Rhodium and iridium amino, amido, and aminyl radical complexes

Article abstract of DOI:10.1002/ejic.200800702

The chlorido-bridged dimeric complex [Rh₂(μ-Cl) ₂(trop₂-NH)₂] [trop₂NH = bis(benzo[a,d]cycloheptenyl)amine] or the acetonitrile complexes [Rh(trop ₂NH)(MeCN)₂]⁺ (CF₃SO ₃^-) and [IrCl(MeCN)(trop₂NH)] are well-suited precursor complexes for phenanthroline-type complexes [M(trop ₂NH)(R,Rphen)]⁺A^- (M = Rh, Ir; R = H, Me, Ph substituents in the 4,7- or 5,6-positions of the phen ligand, A^- = CF₃SO₃^-, PF₆^-). These complexes contain 18-valence-electron configured metal centers in a trigonal-bipyramidal coordination sphere with the amino (NH) group in an axial position and each of the olefinic C=C_trop units is in an equatorial position. The cationic amino complexes [M(trop₂NH)(R,R-phen)] ⁺ are sufficiently acidic (pK_a in dmso: 18.2-19.0) to be quantitatively deprotonated by one equivalent of KOtBu to give neutral amido complexes [M(trop₂N)(R,R-phen)] (M = Rh, Ir). These can be easily oxidized to give aminyl radical complexes [M(trop₂N ^.)(R,R-phen)]⁺A^-, which for M = Rh can be isolated as green crystals. The iridium complex [Ir(trop₂N ^.)(phen)]⁺ is unstable. High-resolution pulse EPR spectroscopy was used to gain insight into the electronic structure of the aminyl radical complexes. Remarkably, the rhodium and iridium complexes have a very similar electronic structure, as revealed by their EPR parameters {[Rh(trop₂N^.)(phen)]⁺: g_1,2,3 = 2.084(2), 2.049(2), 2.027(2); |A_iso| = 45.4 (N1), 10.4 (N2), 3.1 (N3) 27.0 (Rh) MHz; [Ir(trop₂N^.)(phen)]⁺: g _1,2,3 = 2.140(2), 2.107(2), 2.015(2); |A_iso| = 47 (N1), 7.9 (N2), 3.5 (N3), 26.8 (Ir) MHz} and these show that about 60% of the spin population is localized on the nitrogen center (N1) of the trop₂N ligand. In reactions with stannanes (R₃SnH) and thiols (RSH), H-atom transfer to the trop₂N nitrogen atom is observed, [M(trop ₂N^.)(phen)]⁺ + EH → [M(trop ₂NH)(phen)]⁺ + 1/2HE-EH. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800702

FULL PAPER
DOI: 10.1002/ejic.200800702
Rhodium and Iridium Amino, Amido, and Aminyl Radical Complexes
Nicola Donati,[a] Daniel Stein,[a] Torsten Büttner,[a] Hartmut Schönberg,[a] Jeffrey Harmer,[b]
Sreekanth Anadaram,[a] and Hansjörg Grützmacher*[a]
Keywords: Cyclic voltammetry / Iridium / Organometallic compounds / Phosphanes / Reaction mechanisms / Rhodium
The chlorido-bridged dimeric complex [Rh2(µ-Cl)2(trop2-
as green crystals. The iridium complex [Ir(trop2N·)(phen)]+ is
unstable. High-resolution pulse EPR spectroscopy was used
to gain insight into the electronic structure of the aminyl radi-
NH)2] [trop2NH = bis(benzo[a,d]cycloheptenyl)amine] or the
–
acetonitrile complexes [Rh(trop2NH)(MeCN)2]+ (CF3SO3
)
and [IrCl(MeCN)(trop2NH)] are well-suited precursor com- cal complexes. Remarkably, the rhodium and iridium com-
plexes for phenanthroline-type complexes [M(trop2NH)(R,R-
phen)]+A– (M = Rh, Ir; R = H, Me, Ph substituents in the 4,7-
or 5,6-positions of the phen ligand, A– = CF3SO3–, PF6–).
These complexes contain 18-valence-electron configured
metal centers in a trigonal–bipyramidal coordination sphere
with the amino (NH) group in an axial position and each of
the olefinic C=Ctrop units is in an equatorial position. The cat-
ionic amino complexes [M(trop2NH)(R,R-phen)]+ are suffi-
ciently acidic (pKa in dmso: 18.2–19.0) to be quantitatively
deprotonated by one equivalent of KOtBu to give neutral
amido complexes [M(trop2N)(R,R-phen)] (M = Rh, Ir). These
can be easily oxidized to give aminyl radical complexes
[M(trop2N·)(R,R-phen)]+A–, which for M = Rh can be isolated
plexes have a very similar electronic structure, as revealed
by their EPR parameters {[Rh(trop2N·)(phen)]+: g1,2,3
=
2.084(2), 2.049(2), 2.027(2); |Aiso| = 45.4 (N1), 10.4 (N2), 3.1
(N3) 27.0 (Rh) MHz; [Ir(trop2N·)(phen)]+: g1,2,3 = 2.140(2),
2.107(2), 2.015(2); |Aiso| = 47 (N1), 7.9 (N2), 3.5 (N3), 26.8 (Ir)
MHz} and these show that about 60% of the spin population
is localized on the nitrogen center (N1) of the trop2N ligand.
In reactions with stannanes (R3SnH) and thiols (RSH), H-
atom transfer to the trop2N nitrogen atom is observed,
[M(trop2N·)(phen)]+ + EHǞ[M(trop2NH)(phen)]+ + 1/2HE–EH.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
as an blue-black microcrystalline powder, is a low-spin d5
MnII complex with an amido ligand (no N14 hyperfine
coupling could be observed).[3] The first compounds that
were unambiguously characterized by a variety of spectro-
scopic techniques as aminyl radical complexes are the co-
balt(III) anilino radical complex C and some related MnIV
complexes with one, two, and three coordinated amilino
radicals.[4] Complexes D–G could be isolated and were thor-
oughly investigated including structural analyses for A, E,
and G.[5–8] With the exception of E, which is better de-
scribed as a d5 RuIII amido complex with a relatively small
portion of the spin population on the nitrogen center,[6]
these complexes can be formulated as aminyl radical com-
plexes; that is, the major part of the spin population resides
on the N center.
Introduction
Aminyl radicals are short-lived intermediates that ef-
ficiently abstract hydrogen atoms from organic substrates
or add to unsaturated bonds.[1] More persistent radicals can
be obtained with π-conjugated, lone-pair carrying, and/or
bulky substituents bonded to the nitrogen center. Also,
metal fragments can stabilize aminyl radicals to an extent
that they become detectable or even isolatable. Examples
are shown in Scheme 1. It is a priori not always possible to
properly assign the electronic state of such a complex,
which can be formulated with two limiting resonance struc-
tures, [M]-(·NR2) (aminyl radical complex), or [M+·]-(–NR2)
(metal amide). Early examples are A and B, which were
both discussed as aminyl radical complexes. On the basis of
the EPR data, the unstable (t1/2 ≈ 90 s at 25 °C in water)
red-violet NiII complex A, obtained by deprotonation of
a NiIII amine precursor complex, was formulated with a
macrocyclic aminyl radical as ligand.[2] In contrast, spectro-
scopic and computational data clearly show that B, isolatable
A limited amount of data concerning the reactivity of
aminyl radical complexes is available. Care must be taken
when conclusions concerning the spin population are made.
For example, on the one side, MnII amido complex B reacts
as if it is an aminyl radical complex in the sense that H
atoms are abstracted from the solvent or boranes to give
the amine complex [Mn(Cp)(CO)2(NH2R)].[3b] On the other
side, Ru complex E with 8% of the spin population ρ at
the N center does indeed not show N-centered reactivity.[6]
[a] Department of Chemistry and Applied Biosciences, ETH
Zürich,
Wolfgang-Pauli Str. 10, 8093 Zürich, Switzerland
[b] CAESR, Inorganic Chemistry, University of Oxford,
South Parks Road, OX1 3QR, United Kingdom
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Complexes D (ρN = 57%),[5] G (ρN = 57%),[8] and H (ρN
=
2ϫ28%),[9] which carry a substantial amount of spin den-
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H. Grützmacher et al.
FULL PAPER
with the amine trop2NH (2; Scheme 2). The other complex
that serves as a precursor to Rh(trop2NH)-type com-
plexes[13,8] is the cationic bis(acetonitrile) complex
–
[Rh(trop2NH)(MeCN)2]OTf (5; OTf = CF3SO3 ). This
complex is obtained in quantitative yield as yellow (micro)
crystals either by treating 3 in acetonitrile with AgOTf or
by treating the bis(cod) complex [Rh(cod)2]OTf with amine
2 in acetonitrile. Both 3 and 5 can be stored at ambient
temperature in closed vessels for years without signs of de-
composition.
Scheme 1. Selected aminyl radical complexes.
sity at the nitrogen center, undergo the expected H-abstrac-
tion reactions leading to the corresponding amine com-
plexes. Specifically, [Rh(trop2N·)(bipy)]+ (G) (trop
=
benzo[a,d]cycloheptenyl) reacts rapidly with stannanes
(R3SnH) and thiols (RSH) to give [Rh(trop2NH)(bipy)]+
and R3Sn–SnR3 or RS–SR, respectively.
Ruthenium aminyl radical complexes related to F may
serve as catalysts for the electrochemical oxidation of
alcohols to carbonyls.[10] We reported that an iridium com-
plex related to H is a very efficient catalyst for the chemose-
lective dehydrogenation of a wide range of primary alcohols
to aldehydes in combination with para-benzoquinone as ox-
idant.[11] Curiously, rhodium complex H is inactive.
