The first example of facile oxidative addition of carbon-tellurium bonds to zero-valent Pt,Pd, and Ni complexes

Full text of DOI:10.1021/ja963798o

J. Am. Chem. Soc. 1997, 119, 1795-1796
The First Example of Facile Oxidative Addition of
1795
Carbon-Tellurium Bonds to Zero-Valent Pt, Pd,
and Ni Complexes
Li-Biao Han, Nami Choi, and Masato Tanaka*
National Institute of Materials and Chemical Research
Tsukuba, Ibaraki 305, Japan
ReceiVed NoVember 1, 1996
Figure 1. Molecular structure of trans-PtPh(PhTe)(PEt3)2 (1a). Selected
bond lengths (Å) and angles (deg): C(1)-Pt ) 2.032(1), Te-Pt )
2.693(2), P(1)-Pt ) 2.304(4), P(2)-Pt ) 2.299(4); C(1)-Pt-P(2) )
91.5(4), C(1)-Pt-P(1) ) 89.0(4), P(1)-Pt-Te ) 87.6, P(2)-Pt-Te
) 91.9(1), C(1)-Pt-Te ) 174.9(4), P(1)-Pt-P(2) ) 178.9(2), C(2)-
C(1)-Pt-P(1) ) 92.0(1).
Oxidative addition of a carbon-heteroatom bond to a
transition metal complex constitutes the key catalytic step
involved in a number of transition metal-catalyzed transforma-
tions.1 Particularly successful examples in view of organic
synthesis are those that involve carbon-halogen bonds. Or-
ganotelluriums, easily accessible Via reactions of tellurium
tetrachloride, metallic tellurium, or alkali tellurides, are playing
increasingly important roles in organic synthesis2 and materials
chemistry.3 Some of the synthetic reactions starting with
organotelluriums are efficiently promoted by transition metal
compounds added as reagent or catalyst.4 In addition, similar
to diorganyl sulfides and selenides, diorganyl tellurides are
known to coordinate to a variety of transition metals.5 However,
to our knowledge, oxidative addition of a carbon-tellurium
bond to a transition metal has never been documented. Herein
we disclose the first example of facile oxidative addition of a
C-Te bond of diorganyl tellurides (R2Te) with group 10
transition metal complexes M(PEt3)n (M ) Pt, Pd, Ni; n ) 3,
4) affording MR(RTe)(PEt3)2 in high yields.
When Ph2Te (61.9 mg, 0.220 mmol) was slowly added to
Pt(PEt3)3 (0.135 mmol) in benzene (0.5 mL) at 25 °C, the color
of the solution immediately changed from brown to pale yellow.
As evidenced by 31P NMR, the starting Pt(PEt3)3 (δ 41.5 ppm)
was consumed within 0.5 h while two new singlets ascribable
to free PEt3 (δ -19.8 ppm) and trans-PtPh(PhTe)(PEt3)2 (1a,
δ 5.1 ppm, JPPt ) 2688 Hz) were emerging. Evaporation of
the solvent in Vacuo followed by recrystallization from hexane
at -30 °C afforded pure 1a as a deep yellow solid in 92% yield
(88.6 mg, 0.124 mmol) (eq 1). Both 1H and 13C NMR spectra
were in good agreement with the proposed structure; in the 1H
NMR spectra, the ortho-protons of the phenyl group bonded to
platinum showed a satellite due to platinum (3JHPt ) 56.2 Hz)
while those of the other phenyl (PhTe) did not. 13C NMR
displayed, at 152 ppm as a triplet due to the coupling with the
two cis-PEt3 ligands, the platinum-bound ipso-carbon, which
was also accompanied by a satellite arising from coupling with
platinum (1JCPt ) 819.7 Hz).6 The structure of the complex
was confirmed by X-ray crystallography (Figure 1). Complex
1a has a slightly distorted square planar geometry with the two
PEt3 ligands (Ph and PhTe groups) trans to each other. The
phenyl group bonded to Pt lies almost perpendicular to the
CTePtP2 mean plane. The C-Pt bond length of 1a is
2.032(12) Å, longer than the 1.98 Å expected for a typical sp2
C-Pt bond,7a reflecting a moderate trans-influence of PhTe.7
A similar yield of 1a (89%) could be obtained when Pt(PEt3)4
was used instead of Pt(PEt3)3. Pd(PEt3)4 also reacted efficiently
to afford 1b as an orange solid in 94% isolated yield. The
reaction of Ph2Te with Ni(PEt3)4, which proceeded as fast as
its Pd and Pt analogues, produced 1c as a deep red oil. Although
pure 1c has not been isolated, its formation is strongly supported
by NMR spectroscopy; first, monitoring the reaction at 25 °C
by 31P NMR revealed that the starting Ni(PEt3)4 completely
disappeared within 10 min; singlets for 1c at δ 10.3 ppm and
free PEt3 were the only recognizable signals. Secondly, the 1H
NMR exhibited a coupling pattern similar to 1a and 1b.
