Experimental and computational investigations of tautomerism and fluxionality in PCP- and PNP-bridged heavy chalcogenides

Article abstract of DOI:10.1002/ejic.201201378

The reaction of H₂C(PCl₂)₂ with four equivalents of iPrMgCl produces H₂C(PiPr₂)₂, which was treated with tellurium in boiling toluene, or selenium in toluene at room temperature, to give the monochalcogenides EPiPr₂CH ₂PiPr₂ (E = Te, 4a; E = Se, 4b) in high yields. X-ray structural determinations show that 4a and 4b exist as the CH₂ tautomers in the solid state with E-P-C-P dihedral angles of 56.1(2)° and 56.7(1)°, respectively. DFT calculations were carried out for the isolectronic series EPR₂CH₂PR₂ and EPR ₂NHPR₂ (E = Se, Te; R = Me, iPr, tBu, Ph) and for their non-chalcogenated precursors in order to elucidate the factors that determine the preference for PH tautomers in some PNP-bridged systems. Compounds 4a and 4b were also characterized by multinuclear (¹H, ¹³C, ³¹P, ⁷⁷Se, ¹²⁵Te) NMR spectroscopy. In solution, 4a exhibits fluxional behavior, which has been investigated by variable-temperature and variable-concentration multinuclear NMR spectroscopy. The observed behavior is consistent with an intermolecular tellurium transfer with an activation energy of 21.9 ± 3.2 kJ mol^-1; consideration of selenium exchange in 4b indicates a much higher energetic barrier. DFT calculations provide insights into the pathway for the chalcogen exchange process in 4a (ΔE = 20.4 kJ mol^-1). The outcome of reactions of 4a with selenium and nBuLi reflects the lability of the P-Te functionality. The monochalcogenides EPiPr₂CH₂PiPr ₂ (E = Se, Te) exist as CH₂ tautomers in the solid state; the contrast in this finding with that of the preferential formation of PH tautomers by PNP-bridged analogues is addressed through DFT calculations. In solution, the PCP-bridged tellurium derivative undergoes rapid intermolecular tellurium exchange with an activation energy of 21.9 ± 3.2 kJ mol ^-1. Copyright

Full text of DOI:10.1002/ejic.201201378

FULL PAPER
DOI:10.1002/ejic.201201378
Experimental and Computational Investigations of
Tautomerism and Fluxionality in PCP- and PNP-Bridged
Heavy Chalcogenides
[a]
[a]
Philip J. W. Elder, Tristram Chivers,* and
Ramalingam Thirumoorthi[
a]
Keywords: P ligands / Chalcogens / Tautomerism / Fluxionality / Density functional calculations
The reaction of H
produces H C(PiPr
boiling toluene, or selenium in toluene at room temperature,
to give the monochalcogenides EPiPr CH PiPr (E = Te, 4a;
E = Se, 4b) in high yields. X-ray structural determinations
show that 4a and 4b exist as the CH tautomers in the solid
2
C(PCl
2
)
2
with four equivalents of iPrMgCl
pounds 4a and 4b were also characterized by multinuclear
1
13
31
77
125
2
2
)
2
, which was treated with tellurium in
( H, C, P, Se,
Te) NMR spectroscopy. In solution, 4a
exhibits fluxional behavior, which has been investigated by
variable-temperature and variable-concentration multinu-
clear NMR spectroscopy. The observed behavior is consistent
with an intermolecular tellurium transfer with an activation
2
2
2
2
–
1
state with E–P–C–P dihedral angles of 56.1(2)° and 56.7(1)°,
respectively. DFT calculations were carried out for the isolec-
energy of 21.9Ϯ3.2 kJmol ; consideration of selenium ex-
change in 4b indicates a much higher energetic barrier. DFT
calculations provide insights into the pathway for the chalco-
tronic series EPR
Me, iPr, tBu, Ph) and for their non-chalcogenated precursors
in order to elucidate the factors that determine the prefer- come of reactions of 4a with selenium and nBuLi reflects the
2 2 2 2 2
CH PR and EPR NHPR (E = Se, Te; R =
–
1
gen exchange process in 4a (ΔE = 20.4 kJmol ). The out-
ence for PH tautomers in some PNP-bridged systems. Com-
lability of the P-Te functionality.
Introduction
Extensive studies of the redox chemistry and coordina-
tion complexes of tellurium-centered PNP-bridged ligands
–
–
of the type [TePR NPR ] (1) and [N(PR Te) ] (2) (R =
2
2
2
2
iPr, tBu) have been reported recently.[ In certain cases,
metal complexes of 2 serve as suitable single-source precur-
sors for binary metal tellurides in the form of thin films or
1]
[
2,3]
nanocrystals.
The synthesis of these tellurium-centered
ligands requires a different approach than that employed
for the lighter chalcogen analogues because tellurium is a
III
weaker oxidant than sulfur or selenium towards the P
centers in the neutral precursors HN(PR ) . For example,
2
2
In early work, Lusser and Peringer generated the mono-
when R = Ph, tellurium is inert even in boiling toluene;
however, for R = iPr, the monotelluride is obtained in high
yield as the PH tautomer HPiPr NP(Te)iPr (3a) upon
–
telluro PCP-bridged anion [TePPh C(H)PPh ] as the Li de-
2
2
III III
rivative by a metallation-first approach in which the P /P
precursor Ph PCH PPh was lithiated with nBuLi prior to
2
2
2
2
2
treatment of HN(PiPr ) with one equivalent of tellurium
2
2
[7]
oxidation with tellurium. This in situ reagent was then
in n-hexane at 23 °C.[ The selenium analogue 3b also
4]
II
used to prepare a homoleptic Hg complex that was char-
forms the PH tautomer both in the solid state and in solu-
acterized only by 31P and
199
Hg NMR spectroscopy. In
009, we obtained an X-ray crystal structure of (TMEDA)-
Li[TePPh C(H)PPh ], which comprises a centrosymmetric
[7]
[
5]
tion. The monotelluride 3a is readily metallated with
nBuLi to give 1 (R = iPr), which, although it is unstable
towards disproportionation, can be used as an in situ rea-
gent for the synthesis of homoleptic group 11 and 12 com-
2
2
2
dimer incorporating a weak Te···Te contact [3.514(1) Å].[
8]
However, this lithium complex is extremely moisture-sensi-
[
6]
plexes.
[
8]
tive and disproportionates readily in solution.
[
a] Department of Chemistry, The University of Calgary,
Calgary, AB, T2N 1N4, Canada
Fax: +1-403-289-9488
Tellurium-centered PCP-bridged ligands with P-alkyl
substituents have not been characterized. In this investiga-
tion, we intended to compare the structure, properties, and
reactions of the PCP-bridged monochalcogenides
E-mail: chivers@ucalgary.ca
Homepage: www.ucalgary.ca/chem/
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EPiPr CH PiPr (E = Te, 4a; E = Se, 4b) with those of the
2
2
2
PNP-bridged analogues 3a and 3b. In particular, we sought
to ascertain whether 4a and 4b form the CH tautomer in
2
preference to the PH tautomer. In that context, we report
here high-yield syntheses of 4a and 4b together with their
X-ray crystal structures. In view of this finding, we carried
out a comprehensive DFT computational study for the iso-
electronic series EPR CH PR and EPR NHPR (E = Se,
2
2
2
2
2
Te; R = Me, iPr, tBu, Ph) and for their non-chalcogenated
precursors that provides a clarification of the factors, which
determine the preference for PH tautomers in some cases.
The solution behavior of 4a and 4b has been investigated in
detail by variable-temperature and, in the case of 4a, vari- Figure 1. Crystal structure of TePiPr CH PiPr (4a). Hydrogen
2
2
2
1
31
125
able-concentration multinuclear ( H, P, and Te) NMR atoms of the iso-propyl groups have been omitted for clarity. Ther-
mal ellipsoids are shown at 95% probability, H atoms are indicated
spectroscopy, which reveals fluxional behavior involving
tellurium exchange. DFT calculations have been conducted
by spheres of 0.30 Å radius.
in order to elucidate the pathway of the tellurium-transfer
process. The reactions of 4a with selenium, tellurium, and 4b.
Table 1. Selected bond lengths [Å] and bond angles [°] in 4a and
nBuLi have also been studied with a view to evaluating the
influence of the labile P–Te bond on oxidation or deproton-
ation processes.
Bond lengths [Å]
4a (E = Te)
4b (E = Se)
E1–P1
P1–C13
P1–C1
P1–C4
P2–C7
P2–C13
P2–C10
2.3603(7)
1.824(3)
1.841(3)
1.846(3)
1.857(3)
1.868(3)
1.869(3)
2.1155(6)
1.815(3)
1.844(3)
1.815(2)
1.867(3)
1.867(2)
1.858(2)
Results and Discussion
Synthesis and X-ray Structures of TePiPr CH PiPr (4a)
2
2
2
and SePiPr CH PiPr (4b)
2
2
2
We recently developed a high-yield route to the diseleno
Bond angles [°]
4a (E = Te)
–
+
4b (E = Se)
PCP-bridged anion [HC(PiPr Se) ] as the Li derivative
2
2
using the commercially available bis(dichlorophosphinoyl)- P1–C13–P2
111.93(15)
105.04(13)
103.59(13)
108.63(13)
111.63(10)
112.95(10)
114.20(9)
99.78(13)
105.67(15)
99.16(14)
112.05(10)
103.72(9)
105.01(9)
108.54(9)
111.46(7)
113.92(6)
113.39(7)
99.24(9)
[8]
C13–P1–C1
C13–P1–C4
C1–P1–C4
C13–P1–E1
methane H C(PCl ) in a three-step process. In this work,
a similar approach led to the isolation of the monotelluride
2
2 2
TePiPr CH PiPr (4a) as a pale yellow powder in 98% yield
2
2
2
and the monoselenide SePiPr CH PiPr (4b) as clear, color- C1–P1–E1
2
2
2
less crystals in 78% yield [Equation (1)] and [Equation (2)]. C4–P1–E1
C7–P2–C13
(1) C7–P2–C10
C13–P2–C10
[
H
2
2
C(PCl
2
)
2
] + 4 iPrMgCl Ǟ [H
2
C(PiPr
PiPr
2
)
2
] + 4 MgCl
2
104.97(9)
100.56(9)
[
H
C(PiPr
2
)
2
] + E(s) Ǟ EPiPr
2
CH
2
2
(2)
bond length of 2.3603(7) Å in 4a is slightly shorter (by ca.
X-ray quality crystals of 4a were obtained by slowly 0.02 Å) than that in 3a and can be compared directly with
[
9,10]
cooling a hot hexanes solution, and the crystal structure is the value of 2.365 Å reported for iPr
PTe.
The disparity
3
illustrated in Figure 1. Crystals of 4b were obtained by slow of 0.044 Å in the P–C bond lengths of the PCP-bridge is
evaporation of a hexanes solution, and the molecular struc- attributed to the different oxidation states of the two phos-
ture is analogous to that of 4a. Selected bond lengths and phorus atoms.
bond angles for 4a and 4b are given in Table 1.
The monotelluride 4a crystallizes in the monoclinic space group P2
group P2 /n with four molecules in the unit cell. The hydro- hydrogen atoms of the CH
The monoselenide 4b crystallizes in the monoclinic space
/c, also with four molecules in the unit cell. The
group were again located from
1
1
2
gen atoms of the CH group were located from the Fourier the Fourier density map. The Se–P–C–P dihedral angle in
2
density map. Thus, in contrast to the isoelectronic PNP- 4b is 56.7(1)° and an Se–H(iPr) intermolecular contact is ob-
bridged monotelluride 3a,[ the PCP-bridged analogue 4a served with a distance of 2.922 Å. The P–Se bond length
4a]
forms the CH tautomer in preference to the PH tautomer of 2.1155(6) Å in 4b, cf. a value of 2.1212(9) Å found for
2
[
11]
in the solid state. The closest intermolecular contact in 4a iPr
PSe.
3
is a single Te–H interaction at 2.96 Å to one iPr CH group.
3
The Te–P–C–P dihedral angle in 4a is 56.1(2)°, whereas the
Computational Studies: P-H and C/N-H Tautomerism
corresponding Te–P–N–P dihedral angle in 3a is only
[
4a]
3
.2(2)°. The formation of different tautomers for 4a and
A detailed computational study was carried out in order
3a may explain this major structural divergence. The P–Te to explain the solid-state structures of 4a and 4b relative to
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those of their PNP-bridged analogues 3a and 3b. Specifi- isoelectronic systems, the substituents on phosphorus do
cally, the relative stabilities of the PH tautomers compared have a noticeable influence within the PNP-bridged series
to the corresponding NH or CH tautomers for the PNP- of compounds. Thus, in contrast to the iPr and tBu deriva-
2
and PCP-bridged monotellurides were of interest. In calcu- tives, Me or Ph substituents show only small energy differ-
lating the relative total bonding energies of the tautomers ences of Ͻ4.8 kJmol–1 between the two tautomeric forms
–1
of PNP- and PCP-bridged monotellurides, the influence of for E = Te. However, a slight preference (ca. 5 kJmol ) for
the substituent on phosphorus and the nature of the chalco- the N–H tautomer is indicated for R = Ph, E = Se, consis-
[
12]
gen were also included by performing the calculations for tent with the experimental observations. Thus, the com-
the series EPR CH PR and EPR NHPR (R = Me, iPr, putational results support the notion that substituents that
2
2
2
2
2
tBu, Ph and E = Te, Se) (see 5a–h and 6a–h). The inclusion increase the basicity of the lone pair on the phosphorus
of R = Ph in these calculations was prompted by the reports atom favor the formation of the PH tautomer in the case
[
4a]
that the monochalcogenides EPPh NHPPh (E = S, Se) ex- of the PNP-bridged systems.
A cogent manifestation of
2
2
ist exclusively as the NH tautomer, both in solution and in this viewpoint is the predisposition for the PH tautomer in
[
12,13]
the solid state.
the asymmetrical PNP-bridged system HP(NMe2)
PNPPh S, presumably as a result of the electron-donating
2
2
[
14]
Me N substituent. In this regard, we also note that elec-
2
tron-withdrawing groups on nitrogen make the NH group
more
acidic,
again
favoring
the
PH
form
in phosphanylsulfonamide derivatives of the type
[15,16]
RSO NHPRЈ , which have been exploited in catalysis.
2
2
The different electronic effects of the PCP and PNP
backbones are also apparent in the models of the non-
chalcogenated species (Table 3). In both cases, regardless of
the substituent, the P–H tautomer is always higher in en-
ergy, but the magnitude of the energy difference is depend-
ent on the central atom. With a methylene bridge, the CH
2
–1
tautomer is preferred by more than 80 kJmol , while a cen-
tral N atom provides a much lower energy difference (less
Gas-phase structures of 5a–h and 6a–h and those of the
corresponding PH tautomers were optimized. The total
bonding energies of these tautomers, as well as the differ-
ence in their energies calculated according to Equation (3),
are summarized in Table 2.
–1
than 43 kJmol ). These energy barriers are too high for
the PH tautomer to be observed in solution, except in the
case of tBu substitution. In this case, the energy difference
–1
is only 18 kJmol , which is low enough that solvent effects
and ambient temperature could allow for both tautomers
to co-exist in solution. Indeed, we have previously observed
experimentally that a mixture of NH and PH tautomers
(ca. 70:30) is present in a toluene solution of this derivative
ΔE = ENH/CH2 – EPH
(3)
Table 2. Differences in total bonding energy for PH and NH/CH
2
tautomers of 5a–h and 6a–h.[ All values corrected for zero-point
a]
[
4b]
at room temperature.
energy.
–
1
ΔE [kJmol–1]
ΔE [kJmol ]
Table 3. Differences in energy for PH and NH/CH tautomers of
2
(
E
CH2 – EPH
)
(ENH – EPH
)
CH (PR ) and HN(PR ) (R = Me, iPr, tBu, Ph). All values cor-
2
2 2
2 2
rected for zero-point energy.
5
5
5
5
5
5
5
5
a
b
c
d
e
f
–76.1
–59.0
–53.5
–70.5
–77.5
–61.6
–58.1
–72.2
6a
6b
6c
6d
6e
6f
4.8
23.3
17.6
2.9
ΔE [kJmol–1]
ΔE [kJmol–1]
(ENH – EPH)
(
ECH2 – EPH
)
CH
CH
CH
CH
2
2
2
2
(PMe
(PiPr
(PtBu
(PPh
2
)
2
–101.1
–85.5
–81.5
NH(PMe
NH(PiPr
NH(PtBu
NH(PPh
2
)
)
2 2
)
2 2
2 2
)
2
–42.3
–29.9
–18.0
–39.7
0.6
)
2
20.3
14.6
–4.5
2
)
2
2
g
h
6g
6h
2
)
2
–102.4
[
a] Compounds 5b, 6b, 5f, 6f are 4a, 3a, 4b, 3b, respectively, in the
The influence of the alkyl substituent on the nucleophil-
icity of the phosphorus center was modeled by comparing
previous section.
The electronic effects of the PCP backbone appear to be the charges on phosphorus. By using the ADF computa-
[
17]
very different from those of the PNP fragment. For the tional package, charges are provided as Mulliken, Hirsh-
[
18]
[19]
series 5a–h, the CH tautomer is more stable than the PH feld, and Voronoi deformation density (VDD) values.
2
–
1
tautomer by more than 53 kJmol . By contrast, the PH Mulliken population analysis results in equal sharing of
–
1
tautomer is favored by 18–23 kJmol for the PNP-bridged electron density between centers and is known to exaggerate
species when R = iPr, tBu; E = Te, Se, which suggests that the charges; Hirshfeld and VDD methods more effectively
the donor ability of the central nitrogen atom is the likely parse the density and are said to be more accurate.[ It
cause of the difference. Although the nature of the back- should be noted that despite these differences, the trends in
bone is paramount in directing tautomer formation in these the data are consistent between the three methods (Table 4).
20]
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In each of the systems, the charge on the phosphorus atoms 258 K. There was no evidence for the existence of the PH
increases modestly with inductive strength of the alkyl tautomer in solution throughout the temperature range.
group, Me Ͻ iPr Ͻ tBu. These changes are moderate how-
ever, increasing by ca. 0.2 a.u. for Mulliken, 0.03 a.u. for
Hirshfeld, and 0.02 a.u. for VDD.
Table 4. Calculated average charges[a] (in a.u.) of phosphorus atoms
in CH
2
(PR
2
)
2
and HN(PR
2
)
2
(R = Me, iPr, tBu, Ph).
CH Tautomer
2
PH Tautomer
Mulliken Hirshfeld VDD
Mulliken Hirshfeld VDD
CH
CH
CH
CH
2
(PMe
(PiPr
(PtBu
(PPh
2
)
)
2 2
)
2 2
2 2
)
2
0.208
0.301
0.436
0.253
0.136
0.151
0.175
0.139
0.050
0.056
0.073
0.062
0.428
0.634
0.723
0.527
0.204
0.217
0.228
0.198
0.162
0.165
0.175
0.168
2
2
2
NH Tautomer
PH Tautomer
NH(PMe
NH(PiPr
NH(PtBu
NH(PPh
2
)
)
2
)
2 2
2 2
)
2
0.332
0.390
0.482
0.354
0.169
0.106
0.103
0.116
0.110
0.542
0.733
0.793
0.586
0.232
0.190
0.204
0.219
0.204
2
0.176
0.199
0.163
0.254
0.268
0.232
[
a] As a result of differences in the molecular geometry, there is
occasionally a slight variation in atomic charge between atoms.
Solution Behavior of EPiPr CH PiPr (4a, E = Te; 4b, E
2
2
2
=
Se): Multinuclear NMR Spectroscopy Studies
The 31P{ H} NMR spectrum of 4a in [D ]toluene at
1
8
2
98 K exhibits two broad resonances at 21.1 and –2.6 ppm,
V
III
which correspond to the P and P centers, respectively;
the broadness of the peaks prevented the determination of
coupling constants at room temperature. Attempts to deter-
mine the Te NMR chemical shift at 298 K were also un-
successful. In the H NMR spectrum, four resonances are
observed at 298 K: (a) two independent doublets of dou- Figure 2. Variable-temperature 31P NMR spectra for TePiPr CH -
1
25
1
2
2
blets at δ = 0.99 and 1.02 ppm, which correspond to the PiPr
isopropyl CH groups and exhibit coupling to nearby phos-
2
(4a) in [D
8
]toluene (a) in the temperature range 218–338 K
* = shown at 1/2 vertical scale, † = shown at 4ϫ vertical scale),
and (b) expansion of the 218 K spectrum to show P–P coupling.
(
3
3
1
31
3
1
1
phorus [ J( H, P) = 15 Hz] and hydrogen nuclei [ J( H, H)
7.0 Hz], (b) a partially resolved broad resonance at δ =
=
In the 1H NMR spectrum, cooling of the sample to
1
.85 ppm, which can be attributed to CH hydrogen atoms 218 K results in a deceleration of the exchange process on
of the four isopropyl groups, and (c) a pseudo-triplet at δ = the NMR time scale. As illustrated in Figure 3, the triplet
.93 ppm, which results from the coupling of CH protons corresponding to the CH resonance begins to separate into
1
2
2
in the PCP backbone to the two phosphorus nuclei a doublet at δ = 1.69 ppm, while the previously poorly re-
2
1
31
[
J( H, P) = 6 Hz]; the coupling of these protons to the solved isopropyl C–H resonance separates into two dis-
two phosphorus nuclei appears to be equivalent at room tinctly different broad resonances centered at δ = 1.59 and
temperature. In summary, the multinuclear NMR spec- 1.98 ppm. When the solution is heated, these two reso-
troscopy data for 4a clearly indicate fluxional behavior in nances collapse to give a broad resonance at 278 K, which
solution.
becomes well-resolved to reveal couplings to the CH hy-
3
In order to probe the nature of this exchange process, we drogen atoms at 338 K. Interestingly, the resonances corre-
1
31
125
carried out a multinuclear ( H, P and Te) NMR study sponding to the isopropyl CH protons approach equiva-
3
of 4a in [D ]toluene over the temperature range 218–338 K. lence upon heating. Whereas below room temperature the
8
1
3
1
In the P{ H} NMR spectrum, the two broad resonances two different resonances for the isopropyl CH groups on
3
observed at room temperature sharpen markedly with lower the P and PV centers are easily differentiated, their posi-
III
2
31 31
temperatures (Figure 2a), and at 218 K the J( P, P) cou- tions and intensities are nearly identical at 338 K (Δδ =
1
25
plings (63 Hz) and
Te satellites are clearly visible 9.0 Hz). Upon cooling, this equivalence is again lost, and
1
31 125
J( P, Te) = 1735 Hz (cf. 1735 Hz for iPr PTe) (Fig- at 238 K one set has almost completely broadened into the
3
ure 2b). This value was corroborated by the 125Te NMR baseline. It is expected that at these low temperatures, bond
[9]
spectrum at 218 K, which exhibits a well-resolved doublet rotations may be slow on the NMR timescale, which leads
1
31 125
with J( P, Te) = 1734 Hz; however, upon warming the to a notable inequivalence of the isopropyl groups on the
III
V
solution, this doublet collapses and is lost in the baseline at
P
and P centers.
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the rate of exchange, was affected; the most concentrated
sample showed two broad resonances at room temperature,
but with lower concentrations, the peaks sharpened signifi-
cantly.
The rate of exchange for each sample at a specific tem-
perature can be approximated by using the full-widths at
III
V
half-maximum (FWHM) of the P or P resonance [Equa-
tion (4)]. For the purposes of this analysis, the PIII reso-
nance was used, because of the sharper line-shapes in the
intermediate temperature range. A linear relationship be-
tween the observed rate and the concentrations of 4a indi-
cates a first-order reaction with respect to 4a (Table 5). An
Arrhenius plot (Figure 4) was thus used to determine an
activation energy of 21.9Ϯ3.2 kJmol–1 for this process.
[23]
Rate = k[4a] = π(FWHM – FWHM
0
)
(4)
1
Figure 3. Variable-temperature H NMR spectra for TePiPr
2 2
CH -
PiPr (4a) in [D ]toluene in the temperature range 218–348 K. The
2
8
3
portion of the spectra corresponding to CH groups is presented
at 1/2 vertical scale.
Figure 4. Experimental Arrhenius plot for the Te-transfer process
observed in 4a between 230 and 307 K.
In summary, the variable temperature NMR spec-
troscopy data are consistent with an exchange process that
is rapid on the NMR time scale at room temperature. We
The behavior of the selenium derivative SePiPr CH PiPr
2
2
2
1
25
note that the
urides R PTe (R = nBu, tBu, Ph ) are observed to col- 298 K, the P{ H} NMR spectrum in [D ]toluene exhibits
Te NMR spectra of the phosphane tell- (4b) in solution is more straightforward than that of 4a. At
[21]
31
1
3
8
lapse from a well-resolved doublet into a broad resonance two narrow, well-separated doublets at 57.8 and –4.8 ppm,
in the presence of excess R P. In the case of 4a, the pres- which correspond to the PV and P centers, respectively;
[
22]
III
3
III
2
31 31
ence of the P center could provide the site for tellurium each resonance is mutually coupled [ J( P, P) = 49 Hz],
exchange between the two phosphorus centers through and Se satellites are clearly visible on the P center
either an inter- or an intramolecular process.
77
V
1
31 77
[11]
77
[ J( P, Se) = 720 Hz, cf. 708 Hz for iPr PSe]. The Se
3
In order to differentiate between these two exchange NMR chemical shift is observed at –429.6 ppm at this same
[
11]
1
pathways, a VT-NMR study was undertaken, in which the temperature (cf. –489.9 ppm for iPr PSe).
and exhibits
3
1
concentration was also varied; an intermolecular process is the same J coupling to phosphorus. In the H NMR spec-
expected to exhibit concentration dependence, which would trum, the following resonances are observed: (a) two inde-
3
1
1
not be evident for intramolecular exchange. P{ H} NMR pendent doublets of doublets at δ = 1.01 and 1.06 ppm,
spectra of four solutions involving one-half serial dilutions which correspond to the isopropyl CH groups, exhibit cou-
3
–
1
3
1
31
of a 0.053Ϯ0.002 molL sample were collected over the pling to nearby phosphorus [ J( H, P) = 17 Hz] and hy-
3
1
1
temperature range 215–355 K. It was immediately apparent drogen nuclei [ J( H, H) = 7.0 Hz], (b) a multiplet at δ =
that, although the chemical shifts were unaffected by the 1.91 ppm, which can be attributed to the four CH hydrogen
concentration, the broadness of the resonances, and hence atoms of the four isopropyl groups, and (c) an apparent
Table 5. Experimentally determined rate data for the Te-transfer process observed in 4a between 230 and 307 K.
–1
Rate [s–1]
252 K
Rate [s–1]
263 K
Rate [s–1]
274 K
Rate [s–1]
285 K
Rate [s–1]
296 K
Rate [s–1]
307 K
Concentration
Rate [s ]
230 K
–1
[molL ]
0
0
0
0
0
.003
.007
.013
.027
.053
10
13
22
107
110
2419
100
74
123
272
493
9521
99
93
160
457
612
12671
113
148
241
507
1019
19169
137
174
401
763
1300
25565
142
215
499
1066
1794
35102
225
329
625
1224
2384
45268
–1 –1
k (Lmol s )
Eur. J. Inorg. Chem. 2013, 2867–2876
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FULL PAPER
doublet at δ = 1.76 ppm, which corresponds to the CH2 of the experimentally observed concentration dependence,
protons in the PCP backbone. the exchange must occur between two molecules, but, as a
The latter observation represents a notable difference comparison, the energetic pathway for intramolecular tel-
compared to the corresponding signal for 4a, which was lurium exchange was considered first. An intramolecular
only partially resolved into a pseudo-doublet at 218 K (Fig- tellurium-transfer model was calculated by varying the dif-
ure 3). This disparity may arise from the rapid tellurium ference of the d and d distances [Scheme 1, defined as x
2
1
exchange that occurs for 4a at ambient temperature. Selec- in Equation (5)] in 0.2 Å steps from x = –2.2 Å to 2.2 Å. A
1
31
tive H{ P} decoupling experiments for 4a at room tem- plot of the potential energy at each value of x (Figure 5)
perature resulted in a collapse of the triplet to a single peak, indicates one energetic maximum at x = 0 and two energy
which suggests that the coupling to the two phosphorus wells when x is equal to 1.8 Å and –1.8 Å (representing the
atoms is indeed averaged at room temperature. Similar ex- two isomers of 4a). The maximum has an energy of
periments for 4b, where there is no apparent fluxionality at 168 kJmol–1 relative to the minimum, well beyond what
V
2
98 K, led to a partial collapse of the doublet when the P
could be achieved in the temperature range studied experi-
III
center was decoupled. Decoupling of the P center led to mentally. At the minima on the curve, the long P–Te dis-
no visible change in the shape of the CH resonance. These tance of 4.20 Å [Σvdw(P,Te) = 4.05 Å] suggests that there is
2
data suggest that the doublet is in fact a doublet of dou- no intramolecular bonding contribution to the intermo-
V
2
1
31
blets, which exhibits a large coupling to P [ J( H, P) = lecular Te transfer.
III
1
2 Hz] and a very small coupling to P (could not be mea-
sured). It then follows that in the absence of exchange, 4a
should also exhibit this coupling pattern.
d
2
–d
1
= x
(5)
Although the multinuclear NMR spectroscopy data for
4b do not immediately suggest fluxional behavior in solu-
tion at room temperature, evidence of a slow exchange pro-
cess was apparent from the line-broadening observed in the
3
1
1
P{ H} NMR spectra collected over the temperature range
298–355 K. The nature of this exchange is likely comparable
Scheme 1.
to that of 4a, but 4b exhibits a much higher activation bar-
rier as the peaks do not approach equivalence as in 4a. It
is expected that this is a result of the more electronegative
[
24]
Se atom and a stronger P–Se bond than the P–Te bond.
In an attempt to evaluate the influence of the phos-
phorus substituents on the energy barriers for chalcogen
exchange, the synthetic procedure outlined in Equations (1)
and (2) was applied to the synthesis of the tetramethyl de-
rivative TePMe CH PMe . Surprisingly, the methyl-substi-
2
2
2
tuted PCP-bridged precursor Me PCH PMe , which was
2
2
2
obtained as a clear, colorless liquid,[ failed to react with
25]
either elemental tellurium or the tellurium-transfer reagents
[26]
R PTe (R = Et, tBu)
3
even in boiling toluene. By com-
parison with the high-yield synthesis of 4a, the lack of for-
mation of the monotelluride TeMe PCH PMe under these
2
2
2
conditions is puzzling, especially in the light of a literature
report that describes the ditelluration
Me PCH CH PMe with Et PTe in toluene at room tem- transfer process in 4a. (--- indicates x = 0 Å).
of Figure 5. Potential energy curve for a possible intramolecular Te-
2
2
2
2
3
[
27]
perature to give TePMe CH CH PMe Te in 51% yield.
2
2
2
2
Unfortunately, it was not possible to extend this investiga-
A simple intermolecular transfer model would involve a
tion to the tert-butyl derivative TetBu PCH PtBu because single point of attachment between two molecules of 4a. As
2
2
2
the reaction of H C(PCl ) with tert-butylmagnesium chlor- a first approximation, the difference in the distances d and
2
2 2
2
ide produces the six-membered ring 1,4-(CH ) (PtBu)
d1 [Scheme 2, defined as x in Equation (5)] was varied in
2
2
4
through a reductive coupling process rather than the ex- 0.1 Å steps between x = –1.4 Å and 1.4 Å, with all other
[28,29]
pected acyclic product tBu PCH PtBu .
geometric parameters allowed to optimize at each step. In
this manner, an approximation of the intermolecular trans-
fer pathway was made. A plot of the total bonding energy
showed two well-defined minima, and a single maximum.
By using the molecular geometries at these points, the struc-
2
2
2
Models of Tellurium Exchange
To compliment these experimental studies, a series of cal- tures were reoptimized without constraints (but with tighter
culations were performed in an attempt to model the reac- convergence criteria and a higher integration accuracy) to
tion pathway for the tellurium transfer in 4a. On the basis provide more accurate structures and energies; a transition-
Eur. J. Inorg. Chem. 2013, 2867–2876
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state search for the geometry at the maximum was used to
The dimeric structure (Figure 7a) is lower in energy by
model the activation barrier. The energies and values for x 11.4 kJmol–1 when compared to the CH (PiPr ) /
2
2 2
at these points are shown in Figure 6.
CH (PiPr Te) adduct (Figure 7c). The calculated energetic
2 2 2
barrier for transfer of the tellurium atom to a second mole-
–1
cule is 20.4 kJmol , while that for the reverse reaction is
–1
9
.1 kJmol . This suggests that, although the dimer of 4a
is preferred, conversion between the two minima would be
expected in solution at room temperature. This energy bar-
rier correlates very well with the experimentally observed
–1
E of 21.9Ϯ3.2 kJmol , which suggests that this is indeed
a
the transfer process observed in the NMR experiments.
This model, however, is inconsistent with the experimen-
tally observed coalescence of the two P resonances, as
Scheme 2.
31
such a model would require all phosphorus environments
to be the same as a result of the transfer. This discrepancy
could be accounted for by the occurrence of multiple inter-
molecular Te-exchange processes that would give rise to a
single 31P NMR chemical shift.
Consideration of a simple dimer with two points of at-
tachment (Scheme 3) gave intermolecular P–Te bond
lengths well in excess of the sum of van der Waals radii
(4.116, 4.354 Å). This result seems to rule out a symmetrical
intermediate in the exchange process. A contraction of the
molecular Te–P–C–P dihedral angle required to achieve this
geometry (ca. 60° relative to 90° in the free molecule) likely
contributes to the long P–Te distances. Consequently, a
more accurate model should be sufficiently large to allow
for a more relaxed geometry. Such an extended system,
Figure 6. Energy diagram for the intermolecular Te-transfer pro- however, is beyond our computational resources at this
cess in 4a. (--- indicates x = 0 Å).
time.
The minima can best be described as a dimer of 4a
(
where x = 0.905 Å) and an adduct of CH (PiPr ) and
2 2 2
CH (PiPr Te) (where x = –0.685 Å), while the maximum
2
2
2
(where x = –0.147 Å) represents a transition state where the
Te atom is bridged between molecules (Figure 7). The P1–
Te1–P2 bond angles (176.2° for structure a, 177.4° for struc-
ture b and 176.8° for structure c) are all in good agreement
with the solid-state structure of (Ph P) Te, which exhibits a
3
2
80° P–Te–P angle.[ Although the presence of a second Scheme 3.
21]
1
tellurium atom is expected to have an effect on the calcu-
lated energies, the observation that the P–Te2 bond length
and the Te2–P–C–P dihedral angle remain unchanged
throughout the reaction pathway indicates that such a per- Reactions of 4a with Chalcogens and nBuLi
turbation is relatively minor.
In our previous attempts to sequentially oxidize the two
PIII centers in HN(PiPr ) with different chalcogens, only
2
2
III
[5]
one of the P centers could be oxidized. For comparison,
we attempted to prepare a mixed-chalcogen ligand by reac-
tion of 4a with elemental selenium in toluene at room tem-
perature. The occurrence of a reaction under these condi-
tions was readily evident from the formation of a precipitate
of tellurium. However, the 31P NMR spectrum of the super-
natant revealed the formation of the known diseleno deriva-
[
8]
tive H C(PiPr Se) , in addition to unreacted 4a, which
2
2
2
demonstrates the lability of the P–Te bond in 4a. Attempts
to prepare the ditelluro derivative TePiPr CH PiPr Te by
2
2
2
Figure 7. Optimized structures of (a) the dimer of 4a, (b) the transi-
tion state for tellurium transfer, and (c) the CH (PiPr
CH (PiPr Te) adduct.
reaction of iPr PCH PiPr with 2.2 equiv. tellurium in boil-
2
2
)
2
/
2
2
2
2
2
2
ing toluene for 4 d gave only the monotelluride 4a; the Te-
Eur. J. Inorg. Chem. 2013, 2867–2876
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3 4
transfer reagents Et PTe or tBu PTe were also ineffective in spectra are referenced externally to an 85% solution of H PO at
3
3
7
7
III
0 ppm, Se spectra to an external reference of Ph Se in CDCl at
oxidizing the second P center.
2
2
3
1
25
δ = 463 ppm, and Te spectra to Ph
Mass spectra (EI/CI) were obtained with a Thermo Finnigan
SSQ7000 mass spectrometer with a direct insertion probe.
2
Te
2
in CDCl
3
at δ = 422 ppm.
A second manifestation of the lability of the P–Te bond
in 4a was provided by the attempted lithiation of 4a with
nBuLi in THF at –78 °C, followed by warming to room
temperature. Under these conditions, the only detectable
product in the P NMR spectrum was the P /P precur-
sor H C(PiPr ) , presumably formed as a result of cleavage
X-ray Crystallography: Crystallographic data for 4a and 4b are
summarized in Table 6. Crystals of 4a and 4b were coated with
Paratone 8277 oil and mounted on a nylon loop. Diffraction data
were collected on a Nonius KappaCCD diffractometer by using
3
1
III III
2
2 2
of the P–Te bond.
α
monochromated Mo-K radiation (λ = 0.71073 Å) at –150 °C (4a)
and –100 °C (4b). An absorption correction was applied during the
data collection by using the SORTAV program.[ The structures
32]
Conclusions
were solved by direct methods by using SHELXS-97 and refined
by using SHELXL-97.[
33,34]
After full-matrix least-squares refine-
In contrast to their PNP-bridged analogues, the PCP-
bridged monochalcogenides EPiPr CH PiPr (E = Te, Se)
exist as the CH tautomer in the solid state. DFT calcula-
tions provide support for the higher stability of the PH tau-
tomer in the case of the alkyl-substituted PNP-bridged
monochalcogenides, 6b, 6c, 6f, and 6g, and indicate that
ment of the non-hydrogen atoms with anisotropic thermal param-
eters, the hydrogen atoms were placed in idealized locations by
using the appropriate riding models. The locations of the hydrogen
atoms bonded to the PCP carbon atom were located from the Fou-
rier density map and were refined.
2
2
2
2
this preference can be attributed to the different electronic Table 6. Crystallographic data for 4a and 4b.
effects of the PNP relative to PCP bridge. In solution, how-
ever, the monotelluride 4a undergoes a rapid intermolecular
4
a
4b
Empirical formula
Formula weight
Crystal system
C
13
H
30 2
P Te
13 30 2
C H P Se
tellurium exchange with an activation energy of ca.
375.91
monoclinic
P2 /n
10.7740(4)
11.9480(2)
14.0990(5)
90.00
107.8230(11)
90.00
1727.83(9)
4
–150
1.445
1.886
0.19ϫ0.11ϫ0.07
760
327.27
monoclinic
P2 /c
10.7760(3)
11.7200(3)
14.2610(5)
90.00
114.7410(11)
90.00
1677.06(7)
4
–100
1.296
2.409
0.12ϫ0.10ϫ0.08
688
2.32–27.55
14118
3854
0.0336
3396
0.0293
0.0687
1.057
0.991
–
1
2
2 kJmol as determined by NMR spectroscopy studies
supported by DFT calculations. In contrast, the monoselen- Space group
1
1
a [Å]
ide, 4b, undergoes slow exchange, likely because of a much
b [Å]
larger activation energy. Although the lability of the P–Te
c [Å]
bond in 4a preempts the direct formation of a lithium deriv-
α [°]
ative for metathesis reactions, the coordination chemistry of β [°]
the neutral ligands 4a and 4b, which incorporate both heavy γ [°]
3
III
V [Å ]
Z
chalcogen and P donor centers, merits detailed investiga-
tion.
T [°]C
ρ
calcd. [mg/m3]
–
1
μ(Mo-K
Crystal size [mm ]
F(000)
α
) [mm ]
3
Experimental Section
Reagents and General Procedures: All reactions and the manipula-
tion of products were performed under an atmosphere of argon by
θ Range [°]
2.1–27.40
No. of reflections collected 6630
using standard Schlenk techniques. The compounds [H
2
C(PCl
2
)
2
]
No. of unique reflections
3698
0.0246
R
int
(Strem Chemicals, Ͼ90%), MeMgCl (Aldrich, 3.0 m solution in
no. of reflections [IϾ2σ(I)] 3450
THF), iPrMgCl (Aldrich, 2.0 m solution in THF), tBuMgCl (Ald-
rich, 1.0 m solution in THF), nBuLi (Aldrich, 2.5 m solution in hex-
anes), and elemental Te (Aldrich, 30 mesh, 99.997%), and Se (Ald-
rich, 200 mesh, 99.5+%) were used as received. The solvents n-hex-
ane, toluene, diethyl ether, and THF were dried by distillation over
sodium/benzophenone under an argon atmosphere prior to use.
R1 [IϾ2σ(I)]
wR2 (all data)
0.0311
0.0726
1.127
0.982
2
GOF on F
Completeness
[
30]
[31]
Samples of Et
to literature procedures. The compound H
as a clear, colorless, highly air-sensitive liquid from the reaction of
C(PCl ] with MeMgCl in diethyl ether according to the litera-
ture procedure and was shown to be pure by NMR spectroscopy [δ
3
PTe
and tBu
3
PTe
were synthesized according
CCDC-910200 and -910201 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
2
C(PMe was obtained
2 2
)
[
H
2
2 2
)
Computational Details: The structures considered in these studies
3
1
1
[25]
P( H) = –55.0 (s) in reagent toluene, lit. value –55.8]. Elemental
were optimized by using the ADF DFT package, version
analyses were performed on a Perkin Elmer 2400 elemental ana-
lyzer equipped to measure C, H and N.
Spectroscopy Methods: The 1H, 13C, 31P, 77Se, and 125Te NMR
012.01.[35–37] The adiabatic local density approximation (ALDA)
2
[38,39]
was used for the exchange-correlation kernel,
and the differen-
tiated static LDA expression was used with the Vosko–Wilk–Nusair
parameterization.[ Calculations of model geometries were gradi-
40]
8
spectra were obtained in [D ]toluene between 218–338 K on a
Bruker DRX 400 spectrometer operating at 399.46, 100.46, 161.71,
ent corrected with the exchange and correlation functionals pro-
1
13
[41,42]
76.13, and 125.90 MHz, respectively. H and C-DEPT135 NMR
posed in 1991 by Perdew and Wang (PW91).
The structures
spectra are referenced to the solvent signal, and the chemical shifts
were refined by using a triple-ζ all-electron basis set with two polar-
13
are reported relative to (CH
3
)
4
Si. C δ chemical shift assignments
ization functions and by applying the zeroth order regular approxi-
3
1
[43–47]
were confirmed by using 2D techniques (HSQC and HMBC).
P
mation (ZORA)
formalism with the specially adapted basis
Eur. J. Inorg. Chem. 2013, 2867–2876
2874
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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FULL PAPER
1
31 77
2
31 31
sets. The validity of all optimized structures was confirmed by
using frequency calculations; all calculated energies have been cor-
rected for zero-point energies and basis set superposition error
where applicable.
(25 °C): δ = 57.8 [s, J( P, Se) = 720 Hz, J( P, P) = 50 Hz, 1 P,
V
2
31 31
III
77
P ], –4.8 [s, J( P, P) = 50 Hz, 1 P, P ] ppm. Se NMR (25 °C): δ
1
77
31
= –429.6 [d, J( Se, P) = 720 Hz] ppm.
Reaction of 4a with Selenium: A solution of 4a (0.101 g, 0.26 mmol)
in toluene (5 mL) was transferred onto elemental selenium (0.021 g,
0.26 mmol) and stirred with reflux for 18 h. Once the stirring was
stopped, extruded tellurium was allowed to settle, and a P NMR
spectrum of the supernatant solution showed a mixture of 4a and
2 2 2 2 2 2
Synthesis of TePiPr CH PiPr (4a): A solution of [H C(PCl ) ]
(0.953 g, 4.38 mmol) in THF (30 mL) was cooled to –78 °C prior
3
1
to the addition of iPrMgCl (9.6 mL of a 2.0 m solution in THF)
dropwise by syringe. The reaction mixture was stirred for 1 h at
–
78 °C, 30 min at 23 °C, and finally heated for 3 h at 50 °C. The
solvent was removed under vacuum, and the oily product was ex-
tracted with ca. 40 mL of Et O. The solution was passed through a
PTFE disk to remove solid MgCl , the solvent was removed under
vacuum, and the sample of [H C(PiPr ] was redissolved in toluene
30 mL). This solution was then transferred into a flask containing
the diseleno-substituted species H C(PiPr Se) [δ
J( P, Se) = 725 Hz], lit. values [δ = 56.8, J( P, Se) = 726 Hz
=
57.3,
2
2
2
1
31 77
1
31 77
[8]
2
in [D ]THF].
8
2
Reaction of 4a with nBuLi: nBuLi (0.23 mL of a 2.5 m solution in
THF) was added dropwise with stirring to a solution of 4a (0.211 g,
.56 mmol) in THF (10 mL) cooled to –78 °C. The reaction mix-
ture was stirred at this temperature for 30 min and then warmed to
room temperature over 1 h. A P NMR spectrum of the resulting
2
2 2
)
(
0
elemental tellurium (0.619 g, 4.85 mmol) and was heated at reflux
for 21 h. Once cooled, this solution was filtered through a PTFE
disk to remove unreacted tellurium. Solvent removal resulted in a
yellow solid, which was extracted repeatedly with hexanes to yield
3
1
III III
2 2 2
solution showed only the parent P /P compound H C(PiPr ) (δ
8]
=
–1.6 in toluene), lit. value: δ = –1.3 in [D
8
]THF.[
4a as a pale yellow powder (1.595 g, 4.27 mmol, 98%). M.p. 95–
9
8 °C. C13 Te (395.91): calcd. C 41.50, H 8.00; found C 41.57,
40 2
H P
1
]toluene, 23 °C): δ = 1.93 [t, 2J( H, P) =
1
31
H 7.94. H NMR ([D
3 2
Hz, 2 H, CH of the PCP carbon], 1.85 [m, 4 H, CH(CH )
8
Acknowledgments
6
], 1.02
3
1
1
3
1
31
V
[dd, J( H, H) = 7, J( H, P) = 15 Hz, 12 H, CH(CH
3
)
2
on P ],
on
8
]toluene, –55 °C): δ = 1.98 [m, 2 H,
We thank the Natural Sciences and Engineering Council of Canada
NSERC) for continuing financial support. We would also like to
3
1
1
3
1
31
0
P
3 2
.99 [dd, J( H, H) = 7, J( H, P) = 14 Hz, 12 H, CH(CH )
(
III
] ppm. 1H NMR ([D
acknowledge Drs. M. Krykunov and M. Seth for their invaluable
advice regarding ADF methods. We are grateful to Prof. T. Ziegler
for access to computational resources.
V
2
1
31
CH(CH
3
)
2
on P ], 1.69 [d, J( H, P) = 12 Hz, 2 H, CH
2
of the
III
PCP carbon], 1.59 [m, 2 H, CH(CH
CH(CH
H, CH(CH
3
)
2
on P ], 1.06 [br. m, 12 H,
) on P ], 0.96 [dd, J( H, H) = 7, J( H, P) = 14 Hz, 12
3 2
V
3
1
1
3
1
31
III
13
3
)
2
on P ] ppm. C-DEPT135 NMR (25 °C): δ = 19.9
(
br. s, 1C, C of PCP), 19.8 [br. s, 4C, CH(CH ], 18.9 [br. s, 8C, [1] For a review, see T. Chivers, J. S. Ritch, S. D. Robertson, J.
3 2
)
] ppm. 31P{ H} NMR (23 °C): δ = 21.1 (br. s, 1 P, P ),
1
V
Konu, H. M. Tuononen, Acc. Chem. Res. 2010, 43, 1053.
[2] For a review, see J. S. Ritch, T. Chivers, M. Afzaal, P. O’Brien,
Chem. Soc. Rev. 2007, 36, 1622.
CH(CH
3
)
2
III
31
1
–
2.6 (br. s, 1 P, P ) ppm. P{ H} NMR (–55 °C): δ = 22.2 [d,
J( P, P) = 60, J( P, Te) = 1735 Hz, 1 P, P ], –2.6 [d,
J( P, P) = 60 Hz, 1 P, P ] ppm.
940.29 [d, J( Te, P) = 1735 Hz] ppm. X-ray quality crystals of
2
31 31
1
31 125
V
2
31 31
III
125
2 3
[3] For specific examples, see a) Sb Te : S. S. Garje, D. J. Eisler,
Te NMR (–55 °C): δ =
1
125
31
J. S. Ritch, M. Afzaal, P. O’Brien, T. Chivers, J. Am. Chem.
Soc. 2006, 128, 3120; b) PbTe: J. S. Ritch, T. Chivers, K. Ah-
mad, M. Afzaal, P. O’Brien, Inorg. Chem. 2010, 49, 1198; c)
CdTe: K. Ahmad, M. Afzaal, J. S. Ritch, T. Chivers, P. O’Brien,
J. Am. Chem. Soc. 2010, 132, 5964.
–
4
a were obtained by dissolving a sample in hot hexanes, then al-
lowing the solution to cool slowly in a warm water bath.
Synthesis of SePiPr CH PiPr (4b): The reagent [H C(PiPr
prepared from [H C(PCl ] (0.403 g, 1.85 mmol) and iPrMgCl
3.8 mL of a 2.0 m solution in THF) and isolated as described
above for the synthesis of 4a. A solution of [H C(PiPr
1.85 mmol) in toluene (30 mL) was then cooled to 0 °C and trans-
2
2
2
2
2 2
) ] was
[
4] a) T. Chivers, D. J. Eisler, J. S. Ritch, H. M. Tuononen, Angew.
Chem. 2005, 117, 5033; Angew. Chem. Int. Ed. 2005, 44, 4953;
b) J. S. Ritch, T. Chivers, D. J. Eisler, H. M. Tuononen, Chem.
Eur. J. 2007, 13, 4643.
2
2 2
)
(
2
2 2
) ]
(
[
[
5] S. D. Robertson, T. Chivers, Dalton Trans. 2008, 1765.
6] a) J. S. Ritch, T. Chivers, Dalton Trans. 2008, 957; b) J. S. Ritch,
T. Chivers, Inorg. Chem. 2009, 48, 3857.
ferred into a flask containing a rapidly stirred slurry of elemental
selenium (0.145 g, 1.84 mmol) in toluene (5.0 mL), also at 0 °C.
This mixture was then warmed slowly to room temperature with
stirring over 21 h. The reaction mixture was then filtered through
[7] M. Lusser, P. Peringer, Inorg. Chim. Acta 1987, 127, 151.
[8] J. Konu, H. M. Tuononen, T. Chivers, Inorg. Chem. 2009, 48,
11788.
a PTFE disk to remove unreacted selenium. 31P{ H} NMR spec-
1
[
9] N. Kuhn, G. Henkel, H. Schumann, R. Fröhlich, Z. Natur-
forsch. B 1990, 45, 1010.
troscopy of this crude reaction mixture showed complete conver-
sion to monosubstitution, with ca. 6% diselenide SePiPr
PiPr Se as a minor impurity. The solvent was removed from the
reaction mixture, and the residue was redissolved in hexanes. Slow
evaporation of the solvent resulted in precipitation of clear, color-
less crystals of 4b (0.467 g, 1.43 mmol, 78%). M.p. 68–70 °C.
C
9
2 2
CH -
[
10] Values in the range 2.288(5)–2.368(4) Å have been reported for
a variety of phosphane tellurides. G. G. Briand, T. Chivers, M.
Parvez, G. Schatte, Inorg. Chem. 2003, 42, 525, and references
therein.
2
[11] C. G. Hrib, F. Ruthe, E. Seppäla, M. Bätcher, C. Drucken-
brodt, C. Wismach, P. G. Jones, W.-W. du Mont, V. Lippolis,
F. A. Devillanova, M. Bühl, Eur. J. Inorg. Chem. 2006, 88.
[12] P. Bhattacharyya, A. M. Z. Slawin, D. J. Williams, J. D. Wool-
lins, J. Chem. Soc., Dalton Trans. 1995, 3189.
[13] P. Bhattacharyya, A. M. Z. Slawin, M. B. Smith, J. D. Woollins,
Inorg. Chem. 1996, 35, 3675.
13
H
40
1
P
2
Se (327.27): calcd. C 47.71, H 9.24; found C 48.26, H
]toluene, 25 °C): δ = 1.91 [m, 4 H, CH(CH ],
], 1.06 [dd, J( H, H) = 7,
.07. H NMR ([D
8
3 2
)
2
1
31
3
1
1
1
.76 [d, J( H, P) = 12 Hz, 1 H, CH
2
3
1
31
V
3
1
1
3 2
J( H, P) = 17 Hz, 12 H, CH(CH ) on P ], 1.01 [dd, J( H, H)
3
1
31
III
13
=
3 2
7, J( H, P) = 16 Hz, 12 H, CH(CH ) on P ] ppm. C-
1
13
31
3
13
DEPT135 NMR (25 °C): δ = 28.4 [dd, J( C, P) = 42, J( C,
[
14] A. Schmidpeter, H. Rossknecht, Angew. Chem. 1969, 81, 572;
Angew. Chem. Int. Ed. Engl. 1969, 8, 614.
3
1
V
1
13
31
3
13
P) = 2 Hz, 2 C, CH
P) = 7 Hz, 2 C, CH
3
on P ], 24.3 [dd, J( C, P) = 18, J( C,
3
1
III
1
13
31
3
13
on P ], 20.0 [d, J( C, P) = 39 Hz, 1 C,
[
15] a) T. León, M. Parera, A. Roglans, A. Riera, X. Verdaguer,
Angew. Chem. 2012, 124, 7057; Angew. Chem. Int. Ed. 2012,
51, 6951; b) M. Revés, C. Ferrer, T. León, S. Doran, P. Etayo,
1
31
V
3
C of PCP], 19.0 [d, J( C, P) = 11 Hz, 4 C, CH on P ], 19.0 [d,
2
13
31
III
31
1
J( C, P) = 29 Hz, 4 C, CH
3
on P ] ppm. P{ H} NMR
Eur. J. Inorg. Chem. 2013, 2867–2876
2875
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
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[
24] The PE bond energies in Me
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1
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[
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20.
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Published Online: April 15, 2013
Eur. J. Inorg. Chem. 2013, 2867–2876
2876
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim