Synthesis of trifunctional ligands containing thiophosphoryl, pyridine and pyridine N-oxide donor groups

Article abstract of DOI:10.1039/b309336k

The trifunctional mixed donor ligands 2,6-[R₂P(S)CH₂]₂C₅H₃N 1 (R = Ph 1a, Tol 1b, n-Bu, 1c) and 2,6-[R₂P(S)-CH₂]₂C₅H₃NO 2 (R = Ph 2a, Tol 2b, n-Bu, 2c) have been prepared and characterized by spectroscopic (MS, IR, NMR) techniques. The coordination chemistry of one derivative 1a has been examined and the complex {[Ph₂P(S)-CH₂]₂ C₅H₃N} Ni(NO₃)₂ has been crystallized and characterized by single-crystal X-ray diffraction methods. The structure contains a six coordinate Ni(II) ion bonded to a tridentate ligand 1a with Ni-N_pyr 2.110(3) A and Ni-S 2.481(1) and 2.402(1) A, a bidentate nitrate anion and a monodentate NO₃^- anion.

Full text of DOI:10.1039/b309336k

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Synthesis of trifunctional ligands containing thiophosphoryl,
pyridine and pyridine N-oxide donor groups
Xin-min Gan, Eileen N. Duesler, Sahrah Parveen and Robert T. Paine*
Department of Chemistry, University of New Mexico, Albuquerque, NM 87131, USA.
E-mail: rtpaine@unm.edu
Received 5th August 2003, Accepted 7th October 2003
First published as an Advance Article on the web 10th November 2003
The trifunctional mixed donor ligands 2,6-[R2P(S)CH2]2C5H3N 1 (R = Ph 1a, Tol 1b, n-Bu, 1c) and 2,6-[R2P(S)-
CH2]2C5H3NO 2 (R = Ph 2a, Tol 2b, n-Bu, 2c) have been prepared and characterized by spectroscopic (MS, IR,
NMR) techniques. The coordination chemistry of one derivative 1a has been examined and the complex {[Ph2P(S)-
CH2]2C5H3N}Ni(NO3)2 has been crystallized and characterized by single-crystal X-ray diffraction methods. The
structure contains a six coordinate Ni() ion bonded to a tridentate ligand 1a with Ni–Npyr 2.110(3) Å and Ni–S
2.481(1) and 2.402(1) Å, a bidentate nitrate anion and a monodentate NO3Ϫ anion.
intermediate 2,6-bis[(diphenylphosphino)methyl]pyridine was
Introduction
treated, without isolation, with sulfur and the mixture, after
standard workup, gave 2,6-bis[(diphenylphosphino)methyl]-
pyridine P,PЈ-disulfide, 1a, as a white solid in 89% yield. The
compound shows modest solubility in CHCl3, but little solubil-
ity in other common organic solvents. The compound also can
be obtained from the combination of Ph2P(S)Li and 2,6-bis-
(chloromethyl)pyridine, but the yield is significantly lower.
Attempts to prepare the corresponding N-oxide derivative 2a
by peroxide oxidation of the pyridine nitrogen atom in 1a led to
replacement of the sulfur atoms on phosphorus by oxygen
atoms with formation of 2,6-bis[(diphenylphosphino)methyl]-
pyridine N,P,PЈ-trioxide. However, 2a was obtained in 86%
yield by combination of two equiv. of KPPh2 with 2,6-bis(chlo-
romethyl)pyridine N-oxide in THF followed by treatment,
without isolation, of the bis-phosphine with sulfur. The 2,6-
bis[(diphenylphosphino)methyl]pyridine N-oxide P,PЈ-disulfide
was obtained as a white solid that is moderately soluble in
CHCl3 but insoluble in aliphatic and aromatic hydrocarbons.
The success of this reaction may seem surprising since phos-
phines have been used to deoxygenate pyridine N-oxides.14
However, room temperature deoxygenation reactions typically
employ a highly electrophilic phosphine such as PCl3 or PBr3.
More electron rich phosphines, e.g. Ph3P, generally require
forcing conditions to accomplish oxygen atom transfer. The
electron rich diphenyl phosphide clearly prefers to undergo the
chloride displacement chemistry.
Due to the modest solubilities of 1a and 2a, syntheses for
derivatives with tolyl and n-butyl substituents were explored.