Furthermore, in 13C NMR, the ipso-carbon bound to Ni was
clearly observed at 162.3 ppm as a triplet due to the coupling
with two PEt3 ligands (JPC ) 30.9 Hz). Unlike its Pd and Pt
analogues, however, 1c slowly decomposed at room temperature
to deposit black solids.8
(1) (a) Chaloner, P. A. Handbook of Coordination Catalysis in Organic
Chemistry; Butterworth: London, 1986. (b) Collman, J. P.; Hegedus, L.
S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransi-
tion Metal Chemistry; University Science Books: Hill Valley, CA, 1987.
(c) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis; John Wiley &
Sons: New York, 1992.
(2) (a) Irgolic, K. Y. The Organic Chemistry of Tellurium; Gordon and
Breach: New York, 1974. (b) The Chemistry of Organic Selenium and
Tellurium Compounds; Patai, S., Rapport, Z., Eds.; John Wiley & Sons:
New York, 1986; Vol. 1. Ibid. 1987; Vol. 2. (c) ComprehensiVe Organo-
metallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon: Oxford, U.K., 1995; Vol. 11, pp 571-601. (d) Petragnani, N.
Tellurium in Organic Synthesis; Academic Press: London, 1994.
(3) Organotelluriums are important precursors for the controlled synthesis
of binary materials. For example, see: (a) Siemeling, U. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 67. (b) Stein, A.; Keller, S. W.; Mallouk, T. E.
Science 1993, 259, 1558. (c) Khasnis, D. V.; Brewer, M.; Lee, J.; Emge,
T. J.; Brennan, J. G. J. Am. Chem. Soc. 1994, 116, 7129. (d) Fischer, J. M.;
Piers, W. E.; Pearce Batchilder, S. D.; Zaworotko, M. J. J. Am. Chem. Soc.
1996, 118, 283 and references cited therein.
Dibutyl telluride (n-Bu2Te) was as reactive as Ph2Te toward
Pt(PEt3)3 to quantitatively give trans-Pt(n-Bu)(n-BuTe)(PEt3)2
(6) 31P and 13C NMR of Transition Metal Phosphine Complex; Pregosin,
P. S., Kunz, R. W., Eds.; NMR, basic principles and progress, 16; Springer-
Verlag: Berlin and Heidelberg, 1979.
(7) (a) ComprehensiVe Organometallic Chemistry; Wilkinson, G., Stone,
F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982; Vol. 6, pp
471-762. (b) ComprehensiVe Organometallic Chemistry II; Abel, E. W.,
Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, U.K., 1995; Vol.
9, pp 431-531. By comparison with typical C-Pt bond lengths of similar
complexes collected in these references, the PhTe ligand can be ranked, in
the trans-influence, approximately between Cl and tertiary phosphines:
higher than Cl but lower than (close to) R3P.
(4) (a) Bergman, J. Tetrahedron 1972, 28, 3323. (b) Bergman, J.;
Engman, L. Tetrahedron 1980, 36, 1275. (c) Barton, D. H. R.; Ozbalik,
N.; Ramesh, M. Tetrahedron Lett. 1988, 29, 3533. (d) Uemura, S.;
Takahashi, H.; Ohe, K. J. Organomet. Chem. 1992, 423, C9. (e) Uemura,
S.; Fukuzawa, S.-I.; Patil, S. R. J. Organomet. Chem. 1983, 243, 9. (f)
Chieffi, A.; Comasseto, J. V. Tetrahedron Lett. 1994, 35, 4063. (g)
Kawamura, T.; Kikukawa, K.; Takagi, M.; Matsuda, T. Bull. Chem. Soc.
Jpn. 1977, 50, 2022. (h) Uemura, S.; Wakasugi, M.; Okano, M. J.
Organomet. Chem. 1980, 194, 277. (i) Bergman, J.; Engman, L. J.
