Organometallics 1986, 5, 585-587
of 3, an intense band at 1999 cm-' and a weak band at 1957 cm-' established the presence of cis terminal carbonyl groups. 3 is most likely the stereoisomer shown since this structure has the ester group in the least congested site. When the conversion of 1 to 3 was followed by NMR, a second diastereomer, 4,5was seen at early times but it was eventually converted to 3. Cyclopropylidene complex 3 undergoes regiospecific acid-catalyzed cyclopropane ring opening upon exposure to acidic conditions. For example, attempted chromatography of 3 on silica gel led to isolation of alkylidene complex b6 in 45% yield from 2. Treatment of 3 with HBF4 in diethyl ether also led to ring opening to 5. This regiospecific ring opening is best explained by initial protonation a t the ester carbonyl group. Photolysis of a solution of 2 (20 mg, 0.57 mmol) and ethyl diazoacetate (3.4 mmol) in CHzClz at 0 "C for 4 h gave no detectable cyclopropylidene complex 3. Instead, the only product seen by IR and by 'H NMR was the novel allene complex 6.7 In the formation of 6, one CO is lost. The complex contains only terminal CO groups [IR (CH,Cl,) 1974 (s), 1921 (s), 1693 (s) cm-'I. In the 'H NMR of 6, the hydrogens on the complexed allene give rise to three separate doublets of doublets at 6 3.29 (J = 1.2, 2.3 Hz), 3.49 ( J = 4.1, 2.3 Hz), and 3.84 ( J = 4.1, 1.2 Hz). Related dimanganese,6 d i m ~ l y b d e n u mand , ~ diiron complexesl0 are known. The possibility that photolysis of 2 and ethyl diazoacetate initially produces cyclopropylidene complex 3 which then photolytically ring opens to give allene complex 6 can be rejected on the basis of two observations. First, during the photolysis of 2 and the diazo ester, none of the cyclopropylidene complex 3 was detected by lH NMR. Second, while photolysis of the cyclopropylidene complex 3 slowly produces allene complex 6, the rate of conversion of 3 to 6 is much slower than the rate of formation of allene complex 6 from 2. We suggest that under photolysis 2 loses CO prior to reaction with ethyl diazoacetate to generate a complex containing a carbomethoxy carbene ligand and an ethenylidene ligand which then couple to produce a complexed allene. Acknowledgment. Support from the National Science Foundation is gratefully acknowledged. We thank Dr. Elvin Hoel for keeping us informed of his related studies. Registry No. 2, 86420-26-0; 3, 99326-80-4; 4, 99395-44-5; 5, 99326-81-5; 6,99326-82-6; Nz=CHCOZEt, 623-73-4; CUI, 7681-65-4. (6) 5: 'H NMR (acetone-d,, 270 MHz) 6 7.16 (dd, J = 7.9, 6.8 Hz, C=CH), 5.04 (s, C5H5),4.93 (s, C,H,), 4.16 (q, J = 7.1 Hz, OCH2),3.74 ( d a , J = 15.2, 7.9 Hz,CHCHH), 3.62 ( d a , J = 15.2,6.8 Hz, CHCHH),1.26 (t, 3 = 7.1 Hz, CH,); 13C{1H} NMR (acetone-d,, 0.07 M Cr(acac),, 50.1 MHz) 6 270.4 (u-CO).270.1 (u-C). 212.7 (CO). 212.5 (CO). 173.3 ((20,). 131.6 (CH), 89.0 (C,H5), 88 2 (C,H,), 60.6 (CH,CH,), 42 7 (CHCHJ, 16.7 (CH,); IR (CH,Cl,) 2000 (s), 1962 (m), 1790 (s), 1720 (m) cm-'; HRMS calcd for C,sH,aFelOK437.9847. found 437.9853 (7) 6: 'H"NMRia&tone-d,, 200 MHz) 6 4.39 (s, C,H5), 4.28 (s, C5H5), 4.06 (4, J = 7.1 Hz, OCH,), 3.84 (dd, J = 4.1, 1.2 Hz, 1 H), 3.49 (dd, J = 4.1, 2.3 Hz,1 H), 3.29 (dd, J = 1.2, 2.3 Hz,1 HI,1.24 (t, J = 7.2 Hz, CH,); NMR (acetone-d,, 0.07 M Cr(acac),, 50.1 MHz) 6 227.8 (CO), 226.5 (CO), 219.3 (p-C), 173.2 ( C O J , 83.6 (d, J = 176 Hz, C,Hj), 59.9 (t, J = 146 Hz, CHZCH,), 36.2 (t, J = 150 Hz, =CHp), 34.6 (d, J = 168 Hz, =CHCOJ, 15.0 (q,J = 128 Hz, CHJ; IR (CHzClJ 1947 (E), 1921 (s), 1693 (s) cm-*; HRMS calcd for C18H,8Fe204409.9904, found 409.9911. (8) Lewis, L. N.; Huffman, J. C.; Caulton, K. G. J. Am. Chem. S O C . 1980, 102,403. (9) Bailey, W.I., Jr.; Chisholm, M. H.; Cotton, F. A.; Murillo, C. A.; Rankel, L. A. J. Am. Chem. S O C .1978. 100. 802. Dohertv. N.M.: Elschenbroich, C.; Kneuper, H.-J.; Knox, S. A. R. J. Chem.-Soc., Chem. Commun. 1985, 170. (10) Hoel, E. L.;Ansell, G. B.; Leta, S. Organometallics, following paper in this issue.