Since the precursor phosphines Tol2PH and Bu2PH are expen-
sive and/or less readily available from commercial suppliers,
alternative synthetic routes for 1b, 2b (Tol) and 1c, 2c (Bu) were
sought. The method selected here involved treatment of com-
mercially available (EtO)2P(O)H with Lawesson’s reagent which
afforded (EtO)2P(S)H in 82% yield.15,16 This reagent was treated
with the appropriate organolithium reagent, TolLi or BuLi, and
the resulting mixtures combined directly with 2,6-bis(chloro-
methyl)pyridine (0.5 equiv.) to give 1b and 1c, respectively, or
2,6-bis(chloromethyl)pyridine N-oxide (0.5 equiv.) to give 2b
and 2c. In each case, 31P NMR analysis of the crude reaction
mixtures showed that the desired compounds were formed in
>80% yield. Unfortunately, the crude 1b and 2b are sticky solids
that proved difficult to rid of pesky impurities. The compounds
were purified by repeated recrystallization from cold (Ϫ20 ЊC)
acetone or CHCl3–acetone mixtures, but with significant loss of
material. Pure samples were recovered with 17 and 33% yields,
respectively.17
The coordination chemistry of lanthanide, Ln(), and actinide,
An(), ions in aqueous solutions, in many respects, is very simi-
lar.1 Therefore, the logical design of ligands that might select-
ively coordinate with one of these ions or a small group of ions
in a complex matrix represents a great challenge.2 Both classes
of ions are normally considered to be “hard” and they tend to
bind relatively strongly to neutral and anionic ligands contain-
ing oxo-donor sites,1,2 e.g. phosphine oxides and N-oxides. In
this regard, we have prepared and studied a number of bifunc-
tional and trifunctional ligands that contain phosphine oxide
and pyridine N-oxide donor groups3,4 and it is observed that
the ligands with proper “backbone” designs strongly chelate
with Ln(), An() and An() cations. Further, it appears that
An() binding in the case of Am() is slightly favored over
Eu() binding.5,6 It has been previously suggested that “softer”
donors (N and S) might more strongly favor coordination with
An() ions over Ln() ions of similar size7–13 and limited
liquid–liquid extraction data support this proposal. As a result,
our group has been attempting to prepare “softened” deriv-
atives of the oxo ligands previously reported by us. This
includes examples where the pyridine N-oxide group is replaced
by a pyridine fragment and the phosphine oxide group is
replaced by phosphine sulfide. Of course, this ligand softening
opens up the possibility that these new ligands may coordinate
effectively with main group or transition metal cations. In this
regard, we report here the synthesis of two trifunctional ligand
types, 2,6-[R2P(S)CH2]2C5H3N 1 (R = Ph 1a, Tol 1b and n-Bu
1c) and 2,6-[R2P(S)CH2]2C5H3NO 2 (R = Ph 2a, Tol 2b and
n-Bu 2c), and the coordination chemistry of 1a toward Ni().
Results and discussion
The oxophilicity of phosphorus somewhat limits the synthetic
approaches that may be employed to successfully prepare the
trifunctional phosphinomethylpyridine P,PЈ-disulfides, 1, and
phosphinomethylpyridine N-oxide P,PЈ-disulfides, 2. Nonethe-
less, the chemistry outlined in Schemes 1 and 2 provides good to
modest yields of the target compounds. Compound 1a was
most conveniently obtained by allowing 2,6-bis(chloromethyl)-
pyridine to react with two equivalents of KPPh2 in THF. The
The Bu derivatives 1c and 2c were prepared in similar fash-
ions to 1b and 2b and the crude yields of orange oily products
D a l t o n T r a n s . , 2 0 0 3 , 4 7 0 4 – 4 7 0 8
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
4704

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Scheme 1
Scheme 2
were >80%. These compounds show significant solubility in
P,PЈ-disulfide, 620 cmϪ1 20 The 31P{1H} NMR spectra of
.
chlorinated solvents, Et2O, benzene, toluene, xylene and cyclo-
hexane, but they are insoluble in hexane. The greater solubility
complicated efforts to purify these compounds and analytically
pure samples of 2c were obtained only after column chromato-
graphy on silica gel. This led to significant loss of material:
8–40% isolated yields as faintly orange oils.
purified samples contain a single resonance in the region
expected for thiophosphoryl compounds:21 1a 42.4 ppm; 1b
40.9 ppm; 1c 49.6 ppm; 2a 43.2 ppm; 2b 40.2 ppm; 2c 52.8 ppm.
1
The H and 13C{1H} spectra are consistent with the organic
backbones present in the compounds.
