Organometallics 1986,5, 587-588 in this soluble diiron complex is not necessarily the same as that which could occur on heterogeneous FischerTropsch synthesis catalysts. Nonetheless, the availability of a low-energy, thermal pathway to allene reduces the likelihood that the cyclopropylidene pathway is a major contributor to Fischer-Tropsch synthesis. Further investigations to define the general scope of this chemistry and mechanistic details for the thermal, photochemical, and protonation/deprotonation pathways for hydrocarbon ligand rearrangements are in progress, not only for the diiron system but also for similar diruthenium and dicobalt cyclopropylidene complexes.
Acknowledgment, We are indebted to Dr. Larry McCandlish and Prof. John Bercaw for helpful discussions. The laboratory assistance of E. G. Habeeb is also gratefully acknowledged. Registry No. IC, 91547-48-7; It, 91443-97-9;3,100021-54-3; 4, 12154-95-9; Fe, 7439-89-6; H,C=C=CH2, 463-49-0. Supplementary Material Available: Preliminary crystal structure results for 3 and tables of atomic positional and thermal parameters, bond lengths, bond angles, and structure factor amplitudes (16 pages). Ordering information is given on any current
587
Fe 2c
- Fe
Fe - Fe /
3
f
\
5
H2C=CH,
H
A@ /\
Fe - Fe 4
Scheme I1
H,
/CHI C
II
C
I \
Fe-Fe 5
I
C'B
/\
masthead page.
Fe-Fe
Protonation/Deprotonatlon Rearrangements of Bridging Cyclopropylidene Ligands In Dilron Complexes. Stepwise Hydrocarbon Chain Growth via Cyclopropylldene Intermedlates Elvln L. Hoe1 Corporate Research Science Laboratories Exxon Research and Engineering Company Annandale, New Jersey 0880 1 Received October 21. 1985
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Summary: Protonation of the bridging cyclopropylidene ligand in Cp,Fe,(CO),(p-CCH,CH,) leads to the bridging propylidyne complex [Cp,Fe,(CO),(p-CCH,CH3)] which when deprotonated provides the methylvinylidene Cp,Fe,(CO),(p-C=CHCH,). Cyclopropanation of this vinylidene ligand followed by protonation/deprotonation leads exclusively to the dimethylvinylidene complex; none of the linear ethylvinylidene is formed. +
In the preceding communication,' we reported on the thermal and photochemical rearrangement chemistry of the bridging cyclopropylidene ligand in Cp,Fe,(CO),(pCO)(p-CCH,CH,) (2) (Cp = q5-CsHs)which was synthesized from the reaction of diazomethane with Cp2Fe2(CO),(p-CO)(p-C=CH,) (1)2 to model the novel methylene/vinylidene Fischer-Tropsch mechanism proposed by M~Candlish.~ Although the thermal and photochemistry of 2 do not support the proposed mechanism, we find that hydrocarbon chains can be grown via cyclopropylidene intermediates, by using protonation/deprotonation chemistry to effect the rearrangement to the homologous vi-
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(1) Hoel, E. L.; Ansell, G. B.; Leta, s. Organometallics, second of three papers in this issue. (2) Hoel, E. L.; Ansell, G. B.; Leta, S. Organometallics 1984, 3, 1633-1637. (3) McCandlish, L. E. J . Catal. 1983, 83, 362-370.
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nylidene ligand. Employment of this route through several stepwise cycles, however, results in the exclusive formation of the branched hydrocarbon chain, in contrast to the primarily linear chain growth observed in Fischer-Tropsch ~ynthesis.~,~ Protonation of 2 with strong acids such as HBFl or CF3COOH gives the propylidyne complex 3 in high yield. This is consistent with Casey's suggestion that an edgeor corner-protonated form of 2 might be a possible intermediate in the hydrocarbation reaction of ethylene with the methylidyne complex 4.5 NMR experiments with CF3COOD as the proton source confirm that the added proton ends up on the methyl of the propylidyne ligand. Bridging alkylidynes in this system are readily deprotonated with a variety of bases to give the bridging vinylidene c o m p l e x e ~ . ~In , ~this instance, 3 is deprotonated to yield the methylvinylidene complex 5,' which is the rearranged hydrocarbon species equivalent to C in Scheme I of the preceding communication.l Thus, although the cyclopropylidene ligand does not rearrange to the homologous vinylidene either thermally or photochemically, it does so rearrange via a protonation/deprotonation sequence.8 (4) Pichler, H.; Schulz, H.; Kuhne, D. Brennst.-Chem. 1968,49, 344. (5) (a) Casey, C. P.; Fagan, P. J. J. Am. Chem. SOC.1982, 104, 4950-4951. (b) Casey, C. P.; Fagan, P. J.; Miles, W. H.; Marder, S.R. J. Mol. Catal. 1983,21, 173-188. (6) (a) Dawkins, G. M.; Green, M.; Jeffery, J. C.; Sambale, C.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1983,499-506. (b) Kao, S. C.; Lu, P. P. Y.; Pettit, R. Organometallics 1982,1,911-918. (c) Diazomethane also deprotonates 3 to give 5; Hoel, E. L., unpublished results. (7) cis-CpzFez(C0)z(~-CO)(~C=CHCH3) (5): IR (hexane) 2000 (vs), 1966 (m), 1805 (s), 1612 (w) cm-'; 'H NMR (400 MHz, CDC13)6 7.14 (9, J = 6.6 Hz, 1 H, =CH-), 4.83 (8,5 H, Cp), 4.75 (s, 5 H, Cp), 2.38 (d, J = 6.6 Hz, 3 H, CH,). Anal. Calcd for C16H,,03Fe2:C, 52.51; H, 3.86; Fe, 30.52. Found C, 52.31; H, 3.72; Fe, 30.33. (8) A substituted cyclopropylidene complex has been prepared from 1 and ethyl diazoacetate. This complex readily rearranges over silica gel t o the linear vinylidene, presumably via a protonation/deprotonation pathway. Casey, C. P.; Austin, E. Organometallics, first of three papers in this issue.
0 1986 American Chemical Society
Organometallics 1986, 5 , 588-590
588
The cycloprotonation process can be repeated to give the methylcyclopropylidene complex 6.' A t this point, protonation might possibly lead to either the linear (7) or the branched (8) alkylidyne complex, or both, depending on the selectivity of the proton attack. As shown in Scheme 11, we find that attack is selectively at the less substituted carbon, none of the linear isomer is visible in the 'H NMR spectrum of a solution obtained by addition of CF3COOH to 6 in CDC1,. The isobutylidyne complex is seen to be in equilibration with the dimethylvinyl complex 9,1°with an equilibrium ratio of 8:9 = 2:3. Casey found this equilibration to be a general feature of alkylidynes with tertiary carbons next to the bridging carbon atom." Deprotonation of the mixture of cationic complexes led exclusively to the branched vinylidene complex 1012-none of the linear isomer 11 could be detected by 'H NMR. The pentylidyne analogue of 7, prepared by different routes, has been shown to deprotonate smoothly to the linear vinylidene without rearrangement.",13 Further investigations to define the general scope of this chemistry and mechanistic details for the thermal, photochemical, and protonationjdeprotonation pathways for hydrocarbon ligand rearrangements are in progress, not only for the diiron system but also for similar diruthenium and dicobalt cyclopropylidene complexes. However, the facile, low-energy chemistry of the cyclopropylidene ligand in this diiron system, rearranging readily to allene via thermal and photochemical processes' and leading exclusively to branched vinylidene ligands via the protonation/deprotonation pathway, argues against the cyclopropylidene pathway as a major contributor to a Fischer-Tropsch synthesis on heterogeneous catalysts. Acknowledgment. We are indebted to Dr. Larry McCandlish, Dr. Tom Upton, and Prof. John Bercaw for helpful discussions. The laboratory assistance of E. G. Habeeb is also gratefully acknowledged. Registry No. 2, 91547-48-7; 3, 82621-28-1; 5 , 99923-10-1; 6, 99923-11-2; 8, 99923-07-6; 9, 99923-09-8; 10, 99923-12-3.
I
(6): IR (hexane) 1993 (9) (a) cis-Cp,Fe,(C0)2(p-CO)(p-CCH,CHCH~) (vs), 1958 (m), 1798 (s) em-'; 'H NMR (400 MHz, CDCl3) 6 4.60 (s, 5 H, Cp), 4.56 (s,5 H, Cp), 2.08 (dd, J i 2 = -7.9, J1,3 = 9.7 Hz, 1 H, Hi), 1.82 (ddq, J , , = 9.7, J Z 3= 5.5, J34= 6:2 Hz, 1 H, H3), 1.49 (d, Js,4= 6.2 Hz, 3 H, H4), 1.38 (dd,'J,, = -7.9,J2,,= 5.5 Hz, 1 H, H2). Anal. Calcd for C,;H1,OIFe,: C, 53.73; H, 4.24; Fe, 29.39. Found: C, 53.55; H , 4.24; Fe, 29.62.
C-
/\ Fe-Fe (h) The X-ray crystal structure has been published: Ansell, G. B.; Leta,
S.;Hoel, E. L.; Habeeb, E. G. Acta Crystallogr., Sect. C:
Cryst. Struct.
Commun., in press. (10) (a) [Cp,Fe,(C0),(p-CO)(p-CCH(CH~)2)]+[CF3COO](8): 'H NMR (400 MHz, CDClJ 6 5.30 (s, 10 H, CP), 1.80 (d, J = 7 Hz, 6 H, CHd, septet for tertiary hydrogen not observed, presumed to be under Cp resonances. (b) [Cp2Fe2(CO),(p-CO)(~-CH=C(CH,),)IC[CF,CoO]-(9): 'H NMR (400 MHz, CDC13) 6 11.36 (s, 1 H, -CH=), 5.24 (s, 10 H , Cp), 2.31 (s, 3 H, CH,), 1.47 (s, 3 H, CH3). The presence of only one Cp resonance implies rapid oscillation of the @-vinylbonding between the metal atoms at 20 oC.5 (11) Casey, C.P.;Marder, S. R.; Fagan, P. J. J . Am. Chem. Sac. 1983. 105, '719777198. (12) cis-CpzFez(CO)z(r-CO)(@-C=C(CH3),)(10): IR (hexane): 1999 (vs), 1965 (m), 1804 (s), 1630 (w) em-'; 'H NMR (400 MHz, CDC13) 6 4.80 (s, 10 H , Cp), 2.47 (s, 6 H, CH,). (13) Hoel, E. L., unpublished results.
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Cobalt-Mediated Diene Activation: Facile Addition of Nucleophiles to [(q4-1,&Butadiene)Co( CO),]BF, Lucio S. Barinelii, Ke Tao, and Kenneth M. Nicholas* Department of Chemistry, University of Oklahoma Norman, Oklahoma 730 19 Received October 8, 1985
Summary: [(q4-l,3-Butadiene)Co(CO),] BF, (1) reacts regiospecifically by attack at the diene C-1 under mild conditions with a variety of nucleophiles including NaBH,CN(H-), pyridine, PhMgBr, and PMe, to give (anfi-q3CH,CHCHCH,Nu)Co(CO), (2). Regio- and stereospecific 1,4-difunctionaIization of butadiene can be achieved by sequential double nucleophilic addition to 1.
Although metal carbonyl r-complexes of conjugated dienes are among the oldest of organo-transition-metal compounds,' their reactivities have been surprisingly little studied. In this context it is particularly interesting to contrast recent reports of selective C-2 attack by nucleophiles on ( ~ ~ - d i e n e ) F e ( C Owith ) , ~ those of selective C-1 Described herein are attack on [CpM~(q~-diene)(CO)~]+.~ nucleophilic reactions of the parent compound (q4-butadiene)Co(CO),BF, ( 1),4isoelectronic with the prototypical diene complex (q4-butadiene)Fe(CO) [ (q4-Butadiene)Co(CO),]BF, (1) was prepared by an improved route via oxidation of [ (q4-butadiene)Co(CO),1, with (C5HS)zFeBF4.5 The high reactivity of 1 toward nucleophiles was foreshadowed by remarkably high v(C0) = 2150 and 2102 cm-' (cf. v(free CO) = 2143 cm-'). Indeed, treatment of CHBNOzsolutions or T H F or CHZC1,suspensions of 1 with various prospective nucleophiles at -78 0 "C caused generally rapid (min) disappearance of the IR bands at 2150 and 2102 cm-' and their clean replacement with two new bands at ca. 2060 and 1995 cm-', typical for (q3-allyl)Co(CO), derivative^.^ Nucleophiles found to react include pyridine, NaBH,CN(H-), PhMgBr, PMe,, PPh,, P(OMe),, NaCH(C02Me)2, (allyl)SiMe,, 1-(trimethylsiloxy)cyclohexene, and MeOH. Somewhat unstable adducts of 1 with the first four nucleophiles have been isolated in moderate to good yields, and their structures
,.
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(1) Riehlen, H.; Gruhl, A.; Von Hessling, G.; Pfengle, 0. Justus Liebigs Ann. Chem. 1930, 482, 161. (2) (a) Semmelhack, M.F.; Herndon, J. W. J . Organomet. Chem. 1984, 265,C15. (b) Semmelhack, M. F.; Herndon, J. W.; Springer, J. P. J . Am. Chem. Soc. 1983, 105, 2497. (c) Semmelhack, M.F.; Herndon, J. W. Organometallics 1983, 2, 363. (3) (a) Green, M. L. H.; Mitchard, L. C.; Silverthorn, W. E. J . Chem. Soc. Dalton Trans. 1973, 1952. (b) Faller, J. UT.; Rosan, A. M. J . Am. Chem. Soc. 1977, 99,4858, Faller, J. W.;Murray, H. H.; White, D. L.; Chao, K. H. Organometallics 1983,2, 400. (c) Pearson, A. J.; Khan, M. N. I.; Clardy, J. C.; Cun-heng, H. J . Am. Chem. Soc. 1985, 107, 2748. (4) Chaudury, F. M.; Pauson, P. L. J . Organomet. Chem. 1974, 69, C31. (5) Stirring a CHZC12solution of [(butadiene)C~(CO)~]~ (prepared from C O ~ ( C O+) butadiene ~ in 90% yield according to ref 6) with 2 molar equiv of (C,H,),FeBF, at 20 "C (for 4-6 h) under N2 followed by filtration and reprecipitation of the solid (2-3 times) from CH,N02/Et20 affords 1 as a moisture sensitive yellow solid (30-40%). Because of the deficiency of CO's, 50% is the maximum possible yield of 1 from [(C4H6)Co(CO)z]2. Running the reaction under 15-200 psi of CO had no effect on the yield. Comparable results have been obtained in the preparation of (isoprene)and (1,3-cyclohexadiene)Co(C0)3BF,.More efficient routes to 1 are being examined. 1: IR (CH,NO,) 2150,2102 (MC=O), 1050 (BF,3 cm-'; 'H NMR (CD3N02)6 6.7 (m, 2 H), 3.6 (dd, J = 3.5 Hz, 2 H), 2.5 (dd, J = 3, 10 Hz, 2 HI. (6) Fischer, E. 0.; Kuzel, P.; Fritz, H. P. 2. Naturforsch.,B: Anorg. Chern., Org. Chem., Biochem., Biophys., Biol. 1961, 16B, 138. (7) Heck, R. F.; Breslow, D. S. J . Am. Chem. Soc. 1961, 83, 1097.
0 1986 American Chemical Society
