Synthesis of metal dithiolene complexes by Si-S bond cleavage of a bis(silanylsulfanyl)alkene

Article abstract of DOI:10.1016/j.ica.2005.09.067

A new method for the synthesis of metal dithiolenes with alkyl-substituted chelate rings has been investigated. The utility of the protected ene-1,2-dithiolate 3,4-bis-triisopropylsilanyl-sulfanyl-hex-3-ene as a precursor in reactions with metal halide and oxyhalide complexes was examined. Reaction conditions involve a 2:1 or 3:1 mol ratio of reactants in acetonitrile/THF or toluene at 50-80°C for 24-36 h. Complex formation was observed as a result of Si-S bond cleavage by bound or free halide and oxo ligands. Members of four major structural families of dithiolene complexes were prepared in ca. 25-70% yields, including planar [Ni(S₂C₂Et₂) ₂], square pyramidal [MI(S₂C₂Et ₂)₂] (M = Co, Fe), [Fe(py)(S₂C ₂Et₂)₂]^1-, and [ReO(S ₂C₂Et₂)₂]^1-, centrosymmetric [M₂(S₂C₂Et₂) ₄]^2- (M = Co, Mn), [M(S₂C₂Et ₂)₃]^1- (M = V, Nb), and trigonal prismatic [M(S₂C₂Et₂)₃] (M = Mo, W). Seven X-ray structure proofs are provided. It is concluded that the method is feasible and potentially extendable to other ring substituents, whose primary effects are on solubility and modulation of redox potentials.

Full text of DOI:10.1016/j.ica.2005.09.067

Inorganica Chimica Acta 359 (2006) 1427–1434
www.elsevier.com/locate/ica
Synthesis of metal dithiolene complexes by Si–S bond cleavage of
a bis(silanylsulfanyl)alkene
*
Simone Friedle, David V. Partyka, Miriam V. Bennett, R.H. Holm
Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA
Received 31 August 2005; accepted 21 September 2005
Available online 18 January 2006
Abstract
A new method for the synthesis of metal dithiolenes with alkyl-substituted chelate rings has been investigated. The utility of the
protected ene-1,2-dithiolate 3,4-bis-triisopropylsilanylsulfanyl-hex-3-ene as a precursor in reactions with metal halide and oxyhalide
complexes was examined. Reaction conditions involve a 2:1 or 3:1 mol ratio of reactants in acetonitrile/THF or toluene at 50–80 ꢀC
for 24–36 h. Complex formation was observed as a result of Si–S bond cleavage by bound or free halide and oxo ligands. Members
of four major structural families of dithiolene complexes were prepared in ca. 25–70% yields, including planar [Ni(S2C2Et2)2], square
pyramidal [MI(S2C2Et2)2] (M = Co, Fe), [Fe(py)(S2C2Et2)2]1ꢀ, and [ReO(S2C2Et2)2]1ꢀ, centrosymmetric [M2(S2C2Et2)4]2ꢀ (M = Co,
Mn), [M(S2C2Et2)3]1ꢀ (M = V, Nb), and trigonal prismatic [M(S2C2Et2)3] (M = Mo, W). Seven X-ray structure proofs are provided.
It is concluded that the method is feasible and potentially extendable to other ring substituents, whose primary effects are on solubility
and modulation of redox potentials.
ꢁ 2005 Elsevier B.V. All rights reserved.
Keywords: Metal dithiolenes; Bis(silanylsulfanyl)alkene; Si–S bond cleavage
1. Introduction
scope of each family. In general, complexes are prepared
from derivatized ligands by removing protecting groups
to generate an ene-1,2-dithiolate, which is captured by
the metal. This is the case in the original acyloin/ben-
zoin/P4S10 procedure [2,3], which in our hands works best
for R = aryl. While the simplest dithiolene reagent,
Na2[S2C2H2], has been prepared [4,5], only one dialkyl
dithiolene salt has been isolated and used as a reagent in
the synthesis of complexes [6]. Dialkyl ligands are of partic-
ular interest because of their close relationship to the che-
lating portion of the pyranopterindithiolene cofactor
ligand of molybdenum and tungsten enzymes [7–9]. In
our development of active site analogues and analogue
reaction systems of these enzymes [9], we have employed
extensively the ligand with R = Me. This ligand was not
isolated but was transferred from [Ni(S2C2Me2)2] to
[M(CO)3(MeCN)3] to afford [M(S2C2Me2)2(CO)2] (M =
Mo, W) [10,11], which are subject to carbonyl substitution
reactions leading to a wide variety of complexes including
accurate site analogues.
Numerous methods exist for the preparation of metal
dithiolene complexes, which contain the generalized ligand
cis-1,2-[S2C2R2]z (z = 2ꢀ, 1ꢀ, 0; R = alkyl, aryl, CN, CF3;
RR = 1,2-C6H4 or other ring systems). Dithiolenes form
large families of complexes, prominent among which are
planar [M(S2C2R2)2]z, square pyramidal [ML(S2C2R2)2]z,
lateral dimeric [M2(S2C2R2)4]z, (z = 2ꢀ, 1ꢀ, 0; L = vari-
able ligand), and octahedral to trigonal prismatic
[M(S2C2R2)3]z (z = 3ꢀ to 0). Synthetic methods are often
dependent on the substituent R or the backbone ring struc-
ture of which the chelating dithiolene fragment is a part.
Procedures have been systematized and summarized by
Rauchfuss [1]. Once formed, complexes are often suscepti-
ble to reversible redox reactions, accounting for the large
*
Corresponding author. Tel.: +1 617 495 0853; fax +1 617 495 9289.
E-mail address: holm@chemistry.harvard.edu (R.H. Holm).
0020-1693/$ - see front matter ꢁ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.09.067

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S. Friedle et al. / Inorganica Chimica Acta 359 (2006) 1427–1434
Fig. 1. Synthesis of dithiolene complexes.
˚
In seeking additional and possibly more convenient and
benzophenone ketyl; acetonitrile-d3 was stored over 4-A
molecular sieves. All other reagents were commercially
available and used as received. In the following prepara-
tions, volume reduction steps were performed in vacuo.
Redox potentials are referenced to the SCE. Compounds
were identified by a combination of mass spectrometry,
elemental analysis, and X-ray structure determinations.
general routes to dialkyl and other dithiolene complexes,
we noted preparation of the protected ene-1,2-dithiolate
3,4-bis-triisopropylsilanylsulfanyl-hex-3-ene [12] (1). 1 and
its related compounds are obtained by a Pd0-catalyzed
cross-coupling reaction between an alkyne and bis(triiso-
propylsilyl)disulfide (2) to produce isolable bis(silanylsulfa-
nyl)alkenes [12,13]. The reaction affording 1 is shown in
Fig. 1. The possibility that cleavage of the Si–S bonds in
1 might lead to dithiolene complexes is suggested by the
ready occurrence of reaction (1), based on 1,2-bis(trimeth-
ylsilylthio)benzene [14] and leading to monodithiolene
complexes (M = Mo, W) in 70–80% yield [15]. In this
investigation, we have examined the feasibility of 1 as a
dithiolene precursor in a set of reactions with diverse metal
halide sources intended to produce members of the afore-
mentioned dithiolene families
2.1.1. [Ni(S2C2Et2)2]
To
0.087 mmol) in 8 mL of acetonitrile was added a solution
of 3,4-bis-triisopropylsilanylsulfanyl-hex-3-ene [12]
a
solution of (Et4N)2[NiCl4] [16] (40 mg,
(84 mg, 0.18 mmol) in 1 mL of THF. The reaction mixture
was stirred at 60 ꢀC for 24 h and concentrated to dryness.
The residue was washed with hexane and dissolved in
2 mL of acetonitrile. A solution of iodine (66 mg,
0.26 mmol) in 6 mL of THF was added dropwise, and
the suspension was stirred for 90 min. The mixture
was concentrated to dryness in vacuo and the residue was
extracted with toluene/hexane (1:1 v/v). The extract was
chromatographed on a small pad of silica gel twice (using
the same solvent combination as eluent). The violet band
was collected and taken to dryness to give the product as
11 mg (36%) of a dark solid. IR (KBr): 561 (s, br), 1043
[MO4]2ꢀ + 1,2-C6H4(SSiMe3)2
! [MO3(S2C6H4)]2ꢀ + (Me3Si)2O
ð1Þ
2. Experimental
2.1. Preparation of compounds
(m), 1244 (vs, br), 1383 (s, mC@C) cmꢀ1. H NMR (C6D6):
1
d 2.34 (q, 2), 1.11 (t, 3). 13C NMR (C6D6): d 15.10
(CH3), 31.61 (CH2), 185.90 (C–S). Absorption spectrum
(THF): kmax (ꢀM) 280 (22000), 305 (26000), 410 (sh,
2000), 570 (2000), 774 (19000) nm. Voltammetry (0.1 M
LiClO4, DMF): E1/2 = ꢀ0.10 V, ꢀ1.13 V. EI-MS: m/z
All operations were performed under a pure dinitrogen
atmosphere using standard Schlenk techniques or in an
inert atmosphere box. Acetonitrile, ether, and THF were
purified with an Innovative Technology solvent purifica-
tion system. Hexane and toluene were distilled over sodium

S. Friedle et al. / Inorganica Chimica Acta 359 (2006) 1427–1434
1429
349.98 (M+). In multiple preparations with and without the
chromatography step, yields as high as 66% were obtained.
collected and extracted into dry pyridine. The deep black-
brown solution was filtered through Celite, and ether was
diffused into the filtrate. After about 2 days, the product
was obtained as large black crystals (18 mg, 50%). Absorp-
tion spectrum (pyridine): kmax (ꢀM) 356 (10800), 442 (6100),
470 (3850), 580 (2470) nm. Voltammetry (0.1 M
(Bu4N)PF6, pyridine): E1/2 = ꢀ0.22 V. Anal. Calc. for
C25H45FeN2S4: C, 53.84; H, 8.13; N, 5.02; S, 35.98. Found:
C, 53.46; H, 7.92; N, 4.74; S, 35.51%.
2.1.2. [CoI(S2C2Et2)2]
To
a
solution of (Et4N)2[CoCl4] [16] (30 mg,
0.065 mmol) in 8 mL of acetonitrile was added a solution
of 3,4-bis-triisopropylsilanylsulfanyl-hex-3-ene (90 mg,
0.20 mmol) in 1 mL of THF. The reaction mixture was stir-
red at 50–55 ꢀC for 24 h and taken to dryness. The residue
was washed thoroughly with ether twice and dissolved in
2 mL of acetonitrile. A solution of iodine (49 mg,
0.20 mmol) in 4 mL of THF was added dropwise, and
the mixture was stirred for 1 h. The solution was concen-
trated to dryness in vacuo, extracted into 12 mL of tolu-
ene/hexane (1:1 v/v), and filtered. The intense blue-green
solution was reduced to dryness, the residue was extracted
with toluene/hexane, and the extract was filtered. Upon
reduction of the filtrate volume, the product was obtained
as a black solid (11 mg, 35%). IR (KBr): 1046 (m), 1362,
2.1.5. (Ph4P)[ReO(S2C2Et2)2]
To a suspension of [ReOCl3(PPh3)2] [17] (37 mg,
0.044 mmol) in 8 mL of acetonitrile was added Ph4PCl
(18 mg, 0.048 mmol). After the mixture was stirred for
5 min, a solution of 3,4-bis-triisopropylsilanylsulfanyl-
hex-3-ene (42 mg, 0.091 mmol) in 1 mL toluene was added.
The solution was heated at 80–85 ꢀC for 24 h. The orange
solution was concentrated to a residue, which was washed
with hexane and ether. The residue was extracted into a
minimum volume of acetonitrile, the solution was filtered,
and ether was diffused into the filtrate. The solid that crys-
tallized was washed with isopropanol and ether and dried.
The product was collected as an orange, microcrystalline
1
1384 (s, mC@C) cmꢀ1. H NMR (C6D6): d 2.54 (q, 2), 1.01
(t, 3). 13C NMR: d 14.54 (CH3), 34.11 (CH2), 203.45 (C–
S). Absorption spectrum (toluene): kmax (ꢀM) 290 (24100),
394 (sh, 5500), 485 (sh, 4200), 655 (9500). Voltammetry
(0.1 M (Bu4N)PF6, acetonitrile): E1/2 = ꢀ0.25 V, ꢀ1.22 V.
Anal. Calc. for C12H20CoIS4: C, 30.13; H, 4.21; S, 26.81.
Found: C, 30.38; H, 4.25; S, 26.84%.
solid (18 mg, 50%). IR (KBr): 943 (s, mReO) cmꢀ1 1H
.
NMR (CD3CN, anion): d 2.74 (m, 2), 1.01 (t, 3). Absorp-
tion spectrum (acetonitrile): kmax (ꢀM) 290 (5910), 306
(5790), 348 (2800) nm. Voltammetry (0.1 M (Bu4N)PF6,
acetonitrile): E1/2 = 0.57 V. Anal. Calc. for C36H40OPReS4:
C, 51.84; H, 4.83; S, 15.38. Found: C, 51.85; H, 4.68; S,
15.15%.
2.1.3. [FeI(S2C2Et2)2]
To a solution of (Et4N)2[FeCl4] [16] (18 mg, 0.039 mmol)
in 8 mL of acetonitrile was added a solution of 3,4-bis-tri-
isopropylsilanylsulfanyl-hex-3-ene (56 mg, 0.12 mmol) in
THF. The reaction mixture was stirred at 60 ꢀC for 24 h,
and concentrated to dryness. The residue was washed twice
with ether and was suspended in 2 mL acetonitrile. To the
suspension was added dropwise a solution of iodine
(30 mg, 0.12 mmol) in 6 mL of THF. The mixture was stir-
red for 45 min, resulting in a deep green color, and was con-
centrated to dryness. The residue was extracted with
toluene/hexane (1:2 v/v) and filtered. Solvent was removed
and the extraction procedure was repeated affording the
product as a black solid (12 mg, 64%). IR (KBr): 1047 (s,
br), 1370, 1374 (m, mC@C) cmꢀ1. Absorption spectrum
(toluene): kmax (ꢀM) 302 (15000), 382 (sh, 6000), 458 (sh,
8400), 517 (sh, 6000), 607 (7700) nm. Voltammetry (0.1 M
(Bu4N)PF6, acetonitrile): E1/2 = ꢀ0.22, ꢀ0.57, ꢀ1.19 V.
EPR (toluene, 150 K): g1 = 2.03, g2 = 2.18, g3 = 2.26. Anal.
Calc. for C12H20FeIS4: C, 30.32; H, 4.24; S, 26.99. Found:
C, 30.53; H, 4.29; S, 26.86%.
2.1.6. (Ph4P)[V(S2C2Et2)3]
To a solution of VOF3 (11 mg, 0.089 mmol) in 8 mL of
acetonitrile was added Ph4PCl (34 mg, 0.091 mmol). The
mixture was stirred for 5 min; to the solution was added
dropwise a solution of 3,4-bis-triisopropylsilanylsulfanyl-
hex-3-ene (124 mg, 0.027 mmol) in 1 mL of toluene. The
reaction mixture was stirred at 50–55 ꢀC for 36 h to give
a blue-violet solution, which was concentrated to dryness
and washed sequentially with hexane and ether. The resi-
due was extracted into a minimum volume of acetonitrile
and the solution was filtered. Ether (2–3 vol. equiv.) was
diffused into the acetonitrile solution, which was added to
a roughly equal volume of cold ether (ꢀ10 ꢀC), and the
mixture was stored at this temperature overnight. The deep
blue-violet solution and solid that formed were decanted
from a small amount of colorless crystals and allowed to
stand for several hours. The product was collected as a blue
1
solid (18 mg, 24%). H NMR (CD3CN): d 2.93 (q, 2), 1.17
2.1.4. (Et4N)[Fe(C5H5N)(S2C2Et2)2]
(t, 3). Absorption spectrum (acetonitrile): kmax (ꢀM) 370
(3510), 532 (7120), 597 (10100), 678 (6380) nm. Voltamme-
try (0.1 M (Bu4N)PF6, acetonitrile): E1/2 = 0.04, ꢀ0.92 V.
ES-MS: m/z 489 (Mꢀ).
To a solution of (Et4N)2[FeCl4] (30 mg, 0.065 mmol) in
8 mL of acetonitrile was added a solution of 3,4-bis-tri-
isopropylsilanylsulfanyl-hex-3-ene (93 mg, 0.20 mmol) in
1 mL of THF. The reaction mixture was stirred at 55 ꢀC
for 24 h during which a black solid deposited. The mixture
was concentrated to dryness, washed thoroughly with hex-
ane followed by isopropanol and ether. The black solid was
2.1.7. (Et4N)[Nb(S2C2Et2)3]
To
a solution of (Et4N)2[NbOCl5] [18] (30 mg,
0.055 mmol) in 8 mL of acetonitrile was added a solution

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S. Friedle et al. / Inorganica Chimica Acta 359 (2006) 1427–1434
of 3,4-bis-triisopropylsilanylsulfanyl-hex-3-ene (77 mg,
0.17 mmol) in 1 mL of toluene. The reaction mixture was
stirred at 50 ꢀC for 30 h, and the brown-red solution was
concentrated to dryness. The residue was washed with
ether, extracted into THF, and filtered. Solvent was
removed from the filtrate and the extraction procedure
was repeated. The residue was dissolved in a minimum vol-
ume of acetonitrile and stored at ꢀ20 ꢀC. The product was
was taken to dryness; hexane was added and thoroughly
mixed with the residue. The suspension (the product is par-
tially soluble) was placed on a 2-in. pad of dry silica,
flushed with several volume equivalents of hexane
(ꢁ50 mL), and eluted with 2:1 hexane/toluene (v/v). The
product (30 mg, 69%) was isolated as above and shown
to be analytically and spectroscopically identical to the
product of Method A.
1
obtained as a red solid (11 mg, 30%). H NMR (CD3CN,
anion): d 2.68 (q, 2), 1.14 (t, 3). Absorption spectrum (ace-
tonitrile): kmax (ꢀM) 411 (3600), 493 (3130), 554 (2190) nm.
2.2. X-ray structure determinations
Voltammetry (0.1 M (Bu4N)PF6, acetonitrile): E1/2
=
The structures of the seven compounds in Table 1 were
determined. Diffraction-quality crystals were obtained
from the indicated solvents: (Et4N)2[Co(S2C2Et2)]2, aceto-
nitrile/ether; [FeI(S2C2Et2)2], toluene; [CoI(S2C2Et2)2], tol-
uene:hexane (1:1 v/v); (Et4N)[Fe(py)(S2C2Et2)2], pyridine;
(Et4N)2[Mn(S2C2Et2)]2, DMF/ether; [Mo(S2C2Et2)3], tolu-
ene/hexane, ꢀ30 ꢀC; (Ph4P)[ReO(S2C2Et2)2], acetonitrile/
ether. Crystals were coated in Paratone oil and mounted
by means of glass capillary fibers on a Bruker CCD area
detector instrument operated by the SMART software pack-
age. For each crystal, a hemisphere of data was collected
at 193 K in 30 or 45 s frames using scans of 0.3 deg/
frame. Data reduction were performed with SAINT, which
corrects for Lorentz polarization and decay. Absorption
corrections were applied using SADABS, and space groups
were assigned using XPREP. All structures were solved by
direct methods with SHELXTL and refined against all data
by full-matrix least squares on F2. Hydrogen atoms were
attached at idealized positions on carbon atoms and were
refined as riding atoms with uniform isotropic thermal
parameters. The terminal carbon atom of one ethyl group
of [M2(S2C2Et2)4]2ꢀ (M = Mn, Co) and [Mo(S2C2Et2)3]
was disordered over two positions and was refined
accordingly. The latter compound and (Ph4P)[ReO(S2-
C2Et2)2] contain two molecules in the asymmetric unit.
All structures converged in the final stages of refinement,
showing no movement in atom positions. Use of the
checking program PLATON did not identify any missing
or higher symmetry. Crystallographic parameters and
agreement factors are presented in Table 1.
ꢀ1.11 V. ES-MS: m/z 531 (Mꢀ).
2.1.8. [Mo(S2C2Et2)3]
To a solution of [MoOCl4] (15 mg, 0.059 mmol) in
8 mL of toluene was added 3,4-bis-triisopropylsilanylsulfa-
nyl-hex-3-ene (84 mg, 0.18 mmol) in 1 mL of toluene. The
reaction mixture was stirred for 24 h at 60–65 ꢀC. By the
end of the reaction, the solution color was an intense, deep
green. Solvent was removed and the residue was sus-
pended in 5 mL of hexane. The suspension was deposited
on a 2-in. pad of dry silica, flushed several times with hex-
ane, and eluted with toluene:hexane (3:1 v/v). The bright
green band was collected, the solvent was removed to give
1
the product as a red-violet solid (18 mg, 57%). H NMR
(C6D6): d 2.67 (q, 2 ), 1.00 (t, 3). Absorption spectrum
(toluene): kmax (ꢀM) 309 (6110), 434 (9990), 642 (12200)
nm. Voltammetry (0.1 M (Bu4N)PF6, acetonitrile/THF
2:1 v/v): E1/2 = ꢀ0.36, ꢀ0.90 V. Anal. Calc. for
C18H30MoS6: C, 40.43; H, 5.65; S, 35.98. Found: C,
41.40; H, 4.91; S, 35.51%.
2.1.9. [W(S2C2Et2)3]
Method A: To a violet solution of [WCl6] (23 mg,
0.058 mmol) in 6 mL of toluene was added dropwise a
solution of 3,4-bis-triisopropylsilanylsulfanyl-hex-3-ene
(83 mg, 0.18 mmol) in 1 mL of toluene; the color became
deep brown. The reaction mixture was stirred at 65–70 ꢀC
for 24 h to yield a deep turquoise-blue solution that was
concentrated to dryness. To the residue was added 10 mL
of hexane. The suspension was deposited onto a 2-in. pad
of dry silica. The suspension was flushed several times with
hexane and eluted with toluene. The turquoise-blue band
was collected and the solvent was removed to afford the
2.3. Other physical measurements
1H NMR spectra were obtained with Bruker AM 400N/
500N/600N spectrometers. FT-IR spectra were taken on
recrystallized solid samples in KBr on a Nicolet Nexus
470 FT-IR spectrometer, and UV–Vis spectra were
recorded on a Varian Cary 50 Bio spectrophotometer.
Electrospray mass spectra were recorded on a Platform II
quadrupole mass spectrometer (Micromass Instruments,
Danvers, MA).
1
product as a violet solid (21 mg, 59%). H NMR (C6D6):
d 2.72 (q, 2), 1.01 (t, 3). Absorption spectrum (toluene):
kmax (ꢀM) 390 (4310), 505 (2840), 608 (6380) nm. Voltam-
metry (0.1 M (Bu4N)PF6, acetonitrile/THF 2:1 v/v):
E1/2 = ꢀ0.37, ꢀ0.97 V. ES-MS: m/z 622 (Mꢀ). Anal. Calc.
for C18H30S6W: C; 34.72; H, 4.86; S, 30.90. Found: C,
34.62; H, 4.78; S, 31.08%.
Method B: To
a solution of [WOCl4] (24 mg,
0.070 mmol) in 6 mL of toluene was added a solution of
3,4-bis-triisopropylsilanylsulfanyl-hex-3-ene (99 mg, 0.21
mmol) in 2 mL of toluene. The solution was stirred at
70 ꢀC for 30 h and allowed to cool. The reaction mixture
3. Results and discussion
The purpose of this work was to assess the utility of a
particular type of protected ene-1,2-dithiolate, a bis(silan-

S. Friedle et al. / Inorganica Chimica Acta 359 (2006) 1427–1434
1431
Table 1
Crystallographic dataa
(Et4N)2
[Co(S2C2Et2)2]2
[CoI(S2C2Et2)2] [FeI(S2C2Et2)2] (Et4N)[Fe(py)- (Et4N)2-
[Mo(S2C2Et2)3] (PPh4)[ReO-
(S2C2Et2)2]
(S2C2Et2)2]
[Mn(S2C2Et2)2]2
Formula
Crystal system
Fw
C40H80Co2N2S8 C12H20CoIS4
C12H20FeIS4
tetragonal
475.27
P41
10.571(1)
10.571(1)
16.066(3)
90
90
90
1795.4(4)
4
1.563
C25H45FeN2S4 C40H80Mn2N2S8 C36H60Mo2S12
C72H80O2P2Re2S8
monoclinic
1668.18
P21
9.998(2)
20.049(4)
18.051(4)
90
90.93(3)
90
3617.8(1)
2
monoclinic
963.40
P21/c
triclinic
478.35
monoclinic
557.72
P21/n
monoclinic
955.42
P21/c
triclinic
1069.44
ꢀ
ꢀ
Space group
P1
P1
˚
a (A)
11.896(4)
17.745(5)
12.149(4)
90
104.931(9)
90
7.646(1)
9.024(2)
13.362(2)
82.193(3)
75.076(3)
75.265(4)
859.2(3)
2
8.807(1)
16.782(3)
20.328(4)
90
94.64(3)
90
11.976(2)
17.763(4)
12.314(3)
90
104.89(3)
90
11.610(2)
13.628(3)
15.635(3)
100.36(3)
105.14(3)
97.51(3)
2307.4(8)
2
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
c (ꢀ)
3
˚
V (A )
2478(1)
2
2994.5(1)
4
2531.5(9)
2
Z
qcalc (g/cm3)
2h Range (ꢀ)
1.291
1.849
1.237
1.253
1.539
1.531
2.26–56.58
1.105
3.54–52.74
3.16–56.62
1.021
3.86–56.58
1.036
2.92/5.86
4.02–56.58
1.014
3.52–56.60
1.102
3.10–50.00
1.115
Goodness-of-fit (F2) 1.026
c
R1b/wR2 (%)
4.48/11.85
3.42/7.28
4.98/11.55
6.51/12.21
5.15/10.78
7.07/13.55
a
˚
Collected using graphite monochromated Mo Ka radiation (k = 0.71073 A) at T = 193 K.
P
P
b
c
R1 = iFoj ꢀ jFci/ jFoj.
P
P
2
2
1=2
wR2 ¼ f ½wðF 2o ꢀ F c2Þ = ½wðF 2oÞ ꢂg
.
ylsulfanyl)alkene, as a precursor to metal dithiolenes.
Compound 1 was selected because it is accessible from
readily handled 3-hexyne (b.p. 81–82 ꢀC) and the disulfide
2 is obtainable by iodine oxidation of the anion of com-
mercial thiol Pri3SiSH [12]. Deprotection by Si–S bond
cleavage with coordinated or free halide and (possibly)
coordinated oxide is suggested by the bond dissociation
energy order 2 [19–21], against which must be balanced
the energies of M–X and M@O bonds of the reactant.
Product formation is additionally promoted by formation
of strong covalent M–S bonds in stable delocalized che-
late rings [22]. While only one other diethyldithiolene
complex has been reported ([Ni(S2C2Et2)2] [2]), the main
issue is not the preparation of new compounds nor a
detailed structural/electronic analysis of those prepared.
Rather, it is a test of potential precursor 1 in the forma-
tion of examples in the main families of dithiolene com-
plexes, whose structural features have been summarized
[23].
3.1. Bis(dithiolene) complexes
In one set of reactions, the complexes [MCl4]2ꢀ
(M = Ni, Co, Fe) were reacted with 2–3 equiv. of 1 in ace-
tonitrile/THF at 50–60 ꢀC for 24 h. The initial complexes
formed are the readily oxidized species [M(S2C2Et2)2]2ꢀ
(not isolated) which upon treatment with iodine in THF
afford [Ni(S2C2Et2)2] (3, 36–66%), [CoI(S2C2Et2)2] (4,
35%), and [FeI(S2C2Et2)2] (5, 64%, S = 1/2 ground state)
or with pyridine [Fe(py)(S2C2Et2)2]1ꢀ (6), isolated as the
Et4N+ salt (50%). As is typical for [Ni(S2C2R2)2]
complexes, 3 exhibits an intense near-IR transition at
774 nm and a three-member electron transfer series
[Ni(S2C2Et2)2]2ꢀ/1ꢀ/0 at E1/2 = ꢀ0.10 and ꢀ1.13 V. The
compound is highly similar to planar [Ni(S2C2Me2)2] (771
(21500) nm; ꢀ0.15, ꢀ1.05 V) [25]. Complex 3 is formed
by the apparent stoichiometry of reaction (3) (M = Ni);
analogous reactions with 3/2 I2 apply to the formation of
4 and 5. Evidently under workup conditions [Fe(S2-
C2Et2)2]2ꢀ or its pyridine adduct underwent a one-electron
oxidation. (Note the ready oxidizability of closely related
FeII complexes in the couples [Fe(S2C2H4)2]2ꢀ/1ꢀ
(ꢀ1.12 V)), [Fe(S2C6H4)2]2ꢀ (ꢀ0.99 V), and [Fe(S2C6H3-4-
Me)2]2ꢀ/1ꢀ (ꢀ0.91 V) [28,29]. Reaction (4) produces
[ReO(S2C2Et2)2]1ꢀ (7, 50%) in a process requiring an addi-
tional equivalent of chloride for stoichiometric discharge of
all Si–S bonds. It is noteworthy that the oxo ligand is not
silylated in, or silylated and removed from, the isolable
product of the reaction.
SiAF(160) > SiAO > (123–136) > SiACl (113) >
SiAN (92–109) > SiAS (K90) kcal/mol
ð2Þ
Synthetic experiments are summarized in Fig. 1.
Quoted yields are averages of at least two preparations
but are not necessarily optimal. All products evidence
redox reactions; only one oxidation state of each was iso-
lated. For simplicity, the ligand oxidation state is
depicted as an ene-1,2-dithiolate, except for [Ni(S2-
C2Et2)2]. The non-innocent behavior of dithiolene ligands
in oxidized complexes is well-recognized and has been
considered in some detail recently [24]. While the matter
is beyond the purview of this report, we note recent
experimental and theoretical investigations of non-
innocent bis(dithiolene)nickel and related complexes
[22,25–27].
2ꢀ
½MCl4ꢂ þ 2Et2C2ðSSiPri Þ þ I2
3
2
! ½MðS2C2Et2Þ ꢂ þ 2Iꢀ þ 4Pr3i SiCl
ð3Þ
ð4Þ
2
½ReOCl3ðPPh3Þ ꢂ þ 2Et2C2ðSSiPri Þ þ Clꢀ
2
3
2
1ꢀ
! ½ReOðS2C2Et2Þ2ꢂ þ 4Pri3SiCl

1432
S. Friedle et al. / Inorganica Chimica Acta 359 (2006) 1427–1434
Complexes 4–7 exhibit square pyramidal stereochemis-
˚
try in which the metal atom is displaced 0.31 A (4) to
˚
0.72 A (7) from the S4 mean plane toward the axial ligand.
Structures are shown in Figs. 2 and 3 and metric parame-
ters are summarized in Table 2. Average bond lengths
and angle are given for the bis(dithiolene) portions;
numerically designated bonds and angles are averages of
two of the same type. Complex 7 is precedented by square
pyramidal [ReO(S2C6H4)2]1ꢀ [30,31], with which it is iso-
structural. The chelate ring C–S and C–C bond lengths in
6 and 7 are biased toward an enedithiolate ligand descrip-
˚
tion with a single C–S bond (1.82 A) and a double C–C
Fig. 3.
˚
bond (1.33 A). Those of 4 and 5, which are clearly nonclas-
sical molecules, are intermediate between a dithiolate and
dithione in terms of C–S distances.
3.2. M–S dinuclear complexes
Two complexes in this structural category [23] were
obtained, but not in analytical purity; consequently
detailed preparations are not given. However, both com-
plexes were identified by X-ray structure determinations,
justifying their inclusion. Reaction of [MCl4]2ꢀ with
2 equiv. of 1 were performed under conditions used for
bis(dithiolene) complexes except that the reaction with
M = Mn was conducted without exclusion of air. With
M = Co, a limited amount of black crystals was isolated.
This material was shown to contain the dinuclear dianion
[Co2(S2C2Et2)4]2ꢀ (8) as the Et4N+ salt. The complex
shows a well-defined reduction at ꢀ1.22 V and an oxida-
tion at ꢀ0.26 V in acetonitrile. With M = Mn, a mixture
of colorless and red crystals was obtained after standard
workup and recrystallization from DMF/ether. The red
crystals were shown to contain [Mn2(S2C2Et2)4]2ꢀ (9) as
the Et4N+ salt. The structures of 8 and 9, provided in
Fig. 4, are centrosymmetric lateral dimers whose bridging
portion is a M2(l2-SR)2 rhomb in which the metal atom
has an irregular five-coordinate geometry. The structure
of 8 is analogous to that of [Co2(S2C6Cl4)4]2ꢀ [32] while 9
Fig. 2.

S. Friedle et al. / Inorganica Chimica Acta 359 (2006) 1427–1434
1433
Table 2
Selected interatomic distances (A) and angles (ꢀ)
Table 3
˚
˚
Selected interatomic distances (A) and angles (ꢀ)
[CoI-
(S2C2Et2)2]
[FeI-
(S2C2Et2)2]
(Et4N)[Fe(py)-
(S2C2Et2)2]
[ReO-
(S2C2Et2)2]
(Et4N)2[Co(S2C2Et2)2]2
(Et4N)2[Mn(S2C2Et2)2]2
M–S1
M–S2
M–S3
M–S4
M–S10
2.194(1)
2.175(1)
2.195(1)
2.195(1)
2.411(1)
3.274(1)
1.75(1)
1.340(5)
90.47(3)
88.95(4)
89.06(4)
90.10(4)
89.50(4)
174.95(4)
152.57(4)
89.53–104.46
105.7(2)
0.31
2.332(1)
2.317(1)
2.297(1)
2.290(1)
2.618(1)
3.463(1)
1.768(9)
1.339(1)
87.70(3)
87.02(4)
87.17(4)
90.55(4)
89.92(4)
170.12(4)
148.62(4)
92.3–106.66
104.8(3)
0.41
M–L
2.564(1)
2.150(1)
1.686(7)
1.340(8)
98(2)
88.9(4)
164(4)
106.6(2)
118.7(3)
0.31
2.558(1)
2.183(4)
1.699(2)
1.382(7)
102(2)
87.7(5)
157(2)
107.6(2)
118.7(4)
0.44
2.172(2)
2.227(4)
1.762(7)
1.334(2)
99(2)
88.5(6)
161.5(9)
105.9(4)
119.9(5)
0.36
1.714(1)
2.307(5)
1.78(2)
1.32(4)
108(1)
84.4(9)
143(2)
107.1(6)
120(2)
M–Sa
S–Ca
C1–C2a
L–M–Sa
S1–M–S2a
S1–M–S3a
C–S–Ma
C2–C1–S1a
d^ (M)b
a
M–M
S–Ca
C–Cb
M–S1–M0
S1–M–S2
S3–M–S4
S2–M–S3
S1–M–S4
S1–M–S3
S2–M–S4
0.73(1)
Mean values.
b
Perpendicular displacement of M from the mean [S1,S2,S3,S4] plane.
c
S–M–S10
C–S–Ma
d^(M)d
a
Mean values.
b
c
Average of chelate ring C–C bond distance.
Range of 4.
Perpendicular displacement of M from the mean [S1,S2,S3,S4] plane.
d
Symmetry equivalents are denoted by primed atoms.
at 50–70 ꢀC for 24–36 h. This procedure yields
[M(S2C2Et2)3]1ꢀ M = V (10, 24%), Nb (11, 30%) and
[M(S2C2Et2)3] M = Mo (12, 57%), W (13, 59%, 69%) by
two methods. Reaction stoichiometries are simply formu-
lated; e.g., reactions (5) and (6) for the formation of 13
and 11, respectively. Note that in contrast to reaction (4),
the oxo ligand has been
½WCl6ꢂ þ 3Et2C2ðSSiPri3Þ2 ! ½WðS2C2Et2Þ3ꢂ þ 6Pri3SiCl ð5Þ
2ꢀ
½NbOCl5ꢂ þ 3Et2C2ðSSiPri Þ
3
2
1ꢀ
! ½NbðS2C2Et2Þ ꢂ þ 4Pri3SiCl þ ðPr3i SiÞ2O þ Clꢀ
ð6Þ
3
removed in reaction (6) and in the formation of 10 and 12.
A characteristic feature of tris(dithiolene) complexes in oxi-
dized forms is their close approach to or achievement of tri-
gonal prismatic stereochemistry [23]. This feature is
described by the trigonal twist angle h and the trans-SMS
angle, whose values are 0ꢀ and 136ꢀ, respectively, for a tri-
gonal prism and 90ꢀ and 180ꢀ for an octahedron. For 12,
which crystallizes with two independent isostructural mol-
ecules in the asymmetric unit, mean values are h = 0.3ꢀ and
a trans angle of 135ꢀ, indicating that the complex is at the
trigonal prismatic limit. The mean chelate ring C–C
(1.368(5) A) and C–S (1.714(7) A) bond distances indicate
an intermediate ligand oxidation state. Of previously re-
ported complexes, 12 is essentially isostructural with
[Mo(S2C6H4)3] (h = 0ꢀ, trans-SMS = 136ꢀ) [36] and
[Mo(S2C2Me2)3] (h = 3ꢀ, trans-SMS = 137ꢀ) [11]. On this
basis, 13 is expected to the isostructural with
[W(S2C2Me2)3] (h = 2ꢀ, trans-SMS = 137ꢀ) [37]. Diffraction
quality crystals of the Et4N+ salts of 10 and 11 were not
obtained.
Fig. 4.
is essentially isostructural with [Mn2(S2C2H4)4]2ꢀ [33] and
similar to [Mn2(C3S5)4]4ꢀ [34]. This complex is one of only
a small number of homoleptic manganese dithiolenes,
which include a group of MnII,III complexes derived from
toluene-3,4-dithiolate(2-) [35]. Bond distances and angles
for 8 and 9 are collected in Table 3.
˚
˚
3.3. Tris(dithiolene) complexes
These complexes were prepared by reaction of a metal
halide or oxyhalide precursor with three equivalents of 1

1434
S. Friedle et al. / Inorganica Chimica Acta 359 (2006) 1427–1434
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This study contributes a new method of synthesis of
metal dithiolenes by Si–S bond cleavage of a bis(silan-
ylsulfanyl)alkene (1), exemplified by the preparation of
complexes belonging to four major structural families:
[M(S2C2R2)2]z (3), [ML(S2C2R2)2]z (4–7), [M2(S2C2R2)4]z
(8, 9), and [M(S2C2R2)3]z (10–13). Seven X-ray structure
proofs are provided. The procedure introduced here is an
elaboration of reaction (1), which is the first example of
dithiolene complex formation by Si–S bond cleavage. Stoi-
chiometric reactions require sufficient equivalents of bound
or free halide and/or bound oxide to deprotect the ligand
precursor by formation of R3SiX or (R3Si)2O. The method
appears capable of extension. Symmetrical and unsymmet-
rical alkynes R–C„C–R0 with primary, secondary, and
tertiary alkyl groups form bis(triisopropylsilanylsulfa-
nyl)alkenes in reported yields of 42–96% [12]. Published
results suggest that hydroxyl groups removed from the tri-
ple bond by one or more carbon atoms are tolerated in
reactions affording the protected ligand [13]. Hence, the
potential exists for substantial variation in chelate ring sub-
stituents. These influence solubility in non-aqueous and
aqueous media and modulate redox potentials [38]. Lastly,
the use of a disulfide reagent (R3SiS)2 with substituents
smaller than R = Pri may improve yields and eliminate
heating the reaction mixture. This is the case with reaction
(1), which proceeds readily at room temperature.
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5. Supplementary material
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¨
Crystallographic data for structural analysis have been
deposited at the Cambridge Crystallographic Data Center.
Copies of this information can be obtained free of charge
from The Director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK, e-mail: deposit@ccdc.cam.ac.uk or
www:www.ccdc.cam.ac.uk.
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Acknowledgments
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This research was supported by NSF Grant CHE
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