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13C NMR investigation of rhodium PI-complexes
INORG.
NUCL.
CHEM. LETTERS
Vol. 9,
pp. 885-889,
1973. Pergamon Press.
Printed
in
Great Britain.
13C NMR INVESTIGATION OF R H O D I U M P I - C O M P L E X E S D.E. Axelson, Dept. of Chemistry,
C.E. Holloway and A.J. Oliver
York University,
Downsview
(Toronto) Ontario,
Canada
(ReceiuedSAprill~3) Carbon nuclear
rhodium-olefin
magnetic
complexes
(1,2,3).
carbon atoms is not large is zero.
resonance
has
been
used
It was reported
for
several
studies
(i) that iJRh C for olefinic
(i0 ~ 14 Hz), and for the cyclopentadlenyl
This was a t t r i b u t e d
to the predominance
classification
group it
of T-type interactions
metal-ring bonding scheme, although with molecules of low symmetry, ~-C5H5RhL2,
of
in the
such as
of o-and T-bonding loses much of its significance.
An estimate of 15% s-character was made for the olefin-carbon AO used in bonding to the rhodium,
on the basis of an equation
the dominance of the Fermi Contact contribution.
(i) (p = 0.96 JRhC ) , assuming However,
this transfer of
s-character
into the metal-olefin bond does not seem to be countered by a de1 crease in s-character of the olefin C-H bonds as measured by JCH" Indeed an increase in IJcH seems to occur on coordination, noted in other ~-eomplexes s-character
of metals
in these complexes,
(4).
and similar effects have been
Insofar as JCH can be related to
which is not altogether
unlikely that the ligands are undergoing appreciable been pointed out (5) for Pt-olefin
complexes
certain,
it seems
internal change.
It has
that the spin coupling via a
Fermi Contact mechanism must occur through the ligand - metal o-bond in order to involve the metal s-orbital.
An MO calculation has suggested
(6) that the
Pt 6s-orbital does not contribute at all to the bonding in these complexes because of the relatively donor orbital.
large energy separation between it and the ligand
At the very least this does suggest that metal s-orbital
participation may be quite small.
If so, then relatively small changes of the
885
886
RHODIUM PI-COMPLEXES
Vol. 9, N o . 8
metal s-orbital participation in the ligand -- metal o-bond would have a marked effect on JMC'
At the same time other o-bonding contributions could be un-
changed or even enhanced via increased participation of other metal orbitals. The Table lists the 13C data obtained on some rhodium olefin and carbonyl derivatives in this study.
In these cases, splitting of the cyclopentadienyl
carbons by rhodium was clearly resolved.
Coupling to the olefinic carbon
atoms was in agreement with the previously reported data (i).
The magnitude of
JRhC for the cyclopentadienyl ligand is much smaller than for the olefinic case, the largest variations being observed for the rhodium(III) derivatives. The coupling also appears more sensitive to the other ligands on the metal, tending to decrease with increasing trans effect. (7) in JRhP"
A similar trend is observed
It is interesting to compare the reduced coupling constants of
platinum (8) and rhodium olefin derivatives.
In [(COD)RhCI] 2 the reduced
carbon-rhodium coupling is 14.8 x 1021 cm -3, and in (CODPt(CH3)~and (CODPt(CF3) 2 the reduced coupling is 8 x 1021 cm -3, which increases to 18.1 x 1021cm -3 for (COD)PtI 2.
Comparison of the ethylene derivatives (1,8) yields
KRh C = 10.5 to 14.8 x 1021 cm -3 and ~ t C
= 7.3 x 1021 cm -3 ~rans-[PtCH3(C2H4)-
~ ( C H 3 ) 2 ~ 2 ] P F 6 ) , and 28.5 x 1021 cm -3 ((C2H4)Pt(CI3)2).
The much larger varia-
tion in the platinum ethylene derivatives is reflected by a much larger variation in 13C coordination shift (8), although there is no clear relationship between the two.
This is not unexpected if coupling changes are due mainly to
changes in metal s-orbital participation. Coupling between rhodium and a carbonyl carbon has been reported for two derivatives, a cluster (2) RhN(CO) I2 and a dimer (3) [(C5H5)RhCO]2CO.
In the
monomeric derivative (C5H5)Rh(CO) 2 a value (Table) of 83.5 Hz is observed for IJRh C.
The correlation of s-characters and JRhC suggested by a previous study
(i) does not fit this compound, assuming the carbon s-character is 50%.
The
large value of the coupling suggests a greater involvement of rhodium s-orbital in this metal-carbon bond.
It has been noted elsewhere (9) that the reduced
~
62.1
All
downfie]d relative to TMS.
5.2
88.6
C5H5Rh[(CH3)2CHNC]I 2
*
0
93.3
CsHsRhP#3(COCH3)I
80.3
3.8
ppm
(COD)Rh(2.4.Leutidine)Cl
86.2
CsH5Rh(COD)
2.4
6
78.5
82.5
C5H5Rh(CO)P~ 3
3.0~0.2
JHz
Olefln
12.5
13.9
13.9
JHz
Isonitrile
P~3
Acetate
2.4 Leut:
It
"
It
(PC) " "
(RHC)
JHz
23.0 n4ogtSsee~
CH 3
not seen 133.8 (PC) 127.7 " 130.1 "
55.7
30.9 148.0 133.9 138.4 18.2
30.9
32.3
132.2 127.0 128.9
CH N~C
C:O ortho meta para
CH 3
CH3
ortho meta para
"
ppm
Carbons
19.9
Other
ortho meta para
(COD) aliphatie
P$3
CO
13C Data for Rhodium Com p lexes
[(COD)RhCI] 2
87.6
ppm
Cyclopentadlenyl
C5HsRh(CO) 2
Compound
Table
10.3 10.4 0
12.7 10.5 1.7
83.5
.o
888
RltODIUM P I - C O M P L E X E S
Vol. 9, No. 8
coupling KMC in the first row transition metal carbonyls increases left to right.
The reduced coupling for the rhodium complex (88.5 x 1021cm -3)
is intermediate between those of the first row carbonyls (14 to 40 x i0 21cm-3) and that of a third row derivative (durene)W(CO)3 (168 x i021cm-3).
The same
coupling has been observed for the dimer (3), the values of 2JRh C and IJRh. R h being near zero, the latter suggesting very little s-character in this bond. Only an averaged coupling is obtained for the cluster (2), however, similar values of
JRhC can fit the observed spectrum on taking into account that the
averaged spectrum is made up of nine iJRh C (terminal) plus three iJRh C (bridging) and thirty-three 2JRh C.
If values of 83 and 45 respectively are taken for
the iJRh C parameters and zero for 2JRh C an average of 19 Hz is obtained, compared to the experimental value of 17.1 Hz.
If 2JRh C is small but of opposite
sign to 1JRhc, which is consistent with the sign alternation observed in other couplings, then a closer fit could be obtained with only minor changes in the iJRh C parameters.
On the other hand, substituent effects can be quite large,
as the value of 68.8 Hz for JRhC in dicarbonyl rhodium chloride dimer (2) indicates.
This resonance, along with the carbonyl resonances of C5H5Rh(CO)P~3
and C5H5Rh(P~3)(COCH3)I ,
could not be observed in natural abundance in this
study.
Acknowledgements The authors thank Varian Associates for loan o£ an NV-14 FT NMR spectrometer.
Vol. 9, No. 8
RHODIUM P I - C O M P L E X E S
889
References i.
G.M. Bodner, B.N. Storhoff, D. Doddrell and L.J. Todd, Chem. Comm. 1530 (1970).
2.
F.A. Cotton, L. Kruczynski and B.L. Shapiro, J.Amer. Chem. Soc. 94, 6191 (1971).
3.
J. Evans, B.F.G. Johnson, J. Lewis and J.R. Norton, Chem. Comm. 79 (1973).
4.
Lauterbur, ~.Amer. Chem. Soc. 83, 1838 (1961)~ H.S. Gutowsky, J.Amer.Chem. Soc. 88, 1585 (1966).
5.
P.S. Braterman, Inorg. Chem. ~, 1066 (1966).
6.
K.S. Wheelock, J.H. Nelson, L.C. Cusachs and H.B. Jo~assen, J.Amer. Chem. Soc., 92, 5110 (1970).
7.
T.H. Brown and P.J. Green, J.Amer. Chem. Soc. 91, 3378 (1969).
8.
M.H. Chisholm, H.C. Clark, L.E. Manzer and J.B. Stothers, J.Amer. Chem. Soc 94, 5087 (1972).
9.
B.E. Mann, Chem. Comm. 976 (1971)
NUCL.
CHEM. LETTERS
Vol. 9,
pp. 885-889,
1973. Pergamon Press.
Printed
in
Great Britain.
13C NMR INVESTIGATION OF R H O D I U M P I - C O M P L E X E S D.E. Axelson, Dept. of Chemistry,
C.E. Holloway and A.J. Oliver
York University,
Downsview
(Toronto) Ontario,
Canada
(ReceiuedSAprill~3) Carbon nuclear
rhodium-olefin
magnetic
complexes
(1,2,3).
carbon atoms is not large is zero.
resonance
has
been
used
It was reported
for
several
studies
(i) that iJRh C for olefinic
(i0 ~ 14 Hz), and for the cyclopentadlenyl
This was a t t r i b u t e d
to the predominance
classification
group it
of T-type interactions
metal-ring bonding scheme, although with molecules of low symmetry, ~-C5H5RhL2,
of
in the
such as
of o-and T-bonding loses much of its significance.
An estimate of 15% s-character was made for the olefin-carbon AO used in bonding to the rhodium,
on the basis of an equation
the dominance of the Fermi Contact contribution.
(i) (p = 0.96 JRhC ) , assuming However,
this transfer of
s-character
into the metal-olefin bond does not seem to be countered by a de1 crease in s-character of the olefin C-H bonds as measured by JCH" Indeed an increase in IJcH seems to occur on coordination, noted in other ~-eomplexes s-character
of metals
in these complexes,
(4).
and similar effects have been
Insofar as JCH can be related to
which is not altogether
unlikely that the ligands are undergoing appreciable been pointed out (5) for Pt-olefin
complexes
certain,
it seems
internal change.
It has
that the spin coupling via a
Fermi Contact mechanism must occur through the ligand - metal o-bond in order to involve the metal s-orbital.
An MO calculation has suggested
(6) that the
Pt 6s-orbital does not contribute at all to the bonding in these complexes because of the relatively donor orbital.
large energy separation between it and the ligand
At the very least this does suggest that metal s-orbital
participation may be quite small.
If so, then relatively small changes of the
885
886
RHODIUM PI-COMPLEXES
Vol. 9, N o . 8
metal s-orbital participation in the ligand -- metal o-bond would have a marked effect on JMC'
At the same time other o-bonding contributions could be un-
changed or even enhanced via increased participation of other metal orbitals. The Table lists the 13C data obtained on some rhodium olefin and carbonyl derivatives in this study.
In these cases, splitting of the cyclopentadienyl
carbons by rhodium was clearly resolved.
Coupling to the olefinic carbon
atoms was in agreement with the previously reported data (i).
The magnitude of
JRhC for the cyclopentadienyl ligand is much smaller than for the olefinic case, the largest variations being observed for the rhodium(III) derivatives. The coupling also appears more sensitive to the other ligands on the metal, tending to decrease with increasing trans effect. (7) in JRhP"
A similar trend is observed
It is interesting to compare the reduced coupling constants of
platinum (8) and rhodium olefin derivatives.
In [(COD)RhCI] 2 the reduced
carbon-rhodium coupling is 14.8 x 1021 cm -3, and in (CODPt(CH3)~and (CODPt(CF3) 2 the reduced coupling is 8 x 1021 cm -3, which increases to 18.1 x 1021cm -3 for (COD)PtI 2.
Comparison of the ethylene derivatives (1,8) yields
KRh C = 10.5 to 14.8 x 1021 cm -3 and ~ t C
= 7.3 x 1021 cm -3 ~rans-[PtCH3(C2H4)-
~ ( C H 3 ) 2 ~ 2 ] P F 6 ) , and 28.5 x 1021 cm -3 ((C2H4)Pt(CI3)2).
The much larger varia-
tion in the platinum ethylene derivatives is reflected by a much larger variation in 13C coordination shift (8), although there is no clear relationship between the two.
This is not unexpected if coupling changes are due mainly to
changes in metal s-orbital participation. Coupling between rhodium and a carbonyl carbon has been reported for two derivatives, a cluster (2) RhN(CO) I2 and a dimer (3) [(C5H5)RhCO]2CO.
In the
monomeric derivative (C5H5)Rh(CO) 2 a value (Table) of 83.5 Hz is observed for IJRh C.
The correlation of s-characters and JRhC suggested by a previous study
(i) does not fit this compound, assuming the carbon s-character is 50%.
The
large value of the coupling suggests a greater involvement of rhodium s-orbital in this metal-carbon bond.
It has been noted elsewhere (9) that the reduced
~
62.1
All
downfie]d relative to TMS.
5.2
88.6
C5H5Rh[(CH3)2CHNC]I 2
*
0
93.3
CsHsRhP#3(COCH3)I
80.3
3.8
ppm
(COD)Rh(2.4.Leutidine)Cl
86.2
CsH5Rh(COD)
2.4
6
78.5
82.5
C5H5Rh(CO)P~ 3
3.0~0.2
JHz
Olefln
12.5
13.9
13.9
JHz
Isonitrile
P~3
Acetate
2.4 Leut:
It
"
It
(PC) " "
(RHC)
JHz
23.0 n4ogtSsee~
CH 3
not seen 133.8 (PC) 127.7 " 130.1 "
55.7
30.9 148.0 133.9 138.4 18.2
30.9
32.3
132.2 127.0 128.9
CH N~C
C:O ortho meta para
CH 3
CH3
ortho meta para
"
ppm
Carbons
19.9
Other
ortho meta para
(COD) aliphatie
P$3
CO
13C Data for Rhodium Com p lexes
[(COD)RhCI] 2
87.6
ppm
Cyclopentadlenyl
C5HsRh(CO) 2
Compound
Table
10.3 10.4 0
12.7 10.5 1.7
83.5
.o
888
RltODIUM P I - C O M P L E X E S
Vol. 9, No. 8
coupling KMC in the first row transition metal carbonyls increases left to right.
The reduced coupling for the rhodium complex (88.5 x 1021cm -3)
is intermediate between those of the first row carbonyls (14 to 40 x i0 21cm-3) and that of a third row derivative (durene)W(CO)3 (168 x i021cm-3).
The same
coupling has been observed for the dimer (3), the values of 2JRh C and IJRh. R h being near zero, the latter suggesting very little s-character in this bond. Only an averaged coupling is obtained for the cluster (2), however, similar values of
JRhC can fit the observed spectrum on taking into account that the
averaged spectrum is made up of nine iJRh C (terminal) plus three iJRh C (bridging) and thirty-three 2JRh C.
If values of 83 and 45 respectively are taken for
the iJRh C parameters and zero for 2JRh C an average of 19 Hz is obtained, compared to the experimental value of 17.1 Hz.
If 2JRh C is small but of opposite
sign to 1JRhc, which is consistent with the sign alternation observed in other couplings, then a closer fit could be obtained with only minor changes in the iJRh C parameters.
On the other hand, substituent effects can be quite large,
as the value of 68.8 Hz for JRhC in dicarbonyl rhodium chloride dimer (2) indicates.
This resonance, along with the carbonyl resonances of C5H5Rh(CO)P~3
and C5H5Rh(P~3)(COCH3)I ,
could not be observed in natural abundance in this
study.
Acknowledgements The authors thank Varian Associates for loan o£ an NV-14 FT NMR spectrometer.
Vol. 9, No. 8
RHODIUM P I - C O M P L E X E S
889
References i.
G.M. Bodner, B.N. Storhoff, D. Doddrell and L.J. Todd, Chem. Comm. 1530 (1970).
2.
F.A. Cotton, L. Kruczynski and B.L. Shapiro, J.Amer. Chem. Soc. 94, 6191 (1971).
3.
J. Evans, B.F.G. Johnson, J. Lewis and J.R. Norton, Chem. Comm. 79 (1973).
4.
Lauterbur, ~.Amer. Chem. Soc. 83, 1838 (1961)~ H.S. Gutowsky, J.Amer.Chem. Soc. 88, 1585 (1966).
5.
P.S. Braterman, Inorg. Chem. ~, 1066 (1966).
6.
K.S. Wheelock, J.H. Nelson, L.C. Cusachs and H.B. Jo~assen, J.Amer. Chem. Soc., 92, 5110 (1970).
7.
T.H. Brown and P.J. Green, J.Amer. Chem. Soc. 91, 3378 (1969).
8.
M.H. Chisholm, H.C. Clark, L.E. Manzer and J.B. Stothers, J.Amer. Chem. Soc 94, 5087 (1972).
9.
B.E. Mann, Chem. Comm. 976 (1971)