Diamido rhodates(1-)

Article abstract of DOI:10.1002/anie.200502036

(Chemical Equation Presented) The filled/filled repulsion model can be used to explain qualitatively the trends in the acidity of the coordinated NH groups, the redox potentials of the amides, and the UV/Vis absorptions in different aggregates between a c

Full text of DOI:10.1002/anie.200502036

Angewandte
Chemie
Rhodium Complexes
which is only stable in the presence of an excess of anilide in
solution, the NHPh groups are likely rotated such that they
are orientated perpendicular to the central plane, and the lone
pairs are involved in the complexation of the alkali-metal
cation.
Previously, we reported the stable neutral rhodium(i)
amides B and C, which were isolated and fully characterized
(see Table 1 for pertinent data). The pentacoordinate 18-
electron complex B adopts the expected trigonal-bipyramidal
structure with the nitrogen atom in an apical position.[4,5] The
DOI: 10.1002/anie.200502036
Diamido Rhodates(1ꢀ)**
Pascal Maire, Frank Breher, and
Hansjörg Grützmacher*
Dedicated to Professor Herbert W.Roesky
on the occasion of his 70th birthday
[Rh(trop2N)(L\L)] amides
B (trop2N = bis(5H-dibenzo-
[a,d]cycloheptene-5-yl)amide; L\L = tropNH2, bipy) are
reversibly oxidized at about ꢀ0.5 V (versus the ferroce-
nium/ferrocene, Fc+/Fc, couple) to the aminyl radical com-
plexes [Rh(trop2N)(L\L)]+C. Their conjugated acids, [Rh-
(trop2NH)(L\L)]+, have pKa values of about 19 in DMSO.[5]
In the neutral tetracoordinate 16-electron complex [Rh(trop2-
dachꢀH)], C, the NR2 group is approximately coplanar with
the central plane, which leaves the amide nitrogen lone pair in
The M N bond in late transition-metal amides[1] is susceptible
ꢀ
to a number of useful synthetic transformations.[2] Some years
ago, Brunet et al. reported the only known bis-
(amido)rhodium(i) complexes, which were characterized in
rather complex equilibria in the reaction of [RhnClm(PR3)l]
compounds with anilide, MNHPh (M = Li, Na).[3] Based on
NMR data, the structure A was proposed for {Li(solv)x-
[Rh(NHPh)2(PR3)2]} (Scheme 1). In this intimate ion pair,
a
perpendicular position (trop2dach = (R,R)-N,N’-bis(5H-
dibenzo[a,d]cyclohepten-5-yl)-1,2-diaminocyclohexane; the
“ꢀH” indicates mono-deprotonation).[6] This complex is less
readily oxidized (ꢀ0.34 V versus Fc+/Fc) and the pKaDMSO of
the conjugated acid [Rh(trop2dach)]+ (15.7) is significantly
lower than in B. We now report the first stable and fully
characterized diamido rhodates(1ꢀ) and some of their
properties. Interestingly, we observe different aggregates
between the countercation, [M(solv)n]+ (solv = solvent mol-
ecules), and the diamido rhodate(1ꢀ) anion.
For this purpose, we used the chiral tetrachelating amino
olefin (S,S)-N,N’-bis(5H-dibenzo[a,d]cyclohepten-5-yl)-1,2-
diphenyl-1,2-ethylenediamine ((S,S)-trop2dpen = (S,S)-1)[6]
as ligand (Scheme 2). The reaction of ligand (S,S)-1 with
[Rh(cod)2]OTf was straightforward and gave the orange-red
Scheme 1. The diamido rhodate(1ꢀ) A reported by Brunet et al. [3]
,
and isolated 18-electron and 16-electron rhodium(i) amides B and C,
respectively (L\L=tropNH2, bipy).
Table 1: Selected structural and physical data of B, C, (S,S)-3, (S,S)-4, (S,S)-5hip, (S,S)-5cip, and (S,S)-5sip. ꢀ8 denotes the sum of bond angles
around the nitrogen atom. d(103Rh) in ppm ([D8]THF, 298 K).
ꢀ8(N1)[a]
ꢀ8(N2)
pKDa MSO[b]
Eoox[V][c]
lmax [nm]
d(103Rh)
ꢀ
Rh N1
ꢀ
Rh N2
B
2.05
340.0
19
ꢀ0.5
>0.6
ꢀ0.34
–
ꢁ380
470
516
506
545
598
599
>1000
897
(S,S)-3
C
(S,S)-4
(S,S)-5hip
(S,S)-5cip
(S,S)-sip
2.093(3)
1.962(2)
–
1.955(2)
1.964(4)
1.992(3)
2.083(3)
2.110(2)
–
2.030(2)
2.002(4)
1.976(3)
342.7(2)
351.1(2)
–
358.8(2)
355.7(4)
347.3(3)
339.8(3)
337.4(2)
–
340.0(2)
343.8(4)
350.9(3)
15.7(2)
–
736
702
–
577
21–23
ꢀ1.09
665[d]
682
[a] N1 denotes the amido nitrogen center, N2 is NH in C and N-K in (S,S)-5hip. [b] Data of the corresponding acids with the protonated ligand.
[c] Potentials versus Fc+/Fc in a THF/nBu4NPF6 electrolyte at T=208C, scan rate 100 mVsꢀ1, Pt working electrode. [d] (S,S)-5 sip in [D6]DMSO:
d(103Rh)=666 ppm.
complex (lmax = 470 nm) (S,S)-3. When an orange solution of
(S,S)-3 in THF was treated with one equivalent of KOtBu, the
solution immediately turned red to furnish the amide (S,S)-4
quantitatively. This compound was not isolated but was
[*] Dr. P. Maire, Dr. F. Breher, Prof. Dr. H. Grützmacher
Department of Chemistry and Applied Biosciences
ETH-Hönggerberg
8093 Zürich (Switzerland)
Fax: (+41)44-633-1032
characterized by NMR and UV/Vis spectroscopy, which show
that it is very similar to C (see Table 1 for selected data).
Subsequently, (S,S)-4 was further deprotonated under differ-
ent reaction conditions: a) in THF, b) in the presence of three
equivalents of [18]crown-6 (18C6), and c) in the presence of
[2.2.2]cryptand (C222) (see Scheme 2). In case (a), an
E-mail: gruetzmacher@inorg.chem.ethz.ch
[**] This work was supported by the LANXESS AG and the Swiss
National Science Foundation.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2005, 44, 6325 –6329
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6325

Communications
Figure 1 a). Such arene–potassium interactions were
recently proposed to account for the performance of
ruthenium(ii) amides as hydrogenation catalysts.[9] Note
+
ꢀ
that the coordination of the K ion to N2 causes the Rh
N2 bond (2.030(2) Š) to be significantly longer and the N2
coordination sphere to be more pyramidal (sum of angles
ꢀ8 = 340.0(2)8) compared to N1 which binds at a remark-
able short distance (1.955(2) Š) to Rh and resides in an
almost planar coordination sphere (ꢀ8 = 358.8(2)8).
In the crown-ether complex (S,S)-5cip, the [K(18C6)-
(thf)]+ and [Rh(trop2dpenꢀ2H)]ꢀ form a loose contact ion
pair; the potassium ion binds at about 3.2 Š in an h2-
fashion to one benzo group from the outside of the anion
(Figure 2). In the two crystallographically independent
ꢀ
molecules in (S,S)-5cip the slightly shorter Rh N bond
lengths (1.968(4) Š) correlate with a larger sum of bond
ꢀ
angles ꢀ8(N) = 354.58 (ꢀ8(N) = 344.18 for the longer Rh
N distances, 1.994(4) Š; averaged data).
In
[K(C222)][Rh(trop2dpenꢀ2H)]·Et2O·1.5THF,
(S,S)-5sip (Figure 3), the potassium ion has no direct
contact to the anion and is encapsulated by the
[2.2.2]cryptand. A “free” diamido rhodate(1ꢀ) ion is
ꢀ
observed with short Rh N distances (1.984(3) Š) and
flattened coordination spheres at N1 and N2 (ꢀ8(N) =
ꢀ
349.1(3)8) compared to the situation in (S,S)-3 (R N
2.09 Š, ꢀ8(N) = 341.28). Taking the average over all
ꢀ
structures, the Rh N distance to an amido nitrogen
atom, NR2, is about 5% shorter than to an amino nitrogen
atom, NR3.
Figure 4 shows the UV/Vis spectra of the cationic
complex (S,S)-3, the neutral rhodium amide (S,S)-4, the
Scheme 2. Synthesis of the amidorhodium(i) complex (S,S)-4, and the various ion
pairs (S,S)-5hip, (S,S)-5cip, and (S,S)-5 sip.
intensely deep red solution was obtained. In cases (b) and (c),
deep green solutions were obtained. Double deprotonation of
(S,S)-3 in DMSO as solvent with two equivalents of KOtBu
1
also gave green solutions. The H NMR spectra indicated in
each case, that the doubly deprotonated diamido rho-
date(1ꢀ), (S,S)-[Rh(trop2dpenꢀ2H)]ꢀ was obtained.
The products obtained under the conditions a)–c) in
Scheme 2 were crystallized and the results of the X-ray
diffraction studies are displayed in Figures 1–3, respectively.[7]
From experiment (a), darkred crystals of the composition
(S,S)-{K[Rh(trop2dpenꢀ2H)](thf)3}, (S,S)-5hip, precipitated
(> 80% yield) after the reaction mixture had been layered
with n-hexane. From experiments (b) and (c), darkgreen
needles of the composition (S,S)-{[K(18C6)(thf)][Rh(trop2-
dpenꢀ2H)]}·0.5Et2O, (S,S)-5cip, and (S,S)-[K(C222)]
[Rh(trop2dpenꢀ2H)]·Et2O·1.5THF, (S,S)-5sip, were ob-
tained from solutions of the respective complexes in THF
layered with Et2O (ꢂ 80% yield).
Figure 1. a) Structure of the complex (S,S)-5hip. Thermal ellipsoids are
drawn at 30% probability; the three THF molecules are depicted as
ball-and-stick models; hydrogen atoms apart from those in the
ethylene bridge are omitted for clarity. Selected bond lengths [Š] and
ꢀ
ꢀ
ꢀ
ꢀ
angles [8]: Rh N1 1.955(2), Rh N2 2.030(2), Rh C4 2.141(3), Rh C5
ꢀ
ꢀ
ꢀ
ꢀ
2.121(3), Rh ct1 2.010(3), Rh C19 2.126(3), Rh C20 2.130(3), Rh ct2
The structure of (S,S)-5hip is best described as an
electrostatically enforced host–guest complex,[8] in which the
cationic [K(thf)3]+ fragment is embedded in the ligand
frameworkof the anion (see Figure 1b). The potassium ion
has short contacts to the rhodium(i) atom, one amide nitrogen
atom, one hydrogen atom in the ethylene bridge, and four
carbon atoms of one of the adjacent benzo rings (see
=
=
ꢀ
ꢀ
2.004(3), C4 C5trop 1.418(4), C19 C20trop 1.430(4), Rh K 3.3596(9), K
ꢀ
ꢀ
ꢀ
ꢀ
N2 2.856(3), K O1 2.727(3), K O2 2.635(3), K O3 2.736(4), K C17
ꢀ
ꢀ
ꢀ
ꢀ
3.424(3), K C18 3.387(3), K C23 3.908(3), K C26 3.797(3), K H31
2.81; N1-Rh-N2 80.5(1), N1-Rh-ct1 90.8(1), N2-Rh-ct2 92.4(1), ct1-Rh-
=
ct2 96.8(1); f=7.68; (ct=centroids of the C Ctrop units; f is the inter-
section of the planes spanned by the rhodium atom, the N atom and
ct of each bischelate ligand). b) Space-filling model of (S,S)-5hip.
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Angewandte
Chemie
Figure 3. Structure of one of the two independent ion pairs in (S,S)-
5sip. a) Structure of the anion, hydrogen atoms are omitted for clarity.
Thermal ellipsoids are drawn at 30% probability. Selected bond lengths
[Š] and angles [8] (data for the second molecule are given in italics):
Figure 2. Structure of one of the two independent molecules in
(S,S)-5cip. a) A diethyl ether molecule in the crystal lattice and hydro-
gen atoms are omitted for clarity. Thermal ellipsoids are drawn at 30%
probability. Selected bond lengths [Š] and angles [8] (data for the
ꢀ
ꢀ
ꢀ
ꢀ
Rh1 N1 1.992(3), Rh1 N2 1.976(3), Rh2 N3 1.995(3), Rh2 N4
ꢀ
ꢀ
ꢀ
1.970(3), Rh1 C4 2.145(4), Rh1 C5 2.110(4), Rh2 C104 2.136(3),
ꢀ
ꢀ
ꢀ
ꢀ
Rh2 C105 2.113(4), Rh1 C19 2.161(4), Rh1 C20 2.114(4), Rh2 C119
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2.134(4), Rh2 C120 2.119(4), Rh1 ct1 2.004(4), Rh1 ct2 2.014(4),
second molecule are given in italics): Rh1 N1 1.964(4), Rh1 N2
ꢀ
ꢀ
=
=
Rh2 ct3 2.001(4), Rh2 ct4 2.004(4), C4 C5trop 1.429(6), C19 C20trop
ꢀ
ꢀ
ꢀ
ꢀ
2.002(4), Rh2 N3 1.986(4), Rh2 N4 1.972(4), Rh1 C4 2.144(5), Rh1
=
=
1.434(6), C104 C105trop 1.427(5), C119 C120trop 1.422(5), N1-Rh1-N2
81.9(1), N1-Rh1-ct1 91.4(2), N2-Rh1-ct2 91.2(2), ct1-Rh1-ct2 97.9(2),
N3-Rh2-N4 82.0(1), N3-Rh2-ct3 92.0(2), N4-Rh2-ct4 91.3(2), ct3-Rh2-
ꢀ
ꢀ
ꢀ
C5 2.134(5), Rh2 C53 2.156(5), Rh2 C54 2.109(5), Rh1 C19 2.135(4),
ꢀ
ꢀ
ꢀ
ꢀ
Rh1 C20 2.120(5), Rh2 C68 2.159(5), Rh2 C69 2.144(5), Rh1 ct1
ꢀ
ꢀ
ꢀ
ꢀ
2.022(5), Rh1 ct2 2.006(5), Rh2 ct4 2.008(5), Rh2 ct5 2.028(5), Rh1
=
ꢀ
=
=
ct4 97.3(2); f=16.68, f=17.18; (ct=centroids of the C Ctrop units;
ct3 3.164(6), Rh2 ct6 3.217(6), C4 C5trop 1.397(8), C19 C20trop
1.416(8), C53 C54trop 1.436(8), C68 C69trop 1.439(8), K1 C24 3.179(6),
=
=
f is the intersection of the planes spanned by the rhodium atom, the
N atom and ct of each bischelate ligand). b) Space-filling model of
(S,S)-5sip.
ꢀ
ꢀ
ꢀ
K2 C62 3.255(6), K1 O(18C6) 2.729(4)–2.861(4), K2-O(18C6) 2.760(4)–
2.833(4), N1-Rh1-N2 80.5(2), N3-Rh2-N4 81.0(2), N2-Rh1-ct2 91.9(2),
N3-Rh2-ct4 91.9(2), N1-Rh1-ct1 90.5(2), N4-Rh2-ct5 91.6(2), ct1-Rh1-
ct2 97.4(2), ct4-Rh2-ct5 97.8(2); f=6.48, f=16.28; (ct=centroids of
=
C C bonds; f is the intersection of the planes spanned by the
rhodium atom, the N atom and ct of each bischelate ligand). b) Space-
filling model of (S,S)-5cip.
intimate ion pair (S,S)-5hip, and the diamido rhodate(1ꢀ) salt
(S,S)-5sip in THF. Note the progressively red-shifted absorp-
tion lmax in the series: (S,S)-3!(S,S)-4 (Dlmax ꢁ 40 nm), (S,S)-
4!(S,S)-5hip (Dlmax ꢁ 40 nm), and (S,S)-5hip!(S,S)-5 sip
(Dlmax ꢁ 50 nm).
We believe that the deep red color (lmax = 545 nm)
characterizes the host–guest ion pair (S,S)-5hip. Furthermore
we assume that (S,S)-5cip and (S,S)-5 sip both dissociate in
solution and the green color (lmax = 598 nm) indicates the
presence of the solvent separated “free” anion [Rh(trop2-
dpenꢀ2H)]ꢀ. 1H NMR spectroscopy did not allow us to
distinguish between both situations, but the 103Rh NMR
resonance signal of a red solution of (S,S)-5hip is observed at
d = 580 ppm, whereas the green solutions of (S,S)-5cip and
(S,S)-5sip showed d(103Rh) ꢁ 670 ppm (Table 1).
Figure 4. UV/Vis spectra of (S,S)-3, (S,S)-4, (S,S)-5hip, and (S,S)-5sip
in solution in THF.
A cyclic voltammogram (Pt electrode, 0.1m nBu4NPF6/
THF electrolyte at T= 208C, scan rate 100 mVsꢀ1) of a green
solution of (S,S)-5 in DMSO shows a reversible redox wave
for the process (1) at a remarkably low oxidation potential
(ꢀ1.09 V, versus Fc+/Fc):
(S,S)-3, (S,S)-4, (S,S)-5hip, and (S,S)-5sip (Table 1) can be
interpreted within the concept of filled/filled repulsions
(FFR) elegantly developed by Caulton (see Figure 5).[10,11]
In a pentacoordinate 18-electron rhodium amide I, the
lone pair at the amide nitrogen atom undergoes a strong and
repulsive two-center–four-electron interaction with the occu-
pied dxz orbital at the metal center. This orbital is directed
towards the filled p-type orbital at the nitrogen center and is
C
½Rhðtrop2dpenꢀ2HÞꢃꢀꢀeꢀ ! ½Rhðtrop2dpenꢀ2HÞꢃ
ð1Þ
The relative differences between the pKa values, redox
potentials, Eoox, and UV/Vis absorptions in the complexes B, C,
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Communications
Experimental Section
General: Solvents were freshly distilled under argon from sodium/
benzophenone (THF, Et2O) or from sodium/diglyme/benzphenone
(n-hexane). Air-sensitive compounds were stored and weighed in a
glovebox (Braun MB 150 B-G system), and reactions on small scales
were performed directly in the glovebox. NMR spectra were recorded
on Bruker Avance 400 or 500 systems. The chemical shifts are given as
d values and were referenced against tetramethylsilane (TMS) for 1H
and 13C. 103Rh NMR spectra were calibrated with the frequency
reference X = 3.16 MHz. IR spectra were measured with the attenu-
ated total reflection technique (ATR) on a Perkin-Elmer 2000 FT-IR
spectrometer in the range from 4000 cmꢀ1 to 600 cmꢀ1 using a KBr
beam splitter. The UV/Vis spectra were measured with a Perkin-
Elmer UV/Vis/NIR Lambda 19 spectrometer in 0.5-cm quartz
cuvettes.
(S,S)-{K[Rh(trop2dpenꢀ2H)](thf)3} ((S,S)-5hip): To an orange
solution of (S,S)-[Rh(trop2dpen)]SO3CF3 ((S,S)-3) (84 mg,
0.10 mmol) in THF (2 mL) was added KOtBu (25 mg, 0.22 mmol).
The color turned immediately to darkred and the solution was
layered with n-hexane (10 mL). Darkred crystals of ( S,S)-5hip
(80 mg, 0.84 mmol; 84%) suitable for x-ray structure analysis grew
overnight. M.p. > 1308C (decomp); 1H NMR (400.1 MHz, [D8]THF):
d = 3.30 (d, 3JH,H = 8.9 Hz, 2H; CHolefin), 3.91 (s, 2H; CH(Ph)(N)),
Figure 5. Schematic diagram showing the interaction of filled metal
located and filled nitrogen located orbitals in a pentacoordinate 18-
electron amido complex I, a tetracoordinate 16-electron amino amido
complex II, and a bisamido complex III [filled/filled repulsion
(FFR) model]. Only the energetically high-lying antibonding orbital
interactions based on extended Hückel calculations are presented.
3
4.21 (d, JH,H = 8.9 Hz, 2H; CHolefin), 4.35 (s, 2H; CHbenzyl), 6.60–7.03
(m, 22H; CHar), 7.37–7.45 ppm (m, 4H; CHar); 13C NMR (100.6 MHz,
1
only slightly perturbed by the olefins which lie in the nodal
plane (see Figure 5a). In a tetracoordinate 16-electron amino
amido complex II, the lone pair at N also suffers from a
repulsive interaction (seen in the red shift of lmax in (S,S)-4
compared to that in (S,S)-3). However, less so because the
filled dxz and dyz orbitals at the metal center are involved in
[D8]THF): d = 68.4 (br, CHolefin), 70.8 (CHbenzyl), 74.5 (d, JRh,C
=
13.0 Hz; CHolefin), 83.4 (CH(Ph)(N)), 123.6–129.0 (CHar), 141.1–
148.2 ppm (Cquart); 103Rh NMR (12.7 MHz, [D8]THF): d = 577 (s);
ATR-IR (neat): n˜ = 3061w, 2972m, 2866m, 1594m, 1482m, 1466s,
1404m, 1259m, 1052s, 1016m, 896m, 750s, 699s cmꢀ1; UV/Vis
(THF): lmax (e) = 545 (2210), 339 (7760), 277 nm (25680).
(S,S)-{[K([18]crown-6)(thf)][Rh(trop2dpen)]} ((S,S)-5cip): To an
orange solution of (S,S)-[Rh(trop2dpen)]SO3CF3 ((S,S)-3) (84 mg,
0.10 mmol) in THF (2 mL) was added KOtBu (25 mg, 0.22 mmol)
followed by [18]crown-6 (79 mg, 0.3 mmol). The resulting darkgreen
solution was layered with Et2O. Darkgreen crystals of ( S,S)-5cip
(101 mg, 0.080 mmol; 80%) grew overnight. M.p. > 1558C (decomp);
1H NMR (400.1 MHz, [D8]THF): d = 3.08 (d, 3JH,H = 8.9 Hz, 2H;
CHolefin), 3.53 (m, 24H; OCH2CH2O), 3.96 (s, 2H; CH(Ph)(N)), 3.99
=
M!L back-bonding into the p*(C C) orbitals and are
polarized towards the coordinated olefins (see Figure 5b).
In that respect, the coordinated olefins contribute to the
remarkable stability of late transition metal. Consequently,
the strongly destabilized amide I is easy to oxidize and the NH
function in its conjugated acid has a low acidity (large pKa).
On the other hand, the pKa value of the NH function of a 16-
electron amine complex such as (S,S)-3, which gives amide
(S,S)-4 upon deprotonation, is more acidic (by approximately
four orders of magnitude). However, double deprotonation of
a diamino complex to give a diamido complex III gives rise to
two destabilizing interactions between the nitrogen lone pairs
and the filled dxz and dyz orbitals at the metal center (see
Figure 5c). Consequently, lmax is red-shifted to about 600 nm
in compounds of type III. The facile oxidation of III can be
taken as a further indication of this destabilization. The pKa
value of the NH function in the amine amide complex of type
II falls in the region (21 < pKDa MSO < 23).[12] In the host–guest
ion pairs, the destabilizing interaction is diminished (blue shift
of lmax ((S,S)-5sip!(S,S)-5hip) by about 50 nm) because of
the interaction of the nitrogen lone pair with the potassium
cation.
(d, 3JH,H = 8.9 Hz, 2H; CHolefin), 4.27 (d, 3JRh,H = 1.8 Hz, 2H; CHbenzyl),
3
6.56–6.59 (m, 4H; CHar), 6.67–6.94 (m, 18H; CHar), 7.30 (d, JH,H
=
7.4 Hz, 2H; CHar), 7.35 ppm (d, 3JH,H = 7.4 Hz, 2H; CHar); 13C NMR
(100.6 MHz, [D8]THF): d = 67.6 (d, 1JRh,C = 10.5 Hz; CHolefin), 70.5
1
(OCH2CH2O) 71.3 (CHbenzyl), 73.5 (d, JRh,H = 12.8 Hz, CHolefin), 84.6
(CH(Ph)(N)), 122.4–129.7 (CHar), 142.3–148.6 ppm (Cquart); 103Rh
NMR (12.7 MHz, [D8]THF): d = 665 ppm (s); ATR-IR (neat): n˜ =
2879m, 1593w, 1480w, 1463m, 1349m, 1246s, 1099s, 960m,
835m cmꢀ1; UV/Vis (THF): lmax (e) = 598 (2420), 412 (8310), 339
(15360), 275 nm (26370).
(S,S)-{[K(C222)][Rh(trop2dpenꢀ2H)]} ((S,S)-5 sip): To an
orange solution of (S,S)-[Rh(trop2dpen)]SO3CF3 ((S,S)-3) (32 mg,
0.038 mmol) in THF (0.5 mL) was added KOtBu (9 mg, 0.08 mmol,
2.1 equiv) followed by [2.2.2]cryptand (30 mg, 0.08 mmol, 2.1 equiv).
The resulting darkgreen solution was layered with Et O (2.5 mL).
2
Darkgreen crystals of ( S,S)-5 sip (41 mg, 0.031 mmol; 80%) grew
overnight. M.p. > 2108C (decomp); 1H NMR (500.1 MHz,
3
[D8]THF): d = 2.55- 2.57 (m, 12H; NCH2CH2O), 3.06 (d, JH,H
=
Caultonꢀs FFR concept qualifies nicely as a model to
interpret the results presented here with a set of structurally
very closely related and rare dialkylamine/amide complexes.
On the other hand, the fact that the NH functions in d8
rhodium complexes are remarkably acidic[13] (note that the
diamide (S,S)-5 is even stable in presence of small amounts of
9.0 Hz, 2H; CHolefin), 3.54–3.56 (m, 12H; NCH2CH2O), 3.60 (s,
12H; OCH2CH2O), 3.95 (d, 3JH,H = 9.0 Hz, 2H; CHolefin), 3.98 (s, 2H;
CH(Ph)(N)), 4.27 (d, 3JRh,H = 2.2 Hz, 2H; CHbenzyl), 6.56–6.96 (m,
22H; CHar), 7.28–7.36 ppm (m, 4H; CHar); 13C NMR (125.8 MHz,
1
[D8]THF): d = 54.3 (NCH2CH2O), 67.5 (d, JRh,C = 10.0 Hz; CHolefin),
67.9 (NCH2CH2O), 70.7 (OCH2CH2O), 71.3 (CHbenzyl), 73.3 (d,
1JRh,H = 12.7 Hz; CHolefin), 84.7 (CH(Ph)(N)), 122.2–129.8 (CHar),
142.8–149.7 ppm (Cquart); 103Rh NMR (15.8 MHz, [D8]THF): d =
682 ppm (s); ATR-IR (neat): n˜ = 3055w, 2965w, 2868s, 1593m,
1479m, 1461m, 1352m, 1256m, 1100s, 946m, 747s, 700m cmꢀ1; UV/
ꢀ
methanol or water) and that the Rh N bond shortens upon
deprotonation must await a more deep-sighted (computa-
tional) analysis.
6328
www.angewandte.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2005, 44, 6325 –6329

Angewandte
Chemie
Vis (THF): lmax (e) = 599 (2160), 412 (8300), 339 (15750), 275 nm
refinement against full matrix (versus F2) with SHELXTL (ver.
(23160).
6.12) and SHELXH-97, 1508 parameters, 22 restraints, R1 =
0.0424 and wR2 (all data) = 0.1106, max./min. residual electron
density 0.660/ꢀ0.618 eŠꢀ3. For all reported x-ray crystal struc-
tures the non-hydrogen atoms were refined anisotropically. Only
one carbon atom of a Et2O solvent molecule in (S,S)-5sip had to
be refined using the ISOR restraint. The contribution of the
hydrogen atoms, in their calculated position, was included in the
refinement using a riding model. Upon convergence, the final
Fourier difference map showed no significant peaks. CCDC-
267206 ((S,S)-5hip), CCDC-267207 ((S,S)-5cip), and CCDC-
272867 ((S,S)-5sip) 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.
Received: June 13, 2005
Keywords: alkene ligands · amides · binding models · redox
.
chemistry · rhodium
[1] a) The first rhodium(i) amide was reported by: B. Cetinkaya,
M. F. Lappert, S. Torroni, J.Chem.Soc.Chem.Commun.
1979,
843; for reviews see: b) M. F. Lappert, P. P. Power, A. R. Sanger,
R. C. Shrivastava, Metal and Metalloid Amides, Ellis Horwood,
Chichester, UK, 1980; c) H. E. Brynzda, W. Tam, Chem.Rev.
1988, 88, 1163; d) M. D. Fryzuk, C. D. Montgomery, Coord.
Chem.Rev. 1989, 95, 1; e) J. R. Fulton, A. W. Holland, D. J. Fox,
R. G. Bergman, Acc.Chem.Res. 2002, 35, 44.
[8] Because the coordination sphere of the unsaturated [K(thf)3]+
fragment is completed by direct and close contacts within the
cavity of the [Rh(trop2dpenꢀ2H]ꢀ ion, we denote (S,S)-5hip as a
host–guest ion pair held together by electrostatic forces.
Similarly, (S,S)-5cip is considered as contact ion pair because
the one open coordination site in the [K(18C6)(thf)]+ ion is
completed by one contact with the anion, however, outside of its
cavity. The ion pair (S,S)-5sip is denoted as a separated ion pair
because of the lackof a direct contact between the potassium ion
and the anion although the cryptand penetrates the anion in the
solid state. For further definitions see, G. Boche, Angew.Chem.
[2] Selected recent reviews: a) S. E. Clapham, A. Hadzovic, R. H.
Morris, Coord.Chem.Rev. 2004, 248, 2201; b) F. Alonso, I. P.
Beletskaya, M. Yus, Chem.Rev. 2004, 104, 3079; c) R. Noyori, T.
Ohkuma, Angew.Chem. 2001, 113, 40; Angew.Chem.Int.Ed.
2001, 40, 40.
[3] a) J.-J. Brunet, G. Commenges, D. Neidbecker, K. Phillipot, L.
Rosenberg, Inorg.Chem. 1994, 33, 6373; b) J.-J. Brunet, G.
Commenges, D. Neidbecker, K. Phillipot, L. Rosenberg, J.
Organomet.Chem. 1996, 522, 117; polyanionic amides of
rhodium(iii) have been reported: R. Zhou, C. Wang, Y. Hu,
T. C. Flood, Organometallics 1997, 16, 434.
1992, 104, 742; Angew.Chem.Int.Ed.Engl.
1992, 31, 731, and
references therein. For a review on ion pairing in organo-
metallics see: A. Macchioni, Chem.Rev. 2005, 105, 2039.
[9] R. Hartmann, P. Chen, Angew.Chem. 2001, 113, 3693; Angew.
Chem.Int.Ed. 2001, 40, 3581.
[4] T. Büttner, F. Breher, H. Grützmacher, Chem.Commun. 2004,
2820.
[5] T. Büttner, J. Geier, G. Frison, J. Harmer, C. Calle, A. Schweiger,
H. Schönberg, H. Grützmacher, Science 2005, 307, 235.
[6] P. Maire, F. Breher, H. Schönberg, H. Grützmacher, Organo-
metallics 2005, 24, 3207.
[10] K. G. Caulton, New J.Chem. 1994, 18, 25.
[11] D. Conner, K. N. Jayaprakash, T. B. Gunnoe, P. D. Boyle, Inorg.
Chem. 2002, 41, 3042, and references therein.
[12] The pKa of (S,S)-4 could not be determined exactly but was
estimated by using indole (pKdamso = 20.95) and benzamide
(pKdamso = 23.35) as reference substances. Green solutions of
(S,S)-5sip in DMSO react with a slight excess ( ꢁ 10%) of indole
to give red (S,S)-4, which can be deprotonated with lithium
benzamide to give backthe green solution characteristic for the
diamido rhodate(1ꢀ), (S,S)-5sip.
[7] Crystal structure of (S,S)-5hip: Red, highly air-sensitive crystals
were obtained from a THF solution which was layered with n-
hexane at room temperature; C56H58KN2O3Rh, orthorhombic,
space group P2(1)2(1)2(1); a = 11.102(1), b = 16.690(1), c =
24.797(1) Š, V= 4594.4(4) Š3; Z = 4; 1calcd = 1.372 Mgmꢀ3; crys-
tal dimensions 0.58 ” 0.23 ” 0.23 mm; diffractometer Bruker
SMART Apex; MoKa radiation, 200 K, 2Vmax = 56.768; 48252
reflections, 11474 independent (Rint = 0.0779), direct methods;
refinement against full matrix (versus F2) with SHELXTL (ver.
6.12) and SHELXL-97, 568 parameters, 36 restraints, R1 =
0.0434 and wR2 (all data) = 0.0914, max./min. residual electron
density 0.980/ꢀ0.706 eŠꢀ3. Crystal structure of (S,S)-5cip: Dark
green single crystals were obtained from a THF/Et2O solution at
room temperature; C120H132K2N4O14Rh2·Et2O, monoclinic, space
group P2(1); a = 12.842(1), b = 23.010(1), c = 18.969(1) Š, b =
101.780(1)8; V= 5487.1(5) Š3; Z = 2; 1calcd = 1.339 Mgmꢀ3; crys-
tal dimensions 0.60 ” 0.32 ” 0.30 mm; diffractometer Bruker
SMART Apex; MoKa radiation, 200 K, 2Vmax = 52.748; 40465
reflections, 21957 independent (Rint = 0.0285), direct methods;
empirical absorption correction SADABS (ver. 2.03); refine-
ment against full matrix (versus F2) with SHELXTL (ver. 6.12)
and SHELXL-97, 1326 parameters, 1 restraint, R1 = 0.0457 and
wR2 (all data) = 0.1124, max./min. residual electron density
0.775/ꢀ0.429 eŠꢀ3. Crystal structure of (S,S)-5 sip: Darkgreen
single crystals were obtained from a THF solution which was
[13] For rather basic amide complexes (pKTa HF > 22) see: D. Rais,
R. G. Bergman, Chem.Eur.J. 2004, 10, 3970; and references
therein.
layered
124H140K2N8O12Rh2·3THF·2Et2O, triclinic, space group P1;
a = 12.078(1), b = 14.324(1), c = 21.272(2) Š, a = 80.882(1), b =
with
Et2O
at
room
temperature;
C
85.728(2), g = 68.406(1)8; V= 3378.1(5) Š3; Z = 1; 1calcd
=
1.270 Mgmꢀ3; crystal dimensions 0.54 ” 0.48 ” 0.47 mm; diffrac-
tometer Bruker SMART CCD1k; MoKa radiation, 200 K,
2Vmax = 56.508; 28372 reflections, 25863 independent, direct
methods; empirical absorption correction SADABS (ver. 2.03);
Angew. Chem. Int. Ed. 2005, 44, 6325 –6329
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 6329