Organometallics 1983, 2, 195-197 Scheme I
..
L"
i
L
co
2
a
L=:3
b
:=PPh3
c
LsPIOFh!3
4
L=PPhZNEt2
5-
R = C Y 2 CH=CH2
78
6
l-Ch2Ph
91
4.u.
84%
RX 32
LT&
'R
9 =Fh
aspect of the chemistry, we prepared iron acyls lc4 and ld6 but found that IC did not give a stable enolate and although Id formed a stable enolate, reaction with pivaldehyde gave only a 6040 mixture of diastereomeric aldol products 9d in 53% yield (31% recovered starting material).5 The acyl-iron bond is readily cleaved in these complexes to give high yields of esters. For example, slow addition of a CH2C12solution of N-bromosuccinimide to a solution of iron acyl 6b in 1:l CHzClz/ethanol a t -42 "C resulted in oxidative cleavage, giving ethyl dihydrocinnamate in 89% yield (eq 2). NBS
sb
The experimental procedures for the synthesis and subsequent cleavage or iron acyl 6b are typical. Diisopropylamine (190 ML,1.36 mmol) was added to a solution of n-butyllithium (825 pL of 1.6 M hexane solution, 1.32 mmol) in THF (8 mL) maintained at 0 "C under Np After the mixture was stirred a t 0 "C for 20 min, the flask was cooled in a dry ice/CH3CN bath (ca. -42 "C). To this solution of LDA was added a solution of iron acyl l b (500 mg, 1.10 mmol) in T H F (4 mL) dropwise by syringe. During the addition the initial orange color of l b turned to deep red. After the mixture was stirred at -42 "C for 90 min, the enolate was quenched by the addition of benzyl bromide (170 ML,1.43 mmol) that caused an immediate color change from red to dark orange. The reaction mixture was allowed to warm to room temperature, and after 30 min aqueous ammonium chloride (5%, 30 mL) was added followed by CHzC12(30 mL) and 1.2 N HCl(20 mL). After the organic layer was separated, the aqueous layer was extracted with CH2C12(2 X 30 mL) and the CH2C12 extracts were combined and dried over Na2S04. Filtration and removal of volatiles on a rotary evaporator left an orange oil that was chromatographed on activated alumina (2 X 15 cm, CH2C12)and gave 542 mg (91%) of iron complex 6b as a deep orange solid: mp 128-131 "C (CH2C12/petroleumether); IR (CHC13,cm-I) 3050, 3010, 1920,1600,1490,1440; 6O-MHz 'H NMR (CDC13,6) 7.6-6.8 (m, 20 H), 4.3 (d, J = 2 Hz, 5 H), 3.2-2.0 (m, 4 H). Cleavage of the metal-acyl bond was effected by dissolving (6) Prepared according to standard procedures4 from CpFe(C0)&H3 and Ph2PNEt2.
0276-7333/S3/2302-0195$01.50/0
195
iron complex 6b (389 mg, 0.715 mmol) in CHzClz(5 mL) and diluting with an equal volume of EtOH. After the solution was cooled in a dry ice/CH3CN bath (ca. -42 "C), N-bromosuccinimide (142 mg, 0.793 mmol) dissolved in CHZCl2(5 mL) was added dropwise. The color of the solution slowly changed from orange to deep green. After the addition, the solution was allowed to warm to room temperature and after 45 min was transferred to a separatory funnel with the aid of CHZClzand then washed with 1 N NaOH. After the aqueous solution was backextracted with CH2C12,the combined CH2C12layers were dried over NazS04. Filtration followed by removal of volatiles on a rotary evaporator at room temperature left a green semi-solid residue that was triturated several times with Et20. The combined ether fractions were condensed to an oil which after filtration through a short alumina column with petroleum ether gave 114 mg (89%) of ethyl dihydrocinnamate, identical with an authentic sample. The generation of these iron acyl enolates and their reaction with electrophdes are comparable to the formation and reaction of organic ester enolates under strongly basic, aprotic conditions. Although the chiral iron center, in the present work, did not significantly control the formation of any new asymmetric carbon atoms, further work with conformationally restricted iron acyl enolates may overcome this limitation.
Acknowledgment is made to the National Cancer Institute, D.H.E.W. (Grant CA 26374), for support of this work. We thank Professor John Selegue for an early discussion of this chemistry. Octafluorocyclooctatetraene lransltlon-Metal Compounds. Novel Transannular Ring Closures and a Formal Intramolecular Redox Equilibrium between 1,2,5,6-7 and 1,2,3,6-7 Ligands Russell P. Hughes"' and Deborah E. Samkoff Department of Chemistry, Dartmouth College Hanover, New Hampshire 03755 Raymond E. Davis" and Brian B. Laird Department of Chemistry, University of Texas at Austin Austin, Texas 78712 Received September 27, 1982
Summary: Octafluorocyclooctatetraene (OFCOT) reacts , with [CO(CO),(T~C,M~,)] to give [Co(q-C,Me,)(C,F,)] which is in dynamic redox equilibrium between the 1,2,5,6-7 and 1,2,3,6-7 forms of coordinated OFCOT. The molecular structure of a cobalt product derived from transannular ring closure of OFCOT is also reported, and structure reassignments for some R-OFCOT compounds are proposed.
The recent synthesis2 and structural characterization3 of octafluorocyclooctatetraene (OFCOT) have allowed its organometallic chemistry to be compared to that of its thoroughly studied hydrocarbm a n a l ~ g u e . ~We have (1)Alfred P. Sloan Research Fellow, 1980-1984. (2) Lemal, D. M.; Buzby, J. M.; Barefoot, A. C., 111; Grayston, M. W.; Laganis, E. D. J. Org. Chem. 1980, 45, 3118-3120. (3) Laird, B. B.;Davis, R. E. Acta Crystallogr., Sect. B 1982, B38, 678-680. (4) For reviews of cyclooctatetraene chemistry see: Deganello, G.
'Transition Metal Complexes of Cyclic Polyolefins"; Academic Press: New York, 1979. Fray, G. I.; Saxton, R. G. 'The Chemistry of Cyclooctatetraene and Its Derivatives"; Cambridge University Press: Cambridge, 1978.
0 1983 American Chemical Society
196 Organometallics, Vol. 2, No. 1, 1983
Communications Table I.
"F Chemical Shifts'" 6
4
197.7 193.3 168.9 129.3
5a
3 1 [ML, =
138.8 154.7 135.4 1 5 9 . 1 182.4 130.3 1 6 4 . 4 127.9
156.6 185.9 112.6 115.4
144.8 141.3 216.3 171.8
Fe(CO)3 1 '" p p m
upfield f r o m internal CFCl, ; in CDC1, ; 20 "C.
Table 11. Fractional Atomic Coordinates and Thermal Parameters f o r 4'
Figure 1. ORTEP drawing of 4. Selected bond lengths (A):C d 4 = 1.993 (2), COC6 = 1.986 (2), C d p ring centroid = 1.711, range of C o C p carbon = [2.048 (2)-2.117 (2)], C 4 C 5 = 1.525 (3), C W 6 = 1.526 (3), C 3 C 4 = 1.470 (2), C 6 C 7 = 1.471 (2), C 2 C 3 = 1.326 (2), C7-C8 = 1.322 (2), C1-C2 = 1.478 (3), C8-Cl = 1.484 (3), and Cl-C5 = 1.568 (2). Selected bond angles (deg): C4-Co-C6 = 72.87 (7), C4-Co-C9 = 90.68 (a), and C6-Co-C9 = 91.46 (8). Selected dihedral angles (deg): C p ring with (Co-C4-C5-C6) = 52.2, (Cl-C2-C3-C4-C5) with (Co-C4-C5-C6) = 61.5, (Cl-C5C6-C7-C8) with (Co-C4-C5-C6) = 61.1, and (Co-C4-C6) with (C4-C5-C6) = 4.1.
previously described an intramolecular oxidative addition of OFCOT, which afforded the crystallographically characterized 1,2,3,6-0 compound 1 [ML, = Fe(CO)3].5 We 1
FB F7 &4 E 3
co F1 F2 F3 F4 F5 F6 F7
F8 0
c1 c2 c3 c4 c5 C6 c7 C8 c9 c10
c11
I.
also reported that the reaction of OFCOT with zerovalent platinum compounds afforded products of general formula [Pt(C,FJL,] (L = PPh,, PMezPh, PPh,Me), which on the basis of 19Fand 31PNMR data were suggested to have structure 1 (ML, = PtL,)., This communication outlines some cobalt-OFCOT chemistry that provides the first example of a formal redox equilibrium between valence isomers of a cobalt complex and also defines a novel transannular carbon-carbon bond formation that leads to the octafluorobicyclo[3.3.0]octa-2,7-diene-4,6-diyl ligand. A reassignment of the structure of [PtL,(C,F,)] is also described. Reaction of [CO(~-C,M~,)(CO),]~ with OFCOT in refluxing hexanes (84h) afforded, after column chromatography, a mixture of two isomeric [Co(&,Me,)(C,F,)] compounds in 60% overall yield. A combination of spectroscopic techniques clearly identified the structures of these isomers as 2a7and 3., A comparison of 19FNMR
c12 C13 C14 H10 H11 H12 H13 H14 Cpring centroid
2376.5 ( 3 ) 2 8 2 8 (1) 4 7 5 9 (1j 5 8 8 4 (1) 4 5 0 3 (1) 2410 ( 1 ) 1 4 6 (1) -490 (1) 1332 (1) 1977 ( 2 ) 2773 ( 2 ) 4177 ( 2 ) 4681 ( 2 ) 3738 ( 2 ) 2525 ( 2 ) 1217 (2) 675 (2) 1493 (2) 2135 ( 2 ) 1528 (2) 3045 ( 2 ) 3722 ( 2 ) 2626 ( 3 ) 1273 (2) 80 (2) 354 ( 2 ) 474 ( 2 ) 277 ( 2 ) 32 ( 2 ) 2439
'" U for H, U,, for non-hydrogen. All values X104 (except for H atoms; X103). Numbers in parentheses indicate estimated standard deviations in last digit shown.
data for 3 and 1 [M = Fe(CO),] (Table I) shows that fluorines attached to carbons that are directly bound to the metal suffer the greatest chemical shift perturbation on changing the metaLg While 2a and 3 could be sepaMe
P
Co F
(5) Barefoot, A. C., 111; Corcoran, E. W., Jr.; Hughes, R. P.; Lemal, D. M.; Saunders, W. D.; Laird, B. B.; Davis, R. E. J.Am. Chem. SOC.1981, 103, 970-972. (6) (a) Frith, S. A.; Spencer, J. L. Inorg. Synth., submitted for publication. (b) King, R. B.; Bisnette, M. B. J. Organomet. Chem. 1967,8, 287-297. (c) King, R. B.; Efraty, A. J. Am. Chem. SOC.1972, 94, 3773-3779. (7) Compound 2a: 'H NMR (CDCl,, 20 "C) 6 (downfield from Me&) 1.80 (s, C,Me,); 13C{'H}NMR (CDCl,, 20 "C) 6 (downfield from Me&) 105.7 (s, C5Me,), 10.0 (quintet, Jiq-19~ = 2.5 Hz, C&fe5);19FNMR (CDCI,, 20 "C) 6 (upfield from CFCl,) 117.1 (F2),188.3 (Fl); IR (hexane) v1736 cm-'; mass spectrum, m/e 442 (P'). Anal. C, H. 2b: 'H NMR 6 5.29 (s, C,H,); "T NMR 6 114.0 (F2),163.9 (F'); mass spectrum, m/e 372 (P+); IR (hexanes) uC+ 1734 cm-'. Anal. C, H. (8) Compound 3 (all spectral conditions as described in ref 7): 'H NMR 6 1.70 ( 8 , C&fe,); 13C(1H} NMR 6 102.5 (s, C5Me5),9.2 (doublet of quartets, JCF = 4 Hz, 1.5 Hz, C&fe,); IgF NMR (Table I); IR vc4 1736 cm-'; mass spectrum, m/e 442 (P'). Anal. C, H.
1 5 2 (1) 292 ( 4 ) 3 5 5 (4 j 321 ( 4 ) 305 ( 4 ) 297 ( 4 ) 266 ( 4 ) 255 ( 4 ) 292 ( 4 ) 402 ( 6 ) 202 ( 6 ) 241 ( 6 ) 231 ( 6 ) 209 ( 6 ) 192 (6) 181 ( 5 ) 185 (5) 196 ( 5 ) 251 ( 6 ) 237 ( 6 ) 280 ( 7 ) 327 ( 7 ) 302 ( 7 ) 261 (6) 24 ( 5 ) 41 (6) 37 ( 6 ) 37 ( 6 ) 30 (6)
1352.9 ( 2 ) 1788.3 ( 3 ) 6 1 6 9 (1) 287 (1) 6056 (I j 3 4 2 0 (1j 3 0 9 1 (1) 2790 (1) 1 7 2 4 (1) -618 (1) 3 5 0 4 (1) -1564 (1) -383 (1) 2 4 4 4 (1) 4147 (1) 3 1 2 8 (1) 6 6 2 3 (I) 3 6 0 2 (1) -608 (1) -1647 ( 2 ) 5108 ( 2 ) 1320 (2) 2275 (2) 4924 (2) 1999 ( 2 ) 3548 ( 2 ) 790 (2) 2526 ( 2 ) 3520 (2) 225 (2) 2942 ( 2 ) 936 (2) 4214 ( 2 ) 2214 ( 2 ) 5366 ( 2 ) 2420 ( 2 ) 157 (2) -313 ( 2 ) -40 ( 2 ) 3302 ( 2 ) -296 ( 2 ) 3203 ( 2 ) 1019 (2) 3960 ( 3 ) 2101 ( 2 ) 4478 ( 2 ) 4110 ( 2 ) 1434 (2) -75 ( 2 ) 285 (2) -122 ( 2 ) 268 ( 3 ) 114 (2) 402 (3) 307 ( 2 ) 500 (3) 197 ( 2 ) 433 (2) 844 3810
5
F
213.R z M e 2b.
F'
M
Fc
F F7
2
F3
3.
R=H
rated by preparative TLC, they slowly equilibrated on standing in solution [2-3 days, 20 "C; K,,(CDCl3, 20 "C, 2a 2 3) = 0.31. A similar reaction of [CO(~-C,H,)(CO)~] with OFCOT in refluxing rz-octane (48 h) afforded only poor yields (4-5%) of 2b.' No evidence for any compound with structure analogous to 3 was observed, nor d i d 2b (9) A complete analysis of the 19F NMR spectra will be published separately.
Organometallics 1983,2, 197-199 undergo any detectable valence isomerization in solution. The reaction of [Co(q-C5H5)(C0),]neat with OFCOT (80 "C, 72 h) yielded a second yellow crystalline product in execrable yield (
