590
Organometallics 1986, 5 , 590-591
(C5H5)2FeBF4,1282-37-7; C5H5N,110-86-1;N&H3CN, 25895-60-7; P h M g B r , 100-58-3;PMe3, 594-09-2;PPh3, 603-35-0; P(OMe)3, 512-56-1;NaCH(C02Me)2, 18424-76-5;(allyl)SiMe,, 762-72-1;
MeOH, 67-56-1;1-(trimethylsiloxy)cyclohexene,6651-36-1; ( a - 2 - b u t e n y l dimethylmalonate, 99922-88-0; dimethylmalonate, 64963-86-6; 1,1,6,6-tetracarbomethoxy-(z)-3-hexene, 93915-00-5.
The Activation of Methane by Rhenium. Catalytic HID Exchange In Alkanes wlth CpRe(PPh,),H, William D. Jones"?and John A. Maguire Department of Chemistry, University of Rochester Rochester, New York 14627 Received October 7, 1985
Summary: The complex CpRe(PPh,),H, is found to undergo photochemical loss of phosphine. The intermediate formed is capable of catalyzing HID exchange between benzene, THF, and a variety of alkanes including methane.
In recent years several metal complexes that are capable of activating alkanes have been discovered in which the C-H cleavage reaction proceeds by either an electrophilic14 or n~cleophilic~-'~ pathway. In a few of these cases methane has been observed to undergo C-H bond cleavage to give a metal-methyl complex.14~7~8~10 Not since the first reports of alkane activation with Pt(I1) by Shilov'l and WebsterI2have H/D exchange reactions with alkanes been observed. We report here the catalytic exchange of deuterium from C6D6and THF-d8 into alkanes upon photochemical activation of CpRe(PPh,),H,. As an analogue of the known (C,Me5)M(PMe3)H, (M = Ir, Rh) complexes that lose Hz upon irradiation and undergo oxidative addition of alkane^,^^^ we have examined the photochemical behavior of the complexes CpReAlfred P . Sloan Fellow, 1984-1986. Camille and Henry Dreyfus Teacher-Scholar, 1985-1986. (1) Watson, P. L. J. A m . Chern. SOC.1983, 105, 6491-6493. (2) Thompson, M. E.; Bercaw, J. E. f i r e Appl. Chem. 1984,56,1-11. (3) Bruno, J. W.; Marks, T. J.; Day, V. W. J. A m . Chem. SOC.1982, 104,7357-7360. Fendrick, C. M.; Marks, T. J. J . Am. Chern. SOC.1984, 106, 2214-2216. (4) Kitajima, N.; Schwartz, J. J. Am. Chem. SOC.1984,106,2220-2222. ( 5 ) Crabtree, R. H.; Mihelcic, J. M.; Quirk, J. M. J . A m . Chem. SOC. 1979, 101, 7738-7740. Crabtree, R. H.; Mellea, M. F.; Mihelcic, J. M.; Quirk, J. M. J . Am. Chem. SOC.1982, 104, 107-113. Crabtree, R. H.; Demou, P. C.; Eden, D.; Mihelcic, J. M.; Parnell, C. A.; Quirk, J. M.; Morris, G. E. J . Am. Chem. SOC.1982, 104,6994-7001. (6) Baudry, D.; Ephritikhine, M.; Felkin, H. J . Chem. SOC.,Chem. Commun. 1980, 1243-1244. Felkin, H.; Fillebeen-Khan, T.; Gault, Y. Holmes-Smith, R.; Zakrzewski, J. Tetrahedron Lett. 1984,25,1279-1282. Baudry, D.; Ephritikhine, M.; Felkin, H.; Zakrzewski, J. Tetrahedron Lett. 1984, 25, 1283-1284. (7) Janowicz, A. H.; Bergman, R. G. J . A m . Chem. SOC.1982, 104, 352-354. Bergman, R. G.; Janowicz, A. H. J. Am. Chem. SOC.1983,105, 3929-3939. Wax, M. J.; Stryker, J. M.; Buchanan, J. M.; Kovac, C. A.; Bergman, R. G. J. Am. Chem. SOC. 1984, 106, 1121-1122. (8) Hoyano, J. K.; Graham, W. A. G. J. A m . Chem. SOC.1982, 104, 3723-3725. Hoyano, J. K.; McMaster, A. D.; Graham, W. A. G. J. Am. Chem. SOC.1983, 105, 7190-7191. Rest, A. J.; Whitwell, 1.; Graham, W. A. G.; Hoyano, J. K.; McMaster, A. D. J . Chem. SOC.,Chern. Commun. 