Synthesis of a rhodaazacyclopropane and characterization of its radical cation by EPR spectroscopy

Article abstract of DOI:10.1002/anie.200504382

(Chemical Equation Presented) Rh steps into the ring: The radical cation shown is best described as a rhodaazacyclopropane (A) rather than as a Rh ^I iminium ion complex (B). EPR and DFT data indicate that the delocalization of the unpaired electron into the ligand framework contributes to the stability of A (see plot of the singly occupied molecular orbital).

Full text of DOI:10.1002/anie.200504382

Angewandte
Chemie
Metallacycles
tropCl (Scheme 1). Subsequently, 1 was treated with [Rh2(m2-
Cl)2(cod)2] (cod = 1,5-cyclooctadiene) to yield [Rh2(m2-Cl)2-
(trop2NMe)2], which was treated with PPh3 to give [RhCl-
(trop2NMe)(PPh3)] (2). Addition of AgOTf (OTfꢀ =
CF3SO3ꢀ) led to the isolation of [Rh(trop2NMe)(PPh3)]OTf
(3) as red needles in 78% overall yield (for details, see the
Supporting Information). The 13C- and D3-labeled iodide
complexes [13C]5 and [D3]5 were prepared from the reactions
of the rhodium(i)amide 4[5] with 13CH3I and CD3I, respec-
tively. The NMR data indicate that 2 and 5 form trigonal
bipyramidal 18-electron complexes in CDCl3 solution with
DOI: 10.1002/anie.200504382
Synthesis of a Rhodaazacyclopropane and
Characterization of Its Radical Cation by EPR
Spectroscopy**
Pascal Maire, Anandaram Sreekanth, Torsten Büttner,
Jeffrey Harmer,* Igor Gromov, HeinzRüegger,
Frank Breher, Arthur Schweiger, and
Hansjörg Grützmacher*
=
the halide atoms and the C Ctrop units in the equatorial
Cyclopropane and its derivatives
(ER2)3 (E = C, Si, Ge, Sn), bicyclobu-
tanes, and other strained hydrocarbons
have remarkably low oxidation poten-
tials when compared to their unstrained
linear counterparts.[1–3] Can this prop-
erty be translated to transition-metal
complexes, such that small rings incor-
porating the transition metal lead to
more facile oxidation? With this ques-
tion in mind, we characterized a d8 Rh
complexthat has a metal center incor-
porated in a three-membered ring.
Furthermore, we report the results
from high-resolution pulse EPR spec-
troscopy, which, in combination with
density functional theory (DFT) calcu-
lations, allowed us to characterize in
detail the electronic structure of the
corresponding radical cation.
In analogy to the preparation of
trop2NH[4] (trop = tropylidenyl = 5H-
dibenzo[a,d]cyclohepten-5-yl), we pre-
pared the N-methyl derivative
Scheme 1. Synthesis of complexes 3, [13C]5, [D3]5, 6, [13C]6, [D2]6, and radical cations 6C+, [13C]6C+, and
[D2]6C+.
trop2NMe (1) from (Me3Si)2NMe and
positions. Complex 3 forms an ion pair in solution, such that
the OTfꢀ ion binds remotely from the metal in a pocket
between the NMe group and the benzylic protons of the
trop2NMe ligand.
[*] Dr. A. Sreekanth, Dr. J. Harmer, Dr. I. Gromov,
Prof. Dr. A. Schweiger[+]
An ion pair is also observed for 3 in the solid state, again
Laboratorium für Physikalische Chemie
Departement Chemie und Angewandte Biowissenschaften
ETH Zürich
8093 Zürich (Switzerland)
Fax: (+41)44-632-1021
with the OTfꢀ ion bound remotely from the metal center and
embedded between the arene groups of the tropylidenyl and
PPh3 ligands (Figure 1b).[6] The [Rh(trop2NMe)(PPh3)]+ ion
has an unusual “saw-horse” structure (Figure 1a) which is
nonplanar and resembles a trigonal bipyramid with one
equatorial ligand missing (selected bond lengths and angles
are listed in Table 1). Structures of this type have rarely been
observed for stable 16-electron complexes; some examples
include the neutral amide 4[5] and the Ru complexes
[Ru(CO)2L2] (I) and [Ru(CO)(NO)L2]+ (II; L =
PtBu2Me).[7] The N-Rh-P bond angle in 3 (158.2(1)8) and
the P-Ru-P bond angle in II (157.38) are slightly more acute
than the corresponding bond angles in the neutral complexes
4 (166.28) and I (165.68). The ct-Rh-ct angle (134.5(2)8; ct =
centroid of the coordinated double bond) is similar to the
corresponding angles in 4 and I (ca. 1358), but larger than that
E-mail: harmer@phys.chem.ethz.ch
Dr. P. Maire, Dr. T. Büttner, Dr. H. Rüegger, Dr. F. Breher,
Prof. Dr. H. Grützmacher
Laboratorium für Anorganische Chemie
Departement Chemie und Angewandte Biowissenschaften
ETH Zürich
8093 Zürich (Switzerland)
Fax: (+41)44-633-1418
E-mail: gruetzmacher@inorg.chem.ethz.ch
[+] Deceased on January 4, 2006
[**] This work was supported by the Swiss National Science Foundation.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3265

Communications
Figure 1. Structure of 3·3CH2Cl2. a) Thermal ellipsoids are set at 30%
Figure 2. Structure of 6·toluene. Thermal ellipsoids are set at 30%
probability. The toluene molecule and hydrogen atoms, apart from
those in the methylene bridge and at the olefinic carbon atoms, are
omitted for clarity. Selected bond lengths and angles are listed in
probability. The three CH2Cl2 molecules, the OTfꢀ counteranion, and
the hydrogen atoms, apart from those in the N-methyl group and at
the olefinic carbon atoms, are omitted for clarity. Selected bond
=
=
lengths and angles are listed in Table 1 (ct=centroids of the C Ctrop
Table 1 (ct=centroids of the C Ctrop units).
units). Additional angles [8]: C100-P1-C100’ 102.4(3), C200-P1-C100/
100’ 108.0(2), Rh-P1-C100/100’ 124.4(1). b) Space-filling model of 3
showing the position of the anion.
in the nitrosyl complex II (1208). The small Rh1-P1-C200
angle (86.1(2)8) and relatively short Rh···C200 distance (2.80
vs. > 3.6 Š for the other Rh···Cphenyl distances) in 3 are
especially noteworthy and indicate a hyperconjugative inter-
ꢀ
action between the P C bond and the metal center.
The triflate complex 3 reacts cleanly with KOtBu to give
complex 6. The compounds [13C]6 and [D2]6, in which the N-
methylene group is 13C- and D-labeled, were obtained from
the respective iodide complexes [13C]5 and [D3]5. The result
of an X-ray structure analysis on orange crystals of 6 is shown
in Figure 2; selected bond lengths and angles are given in
Table 1.
Interactions between a metal M and an unsaturated ligand
X Y can be considered with regard to the limiting cases
Scheme 2. Selected resonance structures for 6 and 6C+.
=
represented by the heterocyclic metallacyclopropane form
=
(type A, Scheme 2) and a X Y!M donor–acceptor complex
(type B).[8] Complex 6 can be described either as a rhoda-
azacyclopropane 6A or a rhodium iminium ion complex 6B.
In the first case, the Rh center has a formal oxidation state of
+ 1, and in the latter case a formal oxidation state of ꢀ1.
the rhodaazacyclopropane description 6A, which is expected
ꢀ
in view of the energetically low-lying p* orbital of the N C
bond and the consequently strong metal-to-ligand back
ꢀ
donation. N C bond lengths similar to that in 6 have been
ꢀ
The Rh N bond in 6 (2.059(3) Š) is shorter than in 3
observed in the few comparable metalla-aza-cyclopro-
(2.131(5) Š). Also, the N CH2 bond in 6 (1.446(5) Š) is
panes.[11] The large change in the 13C NMR spectroscopic
ꢀ
ꢀ
=
significantly shorter than the N CH3 bond in 3 (1.505(7) Š),
resonances (Dd = dcomplexꢀdligand) of the C Ctrop units (Dd =
=
but considerably longer than the N C bonds in iminium ions
ꢀ75.8 and ꢀ67.0 ppm) on coordination to the Rh center in 6 is
particularly noteworthy, thus indicating significant cyclopro-
pane character for the RhC2 units.
(1.274–1.301 Š)[9] and close in length to the N C bonds in
ꢀ
aziridines (1.440–1.471 Š).[10] Hence, the structural data favor
Table 1: Selected bond lengths [Š] and angles [8] of 3 (experimental), 6 (experimental), and 6C+ (calculated by DFT).[a]
=
C Ctrop
Compound Rh-C16
Rh-N
N-C16
Rh-P
Rh-ct
N-Rh-P
ct-Rh-ct
Rh-N-C16 N-C16-Rh C16-Rh-N
3exp
6exp
6C+
–
2.131(5) 1.505(7) 2.254(1) 2.075(4) 1.413(6) 158.2(1)
134.5(2) 103.1(3)
–
–
2.117(4) 2.059(3) 1.446(5) 2.254(1) 2.065(3) 1.419(4) 160.35(9) 132.6(1)
2.090 2.164 1.417 2.367 2.179 1.422 158.50 136.05
71.9(2)
67.75
67.6(2)
73.37
40.5(1)
38.88
calcd
=
[a] ct indicates the midpoint of the coordinated C Ctrop bond.
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Angewandte
Chemie
A cyclic voltammogram recorded in a THF solution
(0.1m nBu4NPF6 electrolyte, T= 298 K, Pt electrode, scan rate
100 mVsꢀ1) of the rhodaazacyclopropane 6 showed one
the olefinic 13C nuclei, the olefinic protons, and the 31P nucleus
(see the Supporting Information). To assign the methylene
proton signals unambiguously, the corresponding spectra of
[D2]6C+ were also recorded (Supporting Information).
reversible wave at a remarkably low potential (E1o=2
=
ꢀ0.510 V vs. the ferrocenium/ferrocene couple), correspond-
In Figure 3b,
a
representative hyperfine-correlated
+
+
ing to the oxidation 6!6C+.[12] The high stability of 6C allowed
ENDOR (HYEND) spectrum of [13C]6C is displayed which
contains 103Rh and 13C ENDOR frequencies (nENDOR axis) that
are correlated with their corresponding hyperfine frequencies
(nHF axis). In Figure 3c, a representative Q-band HYSCORE
the first detailed study of the electronic structure of a
rhodaazacyclopropyl radical cation by continuous-wave
(CW) and pulse EPR spectroscopy.[13] For this study, 6 as
well as the 13C- and D2-labeled derivatives [13C]6 and [D2]6
were oxidized with ferrocenium triflate to give the radical
+
spectrum of 6C is shown which contains peaks from the
103Rh nucleus, the 13C nuclei of the olefinic C5 atoms, and the
14N and 31P nuclei. The EPR parameters were obtained from
the spectrum by matching the position of the experimental
cross-peaks with those calculated from the relevant spin
Hamiltonian. A complete set of experimentally derived
parameters is given in Table 2, along with the data obtained
from DFT calculations.[16] The experimental spin populations
were calculated from their respective hyperfine couplings.[17]
Overall, the agreement between experimentally derived
and calculated EPR parameters and spin populations is
excellent. According to the DFT calculations, the main part of
the spin density is located on the rhodium center (47%), the
methylene carbon atom (14%), and the four olefinic carbon
atoms (C5 2 ” 15%, C4 2 ” ꢀ3%). This distribution of spin
density can be seen by inspection of the spin-density plot
+
+
+
cations 6C , [13C]6C , and [D2]6C , respectively. The half-life of
+
6C in THF solution (ca. 0.1 mm) is about five hours at room
temperature.[14]
+
The frozen-solution X-band CW-EPR spectra of 6C and
[13C]6C are shown in Figure 3a. Both spectra are well-
+
resolved at the high-field end (g2 = 2.0155, g3 = 2.0145) and
+
show splittings from the 103Rh nucleus (I = 1/2) for 6C and
+
from the 103Rh and 13C nuclei (I = 1/2) for [13C]6C . At the low-
field end (g1 = 2.121), the spectra are poorly resolved.[15] Pulse
ENDOR (electron nuclear double resonance) and HYS-
CORE (hyperfine sublevel correlation) spectroscopies were
used to determine the complete set of hyperfine parameters
of the 103Rh and 13C nuclei of the methylene unit, as well as of
the two methylene 1H nuclei, the weakly coupled 14N nucleus,
Figure 3. a) Experimental (Exp.) and simulated (Sim.) second-derivative X-band CW-EPR spectra of 6C+ and [13C]6C+ in THF measured at 115 K.
b) X-band HYEND spectrum of [13C]6C+ in THF measured at 15 K at the observer position g2. The dashed lines are separated by twice the nuclear
Zeeman interaction (2nI) of 103Rh and 13C, and cross the nENDOR and nHF axes at nI(103Rh) and nI(13C), respectively. c) Q-band HYSCORE spectrum
of 6C+ in THF measured at 15 K near to the g3 observer position. Cross-peaks from 13C(in natural abundance), 103Rh, 31P, and 14N are labeled.
d) Spin density of compound 6C+, plotted with an isosurface level of 0.004.
