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pressure heads. These were constructed to allow purging with 02,as well as sampling of the solution under reaction conditions during the course of the reactions. 2-Hexanone production was measured by GLC. A typical catalytic reaction was run as follows: to a 250-mL Parr bottle were added 0.074 mmol of [Rh(CO),S',]BF, (prepared as earlier reported2 and used immediately), 0.0171 g of C U ( N O ~ ) ~ . ~ (0.074 .~H~O mmol), 0.0219 g of NaCl (0.375 mmol-for the case in which a 5:l mole ratio chloride/rhodium was desired), 0.41 mL of 0.36 M H2S04(0.148 mmol; as an ethanol solution prepared from aqueous concentrated H2S04),0.568 mmol of 2-heptanone, 45 mL of absolute ethanol, and 15 mL of I-hexene (purged through alumina to remove peroxides). This mixture was purged 5 times with 60 psi of 02, set to 40 psi of 02,and the reaction initiated by placing in a 70 OC oil bath. Preparation of RhC13(H,0),.CH,CH20H (11). Compound C was prepared for characterization studies most easily under 40 psi of 0, at 70 OC by mixing 0.0514 g of [Rh(CO),CI], (0.132 mmol), 1.10 mL of 0.48 M HCI (in ethanol, 0.528 mmol), and 15 mL of ethanol. This produced a bright orange solution after a reaction overnight, from which C was isolated by rotovaping to dryness and drying in vacuo. M,for H,O,CI,Rh calcd, 245; found, 226. Anal. Calcd for C2HloO3CI3Rh:C, 8.24; H, 3.46; CI, 36.50. Found: C, 8.41; H, 2.69; CI, 37.17. Determination of Acetone Production. (A) In Presence of 1-Hexene. The measurement of acetone produced in the initial stage of the Rh/ Cu-catalyzed oxidation of I-hexene with isopropyl alcohol as solvent was made by G L C as follows: To a 50" round-bottom flask were added to 0.159 g of RhC13.3H20 (0.604 mmol), 0.137 g of C U ( N O , ) ~ . ~ . ~ H , O (0.589 mmol), and a stir bar. This was purged 20 min with O2 at 40 OC and 30 mL of an 02-purged, 9/1 (v/v) solution of isopropyl alcohol/lhexene added to initiate the reaction. GLC's were recorded after 4, 8, 17, 25, and 40 min. The amount of acetone produced was determined by comparison of peak heights with standards at the same time under identical conditions. When this 1:l C u / R h ratio was used, 0.5 mol of acetone was formed per mole or rhodium in the first 4-8 min. N o further
production was observed. When a 2:1 Cu/Rh mole ratio was used, continuous, catalytic production of acetone was observed. (B)In Absence of I-Hexene. The catlaytic production of acetone from the 0, oxidation of isopropyl alcohol was observed when I-hexene was excluded from the solutions. RhCI,.3H20, C U ( N O ~ ) ~ . ~ . ~and H~O, HClO, were all used as catalysts for this reaction. In a typical run, 0.0369 g of RhCI3.3H20 (0.140 mmol) and a stir bar were placed in a 15" round-bottom flask and purged 20 min with 0, at 40 OC. Into this was syringed 7 mL of isopropyl alcohol, purged itself with O2at 40 OC, to initiate the reaction. Acetone production was measured as described above. Titration of [Rh(CO),CI], with HOOH. Because the reaction of H O O H with [Rh(CO),CI], (A) is quite slow in ethanol, it was run at 40 OC. The visible spectrum of the intermediate, H,[Rh(CO)CI,(OOH)] (B), is most clearly observed by first adding 1.0 equiv of HOOH, followed an hour later by 0.5 equiv. The first addition causes the reaction of much of the starting material A (which overlaps the band at 385 nm), so that after the second addition the band due to C at 385 nm is easily observable in the electronic absorption spectrum. Intermediate B is easily detected in the oxidation of A by H O O H by using FT IR. Since there is no overlap of the carbonyl bands of A and B, the intermediate is detected in the first addition of HOOH. H O O H was diluted in ethanol immediately before use. Aqueous dilution causes the addition of too much H 2 0 , which retards the reaction considerably.
Acknowledgment. We gratefully acknowledge t h e generous support of this research by the National Science Foundation a n d t h e Office of N a v a l Research. Registry No. 02,7782-44-7; Cu(N03),, 3251-23-8; NaCI, 7647-14-5; [Rh(CO),CI]2, 14523-22-9; [RhCIj(H20)2*CH3CH,OH], 85236-98-2; HOOH, 7722-84-1; 1-hexene, 592-41-6; 2-hexanone, 591-78-6; chloride, 16887-00-6.
Activation of Methane with Metal Atoms at 10 K without Photolysis Kenneth J. Klabunde* and Yasutaka Tanaka Contribution from the Department of Chemistry, Kansas State University, Manhattan, Kansas 66506. Received November 8, 1982
Abstract: Codeposition of methane with metal atoms a t 10 K leads to reaction with AI atoms but not with Mg, C a , Ti, Cr, Fe, Co, Ni, Pd, Cu, Ag, Au, G a , In, or Sn. T h e unusual reactivity of AI is ascribed to its 2P radical character, coupled with comparatively high AI-H and A1-C bond strengths.
Activation of alkanes by small "naked" nickel clusters has been accomplished as low as -130 O C . ] Clean metal surfaces of other group 8 metals have shown similar high reactivities at relatively low temperatures2 Also, it has been reported that Zr atoms react with alkanes as low as -196 O C 3 Under m a t r i x isolation conditions of 10-50 K (-263 to -223 "C) no evidence of reaction of bare metal a t o m s or clusters with alkanes has been found, although m a n y attempts have been made. Ozin a n d co-workers have studied V a t o m s in a variety of alkane media in t h e 10-50 K range.4 Likewise, w e have carried o u t similar studies with N i atoms a n d other metals. Photolytic activation of alkanes using metal a t o m s is q u i t e different, however. Gas-phase M*-alkane reactions have been
known for m a n y years.5 A n d recently this approach h a s been extended t o matrix-isolated m e t a l a t o m s i n frozen m e t h a n e and ethane.6,7 Billups a n d co-workers6 reported photolytic activity of M n , Fe, Co, C u , Zn, Ag, and A u a t o m s with CHI. O z i n and co-workers7 reported activity for Cu a t o m s with both CH4 and C2H6 (C-H cleavage only).7 We have recently reported unusually high activities of certain m e t a l a t o m s with C H 3 B r at 10 K, especially A1 and Ga, and attributed this t o t h e low ionization potentials of these a t o m s coupled with their high M-Br bond strengths.* N o t e t h a t n o photolytic activation was necessary. Likewise, Hauge, Kauffman, a n d Margrave have elucidated t h e spontaneous reaction of AI and G a a t o m s with H20.9
(1) Davis, S. C.; Klabunde, K. J. J . Am. Chem. SOC.1978, 100, 5973. Davis, S.C.; Severson, S.; Klabunde, K. J. J. Am. Chem. Soc. 1981,103,3024. (2) Weinberg, W. H. 183rd National Meeting of the American Chemical Society, Las Vegas, Nevada, Mar 1982; American Chemical Society: Washington, D.C., 1982; PETR, paper 3. (3) Remick, R. J.; Asunta, T. A,; Skell, P. S . J . Am. Chem. SOC.1979,101, 1320. (4) Klotzbucher, W. E.; Mitchell, S. A.; Ozin, G. A. Inorg. Chem. 1977, 16. 3063.
( 5 ) Steacie, E. W. R. "Atomic and Free Radical Reactions", 2nd ed.;Van Nostrand-Reinhold: Princeton, 1954; Vol. I, pp 413-416. (6) Billups, W. E.; Konarski, M. M.; Hauge, R. H.; Margrave, J. L. J . Am. Chem. Soc.-1980, 102, 7393. (7) Ozin, G. A,; McIntosh, D. F.; Mitchell, S. A.; Garcia-Prieto, J. J . Am. Chem. SOC.1981, 102, 1574. Also, private communications with Professor Ozin. (8) Tanaka, Y.;Davis, S. C.; Klabunde, K. J. J. Am. Chem. SOC.1982,
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104. 1013.
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Activation of Methane with Metal Atoms
Table 1. Bands Observed in CH,/Al and CD,/Al Reactions (without and with Photolvsis)a reactant/ metal CH,IAl CD,/Al CH,/AIC
proposed species H-A1-CH,
H-Al(CH,), H,AlCH,” CH,/GaC H-Gd-CH, (no product without photolysis)
VAI-H, cm-’ 1777 1275 1764,1746 1828 1723,1710
ssym(CH,)> fJasym(CH,)> cm-’ cnP 579,61Sb 575,553&519 732,615 ? 9 6 5 , 612b
912 960,885 1165,1042 1
1269
a All experiments were carried out at 10 K with 1OOO:l excesses of methane to metal. Could be free .CH,.” After 1-h photolysis with an unfiltered 140-W medium-pressure mercury UV lamp. The 615-cm-’ band grew in intensity upon photolysis which supports the idea that a radical reaction is promoted by LIV.
,
I
I
i
I.
-\,
,
.LiJ
>.
--------Tr
.li
.v
.3.
.iT
+
’J
la
1x
--
I
~
--7-
,e*-.
r-
. v‘
----7FdL-T;-: a w
Figure 1. A. Aluminum atoms d e p o s i t e d with 100-fold Excess of pure CH4. B. After 1-h photolysis. C. After 3-h photolysis. D. After annealing a t 30 K for 1 min.
This background led us to consider what properties of metal atoms may be necessary for 10 K reactions to occur with CHI without photolysis. We decided to survey some of the catalytically important transition-metal atoms as well as main-group atoms for activity with CH4 (at 10 K without photolysis). Our survey led to one simple observation: AI atoms react but Mg, Ca, Ti, Cr, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Zn,Sn,Pb, Ga, and In do not. Furthermore, we have observed photolytic reactivity for one previously unstudied atom.
Results Aluminum. Figure 1A illustrates the spectrum obtained when a 1000-fold excess of pure CH4 is d e p o s i t e d with AI atoms. The absorption of 1777 cm-’ can be assigned to v ~ although ~ - not ~ diatomic AI-H which absorbs at 1593 cm-l.Io The absorptions at 962,615, and 579 cm-l can be assigned to C-H bending modes; it is possible the 615-cm-’ band is due to the free methyl radical.” ~ 8CH, - ~ Photolysis of the matrix for 1 h caused additional v ~ and bands to appear (Figure 1B). The original bands did not change appreciably. However, prolonged photolysis (Figure 1C) caused an additional Y ~ band ~ to - appear ~ and several other 6CH, bands to appear but with simultaneous decreases in the original bands. These results suggest that upon deposition only a portion of the (9) Hauge, R.; Kauffman, J.; Margrave, J. L. J . Am. Chem. SOC.1980, 102, 6005.
(10) Wright, R. B.; Bates, J. K.; Gruen, D. M. Inorg. Chem. 1978, 17, 2275.
(1 1) (a) Andrews, L.; Rmentel, G. C. J . Chem. Phys. 1967,47, 3637. (b) Milligan, D. E.; Jacox, M. E. Ibid. 1967, 47, 5146. (c) Andrews, L. In ‘Cryochemistry”; Ozin, G. A., MosKovits, M., Eds.; Wiley-Interscience: New York, 1976; p 197.
AI atoms react, and more complete reaction is forced by short photolysis.I2 Prolonged photolysis causes the destruction of the original species with the production of more new species. Likewise, annealing (Figure 1D) caused AI-H bands to almost disappear, which is probably due to association and band broadening. Experiments with CD4/A1 and CH4/CD4/Alindicated that the products were mainly one methyl/one hydrido species. Thus, a 1:l mixture of CH,/CD4 with AI yielded a spectrum that was very nearly a direct combination of the separate CH4 and CD, spectra. Gallium. Gallium did not insert or break the C-H bond without UV photolysis. Upon photolysis vGa-H bands at 1723 and 17 10 cm-I appeared and bCH3 bands at 1269, 965, and 612 cm-I. Prolonged photolysis caused a slight increase in these absorptions. Experiments with CH4/CD4indicated that only one methyl and one hydrido group were involved. This suggests that CH,GaH is formed upon photolysis and it is stable toward photolytic decomposition. Indium. This metal atom was unreactive during deposition and upon photolysis. Other Metals. Metals listed previously were all unreacted upon codeposition with CHI at 10 K. Photolytic activity was observed with those previously r e p ~ r t e d . ~ , ~
Discussion Strict assignment of bands is difficult, but the literature is - ~comhelpful. In the absence of donor solvents v ~ in ~R2A1H pounds is in the 1750-1790-cm-’ range,I3 with [HAI(C,H,),], absorbing at 1777 cm-I. Other studies show that HAI(C2H,), and HAl(CH3)2have v ~ at ~1780 - cm-’ ~ and uAI-D for DAI(C2H5), at 1290 cm-’.13 Furthermore, although diatomic AI-H absorbs at a low value of 1593 cm”,” “free” AIH, is estimated - ~ range.I5 Also relevant are to have v ~ in ~the 1850-1900-cm-’ the v ~ and~ v - ~ values ~ ~ observed - ~ for matrix-isolated HOAIH (1 743 cm-I) and HOGaH (1670 cm-I) .9 Examination of several X-A1(CH3)2 and X-A1(CD3), derivatives indicates that strong aCH, bands appear at 1212, 720, and 588 cm-’ and 1010, 980, 950, 680, and 595 cm-I, respectively.I6 Since the bands observed in our experiments with CH4 and CD, do not match with these but are in a range consistent with absorptions in general, we conclude that HAI(CH,), and DAI(CD3)2 are not the primary products even though v ~ is con~ sistent. Thermodynamically these compounds would not be favored since the formation of HAl(CH3)*from 2CH4 and AI would be endothermic by 8 k ~ a l / m o l . ’ ~However, the formation of (12) Low concentrations of AI atoms still led to reaction, indicating that AI atoms rather than (Al), clusters are the reacting species. (13) Schomberg, G.; Hoffman, E. G . 2. Electrochem. 1957, 61, 1110. Hoffman, E. G.; Schomberg, G. Z . Electrochem. 1957, 61, 1101. (14) Mole, T.; Jeffrey, E. A. ‘Organoaluminum Compounds”; Elsevier: Amsterdam, 1972; p 58. (1 5) Wiberg, E.; Amberger, E. “Hydrides of the Elements of Main Group I-IV”; Elsevier: Amsterdam, 1971; pp 432, 433. (16) Gray, A. P. Con.J . Chem. 1963, 41, 1511. Gray, A. P.; Callear, A. B.; Edgecombe, F. H. C. Ibid. 1963, 41, 1502.
~
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J. Am. Chem. Soc. 1983, 105, 3546-3556
H-AI-CH, from CH4 and A1 would be 34 kcal e ~ 0 t h e r m i c . l ~ We conclude that the primary species formed is HAlCH, (or DA1CD3) on the basis of energetic considerations as well as comparing the observed vAI+ and 6CH3 with known organoaluminum hydrides. Photolysis of the deposited CH4/A1 and CD4/Al matrices initially led to a slight increase in product bands but with simultaneous production of new bands. The new bands appear in regions similar to those reported for (R2A1H)2and (R2AIC1), species (some differences would be expected since in the matrices "free" species would be present). The following scheme seems consistent:
,A. :AI*
t CH4
[ H I - - - - CH31
*CH3 t *H t H-AI(CH&
t
-
H2AICH3
ground-state AI atoms are in a 2Pstate (3s23p1),and it would be expected that A1 atoms would possess reactive radical-like propertie~.'*-'~ Also note that ground-state A1 atoms are in the same electronic state as photoexcited Cu atoms, which are also reactive with CHI at 10 K.7 It seems reasonable to conclude that A1 atoms are able to react by a homolytic bond cleavage process, and the driving force is the formation of AI-H and A1-C bonds. The 2P state appears to be uniquely reactive.
H-AI-CH3
Experimental Section The apparatus and procedures have been described in a previous publication.8 The photolytic experiments were carried out for I - , 2-, or 3-h periods by using a medium-pressure mercury UV lamp (140 W, unfiltered).
-
Acknowledgment. The donors of the Petroleum Research Fund, administered by the American Chemical Society, are acknowledged with gratitude.
worm
association and AI-H braoadening
The most important question remains: "Why are A1 atoms reactive (without photolysis) over other metal atoms?" Two considerations come to mind. First, AI-H and AI-C bonds are comparatively strong (68 and 66 kcal, respectively). Second,
Registry No. CH4, 74-82-8; Al, 7429-90-5; Mg, 7439-95-4; Cu, 7440-70-2;Ti, 7440-32-6; Cr, 7440-47-3; Mn, 7439-96-5; Fe, 7439-89-6; Co, 7440-48-4; Ni, 7440-02-0; Pd, 7440-05-3; Cu, 7440-50-8; Ag, 7440-22-4;Au, 744047-5; Zn,7440-66-6;Sn, 7440-31-5;Pb, 7439-92-1; Ga, 7440-55-3; In, 7440-74-6.
(17) Taking the AI-C bond as 66 and the AI-H bond as 68 with H-CH3 as 104 kcal/mol; ref 14, p 95. "Handbook of Chemistry and Physics", 56th ed.; Weast, R. C., Ed.; CRC Press: Cleveland, OH, 1975-1976; pp F-224, F-215.
(18) Hertzberg, G. "Atomic Spectra and Atomic Structure"; Dover Publications: New York, 1944; pp 132, 140. (19) For studies of AI atom-benzene interactions and related work, see: Kasai, P.H.;McLeod, D. J . Am. Chem. SOC.1979, 101, 5860.
Coordinately Unsaturated Clusters. A Novel Catalytic React ion R. R. Burch,+A. J. Shusterman,+E. L. Muetterties,*+R. G. Teller,t and Jack M. Williams** Contribution from the Department of Chemistry, University of California, Berkeley, California 94720, and Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439. Received October 20, 1982
Abstract: The dinuclear rhodium hydride ((p-H)Rh[P(O-i-C3H7),]2)2 is a catalyst precursor for stereoselective hydrogenation of dialkylalkynes and diarylalkynes to the corresponding trans-alkenes. Both H2and the alkyne compete for reaction with the dimer with the respective products being (H)(p-H),Rh,[P(O-i-C3H7)3]4 and (p-H),(p-q2-RC2R)Rh2[P(O-i-C3H7),],. The further reaction of the tetrahydride complex with alkyne and also the rearrangement of the q2-alkynecomplex yield a bridged 3, which has a trans arrangement of alkyl or aryl groups as vinyl derivative, (p-H)[p-q2-RC=C(H)R]Rh2[P(0-i-C3H7),],, established by X-ray crystallographic studies. The rate-determining step in the catalytic cycle appears to be hydrogen addition to the vinyl derivative. Competitive with hydrogen addition to the vinyl derivative is diarylalkyne addition and insertion to give the mononuclear complex [R(H)C=C(R)(R)C=CR]Rh[P(O-i-C3H7),I2, which was also defined by an X-ray crystallographic study. The latter is a catalyst precursor for alkyne hydrogenation to form cis-alkenes. Dynamic stereochemical features of the vinyl complexes in the solution state are described as well as intermolecular alkyne exchange between free alkyne and the vinyl complexes.
.
Introduction A major focus of our metal cluster research has been the design of coordinately unsaturated clusters, specifically clusters in which most or all of the metal atoms have open coordination sites. Presently, this class of clusters is comprised largely of the (pH)RhL2 group in which the immediate coordination sphere of each rhodium(1) atom has a planar set of 2 H (bridging) and 2 L These polynuclear rhodium hydrides are very active catalyst precursors for hydrogenation reaction^,^,^ and this cluster catalysis is the subject of this article. 'University of California. Argonne National Laboratory.
*
0002-7863/83/l505-3546$01.50/0
Cluster catalysislOJ1has a potential for chemoselective and stereoselective reactions that may be unavailable to mononuclear (1) Day, V. W.; Fredrich, M. F.; Reddy, G. S . ; Sivak, A. J.; Pretzer, W.
R.; Muetterties, E. L. J . Am. Chem. SOC.1977, 99, 8091. (2) Brown, R. K.; Williams, J. M.; Fredrich, M. F.; Day, V. W.; Sivak, A. J.; Muetterties, E. L. Proc. Natl. Acad. Sci. U.S.A. 1979, 76, 2099. (3) Sivak, A. J.; Muetterties, E. L. J . Am. Chem. SOC.1979, 101, 4878. (4). Muetterties, E. L.; Sivak, A. J.; Brown, R. K.; Williams, J. M.; Fredrich, M. F.; Day, V. W. "Fundamental Research in Homogeneous Catalysis"; Plenum Publishing: New York, 1972; Vol. 3, p 487. ( 5 ) Brown, R. K.; Williams, J. M.; Sivak, A. J.; Muetterties, E. L. Inorg. Chem. 1980, 19, 370. ( 6 ) Burch, R. R.; Muetterties, E. L.; Schultz, A. J.; Gebert, E. G.; Williams, J. M. J . Am. Chem. SOC.1981, 103, 5517.
0 1983 American Chemical Society