The motivation for the present study was to extend our
understanding of the properties and reactivity of late-transi-
tion-metal aminyl radical complexes. We aimed at com-
plexes of type G because this aminyl radical complex is re-
markably stable, albeit reactive.[8] In this paper, we report a
second complete set of a RhI amine, amido, and aminyl
radical complexes of type G and the synthesis of the first
analogous IrI aminyl radical complex. Furthermore, we de-
scribe in detail the synthesis of various rhodium and irid-
ium trop2NH complexes.
Scheme 2. Syntheses of precursor complexes 3 and 5.
A CD3CN solution of [Rh(trop2NH)(MeCN)2]OTf (5)
shows two sharp and distinct resonances for coordinated
MeCN [δ(1H) = 2.4 ppm] and one uncoordinated MeCN
molecule [δ(1H) = 1.96 ppm]. We assign the first resonance
to the kinetically inert axial bonded MeCN in 5, whereas
the MeCN molecule in the equatorial position is labile and
displaced by the CD3CN solvent molecules.[14]
The syntheses leading to complexes 6a–d with phenan-
throline (phen) and its derivatives Rphen as ligands is dis-
played in Scheme 3. Complex 6a is simply prepared by
treating phen with chlorido-bridged dimer 3 in the presence
of AgOTf in boiling thf. For the complexes carrying the
substituted phenanthroline derivatives, bis(acetonitrile)
complex 5 proved to be the better precursor. All complexes
6a–d were obtained as stable yellow to bright orange
(micro)crystalline powders in good isolated yields (≈80%).
Neutral acetylacetonate (acac) complex 7 was prepared
from [Rh2(µ-Cl)2(trop2NH)2] and acetylacetone (Hacac) in
the presence of KOtBu as base.
Results
Syntheses
The synthesis of the iridium phenanthroline complex
For the synthesis of [Rh(trop2NH)(LʝL)] complexes [Ir(trop2NH)(phen)]PF6 (11) requires harsher reaction con-
(LʝL = bidentate ligand) two routes proved to be useful. ditions. First, the yellow dimeric species [Ir2(µ-Cl)2(trop2-
The first one employs the chlorido-bridged dimer [Rh2(µ- NH)2] (9) was prepared in moderate yield by treating the
Cl)2(trop2NH)2] (3) as a precursor,[12a,12b] which is easily cyclooctene (coe) complex [Ir2(µ-Cl)2(coe)4] with trop2NH
obtained as red crystals by treating the commercially avail- in boiling toluene for 2 d. This complex cannot be con-
able cyclooctadiene (cod) complex [Rh2(µ-Cl)2(cod)2] (1) verted directly into 11 in a similar manner, as found for
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Rhodium and Iridium Amino, Amido, and Aminyl Radical Complexes
sponding neutral amido complexes 12a–c by using one
equivalent of KOtBu as base in thf as solvent. Neutral com-
plex 7, however, did not react to identifiable products under
the same reaction conditions. Iridium complex 11 is again
quantitatively deprotonated by one equivalent of KOtBu to
give neutral iridium amido complex 13. All amido com-
plexes can be isolated as red (12a), red-brown (12b,c), or
green-brown (13) air-sensitive microcrystalline powders (see
Scheme 5).
Scheme 5. Syntheses of amido complexes 12a–13 and aminyl radi-
cal complexes 14a,b and 15.
Scheme 3. Syntheses of amine olefin phenanthrolin complexes
6a–d and acetylacetonato complex 7.
From the radical cation complexes obtained by chemical
oxidation of amido complexes 12a,b (M = Rh) or 13 (M =
Ir) with ferrocenium triflate in thf, compounds 14a and 14b
were isolated as dark-green powders after precipitation with
n-hexane. From a concentrated solution, dark-red single
crystals of 14a were obtained. Despite many attempts, irid-
ium analogue 15 could not be isolated. This compound
rapidly decomposes and can only be characterized by EPR
spectroscopy (vide infra).
the analogous rhodium complex. Instead, 9 needed to be
converted into mono(acetonitrile) complex 10. This com-
plex is also obtained when the cycooctadiene complex
[Ir2(µ-Cl)2(cod)2] is treated with trop2NH (2) in acetonitrile
as solvent (not included in Scheme 4). Finally, when color-
less complex 10 was dissolved in chlorobenzene in the pres-
ence of phen and TlPF6, a deep-red solution was obtained
that turns into a bright orange suspension after heating at
reflux overnight. Desired product 11 could be obtained in
high yield (Ͼ90%) as a yellow powder.
NMR Spectroscopic Data
1
Selected 13C and H NMR spectroscopic data of com-
plexes 3, 5, 6a–d, 7, 9–11, 12a–c, and 13 are listed in Table 1
and are in accord with Cs-symmetric structures. The NMR
spectroscopic data for phenanthroline complexes 6a and
12a are very similar to the reported data for the 2,2Ј-bipyr-
idine complexes [Rh(trop2NH)(bipy)]OTf[8] and [Rh-
(trop2N)(bipy)]. A significant low-frequency coordination
shift of the olefinic 13C resonances {M = Rh: 60–67 ppm,
M = Ir 77–86 ppm with respect to 2 [δ (13Col) ≈ 130 ppm]}
indicates significant back bonding and tight binding. The
resonance of the acidic NH proton is sensitively influenced
by the solvent and is shifted to higher frequencies in [D6]-
dmso (Ͼ5 ppm) relative to that in CD3CN, [D8]thf, or
CDCl3. The deprotonation of the NH group of cationic
rhodium complexes 6a–c or that of iridium complex 11 has
13
a relatively small effect on the
C
resonances indicating
ol
Scheme 4. Syntheses of iridium complexes 9–11.
no significant alteration of the MǞL back donation in the
The rhodium complexes with phen (6a), 4,7-dimethyl- amido complexes. The deprotonation has an effect on the
phenanthrolin (6b), and 4,7-diphenylphenanthroline (6c) as 103Rh resonances, which are shifted by about 500 ppm to
ligands can be quantitatively deprotonated to the corre- lower frequencies in the amido complexes.
Eur. J. Inorg. Chem. 2008, 4691–4703
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H. Grützmacher et al.
FULL PAPER
Table 1. Selected physical data for complexes 3, 5, 6a–d, 7, 9–11, 12a–c, and 13. Chemical shifts are given on the δ scale in ppm, the
redox potentials (E°1/2) were referenced against the Fc+/Fc couple and are given in V, and the bond dissociation energies (BDE) in
kJmol–1. All data were obtained in dmso as solvent. n.d. = not determined; n.r. = not resolved.
Compound
Metal
Solvent
δ olefinic Ha/Hb
δ olefinic 13
C
δ NH
pKa
E°1/2
BDE
δ 103Rh
3
Rh
Rh
Rh
Rh
Rh
Rh
Rh
Ir
Ir
Ir
Rh
Rh
Rh
Ir
CD2Cl2
CD3CN
[D6]dmso
CD3CN
[D6]dmso
CD3CN
CDCl3
CDCl3
CDCl3
[D8]thf
[D8]thf
5.97/6.20
5.36/5.77
3.99/5.56
4.04/5.50
4.13/5.59
4.07/5.54
4.83/5.19
5.58/5.83
4.48/5.00
3.26/5.18
2.73/4.81
3.45/5.01
3.55/5.12
2.72/4.81
71.4 (n.r.)
70.3/71.0
68.0/69.3
67.9/69.2
67.6/69.1
68.0/69.5
66.8/69.9
51.1/52.6
45.6/53.7
47.9/51.1
63.3/64.1
64.3/67.3
65.3/66.9
44.0/50.8
2.90
4.03
5.04
3.79
5.17
3.83
2.92
3.67
4.40
4.78
–
n.d.
n.d.
18.6(2)
19.0(2)
18.7(2)
n.d.
n.d.
n.d.
n.d.
18.2(1)
–
n.d.
n.d.
n.d.
n.d.
361(2)
361(2)
361(2)
n.d.
n.d.
n.d.
n.d.
353(1)
–
2992
2311
2111
2099
2096
2093
2998
–
–
–
1570
1547
1562
–
5
6a
6b
6c
6d
7
n.d.[a]
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
–0.541
–0.568
–0.544
–0.602
9
10
11
12a
12b
12c
13
[D8]thf
[D6]dmso
[D8]thf
–
–
–
–
–
–
–
–
–
[a] The redox potential measured in thf was –0.636 V. Cyclic voltammograms were recorded for the related 2,2Ј-bipyridine (bipy) complex
[Rh(trop2NH)(bipy)]OTf[8] in a thf/nBu4NPF6 electrolyte: E°1 = +0.588 V (RhI/RhII); E°2 = –1.77 V/RhI(bipy)/RhI(bipy·–).
1/2
1/2
Determination of the pKa of 6a–c and 11
(amino)tris(olefin) complex [Rh(trop2NH)(tropNH2)]OTf is
higher [pKa = 20.6(1)].[13] Remarkably, the pKa of the irid-
ium complex [Ir(trop2NH)(phen)]OTf (11) is almost the
same as in the analogous rhodium species 6a. This is in
contrast to the observation we made for the tetracoordinate
16-electron bis(amino) complexes [M(trop2dach)]+ of type
H (see Scheme 1), where the iridium complex has a pKa
value (pKa1 = 10.5; pKa2 = 19.6) about five orders of magni-
Dimethyl sulfoxide is widely used as nonprotic solvent
for the determination of the pKa of a wide range of organic
substrates.[15] This solvent is a sufficiently strong solvent in
order to suppress ion pairing, which otherwise renders the
determination of pKa values rather difficult. A serious
drawback with organometallic complexes is that dmso
might act as a ligand, and especially, it can displace weakly
bound ligands from the metal center. However, this was not
detected with saturated 18-electron complexes 6a–c and 11,
and the pKa of the coordinated amino group could be easily
determined by using 1H NMR spectroscopy. The pKa of the
sample complex [M(NH)]+ is obtained through Equa-
tion (1).
