4,5-Bis(diphenylthiophosphinoyl)-1,2,3-triazole, LT-S2: A new varidentate ligand containing diphenylthiophosphinoyl moieties

Article abstract of DOI:10.1016/S0020-1693(01)00706-X

The novel ligand 4,5-bis(diphenylthiophosphinoyl)-1,2,3-triazole, L^T-S2H, has been synthesized, converted to the triethylamine salt, and to the palladium complexes Pd[L^T-S2]₂ and Pd[L^T-S2][η³-methallyl]. Structures of L^T-S2H, of its 2-acetyl derivative, of Pd[L^T-S2]₂ and Pd[L^T-S2][η³-methallyl] were determined by X-ray crystallography. In the last two complexes the L^T-S2 ligand was N,S-bonded.

Full text of DOI:10.1016/S0020-1693(01)00706-X

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Inorganica Chimica Acta 330 (2002) 38–43
4,5-Bis(diphenylthiophosphinoyl)-1,2,3-triazole, LT-S2: a new
varidentate ligand containing diphenylthiophosphinoyl moieties
Arnold L. Rheingold, Louise M. Liable-Sands, Swiatoslaw Trofimenko *
Department of Chemistry and Biochemistry, Uni6ersity of Delaware, Newark, DE 19716, USA
Received 18 May 2001; accepted 13 June 2001
In memory of Luigi M. Venanzi
Abstract
The novel ligand 4,5-bis(diphenylthiophosphinoyl)-1,2,3-triazole, LT-S2H, has been synthesized, converted to the triethylamine
salt, and to the palladium complexes Pd[LT-S2
]
and Pd[LT-S2][h3-methallyl]. Structures of LT-S2H, of its 2-acetyl derivative, of
2
Pd[LT-S2]2 and Pd[LT-S2][h3-methallyl] were determined by X-ray crystallography. In the last two complexes the LT-S2 ligand was
N,S-bonded. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structures; Palladium complexes; Polydentate ligand complexes; Thiophosphinoyl complexes
structure LT-E2H,1 where E can be O, S, Se, NR% or
1. Introduction
NAr, while R may be a variety of alkyl or aryl groups.
The design of ligands to enable a desired function of
a coordinated metal spans the whole range of inorganic
and bioinorganic fields, either in the extraction of metal
ions, in providing the proper steric and electronic envi-
ronment for catalysis in chemical industry, or in the
modeling of biologically important enzymatic pro-
cesses. Yet, truly novel ligands with impressive proper-
ties do not appear very often.
We have reported recently a novel and versatile
There exist other ligands containing the ꢀP(E)Ph2
grouping, exemplified mainly by structures A or B,
where E can be O, S, Se, or NR% (R is most often Ph or
Me). They usually coordinate as the deprotonated an-
ions, although examples of complexes without deproto-
nation, as in the five-coordinate Sb{H2C[P(O)Ph2]2}Cl3,
are also known [2].
ligand,
4,5-bis(diphenylphosphinoyl)-1,2,3-triazole,
LT-O2H, which is thermally, oxidatively and hydrolyti-
cally very stable, and thus can be used under harsh
conditions [1]. It combines the coordinating ability of
the two ꢀP(O)Ph2 groups with the nitrogen donor
atoms of the triazole ring, and is the prototype of a
much broader family of ligands, having the general
1 In Ref. [1] the abbreviation LT was used for the 4,5-bis(-
diphenylphosphinoyl)-1,2,3-triazole ligand. Since more ligands of this
type are now being prepared, the abbreviation has been modified, to
specify the phosphorus substituents. Thus, LT-E2H will denote the
4,5-bis(diphenylphosphino)-1,2,3-triazole, where each phosphorus
contains a PꢁE bond. When the phosphorus E substituents are
different, the abbreviation will be LT-E,E%, as for instance LT-O,S
,
* Corresponding author. Tel.: +1-302-831 0716; fax: +1-302-831
6335.
E-mail address: trofimen@udel.edu (S. Trofimenko).
LT-O,Se, and so forth. The designation LTH will be reserved for the
parent compound, 4,5-bis(diphenylphosphino)-1,2,3-triazole.
0020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00706-X

A.L. Rheingold et al. / Inorganica Chimica Acta 330 (2002) 38–43
39
Ph2PCꢂCPPh2 (0.26 mol) plus 32 g (1.0 mol) sulfur was
heated with stirring in 500 ml THF. A vigorous reac-
tion ensued and the solids dissolved forming a red
solution, except for the excess sulfur. After 2 h the
liquid layer was decanted, the sulfur residue was
washed with a small amount of acetone, and the com-
bined washings were concentrated down to a thick
slurry. Filtration and washing with acetone yielded a
pinkish solid (102 g, 86.5%). Further evaporation of the
filtrates yielded a second crop of 16 g. Both crops were
slightly contaminated with sulfur, but this did not
interfere with the next step.
Most often the lithium salt of A was prepared (the
dilithio salt had a complicated structure) [3,4] and then
treated with various metal salts. These reactions were
not always clean, and products often contained four-
membered rings, involving bonding to the central car-
bon [5–8], and sometimes six-membered rings [9–13].
Similarly, the imidophosphonates B containing NH in
place of the central CH2 unit have also been prepared
[14–19], and converted to chelates, such as
M[N(P(S)R2)]2 for Mn(II), Fe(II), Ni(II) and Cu(II),
where R was Ph or Me [20–25]. In general, ligands of
type A and B do not possess good stability, nor do the
complexes derived therefrom.
2.2. 4,5-Bis(diphenylthiophosphinoyl)-1,2,3-triazole,
[LT-S2]H
The whole crude batch from the above reaction was
stirred with 19.2 g NaN3 (small excess) in 500 ml DMF,
and after the moderately exothermic reaction subsided,
the red solution was decanted from a small amount of
undissolved sulfur into 3 l of water containing 200 ml
of concentrated HCl. The precipitated creamy solid was
filtered off, washed with several portions of water, plus
a few small portions of acetone, and was dried. The
yield was 97.4 g (76.0% over-all for the two steps).
After recrystallization from DMF the compound
melted at 300 °C. Calc. C26H21N3P2S2: C, 62.3; H, 4.19;
N, 8.38. Found: C, 63.1; H, 4.30; N, 8.16%.
To overcome some of the limitations of previous
thiophosphinoyl ligands, we have prepared the second
member of the [LT-E2]H ligand class with E=S, [LT-
S2]H, and are reporting here some of the preliminary
results. As can be seen from structures C and D there
are two possible modes of chelation for the [LT-S2 −
]
ligand: a symmetric one (C26), through the two S
termini, forming a seven-membered chelate ring, and an
asymmetric one, through one S and the nearest N,
resulting in a five-membered ring.
2.3. 2-Acetyl-4,5-bis(diphenylthiophosphinoyl)-
1,2,3-triazole
A small sample of [LT-S2]H was boiled for 5 min in
excess acetic anhydride, and the solution was evapo-
rated. The residue was recrystallized from xylene; m.p.
1
173–175 °C. IR (cm−1): w(CO) 1719. H NMR (ppm):
2.54 (s, 3H, Me), 7.38 (m, 8H, Ph), 7.48 (m, 4H, Ph),
7.72 (m, 8H, Ph). 31P NMR (ppm): singlet at 31.2. Calc.
C28H23N3OP2S2: C, 61.9; H, 4.24; N, 7.73. Found: C,
62.2; H, 4.47; N, 7.58%.
2. Experimental
All chemicals were of commercial reagent grade and
were used as received. Elemental analyses were done by
Microanalysis, Inc., Wilmington, DE. Infrared spectra
were obtained as Nujol mulls or as KBr pellets with a
Perkin–Elmer 1625 FTIR spectrophotometer, using 16
scans. Proton NMR spectra were obtained with a Nico-
let NT360WB spectrometer. The compounds were stud-
ied under typical conditions of 16 K data points, a
sweep width of 3000–4000 Hz, 90° pulse angles, and a
recycle time of 4–5 s.
2.4. Triethylamonium salt of 4,5-bis(diphenyl-
thiophosphinoyl)-1,2,3-triazole, [LT-S2][HNEt3]
Adding an excess of triethylamine to a stirred slurry
of [LT-S2]H in methanol resulted in a clear solution,
which was evaporated, and the residue was slurried
with acetone, in which the salt is poorly soluble, and
filtered producing, after drying, the pinkish salt in 94%
yield. It was recrystallized from DMF. M.p. sinters
1
from 188 °C, dec. 196–198 °C. H NMR (ppm): 1.02
2.1. 4,5-Bis(diphenylthiophosphinoyl)acetylene
(t, 12H, Me), 3.00 (q, 8H, CH2), 7.16 (m, 8H, Ph), 7.27
(m, 4H, Ph), 7.63 (m, 8H, Ph). 31P NMR (ppm): 32.6.
Calc. for C32H36N4P2S2: C, 63.8; H, 5.98; N, 9.30.
Found: C, 64.0; H, 6.15, N, 9.13%.
The synthesis described below is an improvement
over the literature procedure [26]. A mixture of 102 g

40
A.L. Rheingold et al. / Inorganica Chimica Acta 330 (2002) 38–43
2.5. Pd[LT-S2][p3-methallyl]
2.7. Crystallography
An equimolar mixture of [LT-S2][HNEt3] and [Pd(h3-
methallyl)Cl]2 was stirred in methylene chloride at room
temperature for 1 h. Water was added, the layers were
separated, the pale yellowish organic layer was filtered
through alumina, and evaporated. The residue was
recrystallized from toluene. The compound starts yel-
lowing from 188 °C, and decompose to a red froth at
Crystallographic data are collected in Table 1. All
specimens were mounted in Paratone N mineral oil and
placed in the cold stream. Corrections for absorption
were applied using SADABS. Systematic absences
uniquely determined the space group for 3, and for the
others the centrosymmetric option was chosen by the
results of refinement. All structures were solved by
direct methods. All non-hydrogen atoms were refined
with anisotropic thermal parameters, and hydrogen
atoms were treated as idealized contributions. For 1 the
asymmetric unit is a half molecule residing on a two-
fold axis. The Pd complex in 4 is accompanied by two
molecules of pyridine. All software is contained in the
SHELXTL (5.1) library (G.M. Sheldrick, Bruker AXS,
Madison, WI, USA).
1
210–212 °C. H NMR (ppm): 2.01 (S, 3H, Me), 2.67
(s, 1H, anti ), 3.44 (s, 1H, anti ), 3.65 (d, 1H, syn), 4.60
(d, 1H, syn), 7.24 (m, 8H, phenyl), 7.40 (m, 4H,
phenyl), 7.53 (m, 4H, phenyl), 7.73 (m, 4H, phenyl). 31P
NMR (ppm): 46.8, 28.8. Calc. for C30H27N3P2PdS2: C,
54.5; H, 4.08; N, 6.35. Found: C, 54.4; H, 4.19; N,
6.25%.
2.6. Pd[LT-S2]2·2py
3. Results and discussion
To a stirred methanolic solution of 2 equiv. of
[LT-S2][HNEt3] was added dropwise 1 equiv. of a
methanolic solution of Na2PdCl4, and after 1 h the
solution was diluted with more water. The precipitated
solid was filtered off, washed with three portions of
water, and dried. It was recrystallized from pyridine,
forming a yellow bissolvate. After drying at 150 °C/0.1
Torr to remove pyridine, it did not melt up to 310 °C.
Calc. for C52H40N6P4PdS4: C, 56.4; H, 3.62; N, 7.59.
Found: C, 56.6; H, 3.81; N, 7.56%.
The sodium salts of [LT-S2]H and Na[LT-S2] were
obtained directly in one step by the reaction of sodium
azide with bis(diphenylthiophosphinoyl)acetylene in
DMF [Eq. (1)], and this solution could be used for the
preparation of metal complexes, or for obtaining the
free acid, [LT-S2]H, through acidification with hydro-
chloric acid. The addition of azide anion to bis-
(diphenylthiophosphinoyl)acetylene required DMF as
solvent, rather than methanol, as was the case in the
Table 1
Crystal data and structure refinement parameters for 1–4
1
2
3
4
Empirical formula
C
26H21N3P2S2
C28H23N3OP2S2
C30H27N3P2PdS2
C62H50N8P4PdS4
Formula weight
Crystal system
Space group
501.52
monoclinic
C2/c
543.55
triclinic
662.01
monoclinic
P21/n
1265.62
triclinic
(
(
P1
P1
Unit cell dimensions
,
a (A)
15.9311(3)
7.2861(2)
23.1967(2)
9.0061(2)
9.6793(2)
15.6127(3)
88.4379(9)
79.5000(9)
81.2939(6)
1322.78(3)
2, 1
9.892(2)
25.041(9)
12.336(4)
9.2097(2)
10.9655(2)
28.3762(6)
95.0766(5)
94.1875(2)
90.5218(3)
2846.46(18)
2, 1
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
105.5155(8)
98.57(2)
3
,
2553.20(8)
4, 0.5
3021.7(13)
4, 1
Z, Z%
Crystal color
colorless
1.305
3.53
colorless
1.365
3.50
pale yellow
1.455
8.82
yellow
1.477
6.34
173
Dcalc (g cm−3
)
v (Mo Ka) (cm−1
Temperature (K)
Radiation
)
173
173
235
,
Mo Ka (u=0.71073 A)
Reflections collected
Independent reflections
R(F) (%)
5528
2789
4.23
7459
5139
7.67
5703
4611
4.26
18 100
10 873
6.55
R(wF) (%)
15.06
0.519
20.70
1.073
9.98
0.901
16.04
1.424
−3
,
D(z) (e A
)

A.L. Rheingold et al. / Inorganica Chimica Acta 330 (2002) 38–43
41
acidic enough to form the stable, halocarbon-soluble
triethylamine salt, [LT-S2][Et3NH], which can be used
for reactions of the [LT-S2 −
ligand in organic solvents.
]
The NMR spectrum of [LT-S2][HNEt3] was consistent
with a symmetrical structure of the anion, and the 31P
was at 32.6 ppm, and thus in the typical PꢁS range.
Acetylation of [LT-S2]H with acetic anhydride oc-
curred exclusively at 2-N, and the C26 symmetry of
acylated product, [LT-S2][2-Ac] (2) was confirmed by
NMR, which exhibited a single 31P signal at 31.2 ppm,
as well as by X-ray crystallography (Fig. 2). The PꢁS
distances were 1.9380(14) and 1.9415(12), respectively,
the slightly longer value found in the PꢁS ‘trans’ to the
acyl oxygen.
Fig. 1. ORTEP plot of the structure of [LT-S2]H, 1. Selected bond
We also wanted to check whether the coordination of
,
distances (A) and angles (°): P(1)ꢀS(1) 1.9633(7); P(1)ꢀC(1)
the [LT-S2 −
ligand with Pd(II) will lead to the five-
]
1.8263(17); C(1)ꢀN(2) 1.254(2); N(1)ꢀN(2) 1.337(2); C(13)ꢀP(1)ꢀC(7)
105.75(8); C(13)ꢀP(1)ꢀS(1) 114.30(6); C(7)ꢀP(1)ꢀS(1) 114.00(7);
C(13)ꢀP(1)ꢀC(1) 106.43(8); C(1)ꢀP(1)ꢀC(7).
membered S,N chelate ring, or to the seven-membered
S,S-chelate ring. In the case of [LT-O2]H, several exam-
ples of both types of complexes have been synthesized,
and structurally characterized [1]. The reaction of the
salt [LT-S2][Et3NH] in chloroform with [Pd(h3-methal-
lyl)]2 produced the heteroleptic complex Pd[LT-S2][h3-
methallyl] (3). The fact that its structure was of type D
was suggested by the presence of two very different 31P
signals at 46.8 and 28.8 ppm, assigned to the coordi-
nated and uncoordinated PꢁS, respectively, since the
latter value is much closer to the one found in [LT-
S2][Et3NH]. Asymmetry of the molecule also caused
each of the methallyl syn and anti protons to be unique.
The structure was confirmed by X-ray crystallography
(Fig. 3).
The molecule contains two different PꢁS bonds: the
,
uncoordinated PꢁS bond is 1.9519(17) A, while the
Fig. 2. ORTEP plot of the structure of [LTꢀS2][2-Ac], 2. Selected bond
,
coordinated one is distinctly longer, at 2.0084(18) A.
,
distances (A) and angles (°): P(1)ꢀC(8) 1.821(4); P(1)ꢀS(1) 1.9380(14);
Similarly, the distances from P to the triazole carbon
were different: for the coordinated CꢀP(S)Ph2 group,
P(1)ꢀC(14) 1.812(3); P(1)ꢀC(2) 1.830(3); C(14)ꢀP(1)ꢀC(8) 105.13(16);
C(14)ꢀP(1)ꢀC(2)
104.24(14);
C(8)ꢀP(1)ꢀC(2)
104.51(17);
C(14)ꢀP(1)ꢀS(1) 116.27(14); C(2)ꢀP(1)ꢀS(1) 111.41(12).
synthesis of Na[LT-O2], and longer reaction time. This
reaction was only mildly exothermic, commensurate
with the stronger electron-withdrawing power of a
ꢀP(O)Ph2 group as compared with ꢀP(S)Ph2.
(1)
[LT-S2]H (1) is thermally quite stable, melting sharply
at 300 °C. Its structure was confirmed by X-ray crystal-
,
lography (Fig. 1). The PꢁS distance was 1.9633(7) A,
which is significantly longer compared to the PꢁS dis-
Fig. 3. ORTEP plot of the structure of Pd[LT-S2][h3-methallyl], 3.
,
Selected bond distances (A) and angles (°): Pd(1)ꢀN(1) 2.070(4);
,
tance of 1.881(4) A in HN[P(S)Ph2][P(O)Ph2] [28].
The 4,5-bis(diphenylthiophosphinoyl)-1,2,3-triazole is
Pd(1)ꢀC(27) 2.104(5); Pd(1)ꢀC(29) 2.124(5); Pd(1)ꢀC(28) 2.132(6);
Pd(1)ꢀS(2) 2.3796(14); S(1)ꢀP(1) 1.9519(17); S(2)ꢀP(2) 2.0084(18);
P(1)ꢀC(2) 1.810(4); P(2)ꢀC(1) 1.789(4).
not as acidic as the oxo analogue, LT-O2H, but is still

42
A.L. Rheingold et al. / Inorganica Chimica Acta 330 (2002) 38–43
shortening of the PꢀC bonds. By comparison, in com-
plex Pd[N(P(S)Ph2)2]2 the PꢁS bond lengths were very
,
similar, 2.0255(13) and 2.258(11) A, to the coordinated
PꢁS of compound 4. The PdꢀS bond lengths were
,
2.3478(8) and 2.3333(8)
Pd[N(P(S)Ph2)2]2, and 2.3159(13) and 2.3228(13) A in
complex 4.
A
in the complex
,
Fig. 4. ORTEP plot of the structure of Pd[LT-S2]2·2py, 4. The two
uncoordinated molecules of pyridine have been omitted. Selected
We have also found that the anion [LT-S2 −
extracts
]
,
bond distances (A) and angles (°): Pd(1)ꢀN(4) 1.997(4); Pd(1)ꢀN(1)
readily transition metals from aqueous solutions into
chloroform or into dichloromethane. These and other
2.003(4); Pd(1)ꢀS(4) 2.3159(13); Pd(1)ꢀS(2) 2.3228(13); S(1)ꢀP(1)
1.9476(19); S(2)ꢀP(2) 2.0187(18); S(3)ꢀP(3) 1.949(2); S(4)ꢀP(4)
2.0306(17); N(4)ꢀPd(1)ꢀN(1) 179.63(18); N(4)ꢀPd(1)ꢀS(4) 88.83(12);
reactions of the [LT-S2 −
ligand are being investigated,
]
N(l)ꢀPd(l)ꢀS(4)
90.94(12);
N(4)ꢀPd(1)ꢀS(2)
91.45(12);
and will be reported in due course.
In summary, the second member of the LT-E2H fam-
ily, LT-S2H, has been synthesized, and found to form
homo- and heteroleptic S,N-bonded complexes with
Pd(II), all of which were structurally characterized.
N(1)ꢀPd(1)ꢀS(2) 88.79(12); S(4)ꢀPd(1)ꢀS(2) 179.53(5); P(2)ꢀS(2)ꢀPs(1)
100,26(6); P(4)ꢀS(4)ꢀPd(1) 101.06(6).
,
the PꢀC bond was 1.789(4) A, while for the uncoordi-
,
nated CꢀP(S)Ph2 group the PꢀC bond was 1.8109(4) A.
Thus, coordination of sulfur from the CꢀP(S)Ph2 group
leads to a lengthening of the PꢁS bond, and to shorten-
ing of the PꢀC bond. The PdꢀS distance was 2.3796(14)
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The homoleptic complex Pd[LT-S2]2 (4) was also syn-
thesized by the reaction of the triethylamine salt of
LT-S2H with Na2PdCl4 in methanol. Considering that
the chelation of LT-S2 in 3 was of type D, involving
N,S-bonding, one could have expected the presence of
cis- and trans-isomers. However, X-ray crystallography
showed that the complex was the trans-isomer (Fig. 4).
The reason why no S,S-bonded structure was obtained
is not clear, since other S4 tetracoordinated Pd com-
plexes, for instance Pd[N(P(S)Ph2)2]2, have been re-
ported. In complex 4 the coordinated PꢁS bond lengths
,
were 2.0187(18) and 2.0306(17) A, the uncoordinated
,
ones were 1.9476(19) and 1.9492(2) A, the PꢀC bonds
[15] A. Schmidpeter, H. Groeger, Z. Anorg. Allg. Chem. 345 (1966)
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[16] A. Schmidpeter, H. Groeger, Chem. Ber. 100 (1967) 3979.
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[18] E. Fluck, F.L. Goldman, Chem. Ber. 96 (1963) 3091.
,
to the triazole carbon were 1.814(5) and 1.819(5) A for
the free ꢀP(S)Ph2 groups, and for the coordinated ones
they were 1.794(5) and 1.790(5) A. Again, coordination
,
to Pd resulted in lengthening of the PꢁS bonds, and

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