Synthesis and characterization of novel guanidine ligands featuring biphenyl or binaphthyl backbones

Article abstract of DOI:10.1002/ejic.201000981

In this paper we report on the synthesis and characterization of several new 2,2′-bisguanidino-1,1′-biphenyl and -binaphthyl ligands as well as the electron donor 3,3′,4,4′-tetrakis(tetramethylguanidino)-1, 1′-biphenyl. Chiral bisguanidine ligands were pr

Full text of DOI:10.1002/ejic.201000981

FULL PAPER
DOI: 10.1002/ejic.201000981
Synthesis and Characterization of Novel Guanidine Ligands Featuring Biphenyl
or Binaphthyl Backbones
Astrid Maronna,[a] Elvira Bindewald,[a] Elisabeth Kaifer,[a] Hubert Wadepohl,[a] and
Hans-Jörg Himmel*[a]
Keywords: Platinum / Coordination modes / Guanidine / Biaryl compounds
In this paper we report on the synthesis and characterization
of several new 2,2Ј-bisguanidino-1,1Ј-biphenyl and -bi-
naphthyl ligands as well as the electron donor 3,3Ј,4,4Ј-tetra-
kis(tetramethylguanidino)-1,1Ј-biphenyl. Chiral bisguanid-
ine ligands were prepared with binaphthyl backbones. The
solid-state structures were analysed by single-crystal X-ray
diffraction. UV/Vis and Raman spectra provided a qualitative
insight into the rotational barriers in solution and in the solid
state. Finally, late-transition-metal complexes of two of these
ligands were prepared. These complexes prefer a κ1 rather
than a κ2 coordination mode. The discussion of the experi-
mental results is complemented by quantum chemical (DFT)
calculations. Finally, we report on the first catalytic test reac-
tions.
One example is the Zn–guanidine–amine complex shown in
Scheme 1,[13] which has been employed in asymmetric ni-
troaldol reactions.[14] Guanidines are much stronger bases
than amines [e.g., pKA = 13.6 for HN=C(NH2)2][15] and can
form not only strong σ bonds, but also π bonds to metal
ions.[16] Therefore it would be interesting to test the per-
formance of transition-metal complexes of 2,2Ј-bisguanid-
ine-substituted 1,1Ј-binaphthyls and related systems in
asymmetric catalysis. An interesting point is that the guani-
dino group, although sterically demanding, leaves enough
free space at the imino N atom to allow coordinative bond-
ing to a metal ion. An informative example is provided by
the proton sponge 1,8-bis(tetramethylguanidino)naphth-
alene.[17] In contrast to the corresponding bis(dimethyl-
amino)naphthalene,[18] which is barely suitable as a chelat-
ing ligand (only one complex is known to date[19]), we have
shown that 1,8-bis(tetramethylguanidino)naphthalene exhi-
bits an interesting and rich coordination chemistry.[20]
Introduction
Asymmetric catalysis is a very active field of research
with enormous significance for the manufacture of pharma-
ceuticals, animal health products, agrochemicals, fungicides
and other high-value products. Ligand design is a key issue
in the development of new chiral complexes for homogen-
eous catalysts. One of the most attractive molecules in this
context is binap [2,2Ј-bis(diphenylphosphanyl)-1,1Ј-bi-
naphthyl].[1,2] Applications, for example, of binap–RuII di-
carboxylate complexes in asymmetric hydrogenations or of
cationic binap–Rh complexes in the asymmetric isomeriza-
tion of allylic amines are well documented.[1] The first
attempts to synthesize binap stereospecifically starting with
optically pure 2,2Ј-diamino-1,1Ј-binaphthyl turned out not
to be practical due to racemization at an intermediate
stage.[3] Routes involving optical resolution starting with ra-
cemic 2,2Ј-disubstituted 1,1Ј-binaphthyls were therefore de-
veloped. One of the characteristics of binap systems is the
large degree of flexibility in the torsional angle between the
two naphthyl groups of the binaphthyl backbone.
The suitability of guanidines, especially chiral bicyclic de-
rivatives, in metal-free asymmetric catalysis has already
been demonstrated.[4] At the same time, guanidines and gu-
anidinates are well established versatile ligand systems.[5–12]
However, surprisingly little is known about the suitability
of metal complexes of guanidines in asymmetric catalysis.
Scheme 1.
[a] Anorganisch-Chemisches Institut, Ruprecht-Karls-Universität
Heidelberg,
Herein we report on the synthesis of achiral bisguanid-
ines with a biphenyl backbone and chiral bisguanidines
with a binaphthyl backbone. In addition, we present the
first biphenyl with four guanidino substituents. This mole-
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: +49-6221-545707
E-mail: hans-jorg.himmel@aci.uni-heidelberg.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000981.
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Novel Guanidine Ligands
cule is a new member of a class of electron-donor com-
pounds and redox-active ligands recently developed by our
group that feature at least four guanidino groups attached
directly through the imino N atom to aromatic systems and
are referred to as GFAs (guanidino-functionalized aromatic
compounds).[21–24] Representatives already known include
1,2,4,5-tetrakis(tetramethylguanidino)benzene (ttmgb),[21]
the related (but in its reactivity, remarkably different) com-
pound 1,2,4,5-tetrakis(N,NЈ-dimethyl-N,NЈ-ethyleneguanid-
ino)benzene (tdmegb)[23] and 1,4,5,8-tetrakis(tetramethyl-
guanidino)naphthalene (ttmgn;[24] see Scheme 2). Quantum
chemical calculations indicate that in the gas-phase ttmgb is
an even stronger electron donor than bis(imidazolylidene)-
tetraazafulvalene,[25] which was recently praised as “organic
sodium”.[26]
Scheme 3.
Ligand Synthesis and Structural Characterization
All the ligands were synthesized starting with the corre-
sponding amines and N,N,NЈ,NЈ-tetramethylurea or N,NЈ-
dimethyl-N,NЈ-ethyleneurea. The ureas were activated with
oxalyl chloride (to give Vilsmeier salts) prior to reaction
with the amines. In contrast to the situation for binap, chi-
ral 2,2Ј-bisguanidino-substituted 1,1Ј-binaphthyls can be
synthesized in this way starting from optically pure 2,2Ј-
diamino-1,1Ј-binaphthyl (binam) by stereospecific synthe-
sis. Although the synthesis of 2–5 has not previously been
described, 2,2Ј-bis(tetramethylguanidino)-1,1Ј-biphenyl (1)
has already been reported in the literature.[27] However, only
the diprotonated ligand [1H2]2+ and not the neutral one was
structurally characterized. In our experiments we succeeded
in the crystallization and structural characterization of all
five neutral molecules. The structures are visualized in Fig-
ures 1, 2, and 3. As anticipated, the two phenyl or naphthyl
Scheme 2.
Results and Discussion
In the following we report on the synthesis of the new units in the crystallized ligands 1–4 are not coplanar. The
guanidine ligands 1–5 shown in Scheme 3. The central C– torsional angles were determined to be around 55° in 1, 53°
C single bond, which is common to all these ligands, allows in 2, 66° in 3 and 67° in 4. For comparison, the torsional
flexibility due to a low rotational barrier. Although achiral angle between the two twisted phenyl planes of biphenyl in
molecules result for 1, 2 and 5 with a biphenyl backbone, its lowest-energy form measures 44.4Ϯ1.2°.[28] The increase
3 and 4 with a binaphthyl backbone are chiral molecules. in the torsional angle in all the guanidine ligands relative
Subsequently, we discuss some preliminary aspects of the to biphenyl reflects the steric demands of the two guanidino
coordination chemistry of some of these new guanidine li- groups in the ortho positions. Interestingly, the two phenyl
gands.
rings in solid 5 (ortho positions not substituted) are copla-
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H.-J. Himmel et al.
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nar. The C–C bond length connecting the two phenyl or
naphthyl units is slightly longer in compounds
2
[149.4(2) pm] and 4 [149.1(2) pm], which feature N,NЈ-di-
methyl-N,NЈ-ethyleneguanidino substituents, than in com-
pounds 1 [148.8(2) pm], 3 [148.9(3) pm] and 5 [148.6(4) pm],
which feature tetramethylguanidino substituents. The imino
N=C bond lengths in all the ligands fall into the range typi-
cal of guanidino groups [129.03(12)/129.45(13) pm in 1,
128.85(18)/128.45(18) pm in 2, 130.58(3)/129.3(2) pm in 3,
127.5(2)/129.6(2) in 4 and 128.8(3)/129.2(3) pm in 5].
Figure 2. Molecular structures of 3 and 4. Vibrational ellipsoids
drawn at the 50% probability level. Selected bond lengths [pm] and
bond angles [°] for 3: C1–N1 139.3(3), N1–C21 130.5(3), N2–C21
137.4(3), N3–C21 137.9(3), N4–C11 140.7(3), N4–C26 129.3(3),
N5–C26 137.8(3), N6–C26 137.9(3), C1–C10 140.0(3), C10–C20
148.9(3), C11–C20 138.2(4), C1–N1–C21 124.8(2), N2–C21–N3
114.8(2), C11–N4–C26 124.5(2), N5–C26–N6 114.4(2), C1–C10–
C20–C11 –65.9(11). Selected bond lengths [pm] and bond angles
[°] for 4: N1–C1 139.9(2), N1–C21 127.5(2), N2–C21 139.0(2), N3–
C21 138.2(2), N4–C11 139.5(2), N4–C26 129.6(2), N5–C26
136.9(2), N6–C26 138.5(2), C1–C10 139.3(2), C10-C20 149.1(2),
C11–C20 139.6(2), C1–N1–C21 128.14(15), N2–C21–N3
108.39(14), C11–N4–C26 124.91(14), N5–C26–N6 108.35(15), C1–
C10–C20–C19 66.8(7).
280 nm.[29] The relatively broad absorption bands in the re-
gion 220–280 nm are usually attributed to resonance inter-
actions involving the two benzenoid rings and consequently
the introduction of ortho substituents onto the biphenyl
brings about dramatic changes in its spectrum (especially
Figure 1. Molecular structures of 1 and 2. Vibrational ellipsoids
drawn at the 50% probability level. Selected bond lengths [pm] and
bond angles [°] for 1: N1–C2 140.18(13), N1–C1 129.03(12), N2–
C13 138.89(12), N3–C13 137.82(12), N4–C8 140.30(13), N4–C18
129.45(13), N5–C18 137.48(12), N6–C18 138.53(13), C1–C2
140.90(13), C6–C7 148.88(13), C7–C8 141.42(13), C1–N1–C13
121.74(8), C8–N4–C18 122.60(8), N2–C13–N3 113.83(8), N5–C18– with respect to the extinction coefficients).[30] Figure 4 (a)
N6 114.40(9), C1–C2–C7–C12 –55.3(9). Selected bond lengths [pm]
shows the UV/Vis spectra of 1 (two guanidino substituents
and bond angles [°] for 2: N1–C1 140.29(18), N1–C13 128.85(18),
ortho to the central C–C bond) and 5 (four guanidino sub-
N2–C13 138.41(18), N3–C13 138.69(18), N4–C12 141.34(17), N4–
stituents meta and para to the central C–C bond). Whereas
C18 128.45(18), N5–C18 138.67(18), N6–C18 138.51(17), C1–C6
the spectrum of 1 features bands near 216 and 274 nm, the
spectrum of 5 is characterized by three absorptions centred
at 217, 270 and 339 nm. Most importantly, the extinction
coefficients are much higher for 5 than for 1. The reason
for this difference is that for 1 but not 5, the degree of free-
dom of rotation around the central C–C bond is restricted
due to the presence of guanidino substituents at the ortho
140.98(19), C6–C7 149.4(2), C7–C12 140.5(2), C1–N1–C13
122.69(13), N2–C13–N3 108.01(11), C12–N4–C18 120.33(12), N5–
C18–N6 108.40(12), C1–C6–C7–C8 –52.8(6).
UV/Vis Spectra of the Free Ligands
UV/Vis spectra were recorded for all five ligands in positions. The UV/Vis spectra of 2 and 4 (both featuring
CH3CN solution (see Exp. Sect.). They provide some in- the same guanidino substituents but different backbones)
sight into the dynamic behaviour of the molecules in solu- in the region 200–550 nm are displayed in Figure 5. The
tion. The UV/Vis spectrum of biphenyl contains three in- extinction coefficients for these two compounds are similar,
tense absorption areas at around 170, 190 and 220– which suggests a similar degree of rotational freedom. Two
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Novel Guanidine Ligands
Figure 3. Molecular structure of 5. Vibrational ellipsoids drawn at
the 50% probability level. Selected bond lengths [pm] and bond
angles [°]: N1–C1 140.0(3), N1–C7 128.8(3), N2–C2 141.4(3), N2–
C12 129.2(3), N3–C7 140.1(3), N4–C7 137.0(3), N5–C12 138.2(3),
N6–C12 137.6(3), C1–C2 140.4(3), C2–C3 139.2(3), C3–C4
139.6(3), C4–C4Ј 148.6(4), C1–N1–C7 123.02(19), C2–N2–C12
118.77(19), N3–C7–N4 112.97(19), N5–C12–N6 114.46(19), C3–
C4–C4Ј–C3Ј 180.00(6), N51–C51 140.3(3), N51–C57 129.2(3),
N52–C52 141.0(3), N52–C62 128.8(3), N53–C57 138.4(3), N54–
C57 137.2(3), N55–C62 137.4(3), N56–C62 138.8(3), C51–C52
141.1(3), C52–C53 138.9(3), C53–C54 139.5(3), C54–C54Ј 148.5(4),
C51–N51–C57 122.86(19), C52–N52–C62 120.39(18), N53–C57–
N54 114.34(19), N55–C62–N56 114.11(19), C53–C54–C54Ј–C53Ј
180.00(6).
Figure 4. a) UV/Vis spectra of 1 and 5. b) Raman spectra of (i) 2,
(ii) 4 and (iii) 5 (excited with the 415 nm line of an Ar+ ion laser,
100–300 mW).
absorption maxima are visible in the spectrum of 2 (Fig-
ure 5, a), with the absorption maxima (210 and 275 nm)
only slightly shifted with respect to 1. In the spectrum of 4
(Figure 5, b), four absorption bands are clearly visible at spectra. Therefore we performed the measurements under
around 214, 265, 305 and 353 nm (shoulder). Of these, the non-resonance conditions. Nevertheless, the solid samples
band at 265 nm seems to show some fine structure with showed signs of beam damage after prolonged exposure to
maxima at 262 and 268 nm. For comparison, the spectrum the laser beam. In particular, in the Raman spectra of 1 and
of 1,1Ј-binaphthyl shows an intense absorption band at 3 (see the Raman spectrum of 1 in the Supporting Infor-
around 220 nm and a weaker band containing some vi- mation), broad and large fluorescence signals are observed.
brational structure at around 290 nm.[31] The UV/Vis spec- Therefore only the Raman spectra of 2, 4 and 5, some parts
trum of 3 is displayed in the Supporting Information, to- of which are shown in Figure 4 (b), will be discussed herein.
gether with that of 1. It is similar to that of 4, with absorp- In the case of the ligands 2 and 4, in which rotation is re-
tion maxima at 214, 255, 304 and 351 nm (shoulder).
stricted due to the guanidino groups at the ortho positions,
we observed sharp signals in the low-energy region of the
Raman spectra [at 28.5, 43.5, 68.8 (with a shoulder at 59.9),
91.9, 103.6 and 126.6 cm–1 for 4 and 31.3, 41.1/44.9, 82.0,
91.4 and 106.0 cm–1 for 2]. On the other hand, the spectrum
of 5 shows a single very broad signal at around 88 cm–1. A
second broad feature was centred out of the range of detec-
tion at around 20 cm–1.
