New functional cyclic aminomethylphosphine ligands for the construction of catalysts for electrochemical hydrogen transformations

Article abstract of DOI:10.1002/chem.201304234

Eight-membered cyclic functional bisphosphines, namely 1,5-di-aryl-3,7- di(2-pyridyl)-1,5-diaza-3,7-diphosphacyclooctanes (aryl=2-pyridyl, m-tolyl, p-tolyl, diphenylmethyl, benzyl, (R)-(+)-(α-methyl)benzyl), with 2-pyridyl substituents on the phosphorus atoms have been synthesized by condensation of 2-pyridylphosphine, formaldehyde, and the corresponding primary amine. The structures of some of these bisphosphines have been investigated by X-ray crystallography. The bisphosphines readily form neutral P,P-chelate complexes [(κ²-P,P-L)MCl₂], cationic bis-P,P-chelate complexes [(κ²-P,P-L)₂M]²⁺, or a five-coordinate complex [(κ²-P,P-L)₂NiBr]Br. The electrochemical behavior of two of the nickel complexes, and their catalytic activities in electrochemical hydrogen evolution and hydrogen oxidation, including the fuel-cell test, have been studied. 1,5-Diaza-3,7-diphosphacyclooctanes with 2-pyridyl substituents on the phosphorus atoms have been synthesized by a Mannich-like condensation and readily form P,P-chelate complexes (see scheme). The catalytic activity of a cationic nickel(II) bis-P,P-chelate complex for electrochemical hydrogen evolution was studied.

Full text of DOI:10.1002/chem.201304234

DOI: 10.1002/chem.201304234
Full Paper
&
Bisphosphines
New Functional Cyclic Aminomethylphosphine Ligands for the
Construction of Catalysts for Electrochemical Hydrogen
Transformations
Elvira I. Musina,*[a] Vera V. Khrizanforova,[a] Igor D. Strelnik,[a] Murad I. Valitov,[a]
Yulia S. Spiridonova,[a] Dmitry B. Krivolapov,[a] Igor A. Litvinov,[a] Marsil K. Kadirov,[a]
Peter Lçnnecke,[b] Evamarie Hey-Hawkins,[b] Yulia H. Budnikova,[a] Andrey A. Karasik,[a] and
Oleg G. Sinyashin[a]
Abstract: Eight-membered cyclic functional bisphosphines,
namely 1,5-di-aryl-3,7-di(2-pyridyl)-1,5-diaza-3,7-diphosphacy-
clooctanes (aryl=2-pyridyl, m-tolyl, p-tolyl, diphenylmethyl,
benzyl, (R)-(+)-(a-methyl)benzyl), with 2-pyridyl substituents
on the phosphorus atoms have been synthesized by con-
densation of 2-pyridylphosphine, formaldehyde, and the cor-
responding primary amine. The structures of some of these
bisphosphines have been investigated by X-ray crystallogra-
phy. The bisphosphines readily form neutral P,P-chelate com-
plexes [(k2-P,P-L)MCl2], cationic bis-P,P-chelate complexes
[(k2-P,P-L)2M]2+
, or a
five-coordinate complex [(k2-P,P-
L)2NiBr]Br. The electrochemical behavior of two of the nickel
complexes, and their catalytic activities in electrochemical
hydrogen evolution and hydrogen oxidation, including the
fuel-cell test, have been studied.
Introduction
Complexes of pyridylphosphines with a noncoordinated ni-
trogen atom from the pyridyl substituent are examples of
functionalized systems in which the pyridyl group exhibits
basic properties and is capable of secondary interactions, such
as hydrogen bonding or proton transfer in the coordination
sphere.[12] The ability of the pendant pyridyl groups to interact
with weak proton donors suggests the possibility for use of
the hydride complexes as catalyst precursors for a number of
transformations in polar media, such as nitrile hydration reac-
tions.[13,14] Protonation of the pyridyl group leads to increased
water solubility of the corresponding metal complexes and can
explain the enzyme-like catalytic activity of the RuII complexes
in the hydration of terminal alkynes.[12,15,16]
Pyridylphosphines are multifunctional ligands which have the
ability to act as hybrid P,N-ligands, as well pyridyl functional-
ized phosphines. The different donor abilities of phosphorus
and nitrogen in pyridylphosphines as hybrid ligands reflects
their versatile coordination behavior, which has been har-
nessed in precatalysts for a variety of processes,[1] for example,
Pd-catalyzed hydrocarboxylation of acetylene[2] or oxidative
carbonylation of phenol,[3] Ni-catalyzed olefin oligomeriza-
tion,[4–6] Ru-catalyzed hydrogenation of bicarbonate[7] and ke-
tones,[8] and Fe-mediated atom-transfer radical styrene poly-
merization.[9,10] Moreover, the ability of the phosphorus and ni-
trogen atoms of pyridyl diphosphine to form coordinate bonds
to CuI has recently been used in the self-assembly of metal–or-
ganic frameworks (MOFs).[11]
On the other hand, cyclic aminomethylphosphines are com-
pounds with phosphorus and nitrogen atoms incorporated
into one cyclic system, such that these atoms influence one
another. Despite the presence of two different heteroatoms,
this system is not a hybrid ligand because the nitrogen atom is
not usually coordinated,[17–19] but rather acts as pendant amine
in the secondary coordination sphere of the corresponding
metal.[20,21] Recently, the catalytic activity of PdII complexes of
1,5,3,7-diazadiphosphacyclooctanes for Suzuki–Miyaura cross-
coupling in neat water without additional phase-transfer re-
agent was demonstrated.[22] Moreover, it has been shown that
NiII complexes of some cyclic aminomethylphosphines (1,5-
diaza-3,7-diphosphcyclooctanes and 1-aza-3,7-diphosphacyclo-
heptanes) are the fastest synthetic catalysts known to date for
hydrogen production[21,23] and oxidation,[24] reduction of
oxygen,[25] and electrocatalytic oxidation of formate.[26] Reversi-
ble catalysis has been demonstrated for these catalysts in solu-
[a] Dr. E. I. Musina, V. V. Khrizanforova, I. D. Strelnik, M. I. Valitov,
Y. S. Spiridonova, Dr. D. B. Krivolapov, Dr. I. A. Litvinov, Dr. M. K. Kadirov,
Prof. Dr. Y. H. Budnikova, Prof. Dr. A. A. Karasik, Prof. Dr. O. G. Sinyashin
A. E. Arbuzov Institute of Organic and Physical Chemistry
Russian Academy of Sciences, Kazan Scientific Center
Arbuzov str. 8, 420088 Kazan (Russian Federation)
Fax: (+7)8432752253
E-mail: elli@iopc.ru
[b] Dr. P. Lçnnecke, Prof. Dr. E. Hey-Hawkins
Institut fꢀr Anorganische Chemie
Universitꢁt Leipzig
Johannisallee 29
04103 Leipzig (Germany)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201304234.
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tion[27] and on modified electrodes.[28] The mechanism of hy-
drogen production/oxidation and the role of proton delivery
and removal in these processes have been studied in detail.[29]
It has been shown that the electronic and steric properties of
substituents on both phosphorus and nitrogen can be used to
tune these catalysts.[30]
The reaction of pyridylphosphine (1) with paraformaldehyde
at 100–1058C led to bis(hydroxymethyl)(2-pyridyl)phosphine
1
(2) as a viscous oil. According to 31P{H} and H NMR spectrosco-
py compound 2 was obtained with 90% purity and was used
without purification. Condensation reactions of 2 with primary
amines, namely 2-pyridylamine, m- and p-toluidine, diphenyl-
methylamine, benzylamine, and (R)-(+)-methylbenzylamine in
ethanol at 60–708C led to the air-stable crystalline products
3–8, respectively (Scheme 2). Compounds 3–5 are soluble in
common organic solvents (benzene, chloroform, acetone, and
DMF), 6a and 8a are less soluble, and 7a is only soluble in hot
DMSO.
Various cyclic and macrocyclic aminomethylphosphines with
a variety of properties have been obtained by using diverse
primary or secondary phosphines, aldehydes, and primary or
secondary amines in a Mannich-like condensation reaction.[31]
The substituents on the phosphorus atoms included aryl (phe-
nyl,[23f,26,32] mesityl,[33] 2,4,6-tri-isopropylphenyl)[33], alkyl (meth-
yl,[32b] tert-butyl,[34] cyclohexyl,[24,29a] menthyl,[35] butyl, 2,4-dime-
thylpentyl,[30] and benzyl),[30,36] ferrocenyl,[37] and ferrocenyl-
methyl[38] groups. However, only a few examples of aminome-
thylphosphines with functionalized substituents on the phos-
phorus atoms were derived from ortho-phosphinophenol.[39]
In the present work, we designed new pyridylphosphines
based on the cyclic aminomethylphosphine platform to com-
bine the properties of two systems—pyridylphosphine and
aminomethylphosphine. The introduction of ortho-pyridyl sub-
stituents should expand the coordination modes of these li-
gands by introduction of an additional intramolecular pendant
base situated in close proximity to the first coordination
sphere of the corresponding transition metal and provide pos-
sibilities for nucleophilic activation of hydrogen in the course
of electrochemical H2 production or hydrogen oxidation in fuel
cells.
Scheme 2. Synthesis of 1,5,3,7-diazadiphosphacyclooctanes 3–8. *31P{H} NMR
spectrum of 7 was recorded in [D6]DMSO.
31P{H} NMR spectra of compounds 3–8 showed one signal in
the range d=ꢀ33 to ꢀ63 ppm. The chemical shifts strongly
depend on the nature of the substituent at the nitrogen atom
and are shifted to low field in the order: CH(CH3)Ph<benzyl<
Herein, we report the synthesis and crystal structures of sev-
eral 1,5-diaza-3,7-diphosphacyclooctanes with ortho-pyridyl
substituents on the phosphorus atoms, their neutral P,P-che-
late complexes with platinum(II), palladium(II), and tungsten(0),
and their cationic bis-P,P-chelate complexes with platinum(II),
palladium(II), and nickel(II). The catalytic activity of the cationic
nickel(II) bis-P,P-chelate complexes in electrochemical hydrogen
evolution and the changes to the power density of a micro
fuel cell with the complexes introduced into the near-electrode
layer will be discussed.
CH(Ph)Ph<p-tolyl<m-tolyl<2-pyridyl.
Diazadiphosphacy-
clooctane 3, with a strong electron-withdrawing 2-pyridyl sub-
stituent on the nitrogen atom, showed a signal at d=
ꢀ33 ppm, whereas analogous compounds 4 and 5, with weak
electron-withdrawing aryl substituents, showed a signal at dꢁ
ꢀ44 ppm, and compounds 6–8, with electron-donating benzyl
groups, have broad signals at dꢁꢀ60 ppm. In addition, the
yield also depends on the nature of the nitrogen substituents.
The best yields (75–85%) were obtained for aryl-substituted
heterocycles 4 and 5, moderate yields (50–63%) for benzyl-
substituted compounds 6a–8a, whereas compound 3 was
only obtained in low yield (20%), perhaps due to the low nu-
cleophilicity of 2-pyridylamine. In the case of the benzyl-substi-
tuted amines, the six-membered 1,3-diaza-5-phosphacyclohex-
anes 6b and 8b were isolated as byproducts in 8% and 3%
yield, respectively. The analogous heterocycle 7b was detected
in the reaction mixture by 31P{H} NMR spectroscopy
(Scheme 3). The formation of six-membered heterocycles was
observed earlier for some Mannich-type condensation reac-
tions between primary phosphines, formaldehyde, and primary
amines.[38,39]
Results and Discussion
Preparation and characterization of 1,5-diaza-3,7-diphospha-
cyclooctanes
2-Pyridylphosphine was synthesized by conventional reduction
of diethyl-(2-pyridyl)phosphonate with LiAlH4 (Scheme 1).[40] Di-
ethyl-(2-pyridyl)phosphonate was obtained by an improved
method[41] from N-pyridyl oxide, dimethyl sulfate, and diethyl-
phosphite.
The signals of 6b–8b in the 31P{H} NMR spectra (d=ꢀ58.2,
ꢀ52.5, and ꢀ58.1 ppm for 6b, 7b, and 8b, respectively) are
observed at slightly lower field than those of the correspond-
ing diazadiphosphacyclooctanes.
1
The H NMR spectra of compounds 3–5 in CDCl3 show simi-
Scheme 1. Synthesis of bis(hydroxymethyl)(2-pyridyl)phosphine (2).
lar patterns for the heterocyclic methylene protons. The pro-
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Scheme 3. The formation of six-membered heterocycles as co-products.
Figure 2. Molecular structure of 7a.
tons of the PꢀCH2ꢀN fragments appear as an ABX system and
reveal inequivalence of the two diastereotopic hydrogen
2
atoms. A notable difference in the values of the J(P,H) cou-
359.7(4)8, respectively) (Figure 1), whereas for compounds 7a
and 8a, the nitrogen atoms bonded to sp3-carbon atoms are
trigonal pyramidal (the sum of the bond angles is 340.3(4) and
340.7(4)8, respectively; Figure 2). The orientation of the P-pyrid-
yl groups varies from orthogonal to parallel relative to the
plane of the heterocycle.
pling constants (2J(P,H)A ꢁ5 Hz, 2J(P,H)B ꢁ7–15 Hz) was ob-
served. This pattern is typical for diazadiphosphacylcooctanes
in the crown conformation with a diaxial orientation of the
lone pairs of electrons of the phosphorus atoms.[42] For 6a in
CDCl3 and 7a in DMSO these protons are observed as two
doublets or a broad singlet, respectively. The heterocyclic
1
methylene groups in 8a are inequivalent in the H NMR spec-
Preparation of platinum, palladium, nickel, and tungsten
complexes
trum due to the presence of chiral substituents at the 1- and
5-positions of the heterocycle and form two (AA’)X spin sys-
tems, already observed for 1,5-diaza-3,7-diphosphacyclooc-
tanes with chiral exocyclic substituents.[32d,37] The m-pyridyl
protons H-5 and H-3 (numbering is shown in Scheme 2) of the
benzyl-substituted diazadiphosphacyclooctanes 6a–8a were
observed at higher field (d=6.30–7.20 ppm) than in the corre-
sponding diazaphosphacyclohexanes 6b and 8b (d=7.12–
7.44 ppm). X-ray structure analyses of compounds 3–5, 7a,
and 8a were performed and confirmed the proposed struc-
tures. The crystal structures of 5 and 7a are shown in Figures 1
It has been shown previously that 1,5-diaza-3,7-diphosphacy-
clooctanes readily form chelate complexes with group 10 tran-
sition metals.[23a,b,32d,35,38,39] Furthermore, the heterocyclic back-
bone of 3–8 resembles that of previously described ligands
that contain two noncoordinating pendant amines, which
function as proton relays in the corresponding NiII complexes,
and dramatically increase the rates of intra- and inter-molecu-
lar proton transfer and assist in heterolytic cleavage/formation
of the HꢀH bond.[20,21] As a result, complexes that contain
these pendant bases are much faster electrocatalysts for both
H2 production and oxidation and operate at much lower over-
potentials than analogous complexes without pendant
amines.[23–26,43] The ligands with P-pyridyl substituents have ad-
ditional coordination or pendant basic sites and, therefore, can
either act as P,N-chelates or P,P-chelates with cyclic and exocy-
clic pendant bases capable of secondary interactions, such as
hydrogen bonding or proton transfer. Ligands 5, 7a, and 8a
were chosen as typical representatives of 1,5,3,7-diazadiphos-
phacyclooctanes with aryl-, benzyl, and chiral substituents on
the nitrogen atoms. We studied the coordination properties of
the pyridyl-containing 1,5,3,7-diazadiphosphcyclooctanes de-
scribed above to group 10 transition metals NiII, PdII, and PtII,
which display similar behavior towards diphosphine ligands
and prefer to adopt square-planar or tetrahedral coordination
geometries. These d metals were supplemented by a tung-
sten(0)–carbonyl system that preferred octahedral coordination
and was suitable for P,N-chelation in fac-P,P,N-complexes. 3,7-
Di(2-pyridyl)-1,5-diaza-3,7-diphosphacyclooctanes 5, 7a, and
8a readily react with [PtCl2(cod)], [PdCl2(cod)] (cod=1,5-cyclo-
octadiene), [NiBr2(dme)] (dme=dimethoxyethane), and [Ni-
(CH3CN)6][BF4]2 as bidentate ligands to form mononuclear neu-
tral P,P-chelate complexes 9–11 (Scheme 4) or cationic bis-P,P-
chelate complexes 12–17, dependent on the M/L ratio em-
ployed (Scheme 5). Ligand 5 forms also a stable P,P-chelate
complex 18 with [W(CO)4(cod)] (Scheme 4). Table 1 summarizes
Figure 1. Molecular structure of 5. The noncoordinating toluene molecule is
omitted for clarity.
and 2. Crystals of compounds 3, 4, and 7a contain only the
said molecules, but 5 and 8a crystallize with toluene and ben-
zene, respectively (solvate molecule is disordered). The hetero-
cyclic molecules have a crown (chair–chair) conformation with
equatorial orientation of both P-pyridyl groups and a syn orien-
tation of the lone pairs of electrons on phosphorus, suitable
for metal chelation. The nitrogen atoms of compounds 3–5
with aromatic substituents are in an almost planar environ-
ment (the sum of the bond angles is 359.6(9), 358.6(5), and
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bands in the FTIR spectra for the MꢀCl vibrations (n˜ =290 and
317 cmꢀ1 for 10; n˜ =282 and 296 cmꢀ1 for 11) is further evi-
dence of square-planar coordination with a cis orientation of
the chloro ligands. Four carbonyl bands are observed at n˜ =
2014, 1920, 1902, and 1863 cmꢀ1 for 18, which is also consis-
tent with the formation of a tetracarbonyl bisphosphine che-
late complex.
The ABX spin system produced by the protons of the Pꢀ
CH2ꢀN fragments of 9–18 is observed as two complex multip-
lets in the 1H NMR spectra. Interestingly, in complex 12 (in
CDCl3 or CD2Cl2) one of the protons of the PꢀCH2ꢀN fragment
is observed as a doublet with 3J(Pt,H) satellites (3J(Pt,H)=
42.2 Hz). The platinum and palladium complexes 12–14 are
highly soluble in water due to the presence of four pyridyl
groups and the ionic structure. The chemical shifts of 12 and
14 in the 31P{H} NMR spectra in D2O and CDCl3 are similar but
Scheme 4. Synthesis of complexes 9–11 and 18.
1
the J(Pt,P) coupling constants are approximately 150 Hz lower
in D2O (Table 1)
The phosphorus signal of the Pd complex 13 in D2O was
shifted upfield compared to CDCl3 (d=ꢀ9.8 ppm). In D2O, only
one broad singlet is observed for the protons of the PꢀCH2ꢀN
fragment. In contrast to 12–14, the 31P{H} NMR spectra of nick-
el(II) complex 15 showed two multiplets of an AA’XX’ spin
system at d=ꢀ11.4 and 35.9 ppm, which indicates the inequi-
valence of the phosphorus atoms in this complex, possibly due
to a d8 low-spin five-coordinate nickel(II) ion with trigonal-bi-
pyramidal coordination as described for [NiCl(PMe3)4]Cl[45] (two
triplets at d=ꢀ1.5 and +28.6 ppm, J(P,P)=79 Hz, at 114 K),
which exhibits axial–equatorial exchange of the PMe3 groups.
The exchange rate of 15 is much lower than that of [NiCl-
(PMe3)4][Cl] due to presence of chelate cyclic bisphosphines.
MALDI mass spectrometry (m/z: 1107, [MꢀBr]+) confirmed the
formation of the cationic five-coordinate nickel(II) complex
[NiBrL2][Br]. In the case of the four-coordinate nickel complexes
16 and 17, with tetrafluoroborate as the counterion, all four
phosphorus atoms are equivalent in the 31P{H} NMR spectra
(16: d=0.7 ppm, s; 17: d=5.4 ppm, s).
The model five-coordinate nickel(II) complex [(k2-P,P-L)2NiCl]
[Cl] (19), in which L=1,3,5,7-tetraphenyl-1,5-diaza-3,7-diphos-
phacyclooctane, was synthesized from 1,3,5,7-tetraphenyl-1,5-
diaza-3,7-diphosphacyclooctane and NiCl2. MALDI mass spec-
trometry (m/z: 1003, [MꢀCl]+) confirmed the formation of the
cationic five-coordinate nickel(II) complex [NiClL2]Cl. The NMR
spectra of 19 are similar to those of 15 and show two multip-
lets at d=ꢀ14.0 and 21.6 ppm, which demonstrated the anal-
ogous structures of both complexes in solution.
Scheme 5. Synthesis of complexes 12–17.
the 31P NMR spectroscopic data for complexes 9–18. Compared
to the free ligand, the signals for complexes 9–14 and 16–18
are shifted downfield (Dd=30–50 ppm), consistent with the
reported deshielding of the P nuclei in six-membered chelate
rings.[44]
The 1J(P,Pt) values for complexes 9 and 10 (J=2910 and
3054 Hz, respectively) and 12 and 14 (J=2242 and 2259 Hz, re-
spectively) are in the range expected for P nuclei in a cis and
trans orientation, respectively. The presence of two broad
Table 1. 31P{H} NMR spectroscopic data of complexes 9–18.
Solvent
d31P
Dd
[ppm][a]
1J(M,P)
[Hz]
[ppm]
9
CDCl3
CDCl3
CDCl3
CD2Cl2
CDCl3
D2O
CDCl3
D2O
CDCl3
D2O
ꢀ24.2
ꢀ12.5
3.5
36.1
31.8
47.7
28.8
30.0
29.4
43.7
34.5
51.4
52.3
–
2910[b]
3054[b]
–
2274[b]
2242[b]
2082[b]
–
10
11
12
12
12
13
13
14
14
15
16
17
18
ꢀ15.4
ꢀ14.3
ꢀ14.8
ꢀ0.6
Molecular structures of transition-metal bisphosphine com-
plexes
ꢀ9.8
–
The molecular structures of the neutral monochelate com-
plexes 10, 11, and 18 and cationic bis-P,P-chelate complexes
12, 13, and 16 were unambiguously established by X-ray crys-
tallography. Complexes 10 and 11 are very similar and show
square-planar geometry around the metal center with a cis ar-
rangement of the two coordinating Cl atoms (Figure 3). The P-
M-P bite angles are 83.5(2) (10) and 82.7(4)8 (11).
ꢀ11.7
ꢀ10.8
ꢀ11.4, 35.9
0.7
2259[b]
2096[b]
–
CD3CN
CD3CN
CD3CN
CDCl3
43.5
49.6
46.9
–
–
5.4
2.62
204[c]
[a] Dd=dligandꢀdcomplex. [b] M=Pt. [c] M=W.
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of complexes of group 10 metals. The environment of the in-
tracyclic nitrogen atom N1 of the boat part of the bicyclono-
nane system is nearly planar (sum of bond angles is 353.4(3)8).
In the chair part the N5 atom is nearly pyramidal (sum of bond
angles is 344.4(2)8). The bond lengths N5ꢀCexo and N1ꢀCexo
(1.434(4) and 1.412(4) ꢁ, respectively) correlate with the coordi-
nation of the nitrogen atoms. The average bond length ob-
served for the WꢀC(carbonyl) bond trans to the phosphorus
atom (1.994(3) ꢁ) is shorter than that of common bisphosphine
complexes (2.029(4) ꢁ on average).[47]
Crystals of the cationic bis(P,P)-chelate complexes 12 and 13
were grown by slow evaporation from solutions in chloroform.
Crystals of the corresponding nickel complex 16 were obtained
by slow diffusion of ethanol into a solution of 16 in acetone.
The molecular structures of 12, 13, and 16 consist of discrete
cations formed by two bisphosphine ligands and platinum(II),
palladium(II), or nickel(II) and two noncoordinating chloride
(12 and 13) or tetrafluoroborate (16) anions. Cations of the
complexes 12 and 13 are isostructural. The platinum and palla-
dium atoms are located on a crystallographic twofold axis. The
symmetry independent part of the molecule contains one che-
late ligand. The molecular structures of the cations 13 and 16
are shown in Figures 5 and 6.
Figure 3. Molecular structure of 10. Solvent molecules are omitted for clari-
ty.
The heterocyclic ligands in 10 and 11 have a different con-
formation than the chair–chair conformation of the free het-
erocycle (5). The metal atoms are included in the bicyclic (bicy-
clononane) system, so the conformation may be analyzed as
two six-membered metallacycles: one of them has a chair con-
formation, the other has a boat conformation. The N1 nitrogen
atom of the boat part of the heterocycle is nearly trigonal pyr-
amidal (sum of C-N-C bond angles are 346.4(2) and 347.6(2)8
for 10 and 11, respectively) and is in close proximity to the
metal center (Pt···N1=3.317 ꢁ, Pd···N1=3.280 ꢁ, sum of the
van der Waals radii=3.27 and 3.18 ꢁ,[46] respectively). The N5
nitrogen atom in the chair part of the molecule is trigonal
planar in 10 (sum of C-N-C bond angles is 359.6(2)8), and trigo-
nal pyramidal in 11 (sum of C-N-C bond angles is 345.0(2)8).
The pyridyl group on the phosphorus atom P7 is nearly or-
thogonal to the MP2Cl2 plane (dihedral angles: 75.98 for 10
and 86.88 for 11). Thus, the pyridyl N atoms located above or
below the MP2Cl2 plane are suitable for controlling the direc-
tion of incoming substrates.
Crystals of the P,P-chelate tungsten complex 18 were ob-
tained by slow diffusion of n-hexane into a solution of 18 in
CDCl3. Complex 18 represents an example of a distorted octa-
hedral 1,5-diaza-3,7-diphosphacyclooctane complex (P3ꢀWꢀ
P7=73.70(2)8). The average WꢀP bond length (2.4779(8) ꢁ) is
slightly shorter than that typical for P,P-chelate complexes of
tungsten(0) (2.50–2.52 ꢁ).[47] A chair–boat conformation of the
ligand is observed in 18 (Figure 4), similar to the conformation
Figure 5. Molecular structure of the cation of 13. Counterions and solvate
molecules are omitted for clarity. The corresponding Pt complex 12 is iso-
structural.
Figure 6. Molecular structure of the cation of 16. Counterions and solvate
Figure 4. Molecular structure of 18.
molecules are omitted for clarity.
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In contrast to complexes 10 and 11, complexes 12, 13, and
16 exhibit a slightly (12, 13) or noticeably (16) distorted
square-planar geometry around the metal center. The dihedral
angle between the P3-M1-P7 and P3A-M1-P7A planes is 10.08
for 12, 10.58 for 13, and 22.98 for 16. The PtꢀP bond lengths
are typical for platinum(II) complexes with similar bidentate
phosphine ligands.[17] The P-M-P bond angles of 81.4(1),
81.62(6), and 84.36(4)8 for 12, 13, and 16 are slightly smaller
than those of linear bisphosphines.[17,48] Both heterocyclic li-
gands of the complexes 12, 13, and 16 have a chair–boat con-
formation. The N1 nitrogen atom of the boat part of the het-
erocycle is close to the metal center (Pt···N1=3.319 ꢁ in 12,
Pd···N1=3.330 ꢁ in 13, and Ni···N1 and Ni···N1A=3.371 and
3.394 ꢁ in 16. The geometry is nearly trigonal planar in 12 and
13 (sum of C-N1-C bond angles is 353.0 and 351.88, respective-
ly) and distorted trigonal pyramidal in 16 (sum of C-N1-C and
C-N1A-C bond angles is 347.1 and 347.98). The remote nitro-
gen atom N5 of the chair part has a trigonal pyramidal config-
uration (sum of bond angles is 342.18 for 12, 339.88 for 13,
and 339.5 and 343.38 for 16). The P-pyridyl substituents of 12
and 13 are arranged in a nearly parallel fashion (dihedral
angles between the planes of close pyridyl rings are 23.9 and
6.08 for 12 and 23.2 and 3.68 for 13). The distance between
the centroids of the pyridyl rings is approximately 3.45 ꢁ. Two
pyridyl groups are nearly orthogonal to the MP4 plane (dihe-
dral angles are 85.08 in 12 and 87.68 in 13) with the basic ni-
trogen atom located above and below this plane. In 16, all pyr-
idyl groups have dihedral angles with the NiP4 plane that vary
from 31.8–45.28. Unlike the structure of NiII complexes with
phenyl groups on phosphorus,[23a] in which both nitrogen
atoms in the boat part of the ligands are located on one side
relative to the medium NiP4 plane, in 16 these nitrogen atoms
are located on opposite sides relative to this plane. As a result,
the BF4 counterion in P-phenyl substituted complexes is close
to the nickel ion,[23a] whereas in 16 it is remote from the
cation.
Figure 7. Molecular structure of 19. Counterion is omitted for clarity.
course of an electrochemical oxidation or the production of
hydrogen.
Electrochemical studies of nickel complexes 16 and 17
It was found that the complexes of the type [(k2-P,P-L)2Ni][BF4]2
(16 and 17) are able to activate and oxidize hydrogen in the
coordination sphere, similarly to hydrogenases[49] and to cata-
lyze hydrogen evolution. Therefore, the electrochemical fea-
tures of nickel complexes 16 and 17 were studied. It should be
mentioned that the data obtained for the electrochemical re-
duction of complexes 16 and 17, generated in situ from the
corresponding ligand and Ni(BF4)2, are the same. Both nickel
complexes 16 and 17 display two distinct reversible reduction
waves with a peak-to-peak separation (DEp) for each wave of
50–81 mV in acetonitrile (Table 2 and Figure 8; Figure S1 in the
Supporting Information).
Table 2. Electrochemical data for nickel complexes 16 and 17 in acetoni-
trile.
E1/2 [V]
DEp [mV]
ia/ic[a]
Single crystals of complex 15 suitable for X-ray structure
analysis could not be obtained, but single crystals of model
complex 19 were obtained by slow evaporation of its solution
in chloroform. The compound crystallizes in the space group
C2/c with eight molecules in the unit cell and confirmed the
proposed trigonal bipyramidal structure of the cationic bis-che-
late complex 19, with chlorine and two phosphorus atoms of
different chelate ligands in the equatorial positions and two
phosphorus atoms in the axial positions (Figure 7).
NiII/I
ꢀ0.82
ꢀ0.90
NiI/0
ꢀ1.00
ꢀ1.12
16
17
50
81
0.82
0.86
16
17
58
58
1.1
1.1
[a] ia =anodic current, ic =cathodic current.
The endocyclic amine groups of both ligands located in the
chair parts of the chair–boat ligands point out towards the
chloro ligand. In total, the structure of cation 19 is similar to
one reported by Kilgore[23a] that contained the tetrafluorobo-
rate anion proximal to the nickel center rather than coordinat-
ed chlorine. In summary, the molecular structures indicate that
both the endo- and exo-cyclic basic sites of the ligands are lo-
cated in close proximity to the first coordination sphere of the
transition-metal complexes. Thus, both types of basic site have
the potential to participate in hydrogen activation by the
metal center or in proton transfer to the metal center in the
Figure 8. Cyclic voltammogram of a solution of 17 in acetonitrile
(c=1.5 mm). Conditions: scan rate=0.1 Vsꢀ1, Bu4NBF4 (0.1m), glassy-carbon
working electrode.
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The two waves are assigned to the NiII/I and NiI/0 couples.
Plots of the peak current (ip) versus the square root of the scan
rate display linear relationships for both couples, which indicat-
ed that these redox processes are diffusion controlled (see the
Supporting Information, Figure S2). Values of E1/2 for the nickel-
(II/I) and nickel(I/0) couples range from E1/2 =ꢀ0.82 to ꢀ0.90 V
and E1/2 =ꢀ1.00 to ꢀ1.12 V, respectively, and are comparable
to that of the previously described analogues with P-phenyl
and P-benzyl substituents.[23a,30a]
tammograms represented in traces 2–7 (Figure 9) were record-
ed in the presence of increasing acid concentration. A signifi-
cant increase in the current near the nickel(I/0) couple is de-
tected as rising amounts of acid are added (Figure 9). The
wave of the nickel(II/I) couple remained at constant current
and was positively shifted by 50–100 mV in the presence of
acid relative to the acid-free environment. The electrocatalysis
occurs at a potential of ꢀ1.4 V for complex 16 and ꢀ1.5 V for
complex 17. We observed intensive gas evolution on the sur-
face of the working electrode at these potentials. An analo-
gous hydrogen evolution phenomenon has been described for
nickel complexes of cyclic aminomethylphosphines.[23c] The cat-
alytic enhancement at the NiI/0 reduction peak is not consistent
with the catalytic cycle proposed for catalysts that contain
P-phenyl or P-benzyl substituents; in these cases, a catalytic in-
crease of current at the NiII/I peak was observed.[23f,49a]
Catalytic hydrogen production
The nickel complexes 16 and 17 were tested as electrocatalysts
for hydrogen production. The electrocatalytic experiments
were performed in dry CH3CN with CF3COOH as a proton
source (pKa(CH3CN)=12.7).[50] The H2 production activity was
measured by cyclic voltammetry (CV) of reaction mixtures for
which the acid concentrations were systematically increased
until the icat/ip ratio remained constant—the acid-independent
region (Figures 9 and 10 for 17; see the Supporting Informa-
Equation (1) [see the Experimental section] has been used to
calculate a turnover frequency (TOF) of 3050 sꢀ1 for 16 and
5200 sꢀ1 for 17 in the acid-independent region. These results
show that complexes 16 and 17, with pyridyl-substituted li-
gands, display higher TOFs in organic media than the corre-
sponding phenyl- and benzyl-substituted nickel complexes re-
ported earlier.[23a,e,30,32e] However the overpotentials of catalysts
16 and 17, calculated by the method of Evans et al.[51] range
from 0.5–0.6 V for 16 and 17, respectively (Table 3) and are
slightly higher than for other complexes of this type.[23a,e,30,32e]
Table 3. Electrocatalytic data for hydrogen production.
16
17
potential of catalysis [V]
ꢀ1.4
ꢀ1.5
[CF3COOH] [m]
0.14
3050
21000
0.5
0.11
5200
47000
0.6
kobs [sꢀ1
]
Figure 9. Cyclic voltammograms of solutions of 17 in acetonitrile
(c=1.5 mm) in the presence of various amounts of CF3COOH. Conditions:
scan rate=10 Vsꢀ1, (Bu4N)BF4 (0.1m), glassy-carbon electrode.
k [mꢀ1 sꢀ1
overpotential [V]
]
Probably, the increase of overpotential is caused primarily by
current enhancement of the nickel(I/0) reduction peak in the
catalytic process. Detailed determination of the reasons of the
higher overpotential and the mechanism of H2 production is
outside the scope of this work and will be discussed at
a future date.
The dependence of the catalytic current on catalyst concen-
tration at a constant acid concentration has linear character
(see Figure S6 in the Supporting Information). The second-
order rate constants (first order in acid and first order in cata-
lyst) were determined from plots of kobs versus [H+] (Figure 11
for 17; Figure S8 in the Supporting Information for 16); k=
21000 and 47000mꢀ1 sꢀ1 for 16 and 17, respectively (Table 3).
Thus, the catalytic activities of nickel complexes 16 and 17 for
electrochemical hydrogen evolution in CH3CN are rather high
and are comparable to, or even better than, similar catalysts
based on 1,5-diaza-3,7-diphosphcyclooctanes described to
date.
Figure 10. Plot of icat/ip versus [CF3COOH] for 17 in acetonitrile.
tion, Figures S5 and S7 for 16). The duration of these experi-
ments was restricted to approximately 30 min and minimal
(<5%) catalyst decomposition was observed, determined by
UV/Vis spectroscopy for each complex (see the Supporting In-
formation, Figure S3). Trace 1 in Figure 9 corresponds to the re-
duction of complex 17 in the absence of acid. The cyclic vol-
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Figure 11. Plots of kobs versus [CF3COOH] for hydrogen evolution in acetoni-
trile catalyzed by 17.
Figure 13. CV spectra of 16 in CH3CN (c=2 mm). Conditions: scan
rate=0.1 Vsꢀ1, (Bu4N)BF4 (0.1m). 1) Complex 16, 2) complex 16 after expo-
sure to H2.
Fuel-cell tests
It has been demonstrated that hydrogen reacts with 17. The
red solution of 17 in CD3CN became light yellow after expo-
sure to a hydrogen flow for 1 h, and the 31P NMR spectrum
showed almost complete disappearance of the signal for com-
plex 17 and the appearance of several new peaks in the range
d=9.8–16.1 ppm. Similar spectral changes have been de-
scribed for the formation of protonated Ni0 complexes as
a result of the interaction of analogous NiII complexes with hy-
drogen.[23b,24] The presence of several signals indicates that
a mixture of isomers is present, but the positions of the pro-
tons that resulted from the H2 oxidation are not yet completely
determined. It should be mentioned that the appearance of
The aim of the experiments was to determine the influence of
the introduction of solutions of 16 and 17 in dichloromethane
at the anode side of the membrane-electrode assembly (MEA)
on the power density of the FC (see the Experimental section
and Supporting Information). Carbon-containing molecules (in-
cluding CH2Cl2) in “cold combustion” in the FC are able to pro-
duce carbon monoxide, which contaminates the platinum cat-
alyst and degrades the diagnostic characteristics. To reduce the
negative impact of carbon monoxide contamination, we used
a MEA with a platinum density of 4 mgcmꢀ2. The resultant di-
agnostic curves (power density versus current density;
Figure 14; see the Supporting Information, Figure S12) demon-
strate that treatment of the fuel cell with compound 16 or 17
improves the power density of the FC by 25–30 and 45-52%,
respectively, when applied on the anode side in equal volumes
of dichloromethane.
1
a peak at d=8.84 ppm in the H NMR spectrum suggests pro-
tonation of the pyridyl nitrogen centers and the endocyclic ni-
trogen atoms. The nearly complete disappearance of the initial
peaks in the CV spectra of 17 after exposure to hydrogen was
observed (Figure 12) and was consistent with the chemical re-
Figure 14. FC diagnostic curves with 4.0 mgcmꢀ2 Pt/Nf MEA (Nf=Nafion) by
Figure 12. CV spectra of 17 in CH3CN (c=2 mm). Conditions: scan
rate=0.1 Vsꢀ1, (Bu4N)BF4 (0.1m). 1) complex 17, 2) complex 17 after expo-
sure to H2.
&
*
addition of ( ) CH2Cl2 (10 mL), ( ) a solution of 16 in CH2Cl2
(c=5ꢂ10ꢀ4 mollꢀ1), and ( ) 17 in CH2Cl2 (c=5ꢂ10ꢀ4 mollꢀ1) at the anode
~
side.
duction of 17 to the corresponding nickel(0) complex and con-
comitant hydrogen oxidation. In the case of 16, two peaks in
the CV spectra merged into one after hydrogen was passed
through a solution of complex 16 in CH3CN (Figure 13). The 31P
and H NMR spectra of 16 were unchanged after exposure to
a flow of hydrogen for several hours.
Conclusions
The reaction of 2-pyridylphosphine, formaldehyde, and various
primary amines resulted in eight-membered cyclic pyridyl-sub-
stituted bisphosphines, the structures and coordination prop-
erties of which were similar to those of other 1,5-diaza-3,7-di-
phosphacyclooctanes. These ligands form mono-P,P-chelate
and cationic bis-P,P-chelate complexes with group 10 transition
1
The catalytic properties of 16 and 17 in the oxidation of hy-
drogen were investigated in a specially constructed miniature
fuel cell (FC) [see the Supporting Information, Figure S11].[52]
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added by microsyringe (10 mL increments) until the catalytic cur-
rent (icat) no longer increased. The catalytic current was measured
at ꢀ1.4 and ꢀ1.5 V. The ratio of icat/ip versus the acid concentration
were plotted and the icat/ip ratio in the acid-independent region
was used to determine the catalytic rate constant according to
Equation (1),[23c,53]
metals and tungsten(0). An important advantage to the intro-
duction of a pyridyl substituent on the phosphorus atom of
1,5-diaza-3,7-diphosphacyclooctanes is the improved water sol-
ubility of the resultant transition-metal complexes, which
makes them potentially useful for biphasic catalysis and appli-
cations in medicine. The nitrogen atoms of the pyridyl groups
were not involved in coordination in the transition-metal-com-
plex studies, even when an excess of the metal salt was used.
However, they are located in close proximity to the first coordi-
nation sphere of the transition metal and participate as pend-
ant bases in electrochemical hydrogen oxidation/evolution.
The catalytic activity of the cationic bis-P,P-chelate complexes
with nickel(II) in electrochemical hydrogen evolution is compa-
rable to the best catalytic systems in organic media described
to date. Finally, preliminary results indicate that introduction of
the nickel complexes 16 and 17 into the near-electrode layer
of a real fuel cell increased the power density by up to 52%.
ꢀ
ꢁ
i
cat=ip
kobs ¼ n
ð1Þ
0:72
in which kobs is the observed rate constant, u is the scan rate
[Vsꢀ1], and a two-electron process is assumed.
Fuel-cell (FC) tests
Diagnostic curves of the MEAs studied were measured with a gas-
flow-controlling unit MTS-A-150 and potentiostat ESL 450 (both
Electro Chem Co.) in a specially constructed miniature FC[52] (see
the Supporting Information, Figure S11). The FC consists of two
teflon half-cylinders. Gas-feeding channels inside each half-cylinder
admit oxygen and hydrogen. The active part includes a Pt mesh
spacer that allows gas distribution and at the same time provides
electrical contact, and a MEA (the membrane with Pt electrodes
deposited on both sides). Nafion 117 (Nf) manufactured by DuPont
is available commercially. Platinum catalyst was deposited on the
membrane from a suspension of platinum black particles with
sizes of 30–50 nm in an aqueous solution of Nafion (5%). Plati-
num–Nafion (Pt/Nf) MEAs with platinum densities=1, 2, and
4 mgcmꢀ2 were fabricated by pressing for 7 min at 1778C under
a pressure of 35 atm. Experiments were carried out with a H2/O2
FC. The flow rate of hydrogen was 14 cm3 minꢀ1 and that of
oxygen was 7 cm3 minꢀ1. Diagnostic curves have been measured
for the above-mentioned MEA and with the addition of a solution
(5ꢂ10ꢀ4 mollꢀ1; 10 mL) of the studied complexes at the anodic
side. Each measurement was repeated (ꢂ3); see the Supporting In-
formation.
Experimental Section
General
All reactions and manipulations were carried out under a dry
argon atmosphere by using standard vacuum-line techniques. Sol-
vents were purified, dried, deoxygenated, and distilled before use.
EI-MS (70 eV) were recorded with a DFS Thermo Electron Corpora-
tion (Germany) spectrometer with direct sample admission into the
ion source (ion-source temperature=2808C; vaporizer temperature
programmed from 50–3508C). The XCalibur program was used to
process the mass spectrometry data. The mass spectra are report-
ed as m/z values with relative intensities (Irel) [%]. MALDI mass
spectra were obtained with a Bruker ULTRAFLEX III mass spectrom-
eter (Nd: YAG Smartbeam laser, l=355 nm) in a linear mode, with-
out accumulation of mass spectra. 1H NMR (400 MHz), 13C NMR
(101 MHz), and 31P NMR (162 MHz) spectra were recorded with
a Bruker Avance-DRX 400 spectrometer. Chemical shifts (d) are re-
ported in ppm relative to SiMe4 (1H, 13C; internal standard) and
85% H3PO4 (aq) [31P; external standard]. Coupling constants (J) are
reported in Hz. Atom numbering is shown in Schemes 2 and 3. IR
spectra were recorded on an FTIR spectrometer Tensor 27 (Bruker)
in the range n˜ =4000–400 cmꢀ1, and far-IR spectra of solid samples
in Nujol, placed between polyethylene plates, on an FTIR spec-
trometer IFS-66v/s (Bruker) in the range n˜ =600–100 cmꢀ1, both at
X-ray crystallography
The X-ray data for 4, 5, and 7a were collected on a Gemini diffrac-
tometer (Agilent Technologies) at T=130(2) K and the data for 3,
8a, 10–13, 16, 18, and 19 were collected on Bruker Smart Apex II
CCD diffractometer at T=296(2) [3, 11, 13, 18, 19], 293(2) [8a, 10,
12], and 150(2) K (16), by using MoKa radiation (l=0.71073 ꢁ).
