Electromeric rhodium radical complexes

Article abstract of DOI:10.1002/anie.200903201

Chemical Equation Presented Radical changes: One single P-Rh-P angle determines whether the odd electron in the paramagnetic complex [Rh(trop₂PPh)(PPh₃)] is delocalized over the whole molecule (see picture, blue) or is localized on the P - Rh unit (red). The two energetically almost degenerate electromers exist in a fast equilibrium, and the red complex has the highest spin density at Rh of all low valent Rh complexes observed to date.

Full text of DOI:10.1002/anie.200903201

Angewandte
Chemie
DOI: 10.1002/anie.200903201
Electronic Structure
Electromeric Rhodium Radical Complexes**
Florian Frank Puschmann, Jeffrey Harmer, Daniel Stein, Heinz Rꢀegger, Bas de Bruin,* and
Hansjꢁrg Grꢀtzmacher*
Dedicated to Professor Martin Quack
Electromers are species with significantly different electronic
but only slightly different geometrical structures, whereby
each species corresponds to a local minimum on the energy
hypersurface.[1a–c] Although they have been discussed several
times in the literature, direct observation of “electroisom-
ers”—the synonyms “redox isomers” or “valence isomers”
are likewise used—is rare.[2] Paramagnetic transition-metal
complexes are ideally suited to the study of this phenomenon,
and the localization of the spin on either the metal MC(L) or
the ligand M+(LCÀ) can be characterized by EPR spectrosco-
py.[3] We report herein a striking example in which two
electromers of paramagnetic rhodium complexes coexist in a
À
À
rapid equilibrium and the distortion of only one P Rh P
angle results in a substantial redistribution of the spin density.
We previously reported paramagnetic [M(troppPh)2]0
complexes (Scheme 1; M = Rh, Ir),[4a–d] which exist as rapidly
exchanging trans/cis mixtures (kisom ꢀ 1 ꢀ 104 sÀ1) in solution.
Both isomers have tetrahedrally distorted structures and their
EPR spectra and consequently electronic structures are quite
similar. They are best described as strongly delocalized
organometallic radicals with less than 30% of the spin density
localized on the metal centers.[4e] We have now synthesized
the rhodium complexes 5a,b, which likewise contain two
olefin and two phosphane binding sites in mutual trans
positions, but the constraints within the ligand system do not
allow trans to cis isomerization.
Scheme 1. Synthesis of trop2PPh (2) and the Rh complexes 5a and 5b.
The syntheses of the ligand trop2PPh 2 and the deep red
complexes [Rh(trop2PPh)(PPh3)]+AÀ (5a: AÀ = PF6À, 5b:
AÀ = BArFÀ) are straightforward and proceed with excellent
yields as shown in Scheme 1 (trop = 5H-dibenzo[a,d]-cyclo-
hepten-5-yl). Exchange of the PF6À anion by the BArFÀ anion
(BArFÀ = tetrakis[(3,5-trifluoromethyl)phenyl]borate)[5]
enhances significantly the solubility of 5b (in diethyl ether,
THF, or toluene). The structures of the ligand 2 and complex
5a are shown in Figure 1.[6a,b] The rigid tripodal diolefin
phosphane 2 is preorganized for binding a transition-metal
[*] Dipl.-Chem. F. F. Puschmann, Dr. D. Stein, Dr. H. Rꢀegger,
Prof. Dr. H. Grꢀtzmacher
Department of Chemistry and Applied Biology
ETH-Hꢁnggerberg, 8093 Zꢀrich (Switzerland)
E-mail: gruetzmacher@inorg.chem.ethz.ch
À
ion in its cleft. Only a small rotation around the P Ctrop bonds
is necessary to convert 2 into the conformation it adopts in 5a,
explaining the high stability of this complex. As observed with
the related amino ligand trop2NH,[7] 5a shows a distorted
“sawhorse” (SH) type structure (a trigonal bipyramid with
Dr. B. de Bruin
Universiteit van Amsterdam, Faculty of Science
Van’t Hoff Institute for Molecular Sciences, Homogeneous and
Supramolecular Catalysis, Nieuwe Achtergracht 166
1018 WV Amsterdam (The Netherlands)
E-mail: b.debruin@uva.nl
one missing edge in the equatorial plane):[8] the P1 Rh P2
À
À
À
À
angle is 160.98 and the ct Rh1 ct angle is 134.88 (ct = cent-
=
roid of the coordinated C Ctrop bond). The NMR data for all
Dr. J. Harmer
Inorganic Chemistry, University of Oxford (UK)
these complexes indicate that Cs-symmetrical SH-type struc-
tures are retained in solution and that there are no significant
cation anion interactions (31P nuclei in trans positions,
inequivalent olefinic protons, superimposable data for 5a
and 5b).
[**] This work was supported by the Swiss National Science Foundation
(SNF), the Netherlands Organisation for Scientific Research (NWO-
CW), the European Research Council (ERC Starting Grant 202886),
the University of Amsterdam (UvA), and the ETH Zꢀrich.
À
A cyclic voltammogram of 5a in THF/1m nBu4N+PF6
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200903201.
shows two reversible waves at E18 = À1.339 V and E28 =
Angew. Chem. Int. Ed. 2010, 49, 385 –389
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
385

Communications
Figure 1. A) ORTEP plot (at 30% ellipsoid probability) showing the
structure of 2. Only one of the two crystallographically independent
molecules is shown. Hydrogen atoms are omitted for clarity. Selected
bond lengths [ꢂ] and angles [8] (bond length of the second molecule
=
=
are given in italics): C4 C5 1.338(3), 1.339(3), C19 C20 1.340(3),
1.343(3), S8(C-P-C) 300.7(2), 301.3(2). B) ORTEP plot (at 30% ellip-
soid probability) showing the structure of the cation of 5a·2CH2Cl2.
À
The PF6 anion, the CH2Cl2 solvent molecules, and hydrogen atoms
À
are omitted for clarity. Selected bond lengths [ꢂ] and angles [8]: Rh1
À
À
À
P1 2.231(1), Rh1 P2 2.359(1), Rh1 ct 2.099(3), Rh1 C4 2.194(3),
À
=
À
À
Rh1 C5 2.233(3), C4 C5 1.405(4), Rh1 C22 3.712(5), Rh1 C28
2.905(4), P1-Rh1-P2 160.9(1), ct-Rh1-ct’ 134.8(2), Rh1-P2-C22 124.9(3),
Rh1-P2-C28 87.0(2), S8(C-P1-C) 314.7(8), S8(C-P2-C) 317.2(7).
À1.965 V (vs. ferrocenium/ferrocene) for the redox couples
[Rh(trop2PPh)(PPh3)]+/[Rh(trop2PPh)(PPh3)]0 and [Rh-
(trop2PPh)(PPh3)]0/[Rh(trop2PPh)(PPh3)]À1, respectively.
Chemically, 5b can be reduced by one electron with
elemental sodium, sodium naphthalide, or [CoCp*2][9] (Cp* =
1,2,3,4,5-pentamethylcyclopentadienyl) in THF (Scheme 2).
The EPR spectrum of the X band (T= 120 K) and W band
(T= 20 K) of a frozen solution clearly supports two para-
magnetic rhodium complexes 6LC and 6MC (Figure 2A,B),
which were fully characterized by high-resolution pulse EPR
spectroscopy of the X, Q, and W bands (see the Supporting
Information for details).[10] In contrast to the cis/trans-[Rh-
(troppPh)2]C complexes (Scheme 1), which are highly persistent
Figure 2. A) X-band (9.5065 GHz) continuous wave (CW) EPR spec-
trum of a mixture of 6LC and 6MC measured at T=120 K in a toluene/
THF mixture. The upper trace (black, bold) displays the experimental
spectrum; the second trace (magenta) the simulated spectrum
comprising 0.87 6LC+0.13 6MC. The lower traces show the simulated
EPR spectra of the single components. B) W-band (94.2947 GHz) FID-
detected EPR spectrum measured at T=20 K in a toluene/THF
mixture. The g values of 6LC were resolved at this microwave frequency.
Isomer 6MC displays an axial spectrum with a resolved doublet from a
large 31P hyperfine interaction. C) X-band (9.4793 GHz) CW EPR
spectra of a mixture of 6LC and 6MC in THF recorded at T=190–340 K.
The simulated spectra describing the 6LCQ6MC ratios are displayed in
magenta. D) Van’t Hoff plot, ln(Keq) vs. 1/T, for the ratio Keq =6MC/6LC
from the simulation at each temperature in (C), used to evaluate the
thermodynamic stabilities. E) Computed structure of 6LC. Selected
À
À
À
bond lengths [ꢂ] and angles [8]: P1 Rh 2.259, P2 Rh 2.397, Rh ct1
À
2.114, Rh ct2 2.106, P1-Rh-P2 165.5, ct1-Rh-ct2 134.5. F) Computed
À
structure of 6MC. Selected bond lengths [ꢂ] and angles [8]: P1 Rh
À
À
À
2.257, P2 Rh 2.444, Rh ct1 2.097, Rh ct2 2.094, P1-Rh-P2 122.0, ct1-
Rh-ct2 131.2. G) Computed (b3-lyp, TZVP) spin density of 6LC.
H) Computed (b3-lyp, TZVP) spin density of 6MC.
Scheme 2. Reduction of 5b to give a mixture of 6LC and 6MC.
386
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Angewandte
Chemie
in solution, the radicals 6LC and 6MC react to give a mixture of
diamagnetic products.[11]
species are denoted as 6LCcal, 6L’Ccal, and 6MCcal, respectively.
The most- and least-stable isomers 6LCcal (Erel = 0.0 kJmolÀ1)
and 6L’Ccal (Erel = + 2.1 kcalmolÀ1), respectively, are rotamers
obtained by rotation of the PPh3 group (see the Supporting
Information). Both have structures closely related to that of
the cation of diamagnetic precursor 5a.
The EPR spectra of the X band of the deep brown
solutions in the temperature range 190–340 K are shown in
Figure 2C. The changes in the spectra are fully reversible and
indicate an equilibrium between two electronically different
species that rapidly exchange on the EPR time scale
(ca. 1 GHz).
The second most stable isomer 6MCcal is 2.0 kcalmolÀ1
higher in energy than 6LCcal and has a structure in which the
À
À
The exchange process in solution is fast on the EPR time
scale at all temperatures and only an averaged spectrum is
observed. Lowering the temperature shifts the fast equilibri-
um 6LCQ6MC strongly towards 6LC (the concentration of
isomer 6LC is approximately 66% at 340 K and 88% at
190 K). However, the very different electronic structure and
therefore markedly different g values and hyperfine couplings
of 6LC and 6MC render the averaged spectrum very sensitive to
its temperature-dependent ratio. This behaviour allowed us to
evaluate the equilibrium constant 6MC/6LC = Keq at each
temperature T through spectral simulation. The relative
thermodynamic stabilities were estimated through a Vanꢁt
Hoff plot (lnKeq vs. 1/T; Figure 2D). Accordingly, 6LC is more
stable than 6MC by DH8 = (À1.2 Æ 1) kcalmolÀ1 and DS8 =
(3.9 Æ 4) calmolÀ1 KÀ1. In agreement with the experimentally
observed fast exchange process, DFT computations based on
smaller models of 6LC and 6MC (see the Supporting Informa-
tion) reveal a small energy barrier (ca. 3 kcalmolÀ1).[12] Both
species are detected in frozen solution upon rapid freeze-
quenching with liquid nitrogen (i.e. under non-equilibrium
conditions).
P1 Rh P2 angle closes from 165.58 to 122.08. Concomitantly,
À
the distance of Rh to the PPh3 group becomes longer (Rh P2
in 6LCcal: 2.397 ꢂ; in 6MCcal: 2.444 ꢂ). This result points to a
shift of the electron density onto the metal on going from 6LC
to 6MC (see below). Structure 6MCcal approaches the extreme
À
À
case of a trigonal pyramid, in which the P Rh P angle would
be 908. This structural feature was recently observed for the
bistropsilyl complex [Rh(trop2SiMe)(PPh3)] for which we
assumed—because of the strong s-electron donation of the
silyl group—a strong contribution of the resonance form A
(Scheme 2) and enhanced electron density at the metal
center.[13] A more detailed interpretation of the different
electronic structures of 6LC and 6MC is given in the Supporting
Information.
The computed EPR parameters of the lowest energy
species 6LCcal fit best to the experimental values of the more
stable major isomer 6LC, whereas the computed data for the
somewhat higher energy species 6MCcal are in good accord
with the experimental values of the less abundant isomer 6MC
(Table 1). The experimental giso values of both isomers differ
significantly from ge = 2.0023 and indicate spin density at the
metal center. In 6MC, the larger anisotropy of the g tensor
(6LC: Dg = 0.043; 6MC: Dg = 0.101) shows that the spin density
is higher at the Rh center. Note the large difference of the
hyperfine couplings of the 31P nucleus of the trop2PPh ligand
in 6MC (APiso = (602 Æ 5) MHz) and 6LC (APiso = (53 Æ
8) MHz), which demonstrate the very different electronic
structure of both electromers. Our
To gain insight into the electronic structures of 6LC and
6MC, we performed DFT calculations with the complete
molecule [Rh(trop2PPh)(PPh3)]C. Table 1 lists the experimen-
tal and computed EPR data. Structure optimizations led to
three stable species, which are close in energy. On the basis of
comparison with the experimental data of 6LC and 6MC, these
DFT computations support this
Table 1: Experimental and DFT calculated (values in italics) g values, hyperfine coupling constants
(A [MHz]), and spin densities 1 of compounds 6LC and 6MC.[a]
picture. In 6LCcal, only 33% of the
spin density is located at Rh, 12%
at P1, and 9% at P2, with the
residual spin density delocalized
over the trop2PPh and PPh3
ligand. In 6MCcal, more than half
of the spin density [1(Rh) 58%] is
located at Rh. Another 28%
resides on P1 and only 14% is
delocalized over P2 [1(P2) 3%]
and the hydrocarbon framework.
Electromer 6LC is best described as
a strongly delocalized organome-
tallic radical, whereas 6MC should
be considered as a metallo radical
with a high localization of the spin
6LC (major species detected in the experimental EPR spectra)
exp
calcd
g
g
11 =2.063Æ1
11 =2.048
g
g
22 =2.043Æ1
22 =2.035
g
g
33 =2.020Æ1
33 =2.008
g
g
iso =2.042Æ1
iso =2.034
1
A11
A22
A33
Aiso
53
40
À32
+5
À10
À19
–
22Æ10
22Æ10
115Æ5
12.2%
–
9.0%
–
22
27
70
31P2 exp
calcd
À56Æ5
À7
À50Æ5
À3
10Æ15
+24
103Rh exp
calcd
17Æ5
+2
À17Æ10
À32Æ2
32.8%
À20
À39
6MC (minor species detected in the experimental EPR spectra)
exp.
calcd
g
g
11 =2.100Æ1
11 =2.084
g
g
22 =2.100Æ1
22 =2.078
g
g
33 =1.999Æ1
33 =1.999
g
g
iso =2.066Æ1
iso =2.054
1
A11
A22
A33
Aiso
602
506
–
31P1 exp
calcd
–
575Æ5
575Æ5
655Æ5
À
density in the Rh P1 bond.
28.2%
–
3.1%
–
457
459
601
31P2 exp
calcd
0 to À22
À30
In this report, we provide com-
pelling evidence for the existence
of interconverting and energeti-
cally almost degenerate organome-
tallic electromers, which could be
À35
24Æ2
26
À10
À25
103Rh exp
calcd
24Æ5
18
À38Æ2
3
58%
À41
1
[a] The signs of the experimental hyperfine couplings are assigned according to the DFT results.
Angew. Chem. Int. Ed. 2010, 49, 385 –389
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
387

Communications
de Meijere, J. Am. Chem. Soc. 2005, 127, 1983; c) B. Mꢃller, T.
Bally, F. Gerson, A. de Meijere, M. von Seebach, J. Am. Chem.
Soc. 2003, 125, 13776.
detected through the observation of the paramagnetic
rhodium complex [Rh(trop2PPh)(PPh3)]C by EPR spectrosco-
py under ambient conditions. It remains to be explored how
far the reactivity of the highly delocalized radical 6LC and the
metalloradical 6MC can be distinguished.
[2] The observation of two or more forms of electromers has been
especially achieved with complexes carrying “non-innocent”
ligands, such as the semiquinone/catecholate pair, which are
involved in intramolecular redox processes: Mz(sq·À)QMz+1
-
(cat2À): Reviews: a) E. Evangelio, D. Ruiz-Molina, Eur. J. Inorg.
Chem. 2005, 2957; b) P. Gꢃtlich, A. Dei, Angew. Chem. 1997,
109, 2852; Angew. Chem. Int. Ed. Engl. 1997, 36, 2734; c) for an
EPR study of paramagnetic Rh “redox isomers”, see: B. V.
Lebedev, N. N. Smirnova, G. A. Abakumov, V. K. Cherkasov,
M. P. Bubnov, J. Organomet. Chem. 1989, 485, 341; d) for
CuI(QCÀ)/CuII(Q2À) “redox isomers” (Q = quinone type ligand),
Experimental Section
All manipulations were performed under an inert atmosphere of
argon using standard Schlenk techniques. Selected analytical data are
given below (see the Supporting Information for more details).
trop2PPh (2): trop-Cl (8.20 g, 36 mmol) and phenylphosphane
(1.9 mL, 17.3 mmol) were dissolved in toluene (100 mL). 1,4-
Diazabicyclo[2.2.2]octane (dabco) (3.87 g, 34.5 mmol) dissolved in
toluene (200 mL) was added dropwise under vigorous stirring. The
mixture was heated at reflux for 2 h, and dabco hydrochloride was
filtered off while the mixture was still hot. The mixture was reduced in
volume to 30 mL under reduced pressure, and the product crystallized
within 12 h to give 7.11 g (14.5 mmol, 84%) of colorless microcrystals.
1H NMR (300 MHz, CD2Cl2, 298 K): d = 6.70 (br d, 3JHH = 11.7 Hz,
2H, Holefin), 6.60 (br d, 3JHH = 11.7 Hz, 2H, Holefin), 4.53 ppm (br d,
2JPH = 3.6 Hz, 2H, 2Hbenz); 13C{1H} NMR (75.5 MHz, CD2Cl2, 298 K):
d = 132.4 (d, 4JPC = 5.1 Hz, Colefin), 131.7 (d, 4JPC = 4.3 Hz, Colefin),
55.6 ppm (d, JPC = 26 Hz, Cbenz); 31P{1H} NMR (121.5 MHz, CD2Cl2,
238C): d = À7.0 ppm; m.p.: 218 Æ 28C.
ˇ
see: W. Kaim, M. Wanner, A. Knꢄdler, S. Zꢅlis, Inorg. Chim.
Acta 2002, 337, 163, and references therein; e) for Pd complexes
II
I
·
À =
À À
with benzonitroso ligands Pd (R N O)/Pd (R N O ), see:
G. M. Larin, T. A. Stromnova, S. T. Orlova, Russ. Chem. Bull.
Int. Ed. 2005, 54, 1798; f) for ligand-based “redox isomers”
ZnII(L2À)(L0)/ZnII(LCÀ)(LCÀ), see: P. Chaudhuri, M. Hess, K.
Hildenbrand, E. Bill, T. Weyhermꢃller, K. Wieghardt, Inorg.
Chem. 1999, 38, 2781 – 2790; g) for an unspecified example that
may involve a RhII(dbt)/RhI(dbtCÀ) equilibrium (dbt = o-diben-
zodithiolato), see: C. A. Ghilardi, F. Laschi, S. Midollini, A.
Orlandini, G. Scapacci, P. Zanello, J. Chem. Soc. Dalton Trans.
1995, 531; for computational analysis of the multistate epox-
idation of ethene by [FeIIIO(porC+)] and [FeIVO(por)] “electro-
mers” (por= porphyrin ligand), see: S. P. de Visser, F. Ogliaro,
N. Harris, S. Shaik, J. Am. Chem. Soc. 2001, 123, 3037.
[Rh(PPh3)(trop2PPh)]PF6 (5a): [Rh2(m-Cl)2(cod)2] (105 mg,
0.212 mmol; cod = 1,5-cyclooctadiene) and trop2PPh (221 mg,
0.45 mmol) were dissolved in THF (15 mL). After several minutes,
the solution changed color from yellow to orange and [Rh2(m-
Cl)2(trop2PPh)2]·1.5THF started to precipitate. After 1 day at T=
298 K, 271 mg (0.198 mmol, 94%) of the air stable product was
collected as an orange microcrystalline powder. This product was
dissolved in THF (40 mL) and heated at reflux for 12 h in the
presence of PPh3 (115 mg; 0.438 mmol) and TlPF6 (210 mg;
0.601 mmol). Subsequently, the solvent was removed under reduced
pressure, and the remaining red solid was treated with CH2Cl2
(150 mL). Insoluble material (TlCl) was filtered off over celite, and
the filtrate was reduced in volume to 15 mL and layered with diethyl
ether (50 mL) to give 400 mg (0.400 mmol, 100%) of 5a as air-stable
red microcrystals. 1H NMR (400 MHz, CD2Cl2, 298 K): d = 6.63 (ddd,
[3] For a Review covering Rh-, Ir-, Pd-, and Pt-based radicals, see:
B. de Bruin, D. G. H. Hetterscheid, A. J. J. Koekoek, H. Grꢃtz-
macher, Prog. Inorg. Chem. 2007, 55, Chapter 5.
[4] a) H. Schꢄnberg, S. Boulmaꢆz, M. Wꢄrle, L. Liesum, A.
Schweiger, H. Grꢃtzmacher, Angew. Chem. 1998, 110, 1492;
Angew. Chem. Int. Ed. Angew. Chem. Int. Ed. Engl. 1998, 37,
1423; b) H. Grꢃtzmacher, H. Schꢄnberg, S. Boulmaꢆz, M.
Mlakar, S. Deblon, S. Loss, M. Wꢄrle, Chem. Commun. 1998,
2623; c) S. Deblon, L. Liesum, J. Harmer, H. Schꢄnberg, A.
Schweiger, H. Grꢃtzmacher, Chem. Eur. J. 2002, 8, 601; d) F.
Breher, H. Rꢃegger, M. Mlakar, M. Rudolph, S. Deblon, S.
Boulmaꢆz, H. Schꢄnberg, J. Thomaier, H. Grꢃtzmacher, Chem.
Eur. J. 2004, 10, 641 – 653; e) B. de Bruin, J. C. Russcher, H.
Grꢃtzmacher, J. Organomet. Chem. 2007, 692, 3167.
3JHH = 8.8 Hz, 3JPH = 4.0 Hz, 3JPH = 4.0 Hz, 2H, Hol), 5.43 (ddd, 3JHH
=
8.8 Hz, 3JHP = 2.8 Hz, 3JHP = 2.8 Hz, 2H, Hol), 5.31 ppm (dd, JPH
=
2
14.6 Hz, 3JRhH = 7.6 Hz, 2Hbenz); 13C{1H} NMR (75.5 MHz, CD2Cl2,
[5] N. A. Yakelis, R. G. Bergman, Organometallics 2005, 24, 3579.
[6] Crystal structure data: a) trop2PPh (2): Colorless, air-sensitive
single crystals of 2 were obtained by slow diffusion of hexane
1
1
298 K): d = 90.3 (d, JRhC = 10.8 Hz, Col), 78.0 (d, JRhC = 4.8 Hz, Col),
49.6 ppm (d, 1JPC = 15.9 Hz, Cbenz); 31P{1H} NMR (121.5 MHz, CD2Cl2,
238C): d = 166.3 (dd, 1JRhP = 145.2 Hz, 2JPP = 327.6 Hz, trop2PPh), 24.4
(dd, 1JRhP = 107.0 Hz, 2JPP = 327.6 Hz, PPh3), À144.06 ppm (sept,
1JPF = 714.5 Hz, PF6). mp: 238 Æ 28C (decomposition); for a descrip-
tion of the anion exchange leading to 5b see the Supporting
Information.
ꢀ
into a THF solution of 2; C36H27P; triclinic; space group P1; a =
11.2327(5), b = 13.3384(6), c = 19.7300(9) ꢂ, a = 106.945(1), b =
99.145(1), g = 105.070(1)8; V= 2640.9(2) ꢂ3; Z = 4; 1calcd
=
1.234 gcmÀ3; crystal dimensions 0.52 ꢀ 0.47 ꢀ 0.22 mm3; diffrac-
tometer Bruker SMART Apex with CCD area detector; MoKa
radiation (0.71073 ꢂ), 298 K, 2Vmax = 54.208; 11483 reflections,
7889 independent (Rint = 0.0421); direct methods; empirical
absorption correction SADABS (ver. 2.03); refinement against
full matrix (versus F2) with SHELXTL (ver. 6.12) and SHELXL-
97; 667 parameters, R1 = 0.0410 and wR2 (all data) = 0.1053,
max./min. residual electron density 0.294/À0.221 eꢂÀ3. All non-
hydrogen atoms were refined anisotropically. The contribution
of the hydrogen atoms, in their calculated positions, was included
in the refinement using a riding model; b) [Rh(trop2PPh)-
(PPh3)]PF6·2CH2Cl2 (5a): red single crystals were obtained by
slow diffusion of hexane into a solution of 5a in CH2Cl2;
C56H46P3Cl4F6Rh; orthorhombic; space group Pnma; a =
23.914(10), b = 12.033(8), c = 12.070(5) ꢂ; V= 5205(4) ꢂ3; Z =
4; 1calcd = 1.494 gcmÀ3; crystal dimensions 0.42 ꢀ 0.31 ꢀ 0.29 mm3;
diffractometer Bruker SMART Apex with CCD area detector;
MoKa radiation (0.71073 ꢂ), 298 K, 2Vmax = 56.528; 6504 reflec-
Received: June 13, 2009
Revised: July 22, 2009
Published online: December 2, 2009
Keywords: EPR spectroscopy · radicals · redox chemistry ·
.
rhodium · valence isomerization
[1] a) We refer to the definition given by G. N. Lewis and G. T.
Seaborg who in 1939 defined the term “electromer” as two forms
of a molecule with the atoms in the same, or nearly the same,
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388
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Angewandte
Chemie
tions, 5455 independent (Rint = 0.0409); direct methods; refine-
ment against full matrix (versus F2) with SHELXTL (ver. 6.12)
and SHELXL-97; 337 parameters, R1 = 0.0486 and wR2 (all
data) = 0.1406, max./min. residual electron density 1.207/
À0.678 eꢂÀ3. All non-hydrogen atoms were refined anisotropi-
cally. The contribution of the hydrogen atoms, in their calculated
positions, was included in the refinement using a riding model.
CCDC 706734 (2) and 706733 (5a) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
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[11] These products and the mechanism leading to their formation is
currently under investigation and will be published elsewhere.
[12] For the real (nonsimplified) molecules, this barrier could be
somewhat higher because of steric reasons.
[7] a) P. Maire, T. Bꢃttner, F. Breher, P. Le Floch, H. Grꢃtzmacher,
Angew. Chem. 2005, 117, 6477; Angew. Chem. Int. Ed. 2005, 44,
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[8] The SH structure is proposed for the transient carbonyls
[M(CO)4] (M = Fe, Ru, Os): a) M. Poliakoff, J. J. Turner,
Angew. Chem. Int. Ed. 2010, 49, 385 –389
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