Cationic methyl complexes of rhodium(III): Synthesis, structure, and some reactions

Article abstract of DOI:10.1016/j.jorganchem.2004.02.041

Cationic methyl complex of rhodium(III), trans-[Rh(Acac) (PPh₃)₂(CH₃) (CH₃CN)] [BPh₄] (1) is prepared by interaction of trans-[Rh(Acac) (PPh₃)₂(CH₃)I] with AgBPh₄ in acetonitrile. Cationic methyl complexes of rhodium(III), cis-[Rh(Acac)(PPh₃)₂ (CH₃) (CH₃CN)][BPh₄] (2) and cis-[Rh(BA) (PPh₃)₂(CH₃) (CH₃CN)] [BPh₄] (3) (Acac, BA are acetylacetonate and benzoylacetonate, respectively), are obtained by CH₃I oxidative addition to rhodium(I) complexes [Rh(Acac)(PPh₃)₂] and [Rh(BA)(PPh₃)₂] in acetonitrile in the presence of NaBPh₄. Complexes 2 and 3 react readily with NH₃ at room temperature to form cis-[Rh(Acac)(PPh₃)₂ (CH₃) (NH₃)][BPh₄] (4) and cis-[Rh(BA)(PPh₃)₂(CH₃)(NH₃)] [BPh₄] (5), respectively. Complexes 1-5 were characterized by elemental analysis, ¹H and ³¹P{¹H} NMR spectra. Complexes 1, 2, 3 and 4 were characterized by X-ray diffraction analysis. Complexes 2 and 3 in solutions (CH₂Cl₂, CHCl₃) are presented as mixtures of cis-(PPh₃)₂ isomers involved into a fluxional process. Complex 2 on heating in acetonitrile is converted into trans-isomer 1. In parallel with that isomerization, reductive elimination of methyl group with formation of [CH₃PPh₃][BPh₄] takes place. Replacement of CH₃CN in complexes 1 and 2 by anion I^- yields in both cases the neutral complex trans-[Rh(Acac) (PPh₃)₂(CH₃)I]. Strong trans influence of CH₃ ligand manifests itself in the elongation (in solid) and labilization (in solution) of rhodium-acetonitrile nitrogen bond.

Full text of DOI:10.1016/j.jorganchem.2004.02.041

Journal of Organometallic Chemistry 689 (2004) 1930–1943
www.elsevier.com/locate/jorganchem
Cationic methyl complexes of rhodium(III): synthesis, structure,
and some reactions
a
a,
b
Elizaveta P. Shestakova , Yuri S. Varshavsky *, Konstantin A. Lyssenko ,
b
b
Alexander A. Korlyukov , Viktor N. Khrustalev , Marina V. Andreeva
a
a
Institute of Chemistry, St. Petersburg State University, Petrodvorets, Universitetskii Pr., 26, St. Petersburg 198504, Russian Federation
b
Nesmeyanov Institute of Organoelement Compounds, Vavilova Str., 28, Moscow 117813, Russian Federation
Received 30 November 2003; accepted 23 February 2004
Abstract
Cationic methyl complex of rhodium(III), trans-[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] (1) is prepared by interaction of trans-
[Rh(Acac)(PPh3)2(CH3)I] with AgBPh4 in acetonitrile. Cationic methyl complexes of rhodium(III), cis-[Rh(Acac)(PPh3)2-
(CH3)(CH3CN)][BPh4] (2) and cis-[Rh(BA)(PPh3)2(CH3)(CH3CN)][BPh4] (3) (Acac, BA are acetylacetonate and benzoylacetonate,
respectively), are obtained by CH3I oxidative addition to rhodium(I) complexes [Rh(Acac)(PPh3)2] and [Rh(BA)(PPh3)2] in
acetonitrile in the presence of NaBPh4. Complexes 2 and 3 react readily with NH3 at room temperature to form cis-
[Rh(Acac)(PPh3)2(CH3)(NH3)][BPh4] (4) and cis-[Rh(BA)(PPh3)2(CH3)(NH3)][BPh4] (5), respectively. Complexes 1–5 were char-
1
acterized by elemental analysis, H and 31P{1H} NMR spectra. Complexes 1, 2, 3 and 4 were characterized by X-ray diffraction
analysis. Complexes 2 and 3 in solutions (CH2Cl2, CHCl3) are presented as mixtures of cis-(PPh3)2 isomers involved into a fluxional
process. Complex 2 on heating in acetonitrile is converted into trans-isomer 1. In parallel with that isomerization, reductive
elimination of methyl group with formation of [CH3PPh3][BPh4] takes place. Replacement of CH3CN in complexes 1 and 2 by anion
Iꢀ yields in both cases the neutral complex trans-[Rh(Acac)(PPh3)2(CH3)I]. Strong trans influence of CH3 ligand manifests itself in
the elongation (in solid) and labilization (in solution) of rhodium–acetonitrile nitrogen bond.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Rhodium methyl complexes; Oxidative addition; X-ray; NMR
1. Introduction
In the cases which are not complicated by subsequent
reactions, such as elimination or insertion of ligands, the
final products of methyl iodide oxidative addition to
planar rhodium(I) complexes are octahedral complexes
of rhodium(III). For instance, in reactions
The interaction of planar rhodium(I) complexes with
methyl iodide keeps drawing attention as a simple and
convenient model of the reaction of oxidative addition,
one of the key stages of important catalytic processes.
Mechanistic concepts suggest in many cases the methyl
iodide oxidative addition to proceed through interme-
diates with separated charges, [LnM(CH3)]þIꢀ [1, 2].
The existence of such intermediates is not yet clearly
documented, and their structure remains so far a subject
of speculation [3].
O
O
H3C
H3C
L
L
+ CH3I
Rh
[Rh(Acac)L2(CH3)]+I–
[Rh(Acac)L2(CH3)I]
[Rh(Acac)L2], L = P(OPh)3, PPh3
* Corresponding author.
E-mail address: yurel@peterlink.ru (Y.S. Varshavsky).
the final products are octahedral complexes with differ-
ent mutual disposition of ligands [2b, 4, 5]:
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.02.041

E.P. Shestakova et al. / Journal of Organometallic Chemistry 689 (2004) 1930–1943
1931
2. Results and discussion
L
Rh
L
CH3
H3C
H3C
O
O
CH3
H3C
H3C
O
O
L
2.1. Synthesis and characterization of trans-[Rh-
(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] (1)
Rh
I
I
L
Stirring of suspension of orange crystals of trans-
[Rh(Acac)(PPh3)2(CH3)I] and white solid AgBPh4 in
acetonitrile or acetone/acetonitrile mixture at room
temperature results in formation of a yellow solution
and a pale yellow precipitate. The reaction mixture was
filtered, and solvent was removed from yellow filtrate.
The yellow solid obtained by evaporation of the solvent
was dissolved in chloroform, filtered, and then, on re-
moval of chloroform, dissolved in acetonitrile. A very
fine precipitate contained in the solution was removed
by thorough filtration. The product was isolated by
evaporation of acetonitrile solution and then recrystal-
lized from acetonitrile. An elemental analysis of the
yellow crystalline product and X-ray study of the crystal
grown from acetonitrile showed the substance obtained
to be a salt of cationic rhodium(III) complex containing
[BPh4]ꢀ as an anion and solvated with acetonitrile (1:1),
trans-[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] Æ CH3CN.
A view of the molecular geometry is shown in Fig. 1.
The positions of the cations trans-[Rh(Acac)(PPh3)2-
(CH3)(CH3CN)]þ, anions [BPh4]ꢀ, and molecules
CH3CN in the unit cell are presented in Fig. 2.
L = P(OPh)3
L = PPh3
In both examples above, methyl iodide adheres to
planar rhodium(I) complexes with the initial cis-dispo-
sition of P-donor ligands. In the case of trip-
henylphosphite, the P-ligands retain their initial
disposition (trans-addition of methyl iodide), whereas in
the case of triphenylphosphine, P-ligands migrate to the
mutual trans-positions (cis-addition of methyl iodide). It
can be supposed that the mutual disposition of ligands
in the final product is determined by an intramolecular
rearrangement of the intermediate pentacoordinate
cationic methyl complex before the iodide anion enters
the coordination sphere, and the complex attains its fi-
nal octahedral configuration.
Study of structure, isomerization, and reactivity of
cationic methyl intermediates might shed more light on
the mechanism of oxidative addition, but high reactivity
of these intermediates prevents their study directly in the
reaction mixtures. For instance, the intermediates
formed in the course of the reactions [Rh(b-di-
ket)(PPh3)2] + CH3I in benzene solutions (NMR at a
temperature just above the melting point of benzene)
instantly convert into the final octahedral complexes on
heating the reaction mixture to room temperature [6].
However, in some cases, in the course of oxidative ad-
dition reactions, it was possible to isolate cationic me-
thyl complexes as sufficiently stable salts with bulk
anions, for instance, [CpIr(CO)2(CH3)]þ[BPh4]ꢀ [7] and
[CpRh(CO)(PPhMe2)(CH3)]þ[BPh4]ꢀ [8]. Some stable
cationic complexes were also obtained on interaction of
the halogen containing neutral complexes with silver
salts, for instance, AgBF4 or AgPF6 [9,10]:
The cation trans-[Rh(Acac)(PPh3)2(CH3)(CH3CN)]þ
retains the octahedral structure of the parent neutral
complex with the only difference that the ligand Iꢀ in the
rhodium-(b-diketonate) plane (the equatorial plane in
½LnMClꢁ þ AgX ! ½LnMꢁþXꢀ þ AgCl
We describe here synthesis of isomers of cationic
methyl rhodium(III) complexes, [Rh(b-diket)(PPh3)2-
(CH3)(CH3CN)]þ[BPh4]ꢀ, where b-diket is acetylaceto-
nate or benzoylacetonate ligand, report structures of
these complexes in the crystalline state and in solutions,
and present data on some of their reactions. We believe
that data on structure and reactivity of cationic methyl
complexes isolated in the form of stable salts may give
an insight into chemistry of their unstable analogs. Data
presented in this paper have been partially published in
our communications [11,12].
Fig. 1. The structure of the cation of compound trans-
[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] (1) (50% probability ellip-
soids).

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E.P. Shestakova et al. / Journal of Organometallic Chemistry 689 (2004) 1930–1943
angle (176.07(9)ꢁ) in complex 1 is statistically identical
with the P(1)–Rh–P(2) angles of the related complexes,
[Rh(Acac)(PPh3)2(CH3)I] [5] and
(177.34(11)ꢁ)
[Rh(Acac)(PPh3)2I2] (177.5(3)ꢁ) [13]. The averaged
(2.390 A) Rh–P bond length in 1 compares well with the
ꢀ
ꢀ
average of 2.385 and 2.391 A found in [Rh(Acac)-
(PPh3)2(CH3)I] [5] and [Rh(Acac)(PPh3)2I2] [13], re-
spectively. The two Rh–O bonds in complex 1 differ
ꢀ
significantly, by 0.116 A, due to the difference in the
trans-influence of the methyl and acetonitrile ligands.
The longer Rh–O(2) bond, trans to methyl ligand, is of
ꢀ
the same length, 2.141(5) A, as in the parent neutral
complex. The Rh–CH3 bond length in 1 is slightly
shorter than that in [Rh(Acac)(PPh3)2(CH3)I].
The 31P{1H} NMR spectrum of 1 (CDCl3 solvent,
Table 2) shows a doublet at d 21.2 ppm with coupling
constant J(Rh–P) 99.6 Hz, which indicates the phos-
1
phine ligands to be equivalent. The parent neutral
complex trans-[Rh(Acac)(PPh3)2(CH3)I] with axial po-
sitions of triphenylphosphine ligands has close 31P
NMR spectroscopic parameters, a doublet at d 20.0
ppm with coupling constant 1J(Rh–P) 106.1 Hz (CDCl3
solvent) [4].
Fig. 2. The crystal structure of trans-[Rh(Acac)(PPh3)2(CH3)-
(CH3CN)][BPh4] (1).
our further discussion) is replaced by the CH3CN mol-
ecule coordinated via the nitrogen atom. Table 1 pre-
sents values of the important bond lengths and angles in
the cation trans-[Rh(Acac)(PPh3)2(CH3)(CH3CN)]þ.
For comparison, the corresponding values are given for
the parent neutral complex trans-[Rh(Acac)(PPh3)2-
(CH3)I] [5] and for the closely related complex trans-
[Rh(Acac)(PPh3)2I2] [13].
The trans-position of phosphine ligands in complex 1
1
in solution is confirmed by H NMR spectral data.
1
The H NMR spectrum of complex 1 (CDCl3, Table
3) contains three groups of signals. In the region 6.8–7.5
ppm there are signals of phenyl protons of ligands PPh3
and anion [BPh4]ꢀ. A singlet at d 4.22 ppm (1H) belongs
to the methine proton of the acetylacetonate ligand [4].
Present in the region 0–2 ppm are four singlets, at d 2.00
(3H), 1.43, and 1.40 (two latter are partially superim-
posed, 9H in the total), and 0.68 (3H) ppm. The first of
them, the signal at d 2.00 ppm, is to be assigned to
acetonitrile, which passes into solution on dissolving the
solvated complex in chloroform. This assignment is
founded on the following considerations: (i) the 1H
chemical shift of free acetonitrile in chloroform solution
is d 1.98 ppm [14]; (ii) the signal disappeared on re-
crystallization of the complex from methylene chloride;
(iii) this signal is absent in the spectrum of the complex
10, trans-[Rh(Acac)(PPh3)2(CH3)(CD3CN)][BPh4] Æ CD3-
CN, synthesized in deuterated solvent, CD3CN, and
recrystallized from CD3CN. In order to analyze the two
close signals at d 1.43 and 1.40 ppm (the total of 9H; the
first signal is more intense), we synthesized a complex
containing the deuterated methyl ligand, trans-[Rh(A-
cac)(PPh3)2(CD3)(CH3CN)][BPh4] Æ CH3CN (100). Inten-
sity of signals at d 1.43 and 1.40 ppm in the spectrum of
100 turned out equal (3H and 3H). Thus, we may con-
clude that these signals in the spectra of both 1 and 100
belong to two non-equivalent methyl groups of the
acetylacetonate ligand, and in the spectrum of 1, one of
these signals (d 1.43 ppm) coincides with the signal from
methyl ligand, CH3(–Rh). This overlapping makes the
splitting of CH3(–Rh) signal almost unobservable. The
Two phosphine ligands in all these structures occupy
axial positions trans to each other. The P(1)–Rh–P(2)
Table 1
ꢀ
Selected bond lengths (A) and angles (ꢁ) for complexes trans-
[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] (1) (this work), trans-
[Rh(Acac)(PPh3)2(CH3)I] [5], and trans-[Rh(Acac)(PPh3)2I2] [13] with
estimated standard deviations in parentheses
Complex 1
Trans- Trans-
[Rh(Acac)- [Rh(Acac)-
(PPh3)2(CH3)I] (PPh3)2I2]
Rh–C(1)
Rh–O(1)
Rh–O(2)
Rh–P(1)
Rh–P(2)
Rh–N(1)
Rh–I(1)
Rh-I(2)
2.085(7)
2.025(5)
2.141(5)
2.405(2)
2.376(2)
1.988(7)
–
2.11(2)
2.073(7)
2.141(7)
2.394(3)
2.377(3)
–
–
2.07(2)
2.07(2)
2.395(8)
2.388(8)
–
2.611(2)
–
2.606(3)
2.637(4)
–
P(1)–Rh–P(2)
O(1)–Rh–O(2)
P(1)–Rh–O(1)
P(1)–Rh–O(2)
P(2)–Rh–O(1)
P(2)–Rh–O(2)
P(1)–Rh–C(1)
P(2)–Rh–C(1)
P(1)–Rh–N(1)
P(2)–Rh–N(1)
176.07(9)
91.9(2)
177.34(11)
89.7(3)
92.3(2)
92.6(2)
90.0(2)
92.6(2)
91.3(11)
87.5(11)
–
177.5(3)
90.2(8)
89.3(6)
92.0(6)
92.1(6)
90.0(6)
–
93.45(15)
91.47(15)
88.71(15)
91.74(15)
87.1(2)
89.6(2)
87.32(19)
90.43(19)
–
–
–
–

Table 2
31P{1H} NMR spectral parameters of cationic methyl complexes of rhodium(III) 1–5 (solvent CDCl3)
Compound
Cation
20 ꢁC
)50 ꢁC
d, ppm/1J(RhP), Hz
2J(PP), Hz
d, ppm/1J(RhP), Hz
2J(PP), Hz
1
2
Trans-[Rh(Acac)(PPh3)2(CH3)CH3CN]þ
Cis-[Rh(Acac)(PPh3)2(CH3)CH3CN]þ
Single isomer
21.2/99.6
–
21.2/99.4
–
Major isomer 2a
Minor isomer 2b
29.8/137.8a
29.6/138.1a
–
–
29.7 /136.0
27.3/143.1
23.6 /128.4
–
36.9
3
Cis-[Rh(BA)(PPh3)2(CH3)CH3CN]þ
Major isomer 3a
31.1/135.1
28.8/138.0
27.4/142.9
24.4/128.7
38.5
36.0
Minor isomers (3b, 3b0)b
4
5
Cis-[Rh(Acac)(PPh3)2(CH3)NH3]þ
Cis-[Rh(BA)(PPh3)2(CH3)NH3]þ
Single isomer
26.7/133.8
24.0/128.6
35.2
27.0/134.2
23.0/127.2
35.5
Isomer0
Isomer00
27.3/134.1
24.0/128.3
26.9/134.8
23.4/128.2
34.8
35.4
27.5/134.6
23.3/126.7
27.2/134.8
22.8/127.0
35.2
35.6
a Spectral parameters of averaged spectrum.
b We failed to measure spectral parameters for one of the minor isomers of 3 (3b or 3b0) due to partial overlapping of their signals (Fig. 6).
Table 3
1H chemical shifts of methyl, b-diketonate, CH3CN, and NH3 ligands in complexes 1–5 (solvent CDCl3)
Compound
Cation
T (ꢁC)
CH3–Rh
CH3(b-diketonate) CH (b-diketonate) CH3CN–Rh
NH3–Rh
1
Trans-[Rh(Acac)(PPh3)2(CH3)CH3CN]þ
Single isomer
ꢂ20
)50
ꢂ1.43
ꢂ1.37
1.43; 1.40
1.38, 1.37
4.22
4.22
0.68
0.51
–
–
a
2
3
4
5
Cis-[Rh(Acac)(PPh3)2(CH3)CH3CN]þ
Cis-[Rh(BA)(PPh3)2(CH3)CH3CN]þ
Cis-[Rh(Acac)(PPh3)2(CH3)NH3]þ
Cis-[Rh(BA)(PPh3)2(CH3)NH3]þ
ꢂ20
)50
1.90
1.46
1.70
1.80
5.40
5.35
1.40
1.65
–
–
Major isomer 2ab
a
ꢂ20
)50
2.04
b
1.84
1.95
6.10
6.00
1.30
1.65
–
–
Major isomer 3ab
–
Single isomer
ꢂ20
)50
1.33
1.24
1.92; 1.64
1.92; 1.65
4.72
4.70
–
–
0.20
)0.30
Isomer0
Isomer000
Isomer
Isomer00
ꢂ20
)50
1.42
1.47
1.36
1.39
1.82
2.06
1.82
2.06
5.45
5.40
5.45
5.40
–
–
–
–
0.32
0.32
)0.19
)0.19
a Spectral parameters of averaged spectrum.
b We failed to make a reliable assignment of 1H resonances for the minor isomers (2b, 3b and 3b0) and for the methyl ligand in the major isomer 3a due to partial overlapping or/and low intensities
of signals.

1934
E.P. Shestakova et al. / Journal of Organometallic Chemistry 689 (2004) 1930–1943
splitting of this signal is more pronounced in the spec-
trum of 1 recorded in the CD3CN solution, triplet of
doublets at d 1.42 ppm with 2J(RhH) 1.8 Hz; 3J(PH) 5.4
Hz. These parameters are close to those of the CH3
(–Rh) group in the spectrum of the parent neutral
complex, [Rh(Acac)(PPh3)2(CH3)I], triplet of doublets
at d 1.39 ppm with J(RhH) 2.1 Hz; J(PH) 5.7 Hz (in
CDCl3 solution) [4]. Finally, the signal at d 0.68 ppm is
to be assigned to methyl group of coordinated acetoni-
trile, as this signal is absent in the spectrum of the
complex 10 containing deuterated acetonitrile. The non-
equivalence of methyl groups of the acetylacetonate li-
gand in 1 is due to the different nature of the ligands,
CH3 and CH3CN, lying in the equatorial plane in trans-
positions to acetylacetonate oxygens. This proves that
when in solution complex 1 retains its solid-state octa-
hedral geometry.
[BPh4] Æ 0.5CH2Cl2. Thus, the formation of cis-
[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4]
represented by following scheme:
may
be
H3C
H3C
O
O
PPh3
PPh3
Rh
+
+
CH3I
NaBPh4
+
2
3
CH3
Rh
NCCH3
CH3CN
PPh3
H3C
H3C
O
–
+
BPh4
NaI
O
PPh3
The structure of the cation is shown in Fig. 3. The
positions of the cations cis-[Rh(Acac)(PPh3)2-
(CH3)(CH3CN)]þ, anions [BPh4]ꢀ, and molecules
CH2Cl2 in the unit cell are presented in Fig. 4. Selected
bond lengths and angles are given in Table 4.
The 31P{1H} NMR spectrum of 1 is temperature in-
variant down to )50 ꢁC. In the 1H NMR spectrum, only
minor changes in the positions of signals were observed
with a decrease of temperature (Tables 2 and 3).
Acetonitrile ligand in complex 1 could be replaced by
anion Iꢀ on heating with potassium iodide in the
acetone solution. As a result, 1 is quantitatively
transformed into the parent neutral complex
[Rh(Acac)-(PPh3)2(CH3)I] [4] that was isolated from the
reaction mixture and characterized by elemental
According to the X-ray diffraction data, the cation
has geometry of distorted octahedron with phosphines
in the equatorial plane and the CH3 and CH3CN ligands
in axial positions. The C(1)–Rh–N(1) angle, 167.59(11)ꢁ,
differs markedly from the ideal value of 180ꢁ, the ace-
tonitrile molecule being deflected towards the acetyl-
acetonate ligand. The angle P(1)–Rh–P(2) amounts to
99.14(3)ꢁ, which markedly exceeds the value of the
corresponding angle in the bisphosphite complex cis-
[Rh(CH3COCHCOCF3)(P(OPh)3)2I2] (91.3(3)ꢁ) [15].
This difference can result from a larger cone angle for
triphenylphosphine [16]. It is to be noted that the Rh–
N(1) bond trans to the methyl ligand (complex 2) is
1
analysis, 31P{1H}, and H NMR spectra.
PPh3
H3C
H3C
CH3
–
[BPh4]
KI
Rh
NCCH3
PPh3
PPh3
Rh
H3C
H3C
CH3
I
+ 40˚C
acetone
KBPh4
CH3CN
PPh3
2.2.
Synthesis
and
characterization
of
cis-
[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] (2) and
cis-[Rh(BA)(PPh3)2(CH3)(CH3CN)][BPh4] (3)
We have also prepared cationic methyl complexes of
rhodium(III) by action of methyl iodide on rhodium(I)
complexes, [Rh(b-diket)(PPh3)2], in the presence of so-
dium tetraphenylborate in acetonitrile. In the case of b-
diket ¼ Acac, a light-yellow crystalline product was
formed. Crystal for the structure investigation was ob-
tained by recrystallization from methylene chloride/di-
ethyl ether solution. According to the results of
elemental analysis and X-ray study, the product is cat-
ionic complex cis-[Rh(Acac)(PPh3)2(CH3)(CH3CN)]-
Fig. 3. The structure of the cation of compound cis-
[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] (2) (50% probability ellip-
soids).

