Tetrapodal pentadentate ligands with NS4 and NP4 donor sets: An elusive tetrathiol, and a sterically encumbered tetraphosphane

Article abstract of DOI:10.1515/znb-2002-1110

With the intention of preparing tetrapodal pentadentate ligands having NS₄ or NP₄ donor sets, we investigated reactions of the previously reported tetratosylate 2,6-C₅H₃N[CMe(CH₂OTs)₂] ₂ (2) with thiourea or diphenylphosphide, but found them not to proceed cleanly, and to give mixtures of products. A derivative of 2 better suited to nucleophilic substitution is the corresponding tetrabromide 2,6-C₅H₃N[CMe(CH₂Br)₂] ₂(2,6-bis-(2-bromo-1-bromomethyl-1-methyl-ethyl)-pyridine, 3), which is obtained in excellent yield from 2 by treatment with LiBr in dimethylsulfoxide. The reaction of 3 with 4 eq of thiourea in refluxing ethanol gives a single product. Substitution is not quantitative, however, and the product likely is a bis(thiouronium) bis(bromide) salt. Similarly, the reaction of 3 with 4 eq of potassium Oethyl xanthogenate displaces only two out of the four bromo substituents under the chosen conditions; workup then leads to what is formulated as a bis(thietane) derivative formed by intramolecular cyclisation. By contrast, nucleophilic substitution with NaSEt in ethanol is quantitative, and the thioether 2,6-C₅H₃N[CMe(CH₂SEt)₂] ₂ (2,6-bis-(2-ethylsulfanyl-l-ethylsulfanylmethyl-1-methyl-ethyl)-pyridine, 4) has been isolated in close to 60% yield. Likewise, and in spite of the considerable steric bulk amassed in the molecule, the reaction of 3 with an excess of KPPh₂ in THF proceeds smoothly (even at -50°C), to give the tetraphosphane 2,6-C₅H₃N[CMe(CH₂PPh₂) ₂]₂ (2,6-bis-{2-(diphenyl-phosphanyl)-1- [(diphenyl-phosphanyl)-methyl]-1-methyl-ethyl}-pyridine, 5) in 65% yield. In order to assess possible pathways of oxidative degradation relevant to the coordination chemistry of this ligand, 5 was treated with NO in CH₂Cl₂ or ether at different temperatures. In two cases, reaction was observed to produce the oxide 2,6-C₅H₃N[CMe(CH₂P(O)Ph₂) ₂]₂ (6) as a colourless solid in near quantitative yield, with concomitant formation of N₂O. All compounds have been characterised by ¹H ¹³C and ³¹p NMR spectroscopy (as applicable); IR spectroscopic and elemental analysis data are reported, and the crystal structure of 6 has been determined.

Full text of DOI:10.1515/znb-2002-1110

Tetrapodal Pentadentate Ligands with NS4 and NP4 Donor Sets:
An Elusive Tetrathiol, and a Sterically Encumbered Tetraphosphane
Christopher Zimmermanna, Walter Bauerb, Frank W. Heinemanna, and Andreas Grohmanna
a
Institut fu¨r Anorganische Chemie, Universita¨t Erlangen-Nu¨rnberg,
Egerlandstraße 1, D-91058 Erlangen, Germany
b Institut fu¨r Organische Chemie, Universita¨t Erlangen-Nu¨rnberg,
Henkestraße 42, D-91054 Erlangen, Germany
Reprint requests to Priv.-Doz. Dr. A. Grohmann. Fax: 09131-852 7367;
E-mail: grohmann@anorganik.chemie.uni-erlangen.de
Z. Naturforsch. 57 b, 1256–1264 (2002); received August 5, 2002
Tetrapodal Pentadentate Ligand, Polythiols, Polyphosphanes
With the intention of preparing tetrapodal pentadentate ligands having NS4 or NP4 donor sets,
we investigated reactions of the previously reported tetratosylate 2,6-C5H3N[CMe(CH2OTs)2]2
(2) with thiourea or diphenylphosphide, but found them not to proceed cleanly, and to
give mixtures of products. A derivative of 2 better suited to nucleophilic substitution is the
corresponding tetrabromide 2,6-C5H3N[CMe(CH2Br)2]2(2,6-bis-(2-bromo-1-bromomethyl-1-
methyl-ethyl)-pyridine, 3), which is obtained in excellent yield from 2 by treatment with
LiBr in dimethylsulfoxide. The reaction of 3 with 4 eq of thiourea in refluxing ethanol
gives a single product. Substitution is not quantitative, however, and the product likely is a
bis(thiouronium) bis(bromide) salt. Similarly, the reaction of 3 with 4 eq of potassium O-
ethyl xanthogenate displaces only two out of the four bromo substituents under the chosen
conditions; workup then leads to what is formulated as a bis(thietane) derivative formed by
intramolecular cyclisation. By contrast, nucleophilic substitution with NaSEt in ethanol is
quantitative, and the thioether 2,6-C5H3N[CMe(CH2SEt)2]2(2,6-bis-(2-ethylsulfanyl-1-ethyl-
sulfanylmethyl-1-methyl-ethyl)-pyridine, 4) has been isolated in close to 60% yield. Likewise,
and in spite of the considerable steric bulk amassed in the molecule, the reaction of 3 with an
excess of KPPh2 in THF proceeds smoothly (even at –50 C), to give the tetraphosphane
2,6-C5H3N[CMe(CH2PPh2)2]2 (2,6-bis- 2-(diphenyl-phosphanyl)-1-[(diphenyl-phosphanyl)-
methyl]-1-methyl-ethyl -pyridine, 5) in 65% yield. In order to assess possible pathways of
oxidative degradation relevant to the coordination chemistry of this ligand, 5 was treated with
NO in CH2Cl2 or ether at different temperatures. In two cases, reaction was observed to pro-
duce the oxide 2,6-C5H3N[CMe(CH2P(=O)Ph2)2]2 (6) as a colourless solid in near quantitative
yield, with concomitant formation of N2O. All compounds have been characterised by 1H, 13
C
and 31P NMR spectroscopy (as applicable); IR spectroscopic and elemental analysis data are
reported, and the crystal structure of 6 has been determined.
+
Introduction
ments of the type [M(NH3)5] , which contain only
monodentate donors. Whereas complexes such as
[FeII(NH3)5)X]+ (X = halide)are unknown, chelated
[(1)FeIIBr]+ is stable under ambient conditions and
has been used to prepare a series of derivatives
In octahedral complexes, tetrapodal pentadentate
ligands help to create a single “labile” coordina-
tion site for reactivity studies of small monoden-
tate ligands. We chose to investigate systems of
high overall symmetry, and introduced the pen-
taamine 1 [1, 2]. Its NN4 donor set, while hav-
ing a geometry similar to that of a porphyrin with
an additional axial base, is unique for its predomi-
nant donor character. We expect transition metal
ions complexed by 1 to be electron-rich and at the
+
[(1)FeIIL] (L = CO, NO, NO+, NO2 ) by lig-
and exchange. The reactivity of the nitro complex
is unusual in that coordinated nitrite can be reduced
to NO in the presence of protons and a suitable re-
ducing agent (MeOH), a pattern reminiscent of the
action of heme-dependent nitrite reductases [3].
The pentaamine 1 is obtained by a sequence of
same time stabilised with respect to complex frag- reactions that enables, in principle, the variation of
c
¨
¨
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C. Zimmermann et al. · Tetrapodal Ligands with NS4 and NP4 Donor Sets
1257
We expected the product to be sufficiently volatile
to allow distillation, and decomposition with am-
monium fluoride was envisaged to regenerate the
tetraalcohol. Even kugelrohr distillation, however,
failed to achieve appreciable purification, and this
approach was abandoned.
the basal donor set, which is introduced towards the
end of the sequence by nucleophilic substitution.
As the redox potential of a complex fragment is to a
large part also a function of the nature of the donor
atoms, we extended our study to include thiol and
phosphane ligands, and aimed to derive NS4 and
NP4 ligands from intermediates in the synthesis of
1. We report here on attempts to obtain pure samples
of the tetraalcohol 2,6-C5H3N[CMe(CH2OH)2]2,
on the reactivity of the tetratosylate 2,6-
C5H3N[CMe(CH2OTs)2]2 (2) and the tetrabromide
2,6-C5H3N[CMe(CH2Br)2]2 (3) towards thiourea,
potassium O-ethyl xanthogenate, sodium ethanethi-
olate and potassium diphenylphosphide, and on
the complete oxidation of the tetraphosphane 2,6-
C5H3N[CMe(CH2PPh2)2]2 (5) to give the oxide,
2,6-C5H3N[CMe(CH2P(=O)Ph2)2]2 (6). Complex-
ation studies with 5 are in progress and will be
reported elsewhere.
2,6-C5H3N[CMe(CH2X)2]2 (X = Cl; X = Br: 3)
We pursued the synthesis of tetrahalide ana-
logues of the tetraalcohol in order to obtain use-
ful starting materials for nucleophilic substitu-
tion reactions. Attempts to prepare a tetrachloride
from the tetraalcohol by reaction with SOCl2 in
pyridine [6] were hampered by the presence of
water and invariably gave mixtures of products.
An intense signal in the mass spectrum (FD) at
m/z = 351 (90 %) is assigned to the bis(ester)
4
of sulfurous acid [7], 2,6-bis-(5-methyl-2-oxo-2
-
[1,3,2]dioxathian-5-yl)-pyridine, shown in Formula
B, but a signal for the desired chloro derivative is not
observed. We therefore focussed on the synthesis of
a tetrabromide.
Results and Discussion
Attempted purification of the tetraalcohol
2,6-C5H3N[CMe(CH2OH)2]2
Pure tetraalcohol had been obtained previously
as the hemihydrate [4], but its water content proved
a disadvantage in a number of subsequent reactions
(see the attempted synthesis of a tetrachloride, be-
low). Also, we sought a straightforward method for
purifying tetraalcohol that had been obtained in an
impure form. To this end, crude tetraalcohol was
deprotonated with potassium hydride in hexane and
treated with 4 eq of trimethylsilylchloride, to give
a brown oil containing the tetrakis(trimethylsilyl)-
ether (Formula A, 2,6-bis-[1-methyl-2-(trimethyl-
silanyloxy)-1-(trimethyl-silanyloxymethyl)-ethyl]-
pyridine) as the main product. The mass spectrum
(FD) has the expected parent ion as the most in-
tense peak at m/z = 543. In addition to signals due
The reaction of pure tetratosylate 2 with an ex-
cess of LiBr in anhydrous DMSO at elevated tem-
perature yields, after aqueous workup, a yellow-
brown viscous oil, which is the virtually pure tetra-
bromide “pyBr4”, 3 (2,6-bis-(2-bromo-1-bromom-
ethyl-1-methyl-ethyl)-pyridine). The isolated yield
is close to 99% (eq. (1)). In the mass spectrum of 3
(FD), the parent ion signal clusters around m/z = 507
(= M[py(79Br)4] + 4) and shows the isotope pattern
1
to impurities, the H NMR spectrum shows sig-
nals for the pyridine, the diastereotopic methylene,
the methyl and the trimethylsilyl protons having
the expected patterns and correct intensities [5].
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C. Zimmermann et al. · Tetrapodal Ligands with NS4 and NP4 Donor Sets
expected for a tetrabromo derivative. In the 1H NMR tion under the chosen conditions is thus incomplete,
spectrum, the protons on the pyridine ring give rise and it has not been pursued further.
to a triplet (7.69 ppm) and doublet (7.23 ppm) with
correct integrated intensities (1 : 2, AB2 system),
while the diastereotopic methylene protons show a
characteristic set of two doublets (AB system) at
ca. 3.9 ppm, and the six methyl protons give rise
to a singlet at 1.61 ppm. The compound dissolves
easily in ether, CH2Cl2, and THF. Its ready forma-
tion parallels the near quantitative reaction of the
tetratosylate with sodium azide under similar con-
ditions in the original synthesis of the pentaamine
1 [8].
Reaction of 2,6-C5H3N[CMe(CH2Br)2]2 with
potassium O-ethyl xanthogenate
Instead of thiourea, potassium O-ethyl xan-
thogenate [13, 14] or potassium thioacetate [15, 16]
have also been used as “masked” sulfhydryl group
equivalents. The reaction of the tetrabromide 3 with
an excess (6 eq) of potassium O-ethyl xanthogenate
in DMSO at 70 C for 72 h, followed by aqueous
work-up, gives a yellow paste whose MS data sug-
gest a derivative containing a maximum of three
xanthogenate residues. Treatment of this paste with
ethylenediamine at 40 C, followed by hydrolysis
as described in the literature [14], and final purifi-
cation (cf. Experimental) give a yellowish powder
Reaction of 2,6-C5H3N[CMe(CH2Br)2]2 with
thiourea
A general method for the preparation of alkylthi-
ols starts from the corresponding alkyl halide, which
is converted into an S-alkyl thiouronium salt by
reaction with thiourea, and subsequently decom-
posed in alkaline solution [9 - 12]. The reaction of
the tetrabromide 3 with a slight excess (4.4 eq) of
thiourea in refluxing ethanol yields, after work-up,
a yellow paste whose 1H NMR spectrum indicates a
mixture of products. After treatment of this mixture
with aqueous NaOH, neutralisation with aqueous
HCl, and extraction with diethyl ether, the obtained
material shows no indication ofthe desired tetrathiol
(1H NMR, MS). However, crystallisation of the ini-
tially obtained mixture of products from aqueous
picric acid provides a yellow microcristalline mate-
rial. Its 1H NMR spectrum has a broadened two-line
feature at 9.03 ppm assigned to the diastereotopic
NH2 protons of a thiouronium salt and a singlet for
the picrate protons at 8.58 ppm. From a comparison
of integrals of these and the methylene group sig-
nals we conclude that the product is best formulated
as a bis(thiouronium) salt, in which only two out of
four bromo substituents have been replaced with
a thioureido group (Formula C shows one of the
three possible isomers, in which like substituents
are diametrically opposite). The substitution reac-
1
whose MS and H NMR data are compatible with
the formulation of a bis(thietane) (2,6-bis-(3-me-
thyl-thietan-3-yl)-pyridine, Formula D). The molec-
ular mass of this material corresponds to the peak
of highest intensity in the mass spectrum, and the
1H NMR spectrum is conspicuous for the absence
of SH signals, while showing all the other expected
signals with correct integrated intensities. Thietane
formation is known to be facile in 1,3-disubstitu-
ted trimethylene derivatives, in which an initially
introduced thiolate function displaces, in a second
step, a leaving group in the 3-position by nucle-
ophilic substitution [17]. Therefore, the bis(thio-
uronium) salt shown in Formula C is expected also
to give the bis(thietane) product when worked up
with ethylenediamine [17].
2,6-C5H3N[CMe(CH2SEt)2]2 (4)
In contrast to the other reactions described here
which involve sulfur nucleophiles, the reaction of
the tetrabromide 3 with sodium ethanethiolate (in
refluxing ethanol) proceeds smoothly and with com-
plete substitution (eq. (2)). Sodium bromide pre-
cipitates and may thus be conveniently removed.
Evaporation of the solvent leaves 4 as a yellow oil
(isolated yield: 58%), with 1H and 13C patterns char-
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C. Zimmermann et al. · Tetrapodal Ligands with NS4 and NP4 Donor Sets
1259
and 1H 13C NMR spectra has allowed the com-
plete assignment of the carbon resonances (see Ex-
perimental). In the 31P spectrum, a broad signal at
–24.7 ppm is assigned to the phosphorus atoms
of the diphenylphosphanyl groups. The chemical
shifts of the methylene protons and carbon and
phosphorus atoms in 3 are comparable to those de-
termined for other poly(diphenylphosphanyl) com-
pounds [25, 28]. The mass spectrum has a prominent
signal (> 90% intensity) due to the molecular ion
at m/z = 928, as expected. The tetraphosphane is
readily soluble in CH2Cl2, THF, toluene, ether and
refluxing ethanol, and sparingly soluble in hexane.
It is insoluble in ethanol and methanol at room tem-
perature. Oxidation of the solvent-free solid by aer-
obic oxygen is sluggish (if it occurs at all; no change
in the 31P spectrum is observed after several hours),
and the compound may be stored indefinitely under
dry dinitrogen at room temperature.
acteristic of a C2v-symmetrical derivative (see Ex-
perimental). Future work will address the question
whether the derivatisation is similarly straightfor-
ward with benzylthiolate, as benzyl thioethers may
be cleaved selectively on the benzyl side to leave
the corresponding thiol [18], so that this reaction
may finally provide a viable route to the tetrathiol
2,6-C5H3N[CMe(CH2SH)2]2.
2,6-C5H3N[CMe(CH2PPh2)2]2 (5)
The reaction of polytosylates with alkali phos-
phides is an established method of preparation for
polyphosphanes [19 - 21]. An initial series of ex-
periments, however, employing the tetratosylate 2
and LiPPh2 or KPPh2, gave ill-defined brown mix-
tures of products, and neither NMR spectroscopy
nor mass spectrometry indicated the formation of
the target molecule. One of the underlying rea-
sons may be the basicity of the phosphide anion,
and its abstraction of tosylate methyl protons, in-
stead of reacting by nucleophilic displacement of
the leaving group [22, 23]. As an alternative start-
ing material in the synthesis of polyphosphanes,
polyhalides have been used to advantage, some of
them having neopentyl-like residues as in our sys-
tem [24 - 26]. This motivated our synthesis of the
tetrabromide 3, as described above. Treatment of a
solution of 3 in THF at –50 C with a slight ex-
cess (0.2 eq) of potassium diphenylphosphide [27],
followed by raising the temperature slowly and re-
fluxing for 12 h, gives a mixture from which, af-
ter aqueous workup, the tetraphosphane 5 may be
isolated as a colourless foamy solid in up to 65%
2,6-C5H3N[CMe(CH2P(=O)Ph2)2]2 (6)
With a view to the later synthesis of tetraphos-
+
phane complexes of the type [(5)M(NO)] (M =
Ru, Fe), we studied conditions under which the lig-
and would be susceptible to oxidation by nitric ox-
ide (nitrogen monoxide, NO). Since the reaction
may be expected to produce the phosphane oxide,
with concomitant formation of nitrous oxide (dini-
trogen oxide, N2O) [29, 30], we chose a 1 : 2 sto-
ichiometry (RPPh2:NO). Solutions of 5 in CH2Cl2
at –78 C, 0 C, and 25 C, respectively, were each
treated with 8 eq of NO gas, and their IR spectra
recorded periodically. Whereas no reaction was ob-
served at –78 C and 0 C, a ready reaction occurred
at 25 C to produce the oxide 6 (2,6-bis-[2-(diphe-
nyl-phosphinoyl)-1-(diphenyl-phosphinoylmethyl)-
1-methyl-ethyl]-pyridine; (eq. (4)). The formation
of N2O is conveniently followed by monitoring a
growing band at 2222 cm 1, which is due to the
N=N stretching vibration.
1
yield (eq. (3)). In the H NMR spectrum, the di-
astereotopic methylene protons (AB system) give
rise to two characteristic doublets of doublets be-
For quantitative formation of the oxide, the
tetraphosphane is best treated with an excess of
NO in diethylether at room temperature (see Ex-
perimental) [29]. Compound 6 has been isolated
1
tween 2.5 and 2.8 ppm, due to geminal H1H and
1H31P coupling. Comparison of the 1H 31P 13C
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C. Zimmermann et al. · Tetrapodal Ligands with NS4 and NP4 Donor Sets
(111.1 - 114.1 and 106.7 - 109.8 , respec-
tively) [31].
Concluding Remarks
The present work shows that ligands with
square-pyramidally juxtaposed donor sets other
than NN4 are, in principle, accessible from inter-
mediates of the synthesis of the pentaamine 2,6-
C5H3N[CMe(CH2NH2)2]2. While the tetratosylate
2 is unsuitable for a direct tetraphosphane synthesis,
it may be converted into the corresponding tetra-
Fig. 1. Molecular structure of one of the two symmetry-
independent molecules in 6 (for clarity, a ball-and-stick
representation is shown, and hydrogen atoms have been
omitted).
bromide 3 in high yield, which then undergoes
a clean reaction with KPPh2 to yield the corre-
sponding NP4 ligand. The tetraphosphane 5 is the
first polyphosphane of this topology. Preliminary
experiments show that, inspite of its considerable
steric bulk, 5 does indeed form mononuclear com-
plexes (M = Ru, Co) in which the ligand acts as
a square-pyramidal coordination cap. The prepa-
ration of a tetrathiol (NS4) from the tetrabromide
and thiourea was unsuccessful under the chosen
conditions. However, NMR spectroscopic results
indicate that substitution (albeit incomplete) does
occur in ethanol. Current work addresses the ques-
tion whether a more nucleophilic sulfhydryl equiv-
alent (such as thioacetate) may effect complete sub-
stitution. Alternatively, since complete substitution
has been achieved with ethanethiolate as the nu-
cleophile, the analogous reaction with benzylthio-
late and subsequent cleavage of the corresponding
thioether may finally provide access to a tetrapodal
polythiol having an NS4 donor set.
as a colourless powder in 94% yield. The product
is characterised by a new strong absorption in the
IR spectrum at 1183 cm 1, which is assigned to
the P=O stretching vibration. The 1H, 13C, and 31
P
NMR data reflect the pairwise diastereotopicity of
the phenyl rings but are otherwise in accord with
values reported for other , -bis(diphenyl-phos-
phinoyl) alkanes [31]. The only striking difference
1
is in the J(P-C) coupling constants involving the
ipso carbon atoms. At ca. 190 Hz in the case of 6,
these coupling constants are almost three times as
large as in the case of the diphosphane-derived ox-
ides [31]. Compound 6 dissolves easily in CH2Cl2
but is virtually insoluble in diethyl ether.
The tetraphosphane oxide crystallises from
methylene chloride as the hydrate with 0.5 equiv-
alents of CH2Cl2 (6 H2O 0.5 CH2Cl2). Sin-
gle crystals were of sufficient quality to allow de-
termination of the solid-state structure (Fig. 1).
The substituents on the phosphorus atoms adopt
a distorted tetrahedral geometry. The P=O bond
lengths involving P12, P13 and P15 are similar (av-
erage value: 147.5 pm), while the P=O bond at
P14 is significantly shorter (140.0 pm). The av-
erage P-C bond length (P-CAryl and P-CAlkyl) is
182.0 pm. These values, with the exception of
the P=O bond length involving P14, are compa-
rable to those found for 1,3-bis-(diphenyl-phos-
phinoyl)-propane: d(P-CAryl/CAlkyl) = 179.9 pm,
d(P=O) = 149.1 pm [31]. Likewise, the angles
(OPCAryl Alkyl) and (CAryl AlkylPCAryl Alkyl) are in
the ranges 110.8(4) - 118.4(4) and 100.5(4) -
109.7(4) , respectively, and thus of the same magni-
Experimental Section
Materials and instrumentation: Manipulations were
performed under an atmosphere of dried nitrogen, using
standard Schlenk techniques. Reagents were AR grade
or better and were purchased from Merck, Fluka, and
Aldrich. The tetratosylate 2,6-C5H3N[CMe(CH2OTs)2]2
and KPPh2 2 THF were prepared as described previ-
ously [4, 27]. IR spectra (KBr discs or solutions in CaF2
cuvettes) were recorded on a Perkin Elmer 16PC FT-IR
instrument; solution spectra were compensated for sol-
vent absorptions. NMR spectra were measured on JEOL
JNM-EX 270, Lambda LA 400 and ALPHA 500 spec-
trometers, and mass spectra on a JEOL MSTATION 700
spectrometer. Only the absolute values of NMR coupling
constants have been determined. Elemental analyses were
tude as in 1,3-bis-(diphenyl-phosphinoyl)-propane performed using a Carlo Erba Elemental Analyser 1106.
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C. Zimmermann et al. · Tetrapodal Ligands with NS4 and NP4 Donor Sets
1261
2,6-C5H3N[CMe(CH2Br)2]2 (3). To a warm solution room temperature, and subsequently heated to reflux for
(70 C) of the tetratosylate 2 (26.02 g, 29.84 mmol) in 12 h. Upon cooling to room temperature, the mixture
DMSO (430 ml) was added dry LiBr (15.55 g, 179 mmol, was further cooled to 0 C in an ice bath, and quenched
6 eq) in one portion, and the mixture stirred at 70 C for with degassed water (120 ml). The organic phase was
72 h. The added LiBr dissolved within 30 min, and to- separated, and the aqueous phase extracted with abso-
wards the end of the reaction the solution had taken on a lute ether (5
100 ml). The combined organic phases
light brown colour. Workup was then carried out in air, were dried over Na2SO4, taken to dryness, and the re-
with no precautions taken to exclude water from the sol- maining yellowish paste dried in vacuo. It was triturated
vents. After the solution had cooled to room temperature, with absolute ethanol (50 ml) with stirring at 50 C for
water (690 ml) was added with stirring to give a white 2 h. Upon decantation of the yellowish liquid, the re-
milky precipitate. Stirring was continued for 10 min, and maining colourless paste was triturated with n-hexane
the mixture then extracted with ether (5 200 ml). The overnight. The hexane solution was then decanted, the
combined ether phases were extracted once with water sirupy paste dissolved in absolute CH2Cl2, the solution
(70 ml), and dried over Na2SO4. Ether was distilled off taken to dryness, and the residue dried in vacuo to yield
on a rotary evaporator to leave the tetrabromide 3 as a the tetraphosphane as a colourless foamy solid. The hex-
yellow oil which was dried in vacuo. The material is ane solution deposited further product upon cooling to
virtually pure (1H NMR) and was used in subsequent re- –20 C for 24 h. Yield: 9.04 g (65.0%). The elemental
actions without further purification. Yield: 14.9 g (99%). analysis is as yet unsatisfactory due to variable amounts
MS (FD+, THF): m/z(%) = 507 [py(Br)4]+ (100). 1H NMR of occludedsolvent:C61H57NP4 (928.03):calcd. C, 78.95;
(270 MHz, CDCl3, R. T.): /ppm = 7.69 (AB2, 3 lines, 1 H, 6.19; N, 1.51; found C, 75.41; H, 5.81; N, 1.33 C. IR
H, py-H4), 7.23 (AB2, 2 lines, 2 H, py-H3 5), 3.93 (d, (KBr, cm 1): 3048, 2959, 1583, 1573, 1479, 1455, 1432
2
2J(HH) = 9.9 Hz, 4 H, -CHH-Br), 3.84 (d, J(HH) = (P-Ph), 738, 694, 508. MS (FD+, CH2Cl2): m/z (%) = 928
1
9.9 Hz, 4 H, -CHH-Br), 1.61 (s, 6 H, -CH3). 1H 13C [py(PPh2)4]+ (90). H NMR (400 MHz, CD2Cl2, R. T.):
NMR (270 MHz, DMSO-d6, R. T.): /ppm = 159.64 (py-
/ppm = 7.31 - 6.89 (m (br), 43 H, py-H4, py-H3 5, Cortho
-
C2/6), 137.31 (py-C4), 119.40 (py-C3/5), 45.60 (>C<), H, Cortho'-H, Cmeta-H, Cmeta'-H, Cpara-H, Cpara'-H), 2.76 (dd
42.14 (-CH2-), 22.53 (-CH3).
(br), 2J(HH) = 14.15 Hz, 2J(HP) = 4.64 Hz, 4H, -CHH-),
2.52 (dd (br), 2J(HH) = 14.13 Hz, 2J(HP) = 1.46 Hz, 4 H,
-CHH-), 1.24 (s (br), 6 H, -CH3). 31P NMR (400 MHz,
CD2Cl2, R. T.): /ppm = –24.72 (s (br)). 1H 31P 13C
NMR/ 1H 13C NMR (500 MHz, CD2Cl2, R. T.): /ppm =
2,6-C5H3N[CMe(CH2SCH2CH3)2]2 (4). To a solution
of sodium metal (freshly cut under hexane, 1.27 g,
55.2 mmol) in ethanol (50 ml) was added ethanethiol
(3.42 g, 4.1 ml, 55.0 mmol), and the mixture stirred at
room temperature for 15 min. A solution of the tetrabro-
mide 3 (5.58 g, 11.0 mmol) in ethanol (10 ml) was then
added, and the mixture refluxed for 12 h. A crystalline pre-
cipitate (NaBr) began to appear after 1 h. The suspension
was allowed to cool to room temperature, filtered, and the
filtrate taken to dryness to leave 4 as a yellow oil. Yield:
2.74 g (58 %). 1H NMR (270 MHz, CDCl3, R. T.): /ppm
= 7.56 (AB2, 3 lines, 1 H, py-H4), 7.14 (AB2, 2 lines,
2 H, py-H3 5), 3.13 (d, 2J(HH) = 12.6 Hz, 4 H, -CHH-),
3
165.51 (t, J(CP) = 3.1 Hz, 2 C, py-C2/6), 140.80 (d,
1J(CP) = 12.93 Hz, 4 C, Cipso/Cipso'), 140.78 (d, 1J(CP) =
14.48 Hz, 4 C, Cipso/Cipso'), 136.46 (s, 1 C, py-C4), 133.64
2
(d, J(CP) = 20.69 Hz, 8 C, Cortho/Cortho'), 133.31 (d,
2J(CP) = 20.18 Hz, 8 C, Cortho/Cortho'), 128.88 (d, 3J(CP) =
7.76 Hz, 8 C, Cmeta/Cmeta'), 128.82 (s, 4C, Cpara/Cpara'),
3
128.75 (d, J(CP) = 6.72 Hz, 8 C, Cmeta/Cmeta'), 128.59
(s, 4C, Cpara/Cpara'), 118.47 (s, 2 C, py-C3/5), 44.93 (t,
2J(CP) = 15.26 Hz, 2 C, >C<), 43.37 (dd, 1J(CP) =
16.29 Hz, 3J(CP) = 9.57 Hz, 4 C, -CH2-), 26.79 (t,
3J(CP) = 10.6 Hz, 2 C, -CH3).
2
2.96 (d, J(HH) = 12.5 Hz, 4 H, -CHH-), 2.31 (quart,
3J(HH) = 7.4 Hz, 8 H, -CH2-CH3), 1.50 (s, 6 H, -CH3),
3
1.11 (t, J(HH) = 7.4 Hz, 12 H, -CH2-CH3). 1H 13C
2,6-C5H3N[CMe(CH2P(=O)Ph2)2]2 (6). Reactivity
studies with NO: Three solutions of 100 mg aliquots of
5 (0.11 mmol) in CH2Cl2 (10 ml) were kept at –78 C,
0 C, and 25 C, respectively, and to each was added NO
(19.3 ml, 0.86 mmol). Solution IR spectra were recorded
NMR (270 MHz, CDCl3, R. T.): /ppm = 162.96 (py-
C2/6), 136.15 (py-C4), 118.63 (py-C3/5), 46.34 (>C<),
43.36 (-CH2-), 27.93 (-CH2-CH3), 23.12 (-CH3), 14.96
(-CH2-CH3).
2,6-C5H3N[CMe(CH2PPh2)2]2 (5). A suspension of at hourly intervals. No reaction was observed in the first
KPPh2 2 THF (25.4 g, 63.5 mmol) in THF (150 ml) was two cases after 4 h, and the mixtures were discarded. The
cooled to –50 C in an acetone/dry ice bath. To this was mixture at room temperature showed a prominent band
1
added a solution of 3 (7.6 g, 15 mmol) in THF (50 ml) at 2222 cm (N2O, N=N str) already after 1 h. Reaction
during 4 h, during which time the suspension changed was allowed to proceed for 16 h, after which time the mix-
colour from red to yellow-orange. The reaction mixture ture was taken to dryness to leave 6 as a colourless powder
was allowed, together with the cold bath, to warm to whose spectroscopic data were identical to those of ma-
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1262
C. Zimmermann et al. · Tetrapodal Ligands with NS4 and NP4 Donor Sets
terial obtained by the following procedure. Preparative R. T.): /ppm = 7.69 (AB2, 3 lines, 1 H, py-H4), 7.27
scale: Into a clear, colourless solution of the tetraphos- (AB2, 2 lines, 2 H, py-H3 5), 3.84 (d, 2J(HH) = 10.8 Hz,
2
phane 5 (1.85 g, 2.0 mmol) in ether (40 ml), cooled to 0 C, 4 H, -CHH-OSiMe3), 3.77 (d, J(HH) = 10.8 Hz, 4 H,
was passed a gentle stream of NO during 5 min. A fine, -CHH-OSiMe3), 1.29 (s, 15 H, 6 H, -CH3 [+ impurities]),
powdery solid began to appear after ca. 30 s. Stirring was 0.0 (s, 36 H, -Si(CH3)3).
