Unexpected one-electron oxidation of a secondary phosphite selenide Cp(CO)2FeP(Se)(OiPr)2 by GaCl3 and InCl 3 - Rare examples of Di- and triselenide formation

Article abstract of DOI:10.1002/ejic.201201322

The reactions of the neutral phosphonoselenoate [Cp(CO)₂FeP(Se) (OiPr)₂] (1) with Lewis acids (GaCl₃, InCl₃) produce dicationic complexes [{Cp(CO)₂FeP(OiPr)₂} ₂Se_n][GaCl₄]₂, [n = 2 (2), 3 (3)] and [{Cp(CO)₂FeP(OiPr)₂}₂Se_n] [InCl₄]₂ [n = 2 (4), 3 (5)] in good yields; the complexes comprise an Se₃ (or Se₂) chain that bridges two FpP(OiPr)₂ groups [Fp = Cp(CO)₂Fe]. These compounds are the one-electron oxidation products of secondary phosphite selenide 1 by group 13 (Ga, In) trichlorides. On the other hand, the reaction of GaCl₃ with (iPrO)₂PSe₂^- (dsep) yields only the Lewis adduct tris(O,O-diisopropyldiselenophosphate)gallium (6). The ³¹P NMR spectrum of 6 at 183 K reveals that the gallium(III) center is surrounded by one chelating and two pendant dsep ligands, which is in line with the obtained X-ray structure. In addition, the two-electron oxidation of 1 leads to phosphite [Cp(CO)₂FeP(O)(OiPr)₂] formation. Copyright

Full text of DOI:10.1002/ejic.201201322

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DOI:10.1002/ejic.201201322
Unexpected One-Electron Oxidation of a Secondary
Phosphite Selenide Cp(CO)2FeP(Se)(OiPr)2 by GaCl3 and
InCl3 – Rare Examples of Di- and Triselenide Formation
Vladimir A. Kuimov,[a] Ping-Kuei Liao,[b] Ling-Song Chiou,[b]
Hong-Chih You,[b] Ching-Shiang Fang,[b] and C. W. Liu*[b]
Keywords: Selenium / Gallium / Indium / Structure elucidation / Oxidation
The reactions of the neutral phosphonoselenoate
[Cp(CO)2FeP(Se)(OiPr)2] (1) with Lewis acids (GaCl3, InCl3)
produce dicationic complexes [{Cp(CO)2FeP(OiPr)2}2-
Sen][GaCl4]2, [n = 2 (2), 3 (3)] and [{Cp(CO)2FeP(OiPr)2}2-
Sen][InCl4]2 [n = 2 (4), 3 (5)] in good yields; the complexes
comprise an Se3 (or Se2) chain that bridges two FpP-
(OiPr)2 groups [Fp = Cp(CO)2Fe]. These compounds are the
one-electron oxidation products of secondary phosphite sele-
nide 1 by group 13 (Ga, In) trichlorides. On the other hand,
the reaction of GaCl3 with (iPrO)2PSe2– (dsep) yields only the
Lewis adduct tris(O,O-diisopropyldiselenophosphate)gallium
(6). The 31P NMR spectrum of 6 at 183 K reveals that the
gallium(III) center is surrounded by one chelating and two
pendant dsep ligands, which is in line with the obtained X-
ray structure. In addition, the two-electron oxidation of 1
leads to phosphite [Cp(CO)2FeP(O)(OiPr)2] formation.
undertaken systematic studies on this class of compounds.
We discovered that the stable phosphonoselenoate reagent
FpP(Se)(OiPr)2 (1), a conjugated base of a secondary phos-
phite selenide, can be readily prepared from dsep and Fp
dimer.[6] The latter is a high-potential precursor for the fab-
rication of new Lewis adducts (in reactions with soft Lewis
acids such as CuI, AgI, CdII, and HgII cations),[6,7] charge-
transfer adducts (with iodine)[6b] or Se-methylated products
(with Meerwein’s reagent).[6b]
To gain further insights into the factors that govern the
coordination chemistry of phosphite selenides and to ex-
plore this chemistry in more detail, we have initiated a study
of 1 with borderline Lewis acids (LAs) of group 13 (Ga, In)
trichlorides.[8] InCl3 can complex such soft Lewis bases
(LBs) as (RO)2PSe2– or R2PSe2–,[9] in which the P atom has
a +5 oxidation state. Also, O’Brien et al. prepared Lewis
acid–base adducts, M(iPr2PSe2)3, from both GaCl3 and
InCl3 with soft LBs, (R2PSe)2Se.[10] Notably, the
[(SePPh2)2N]– anion has also formed stable tris-chelates
with InCl3.[11] In addition, dsep can be oxidized by some
borderline LAs (FeCl3, VCl3, VOSO4)[12] to form
[{(RO)2PSe}2Sen] products, which suggests that there is a
significant energy difference in the frontier orbitals of the
reactants. Thus, the differences in the electron-cloud distri-
bution and the size of the energy gap between selenophos-
phoryl compounds and various LAs can yield different
types of HOMO–LUMO interactions: (a) Lewis adducts in
the case of sufficiently soft LAs, (b) oxidation products for
borderline LAs as a result of the mismatched Lewis pair.
This is due to the lower softness and high reduction poten-
tial (E0r)[13] values for these LAs. On the basis of these fun-
Introduction
H-Phosphonoselenoates (secondary phosphite selenides)
are a largely unexplored class of phosphorus compounds
and are potentially useful synthetic intermediates. Although
they have been known for a long time, they remain rare
and synthetically hardly accessible.[1] In general, the known
routes to H-phosphonoselenoates suffer from the use of
highly toxic H2Se and aggressive dialkylphosphoro chlor-
ides or are achievable by particular condensing agents.[2] At
the same time, H-phosphonoselenoates have been success-
fully used for oxidative phosphorylation of 3Ј-O-(tert-butyl-
dimethylsilyl)thymidine to produce dinucleoside phos-
phoroselenoates with a modified 3Ј–5Ј internucleotide link-
age.[3] Some oxidative transformations of dinucleoside H-
phosphonoselenoate were studied by Stawinski.[4] However,
transformation of the P=Se moiety (in which the oxidation
state of the P atom is +3) was either not touched upon or
almost neglected owing to the unstable nature of H-phos-
phonoselenoates with respect to disproportionation. Owing
to the potential applications of H-phosphonoselenoates as
precursors to various biologically important phosphate es-
ters and their analogs in selenium biomedicine,[5] we have
[a] A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch
of the Russian Academy of Sciences,
1 Favorsky Str., 664033 Irkutsk, Russian Federation
[b] Department of Chemistry, National Dong Hwa University,
Hualien, Taiwan 97401, R.O.C.
Fax: +886-3-8633570
E-mail: chenwei@mail.ndhu.edu.tw
Homepage: http://faculty.ndhu.edu.tw/~cwl/index.htm
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201201322.
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damental facts, it could be anticipated that 1 would react air moisture. This feature is particular for the similar com-
with GaCl3 and InCl3 to yield Lewis adducts; however, pounds.[19] There appears to be no literature reports to date
some electronic arguments make these facts implausible on the oxidation of phosphonoselenoates by any LAs ex-
(vide infra). Thus, oxidation products of the type [{Cp- cept BiCl3.[18a]
(CO)2FeP(OiPr)2}2Sen]2+ that contain a catenated selenium
chain are formed. To the best of our knowledge, until now
there have been no reports of iron-containing selenophos-
phoryl compounds with an Fe–P–(Se)n–P–Fe linkage. Al-
though oxidative couplings of some seleno-organic com-
pounds with different LAs have been reported in the litera-
ture,[14] condensation reactions of PIII=Se fragments are not
well known. The most commonly encountered P–Sen–P
linkages in organoselenophosphorus chemistry connect
neutral phosphorus(V)[2a,15] atoms or are generated by one-
electron oxidation of diselenophosph(in)ates[16] as unineg-
atively charged ligands. In the literature, there are only a
few examples of oxidation reactions of the P=Se fragment
in (Me2N)3P=Se and 1,1Ј-bis(di-tert-butylphosphorose-
lenoyl)ferrocene {Fc-1,1Ј-[PSe(tBu)2]2} by a strong LA
Figure 1. Perspective view of the dicationic complex in 3 with H
atoms omitted for clarity. Selected bond lengths [Å] and angles [°]:
(BiCl3) or acidic metallocene (acetylferrocenium tetra-
fluoroborate)[17] to form dicationic [P–Se–Se–P]2+ moieties,
which were confirmed by X-ray analyses.[18] Nevertheless,
the P atom in these two compounds is pentavalent. No one
has succeeded in the one-electron oxidation of secondary
Se(1)–P(1) 2.2580(15), Se(1)–Se(3) 2.3349(10), Se(2)–Se(3)
2.3154(9), Se(2)–P(2) 2.2688(13), Fe(1)–P(1) 2.1730(16), Fe(2)–P(2)
2.1661(14);
Se(2)–Se(3)–Se(1)
107.09(4),
P(1)–Se(1)–Se(3)
104.16(5), P(2)–Se(2)–Se(3) 101.50(4), Fe(2)–P(2)–Se(2) 119.71(6),
Fe(1)–P(1)–Se(1) 108.68(7); P(1)–Se(1)–Se(3)–Se(2) 96.14, P(2)–
Se(2)–Se(3)–Se(1) 85.97.
phosphite selenides or their conjugate bases on Se=PIII
.
Results and Discussion
Two gallium(III) complexes, [{FpP(OiPr)2}2Sen][GaCl4]2
[n = 2 (2), 3 (3)], and two indium(III) complexes,
[{FpP(OiPr)2}2Sen]2[InCl4]2 [n = 2 (4), 3 (5)], were obtained
by the reactions of 2 equiv. of LA with 1 in dichlorometh-
ane (DCM) at –30 °C and 5 °C, respectively (Scheme 1). In
all cases, compounds 2, 3 and 4, 5 were obtained as insepa-
rable mixtures in 71 and 77% yields, respectively. The pres-
ence of catenated selenium chains with different numbers
of selenium atoms (Se2 for 2 and 4 and Se3 for 3 and 5)
was authenticated by X-ray crystallographic (for 3 and 4,
Figures 1 and 2) and chemical investigations (for a mixture
of 2 and 3, vide infra). Interestingly, the oxidation does not
stop in the coupling process but proceeds with dismutation
and gives mixtures of catenates. However, separation of
both catenates was not feasible by virtue of their similar
Figure 2. Perspective view of the dicationic complex in 4 with H
atoms omitted for clarity. Selected bond lengths [Å] and angles [°]:
Se(1)–P(1) 2.2565(18), Se(1)–Se(1A) 2.3490(13), Fe(1)–P(1)
2.1732(17);
P(1)–Se(1)–Se(1A)
103.05(5),
Fe(1)–P(1)–Se(1)
109.65(7); P(1)–Se(1)–Se(1A)–P(1A) 120.15, Fe(1)–P(1)–Se(1)–
solubility in organic solvents and exceptional sensitivity to Se(1) –171.82.
Scheme 1. Reactivities of GaCl3 and InCl3 toward 1.
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[9b]
GaCl3 and InCl3
react with ammonium diisopropyl
diselenophosphate in methanol at 0 °C to yield the galli-
um(III) tris(diselenophosphate) 6 and the indium(III) tris-
(diselenophosphate) 7 in 85 and 70% yields, respectively
(Scheme 2).
Scheme 3. Two-electron oxidation of 1.
3 and 4 suitable for X-ray diffraction studies, which allowed
us to solve their molecular structures. Previously, it has
been reported that similar selenophosphorus compounds
are rather unstable and decompose rapidly when the solu-
tion is exposed to air or moisture.[25] We have found these
complexes seem to be stable at –20 °C for several days un-
der dry nitrogen. The complexes in solution gradually de-
compose at room temperature under daylight. However,
separation of these catenates was not feasible by virtue of
their similar solubility in organic solvents and exceptional
sensitivity to air moisture. The X-ray structures of 3 and 4
(Figures 1 and 2) confirm the presence of the P–(Se)n–P
linkage (n = 2 or 3). The gallium(III) diselenophosphate 6
is more stable than 2–5. The structure consists of one che-
lating and two pendant dsep ligands in a distorted tetrahe-
dral geometry around the gallium center (Figure 3). It is
isostructural with its diselenophosphinate analogue,
[Ga{Se2P(iPr)2}3].[10] Compound 8 is an oily product and is
highly soluble in common organic solvents. The presence of
the phosphito moiety was primarily ascertained by 31P
NMR and IR spectroscopy, and the composition of 8 was
fully confirmed by MALDI-TOF mass spectrometry (vide
infra).
Scheme 2. Reaction of GaCl3 and InCl3 with dsep.
Apparently, the energies of the highest occupied molecu-
–
lar orbital (HOMO) in (RO)2PSe2 and the lowest unoccu-
pied molecular orbitals (LUMOs) in GaCl3 and InCl3
match well with each other. They are in sharp contrast to
those of the neutral species 1 owing to the considerably
larger energy differences between the HOMO of 1 and the
LUMOs of the LAs.[20] In accordance with the Klopman
equation,[21] the difference postulates that no adducts can
be formed, but only transfer of electrons from Se in 1 to
LAs can take place. Notably, rather hard FeCl3 reacts with
1 or dsep to give oxidized products owing to its lower soft-
϶
ness (softness parameter En = –0.73 eV in DCM) and
r
higher E0 in comparison with those of Ga3+ and In3+ [13]
.
In contrast, the reactions of AlCl3 (hard LA) with both 1
and dsep did not lead to either oxidized products or the
Lewis adducts, and this fact correlates well with the hard
and soft acids and bases (HSAB) concept. Notably, the
softer Te atom of the [TePR2]2N– anion reacted with GaCl3
in a nonpolar solvent such as toluene at –78 °C to yield at
first an unstable adduct, Ga[(TePR2)2N]3, which then
underwent an internal redox process followed by consecu-
tive rearrangement and dimerization.[22] On this account
GaCl3 is believed to be a borderline Lewis acid, and its very
r
low E0 allows for the formation of a Lewis adduct with
dsep without any further redox reactions. In other words,
the course of the reaction depends on reduction potentials,
relative softness in a given solvent, and the energy gap be-
tween the frontier orbitals of the reactants. Thus, as the
oxidation potentials for 1 and dsep are so different, 0.81
and 0.24 V, respectively,[7a,23] it is not surprising that 1 is
easily oxidized in the reaction with borderline LAs (GaCl3
and InCl3), whereas dsep gives Lewis acid–base adducts.[9b]
Two-electron oxidations of chalcogenophosphorus com-
pounds proceed by means of powerful oxidants. A standard
oxidation method for the conversion of thio- and seleno-
phosphoryl compounds to oxophosphoryl ones by using
Oxone has been reported.[24] Thus, phosphonoselenoates
were treated with 2 equiv. of Oxone (0.1 m aq. solution) in
Figure 3. Perspective view of 6. Selected bond lengths [Å] and
angles [°]: Ga(1)–Se(1) 2.4496(12), Ga(1)–Se(2) 2.4450(12), Ga(1)–
Se(3) 2.3600(13), Ga(1)–Se(5) 2.3690(12), Se(1)–P(1) 2.173(2),
Se(2)–P(1) 2.174(2), Se(3)–P(2) 2.221(2), Se(4)–P(2) 2.079(3), Se(5)–
P(3) 2.187(2), Se(6)–P(3) 2.088(2); Se(2)–Ga(1)–Se(1) 89.82(4),
an MeOH/THF mixture (1:1) to cleanly produce phosphite Se(3)–Ga(1)–Se(5) 119.47(5), Se(1)–P(1)–Se(2) 105.28(8), Se(4)–
P(2)–Se(3) 115.80(11), Se(6)–P(3)–Se(5) 115.52(11).
8 in 90% yield (Scheme 3).
All the compounds have been characterized by spec-
troscopy (multinuclear NMR, IR) and microanalyses. Com-
pounds 2–5 are soluble in common polar organic solvents
and were crystallized by the slow diffusion of hexane into
Compound 3
DCM solutions to yield transparent colorless crystals. For-
Compound 3 crystallizes in the orthorhombic space
tunately, we have succeeded in obtaining single crystals of group Pna21 with four molecules per unit cell. X-ray analy-
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sis revealed that the dicationic salt comprises an Se3 chain tified in [(iPr2PSe2)3Ga].[10] The angles around the GaIII
that bridges two (iPrO)2PFp groups. The P–Se distances in center, in the range 89.82(4)–119.47(5)°, indicate pseudotet-
3 [mean 2.263(2) Å] are significantly longer than the corre- rahedral geometry. The four-membered Se–P–Se–Ga che-
sponding distance in 1 [2.128(1) Å], which suggests that a late is approximately planar. The structure is different to
P–Se single bond exists in the former. They are similar to that of its heavier congener, [{(iPrO)2PSe2}3In], which has
the average P–Se bond length found in [(Me2N)3PSe–]2- three chelating dsep ligands around the InIII center in a dis-
[Bi2Cl8] (2.230 Å)[18a] and [dtbpfSe2][BF4]2 [2.275 Å, dtbpf torted octahedral geometry.[9b]
=
1,1Ј-bis(di-tert-butylphosphanyl)ferrocene].[18b] Within
the Se3 chain, the Se–Se bond lengths are unequal [Se1–Se3
2.3349(10), Se2–Se3 2.3154(9) Å] and almost identical to
those in the (Se)P–Se3–P(Se) moiety of [(EtO)2P(Se)]2Se3
[2.3448(6) and 2.3439(6) Å].[12b] The torsion angles of 96.14
[P(1)–Se(1)–Se(3)–Se(2)] and 85.97° [P(2)–Se(2)–Se(3)–
Se(1)] indicate that these planes are nearly perpendicular
and comparable to those in [dtbpfSe2][BF4]2 (–96.19°) and
[(EtO)2P(Se)]2Se3 (–87.8°).[12b] The arrangement of three Se
atoms looks like a spiral along the P–P axis. The Fe–P···P–
Fe torsion angle is 85.78°. In addition, two FpP(OiPr)2
moieties lie at each side of the Se3 plane. It should be noted
that the torsion angles of Se–P–Fe–XCp are inequivalent
(49.51 and –60.21°); this difference can be explained by the
presence of strong van der Waals contacts between two
chloride atoms (Cl5 and Cl8) of the tetrachlorogallate with
two neighboring Se atoms (Se2 and Se3). The Se3···Cl5 and
Se2···Cl8 nonbonded distances of 3.542 and 3.557 Å,
respectively, are slightly shorter than the sum of their
van der Waals radii (3.65 Å).[26]
Infrared Spectroscopy
The IR spectra of the dicationic complexes 2–5 showed
no ν(P=Se) absorption bands at 540–600 cm–1 in contrast
with their parent compound, 1. Instead, the P–Se stretching
frequency was identified in the range 320–374 cm–1, and the
Se–Se absorption bands were identified in the range 226–
251 cm–1 for 2–5. The Se–Se stretching of Cs4Th4P4Se26 was
observed at 252 cm–1.[16a] The IR spectra of 3 and 4 re-
vealed the characteristic peaks for symmetric and antisym-
metric stretching frequencies of two CO groups at 2014–
2015 and 2057–2058 cm–1, respectively, which confirms the
conservation of the iron oxidation state (+2) in both mole-
cules. The ν(CO) band is about 20 cm–1 higher in these
compounds than that of their precursor 1. The IR spectrum
of 8 shows typical ν(CO) bands at 1985 and 2036 cm–1, a
phosphoryl group ν(P=O) band at 1142 cm–1, and aliphatic
phosphate group ν(POC) bands at 977 and 970 cm–1.
Mass Spectrometry
Compound 4
Unfortunately, molecular ion peaks were not detected in
the positive MALDI-TOF mass spectrum for dication com-
plexes 2–5. However, fragment peaks of 2 and 3 at m/z =
429.81, 391.02, and 349.91 (428.94, 391.17, and 350.06 for
Compound 4 crystallizes in the monoclinic space group
C2/c. X-ray analysis of 4 revealed that two FpP(OiPr)2 frag-
ments are connected through an Se2 bridge and that the
structure consists of a discrete [Fp(OiPr)2PSe–]2 dication
and two tetrachloroindate anions. In the Se2 bridge, the Se–
Se bond length is 2.349(1) Å, typical of an Se–Se single
bond,[27] and the structure is centrosymmetric. The P–Se–
Se–P torsion angle (120.15°) in 4 is significantly larger than
those in [dtbpfSe2][BF4]2 (–96.19°)[18b] and [(Me2N)3PSe–]2-
[Bi2Cl8] (–112.4°).[18a] The Se–P–Fe–XCp torsion angles
(–58.56°) are comparable to those in the n-propyl derivative
of 1.[6b] Contrary to the structure reported by Willey et
al.,[18a] the counterion in [(Me2N)3PSe–]2[Bi2Cl8] exists as a
polymeric anionic chain [(BiCl4)2]n2n–; however, tetrachloro-
gallate and tetrachloroindate are discrete anions in 3 and 4,
respectively.
4 and 5), which corresponded to [{FpP(OiPr)2}2Se3
–
CO]2+ (m/z = 430.55), [{FpP(OiPr)2}2Se2 – CO]2+ (m/z =
391.07), and [{FpP(OiPr)2}2Se2 – 4 CO]2+ (m/z = 349.05),
respectively, were observed. On the other hand, peaks corre-
–
–
sponding to GaCl4 and InCl4 were identified in the nega-
tive-ion mass spectra. A positive MALDI-TOF mass spec-
trum of 8 displays the molecular ion peak at m/z = 343.04
(Mcalcd. 342.20 [M + H]), which provides further evidence
in support of the structural assignment for 8.
NMR Studies
The 31P NMR spectra of 2–5 at 223 K show only singlets
flanked by a pair of 77Se satellite peaks (JP,Se = 511, 513,
525, and 523 Hz for 2, 3, 4, and 5, respectively). The de-
crease of the coupling constants in 2–5 with respect to that
Compound 6
Compound 6 crystallizes in the monoclinic space group of the precursor 1 (JP,Se = 713 Hz) indicates that the P–Se
C2/c with eight molecules per unit cell. The gallium atom bond order has decreased and is consistent with those for
is coordinated by two dsep ligands in a monodentate fash- a typical P–Se single bond.[28] The 31P chemical shift of the
ion and a chelating dsep ligand. Although the bidentate products is approximately 10 ppm downfield of that of their
Ga–Se distances [2.4496(12) and 2.4450(12) Å] are almost precursor 1. Similar downfield shifts were also noted for the
the same as those reported in [(iPr2PSe2)3Ga], the mono- above-mentioned diselenium salts, [(Me2N)3PSe–]2[Bi2Cl8]
–
–
dentate Ga–Se distances [2.3600(13) and 2.3690(12) Å] are and [dtbpfSe2][BF4]2. Interestingly, the GaCl4 and InCl4
slightly shorter than those [2.385(5) and 2.396(4) Å] iden- counterions have little effect on the 31P chemical shifts,
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which is apparently due to the strong solvation of ions in creases dramatically. However, their integration ratio re-
the deuterated solvent. For InCl3, both complexes (4 and 5) mains roughly the same (2:1, Figure S1). The sharp reso-
have just one 31P NMR resonance at room temperature (δ nance at 183 K, which is broad at 293 K, is the chemical
= 176.3 ppm) and two overlapped resonances at 223 K shift of the chelating dsep ligand, for which the chelating–
(179.5 and 179.8 ppm), whereas the two 31P NMR reso- dangling interchange is fast at 293 K but slow at 183 K.
nances for 2 and 3 remain well separated regardless of tem- A similar exchange for dsep ligands in solution has been
perature (Figure 4). However, the 1JP,Se values for gallates 2 identified in its heavier congener, In(dsep)3.[9b] As there are
and 3 are smaller than those of indates 4 and 5, which re- two pendant dsep ligands in the solid-state structure of 6
flects the strong van der Waals contacts of two chloride (vide supra), two sets of selenium satellite peaks instead of
atoms in the tetrachlorogallate (Cl5 and Cl8) with the two one are expected for the peak at δ = 63.0 ppm.
neighboring Se atoms (vide supra). Curiously, we were un-
Presumably, intramolecular exchange involving simulta-
able to detect a 77Se NMR resonance for any of the dicat- neous formation of the Ga1–Se6 (Ga1–Se4) bond and
ionic complexes over the temperature range 298–253 K, cleavage of the Ga1–Se5 (Ga1–Se3) bond is so fast at 293 K
presumably because of line broadening resulting from fast that the phosphorus nuclei do not experience any difference
relaxation of the selenium nuclei in these large and asym- between the two Se atoms attached. Slower exchange at
metric molecules. Only at 223 K did the 77Se NMR studies 183 K helps assign the broad resonance at δ = 64.5 ppm to
reveal two doublets at δ = 212 (1JP,Se = 508 Hz, 2) and two pendant dsep units. In contrast, the 77Se NMR spec-
186.9 ppm (1JP,Se = 512 Hz, 3) for the gallates and δ = 127.6 trum at ambient temperature shows two doublets at δ =
(1JP,Se = 503 Hz, 4) and 150.4 ppm (1JP,Se = 526 Hz, 5) for 252.4 (1JP,Se = 616 Hz) and 311.4 ppm (1JP,Se = 584 Hz),
1
the indates (Figure 4). The H and 13C NMR spectra of 2– which strongly suggests that the Ga–Se bonds are labile.
5 only corroborate the presence of ligand molecules.
Overall, the variable-temperature (VT) 31P NMR spectra
clearly demonstrate that two distinct chemical environments
are unequivocally observed in solution for the P atoms of
the dsep ligands; this is in agreement with the solid-state
structure obtained by X-ray analysis.
The absence of selenium in 8 is supported by the fact
that no typical satellite peaks were observed for the singlet
1
at δ = 105.5 ppm in the 31P NMR spectrum. The H NMR
spectrum displays peaks at δ = 1.24 and 4.71 ppm for
OCH(CH3)2 groups and at δ = 5.03 ppm for the Cp group.
Mechanistic Studies
A plausible mechanism for the one-electron oxidation
can be rationalized as follows: In the first step it is reason-
able to propose that the LA (GaCl3 or InCl3) contacts with
the lone pair of electrons on the Se atom. This complex
is unstable due to the mismatched Lewis pair and rapidly
disproportionates followed by a redox process. For example,
GaCl3 exists as a dimer (a mixed salt of [GaCl2]GaCl4)[29]
and readily accepts 2 e–, each from one Se atom of 1, to
release stable tetrachlorogallate anions and selenophos-
phoryl radical cations (Scheme 4). Notably, a white solid
formed during the reaction and appears to be GaI-
[GaIIICl4].[30] Recently, Bertrand and co-workers showed
that borylene–bis[cyclic(alkyl)(amino)carbene] adducts can
Figure 4. (a) 31P NMR spectrum of 2 and 3 in [D6]acetone at
223 K; (b) 77Se NMR spectrum of 2 and 3 in [D6]acetone at 223 K;
(c) 31P NMR spectrum of 4 and 5 in [D6]acetone at 223 K; (d) 77Se
NMR spectrum of 4 and 5 in [D6]acetone at 223 K.
readily undergo one-electron oxidation with GaCl3 to give
– [31]
a stable radical cation stabilized by GaCl4 .
Phosphane
sulfides can reduce some borderline LAs such as CuII and
31P NMR spectroscopic studies of 6 in CD2Cl2 con- AuIII ions to CuI and AuI,[32] and, to some extent, FeIII to
firmed the formation of the tris(diselenophosphato)galli- FeII,[33] whereas phosphane sulfides easily lose 1 e– to yield
um(III) compound. Two chemical shifts are observed at a radical cation followed by a rapid coupling. This mecha-
ambient temperature: one sharp resonance at δ = 63.0 ppm nism is in good agreement with the data obtained for the
with a set of selenium satellite peaks (1JP,Se = 617 Hz) and electrochemical and chemical oxidations of C=S,[34]
a small, slightly broad resonance at δ = 53.9 ppm (1JP,Se
=
P=S,[25b] and P=Se[18] species to form dications by coupling
584 Hz). As the temperature is lowered to 183 K, the sharp of the radical cations.
signal broadens and shifts ca. 1.5 ppm downfield. The sec-
At the same time, it is known that some hard–soft Lewis
ond peak (δ = 55.4 ppm) sharpens, and its intensity in- adducts (for instance, dithiophosphato[9a,35] complexes of
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Scheme 4. Tentative mechanism for the reaction of GaCl3 with 1. Presumably, the reaction with InCl3 follows the same mechanism.
Cu2+, Au3+, Tl3+, Co3+, Fe3+, and VO2+ or a diselenophos- The reaction of excess Ph3P with the mixture was moni-
phinate complex[36] of Cu2+) are so unstable that they un- tored by 31P NMR spectroscopy and revealed a consecutive
dergo an internal redox process to form Cu+, Au+, Tl+, reduction of both salts in 48 h. The signal at δ = 173.6 ppm
Co2+, Fe2+, and V3+ complexes (soft–soft) and the corre- (Se3) significantly decreases with respect to the signal at δ
sponding polysulfides [(RO)2P(S)]2Sn or [R2P(S)]2Sn (n = 1– = 172.3 ppm (Se2), and eventually an integration ratio of
3). Apparently, the dichalcogenophosph(in)ates, which are ca. 4:1 is reached (Figure S2c). There are new signals for
evidently not very well suited for the stabilization of high- both Ph3P=Se (δ = 36.4 ppm) and 1 (δ = 167.4 ppm,
oxidation-state metal (hard LA) complexes, behave as Scheme 5). After 3 d, the 31P spectrum shows two main
strong reducing agents owing to their high reduction poten- peaks corresponding to Ph3P=Se and 1 with two new small
tials. Therefore, an appropriate combination of E0, softness doublets. It is possible that both doublets belong to one
(in a given solvent), and energy differences in the frontier intermediate, a dicationic unit [FpP(OiPr)2–Se–PPh3]2+ (i),
orbitals of the reactants dictates the direction of the reac- which is indicated by the similarity of their coupling con-
2
tion toward either oxidation or adduct formation.
stants (δ = 160.9 ppm, JP,P = 24.7 Hz and δ = 31.6 ppm,
To exclude the effect of trace oxygen in the one-electron 2JP,P = 24.4 Hz, Figure S2d). This dicationic intermediate i
oxidation process, we have attempted to carry out a direct can accept 1 e– from Ph3P=Se to give 1 and another un-
oxidation of 1 by dry air (LA, CH2Cl2, –30 °C, overnight). identified species (δp = 30.7 ppm, JP,P = 19.6 Hz), which
However, the 31P NMR spectrum of the solution remains can be attributed to a monoselenium triphenylphosphane
the same as those performed in an inert atmosphere. Appar- gallate species.
ently, the oxygen in air does not have any influence on the
Apparently, the released [GaCl4]– reacts with Ph3P to
result of oxidation, though trace oxygen can initiate reoxi- form a complex, [GaCl3(Ph3P)], which cannot be detected
dation of the remaining salt (M2+) to a stable trivalent state by 31P NMR spectroscopy at ambient temperature.[38] The
(M3+), which continues the reaction. In the absence of LAs, experiment indicates that the signal at δ = 173.6 ppm can be
no reactions occur between oxygen and 1.
unambiguously assigned to the triselenide 3, which should
As GaCl3 and InCl3 are generally referred to as rather rapidly lose one Se atom to yield diselenide 2 (δ =
strong LAs,[8] oxidations are complicated by a follow-up 172.3 ppm), which is then slowly reduced to the initial
dismutation process that proceeds even at low temperatures phosphonoselenoate 1. The reaction of the mixture of 2 and
(–50 °C) and in which the molar ratio of Se2/Se3 remains 3 with secondary phosphane RЈ2PH[39] instantly leads to 1
almost unchanged (ca. 2:1) in all cases. Barnard and Wood- and RЈ2P(Se)H (δP = 3.5 ppm, JP,Se = 712 Hz, Figure S3).
bridge[37] have proposed that such kind of diselenide can be
At the same time, a new singlet (δ = 53.8 ppm) appears
unstable and disproportionates to the mono- and triselenide in the 31P NMR spectrum and is assigned to the chloro-
by intermolecular rearrangement. However, this mechanism phosphane–gallium chloride represented in Equation (1).
is not suitable to explain our results. Our NMR investi-
gations reveal that only traces of monoselenide form in the
reaction (vide infra).
To authenticate that the solid-state structure of 3 is rel-
evant to the signal at δ = 173.6 ppm (CDCl3) in the 31P
NMR spectrum, we attempted to reduce the mixture of sel-
enides 2 and 3 (molar ratio as 2:1) with soft reducing agents.
(1)
Scheme 5. Reduction of 3 by Ph3P.
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The new resonance at δ = 53.8 ppm lies in the range of slowly form diselenide and then the initial compound, 1. In
the known chemical shifts of chlorophosphane–gallium contrast, the reaction of GaCl3 with dsep anions cleanly
chloride complexes.[40] These investigations confirm that the gives the Lewis adduct [{(iPrO)2PSe2}3Ga] as colorless crys-
initial reaction mixture consists of only Se2 and Se3 deriva- tals in a high-yield (85%) process. The formation of [(iPrO)2-
tives, and only one form preferentially crystallizes.
PSe2]3Ga can be easily understood on the basis of the small
To gain insight into the probable interactions between energy gap between the HOMO of dsep and the LUMO of
the mixtures of selenides (2 and 3) with Ph3P, we carried GaCl3. On the other hand, strong oxidants such as oxone
out selenium exchange reactions between RЈ2PH and 1. The in reaction with FpP(Se)(OiPr)2 gave iron complexes of sec-
results shown below demonstrated that the above-men- ondary phosphites. These results contribute to both funda-
tioned reactions (Scheme 5) would proceed through a mental and synthetic chemistry of selenophosphorus com-
monoselenide intermediate like i. Thus, the secondary phos- pounds. As the Se–Se bond is labile and can be broken eas-
phane slowly reduced 1 to form the key intermediate ily, studies to apply these P–Se iron-containing diselenides
[FpP(OiPr)2–Se–PHRЈ2] based on a mechanism[41] involv- as synthetic precursors are currently underway.
ing reoxidation by selenophilic attack in a linear transition
state. The 31P{1H} NMR spectrum of the intermediate
Experimental Section
[FpP(OiPr)2–Se–PHRЈ2] displays two doublets (δ = 42.8
2
and 187.9 ppm, Figure S4a) with identical JP,P coupling
Caution! Selenium and its derivatives are toxic. These materials
should be handled with great caution.
constants (82.4 Hz), which is a typical value for such sys-
tems.[42] The peak at δ = 187.9 ppm corresponds to the
FpP(OiPr)2 unit, and the peak at δ = 42.8 ppm corresponds
to the RЈ2PH moiety. These two doublets are each flanked
Materials and Measurements: All chemicals were purchased from
commercial sources and used as received. Commercial GaCl3 and
InCl3 were purchased as crystalline solids and stored in a glovebox.
Solvents were purified by applying standard protocols.[44] All reac-
tions were performed in oven-dried Schlenk glassware by using
standard inert-gas techniques. Elemental analyses were carried out
with a Perkin–Elmer 2400 CHN analyzer. NMR spectra were re-
corded with a Bruker Avance DPX300 FT-NMR spectrometer,
which operates at 300 MHz for 1H, 75.5 MHz for 13C, 121.49 MHz
for 31P, and 57.24 MHz for 77Se. 31P{1H} and 77Se{1H} NMR spec-
tra were referenced externally against 85% H3PO4 (δ = 0 ppm) and
(PhSe)2 (δ = 463 ppm), respectively. Chemical shifts (δ) and cou-
pling constants (J) are reported in ppm and Hz, respectively. CDCl3
and (CD3)2CO NMR solvents were dried with 4 Å molecular sieves
prior to use. IR spectra were recorded with a Bruker Optics FTIR
TENSOR 27 spectrometer (180–4000 cm–1) at 20 °C with CsI
plates. FpP(Se)(OiPr)2 (1) was prepared according to a reported
method.[6] MALDI-TOF spectra were acquired with an Autoflex
time-of-flight mass spectrometer (Bruker Daltonic, Bremen)
equipped with a 337 nm nitrogen laser (10 Hz, 3 ns pulse width).
Spectral data were obtained in the reflection mode with an acceler-
ation voltage of 20 kV. A 0.5 μL aliquot of the sample solution
was applied on the target plate and dried before MALDI-TOF MS
analysis. Each mass spectrum was derived from 100 summed scans.
1
by a set of selenium satellite peaks with unequal JP,Se cou-
pling constants (670 and 542 Hz, respectively) presumably
owing to different P–Se bond lengths (Figure S4b). Both
coupling constants are smaller than those for 1 (JP,Se
713 Hz) and secondary phosphane selenide (JP,Se
=
712 Hz). This indicates the decrease of the P–Se bond order
in [FpP(OiPr)2–Se–PHRЈ2] and corresponds to a bond or-
der of 1.5.[43] The presence of a proton on the RЈ2P moiety
1
has been proved by the H-coupled 31P NMR spectrum,
1
which displays a doublet of doublets with a JP,H coupling
constant of 366 Hz (Figure S4c). An increase in the latter
with respect to that of the initial secondary phosphane
(1JP,H = 198 Hz) indicated that the phosphorus atom is
combined with the Se atom from 1. In the 31P{1H}–31P{1H}
COSY spectrum there are two cross peaks between these
doublet peaks, which confirms that these two resonances
belong to one compound with two different phosphorus
atoms (Figure S5). Meanwhile, it must be emphasized that
Ph3P practically does not react with 1 at ambient tempera-
ture.
[{Cp(CO)2FeP(OiPr)2}2Sen][GaCl4]2 (2, n = 2; 3, n = 3): In a
glovebox, GaCl3 (0.070 g, 0.40 mmol) was added to a 100 mL
round-bottomed Schlenk flask and then dissolved in DCM (30 mL)
and stirred at –30 °C for 10 min. After 1 (0.081 g, 0.20 mmol) had
been added and the mixture stirred overnight at –30 °C, a yellow-
brown solution formed, which was filtered, and the filtrate was con-
centrated to dryness under vacuum. It was then extracted with ace-
Conclusions
The study on the one-electron oxidation process of sec-
ondary phosphite selenide 1 by group 13 (Ga, In) trichlo-
rides described here contributes to the understanding of the tone (10 mL) to afford a yellow-brown solution, which on concen-
tration formed yellow-brown oils. Yield 0.097 g (71%).
(C26H38Cl8Fe2Ga2O8P2Se3)0.33(C26H38Cl8Fe2Ga2O8P2Se2)0.66
reactivities of phosphonoselenoates [RPSe(ORЈ)2] with
strong LAs. They gave rise to [{Cp(CO)2FeP(OiPr)2}2Sen]-
[GaCl4]2 and [{Cp(CO)2FeP(OiPr)2}2Sen][InCl4]2, which
contain an Se3 or Se2 unit between two FpP(OiPr)2 groups.
These are rare examples of the one-electron oxidation of a
selenophosphoryl moiety. Moreover, 3 and 4 are the first
structurally characterized iron–selenophosphoryl dicationic
salts with an Fe–P–Sen–P–Fe linkage. Evidence to support
the Se2 and Se3 assignment in the 31P NMR spectra has
·
0.5C3H6O (1275.97): calcd. C 25.64, H 3.21; found C 26.01, H 3.13.
3
1H NMR ([D6]acetone): δ = 1.38 (d, JH,H = 5 Hz, 24 H, CH3),
4.83 (m, 4 H, OCH), 5.32 (s, 10 H, Cp) ppm. 13C NMR ([D6]-
2
acetone): δ = 209.4 (d, JP,C = 34 Hz, CO), 88.6 (Cp, 3), 88.7 (Cp,
2
2), 77.3 (d, JP,C = 9.9 Hz, OCH), 23.4 (CH3, 2), 23.8 (CH3, 3)
1
ppm. 31P{1H} NMR ([D6]acetone, room temp.): δ = 174.9 (s, JP,Se
1
= 511.7 Hz, 2), 176.1 (s, JP,Se = 513.0 Hz, 3); 223 K: δ = 177.4 (s,
1
1JP,Se = 511.0 Hz, 2), 179.5 (s, JP,Se = 513.0 Hz, 3) ppm; (CDCl3,
1
1
been obtained by the sequential deselenization by Ph3P to room temp.): δ = 172.3 (s, JP,Se = 511.7 Hz, 2), 173.6 (s, JP,Se
=
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511.7 Hz, 3) ppm; relative ratio ca. 2:1. 77Se{1H} NMR ([D6]acet-
(30 mL) and the solution filtered. The colorless filtrate was concen-
trated to dryness under vacuum to obtain the product as a pale
yellow powder of 6. Yield 0.255 g (85%). M.p. 157 °C. C18H42Ga-
O6P3Se6 (990.93): calcd. C 21.82, H 4.27; found C 21.36, H 4.38.
1
1
one, 223 K): δ = 186.9 (d, JP,Se = 512 Hz, 2), 212.0 (d, JP,Se
=
507.8 Hz, 3) ppm. IR (KBr): ν = 251 [ν(Se–Se)], 345, 374 [ν(P–Se)],
˜
963 [ν(POC)], 2015, 2058 [ν(CO)] cm–1.
3
1H NMR (CDCl3): δ = 1.41 (d, JH,H = 6.2 Hz, 36 H, CH3), 4.96
[{Cp(CO)2FeP(OiPr)2}2Sen][InCl4]2 (4, n = 2; 5, n = 3): The same
procedure as that described for 2 was used. However, InCl3
(0.076 g, 0.34 mmol) was used instead of GaCl3, and a 2:1 ratio of
LA to initial precursor at 5 °C was maintained. Yield 0.096 g
(m, 6 H, OCH) ppm. 31P{1H} NMR (CDCl3, room temp.): δ =
1
1
63.0 (s, JP,Se = 617 Hz), 53.8 (br. s, JP,Se = 584 Hz) ppm. 77Se
1
NMR (CDCl3, room temp.): δ = 252.4 (d, JP,Se = 616 Hz), 311.4
(d, JP,Se = 584 Hz) ppm.
1
(77%). (C26H38Cl8Fe2In2O8P2Se2)0.33(C26H38Cl8Fe2In2O8P2Se3)0.66
·
1.5C3H6O (1449.39): calcd. C 25.06, H 3.24; found C 24.99, H 2.84.
[Cp(CO)2FeP(O)(OiPr)2] (8): To a vigorously stirred solution of 1
(0.708 g, 1.75 mmol) in THF/MeOH (1:1, v/v; 35 mL), a solution
of Oxone (37 mL, 0.1 m) was added in one portion. The tempera-
ture of the reaction mixture increased to 40 °C, and the mixture
was stirred for 30 min. Solid precipitates were removed by centri-
fuge, the filtrates were extracted with DCM (3ϫ 20 mL), and the
combined organic phase was washed with water three times. The
solution was dried with Na2SO4, and the solvent was removed from
the filtrate to yield a yellow-brown oil. Yield 0.538 g (90%).
C13H19FeO5P·THF (414.21): calcd. C 49.28, H 6.57; found C 49.33,
H 6.71. 1H NMR (CDCl3): δ = 1.24 (t, 3JH,H = 9.7 Hz, 12 H, CH3),
4.71 (m, 2 H, OCH), 5.03 (s, 5 H, Cp) ppm. 31P{1H} NMR
3
1H NMR ([D6]acetone): δ = 1.46 (d, JH,H = 3 Hz, 24 H, CH3),
4.97 (m, 4 H, OCH), 5.51 (s, 10 H, Cp) ppm. 13C NMR ([D6]-
acetone): δ = 209.3 (d, 2JP,C = 32 Hz, CO), 89.3 (Cp), 77.4 (d, 2JP,C
= 10.9 Hz, OCH), 23.9 (CH3, 4), 24.0 (CH3, 5) ppm. 31P{1H}
1
NMR ([D6]acetone, room temp.): δ = 176.3 (s, JP,Se = 531.0 Hz):
1
1
223 K δ = 179.5 (s, JP,Se = 525.0 Hz), 179.8 (s, JP,Se = 523.0 Hz)
ppm. 77Se{1H} NMR ([D6]acetone, 223 K): δ = 127.6 (d, JSe,P
502.5 Hz, 5), 150.4 (d, JSe,P = 525.9 Hz, 4) ppm. IR (KBr): ν =
=
1
1
˜
226 [ν(Se–Se)], 320, 330 [ν(P–Se)], 955 [ν(POC)], 2014, 2057 [ν(CO)]
cm–1.
Reactions of 2 and 3 with a Tertiary (or Secondary) Phosphane:
Treatment of a mixture of 2 and 3 (30 mg) with a slight excess of
Ph3P in CDCl3 (NMR tube under Ar) for 3 d resulted in the forma-
tion of 1 together with Ph3P=Se (δP = 36.4 ppm, JP,Se = 727 Hz)
and a new intermediate cationic species (see NMR section). The
formation of 1 and Ph3P=Se was monitored by 31P NMR spec-
troscopy. With bis(2-phenethyl)phosphane (RЈ2PH),[39] 2 and 3 im-
mediately and quantitatively produced 1, RЈ2P(Se)H, and an un-
known RЈ2PCl–gallium(III) chloride complex. The reaction of 1
with RЈ2PH formed new cationic diphosphorus monoselenium spe-
cies together with RЈ2P(Se)H (vide supra).
(CDCl ): δ = 105.5 (s) ppm. IR (KBr): ν = 970 and 977 [ν(POC)],
˜
3
1145 [ν(P=O)], 1985, 2026 [ν(CO)] cm–1. MS (MALDI-TOF): m/z
(calcd.) = 343.0 (342.2).
Crystal Structure Determinations: Single crystals of 3, 4, and 6 suit-
able for X-ray crystallography were obtained by diffusing hexane
into DCM solutions of the compounds. The crystals were mounted
on the tips of glass fibers with epoxy resin, and the data were col-
lected with an APEX II CCD diffractometer with graphite-mono-
chromated Mo-Kα radiation (λ = 0.71073 Å). Data reduction was
performed with SAINT,[45] which corrects for Lorentz and polar-
ization effects. A multiscan absorption correction based on SAD-
[{(iPrO)2PSe2}3Ga] (6): NH4[Se2P(OiPr)2] (0.3 g, 1 mmol) was dis-
solved in MeOH (20 mL) in a 100 mL Schlenk flask, and GaCl3 ABS was applied. Structures were solved by the use of direct meth-
(0.06 g, 0.34 mmol) was added. The resulting mixture was stirred
for 1 h (0 °C, N2). The solution was then concentrated to dryness
under vacuum. The powder formed was redissolved in DCM
ods, and the refinements were performed by the least-squares
method on F2 with the SHELXL-97 package,[46] incorporated in
SHELXTL/PC V5.10.[47] Crystallographic data are presented in
Table 1. Selected crystallographic data for 3, 4, and 6.
3
4
6
Empirical formula
Formula mass
C26H38Cl8Fe2Ga2O8P2Se3
1312.16
C26H38Cl8Fe2In2O8P2Se2
1323.29
C18H42GaO6P3Se6
990.91
Crystal system
Space group
orthorhombic
Pna21
monoclinic
C2/c
monoclinic
C2/c
a [Å]
b [Å]
c [Å]
α [°]
22.5285(8)
13.9131(5)
15.3894(5)
90
15.751(3)
13.084(3)
23.041(5)
90
30.363 (2)
13.7567 (9)
20.6389 (14)
90
β [°]
90
90
4823.7(3)
4
1.807
95.024(5)
90
4730.2(18)
8
1.858
3.660
119.802 (2)
90
7480.7 (9)
8
1.760
6.729
γ [°]
V [Å3]
Z
ρcalcd. [gcm–3]
μ [mm–1]
4.506
T [K]
296(2)
48598
296(2)
31188
296
7366
Reflections collected
Independent reflections
Final R indices [IϾ2σ(I)][a,b]
10945 (Rint = 0.0654)
R1 = 0.0388
wR2 = 0.0778
R1 = 0.0850,
wR2 = 0.0897
0.994
5676 (Rint = 0.0424)
R1 = 0.0510
wR2 = 0.1447
R1 = 0.0880
wR2 = 0.1662
1.040
4358(Rint = 0.049)
R1 = 0.0583
wR2 = 0.1749
R1 = 0.1044
wR2 = 0.1937
1.093
R indices (all data)[a,b]
Goodness of fit
Largest difference peak/hole [eÅ–3]
0.427/–0.378
1.537/–0.739
2.683/–1.170
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2
.
2
2 2
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[10]
[11]
[12]
a) C. Q. Nguyen, A. Adeogun, M. Afzaal, M. A. Malik, P.
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919.
Table 1. CCDC-858704 (for 3), -858705 (for 4), and -858706 (for 6)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic
data_request/cif.
Data
Centre
via
www.ccdc.cam.ac.uk/
Supporting Information (see footnote on the first page of this arti-
a) H. Hertel, W. Kuchen, Chem. Ber. 1971, 104, 1740; b) V.
Béreau, J. A. Ibers, Acta Crystallogr., Sect. C: Cryst. Struct.
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cle): 31P NMR spectra (S1–S5).
Acknowledgments
As the softness parameter (En϶) depends on the dielectric con-
stant (ε) of the solvent used, it was evaluated based on the
Klopman equation in the solvent in which the reaction was
performed; En϶(Fe3+, acetone) = 1.11 eV; En϶(V3+, EtOH) =
2.70 eV; En϶(VO2+, iPrOH) = 2.01 eV; En϶(Ga3+, DCM) =
[13]
We thank the National Science Council of Taiwan (grant NSC 100-
2923-M259-001-MY3) and the Russian Foundation for Basic Re-
search (joint grant Russia-Taiwan 11-03-92003-HHC_a) for finan-
cial support.
϶
–1.54 eV; En϶(In3+) = –2.08 eV (DCM), –25.60 (toluene); En
(P=Se, DCM) ≈ –4.11 eV; Em϶(P–Se–) ≈ –6.93 eV; Em϶(HSe–,
DCM) ≈ –7.19 eV. Reduction and oxidation potential data
adopted from: C. E. Housecroft, A. G. Sharpe, Inorganic
Chemistry, 2nd ed., Pearson Education Limted, Harlow, 2005.
[1] a) J. Michalski, C. Krawiecki, Rocz. Chem. 1957, 31, 715; b) C.
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Phosphorus Relat. Group V Elem. 1973, 2, 273.
[2] a) J. Michalski, Ann. N. Y. Acad. Sci. 1972, 192, 90; b) F. R.
Hartley in The Chemistry of Organophosphorus Compounds:
Phosphine oxides, sulfides, selenides and tellurides (Ed.: F. R.
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Bollmark, J. Stawinski, Collect. Czech. Chem. Commun. 2006,
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[3] a) C. J. Wilds, R. Pattanayek, C. L. Pan, Z. Wawrzak, M. Egli,
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M. Wojcik, B. Rebowska, G. Nowak, W. J. Stec, FEBS J. 2007,
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Chem. 2008, 73, 5029.
[4] M. Kullberg, M. Bollmark, J. Stawinski, Collect. Czech. Chem.
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r
r
r
E0 (Fe3+/Fe2+) = +0.77 V; E0 (VO2+/V3+) = +0.34 V; E0 (V3+
/
r
r
V2+) = –0.26 V; E0 (Ga3+/Ga+) = –0.75 V; E0 (In3+/In+) =
–0.44 V; E0°(10/+) = 0.81 V (from ref.[7a]); E0°(dsep0/–) = 0.24 V
(from ref.[23]).
[14]
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Eur. J. Inorg. Chem. 2013, 2083–2092
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
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Received: November 1, 2012
Published Online: February 7, 2013
Eur. J. Inorg. Chem. 2013, 2083–2092
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim