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An infrared spectroscopic study of some phosphine chalcogenide derivatives of chromium and tungsten hexacarbonyls
INORG.
NUCL.
CHEM. LETTERS
Vol. 9, pp. 941-945, 1973.
Perganum Press.
Printed in Great Britain.
AN INFRARED SPECTROSCOPIC STUDY OF SOME PHOSPHINE CHALCOGENIDE DERIVATIVES OF CHROMIUMAND TUNGSTEN HEXACARBONYLS
P. M. Boorman , S. A. Clow, D. Ports and H. Wieser Department of Chemistry, The University of Calgary Calgary, Alberta, Canada (Receioed 10 April l ~ 3 )
The bonding in phosphine sulfidesand selenides has been of considerable interest in recent years (i). Likewise, the coordination properties of these compounds has attracted attention (2). However, most of these studies have related to their basicity and o-donor properties rather than to their possible ~-acceptor ability. Consequently, we report here the infrared spectroscopic properties of compounds of the type M(CO)5L, where H = Cr or W, and L = PhsPS(Se), CYsPS(Se), MesPS and (Me2N)sPS.
During the course of our work the complexes in which
L = Ph3PS and Me3PS were reported by Brodie and co-workers (3), but none of the other compounds has been previously described.
The present work is the
first detailed investigation of the ir spectra of complexes of this type.
Experimental
The compounds were prepared by UV photolysis of solutions of the appropriate ligand and metal carbonyl in tetrahydrofuran. analyses were obtained for all the new compounds.
Satisfactory elemental
Other synthetic methods
always gave rise to metal chalcogenides, and even the photolytic method gave rise to unstable oils with the ligands BusPS(Se) and (EtO)sPS , whereas PhsAsS and Ph3SbS yielded analytically pure samples of M(CO)sPh3As and M(CO)5PhsSb , respectively. Infrared spectra were carefully measured in hexane solution in 0 . 1 m m KBr solution cells, using a calibrated Perkin Elmer 621 spectrophotometer.
941
PHOSPHINE CHALCOGENIDE DERIVATIVES
942
VoL 9, No. 9
Infrared Spectra
In distinct contrast to previous work (3) we find that only in certain cases does the X3PS(Se) ligand cause a carbonyl spectrum (Table i) that deviates significantly from that expected for an idealized C~v mlcrosymmetry. ments are based on arguments presented by several authors (4,5,6).
Our assignThe compounds
containing Ph3PS , Ph3PSe and (Me2N)3PS all yield simple C4v spectra (2A I + E) although the infrared forbidden B! mode does sometimes occur very weakly.
In
other instances (L = Me3PS , Cy3PS(Se)) the E band is split, as implied by Brodie (3).
Another point of difference between our spectra and the spectrum previously
reported (3) is our characterization of free metal hexacarbonyls as decomposition products of the phosphine chalcogenide complexes.
Bands at 1984 cm -I (Cr com-
plexes) and 1890 cm -I (W complexes) appeared in spectra of the derivatives and these increased in intensity with time.
TABLE i
Solution (Hexane) Spectra of the Complexes M(CO)bL and their Assignments (on the basis of C~v Syam~etry) Carbonyl Stretching Vibrations (cm-I)
Compound
AI
(i)
BI
E
AI
(2)
Cr(CO)5SePPh 3
2059 m,sp
1979 w
1939 vs
1914 s,sp
Cr(CO)5SPPh 3
2063 m, sp
--
1947 s
1912 m,sp
W(CO)bSePPh 3
2066 m,sp
1975 w
1935 vs
1910 s,sp
W(CO)bSPPh 3
2068 m,sp
1977 w
1935 vs
1909 s,sp
Cr(CO)5SP(NMe2) 3 2062 m,sp
1980 m
1935 s,br
1909 s,sp
1922 s,br
1906 s,sp
W(CO)5SP(NMe2) 3
2068 m,sp
1975 m
W(CO)5SPMe 3
2070 m,sp
---
1939 s,sp 1924 s,sp
1908 s,sp
Cr(CO)bSPMe 3
2064 m,sp
1946 s,sp 1927 s,sp
1909 s,sp
W(CO)5SePCy 3
2065 m, sp
1975 m, sp
1935 s,sp 1922 s,sp
1906 s,sp
Cr(CO)bSePCy 3
2057 m,sp
1979 w
1941 s,sp 1925 s,sp
1910 s,sp
W(CO)5SPCy 3
2067 m,sp
1976 m,sp
1933 s,sp 1922 s,sp
1905 s,sp
Vol. 9, No. 9
PHOSPI']IINE CHALCOOENIDE DERIVATIVES
943
Bands associated with P = S(Se) stretching modes are shown in Table 2.
