The first metal complexes of the proton sponge 1,8-bis(N,N,N′, N′-tetramethylguanidino)naphthalene: Syntheses and properties

Article abstract of DOI:10.1002/ejic.200800677

In this work we report on the syntheses and properties of the first transition metal complexes of the proton sponge 1,8-bis(N,N,N′,N′- tetramethylguanidino)naphthalene (btmgn). Of the three complexes [(btmgn)PdCl₂], [(btmgn)PtCl₂] and [(btmgn)PtCl ₂(C₂H₄)], the first two feature a chelating btmgn ligand that is bound to the metal atom through two nitrogen atoms. Only one metal-N bond is established in [(btmgn)-PtCl₂(C₂H ₄)]. The molecular structures of [(btmgn)PdCl₂] and [(btmgn)PtCl₂] show some interesting details. X-ray crystallographic studies reveal that the naphthyl aromatic systems in both complexes are not planar, the metal atoms reside above the best-plane of the naphthyl systems and the compounds adopt a chiral conformation in the crystalline phase. Several dynamic processes of the two guanidinyl groups in solution were identified by line-shape analysis of the temperature-dependent NMR spectra. The complex [(btmgn)-PtCl₂(C₂H₄)] eliminates ethylene at elevated temperature to give [(btmgn)PtCl₂]. Quantum chemical (DFT) calculations indicate that the ΔG⁰ value for this reaction is close to zero. Indeed the compound [(btmgbp)PtCl₂] {btmgbp = 2,2′-bis(N,N,N′,N′-tetramethylguanidino)biphenyl} in which the naphthyl group is replaced by a biphenyl group is not amenable to ethylene elimination. First experiments point to interesting catalytic properties of the new complexes. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800677

FULL PAPER
DOI: 10.1002/ejic.200800677
The First Metal Complexes of the Proton Sponge 1,8-Bis(N,N,NЈ,NЈ-
tetramethylguanidino)naphthalene: Syntheses and Properties
Ute Wild,[a] Olaf Hübner,[a] Astrid Maronna,[a] Markus Enders,[a] Elisabeth Kaifer,[a]
Hubert Wadepohl,[a] and Hans-Jörg Himmel*[a]
Keywords: Proton sponge / Coordination compounds / Palladium / Platinum / Guanidine / Chelates
In this work we report on the syntheses and properties of
the first transition metal complexes of the proton sponge 1,8-
bis(N,N,NЈ,NЈ-tetramethylguanidino)naphthalene (btmgn).
Of the three complexes [(btmgn)PdCl2], [(btmgn)PtCl2] and
[(btmgn)PtCl2(C2H4)], the first two feature a chelating btmgn
ligand that is bound to the metal atom through two nitrogen
atoms. Only one metal–N bond is established in [(btmgn)-
PtCl2(C2H4)]. The molecular structures of [(btmgn)PdCl2] and
[(btmgn)PtCl2] show some interesting details. X-ray crystal-
lographic studies reveal that the naphthyl aromatic systems
in both complexes are not planar, the metal atoms reside
above the “best-plane” of the naphthyl systems and the com-
pounds adopt a chiral conformation in the crystalline phase.
Several dynamic processes of the two guanidinyl groups in
solution were identified by line-shape analysis of the tem-
perature-dependent NMR spectra. The complex [(btmgn)-
PtCl2(C2H4)] eliminates ethylene at elevated temperature to
give [(btmgn)PtCl2]. Quantum chemical (DFT) calculations
indicate that the ∆G0 value for this reaction is close to zero.
Indeed the compound [(btmgbp)PtCl2] {btmgbp
= 2,2Ј-
bis(N,N,NЈ,NЈ-tetramethylguanidino)biphenyl} in which the
naphthyl group is replaced by a biphenyl group is not ame-
nable to ethylene elimination. First experiments point to
interesting catalytic properties of the new complexes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
atoms of PS3 are sterically less shielded than the nitrogen
lone pairs in PS1. Many transition metal complexes featur-
ing ligands with tetramethylguanidino groups were synthe-
sized in the recent years. Because of the strong basicity of
guanidines, interesting properties are expected for these
complexes. To name two examples, Henkel et al. synthe-
sized several complexes (especially of Fe and Cu) of bis-
guanidines, using e.g. 1,3-bis(N,N,NЈ,NЈ-tetramethylguani-
dino)propane [(Me2N)2CN(CH2)3NC(NMe2)2],[8] and also
published valuable work on the synthetic routes to such li-
gands.[9] Very recently, the first 1:1 Cu/O2 complex featuring
Introduction
The first example of a proton sponge, 1,8-bis(dimethyl-
amino)naphthalene (PS1) (see Scheme 1), was reported in
1968 by Alder et al.[1] and features two dimethylamino
groups in close proximity. While PS1 has a high affinity
towards H+, it is indifferent to other electrophiles, which is
in contrast to usual nitrogen bases. This implies that PS1 is
not ready to act as ligand in coordination complexes. In-
deed, up to date only one complex[2] of the archetypal pro-
ton sponge PS1 is known.[3] Other examples for proton
sponges include quino[7,8-h]quinoline (PS2)[4] and 1,8-
bis(N,N,NЈ,NЈ-tetramethylguanidino)naphthalene (PS3).[5]
On the basis of quantum chemical calculations, PS4 was
suggested to be a superior chiral proton sponge.[6] However,
its synthesis has not yet been achieved. Recently, the first
transition metal complexes of the proton sponge PS2 were
reported.[7] Herein we report the syntheses, characterization
and reactivity of the first metal complexes of the proton
sponge PS3 that exhibit unusual structures and interesting
reactivity. Complex formation in the case of PS3 is easier
than for PS1 because the lone pairs at the imine-nitrogen
[a] Anorganisch-Chemisches Institut, Ruprecht-Karls-Universität
Heidelberg,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: +49-6221-54-5707
E-mail: hans-jorg.himmel@aci.uni-heidelberg.de
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Scheme 1.
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Metal Complexes of 1,8-bis(N,N,NЈ,NЈ-tetramethylguanidino)naphthalene
end-on coordinated O2 was reported.[10] In this complex, were obtained from CH2Cl2/Et2O solutions. The molecular
Cu is coordinated by the tripodal, superbasic and sterically structure of 1 is illustrated in Figure 1. Selected structural
encumbered tris(tetramethylguandino)tren (tmg3tren) li- parameters can be found in Table 1. The most remarkable
gand.
features of the structure are the non-planarity of the naph-
thalene aromatic system and the location of the Pd atom
133.8(7) pm above the “best plane” of the aromatic sys-
tem.[11] Furthermore, 1 is chiral (see Figure 1) and contains
two pairs of enantiomers in the unit cell.
Results and Discussion
Reaction of [(1,5-cod)PdCl2] (1,5-cod = 1,5-cycloocta-
diene) and PS3 in CH2Cl2 yielded the new Pd complex
[(PS3)PdCl2] (1). Red crystals suitable for X-ray diffraction
Table 1. Selected bond lengths [pm] and angles [°] for 1.
Pd–Cl1
Pd–N1
N1–C1
N1–C11
C11–N2
C11–N3
C1–C10
C1–C2
C4–C5
C3–C4
232.62(13)
205.3(5)
140.6(7)
135.2(7)
135.8(8)
134.1(7)
146.0(8)
138.6(8)
141.1(9)
136.0(9)
139.5(8)
142.4(8)
89.53(6)
92.84(14)
116.5(4)
123.3(5)
Pd–Cl2
Pd–N4
N4–C9
N4–C16
C16–N6
C16–N5
C9–C10
C8–C9
C5–C6
C6–C7
C7–C8
231.09(16)
201.0(5)
143.2(7)
132.4(7)
135.1(7)
135.4(8)
143.6(8)
136.8(8)
142.4(9)
135.8(9)
141.5(8)
C2–C3
C5–C10
Cl1–Pd–Cl2
Cl1–Pd–N1
C1–N1–Pd
C1–N1–C11
N1–Pd–N4
Cl2–Pd–N4
C9–N4–Pd
C9–N4–C16
81.92(19)
96.29(14)
109.0(3)
121.1(5)
C1–N1–C11–N2 –38.7
C1–N1–C11–N3 141.7
Variable low-temperature 1H NMR studies of 1 were car-
ried out to analyze the flexibility of the guanidinyl groups
1
in solution (Figure 2). The H NMR spectra at room tem-
perature show a symmetric naphthalene unit (three reso-
nances for ortho, meta and para H atoms) and one single
resonance for the eight N–CH3 groups. Upon cooling, the
N–CH3 signal splits into four signals and by further lower-
ing of the temperature, the Pd complex 1 gives eight distinct
signals for the methyl groups, and the ortho and para H
atoms of the naphthalene moiety are split into two pairs of
signals. This pattern is in accordance with the structure in
the solid state, where the symmetry of the naphthalene unit
Figure 1. Molecular structure of complex 1 (in front view and the
two enantiomers in side view). Ellipsoids are drawn at the 50%
probability level.
Figure 2. Experimental variable-temperature 1H NMR spectra of 1 (left) and corresponding simulated spectra (right). The aromatic
resonances were simulated only for the fast low-temperature process (178 K–198 K). The signal at δ = 5.3 ppm arises from traces of
CHDCl2. For the corresponding rate constants see Table 2.
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H.-J. Himmel et al.
FULL PAPER
is lowered by the significantly different orientation of the hand, reaction of Zeise’s dimer [Pt2(C2H4)2Cl4] with the hy-
two guanidine units. In order to get further insight into the drogen sponge PS3 in CH2Cl2 at room temperature gave
dynamic processes, we simulated the variable-temperature the new complex 2 [see Equation (1)].
1H NMR spectra with the aid of a line-shape analysis mod-
ule[12] and extracted rate constants by fitting the simulated
spectra with the experimental spectra. As a result, three
well-separated rate constants of four different fluxional pro-
cesses have been determined. The fastest process which
leads to a symmetric naphthalene unit and four N–CH3 res-
onances can be described by reorientation of the two guani-
dine units without complete rotation around the N1–C
bonds (see Scheme 2). The fitting of the rate constant for
this process results in a value of 78 Hz at a temperature of
178 K. By further analysis of the line shape behavior a
The NMR spectroscopic data of 2 indicates the presence
Gibbs free activation energy ∆G‡ of 36 kJmol–1 has been of an ethylene unit. The isolation of an ethylene complex in
determined. This process results in racemization of the en- the case of Pt but not Pd is in agreement with the larger
antiomeric complexes observed in the crystal. A complete stability of PtII alkene complexes compared to their PdII
rotation of the guanidine units can be ruled out, as this counterparts.[13] Yellow crystals of the complex were ob-
would lead to a spectrum with only two different N–CH3 tained from toluene layered by petroleum ether (PE) 40/60
resonances. Rotation around the N2–C bond and the N3– and Figure 3 illustrates the molecular structure as deter-
C bond occurs at two different reaction rates. The slower mined by X-ray diffraction (see Table 3 for selected struc-
rotation is accompanied by a complete rotation of the gua- tural parameters). Only one of the guanidinyl groups in 2
nidine units (rotation around the N1–C bond, Scheme 2). is bound to Pt. As in the [PtCl3(C2H4)]– anion of Zeise’s
Table 2 summarizes the results of the line-shape analysis.
salt,[14] the ethylene moiety is oriented perpendicularly to
the plane hosting the Pt atom, the two Cl atoms and the N
atom attached to Pt. With a value of 135.7(9) pm, the C=C
distance is, as anticipated, elongated with respect to that in
free ethylene [133.7(2) pm].[15] The two Pt–C distances are
slightly different and have values of 213.8(7) and
211.9(6) pm, which are comparable with the Pt–C distances
in Zeise’s salt [212.8(3) and 213.5(3) pm]. The Pt–N dis-
tance in 2 is 206.9(4) pm. For comparison, in cis- and trans-
[(hppH)2PtCl2] (hppH = 1,3,4,6,7,8-hexahydro-2H-pyrim-
ido[1,2-a]pyrimidine) values of 202.2(3)/202.3(3) and
203.3(2) pm, respectively, were determined.[16] The relatively
large Pt–N distance in 2 can be explained by the strong
trans effect of coordinated ethylene. Complex 2 is stable in
toluene at room temperature. However, in refluxing CH2Cl2
it eliminates ethylene to give the new complex 3. The NMR
spectroscopic data of 3 shows the disappearance of the sig-
nals from the ethylene group. Orange crystals of 3 were
grown by layering a CH2Cl2 solution with PE 40/60. The
single-crystal X-ray diffraction analysis confirms that 3 is
the homologue of 1, namely the complex [(PS3)PtCl2], in
which both guanidinyl groups are bound to the Pt atom
(see Figure 4 and Table 4). As a consequence of the η2-co-
ordination mode, the naphthyl group again abandons its
planar structure. Moreover, the Pt atom is located 133.1 pm
above the “best plane” of the aromatic system.[7] This un-
usual structure is in clear contrast to that of e.g. [(btmgb)-
PtCl2] (4) {btmgb = 1,2-bis(N,N,NЈ,NЈ-tetramethylguani-
dino)benzene}, in which the Pt atom lies in the plane de-
fined by the C6 aromatic ring.[17] Like its Pd analogue, 3
features two pairs of enantiomers in the unit cell. Some
Scheme 2.
Table 2. Estimated rate constants and Gibbs free activation energy
barriers ∆G‡ for the different processes observed in the tempera-
ture-dependent NMR spectra.
T [K]
Rate constants [s–1]
Process 2[b]
Process 1[a]
Process 3[c]
178
188
198
208
218
228
238
248
258
78
300
1150
230
470
1000
4000
10000
20000
11
25
100
310
920
3500
∆G‡ [kJmol–1]
36 (200 K)
42 (250 K)
46 (250 K)
[a] Reorientation of the guanidine units without complete rotation.
[b] Rotation of NMe2 unit. [c] Rotation of second NMe2 unit. A
simultaneous rotation around N1–C has been presumed with the
same reaction rate for the simulation of this parameter.
First experiments aiming at the synthesis of Pt complexes variable low-temperature 1H NMR spectra recorded for this
of PS3 with the compound PtCl2(dmso)2 as precursor gave complex in solution are shown in Figure 5. As in the case
no results. The only complex that could be isolated in small of 1, the spectrum at room temperature displays only one
amounts was the salt [PS3H]+[PtCl3(dmso)]–. On the other signal at δ = 2.83 ppm for all eight methyl groups. However,
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Metal Complexes of 1,8-bis(N,N,NЈ,NЈ-tetramethylguanidino)naphthalene
the splitting into four CH3 signals occurs at lower tempera-
ture than in the case of 1 indicating more facile rotation
around the C–N bonds of the guanidinyl groups. The spec-
trum recorded at 178 K still shows four signals, which me-
ans that the rate for interconversion of the two enantiomers
is higher for 3 than for 1. It is obvious that the bond order
of the N=C double bonds in PS3 before coordination is
considerably reduced after coordination relative not only to
the free ligand but also to the situation in complex 1. This
is also manifested in the C1–N1–C11–N3 and C1–N1–C11–
N2 torsion angles of 41.7° and –139.8°.
Figure 4. Molecular structure of complex 3 in front and side view.
Ellipsoids are drawn at the 50% probability level. The H atoms of
the methyl groups were omitted for clarity.
Figure 3. Molecular structure of complex 2. Ellipsoids are drawn
at the 50% probability level. The H atoms of the methyl groups
were omitted for clarity.
Table 4. Selected bond lengths [pm] and angles [°] for 3.
Pt–Cl1
Pt–N1
N1–C1
N1–C11
C11–N2
C11–N3
C1–C2
C2–C3
C3–C4
C4–C5
C1–C10
C5–C10
Cl1–Pt–Cl2
Cl1–Pt–N1
C1–N1–Pt
N1–C11–N2
N1–C11–N3
N2–C11–N3
232.62(12)
204.6(3)
141.6(5)
135.7(5)
134.3(5)
134.5(5)
138.4(5)
140.3(6)
136.4(6)
140.7(6)
145.6(5)
142.6(5)
88.50(4)
92.45(9)
117.6(2)
117.8(4)
123.9(4)
118.3(3)
Pt–Cl2
Pt–N4
230.71(11)
202.8(3)
142.5(5)
133.5(5)
135.5(5)
135.5(5)
137.7(5)
140.9(6)
134.0(6)
142.9(6)
143.0(5)
Table 3. Selected bond lengths [pm] and angles [°] for 2.
N4–C9
N4–C16
C16–N5
C16–N6
C8–C9
C7–C8
C6–C7
C5–C6
C9–C10
Pt–Cl1
Pt–C21
Pt–N1
N1–C1
N1–C11
C11–N2
C11–N3
C1–C2
C2–C3
C3–C4
229.63(15)
213.8(7)
206.9(4)
142.8(6)
132.9(6)
135.7(6)
135.7(6)
138.5(7)
140.0(7)
134.2(7)
142.2(7)
143.8(7)
144.6(7)
Pt–Cl2
230.35(15)
211.9(6)
458.5(3)
139.9(6)
129.0(6)
137.3(7)
139.6(7)
138.2(7)
139.2(8)
135.2(8)
142.2(8)
144.4(7)
135.7(9)
97.4(19)/97(2)
37.2(3)
Pt–C22
Pt···N4
N4–C9
N4–C16
C16–N5
C16–N6
C8–C9
C7–C8
C6–C7
C5–C6
C9–C10
C21–C22
N1–Pt–N4
Cl2–Pt–N4
C9–N4–Pt
N4–C16–N5
N4–C16–N6
N5–C16–N6
82.06(12)
97.21(10)
109.0(3)
119.8(4)
123.0(4)
117.2(4)
C4–C5
C1–C10
C5–C10
C21–H
Cl1–Pt–Cl2
N1–Pt–Cl1
Cl1–Pt–C21
C1–N1–Pt
N1–C11–N2
N2–C11–N3
N4–C16–N6
97.4(19)/96(2) C22–H
178.36(6)
91.32(12)
91.0(2)
C21–Pt–C22
N1–Pt–Cl2
Cl1–Pt–C22
C11–N1–Pt
N1–C11–N3
N4–C16–N5
N5–C16–N6
89.56(12)
87.9(2)
120.6(3)
120.2(4)
120.7(5)
113.3(4)
C1–N1–C11–N2 –139.8
C1–N1–C11–N3 41.7
118.6(3)
122.6(4)
117.1(5)
125.9(5)
bone of the bisguanidine ligand system could turn ∆G0 to
positive values. To gain further insight, we prepared a re-
Quantum chemical calculations [18] suggest that the elimi- lated Pt ethylene complex, namely [(btmgbp)PtCl2(C2H4)]
nation of ethylene from 2 to give 3 is associated with a (5) {btmgbp = 2,2Ј-bis(N,N,NЈ,NЈ-tetramethylguanidino)-
change in energy and Gibbs free energy (at 298 K, biphenyl}, in which the naphthyl group is replaced by bi-
1013 mbar) of 45.4 and –3.2 kJmol–1, respectively. Inspec- phenyl. Complex 5 can be obtained in a similar way as 2
tion of the isodensity surfaces (see Supporting Information) from btmgbp and [Pt2(C2H4)2Cl2], and Figure 6 displays its
of the HOMO orbitals of 2 and 3 shows that the HOMO molecular structure (see Table 5 for selected structural pa-
is concentrated at the PS3 ligand for 2, but at the Pt and rameters). Similar to the situation in 2, the bisguanidine
Cl atoms for 3. In contrast, the LUMO is concentrated at unit is bound only through one N atom to Pt. However, in
Pt and Cl for 2 and at the PS3 ligand for 3. The calculated this case even prolonged heating of a CH2Cl2 solution (and
∆G0 value close to zero for ethylene elimination from 2 to also of a CH3CN solution) of 5 to reflux for 24 h did not
give 3 implies that even slight modifications in the back- cause formation of [(btmgbp)PtCl2].
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As a consequence of the unusual molecular structures,
interesting chemical properties are expected for the three
complexes 1–3. As first examples, we briefly inspected two
different catalytic reactions: (i) Heck reaction between sty-
rene and phenyl iodide to give trans-stilbene catalyzed by
complex 1. As detailed in the Experimental Section, com-
plex 1 turned out to be a good catalyst for this reaction
yielding nearly quantitative amounts of trans-stilbene. The
number of turnovers was 45, and the turnover frequency
[TOF, (mol product)/(mol catalystϫtime)] is roughly 9 h–1.
Thus, the process is quite fast, although catalysts with
higher TOF are known.[19] (ii) Hydrosilylation between Et3-
SiH and Me3SiC(H)CH2 to give Me3SiC(H)CH(SiEt3) at
room temperature in the presence of the Pt complexes 2 or
3. In this case we followed the product yield with GC/MS.
The applied conditions were similar to that used previously
in a study which compared the catalytic activity of several
Pt0 olefin complexes with that of the archetypical Karstedt
catalyst.[20] Our results (see Figure 7) show that complex 2
is a highly active catalyst for this reaction. The number of
turnovers was ca. 500, and the turnover frequency can be
estimated to be 302 h–1 from the plot shown in Figure 5 [for
this estimate, the linear curve section (16–96 min) was used].
There was no sign of an induction period and the product
yield reached Ͼ95% after less than 200 min. No colloid for-
mation or precipitate was observed indicating a homogen-
eous process. Interestingly, complex 3 showed no or only
very low catalytic activity, in contrast to 2; even after
140 min no significant product formation was detectable.
Only after addition of CH2Cl2 (increasing the solubility of
3) the reaction started slowly with ca. 10% yield after
550 min.
Figure 5. Experimental variable-temperature 1H NMR spectra of
3.
Figure 6. Molecular structure of complex 5. Ellipsoids are drawn
at the 50% probability level. The H atoms of the methyl groups
were omitted for clarity.
Table 5. Selected bond lengths [pm] and angles [°] for 5..
Pt–Cl1
Pt–C23
Pt–N1
N1–C1
N1–C13
C13–N2
C13–N3
C1–C6
229.23(13)
2.156(5)
2.066(3)
1.430(4)
1.333(4)
1.346(5)
1.343(4)
1.404(5)
1.484(5)
178.41(4)
87.95(8)
89.8(2)
Pt–Cl2
2.3016(13)
2.147(5)
663.9(6)
1.408(5)
1.284(5)
1.388(5)
1.380(5)
1.407(5)
Pt–C24
Pt···N4
N4–C12
N4–C18
C18–N5
C18–N6
C7–C12
Figure 7. Product yield (according to GC/MS) in the hydro-
silylation reaction between Et3SiH and Me3SiCHCH2 to give Me3-
SiC(H)CH2(SiEt3) using complex 2 and 3 as catalyst. The arrow
marks the point at which CH2Cl2 was added to increase the solubil-
ity of complex 2.
C6–C7
Cl1–Pt–Cl2
N1–Pt–Cl1
Cl1–Pt–C23
C1–N1–Pt
N1–C13–N2
N2–C13–N3
N4–C18–N6
C23–Pt–C24
N1–Pt–Cl2
Cl1–Pt–C24
C13–N1–Pt
N1–C13–N3
N4–C18–N5
N5–C18–N6
36.9(2)
90.63(8)
91.49(18)
120.7(2)
122.8(3)
127.3(4)
114.0(4)
Conclusions
116.3(2)
120.0(3)
117.2(3)
118.7(4)
In this work we report the syntheses of the first transition
metal complexes of the proton sponge 1,8-bis(N,N,NЈ,NЈ-
tetramethylguanidino)naphthalene (btmgn). In the com-
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Metal Complexes of 1,8-bis(N,N,NЈ,NЈ-tetramethylguanidino)naphthalene
X-ray Crystallographic Studies: Suitable crystals were taken directly
plexes [(btmgn)PdCl2] (1) and [(btmgn)PtCl2] (3), the btmgn
ligand acts as a chelating ligand, that is bound to the metal
atom through two nitrogen atoms. The most remarkable
structural features of both complexes [(btmgn)PdCl2] and
[(btmgn)PtCl2] are the non-planarity of the naphthyl aro-
matic system, the location of the metal atom above the
“best plane” of the aromatic systems, and the chirality of
the molecules in the crystalline phase. A line-shape analysis
of dynamic NMR spectra showed that ca. 80 interconver-
out of the mother liquor, immersed in perfluorinated polyether oil,
and fixed on top of a glass capillary. Measurements were performed
at low temperature with a Bruker AXS Smart 1000 diffractometer
and with a Nonius-Kappa CCD diffractometer (Mo-Kα radiation,
graphite monochromated, λ = 0.71073 Å). The data collected were
processed using the standard Bruker and Nonius software.[21] The
structures were solved by the heavy atom method combined with
structure expansion by direct methods applied to difference struc-
ture factors (complex 1)[22] or by conventional direct methods[23]
sions per second between the two enantiomers of [(btmgn)- and refined by full-matrix least-squares methods based on F2
against all reflections.[19] All non-hydrogen atoms were given aniso-
tropic displacement parameters. Hydrogen atoms were fixed at cal-
culated positions and refined with a riding model. CCDC-686257
(compound 1), -686258 (compound 2), -686259 (compound 3)
and -693423 (compound 5) contain the supplementary crystallo-
graphic data (excluding structure factors) for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via http://www.ccdc.cam.ac.uk/ data_request/
cif.
PdCl2] occur already at 178 K (∆G‡ ≈ 36 kJmol–1), making
an isolation of one enantiomer virtually impossible. In the
case of [(btmgn)PtCl2], the interconversion is even faster.
The NMR studies also provide information about the rates
and Gibbs free energies for rotations around the guanidinyl
C–N bonds.
In contrast to the situation in [(btmgn)PdCl2] and
[(btmgn)PtCl2], only one N–Pt bond is established in the
complex [(btmgn)PtCl2(C2H4)] (2), which eliminates ethyl-
ene at elevated temperatures to give [(btmgn)PtCl2]. Quan-
tum chemical (B3LYP) calculations predict a ∆G0 value (at
298 K, 1 bar) of not more than –3.2 kJmol–1 for this pro-
cess. To obtain further information, the compound
[(PS3)PdCl2] (1): [(1,5-cod)PdCl2] (30 mg, 0.11 mmol) was dis-
solved in CH2Cl2 (10 mL) and stirred under reflux. PS3 (56 mg,
0.16 mmol, 0.145 equiv.) in CH2Cl2 (10 mL) was added dropwise
to this solution over a period of 30 min. The orange-colored clear
solution was stirred for additional 2 h and afterwards filtered
[(btmgbp)PtCl2(C2H4)] was synthesized. Elimination of through a silica frit. The solvent was removed in vacuo and the
orange residue was washed several times with diethyl ether and PE
40/60 yielding an orange powder. Red crystals (27 mg, 47%) of 1
were obtained by layering a CH2Cl2 solution of this powder with
diethyl ether. C20H30Cl2N6Pd (531.80): calcd. C 45.17, H 5.69, N
15.80; found C 44.34, H 5.65, N 15.21. 1H NMR (399.89 MHz,
CD2Cl2, 296.2 K): δ = 7.497 (d, 1JH-H = 8.1 Hz, 2 H), 7.30 (t,
1JH-H = 7.8 Hz, 2 H), 6.61 (s, 1JH-H = 7.5 Hz, 2 H), 2.82 (s, 24
H, CH3) ppm. 13C NMR (100.56 MHz, CD2Cl2, 296 K): δ = 165.7
(CN3), 141.7, 136.7, 126.3, 125.7, 122.4, 113.8 (CArom.), 40.9 (CH3)
ppm. MS (EI): m/z (%) = 532 (50) [M]+, 496 (20) [(tmgn)PdCl]+,
C2H4 should be less favorable in this case (formation of a
seven-membered ring), and indeed this reaction is not ob-
served.
Finally, first catalytic tests were carried out on [(btmgn)-
PdCl2], [(btmgn)PtCl2], and [(btmgn)PtCl2(C2H4)]. Al-
though much more research is necessary to fully explore the
catalytic potential of these complexes, these preliminary
tests show interesting results. Heck reactions with [(btmgn)-
PdCl2] proceed smoothly, although catalysts with larger
turn-over frequencies are known. The most remarkable re- 460 (77) [(tmgn)Pd]+. UV/Vis: λ = 290, 355 nm. IR: ν = 1561
˜
[ν(C=N)] cm–1. Crystal data for 1: C20H30Cl2N6Pd·CH2Cl2, Mr =
sult is that [(btmgn)PtCl2(C2H4)] seems to be a good cata-
lyst for hydrosilylation reactions (TOF of ca. 300 h–1), while
616.73, 0.30ϫ0.10ϫ0.10 mm, monoclinic, space group P21/c, a =
10.2408(8), b = 16.5023(13), c = 14.9271(12) Å, β = 95.456(2)°, V
[(btmgn)PtCl2] does not seem to catalyze hydrosilylation.
= 2511.2(3) Å3, Z = 4, dcalcd. = 1.631 Mgm–3, T = 100 K, θ range
1.8 to 26.4°. Reflections measured 46844, independent 5135 (Rint
= 0.0974), observed [IϾ2σ(I)] 3231, semiempirical absorption cor-
rection. Final R indices [Fo Ͼ 4σ(Fo)]: R(F) = 0.0437, wR(F2) =
Experimental Section
0.0901.
All reactions were carried out under a dry argon atmosphere using
standard Schlenk techniques. All solvents were dried using the
standard methods followed by distillation. [(1,5-cod)PdCl2] was
either prepared from dichloridobis(benzonitrile)palladium(II)
(99% purity, ABCR) or purchased from ABCR (99% purity). For
the synthesis of [(1,5-cod)PdCl2], 1,5-cod (0.9 mL, 7.3 mmol) was
[(PS3)PtCl2(C2H4)] (2): [PtCl(C2H4)(µ-Cl)]2 (60 mg, 0.102 mmol)
was dissolved in CH2Cl2 (10 mL). A solution of PS3 (71 mg,
0.2 mmol) in CH2Cl2 (10 mL) was then added dropwise over a
period of 30 min. The yellow solution was stirred for additional
30 min at room temperature and the solvent was removed in vacuo
afterwards. The remaining yellow powder was redissolved in tolu-
ene and filtered through silica. A yellow powder (83 mg) was ob-
tained, which was washed several times with PE 40/60. Yellow crys-
tals of 2 were grown at –20 °C by layering a toluene solution with
PE 40/60. 1H NMR (399.89 MHz, CD2Cl2, 296 K): δ = 8.59 (d,
1JH-H = 7.3 Hz, 1 H), 7.51–7.15 (m, 4 H), 6.16 (d, 1JH-H = 7.2 Hz,
added
to
dichloridobis(benzonitrile)palladium(II)
(50 mg,
0.13 mmol). The solution was carefully heated with a heat gun for
some time until reflux. Afterwards, it was stirred for 1 h at room
temperature. PS3 and the dinuclear complex di-µ-chlorido-
dichloridobis(ethylene)diplatinum(II) [PtCl(C2H4)(µ-Cl)]2 used in
the syntheses of the Pt complexes were purchased from Fluka (pu-
rum) and ABCR (97% purity), respectively. IR spectra were re-
corded with a BIORAD Excalibur FTS 3000 spectrometer. NMR
spectra were measured with a Bruker Avance II 400 spectrometer.
The variable-temperature NMR measurements were recorded with
a Bruker DRX 300 spectrometer. A Perkin–Elmer Lambda 19 spec-
trometer was used to obtain UV/Vis spectroscopic data.
1
1 H), 4.45 (m, JPt-H = 82 Hz, 4 H), 3.76 (s, 3 H, CH3), 2.90 (s,
15 H, CH3), 2.63 (s, 3 H, CH3), 1.96 (s, 3 H, CH3) ppm. 13C NMR
(100.56 MHz, CD2Cl2, 296 K): δ = 168.8, 160.5 (CN3), 150.1,
147.5, 137.0, 126.4, 125.6, 124.9, 124.8, 124.2, 121.0, 117.8 (CArom.),
70.6 (C2H4), 41.1, 40.4 (br.), 39.6, 38.9 (CH3) ppm. 195Pt NMR
(85.96 MHz, CD2Cl2, 296 K): δ = –2787 (br.) ppm. MS (FAB): m/z
(%): 649 (66) [M + H]+, 548 (100) [(tmgn)Pt]+, 620 (90) [(tmgn)-
Eur. J. Inorg. Chem. 2008, 4440–4447
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4445

H.-J. Himmel et al.
FULL PAPER
PtCl2]+, 584 (68) [(tmgn)PtCl]+. Crystal data for 2: C22H34Cl2N6Pt,
Mr = 648.54, 0.30ϫ0.10ϫ0.10 mm, monoclinic, space group P21/
n, a = 10.619(2), b = 15.451(3), c = 15.965(3) Å, β = 107.16(3)°, V
= 2502.8(9) Å3, Z = 4, dcalcd. = 1.721 Mgm–3, Mo-Kα radiation
(graphite monochromated, λ = 0.71073 Å), T = 200 K, θrange 1.88
0.71073 Å), T = 200 K, θrange 1.70 to 27.57°. Reflections measured
47990, independent 6340, Rint = 0.0686, semiempirical absorption
correction. Final R indices [IϾ2σ(I)]: R1 = 0.0321, wR2 = 0.0734.
Heck Reaction: NaOAc (360 mg, 4.4 mmol), styrol (0.64 mL,
5.6 mmol) and iodobenzene (0.445 mL, 4 mmol) were dissolved in
dmf (5 mL). Subsequently, Pd complex 1 (8.5ϫ10–3 mmol) was
added. The reaction mixture was stirred for 5 h at ca. 135 °C. Sub-
sequently, the reaction was stopped by addition of H2O (ca.
10 mL). The product was then extracted by addition (2 times) of
CH2Cl2 (ca. 15 mL). The CH2Cl2 solution was shaken five times
with H2O, dried with MgSO4 and filtered. After removal of the
solvent, trans-stilbene was obtained with more than 95% yield.
to 27.50°. Reflections measured 11425, independent 5740, Rint
=
0.0603, semiempirical absorption correction. Final
R indices
[IϾ2σ(I)]: R1 = 0.0391, wR2 = 0.0860.
[(PS3)PtCl2] (3): As for the preparation of 2, [PtCl(C2H4)(µ-Cl)]2
(50 mg, 0.085 mmol) was dissolved in CH2Cl2 (10 mL) and a solu-
tion of PS3 (86 mg, 0.243 mmol, 1.4 equiv.) in CH2Cl2 (10 mL) was
added dropwise over a period of 30 min. In contrast to the prepara-
tion of 2, the reaction mixture was stirred for a period of 20 h
under reflux. After removal of the solvent, the orange residue was
redissolved in toluene and filtered through a silica frit. Complex 3
remained on the frit and was washed several times with toluene. It
was then redissolved in CH2Cl2 and removed from the silica. An
orange powder was obtained after solvent removal. Orange crystals
(25 mg, 24%) were grown at room temperature from a CH2Cl2
solution layered with PE 40/60. C20H30Cl2N6Pt (620.49): calcd. C
Hydrosilylation: Et3SiH (0.48 mL, 3 mmol) and Me3SiCHCH2
(0.87 mL, 6 mmol) were dissolved in n-hexane (30 mL). Sub-
sequently, the potential catalyst (complex 2 or 3, 6ϫ10–3 mmol)
was added. The reaction (at 30 °C) was followed by GC/MS mea-
surements. For these measurements, 0.1 mL of the reaction mixture
was filtered through a silica frit. The product [Me3SiC(H)-
CH2(SiEt3)] was redissolved and removed from the silica with n-
hexane (1 mL), before being injected into the GC/MS machine.
1
38.71, H 4.87, N 13.54; found C 38.65, H 4.89, N 12.89. H NMR
Supporting Information (see footnote on the first page of this arti-
cle): NMR spectroscopic data of [btmgnH]+[PtCl3(C2H4)]–, IR
spectra recorded for complexes 1 and 3, UV/Vis spectra recorded
for complexes 1 and 3, and isodensity surfaces of the HOMOs and
LUMOs of 2 and 3
1
(399.89 MHz, CD2Cl2, 296 K): δ = 7.44 (d, JH-H = 8.1 Hz, 2 H),
1
1
7.25 (t, JH-H = 7.8 Hz, 2 H), 6.54 (s, JH-H = 7.5 Hz, 2 H), 2.83
(s, 24 H, CH3) ppm. 13C NMR (100.56 MHz, CD2Cl2, 296 K): δ =
165.8 (CN3), 142.5, 125.8, 122.0, 112.8 (CArom.), 40.814 (CH3) ppm.
195Pt NMR (85.96 MHz, CD2Cl2, 296 K): δ = –1807 (br.) ppm. MS
(EI): m/z (%) = 620 (100) [M]+, 548 (70) [(tmgn)PtCl]+, 584 (32)
[(tmgn)PtCl]+. UV/Vis: λ = 358 (br.) nm. Crystal data for 3:
C20H30Cl2N6Pt·CH2Cl2, Mr = 705.420, 0.40ϫ0.30ϫ0.30 mm, mo-
noclinic, space group P21/c, a = 10.283(2), b = 16.653(3), c =
Acknowledgments
15.044(3) Å, β = 96.46(3)°, V = 2559.80 Å3, Z = 4, dcalcd.
=
We gratefully acknowledge the Deutsche Forschungsgemeinschaft
for their continuous financial support.
1.830 Mgm–3, Mo-Kα radiation (graphite monochromated, λ =
0.71073 Å), T = 200 K, θrange 1.83 to 27.73°. Reflections measured
11615, independent 5912, Rint = 0.0643, semiempirical absorption
correction. Final R indices [IϾ2σ(I)]: R1 = 0.031, wR2 = 0.0847.
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dissolved in CH2Cl2 (5 mL) was added dropwise to a solution of
btmgbp (110.3 mg, 0.34 mmol) in CH2Cl2 (1 mL). The reaction
mixture was stirred for 1 h at room temperature. After removal of
the solvent in vacuo, a yellow powder was obtained, which was
washed three times with PE 40/60 (10 mL). Yield: 108.4 mg (47%).
Needle-shaped crystals were grown by slow diffusion of PE 40/60
into a toluene solution of 5. C24H36Cl2N6Pt (674.58): calcd. C
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1
42.73, H 5.38, N 12.46; found C 42.20, H 5.29, N 11.90. H NMR
3
4
(399.89 MHz, CD2Cl2, 296 K): δ = 8.38 (dd, J = 8.0, J = 1.1 Hz,
3
4
1 H, H11), 7.61 (dd, J = 7.6, J = 1.46 Hz, 1 H, H5), 7.3–7.2 (m,
1 H, H10), 7.20–7.13 (m, 1 H, H8), 7.10–7.02 (m, 1 H, H3), 6.99
(dt, J = 7.60, 7.56, J = 1.3 Hz, 1 H, H9), 6.80 (dt, J = 7.4, J =
1.2 Hz, 1 H, H4), 6.47 (dd, J = 8.0, J = 1.0 Hz, 1 H, H2), 4.60–
4.57 (m, 2JPt-H = 53.0 Hz, 2 H, HEthylene), 4.39–4.36 (m, 2JPt-H
= 51.71 Hz, 2 H, HEthylene), 3.60 (s, 3 H, CH3), 2.67 (s, 12 H), 2.59
(s, 3 H, CH3), 2.41 (s, 3 H, CH3), 2.21 (s, 3 H, CH3) ppm. 13C
NMR (100.56 MHz, CD2Cl2, 296 K): δ = 165.7 (C13), 159.0 (C18),
3
4
3
4
3
4
149.7 (C1), 148.1 (C12), 134.8 (C7), 132.3 (C8), 131.0 (C5), 129.9 [10] C. Würtele, E. Gaoutchenova, K. Harms, M. C. Holthausen,
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(CAryl), 119.7 (C4), 71.6 (2 C, C2H4), 41.5 (CH3), 41.5 (CH3), 40.1
(4 C, CH3), 39.9 (CH3), 39.4 (CH3) ppm. 195Pt NMR (85.96 MHz,
CD2Cl2, 296 K): δ = –2831 ppm. MS (ESI+): m/z (%) = 674.2 (100)
[MH]+, 673.2 (75) [M]+. UV/Vis (CH2Cl2): λ = 281 nm. Crystal
data for 5: C24H36Cl2N6Pt, Mr = 674.58, 0.35ϫ0.25ϫ0.20 mm,
monoclinic, space group P21/c, a = 9.2180(18), b = 19.928(4), c =
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root-mean-square deviations of fitted atoms are 9.98 pm for 1
and 10.74 pm for 3.
15.569 Å, β = 105.10(3)°, V = 2761.2(9) Å3, Z = 4, dcalcd.
1.623 Mgm–3, Mo-Kα radiation (graphite monochromated, λ =
=
[12] DNMR Lineshape Analysis module as part of the Topspin
software package, TOPSPIN 2.1, 2008, Bruker Biospin.
4446
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 4440–4447

Metal Complexes of 1,8-bis(N,N,NЈ,NЈ-tetramethylguanidino)naphthalene
[13]
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[18] Quantum chemical calculations within the framework of den-
sity functional theory were performed with the program pack-
age TURBOMOLE.[24] For all calculations, the B3LYP func-
tional was used,[25] which is based on a three-parameter func-
tional by Becke[26] and incorporates the correlation functional
by Lee, Yang, and Parr.[27] The structures of the different sys-
tems are optimized and vibrational frequencies are calculated
analytically.[28] The determination of the electronic energies
used the def2-TZVP basis set.[29] Zero point vibrational ener-
gies and thermodynamic contributions were obtained with the
smaller def2-SV(P) basis set[29] only.
[19] See, for example: E. Peris, J. A. Loch, J. Mata, R. H. Crabtree,
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Received: July 8, 2008
Published Online: August 26, 2008
Eur. J. Inorg. Chem. 2008, 4440–4447
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4447