Reactivity of cationic methyl rhodium(III) complexes cis-[Rh(β-diket) (PPh3)2(CH3)(CH3CN)][BPh 4] toward ligands of different character: Pyridine, carbon monoxide, and triphenylphosphine

Article abstract of DOI:10.1016/j.jorganchem.2005.02.054

Cationic methyl complex of rhodium(III), cis-[Rh(Acac)(PPh ₃)₂(CH₃)(Py)][BPh₄] (1) as a single isomer with Py in the trans to PPh₃ position, is formed upon the reaction of cis-[Rh(Acac)(PPh₃)₂(CH₃)(CH ₃CN)][BPh₄] with pyridine in methylene chloride solution.Complex 1 was characterized by elemental analysis and by ³¹P{¹H} and ¹H NMR spectra.Cationic pentacoordinate acetyl complexes, trans-[Rh(Acac)(PPh₃) ₂(COCH₃)][BPh₄] (2) and trans-[Rh(BA)(PPh ₃)₂(COCH₃)][BPh₄] (3), are prepared by action of carbon monoxide on cis-[Rh(Acac)(PPh₃) ₂(CH₃)(CH₃CN)][BPh₄] and cis-[Rh(BA)(PPh₃)₂(CH₃)(CH₃CN)] [BPh₄], respectively, in methylene chloride solutions.Complexes 2 and 3 were characterized by elemental analysis and by IR, ³¹P{ ¹H}, ¹³C{¹H} and ¹H NMR. According to NMR data, 2 and 3 in solution are non-fluxional trigonal bipyramids with β-diketonate and acetyl ligands in the equatorial plane and axial phosphines.In solutions, 2 and 3 gradually isomerize into octahedral methyl carbonyl complexes trans-[Rh(Acac)(PPh₃)₂(CO)(CH ₃)][BPh₄] (4) and trans-[Rh(BA)(PPh₃) ₂(CO)(CH₃)][BPh₄] (5), respectively.Complexes 4 and 5 were characterized by IR, ³¹P{¹H}, ¹³C{¹H} and ¹H NMR, without isolation.Upon the action of PPh₃ on cis-[Rh(Acac)(PPh₃)₂(CH ₃)(CH₃CN)][BPh₄] and cis-[Rh(BA)(PPh ₃)₂(CH₃)(CH₃CN)] [BPh₄], reductive elimination of the methyl ligand as a phosphonium salt, [CH ₃PPh₃][BPh₄], occurs to give square planar rhodium(I) complexes [Rh(Acac)(PPh₃)₂] and[Rh(BA)(PPh ₃)₂], respectively. The reaction products were identified in the reaction mixtures by ³¹P{¹H} and ¹H NMR.

Full text of DOI:10.1016/j.jorganchem.2005.02.054

Journal of Organometallic Chemistry 690 (2005) 3397–3404
www.elsevier.com/locate/jorganchem
Reactivity of cationic methyl rhodium(III) complexes
cis-[Rh(b-diket)(PPh3)2(CH3)(CH3CN)][BPh4] toward ligands
of different character: pyridine, carbon monoxide,
and triphenylphosphine
*
Elizaveta P. Shestakova, Yuri S. Varshavsky , Aleksei B. Nikolskii
Institute of Chemistry, St. Petersburg State University, Petrodvorets, Universitetskii Pr., 26, 198504 St. Petersburg, Russia
Received 8 November 2004; revised 14 February 2005; accepted 14 February 2005
Available online 15 June 2005
Abstract
Cationic methyl complex of rhodium(III), cis-[Rh(Acac)(PPh3)2(CH3)(Py)][BPh4] (1) as a single isomer with Py in the trans to
PPh3 position, is formed upon the reaction of cis-[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] with pyridine in methylene chloride solu-
1
tion. Complex 1 was characterized by elemental analysis and by 31P{1H} and H NMR spectra. Cationic pentacoordinate acetyl
complexes, trans-[Rh(Acac)(PPh3)2(COCH3)][BPh4] (2) and trans-[Rh(BA)(PPh3)2(COCH3)][BPh4] (3), are prepared by action of
carbon monoxide on cis-[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] and cis-[Rh(BA)(PPh3)2(CH3)(CH3CN)][BPh4], respectively, in
1
methylene chloride solutions. Complexes 2 and 3 were characterized by elemental analysis and by IR, 31P{1H}, 13C{1H} and H
NMR. According to NMR data, 2 and 3 in solution are non-fluxional trigonal bipyramids with b-diketonate and acetyl ligands
in the equatorial plane and axial phosphines. In solutions, 2 and 3 gradually isomerize into octahedral methyl carbonyl complexes
trans-[Rh(Acac)(PPh3)2(CO)(CH3)][BPh4] (4) and trans-[Rh(BA)(PPh3)2(CO)(CH3)][BPh4] (5), respectively. Complexes 4 and 5 were
1
characterized by IR, 31P{1H}, 13C{1H} and H NMR, without isolation. Upon the action of PPh3 on cis-[Rh(Acac)(PPh3)2(CH3)-
(CH3CN)][BPh4] and cis-[Rh(BA)(PPh3)2(CH3)(CH3CN)] [BPh4], reductive elimination of the methyl ligand as a phosphonium salt,
[CH3PPh3][BPh4], occurs to give square planar rhodium(I) complexes [Rh(Acac)(PPh3)2] and [Rh(BA)(PPh3)2], respectively. The
1
reaction products were identified in the reaction mixtures by 31P{1H} and H NMR.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Rhodium; Methyl complexes; Acetyl complexes; Reductive elimination; IR; NMR
1. Introduction
or benzoylacetonate ligand) [6], which may be consid-
ered as stable analogs of unstable ionic intermediates.
According to X-ray data, both phosphines in these cat-
ions in the solid state lie in the same (‘‘equatorial’’) plane
with the b-diketonate ligand. As might be expected,
these cationic complexes showed a high reactivity with
respect to acetonitrile replacement reactions and struc-
tural rearrangements. Thus, the CH3CN ligand in cis-
[Rh(b-diket)(PPh3)2(CH3)(CH3CN)]+ cations is readily
and quantitatively replaced by NH3 or Iꢀ even at ambi-
ent temperature, and the positions of PPh3 ligands in the
resultant complexes differ from their positions in the
In current publications on methyl iodide oxidative
addition to square planar rhodium(I) complexes, the
reaction mechanisms involving intermediates with
separated charges are widely discussed [1–5]. Recently,
we isolated and characterized two cationic methyl
complexes of rhodium(III), cis-[Rh(b-diket)(PPh3)2-
(CH3)(CH3CN)]+[BPh4]ꢀ (b-diket is acetylacetonate
*
Corresponding author.
E-mail address: yurel@peterlink.ru (Y.S. Varshavsky).
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.02.054

3398
E.P. Shestakova et al. / Journal of Organometallic Chemistry 690 (2005) 3397–3404
+
initial complexes. The ammonia complexes contain one
equatorial and one axial phosphine ligand, whereas the
action of Iꢀ yields the neutral complexes trans-[Rh(b-di-
ket)(PPh3)2(CH3)I] with two axial trans phosphines.
Here, we report reactions of the complexes cis-[Rh(b-di-
ket)(PPh3)2(CH3)(CH3CN)][BPh4] with three ligands,
pyridine, carbon monoxide and triphenylphosphine,
widely differing in their electronic properties and
reactivity.
PPh3
H3C
H3C
PPh3
CH3
O
O
Rh
Py
2.2. Reaction of cis-[Rh(b-diket)(PPh3)2(CH3)-
(CH3CN)][BPh4] complexes with CO
2. Results and discussion
Complexes trans-[Rh(Acac)(PPh3)2(COCH3)][BPh4]
(2) and trans-[Rh(BA)(PPh3)2(COCH3)][BPh4] (3) are
easily formed at ambient temperature by passing a
stream of CO for 15 min through methylene
chloride solutions of complexes cis-[Rh(Acac)(PPh3)2-
(CH3)(CH3CN)][BPh4] and cis-[Rh(BA)(PPh3)2(CH3)-
(CH3CN)] [BPh4], respectively. Complexes 2 and 3 were
characterized by elemental analysis and by IR, 31P{1H}
and 1H NMR spectra. The 13C NMR spectra were
taken for a sample of [Rh(Acac)(PPh3)2(13COCH3)]
[BPh4] (20) obtained using carbon monoxide enriched
in 13C (76.6%).
2.1. Reaction of cis-[Rh(Acac)(PPh3)2(CH3)-
(CH3CN)][BPh4] complex with pyridine
Treatment of cis-[Rh(Acac)(PPh3)2(CH3)(CH3CN)]-
[BPh4] in methylene chloride with excess pyridine at
ambient temperature yields cis-[Rh(Acac)(PPh3)2(CH3)-
(Py)][BPh4] (1). Complex 1 was isolated as a yellow
crystalline solid in 77% yield and was characterized
1
by elemental analysis and by 31P{1H} and H NMR
spectra. The 31P{1H} NMR spectrum of 1 in chloro-
form represents two doublets of doublets (d 23.1
ppm, 1J(PRh) 134.5 Hz and d 21.5 ppm, 1J(PRh)
The IR spectra of complexes 2 and 3 display intense
bands with maxima at 1726 cmꢀ1 (2) and 1728 cmꢀ1
(3), which correspond to the m(CO) stretching vibration
in the –C(@O)Me group of acetyl rhodium(III) com-
plexes [3,5,8–17].
2
129.3 Hz, J(PP) 35.2 Hz) that corresponds to the com-
plex with two inequivalent phosphine ligands, which is
present in solution as a single isomer. Spin–spin cou-
1
2
pling constants J(PRh) and J(PP) of complex 1 are
rather close to those of the previously reported ammo-
nia complex cis-[Rh(Acac)(PPh3)2(CH3)(NH3)][BPh4], d
The 13C NMR spectrum of a freshly prepared chloro-
form solution of 20 displays doublet of triplets from ace-
1
1
1
2
26.7 ppm, J(PRh) 133.8 Hz and d 24.0 ppm, J(PRh)
tyl carbon at d 207.2 ppm, J(CRh) 28.9 Hz, J(CP) 6.2
Hz [13–17], split by spin–spin coupling with 103Rh and
two equivalent 31P nuclei. The 31P{1H} NMR spectra
of freshly prepared chloroform solutions of complexes
2 and 3 display in each case one sharp doublet at d
2
1
128.6 Hz, J(PP) 35.2 Hz [6]. The H NMR spectrum
of complex 1 consists of a group of signals of phenyl
protons (d 6.8–7.5 ppm), signals of coordinated pyri-
dine (d 6.74 and 8.09 ppm),1 a signal from methine
proton of the acetylacetonate ligand (d 4.37 ppm)
and a number of signals from methyl protons in the re-
gion d 1–2 ppm. Two sharp signals within the last re-
gion at d 1.88 (3H) and 1.49 ppm (3H) belong to
protons of two inequivalent methyl groups of the acet-
ylacetonate ligand. The signal at d 1.78 ppm, which ap-
pears as a broadened singlet, should be assigned to the
methyl ligand (H3C–Rh). The coupling to 103Rh and
two inequivalent 31P nuclei is not resolved. On the
basis of NMR spectra, we assign to the cation of 1
the following structure, akin to the structure of
cation cis-[Rh(Acac)(PPh3)2(CH3)(NH3)]+, which has
been determined by NMR spectra and X-ray
analysis [6].
1
30.5 ppm, J(PRh) 151.9 Hz (2) and at d 31.0 ppm,
1J(PRh) 152.6 Hz (3). The P NMR spectrum of 20
31
2
shows an additional splitting arising from J(PC) 6.1
Hz. No line broadening was observed which might indi-
cate a fluxional behavior of these complexes. As is evi-
dent from these spectral data, complexes 2 and 3 exist
in solutions in single isomeric forms containing two
phosphine ligands in the equivalent positions trans to
each other.
1
The H NMR spectra of complexes 2 and 3 contain
three groups of signals. In the region d 6.8–7.8 ppm, there
are signals from phenyl protons of phosphine and ben-
zoylacetonate ligands and the [BPh4]ꢀ anion. Signals
from methine protons for complexes 2 and 3 are located
at d 5.67 and 6.44 ppm, respectively. Signals from methyl
protons represent the third group lying in the region d
1.7–2.5 ppm. In the spectrum of 2 the signal at d 2.27
ppm (3H) should be assigned to the methyl group of
the acetyl ligand as this signal is split into doublet in
1
We observed only these two signals because the third one was
obscured by the assemblage of phenyl proton signals; the 1H NMR
data for coordinated pyridine see, for example, in [5,7].
13
the spectrum of C enriched complex 20 (2J(HC) 5.8

E.P. Shestakova et al. / Journal of Organometallic Chemistry 690 (2005) 3397–3404
3399
Hz). The intense signal at d 1.73 ppm (6H) should be as-
signed to two equivalent methyl groups of the acetylacet-
onate ligand. By analogy, we assign the signals at d 2.47
(3H) and 1.85 ppm (3H) in the spectrum of complex 3 to
methyl groups of acetyl and benzoylacetonate ligands,
respectively. It is easy to verify that a trigonal bipyramid
with trans-phosphines and the acetyl group in the equa-
torial position fits all the experimental data:
The 13C NMR spectrum (in CDCl3) of the mixed
product obtained from complex 20, along with signal
from acetyl carbon, showed a doublet of triplets at d
1
2
186.2 ppm, J(CRh) 61.9 Hz, J(CP) 13.8 Hz, which is
characteristic of carbonyl carbon in rhodium(III) bis-
phosphine complexes with two equivalent 31P nuclei
[13–17,28]. The 31P{1H} NMR spectrum of the mixed
product obtained from 2, in addition to doublet from
the initial acetyl complex, contained one more doublet
1
of sharp lines at d 24.3 ppm, J(PRh) 87.6 Hz (doublet
2
of doublets with J(PC) 13.8 Hz in the case of 20) that
PPh3
Rh
+
R1
O
O
O
C
is in concordance with the above data and confirms
the equivalence of two phosphine ligands in the isomer-
ization product.
CH3
2
R
In the 31P{1H} NMR spectrum of the mixed product
obtained from 3, alongside with a doublet from the ini-
tial acetyl complex, two doublets were observed, d 24.8
PPh3
2: R1 = R2 = CH3
3: R1 = CH3; R2 = Ph
1
1
ppm, J(PRh) 87.4 Hz and d 24.4 ppm, J(PRh) 86.7
Hz (Fig. 1).
Obviously in the case of the unsymmetrical b-diketo-
nate ligand, BA, two isomeric methyl carbonyl com-
plexes with equivalent phosphines were formed, which
points to the mutual trans position of phosphine ligands.
Taking into account the close resemblance between
NMR spectra of the isomerization products, we can
conclusively assign the following structures to them:
Acyl complexes of rhodium(III) usually exist in a pen-
tacoordinate form, and their typical solid-state geometry
is square pyramid (sp) with apical acyl ligand [4,9,10,
18–23]. The same geometry was evidenced for these
complexes in solutions. Complexes 2 and 3 (at least in
solution) belong to a less common structural type, tri-
gonal bipyramid (tbp). The similar geometry with
axial phosphine ligands was found for the neutral
complex [RhCl2(PPh3)2(COCH2Ph)] in solution as well
as in the solid state [24]. The neutral complex
[Rh(Ph2P(CH2)3PPh2)(COCH3)I2] was described as a dis-
torted pyramid approximated to the tbp form in the solid
state [25]. Interestingly, contrary to the most pentacoordi-
nate rhodium(III) complexes, the acyl complexes, both sp
and tbp, do not exhibit fluxional behavior in solution. As
mentioned above, we also did not mark any signs of fluxi-
onality in the room-temperature NMR spectra of 2 and 3.
We noticed that several new signals appear in the
NMR spectra of solutions of complexes 2 and 3 held
at ambient temperature under an inert atmosphere. As
the isomerization of rhodium(III) acyl complexes into
alkyl carbonyl complexes
+
PPh3
R1
O
O
CH3
Rh
PPh3
2
R
CO
4: R1 = R2 = CH3
5a, 5b: R1, R2 = CH3, Ph
The 1H NMR spectra of mixtures of acetyl complexes
and products of their isomerization are complicated,
and therefore, we succeed in the complete assignment
of the proton signals only for complex 4. The methyl
groups of the acetylacetonate ligand show two singlets
of equal intensity, d 1.45 and 1.38 ppm. The signal from
protons of the methyl ligand (H3C–Rh) in the spectrum
of 4 at d 1.32 ppm appears as a triplet of doublets due to
spin–spin coupling with 103Rh and two equivalent 31P
nuclei (2J(HRh) 1.81 Hz, 3J(HP) 4.90 Hz). All these data
confirm the geometry of 4 derived from 31P and 13C
NMR data. We did not try to make an assignment of
1H resonances for isomers of complex 5 in the region
1–2 ppm because of abundance of partially overlapped
signals. Singlets from methine protons are located at d
4.15 ppm (4) and 4.91 and 4.85 ppm (isomers of 5).
It is worth noting that acyl–alkyl isomerization of
sp complexes with apical acyl ligand requires a free
equatorial position capable of accepting the methyl
R–CðOÞ–RhLn ! R–RhðCOÞLn
is a well-documented phenomenon [9,11,12,24,26,27], we
assumed that the new signals belong to the products of
this kind. With this assumption, we studied the IR and
NMR spectra of residues obtained by evaporation of
dichloromethane solutions of 2 and 3 after 24 h storage.
As expected, the IR spectra of these mixed products (in
CH2Cl2), alongside with acetyl m(CO) absorption bands
of initial 2 and 3 at 1726 and 1728 cmꢀ1, contained
m(CO) bands at 2060 and 2058 cmꢀ1, respectively, which
are characteristic of terminal carbonyl ligands in rho-
dium(III) complexes [3,5,8,9,11–17,27,28].

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E.P. Shestakova et al. / Journal of Organometallic Chemistry 690 (2005) 3397–3404
Fig. 1. The 31P{1H} NMR (CDCl3) spectrum of trans-[Rh(BA)(PPh3)2(COCH3)][BPh4] (3) after 24 h ageing of solution in CH2Cl2 at ambient
temperature.
ligand, i.e. a considerable rearrangement of ligands
should accompany this isomerization. In the case of
isomerization
There is no doubt that this dynamic isomerization pro-
ceeds through acetonitrile dissociation, which produces
a variety of undetectable fluxional pentacoordinate spe-
cies of sp and tbp configurations. The adjunction of
carbon monoxide molecule to some of these species
may generate short-lived intermediates containing
methyl and carbonyl ligands in cis position and thus
appropriate to the transformation into acetyl com-
plexes by migratory insertion. Having no positive data
on the possible structure of immediate precursors of
the acetyl complex, we can envision these precursors
as octahedral cationic methyl carbonyl complexes con-
taining phosphine ligands in cis positions. We consider
the trans-(PPh3)2 geometry as less credible, because
trans-(PPh3)2 carbonyl complexes were detected as rel-
atively stable moieties 4 and 5 resulted from the isom-
erization of acyl complexes 2 and 3. In the case of
cis-(PPh3)2 precursor, the CO insertion stage obviously
should be accompanied by an rearrangement of phos-
phine ligands.
2 ð3Þ ! 4 ð5Þ
the process seems to include only the methyl ligand
migration within the equatorial plane, and moreover,
the presence of b-diketonate ligand with a bite angle va-
lue of ꢁ90° [6,29–36] could facilitate this migration
making two other equatorial angles more capacious
then in the ideal tbp [37]. Observed incompleteness of
the isomerization reactions for 24 h may be caused
either by equilibrium between acyl and methyl carbonyl
complexes [9,24,26,27] or by kinetic reasons. A pro-
longed examination of these reactions is hindered by a
further transformation of carbonyl complexes that pro-
duce a number of new signals from unidentified prod-
ucts in NMR spectra of reaction mixtures.
The presented data allow us to make some preliminary
comments concerning mechanism of the acetyl complex
formation. Recently [6], we detected two dynamically ex-
changed isomeric forms of the cation in solution ofthe salt
cis-[Rh(b-diket)(PPh3)2(CH3)(CH3CN)][BPh4]:
2.3. Reaction of cis-[Rh(b-diket)(PPh3)2(CH3)-
(CH3CN)][BPh4] complexes with triphenylphosphine
Preliminary experiments have shown that the
31P{1H} NMR spectra of reaction mixtures of cis-
[Rh(b-diket)(PPh3)2(CH3)(CH3CN)][BPh4] with PPh3
in chloroform at room temperature, alongside with
numerous signals of unidentified products, exhibit an in-
tense singlet due to phosphine oxide (d 30.5 ppm), which
CH3
PPh3
Rh
+
+
PPh3
PPh3
PPh3
CH3
O
O
O
O
Rh
NCCH3
major
NCCH3
minor

E.P. Shestakova et al. / Journal of Organometallic Chemistry 690 (2005) 3397–3404
3401
points to the sensitivity of the initially formed products
to oxygen traces. Therefore, to detect primary reaction
products, we carried out these reactions directly in the
NMR tube (CDCl3 as a solvent).
Thus, the main reaction occurring on action of tri-
phenylphosphine on rhodium(III) methyl complexes
can be described as reductive elimination
cis-½Rhðb-diketÞðPPh3Þ ðCH3ÞðCH3CNÞꢂ½BPh4ꢂ þ PPh3
The 31P{1H} NMR spectra of the reaction mixtures
obtained at a molar ratio PPh3:Rh = 1:1 show one dou-
2
! Rhðb-diketÞðPPh3Þ þ ½CH3PPh3ꢂ½BPh4ꢂ þ CH3CN
2
1
blet (d 56.6 ppm, J(PRh) 193.1 Hz) in the low-field re-
gion in the case of the Acac complex, and two doublets
Alongside with signals from the reaction products, the
room-temperature 31P{1H} NMR spectrum of each of
reaction mixtures shows signals corresponding to
unconverted reactants, namely, the extremely broadened
doublet centered at d ꢁ 30 ppm due to the initial rho-
dium(III) complex and the broadened singlet at d ꢀ4.2
ppm from free triphenylphosphine (19.0 Hz as opposed
to 4.0 Hz for individual PPh3). The broadening of the
last signal indicates that free triphenylphosphine takes
part in an exchange process. Interestingly, signals of
the rhodium(I) bisphosphine complexes in the spectra
of reaction mixtures are as narrow as in the spectra of
corresponding individual compounds (for instance, 4.5
Hz for [Rh(Acac)(PPh3)2]). Thus, it appears that no rho-
dium(I), but only rhodium(III) complexes are involved
in the fast exchange with free phosphine in these condi-
tions. Such behavior of the rhodium(I) complexes seems
to be unusual, as square planar rhodium(I) complexes
1
of doublets (d 59.0 ppm, J(P1Rh) 195.5 Hz, and d 54.4
ppm, 1J(P2Rh) 191.4 Hz; 2J(P1P2) 56.4 Hz) in the case of
the BA complex (Fig. 2).
These signals may be assigned with certainty to the
rhodium(I) square planar complexes, [Rh(A-
cac)(PPh3)2] and [Rh(BA)(PPh3)2], respectively, which
we studied earlier [38] and also used to obtain cis-
[Rh(b-diket)(PPh3)2(CH3)(CH3CN)][BPh4] [6]. In addi-
tion, a sharp singlet (d 22.2 ppm) is also present in
the spectra of the both reaction mixtures. We ascribed
this singlet to the cation [CH3PPh3]+. This conclusion
was confirmed by the synthesis of the salt
[CH3PPh3][BPh4] and measurement of its 1H and
31P{1H} NMR spectra [6]. The cation [CH3PPh3]+
could form as a result of intramolecular methyl ligand
transfer from the rhodium(III) to coordinated
triphenylphosphine.
Fig. 2. The 31P{1H} NMR (CDCl3) spectrum of the reaction mixture {cis-[Rh(BA)(PPh3)2(CH3)(CH3CN)][BPh4] + PPh3} (1:1 mol) immediately
after mixing of reactants.

3402
E.P. Shestakova et al. / Journal of Organometallic Chemistry 690 (2005) 3397–3404
generally are susceptible to a fast intermolecular ex-
change. As an example, the presence of free phosphine
in a solution containing related monophosphine com-
plex, [Rh(Acac)(PPh3)(CO)], causes a fast exchange be-
tween free and coordinated triphenylphosphine, which
leads to disappearance of the Rh–P coupling [39].
Reactions of cis-[Rh(b-diket)(PPh3)2(CH3)(CH3CN)]-
[BPh4] with triphenylphosphine were also carried out at
a molar ratio PPh3:Rh = 0.5. The 31P{1H} NMR spectra
of these reaction mixtures are characterized by higher
relative intensities of the signals from the initial rho-
dium(III) complexes.
The presence of signals of the initial rhodium(III)
complexes and triphenylphosphine in the 31P{1H}
NMR spectra of the reaction mixtures implies that the
reactions under discussion do not proceed to completion
under these conditions. However, an elongation of reac-
tion time led to the appearance of signals presumably re-
lated to products of decomposition of the formed
3. Concluding remarks
In this work and in our previous paper [6], we have
reported the reactions of the cationic methyl complexes
cis-[Rh(b-diket)(PPh3)2(CH3)(CH3CN)][BPh4] with sev-
eral ligands of different nature, namely Iꢀ, NH3, pyri-
dine, CO, PPh3. As shown above, these complexes
readily react with all these ligands at ambient tempera-
ture. The high rate of these reactions seems to be
caused by the fact that the acetonitrile ligand is easily
detached from the starting complex to give pentacoor-
dinate moieties, which are involved into a fast intercon-
version. It suggests that in these reactions the first and
the slowest stage of a substitution reaction occurs
spontaneously on the dissolution of a starting com-
pound, and hence the entire reaction has a very low
activation barrier. It is worth noting that both NH3
and pyridine derivatives are formed as a single isomer
each. It is very likely that in the all cases an entering
ligand does occupy the position cis to the CH3 ligand.
In the cases of ligands, which are subject to methyla-
tion (CO, PPh3), this location is of the key importance
because it provides a possibility for further transforma-
tions, namely migratory insertion or reductive
elimination.
rhodium(I)
bisphosphine
complexes,
Rh(b-di-
ket)(PPh3)2, as a result of their interaction with traces
of oxygen (the singlet of phosphine oxide at d 30.5
ppm) [40] and chlorinated solvent [36,41].
The reaction mixtures have been examined by 1H
NMR spectroscopy. As it could be expected, in the re-
gion d 5–6.5 ppm we observed singlets from methine
protons of b-diketonate ligands both of formed rho-
dium(I) complexes, 5.26 ppm (Acac) and 6.02 ppm
(BA) [38], and of initial rhodium(III) complexes, 5.34
ppm (Acac) and 6.04 ppm (BA) [6]. The intensity of
singlets from methine protons of rhodium(I) complexes
increased with increasing PPh3:Rh molar ratio in reac-
tion mixtures.
4. Experimental
4.1. Preparation of complexes
All operations were performed under an atmosphere
of dry argon. The rhodium complexes cis-[Rh(Acac)-
(PPh3)2(CH3)(CH3CN)][BPh4], cis-[Rh(Acac)(PPh3)2-
(CD3)(CH3CN)][BPh4], cis-[Rh(BA)(PPh3)2(CH3)(CH3-
CN)][BPh4], cis-[Rh(BA)(PPh3)2(CD3)(CH3CN)][BPh4]
were synthesized by published procedures [6]. Gaseous
CO was prepared by standard method [42]. Carbon
monoxide enriched in 13C (76.6%) was obtained from
commercial sources. Solvents were dried and purified
by known procedures [43] and distilled under argon.
Elemental analyses were performed on a Hewlett–
Packard 185 microanalyzer.
In the region 1–2 ppm, where signals due to CH3
groups of the initial complex and final products could
1
be expected [6,38], the H NMR spectra of the reaction
mixtures were complicated owing to overlapping of
numerous signals. The use of rhodium(III) complexes
with a deuterated methyl ligand (D3C–Rh) allowed us
to identify a part of these signals. Thus, it was possible
to distinguish a doublet due to the cation [CH3PPh3]+
2
(d 1.39 ppm, J(HP) 12.7 Hz), and singlets of methyl
groups of b-diketonate ligands in [Rh(b-diket)(PPh3)2]:
d 1.41 ppm (Acac) and 1.53 ppm (BA). In the spectra
of reaction mixtures at a molar ratio PPh3:Rh = 0.5, we
could detect resonances of initial rhodium(III) com-
plexes: broadened singlets due to methyl ligand, H3C–
Rh, at d 1.90 ppm (Acac) and 2.04 ppm (BA), and sharp
singlets due to methyl groups of the b-diketonate ligand
at d 1.70 (Acac) and 1.84 (BA). In the 1H NMR spectra
of 1:1 reaction mixtures, signals from the methyl ligand,
CH3–Rh, could not be detected, whereas the positions of
sharp singlets at d 1.70 ppm (Acac) and 1.84 ppm (BA)
remained unchanged. We ascribe this peculiarity to
chemical exchange processes in rhodium(III) complexes,
which also were evidenced by the 31P{1H} NMR spectra.
4.1.1. Preparation of cis-[Rh(Acac)(PPh3)2(CH3)-
(Py)][BPh4] (1)
Mixture of cis-[Rh(Acac)(PPh3)2(CH3)(CH3CN)]
[BPh4] (0.13 g, 0.11 mmol), excess pyridine (0.7 ml, 8.7
mmol) and methylene chloride (2 ml) was stirred at
ambient temperature for 2 h. Then solvent and excess
pyridine were removed in vacuo. Recrystallization from
methylene chloride/diethyl ether provided yellow crys-
tals of 1. Yield: 0.10 g (77%). Anal. Calc. for
C71H65BNO2P2Rh: C, 74.81; H, 5.75. Found: C, 74.31;
H, 5.66%. 1H NMR (CDCl3): d 6.8–7.5 (m, C6H5),
8,09 (s, 2H), 6.74 (s, 2H) (C5H5N), 1.78 (br s, 3H,

E.P. Shestakova et al. / Journal of Organometallic Chemistry 690 (2005) 3397–3404
3403
H3C–Rh), 4.37 (s, 1H), 1.88 (s, 3H), 1.49 (s, 3H)
(OC(CH3)CH(CH3)CO). 31P{1H} NMR (CDCl3): d
23.1 (dd, J(PRh) 134.5 Hz, J(PP) 35.2 Hz), 21.5 (dd,
4.1.5. Isomerization of trans-[Rh(Acac)(PPh3)2-
(13COCH3)][BPh4] (20)
1H NMR (CDCl3): d 6.8–7.5 (m, C6H5), 5.67 (s), 1.73
(s) (OC(CH3)CH(CH3)CO), 2.27 (d, CH3(13CO)–Rh,
2J(HC) 5.8 Hz) (complex 20); 4.15 (s), 1.45 (s), 1.38 (s),
1
2
1J(PRh) 129.3 Hz, J(PP) 35.2 Hz).
2
2
3
4.1.2. Preparation of trans-[Rh(Acac)(PPh3)2-
(COCH3)][BPh4] (2)
A stream of CO was passed through a solution of
1.32 (td, J(HRh) 1.81 Hz, J(HP) 4.90 Hz). 31P{1H}
1
2
(CDCl3): d 30.5 (dd, J(PRh) 151.9 Hz, J(PC) 6.1 Hz)
1
2
(complex 20), 24.3 (dd, J(PRh) 87.6 Hz, J(PC) 13.8
complex
cis-[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4]
Hz). 13C{1H} NMR (CDCl3): d 207.2 (dt, 1J(CRh)
2
(0.30 g, 0.26 mmol) in methylene chloride (4 ml) for
15 min at ambient temperature. Then solvent was re-
moved in vacuo, and yellow solid 2 was thus obtained.
Yield: 0.26 g (91%). Anal. Calc. for C67H60BO3P2Rh:
C, 73.90; H, 5.55. Found: C, 73.83; H, 5.75%. IR
(CH2Cl2), m(CO)/cmꢀ1: 1726s. 1H NMR (CDCl3):
6.8–7.5 (m, C6H5), 5.67 (s, 1H), 1.73 (s, 6H)
(OC(CH3)CH(CH3)CO), 2.27 (s, 3H, CH3(CO)–Rh).
31P{1H} NMR (CDCl3): d 30.5 (d, 1J(PRh) 151.9
Hz). trans-[Rh(Acac)(PPh3)2(13COCH3)][BPh4] (2). 1H
NMR (CDCl3): d 6.8–7.5 (m, C6H5), 5.67 (s, 1H),
1.73(s, 6H) (OC(CH3)CH(CH3)CO), 2.27 (d, 3H,
2J(HC) 5.8 Hz, CH3(13CO)–Rh). 13C{1H} NMR
(CDCl3): d 207.2 (dt, 1J(CRh) 28.9 Hz, 2J(CP) 6.2
Hz). 31P{1H} NMR (CDCl3): d 30.5 (dd, 1J(PRh)
28.9 Hz, J(CP) 6.2 Hz) (complex 20); 186.2 (dt,
1J(CRh) 61.9 Hz, J(CP) 13.8 Hz).
2
4.1.6. Isomerization of trans-[Rh(BA)(PPh3)2-
(COCH3)][BPh4] (3)
The solution of complex 3 (0.1 g, 0.08 mmol) in meth-
ylene chloride (1.5 ml) was stored for 24 h at ambient
temperature. Then solvent was removed in vacuo. IR
(CH2Cl2), m(CO)/cmꢀ1: 1728, 2058. 31P{1H} NMR
(CDCl3): d 31.0 (d, 1J(PRh) 152.6 Hz) (complex 3),
1
1
24.8 (d, J(PRh) 87.4 Hz), 24.4 (d, J(PRh) 86.7 Hz);
intensities of signals of 3 and resultant carbonyl com-
plexes are in ratio 3:1.
4.1.7. The reaction of cis-[Rh(Acac)(PPh3)2(CH3)-
(CH3CN)][BPh4] and cis-[Rh(BA)(PPh3)2(CH3)-
(CH3CN)][BPh4] with PPh3 in CDCl3
2
151.9 Hz, J(PC) 6.1 Hz).
4.1.3. Preparation of trans-[Rh(BA)(PPh3)2(COCH3)]-
[BPh4] (3)
A stream of CO was passed through a solution of the
CDCl3 (0.6 ml) was added directly in the NMR tube
to a mixture of complex cis-[Rh(Acac)(PPh3)2(CH3)
(CH3CN)][BPh4] (0.014 g, 0.012 mmol) or complex
cis-[Rh(BA)(PPh3)2(CH3)(CH3CN)][BPh4] (0.016 g,
0.013 mmol) with appropriate amount of PPh3 at ambi-
ent temperature. The mixtures was intensively shaken
for 10–15 s and immediately after that transferred to
NMR probe.
complex
cis-[Rh(BA)(PPh3)2(CH3)(CH3CN)][BPh4]
(0.47 g, 0.38 mmol) in methylene chloride (5 ml) for 20
min at ambient temperature. Then solvent was removed
in vacuo, and yellow solid complex 3 was thus obtained
as CH2Cl2 0.5:1 solvate. Yield: 0.44 g (97%). Anal. Calc.
1
2
for C72H62BO3P2Rh ꢃ CH2Cl2: C, 72.96; H, 5.32.
Found: C, 72.52; H, 5.38%. IR (CH2Cl2), m(CO)/cmꢀ1
:
4.2. NMR and IR measurements
1
1728s. H NMR (CDCl3): d 6.8–7.8 (m, C6H5), 6.44 (s,
1H), 1.85 (s, 3H), (OC(CH3)CH(C6H5)CO), 2.47 (s,
The NMR spectra were measured in deuterochloro-
form solutions at room temperature on Bruker AM-
300 spectrometer operating in the Fourier-transform
mode with noise proton decoupling for 31P and 13C.
1
2
3H, CH3(CO)–Rh), 5.30 (s, 1H, CH2Cl2, solvent mole-
cules in the solvated crystals). 31P{1H} NMR (CDCl3):
1
31.0 (d, J(PRh) 152.6 Hz).
1
The H and 13C spectra were recorded with solvent as
1
4.1.4. Isomerization of trans-[Rh(Acac)(PPh3)2-
(COCH3)][BPh4] (2)
internal standards (d H of residual proton 7.25 ppm;
d
13C 77.0 ppm in CDCl3). The 31P chemical shifts were
The solution of complex 2 (0.1 g, 0.09 mmol) in meth-
ylene chloride (1.5 ml) was stored for 24 h at ambient
temperature. Then solvent was removed in vacuo.
IR (CH2Cl2), m(CO)/cmꢀ1: 1726, 2060. 1H NMR
(CDCl3): d 6.8–7.5 (m, C6H5), 5.67 (s), 1.73 (s)
(OC(CH3)CH(CH3)CO), 2.27 (s, CH3(CO)–Rh) (com-
plex 2); 4.15 (s), 1.45 (s), 1.38 (s) (OC(CH3)CH(CH3)-
CO), 1.32 (td, 2J(HRh) 1.81 Hz, 3J(HP) 4.90 Hz).
measured with 85% phosphoric acid as external stan-
dard, d 31P 0.0 ppm. The IR spectra were recorded on
a Specord 75 IR spectrometer.
Acknowledgements
We thank Dr. N.G. Antonov and Dr. S.N. Smirnov
for NMR measurements. Financial support from the
Russian Federation Ministry of Education (‘‘Universi-
ties of Russia’’ Program, UR.05.01.032 and
UR.05.01.314) is gratefully acknowledged.
1
31P{1H} NMR (CDCl3): d 30.5 (d, J(PRh) 151.9Hz)
(complex 2), 24.3 (d, 1J(PRh) 87.6 Hz); intensities of sig-
nals of 2 and resultant carbonyl complex are in ratio
1.7:1.

3404
E.P. Shestakova et al. / Journal of Organometallic Chemistry 690 (2005) 3397–3404
[22] L.J. Damoense, W. Purcell, A. Roodt, Rhodium Express 14
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