Probing solid iminobis(diorganophosphine chalcogenide) systems with multinuclear magnetic resonance

Article abstract of DOI:10.1139/V08-150

A ³¹P and ⁷⁷Se solid-state NMR investigation of the iminobis(diorganophosphine chalcogenide) HN(R₂PE)₂ (R = Ph, ⁱPr; E = O, S, Se) systems is presented. The NMR results are discussed in terms of the k

Full text of DOI:10.1139/V08-150

348
Probing solid iminobis(diorganophosphine
chalcogenide) systems with multinuclear magnetic
resonance1
Bryan A. Demko and Roderick E. Wasylishen
Abstract: A 31P and 77Se solid-state NMR investigation of the iminobis(diorganophosphine chalcogenide) HN(R2PE)2
(R = Ph, iPr; E = O, S, Se) systems is presented. The NMR results are discussed in terms of the known HN(R2PE)2
structures available from X-ray crystallography. The phosphorus chemical shift tensors are found to be sensitive to the
nature of the alkyl and chalcogen substituents. The nature of the R group also influences the selenium chemical shift
i
tensors of HN(R2PSe)2 (R = Ph, Pr), which are shown to be sensitive to hydrogen bonding in the dimer structure of
HN(Ph2PSe)2 and to the presence of disorder in the case of HN(iPr2PSe)2. Scalar relativistic ZORA DFT nuclear mag-
netic shielding tensor calculations were performed yielding the orientations of the corresponding chemical shift tensors.
A theoretical investigation into the effect of the E-PLP-E “torsion” angle on the phosphorus and selenium chemical
shift tensors of a truncated HN(Me2PSe)2 system indicates that the electronic effect of the alkyl group on the respective
nuclear magnetic shielding tensors are more important than the steric effect of the E-PLP-E torsion angle.
Key words: iminobis(diorganophosphine chalcogenide), solid-state NMR, 31P NMR, 77Se NMR, ZORA DFT.
Résumé : On a effectué une étude basée sur les RMN du 31P et du 77Se à l’état solide d’iminobis(chalcogénure de
i
diorganophosphine) HN(R2PE)2 (R = Ph, Pr; E = O, S, Se). On discute des résultats de la RMN en fonction de struc-
tures HN(R2PE)2 connues, disponibles à partir de la diffraction des rayons X. On a trouvé que les tenseurs du déplace-
ment chimique du phosphore sont sensibles à la nature du groupe alkyle et des substituants chalcogènes. La nature du
i
groupe R influence aussi les tenseurs du déplacement chimique du sélénium de HN(R2PSe)2 (R = Ph, Pr) et on a dé-
montré qu’ils sont aussi sensibles à la liaison hydrogène dans la structure dimère du HN(Ph2PSe)2 et à la présence de
désordre dans le cas du HN(iPr2PSe)2. On a effectué des calculs de théorie de la fonctionnelle de densité ZORA scalai-
res relativistiques du tenseur de blindage magnétique qui ont permis d’obtenir les orientations correspondantes des ten-
seurs de déplacements chimiques. Une investigation théorique de l’effet de l’angle de torsion E-PLP-E sur les tenseurs
du déplacement chimique du phosphore et du sélénium d’un système HN(Me2PSe)2 tronqué indique que l’effet électro-
nique du groupe alkyle sur les tenseurs respectifs de blindage magnétique nucléaire sont plus importants que l’effet sté-
rique de l’angle de torsion E-PLP-E.
Mots-clés : iminobis(chalcogénure de diorganophosphine), RMN à l’état solide, RMN du 31P, RMN du 77Se, calculs de
théorie de la fonctionnelle de densité ZORA.
[Traduit par la Rédaction] Demko and Wasylishen 360
Introduction
of research interest. Acetylacetonate (acac) and its β-
diketonate derivatives represent the ideological figurehead
of monoanionic bidentate coordination chemistry (1). Re-
cently, β-diketonate precursors have been utilized in the fab-
rication of metal oxide thin films (2) and other chemical
vapor deposition applications (3). Interest in related metal
chalcogenide materials has spurred the investigation of
monoanionic bidentate ligands possessing the corresponding
elements of Group 16. Some sulfur- and selenium-
containing ligands such as dialkyldichalcogenophosphates,
dialkyldichalcogenophosphinates, and dialkyldichalcogeno-
carbamates have appeared in the literature (4–6); however,
their small chalcogen–chalcogen interatomic distances result
in the formation of complexes primarily in an anisobidentate
fashion (7). The iminobis(diorganophosphine chalcogenide)
compounds, the so-called non-carbon (main group) ana-
logues of acetylacetone, offer the opportunity to vary the do-
nor chalcogen atom. Also, variation of the alkyl group in
these ligands is more easily accessible than for the organic
The coordination of monoanionic bidentate ligands with
metal and non-metal centers continues to provide a vast area
Received 13 June 2008. Accepted 25 August 2008. Published
on the NRC Research Press Web site at canjchem.nrc.ca on
21 November 2008.
This paper is dedicated to Professor Richard J. Puddephatt in
honour of his outstanding contributions to Canadian
chemistry.
B.A. Demko and R.E. Wasylishen.2 Department of
Chemistry, Gunning–Lemieux Chemistry Centre, University
of Alberta, Edmonton, AB T6G 2G2, Canada.
1This article is part of a Special Issue dedicated to Professor
R. Puddephatt.
2Corresponding author (e-mail:
roderick.wasylishen@ualberta.ca).
Can. J. Chem. 87: 348–360 (2009)
doi:10.1139/V08-150
© 2008 NRC Canada

Demko and Wasylishen
349
Scheme 1. Similarities between the structures of acetylacetone
and the iminobis(diorganophosphine chalcogenide) systems.
the appropriate chlorodiorganophosphine R2PCl (Sigma-
Aldrich) (55, 61). Briefly, R2PCl in toluene is added
dropwise to a hot toluene solution of HN(SiMe3)2 and is
maintained above 80 °C for at least two hours to remove the
chlorotrimethylsilane by-product by distillation. Oxidation to
the corresponding iminobis(diorganophosphine chalcogenide)
was achieved from the subsequent reaction with hydrogen
peroxide in an ice bath (55, 62) and via reflux with either el-
emental sulfur (55) or elemental selenium (10, 20). X-ray
crystal structures from the literature, for each of the investi-
gated iminobis(diorganophosphine chalcogenide) systems,
analogues (8). The fine-tuning available for specific metal
complexation permits comparisons between the bonding in
organic and inorganic analogues, knowledge widely sought
throughout the chemistry community (9). While not
isoelectronic, acac and dichalcogenoimidodiphosphinate sys-
tems are closely related (Scheme 1). An early example of
the Group 10 complexes of [N(Ph2PSe)2]– contained
heterocyclic MSe2P2N rings that were puckered (10), unlike
those of acetylacetonate that contain planar six-membered
rings (11, 12). This difference has been attributed to the
ability of the dichalcogenoimidodiphosphinate ligands to
form delocalized systems utilizing low lying d orbitals (10,
13, 14). The structures of these complexes are known to de-
pend on the choice of chalcogen, alkyl group, and metal (13,
15–19). Often, the complexes exhibit symmetrical coordina-
tion patterns with the donor chalcogen atoms (8, 20).
Numerous reviews of the versatile dichalcogenoimidodi-
phosphinate ligands exist in the literature (15, 21–23). In
addition to applications as single-source precursors for solid-
state metal chalcogenide materials (4–6, 20, 24–29), these
bidentate ligands have found uses in the search for stereo-
chemically active lone pairs (10, 19, 30–32), in catalysis
(33–35), and in metal extraction processes (15, 36–39), as
lanthanide shift reagents (40, 41), luminescent materials
(42), and as enzyme mimetics (43–45).
i
HN(R2PE)2 (E = O; R = Ph (50) and Pr (31), E = S; R = Ph
(50–52) and iPr (47), E = Se; R = Ph (10) and iPr (31)), have
been previously reported.
NMR experiments
Solid-state NMR investigations of powdered samples of
HN(R2PE)2]2 (E = O, S, Se; R = Ph, iPr) were obtained using
4.70 T, 7.05 T, and 11.75 T NMR spectrometers. The sam-
ples were packed in 4 mm (7.05 T and 11.75 T) and 7.5 mm
(4.70 T) o.d. zirconium oxide rotors and were placed within
probes suitable for magic angle spinning, MAS, NMR ex-
periments. A ramped amplitude cross polarization (RACP)
pulse sequence was used to acquire all spectra (63). Two-
pulse phase-modulation (TPPM) (64) and proton decoupling
fields of approximately 60 kHz were utilized. The 31P NMR
spectra were referenced with respect to 85% aq. H3PO4 by
setting the isotropic 31P NMR peak of solid (NH4)H2PO4 to
0.81 ppm (65). Selenium-77 NMR spectra were referenced
to Me2Se (l) by setting the isotropic peak of solid ammo-
nium selenate (NH4)2SeO4 to 1040.2 ppm (65, 66).
Solid-state 31P NMR experiments were performed at
Larmor frequencies of 81.0, 121.6, and 202.5 MHz, and at
spinning frequencies ranging from 3.0 to 7.2 kHz. A total of
between 64 and 128 scans were acquired per spectrum. Con-
tact times between 1.5 and 6.5 ms, and pulse delays between
600 and 840 s for HN(Ph2PE)2 systems and between 7 and
18 s for the HN(iPr2PE)2 systems were employed.
Solid-state 77Se NMR measurements were performed at
Larmor frequencies of 38.2, 57.3, and 95.4 MHz, and at
spinning frequencies ranging from 2.0 to 14.0 kHz. A total
of between 384 and 16 384 scans were acquired per spec-
trum. Contact times between 6.5 and 10.0 ms, and pulse de-
lays between 600 and 840 s for HN(Ph2PE)2 species and
between 5 and 14 s for the HN(iPr2PE)2 systems were em-
ployed.
The principal components of the respective phosphorus
and selenium chemical shift tensors, δ11 ≥ δ22 ≥ δ33, were de-
termined from the experimental spectra using the procedure
of Herzfeld and Berger (67, 68). All experimental solid-state
NMR spectra were simulated using the determined values
with the program WSOLIDS (69) to assess the quality of the
obtained parameters. This procedure results in errors of
Despite the considerable interest in the properties and chem-
istry of the complexes of dichalcogenoimidodiphosphinate
ligands, relatively little is known about the neutral
iminobis(diorganophosphine chalcogenide) HN(R2PE)2 de-
rivatives (46). Characterization of these systems has predom-
inantly been performed by X-ray crystallography (10, 31,
47–53), often accompanied by IR (31, 54–57), Raman (56,
57), and (or) solution NMR spectroscopy (10, 31, 47, 54,
58). Solid-state NMR, being potentially more informative
than solution NMR spectroscopy, would appear to be an ap-
propriate technique for characterizing the HN(R2PE)2 lig-
ands. Recently, we have demonstrated the use of solid-state
NMR spectroscopy in the characterization of the metal(II)
complexes of the [N(iPr2PSe)2]– ligand (59, 60). Herein we
present a solid-state 31P and 77Se NMR investigation of the
i
HN(R2PE)2 (E = O, S, Se; R = Ph, Pr) systems representing
the first solid-state NMR investigation of the iminobis(di-
organophosphine chalcogenides). Comparisons of the solid-
state NMR results obtained herein with those of the
M[N(iPr2PSe)2]2 complexes previously investigated are
made, where appropriate (59, 60).
0.2 ppm in the isotropic chemical shift, δiso = (1/3)(δ11
+
δ22 + δ33), and errors in the principal components of approxi-
mately 1%–3% of the span, Ω = δ11 – δ33, of the respective
chemical shift tensors. Another useful quantity for describ-
ing the appearance of chemical shift powder patterns is the
skew, κ = 3(δ22 – δiso)/Ω, where axial symmetry is described
by κ = +1 or –1 (70).
Experimental
Sample preparation
The phenyl and isopropyl variants of bis(diorgano-
phosphino)amine HN(R2P)2 were prepared via the condensa-
tion reaction between hexamethyldisilazane HN(SiMe3)2 and
© 2008 NRC Canada

350
Can. J. Chem. Vol. 87, 2009
Fig. 1. Common conformations encountered in iminobis(diorgano-
phosphine chalcogenide), HN(R2PE)2 (E = O, S, Se), systems.
DFT computations
Theoretical calculations of NMR parameters were per-
formed on isolated molecules. Cartesian coordinates of the
atoms were generated from the reported crystal structures
placing hydrogen atoms at idealized locations (rCH = 1.08 Å
i
(R = Ph), 1.09 Å (R = Pr)). Magnetic shielding tensors σ
were calculated using the NMR module (71–73) of the Am-
sterdam density functional (ADF) program package (74–78).
The Vosko–Wilk–Nusair (79) local density approximation
with the Becke88–Perdew86 (80–82) generalized gradient
approximation were used for the exchange-correlation func-
tional. Scalar relativistic corrections were carried out based
on the implementation of the zero-order regular approxima-
tion (ZORA) formalism (83–86). Triple-ζ doubly polarized
(TZ2P) Slater-type ZORA basis sets were used for all atoms
except for hydrogen, where double-ζ quality (DZ) basis
functions were utilized. The corresponding phosphorus and
selenium chemical shift tensors were obtained from the
magnetic shielding tensors using the relationship,
choice of R group and (or) chalcogen where applicable. DFT
computations are used to provide the orientations of the
phosphorus and selenium nuclear magnetic shielding ten-
sors.
Solid-state 31P NMR
The 31P NMR parameters obtained for each of the
i
HN(R2PE)2 (E = O, S, Se; R = Ph, Pr) samples investigated
σiso (ref) −σii (sample)
are given in Table 1, along with theoretical calculations of
the corresponding phosphorus chemical shift tensors. Exper-
imental solid-state 31P NMR spectra for HN(R2PO)2,
HN(R2PS)2, and HN(R2PSe)2 are given in Figs. 2, 5, and 6,
respectively.
[1]
δii (sample) =
1−σiso (ref)
where σiso(ref) is the isotropic shielding of a standard refer-
ence. The absolute shielding scale for 31P has been deter-
mined, and the value of σiso (85% aq. H3PO4) has been
established to be 328.35 ppm (87). We have previously in-
vestigated the selenium chemical shift tensors in a wide
range of selenium-containing compounds and used the value
of 1580 ppm determined therein for the isotropic reference
shielding of a neat liquid of dimethyl selenide at 23 °C (88).
i
HN(R2PO)2 (R = Ph, Pr)
For the phenyl derivative, the imidodiphosphinic acid
tautomer Ph2P(OH)NP(O)Ph2 (50) was found instead of the
initially hypothesized HN(Ph2PO)2 structure (48, 49), which
possesses an acidic N-H proton. As
a
result,
Ph2P(OH)NP(O)Ph2 has a considerably different structure
from the other iminobis(diorganophosphine chalcogenide)
systems investigated that all display acidic N-H protons.
Similar to the HN(Ph2PE)2 (E = S, Se) molecules that pos-
sess a solid-state structure in which the EPNPE backbone
adopts an anti conformation, Ph2P(OH)NP(O)Ph2 is trans
with an O-PLP-O “torsion” angle of 180° (50). However,
unique to the Ph2P(OH)NP(O)Ph2 system is a linear P-N-P
angle of 180° (50). The solid-state 31P NMR spectrum is
given, along with its simulation, in Fig. 2a. Contrary to the
single phosphorus environment expected from the crystal
structure of Ph2P(OH)NP(O)Ph2 (50), two phosphorus chem-
ical shift tensors were extracted (Table 1), which possess
isotropic chemical shifts and spans that differ by more than
20 ppm despite the two tensors possessing similar skews. As
the 31P NMR spectrum (not shown) of a chloroform solution
of Ph2P(OH)NP(O)Ph2 displays only a single peak, the solid
sample investigated, as obtained from a methylene chloride
– hexanes recrystallization, must be of a different polymorph
of Ph2P(OH)NP(O)Ph2 than the reported structure from a
crystal grown in glacial acetic acid (50).
Phosphorus chemical shift tensors from the DFT computa-
tions of a single Ph2P(OH)NP(O)Ph2 unit from the reported
crystal structure (50) (Table 1) produce comparable values
of δiso, δii, Ω, and κ with the experimentally determined pa-
rameters; however, they do not predict an equally large dif-
ference between the two respective isotropic chemical shifts.
This discrepancy is likely a result of using the geometry
from the reported crystal structure, which is not entirely rep-
resentative of the actual solid-state structure of the solid
Results and discussion
i
A common difference between the R = Ph and R = Pr
structures of the HN(R2PE)2 systems is that while the
EPNPE backbones in iminobis(diphenylphosphine chalco-
genide) species are oriented anti, the HN(iPr2PE)2 (E = O, S,
Se) molecules all possess gauche conformations (Fig. 1).
X-ray diffraction studies of each of the iminobis(diorgano-
phosphine chalcogenides) investigated here indicate that the
crystals contain one molecule in the asymmetric unit. The
reported structure for HN(Ph2PO)2 contains an inversion
center providing chemical equivalence between the two
phosphorus atoms such that only a single phosphorus chemi-
cal shift tensor is expected for this sample. The remaining
samples investigated, HN(Ph2PE)2 (E
= S, Se) and
HN(iPr2PE)2 (E = O, S, Se), do not possess any symmetry
elements within their respective molecular structures provid-
ing chemical equivalence between the two phosphorus (or
two selenium) atoms, thus two distinct phosphorus (or sele-
nium) chemical shift tensors are expected in the experimen-
tal NMR spectra. The obtained phosphorus chemical shift
tensors for the iminobis(diorganophosphine chalcogenide)
systems are presented first, followed by the results of a
solid-state 77Se NMR study on HN(R2PSe)2 (R = Ph, iPr). As
the syntheses of the phenyl-derivatized species were re-
ported prior to the isopropyl variants, the results for
HN(Ph2PE)2 will precede those for HN(iPr2PE)2. The ex-
tracted NMR parameters are discussed in terms of the
known molecular structures, highlighting the impact in the
© 2008 NRC Canada

Demko and Wasylishen
Table 1. Solid-state 31P NMR parameters for HN(R2PE)2 (E = O, S, Se; R = Ph, Pr).
351
i
1J(Se,P)iso
(Hz)
a
δiso
(ppm)
δ11
(ppm)
δ22
(ppm)
δ33
(ppm)
Ω
(ppm)
E
R
κ
8.2
28.4
19.0
24.4
52.5
57.7
62.2
68.9
59.1
69.1
54.7
57.1
75.4
76.5
89.1
90.6
102.2
108.2
48.9
52.4
98.6
101.8
88.8
91.1
129.8
130.3
129.9
130.5
79.6
109.5
85.7
13.3
38.6
35.8
51.6
101.8
89.2
124.0
123.9
122.3
124.0
77.5
–68.2
O
Ph
(Exptl.)
147.8
172.3
150.3
233.3
147.8
141.5
213.1
205.7
207.3
206.1
224.9
249.5
310.8
279.1
164.4
172.7
248.0
220.2
214.7
243.5
313.6
347.1
151.3
157.8
272.3
232.3
268.0
243.5
0.10
0.18
0.34
0.35
1.00
0.67
0.87
0.80
0.92
0.80
0.30
0.43
0.52
0.45
0.60
0.48
0.49
0.76
0.19
0.34
0.39
0.45
0.49
0.36
0.44
0.81
0.46
0.66
–62.8
–64.6
–105.9
–46.0
–28.8
–75.2
–61.4
–76.2
–61.4
–69.2
–85.5
–106.9
–83.8
–9.4
(Calcd.)
(Exptl.)
127.4
101.8
112.7
137.9
144.3
131.1
144.7
155.7
164.0
203.9
195.3
155.0
163.0
206.1
190.3
149.5
160.4
235.0
249.3
152.0
160.4
245.8
215.2
243.4
225.2
iPr
(Calcd. a)
(Calcd. b)
(Exptl.)
S
Ph
iPr
Ph
iPr
92.7
(Calcd.)
(Exptl.)
129.2
118.0
121.7
118.5
142.6
164.3
62.5
–9.7
(Calcd.)
(Exptl.)
–41.9
–29.9
–65.2
–83.1
–78.6
–97.8
0.7
Se
–720
–740
79.9
(Calcd.)
(Exptl.)
139.3
153.9
113.7
110.3
170.2
192.8
170.9
184.4
–740
–735
2.6
(Calcd. a)
(Calcd. b)
–26.5
–17.1
–24.6
–18.3
1
aFor directly bonded selenium-77 and phosphorus-31 spin pairs; signs of J(77Se,31P)iso are known to be negative for
numerous analogous systems (95, 96).
sample investigated, as well as the neglect of intermolecular
effects including potential hydrogen bonding between
Ph2P(OH)NP(O)Ph2 molecules. Additionally, the computa-
tions indicate that the phosphorus bearing the hydroxyl
group is more shielded than the P=O phosphorus in
Ph2P(OH)NP(O)Ph2. The calculated orientations of the two
phosphorus chemical shift tensors are also different, as
shown in Fig. 3a. The computed P-OH phosphorus chemical
shift tensor is oriented with δ11 perpendicular to the local
O-P-N plane, and δ33 approximately parallel to the P-N vector
with δ22 within the O-P-N plane and perpendicular to P-N.
The calculated P=O phosphorus chemical shift tensor places
δ11 perpendicular to the local O-P-N plane, while in contrast
δ33 is oriented nearly parallel to the P-O vector with δ22
within the O-P-N plane and perpendicular to P-O. The orien-
tation of the P=O phosphorus chemical shift tensor is similar
to what is consistently found for tris-organophosphine ox-
ides (89).
One of the largest differences between HN(iPr2PO)2 and
Ph2P(OH)NP(O)Ph2 is that iminobis(diisopropylphosphine
oxide) possesses an acidic N-H proton leading to a P-N-P
angle of 130° (31). The gauche conformation of HN(iPr2PO)2,
reflected in a 52° O-PLP-O “torsion” angle, yields a chain-
like arrangement of HN(iPr2PO)2 units in its solid state
structure (31). The X-ray structure of HN(iPr2PO)2 displays
some disorder in that one methyl carbon on one isopropyl
group possesses two 50% occupancy sites (31). There exists
three spinning sideband manifolds corresponding to three
discernable signals in the 31P MAS spectrum of HN(iPr2PO)2
given in Fig. 2b; however, as one of the three signals is sig-
nificantly less intense than the other two it is considered to
be a minor impurity in the sample rather than resulting from
disorder in the structure. The impurity can be readily identi-
fied in Fig. 2b by comparison of the experimental with the
simulated spectrum. The two isotropic phosphorus chemical
shifts obtained (Table 1) are in good agreement with the
31P NMR value from a chloroform solution of HN(iPr2PO)2,
i.e., 55.5 ppm (31). The phosphorus environments are
deshielded with respect to those of Ph2P(OH)NP(O)Ph2 and
possess slightly smaller spans and larger positive skews. The
steric or electronic source of this difference will be dis-
cussed later. One phosphorus environment indicates an axi-
ally symmetric chemical shift tensor despite there being no
symmetry reasons for attaining this axial symmetry.
Methods for obtaining accurate principal components of the
chemical shift tensor from spectra of MAS samples are
known to have the greatest difficulty with axially or near ax-
ially symmetric species (90).
Calculated phosphorus chemical shift tensors were ob-
tained for both of the 50% occupancy structures (31), la-
beled “a” and “b” in the Table 1. Both phosphorus chemical
shift tensors computed for each of the two structures are in
© 2008 NRC Canada

352
Can. J. Chem. Vol. 87, 2009
Fig. 2. (a) RACP MAS 31P NMR spectrum (lower trace) for Ph2P(OH)NP(O)Ph2 and its simulation (upper trace). Experimental
conditions: 11.75 T, 64 scans, MAS at 3.0 kHz, 10 Hz of line broadening, 3.0 ms contact time, and 900 s recycle delay. (b) RACP MAS
31P NMR spectrum (lower trace) for HN(iPr2PO)2 and its simulation (upper trace). Experimental conditions: 11.75 T, 128 scans, MAS
at 3.0 kHz, 10 Hz of line broadening, 3.0 ms contact time, and 18 s recycle delay. The isotropic peaks are marked with an asterisk (*).
reasonable agreement with the experimental values. The val-
ues of δii(calcd.) are quite similar for structures “a” and “b”,
suggesting that the presence of disorder in the methyl group
does not significantly affect the phosphorus shielding in
HN(iPr2PO)2. This is consistent with the solid-state 31P
NMR spectrum (Fig. 2b) where no discernable difference in
the obtained line widths or line shapes of the two phospho-
rus environments was detected. In contrast to the calculated
orientations of the phosphorus chemical shift tensors in
Ph2P(OH)NP(O)Ph2, all phosphorus tensors for HN(iPr2PO)2
are oriented similarly (Fig. 3b). The computations place δ33
approximately along the O-P vector, and δ22 perpendicular to
the local O-P-N plane, with δ11 perpendicular to O-P within
the O-P-N plane.
phosphorus chemical shift tensors of HN(Ph2PS)2 describe
phosphorus nuclei that are more deshielded, possess larger
spans, and have slightly more positive values of κ than those
obtained for Ph2P(OH)NP(O)Ph2.
The DFT computations were performed on a dimer of
HN(Ph2PS)2 units. The calculated principal components of
the respective phosphorus chemical shift tensors slightly
overestimate the corresponding experimental values. The
orientations of the two calculated phosphorus chemical shift
tensors (Fig. 3c) are nearly identical and most closely resem-
ble those calculated for the P=O phosphorus of
Ph2P(OH)NP(O)Ph2, with δ33 approximately parallel to the
P-S vector, δ11 perpendicular to the local S-P-N plane, and
δ22 nearly within the S-P-N plane perpendicular to P-S.
These orientations are consistent with those obtained for
tris-organophosphine sulfide systems (89) and similar to
those found in tetramethyldiphosphine disulfide (91).
Similar to that of HN(iPr2PO)2, the structure of
HN(iPr2PS)2 contains a 132° P-N-P angle; however, the
S-PLP-S torsion angle is slightly larger at 79° and the X-ray
structure reports no evidence of disorder (47). The solid-
state 31P NMR spectrum of HN(iPr2PS)2 is given in Fig. 5b.
The isotropic chemical shifts for the two phosphorus envi-
ronments are in good agreement with the value of 91.2 ppm
reported for HN(iPr2PS)2 in CDCl3 (47). Similar to the
chemical shift tensors describing the phosphorus shielding
of HN(Ph2PS)2 and Ph2P(OH)NP(O)Ph2, the two phosphorus
i
HN(R2PS)2 (R = Ph, Pr)
The anti conformation of HN(Ph2PS)2, with a S-PLP-S
torsion angle of 156° is similar to that of
Ph2P(OH)NP(O)Ph2, while the P-N-P angle of 133° is con-
sistent with a PNP backbone that possesses a protonated ni-
trogen (50–52). The solid state structure consists of two
HN(Ph2PS)2 molecules hydrogen bonded to form dimer
pairs (Fig. 4) (50–52). The 31P NMR parameters obtained
from the RACP MAS spectrum for HN(Ph2PS)2 (Fig. 5a)
are given in Table 1. The isotropic chemical shifts obtained
are in good agreement with the solution 31P NMR values of
55.1 ppm in THF (54) and 58.2 ppm in CDCl3 (58). The
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353
Fig. 3. Calculated phosphorus chemical shift tensor orientations for (a) Ph2P(OH)NP(O)Ph2, (b) HN(iPr2PO)2, (c) HN(Ph2PS)2,
(d) HN(iPr2PS)2, (e) HN(Ph2PSe)2, and (f) HN(iPr2PSe)2.
Fig. 4. Dimer structure of HN(Ph2PE)2 (E = S, Se).
environments of HN(iPr2PS)2 are more deshielded and pos-
sess larger spans than those for HN(iPr2PO)2. Solution 31P
i
NMR for the mixed chalcogen system Pr2P(O)NHP(S)iPr2
displays a comparable difference in the values of δiso(31P),
54.8 and 90.9 ppm (31). Additionally, as with the E = O
compounds, the phosphorus sites in HN(iPr2PS)2 are more
deshielded and have larger positive skews than the phenyl
derivative.
Calculated phosphorus chemical shift tensors for
HN(iPr2PS)2 are given in Table 1. The computed values of
δiso, δii, Ω, and κ are in reasonable agreement with the exper-
imentally obtained parameters. As observed with the calcu-
lated orientation of the tensors in HN(iPr2PO)2, the two
phosphorus chemical shift tensors for HN(iPr2PS)2 (Fig. 3d)
are approximately identical and place δ33 nearly parallel to
the E-P vector; however, the directions of δ11 and δ22 are es-
sentially reversed in HN(iPr2PS)2 with respect to
HN(iPr2PO)2, with δ11 perpendicular to the local S-P-N plane
and δ22 within the S-P-N plane perpendicular to S-P.
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Can. J. Chem. Vol. 87, 2009
Fig. 5. (a) RACP MAS 31P NMR spectrum (lower trace) for HN(Ph2PS)2 and its simulation (upper trace). Experimental conditions:
11.75 T, 64 scans, MAS at 3.0 kHz, 10 Hz of line broadening, 3.0 ms contact time, and 900 s recycle delay. (b) RACP MAS 31P
NMR spectrum (lower trace) for HN(iPr2PS)2 and its simulation (upper trace). Experimental conditions: 11.75 T, 128 scans, MAS at
3.0 kHz, 5 Hz of line broadening, 3.0 ms contact time, and 9 s recycle delay. The isotropic peaks are marked with an asterisk (*).
i
Se-P-N plane perpendicular to P-Se. This orientation is simi-
lar to that found for tris-organophosphine selenides (89).
HN(R2PSe)2 (R = Ph, Pr)
Isomorphous with HN(Ph2PS)2, the dimer structure of
HN(Ph2PSe)2 possesses an anti conformation with a Se-PLP-Se
torsion angle of 154° and a P-N-P angle of 132° (10). The
phosphorus chemical shift parameters, along with an estima-
tion of the one-bond selenium–phosphorus indirect spin–spin
The structure of HN(iPr2PSe)2 more closely resembles
that of HN(iPr2PS)2 with an 80° Se-PLP-Se torsion angle
and a P-N-P angle of 131° (31). However, similar to the
structure of HN(iPr2PO)2, the selenium analogue was refined
where the location of one methyl carbon on one isopropyl
group contained two 50% occupancy locations (31). The iso-
tropic chemical shifts and 1J(77Se,31P)iso values extracted
(Table 1) from the simulation of the solid-state 31P NMR
spectrum of HN(iPr2PSe)2 (Fig. 6b) are in good agreement
with those from a chloroform solution 31P NMR study,
89.5 ppm and (–)757 Hz (31). Similar to the solid-state
31P NMR spectrum of HN(iPr2PO)2 (Fig. 2b), no evidence
for the disorder in the methyl group was detected in the
corresponding spectrum for iminobis(diisopropylphosphine
selenide). As with the phosphorus chemical shift tensors of
HN(Ph2PE)2 (E = S, Se), the two tensors for HN(iPr2PSe)2
are comparable to those found for HN(iPr2PS)2 (Table 1).
The isotropic phosphorus chemical shifts of the mixed
coupling constant J(77Se,31P)iso from the MAS 31P NMR
1
spectrum (Fig. 6a) are reported in Table 1. The values of
δiso(31P) and J(77Se,31P)iso obtained are in good agreement
1
with those from 31P NMR of methylene chloride and chloro-
form solutions of HN(Ph2PSe)2, 53.0 ppm and (–)793 Hz
(10), and 53.2 ppm (58), respectively. The principal compo-
nents of the phosphorus chemical shift tensors are very simi-
lar to those found for HN(Ph2PS)2 (Table 1) indicating that
the impact of exchanging oxygen for sulfur in HN(Ph2PE)2
is larger than exchanging sulfur for selenium.
The phosphorus chemical shift tensors were calculated for
a dimer of HN(Ph2PSe)2 molecules (10). The calculations
overestimate the values of δiso and Ω, indicating that scalar
relativistic effects may not be sufficient to accurately de-
scribe the shielding environment for HN(Ph2PSe)2, and that
spin–orbit relativistic effects may be important. Similar to
those of HN(Ph2PS)2, the calculated orientations of the
phosphorus chemical shift tensors in HN(Ph2PSe)2 (Fig. 3e)
place δ11 perpendicular to the local Se-P-N plane, δ33
approximately along the P-Se vector, and δ22 within the
i
chalcogen compound Pr2P(S)NHP(Se)iPr2 from a chloro-
form solution 31P NMR study are also very similar at 89.2
and 92.1ppm (31).
Phosphorus chemical shift tensors were calculated for
both of the 50% occupancy structures (31), labeled “a” and
“b” in Table 1. The scalar relativistic calculated phosphorus
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Demko and Wasylishen
355
Fig. 6. (a) RACP MAS 31P NMR spectrum (lower trace) for HN(Ph2PSe)2 and its simulation (upper trace). Experimental conditions:
11.75 T, 64 scans, MAS at 3.0 kHz, 10 Hz of line broadening, 3.0 ms contact time, and 900 s recycle delay. (b) RACP MAS 31P NMR
spectrum (lower trace) for HN(iPr2PSe)2 and its simulation (upper trace). Experimental conditions: 11.75 T, 128 scans, MAS at
3.0 kHz, 10 Hz of line broadening, 3.0 ms contact time, and 18 s recycle delay. The isotropic peaks are marked with an asterisk (*).
chemical shift tensors for HN(iPr2PSe)2, as with those for
HN(Ph2PSe)2, overestimate the experimental values. Analo-
gous to those for HN(iPr2PO)2, the calculated phosphorus
chemical shift tensors for HN(iPr2PSe)2 structures “a” and
“b” are nearly identical and suggest that evidence for the
disorder is unlikely to come from the solid-state 31P NMR
spectrum. As with the calculated orientations of the phos-
phorus chemical shift tensors in HN(iPr2PO)2, all four
tensors for iminobis(diisopropylphosphine selenide) are
identical, as shown in Fig. 3f. They are all oriented similarly
to those of HN(iPr2PS)2 with δ33 near the P-Se vector, δ11
perpendicular to the local Se-P-N plane, and δ22 within the
Se-P-N plane perpendicular to the P-Se vector.
sistent with the less symmetric environment of selenium in
the iminobis(diorganophosphine chalcogenide) systems and
the larger chemical shift range of selenium with respect to
that of phosphorus (92, 93).
The dimer structure of HN(Ph2PSe)2 (Fig. 4) was used to
calculate the selenium chemical shift tensors. The computed
principal components are in good agreement with the experi-
mental values, particularly in the difference in shielding be-
tween the two chemical shift tensors. The calculations
indicate that the selenium that participates in hydrogen
bonding between the two HN(Ph2PSe)2 molecules is less
shielded than the selenium that is not involved in hydrogen
bonding. The calculated orientations of the two selenium
chemical shift tensors are also different (Fig. 8a). For the se-
lenium involved in hydrogen bonding between the dimers,
δ33 is nearly parallel to the Se-P vector, δ11 is perpendicular
to the local Se-P-N plane, and δ22 is within the Se-P-N plane
perpendicular to Se-P. The selenium that is not involved in
hydrogen bonding possesses a chemical shift tensor that ori-
ents δ22 approximately along Se-P, with δ11 perpendicular to
the local Se-P-N plane, and δ33 within the Se-P-N plane per-
pendicular to Se-P.
Solid-state 77Se NMR
The solid-state 77Se NMR spectrum for HN(Ph2PSe)2 is
given in Fig. 7a and the 77Se NMR parameters extracted
from its simulation are reported in Table 2. The values of
1J(77Se,31P)iso obtained are in agreement with those from
solution 31P NMR (10) and with our solid-state 31P NMR
values (Table 1) above. Similar to the large difference in
isotropic phosphorus chemical shifts observed for
Ph2P(OH)NP(O)Ph2, there is a significant difference be-
tween the two values of δiso(Se) in HN(Ph2PSe)2. The spans
of the selenium chemical shift tensors are both larger than
any of the phosphorus chemical shift tensors, which is con-
The 77Se NMR parameters obtained from the solid-state
77Se NMR spectrum for HN(iPr2PSe)2 (Fig. 7b) are given in
1
Table 2. The two J(77Se,31P)iso obtained are in good agree-
ment with the reported values from solution (31) and solid-
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Can. J. Chem. Vol. 87, 2009
Fig. 7. (a) RACP MAS 77Se NMR spectrum (lower trace) for HN(Ph2PSe)2 and its simulation (upper trace). Experimental conditions:
11.75 T, 384 scans, MAS at 3.0 kHz, 50 Hz of line broadening, 10.0 ms contact time, and 840 s recycle delay. (b) RACP MAS 77Se
NMR spectrum (lower trace) for HN(iPr2PSe)2 and its simulation (upper trace). Experimental conditions: 11.75 T, 5288 scans, MAS at
6.0 kHz, 50 Hz of line broadening, 6.5 ms contact time, and 14 s recycle delay. The isotropic peaks are marked with an asterisk (*).
state (above) 31P NMR. Unlike those for HN(Ph2PSe)2,
the two isotropic selenium chemical shifts for iminobis-
(diisopropylphosphine selenide) are more shielded and sig-
nificantly closer together. In contrast to the solid-state 31P
NMR spectra for HN(iPr2PE)2 (E = O, Se), the solid-state
77Se NMR spectrum for HN(iPr2PSe)2 appears to be sensi-
tive to the disorder of the methyl group in the structure (31).
Figure 9 displays the isotropic region of the solid-state 77Se
Se-P-N plane; however, the P-Se vector nearly bisects the
δ22-Se-δ33 angle within the Se-P-N plane.
Iminobis(diorganophosphine selenide) vs.
diselenoimidodiphosphinato complexes
Upon comparison with the phosphorus and selenium
chemical shift tensors of the M[N(iPr2PSe)2]2 complexes
previously investigated (59, 60), there are some consistent
changes in the calculated orientations of the phosphorus and
selenium chemical shift tensors of HN(iPr2PSe)2 upon
deprotonation and complexation with a cationic center. The
phosphorus chemical shift tensors in the diselenoimido-
diphosphinato complexes are all oriented similarly, with δ33
nearly parallel to the P-N bond vector, δ11 perpendicular to
the local Se-P-N vector, and δ22 within the Se-P-N plane per-
pendicular to the P-N vector (59, 60). This is in contrast to
the majority of the phosphorus chemical shift tensors where
δ33 is nearly parallel to the P-E vector, and most closely re-
sembles the orientation of the phosphorus chemical shift ten-
sor for the P-OH environment in Ph2P(OH)NP(O)Ph2. The
change in the orientation of the selenium chemical shift ten-
sor upon complexation is not quite as predictable. When
[N(iPr2PSe)2]– is coordinated with a Group 10 (Pd or Pt) or
12 (Zn, Cd or Hg) metal center, the orientation of the sele-
nium chemical shift tensor remains essentially identical to
that found in HN(iPr2PSe)2 with δ33 nearly parallel to the
P-Se vector, δ11 perpendicular to the local Se-P-N plane, and
i
NMR spectra for HN(R2PSe)2 (R = Ph, Pr), where one of
the two J-coupled isotropic peaks for HN(iPr2PSe)2 is visi-
bly broader than the other.
The two calculated selenium chemical shift tensors for
each of the two 50% occupancy structures also suggest that
the impact of the disorder of the methyl group should be
more pronounced in the solid-state 77Se NMR spectrum;
however, the calculations indicate that both selenium envi-
ronments should be influenced by the disorder. The calcula-
tions predict that the selenium environment that is furthest
from the methyl group should be affected more than the
proximal selenium. The calculated orientations of the sele-
nium chemical shift tensors (Fig. 8b) are identical for struc-
tures “a” and “b”, yet distinct. The chemical shift tensor for
the selenium distal to the methyl disorder is oriented such
that δ33 is nearly along the Se-P vector, δ11 is perpendicular
to the local Se-P-N plane, while δ22 lies within the Se-P-N
plane perpendicular to Se-P. The selenium nearest the
methyl disorder possesses a calculated chemical shift tensor
that also places δ11 approximately perpendicular to the local
δ
22 perpendicular to the P-Se vector (59, 60). However, when
© 2008 NRC Canada

Demko and Wasylishen
Table 2. Solid-state 77Se NMR parameters for HN(R2PSe)2 (R = Ph, Pr).
357
i
a
δiso
(ppm)
δ11
(ppm)
δ22
(ppm)
δ33
(ppm)
Ω
(ppm)
1J(Se,P)iso
(Hz)
R
κ
–41
79
–30
Ph
(Exptl.)
–184
–101
–201
–115
–355
–322
–495
–436
–518
–465
–219
–146
–248
–133
–419
–352
–609
–512
–608
–528
–291
–236
–325
–331
–511
–435
–735
–575
–638
–603
250
317
295
408
376
256
595
353
331
337
–0.42
–0.43
–0.48
–0.13
–0.51
–0.36
–0.58
–0.64
–0.82
–0.55
–800
–740
(Calcd.)
(Exptl.)
97
iPr
–135
–179
–140
–222
–307
–265
–760
–720
(Calcd. a)
(Calcd. b)
1
aFor directly bonded selenium-77 and phosphorus-31 spin pairs; signs of J(77Se,31P)iso are known to be negative for
numerous analogous systems (95, 96).
Fig. 9. Isotropic region of the 77Se NMR spectrum for
Fig. 8. Calculated orientations of the selenium chemical shift
(a) HN(Ph2PSe)2 and (b) HN(iPr2PSe)2 (lower traces) and their
tensors for (a) HN(Ph2PSe)2 and (b) HN(iPr2PSe)2.
simulations (upper traces).
anti E-PLP-E torsion angles, are all more shielded than their
HN(iPr2PE)2 counterparts that have gauche torsion angles.
Conversely, in Table 2 the selenium nuclei of HN(Ph2PSe)2
are both less shielded than those of HN(iPr2PSe)2. The con-
sistent differences observed in the isotropic chemical shifts
between the phenyl and isopropyl variants of HN(R2PE)2
(E = O, S, Se) are likely to arise from a combination of the
electronic effects of the chosen R group and the common
steric differences between the structures. To probe the nature
of these differences, nuclear magnetic shielding calculations
were performed on a truncated system, HN(Me2PSe)2. The
HN(Me2PSe)2 structure was achieved by replacing the
isopropyl groups of one of the two 50% occupancy struc-
tures of HN(iPr2PSe)2 with methyl groups. Figure 10 dis-
plays the effect of rotation about the E-PLP-E torsion angle
from an eclipsed orientation of 0° to a trans conformation of
180° in 15° increments. For both the computed phosphorus
coordinated to a Group 16 (Se or Te) center, the orientation
of the selenium chemical is significantly different in that δ33
is directed nearly parallel to the Se-Se or Te-Se vector, δ11
nearly parallel to the Se-P vector, and δ22 perpendicular to
the Se-Se-P/Te-Se-P plane (60).
The influence of the E-PLP-E torsion angle on 31P and
77Se NMR parameters
From Table 1, it is clear that the phosphorus environments
in the HN(Ph2PE)2 (E = O, S, Se) systems, which all possess
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358
Can. J. Chem. Vol. 87, 2009
Fig. 10. Effect of rotation about the E-PþP-E torsion angle for
HN(Me2PSe)2 on (a) δiso(31P) and (b) δiso(77Se).
of the HN(Ph2PE)2 (E = O, S, Se) systems are all more
shielded, with larger spans and smaller skews than the
corresponding
HN(iPr2PE)2
systems.
Aside
from
Ph2P(OH)NP(O)Ph2, the calculated orientations of the two
phosphorus chemical shift tensors in each HN(R2PE)2 sys-
tem are essentially identical with δ33 oriented nearly parallel
to the P-E vector as expected from tris-organophosphine
chalcogenide systems (89). The experimental and theoretical
selenium chemical shift tensors in HN(Ph2PSe)2 were found
to be sensitive to the presence of hydrogen bonding in its
solid state dimer structure, while those of HN(iPr2PSe)2 were
susceptible to the disorder found in its structure. The impact
of the conformation of the EPNPE backbone via the E-PLP-E
torsion angle was studied by DFT nuclear magnetic shield-
ing calculations on a truncated system, HN(Me2PSe)2. The
steric impact of the Se-PLP-Se angle on the computed phos-
phorus and selenium isotropic chemical shifts was found to
have the opposite effect to what was observed experimen-
tally, suggesting that the choice of phenyl or isopropyl group
is more important than the conformational contributions to
the phosphorus and selenium shielding in these systems.
Finally, this study further demonstrates the feasibility of
the measurement of phosphorus and selenium chemical shift
tensors for these important ligands. Furthermore, the sensi-
tivity of these tensors to subtle structural effects is apparent.
Acknowledgements
We thank the Natural Sciences and Engineering Research
Council of Canada, the Alberta Ingenuity Fund, and the
University of Alberta for research grants and scholarships.
REW is a Canada Research Chair in Physical Chemistry at
the University of Alberta. The authors wish to thank
Dr. Devin Sears for use of his computational resources.
and selenium chemical shifts, the calculations predict the op-
posite effect to what was observed experimentally; that is,
the anti structures of HN(Me2PSe)2 possess less shielded
phosphorus and more shielded selenium environments than
any of the gauche structures. The outcome of these calcula-
tions suggest that the electronic effect of the chosen R group
dominates the impact of the E-PLP-E torsion angle, which
is supported by the solution 31P NMR reported for the mixed
alkyl system Ph2P(S)NHP(S)iPr2 (94). The isotropic phos-
phorus chemical shifts of Ph2P(S)NHP(S)iPr2, 100.0 and
51.5 ppm, display an even larger separation than those found
between the phenyl and isopropyl compounds studied
herein, HN(R2PE)2 (E = O, S, Se) (Table 1). Rotation of the
S-PLP-S angle in solution may effectively average the
conformational impact on the phosphorus chemical shift
present in the solid state. Thus, the electronic effect of R
groups on the phosphorus shielding is not opposed to the
same extent by the conformation of the EPNPE backbone
and the isotropic phosphorus chemical shifts are found to be
further apart.
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