Functionalized cyclodiphosphazanes cis-[tBuNP(OR)]2 (R=C6H4OMe-o, CH2CH2OMe, CH2CH2SMe, CH2CH2NMe2) as neutral 2e, 4e or 8e donor liga

Article abstract of DOI:10.1016/j.jorganchem.2007.01.048

Cyclodiphosphazanes having donor functionalities such as cis-[^tBuNP(OR)]₂ (R = C₆H₄OMe-o (2); R = CH₂CH₂OMe (3); R = CH₂CH₂SMe (4); R = CH₂CH₂NMe

Full text of DOI:10.1016/j.jorganchem.2007.01.048

Journal of Organometallic Chemistry 692 (2007) 2642–2648
www.elsevier.com/locate/jorganchem
Functionalized cyclodiphosphazanes cis-[tBuNP(OR)]2
(R=C6H4OMe-o, CH2CH2OMe, CH2CH2SMe, CH2CH2NMe2)
as neutral 2e, 4e or 8e donor ligands
Maravanji S. Balakrishna*, P. Chandrasekaran, Ramalingam Venkateswaran
Phosphorus Laboratory, Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400 076, India
Received 15 October 2006; received in revised form 26 January 2007; accepted 26 January 2007
Available online 3 February 2007
Abstract
Cyclodiphosphazanes having donor functionalities such as cis-[tBuNP(OR)]2 (R = C6H4OMe-o (2); R = CH2CH2OMe (3);
R = CH2CH2SMe (4); R = CH2CH2NMe2 (5)) were obtained in good yield by reacting cis-[tBuNPCl]2 (1) with corresponding nucleo-
philes. The reactions of 2–5 with [RuCl2(g6-cymene)]2, [MCl(COD)]2 (M = Rh, Ir), [PdCl2(PEt3)]2 and [MCl2(COD)] (M=Pd, Pt) result
in the formation of exclusively monocoordinated mononuclear complexes of the type cis-[{tBuNP(OR)}2MLn-jP] irrespective of the
reaction stoichiometry and the reaction conditions. In contrast, 2–5 react with [RhCl(CO)2]2, [PdCl(g3-C3H5)]2, CuX (X=Cl, Br, I)
to give homobinuclear complexes. Interestingly, CuX produces both mono and binuclear complexes depending on the stoichiometry
of the reactants and the reaction conditions. The mononuclear complexes on treatment with appropriate metal reagents furnish hetero-
metallic complexes.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Cyclodiphosphazanes; Transition metals; Monodentate; Bidentate; Heterometallic complexes; Coordination polymers
1. Introduction
nuclear complexes of group 6 and 8 metals with cyclodiphos-
phazanes showing both mono- and bridged bidentate modes
of coordination. Recently, we have reported [5–8] on the
synthesis, reactivity and transition metal chemistry of sev-
eral functionalized cyclodiphosphazanes of the type cis-
[ROP(l-NtBu)]2(R=C6H4OMe-o (2), CH2CH2OMe (3),
CH2CH2SMe (4), CH2CH2NMe2 (5)) and the details are
summarized in this account.
The main group and transition metal chemistry of dian-
ionic bis(amido)cyclodiphophazanes, cis-[tBuNP(tBuNÀ)]2
and their chalcogen derivatives, cis-[tBuNP(E)(tBuNÀ)]2
(E = S or Se) has been extensively studied by Chivers [1]
and Stahl [2]. Several other groups have explored the reactiv-
ity of chloro derivative cis-[tBuNPCl]2 (1) which resulted not
only in the isolation of dimeric to pentameric macrocycles
but also in understanding the thermodynamics and mecha-
nistic aspects involved in these reactions [3]. Surprisingly,
the coordination chemistry of neutral cyclodiphosphazanes
is scant in spite of their ability to show monodentate and
bridged bidentate modes of coordination. Krishnmurthy
and coworkers [4] have reported some homo- and heterobi-
2. Synthesis of functionalized cyclodiphosphazanes
Cyclodiphosphazanes of the type [ROP(l-NtBu)]2
(R = C6H4OMe-o (2), CH2CH2OMe (3), CH2CH2SMe
(4), CH2CH2NMe2 (5)) containing donor functionalities
have been prepared by reacting [ClP(l-NtBu)]2 (1) with
two equivalents of 2-(methoxy)phenol or 2-substituted
ethanols, HOCH2CH2E (E = OMe, SMe, NMe2) as
shown in Scheme 1. The reactions were carried out either
in presence of Et3N or by using the sodium salts of
*
Corresponding author. Fax: +91 22 2572 3480.
E-mail address: krishna@chem.iitb.ac.in (M.S. Balakrishna).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.01.048

M.S. Balakrishna et al. / Journal of Organometallic Chemistry 692 (2007) 2642–2648
2643
MeO
t Bu
N
OMe
O
O
P
P
N
tBu
2
t Bu
N
2HOCH2CH2EMe
Et3N, Et2O
O
O
P
EMe
2 HOC6H4OMe-
Et3N, Et2O
o
P
EMe
N
t Bu
t Bu
N
3; E = O, 4; E = S
Cl
Cl
P
P
N
tBu
tBu
O
N
O
2NaOCH2CH2NMe2
THF
P
NMe2
1
P
NMe2
N
t Bu
5
Scheme 1.
respective alkoxide derivatives. The phenol derivative 2 is
a crystalline solid whereas the others are oily liquids
which are purified by vacuum distillation [5,6]. All these
compounds exist as cis isomers as confirmed by their
31P NMR spectral data (31P NMR data (dP in ppm): 2,
145.6; 3, 133.8; 4, 134.1; 5, 133.7). The phosphorus-31
chemical shifts due to cis-isomers are more shielded rela-
tive to that of trans-isomers.
4. Rhodium(I) and ruthenium(II) derivatives
The reactions of cyclodiphosphazane derivatives with
[Rh(CO)2Cl]2 afford a variety of products, depending upon
the stoichiometry of the reactants, reaction conditions and
also on the nature of the donor functionalities present in
the pendant groups as shown in Schemes 2 and 3 [5,6].
The tetranuclear complexes 6 and 7 containing two
[Rh(l-Cl)]2 units and two bridging cyclodiphosphazanes
are obtained when the [Rh(CO)2Cl]2 and 2 or 3 were used
in 1:1 molar ratios. Treatment of [Rh(CO)2Cl]2 with four
3. Transition metal chemistry of cyclodiphosphazanes
The cyclodiphosphazanes 2–5 containing a donor arm
on each phosphorus(III) center can act as 2e, 4e, 6e or
8e donor ligands depending on the nature of the metal
derivatives employed, stoichiometry and the reaction con-
ditions (Chart 2). Compounds 2 and 3 have shown only
the bidentate mode and the side arms did not coordinate
to the transition metals whereas the compounds 4 and 5
perform as bischelating ligands with platinum metals
(see Chart 1).
equivalents of 2 afforded trans-[Rh(CO)Cl{(RO)P(l-
NtBu)2P(OR)}2] (10) in quantitative yield [5]. Interestingly,
the reaction of 4 and 5 with one equivalent of [Rh(CO)2Cl]2
in acetonitrile under reflux conditions afforded the dinu-
clear bischelated Rh(I) complexes 8 and 9, respectively,
as shown in Scheme 2. These are the first examples of
cyclodiphosphazanes acting as 8eÀ bischelating ligands.
The 31P NMR spectra of complexes 6–9 show multiplets
with chemical shifts in the range of 115–124 ppm. The
tBu
tBu
N
tBu
O
O
O
O
N
O
O
N
E
E
E
E
P
P
E
P
P
E
P
P
N
tBu
N
tBu
N
tBu
M (or M')
M (or M')
M
M
M
tBu
N
tBu
N
O
O
O
O
E
E
E
E
P
P
P
P
N
tBu
N
tBu
M (or M')
M
M
M
M
M
(or M')
Chart 1. Possible coordination modes of cyclodiphosphazanes with donor functionalities.

2644
M.S. Balakrishna et al. / Journal of Organometallic Chemistry 692 (2007) 2642–2648
tBu
N
tBu
N
RO
OR
RO
OR
P
P
P
P
OC
Cl
CO
Cl
[Rh(CO)2Cl]2
CH3CN
N
N
Rh
tBu
Rh
tBu
2-5
reflux, 4 h
Cl
Cl
[Rh(CO)2Cl]2
CH3CN
tBu
N
Rh
Rh
OC
CO
P
P
N
tBu
OR
RO
tBu
N
O
P
O
E
6 R = C6H4OMe-
o
P
E
7 R = CH2CH2OMe
N
tBu
Rh
Rh
Cl
OC
CO
Cl
8 E = S
9 E = NMe2
Scheme 2.
tBu
N
RO
OC
Rh
OR
P
P
CO
Rh
N
tBu
1:1
[Rh(CO)2Cl]2
tBu
N
Cl
Cl
Cl
Cl
P
RO
P
OR
tBu
N
Rh
P
Rh
CO
OC
N
P
tBu
N
RO
OR
tBu
2 R = C6H4OMe-
o
6
2:1
4:1
[Rh(CO)2Cl]2
[Rh(CO)2Cl]2
[Rh(CO)2Cl]2
2 L
tBu
CO
Rh
OR
tBu
OR
P
OR
OR
tBu
N
N
N
P
P
P
Cl
Cl
CO
Rh
CO
Rh
OR
RO
0.5
N
N
P
N
P
tBu
OR
tBu
RO
tBuN
RO
tBu
[Rh(CO)2Cl]2
tBu
Cl
Cl
P
P
tBu
tBu
N
N
N
10
4 L
P
P
Cl
tBu
N
OR
Rh
Rh
CO
CO
P
P
N
OR
11
OR
tBu
Scheme 3.
2
2JPP and JRhP couplings are in the range 42–47 Hz and
230–250 Hz, respectively. The IR spectra of complexes 6–
10 show two absorptions in the range 1993–2034 cmÀ1
which is clearly consistent with the cis related CO/phos-
phine structures proposed for these complexes [10]. The
structures of compounds 6, 7 and 9 were further confirmed
by low temperature single-crystal X-ray diffraction studies
[5,6].
The NMR tube reaction of complexes 6 and 10, respec-
tively, with 6 equivalents of ligand and 1.5 equivalents of
[RhCl(CO)2]2 showed quantitative conversion into each
other with complex [RhCl(CO){ROP(l-NtBu)}2]4 (11) as
an intermediate as revealed by the 31P NMR spectroscopic
data [10]. Both mono- and tetranuclear complexes have
been structurally characterized. In a separate reaction,
treatment of [Rh(CO)2Cl]2 with {ROP(l-NtBu)}2 in 1:1

M.S. Balakrishna et al. / Journal of Organometallic Chemistry 692 (2007) 2642–2648
2645
ratio afforded the complex 11 in quantitative yield which
5. Palladium and platinum derivatives
shows a doublet at 105 ppm in its 31P NMR spectrum with
1JRhP = 246 Hz. Attempts to grow suitable crystals of 11
for X-rays studies have been unsuccessful.
The reactions of cis-[tBuNP(OC6H4OMe-o)]2 (2) with
[M(COD)Cl2] (M = Pd or Pt), are independent of stoichi-
ometry and the reaction conditions, and afford exclusively
cis complexes, 15 and 16 with the ligand exhibiting mono-
dentate coordination. In contrast, the reaction of two equiv-
alents of 2 with [Pd(NCPh)2Cl2] in dichloromethane affords
a mononuclear trans palladium(II) derivative 17 as shown
in Scheme 4. The 31P NMR spectra of complexes 15 and
The reaction between [MCl(COD)]2 and 2 gave exclu-
sively the monocoordinated complexes, [(COD)MCl-
{ROP(l-NtBu)}2] (12 M = Rh, dPA = 102.8 ppm (1JRhP
=
229 Hz), dPX = 131.7 ppm; 13 M = Ir, dPA = 88.5 ppm;
PX = 133 ppm;) irrespective of the stoichiometry of the
d
reactants and the reaction conditions. The rhodium(I)
complex 12 containing a free phosphorus(III) center is used
as a metalloligand to generate a series of heterometallic
complexes and the details are summarized later in Scheme
6.
The mononuclear Ru(II) complex 14 was prepared [6]
by reacting two equivalents of cis-[tBuNP(OC6H4OMe-
o)]2 (2) with [Ru(g6-p-cymene)Cl2]2 in dichloromethane.
Even, with an excess of metal reagent, only the mononu-
clear product was obtained. In the 31P NMR spectrum of
14, the uncoordinated phosphorus appears as a doublet
centered at 133.5 ppm whereas the chemical shift due to
the coordinated phosphorus appears at 109.6 ppm. The
2JPP coupling is 8.7 Hz.
2
16 show two doublets with a JPP coupling of 53 Hz and
7.3 Hz, respectively. The platinum complex shows a large
1JPtP coupling of 4861 Hz, which is consistent with the pro-
posed cis geometry 16 [9]. The trans-palladium(II) complex
17 exhibits two single resonances at 128.3 and 84.6 ppm,
respectively, for uncoordinated and coordinated phospho-
2
rus centers and no JPP coupling was observed. Treatment
of cis-[tBuNP(OC6H4OMe-o)]2 (2) with palladium(II)
dimer, [Pd(PEt3)Cl2]2 in an equimolar ratio also affords a
mononuclear complex 18 containing monodentate cyclodi-
phosphazane and PEt3 ligands in mutually cis orientations.
The 31P NMR spectrum of complex 18 consists of three
resonances; uncoordinated phosphorus of cyclodiphosp-
hazane and PEt3 appear as doublets at 127.2 (2JPP
=
3.9 Hz) and 35.8 ppm (2JPP = 16.8 Hz) respectively and
are coupled to the coordinated phosphorus, which appears
as a doublet of doublets centered at 85.7 ppm. Further
structural evidence come from 1H NMR and mass spectral
data, elemental analysis and single crystal X-ray diffraction
studies in case of complexes 17 and 18 [6]. The 1:1 reac-
tion between 2 and [PdCl(g3-C3H5)]2 in dichloromethane
affords dinuclear palladium(II) complex, [(PdCl(g3-C3H5))2-
t Bu
N
t Bu
N
RO
M
RO
OR
OR
P
P
P
A
P
X
A
X
Cl
N
N
t Bu
t Bu
Ru
Cl
Cl
R = C6H4OMe-
o
12, M = Rh
13, M = Ir
14
OR
tBu
tBu
N
OR
OR
Pd
N
P
P
RO
P
Cl
P
P
P
N
tBu
N
N
Cl
Cl
tBu
tBu
M
Cl
P
tBu
N
N
tBu
[M(COD)Cl2]
CH2Cl2
RO
17
OR
[Pd(NCPh)2Cl2]
CH2Cl2
RO
N
P
tBu
15, M = Pd
16, M = Pt
OR
tBu
N
RO
OR
P
P
[Pd(PEt3)Cl2]2
CH2Cl2
N
tBu
3
[PdCl( C3H5)]2
2
R = C6H4OMe-
o
CH2Cl2
tBu
N
RO
P
OR
Pd
tBu
N
RO
OR
P
P
PEt3
Cl
P
N
tBu
Pd
Cl
N
tBu
Pd
Cl
19
Cl
18
Scheme 4.

2646
M.S. Balakrishna et al. / Journal of Organometallic Chemistry 692 (2007) 2642–2648
{(tBuNP(OC6H4OMe-o))2-jP}] (19) with cyclodiphosphaz-
ane acting as a bridging ligand. The 31P NMR spectrum of
19 shows a sharp singlet at 121.1 ppm indicating the sym-
metrical coordination of cyclodiphosphazane.
polymers [Cu2X2{tBuNP(OC6H4OMe-o)}2]n (20; X = Cl,
21; X = Br, 22; X = I). The crystal structures of 20 and
22 reveal a zig-zag arrangement of [P(l-N)2P] and [Cu(l-
X)2Cu] units in an alternating manner to form one dimen-
sional copper(I) coordination polymers. The reaction
between cis-[tBuNP(OC6H4OMe-o)]2 (1) and CuX in a
2:1 ratio afforded mononuclear tricoordinated copper(I)
complexes of the type [CuX{(tBuNP(OC6H4OMe-o))2}2]
(23; X = Cl, 24; X = Br, 25; X = I). The single crystal X-
ray structures were established for the mononuclear cop-
per(I) complexes 23 and 24. When the reactant ratios are
1:1, the formation of a mixture of polymeric and mononu-
clear products was observed. The Cu(I) polymers (20–22)
were converted into the mononuclear complexes (23–25)
by reacting with three equivalents of cis-[tBuNP(O-
C6H4OMe-o)]2 (1) in DMSO. Similarly, the mononuclear
complexes (23–25) were converted into the corresponding
polymeric complexes (20–22) with three equivalents of cop-
per(I) halide under mild reaction conditions. The com-
plexes are the first examples coordination polymers
containing cyclodiophosphazanes [8] (see Scheme 5).
6. Copper(I) derivatives
Cyclodiphosphazanes containing two P(III) centers in a
mutually cis-orientations can interact with CuX, which
prefers either trigonal planar or tetrahedral geometries, to
give a variety of products as shown in Chart 2. In these
reactions, the choice of the product formation depends
on the stoichiometry of the reactants and the reaction con-
ditions which is also guided by both the kinetic and the
thermodynamic aspects. So far, the stoichiometry con-
trolled reactions have yielded products of the type I–III
[8] and attempts are being made to synthesize the products
of the type IV and V.
The reactions of cyclodiphosphazane, cis-[tBuNP(O-
C6H4OMe-o)]2 (1) with two equivalents of CuX in acetoni-
trile afforded one dimensional copper(I) coordination
CuX
M
+
L
tBu
N
P
tBu
N
OMe
MeO
L =
O
O
P
X
L:M
1:1
I
X
2:1
1:2
II
X
X
III
1.5:1
3:1
IV
V
Chart 2. Structural possibilities in the reactions of cis-[tBuNP(OC6H4OMe-o)]2 with CuX (X=Cl, Br, I).

M.S. Balakrishna et al. / Journal of Organometallic Chemistry 692 (2007) 2642–2648
2647
tBu
RO
OR
Cu
N
2CuX
P
P
N
CH3CN
X
tBu
tBu
N
20, X = Cl
21, X = Br
22, X = I
X
Cu
RO
OR
n
P
P
3[(RO)P( -NtBu)]2
3 CuX
N
tBu
2
X
tBu
tBu
N
R = C6H4OMe-
o
N
P
Cu
OR
0.5 CuX
CH3CN
23, X = Cl
24, X = Br
25, X = I
OR
P
P
N
P
tBu
N
RO
OR
tBu
Scheme 5.
7. Heterometallic complexes of cyclodiphosphazanes
bimetallic complexes bridged by the cyclodiphosphazane,
cis-[tBuNP(OC6H4Me-p)]2. Apart from this, there are no
reports on any other heterometallic complexes of cyclo-
diphosphazanes. Our recent studies on transition metal
chemistry of cyclodiphosphazane have shown the follow-
ing preferential coordination modes (Chart 3) depending
upon the type of metal derivatives employed in the com-
plexation reactions. From the chart it is clear that some of
the rhodium(I), palladium(II) and ruthenium(II) deriva-
tives preferably form monocoordinated complexes leaving
the other phosphorus(III) center uncoordinated. Interest-
ingly, these isolated complexes containing a free phospho-
rus(III) end react further with various metal derivatives to
give a series of heterometallic complexes [10,11] as shown
in Scheme 6.
Previously Krishnamurthy and coworkers have
reported [4b,4c] molybdenum(0) based homo- and hetero-
t Bu
N
t Bu
N
RO
OR
RO
OR
P
P
P
P
A
X
A
X
N
N
t Bu
t Bu
MLn
MLn
MLn
R = C6H4OMe-
[RuCl2( 6-cymene)]2
[MCl(COD)]2 (M = Rh, Ir)
[PdCl2(PEt3)]2
[RhCl(CO)2]2
[PdCl( 3-C3H5)]2
CuX (X = Cl, Br, I)
AuClSMe2
o
[MCl2(COD)] (M = Pd, Pt)
The complex 12 reacts with AuCl(SMe2) to give hetero-
binuclear complex 26 in quantitative yield. Treatment of 12
Chart 3. Preferred coordination modes for various transition metals.
tBu
N
RO
OR
P
P
X
A
N
Rh
tBu
Cl
AuCl(SMe2)
0.5 [PdCl(C3H5)]2
CH2Cl2
CH2Cl2
tBu
N
tBu
N
RO
RO
OR
OR
Rh
2CuX
P
P
P
P
X
A
X
A
N
N
Au
Cl
Pd
Rh
Cl
tBu
tBu
Cl
Cl
26
27
tBu
OR
tBu
N
RO
RO
Cu
OR
N
P
P
P
P
X
A
X
A
X
X
N
N
Rh
Cl
Rh
Cu
tBu
tBu
Cl
(28, X = Cl; 29, X = Br; 30, X = I)
Scheme 6.

2648
M.S. Balakrishna et al. / Journal of Organometallic Chemistry 692 (2007) 2642–2648
with 0.5 equivalent of [PdCl(g3-C3H5)]2 produces Pd/Rh
complex 27, whereas the reaction between 12 and CuX
(X = Cl, Br, I) produces tetranuclear (2RhI/2CuI) com-
plexes (28–30) containing rhombic [Cu(l-X)2Cu] units as
shown in Scheme 6. The 31P NMR spectrum of 26 consists
of two sets of doublet of doublets centered at 104.7 and
94.1 ppm assigned to gold- and rhodium-coordinated phos-
phorus centers respectively. The gold bound phosphorus
Acknowledgements
We are grateful to the Department of Science and Tech-
nology (DST), New Delhi, for funding and Prof. J. T. Ma-
gue for X-ray diffraction studies.
References
3
2
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center shows JRhP of 5.5 Hz along with a JPP of 30 Hz.
1
The rhodium bound phosphorus center shows JRhP cou-
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at 130.6 ppm (2JPP = 37 Hz) for palladium coordinated
phosphorus center and a doublet of doublets centered at
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The cyclodiophosphazanes containing donor function-
alities exhibit versatile coordination properties. The exclu-
sive formation of either cis or trans palladium(II)
complexes was achieved by using appropriate metal
reagents. The reactions with RhI, IrI, PdII and RuII metal
dimers selectively afforded the corresponding mononu-
clear complexes which are effectively used as metallo-
ligands to generate a series of heterometallic complexes.
Cyclodiphosphzanes containing ether functionalities were
found to preferably form tetranuclear rhodium(I) com-
plexes, whereas those with thioether and amine function-
alities gave the corresponding bischelated complexes. The
latter complexes are the first examples of cyclodiphospha-
zanes performing as eight-electron donor tetradenate
ligands. The CuI coordination polymers of cyclodiphos-
phazanes undergo rare reversible transformations into
the corresponding mononuclear complexes. Although,
cis conformers are not kinetically suited for extending
the linear propagation to give the coordination polymers,
the formation of rhombic [Cu(l-X)]2 units during the
reaction and their flexible orientations and variable coor-
dination numbers of CuI centers facilitated the formation
of coordination polymers. Further preparation of polynu-
clear complexes and high nuclearity clusters of platinum
metals is in progress.
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