Synthesis and structure of heavier group 2 metal complexes with diselenoimidodiphosphinato ligand containing SreSe and BaeSe direct bonds

Article abstract of DOI:10.1016/j.jorganchem.2013.04.056

We report the mononuclear diselenoimidodiphosphinato strontium and barium complexes of the molecular formula [{h²-N(PPh₂Se) ₂}₂Sr(THF)₂] (2) and [{h²-N(PPh ₂Se)₂}₂Ba(THF)3] (3) which can be obtained by two routes, either by the treatment of metal bis(trimethylsilyl)amide and diselenoimidodiphosphine (1) via the elimination of silylamine or salt metathesis reaction involving metal diiodide and potassium salt of diselenoimidodiphosphine. In the solid state structures of 2 and 3, each of the metal atom is ligated by four selenium atoms from two diselenoimidodiphosphinato ligand moieties and two (for 2) and three (for 3) THF molecules to adopt a distorted octahedral geometry around the strontium atom and distorted pentagonal bipyramidal geometry for barium ion. In the complexes 2 and 3, a direct metal selenium contact is observed. Additionally we also report the synthesis and structure of lithium complex [h²-N(PPh₂Se) ₂Li(THF)₂] (4) which was synthesized by using 1 and LiCH₂SiMe₃ in THF solution.

Full text of DOI:10.1016/j.jorganchem.2013.04.056

Journal of Organometallic Chemistry 740 (2013) 104e109
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and structure of heavier group 2 metal complexes
with diselenoimidodiphosphinato ligand containing SreSe and
BaeSe direct bonds
*
Ravi K. Kottalanka, Srinivas Anga, Salil K. Jana, Tarun K. Panda
Department of Chemistry, Indian Institute of Technology Hyderabad, Ordnance Factory Estate, Yeddumailaram, 502205 Andhra Pradesh, India
a r t i c l e i n f o
a b s t r a c t
Article history:
We report the mononuclear diselenoimidodiphosphinato strontium and barium complexes of the
molecular formula [{h h
2-N(PPh2Se)2}2Sr(THF)2] (2) and [{ 2-N(PPh2Se)2}2Ba(THF)3] (3) which can
Received 5 March 2013
Received in revised form
25 April 2013
be obtained by two routes, either by the treatment of metal bis(trimethylsilyl)amide and dis-
elenoimidodiphosphine (1) via the elimination of silylamine or salt metathesis reaction involving metal
diiodide and potassium salt of diselenoimidodiphosphine. In the solid state structures of 2 and 3, each of
the metal atom is ligated by four selenium atoms from two diselenoimidodiphosphinato ligand moieties
and two (for 2) and three (for 3) THF molecules to adopt a distorted octahedral geometry around the
strontium atom and distorted pentagonal bipyramidal geometry for barium ion. In the complexes 2 and
3, a direct metal selenium contact is observed. Additionally we also report the synthesis and structure of
Accepted 30 April 2013
Keywords:
Diselenoimidodiphosphine
Metallacycle
Strontium
lithium complex [
h
2-N(PPh2Se)2Li(THF)2] (4) which was synthesized by using 1 and LiCH2SiMe3 in THF
Barium
solution.
Selenium
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
of the alkaline earth metal complexes can be controlled via the
well-defined nitrogen-based ligand architecture.
Due to the oxophilic and electropositive nature compared to
those of early d-transition metals, homoleptic and heteroleptic
alkaline earth metal complexes are attractive to the organometallic
chemists [1,2]. The alkaline earth metal compounds have recently
employed in various catalytic applications to ring-opening poly-
merization of various cyclic esters [3,4], polymerization of styrene
and dienes [5e7], and hydroamination and hydrophosphination
reactions of alkenes and alkynes [8]. Exploration of the structure
and reactivity of alkaline earth metal species is one of the most
important steps to the design and development of efficient ho-
mogeneous catalysts; however, full realization of the catalytic po-
tential of these elements still requires substantial advances in
understanding their basic coordination and organometallic chem-
istry. To stabilize these extremely oxophilic and electropositive
metals, a wide variety of nitrogen-based ancillary ligands, such as
Another important application of alkaline earth metal chalcoge-
nolates is in high temperature superconductors and ferroelectrics. In
particular, alkaline earth metal oxide compounds used as suitable
precursors [18]. Much less attention has been paid to the alkaline
earth metal thiolates and selenates, although many heavier chal-
cogenates are known as potential dopants for chalcogen-based
semiconductors [19]. The chelating ligands having selenium as the
donor atom to stabilize the heavier alkaline earth metal complexes
are rare. Over the last few years very fewcalcium selenides have been
reported, such as [(TMEDA)2Ca(SeSi(SiMe3)3)] [20], but to date only
the solid state structures of [(THF)4Ca(SeMes’)2] [21] and [(THF)2Ca
{(PyCH)e(Se)PPh2}2] [22] have been reported. Full structural char-
acterization of strontium selenides is even scarce [23,24]. The com-
plex having barium selenium bond is limited as the structurally
authenticated examples are mostly restricted for the various sulfur
derivatives [{(H2O)2Ba(tmtH2)2}n] (tmt ¼ 2,4,6-trimarcaptotriazine,
S3C3N3) [25], [([17] crown-6)Ba(hmpa)SMes*][SMes*](Mes* ¼ 2,4,6-
tris(pyrazolyl)borates [1], aminotroponiminates [9],
b-diketimi-
nates [10e12], and iminopyrroles [13e15], 1,4-diaza-1,3-butadiene
[16,17] have been introduced to prepare well-defined alkaline earth
metal complexes revealing that the catalytic activity and selectivity
tBu3C6H2)
[26],
[Ba(hmpa)3{NaPhNNNNC(S)}2] [27],
[Ba-
(hmpa)3(C(S)NOPh2] [28], and few more examples including
[Ba(SCMe3)2 [29], [Ba(tmeda)2(SeSi(SiMe3)3)2] [20] are reported.
Ruhlandt-Senge et al. reported barium selenoates like [Ba(TH-
F)4(SeMes*)2], [([26] crown-6)Ba(hmpa)2(SMes*)2], [Ba(Py)3(THF)(-
SeTrip)2}2] (Trip ¼ 2,4,6 iPr3C6H2), and [Ba( [17]crown-6)(SeTrip)2]
* Corresponding author. Tel.: þ91 4023016036; fax: þ91 4023016032.
E-mail address: tpanda@iith.ac.in (T.K. Panda).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.04.056

R.K. Kottalanka et al. / Journal of Organometallic Chemistry 740 (2013) 104e109
105
[30], however vast potential of this field of chemistry is still to
be developed. Recently we also have reported the heavier alkaline
earth metal selenium containing complexes [M(THF)2{Ph2P(Se)
N(CHPh2)}2] (M ¼ Ca, Sr, Ba) to enrich the field of heavier group 2
metal seleno complexes [31]. In that work we showed that phos-
phinoselenoic amide ligand are capable to stabilize heavier alkaline
earth metals via the formation of a selenium metal bond. In contin-
uation of our study regarding heavier group 2 metal selenoates
complexes, we observed that diselenoimidodiphosphinato ligand is
introduced to a wide range of metal coordination sphere including
alkali metals [32,33], group 12 [34]; group 13 [35,36], group 14
[34,37,38], group15[39], group16[40,41], transitionmetals (VandCr
[42]; Mn [43,44] and Re [45]; Ru, Rh, Ir [33,46,47]; Os [48], Co [49];
group 10: Ni [50], Pd [50e53], Pt [32,46,50] and group 11 [53]: and to
rare earth metals [54,55]: and this can be due to the flexible nature of
the ligand moieties to adopt several metallacyclic ring depending
upon coordination tothe metalcenter. To our surprise, thereportsfor
heavier alkaline earth metal diselenoimidodiphosphinato are
missing in this series which could give more information about the
alkaline earth metal selenoates and therefore there is a scope to
develop the heavier alkaline earth metal complexes with dis-
elenoimidodiphosphinato ligand.
SrI2 (74.0 mg, 0.172 mmol) in 10 mL of THF solvent at ambient
temperature and stirred for 12 h. The white precipitate of KI was
filtered off and filtrate was dried under vacuo. The resulting white
compound was further purified by washing with pentane and
crystals of 2 suitable for X-ray analysis can be grown from THF/
pentane (1:2 ratios) mixture at ꢀ40 ꢁC. Yield 196.3 mg (86%).
1H NMR (400 MHz, C6D6):
d 8.07 (bs, 8H, ArH), 6.90 (bs, 12H,
ArH), 3.58 (m, 8H, CH2 of THF), 1.39 (m, 8H, CH2 of THF) ppm. 13
C
{1H} NMR (100 MHz, C6D6): 128.2 (ArC), 127.9 (ArC), 127.7(ArC),
67.8 (THF), 25.6 (THF) ppm. 31Pe{1H}NMR (161.9 MHz, C6D6):
43.3 ppm. FT-IR (selected frequencies): 1433 (PeC), 899 (PeN), 539
(P¼Se) cmꢀ1
.
Elemental analysis: C56H56N2O2P4Se4Sr (1316.37) calcd. C 51.09
H 4.29 N 2.13; found C 50.88 H 4.06 N 2.01.
2.3. Synthesis of [{h
2-N(PPh2Se)2}2Ba(THF)3] (3)
Route 1: in a 10 mL sample vial two equivalents (200 mg,
0.368 mmol) of ligand 1 and 1 equivalent of [Ba{N(SiMe3)2}2(THF)2]
(110.8 mg, 0.184 mmol) were mixed together with 2 mL of THF.
After 3 h of stirring at ambient temperature, 2 mL of n-pentane was
added to it and the reaction mixture was kept in ꢀ40 ꢁC freezer.
After 12 h pale green colored crystals of 3 were obtained. Yield
225.0 mg (85%).
In this context, the heavier alkaline earth metal selenium
containing complexes [{h -
2-N(PPh2Se)2}2Sr(THF)2] (2) and [{h2
N(PPh2Se)2}2Ba(THF)3] (3) are presented, which can be prepared in
good yield and high purity by two synthetic routes. Thus heavier
alkaline earth metal complexes reported herein, 2e3, can be the
examples of fewer class of complexes, with a direct selenium-
alkaline earth metal contact. Additionally we also present the
Route 2: in a 50 mL pre-dried Schlenk flask potassium salt of
ligand 1 [K{N(Ph2PSe)2}] (200 mg, 0.344 mmol) was mixed with
BaI2 (67.3 mg, 0.172 mmol) in 10 mL THF solvent at ambient tem-
perature and stirred for 12 h. The white precipitate of KI was
filtered off and filtrate was dried under vacuo. The resulting white
compound was further purified by washing with pentane and
crystals suitable for X-ray analysis are grown from THF/pentane
(1:2 ratios) mixture solvent at ꢀ40 ꢁC. Yield 202.0 mg (82%).
synthesis and structure of lithium complex
[h
2-N(PPh2Se)2
-
Li(THF)2] (4) which were obtained by using 1 and LiCH2SiMe3 in
THF solution.
1H NMR (400 MHz, C6D6):
d 8.16 (bs, 8H, ArH), 6.93e6.98 (m,
2. Experimental
12H, ArH), 3.57(m, 12H, CH2 of THF), 1.38 (m, 12H, CH2 of THF) ppm.
13Ce{1H}NMR (100 MHz, C6D6): 131.7 (P attached o-ArC), 129.9(P
attached ArC), 128.1 (P attached p-ArC), 127.9 (P attached m-ArC),
67.8 (THF), 25.6 (THF) ppm. 31Pe{1H}NMR (161.9 MHz, C6D6):
43.7 ppm. FT-IR (selected frequencies): 1434 (PeC), 934 (PeN), 538
2.1. General information
All manipulations of air-sensitive materials were performed
with the rigorous exclusion of oxygen and moisture in flame-dried
Schlenk-type glassware either on a dual manifold Schlenk line,
interfaced to a high vacuum (10ꢀ4 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 benzophenone ketyl prior to use.
Hydrocarbon solvents (toluene and n-pentane) were distilled un-
der nitrogen from LiAlH4 and stored in the glove box. 1H NMR
(400 MHz), 13C{1H} (100 MHz) 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. Diselenoimidodiphosphine
[56], [K{N(Ph2PSe)2}] [33], [M{N(SiMe3)2}2(THF)2] [57,58] (M ¼ Sr,
Ba), and LiCH2SiMe3 [59] were prepared according to the literature
procedures. SrI2 and BaI2 were purchased from Sigma Aldrich and
used without further purification.
(P¼Se) cmꢀ1
.
Elemental analysis: C60H64BaN2O3P4Se4 (1438.22) calcd. C 50.11
H 4.49 N 1.95; found C 50.02 H 3.93 N 1.73.
2.4. Synthesis of [h
2-N(PPh2Se)Li(THF)2] (4)
In a 10 mL sample vial one equivalent (100 mg, 0.184 mmol) of
ligand 1 and one equivalent of LiCH2SiMe3 (17.4 mg, 0.184 mmol)
were mixed together along with 2 mL of THF. After 6 h of stirring at
ambient temperature, 2 mL of n-pentane was added onto it and
kept in ꢀ40 ꢁC. After 3 h cube shaped colourless crystals of 4 were
obtained. Yield 114.8 mg (90%). 1H NMR (400 MHz, C6D6):
d 8.38e
8.44 (m, 8H, ArH), 7.04e7.08 (m, 8H, ArH), 6.95e6.99 (m, 4H, ArH),
3.49 (m, 8H, CH2 of THF), 1.26 (m, 8H, CH2 of THF) ppm. 13Ce{1H}
NMR (100 MHz, C6D6):
d 142.6 (P-ArC),141.7 (P-ArC), 131.6 (P
attached o-ArC), 131.5 (P attached o-ArC), 129.6 (P attached p-ArC),
128.1 (P attached m-ArC), 127.6 (P attached m-ArC), 68.3 (THF), 25.3
2.2. Synthesis of [{
h
2-N(PPh2Se)2}2Sr(THF)2] (2)
(THF) ppm. 31Pe{1H}NMR (161.9 MHz, C6D6):
d
42.9 ppm. FT-IR
(selected frequencies):
n
¼ 1432 (PeC), 931 (PeN), 540 (P¼Se)
Route 1: in a 10 mL sample vial 2 equivalents (200 mg,
0.368 mmol) of ligand 1 and 1 equivalent of [Sr{N(SiMe3)2}2(THF)2]
(101.6 mg, 0.184 mmol) are mixed together with 2 mL of THF. After
6 h of stirring, 2 mL of n-pentane was added to the top of it and the
reaction mixture was placed in ꢀ40 ꢁC freezer. After 12 h, pale
green colored crystals of 2 were obtained. Yield 218.3 mg (90%).
Route 2: in a 50 mL pre-dried Schlenk flask potassium salt of
ligand 1 [K{N(Ph2PSe)2}] (200 mg, 0.344 mmol) was mixed with
cmꢀ1
.
Elemental analysis: C32H36LiNO2P2Se2 (693.42) calcd. C 55.43 H
5.23 N 2.02; found C 54.99 H 5.01 N 1.87.
2.5. Single crystal X-ray structure determinations
Single crystals of compounds 2e4 were grown from a solution of
THF/pentanemixture (1:2) underinertatmosphereat a temperature

106
R.K. Kottalanka et al. / Journal of Organometallic Chemistry 740 (2013) 104e109
of ꢀ40ꢁC. In each case a crystal of suitable dimensions was mounted
on a CryoLoop (Hampton Research Corp.) with a layer of light min-
eral oil and placed in a nitrogen stream at 150(2) K. All measure-
3. Results and discussion
The heavier alkaline earth metal complexes 2 and 3 were pre-
pared in good yield by two synthetic routes. In the first route the
diselenoimidodiphosphine (1) is treated with alkaline earth metal
bis(trimethylsilyl)amide in THF at ambient temperature to afford
the respective strontium and barium complexes of molecular
ments were made on an Oxford Supernova X-calibur Eos CCD
ꢀ
detector with graphite-monochromatic CuK
a
(1.54184 A) radiation.
Crystal data and structure refinement parameters are summarized
below. The structures were solved by direct methods (SIR92)
[60] and refined on F2 by full-matrix least-squares methods; using
SHELXL-97 [61]. Non-hydrogen atoms were anisotropically refined.
H-atoms were included in the refinement on calculated positions
formula [{h h
2-N(PPh2Se)2}2Sr(THF)2] (2) and [{ 2-N(PPh2Se)2}2
-
Ba(THF)3] (3) via the elimination of volatile bis(trimethylsilyl)
amine. In second method, the compounds 2 and 3 can also be ob-
tained by the reaction of respective alkaline earth metal diiodides
with potassium salt of diselenoimidodiphosphine [K{N(Ph2PSe)2}]
which was prepared according to the literature procedure involving
1 and potassium bis-trimethylsilylamide [33]. The novel alkaline
earth metal complexes 2e3 were characterized by analytical/
spectroscopic techniques and the molecular structures of
both strontium and barium diselenoimidodiphosphinato com-
plexes were determined by single crystal X-ray diffraction analyses
(Scheme 1).
riding on their carrier atoms. The function minimized was
P
[
w(Fo2
ꢀ
F2c)2] (w
¼
1/[
s
s
2(Fo2)
þ
(aP)2
þ
bP]), where
P ¼ (Max(Fo2,0) þ 2F2c)/3 with
2(Fo2) from counting statistics. The
function R1 and wR2 were (SjjFoj ꢀ jFcjj)/SjFoj and [Sw(Fo2 ꢀ Fc2)2/
S(wFo4)]1/2, respectively. The ORTEP-3 programwas used to draw the
molecule. Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as a supplementary publi-
cation no. CCDC 926079 (2), 926077 (3), 926078 (4). Copies of the
data can be obtained free of charge on application to CCDC,12 Union
Road, Cambridge CB21EZ, UK (fax: þ (44)1223 336 033; email:
deposit@ccdc.cam.ac.uk).
A strong absorption at 539 cmꢀ1 (for 2), and 538 cmꢀ1 (for 3)
in FT IR spectra indicates the evidence of P¼Se bond into the each
complex. However, the P¼Se bond stretching frequencies for
compound 2 and 3 is shifted to lower value compared to the
neutral ligand 1 (595 cmꢀ1) due slight elongation of PeSe bond
[56]. In 1H NMR spectra, the amino proton of the ligand 1 which
was present at 4.42 ppm is absent. The multiplet signals at 3.49
and 1.26 ppm (for 2) 3.58 and 1.39 ppm (for 3) can be assigned
for solvated THF molecules coordinated to the metal centre. One
set of signals for the phenyl protons are also observed which is in
the same range to that of ligand 1 indicating no significant effect
of metal atoms onto the phenyl groups due to complex forma-
tion. In 31P{1H} NMR spectra, in complexes 2e3, all the phos-
phorus atoms present in the two diselenoimidodiphosphinato
moieties are chemically equivalent and show only one signal at
43.3 ppm and 43.7 ppm respectively and these values are
significantly high field shifted to that of compound 1 (52.6 ppm)
upon coordination of strontium or barium atom onto the sele-
nium atom of the diselenoimidodiphosphinato ligand. This
observation is opposite to our previous studies where we noticed
a down field shift for the resonance of phosphorus atoms
(71.9 ppm for Ca, 71.8 ppm for Sr and 71.9 for Ba) bound to
heavier alkaline earth metals compared to free phosphinosele-
noic amido ligand (58.0 ppm) [31].
2: C56H56N2O2P4Se4Sr; FW ¼ 1316.37; (CCDC 926079), Ortho-
ꢀ
ꢀ
rhombic, P b c a; lattice constants a ¼ 10.9194(6) A, b ¼ 17.2140(6) A,
3
ꢀ
ꢁ
ꢀ
c ¼ 29.4632(9) A;
a
¼
b
¼
g
¼ 90 ; V ¼ 5538.1(4) A ; T ¼ 150(2) K,
l
¼ 1.54184 A; Z ¼ 4; Dcalc ¼ 1.579 g cmꢀ3
;
m
(Cu-Ka) ¼ 5.781 mmꢀ1
;
ꢀ
qmax. ¼ 70.77; 14,408 [Rint ¼ 0.0423] independent reflections
measured, of which 5242 were considered observed with I > 2s(I);
max. residual electron density 0.547 and ꢀ0.601 e/Aꢀ3; 313 pa-
rameters, R1 (I > 2
s
(I)) ¼ 0.0370; wR2 (all data) ¼ 0.1045.
3: C60H64BaN2O3P4Se4; FW ¼ 1438.18; (CCDC 926077), mono-
ꢀ
ꢀ
3
ꢀ
clinic, C 2/c; lattice constants a ¼ 33.7336(18) A, b ¼ 11.8971(10) A,
c ¼ 18.1604(10) A;
a
¼
g
¼ 90ꢁ,
b
¼ 104.155; V ¼ 7067.1(8) A ;
ꢀ
T ¼ 150(2) K,
l
¼ 1.54184 A; Z ¼ 4; Dcalc ¼ 1.352 g cmꢀ3
; m(Cu-
ꢀ
Ka) ¼ 7.88 mmꢀ1
qmax. ¼ 70.96; 14,980 [Rint ¼ 0.0392] independent
;
reflections measured, of which 6696 were considered observed with
I > 2
s
(I); max. Residual electron density 2.720 and ꢀ0.819 e/Aꢀ3
;
335 parameters, R1 (I > 2
s
(I)) ¼ 0.0688; wR2 (all data) ¼ 0.2321.
4: C32H36LiNO2P2Se2; FW ¼ 693.42; (CCDC 926078), monoclinic,
ꢀ
ꢀ
C
c; lattice constants
a
¼
22.0095(5) A,
b
b
¼
9.1496(2) A,
3
ꢀ
c ¼ 17.3861(5) A;
a
¼
g
¼ 90ꢁ,
¼ 113.821(3); V ¼ 3202.92(14) A ;
ꢀ
T ¼ 150(2) K,
l
¼ 1.54184 A; Z ¼ 4; Dcalc ¼ 1.438 g cmꢀ3
; m(Cu-
ꢀ
Ka) ¼ 4.052 mmꢀ1
qmax. ¼ 70.69; 6127 [Rint ¼ 0.0200] independent
;
reflections measured, of which 3804 were considered observed
Although there has been ongoing interest in alkaline earth or-
ganometallics [62] and particularly in the cyclopentadienyl chem-
istry of these elements [63], 2e3 represents e to the best of our
knowledge e the first diselenoimidodiphosphinato alkaline earth
with I > 2
Aꢀ3
335 parameters, R1 (I
data) ¼ 0.0770.
s
(I); max. residual electron density 0.538 and ꢀ0.642 e/
;
>
2
s
(I)) 0.0292; wR2 (all
¼
Scheme 1. Synthesis of diselenoimidodiphosphinato strontium (2) and barium (3) complexes by two synthetic routes.

R.K. Kottalanka et al. / Journal of Organometallic Chemistry 740 (2013) 104e109
107
ꢀ
Fig. 1. ORTEP diagram of 2 with thermal displacement parameters drawn at the 30% probability level; hydrogen atoms were omitted for clarity. Selected bond lengths [A] and bond
angles [ꢁ]. P(1)eN(1) 1.588(3), P(2)eN(1) 1.581(3), P(1)eSe(1) 2.1515(8), P(2)eSe(2) 2.1583(8), P(1)eC(1) 1.822(3), P(1)eC(7) 1.819(3), P(2)eC(13) 1.821(3), P(2)eC(19) 1.823(3),
Sr(1)eSe(1) 3.1013(4), Sr(1)eSe(1)i 3.1013(3), Sr(1)eSe(2) 3.1262(3), Sr(1)eSe(2)i 3.1262(3), Sr(1)eO(1) 2.523(2) Sr(1)eO(1)i 2.523(2) N(1)eP(1)eSe(1) 120.79(10), N(1)eP(2)eSe(2)
120.01(10), P(1)eN(1)eP(2) 141.44(18), Se(1)eSr(1)eSe(2) 94.512(9), P(1)eSe(1)eSr(1) 104.96(2), P(2)eSe(2)eSr(1) 103.23(2), N(1)eP(1)eC(1) 106.95(14), N(1)eP(1)eC(7)
105.39(14), N(1)eP(2)eC(13) 105.45(14), N(1)eP(2)eC(19) 110.25(14), O(1)eSr(1)eSe(1) 91.43(6), O(1)ieSr(1)eSe(1) 88.57(6), O(1)ieSr(1)eO(1) 180.0, O(1)eSr(1)eSe(2) 86.89(6),
O(1)eSr(1)eSe(2)i 93.11(6).
metal complexes. Therefore, their molecular structures in the solid
state were determined by X-ray diffraction analysis. The strontium
complex 2 crystallizes in orthorhombic space group P bca having
four molecules in the unit cell. Structural parameters for compound
2 are given in experimental section. The molecular structure of
compound 2 is shown in Fig. 1. In the centrosymmetric molecule 2,
the coordination polyhedron is formed by two monoanionic
{N(Ph2P(Se))}ꢀ ligands, and two THF molecules which are trans to
each other. Each {N(Ph2P(Se)}ꢀ ligand coordinates to the strontium
atom via chelation of two selenium atoms having a distance of
In contrast to the strontium complex 2, barium dis-
elenoimidodiphosphinato complex 3 crystallizes in the monoclinic
space group C2/c having four molecules of 3 in the unit cell. The
details of the structural parameters are given in the experimental
section. The solid state structure of the complex 3 is given in Fig. 2.
Similar with strontium complex, in the barium complex 3, the co-
ordination polyhedron is formed by two {{N(Ph2PSe)2}ꢀ ligands,
and three THF molecules. As expected from the larger atomic radius
of Ba2þ [64], Ba1eO (2.707(5), 2.796(8) A), and Ba1eSe (3.3842(8),
ꢀ
ꢀ
3.3524(8) A) distances are elongated in comparison with the cor-
responding values determined for the Sr2þ complexes 2 (SreO
ꢀ
3.1013(4) A. The amido nitrogen is not coordinating to the stron-
ꢀ
ꢀ
ꢀ
tium atom as Sr1eN1 distance of 4.422 A is very high. The Sr1eSe
2.523(2) A and SreSe 3.1013(4) and 3.1262(3) A). However the Bae
O and BaeSe distances are within the range to that (BaeO 2.716(6)
ꢀ
distance (3.1013(4) and 3.1262(3) A) are within the range of SreSe
ꢀ
ꢀ
distance 3.1356(9) A for [Sr(THF)2{Ph2P(Se)N(CHPh2)}2] reported
and BaeSe 3.3553(10) A) our previously observed barium com-
ꢀ
by us [31], (3.138(7)e3.196(9) A) for [(THF)3Sr(Se2PPh2)2] published
pound [Ba(THF)2{Ph2P(Se)N(CHPh2)}2] [31] and also within the
ꢀ
ꢀ
very recently by Westerhausen et al., and (3.066(1) A) for the
range of reported value 3.2787(11) A for the complex [Ba(TH-
ꢀ
complex [Sr{Se(2,4,6-tBu3C6H2)}2(THF)4] [24]. The center metal is
additionally ligated by two THF molecules having SreO distance of
F)4(SeMes*)2] (Mes*
¼
2,4,6-tBu3C6H2) and 3.2973(3)
A
for
[Ba(Py)3(THF)-(SeTrip)2}2] (Trip ¼ 2,4,6 iPr3C6H2) reported by
Ruhlandt-Senge et al. [23]. Thus the central atom barium adopts a
distorted pentagonal bipyramidal geometry due to coordination
from two 1 moieties and three THF molecules. Two six-membered
metallacycles Ba1eSe1eP1eN1eP2eSe2 and Ba1eSe1ieP1ieN1ie
P2ieSe2i are formed due to ligation of two ligand moieties via se-
lenium atoms. In complex 3, the six-membered BaSe2P2N metal-
lacycle is nonplanar and adopts a twisted boat conformation similar
to that of strontium complex 2. For the metallacycle Ba1eSe1eP1e
ꢀ
2.523(2) A to adopt the strontium atom distorted octahedron ge-
ometry. The P1eN1eP2 angle of 141.44(18)ꢁ is slightly more than
that (130.3(3)ꢁ and 133.1(3))ꢁ of diselenoimidodiphosphinato co-
balt complex [Co{N(Ph2PSe)2}2] reported by Novosad et al. [49]
Thus two six-membered metallacycles Sr1eSe1eP1eN1eP2eSe2
and Sr1eSe1ieP1ieN1ieP2ieSe2i are formed due to ligation of two
ligand moieties via selenium atoms. The plane containing P1, Se1,
Sr1 makes a dihedral angle of 28.39ꢁ with the plane having P2, Se2,
Sr1 atoms. The six-membered SrSe2P2N metallacycle is nonplanar
and adopt a twisted boat conformation. For the metallacycle Sr1e
ꢀ
ꢀ
N1eP2eSe2, the atoms P2 and Se1 reside 0.437 A and 0.527 A
above the mean plane having Ba1, Se1, P1, N1, P2, Se2 atoms
ꢀ
ꢀ
ꢀ
ꢀ
Se1eP1eN1eP2eSe2, the atoms P2 and Se1 reside 0.668 A and
respectively whereas Ba1 (0.140 A), Se2 (0.129 A), N1(0.083 A) and
ꢀ
ꢀ
0.521 A above the mean plane having Sr1, Se1, P1, N1, P2, Se2 atoms
P1(0.613 A) are located below the mean plane. Similar to strontium
ꢀ
ꢀ
ꢀ
respectively whereas Sr1 (0.076 A), Se2 (0.092 A), N1(0.046 A) and
complex, no interaction between the amido nitrogen and barium
atom was observed. Nevertheless complex 3 is another example of
barium seleno complex having barium selenium direct contact.
Lithium complex: alkali metal salts are important precursors for
salt metathesis reaction. Various alkali metal salts of {N(PR2Se)2}
ligand are known, however the [Li{N(P(ipr)2Se)2}] was prepared by
ꢀ
P1(0.312 A) are located below the mean plane.
The PeSe bond distances (2.1515(8) and 2.1583(8) A) and PeN
bond distances (1.588(3) and 1.581(3) A) are within the range to
that of (2.0992(14) and 2.1913(13) A) and (1.577(7) and 1.609(4) A)
respectively for [Co{N(Ph2PSe)2}2] [49].
ꢀ
ꢀ
ꢀ
ꢀ

108
R.K. Kottalanka et al. / Journal of Organometallic Chemistry 740 (2013) 104e109
ꢀ
Fig. 2. ORTEP diagram of 3 with thermal displacement parameters drawn at the 30% probability level; hydrogen atoms were omitted for clarity. Selected bond lengths [A] and bond
angles [ꢁ]. P(1)eN(1) 1.588(5), P(2)eN(1) 1.585(5), P(1)eSe(1) 2.1393(14), P(2)eSe(2) 2.1440(17), P(1)eC(1) 1.818(6), P(1)eC(7) 1.819(6), P(2)eC(13) 1.821(7), P(2)eC(19) 1.811(6),
Ba(1)eSe(1) 3.3842(8), Ba(1)eSe(1)i 3.3842(8), Ba(1)eSe(2) 3.3524(8), Ba(1)eSe(2)i 3.3524(8), Ba(1)eO(1) 2.796(8), Ba(1)eO(2) 2.707(5), Ba(1)eO(2)i 2.707(5), N(1)eP(1)eSe(1)
119.5(2), N(1)eP(2)eSe(2) 121.0(2), P(1)eN(1)eP(2) 135.3(3), Se(1)eBa(1)eSe(2) 82.371(19), P(1)eSe(1)eBa(1) 101.68(4), P(2)eSe(2)eBa(1) 114.06(5), N(1)eP(1)eC(1) 103.8(3),
N(1)eP(1)eC(7) 110.1(3), N(1)eP(2)eC(13) 107.9(3), N(1)eP(2)eC(19) 105.0(3), O(2)eBa(1)eO(1) 76.69(14), O(2)eBa(1)eO(2)i 153.4(3), O(1)eBa(1)eSe(2) 67.253(17), O(2)eBa(1)e
Se(2) 78.68(11).
Chivers et al. involving the reaction of n-BuLi and [HN(P(iPr)2Se)2]
in the presence of TMEDA at ꢀ78ꢁ [32]. Here we report an
alternative method to synthesize the lithium salt of dis-
elenoimidodiphosphinato ligand without using TMEDA. The
treatment of 1 with LiCH2SiMe3 in 1:1 M ratio in THF at ambient
previously reported [
h
2-N(P(ipr)2Se)Li(TMEDA)] complex [32]. The
ꢀ
LieO distances of 1.950(7) and 1.932(7) A are within the reported
values. The lithium atom adopts a distorted tetrahedral geometry
due to the ligation of two selenium atoms and two THF molecules.
temperature afforded the lithium salt of molecular formula [h2
-
N(PPh2Se)Li(THF)2] (4) through the elimination of volatile tetra-
methylsilane in good yield (Scheme 2). The compound 4 was
characterized by analytical/spectroscopic technique and the solid
state structure of the complex 4 was determined by single crystal X-
ray diffraction analysis.
In 1H NMR spectra of 4, the coordinated THF molecules appear at
3.49 and 1.26 ppm as multiplet along with the phenyl protons in the
expected range. The 31P{1H} NMR spectra one singlet is observed at
42.9 ppm indicating both the phosphorus atoms are magnetically
equivalent. Compound 4 was recrystallized from THF/pentane (1:2)
and crystallizes in monoclinic space group Cc having four molecules
in the unit cell. The solid state structure of the complex 4 is given in
Fig. 3. The details of the structural parameters are given in Section
2. The coordination polyhedron of the complex 4 is formed by the
chelation of two selenium atoms of the ligand moiety along with
two THF molecules. No interaction between amido nitrogen and
lithium atoms was observed. LieSe distances 2.598(7) and
ꢀ
ꢀ
2.606(7) A are within the range to that of (2.556(9) and 2.52(8) A)
Fig. 3. ORTEP diagram of 4 with thermal displacement parameters drawn at the 30%
ꢀ
probability level; hydrogen atoms were omitted for clarity. Selected bond lengths [A]
and bond angles [ꢁ]. P(1)eN(1) 1.594(3), P(2)eN(1) 1.597(3), P(1)eSe(2) 2.1453(9),
P(2)eSe(1) 2.1462(9), P(1)eC(1) 1.827(3), P(1)eC(7) 1.819(4), P(2)eC(13) 1.822(3),
P(2)eC(19) 1.825(3), Li(1)eSe(1) 2.598(7), Li(1)eSe(2) 2.606(7) Li(1)eO(1) 1.950(7),
Li(1)eO(2) 1.932(7), N(1)eP(1)eSe(2) 120.19(12), N(1)eP(2)eSe(1) 119.79(11), P(1)e
N(1)eP(2) 133.7(2), Se(1)eLi(1)eSe(2) 113.2(2), P(1)eSe(2)eLi(1) 93.27(15), P(2)e
Se(1)eLi(1) 98.44(15), N(1)eP(1)eC(1) 108.56(16), N(1)eP(1)eC(7) 103.27(16), N(1)e
P(2)eC(13) 104.41(16), N(1)eP(2)eC(19) 108.17(17), O(2)eLi(1)eO(1) 109.7(3), O(2)e
Li(1)eSe(1) 105.5(3), O(1)eLi(1)eSe(1) 105.5(3), O(2)eLi(1)eSe(2) 111.9(3).
Scheme 2. Synthesis of diselenoimidodiphosphinato lithium compound 4.

R.K. Kottalanka et al. / Journal of Organometallic Chemistry 740 (2013) 104e109
109
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ꢀ
ꢀ
Li1eSe1eP2eN1eP1eSe2, the atoms Se2 (0.403 A), P2 (0.509 A),
ꢀ
N1 (0.013 A) above the weighted least-squares best plane having
ꢀ
ꢀ
Ba1, Se1, P1, N1, P2, Se2 atoms whereas Li1 (0.053 A), P1 (0.566 A)
ꢀ
and Se1 (0.280 A) are located below the mean plane.
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In conclusion, we have reported the missing group 2 metal
complexes of diselenoimidodiphosphinato by synthesizing stron-
tium and barium complexes via two synthetic routes using dis-
elenoimidodiphosphinato ligand. In first method silylamide route
and in the second method salt metathesis route was used to
prepare the target compounds. Strontium complex 2 adopted
distorted octahedral geometry whereas geometry of the larger
barium atom in complex 3 can be best described as distorted
pentagonal bipyramidal and the MeSe bond distances are
increasing from SreSe to BaeSe bond. Finally, synthesis of the
lithium diselenoimidodiphosphonato complex was achieved by
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the X-ray analysis.
Acknowledgements
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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. thanks
UGC, India and S.A. thanks CSIR, India for their PhD fellowship.
Generous support from K. Mashima, Osaka University, Japan is
gratefully acknowledged. We thank to the reviewers for their
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Appendix A. Supplementary data
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