1984, 624-626. (9) Jones, W. D.; Feher, F. J. Organometallics 1983,2,562-563. Jones, W. D.; Feher, F. J. J . A m . Chem. SOC.1984,106, 1650-1663. Jones, W. D.; Feher, F. J. J . A m . Chem. SOC. 1985, 107, 620-631. (10) Bergman, R. G.; Seidler, P. F.; Wenzel, T. T. J . Am. Chem. SOC. 1985, 107, 435f3-4359. (11) Gol'dshleger, N. F.; Tyabin, M. B.; Shilov, A. E.; Shteinman, A. A. Russ. J . Phys. Chem. (Engl. Trans) 1969, 43, 1222-1223. (12) Hodges, R. J.; Webster, D. E.; Wells, P. B. J . Chem. SOC.,Chem. Commun. 1971. 462-463.
Table I. Turnover Numbers and Rates for Exchange of Deuterium from C,D, into Alkanes by CDRe(PPh2),HIn alkane methane ethane propane cyclopropane
irradiation time, min 180 300 60 120 180 40
[alkane], M -0.4 2 2
5
$0 cyclopentane
120 180 30
1.2
10 THFb
120 300 60 100
6.2
no. of turnovers 68 33 51,c 2 9 12,' 4.0d 71,' 4.0d 250 369 409 423 42 74 87 90 488,' 840' 520,e 8951
"[CpRe(PPh,),H,] = 1.2 mM. b[CpRe(PPh3)2H,] = 0.6 mM. Primary exchange. dSecondary exchange. e p exchange. 1, exchange.
Scheme I
0 H
/:'\-
R3P
hw
PR
R=Ph
H
I
-PR3
(PR3),H2(R = alkyl, aryl). Contrary to the behavior of the rhodium and iridium complexes, the dihydride CpRe(PPh,),H, (1) loses PPh, rather than H2 upon photolysis,13 apparently due to the trans disposition of the hydride ligand^.'^ Irradiation of 1 in THF solution in the presence of other phosphines results in the stepwise formation of CpRe(PPh,)(PR,)H, and CpRe(PR,),H, (R = p-tolyl, methyl, C,D,) in quantitative yield (eq l).',
(13) Photochemical phosphine loss has been observed previously: (a) Green, M. A,; Huffman, J. C.; Caulton, K. G.: Rybak, W.K.; Ziolkowski, J. J. J . Organornet. Chem. 1981, 218, C39-C43. (b) Roberts, D. A.; Geoffroy, G. L. J. Organornet. Chern. 1981,214, 221-231. (14) Preliminary X-ray studies of CpRe(F'Ph,)zHz*CeH, show a symmetrical trans disposition of the two PPh, ligands. (15) The UV spectrum of 1 displays a well-resolved absorption with A, = 328 nm. 'H NMR (C6D6): 1,6 4.268 (s, 5 H), 7.621 (m, 12 H), 6.973 (m, 18 H), -9.953 (t,J = 40.1 Hz, 2 H); CpRe(PMeJzH2, 6 4.553 (s, 5 HI, 1.537 (d, J = 7.3 Hz, 18 H), -12.130 (t, J = 43.6 Hz, 2 H); CpRe[P(pt 0 1 y l ) ~ ] ~ 6H4.404 ~ , (s, 5 H), 7.641 (t,J = 9.0 Hz, 12 H), 6.902 (d, J = 9.0 Hz, 1 2 H), 2.031 (s, 18 H), -9.901 (t, J = 40.2 Hz, 2 H); CpRe(PMe,)(PPh3)H2,6 4.531 (s, 5 H), 7.800 (m, 6 H), 7.060 (m, 9 H), 1.218 (d, J = 8.9 Hz, 9 H), -11.186 (dd, J = 44.7, 40.7 Hz, 2 H); CpRe[P(tolyl),](PPh,)H,, 6 4.342 (s, 5 H), 7.680 (m, 6 H), 7.35 (m, 6 H), 6.95 (m, 15 H), 2.040 (s, 9 H), -9.923 (t, J = 40.1 Hz, 2 H).
0276-7333/86/2305-0590$01.50/0C 1986 A m e r i c a n C h e m i c a l Society
Organometallics 1986,5, 591-593 Irradiation of 1 in C6D6solvent containing an excess of alkane results in the catalytic scrambling of deuterium between the benzene and the alkane (eq 2). In a typical experiment, 5 mg of 1 in 0.4 mL of C6D6along with -300 equiv of methane were sealed in an NMR tube under vacuum.16 Upon irradiation (200-W Hg lamp, Pyrex filter) the appearance of CH,D is observed by 2H NMR spectroscopy at 6 0.115. The quartet nature of the resonance ( J = 2.0 Hz) is consistent with a single H/D exchange per encounter and is identical with the ,H NMR spectrum of authentic CH,D. Added c-C6Dlzas an internal standard (2 equiv relative to Re) shows 68 turnovers after 3 h of irradiation. During this period, the appearance of free PPh, is observed in the 'H NMR as well as a new unidentified rhenium side product (20%) displaying a cyclopentadienyl singlet at 6 4.47. Details of the turnover numbers and rates based on similar experiments with ethane, propane, cyclopropane, cyclopentane, and THF are shown in Table I. As the irradiation proceeds, 1 is depleted, free PPh, appears, and the initial turnover rates are observed to drop off. Irradiation of 1 in THF-d8solvent also serves as an efficient method for exchanging deuterium into alkanes. Methane is readily deuterated upon photolysis in this solvent. Turnover numbers for C6D6/THFH/D exchange exceed 1000.
The loss of PPh3 from 1 appears to generate the species [CpRe(PPh,)H,] that is active in the H/D exchange. The addition of 3 equiv of PPh, completely inhibits the isotopic scrambling between C6D6and ethane. Slow photochemical decomposition of 1 also produces free PPh,, accounting for the inhibition of the reaction upon prolonged photolysis. Added O2 (20 equiv) has little effect upon the scrambling rate or products, suggesting that alkyl radicals are not involved. A proposed mechanism for the reaction is suggested in Scheme I, in which the intermediates CpRe(PPh,)H,R are similar to the known CpRe(PPh3)H4.13a The kinetic selectivity of the reactive intermediate was investigated by photolysis of C6D6solutions of 1 containing both an alkane and methane. Integration of the R-D resonances in the 2H NMR spectrum corrected for the relative amounts of alkane present showed only small preferences for methane over ethane (2.0:l) and m e t l p e over cyclopentane (1.6:l). The preference for primary over secondary activation in propane was observed to be 20:l. THF displayed a 1.7:l ratio of a:p exchange. Competition between propane and benzene in THF-$ solvent shows an 8.2:l ratio of arene:alkane H/D exchange, indicating comparable reactivity between aromatic and primary aliphatic C-H bonds. There are two interesting features of this system. First, the recent studies by Bergman and co-workers10 using CpRe(PMe,), and derivatives provides a means of circumventing the inability to labilize Hz in CpRe(PPh,),H,. Photochemical loss of PMe, from this compound resulted in the formation of alkane oxidative addition adducts in which it is not possible to exchange hydrogen and deuterium between C-H and C-D containing substrates. The intermediate species responsible for alkane activation in the system reported here must contain at least one hydrogen ligand and therefore has to be fundamentally ~~
(16) The pressure of methane in the NMR tube exceeds 10 atm under these conditions, and great care must be exercized in handling the sample to avoid explosion.
0276-7333/86/2305-0591$01.50/0
591
different from the one reported by Bergman. Second, the presence of more than one hydrogen combined with the assumption that an even-electron intermediate is involved means that a Re(III)/Re(V) couple is probably responsible for the alkane activation. Felkin also proposed a Re(III)/Re(V) couple for the activation of alkanes by Re(PPh3)zH7.6The catalytic H/D exchange by CpRe(PPh,),H, represents C-H bond activation by a complex in an intermediate oxidation state, probably involving an intermediate that is neither electrophilic nor nucleophilic in nature.
Acknowledgment. We thank the U.S. Department of Energy (83ER13095) for their support of this work. ~H~, Registry No. 1, 81422-70-0; C P R ~ ( P M ~ , ) 97577-92-9; CpRe[P(p-t0ly1)3]~H,,100164-66-7; CpRe(PMe3)(PPh3)H2, 100082-36-8; CpRe[P(p-toyl),](PPh3)H2, 100082-37-9; THF, 109-99-9;THF-dg, 1693-74-9;C6D6,1076-43-3;methane, 74-82-8; ethane, 74-84-0;propane, 74-98-6; cyclopropane, 75-19-4; cyclopentane, 287-92-3.
Transformation of an y4-Cycloocta-1,5-dlene (cod) Ligand into an Vl-Alkenyl Group from Reactlons of CpRuH(cod) (Cp = q5-C5H,) with Diphosphlnes: The X-ray Structural Determination of the Orange and Yellow Forms of CpRu( ~ - U - C ~ H ,Ph,PCH,PPh,) ~)( Davld C. Llles, Hester E. Oosthulzen, Alan Shaver,+ Erlc Singleton," and Manfred B. Wiege National Chemical Research Laboratory Council for Scientific and Industrial Research Pretoria 000 1, Republic of South Africa Received November 5, 1985
Summary: Treatment of [RuH(cod)(NH,NMe,),] PF, (cod = cycloocta-l,5diene) with TlCp (Cp = $-C5H,) gave the novel hydride complex CpRuH(cod). With monodentate ligands, hydride migration occurred to give the v3-allyl complexes CpRuL($-C,H,,) (L = PPh,, CNxylyl; xylyl = 2,6dimethylphenyl) whereas with chelating diphosphines transformation of the hydride complex to the aikenyl derivative C~RUL,(~-U-C,H,~)was found to take place. Restricted rotation about the RU-C bond in CpRu(Ph,PCH,PPh2)( 1-a-C,H13) produces yellow and orange forms of this compound, both of which have been characterized by X-ray diffraction. The chemistry of half-sandwich complexes of ruthenium(I1) and osmium(I1)received considerable impetus with recent reports' of new high yield syntheses of CpRuCl(cod) and Cp'MCl(cod) (M = Ru, Os; Cp' = q5-C5Me5;cod = cycloocta-1,5-diene). The cyclooctadiene and chloro ligands in these compounds are highly labile, providing facile routes into a wealth of cyclopentadienyl and pentamethylcyclopentadienyl derivatives of ruthenium and osmium. In this paper we wish to report the synthesis of the Senior Visiting Scientist from the Department of Chemistry, McGill University, Montreal, Quebec, Canada. (1) (a) Albers, M. 0.; Oosthuizen, H. E.; Robinson, D. J.; Shaver, A.; Singleton, E. J. Organornet. Chern. 1985, 282, C49. (b) Oshima, N.; Suzuki, H.; Moro-oka, Y. Chern. Lett. 1984, 1161. (c) Liles, D.C.; Shaver, A.; Singleton, E., Wiege, M. B. J. Organornet. Chem. 1985, 288, C33.
0 1986 American Chemical Society
