Reactions of the hexaaquarhodium(III) cation with bis(benzimidazol-2- ylmethyl)methylamine and PPh3: Syntheses and properties of new hydrido- and carbonylrhodium complexes

Article abstract of DOI:10.1016/j.ica.2003.10.020

Hexaaquarhodium(III) perchlorate has been found to be an interesting starting material for the preparation of rhodium compounds. New mononuclear hydrido- and carbonylrhodium compounds with bis(benzimidazol-2-ylmethyl) methylamine (L) and PPh₃ o

Full text of DOI:10.1016/j.ica.2003.10.020

Inorganica Chimica Acta 357 (2004) 2483–2493
www.elsevier.com/locate/ica
Reactions of the hexaaquarhodium(III) cation with
bis(benzimidazol-2-ylmethyl)methylamine and PPh3: syntheses
and properties of new hydrido- and carbonylrhodium complexes
*
ꢀ ꢀ
ꢀ
Monika Moszner , Ewa Kwaskowska-Chßec, Jozef J. Ziołkowski
Faculty of Chemistry, University of Wrocław, 14 F. Joliot-Curie Str., 50-383 Wrocław, Poland
Received 18 July 2003; accepted 25 October 2003
Available online 18 May 2004
Abstract
Hexaaquarhodium(III) perchlorate has been found to be an interesting starting material for the preparation of rhodium com-
pounds. New mononuclear hydrido- and carbonylrhodium compounds with bis(benzimidazol-2-ylmethyl)methylamine (L) and
PPh3 of the type [Rh(H)L(PPh3)2](ClO4)2 (1) and [Rh(CO)L(PPh3)2](ClO4) (2) have been synthesized. The monomeric Rh(II)
compound was identified as an intermediate. Complexes 1 and 2 were characterized by elemental analysis, mass spectrometry and
IR, and NMR spectroscopies. The fluxional behaviour of 2 was studied by variable-temperature 1H and 31P{H} NMR experiments.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Rhodium complexes; Aqua complexes; Benzimidazolato complexes; Hydrides; Carbonyls
1. Introduction
in metalloproteins. One of these is bis(benzimidazol-2-
ylmethyl)methylamine (L) (Fig. 1).
The versatile behaviour of transition metal chelates of
N-donor ligands is the subject of ongoing research.
Many chemists have incorporated imidazole groups in
stable chelates to obtain ligand systems [1,2]. A certain
flexibility of the ligand, whereby the coordination ge-
ometries may adapt to oxidation state changes and to
one or two ‘‘open’’ positions at the metal ion site [3], may
facilitate catalytic reactions. Synthesis of metal com-
plexes of bridged bis(benzimidazole) ligands of various
bridge type donor groups is of great interest for their
physiological activity and interesting stereochemistry.
Complexes of bridged bis(imidazole) and bis(benz-
imidazole) ligands of various bridge types with transi-
tion metals were examined as potential models of the
structure and mobility of biological metal binding sites
Interest in the chemistry of rhodium compounds
stems from their activity in many homogeneous catalytic
processes, such as hydrogenation [4], hydroformylation
[4d,5] decarbonylation [4e], carbonylation [5e,6], hy-
drosililation [7], reductive amination [8], oxidation [9–
12], cyclopropanation and cycloaddition [13]. Rhodium
compounds show interesting antitumour activity and
represent the most promising candidates for the devel-
opment of structurally related platinum analogues [14].
Antibacterial action of some rhodium complexes in
structures of the type [RhCl2(py)4]Cl, [Rh2X2(RCOO)2
(N-N)2] and [Rh2(RCOO)2(N-N)2(H2O)2]2þ(X ¼ Cl, Br,
I; R ¼ H, Me, PhCHOH; N-N ¼ 2,20-bipyridine, 1,10-
phenantroline and their derivatives) has also been
demonstrated [15].
Numerous publications have appeared regarding
metals like Cu [16–19], Zn, Pd, Pt [19], Fe [1,2,20,21] Mn
[1,2,22], Co [19,23], Ni [19,24], Ru [25], but only a few
reports are available on rhodium compounds with the
ligand in question [26–28]. There is no data on this type
of compound containing simultaneously coordinated
* Corresponding author. Tel.: (+48)-(71)-3757-228; fax: (+48)-(71)-
328-23-48.
E-mail address: mm@wchuwr.chem.uni.wroc.pl (M. Moszner).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.10.020

2484
M. Moszner et al. / Inorganica Chimica Acta 357 (2004) 2483–2493
2.2. Syntheses of the complexes
2.2.1. RhL(H)(PPh3)2](ClO4)2 (1)
(a) To
a
1–3
M
HClO4/EtOH solution of
[Rh(H2O)6](ClO4)3 (0.273 mmol, 4 cm3) heated to 348 K
under a nitrogen atmosphere was slowly added deoxy-
genated L (0.273 mmol, 79 mg) in 10 cm3 of EtOH and
next a deoxygenated solution of PPh3 (0.819 mmol, 215
mg) in 10 cm3 EtOH. The resulting red mixture was
stirred under an inert atmosphere at 348 K for 5 h, next
oxygenated with O2 until the colour changed to yellow,
and further stirred at room temperature for 20 h under
N2. The deposited greyish-white precipitate was filtered
off and washed with deaerated EtOH and Et2O. The
crude product was dissolved in acetone and EtOH (1:1).
Careful evaporation under a slow flow of nitrogen af-
forded white precipitate of 1. It was filtered off and
vacuum dried.
Yield: 214 mg (70%). Found: C, 56.75; H, 4.22; N,
6.18; Cl, 5.56%. C53H48N5P2O8Cl2Rh (M ¼ 1118:72)
requires: C, 56.90; H, 4.33; N, 6.26; Cl, 5.54%. Posi-
tive-ion ESI-MS (CHCl3) m=z 1018.7 [{RhL(H)
(PPh3)2}(ClO4)]þ; 919.9 [RhL(H)(PPh3)2]2þ. Selected
IR absorption bands (KBr, cmꢁ1): 1624 m, 1480 s,
1437 s, 1185 sh, 1092 vs, br, 746 s, 699 s, 624 s, 520 s;
(nujol) 2180 m m(Rh–H). NMR spectra, d (ppm), 1H
(acetone-d6): )14.4 (dt, 1H JP;H ¼ 18.4, JRh;H ¼ 25.1
Hz); 3.36 (s, 3H, N1–CH3); 3.49, 4.35 (dd, 4H, 2Ha,
Fig. 1. Bis(benzimidazol-2-ylmethyl)methylamine (L).
hydride anions or carbonyl ligands. It has been demon-
strated that different rhodium(III) substrates, like RhCl3 ꢀ
3H2O and [R(H2O)6](ClO4)3, used as the reagents for
syntheses of rhodium compounds, affect the stoichiome-
try of the substitution products [27,28, 29a,29b].
As a continuation of the research performed in this
laboratory over the past several years, aimed to inves-
tigate the chemistry of homoleptic aqua rhodium com-
plexes [27–29], we have examined the reactivity of
[Rh(H2O)6](ClO4)3 in substitution reaction with
bis(benzimidazol-2-ylmethyl)methylamine and PPh3.
Here, we report on the preparation and characterization
of the title complexes.
2. Experimental
2.1. Materials and physical measurements
0
0
0
2Hb, Jab ¼ 17.5 Hz); 7.05–7.32 (m, 8H H6;6 , H7;7 , H8;8
,
0
0
RhCl3 ꢀ 3H2O was purchased from Pressure Chemical
Co. All other chemicals were reagent grade and were
used as commercially available. Infrared spectra were
recorded on a FT-IR Nicolet Impact 400 spectrometer
in the 4000–400 cmꢁ1 range as KBr disks or Nujol mulls.
The NMR spectra were collected on a Bruker AMX-300
spectrometer (1H at 300.13 MHz, 31P at 121.496 MHz)
and on a Bruker Avance–500 spectrometer (1H at 500.13
MHz, 13C at 125.76 MHz) with TMS as internal stan-
H9;9 + 30 H P(C6H5)3); 12.1 (s, 2H, N3;3 –H); 31P{H}:
35.17 (d, JRh;P ¼ 116.8 Hz); (CD2Cl2): )14.74 (dt, 1H,
JP;H ¼ 18.0 Hz); 2.93 (s, 3H, N1–CH3); 2.87, 3.95 (dd,
4H, 2Ha, 2Hb, Jab ¼ 17.6 Hz); 6.92–7.65 (m, 38 H aryl
0
H); 12.24 (s, 2H, N3;3 –H); 31P{H}: 35.1 (d,
JRh;P ¼ 116.9 Hz).
(b) The above procedure was applied to the reaction
carried out in MeOH. A greyish-white solid was pre-
cipitated and was filtered off, washed with MeOH and
Et2O, and dried in vacuo. Yield: 183 mg (60%). Found:
C, 56.50 5; H, 4.52; N, 6.20; Cl, 5.46%.
C53H48N5P2O8Cl2Rh (M ¼ 1118:72) requires: C, 56.90;
H, 4.33; N, 6.26; Cl, 5.54%. Positive-ion ESI-MS
(CHCl3) m=z 1018.7 [{RhL(H)(PPh3)2}(ClO4)]þ; 919.9
1
dard for H and 13C{H}, and 85% H3PO4 as external
standard for 31P{H}. ESR spectra were monitored for
solutions and solids on a Bruker ESP 300E spectrome-
ter. Elemental analyses were performed at the Elemental
Analysis Centre of Wrocław University on a Perkin–
Elmer Elemental Analyser 2400 for CHN. Mass spectra
were measured on a Finnigan Mat. TSQ 700. Catalytic
reaction products were analysed on a GS-MS Hewlett–
Packard instrument: HP 5890 II chromatograph with
HP 5971a mass detector. Bis(benzimidazol-2-ylm-
ethyl)methylamine (L) was synthesized as described
[27,28]. [Rh(H2O)6](ClO4)3 was prepared according to
the method of Ayres and Forrester [30] in the reaction of
RhCl3 ꢀ 3H2O with concentrated perchloric acid and
standardized spectrophotometrically using the known
UV–Vis spectrum of [Rh(H2O)6](ClO4)3 with peaks at
396 nm (e ¼ 62 Mꢁ1 cmꢁ1) and 316 nm (e ¼ 67:4 Mꢁ1
cmꢁ1) as described by Reynolds and coworkers [31].
[RhL(H)(PPh3)2]2þ
. Selected IR absorption bands
(Nujol, cmꢁ1): 2176 m m(Rh–H), 1624 m, 1076 br s,749 s,
696 s, 612 s, 523 s. NMR spectra (CD3CN), d (ppm), 1H:
)14.43 (dt, 1H JP;H ¼ 17.4, JRh;H ¼ 24.8 Hz); 3.24 (s, 3H,
N1–CH3); 3.38, 4.22 (dd, 4H 2Ha, 2Hb, Jab ¼ 17.5 Hz));
0
6.94–7.43 (m, 38H aryl H), 12.1 (s, 2H, N3;3 –H);
1
31P{H}: 35.3 (d, JRh;P) ¼ 117.1 Hz).
2.2.2. RhL(CO)(PPh3)2](ClO4) (2)
To
a
1–3
M
HClO4/EtOH solution of
[Rh(H2O)6](ClO4)3 (0.273 mmol, 4 cm3) heated to 348 K
under an argon atmosphere was slowly added deoxy-
genated L (0.273 mmol, 79 mg) in 10 cm3 EtOH and

M. Moszner et al. / Inorganica Chimica Acta 357 (2004) 2483–2493
2485
next a deaerated solution of PPh3 (0.819 mmol, 215 mg)
in 10 cm3 EtOH. The resulting red mixture was stirred
under argon at 348 K for 5 h and next for 20 h at room
temperature. A deposited pale-yellow solid was filtered
and washed with degassed EtOH and Et2O. The crude
product was dissolved in a mixture of CH2Cl2, CHCl3
and EtOH (1:1:1) and gently evaporated under a nitro-
gen flow. The pale yellow micro-crystals were collected
by filtration, washed with cold ethanol, and vacuum
dried. Yield: 171 mg (60%). Found: C, 60.98; H, 4.46; N,
6.45%. C54H47N5P2O5Cl1Rh1 (M ¼ 1046:29 requires: C,
61.99; H, 4.53; N, 6.69%. Positive-ion ESI-MS (CHCl3)
m=z 946.6 [RhL(CO)(PPh3)2]þ. Selected IR absorption
bands (KBr, cmꢁ1): 2002 vs, 1481 m, 1458 m, 1436 s,
1115 sh, 1094 br vs, 746 s, 698 s, 623 m, 521 s; (Nujol)
2006 s. NMR spectra (CDCl3), d (ppm), 1H: 0.36 (s, 3H,
N1–CH3), 2.66 and 3.98 (dd, 4H, 2Ha, 2Hb, Jab ¼ 17.2
Scheme 1.
Dropwise addition of ethanolic solution containing L
to a solution of [Rh(H2O)6]3þ in 1–3 M HClO4/EtOH,
warmed up to 348 K, leads to a colour change from
yellow to yellow-brown. Subsequent addition of PPh3 in
EtOH causes a discernible darkening to dark red after
several minutes for reactions carried out both under an
N2 and Ar atmosphere.
The ESR spectrum of the resulting mixture in liquid
nitrogen exhibits near axial symmetry with gxx;yy ¼ 2:29,
gzz ¼ 1:99 (gav ¼ 2:19) (Fig. 2(a)), comparable with
those published for other monomeric rhodium(II)
compounds [32].
0
0
0
0
Hz), 7.69–6.74 (m, 8H, H6;6 ,0 H7;7 , H8;8 , H9;9 + 30H
P(C6H5)3), 11.23 (s, 2H, N3;3 –H); 31P{H}: 29.46 (dd,
1JRh;P ¼ 128.8 Hz, JP;P ¼ 28.9Hz); (CD2Cl2): 0.47 (s, 3H,
N1–CH3), 4.0–3.5 (s br, 4H, 4 Ha;b), 7.6–6.78 (m, 38 H
0
aryl H), 11.34 (s, 2H, N3;3 –H); 31P{H}: 29.25 (d,
1
1JRh;P ¼ 128.8 Hz); (acetone-d6): H: 0.57 (s, 3H, N1–
CH3), 3.42–3.38 (m, 4H, 4Ha;b), 8.0–6.83 (m, 38H aryl
H), 11.56 (s, 2H, N3;3 –H); 31P{H}: 30. 57 (d,
0
1
1JRh;P ¼ 128.1 Hz). 13C{H}: 189.1 (dt, JRh;C ¼ 68.3 Hz,
2JCRhP ¼ 17.2 Hz).
Catalytic runs. To a 1–3 M HClO4/ROH (R ¼ Me,
Et) solution of [Rh(H2O)6](ClO4)3 (0.225 mmol) heated
to 348 K under a nitrogen atmosphere was slowly added
deoxygenated L (0.225 mmol) in 10 cm3 of ROH and
next a deoxygenated solution of PPh3 (0.675 mmol) in
10 cm3 ROH. The unsaturated substrate like 1-hexene
or cyclohexene (2.25 mmol) was added subsequently.
The resulting mixture was stirred under an inert atmo-
sphere at 348 K for 3 h. Organic products were analysed
with GC–MS after separation from the rhodium com-
plexes by vaccum transfer.
This indicates that the reduction of Rh(III) to Rh(II)
takes place during the first reaction steps, reaction (1).
½RhIIIðH2OÞ ꢂ3þ þ L þ PPh3
6
H
þ=H2O=EtOH
2þ
½RhIILðPPh Þ ꢂ
ð1Þ
ƒƒƒƒƒƒƒ!
3
2
D N2ðArÞ
The stoichiometry of the final products suggests that
the Rh(II) species is a monomeric [RhL(PPh3)2]2þ cat-
Caution. Although no accident occurred with the
rhodium perchlorate complexes during the experimental
work, it should be remembered that perchlorates are
potentially explosive. They should be prepared in small
quantities and handled with care.
3. Results and discussion
3.1. Synthesis, ESR and IR characterization
The preparations and principal reactions of com-
plexes described in this paper are presented in Scheme 1.
Hexaaquarhodium(III) perchlorate in acidic water
ethanolic solution has been found to react with L giving
complexes [RhL(H2O)2(ClO4)](ClO4)2 and [RhL2]-
(ClO4)3 ꢀ 3H2O for 1:1 and 1:2 metal-to-ligand molar
ratios, respectively [27,28].
Fig. 2. ESR spectra (a) of [RhL(PPh3)2]2þ, [Rh(II)], in reaction mixture
solution, in liquid nitrogen, (b) after reaction of [Rh(II)] with O2.

2486
M. Moszner et al. / Inorganica Chimica Acta 357 (2004) 2483–2493
ion, [RhII]. Bulky tertiary phosphines have been found
to reduce rhodium(III) either by a two electron process
to rhodium(I) or by one-electron reduction to
rhodium(II), e.g., RhCl2(PBut2R)2 (R ¼ Me, Et, Prn)
[33], RhCl2{((o-tol)3P}2 [34], [Rh(PPh3)2Cl2] [35], [Rh
(tmpp)2](BF4)2 (tmpp ¼ 2,4,6-trimethoxyphenyl)phos-
phine [36]. Many Rh(II) complexes with N and N-O
donor ligands have also been described [32b,37]. Cool-
ing the reaction mixture in liquid nitrogen afforded a
small amount of a yellow, unstable solid, whose IR
spectrum displayed a strong band at 1640 cmꢁ1, char-
acteristic for the acetyl group, as demonstrated for
for more then 20 h affords the hydride compound
[Rh(H)L(PPh3)2](ClO4)2 (1).
The reaction performed in MeOH led only to the
formation of 1.
A reasonable explanation for the experimental ob-
servations is to suppose that in its interactions the rho-
dium(II) compound may follow a few different reaction
pathways. The stability of Rh(III) (4d6) or Rh(I) (4d8)
relative to Rh(II) (4d7) allows easy one-electron oxida-
tion or reduction reactions of Rh(II) intermediates to
occur.
Thus it can be tentatively assumed that 1 is formed
according to reaction (2), while the formation of 2 fol-
lows reactions (3) and/or (4).
complexes [RhBr2(COCH3)(CO)(PEt2Ph)2] (1667 cmꢁ1
)
and [RhCl2(COCH3)(CO)(PEt2Ph)2] (1660 cmꢁ1) [38]
and postulated for compounds [M(CF3COO)2(CO)
(PPh3)2] (M ¼ Ru, Os), which have been found to be
readily attacked by primary and secondary alcohols to
liberate aldehydes and ketons, respectively, with con-
comitant formation of the hydride species [MH(CF3
COO)(CO)(PPh3)2] [39].
2½RhðIIÞꢂ þ C2H5OH ! 2½RhIIIHꢂ þ CH3CHO
2½RhðIIÞꢂ þ C2H5OH ! 2½RhIðCOÞꢂ þ H2 þ CH4
½RhðIIÞꢂ þ CH3CHO ! ½RhIðCOÞꢂ þ CH4
ð2Þ
ð3Þ
ð4Þ
The reaction performed in the presence of nitrogen
gives a mixture of [Rh(H)L(PPh3)2](ClO4)2 (1) and
[Rh(CO)L(PPh3)2]ClO4 (2) in a ratio of ca. 5:1 (based on
1H NMR spectra) under the reaction conditions de-
scribed. Fractional crystallization, under vacuum, from
the solution of CHCl3/EtOH (1:1), affords 1 and 2 as
individual solids, 2 precipitating as the first one.
The analogous reaction performed in an argon
atmosphere leads to the formation of [Rh(CO)L
(PPh3)2](ClO4) (2) as the main product. Some amounts
of the compounds [RhL2](ClO4)3 and [RhL(H2O)2
(ClO4)](ClO4)2 [27,28] as well as OPPh3 were identified
in the mother liquors.
The reaction solution, containing the [Rh(II)] moiety
affected by oxygen, changes its colour from red to pale-
yellow. Its ESR spectrum (g1 ¼ 2:099, g2 ¼ 2:028,
g3 ¼ 2:007; gav ¼ 2:045) (Fig. 2(b)) is indicative of a
superoxo Rh(III) derivative [RhIII(O2ꢁ)]2þ by compari-
son with literature data [29d,37c,37d,38,40–42]. Further
stirring of the oxygenated solution under nitrogen flow
The positive effect of oxygen on the formation of 1
suggests that the superoxide coordinated to the Rh
centre acts as a base that abstracts Hþ from alcohol
affording an acyl derivative subsequently converted to
rhodium hydride (reaction 5). The base has been found
to play a crucial role in the formation both of hydrides
[38,43] and carbonyls [39] by dehydrogenation of alco-
hols. All the reported studies were carried out in strong
acidic conditions. Thus, a plausible reaction is given by
½RhðIIÞꢂ þ O2 ! ½RhIIIðOꢁÞꢂ
½RhIIIðHÞꢂ
2
þ CH3COOH þ H2O
We have investigated appropriate chemical routes in an
ð5Þ
effort to isolate intermediate products.
The IR spectrum of 1, in a Nujol mull, displays a
band at 2180 cmꢁ1, which is assigned to Rh–H
stretching vibration. This frequency falls within the
range for Rh(III) hydrides, Table 1, [44–48].
Table 1
Spectral data for hydrido-complexes of rhodium(III)
Compound
m(Rh–H) (cmꢁ1
)
dH
JRh;H (Hz)
JP;H (Hz)
Reference
[Rh(H)L(PPh3](ClO4)2
cis-[Rh(H)(Cl)L1](ZnCl4)
trans-[Rh(H)(Cl)L1](ZnCl4)
[Rh(H)(NH3)5](SO4)
[Rh(H)(NH3)5](ClO4)2
trans-[Rh(NH3)4
2180
2119
2124
2079
2126
2146
)14.3
25.1
36.4
34.4
14.5
18.4
this work
[44]
[44]
)20.70
)20.34
)17.1
[45]
[45]
[45]
(H2O)(H)](SO4)
trans-[Rh(H)(en)2Cl]þ
cis-[Rh(H)(en)2Cl]þ
cis-[Rh(H)trienCl]þ
K2[Rh(H)(CN)4(H2O)]
[Rh(H)py4Cl]Cl
2100
2093
2081
1976
2000
)21
)21
)18.8
31.0
31
[45]
[46]
[46]
[47]
[48]
27.0
)18.5
L1 ¼ [14] and N4; triene ¼ ethylenetetramine.

M. Moszner et al. / Inorganica Chimica Acta 357 (2004) 2483–2493
2487
Table 2
IR m(CO) and 13C NMR data for rhodium(I) complexes
Compound
m(CO) (cmꢁ1
)
Solvent
CD2Cl2
T (K)
d(CO)
1JRh;C (Hz)
JCRhP (Hz)
Reference
this work
[Rh(CO)L(PPh3)2]ClO4
2002a
2006b
2001
2000
2000
2001
243
189.1
68.5
17.0
[Rh(CO)(PPh3)2L2]PF6
[Rh(CO)(PPh3)2L3]PF6
[Rh(CO)(PPh3)42]PF6
[49]
[49]
[49]
[49]
[50]
[50]
[50]
[51]
[51]
[51]
[Rh(CO)(PPh3)52]PF6
trans-[Rh(CO)F(PPh3)2]
trans-[Rh(CO)(ONO2)(PPh3)2]
trans-[Rh(CO)Cl(PPh3)2]
trans-[Rh(Sp)2COCl]2ꢁd
[Rh(Sp)COCl2]2ꢁ
CD2Cl2
CDCl3
CDCl3
CH3OH
H2O
243
243
243
298
298
298
190.6
190.6
187.8
187.8
184.7
189.5
68.8
74.7
74.3
74.5
79.7
76.3
16.8
16.9
16.0
15.8
17.0
24.0
1982c
1979.5c
[Rh(acac)(Sp)CO]ꢁ
H2O
a KBr.
b Nujol.
c THF solution, L2 ¼ imidazole, L3 ¼ benzimidazole, L4 ¼ 2-methylbenzimidazole, L5 ¼ 2-ethylbenzimidazole.
d Sp ¼ [PPh2(C6H4SO3]ꢁ.
Fig. 3. NMR spectra of [Rh(H)L(PPh3)2](ClO4)2 (1) in acetone-d6: (a) 1H, (b) 31P{H}.

2488
M. Moszner et al. / Inorganica Chimica Acta 357 (2004) 2483–2493
Replacement of hydrogen by halogen was found to take
place easily for [PtHCl(PEt3)2] [43].
A Rh–CO stretching vibration appears in the IR
spectrum of 2 as a very strong band at 2002 cmꢁ1, which
shifted to 2006 cmꢁ1 in a Nujol mull (Table 2).
It has been reported that some rhodium(III) complexes
in the presence of tertiary phosphines react with primary
alcohols to give rhodium(I) carbonyl compounds, e.g.,
[Rh(CO)(ONO2)(PPh3)2] [51], trans-[RhCl(CO)(PR3)2],
(PR3 ¼ PMe2Ph, PEt2P, PEt2Ph) [38].
3.2. NMR studies of 1 and 2
Fig. 4. Schematic structure of 1.
The m(Rh–H) frequency disappears when the spec-
trum is measured as KBr pellets. This indicates that the
hydridic hydrogen is replaced by halide, giving most
probably the halide complex [RhBrL(PPh3)2](ClO4)2.
The proton NMR of compound 1 (Fig. 3) in the
hydridic region shows a quartet at )14.3 ppm. The
presence of a quartet can be rationalized as being gen-
erated by the coupling between the hydrogen atom and
Fig. 5. MR spectra of [Rh(CO)L(PPh3)2]ClO4 (2) in CDCl3 (a) 1H, (b) 31P {H}, 298 K.

M. Moszner et al. / Inorganica Chimica Acta 357 (2004) 2483–2493
2489
the two equivalent phosphorous atoms, giving rise to a
triplet, which is further split by rhodium to form a
triplet of doublets. The appearance of a quartet can then
be explained by assuming that JP;H is almost equal to
JRh;H. Actually, they are slightly unequal, as evidenced
by shoulders seen on the individual peaks of the quartet.
From the fine structure of that multiplet, the individual
coupling constants were calculated to be JP;H ¼ 18.4 and
downfield shifted in comparison with the free ligand
(3.27 ppm) [27,28], and an unresolved aromatic group of
signals in a 7.0–7.6 ppm region from the ligands L and
PPh3 are consistent with the molecular structure of the
complex with a facial L ligand, two axial phosphines,
and the hydride ion trans to N1 and cis to both phos-
0
phines. The N3H + N3 H singlet resonance appears at
12.1 ppm.
1
JRh;H ¼ 25.1 Hz. The latter was confirmed by a H{P}
The 31P NMR spectrum (Fig. 3(b)) displays one
doublet at 35.1 ppm with 1JRh;P ¼ 116 Hz. This indicates
that both PPh3 ligands are equivalent and mutually cis.
NMR experiment, which resulted in the collapsing of
the quartet into a doublet centred at )14.3 ppm. The
JRh;H value of 25.1 Hz indicates that two phosphine li-
gands are cis-coordinated to the hydride [52]. The 2- and
20CH2 resonances show an AB system with considerable
magnetic non-equivalence of methylene protons
(da ¼ 4:35; db ¼ 3:52 ppm with JAB ¼ 16.5 Hz). The
additional singlet resonance from N1CH3 at 3.37 ppm,
1
Both H and 31P{H} NMR data are entirely in ac-
cord with the schematic structure of 1 in Fig. 4.
The 1H and 31P{H} NMR spectra of 2 in chloroform-
d are presented in Fig. 5.
The characteristic features of 2 are the presence of an
AB-type spectrum of methylene protons (C(2)–H2 and
Fig. 6. 13C{H} NMR spectrum of 2 in CD2 Cl2 at 243 K.
Fig. 7. Variable-temperature (a) 1H and (b) 31P{H} NMR spectra of 2 in CD2Cl2.

2490
M. Moszner et al. / Inorganica Chimica Acta 357 (2004) 2483–2493
Fig. 8. Schematic representation of interconversions observed in variable-temperature NMR spectra of 2.
C(20)–H2) and the concomitant presence of a doublet of
doublets in the 31P NMR spectrum. It is noteworthy
that the N1–CH3 resonance (d ꢃ 0:4 ppm) is consider-
ably upfield shifted in comparison with 1. The presence
of a doublet of triplets at 189.1 ppm with JRh–C ¼ 68.5
Hz and JCRhP ¼ 17 Hz in the 13C{H} NMR spectrum of
2 (Fig. 6), taken at 243 K in dichloromethane-d2, cor-
responding to a carbonyl group, is indicative of rho-
dium(I) complexes in a square planar environment
(Table 2) [50,51].
In dichloromethane-d2, at 298 K, the methylene
protons of 2 give one broad singlet resonance centred at
about 3.2 ppm and a broad doublet at 29.2 ppm in H
1
and 31P{H} NMR spectra, respectively. As the temper-
ature drops below the coalescence point (298 K), the
methylene proton signal splits into two separate broad
1
singlets at 3.70 ppm and 2.63 ppm at 273 K in the H
NMR spectrum, and an additional splitting of compo-
nents of the doublet in the 31P{H} NMR spectrum is
found, leading to a doublet of doublets (d ¼ 29:5,
JP–Rh ¼ 128.8 Hz, JP–P ¼ 28.5 Hz). Further decrease of
temperature results in the sharpening of resonances of
the typical AB pattern and disappearance of the
P–P homonuclear splitting in the 31P NMR spectrum,
which eventually becomes a well-resolved doublet. The
Thus, two phosphine ligands are equivalent in 2 and
coordinated cis to the carbonyl ligand. The fourth co-
ordination site is occupied by L, which is coordinated in
symmetrical fashion (only one set of resonances from
benzimidazolyl groups is observed). This implies that L
serves as a monodentate ligand, coordinated with the
central rhodium(I) through N1 trans to a CO molecule.
Varied coordination behaviour of multidentate N-het-
erocycles has been observed in [M(BbzIR2py2)]ClO4
(R ¼ H – 2,6-bisbenzimidazolyl)pyridine; R ¼ Me – 2,6-
bis(N-methylbenzimidazol)pyridine;
M ¼ Cu,
Co)
[26,53]. Such coordination results in flexibility of L, re-
flected in a dynamic behaviour observed in variable-
1
temperature H and 31P NMR experiments (Fig. 7).
Fig. 9. Schematic structure of 2.

M. Moszner et al. / Inorganica Chimica Acta 357 (2004) 2483–2493
2491
Table 3
Isomerization and hydrogenation of olefins over the system {[Rh(H2O)6]3þ + L + PPh3]} in 1 M HClO4/EtOH solution
Olefin
Solvent
1-Hexene
R cis-,trans-2-Hexene
Hexane
5.9
Cyclohexene
Cycohexane
1-Hexene
EtOH
MeOH
2.56
25.26
91.95
74.74
Cyclohexene
EtOH
MeOH
95.61
99.0
4.39
0.47
[Rh(H2O)6]3þ ¼ 8 ꢄ 10ꢁ3 M; [L] ¼ 8 ꢄ 10ꢁ3 M; [PPh3] ¼ 2.4 ꢄ 10ꢁ2; [olefine] ¼ 8 ꢄ 10ꢁ2; 348 K; 3 h; N2. Further studies are underway.
described spectral change observed in dichloromethane
can be attributed only to the conformational changes
around the metal centre due to L. The central nitrogen
atom N1 in the free ligand has roughly sp3-hybridiza-
tion, with C(CH3)–N(1)–C(2 or 20) and C(2)–N(1)–C(20)
tetrahedral angles of ca. 104–110° [27,28]. It still remains
sp3-hybridized when coordinated through N(1) to rho-
dium(I). However, it interconverts rapidly with inver-
sion of the configuration at N(1), as can be concluded
from the coalescence of Ha and Hb resonances at 298 K.
This interconversion between isomers B and B0 and/or C
and C0 can be represented by form A as virtual average
species observed at 298 K. When temperature goes
down below 298 K, the forms B and B0 interconvert
slowly on the NMR time-scale, the Ha and Hb protons
are diastereotopic and an AB-type 1H NMR spectrum is
observed, and at the same time the phosphine ligands
are non-equivalent and mutually coupled resulting in the
presence of a doublet of doublets in the 31P NMR
spectrum. This situation takes place within the 283–263
K temperature range. Further decrease of temperature
results in the disappearance of the non-equivalence of
the phosphine ligands and the appearance of a sharp
doublet in the 31P NMR spectrum below 260 K. These
spectra can be attributed to slowly interconverting forms
C and C0, in which Ha and Hb protons are still diaste-
reotopic (an AB-type spectrum is observed across the
entire 263–233 K temperature range) and the phos-
phines become equivalent (Fig. 8).
tions at 540 and 727 cmꢁ1 and the 31P{H} spectrum
shows a band at ca. 33 ppm, attributable to OPPh3.
3.3. Catalytic activity
Preliminary studies indicated a double-bond mi-
gration to be a result of the interaction of the system
consisting of [Rh(H2O)6]3þ, L, and PPh3 with olefins,
for reactions carried out in situ under a nitrogen
atmosphere. Some hydrogen transfer and formation
of saturated hydrocarbons were also observed
(Table 3).
4. Conclusions
In this paper we have shown that reaction between
[Rh(H2O)6]3þ and L carried out in the presence of
PPh3 results in the formation of a metalloradical
Rh(II) species. The data obtained implies that the
observed dehydrogenation and decarbonylation of
ethanol is effected by the latter. Both the hydride
[Rh(H)L(PPh3)2](ClO4)2 (1) and the carbonyl [Rh-
(CO)L(PPh3)2](ClO4) (2) complexes have been isolated
and determined. Dynamic properties of 2 evidence
the ability of L to adapt its geometry to the electronic
and geometric preferences of the metal centre. It may
be beneficial for catalytic reactions to occur.
In more polar solvents (chloroform, acetone) in
comparison with methylene dichloride, the B () B0
interconversion is slow at 298 K on both the 1H and 31
P
Acknowledgements
NMR time-scales, and consequently the AB spectrum
from C(2 and 20)–H2 in the 1H and a doublet of doublets
in 31P NMR spectra are observed.
All the obtained data correspond to the formula of 2
and its proposed structure is depicted in Fig. 9.
We thank Professor S. Wołowiec for helpful discus-
sion.
The hydride 1 dissolves well in acetone, moderately in
chloroform, methanol, and acetonitrile, and sparingly
in ethanol. The carbonyl compound 2 dissolves well in
chlorinated solvents, moderately in acetone, and spar-
ingly in ethanol. Complexes 1 and 2 are stable in the
solid state and in solutions under an inert atmosphere.
Prolonged exposure of the solutions to air results in
their decomposition. The IR spectrum exhibits vibra-
References
[1] H. Adams, N.A. Bailey, D.J. Crane, D.E. Fenton, J.M. Latour,
J.M. Williams, J. Chem. Soc., Dalton Trans. (1990) 1727.
[2] J.D. Crane, D.E. Fenton, J. Chem. Soc., Dalton Trans. (1990)
3647.
[3] G. Tabbi, W.L. Driesse, J. Reedijk, N. Veldman, A.L. Spec,
Inorg. Chim. Acta 288 (1999) 239.

2492
M. Moszner et al. / Inorganica Chimica Acta 357 (2004) 2483–2493
€
~
[4] (a) J.-E. Backvall, J. Organomet. Chem. 652 (2002) 105;
[15] (a) M. Bien, F. Pruchnik, A. Seniuk, T.M. Lachowicz, P.
ꢀ
(b) J.A. Casares, P. Espinet, J.M. Martın-Alvarez, G. Espino, M.
Perez-Manrique, F. Vattier, Eur. J. Inorg. Chem. (2001)
Jakimowicz, J. Inorg. Biochem. 73 (1999) 49;
(b) R.J. Bromfield, R.H. Dainity, R.D. Gillard, B.T. Heaton,
Nature 223 (1969) 735.
ꢀ
289;
(c) A.M. Trzeciak, J.J. Ziokowski, J. Organomet. Chem. 597
ꢀ
[16] J.C. Lockhart, W. Clegg, M.N.S. Hill, D.J. Rushton, J. Chem.
Soc., Dalton Trans. (1990) 3541.
(2000) 69;
(d) M. Moszner, A.M. Trzeciak, J.J. Ziołkowski, J. Mol. Catal. A:
ꢀ
[17] (a) H.P. Berends, W. Stephan, Inorg. Chim. Acta 93 (1984)
173;
Chem. 130 (1998) 241;
(e) B.R. James, D. Mahajan, Can. J. Chem. 57 (1979) 180.
(b) M. Palaniandavar, T. Pandiyan, M. Lakshminarayanan, H.
Manohar, J. Chem. Soc., Dalton Trans. (1995) 455.
[18] T. Pandiyan, M. Murali, M. Palaniandavar, Trans. Met. Chem. 20
(1995) 440.
ꢀ
[5] (a) F. Ungvary, Coord. Chem. Rev. 228 (2002) 61;
ꢀ
(b) J. Wrzyszcz, M. Zawadzki, A.M. Trzeciak, J.J. Ziołkowski, J.
Mol. Catal. 189 (2002) 203;
ꢀ
(c) A.M. Trzeciak, E. Wolszczak, J.J. Ziołkowski, New J. Chem.
20 (1996) 365;
[19] S.K. Chawla, B.K. Gill, Polyhedron 16 (1997) 1315.
[20] S. Wang, Q. Luo, X. Wang, K. Yu, J. Chem. Soc., Dalton Trans.
(1995) 2045.
ꢀ
(d) F. Ungvary, Coord. Chem. Rev. 147 (1996) 547;
(e) M. Beller, B. Cornils, C.D. Frohning, C.W. Kohlpaintner, J.
Mol. Catal. A 104 (1995) 17.
[21] R. Boca, P. Baran, L. Dlhan, H. Fuess, W. Haase, F. Renz, W.
Linert, I. Svoboda, R. Werner, Inorg. Chim. Acta 260 (1997) 129.
[22] (a) A.R. Oki, P.R. Bommarreddy, H. Zhang, N. Hosmane, Inorg.
Chim. Acta 231 (1995) 109;
[6] Qiang Xu, Coord. Chem. Rev. 231 (2002) 83.
[7] (a) S. Sakaki, M. Sumimoto, M. Fukuhara, M. Sugimoto, H.
Fujimoto, S. Matsuzaki, Organometallics 21 (2002) 3788;
(b) M.D. Fryzuk, L. Rosenberg, S.J. Rettig, Organometallics 15
(1996) 2871;
(b) M.S. Lah, H. Chun, Inorg. Chem. 36 (1997) 1782.
ꢀ
ꢀ
[23] (a) E. Kwaskowska-Chßec, M. Kubiak, T. Głowiak, J.J. Ziołkow-
ski, J. Chem. Crystallogr. 25 (1995) 833;
ꢀ
ꢀ
(c) D. Steinborn, U. Sedlak, M. Dargatz, J. Organomet. Chem.
415 (1991) 407;
(b) E. Kwaskowska-Chßec, M. Kubiak, T. Głowiak, J.J. Ziołkow-
ski, Trans. Met. Chem. 23 (1998) 641.
ꢀ
[24] T. Pandiyan, S. Bernes, C. Duran de Bazua, Polyhedron 16 (1997)
ꢀ
ꢀ
(d) E.N. Salnikova, M.L. Khidekel, Izv. Akad. Nauk SSSR, Ser.
Khim. (1967) 223.
2819.
[8] M.V. Klujev, M.L. Khidekel, V.V. Strelets, Trans. Met. Chem. 3
(1978) 380.
[25] X. Xiaoming, M. Haga, T. Matsumura-Inoue, Y. Ru, A.W.
Addison, K. Kano, J. Chem. Soc., Dalton Trans. (1993) 2477.
[26] V. Gayathri, E.G. Leelamani, N.M.N. Gowda, G.N.K. Reddy,
Polyhedron 16 (1997) 1169.
[9] R.A. Sheldon, J.K. Kochi, Metal Catalyzed Oxidations of
Organic Compounds, Academic Press, New York, 1981.
[10] H. Mimoun, in: J. Portefaix, F. Figueres (Eds.), Chemical and
Physical Aspects of Catalytic Oxidation, CMRS, Paris,
1980.
ꢀ
[27] M. Moszner, E. Kwaskowska-Chßec, S. Wołowiec, L.B. Jer-
ꢀ
zykiewicz, J.J. Ziołkowski, J. Chem. Res. (S) (1999) 642.
ꢀ
[28] M. Moszner, E. Kwaskowska-Chßec, S. Wołowiec, L.B. Jer-
ꢀ
[11] B.R. James, in: L.I. Simandi (Ed.), Dioxygen Activation and
Homogeneous Catalytic Oxidation, Elsevier, Amsterdam, 1991, p.
195.
zykiewicz, J.J. Ziołkowski, J. Chem. Res. (M) (1999) 2727.
[29] (a) M. Moszner, F. Asaro, S. Geremia, G. Pellizer, C. Tavagn-
acco, Inorg. Chim. Acta 261 (1997) 161;
ꢀ
(b) M. Moszner, T. Głowiak, M. Kubiak, J.J. Ziołkowski, G.
Costa, C. Tavagnacco, Polyhedron 16 (1997) 307;
[12] (a) C. Tavagnacco, M. Moszner, S. Cozzi, S. Peressini, G. Costa,
J. Electroanal. Chem. 448 (1998) 41;
ꢀ
ꢀ
ꢀ
(c) M. Moszner, J.J. Ziołkowski, J. Organomet. Chem. 411 (1991);
(d) M. Moszner, J.J. Ziołkowski, Inorg. Chim. Acta 154 (1988)
(b) E. Kwaskowska-Chßec, J.J. Ziołkowski, Oxid. Commun. 16
(1993) 210;
ꢀ
ꢀ
ꢀ
(c) E. Kwaskowska-Chßec, J.J. Ziołkowski, Oxid. Commun. 11
(1988) 117.
299.
[30] G.H. Ayres, J.S. Forrester, J. Inorg. Nucl. Chem. 3 (1957) 365.
[31] W.C. Wolsey, C.A. Reynolds, J. Kleinberg, Inorg. Chem. 2 (1963)
463.
[13] (a) M.P. Doyle, W.R. Winchester, M.N. Protopopova, A.P.
Kazala, L.J. Westrum, Org. Synth. 73 (1996) 13;
(b) H.M.L. Davies, P.R. Bruzinski, D.H. Lake, N. Kong, M.J.
Fall, J. Am. Chem. Soc. 118 (1996) 6897;
[32] (a) D. Menglet, A.M. Bond, K. Coutinho, R.S. Dickson, G.G.
Lazarev, S.A. Olsen, J.R. Pilbrow, J. Am. Chem. Soc. 120 (1998)
2086;
(c) P. Muller, C. Band, Y. Jacquier, M. Moran, I. Negeli, J. Phys.
Org. Chem. (1996) 341.
(b) D.G. DeWit, Coord. Chem. Rev. 147 (1996) 209;
(c) N.G. Connely, D.J.H. Emslie, B. Metz, A.G. Orpen, M.J.
Quayle, Chem. Commun. (1996) 2289;
ꢀ
[14] (a) B.P. Esposito, R. Najjar, Coord. Chem. Rev. 232 (2002) 137;
ꢀ
ꢀ
(b) K. Sorasaenee, J.R. Galan-Mascaros, K.R. Dunbar, Inorg.
Chem. 41 (2002) 433;
(c) F. Pruchnik, P. Jakimowicz, Z. Ciunik, J. Zakrzewska-
ꢀ
(d) H.R. Jimenez, M. Momenteau, Inorg. Chim. Acta 244 (1996)
171.
~
Czerwinska, A. Opolski, J. Wietrzyk, E. Wojdat, Inorg. Chim.
Acta 334 (2002) 59;
[33] C. Masters, B.L. Shaw, J. Chem. Soc. (A) (1971) 3679.
[34] M.A. Bennett, P.A. Lonstaff, J. Am. Chem. Soc. 91 (1969) 6266.
[35] C.A. Ogle, T.C. Masterman, J.L. Hubbard, J. Chem. Soc., Chem.
Commun. (1990) 1733.
(d) P.K.-L. Fu, P.M. Bradly, C. Turro, Inorg. Chem. 40 (2001)
2476;
(e) J.M. Asara, J.S. Hess, E. Lozada, K.R. Dunbar, J. Allison, J.
Am. Chem. Soc. 122 (2000) 8;
[36] K.R. Dunbar, S.C. Haefner, L.E. Pence, J. Am. Chem. Soc. 111
(1989) 3504.
(f) J.M. Asara, J.S. Hess, E. Lozada, K.R. Dunbar, J. Am. Chem.
Soc. 122 (2000) 8;
[37] (a) D.J. Anderson, R. Eisenberg, Inorg. Chem. 33 (1994) 5378;
(b) A.G. Bunn, M. Wei, B.B. Wayland, Organometallics 13 (1994)
3390;
(g) C.A. Crawford, J.H. Matonic, J.C. Huffman, K. Foltig, K.R.
Dunbar, G. Christou, Inorg. Chem. 36 (1997) 2361;
(h) H.T. Chifotides, K.R. Dunbar, J.H. Matonic, Inorg. Chem. 31
(1992) 4828;
(c) S. Calmotti, A. Pasini, Inorg. Chim. Acta 85 (1984) L55;
(d) J.E. Anderson, T.P. Gregory, Inorg. Chem. 28 (1989) 28;
(e) B.B. Wayland, A.R. Newman, J. Am. Chem. Soc. 101 (1979)
6472.
(i) N. Farrell, Transition Metal Complexes as Drugs and
Chemotherapeutic Agents, Kluwer Academic Publishers,
Dordrecht, 1989.
[38] J. Chat, B.L. Shaw, J. Chem. Soc. (A) (1966) 1437.
[39] A. Dobson, S.D. Robinson, Inorg. Chem. 16 (1997) 137.

M. Moszner et al. / Inorganica Chimica Acta 357 (2004) 2483–2493
2493
ꢀ
[40] (a) M. Moszner, J.J. Ziołkowski, Pol. J. Chem. 72 (1998) 2357;
(b) I.J. Ellison, R.D. Gillard, M. Moszner, M. Wilgocki, J.J.
[48] B.N. Figgis, R.D. Gillard, R.S. Nyholm, G. Wilkinson, J. Chem.
Soc. (1964) 5189.
ꢀ
Ziołkowski, J. Chem. Soc., Dalton Trans. (1994) 2531;
(c) I.J. Ellison, R.D. Gillard, M. Moszner, M. Wilgocki, J.J.
[49] C. Woods, C. Daffron, Inorg. Chim. Acta 101 (1985) 13.
[50] B.T. Heaton, J.A. Iggo, C. Jacob, H. Blanchard, M.B. Hurst-
house, I. Ghatak, M.E. Harman, R.G. Somerville, W. Heggie,
P.R. Page, I. Villax, J. Chem. Soc., Dalton Trans. (1992) 2533.
[51] J.C. Varshavskii, T.G. Tsherkasova, N.W. Kisieleva, L.S. Breslev,
A.S. Khatshaturov, Koord. Khim. 13 (1987) 1490.
[52] J.A. Osborn, F.J. Jardin, J.F. Jung, G. Wilkinson, J. Chem. Soc.
(A) (1966) 1711.
ꢀ
Ziołkowski, Polyhedron 13 (1994) 1354;
(d) M. Moszner, J.J. Ziołkowski, Trans. Met. Chem. 18 (1993) 248;
ꢀ
ꢀ
(e) M. Moszner, M. Wilgocki, J.J. Ziołkowski, J. Coord. Chem. 20
(1989) 219.
[41] A. Vigalok, Y. Ben-David, D. Milstein, Organometallics 15 (1996)
1839.
[42] A. Bakac, I.A. Guzei, Inorg. Chem. 39 (2000) 736.
[43] J. Chatt, B.L. Shaw, J. Chem. Soc. (1962) 5075.
[44] A. Bakac, L.M. Thomas, Inorg. Chem. 35 (1996) 5880.
[45] K. Thomas, J.A. Osborn, A.R. Powell, G. Wilkinson, J. Chem.
Soc. (A) (1968) 1801.
[53] (a) S.B. Sanni, H.J. Behm, P.T. Beurskens, S.B.G.A. Van
Alabada, J. Reedijk, A.T.H. Lenstra, A.W. Addisosn, M. Palani-
andavar, J. Chem. Soc., Dalton Trans. (1998) 1429;
(b) V. Shklover, I.L. Eremenko, H. Berke, R. Nesper, Md.S.M.
Zakeerudin, K. Nazeerudin, M. Gratzel, Inorg. Chim. Acta 219
(1994) 11;
[46] R.D. Gillard, G. Wilkinson, J. Chem. Soc. (1963) 3594.
[47] D.N. Lawson, M.J. Mays, G. Wilkinson, J. Chem. Soc. (A) (1966)
52.
(c) V. Gayathari, N. Shashikala, N.M.N. Gowda, G.K.N. Reddy,
Indian J. Chem. 32A (1993) 33.