and
PhCtCCF3 at 70 °C overnight produced 3b in 51% yield.
The product was obtained as a mixture of two isomers (90%
isomer with the CF3 group trans to P, 10% isomer with the
CF3 group cis to P). The 31P{1H} NMR spectrum of the
major isomer of 3b shows a quartet at δ 64.7 (JP-Pt=3844 Hz,
JP-F=16 Hz), and the minor isomer appears as a singlet at
δ 66.6 (JP-Pt=3633 Hz).
The single-crystal structures of 1b-3c have been deter-
mined and are shown Figure 1. Table 1 lists similar bond
distances and angles for the compounds. While d10 Pt0
complexes might be expected to have a tetrahedral geometry,
the structural analysis revealed a distorted trigonal geometry
at the metal center with the alkyne ligand in the P-Pt-P
plane. One can notice asymmetrical binding of the trifluor-
omethylphenylacetylene derivatives, in that the Pt-C(2)
bond is noticeably shorter in 1b and 2b, but not in 3b. The
CtC-C bending of the alkyne substituents ranges from
135° to 145°, indicative of strong π-back-bonding.18,19 The
presence of an elongated C-C triple bond compared to free
Similarly, (dippdmae)Pt(η2-PhCtCC(CH3)3) (3c) also
proved to be thermally sensitive. Upon heating 3c at 55 °C
for 2 days, similar to the case for 3b, a new complex appears
with a doublet at δ 27.8 (JP-P=28 Hz; JP-Pt=3208 Hz) and
another doublet at δ 34.1 (JP-P=28 Hz; JP-Pt=3483 Hz).
Comparison to the literature data for (dippdmae)2Pt(η2-
PhCtCPh)23 suggests that the new complex was (dip-
pdmae)2Pt(η2-PhCtCC(CH3)3) (Scheme 1). Heating 3c at
75 °C for 1 day caused decomposition.
Our previous studies showed that aryl-alkyne C-C bonds
undergo oxidative addition upon photolysis.6 Therefore, com-
pound 1a was irradiated with UV light (λ > 300 nm) in C6D6
solution. After irradiation overnight, no evidence for activa-
tion product was seen, and only 1a remained. Similar
irradiation of 1c also showed no evidence for C-C cleavage.
Irradiation of 1b for 10 days, however, showed the formation
of a new product (60%) whose 31P NMR spectrum showed
multiplets at δ 63.95 (JPt-P =2251 Hz) and 71.90 (JPt-P
=
(18) Otsuka, S.; Nakamura, A. Adv. Organomet. Chem. 1976, 14, 245,
and references therein..
1566 Hz). These chemical shifts and coupling constants are
consistent with the formation of the C-C insertion product
(dippe)Pt(Ph)(CtCCF3), 4b.6 As further evidence for aryl-
alkyne C-C cleavage, the 1H NMR spectrum showed a
change in the ortho C-H resonance of the alkyne phenyl
group from δ 8.10 (d, J=7 Hz) in 1b to δ 7.75 (t, J=7 Hz)
with platinum satellites (JPt-H=27 Hz) in 4b (see Supporting
Information for spectra). Irradiation for 18 days showed
∼80% conversion to 4b, but the product could not be
isolated cleanly. No evidence for sp-sp3 bond cleavage
was seen.
In contrast to 1a, irradiation of 2a in C6D6 with UV light
(λ > 300 nm) for 20 h led to the complete conversion to a PtII
product, as observed by 31P NMR spectroscopy. The pro-
duct that appeared displayed a 1:1:1 triplet (J=30 Hz) at δ
83.8 with platinum satellites (JP-Pt=1721 Hz) and a singlet
(19) (a) Bartik, T.; Happ, B.; Iglewsky, M.; Bandmann, H.; Boese, R.;
Heimbach, P.; Hoffmann, T.; Wenschuh, E. Organometallics 1992, 11,
1235. (b) Rosenthal, U.; Schulz, W. J. Organomet. Chem. 1987, 321, 103.
(c) Tatsumi, K.; Hoffmann, R.; Templeton, J. L. Inorg. Chem. 1982, 21, 466.
(d) Hey, E.; Weller, F.; Dehnicke, K. Z. Anorg. Allg. Chem. 1984, 514, 18.
(e) Dewar, M. J. S.; Ford, G. P. J. Am. Chem. Soc. 1979, 101, 783. (f) Hartley,
F. R. Angew. Chem. 1972, 84, 657. (g) Nelson, J. H.; Wheelock, K. S.;
Cusachs, L. C.; Jonassen, H. B. J. Am. Chem. Soc. 1969, 91, 7005.
(h) Greaves, E. O.; Lock, C. J. L.; Maitlis, P. M. Can. J. Chem. 1968, 46,
3879. (i) Dewar, M. J. S. Bull. Soc. Chim. Fr. 1951, 18, C79. (j) Chatt, J.;
Duncanson, L. A. J. Chem. Soc. 1953, 2939.
(20) Mavriris, A.; Moustakali-Mavridis, I. Acta Crystallogr. 1977,
B33, 3612. The CtC bond length in free diphenylacetylene is 1.198(4) Å.
€
(21) Rosenthal, U.; Oehme, G.; Gorls, H.; Burlakov, V. V.; Yanovsky,
A. I.; Struchkov, Y. T. J. Organomet. Chem. 1990, 390, 113. Rosenthal,
U.; Oehme, G.; Burlakov, V. V.; Petrovskii, P. V.; Vol'pin, M. E.
J. Organomet. Chem. 1990, 391, 119. Rosenthal, U.; Nauck, C.; Arndt, P.;
€
Pulst, S.; Baumann, W.; Burlakov, V. V.; Gorls, H. J. Organomet. Chem.
1994, 484, 81.
(22) (a) Rosenthal, U.; Oehme, G.; Gorls, H.; Burlakov, V. V.;
€
Yanovsky, A. I.; Struchkov, Y. T. J. Organomet. Chem. 1990, 389,
251. (b) Boag, N. M.; Green, M.; Grove, D. M.; Howard, J. A. K.; Spencer,
J. L.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1980, 2170.
€
(23) Muller, C.; Lachicotte, R. J.; Jones, W. D. Organometallics 2002,
21, 1118.

6526 Organometallics, Vol. 28, No. 22, 2009
Gunay et al.
Figure 1. Molecular structures of (chelate)Pt(η2-PhCtCR) (1b, 1c, 2a, 2b, 2c, 3b, and 3c) where chelate=dippe (1), dtbpe (2), or
dippdmae (3) and R=CH3 (a), CF3 (b), or t-Bu (c) (50% probability ellipsoids).
˚
Table 1. Selected Bond Lengths (A) and Bond Angles (deg) for 1a-3c
Bond Lengths
1b
1c
2a
2b
2c
3b
3c
Pt(1)-P(1)
Pt(1)-P(2)/N(1)a
Pt(1)-C(1)
Pt(1)-C(2)
C(1)-C(2)
2.2527(10)
2.2638(10)
2.040(4)
2.006(4)
1.299(5)
1.463(5)
1.471(5)
2.2603(5)
2.2589(5)
2.0411(17)
2.0497(17)
1.303(2)
2.2862(8)
2.2783(8)
2.060(3)
2.023(3)
1.310(4)
1.456(4)
1.463(4)
2.276(4)
2.299(4)
2.098(16)
2.027(15)
1.342(18)
1.37(2)
2.2798(10)
2.2788(9)
2.043(3)
2.060(3)
1.285(5)
1.459(5)
1.528(5)
2.2502(9)
2.221(3)a
1.998(4)
2.022(4)
1.301(5)
1.465(5)
1.457(5)
2.249(3)
2.242(6)a
2.067(7)
1.995(7)
1.302(9)
1.449(9)
1.497(9)
C(1)-C(3)
1.458(2)
1.503(2)
C(2)-C(9)
1.50(2)
Bond Angles
1b
1c
2a
2b
2c
3b
3c
P(1)-Pt(1)-P(2)/N(1)a
C(1)-Pt(1)-C(2)
C(3)-C(1)-C(2)
87.12(4)
87.244(18)
88.51(3)
37.41(13)
140.0(3)
143.9(3)
88.32(12)
88.34(4)
36.51(13)
142.6(4)
138.1(3)
84.21(9)a
37.76(14)
143.2(4)
140.4(4)
83.7(4)a
37.3(3)
144.8(7)
144.2(7)
37.44(15)
142.1(4)
140.5(4)
37.14(7)
145.31(17)
140.34(16)
37.9(5)
135.3(17)
141.9(16)
C(9)-C(2)-C(1)
a Replace P(2) with N(1) in these compounds.

Article
Organometallics, Vol. 28, No. 22, 2009 6527
Scheme 1. Reactivity of Alkyne Complexes
Figure 3. 31P NMR spectrum upon irradiation of 2b in C6D6 for
4 days.
˚
Table 2. Selected Bond Lengths (A) and Bond Angles (deg) for 2D
Bond Lengths
Pt(1)-P(1)
Pt(1)-P(2)
2.2880(10)
2.3317(10)
Pt(1)-C(1)
Pt(1)-D(1)
2.084(4)
1.5854
Bond Angles
D(1)-Pt(1)-P(1)
P(2)-Pt(1)-P(1)
C(1)-Pt(1)-P(2)
90.2
87.74(4)
99.90(11)
D(1)-Pt(1)-C(1)
Pt(1)-P(1)-C(31)
Pt(1)-P(2)-C(32)
82.1
108.47(13)
106.61(13)
Likewise, photolysis of 3b with UV light for 9 h showed
evidence for the slow formation of a new product (60%) with
JPt-P = 2802 Hz. This product is assigned to the C-C
cleavage product (dippdmae)Pt(Ph)(CtCCF3) (6b). As with
1
5b, the H NMR spectrum showed a change in the ortho
C-H resonance of the alkyne phenyl group from δ 7.96 (d,
J=7 Hz) in 3b to δ 7.64 (d, J=7 Hz) with platinum satellites
(JPt-H = 66 Hz) in 6b (see Supporting Information for
spectra). Longer irradiation led to decomposition, which
prevented isolation of 6b.