continued for 30 min at 0 C and for a further 30 min
at room temperature. The solid was then filtered off,
washed with ether (3 8 ml), and dried in vacuo. Yield:
1.93 g (94.0 %). 6 0.5 Et2O, C61H57NO4P4 0.5 Et2O
(1029.09): calcd. C 73.53, H 6.07, N 1.36; found C 73.78,
H 6.35, N 1.24. IR (KBr, cm 1): 3053, 2964, 1576, 1482,
1457, 1436 (P-Ph), 1261, 1183 (P=O), 1116, 1100, 1067,
1026, 997, 804, 742, 714, 696, 593, 556, 508. MS (FD+,
CH2Cl2): m/z (%) = 992 [py(P(O)Ph2)4]+ (100). 1H NMR
(270 MHz, CD2Cl2, R. T.) /ppm = 7.61 - 6.91 (m (br), 43
H, py-H4, py-H3 5, Cortho-H, Cortho'-H, Cmeta-H, Cmeta'-H,
Cpara-H, Cpara'-H), 3.44 (dd, 2J(HH) = 15.03 Hz, 2J(HP) =
Reaction of the tetrabromide 3 with thiourea. A solu-
tion of 3 (2.53 g, 5.0 mmol) in THF (10 ml) was added
dropwise to a suspension of thiourea (1.37 g, 22.0 mmol,
4.4 eq) in ethanol (30 ml), and the mixture heated to reflux
for 6 h. A clear solution resulted upon warming, whose
colour gradually turned yellow. No precipitate formed
upon cooling to room temperature at the end of the re-
action, and the solution was taken to dryness to leave
a yellow paste (ca. 2.3 g) which was dried in vacuo.
Half of this was hydrolysed with base following the pro-
cedure of Harley-Mason et al. [9], but analysis of the
product provided no indication for the formation of the
target tetrathiol. The other half was dissolved in reflux-
ing ethanol, and the hot solution added to a refluxing
aqueous solution of picric acid (1% m/m). Upon cool-
ing to room temperature, the solution deposited a yellow
microcrystalline powder which was filtered off, washed
with ethanol/ether (1:1), and dried in a stream of dry
2
9.95 Hz, 4 H, -CHH-), 2.89 (ddd, J(HH) = 14.37 Hz,
4
2J(HP) = 12.02 Hz, J(HP) = 1.17 Hz, 4 H, -CHH-),
1.49 (s, 6 H, -CH3). 31P NMR (400 MHz, CD2Cl2, R. T.):
/ppm = 26.97 (s). 1H 13C NMR (270 MHz, CD2Cl2,
3
R. T.): /ppm = 163.01 (t, J(CP) = 29.91 Hz, 2C, py-
C2/6), 136.62 (s, 1 C, py-C4), 135.66 (d, 1J(CP) = 193.87
Hz, 4 C, Cipso/Cipso'), 135.57 (d, 1J(CP) = 192.86 Hz, 4 C,
1
dinitrogen. H NMR data suggest this material to be a
C
ipso/Cipso'), 131.18 (s (br), 8 C, Cpara/Cpara'), 130.65 (d,
bis(thiouronium) bis(picrate) derivative of the tetrabro-
mide 3: 1H NMR (270 MHz, DMSO-d6, R. T.): /ppm =
9.03 (d (br), 2J(HH) = 9.4 Hz, 8 H, thiouronium-), 8.58
(s, 4 H, picrate), 7.90 (''t'', 1H, py-H4), 7.45 (''d'', 2 H,
py-H3 5), 3.78 - 3.53 (m, 8 H, -CH2-), 1.52 (s, 6 H, -CH3).
Reaction of the tetrabromide 3 with potassium O-ethyl
xanthogenate. A solution of 3 (5.07 g, 10.0 mmol) in
DMSO (150 ml) under dry dinitrogen was warmed to
70 C with stirring, solid potassium O-ethyl xanthogenate
(9.62 g, 60.0 mmol) – which had previously been dried
2J(CP) = 22.69 Hz, 4 C, Cortho/Cortho'), 130.52 (d, 2J(CP) =
23.72Hz, 4 C, Cortho/Cortho'), 128.56 (d, 3J(CP) =22.68 Hz,
3
4 C, Cmeta/Cmeta'), 128.53 (d, J(CP) = 22.68 Hz, 4 C,
Cmeta/Cmeta'), 117.82 (s, 2 C, py-C3/5), 43.91 (t, 2J(CP) =
1
15.47 Hz, 2 C, >C<), 40.11 (dd, J(CP) = 139.23 Hz,
3J(CP) = 25.77 Hz, 4 C, -CH2-), 26.33 (t, 3J(CP) =
19.59 Hz, 2 C, -CH3).
Attempted derivatisations and purifications
2,6-C5H3N[CMe(CH2OSiMe3)2]2. Potassium hydride in an oil pump vacuum – added in one portion, and the
(0.45 g, 11.2 mmol) was suspended in hexane (10 ml), and mixture stirred at 70 C for 72 h. The xanthogenate ini-
the mixture cooled to 0 C in an ice bath. After addition tially formed a yellow sludge, which dissolved within
of a solution of crude tetraalcohol (0.71 g, 2.8 mmol) 2 h to give a clear solution, which gradually took on
in THF (7 ml), stirring was continued for 15 min at 0 C. a yellowish colour. Workup was performed in air. Af-
The mixture was then allowed to warm to room tempera- ter the solution had cooled to room temperature, water
ture during 30 min, and gas evolution (H2) was observed. (240 ml) was added, the mixture stirred for 10 min, and
The resulting yellow-brown suspension was cooled to – then extracted with ether (5 100 ml). The combined
60 C in a methanol / dry ice bath, and a solution of ether phases were extracted with water (30 ml) and dried
Me3SiCl (1.42 ml, 11.2 mmol) in hexane (10 ml) added over Na2SO4. After removal of the solvent and drying
dropwise. After the addition, stirring was continued for in vacuo, the remaining yellow paste was treated with
1 h at –60 C and another 12 h at room temperature, ethylenediamine (20 ml) at 40 C for 12 h. After cooling
during which time the colour of the suspension changed to room temperature, the solution was added to a water /
from brown to yellow. Precipitated KCl was removed by ice mixture (80 ml) to produce a milky precipitate. The
filtration / centrifugation, and the yellow filtrate taken to pH was adjusted to 5 by addition of aqueous HCl, and the
dryness in an oil pump vaccum, to leave a brown oil. suspension extracted with ether (5 100 ml). The com-
Kugelrohr (bulb-to-bulb) distillation failed to achieve ap- bined ether phases were dried over Na2SO4. Removal of
preciable purification. MS (FD+, CH2Cl2): m/z (%) = 543 the solvent and drying in vacuo gave a yellowish pow-
1
[py(OTMS)4]+ (100). H NMR (270 MHz, DMSO-d6, der formulated as the bis(thietane) derivative: MS(FD+,
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C. Zimmermann et al. · Tetrapodal Ligands with NS4 and NP4 Donor Sets
Table 1. Crystallographic data for compound 6.
1263
(AB2, 3 lines, 1 H, py-H4), 7.17 (AB2, 2 lines, 2 H, py-
H3 5), 3.79 (d, 2J(HH) = 4.5 Hz, 4 H, (-CHH)2S), 3.01 (d,
2J(HH) = 4.5 Hz, 4 H, (-CHH)2S), 1.66 (s, 6 H, -CH3)
(no signals for -SH).
Composition
6 H2O 0.5 CH2Cl2
C61 5H60ClNO5P4
1052.43
Empirical formula
Formula weight
Crystal system
Space group (no.)
orthorhombic
Pca21 (no. 29)
26.914(3)
Crystallography
˚
a [A]
Selected distances and angles for compound 6 are dis-
cussed in the text; crystal data are given in Table 1. The
structure was solved by direct methods and refined by full-
matrix least-squares procedures on F2 using SHELXTL
NT 5.10 (Bruker AXS, 1998). The unit cell contains
two symmetry-independent molecules. One of the solvent
water molecules is disordered, with alternative occupa-
tions of 76(2)% (O2) and 24(2)% (O4). The hydrogen
atoms were calculated in geometrically optimised posi-
tions, and their isotropic displacement parameters tied to
those of the adjacent carbon or oxygen atoms by a fac-
tor of 1.2 and 1.5, respectively. Positions for the hydrogen
atoms of the water molecules were obtained from a differ-
ence Fourier synthesis and not refined. Crystallographic
data (excluding structure factors) for this structure have
been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC 195312.
Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK [Fax: int. code +44 (1223) 336-033; E-mail:
deposit@ccdc.cam.ac.uk]
˚
b [A]
14.090(1)
˚
c [A]
28.732(3)
Z
8
3
˚
V [A ]
10896(2)
3
calcd [g cm
]
1.283
Diffractometer
Siemens P4
0.71073
[a]
˚
[A]
Crystal size [mm3]
T [ C]
0.70 0.62 0.48
200(2)
psi scans
0.651/0.687
Absorption correction
Tmin/Tmax
Scan
2
Range
4
52
Measured reflections
Unique reflections
15976
12041
6305
0.238
1316
9.2
0.1934
0.0747
0.608/–0.385
Observed reflections[b]
1
(Mo-K ) [mm
]
Refined parameters
Data/parameter ratio
wR2 (all data)[c]
R1 (obs. data)[d]
3
˚
fin (max/min) [e A
]
Weighting scheme[e]
Abs. structure parameter
k = 0.0792 / l = 0.08784
–0.01(12)
Acknowledgements
[a] Mo-K , graphite monochromator; [b] with Fo 4 (F);
[c] wR2 = ( Σ [w(Fo2 – Fc )2]
Σ w(Fo )2] )0 5
;
[d] R1 =
We thank Professor H. H. Karsch (Technische Univer-
sita¨t Mu¨nchen) and Professor D. Uguen (ECPM, Stras-
bourg) for valuable discussions, and we are grateful to
Professor D. Sellmann for support of this work. Finan-
cial support by the Deutsche Forschungsgemeinschaft is
gratefully acknowledged.
2
2
Σ |Fo| – |Fc| Σ |Fo| for F > 4 (F); [e] w = 1/[ 2(Fo ) +
2
2
2
(k P)2 + l P] and P = (Fo + 2 Fc )/3.
CH2Cl2): m/z (%) = 251 [py(S)2]+ (100), 283 [py(S)(S2)]+
(10). 1H NMR (270 MHz, DMSO-d6, R. T): /ppm = 7.76
[6] J. P. Mason, D. J. Gasch, J. Am. Chem. Soc. 60,
2816 (1938).
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