Carbon-13 magnetic resonance studies on the formation of secondary α-ferrocenyl carbocations from tertiary carbinols

Jour&ofO~jpnometal~ic

Chemistry,118(1976)C47--C52 0 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands

Preliminary communication CARBON-13 MAGNETIC RESONANCESTUDIES ON THE FORMATION OF SECONDARY a-FERROCENYL CARBOCATIONS FROM TERTIARY CARBINOLS C.C.

LEE*,

S.C.

CHEN, W.J.

PANNEKOEK and R.G.

SUTHERLAND

Departmentof Chemistryand ChemicalEngineering,Universityof Saskatchewan, Saskatoon.Saskatchewan S7N OWO (Canada) (Received July 13th. 1976)

Sumnary

with

The same secondary

ferrocenylisopropylcarbenium

concentrated

at

methyl dimethyl

H,SO,

carbinol

ion was obtained

occurrence

thus

providing

substituted

or the the

of

ion

tertiary

to

report

(Ia)

shifts

with

CF3COOH

converting

or ferrocenyl-

diphenylmethyl

carbenium

or ferrocenyl-

at 5OC. The results tertiary

indicate

to secondary

demonstration

of the

extraordinary

the

of the

same secondary

fmm

formation

either

the

secondary

stability

carbocations, of

a-ferrocenyl

methyldiphenylcarbinol

(IIIa),

ferrocenyldiphenylmethylcarbenium

ferrocenyldiphenylmethylcarbinol (IIIb).

ferrocenylisopropyl-

fermcenylisopropylcarbinol

ferrocenylmethyldimethylcarbinol

same secondary

secondary

ferrocenyl

ferrocenyldiphenylmethylcarbinol

1,2-hydride

a novel

ferrocenylisopropylcarbinol

same secondary

was treated

from treatment

carbocations.

We wish cakbenium

and the

when either

methyldiphenylcarbinol the

10°C of either

ion was formed

(IIb)

and the ion

or the

(Ib) tertiary

formation

from either ferrocenyl-

(IIa) of the

C48

L

3

I

4

5

67 1

+“-CH(R)p a

6

I

Fe

Fe 4’

5’

1’

3’ 6

II

I

2

CH2-k(R)2 a

0

Ia,

IIa,

IIIa

R = CH3

Ib,

Ifb,

IIIb

R = CSHS

Fe

da III

13 C

Data from the 1H-decoupled Ia from treatment in Table of

7.

are essentially

identical

to those

di astereotopi

cyclopentadienyl

the CH3 groups of

of

have recently

IIIa

reported

data for

IIa [l]_

to five

Similarly.

due to the presence_of

ion

the 13C Nfi spectrum

Ia and IIa

by these workers

rise

and carbenium

H2S04 at 10°C are summarized

at C-a in Iia renders

c, thus giving

ring of

IIa is also

observed

center

IIa,

in concentrated

from ITa in CF3COOD. The present

out that the asymnetric

pai rs of carbons stituted

IIa or IIIa

Braun, Abram and Watts [1]

Ia generated

pointed

of either

spectra

NMR

[ll-

(Table

1)

It has been

the C-2,5. and C-3,4

iignals

for

the sub-

the n&equivalence the asyinnetric

center,

.of a

c49

TABLE 1 13C NMR SPECTRA OF FERROCENYLISOPROPYLCARBINOL

DATA FROM THE 'H-DECOUPLED

(IIIa).

FERROCENYLMETHYLDIMETHYLCARBINOL

(IIa),

ANDTHE FERR9CENYLISOPROPYLCARBENIUM

ION

(Ia). Chemical Shifts, ppma

IIab (CDCl3)

IIa (Acetone-s) C-l

93.7

IIIa

Iab (i-$504)

(Acetone-&)

93.4

85.4

104.7

c-z,5

66.1,68.3

64.9,68.9

68.0

87.4,82-l

c-3,4

67.7

67.6,67-g

70.8

95.1.95.6

c-l'-C-5'

69.1

68.3

69.1

82.1

C-a

75.2

75.1

45.7

133.4

C-0

36.3

34.9

---

35.5

C"3

18.2,19-O

a

18.6.18.8

29.4

22.5,28.7

from external TMS in a capillary

Chemical shifts were measured

contained

some CD3N02 as a locking compound in studies

identical

results

were reported

in ref.

1 for

IIa

with

tube which also Ia.

The C-2.5

and C-3,4

equivalent

in carbocation

attributed

to a restricted

substituted rise

carbocation

to Ia indicates

Ia,

pairs

[1,3].

ferrocenylmethyldimethylcarbenium

secondary

carbocation

Ia.

of this

about the C-1-C-a

The fact

the occurrence

by Roberts

of carbons and the CH3 groups are

and the origin

rotation

Essentially

in CDC13 and Ia in CF3COOD.

finding that was first observed for 'asymmetric isopropylcarbinols et al [2].

b

that

tertiary

nonequivalence

also

non-

has been

bond in the a-ferrocenyl carbinol

IIIa

also

gave

of a 1,2-hydride shift, converting the tertiary ion to the more stable a-ferrocenyl

substituted

_

cm Xn sfmflar

studied-

with

IIb

and IIIb,

it was found that treatment of either

of these aTcohoTs wft’thconcentrated H2S04 gave rise to extensive decomposition. Carbocation

Ib, however, was obtained by dissolving

data from the

73

Whentertiary

alcohol

C NMR

spectra of IIb, IIlb

was treated

IIIb

and ion

with

neat

IIb

at 5’C.

in CF$DOH

The

in Table 2.

Ib are summarized

CF3COOH, decompositik

also

TABLE 2

DATA FROMTHE ‘H-DECOUPLED l3 C NMR SPECTRA OF FERROCENYLDIPHENYLMETHYLCARBINOL (IIb),

FERROCENYLMETHYLDIPHENYLCARBINOL(IIIb) AND THE FERROCENYLDIPHENYLMETHYL-

CARBENIUM ION (Ib).

Chemical Shifts,

ppma

IIIb

IIb

(Acetone-&)

(CF!$X~H)

(Acetone-%) 83.6

104.9

67.8

79.9,81.2

67.7

71.3

94.5,94.7

69.1

69.1

C-a

72.9

43.8

140.3

C-B

61.5

78.9

56.0b

C-l

c-2.5 c-3,4

C-l ’ -c-5 ’

Aromatic

94.5

66.3,68.6

126.8,128.7

81.7

124.3,127.8,128.2

127.0,128.3

129_7,130.1

Aromatic quaternary

a

Chemical shifts

143.7,144.3

148.7

-W-B

were measured from external TMSin a capillary

contained some CD3N02 a doublet in off

129,5.130.0,130.5

as a locking compound in studies with

resonance

studies,

indicating

the

presence

lb. of

tube which also b

Becomes

1H at C-B.

C51

0CC”rl-i.

Ion Ib was generated from IIIb when CF-$OOH (about 10%) was added to a of IIIb in CDCl3 at 5OC and the 13C NMRspectrum was recorded after a

SOlUtiOn

relatively

short contact time (about 4000 scans)

The identification

of

Ib as the

secondary

is based on the general similarity

in order to minimize

decomposition

ferrocenyldiphenylmethylcarbenium

ion

of its 13C NMRspectra with that of Ia, the

nonequivalence of the C-2,5 and C-3,4 pairs of carbon atoms, and the fact that off

resonance gave a doublet for the C-B absorption

H on of ion

this carbon.

a 1.2-hydride to the

showing the presence of one

The formation of Ib from IIIb again indicates shift

secondary

converting the tertiary

ferrocenylmethyldiphenylcarbenium

ferrocenyldiphenylmethylcarbenium

The great stability

of a-ferrocenyl

known. The early 1iterature

ion.

substituted

carbenium ions is well

has been reviewed by Cais [43.

NMR[1,31 and other techniques 15-81 have been applied a-ferrocenylcarbenium

rearrangement Tertiary

ions.

of secondary to tertiary

carbccations

undergo 1 .Z-shifts substituent.

The present

) including

results

therefore,

tertiary

containing

constitute

demonstration of the extraordinary stability

in studies

a reversal

substituted

to give secondary carbocations

These findings,

More recently,

13C

of stable

show that instead of the usual

carbocations,

a diphenyl

the occurrence

has taken place. cation,

could

an a-ferrocenyl

another. but rather novel,

of a-ferrocenyl

substituted

car-

bocations.

Acknowledgement

Be thank the National

Research Council

of Canada for financial

support.

References l-

S- Braun. T-S.

2.

J.I.

J. Organornet. Chem., 97 (1975)

Kroschwitt, M. Winokur, H.J. Reich,

91 (1969)

3_

Abram, and W.E. Watts,

and J-D.

Roberts,

5927.

G-A- Olah and 6. Liang, J. Org. Chem., 40 (1975)

1849.

429.

.I_ ARh Chem.

SOL,

c62 <’

4.

M. Cair, Drganomet.

5,

G.

Cerichelli,

6.

D.

Kaufman and R. Kupper, J. Org. Chem., 39 (1974)

7.

J-W.

8.

W_ Crawford and

Chem.

Rev.. 1 (1966)

435,

_

B, Floris, and G.-Ortaggi, J. Organomet. Chem,, 78 (1974) 241

Larsen and P, Ashkenazi, W.E. Watts,

J, Am. Chem. Sac.,

1437.

97 (1975) 2140.

J. Organomet. Chem.. 110 (1976) 257.