Rh(I) carbonyl carboxylato complexes: Spectral and structural characteristics. Some reactions of coordinated formate group

Article abstract of DOI:10.1007/s11173-005-0008-3

Complexes [Rh(μ-RCOO)(CO₂)]₂, where R = H, CH ₃, CF₃ (I, II, III, respectively) are synthesized by reacting anhydrous carboxylic acids with Rh(Acac)(CO₂) crystals. In compounds I, II, III, and trans-Rh(RCOO)(PPh₃)₂(CO), where R = H, CH₃, CF₃ (IV, V, VI, respectively), ν(CO) and ¹J(CRh) increase and δ¹³C decreases with the increasing electronegativity of R (CH₃ < H < CF₃). In the case complexes IV, V, and VI, the values of δ³¹P and ¹J(PRh) decrease in the same order. Complexes I and V are studied by X-ray diffraction analysis. Intramolecular (2.946 A) and intermolecular (3.127 A) Rh-Rh distances in a columnar structure I are close, i.e., the structure contains infinite chains of metal atoms. Interaction of IV with chlorinated solvents results in trans-RhCl(PPh₃)₂(CO). When heated with an excess of PPh₃ in propanol-2, compound IV transforms to HRh(PPh₃)₃(CO). The latter reaction was suggested as a basis of a new method that can be used to obtain HRh(PPh ₃)₃(CO).

Full text of DOI:10.1007/s11173-005-0008-3

Russian Journal of Coordination Chemistry, Vol. 31, No. 2, 2005, pp. 121–131. Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 2, 2005, pp. 132–142.
Original Russian Text Copyright © 2005 by Varshavskii, Cherkasova, Podkorytov, Korlyukov, Khrustalev, Nikol’skii.
Rh(I) Carbonyl Carboxylato Complexes: Spectral and Structural
Characteristics. Some Reactions of Coordinated Formate Group
Yu. S. Varshavskii*, T. G. Cherkasova*, I. S. Podkorytov**, A. A. Korlyukov***,
V. N. Khrustalev***, and A. B. Nikol’skii*
*Research Institute of Chemistry, St. Petersburg State University,
Universitetskii pr. 26, Petrodvorets, St. Petersburg, 198504 Russia
**Research Institute of Synthetic Rubber, Gapsal’skaya ul. 1, St. Petersburg, 198035 Russia
***Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
ul. Vavilova 28, Moscow, 119991 Russia
Received March 30, 2004
Abstract—Complexes [Rh(µ-RCOO)(CO)2]2, where R = H, CH3, CF3 (I, II, III, respectively) are synthesized
by reacting anhydrous carboxylic acids with Rh(Acac)(CO)2 crystals. In compounds I, II, III, and trans-
1
Rh(RCOO)(PPh3)2(CO), where R = H, CH3, CF3 (IV, V, VI, respectively), ν(CO) and J(CRh) increase and
δ13C decreases with the increasing electronegativity of R (CH3 < H < CF3). In the case complexes IV, V, and
VI, the values of δ31P and 1J(PRh) decrease in the same order. Complexes I and V are studied by X-ray diffrac-
tion analysis. Intramolecular (2.946 Å) and intermolecular (3.127 Å) Rh–Rh distances in a columnar structure
I are close, i.e., the structure contains infinite chains of metal atoms. Interaction of IV with chlorinated solvents
results in trans-RhCl(PPh3)2(CO). When heated with an excess of PPh3 in propanol-2, compound IV transforms
to HRh(PPh3)3(CO). The latter reaction was suggested as a basis of a new method that can be used to obtain
HRh(PPh3)3(CO).
Dirhodium(I) di(µ-carboxylato) tetracarbonyls phines) were studied more intensively than other car-
[Rh(µ-RCOO)(CO)2]2 were obtained for the first time
by reacting rhodium(I) carbonyl chloride dimer [Rh(µ-
Cl)(CO)2]2 with silver carboxylates [1]. The authors [1]
synthesized and characterized acetate, trifluoroacetate,
p-fluorobenzoate, and phthalate complexes of this type
and some bis(phosphine) derivatives, such as trans-
Rh(RCOO)(PPh3)2(CO). Later, some other methods
boxylate derivatives. This is quite natural, since
formate group is a C1 ligand with composite structure
and high reactivity.
It is noteworthy that though separate IR and NMR
parameters of Rh(I) carbonyl carboxylate complexes
were reported in some of the above-mentioned papers,
were developed for synthesizing [Rh(µ-RCOO)(CO)2]2 their comparison is difficult, since they were deter-
complexes with R = CH3 (II), CF3 (III) [2–4] and their
monocarbonyl triphenylphosphine derivatives trans-
Rh(RCOO)(PPh3)2(CO) [2, 5–12]. The authors of [4]
reported the results of X-ray diffraction study of [Rh(µ-
mined under different conditions.
In this work, simple reaction is suggested that can be
used to synthesize [Rh(µ-HCOO)(CO)2]2 complex and
its crystal structure is determined. The latter complex is
shown to be suitable starting reagent in synthesis of
Rh(I) carbonyl hydride HRh(PPh3)3(CO). X-ray dif-
fraction data available in the literature for bis(triphenyl-
phosphine) complexes of the composition trans-
Rh(RCOO)(PPh3)2(CO) with R = H, CF3 [13, 17] are
supplemented with the data we obtained for analogous
acetate complex. IR and NMR measurements of carbonyl
formate complexes [Rh(µ-HCOO)(CO)2]2 and of
trans-Rh(HCOO)(PPh3)2(CO) together with their ace-
tate and trifluoroacetate analogs made it possible to
obtain for the first time a set of comparable spectral
parameters that indicates a transfer of electronic effects
of the ligands through a central atom. The results of this
work were partially reported in the previous publica-
CF3COO)(CO)2]2.
The
structure
of
trans-
Rh(CF3COO)(PPh3)2(CO) was previously determined
in [13].
Rhodium(I) formate complexes became available
considerably later. Thus, the carbonyl formate dimer
[Rh(µ-HCOO)(CO)2]2 (I) was synthesized for the first
time via a reaction of dirhodium(II) tetraacetate with
carbon monoxide in formic acid [14]. Some other
methods of synthesis of this compound were reported
later on in [15, 16]. A series of bis(phosphine) com-
plexes trans-Rh(HCOO)(PR3)2(CO) was also synthe-
sized [17–19]. The molecular structure of trans-
Rh(HCOO)(PPh3)2(CO) (IV) was determined by X-ray
diffraction method [17]. It should be noted that in sub-
sequent years, rhodium(I) formate complexes with car-
bonyl and some other π-acceptor ligands (olefins, phos- tions [20–22].
1070-3284/05/3102-0121 © 2005 Pleiades Publishing, Inc.

122
VARSHAVSKII et al.
C(4)
O(6)
O(4)
C(3)
O(3)
O(5)
Rh(2)
Rh(1)
C(6)
C(2)
C(5)
C(1)
O(8)
O(2)
O(7)
O(1)
Fig. 1. The molecular structure of [Rh(µ-HCOO)(CO) ] (thermal ellipsoids correspond to 50% probability; hydrogen atoms are
2 2
not shown).
RESULTS AND DISCUSSION
Molecular and crystal structure of [Rh(m-
HCOO)(CO)2]2 (I). According to a preliminary study,
compound I forms twin crystals unsuitable for X-ray
diffraction measurements. Nevertheless, we managed
to obtain, in a general form, the molecular and crystal
parameters of structure I, though R-factor was very
large, and thus the bond lengths and angles obtained
should be considered as approximate ones.
Synthesis of dirhodium(I) di-m-carboxylato tet-
racarbonyls.
Acetylacetonate
ligand
in
Rh(Acac)(CO)2 complex can be easily replaced with
another anionic ligands. In particular, it is readily
detached when treated with protic acids. The authors
[2] used this reaction in synthesis of dicarbonyl com-
plexes [Rh(µ-RCOO)(CO)2]2 with fluorinated carboxy-
late groups, R = CF3 and i-C3F7:
The molecular structure of I is shown in Fig. 1. The
bond lengths and bond angles in the nearest surround-
ing of Rh atoms are as follows: Rh(1)–Rh(2) 2.946(2),
Rh(1)–C(1) 1.87(2), Rh(1)–C(2) 1.87(2), Rh(1)–O(3)
2.089(16), Rh(1)–O(4) 2.088(15), C(1)–O(1) 1.09(3),
C(2)–O(2) 1.05(3) Å; C(1)Rh(1)C(2) 88.9(11)°,
C(1)Rh(1)O(3) 93.2(9)°, C(1)Rh(1)O(4) 178.8(9)°,
C(1)Rh(1)Rh(2) 98.0(7)°, O(3)Rh(1)O(4) 85.7(6)°,
Rh(1)C(1)O(1) 178(2)°, Rh(1)C(2)O(2) 178(2)°. One
can see that structure of I is very close to that of its tri-
fluoroacetate analog [4]. In terms of a general configu-
ration and geometric parameters of the bridging carb-
oxylate groups, molecule I is also similar to molecules
of Rh(I) binuclear carboxylate complexes, such as
2Rh(Acac)(CO)2 + 2RCOOH
[Rh(µ-RCOO)(CO)2]2 + 2HAcac.
We modified the procedure described in [2] and
obtained also the derivatives of nonfluorinated acids
with R = H and CH3. When crystalline Rh(Acac)(CO)2
was treated with anhydrous carboxylic acids in the
presence of diethyl ether, complexes I–III were
obtained in the form of needle-shaped crystals with a
bronze luster. The products were isolated from a reac-
tion mixture in a high yield and did not require further
purification.
The reaction completeness depends on the carboxy- [Rh(µ-HCOO)(Cod)]2 (Cod is cyclooctadiene-1,5)
lic acid strength. In accordance with the values of pKa [16], [Rh(µ-ëF3COO)(Cod)]2 [4], and [Rh(µ-
(4.75, 3.75, 0.23 for R = CH3, H, CF3, respectively CH3COO)(Nbd)]2 (Nbd is norbornadiene) [24]. The
[23]), the reaction of complex III formation proceeds Rh–C and C–O bond lengths characterizing carbonyl
almost completely and instantaneously, while in the groups are close to the corresponding values in another
case of complexes I and II, this substitution reaction is Rh(I) complexes with the Rh(CO)2 fragment, both
reversible, which requires that liberated acetylacetone binuclear and mononuclear complexes, for example,
be removed from the reaction mixture by repeated [Rh(µ-Cl)(CO)2]2 [25], RhAcac(CO)2 [26], etc. Note
decantation and further addition of a fresh portions of that intramolecular Rh–Rh distances in carbonyl com-
formic or acetic acid.
plexes are shorter than the respective distances in their
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 31 No. 2 2005

Rh(I) CARBONYL CARBOXYLATO COMPLEXES
123
olefin analogs: 2.946(2) Å for [Rh(µ-HCOO)(CO)2]2
r(Rh– Rh), Å
3.6
3.4
3.2
3.0
and 2.984(1)/2.994(1) Å for [Rh(µ-ëF3COO)(CO)2]2
[4] as compared to 3.39 Å (without a standard devia-
tion) in [Rh(µ-HCOO)(Cod)]2 [16], 3.4844(6) Å in
[Rh(µ-ëF3COO)(Cod)]2 [4], and 3.1050(7) Å in [Rh(µ-
CH3COO)(Nbd)]2 [24].
13
12
11
10
Rh(I), 2 bridges
olefin ligands
2.8
Rh(I), 2 bridges
carbonyl ligands
6
The authors of [24] discussed the ratio of the Rh–Rh
distances (r) and dihedral angle (θ) formed by coordi-
nation planes of the Rh atoms in binuclear Rh(I) com-
plexes. It is not surprising that in a binuclear complex
with chloride bridges, namely, [Rh(µ-Cl)(CO)2]2
(according to data in [20], θ ≈ 123°), the value of r
(3.133(2) Å) is larger than that in the molecules of both
investigated carboxylate analogs, where coordination
planes of the Rh atoms form considerably smaller angle
with one another (26.7° and 2.946 Å for formate com-
plex; ~29° and 2.984/2.994 Å for trifluoroacetate com-
plex).
