3149 References and Notes (1)Paper XXX: M. Gouterman and G.-E. Khalil, J. Mol. Spectrosc., 53, 88 (1974). (2)Spectroscopic studies from Ph.D. thesis of L.K.H. and M.Sc. thesis of G.-E.K.; chemical studies in part from Ph.D. thesis of K.R.
(3)(a) University of Washington: (b) Technische Hochschule Aachen; (c) University of British Columbia.
(4)J. W. Buchler, G. Eikelmann. L. Puppe. K. Rohbock, H. H. Schneehage. and D. Weck. Justus Liebigs Ann. Chem., 745, 135 (1971). ( 5 ) J. W. Buchler and H. H. Schneehage, Z. Naturforsch.. Tell B, 28, 432 (1973). (6)J. W. Buchler and K. Rohbock, lnorg. Nucl. Chem. Lett., 8 , 1073 (1972). (7)J. W. Buchler, L. Puppe, K. Rohbock. and H. H. Schneehage, Ann. N.Y. Acad. Scb, 206. 116 (1973). (6)M. Tsutsui, R. A. Velapoldi, K. Suzuki, F. Vohwinkel, M. Ichakawa, and T. Koyano, J. Am. Chem. SOC.,91, 6262 (1969):M. Tsutsui, R. A . Veiapoldi, K. Suzuki, and T. Koyano, Angew. Chem.. 60,914(1968). (9)J.-H. Fuhrhop, Tetrahedron Lett.. 3205 (1969). (10) D. Ostfeld and M. Tsutsui. Acc. Chem. Res., 7 , 52 (1974). (11) M. Gouterman, "Excited States of Matter", Vol. 2,C. W. Shoppee. Ed., Texas Tech University, Lubbock, Texas, 1973,p 63. (12)R. S.Becker and J. B. Allison, J. Phys. Chem., 67, 2662,2669 (1963). (13)A. T. Gradyushko, V. A. Mashenkov, A. N. Sevchenko. K. N. Solov'ev, and M. P. Tsvirko, Dokl. Akad. Nauk SSSR, 182, 64 (1968)[Sov. Phys.Dokl.. 13,869 (1969)]. (14)A. T. Gradyushko and M. P. Tsvirko, 0 t Spetrosk., 31, 548 (1971) [Opt. Spectrosc. (USSR), 31,291 (1971)f' (15)Paper XXVII: M. Gouterman, F. P. Schwarz, P. D. Smith, and D. Dolphin, J. Chem. Phvs.. , ~59. , . 676 (1973). (16)Paper XXIV: L. K. Hanson, M'. Gouterman, and J. C. Hanson, J. Am. Chem. Soc., 95,4822 (1973). (17)A. Antipas. M. Gouterman, D. B. Howell, J. W. Buchler, and D. Dolphin,
(18) Paper XVIII: D. Eastwood and M. Gouterman, J. Mol. Specfrosc., 35, 359 (1970). (19) Paper XXII: J. B. Callis, M. Gouterman, Y. M. Jones, and B. H. Henderson, J. Mol. Specfrosc.. 39,419(1971). (20)Paper XII: D. Eastwood and M. Gouterman, J. Mol. Spectrosc., 30, 437 (1969). (21)B. E. Smith and M. Gouterman, Chem. Phys. Lett., 2, 517 (1968). (22)Paper XIX: M. Gouterman. R. M. Mathies. B. E. Smith, and W. S. Caughey, J. Chem. Phys., 52,2795 (1970). (23)J. Bohandy. 8. F. Kim, and C. K. Jen, J. Mol. Spectrosc., 49, 365 (1974). (24)L. K. Hanson, Ph.D. Thesis, Department of Chemistry, University of Washington, Seattle, Wash.. 1973. (25)Paper XXXII: M. Gouterman. L. K. Hanson, G.-E. Khalil, W. R. Leenstra. and J. W. Buchler, J. Chem. Phys., 62,2343 (1975). (26)Paper XIV: R. L. Ake and M. Gouterman, Theor. Chlm. Acta, 15, 20 (1969). (27)G.-E. Khalil, M.Sc. Thesis, Department of Chemistry, University of Washington, Seattle. Wash.. 1973. (28) M. Gouterman, D. B. Howell. and J. Wannlund, unpublished results. (29)K. Rohbock, Dissertation, Technische Hochschule Aachen, 1972. (30)Paper XIII: P. G. Seybold and M. Gouterman. J. Mol. Spectrosc., 31, 1 (1969). (31)M. Gouterrnan, J. Chem. Phys., 30, 1139 (1959). (32)M. Gouterman, D. Holten, and E, Lieberman, work in progress. (33)R. C. Pettersen, J. Am. Chem. SOC.,93,5629 (1971). (34)J. van Kaam, Diplomarbeit. Technische Hochschule Aachen, 1972. (35)N. Kim, J. W. Buchler, and J. L. Hoard, to be published. (38)M. H. Perrin. M. Gouterman, and C. L. Perrin, J. Chem. Phys., 50, 4137 (1969). (37)J. S. Bonham, M. Gouterman. and D. 5. Howell, submitted for publication.