Angew. Chem. Int. Ed. 2006, 45, 3265 –3269
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3267

Communications
Table 2: EPR parameters and spin populations of compound 6C+. DFT
values are given in brackets.[a]
+
assignment of an oxidation state to the metal center in 6C is
not meaningful,[21] and this complexis best described as a
radical with a delocalized unpaired electron.
Group
Nucleus A1 [MHz]
A2 [MHz]
A3 [MHz] Spin
population
–
Rh1
29ꢁ2
(26.3)
19ꢁ2
(16.3)
ꢀ11ꢁ1
(ꢀ7.9)
25ꢁ2
(22.6)
20ꢁ2
(16.8)
0ꢁ2
ꢀ18ꢁ2
–
Experimental Section
(ꢀ12.2) (47%)
Selected spectroscopic data of diagnostic value are given; for details,
see the Supporting Information.
methylene C16
methylene H16
66ꢁ2
(47.8)
3ꢁ1
15%
(14%)
3: CH2Cl2 (10 mL) and THF (10 mL) were added to [RhCl-
(trop2NMe)(PPh3)] (162 mg, 0.200 mmol) and AgSO3CF3 (51 mg,
0.200 mmol). The resulting red suspension was stirred at room
temperature for 1 h and filtered over celite to remove AgCl. The
solvents were evaporated in vacuo, and the residue was recrystallized
from CH2Cl2/hexanes to yield 3 (175 mg, 0.189 mmol, 94%) as red
2”ꢀ0.2%
(0.1)
(4.2)
(2”ꢀ0.1%)
amine
PPh3
N1
P1
C5
ꢀ1.6ꢁ0.2 ꢀ0.9ꢁ0.2 0.2ꢁ0.2 ꢀ0.5%
(ꢀ1.6)
0 to 15
(0.4)
(ꢀ0.8)
0 to 15
(4.3)
(0.4)
0 to 15
(17)
(ꢀ0.5%)
–
needles. M.p. > 1908C (decomp); 1H NMR (300.1 MHz, CD2Cl2): d =
(2.5%)
1.85 (d, 4JPH = 2.9 Hz, 3H, NCH3), 4.88 (dd, 3JHH = 8.9 Hz, JPH
=
3
olefin
21ꢁ5
21ꢁ5
(ꢀ0.1)
(ꢀ4.2)
4ꢁ2
55ꢁ5
(40.3)
(ꢀ2.7)
4ꢁ1
2”11%
(2”15%)
(2”ꢀ3%)
2”ꢀ0.1%
(2”ꢀ0.2%)
2”0.5%
(2”0.3%)
2.0 Hz, 2H, CHolefin), 6.61 ppm (ddd, 3JHH = 8.9 Hz, 3JPH = 2.9 Hz,
(ꢀ0.2)
4 ꢀ8.6) (
ꢀ11ꢁ1
(ꢀ10.8)
5ꢁ1
2JRhH = 2.9 Hz, 2H, CHolefin); 13C NMR (75.5 MHz, CD2Cl2): d = 44.6
C
H5
(s, NCH3), 78.6 (d, 1JRhC = 7.3 Hz, CHolefin), 88.5 ppm (d, JRhC
=
1
olefin
13.1 Hz, CHolefin); 31P NMR (121.5 MHz, CD2Cl2): d = 39.2 ppm (d,
1JRhP = 138 Hz); 103Rh NMR (12.6 MHz, CDCl3): d = 1272 ppm (d,
1JRhP = 138 Hz); HRMS (MALDI): m/z: 776.1975 (calcd for
C49H40NPRh+: 776.1948).
(1.3)
(2.3)
H4
5ꢁ2
10ꢁ1
(3.5)
(5.2)
(9.3)
[a] The signs of the experimental hyperfine couplings A1,2,3 are assigned
according to the DFT results; principal axis directions are given in the
Supporting Information. g1 =2.121ꢁ0.001 (2.1050), g2 =2.0155ꢁ
0.0005 (2.0174), g3 =2.0145ꢁ0.0005 (2.0163).
6: A solution of KOtBu (18.2 mg, 0.162 mmol) in THF (2 mL)
was added to a suspension of 3 (150 mg, 0.162 mmol) in THF (5 mL).
The resulting orange solution was filtered over a plug of alumina and
concentrated to 1 mL under reduced pressure. The product crystal-
lized upon addition of toluene (1 mL) and hexanes (10 mL). The
mother liquor was decanted, and orange crystals of 6 were dried
in vacuo. Yield: 88 mg (0.114 mmol, 70%); m.p. > 1658C (decomp);
given in Figure 3d. There is some spin delocalization to the
two benzo moieties (2 ” 6%) of the trop ligand, with the
alternating sign of the hyperfine couplings of adjacent carbon
1H NMR (400.1 MHz, [D8]THF): d = 2.89 (dd, JPH = 3.3 Hz, JRhH
=
=
3
2
2.0 Hz, 2H, CH2), 3.83 (ddd, 3JHH = 9.5 Hz, 3JPH = 8.5 Hz, JRhH
2
1.5 Hz, 2H, CHolefin), 4.37 ppm (dd, 3JHH = 9.5 Hz, 2JRhH = 2.0 Hz,
nuclei indicating
a spin-polarization (hyperconjugation)
2H, CHolefin); 13C NMR (62.9 MHz, [D8]THF): d = 54.7 (d, JRhC
=
=
1
mechanism. Both experimental and calculated data show
small hyperfine couplings and thus small spin populations on
the nitrogen and phosphorus nuclei. A comparison of 6 and
1
1
9.7 Hz, CHolefin), 62.4 (d, JRhC = 17.0 Hz, CH2), 63.5 ppm (d, JRhC
8.7 Hz, CHolefin); 31P NMR (162.0 MHz, [D8]THF): d = 63.8 ppm (d,
1JRhP = 185 Hz); 103Rh NMR (12.6 MHz, [D8]THF): d = ꢀ229 ppm (d,
1JRhP = 185 Hz); HRMS (MALDI): m/z: 776.1937 (calcd for
C49H40NPRh+: 776.1948); EPR samples of 6C+ were prepared by
adding a solution containing one equivalent of ferrocenium triflate
(5 mm in THF) to a solution of 6 (5 mm in THF). Sample tubes were
degassed by three freeze-pump-thaw cycles, sealed, and stored in
liquid nitrogen.
+
6C shows that the gross structural features are retained.
In summary, X-ray, NMR, and EPR spectroscopic data
+
strongly support the proposal that 6 and 6C are best formulated
as RhNC metallacycles. In such a formulation, the interaction
of the filled p(C N) orbital (polarized towards the N atom)
with unoccupied metal orbitals represents the Rh N bond,
and the interaction of the unoccupied p*(C N) orbital
(polarized towards the C atom) with occupied metal orbitals
represents the Rh C bond, which lies higher in energy.
ꢀ
ꢀ
ꢀ
Received: December 9, 2005
Revised: January 16, 2006
Published online: April 18, 2006
ꢀ
ꢀ
Therefore, oxidation of 6 mainly affects the Rh C bond, and
consequently the spin population at the carbon atom in 6C+ is
significant, but very low at the nitrogen atom.
Keywords: density functional calculations · EPR spectroscopy ·
.
heterocycles · redox chemistry · rhodium
It has been convincingly demonstrated that constraints
imposed by the ligand sphere can be used to control the redox
potential of transition-metal complexes,[18] and we have
reported that four-coordinate d8 Rh complexes have large
negative reduction potentials when the ligand sphere is not
flexible enough to allow for a tetrahedral distortion.[19]
However, as a result of a lack of suitable reference
compounds, the present study does not allow the firm
conclusion that small-ring metalla-heterocycles are more
easily oxidized than corresponding larger-ring complexes or
comparable acyclic compounds, and it remains an open
question whether compounds such as 6 are strained mole-
[1] Cyclopropanes and strained hydrocarbons: a) P. G. Gassmann,
R. Yamaguchi, Tetrahedron 1982, 38, 1113; b) P. G. Gassmann,
R. Yamaguchi, J. Am. Chem. Soc. 1979, 101, 1308.
[2] Cyclotrisilane: a) Z.-R. Zhang, J. Y. Becker, R. West, J. Appl.