4
8
9
2.6
2.4
2.2
3
2
1
7
5
Rh(II), 2 bridges
Rh(II), 4 bridges
0
0.1
0.2
0.3
0.4
0.5
0.6
sin(θ/2)
Fig. 2. Correlation of intramolecular Rh–Rh distance with
dihedral angle between equatorial coordination planes of Rh
atoms in binuclear carboxylate complexes of Rh(I) and Rh(II)
(correlation factor 0.971; r = 2.4026 + 1.9049sin(θ/2); our
data; ꢀ data in the literature: (1) Rh (CH COO) (H O) [27];
2
3
4
2
2
(2)
Rh (CH COO) (P(OCH ) )
3 3 2
[Rh (CH COO) Cl ][(CH ) NH]
[28];
(3)
(4)
2
3
4
2
3 2
2
[29];
2
3
4
It is interesting to establish a relationship between r
and θ in a series of Rh binuclear carboxylate com-
plexes, including both Rh(I) and Rh(II) complexes. If
the differences in the Rh–O distances and internal geo-
metric parameters of carboxyl groups (the C–O bond
lengths and OCO bond angles) are considered unessen-
tial, then, in the first approximation, the values of r and
sin(θ/2) are expected to show a linear dependence. Data
available in the literature [27–34] confirm this expecta-
tion (Fig. 2). One can see that the observed relationship
has “isle” nature. It is natural to assign the gap between
the first and second sets of points (with Rh(II) com-
plexes in both sets) and between the third and fourth
sets (with Rh(I) complexes in the latter sets) to geomet-
ric factors; the gap between the second and third sets of
points is mainly determined by different electronic con-
figuration of a central atom (d7 and d8, respectively).
Previously [32], we briefly touched upon this question.
[Rh (CF CONH) (Phen) Py ][PF ] (Phen is phenanthro-
2
3
2
2
2
6 2
line) [3]; (5) [Rh (CH COO) (Phen) Py ][PF ] [30]; (6)
2
3
2
2
2
6 2
Rh (i-C H COO) (COOCH ) (CO) (PPh )
[31]; (7)
[32]; (8)
Rh (CH COO) (Dmg) (PPh ) (Dmg is dimethylglyoxime)
2
3
7
2
3 2
2
3 2
Rh (CH COO) (COOCH ) (CO) (CH OH)
2
3
2
3 2
2
3
2
2
3
2
2
3 2
[33]; (9) Rh (i-C H COO) (COOCH ) (CO) (CH OH)
2
3
7
2
3 2
2
3
2
[31]; (10) Rh (HCOO) (CO) [in this work]; (11)
2
2
4
Rh (CF COO) (CO) [4]; (12) Rh (CH COO) (Nbd)
2
3
2
4
2
3
2
2
[23]; (13) Rh (HCOO) (Cod) [16].
2
2
2
plex trans-Rh(HCOO)(PPh3)2(CO) was obtained for the
first time and characterized significantly later [15]. We
synthesized bis(triphenylphosphine) complexes trans-
Rh(HCOO)(PPh3)2(CO)
Rh(CH3COO)(PPh3)2(CO)
(IV),
(V),
trans-
trans-
and
Rh(CF3COO)(PPh3)2(CO) (VI) by reacting triphenyl-
phosphine with binuclear complexes [Rh(µ-
RCOO)(CO)2]2 (taken in a molar ratio PPh3 : Rh = 2) in
propanol-2 at room temperature.
In line with the data obtained, intramolecular dis-
tance Rh–Rh in [Rh(µ-HCOO)(CO)2]2 crystal
(2.946 Å) is only slightly shorter than intermolecular
distance (3.127 Å), i.e., this crystal contains infinite
chains of the metal atoms; an average value of RhRhRh
angle being 170.49(10)° (Fig. 3). In this respect, the
compound under study is similar to its trifluoroacetate
analog (2.989, 3.092 Å, respectively) [4]. This fact is
likely to be an answer to the question put by the authors
of [4]: the presence of fluorinated substituent in carbox-
ylate group is not a necessary condition for realization
of a chain structural motif. Although Rh–Rh distances
determined in [35] are considered too long for the
metal–metal interaction to be treated as a valent inter-
action, the metal luster of [Rh(µ-RCOO)(CO)2]2 crys-
tals suggests a considerable delocalization of electrons
along the metal atom chain.
The data we obtained for the molecular structure of
complex V (Fig. 4) agree well with those for formate
(IV) [17] and trifluoroacetate (VI) [13] analogs. The
bond lengths and bond angles in the nearest surround-
ing of Rh atoms in molecular structure of compound V
are: Rh(1)–C(3) 1.812(4), Rh(1)–O(1) 2.084(2),
Rh(1)–P(1) 2.3352(11), Rh(1)–P(2) 2.3147(11), C(3)–
O(3) 1.149(4) Å; C(3)Rh(1)P(1) 89.61(12)°,
C(3)Rh(1)P(2) 92.16(12)°, C(3)Rh(1)O(1) 174.03(13)°,
P(1)Rh(1)P(2) 169.62(3)°, O(1)Rh(1)P(1) 91.42(7)°,
O(1)Rh(1)P(2) 87.88(8)°, Rh(1)C(3)O(3) 173.8(3)°.
All the three compounds are mononuclear tetracoor-
dinated complexes. It was noted in [13] that almost
orthogonal arrangement of a plane of carboxylate
group with respect to that of coordination tetragon and
a relatively short contact (~3.34 Å) between the Rh
atom and noncoordinated carboxylate oxygen favor
Bis(triphenylphosphine)
complexes
trans-
Rh(RCOO)(PPh3)2(CO). Acetate and some other
carboxylate bis(triphenylphosphine) carbonyl com-
plexes of the composition trans-Rh(RCOO)(PPh3)2(CO)
nonvalent interaction Rh
O=C in trans-
Rh(CF3COO)(PPh3)2(CO) crystal. Such an interaction
were reported long ago [1, 2, 5–12]. The formate com- is likely to occur also in crystal V, where the dihedral
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 31 No. 2 2005

124
VARSHAVSKII et al.
x
z
0
y
Fig. 3. The packing of molecules in [Rh(µ-HCOO)(CO) ] crystal (I).