Data reduction of 4, 5, and 7a was performed with CrysAlis Pro
software,[54] and included the program SCALE3 ABSPACK[55] for em-
pirical absorption correction. Data reduction of 3, 8a, 10–13, 16,
18, and 19 was performed with the APEX2[56] program, and includ-
ed the program SAINT[56] and SADABS.[57] All structures were solved
by direct methods[58,59] and refined with SHELXL-97.[59] Non-hydro-
gen atoms were refined with anisotropic thermal parameters, with
the exception of the minor (17%) disordered part of the structure
of 4. Hydrogen atoms in 4, CH3 substituents, and disordered parts
in 5 were calculated on idealized positions by using the riding
model, whereas all other hydrogen atoms are located at the end
of the structure refinement by using a difference-density Fourier
map. Hydrogen atoms in 3, 8a, 10–13, 16, 18, and 19 were refined
as riding atoms. Structure representations were generated with DI-
AMOND-3.[60] The crystallographic data and summary of data col-
lection and refinement are presented in Table S1 (see the Support-
ing Information).
an optical resolution of 4 cmꢀ1
.
Electrochemical methods
CV measurements were performed with a BAS Epsilon (USA) E2P
potentiostat comprised of a measuring block, Dell Optiplex 320
computer with installed Epsilon ES-USB-V200 program, and a C3
electrochemical cell. A stationary glassy-carbon electrode was used
as the working electrode. A Fc+/Fc (Fc=ferrocenyl) system served
as the reference electrode. A platinum wire with a diameter of
0.5 mm was used as the auxiliary electrode. Measurements were
performed under an argon atmosphere.
H2 production measurements
A solution of the nickel complex (1.5 mm) in acetonitrile (5 mL)
that contained (Bu4N)BF4 (0.1m) was prepared. Nickel complexes
were titrated with trifluoroacetic acid (TFA). Aliquots of acid were
CCDC-93002 (3), CCDC-932709 (4), CCDC-932710 (5), CCDC-932711
(7a), CCDC-933003 (8a), CCDC-932995 (10), CCDC-932996 (11),
Chem. Eur. J. 2014, 20, 3169 – 3182
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3
4
CCDC-932997 (12), CCDC-932998 (13), CCDC-93299 (16). CCDC-
933000 (18), and CCDC-93001 (19) contain the supplementary crys-
tallographic 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.
7.8 Hz, 2H; H-9), 6.68 (dd, J(H,H)=8.3 Hz, J(H,H)=2.4 Hz, 2H; H-
3
10), 6.64 (brs, 2H; H-7), 6.54 (d, J(H,H)=7.8 Hz, 2H; H-8), 4.59 (dd,
2J(H,H)ꢁ J(P,H)ꢁ14.7 Hz, 4H; H-1eq), 4.14 (dd, 2J(H,H)=14.7 Hz,
2
2J(P,H)=4.4 Hz, 4H; H-1ax), 2.27 ppm (s, 6H; H-6); 13C NMR
(101 MHz, CDCl3): d=162.6 (m, 1J(C,P)=11.1 Hz; ipso-CꢀP), 150.53
(dddd, 1J(C,H)=178.6 Hz, 2J(C,H)=6.6 Hz, 3J(C,P)ꢁ J(C,H)=3.3 Hz;
3
C-2), 146.07 (m; ipso-CꢀN), 138.82–138.51 (m; ipso-CꢀC), 135.59
Synthesis of starting materials
(ddd, 1J(C,H)=162.9 Hz, 2J(C,H)=6.6, 7.5 Hz; C-4), 129.02 (ddd,
1J(C,H)=163.6 Hz, J(C,H)=6.6 Hz, J(C,P)=33.7 Hz; C-5), 128.98 (d,
2
2
[PtCl2(cod)] was prepared from H2[PtCl6]·6H2O according to a modi-
fied procedure (see the Supporting Information).[61] [PdCl2(cod)],[62]
[Ni(NCMe)6][BF4]2,[63] and [NiBr2(dme)][64] were prepared by pub-
lished procedures. [W(CO)4(cod)] was purchased from Aldrich. O,O-
Diethyl(pyrid-2-yl)phosphonate was obtained from pyridine-N-
oxide and sodium diethylphosphonate by an improved Redmors[41]
method (see the Supporting Information). 2-Pyridylphosphine (1)
was obtained from O,O-diethyl(pyrid-2-yl)phosphonate by reduc-
tion with LiAlH4 in diethyl ether.[40]
1J(C,H)=157.1 Hz; C-7), 122.73 (ddd, J(C,H)=164.3 Hz, J(C,H)=7.5,
1
2
6.6 Hz; C-3), 117.85 (ddd, 1J(C,H)=158.6 Hz, 2J(C,H)=11.6 Hz,
3J(C,H)=6.4 Hz; C-8) 113.75 (brd, J(C,H)=155.5 Hz; C-9), 110.17 (d,
1
1J(C,H)=157.1 Hz; C-10), 56.45 (tdd, 1J(C,H)=140.8 Hz, 1J(C,P)=
16.5 Hz, 3J(C,P)=4.6 Hz; C-1), 22.08 ppm (qdd, 1J(C,H)=126.1 Hz,
3J(C,H)ꢁ J(C,H)=4.6 Hz; C-6); 31P{1H} NMR (162 MHz, CDCl3): d=
3
ꢀ43.4 ppm; elemental analysis calcd (%) for C28H30N4P2: C 69.41, H
6.24, N 11.56, P 12.79; found: C 69.43, H 6.26, N 11.62, P 12.76.
Compound 5: Compound 5 (1.12 g, 85%) was prepared by the
procedure described above for 4 from 2 (0.92 g, 5.4 mmol) and p-
toluidine (0.58 g, 5.4 mmol), except the reaction mixture was
stirred at ambient temperature for 30 min. Single crystals of 5 suit-
able for X-ray crystal structure analysis were obtained by recrystalli-
sation of crude 5 from toluene. M.p. 1708C; 1H NMR (400 MHz,
Synthesis
Compound 2: A mixture of 2-pyridylphosphine (1.39 g, 12.5 mmol)
and paraformaldehyde (0.75 g, 25.0 mmol) was stirred at 1108C
1
until homogenization was observed. H NMR (400 MHz, CDCl3): d=
3
3
8.59 (d, J(H,H)=4.4 Hz, 1H; H-2), 7.70 (dddd, J(H,H)=7.3, 7.8 Hz,
3
CDCl3): d=8.73 (brd, J(H,H)=4.7 Hz, 2H; H-2), 7.69–7.65 (m, 4H;
4
4J(H,H)ꢁ J(P,H)ꢁ2 Hz, 1H; H-4), 7.63 (ddd, 3J(H,H)=7.8, 4.4 Hz,
3
H-3+H-4), 7.24–7.21 (m, 2H; H-5), 7.01 (d, J(H,H)=7.8 Hz, 4H; H-
4J(H,H)ꢁ2 Hz, 1H; H-3), 7.28 (ddd, 3J(H,H)=7.3 Hz, 3J(P,H)ꢁ4 Hz,
8), 6.76 (d, 3J(H,H)=7.8 Hz, 4H; H-7), 4.60 (dd, 2J(H,H)=15.0 Hz,
2J(P,H)~12.5 Hz, 4H; H-1eq), 4.12 (dd, 2J(H,H)=15.0 Hz, 2J(P,H)=
4.8 Hz, 4H; H-1ax), 2.20 ppm (s, 6H, H-6); 31P{1H} NMR (162 MHz,
CDCl3): d=ꢀ44.2 ppm; MS (EI): m/z (%): 484 (1.3) [M]+, 406 (0.67)
[MꢀC5H4N]+, 374 (4.22) [MꢀC5H5NP]+, 350 (10.68) [MꢀC7H5NP]+,
255 (7.32) [MꢀC13H14N2P]+, 122 (46.84) [C6H5NP] +, 91 (100.0)
[C7H7]+; elemental analysis calcd (%) for C28H30N4P2: C 69.41, H 6.24,
N 11.56, P 12.79; found: C 69.54, H 6.26, N 11.47, P 12.76.
4J(H,H)ꢁ2 Hz, 1H; H-5), 5.59–4.95 (brm, 2H; OH), 4.63 (dd,
2J(H,H)=13.2 Hz, J(P,H)=7.8 Hz, 2H; H-1A), 4.51 ppm (dd, J(H,H)=
2
2
2
13.2 Hz, J(P,H)=10.8 Hz, 2H; H-1B); 31P{1H} NMR (162 MHz, CDCl3):
d=ꢀ16.7 ppm. Compound 2 was synthesized immediately before
use.
Compound 3: Compound 2 (2.21 g, 12.9 mmol) was dissolved in
dry ethanol (10 mL) and a solution of 2-pyridylamine (1.24 g,
13.2 mmol) in dry ethanol (7 mL) was added. The mixture was
stirred at 708C for 72 h. The precipitate formed was filtered off,
washed carefully with ethanol, and dried at 0.05 torr for 3 h. The
filtrate was heated at 708C for 24 h and the precipitate formed
was filtered off (ꢂ2). The combined precipitates were washed with
ethanol and dried at 0.05 torr for 3 h to give 3 (0.6 g, 20%). Single
crystals of 3 suitable for X-ray crystal structure analysis were ob-
tained by recrystallisation of the crude product from ethanol. M.p.
196–1988C; 1H NMR (400 MHz, CDCl3): d=8.71 (ddd, 3J(H,H)=
4.8 Hz, 4J(H,H)=2.0 Hz, 5J(H,H)=1.0 Hz, 2H; H-2), 8.19 (ddd,
3J(H,H)=4.9 Hz, 4J(H,H)=1.9 Hz, 5J(H,H)=0.7 Hz, 2H; H-6), 7.88
(ddd, 3J(H,H)=7.7, 4.8 Hz, 4J(H,H)=1.1 Hz, 2H; H-3), 7.69 (dddd,
Compounds 6a and 6b: Compound 6a (1.70 g, 63%) was pre-
pared by the procedure described above for 4 from 2 (1.45 g,
8.47 mmol) and diphenylmethylamine (1.55 g, 8.47 mmol), except
that the reaction time was 15 min. M.p. 194–1968C; 1H NMR
(400 MHz, CDCl3): d=8.16 (brd, 3J(H,H)=4.4 Hz, 2H; H-2), 7.60
(brd, 3J(H,H)=7.3 Hz, 8H; H-7), 7.21 (dd, 3J(H,H)=7.3, 7.9 Hz, 8H;
H-8), 7.16–7.09 (m, 3J(H,H)=7.9 Hz, 6H; H-9+H-4), 6.80 (dd,
3J(H,H)=6.9, 4.9 Hz, 2H; H-3), 6.30 (d, 3J(H,H)=7.8 Hz, 2H; H-5),
2
5.71 (s, 2H; H-6), 3.94 (brd, J(H,H)=14.7 Hz, 4H; H-1A), 3.64 ppm
(brd, 2J(H,H)=14.7 Hz, 4H; H-1B); 31P{1H} NMR (162 MHz, CDCl3):
d=ꢀ60.5 ppm; elemental analysis calcd (%) for C40H38N4P2: C
75.46, H 6.02, N 8.80, P 9.73; found: C 75.38, H 6.16, N 8.87, P 9.76.