Electrochem. 1998, 28, 517; b) cyclotristannane: I. S. Orlov,
A. A. Moiseeva, K. P. Butin, L. R. Sita, M. P. Egorov, O. M.
Nefedov, Mendeleev Commun. Electronic Version 2002, 4, 1; I. S.
Orlov, M. P. Egorov, O. M. Nefedov, A. A. Moiseeva, K. P.
Butin, D. Ostendorf, M. Weidenbruch, Mendeleev Commun.
Electronic Version 2002, 3, 1.
=
cules. Certainly, the coordination of the C Ctrop units to the
metal center also contributes to the low oxidation potential of
6 and the high stability of its radical cation 6C .
[3] a) H. Bock, Angew. Chem. 1989, 101, 1659; Angew. Chem. Int.
Ed. Engl. 1989, 28, 1627; b) M. Driess, H. Grützmacher, Angew.
Chem. 1996, 108, 901; Angew. Chem. Int. Ed. Engl. 1996, 35, 828.
+ [20]
An
3268
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Angew. Chem. Int. Ed. 2006, 45, 3265 –3269

Angewandte
Chemie
[4] T. Büttner, F. Breher, H. Grützmacher, Chem. Commun. 2004,
2820.
[5] P. Maire, T. Büttner, F. Breher, P. Le Floch, H. Grützmacher,
Angew. Chem. 2005, 117, 6477; Angew. Chem. Int. Ed. 2005, 44,
6318.
[15] The poor resolution is probably a result of considerable g strain
caused by a distribution of different molecular conformations
and poor glass formation in frozen solution.
[16] DFT calculations were performed with the Amsterdam Density
Functional (ADF 2005.01) package. Details are given in the
Supporting Information.
[17] J. R. Morton, K. F. Preston, J. Magn. Reson. 1978, 30, 577.
[18] The classical way to influence the redoxpotential of a transition-
metal complexis to destabilize the ground-state structure of one
partner in a redoxcouple. For examples of this strategy, see:
a) C. O. Dietrich-Buchecker, J. Guilhem, J.-M. Kern, C. Pascard,
J.-P. Sauvage, Inorg. Chem. 1994, 33, 3498, and references
therein; b) C. Dietrich-Buchecker, J.-P. Sauvage, J.-M. Kern, J.
Am. Chem. Soc. 1989, 111, 7791.
[6] 3·3CH2Cl2: C53H44Cl6F3NO3PRhS, red needles, orthorhombic,
space group Pnma, a = 23.791(4), b = 17.642(3), c = 12.192(2) Š,
V= 5117(1) Š3, Z = 4, 1calcd = 1.530 Mgmꢀ3
,
MoKa
, 200 K,
2qmax = 52.748, 30414 reflections, 5403 independent (Rint
=
0.0679), Patterson, empirical absorption correction SADABS
(version 2.03), refinement against full matrix(versus F2) with
SHELXTL (version 6.12) and SHELXL-97, 341 parameters,
R1 = 0.0598, wR2 = 0.1568 (all data), max./min. residual electron
ꢀ3
density 1.339/ꢀ1.624 eŠ
. 6·toluene: C56H47NPRh, orange
[19] C. Laporte, F. Breher, J. Geier, J. Harmer, A. Schweiger, H.
Grützmacher, Angew. Chem. 2004, 116, 2621; Angew. Chem. Int.
Ed. 2004, 43, 2567.
crystals, orthorhombic, space group Pnma, a = 25.397(1), b =
13.634(1), c = 12.052(1) Š, V= 4173.0(4) Š3, Z = 4, 1calcd
=
1.381 Mgmꢀ3, MoKa, 250 K , 2qmax = 52.748, 25675 reflections,
4450 independent (Rint = 0.0711), direct methods, refinement
against full matrix(versus F2) with SHELXTL (version 6.12) and
[20] Olefins as non-innocent ligands in IrII compounds: D. G. H.
Hetterscheid, J. Kaiser, E. Reijerse, T. P. J. Peters, S. Thewissen,
A. N. J. Blok, J. M. M. Smits, R. de Gelder, B. de Bruin, J. Am.
Chem. Soc. 2005, 127, 1895; D. G. H. Hetterscheid, M. Bens, B.
de Bruin, Dalton Trans. 2005, 5, 979.
SHELXL-97, 291 parameters, R1 = 0.0415, wR2 = 0.0933 (all
ꢀ3
data), max./min. residual electron density 0.823/ꢀ0.594 eŠ
.
CCDC-290105 (3) and CCDC-290104 (6) contain the supple-
mentary 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. For fur-
ther details, see also the Supporting Information.
[21] Formally, 6C+ could be described as a RhII complex, but the
g values of such complexes are significantly different: K. K.
Pandey, Coord. Chem. Rev. 1992, 121, 1.
[7] a) M. Ogasawara, D. Huang, W. E. Streib, J. C. Huffman, N.
Gallego-Planas, F. Maseras, O. Eisenstein, K. G. Caulton, J. Am.
Chem. Soc. 1997, 119, 8642, and references therein; related C2v
structures were found by IR spectroscopy and calculations for the
carbonyl complexes [M(CO)4] (M=Fe, Ru, Os; isolated only at
very low temperatures in inert matrices): b) M. Poliakoff, J. J.
Turner, J. Chem. Soc. Dalton Trans. 1974, 2276; c) M=Ru: P. L.
Bogdan, E. Weitz, J. Am. Chem. Soc. 1989, 111, 3163; d) J. Li, G.
Schreckenbach, T. Ziegler, J. Am. Chem. Soc. 1995, 117, 486; also
for [RhH(CO)3] and trans-[RhH(CO)2(PH3)], possible intermedi-
ates in hydroformylation reactions, nonplanar structures were
calculated, but the distortions are much smaller: e) R. Schmid,
W. A. Herrmann, G. Frenking, Organometallics 1997, 16, 701.
[8] For a recent review, see: G. Frenking, K. Wichmann, N. Frꢀhlich,
C. Loschen, M. Lein, J. Frunzke, V. M. Rayꢁn, Coord. Chem.
Rev. 2003, 238–239, 55.
[9] See, for example: S. Hollenstein, T. Laube, Angew. Chem. 1990,
102, 194; Angew. Chem. Int. Ed. Engl. 1990, 29, 188.
[10] See, for example: S. Brückner, L. Malpezzi, A. V. Prosyanik,
S. V. Bondarenko, Acta Crystallogr. Sect. C 1985, 41, 215.
[11] CoNC heterocycles: a) R. Dreos, A. Felluga, G. Nardin, L.
Randaccio, G. Tauzher, Organometallics 2003, 22, 2486, and
references therein; b) R. M. Hartshorn, S. G. Telfer, J. Chem.
Soc. Dalton Trans. 2000, 2801; c) D. M. Tonei, L.-J. Baker, P. J.
Brothers, G. R. Clark, D. C. Ware, Chem. Commun. 1998, 2593;
d) L. G. Marzilli, S. M. Polson, L. Hansen, S. J. Moore, P. A.
Marzilli, Inorg. Chem. 1997, 36, 3854; e) ZrNC heterocycle: J.
Pflug, A. Bertuleit, G. Kehr, R. Frꢀhlich, G. Erker, Organo-
metallics 1999, 18, 3818; f) PdNC heterocycle: C. C. Lu, J. C.
Peters, J. Am. Chem. Soc. 2004, 126, 15818.
[12] For comparison, the neutral pentacoordinate 18-electron com-
plex 2 is oxidized at + 0.33 V (in THF, 0.1m nBu4NPF6), the
cationic complex
3
at + 0.26 V (in 5:1 THF/CH2Cl2,
0.1m nBu4NPF6), and the labile pentacoordinate 18-electron
complex[Rh(MeCN)(trop 2NMe)(PPh3)]+ (K ꢂ 4 Lmolꢀ1
+ 0.753 V (in MeCN, 0.1m nBu4NPF6).
) at
[13] A. Schweiger, G. Jeschke, Principles of Pulse Electron Para-
magnetic Resonance, Oxford Press, Oxford, 2001.
[14] The decomposition of 6C+ gives about 20% [Rh(trop2NMe)-
(PPh3)]OTf (3) and three other rhodium phosphane complexes
of unknown structure.
Angew. Chem. Int. Ed. 2006, 45, 3265 –3269
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