585
Thermal and Photochemical Rearrangements of a Bridging Cyciopropyiidene Ligand to Aliene in a Diiron Complex Elvln L. Hoel," Gerald B. Ansellt and Susan Letat Corporate Research Science Laboratories and Analytical Division Exxon Research and Engineering Company Annandale, New Jersey 0880 1
Summary:
-
Received October 21, 1985
The bridging cyclopropylidene ligand in
Cp,Fe,(CO),(p-CCH,CH,) (Cp = q5-C,H,) rearranges at 100 OC or photochemically at 10 OC to the thermally unstable allene complex Cp,Fe,(CO),(p-CH,=C=CH,). The relevance of this chemistry to a recently proposed Fischer-Tropsch mechanism is discussed.
We recently prepared diiron cyclopropylidene complexes so that the chemistry of the previously unknown cyclopropylidene ligand could be studied as a model for the novel methylene/vinylidene Fischer-Tropsch mechanism proposed by McCandlish (Scheme I).l The complexes IC and It (with CO and Cp (Cp = 775-C5H5)ligands cis and trans, respectively, to the plane of the metal atoms and bridging ligands) were prepared by reaction of the corresponding p-vinylidene complexes 2c and 2t with diazomethane in the presence of CuCl,, a synthesis formally equivalent to A B. We find that the thermal and photochemistry of 1 do not support the proposed mechanism; however, as detailed in the accompanying communication, hydrocarbon chains can be grown via cyclopropylidene intermediates by using protonation/deprotonation chemistry to effect the rearrangement of the homologous vinylidene ligand.3 Solutions of IC or I t in octane were heated under argon and the couse of reaction was followed by IR spectroscopy. The first observed change was interconversion of the cis and trans isomers, beginning at about 60 "C. An equilibrium appeared to be established after about 30 min at 80 "C. At about 100 "C two new peaks, subsequently identified as belonging to 3 (see below), began to show at 1939 (m) and 1919 (s) cm-'. At 125 "C, bands due to Cp2Fez(C0)4(2006 (w), 1959 (s), 1793 (s) cm-l) (4) began to appear. The bands for 3 appeared to reach a steadystate concentration while the bands for 1 disappeared and those for 4 grew. After several hours at 125 " C the only significant carbonyl bands were those for 4. Upon cooling, 4 crystallizes from the solution and could be isolated in
-
Scheme I RH&\ Linear
H ,
s A,, C
Branched Growth
* Corporate
Research Science Laboratories.
* Analytical Division.
0276-7333/86/2305-0585$01.50/0 0 1986 American Chemical Society
R, ,CH3
F
-774D777
586 Organometallics, Vol. 5, No. 3, 1986
Communications Scheme I1
C
hea/
\&+
A'
co
'c/ 0
'fl
IC
80°C
-Fe
, /
H,C-CH, oc%F,F 'e\-e \/,
2c
/ \
Fe
11
It
yields up to 80% of theoretical based on CO. When argon was bubbled through the solution at reflux, the gaseous products were swept into a sampling bag. GC analysis identified allene as the only significant hydrocarbon product, in isolated yields up to 47 % . When the thermolysis was done under a CO atmosphere, 4 was isolated from the solution in 86% yield (based on Fe) and allene was still the only significant gaseous product. Complex 3 was obtained in good yield by the photolysis of IC in T H F solution a t 10 "C (1.0 g of IC dissolved in 350 mL of T H F and exposed to a 450-W Hg lamp for 1 h) followed by chromatography on alumina II.* Dark green prisms were obtained by recrystallization from hexane at low temperatures. The IR and 'H NMR spectra of 35 were consistent with the structure confirmed by X-ray crystallography (see supplementary material) and shown in Figure 1. This allene complex is similar in structure and 'H NMR spectrum to known dimolybdenum6 and dimanganese' complexes of allene. Solutions of complex 3 decompose slowly at room temperature and faster at elevated temperatures to liberate allene and deposit an insoluble brown powder, which has not been further characterized. Examination of the photolysis solution by IR spectroscopy early in the conversion shows that the rearrangement to the allene ligand is preceded by a very rapid equilibration of IC with It. This is especially evident when starting with It, as the equilibrium ratio of 1c:lt is about 4.8:1.* In light of a recent report that cationic cyclopropylidene complexes, including [CpFe(CO),(=CCH,CH,)]+ ( 5 ) , re-
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(1) McCandlish, L. E. J . Catal. 1983, 83, 362-370. (2) Hoel, E. L.; Ansell, G. B.; Leta, S. Organometallics 1984, 3, 1633-1637. (3) Hoel, E. L. Organometallics, third of three papers in this issue. (4) A substituted allene complex has been synthesized directly from the photochemical reaction of ethyl diazoacetate with 2. Casey, C. P.; Austin, E. Organometallics, first of three papers in this issue. (5) CpzFe,(CO),(p-H2C=C=CH2) (3): IR (hexane) 1939 (m), 1919 (s) em-'; 'H NMR (400 MHz, CDC1,) 6 4.24 (s, 10 H, Cp), 3.41 (dd, J = 2.4, 2.7 Hz, 1 H, AA'), 2.89 (dd, J = 2.4, 2.7 Hz, 1 H, XX'); l3CI1HJNMR (75 MHz, CD,Cl,) 6 227.73 (CO), 216.08 (=C=), 82.70 (Cp), 30.17 ICH,). (6) (a) Bailey, W. I., Jr.; Chisholm, M. H.; Cotton, F. A.; Murillo, C. A,; Rankel, L. A. J . Am. Chem. SOC. 1978,100,802-807. (b) Doherty, N. M.; Elschenbroich, C.; Kneuper, H.-J.; Knox, S. A. R. J . Chem. Soc., Chem. Commun. 1985, 170-171. (7) Lewis, L. N.; Huffman, J. C.; Caulton, K. G. J . Am. Chem. SOC. 1980, 102, 403-404.
>1ooocp
H,C =C =CH,
[ ] 3
+
-b
Cp,Fez(CO), 4
+
\
-\
insolubles
t
J
Figure 1. Structure of 3, Cp2Fe2(C0)2(H,C=C=CH2). Bond
lengths (A): Fe(l)-Fe(2) = 2.689 (l),Fe(l)-C(3) = 2.100 ( 5 ) , Fe(2)4(5) = 2.095 (4), Fe(l)-C(4) = 1.908 (4),Fe(2)4(4) = 1.929 (4), Fe(l)-C(l) = 1.737 (5), Fe(2)-C(2) = 1.738 (4), C(3)-C(4) = 1.342 (7), C(4)-C(5) = 1.416 ( 7 ) ,C(1)-O(1) = 1.160 ( 5 ) , and C(2)-0(2) = 1.151 (5). Angles (deg): C(3)-C(4)-C(5) = 146.8 (4) and Fe(l)-C(4)-Fe(2) = 89.0 (2).
arrange very rapidly to allene complexes,s it is interesting that both thermal and photochemical cis/ trans equilibrations proceed so readily relative to rearrangement to the allene complex. As isomerization probably involves species with terminal cyclopropylidene ligands as interm e d i a t e ~ , ~the , ' ~implication is that cyclopropylidene is a rather stable ligand in neutral complexes. The difference, we believe, is a consequence of the expected instability of the cyclopropyl cation resonance structure of 5, a cation which in the organic analogue opens exceedingly easily to the allyl cation." It should be clear that the chemistry of cyclopropylidene (8) Lisko, J. R.; Jones, W. M. Organometdllics 1985, 4, 612-614. (9) Thermal isomerization: (a) Dawkins, G. M.; Green, M.; Jeffery, J. C.; Sambale, C.; Stone, F. G. A. J . Chem. SOC.,Dalton Trans. 1983, 499-506. (b) Evans, J. Adu. Organomet. Chem. 1977, 16, 323-326. (10) Although the photoisomerization may occur similarly to the thermal, it might instead proceed according to the photochemical reactions of CpzFez(CO),, i.e. by breaking the Fe-Fe bond and moving the bridging carbonyl to a terminal positicn, leaving the cyclopropylidene in a bridging position during C-Fe bond rotation: Tyler, D. R.; Schmidt, M. A,; Gray, H. B. J . Am. Chem. Soc. 1983, 105, 6018-6021. (11) Olah, G. A,; Liang, G.; Ledlie, D. B.; Costopoulos, M. G. J . Am. Chem. Soc. 1977, 99, 4196-4198.
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 masthead page.
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.
0276-7333/86/2305-0587$01.50/0
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
/\
Fe-Fe
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