Organomet. Chem. 1979, 175, 233. (j) Ohe, K.; Takahashi, H.; Uemura,
S.; Sugita, N. J. Org. Chem. 1987, 52, 4859.
(8) Heating the solution accelerated the decomposition. After a toluene
solution of the complex was refluxed overnight, 1c disappeared completely
to afford biphenyl in a quantitative yield.
(5) Gysling, H. J. Coord. Chem. ReV. 1982, 42, 133.
S0002-7863(96)03798-5 CCC: $14.00 © 1997 American Chemical Society

1796 J. Am. Chem. Soc., Vol. 119, No. 7, 1997
Communications to the Editor
(1d) as a yellow oil.9 Other dialkyl tellurides also reacted
smoothly. Although the complexes obtained from n-Bu2Te,
Me2Te, and (PhCH2CH2)2Te failed to crystallize, orange crystals
of Pt(t-BuCH2)(t-BuCH2Te)(PEt3)2 (1e) were successfully iso-
lated from the reaction of (t-BuCH2)2Te with Pt(PEt3)3 (83%
yield). As expected, two nonequivalent neopentyl groups of
in 76% yield (in 6 h).10-12 Ph2Se showed higher reactivity
toward Pt(PEt3)3 than Ph2S; the reaction of Ph2Se with Pt(PEt3)3
readily took place at 50 °C over 5 h to produce trans-PtPh-
(PhSe)(PEt3)2 (3a) in 90% yield as orange crystals.12 Therefore,
the ease of oxidative addition of a carbon-chalcogen bond to
Pt(PEt3)3 can be concluded to decrease in the order C-Te >
C-Se > C-S, which is the reverse of the order of their bond
strengths.2b
1
1e were observed in H NMR; the methylene group bonded
directly to platinum was observed at δ 1.78 ppm as a triplet
due to the coupling with PEt3 (JHP ) 8.0 Hz), accompanied by
a satellite due to platinum (2JHPt ) 65.6 Hz).
Interesting regioselectivity of the oxidative addition of C-Te
bonds with the platinum complex was encountered when an
unsymmetrical telluride was employed as the substrate (eq 2).
Finally, it is interesting to note that the C-Te bond reacts
with Pd(PEt3)4 eVen faster than the corresponding C-I bond,
known as one of the most reactive bonds. As shown in eq 4,
when Pd(PEt3)4 was treated at room temperature with an
equimolar mixture of Ph2Te (11 equiv) and PhI (11 equiv), 1b
was formed as the major product in 20 min and the ratio of
1b/4b remained unchanged under these conditions over a period
of 5 h.13 A separate experiment, in which pure 1b was treated
with pure 4b in benzene at room temperature, also confirmed
no reaction occurring between these complexes. Accordingly
the ratio observed in eq 4 is likely to reflect kinetic control,
indicating that Ph2Te reacts about 4 times faster than PhI.
The reaction of n-BuTePh with Pt(PEt3)3 quantitatively produced
1f and 1f′, as a result of the oxidative addition of Ph-Te and
n-Bu-Te bonds, respectively, in 77:23 ratio. i-PrTePh more
selectively reacted to afford only trans-1g, the product arising
from the exclusive Ph-Te bond oxidative addition.
The mechanism of the oxidative addition remains to be further
clarified. However, the following comments merit consider-
ation. When the two C-Te bond strengths of the tellurides
are compared, the foregoing regioselectivity appears opposite
to what would be expected if the reaction of the telluride with
Pt(PEt3)3 took place Via a radical mechanism, which was
proposed for most cases of sp3 carbon-halogen bond oxidative
additions.7a Alternatively, the C-Te bond oxidative addition
to the platinum complex can be envisioned to occur by the
insertion of the nucleophilic platinum(0) to the more positively
charged C-Te bond of the telluride, resulting in the preferential
cleavage of the C-Te bonds (i.e., Ph-Te rather than n-Bu-
Te or i-Pr-Te). An NMR study strongly indicated that the
oxidative addition of the C-Te bonds took place in a cis fashion
to afford a cis-complex, which isomerized rapidly to the trans-
form on standing. Thus, monitoring of the reaction of i-PrTePh
with Pt(PEt3)3 at 25 °C by 31P NMR revealed that Pt(PEt3)3
disappeared within 5 min to form cis-1g (JPPt (trans to Ph) )
1771.2 Hz, JPPt (trans to i-PrTe) ) 2944.1 Hz) and trans-1g
(JPPt ) 2722.7 Hz) in 95:5 ratio (eq 3). Upon standing the
solution at room temperature, cis-1g isomerized completely to
trans-1g within 0.5 h, leaving trans-1g as the sole complex in
the solution.
