The structure and bonding of ferrocenylcarbonium ions

Tetrahedron

Vol. 29, pp 1575 to 1584.

P~IWUIMXIPress.

1973.

Pnnted m Gnat

Bntam

THE STRUCTURE AND BONDING OF FERROCENYLCARBONIUM IONS J. J. DANNENBERG,* M. K. LEvnNnERGt and J. H. RICHARDS Contribution No. 3790 from the Gates and Crellin Laboratoriesof Chemistry, California Institute of Technology, Pasadena,California9 1109. (Received in USA 3 1 July 1972; Received in UKforpublication

22 January 1973)

Abstract-Studies of NMR and Miissbauer spectra of a-ferrocenylcarbonium ions are discussed in terms of three models for these ions. Agreement seems best between the observed results and expecta-

tions based on a model for the carbonium ion in which there is bonding between the iron atom and the

a-carbon.

Carbonium ions bearing an adjacent ferrocenyl nucleus (1) possess unusual stability.1-17 In attempting to rationalize this stability structures have been

(0)

advocated in which there is1-4.1s-zo and there is not14-17*21-22interaction of the Fe with the cationic center. This paper examines the NMR and Mossbauer spectra of 2-methyl and 2-deuteroferrocenylcarbonium ions.

+5oc/s4

RESULTS NMR Spectroscopy

Fig 1 shows the NMR spectrum of a solution of ferrocenylcarbinol in cone snlfuric acid. Measurement of the freezing point depression of such a solution shows that four moles of ions are formed per mole of carbinol dissolved (one mole of ferrocenylcarbonium ion, one mole of hydronium ion, and two moles of bisulfate). Fig 1 also shows the NMR spectra of mixtures containing (i) 65% crmethylferrocenylcarbinol and 35% ferrocenylcarbinol and (ii) 65% cr-deuteroferrocenylcarbinol and 35% ferrocenylcarbinol. Table 1 lists the chemical shifts. The derivatives substituted in the ar-position of the ring bearing the carbinyl carbon were prepared *Present address: Department of Chemistry, Hunter College of the City University of New York, 695 Park Avenue, New York, N.Y. 10021. tPresent address: Abbott Laboratories, North Chicago, Illinois.

Fig 1. Spectra of (a) ferrocenycarbonium ion; (b) a mixture of approximately 65% o-deuterofetrocenylcarbonium ion, 35% ferrocenylcarbonium ion; (c) a mixture of approximately 65% a-methylferrocenylcarbonium ion, 35% ferrocenylcarbonium ion. All spectra were taken in concentrated sulfuric acid.

1575

J. J. DANNENBERG,M. K. LEVENBERGand J. H. RICHARDS

1576

Table 1. Chemical shti assignments of ferrocenylcarbonium ions Carbonium

ion

CH$

Chemical shifts a-H P-H

C&

5.90

4.68 triplet

6.28 triplet

5.23

590

4.68 triplet

6.28 doublet

5.23

Me 5*80,6.12

4.51 triplet

6.13 doublet

5.03

The chemical shiis listed were measured using tetramethylammonium chloride (3.106) as a standard. All shifts are in ppm. from TMS. by the specific lithiation of ferrocenylcarbinyl dimethyl aminez3 followed by hydrolysis with deuterium oxide (to yield a-deuteroferrocenylcarbinyl dimethyl amine) or treatment with methyl iodide (to yield a-metbylferrocenylcarbinyl dimethyl amine). Further treatment with methyl iodide afforded the quatemary ammonium salts which on basic hydrolysis afforded the corresponding carbinols 6 and 7. (Scheme 1). The NMR spectrum of the sample of a-methylferrocenylcarbinol prepared by the above procedure shows it to be contaminated with significant amounts of unsubstituted carbonium ion 1. Nevertheless, the spectrum of 9 can be ascertained by subtracting the spectrum of 1 from the spectrum of the mixture. Integration of the unsubstituted ring peaks in the spectrum of the mixture indicates that the compound with an a-Me group accounts for about 65% of the mixture. Integration of the substituted ring peaks for the deuterated carbonium ion 8 gives a ratio of 1.37: 2.00 for a-proton to p-proton. This ratio corresponds to about 60-65% deuteration which accords well with the results on methylation since both derivatives were prepared from the same lithiated intermediate, 3.

In any event, the spectra of Fig 1 clearly indicate that the resonances at higher field are due to the a-ring protons since these peaks decrease in intensity when a deuterium or a Me group is substituted for one of the a-ring hydrogens. In the asubstituted carbonium ion, the /3-protons should exist as doublets. (In the unsubstituted carbonium ion 1, both the a- and &ring protons occur as triplets.) Use of coupling constants previously reportedz4 between ring protons and the assumption that these protons couple only with each other support this expectation. The spectrum of the amethyl carbonium ion 9 in which the resonance of the p-protons is not obscured shows them as a doublet. Superposition of the doublet attributable to the &protons of the a-deuterated carbonium ion 8 upon the triplet attributable to the p-protons of the unsubstituted ion 1 with which 8 is contaminated accounts for the unresolved multiplet observed in spectrum B of Fig 1. In all cases, the a-protons appear as triplets as expected. In the spectra of the unsubstituted carbonium ion, 1, and the a-deuterated ion, 8, the methylene protons appear as sharp singlets. In the spectrum of 9, however, the metbylene protons are nonequivalent and appear as an AB quartet. The low field lines in the spectrum of 9 are attributed to the two @ring protons and the two methylene protons. The two large lines at lowest field are assigned to the P-protons since the coupling is the same as for the triplet due to the a-protons at highest field. The high field wing of the AB quartet of the methylene protons is easily identifiable in Fig 1; the wing at lower field is partially obscured by the /3-proton resonances of the unsubstituted carbonium 1 present as a contaminant. An interesting implication of the non-equivalence of the two methylene protons of the carbonium ion 9 is that rotation of the methylene carbon relative to the ring must be highly restricted. A similar conclusion had been reached earlier based on studies of solvolysis of substituted ferrocenylcarbinyl acetates,4 and in studies” of the NMR spectra of methyl cyclobutadienyl iron tricarbonyl carbonium ion. DISCUSSION

resonance model. A model for ferrocenylcarbonium ion which includes contributions from canonical forms such as 10 and 11 may be considered. In this model of the carbonium ion, the iron occupies a symmetrical position relative to both rings and there is no direct interaction between the Fe atom and the carbinyl carbon. In such a cation, the positive methylene group should be strongly electron withdrawing. Various studies have shown a correlation between the chemical shift of a hydrogen that is directly bonded to an aromatic ring and the charge density on the carbon The

The structure and bonding of ferrocenylcarbonium

+

MqNCH,NM%

J

4A

NaOH

9

8

SCHEME

1

ion

1577

1578

J. J. DANNENBERG, M. K. LEVENBERG and J. H. RICHARDS

-

Fe

11

10

to which this hydrogen is bonded.22*26 Table 3 shows that Hilckel treatment of a fulvene system (here taken as a first approximation to the substituted ring of 1) containing between 5 and 6 r-electrons, predicts that the B-carbons will have a higher electron density than the a-carbons. In phenylcarbonium ionz7*2* and phenylcarbanion,20 the observed shifts agree well with those calculated on the basis of simple Hilckel theory and the suggested relationship between charge density at a carbon in an aromatic ring and the chemical shift of an attached hydrogen. In addition, the inductive effect in a canonical structure such as 10 will tend to make the a-carbons more positive than the pcarbons. On the basis of charge densities, the resonance mcodel (10 * 11) would be expected to have the a-hydrogens more deshielded (to lower field) than the &hydrogens. Moreover the effect of the magnetic anisotropy of the double bond between the methylene carbon and the ring in 11 would also tend to deshield the a-protons more than the p-protons.31,3Z In fact the experimental spectra of ferrocene derivatives with electron withdrawing groups typically exhibit resonances of a-protons at lower field than resonances of p-protons,33*34 in accord with the considerations just discussed. In Table 2. Mossbauer spectra data*

Ferrocenylcarbinol Ferrocenylcarbonium ion, 1

Isomer shit? (mmlsec)

Quadrupole splitting (mmlsec)

0.56 0.57

199 2.29

*These spectra were observed at 137°Kin frozen solution. The value for tbe quadrupole splitting in the spectra of ferrocenylcarbinol is different from that reported in Ref 4 1. This difference is undoubtably due to the different experimental conditions used in Ref 4 1. Table 3. Charges calculated for (Y-and 8_protons of fulvene svstems with 5 and 6 n-electrons” Electrons in system 5

6

Huckel theory Omega techniqueb (Y P ff B 0.270 o-065 0.240 0.110 -0.092 -0.073 -0.074 -o@l5

“See reference 30 for a description of the methods used. Omega was taken as 1.O.

contrast, the relative positions of the (Y-and IS-ring protons differ very significantly from those anticipated on the basis of this model (10 f, 11). Studies’* of substituent effects also accentuate the difllculties of the resonance model. A correlation has been made between the chemical shifts of the methine protons and the substituent-Y for carbonium ions of the type 12 (Table 4). As -Y becomes more electron withdrawing, the methine proton becomes more shielded; this is the exact opposite of the result anticipated for the resonance model, but one that is predicted by the iron participation model (see subsequent discussion).

