Photo-and-thiol-driven trans insertion of phenylacetylene into H - Pt bonds

Article abstract of DOI:10.1021/ja027237a

The photo-and-thiol-driven trans insertion of phenylacetylene into H-Pt bonds of Pt(X)(H)(PPh₃)₂ (X = SAr, Cl, Br, and I) took place to afford Pt[(Z)-C(H)=CH(Ph)](X)(PPh₃)₂ in good yields. Copyright

Full text of DOI:10.1021/ja027237a

Published on Web 11/09/2002
Photo-and-Thiol-Driven Trans Insertion of Phenylacetylene into H-Pt Bonds
Atsushi Ohtaka, Hitoshi Kuniyasu,* Masanori Kinomoto, and Hideo Kurosawa*
Department of Molecular Chemistry and Frontier Research Center, Graduate School of Engineering,
Osaka UniVersity, Suita, Osaka 565-0871, Japan
Received June 10, 2002
Insertion (IS) of unsaturated molecules into the H-M bonds is
among the most basic topics in organometallic chemistry.1 As to
the mechanism, cis IS has been widely established, although a
limited number of trans ISs, mostly exploiting activated alkynes
such as DMAD, have been reported.2,3 In connection with the
mechanisms of some Pt-catalyzed reactions including thiols and
alkynes as substrates4 and our study on the reactions of unsaturated
molecule with thiolato palladium and platinum complexes,5,6 we
were initially interested in the reactivity of alkynes toward the
complexes having H-Pt-SAr fragment. Herein we wish to report
on our findings that trans IS of phenylacetylene (1) into the H-Pt
bonds took place with the assistance of unexpected factors.
First, the reaction of 1 (0.05 mmol) with trans-Pt(H)(SAr)(PPh3)2
(2, Ar ) C6H4Cl-p) (0.01 mmol), which was prepared in situ by
the reaction of Pt(PPh3)2(C2H4) (0.01 mmol) with ArSH (3, Ar )
C6H4Cl-p) (0.06 mmol),7 was carried out in C6D6 (0.5 mL) using
OdP(tol-p)3 as an internal standard under N2 atmosphere at 25 °C
under room light (just without covering the NMR tube). The 31P
NMR spectra indicated the formation of a platinum complex Z-4
in 36% (cis/trans ) 64/36)8 and 81% (cis/trans ) 64/36) yields
after 2 and 5 h, respectively (eq 1, run 1 of Table 1). In stark
Figure 1. ORTEP diagram of cis-Z-4 (Ph on PPh3 omitted).
When the reaction of 1 (0.05 mmol) with 2 (0.01 mmol) in the
presence of 3 (0.05 mmol) was performed under the irradiation of
500-W tungsten lamp at 10 °C, the reaction finished within 10 min
to afford Z-4 in 77% (cis/trans ) 73/27) and 85% (cis/trans )
85/15) yields in C6D6 and acetone-d6, respectively (runs 3 and 4).9
The complex Z-4 was isolated from a preparative-scale reaction
(0.1 mmol of 2) in 65% (cis/trans ) 78/22) yield (run 5), and the
X-ray single-crystal structure analysis of its cis-isomer proved the
structure to be cis-Pt[(Z)-C(H)dC(H)(Ph)](SAr)(PPh3)2 (cis-Z-4)
(Figure 1), implying that 1 inserted into the H-Pt bond of 2 with
Pt bound at terminal position in a trans-fashion.10 Because the
isolated Z-4 isomerized to the “cis IS” product Pt[(E)-C(H)dCH(Ph)]-
(SAr)(PPh3)2 (E-4) under photoirradiation for 30 min (E/Z ) 32/68),
the possibility of kinetic formation of E-4 and subsequent isomer-
ization to Z-4 can be ruled out.11
Table 1. Reaction of 1 with 2a
ArSH (3)
(mmol) (°C)
T
Z-4,
yield %
In the case of lapping the tube in aluminum foil, the reaction
was significantly retarded even in the presence of 3; only 8% of
Z-4 was formed even after 20 h (run 6). No reaction took place
without the addition of 3 even when the tube was irradiated with
500-W tungsten lamp (run 7). The reaction of 1 (0.05 mmol) with
2 (0.01 mmol) carried out in the presence of AIBN (0.01 mmol)
and 3 (0.05 mmol) at 60 °C also furnished Z-4 in 76% (only trans)
yield (run 8), while the reaction in the presence of AIBN without
3 produced only 3% of Z-4 even after 3 h (run 9), showing that the
role of photoirradiation was replaceable by AIBN, but the presence
of 3 was crucial to obtain Z-4 effectively.
b
run
condition
room light
time
(cis/trans)c
1
0.05d 25
2 h
5 h
36
81
0
77
85
65g
8
0
76
3
(64/36)
(64/36)
2
3
room light
0
25 48 h
10 10 min
10 10 min
10
25 20 h
10 10 min
60
60
500-W tungsten lamp 0.05
(73/27)
(85/15)
(78/22)
(42/58)
4e 500-W tungsten lamp 0.05
5f 500-W tungsten lamp 0.5
1 h
6
7
under dark
500-W tungsten lamp
0.05
0
0.05
0
8h under dark
9h under dark
1 h
3 h
(only trans)
(only trans)
a Unless otherwise noted, 0.05 mmol of 1, 0.01 mmol of 2 in C6D6 (0.5
mL) in a Pyrex NMR glass tube. b NMR yield. c Stereochemistry of two
PPh3 on Pt. d 2 was prepared in situ by the reaction of Pt(PPh3)2(C2H4)
(0.01 mmol) with 3 (0.06 mmol). e In acetone-d6 (0.5 mL). f Preparative
scale (0.1 mmol of 2). g Isolated yield. h 0.01 mmol of AIBN.
Prompted by these intriguing results, the generality of the
trans IS has been next tested. It became evident that the present
protocol was also applicable to the complexes trans-Pt(H)(X)(PPh3)2
(6: X ) Cl, 7: X ) Br, 8: X ) I). When the reaction of 1 with
6 was carried out in the presence of 5 equiv of 3 under the
irradiation of 500-W tungsten lamp at 10 °C for 30 min, the
selective formation of the trans IS product Pt[(Z)-C(H)dC(H)(Ph)]-
(Cl)(PPh3)2 (Z-9)12 was confirmed in 79% (cis/trans ) 79/21) yield
after 30 min (eq 2, run 1 of Table 2). Similarly to the case of
reaction of 1 with 2, photoirradiation can be replaced by AIBN to
furnish Z-9 in 74% (only trans) yield after 1 h at 70 °C (run 2) and
contrast, no reaction took place in the reaction of 1 with isolated 2
under otherwise identical conditions even after 48 h (run 2). After
many trials, it was found that both of the presence of 3 and
photoirradiation were essential for the successful formation of Z-4.
* To whom correspondence should be addressed. E-mail: kuni@
ap.chem.eng.osaka-u.ac.jp.
9
14324
J. AM. CHEM. SOC. 2002, 124, 14324-14325
10.1021/ja027237a CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
3 was again indispensable (runs 3 and 4). The reaction of 1 with 7
in the presence of 3 under photoirradiation afforded the trans IS
product Z-1013 in 83% (cis/trans ) 16/84) yield after 30 min
(run 5). Although accompanied by the Z-to-E isomerization, vinyl-
platinum 11 was also obtained from 8 in 42% yield after 30 min
(run 6).14
under photoirradiation or in the presence of AIBN17 would play a
pivotal role for the present trans IS methodology.
In summary, this study demonstrated that both modes of cis
and trans IS of alkynes into H-M bonds could be achieved by
employing different reaction conditions. The work to elucidate the
scope and limitations of the present trans IS into H-M bonds as
well as the participation of trans IS in Pt-catalyzed reactions4 is
now in progress.
Table 2. Reaction of 1 with H-Pt Bonds of Pt(X)(H)(PPh3)2 (X )
Cl, Br, and I)a
b
run
X
condition
T (°C)
time
yield %
(cis/trans)
(79/21)
Acknowledgment. Partial support of this work through Grant-
in-Aid for Scientific Research, Ministry of Education, Science and
Culture, the JSPS research fellowship for young scientists, and
CREST of Japan Science and Technology Corporation is gratefully
acknowledged.
1
Cl 500-W tungsten lamp
under dark
10
70
10
70
10
10
30 min
1 h
30 min
1 h
30 min
10 min
30 min
79
74
0
2c
3d
4c,d
5
(only trans)
500-W tungsten lamp
under dark
0
Br 500-W tungsten lamp
I
83
11
42e
(16/84)
(only trans)
(only trans)
6
500-W tungsten lamp
Supporting Information Available: Listing of experimental
procedures and analysis data for the compounds in this communication
(PDF). This material is available free of charge via the Internet at http://
pubs.acs.org.
a Unless otherwise noted, 0.05 mmol of 1, 0.01 mmol of Pt complex,
0.05 mmol of 3 in C6D6 (0.5 mL). b NMR yield. c 0.01 mmol of AIBN.
d Without 3. e 12% of E-11 was included.
References
(1) (a) Crabtree, R. H. The Organometallic Chemistry of the Transition Metals,
3rd ed.; John Wiley & Sons: New York, 2000. (b) Collman, J. P.;
Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Application
of Organotransition-Metal Chemistry; University Science Books: Mill
Valley, CA, 1987.
(2) Clark, H. C.; Ferguson, G.; Goel, A. B.; Janzen, E. G.; Ruegger, J. H.;
Siew, P. Y.; Wong, C. S. J. Am. Chem. Soc. 1986, 108, 6961 and
references therein.
(3) The involvement of trans IS of alkyne into H-Rh bond has been proposed
in a Rh-catalyzed reaction. Tanaka, K.; Fu, G. C. J. Am. Chem. Soc. 2001.
123, 11492.
(4) (a) Ogawa, A.; Ikeda, T.; Kimira, K.; Hirao, T. J. Am. Chem. Soc. 1999,
121, 5108. (b) Kuniyasu, H.; Ogawa, A.; Sato, K.; Ryu, I.; Kambe, N.;
Sonoda, N. J. Am. Chem. Soc. 1992, 114, 5902. (c) Ogawa, A.; Kawakami,
J.; Mihara, M.; Ikeda, T.; Sonoda, N.; Hirao, T. J. Am. Chem. Soc. 1997,
119, 12380.
As to the reaction of 1 with 6, the IS of 1 into the H-Pt bond
has been already reported to yield trans-Pt[C(Ph)dCH2](Cl)(PPh3)2
(12).15 Actually, when the reaction of deuterated phenylacetylene
(1-d) with 6 was conducted at 70 °C under dark, the cis IS product
12-d was formed in 57% (only trans) yield after 20 h (eq 3). That
is, both the stereo- and regiochemistry of IS of 1 into the H-Pt
bonds could be controlled by simply switching the reaction
conditions; the conventional thermal reaction produced cis IS
product with Pt bound at the internal carbon, while the present
photo-and-thiol-driven reaction produced trans IS product with Pt
bound at the terminal carbon (Scheme 1).
(5) (a) Kuniyasu, H.; Sugoh, K.; Moon, S.; Kurosawa, H. J. Am. Chem. Soc.
1997, 119, 4669. (b) Kuniyasu, H.; Hiraike, H.; Morita, M.; Tanaka, A.;
Sugoh, K.; Kurosawa, H. J. Org. Chem. 1999, 64, 7305. (c) Sugoh, K.;
Kuniyasu, H.; Sugae, T.; Ohtaka, A.; Takai, Y.; Tanaka, A.; Machino,
C.; Kambe, N.; Kurosawa, H. J. Am. Chem. Soc. 2001, 123, 5108. (d)
Sugoh, K.; Kuniyasu, H.; Kurosawa, H. Chem. Lett. 2002, 106.
(6) (a) Kuniyasu, H. In Catalytic Heterofunctionalization; Togni, A., Grutz-
macher, Eds.; Wiley-VCH: Weinheim, 2001; Chapter 7. (b) Kuniyasu,
H.; Kurosawa, H. Chem. Eur. J. 2002, 8, 2660.
(7) (a) Keskinen. A. E.; Senoff, C. V. J. Organomet. Chem. 1972, 37, 201.
(b) Ugo, R.; La Monica, G.; Cenini, S. J. Chem. Soc. A 1971, 522.
(8) “cis/trans” and “E/Z” refer to the stereochemistry of two PPh3 on Pt and
the geometry of vinyl moiety, respectively.
Scheme 1. Photo-and-Thiol-Driven Trans IS vs Conventional
Thermal Cis IS of 1 into H-Pt Bonds
(9) It must be noted that the radical addition of 3 to 1 to give (Ph)(H)Cd
C(H)(SAr) (5) was significantly suppressed by the presence of 2; the
formation of 5 was confirmed in 12% (only Z isomer) yield by 1H NMR
spectrum in run 3, while the reaction conducted without 2 produced 5 in
76% (E/Z ) 23/77) yield. Similar suppression of radical addition by Fe-
(CO)5 has been reported, See: Kandror, I. I.; Petrova, R. G.; Petrovski,
P. V.; Freidlina, R. Kh. IzV. Akad. Nauk SSSR, Ser. Khim. 1969, 7, 1621.
(10) Crystal data of cis-Z-4: space group P-1 (no. 2) with a ) 16.721(2) Å,
b ) 19.129(3) Å, c ) 15.646(2) Å, R ) 110.955(4)°, â ) 99.908(6)°, γ
) 106.192(5)°, Z ) 4, F ) 1.50 g/cm3, R ) 0.047, and Rw ) 0.089.
(11) Considering the steric hindrance, the isomerization of the possible three-
coordinate intermediate Pt[(E)-C(H)dC(H)(Ph)](SAr)(PPh3) to Pt[(Z)-
C(H)dC(H)(Ph)](SAr)(PPh3) prior to the formation of Z-4 is also unlikely.
Huggins, J. M.; Bergman, R. G. J. Am. Chem. Soc. 1981, 103, 3002.
(12) The structure of trans-Z-9 was unambiguously determined by X-ray
analysis. See the SI for more details.
Finally, to get the information on the reaction course of trans
IS, deuterium-labeling experiments were conducted as follows. The
reaction of 1-d with 6 in the presence of AIBN and 3 to produce
trans-Z isomer (Table 2, run 2) was performed at 70 °C under dark
for 1 h, and the resultant complex was analyzed by 1H NMR
spectrum. Although a small portion of D-H exchange was
suggested (91%-d to 84%-d), D was selectively incorporated into
the R-carbon, denying the involvement of vinylidene intermediate
(eq 4). Unfortunately, the attempt to specify the origin of
â-hydrogen failed due to the faster D-H scrambling between trans-
Pt(H)(X)(PPh3)2 (2: X ) SAr, 6: X ) Cl) and ArSD (3-d, Ar )
C6H4Cl-p) than IS,16 and the reaction mechanism still remains
elusive; however thiyl radical, which could be generated from 3
(13) Mann, B. E.; Shaw, B. L.; Tucker, N. I. J. Chem. Soc. A 1971, 2667.
(14) The authentic 11 was synthesized separately.
(15) Furlani, A.; Russo, M. V.; Villa, A. C.; Manfredotti, A. G.; Guastini, C.
J. Chem. Soc., Dalton Trans. 1977, 2154.
(16) The reaction of 2 (0.01 mmol) or 6 (0.01 mmol) with 3-d (94%-d, 0.05
mmol) in C6D6 afforded trans-Pt(D)(X)(PPh3)2 (X ) SAr; 0.035 mmol,
X ) Cl; 0.0054 mmol) after 5 min.
(17) Griesbaum, K. Angew. Chem., Int. Ed. Engl. 1970, 9, 273.
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