TABLE 2
P = S(Se) Stretching Frequencies (IR) for M(CO)5L Complexes and Uncoordinated Ligands in Hexane Solutions
Compound
v~P = S~Se))
Compound
_
~P
- S~Se))
Cr(CO)sSePPh 3
544
W(CO)5SPMe 3
540
Cr(CO)sSPPh 3
600
Cr(CO)5SPMe 3
540
W(CO)5SePPh 3
543
Ph3PSe
564
W(C0)5SPPh 3
599
Ph3PS
645
Cr(CO) 5SP(Me2N)3
544
(Me2N)3PS
560
W(CO)5SP(Me2N) 3
545
Me3PS
566
The d e c r e a s e s reported (2).
for
i n ~ ( P = S) a n d ~(P = Se) a r e o f a s i m i l a r these
Surprisingly
ligands , though,
in adducts
with metals
magnitude
in positive
to those
oxidation
t h e c h a n g e i n v ( P = S) u p o n c o o r d i n a t i o n
states
o f He3PS
(-26 cm -I) is smaller than that of Ph3PS (A~ = -45 cm -I) even though Me3PS causes the E carbonyl mode to lose its degeneracy whereas Ph3PS does not,
A
likely explanation is that in the free PhsPS molecule there is a greater degree of d~ + pw interaction in the P = S bond, which is weakened upon coordination to the metal. series Ph3PS
Since the strength of such dw + p~ bonding decreases in the >
triphenyl case.
Me3PS
)
(Me2N)3PS ,
Av(P = S) is most pronounced in the
On this basis one would predict that metal-sulfur d~-d~
interaction would be rather limited, since this would tend to strengthen the P-S ~ bond. The u s e o f v i b r a t i o n a l metal-ligand tention
(7).
q-bonding
spectroscopic
in carbonyl
data
to examine the extent
complexes has been a matter
of
o f some c o n -
It seems clear that there is no simple way of identifying the
relative importance of o-donation and w-acceptamce of a ligand L.
However.
either carbonyl frequencies or Cotton-Kraihanzel (5) force constants may be
PHOSPHINE CHALCOGENIDE DERIVATIVES
944
Vol. 9, No. 9
used (7) as the basis for comparing the overall (e-~) donation from the ligand to the metal in a series of complexes M(CO)hL.
We have used the Sum of the C-K
stretching force constants as the basis for our comparisons since these reflect all the IR bands and act as a good confirmation of our band assignments. In Table 3 the ligands Ph3PS , Ph3PSe and (Me2N)3PS are placed in their relative positions in a series in which increasing amounts of charge are transferred from the ligand to the metal for the compounds W(CO)5L.
It will be noted that the
ligands occur above cyclohexylamine in the series for which compound no ~-bonding would be expected.
From this it may be implied that the chalcogenides do possess
some ~-acceptor characCer (8).
TABLE 3
Force Constants for W(CO)5L Complexes
Compound
kI
x
+ k2
ki
**
W(CO)sPPh3 #
15.58
15.85
0.30
W(CO)sSePPh 3
14.97
15.74
0.33
W(CO)5SPPh 3
14.89
15.78
0.33
W(CO)5SP(NMe2) 3
14.85
15.73
0.34
W(C0)5C6HIINH2 #
14.65
15.74
0.35
W(CO)5C2H50H#
14,53
15.73
0.35
W(CO)5(DMF) #
13.93
15.58
0.36
Force constants obtained from Ref. 8. x
k I refers to CO trans to L.
+
k 2 refers to CO cis to L.
**
K i refers to CO stretch-stretch interaction constant.
The relative (a-~) donor characters of all of the R3PX llgands studied (including those which gave more complex spectra), may be compared on the basis of the averaged stretching frequencies for the 2Almodes for both W and Cr carbonyls,
The approximate order of the llgands is: -
Cy3PSe > Cy3PS > (Me2N)3PS ~ Ph3PSe ~ Me3PS > Ph3PS.
Vol. 9, No. 9
PHOSPHINE CHALCOGENIDE DERIVATIVES
945
There seems to be no simple correlation between this sequence and the complexity of the carbonyl spectra, nor with the relative changes in the v(PS) stretching frequencies.
For these reasons we are presently engaged in x-ray
crystallographic studies of selected compounds in an attempt to gain further insight into the problem. We thank the National Research Council of Canada for financial support, and H$ss V. Miasek for the preparation of two of the complexes.
References
i.
See for example R. F. HUDSON, Structure and Mechanism in Organophosphorus Chemistry, Chapter 3 Academic Press, New York (1965).
2.
N.M.
KARAYANNIS, C. M. MIICULSKI and L. L. PYTLEWSKI, Inorg. Chim. Acta.
Rev., 5, 82 (1971). 3.
E. W. AINSCOUGH, A. M. BRODIE and A. R. FURNESS, Chem. Co~anun., 1357 (1971).
4.
L. E. ORGEL, Inorg. Chem., I, 25 (1962).
5.
F. A. COTTON and C. S. KRAIHANZEL, J. Am. Chem. Soc., 84, 4432 (1962).
6.
F. A. COTTON and C. S. KRAIHANZEL, Inorg. Chem., 2, 533 (1963).
7.
L. M. HAINES and M. H. B. STIDDARD, Adv. Inorg. Chem. Radiochem., 12, 53
(1969). 8.
F. A. COTTON, I n o r g . Chem., 3, 702 (1968).
NUCL.
CHEM. LETTERS
Vol. 9, pp. 941-945, 1973.
Perganum Press.
Printed in Great Britain.
AN INFRARED SPECTROSCOPIC STUDY OF SOME PHOSPHINE CHALCOGENIDE DERIVATIVES OF CHROMIUMAND TUNGSTEN HEXACARBONYLS
P. M. Boorman , S. A. Clow, D. Ports and H. Wieser Department of Chemistry, The University of Calgary Calgary, Alberta, Canada (Receioed 10 April l ~ 3 )
The bonding in phosphine sulfidesand selenides has been of considerable interest in recent years (i). Likewise, the coordination properties of these compounds has attracted attention (2). However, most of these studies have related to their basicity and o-donor properties rather than to their possible ~-acceptor ability. Consequently, we report here the infrared spectroscopic properties of compounds of the type M(CO)5L, where H = Cr or W, and L = PhsPS(Se), CYsPS(Se), MesPS and (Me2N)sPS.
During the course of our work the complexes in which
L = Ph3PS and Me3PS were reported by Brodie and co-workers (3), but none of the other compounds has been previously described.
The present work is the
first detailed investigation of the ir spectra of complexes of this type.
Experimental
The compounds were prepared by UV photolysis of solutions of the appropriate ligand and metal carbonyl in tetrahydrofuran. analyses were obtained for all the new compounds.
Satisfactory elemental
Other synthetic methods
always gave rise to metal chalcogenides, and even the photolytic method gave rise to unstable oils with the ligands BusPS(Se) and (EtO)sPS , whereas PhsAsS and Ph3SbS yielded analytically pure samples of M(CO)sPh3As and M(CO)5PhsSb , respectively. Infrared spectra were carefully measured in hexane solution in 0 . 1 m m KBr solution cells, using a calibrated Perkin Elmer 621 spectrophotometer.
941
PHOSPHINE CHALCOGENIDE DERIVATIVES
942
VoL 9, No. 9
Infrared Spectra
In distinct contrast to previous work (3) we find that only in certain cases does the X3PS(Se) ligand cause a carbonyl spectrum (Table i) that deviates significantly from that expected for an idealized C~v mlcrosymmetry. ments are based on arguments presented by several authors (4,5,6).
Our assignThe compounds
containing Ph3PS , Ph3PSe and (Me2N)3PS all yield simple C4v spectra (2A I + E) although the infrared forbidden B! mode does sometimes occur very weakly.
In
other instances (L = Me3PS , Cy3PS(Se)) the E band is split, as implied by Brodie (3).
Another point of difference between our spectra and the spectrum previously
reported (3) is our characterization of free metal hexacarbonyls as decomposition products of the phosphine chalcogenide complexes.
Bands at 1984 cm -I (Cr com-
plexes) and 1890 cm -I (W complexes) appeared in spectra of the derivatives and these increased in intensity with time.
TABLE i
Solution (Hexane) Spectra of the Complexes M(CO)bL and their Assignments (on the basis of C~v Syam~etry) Carbonyl Stretching Vibrations (cm-I)
Compound
AI
(i)
BI
E
AI
(2)
Cr(CO)5SePPh 3
2059 m,sp
1979 w
1939 vs
1914 s,sp
Cr(CO)5SPPh 3
2063 m, sp
--
1947 s
1912 m,sp
W(CO)bSePPh 3
2066 m,sp
1975 w
1935 vs
1910 s,sp
W(CO)bSPPh 3
2068 m,sp
1977 w
1935 vs
1909 s,sp
Cr(CO)5SP(NMe2) 3 2062 m,sp
1980 m
1935 s,br
1909 s,sp
1922 s,br
1906 s,sp
W(CO)5SP(NMe2) 3
2068 m,sp
1975 m
W(CO)5SPMe 3
2070 m,sp
---
1939 s,sp 1924 s,sp
1908 s,sp
Cr(CO)bSPMe 3
2064 m,sp
1946 s,sp 1927 s,sp
1909 s,sp
W(CO)5SePCy 3
2065 m, sp
1975 m, sp
1935 s,sp 1922 s,sp
1906 s,sp
Cr(CO)bSePCy 3
2057 m,sp
1979 w
1941 s,sp 1925 s,sp
1910 s,sp
W(CO)5SPCy 3
2067 m,sp
1976 m,sp
1933 s,sp 1922 s,sp
1905 s,sp
Vol. 9, No. 9
PHOSPI']IINE CHALCOOENIDE DERIVATIVES
943
Bands associated with P = S(Se) stretching modes are shown in Table 2.
TABLE 2
P = S(Se) Stretching Frequencies (IR) for M(CO)5L Complexes and Uncoordinated Ligands in Hexane Solutions
Compound
v~P = S~Se))
Compound
_
~P
- S~Se))
Cr(CO)sSePPh 3
544
W(CO)5SPMe 3
540
Cr(CO)sSPPh 3
600
Cr(CO)5SPMe 3
540
W(CO)5SePPh 3
543
Ph3PSe
564
W(C0)5SPPh 3
599
Ph3PS
645
Cr(CO) 5SP(Me2N)3
544
(Me2N)3PS
560
W(CO)5SP(Me2N) 3
545
Me3PS
566
The d e c r e a s e s reported (2).
for
i n ~ ( P = S) a n d ~(P = Se) a r e o f a s i m i l a r these
Surprisingly
ligands , though,
in adducts
with metals
magnitude
in positive
to those
oxidation
t h e c h a n g e i n v ( P = S) u p o n c o o r d i n a t i o n
states
o f He3PS
(-26 cm -I) is smaller than that of Ph3PS (A~ = -45 cm -I) even though Me3PS causes the E carbonyl mode to lose its degeneracy whereas Ph3PS does not,
A
likely explanation is that in the free PhsPS molecule there is a greater degree of d~ + pw interaction in the P = S bond, which is weakened upon coordination to the metal. series Ph3PS
Since the strength of such dw + p~ bonding decreases in the >
triphenyl case.
Me3PS
)
(Me2N)3PS ,
Av(P = S) is most pronounced in the
On this basis one would predict that metal-sulfur d~-d~
interaction would be rather limited, since this would tend to strengthen the P-S ~ bond. The u s e o f v i b r a t i o n a l metal-ligand tention
(7).
q-bonding
spectroscopic
in carbonyl
data
to examine the extent
complexes has been a matter
of
o f some c o n -
It seems clear that there is no simple way of identifying the
relative importance of o-donation and w-acceptamce of a ligand L.
However.
either carbonyl frequencies or Cotton-Kraihanzel (5) force constants may be
PHOSPHINE CHALCOGENIDE DERIVATIVES
944
Vol. 9, No. 9
used (7) as the basis for comparing the overall (e-~) donation from the ligand to the metal in a series of complexes M(CO)hL.
We have used the Sum of the C-K
stretching force constants as the basis for our comparisons since these reflect all the IR bands and act as a good confirmation of our band assignments. In Table 3 the ligands Ph3PS , Ph3PSe and (Me2N)3PS are placed in their relative positions in a series in which increasing amounts of charge are transferred from the ligand to the metal for the compounds W(CO)5L.
It will be noted that the
ligands occur above cyclohexylamine in the series for which compound no ~-bonding would be expected.
From this it may be implied that the chalcogenides do possess
some ~-acceptor characCer (8).
TABLE 3
Force Constants for W(CO)5L Complexes
Compound
kI
x
+ k2
ki
**
W(CO)sPPh3 #
15.58
15.85
0.30
W(CO)sSePPh 3
14.97
15.74
0.33
W(CO)5SPPh 3
14.89
15.78
0.33
W(CO)5SP(NMe2) 3
14.85
15.73
0.34
W(C0)5C6HIINH2 #
14.65
15.74
0.35
W(CO)5C2H50H#
14,53
15.73
0.35
W(CO)5(DMF) #
13.93
15.58
0.36
Force constants obtained from Ref. 8. x
k I refers to CO trans to L.
+
k 2 refers to CO cis to L.
**
K i refers to CO stretch-stretch interaction constant.
The relative (a-~) donor characters of all of the R3PX llgands studied (including those which gave more complex spectra), may be compared on the basis of the averaged stretching frequencies for the 2Almodes for both W and Cr carbonyls,
The approximate order of the llgands is: -
Cy3PSe > Cy3PS > (Me2N)3PS ~ Ph3PSe ~ Me3PS > Ph3PS.
Vol. 9, No. 9
PHOSPHINE CHALCOGENIDE DERIVATIVES
945
There seems to be no simple correlation between this sequence and the complexity of the carbonyl spectra, nor with the relative changes in the v(PS) stretching frequencies.
For these reasons we are presently engaged in x-ray
crystallographic studies of selected compounds in an attempt to gain further insight into the problem. We thank the National Research Council of Canada for financial support, and H$ss V. Miasek for the preparation of two of the complexes.
References
i.
See for example R. F. HUDSON, Structure and Mechanism in Organophosphorus Chemistry, Chapter 3 Academic Press, New York (1965).
2.
N.M.
KARAYANNIS, C. M. MIICULSKI and L. L. PYTLEWSKI, Inorg. Chim. Acta.
Rev., 5, 82 (1971). 3.
E. W. AINSCOUGH, A. M. BRODIE and A. R. FURNESS, Chem. Co~anun., 1357 (1971).
4.
L. E. ORGEL, Inorg. Chem., I, 25 (1962).
5.
F. A. COTTON and C. S. KRAIHANZEL, J. Am. Chem. Soc., 84, 4432 (1962).
6.
F. A. COTTON and C. S. KRAIHANZEL, Inorg. Chem., 2, 533 (1963).
7.
L. M. HAINES and M. H. B. STIDDARD, Adv. Inorg. Chem. Radiochem., 12, 53
(1969). 8.
F. A. COTTON, I n o r g . Chem., 3, 702 (1968).