The lack of C-C cleavage in 1a, 2a, 1c, and 2c was
unexpected on the basis of prior reactivity seen in other
L2Pt(acetylene) complexes.6 Evidently, 1-phenyl-1-propyne
and tert-butylphenylacetylene do not coordinate sufficiently
strongly so that upon irradiation dissociation occurs prior to
C-C cleavage. The vacant coordination site can then be
occupied by C6D6, which is then activated. As these alkynes
have an electron-donating alkyl group on the acetylene, this
electron donation may cause poor back acceptance by the
acetylene, and hence a weaker coordination. Therefore, a
similar substrate with an electron-withdrawing substituent
may show a better coordination to the platinum and facil-
itate C-C activation, as seen with trifluoromethylphenyla-
cetylene.
Figure 2. Product (dippe)Pt(D)(C6D5) (2D) arising from irra-
diation of 2a in C6D6 (50% probability ellipsoids).
at δ 102.0 (JP-Pt=1794 Hz). This sample was crystallized, and
the X-ray structure of the product was determined (Figure 2,
Table 2), indicating that the product was (dtbpe)Pt(D)(C6D5)
(2D), arising from reaction with the solvent (C6D6) rather
than the C-C activation of 1-phenyl-1-propyne (Scheme 1).
Irradiation of 2c gives a similar result, producing 2D.
A related result was reported earlier describing the formation
of C6H6-activated product (dtbpe)Pt(H)(C6H5) upon photo-
lysis of (dtbpe)PtH2 in benzene.24
Irradiation of 2b in C6D6 also led to the formation of a new
PtII product, 5b. In this case, however, the 31P NMR
spectrum showed two distinct singlets, each with platinum
While the detailed mechanism of the photoinduced C-C
cleavage is not known, a pathway involving orthometalation
can be ruled out, as para-substituents on the aryl ring remain
para in the Pt-aryl product.6b We propose that the mechan-
ism of cleavage is the same as seen in the isoelectronic C-CN
cleavage of benzonitrile by [Ni(dippe)], which was estab-
lished by experiment and DFT theory.25 In this mechanism,
coordination to the triple bond is not important for C-C
cleavage. The molecule must first rearrange to the η2-arene
complex, which then undergoes C-C oxidative cleavage, as
satellites (Figure 3, δ 71.1, JP-Pt = 2564 Hz; 80.0, JP-Pt
=
1547 Hz). Complete conversion to 5b was not observed even
after 8 days of irradiation by UV light, the highest conversion
reaching 60%, suggesting attainment of a photostationary
state. These chemical shifts and coupling constants are
consistent with the formation of the C-C insertion product
(dtbpe)Pt(Ph)(CtCCF3), 5b.6
(24) Boaretto, R.; Sostero, S.; Traverso, O. Inorg. Chim. Acta 2002,
330, 59.
´
(25) Ates-in, T. A.; Li, T.; Lachaize, S.; Garcıa, J. J.; Jones, W. D.
Organometallics 2008, 27, 3811.

6528 Organometallics, Vol. 28, No. 22, 2009
Gunay et al.
Scheme 2. Mechanism of C-C Cleavage in Benzonitrile and
Proposed Mechanism for Phenylacetylenes
acetylene,28 1,2-bis(diisopropylphosphino)ethane (dippe),29
1-diisopropylphosphino-2-dimethylaminoethane (dippdmae),30
1,2-bis(di-tert-butylphosphino)ethane (dtbpe),31 and tert-butyl-
phenylacetylene32 were synthesized according to the reported
procedures.
Preparation of (dippe)Pt(η2-PhCtCCH3) (1a). 1-Phenyl-1-
propyne (2.82 mg, 0.024 mmol, 3.04 μL) was dissolved in 0.5 mL
of C6D6 and transferred onto Pt(COD)2 (10 mg, 0.024 mmol)
powder. The color of the solution became dark brown. Then
0.5 mL of C6D6 solution of dippe (6.37 mg, 0.024 mmol) was
added, and the solution was placed into a resealable NMR tube,
which was heated at 70 °C overnight, whereupon the color
turned light orange. The solvent and the free COD were
removed under vacuum, and the light yellow powder was
redissolved in C6H6. Colorless crystals of 1a were obtained via
1
solvent evaporation at 23 °C. Yield: 7.5 mg, 54%. For 1a: H
NMR (C6D6): δ 0.83 (dd, JH-P =13 Hz, JH-H =7 Hz, 6 H,
CHMe2), 0.9 (dd, JH-P=14 Hz, JH-H=7 Hz, 6 H, CHMe2), 1.08
(dd, JH-P=7 Hz, JH-H=3 Hz, 6 H, CHMe2), 1.12 (dd, JH-P=
shown in Scheme 2. Perhaps the role of photolysis is to
destabilize the metal-alkyne interaction and promote the
migration to the phenyl ring. This pathway would also
account for the lack of sp-sp3 C-C cleavage. Since only
the CF3-containing phenylalkynes undergo C-C activation,
perhaps the stronger binding of this alkyne leads to the η2-
arene complex upon photolysis rather than dissociation, as
seen with the Me- and t-Bu-substituted alkynes. Addition-
ally, the initial coordination of the [L2Pt] fragment to the
alkyne triple bond is apparently faster than the rate of
coordination to the arene π-system, since no C-C cleavage
is seen thermally when the η2-alkyne complexes were synthe-
sized.
7 Hz, JH-H=3 Hz, 6 H, CHMe2), 1.18 (m, 4 H, CH), 1.65 (s, 3 H,
CtCCH3), 1.85 (m, 2 H, CH2), 2.05 (m, 2 H, CH2), 7.13 (pseudo
t, JH-H=9 Hz, 1 H, p-C6H5), 7.39 (t, JH-H=9 Hz, 2 H, m-C6H5),
7.95 (d, JH-H=10 Hz, 2 H, o-C6H5). 13C{1H} NMR (C6D6):
δ 18.3 (s, CHMe2), 18.7 (s, CHMe2), 19.0 (s, CtC-CH3), 19.4
(s, CHMe2), 19.8 (s, CHMe2), 24.48 (m, CH2), 25.7 (d, JC-P
=
21 Hz, CH), 26.4 (d, JC-P=21 Hz, CH), 124.8, 130.5, 131.6 and
obscured by C6D6 (s, Ph), 135.9 (s, CtC), 141.2 (s, CtC).
31P{1H} NMR (C6D6): δ 77.5 (d, JP-P=48 Hz, with platinum
satellites JP-Pt=2944 Hz, P trans to C-CH3), 79.8 (d, JP-P
=
48 Hz, with platinum satellites JP-Pt = 3041 Hz, P trans to
C-C6H5).
Preparation of (dtbpe)Pt(η2-PhCtCCH3) (2a). A 0.5 mL
portion of a C6D6 solution of 1-phenyl-1-propyne (8.5 mg,
0.073 mmol, 9.2 μL) was added to Pt(COD)2 (30 mg, 0.073 mmol),
followed by 0.5 mL of a C6D6 solution of dtbpe (23.2 mg,
0.073 mmol). The color of the solution turned brown-red. The
sample was heated at 100 °C to obtain the Pt0 product, where-
upon the solution turned red. The volatiles were removed under
vacuum, and the red powder was redissolved in C6H6 for
recrystallization by evaporation. Colorless crystals of 2a were
collected. Yield: 25.7 mg, 56%. For 2a, 1H NMR (C6D6): δ 0.97
(d, JH-P=14 Hz, 2 H, CH2), 1.12 (s, 3 H, CtCCH3), 1.16 (d,
Conclusions
Pt0 complexes of η2-coordinated asymmetric acetylene
derivatives 1-phenyl-1-propyne, trifluoromethylphenylace-
tylene, and tert-butylphenylacetylene have been synthesized
and characterized. Only the Pt0 complexes with the electron-
deficient trifluoromethylphenylacetylene ligand showed evi-
dence for C-C cleavage. The strong donor chelate dtbpe on
platinum showed evidence for C-H activation of benzene
solvent following alkyne loss. In no case was evidence for
sp-sp3 C-C cleavage observed.
JH-P=7 Hz, 18 H, CMe3), 1.19 (d, JH-P=7 Hz, 18 H, CMe3),
1.28 (d, JH-P=12 Hz, 2 H, CH2), 7.07 (pseudo t, JH-H=8 Hz,
1 H, p-C6H5), 7.33 (t, JH-H=9 Hz, 2 H, m-C6H5), 7.80 (d, JH-H
=
9 Hz, 2 H, o-C6H5). 13C{1H} NMR (C6D6): δ 17.1 (s,
CtC-CH3), 25.8 (m, CH2), 29.9 (d, JC-P=12 Hz, C(CH3)3),
30.1 (d, JC-P=12 Hz, C(CH3)3), 34.0 (m, P-Cs), 124.0 (s, ipso-
C), 129 (s, C in Ph), the additional resonances obscured by C6D6
solvent (aromatic carbons), 141.2 (m, CtC). 31P{1H} NMR
Experimental Section
General Considerations. All experiments were carried out
under a nitrogen atmosphere, either on a high-vacuum line
using modified Schlenk techniques or in a Vacuum Atmospheres
Corporation glovebox, unless otherwise stated. The solvents
were available commercially and distilled from dark purple
solutions of benzophenone ketyl. 1H, 13C{H}, and 31P{H}
NMR spectra were recorded on Bruker Avance-400, Bruker
AMX-400, and Bruker Avance-500 spectrometers. All 1H che-
mical shifts were referenced to residual proton resonances or to
TMS in the deuterated solvents. An external standard of 85%
H3PO4 was used to reference the 31P{H} NMR data. All crystal
structures were determined by using a Siemens-SMART 3-circle
CCD diffractometer. All photolysis experiments were per-
formed in sealed NMR tubes with an Oriel arc source using
a 200 W Hg(Xe) bulb. Elemental analyses were obtained
from Desert Analytics. 1-Phenyl-1-propyne was obtained from
commercial sources, and Pt(COD)2,26,27 trifluoromethylphenyl-
(C6D6): δ 96.6 (d, JP-P=55 Hz, with platinum satellites JP-Pt
3016 Hz, 1 P), 97.5 (d, JP-P=54 Hz, with platinum satellites JP-Pt
=
=
3155 Hz, 1 P).
Preparation of (dtbpe)Pt(D)(C6D5) (2D). A 10 mg (0.016 mmol)
portion of 2a was dissolved in 1 mL of C6D6 and placed into a
resealable NMR tube with a Teflon stopcock. The sample was
irradiatedwithUV light(λ >300nm) for 20 h. A 95%conversion
to the solvent activated complex was observed by 31P NMR
spectroscopy. Colorless crystals of 2D were obtained by solvent
1
evaporation. Yield: 7.0 mg, 74%. For 2D, H NMR (CDCl3):
(28) Kobayashi, Y.; Yamashita, T.; Takahashi, K.; Kuroda, H.;
Kumadaki, I. Chem. Pharm. Bull. 1984, 32 (11), 4402.
(29) (a) Fryzuk, M. D.; Jones, T.; Einstein, F. W. B. Organometallics
1984, 3, 185. (b) Burg, R. J.; Chatt, J.; Hussain, W.; Leigh, G. J.
J. Organomet. Chem. 1979, 182, 203.
(30) Werner, H.; Hampp, A.; Peters, K.; Peters, E. M.; Walz, L.; von
(26) Green, M.; Howard, J. A. K.; Spencer, J. L.; Stone, F. G. A.
J. Chem. Soc., Dalton Trans. 1977, 271.
(27) Ogoshi, S.; Morita, M.; Inoue, K.; Kurosawa, H. J. Org. Chem.
Schnering, H. G. Z. Naturforsch. 1990, 45b, 1548.
€
€
(31) Porschke, K. R.; Pluta, C.; Proft, B.; Lutz, F.; Kruger, C. K. Z.
Naturforsch. B: Chem. Sci. 1993, 48, 608–626.
2004, 689, 662.
(32) Bock, H.; Alt, H. Chem. Ber. 1970, 103, 1784.

Article
Organometallics, Vol. 28, No. 22, 2009 6529
δ 1.32 (m, 36 H, CMe3), 1.54 (d, JH-P = 13 Hz, 4 H, CH2).
13C{1H} NMR (CDCl3): δ 30.8 (m, C(CH3)3), 30.3 (m, C(CH3)3),
36.2 (d, JC-P=16 Hz, CH2), 36.9 (d, JC-P=27 Hz, CH2), 124.0,
127.3, 128.1, and 131.5 (Ph). 31P{1H} NMR (C6D6): δ 83.8
(t, JP-D=30 Hz, with platinum satellites JP-Pt=1721 Hz, 1 P,
P trans to D), 102.0 (s, with platinum satellites JP-Pt=1794 Hz,
1 P, P trans to C6D5).
6 H, CHMe2), 1.31 (s, 9 H, t-Bu), 1.58 (m, 4 H, CH), 2.07 (m,
2 H, CH2), 2.21 (m, 2 H, CH2), 6.9 (t, JH-H=7 Hz, 1 H, p-C6H5),
7.13 (pseudo t, JH-H=8 Hz, 2 H, m-C6H5), 7.25 (d, JH-H=8 Hz,
2 H, o-C6H5). 13C{1H} NMR (C6D6): δ 18.0 (s, CHMe2), 18.4
(s, CHMe2), 20.0 (s, CHMe2), 20.4 (s, CtC-C-), 20.6
1
2
(s, CHMe2), 23.1 (dd, JC-P = 74 Hz, JC-P = 47 Hz, CH2),
25.0 (dd, 1JC-P=83 Hz, 2JC-P=57 Hz, CH2), 26.2 (d, JC-P
=
Preparation of (dippe)Pt(η2-PhCtCCF3) (1b). Trifluoro-
methylphenylacetylene (13.2 mg, 0.08 mmol) was dissolved in
C6D6 (0.5 mL) and added to Pt(COD)2 (32.9 mg, 0.08 mmol). A
purple solution was formed, which was transferred to a vial
containing dippe (21.0 mg, 0.08 mmol), producing an orange
solution. Following evaporation of benzene the compound was
dissolved in a 1:4 mixture of petroleum ether and dichloro-
methane and stored at -20 °C, forming yellow crystals. Yield:
25.0 mg, 50%. For 1b, 1H NMR (C6D6): δ 0.74 (dd, JH-P=14 Hz,
75 Hz, CH), 32.7 (s, C(CH3)3), 124.2, 128.7, 131.2 and obscured
by C6D6 (s, Ph), 143.1 and 143.3 (s, CtC). 31P{1H} NMR
(THF-d8): δ 74.7 (d, with platinum satellites, JP-P=47 Hz, JP-Pt
=3111 Hz), 75.4 (d, with platinum satellites, JP-P=48 Hz, JP-Pt
=2970 Hz). Anal. Calcd (found) for C26H46P2Pt: 50.72 (50.54)
C, 7.53 (7.47) H.
Preparation of (dtbpe)Pt(η2-PhCtCC(CH3)3) (2c). tert-Bu-
tylphenylacetylene (3.84 mg, 0.024 mmol) was dissolved in
0.5 mL of C6D6 and added to Pt(COD)2 (10 mg, 0.024 mmol)
at room temperature. Then 0.5 mL of a C6D6 solution of dtbpe
(7.74 mg, 0.024 mmol) was added, and the solution became light
yellow. The sample was heated at 100 °C overnight to obtain
only the η2-coordinated Pt0 complex. However, 31P NMR data
showed that only 50% of the products were the target Pt0-η2
complex, 2c, with ∼50% (dtbpe)Pt(COD) still remaining. To
obtain only the Pt0-η2 complex, an additional 19 equiv of the
alkyne was added to the solution and the sample was heated at
100 °C overnight, producing only 2c. Excess alkyne was required
to obtain high conversions. The volatiles were removed under
vacuum and the white-yellow powder was recrystallized from
C6H6, yielding colorless and air-sensitive crystals of 2c. Yield:
11.8 mg, 72%. For 2c, 1H NMR (C6D6): δ 1.02 (d, JH-P=12 Hz,
18 H, CMe3), 1.12 (m, 2 H, CH2), 1.26 (d, JH-P=12 Hz, 18 H,
CMe3), 1.41 (m, 2 H, CH2), 1.63 (s, 9 H, CtCCMe3), 6.99 (t, 1
H, p-C6H5), 7.25 (t, 2 H, m-C6H5), 7.37 (d, 2 H, o-C6H5).
13C{1H} NMR (C6D6): δ 24.9 (m, P-C), 26.9 (m, P-C), 29.7
(d, JC-P=48 Hz, CMe3), 29.9 (s, CtCC), 30.2 (d, JC-P=48 Hz,
CMe3), 32.8 (s, CCMe3), 33.7 (dd, JC-P=70 Hz, JC-P=28 Hz,
CH2), 34.4 (dd, JC-P=68 Hz, JC-P=28 Hz, CH2), 123.2 (s, ipso-
C), resonances overlapping with C6D6 (Ph), 144.5 and 146.0 (s,
CtC). 31P{1H} NMR (C6D6): δ 96.6 (d, JP-P =55 Hz, with
platinum satellites JP-Pt=3016 Hz, 1 P), 97.5 (d, JP-P=54 Hz,
with platinum satellites JP-Pt = 3155 Hz, 1 P). Anal. Calcd
(found) for C30H54P2Pt: 53.64 (53.20) C, 8.10 (8.40) H.
J
H-H =8 Hz, 6 H, CHMe2), 0.82 (dd, JH-P =16 Hz, JH-H
12 Hz, 6 H, CHMe2), 0.98 (dd, JH-P=17 Hz, JH-H=7 Hz, 6 H,
CHMe2), 1.07 (m, 4 H, P-CH-), 1.12 (dd, JH-P=16 Hz, JH-H
7 Hz, 6 H, CHMe2), 1.95 (m, 4 H, CH2), 7.08 (t, JH-H=7 Hz, 1 H,
p-C6H5),7.27(pseudot,JH-H=8 Hz, 2 H, m-C6H5),8.02(d,JH-H
8 Hz, 2 H, o-C6H5). 31P{1H} NMR (C6D6): δ 76.8 (dq, JP-P
=
=
=
=
34 Hz, JP-F=10 Hz, JP-Pt =3248 Hz), 78.9 (d, with platinum
satellites, JP-P=34 Hz, JPt-P=2999 Hz). 19F{1H} NMR (C6D6):δ
6.7 (d, with platinum satellites, JF-P = 10 Hz, JF-Pt =57 Hz).
13C{1H} NMR (C6D6): δ 18.5 (s, CHMe2), 18.7 (s, CHMe2), 19.4
(s, CHMe2), 20.0 (s, CHMe2), 23.5 (dd, JC-P =27 Hz, JC-P
13 Hz, CH2), 24.0 (dd, JC-P=27 Hz, JC-P=13 Hz, CH2), 25.6 (d,
C-P=23 Hz, CH), 26.7 (d, JC-P=23 Hz, CH), 125.0, 126.9, 128.0,
=
J
and 128.3 (s, Ph), 131.4 (m, CF3), 132.0 (s, CtC), 134.0 (t, CtC).
Anal. Calcd (found) for C23H37F3P2Pt: C, 44.02 (44.13); H, 5.94
(5.72).
Preparation of (dtbpe)Pt(η2-PhCtCCF3) (2b). Trifluoro-
methylphenylacetylene (4.13 mg, 0.0243 mmol) dissolved in
0.5 mL of C6D6 was added to a vial containing Pt(COD)2
(10 mg, 0.0243 mmol), producing a light pink solution. Then
0.5 mL of a C6D6 solution of dtbpe (7.73 mg, 0.0243 mmol) was
added, and the sample was heated at 100 °C to obtain a light
orange solution of 2b (full conversion by 31P NMR spectro-
scopy). The volatiles were removed under vacuum, and the
sample was recrystallized from C6H6, producing colorless crys-
1
tals of 2b. Yield: 12.8 mg, 77%. For 2b, H NMR (CDCl3): δ
Preparation of (dippdmae)Pt(η2-PhCtCCF3) (3b). Pt(COD)2
(36.7 mg, 0.089 mmol) was dissolved in a solution of trifluor-
omethylphenylacetylene (15.2 mg, 0.089 mmol) in C6D6 (0.5 mL)
to give a purple solution. (i-Pr)2PCH2CH2NMe2 (16.9 mg,
0.089 mmol, 18.9 μL) was added, producing a dark orange
solution that was heated to 70 °C overnight. The volatiles were
evaporated under vacuum, and the remaining solid was recrys-
tallized from petroleum ether (0.5 mL) containing a few drops of
dichloromethane at -20 °C. The product was obtained as
orange crystals as a mixture of isomers (90% isomer with the
CF3 group trans to P, 10% isomer with the CF3 group cis to P).
1.27 (d, JH-P=13 Hz, 18 H, CMe3), 1.39 (d, JH-P=13 Hz, 18 H,
CMe3), 1.85 (m, 4 H, CH2), 7.21 (t, J=7 Hz, 1 H, p-H), 7.38 (t,
J=7 Hz, overlapping with the solvent resonance, 2 H, m-H),
7.45 (d, J=7 Hz, 2 H, o-H). 13C{1H} NMR (CDCl3): δ 25.6 (m,
C), 30.0 (m, (CH3)3), 34.5 (m, CH2), 125.4, 127.3, 127.5, and
128.6 (s, aromatic C’s), 132.2 and 133.7 (m, CtC), 139.0
(m, CF3). 19F{1H} NMR (CDCl3): δ 10.4 (d, with platinum
satellites, JF-P=13 Hz, JF-Pt=84 Hz). 31P{1H} NMR (C6D6):
δ 94.1 (dq, JP-P=39 Hz, JP-F=12 Hz, with platinum satellites
JP-Pt=3342 Hz, 1 P, P trans to CF3), 95.3 (d, JP-P=39 Hz, with
platinum satellites JP-Pt=3116 Hz, 1 P, P trans to Ph). 31P{1H}
NMR (CDCl3):δ93.7 (m, with platinum satellites JP-Pt=3339 Hz,
1 P, P trans to CF3), 94.9 (d, JP-P = 58 Hz, with platinum
satellites JP-Pt = 3116 Hz, 1 P, P trans to Ph). Anal. Calcd
(found) for C27H45F3P2Pt: 47.43 (48.74) C; 6.63 (6.17) H.
Preparation of (dippe)Pt(η2-PhCtCC(CH3)3) (1c). tert-Bu-
tylphenylacetylene (10.5 mg, 0.0664 mmol) was dissolved in
THF-d8 (0.5 mL) and cooled to -20 °C. This solution was
transferred onto Pt(COD)2 (27.3 mg, 0.0664 mmol), forming a
dark orange solution, which was added to a vial containing 17.4
mg of dippe (0.0664 mmol). This solution was heated to 100 °C
for 20 h, whereupon the color changed to bright yellow
(complete conversion to the η2-alkyne complex was confirmed
by 31P NMR spectroscopy). The solvent was evaporated under
vacuum and the product recrystallized from pentane/dichlor-
Yield: 25.0 mg, 51%. For 3b, 1H NMR (C6D6): δ 0.79 (dd, JH-P
13 Hz, JH-H=7 Hz, 6 H, CHMe2 (major)), 0.86 (dd, JH-P=14 Hz,
JH-H=7 Hz, 6 H, CHMe2 (minor)), 1.02(dd, JH-P=17 Hz, JH-H
=
=
7 Hz, 6 H, CHMe2 (major)), 1.10 (dd, JH-P=16 Hz, JH-H=7 Hz,
6 H, CHMe2 (minor)), 1.80 (m, 2 ꢀ 6 H, CH2, CH (both)), 2.63
(s, with platinum satellites, JH-Pt=11 Hz, 6 H, NMe2 (minor)),
2.70 (s, with platinum satellites, JH-Pt = 11 Hz, 6 H, NMe2
(major)), 7.06 (t, JH-H=7 Hz, 1 H, p-C6H5 (major)), 7.08 (t, J=
7 Hz, p-C6H5 (minor)), 7.19 (pseudo t, JH-H=7 Hz, 2 H, m-C6H5
(major)), 7.26 (pseudo t, JH-H=7 Hz, 2 H, m-C6H5 (minor)), 7.85
(d, JH-H=7 Hz, 2 H, o-C6H5 (minor)), 7.97 (d, JH-H=7 Hz, 2 H,
o-C6H5 (major)). 31P{1H} NMR (C6D6): δ 64.7 (q, with platinum
satellites, JP-F=16 Hz, JP-Pt =3844 Hz (major)), 66.6 (s, with
platinum satellites, JP-Pt=3633 Hz (minor)). Anal. Calcd (found)
for C19H29F3NPPt: 41.15 (41.04) C, 5.27 (5.33) H, 2.53 (2.32) N.
Preparation of (dippdmae)Pt(η2-PhCtCC(CH3)3) (3c). Pt-
(COD)2 (20.1 mg, 0.049 mmol) was suspended in C6D6 (0.5 mL),
and (i-Pr)2PCH2CH2NMe2 (9.3 mg, 0.049 mmol, 10.3 μL) was
1
omethane at -20 °C. Yield: 31.4 mg, 77%. For 1c, H NMR
(THF-d8): δ 0.96 (m, 12 H, CHMe2), 1.06 (dd, JH-P=12 Hz,
JH-H=7 Hz, 6 H, CHMe2), 1.17 (dd, JH-P=15 Hz, JH-H=7 Hz,

6530 Organometallics, Vol. 28, No. 22, 2009
Gunay et al.
added. A yellow solution formed, which was added to tert-
butylphenylacetylene (7.7 mg, 0.049 mmol). The resultant solution
was heated to 55 °C overnight. The volatiles were evaporated
under vacuum, and the dark orange oil that remained was
dissolved in petroleum ether (0.2 mL) containing a few drops
of THF. Recrystallization at -20 °C produced yellow crystals of
3c. Yield: 12.7 mg, 48%. For 3c, 1H NMR (C6D6): δ 0.92 (dd,
sample was placed into a resealable NMR tube. The tube was
irradiated with UV light, and a maximum conversion of 60% to
the activated complex 5b was observed by 31P NMR after 8 days
of photolysis. Longer photolysis resulted in decomposition.
=
2564 Hz, 1 P, P trans to acetylide), 80.0 (s, with platinum
satellites JP-Pt=1547 Hz, 1 P, P trans to Ph).
31P{1H} NMR (C6D6): δ 71.1 (s, with platinum satellites JP-Pt
J
H-P=13 Hz, JH-H=7 Hz, 6 H, CHMe2), 1.08 (m, 2 H, CH),
Generation of (dippdmae)Pt(Ph)(CtCCF3) (6b). A 38 mg
(0.068 mmol) sample of 3b was dissolved in 0.6 mL of C6D6
and placed in a resealable NMR tube. The solution was irra-
diated for 10 days, and NMR spectra were recorded periodi-
cally. The Supporting Information shows typical data, showing
the conversion of 3b into a new product assigned as
(dippdmae)Pt(Ph)(CtCCF3) (6b, ∼60% after 4 days; ∼70%
after 10 days). For 6b, 1H NMR (C6D6): δ 7.643 (d, J=7 Hz,
1.17 (dd, JH-P=16 Hz, JH-H=6 Hz, 6 H, CHMe2), 1.51 (s, 9 H,
t-Bu), 1.85 (m, 4 H, CH2), 2.65 (m, br, 6 H, NMe2), 7.05 (t, JH-H
=7 Hz, 1 H, p-C6H5), 7.31 (pseudo t, JH-H =7 Hz, 2 H, m-
C6H5), 7.62 (d, br, JH-H=6 Hz, 2 H, o-C6H5). 31P{1H} NMR
(C6D6): δ 65.8 (s, with platinum satellites, JP-Pt = 3717 Hz).
Anal. Calcd (found) for C22H38NPPt: 48.70(48.18) C, 7.06(5.88)
H, 2.58(1.85) N.
Generation of (dippe)Pt(Ph)(CtCCF3) (4b). A 32 mg (0.052
mmol) amount of 1b was dissolved in 0.6 mL of C6D6 and placed
in a resealable NMR tube. The solution was irradiated for 10
days, and NMR spectra were recorded periodically. The Sup-
porting Information shows typical data, showing the conversion
of 1b into a new product assigned as (dippe)Pt(Ph)(CtCCF3)
(4b, ∼60% after 10 days; 80% after 18 days). For 4b, 1H NMR
(C6D6): δ 7.753 (t, J=7 Hz, JPt-H=27 Hz, 2 Hortho), 7.285 (t, J=
7 Hz, 2 Hmeta), 7.043 (t, J=7 Hz, 1 Hpara), 2.17 (m, 2 H, CH2),
1.87 (m, 2 H, CH2), 1.24 (dd, J=16, 8 Hz, 6 H, CHMe2), 0.81
(dd, J=16, 8 Hz, 6 H, CHMe2), 0.69 (dd, J=16, 8 Hz, 6 H,
CHMe2), 0.67 (dd, J = 16, 8 Hz, 6 H, CHMe2), CHMe2
obscured. 31P{1H} NMR (C6D6): δ 63.95 (m, JPt-P = 2551
Hz), 71.90 (m, JPt-P = 1566 Hz). 19F{1H} NMR (C6D6): δ
13.62 (s, JPt-F=28 Hz).
JPt-H=66 Hz, 2 Hortho), 7.091 (t, J=7 Hz, 2 Hmeta), 6.947 (t, J=
7 Hz, 1 Hpara), 3.575 (t, J=6 Hz, 2 H, CH2), 2.385 (s, JPt-H=18 Hz,
6 H, NMe2), 1.70 (m, 4 H, CH2 þ, CHMe2), 0.67 (dd, J=16, 8 Hz,
6 H, CHMe2), 0.63 (dd, J=16, 8 Hz, 6 H, CHMe2). 31P{1H}
NMR (C6D6): δ 49.1 (s, JPt-P = 2802 Hz). 19F{1H} NMR
(C6D6): δ 4.356 (s, JPt-F=155 Hz).
Acknowledgment is made to the U.S. Department of
Energy, grant FG02-86ER13569, for their support of this
work.
Supporting Information Available: 1H and 31P NMR spectra
for the photolyses of 1b, 2b, and 3b. Structural data for 1b, 1c,
2a, 2b, 2c, 3b, 3c, and 2D have been deposited with the Cam-
bridge Crystallographic Data Centre, CCDC #732792-732799.
This material is available free of charge via the Internet at http://
pubs.acs.org.
Generation of (dtbpe)Pt(Ph)(CtCCF3) (5b). A 10 mg (0.015
mmol) amount of 2b was dissolved in 1 mL of C6D6, and the