2 2
C(25)
angle between the OCO plane of acetate ligand and
coordination plane of the Rh atom is 107.3° and the
Rh···O(=C) distance is equal to ~2.9 Å.
C(24)
C(23)
C(39)
C(32)
C(33)
C(26)
Spectral characteristics of carbonyl carboxylate
complexes. Parameters of IR and NMR spectra of carb-
oxylate complexes are given in Table 1. Although many
spectral parameters of compounds I–VI were previ-
ously reported in the above-mentioned papers, we
decided to measure them again and to obtain the same
set of parameters suitable for comparison for the whole
group of compounds. IR spectra of solutions of binu-
clear complexes contain three absorption bands in the
range of stretching vibrations of carbonyl group. Three
maxima ν(CO) are observed also for the other com-
plexes, whose molecules contain two Rh(CO)2 frag-
ments bonded to one another, and are due to interaction
of vibrations of these fragments [36, 37].
The 13C NMR parameters of compounds I, II, and
III lie in the region typical of Rh(I) complexes contain-
ing Rh(CO)2 fragments [38, 39]. The transition to
bis(phosphine) derivatives is usually attended by a
decrease in the ν(CO) values and by an increase in the
δ13ë chemical shift.
C(38)
C(37)
C(36)
C(27)
C(28)
C(31)
C(22)
P(2)
C(34)
C(35)
C(30)
C(29)
O(1)
Rh(1)
C(1)
C(3)
O(3)
C(2)
O(2)
C(14)
C(15)
C(21)
C(16)
P(1)
C(20)
C(10)
C(11)
C(13)
C(5)
C(12)
C(4)
Data in Table 1 reveal correlation between the spec-
tral characteristics of carboxylate complexes and elec-
tronegativity of radical R in the carboxylic acid anion.
As electronegativity of R increases in a series CH3, H,
CF3, the frequency of stretching vibrations of carbonyl
groups is increased, while the δ13C chemical shift is
decreased and the 1J(CRh) values are increased both in
compounds containing dicarbonyl fragments (I–III)
and in monocarabonyl bis(phosphine) complexes
(IV–VI). In compounds IV–VI, the highest frequency
ν(CO) (trifluoroacetate complex) corresponds to the
C(19)
C(17)
C(6)
C(18)
C(9)
C(8)
C(7)
Fig.
4.
The
molecular
structure
of
Rh(CH COO)(PPh ) (CO) (V) (thermal ellipsoids corre-
3
3 2
spond to 50% probability; hydrogen atoms are not shown).
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 31 No. 2 2005

Rh(I) CARBONYL CARBOXYLATO COMPLEXES
125
Table 1. Spectral parameters of Rh(I) carbonyl carboxylate complexes (in CHCl3)
δ13C (Rh CO), ppm
δ31P, ppm
δ1H,
δ19F,
Compound
ν(CO), cm–1
(1J(CRh); 2J(CRhP), Hz) (1J(PRh), Hz)
ppm
ppm
[Rh(µ-HCOO)(CO)2]2 (I)
2104, 2082, 2030 181.18 (73.7)
2102, 2078, 2028 181.86 (73.7)
2116, 2096, 2048 179.37 (75.9)
8.01*
2.02
[Rh(µ-CH3COO)(CO)2]2 (II)
[Rh(µ-CF3COO)(CO)2]2 (III)
trans-Rh(HCOO)(PPh3)2(CO) (IV)
–77.54
1980
1975
1984
189.93 (69.5, 16.9)
31.61 (134.8)
7.08
191.68 (68.6, 16.9)**
190.12 (68.7, 16.9)
192.07 (67.8, 16.9)**
189.56 (71.2, 16.9)
191.25 (71.2, 16.1)**
32.08 (136.1)** 7.78**
32.82 (137.9) 0.76
32.98 (138.6)** 1.22**
31.19 (132.2)
trans-Rh(CH3COO)(PPh3)2(CO) (V)
trans-Rh(CF3COO)(PPh3)2(CO) (VI)
–78.53
31.53 (132.2)**
3
* t., J(HCORh), 2.9 Hz.
** In C D .
6
6
13
shortest C–O bond length in carbonyl group: 1.138(6) carbonyl region of the C spectrum contains, in addi-
[13] as compared to 1.150(5) Å in formate [17] and tion to a signal of the studied compound (doublet of
1.149(4) Å in acetate (in this work) analogs.
triplets, Table 1), one more signal of the same form and
comparable intensity. The 31P spectrum of solution of
IV also exhibits an intense additional signal (doublet).
The parameters of these signals, δ13C and δ31P,
1J(CRh), 1J(PRh), and 2J(CP) coincide with parameters
of the known complex, namely, RhCl(PPh3)2(CO). Yel-
low crystals of individual compound with the same
spectral parameters are separated from a solution of
complex IV in methylene chloride. A complete conver-
sion of formate complex into chloride complex occurs
on heating (40°ë) of a solution of IV in CH2Cl2 for 2 h;
the reaction is attended by liberation of CO2. The reac-
tion product was identified as trans-RhCl(PPh3)2(CO)
on the basis of comparison of its IR and NMR spectra
with the spectra of a sample synthesized according to
the procedure described in [46].
The effect of substituent CF3 on the spectral param-
eters of carbonyl groups in Rh(I) complexes was
observed previously in both carboxylate [1, 5, 8] and in
β-diketo and β-ketoimino complexes [40–42]. The 31P
NMR data also turned sensitive to the electronic effect
of substituent in carboxylate group: as its electronega-
1
tivity increases, δ31P and J(PRh) decrease. As it is
always observed, the ν(CO) values in IR spectra of
triphenylphosphine complexes IV–VI are considerably
higher than those in the spectra of analogous complexes
with aliphatic phosphines PCy3 (Cy is cyclohexyl), Pi-
Pr3 [15, 18, 19, 43, 44].
The above bis(phosphine) complexes IV–VI are the
final products of interaction of complexes I–III with
triphenylphosphine taken at a molar ratio PPh3 : Rh = 2.
The authors of [9] studied the spectra of reaction mix-
Crystallographic characteristics of the isolated com-
tures Rh2(µ-RCOO)2(CO)4 + PPh3 at lower PPh3 : Rh pound agree well with the data for orthorhombic modifi-
ratios and observed the formation of some products cation of trans-RhCl(PPh3)2(CO) · 2CH2Cl2 [47]. The
with intermediate composition. One of them, i.e., the transformation of formate complex to chloride complex
acetate complex Rh2(µ-CH3COO)2(PPh3)(CO)3, was is likely to occur through oxidative addition of methyl-
isolated and characterized. In paper [45], [Rh(µ-
CH3COO)(PPh3)(CO)]2 complex was also studied. In
addition to data in [9, 45], we measured the 1H, 13C, and
31P NMR spectra of reaction mixtures [Rh(µ-
CH3COO)(CO)2]2 + PPh3 in chloroform at a molar ratio
PPh3 : Rh = 1 and determined the spectral parameters of
these complexes (see in experimental section)
ene chloride to complex IV and formation of unstable
Rh(III) complex Rh(HCOO)(PPh3)2(CO)(CH2Cl)Cl that
is further transformed with elimination of CO2 (and,
presumably, CH3Cl) to trans-RhCl(PPh3)2(CO). The
ability of Rh(I) complexes to enter such type of reac-
tions with chlorinated solvents was noted in [48].
Reaction with triphenylphosphine. Formation of
HRh(PPh3)3(CO). When heated with excess triphenyl-
phosphine in propanol-2, compound IV gives the
known complex HRh(PPh3)3(CO) (VII) in a high yield.
The reaction occurs at a high rate and results in com-
plex VII that precipitates as well formed lustrous mus-
tard-colored crystals. The comparison of IR and NMR
Some reactions of formate ligand in complex,
trans-Rh(HCOO)(PPh3)2(CO) (IV). Formate ligand
in
bis(phosphine)
complex
IV,
trans-
Rh(HCOO)(PPh3)2(CO) can enter some reactions that
almost quantitatively transform IV to nonformate
derivatives of Rh(I).
Reactions with chlorinated solvents. Formation (1H, 13C, and 31P) spectra of the obtained compound
of trans-RhCl(PPh3)2(CO). When measuring NMR with those of HRh(PPh3)3(CO) synthesized following
spectra of complex IV in CDCl3, we discovered that the the procedure [49] and the results of elemental analysis
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 31 No. 2 2005

126
VARSHAVSKII et al.
confirm its identification. The reaction is attended by solvent) contain the absorption bands due to carbonyl
liberation of CO2 (1 mol per g-atom of rhodium):
groups in the range of 1990–2030 and 1800–1880 cm–1.
The solutions are unstable; even when kept in an inert
atmosphere, the absorption bands due to terminal car-
bonyl groups gradually shift toward low frequencies.
One can assume that in these experiments, we observed
the formation of anionic polynuclear clusters similar to
those previously described by the authors [57], who
studied the reducing carbonylation of Rh(III) chloride
and Rh(I) carbonyl chloride on silica gel surface.
Rh(HCOO)(PPh3)2(CO) + PPh3
HRh(PPh3)3(CO) + CO2.
Experiment with deuterated complex IV
Rh(DCOO)(PPh3)2(CO) gives deuterated analog of
complex VII, namely, DRh(CO)(PPh3)3. This fact
implies that formate group of the starting complex IV
serves the source of hydride ligand in complex VII.
This reaction is a new and remarkable example of trans-
formations RhLn(HCOO)
HRhLn + CO2 described
EXPERIMENTAL
in [16, 50]. The possible mechanisms of these reactions
and of reversible reactions of CO2 introduction at a
metal–hydrogen bond were extensively discussed in the
literature [16, 18, 50–55].
We also found that complex VII can be obtained
directly from I, without the stage of complex IV isola-
tion. Taking into account a high yield and an adequate
quality of the product obtained in this way, we believe
that this reaction can be used as an alternative method
in synthesis of HRh(PPh3)3(CO). It should be noted that
insignificant amount of hydride complex VII formed as
a byproduct was also observed by us in reaction of com-
plex I with triphenylphosphine (P : Rh > 2) in methanol,
diethyl ether, or toluene.
All reactions were carried out in dried solvents, in
the atmosphere of dry argon, using common Schlenk
technique (synthesis of compounds I–III do not require
an inert atmosphere). Rh(Acac)(CO)2 was obtained by
procedure [58]. Samples of complexes for measuring
the 13C NMR spectra were obtained from enriched
Rh(Acac)(CO)2 preparation, which was prepared by
bubbling 13CO (76.6% 13C) through a suspension of
Rh(Acac)(C2H4)2 [59] in hexane. Samples of
RhCl(PPh3)2(13CO) and HRh(PPh3)3(13CO) were pre-
pared following the known procedures [39] and [49],
respectively. Triphenylphosphine was recrystallized
from ethanol
The 1H, 13C, 31P, and 19F spectra were measured on
Transformations
of
[Rh(m-HCOO)(CO)2]2
a Bruker AM-500 spectrometer at 500, 125, 202, and
heated in propanol-2. On heating a suspension of
[Rh(µ-HCOO)(CO)2]2 in propanol-2, a solution of dark
brown color is formed and a small amount of brown
precipitate. After the precipitate is treated with chloro-
form, the known cluster Rh6(CO)16 can be extracted
that was identified from IR spectrum in [56]. IR spectra
of the filtrate contain intense absorption bands with
composite profile that are typical of polynuclear Rh
carbonyl clusters: 2040–2060 cm–1 (terminal carbonyl
groups) and 1840–1880 cm–1 (bridging carbonyl
groups). Judging from the positions and shapes of these
bands, the solutions contain anionic polynuclear clus-
ters whose composition depends on the heating time
(from 5 min to 7 h). It is worthwhile noting that IR
spectra of filtrates always contain absorption band with
a sharp maximum at 1716 cm–1 that can be assigned to
acetone, i.e., the product of propanol-2 oxidation. The
solutions are stable when stored in an inert atmosphere,
but when their IR spectra are recorded once again, they
show some changes in positions of the bands due to
absorption of carbonyl groups; the indicated changes
are likely to occur as a result of partial loss of CO.
When these solutions are treated with CO, their IR
spectra acquire the initial form. The preliminary mea-
surements of the 13C and 1H NMR spectra indicate that
solutions contain anionic polynuclear clusters. The
addition of salts of large cations, for example,
(PPh3)2NCl, PPh4Cl, to the reaction mixtures gives pre-
cipitates of brown color readily soluble in acetonitrile
1
470 MHz, respectively. An internal standard in the H
and 13C spectra was a solvent (δ1ç of the residual pro-
tons in CDCl3, C6D6, and CD3C6D5 were 7.25, 7.16,
and 2.09 ppm, respectively; δ13C for CDCl3 77.0 ppm,
for C6D6 128.69 ppm). The 31P chemical shifts were
referenced to 85% orthophosphoric acid used as an
external standard, δ31P 0.0 ppm. The 19F chemical shifts
were referenced to CFCl3, δ19F 0.0 ppm. IR spectra
(nujol mulls, solutions in CHCl3) were recorded on a
Specord 75 IR spectrometer.
X-ray diffraction analysis. The main experimental
parameters and crystallographic data are listed in Table 2.
All diffraction measurements were carried out on a
Bruker Smart 1000 CCD diffractometer (MoKα radia-
tion, λ = 0.71073 Å, ϕ and ω scan mode) with SMART
program [60]. The obtained three series of frames, cor-
responding to half sphere of reciprocal space, were pro-
cessed with SAINT-Plus program [60] and averaged
with SADABS program [60]. The structures were
solved by direct methods and refined by full-matrix
anisotropic-isotropic approximation on F2. Hydrogen
atoms were calculated geometrically and refined in a
rigid body model with U(H) = 1.5Ueq(C), where C and
H are carbon and hydrogen atoms. All calculations
were performed with SHELXTL-Plus program pack-
age [61].
As was mentioned above, the discrepancy factors R1
and acetone (presumably salts of anionic clusters). IR and wR2 obtained in refinement of structure I are very
spectra of solutions of these precipitates (with CH3CN high because of insufficient quality of the crystals used.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 31 No. 2 2005

Rh(I) CARBONYL CARBOXYLATO COMPLEXES
127
Table 2. Crystallographic parameters and details of data collection and refinement of structures I and V
Value
Parameter
I
V
M
407.90
110(2)
714.50
110(2)
Temperature, K
Space group
P1
0.4 × 0.3 × 0.1
6.7185(19)
7.604(2)
10.307(3)
96.710(5)
100.963(6)
102.294(6)
498.3(2)
2
P1
0.4 × 0.2 × 0.2
10.829(3)
12.629(4)
12.659(4)
86.239(7)
80.412(7)
73.116(6)
1633.3(8)
2
Crystal size, mm
a, Å
b, Å
c, Å
α, deg.
β, deg.
γ, deg.
V, Å3
Z
ρ(calcd.), g/cm3
µ
2.719
1.453
Mo, cm–1
49.24
6.58
F (000)
454
732
Range of 2θ, deg
4.08–51.36
3505
4.42–60.08
13649
Total number of reflections
Number of unique reflections (Rint)
Number of reflections with I > 2σ(I)
Number of refined parameters
R1 (for reflections with I > 2σ(I))
wR2 (for all reflections)
GOOF
1735 (Rint = 0.499)
1308
9346 (Rint = 0.499)
5947
145
538
0.1245
0.0591
0.3154
0.1208
2.155
1.055
ρ
max/ρmin (eÅ–3)
8.529/–4.614
1.956/–1.120
X-ray diffraction study of the product of reaction 15 min until the crystals of the initial complex with
characteristic red-green dichroism disappeared com-
pletely.
The product was filtered, washed with ether, and
dried in vacuum. The yield was 0.39 g (83%).
between Rh(HCOO)(PPh3)2(CO) and CH2Cl2 was per-
formed using the same experimental parameters as in
the case of I and V. The analysis of difference Fourier
syntheses showed that in the structure of
RhCl(PPh3)2(CO) formed, the Cl atom and carbonyl
group at the Rh atom overlap. The refinement of popu-
lations of two positions linked by the inversion center
gave the ratio 1 : 1. The discrepancy factors: R1 (for
reflections with I > 2σ(I)) 0.0526, wR2 (for all reflec-
tions) 0.1329; GOOF 1.062.
The completeness of transformation was confirmed
by the absence of the band due to acetylacetonate
ligand at 1530 cm–1 in IR spectrum of the product sam-
ple dissolved in CHCl3. The spectral data (IR and
NMR) agree well with the data of [14, 16]. For
ë3HO4Rh anal. calcd. (%): C, 17.67. Found (%): C,
17.69.
[Rh(m-CH3COO)(CO)2]2. Glacial acetic acid
(2 ml) was added to a suspension of Rh(Acac)(CO)2
(0.5 g, 1.94 mmol) in diethyl ether (2 ml), which was
followed by precipitation of needle-shaped brown crys-
tals with a bronze luster. The reaction mixture was
[Rh(m-HCOO)(CO)2]2. Anhydrous formic acid
(1.5 ml) was added to a suspension of Rh(Acac)(CO)2
(0.5 g, 1.94 mmol) in diethyl ether (1.5 ml). Needle-
shaped brown crystals with a bronze luster precipitated.
The reaction mixture was stirred for 30 min. The solu-
tion was decanted, and another portion of formic acid
(0.7 ml) was added to the residue and stirred for another stirred for 1 h, the solution was decanted, and another
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 31 No. 2 2005

128
VARSHAVSKII et al.
portion of acetic acid (7 ml) was added; the mixture was 0.27 g (83%). The spectral data of the product (IR and
NMR) are consistent with the data in [15, 17].
stirred for another 15 min until the crystal of the initial
complex disappeared completely. The precipitate was
filtered, washed with ether, and dried in vacuum. The
yield was 0.33 g (79%). The completeness of reaction
was confirmed as described above. IR spectrum of the
compound is consistent with the data in [1, 14].
For C38H31O3P2Rh
anal. calcd. (%):
Found (%):
C, 65.15;
C, 64.65;
H, 4.42.
H, 4.42.
trans-Rh(CH3COO)(PPh3)2(CO).
[Rh(µ-
For C4H3O4Rh
ëH3COO)(CO)2]2 (0.1 g, 0.229 mmol) and triphenyl-
phosphine (0.24 g, 0.92 mmol) were placed in a reac-
tion vessel, and propanol-2 (3.5 ml) was added. The
suspension obtained was stirred for 1 h. The precipi-
tated crystalline product of a yellow color was filtered
and washed with ether. The yield was 0.26 g (80%). The
anal. calcd. (%):
Found (%):
C, 22.04;
C, 22.10;
H, 1.10.
H, 1.00.
[Rh(m-CF3COO)(CO)2]2. To a suspension of
Rh(Acac)(CO)2 (0.5 g, 1.94 mmol) in diethyl ether spectral parameters (IR and NMR) agree well with
those in [5, 7, 9, 12].
(1 ml), trifluoroacetic acid (0.8 ml) was added, and the
precipitation of needle-shaped brown crystals with a
bronze luster was observed. The reaction mixture was
stirred for 10 min. The precipitate was filtered, washed
with ether, and dried in vacuum. The yield was 0.47 g
(89%). IR spectrum of the product agrees well with the
data of [1, 2, 4]. For ë4O4F3Rh anal. calcd. (%): C,
17.66. Found (%): C, 17.99.
For C39H33O3P2Rh
anal. calcd. (%):
Found (%):
C, 65.55;
C, 65.43;
H, 4.62;
H, 4.80;
Rh, 14.40.
Rh, 14.41.
Reaction of [Rh(m-CH3COO)(CO)2]2 with PPh3
at PPh3 : Rh = 1. [Rh(µ-CH3COO)(CO)2]2 (0.057 g,
0.132 mmol) was placed in a reaction vessel and a solu-
tion of PPh3 (0.069 g, 0.264 mmol) in CHCl3 (4 ml) was
added. The obtained yellow solution was evaporated at
a reduced pressure to dryness. The residue was dis-
solved in CDCl3 (2 ml) and used in the 1H, 13ë, and 31P
NMR measurements. The parameters of the signals
observed and their assignment to the reaction products
trans-Rh(HCOO)(PPh3)2(CO).
[Rh(µ-
HCOO)(CO)2]2 (0.1 g, 0.245 mmol) and PPh3 (0.26 g,
0.99 mmol) were placed in a reaction vessel, and pro-
panol-2 (3.5 ml) was added. The suspension was stirred
for 1 h. The precipitated crystalline product of a yellow
color was filtered and washed with ether. The yield was are shown below.
δ13C, ppm
δ31P, ppm
Compound
δ1H, ppm
(1J(CRh), 2J(CP), Hz)
(1J(PRh), Hz)
(Y1)
(Y2)
(X2)
183.4 (73.7) d.
50.4 (175.5) d.
1.05
2.08
CH3
C
187.0 (75.4, 22.1) d.d.
Ph3P
OC
O
O
O
O
CO
CO
Rh
Rh
Rh
C
CH3
188.4 (75.4, 22.9) d.d.
190.1 (~69) broad
48.8 (180.6) d.
32.8 (137.6) d.
1.41
0.87
CH3
C
O
Ph3P
OC
O
O
CO
Rh
O
C
PPh3
CH3
Ph3P
CO
Rh
H3C
O
C O
PPh3
13
31
for the analogous complexes occurring in the reaction
The above assignment of the C and P signals is
based on the comparison of their relative intensities and
mixtures [Rh(µ-Cl)(CO)2]2 + PPh3. A sharp doublet at
was performed taking into account data in [45, 62, 63] 183.4 ppm in the 13C spectrum of the obtained mixture
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 31 No. 2 2005

Rh(I) CARBONYL CARBOXYLATO COMPLEXES
129
of the products is assigned to dicarbonyl fragment in washed with ether and dried in vacuum. The yield was
composition Y1; doublets of doublets with higher δ13C
0.20 g (89%). In terms of the spectral parameters, the
product is identical to a complex produced from [Rh(µ-
belong to monocarbonyl fragments in composition Y1
and Y2. Broadening of signal at 190.1 ppm correspond-
ing to complex V is likely to be explained by some
exchange processes in a solution. Of the two δ1H values
in Y1 spectrum, a lower value was presumably assigned
to a methyl group in syn-position to PPh3.
HCOO)(CO)2]2.
3.
DRh(PPh3)3(CO).
In
synthesis
of
DRh(PPh3)3(CO), use was made of deuterated prepara-
tion of formate complex, namely, Rh(µ-DCOO)(CO)2
obtained according to the above procedure with the use
of DCOOH (enriched by 99%). IR spectrum (nujol
mulls): ν(CO) 1945 cm–1, ν(RhD)—the band is over-
lapped by triphenylphosphine absorption. NMR (tolu-
ene-d8): δ2D 9.32 ppm; δ31P 40.8 ppm, 1J(PRh)
155.2 Hz.
trans-Rh(CF3COO)(PPh3)2(CO). A mixture of
[Rh(µ-ëF3COO)(CO)2]2 (0.1 g, 0.184 mmol) and
triphenylphosphine (0.19 g, 0.74 mmol) was placed in
a reaction vessel and propanol-2 (3.5 ml) was added.
The suspension was stirred for 30 min. The obtained
crystalline product of a yellow color was filtered and
washed with ether. The product yield was 0.23 g (82%).
IR spectrum of the compound is consistent with data in
[6, 8].
4. Reaction of trans-Rh(HCOO)(PPh3)2(CO) with
methylene chloride. Compound IV (0.25 g) was dis-
solved in CH2Cl2 (10 ml) and the obtained suspension
was refluxed at 40°ë for 2 h. Then, the precipitate was
filtered, washed with diethyl ether, and dried in vac-
uum. The yield was 0.20 g. IR and NMR spectra (in
chloroform) of the product (ν(CO) 1978 cm–1, δ13C
For C39H30O3P2F3Rh
anal. calcd. (%):
Found (%):
C, 60.95,
C, 60.69,
H, 3.90.
H, 3.97.
1
2
187.2 ppm, J(CRh) 73.7 Hz, J(CP) 16.1 Hz; δ31P
1
29.2 ppm, J(PRh) 125.9 Hz) coincide with those of
trans-RhCl(PPh3)2(CO) sample synthesized by the
known procedure [46]. The integrated intensity of the
band ν(CO) in IR spectrum of a solution of the reaction
product almost equals the intensity of this band in the
spectrum of a standard sample. Crystallographic char-
acteristics of the crystals of compounds chosen from
mother liquor (space group Pbca, orthorhombic cell
with unit cell parameters a = 23.074(5) Å, b =
7.8978(16) Å, c = 20.272(4) Å) satisfactorily agree
with the literature data for orthorhombic modification
of trans-RhCl(PPh3)2(CO) · 2CH2Cl2 [47]. The 31P
NMR spectrum of a filtrate, obtained after separation of
RhCl(PPh3)2(CO), does not contain a signal from the
starting trans-Rh(HCOO)(PPh3)2(CO), but has a dou-
blet from trans-RhCl(PPh3)2(CO) and a singlet at
29.25 ppm from triphenylphosphine oxide. The trans-
formation of formate complex to chloride complex
occurs also at room temperature, but in this case, the
reaction is complete in 2 days.
HRh(PPh3)3(CO). 1. Synthesis from [Rh(µ-
HCOO)(CO)2]2. A mixture of [Rh(µ-HCOO)(CO)2]2
(0.1 g, 0.245 mmol) and triphenylphosphine (0.64 g,
2.44 mmol) was placed in a reaction vessel, and pro-
panol-2 (13 ml) was added. The precipitate of a yellow
color formed. The reaction vessel was placed in a water
bath preliminarily heated to 90°C. The mixture was
refluxed for 30 min. The precipitate dissolved during
the first minutes, and a yellow solution formed, from
which crystals of the final product precipitated immedi-
ately. The reaction was accompanied by a release of
CO2. The reaction mixture was cooled to room temper-
ature, and mustard-colored crystals were filtered,
washed with ether, and dried in vacuum. The product
yield was 0.40 g (89%). Titration with baryta water
showed that one mol of ëé2 per one g-atom of Rh is
released in the reaction. IR spectrum (essential oil
mulls, cm–1): ν(RhH) 2042, ν(CO) 1926; NMR (tolu-
ene-d8): δ1H 9.36 ppm; 2J(HP) 14.1 Hz; 31P 40.8 ppm,
1 1J(PRh) 154.5 Hz.
Rh(I) formate complexes are of great interest for
researchers due to extensive development of chemistry
of C1 ligands. In this work, we suggested a suitable pro-
cedure of synthesizing [Rh(µ-HCOO)(CO)2]2, charac-
terized the crystal and molecular structures of this com-
plex, and described some reactions of its triphenylphos-
For C55H46OP3Rh
anal. calcd. (%):
Found (%):
C, 71.89;
C, 72.29;
H, 5.01.
H, 5.08.
phine
derivative
trans-Rh(HCOO)(PPh3)2(CO)
2. Synthesis from trans-Rh(HCOO)(PPh3)2(CO).
trans-Rh(HCOO)(PPh3)2(CO) (0.172 g, 0.245 mmol)
and triphenylphosphine (0.167 g, 0.61 mmol) were
placed in a reaction vessel and propanol-2 (7 mol) was
added. The reaction vessel was placed in a water bath
preliminarily heated to 90°C. The reaction mixture was
occurring with destruction of formate ligand and
release of CO2. One of these reactions was suggested as
the basis of a new and efficient method of synthesizing
carbonyl hydride complex HRh(PPh3)3(CO).
X-ray diffraction and spectral (IR and NMR) data
refluxed for 30 min. Crystals of the final product we obtained made it possible to systematize character-
formed rapidly. The reaction was accompanied by lib- istics of Rh(I) carbonyl carboxylate complexes [Rh(µ-
eration of CO2. The mixture was cooled to room tem- RCOO)(CO)2]2 and trans-Rh(RCOO)(PPh3)2(CO) (R =
perature, and mustard-colored crystals were filtered, H, CH3, CF3) and to compare the structural and spectral
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 31 No. 2 2005

130
VARSHAVSKII et al.
(20 Int. Chugaev Conf. on Coordination Chemistry),
Rostov-on-Don, 2001, p. 160.
parameters of formate complexes with the correspond-
ing parameters of their analogs.
21. Varshavsky, Yu., Cherkasova, T., Korlyukov, A., et al.,
Abstracts of Papers, 35th Int. Conf. on Coordination
Chemistry, Heidelberg, 2002, p. 664.
ACKNOWLEDGMENTS
22. Varshavsky, Yu.S., Cherkasova, T.G., and Podkorytov, I.S.,
The authors are grateful to Z.A. Starikova for her
concern about this work and fruitful discussion.
Inorg. Chem. Commun., 2004, vol. 7, no. 4, p. 489.
23. Gordon, A.J. and Ford, R.A., A Handbook of Practical
Data, Techniques, and References, New York: Wiley,
1972.
24. Reis, A.H., Jr., Willi, C., Siegel, S., and Tani, B., Inorg.
Chem., 1979, vol. 18, no. 7, p. 1859.
This work was supported by the RF Ministry of
Education (project no. UR.05.01.032). X-ray diffrac-
tion experiments were conducted in the Center for
X-ray Diffraction Study and were supported by the
Russian Foundation for Basic Research (projects
nos. 00-03-32807a, 00-15-97359).
25. Potekhin, K.A., Batsanov, A.S., and Struchkov, Yu.T.,
Rhodium Express, 1993, no. 1, p. 3.
26. Huq, F. and Skapski, A.C., J. Cryst. Mol. Struct., 1974,
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