Infrared spectra and structure of [(η-C5H5)Fe(CO)2]2 adsorbed on oxide surfaces

Journal of Molecular Structure, 174 (1988) 325-330 Elsevier Science Publishers B.V., Amsterdam-Printed

INFRARED OXIDE

S.

SPECTRA

AND STRUCTURE

OF

325

in The Netherlands

[(r)-C5H5)Fe(C012]2

ADSORBED

ON

SURFACES

Dobos' , S. Nunziante-Cesaro2

and B. V. Lokshin3

1

Hungarian Institute of Isotopes, Budapest, P.O.B. 77 (Hungary) 2

Centro Studi A. More, Rome

Termodin. (Italy)

Chim.

Alte

Academy

Temp.,

3 Institute of Organo-Element Compounds, Vavilova 28, Moscow B-312 (USSR)

of

Sciences,

University

H-1525

of Rome,

USSR Academy

of

P.le

Sciences,

ABSTRACT The surface reaction of [(n-C H )Fe(CO) ] adsorbed on hydrated silica and alumina has been studie 5 3 by FTI6 gpectroscopy. Hydrogen bonding of one or both bridging carbonyls of the molecule with the protonation on metal-metal bonds, surface hydroxo groups, and forming adducts with Lewis acidic sites of the surface have been of surface taken into consideration, and a series species was detected suggesting a co-existance of most above surface stabilised Fe-Fe reactions. Cyclopentadienyl group has frame, cleavage of metal-metal bond in a small rate was only detected.

INTRODUCTION Catalyst

precursor

hydroxilated

oxide

ions by cleavage

and Fe3+ ligands

(refs.

important

role

1,2).

reactions

substitution oxidation with

surface

between

basic

cations

may occur.

around

modes

makes

002%2860/88/$03.50

and

There

is an

at molecules

and

with

surface

02-

and

Lewis

of

carbonyls

0 1988 Elsevier Science Publishers B.V.

all

CO

play

an

cluster surface

(OH)-

ligands,

oxidation

of metal

interaction

unsaturated

scrambling

a low

on Fe2+

hydroxiles,

acid-basis

coordinatively

many

between

series

and the coupling with

loosing

in general

hydroxiles,

allover

surface

a

because

surface

consequently

state

bonds, groups

CO groups

surface

hydroxiles

frame,

in bridged

with

into

of the interaction

3,41,

with

CO groups

the metal

are only

steps

between

of CO groups

of CO groups

carbonyl

supported

Fe3(C0),2,

decompose

of metal-metal

(refs.

like bonding

like

quickly

Bridging

in initial

surface

and oxide

atoms

carbonyls,

surfaces

portion between

surface

of

carbonyls

of C-O

difficult

molecules stretching to

clearly

326

0

0.

'HO-

'Al

IV

III

II

I

0

HO-

$:&p($fi_Fp)~~~*(fFi&e+) co

c

0

co

-Al

V

co

co

VI

co

c

c

0

0

VIII

VII

Fig. 1. Characteristic structures derived from [ (n-C5Hg)Fe(C0)2]2.

TABLE 1 Spectral data of complexes derived from [(n-C5Hg)Fe(C0)2]2. I(nn-C5H5)Fe(C0)2]2

Frequencies (cm-')

Assignment

cyclohexane

2004 1960 1796

I

m-cresol

1997 1958 1807 (1781) 1733

(I)+II+III ref.6

liquid xenon + (CF3)3COH

2015 1973 1817 1733 2022 1983 1733 2069 2033

II III VI

ref.11

AIR 2 BC13 A;1R3

2026 1985 1828 1682 2042 2004 1682 2038 2020 1845 1463

IV V IV'

ref.10

uv,

2060 2012

VII

ref.12

1812

VIII.

ref.13

ccl4

pvc matrix, UV

ref.5

ref.15

327

distinguish

between

all

infrared

spectra.

contains

two bridging

terminal

ones,

bridging

carbonyls

above

possibilities,

The molecule

of

carbonyls

offers

simple

model.

have been

widely

studied

vibrational

published

(refs.

the

[(n-C5Hg)Fe(C0)2]2

of extremely

a very

complete

on

spectroscopic

basis which

high basicity

of

and elucidated

background

has

only

and two

reactions

The

of

its

and

also

a

been

5-10).

