Synthesis of 6,6′-bis(dimethylamino)- and 6,6′-dibromo- substituted 2,2′-diphosphanylbiphenyls and their palladium complexes

Article abstract of DOI:10.1002/ejic.201300473

New 6,6′-dibromo- and 6,6′-bis(dimethylamino)-substituted 2,2′-diphosphanylbiphenyl ligands 11-14 were prepared starting from 2,2′-dibromo-4,4′-dimethyl-6,6′-dinitro-1,1′-biphenyl (4). Depending on the phosphane groups [diphenylphosphanyl (11, 13) or diis

Full text of DOI:10.1002/ejic.201300473

FULL PAPER
DOI:10.1002/ejic.201300473
Synthesis of 6,6Ј-Bis(dimethylamino)- and 6,6Ј-Dibromo-
Substituted 2,2Ј-Diphosphanylbiphenyls and Their
Palladium Complexes
Holm Petzold,*[a] Albara I. S. Alrawashdeh,[a,b] Silvio Heider,[a]
Linda Haufe,[a] and Tobias Rüffer[a]
Keywords: Phosphane ligands / Biphenyl / Palladium / Suzuki–Miyaura coupling / VT NMR spectroscopy / Cross-coupling
New 6,6Ј-dibromo- and 6,6Ј-bis(dimethylamino)-substituted
2,2Ј-diphosphanylbiphenyl ligands 11–14 were prepared
starting from 2,2Ј-dibromo-4,4Ј-dimethyl-6,6Ј-dinitro-1,1Ј-bi-
phenyl (4). Depending on the phosphane groups [diphenyl-
phosphanyl (11, 13) or diisopropylphosphanyl (12, 14)] the
palladium dichloride complexes show different coordination
symmetry. Whereas the smaller diphenylphosphanyl groups
lead to C2-symmetric complexes, the respective bis(diiso-
propyl)phosphanes 12 and 14 form C1-symmetric complexes
that show fluxional behavior due to the restricted rotation of
the isopropyl groups as well as the exchange of atom posi-
tions within the C1-symmetric conformer. All complexes have
been tested as precatalysts in the Suzuki–Miyaura cross cou-
pling reaction of 2-bromotoluene and phenylboronic acid.
The activity of the catalytic system increases with the size of
the diphosphanes and the donating ability of the ligand. In
contrast to C2-symmetric palladium complex 15, platinum
complex 19 was found to be C1-symmetric in the solid state
despite the fact that both complexes have the small bis-
(diphenylphosphanyl)-substituted diphosphane ligand 11 in
common. NiBr2 adduct 20 with a similar diphosphane 13 ex-
ists as a mixture of distorted square-planar and tetrahedral
coordination sphere geometries in equilibrium with each
other.
Introduction
Diphosphanes with general structure A (Scheme 1) em-
ploying a 1,1Ј-biphenyl-2,2Ј-diyl bridge have attracted much
interest as supporting ligands in numerous transition-metal-
catalyzed transformations,[1–3] including Suzuki–Miyaura
cross coupling reactions,[4] amination reactions,[5] Mizo-
roki–Heck reactions,[6,7] hydroaminations,[8] hydrogena-
tions,[9] additions,[10–14] N-heterocyclizations[15] and
others.[16–18]
Not only the employed phosphane substituents but also
the size and electronic properties of the substituents at the
6- and 6Ј-position affect the catalytic activity of the derived
transition metal complexes.[3,19,20] In conjunction with our
recent efforts to synthesize 2,2Ј,6,6Ј-tetraphosphanylbi-
phenyls[21] we gained access to valuable 2,2Ј,6,6Ј-tetrasub-
stituted biphenyls that allow the syntheses of new members
of the above-mentioned class of diphosphanes. In this ac-
count we wish to present the syntheses of 6,6Ј-dibromo-
and 6,6Ј-bis(dimethylamino)-substituted 2,2Ј-diphosphan-
ylbiphenyls and their palladium complexes. These diphos-
Scheme 1. 1,1Ј-Biphenyl-2,2Ј-diyl-bridged diphosphanes discussed
below and the numbering for relevant positions.
phanes are of interest, as the large bromo substituents in
the ortho positions lead to high activation barriers for the
rotation around the central C–C bond.[22] Additionally, the
dimethylamino groups can increase the electron density of
the biphenyl system,[23] act as additional hemilabile do-
nors[24] or form proton sponge systems.[25–27]
Results and Discussion
[a] TU Chemnitz, Institut für Chemie, Anorganische Chemie,
Straße der Nationen 62, 09111 Chemnitz, Germany
E-mail: holm.petzold@chemie.tu-chemnitz.de
Ligands based on 2-phosphanyl- and 2,2Ј-diphosphanyl-
biphenyls are accessible by various methods employing elec-
trophilic,[28] nucleophilic,[29] and radical chemistry[30] as
well as transition-metal-catalyzed[31,32] reactions. A particu-
larly effective method has been the treatment of a 2,2Ј-di-
Homepage: http://www.tu-chemnitz.de/chemie/anorg/hpetzold/
[b] Tafila Technical University, Department of Chemistry,
Tafila 66110, Jordan
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300473.
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lithiated biphenyl with a chlorophosphane.[28,33,34] Dilithi- Therefore, to find optimal conditions for complete forma-
ated biphenyl species are easily prepared by halogen/lithium tion of 10 (but at the same time avoiding degradation of
exchange from the 2,2Ј-diiodo-/2,2Ј-dibromobiphenyls. We the solvent and of dilithiated species 10) this reaction was
prepared diiodobiphenyl 6 and dibromobiphenyl 7 by the monitored by sampling small quantities from a reaction
route depicted in Scheme 2.[35,36] The known diamine deriv- mixture of 7 and 3 equiv. of nBuLi in diethyl ether solution
1
ative 5 can be prepared from inexpensive and commercially stirred at 0 °C. Reaction samples were analyzed by H and
available 4-methyl-2-nitroaniline (1). The methyl group in 13C{1H}-DEPT90 NMR spectra following a small-scale
the 4-position blocks the C-4 atom from electrophilic attack water quench. Samples taken after 5 and 15 min reaction
by bromine in the first step to derivative 2; consequently, 2 times revealed incomplete reaction. All NMR signals for 7
is the only isolable regioisomer.[37] Moreover, the 4-methyl as well as quenched 9 and 10 were assigned by 2D NMR
group improves the solubility of all compounds and simpli- methods. Comparisons between different spectra, especially
fies workup procedures. The key step in the synthesis is an 13C{1H}-DEPT90 data sets, allowed rough quantitation of
Ullmann[35,38] homo-coupling of iodo compound 3 to form compound ratios in the reaction mixtures. Another sample
the central C–C bond in 4. This reaction is highly selective taken after 45 min revealed almost complete reaction, and
and proceeds smoothly under relatively mild conditions in only small amounts of quenched 9 were found after 2 h. At
good yields due to the activating nitro group in the ortho this point the remaining reaction mixture was quenched
position.[35] Side products (e.g. 1-bromo-3-methyl-5-nitro- using D2O. The absence of vicinal coupling in 10, which
benzene) are effectively removed by washing crude biphenyl was quenched with D2O, points to the low reactivity of 10
4 with ethanol. Following reduction of 4 with Zn/HCl[36] towards the organic solvent in the sense of proton abstrac-
yields 5 neatly. Altogether, 5 can be prepared by this route tion (Figure S1).
on a 20 g scale in a cost-effective manner that does not re-
quire column chromatography.
Scheme 3. Syntheses of dilithiated reagents 8 and 10.
Treatment of lithiated species 8 or 10 with a slight excess
of chlorodiphenyl- or chloro(diisopropyl)phosphane led to
the formation of diphosphanes 11–14 (Scheme 4). Attempts
to make 8 or 10 react with di-tert-butyl(chloro)phosphane
failed; even under reflux conditions only quenched 10 [2,2Ј-
bis(dimethylamino)-4,4Ј-dimethylbiphenyl] was identified
following workup. It is worth noting that, for the synthesis
Scheme 2. Synthetic route to biphenyl species 6 and 7 used for sub-
of the PPh2-substituted diphosphane 11, a “one shot” or
sequent modifications.
inverse addition is recommended to avoid formation of a
Starting from diamine 5, diiodo derivative 6[36] as well monolithiated monophosphane species that likely decom-
as bis(dimethylamino) derivative 7[26,27] were obtained by poses by P–C bond cleavage to a phosphafluorene deriva-
Sandmeyer (6) or N-methylation (7) reactions, respectively tive.[32,39]
(Scheme 2). The iodide/lithium exchange with 6 to form di-
It appears that dibromo-substituted diphosphanes 13
lithiated species proceeds quickly in diethyl ether solution and 14 can be handled in air without significant oxidation.
at low temperatures (–80 °C) with n- or tBuLi (Scheme 3). In contrast, both dimethylamino-substituted phosphanes 11
Even when using excess n- or tBuLi, only dilithiated species and 12 are significantly more sensitive to oxidation.[40] The
8 was generated. Due to the electron-rich aromatic system dibromo-substituted diphosphane 14 crystallized as well-
in 7 the bromine/lithium exchange is considerably slower. shaped crystals and was therefore further investigated by X-
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Scheme 4. Syntheses of diphosphanes 11–14 and complexes 15–20.
ray structure analysis (Tables S2 and S3). In the asymmetric hindered rotation of one or more isopropyl groups; PA1 ex-
unit one molecule of 14 is found with C1 symmetry. How- changes with PA2 as well as PB1 exchanges with PB2; the
ever, the deviation from the expected C2 symmetry is small index A and B defines the position of the phosphorus atom
and can be fully explained by packing effects. Figure S14 in the molecule, and the number defines the conformer
(left side) depicts the molecular structure of 14. The two (Figure 1).
aromatic rings of the biphenyl core are twisted by about
80 °, the electron lone pairs of the phosphane substituents
are directed towards the indirectly bound aromatic ring of
the biphenyl moiety, and the intramolecular distance be-
tween the two phosphorus atoms is 3.7280(10) Å.
All phosphanes 11–14 were treated with [Pd(cod)Cl2]
(cod = 1,5-cyclooctadiene) to generate corresponding palla-
dium complexes 15–18. Phosphane 11 was additionally
treated with [Pt(cod)Cl2] to yield complex 19, and phos-
phane 13 was treated with NiBr2 to yield nickel complex
20. The 31P{1H} NMR spectra of the PPh2 complexes 15,
17 and 19 show a single sharp signal. In contrast, spectra
of the P(iPr2)-substituted complexes 16 and 18 revealed one
very broad singlet. Similar broadening was also found in
1
the H NMR spectra, but to a smaller extent. Obviously,
Figure 1. 31P{1H} VT-NMR spectra (in CD2Cl2 from 20 °C to
–90 °C) of complex 18. Signals PA and PB undergo mutual ex-
change only at higher temperatures (above 0 °C). Splitting of the
signals PA and PB is due to the presence of two different conformers
that have some minor differences regarding the coordination geom-
etry and that slowly interconvert.
complexes 16 and 18 show fluxional behavior. Indeed, when
16 was dissolved in [D7]dmf (dmf = N,N-dimethylform-
amide) and 31P{1H} NMR spectra were recorded at 100 °C
(Figure S2), a single sharp singlet was formed revealing the
equivalence of the two phosphorus atoms in averaged spec-
tra at high temperature that corroborate the expected struc-
ture. For further investigation of the dynamics in this sys-
The variable-temperature 31P{1H} NMR spectroscopic
tem, VT-NMR experiments were performed. Lowering the data obtained for 18 were used in a line-shape analysis (Fig-
temperature of a solution of 18 in CD2Cl2 led to the ap- ure S6) by exploiting the calculated spectra, and assuming
pearance of two broad singlets with equal intensity but dif- the above discussed exchange scheme the agreement with
ferent broadening, clearly visible at –35 °C. These two sing- the experimental spectra is reasonably good. The calculated
lets each split into two broad singlets with different inten- rate constants (Table S1) were further used in an Arrhenius
sities (45:55 for 18 at –90 °C in CD2Cl2), the ratio between plot (Figure S7). Interestingly, the activation energy Ea for
the intensities of these two pairs of signals is the same (Fig- mutual exchange [Ea
ure 1). This behavior is consistent with a lowering of the 149(+121/–67) GHz] is almost identical to that obtained for
symmetry in complex 18 from C2 symmetry to C1 symmetry the interconversion between the two conformers [Ea
= 30.5(1.1) kJ/mol and A =
=
that would lead to the appearance of two singlets with equal 30.0(2.5) kJ/mol and A = 0.8(+1.8/–0.55) GHz]. The differ-
intensity; PA mutually exchanges slowly with PB, in the ences in reaction rate seem to solely result from the fre-
sense that they exchange the chemical environment but quency factor, which differs by two orders of magnitude.
keeping all bonds intact. Such behavior was also observed
Complex 16 also showed fluxional behavior, in this case
in similar systems.[4] Additional splitting can be explained the 31P{1H} NMR spectrum at –90 °C (CD2Cl2) shows five
by a slow fluctuation between two different C1-symmetric broad singlets in a ratio of 0.23:0.44:0.44:1.23:1 (Figure S3).
conformers with different stability, most likely caused by Similar to the related complex 18, complex 16 was found to
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exist in different conformers at low temperatures (Fig- were investigated by single-crystal X-ray structure analysis.
ures S2 and S3). To gain more insight into the signal assign- All investigated complexes crystallize as a racemic mixture
ment, 31P EXSY spectra were recorded (Figure S4). These of both enantiomers. Only complex 17 crystallizes as a C2-
spectra allowed the grouping of the signals into two groups symmetric molecule with a crystallographic C2 axis perpen-
(PA and PB); exchange within these two groups was ob- dicular to the central C–C bond of the biphenyl backbone
served at –90 °C (max. 0.5 s mixing time), and the inten- (Figure S13). Nevertheless, all palladium complexes with
sities summed together equally. Assuming that the strongest PPh2 substituents show molecular structures close to the
signal at δ = 47.66 ppm is coincidently an overlay of two expected C2 symmetry; only small deviations due to pack-
signals, each of the two groups include three signals with a ing effects are apparent. On the other hand complexes with
ratio of 0.23:0.44:1. In summary, we can conclude that, in P(iPr)2 substituents were considerably distorted from the C2
the case of complex 18, the most stable conformer is also symmetry (Figures 2 and S14) which reflects the observa-
C1-symmetric. This isomer undergoes a dynamic exchange tion in the low-temperature NMR spectra. Substituents in
with two other C1-symmetric conformers (Figure S4). The the 6- and 6Ј-positions of the biphenyl backbone exert only
positions of PA and PB in 18 do not exchange at low tem- minor effects on the coordination environment of the palla-
peratures, and the mutual exchange between PA and PB is dium complexes. Not surprisingly, structures found in the
significantly less likely. Due to the complicated exchange solid state of complexes 15/17 and 16/18, respectively, are
between six positions and four different time constants, de- nearly superimposable. The molecular structure of platinum
termination of the dynamic parameters was not possible. complex 19 is remarkably different from that of palladium
All palladium complexes bearing PPh2 groups failed to ex- analogue 15 (Figures S10 and 2).
hibit any broadening of NMR signals at low temperatures.
In contrast to 15, Pt complex 19 is highly distorted from
The 31P{1H} NMR spectra of complex 19 showed the ex- C2 symmetry, analogous to the P(iPr)2-substituted palla-
pected singlet with 195Pt satellites, and again no broadening dium complexes 18/16 (Figure S12). Complexes 16, 18 and
at low temperatures was observed. However, one of the two 19 all have a more perfect planar coordination environment
phenyl groups seems to be rotationally hindered as indi- in common. Conversely, in the PPh2-substituted Pd com-
cated by splitting of the 1H NMR signal below –40 °C (Fig- plex 17 the two chlorido ligands are skewed along the C2
ure S5). Attempts to record 31P{1H} NMR spectra of the axis out of the plane. This can be explained by close con-
nickel complex 20 failed, this might be due to the low solu- tacts of the phenyl substituents (PPh2) with the Cl atoms
bility as well as the presence of an equilibrium between the bonded to the metal center (Figure S10). The larger ligand
respective square-planar (S = 0) and tetrahedral (S = 1) field splitting in the Pt complex 19 and the higher rigidity
isomers.[41] This is further supported by some broadening of the coordination sphere in the case of platinum does not
and unusually large shifts of the proton resonances, which allow such a distortion. As a result the ligand is distorted
1
is a typical behavior of resonances in the H NMR spectra to a C1 symmetry allowing the Pt atom to have an almost
for such compounds (Figure S8); signals broaden and shift perfect square-planar coordination sphere (Figure S10). Re-
to unusually high or low field with increasing tempera- placement of the phenyl groups by isopropyl groups in-
ture.[42–45]
creases the strain between the chlorido ligands and the
The platinum as well as the palladium complexes crys- phosphane moieties. Consequently, Pd complexes 16 and 18
tallize well from CH2Cl2/diethyl ether solutions mostly as appear to benefit from similar stabilizing forces, which in-
CH2Cl2 solvates. Consequently, all complexes, except 20, voke a distorted backbone. A close contact between the iso-
Figure 2. ORTEP[46] plot of the C2-symmetric complex 15 (left, viewed along the crystallographic C2 axis) and the C1-symmetric complex
16 (right).
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propyl group and one chlorido ligand is a common feature crowded and electron-rich phosphane ligands, as in 12, af-
of complexes 16 and 18 and results in remarkable bending ford complexes with higher activity in Suzuki–Miyaura
of one of the two Pd–Cl bonds out of the planar coordina- cross couplings. The reduced activity of bromo-substituted
tion sphere (by about 0.5 Å). Although no crystals suitable complexes 17 and 18 might also be attributed to deactiva-
for X-ray analysis were obtained for the Ni complex 20, a tion by an oxidative addition to the C–Br bond. For exam-
larger distortion of the square-planar coordination sphere ple, Leroux reported a phosphanylation of biphenyls that
for the nickel atom that retains C2 symmetry would lead to involved very similar intermediates but at temperatures sub-
a tetrahedral coordination sphere. This is, at least, partly stantially higher than 100 °C.[32] However, thus far we have
the case for 20 as deduced from NMR data (vide supra, not found C–Br bond activation in the Pd2+ complexes.
Figure S8). Due to metal–phosphane coordination, the Further investigations will be necessary to evaluate this
N(1)···N(2) distances in 15, 16 and 19 (3.23 Å, 3.02 Å, point and to test the catalytic activities in detail.
3.10 Å) are close to or slightly smaller than the sum of the
van der Waals radii (1.55 Å)[22] indicating a small interac-
Conclusions
tion of the lone pairs at the nitrogen atoms. Protonation
of complex 16 with 1 equiv. of weakly coordinating acid
[H(OEt2)][B(C6F5)4][47] leads to broadening of the proton
resonances and the appearance of a new signal at δ =
12 ppm. This resonance can be assigned to a protonated
dimethylamino group involved in hydrogen bonding. In
proton sponge systems downfield shifts up to 18 ppm are
often found.[26] Similarly, the Br···Br distance in 17 and 18
(3.62 Å both) are equal to the sum of the van der Waals
radii (1.85 Å);[22] the Br···Br distance is only 0.2 Å longer
than in the highly strained 4,5-dibromophenanthrene.[48]
As mentioned in the introduction, crowded phosphanes
with a biphenyl backbone have found widespread use in
catalysis. As a preliminary experiment all four Pd com-
plexes 15–18 were tested as (pre)catalysts in the Suzuki–
Miyaura cross coupling of 2-bromotoluene as a non-acti-
vated substrate with phenylboronic acid. Reactions were
monitored by successive investigation of small samples
New 6,6Ј-dibromo- and 6,6Ј-bis(dimethylamino)-substi-
tuted 2,2Ј-diphosphanylbiphenyls were prepared by a multi-
step synthesis. Depending on the phosphanyl groups used
the resulting nickel, palladium and platinum complexes
show different symmetry and coordination spheres. Free ro-
tation of the isopropyl groups is remarkably hindered with
C2 symmetry being found in the solid state for complexes
employing diphenylphosphanyl-substituted ligands. Con-
versely, complexes with isopropyl-substituted phosphanes
were found to be C1-symmetric in the solid state as well as
in solution. These differences in steric hindrance and com-
plex symmetries seem to minimally influence catalytic ac-
tivity. Further work to evaluate the catalytic scope of these
complexes is underway.
Experimental Section
1
using H NMR spectroscopy with acetyl ferrocene as an
internal standard.[49–52] Figure 3 depicts the results of time
course experiments. After 60 min in every case, quantitative
conversions had been achieved. Complex 16 (R = NMe2,
RЈ = iPr) was the most active catalyst in the series and
enabled Ͼ 90% conversion after only 20 min. The activities
observed for these complexes follow the expected trend that
General: All reactions handling sensitive chemicals were carried out
under argon using standard Schlenk and cannula techniques. NMR
spectra were recorded with a Bruker Avance III 500 spectrometer;
chemical shifts for 1H and 13C NMR are referenced internally to
the residual protons and to the 13C NMR signal of the deuterated
solvent.[53] Elemental analyses were performed by using a Thermo
FlashAE 1112 analyzer. Infrared spectra were recorded with a Nic-
olet IR200 FT-IR spectrometer. Mass spectra were recorded with a
Bruker micrOTOF-QIIa mass spectrometer operating in ESI mode.
CCDC-932246 (14), -932247 (15), -932248 (16), -932249 (17),
-932250 (18) and -932251 (19) contain the supplementary crystallo-
graphic 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.
Materials: Diethyl ether and thf were purified by distillation from
sodium/benzophenone ketyl. Ethanol was purified by distillation
from magnesium and acetonitrile by distillation from calcium hy-
dride. Diphosphane 14 (6,6Ј-dibromo-4,4Ј-dimethyl-1,1Ј-biphenyl-
2,2Ј-diyl)bis(diisopropylphosphane) was synthesized according to
published procedures.[21] All other chemicals were purchased by
commercial suppliers and were used without further purification.
Synthesis of 2-Bromo-4-methyl-6-nitroaniline (2) (Modification from
Refs.[36,37]): 4-Methyl-2-nitroaniline (1, 61.5 g 0.40 mol) was dis-
solved in acetic acid (470 mL, 98%) in a 2 L flask by gentle heating.
The flask was placed in an ice bath, and bromine (71.5 g 0.45 mol)
dissolved in acetic acid (100 mL) was added over 30 min with a
dropping funnel; during the addition the temperature was kept be-
low 10 °C. After addition of about 1/3 of the bromine, an orange
Figure 3. Time course of the Suzuki–Miyaura cross coupling of 2-
bromotoluene with phenylboronic acid [reaction conditions:
1 mmol 2-bromotoluene, 1.2 mmol phenylboronic acid, 3 mmol
base, 0.5 mol-% palladium complex, 10 mL of dioxane/water (2:1),
85 °C].
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solid started to precipitate (protonated 1). After completed ad-
dition, the reaction mixture was stirred at 0 °C for additional
20 min and at ambient temperature for another 2 h. Completeness
of the reaction was checked by sampling a small quantity and re-
ppm. IR (KBr): ν = 3075 (s, νC-H), 1528 (s, νN-O), 1352 (s, νC-N),
1040 (s). M.p. 202–207 °C.
˜
Synthesis of 2,2Ј-Diamino-6,6Ј-dibromo-4,4Ј-dimethyl-1,1Ј-biphenyl
(5) (Modification from Ref.[36]): The dinitrobiphenyl 4 (30.9 g,
0.072 mol) was suspended in methanol (150 mL), and zinc dust
(33 g, 0.505 mol) was added. The reaction mixture was refluxed
for a few minutes, and concentrated hydrochloric acid was added
dropwise until a clear solution with small residues of zinc dust had
formed. The completeness of the reaction was checked by means
1
cording the H NMR spectrum. To the reaction mixture NaHCO3
(20 g, 0.24 mol) was carefully added (gas develops with delay), then
water (500 mL) and another portion of NaHCO3 (20 g, 0.24 mol)
were added. The crude product precipitated from the solution and
was separated by suction filtration and carefully washed with water
to remove acetic acid completely. The crude product was dissolved
in CH2Cl2, the organic phase was washed with water (200 mL),
dried with MgSO4, and the solvent was removed by rotary evapora-
tion to yield pure 2 as orange solid (88.2 g, 0.38 mol, 94% based
on 1). 1H NMR (500 MHz, CDCl3): δ = 7.94 (dd, 4J(H,H) =
2.0 Hz, 4J(H,H) = 0.9 Hz, Ar-H, 1 H), 7.55 (dd, 4J(H,H) = 2.0 Hz,
4J(H,H) = 0.9 Hz, Ar-H, 1 H), 6.45 (br s, NH2, 2 H), 2.27 (s, CH3,
3H) ppm. 13C{1H} NMR (126 MHz, CDCl3): δ = 140.32, 140.08,
1
of H NMR spectroscopy. To the cooled solution ammonia (25%
in water) was added until the solution became basic and was sub-
sequently extracted with dichloromethane (2ϫ 100 mL) to yield a
clear organic phase. The combined extracts were washed with di-
luted ammonia (10% in water) and dried with MgSO4. The solvent
was removed by rotary evaporation, and the crude product was
dissolved in diethyl ether (100 mL), the solution was then filtered
through aluminum oxide and once again concentrated to dryness
to yield diamine 5 as white solid (23.7 g, 0.064 mol, 89%). 1H
NMR (500 MHz, CDCl3): δ = 6.95 (d, 4J(H,H) = 2.0 Hz, Ar-H,
2 H), 6.56 (d, 4J(H,H) = 2.0 Hz, Ar-H, 2 H), 3.54 (br. s, NH2, 4 H),
2.28 (s, CH3, 6H) ppm. 13C{1H} NMR (126 MHz, CDCl3): δ =
145.99, 140.89, 125.56, 123.40, 120.73, 115.24, 32.2 (CH3) ppm. IR
132.7, 126.56, 125.58, 112.02, 20.01 (CH ) ppm. IR (KBr): ν =
˜
3
3484 (s, νN-H), 3368 (s), 1576 (s), 1509 (s, νN-O), 1347 (s, νC-N), 1085
(m) cm–1. C14H14Br2N2O2 (231.05): calcd. C 36.93, H 3.05, N
12.12; found C 36.40, H 3.01, N 12.13. M.p. 67–69 °C (ref.[37] 68.6–
68.9 °C).
(KBr): ν = 3361 (s, νN-H), 3010 (s, νC-H), 1612 (s), 1549 (s), 1302 (s,
˜
Synthesis of 1-Bromo-2-iodo-5-methyl-3-nitrobenzene (3) (Modifica-
tion from Ref.[36]): Fairly grinded 2 (88.1 g, 0.38 mol) was suspended
in diluted sulfuric acid (63 mL of concd. acid in 300 mL of water)
at 0 °C. To this mixture NaNO2 (43 g, 0.623 mol) dissolved in H2O
(120 mL) was added slowly with vigorous stirring during 45 min.
The suspension was stirred at ambient temperature for another
30 min. The solution was filtered, and the filtrate was directly
poured into a well-stirred solution of KI (120 g, 0.72 mol) dissolved
in water (100 mL). The filter cake was washed with water, extracted
with dichloromethane, filtered through silica gel and was recrys-
tallized from ethanol to yield 25 g of unreacted aniline derivative
2. The aqueous solution containing the diazonium salt and KI was
stirred at 70 °C for 1 h. The cooled solution was then extracted
with dichloromethane (3ϫ 100 mL). The organic phases were com-
bined and washed with bicarbonate solution, sodium sulfite solu-
tion, and water, then dried with MgSO4. Evaporation of the solvent
yielded 3 (68.2 g, 0.20 mol, 52%) as a yellow to brown crystalline
solid of sufficient purity. 1H NMR (500 MHz, CDCl3): δ = 7.67
(dd, 4J(H,H) = 1.9 Hz, 4J(H,H) = 0.7 Hz, Ar-H, 1 H), 7.35 (dd,
4J(H,H) = 1.9 Hz, 4J(H,H) = 0.7 Hz, Ar-H, 1 H), 2.37 (s, CH3, 3H)
ppm. 13C{1H} NMR (126 MHz, CDCl3): δ = 156.28, 141.32,
νC-N), 1034 (s) cm–1. ESI-TOF MS: calcd. for [C14H14Br2N2+nH]+
370.957; found 370.955. C14H14Br2N2 (370.082): calcd. C 45.44, H
3.81, N 7.57; found C 46.04, H 3.80, N 7.66. M.p. 131–134°C
(ref.[36] 135–136 °C).
Synthesis of 6,6Ј-Dibromo-2,2Ј-diiodo-4,4Ј-dimethyl-1,1Ј-biphenyl
(6) (Modification from Ref.[36]): Diamine 5 (12 g, 0.032 mol) was
suspended in diluted sulfuric acid (18 mL of concd. acid in 100 mL
of water) and cooled to 0 °C. Sodium nitrite (6.9 g, 0.10 mol) dis-
solved in water (60 mL) was added dropwise within 30 min. The
diazonium salt solution was added to a vigorously stirred solution
of KI (20 g) in water (60 mL). After complete addition, the reaction
mixture was stirred at 70 °C for 90 min and chilled to ambient tem-
perature. The reaction mixture was extracted with dichloromethane
(5ϫ 80 mL) and washed with NaHCO3 solution and Na2SO3 solu-
tion. The combined extracts were concentrated to dryness, and the
crude product was purified by column chromatography (SiO2; hex-
ane/dichloromethane 5:1) to yield the crude product as white solid,
which was recrystallized from hexane to yield the pure product 6
1
as colorless crystalline solid (6.37 g, 0.011 mol, 33.2%). H NMR
(500 MHz, CDCl3): δ = 7.75 (dd, 4J(H,H) = 1.5 Hz, 4J(H,H) =
136.20, 133.02, 123.64, 90.66, 20.75 (CH ) ppm. IR (KBr): ν =
0.7 Hz, Ar-H, 2 H), 7.51 (dd, J(H,H) = 1.5 Hz, 4J(H,H) = 0.7 Hz,
˜
4
3
3075 (s, νAr-H), 1530 (s, νN-O) 1347 (s, νC-N), 1259 (s), 1048 (s) cm–1.
Ar-H, 2 H), 2.37 (br. s, CH3, 6 H) ppm. 13C NMR (125 MHz,
CDCl3): δ = 145.4, 141.7, 139.0, 133.5, 100.0, 67.1, 20.6 (CH3)
M.p. 70–73 °C.
ppm. IR (KBr): ν = 2906 (m, νC-H), 1612 (s), 1580 (s), 1521 (s),
˜
Synthesis of 2,2Ј-Dibromo-4,4Ј-dimethyl-6,6Ј-dinitro-1,1Ј-biphenyl
(4) (Modification from Refs.[35,36]): Compound 3 (68 g, 0.2 mol) was
dissolved in dry DMF (80 mL) under argon. To the stirred solution
copper powder (84 g, 1.3 mol) was added at 100 °C in three por-
tions in 30 min intervals. After cooling to ambient temperature,
dichloromethane (160 mL) was added, and the reaction mixture
was filtered, the filter cake was washed several times with ad-
ditional portions of dichloromethane, the combined organic phases
were washed with 2.5 m hydrochloric acid (5ϫ 100 mL). The sol-
vents were removed by rotary evaporation; the crude product was
washed with ethanol (100 mL) under heating and stirring to yield
the desired product 4 in analytical purity as yellow solid (31 g,
1030 (s) cm–1. C14H10Br2I2 (591.846): calcd. C 28.41, H 1.70; found
C 29.00, H 1.69. M.p. 205 °C (ref.[36] 212–213 °C).
Synthesis of 2,2Ј-Dibromo-6,6Ј-bis(dimethylamino)-4,4Ј-dimethyl-
1,1Ј-biphenyl (7) (Modification from Ref.[27]): Diamine 5 (11 g,
0.03 mol) was dissolved in thf (200 mL), sodium hydride (4.4 g,
0.18 mol) and dimethyl sulfate (15.1 mL, 0.18 mol) were added.
The reaction mixture was refluxed for 35 h; after cooling to ambi-
ent temperature, an excess of ammonia (10% in H2O) was added.
The mixture was extracted with dichloromethane (3ϫ 60 mL). The
combined organic extracts were filtered through silica and reduced
to dryness to afford the crude product. Recrystallization from
0.072 mol, 72.5%). 1H NMR (500 MHz, CDCl3): δ = 8.01 (d, methanol yielded the desired product 7 as white semi-crystalline
4J(H,H) = 2.0 Hz, Ar-H, 2 H), 7.80 (d, 4J(H,H) = 2.0 Hz, Ar-H,
2 H), 2.52 (s, CH3, 6H) ppm. 13C{1H} NMR (126 MHz, CDCl3):
solid (8.9 g, 0.021 mol, 70%). 1H NMR (500 MHz, CDCl3): δ =
7.15 (s, Ar-H, 2 H), 6.85 (s, Ar-H, 2 H), 2.49 (s, N-CH3, 12H), 2.34
δ = 149.44, 141.47, 138.62, 131.34, 125.16, 124.83, 21.13 (CH3) (s, Ar-CH3, 6 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 154.0,
Eur. J. Inorg. Chem. 2013, 4858–4866
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139.3, 132.6, 127.2, 126.9, 119.8, 43.8, 21.4 (CH3) ppm. ESI-TOF
of nBuLi (0.665 mL, 1.6 m in n-hexane, 1.06 mmol). The resulting
slightly opaque mixture was stirred at –95 °C for 25 min, and then
a solution of Ph2PCl (232.6 mg, 1.06 mmol) in diethyl ether (5 mL)
was added. The mixture was allowed to attain room temperature
within 2 h. At ca. –65°, the precipitation of a white solid occurred.
After stirring at ambient temperature for 4 h, the mixture was con-
centrated to dryness under reduced pressure (oil pump vacuum) for
1 h, then a new portion of Et2O (5 mL) was added. The mixture
was quenched by addition of 10 mL of degassed H2O, extracted
with dichloromethane (3ϫ 10 mL) under Ar. The combined or-
ganic extracts were dried with MgSO4 and concentrated under re-
duced pressure. The crude material obtained was filtered through
silica gel by using DCM as eluent and then concentrated under
reduced pressure. The resulting colorless oil was recrystallized from
EtOH to yield 204 mg (56%) of the title compound as white crys-
MS: calcd. for [C18H22Br2N2 + H]+ 427.02; found 427.02. IR
(KBr): ν = 3053 (s), 1593 (s), 1544 (s), 1346 (s), 1303 (m), 1210
˜
(m), 1046 (m), 738 (s) cm–1. C18H22Br2N2 (426.19): calcd. C 50.73,
H 5.20, N 6.57; found C 50.72, H 5.27, N 6.41. M.p. 137–140 °C.
Synthesis of 6,6Ј-Bis(diphenylphosphanyl)-N2,N2,N2Ј,N2Ј,4,4Ј-hexa-
methyl-1,1Ј-biphenyl-2,2Ј-diamine (11): To a solution of 7 (400 mg,
0.94 mmol) in diethyl ether (8 mL) nBuLi (1.6 m, 1.76 mL,
2.8 mmol) was added at 0 °C, and the reaction mixture was stirred
at this temperature for 3 h. The solution was cooled to –40 °C,
and chlorodiphenylphosphane (723 mg, 3.3 mmol) in diethyl ether
(4 mL) was added in one portion. The reaction mixture was stirred
for 72 h, and subsequently water (5 mL) was added. The reaction
mixture was extracted with dichloromethane (3ϫ 5 mL), the com-
bined organic extracts were washed with water and dried with
MgSO4. The organic phase was filtered through silica gel and con-
centrated to dryness. The resulting solid was washed with ethanol
to afford 11 as white solid (370 mg, 0.51 mmol, 54%). The product
can be further purified by recrystallization from ethanol/dichloro-
methane (1:2). 1H NMR (500 MHz, C6D6, 25 °C): δ = 7.32–7.37
(m, PPh2, 8 H), 7.28 (d, J = 7 Hz, 2H, Ar-H), 7.07 (m, 6 H), 6.95
(t, PPh2, J(P,H) = 6 Hz, 4 H), 6.80 (br. s, PPh2, 4 H), 2.27 (s, CH3,
6 H), 2.08 (s, N(CH3)2, 12 H) ppm. 31P{1H} NMR (202.5 MHz,
1
tals. H NMR (500 MHz, CDCl3, 25 °C): δ = 7.38 (d, Ar-H, 2 H),
7.08–7.70 (m, Ph, 20 H) 6.97 (s, Ar-H, 2 H), 2.01 (s, biphen-CH3,
6 H) ppm. 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ =
–12.0 ppm. IR (KBr): ν = 3051 (s, νC-H, Aryl-H), 1580 (m), 1478
˜
(m, νCH3, Aryl-CH3), 1434 (s), 1208 (s), 1068 (s, νC-Br, Aryl-Br)
cm–1. ESI-TOF MS: calcd. for [C38H30Br2P2 + H]+ (100%) 709.25;
found 709.011. C38H30Br2P2 (708.40): calcd. C 64.43, H 4.27; found
C 64.60, H 4.59.
Synthesis of Palladium Complexes 15–18 and Platinum Complex 19:
To a solution of the appropriate diphosphane (0.2 mmol) in DCM
(5 mL) a solution of [Pd(COD)Cl2]/[Pt(COD)Cl2] (COD = cy-
cloocta-1,5-diene) (0.2 mmol) in DCM (5 mL) was added. This
solution was stirred for 12 h and then concentrated to dryness to
yield the crude products, which were subsequently crystallized by
vapor diffusion of diethyl ether or pentane to a solution of the
complex in DCM.
CDCl ): δ = –11.60 ppm. IR (KBr): ν = 3051 (m, νC-H), 1589 (s),
˜
3
1545 (m), 1476 (m), 1309 (s), 1429 (s), 1130 (s) cm–1. ESI-TOF
MS: calcd. for [C42H42N2P2 + H]+ (100%) 637.289; found 637.275.
C42H42N2P2·CH2Cl2 (636.74): calcd. C 71.56, H 6.15, N 3.88;
found C 71.32, H 6.49, N 3.65. M.p. 229 °C (dec.).
