Electron transfer behavior of pincer-type {RhNO}8 complexes: Spectroscopic characterization and reactivity of paramagnetic {RhNO}9 complexes

Article abstract of DOI:10.1021/om4008746

The electrochemistry of the {RhNO}⁸ complexes [Rh(PCP ^tBu)(NO)][BF₄] (1⁺), [Rh(PCP ^tBuCH₂)(NO)][BF₄] (2⁺), and Rh(PCP^tBu)(NO)Cl (3) was studied. Both four-coordinate complexes 1⁺ and 2⁺ exhibit a reversible reduction within the CH₂Cl₂ solvent window. Nevertheless, the chemical or electrochemical reduction of 1⁺ and 2⁺ in CH ₂Cl₂ led to the formation of the five-coordinate {RhNO}⁸ complexes 3 and Rh(PCP^tBuCH₂)(NO)Cl (4), respectively, through chloride abstraction from CH₂Cl ₂ by the one-electron-reduced {RhNO}⁹ species [Rh(PCP ^tBu)(NO)]^? (1^?) and [Rh(PCP ^tBuCH₂)(NO)]^? (2^?), as has been observed for many other 17-electron paramagnetic complexes. The new complex 4 was fully characterized by multinuclear NMR techniques, IR, X-ray diffraction, CV, UV-vis, and elemental analysis. On the other hand, the five-coordinate complexes 3 and 4 show only one irreversible oxidation in CH₂Cl₂ and two irreversible reductions in THF. The {RhNO}⁹ complex 1^? could be obtained quantitatively by one-electron reduction of 1⁺ with cobaltocene in nonchlorinated solvents and was characterized by IR, EPR, and ¹H NMR in solution. Activation of carbon-halogen bonds by complex 1^? was observed by studying the reactivity of 1^? with some aryl halides, giving in all cases the {RhNO}⁸ Rh(PCP^tBu)(NO)X (X = Cl ^-, 3, or X = I^-, 6) as the only rhodium complex, while a complex with coordination of the aryl moiety was not observed as a stable final product in any case. The fate of the aryl organic radicals could be determined in some cases. In addition, DFT calculations were performed to elucidate the electronic structure of 1^? and to support the observed reactivity.

Full text of DOI:10.1021/om4008746

Article
pubs.acs.org/Organometallics
8
Electron Transfer Behavior of Pincer-Type {RhNO} Complexes:
Spectroscopic Characterization and Reactivity of Paramagnetic
9
{
RhNO} Complexes
†
†
‡
,†
Juan Pellegrino, Carina Gaviglio, David Milstein, and Fabio Doctorovich*
†
́
Departamento de Química Inorganica, Analítica, y Química Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos
Aires, INQUIMAE-CONICET, Ciudad Universitaria, Pab. 2, C1428EHA, Buenos Aires, Argentina
‡
Department of Organic Chemistry and Department of Chemical Research Support, The Weizmann Institute of Science, Rehovot,
6100, Israel
7
*
S Supporting Information
8
ABSTRACT: The electrochemistry of the {RhNO} complexes
t
+
t
+
[
Rh(PCP Bu)(NO)][BF ] (1 ), [Rh(PCP BuCH )(NO)][BF ] (2 ),
4 2 4
t
and Rh(PCP Bu)(NO)Cl (3) was studied. Both four-coordinate
complexes 1 and 2+ exhibit a reversible reduction within the
CH Cl solvent window. Nevertheless, the chemical or electrochemical
reduction of 1 and 2 in CH Cl led to the formation of the five-
coordinate {RhNO} complexes 3 and Rh(PCP BuCH )(NO)Cl (4),
+
2
2
+
+
2
2
8
t
2
respectively, through chloride abstraction from CH Cl by the one-
2
2
9
t
•
•
electron-reduced {RhNO} species [Rh(PCP Bu)(NO)] (1 ) and
Rh(PCP BuCH )(NO)] (2 ), as has been observed for many other 17-electron paramagnetic complexes. The new complex 4
t
•
•
[
2
was fully characterized by multinuclear NMR techniques, IR, X-ray diffraction, CV, UV−vis, and elemental analysis. On the other
hand, the five-coordinate complexes 3 and 4 show only one irreversible oxidation in CH Cl and two irreversible reductions in
2
2
9
•
+
THF. The {RhNO} complex 1 could be obtained quantitatively by one-electron reduction of 1 with cobaltocene in
nonchlorinated solvents and was characterized by IR, EPR, and H NMR in solution. Activation of carbon−halogen bonds by
complex 1 was observed by studying the reactivity of 1 with some aryl halides, giving in all cases the {RhNO}
Rh(PCP Bu)(NO)X (X = Cl , 3, or X = I , 6) as the only rhodium complex, while a complex with coordination of the aryl
moiety was not observed as a stable final product in any case. The fate of the aryl organic radicals could be determined in some
cases. In addition, DFT calculations were performed to elucidate the electronic structure of 1 and to support the observed
1
•
•
8
t
−
−
•
reactivity.
INTRODUCTION
well-defined structure, and steric protection) with the non-
■
•
innocence of the NO ligand (electronic reservoir) in the
For many years, the chemistry of NO has been a topic of great
interest to inorganic chemists, and nitrosyl complexes have
experienced renewed attention since the discovery of the nitric
n
reactivity of {RhNO} complexes.
While there have been many reports on the structure,
reactivity, and redox interconversion for five- and six-coordinate
•
1
oxide radical NO as a physiologically essential agent. The rich
n
1,3
{
MNO}8 complexes (n = 6, 7, and 8),
square-planar
coordination chemistry of the “simple” NO ligand is based on
n
•
{MNO} complexes are rare. Only a few complexes with
iridium were reported many years ago, but their redox behavior
its redox activity, which gives rise to three limiting (M -NO ,
n+1
−
n−1
+
M
-NO , and M -NO ) and countless intermediate
1c,4
5
was not studied.
In a recent paper, we reported the
electronic states for metal nitrosyl complexes. In recognition
of the covalent nature of the M−NO bond, nitrosyl complexes
are described as {MNO} (regardless of the coligands), where n
synthesis of a family of {RhNO}8 pincer-type complexes
I
n
(square-planar four-coordinate, formally Rh , and square-
III
pyramidal five-coordinate, formally Rh complexes). Also
stands for the number of electrons in the metal d and π* NO
1
d
spectroscopic and structural characterization was presented,
and their reactivity was studied. Now we wish to focus on the
orbitals. On the other hand, complexes with pincer ligands
constitute an extensive family of compounds that have been
steadily attracting increasing interest in view of their important
8
electron transfer behavior of {RhNO} complexes to study the
n
2
electronic structure and the reactivity of {RhNO} pincer-type
roles in synthesis, bond activation, and catalysis. It has been
complexes with n ≠ 8, with special interest in paramagnetic
complexes. Since many years ago odd-electron complexes have
demonstrated that the superiority of pincer-complex catalysts
over the traditional ones is based on the high stability and well-
defined structure and stoichiometry of these species. So it
seems interesting to explore the possible “synergistic effect” of
the combination of robust bulky pincer ligands (high stability,
Received: August 30, 2013
Published: October 31, 2013
©
2013 American Chemical Society
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Organometallics
Article
attracted much attention for their use in organic trans-
formations, and there have been several reports on the role
resulting in C−X bond activation; this reactivity has been not
9
documented for the previously reported {RhNO} system.
7
of monomeric d 17-electron complexes in the activation of
6,7
carbon−halogen bonds. Also some C−H activation reactions
RESULTS AND DISCUSSION
■
(
8
have been observed for Rh(0) complexes.
8
Cyclic Voltammetry. The {RhNO} complex [Rh-
An interesting approach is the use of redox “noninnocent”
ligands as reservoirs of electrons for bond-making and bond-
breaking reactions at coordinatively unsaturated metals, with
the possibility to store electrons in the ligand, followed by
metal-centered reactions. For example, in 2006 Frech et al.
reported that the one-electron reduction product of the
t
+
PCP Bu)(NO)][BF ] (1 ) exhibits in CH Cl one accessible
4 2 2
redox process at E1/2 = −1.16 V within the solvent window
(
Figure 2a), which can be represented by eq 1.
t
+
−
t
•
[Rh(PCP Bu)(NO)] + e → [Rh(PCP Bu)(NO)]
+
•
1
1
i
rhodium(I) pincer naphthyl complex [(C H (CH P Pr ) )Rh-
1
0
5
2
2 2
E1/2 = −1.16 V
(1)
1
(
η -N )] shows metal-centered reactivity with water and benzyl
2
chloride, although EPR proved the unpaired electron to be
9
centered at the PCP ligand. More recently, Zhu et al. showed
that the formally Co(0) complex LCo(N ) (L = 2,6-bis(2,6-
2
dimethylphenyliminoethyl)pyridine) with a redox-active imi-
nopyridine ligand reacts with many alkyl and aryl halides RX,
including aryl chlorides, to give a mixture of LCoR and LCoX
(
binuclear oxidative addition) in a halogen atom abstraction
1
0
mechanism. So, it seems interesting to explore the one-
electron reduction products of {RhNO} complexes, which
8
would be isoelectronic with the formally Rh(0) and Co(0)
complexes mentioned above and could exhibit similar reactivity.
9
To our knowledge, very few {MNO} complexes were
n
previously reported, in contrast with the several {MNO}
systems reported for n = 4, 5, 6, 7, 8, and 10, with n = 9
1
being by far the number with fewer examples. Three of these
9
{
MNO} systems are cobalt complexes, and crystal structures
1
1−13
were reported,
while the other one is a rhodium complex
with an anionic PNP pincer ligand, much more related to our
system because of the metal and the similar ligand environ-
1
4
ment. Very recently, Wieghardt and co-workers could provide
a qualitative description of the Co−NO bonding in the four-
9
coordinate {CoNO} species Tp*Co(NO) (Tp* = hydrotris-
(
3,5-Me -pyrazolyl)borate): through a variety of spectroscopic
2
measurements and DFT calculations, they described it as a
Co(II) (SCo = 3/2) metal center, antiferromagnetically coupled
−
13
to a triplet NO anion (S = 1). On the other hand, the
NO
9
only {RhNO} complex reported, Rh(PNP)NO (PNP =
N( Bu PCH SiMe ) ), could not be isolated but was
characterized by IR, NMR, and EPR in solution, and a Rh NO
structure was supported by DFT calculations.
In this article we report the electron transfer behavior of the
t
2
2
2 2
I
•
14
+
+
Figure 2. Cyclic voltammograms of 1 (a) and 2 (b) in CH Cl /0.1
2
2
8
t
four-coordinate {RhNO} complexes [Rh(PCP Bu)(NO)]-
M Bu NPF .
4 6
+
t
+
[
BF ] (1 ) and [Rh(PCP BuCH )(NO)][BF ] (2 ) and the
4 2 4
8
t
five-coordinate {RhNO} complex Rh(PCP Bu)(NO)Cl (3)
8
t
The related {RhNO} complex [Rh(PCP BuCH )(NO)]-
4
(
Figure 1).
2
+
Both complexes 1+ and 2+ show accessible reduction
1/2
[
2
BF ] (2 ) shows a reversible reduction at E = −1.41 V (eq
), which is shifted by −250 mV from the corresponding value
potentials, thanks to the presence of the reducible NO moiety9,
+
of 1 (Figure 2b).
exhibiting a reversible one-electron reduction to a {RhNO}
9
•
species. The novel {RhNO} species 1 was well characterized
in solution and its reactivity with organic halides was studied,
t
+
−
•
[
Rh(PCP BuCH )(NO)] + e
2
+
2
t
→
[Rh(PCP BuCH )(NO)] E1/2 = −1.41 V
2
•
(2)
2
This similar response on electrochemical reduction was
expected since both complexes are four-coordinated mono-
cationic nitrosyl Rh(I) complexes, with very similar coligands:
t
+
t
+
phenyl PCP Bu for 1 and benzyl PCP BuCH for 2 .
2
+
The reduction process of complex 2 is less favorable than
that of 1 , consistent with the stronger donation of the benzilic
8
+
Figure 1. {RhNO} complexes used in this study.
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Organometallics
Article
moiety, as reflected also by its low-energy-shifted NO
−1
+
+
stretching frequency (1834 vs 1726 cm for 1 and 2 in
CH Cl , respectively). In contrast with the accessible one-
2
2
+
+
electron reduction of complexes 1 and 2 , the structurally
related Rh(I) complex Rh(PCP Bu)(CO) shows no reduc-
tion process in the whole broad window of the THF solvent, up
t
15
+
to −3.0 V, while complex 1 shows a second (irreversible) wave
+
at −2.49 V in that solvent (see CV of 1 in THF in the
Supporting Information, Figure S1). This proves the ability of
the NO ligand to access low oxidation states in these PCP
complexes.
In contrast with the reversible reductions observed for the
four-coordinate {RhNO} complexes 1+ and 2 , the five-
8
+
8
coordinate {RhNO} complex 3 shows only an irreversible
oxidation at 0.65 V in CH Cl and two irreversible reductions
2
2
at −2.14 and −2.52 V in THF (Figure 3, eqs 3−6).
t
−
t
−•
[
Rh(PCP Bu)(NO)Cl] + e → [Rh(PCP Bu)(NO)Cl]
−
•
3
3
E1/2 = −2.14 V
(3)
t
−•
t
•
−
[
Rh(PCP Bu)(NO)Cl] → [Rh(PCP Bu)(NO)] + Cl
−
•
•
3
1
(4)
t
•
−
t
−
[
Rh(PCP Bu)(NO)] + e → [Rh(PCP Bu)(NO)]
•
−
1
1
E1/2 = −2.52 V
(5)
t
−
t
+·
[
Rh(PCP Bu)(NO)Cl] − e → [Rh(PCP Bu)(NO)Cl]
+
•
3
3
Figure 3. Cyclic voltammogram of 3 in CH Cl (a) and THF (b)/0.1
2
2
M Bu NPF .
4
6
E1/2 = +0.65 V
(6)
The potential of the last reduction wave is almost identical to
+
that of the second wave of 1 in THF (Figure S1), suggesting
that the chloride ligand is lost after the first reduction of 3,
•
giving 1 , eqs 3−5. The irreversibility of the last reduction (eq
5
) could be due to loss of the NO and/or the PCP ligand. In
the case of the oxidation, the observation of the reduction wave
at −1.16 V of the couple 1 /1 when scanning the potential in
the reverse direction after having reached the oxidation
potential of 3 suggested that 1 is generated from 3 . Also
when the chemical or the electrochemical oxidation of 3 was
performed, the IR spectra (Figure S2) showed the appearance
of the νNO stretching frequency of 1 . These results suggest the
loss of chloride radical from 3 .
+
•
+
+•
+
+
•
Spectroelectrochemistry and Chemical Reduction of
+
+
Complexes 1 and 2 . The reversibility of the reduction wave
+
+
of complexes 1 and 2 in CH Cl solution inspired us to
2
2
explore the electrochemical reduction through IR spectroelec-
trochemistry, since the νNO stretching band is known to be very
sensitive to the oxidation state of this noninnocent ligand in
1
,3
Figure 4. IR spectral changes observed during the electrochemical
metal complexes.
+
The IR spectra obtained on electrochemical reduction of 1+
reduction of 1 in CH
2
Cl
2
/0.1 M Bu NPF .
4 6
are presented in Figure 4. The electrolytic reduction of the
+
•
monocation 1 in CH Cl /0.1 M Bu NPF is accompanied by a
reactive 17-electron species 1 , although stable on the CV scale,
could not be observed under these conditions, and complex 3 is
formed, probably by chloride abstraction from CH Cl .
2
2
4
6
1
2
1
09 cm− low-energy shift of the NO stretching band from
−
1
834 to 1625 cm (Figure 4). Surprisingly, despite the
2
2
reversibility under CV conditions, reversing the potential did
not result in the recovery of the starting material 1 . Moreover,
In order to confirm the formation of complex 3 by the
electrochemical reduction, the chemical reduction of complex
+
+
the νNO stretching band observed for the product is the same as
1 was tried in CH Cl . Considering the reversible reduction
2
2
t
+
that of the known complex Rh(PCP Bu)(NO)Cl (3), obtained
wave of 1 at E1 = −1.16 V, cobaltocene, Co(Cp) (Cp =
cyclopentadienyl) (E1/2 = −1.33 V), was chosen as the proper
/2
2
+
5
16
by reaction of 1 with chloride. Consequently, the expected
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Organometallics
Article
Scheme 1
Scheme 2
+
8
reducing agent. Reaction of 1 with 1 equiv of Co(Cp) in
square-pyramidal {MNO} complexes, as several reported five-
17
2
CH Cl resulted in quantitative formation of 3 and [Co(Cp) ]-
BF ], confirming the initial formation of the one-electron-
reduced {RhNO} species 1 (Scheme 1). The identity of 3 was
confirmed by P and H NMR, FTIR, and UV−vis. The UV−
vis spectra for complexes 1 , 2 , and 3, not previously reported,
are presented in the Supporting Information, Figure S3 and
Table S1. So, although the reduced species (1 ) is best
coordinate nitrosyl cobalt(III) complexes and the related five-
coordinate nitrosyl rhodium(III) complex 3. The assignment
of the band was confirmed by use of the N-labeled derivative
2
2
2
5
[
4
9
•
15
31
1
5
t
15
−1
Rh(PCP BuCH )( NO)Cl, with a frequency at 1572 cm .
2
5
+
+
These data are consistent with a bent RhNO moeity.
The molecular structure of 4 was confirmed by an X-ray
diffraction study of single crystals obtained by slow diffusion of
•
•
described as a Rh(I) with a reduced NO ligand (see below), it
shows similar reactivity to 17-electron metal-centered radi-
pentane into a concentrated solution of 4 in CH Cl at −30 °C
(Figure 5). Selective bond lengths and bond angles are given in
2 2
6
,7
cals,
as mentioned in the Introduction. However, one
important difference is that in our system the alkyl moiety
did not end coordinated to rhodium. The fate of the organic
•
radical (CH Cl ) was not determined in this experiment, but it
2
•
could be identified in the reaction between 1 and some aryl
halides (see below).
IR spectroelectrochemistry experiments of complex 2 show
the same results as complex 1 ; the reduced species 2 is not
+
+
•
+
stable in CH Cl . Chemical reduction of 2 allowed us to
2
2
t
isolate and fully characterize complex Rh(PCP BuCH )(NO)Cl
2
(
4).
Reaction of 2+ with CoCp * in CH Cl Solution.
2
2
2
Formation of 4. Considering the reduction potential of
complex 2 , Co(Cp*) (Cp* = 1,2,3,4,5-pentamethylcyclopen-
tadienyl) (E1/2 = −1.94 V) was chosen as the reducing agent.
Treatment of complex 2 with 1 equiv of Co(Cp*)2 in
+
2
16
+
dichloromethane solution resulted in quantitative formation of
Figure 5. ORTEP plot of complex 4 at the 50% probability level.
Hydrogen atoms are omitted for clarity.
4
as a single new product, also by chloride abstraction from
9
•
CH Cl by the one-electron-reduced {RhNO} species 2
2
2
(
Scheme 2).
The new complex 4 was fully characterized by multinuclear
NMR techniques, IR, X-ray diffraction, CV, UV−vis, and
Table 1. The rhodium atom is located in the center of a square
pyramid with a bent apical nitrosyl group occupying the
position trans to the empty coordination site and the Cl ligand
trans to the methylene carbon (C1), with a C(1)−Rh(1)−
Cl(1) angle of 176.39(11)°. Also, it is worth mentioning that
the coordinated methylene is tilted out of the plane, with a Rh−
3
1
1
elemental analysis. The P{ H} NMR spectrum of 4 (Figure
1
S4) exhibits a doublet at δ 117.7 with a J
of 176.7 Hz,
Rh,P
indicative of two chemically equivalent phosphorus nuclei
1
coordinated to rhodium (Figure S4). In the H NMR (Figure
5
S5), the methylene group of RhCH Ar gives rise to a triplet of
C1−C2 angle of 101.5(2)°. As in the case of complex 3, the
2
2
3
doublets positioned at 3.4 ppm ( J = 1.9 Hz, J = 7.0 Hz).
rhodium atom in complex 4 can be described as Rh(III) with a
Rh−N−O angle of 129.6(4)°, confirming the bent NO
character of the nitrosyl ligand, and a N−O bond distance of
1.175(6) Å, both in the range observed for complex 3
RH
PH
1
3
1
The methylene group appears in the C{ H} NMR as a
1
2
doublet of triplets at 13.4 ppm ( J = 16.8 Hz, J = 2.6 Hz).
RH
PH
1
5
In the N NMR (Figure S6), there is only one signal due to
the 15N-enriched nitrosyl complex 4, which appears at 831.4
ppm as a broad singlet, characteristic of a bound bent
5
(127.4(3)° and 1.184(4) Å, respectively).
The redox behavior of 4 was studied by cyclic voltammetry;
the five-coordinate {RhNO}8 complex 4 exhibits only an
irreversible oxidation at 0.65 V in CH Cl (Figure S8), at the
1
7,5
nitrosyl.
shows a signal characteristic of a nitrosyl ligand at 1605 cm
Figure S7), similar to the νNO stretching frequency of other
The IR spectrum obtained in the solid state
−1
2
2
(
same potential observed for complex 3. In order to compare,
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Organometallics
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Table 1. Selected Bond Lengths (Å) and Angles (deg) for 4
Scheme 3
Rh(1)−C(1)
C(1)−C(2)
Rh(1)−N(1)
N(1)−O(1)
Rh(1)−P(1)
Rh(1)−P(2)
2.090(4)
1.460(5)
1.890(4)
1.175(6)
2.4420(10)
2.4097(10)
C(2)−C(3)
C(3)−C(4)
C(4)−C(5)
C(5)−C(6)
C(6)−C(7)
C(7)−C(2)
Rh(1)−Cl(1)
Rh(1)−C(1)−C(2)
C(3)−C(2)−C(7)
C(4)−C(5)−C(6)
C(2)−C(3)−C(4)
C(3)−C(4)−C(5)
P(1)−Rh(1)−Cl(1)
P(2)−Rh(1)−Cl(1)
1.416(6)
1.397(6)
1.398(6)
1.387(6)
1.403(6)
1.411(6)
2.4615(10)
101.5(2)
120.3(4)
123.5(4)
119.2(4)
118.3(4)
97.85(3)
97.31(4)
−
37.2 (s, 1H) (Figure S9). The signals are quite broad, and the
Rh(1)−N(1)−O(1)
N(1)−Rh(1)−P(1)
N(1)−Rh(1)−P(2)
N(1)−Rh(1)−C(1)
P(2)−Rh(1)−P(1)
N(1)−Rh(1)−Cl(1)
C(1)−Rh(1)−Cl(1)
129.6(4)
1
31
103
partitions due to the H coupling with the nuclei P and Rh,
usually found in related diamagnetic complexes, are not
104.75(13)
105.06(12)
89.07(17)
145.18(4)
94.54(14)
176.39(11)
1
31
1
observed. Also consistent with H NMR, the P{ H} NMR
shows only very weak signals attributed to diamagnetic
byproducts, one of those identified as the known Rh(PCP Bu)-
t
18
(
N ) (5).
2
•
The IR spectrum of 1 in THF solution (Figure 6) exhibits a
−1
very strong band at 1614 cm , assigned, on the basis of its
the electrochemical data for all complexes is summarized in
Table 2, along with their νNO stretching frequencies. The
Table 2. Formal Electrode Potentials and νNO of the
8
{
RhNO} Complexes in CH Cl
2
2
a
νNO (cm−1
)
complex
E (ΔE); volts
1+
2+
3
−1.16 (0.072)
−1.41 (0.083)
+0.65
1834
1726
1625
1615
4
+0.65
a
E1/2 (ΔE) for reversible couples and Epa for irreversible processes.
8
striking result is that, while for the four-coordinate {RhNO}
+
+
complexes 1 and 2 there is an important difference in the
electronic structure between the phenyl and benzyl PCP
complexes, as concluded by the gap observed in E and νNO, for
8
•
the five-coordinate {RhNO} complexes 3 and 4 the difference
Figure 6. IR spectrum of 1 in THF.
is negligible. This is consistent with the description of the four-
I
+
coordinate complexes as Rh NO , with a dominant back-
donation of electron density from the metal center, very
influenced by the donor properties of the coligands. On the
other hand, the five-coordinate complexes are best described as
•
relative intensity and position, to the N−O stretching of 1 ,
while the strong ν of 5 at 2123 cm− is not observed,
1
N2
confirming it is a minor byproduct.
III
−
•
Rh NO , for which the back-donation is less important, and
accordingly the different donor properties of the phenyl and
benzyl ligands are not so relevant to the electronic structure.
The EPR spectrum of 1 in THF solution (Figure S10)
shows a signal at g = 2.0011, but the partition due to coupling
iso
14
15
with the9 N or N nucleus was not observed. The related
9
Stable {RhNO} Complex: Preparation and Character-
{RhNO} complex, Rh(PNP)NO, showed a triplet at g
=
iso
9
14
ization. We are interested in obtaining the {RhNO} complex
2.0064 with a hyperfine coupling constant Aiso = 13 G. The
absence of partition could indicate a lower localization of the
spin on NO for 1 , which is also consistent with the highly
shifted signals in the H NMR spectrum, in the range +24 to
•
1
to characterize its electronic structure and explore its
•
reactivity with other organic halides. As stated in the
n
1
Introduction, {MNO} complexes with n = 9 are rare. The
9
only square-planar {RhNO} complex previously reported,
−37 ppm.
However, the large change of 220 cm− in the ν observed
1
Rh(PNP)NO, was obtained by reaction of a convenient
NO
•
8→9
+
•
precursor with NO , but its reactivity with organic halides
upon the {RhNO}
conversion from 1 to 1 (1834 to 1614
cm ) suggests a highly NO-centered reduction, converting a
−1
was not studied.
Since the reduction of 1 in CH Cl led to the fast and
+
8
I
+
9
{RhNO} complex described mainly as Rh NO to a {RhNO}
2
2
I
•
quantitative formation of 3, without observing the intermediate
species with a predominant Rh NO character, in marked
9
•
II
−
{
RhNO} complex 1 , we decided to explore the reduction in
contrast with the Co NO formulation found for Tp*Co-
13
•
•
nonchlorinated solvents. 1 was obtained in nearly quantitative
yield when THF or benzene was added to a mixture of 1 and
(NO). This distinct description for 1 as compared to
Tp*Co(NO) was expected, given the different series of the
transition metal center and the very different nature of the
tridentate ligands Tp* and PCP.
+
Co(Cp) , both in solid form, under argon (Scheme 3),
2
obtaining a very intense brown solution and a yellow precipitate
+
−
of [Co(Cp) ] [BF ] within a few minutes.
The predominant participation of the NO orbitals in the
2
4
•
8→9
+
•
The paramagnetic nature of 1 was immediately apparent
from the H NMR of the supernatant, with broad resonances
{RhNO}
conversion from 1 to 1 is similar to what has
1
6→7
been found in the {MNO}
one-electron conversion for
II
occurring at δ 24.3 (s, 4H), 3.0 (s, 36H), −11.1 (s, 6H), and
many different systems (five- or six-coordinate), with M = Fe ,
6
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Organometallics
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II
II
III 1b,3
•
Ru , Os , and Ir . This suggests that the NO ligand in five-
of 1 have a very important contribution of the π* NO orbital,
6
or six-coordinate {MNO} and in the square-planar four-
which suggests a highly NO-centered reduction. Consistent
with this, DFT calculations predict a 148 cm decrease of ν
8
+
−1
coordinate {RhNO} complexes (such as 1 ) has similar
NO
electron density, and both systems are best described as NO+
+
•
−1
for the reduction of 1 to 1 (from 1816 to 1668 cm ), a
rather lower shift than the 220 cm− decrease observed in the
experiment. However, DFT functionals usually tend to
overestimate the electronic density delocalization, thus
predicting a smaller ΔνNO for the electron transfer process, as
have been already observed previously for calculations in other
1
complexes, reflected in the high stretching ν frequencies in
the range 1800−1950 cm and the linear M−N−O angle
found for these systems.
the rather low Rh−N−O angle of 159.9° are due to strong
sigma-donation by the aryl ring, as discussed previously. On
the other hand, the unpaired electron in both reduced species
NO
−1
1
,3,5
+
The relatively low ν of 1 and
NO
5,19
20
nitrosyl complexes. So, the IR results along with the DFT
7
9
I
•
•
{
MNO} and {RhNO} is partially located on the NO ligand,
calculations support a predominant Rh NO description for 1 ,
also in agreement with the calculated spin densities of 0.16 on
Rh, 0.47 on N, and 0.27 on O.
The optimized structure of 1 is shown in Figure 8, while
relevant bond distances and angles, compared to those of 1 ,
•
yielding NO complexes, with ν in the range 1600−1700
NO
−
1
1,3
cm and M−N−O angles between 140° and 150° (see the
9
•
•
DFT-optimized structure for the {RhNO} complex 1 below).
+
7
However, there are no reports on {MNO} complexes
describing halogen−carbon activation reactivity, in contrast to
9
•
what we have found for the {RhNO} species 1 .
•
Reactivity of 1 toward RX Compounds. With the aim
to explore the activation of carbon−halogen bonds, the reaction
•
•
of 1 with some aryl halides was studied. The reactions of 1
with iodobenzene, 2-iodofluorobenzene, CH Cl , and 4-chloro-
2
2
α,α,α-trifluorotoluene, were performed in benzene or toluene.
•
When the reaction of 1 with iodobenzene was performed in
t
toluene, almost quantitative conversion to Rh(PCP Bu)(NO)I
3
1
1
(
6) was observed after some minutes, as judged by P{ H}
•
NMR. In the case of the reaction of 1 with 2-
iodofluorobenzene in benzene, quantitative conversion to 6
was observed within minutes, while the product 2-fluorobi-
1
9
phenyl was detected by F NMR (Figure S12) and GC-MS.
The identity of 6 was also confirmed by its independent
+
preparation from 1 and KI (see the Supporting Information).
•
In the case of the reaction of 1 with CH Cl in toluene, also
2
2
•
Figure 8. DFT-optimized structure of 1 (hydrogen atoms are omitted
for clarity).
quantitative conversion to 3 was observed within hours, as
judged by 31P{ H} NMR.
1
•
When the reaction of 1 with 4-chloro-α,α,α-trifluorotoluene
was performed in benzene, quantitative conversion of 1 to 3
•
was observed within hours (Figure S11), but no new signal
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Calculated Structures of 1 and 1
19
appeared in the F NMR, probably due to a similar shift of the
substrate 4-chloro-α,α,α-trifluorotoluene and the possible
products such as 4-trifluoromethylbiphenyl. Fortunately the
product 4-trifluoromethylbiphenyl could be identified by GC-
MS.
+
•
1+
a
1•
d(Rh−Cipso)
d(Rh−N)
d(N−O)
2.072 (2.085)
1.812 (1.763)
1.175 (1.175)
2.102
1.902
1.205
148.8
•
8
t
The conversion of 1 to {RhNO} Rh(PCP Bu)(NO)X (X =
−
−
Cl , 3, or X = I , 6) as the only rhodium complex was observed
in all cases, while a complex with coordination of the aryl
moiety was not observed as a stable final product in any case.
DFT Calculations. Density functional theory calculations
were performed to obtain more insight into the electronic
structure of the {RhNO} 1 and to support the proposed
reactivity of 1 and 2 with organic halides.
Figure 7 shows the HOMO and LUMO of 1 and the
∠
Rh−N−O
154.5 (159.9)
5
a
Experimental values in parentheses.
9
•
are given in Table 3. The lengthening of the Rh−N and N−O
distances and the decreasing of the Rh−N−O angle upon the
•
•
{RhNO}8
→9
conversion from 1+ to 1 (Table 3) are
•
+
6→7
•
+
reminiscent of what is typically observed for the {MNO}
conversion of previously reported systems, reflecting a high
degree of NO reduction.
SOMO of 1 . As can be seen, the LUMO of 1 and the SOMO
1
,3
It has been proposed previously that the initial step for the
reaction of a 17-electron paramagnetic complex with organic
6
a,b,7,10
halides is halogen abstraction,
and we propose the same
•
•
for 1 and 2 . As a difference from previously reported systems,
•
•
the reactions of 1 and 2 with CH Cl give exclusively the five-
2
2
coordinate complexes with Cl− as a fifth ligand, and the
−
complex with the alkyl fragment, i.e., CH Cl , is not observed.
2
The following sequence of reactions is proposed to explain the
observed reactivity for 1 and 2 , represented as Rh(L)(NO)
+
•
•
•
•
Figure 7. Frontier orbitals of 1 and 1 .
6
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Organometallics
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t
t
(
L as a generic representation of PCP Bu and PCP BuCH ),
Table 5. Calculated Energies (kcal/mol) for the Reactions of
1 with Aryl Halides
2
•
supported by DFT calculations (Table 4).
•
•
Rh(L)(NO) + CH Cl → Rh(L)(NO)Cl + CH Cl
RX
chlorobenzene
H
K
L
2
2
2
(
A)
+20
+6
−25
−39
−39
−46
−27
−53
−67
−67
−63
−53
•
bromobenzene
iodobenzene
2
CH Cl → ClCH CH Cl
(B)
(C)
2
2
2
+6
•
•
2
4
-iodofluorobenzene
+6
Rh(L)(NO) + CH Cl → Rh(L)(NO)CH Cl
2
2
-chloro-α,α,α-trifluorotoluene
+20
2
Rh(L)(NO)CH Cl → 2Rh(L)(NO)Cl + CH CH
2
2
2
(
D)
•
2
Rh(L)(NO)CH Cl → 2Rh(L)(NO)H + ClCHCHCl
2
with the quantitative conversion of 1 to the five-coordinate
t
(E)
Rh(PCP Bu)(NO)X, with X = Cl or I, observed in the reaction
•
of 1 with aryl halides.
•
2A + B = 2Rh(L)(NO) + 2CH Cl
2
2
As the expected coupling products dichloroethane
(
ClCH CH Cl) and (Aryl) were not detected in the reactions
→
2Rh(L)(NO)Cl + ClCH CH Cl
(F)
2 2 2
2
2
•
of 1 with CH Cl and aryl halides, respectively, we can
2
2
•
conclude that the thermodynamically feasible reactions B and I
do not compete favorably with other faster reactions of the
initially generated alkyl and aryl radicals. One of such reactions
could involve the solvent, giving the 4-trifluoromethylbiphenyl
and 2-fluorobiphenyl products, observed in the reactions of 1
with 4-chloro-α,α,α-trifluorotoluene and 2-iodofluorobenzene
A + C = 2Rh(L)(NO) + CH Cl
2
2
→
Rh(L)(NO)Cl + Rh(L)(NO)CH Cl
(G)
2
•
Table 4. Calculated Energies (kcal/mol) for Reactions A and
D−G
in benzene, respectively. The attack of an aryl radical to
benzene has been already proposed in the literature. Also, it is
1•
2•
21
A
F
+4
+9
possible that the five-coordinate complexes Rh(L)(NO)CH Cl
2
t
−83
−32
−67
+16
−37
−23
−69
−4
and Rh(PCP Bu)(NO)Aryl are never formed due to the fast
•
•
G
D
E
reaction of the CH Cl and Aryl radicals with the solvent.
2
CONCLUSIONS
■
8
The electron transfer behavior of pincer-type {RhNO}
complexes was studied. The five-coordinate complex 3 shows
As can be seen, the DFT calculations predict a favorable
chloride abstraction from dichloromethane for both 1 and 2
entries 1, 2, and 3 in Table 4). The low stability of the five-
coordinate alkyl complex (not observed) is also well
reproduced, since if it is transiently formed, it will decompose,
giving the five-coordinated chloride complexes (the only
products observed) (entries 4 and 5 in Table 4). The calculated
energies for reactions D and E are also consistent with the
absence of a five-coordinated hydride complex (not observed)
as a final stable product.
•
•
only irreversible processes due to loss of chloride, while the
(
+
+
four-coordinate complexes 1 and 2 exhibit reversible one-
8
→9
electron reductions in CH Cl . While these {RhNO}
2
2
conversions are reversible under the cyclic voltammetry+
conditions, the electrochemical or chemical reduction of 1
+
9
and 2 in CH Cl did not yield the paramagnetic {RhNO}
2
2
•
•
complexes 1 and 2 , but the diamagnetic five-coordinate
RhNO} complexes 3 and 4, by reaction with CH Cl . The
halogen−carbon bond activation reactivity of complex 1 was
not limited only to its reaction with CH Cl . Complex 1 ,
obtained by reduction of 1 with cobaltocene in nonchlorinated
solvents, also reacted with other organic halides, including aryl
chlorides, added in slight excess (no more than 5 equivalents).
In the absence of halogenated substrates, 1 is stable enough to
be well characterized in solution. The −220 cm shift observed
for the ν upon the {RhNO}
8
{
2 2
•
•
DFT calculations also predict favorable reactions of 1 with
aryl halides as concluded by the calculated energies for
reactions H, K, and L for different aryl halides (Table 5).
•
2
2
+
t
•
t
•
[
Rh(PCP Bu)(NO)] + RX → Rh(PCP Bu)(NO)X + R
·
•
(
H)
−1
8→9
2
R• → R
(I)
(J)
conversion is indicative of a
2
NO
highly NO-centered reduction, similar to what was previously
observed for the {MNO}6 conversion for many five- or six-
coordinate complexes. This, along with the DFT calculations,
t
•
•
t
→7
[
Rh(PCP Bu)(NO)] + R → Rh(PCP Bu)(NO)R
t
•
I
•
•
H + J = 2[Rh(PCP Bu)(NO)] + RX
supports a predominant Rh NO description for 1 . The odd
·
•
electron in 1 is highly located on the NO ligand, as has been
found for many five- or six-coordinate {MNO} complexes,
t
t
→
Rh(PCP Bu)(NO)X + Rh(PCP Bu)(NO)R
7
−1
(
K)
which show νNO in the range 1600−1700 cm , matching well
−
1
•
t
with the value of 1614 cm found for 1 . However, the metal-
H − J + I = Rh(PCP Bu)(NO)R + RX
•
centered reactivity found for 1 , i.e., its reaction with organic
halides, has not been documented for the {MNO} systems or
for the few {MNO} systems previously reported. Studies on
the redox behavior of four-coordinate {RhNO} complexes
·
7
t
→
Rh(PCP Bu)(NO)X + R2
(L)
9
8
As can be observed, DFT calculations predict that reaction L
is favorable in all cases, supporting the instability of the five-
coordinate aryl complexes Rh(PCP Bu)(NO)R, in agreement
with other pincer ligands with different electronic and steric
properties are under way.
t
6
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Organometallics
Article
of 4 as a single product. After solvent evaporation it was redisolved in
toluene. After filtration and evaporation of the solvent the new
complex 4 was obtained in nearly quantitative yield. Single crystals
suitable for X-ray diffraction were obtained by crystallization from a
concentrated solution of 4 in dichloromethane at −30 °C.
EXPERIMENTAL SECTION
■
1
. Syntheses. All experiments with metal complexes and
phosphine ligands were carried out under an atmosphere of purified
nitrogen in an MBraun glovebox or using standard Schlenk techniques
under an argon atmosphere. All solvents were analytical grade or
better. CH Cl was distilled over calcium hydride under nitrogen. All
31
1
1
Characterization of 4. P{ H} NMR (CD Cl ): 117.70 (d, J
=
=
2
2
RhP
1
3
2
2
1
76.7 Hz). H NMR (CD Cl ): 6.53 (s, 1H, Rh-Ar), 3.42 (vdt, J
2 2 PH
other nondeuterated solvents were refluxed over sodium/benzophe-
none ketyl and distilled under nitrogen. Deuterated solvents were
dried over 3 Å molecular sieves. Commercially available reagents were
used as received, except for CoCp and CoCp *, which were purified
2
7
.0 Hz, J
= 1.9 Hz, 2H, Ar-CH -Rh), 3.35 (dq, left part of ABq,
JHH = 14.7 Hz, 2H, Ar-CH -P), 3.11 (br d, right part of ABq, J
4.8 Hz, 2H, Ar-CH -P), 2.27 (s, 6H, 2 Ar-CH ), 1.26 (vt, J = 5.9
Hz, 18H, 2 (CH ) C-P), 1.23 (br s, 18H, 2 (CH ) C-P). C{ H}
RhH 2
2
2
=
HH
2
3
1
2
3
PH
13
2
2
1
3
3
3 3
by sublimation. 4-Chloro-α,α,α-trifluorotoluene, iodobenzene, and 2-
iodofluorobenzene were stored over 3 Å molecular sieves. [Rh-
3
NMR (CD Cl ): 143.67 (br s, Rh-Ar), 132.22 (vt, J = 2.1 Hz, Rh-
2
2
PC
Ar), 131.52 (s, Rh-Ar), 126.90 (s, Rh-Ar), 38.87 (br s, (CH ) C-P),
t
t
3 3
(
(
PCP Bu)(NO)][BF ], [Rh(PCP BuCH )(NO)][BF ], and Rh-
1
2
4
2
4
3
(
8.26 (vt, J = 2.8 Hz, (CH ) C-P), 30.94 (vt, JPC = 1.7 Hz,
t
5
PC 3 3
PCP Bu)(NO)(Cl) were prepared as described in a previous work,
2
1
CH ) C-P), 29.40 (vt, J = 1.8 Hz, (CH ) C-P), 20.20 (vt, J
=
PC
t
3
3
PC
3
3
with some minor modifications as follows: [Rh(PCP Bu)(NO)][BF ]
was prepared in toluene instead of dioxane, and [Rh(PCP BuCH )-
1
4
6
.2 Hz, Ar-CH -P), 19.83 (s, CH -Ar), 13.39 (br dt, J
= 16.8 Hz,
t
2
3
RhC
2
2
13
1
JPC = 2.6 Hz, Ar-CH -Rh) (assignment of C{ H} NMR signals was
confirmed by C DEPT135). IR ν (solid state, cm ): 1605 (s, NO).
Anal. Calcd: C, 53.69; H, 8.18. Found: C, 53.77; H, 8.24.
2
(
NO)][BF ] was further purified by repeated recrystallizations from
4
13
−1
CH Cl −dioxane.
2
2
2
. Physical Measurements. Cyclic voltammetry was carried out
X-ray Structural Analysis of 4. Crystal Data: C H ClNOP Rh,
2
7
49
2
at a 100 mV/s scan rate in dry and deoxygenated CH Cl /0.1 M
2
2
3
red, plate, 0.60 × 0.40 × 0.30 mm , monoclinic; P 1 21/n 1; a =
0.4103(4) Å, b = 23.0450(7) Å, c = 12.0078(4) Å; β = 94.001(3)°,
from 25 degrees of data; T = 150(2) K; V = 2873.71(17) Å , Z = 4; fw
Bu NPF using a three-electrode configuration (glassy carbon or Pt
4
6
1
working electrode, Pt counter electrode, Pt wire pseudoreference
electrode) and a TEQ 03 potentiostat. The ferrocenium/ferrocene
3
3
−1
=
603.97; D = 1.396 g/cm ; μ = 0.819 mm . Data Collection and
+
/0
c
(
Fc ) couple served as an internal reference. All the potentials are
Processing: Oxford Gemini E CCD area detector diffractometer, Mo
Kα (λ = 0.71073 Å), graphite monochromator; −14 ≤ h ≤ 10, −27 ≤
k ≤ 30, −16 ≤ l ≤ 15, 23 053 reflections collected, 6736 independent
+
/0
expressed against Fc .The solutions were prepared under an
atmosphere of purified nitrogen or argon as described before at
concentrations of approximately 1 mM. UV−vis spectra were acquired
on a Hewlett-Packard HP8453 diode array spectrometer with 1 cm
reflections (R = 0.0281). For data collection, cell refinement, and
int
data reduction CrysAlisPro software was used. Absorption correction
was made by multiscan. Solution and Refinement: The structure was
solved by direct methods with SHELXS-97. Full-matrix least-squares
path length cells, under Ar or N , preparing the solutions in a drybox
2
or using standard Schlenk techniques. IR spectra were obtained using a
Nicolet Avatar FTIR spectrophotometer. Spectroelectrochemistry was
performed by use of an OTTLE cell, in dry and deoxygenated
2
refinement based on F with SHELXL-97; 302 parameters with 0
2
restraints, final R = 0.0531 (based on F ) for data with I > 2 σ(I), and
1
13
15
19
31
1
CH Cl /0.1 M Bu NPF . H, C, N, F, and P NMR spectra were
2
2
2
4
6
R = 0.0620 on 6736 reflections, goodness-of-fit on F = 1.044, largest
1
1
recorded using a Bruker 500 MHz NMR spectrometer. H and
−3
electron density peak = 4.231 e Å .
1
3
1
C{ H} NMR chemical shifts are reported in ppm downfield from
t
15
+
Reaction of [Rh(PCP BuCH )( NO)][BF ] (2 ) with CoCp * in
CH Cl Solution. Formation of Rh(PCP Bu)(CH )( NO)Cl (4). It was
prepared as described above, using NOBF .
Characterization of N-Labeled 4. N NMR (CD Cl ): 831.38
1
2
4
2
tetramethylsilane. H NMR chemical shifts were referenced to the
t
15
2
2
2
2
3
residual hydrogen signal of the deuterated solvent (7.15 ppm, benzene;
15
4
.32 ppm, dichloromethane). In 13C{ H} NMR measurements the
1
5
15
15
2
2
signals of deuterated benzene (128.0 ppm) or deuterated dichloro-
methane (53.8 ppm) were used as a reference. 31P NMR chemical
shifts were reported in ppm downfield from H PO and referenced to
−1
15
(
br s). IR ν (solid state; cm ): 1572 (s, NO).
t
+
Reaction of [Rh(PCP Bu)(NO)][BF ] (1 ) with CoCp in Non-
4
2
t
•
•
3
4
chlorinated Solvents. Formation of [Rh(PCP Bu)(NO)] (1 ). THF or
benzene (0.85 mL), deaerated through several freeze−pump−thaw
1
5
an external 85% solution of phosphoric acid in D O. N NMR
2
+
chemical shifts were reported in ppm relative to liquid ammonia.
Abbreviations used in the description of NMR data are as follows: br,
broad; s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; v,
virtual. EPR measurements were recorded on a Bruker EMX Plus
spectrometer. Elemental analysis was performed in a Carlo Erba EA
108. GC-MS was measured in a Shimadzu, QP-5000.
. Computational Methodology. All calculations were carried
cycles and argon refilling, was added to a mixture of 1 (12 mg, 0.019
mmol) and CoCp (3.6 mg, 0.019 mmol) under argon. Inmediately a
2
strong brown solution and a light brown precipitate were obtained.
1
19
The precipitate (identified as [CoCp ][BF ] by H and F NMR) was
2
4
separated by filtration. 31P{ H}, H NMR, IR, and EPR of the solution
1
1
•
1
indicate nearly quantitative formation of 1 .
•
1
3
Characterization of 1 . H NMR (THF): 24.32 (br s, 4H, 2 Ar-
2
2
out with the program package Gaussian03. The structures of all
molecules were fully geometry optimized at the DFT level, using the
PBE exchange−correlation functional. The LANL2DZ basis set and
pseudopotential were used for the rhodium atom. For the H, N, O, C,
P, and F atoms the 6-31G** basis set was used, while for Br and I
atoms the LANL2DZ basis set and pseudopotential were used. The
vibrational frequencies were calculated on optimized structures using
the same functional and basis set.
CH -P), 3.00 (br s, 36H, 4 (CH ) C-P)), −11.12 (br s, 6H, 2 Ar-
2
3 3
−1
CH ), −37.22 (br s, 1H, Rh-Ar). IR ν (in THF solution, cm ): 1614
3
(s, NO).
t
•
•
Reaction of [Rh(PCP Bu)(NO)] (1 ) with RX Halides in Benzene or
Toluene. Formation of Rh(PCP Bu)X(NO). Complex 1 was prepared
t
•
as previously described, and then the RX halide was added. The
1
19
31
reaction was followed in time by H, F, and P NMR. Also GC-MS
was used to identify the possible organic products.
t
+
t
+
Reaction of [Rh(PCP Bu)(NO)][BF ] (1 ) with CoCp in CH Cl
Reaction of [Rh(PCP Bu)(NO)][BF
4
] (1 ) with KI. Formation of
OH (0.5 mL) were
4
2
2
2
t
t
Solution. Formation of Rh(PCP Bu)(NO)Cl (3). Dichloromethane was
Rh(PCP Bu)(NO)I (6). CH
2
Cl
2
(1 mL) and CH
3
+
+
added to a mixture of solid 1 (8 mg, 0.012 mmol) and solid CoCp2
added to a mixture of 1 (8.5 mg, 0.013 mmol) and KI (3.5 mg, 0.021
mmol). A brown solution was obtained after some minutes’ stirring,
and through FTIR quantitative formation of 6 was observed. The
solvent was removed under vacuum, and the remaining solid was
extracted with benzene. The new compound 6 was quantitatively
obtained after solvent evaporation.
(
2.4 mg, 0.012 mmol). Immediately a brown solution and a yellow
precipitate were obtained. After filtration and evaporation of the
solvent the known complex 3 was obtained in nearly quantitative yield.
3
1
1
1
5
P{ H} and H NMR and IR were the same as reported before.
t
+
Reaction of [Rh(PCP BuCH )(NO)][BF ] (2 ) with CoCp * in
CH Cl Solution. Formation of Rh(PCP Bu)(CH )(NO)Cl (4). Dichloro-
2
4
2
t
31
1
): 75.40 (d, 1JRhP
): 6.66 (s, 1H, Rh-Ar), 3.14 (AB quartet,
-P), 2.19 (s, 6H, 2 Ar-CH ), 1.21 (vt, JPH
8.3 Hz, 18H, 2 (CH ) C-P), 1.19 (vt, J = 7.7 Hz, 18H, 2 (CH ) C-
Characterization of 6. P{ H} NMR (C
D
6
=
2
2
2
6
+
1
methane was added to a mixture of solid 2 (15 mg, 0.023 mmol) and
143.7 Hz). H NMR (C D
6 6
2
solid CoCp * (7.5 mg, 0.023 mmol). Immediately a reddish-brown
J
HH = 14.5 Hz, 4H, Ar-CH
2
3
=
2
31
1
solution was obtained. P{ H} NMR revealed quantitative formation
3
3
PH
3 3
6
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Organometallics
Article
P). 13C{ H} NMR (C D ): 169.98 (d, J = 40.2 Hz, Cipso, Rh-Ar),
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6
6
RhC
45.07 (vt, JPC = 7.9 Hz, Rh-Ar), 130.81 (vt, JPC = 8.4 Hz, Rh-Ar),
28.58 (s, Cpara,Rh-Ar), 37.34 (vt, JPC = 6.9 Hz, (CH ) C-P), 36.34 (vt,
JPC = 7.3 Hz, (CH ) C-P), 31.70 (vtd, J = 10.5 Hz, J = 2.0 Hz,
Ar-CH -P), 30.80 (vt, J = 2.2 Hz, (CH ) C-P), 28.86 (vt, J = 2.3
Hz, (CH ) C-P), 22.51 (s, CH -Ar) (assignment of C{ H} NMR
signals was confirmed by C DEPT135). IR ν (solid state; cm ):
616 (s, NO). Anal. Calcd: C, 47.65; H, 7.23. Found: C, 47.42; H,
1
3
3
2
II
3
3
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RhC
Os : (h) Singh, P.; Sarkar, B.; Sieger, M.; Niemeyer, M.; Fiedler, J.;
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ASSOCIATED CONTENT
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of 1 with 2-iodofluorobenzene; P{ H}, H, and C{ H}
spectra of 6; Cartesian coordinates from optimizations for all
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AUTHOR INFORMATION
■
Corresponding Author
*E-mail: doctorovich@qi.fcen.uba.ar.
Notes
(9) Frech, C. M.; Ben-David, Y.; Weiner, L.; Milstein, D. J. Am. Chem.
Soc. 2006, 128, 7128−7129.
The authors declare no competing financial interest.
(10) (a) Zhu, D.; Budzelaar, P. H. M. Organometallics 2010, 29,
ACKNOWLEDGMENTS
5759−5761. (b) Zhu, D.; Korobkov, I.; Budzelaar, P. H. M.
■
Organometallics 2012, 31, 3958−3971.
This work was financially supported by the University of
Buenos Aires (UBACYT X065), ANPCyT (PICT 2010-2497),
PME 01113, and CONICET. D.M. is the holder of the Israel
Matz Professorial Chair of Organic Chemistry. The OTTLE
cell was kindly provided by Prof. Dr. Wolfgang Kaim. We thank
Prof. Dr. Carlos Brondino for supporting EPR measurements.
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