Table 4. Chemical shifts of carbinyl protons of selected cations Chemical shiis (ppm from TMS)

Cation Ferrocenylcarbinyl a-Methylferrocenylcarbmyl Ferrocenyhnethylcarbinyl Ferrocenylisopropylcarbinyl Ferrocenyl-r-butylcarbinyl Ferrocenylphenylcarbinyl Ferrocenyl-p-methylphenylcarbinyl Ferrocenyl-p-methoxyphenylcarbinyl Ferrocenyl-p-carbomethoxyphenylcarbinyl Benzhydryl p-Methoxybenzhydryl

590 5.80,6*12” 7.03” 6.98” 7.07b 7*92b 7.94b 7.%b 7.67b 9*8W 9.06b

Two nonequivalent protons, bRef.20 “Ref. 37.

The diene-iron wcomplex model. In this model,” the Fe is bonded only to four carbons of the fulvene system and the methylene carbon is attached to the system by alocalized double bond, 13. The Fe atom is shifted away from the methylene carbon so that the bonding with the butadiene system may be =CH,

The structure and bonding of ferrocenylcarbonium ion optimized. This structure was suggested as the analogue to the proposed” structure for the cyclobutadienyl iron tricarbonyl carbonium ion, 14. In both structures, 13 and 14, the positive charge is distributed over the remainder of the system, excluding the methylene carbon and the ring carbon to which it is attached.

14

The NMR spectrum of 14 is analogous to that of 1 in that the cu-protons are more shielded than the /?-proton. Much of the support for a structure such as 14 was based on the assumption that the magnetic resonance of the terminal (a) protons of an allylic system, such as 14, should come at higher field than the central (8) proton. Also, it was thought” that a structure such as 15, which is the analogue of one of the proposed structures for ferrocenylcarbonium ion, 1, could not account for the observed R spectrum. However, some

15

recent evidence% indicates that the central proton and the terminal syn (relative to the central proton) proton of various ~-ally1 tricarbonyl cations (such as 16) have approximately the same chemical shift, respectively 5.68 and 5.45 ppm from TMS, when the terminal carbon in question also carries a Me substituent. Moreover, the vinyl group with which the terminal carbons of the allylic system 14 are substituted should have a greater deshielding effect than a Me group (as in 16), suggesting that the (rprotons of a structure such as 16 should be deshielded relative to the P-proton, and that a preferable structure for the cyclobutadienyl iron tricarbonyl carbonium ion would be 15, the analogue ofl.

r

H

16

1'

1579

Structures such as 14 also pose a conceptual difficulty in that the Fe atom coordinates only 16 rather than 18 electrons in its valence shell despite the availability of the two additional electrons needed to attain the closed-shell krypton configuration. In the absence of an anomalous effect that could preferentially stabilize 13 or 14, one would expect these structures to be less stable than 1 or 15. Fe bonds only to two double bonds in systems such as tropilium iron tricarbonyl cation presumably because bonding to the entire 7r-electron system of the ligand would require Fe to coordinate more than 18 electron.37 Fe coordinates only 16 electrons in the ally1 iron tricarbonyl cations and their true salts. However, these species are rather unstable as indicated by the spontaneous decomposition of such salts in aqueous solution.38 The ally1 iron tricarbonyl chlorides are not true salts, as the Fe satisfies its need for the two additional electrons by forming a covalent bond to chlorine.39 The possibility remains that Fe may acquire an additional pair of electrons by coordination of solvent to stabilize 13 or 14. However, one would expect this intermolecular participation to be less effective means to achieve the krypton configuration than by intramolecular interaction with the remaining two P-electrons. The MGssbauer spectrum of ferrocenylcarbonium ion provides additional evidence against 13. As shown by the results in Table 2, ferrocenylcarbonium ion has the same isomer shift as ferrocenylcarbinol,40 which in turn has the same isomer shift as ferrocene.41 The isomer shift is a sensitive measure of the relative density of s-electrons at the nucleus.42 Formation of 13 from ferrocenylcarbinol would cause a reduction of the valence electrons coordinated by Fe from 18 to 16. Such a reduction should be expected to cause a significant change in the isomer shift since even changes in p- or d-orbital populations are known to change the shielding of the s-orbitals and thereby the s-density at the nucleus. In fact, the isomer shift of 13 is found to be the same as that of ferrocenylcarbinol. The change in quadrapole splittings between ferrocenylcarbinol and ferrocenylcarbonium ion can be explained on the basis of difference in the r-bonding ligand in ferrocenylcarbinol (cyclopentadienyl) and the carbonium ion (fulvene). Wertheim and Herber”vU have explained the small range of quadrapole splittings observed for ferrocene derivatives by suggesting that the electric field gradient at the Fe nucleus is affected much more by changes in r-bonding ligands than by substituents joined by u-bonds to the r-ligands. The iron-participation model. This model depicts a carbonium ion, as in 1, in which the substituted ring is planar and conjugated as in fulvene. The Fe is shied somewhat away from the center of the substituted ring toward the methylene group; the unsubstituted ring is still unshifted relative to

1580

J. J. DANNENBERG.M. K. LEVENBERGand J. H. RICHARDS

the Fe, but is shifted (with the Fe) relative to the substituted ring. Ferrocene can be considered as two cyclopentadienyl entities which are bonded to an Fe atom by means of interactions of the cyclopentadienyl molecular orbitals with the Fe orbitals of the same symmetry.45 In an analogous sense, the carbonium ion can be described as one cyclopentadienyl and one fulvene entity bonded to an Fe atom by similar interactions. The Hiickel molecular orbitals for cyclopentadienyl and fulvene are shown in Fig 2.4s All the cyclopentadienyl orbitrds are of proper symmetry for bonding with the iron 3d, 4s and 4p orbitals.45 Fulvene orbitals numbered a, b, c and e have the same symmetry as the cyclopentadienyl orbitals numbered a, b, c and e in Fig 2. The center of fulvene orbitals a and b lie somewhat to the methylene side of the center of the ring and these orbitals, together with the electron density on the carbinyl carbon of the fulvene molecular orbital d, should account for the postulated movement of the substituted ring relative to the Fe and unsubstituted ring. A recent self-consistant charge calculation based on Extended Hiickel Theory predicts interaction of the Fe with the cationic site, althoughthe predicted geometry is somewhat different from 1.47 A model such as 1 readily accounts for the NMR data. If the Fe is shied as in 1, it should be nearer and therefore more strongly bonded to the (Ya

0.477

0

b

0.477

0.477

carbons than to the 8-carbons. This might decrease somewhat the positive charge density on the (Ycarbons relative to the @ubons. The effect of the magnetic anisotropy of the Fe in the structure 1 is probably more important. The magnetic anisotropy of unsymmetrical atoms, such as Fe, can effect the magnetic environment of neighboring atoms, thereby infhiencing the chemical shifts of nearby protons4* For the case of unsubstituted ferrocene, the effect of the anisotropy of Fe upon the ring protons has been estimated to decrease their chemical shift by 2.16 ppm.@ As the protons are moved nearer the Z axis of the Fe (the rotational axis of ferrocene) the anisotropic shielding should increase. As a result of such movement, the cY-protons of 1 should be more shielded by virtue of Fe anisotropy than the P-protons. This is supported by the report that the resonances of the ?r-ring protons are much more shielded in ferrocenylphenylcarbinyl cation than in 6-phenylfulvene.” This supposition was also confirmed by a recent study of ferrocenophones.W Finally, the ring current of the unsubstituted ring should exert an anisotropic effect similar to,“’ but of smaller magnitude,& than that due to Fe. These three effects are additive and each should cause the cu-protons to become shielded relative to the pprotons. Such a model readily accounts for the NMR data. If the iron is positioned as in 14, it should be nearer and therefore more closely bonded to the p-carbons C

0.632

O*y

0.477 0.477 E = a+0.618@

E= a+2.000/3

e

d

0.632

E=a+0618/!3 0-y

-0.372

0.602 E=a-1

E = cc- I.6188 a

0.247

E= 01+2.115B d

0.749

b

-0.500

E=a+l.OOO~

e.

6188

c

o.ooo

E = a+O.618p

O.tjOO --- --- 0.664

-0.439‘ ,:‘-‘:, *-il.439 0.153 0.153.b E = a-0.254/S Fig 2.

E = a-1.618p

E=a-1.861p

Hiickel molecular orbitalsfor cyclopentadienyland fulvene.

1581

The structure and bonding of ferrocenylcarbonium ion than the a-carbons. Hence, we expect the positive charge on the S-carbons to be more stabilized by the Fe than that on the a-carbons. These effects, thus, offer an explanation for the observed NMR spectrum of ferrocenylcarbonium ion and also of the observed substituent effects on the methine resonance in 12.18 When an electrondonating group is in the para-phenyl position of 12, the charge on the methine carbon is more effectively stabilized by interactions with the phenyl part of the molecule than if the para-substituent of the benzene ring be electron-withdrawing. In the former case, the Fe need not stabilize as much positive charge as in the latter case. Since the Fe loses bonding energy with the @carbons by moving toward the methine position, it should move farther toward the methine carbon as the para-phenyl substituent becomes more electron-withdrawing. In other words, the potential energy surface of the carbonium ion is at a minimum with the Fe less shifted from its “normal’* position when the paraphenyl substituent is electron-donating. Charge stabilization is only one of the three ways in which the Fe shields the methine proton since all of the above arguments concerning the shielding of the a-protons apply to the methine protons, as well. The methine proton, consequently, is not as well shielded by the anisotropic magnetic fields of the Fe and the unsubstituted ring when the charge is partially stabilized through the phenyl ring and these effects of magnetic anisotropy dominate effects due to charge density. This interpretation is in good agreement with the experimental results of Table 4. We anticipate that an increase in the electrondonating capacity of the substituted phenyl ring in 11 should have a greater effect upon the amount of Fe shift when the potential minimum requires that the iron is not near its symmetrical ferrocene position. In other words, the change in chemical shift per unit of electron-withdrawing capacity da/da is not linear and should decrease as u+ increases. Fig 3 demonstrates that this anticipated relationship is valid. An analogous explanation accounts for the observed decrease in shielding of the average of the methylene protons of 9 relative to 1 and 8 mentioned previously. As the Me group at the a-ring position increases the amount of stabilization of the positive character that is directly conducted through the cyclopentadienyl ring, the distance the Fe must move is, accordingly, decreased. Rosenblum’s conclusion that iron displacement is probably not important in several tertiary ferrocenylcarbonium ionsZZ is not in disagreement with this conception. Solvolysis

Much of the objection to the concept of Fe participation in ferrocenylcarbonium ions comes from solvolytic studies of ferrocenylcarbinyl

751 -IO

I -05

I 0

I 05

I IO

Fig 3. Plot of chemical shifts ofpara-substituted phenylferrocenylcarbonium ions, 11, against CT+and u- valueP of the paru-substituents.

chloride and derivatives which have ferrocenyl groups insulated from the carbinyl carbon by phenyl (p-ferrocenylphenylcarbinyl chloride), groups comparisons between ferrocenylcarbinyl chloride and chloromethyl methyl ether, and the existence of linear relationships between these solvolytic data and IR CO stretching frequencies of related ketones or esters.14’-16 The observed results diier from those anticipated on the basis of the known effects of sulfur, for example, as aneighboring group. There is considerable question of the extent to which the contribution of an interaction between Fe and the carbinyl carbon to the stabilization of 1 is analogous to neighboring group participation by sulfur. In addition, there is another point which may alleviate some of the present discrepancies in interpretations of the bonding and structure of these cations. On an energy surface between ground state and completely ionized carbonium ion, three distinctly different regions have been considered. The early work dealt with solvolysis of acetates.‘-’ The work of Traylor et a1.1c-16deals with solvolysis of chlorides. The physical studies in this paper deal with the completely ionized carbonium ions. As shown by Hill” (data are collected in Table 5), ferrocenylcarbinyl chloride is much more reactive than the corresponding acetate. Hammond= has correlated the degree to which the structure of a transition state resembles a ground state reactant or an intermediate with the difference in energies between reactant and intermediate. The smaller this difference the more the transition state will have the structural characteristics of reactants. Thus, the transition state in the solvolysis of ferrocenylcarbinyl chloride will have more characteristics of the ground state of the reactant than will

1582

J. J. DANNENBERG,M. K. LEVENBERGand J. H. RICHARDS

Table 5.

Activation parameters for a-ferrocenylethyl chloride and related solvolyses

Solvolysis a-Ferrocenylethyl chloride 60% ether40% ethanol Triphenylmethyl chloride 60% ether40% ethanol a-Ferrocenylcarbinyl acetate 80% acetone Triphenylmethyl acetate 80% acetone

Temp “C

AH* kcal

APeu

-42 to -82

10*9& 0.7

-22

oto25

13.2

-23

oto35

19.0

-13

15to45

22.1

-7

the transition

state for the solvolysis of the significantly less reactive ferrocenylcarbinyl acetates. If interaction between the iron and the carbinyl carbon, with concomitant rearrangement of the ferrocene geometry, is important in the fully formed carbonium ion 1,it will be less manifest in

the transition state for solvolysis of ferrocenylcarbinyl acetates and still less manifest (and possibly unobservable) in solvolytic studies of ferrocenylcarbinyl chloride. The observation that the pkr’s do not correlate with the rates of solvolysis for ferrocenyl and triphenyl carbonium ions55*5s further clouds the relevence of solvolysis rates to cation structure. EXPERIMENTAL Ferrocenylcarbinyldimethylamine, 2. Ferrocene (46 g, 0.25 moles) was added slowly to a mixture of 43 g bis (dimethylamino)methane (see below), 54 g phosphoric acid and 400 ml AcOH in a l-liter, 3-neck, round-bottom flask equipped with a magnetic stirrer, Nz inlet, and a condenser. The flask was heated and kept between 100 and 110” for 8f hr. The mixture was then diluted (in two parts) with 500ml water and extracted with ether to remove the excess ferrocene. The water layer was neutralized with 2468 NaOH pellets (added slowly, with stirring). The resulting semisolid was considerably diluted with water and then extracted with ether 3 times. The ether extracts were combined, dried over MgSO,, and evanorated to leave a red oil. The oil was distilled. The fraction which boiled 89-96”/05-0.25mm Hg was collected and stored under N, in the refrigerator. The bis(dimethylamino)methane used in this synthesis was prepared by hydrolyzing an aqueous soln of 123 g MqNH.HCl with an aqueous soln of 60 g NaOH. The resulting MezNH soln was added slowly to 65 ml 37% aqueous formaldehyde soln, cooled m an ice bath. The temp was kept below 159 The reaction was stirred in an ice bath for 45 min. Then, 150 g KOH was added in 5 portions. The mixture separated into 2 layers. The upper layer was collected and distilled from KOH pellets. The fraction distilling between 80-86” was used for further reactions.

a-Lithioferrocenylcarbinyldimethylamine, 3. Compound 2, (244 g, 0.01 moles) and 10 ml anhyd ether (fresh can) were added to a 25 ml, 3-neck, round-bottomed flask fitted with a condenser, Nz inlet, and a dropping funnel. The system was flushed with NP 15% n-Buli (8 ml) in heptane (Foote, lot no. 401-02) was added dropwise through the dropping funnel. The mixture was allowed to stand 1 hr under N, The soln was then used directly. This preparation affords only the a-lithiated compound, 3.= a-Deuteroferrocenylcarbinyldimethylamine, 4A. To the soln of 3, described above was added dropwise approximately 2 ml D,O. When reaction no longer occurred upon the addition of more Da, water was added and the mixture extracted with ether. The ether layer was collected, dried over anhyd MgSO, evaporated to yield 4Ae8 a-Deuteroferrocenylcarbinyltrimethylammonium iodide, 4. Unpurified 4A, was dissolved in 15 ml MeOH. After cooling, 2f ml Me1 was refluxed for 2f hr. Upon addition of ether, a ppt formed. This ppt was collected and washed with ether, yield: 2.43 g 4. wDeuteroferrocenylcarbino1, 6. To 20 ml of 1 M NaOH in a round-bottomed flask flushed with Nz was added 2.Og of 4. The mixture was refluxed under N) for 2 hr. The mixture was then extracted with ether. The ether extract was washed with water until it became neutral, dried over MgSO.,, and evaporated. The resulting solid was recrystallized from n-heptane. a-Methylferrocenylcarbinyltrimethylammonium iodide, 5. Me1 (5 ml) was added dropwise to a soht of 3, as described. MeOH was added to dissolve as much of the mixture as was possible. The MeOH soln was decanted from the solid. A large quantity of ether was added which caused the formation of a ppt. The ppt was collected and washed with ether, yield: 2.8 g 7, m.p. 170-5” dec. a-Methylferrocenylcarbinol, 7. To 1 M NaOH (20 ml) in a round-bottomed flask was added 2.0 g of 5. The mixture was refluxed for 2 hr and extracted with ether. The ether was washed with water until it became neutral, dried over MgS04, and evaporated, leaving a red oil. An NMR spectrum of the oil showed it to be a mixture of 7 and of ferrocenylcarbinol. Carbonium ions. Carbonium ions were prepared by dissolving the carbinol in cone HSO,. Deep red solns were immediately formed. Occasionally, a brown or green soln formed, mdicating that some oxidation had occurred. Oxidation was minimized by pre-chilling the HSO, and the mixing vessel and by flushing the mixing vessel with Nb NMR spectra. The spectra were taken with the aid of a Varian A-60 NMR spectrometer immediately after preparation of the carbonium ions. HSO, was used as the NMR solvent and tetramethylammonium chloride as a reference (3.10). Calculated NMR transitions were obtained with the aid of the computer program written by Ferguson and Marquardt.s7 All computations were carried out on an IBM 7094 digital computer. Miissbauer spectra. Solns of the samples in small polyethylene envelopes were placed between two Bakelite plates approximately spaced with washers. The solns were then frozen in liquid N, and clipped to a Cu-holder which was immersed in a standard liquid N2 Dewar flask so that only the part holding the sample extended out of the Dewar flask. The top of the Dewar flask was then covered with Styrofoam. At thermal equilibrium the temp of the sample was 137°K. Mossbauer spectra of the samples were taken through the Styrofoam using equip-

The structure and bondii ment designed and loaned to the authors by Dr. E. Kankeleit. Freezing point depression. The cryostat used to measure the freezing points is described by Newman.= A stock soln was made of slightly fuming HSOl by mixing 380 ml cone HSO, with 1 lb of 30% fuming HSO+ This mixture was found to be slightly higher than the desired concentration of SO, to produce the highest freezing point. The addition of 0.7ml water per sample brought the HSO, to the desired concentration just past the freezing point maximum. A weighed quantity (approximately 90 g) of HSO, was poured into the cryostat. The unit was assembled and all joints greased. The required 0.7 ml water was added. The cryostat was allowed to equilibrate for several hr, so that the inside surface would lose any water film which may have adhered. The outer can was filled with an ice-water slurry. The HSO, soln was stirred and its temp was recorded every min. The temp was estimated to O+Ol degree wtth a Beckman thermometer. When the temp fell to the freezing point of the HSO, a piece of dry ice was placed against the surface of the inner vessel. The dry ice was held there 1 min, and upon removal, white crystals of HSO, could be seen. The temp would continue to drop for several more min. It would then suddenly shoot up a degree or two and stay there for from 2 to 15 min, depending on the concentration of solute. This maximum point was taken as the freezing point. Samples were introduced into the soln as compressed pellets and dropped down a glass tube to the surface of the acid. This method of introducing samples required an hr to dissolve each sample. The method was, however, found to be a superior way of insuring that the entire sample reached the acid. Once the freezing point was obtained for the sample, the inner vessel was removed from the rest of the apparatus and allowed to warm up to room temp. A sample pellet was introduced into the acid and allowed to dissolve. The freezing cycle was then repeated. The data obtained in this way were used to calculate the Van? Hoff i Factor, using the formula AT 1=Amx6~154(1-08047r) where Am is the molahty of solute in solvent, AT is the change in freezing point when solute is added and t is the mean depression (freezing point of pure HSO,-freezing point of soln).59 Corrections were made for supercooling,BOand for exposed thermometer stem.B1 REFERENCES

?1. H. Richards and E. A. Hill, J. Am. Chem. Sot. 81, 3484 (1959) *D. S. Trifan and R. Backsai, Tetrahedron Letters No. 13, l(1960) 3E. A. Hill and J. H. Richards, J. Am. Chem. Sot. 83, 3840(1961) ‘E. A. Hill and J. H. Richards, Ibid. 83,4216 (1961) 5K. Schlozl and A. Mohar, Monatsh. Chem. 92, 219 (1961) BK. Schlogl and A. Mohar, Naturwissenschaften 9, 376 (1961) ‘R. Taylor, Chem. & Ind. 1122 (1959) 8A. N. Nesmeyanov, E. G. Perevalova and Y. A. Ustynyuk, Doki. Akad. NaukSSSR 133,1105 (1960) gA. N. Nesmeyanov, I. I. Kritskaya and T. V. Antipina, Izv.Akad. NaukSSSR, Otd. Khim. Nauk 1777 (1962)

of ferrocenylcarbonium

ion

1583

‘OM. Rosenblum, A. K. Banetjee, N. Danieli, R. W. Fish and V. Schlatter. J. Am. Chem. Sot. 85.3 16 (1963) “M. J. N-ugent, d. E. Carter and J. H. Richards, Ibid. 91, 6195 (1969) ‘*M. J. Nugent, R. Kummer and J. H. Richards, Ibid. 91, 6138 (1969) 13M.J. Nugent, R. Kummer and J. H. Richards, Ibid. 91, 6141(1969) 14J.C. Ware and T. G. Traylor, Tetrahedron Letters 1295 (1965) 15T. T. Tidwell and T. G. Traylor, J. Am. Chem. Sot. 88, 3442 (1966) IV. G. Traylor and J. C. Ware, Ibid., 89, 2304 (1967); T. G. Traylor, W. Hanstein, H. J. Berwin, N. A. Clinton and R. S. Brown. Ibid. 93.5715 (1971) “5. D. Fitzpatrick, L. Watts and R.‘Pettit, Tetrahedron Letters 1299 (1966) ‘*M. Cais, J. J. Dannenberg, A. Etsenstadt, M. I. Levenberg and J. H. Richards, Ibid. 1695 (1966) 1°M. Hisatome and K. Yamakawa, Ibid., 3533 (1971) *OM.Hisatome and K. Yamakawa. Tetrahedron 27.2101 (1971) ZIC. P. Lillya and R. Sahatjian, J. Organomet. Chem. 32, 371(1971) *51.Feinberg and M. Rosenblum, J. Am. Chem. Sot. 91, 4324(1971) P3D. W. Slocum, B. W. Rockett and C. R. Hauser, Ibid., 87,1241(1965) 24M. I. Levenbcrg and J. H. Richards, Ibid., 86, 2634 (1964) W. Fraenkel, R. E. Carter, A. McLachlan and J. H. Richards, Ibid., 82,5846 (1960) *aT. Schaefer an W. G. Schneider. Canad. J. Chem. 41. 966 (1963) e7G. A. Oh&J. Am. Chem. Sot. 86,934 (1964) **D. G. Famum, Ibid. 86,934 (1964) W. R. Sandel and H. H. Freeman, Ibid. 85,2328 (1963) 3oA. Streitwieser, Molecular Orbital Theory for Organic Chemists. D. 115. Wiley. New York (1961) 31L. M. J&man, Applications of ‘N&ear Magnetic Resonance in Organic Chemistry p. 129. Pergamon Press, New York (1959) s2A. A. Bothner-By and J. A. Pople, Ann. Rev. Phys. Chem. 16,43 (1965) “M. Rosenblum, Chemistry of the Iron Group Metallocenes: Ferrocene, Ruthenocene and Osmocene, Part I. p. 44. Wiley, New York (1965) 34G. G. Dvoryantseva, S. L. Portnova, K. I. Grandberg, S. P. Gubin and Yu. N. Sheinker, Dokl. Akad. Nauk SSSR 160,1075 (1965) a5N. C. Deno, Prog. Phys. Org. Chem. 2,129 (1964) 3sc. Tanzer and J. H. Richards, unpublished results. 37J.E. Mahler, D. A. K. Jones and R. Pettit, J. Am. Chem. Sot. 86,3589 (1964) 38G. F. Emerson, J. Mahler and R. Pettit, Chem. & Ind. 836 (1964); G. F. Emerson, and R. Pettit,J. Am. Chem. Sot. 84,4591(1962) 38Nesmeyanov,j. Organometal. Chem. 14,395 (1968) 9. J. Dannenbera and J. H. Richards. Tetrahedron Letters 4747 (1967r ‘IA. V. Lesikar, J. Chem. Phys. 40,2746 (1964) %. K. Wertheim, Mossbauer Effect, Principles and Application, Chap. 5. Academic Press, New York (1964) 45G. K. Wertheim and R. H. Herber, J. Am. Chem. Sot. 84,2274 (1962) UG. K. Wertheim and R. H. Herber, J. Chem. Phys. 38, 2106 (1963)

1584

J. J. DANNENBERG,M. K. .LEVENBERGand J. H. RICHARDS

&F. A. Cotton, Chemical Applications of Group Theory p. 168. Interscience, New York (1963) ‘6c. A. Coulson and A. Streitwieser, Dictionary of mElectron Calculations pp. 123, 209. Pergamon Press, New York (1965) %. Gleiter and R. Seeger, Helo. Chim. Acta 54, 1217 (1971) ‘BJ.A. Pople, W. C. Schneider and H. J. Bernstein, High Resolution Nuclear Magnetic Resonance p. 176. McGraw-Hill, New York (1959) ‘SM. I. Levenberg, Ph.D. Thesis, California Institute of Technology (1965) T. D. Turbitt and W. E. Watts, Tetrahedron 28, 1227 (1972)

51Ref. 49, p. 180 52H. H. Jaffe, Chem. Rev. 53,191(1953) %. A. Hill,J. Org. Chem. 28,3586 (1963) 54G. S. Hammond,J. Am. Chem. Sot. 77,334 (1955) J5E. A. Hill and R. Wiesner, Ibid. 91,509 (1971) JdE. A. Hill, J. Organomet. Chem. 24,457 (1970) %. C. Ferguson and D. W. Marquardt, J. Chem. Phys. 41,2087 ( 1964) %I. S. Newman, H. G. Kuivila, and A. B. Garrett, J. Am. Chem. Sot. 67,704 (1945) 59J.L. O’Brien and C. Niemamr, Ibid. 73,4264 (195 1) B”R. J. Gillespie, E. D. Hughes, and C. K. Ingold, J. Chem. Sot. 2473 (1950) B’Handbook of Chemistry and Physics, 39,2 144 (1957)