EXPERIMENTAL Alumina

and silica

were

CABOT

CORPORATION

vacua

at 573 K for 6 hours

silica 60%

still

(refs.

remained

1,2)),

Calculated

metal

loadings

reported

resolution equipped Nujol

were

RESULTS

mull

In Fig.

have

1

we

NOVA

collected had

reactions

metal-Lewis formation.

been

and about

solution under

Spectra

3 computer.

basis

structures complex

of

of

of

vacuum. supported

recorded.

Silica

with

formation

For

all

alumina

or

we

in the reactions surfaces.

Table

corresponding

terminal

CO stretching

active

bridging

stretching

in

two bridging

ones at 1796 and around to the symmetric intensity,

C-O bonds

is near

0.

.

about

The

1820

combination, the

of

adduct

these

The

only

1962

cis

parent

one and

conformer

at 2005 and cm-'.

with

of

as a mixture

form with

at

-1

During

data.

1962,

The

however,

in

identified

prototypes

is present trans

CO stretches

because

type

bridged

[(n-C5H5)Fe(C0)2]2

spectral

frequency

has two terminal

bridging

of

infrared

at 1796 cm

structures obtained

the

of ligand

1 contains

C2v symmetry

0)

products

simultaneously

in solution

active

(near

as

of the centrosymmetric

belongs

characteristic

and of

surprise,

[(n-C5H5)Fe(C012]2

two conformers

most

identified

[(n-C5H51Fe(C0)2]2

adduct

structures

and alumina

the

been

To our great

all above

weak

pentane

in

as references.

which

different

which

1%.

alumina coverage

was dried

and

AND DISCUSSION

(I-VIII),

silica

in Nujol

the

cluster

about

were

DATA GENERAL

used

with

the

monolayer

C)

heated

a 200-scan data accumulation was carried out at a -1 FTS-2OC a DIGILAB interferometer cm , using

of 2 with

contacted

(Alon and

treatment

hydroxile

The supported

[( nJ.Z5H5)Fe(C0)2]2 spectra

this

(by

DEGUSSA

respectively,

HS51,

hydrated:

then

[(n-C5H5)Fe(C012]2.

from

obtained

(Cab-0-Sil

last has

angle

between

formation

of

a the

adduct

of ir one with and one, very two with

(Cl 15m - Om

2h - Ih

4h - 2h

20h - 2h

1p . 70h -2Oh

III III1

I I I

IN

III

I I

IVII

n

VII II IT1 I I VII I I

2000

‘II I IIII II [II II I aI I m J II l II v1 f I VII

VIII 1

1700

1 I 2000

I 1700

I Il

IIIU

IVII w

I

1

n n

II v1 I I VII

VIII

Fig. 2. Infrared spectra of (B)

III IIll

1 1 2000

VIII

I 1700 -1 v,cm

(A) [(~-C5H5)Fe(CO)2]2/A120x/Nujol [(q-C5H5)Fe(CO)2]2/Si02/Nujol systems and (C) difference

spectra calculated from spectra in (A).

329

Lewis

the CO system

acids,

lowering

of the bridging

in

slight

the

increasing

The frequency

involved.

The lowest

acid.

strength

of Lewis

of frequency

Fe-Fe

bond

acid

results

perturbed

therefore,

transform

of the

resultant

of to

it

occur

a

may

10,lS).

of bridging

bands

in

not

the wide

Protonation carbonyl

terminal

terminal

and

Lewis

sensitive

into

the

carbonyl

is very

cm -' (refs.

in the disappearing CO-s

of

strength

the

on

in

in the adduct,

frequency

the

CO frequency

and,

resulting

involved

depends

of 1700-1400

bridging

frequencies

be

of

shift

bridging

range

because

will

CO frequency

appear

bands,

and

ones,

on

at

the

higher

frequencies. In figs. alumina

2A-B the spectra

(2A) and on silica

by Nujol

the reaction

(2B) in Nujol

of the complex

down

and it can be also modified

with

it in occupying

the figures I-VIII.

Taking

prototype figs.

2A-B can easily

prototypes First surface

found

of all in the

takes

bridging

slown

(ref.

2).

In

to the structures

spectral

sets

for the bands

which

surprisingly

also

surface

which

in

certainly

well

at 1814 and to

to

the

1742 cm-l.

between

type

the

perturbes

molecules

variety

on silica

(of both

carbonyl

hydroxiles

large

a

reaction,

hydroxiles

slightly

bridging

belongs

system

Nujol

of

As dominating

with

CO, but with

band

is

competition

frequencies

the

into

separated

presence

in the

new bands

supposingly

broad

place, but,

assigned

1,

corresponding

occurs.

of adducts

stretches,

into

on the surface

in Table

Remember,

surface

entering

on

in solutions.

complexes

formation

produces

be

species

supported

are shown.

the

the characteristic

collected

surface

when sites

mull

with

the sets of bands

into account

adducts

represent

III)

different

we marked

complex

of the parent

II

and

terminal

CO

region

it

stretching A new band

in

of higher

at 1700

hydrogen acidic

1645 - 1620 cm-'

of (2B),

bonding

character.

indicates

adducts

cm-' on The of

type

IV and V, with further electrophiles. The terminal CO band at -1 2062 cm with its pair about 2015 cm -I (shoulder), belongs to the structures

IV and V. The band

not practically On alumina II-III

and

change

essentially IV-V

relativeintensities. in spectra several

system

on silica

can The

the same phenomena be

identified

system,

reactions

occur,

with

however,

in fig. 2A and in the difference

simultaneous

is stable:

it

does

in time.

take place.

structures

somewhat

is not stable. spectra

in

The difference

I,

differing As fig.

seen 2C,

spectra

330 recorded on expanded scale, show that the

decrease

pair at about 2055 and

be

2015

cm-'

might

a

of

result

overlapping pairs of bands, because changes in

its

not parallel with the intensity changes in the

bridging

region. It means that it is to be partly

assigned

the

band

of

more

intensity to

do

carbonyl nonbridged

species, like VI. An assignment to the monomer species of type VII bonded to the surface through oxygen atoms (CpFe(C0)2-O-)

is

not

excluded, either. It is very important to notice that a series

of

different adducts with the surface

of the types IV and V is indicated by the presence of a series of bands in the range of -1 1700-1600 cm , referring to a series of different acidic sites on

the surface. It is very important to mention that almost all surface species traced in

our

experiments

have

reserved

ligands. This fact is quite unusual in

Fe-Fe

the

case

iron carbonyls because they generally quickly carbonyls when

contacted

with

hydroxilated

surfaces (refs. 1,2). We believe that

the

bonds of

and

CO

polynuclear

oxidize

and

alumina

or

cyclopentadienyl

stabilizes Fe-Fe bonds, supposingly by both electronic and

loose silica ring steric

effects. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14

15

S. Dobos, I. B&sz&m&yi, J. Mink and L. Guczi, Inorg. Chim. Acta, 120 (1986) ?_35;143. S. Dobos, I. B%zormenyi, J. Mink and L. Guczi, Inorg. Chim. Acta, 120 (1986) 145-152. S. Dobos, A. Beck, S. Nunziante-Cesaro and M. Barbeschi, Inorg. Chim. Acta, 130 (1987) 65-73. S. Dobos, I. B%z.drm&yi, J. Mink and L. Guczi, Inorg. Chim. Acta, in press. A. R. Manning, J. Chem. Sot., A (1968) 1319-1324. A (1970) P. McArdle and A. R. Manning, J. Chem. sot., 2133-2136. A. R. Manning, Coord. Chem. Rev., 51 (1983) 41-67. A. Alich, N. J. Nelson and D. F. Shriver, Chem. Commun., (1971) 254-255. N. E. Kim, N. J. Nelson and D. F. Shriver, Inorg. Chim. Acta, 7 (1973) 393-396. D. F. Shriver, J. Organometal. Chem., 94 (1975) 259-271. B. V. Lokshin, private communication. D. R. Tyler, M. A. Schmidt and H. B. Gray, J. Am. Che. sot., 105 (1983) 6018-6021. Commun ., R. H. Hooker, K. A. Mahmoud and A. J. Rest, Chem. (1983) 1022-1024. D. C. Harris and H. B. Gray, Inorg. Chem., 14 (1975) 1215-1217. J. S. Kristoff and D.F. Shriver, Inorg. Chem., 13 (1974) 499-505.