Coordination behavior of the (diphenylphosphanyl)[α-(2-pyridyl) benzyl]amide anion toward lithium and zinc cations

Article abstract of DOI:10.1002/ejic.201000039

A two-step synthesis allows the preparation of [α-(2-pyridyl)benzyl] amine (1) in good yield. Phosphanylation in the presence of triethylamine gives (diphenylphosphanyl)[α-(2-pyridyl)benzyljamine (2), which crystallizes as a racemate in the centrosymmetric triclinic space group P1. The P-N bond lengths exhibit an average value of 168.3 pm. Lithiation of 2 with n-butyllithium yields dimeric semi(tetrahydrofuran)lithium (diphenylphosphanyl)[α-(2- pyridyl)benzyl]amide (3) with the lithium atoms in different environments. One Li atom, is in a distorted, tetrahedral environment and the other in a trigonal-planar coordination sphere with bridging amide moieties (av. Li-N 201.8, Li-O 192.4 pm). Zincation of 2 with dimethylzinc leads to the formation of dimeric methylzinc (diphenylphosphanyl)[α-(2-pyridyl)benzyr]amide (4) with a central six-membered (ZnNP)₂ ring in a boat conformation (av. Zn-N 201.8, Zn-P 245.9 pm). The endocyclic P-N bonds are rather short (av. value 162.7 pm).

Full text of DOI:10.1002/ejic.201000039

FULL PAPER
DOI: 10.1002/ejic.201000039
Coordination Behavior of the (Diphenylphosphanyl)[α-(2-pyridyl)benzyl]amide
Anion toward Lithium and Zinc Cations
Dirk Olbert,[a] Helmar Görls,[a] Delf Conrad,[a] and Matthias Westerhausen*[a]
Keywords: Pyridylmethylamines / Lithium / Zinc / Metalation reactions / C–C coupling reactions
A two-step synthesis allows the preparation of [α-(2-pyridyl)-
benzyl]amine (1) in good yield. Phosphanylation in the pres-
ence of triethylamine gives (diphenylphosphanyl)[α-(2-pyr-
atom is in a distorted tetrahedral environment and the other
in a trigonal-planar coordination sphere with bridging amide
moieties (av. Li–N 201.8, Li–O 192.4 pm). Zincation of 2 with
idyl)benzyl]amine (2), which crystallizes as a racemate in the dimethylzinc leads to the formation of dimeric methylzinc
¯
centrosymmetric triclinic space group P1. The P–N bond
(diphenylphosphanyl)[α-(2-pyridyl)benzyl]amide (4) with a
central six-membered (ZnNP)2 ring in a boat conformation
(av. Zn–N 201.8, Zn–P 245.9 pm). The endocyclic P–N bonds
are rather short (av. value 162.7 pm).
lengths exhibit an average value of 168.3 pm. Lithiation of 2
with n-butyllithium yields dimeric semi(tetrahydrofuran)lith-
ium (diphenylphosphanyl)[α-(2-pyridyl)benzyl]amide (3)
with the lithium atoms in different environments. One Li
The redox potential of the organometallics determines
whether an oxidative C–C coupling reaction occurs. Organo-
lithium and -magnesium reagents are able to doubly depro-
tonate (2-pyridylmethyl)amines to give (L)2–, but the redox
potentials of these metals prevent an oxidative C–C coupling
reaction.[2,5] Oxidation can be achieved by addition of an
oxidizing reagent. Thus, addition of white phosphorus to a
solution of Li2(L) leads to the formation of Li2(Lox12) and
Li3P7.[9] Dialkylzinc is a weaker metalating reagent, and
higher temperatures are necessary to perform a double de-
protonation. However, under these reaction conditions the
dianion is immediately oxidized, and zinc metal precipitates
from the reaction mixture, thus yielding the dinuclear zinc
complex of (Lox12)2–, namely, (RZn)2(Lox12).[1,2] Even
stronger oxidizing reagents such as iron(III) compounds are
necessary to prepare the imines (Lox2)0 by means of a second
oxidation step.[16] It is noteworthy that the oxidative C–C
coupling reaction occurs only with deprotonated (2-pyr-
idylmethyl)amines, whereas (2-pyridylmethyl)amine (H2L)
itself can act as a ligand even for iron(III) if deprotonation
is impossible due to a lack of nucleophilicity of the anion
[see, for example, the (H2L) complexes of iron chlorides].[17]
Also, adducts of (2-pyridylmethyl)amine with zinc(II) are
well known without deprotonation reactions if anions with-
out nucleophilic character are present {see, for example, the
complexes of zinc(II) halide of the types [(H2L)ZnX2], [(H2L)2-
ZnX2], and [(H2L)3ZnX2]}.[18]
Introduction
Primary and secondary (2-pyridylmethyl)amines (H2L)
offer a surprisingly wide spectrum of reactivity depending
on the N-substituent. Deprotonation with organometallics
such as LiR and ZnR2 leads to the formation of the corre-
sponding lithium and zinc amides.[1–8] Starting from these
amides (HL)– (Scheme 1) a fascinating chemistry opens up.
A second metalation step yields the dianion (L)2–, which is
stabilized by delocalization of the negative charge and be-
haves mostly as a bis(amide).[2,5] These bis(amides) can be
oxidized, thereby leading to radical anions (Lox1)·–, which
easily dimerize with C–C bond formation to (Lox12)2–.[1–3,9]
Another single-electron oxidation yields the neutral imines
(Lox2)0. The reaction behavior of the secondary (2-pyr-
idylmethyl)amines strongly depends on the metalating
power of the organometallics, the redox potential of the
metals, and also on the nature of the N-bound group R, the
bulkiness and electronic properties of which play a key role.
If R represents a tert-butyl group, an equilibrium between
the radical anion (Lox1 ·–
)
and its dimer (Lox1
)
was ob-
2–
2
served in solution,[10–13] whereas in the solid state only the
dimer was found.[13,14] If trialkylsilyl groups are bound at
the amide nitrogen atom, the radical anion (L )
ox1 ·– was nei-
ther detected in solution nor in the solid state.[1,2] However,
the metathesis reaction of Na(Lox1) with ZnCl2 allowed the
isolation of crystalline Zn(Lox1)2 when bulky aryl groups
were bound at the amido group.[15]
The influence of another Lewis base at the amide nitro-
gen atom was investigated by using (diphenylphos-
phanyl)(2-pyridylmethyl)amine.[19] The N-bound diphenyl-
phosphanyl group allows the detection of the reaction by
means of 31P{1H} NMR spectroscopy; however, it also in-
fluences the chemistry of the (2-pyridylmethyl)amines. On
[a] Institut für Anorganische und Analytische Chemie, Friedrich-
Schiller-Universität Jena,
August-Bebel-Str. 2, 07743 Jena, Germany
Fax: +49-3641-948102
E-mail: m.we@uni-jena.de
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D. Olbert, H. Görls, D. Conrad, M. Westerhausen
FULL PAPER
Scheme 1. Reactivity pattern of (2-pyridylmethyl)amines. The upper line shows the deprotonation/protonation equilibria, the right column
the oxidation/reduction equilibria.
the one hand, another coordination site at the phosphorus
moiety is available; on the other hand, the oxidative C–C
Results and Discussion
Synthesis of [α-(2-Pyridyl)benzyl]amine (1)
coupling reaction is hindered in comparison to compounds
with N-bound trialkylsilyl groups.[19]
The synthesis of 1 was accomplished by means of a two-
Several experiments showed that delocalization of the an-
ionic charge represents a requirement for the oxidation of
these amines. Therefore, [2-(2-pyridyl)ethyl]amine can only
be deprotonated once, and no C–C coupling occurs under
similar reaction conditions.[20] Other preparative procedures
are necessary to synthesize 1,4-diamino-2,3-bis(2-pyridyl)-
butanes.[21] We were interested in the influence of a phenyl
group at the methylene moiety of the (2-pyridylmethyl)-
amines on the coordination behavior of ligand (HL)–. Due
to the fact that a phenyl group raises the acidity of the re-
maining proton and would be able to interfere with the
charge after a second deprotonation, the diphenylphos-
phanyl group was chosen to suppress a second deprotonation
step, thus avoiding the formation of (phosphanyl)[α-(2-pyr-
idyl)benzylidene]amines. Dyer et al.[22] already showed that
these compounds act as N,P-chelating ligands for rhodi-
um(II), palladium(II), and platinum(II) and that these com-
plexes are able to copolymerize carbon monoxide and alkene.
In addition, an equilibrium according to Equation (1) was
observed depending on the P-bound substituents. With R =
Ph the monocyclic “open” form is favored,[22] whereas the
bicyclic “closed” form with the broken aromaticity is the
major component for R = NiPr2.[23]
step procedure starting from commercially available phenyl
2-pyridyl ketone according to a literature procedure.[24]
A
subsequent reduction of the oxime in a heterogenic mixture
of zinc, ammonium acetate, and ammonia in ethanol
yielded racemic 1 as a light yellow oil after distillation in
vacuo according to Equation (2).[25] Our present investi-
gations focus on the coordination chemistry of these biden-
tate bases, and therefore (S) and (R) enantiomers of 1 were
not separated.
(2)
The introduction of N-phosphanyl substituents[19] at the
amide functionality of (2-pyridylmethyl)amine is possible
through a two-step sequence that involves lithiation of the
amine at –78 °C followed by a metathesis reaction with
chlorodiphenylphosphane to yield (diphenylphosphanyl)(2-
pyridylmethyl)amine. The additional phenyl group at the
methylene unit did not hinder this reaction sequence, but
we also obtained at least two minor byproducts, namely,
bis(diphenylphosphanyl)[α-(2-pyridyl)benzyl]amine
and
tetraphenyldiphosphane. Due to the fact that purification
of (diphenylphosphanyl)[α-(2-pyridyl)benzyl]amine (2)
through distillation or sublimation in vacuo failed, all reac-
(1) tions were accompanied by traces of these byproducts. To
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Coordination Behavior of (2-Pyridylmethyl)amide Anions
suppress these side reactions, attempts were undertaken to observed for bis(diphenylphosphanyl)(2-pyridylmethyl)-
employ milder deprotonation reagents. A mixture of trieth- amine[19] as well as for N-trialkylsilyl-substituted (2-pyr-
ylamine and catalytic amounts of 4-(dimethylamino)pyr- idylmethyl)amines.[26,27]
idine (dmap) was added to a solution of amine 1 in tetra-
hydrofuran. Whereas deprotonation and phosphanylation
succeeded without formation of any byproduct, separation
of the desired product 2 from an excess of dmap proved to
be challenging. Therefore, we tested this reaction without
the addition of catalytic amounts of dmap according to
Equation (3). If an excess amount of NEt3 (20 mol-%) was
applied, product 2 was obtained in good yield after removal
of solid triethylammonium chloride by filtration and excess
triethylamine by distillation under reduced pressure.
Metalation of (Diphenylphosphanyl)[α-(2-pyridyl)-
benzyl]amine (2)
Lithiation of 2 with n-butyllithium yielded colorless di-
meric semi(tetrahydrofuran)lithium (diphenylphosphan-
yl)[α-(2-pyridyl)benzyl]amide (3) according to Scheme 2. In
this dinuclear complex, the lithium atoms show different
coordination environments. One lithium atom is sur-
rounded tetrahedrally by four nitrogen atoms, whereas the
other one is in a trigonal-planar environment of the two
amide functionalities and an oxygen atom of the tetra-
hydrofuran molecule. A very similar molecular structure
was observed for dimeric semi(tetrahydrofuran)lithium
(tert-butyldimethylsilyl)(2-pyridylmethyl)amide.[5] Metala-
tion of 2 with dimethylzinc gave heteroleptic complexes of
colorless methylzinc (diphenylphosphanyl)[α-(2-pyridyl)-
benzyl]amide (4), which crystallized from a solution in tolu-
ene as a dimer with tetracoordinate zinc atoms. In contrast
to the lithium derivative, the zinc compound showed a dif-
ferent molecular structure from its trialkylsilyl congener,
which formed a four-membered Zn2N2 ring.[1,2]
(3)
Figure 1 shows the molecular structure and numbering
scheme of the (S) isomer of 2. However, due to the centro-
symmetric space group, the crystalline material contains a
racemate of 2. The hydrogen atom at N1 was refined freely,
and the environment of the nitrogen atom N1 is nearly
planar considering the estimated standard deviation (e.s.d.)
values. The phosphorus atom P is embedded in a trigonal-
pyramidal environment. The P–N1 bond of 168.3(2) pm is
rather short, which can be understood as a consequence of
a negative hyperconjugation from the pz(N1) lone pair into
a σ*(P–C19) orbital. This fact would also explain the slight
elongation of the P–C19 bond [184.4(2) pm] relative to the
P–C13 distance of 182.7(2) pm. Similar effects have been
Scheme 2. Metalation of 2.
Spectroscopic Characterization
Selected NMR spectroscopic data of 1, 2, 3, and 4 are
compared in Table 1. Due to the low solubility of 4 in hy-
drocarbons, the NMR spectroscopic data of this zinc com-
pound were recorded as solutions in [D8]thf. The reso-
nances of the methine proton, of the tertiary carbon atom
as well as of the 31P atom, are shifted towards higher fields
Figure 1. Molecular structure of the (S) isomer of 2. The ellipsoids
represent a probability of 40%. Aryl hydrogen atoms are omitted
for clarity reasons. Selected bond lengths [pm] and angles [°]: P–N1
168.3(2), P–C13 182.7(2), P–C19 184.4(2), N1–C1 146.0(3), N1–H
83.0(2), C1–C2 152.4(3), C1–C7 152.5(3); C1–N1–P 124.64(15),
C1–N1–H 115.0(16), P–N1–H 113.7(16), N1–P–C19 130.09(11),
N1–P–C13 103.27(10), C19–P–C13 100.62(11).
Eur. J. Inorg. Chem. 2010, 1791–1797
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D. Olbert, H. Görls, D. Conrad, M. Westerhausen
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upon phosphanylation and metalation due to an enhanced
As already mentioned, the lithium atoms show different
shielding of the nitrogen atom. Metalation also leads to sig- coordination environments. One lithium atom (Li2) is lo-
3
nificantly larger J(H,P) coupling constants.
cated in the center of a distorted tetrahedron and coordi-
nated by two amide moieties and two pyridyl units. The
other lithium cation (Li1) is situated in a trigonal-planar
environment and binds to two nitrogen atoms and one
Table 1. Comparison of selected NMR spectroscopic data (chemi-
cal shifts, δ [ppm]; coupling constants, J [Hz]) of the unsubstituted
amine 1 (in CDCl3), the N-phosphanyl-substituted ligand 2 (in
C6D6), the lithium salt 3 (in C6D6), and the methylzinc complex 4 tetrahydrofuran molecule. Similar structures of N-trialkyl-
(in [D8]thf).
silyl-substituted (2-pyridylmethyl)amides were observed
earlier,[5] whereas lithium (diphenylphosphanyl)(2-pyridyl-
1
2
3
4
methyl)amide adopts a different structure.[28] The bridging
fashion of the amide functionality and the higher coor-
dination number of the nitrogen atoms lead to significant
changes of the structural parameters. Nevertheless, rather
short P–N bonds [165.7(3) and 165.9(3) pm] are observed
in compound 3, but in comparison to the free amine 2 they
are only slightly shorter (Table 2). The reason for this short-
ening is the higher electrostatic attraction between the de-
protonated amide function and the phosphanyl group.
1H NMR
δ(CHalkyl
)
5.17
–
5.48
8.4
5.76
21.4
5.46
17.2
3J(H,P)
13C{1H} NMR
δ(CHalkyl
)
60.7
–
65.8
22.4
71.6
13.7
67.7
20.8
2J(P,C)
31P{1H} NMR
δ(P)
–
42.2
52.4
46.8
Molecular Structures
Table 2. Selected average bond lengths [pm] and angles [°] of 2 and
its lithium (3) and zinc derivative (4).
The molecular structure of dimeric 3 is displayed in Fig-
ure 2. In principle, the three different (S,S), (R,R), and
(S,R) isomers are possibly based on the chirality of the terti-
ary carbon atoms C6 and C30. This dimer nearly adopts
C2 symmetry and crystallizes in a centrosymmetric space
group. Therefore, the crystalline material contains a race-
mate of the (S,S) and (R,R) isomers.
