1
60
A.M. Trzeciak et al.rJournal of Organometallic Chemistry 552 (1998) 159–164
According to our earlier studies, rhodium
plexes with N-pyrrolyl phosphines NC H
PPh
NC H4.2 , PPh2 NC H4.. as well as rhodium
Ž
I
.
com-
species, like HRh
ucts.
CO
Ž .wPŽNC H4.3x3, in reaction prod-
4
Ž
P
Ž
.
3,
4
4
Ž
Ž
Ž
I
.
4
4
phosphite complexes are similar in H2 splitting via
oxydative addition to metal center at mild conditions
2.1. Hydrogen actiÕation by the system:
Rh(acac)(CO)(PPh )qH qPPh qPPh (NC H )
4 3y x
3
2
3
x
4
Ž
0.1 MPa, room temperature
that HRh CO NC H
. x -type complexes are
4 3yx 3
.
. Moreover it was found
Ž
.
wPPh
Ž
In contrast to the rhodium I complexes with P OPh
Ž . .
Ž
x
4
3
active catalysts for hex-1-ene hydroformylation w18x.
or N-pyrrolyl phosphines, similar complexes with PPh3
In this paper we present the studies of catalytic
Ž
.
weaker p-acceptor
form only traces of
.
HRh CO PPh in reaction with H under 0.1 MPa.
3 3
activity of two hydrido complexes—HRhwP
and HRh CO NC H
. x synthesised under 0.1 MPa
4 3 3
Ž
NC H
.
x
Ž
.Ž
4
4
3 4
2
Ž
.
wP
Ž
4
To split dihydrogen molecule effectively the application
of higher pressure is required. We have found as quite
interesting that even small amounts of N-pyrrolyl phos-
phines added to the system containing
of H in hydrogenation of aromatics and cyclic olefins.
2
The investigations of H2 activation mechanism by
rhodium
Ž
I
.
N-pyrrolyl phosphino complexes leading to
the formation of HRh
Ž
CO.ŽPPh3.3 are also reported.
Rh acac CO PPh and PPh3 facilitate this reaction
.Ž .Ž
Ž
.
3
and ca. 80% of HRh
In order to elucidate the most important steps of
HRh
CO.ŽPPh3.3 complex formation at the presence of
N-pyrrolyl phosphines the spectroscopic studies have
ŽCO.ŽPPh3.3 could be obtained.
2
. Results and discussion
The passing of a mixture of H rCO
Ž
Ž
0.1 MPa
acac.ŽCO.2 and a
proceeds with
formation of the rhodium hydrido complexes of formula
HRh CO
wPPhxŽNC H4. x w18x. The corresponding
.
2
3
1
through a solution containing Rh
PPhx
4 4
N-pyrrolyl phosphine NC H .3yx
Ž .
Ž
been done. In P NMR spectrum of the solution con-
taining equimolar concentration of Rh
acac.ŽCO.ŽPPh3
qP
NC H4.3 briefly after mixing two above compo-
nents, the doublet, typical for Rh
Ž
Ž
.
Ž
4
Ž
.
Ž
acac NC H4.
.wPŽ x
4 3 2
4
3yx
3
reaction with only H leads to the formation of two
complexes: HRh
HRhwPPhxŽNC H4
was observed. Other complexes present in solution were
in dynamic exchange with phosphine ligands. This
2
Ž
CO
.
wPPh
Ž
NC H
. x
and
x
4
4 3y x 3
1
.
x in the ratio dependent on the
was indicated by the presence of the H NMR signal at
4
3yx 4
1
.84 ppm
Rh acac
wP
C H 3 acac
Rh
acac.ŽCO.wPŽNC H4.3x complexes. At the same
Ž
next to 1.71 ppm derived from
NC H4.
which is an average signal of
in R h and
acac.ŽC O .ŽP P h 3
initial concentration of N-pyrrolyl phosphine. Higher
N-pyrrolyl phosphine concentrations favour formation
of the corresponding hydrido complex without CO
in coordination sphere, so that at the concentration ratio
Ž
.
Ž
x .
3 2
4
Ž
.
Ž
.
Ž
4
3
1
wR h
Ž
a c a c . Ž C O . 2 x:wP
Ž
N C 4 H 4 . 3 x s 1 :5 ,
time, in P NMR spectra two broad lines at ca. 40 ppm
HRhwP
Ž
NC H4.
x
is the only reaction product. Its
and ca. 85 ppm assigned for complexes with PPh and
4
3 4
3
P
ŽNC H4.3 respectively, were observed. The spectra
structure was confirmed by quintet of doublets observed
4
1
in H NMR spectrum at dsy10.2 ppm. The spectrum
are changing in time and after several hours the mixed
ligand complex of formula Rh
acac.ŽPPh3.Ž NC H . .
was identified in reaction mixture by the characteristic
Ž
P
Ž
was recorded directly for the reaction mixture because
of very low solubility of the complex in organic sol-
4
4 3
3
1
vents. Stirring the suspension of HRhwP
toluene in CO atmosphere 0.1 MPa pressure applied
causes in 5 min formation of totally transparent solution
from which HRh CO
wP NC H4.3x3 was isolated as the
only product according to the reaction:
HRh P
NC H .3 4 qCO
HRh
Ž
NC H4. x in
P NMR spectrum
It can be concluded, that N-pyrrolyl phosphine la-
bilises the coordination sphere of Rh
acac.ŽCO.ŽPPh3
Table 1 .
Ž .
4
3 4
Ž
.
Ž
.
Ž
.
Ž
and partially substitutes PPh and CO leading to the
4
3
formation of the mixture of complexes according to the
reaction:
Ž
4
4
P
Ž
NC H 4.3
4
™
Ž
CO
.
P
Ž Ž
NC H .3 3 qP NC H .3
4
4
4
4
nRh
Ž
acac. ŽCO. ŽPPh3
.
™
Rh
Ž
acac
.
The formation of hydride complexes of
HRhwPPhxŽNC H4.3yx x type have the similar course
4
4
=
P
Ž
NC H .3 2 qRh
Ž
acac. ŽCO
.
P
Ž
NC H .3
4
4
4
4
Ž
reaction below
.
for all N-pyrrolyl phosphines and in
each case the compound of low solubility was obtained.
Rh
acac. ŽCO.2 q4PPhx
HRh PPhx
NC H .3yx 4 qHacacq2CO
This reaction is analogues to the earlier described
synthesis of phosphite complex HRhwP OPh.3x4 w15x. It
was found convenient to use Rh
acac.ŽC H4. instead
of Rh
acac.ŽCO.2 as starting rhodium complex to pre-
vent formation even traces of carbonyl containing
qRh
Ž
acac. ŽPPh3
.
P
Ž
NC H .3
4
4
Ž
™
Ž
NC H .3yx qH2
4 4
The presence of N-pyrrolyl phosphine, PPh NC
Ž
2
4
.
Ž
H4
.
, facilitates the reaction of Rh
Ž
acac.ŽCO.ŽPPh3
CO
is formed within 1 h of the reaction:
4
4
complex with dihydrogen and HRh
Ž
.
wPPh2ŽNC4
H4
.
Ž
™
x2
Ž
PPh3
.
Ž
Ž
2
2
Rh
acac. ŽCO. ŽPPh3
HRh CO
.
q2PPh2
Ž
NC H
.
qH2
4
4
Ž
Ž
.
PPh2
Ž
NC H . 2
Ž
PPh3
.
qHacac
4
4