Synthesis of 6,6Ј-Bis(diisopropylphosphanyl)-N2,N2,N2Ј,N2Ј,4,4Ј-
hexamethyl-1,1Ј-biphenyl-2,2Ј-diamine (12): To a solution of 7
(498 mg, 1.16 mmol) in diethyl ether (15 mL) nBuLi (1.6 m, 2.4 mL,
3.84 mmol) was added at 0 °C and the solution was stirred at this
temperature for 2.5 h. After a few minutes a white precipitate had
formed. To the reaction mixture chlorodiisopropylphosphane
(1.15 g, 7.6 mmol) dissolved in diethyl ether (3 mL) was added at
0 °C. The reaction mixture was stirred at ambient temperature
overnight and concentrated to dryness. Degassed sodium hydrogen
carbonate solution was added, and the reaction mixture was ex-
tracted with dichloromethane (3ϫ 30 mL). The combined organic
extracts were dried with MgSO4, and the solution was subjected to
flash chromatography on SiO2 (dichloromethane). Evaporating the
solvent to dryness afforded a colorless oil that solidified upon stir-
ring with ethanol. The crude product was recrystallized from eth-
anol (10 mL) to yield the pure compound 12 as white, slightly air-
sensitive solid (240 mg, 0.48 mmol, 41%). 1H{31P} NMR
(500 MHz, CDCl3, 25 °C): δ = 7.00 (s, Ar-H, 2 H), 6.71 (s, Ar-H,
2 H), 2.26 (s, biphen-CH3, 6 H), 2.30 (s, N(CH3)2, 12 H), 2.23 (sept,
3J(H,H) = 6.9 Hz, CH(Me)2, 2 H), 1.71 (sept, 3J(H,H) = 7.2 Hz,
(11-κP-κPЈ)PdCl2 (15) (R = NMe2; RЈ = Ph): The crude product
was recrystallized from CH2Cl2/diethylether yielding a yellow pow-
der (85.9%). M.p. 260 °C (dec.). 1H{31P} NMR (500 MHz, CDCl3,
25 °C): δ = 7.92 (d, J(P,H) = 7.5 Hz, 4 H), 7.84 (d, J(P,H) = 7.5 Hz,
4 H), 7.39 (m, 6 H), 7.31 (t, J(P,H) = 7.5 Hz, 2 H), 7.17 (d, J(P,H)
= 7.5 Hz, 4 H), 6.55 (s, 2 H), 6.05 (s, 2 H), 2.40 (s, N(CH3)2, 12 H),
2.02 (s, CH3, 6 H) ppm. 31P{1H} NMR (202.5 MHz, CDCl3,
25 °C): δ = 31.6 ppm. IR (KBr): ν = 3057 (s, νC-H, Aryl-H), 1589
˜
(s), 1543 (s, νCH3, Aryl-CH3), 1433 (s), 1349 (s, νC-N, ArylN), 1591
(s), 1093 (s, νC-N, Alkyl-N) cm–1. ESI-TOF MS: calcd. for
[C42H42ClN2P2Pd2
–
Cl
+
H]+ 777.155; found 777.140.
C42H42N2P2Pd·1.5CH2Cl2 (814.07): calcd. C 55.49, H 4.82, N 2.98;
found C 55.73, H 5.00, N 2.87.
(12-κP-κPЈ)PdCl2 (16) (R = NMe2; RЈ = iPr): The crude product
was recrystallized from CH2Cl2/diethyl ether to yield a yellow pow-
der (75%). 1H NMR (500 MHz, CDCl3, 25 °C): δ = 7.08 (d,
3J(P,H) = 9 Hz, Ar-H, 2 H), 6.86 (s, Ar-H, 2 H), 2.56 (s, N(CH3)2,
12 H), 2.38 (s, biphen-CH3, 6 H), 1.55 (br., CH(Me)2, 12 H), 1.28
(br., CH(Me)2, 6 H), 1.01 (dd, 3J(P,H) = 15 Hz, 3J(H,H) = 7.15 Hz,
CH(CMe2)2, 6 H) ppm. 31P{1H} NMR (202.5 MHz, CDCl3,
3
CH(Me)2, 2 H), 1.10 (d, J(H,H) = 6.9 Hz, CH(CH3)2, 6 H), 0.98
3
3
(d, J(H,H) = 7.2 Hz, CH(CH3)2, 6 H), 0.97 (d, J(H,H) = 6.6 Hz,
CH(CH3)2, 6 H), 0.79 (d, 3J(H,H) = 7.23 Hz, CH(CH3)2, 6 H)
ppm. 13C NMR (125 MHz, CDCl3): δ = 150.8 (dd, J(P,C) = 8.8,
2.0 Hz), 139.2 (d, J(P,C) = 14.3 Hz), 136.1, 135.2 (dd, J(P,C) = 32.0,
5.4 Hz), 125.9 (d, J(P,C) = 2.2 Hz), 119.8, 43.17, 25.0 (d, J(P,C) =
16.9 Hz), 23.6 (d, J(P,C) = 16.3 Hz), 23.2 (d, J(P,C) = 23.5 Hz),
22.0 (d, J(P,C) = 20.8 Hz), 21.8, 19.3 (d, J(P,C) = 13.9 Hz), 18.2
(d, J(P,C) = 9.0 Hz) ppm. 31P{1H} NMR (202.5 MHz, CDCl3): δ
= –1.4 ppm. C30H50P2N2 (500.68): calcd. C 71.97, H 10.70, N 5.60;
found C 71.67, H 10.32, N 5.63.
25 °C): δ = 46.4 (br.) ppm. IR (KBr): ν = 2975, 2959, 2919, 2866,
˜
2792 (s, νC-H), 1589, 1540, 1486, 1456, 1403, 1229, 1061, 665, 628,
501 cm–1. ESI-TOF MS: calcd. for [C30H50ClN2P2Pd]+ 641.2199;
found 641.2175. C30H50Cl2N2P2Pd (678.00): calcd. C 53.14, H 7.43,
N 4.13; found C 52.71, H 7.45, N 4.08.
(13-κP-κPЈ)PdCl2 (17) (R = Br; RЈ = Ph): The crude product was
recrystallized from CH2Cl2/pentane to yield a yellow powder
1
(85.2%). M.p. 268 °C (dec.). H NMR (500 MHz, CDCl3, 25 °C):
Synthesis of 6,6Ј-Dibromo-4,4Ј-dimethyl-1,1Ј-biphenyl-2,2Ј-diylbis-
δ = 8.01 (dd, 3J(P,H) = 12.45 Hz, 3J(H,H) = 7.64 Hz, Ph, 4 H),
(diphenylphosphane) (13): To a solution of 6 (300 mg, 0.506 mmol) 7.81 (m, Ph, 4 H), 7.49–7.41 (m, Ph, 8 H), 7.37 (m, Ph, 4 H), 7.03
in diethyl ether (6 mL) was added at –95 °C within 5 min a solution
(s, Ar-H, 2 H), 6.90 (d, 3J(P,H) = 11.74 Hz, Ar-H, 2 H), 2.05 (s,
Eur. J. Inorg. Chem. 2013, 4858–4866
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biphen-CH3, 6 H) ppm. 31P{1H} NMR (202.5 MHz, CDCl3,
25 °C): δ = 31.6 ppm. IR (KBr): ν = 3013 (m, νC-H, Aryl-H), 1586
˜
[1] H. Shimizu, I. Nagasaki, T. Saito, Tetrahedron 2005, 61, 5405–
5432.
(s, νCH3, Aryl-CH3), 1523 (m), 1479 (m), 1435 (s), 1097 (s, νC-Br
,
Aryl-Br) cm–1. ESI-TOF MS: calcd. for [C26H38Br2Cl2P2Pd – Cl +
H]+ 850.889; found 850.866. C38H30Br2Cl2P2Pd (885.73): calcd. C
51.53, H 3.41; found C 51.05, H 3.42.
[2]
[3]
M. McCarthy, P. J. Guiry, Tetrahedron 2001, 57, 3809–3844.
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K. Mikami, T. Miyamoto, M. Hatano, Chem. Commun. 2004,
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(14-κP-κPЈ)PdCl2 (18) (R = Br; RЈ = iPr): The crude product was
S. Shekhar, P. Ryberg, J. F. Hartwig, J. S. Mathew, D. G. Black-
mond, E. R. Strieter, S. L. Buchwald, J. Am. Chem. Soc. 2006,
128, 3584–91.
recrystallized from CH2Cl2/pentane to yield a yellow powder
1
(77.3%). M.p. 168–171 °C. H NMR (500 MHz, CDCl3, 25 °C): δ
= 7.70 (s, Ar-H, 2 H), 7.51 (d, 3J(P,H) = 9 Hz, Ar-H, 2 H), 3.84
(m, CH(Me)2, 2 H), 2.45 (s, biphen-CH3, 6 H), 2.35 (br. s,
CH(Me)2, 2 H), 1.23 (br., CH(CMe2)2, 6 H), 1.24 (br., CH(Me)2,
12 H), 1.03 (dd, 3J(P,H) = 16 Hz, 3J(H,H) = 6.41 Hz, CH(Me)2,
6 H) ppm. 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ = 45.0
[6]
[7]
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5719.
(br.) ppm. IR (KBr): ν = 3030 (s, νC-H, Aryl-H), 2969 (m), 2876
˜
(m), 1534 (m, νCH3, Aryl-CH3), 1583 (s), 1452 (s), 1375 (s), 1221
(s), 1156 (s), 1041 (s, νC-Br, Aryl-Br) cm–1. ESI-TOF MS: calcd. for
[10]
[11]
[C26H38Br2Cl2P2Pd
– Cl +
H]+ 714.951; found 714.941.
C26H38Br2Cl2P2Pd (749.66): calcd. C 41.66, H 5.12; found C 41.45,
H 5.17.
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
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A. Kina, H. Iwamura, T. Hayashi, J. Am. Chem. Soc. 2006,
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(11-κP-κPЈ)PtCl2 (19) (R = NMe2; RЈ = Ph): The crude product
was recrystallized from CH2Cl2/diethyl ether to yield a yellow pow-
1
der (91%). M.p. 218 °C (dec.). H{31P} NMR (500 MHz, CDCl3,
25 °C): δ = 7.84 (d, J(H,H) = 7.8 Hz, Ph, 4 H), 7.45 (d, J(H,H) =
7.5 Hz, Ph, 4 H), 7.32 (m, Ph, 6 H), 7.23 (t, J(H,H) = 7.5 Hz, 2 H),
7.08 (t, J(H,H) = 7.8 Hz, 4 H), 6.52 (s, Ar-H, 2 H), 5.88 (s, Ar-H,
2 H), 2.31 (s, biphen-N(CH3)2, 12 H), 1.92 (s, biphen-CH3, 6 H)
ppm. 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ = 11.8
(J(Pt,P)= 3600 Hz) ppm. ESI-TOF MS: calcd. for
[C42H42ClN2P2Pd2
–
Cl
+
H]+ 867.216; found 867.201.
C42H42N2P2Pt·0.75CH2Cl2 (902.73): calcd. C 53.13, H 4.54, N 2.90;
found C 53.23, H 4.78, N 2.74.
Synthesis of (13-κP-κPЈ)NiBr2 (20) (R = Br; RЈ = Ph): To a suspen-
sion of NiBr2 (9 mg, 0.041 mmol) in anhydrous thf (8 mL) diphos-
phane 13 (40 mg, 0.057 mmol) was added. The reaction mixture
was refluxed for 12 h, and the resulting light green reaction mixture
was filtered through Celite to remove unreacted NiBr2 and then
concentrated to dryness. The residue was washed with small
amounts of dry DCM and diethyl ether and dried in oil pump
vacuum to afford a light green-grey powder (25 mg, 0.027 mmol,
67%). 1H NMR (500 MHz, CDCl3, 25 °C): δ = 1.13 (s, 6 H, CH3),
A. Aranyos, D. W. Old, A. Kiyomori, J. P. Wolfe, J. P. Sadighi,
S. L. Buchwald, J. Am. Chem. Soc. 1999, 121, 4369–4378.
D. W. Old, J. P. Wolfe, S. L. Buchwald, J. Am. Chem. Soc. 1998,
120, 9722–9723.
3
4.17 (s, 2 H), 4.64 (s, 2 H), 6.52 (t, J(H,H) = 6.7 Hz, 2 H), 7.22 (t,
[25]
[26]
S. T. Howard, J. Am. Chem. Soc. 2000, 122, 8238–8244.
T. Saupe, C. Krieger, H. A. Staab, Angew. Chem. 1986, 98, 460–
462.
3J(H,H) = 6.6 Hz, 2 H), 7.95 (br. s, 4 H), 8.08 (s, 4 H), 8.58 (s, 4 H),
8.99 (d, 3J(H,H) = 6.3 Hz, 4 H) ppm. IR (KBr): ν = 3052, 2912,
˜
1585, 1479, 1435, 1096, 741, 694, 515, 501 cm–1. ESI-TOF MS:
calcd. for [C38H30P2Br3Ni+] 846.8680; found 846.8699.
C38H30P2Br4Ni (926.90): calcd. C 49.24, H 3.26; found C 49.02, H
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Received: April 11, 2013
Published Online: July 19, 2013
Eur. J. Inorg. Chem. 2013, 4858–4866
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim