A structural and spectroscopic investigation of octahedral platinum bis(dithiolene)phosphine complexes: Platinum dithiolene internal redox chemistry induced by phosphine association

Article abstract of DOI:10.1021/ic501273b

The complexes [Pt(mdt)₂] (4; mdt = methyldithiolene, [Me ₂C₂S₂]^n-), [Pt(adt)₂] (5; adt = p-anisyldithiolene, [(MeO-p-C₆H₄)₂C ₂S₂]^n-), and [Pd(adt)₂] (10) have been prepared in yields of >90% via transmetalation reactions with the corresponding [R₂Sn(S₂C₂R′₂)] complexes (R = ⁿBu, R′ = Me; R = Me, R′ = -C ₆H₄-p-OMe, 3). Intraligand C-S and C-C_chelate bond lengths (～1.71 and ～1.40 A, respectively) obtained by X-ray crystallography show these compounds to be comprised of radical monoanions mdt^?- and adt^?-. The six-coordinate octahedral adducts [Pt(adt)₂(dppe)] [6; dppe = 1,2-bis(diphenylphosphino)ethane] , trans-[Pt(adt)₂(PMe₃)₂] (8), and trans-[Pt(mdt)₂(PMe₃)₂] (9) have also been prepared, and crystal structures reveal dithiolene ligands that are fully reduced ene-1,2-dithiolates (C-S and C-C_chelate = ～1.77 and 1.35 A, respectively). Reduction of the dithiolene ligand thus occurs to accommodate the +IV oxidation state typical of octahedral six-coordinate platinum. The cyclic voltammogram of 5 shows two fully reversible reductions at -0.11 and -0.84 V in CH₂Cl₂ (vs Ag/AgCl), attributed to successive (adt^?- + e^- → adt^2-) processes, and a reversible oxidation at +1.01 V. The cyclic voltammogram of 9 shows two reversible oxidations at +0.38 and +0.86 V, which are assigned as successive (adt^2- → adt^?- + e^-) oxidations. Consistent with their formulation as having fully reduced dithiolene ligands, the UV-vis spectra for 6, 8, and 9 show no low-energy absorptions below 700 nm, and the S K-edge XAS spectra of 6 and 8 show dithiolene sulfur that is reduced relative to that in 5. The introduction of PMe₃ to 10 did not produce the palladium analogue of 8 but rather [Pd(adt)(PMe ₃)₂] (11). The reaction of [PdCl₂(PPh ₃)₂] with Li₂(mdt) produced a mixture of [Pd(mdt)(PPh₃)₂] (12, 20%) and [(Ph₃P)Pd(μ- 1,2-mdt-S,S′:S)₂Pd(PPh₃)] (13, 28%), with the latter having C₂ symmetry with a Pd₂S₂ core structure folded along the S···S axis.

Full text of DOI:10.1021/ic501273b

Article
pubs.acs.org/IC
A Structural and Spectroscopic Investigation of Octahedral Platinum
Bis(dithiolene)phosphine Complexes: Platinum Dithiolene Internal
Redox Chemistry Induced by Phosphine Association
P. Chandrasekaran,*,† Angelique F. Greene,‡ Karen Lillich,‡ Stephen Capone,‡ Joel T. Mague,‡
Serena DeBeer,§,⊥ and James P. Donahue*,‡
†Department of Chemistry and Biochemistry, Lamar University, Beaumont, Texas 77710, United States
‡Department of Chemistry, Tulane University, 6400 Freret Street, New Orleans, Louisiana 70118, United States
§Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
⊥Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34−36, D-45470 Mulheim an der Ruhr, Germany
̈
S
* Supporting Information
ABSTRACT: The complexes [Pt(mdt)2] (4; mdt = methyldithiolene, [Me2C2S2]n−), [Pt(adt)2] (5; adt = p-anisyldithiolene,
[(MeO-p-C6H4)2C2S2]n−), and [Pd(adt)2] (10) have been prepared in yields of ≥90% via transmetalation reactions with the
corresponding [R2Sn(S2C2R′2)] complexes (R = nBu, R′ = Me; R = Me, R′ = −C6H4-p-OMe, 3). Intraligand C−S and C−Cchelate
bond lengths (∼1.71 and ∼1.40 Å, respectively) obtained by X-ray crystallography show these compounds to be comprised of
radical monoanions mdt•− and adt•−. The six-coordinate octahedral adducts [Pt(adt)2(dppe)] [6; dppe = 1,2-
bis(diphenylphosphino)ethane], trans-[Pt(adt)2(PMe3)2] (8), and trans-[Pt(mdt)2(PMe3)2] (9) have also been prepared, and
crystal structures reveal dithiolene ligands that are fully reduced ene-1,2-dithiolates (C−S and C−Cchelate = ∼1.77 and 1.35 Å,
respectively). Reduction of the dithiolene ligand thus occurs to accommodate the +IV oxidation state typical of octahedral six-
coordinate platinum. The cyclic voltammogram of 5 shows two fully reversible reductions at −0.11 and −0.84 V in CH2Cl2 (vs
Ag/AgCl), attributed to successive (adt•− + e− → adt2−) processes, and a reversible oxidation at +1.01 V. The cyclic
voltammogram of 9 shows two reversible oxidations at +0.38 and +0.86 V, which are assigned as successive (adt2− → adt•− + e−)
oxidations. Consistent with their formulation as having fully reduced dithiolene ligands, the UV−vis spectra for 6, 8, and 9 show
no low-energy absorptions below 700 nm, and the S K-edge XAS spectra of 6 and 8 show dithiolene sulfur that is reduced relative
to that in 5. The introduction of PMe3 to 10 did not produce the palladium analogue of 8 but rather [Pd(adt)(PMe3)2] (11).
The reaction of [PdCl2(PPh3)2] with Li2(mdt) produced a mixture of [Pd(mdt)(PPh3)2] (12, 20%) and [(Ph3P)Pd(μ-1,2-mdt-
S,S′:S)2Pd(PPh3)] (13, 28%), with the latter having C2 symmetry with a Pd2S2 core structure folded along the S···S axis.
Mayweg also detailed the preparation and isolation of six-
coordinate [M(S2C2R2)2(PPh3)2] species (M = Pd, R = Ph; M
= Pt, R = Ph or Me),13 but a subsequent report by Davison and
Howe disputed the identity of the species formed under the
given conditions, identifying them instead as [M(S2C2R2)-
(PR3)2] complexes.14 In a reexamination of the compound
type, Schrauzer and Mayweg affirmed the preparation and
isolation of blue [Pt(S2C2Ph2)2(PR3)2] (PR3 = 1/2dppe, PnBu3)
and brown [Ni(S2C2Ph2)2(PR3)2] (PR3 = PPh3, PnBu3), albeit
from room temperature reactions rather than from refluxing
conditions as initially described.15 The nickel compounds were
noted as being markedly less stable than the platinum
INTRODUCTION
■
Metallodithiolene complexes, both homoleptic and hetero-
leptic, have enjoyed continuous scrutiny over the several
decades since their initial syntheses and property investigations
were disclosed. Much of this activity has been motivated by the
promise of applications as catalysts1 or advanced materials.2−7
Among heteroleptic complexes, two large classes have been
developed, one being mono- and bis(dithiolene) complexes of
molybdenum and tungsten because of their biological
relevance8 and the second being mono(dithiolene) complexes
of the group 10 metals, in large part owing to the photophysical
properties of [Pt(S2C2R2)L2] complexes.3−5,9−11
Compounds of the type [M(S2C2R2)(phosphine)2] (M = Ni,
Pd, Pt) were among the first of this latter class to be
described.12 An early communication by Schrauzer and
Received: May 31, 2014
© XXXX American Chemical Society
A
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 1. Summary of Known Platinum Dithiolenebis(phosphine) Complexes
compound
reference
18, 19
compound
reference
39
b
[(mnt)Pt(dppe)] [mnt = maleonitriledithiolate(2−) =
[(SCS2C2S2)Pt(DPCB-phen)]
[(NC)2C2S2]2−); dppe = Ph2PCH2CH2PPh2]
[(dddt)Pt(PPh3)2] [dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate 21
[(mnt)Pt(P−P)] [P−P = Ph2PCHCHPPh2, 1,2-(Ph2P)2C6H4, 18
(2−)]
[(dddt)Pt(dppe)]
or Cy2PCH2CH2PCy2]
40
40
38
38
[(mnt)Pt(Ph2PCH2PPh2)]
20
[(dddt)Pt(3,4-Me2-3′,4′-(Ph2P)2ttf)]
[(dddt)Pt(dppf)]
[(mnt)Pt(PR2R′)2] (R = R′ = Ph;12,18,21 R = Me, R′ = Ph;18,22
R
12, 18,
21, 22
= R′ = Et22
)
[(mtdt)Pt(dppf)] [mtdt = 1,2-bis(methylthio)ethylene-1,2-
[(mnt)Pt(P(CH2OH)3)2]
23
20
24
dithiolate(2−)]
[(mnt)Pt(P(OR)3)2] (R = Et or Ph)
[(phdt)Pt(dppf)] [phdt = 6-hydro-5-phenyl-1,4-dithiin-2,3-
38
38
[(mnt)Pt(abpcd)] [abpcd = 2-(9-anthracenylidene)-4,5-bis
(Ph2P)-4-cyclopenten-1,3-dione]
dithiolate(2−)]
[(dphdt)Pt(dppf)] [dphdt = 5,6-diphenyl-1,4-dithiin-2,3-
[(mnt)Pt(fbpcd)] [fbpcd = 2-(ferrocenylidene)-4,5-bis(Ph2P)-4- 25
cyclopenten-1,3-dione]
dithiolate(2−)]
[(bdt)Pt(PPh3)2] [bdt = benzene-1,2-dithiolate(2−)]
[(bdt)Pt(dppf)]
41
[(H2C2S2)Pt(PnBu3)2]
26
42
[(H2C2S2)Pt(PR2R′)2] (R = R′ = Et; R = Me, R′ = Ph)
[(H2C2S2)Pt(PPh3)2]
22
[(bdt)Pt(3,4-Me2-3′,4′-(Ph2P)2ttf)]
40
a
21
[(bdt)Pt(DPCB)]
39
b
[((CF3)2C2S2)Pt(PPh3)2]
12
[(bdt)Pt(DPCB-phen)]
39
[((MeO2C)2C2S2)Pt(PPh3)2]
27
[(bdt)Pt(PPh2(CCPh))2]
43
[((RO2C)2C2E2)Pt(dppe)] (R = Me or Et; E = S or Se)
[((MeO2C)2C2S2)Pt(P(OMe)3)2]
28
[(bdt)Pt(μ-Ph2PCCPPh2)2Pt(bdt)]
44
29
[(2,6-Cl2-bdt)Pt(dppf)]
42
[(Ph2C2S2)Pt(P−P)] (P−P = dppe or 2PPh3)
[((tBu-p-C6H4)2C2S2)Pt(PPh3)2]
16
[(2,6-Cl2-bdt)Pt(μ-Ph2PCCPPh2)2Pt(2,6-Cl2-bdt)]
[{4-[(4-methylphenyl)azo]-1,2-bdt}Pt(dppe)]
[(tdt)Pt(dppf)] [tdt = toluene-3,4-dithiolate(2−)]
[(tdt)Pt(pbpcd)] [pbpcd = 2-(pyrene-1-ylidene)-4,5-bis(Ph2P)-4- 48
cyclopenten-1,3-dione]
44
30
45, 46
42, 47
[((ArH)C2S2)Pt(dppe)] (Ar = 2-pyridyl,31 3-pyridyl,31 2-
31, 32
quinoxalinyl,31,32 2-pyrazinyl31
)
[(OCS2C2S2)Pt(P−P)] (P−P = dppe or 2PPh3)
21, 33, 34
[(SCS2C2S2)Pt(PPh3)2] [SCS2C2S2 = 1,3-dithiole-2-thione- 21, 33, 35
[(tdt)Pt(bpcd)] [bpcd = 4,5-bis(Ph2P)-4-cyclopenten-1,3-dione] 48
4,5-dithiolate(2−)]
[(SCS2C2S2)Pt(PEt3)2]
[(tdt)Pt(μ-Ph2PCCPPh2)2Pt(tdt)]
44
36
35
37
[(qdt)Pt(PR2R′)2] [qdt = quinoxaline-2,3-dithiolate(2−); R = R′ 22
= Et; R = Me, R′ = Ph]
[(SCS2C2S2)Pt(Ph2PCH2CH2PPh2)]
[(SCS2C2S2)Pt(3,4-Me2-3′,4′-(Ph2P)2ttf] (ttf =
a
DPCB
= 1,2-diphenyl-3,4-bis[(2,4,6-tri-tert-butylphenyl)-
b
tetrathiafulvalene)
phosphinidene]cyclobutene. DPCB-phen = phenanthrene-1,2-diyli-
[(SCS2C2S2)Pt(dppf)] [dppf = 1,1′-bis(diphenylphosphino)
38
39
dene-3,4-bis[(2,4,6-tri-tert-butylphenyl)phosphinidene]cyclobutene.
ferrocene = (C5H4(Ph2P))2Fe]
a
[(SCS2C2S2)Pt(DPCB)]
analogues. Since that time, apart from a note of cyclic
voltammetry data for [Pt(S2C2Ph2)2(dppe)]16 [dppe = 1,2-
bis(diphenylphosphino)ethane] and a later report describing its
use as a dithiolene transfer agent,17 no published work of which
we are aware has revisited these compounds and addressed the
correctness of their formulation by Schrauzer and Mayweg or
sought to characterize them more thoroughly.
coordination sphere is accommodated. Related complexes of
palladium are also reported here.
EXPERIMENTAL SECTION
■
General Considerations. Air- and moisture-sensitive compounds
were prepared and handled under a N2 atmosphere using a drybox or
standard Schlenk-line techniques. Published procedures were
employed in the syntheses of [(Me2C2S2)Sn(nBu)2]49 and
Me2C2S2CO.50 All other reagents were purchased from commercial
sources and used as received [K metal, CS2, desoxyanisoin, N-
bromosuccinimide (NBS), 2,2′-azobis(2-methylpropionitrile) (AIBN),
H2SO4, nBuLi (1.6 M in hexanes), Me2SnCl2, PtCl2, PdCl2, cis-
[Pd(PPh3)2Cl2], I2, PMe3 (1.0 M in toluene), 10% LiOMe in MeOH,
and 1,2-bis(diphenylphosphino)ethane (dppe)]. Solvents were dried
with a system of drying columns from the Glass Contour Company
[CH2Cl2, tetrahydrofuran (THF), and Et2O], were freshly distilled
according to standard procedures (MeOH, MeCN, and 1,2-dichloro-
ethane),51 or were used as received (CCl4 and iPrOH). Silica columns
were run in the open air using 60−230 μm silica (Dynamic
Adsorbents). The compounds reported and their supporting ligands
are hereafter referred to by the numerical designations and
abbreviations given in Chart 1.
As part of a program of research aimed at a “bottom-up”
approach to the synthesis of complex metallodithiolene
materials, we have made observations that corroborate Mayweg
and Schrauzer’s report of isolable [M(S2C2R2)2(PR3)2]
complexes,15 at least with platinum. Considering the fairly
extensive corpus of [M(S2C2R2)(PR3)2] (M = Ni, Pd, Pt)
complexes that has been developed since Mayweg and
Schrauzer’s work (Table 1), it is surprising that Schrauzer’s
six-coordinate [Pt(S2C2R2)2(PR3)2] compounds have not been
reexamined using modern physical methods of analysis and
characterization. Herein we describe the properties and
characterization of [Pt(S2C2R2)2(PR′3)2] [R = p-anisyl or Me,
R′ = Me; R = p-anisyl, (PR′3)2 = 1,2-bis(diphenylphosphino)-
ethane] structurally by X-ray crystallography and spectroscopi-
cally by S K-edge X-ray absorption spectroscopy (XAS). The
latter technique is decisive in showing how the redox
noninnocent nature of the dithiolene ligand enables internal
redox change between metal and the dithiolene ligand such that
the PtIV oxidation state is created and the expanded
Instrumentation. All NMR spectra were recorded at 25 °C with a
Varian Unity Inova spectrometer operating at 400, 100.5, and 161.8
MHz for 1H, 13C, and 31P nuclei, respectively. Spectra were referenced
to the protonated solvent residual for 1H and 13C NMR, whereas 85%
H3PO4 was used as an external standard for 31P NMR. IR spectra were
taken as pressed KBr pellets with a Thermo Nicolet Nexus 670 Fourier
transform infrared instrument in absorption mode, while UV−vis
spectra were obtained at ambient temperature with a Hewlett-Packard
B
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
several portions of hexanes were added over a period of 4 h to 2-
propanol under a N2 flow. Vigorous evolution of H2 gas and moderate
warming of the flask ensued. During this time, the 2-propanol solution
thickened visibly. The mixture was gradually warmed to ambient
temperature, and stirring was continued for approximately 8 h until all
K metal had been consumed. With a flow of N2 outward, the central
neck of the Schlenk flask was replaced with a 125 mL pressure
equalizing addition funnel fitted with a Teflon stopcock. The K+PriO−/
PriOH mixture was cooled again to 0 °C in an ice bath. Carbon
disulfide (100 mL, 126 g, 1.65 mol) was added to the addition funnel
and admitted dropwise to the isopropoxide solution over the course of
2 h. A fine, pale-yellow precipitate formed immediately. The reaction
vessel was maintained in the ice bath because of the moderate
exothermicity of the reaction. Before the addition was complete, the
mixture thickened significantly. After the complete addition of CS2, the
addition funnel was replaced with an overhead mechanical stirrer fitted
to a Teflon paddle with a suitable adaptor supporting the glass shaft of
the stirrer in the neck of the flask. The reaction mixture was warmed to
room temperature and subjected to vigorous stirring for 1 h. The thick,
pasty potassium O-isopropylxanthate was then collected on a large
Buchner funnel in the open air and washed with diethyl ether (5 × 100
mL). The slightly moist filter cake was transferred to a clean 1000 mL
Schlenk flask, dried at 0.1 Torr at room temperature for 24 h, and
obtained as a loose, pale-yellow solid in a yield of 95% (254 g, 1.46
mol). Potassium O-isopropylxanthate thus obtained is stable to air,
moisture, and light and is of sufficient purity for the following step.
[(MeO-p-C6H4)C(O)CH(SC(S)OiPr)(C6H4-p-OMe)] (1). A 500
mL Schlenk flask with a stir bar was charged with desoxyanisoin (15.0
g, 58.5 mmol), NBS (10.42 g, 58.54 mmol), and AIBN (0.020 g)
under an atmosphere of N2. Following the addition of CCl4 (200 mL),
a reflux condenser was fit to the Schlenk flask and the mixture was
heated to 70 °C for 6 h under N2. After this reaction vessel cooled to
room temperature, solid potassium O-isopropylxanthate (10.2 g, 58.5
mmol) was added to the reaction mixture in a single portion. With
vigorous stirring, the resulting pale-yellow reaction mixture was heated
to reflux for 4 h. The mixture was permitted to cool and then was
poured over ice water and extracted with portions of CH2Cl2 (3 × 150
mL). The combined organic fractions were washed thoroughly with
deionized water, dried over MgSO4, and separated from the drying
agent by filtration. The filtrate was concentrated under reduced
pressure to afford a brown paste. The addition of MeOH to this pasty
brown solid residue produced a white solid precipitate, which was
collected onto a glass frit by filtration and then dried under vacuum to
afford 1. Yield: 17.73 g, 45.40 mmol, 78%. Mp: 83−85 °C. Rf = 0.52
(3:1 CH2Cl2/hexanes). 1H NMR (δ, ppm in CDCl3): 7.99 (d, J = 9.2
Hz, 2H, Ph), 7.33 (d, 2H, Ph), 6.88 (d, J = 9.2 Hz, 2H, Ph), 6.81 (d,
2H, Ph), 6.48 (s, 1H, CH), 5.64 (sep, J = 6.4 Hz, 1H, CH(CH3)2),
3.82 (s, 3H, −OCH3), 3.73 (s, 3H, −OCH3), 1.24 (m, 6H,
(CH3)2CH). 13C NMR (δ, ppm in CDCl3): 212.91 (s, CO), 192.87
(CS), 164.34 (s, Ph), 160.38 (s, Ph), 131.99 (s, Ph), 130.95 (s, Ph),
129.24 (s, Ph), 125.95 (s, Ph), 115.30 (s, Ph), 114.58 (s, Ph), 79.00
(CS), 59.98 (CH(CH3)2), 56.17 (s, −OCH3), 55.94 (s, −OCH3),
21.93 (s, CH(CH3)2. IR (cm−1 in KBr): 2977 (w), 1671 (s), 1597 (s),
1509 (s), 1462 (m), 1242 (s), 1171 (s), 1087 (s), 1039 (s), 864 (w),
782 (m), 597 (m), 530 (m). ESI-MS+: m/z 391.10 (M + H+). Anal.
Calcd for C20H22S2O4: C, 61.51; H, 5.67. Found: C, 61.82; H, 5.69.
[(MeO-p-C6H4)2C2S2CO] (2). A 250 mL three-necked flask
equipped with an addition funnel was charged with 1 (17.73 g, 45.4
mmol) and a magnetic stir bar. Over a period of 30 min at 0 °C, 100
mL of 80% aqueous H2SO4 was added dropwise directly onto solid 1.
The resulting reaction mixture was stirred well for the ensuing 4 h,
during which time it darkened progressively to a brown color. It was
then poured over ice and extracted with portions of CH2Cl2 (3 × 100
mL). The combined CH2Cl2 extracts were washed with saturated
aqueous NaHCO3 and then deionized water. This organic solution was
then dried over MgSO4, separated from the drying agent by filtration,
and reduced to a pasty solid with the use of a rotary evaporator.
Methyl alcohol (∼100 mL) was added to this solid residue until a
clean product was precipitated. Yield: 12.73 g, 38.52 mmol, 85%. Mp:
Chart 1. Numerical Identification System for Compounds
Footnote a: adt = cis-1,2-di-p-anisyldithiolene, [(MeO-p-
C6H4)2C2S2]n−. Footnote b: mdt = cis-1,2-dimethyldithiolene,
[Me2C2S2]n−. Footnote c: dppe = 1,2-bis(diphenylphosphino)ethane.
8452A diode-array spectrophotometer. Electrospray ionization mass
spectrometry (ESI-MS) spectra were obtained with either a Bruker
Daltonics or a PESciex Qstar instrument. Electrochemical measure-
ments were made with a CHI620C electroanalyzer workstation using a
Ag/AgCl reference electrode (or silver wire electrode for [Pt-
(adt)2(dppe)]), a platinum disk working electrode, a platinum wire
auxiliary electrode, and [nBu4N][PF6] as the supporting electrolyte.
Under these conditions, the [Cp2Fe]+/Cp2Fe couple consistently
occurred at +440 mV. Elemental analyses were performed by Midwest
Microlab, LLC, of Indianapolis, IN. Descriptions of the instrumenta-
tion and procedures employed in X-ray diffraction data collection and
processing, and for the structure solutions and refinements, are
deferred to the Supporting Information (SI), as are figures showing the
complete atom labeling for all compounds (Figures S1−S16 in the SI).
Unit cell data and refinement statistics for all structures reported are
presented in Table 2.
XAS. XAS spectra were measured at the Stanford Synchrotron
Radiation Lightsource (SSRL). S K-edge data were obtained using the
20-pole wiggler beamline 4-3. Detailed S K-edge data collection and
normalization procedures were followed as previously described.52 Pt
L-edge XAS were measured on the 20-pole wiggler beamline 7-3.
Samples for Pt L-edge XAS were prepared by dilution in boron nitride
(BN), pressed into a pellet, and sealed between 38 μm Kapton tape
windows in a 0.5 mm aluminum spacer. Data were measured in
transmittance mode, and samples were maintained at 10 K using an
Oxford Instruments CF1208 continuous-flow liquid-helium cryostat.
Internal energy calibrations were performed by simultaneous measure-
ment of the Pt reference foil placed between the second and third
ionization chambers with inflection points assigned as 13879.9 eV for
the L1-edge. Data were averaged using EXAFSPAK53 and normalized
by subtracting the spline and normalizing the postedge to 1.0. The S K
pre-edge features were modeled with line shapes having fixed mixing
ratios (1:1) of Lorentzian and Gaussian functions (pseudo-Voigt)
using the program EDG_FIT.53
Syntheses. Potassium O-Isopropylxanthate. A 1000 mL Schlenk
flask was charged with a large stir bar and 2-propanol (700 mL, 550 g,
9.15 mol), capped with a rubber septum, and affixed to a Schlenk line
via its side stopcock. While being vigorously stirred, 2-propanol was
thoroughly sparged for 15 min with dry N2 delivered from the inert gas
manifold of a Schlenk line through a long syringe needle penetrating
the septum and vented through a second, smaller syringe needle. After
thorough degassing, 2-propanol was maintained under a positive N2
pressure applied through the side stopcock of the flask and was cooled
to 0 °C with an ice bath. Note! It is important for safety reasons that
iPrOH be completely oxygen free. H2(g) evolved by the reaction of K0 with
iPrOH is very flammable and should be vented through the pressure release
system of the Schlenk line into the back of a well-ventilated fume hood.
Pieces of freshly cut K metal (60.1 g total, 1.53 mol) washed with
1
138−140 °C. Rf = 0.61 (3:1 CH2Cl2/hexanes). H NMR (δ, ppm in
C
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 2. Unit Cell and Refinement Data for Compounds 1−13
1
2
3
4
formula
fw
C22H22O4S2
390.50
C17H14O3S2
330.40
C18H20O2S2Sn
C8H12PtS4
431.51
451.15
cryst syst
space group
color, habit
a, Å
monoclinic
P21/c
triclinic
monoclinic
triclinic
P1
̅
P21/n
P1
̅
colorless, parallelpiped
11.527(1)
16.947(2)
10.322(1)
90
colorless, parallelpiped
5.4968(4)
11.7792(9)
12.5653(9)
113.349(1)
94.108(1)
94.857(1)
739.33(9)
100
colorless, parallelpiped
black, prism
6.9778(14)
7.1911(14)
7.5203(15)
62.622(3)
62.445(2)
88.558(3)
288.52(10)
100
13.4064(19)
b, Å
10.7853(15)
c, Å
25.900(4)
α, deg
90
β, deg
102.779(2)
90
99.379(2)
γ, deg
V, Å3
90
1966.5(4)
100
3694.8(9)
T, K
100
Z
4
2
8
1
density, g·cm−1
μ, mm−1
cryst size, mm
1.319
1.484
1.622
2.483
0.292
0.369
1.615
12.833
0.10 × 0.11 × 0.17
0.0710, 0.1492
1.222
0.09 × 0.09 × 0.25
0.0288, 0.0749
1.065
0.10 × 0.19 × 0.33
0.0194, 0.0485
0.05 × 0.05 × 0.11
0.0160, 0.0390
a
b
R1, wR2
c
GOF
1.069
1.031
5·DCE
6
7·DCE
8
9
formula
fw
C34H32Cl2O4PtS4
C58H52O4P2PtS4
1198.27
orthorhombic
Pccn
C44H42Cl2O2P2PtS2
994.83
C38H46O4P2PtS4
952.02
C14H30P2PtS4
583.65
898.83
cryst syst
triclinic
monoclinic
P21/n
monoclinic
P21/n
orthorhombic
Cmca
space group
color, habit
a, Å
P1
̅
orange, plate
9.140(6)
12.279(8)
17.818(12)
109.932(9)
95.950(10)
109.328(8)
1720(2)
100
blue, plate
17.8597(12)
18.7052(12)
16.6577(11)
90
yellow, slat
23.093(4)
13.429(2)
27.953(5)
90
orange, column
8.4203(9)
13.7295(14)
33.591(4)
90
orange, plate
15.543(3)
12.222(2)
11.3826(18)
90
b, Å
c, Å
α, deg
β, deg
90
110.592(2)
90
93.757(1)
90
90
γ, deg
V, Å3
90
90
5564.8(6)
100
8115(2)
100
3875.0(7)
100
2162.2(6)
195
T, K
Z
2
4
8
4
4
density, g·cm−1
μ, mm−1
cryst size, mm
1.735
1.430
1.629
1.632
1.793
4.513
2.773
3.809
3.958
7.017
0.02 × 0.08 × 0.09
0.0562, 0.1384
1.012
0.02 × 0.10 × 0.21
0.0236, 0.0538
1.091
0.10 × 0.16 × 0.28
0.0262, 0.0520
1.035
0.08 × 0.12 × 0.18
0.0193. 0.0426
1.046
0.05 × 0.10 × 0.13
0.0178, 0.0442
1.076
a
b
R1, wR2
c
GOF
10
11
12
13
formula
fw
C32H28O4PdS4
711.18
C22H32O2P2PdS2
560.94
C40H36P2PdS2
749.15
C44H42P2Pd2S4
973.76
cryst syst
space group
color, habit
a, Å
triclinic
monoclinic
P21/c
monoclinic
Pn
triclinic
P1
̅
P1
̅
orange, parallelpiped
orange, slab
8.9483(6)
20.1445(14)
14.4855(10)
90
blue, block
9.0024(4)
10.9590(4)
17.4224(7)
90
red, block
9.8658(3)
10.4704(3)
21.2026(7)
85.809(1)
83.237(1)
68.470(1)
2022.15(11)
100
9.792(3)
b, Å
12.201(3)
14.106(4)
104.443(4)
104.466(4)
105.890(4)
1475.3(7)
100
c, Å
α, deg
β, deg
106.924(1)
90
99.862(10)
90
γ, deg
V, Å3
2498.1(3)
100
1693.5(1)
100
T, K
Z
2
4
2
2
density, g·cm−1
μ, mm−1
cryst size, mm
1.601
1.491
1.469
1.599
0.949
1.054
0.794
1.207
0.03 × 0.03 × 0.08
0.0523, 0.1218
0.977
0.11 × 0.16 × 0.23
0.0215, 0.0535
1.058
0.13 × 0.18 × 0.23
0.0169, 0.0446
1.131
0.10 × 0.13 × 0.13
0.0208, 0.0509
1.056
a
b
R1, wR2
c
GOF
D
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 2. continued
a
b
c
2
2
2
2
2
R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = {[∑w(Fo − Fc2)/∑w(Fo )2}1/2; w = 1/[σ2(Fo ) + (xP)2], where P = (Fo + 2Fc2)/3. GoF = {∑[w(Fo
−
Fc2)2]/(n − p)}1/2, where n = number of reflections and p= total number of parameters refined.
CDCl3): 7.11 (d, J = 9.2 Hz, 4H, Ph), 6.76 (d, 4H, Ph), 3.76 (s, 6H,
−OCH3). 13C NMR (δ, ppm in CDCl3): 191.36 (s, CO), 160.02 (s,
olefinic C), 131.14 (s, Ph), 127.84 (s, Ph), 124.45 (s, Ph), 114.53 (s,
Ph), 55.66 (OCH3). IR (cm−1 in KBr): 1658 (m), 1631 (s), 1600 (m),
1511 (s), 1294 (m), 1248 (vs), 1186 (m), 1027 (m), 832 (s), 584 (w),
518 (w). ESI-MS+: m/z 331.04 (M + H+). Anal. Calcd for
C17H14S2O3: C, 61.79; H, 4.27. Found: C, 61.68; H, 4.29.
8.4 Hz, dithiolene-Ph), 6.61 (d, 4H, JHH = 8.8 Hz, dithiolene-Ph), 3.69
(s, 6H, −OCH3), 2.58−2.48 (m, 4H, dppe −CH2). 13C NMR (δ, ppm
in CD2Cl2): 133.82 (br, m), 131.35 (s), 128.91 (s), 128.86 (s), 128.81
(s), 112.89 (s), 55.25 (s), 43.67 (s). 31P NMR (δ, ppm in CD2Cl2):
45.02 (s, 1JPtP = 2746.73 Hz). Absorption spectrum [CH2Cl2; λmax, nm
(εM, M cm−1)]: 330 (43300), 432 (sh, 5000). Anal. Calcd for
C42H38O2P2S2Pt: C, 56.30; H, 4.27; P, 6.91. Found: C, 54.36; H, 4.39;
P, 7.31.
[(adt)SnMe2] (3). A stirred solution of 2 (4.00 g, 12.1 mmol) in
[Pt(adt)2(PMe3)2] (8). A stirred solution of 5 (0.100 g, 0.125 mmol)
in CH2Cl2 (20 mL) was treated with PMe3 in toluene (0.5 mL, 1.0 M
solution) delivered via syringe, which induced a change in color from
deep red to pale yellow. This reaction mixture was stirred for 24 h at
ambient temperature, after which time the solvent was removed under
reduced pressure and the resulting solid residue was washed with Et2O
(2 × 10 mL) and dried. Yield: 0.102 g, 0.107 mmol, 86%. 1H NMR (δ,
THF (80 mL) under N2 in a 200 mL Schlenk flask was cooled to 0 °C
and treated with BuLi in hexanes (1.6 M, 15.13 mL, 24.21 mmol)
n
delivered via syringe. The mixture was stirred for 24 h at ambient
temperature, whereupon a solution of Me2SnCl2 (2.65 g, 12.10 mmol)
in THF (20 mL) was transferred via a cannula at room temperature.
This mixture was stirred overnight, quenched by pouring over ice, and
then extracted with portions of CH2Cl2 (3 × 100 mL). The combined
organic fractions were dried over MgSO4. Following removal of
MgSO4 and the solvent, the crude product was purified on a silica
column eluted with 3:1 CH2Cl2/hexanes. Yield: 4.10 g, 8.79 mmol,
ppm in CD2Cl2): 7.01 (d, 8H, JHH = 8.8 Hz, Ph), 6.64 (d, 8H, JHH
=
8.8 Hz, Ph), 3.71 (s, 12H, −OCH3), 1.81 (t, 18H, J = 4 Hz, P(CH3)3).
13C NMR (δ, ppm in CD2Cl2): 158.54 (s), 135.01 (s), 130.96 (s),
129.95 (s), 113.64 (s), 55.62 (s), 9.24 (t, P(CH3)3). 31P NMR (δ, ppm
1
73%. Mp: 173−175 °C. Rf = 0.66 (CH2Cl2). H NMR (δ, ppm in
1
CDCl3): 7.02 (d, J = 8.8 Hz, 4H, Ph), 6.60 (d, J = 9.2 Hz, 4H, Ph),
3.69 (s, 6H, −OCH3), 1.01 (s, J119Sn−H = 61.6 Hz, J117Sn−H = 58.8 Hz,
6H, Sn(CH3)2). 13C NMR (δ, ppm in CDCl3): 158.53 (s, olefinic C),
133.91 (s, Ph), 133.41 (s, Ph), 130.42 (s, Ph), 113.66 (s, Ph), 55.63 (s,
−OCH3), 3.55 (s, Sn(CH3)2). ESI-MS+: m/z 452.99 (M + H+). Anal.
Calcd for C18H20O2S2Sn: C, 47.92; H, 4.47; S, 14.21. Found: C, 48.06;
H, 4.49; S, 14.03.
in CD2Cl2): −18.28 (s, JPtP = 1740 Hz). Absorption spectrum
[CH2Cl2; λmax, nm (εM, M cm−1)]: 256 (83500), 314 (33900), 428
(sh, 1980). Anal. Calcd for C38H46O4P2S4Pt: C, 47.94; H, 4.87; P, 6.51.
Found: C, 47.86; H, 4.72; P, 6.45.
[Pt(mdt)2(PMe3)2] (9). The procedure used in the synthesis of 9 was
analogous to that described for 8. The scale employed for the reaction
involved 0.100 g of [Pt(S2C2Me2)2] (0.232 mmol) and 1.0 mL of
1
PMe3 in toluene (1.00 mmol). Yield: 0.113 g, 0.194 mmol, 84%. H
[Pt(mdt)2] (4). A procedure similar to that implemented for the
synthesis of [Pt(adt)2] (5) was followed on a scale employing 0.264 g
of [(mdt)Sn(nBu)2] (0.989 mmol), 0.100 g of PtCl2 (0.376 mmol),
NMR (δ, ppm in CDCl3): 1.78 (d, 18H, JPH = 13.2 Hz, P(CH3)3),
1.61 (s, 12H, dithiolene −CH3). 13C NMR (δ, ppm in CDCl3): 122.61
(S, dithiolene CC), 21.25 (s, dithiolene −CH3)), 9.24 (t, P(CH3)3).
1
and 0.095 g of I2 (0.374 mmol). Yield: 0.156 g, 0.362 mmol, 96%. H
1
31P NMR (δ, ppm in CD2Cl2): −19.40, JPtP = 1775 Hz). Absorption
NMR (δ, ppm in CDCl3): 2.59 (s, 12H, −CH3). 13C NMR (δ, ppm in
CDCl3): 177.34 (s), 160.70 (s).
spectrum [CH2Cl2; λmax, nm (εM, M cm−1)]: 232 (29400), 272 (sh,
7100). Anal. Calcd for C14H30P2S4Pt: C, 28.80; H, 5.18; P, 10.61.
Found: 28.88; H, 5.10; P, 10.85.
[Pt(adt)2] (5). A 50 mL Schlenk flask with stir bar was charged with
CH2Cl2 (30 mL), 3 (0.351 g, 0.778 mmol), and PtCl2 (0.100 g, 0.376
mmol). The resulting reaction mixture was stirred for 12 h at ambient
temperature, after which time I2 (0.095 g, 0.374 mmol) was added in a
single portion under a N2 flow. The dark reaction mixture that resulted
was stirred an additional 4 h. The solvent was removed under reduced
pressure, and the solid residue was washed with MeOH (2 × 10 mL),
followed by Et2O (3 × 10 mL). The resulting dark solid was dried
under vacuum for 24 h. Yield: 0.281 g, 0.351 mmol, 94%. 1H NMR (δ,
ppm in CDCl3): 7.23 (d, 8H, JHH = 8.8 Hz, Ph), 6.79 (d, 8H, JHH = 8.8
Hz, Ph), 3.80 (s, 12H, −OCH3). 13C NMR (δ, ppm in CDCl3): 177.34
(s), 160.70 (s), 134.64 (s), 130.90, (s), 114.26 (s), 55.86 (s).
Absorption spectrum [CH2Cl2; λmax, nm (εM, M cm−1)]: 464 (2990),
860 (52700). Anal. Calcd for C32H28O4S4Pt·ClCH2CH2Cl: C, 45.43;
H, 3.59; S, 14.27. Found: C, 45.14; H, 3.44; S, 11.99.
[Pd(adt)2] (10). The procedure employed for the synthesis of 10
was analogous to that used for 5. The scale on which the reaction was
performed involved 0.53 g (1.17 mmol) of 3, 0.100 g (0.564 mmol) of
PdCl2, and 0.143 g (0.563 mmol) of I2. Yield: 0.359 g, 0.505 mmol,
89%.
[Pd(adt)(PMe3)2] (11). Trimethylphosphine in toluene (1 M
solution, 0.56 mL, 0.56 mmol) was delivered via syringe to a stirring
solution of [Pd(S2C2(C6H4-p-OMe)2)2] (0.100 g, 0.141 mmol) in
CH2Cl2 (25 mL) at ambient temperature. The reaction mixture
immediately assumed an orange color. Stirring was continued for 12 h,
after which time the solvent was removed under reduced pressure and
the resulting solid residue was washed with Et2O (2 × 10 mL) and
dried under vacuum. Crystals were grown by the diffusion of hexanes
vapor into a C6H6 solution. Yield: 0.061 g, 0.109 mmol, 77%. 1H NMR
(δ, ppm in CD2Cl2): 7.08 (d, J = 9.2 Hz, 4H, Ph), 6.64 (d, J = 9.2 Hz,
4H, Ph), 3.32 (s, 6H, −OCH3), 1.60 (d, 18H, JPH = 9.2 Hz, P(CH3)3).
13C NMR (δ, ppm in CD2Cl2): 158.19 (s, Ph), 137.20 (s, olefinic C),
134.75 (s, Ph), 131.46 (s, Ph), 128.83 (s, Ph), 113.27 (s, Ph), 55.59 (s,
−OCH3), 17.55 (t, P(CH3)3). 31P NMR (δ, ppm in CD2Cl2): −18.49
(s). Absorption spectrum [CH2Cl2; λmax, nm (εM, M cm−1)]: 222
(26700), 266 (44000), 338 (sh, 3560).
[Pt(adt)2(dppe)] (6). A mixture of solid 5 (0.100 g, 0.125 mmol)
and dppe (0.100 g, 0.251 mmol) was dissolved in CH2Cl2 (25 mL) to
form a deep-blue reaction mixture. The resulting blue solution was
stirred vigorously at ambient temperature for 4 h, after which time the
solvent was removed under reduced pressure. The residual solid was
washed with Et2O (2 × 10 mL) and then dried under vacuum to afford
6 as a blue solid. Yield: 0.115 g, 0.096 mmol, 77%. 31P NMR (δ, ppm
1
in C6D6): 3.01 (s, JPtP = 1756.3 Hz). Absorption spectrum [CH2Cl2;
λmax, nm (εM, M cm−1)]: 260 (11100), 315 (sh, 32500), 580 (2080).
[Pt(adt)(dppe)] (7). A vigorously stirred mixture of 5 (0.050 g, 0.063
mmol) and dppe (0.025 g, 0.063 mmol) in 1,2-dichloroethane (15
mL) was heated to 70 °C for 6 h. The deep-blue color formed initially
changed to yellow during the course of the reaction. The solvent was
removed under pressure, and the solid residue was washed with Et2O
(2 × 10 mL) and dried under vacuum to afford 7 as a yellow solid.
Yield: 0.046 g, 0.051 mmol, 82%. 1H NMR (δ, ppm in CD2Cl2): 7.87−
[Pd(mdt)(PPh3)2] (12) and [Pd2(μ-mdt)2(PPh3)2] (13). A portion of
Me2C2S2CO (0.063 g, 0.431 mmol) in MeOH (10 mL) was
deprotected by the addition of 10% LiOMe in MeOH (0.4 mL, 0.872
mmol). The resulting clear reaction mixture was stirred for 2 h at
ambient temperature and then was transferred via a cannula to a
Schlenk flask containing cis-[Pd(PPh3)2Cl2] (0.305 g, 0.436 mmol) in
CH2Cl2 (20 mL). The reaction mixture assumed a dark-brown color.
Stirring was continued overnight, and the solvent was then removed
under reduced pressure. Analysis of the crude product by 31P NMR
7.82 (m, 8H, dppe-Ph), 7.49 (br, s, 12H, dppe-Ph), 7.07 (d, 4H, JHH
=
E
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
indicated the presence of two different compounds, which were
subsequently separated on a silica column eluted with 1:1 CH2Cl2/
hexanes. Both compounds were readily crystallized by slow
evaporation of the eluant. 12. Yield: 0.063 g, 0.084 mmol, 19%. Rf:
1
0.31 (1:1 CH2Cl2/hexanes). H NMR (δ, ppm in CDCl3): 7.43−7.39
(m, 12H, Ph), 7.26 (t, JHH = 8 Hz, 6H, Ph), 7.10 (t, JHH = 7.2 Hz, 12H,
Ph), 1.89 (s, 6H, −CH3). 31P NMR (δ, ppm in CDCl3): 26.40 (s).
Absorption spectrum [CH2Cl2; λmax, nm (εM, M cm−1)]: 288 (60000).
Anal. Calcd for C40H36P2S2Pd: C, 64.12; H, 4.84. Found: C, 63.49; H,
4.92. 13. Yield: 0.070 g, 0.072 mmol, 33%. Rf: 0.17 (1:1 CH2Cl2/
1
hexanes). H NMR (δ, ppm in CDCl3): 7.67−7.62 (m, 12H, Ph),
7.43−7.34 (m, 18H, Ph), 1.36 (s, 6H, −CH3), 0.83 (s, 6H, −CH3). 13
C
NMR (δ, ppm in CDCl3): 135.26 (s), 135.20 (s), 135.14 (s), 130.96
(s), 130.66 (s), 130.51 (s), 128.30 (s), 128.25 (s), 128.19 (s), 115.21
(s), 25.22 (s, −CH3), 21.57 (s, −CH3). 31P NMR (δ, ppm in CDCl3):
32.23 (s). Absorption spectrum [CH2Cl2; λmax, nm (εM, M cm−1)]:
224 (103000), 320 (23500), 420 (12200), 584 (1700). Anal. Calcd for
C44H42P2S4Pd2: C, 54.26; H, 4.34. Found: C, 54.10; H, 4.44.
RESULTS AND DISCUSSION
Syntheses and Structure. The synthesis of 4,5-di-p-anisyl-
1,3-dithiol-2-one (2; Scheme 1) was undertaken via the acid-
■
Scheme 1. Synthesis of the p-Anisyl-Substituted Dithiolene
Ligand
catalyzed cyclization of O-isopropyl rac-(4-methoxyphenyl-4-
methoxyphenacyl)dithiocarbonate (1; Scheme 1), a reaction of
some generality reported by Bhattacharya and Hortmann.54
Compound 1 was itself readily obtained in good yield (78%) by
an in situ bromination of commercially available desoxyanisoin
followed immediately by treatment with potassium O-
isopropylxanthate. Prepared as a racemic mixture, compound
1 crystallizes as such in centric space group P21/c (Table 2);
the S enantiomer is presented in Figure 1 and shows the syn
disposition of the p-anisyl groups that is necessary for ring
cyclization. Selected bond distances and angles are gathered in
Table S1 in the SI. While a fair number of dialkyl
dithiocarbonate type molecules have been identified structur-
ally, few of these are compounds in which the dithiocarbonate
functionality is positioned α to a carbonyl group. The molecule
closest in kind to 1 that has been characterized by X-ray
crystallography is (4-pyridyl)C(O)CH2SC(S)OiPr.53
Compound 2 is a convenient protected form of the
dithiolene ligand that is readily unmasked via base hydrolysis
and then coordinated to the desired transition complex, usually
by the displacement of halide ligands. Bond lengths and angles
for 2 (Table S2 in the SI) are similar to those reported for
related compounds that have been characterized structur-
ally.49,55−59 One of the types of metal complexes readily formed
from an in situ generated ene-1,2-dithiolate is a dialkyltin
dithiolene compound, such as 3 (Scheme 1 and Figure 1). Two
Figure 1. Thermal ellipsoid plots of 1 (a), 2 (b), and 3 (c) at the 50%
probability level. Hydrogen atoms are omitted for clarity except for
that at the chiral center C(9) in part a.
independent molecules of 3 occur in the asymmetric unit of the
cell, one of which is presented in Figure 1, and form relatively
close nonbonding intermolecular Sn···S contacts via an offset
head-to-head packing arrangement (Figure S17 in the SI). Such
intermolecular contacts are typical of this compound type.60−63
Selected metric parameters for 3 are gathered in Table S3 in the
SI and are similar to those observed in related com-
pounds.49,60−63
Dialkyltin species such as 3 have utility themselves in
transmetalation reactions that afford transition-metal dithiolene
complexes and often result in cleaner synthesis compared to
reactions employing the alkali-metal ene-1,2-dithiolate salts.
Compound 3 and its methyl dithiolene (mdt) variant were thus
employed for the preparation of [M(S2C2R2)2] [M = Pt, R =
Me (4) or p-anisyl (5); M = Pd, R = p-anisyl (10)]. We find
this synthetic approach (Scheme 2) to be consistent in
producing good yields of ∼90% and decidedly preferable to
the older P4S10/acyloin method devised by Schrauzer and
Mayweg,13 at least with these more expensive noble metals.
Structural characterization by X-ray crystallography (Figure
2a,b and Tables 2 and 3) revealed idealized D2h point group
F
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 2. Synthesis of Platinum and Palladium Dithiolenephosphine Complexes
symmetry for 4 but only C2 symmetry for 5 and 10 owing to
the disruption of all mirror planes by the canting angles of the
dithiolene p-anisyl substituents. An appreciable number of
homoleptic platinum and palladium bis(dithiolene) complexes
have been identified structurally, although the great majority of
these are anionic species with the dicyanoethylene(2−) ligand
(mnt2−). Only [Pt(S2C2R2)2] (R = Ph,64 p-anisyl,65 p-tBu-
C6H4,30 CF366), [Pt(dddt)2]67 [dddt = 5,6-dihydro-1,4-dithiin-
2,3-dithiolate(2−)], and [Pt(tmdt)2] [tmdt = trimethylenete-
trathiafulvalenedithiolate(2−)]68 are prior examples of mono-
nuclear charge-neutral platinum complexes for which a crystal
structure is reported. Crystallographically characterized palla-
d i u m c o m p l e x e s a r e f e w e r s t i l l , w i t h [ P d -
(norbornylenedithiolate)2]69 and [Pd(pttdt)2] [pttdt = di-n-
propylthiotetrathiafulvalenedithiolate(2−)]70 and [Pd-
(Et2timdt)2] (Et2timdt = monoanion of 1,3-diethylimidazoli-
dine-2,4,5-trithione)71 being the only precedents. Selected
structural parameters for 4, 5, and 10 are collected in Table 3
and compared with the corresponding values for [Ni(mdt)2]72
and [Ni(adt)2].73 The similarity of the values confirms the
description of 4, 5, and 10 as divalent metal ions coordinated
by radical monoanions, with the description given for
[Ni(mdt)2] on the basis of detailed structural, S K-edge XAS,
and computational studies.72,75 We note that [M(adt)2]n (M =
Ni, Pd, Pt) is the only series with n = 0 for the group 10 triad
for which crystallographic characterization is complete.
crystallography (Figure 2d), while the related dppe complex has
phosphine chelating in the cis fashion, as opposed to bridging
between metal atoms in a 1D coordination polymer76 or cyclic
species.77 Compound 8 (Figure 2d) occurs on a general
position in monoclinic P21/n but shows only Ci point
symmetry, if the staggered arrangement of PMe3 ligands and
the “two down, two up” orientation of the anisyl substituents
are considered. Compound 9 crystallizes on a special position
in orthorhombic Cmca such that the whole molecule is
generated from one unique fourth by reflection and inversion
operations. The point symmetry in compound 6 is limited to
only C2 rotational symmetry, with the C2 axis bisecting the
S(2)−Pt(1)−S(2A) and P(1)−Pt(1)−P(1A) angles. As noted
earlier, compounds 6, 8, and 9 are noteworthy as the first such
six-coordinate bis(phosphine) adducts of group 10 bis-
(dithiolene) complexes to be structurally characterized.
Selected averaged bond lengths for 6, 8, and 9 are presented
in Table 4. Comparison of M−S, S−C, and C−Cchelate bond
lengths with corresponding values for 4 and 5 in Table 3 shows
that the first two bond distances increase, while the third
decreases, with the changes being significant within the
resolution of the data. The nature and magnitude of these
bond-length changes in 6, 8, and 9 are indicative of a reduction
of the dithiolene ligand from a radical monoanion to fully
reduced ene-1,2-dithiolate (Scheme 3b→a). This dithiolene
ligand reduction occurs to accommodate the oxidation of PtII to
PtIV, its typical oxidation state in a six-coordinate octahedral
environment. While expansion of a metal’s coordination
number by association of the phosphine ligands is not usually
an oxidative addition reaction, the reactions of 4 and 5 to afford
6, 8, and 9 are special cases in which this is so. The reducing
equivalents that would normally pass from metal to the species
The introduction of 2 equiv of PMe3 or 1 equiv of dppe to
CH2Cl2 solutions of [Pt(S2C2R2)2] at ambient temperature
cleanly affords the six-coordinate bis(phosphine) adducts
(compounds 6, 8, and 9; Scheme 2). The PMe3 complexes
1
revealed a trans disposition for the phosphine ligands by H
NMR spectroscopy, a matter subsequently confirmed by X-ray
G
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 2. Thermal ellipsoid plots of 4 (a), 10 (b), 7 (c), trans-8 (d), 6 (e), and 13 from top (f) and side (g) views. All hydrogen atoms are omitted
for greater clarity.
a
Table 3. Selected Interatomic Distances (Å) and Angles (deg) for [M(S2C2R2)2] Complexes
[Pt(mdt)2] (4)
[Ni(mdt)2]72
[Pt(adt)2] (5)
[Pd(adt)2] (10)
[Ni(adt)2]73
M−S
S−C
2.2550[6]
1.705[2]
1.388(5)
87.86(3)
92.14(3)
180.0
2.1285[10]
1.714[4]
1.365(9)
88.64(5)
91.36(5)
180.0
2.244[1]
1.707[4]
1.397[8]
87.68[5]
92.41[6]
176.65[5]
106.0[2]
120.1[3]
2.2578[9]
1.708[3]
1.414[6]
87.89[4]
92.19[4]
176.63[5]
105.8[1]
120.1[3]
2.1241[3]
1.7118[10]
1.392[2]
C−Cchelate
S−M−Schelate
S−M−Scis
S−M−Strans
C−S−M
C−C−S
91.08[1]
89.01[1]
176.43[1]
105.77[4]
118.56[7]
105.37[8]
120.7[1]
105.0[1]
119.4[3]
a
Chemically identical, crystallographically independent values are averaged. Uncertainties are propagated according to the general formula for
uncertainty as a function of several variables, as detailed in ref 74.
that is oxidatively adding are instead transferred to the partially
oxidized dithiolene ligands.
Under the same mild conditions as those employed for the
synthesis of compound 8, the analogous six-coordinate
diphosphine adduct of palladium complex 10 was not observed.
Although probable as an initially formed species, [Pd-
(adt)2(PMe3)2] is apparently less stable thermally and yields
readily to the formation of square-planar C2v-symmetric 11
(Scheme 2). The fate of the substituted dithiolene ligand was
not established. The related platinum complex 7 (Scheme 2c
and Figure 2) was found to form if the reaction between 5 and
dppe was attended by moderate heating (70 °C). Although not
H
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
a
Table 4. Selected Interatomic Distances (Å) and Angles (deg) for [M(S2C2R2)2] Complexes
[M(S2C2R2)2(PR′3)2]
[M(S2C2R2)(PR′3)2]
6
8
9
7
11
12
b
c
M−S
M−P
S−C
2.3654(5), 2.3688(5)
2.3376(6)
2.3656[3]
2.3597[4]
1.7683[10]
1.343[2]
2.3619(8)
2.3625(12)
1.769(4)
1.345(7)
88.27(4)
91.73(4)
180.0
2.2923[4]
2.2586[4]
1.764[2]
1.347[3]
87.95[2]
2.2918[3]
2.3054[3]
1.7627[11]
1.353(2)
2.2922[3]
2.3142[3]
1.7639[12]
1.335(2)
b
c
1.762(2), 1.776(2)
C−Cchelate
S−M−Schelate
S−M−Scis
S−M−Strans
P−M−P
P−M−Scis
P−M−Strans
C−S−M
C−C−S
1.356(3)
88.085(19)
88.468[12]
91.535[12]
179.428[12]
179.437(18)
89.999[7]
87.124(13)
87.341(14)
b
c
86.189(19), 93.65(3)
171.63(3)
86.41(3)
180.0
86.18[2]
93.17[2]
174.24[2]
104.50[5]
121.4[1]
96.368(16)
88.303[11]
174.681[11]
105.62[4]
97.605(14)
88.804[10]
166.651[10]
104.65[4]
b
c
c
92.38(2), 89.995(19)
90.00[2]
176.035(19)
b
102.35(8), 102.94(7)
102.11[4]
123.61[7]
102.53(12)
123.32(12)
b
c
124.46(17), 121.49(16)
120.81[8]
121.23[8]
a
Chemically identical, crystallographically independent values are averaged. Uncertainties are propagated according to the general formula for
b
c
uncertainty as a function of several variables, as detailed in ref 74. Bond length/angle involving S(1). Bond length/angle involving S(2).
Scheme 3. Redox Levels for a Dithiolene Ligand with Typical C−S and C−C Bond Lengths Indicated
confirmed in a deliberate experiment, these observations
suggest strongly that solutions of 6 would lead to 7 if subjected
to the same temperature for a similar duration of time.
Table 5. Selected Interatomic Distances (Å) and Angles
(deg) for 13
a
Pd···Pd
2.9650(2)
2.2816[3]
2.3171[3]
2.3844[3]
2.2857[3]
1.7730[12]
1.7574[12]
1.344[1]
S−Pd−Schelate
Sbridging−Pd−Sbridging
S−Pd−Strans
87.654[11]
78.621[10]
165.315[11]
102.588[10]
177.553[11]
91.151[11]
78.181[9]
73.9
The obvious approach to the synthesis of [M(S2C2R2)-
(PR′3)2] via halide displacement from [MCl2(PR′3)2] by an
ene-1,2-dithiolate salt was examined with in situ generated
Li2(mdt) and [PdCl2(PPh3)2]. The anticipated 12 (Scheme 2)
was isolated in a modest yield of 19% along with a comparable
amount (33%) of the dipalladium species [(Ph3P)Pd(μ-
mdt)2Pd(PPh3)] (13; Scheme 2). Dinuclear compound 13 is
of a type first prepared by Mayweg and Schrauzer,15 although
the specific nature of the dimerically formulated compound was
not then established. Compound 13 shows square-planar
palladium(II) centers, with each metal ion coordinated by a
single PPh3 ligand and chelated by a single mdt ligand, one
sulfur atom of which forms a bridge to the other palladium(II)
ion (Figure 2f). The two square-planar palladium(II) centers
are thus hinged by two bridging thiolate-type sulfur atoms and
form a dihedral angle of 73.4° along the S(2)···S(4) interatomic
axis (Figure 2g). The S−C and C−Cchelate bond lengths in the
mdt ligands are indicative of a fully reduced ene-1,2-dithiolate
ligand (Table 5). The bridging is asymmetric, with the bridging
sulfur atom being ∼0.036 Å nearer to the palladium ion to
which the other sulfur atom of the same ligand is bound.
Pd−Snonbridging
Pd−Sbr,short
Pd−Sbr,long
Pd−P
S−Cbridging
S−Cnonbridging
C−Cchelate
P−Pd−Sbridging,cis
P−Pd−Sbridging,trans
P−Pd−Snonbridging,cis
Pd−S−Pd
b
θ
a
Chemically identical, crystallographically independent values are
averaged. Uncertainties are propagated according to the general
formula for uncertainty as a function of several variables as detailed in
b
ref 74. Fold angle between mean PdS3P planes.
C2/c.79 The same folded butterfly motif occurs with [(Ph3P)-
Pd(μ-1,2-ethanedithiolato-S,S′:S)2Pd(PPh3)],80 in which the
dithiolate ligand is fully reduced, but fully planar or nearly
planar Pd(μ-S)2Pd core structures are typical for related
complexes bearing monodendate thiolate ligands, such as
[(Ph3P)(SPh)Pd(μ-SPh)2Pd(SPh)(PPh3)],81 [(Ph3P)(SC6F5)-
Pd(μ-SC6F5)2Pd(SC6F5)(PPh3)],82−84 and [((iPrO)3P)(SPh)-
Pd(μ-SPh)2Pd(SPh)((P(OiPr)3)].85 It is likely that the folded
Pd(μ-S)2Pd core seen in 13 and in [(Ph3P)Pd(μ-1,2-ethyl-
enedithiolato-S,S′:S)2Pd(PPh3)] is a consequence of the
restricted intraligand S−S separation imposed by the chelating
ligand. The intraligand distances between terminal and bridging
sulfur atoms in 13 average to 3.185 Å, somewhat less than the
corresponding distance of 3.389 Å found, for example, in
[(Ph3P)(SPh)Pd(μ-SPh)2Pd(SPh)(PPh3)].81 We note that the
interpalladium separation of 2.9650(2) Å is substantially shorter
Although it occurs on a general position in P1, 13 shows C
point group symmetry overall.
̅
2
We note a recent report of closely related [(Ph3P)Pd(μ-1,2-
ethylenedithiolato-S,S′:S)2Pd(PPh3)],78 which was formed in a
serendipitous reaction between [Pd(PPh3)4] and tetrathiafulva-
lene. This compound is isostructural to 13 but differs
crystallographically by occurring on a 2-fold rotation axis in
I
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
than twice the van der Waals radius of this element (3.26 Å)86
and close enough to support potential interaction between the
two ions.
Electrochemistry. The cyclic voltammetry for bis-
(dithiolene) complex 5, shown in Figure 3, reveals two
attributed to the adt ligand, the second of which creates the
fully oxidized α-dithione form (Scheme 3c). The full range of
dithiolene redox levels has also been observed electrochemically
in the related complexes [(adt)M(μ-tpbz)M(adt)] [M = Ni,
Pd, Pt; tpbz = 1,2,4,5-tetrakis(diphenylphosphino)benzene].87
UV−Vis and XAS. The UV−vis spectra of 5 and of the
phosphine complexes 6−8 are presented in Figure 4. The
Figure 3. Cyclic voltammetry for 5−8 in CH2Cl2 recorded with
[nBu4N][PF6] as the supporting electrolyte at 25 °C (−78 °C for 6
with a scan rate of 100 mV·s−1.
Figure 4. UV−vis spectra (CH2Cl2, 25 °C) for 5−8.
arresting feature in the spectrum of 5 is the low-energy intense
absorption band at 860 nm, a ligand-to-ligand charge-transfer
(LLCT) transition and well-known spectroscopic marker for
the presence of π-radical monoanionic dithiolene ligands
(Scheme 3b). In the spectra of all of the phosphine adducts,
this absorption is conspicuously absent, which confirms the
crystallographic interpretation of fully reduced ene-1,2-
dithiolates coordinated to platinum (Scheme 3a). The
spectrum for 6 shows a broad band of low intensity at 580
nm, which does not have a counterpart in the spectrum of 8.
Although an assignment for this transition has not been
attempted with computational assistance, it is probable that it
appears in 6 and not 8 because of the lack of inversion
symmetry and differently constituted and ordered frontier MOs
in the former. Complex 4 shows a LLCT absorption at 739 nm,
which accords with the ordering of ligand substituent influences
previously tabulated for nickel bis(dithiolene) complexes.5
To assist the description of the redox levels of the dithiolene
ligand and platinum metal in compounds 5−8, both S K-edge
and Pt L1-edge XAS spectra were obtained, the results of which
are presented in Figure 5. The energies of the pre-edge
absorption maxima, which were determined after a pseudo-
Voigt deconvolution of overlapping features in the pre-edge
region (Figures S20−S23 in the SI), are given in Table 6. These
pre-edge absorptions in the S K-edge X-ray spectra arise from
transitions from S 1s orbitals to acceptor MOs bearing S p
character and manifest intensity according to the degree of their
S p character.88 Rising-edge energies in both the S K-edge and
Pt L1-edge XAS were identified as the inflection points in the
second derivatives of the XAS spectra in the rising-edge region
(Figures S24−S27 in the SI).
reversible reductions at E1/2 = −0.11 and −0.84 V and a single
reversible oxidation at E1/2 = +1.01 V. The similarity of these
redox features with corresponding reductions and an oxidation
for [Ni(adt)2] and 10 (Figures S18 and S19 in the SI) supports
their assignment as dithiolene-ligand-based processes in which
the metal remains in an invariant MII divalent state. This
interpretation is affirmed by inspection of the frontier
molecular orbitals (MOs) of 5 following a geometry
optimization, which shows both the highest occupied molecular
orbital (HOMO) and lowest unoccupied molecular orbital
(LUMO) to be largely comprised of the dithiolene C2S2 π
system (vide infra; Figure S28 in the SI), although the latter
does have a modest degree of metal d character.
The cyclic voltammogram for 8 shows reversible oxidations
at +0.38 and +0.86 V, which are assigned as successive
oxidations of the two dithiolene ligands, with platinum being
already at a high oxidation level (PtIV) and the dithiolene
ligands being fully reduced, as indicated by the crystallographic
data (vide supra). The voltammogram for 6 displays two
oxidation features, the first being a reversible oxidation at +0.59
V and the second an irreversible process at ∼+1.04 V. The
potential for the first oxidation of 6 is ∼0.2 V more positive
than the first oxidation for 8, a difference attributable to the
greater basicity of the PMe3 ligand. What effect the cis
arrangement of the phosphine ligand has on the electro-
chemistry of 6, as opposed to the trans configuration as found
in 8, is unclear but is presumably slight. In 7, the presence of
only oxidation features, the first of which (at +0.45 V) is fully
reversible, and the absence of any reduction processes are
consistent with the compound being composed of fully reduced
ene-1,2-dithiolate ligands and a divalent metal ion, neither of
which is capable of further reduction. Both oxidations in 7 are
The S K-rising-edge energy for 5 at 2473.8 eV is ∼1.3 eV
higher in energy than that for 6 and 8, which is consistent with
J
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
from inspection of the LUMOs, as a S 1s → LUMO+1
2
2
excitation. Composed of the Pt dx −y and four S p orbitals in σ*
combination (Figure S28 in the SI), the LUMO+1 is the only
other nearby unoccupied MO with appreciable S p character.
Related [(M(dithiolene)2]z complexes have been interrogated
spectroscopically by S K-edge XAS and analyzed computation-
ally in considerable detail (M = Ni; dithiolene = mdt; z = 0, 1−,
2−;75 M = Ni, dithiolene = mnt, z = 1−, 2−;89 M = Ni, Pd or
Pt, dithiolene = bdt, z = 1−, 2−;90 M = Ni, Pd, or Pt, dithiolene
= 3,5-di-tert-butylbenzenedithiolate, z = 0, 1−, 2−).91 The
nature and intensity of the two pre-edge transitions in the S K-
edge spectrum of 5 are essentially identical with those described
for the charge-neutral [(M(dithiolene)2]z complexes noted in
the studies above.
To assist a definitive assignment of the pre-edge transitions
in their S K-edge XAS spectra, the geometries of 6 and 8 were
optimized. The LUMO and LUMO+1 for these compounds,
both possible acceptor orbitals for these transitions, are
presented in Figure 6, while Table 7 summarizes the
Figure 5. Normalized S K-edge (top panel) and Pt L1-edge (bottom
panel) XAS spectra for 5−8.
Table 6. S K-Pre-edge, S K-Edge, and Pt L1-Edge Energies
(eV) for 5−8
S K-pre-edge S 1s →
S K-edge
(eV)
Pt L1-edge
(eV)
LUMO
energy
(eV)
compound
intensity S 1s → 4p
Pt 2s → 6p
[Pt(adt)2] (5)
2470.3
2472.5
2471.0
2471.9
2472.7
2471.2
1.30
1.46
1.51
0.70
0.41
1.83
2473.8
13878.9
Figure 6. Images of the LUMO and LUMO+1 for 6 (a) and 8 (b)
drawn at the 0.035 contour level. Energies are relative to the HOMO
(not shown).
[Pt(adt)2(dppe)] (6)
[Pt(adt)(dppe)] (7)
2472.5
2473.5
13880.1
13877.9
[Pt(adt)2(PMe3)2]
(8)
2472.5
13879.8
contributions of the Pt d and S p atomic orbitals to their
composition, as given by a Loewdin orbital population analysis.
The LUMOs of both 6 and 8 are of similar description, being
the partially oxidized (radical) character of its dithiolene
ligands, compared to the fully reduced ene-1,2-dithiolate
ligands indicated for 6−8 on the foregoing combined evidence
of crystallography, electrochemistry, and UV−vis absorption
spectroscopy. The lowest-energy pre-edge feature for 5 at
2470.3 eV is a S 1s → LUMO transition (Table 6), which owes
its intensity to the substantial S p character in the acceptor MO
(Figure S28 in the SI). This kind of low-energy pre-edge
excitation in the S K-edge XAS is diagnostic of the presence of a
dithiolene ligand with radical monoanionic character. The
higher-energy pre-edge transition for 5, at 2472.5 eV, is of an
intensity comparable to the lower-energy feature and assigned,
2
2
σ* in nature between the metal dx −y and ligand p orbitals. The
LUMO for 8 differs from that of 6 in that its p orbital
contributions arise only from sulfur, whereas the latter has both
P p and S p character. The greater S p character to the LUMO
versus LUMO+1 for both 6 and 8 identifies it as the more likely
acceptor orbital for the lowest-energy pre-edge transition
(Figures S29 and S30 in the SI and Table 7). This assignment
is confirmed by time-dependent density functional theory (TD-
DFT) simulation of these excitations (Figure S32 in the SI).
The rising edges for both 6 and 8 show unresolved additional
feature(s) that may arise from, at least in part, transitions to the
K
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 7. Composition of Frontier MOs for 5−8
[Pt(adt)2] (5)
[Pt(adt)2(dppe)] (6)
[Pt(adt)(dppe)] (7)
% Pt d % S p
3.0 32.2
[Pt(adt)2(PMe3)2] (8)
% Pt d
% S p
% Pt d
% S p
% Pt d
% S p
HOMO
LUMO
0.4
14.3
30.8
16.6
46.8
32.9
4.6
1.3
44.3
52.8
19.9
8.0
31.8
33.3
49.4
40.0
17.4
13.2
3.0
9.6
1.1
LUMO+1
22.4
LUMO+1 because both of these orbitals are constituted with a
moderate degree of S p character. Compound 7, in contrast to
6 and 8, shows no well-resolved pre-edge transitions at ∼2471
eV but rather higher-energy features at ∼2471.9 and 2472.7 eV
that overlap with the rising edge. Inspection of the frontier
MOs for 7 (Figure S31 in the SI and Table 7) identifies the
LUMO again as the empty orbital most suited by virtue of S p
character to serve as an acceptor MO. Although more
complicated by having substantial contribution from the dppe
ligand, the LUMO in 7 has some similarity to those of 6 and 8
2PR3 → [PtIV(adt2−)2(PR3)2], such that the expanded ligand
set can be accommodated.
In their report reaffirming their claim of the synthesis of
[Pt(S2C2R2)2(phosphine)2] compounds,15 Mayweg and
Schrauzer noted the pronounced differences in their electronic
absorption and vibrational spectra compared to those of the
homoleptic bis(dithiolene) precursors. Although the ideas and
associated language of ligand redox noninnocence were
undeveloped at that time, they correctly attributed these
observations to an alteration of the dithiolene ligands from a
delocalized electronic description and commented on the useful
insight into these compounds that X-ray crystal structures
would offer. A surprising 48 years after Mayweg and Schrauzer’s
work, this report shows through a combination of crystallog-
raphy, cyclic voltammetry measurements, and spectroscopic
characterization by UV−vis and XAS that phosphine
association to [Pt(S2C2R2)2], which is generally not a redox
process, can in this case be described as oxidative addition. This
behavior is an example of dithiolene redox noninnocence that is
distinctly different from the other manifestations of the
phenomenon that we have recently noted, such as variations
in dithiolene reduction in formally isoelectronic complexes as a
function of ancillary ligands93 and internal metal dithiolene
redox reorganization induced by a coordination geometry
2
2
in having σ* character between the S p and Pt dx −y orbitals.
TD-DFT simulations affirm that excitation to the LUMO of 7
is the first and most important contribution to its pre-edge
features in the S K-edge XAS spectrum (Figure S32 in the SI).
The effective nuclear charge at platinum, Zeff, can be gauged
in a direct way from the Pt L1-edges, which have their basis in
electric-dipole-allowed Pt 2s → 6p transitions. The platinum-
(II) species 5 and 7 exhibit rising-edge energies of 13878.9 and
13877.9 eV, respectively, whereas octahedral 6 and trans-8
show rising-edge energies that are positively shifted to higher
energy at 13880.1 and 13879.8 eV. Qualitatively, the higher
rising-edge energies for 6 and 8 are consistent with their
formulation as platinum(IV) species, as suggested by the
appearance of fully reduced dithiolene ligands in their crystal
structures and as expected for six-coordinate octahedral
platinum. In measurements of W L1-edge XAS spectra of a
variety of six-coordinate compounds, a change of ∼0.5 eV
suggested itself as a typical energy change for a third-row metal
L1-rising-edge energy upon a change of metal formal oxidation
state by one unit.92 The difference of ∼1.0 eV in the rising-edge
energies for 5 versus 6 and 8 is consistent with this observation
but may be simply fortuitous. Differing ligand-field effects
arising from the different coordination numbers and geometries
for 5 and 7 versus 6 and 8 complicate the comparison of Pt L1-
rising-edge energies between the two sets and may contribute
to the greater difference of ∼2.0 eV seen for 7 versus 6 and 8.
change.94 Because the [PtII(adt•−)2] + 2PR3
→
[PtIV(adt2−)2(PR3)2] reaction that is highlighted in this report
involves internal redox reorganization between a metal and a
ligand in a net nonredox process, it is necessarily an instance of
redox innocence involving the combination of both a metal and
a ligand, as opposed to a ligand alone, as discussed by Ward and
McCleverty.95
ASSOCIATED CONTENT
* Supporting Information
■
S
Full description of procedures for crystal growth, diffraction
data collection and processing, and structure solution and
refinement, complete crystallographic data for all new
structures in CIF format, thermal ellipsoid plots with complete
atom labeling, tables of selected bond lengths and angles for
compounds 1−3, Figures S1−S32, and description of computa-
tional methods and coordinates for geometry-optimized
structures. This material is available free of charge via the
Internet at http://pubs.acs.org.
SUMMARY AND CONCLUSIONS
■
In this contribution, we have reported high-yielding syntheses
of 4 and 5 via transmetalation reactions with R′2Sn(S2C2R2) (R
= Me, −C6H4-p-OCH3) complexes. Bis(phosphine) adducts of
these platinum complexes have been prepared and charac-
terized spectroscopically, electrochemically, and structurally by
X-ray diffraction. These six-coordinate complexes display
octahedral geometries, a noteworthy contrast with trigonal-
prismatic [W(S2C2Me2)2(PMe3)2] and [W(S2C2Me2)2(dppe)].
The dithiolene ligand C−S and C−Cchelate bond lengths, as
determined crystallographically, are indicative of fully reduced
ene-1,2-dithiolates in all phosphine adducts, both for six-
coordinate [Pt(S2C2R2)2(phosphine)2] and four-coordinate
[Pt(S2C2R2)(phosphine)2] complexes. The UV−vis spectra of
these complexes corroborate this interpretation. Thus, the
coordination of two phosphine ligands to [PtII(adt)2] occasions
an internal metal-to-ligand charge transfer, [PtII(adt•−)2] +
AUTHOR INFORMATION
Corresponding Authors
*E-mail: chandru@lamar.edu.
*E-mail: donahue@tulane.edu.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The Louisiana Board of Regents is thanked for enhancement
Grant LEQSF-(2002-03)-ENH-TR-67, with which Tulane’s X-
L
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(30) Pap, J. S.; Benedito, F. L.; Bothe, E.; Bill, E.; DeBeer George, S.;
ray diffractometer was purchased, and Tulane University is
acknowledged for its ongoing support with operational costs for
the diffraction facility. Support from the National Science
Foundation (Grant CHE-0845829 to J.P.D.) and from the
Georges Lurcy Grant and Tulane Provost Fund for Under-
graduate Research (to S.C.) is gratefully acknowledged. Use of
the SSRL, SLAC National Accelerator Laboratory, is supported
by the U.S. Department of Energy, Office of Science, Office of
Basic Energy Sciences, under Contract DE-AC02-76SF00515.
Weyhermuller, T.; Wieghardt, K. Inorg. Chem. 2007, 46, 4187−4196.
̈
(31) Kaiwar, S. P.; Hsu, J. K.; Liable-Sands, L. M.; Rheingold, A. L.;
Pilato, R. S. Inorg. Chem. 1997, 36, 4234−4240.
(32) Kaiwar, S. P.; Vodacek, A.; Blough, N. V.; Pilato, R. S. J. Am.
Chem. Soc. 1997, 119, 3311−3316.
(33) Keefer, C. E.; Purrington, S. T.; Bereman, R. D.; Knight, B. W.;
Bedgood, D. R., Jr.; Boyle, P. D. Inorg. Chim. Acta 1998, 282, 200−
208.
(34) Vicente, R.; Ribas, J.; Cassoux, P. Nouv. J. Chim. 1984, 8, 653−
658.
REFERENCES
(35) Vicente, R.; Ribas, J.; Solans, X.; Font-Altaba, M.; Mari, A.; De
Loth, P.; Cassoux, P. Inorg. Chim. Acta 1987, 132, 229−236.
(36) Guyon, F.; Knorr, M.; Garillon, A.; Strohmann, C. Eur. J. Inorg.
Chem. 2012, 282−291.
■
(1) McNamara, W. R.; Han, Z.; Yin, C.-J.; Brennessel, W. W.;
Holland, P. L.; Eisenberg, R. Proc. Natl. Acad. Sci. U.S.A. 2012, 109,
15594−15595.
(2) Faulmann, C.; Cassoux, P. Prog. Inorg. Chem. 2004, 52, 399−490.
(3) Pilato, R. S.; van Houten, K. A. Prog. Inorg. Chem. 2004, 52, 369−
398.
́ ̀
(37) Shin, K.-S.; Jung, Y.-J; Lee, S.-K.; Fourmigue, M.; Barriere, F.;
Bergamini, J.-F.; Noh, D.-Y. Dalton Trans. 2008, 5869−5871.
(38) Noh, D.-Y.; Seo, E.-M.; Lee, H.-J.; Jang, H.-Y.; Choi, M.-G.;
Kim, Y. H.; Hong, J. Polyhedron 2001, 20, 1939−1945.
(4) Cummings, S. D.; Eisenberg, R. Prog. Inorg. Chem. 2004, 52,
(39) Nakajima, Y.; Nakatani, M.; Hayashi, K.; Shiraishi, Y.; Takita, R.;
Okazaki, M.; Ozawa, F. New J. Chem. 2010, 34, 1713−1722.
315−368.
(5) Mueller-Westerhoff, U. T.; Vance, B.; Yoon, D. I. Tetrahedron
1991, 47, 909−932.
̀
(40) Lee, S.-K.; Shin, K.-S.; Noh, D.-Y.; Jeannin, O.; Barriere, F.;
Bergamini, J.-F.; Fourmigue,
́
M. Chem.Asian J. 2010, 5, 169−176.
(6) Robertson, N.; Cronin, L. Coord. Chem. Rev. 2002, 227, 93−127.
(7) Cassoux, P.; Valade, L.; Kobayashi, H.; Kobayashi, A.; Clark, R.
A.; Underhill, A. E. Coord. Chem. Rev. 1991, 110, 115−160.
(8) Enemark, J. H.; Cooney, J. J. A.; Wang, J.-J.; Holm, R. H. Chem.
Rev. 2004, 104, 1175−1200.
(41) Lesley, M. J. G.; Clegg, W.; Marder, T. B.; Norman, N. C.;
Orpen, A. G.; Scott, A. J.; Starbuck, J. Acta Crystallogr., Sect. C 1999,
55, 1272−1275.
(42) Maisela, L. L.; Crouch, A. M.; Darkwa, J.; Guzei, I. A. Polyhedron
2001, 20, 3189−3200.
(9) Zarkadoulas, A.; Koutsouri, E.; Mitsopoulou, C. A. Coord. Chem.
Rev. 2012, 256, 2424−2434.
́
(43) Berenguer, J. R.; Bernechea, M.; Fornies, J.; García, A.; Lalinde,
(10) Geary, E. A. M.; McCall, K. L.; Turner, A.; Murray, P. R.;
McInnes, E. J. L.; Jack, L. A.; Yellowlees, L. J.; Robertson, N. Dalton
Trans. 2008, 28, 3701−3708.
E.; Moreno, M. T. Inorg. Chem. 2004, 43, 8185−8198.
(44) Shin, K.-S.; Son, K.-I.; Kim, J.-I.; Hong, C. S.; Suh, M.; Noh, D.-
Y. Dalton Trans. 2009, 1767−1775.
(11) Cocker, T. M.; Bachman, R. E. Inorg. Chem. 2001, 40, 1550−
1556.
(45) Nihei, M.; Kurihara, M.; Mizutani, J.; Nishihara, H. Chem. Lett.
2001, 852−853.
(12) Davison, A.; Edelstein, N.; Holm, R. H.; Maki, A. H. Inorg.
Chem. 1964, 3, 814−823.
(46) Nihei, M.; Kurihara, M.; Mizutani, J.; Nishihara, H. J. Am. Chem.
Soc. 2003, 125, 2964−2973.
(13) Schrauzer, G. N.; Mayweg, V. P. J. Am. Chem. Soc. 1965, 87,
1483−1489.
(47) Bacsa, J.; Darkwa, J.; Maisela, L. L. Acta Crystallogr., Sect. E 2001,
57, m109−m110.
(14) Davison, A.; Howe, D. V. Chem. Commun. 1965, 290−291.
(15) Mayweg, V. P.; Schrauzer, G. N. Chem. Commun. 1966, 640−
641.
(48) Hunt, S. W.; Yang, L.; Wang, X.; Nesterov, V.; Richmond, M. G.
J. Inorg. Organomet. Polym. 2010, 20, 457−467.
́
(49) Chandrasekaran, P.; Arumugam, K.; Jayarathne, U.; Perez, L.
(16) Bowmaker, G. A.; Boyd, P. D. W.; Campbell, G. K. Inorg. Chem.
M.; Mague, J. T.; Donahue, J. P. Inorg. Chem. 2009, 48, 2103−2113.
(50) Chandrasekaran, P.; Donahue, J. P. Org. Synth. 2009, 86, 333−
343.
1983, 22, 1208−1213.
(17) Nomura, M.; Okuyama, R.; Fujita-Takayama, C.; Kajitani, M.
Organometallics 2005, 24, 5110−5115.
(51) Armarego, W. L. F.; Perrin, D. D. Purification of Laboratory
Chemicals, 4th ed.; Butterworth-Heinemannn: Oxford, U.K., 2000.
(52) Pollock, C. J.; Tan, L. L.; Zhang, W.; Lancaster, K. M.; Lee, S.
C.; DeBeer, S. Inorg. Chem. 2014, 53, 2591−2597.
(53) George, G. N. EXAFSPAK; Stanford Synchrotron Radiation
Laboratory, Stanford Linear Accelerator Center, Stanford University:
Stanford, CA, 2001.
(18) Bevilacqua, J. M.; Zuleta, J. A.; Eisenberg, R. Inorg. Chem. 1994,
33, 258−266.
(19) Landis, K. G.; Hunter, A. D.; Wagner, T. R.; Curtin, L. S.; Filler,
F. L.; Jansen-Varnum, S. A. Inorg. Chim. Acta 1998, 282, 155−162.
(20) Johnson, C. E.; Eisenberg, R.; Evans, T. R.; Burberry, M. S. J.
Am. Chem. Soc. 1983, 105, 1795−1802.
(21) Keefer, C. E.; Bereman, R. D.; Purrington, S. T.; Knight, B. W.;
Boyle, P. D. Inorg. Chem. 1999, 38, 2294−2302.
(22) Fitzmaurice, J. C.; Slawin, A. M. Z.; Williams, D. J.; Woollins, J.
D.; Lindsay, A. J. Polyhedron 1990, 9, 1561−1565.
(23) Foguet, R.; Sampedro, F.; Ortiz, J. A.; Cayuela, S.; Castello, J.
M.; De Andres, L.; Bonal, J. Eur. Pat. Appl.EP 258655 A2 19880309,
1988.
(54) Bhattacharya, A. K.; Hortmann, A. G. J. Org. Chem. 1974, 39,
95−97.
(55) Levi, O. P.-T.; Becker, J. Y.; Ellern, A.; Khodorkovsky, V.
Tetrahedron Lett. 2001, 42, 1571−1573.
(56) Arumugam, K.; Clark, D. S.; Mague, J. T.; Donahue, J. P. Acta
Crystallogr., Sect. C 2011, 67, o446−o449.
(57) Xue, G.; Fang, Q.; Yu, W.-T.; Chen, X.; Lei, H. J. Chem.
Crystallogr. 2008, 38, 65−69.
(24) Hunt, S. W.; Wang, X.; Richmond, M. G. J. Mol. Struct. 2009,
919, 34−40.
(58) Xue, G.; Fang, Q.; Yu, W. Acta Crystallogr., Sect. C 2003, 59,
o653−o655.
(25) Poola, B.; Hunt, S. W.; Wang, X.; Richmond, M. G. Polyhedron
2008, 27, 3693−3699.
(59) Simonsen, O.; Varma, K. S.; Clark, A.; Underhill, A. E. Acta
Crystallogr., Sect C 1990, 46, 804−807.
(26) Sato, M.; Sensui, M.-A. J. Organomet. Chem. 1997, 538, 1−8.
(27) Dudis, D. S.; King, C.; Fackler, J. P., Jr. Inorg. Chim. Acta 1991,
181, 99−102.
(60) Ma, C.; Han, Y.; Li, D. Polyhedron 2004, 23, 1207−1216.
(61) Allan, G. M.; Howie, R. A.; Skakle, J. M. S.; Wardell, J. L.;
Wardell, S. M. S. V. J. Organomet. Chem. 2001, 627, 189−200.
(62) Chohan, Z. H.; Howie, R. A.; Wardell, J. L. J. Organomet. Chem.
1999, 577, 140−149.
(28) Ford, S.; Lewtas, M. R.; Morley, C. P.; Di Vaira, M. Eur. J. Inorg.
Chem. 2000, 933−938.
(29) Bevilacqua, J. M.; Eisenberg, R. Inorg. Chem. 1994, 33, 2913−
2923.
M
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(63) Doidge-Harrison, S. M. S. V.; Irvine, J. T. S.; Khan, A.; Spencer,
G. M.; Wardell, J. L.; Aupers, J. H. J. Organomet. Chem. 1996, 516,
199−205.
(92) Jayarathne, U.; Chandrasekaran, P.; Greene, A. F.; Mague, J. T.;
DeBeer, S.; Lancaster, K. M.; Sproules, S.; Donahue, J. P. Inorg. Chem.
2014.
(93) Yan, Y.; Keating, C.; Chandrasekaran, P.; Jayarathne, U.; Mague,
J. T.; DeBeer, S.; Lancaster, K. M.; Sproules, S.; Rubtsov, I. V.;
Donahue, J. P. Inorg. Chem. 2013, 52, 6743−6751.
(94) Yan, Y.; Chandrasekaran, P.; Mague, J. T.; DeBeer, S.; Sproules,
S.; Donahue, J. P. Inorg. Chem. 2012, 51, 346−361.
(95) Ward, M. D.; McCleverty, J. A. Dalton Trans. 2002, 275−288.
(64) Dessy, G.; Fares, V.; Bellitto, C.; Flamini, A. Cryst. Struct.
Commun. 1982, 11, 1743−1745.
(65) Hursthouse, M. B.; Malik, K. M. A.; Underhill, A. Private
Communication to CSD, 2003, Entry QAYMOT.
(66) (a) Kogut, E.; Tang, J. A.; Lough, A. J.; Widdifield, C. M.;
Schurko, R. W.; Fekl, U. Inorg. Chem. 2006, 45, 8850−8852. (b) Tang,
J. A.; Kogut, E.; Norton, D.; Lough, A. J.; McGarvey, B. R.; Fekl, U.;
Schurko, R. W. J. Phys. Chem. B 2009, 113, 3298−3313.
́
(67) Gritsenko, V. V.; Dyachenko, O. A.; Cassoux, P.; Kotov, A. I.;
Laukhina, E. E.; Faulmann, C.; Yagubskii, E. B. Russ. Chem. Bull. 1993,
42, 1149−1151.
(68) Zhou, B.; Kobayashi, A.; Okano, Y.; Nakashima, T.; Aoyagi, S.;
Nishibori, E.; Sakata, M.; Tokumoto, M.; Kobayashi, H. Adv. Mater.
2009, 21, 3596−3600.
(69) Okuma, K.; Munakata, K.; Tsubota, T.; Kanto, M.; Nagahora,
N.; Shioji, K.; Yokomori, Y. Tetrahedron 2012, 68, 6211−6217.
(70) Suzuki, W.; Fujiwara, E.; Kobayashi, A.; Hasegawa, A.;
Miyamoto, T.; Kobayashi, H. Chem. Lett. 2002, 936−937.
(71) Arca, M.; Demartin, F.; Devillanova, F. A.; Garau, A.; Isaia, F.;
Lelj, F.; Lippolis, V.; Pedraglio, S.; Verani, G. J. Chem. Soc., Dalton
Trans. 1998, 3731−3736.
(72) Lim, B. S.; Fomitchev, D. V.; Holm, R. H. Inorg. Chem. 2001, 40,
4257−4262.
(73) Arumugam, K.; Bollinger, J.; Fink, M.; Donahue, J. P. Inorg.
Chem. 2007, 46, 3283−3288.
(74) Taylor, J. R. An Introduction to Error Analysis; University Science
Books: Sausalito, CA, 1997; pp 73−77.
(75) Szilagyi, R. K.; Lim, B. S.; Glaser, T.; Holm, R. H.; Hedman, B.;
Hodgson, K. O.; Solomon, E. I. J. Am. Chem. Soc. 2003, 125, 9158−
9169.
(76) Samar, D.; Harvey, P. D. J. Inorg. Organomet. Polym. 2007, 17,
251−258.
(77) Lobana, T. S.; Sharma, R.; Bermejo, E.; Castineiras, A. Inorg.
Chem. 2003, 42, 7728−7730.
(78) Pop, F.; Branzea, D. G.; Cauchy, T.; Avarvari, N. C. R. Chim.
2012, 15, 904−910.
(79) In ref 78, the structure of [(Ph3P)Pd(μ-S2C2H2)2Pd(PPh3)] is
incorrectly described as residing on an inversion center. The molecule
occurs on a 2-fold rotation axis.
(80) Cao, R.; Jiang, F.; Liu, H. Acta Crystallogr., Sect. C 1995, 51,
1280−1282.
(81) Nakanishi, I.; Tanaka, S.; Matsumoto, K.; Ooi, S. Acta
Crystallogr., Sect. C 1994, 50, 58−61.
(82) Fenn, R. H.; Segrott, G. R. J. Chem. Soc. A 1970, 3197−3201.
(83) Fenn, R. H.; Segrott, G. R. J. Chem. Soc., Dalton Trans. 1972,
330−333.
́ ́
(84) Estudiante-Negrete, F.; Redon, R.; Hernandez-Ortega, S.;
Toscano, R. A.; Morales-Morales, D. Inorg. Chim. Acta 2007, 360,
1651−1660.
(85) Ananikov, V. P.; Kabeshov, M. A.; Beletskaya, I. P.; Khrustalev,
V. N.; Antipin, M. Y. Organometallics 2005, 24, 1275−1283.
(86) See http://periodictable.com/Elements/046/data.html (last
accessed: May 19, 2014).
(87) Arumugam, K.; Shaw, M. C.; Mague, J. T.; Bill, E.; Sproules, S.;
Donahue, J. P. Inorg. Chem. 2011, 50, 2995−3002.
(88) Glaser, T.; Hedman, B.; Hodgson, K. O.; Solomon, E. I. Acc.
Chem. Res. 2000, 33, 859−868.
(89) Sarangi, R.; DeBeer George, S.; Rudd, D. J.; Szilagyi, R. K.;
Ribas, X.; Rovira, C.; Almeida, M.; Hodgson, K. O.; Hedman, B.;
Solomon, E. I. J. Am. Chem. Soc. 2007, 129, 2316−2326.
(90) DeBeer George, S.; Neese, F. Inorg. Chem. 2010, 49, 1849−
1853.
(91) Ray, K.; DeBeer George, S.; Solomon, E. I.; Wieghardt, K.;
Neese, F. Chem.Eur. J. 2007, 13, 2783−2797.
N
dx.doi.org/10.1021/ic501273b | Inorg. Chem. XXXX, XXX, XXX−XXX