584
Organometallics 1986, 5 , 584-585
carbonyl d i m e r ~ . ~An J ~ important consequence of this mechanism is that only two of the carbonyls ( x and y, Scheme 11) exchange between the two metals while the third ( 2 ) remains terminally bound in a position "trans" to the phosphine. Thus, in the 13CNMR spectrum, carbonyl x and y should give rise to a singlet and a doublet tJcp) a t the low-temperature limit and to a doublet ( J '/JrP) a t high temperature, while carbonyl z should remain a singlet throughout. confirmation of these predictions was accomplished by acquisition of variable-temperature (-75 "C to +55 "C) 13C NMR data for I3CO-labeled 5." Line-shape analysis'2 of the four spin system, assuming exchange between only two spins as dictated by the proposed mechanism, allowed calculation of the activation parameters for the fluxional process: AGtZg8= +12.0 (1)kcal mol-l, AH* = +8.8 (2) kcal mol-', and AS* = -10.6 (1.0) eu. A bridging dicarbonyl intermediate or transition state of the type depicted in Scheme I1 has never been observed in any of the other known carbonyl FvM, complexes, unlike the situation encountered in the CP,M,(CO)~ (M = Fe, Ru) dimers where it is thermodynamically stable.Ioa Acknowledgment. This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Chemical Sciences Division of the U S . Department of Energy, under Contract DE-AC03-76SF00098. W.B.T. is the recipient of a W. R. Grace Fellowship (1984-1985) and K.P.C.V. is a Miller Research Professor in Residence (1985-1986). Support from Nicolet Instruments, Madison, WI, is gratefully acknowledged by R.B. as well as the assistance of D. Blaser (University of Essen). Supplementary Material Available: Listings of positional a n d thermal parameters, bond lengths a n d angles, and structure factors of 6, variable-temperature 13C NMR spectra of 13CO-labeled 5 , a n d melting point, spectral, a n d analytical d a t a on 4-6 a n d 8 (48 pages). Ordering information is given on any current masthead Page. (9) Adams, R. D.; Cotton, F. A. J . Am. Chem. Soc. 1973, 95,6589. (10) (a) Gansow, 0. A,; Burke, A. R.; Vernon, W. D. J. Am. Chem. Soc. 1976,98,5817. (b) Haines, R. J.; DuPreez, A. L. Inorg. Chem. 1969,8, 1459. Adams, R. D.; Brice, M.; Cotton, F. A. J . Am. Chem. SOC.1973,95, 6594. Kirchner, R. M.; Marks, T. J.; Kristoff, J. S.; Ibers, J. A. Ibid. 1973, 95,6602. Howell, J. A. S.; Rowan, A. J. J . Chem. Soc., Dalton Trans. 1980,1845. (11) 'jCO-labeled 5 was prepared via the reaction of PEt, with ':'COlabeled 3,which was in turn synthesized from the reaction of I3CO with 3 (50 psi of I3CO, 130 "C, THF, 50 h, approximately 20% incorporation by IR and I3C NMR). (12) Line-shape analysis was performed at the UCB Computer Center using DYXAMAR, a modified version of a program developed by: Meakin, P.; Muetterties, E. L.; Tebbe, F. N.; Jesson, J. P. J . Am. Chem. SOC.1971, 93,4701. Jesson, J. P.; Meakin, P. Acc. Chem. Res. 1973,6.269. Data were plotted according to the Eyring equation In (nhk/khT)= -AH*/RT + S * / R and fitted to a straight line using linear least-squares program ACTPAR: a modified version of a program developed by: Binsch, G.; Kessler. H. Angeu. Chem.. Int. Ed. Engl. 1980, 19, 411.
Reaction of a p-Ethenylidene Diiron Complex with Ethyl Dlazoacetate Charles P. Casey' and Edwln A. Austin Department of Chemistry, University of Wisconsin Madison, Wisconsin 53706 Received October 8, 1985
Summary: The g-ethenylidene complex [(C,H,)(CO)Fe] 2(p-C=CH2)(2) reacted with ethyl diazoacetate in the presence of CUI to produce the cyclopropylidene com0276-7333/S6/2305-0504$01.50/0
plex [(C,H,)(CO)Fe] ,(p-CO)(p-CCH2CHC02Et) (3). Cyclopropylidene complex 3 underwent acid-catalyzed ring opening to give palkenylidene compound [(C,H,)(CO)(5). Photolysis of 2 and ethyl Fe] ,(pC=CHCH,CO,Et) diazoacetate gave the allene complex [(C,H,)(CO)Fe] 2(/L-CH,=C=CHCO~E~) (6).
For the past several years, we have been studying new carbon-carbon bond-forming reaction of diiron complexes with bridging hydrocarbon ligands. We discovered the addition of the C-H bond of the cationic bridging methylidyne complex [ (C,H,)(CO)Fe],(p-CO)(p-CH)+ (1) across the carbon-carbon double bond of alkenes which produces new p-alkylidyne complexes.lJ We have also found that neutral p-alkenylidene complexes (in equilibrium with cationic p-alkylidyne complexes) condense with aldehydes under acidic conditions to produce vinylcarbyne diiron complexes.3 Hoel's recent report* of the coppercatalyzed cyclopropanation of the p-ethenylidene complex (CjH5)2(CO)zFe,(p-CO)(p-C=CH2) (2) with diazomethane sparked our interest in the reactions of diazoesters with p-alkenylidene complexes. Here we report three different selective reaction pathways for the reaction of p-ethenylidene complex 2 with ethyl diazoacetate that lead to bridging cyclopropylidene, alkenylidene, and allene complexes. Ethenylidene complex 2 reacts with ethyl diazoacetate only in the presence of a copper catalyst or upon photolysis. Ethenylidene complex 2 (250 mg, 0.71 mmol), excess ethyl diazoacetate (2.8 mmol), and CUI (1.3 mmol) were heated in 50 mL of refluxing CH2C1, for 19 h. After filtration and evaporation of solvent the oily residue was crystallized from hexane-CH2C1, to give a single isomer of the cyclopropylidene complex 3 (185 mg, 60%).5 In the 'H NMR of 3, the ABC pattern of the cyclopropane hydrogens (Jcis = 8.0 Hz, Jtrans = 4.5 Hz, J,,, = -8.5 Hz) helped to establish the structure of 3. In the IR spectrum
(1)Casey, C. P.; Fagan, P. J. J . Am. Chem SOC.1982,104, 4950. ( 2 ) Casey, C. P.; Fagan, P. J.; Miles, W. H.; Marder. S. R. J . Mol. Catal. 1983, 21, 173. (3) Casey, C. P.; Konings, M. S.; Palermo, R. E.; Colborn, R. E. J . Am. Chem. Soc. 1985, 107, 5296. (4) Hoel, E. L.; Ansell, G. B.; Leta, S. Organometallics 1984,3,1633. (5)3,major isomer: 'H NMR (acetone-d,, 270 MHz) 6 4.84 (s, CsH,), 4.80 (s, C,H,), 4.05 (dq, J = 11.0, 7.2 Hz, OCHHCH3), 3.94 (dq, J = 11.0, 7.2 Hz, OCHHCHJ, 2.67 (dd, J = 8.0, 4.5 Hz, CHCO,Et), 2.56 (dd, J = -8.5, 8.0 Hz, CHHCHC02Et), 2.53 (dd, J = -8.5, 4.5 Hz, CHHCO,Et), 1.13 (t, J = 7.2 Hz, CHJ. I3C NMR (acetone-d,, 0.07 M Cr(acac),, 50.1 MHz) 6 269.9 (w-CO),213.0 (CO), 212.3 (CO), 175.2 (CO*), 155.9 (w-C), 89.8 (d, J = 183 Hz, C5H5),89.5 (d, J = 180 Hz, C5H5),5.97 (t, J = 148 Hz, CH2CH3), 34.0 (t, J = 165 Hz, CCH,CH), 32.7 (d, J = I70 Hz, CHCO,Et), 14.3 (4, J = 125 Hz, CH,); IR (CH2C1,) 1999 (4, 1957 (m), 1788 (m), 1704 (m) cm-'; HRMS calcd for C,9Hl,Fe20j 437.9847, found 437.9852. 4, minor isomer: 'H NMR (acetone-d,, 270 MHz) 6 4.75 (s, C5HJ, 4.70 (s, C5H5),4.14 (m, OCH2),2.95 (dd, J = 8.5, 4.9 Hz, 1 H), 2.48 (dd, J = 8.5, 4.9 Hz, 1 H), 2.37 (t, J = 8.5 Hz, 1 H), 1.20 (t, J = 6.8 Hz, CH,)
0 1986 American C h e m i c a l S o c i e t y
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 a t 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 a t 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 a t 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. SOC. 1980, 102,403. (9) Bailey, W.I., Jr.; Chisholm, M. H.; Cotton, F. A.; Murillo, C. A.; Rankel, L. A. J. Am. Chem. SOC.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:
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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 cyclopropylidenecomplexes 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 a t about 60 "C. An equilibrium appeared to be established after about 30 min a t 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 a t 125 " C the only significant carbonyl bands were those for 4. Upon cooling, 4 crystallizes from the solution and could be isolated in
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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
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