The chelation properties of 1 and 2 toward selected metal
ions is of interest and studies of the coordination chemistry
with Ln() ions and Pu() are in progress. In addition, initial
surveys of the liquid–liquid extraction performance of 1c and
2c are underway. Anticipating that derivatives of 1, in particu-
lar, might also coordinate with and extract selected d- and
p-block metals, the molecular coordination chemistry with
Ni() has been examined. The 1 : 1 combination of 1a with
Ni(NO3)2 gave Ni{[Ph2P(S)CH2]2C5H3N}(NO3)2 in analytically
pure form. The complex forms green crystals that display an
infrared spectrum with an absorption at 599 cmϪ1. This is ten-
tatively assigned to a coordinated P᎐S group with ν 15 cmϪ1
The new compounds was characterized by CHN analyses,18
high or low resolution FAB-MS, IR and 1H, 13C{1H} and
31P{1H} NMR spectroscopy. Compounds 1a, 2a, 2b and 2c gave
satisfactory analytical data. The HRFAB mass spectra of 1a, 1c
and 2a–c display a (M ϩ Hϩ) parent ion that is the most intense
ion and the m/z values agree well with the calculated molecular
weights. A low-resolution FAB MS was obtained for 1b, and it
showed an intense ion at the expected mass for (M ϩ Hϩ). The
infrared spectra of 2a–c contain a band at 1230, 1238 and 1248
cmϪ1, respectively, that may be tentatively assigned to νNO
.
These assignments are supported by the absence of a band in
this region in 1a–c and the appearance of similar absorptions
for 2,6-bis[(phosphino)methyl]pyridine N,P,PЈ-trioxides, 1260–
᎐
PS
lower in frequency than in 1a. This is consistent with a P᎐S–Ni
᎐
coordination interaction.
1240 cm
.
Ϫ1 3,4 Assignment of observed absorptions to νPS are less
The molecular structure of the complex was subsequently
determined by single crystal X-ray diffraction methods. The
complex crystallizes in the orthorhombic space group Pbca
with eight molecules per unit cell with no solvent molecules or
disordered atoms. A view of the molecule is shown in Fig. 1 and
selected bond lengths are summarized in Table 1. There is one
ligand 1a in the complex and it acts as a tridentate chelate
binding in a facial mode to the Ni() ion through the pyridine
nitrogen atom and the two thiophosphoryl sulfur atoms. The
certain; however, we propose the following assignments: 1a 615
cmϪ1; 1c 731 cmϪ1; 2a 623 cmϪ1; 2b 656 cmϪ1; 2c 731 cmϪ1. The
νP᎐S bands for the alkyl phosphine sulfides appear at higher fre-
quency as expected19 and the νP᎐S bands for the aryl phosphine
sulfides are comparable with᎐ data reported for 2-bis[(di-
phenylphosphino)methyl]-6-methylpyridine P,PЈdisulfide, 625
cmϪ1, 2-[(diphenylphosphino)methyl]-6-methylpyridine P sul-
fide, 620 cmϪ1, and 2-bis[(diphenylphosphino)methyl]pyridine
D a l t o n T r a n s . , 2 0 0 3 , 4 7 0 4 – 4 7 0 8
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Table 1 Selected bond lengths (Å) Ni{[Ph2P(S)CH2]2C5H3N}(NO3)2
Experimental
The organic reagents were purchased from Aldrich Chemical
Co. Organic solvents were obtained from VWR and dried by
standard methods. The Ni(NO3)2ؒ6H2O was purchased from
Fisher Scientific. Infrared spectra were recorded on a Mattson
2020 FTIR instrument and NMR spectra were obtained with
Bruker FX-250 and JEOL GSX-400 spectrometers using Me4Si
(1H, 13C) and 85% H3PO4 (31P) as shift standards. All downfield
Ni–S(1)
Ni–S(2)
Ni–N(1)
P(1)–S(1)
P(2)–S(2)
C(1)–C(6)
C(5)–C(7)
N(2)–O(1)
N(2)–O(2)
N(2)–O(3)
2.481(1)
2.402(1)
2.110(3)
1.980(2)
1.981(2)
1.501(5)
1.507(5)
1.276(4)
1.271(4)
1.208(4)
Ni–O(1)
Ni–O(2)
Ni–O(4)
P(1)–C(6)
P(2)–C(7)
C(1)–N(1)
C(5)–N(1)
N(3)–O(4)
N(3)–O(5)
N(3)–O(6)
2.154(3)
2.136(3)
2.061(3)
1.825(4)
1.811(4)
1.347(5)
1.356(5)
1.268(5)
1.199(5)
1.220(5)
shifts from the standards are assigned as ϩδ and the 1H and 13
C
peak assignments are based upon assignments made previously
for related ligands.3,4 The mass spectra were obtained at
the Midwest Center for Mass Spectrometry, University of
Nebraska and elemental analyses were acquired from Galbraith
Laboratories.
Ligand syntheses
2,6-Bis(chloromethyl)pyridine was prepared as described by
Rezzonico and Grignon-Dubois.27 CAUTION: Handling of
this reagent and its solutions should be done in a well ventilated
hood. Skin and eye contact must be carefully avoided since the
compound is an aggressive irritant. The compound has a small
vapor pressure at 23 ЊC and it can cause bronchial irritation
as well. We find considerable variation in the intensity of irri-
tation between individuals, so care should be exercised when
preparing and handling this reagent.
Fig. 1 Molecular structure and atom labeling scheme for Ni{[Ph2P-
(S)CH2]2C5H3N}(NO3)2.
2,6-Bis[(diphenylphosphino)methyl]pyridine
P,PЈ-disulfide
4
(1a). Under dry nitrogen, a red solution of KPPh2 (40 mL,
0.5 M in THF, 20 mmol) was added dropwise (30 min) at 23 ЊC
to a stirred solution of 2,6-bis(chloromethyl)pyridine (1.76 g,
10 mmol) in dry tetrahydrofuran (THF, 40 mL). The red color
changed immediately and an orange, cloudy mixture formed.
The mixture was stirred at 23 ЊC for an additional period (1 h)
and then sulfur (0.7 g, 22 mmol) in benzene (40 mL) was added.
This combination was stirred at 23 ЊC (1 h) and then poured
into water (100 mL). The resulting mixture was extracted with
CHCl3 (2 × 100 mL), the organic and aqueous phases separated
and the organic phase dried over Na2SO4. The CHCl3 solution
was decanted, vacuum evaporated and the solid residue was
treated with acetone (50 mL). The suspension was stirred (1 h),
the white solid collected by filtration, and rinsed with acetone
(2 × 20 mL). The solid was vacuum dried overnight leaving a
white solid 1a (4.8 g, 89%). The solid was recrystallized from
CHCl3–acetone (2 : 1) resulting in a colorless crystalline solid,
mp 217–218 ЊC. Soluble in CHCl3 (7 × 10Ϫ2 M). Found: C,
68.75; H, 4.97; N, 2.53%. C31H27NP2S2 requires C, 69.07; H,
5.05; N, 2.60%. HRFAB-MS: m/z (M ϩ Hϩ) 540.1115;
C31H28NP2S2 requires 540.1138. NMR (23 ЊC, CDCl3): 31P{1H}
δ 42.4; 1H δ 3.86 (d, J = 14.2 Hz, CH2), 7.13 (d, J = 7.6 Hz), 7.37–
7.47 (m); 7.76–7.84 (m); 13C{1H} δ 43.36 (d, J = 50.1 Hz, C1),
123.54 (C3), 128.32 (d, J = 12.4 Hz, C7), 131.41 (C8), 131.80
(d, J = 9.3 Hz, C6), 132.52 (d, J = 81.5 Hz, C5), 135.96 (C4),
151.66 (d, J = 7.2 Hz, C2). IR (KBr, cmϪ1): 3047 (m), 2945 (m),
2893 (m), 1585 (m), 1481 (w), 1437 (s), 1396 (m), 1273 (w), 1101
(s), 995 (w), 823 (s), 744 (s), 704 (s), 692 (s), 615 (m), 505 (m),
476 (m).
coordinate bond lengths involving 1a are relatively dissimilar:
Ni–S(1) 2.481(1) Å, Ni–S(2) 2.402(1) Å and Ni–N(1) 2.110(3)
Å. The Ni–N(1) bond length is similar to Ni–N bond
lengths (2.04–2.14 Å) found in a large number of complexes
containing high-spin Ni().22 It is interesting to compare the
Ni–N(1) bond length to that in the complex [Ph2P(O)CH-
2C5H4N]2NiCl2 where the Ni–N bond length is 2.133(3) Å.23 In
the latter, Ph2P(O)CH2C5H4N acts as a bidentate chelating lig-
and. In that complex the P(O)–Ni coordinate bond length is
2.053(2) Å which is, as expected, significantly shorter than the
Ni–(S)P distances in Ni(1a)(NO3)2. The Ni–S bond lengths are
similar to those found in a six-coordinate Ni() complex con-
taining two neutral tridentate 2-pyridineformamide-N(4)-
methylthiosemicarbazone ligands: Ni–S 2.420(2) and 2.416(2)
Å.24 The Ni–N distances, 2.099(6) and 2.117(6) Å, are also
comparable to the distances in Ni(1a)(NO3)2. The remaining
three coordination sites on the Ni() are occupied by oxygen
atoms from one bidentate nitrate ion and one monodentate
nitrate ion. The bidentate nitrate coordination is relatively
symmetric with Ni–O(1) 2.154(3) Å and Ni–O(2) 2.136(2) Å.
The second nitrate ion provides Ni–O(4) 2.061(3) Å and
Ni ؒ ؒ ؒ O(5) 3.183 Å. The former is clearly a bonding inter-
action while the latter is nonbonding. It is interesting to note
that the short, monodentate interaction Ni–O(4) is approx-
imately trans[O(4)–Ni–S(1) 168.5(1)Њ] to the longer Ni–S(1)
interaction. Despite the range in Ni–S and Ni–N coordinate
bond lengths the ligand–Ni docking footprint is very symmetric
forming a nonbonded nearly equilateral triangle: N(1) ؒ ؒ ؒ S(1)
3.348 Å, N(1) ؒ ؒ ؒ S(2) 3.503 Å, S(1) ؒ ؒ ؒ S(2) 3.394 Å; internal
internal angles at N(1) 59.3Њ, S(1) 62.6Њ, S(2) 58.0Њ. This sym-
metry is distinct from the asymmetric footprints displayed
by bis(phosphinomethyl)pyridine N,P,PЈ-trioxide ligands on
Ln() and An() ions2,3,25,26 which typically form isosceles tri-
2,6-Bis[(diphenylphosphino)methyl]pyridine N-oxide P,PЈ-
disulfide (2a). Under dry nitrogen a red solution of KPPh2
(15 mL, 0.5 M in THF, 7.5 mmol) was added dropwise (5 min)
at 23 ЊC to a stirred THF (15 mL) solution of 2,6-bis(chloro-
methyl)pyridine N-oxide28 (0.72 g, 3.75 mmol). The red
color was discharged immediately producing an orange, cloudy
mixture. Stirring was continued at 23 ЊC (1 h). Sulfur (0.264 g,
8.2 mmol) in THF (15 mL) was added, stirred (1 h) and the
THF removed by vacuum evaporation. The remaining residue
was poured into a mixture of aqueous NaHCO3 (50 mL sat.
solution ϩ 50 mL water). This mixture was extracted with
angles with the nonbonding P᎐O ؒ ؒ ؒ O᎐P edge showing a large
᎐
᎐
variation depending upon the size of the metal ion. The two
P᎐S bond lengths are identical, 1.980(2) Å, suggesting that
᎐
the asymmetry in Ni–S distances does not impact the P᎐S
᎐
donor groups in a significant fashion. Given the interesting
bonding mode, further studies of related ligands with d-block
and p-block metals will be undertaken, and findings described
in the future.
D a l t o n T r a n s . , 2 0 0 3 , 4 7 0 4 – 4 7 0 8
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CHCl3 (2 × 150 mL) and the combined CHCl3 fractions dried
over Na2SO4. The CHCl3 solution was decanted, evaporated to
dryness and the residue treated with acetone (30 mL). This sus-
pension was stirred (1 h) at 23 ЊC and the white solid collected
by filtration and washed with acetone (2 × 10 mL). The solid
was dried in vacuo (12 h) and was obtained as a white solid 2a
(1.8 g, 86%). The solid was recrystallized from CHCl3/acetone
(2:1), and colorless crystals were obtained, mp 239–240 ЊC
(decomp.). Soluble in CHCl3 (1 × 10Ϫ2 M). Found: C, 66.31; H,
4.73; N, 2.50%. C31H27NOP2S2 requires C, 67.01; H, 4.90; N,
2.52%. HRFAB-MS: m/z (M ϩ Hϩ) 556.1083; C31H28NOP2S2
mmol) was added with stirring (1 h) at 0 ЊC to a solution of
diethylthiophosphite (1.7 g, 11 mmol) in cyclohexane (40 mL).
The mixture was warmed to 23 ЊC, stirred for an additional
hour and a solution of 2,6-bis(chloromethyl)pyridine (0.88 g,
5.45 mmol) in cyclohexane (30 mL) was added. This mixture
was stirred (4 h) then poured into sat. aqueous NH4Cl solution
(50 mL) which was then extracted with diethyl ether–CH2Cl2
(1 : 1) solution (2 × 40 mL). The combined organic phase was
dried over Na2SO4 and evaporated to dryness leaving an orange
oil 1c (2.4 g). This was further purified by chromatography on
silica gel using MeOH–CHCl3 as the eluent (0.18 g, 7.8%).
Soluble in CHCl3, Et2O, cyclohexane C6H6, toluene, xylene.
HRFAB-MS: m/z (M ϩ Hϩ) 460.2382; C23H44NP2S2 requires
1
requires 556.108. NMR (23 ЊC, CDCl3): 31P{1H} δ 43.2; H
δ 4.30 (d, J = 14.0 Hz, CH2), 7.02 (t, J = 6.0 Hz), 7.39–7.47 (m),
7.66 (d, J = 7.4 Hz), 7.85–7.93 (m); 13C{1H} δ 34.86 (d, J = 53.0
Hz, C1), 123.56 (t, J = 2.8 Hz, C4), 126.08 (t, J = 3.7 Hz,
C3), 128.49 (d, J = 12.4 Hz, C7), 131.35 (d, J = 10.5 Hz, C6),
131.69 (d, J = 2.7 Hz, C8), 132.16 (d, J = 72.6 Hz, C5), 143.46 (d,
J = 7.3 Hz, C2). IR (KBr, cmϪ1): 3049 (m), 2966 (m), 2885 (m),
1564 (w), 1481 (m), 1435 (m), 1410 (m), 1386 (m), 1265 (w),
1230 (s), 1103 (s), 1026 (w), 950 (w), 854 (s), 800 (s), 752 (s), 698
(s), 623 (m), 499 (m).
1
460.2390. NMR (23 ЊC, CDCl3): 31P{1H} δ 49.6; H δ 0.93 (t,
J = 7.2 Hz, 12 H, CH3), 1.37–1.89 (m, 24 H, CH2), 3.42 (d,
J = 14.1 Hz, 4 H, CH2), 7.25 (m, 2H), 7.64 (t, J = 7.7 Hz,
1 H); 13C{1H} δ 13.52 (C8), 23.75 (d, J = 16.0 Hz, C7), 24.17 (d,
J = 3.5 Hz, C6), 30.27 (d, J = 50.8 Hz, C5), 41.57 (d, J = 43.1 Hz,
C1) 122.97 (C3), 136.79 (C4), 152.92 (d, J = 9.6 Hz, C2). IR (KBr,
cmϪ1): 2957 (s), 2931 (s), 2868 (s), 1585 (m), 1452 (s), 1402 (m),
1276 (m), 1221 (m), 1089 (m), 1053 (w), 906 (s), 831 (m), 783
(m), 731 (s), 441 (w).
2,6-Bis[(ditolylphosphino)methyl]pyridine P,PЈ-disulfide (1b).
Under dry nitrogen, tolyllithium29 (2.6 g, 26.5 mmol) in Et2O
(50 mL) was added with stirring to diethylthiophosphite15,16
(1.36 g, 8.84 mmol) in Et2O (30 mL) at 0 ЊC. The mixture was
warmed to room temperature and stirred (2 h). A white suspen-
sion formed and this solution was combined with 2,6-bis-
(chloromethyl)pyridine (0.72 g, 4.09 mmol) in THF (20 mL) at
23 ЊC. After stirring (2 h), a clear, light orange colored solution
was obtained. The mixture was evaporated and the residue
treated with aqueous saturated NH4Cl solution (50 mL). This
mixture was then extracted with Et2O–CH2Cl2 solution (1 : 1)
(2 × 50 mL) and the recovered organic phase was dried over
Na2SO4. The solvent was evaporated leaving a sticky white solid
1b that was recrystallized from acetone or CHCl3–acetone (0.4 g,
17%). Soluble in CHCl3. LRFAB-MS: m/z (M ϩ Hϩ) 596; C35H36-
NOP2S2 requires 596. NMR (23 ЊC, CDCl3):31P{1H} δ 40.9.
2,6-Bis[(dibutylphosphino)methyl]pyridine N-oxide P,PЈ-
disulfide (2c). n-Butyllithium (20.6 mL, 1.6 M in hexane, 33
mmol) was added with stirring at 0 ЊC to a solution of di-
ethylthiophosphite (1.7 g, 11 mmol) in cyclohexane (40 mL).
The mixture was warmed to 23 ЊC, stirred (1 h) and then added
to a solution of 2,6-bis(chloromethyl)pyridine N-oxide (0.96 g,
5.45 mmol) in THF (20 mL) at 23 ЊC. This mixture was stirred
(2 h), poured into saturated aqueous NH4Cl (100 mL) and then
treated with CH2Cl2 (2 × 50 mL). The organic phase was separ-
ated, dried over Na2SO4, and solvent removed in vacuo. An
orange oil (2c) (2.8 g) was collected and further purified by
column chromatography (silica gel, MeOH–CHCl3 1 : 1 eluant)
(0.9 g, 37.8%). Soluble in CHCl3, Et2O, C6H6, toluene, xylene.
Found: C, 57.66; H, 9.46; N, 2.74%; C23H43NOP2S2 requires
C, 58.08; H, 9.11; N, 2.94%. HRFAB-MS: m/z (M ϩ Hϩ)
476.2341; C23H44NOP2S2 requires 476.2340. NMR (23 ЊC,
1
2,6-Bis[(ditolylphosphino)methyl]pyridine N-oxide P,PЈ-
disulfide (2b). A solution of p-tolyllithium29 (2.6 g, 26.5 mmol)
in diethyl ether (50 mL) was added dropwise (1 h) with stirring
at 0 ЊC to a solution of diethylthiophosphite15,16 (1.36 g, 8.84
mmol) in diethyl ether (30 mL). The mixture was warmed to
23 ЊC and stirred (2 h). To this mixture a solution of 2,6-bis-
(chloromethyl)pyridine N-oxide27 (0.78 g, 4.43 mmol) in THF
(40 mL) was added and stirred (2 h). The solvent was then
vacuum evaporated and the residue treated with saturated
aqueous NH4Cl (50 mL). This mixture was extracted with
CH2Cl2 (2 × 50 mL), the organic phase collected, dried over
Na2SO4 and the solvent removed by vacuum evaporation. The
remaining residue was washed with cold acetone (2 × 25 mL)
and a white solid was recovered (2.4 g). Further recrystalliz-
ation from acetone gave pure samples of 2b (0.80 g, 33%), mp
198–199 ЊC. Soluble in CHCl3 (2 × 10Ϫ2 M). Found: C, 67.53;
H, 5.63; N, 2.23%. C35H35NOP2S2 requires C, 68.72; H, 5.77; N,
2.29%. HRFAB-MS: m/z (M ϩ Hϩ) 612.1708; C35H36NOP2S2
CDCl3): 31P{1H} δ 52.8. H δ 0.93 (t, J = 7.2 Hz, 12 H, CH3),
1.40–2.04 (m, 24 H, CH2), 3.72 (d, J = 13.4 Hz, 4H, CH2), 7.21
(t, 1 H), 7.47 (m, 2 H); 13C{1H} δ 13.49 (C8), 23.71 (d, J = 16.4
Hz, C7), 24.39 (d, J = 3.8 Hz, C6), 31.79 (d, J = 49.9 Hz, C5),
34.10 (d, J = 44.5 Hz, C1), 124.04 (s, C4), 126.66 (C3), 143.80 (d,
J = 10.7 Hz, C2).
Preparation of complex
A solution of Ni(NO3)2ؒ6H2O (29.1 mg, 0.1 mmol) in acetone
(10 mL) was combined with a solution of 1a (54 mg, 0.1 mmol)
in CHCl3 (10 mL) and stirred (5 min). The mixture was filtered
and the solvent allowed to slowly evaporate. The resulting crys-
tals were suitable for crystallographic analysis. IR (KBr, cmϪ1):
3061 (w), 2985 (w), 2924 (w), 1606 (w), 1574 (w), 1481 (s), 1444
(s), 1294 (s), 1103 (m), 1020 (m), 1030 (m), 945 (w), 852 (m), 746
(m), 694 (s), 599 (s), 489 (m).
X-Ray diffraction analysis
1
requires 612.171. NMR (23 ЊC, CDCl3): 31P{1H} δ 40.2; H
δ 2.34 (12 H, CH3), 4.28 (d, J = 14.0 Hz, 4H, CH2), 6.94 (t,
J = 8.0 Hz, 1H), 7.16–7.21 (m, 8H), 7.66 (d, J = 8.04 Hz, 2H),
7.72–7.81 (m, 8H); 13C{1H} δ 21.32 (C9), 34.61 (d, J = 53.6 Hz,
C1), 123.39 (C4), 125.79 (C3), 128.93 (d, J = 84.3 Hz, C5), 129.10
(d, J = 12.9 Hz, C7), 131.16 (d, J = 11.1, C6), 141.97 (d, J = 2.5
Hz, C2), 143.49 (C8). IR (KBr, cmϪ1): 3047 (m), 3021 (m), 2961
(m) 2901 (m), 2866 (m), 1597 (m), 1560 (w), 1489 (m), 1447 (m),
1400 (s), 1238 (s), 1186 (m), 1101 (s), 1035 (m), 995 (w), 854 (m),
810 (s), 752 (m), 713 (m), 656 (s), 586 (m), 509 (s), 434 (m).
A single crystal (0.3 × 0.3 × 0.18 mm) was mounted on a glass
fiber and data were collected on a Siemens R3m/V diffract-
ometer equipped with a graphite monochromator and using
Mo-Kα radiation (λ = 0.71073 Å). Crystal data: C31H27N3-
NiO6P2S2,
M
=
722.33, orthorhombic, space group
Pbca, a = 15.431(2), b = 18.055(3), c = 22.931(4) Å, V =
6388.7(17) Å3, Z = 8, µ = 0.887 mmϪ1, T = 20 ЊC, 11094 reflec-
tions collected, 5623 independent reflections (Rint = 0.0632)
which were used in all calculations. The final refinement indices
were R1 = 0.0508, wR2 = 0.1044 [I > 2σ(I )], R1 (all data) =
0.1026. All calculations were performed with XSCANS30
Version 2.10 and the absorption correction used XPREP31
2,6-Bis[(dibutylphosphino)methyl]pyridine P,PЈ-disulfide (1c).
A solution of n-butyllithium (20.6 mL, 1.6 M in hexane, 33
D a l t o n T r a n s . , 2 0 0 3 , 4 7 0 4 – 4 7 0 8
4707

View Article Online
14 A. Albini and S. Pietra, Heterocyclic N-Oxides, CRC Press, Boca
Version 5.03. The structure was solved by direct methods
(SHELXL-97).32 The refinement was well behaved and all non-
hydrogen atoms were refined anisotropically. The H-atoms were
allowed to vary in position with Uiso = 1.25Uequiv of the parent
atom.
CCDC reference number 215637.
See http://www.rsc.org/suppdata/dt/b3/b309336k/ for crystal-
lographic data in CIF or other electronic format.
Raton, FL, 1991, p. 120, and references therein.
15 N. G. Zabirov, R. A. Cherkasov, I. S. Khalikov and A. N. Pudovik,
Zh. Obshch. Khim, 1989, 59, 1493.
16 S. Rashad, A. A. El-Kateb and F. H. Osman, Chem. Ind. (London),
1984, 553.
17 The synthesis and purification schemes for 1b and 2b were not
optimized since the tolyl substituents did not significantly enhance
the organic solvent solubilities compared to 1a and 2a.
18 Compounds 1b and 1c consistently gave carbon analytical results
that suggested the presence of minor impurities or incomplete
combustion. Carbon analyses for some other pyridylphosphine
oxides prepared in our group have provided similar low carbon
contents and it is generally thought that this results from incomplete
combustion.
Acknowledgements
Financial support for this study came from the U.S. Depart-
ment of Energy, Office of Basic Energy Sciences, Grant No.
DE-FG03-94ER 14446.
19 D. E. C. Corbridge, Top. Phosphorus Chem, 1969, 6, 235.
20 S. M. Nelson, M. Perks and B. J. Walker, J. Chem. Soc. A, 1976,
1205.
21 M. M. Crutchfield, C. H. Dungan, J. M. Letcher, V. Mark and
J. R. VanWazer, Top. Phosphorus Chem., 1967, 5, 365.
22 L. Sacconi, F. Mani and A. Bencini, Comprehensive Coordination
Chemistry, ed. G. Wilkinson, R. D. Gillard and J. A. McCleverty,
Perganon Press, New York, 1987, vol. 5, p. 86.
23 J. T. Mague and J. L. Krinsky, Inorg. Chem., 2001, 40, 1962.
24 I. Garcia, E. Bermejo, A. K. El Sawaf, A. Castiñeiras and
D. X. West, Polyhedron, 2002, 21, 729.
25 Y.-C. Tan, X.-M. Gan, J. L. Stanchfield, E. N. Duesler and
R. T. Paine, Inorg. Chem., 2001, 40, 2910.
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28 This reagent was prepared by combination of 2,6-dichloro-
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mL, 30%). The solution was stirred and heated (70 ЊC, 15 h) and the
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was dissolved in CH2Cl2 (50 mL) and extracted with aqueous
NaHCO3–Na2CO3 (1 : 1) solution (50 mL). The CH2Cl2 solution
was washed with fresh aqueous NaHCO3 solution and dried over
Na2SO4. The CH2Cl2 solution was evaporated leaving 2,6-dichloro-
methylpyridine N-oxide as a white solid. Yield: 6.0 g (92%).
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31 Absorption correction used XPREP, Version 5.03, Siemens, 1994.
32 G. M. Sheldrick, SHELXL-97 Programs for the Refinement of
Crystal Structures, University of Gottingen, Germany, 1997.
D a l t o n T r a n s . , 2 0 0 3 , 4 7 0 4 – 4 7 0 8
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