J. Am. Chem. SOC.1993, 115, 3354-3355
3354
Dehydrohalogenation for Facile Generation of Unsaturated Ru(0)
unit. Five inequivalent protons of intensity = 1 correspond to an +allyl group with no molecular mirror plane of symmetry containing the central allyl carbon. All these data are consistent with the product being that of oxidative addition of propylene to Ru(C0)Pz (structure 1).11-13
Richard H. Heyn and Kenneth G. Caulton' Department of Chemistry Indiana University Bloomington, Indiana 47405
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I
Received July 27, 1992
Dehydrohalogenation (eq 1) is the infrequently encountered reverse of the oxidative addition reaction.'q2 The reaction of eq 1 is most common with IrI1' and Rh"' and often requires Brransted base to make the reaction e ~ e r g o n i c .Dehydrohalogenation ~ of
-
L,M"+2(H)(C1)
L,M"
100
16e
+ HC1
(1)
isoelectronic divalent Fe, Ru, or Os might be challenging, however, since 16-electron compounds of these metals (when zerovalent) have to date only been produced under high-energy conditions (high temperature, UV photon, or matrix isolation). Consider, for example, the high temperatures required for reductive elimination from R u H ( P ~ ) ( P M(135 ~ ~ )"C) ~ ~or RuH2(PMe3)s4 (>18OOC)andfromO~R~(CO)~SwhenR =Horalky1(126-163 "C). Once formed, the isoelectronic M(0)L4 (M = Fe, Ru, Os) are sufficiently high-ecergy species that they react with C-H bond^.^,"^ In the special case of the hydrido halide reagent RuHCl(CO)P2,9 ( P = P'Bu2Me), dehydrohalogenation would yield a most unusual 14-electron transient (eq 2). We report
RuH(Cl)(CO)P, + base
-
(Hbase+)Cl- + Ru(CO)P, (2)
here evidence for dehydrohalogenation as a route toward lowtemperature generation of a highly reactive intermediate. Addition of 'BuLi to a toluene solution of RuH(Cl)(CO)P2 and propylene (1 :1:1 mole ratio) at -75 "C gives clean conversion to a single species in which propylene has trapped the primary product of dehydrohalogenation.10 The single vco band shows this to be a monocarbonyl, and the 3IP(lH)N M R spectrum, an AB pattern, has a JAevalue (239 Hz) which requires two mutually trans phosphine ligands. The IH N M R spectrum shows a hydride of intensity = 1 (doublet of doublets), two PMe doublets, and four P'Bu doublets. The inequivalent P'Bu groups show that the molecule has no mirror plane of symmetry containing the P-Ru-P ( I ) Grushin, V. V.; Alchrem, I. S.;Vol'pin, M. E. J . Organomet. Chem. 1989, 371, 403. (2) Grushin, V. V.; Vymenits, A. B.; Vol'pin, M. E. J. Organomer. Chem. 1990, 382, 185. (3) E.&, RhHCI?PI N R , RhClP, [HNR,]CI. This reaction is a
+
-
+
probable mechanistic step in certain examples of heterolytic splitting of H?. See: Brothers, P. J . f r o g . Inorg. Chem. 1980, 28, I . (4) Hartwig, J. F.; Andersen, R. A.; Bergman, R. G. J . A m . Chem. SOC. 1991,113,6492. See also: Koola, J. D.; Roddick, D. M. J . Am. Chem. SOC. 1991, 113, 1450. (5) Norton, J. R. Acc. Chem. Res. 1979, 12, 139. (6) Baker, M. V.; Field, L. D. J. Am. Chem. SOC.1986,108,7433, 7436. (7) An exception is the transient Fe(dmpe)? derived from FeCl?(dmpe)?,
where the high energy input comes from the N a / H g reagent. See: Chatt, J.; Davidson. J. M. J . Chem. SOC..Chem. Commun. 1965, 843. (8) Steric 'pressure" can facilitate the production of unsaturated Os(0). See: Ermer, S. P.; Shinomoto, R. S.; Deming, M. A.; Flood, T. C. Orgonomerallics 1989,8, 1377. Shinomoto, R. S.;Desrosiers, P. J.; Harper, T . G. P.; F1ood.T. C. J. Am. Chem.Soc. 1990, 112, 704. (9) Gill, D. F.;Shaw, B. L. Inorg. Chim. Acra 1979.32.19. Thiscompound has Y( (,= 1904 cm I . (IO) ' H N M R ( 5 0 0 MHz, 25 "C, COD,): b 4.56 (m, 1 H), 3.07 (d, JIIII = 7.0 Hz, 1 H), 2.10 (m, I H ) , 1.75 (1, J11l1= 2.3 Hz, 1 H ) (all are allylic, = 1 1.5 together with one more masked by a 'Bu resonance), 1.34 (d, P'Bu, JI'II Hz, 9 H), 1.32 (d. P'Bu, JI~I = 11.3 Hz, 9 H ) , 1.30 (d, P'Bu, JPII= 11.6 Hz, 9 H), 1.07 (d, P'Bu, Jl.11= 12.2 Hz, 9 H ) , 0.81 (d, PMe, 51'11= 5.5 Hz, 3 H), 0.63 (d, PMe, J I =~4.6~Hz,~3 H), -8.77 (dd, Ru-H, JI.lI = 23.5, 31.5 Hz. 1 H). ' l P ( l H ) N M R(146MHz,C,,D,,): 663.52,61.92. I R v ( C 0 ) (inC,D,,): 1887.
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I
When the reaction is repeated under the above conditions using RuD(Cl)(CO)P2, LiC(CH&, and H3CCHCH2, product I is devoid of deuterium (IH and 2H N M R evidence), which rules out a mechanism where 'BuLi deprotonates either free or coordinated pr0py1ene.I~ It also shows that there is no oxidative addition of the allylic C-H bond when deuteride is still on the metal (these would probably scramble in the Ru(D)(H)(allyl) fragment). Variable-temperature 31P(1H)N M R spectroscopy is useful in identifying the product of reaction of RuHCl(CO)P2 and 'BuLi. At or below 4 0 OC, there is complete conversion to a single species exhibiting a sharp singlet at 70.2 ppm.15 This species is stable for at least 1 h at 4 0 "C. At -10 "C, within 3 h, there is clean conversion to a mixture whose 3lP(lH) N M R spectrum consistsof threesignals between 57.2and 57.4ppm. Thesesignals are similar to the single resonance for the product (RuH( C ~ H S ) ( C O ) Pof~reactionof ) PhLi and RuHCl(C0)Pzin pentane at -10 "C.I6 The 70.2 ppm species thus oxidatively adds toluene solvent. Addition of propylene at 4 0 OC to the species with the 70.2 ppm 31P N M R signal provides immediate, complete conversion to I.)' The same (70.2 ppm) species is also produced from RuHCl(CO)P2 and'BuLi in pentanesolvent, ruling out any form of toluene being present in this species. When the reaction is carried out under the same conditions with R U H F ( C O ) P ~ ~ ~ instead of RuHCl(CO)P2, the same 70.2 ppm signal is observed and no trace of a doublet structure from coordinated fluorine can be detected. This proves that halide is not present in the species showing the 70.2 ppm 3IP N M R signal. Additionally, when the reaction between RuDCI(CO)P2 and 'BuLi is also monitored by 2H N M R spectroscopy at 4 0 "C, only (CH3)jCD is detected.19 ( 1 1) The identity of this product is supported by independent synthesis of the same material from RuHCI(CO)P? and allyl MgCI. (12) The 31PNMRinequivalenceofthephosphorusnucleiat25 'Cindicates slow interconversion between the structureshown and that with the allyl group pointing toward the other phosphine. The JlP(lH)N M R spectrum shows that thecompounddecompnses (-60 'C) beforesiteexchangebeginstobeevident. (13) For other hydrido allyl compounds, see: McGhee, W.D.; Bergman, R. G. J . A m . Chem. SOC.1988, 110. 4246. Zhuang, J.-M.;Sutton, D. P. Organometallics 1991, 10, 1516 and references therein. (14) There is no evidence ("P N M R ) for propylene binding to RuHCI(CO)P? at -80 'C in toluene-&. (15) The ' l P ( i H )N M R signal of RuHCI(C0)P: is broad at 4 0 'C and below due to slowing of rotation about the Ru-P bonds. Since the 70.2 ppm signal is sharp, it is less crowded than the five-coordinate precursor. (16) This compound transforms further in pentane at 20 OC within 1 h to a variety of uncharacterized products. (17) (a) The 70.2 ppm species is also converted to RU(H)?(H?)(CO)P?I'~ by addition of an excess of H ? at 4 0 'C. (b) Gusev, D. G.; Vymenits. A. B.; Bakhmutov, V. 1. Inorg. Chem. 1992. 31, I . (18) This compound shows a J(P-F) of 24 Hz (J. Poulton, private communication). (19) The absence of Me?CCHD indicates that reversible @-hydrogen elimination from a Ru'Bu intermediate is not involved.
OOO2-7863/93/1515-3354$04.00/00 1993 American Chemical Society
Communications to the Editor
Taken together, these results are consistent with identifying this 70.2 ppm species as [RU(CO)P~],.*~ That a hydride and an allyl ligand are formed in this reaction emphasizes the high reactivity of the intermediate produced from 'BuLi and RuHCl(C0)Pz. A 16-electron reagent (ML,) cannot oxidatively add propylene and form an q3-allyl hydride product without dissociation of ligand L. A 14-electron intermediate does have this Dehydrohalogenation is a perhaps underuti(20) Two referees feel that the -70 "C species could be the five-coordinate product of oxidative addition of a 'BuP C-H bond (with the requirement that such oxidative addition is rapidly reversible at -70 "C). We feel this to be unlikely since metalation will move the phosphorus chemical shift at least SO ppm upfield, requiring a rate of 10' s I to achieve coalescence.
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J . Am. Chem. SOC..Vol. 115, No.8, 1993 3355
lized method of producing, under very mild conditions, molecules with a useful combination of characteristics: unsaturated, lowvalent, and neutral. We are currently probing the limits of base strength which will permit this dehydrohalogenation and the range of C-H bond types which can be attacked. Acknowledgment. This work was supported financially by the National Science Foundation and materially by Johnson Matthey/ Aesar. We thank Helmut Rothfuss, Jason Poulton, Joe Kolis, and Bryan Hauger for useful insights and suggestions. (21) For an example of intramolecular C-H bond cleavage from the unsaturated (photogenerated at 260 nm) species Fe(CO),(propene), see: Barnhart, T. M.; McMahon, R. J. J . Am. Chem. SOC.1992, 114. 5434.
