IR spectroscopic studies of the reversible equilibria between Rh(I)(triphos) aryloxides, aryloxycarbonyls, and carbonyls

Article abstract of DOI:10.1016/S0022-328X(98)01022-5

The complex, [Rh(triphos)CO][PF₆] {triphos = bis(2-diphenylphosphinoethyl)phenyl phosphine}, 4, reacts with aryloxides, ArO^- {Ar = C₆H₅, C₆H₄-p-CH₃, C₆H₄-p-OCH₃}. The formation and subsequent chemistry of the resulting aryloxycarbonyl complexes were observed by FTIR spectroscopy. These aryloxycarbonyl complexes are formed and decay via different pathways involving the fac- and mer-isomers of Rh(triphos)(CO)(OAr). Decarbonylation of Rh(triphos)(CO)(OAr) forms Rh(triphos)OAr, {Ar = C₆H₅ (1), C₆H₄-p-CH₃, (2) C₆H₄-p-OCH₃ (3)}, while elimination of the aryloxide via a different pathway can also reform [Rh(triphos)CO][PF₆], 4.

Full text of DOI:10.1016/S0022-328X(98)01022-5

Journal of Organometallic Chemistry 577 (1999) 31–37
IR spectroscopic studies of the reversible equilibria between
Rh(I)(triphos) aryloxides, aryloxycarbonyls, and carbonyls
Anne M. Gull, Julia M. Blatnak, Clifford P. Kubiak *
Department of Chemistry, Purdue Uni6ersity, 1393 Brown Laboratory of Chemistry, West Lafayette, IN 47907, USA
Received 15 June 1998; received in revised form 25 August 1998
Abstract
The complex, [Rh(triphos)CO][PF6] {triphos=bis(2-diphenylphosphinoethyl)phenyl phosphine}, 4, reacts with aryloxides,
ArO− {Ar=C6H5, C6H4-p-CH3, C6H4-p-OCH3}. The formation and subsequent chemistry of the resulting aryloxycarbonyl
complexes were observed by FTIR spectroscopy. These aryloxycarbonyl complexes are formed and decay via different pathways
involving the fac- and mer-isomers of Rh(triphos)(CO)(OAr). Decarbonylation of Rh(triphos)(CO)(OAr) forms Rh(triphos)OAr,
{Ar=C6H5 (1), C6H4-p-CH3, (2) C6H4-p-OCH3 (3)}, while elimination of the aryloxide via a different pathway can also reform
[Rh(triphos)CO][PF6], 4. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Reversible equilibria; Aryloxides; Aryloxycarbonyls; Carbonyls
1. Introduction
the carbonylation of [Pt(triphos)(OAr)][PF6] proceeds
by a similar mechanism [2].
There are two principal mechanisms by which late
transition metal aryloxy complexes can be carbonylated
to their respective aryloxycarbonyls. The first is classi-
cal migratory insertion, where the aryloxy ligand mi-
grates to a carbon monoxide cis to the aryloxy ligand,
Eq. ((1)).
A second type of mechanism that must be considered
in view of the lower M–OAr bond energies expected
for late transition metal aryloxy complexes, is nucle-
ophilic addition of the aryloxide to coordinated carbon
monoxide. This involves substitution of a weakly
bound aryloxy ligand by carbon monoxide, followed by
nucleophilic addition of the displaced aryloxide to the
carbonyl ligand Eq. (2).
LnM−OAr CXO Ln(CO)+
+
−OAr“LnM(C(O)OAr)
(1)
(2)
Bryndza concluded that this mechanism is important
in the carbonylation of the platinum alkoxy complexes,
Pt(dppe)(OMe)(R) (R=OMe, Me; dppe=1,2 bis-
(diphenylphosphino)ethane) [1] and we reported that
Atwood et al. found that nucleophilic addition of ary-
loxide to the coordinated carbon monoxide ligands of
[Ir(CO)2(PPh3)2]+ occurs during the reaction of
Ir(CO)(PPh3)2(OR) (R=Me, Ph) with carbon monox-
ide [3–6]. We describe reactions of a series of aryloxides
{ArO−; Ar=C6H5, C6H4-p-CH3, C6H4-p-OCH3} with
[Rh(triphos)(CO)]+ to afford aryloxycarbonyl com-
plexes, Rh(triphos)(C(O)OAr). We also report FTIR
spectroscopic studies of the reversible decarbonylation
and aryloxide eliminations.
* Corresponding author. Present address: Department of Chem-
istry and Biochemistry, University of California, San Diego, 9500
Gilman Drive, La Jolla, CA 92093-0358, USA. Fax: +1-619-534-
5383; e-mail: ckubiak@ucsd.edu
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01022-5

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A.M. Gull et al. / Journal of Organometallic Chemistry 577 (1999) 31–37
2. Results and discussion
carbonyl complexes have reported values of w(CO) in
the 2023–2029 cm−1 range [15,16].
2.1. Preparation of aryloxide and carbonyl complexes
2.2. Aryloxide additions to coordinated CO
The previously reported complex, Rh(triphos)Cl [7,8]
was used as the starting material for the synthesis of a
series of rhodium aryloxide complexes, 1–3. The com-
plex Rh(triphos)Cl, was reacted with excess sodium
aryloxide NaOAr {Ar=C6H5, C6H4-p-CH3, C6H4-p-
OCH3} in acetone and stirred overnight. The solvent
was removed and the solid was extracted into CH2Cl2
and precipitated with hexanes, to produce Rh(t-
riphos)OAr {1: Ar=C6H5, 2: Ar=C6H4-p-CH3, 3:
Ar=C6H4-p-OCH3}.
The reactions of 4 with various aryloxides were mon-
itored by IR spectroscopy. The complex [Rh-
(triphos)(CO)][PF6], 4, was dissolved in THF and
NaOAr {Ar=C6H5, C6H4-p-CH3, C6H4-p-OCH3} was
added as a solution in THF. Fig. 1 shows a series of IR
spectra taken over time with increasing amounts of
NaOC6H5. Immediately following addition of
NaOC6H5, the phenoxycarbonyl product is observed at
w(CO)=1709 cm−1 (Fig. 1b). Surprisingly, 30 min
later, this band has disappeared and the original band
for 4 at w(CO)=2021 cm−1 has almost completely
been restored (Fig. 1c). The phenoxycarbonyl band
reappears as additional NaOC6H5 is added (Fig. 1d).
This ephemeral product formation followed by rever-
sion to starting material cycle can be repeated several
times by adding more NaOC6H5 and waiting. Signifi-
cantly, two other carbonyl compounds, the fac- and
mer-isomers of Rh(triphos)(CO)(OC6H5), also are ob-
served in small quantities. The fact that both the fac-
and mer-isomers of Rh(triphos)(CO)(OC6H5) are ob-
served is consistent with the expectation that these
isomers may have different stabilities but interconvert
slowly because of the steric requirements of the triphos
ligand. Similar behavior has been observed with fac-
and mer-iridium triphos complexes [17]. The fac-
Rh(triphos)(CO)(OC6H5) complex is characterized by
w(CO)=2005 cm−1, while mer-Rh(triphos)(CO)(OC6-
H5) is observed at w(CO)=2058 cm−1. The assign-
ments of these isomers are based on the energetic
preference of the strongest | and y-donor ligands in
axial positions, as they would be in the fac-isomer. This
|/y donation results in increased backbonding to the
equatorial carbonyl ligand and the lower energy w(CO)
band. It is important to note that the appearance of
phenoxycarbonyl w(CO) absorption and its subsequent
disappearance (Fig. 1) implies that this species forms
and decays by separate pathways. The observation of
both the fac- and mer-isomers, the fac-isomer is consid-
ered more thermodynamically stable, implies that one
of these is an intermediate in the formation of the
phenoxycarbonyl complex, Rh(triphos)(C(O)OC6H5),
while the other isomer is an intermediate in its decay.
The reaction of 4 with a more nucleophilic aryl
oxide, NaOC6H4-p-CH3, eliminates the reaction ‘re-
bound’ phenomenon observed with NaOC6H5. Fig. 2
shows a series of IR spectra taken over time with
increasing amounts of NaOC6H4-p-CH3. The w(CO)
band at 1703 cm−1, corresponding to the aryloxycar-
bonyl, Rh(triphos)(C(O)OC6H4-p-CH3), grows with ad-
dition of NaOC6H4-p-CH3 (Fig. 2c) but does not decay
A few other rhodium aryloxides have been reported
previously,
Rh(PPh3)3OC6H4-p-CH3
including
Rh(PPh3)3OC6H5
[10] and
[9]
trans-
Rh(PPh3)2(CO)OC6H5 [11]. In general, the Rh–PB cou-
pling constant is quite sensitive to the nature of the
ligand trans to it. The magnitude of J(Rh–PB) de-
creases from 164 Hz for Rh(triphos)Cl to ca. 150 Hz
for the aryloxides, 1–3, suggesting that chloride and
aryloxides behave similarly as ligands to rhodium. The
relative trend of the Rh–OAr bonding interactions also
should be reflected in the Rh–PB coupling constants,
but due to the small difference in these values, no trend
is evident. The magnitude of J(Rh–PB) for 1–3 agrees
well with the reported value of 147 Hz for J(Rh–PB) of
Rh(ttp)OC6H5 {ttp=Ph(PCH2CH2CH2PPh2)2} [12].
The carbonyl complex [Rh(triphos)(CO)][PF6] was
prepared by treating Rh(triphos)Cl with AgPF6 in ace-
tone to remove chloride, generating an acetone solvento
complex. The reaction flask was evacuated and then
filled with carbon monoxide. The solution was stirred
for 1 h under CO, then product was precipitated with
diethyl ether to yield [Rh(triphos)(CO)][PF6], 4. The
1H-NMR spectrum shows four multiplets for the
triphos methylene protons at 2.23, 2.91, 3.15 and 3.31
ppm and the phenyl protons in the l 7.41–7.80 ppm
region. The 31P{1H}-NMR spectrum is an A2BX spin
system (l(PA)=55.6 ppm, l(PB)=104.7 ppm) with
2J(PAPB)=28.2 Hz, 1J(RhPA)=128 Hz, and
1J(RhPB)=115 Hz and l(PF6)= −144 ppm. The re-
lated rhodium triphosphine carbonyl complex,
[Rh{PhP(CH2CH2CH2PPh2)2}(CO)][PF6], was reported
by Meek and co-workers [13,14]. The 1J(RhPB) value of
115.2 Hz for their complex agrees well with that for
complex 4. The IR spectrum of 4 shows one terminal
w(CO) band at 2021 cm−1 in THF and at 2026 cm−1 in
KBr. For comparison, other rhodium tris(phosphine)

A.M. Gull et al. / Journal of Organometallic Chemistry 577 (1999) 31–37
33
Fig. 1. IR (THF) of the reaction of 4 with NaOC6H5: (a) 4 only (b) 0.5 equivalents of NaOC6H5 (c) 0.5 h after (b) (d) 0.25 additional equivalents
of NaOC6H5.
fac-isomer. One reason for this is the accumulation of
the fac-isomer whenever the aryloxycarbonyl complex
is observed (Fig. 1b,Fig. 2c,Fig. 3b). Another fact sup-
porting this view is the more persistent formation of the
aryloxycarbonyl species when the stronger nucleophiles,
afterward (Fig. 2d). This behavior differs radically from
that of the NaOC6H5 case. Again, both the fac- and
mer-isomers of Rh(triphos)(CO)(OAr) are observed,
but at w(CO) 2004 and 2057 cm−1, respectively. The
strongest nucleophile of the series, NaOC6H4-p-OCH3,
was also reacted with 4. Fig. 3 shows the IR spectra
taken over time after NaOC6H4-p-OCH3 addition. The
ArO−
=
−OC6H4-p-CH3 and −OC6H4-p-OCH3, are
used. These stronger nucleophiles favor the fac-isomer.
A key point is that the decay pathway of the aryloxy-
carbonyl complex must differ from its formation path-
way. The logic for this comes from the fact that the
aryloxycarbonyl clearly can be formed but over time
reverts to 4 plus aryloxide while a simple equilibrium
between 4 plus aryloxide and the aryloxycarbonyl com-
plex cannot be established. We suggest that decay of
the aryloxycarbonyl complex occurs through the mer-
isomer of Rh(triphos)(CO)(OAr), which is unstable
with respect to 4 plus the aryloxide ligand. The mer-iso-
mer becomes progressively less favored with the more
nucleophilic aryloxides, and this explains the persis-
tence of the aryloxycarbonyl complex when the more
nucleophilic aryloxides are used.
aryloxycarbonyl,
Rh(triphos)(C(O)OC6H4-p-OCH3),
was observed in the IR spectrum at 1700 cm−1 (Fig.
3c). Significantly, only the fac-isomer of Rh-
(triphos)(CO)(OC6H4-p-OCH3) is observed in the IR,
w(CO)=2002 cm−1. The fact that the mer-isomer is
not observed is reasonable since the para-methoxy
group makes this aryloxide a strong | and y donor
such that only the more stable fac-isomer is observed.
The differences in persistence of formation of the ary-
loxycarbonyl complexes based on the nucleophilic
strength of the aryloxide used indicates that the equi-
librium conditions governing this set of reactions are
highly reversible and nearly thermoneutral. A proposed
reaction pathway, Fig. 4, involves the initial formation
of one of the isomers of Rh(triphos)(CO)(OAr) by
addition of the ArO− to 4, followed by the nucleophilic
addition of the aryloxide to the coordinated carbonyl
resulting in the square planar aryloxycarbonyl complex.
We propose that the isomer formed initially is the
Attempts to isolate any of the aryloxycarbonyl com-
plexes, Rh-(triphos)(C(O)OAr) {Ar=C6H5, C6H4-p-
CH3, C6H4-p-OCH3} netted only [Rh(triphos)CO]PF6,
4, and the corresponding aryloxide, Rh(triphos)OAr,
1–3, as observed by 31P{1H}-NMR. The equilibrium

34
A.M. Gull et al. / Journal of Organometallic Chemistry 577 (1999) 31–37
Fig. 2. IR (THF) of the reaction of 4 with NaOC6H4-p-CH3: (a) 4 alone (b) after addition of 1.0 equivalents of NaOC6H4-p-CH3 (c) after addition
of another 0.5 equivalents of NaOC6H4-p-CH3 (d) 0.5 h after (c).
loss of carbon monoxide, Fig. 4, allows for the forma-
tion of Rh(triphos)OAr, 1–3. One way to block the
pathway by which the aryloxycarbonyl decays is to
occupy an additional vacant site on rhodium. This was
attempted with an additional carbonyl ligand. The pres-
ence of a second carbonyl also serves the purpose of
increasing the electrophilicity at the carbonyl carbon
atoms. The complex [Rh(triphos)(CO)][PF6], 4, was dis-
solved in THF and carbon monoxide was bubbled
through the solution, yielding [Rh(triphos)(CO)2][PF6],
5. Attempts to isolate the bis(carbonyl) complex, 5, led
only to recovery of 4. However, the IR spectrum of 5 in
THF clearly shows two terminal w(CO) bands at 2051
and 2006 cm−1. The 31P{1H}-NMR spectrum is an
A2BX spin system (l(PA)=64.0 ppm, l (PB)=104.9
5. These new bands correspond to fac-Rh-
(triphos)(CO)(C(O)OC6H5). The mer-isomer is not ob-
served as there is
a strong preference for the
phenoxycarbonyl ligand to occupy an axial position, as
it does in the facial-isomer. The phenoxycarbonyl is
formed and persists now that there are two carbonyl
ligands. The fact that the mer-isomer is not observed in
this experiment further supports our view that aryloxy-
carbonyl deinsertion occurs through the mer-isomer.
Attempts to isolate the phenoxycarbonyl, Rh-
(triphos)(CO)(C(O)OC6H5), were made, resulting only
in [Rh(triphos)CO]PF6, 4, and Rh(triphos)OC6H5, 1.
Again, the inevitable loss of a carbonyl ligand allows
for the usual pathway to phenoxycarbonyl ligand col-
lapse to carbon monoxide and phenoxide, shown in
Fig. 4.
1
1
ppm) with J(RhPA)=124 Hz, J(RhPB)=92 Hz and
2J(PAPB)=23 Hz. Related examples of rhodium
tris(phosphine) bis(carbonyl) complexes show similar
spectroscopic data [15,16]. The dicarbonyl complex,
3. Conclusion
[Rh(triphos)(CO) ][PF6], 5, was generated in situ by
2
the introduction of 1 atm carbon monoxide over a THF
solution of [Rh(triphos)(CO)][PF6], 4. Next, a THF
solution of NaOC6H5 was added in increments of 0.5
equivalents and the reactions were monitored by IR
spectroscopy. The bis(carbonyl), 5, bands at 2051 and
2006 cm−1 are replaced during the addition of
NaOC6H5 by new bands at 1926 and 1699 cm−1, Fig.
Complex 4, [Rh(triphos)CO][PF6], is attacked at CO
by aryloxide nucleophiles to form aryloxycarbonyl
complexes. These aryloxycarbonyl complexes cannot be
isolated as they decay through a five-coordinate aryl-
oxycarbonyl species to form rhodium triphos aryloxide
complexes, 1–3, and 4. By starting with the five-coordi-
nate bis(carbonyl) complex, 5, the carbonyl aryloxycar-

A.M. Gull et al. / Journal of Organometallic Chemistry 577 (1999) 31–37
35
Fig. 3. IR (THF) of the reaction of 4 with NaOC6H4-p-OCH3: (a) 4 alone (b) after addition of 3.0 equivalents of NaOC6H4-p-OCH3 (c) 0.5 h
after (b).
bonyl complex, Rh(triphos)(CO)(C(O)OAr), can be
formed persistently. This set of reactions comprises a
highly reversible equilibrium, which can be perturbed
by a change in nucleophilic strength of the aryloxides,
or by the presence of carbon monoxide. A surprising
mechanistic detail is that addition of weaker nucle-
ophile aryloxides such as phenoxide to 4 leads to the
prompt formation of a phenoxycarbonyl species, but as
equilibrium is re-established the phenoxycarbonyl spe-
cies ultimately reverts to [Rh(triphos)CO]PF6, 4, and
Rh(triphos)OC6H5, 1.
4. Experimental section
4.1. General procedures
All reactions and manipulations were carried out
under nitrogen using standard Schlenk and dry box
techniques. Solvents were degassed and purified by
distillation under nitrogen from the appropriate drying
agents (sodium/benzophenone for THF, sodium for
toluene, CaH2 for CH2Cl2 and hexanes, 4A Linde
molecular
sieves
for
acetone).
Triphos{bis(2-
diphenylphosphinoethyl) phenylphosphine} was pur-
chased from Aldrich Chemical Company and used as
received. The complex Rh(triphos)Cl was synthesized
according to the published literature procedure [7,8].
Carbon monoxide (99.5%) was purchased from
Matheson Gas Company. The compound NaOAr
{Ar=C6H5, C6H4-p-CH3, C6H4-p-OCH3} was pre-
Fig. 4. Proposed scheme for the reactivity of 4 with aryl oxides.

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A.M. Gull et al. / Journal of Organometallic Chemistry 577 (1999) 31–37
Fig. 5. IR (THF) of the reaction of 5 with NaOC6H5: (a) 5 alone (b) after addition of 2.0 equivalents of NaOC6H5 (c) 0.5 h after (b) (d) after
addition of another 1.0 equivalents of NaOC6H5 (e) 0.5 h after (d).
pared from ArOH and NaH in THF and precipitated
with hexanes. H-NMR spectra were recorded on Gem-
ppm, 2J(PAPB)=33.1 Hz, 1J(RhPA)=153 Hz,
1J(RhPB)=149 Hz. 2: 31P{1H}-NMR (CD2Cl2): A2BX,
1
2
ini 200, Varian XL-200, and QE-300 spectrometers with
chemical shifts reported in ppm referenced to internal
SiMe4. 31P{1H}-NMR spectra were recorded on QE-
300 and Varian XL-200 spectrometers at 121.4 and 81.0
MHz, respectively, with chemical shifts reported in ppm
referenced to external 85% H3PO4. Plasma desorption
mass spectroscopy (PD MS) spectra were collected on
an Applied Biosystems Bio-Ion 20R instrument. IR
Spectra were recorded on Perkin Elmer 1710 and
Mattson Galaxy Infrared Fourier Transform Spectrom-
eters. Elemental analysis were performed by H.D. Lee
of this department.
l(PA)=39.6 ppm, l(PB)=110.6 ppm, J(PAPB)=33.0
Hz, 1J(RhPA)=154 Hz, 1J(RhPB)=150 Hz. 3:
31P{1H}-NMR (CD2Cl2): A2BX, l(PA)=39.5 ppm,
l(PB)=110.4 ppm, 2J(PAPB)=32.0 Hz, 1J(RhPA)=
1
153 Hz, J(RhPB)=148 Hz.
4.3. Preparation of [Rh(triphos)(CO)][PF6], 4
The compound Rh(triphos)Cl (0.156 g, 0.23 mmol)
was allowed to react with AgPF6 (0.058 g, 0.23 mmol)
in 15 ml acetone. The AgCl was filtered off, leaving a
solution of the acetone solvento complex. The flask was
evacuated, then filled 1 atm carbon monoxide and the
solution was stirred for 1 h. Diethyl ether (10 ml) was
used to precipitate 0.16 g of [Rh(triphos)(CO)][PF6], 4.
4.2. Preparation of Rh(triphos)OAr, 1–3
1
Rh(triphos)Cl [7,8] was allowed to react with excess
NaOAr {Ar=C6H5, C6H4-p-CH3, C6H4-p-OCH3} in
acetone and stirred overnight. The solvent was removed
and the solid was extracted into CH2Cl2 and precipi-
tated with hexanes, to produce Rh(triphos)OAr {1:
Ar=C6H5, 2: R=C6H4-p-CH3, 3: R=C6H4-p-
OCH3}. Typical yields were near 70% with the major
impurity being Rh(triphos)Cl. 1: 31P{1H}-NMR
(CD2Cl2): A2BX, l(PA)=39.2 ppm, l(PB)=110.4
The yield was 86%. H-NMR (CD2Cl2): l(CH2)=2.23
ppm (m, 2H), l(CH2)=2.91 ppm (m, 2H), l(CH2)=
3.15 ppm (m, 2H), l(CH2)=3.31 ppm (m, 2H),
l(Ph)=7.41–7.80 ppm (m, 25H). 31P{1H}-NMR
(CD2Cl2): A2BX, l(PA)=55.6 ppm, l(PB)=104.7
ppm, l(PF6)= −144 ppm, 2J(PAPB)=28.2 Hz,
1J(RhPA)=128 Hz, 1J(RhPB)=115 Hz. IR (KBr):
w(CO)=2026 cm−1. IR (THF): w(CO)=2021 cm−1
PDMS: m/z 637.3 (loss of CO). Anal. Calc. for
.

A.M. Gull et al. / Journal of Organometallic Chemistry 577 (1999) 31–37
37
C35H33F6RhOP4: C, 51.85; H, 4.11. Found: C, 51.54; H,
4.06.
resulted in the mono(carbonyl), 4. Yield (by NMR) was
100%. 31P{1H}-NMR (CD2Cl2): A2BX, l(PA)=64.0
ppm,
1J(RhPA)=124 Hz, 1J(RhPB)=92 Hz. IR (THF):
w(CO)=2051, 2006 cm−1
l(PB)=104.9
ppm,
2J(PAPB)=23
Hz,
4.4. Reaction of 4 with NaOC6H5
.
The compound [Rh(triphos)(CO)][PF6], 4, (0.047 g,
0.058 mmol) was dissolved in 2.5 ml THF and
NaOC6H5 was added in 0.5 equivalent increments in
THF to a 5 ml reaction flask with a septum. After each
addition of NaOC6H5, a sample was transferred via a
syringe to an IR cell (b=8×10−3 mm). IR (THF):
After 0.5 equivalents NaOC6H5 was added, w(CO)=
2058, 2020, 2005, 1709 cm−1 and w(C–C)=1589, 1497
cm−1; After 0.5 h, w(CO)=2020 cm−1; After a further
0.5 equivalents NaOC6H5 was added, w(CO)=2058,
2020, 2005, 1710 cm−1 and w(C–C)=1590, 1500
4.8. Reactions of 5 with NaOC6H5
The compound [Rh(triphos)(CO)][PF6], 4, (0.32 g,
0.39 mmol) was dissolved in THF (16 ml) and 1 atm of
carbon monoxide was added to the solution to generate
the bis(carbonyl), 5. Next, a THF solution of NaOC6H5
was added in increments of 0.5 equivalents at a time.
This reaction was monitored by IR spectroscopy with
samples that were transferred via a syringe to an IR cell
(b=8×10−3 mm). IR (THF): w(CO)=2051, 2006,
cm−1; After an additional 0.5 h, w(CO)=2020 cm−1
.
1926, 1698 cm−1 and w(C–C)=1589, 1489 cm−1
.
This oscillation can be repeated several times until the
w(C–C) bands grow large enough to make the w(CO)
bands difficult to see in the noise. 31P{1H}-NMR
(THF/CD2Cl2): (4) 60% A2BX, l(PA)=55.4 ppm,
l(PB)=105.3 ppm, 2J(PAPB)=27.8 Hz, 1J(RhPA)=
Acknowledgements
We thank the Department of Energy (DE-FG22-
93PC93208) and the Petroleum Research Fund, admin-
istered by the American Chemical Society (27338-AC1).
A.M. Gull thanks Amoco Chemical and the Depart-
ment of Education for a National Needs Fellowship.
1
128 Hz, J(RhPB)=112 Hz; (1) 40% A2BX, l(PA)=
39.4 ppm, l(PB)=110.5 ppm, 2J(PAPB)=30.5 Hz,
1
1J(RhPA)=152 Hz, J(RhPB)=150 Hz.
4.5. Reaction of 4 with NaOC6H5-p-CH3
The compound [Rh(triphos)(CO)][PF6], 4, (0.106 g,
0.13 mmol) was dissolved in 6 ml THF and NaOC6H5-
p-CH3 was added in 0.5 equivalent increments in THF.
After each addition of NaOC6H5-p-CH3, a sample was
transferred via a syringe to an IR cell (b=8×10−3
mm). IR (THF): After 1.0 equivalents NaOC6H5-p-CH3
was added, w(CO)=2057, 2021, 2004, 1703 cm−1 and
w(C–C)=1600, 1516 cm−1; After 0.5 h, w(CO)=2058,
2022, 2004, 1703 cm−1 and w(C–C)=1602, 1517
cm−1; The w(CO) band at 1703 cm−1 grows with the
addition of NaOC6H5-p-CH3.
References
[1] H.E. Bryndza, Organometallics 4 (1985) 1686.
[2] D.W. Dockter, P.E. Fanwick, C.P. Kubiak, J. Am. Chem. Soc.
118 (1996) 4846.
[3] K.A. Bernard, W.R. Rees, J.D. Atwood, Organometallics 5
(1986) 390.
[4] W.M. Rees, M.R. Churchill, J.C. Fettinger, J.D. Atwood,
Organometallics 4 (1985) 2179.
[5] W.M. Rees, M.R. Churchill, Y.-J. Li, J.D. Atwood,
Organometallics 4 (1985) 1162.
[6] W.M. Rees, J.D. Atwood, Organometallics 4 (1985) 402.
[7] R.B. King, P.N. Kapoor, R.N. Kapoor, Inorg. Chem. 10 (1971)
1841.
4.6. Reactions of 4 with NaOC6H5-p-OCH3
[8] S.A. Westcott, G. Stringer, S. Anderson, N.J. Taylor, T.B.
Marder, Inorg. Chem. 33 (1994) 4589.
[9] Y. Hayashi, S. Komiya, T. Yamamoto, A. Yamamoto, Chem.
Lett. (1984) 977.
[10] S.E. Kegley, C.J. Schaverien, J.H. Freudenberger, R.G.
Bergman, S.P. Nolan, C.D. Hoff, J. Am. Chem. Soc. 109 (1987)
6563.
[11] K.A. Bernard, M.R. Churchill, T.S. Janik, J.D. Atwood,
Organometallics 9 (1990) 12.
[12] L.M. Green, D.W. Meek, Organometallics 8 (1989) 659.
[13] G.G. Christoph, P. Blum, W.-C. Liu, A. Elia, D.W. Meek,
Inorg. Chem. 18 (1979) 894.
The compound [Rh(triphos)(CO)][PF6], 4, (0.011 g,
0.014 mmol) was dissolved in 4 ml THF and NaOC6H5-
p-OCH3 was added in 0.5 equivalent increments in
THF. After each addition of NaOC6H5-p-OCH3, a
sample was transferred via a syringe to an IR cell
(b=8×10−3 mm). IR (THF): w(CO)=2019, 2002,
1700 cm−1; w(C–C)=1602, 1513 cm−1
.
4.7. Preparation of [Rh(triphos)(CO)2][PF6], 5
[14] J.A. Tiethof, J.L. Peterson, D.W. Meek, Inorg. Chem. 15 (1976)
1365.
[15] T.E. Nappier Jr, D.W. Meek, R.M. Kirchner, J.A. Ibers, J. Am.
Chem. Soc. 95 (1973) 4194.
[16] R.R. Schrock, J.A. Osborn, J. Am. Chem. Soc. 93 (1971) 2397.
[17] A.M. Gull, P.E. Fanwick, C.P. Kubiak, Organometallics 12
(1993) 2121.
The compound [Rh(triphos)(CO)][PF6], 4, was dis-
solved in THF and carbon monoxide was bubbled
through the solution, yielding [Rh(triphos)(CO)2][PF6],
5. Attempts to isolate this bis(carbonyl) complex, 5,