E.P. Shestakova et al. / Journal of Organometallic Chemistry 689 (2004) 1930–1943
1935
one of them the phosphine ligands occupy equivalent
positions, while in the other their positions are non-
equivalent. It is evident that at room temperature these
complexes are involved into a fast interconversion, while
at )50ꢁ these dynamic processes slow down and do not
affect the 31P NMR spectrum. The intense doublet at d
29.7 ppm corresponds to the complex containing two
equivalent phosphines, and should be ascribed to the
major form 2a, that retains in solution the solid-state
geometry of 2 with both PPh3 ligands in the equatorial
plane (Fig. 3). Structure of the minor form, 2b, present
in the solution and containing non-equivalent phos-
phines will be discussed in Section 2.4.
Cationic complex with the benzoylacetonate ligand
cis-[Rh(BA)(PPh3)2(CH3)(CH3CN)][BPh4] (3) was pre-
pared similarly to the complex 2 by action of methyl
iodide on [Rh(BA)(PPh3)2] in acetonitrile in the presence
of NaBPh4. After recrystallization from methylene
chloride/diethyl ether solution, complex 3 was charac-
terized by elemental analysis, and its solid-state struc-
ture was established by X-ray crystallography (Fig. 5).
The complex is solvated with diethyl ether (1:1).
Selected bond lengths and angles are given in Table 4.
As can be seen, in solid state, cation 3, cis-[Rh(BA)-
(PPh3)2(CH3)(CH3CN)]þ, like cation 2, has a distorted
octahedral geometry with two cis-triphenylphosphine
ligands in the equatorial plane and the methyl and
CH3CN ligands in axial positions, trans to each other.
The structural parameters of complex 3 are very close to
those of complex 2.
Fig. 4. The crystal structure of cis-[Rh(Acac)(PPh3)2(CH3)-
(CH3CN)][BPh4] (2), projection along the Y-axis.
Table 4
ꢀ
Selected bond lengths (A) and angles (ꢁ) for complexes
cis-[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] (2), cis-[Rh(BA)(PPh3)2-
(CH3)(CH3CN)][BPh4] (3), and cis-[Rh(Acac)(PPh3)2(CH3)(NH3)]-
[BPh4] (4) with estimated standard deviations in parentheses
2
3
4
Rh–C(1)
Rh–O(1)
Rh–O(2)
Rh–P(1)
Rh–P(2)
Rh–N(1)
2.059(3)
2.062(3)
2.068(2)
2.0775(19)
2.3078(8)
2.3383(9)
2.192(3)
2.075(3)
2.152(2)
2.071(2)
2.3111(7)
2.3291(7)
2.118(2)
2.0829(18)
2.0653(18)
2.3262(8)
2.3032(7)
2.190(2)
The 31P{1H} and 1H NMR spectra of 3, like those of
2, are temperature dependent (Tables 2 and 3, Fig. 6).
The 31P{1H} NMR spectrum of 3 in CDCl3 at room
temperature is averaged and shows a single doublet of
broadened lines, d 29.6 ppm with apparent 1J(RhP)
138.1 Hz. In the spectrum recorded at )20 ꢁC, the
P(1)–Rh–P(2)
O(1)–Rh–O(2)
P(1)–Rh–O(1)
P(1)–Rh–O(2)
P(2)–Rh–O(1)
P(2)–Rh–O(2)
P(1)–Rh–C(1)
P(2)–Rh–C(1)
P(1)–Rh–N(1)
P(2)–Rh–N(1)
C(1)–Rh–N(1)
99.14(3)
90.01(7)
88.31(6)
177.28(6)
170.77(6)
82.74(6)
90.21(9)
90.50(9)
93.16(6)
100.73(6)
167.59(11)
98.81(3)
89.75(8)
84.43(6)
171.22(6)
175.55(6)
87.37(6)
89.31(9)
93.39(9)
101.40(7)
90.70(7)
167.82(10)
99.86(3)
89.21(8)
98.13(6)
169.00(6)
89.77(5)
88.30(6)
89.88(9)
94.43(8)
90.81(7)
168.33(7)
90.27(11)
ꢀ
significantly (0.202 A) longer than Rh–N(1) bond trans
to acetylacetonate oxygen (complex 1). This fact, as well
as the above-mentioned asymmetry in the rhodium–
oxygen bonds in complex 1, displays a strong trans-in-
fluence of the methyl ligand.
1
The 31P{1H} and H NMR spectra of 2 are temper-
ature dependent. At room temperature, its 31P{1H}
spectrum in CDCl3 (Table 2) is averaged and shows a
single doublet of broadened lines at d 29.8 ppm with
1
apparent J(RhP) value of 137.8 Hz, while at )50 ꢁC
two sets of signals are observed, a doublet at d 29.7 ppm
with high intensity and two doublets of doublets (d 27.3
and 23.6 ppm) with very low intensity. This indicates
that two related forms of 2 are present in the solution. In
Fig. 5. The structure of the cation of compound cis-[Rh(BA)(PPh3)2-
(CH3)(CH3CN)][BPh4] (3) (50% probability ellipsoids).

1936
E.P. Shestakova et al. / Journal of Organometallic Chemistry 689 (2004) 1930–1943
Fig. 6. The 31P{1H} NMR spectra of cis-[Rh(BA)(PPh3)2(CH3)(CH3CN)][BPh4] (3) in CDCl3 at various temperatures.
corresponding resonance appears as a combination of
two very broad, poorly resolved bands. The spectrum
measured at )50 ꢁC contains two groups of signals
differing by intensity. The group of signals with a high
intensity consists of two doublets of doublets and be-
longs to a complex with two non-equivalent phosphines
(d 31.1 and 28.8 ppm). We believe this group of signals
to belong to cation 3a that retains in solution the solid-
state structure of 3 with two equatorial phosphines in
the cis-position to each other (Fig. 5). This complex is a
structural analog of 2a, and the non-equivalence of the
phosphine ligands in its structure is a consequence of the
asymmetry of the benzoylacetonate ligand. The second
group of signals has a lower intensity and seems to be
the superimposed spectra of two other cations that
contain phosphines in non-equivalent positions (Fig. 6,

E.P. Shestakova et al. / Journal of Organometallic Chemistry 689 (2004) 1930–1943
1937
Table 2). The structure of these minor forms will be
discussed in Section 2.4.
characterized by elemental analysis, crystal X-ray dif-
fraction study, and 31P{1H} and 1H NMR spectra.
Crystal for the X-ray diffraction analysis was grown
from the methylene chloride/diethyl ether solution. The
structure of the cation is shown in Fig. 7.
Selected bond lengths and angles are given in Table 4.
The equatorial plane of cation 4 contains triphenyl-
phosphine and methyl ligands. The second triphenyl-
phosphine ligand and the ammonia molecule occupy
axial positions, trans to each other. The angle P(1)–Rh–
P(2) amounts to 99.86(3)ꢁ, which is very close to the
angle P(1)–Rh–P(2) in structures 2 and 3 (Table 4).
Lengths of two Rh–O bonds differ significantly (0.081
1
The H NMR spectra of complexes 2 and 3 recorded
at room temperature consist of three groups of signals.
In the region 6.8–7.8 ppm there are signals of phenyl
protons of PPh3, BPhꢀ4 , and benzoylacetonate. Signals
of methine protons for complexes 2 and 3 are located at
d 5.40 ppm (1H) and d 6.10 ppm (1H), respectively.
Signals of methyl protons represent the third group ly-
ing in the region d 0–2.1 ppm. In the spectrum of 2 the
signal at d 1.90 ppm (3H) should be assigned to
the methyl ligand, CH3(–Rh), as this signal is absent in
the spectrum of the complex with deuterated methyl li-
gand, cis-[Rh(Acac)(PPh3)2(CD3)(CH3CN)][BPh4] (20).
Two equivalent methyl groups of the acetylacetonate
ligand give a singlet at d 1.70 ppm with intensity cor-
responding to 6H. Finally, we assign a singlet at d 1.40
ppm to methyl group of coordinated acetonitrile. In the
1H NMR spectrum of complex 3 the signal at d 2.04
ppm should be assigned to the methyl ligand, CH3
(–Rh), as this signal is absent in the spectrum of the
complex with deuterated methyl ligand, cis-
[Rh(BA)(PPh3)2(CD3)-(CH3CN)][BPh4] (30). By anal-
ogy with complex 2, the signals at d 1.84 and 1.30 ppm
should be assigned to the methyl groups of the benzoyl
acetonate and coordinated acetonitrile, respectively. In
the 1H NMR spectra of complexes 2 and 3 are also
present signals from protons of the solvent molecules
contained in the solvated crystals, a singlet at d 5.30 ppm
from CH2Cl2 (complex 2) and two multiplets, quartet at
d 3.50 ppm and triplet at d 1.25 ppm, from diethyl ether
(complex 3). The 1H NMR spectra of complexes 2 and 3
at room temperature evidently are averaged. At )50 ꢁC
the 1H NMR spectra of both complexes contain a
number of overlapping signals, as spectra of major and
minor forms are separated due to deceleration of dy-
ꢀ
A), the bond trans to the CH3 ligand being longer. The
values of angles P(1)–Rh–O(1) (98.13(6)ꢁ), P(1)–Rh–
O(2) (169.00(6)ꢁ), and P(2)–Rh–N(1) (168.33(7)ꢁ) indi-
cate the structure of complex 4 to be a markedly
distorted octahedron, with the NH3 ligand deviating
towards the acetylacetonate ligand.
The 31P{1H} NMR spectrum of complex 4 in chlo-
roform solution (Table 2) at room temperature repre-
sents two doublets of doublets (d 26.7 and 24.0 ppm)
and corresponds to the complex with two non-equiva-
lent phosphine ligands, which is present in solution in
one isomer form. Thus, complex 4 in solution retains its
solid-state geometry (Fig. 7). The 1H NMR spectrum of
complex 4 (Table 3) consists of a group of phenyl proton
signals (d 6.8–7.5 ppm), a signal of methine proton of
acetylacetonate ligand at d 4.72 ppm (1H), and a set of
signals of methyl groups and coordinated ammonia in
the region 0–2 ppm. Within this region, signals at d 1.92
(3H) and 1.64 (3H) ppm belong to protons of two non-
equivalent methyl groups of the acetylacetonate ligand.
The signal with poorly resolved splitting at d 1.33 ppm
(3H) should be assigned to the methyl ligand, CH3-
(–Rh). Splitting of this signal is caused by spin–spin
1
namic exchange processes. By comparing the H NMR
spectra of complexes 2 and 20, we succeeded in assigning
the signals belonging to the major form, 2a, with
equatorial phosphine ligands (Table 3). For 2b and 3b,
and for the methyl ligand CH3(–Rh) in 3a, we failed to
make a reliable assignment of signals due to their
overlapping or low intensity. It is to be noted that in the
spectra of 2 we did not observe splitting of signal from
protons of the CH3(–Rh) ligand at room temperature as
well as at )50 ꢁC.
2.3. Reactions of complexes 2 and 3 with ammonia:
characterization
of
cis-[Rh(Acac)(PPh3)2(CH3)-
(NH3)][BPh4] (4) and cis-[Rh(BA)(PPh3)2(CH3)-
(NH3)][BPh4] (5)
Complex
cis-[Rh(Acac)(PPh3)2(CH3)(NH3)][BPh4]
(4) is easily formed by passing a stream of NH3 through
the methylene chloride solution of 2 or the suspension of
2 in acetonitrile at room temperature. Complex 4 was
Fig. 7. The structure of the cation of compound cis-[Rh(Acac)-
(PPh3)2(CH3)(NH3)][BPh4] (4) (50% probability ellipsoids).

1938
E.P. Shestakova et al. / Journal of Organometallic Chemistry 689 (2004) 1930–1943
interaction of methyl ligand protons with 103Rh and two
non-equivalent 31P nuclei. We assign signal at d 0.20
ppm (3H) to the protons of coordinated ammonia, as
this signal is absent in the spectrum of the deuterated
complex, cis-[Rh(Acac)(PPh3)2(CH3)(ND3)][BPh4] (40),
prepared by action of ND3 gas on 2.
doublet from the octahedral cis-(PPh3)2 complex, 2a,
with equivalent phosphines, contains two doublets of
doublets from other cis-(PPh3)2 moiety, 2b, with non-
equivalent phosphines. The coexisting forms of
complex 2 at room temperature are in the dynamic
exchange:
Complex 3 also reacts readily with ammonia gas at
room temperature to form cis-[Rh(BA)(PPh3)2-
(CH3)(NH3)][BPh4] (5). The obtained compound was
characterized by elemental analysis, 31P{1H} and 1H
NMR spectra. In its 31P{1H} NMR spectrum two sets
of signals differing by intensity could be detected. Each
of these sets represents two doublets of doublets (Table
2), which indicates that complex 5 is formed from 3 in
two isomeric forms with non-equivalent phosphine
ligands. Taking into account close values of 31P{1H}
NMR spectroscopic parameters of the acetylaceto-
nate and benzoylacetonate derivatives (Table 2) and the
X-ray diffraction data for 4, the acetylacetonate analog,
we assign to these isomeric cations the following
structures:
2a ¢ 2b
It is reasonable to assume that the dynamic rear-
rangement of ligands takes place within the fluxional
pentacoordinate moiety formed by dissociation of
acetonitrile from the cation 2a, in which acetonitrile is
subjected to strong trans effect of methyl ligand.
Several geometries are compatible with the low-tem-
perature NMR data for 2b, namely two octahedral
isomers and three pentacoordinate structures formed
by acetonitrile dissociation. We suppose that in the
reaction with ammonia are involved forms, in which
the mutual arrangement of phosphine ligands is fitted
well to the final geometry of ammonia complex, and
tentatively depict below the structure for 2b akin to
the structure of the ammonia complex 4, i.e., as an
isomer of 2a:
+
+
PPh3
Rh
PPh3
Rh
PPh3
CH3
H3C
Ph
O
O
PPh3
CH3
O
O
+
PPh3
H3C
PPh3
CH3
H3C
H3C
O
O
NH3
NH3
Rh
The 1H NMR spectrum of complex 5 consists of three
groups of signals. The region 6.8–7.8 ppm contains
signals of phenyl protons. In the region of methine
protons two singlets differing by intensity are present at
d 5.40 and 5.45 ppm, which correspond to two isomers
of 5. In the region 0–2.1 ppm, signals of methyl groups
and coordinated ammonia are present. Signals at d 1.42
and 1.47 ppm are broadened and exhibit a complex
splitting. Therefore, we assign them to methyl ligands,
CH3(–Rh), in two isomers of 5. Signals at d 1.82 and
2.06 ppm belong to methyl groups of benzoylacetonate
ligands in these two isomers. Signal at d 0.32 ppm
should be assigned to ligand NH3, as this signal is absent
in the complex containing deuterated ammonia. It is to
be noted that the position of this signal is identical for
both isomers of the complex 5. A reduction of temper-
ature to )50 ꢁC produces no essential changes in the
NCCH3
2b
Likewise, we depict structures of two minor moieties,
3b and 3b0, presented in the solutions of 3 as the minor
isomers of the octahedral cation 3a:
+
+
PPh3
PPh3
PPh3
CH3
H3C
Ph
O
O
Ph
O
O
PPh3
CH3
Rh
Rh
H3C
NCCH3
NCCH3
3b
3b'
1
31P{1H} and H NMR spectra of complexes 4 and 5,
1
except for some shifts of the H signals of the methyl
ligand, CH3(–Rh), and of the coordinated ammonia
(Tables 2 and 3).
2.5. Some reactions of the complex cis-[Rh(Acac)-
(PPh3)2(CH3)(CH3CN)][BPh4] (2)
As seen from above data, complexes 2 and 3 in so-
lutions are present in cis-(PPh3)2 forms, and action of
ammonia resulted in the formation of cis-(PPh3)2 com-
plexes with one equatorial and one axial phosphine.
Below we will consider two reactions in which complex
of the trans-(PPh3)2 type is formed with both phos-
phines in the axial positions.
2.4. Discussionofstructureofminorformsofcomplexescis-
[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] (2) and
cis-[Rh(BA)(PPh3)2(CH3)(CH3CN)][BPh4] (3)
As mentioned above, at )50 ꢁC the 31P{1H} NMR
spectrum of complex 2 in CDCl3, alongside with the

E.P. Shestakova et al. / Journal of Organometallic Chemistry 689 (2004) 1930–1943
1939
2.5.1. Isomerization of cis-[Rh(Acac)(PPh3)2(CH3)-
(CH3CN)][BPh4] (2) into trans-[Rh(Acac)(PPh3)2-
(CH3)(CH3CN)][BPh4] (1)
anion Iꢀ in the coordination sphere of the cis-(PPh3)2
cation 2 is the neutral trans-(PPh3)2 complex, i.e., the
substitution is accompanied by a rearrangement of
phosphine ligands. (ii) The trans-(PPh3)2 neutral com-
plex is formed from the cis-(PPh3)2 cation 2 much more
readily than from the structurally related trans-(PPh3)2
cation 1 which reacts with KI only at heating. In these
facts, like in the dynamic behavior of 2, the lability of
acetonitrile ligand in the trans-position to methyl ligand
makes itself evident.
On heating complex 2 in acetonitrile at 75 ꢁC the
solution changes its color from light yellow to orange.
In the 31P{1H} NMR spectrum (CDCl3 solvent) of the
solid isolated from the reaction mixture, the following
signals are present: broadened doublet at d ꢂ 31 ppm
1
with J(RhP) ꢂ 140 Hz, intense sharp doublet at d 21.2
1
ppm with J(RhP) 99.6 Hz, and intense singlet at d 22.2
ppm. The obvious assignment of these signals is as
1
follows. The sharp doublet at d 21.2 ppm, J(RhP) 99.6
Hz belongs to the trans-bisphosphine complex 1 pro-
duced by isomerization of the complex 2; the doublet
with broadened lines centered at d ꢂ 31 ppm belongs to
the unreacted complex 2. The unexpectedly appeared
3. Concluding remarks
In this work, we have synthesized, isolated as tetra-
phenylborate salts, and characterized stable methyl
cationic rhodium(III) complexes in two isomeric
octahedral forms, trans-[Rh(b-diket)(PPh3)2(CH3)-
(CH3CN)][BPh4] with b-diket ¼ acetylacetonate and
cis-[Rh(b-diket)(PPh3)2(CH3)(CH3CN)][BPh4] with b-
diket ¼ acetylacetonate and benzoylacetonate groups.
The trans-(PPh3)2 isomer containing two axial phos-
phines retains its geometry in solution and is kinetically
inert. By contrast, cis-(PPh3)2 isomers containing two
equatorial phosphines are remarkably labile. On disso-
lution, these cis-(PPh3)2 isomers undergo partial trans-
formation with transfer of one PPh3 ligand from an
equatorial to an axial position. That transfer presum-
ably takes place within pentacoordinate species resulting
from CH3CN dissociation. The pentacoordinate species
and octahedral minor cis-(PPh3)2 isomers are involved
into a dynamic structural exchange with initial major
isomers. It seems likely that the main reason of the
readiness of the major cis-(PPh3)2 isomers to generate
these minor moieties is lability of CH3CN ligand, which
is subjected to the strong trans effect of methyl ligand.
CH3CN ligand in cis-[Rh(b-diket)(PPh3)2(CH3)-
(CH3CN)]þ cations is readily and quantitatively re-
placed by NH3 or Iꢀ even at ambient temperature. It is
noticeable that the positions of PPh3 ligands in the re-
sultant complexes differ from their positions in the
starting complexes. The ammonia complexes contain
one equatorial and one axial phosphine ligand, whereas
the action of Iꢀ yields the neutral complexes trans-
[Rh(b-diket)(PPh3)2(CH3)I] with two axial trans dis-
posed phosphines.
singlet at
d 22.2 ppm corresponds to the salt
[CH3PPh3][BPh4], which is confirmed by NMR spectra
of the authentic sample prepared for this purpose [17].
Formation of the methyltriphenylphosphonium salt is
evidence that, in parallel with isomerization of 2 into 1,
cleavage of the Rh–CH3 bond takes place. This re-
ductive elimination reaction must generate some rho-
dium(I) complex, but we failed to detect any.
Comparison of integral intensities of 31P signals corre-
sponding to the complex
1
and to the salt
[CH3PPh3][BPh4] indicated that comparable amounts
of the initial complex 2 undergo isomerization and re-
ductive elimination. The following scheme represents
tentatively this observation:
þ75 ꢁC
CH3CN
f2a ¢ 2bg
1 þ ½CH3PPh3ꢁþBPhꢀ þ \Rh ðIÞ"
ƒƒ!
4
2.5.2. Interaction of cis-[Rh(Acac)(PPh3)2(CH3)-
(CH3CN)][BPh4] (2) with KI
When stirring complex 2 with KI in acetone at room
temperature, formation of an orange crystalline solid is
observed. After separation from KBPh4, the orange
product was characterized by elemental analysis,
31P{1H} and 1H NMR spectra and thus identified as the
neutral octahedral complex trans-[Rh(Acac)(PPh3)2-
(CH3)I]. The quantitative conversion of the initial
complex takes 30–40 min.
+20˚C
Stable methyl cationic cis-(PPh3)2 complexes with
two equatorial phosphines have been synthesized by
methyl iodide oxidative addition to rhodium(I) planar
complexes [Rh(b-diket)(PPh3)2] in acetonitrile solutions
in the presence of NaBPh4. The credible speculation is
that the unstable cationic intermediates, which retain the
initial cis-(PPh3)2 arrangement of phosphine ligands,
could be formed at the primary stages of methyl iodide
oxidative addition to [Rh(b-diket)(PPh3)2] complexes
also in less coordinating solvents.
+
2a
2b
KI
{
}
acetone
PPh
Rh
3
3
H C
O
O
3
CH
I
3
+
+
KBPh
CH CN
3
4
H C
3
PPh
The following peculiarities of this reaction draw at-
tention: (i) The product of acetonitrile substitution for

1940
E.P. Shestakova et al. / Journal of Organometallic Chemistry 689 (2004) 1930–1943
4. Experimental
4.1. Preparation of complexes
trile provided yellow crystals of 1 as CH3CN 1:1 solvate.
Yield: 0.22 g (74%).
4.1.3. Preparation of trans-[Rh(Acac)(PPh3)2(CH3)-
(CD3CN)][BPh4] (10)
The complex was prepared analogously to 1 from
[Rh(Acac)(PPh3)2(CH3)I] (0.30 g, 0.34 mmol) using
CD3CN as solvent. Yield: 0.27 g (69%).
All operations were performed under an atmosphere
of dry argon. Rhodium complexes [Rh(Acac)(PPh3)2],
[Rh(BA)(PPh3)2], [Rh(Acac)(PPh3)2(CH3)I] were syn-
thesized by published procedures [4,18]. Gaseous NH3
and ND3 were prepared by standard methods [19].
Solvents were dried and purified by known procedures
[14] and distilled under argon. Methyl iodide was always
used as freshly distilled samples. Elemental analyses
were performed with Hewlett–Packard 185 microana-
lyzer. The analytical data for complexes 1–5 are pre-
sented in Table 5.
4.1.4. Preparation of trans-[Rh(Acac)(PPh3)2(CD3)-
(CH3CN)][BPh4] (100)
The complex was prepared using the procedure de-
scribed for 1 starting from [Rh(Acac)(PPh3)2(CD3)I]
(0.36 g, 0.41 mmol). Yield: 0.29 g (62%).
4.1.1. Preparation of [Rh(Acac)(PPh3)2(CD3)I]
4.1.5. Preparation of cis-[Rh(Acac)(PPh3)2(CH3)-
(CH3CN)][BPh4] (2)
Product was prepared by a modified literature pro-
cedure [4]. To a suspension of [Rh(Acac)(PPh3)2] (0.30
g, 0.41 mmol) in toluene (10 ml) was added excess of
CD3I (0.20 ml). Reaction mixture was stirred at ambient
temperature for 30 min. The solvent was removed in
vacuo. Recrystallization from benzene/hexane provided
orange fine crystals of [Rh(Acac)(PPh3)2(CD3)I]. Yield:
0.34 g (95%). 31P{1H} NMR (CDCl3): d 21.1 ppm,
To a suspension of [Rh(Acac)(PPh3)2] (0.49 g, 0.67
mmol) and NaBPh4 (0.47 g, 1.37 mmol) in acetonitrile
(15 ml) was added methyl iodide (0.13 ml, 2.09 mmol) at
5 ꢁC. The resulting reaction mixture was stirred for 1 h
at 10 ꢁC. A yellow fine crystalline precipitate was iso-
lated by filtration, washed twice with acetonitrile (5 ml)
and dried in vacuo. Recrystallization from methylene
chloride/diethyl ether provided yellow crystals of 2 as
CH2Cl2 0.5:1 solvate. Yield: 0.67 g (87%).
1
1J(RhP) ¼ 106.1 Hz. H NMR (CDCl3): d 7.8–7.2 ppm
(m, 2PPh3), 4.26 ppm (s, 1H, CH), 1.51 and 0.94 ppm
(both s, 6H, CH3 of Acac).
4.1.2. Preparation of trans-[Rh(Acac)(PPh3)2(CH3)-
(CH3CN)][BPh4] (1)
4.1.6. Preparation of cis-[Rh(Acac)(PPh3)2(CD3)-
(CH3CN)][BPh4] (20)
To a suspension of NaBPh4 (0.10 g, 0.29 mmol) and
AgNO3 (0.05 g, 0.29 mmol) in acetonitrile (15 ml) was
added a suspension of [Rh(Acac)(PPh3)2(CH3)I] (0.22 g,
0.26 mmol) in acetone (10 ml). The reaction mixture was
stirred at ambient temperature until complete exhaus-
tion of orange starting rhodium complex (ꢂ2 h). The
reaction mixture was filtered, and solvent was removed
from yellow filtrate in vacuo. Chloroform (10 ml) was
added to yellow solid yielding a yellow solution con-
taining very fine light precipitate. The precipitate was
filtered off, and solvent was removed from filtrate under
reduced pressure. Acetonitrile (10 ml) was added to
yellow solid formed. Solution was filtered, and solvent
was removed in vacuo. Recrystallization from acetoni-
The complex was prepared using the procedure de-
scribed for 2, starting from [Rh(Acac)(PPh3)2] (0.51 g,
0.70 mmol), NaBPh4 (0.47 g, 1.37 mmol) and CD3I
(0.13 ml, 2.09 mmol). Yield: 0.49 g (61%).
4.1.7. Preparation of cis-[Rh(BA)(PPh3)2(CH3)-
(CH3CN)][BPh4] (3)
The complex was prepared analogously to 2 from
[Rh(BA)(PPh3)2] (0.50 g, 0.63 mmol), NaBPh4 (0.76 g,
2.22 mmol) and methyl iodide (0.12 ml, 1.93 mmol) in
acetonitrile (15 ml). Recrystallization from methylene
chloride/diethyl ether provided yellow crystals of 3 as
(C2H5)2O 1:1 solvate. Yield: 0.70 g (90%).
Table 5
Analytical data for complexes 1, 2, 3, 4, and 5
Compound
Color
Molecular formula
Analyses, found (%) (calc. (%))
C
H
1
2
3
4
5
[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] Æ CH3CN
[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] Æ 1/2CH2Cl2
[Rh(BA)(PPh3)2(CH3)(CH3CN)][BPh4] Æ (C2H5)2O
[Rh(Acac)(PPh3)2(CH3)(NH3)][BPh4]
Yellow
Yellow
Yellow
Yellow
Yellow
74.08 (73.58)
71.83 (71.89)
74.70 (74.70)
73.56 (73.54)
74.75 (74.80)
6.18 (5.82)
5.53 (5.64)
6.08 (6.10)
5.89 (5.89)
5.87 (5.75)
[Rh(BA)(PPh3)2(CH3)(NH3)][BPh4]

E.P. Shestakova et al. / Journal of Organometallic Chemistry 689 (2004) 1930–1943
1941
4.1.8. Preparation of cis-[Rh(BA)(PPh3)2(CD3)-
(CH3CN)][BPh4] (30)
ppm. 1H NMR (CDCl3): d 7.8–6.7 ppm (m, PPh3,
BPh4), 1.37 ppm (d, 3H, CH3), J(H–P) 12.8 Hz.
2
The complex was prepared using the procedure de-
scribed for 2, starting from [Rh(BA)(PPh3)2] (0.50 g,
0.63 mmol), NaBPh4 (0.43 g, 1.26 mmol) and CD3I
(0.13 ml) in acetonitrile (20 ml). Yield: 0.60 g (77%).
4.1.14. The reaction of trans-[Rh(Acac)(PPh3)2(CH3)-
(CH3CN)][BPh4] (1) with KI in acetone
Mixture of 1 (0.04 g, 0.03 mmol), KI (0.02 g, 0.11
mmol) and acetone (1 ml) was stirred for 1.5 h at 40 ꢁC.
The initial yellow suspension turned orange. Then ace-
tone was removed in vacuo. Toluene (10 ml) was added
to dry orange solid. Solution was filtered, and the filtrate
was concentrated to ca. 0.5 ml in vacuo; addition of
hexane (5 ml) led to the precipitation of orange solid.
The solvent was decanted, and the residue was washed
with hexane (2 ml) and dried in vacuo. Yield: 0.026 g
(96%). Found: C ¼ 57.98, H ¼ 4.73%. RhC42H40P2O2I
requires C ¼ 58.08, H ¼ 4.64%. 31P{1H} NMR (CDCl3):
4.1.9. Preparation of cis-[Rh(Acac)(PPh3)2(CH3)-
(NH3)][BPh4] (4)
A stream of gaseous NH3 was passed through a
suspension of complex 2 (0.81 g, 0.71 mmol) in aceto-
nitrile (10 ml) for 30 min at room temperature. Within
10 min the initial complex was completely dissolved to
yield pale yellow solution. Then yellow crystals began to
precipitate. Crystalline precipitate was isolated by fil-
tration, washed with acetonitrile and dried in vacuo.
Recrystallization from methylene chloride/diethyl ether
provided yellow crystals of 4. Yield: 0.51 g (67%).
1
1
d 21.1 ppm, J(RhP) ¼ 106.1 Hz. H NMR (CDCl3): d
7.8–7.2 ppm (m, 2PPh3), 4.26 ppm (s, 1H, CH), 1.51 and
0.94 ppm (both s, 6H, CH3 of Acac), 1.40 ppm (td, 3H,
Rh–CH3), 2J(H–Rh) ¼ 2.1 Hz, 3J(H–P) ¼ 5.7 Hz.
31P{1H} and 1H NMR spectral characteristics of the
resulted product agree well with those of trans-
[Rh(Acac)(PPh3)2(CH3)I] [4].
4.1.10. Preparation of cis-[Rh(Acac)(PPh3)2(CH3)-
(ND3)][BPh4] (40)
The complex 40 was prepared using the procedure
described for 4, starting from complex 2 (0.31 g, 0.27
mmol) and ND3. Yield: 0.20 g (69%).
4.1.11. Preparation of cis-[Rh(BA)(PPh3)2(CH3)-
(NH3)][BPh4] (5)
4.1.15. The reaction of cis-[Rh(Acac)(PPh3)2(CH3)-
(CH3CN)][BPh4] (2) with KI in acetone
A stream of gaseous NH3 was passed through a
suspension of complex 3 (0.075 g, 0.060 mmol) in ace-
tonitrile (2 ml) for 15 min at room temperature. The
initial complex was completely dissolved to yield pale
yellow solution. The reaction mixture was filtered, and
acetonitrile was removed in vacuo. The oily residue
turned into crystalline product on cooling in refrigera-
tor. Yield: 0.065 g (95%).
Mixture of complex 2 (0.09 g, 0.08 mmol), KI (0.02 g,
0.11 mmol) and acetone (1 ml) was stirred at ambient
temperature for 40 min. The initial yellow suspension
turned orange. Acetone was removed in vacuo. Methy-
lene chloride (5 ml) was added to dry orange solid. So-
lution was filtered, and solvent was removed from
filtrate in vacuo. Yield: 0.06 g (90%). Found: C ¼ 58.31,
H ¼ 4.88%. RhC42H40P2O2I requires C ¼ 58.08,
H ¼ 4.64%. 31P{1H} NMR (CDCl3): d 21.1 ppm,
4.1.12. Preparation of cis-[Rh(BA)(PPh3)2(CH3)-
(ND3)][BPh4] (50)
The complex was prepared analogously to 5 from
complex 3 (0.33 g, 0.27 mmol) and ND3. Yield: 0.29 g
(97%).
1
1J(RhP) ¼ 106.1 Hz. H NMR (CDCl3): d 7.8–7.2 ppm
(m, 2PPh3), 4.26 ppm (s, 1H, CH), 1.51 and 0.94 ppm
(both s, 6H, CH3 of Acac), 1.41 ppm (td, 3H, Rh–CH3),
3
1
2J(H–Rh) ¼ 2.1 Hz, J(H–P) ¼ 5.7 Hz. 31P{1H} and H
NMR spectral characteristics of the resulted product
agree well with those of [Rh(Acac)trans-(PPh3)2(CH3)I]
[4].
4.1.13. Preparation of [CH3PPh3][BPh4]
Product was prepared by modifying a literature pro-
cedure [17]. To a solution of triphenylphosphine (1.0 g,
3.80 mmol) in methylene chloride (5 ml) was added
methyl iodide (0.5 ml, 7.6 mmol). Reaction mixture was
stirred at ambient temperature for 10 min. A solvent
was removed in vacuo. The white solid thus obtained
was mixed with NaBPh4 (1.41 g, 4.10 mmol) and
methanol (20 ml) yielding a white fine crystalline prod-
uct. The precipitate was isolated by filtration, washed
twice with methanol (5 ml) and dried in vacuo. Yield:
1.86 g (82%). Found: C ¼ 86.58, H ¼ 6.48%. C43H38PB
requires C ¼ 86.57, H ¼ 6.42%. Melting point (m.p.)
197.0 ꢁC (197.0 ꢁC [17]). 31P{1H} NMR (CDCl3): d 22.2
4.1.16. Heating of cis-[Rh(Acac)(PPh3)2(CH3)-
(CH3CN)][BPh4] (2) in acetonitrile
Complex 2 (0.2 g, 0.17 mmol) in acetonitrile (4 ml)
was heated up to 75 ꢁC for 30 min. Complex 2 was fully
dissolved at 60 ꢁC. Then the pale yellow solution turned
orange. Acetonitrile was removed in vacuo. The orange
solid thus obtained was characterized by 31P{1H} NMR
spectrum (CDCl3): broadened doublet at d ꢂ 31 ppm
1
with J(RhP) ꢂ 140 Hz from unreacted complex 2, sin-
glet at 22.2 ppm from [CH3PPh3][BPh4], doublet at 21.2
1
ppm, J(Rh–P) 99.6 Hz, from complex 1.

1942
E.P. Shestakova et al. / Journal of Organometallic Chemistry 689 (2004) 1930–1943
Table 6
Crystallographic data for complexes 1, 2, 3, and 4
1 Æ CH3CN
2 Æ 1/2CH2Cl2
3 Æ C4H10
O
4
Molecular formula
Formula weight
T (K)
Radiation, k(Mo Ka) (A)
Crystal system
Space group
C70H66BN2O2P2Rh
C68H63BNO2P2Rh Æ 1/2CH2Cl2
1144.32
110(2)
C77H75BNO3P2Rh
1238.04
120(2)
RhC66H63BNO2P2
1077.83
115(2)
1142.91
110(2)
0.71073
ꢀ
0.71073
Orthorhombic
Pbcn
Yellow, prism
19.522(4)
19.313(3)
30.305(4)
90
0.71073
Monoclinic
C2=c
Yellow, prism
51.481(5)
9.8086(16)
30.539(5)
90
0.71073
Monoclinic
P21=c
Yellow, prism
16.6550(18)
16.8739(18)
20.568(2)
90
Triclinic
ꢁ
P1
Colorless, plate
9.780(2)
Color, shape
ꢀ
a (A)
ꢀ
b (A)
15.919(3)
19.496(5)
101.899(7)
96.078(5)
99.853(6)
2894.8(11)
2
ꢀ
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
90
121.861(3)
90
109.934(2)
90
3
ꢀ
V (A )
11426(3)
8
1.330
13097(3)
8
1.256
5434.1(10)
4
1.317
Z
ccalc (g cmꢀ3
)
1.311
3.98
1192
Linear absorption, l (cmꢀ1
)
4.49
4760
3.58
5184
4.20
2248
F ð000Þ
Dimension (mm · mm · mm)
Diffractometer
Scan type
0.20 · 0.10 · 0.03
SMART CCD 1000
u and x
1.90–27.60
17 852 (0.1224)
12 609
0.30 · 0.20 · 0.10
SMART CCD 1000
u and x
1.70–29.30
117 258 (0.0759)
15 093
0.30 · 0.10 · 0.10
SMART CCD 1000
u and x
1.69–28.02
59 344 (0.0526)
15 705
0.30 · 0.20 · 0.10
SMART CCD 1000
u and x
1.82–30.04
64 493 (0.0458)
15 844
h range (ꢁ)
Measured reflections (Rint
Unique reflections
)
Reflections with I > 2rðIÞ
Parameters
3075
588
9378
944
9735
784
11 400
658
Final RðFhklÞ: R1 ½I > 2rðIÞꢁ
0.07520
0.1810
0.0516
0.1194
0.0540
0.1247
0.0588
0.1358
Final RwðFh2klÞ: wR2 [all data]
Goodness-of-fiꢀt3
0.64
1.476/)1.061
1.061
1.335/)0.593
1.000
1.678/)0.533
1.003
2.341/)1.001
ꢀ
q
max=qmin (e A
)
4.2. X-ray analysis
pling for 31P. The 1H chemical shifts were measured with
solvent residual proton as internal standard, d 1H ¼ 7.25
ppm. The 31P chemical shifts were measured with 85%
phosphoric acid as external standard, d 31P 0.0 ppm.
The X-ray diffraction data were collected on Bruker
SMART CCD 1000 diffractometer (k(Mo Ka)-radia-
tion, graphite monochromator, u and h scan mode) and
corrected for Lorentz and polarization effects and for
absorption [20]; details are given in Table 6.
5. Supporting information available
The structure were solved by direct methods and re-
fined by full-matrix least-squares in the anisotropic–
isotropic approximation. The crystal of complex 3
contains a solvate diethyl ether molecules which are
disordered over two sites with occupancies 0.6 and 0.4,
respectively. The hydrogen atoms of all compounds
were placed in calculated positions and refined in riding
model with fixed thermal parameters (Uiso(H) ¼
1.5Ueq(C) for the CH3-groups and Uiso(H) ¼ 1.2Ueq(C)
for the other groups). All calculations were carried out
by use of the SHELXTL (PC Version 5.10) program
package [21].
Tables of atom coordinates, bond lengths and angles,
torsion angles and anisotropic displacement parameters
for 1, 2, 3 and 4: CCDC Nos. 225212, 225213, 225214,
225215, respectively. Ordering information is given on
any current masthead page.
Acknowledgements
We thank Prof. Brian T. Heaton for valuable dis-
cussion that stimulated us to carry out this study. X-ray
studies (A.A.K., K.A.L., and V.N.Kh.) were financially
supported by the Russian Foundation for Basic Re-
search (Projects Nos. 00-03-32807a and 00-15-97359).
We also thank Dr. N.G. Antonov and Dr. S.N. Smirnov
for NMR measurements. Financial support from the
Russian Federation Ministry of Education (‘‘Universi-
4.3. NMR measurements
NMR spectra were measured in deuterochloroform
solutions on Bruker AM-300 spectrometer operating in
the Fourier-transform mode with noise proton decou-

E.P. Shestakova et al. / Journal of Organometallic Chemistry 689 (2004) 1930–1943
1943
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