On the basis of the novel oxidative addition of the C-Te
bond, numerous applications can be developed in organic
synthesis and materials chemistry.
Acknowledgment. We are grateful to the Japan Science and
Technology Corporation (JST) for partial financial support through the
CREST (Core Research for Evolutional Science and Technology)
program and for postdoctoral fellowships to L.-B.H. and N.C.
Supporting Information Available: Experimental details, spectral
and/or analytical data of the tellurium complexes; a perspective view
and tables of crystallographic data, atomic coordinates and thermal
parameters, and bond lengths and angles for 1a (13 pages). See any
current masthead page for ordering and Internet access instructions.
JA963798O
(10) For modeling the hydrodesulfurization process, reactions of thiophenes
with transition metal complexes are of current interests. (a) Angelici, R. J.
Acc. Chem. Res. 1988, 21, 387. (b) Angelici, R. J. Coord. Chem. ReV. 1990,
105, 61. (c) Sa´nchez-Delgado, R. A. J. Mol. Catal. 1994, 86, 287. See
also: (d) Paneque, M.; Taboada, S.; Carmona, E. Organometallics 1996,
15, 2678. (e) Bianchini, C.; Frediani, P.; Herrera, V.; Jime´nez, M. V.; Meli,
A.; Rinco´n, L.; Sa´nchez-Delgado, R.; Vizza, F. J. Am. Chem. Soc. 1995,
117, 4333. (f) Garcia, J. J.; Maitlis, P. M. J. Am. Chem. Soc. 1993, 115,
12200. (g) Jones, W. D.; Chin, R. M.; Crane, T. W.; Baruch, D. M.
Organometallics 1994, 13, 4448. (h) Druker, S. H.; Curtis, M. D. J. Am.
Chem. Soc. 1995, 117, 6366. (i) Smith, V. C. M.; Aplin, R. T.; Brown, J.
M.; Hursthouse, M. B.; Karalulov, A. I.; Malik. K. M. A.; Cooley, N. A.
J. Am. Chem. Soc. 1994, 116, 5180.
(11) Useful Ni-assisted transformations of the C-S bond of dithioacetals
have been developed: (a) Luh, T.-Y. Acc. Chem. Res. 1991, 24, 257. (b)
Luh, T.-Y. Pure Appl. Chem. 1996, 68, 105. See also: (c) Adams, R. D.;
Falloon, S. B. J. Am. Chem. Soc. 1994, 116, 10540. (d) Baranger, A. M.;
Hanna, T. A.; Bergman, R. G. J. Am. Chem. Soc. 1995, 117, 10041.
(12) Comparison of the coupling constants (e.g., 1Jipso-CPt for 1a (819.7
Hz), 2a (797.7 Hz) and 3a (818.8 Hz)) suggests the trans-influence is in
the order PhS > PhSe g PhTe.
At room temperature, the reaction of Ph2S with Pt(PEt3)3 did
not proceed even after 1 day, and heating at 50 °C for an
additional day gave only a trace of trans-PtPh(PhS)(PEt3)2 2a
(<3%). The reaction proceeded slowly at a more elevated
temperature (110 °C) to give complex 2a as off-white crystals
(9) Upon mixing n-Bu2Te (2 equiv) and Pt(PEt3)3 at 25 °C in C6D6, the
starting Pt(PEt3)3 was consumed completely within 20 min. In 31P NMR,
only two singlets which corresponded to 1d (δ 7.8 ppm, JPPt ) 2878 Hz)
and free PEt3 were observed. Further evidence for the oxidative addition
of the n-Bu-Te bond to platinum came from 13C NMR spectroscopy where
the carbon directly bound to platinum displayed a triplet at δ 8.2 ppm (C-
Pt, JPC ) 5.3 Hz, JCPt ) 604.4 Hz).
(13) When the mixture shown in eq 4 was heated at 80 °C in benzene,
however, 4b gradually increased at the expense of 1b; 1b almost completely
disappeared after 6 h heating at 80 °C (1b/4b < 2:98 by 31P NMR).
Likewise, conversion of 1b to 4b was found when a mixture of pure 1b
and PhI in C6D6 was heated at 80 °C for 6 h. These results indicate that
complex 4b is thermodynamically more stable than 1b.