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Methyltriphenylphosphonium[oxy(methylenetriphenylphosphorane)-carbene]pentacarbonylchromium(0): An ylide-carbene complex
Joumal of Prgonometallic Chemisry, 49 (1973) C73-C76 @ Elsevier Sequoia Sk, Lawanne - Printed in The Netherlands
Preliminary
c73
communication
Methyltriphenylphosphonium
[ oxy (methylenetriphenylphosphorane)-
carbene] pentacarbonylchromium(0):
An ytide-carbene complex*
DENNIS K. MITCHELL and WILLIAM C_ KASKA Department
of Chemistry.
University of Gzlifornirr, Santa Barbara, Gdifomti
93106 (iX.4.)
(Received November 7tb, 1972; by publisher January lStb,l973)
The addition
of phosphorus
ylides to transition
metal carbonyl
complexes
gives
ylide-carbene adducts in high yield. This facile addition to the metal coordinated carbon monoxide is in contrast to all previous reports which emphasize only substitution of carbon monoxide by the ylide carbon atomrW2. Thus, the interaction of alkali halide free methylenetriphenylphosphorane3 with chromium hexacarbonyl in a 2/l molar ratio respectively in THF gave a bright yellow addition product, [(CO)sCr(O-PhsPCHs)+_ CHPPhs] (I) m-p. 115-126” (dec.) with satisfactory C, H, 0, and P analyses (yield 0.3%). The 60 MHz NMR spectrum in pyridine showed two doublets at 6 4.65 ppm, J(PCH) 40 Hz and 6 3.05 ppm, J(PCH) 13 Hz in the ratio of l/3 respectively. The same spectrum was obtained in DMSO&. The absorption at 6 3.05 ppm was identified as Ph3PCHs+ and the absorption at 4.65 ppm was assigned to the methynic proton of the complex, I. An IR spectrum of the complex in THF solution showed four Y(CO) bands at 2015w, 1985m, 1890vs,and 1859mcm-!. Ordinarily three IR active bands are observed for C’, v symmetry of pentacarbonyl adducts although an infrared inactive band of Br symmetry can often become allowed if the symmetry of the complex is distorted from idealized Car, symmetry. Although the peak at 1985 cm-’ occurs at the same frequency as Cr(CO)e, there was no evidence for Cr(CO)e as an impurity. After five recrystallizations from THF-pentane, the 1985 cm-’ band showed no diminution in intensity. The presence of THF could, however, induce slight decomposition of the complex. This has often been observed to be the case with carbene complexes’. These results are best described in terms of the following equation which has also been verified by a mass balance accounting of all the materials: PhJP=CHZ
-I-
CrK016
(C0)@--c
fPIesented In part at the Fifth International Moscow, U.S.S.R.
/O\
Conference
Cl+--gPl13
on 0rganometaI.k
Chemistry, August 1971,
.c74-
.
+
.
PRELIMINARY. COhfMUNiCATION
cC0)*Cr-c
CH2=PPn3
\
Ph$--Cl+3
c=PPn3 I H
The initial-carbonyl-ylideladduct
does not elim-inate triphenylphosphine
to give an olefm in the usual Wittig manner but rapidly undergoes transylidations
&oxido ylide adducts of the type reported by Schlosser6. The chromium complex, suspended in toluene, can be methylated atom with CH,OSC&F to give
/
and
I
on the oxygen
of the alkylated
Ph,kH,
OSO,F-.
3
H
An NMR spectrum
to give
OCH3
\C=PPh
(CO)&+c
oxide
product in benzene showed a singlet at
S 3.50 ppm for the methyl group and a doublet at 6 5.40 ppm J(F’CH) 33 HZ for the lone ylidic proton in a 3/l ratio respectively. The methyltriphenylphosphonium fluorosulfonate was identified by comparison with an authentic
sample.
Greco’ has recently reported that equimolar amounts of Group VI transition metal carbonyk and methylenetriphenylphosphorane [(C,H,),wH, - LiBr] generated “in situ” give a l/l adduct instead of the 2/l adduct reported here. A r-allylic structure W5’3P\C
#+,
0 MKO),
t/-
M
=
Cr,Mo.W
with a THF oxonium cation has been postulated_ The following equation wouid describe .the reaction: M (CO16
-I-
(CgH513P=CH2
THF
- LiBr
-
K015M-C
/“-
GtC,H~3LiBr
‘CH;’
/O-
4.
tCO15M--C1CH,~(C6~&.
LiBr
I-
+
2
+ 0 + [
9
I
LIBr-
PRELIMINARY COMMUNICATION
Our studies with transition metal carbonyls In the case of the tungsten 6 4.7O,J(PCH) 41.5 Hz;6
c75
alkali halide free methylenetriphenylphosphorane and Group VI in a l/l molar ratio in THF show the presence of twd prod&s. complex, the NMR spectrum showed a set of three doublets at 3.35,J(PCH) 13.5 Hz;and 6 2_02,J(PCH)‘13 Hz. The fust
two peaks at S 4.7 and 3.35 were in the ratio of l/3 respectively. The third peak was
assigned to a l/l adduct and represented
3% of the reaction mixture: 0-
WKOI,
+
tC,H&P=CH2
-
THF
tCO&w-C
/
(C,H,),&H~
\ / 6 3.35
H~c=P(c6H51 / 6 4.70 (I)
70%
The addition of one molar equivalent of methylenetriphenylphosphorane to the mixture of I and II in THF results in the total disappearance of II and the formation of I. Thus the initial adduct in the reaction is II which subsequently loses a proton to methylenetriphenylphosphorane to form the salt I. The approximate pKa of THF in water’ is -2.1, and the pKa of most conjugate acids of ylides range’ from 5 to 7. Even though these values reflect determinations in water, it does not seem likely that THF is a strong enough base to remove a proton from II at equilibrium. Furthermore, as suggested by Greco*, the postulate of a Ir-allylic structure for the ylide-pentacarbonyl complex I is also unnecessary since it implies that the structures have more electrons than the next inert gas configurationg. ACKNOWLEDGEMENT We thank the donors of the Petroleum Research Fund sponsored by the American Chemical Society and the Research Committee, University of California, Santa Barbara for financial support. REFERENCES 1 W. Hieber, E. Winter and E. Schubert, Chem. Ber., 95 (1962) 3070; H. Bock and H. Tom Dieck, 2. Narurforsch. B, 21 (1966) 739; K.A.O. Starzewski, H. Tom Dieck, K.D. Franz and F. Hohmann, J. OrganometaL Chem., 42 (1972) C3.5; D. Cashman and FJ. Lalor, J. OrganometaL Chem., 32 (1971) 351; B. Barrett, C. Kriiger and Y.H. Tsay, Abstr. Vth Intern. ConJ Organometa?. Chem. VOL I, 1971, p- 155. 2 A. Greco, J. O~anometal. clrem., 43 (1972) 351. 3 R. KLister, D. Simic and M.A. Grossberger,Liebigs Ann. Chem., 739 (1970) 211. 4 M-Y. Darensbourg and DJ. Darensbourg, Inorg. Gem., 9 (1970) 32.
-:
P-NARY
CObQ&JNICATIoN
3 :ZfkXkstma& ch_em. Beri,95-(I&) 58. -6. .M. ‘Schlo$er,.FX. Chrisgma&k Fiskalaand Di Coffinct, Synthesis, (1971) 29. .7 EJ$h-+e~t&&r#wk. Oti.-Chem., l(1963) 223. .8 A.W; Johnson, Yhii Chemisiij’, Acatiehc Press,1966, p_ 661. .9 .-CA Tolmawchem. ~SotL-_Rh., 1 (1972) 337; R.B. King, Tnmsitionhietai O+wtiet&?iic C&mis!m Academic Press,1969, p. 4.
Preliminary
c73
communication
Methyltriphenylphosphonium
[ oxy (methylenetriphenylphosphorane)-
carbene] pentacarbonylchromium(0):
An ytide-carbene complex*
DENNIS K. MITCHELL and WILLIAM C_ KASKA Department
of Chemistry.
University of Gzlifornirr, Santa Barbara, Gdifomti
93106 (iX.4.)
(Received November 7tb, 1972; by publisher January lStb,l973)
The addition
of phosphorus
ylides to transition
metal carbonyl
complexes
gives
ylide-carbene adducts in high yield. This facile addition to the metal coordinated carbon monoxide is in contrast to all previous reports which emphasize only substitution of carbon monoxide by the ylide carbon atomrW2. Thus, the interaction of alkali halide free methylenetriphenylphosphorane3 with chromium hexacarbonyl in a 2/l molar ratio respectively in THF gave a bright yellow addition product, [(CO)sCr(O-PhsPCHs)+_ CHPPhs] (I) m-p. 115-126” (dec.) with satisfactory C, H, 0, and P analyses (yield 0.3%). The 60 MHz NMR spectrum in pyridine showed two doublets at 6 4.65 ppm, J(PCH) 40 Hz and 6 3.05 ppm, J(PCH) 13 Hz in the ratio of l/3 respectively. The same spectrum was obtained in DMSO&. The absorption at 6 3.05 ppm was identified as Ph3PCHs+ and the absorption at 4.65 ppm was assigned to the methynic proton of the complex, I. An IR spectrum of the complex in THF solution showed four Y(CO) bands at 2015w, 1985m, 1890vs,and 1859mcm-!. Ordinarily three IR active bands are observed for C’, v symmetry of pentacarbonyl adducts although an infrared inactive band of Br symmetry can often become allowed if the symmetry of the complex is distorted from idealized Car, symmetry. Although the peak at 1985 cm-’ occurs at the same frequency as Cr(CO)e, there was no evidence for Cr(CO)e as an impurity. After five recrystallizations from THF-pentane, the 1985 cm-’ band showed no diminution in intensity. The presence of THF could, however, induce slight decomposition of the complex. This has often been observed to be the case with carbene complexes’. These results are best described in terms of the following equation which has also been verified by a mass balance accounting of all the materials: PhJP=CHZ
-I-
CrK016
(C0)@--c
fPIesented In part at the Fifth International Moscow, U.S.S.R.
/O\
Conference
Cl+--gPl13
on 0rganometaI.k
Chemistry, August 1971,
.c74-
.
+
.
PRELIMINARY. COhfMUNiCATION
cC0)*Cr-c
CH2=PPn3
\
Ph$--Cl+3
c=PPn3 I H
The initial-carbonyl-ylideladduct
does not elim-inate triphenylphosphine
to give an olefm in the usual Wittig manner but rapidly undergoes transylidations
&oxido ylide adducts of the type reported by Schlosser6. The chromium complex, suspended in toluene, can be methylated atom with CH,OSC&F to give
/
and
I
on the oxygen
of the alkylated
Ph,kH,
OSO,F-.
3
H
An NMR spectrum
to give
OCH3
\C=PPh
(CO)&+c
oxide
product in benzene showed a singlet at
S 3.50 ppm for the methyl group and a doublet at 6 5.40 ppm J(F’CH) 33 HZ for the lone ylidic proton in a 3/l ratio respectively. The methyltriphenylphosphonium fluorosulfonate was identified by comparison with an authentic
sample.
Greco’ has recently reported that equimolar amounts of Group VI transition metal carbonyk and methylenetriphenylphosphorane [(C,H,),wH, - LiBr] generated “in situ” give a l/l adduct instead of the 2/l adduct reported here. A r-allylic structure W5’3P\C
#+,
0 MKO),
t/-
M
=
Cr,Mo.W
with a THF oxonium cation has been postulated_ The following equation wouid describe .the reaction: M (CO16
-I-
(CgH513P=CH2
THF
- LiBr
-
K015M-C
/“-
GtC,H~3LiBr
‘CH;’
/O-
4.
tCO15M--C1CH,~(C6~&.
LiBr
I-
+
2
+ 0 + [
9
I
LIBr-
PRELIMINARY COMMUNICATION
Our studies with transition metal carbonyls In the case of the tungsten 6 4.7O,J(PCH) 41.5 Hz;6
c75
alkali halide free methylenetriphenylphosphorane and Group VI in a l/l molar ratio in THF show the presence of twd prod&s. complex, the NMR spectrum showed a set of three doublets at 3.35,J(PCH) 13.5 Hz;and 6 2_02,J(PCH)‘13 Hz. The fust
two peaks at S 4.7 and 3.35 were in the ratio of l/3 respectively. The third peak was
assigned to a l/l adduct and represented
3% of the reaction mixture: 0-
WKOI,
+
tC,H&P=CH2
-
THF
tCO&w-C
/
(C,H,),&H~
\ / 6 3.35
H~c=P(c6H51 / 6 4.70 (I)
70%
The addition of one molar equivalent of methylenetriphenylphosphorane to the mixture of I and II in THF results in the total disappearance of II and the formation of I. Thus the initial adduct in the reaction is II which subsequently loses a proton to methylenetriphenylphosphorane to form the salt I. The approximate pKa of THF in water’ is -2.1, and the pKa of most conjugate acids of ylides range’ from 5 to 7. Even though these values reflect determinations in water, it does not seem likely that THF is a strong enough base to remove a proton from II at equilibrium. Furthermore, as suggested by Greco*, the postulate of a Ir-allylic structure for the ylide-pentacarbonyl complex I is also unnecessary since it implies that the structures have more electrons than the next inert gas configurationg. ACKNOWLEDGEMENT We thank the donors of the Petroleum Research Fund sponsored by the American Chemical Society and the Research Committee, University of California, Santa Barbara for financial support. REFERENCES 1 W. Hieber, E. Winter and E. Schubert, Chem. Ber., 95 (1962) 3070; H. Bock and H. Tom Dieck, 2. Narurforsch. B, 21 (1966) 739; K.A.O. Starzewski, H. Tom Dieck, K.D. Franz and F. Hohmann, J. OrganometaL Chem., 42 (1972) C3.5; D. Cashman and FJ. Lalor, J. OrganometaL Chem., 32 (1971) 351; B. Barrett, C. Kriiger and Y.H. Tsay, Abstr. Vth Intern. ConJ Organometa?. Chem. VOL I, 1971, p- 155. 2 A. Greco, J. O~anometal. clrem., 43 (1972) 351. 3 R. KLister, D. Simic and M.A. Grossberger,Liebigs Ann. Chem., 739 (1970) 211. 4 M-Y. Darensbourg and DJ. Darensbourg, Inorg. Gem., 9 (1970) 32.
-:
P-NARY
CObQ&JNICATIoN
3 :ZfkXkstma& ch_em. Beri,95-(I&) 58. -6. .M. ‘Schlo$er,.FX. Chrisgma&k Fiskalaand Di Coffinct, Synthesis, (1971) 29. .7 EJ$h-+e~t&&r#wk. Oti.-Chem., l(1963) 223. .8 A.W; Johnson, Yhii Chemisiij’, Acatiehc Press,1966, p_ 661. .9 .-CA Tolmawchem. ~SotL-_Rh., 1 (1972) 337; R.B. King, Tnmsitionhietai O+wtiet&?iic C&mis!m Academic Press,1969, p. 4.