2
3
4
N–H/Li/Zn
N–P
83
168.3
146.0
182.7
184.4
–
124.6
114
115
103.1
103.3
100.6
–
–
–
201.8
165.8
147.5
–
201.8
162.7
145.8
–
N–C
P–CI
P–CII
–
–
P–Zn
–
120.6
–
245.9
122.2
125.2
112.4
109.3
110.4
102.1
107.2
110.5
117.1
P–N–C
P–N–H/Zn
C–N–H/Zn
N–P–CI
N–P–CII
CI–P–CII
N–P–Zn
CI–P–Zn
CII–P–Zn
–
110.8
107.0
99.3
–
–
–
The molecular structure and numbering scheme of di-
meric 4 is displayed in Figure 3. The zinc atoms are located
in distorted tetrahedrons, and each binds to a methyl group,
an amide moiety, a pyridyl unit, and a phosphorus atom.
This fact leads to a large number of possible isomers, based
on the chirality of the zinc atoms and of the tertiary carbon
atoms C6A and C6B. However, the dimeric dinuclear com-
plex exhibits nearly C2 symmetry with a C2 axis perpendicu-
lar to the six-membered (ZnNP)2 ring. Due to this fact,
both carbon atoms and both zinc atoms show the same
configuration. Crystallization in a centrosymmetric space
Figure 2. Molecular structure of dimeric 3. The ellipsoids represent
a probability of 40%. Hydrogen atoms are omitted for reasons of
clarity. Selected bond lengths [pm] and angles [°]: Li1–O1 192.4(7),
Li1–N2 200.1(6), Li1–N4 202.6(6), Li2–N1 199.8(6), Li2–N2 group leads to a racemate in the crystalline state.
204.7(6), Li2–N3 204.3(6), Li2–N4 201.3(6), P1–N2 165.7(3), P2–
N4 165.9(2), N2–C6 148.2(4), N4–C30 146.8(4); O–Li1–N2
Zn2N2 ring, and a six-membered (ZnNP)2 cycle with a boat
127.2(3), O–Li1–N4 126.0(3), N2–Li1–N4 106.5(3), N1–Li2–N4
Steric crowding hinders the formation of a four-membered
conformation is formed. This molecular structure is unique
132.5(3), N1–Li2–N2 85.6(2), N4–Li2–N2 105.3(3), N1–Li2–N3
and stands in contrast to earlier reported structures of zinc-
ated (2-pyridylmethyl)amines in which the dimer is formed by
means of a planar four-membered Zn2N2 ring.[1,2] The ad-
ditional phenyl group puts a larger steric pressure on the mo-
lecule and forces dimerization through the phosphorus atoms.
Despite the larger coordination number of the phosphorus
115.9(3), N4–Li2–N3 85.6(2), N2–Li2–N3 139.5(3), C6–N2–P1
120.1(2), C6–N2–Li1 132.5(3), P1–N2–Li1 99.0(2), C6–N2–Li2
109.5(3), P1–N2–Li2 113.2(2), C30–N4–P2 121.1(2), C30–N4–Li2
109.4(3), P2–N4–Li2 113.3(2), C30–N4–Li1 131.2(3), P2–N4–Li1
98.7(2), N2–P1–C19 110.15(16), N2–P1–C13 107.49(16), C19–P1–
C13 98.97(17), N4–P2–C43 11.43(16), N4–P2–C37 106.53(15),
C43–P2–C37 99.63(15).
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Coordination Behavior of (2-Pyridylmethyl)amide Anions
with triethylamine as a base. Subsequent reaction with chlor-
odiphenylphosphane allowed the synthesis of the desired N-
substituted product 2 in very good yields and with high pu-
rity. According to crystal-structure analysis of the phos-
phanyl-substituted [α-(2-pyridyl)benzyl]amine, the planar
amine functionality allows hyperconjugation and back-do-
nation of electron density into antibonding P–C bonds.
Deprotonation of
2 with n-butyllithium in tetra-
hydrofuran yields a dinuclear lithium(I) complex, which is
structurally related to the N-trialkylsilyl-substituted (2-pyr-
idylmethyl)amides that crystallized from tetrahydrofuran.
The zinc derivative 4 obtained from the zincation of 2 with
ZnMe2 forms a stable six-membered (ZnNP)2 ring in a boat
conformation, which is stabilized by a delocalization of the
anionic charge within the P–N moieties.
Figure 3. Molecular structure of dimeric 4. The ellipsoids represent
a probability of 40%. Aryl hydrogen atoms are omitted for reasons
of clarity. The asymmetric unit contains one additional toluene mo-
lecule, which is not shown in this representation. Selected bond
lengths [pm] and angles [°]: ZnA–C13A 198.3(3), ZnB–C13B
198.4(3), ZnA–N1A 213.8(2), ZnB–N1B 213.6(2), ZnA–N2A
201.4(2), ZnB–N2B 202.2(2), ZnA–P1A 246.21(8), ZnB–P1B
245.52(7) P1A–N2B 163.2(2) P1B–N2A 162.2(2) N2A–C6A
146.0(3) N2B–C6B 145.6(3); C13A–ZnA–N2A 126.87(11), C13–
ZnA–N1A 119.00(12), N2A–ZnA–N1A 79.51(9), C13A–ZnA–P1A
119.33(9), N2A–ZnA–P1A 101.35(7), N1A–ZnA–P1A 102.37(7),
C13B–ZnB–N2B 125.76(12), C13B–ZnB–N1B 119.49(13), N2B–
ZnB–N1B 79.77(9), C13B–ZnB–P1B 121.02(11), N2B–ZnB–P1B
101.02(7), N1B–ZnB–P1B 100.62(6), C6A–N2A–P1B 121.52(18),
C6A–N2A–ZnA 112.21(17), P1B–N2A–ZnA 125.96(13), C6B–
N2B–P1A 122.79(18), C6B–N2B–ZnB 112.62(17), P1A–N2B–ZnB
124.37(13), N2B–P1A–C14A 109.36(13), N2B–P1A–C20A
111.00(12), C14A–P1A–C20A 102.25(13), N2B–P1A–Zn1A
107.56(8), C14A–P1A–Zn1A 110.16(9), C20A–P1A–Zn1A
Experimental Section
General Procedure: All manipulations were carried out under ar-
gon, and the solvents were thoroughly dried. IR spectra were re-
corded with Nujol solutions between KBr windows if not stated
otherwise. The found N and C values of the elemental analyses
deviate from calculated values because weighing of these moisture-
sensitive compounds was challenging and also because of nitride
and carbonate formation during combustion, even though V2O5
was added.
Synthesis of N-Hydroxy-1-phenyl-1-(2-pyridyl)methanimine: Phenyl
(2-pyridyl) ketone (10.0 g, 54.6 mmol) and hydroxylamine hydro-
chloride (6.0 g, 86.0 mmol) were dissolved in a mixture of ethanol
(40 mL) and water (4 mL). While the colorless suspension was
stirred, solid sodium hydroxide (11.0 g, 275.0 mmol) was added
stepwise. This suspension was stirred at room temp. for an ad-
ditional 4 h, during which time the color of the solution turned
yellowish. After addition of water (50 mL), the solution became
clear. Dry ice was added until the oxime precipitated. All solids
were collected and dried in vacuo. Yield: 9.91 g (50.0 mmol, 91%).
116.33(10),
N2A–P1B–C14B
109.31(13),
N2A–P1B–C20B
109.78(13), C14B–P1B–C20B 102.00(13), N2A–P1B–Zn1B
106.74(8), C14B–P1B–Zn1B 110.92(9) C20B–P1B–Zn1B 117.89(9).
1
M.p. 151 °C. H NMR (400 MHz, CDCl3): δ = 9.61 (s, 1 H, OH),
atoms, rather short P–N distances of 163.2(2) pm are ob-
served. This finding can easily be explained by the mesomeric
valence bond structures as shown in Scheme 3.
3
3
8.61 [d, J(H,H) = 4.4 Hz, 1 H, H1], 7.66 [dd, J(H,H) = 7.6 Hz, 1
3
H, H3], 7.55 [d, J(H,H) = 8.0 Hz, 1 H, H4], 7.44 (m, 5 H, PhH),
7.25 [dd, 3J(H,H) = 4.4 Hz, 1 H, H2] ppm. 13C{1H} NMR
(50 MHz, CDCl3): δ = 156.5 (C6), 154.6 (C5), 149.5 (C1), 136.5
(C3), 131.7 (C7), 129.4 (C8, C12), 129.1 (C10), 128.1 (C9, C11), 123.6
(C2), 122.9 (C4) ppm. MS (EI): m/z (%) = 198 (75) [M]+, 181 (12)
[M – OH]+, 167 (100) [M – NOH]+. IR (KBr pellet): ν = 3189 (vs),
˜
3084 (s), 3060 (s), 3011 (m), 2926 (m), 1960 (vw), 1891 (vw), 1584
(s), 1566 (m), 1497 (w), 1469 (vs), 1442 (s), 1428 (s), 1328 (m), 1284
(w), 1246 (vw), 1178 (vw), 1152 (vw), 1095 (w), 1072 (vw), 1051
(w), 1034 (w), 1006 (vs), 993 (s), 946 (vs), 912 (m), 886 (vw), 791
(s), 771 (s), 744 (s), 702 (vs), 685 (m), 654 (w), 623 (w), 570 (vw),
490 (w), 469 (w) cm–1. C12H10N2O (198.22): calcd. C 72.71, H 5.01,
N 14.07; found C 72.24, H 5.08, N 14.13.
Synthesis of 1: N-Hydroxy-1-phenyl-1-(2-pyridyl)methanimine
(9.9 g, 50 mmol) and ammonium acetate (2 g, 26 mmol) were dis-
solved in a mixture of a concentrated aqueous NH3 solution
(250 mL) and ethanol (50 mL). Then zinc dust (13 g, 200 mmol)
was added. The resulting suspension was stirred at reflux for 2 h.
After cooling to room temp., the excess amount of zinc was filtered
off and washed with toluene. The filtrate was extracted with diethyl
ether (3ϫ50 mL). Then a 50% NaOH solution (10 mL) was added.
This solution again was extracted with diethyl ether (2ϫ50 mL).
Scheme 3. Mesomeric valence bond presentations of dimeric 4.
Conclusion
Ligand synthesis by means of metathesis reactions of lithi-
ated (2-pyridylmethyl)amides with chlorophosphanes was
improved by involving a very mild deprotonation protocol The ethereal fractions were combined, dried with Na2SO4, and the
Eur. J. Inorg. Chem. 2010, 1791–1797
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1795

D. Olbert, H. Görls, D. Conrad, M. Westerhausen
FULL PAPER
solvents were removed in vacuo. The remaining oil was distilled in
vacuo to yield a light yellow oily liquid. Yield: 6.0 g (32.7 mmol,
(C3), 131.9 [d, 1J(C,P) = 9.8 Hz, o-C2(PPh2)], 131.5 [d, 1J(C,P) =
9.9 Hz, o-C1(PPh2)], 128.5–127.1 [m-C(PPh2), p-C(PPh2), m-C(Ph),
65%). 1H NMR (400 MHz, CDCl3): δ = 8.49 [d, 3J(H,H) = 4.8 Hz, p-C(Ph)], 122.1 (C4), 121.6 (C2), 65.8 [d, 2J(C,P) = 22.4 Hz, C6]
3
3
1 H, H1], 7.47 [dd, J(H,H) = 7.6 Hz, 1 H, H3], 7.36 [d, J(H,H) = ppm. 31P{1H} NMR (162 MHz, C6D6): δ = 42.2 ppm. MS (EI):
8.4 Hz, 2 H, o-Ph], 7.24 [dd, 3J(H,H) = 8.0 Hz, 2 H, m-Ph], 7.18
m/z (%) = 368 (76) [M]+, 200 (100) [M – HC(Py)(Ph)]+, 183 (77)
[d, J(H,H) = 7.6 Hz, 1 H, H4], 7.15 [dd, J(H,H) = 4.0 Hz, 1 H,
[M – PPh ]+, 168 (45) [M – HNPPh ]+. IR (neat): ν = 3348 (w),
3
3
˜
2
2
p-Ph], 7.02 [dd, 3J(H,H) = 4.8 Hz, 1 H, H2], 5.17 (s, 1 H, H6), 2.14 3053 (s), 3025 (m), 2919 (w), 2849 (w), 1951 (vw), 1888 (vw), 1811
(s, 2 H, NH2) ppm. 13C{1H} NMR (50 MHz, CDCl3): δ = 163.1 (vw), 1752 (vw), 1588 (s), 1569 (m), 1494 (m), 1476 (s), 1452 (m),
(C5), 148.7 (C1), 144.5 (C7), 136.1 (C3), 128.1 (C9, C11), 126.8 (C8,
C10, C12), 121.5 (C2), 121.2 (C4), 60.7 (C6) ppm. MS (EI): m/z (%)
= 184 (70) [M]+, 168 (100) [M – NH2]+, 107 (94) [M – Ph]+. IR
1433 (vs), 1392 (m), 1305 (w), 1282 (w), 1242 (w), 1184 (m), 1148
(m), 1089 (m), 1068 (m), 1047 (w), 1027 (m), 997 (m), 970 (w), 917
(w), 841 (w), 743 (vs), 696 (s), 636 (vw), 613 (w), 550 (w), 516 (m),
465 (m) cm–1.
(Nujol): ν = 3370 (w), 3270 (w), 3060 (w), 2924 (vs), 2854 (vs),
˜
1925 (vw), 1901 (vw), 1588 (s), 1569 (m), 1492 (m), 1467 (s), 1433
(s), 1377 (m), 1266 (w), 1147 (w), 1046 (m), 1027 (m), 994 (m), 907
(w), 811 (m), 747 (s), 699 (s), 653 (w), 617 (w), 598 (w), 556 (w)
cm–1. C12H12N2 (184.23): calcd. C 78.22, H 6.57, N 15.21; found
C 77.66, H 6.57, N 15.01.
Synthesis of 3: A 1.6  solution of n-butyllithium (0.46 mL) in hex-
ane was added dropwise to a cooled (–78 °C) and stirred solution
of 2 (0.27 g, 0.74 mmol) in thf (5 mL). After complete addition, the
solution was slowly warmed to room temp. and stirred overnight.
The solution color changed to deep brown. After removal of all
volatiles, thf (2 mL) was added, and the desired compound crys-
tallized at –78 °C within 2 d. Yield: 246 mg (0.30 mmol, 80%). M.p.
Synthesis of 2: Compound 1 (1.2 g, 6.6 mmol) was dissolved in tol-
uene (20 mL), and then triethylamine (0.80 g, 8.0 mmol) was
added. A solution of chlorodiphenylphosphane (1.46 g, 6.6 mmol)
in toluene (10 mL) was added to this mixture, while stirring was
continued at room temp. During the addition of the chlorodiphen-
ylphosphane solution, colorless triethylamine hydrochloride pre-
cipitated. The reaction solution was stirred at room temperature
overnight. The precipitate was removed, washed with toluene, and
all volatiles were removed in vacuo, thus yielding a clear, almost
colorless oily liquid. Yield: 2.3 g (6.3 mmol, 93%). 1H NMR
1
3
103 °C (dec.). H NMR (200 MHz, C6D6): δ = 7.92 [d, J(H,H) =
3
7.9 Hz, 1 H, H1], 7.72 [d, J(H,H) = 9.4 Hz, 2 H, o-Ph], 7.63 (m, 4
3
H, o-PPh2), 7.16 [dd, J(H,H) = 7.6 Hz, 2 H, m-Ph], 7.28 (m, 9 H,
3
m-PPh2), 6.98 (m, 1 H, p-PPh2), 6.84 [dd, J(H,H) = 7.4 Hz, 1 H,
p-Ph], 6.68 [dd, 3J(H,H) = 7.4 Hz, 1 H, H3], 6.52 [d, 3J(H,H) =
8.0 Hz, 1 H, H4], 6.33 [dd, 3J(H,H) = 5.8 Hz, 1 H, H2], 5.76 [d,
3J(H,P) = 21.4 Hz, 1 H, CH], 3.27 (m, 2 H, OCH2), 1.24 (m, 2 H,
CH2) ppm. 13C{1H} NMR (50 MHz, C6D6): δ = 171.5 (br., C5),
(400 MHz, C6D6): δ = 8.32 [d, 3J(H,H) = 5.2 Hz, 1 H, H1], 7.52 150.5 [i-C(Ph)], 148.3 [d, 1J(C,P) = 30.0 Hz, i-C(PPh2)], 147.5 (C1),
[dd, 3J = 6.0 Hz, 4 H, o-CH1(PPh2)], 7.45 [dd, 3J = 6.0 Hz, 4 H, o- 136.2 (C3), 133.1 [d, 2J(C,P) = 20.3 Hz, o-C(PPh2)], 129.1 [o-C(Ph)],
3
CH2(PPh2)], 7.35 [d, J(H,H) = 7.6 Hz, 2 H, o-Ph], 7.12–6.95 (m,
126.9 [m-C(PPh2)], 126.7 [p-C(PPh2)], 128.3 [m-C(Ph)], 125.8 [p-
9 H, m,p-Ph, m,p-PPh2), 6.86 [dd, 3J(H,H) = 7.6 Hz, 1 H, H3], 6.71 C(Ph)], 123.7 (C4), 120.6 (C2), 71.6 [d, 2J(C,P) = 13.7 Hz, CH],
3
3
[d, J(H,H) = 7.6 Hz, 1 H, H4], 6.48 [dd, J(H,H) = 4.8 Hz, 1 H,
67.9 (OCH2) 25.5 (CH2) ppm. 31P{1H} NMR (81 MHz, C6D6): δ
H2], 5.48 [dd, J(P,H) = 8.4 Hz, 1 H, CH], 4.36 [dd, J(P,H) = 9.0, = 52.4 ppm. 7Li NMR (149 MHz, [D6]benzene): δ = 3.1 (LiN4), 1.6
3
2
3J(H,H) = 5.0 Hz, 1 H, NH] ppm. 13C{1H} NMR (50 MHz, C6D6): (LiN O) ppm. IR (Nujol): ν = 3165 (vw), 3136 (vw), 3053 (m),
˜
2
δ = 162.7 [d, J(C,P) = 6.3 Hz, C5], 149.0 (C1), 145.2 [d, J(C,P) = 2924 (vs), 2854 (vs), 2722 (vw), 2669 (vw), 2607 (vw), 2048 (vw),
3
3
4.0 Hz, i-C(Ph)], 142.8 [d, 1J(C,P) = 14.7 Hz, i-C(PPh2)], 135.9
1957 (w), 1884 (w), 1809 (vw), 1766 (vw), 1722 (vw), 1660 (vw),
Table 3. Crystal data and refinement details for the X-ray structure determinations of 2, 3, and 4.
2
3
4
Empirical formula
Mr [gmol–1]
T [K]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C24H21N2P
368.39
183(2)
C52H48Li2N4OP2·C4H8O
892.87
183(2)
monoclinic
P21/n (no. 14)
10.2964(2)
27.6523(8)
18.7652(5)
90
92.916(2)
90
5335.9(2)
4
1.103
1.23
C50H46N4P2Zn2·C7H8
987.72
183(2)
triclinic
triclinic
¯
¯
P1 (no. 2)
P1 (no. 2)
9.393(1)
9.846(1)
12.248(1)
85.009(5)
71.571(5)
65.452(6)
976.14(18)
2
12.9680(4)
13.9220(5)
16.0896(7)
86.320(2)
74.334(2)
63.121(2)
2489.21(16)
2
γ [°]
V [Å3]
Z
ρ [gcm–3]
1.250
1.5
1.318
10.69
µ [cm–1]
Measurement range [°]
Measured data
4.56 Ͻ 2θ Ͻ 54.88
6457
4685
4.22 Ͻ 2θ Ͻ 54.96
33780
12173
4.34 Ͻ 2θ Ͻ 55.00
17823
11310
Unique data (Rint
)
Data with IϾ2σ(I)
wR2 (all data, on F2)[a]
R1 [IϾ2σ(I)][a]
2826
0.1683
0.0632
1.020
6855
0.2897
0.0876
1.020
8575
0.1185
0.0707
1.008
s[b]
Residual density [eÅ–3]
0.533/–0.629
0.996/–0.391
1.182/–0.413
[a] Definition of the R indices: R1 = (Σ||Fo| – |Fc||)/Σ|Fo|; wR2 = {Σ[w(F2o – F2c)2]/Σ[w(F2o)2]}1/2 with w–1 = σ2(F2o) + (aP)2 + bP; P = [2F2c +
max(F2o)]/3. [b] S = {Σ[w(F2o – F2c)2]/(No – Np)}1/2
.
1796
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 1791–1797

Coordination Behavior of (2-Pyridylmethyl)amide Anions
[5] M. Westerhausen, A. N. Kneifel, N. Makropoulos, Inorg.
Chem. Commun. 2004, 7, 990–993.
[6] M. Westerhausen, A. N. Kneifel, A. Kalisch, Angew. Chem.
2005, 117, 98–100; Angew. Chem. Int. Ed. 2005, 44, 96–98.
[7] C. Koch, A. Malassa, C. Agthe, H. Görls, R. Biedermann, H.
Krautscheid, M. Westerhausen, Z. Anorg. Allg. Chem. 2007,
633, 375–382.
1592 (m), 1569 (m), 1454 (vs), 1377 (vs), 1341 (w), 1306 (w), 1279
(w), 1248 (w), 1195 (w), 1152 (w), 1124 (w), 1110 (w), 1070 (w),
1046 (w), 1027 (w), 998 (w), 974 (w), 942 (w), 917 (w), 884 (w), 860
(w), 843 (w), 737 (m), 722 (m), 697 (m), 666, (vw), 647 (vw), 614
(vw), 543 (w), 515 (w) cm–1. C52H48Li2N4OP2 (820.75): calcd. C
76.10, H 5.90, N 6.83; found C 72.42, H 5.18, N 6.63.
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[10] J. T. B. H. Jastrzebski, J. M. Klerks, G. van Koten, K. Vrieze,
J. Organomet. Chem. 1981, 210, C49–C53.
Synthesis of 4: Compound 2 (0.40 g, 1.1 mmol) was dissolved in
toluene (3 mL) and cooled to 0 °C. A 1.5  solution of dimeth-
ylzinc (0.75 g) in toluene was added dropwise to this stirred solu-
tion. After addition, the color of the solution changed to deep
violet. This clear solution was stirred at room temp. for an ad-
ditional 2 h. After removal of the solvent (2 mL) in vacuo, the re-
maining solution was stored at –20 °C. The crystalline, colorless
product was obtained from this solution after storage at –20 °C for
several days. Yield: 0.33 g (0.75 mmol, 68%). 1H NMR (400 MHz,
[11]
[12]
L. H. Polm, C. J. Elsevier, G. van Koten, J. M. Ernsting, D. J.
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2602–2608.
3
[D8]thf): δ = 8.02 [d, J(H,H) = 4.0 Hz, 1 H, H1] 7.49 [dd, 3J(H,H)
= 8.0 Hz, 1 H, H3], 7.32 (m, 2 H, o-Ph), 7.17 (m, 4 H, o-PPh2),
7.02 (m, 6 H, m-PPh2, p-PPh2), 6.90 (m, 3 H, m-Ph, p-Ph), 7.05
[13]
[14]
[15]
[16]
[17]
[18]
G. van Koten, J. T. B. H. Jastrzebski, K. Vrieze, J. Organomet.
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3
(m, 1 H, H4), 6.94 (m, 1 H, H2), 5.46 [d, J(H,P) = 17.2 Hz, 1 H,
CH], –0.61 (s, 3 H, CH3) ppm. 13C{1H} NMR (100 MHz, [D8]thf):
δ = 166.2 (br., C5), 145.9 [i-C(Ph)], 147.3 (C1), 147.8 [br., i-
C(PPh2)], 138.5 (C3), 133.5 [d, 2J(C,P) = 13.2 Hz, o-C(PPh2)], 133.0
[d, 2J(C,P) = 14.3 Hz, o-C(Ph)], 128.5 [m-C(PPh2), p-C(PPh2)],
127.9 [m-C(Ph), p-C(Ph)], 123.7 (C4), 122.7 (C2), 67.7 [d, 2J(C,P) =
20.8 Hz, C6], –11.8 (CH3) ppm. 31P{1H} NMR (81 MHz, C6D6): δ
= 46.8 ppm. IR (Nujol): ν = 2924 (vs), 2854 (vs), 1603 (w), 1450
˜
(m), 1437 (m), 1377 (w), 1304 (vw), 1264 (vw), 1195 (w), 1152 (w),
1080 (w), 1042 (m), 1019 (w), 802 (vw), 759 (m), 703 (w), 687 (w),
665 (w), 619 (w), 572 (vw), 509 (vw) cm–1. C50H46N4P2Zn2 (895.60):
calcd. C 67.05, H 5.18, N 6.26; found C 66.10, H 5.63, N 6.03.
Structure Determinations: The intensity data for the compounds were
collected with a Nonius KappaCCD diffractometer by using graph-
ite-monochromated Mo-Kα radiation.[29,30] The structures were
solved by Direct Methods (SHELXS[31]) and refined by full-matrix
least-squares techniques against Fo2 (SHELXL-97[32]). All hydrogen
atoms were included at calculated positions with fixed thermal pa-
rameters. All nondisordered non-hydrogen atoms were refined aniso-
tropically.[32] Crystallographic data as well as structure solution and
refinement details are summarized in Table 3. The XP program (Sie-
mens Analytical X-ray Instruments, Inc.) was used for structure rep-
resentations. CCDC-761465 (2), -761466 (3), and -761467 (4) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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Allg. Chem. 2004, 630, 2013–2021.
[28] D. Olbert, A. Kalisch, H. Görls, I. M. Ondik, M. Reiher, M.
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[29] COLLECT, Data Collection Software, Nonius B. V., The Ne-
therlands, 1998.
Acknowledgments
This work was generously supported by the Deutsche Forschungs-
gemeinschaft (DFG, Bonn–Bad Godesberg, Germany). We are also
grateful to the Fonds der Chemischen Industrie (Frankfurt/Main,
Germany) for supporting our research.
[1] M. Westerhausen, T. Bollwein, N. Makropoulos, T. M. Rotter,
T. Habereder, M. Suter, H. Nöth, Eur. J. Inorg. Chem. 2001,
851–857.
[30] “Processing of X-ray Diffraction Data Collected in Oscillation
Mode”: Z. Otwinowski, W. Minor in Methods in Enzymology,
vol. 276 (Macromolecular Crystallography, Part A) (Eds.: C. W.
Carter, R. M. Sweet), Academic Press, 1997, pp. 307–326.
[31] G. M. Sheldrick, Acta Crystallogr., Sect. A 1990, 46, 467–473.
[32] G. M. Sheldrick, SHELXL-97 (version 97.2), University of
Göttingen, Germany, 1997.
[2] M. Westerhausen, T. Bollwein, N. Makropoulos, S. Schnei-
derbauer, M. Suter, H. Nöth, P. Mayer, H. Piotrowski, K. Pol-
born, A. Pfitzner, Eur. J. Inorg. Chem. 2002, 389–404.
[3] M. Westerhausen, T. Bollwein, P. Mayer, H. Piotrowski, A.
Pfitzner, Z. Anorg. Allg. Chem. 2002, 628, 1425–1432.
[4] M. Westerhausen, A. N. Kneifel, I. Lindner, J. Grcic´, H. Nöth,
ˇ
Received: January 16, 2010
Z. Naturforsch., Teil B 2004, 59, 161–166.
Published Online: March 11, 2010
Eur. J. Inorg. Chem. 2010, 1791–1797
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1797