(38)F. P. Dwyer, L. Puppe, J. W. Buchler, and W. R . Scheidt, lnorg. Chem., in press.
work in progress.
Chemistry of Dicarbonyl y5-Cyclopentadienyliron Complexes. General Syntheses of Monosubstituted y2-Olefin Complexes and of 1-Substituted yl-Allyl Complexes. Conformational Effects on the Course of Deprotonation of ( y2-Olefin) Cations A. Cutler, D. Ehntholt, P. Lennon, K. Nicholas, David F. Marten, M. Madhavarao, S. Raghu, A. Rosan, and M. Rosenblum* Contribution from the Department of Chemistry, Brandeis University, Waltham, Massachusetts 02154. Received September 3, 1974
Abstract: Reaction of dicarbonyl vs-cyclopentadienyl(ql-allyl)iron with cationic electrophiles provides a general route to monosubstituted (v2-olefin)iron complexes. Alternatively these may be obtained by an exchange reaction employing the olefin and dicarbonyl vs-cyclopentadienyl(v2-isobutylene)irontetrafluoroborate. Deprotonation of the cationic olefin complexes provides a general route to 1-substituted ql-allyliron complexes. The most stable conformation for the monosubstituted ( q 2 o1efin)iron cation is best represented by 17b. The stereochemistry of the vl-allyliron complexes derived by deprotonation of the complex cations can be accounted for in terms of preferred base abstraction of an allylic proton trans to the iron-olefin bond. Deprotonation of the allyl alcohol complex (3p) leads to the lactone (26) through a conformationally determined stereospecific intramolecular reaction. The I3C N M R spectra of several (v2-olefin)iron cations are recorded and shown to provide useful information relevant to their conformations. Deuteration of dicarbonyl ~s-cyclopentadienyl(vl-cinnamyl)iron with deuteriotrifluoroacetic acid is shown to be nonstereospecific.
+
I n order to examine the synthetic applications of ( 3 n ) cycloaddition reactions1 and of metal-assisted olefin condensations2 employing dicarbonyl ~5-cyclopentadienyl(ql-allyl)iron complexes [hereafter designated as (v1-allyl) Fp complexes], general methods for the preparation of these substances are required. Simple alkyl-substituted (q'-allyl)Fp complexes have been prepared by metallation of the corresponding allyl halides or tosylates with the dicarbonyl q5-cyclopentadienyl ferrate anion ( F P - ) ~ or through deprotonation of the dicarbonyl v5-cyclopentadienyl(o1efin)iron cation [ F p ( ~ l e f i n ) + ] . 'These ~ latter com-
plexes are in turn available either directly from the olefin by an exchange reaction with the Fp(isobuty1ene) cation4 or through a reaction sequence involving the complex iron anion (Fp-) and a n e p ~ x i d e .These ~ transformations a r e summarized below in Figure 1. The present paper provides a general procedure for the introduction of functional groups a t the terminal olefinic carbon atom of (v'-allyl)Fp complexes, and a description of the chemistry of the intermediate Fp(olefin) cations, in particular their conformation and the stereochemistry of their deprotonation.
Rosenblum et al. J Chemistry of Dicarbonyl q5-Cyclopentadienyliron Complexes
3150
E
PFs- or BF,-
1
3
Et,N
L
E=
I
5
4
h, E =
Me-SO,b, Mea,
c,
Figure 1.
d,
E
“F c . 1
LI
Results and Discussion Evidence for the formation of a dipolar intermediate (2) in the reactions of (q’-allyl)Fp complexes with uncharged electrophiles has previously been sumrnarized.ld These intermediates collapse by either anionic attack at the metal or on the activated olefin, affording “insertion” or cycloaddition products (eq 1 and 2).
Fp7_
( J -
e.
CH,CO-
f. PhCO-
i, (MeO),,CHj. OHCk, (MeO),CI, MeOjCm. B r n,
Ph,P+-
0.
MeO-
p. H e
q.
Ph-
4
1
With cationic electrophiles, the intermediate (2, E instead of E-) is incapable of further reaction and may readily be isolated. O n deprotonation with triethylamine, the 1substituted (q’-allyl)Fp complex is obtained, generally in high yield (eq 3).6 These substances, which are isolated as low-melting solids or oils, are readily characterized through their crystalline cycloaddition products with tetracyanoethylene ( T C N E ) . Sulfonylation. The reaction of (q’-allyl)Fp complexes with sulfur dioxide generally affords “insertion” products’ (eq 1). However, in the presence of a suitable additional electrophile, the intermediate (2) may be trapped. Thus, when the parent complex (1) is added to a suspension of trimethyloxonium tetrafluoroborate in liquid S 0 2 , the salt (3a) is isolated in high yield.* Deprotonation of 3a proceeds readily at 0’ to give the trans- 1-methylsulfonylallyliron complex (4a) as the exclusive product in 90% yield. This was further characterized as its T C N E adduct 6a. The formation of 3a in the presence of oxonium salt suggests that 1 is converted rapidly and entirely to the dipolar ion 2 ( E = S o l ) in liquid SO2 solution since the oxonium salt alone may be shown to be sufficiently electrophilic to effect the alkylation of 1. Alkylation. When carried out in methylene chloride solution, the reaction of 1 with trimethyloxonium tetrafluoroborate gives the Fp(1-butenyl) cation (3b) in high yield. In contrast to 3a, deprotonation of this cation gave a mixture of the trans- and cis-2-butenyl complexes (4b and 5b) in a ratio of 3:2. The reaction of tropylium tetrafluoroborate with 1 also proceeds rapidly a t room temperature affording a quantitative yield of the salt (3c). Deprotonation a t Oo gave, as with 3b, a mixture of isomeric complexes 4c and The adduct, obtained on treatment of this product with an equimolar amount of T C N E , is derived exclusively by a ( 3 2) cycloaddition reaction involving the metal-activated double bond, rather than the cycloheptatriene ring, since the adduct preserves the characteristic N M R absorption pattern of a cycloheptatriene ring and fails to exhibit cyclopropane proton absorption.1° Alkylation was also effected with the trichlorocyclopro-
+
6
7
penium ion,” but attempts to deprotonate the product (3d) led instead to regeneration of 1. Acylation. The introduction of an acyl function a t Cl in I may be accomplished by direct acylation a t low temperatures employing acyl cations generated from acyl halides and silver hexafluoroantimonate.I2 The intermediate acylated cations (3e,f), formed with acetyl or benzoyl chloride, were not isolated but were deprotonated in situ by treatment with triethylamine. In each of these reactions, the product was exclusively the trans derivatives (4e,f). A more convenient procedure makes use of dialkoxycarbenium ions as electrophiles. These cations are readily available from orthoformates or 1,3-dioxolanes on treatment with trityl salts,13 and their reactions with 1 take place rapidly a t low temperatures to give the corresponding cations (3) as crystalline, air-stable substances, in high yield. Deprotonation is achieved rapidly a t Oo to give essentially quantitative conversion to the I-substituted allyl complex. In all of the cases examined (3g-i), deprotonation gave the trans isomer (4g-i) apparently as the exclusive product; none of the cis isomers could be detected in the N M R spectra of products of these reactions. The hydrolytic stability of the protected acyl functions in these complexes varies considerably. Protonation of the activated double bond is apparently competitive with protonation of oxygen and may as a consequence retard hydrolysis of the ketal group. Complex 4g resisted hydrolysis in a 10% aqueous dioxane solution of HCI at room temperature, while 4h was converted with 5% HCI principally to the unconjugated demetallated ketone. Hydrolysis of 4i to 4j OCcurs rapidly and quantitatively in 1% HCI. Carboxylation. Trimethoxycarbenium ion, prepared from trimethyl orthocarbonate and trityl cation, serves as a convenient electrophile for the introduction of a carboalkoxy function at C I in complex 1. The cation (3k) is hydrolytically very sensitive and was converted directly to the ester (41). Bromination and Brominolysis. The cleavage of transition metal-carbon 0 bonds by halogen or positive halogen re-
J o u r n a l of the American Chemical Society / 97:ll / M a y 28, 1975
3151 agents is well k n o ~ n . l T~ h~e ' brominolysis ~ of the Fe-C bond in (a1kyl)Fp complexes is a very rapid reaction and may be achieved either with bromine,ls pyridinium perbromide, or N-bromopyridinium bromide,I6 the latter reagent being preferred. The cleavage of the Fp-C bond in 8 and 9 a t -78' with N-bromopyridinium bromide may be effected in high yield. Indeed, so rapid is the brominolysis reaction that it can be carried out selectively in the presence of an isolated center of unsaturation, as is illustrated by the conversion of 10 to 11.
8
9
11
10
When the double bond is activated toward electrophilic attack by conjugation with the Fp-C bond, it becomes the preferred site of reaction. Even at -78', the reaction of 1 with bromine is virtually instantaneous, and the cation (3m), isolated as the hexafluorophosphate, salt, is obtained in high yield. In sharp contrast to preceding experience, deprotonation of this cation led exclusively to the cis- I-bromoallyliron complex (5m), as indicated by the vinyl proton coupling constant of 6.5 Hz. The T C N E adduct prepared from this complex is, not surprisingly, unstable and readily eliminates FpBr. Bromination and deprotonation of the methallyliron complex (12) gave (I-bromo-2-methylally1)Fp (14). Little if
12
13
14
any of the isomeric 2-bromomethallyliron complex is formed in the deprotonation of the intermediate olefin complex (13), and the N M R spectrum of the product shows that it is a single stereoisomer, of as yet unknown stereochemistry. Olefin Exchange Reaction. As an alternative to electrophilic substitution of preformed ( ~ l - a l l y l ) F pcomplexes, we undertook to explore the preparation of Fp(olefin) cations directly from the functionalized olefin by the exchange process shown below (eq 4).
+ olefin ClCH.CH,CI
+~p-j,
) ,
Fp(olefin)+ i-
(4)
Table I. NMR Spectra of Monosubstituted Fp(olefii)+ Complexes (Chemical Shifts, 7 ; Coupling Constants, Hz)
A
"22
HI
3ba 3ca 3pa 3ha 3mb 3Oa 3ea 3 qa 24C
4.39 4.33 4.40 4.30 4.22 4.32 4.32 4.31 5.17
co co
6.54 (15) 6.42 (15) 6.55 (14.5) 6.44 (15) 6.32 (14) 6.44 (15) 6.36 (15) 6.35 (15) 7.18 (11.5)
6.09 (8) 6.0 (8) 6.0 (9) -5.93 (8) 5.98 (8) 5.96 (8) 5.97 (8) 6.02 (8) 6.70 (7.5)
a Taken in nitromethaned',. bTaken in acetoned',. CTaken in CDC1,.
O f t h e three olefin complexes (3n-p) prepared in the exchange reaction, 30 was alternatively prepared by metalation of 3-methoxypropene oxide with Fp- followed by treatment with acid.5 Attempts to prepare a n allyl cyanide olefin complex gave instead the nitrile coordinated cation (FpN=CCH2CH=CH2)+. Deprotonation of the methoxypropeneiron complex (30),like 3m, behaved exceptionally and gave exclusively the cis-1-methoxyallyliron complex (So), as indicated by the vinyl proton coupling constant of 6 Hz. This was characterized as its T C N E and tosyl isocyanate adducts. Like the acetal complexes 4g,h, the vinyl ether complex 50 proved to be resistant to mild acid hydrolysis and was recovered in near quantitative yield after treatment with 3% aqueous HCI a t reflux after 30 min. A discussion of the product formed in the deprotonation of 3p is deferred to the section below. Conformation of Monosubstituted Olefin Complexes. Four extreme conformations of these complexes may be considered (16a,b and 17a,b). Of these, model^'^^'^ clearly indicate that, for conformations 16a,b, in which the olefin axis is either in or near the Fp group symmetry plane, substantial steric interactions exist between ring protons or the carbonyl group and the olefin ligand. A clear distinction cannot be made on steric grounds between 17a and 17b since interactions subsist in each be-
15
A number of simple mono- and dienes had previously been shown to enter successfully into this r e a ~ t i o nThe . ~ exchange reaction has been employed most successfully with monosubstituted olefins, although it is not confined to these, and a number of cycloalkene complexes including C-5, 6, 7, and 8 cycloalkenes,' b,4 cyclohexa- 1,3- and - 1,4-dienes, cycloocta-1 $diene, and norbornadiene4 can be made by this method. The effectiveness of monosubstituted olefins as components in the exchange process is not surprising since efficient conversion to product complex depends on its thermodynamic stability, which is observed to decrease with increasing alkyl substitution of the 01efin.l' An instructive illustration of the importance of steric factors in the exchange reaction is provided by cyclopentene and cyclohexene which give 100 and 2% yields of Fp(olefin)+ complexes, respectively, under identical conditions in the exchange reaction. Models show that a serious steric compression exists in the cyclohexene complex, involving an axial ring proton a t C4 of the cyclohexene ring with the Fp group. Comparable interactions a r e absent in the cyclopentene complex.
R
16b
16a
'oc
co17a
17b
tween the olefin substituent and either ring protons or a carbonyl ligand. However, an examination of the N M R spectral data (Table I ) for a series of these complexes provides grounds for concluding that a conformation close to the idealized form (17b) is favored. The close correspondence of terminal vinyl proton absorptions in these complexes suggests very similar conformational populations. For both
Rosenblum et al. 1 Chemistry of Dicarbonyl q5-CyclopentadienylironComplexes
3152 Table 11. Carbonyl ’% Resonance in Fp(o1efin) Complexes (Chemical Shifts, ppm)a
co
Cation
A
:
209.60
Fp---t(’
209.21
(3rj~p4,
210.96
HH
*
1.75
oc
210.83
(15)FpA
+&
oc
co 18
(3b1Fp