Raman Spectra of the Free Ligands
The low-energy vibrations of biphenyls and binaphthyls
in the ground and excited electronic states have been inten-
sively studied in the past because there is a correlation be-
tween them and the torsional barriers.[32,33] For example,
the torsional mode of 1,1Ј-binaphthyl has been shown to
occur at around 30 cm–1. In the case of biphenyl in its A
ground electronic state, quantum chemical [B3LYP/6-
31G(d)] calculations yielded frequencies of 71, 96, 129 and
1
CV Curves and Redox Chemistry
Biphenyl has a relatively high oxidation potential,
271 cm–1 for the torsional and other inter-ring vibrational around 2 V versus SCE.[34] The situation changes upon the
modes.[32] In our experiments, the spectra were excited with introduction of two guanidino substituents. However, the
the 514 nm line of an Ar+ ion laser. This excitation energy waves are generally broad and non-reversible (see, for exam-
is well below the energy needed for the electronic excitations ple, the CV curves recorded for 2 and 4 in the Supporting
responsible for the absorptions observed in the UV/Vis Information). As anticipated, the introduction of four gua-
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show a reduction in the central C–C bond length from
148.4 pm in neutral 5 to 142.4 pm in 52+. Upon oxidation,
the aromaticity is removed from the two C6 rings, leading
to C–C bond lengths in the range 138.7–148.0 pm. We also
tried to oxidize 5 chemically by reaction with I2. Upon ad-
dition of I2 to a CH3CN solution of 5, the reaction mixture
immediately turned dark green. The NMR spectra indicate
the presence of a mixture of products. The UV/Vis spec-
trum (see the Supporting Information) shows bands at 290
and 353 nm assignable to the I3– anion, which indicates that
a redox reaction indeed has taken place. In addition, a
broad band appears at 705 nm, which is responsible for the
intense colour of the solution and was assigned to oxidized
Figure 5. UV/Vis spectra of a) 2 and [PtCl2(C2H4)(κ1-2)] and b) 4
and [PtCl2(C2H4)(κ1-4)].
nidino substituents in 5 has the greatest impact on the oxi-
dation potential. The CV curve of 5 features two reversible
oxidation/reduction waves located at E = 0.06 and 0.61 V
½
(see Figure 6, a). Measurements in the presence of ferrocene
in solution indicate that both peaks can be assigned to one-
electron oxidation/reduction. Upon two-electron oxidation,
the central C–C bond is transformed from a single to a
double bond [see the Lewis structure in Equation (1)].
Guanidino groups at the para or ortho positions assist this
oxidation and could stabilize the positive charges. In ad-
dition, gas-phase oxidation was analysed with the aid of
quantum chemical (B3LYP/6-311G**) calculations. The
calculated gas-phase structure of the dication 52+ is illus-
Figure 6. a) CV curve [SCE, 100 mVs–1, CH3CN, (nBu4N)(PF6) as
electrolyte] for 5. b) Gas-phase donor strength of several GFAs
measured relative to bis(imidazolylidene)tetraazafulvalene on the
basis of the model electron-transfer reaction [bis(imidazolylidene)-
tetraazafulvalene]2+ + GFA Ǟ bis(imidazolylidene)tetraazaful-
trated in the Supporting Information. The calculations valene + [GFA]2+
.
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Novel Guanidine Ligands
5. In Figure 6 (b) the calculated two-electron gas-phase do- Signals at around 4.6 and 4.3 ppm (the latter showing cou-
nor capacity of 5 is compared with that of other aromatic pling to Pt) directly indicate the presence of an ethylene
compounds featuring four guanidino substituents and of ligand in the product. The number of signals in the aro-
the “organic sodium“ bisimidazolylidene-tetraazafulvalene matic region signals the formation of an unsymmetrical
on the basis of the ΔG0 value of the redox reaction shown product. In line with the other analytical data, the peaks in
in Equation (2). According to these calculations, compound the FAB+ mass spectrum suggest the formation of the com-
5 is a slightly better electron donor than the tetraazaful- plex [PtCl2(C2H4)(κ1-2)]. The product was crystallized and
valene in the gas phase. However, it exhibits a lower donor studied by XRD. Figure 8 (a) shows its molecular structure.
capacity than the three tetrakisguanidine compounds Ligand 2 is indeed κ1-coordinated to PtII, trans to the ethyl-
ttmgb, tdmegb and ttmgn (see Scheme 1 for their Lewis for- ene ligand, in the same way as already reported for
mula).
[PtCl2(C2H4)(κ1-1)].[20] As anticipated, the imino N=C
bond length within the coordinating guanidino group in-
creases to 132.8(4) pm upon coordination and is signifi-
cantly longer than that of the non-coordinating guanidino
group [129.2(4) pm]. The Pt–N bond measures 207.5(2) pm
and compares with a value of 206.9(4) pm measured in the
related complex [PtCl2(C2H4)(κ1-btmgn)] (see Scheme 4).
The torsional angle between the two phenyl rings is around
53°, as in free 2. In the crystalline phase, dimeric assemblies
are formed through two Pt–Cl···H–C contacts of around
261.7(5) pm (see Figure 8, b).
Coordination Chemistry and Preliminary Catalytic Tests
When 2 was allowed to react with Zeise’s dimer,
[Pt2Cl4(C2H4)2], the formation of a new product was de-
tected by NMR spectroscopy. In the 195Pt NMR spectrum,
a single signal is observed at –2849 ppm. Figure 7 (a) shows
1
the H NMR spectra of 2 before and after the reaction.
Figure 8. a) Molecular structure of the complex [PtCl2(C2H4)(κ1-
2)]. Vibrational ellipsoids drawn at the 50% probability level. Se-
lected bond lengths [pm] and bond angles [°]: Pt–N1 207.5(2), Pt–
Cl1 229.48(9), Pt–Cl2 229.52(9), Pt–C23 214.1(3), Pt–C24 213.9(3),
N1–C1 142.8(4), N1–C13 132.8(4), N2–C13 133.8(4), N3–C13
135.2(4), N4–C12 140.1(4), N4–C18 129.2(4), N5–C18 139.0(4),
N6–C18 138.0(4), C1–C6 140.7(4), C6–C7 149.4(4), C7–C12
141.9(4), Cl1–Pt–N1 90.63(8), Cl2–Pt–N1 89.71(8), Pt–N1–C1
117.14(19), Pt–N1–C13 123.9(2), N2–C13–N3 108.8(3), N1–C1–C6
123.0(3), C1–C6–C7 122.3(3), C6–C7–C12 122.0(3), N4–C12–C7
120.8(3), C12–N4–C18 122.5(3), N4–C18–N5 130.1(3), N4–C18–
N6 121.4(3), N5–C18–N6 108.5(2), C1–C6–C7–C8 52.9(17).
b) Molecular structure of the dimeric assembly of complex
[PtCl2(C2H4)(κ1-2)].
According to our analytical data (see the Exp. Sect.),
the reaction between (R)-4 and [Pt2Cl4(C2H4)2] proceeds
similarly to that between 2 and [Pt2Cl4(C2H4)2]. The 1H
NMR spectra obtained for 4 before and after reaction are
Figure 7. 1H NMR spectra recorded for CD2Cl2 solutions of a) 2
and the complex [PtCl2(C2H4)(κ1-2)] (400 MHz) and b) 4
(600 MHz) and the complex [PtCl2(C2H4)(κ1-4)] (400 MHz).
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Scheme 4.
Table 1. Calculated (B3LYP/LANL2DZ) bond lengths and wavenumbers of the two ν(C=C) + δ(CH2) vibrational modes for the com-
pounds discussed in this work.
Compound
d(C=C) [pm] d(Pt–Cl) [pm] d(Pt–N) [pm] d(C=N) [pm]
ν(C=C) + δ(CH2) [cm–1]
C2H4
134.8
142.6
141.1
141.1
–
–
–
–
–
1677.6/1387.5
1544.3, 1543.4/1251.3, 1250.4
[Pt2Cl4(C2H4)2]
[PtCl2(C2H4)(κ1-2)]
[PtCl2(C2H4){(R)-κ1-4}]
238.2/249.1
244.2/243.4
244.2/243.4
208.4
208.5
130.2 (free), 134.8 (coord.) 1550.4/1279.1
130.0 (free), 135.0 (coord.) 1548.9/1277.3
shown together in Figure 7b. Again the presence of a C2H4 10% δ(CH2).[38] Powell et al. suggested a simple method
ligand in the product can be deduced from the signals at for comparing the bonding in ethylene complexes.[39] In this
around 4.4 and 4.2 ppm. The high-resolution FAB+ mass method, the summed percentage lowering of ν(C=C) and
spectrometric data also point to the formation of the com- δs(CH2) is a measure of the decrease of the double bond
plex [PtCl2(C2H4){(R)-κ1-4}]. Unfortunately the crystals character of the olefin upon coordination. The summed
obtained for this species turned out to be of insufficient percentage is 15.4% in the case of [PtCl2(C2H4)(κ1-2)] [with
quality for an XRD analysis. The gas-phase structure de- 1623 and 1342 cm–1 for ν(C=C) and δs(CH2) in free ethyl-
rived from quantum chemical calculations is illustrated in ene]. This value is significantly higher than that derived for
the Supporting Information (see Table 1 for a list of selected standard trans-[PtCl2(C2H4)L] complexes (for example,
properties).
with L a pyridine derivative or CH3CN).[40] In previous
We also recorded the Raman spectra. Unfortunately, the work on NiII complexes we showed that the guanidino N–
spectra recorded for [PtCl2(C2H4)(κ1-4)] suffered from metal bond exhibits a strong σ(NǞNi) and a weaker
visible beam damage. Figure 9 shows the spectra obtained π(NǞNi) donor component,[16] a result that is in line with
for ligand 2 and the corresponding complex [PtCl2(C2H4)- the presence of strong Pt–C2H4 back-bonding. A compari-
(κ1-2)] (the complete spectra are shown in the Supporting son of some of the calculated bonding parameters for
Information.). Two signals at 1501 and 1236 cm–1 (see Fig- [PtCl2(C2H4){(R)-κ1-4}],
[PtCl2(C2H4)(κ1-2)],
[Pt2Cl4-
ure 9, a) were assigned to modes that can be described as (C2H4)2] and free C2H4 in Table 1 also supports this conclu-
mixtures predominantly of ν(C=C) and δs(CH2).[35–37] In sion. Figure 9 (a) also shows the low-energy region of the
the IR spectrum a band at 1502 cm–1 is observed (see the Raman spectra, which reveals that complex formation af-
Supporting Information). A problem with any attempt at fects the torsional and other inter-ring vibrations. Further-
correlating the observed wavenumbers with the properties more, the 250–550 cm–1 region is shown in Figure 9 (b) and
of the Pt–C2H4 bond is that the potential energy distribu- is characteristic of the ν(Pt–Cl), ν(Pt–N) and ν(Pt–C2)
tion changes significantly and almost unpredictably in eth- modes. For example, in (nBu4P)[PtCl3(C2H4)], ν(Pt–Cl) and
ylene–metal complexes. For example, in the [PtCl3(C2H4)]– ν(Pt–C2) occur at 338/332/313 and 512 (νs)/413 (νas) cm–1,
complex anion, the character of the higher-energy mode respectively.[38] In trans-[PtBr2(NH2Ph)(C2H4)], the Pt–N
(now at 1516 cm–1) is 21% ν(C=C) and 36% δ(CH2), and stretching mode, ν(Pt–N), is located at 430 cm–1.[38] In the
for the lower-energy mode (at 1230 cm–1) 76% ν(C=C) and case of [PtCl2(C2H4)(κ1-2)], we tentatively assigned the
1308
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 1302–1314

Novel Guanidine Ligands
doublet at 336.4/330.2 cm–1 to the two ν(Pt–Cl) modes, the quantum chemical calculations, the product of ethylene eli-
two weak features at 424.7 and 372.5 cm–1 to the ν(Pt–C2) mination, [PtCl2(κ2-1)], does not exhibit a planar coordina-
modes and the signal at 396.7 cm–1 to the ν(Pt–N) mode.
tion, but a sawhorse-type structure (see the Supporting In-
formation).
Traces of water had to be rigorously excluded in all our
experiments. When the PtII complex [PtCl2(C2H4)(κ1-1)][20]
was dissolved in CD2Cl2 and the solution exposed to air to
allow reaction with traces of H2O, a small amount of brown
crystalline product precipitated, which turned out to consist
of [(1H)PtCl3] molecular units. Subject to the very same
reaction conditions, red crystals of [(1H)PdCl3] were ob-
tained during the attempt to synthesize the neutral PdII
complex with 1,2-cyclooctadiene as olefin moiety. The mo-
lecular structures of these products derived from an XRD
analysis are provided in the Supporting Information. The
flexibility in the torsional angle between the two phenyl ring
planes allows significant N–H···Cl–M hydrogen-bonding.
Attempts to obtain [(1H)PtCl3] in the absence of traces of
water starting with [(NH4)2PtCl4] failed.
We then tested the catalytic activity of the PtII complexes.
The three complexes [PtCl2(C2H4)(κ1-1)],[20] [PtCl2(C2H4)-
(κ1-2)] and [PtCl2(C2H4){(R)-κ1-4}] were used to catalyse
the hydrosilylation reaction between Et3SiH and Me3-
SiC(H)CH2 to yield Et3SiCH2CH2SiMe3. For this reaction
there are of course already numerous catalysts available.
Nevertheless, this reaction was of interest in the context of
our study because we have previously shown that Pt dichlo-
ride complexes with κ2-coordinated bisguanidine ligands
are catalytically inactive.[20] This implies that ethylene elimi-
nation, as shown in Scheme 4, directly affects the TON. If
[PtCl2(κ1-bisguanidine)] complexes are formed as interme-
diates in the catalytic process (whatever species represents
the active catalyst and no matter if the catalysis is homogen-
eous or heterogeneous), they must be very short-lived be-
cause isomerization to [PtCl2(κ2-bisguanidine)] most likely
extinguishes the catalytic activity.[20] The reaction was fol-
lowed by GC–MS and the results are shown in Figure 10.
All three complexes turned out to be catalytically active.
Complex [PtCl2(C2H4)(κ1-2)] exhibits the smallest turnover
frequency (TOF) at the beginning of the reaction, which
Figure 9.
Raman
spectra
measured
for
(i) 2
and
(ii) [PtCl2(C2H4)(κ1-2)] excited with the 415 nm line of an Ar+ ion
laser (100–300 mW). a) The low-frequency region (20–200 cm–1)
characteristic of torsional and other inter-ring vibrational modes
together with the 1100–1650 cm–1 region containing the two vi-
brational modes with high ν(C=C) + δs(CH2) character (high-
lighted by asterisks). b) The 250–550 cm–1 region containing the
ν(Pt–C2), ν(Pt–Cl) and ν(Pt–N) modes for (i) 2 and
(ii) [PtCl2(C2H4)(κ1-2)].
The complex [PtCl2(C2H4)(κ1-btmgn)] (see Scheme 4) might signal the presence of an induction period. After
was shown to thermally eliminate C2H4 in CH2Cl2 at reflux
to give [PtCl2(κ2-btmgn)].[20] In contrast, the synthesis of
[PtCl2(κ2-1)] in CH2Cl2 at reflux could not be realized.
Attempts to eliminate C2H4 photolytically in CH2Cl2 or tol-
uene also failed. The NMR spectra indicate the formation
of a mixture of products, but it was impossible to isolate
and/or identify a single product. In the light of these experi-
mental findings, quantum chemical (B3LYP/LANL2DZ)
calculations were carried out to compare the thermo-
dynamic properties of the ethylene elimination starting
with the two complexes [PtCl2(C2H4)(κ1-btmgn)] and
[PtCl2(C2H4)(κ1-1)] (see Scheme 4). In the case of
[PtCl2(C2H4)(κ1-btmgn)], ΔG0 (free energy at 298 K, 1 bar)
was previously estimated to be –3 kJmol–1.[20] For
[PtCl2(C2H4)(κ1-1)],[20] a significantly endergonic value was
determined (ΔG0 = +62 kJmol–1). The calculations are thus
Figure 10. Results of the catalytic hydrosilylation of trimethylsilyl-
in line with the experimental results. According to the ethane using the new Pt–guanidine complexes.
Eur. J. Inorg. Chem. 2011, 1302–1314
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1309

H.-J. Himmel et al.
FULL PAPER
= 3051 (w), 3011 (w), 2926 (m), 2886 (m), 2801 (w), 1607 (s), 1577
(s), 1498 (m), 1455 (m), 1428 (m), 1374 (s), 1269 (w), 1236 (m),
1203 (w), 1139 (s), 1061 (w), 1017 (s), 925 (w), 860 (w), 783 (m),
758 (m), 737 (s), 702 (w), 623 (w), 566 (w), 521 (w), 502 (w), 463
(w) cm–1. Raman measurements not possible due to laser beam
damage (even for 100 mW and short exposure times). UV/Vis
(CH3CN, c = 2.53ϫ10–5 molL–1): λ (ε) = 274 (10946), 218
(23878 Lmol–1 cm–1) nm. MS (ESI+): m/z (%) = 381.27561 (100)
[MH]+. C22H32N6 (380.54): C 69.44, H 8.48, N 22.09; found C
69.61, H 8.44, N 22.06.
250 min the conversion to the product was Ͼ95% for all
three catalysts. The TOF for the three complexes
[PtCl2(C2H4)(κ1-1)], [PtCl2(C2H4)(κ1-2)] and [PtCl2(C2H4)-
{(R)-κ1-4}] are around 240, 270 and 190 h–1, respectively
(in the time period 20–100 min after the start of the reac-
tion). The experiments thus indicate that [PtCl2(κ2-1)],
which is likely to be catalytically inactive, is not formed as
an intermediate in the course of the reaction.
Crystal data for 1: C22H32N6, Mr = 380.53, 0.40ϫ0.40ϫ0.40 mm3,
monoclinic, space group P21/n, a = 8.0995(5), b = 15.1232(8), c =
17.9918(10) Å, β = 100.2960(10)°, V = 2168.3(2) Å3, Z = 4, ρcalcd.
= 1.166 Mgm–3, Mo-Kα radiation (graphite-monochromated, λ =
0.71073 Å), T = 100 K, θrange = 1.77–32.33°. Reflections measured
6006, independent 7353, Rint = 0.0557. Final R indices [IϾ2σ(I)]:
R1 = 0.0470, wR2 = 0.1400.
Conclusions
We have reported herein the synthesis and characteriza-
tion of several new guanidine ligands with biphenyl and
binaphthyl backbones. Preliminary experiments on the co-
ordination chemistry of the bisguanidine systems indicate
that they prefer a κ1 bonding mode instead of a chelating
κ2 bonding mode. Thus, the second guanidino group could
act as a hemilabile ligand stabilizing a vacancy at the metal
created in the course of a catalytic cycle. Ongoing research
in our group includes the use of the chiral binaphthyl li-
gands 3 and 4 in asymmetric catalysis. In addition, the re-
dox chemistry of the new electron donor 5 will be explored.
2: Oxalyl chloride (7 mL, 80 mmol, 20 equiv.) was added dropwise
to
a solution of 1,3-dimethylethyleneurea (1.7 mL, 16 mmol,
4 equiv.) dissolved in CHCl3 (30 mL) at room temperature. The re-
action mixture was stirred under reflux for 20 h. After removal of
the solvent in vacuo, the activated urea, 2-chloro-1,3-dimethylethyl-
eneformamidinium chloride, was washed with Et2O (15 mL). Then
the orange solid was redissolved in CH2Cl2 (20 mL) and added to
a solution of 2,2Ј-diamino-1,1Ј-biphenyl (0.74 g, 4 mmol, 1 equiv.)
and triethylamine (3.4 mL, 24 mmol, 6 equiv.) in CH2Cl2 (30 mL)
at 255 K. Subsequently the reaction mixture was warmed to room
temperature and after 2 h stirring at room temperature the mixture
was extracted with 10% aq. HCl. The aqueous solution was washed
with CH2Cl2 and after addition of 25% aq. KOH, the solution was
extracted with toluene. The combined toluene phases were dried
with K2CO3 and the solvent was removed in vacuo. The residue
was recrystallized from toluene/n-hexane to give colourless crystals
Experimental Section
All reactions were carried out under Ar using standard Schlenk
techniques. 2,2Ј-Diamino-1,1Ј-biphenyl was synthesized as de-
scribed in the literature.[41] The dinuclear complex di-μ-chloro-
dichlorobis(ethylene)diplatinum(II) [PtCl(C2H4)(μ-Cl)]2 (97%)
used in the synthesis of the Pt complexes (R)-(+)-2,2Ј-diamino-1,1Ј-
binaphthyl (99%) and N,NЈ-dimethylethyleneurea was purchased
from ABCR. Oxalyl chloride, tetramethylurea, acetonitrile and n-
hexane were used from Aldrich without further purification as well
as chloroform purchased from Acros. Other solvents were dried
using the standard methods and then distilled. NMR spectra were
measured with Bruker Avance II 400 and Avance III 600 spectrom-
eters. A Cary 5000 spectrophotometer was used to record UV/Vis
spectra. IR spectra of CsI discs of the compounds were recorded
with a FT-IR Biorad Merlin Excalibur FT 3000 spectrometer. GC–
MS measurements were performed with an Agilent Technologies
G1530A MSD 5973N device. An EG&G Princeton 273 apparatus
was used for the CV measurements. Raman spectra were recorded
with a T64000 spectrometer from Horiba–Jobin–Yvon. The 514 nm
line of an Ar+ ion laser (100–300 mW) was used for excitation.
1
of 2 (1.16 g, 77%). H NMR (399.89 MHz, CD2Cl2, 295.3 K): δ =
4
7.14 (dd, 3J = 7.50, J = 1.53 Hz, 2 H, 5-H), 7.08–7.04 (m, 2 H, 3-
3
4
H), 6.79 (ddd, J = 8.66, 5.62, J = 1.94 Hz, 4 H, 2-H/4-H), 3.11
(s, 8 H, CH2), 2.56 (s, 12 H, CH3) ppm. 13C NMR (100.56 MHz,
CD2Cl2, 297.5 K): δ = 154.86 (2 C, C-13/C-18), 148.79 (2 C, C-1/
C-12), 133.89 (2 C, C-6/C-7), 131.52 (2 C, C-5/C-8), 126.72 (2 C,
C-3/C-10), 122.93(2 C, C-2/C-11), 119.18 (2 C, C-4/C-9), 48.81 (4
C, CH ), 35.43 (4 C, CH ) ppm. IR (KBr): ν = 3053 (m), 3023 (m),
˜
2
3
2941 (s), 2859 (s), 2850 (s), 2368 (w), 2340 (w), 1661 (s), 1585 (s),
1560 (m), 1466 (m), 1426 (m), 1390 (m), 1274 (s), 1233 (m), 1139
(w), 1110 (w), 1070 (w), 1031 (m), 964 (m), 862 (m), 768 (s), 732
(s), 701 (m), 650 (m), 587 (m), 506 (s) cm–1. Raman (514 nm,
300 mW): ν = 31.3, 41.1/44.9, 82.0, 91.4, 106.0, 319.9, 356.3, 500.8,
512.7, 550.2, 645.5, 691.9, 724.9, 775.2, 1002.7, 1044.1, 1155.6,
1231.2, 1273.9, 1298.8, 1308.6, 1559.3, 1568.7, 1585.5, 1597.8,
1: 2-Chloro-1,1Ј,3,3Ј-tetramethylformamidinium chloride (Vils-
meier salt) was prepared by adding oxalyl chloride (7.6 mL,
88 mmol, 16 equiv.) to a solution of N,N,NЈ,NЈ-tetramethylurea
(2.3 mL, 19.3 mmol, 3.5 equiv.) dissolved in CHCl3 (15 mL) at
room temperature. The reaction mixture was heated at reflux over-
night. After evaporating the solvent, the remaining white solid was
washed with Et2O (2ϫ20 mL). Reaction of the synthesized Vilsme-
ier salt with 2,2Ј-diamino-1,1Ј-biphenyl (1.01 g, 5.5 mmol, 1 equiv.)
was performed according to the experimental procedure described
by Pruszynski et al.[27] Yield 1.44 g (67%). Crystals suitable for X-
ray diffraction were obtained by recrystallization from hot n-hex-
1639.7, 2944.3, 3056.8 cm–1. UV/Vis (CH3CN,
c
=
2.58ϫ10–5 molL–1):
λ (ε) =
275 (10187), 210(24580 Lmol–1
cm–1) nm. MS (ESI+): m/z (%) = 377.24550 (100) [MH]+. C22H28N6
(376.50): calcd. C 70.18, H 7.50, N 22.32; found C 70.18, H 7.46,
N 22.13.
Crystal data for 2: C22H28N6, Mr = 376.50, 0.40ϫ0.30ϫ0.25 mm3,
¯
triclinic, space group P1, a = 9.1410(18), b = 9.934(2), c =
12.142(2) Å, α = 79.57(3), β = 85.82(3), γ = 69.69(3)°, V =
1016.9(3) Å3, Z = 2, ρcalcd. = 1.230 Mgm–3, Mo-Kα radiation
(graphite-monochromated, λ = 0.71073 Å), T = 100 K, θrange
1.71–27.43°. Reflections measured 8637, independent 4620, Rint
0.0293. Final R indices [IϾ2σ(I)]: R1 = 0.0472, wR2 = 0.1122.
=
=
1
ane solution. H NMR (600.13 MHz, CD2Cl2, 295.0 K): δ = 7.06
3
3
(t, J = 6.90 Hz, 4 H, CH), 6.77 (t, J = 7.33 Hz, 2 H, CH), 6.64–
6.68 (m, 2 H, CH), 2.57 (s, 24 H, CH3) ppm. 13C NMR
(150.90 MHz, CD2Cl2, 295.0 K): δ = 158.38, 150.45, 133.56 (Cq),
(R)-3: Oxalyl chloride (5.4 mL, 61.6 mmol, 35 equiv.) was added
131.48, 126.94, 122.39, 119.04 (CH), 39.55 (CH ) ppm. IR (CsI): ν dropwise to a solution of N,N,NЈ,NЈ-tetramethylurea (1.5 mL,
˜
3
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Eur. J. Inorg. Chem. 2011, 1302–1314

Novel Guanidine Ligands
12.3 mmol, 7 equiv.) dissolved in CHCl3 (20 mL) at room tempera-
ture. The reaction mixture was stirred under reflux for 15 h. After
removal of the solvent in vacuo, the remaining solid, 2-chloro-
1,1Ј,3,3Ј-tetramethylformamidinium chloride, was washed with
Et2O (20 mL). Then the white solid was dissolved in CH2Cl2
(20 mL) and added to a solution of (R)-(+)-2,2Ј-diamino-1,1Ј-bi-
naphthalene (0.5 g, 1.76 mmol, 1 equiv.) and triethylamine (1.5 mL,
H/15-H), 7.69 (d, 3J = 8.72 Hz, 2 H, 3-H/13-H), 7.21 (d, 3J =
8.72 Hz, 2 H, 2-H/12-H), 7.19–7.15 (m, 2 H, 6-H/16-H), 7.11–7.07
3
(m, 2 H, 7-H/17-H), 7.05 (d, J = 8.45 Hz, 2 H, 8-H/18-H), 3.17–
2.98 (m, 8 H, CH2), 2.48 (s, 12 H, CH3) ppm. 13C NMR
(150.90 MHz, CD2Cl2, 295.0 K): δ = 155.57 (2 C, C-21/C-26),
147.11 (2 C, C-1/C-11), 134.76 (2 C, C-9/C-19), 129.21 (2 C, C-4/
C-14), 127.77 (2 C, C-5/C-15), 126.91 (2 C, C-3/C-13), 126.14 (2 C,
10.6 mmol, 6 equiv.) in CH2Cl2 (30 mL) at 255 K. The mixture was C-8/C-18), 125.46 (2 C, C-10/C-20), 125.27 (2 C, C-7/C-17), 124.74
stirred for a further 1 h at 255 K and subsequently warmed up to
room temperature. After stirring for 3 h at room temperature the
reaction mixture was extracted with 10% aq. HCl and the aqueous
(2 C, C-2/C-12), 122.35 (2 C, C-6/C-16), 48.66 (4 C, CH2), 35.52 (4
C, CH ) ppm. IR (CsI): ν = 3051 (m), 2937 (s), 2841 (s), 1691 (s),
˜
3
1640 (s), 1607 (s), 1589 (s), 1490 (m), 1442 (w), 1420 (w), 1371 (m),
solution was washed with CH2Cl2. Then 25% aq. NaOH was 1279 (m), 1227 (m), 1142 (w), 1075 (w), 1039 (s), 988 (w), 953 (s),
added and the solution was extracted with toluene. The combined
toluene phases were dried with K2CO3 and the solvent was re-
moved in vacuo. The residue was recrystallized from hot n-hexane
to give colourless crystals of (R)-3 (622.0 mg, 73%). 1H NMR
(600.13 MHz, CD2Cl2, 295.0 K): δ = 7.76 (d, 3J = 8.06 Hz, 2 H, 5-
H/15-H), 7.71 (d, 3J = 8.71 Hz, 2 H, 3-H/13-H), 7.17 (ddd, 3J =
856 (w), 825 (s), 752 (s), 699 (w), 640 (w), 620 (w), 590 (w), 525
(w), 505 (w), 479 (m), 424 (w) cm–1. Raman (514 nm, 300 mW): ν
˜
= 28.5, 43.5, 59.9/68.8, 91.9, 103.6, 126.6, 243.0, 408.6, 428.8,
541.1, 582.4/591.0, 688.5, 849.7, 1138.7, 1144.5, 1368.6, 1422.4,
1428.2, 1562.0, 1589.0, 1608.2 cm–1. UV/Vis (CH3CN,
c =
2.10ϫ10–5 molL–1): λ (ε) = 353 (sh, 3905), 305 (15523), 265
(27980), 214 (30535 Lmol–1 cm–1) nm. MS (ESI+): m/z (%) =
477.27627 (100) [MH]+. C30H32N6 (476.62): calcd. C 75.60, H 6.77,
N 17.63; found C 75.60, H 6.50, N 17.61.
4
8.00, 6.21, J = 1.68 Hz, 2 H, 6-H/16-H), 7.11–7.05 (m, 4 H, 7-H/
17-H/8-H/18-H), 6.99 (d, 3J = 8.71 Hz, 2 H, 2-H/12-H), 2.43 (s,
24 H, CH3) ppm. 13C NMR (100.56 MHz, CD2Cl2, 296.0 K): δ =
158.41(2 C, C-21/C-26), 148.78 (2 C, C-1/C-11), 135.14 (2 C, C-9/
C-19), 129.18 (2 C, C-4/C-14), 128.00 (2 C, C-5/C-15), 127.28 (2 C,
C-3/C-13), 126.60 (2 C, C-8/C-18), 125.18 (2 C, C-7/C-17), 124.94
(2 C, C-2/C-12), 124.35 (2 C, C-10/C-20), 122.27 (2 C, C-6/C-16),
Crystal data for (R)-4: C30H32N6, Mr
=
476.62,
0.50ϫ0.45ϫ0.40 mm3, orthorhombic, space group P212121, a =
8.0800(16), b = 15.223(3), c = 20.610(4) Å, V = 2535.1(9) Å3, Z =
4, ρcalcd. = 1.249 Mgm–3, Mo-Kα radiation (graphite-monochro-
mated, λ = 0.71073 Å), T = 100 K, θrange = 1.66–30.04°. Reflections
measured 7451, independent 7419, Rint = 0.056. Final R indices
[IϾ2σ(I)]: R1 = 0.0489, wR2 = 0.1129.
39.37 (8 C, CH ) ppm. IR (CsI): ν = 3045 (m), 3004 (m), 2936 (s),
˜
3
2882 (s), 2799 (m), 2362 (w), 1601 (s), 1578 (s), 1500 (m), 1454 (w),
1422 (m), 1378 (s), 1316 (w), 1237 (m), 1208 (m), 1140 (s), 1064
(m), 1038 (m), 1021 (m), 976 (m), 952 (w), 915 (w), 860 (w), 825
(s), 756 (s), 739 (s), 683 (w), 652 (m), 616 (w), 572 (m), 534 (m),
486 (m), 427 (m) cm–1. Raman measurements not possible due to
laser beam damage (even for 100 mW and short exposure times).
UV/Vis (CH3CN, c = 3.13ϫ10–5 molL–1): λ (ε) = 351 (sh, 3839),
304 (13927), 255 (27278), 214 (28338 Lmol–1 cm–1) nm. MS (ESI+):
m/z (%) = 482.31070 (33.3) [M(H)2]2+, 481.30731 (100) [MH]+,
383.22298 (63.3) [MH – C5H10N2]+. C30H36N6 (480.65): calcd. C
74.97, H 7.55, N 17.48; found C 74.93, H 7.57, N 17.43.
5: 3,3Ј-Diaminobenzidine (1.714 g, 8.00 mmol) was dissolved in
CH3CN (10 mL). Then NEt3 (14.00 mL) and the activated urea
suspended in CH3CN (30 mL) were added at 0 °C. The red-brown
reaction mixture was stirred for a period of 2 h at 0 °C. During
removal of the solvent in vacuo a beige precipitate formed, which
was filtered off. The solvent was removed from the filtrate and the
brown solid residue redissolved in 10% aqueous HCl solution.
Then 25% aqueous NaOH solution was added. The pale-brown
suspension was extracted with a total amount of Et2O (80 mL).
The combined organic phases were dried with K2CO3. Then the
solvent was removed in vacuo. Sublimation at 160–170 °C and
2ϫ10–2 mbar afforded the product as a white solid. 1H NMR
Crystal data for (R)-3: C30H36N6, Mr
=
480.65,
0.40ϫ0.35ϫ0.30 mm3, orthorhombic, space group P212121, a =
14.926(3), b = 15.625(3), c = 11.382(2) Å, α = 90, β = 90, γ = 90°,
V = 2654.5(9) Å3, Z = 4, ρcalcd. = 1.203 Mgm–3, Mo-Kα radiation
5
(600 MHz, CD3CN): δ = 6.91 (dd, 3J = 7.99, J = 2.22 Hz, 2 H, 6-
(graphite-monochromated, λ = 0.71073 Å), T = 100 K, θrange
1.89–27.48°. Reflections measured 6116, independent 6086, Rint
0.046. Final R indices [IϾ2σ(I)]: R1 = 0.0564, wR2 = 0.1239.
=
=
H/6Ј-H), 6.60 (d, 5J = 2.21 Hz, 2 H, 5-H/5Ј-H), 6.40 (d, 3J =
7.99 Hz, 2 H, 2-H/2Ј-H), 2.648/2.649 (d, 48 H, CH3) ppm. 13C
NMR (150 MHz, CD3CN): δ = 159.16 (C-7/C-7Ј/C-8/C-8Ј), 150.08
(C-7/C-7Ј/C-8/C-8Ј), 145.26 (C-3/C-3Ј), 143.67 (C-4/C-4Ј), 134.39
(C-1/C-1Ј), 122.57 (C-2/C-2Ј), 119.71 (C-5/C-5Ј), 118.69 (C-6/C-6Ј),
(R)-4: Oxalyl chloride (1.8 mL, 20 mmol, 20 equiv.) was added
dropwise to solution of 1,3-dimethylethyleneurea (0.4 mL,
a
4 mmol, 4 equiv.) dissolved in CHCl3 (10 mL) at room temperature.
The reaction mixture was stirred at reflux overnight. After removal
of the solvent in vacuo, the remaining solid, 2-chloro-1,3-dimethyl-
ethyleneformamidinium chloride, was washed with Et2O (15 mL).
Then the orange solid was redissolved in CH2Cl2 (10 mL) and
added to a solution of (R)-(+)-2,2Ј-diamino-1,1Ј-binaphthalene
(284.4 mg, 1 mmol, 1 equiv.) and triethylamine (0.8 mL, 6 mmol,
6 equiv.) in CH2Cl2 (30 mL) at 255 K. The reaction mixture was
warmed to room temperature over 6 h and subsequently extracted
with 10% aq. HCl. After washing the aqueous solution with
CH2Cl2, 25% aq. NaOH was added and the solution was extracted
with toluene. The combined toluene phases were dried with K2CO3
and the solvent was removed in vacuo. The orange residue was
washed with n-hexane to give (R)-4 (347.2 mg, 73%) as a light-
yellow powder. Crystals suitable for X-ray diffraction were ob-
tained by recrystallization from toluene/n-hexane. 1H NMR
(600.13 MHz, CD2Cl2, 295.0 K): δ = 7.75 (d, 3J = 8.03 Hz, 2 H, 5-
39.80/39.74 (CH ) ppm. IR (CsI): ν = 3008 (w), 2931 (w), 2908 (w),
˜
3
2831 (w), 1612 (m), 1496 (m), 1373 (s), 1242 (w), 1142 (s), 1064
(w), 1018 (s), 925 (w), 871 (w), 817 (m) cm–1. Raman (514 nm,
300 mW): λ = ca. 20, ca. 88, 422.1, 480.6, 675.9, 737.4, 781.6, 833.4,
1013.0, 1119.5, 1136.8, 1241.8, 1299.5, 1337.0, 1426.2, 1575.4,
2930.6 cm–1. UV/Vis (CH3CN, c = 6.6ϫ10–5 molL–1): λ (ε) = 266
(2.4ϫ104), 256 (2.6ϫ104 Lmol–1 cm–1) nm. CV (CH3CN, SCE,
scan speed 100 mVs–1): E = 0.06, 0.61 V. MS (FAB+): m/z = 606.5
½
(50) [M]+, 562.8 (100) [M – NMe2]+, 517.7 (9) [MH – (NMe2)2]+.
MS (ESI+): m/z = 607.5 (98) [M + H]+, 1213.9 (100) [2M + H]+.
C32H54N12 (606.87): calcd. C 63.33, H 8.97, N 27.70; found C
63.08, H 9.01, N 27.14.
Crystal
data
for
5:
C32H54N12,
Mr
=
606.87,
0.19ϫ0.13ϫ0.05 mm3, monoclinic, space group P21/c,
a
=
7.320(4), b = 22.786(14), c = 20.857(11) Å, β = 90.593(12)°, V =
3479(3) Å3, Z = 4, ρcalcd. = 1.159 Mgm–3, Mo-Kα radiation (graph-
Eur. J. Inorg. Chem. 2011, 1302–1314
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1311

H.-J. Himmel et al.
ite-monochromated, λ = 0.71073 Å), T = 100 K, θrange = 1.79– 69.81 (2 C, Cethylene), 48.90 (2 C, CH2), 47.06 (2 C, CH2), 35.92
FULL PAPER
25.03°. Reflections measured 53261, independent 6073, Rint
0.0866. Final R indices [IϾ2σ(I)]: R1 = 0.0502, wR2 = 0.1075.
=
(4C, CH ) ppm. IR (CsI): ν = 3041 (w), 2962 (s), 2882 (m), 1630
˜
3
(s), 1605 (s), 1588 (s), 1553 (sh), 1503 (w), 1482 (w), 1438 (w), 1415
(m), 1383 (m), 1294 (m), 1262 (m), 1092 (s), 1038 (s), 954 (w), 856
(m), 806 (s), 747 (m), 698 (w), 623 (w), 599 (w), 496 (m), 482
(m) cm–1. Raman measurements not possible due to laser beam
damage (even for 100 mW and short exposure times). UV/Vis
(CH3CN, c = 1.23ϫ10–5 molL–1): λ (ε) = 352 (3311), 302 (11999),
265 (22597), 243 (24799), 209 (33284 Lmol–1 cm–1) nm. HRMS
(FAB+): m/z (%) = 769.2045 (55.6), 770.2055 (85.8), 771.2028
(100.0), 772.2070 (71.1), 773.2063 (60.3) [MH]+. C32H36Cl2N6Pt
(770.66): calcd. C 49.87, H 4.71, N 10.90; found C 51.02, H 4.88,
N 10.17.
[PtCl2(C2H4)(κ1-2)]: [PtCl2(C2H4)]2 (117.6 mg, 0.2 mmol, 1 equiv.)
dissolved in CH2Cl2 (8 mL) was added to a solution of 2 (147.6 mg,
0.39 mmol, 1.96 equiv.) in CH2Cl2 (12 mL). The resulting clear yel-
low solution was stirred for 1 h at room temperature. After removal
of the solvent in vacuo, a yellow powder was obtained, which was
washed twice with PE (40/60, 8 mL) to give [PtCl2(C2H4)(κ1-2)]
(259.0 mg, 98%). Crystals suitable for X-ray diffraction were ob-
tained by slow diffusion of PE (40/60) into a toluene solution of
the product. 1H NMR (399.89 MHz, CD2Cl2, 295.0 K): δ = 8.14
4
(d, 3J = 7.33 Hz, 1 H, 11-H), 7.4 (dd, 3J = 7.51, J = 1.36 Hz, 1 H,
4
5-H), 7.23 (dt, 3J = 8.06, 8.02, J = 1.62 Hz, 1 H, 10-H), 7.11–7.03
Catalytic Hydrosilylation: Et3SiH (0.48 mL, 3 mmol) and Me3-
SiC(H)CH2 (0.87 mL, 6 mmol) were dissolved in n-hexane (30 mL).
Then the potential catalyst ([PtCl2(C2H4)(κ1-1)], [PtCl2(C2H4)(κ1-
2)] or [PtCl2(C2H4)(κ1-4)], 6ϫ10–3 mmol) was added. The reaction
(at 25 °C) was followed by GC–MS. For these measurements,
0.1 mL of the reaction mixture was filtered through a silica frit.
The product Et3SiCH2CH2SiMe3 was redissolved and removed
from the silica with n-hexane (2 mL) before being injected into the
GC–MS machine.
3
4
(m, 2 H, 8-H/3-H), 6.99 (dt, J = 7.55, 7.53, J = 0.96 Hz, 1 H, 9-
2
H), 6.87–6.78 (m, 2 H, 2-H/4-H), 4.75–4.48 (m, JPt-H = 50.05 Hz,
2 H, Hethylene), 4.46–4.21 (m, JPt-H = 54.75 Hz, 2 H, Hethylene),
2
3.47–3.24 (m, 6 H, CH2), 3.22–3.13 (m, 2 H, CH2), 3.07–2.40 (m,
6 H, 16-H/17-H), 2.56 (s, 6 H, 21-H/22-H) ppm. 195Pt NMR
(85.96 MHz, CD2Cl2, 295.0 K):
δ =
–2849 ppm. 13C NMR
(100.56 MHz, CD2Cl2, 295.0 K): δ = 163.35 (C-13), 155.58 (C-18),
148.91 (C-1), 147.98 (C-12), 136.34 (C-7), 131.81 (C-8), 131.21 (C-
6), 131.11 (C-5), 129.33 (C-11), 127.05 (C-3), 126.77 (C-10), 122.37
(C-2), 121.85 (C-9), 119.78 (C-4), 70.86 (2 C, Cethylene), 48.90 (2 C,
C-14/C-15), 47.73 (2 C, C-19/C-20), 35.43 (4 C, CH3) ppm. IR
X-ray Crystallographic Study: Suitable crystals were taken directly
from the mother liquor, immersed in perfluorinated polyether oil
and fixed on top of a glass capillary. Data were collected with a
Nonius–Kappa CCD diffractometer with a low-temperature unit
using graphite-monochromated Mo-Kα radiation. The temperature
was set to 100 K. The data collected were processed using the stan-
dard Nonius software.[42] All calculations were performed using the
SHELXT-PLUS software package. Structures were solved by direct
methods with the SHELXS-97 program and refined with the
SHELXL-97 program.[43,44] Graphical handling of the structural
data during solution and refinement was performed with
XPMA.[45] Atomic coordinates and anisotropic thermal parameters
of non-hydrogen atoms were refined by full-matrix least-squares
calculations.
(CsI): ν = 3012 (w), 2927 (w), 2871 (m), 1635 (s), 1586 (s), 1558
˜
(s), 1502 (w), 1471 (m), 1420 (m), 1390 (m), 1278 (s), 1238 (m),
1150 (w), 1117 (w), 1032 (m), 967 (m), 869 (w), 833 (w), 783 (m),
748 (s), 694 (w), 652 (w), 586 (w), 559 (w), 510 (s), 471 (w) cm–1.
Raman (514 nm, 300 mW): λ = 28.2, 39.6, 56.3, 90.9, 149.1, 212.2,
330.2/336.6, 372.2, 396.8, 424.9, 468.3, 488.5, 511.7, 561.5, 605.6,
643.5, 724.4, 739.2, 782.6, 1044.6, 1154.6/1160.5, 1230.2, 1245.5,
1298.8, 1497.0, 1553.9, 1563.7, 1589.4, 1600.3, 1632.8,
3044.3 cm–1. UV/Vis (CH3CN, c = 1.56ϫ10–5 molL–1): λ (ε) = 269
(10784 Lmol–1 cm–1) nm. HRMS (FAB+): m/z (%) = 669.1769
(63.4), 670.1799 (81.2), 671.1766 (100.0), 672.1766 (65.8), 673.1758
(60.7) [MH]+. C24H32Cl2N6Pt (670.54): calcd. C 42.99, H 4.81, N
12.53; found C 42.60, H 4.77, N 12.23.
CCDC-790562 (for 2), -790558 [for (R)-3], -790561 [for (R)-4],
-790936 (for 5), -790557 {for [PtCl2(C2H4)(κ1-2)]}, -790559 {for
[(1H)PtCl3]}, -790560 (for [(1H)PdCl3]) 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.
Crystal data for [PtCl2(C2H4)(κ1-2)]: C24H32Cl2N6Pt, Mr = 670.54,
3
¯
0.30ϫ0.25ϫ0.18 mm , triclinic, space group P1, a = 9.934(2), b =
10.492(2), c = 13.034(3) Å, α = 101.96(3), β = 95.39(3), γ =
106.01(3)°, V = 1260.9(5) Å3, Z = 2, ρcalcd. = 1.766 Mgm–3, Mo-
Kα radiation (graphite-monochromated, λ = 0.71073 Å), T =
100 K, θrange = 2.08–30.17°. Reflections measured 13245, indepen-
dent 7327, Rint = 0.0388. Final R indices [IϾ2σ(I)]: R1 = 0.0270,
wR2 = 0.0705.
Quantum Chemical Calculations: Quantum chemical calculations
were carried out with the Gaussian 03[46] and Gaussian 09[47] pro-
gram package. The B3LYP functional together with the LANL2DZ
basis set was used throughout these calculations.
[PtCl2(C2H4){(R)-κ1-4}]: [PtCl2(C2H4)]2 (77.43 mg, 0.13 mmol,
1 equiv.) dissolved in toluene (9 mL) was added to a solution of
(R)-4 in toluene (6 mL). After 30 min the reaction was quenched
by reducing the volume of the reaction mixture to around 4 mL
and adding PE (40/60, 10 mL). A yellow precipitate was filtered off
and washed twice with PE (40/60, 5 mL) to give [PtCl2(C2H4){(R)-
Supporting Information (see footnote on the first page of this arti-
cle): UV/Vis spectra of 1 and 3, Raman spectrum of 1, Raman and
IR spectra of 5, CV curves for 2 and 4 in CH2Cl2, calculated struc-
ture (B3LYP/6-311G**) of dication 52+, UV/Vis spectrum obtained
for the oxidation of 5 with I2 in CH3CN, IR spectra of free 2 and
the complex [PtCl2(C2H4)(κ1-2), molecular structures of [(1H)-
PdCl3] and [(1H)PtCl3], Raman spectra of 2 and [PtCl2(C2H4)(κ1-
2)] and gas-phase structures of [PtCl2(C2H4)(κ1-2)], [PtCl2-
(C2H4)(κ1-4)] and [PtCl2(C2H4)(κ1-1)].
4}] (152.8 mg, 77%) as
a
light-yellow powder. 1H NMR
(399.89 MHz, CD2Cl2, 295.1 K): δ = 8.35 (d, 3J = 8.78 Hz, 1 H,
CH), 7.82 (t, 3J = 7.34, 2 H, CH), 7.74 (d, 3J = 8.03 Hz, 1 H, CH),
7.69 (d, 3J = 8.75 Hz, 2 H, CH), 7.34–7.10 (m, 7 H, CH), 4.56–
4.40 (m, 2 H, Hethylene), 4.32–4.12 (m, 2 H, Hethylene), 3.42–2.95 (m,
8 H, CH2), 2.82 (s, 3 H, CH3), 2.57 (s, 6 H, CH3), 2.07 (s, 3 H,
CH3) ppm. 195Pt NMR (85.96 MHz, CD2Cl2, 294.8 K): δ
=
Acknowledgments
–2853 ppm. 13C NMR (100.56 MHz, CD2Cl2, 296.4 K): δ = 156.58,
140.08, 146.39, 134.41 (Cq), 130.86 (CH), 130.36 (Cq), 128.12, Continued financial support from the Deutsche Forschungsgemein-
127.35, 126.79, 126.63, 126.21, 125.31, 124.42, 123.84, 123.24 (CH), schaft (DFG) is gratefully acknowledged.
1312
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 1302–1314

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Received: September 15, 2010
Published Online: January 26, 2011
1314
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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