Heavier alkaline earth metal complexes with phosphinoselenoic amides: Evidence of direct M-Se contact (M = Ca, Sr, Ba)

Article abstract of DOI:10.1039/c2dt32339g

We report here a series of heavier alkaline earth metal complexes with a phosphinoselenoic amide ligand using two synthetic routes. In the first route, the heavier alkaline earth metal bis(trimethylsilyl)amides [M{N(SiMe ₃)₂}₂(THF)_n] (M = Ca, Sr, Ba) were treated with phosphinoselenoic amine [Ph₂P(Se)NH(CHPh₂)] (3), prepared by the treatment of bulky phosphinamines [Ph ₂PNH(CHPh₂)] (1) with elemental selenium in THF, and afforded homoleptic alkaline earth metal complexes of composition [M(THF) ₂{Ph₂P(Se)N(CHPh₂)}₂] (M = Ca (7), Sr (8), Ba (9)). The metal complexes 7-9 can also be obtained via salt metathesis route where the alkali metal phosphinoselenoic amides of composition [{(THF)₂M'Ph₂P(Se)N(CHPh₂)}₂] (M' = Na (5) and K (6)) were reacted with respective metal diiodides in THF at ambient temperature. The solid state structures of the alkali metal complexes 5-6 and alkaline earth metal complexes 7-9 were established by single crystal X-ray diffraction analysis. In the solid state, alkali metal complexes 5 and 6 are dimeric and form a poly-metallacyclic structural motif. In contrast, complexes 7-9 are monomeric and a direct metal-selenium bond is observed in each case.

Full text of DOI:10.1039/c2dt32339g

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Heavier alkaline earth metal complexes with
phosphinoselenoic amides: evidence of direct
Cite this: Dalton Trans., 2013, 42, 4947
M–Se contact (M = Ca, Sr, Ba)†
Ravi K. Kottalanka,a Kishor Naktode,a Srinivas Anga,a Hari Pada Nayekb and
Tarun K. Panda*a
We report here a series of heavier alkaline earth metal complexes with a phosphinoselenoic amide
ligand using two synthetic routes. In the first route, the heavier alkaline earth metal bis(trimethylsilyl)-
amides [M{N(SiMe3)2}2(THF)n] (M = Ca, Sr, Ba) were treated with phosphinoselenoic amine [Ph2P(Se)NH-
(CHPh2)] (3), prepared by the treatment of bulky phosphinamines [Ph2PNH(CHPh2)] (1) with elemental
selenium in THF, and afforded homoleptic alkaline earth metal complexes of composition [M(THF)2{Ph2P-
(Se)N(CHPh2)}2] (M = Ca (7), Sr (8), Ba (9)). The metal complexes 7–9 can also be obtained via salt meta-
thesis route where the alkali metal phosphinoselenoic amides of composition [{(THF)2M’Ph2P(Se)N-
(CHPh2)}2] (M’ = Na (5) and K (6)) were reacted with respective metal diiodides in THF at ambient temp-
erature. The solid state structures of the alkali metal complexes 5–6 and alkaline earth metal complexes
7–9 were established by single crystal X-ray diffraction analysis. In the solid state, alkali metal complexes 5
and 6 are dimeric and form a poly-metallacyclic structural motif. In contrast, complexes 7–9 are mono-
meric and a direct metal–selenium bond is observed in each case.
Received 4th October 2012,
Accepted 20th December 2012
DOI: 10.1039/c2dt32339g
www.rsc.org/dalton
aminotroponiminates,7 β-diketiminates,8 iminopyrroles,9 and
Introduction
1,4-diaza-1,3-butadiene,10 have been introduced to prepare
Homoleptic and heteroleptic alkaline earth metal complexes well-defined alkaline earth metal complexes revealing that the
are attractive to organometallic chemists because of their oxo- catalytic activity and selectivity of the alkaline earth metal
philic and electropositive nature compare to those of early complexes can be controlled via the well-defined nitrogen-
d-transition metals.1 The alkaline earth metal compounds based ligand architecture.
have recently been employed in various catalytic applications
Another important application of alkaline earth metal chalco-
for ring-opening polymerization of various cyclic esters,2,3 genolates is in high temperature superconductors and ferro-
polymerization of styrene and dienes,4 and hydroamination electrics. In particular, alkaline earth metal oxide compounds
and hydrophosphination reactions of alkenes and alkynes.5 are used as suitable precursors.11 Much less attention has
Determining the structure and reactivity of alkaline earth been paid to the alkaline earth metal thiolates and selenates,
metal species is an important step toward the design and although many heavier chalcogenates are known as potential
development of efficient catalysts; however, full realization of dopants for chalcogen-based semiconductors.12 Chelating
the catalytic potential of these elements still requires substan- ligands having selenium as the donor atom to stabilize the
tial advances in understanding their basic coordination heavier alkaline earth metal complexes are rare. Over the last
and organometallic chemistry. To stabilize these extremely few years very few calcium selenides have been reported, such
oxophilic and electropositive metals, a wide variety of nitro- as [(TMEDA)2Ca(SeSi(SiMe3)3)],13 but to date only the solid-
gen-based ancillary ligands, such as tris(pyrazolyl)borates,6 state structure of [(THF)4Ca(SeMes′)2]14 and [(THF)2Ca{(PyCH)-
(Se)PPh2}2]15 have been reported. Full structural characteriz-
ation of strontium selenides is even scarcer.16 Complexes
aDepartment of Chemistry, Indian Institute of Technology Hyderabad, Ordnance
Factory Estate, Yeddumailaram 502205, Andhra Pradesh, India.
having a barium–selenium bond are limited as the structurally
authenticated examples are mostly restricted for the various
sulfur derivatives [{(H2O)2Ba(tmtH2)2}n] (tmt = 2,4,6-trimer-
captotriazine, S3C3N3),17 [([18]crown-6)Ba(hmpa)SMes*][SMes*]
(Mes* = 2,4,6-tBu3C6H2),18 [Ba(hmpa)3{NaPhNNNNC(S)}2],19
E-mail: tpanda@iith.ac.in; Fax: +91 (40)2301 6032; Tel: +91 (40)2301 6036
bDepartment of Applied Chemistry, Indian School of Mines, Dhanbad,
826004 Jharkhand, India
†CCDC reference numbers 903850–903856. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c2dt32339g
[Ba(hmpa)3(C(vS)NOPh2)]20 and
a
few more examples
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Dalton Transactions
including [Ba(SCMe3)2],21 [Ba(tmeda)2-(SeSi(SiMe3)3)2]22 are
reported but no structural data are available. Ruhlandt-Senge
and coworkers reported barium selenoates like [Ba(THF)4-
(SeMes*)2], [([18]crown-6)Ba(hmpa)2(SMes*)2], [{Ba(Py)3(THF)-
(SeTrip)2}2] (Trip
= 2,4,6-iPr3C6H2), and [Ba([18]-crown-6)-
(SeTrip)2],23 however the vast potential of this field of
chemistry is still to be developed.
Our work is focused towards the exploration of synthetic
methodologies allowing for a facile, clean, and high-yield pro-
duction of the required molecules and determination of the
molecular structure and function. In our on-going project we
have synthesized N-(diphenylphosphino)-2,6-dimethylaniline
[Ph2PNH(2,6-Me2C6H3)] and their chalcogenides [Ph2P(O)NH-
(2,6-Me2C6H3)] and [Ph2P(S)NH(2,6-Me2C6H3)]24 and their
complexes with alkali metals. Recently we also reported a
number of alkali metal poly-cyclic compounds using various
phosphinamine chalcogenide ligands.25 Now we want to intro-
duce new bulky seleno-phosphinamines [Ph2P(Se)NH(CHPh2)] (3)
and [Ph2P(Se)NH(CPh3)] (4) derived from the bulky phosphin-
amines [Ph2PNH(CHPh2)] (1) and [Ph2PNH(CPh3)] (2) respect-
ively with elemental selenium, having (Se,P,N)-chelating
coordination sites, into alkaline earth metal chemistry. This
unique ligand is potentially capable of coordinating through
hard nitrogen and phosphorus donor atoms along with the
soft selenium donor atom. Thus, by deprotonation reactions of
the amine group present in these ligands, the neutral ligands
can be converted to monoanionic ligands which can poten-
tially form complexes with heavier alkaline earth metals via
coordination of three donor atoms (N, P and Se). The work
will enable us to better understand alkaline-earth-metal–
selenium bond strengths and characteristics, and provide
important information on the association and aggregation
behaviour depending on selenium atoms, ligands and
donors.
Scheme 1 Synthesis of phosphinoselenoic amines 3 and 4.
Fig. 1 Solid-state structure of compound 3 (a) and 4 (b); ellipsoids are drawn
to encompass 30% probability. Selected bond lengths [Å] and bond angles [°]:
3: P1–Se1 2.1086(12), P1–N1 1.642(4), P1–C14 1.804(4), P1–C20 1.812(4),
N1–C1 1.459(6), C1–C2 1.543(5), C1–C8 1.541(6), Se1–P1–N1 113.75(14),
P1–N1–C1 124.1(3), C14–P1–C20 104.16(19), C20–P1–Se1 111.19(14),
C14–P1–Se1 114.48(14); 4: P1–N1 1.664(2), P1–Se1(1) 2.1166(8), P1–C20
1.826(3), P1–C26 1.825(3), N1–C1 1.496(4), C1–C2 1.541(4), C1–C14 1.540(4),
C1–C8 1.547(4), P1–N1–C1 129.4(2), N1–P1–Se1 119.90(10), Se1–P1–C20
111.13(11), Se1–P1–C26 112.96(11).
techniques and the solid-state structures were established by
single crystal X-ray diffraction analysis.
In the FT-IR spectrum of compounds 3 and 4, strong
absorptions at 568 cm−1 and 599 cm−1, respectively, are
observed that can be assigned as characteristic PvSe bond
stretchings and are comparable with the reported values
In this context, the selenium-containing heavier alka-
line earth metal complexes [M(THF)2{Ph2P(Se)N(CHPh2)}2]
(M = Ca (7), Sr (8), Ba (9)) are presented, which can be prepared
in good yield and high purity by two synthetic routes. Thus,
the heavier alkaline earth metal complexes reported herein,
[M(THF)2{Ph2P(Se)N(CHPh2)}2] (M = Ca (7), Sr (8), Ba (9)), are
examples of a rare class of complexes with a direct selenium–
alkaline earth metal contact. The full accounts of two synthetic
routes and the solid state structures of all the complexes will
be presented.
555 cm−1 26
The characteristic signal of the methine proton
.
1
(δ 5.62–5.68 ppm) in the H NMR spectrum of compound 3 is
slightly downfield shifted compare to free phosphinamine 1
(δ = 5.26–5.37 ppm). 31P{1H} NMR spectra is more informative
as the compound 3 shows a signal at 58.0 ppm and compound
4 shows a signal at 60.3 ppm, which are slightly downfield
shifted from those of compounds 1 (35.2 ppm) and 2
(26.3 ppm) upon addition of selenium atom to phosphorus
atom.
In the solid state structures, both compounds 3 and 4 crys-
tallize in the monoclinic space group P21/c, having four inde-
pendent molecules along with one THF molecule in the unit
cell (Fig. 1). The details of the structural parameters are given
in Table 1. The P–Se bond distances (2.1086(12) Å for 3 and
2.1166(8) Å for 4) are almost the same and in good agreement
with our previously reported14 values 2.1019(8) Å for [Ph2P(Se)-
NH(2,6-Me2C6H3)], and can be considered as phosphorus–
selenium double bond. P1–N1 bond distances (1.642(4) Å for 3
and 1.664(2) Å for 4) and C1–N1 distances (1.459(6) for 3 and
1.496(4) for 4) are also similar to those of phosphinamine
Results and discussion
Ligands
The phosphinoselenoic amines [Ph2P(Se)NH(CHPh2)] (3) and
[Ph2P(Se)NH(CPh3)] (4) were prepared in quantitative yield by
the treatment of the respective phosphinamines, [Ph2PNH-
(CHPh2)] (1) and [Ph2PNH(CPh3)] (2), respectively, with excess
elemental selenium in 1 : 1.2 molar ratio at ambient tempera-
ture in THF solvent (Scheme 1). Both compounds 3 and 4 have
been characterized by standard analytical/spectroscopic
4948 | Dalton Trans., 2013, 42, 4947–4956
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Table 1 Crystallographic data and structure refinement parameters for complexes 3–9
Compound
3·THF
4·THF
5
6
CCDC No.
Empirical formula
Formula weight
903851
903856
C35H34NOPSe
594.56
903853
C66H74N2Na2O4P2Se2
1225.11
903855
C66H72K2N2O4P2Se2
1257.33
C
29H30NOPSe
518.47
T (K)
λ (Å)
150(2)
1.54184
150(2)
1.54184
150(2)
1.54184
150(2)
1.54184
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Monoclinic
P21/c
9.4326(8)
14.8835(14)
20.239(2)
90
116.921
90
2533.4(4)
4
Monoclinic
P21/c
12.2406(3)
13.6069(4)
20.4841(6)
90
121.334(2)
90
2914.16(14)
4
Triclinic
P1
10.392(17)
12.981(2)
Triclinic
P1
10.4891(10)
13.1334(10)
13.4628(8)
67.483(6)
84.963(6)
66.685(8)
1568.9(2)
ˉ
ˉ
13.463(17)
α (°)
β (°)
γ (°)
109.103(13)
107.189(13)
104.478(14)
1513.8(4)
V (Å3)
Z
1
1
Dcalc (g cm−3
)
1.359
2.760
1072
1.355
2.474
1232
1.344
2.549
636
1.331
3.512
652
μ (mm−1
F (000)
)
Theta range for data collection
Limiting indices
3.85 to 70.86°
−10 ≤ h ≤ 11,
−18 ≤ k ≤ 17,
−19 ≤ l ≤ 24
10946/4807
[R(int) = 0.0516]
98.2%
Multi-scan
0.79 and 0.578
Full-matrix least-squares on F2
4807/0/298
1.028
4.12 to 70.78°
−14 ≤ h ≤ 11,
−16 ≤ k ≤ 16,
−21 ≤ l ≤ 24
12004/5495
[R(int) = 0.0354]
98.1%
Multi-scan
0.660 and 0.560
Full-matrix least-squares on F2
5495/0/352
0.757
3.81 to 70.74°
−11 ≤ h ≤ 12,
−14 ≤ k ≤ 15,
−16 ≤ l ≤ 11
11164/5681
[R(int) = 0.0303]
97.5%
3.56 to 70.72°
−12 ≤ h ≤ 12,
−16 ≤ k ≤ 14,
−16 ≤ l ≤ 15
11473/5891
[R(int) = 0.0445]
97.9%
Reflections collected/unique
Completeness to theta = 71.25
Absorption correction
Max. and min. transmission
Refinement method
Multi-scan
Multi-scan
0.660 and 0.560
Full-matrix least-squares on F2
5681/6/362
0.685 and 0.585
Full-matrix least-squares on F2
5891/6/382
1.063
Data/restraints/parameters
Goodness-of-fit on F2
1.036
Final R indices [I > 2σ(I)]
R indices (all data)
R1 = 0.0595, wR2 = 0.1534
R1 = 0.0761, wR2 = 0.1675
R1 = 0.0426, wR2 = 0.1209
R1 = 0.0562, wR2 = 0.1386
R1 = 0.0379, wR2 = 0.0987
R1 = 0.0452, wR2 = 0.1065
R1 = 0.0470, wR2 = 0.1155
R1 = 0.0635, wR2 = 0.1270
Absolute structure parameter
Largest diff. peak and hole
1.569 and −0.746 e Å−3
1.741 and −0.734 e Å−3
0.337 and −0.452 e Å−3
0.586 and −0.741 e Å−3
Compound
7·2THF
8·2THF
903854
C66H74N2O4P2Se2Sr
1266.75
9
CCDC No.
Empirical formula
Formula weight
T (K)
903852
903850
C66H70CaN2O4P2Se2
C58H58BaN2O2P2Se2
1172.26
150(2)
1215.18
150(2)
150(2)
λ (Å)
1.54184
Triclinic
P1
10.2981(9)
10.9898(9)
14.4141(13)
99.955(7)
101.789(8)
103.034(7)
1514.2(2)
0.71069
1.54184
Monoclinic
P21
15.7828(7)
11.0357(3)
16.9825(7)
90
117.366(5)
90
2626.9(2)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
Triclinic
ˉ
ˉ
P1
10.191(5)
10.912(5)
14.641(5)
99.369(5)
101.195(5)
103.621(5)
1514.7(11)
γ (°)
V (Å3)

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compounds 1 (P1–N1 1.673(6) Å and C1–N1 1.453(8) Å) and 2
(P1–N1 1.691(2) Å and C1–N1 1.494(2) Å) previously observed
by us.24,25
Alkali metal complexes
The dimeric sodium and potassium complexes of molecular
formula [{(THF)2M′Ph2P(Se)N(CHPh2)}2] (M′ = Na (5) and K (6))
were prepared by the reaction of compound 3 and sodium bis
(trimethyl)silylamide (or potassium bis(trimethylsilyl)amide in
case of 6) in toluene through the elimination of volatile bis(tri-
methylsilyl)amine (Scheme 2).27
ˉ
Complex 5 crystallizes in triclinic space group P1 having
one molecule in the unit cell. The solid state structure of
complex 5 is given in Fig. 2. The details of the structural
Scheme 2 Synthesis of alkali metal and alkaline earth metal phosphinoselenoic
amide complexes.
Fig. 2 Solid-state structure of compound 5; ellipsoids are drawn to encompass
30% probability, omitting hydrogen atoms. Selected bond lengths [Å] and bond
angles [°]: Na1–N1i 2.380(2), Na1–Se1 2.9956(12), Na1–Se1i 3.0694(11),
Na1–O1 2.426(2), Na1–O2 2.399(2), Na1–P1i 3.2214(13), N1–P1 1.594(2),
P1–Se1 2.1519(8), Se1–Na1–Se1i 99.14(3), Se1–Na1–N1i 115.92(6), Se1i–Na1–P1i
39.915(19), Se1–Na1–P1i 114.01(4), Se1i–Na1–O1 83.95(6), Se1i–Na1–O2
171.24(6), N1i–Na1–P1i 28.30(5), N1i–Na1–O1 108.79(8), N1i–Na1–O2
112.65(8), N1i–Na1–Se1i 68.15(5), Na1–Se1–Na1i 80.86(3), O1–Na1–Se1i
83.95(6), O2–Na1–Se1i 171.24(6).
4950 | Dalton Trans., 2013, 42, 4947–4956
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Se2A–K–Se2Ai of 91.12(2)° and K–Se2A–Ki of 88.88(2)° is
observed. The K–Se2A and K–Se2Ai bond distances are also
similar at 3.3090(10) and 3.5150(10) Å, respectively. Each of the
selenium atoms is μ-coordinated between each of the two pot-
assium atoms. Additionally, each phosphorus atom is weakly
coordinated to each potassium atom to form highly strained
three-membered metallacycles having P–K-distance 3.5579(13) Å.
Two additional THF molecules are also coordinated to each
potassium atom to adopt a distorted octahedral geometry for
each potassium metal atom. The bond distances K–N 2.725(3),
K–O1 2.659(3), and K–O7 2.695(3) Å are slightly elongated
compare to that of sodium complex 5, but are in the range of
the previously observed potassium complexes reported in lit-
erature. Unlike the analogous sodium complex, a short contact
between potassium and one of the phenyl carbons (K⋯C1C
(3.194(3) Å)) is observed, which can be interpreted as a remote
or secondary M–C interaction. However, in solution all phenyl
carbons appeared equivalent in the 13C{1H} NMR study, pre-
Fig. 3 Solid state structure of compound 6; ellipsoids are drawn to encompass
30% probability, omitting hydrogen atoms. Selected bond lengths [Å] and bond
angles [°]: K–N 2.725(3), K–Se2a 3.3090(10), K–Se2ai 3.5150(9), K–O1 2.659(3),
K–O7 2.695(3), K–C1ci 3.194(3), K–P 3.5579(12), N–P 1.589(3), P–Se2a sumably due to dynamic behaviour of the complex. Thus in
2.1476(9), Se2a–K–Se2ai 91.12(2), Se2a–K–N 61.31(6), Se2a–K–P 36.22(17),
the solid state, two additional five member metallacycles
Se2a–K–O1 171.26(8), Se2a–K–O7 94.77(10), N–K–P 25.09(6), N–K–O1
K1–C1C–C20–P1–Se1 and K1i–C1Ci–C20i–P1i–Se1i are formed.
109.95(10), N–K–O7 102.29(10), N–K–Se2ai 90.75(6), K–Se2a–Ki 88.88(2),
An unusual structural motif is formed by fusion of four three-
member and two five-member metallacycle rings. To the best
of our knowledge, this is the first example of such kind of
structural motif in potassium complexes. Even the complexes
5 and 6 are dimeric in the solid state, only one set of signals
O1–K–Se2ai 88.87(8), O7–K–Se2ai 166.95(9).
parameters are given in Table 1. In the centrosymmetric mole-
cule 5, two phosphinoselenoic amide ligands are coordinated
to each of two sodium atoms by one selenium, one phos-
phorus and one amido nitrogen atom exhibiting a diamond
shaped Na2Se2 core with mean angles Se1–Na–Se1i of 99.14(3)°
and Na1–Se1–Na1i of 80.86(3)°. The Na1–Se1 and Na1–Se1i
bond distances are also almost the same at 2.9956(12) Å and
3.0694(11) Å, respectively. Each of the selenium atoms is
μ-coordinated between the two sodium atoms. Additionally,
each phosphorus atom is weakly coordinated to each sodium
atom to form highly strained three membered metallacycles
having P1–Na1-distance 3.2214(14) Å. In complex 5, two
additional THF molecules are also coordinated to each sodium
atom and the geometry of each sodium atom can be best
described as distorted octahedral. The bond distances Na1–N1
2.380(2), Na1–O1 2.426(2), and Na1–O2 2.399(2) Å are in the
range of the previously observed sodium phosphinthioic
amide complexes reported by us.16 The whole structure con-
sists of four three-member rings fused together forming a
penta-metallacyclo[4.2.0.01,7.02,5.02,4]octane structure. Such a
structural motif in sodium complexes due to the presence of
three adjacent hetero donor atoms selenium, phosphorus and
nitrogen was recently reported by us.25
1
were recorded in the H, 31P{1H} and 13C{1H} NMR spectra in
each case due to the dynamic nature of the complexes in
solution.
Alkaline earth metal complexes
Reaction of 3 with alkaline earth metal bis(trimethylsilyl)-
amides [M{N(SiMe3)2}2(THF)n] (M = Ca, Sr, Ba) in a 2 : 1 molar
ratio in THF followed by crystallization from THF–n-pentane,
homoleptic phosphinoselenoic amido alkaline earth metal
complexes of composition [M(THF)2{Ph2P(Se)N(CHPh2)}2]
(M = Ca (7), Sr (8), Ba (9)) were obtained in good yield via the
elimination of hexamethyldisilazane (Scheme 2).27 The same
alkaline earth metal complexes 7–9 can also be prepared by
another route, salt metathesis reaction involving the alkali
metal phosphinoselenoic amides with alkaline earth metal
diiodides in THF. The silylamide route was followed for all the
three complexes 7–9, whereas both the routes were used for
calcium complex 7 only. The new complexes have been charac-
terized by standard analytical/spectroscopic techniques, and
the solid-state structures were established by single-crystal
X-ray diffraction analysis. A strong absorption at 570 cm−1 (for
7), 569 cm−1 (for 8) and 569 cm−1 (for 9) in FT IR spectra indi-
cates the evidence of PvSe bond into the each complex. The
signals of the methine proton (δ 5.93–5.87 ppm for 7,
The potassium phosphinoselenoic amido complex 6 crystal-
ˉ
lizes in the triclinic space group P1 having one molecule in the
unit cell and is isostructural with the sodium complex 5 due to
the similar ionic radii of sodium and potassium. The details
of the structural parameters are given in Table 1. The solid
state structure of complex 6 is given in Fig. 3. Each potassium
atom in the dimeric complex 6 is coordinated by one {Ph2P(Se)-
N(CHPh2)}− ligand and two THF molecules. Similar to
complex 5, a diamond-shaped K2Se2 core with mean angles
1
5.40–5.33 ppm for 8 and 5.46–5.39 ppm for 9) in the H NMR
spectrum of the diamagnetic complexes 7–9 are unaffected
due to complex formation. In 31P{1H} NMR spectra, complexes
7–9 show only one signal at 71.9 ppm, 71.8 ppm and
71.9 ppm, respectively, and these values are significantly
downfield shifted compared to that of compound 3 (58.0 ppm)
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ligands, and two THF molecules which are trans to each other.
Each {Ph2P(Se)N(CHPh2)}− ligand coordinates to the calcium
atom via chelation of one amido nitrogen atom and one sel-
enium atom and a very weak P–Ca interaction (3.274 Å) of the
{Ph2P(Se)N(CHPh2)}− moiety is observed. Thus the {Ph2P(Se)N-
(CHPh2)}− group can be considered as a pseudo-bidentate
ligand. The central atom calcium adopts a distorted octahedral
geometry due to coordination from two {Ph2P(Se)N(CHPh2)}−
moieties and two THF molecules. The Ca–N distance (2.479(5) Å)
is slightly elongated compare with the calcium–nitrogen
covalent bond (2.361 (2) and 2.335(2)) reported for
[Ca(Dipp2DAD)(THF)4] (Dipp2DAD = N,N′-bis(2,6-diisopropyl-
phenyl)-1,4-diaza-1,3-butadiene in the literature.29 The most
interesting thing is that the Ca–Se bond 2.989(8) Å is within
the same range of Ca–Se bond (2.945(1) Å) reported for
[(THF)2Ca{(PyCH)(Se)PPh2}2]14 and (2.93 to 3.00 Å) reported
for [(THF)4Ca(SeMes′)2] and (2.958(2) to 3.001(2) Å) reported
for [(THF)2Ca(Se2PPh2)2] in the literature.13,15 Thus the com-
pound 7 is one example of the few complexes known having a
direct calcium–selenium bond.11–13 The P–Se distance
(2.1449(2) Å) in complex 5 is slightly elongated (2.111(2) Å) but
within the same range as that of free ligand 3 indicating no
impact on P–Se bond upon coordination of the calcium atom
to the selenium atom. In compound 8, the strontium atom is
hexacoordinated by two selenium atoms, two amido nitrogen
atoms of two {Ph2P(Se)N(CHPh2)}− ligands and two THF mole-
cules. The solvate THF molecules are trans to each other and
the strontium atom adopts a distorted octahedral geometry.
Like compound 5, a weak interaction (P–Sr 3.426(2) Å)
between phosphorus and metal atom is noticed. The stron-
tium–nitrogen bond distance (2.609(3) Å) fits well (2.6512(2)
and 2.669(2) Å) with our previously observed strontium
complex [(ImpDipp)2Sr(THF)3] (ImpDipp = 2,6-iPr2C6H3NvCH)–
C4H3N).30 The Sr–Se bond distance (3.136(9) Å) is slightly
elongated compare to that of Ca–Se bond distance (2.989(8) Å)
observed in complex 7 due to the larger ionic radius of stron-
tium than calcium ion. The observed Sr–Se distance in our
compound 8 is within the range of Sr–Se distances (3.138(7) to
3.196(9) Å) of structurally characterized complex [(THF)3Sr-
(Se2PPh2)2] published very recently by Westerhausen and cow-
orkers16b and that (3.066(1) Å) for the complex [Sr{Se(2,4,6-
tBu3C6H2)}2(THF)4].16a Thus our phosphinoselenoic amido
strontium complex 8 is another example of a fully structurally
characterized strontium complex having direct Sr–Se bond.
Unlike compounds 7–8, the barium complex 9 crystallizes
in the monoclinic space group P21, having two molecules in
the unit cell. The details of the structural parameters are given
in Table 1. The solid-state structure of complex 9 is given in
Fig. 6. Similar to the calcium and strontium complexes, in the
barium complex 9 the coordination polyhedron is formed by
two {Ph2P(Se)N(CHPh2)}− ligands and two trans THF mole-
cules. The amido nitrogen atom along with the selenium
atom of each of the phosphinoselenoic amido ligands coordi-
nates to the barium atoms to adopt a distorted octahedral geo-
metry for the barium atom, considering the {Ph2P(Se)N-
(CHPh2)}− ligand as bidentate. The Ba–P distance is even
Fig. 4 Solid-state structure of compound 7; ellipsoids are drawn to encompass
30% probability, omitting hydrogen atoms for clarity. Selected bond lengths [Å]
and bond angles [°]: Ca1–N1 2.479(5), Ca1–P1 3.2737(16), Ca1–Se1 2.9889(8),
Ca1–O1 2.427(5), N1–Ca1–O1 89.23(17), N1–Ca1–P1 28.95(13), P1–Se1–Ca1
77.31(5), P1–Ca1–Se1 39.73(3), Se1–Ca1 N1 68.20(13), O1–Ca1–Oi 180.000(1),
Se1–Ca–Se1i 180.0.
Fig. 5 Solid state structure of compound 8; ellipsoids are drawn to encompass
30% probability, omitting hydrogen atoms for clarity. Selected bond lengths [Å]
and bond angles [°]: Sr1–N1 2.609(3), Sr1–P1 3.4255(15), Sr1–Se1 3.1356(9),
Sr1–O1 2.567(3), N1–Sr1–O1 91.72(9), N1–Sr1–P1 26.86(6), P1–Sr1–Se1
37.89(2), Se1–Sr1–N1 64.23(7), O1–Sr1–Oi 180.00(10), Se1–Sr–Se1i 180.0.
upon coordination of calcium, strontium or barium atom onto
the selenium atom of the phosphinoselenoic amido ligand.
The two phosphorus atoms present in the two {Ph2P(Se)N-
(CHPh2)}− moieties are chemically equivalent.
The calcium and strontium complexes 7 and 8 crystallize in
ˉ
the triclinic space group P1, having one molecule of either 7 or
8 and two THF molecules as solvate in the unit cell. The
details of the structural parameters are given in Table 1. The
solid-state structures of the complexes 7 and 8 are shown in
Fig. 4 and 5, respectively. Both the complexes 7 and 8 are iso-
structural to each other due to similar ionic radii (1.00 and
1.18 Å for coordination number 6).28
In the centrosymmetric molecule 7, the coordination poly-
hedron is formed by two monoanionic {Ph2P(Se)N(CHPh2)}−
4952 | Dalton Trans., 2013, 42, 4947–4956
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dried Schlenk-type glassware either on a dual manifold
Schlenk line, interfaced to a high vacuum (10−4 Torr) line, or
in an argon-filled M. Braun glove box. THF was pre-dried over
Na wire and distilled under nitrogen from sodium and benzo-
phenone ketyl prior to use. Hydrocarbon solvents (toluene and
n-pentane) were distilled under nitrogen from LiAlH4 and
stored in the glove box. 1H NMR (400 MHz), 13C{1H} and
31P{1H} NMR (161.9 MHz) spectra were recorded on a BRUKER
AVANCE III-400 spectrometer. BRUKER ALPHA FT-IR was used
for FT-IR measurement. Elemental analyses were performed
on a BRUKER EURO EA at the Indian Institute of Technology,
Hyderabad. Sodium and potassium bis(trimethylsilyl)amide
were purchased from Sigma Aldrich and used as such. The
phosphinamines 1, 2,24 and [M{N(SiMe3)2}2(THF)2] (M = Ca,
Sr, Ba)31 were prepared according to literature procedures by
using respective metal diiodides and [KN(SiMe3)2]. The NMR
solvent C6D6 was purchased from Sigma Aldrich and dried
under Na/K alloy prior to use.
Fig. 6 Solid state structure of compound 9; ellipsoids are drawn to encompass
30% probability, omitting hydrogen atoms. Selected bond lengths [Å] and bond
angles [°]: Ba1–N1 2.777(6), Ba1–P1 3.662(2), Ba1–Se1 3.3553(10), Ba1–O1
2.716(6), Ba1–N2 2.778(6), Ba1–P2 3.665(2), Ba1–Se2 3.3314(10), B1–O2
2.734(6), N1–Ba1–O1 91.2(2), N1–Ba1–P1 24.34(15), P1–Ba1–Se1 35.37(4),
Se1–Ba1–N1 59.62(15), O1–Ba1–O2 177.3(2), Se1–Ba–Se2 175.66(3),
N1–Ba1–N2 175.8(2), N2–Ba1–O2 94.8(2), N2–Ba1–Se2 59.46(15).
Preparation of [Ph2P(Se)NH(CHPh2)] (3). N-Benzhydryl-1,1-
diphenylphosphinamine 1 (1.0 gm, 2.72 mol) and elemental
selenium (250 mg, 3.16 mol) were heated to 60 °C in THF
(10 ml) for 12 h. Unreacted excess selenium was filtered off
through a G4 frit and the filtrate was collected. After evapo-
ration of solvent from filtrate in vacuo, a light yellow solid
residue was obtained (yield: 1.20 gm, 99%). The title com-
pound was recrystallized from THF at room temperature.
1H NMR (400 MHz, CDCl3): δ 7.72–7.77 (m, 4H, ArH),
7.12–7.33 (m, 16H, ArH), 5.62–5.68 (dd, 1H, J = 14.8 Hz, 6.4
Hz, CH), 3.17–3.14 (br t, 1H, J = 5.2 Hz, NH) ppm. 13C{1H}
NMR (100 MHz, CDCl3): δ 142.9 (ArC), 142.8 (ArC), 134.2
(P-ArC), 133.3 (P-ArC), 131.9 (P attached o-ArC), 131.8
(P attached o-ArC), 131.6 (P attached p-ArC), 128.4 (m-ArC),
128.3 (P attached m-ArC), 128.1 (P attached m-ArC), 127.8
(o-ArC), 127.2 (p-ArC), 59.8 (CH) ppm. 31P{1H}NMR
(161.9 MHz, CDCl3): δ 58.0 ppm. FT-IR (selected frequencies):
larger (3.662(2) Å) compare to that of complexes 7 (3.2737(16) Å)
and 8 (3.4255(15) Å), indicating a very weak interaction
between the barium atom and phosphorus atom. The Ba–N
distances (2.777(6) and 2.778(6) Å) are similar to the values
(2.720(4) and 2.706(4) Å) for [Ba((Dip)2DAD)(μ-I)(THF)2]2
reported in the literature.30 The Ba–Se distance (3.3553(1) Å) is
the largest among the above mentioned M–Se distances for
calcium and strontium complexes (2.9889(8) and 3.1355(9) Å,
respectively; vide supra) and can be attributed to the larger
ionic radii of the barium atoms compared to calcium and
strontium atoms. The Ba–Se distance (3.3553(1) Å) of com-
pound 9 is similar to the reported values of 3.2787(11) Å
for the complex [Ba(THF)4(SeMes*)2] (Mes* = 2,4,6-tBu3C6H2)
and 3.2973(3) Å for [{Ba(Py)3(THF)(SeTrip)2}2] (Trip = 2,4,6
iPr3C6H2) reported by Ruhlandt-Senge and coworkers.23 Never-
theless complex 9 is a unique example of a barium-seleno
complex where two other heteroatoms, nitrogen and phos-
phorus, coordinate to the barium atom. The P–Se bond
(2.152(2) Å) is slightly elongated upon coordination of
selenium to the barium atom. A weak interaction between
barium and phosphorus (Ba1–P1 3.662(2) and 3.665(2) Å) is
also observed. Upon coordination to the barium atom each of
the ligand fragments form two three-member metallacycles
which are fused together to give a four-member metallacycle
Se1–P1–N1–Ba1. The bite angles (Se1–Ba1–N1 59.62(15)° and
Se2–Ba1–N2 59.46(15)°, P1–Se1–Ba1 80.11(6)° and 80.77(6)°)
indicate a highly strained structure of the molecule.
ν = 3242 (N–H), 1435 (P–C), 898 (P–N), 568 (PvSe) cm−1
.
(C25H22NPSe) Calc. C 67.27, H 4.97, N 3.14; found C 66.99
H 4.43, N 2.93.
Preparation of [Ph2P(Se)NH(CPh3)] (4). Similar to com-
pound 3. Yield 1.20 g, 100%. 1H NMR (400 MHz, C6D6):
δ 7.74–7.79 (m, 4H, ArH), 7.19–7.22 (m, 6H, ArH), 6.59–6.99
(m, 15H, ArH), 3.71 (d, 1H, J = 3.16 Hz, CH), ppm. 13C{1H}
NMR (100 MHz, C6D6): δ 143.9 (ArC), 143.8 (ArC), 136.1
(P-ArC), 135.1 (P-ArC), 130.8 (P attached o-ArC), 130.6
(P attached m-ArC), 129.5 (P attached p-ArC), 129.4 (P attached
p-ArC), 129.1 (o-ArC), 126.7 (m-ArC), 126.1 (p-ArC), 71.3
(CH) ppm. 31P{1H}NMR (161.9 MHz, C6D6): δ 62.6 ppm.
FT-IR (selected frequencies): ν = 3300 (N–H, very week),
1435 (P–C), 910 (P–N), 599 (PvSe) cm−1. (C35H34NOPSe)
(4·THF) Calc. C 70.70, H 5.76, N 2.36; found C 70.13 H 5.39,
N 2.18.
Preparation of [{(THF)2NaPh2P(Se)N(CHPh2)}2] (5). In
10 ml sample vial one equivalent (50 mg, 0.112 mmol) of
ligand 3 and one equivalent of sodium bis(trimethylsilyl)-
a
Experimental
General considerations
All manipulations of air-sensitive materials were performed amide (20.5 mg, 0.112 mmol) were mixed together with a
with the rigorous exclusion of oxygen and moisture in flame- small amount (2 ml) of toluene. After 6 h, a small amount of
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THF (2 ml) and n-pentane (2 ml) were added to it and kept at 127.1 (p-ArC), 67.7 (THF) 59.6 (CH), 25.6 (THF) ppm. 31P{1H}
−40 °C. After 24 h, colorless crystals of 5 were obtained. NMR (161.9 MHz, C6D6): δ 71.9 ppm. FT-IR (selected frequen-
Yield 95%. H NMR (400 MHz, C6D6): δ 7.73–7.67 (m, 4H, cies): ν = 3381 (N–H), 1436 (P–C), 930 (P–N), 570 (PvSe) cm−1
1
.
ArH), 6.96–6.94 (m, 4H, ArH), 6.84–6.66 (m, 12H, ArH), (C66H70CaN2O4P2Se2) (7·2THF) Calc. C 65.23, H 5.81, N 2.31;
5.82–5.76 (dd, 1H, J = 16.0 Hz, 6.0, 8.0 Hz CH) ppm. 13C{1H} found C 64.88 H 5.32, N 2.11.
NMR (100 MHz, C6D6): δ 143.6 (ArC), 143.5 (ArC), 135.4
8: Yield 78%. 1H NMR (400 MHz, C6D6): δ 7.84–7.78 (m, 4H,
(P-ArC), 134.5 (P-ArC), 132.3 (P attached o-ArC), 132.2 ArH), 7.33–7.31 (m, 4H, ArH), 6.95–6.79 (m, 12H, ArH),
(P attached o-ArC), 131.3 (P attached p-ArC), 131.2 (P attached 5.40–5.33 (d, 1H, J = 27.6 Hz, CH) ppm, 3.48 (m, THF), 1.27
p-ArC), 128.4 (P attached m-ArC), 128.2 (m-ArC), 128.0 (o-ArC), (m, THF) ppm. 13C{1H} NMR (100 MHz, C6D6): δ 143.6 (ArC),
127.1 (p-ArC), 59.6 (CH) ppm. 31P–{1H}NMR (161.9 MHz, 143.5 (ArC), 135.4 (P-ArC), 134.5 (P-ArC), 132.3 (P attached
C6D6): δ 71.9 ppm. FT-IR (selected frequencies): ν = 3365 o-ArC), 132.2 (P attached o-ArC), 131.3 (P attached p-ArC),
(N–H), 1435 (P–C), 894 (P–N), 570 (PvSe) cm−1
(C66H74N2Na2O4P2Se2) Calc. C 64.70, H 6.09, N 2.29; found (m-ArC), 127.3 (o-ArC), 127.1 (p-ArC), 68.1 (THF), 59.6 (CH),
C 64.15 H 5.82, N 1.76.
25.5 (THF) ppm. 31P–{1H}NMR (161.9 MHz, C6D6): δ 71.9 ppm.
.
131.2 (P attached p-ArC), 128.8 (P attached m-ArC), 128.4
Preparation of [{(THF)2KPh2P(Se)N(CHPh2)}2] (6). In a 10 ml FT-IR (selected frequencies): ν = 1436 (P–C), 931 (P–N),
sample vial, one equivalent (50 mg, 0.112 mmol) of ligand 3 569 (PvSe) cm−1. (C66H74N2O4P2Se2Sr) (8·2THF) Calc. C 62.58,
and one equivalent of potassium bis(trimethylsilyl)amide H 5.89, N 2.21; found C 62.03 H 5.43, N 2.05.
(22.4 mg, 0.112 mmol) were mixed together with 2 ml of
9: Yield 83%. 1H NMR (400 MHz, C6D6): δ 7.88–7.83 (m, 4H,
toluene. After 6 h, a small amount of THF (2 ml) and ArH), 7.26–7.24 (m, 4H, ArH), 7.06–6.85 (m, 12H, ArH),
n-pentane (2 ml) were added to it and kept at −40 °C. After 5.46–5.39 (d, 1H, J = 26.1 Hz, CH) ppm, 3.47 (m, THF), 1.30
24 h, colorless crystals of 6 were obtained.
(m, THF) ppm. 13C NMR (100 MHz, C6D6): δ 143.6 (ArC), 143.5
1
Yield 90%. H NMR (400 MHz, C6D6): δ 7.88–7.82 (m, 4H, (ArC), 135.4 (P-ArC), 134.5 (P-ArC), 132.3 (P attached o-ArC),
ArH), 7.07–7.06 (m, 4H, ArH), 6.96–6.82 (m, 13H, ArH), 132.2 (P attached m-ArC), 131.3 (P attached p-ArC), 131.2
5.84–5.78 (dd, 1H, J = 8.8 Hz, 6.0 Hz CH) ppm, 3.46 (m, THF), (P attached p-ArC), 128.4 (o-ArC), 128.2 (m-ArC), 127.1 (p-ArC),
1.31 (m, THF) ppm. 13C{1H} NMR (100 MHz, C6D6): δ 143.8 67.7 (THF), 59.6 (CH), 25.6 (THF) ppm. 31P–{1H}NMR
(ArC), 143.7 (ArC), 135.9 (P-ArC), 134.9 (P-ArC), 132.2 (161.9 MHz, C6D6): δ 71.9 ppm. FT-IR (selected frequencies):
(P attached o-ArC), 132.1 (P attached o-ArC), 131.2 (P attached ν = 1437 (P–C), 911 (P–N), 569 (PvSe) cm−1. (C58H58Ba-
p-ArC), 131.1 (P attached p-ArC), 128.4 (P attached m-ArC), N2O2P2Se2) Calc. C 59.42, H 4.99, N 2.39; found C 58.93,
128.2 (m-ArC), 127.9 (o-ArC), 127.1 (p-ArC), 58.9 (CH) ppm. H 5.01, N 2.08.
31P{1H}NMR (161.9 MHz, C6D6): δ 71.9 ppm. FT-IR (selected
X-ray crystallographic studies of 3–9
frequencies): ν = 3373 (N–H), 1436 (P–C), 931 (P–N), 569
(PvSe) cm−1. (C66H74K2N2O4P2Se2) Calc. C 63.04, H 5.93, Single crystals of compounds 3 and 4 were grown from a solu-
N 2.23; found C 62.68 H 5.62, N 1.78.
tion of THF at a temperature of −4 °C; compounds 5–9 were
Preparation of [M(THF)2{Ph2P(Se)N(CHPh2)}2] (M = Ca (7), grown from a THF and pentane mixture at −40 °C under inert
Sr (8), Ba (9)). Route 1: In a 10 ml sample vial, two equivalents atmosphere. In each case a crystal of suitable dimensions was
(100 mg, 0.224 mmol) of ligand 3 and one equivalent of [M{N- mounted on a CryoLoop (Hampton Research Corp.) with a
(SiMe3)2}2(THF)n] (M = Ca, Sr, Ba) were mixed together with layer of light mineral oil and placed in a nitrogen stream at
2 ml of toluene. After 6 h of stirring another 2 ml of THF and 150(2) K. All measurements were made on an Oxford Super-
n-pentane (2 ml) were added to it and kept at −40 °C. After nova X-calibur Eos CCD detector with graphite-monochromatic
24 h, colorless crystals were obtained.
Cu-Kα (1.54184 Å) or Mo-Kα (0.71069 Å) radiation. Crystal data
Route 2: In a 25 ml pre-dried Schlenk flask, potassium salt and structure refinement parameters are summarized in
of ligand 3 (200 mg, 0.32 mmol) was mixed with CaI2 Table 1. The structures were solved by direct methods
(46.8 mg, 0.16 mmol) in 10 ml THF solvent at ambient temp- (SIR92)32 and refined on F2 by full-matrix least-squares
erature and stirring continued for 12 h. The white precipitate methods using SHELXL-97.33 Non-hydrogen atoms were aniso-
of KI was filtered off and filtrate was evaporated in vacuo. The tropically refined. H-atoms were included in the refinement on
resulting white compound was further purified by washing calculated positions riding on their carrier atoms. For com-
with pentane and crystals suitable for X-ray analysis were pound 5 disordered C30 of a coordinated tetrahydrofuran was
grown from THF–pentane (1 : 2 ratio) mixture at −40 °C.
refined with split model with site occupation factor 0.49(2)
1
7: Yield: Route 1 85% and Route 2 80%. H NMR (400 MHz, and for compound 6 disordered carbon atoms of two coordi-
C6D6): δ 7.84–7.78 (m, 4H, ArH), 7.07–7.05 (m, 4H, ArH), nated tetrahydrofuran were refined with split model. C11 in
6.95–6.78 (m, 12H, ArH), 5.93–5.87 (dd, 1H, J = 15.3 Hz, one THF is split with site occupation factor 0.62(4). C13 and
6.5 Hz, CH) ppm, 3.46 (m, THF), 1.31 (m, THF) ppm. 13C{1H} C2D are split with site occupation factors 0.42(10) and 0.48(4),
2
2 2
NMR (100 MHz, C6D6): δ 143.6 (ArC), 143.5 (ArC), 135.4 respectively. The function minimized was [∑w(Fo − Fc ) ]
(P-ArC), 134.5 (P-ArC), 132.3 (P attached o-ArC), 132.2 (w = 1/[σ2(Fo ) + (aP)2 + bP]), where P = (max(Fo ,0) + 2Fc )/3
2
2
2
(P attached o-ArC), 131.3 (P attached p-ArC), 131.2 (P attached with σ2(Fo ) from counting statistics. The function R1 and wR2
2
p-ArC), 128.4 (P attached m-ArC), 128.3 (m-ArC), 128.0 (o-ArC), were (∑||Fo| − |Fc||)/∑|Fo| and [∑w(Fo − Fc ) /∑(wFo )]1/2
,
2
2 2
4
4954 | Dalton Trans., 2013, 42, 4947–4956
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respectively. The ORTEP-3 program was used to draw the mole-
cule. CCDC reference numbers 903850–903856. For crystallo-
graphic data in CIF or other electronic format see DOI:
10.1039/c2dt32339g.
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Conclusions
In conclusion, we have reported a series of heavier alkaline-
earth-metal–selenium complexes having direct metal–
selenium bonds via two synthetic routes using phosphinosele-
noic amide ligand. In the first method the silylamide route
was used to prepare the target compounds, and in the second
method the salt metathesis route was used. Due to similar
ionic radii, calcium and strontium complexes are isostructural,
and also the M–Se bond distances increase from Ca–Se to
Sr–Se and a further increase is observed for the Ba–Se bond.
Further reactivity studies on these complexes are underway in
our laboratory.
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Acknowledgements
This work was supported by the Department of Science and
Technology India (DST) under the SERC Fast Track
Scheme (SR/FT/CS-74/2010) and start-up grant from IIT
Hyderabad. R. K. and K. N. thanks UGC, India and
S. A. thanks CSIR, India for their PhD fellowships. Generous
support from K. Mashima, Osaka University, Japan is gratefully
acknowledged. We also thank the reviewers for their valuable
suggestions.
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