9718
J. Am. Chem. Soc. 2001, 123, 9718-9719
Carbon-Carbon Bond Activation in
Pt(0)-Diphenylacetylene Complexes Bearing
Chelating P,N- and P,P-Ligands
Christian Mu¨ller, Carl N. Iverson, Rene J. Lachicotte, and
William D. Jones*
Department of Chemistry
UniVersity of Rochester
Rochester, New York 14627
ReceiVed July 20, 2001
The cleavage of C-C bonds under mild conditions is currently
an active research area in organometallic chemistry due to its
potential application in the petroleum industry. Oxidative addition
of C-C bonds to metal centers often relies on relief of ring strain
or attainment of aromaticity, although the activation of an
unstrained C-C bond has been achieved in the presence of highly
reactive species, by forcing the target molecule into close
proximity to the metal or by the formation of strong M-aryl
bonds.1,2
Figure 1. Molecular structure of (PN)PtPh(C≡CPh) (4) (ORTEP
diagram; 30% probability ellipsoids).
NMR spectrum of 4 showed a singlet at δ ) 49.8 ppm with Pt-
satellites (1JPt-P ) 2697 Hz). In the 1H NMR spectrum resonances
were observed for two unique phenyl groups. In particular,
platinum satellites for only one set of ortho phenyl protons were
detected, which is characteristic for a phenyl group σ-bonded to
a platinum center. A crystal of 4 suitable for X-ray diffraction
was obtained by recrystallization from THF/pentane at T ) -30
°C. The molecular structure of 4 is illustrated in Figure 1. The
structural analysis confirms that 4 is the C(sp2)-C(sp) cleavage
product. Interestingly, the insertion of the metal center into the
C-C bond of diphenylacetylene is selective, forming only one
isomer with the alkynyl group trans to the phosphorus atom.
The precursor (COD)Pt(PhC≡CPh) was also converted into
symmetrically substituted Pt(0)-alkyne complexes bearing chelat-
ing P,P-ligands. Thus, the reaction of 1 with 1 equiv bis-
(diisopropylphosphino)ethane8 (5) (dippe) or bis(dicyclohexyl-
phosphino)ethane (6) (dcpe) led to the formation of the corre-
sponding η2-alkyne complexes (dippe)Pt(PhC≡CPh) (7) and
(dcpe)Pt(PhC≡CPh)9 (8) (eq 1). 7 and 8 were obtained as yellow,
air- and moisture-sensitive solids in high yields after recrystal-
lization from pentane/CH2Cl2. The 31P{1H} NMR spectra of 7
and 8 in C6D6 showed a singlet with Pt-satellites at δ ) 77.1
ppm (1JPt-P ) 3034 Hz) and δ ) 68.2 ppm (1JPt-P ) 3029 Hz),
respectively. Analogous to compound 3, migration of the metal
center with subsequent insertion into the C-Ph bond was observed
for compounds 7 and 8 upon irradiation with UV light. The C-C
cleavage products (dippe)PtPh(C≡CPh) (9) and (dcpe)PtPh-
(C≡CPh) (10) were quantitatively generated after photolyzing
solutions of 7 and 8 in C6D6 for 12 and 7 h, respectively (eq 2).
We report here on the synthesis of various Pt(0)-diphenyl-
acetylene complexes bearing chelating P,N- or P,P-ligands and
on the cleavage of the C(sp2)-C(sp) bond in diphenylacetylene.
The η2-alkyne complexes were quantitatively converted into the
oxidative addition products under photolytic conditions. While
carbon-alkyne C-C cleavage has been reported in a few isolated
cases,3 aryl-alkyne cleavage is quite difficult.4
Reaction of (COD)Pt(PhC≡CPh)5 (1) with 1 equiv of (diiso-
propylphosphino-dimethylamino)ethane6 (PN, 2) in CH2Cl2 af-
forded the η2-alkyne complex (PN)Pt(PhC≡CPh) (3) as a yellow,
air- and moisture-sensitive solid in high yield after recrystallization
from pentane/CH2Cl2 (eq 1). The 31P{1H} NMR spectrum of 3
in C6D6 displayed a singlet with Pt-satellites at δ ) 65.8 ppm
(1JPt-P ) 3647 Hz).
A solution of 3 in C6D6 was irradiated with UV light,7 and the
reaction was monitored by 31P{1H} NMR spectroscopy. After 2
h the formation of a new species was observed. Within 45 h 3
was quantitatively converted into the product (4) which was
obtained as a colorless solid after recrystallization. The 31P{1H}
(1) For recent reviews on C-C bond activation see: (a) Rybtchinski, B.;
Milstein, D. Angew. Chem., Int. Ed. 1999, 38, 870. (b) Murakami, M.; Ito, Y.
In Topics in Organometallic Chemistry; Murai, S., Ed.; Springer-Verlag: New
York, 1999; Vol. 3, pp 96-129. (c) Rosenthal, U.; Pellny, P.-M.; Kirchbauer,
F. G.; Burlakov, V. V. Acc. Chem. Res. 2000, 33, 119.
(2) Garcia, J. J.; Jones, W. D. Organometallics 2000, 19, 5544 and
references therein.
(3) Baddley, W. H.; Panattoni, C.; Bandoli, G.; Clemente, D. A.; Belluco,
U. J. Am. Chem. Soc. 1971, 93, 5590. Mu¨ller, E.; Segnitz, A. Liebigs Ann.
Chem. 1973, 1583.
Colorless, air- and moisture-stable crystals of 9 and 10 were
isolated after recrystallization. The 31P{1H} NMR spectra of the
generated species each displayed two singlets with Pt-satellites
(4) Anderson, G. K.; Lumetta, G. J.; Siria, J. W. J. Organomet. Chem.
1992, 434, 253.
(5) 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.
(6) Werner, H.; Hampp, A.; Peters, K.; Peters, E. M.; Walz, L.; von
Schnering, H. G. Z. Naturforsch. 1990, 45b, 1548.
(7) All photolysis experiments were conducted with an Oriel arc source
using a 200-W Hg(Xe) bulb in Pyrex vessels or NMR tubes.
(8) (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.
(9) Hackett, M.; Ibers, J. A.; Whitesides, G. M. J. Am. Chem. Soc. 1988,
110, 1436.
10.1021/ja016675z CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/11/2001
Mueller
