A rhodium(I) dicarbonyl complex with a redox-active ferrocenyl phosphine-NHC ligand: Enhanced reactivity of the metal centre through ferrocene oxidation This paper is dedicated to Professor Claude Lapinte on the occasion of his retirement.

Article abstract of DOI:10.1016/j.poly.2014.04.050

A rhodium(I) dicarbonyl complex bearing a bidentate ferrocenyl phosphine-NHC ligand has been synthesized and characterized by NMR, IR spectroscopy, mass spectrometry and X-ray diffraction methods. Its behaviour towards oxidation was investigated and revealed that changing the oxidation state of ferrocene can significantly modify the electron density at rhodium. Oxidation of the rhodium(I) dicarbonyl complex in acetonitrile furnished an air-stable rhodium(III) complex, stabilized by acetonitrile molecules and with an interesting C-H bond activation at ferrocene. This new rhodium(III) complex is active for the hydrosilylation of acetophenone and its derivatives.

Full text of DOI:10.1016/j.poly.2014.04.050

Accepted Manuscript
A rhodium(I) dicarbonyl complex with a redox-active ferrocenyl phosphine-
NHC ligand: enhanced reactivity of the metal centre through ferrocene oxidation
Nathalie Debono, Jean-Claude Daran, Rinaldo Poli, Agnès Labande
PII:
S0277-5387(14)00270-8
DOI:
http://dx.doi.org/10.1016/j.poly.2014.04.050
POLY 10694
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
21 February 2014
26 April 2014
Please cite this article as: N. Debono, J-C. Daran, R. Poli, A. Labande, A rhodium(I) dicarbonyl complex with a
redox-active ferrocenyl phosphine-NHC ligand: enhanced reactivity of the metal centre through ferrocene oxidation,
Polyhedron (2014), doi: http://dx.doi.org/10.1016/j.poly.2014.04.050
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

A rhodium(I) dicarbonyl complex with a redox-active ferrocenyl phosphine-
NHC ligand: enhanced reactivity of the metal centre through ferrocene
oxidation
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
a,b
a,b
a,b,c
*,a,b
Nathalie Debono, Jean-Claude Daran, Rinaldo Poli
and Agnès Labande
a. CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, BP 44099, F-31077 Toulouse
Cedex 4, France. E-mail: agnes.labande@lcc-toulouse.fr; Fax: (+33) 561553003; Tel: (+33) 561333158
b. Université de Toulouse, UPS, INPT, F-31077 Toulouse Cedex 4, France
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
c. Institut Universitaire de France, 103 bd Saint-Michel, F-75005 Paris, France
This paper is dedicated to Professor Claude Lapinte on the occasion of his retirement.
Abstract
A rhodium(I) dicarbonyl complex bearing a bidentate ferrocenyl phosphine-NHC ligand has
been synthesized and characterized by NMR, IR spectroscopy, mass spectrometry and X-Ray
diffraction methods. Its behaviour towards oxidation was investigated and revealed that
changing the oxidation state of ferrocene can significantly modify the electron density at
rhodium. Oxidation of the rhodium(I) dicarbonyl complex in acetonitrile furnished an air-
stable rhodium(III) complex, stabilized by acetonitrile molecules and with an interesting C-H
bond activation at ferrocene. This new rhodium(III) complex is active for the hydrosilylation
of acetophenone and its derivatives.
1
. Introduction
Wrighton et al. first demonstrated in the early 1990s that fine tuning of the electronic
properties of a metal complex could be achieved by the introduction of redox-active ligands,
as they were able to enhance the reactivity of a carbonyl ligand coordinated to rhenium
towards nucleophiles by changing the oxidation state of cobaltocene [1]. In the area of
catalysis, Mirkin also described the use of hemilabile redox-active ligands that presented
charge-dependent behaviour [2]. Later, Gibson and Long showed that they could reversibly
modulate the activity of a titanium polymerisation catalyst with the help of a substitutionally
inert, redox-active ligand [3]. More recent examples include the work of Bielawski [4-6],
Diaconescu [7,8] and Plenio [9,10].
Many redox-active groups have been incorporated, such as the ubiquitous ferrocene [2-5,9-
1
3], or other metallocenes [1,14], quinone [6], terthienyl [15], amidophenolates [16], etc.
However, it was only recently that the redox properties of N-heterocyclic carbenes (NHC)
bearing electroactive groups were exploited in catalysis. The NHC can either be in direct
electronic communication with the electroactive moiety (ferrocene [5], quinone [6]), or
1

simply act as an ancillary ligand or “anchor” to guarantee the stability of the complex
whatever the oxidation state of the electroactive component [9].
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
Our group has a strong interest in the chemistry and catalytic activity of functionalised N-
heterocyclic carbene complexes [17-21]. We have recently investigated the behaviour of a
1
,5-cyclooctadiene (COD) rhodium(I) complex bearing a ferrocenyl phosphine-NHC ligand, 1,
towards oxidation (figure 1) [21]. We have been able to demonstrate that iron oxidation has
dramatic consequences on the reactivity of the rhodium complex, and we then wished to
extend this work to a similar rhodium(I) complex possessing carbonyl ligands in place of
COD. The results of these studies are described here.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
Figure 1. Rhodium(I) complex 1 with redox-active ferrocenyl phosphine-NHC ligand.
2
. Experimental
General considerations
All manipulations were carried out under an inert atmosphere of dry argon by using vacuum
line and Schlenk tube techniques. Solvents for all syntheses were dried and degassed by
standard methods before use, unless otherwise stated.
1
The 1D- and 2D-NMR spectra were recorded on Bruker AV500 and AV400 spectrometers. H
13
and C chemicals shifts (δ) are given in ppm (the residual peak of deuterated solvents was
3
1
used as reference). P chemicals shifts are reported in ppm. Peaks are labelled as singlet (s),
doublet (d), triplet (t), multiplet (m) and broad (br). The proton and carbon assignment were
1
13
1
31
performed by COSY, HSQC, H- C HMBC, H- P HMBC experiments. The IR spectra were
acquired on a Bruker Alpha-P spectrometer equipped with an ATR module (compound 2) or
Perkin-Elmer Spectrum 100 FT-IR with an ATR module (compound 3). The MS spectra were
obtained from the mass spectrometry service of the Paul Sabatier University. The cyclic
voltammetry (CV) experiment was carried out with a PGSTAT-302N potentiostat (Metrohm)
at 25°C using a Pt disk working electrode, a Pt wire counter electrode and a saturated
calomel reference electrode (SCE); a 0.1 M n-Bu BF solution was used as the supporting
4
4
-3
electrolyte. The solution used during the electrochemical study was typically 10 M in
rhodium compound. All electrochemical data are referenced versus ferrocene (in our hands,
+
-1
E°[FcH/FcH ] = 0.54 V/SCE in CH Cl /n-Bu BF , 0.1 V.s , 25°C).
2
2
4
4
2

The rhodium(I) complex 1 [17] and thianthrenium tetrafluoroborate [Th][BF ] [22] were
prepared according to previously reported procedures.
4
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
Abbreviations
P
Cp : cyclopentadienyl ring with the PPh substituent.
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
C
Cp : cyclopentadienyl ring with the NHC substituent.
Fc: ferrocenyl.
Im: imidazol-2-ylidene.
L: ferrocenyl phosphine-NHC ligand.
Syntheses
+
-
[Rh(CO) (L)] BF (2)
2
4
-5
CO was bubbled through a solution of complex 1 (50 mg, 7.0∙10 mole) in CH Cl (30 mL) for
2
2
2h. After partial solvent evaporation, a yellow solid was obtained by precipitation with
pentane. The solution was filtered off and the solid was washed twice with pentane to
remove the 1,5-cyclooctadiene, then dried in vacuo. The solid was obtained as a yellow
-1
powder (42 mg, 91%). IR (ATR): 2085 (s), 2029 (s) cm (C=O). Occasionally, isolated samples
of the product obtained from incomplete carbonylations gave a spectrum featuring a third
-1
1
C=O vibration at 1997 (m) cm , assigned to the monocarbonyl complex (≤5%); H NMR
(400.13 MHz, CDCl , 298 K):  7.71 (1H, d, J = 2.0 Hz, HC=C Im), 7.63-7.53 (6H, m, PPh ),
3
HH
2
7
.50-7.45 (2H, m, PPh ), 7.43 (1H, d, J = 2.0 Hz, HC=C Im), 7.35-7.28 (2H, m, PPh ), 5.17 (1H,
2
HH
2
C
d, J = 14.8 Hz, CH Im), 4.89 (1H, d, J = 15.2 Hz, CH Im), 4.70 (1H, m, Cp ), 4.61 (1H, m,
Cp ), 4.57 (1H, m, Cp ), 4.40 (1H, m, Cp ), 4.28 (1H, m, Cp ), 4.18 (1H, m, Cp ), 3.47 (1H, br s,
Cp ), 3.25 (3H, s, CH ), 2.51 (1H, br s, Cp ). C NMR (100.62 MHz, CDCl , 298 K):  186.7 (dd,
HH
2
HH
2
P
C
P
C
C
P
P
13
3
3
J = 55.7 Hz, J = 16 Hz, CO), 181.8 (dd, J = 61.2 Hz, J = 102.3 Hz, CO), 165.9 (dd, J =
RhC
PC
RhC
PC
RhC
16.2 Hz, J = 42.1 Hz, C
), 133.4 (d, J = 12.5 Hz, CH ), 132.7 (d, J = 12.4 Hz, CHPPh2),
PC
carbene
PC
PPh2
PC
1
32.5 (quat CPPh2), 131.9 (dd, J = 2.0 Hz, J = 10.0 Hz, CH ), 131.1 (d, J = 46.7 Hz, quat
RhC
PC
PPh2
PC
CPPh2), 129.6 (d, J = 10.5 Hz, CH ), 129.0 (d, J = 10.8 Hz, CH ), 125.6 (2*C=C Im), 88.0
PC
PPh2
P
PC
PPh2
C
C
P
(
quat Cp ), 75.1 (d, J = 7.7 Hz, Cp ), 74.4 (Cp ), 73.3 (d, J = 7.5 Hz, Cp ), 72.8 (d, J = 14.4
PC
PC
PC
P
P
C
C
C
Hz, Cp ), 72.0 (d, J = 6.6 Hz, Cp ), 70.1 (Cp ), 69.5 (Cp ), 68.7 (Cp ), 68.4 (d, J = 60.1 Hz, quat
PC
PC
P
31
Cp ), 49.0 (CH Im), 37.6 (CH Im). P NMR (161.98 MHz, CDCl , 298 K): 19.98 (d, J = 132
Hz). MS (ESI): m/z 595 [M-CO] (11), 384 [M-C H N O Rh] (96). HRMS (ES ): calcd for
2
3
3
RhP
+
6
4 2 2
C H FeN O PRh 623.0058; found 623.0061.
2
9
25
2 2
+
-
Oxidation of [Rh(CO)
(L)] BF
(2) in CH
Cl
2
4
2
2
3

In a glovebox, AgBF (10 mg, 0.049 mmol, 1.5 equiv.) was added, as a solid, to a solution of
4
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
complex 2 (23 mg, 0.033 mmol) in CH Cl (3 mL). The solution turned from yellow to deep
2
2
green in a few seconds. Stirring was stopped to allow the silver precipitate to settle and an
aliquot of the solution was deposited on the IR cell. After evaporation of the solvent, the
-
1
green solid was analysed: IR (ATR) 2097 (s), 2045 (s) cm (C=O).
+
-
Oxidation of [Rh(CO) (L)] BF (2) in MeCN: generation of [Rh(CH CN) (L)](BF ) (3)
2
4
3
3
4 2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
-
5
A solution of thianthrenium tetrafluoroborate (27 mg, 8.9∙10 mole, 1.5 equiv.) in CH CN
3
-
5
(
2.5 mL) was added dropwise to a solution of 2 (42 mg, 5.9∙10 mole, 1 equiv.) in CH CN (5
3
mL). The mixture was stirred for 10 min at room temperature and then the solvent was
evaporated in vacuo. The complex was precipitated with a CH CN/Et O (1/9) mixture several
3
2
times until the solution was colourless, then taken up into CH CN and left standing for 48h.
3
The solvent was evaporated in vacuo to give 3 as an orange solid (38.8 mg, 76%). IR (ATR)
-1
νmax/cm 2322, 2293 and 2252 (w) (C≡N ); 1474, 1436 and 1405 (w/m) (C=C ); 1051-999
str.
str.
1
(vs) (BF ); 747, 696 and 684 (m/s) (C-H
). H NMR (500.33 MHz, CD CN, 228 K):  7.65-
4
bend.
3
7
.55 (3H, m, PPh ), 7.53-7.46 (4H, m, HC=C Im + PPh ), 7.43-7.40 (2H, m, PPh ), 7.20 (1H, s,
2
2
2
P
HC=C Im), 7.11 (2H, dd, J = 11.5 Hz, J = 7.5 Hz, PPh ), 5.63 (1H, br s, Cp ), 4.89 (1H, d, J =
HH
HP
C
2
HH
P
P
C
1
4
4
6.1 Hz, CH Im), 4.73-4.66 (4H, m, Cp + 2 x Cp + CH Im), 4.58 (1H, s, Cp ), 4.40 (1H, s, Cp ),
.18 (1H, s, Cp ), 3.98 (3H, s, CH ). C NMR (125.82 MHz, CD CN, 228 K):  147.2 (dd, J =
2
2
C
13
3
3
RhC
7.2 Hz, J = 11.4 Hz, Ccarbene), 133.1-132.6 (m, 2 x o-CHPPh2 + p-CHPPh2), 132.0 (d, J = 9.8 Hz, 2
PC
PC
x o-CHPPh2), 131.3 (d, J = 2.6 Hz, p-CH ), 129.6 (d, J = 10.9 Hz, 2 x m-CHPPh2), 128.5 (d, JPC=
PC
PPh2
PC
1
0.7 Hz, 2 x m-CHPPh2), 128.0 (d, J = 52.2 Hz, quat C ), 126.3 (C=C Im), 124.1 (C=C Im),
PC
PPh2
C
P
123.9 (quat C), 122.17 (d, quat C), 87.2 (br s, quat Cp ), 83.3 (d, J = 9.1 Hz, Cp ), 77.1 (d, J =
1
(d, J = 65.8 Hz, quat Cp ), 70.6 (Cp ), 50.4 (CH Im), 39.1 (CH ). P NMR (202.54 MHz,
PC
PC
P
C
P
P
C
2.6 Hz, Cp ), 75.3 (Cp ), 73.7 (d, J = 7.2 Hz, Cp ), 73.3 (d, J = 6.9 Hz, Cp ), 72.3 (Cp ), 71.4
PC
PC
P
C
31
PC
2
3
CD CN, 228 K): 41.56 (d, J = 138 Hz).
3
RhP
General procedure for the hydrosilylation of acetophenone derivatives
-
6
The rhodium catalyst (4∙10 mole, 1 mol%) was placed in a dry Schlenk tube under argon
-
4
and THF (0.2 mL) and acetophenone (3.9∙10 mole, 1 equiv., 2.0 M in THF) were added.
-
4
Diphenylsilane (4.3∙10 mole, 1.1 equiv.) was then added dropwise at room temperature
and the resulting mixture was stirred for 17h. The solvent was concentrated in vacuo, the
residue taken up into CH Cl and MeOH (1 mL) and stirred for 1h. HCl (2 M, 1 mL) was then
2
2
added and the mixture was stirred for an additional hour. The phases were separated, the
aqueous phase extracted with CH Cl and the organic phases were dried (MgSO ), filtered
2
2
4
1
and concentrated in vacuo. The residue was analysed by H NMR (CDCl ) and the
3
conversions were calculated by integration and comparison of the characteristic signals of
acetophenone ( 2.63, s, 3H) and 1-phenylethanol ( 4.90, q, 1H).
-6
Kinetic follow-up: the rhodium catalyst (8∙10 mole, 1 mol%) was placed in a dry NMR tube
-4
under argon and d -THF (0.4 mL) and acetophenone (7.9∙10 mole, 1 equiv., 2.0 M in THF)
8
4

-
4
were added. Diphenylsilane (8.7∙10 mole, 1.1 equiv.) was then added dropwise at room
temperature and the resulting mixture was shaken. The reaction mixture was analysed by H
NMR and the conversions were calculated by integration and comparison of the
characteristic signals of acetophenone ( 2.50, s, 3H) and diphenyl(1-phenylethoxy)silane (
1.53, d, 3H).
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
1
X-ray structural analyses
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
A single crystal of compound 2 was mounted under inert perfluoropolyether at the tip of a
glass fiber and cooled in the cryostream of an Oxford-Diffraction Xcalibur CCD
diffractometer. The structure was solved by direct methods (SIR97 [23]) and refined by least-
2
squares procedures on F using SHELXL-97 [24]. All H atoms attached to carbon were
introduced in calculation in idealized positions and treated as riding models. The drawing of
the molecules was realized with the help of ORTEP32 [25].
Crystal data for compound 2: yellow needles, C H FeN O PRh·BF , M= 710.05, monoclinic,
29
25
2
2
4
3
a = 9.5352(3), b = 21.1742(7), c = 13.8059(4) Å, = 101.32 (3) °, V = 2734.97(15) Å , T = 180
-1
K, space group P2 /n (no 14), Z= 4, (Mo-K)= 1.25 mm , 29805 reflections measured, 6010
1
unique (R = 0.032) which were used in all calculations, 5029 observed with I 2σ(I), 389
int
2
parameters, 17 restraints. The final R and wR(F ) were 0.027 and 0.067 respectively(all data),
GOF, 0.98.
3
. Results and discussion
1
. Synthesis and characterisation of the rhodium(I) dicarbonyl complex 2
The synthesis of the precursor rhodium complex 1 was reported in a previous work [17]. It is
31
perfectly air stable and was not altered after several months of storage. Its P NMR
1
3
spectrum shows a doublet at δ 19.5 (JRh-P= 158 Hz), whereas the C NMR spectrum shows a
1
2
doublet of doublets situated at δ 176.9 ( J = 49.7 Hz, J = 15.5 Hz), typical of the C2
Rh-C
P-C
carbon in Rh(I) NHC complexes.
Scheme 1. Synthesis of rhodium(I) carbonyl complex 2.
31
The dicarbonyl complex 2 was prepared in quasi-quantitative yield, as verified by P NMR
monitoring, by bubbling CO gas through a solution of 1 in CH Cl (scheme 1). As observed for
2
2
5

other cationic Rh(I) complexes [26,27], the resulting pale yellow solid is moderately stable in
solution and decomposes in a few days when left in air. It is stable under argon in the solid
form, however, and was fully characterised by conventional methods. Its P NMR spectrum
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
3
1
shows a doublet at δ 20.5, with a smaller coupling constant to rhodium (JRh-P= 132 Hz) than
1
that of complex 1. The H NMR spectrum revealed the disappearance of the COD proton
13
signals, whereas typical signals for coordinated CO ligands were attributed in the C NMR
1
2
1
spectrum at δ 186.7 (dd, J = 55.7 Hz, J = 16.0 Hz, cis to P) and 181.8 (dd, JRh-C= 61.2 Hz,
Rh-C
P-C
2
13
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
J = 102.3 Hz, trans to P). The characteristic C NMR signal of the C2 carbon (dd, δ 165.9,
JRh-C= 42.1 Hz, J = 16.2 Hz) was found upfield compared to that of complex 1, which is
P-C
1
2
P-C
consistent with similar Rh(I) NHC complexes [26,28]. Finally infra-red spectroscopy, which is
a very useful tool for the characterisation of carbonyl compounds, showed two intense
-
1
bands for  stretching frequencies at 2084 and 2029 cm , which are in accord with other
CO
cationic NHC-Rh complexes [26,27]. The presence of two bands of equal intensity is
consistent with the expected cis arrangement of the two carbonyl groups.
X-ray quality crystals of 2 were obtained by slow diffusion of pentane into a CH Cl solution
2
2
of the complex under 1 atm of CO, the diffraction analysis of which confirmed the expected
structure (fig. 2), with a typical square-planar geometry about the rhodium atom. The
structure does not present any unusual features. Selected bond lengths and angles are listed
in Table 1. The carbene-rhodium and phosphorus-rhodium bond lengths are consistent with
those measured in related Rh(I)-NHC complexes [28,29] and are similar, within errors, to
those measured for the previously described Rh(I)-NHC COD complex 1 [17]. The Rh-carbonyl
bond lengths are also within the expected range for this type of compounds.
Figure 2. ORTEP representation of the cation in the dicarbonyl complex 2. Ellipsoids are
shown at the 30% probability level. All hydrogen atoms are omitted for clarity.
6

Table 1. Selected bond distances (Å) and angles (°) for the experimental structure of 2 and
comparison with those of 1 [17].
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
Bond
Rh(1)-C(NHC)
Rh(1)-P(1)
Rh(1)-C(L)
(1, L=(COD); 2, L=CO)
Complex 1 [17]
2.047(3)
2.3345(8)
2.215(3), 2.231(3)
2.220(3), 2.217(3)
-
-
Complex 2
2.062(2)
2.3547(6)
1.901(3)
1.886(3)
1.124(3)
1.128(3)
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
O(31)-C(31)
O(41)-C(41)
Angle
C(NHC)-Rh(1)-P(1)
C(41)-Rh(1)-P(1)
C(31)-Rh(1)-C(62)
C(31)-Rh(1)-C(41)
90.83(8)
89.92(7)
91.93(7)
86.78(10)
91.97(10)
-
-
-
2
. Oxidation studies
The rhodium complex 2 was analysed by electrochemical methods. The cyclic
voltammogram of 2 was recorded in CH Cl (fig. 3). Similarly to that of complex 1 [21], the
2
2
voltammogram shows a reversible redox wave for the ferrocene moiety at E = 0.43
1
/2
+
+
V/[FcH/FcH ] followed by an irreversible process at 1.06 V/[FcH/FcH ], that could be
assigned to the oxidation of Rh(I). By analogy with 1, we can assume that the oxidation
process at 0.43 V is a one-electron oxidation of ferrocene to ferrocenium.
1,4E-05
1,2E-05
1,0E-05
8,0E-06
6,0E-06
,0E-06
2,0E-06
4
0
,0E+00
2,0E-06
4,0E-06
6,0E-06
-1,6
-1,1
-0,6
-0,1
0,4
0,9
1,4
-
-
-
E (V) vs [FcH/FcH+]
Figure 3. Cyclic voltammogram on a Pt electrode of complex 2: 1 mM in CH Cl with
2
2
−1
nBu NBF (0.1 M) at a scan rate of 0.2 V s .
4
4
Although it was possible to generate the oxidised complexes by bulk electrolysis, we ruled
this procedure out for preparative purposes since it could be difficult to separate the
7

expected product from the ionic supporting electrolyte. We thus turned to chemical
oxidation. The choice of oxidant was guided by the E1/2 values of the ferrocene/ferrocenium
redox couple, obtained via electrochemical methods, but other parameters had to also be
taken into account, such as the “innocent” character of the reagent and the ease of
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
purification of the oxidised Rh complex [30]. NOBF is a strong oxidant but reacted with the
4
phosphine group, giving a phosphine oxide. AgBF was the most obvious choice, however its
4
oxidation potential is very solvent-dependent and should perform the oxidation of the
+
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
ferrocenyl moiety in 1 and 2 in CH Cl (E°= 0.65 V/[FcH/FcH ]), but not in a coordinating
2
2
+
solvent like MeCN (E°= 0.04 V/[FcH/FcH ]). We therefore focused our attention on
thianthrenium tetrafluoroborate [Th][BF ] (E°= 0.86 V/[FcH/FcH ] in MeCN), the oxidation
+
4
potential of which does not vary much with the solvent [22]. [Th][BF ] gives deep purple
4
solutions in acetonitrile and is insoluble in ether, whereas its reduced form is colourless and
soluble in ether. This means that the reactions can be followed visually and that the oxidised
rhodium complexes may be purified by simple precipitation and washing with Et O.
2
Chemical oxidation of complexes 1 and 2 in dichloromethane
Complex 1 was oxidised in CH Cl , either by addition of solid, anhydrous AgBF [31], or by a
2
2
4
[
Th][BF ] solution in the same solvent at room temperature (scheme 2). The orange
4
dichloromethane solution turned rapidly olive-green, at which point it was concentrated to
ca. 0.5 mL, and diethyl ether was added. A dark green precipitate separated from the light
yellow solution, which was filtered off. The green solid was further rinsed with diethyl ether
1
31
and analysed by H and P NMR in CD Cl (fig. 4).
2
2
Scheme 2. Oxidation of rhodium(I) complex 1 with [Th][BF ] in CH Cl .
4
2
2
8

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
3
1
Figure 4. P NMR spectra: oxidation of complex 1 by [Th][BF ] in CD Cl .
4
2
2
1
The H NMR spectrum showed very broad signals stretching from δ 25 to -10, whereas no or
very weak shifted signals were detected by P NMR. The characteristic colour and the
absence of P NMR signal suggested to us that we had generated paramagnetic
ferrocenium. The reversible nature of this oxidation was demonstrated when excess water
was added to the green CD Cl solution [32]: the solution became orange again and its P
NMR spectrum showed a doublet at δ 19.5 with a coupling constant of 158 Hz. Purification
of the NMR sample by simple drying and filtration on neutral alumina allowed the complete
recovery of the starting Rh(I) complex.
3
1
3
1
3
1
2
2
It has been demonstrated by Wrighton et al. that infra-red CO values in transition metal
carbonyl complexes with ferrocenylphosphino ligands could be increased by up to 20 cm
upon oxidation of ferrocene [11]. More recently, Bielawski et al. measured the values for a
carbonyl rhodium complex bearing a diaminocarbene-ferrocenophane ligand in both
reduced and oxidised states, and found on average a difference of 20 cm between the two
oxidation states [33]. Infra-red thus appeared to us as a powerful tool to demonstrate the
influence of ferrocene oxidation state on the electron density at rhodium in our complexes.
In a typical procedure, solid, anhydrous AgBF
form of carbonyl complex 2 in CH Cl (scheme 3). The colour turned in a few seconds from
light yellow to forest green [34].
-
1
-1
(1.5 equiv.) was used to generate the oxidised
4
2
2
9

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
Scheme 3. Oxidation of rhodium(I) carbonyl complex 2 with AgBF in CH Cl .
4
2
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
Complex 2
AgBF4 + 5min
AgBF4 + 20min
AgBF4 + 45min
2300
2200
2100
2000
1900
1800
red
-1
Figure 5. IR spectra (ATR), oxidation of complex 2 with AgBF
in CH
Cl
. CO(2 ), cm : 2084,
4
2
2
ox
-1
-1
2
029; after 45min,  (2 ), cm : 2097, 2045. The small band at 1997 cm for the initial
CO
solution is attributed to a monocarbonyl impurity (see Experimental section).
IR spectra were taken at intervals and showed the shift of the original  bands to higher
CO
-
1
-1
stretching frequencies by 13 cm for the higher frequency band and by 16 cm for that at
lower frequency (fig. 5) [35]. This is characteristic of a metal centre with a lower electron
density, since decreased backbonding from the d-orbital of the metal to the * antibonding
orbital strengthens the CO bonds and shifts the  bands toward higher frequencies. The
CO
red
ox
-1
average difference between the CO values for 2 and 2 is 14 cm , which is significant
enough to assert that the reactivity at the rhodium centre may be affected by the oxidation
of the ferrocene unit.
Chemical oxidation of complexes 1 and 2 in acetonitrile
+
As AgBF has a redox potential of 0.04 V/[FcH/FcH ] in MeCN [29], it should not be capable
4
of oxidizing the ferrocene moiety of 2. We therefore turned to [Th][BF ], which possesses
4
the additional advantage of being very soluble in this solvent. Typically, a solution of
1
0

[
(
Th][BF ] in MeCN was added dropwise to a solution of complex 2 in the same solvent
scheme 4). As reported earlier in the case of 1, we observed a very different behaviour from
4
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
the reaction in dichloromethane: no colour change to green was detected. Rather, a brown-
orange solution was obtained after the addition of ca. 1.5 equivalent of oxidant. At the end
of the addition, the solvent was evaporated to a minimum and diethyl ether was added to
precipitate the rhodium complex and wash off the products of [Th][BF ] reduction as well as
unreacted 2.
4
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
3
1
The P NMR spectrum of the crude reaction mixture showed one major species appearing as
a doublet at δ 41.5, with a coupling constant of 138 Hz, along with some unreacted 2,
whereas the H NMR spectrum was typical of a diamagnetic compound, and revealed the
1
presence of bound acetonitrile molecules. We demonstrated earlier, for the oxidation of 1 in
acetonitrile, that the species showing a doublet at δ 41.5 is a rhodium(III) complex resulting
from the oxidation of the ferrocene unit to ferrocenium and subsequent electron transfer
from rhodium to ferrocenium [21]. The reorganisation of the coordination sphere around
rhodium to adopt the preferred octahedral geometry implied coordination of acetonitrile
molecules. An unusual C-H activation at ferrocene followed this reorganisation to give the
air-stable rhodium(III) complex 3. Here we demonstrate that the oxidations of complex 1
(bearing a COD ligand) and the dicarbonyl complex 2 lead to the same species (scheme 4).
The full characterization of the product 3, which includes the X-ray diffraction analysis of a
bipy derivative, is reported in our previous contribution [21].
Scheme 4. Oxidation of complexes 1 and 2 with [Th][BF ] in MeCN.
4
3
1
The reaction of the carbonyl complex 2 was also followed by P NMR (fig. 6). The species
giving a doublet at δ 28.7 was previously shown to be the intermediate rhodium(III) species
(4) that has not yet undergone the C-H activation at ferrocene (scheme 5): it was the main
species observed after 10 min, along with some unreacted 2 and an unidentified by-product
at δ ca. 25. Oxidation of rhodium(I) to rhodium(III) is thus very quick and is followed by the
slow C-H activation at ferrocene to give complex 3 as the main species after 24 h.
1
1

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
3
1
Figure 6. P NMR spectra: oxidation of complex 2 by [Th][BF
] in MeCN.
4
I
III
Scheme 5. Intermediate species (4) in the oxidation process of Rh complex 2 to Rh complex 3.
In order to check that ferrocene could efficiently act as an electron relay, complex 2 was first
oxidized in CH Cl with an excess of AgBF (1.5 equiv.), giving rise to the forest-green,
paramagnetic ferrocenium-Rh(I) complex 2 (scheme 6). After filtration of insoluble silver,
the solution was evaporated in vacuo to give a green solid: upon addition of MeCN, the
colour instantly turned to orange-brown. After 24h standing at room temperature, the
solvent was evaporated and the orange residue analysed by P and H NMR. The P NMR
spectrum revealed the presence of two species in ca. 75:25 ratio: the doublet situated at δ
1.6 (JRh-P = 138 Hz), characteristic of complex 3, and a doublet at δ 33.2 (JRh- P= 120 Hz) that
might arise from the reaction of 2 with acetonitrile. The H NMR spectrum confirmed the
presence of complex 3 as the main product. The product distribution is consistent with the
2
2
4
ox
31
1
31
4
red
1
red
oxidation stoichiometry (two oxidizing equivalents are necessary to convert 2 to 3).
1
2

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
ox
Scheme 6. Stepwise oxidation of complex 2 in CH Cl and reaction of 2 in MeCN.
2
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
The above combined results confirm that the reactivity of the rhodium centre can be
enhanced dramatically, simply by changing the oxidation state of a ligand electronically
connected to Rh. Thanks to this stepwise process and to the irreversible character of the
reaction, it even becomes possible to use AgBF , a very common and convenient oxidant
4
which is too weak to operate in acetonitrile.
3
. Hydrosilylation catalysis
III
Rhodium(III) complexes, particularly half-sandwich Rh complexes, are catalysts of choice for
the functionalization of C -H bonds [36-38] and we recently showed the potential of
sp2
complex 3 for this type of reaction [21]. We envisioned that this system may also be suitable
for other types of catalytic reactions, such as the hydrosilylation of carbonyl compounds. We
previously described the use of complex 1 and its analogue bearing a norbornadiene ligand
in place of COD as catalysts for this reaction but both proved rather sluggish, probably due to
their high stability and the difficulty to remove the diene ligand [17].
Thus hydrosilylation of acetophenone and its derivatives were carried out with 1 mol% of
complex 1 or 3 in THF at room temperature (scheme 7, table 2). All reactions were stopped
after 17 h to allow for direct comparison of conversions.
Scheme 7, Table 2. Hydrosilylation of acetophenone derivatives.
Conversion (%) (b)
Entry
Substrate (R, R’)
Product
Complex 1
54 (1)
43 (4)
53 (3)
50 (0)
>99
Complex 3
85 (4)
88 (3)
90 (1)
78 (4)
>99
1
2
3
4
5
5a (H, Me)
5b (Me, Me)
5c (OMe, Me)
5d (F, Me)
6a
6b
6c
6d
6e
5e (H, CF3)
1
3

(
a) Reagents and conditions: acetophenone (1.0 equiv., 2M in THF), diphenylsilane (1.1
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
equiv.), Rh cat. (1mol%), rt, 17 h. (b) Average of two runs, with % difference between the two
runs in parentheses; conversion calculated by integration of characteristic H NMR signals of
acetophenone derivative and 1-phenylethanol derivative in the crude reaction mixture after
hydrolysis of the silyl ether.
1
As a general observation, the rhodium(III) complex 3 shows good activity for the
hydrosilylation of both electron-rich and electron-deficient acetophenones and is a better
catalyst than the rhodium(I) complex 1. The reaction of diphenylsilane with acetophenone
was followed by H NMR in d -THF. The conversion of acetophenone into the expected silyl
ether was plotted against time and the reaction profiles turned out surprisingly different for
1 and 3 (fig. 7) [39]. Comparison of the initial rates shows that the catalytic activity of 3 is 20
times greater than that of 1. For complex 1, the reaction follows a first order rate law,
whereas the data for 3 do not appear consistent with a simple rate law.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
1
8
Figure 7. Reaction of Ph SiH with acetophenone (1 mol% catalyst, d -THF, rt). Conversion (%) of
acetophenone vs. time, circles: complex 1; triangles: complex 3.
2
2
8
Conclusions
A new dicarbonyl rhodium(I) complex bearing an electroactive ferrocenyl phosphine-NHC
ligand has been synthesized and fully characterized. Its behaviour in the presence of a
chemical oxidant has been studied, proving that the electron density at the rhodium centre
could be tuned by oxidation of the ferrocenyl group on the bidentate ligand. This difference
has been highlighted by infra-red spectroscopic measurement of the CO stretching
frequencies. The dicarbonyl rhodium(I) complex has also shown an interesting reactivity in
acetonitrile which parallels that of the related COD complex 1, giving a stable rhodium(III)
1
4

complex after several oxidation-electron transfer processes and complete reorganisation of
the coordination sphere.
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
Acknowledgements
This work was supported by the Agence Nationale de la Recherche (ANR-07-JCJC-0041). We
are also grateful to the CNRS (Centre National de la Recherche Scientifique) for further
financial support.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
Appendix A. Supplementary Data
CCDC 986640 contains the supplementary crystallographic data for compound 2. This data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article: crystal data and refinement parameters for compound 2.
1
5

References
1. I.M. Lorkovic, M.S. Wrighton, W.M. Davis, J. Am. Chem. Soc., 116 (1994) 6220–6228.
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
2
. C.S. Slone, C.A. Mirkin, G.P.A. Yap, I.A. Guzei, A.L. Rheingold, J. Am. Chem. Soc., 119 (1997)
0743–10753.
1
3
. C.K.A. Gregson, V.C. Gibson, N.J. Long, E.L. Marshall, P.J. Oxford, A.J.P. White, J. Am. Chem.
Soc., 128 (2006) 7410–7411.
4. K. Arumugam, C.D. Varnado, S. Sproules, V.M. Lynch, C.W. Bielawski, Chem.-Eur. J., 19 (2013)
0866–10875.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
1
5
. C.D. Varnado, Jr, E.L. Rosen, M.S. Collins, V.M. Lynch, C.W. Bielawski, Dalton Trans., 42 (2013)
13251–13264.
6
7
. A.G. Tennyson, V.M. Lynch, C.W. Bielawski, J. Am. Chem. Soc., 132 (2010) 9420–9429.
. E.M. Broderick, N. Guo, T. Wu, C.S. Vogel, C. Xu, J. Sutter, J.T. Miller, K. Meyer, T. Cantat, P.L.
Diaconescu, Chem. Commun., 47 (2011) 9897–9899.
8
. E.M. Broderick, N. Guo, C.S. Vogel, C. Xu, J. Sutter, J.T. Miller, K. Meyer, P. Mehrkhodavandi,
P.L. Diaconescu, J. Am. Chem. Soc., 133 (2011) 9278–9281.
9
1
. M. Süßner, H. Plenio, Angewandte Chemie International Edition, 44 (2005) 6885–6888.
0. R. Savka, S. Foro, M. Gallei, M. Rehahn, H. Plenio, Chem.- Eur. J., 19 (2013) 10655–10662.
11. T.M. Miller, K.J. Ahmed, M.S. Wrighton, Inorg. Chem., 28 (1989) 2347–2355.
1
2. A.M. Allgeier, C.S. Slone, C.A. Mirkin, L.M. Liable-Sands, G.P.A. Yap, A.L. Rheingold, J. Am.
Chem. Soc., 119 (1997) 550–559.
13. I.V. Kourkine, C.S. Slone, C.A. Mirkin, L.M. Liable-Sands, A.L. Rheingold, Inorg. Chem., 38
1999) 2758–2759.
4. I.M. Lorkovic, R.R. Duff Jr., M.S. Wrighton, J. Am. Chem. Soc., 117 (1995) 3617–3618.
(
1
15. D.A. Weinberger, T.B. Higgins, C.A. Mirkin, L.M. Liable-Sands, A.L. Rheingold, Angew. Chem.
Int. Ed., 38 (1999) 2565–2568.
1
1
1
6. K.J. Blackmore, J.W. Ziller, A.F. Heyduk, Inorg. Chem., 44 (2005) 5559–5561.
7. A. Labande, J.-C. Daran, E. Manoury, R. Poli, Eur. J. Inorg. Chem., (2007) 1205–1209.
8. J. Wolf, A. Labande, J.-C. Daran, R. Poli, Eur. J. Inorg. Chem., (2007) 5069–5079.
19. N. Debono, A. Labande, E. Manoury, J.-C. Daran, R. Poli, Organometallics, 29 (2010) 1879–
882.
0. A. Labande, J.-C. Daran, N.J. Long, A.J.P. White, R. Poli, New J. Chem., 35 (2011) 2162–2168.
21. A. Labande, N. Debono, A. Sournia-Saquet, J.-C. Daran, R. Poli, Dalton Trans., 42 (2013) 6531–
537.
2. B. Boduszek, H. J. Shine, J. Org. Chem., 53 (1988), 5142-5143.
1
2
6
2
23. A. Altomare, M. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A. Guagliardi, A. Moliterni, G.
Polidori, R. Spagna, J. Appl. Cryst., 32 (1999) 115-119.
2
2
2
4. G. M. Sheldrick, Acta Cryst. A, 64 (2008) 112-122.
5. L. J. Farrugia, J. Appl. Cryst., 30 (1997) 565.
6. L.D. Field, B.A. Messerle, K.Q. Vuong, P. Turner, Organometallics, 24 (2005) 4241–4250.
27. L.D. Field, B.A. Messerle, K.Q. Vuong, P. Turner, Dalton Trans., (2009) 3599–3614.
8. S. Burling, L.D. Field, H.L. Li, B.A. Messerle, P. Turner, Eur. J. Inorg. Chem., 2003 (2003) 3179–
184.
29. C.H. Leung, C.D. Incarvito, R.H. Crabtree, Organometallics, 25 (2006) 6099–6107.
0. N.G. Connelly, W.E. Geiger, Chem. Rev., 96 (1996) 877–910.
2
3
3
1
6

3
3
1. The quality of AgBF is crucial since only traces of water lead to the reduction of ferrocenium.
4
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
2. H O reduces ferrocenium back to ferrocene in complex 1 but the nature of the oxidized
2
species was not investigated yet.
33. D.M. Khramov, E.L. Rosen, V.M. Lynch, C.W. Bielawski, Angew. Chem. Int. Ed., 47 (2008)
2
267–2270.
ox
3
3
4. 2 is very sensitive to moisture and turned rapidly from forest green to brown when exposed
to traces of water to give a complex mixture.
-1
5. The third band of medium intensity at 1997 cm may be attributed to the monocarbonyl
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
3
1
complex due to an incomplete reaction ( P NMR: >95% of dicarbonyl complex in this
sample).
3
3
3
3
6. D.A. Colby, R.G. Bergman, J.A. Ellman, Chem. Rev., 110 (2010) 624–655.
7. J. Wencel-Delord, T. Droge, F. Liu, F. Glorius, Chem. Soc. Rev., 40 (2011) 4740–4761.
8. G. Song, F. Wang, X. Li, Chem. Soc. Rev., 41 (2012) 3651–3678.
9. The amount of silyl enol ether by-product was neglected in the calculations since it
represents less than 1% of the total.
1
7

The behaviour of a new dicarbonyl rhodium(I) complex bearing an electroactive ferrocenyl
phosphine-NHC ligand towards oxidation has been studied, proving that the electron density
at the rhodium centre could be tuned by oxidation of the ferrocenyl group. This difference
has been highlighted by infra-red spectroscopic measurements.