3J(H,H)=7.7, 7.4 Hz, 4J(H,H)ꢁ J(P,H)ꢁ2.0 Hz, 2H; H-4), 7.43 (ddd,
4
3J(H,H)=8.5, 7.1 Hz, J(H,H)=1.9 Hz, 2H; H-8), 7.23 (ddd, J(H,H)=
7.4, 3J(P,H)=4.8 Hz, 4J(H,H)=1.1 Hz, 2H; H-5), 6.81 (d, 3J(H,H)=
8.5 Hz, 2H; H-9), 6.57 (ddd, 3J(H,H)=7.1, 4.9 Hz, 4J(H,H)=0.7 Hz,
2H; H-7), 5.10 (dd, 2J(H,H)=14.7 Hz, 2J(P,H)=7.3 Hz, 4H; H-1eq),
4.08 ppm (dd, 2J(H,H)=14.7 Hz, 2J(P,H)=4.4 Hz, 4H; H-1ax);
31P{1H} NMR (162 MHz, CDCl3): d=ꢀ33.5 ppm; elemental analysis
calcd (%) for C24H24N6P2: C 62.88, H 5.28, N 18.33, P 13.51; found: C
62.82, H 5.26, N 18.27, P 13.76.
4
3
Crystals of 6b (0.36 g, 8%) precipitated from the filtrate of the re-
action mixture. They were filtered off, washed with ethanol, and
dried at 0.05 torr for 2 h. M.p. 170–1718C; 1H NMR (400 MHz,
3
3
CDCl3): d=8.58 (brd, J(H,H)=4.4 Hz, 1H; H-2), 7.57 (dd, J(H,H)=
3
7.3, 7.9 Hz, 1H; H-4), 7.44 (brd, J(H,H)=7.3 Hz, 1H; H-3), 7.33–7.31
(m, 4H; H-9), 7.26–7.08 (m, 17H; H-7+H-8+H-5), 4.78 (s, 2H; H-6),
3.46 (dd, 2J(H,H)=11.3 Hz, 4J(H,H)=2.0 Hz, 1H; H-10A), 3.40 (d,
2
2J(H,H)=11.3 Hz, 1H; H-10B), 3.30 (dd, 2J(H,H)ꢁ J(P,H)ꢁ13.2 MHz,
2
2
2H; H-1eq), 3.18 ppm (dd, J(H,H)=13.2 Hz, J(P,H)=4.9 Hz, 2H; H-
1ax); 31P{1H} NMR (162 MHz, CDCl3): d=ꢀ58.0 ppm; elemental anal-
ysis calcd (%) for C34H32N3P: C 79.51, H 6.28, N 8.18, P 6.03; found:
C 79.38, H 6.26, N 8.27, P 6.06.
Compound 4: Compound 2 (2.14 g, 12.5 mmol) was dissolved in
dry ethanol (10 mL) and
a solution of m-toluidine (1.35 g,
12.6 mmol) in dry ethanol (7 mL) was added. The mixture was
stirred at 708C for 6 h, then at rt overnight. The precipitate formed
was filtered off, washed carefully with ethanol, and dried at
0.05 torr for 3 h to give 4 (2.3 g, 75%). Single crystals of 4 suitable
for X-ray crystal structure analysis were obtained by slow evapora-
tion of CDCl3 from an NMR sample. M.p. 161–1658C; 1H NMR
Compound 7a: Compound 7a (1.51 g, 60%) was prepared by the
procedure described above for 4 from 2 (1.78 g, 10.4 mmol) and
benzylamine (1.13 g, 10.6 mmol), except that the reaction mixture
was stirred at 608C for 3 h. An analytically pure sample of 7a was
obtained by recrystallization from toluene. Single crystals of 7a
suitable for X-ray crystal structure analysis were obtained by recrys-
3
(400 MHz, CDCl3): d=8.75 (brd, J(H,H)=4.4 Hz, 2H; H-2), 7.73–7.63
(m, 4H; H-3+H-4), 7.23–7.25 (m, 2H; H-5), 7.11 (dd, 3J(H,H)=8.3,
Chem. Eur. J. 2014, 20, 3169 – 3182
www.chemeurj.org
3178
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
1
1
tallization from toluene. M.p. 1708C; H NMR (400 MHz, [D6]DMSO):
in CH2Cl2. M.p. 2608C; H NMR (400 MHz, CDCl3): d=8.76 (brs, 2H;
d=8.49 (brd, 3J(H,H)=4.4 Hz, 2H; H-2), 7.56 (dd, 3J(H,H)=7.3,
7.8 Hz, 2H; H-4), 7.38 (brd, 3J(H,H)=7.3 Hz, 4H; m-Bn), 7.28–7.32
H-2), 8.24 (m, 2H; H-4), 7.82 (m, 2H; H-3), 7.41 (m, 2H; H-5), 7.13
(d, J(H,H)=7.8 Hz, 4H; H-8), 6.99 (d, J(H,H)=7.8 Hz, 4H; H-7), 4.66
3
3
3
3
2
2
2
(m, J(H,H)=7.3, Hz, 6H, o-+p-Bn), 7.19 (brd, J(H,H)=7.8 Hz, 2H;
H-5), 7.14 (dd, 3J(H,H)=7.3, 4.4 Hz, 2H; H-3), 4.17 (s, 4H; H-6),
3.73 ppm (brs, 8H; H-1); 31P{1H} NMR (162 MHz, [D6]DMSO): d=
ꢀ60.3 ppm; elemental analysis calcd (%) for C28H30N4P2: C 69.41, H
6.24, N 11.56, P 12.79; found: C 69.78, H 6.26, N 11.37, P 12.96.
(d, J(H,H)=14.4 Hz, 4H; H-1A), 4.22 (dd, J(H,H)=14.4 Hz, J(P,H)=
6.4 Hz, 4H; H-1B), 2.27 ppm (s, 6H; H-6); 31P{1H} NMR (162 MHz,
CDCl3): d=ꢀ12.5 ppm (1J(Pt,P)=3054 Hz); IR (nujol): n˜ =290,
317 cmꢀ1 (PtCl); elemental analysis calcd (%) for C28H30Cl2N4P2Pt: C
44.81, H 4.03, Cl 9.45, N 7.47, P 8.25; found: C 44.68, H 4.06, Cl
9.46, N 7.51, P 8.19.
Compounds 8a and 8b: Compound 8a (0.99 g, 50%) was pre-
pared by the procedure described above for 4 from 2 (1.32 g,
7.7 mmol) and (R)-a-methylbenzylamine (0.93 g, 7.7 mmol), except
Compound 11: Compound 11 (0.14 g, 92%) was prepared by the
procedure described above for 10 from 5 (0.11 g, 0.23 mmol) and
[PdCl2(cod)] (0.065 g, 0.23 mmol), except that the reaction time
was 1 d, the reaction mixture was red, and the resultant red solid
was washed with diethyl ether. Single crystals of 11 suitable for X-
ray crystal-structure analysis were obtained by slow diffusion of n-
hexane into a solution of 11 in CH2Cl2. M.p. 2588C; 1H NMR
(400 MHz, CDCl3): d=8.75 (d, 3J(H,H)=4.6 Hz, 2H; H-2), 8.23 (d,
3J(H,H)=7.8, 4.6 Hz, 2H; H-3), 7.80 (ddd, 3J(H,H)=7.8, 10.8 Hz,
4J(H,H)=1.6 Hz, 2H; H-4), 7.41 (m, 2H; H-5), 7.15 (d, 3J(H,H)=
8.2 Hz, 4H; H-8), 7.00 (d, 3J(H,H)=8.2 Hz, 4H; H-7), 4.72 (d,
2J(H,H)=14.0 Hz, 4H; H-1A), 4.06 (dd, 2J(H,H)=14.0 Hz, 2J(P,H)=
3.7 Hz, 4H; H-1B), 2.28 ppm (s, 6H; H-6); 31P{1H} NMR (162 MHz,
CDCl3): d=3.5 ppm; IR (Nujol): n˜ =296, 282 cmꢀ1 (PdCl); elemental
analysis calcd (%) for C28H30Cl2N4P2Pd: C 50.81, H 4.57, Cl 10.71, N
8.47, P 9.36; found: C 50.68, H 4.46, Cl 10.66, N 8.51, P 9.49.
that the reaction time was 2 h. M.p. 132–1338C; [a]D20
=
1
ꢀ15 cm3 gꢀ1 dmꢀ1 (c=0.17 in C6H6); H NMR (400 MHz, CDCl3): d=
3
3
8.50 (brd, J(H,H)=4.6 Hz, 2H; H-2), 7.49 (brd, J(H,H)=7.3 Hz, 4H;
3
m-PhCH), 7.32–7.29 (m, J(H,H)=7.3, 7.4 Hz, 6H; o-+p-PhCH), 7.22
(dd, 3J(H,H)ꢁ J(H,H)ꢁ7.3 Hz, 2H; H-4), 6.97 (dd, 3J(H,H)=7.3,
3
4.6 Hz, 2H; H-3), 6.75 (d, 3J(H,H)=7.3 Hz, 2H; H-5), 4.73 (q,
3J(H,H)=6.6 Hz, 2H; H-6), 4.58 (brd, 3J(H,H)=14.8 Hz, 2H; H-1A),
3
3
3.63 (brd, J(H,H)=14.8 Hz, 2H; H-1B), 3.57 (brd, J(H,H)=14.6 Hz,
2H; H-1A’), 3.46 (brd, 3J(H,H)=14.6 Hz, 2H; H-1B’), 1.49 ppm (d,
3J(H,H)=6.6 Hz, 6H; H-7); 31P{1H} NMR (162 MHz, CDCl3): d=
ꢀ63.1 ppm; MS (EI): m/z (%): 512 (0.06) [M]+, 434 (0.25)
[MꢀC5H4N]+, 407 (0.25) [MꢀC6H5(CH)CH3]+, 402 (4.13)
[MꢀC5H5NP]+, 364 (3.15) [MꢀC10H14N]+, 256 (7.83) [C15H17N2P]+,
151 (19.49) [C5H5NP(CH)CH2N]+, 124 (13.79) [C6H7NP]+, 105 (100.0)
[C8H9]+; elemental analysis calcd (%) for C30H34N4P2: C 70.30, H 6.69,
N 10.93, P 12.09; found: C 70.38, H 6.56, N 11.03, P 12.06.
Compound 12: A solution of [PtCl2(cod)] (0.047 g, 0.13 mmol) in
CH2Cl2 (5 mL) was added to a stirred solution of 5 (0.12 g,
0.25 mmol) in CH2Cl2 (5 mL). The yellow mixture was stirred for
30 min. CH2Cl2 was removed under reduced pressure to give
a light-yellow solid, to which Et2O (5 mL) was added. The solid was
filtered off, washed with diethyl ether, and dried under reduced
pressure to give 12 (0.10 g, 62%). Single crystals of 12 suitable for
X-ray crystal-structure analysis were obtained by slow evaporation
Crystals of 8b (0.09 g, 3%) precipitated from the filtrate of the re-
action mixture. They were filtered off, washed with ethanol, and
dried at 0.05 torr for 2 h. M.p. 92–948C; [a]2D0 =+35 cm3 gꢀ1 dmꢀ1
(c=0.17 in CHCl3); 1H NMR (400 MHz, CDCl3): d=8.58 (brd,
3J(H,H)=4.2 Hz, 1H; H-2), 7.51 (dd, 3J(H,H)=8.2, 7.6 Hz, 1H; H-4),
3
7.18–7.30 (m, 11H; Ph+H-5), 7.10 (dd, J(H,H)=8.2, 4.2 Hz, 1H; H-
3
3
1
3), 3.98 (q, J(H,H)=6.7 Hz, 1H; H-6), 3.84 (q, J(H,H)=6.5 Hz, 1H;
H-6’), 3.62–3.45 (m, 4H; H-10+H-1A), 3.30–3.28 (m, 2H; H-1B), 1.37
of a solution of 12 in CDCl3. M.p. 2008C; H NMR (400 MHz, CD2Cl2):
3
3
d=8.34 (d, J(H,H)=3.8 Hz, 2H; H-2), 7.58 (d, J(H,H)=7.2 Hz, 2H;
3
3
3
3
(d, J(H,H)=6.5 Hz, 3H; H-7’), 1.19 ppm (d, J(H,H)=6.7 Hz, 2H; H-
7); 31P{1H} NMR (162 MHz, CDCl3): d=ꢀ58.1 ppm; elemental analy-
sis calcd (%) for C24H28N3P: C 74.01, H 7.25, N 10.79, P 7.95; found:
C 73.88, H 7.16, N 10.75, P 7.89.
H-5), 7.48 (dd, J(H,H)=7.2, 7.0 Hz, 2H; H-4), 7.16 (dd, J(H,H)=7.0,
3.8 Hz, 2H; H-3), 7.07 (d, 3J(H,H)=8.1 Hz, 4H; H-8), 6.94 (d,
3J(H,H)=8.1 Hz, 4H; H-7), 4.75 (d, J(H,H)=13.9 Hz, 4H; H-1A), 4.15
(d, J(H,H)=13.9 Hz, J(Pt,H)=42.2 Hz, 4H; H-1B), 2.14 ppm (s, 6H;
H-6); H NMR (400 MHz, D2O): d=8.55 (d, J(H,H)=4.6 Hz, 2H; H-2),
2
2
3
1
3
Compound 9: A solution of [PtCl2(cod)] (0.062 g, 0.17 mmol) in
CH2Cl2 (5 mL) was added to a stirred solution of 7a (0.08 g,
0.17 mmol) in CH2Cl2 (5 mL). The mixture was stirred for 30 min.
CH2Cl2 was removed under reduced pressure to give a light-yellow
solid, then Et2O (5 mL) was added. The solid was filtered off and
dried under reduced pressure to give 9 (0.08 g, 62%). M.p.>
2608C; 1H NMR (400 MHz, CDCl3): d=8.61 (brd, 3J(H,H)=4.5 Hz,
2H; H-2), 7.98–7.93 (m, 2H; H-4), 7.78–7.72 (m, 2H; H-3), 7.43 (d,
3J(H,H)=7.0 Hz, 4H; H-8), 7.38–7.31 (m, 3J(H,H)=7.0 Hz, 8H; H-
3
3
3
7.61 (dd, J(H,H)ꢁ J(H,H)ꢁ7.2 Hz, 2H; H-4), 7.44–7.39 (m, J(H,H)=
8.2 Hz, 6H; H-3+H-8), 7.34 (d, 3J(H,H)=8.2 Hz, 4H; H-7), 6.89 (d,
3J(H,H)=7.2 Hz, 2H; H-5), 4.29 (s, 3J(Pt,H)=31.9 Hz, 8H; H-1),
2.30 ppm (s, 6H; H-6); 1H NMR (400 MHz, CDCl3): d=8.43 (d,
3J(H,H)=4.3 Hz, 2H; H-2), 7.67–7.60 (m, 4H; H-5+H-4), 7.28–7.25
(m, 2H; H-3, the signal partially overlaps with the solvent signal),
3
3
7.17 (d, J(H,H)=8.2 Hz, 4H; H-8), 7.03 (d, J(H,H)=8.2 Hz, 4H; H-7),
4.79 (d, 2J(H,H)=13.9 Hz, 4H; H-1A), 4.25 (d, 2J(H,H)=13.9 Hz,
3J(Pt,H)=42.2 Hz, 4H; H-1B), 2.21 ppm (s, 6H; H-6); 31P{1H} NMR
(162 MHz, CD2Cl2): d=ꢀ15.4 ppm (1J(Pt,P)=2274.2); 31P{1H} NMR
(162 MHz, CDCl3): d=ꢀ14.3 ppm (1J(Pt,P)=2241.7 Hz); 31P{1H} NMR
(162 MHz, D2O): d=ꢀ14.8 ppm (1J(Pt,P)=2082.4 Hz); elemental
analysis calcd (%) for C56H60Cl2N8P4Pt: C 54.46, H 4.90, Cl 5.74, N
9.07, P 10.03; found: C 54.68, H 4.86, Cl 5.56, N 9.11, P 9.99.
2
2
7+H-9+H-3), 4.40 (s, 4H; H-6), 3.86 (dd, J(H,H)=14.0 Hz, J(P,H)=
5.8 Hz, 4H; H-1A), 3.78 ppm (dd, 2J(H,H)=14.0 Hz, 2J(P,H)=5.1 Hz,
4H, H-1B); 31P{1H} NMR (162 MHz, CDCl3): d=ꢀ24.2 (1J(Pt,P)=
2910 Hz); IR (nujol): n˜ =288, 315 cmꢀ1 (PtCl); elemental analysis
calcd (%) for C28H30Cl2N4P2Pt: C 44.81, H 4.03, Cl 9.45, N 7.47, P
8.25; found: C 44.78, H 3.96, Cl 9.24, N 7.23, P 8.36.
Compound 10: Compound 10 was prepared by the procedure de-
scribed above for 9 from 5 (0.10 g, 0.21 mmol) and [PtCl2(cod)]
(0.077 g, 0.21 mmol), except that the reaction time was 2 d and
the reaction mixture was yellow. CH2Cl2 was removed under re-
duced pressure to give a light-yellow solid, to which Et2O (5 mL)
was added. The solid was filtered off, carefully washed with cold
CHCl3, and dried under reduced pressure to give 10 (0.10 g, 65%).
Single crystals of 10 suitable for X-ray crystal-structure analysis
were obtained by slow diffusion of n-hexane into a solution of 10
Compound 13: Compound 13 (0.06 g, 55%) was prepared as de-
scribed above for 12 from 5 (0.10 g, 0.21 mmol) and [PdCl2(cod)]
(0.029 g, 0.10 mmol), except that the reaction mixture was red.
Single crystals of 13 suitable for X-ray crystal-structure analysis
were obtained by slow evaporation of a solution of 13 in CDCl3.
M.p.>2608C; 1H NMR (400 MHz, CDCl3): d=8.38 (d, 3J(H,H)=
4.2 Hz, 2H; H-2), 7.70 (d, 3J(H,H)=7.5 Hz, 2H; H-5), 7.58 (dd,
3
3J(H,H)=7.2, 7.5 Hz, 2H; H-4), 7.29 (dd, J(H,H)=7.2, 4.2 Hz, 2H; H-
3
3
3), 7.06 (d, J(H,H)=8.1 Hz, 4H; H-8), 6.96 (d, J(H,H)=8.1 Hz, 4H;
3179 ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2014, 20, 3169 – 3182
www.chemeurj.org

Full Paper
2
2
H-7), 4.82 (d, J(H,H)=13.8 Hz, 4H; H-1A), 3.96 (d, J(H,H)=13.8 Hz,
7+H-8), 7.06 (brd, 3J(H,H)=7.4 Hz, 2H; H-5), 4.42 (d, 2J(H,H)=
13.8 Hz, 4H; H-1A), 3.97 (d, J(H,H)=13.8 Hz, 4H; H-1B), 2.29 ppm (s,
6H; H-6); 31P{1H} NMR (162 MHz, CD3CN): d=0.7 ppm; MS (MALDI):
m/z: 1027 [Mꢀ(BF4)2]+; elemental analysis calcd (%) for
C56H60B2F8N8NiP4: C 55.99, H 5.03, N 9.33, P 10.31; found: C 55.12, H
5.12, N 9.61, P 10.23..
1
2
4H; H-1B), 2.21 ppm (s, 6H; H-6); H NMR (400 MHz, D2O): d=8.62
(d, J(H,H)=4.4 Hz, 2H; H-2), 7.64 (dd, J(H,H)=8.1, 7.2 MHz, 2H; H-
4), 7.46 (d, J(H,H)=8.4 Hz, 4H; H-8), 7.42 (dd, J(H,H)=7.2, 4.4 Hz,
2H; H-5), 7.37 (d, J(H,H)=8.4 Hz, 4H; H-7), 7.09 (d, J(H,H)=8.1 Hz,
2H; H-5), 4.37 (brd, J(H,H)=14.0 Hz, 4H; H-1A), 4.14 (d, J(H,H)=
14.0 Hz, 4H; H-1B), 2.34 ppm (s, 6H; H-6); 31P{1H} NMR (162 MHz,
CDCl3): d=ꢀ0.6 ppm; 31P{1H} NMR (D2O): d=ꢀ9.8 ppm; MS
(MALDI): m/z: 1074 [Mꢀ2Cl]+; elemental analysis calcd (%) for
C56H60Cl2N8P4Pd: C 58.67, H 5.28, Cl 6.19, N 9.77, P 10.81; found: C
58.81, H 5.24, Cl 6.25, N 9.69, P 10.76.