1
tude lower than that of the rhodium complex (pKa = 15.7;
pKa2 Ͼ 21).[9,16] In addition, we looked into the rates of the
deprotonation reactions of rhodium amine complex 6a by
using either imidazolide (Imd–) as base [Equation (3)] or by
inspection of the self-exchange reaction given in Equa-
tion (4).
(3)
pKa[M(NH)] = pKa(Href) – log K
[M(NH)]+ + ref– Ǟ [M(N)] + Href
(1)
(2)
where pKa(Href) is the known pKa value of a reference sys-
tem in the same solvent, Href p H+ + ref–, and K is the
equilibrium constant of the reaction given in Equation (2).
K is determined by measuring suitable 1H resonances of
[M(NH)]+/[M(N)] and ref–/Href. In order to obtained exact
data, it is best to use a reference base that has a pKa value
very close to that expected for the sample. In this case, all
species participating in the Equation (2) have almost equal
1
In the first case, the H NMR spectrum at T = 298 K of
concentrations, and the experimental error in the integra- a 1:1 mixture of 6a and Li+(Imd–) shows averaged sharp
tion of the peak intensities is smallest. We found that the signals for the pairs [Rh(trop2NH)(phen)]+/[Rh(trop2N)-
imidazolide/imidazole reference pair [pKa(dmso) = 18.6(1)] (phen)] and Imd–/HImd. Upon cooling, only a very small
is ideally suited for the determination of the pKa of rho- line-broadening effect for characteristic NMR resonances
dium complexes 6a,b and iridium complex 11, whereas di- [i.e., the olefinic and benzylic 1H resonances of the trop unit
acetamide/diacetamine (no proton resonances in the aro- and the HC(N2) proton of the imidazole] could be observed
matic region) allowed the determination of the pKa of 6c. in the accessible temperature range between 230 and 298 K.
The pKa data are listed in Table 1. The NH acidities lie in The reaction given in Equation (3) remains fast on the
a narrow range of pKa = 18.2–19.0 and compare well with NMR timescale, and we estimate a rate of kobs ≈ 0.5–
the value determined for the analogous bipy complex 1ϫ106 s–1. The NMR spectra of
a
mixture of
[Rh(trop2NH)(bipy)]OTf (pKa = 18.7).[8] The pKa of the co- [Rh(trop2NH)(phen)]OTf (6a) and [Rh(trop2N)(phen)]
ordinated trop2NH ligand in the cationic 18-electron bis- (12a) show broad signals at T = 283 K that sharpen signifi-
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Rhodium and Iridium Amino, Amido, and Aminyl Radical Complexes
cantly upon cooling to T = 213 K meaning that this process
is rather slow on the NMR timescale. Line-shape analysis
by using the MEXICO program package[17] allowed us to
determine the activation barrier ∆G#
= 67(1) kJmol–1
298
and the rate of self-exchange for the reaction give in Equa-
tion (4): k = 11.2 s–1.
Cyclic Voltammetry
The cyclic voltammogram (CV) of the previously
Figure 1. Molecular structure of 3·(CH2Cl2)2. The thermal ellip-
soids correspond to 30% probability. The hydrogen atoms except
at the nitrogen atoms and CH2Cl2 molecules are omitted for clarity.
Selected bond lengths [Å] and angles [°]: Rh1–N1 2.076(5), Rh1–
Cl1 2.384(2), Rh1–Cl1a 2.626(2), Rh–C4 2.165(5), Rh1–C5
2.145(6), Rh–C19 2.141(6), Rh–C20 2.165(6), Rh1–ct1
2.032(6),Rh1–ct2 2.032(6), C4–C5 1.435(8), C19–C20 1.421(8);
N1–Rh1–Cl1 177.1(1), N1–Rh1–Cl1A 91.1(1), N1–Rh1–C5
91.1(1), ct1–Rh1–ct2 136.7(2); ct = centroid of the (C=Ctrop)
bond.
reported
cationic 2,2Ј-bipyridine
(bipy) complex
[Rh(trop2NH)(bipy)]OTf[8] in a thf/nBu4NPF6 electrolyte
shows a reversible redox wave at E°1/2 = –1.77 V (vs.
Fc+/Fc). This reduction is ligand centered and leads to the
neutral complex [RhI(trop2NH)(bipy·–)]. We were unable to
isolate this compound, but the formation of the bipy·– radi-
cal anion is clearly proven by its characteristic EPR spec-
trum.[18,19] A quasireversible redox wave is observed at
E°1/2 = +0.588 V (vs. Fc+/Fc). It is likely that this oxidation
is a metal-centered process giving rhodium(II) complex
[RhII(trop2NH)(bipy)]2+ [20]
We were unable to isolate this
.
complex or characterize it by EPR spectroscopy. In com-
parison to this cationic complex, neutral rhodium amido
complexes 12a–c and iridium amide 13 show markedly dif-
ferent cyclic voltammograms. All compounds are easily oxi-
dized and show a reversible redox wave in a narrow range
between –0.51 and –0.60 V (in dmso, vs. Fc+/Fc). As dis-
cussed below, this oxidation is best described as ligand
centered leading to an aminyl radical complex
[M(trop2N·)(NʝN)]+. With the equation BDE = 5.74pKa +
96.5E°1/2 + C, which has been extensively used by Bordwell
et al.[21] for the determination of the bond dissociation ener-
gies (BDEs) of organic compounds (C is an empirically de-
rived constant of 306.9 kJmol–1 in dmso), the NH dissoci-
ation energy for RhI complexes 6a–c and IrI complex 11
is estimated to be 361(2) and 353(2) kJmol–1, respectively
(Table 1). All data resemble closely those obtained for the
Figure 2. Structure of 5. The thermal ellipsoids are drawn at 30%
probability. The counteranion OTf– and all hydrogen atoms except
at N1 are omitted for clarity. Selected bond lengths [Å] and angles
[°]: Rh1–N1 2.075(3); Rh1–N2 2.191(4); Rh1–N3 2.007(4); Rh1–C4
2.185(4); Rh1–C5 2.169(4); Rh1–C19 213.5(4); Rh1–C20 2.140(5)
Rh1–ct1 2.060(6), Rh1–ct2 2.199(6), C4–C5 1.411(6), C19–C20
1.417(6); N1–Rh1–N3 178.1(2); N1–Rh1–N2 87.0(1); N2–Rh1–
ct(C4,C5) 105.4(2), N2–Rh1–ct(C19,C20) 117.7(2); ct = centroid of
the (C=Ctrop) bond.
[Rh(trop2NH)(bipy)]+/[Rh(trop2N)(bipy)] couple [pKa
18.7(2); E°1/2 = –0.552 V; BDE = 361(2) kJmol–1].[8]
=
Structures from X-ray Diffraction Data
In all complexes, the rhodium centers reside in mildly
distorted trigonal bipyramidal (TBP) coordination spheres
The structures of 3, 5, 7, 6a,d, 12a, and 14a were deter- with the largest deviation seen in the ct–Rh–ct angles, which
mined by X-ray diffraction studies. Plots of the structures are Ͼ130° (ideally 120°). In the idealized structures, the
of 3, 5, 7, and 14a are shown in Figures 1, 2, 3, and 4, trop units are related by mirror symmetry; complex 5 has,
respectively. Selected bond lengths and angles for 3, 5, and in addition, a center of inversion within the planar R2Cl2
7 are given in the Figure captions. For 6a,d, 12a, and 14a, ring. With the exception of 14a (vide infra), the Rh–N1
selected distances and angles are listed in Table 2. Tables 4 bond is longer than 2 Å (2.046 Å in 12a to 2.088 Å in 6a).
and 5 contain information concerning the data collection The distances from the Rh center to the centroids (ct) of
and refinement of the examined structures.
the coordinated C=Ctrop units do not vary greatly (2.003 Å
Eur. J. Inorg. Chem. 2008, 4691–4703
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4695

H. Grützmacher et al.
FULL PAPER
in 7 to 2.199 Å in 5), and neither do the coordinated
C=Ctrop bond lengths, which are about 1.42 Å on average
(the C=C bond in the free trop2NR ligands is about
1.34 Å).[18] The elongation of the coordinated C=Ctrop
bonds (Ͼ1.41 Å) indicate considerable MǞL back do-
nation and tight binding. In agreement with the NMR spec-
troscopic data, the structural data also suggest that the
MǞL back donation is only slightly influenced by the na-
ture of the different chelate ligands or the deprotonation of
the NH group. A further common feature of all complexes
is that, as expected, the labile σ donor (Cl in 3; MeCN in
5; O in 7; N in 6a,d, 12a, and 14a) in the equatorial position
of the TBPs around each Rh center is bound at significantly
longer distances than that found for the corresponding li-
gand in the axial position.
With complexes 6a, 12a, and 14a, respectively, a second
complete series of amino, amido, and aminyl radical com-
plexes could be structurally investigated. The data listed in
Table 2 are very close to those we obtained for the series of
2,2Ј-bipyridine complexes [Rh(trop2NX)(bipy)]n (X = H, n
= +1; X = lone pair, n = 0; X = ·, n = +1).[8] As we observed
in this series, the only significant structural change occurs
when neutral amido complex 12a is oxidized to radical cat-
ion complex 14a. In this complex, the Rh1–N1 bond
[1.947(4) Å] is significantly shorter than that in all other
compounds. Furthermore, the sum of the bond angles
around N1, Σ°(N1), flattens and is close to 360°, whereas in
all other complexes Σ°(N1) is closer to 340°, also in amido
complex 12a. The shortening of the Rh–N bond and the
flattening of the N1 coordination sphere can be explained
under the assumption that the removed electron resides in
a Rh–N antibonding orbital.
Figure 3. Structure of 7·CH2Cl2. The thermal ellipsoids are drawn
at 30% probability. All hydrogen atoms except at N1 and the
CH2Cl2 molecule are omitted for clarity. Selected bond lengths [Å]
and angles [°]: Rh–N1: 2.059(5), Rh–O1: 2.185(4), Rh–O2 2.022(4),
Rh1–C4 2.149(7); Rh1–C5 2.153(6); Rh1–C19 2.134(6); Rh1–C20
2.119(6) Rh1–ct1 2.031(6), Rh1–ct2 2.003(6), C4–C5 1.418(9),
C19–C20 1.424(8); N1–Rh1–O2 178.95(2); N1–Rh–O1 87.66(2);
O1–Rh–O2 92.74(2); ct1–Rh–ct2 137.4(2); ct = centroid of the
C=C bond.
EPR Spectroscopy
In order to gain further insight into the electronic struc-
tures, the aminyl radical complexes [Rh(trop2N·)(phen)]OTf
(14a) and its iridium analogue 15 were investigated with
continuous wave (CW) and high-resolution pulse EPR
methods.[22] Well-resolved CW EPR spectra of
[Rh(trop2N·)(phen)]OTf (14a) were obtained in a thf/ace-
tone (2:1 by vol.) solvent mixture at S-band and T = 298 K,
as shown in Figure 5A. Couplings to one rhodium (I =
1/2), two nitrogen (I = 1), and two hydrogen nuclei (I =
1/2) are resolved. The isotropic hyperfine coupling con-
stants listed in Table 3 were obtained through the simula-
tion.
Figure 4. The structure of aminyl radical cation complex
[Rh(trop2N·)(phen)]+ (14a) is shown as an example (thermal ellip-
soids at 30% probability) and indicates the atom labeling scheme
used for all compounds. The structures of 6a,d and 12a are not
displayed. N1 represents an NH function in 6a,d, an amide nitro-
gen in 12a, and an aminyl center in 14a. Selected bond lengths [Å]
and angles [°] for all compounds are given in Table 2. ct = centroid
of the C=C bond.
Table 2. Selected bond lengths [Å] and angles [°] for 6a·(thf)2, 6d·CH3CN, 12a·(thf)2, and 14a·(thf)2.
Rh–N1
Rh–N2
Rh–N3
Rh-ct1
Rh-ct2 C=Ctrop Σ°(N1)
N1–Rh–
ct1–Rh–
N1–Rh– N2–Rh–N3
N3
ct2
N2
6a·(thf)2
2.088(2)
2.086(4)
2.046(1)
1.947(4)
2.177(2) 2.033(2) 2.034(2) 2.021(2) 1.424(3) 343.2(1)
2.193(3) 2.046(4) 2.060(5) 2.047(5) 1.427(7) 344.6(7)
2.148(1) 2.099(1) 2.018(1) 2.020(1) 1.433(2) 342.3(1)
2.188(4) 2.092(3) 2.084(4) 2.032(4) 1.417(6) 356.7(2)
175.2(1)
175.2(2)
170.9(1)
177.3(2)
134.8(1)
132.6(2)
136.4(1)
140.9(2)
95.8(1)
97.2(2)
92.6(1)
102.1(2)
79.4(1)
78.1(2)
78.3(1)
77.7(2)
6d·CH3CN
12a·(thf)2
14a·(thf)2
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Rhodium and Iridium Amino, Amido, and Aminyl Radical Complexes
The principal values of the rhombic g matrix [g1
=
2.084(2), g2 = 2.049(2), g3 = 2.027(2)] and the large nitrogen
hyperfine coupling of 100 MHz along g3 were determined
from echo-detected EPR frozen solution spectra at Q-band
(see inset in Figure 5B) and W-band (not shown here). Pulse
EPR techniques were applied to obtain a complete picture
of the anisotropic part of the hyperfine interactions and
thus the spin populations. As an example, a Q-band HY-
SCORE (hyperfine sublevel correlation) spectrum of 14a
measured at T = 25 K is shown in Figure 5B along with its
simulation (Figure 5C).
At the chosen observer position of B0 = 1220.9 mT (indi-
cated by the line position in the EPR spectrum displayed in
the inset of Figure 5B), crosspeaks from the nitrogen nuclei
N2 (strong coupling case |A| Ͼ 2|ν14N|) in the (–,+) quad-
rant and N3 (weak coupling case |A| Ͻ 2|ν14N|) in the (+,+)
quadrant are observed. The position of the double-quan-
tum crosspeaks allow initial guesses for the hyperfine coup-
lings (for a small quadrupole interaction), as they are cen-
tered at the hyperfine value A and split by 4ν14N in the
strong coupling case, and in the weak coupling case the
double-quantum peaks are centered at 2ν14N and split by
2A (Figure 5B). Measurements at several observer positions
allowed determination of the principal values of the nitro-
gen hyperfine and nuclear quadrupole tensors listed in
Table 3. The rhodium hyperfine principal values were ob-
tained from the room-temperature and frozen-solution CW
EPR spectra (see Supporting Information) recorded at X-
band.
A paramagnetic iridium aminyl radical complex was sig-
nificantly more difficult to stabilize. When the amide com-
plex [Ir(trop2N)(phen)] (13) was treated with a ferrocenium
salt as oxidant under conditions identical to those used for
the generation of 14 (solutions of which are stable at room
Figure 5. (A) S-band (2.63 GHz) CW EPR spectrum recorded at
room temperature (298 K) of 14a in thf/acetone (2:1). Experimental
(exp.) and simulated (sim.) spectra. (B) Q-band (35.3 GHz)
HYSCORE spectra of 14a in thf measured at 25 K at observer
positions B0 = 1220.9 mT. Selected crosspeaks are assigned to ni- temperature for at least a couple of weeks) no EPR signal
trogen N1, N2, and N3 with labels for nitrogen double-quantum
could be detected and the NMR spectra showed resonances
(d) and single-quantum (s) frequencies. Inset: Q-band echo-de-
for the amine complex [Ir(trop2NH)(phen)]+ (11). Only
tected EPR spectrum (first derivative representation) showing the
when stock solutions of the amide [Ir(trop2N)(phen)] and
observer position used to record the HYSCORE spectrum. (C)
the ferrocenium salt were combined and the reaction mix-
Simulated Q-band HYSCORE spectrum.
Table 3. Hyperfine and nuclear quadrupole parameters for aminyl radical complexes 14a and 15. Numbers in brackets are error estimates.
[Rh(trop2N·)(phen)]OTf (14a)
g1,2,3 = 2.084(2), 2.049(2), 2.027(2)
Nucleus
|Aiso| [MHz]
|A1,2,3| [MHz]
|κ|[a] [MHz]
η[a]
N1
N2
N3
45.4(5)
10.4(5)
3.1(2)
27.0(5)
9.9(5)
18(5), 18(5), 100(3)
12.3(5), 9.6(5), 8.7(5)
3.0(2), 3.2(2), 3.0(2)
48(2), 16(3), 16(3)
–
1.6(2)
3.0(2)
2.6(2)
–
0.7(2)
0.3(1)
0.2(1)
–
Rh
Hbz(ϫ2)
–
–
[Ir{trop2N·(phen)}] (OTf/PF6) (15)
g1,2,3 = 2.140(2), 2.107(2), 2.015(2)
Nucleus
|Aiso| [MHz]
|A1,2,3| [MHz]
|κ|[a] [MHz]
η[a]
N1
N2
47(5)
7.9(5)
3.5(5)
26.8(5)
21(5), 21(5), 100(3)
10.2(5), 7.9(5), 5.7(5)
3.2(2), 4.0(2), 3.2(2)
44(5), 30(5), Ͻ20
1.5(2)
2.1(2)
2.2(2)
–
0.7(2)
0.0(1)
0.0(1)
–
N3
191Ir
[a] Nuclear quadrupole interactions κ = |e2qQ/h| and asymmetry parameter η = (Qx – Qy)/Qz with Qx = –κ(1 – η)/[4I(2I – 1)], Qy = –κ(1
+ η)/[4I(2I – 1)] and Qz = 2κ/[4I(2I – 1)].
Eur. J. Inorg. Chem. 2008, 4691–4703
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4697

H. Grützmacher et al.
FULL PAPER
ture rapidly frozen in liquid nitrogen could an EPR spec- 2p orbital, respectively). For the iridium complex, the
trum of 15 be recorded. Remarkably, the stability of 15 is analysis of the N1 hyperfine coupling gives 3.3% (2s or-
significantly enhanced when a solution contains 10–25 mM bital) and 53% (2p orbital).
of the iridium complex and about 400 mM of nBuN4PF6 as
The hyperfine coupling of N1 with a large isotropic and
electrolyte. Under these circumstances, solutions of 15 re- a pronounced axial dipolar part, and the rather small an-
main EPR active for a couple of hours at room tempera- isotropy of the g matrix characterize these species best as
ture. A frozen-solution (T = 120 K) CW EPR spectrum of RhI or IrI aminyl radical complexes with an estimated spin
15 at X-band (9.53 GHz) is shown in Figure 6A, along with population of about 60% at the aminyl radical center N1.
a satisfactory simulation obtained by employing the three A DFT calculation that we performed for the bipy complex
principal g values and hyperfine couplings from the iridium [Rh(trop2N·)(bipy)]OTf (G) showed that the majority
nucleus and the N1 and N2 nuclei (two and three principal (≈30%) of remaining spin population is localized at the
values were determined independently by HYSCORE metal center.[8] Because the EPR spectra are very similar for
data).[23] In addition, HYSCORE spectra taken at different H, 14a, and 15, we assume that in the latter the spin density
observer positions (for an example see Figure 6B) enabled at the metal center is of the same magnitude. In summary
the determination of the complete set of hyperfine coupling the results show that the MII amide resonance form contrib-
constants of N1, N2, and N3 (see Table 3). As a result, we utes significantly to the electronic ground state and stabi-
found a remarkable similarity between the spin population lizes the complexes.
distribution in rhodium and iridium radical complexes 14
and 15. Moreover, the ligand hyperfine coupling constants
Reactivity
In accord with the electronic structure, the complexes
of both species are almost identical to that of the previously
investigated bipyridine complex [Rh(trop2N·)(bipy)]+ (G;
Scheme 1).[8] From the isotropic (Aiso = (2A1,2 + A3)/3) and
dipolar (T = |A1,2 – Aiso|) parts of the axial hyperfine inter-
action, the spin population for the N1 nucleus of the rho-
dium complex in the 2s orbital is calculated as 45.3/
1443.9 MHz = 3.1% and for the 2p orbital 27.3/49.8 MHz
= 55% (1443.9 and 49.8 MHz are the hyperfine coupling
constant for 14N with 100% spin population in the 2s and
[Rh(trop2N·)(bipy)]OTf (H) and [M(trop2N·)(phen)]OTf
(14a: M = Rh; 15: M = Ir) behave like aminyl radical com-
plexes. In view of their almost-identical EPR spectra, it is
not surprising that bipy complex H and phenanthrolin
complexes 14a and 15 show almost the same reactivity
(Scheme 6).
Scheme 6. Reactivity of 14a and 15 with H atom donors. The reac-
tion between 15 and Et3SiH gives the siloxane (Et3Si)2O, which is
shown in grey.
With hydrogen donors of
a
lower BDE than
360 kcalmol–1, like tributylstannane (BDE = 308.5 kJ
mol–1) or thiophenol (BDE = 348.7 kJmol–1), very clean
and fast reactions to amine complexes 6a or 11 were ob-
served. The H abstractions with the tert-butyl thiol or thio-
glycolic acid methyl ester (estimated BDE Ͼ 380 kJmol–1)
are slightly endothermic and slower, but they are driven by
the formation of the corresponding disulfides, which make
the overall process strongly exothermic by ca.
300 kJmol–1.[24] Phenol does not react because of the
strength of the O–H bond (BDE Ͼ 376 kJmol–1) and the
instability of the peroxide, Ph–O–O–Ph. Although the reac-
tions with silanes (BDE ≈ 360 kJmol–1), phenyl-substituted
methanes (BDE Ͻ 350 kJmol–1), or 9,10-dihydroanthra-
cene (BDE = 315.1 kJmol–1) are thermodynamically fa-
vored, no reaction was observed with rhodium complex 14a
Figure 6. (A) X-band (9.5315 GHz) CW EPR spectra of 15
measured at 120 K in thf, experimental (exp.) and simulated (sim.).
The simulation requires the g-matrix and N1, N2, and Ir hyperfine
couplings. (B) Q-band (35.25 GHz) HYSCORE spectra of 15 in thf
measured at 15 K at B0 = 1200.0 mT. Selected crosspeaks are as-
signed to nitrogen N1, N2, and N3 with labels for nitrogen double-
quantum (d) and single-quantum (s) frequencies. Inset: Q-band
echo-detected EPR spectrum (first derivative) showing the observer
position used to record the HYSCORE spectrum.
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Rhodium and Iridium Amino, Amido, and Aminyl Radical Complexes
indicating a kinetic barrier for the H-abstraction reactions. cal complexes, the Rh–N(trop2) bond shortens significantly
As noted above, the iridium complex [Ir(trop2N·)(phen)]- (≈14 pm) and the coordination sphere around N becomes
OTf (15) behaves slightly differently. This complex is highly trigonal planar. Both effects are in accord with the assump-
unstable in thf solution and gives cleanly within seconds at tion that the electron is removed from a d(M)–p(N) anti-
room temperature amine complex 11. When aminyl com- bonding orbital.
plex 15 is generated in the presence of 9,10-dihydroanthra-
The EPR results in combination with our previous study
cene as H-donor, the expected anthracene is not observed including DFT calculations[8] bolster this picture. Although
although amine complex 11 was cleanly obtained. We were significant spin population (about 30%) is located at the
unable to determine the source of hydrogen that generates metal center, about 60% resides on the nitrogen, which
11 from 15.[25] Whereas rhodium complex 14a remains un- justifies the aminyl radical complex description,
affected in the presence of silane, iridium aminyl complex [M(trop2N·)(phen)]+ (M = Rh: 14a, M = Ir: 15). Moreover,
15 does react rapidly with Et3SiH (BDE = 377 kJmol–1) to hydrogen-abstraction reactions with stannanes and thiols,
form 11 and siloxane Et3Si–O–SiEt3 [δ(29Si) = 9.1 ppm].[26] which give the amine complexes, show that these com-
It is at present unclear by which mechanism the siloxane pounds show the expected reactivity of aminyl complexes.
was formed.
Like in the deprotonation reactions of the amine complexes,
our first experiments indicate that sizeable kinetic barriers
may be associated with these H-abstraction reactions, which
may have steric and/or electronic origins. A puzzle to be
solved remains the apparently higher instability (and reac-
Conclusions
Straight-forward simple routes to fivefold-coordinated tivity) of the iridium complex [Ir(trop2N·)(phen)]+ (15), al-
18-electron rhodium and iridium amine diolefin complexes though its ground-state structure must be very similar to
were developed from readily available starting materials. Es- that of rhodium complex 14a. We have no satisfying expla-
pecially the acetonitrile complexes [Rh(trop2NH)(MeCN)2]- nation for this phenomenon at present, but we note that
OTf (5) and [IrCl(trop2NH)(MeCN)] (10) proved to be suit- iridium radical complexes seemingly show higher reactiv-
able precursor complexes for the syntheses of various phen- ity.[11,20] Whether this is eventually a property of a transi-
anthroline-type complexes [M(trop2NH)(R,R-phen)]+ (6a– tion state on the reaction coordinate in H-abstraction reac-
d, 11; M = RhI or IrI; R = substituents at phen). These tions remains to be investigated.
complexes are quantitatively (judged by 1H NMR spec-
troscopy) deprotonated by one equivalent of KOtBu to give
the neutral amido complexes [M(trop2N)(R,R-phen)] (12a–
c, 13). The pKa of the amine complexes in dmso is in a
narrow range between 18.2 and 19, and it is remarkably
independent of the metal center. We attribute this to the
fact that the olefin moieties are arranged in a perpendicular
fashion with respect to the NH–M-axis. Hence, the MǞL
Experimental Section
General Techniques: All manipulations of air- or moisture-sensitive
compounds were performed with a standard vacuum line in flame-
dried flasks under an atmosphere of argon. The argon was pro-
vided by PANGAS and further purified with an MBraun 100 HP
gas purification system. Solvents were distilled under argon from
back bonding, which is certainly larger in the iridium com-
plexes and stabilizes the amido complex,[16b] has only a neg-
ligible effect on the pKa. The reversible redox potential of
amido complexes 12a–c and 13 lies likewise within a narrow
range of –0.54 to –0.60 V (in dmso vs. Fc+/Fc). The NH
bond energies in all amine complexes are estimated to be
about 360 kJmol–1. Whereas small bases rapidly depro-
tonate the amine complexes to the corresponding amido
complexes, a sizeable kinetic barrier may be encountered
with sterically demanding bases, as indicated by data ob-
tained from the self-exchange reaction [Equation (4), vide
supra].
A second complete set of structures for an amine
(trop2NH), amido (trop2N), and aminyl radical (trop2N·)
complex could be obtained (6a, 12a, 14a), and some general
structural features become apparent: (i) The amine and
amido complexes have rather similar structures; noteworthy
is the pyramidal coordination sphere around the nitrogen
center in the amido complexes. (ii) The ligand in the trans
position to the amido ligand is bonded at slightly longer
distances than in the corresponding amine complexes indi-
cating a stronger trans influence of the amido group. (iii)
sodium (toluene), sodium/benzophenone (thf, dimethoxyethane, di-
ethyl ether), sodium/benzophenone/tetraglyme (n-hexane), sodium–
potassium alloy (benzene), calcium hydride (dichloromethane, ace-
tonitrile). Air-sensitive compounds were stored and weighed in a
glove box (M Braun: lab master 130 or 150B-G). Reactions in small
quantities were performed within a glove box.
Cyclic Voltammetric Investigations: CV spectra were recorded with
a Princeton Applied Research potentiostat/galvanostat model 263A
or model 283. The measurements were performed with an appara-
tus designed by Heinze et al.[27] Working electrode: planar platinum
electrode (approximate surface area 0.785 mm2); reference elec-
trode: silver; counter electrode: platinum wire. At the end of each
measurement, ferrocene was added as internal standard for cali-
bration (–0.352 V vs. Ag/AgCl).
EPR: The S-band CW EPR spectra were measured with a home-
built instrument with a home-built split-ring resonator. The tem-
perature was controlled by a liquid helium cryostat from Oxford,
Inc. Measurements used microwave (mw) power of 11 mW, a mod-
ulation amplitude of 0.1 mT, and a modulation frequency of
100 kHz. The X-band CW EPR spectra were measured with a
Bruker E500 spectrometer equipped with a liquid nitrogen cryostat
by using a modulation amplitude of 0.2 mT and a modulation fre-
quency of 100 kHz. The Q-band spectra were measured with a
Upon oxidation of the amido complexes to the aminyl radi- home-built instrument equipped with a liquid helium cryostat from
Eur. J. Inorg. Chem. 2008, 4691–4703
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4699

H. Grützmacher et al.
FULL PAPER
Oxford, Inc. The echo-detected EPR spectra were recorded at 15 K
by using the two-pulse sequence π/2–τ–π–echo with tπ/2 = 50 ns, tπ
= 100 ns, and a variable τ from 500 to 748 ns in 8 ns steps. Q-band
HYSCORE spectra were measured at 15 K and a repetition rate of
1 kHz by using the sequence π/2–τ–π/2–t1–π–t2–π/2–τ–echo. The
mw pulse lengths were tπ = 16 ns, tπ/2 = 16 ns, with starting times
t1,2 = 96 ns and a time increment ∆t1,2 = 12 ns. EPR data were
simulated with the program EasySpin[28] and HYSCORE spectra
with a program written in-house.[29]
[Rh(trop2NH)(phen)]OTf (6a): To
a
solution of [Rh2(µ-Cl)2-
(trop2NH)2] (3; 300 mg, 0.28 mmol) in thf (100 mL) was added
phenanthroline (114 mg, 0.62 mmol, 2.2 equiv.) and silver triflate
(144 mg, 0.56 mmol, 2.0 equiv.), and the solution was heated at re-
flux overnight. The yellow suspension was filtered through Celite,
and the residual silver chloride was washed with thf (30 mL). The
filtrate was dried in vacuo and recrystallization from CH2Cl2/hex-
ane (1:1) yielded the product as bright-orange needles (360 mg,
78%). Yellow crystals for X-ray structural analysis were grown
from
a
concentrated thf/hexane (1:1) solution. 1H NMR
UV/Vis: Spectra were recorded with a UV/Vis/NIR lambda 19
spectrometer in 5-mm quartz cuvettes (200–1000 nm). Time-de-
pendent measurements were performed with an Analytik Jena Spe-
cord S100 (diode array) spectrometer.
(500.2 MHz, [D6]dmso): δ = 3.99 (d, 3JHH = 9.4 Hz, 2 H, Hol), 4.94
(s, 2 H, Hbzl), 5.04 (s, 1 H, NH), 5.56 (d, JHH = 9.0 Hz, 2 H, Hol)
3
ppm. 13C NMR (100.6 MHz, [D6]dmso): δ = 68.0 (d, JRhC
=
1
7.3 Hz, 2 C, Col), 69.3 (d, JRhC = 12.3 Hz, 2 C, Col), 71.4 (s, 2 C,
Cbzl) ppm. 103Rh NMR (15.8 MHz, [D6]dmso): δ = 2111 (s) ppm.
1
NMR Spectra: NMR spectra were recorded with Bruker Avance
500, 300, or 250 spectrometers. The chemical shifts (δ) were mea-
sured according to IUPAC regulations and expressed in ppm rela-
tive to TMS and H3PO4 for 1H, 13C and 31P, respectively.[30] Excep-
tion is for 103Rh with the frequency reference Ξ = 3.16 MHz. Coup-
ling constants J are given in Hertz [Hz] as absolute values, unless
specifically stated. Where first-order analysis is appropriate, the
multiplicity of the signals is indicated as s, d, t, q, or m for singlets,
doublets, triplets, quartets, or multiplets, respectively. Otherwise,
the spin systems are specified explicitly. The abbreviation br. is
given for broadened signals. The benzylic protons and carbon
atoms are designated as Hbzl and Cbzl, respectively, and the olefinic
protons and carbon atoms as Hol and Col, respectively. Only se-
lected spectroscopic data of diagnostic value are given. For further
details see the Supporting Information.
ATR IR: ν = 3196 (w, N–H stretch) cm–1. C H F N O RhS
˜
43 31
3
3
3
(829.61): calcd. C 62.25, H 3.76, N 5.06; found C 62.31, H 3.81, N
5.02.
General Procedure (GP 1) for [Rh(trop2NH)(R,R-phen)]OTf (6b–d):
To a solution of [Rh(trop2NH)(MeCN)2]OTf (5) in thf (5 mM) was
added the phenanthroline derivative in slight excess (1.2–
1.4 equiv.). The solution was heated at reflux overnight and cooled
to room temperature, and the solvent was removed in vacuo. The
raw product was subsequently recrystallized from CH2Cl2/hexane
(1:1).
[Rh(trop2NH)(4,7-Me2-phen)]OTf (6b): Compound
5 (100 mg,
0.14 mmol) was treated with 4,7-dimethylphenanthroline (35.0 mg,
0.17 mmol) according to GP 1 to give a yellow powder (99 mg,
82%). 1H NMR (400.1 MHz, CD3CN): δ = 2.87 (s, 3 H, CH3),
3
3.00 (s, 3 H, CH3), 3.79 (s, 1 H, NH), 4.04 (dd, JHH = 9.5 Hz,
[Rh2(µ-Cl)2(trop2NH)2] (3): [Rh2(µ2-Cl)2(cod)2] (500 mg, 1.01 mmol)
and trop2NH (806 mg, 2.02 mmol, 2 equiv.) were dissolved in
CH2Cl2 (20 mL). The bright orange-red solution turned dark red
after 30 min, and the mixture was left overnight without stirring.
Dark-red crystals were formed, which were isolated by filtration
and washed with hexane. Drying in vacuo yielded an orange pow-
2JRhH = 1.0 Hz, 2 H, Hol), 4.96 (s, 2 H, Hbzl), 5.50 (dd, JHH
=
3
2
9.3 Hz, JRhH = 2.2 Hz, 2 H, Hol) ppm. 13C NMR (100.6 MHz,
1
CD3CN): δ = 18.5 (s, 1 C, CH3), 18.7 (s, 1 C, CH3), 67.9 (d, JRhC
1
= 7.7 Hz, 2 C, Col), 69.2 (d, JRhC = 12.3 Hz, 2 C, Col), 71.5 (s, 2
C, Cbzl) ppm. 103Rh NMR (12.7 MHz, CD3CN): δ = 2099 (s) ppm.
ATR IR: ν = 3221 (w, NH stretch) cm–1.
˜
1
der (874 mg, 78%). H NMR (400.1 MHz, CD2Cl2): δ = 2.90 (s, 2
3
2
H, NH), 4.44 (s, 4 H, Hbzl), 5.97 (dd, JHH = 9.4 Hz, JRhH
=
[Rh(trop2NH)(4,7-Ph2-phen)]OTf (6c): Compound
5 (100 mg,
2.1 Hz, 4 H, Hol), 6.20 (d, 3JHH = 9.4 Hz, 4 H, Hol) ppm. 13C NMR
(100.6 MHz, CD2Cl2): δ = 71.4 [br. s, 8 C, Col], 73.1 (s, 4 C, Cbzl
ppm. 103Rh NMR (12.7 MHz, CD2Cl2): δ = 2992 (s) ppm. ATR
IR: ν = 3200 (w, NH stretch) cm–1. UV/Vis (CH CN): λ (ε,
0.14 mmol) was treated with and 4,7-diphenylphenanthroline
(64.0 mg, 0.19 mmol) according to GP 1 to give a bright-orange
powder (96 mg, 71%). Bright-orange crystals for X-ray structural
analysis were grown from a concentrated CH2Cl2 solution. 1H
)
˜
3
3
Lmol–1 cm–1)
=
232 (sh.), 289 (45700), 329 (sh.) nm.
NMR (400.1 MHz, [D6]dmso): δ = 4.13 (d, JHH = 9.6 Hz, 2 H,
Hol), 4.96 (s, 2 H, Hbzl), 5.17 (s, 1 H, NH), 5.59 (dd, 3JHH = 9.6 Hz,
2JRhH = 2.2 Hz, 2 H, Hol) ppm. 13C NMR (75.5 MHz, [D6]dmso):
C60H46Cl2N2Rh2 (1071.74): calcd. C 67.24, H 4.33, N 2.61, Cl 6.62;
found C 67.03, H 4.47, N 2.89, Cl 6.77.
1
1
δ = 67.6 (d, JRhC = 8.5 Hz, 2 C, Col), 69.1 (d, JRhC = 12.8 Hz, 2
C, Col), 71.0 (s, 2 C, Cbzl) ppm. 103Rh NMR (12.6 MHz, [D6]dmso):
δ = 2096 (s) ppm.
[Rh(trop2NH)(MeCN)2]OTf (5): To a solution of [Rh2(µ-Cl)2-
(trop2NH)2] (3; 100 mg, 93.4 µmol) in acetonitrile (25 mL) was
added silver triflate (48 mg, 187 µmol, 2 equiv.). The mixture was
heated at reflux overnight and after filtration through Celite all
volatiles were removed in vacuo to give a yellow powder (134 mg,
98%). 1H NMR (400.1 MHz, CD3CN): δ = 2.37 (s, 3 H, axial-
CH3), 4.03 (s, 1 H, NH), 4.78 (s, 2 H, Hbzl), 5.36 (d, 3JHH = 9.4 Hz,
2 H, Hol), 5.77 (dd, 3JHH = 9.4 Hz, 2JRhH = 2.5 Hz, 2 H, Hol) (note:
equatorial CH3CN is exchanged for solvent molecules) ppm. 13C
NMR (100.6 MHz, CD3CN): δ = 4.4 (s, 1 C, axial-CH3), 70.3 (d,
[Rh(trop2NH)(5,6-Me2-phen)]OTf (6d): Compound
5 (50 mg,
64 mmol) was treated with 5,6-dimethylphenanthroline (20 mg,
96 mmol) according to GP 1 to give a yellow powder (46 mg, 79%).
Yellow crystals for X-ray structural analysis were grown from a
1
concentrated CH3CN solution. H NMR (400.1 MHz, CD3CN): δ
= 2.86 (s, 3 H, CH3), 2.89 (s, 3 H, CH3), 3.83 (s, 1 H, NH), 4.07
3
3
(d, JHH = 9.3 Hz, 2 H, Hol), 4.98 (s, 2 H, Hbzl), 5.54 (dd, JHH
=
2
9.5 Hz, JRhH = 2.2 Hz, 2 H, Hol) ppm. 13C NMR (100.6 MHz,
1
1JRhC = 8.0 Hz, 2 C, Col), 71.0 (d, JRhC = 12.3 Hz, 2 C, Col), 71.6
1
CD3CN): δ = 15.1 (s, 1 C, CH3), 15.2 (s, 1 C, CH3), 68.0 (d, JRhC
(s, 2 C, Cbzl) ppm. 103Rh NMR (12.7 MHz, CD3CN): δ = 2311 (s)
1
= 8.2 Hz, 2 C, Col), 69.5 (d, JRhC = 12.8 Hz, 2 C, Col), 71.5 (s, 2
ppm. ATR IR: ν = 3131 (s, NH stretch), 2300 (w, CϵN stretch),
˜
C, Cbzl) ppm. 103Rh NMR (12.6 MHz, CD3CN): δ = 2093 (s) ppm.
2280 (w, CϵN stretch) cm–1. Raman: ν = 2297 (s, CϵN stretch),
˜
ATR IR: ν = 3198 (w, NH stretch) cm–1.
˜
2277(s, CϵN stretch) cm–1. UV/Vis (CH3CN): λmax (ε,
Lmol–1 cm–1) = 211 (55000), 229 (sh.), 284 (24.000), 320 (sh.) nm.
C35H29F3N3O3RhS (731.59): calcd. C 57.46, H 4.00, N 5.74, S 4.38,
F 7.79; found C 57.47, H 4.10, N 5.57, S 4.22, F 7.72.
[Rh(trop2NH)(acac)] (7): To a solution of [Rh2(µ-Cl)2(trop2NH)2]
(3; 250 mg 0.23 mmol) in thf (100 mL) was added a solution
(0.5 mL) prepared from acetylacetone (1.05 mL, 10.2 mmol) and
4700
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 4691–4703

Rhodium and Iridium Amino, Amido, and Aminyl Radical Complexes
KOtBu (1.26 g 11.2 mmol) in methanol (10 mL). The yellow solu-
tion was heated at reflux overnight and cooled to room tempera-
ture, and the solvent was removed in vacuo. The raw product was
recrystallized from CH2Cl2/hexane (1:1) to give a yellow crystalline
solid (226 mg, 82%). Yellow crystals for X-ray structural analysis
solvent signals), 77.5 (s, Cbzl) ppm. 103Rh NMR (12.7 MHz, [D8]-
thf): δ = 1570 (s) ppm. UV/Vis (thf): λmax = 326 nm.
[Rh(trop2N)(4,7-Me2-phen)] (12b): Complex 6b (120 mg,
0.14 mmol) was treated with KOtBu (16 mg, 0.14 mmol) according
to GP 2 to yield a brown powder (89 mg, 90%). 1H NMR
(250.1 MHz, [D8]thf): δ = 2.76 (s, 3 H, CH3), 2.95 (s, 3 H, CH3),
1
were grown from a concentrated CH2Cl2/hexane (1:1) solution. H
NMR (300.1 MHz, CDCl3): δ = 1.65 (s, 3 H, CH3), 1.90 (s, 3 H,
CH3), 2.92 (s, 1 H, NH), 4.40 (s, 2 H, Hbzl), 4.83 (d, 3JHH = 9.3 Hz,
2 H, Hol), 5.38 (dd, 3JHH = 9.3 Hz, 2JRhH = 2.5 Hz, 2 H, Hol) ppm.
13C NMR (75.5 MHz, CDCl3): δ = 27.8 (s, 1 C, CH3), 28.7 (s, 1 C,
3
3.45 (d, JHH = 9.5 Hz, 2 H, Hol), 4.10 (s, 2 H, Hbzl), 5.01 (dd,
2
3JHH = 9.1 Hz, JRhH = 2.0 Hz, 2 H, Hol) ppm. 13C NMR
(62.9 MHz, [D8]thf): δ = 17.6 (s, 2 C, CH3), 17.8 (s, 2 C, CH3), 67.3
(s, 2 C, Col), 79.4 (s, 2 C, Cbzl) ppm. 103Rh NMR (15.8 MHz, [D6]-
dmso): δ = 1547 (s) ppm.
1
1
CH3), 66.8 (d, JRhC = 13.4 Hz, 2 C, Col), 69.9 (d, JRhC = 8.5 Hz,
2 C, Col), 73.0 (s, 2 H, Cbzl) ppm. 103Rh NMR (12.7 MHz, CDCl3):
δ = 2998 (s) ppm. ATR IR: ν = 3063 (w, NH stretch) cm–1.
[Rh(trop2N)(4,7-Ph2-phen)] (12c): Complex 6c (100 mg, 0.10 mmol)
was treated with KOtBu (13 mg, 0.10 mmol) according to GP 2 to
˜
C35H30NO2Rh·CH2Cl2 (684.455): calcd. C 63.17, H 4.71, N 2.34;
found C 62.94, H 4.79, N 2.00.
yield
a
dark red-brown powder (70 mg, 82%). 1H NMR
(250.1 MHz, [D6]dmso): δ = 3.55 (d, 3JHH = 9.3 Hz, 2 H, Hol), 4.10
[Ir2(µ-Cl)2(trop2NH)2] (9): To a suspension of [Ir2(µ2-Cl)2(coe)4]
(1.00 g, 1.11 mmol) in toluene (200 mL) was added trop2NH (2;
887 mg 2.23 mmol), and the reaction mixture was heated at reflux
for 48 h. A yellow suspension formed. The product was isolated by
filtration, and it was then subsequently washed with toluene to give
(s, 2 H, Hbzl), 5.12 (d, JHH = 9.3 Hz, JRhH = 1.6 Hz, 2 H, Hol)
ppm. 13C NMR (100.6 MHz, [D6]dmso): δ = 65.3 (s, 2 C, Col), 66.9
(s, 2 C, Col), 78.9 (s, 2 C, Cbzl) ppm. 103Rh NMR (15.8 MHz, [D6]-
dmso): δ = 1562 (s) ppm.
3
2
yellow microcrystalline solid (809 mg, 58%). 1H NMR
[Ir(trop2N)(phen)] (13): To a solution of complex 11 (100 mg,
0.11 mmol) in thf (4 mL) was added KOtBu (20 mg, 0.18 mmol,
1.6 equiv.) in one portion. An immediate color change from yellow
to very dark green was observed. The volume of the solution was
reduced to approx. 1 mL and then hexane (3 mL) was added. A
green-brown powder precipitated, which was filtered and washed
with hexane to yield a green-brown powder (70 mg, 83%). 1H
a
(300.1 MHz, CDCl3): δ = 3.67 (s, 2 H, NH), 4.58 (s, 4 H, Hbzl),
5.58 (d, JHH = 8.8 Hz, 4 H, Hol), 5.83 (d, JHH = 9.1 Hz, 4 H,
3
3
Hol) ppm. 13C NMR (75.5 MHz, [D6]dmso): δ = 51.1 (s, 2 C, Col),
52.6 (s, 2 C, Col), 70.0 (s, 4 C, Cbzl) ppm. ATR IR: ν = 3199 (w,
˜
N–H stretch) cm–1. C60H46Cl2Ir2N2 (1250.36): calcd. C 63.17, H
4.71, N 2.34; found C 62.94, H 4.79, N 2.00.
3
NMR (300.1 MHz, [D8]thf): δ = 2.72 (d, JHH = 8.8 Hz, 2 H, Hol),
[IrCl(MeCN)(trop2NH)] (10): [Ir2(µ-Cl)2(trop2NH)2] (9; 500 mg,
0.4 mmol) was suspended in CH3CN (75 mL), and the mixture was
heated at reflux overnight whereby a white suspension formed. The
reaction mixture was cooled to room temperature and all volatiles
were removed in vacuo to yield a white flaky solid (515 mg, 97%).
1H NMR (500.1 MHz, CDCl3): δ = 2.50 (s, 3 H, CH3), 4.40 (s, 1
H, NH), 4.48 (d, 3JHH = 8.7 Hz, 2 H, Hol), 4.67 (s, 2 H, Hbzl), 5.00
(d, 3JHH = 8.7 Hz, 2 H, Hol) ppm. 13C NMR (125.8 MHz, CDCl3):
δ = 4.2 (s, 1 C, CH3), 45.6 (s, 2 C, Col), 53.7 (s, 2 C, Col), 72.7 (s,
2 C, Cbzl) ppm.
3
4.30 (s, 2 H, Hbzl), 4.81 (d, JHH = 9.1 Hz, 2 H, Hol) ppm. 13C
NMR (62.9 MHz, [D6]dmso): δ = 44.0 (s, 2 C, Col), 50.8 (s, 2 C,
Col), 77.0 (s, 2 C, Cbzl) ppm.
[Rh(trop2N·)(phen)]OTf (14a): To a solution of amide 12a (50 mg,
74 µmol) in thf (8 mL) was added ferrocenium triflate (25 mg,
74 µmol, 1 equiv.) in one portion. The volume of the solution was
reduced to about 4 mL and hexane (4 mL) was then added where-
upon a dark-green precipitate was formed. The product was fil-
tered, washed with hexane (4 mL) and thoroughly dried in vacuo
to afford radical 14a as a finely divided pale-green powder. Dark-
red crystals for X-ray structural analysis were grown from a satu-
rated thf solution. UV/Vis (thf): λmax = 217, 230, 267, 297 nm.
[Rh(trop2N·)(4,7-Me2-phen)]OTf (14b): To a solution of amide 12b
(18 mg, 26 µmol) in thf (1 mL) was added ferrocenium triflate
(8 mg, 24 µmol, 1 equiv.) in one portion. Hexane (1 mL) was
added, whereupon a dark-green precipitate was formed. The prod-
uct was filtered, washed with hexane (1 mL), and thoroughly dried
in vacuo. Radical 14b was obtained as a pale-green powder.
[Ir(trop2NH)(phen)]PF6 (11): Complex 10 (250 mg, 0.38 mmol),
phenanthroline (70.0 mg, 0.38 mmol, 1 equiv.), and TlPF6 (160 mg,
0.46 mmol, 1.2 equiv.) were dissolved in chlorobenzene (10 mL).
The dark-red solution was heated at reflux overnight, which re-
sulted in the formation of a bright-orange suspension. The product
was filtered and washed with ice-cold chlorobenzene to give a yel-
low powder (330 mg, 96%). 1H NMR (300.1 MHz, [D8]thf): δ =
3
3
3.26 (d, JHH = 8.8 Hz, 2 H, Hol), 4.78 (s, 1 H, NH), 5.18 (d, JHH
= 9.3 Hz, 2 H, Hol), 5.36 (s, 2 H, Hbzl) ppm. 13C NMR (62.9 MHz,
[D6]dmso): δ = 47.9 (s, 2 C, Col), 51.1 (s, 2 C, Col), 71.0 (s, 2 C,
[Ir(trop2N·)(phen)](OTf/PF6) (15): Ferrocenium triflate (22 mg,
66 µmol) and nBu4NPF6 (774 mg, 2 mmol) were dissolved in thf
(5 mL) and neutral amide complex 13 (10 mg, 13 µmol) was dis-
solved in thf (0.5 mL). An aliquot (0.1 mL) of each of these solu-
tions were combined in an EPR tube and sealed off.
Cbzl) ppm. ATR IR: ν = 3233 (w, N–H stretch) cm–1.
˜
General Procedure (GP 2) for the Amido Complexes [Rh(trop2N)-
(R,R-phen)] (12a–c): To a solution of the amine complex in thf
(18 mm) was added KOtBu (1.0 equiv.). The volume of the solution
was reduced to about 20%. n-Hexane was added slowly to reach a
1:1 (by vol.) mixture whereby the product precipitated. The product
was filtered off and washed with n-hexane.
X-ray Crystallography: Crystals of 3 were grown from the mother
liquor (CH2Cl2) overnight at the bottom of the flask and isolated
by decantation. Crystals of 5 were grown from a concentrated
CH3CN solution. Yellow crystals of 7 suitable for analysis were
grown from a concentrated CH2Cl2/hexane (1:1) solution. Crystals
of 6a were grown from a concentrated thf/hexane (1:1) solution.
Crystals of 6d were grown from a concentrated CH3CN solution.
Dark-red crystals of 12a were grown from a saturated thf solution.
Dark-red crystals of 14a were slowly grown from a concentrated
thf solution. To avoid quality degradation, most single crystals were
mounted in perfluoropolyalkyl ether oil on top of a glass fiber and
[Rh(trop2N)(phen)] (12a): Complex 6a (150 mg, 0.18 mmol) was
treated with KOtBu (21 mg, 0.18 mmol) according to GP 2 to give
a dark-red powder (103 mg, 84%). Dark-red crystals for X-ray
structural analysis were slowly grown from a concentrated thf solu-
1
3
tion. H NMR (300.1 MHz, [D8]thf): δ = 2.73 (d, JHH = 9.1 Hz,
2 H, Hol), 4.30 (s, 2 H, Hbzl), 4.81 (d, JHH = 9.1 Hz, 2 H, Hol)
3
ppm. 13C NMR (62.9 MHz, [D8]thf): δ = 63.3 (d, JRhC = 13.0 Hz,
1
2 C, Col), 64.1 (2 C, Col; doublet not resolved due to overlapping
Eur. J. Inorg. Chem. 2008, 4691–4703
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4701

H. Grützmacher et al.
FULL PAPER
then brought into the cold nitrogen stream of a low-temperature
device so that the oil solidified. Data collection for the X-ray struc-
ture determinations were performed with SMART APEX plat-
ment parameters except for of 14a in which the incorporated thf
molecules were refined isotropically, because of high disordering.
The thf molecules (14a) and dichloromethane molecules (7) in the
crystal lattice are slightly (7) or strongly (14a) disordered and a
high number of restraints were used to achieve a satisfactory wR2
value. Hydrogen atoms were placed in their idealized positions and
allowed to ride on the respective carbon atoms. Upon convergence,
the final Fourier difference map of the X-ray structures of 6a,d, 7,
and 14a showed no significant peaks. For 12a, some residual elec-
tron density was located close to the heavy atom rhodium (≈0.65 Å)
even when an absorption correction was applied. Associated crys-
tallographic data and other experimental details are summarized in
Tables 4 and 5.
forms with graphite-monochromated Mo-Kα radiation (λ
=
0.71073 Å). The reflex intensities were measured by CCD area de-
tectors. The collected frames were processed with the proprietary
software SAINT.[31] Solution and refinement of the structures was
performed with SHELXS-97[32] and SHELXL-97,[33] respectively.
The structures were solved by the Patterson-method and successive
interpretation of the difference Fourier maps, followed by full-ma-
trix least-squares refinement (against F2). Moreover, an empirical
absorption correction (SADABS[34]) was applied to all structures.
All non-hydrogen atoms were refined with anisotropic displace-
Table 4. Crystal data and refinement for compounds 3, 5, and 7.
3·(CH2Cl2)2
5
7·CH2Cl2
Empirical formula
Formula mass
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C60H46Cl2N2Rh2·3CH2Cl2
C35H29F3N3O3RhS
731.58
C36H32Cl2NO2Rh
684.44
monoclinic
P21/n
16.1605(10)
13.0108(8)
30.422(2)
90
100.7000(10)
90
666.22
triclinic
monoclinic
P21/n
8.819(1)
32.691(4)
11.023(1)
90
103.379(4)
90
3091.7(6)
4
¯
P1
10.920(3)
12.821(3)
13.328(3)
65.876(5)
66.155(5)
67.821(4)
1506.5(6)
2
α [°]
β [°]
γ [°]
V [Å3]
6285.3(7)
8
Z
F(000)
670
1488
0.41ϫ0.34ϫ0.28
1.572
2800
0.35ϫ0.32ϫ0.05
1.447
Crystal size [mm]
ρcalcd. [gcm–3]
µ [mm–1]
0.27ϫ0.15ϫ0.14
1.469
0.943
0.680
0.746
T [K]
100(2)
8460
5120 [R(int) = 0.0285]
293(2)
19510
5271 [R(int) = 0.0681]
298(2)
26087
9015 [R(int) = 0.0601]
Reflections collected
Unique reflections
Flack parameter
GOF on F2
R1, wR2 [IϾ2σ(I)]
R1, wR2 (all data)
1.053
0.0569, 0.1340
0.0823, 0.1453
1.144
0.0524, 0.0825
0.0780, 0.0886
1.051
0.0508, 0.1016
0.1031, 0.1195
Table 5. Crystal data and refinement for compounds 6a,d, 12a, and 14a.
6a
6d·CH3CN
12a·2thf
14a·2thf
Empirical formula
Formula mass
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C86H60F6N6O6Rh2S2
1657.34
monoclinic
P21/c
18.8761(11)
14.6610(9)
13.7651(8)
90
C47H38F3N4O3RhS
898.78
orthorhombic
P212121
13.073(3)
15.114(4)
19.522(5)
90
C40H36.80N2.40O1.60Rh0.80 C34H30.67F2N2O3.33Rh0.67S0.67
659.05
monoclinic
P21/n
648.59
monoclinic
P21/n
14.0367(4)
18.4891(6)
14.6286(4)
90
13.6004(10)
17.4667(13)
19.7546(15)
90
α [°]
β [°]
110.233(1)
90
3574.3(4)
2
90
90
96.2090(10)
90
3774.23(19)
5
106.6330(10)
90
4496.4(6)
6
γ [°]
V [Å3]
3857.3(18)
4
Z
F(000)
1684
0.48ϫ0.35ϫ0.32
1.540
1840
0.22ϫ0.20ϫ0.17
1.548
1712
0.32ϫ0.25ϫ0.21
1.450
2004
0.21ϫ0.16ϫ0.06
1.437
Crystal size [mm]
ρcalcd. [gcm–3]
µ [mm–1]
0.598
0.562
0.500
0.490
T [K]
200(2)
30835
8869 [R(int) = 0.0289]
298(2)
31550
7880 [R(int) = 0.0864]
0.02(3)
1.003
0.0439, 0.0818
0.0815, 0.0933
150(2)
118008
26075 [R(int) = 0.0543]
200(2)
35606
9198 [R(int) = 0.0669]
Reflections collected
Unique reflections
Flack parameter
GOF on F2
R1, wR2 [IϾ2σ(I)]
R1, wR2 (all data)
1.046
0.0347, 0.0830
0.0414, 0.0865
1.114
0.0619, 0.1207
0.0865, 0.1292
1.047
0.0529, 0.1145
0.1033, 0.1346
4702
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 4691–4703

Rhodium and Iridium Amino, Amido, and Aminyl Radical Complexes
[13]
T. Büttner, F. Breher, H. Grützmacher, Chem. Commun. 2004,
2820–2821.
CCDC-679134 (for 3), -679133 (for 5), -673814 (for 7), -673467 (for
6a), -673466 (for 6d), -673468 (for 12a), and -673465 (for 14a) con-
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[14]
It is well established that the equatorial position in TBP 18-
electron complexes is labile (see standard textbooks on organo-
metallic chemistry). Furthermore, for electronic reasons π-ac-
ceptor ligands bind in the equatorial position, whereas σ-donor
ligands reside in the axial position of TBP; for a classical paper,
see: A. Rossi, R. Hoffmann, Inorg. Chem. 1975, 14, 365.
F. G. Bordwell, Acc. Chem. Res. 1988, 21, 456. For an extensive
listing of pKa values of various acids see: D. A. Ripin, D. A.
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Acknowledgments
This work was supported by the ETH Zürich and the Swiss
National Science Foundation (SNF). H. G. and H. S. thank the
Morgan Motor Company for continuous inspiration.
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Published Online: September 10, 2008
Eur. J. Inorg. Chem. 2008, 4691–4703
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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