3
3
3
3
3
3
2
2
Compound 17:
A
solution of [Ni(CH3CN)6][BF4]2 (0.054 g,
0.14 mmol) in CH3CN (3 mL) was added to a stirred solution of 8a
(0.14 g, 0.27 mmol) in a mixture of CH3CN (3 mL) and CH2Cl2
(2 mL). The mixture was stirred for 1 d. The solvent was removed
under reduced pressure to give 17 (0.17 g, 98%) as a red-violet
solid. M.p. 158–1608C; [a]2D0 =+10 cm3 gꢀ1 dmꢀ1 (c=0.17 in CH3CN);
1H NMR (400 MHz, CDCl3): d=8.35 (d, 3J(H,H)=4.2 Hz, 2H; H-2),
Compound 14: Compound 14 (0.11 g, 92%) was prepared by the
procedure described above for 12 from 8a (0.10 g, 0.19 mmol) and
[PtCl2(cod)] (0.028 g, 0.09 mmol), except that the reaction time was
3
7.43 (dd, J(H,H)=7.2, 7.6 Hz, 2H; H-4), 7.34–7.32 (m, 6H; Ph), 7.24
(dd, 3J(H,H)=7.6, 4.2 Hz, 2H; H-3 partiallly overlaps with phenyl
1 d and the reaction mixture was dark red. M.p. 140–1428C; [a]D20
=
3
+9 cm3 gꢀ1 dmꢀ1 (c=0.03 in CH2Cl2); H NMR (400 MHz, CDCl3): d=
1
group signals), 7.23–7.20 (m, 4H; Ph), 7.03 (d, J(H,H)=7.2 Hz, 2H;
3
2
3
3
H-5), 4.06 (q, J(H,H)=6.9 Hz, 2H; H-6), 3.56 (brd, J(H,H)=13.1 Hz,
8.14 (d, J(H,H)=3.6 Hz, 2H; H-2), 7.68 (d, J(H,H)=7.2 Hz, 2H; H-5),
7.43 (dd, 3J(H,H)=7.2, 7.6 Hz, 2H; H-4), 7.22–7.31 (m, 10H; Ph),
2
2
2H; H-1A), 3.48 (brd, J(H,H)=13.2 Hz, 2H; H-1A’), 3.08 (d, J(H,H)=
13.1 Hz, 2H; H-1B’), 2.99 (d, 2J(H,H)=13.1 Hz, 2H; H-1B), 1.46 ppm
(d, 3J(H,H)=6.9 Hz, 6H; H-7); 31P{1H} NMR (162 MHz, CD3CN): d=
5.4 ppm; MS (MALDI): m/z: 1083 [Mꢀ(BF4)2]+; elemental analysis
calcd (%) for C60H68B2F8N8NiP4: C 57.31, H 5.45, N 8.91, P 9.85;
found: C 57.23, H 5.44, N 8.97, P 9.79.
3
3
7.07 (dd, J(H,H)=7.6, 3.6 Hz, 2H; H-3), 4.28 (q, J(H,H)=6.4 Hz, 2H;
2
2
H-7), 4.18 (d, J(H,H)=13.1 Hz, 2H; H-1A), 4.11 (d, J(H,H)=11.9 Hz,
2H; H-1A’), 3.62 (d, 2J(H,H)=11.9 Hz, 2H; H-1B’), 3.56 (d, 2J(H,H)=
3
1
13.1 Hz, 2H; H-1B), 1.56 ppm (d, J(H,H)=6.4 Hz, 3H; H-6); H NMR
(400 MHz, D2O): d=8.34 (d, 3J(H,H)=4.0 Hz, 2H; H-2), 7.48 (dd,
3J(H,H)=8.2, 7.3 Hz, 2H; H-4), 7.42–7.37 (m, 10H; Ph), 7.27 (dd,
3J(H,H)=4.0, 8.2 Hz, 2H; H-3), 7.01 (d, 3J(H,H)=7.3 Hz, 2H; H-5),
4.31 (q, J(H,H)=6.4 Hz, 2H; H-7), 4.09 (d, J(H,H)=14.5 Hz, 2H; H-
1A), 4.00 (d, 2J(H,H)=14.5 Hz, 2H; H-1B), 3.86 (d, 2J(H,H)=13.9 Hz,
2H; H-1 A’), 3.47 (d, 2J(H,H)=13.9 Hz, 2H; H-1B’), 1.59 ppm (d,
3J(H,H)=6.4 Hz, 3H; H-6); 31P{1H} NMR (162 MHz, CDCl3): d=
ꢀ11.7 ppm (1J(PtP)=2258.5 Hz); 31P{1H} NMR (D2O): d=ꢀ10.8 ppm
(1J(PtP)=2096 Hz); elemental analysis calcd (%) for C60H68Cl2N8P4Pt:
C 55.82, H 5.31, Cl 5.49, N 8.68, P 9.60; found: C 55.75, H 5.36, Cl
5.54, N 8.49, P 9.69.
Compound 18: A solution of ligand 5 (0.10 g, 0.21 mmol) in tolu-
ene (10 mL) was added to a stirred solution of [W(CO)4(cod)]
(0.083 g, 0.21 mmol) in CH2Cl2 (5 mL). The reaction mixture was
heated at 608C for 50 h. CH2Cl2 was removed under reduced pres-
sure and Et2O (5 mL) was added to the remaining solid. The brown
solid was filtered off, washed with diethyl ether, and dried under
reduced pressure to give 18 (0.12 g, 74%). Single crystals of 18
suitable for X-ray crystal structure analysis were obtained by slow
diffusion of n-hexane into a solution of 18 in CDCl3. M.p.>2608C;
1H NMR (400 MHz, CDCl3): d=8.71 (d, 3J(H,H)=5.1 Hz, 2H; H-2),
3
2
3
3
8.03 (m, 2H; H-3), 7.86 (dd, J(H,H)ꢁ J(H,H)=7.3 Hz, 2H; H-4), 7.33
(m, 2H; H-5), 7.05 (d, 3J(H,H)=7.9 Hz, 4H; H-8), 6.98 (d, 3J(H,H)=
7.9 Hz, 4H; H-7), 4.38 (brd, 2J(H,H)=13.3 Hz, 4H; H-1A), 3.91 (d,
2J(H,H)=13.3 Hz, 4H; H-1B), 2.24 ppm (s, 6H; H-6); 31P{1H} NMR
(162 MHz, CDCl3): d=2.6 ppm (1J(W,P)=204 Hz); IR (nujol): n˜ =
2014, 1920, 1902, 1863 cmꢀ1 (CO); elemental analysis calcd (%) for
C32H30N4O4P2W: C 49.25, H 3.87, N 7.18, P 7.94; found: C 49.34, H
3.85, N 7.11, P 7.79.
Compound 15: A solution of [NiBr2(dme)] (0.049 g, 0.16 mmol) in
CH2Cl2 (5 mL) was added dropwise to a stirred solution of 5
(0.163 g, 0.33 mmol) in CH2Cl2 (7 mL). The dark-red reaction mix-
ture was stirred for 1 d. CH2Cl2 was removed under reduced pres-
sure to give a solid, then Et2O (5 mL) was added. The solid was fil-
tered off, washed with diethyl ether, and dried under reduced pres-
1
sure to give 15 (0.12 g, 63%). M.p. 230–2318C; H NMR (400 MHz,
CDCl3): d=8.31 (m, 2H; H-2), 7.64 (m, 2H; H-3 or H-4 or H-5), 7.32
(m, 2H; H-3 or H-4 or H-5), 7.04 (m, 10H; H-3 or H-4 or H-5 + H-7
+ H-8), 4.60 (m, 4H; H-1A), 3.70 (m, 4H; H-1B), 2.28 ppm (s, 6H; H-
Compound 19: Solid NiCl2 (0.05 g, 0.38 mmol) was added to a solu-
tion of 1,3,5,7-tetraphenyl-1,5-diaza-3,7-diphosphacyclooctane[32a,b]
(0.35 g, 0.77 mmol) in DMF (20 mL) and the mixture was stirred for
24 h. The solvent was evaporated under reduced pressure, then
the resultant dark-red powder was washed with ethanol (20 mL),
and dried under reduced pressure to give 19 (0.31 g, 79%). Single
crystals of 19 suitable for X-ray crystal-structure analysis were ob-
tained by slow evaporation of a solution of 19 in chloroform. M.p.
1
3
6); H NMR (400 MHz, CD3CN): d=8.28 (d, J(H,H)=3.6 Hz, 2H; H-
3
2), 7.53–7.41 (m, 2H; H-4), 7.23 (dd, J(H,H)=3.6, 7.5 Hz, 2H; H-3),
7.06–6.96 (m, 10H; H-7+H-8+H-5), 4.54 (d, 2J(H,H)=13.5 Hz, 4H;
H-1A), 3.70 (brd, J(H,H)=13.5 Hz, 4H; H-1B), 2.22 ppm (s, 6H; H-6);
2
31P{1H} NMR (162 MHz, CDCl3): d=22.9 (brm), ꢀ10.6 ppm (brm);
31P{1H} NMR (162 MHz, CD3CN): d=35.9 (brm), ꢀ11.4 ppm (brm);
MS (MALDI): m/z: 1107 [MꢀBr]+; elemental analysis calcd (%) for
C56H60Br2N8NiP4: C 56.64, H 5.09, Br 13.46, N 9.44, P 10.43; found: C
56.81, H 5.12, Br 13.25, N 9.62, P 10.32.
1
179–1838C; H NMR (CD3CN): d=7.76–6.87 (m, 20H; Ph), 4.67–4.43
(m, 4H; PꢀCH2ꢀN), 3.96–3.67 ppm (m, 4H; PꢀCH2ꢀN); 31P{1H} NMR
(CD3CN): d=21.6 (m), ꢀ14.0 ppm (m); MS (MALDI): m/z: 1003
[MꢀCl]+; elemental analysis calcd (%) for C56H56Cl2N4NiP4: C 64.76,
H 5.43, Cl 6.83, N 5.39, Ni 5.65, P 11.93; found: C 64.73, H 5.41, Cl
6.74, N 5.65, Ni 5.63, P 11.62.
Compound 16:
A
solution of [Ni(CH3CN)6][BF4]2 (0.047 g,
0.21 mmol) in CH3CN (5 mL) was added dropwise to a stirred sus-
pension of 5 (0.101 g, 0.21 mmol) in CH3CN (5 mL) The dark-red re-
action mixture was stirred for 1 d. CH3CN was removed under re-
duced pressure to give a solid. The solid was filtered off, washed
with diethyl ether, and dried under reduced pressure to give 16
(0.23 g, 90%). Single crystals of 16 suitable for X-ray crystal struc-
ture analysis were obtained by slow diffusion of ethanol into a solu-
Acknowledgements
Financial support from RFBR (No. 12-03-97083-r_povolzhye_a,
13-03-00139, 13-03-00563), President’s of RF Grant for the sup-
port of leading scientific schools (No. NSh-4428.2014.3), the
Ministry of Science and Education (state contract 8432) and
1
tion of 16 in acetone. M.p. 196–1988C; H NMR (400 MHz, CD3CN):
3
3
d=8.45 (d, J(H,H)=4.0 Hz, 2H; H-2), 7.52 (dd, J(H,H)=7.0, 7.4 Hz,
3
2H; H-4), 7.33 (dd, J(H,H)=7.0, 4.0 Hz, 2H; H-3), 7.21 (brs, 8H; H-
Chem. Eur. J. 2014, 20, 3169 – 3182
www.chemeurj.org
3180
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
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the VolkswagenStiftung, Germany (Az. 85 625) is gratefully ac-
knowledged.
Keywords: diazadiphosphacyclooctanes · electrochemistry ·
hydrogen · metal complexes · pyridylphosphines
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