Di- and tetranulcear RuII complexes of phenylene-1,4-diaminotetra(phosphonite), p-C6H4[N{P(OC6H4OMe-o)2}2]2 and their catalytic investigation towards transfer hydrogen

Article abstract of DOI:10.1016/j.jorganchem.2009.07.002

The stoichiometric reaction of phenylene-1,4-diaminotetra(phosphonite), p-C₆H₄[N{P(OC₆H₄OMe-o)₂}₂]₂ (P₂NF{cyrillic}NP₂) (1) with [RuCl₂(p-cymene)

Full text of DOI:10.1016/j.jorganchem.2009.07.002

Journal of Organometallic Chemistry 694 (2009) 3390–3394
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Di- and tetranulcear RuII complexes of phenylene-1,4-diaminotetra(phosphonite),
p-C6H4[N{P(OC6H4OMe-o)2}2]2 and their catalytic investigation towards
transfer hydrogenation reactions
b
Chelladurai Ganesamoorthy a, Maravanji S. Balakrishna a, , Joel T. Mague
*
a Phosphorus Laboratory, Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400 076, India
b Department of Chemistry, Tulane University, New Orleans, Lousiana 70118, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 May 2009
Received in revised form 22 June 2009
Accepted 1 July 2009
Available online 5 July 2009
The stoichiometric reaction of phenylene-1,4-diaminotetra(phosphonite), p-C6H4[N{P(OC6H4OMe-o)2}2]2
(P2NUNP2) (1) with [RuCl2(p-cymene)]2 in acetonitrile produces cis,cis-[{RuCl2(CH3CN)2}2(P2NUNP2)] (2),
whereas the similar reaction of 1 with [RuCl2(p-cymene)]2 in THF medium affords a tri-chloro-bridged
tetrametallic complex, [{(g l2-Cl)3Cl}2(P2NUNP2)] (3) irrespective of the stoichiometry
6-p-cymene)Ru2(
and reaction conditions. The formation and structure of complexes 2 and 3 are assigned through various
spectroscopic and micro analysis data. The molecular structure of 2 is confirmed by single crystal X-ray
diffraction study. The catalytic activities of complexes 2 and 3 have been investigated in transfer hydro-
genation reactions.
Keywords:
Tetraphosphonite
RuII complexes
Ó 2009 Elsevier B.V. All rights reserved.
Tetradentate ligands
Transfer hydrogenation reactions
1. Introduction
phine), PhN{P(OC6H4OMe-o)2}2 in combination with various
pyridyl ligands to make several multinuclear mixed ligand com-
The design and synthesis of phosphine ligands has been an ac-
tive field of research over several years as their metal complexes
play a major role in various organic transformation reactions [1].
Particularly, aminophosphines (phosphines having P–N bonds)
have generated considerable interest because of their easier syn-
thetic methodologies which facilitate tuning of steric and elec-
tronic properties around phosphorus centers [2]. A variety of
aminophosphines can be readily prepared by treating primary or
secondary amines with halo phosphines (Eq. (1)).
plexes including 2D and 3D coordination polymers [4]. We have
also reported the synthesis of PdII, PtII, RhI and Group 11 com-
plexes, and catalytic applications of
a tetraphosphonite, p-
C6H4[N{P(OC6H4OMe-o)2}2]2 (1) (hereafter referred as P2NUNP2)
[5]. As a part of our interest in the transition metal chemistry of
cyclic and acyclic diphosphazane ligands [6] and their catalytic
applications [7], we describe herein the coordinating behavior of
P2NUNP2 (1) towards RuII derivative and their utility in transfer
hydrogenation reactions.
ð3ꢀxÞEt3
RxPClð3ꢀxÞ þð3 ꢀ xÞR0 NHð3ꢀyÞ
!
N RxPðNR0Þð3ꢀxÞ þ ð3 ꢀ xÞEt3N ꢁ HCl
y
2. Experimental section
x¼0ꢀ3
y¼1 or 2
ð1Þ
2.1. General procedures
Although these reactions look simple the choice of the product
formation depends heavily on the reaction conditions and stoichi-
ometry. Often the reactions lead to the formation of a mixture of
products which can not be separated through conventional column
chromatography other than fractional crystallization or distillation
methods. We have a long standing interest in designing amino-
phosphine ligands appended with additional hetero-donor atoms
to explore their transition metal chemistry and catalytic applica-
tions [3]. Recently, we have utilized a ‘‘short-bite” aminobis(phos-
All manipulations were performed under rigorously anaerobic
conditions using Schlenk techniques. All the solvents were purified
by conventional procedures and distilled prior to use [8]. Com-
pounds p-C6H4[N{P(OC6H4OMe-o)2}2]2 [5c] and [RuCl2(p-cym-
ene)]2 [9] were prepared according to the published procedures.
Other chemicals were obtained from commercial sources and puri-
fied prior to use.
2.2. Instrumentation
* Corresponding author. Tel.: +91 22 2576 7181; fax: +91 22 2576 7152/2572
3480.
The 1H and 31P{1H} NMR (d in ppm) spectra were recorded using
VXR 400 spectrometer operating at the appropriate frequencies
E-mail addresses: krishna@chem.iitb.ac.in, msb_iitb@yahoo.com (M.S. Balakrishna).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.07.002

C. Ganesamoorthy et al. / Journal of Organometallic Chemistry 694 (2009) 3390–3394
3391
using TMS and 85% H3PO4 as internal and external references,
respectively. The microanalyses were performed using Carlo Erba
Model 1112 elemental analyzer. The melting points of compounds
were observed in capillary tubes and are uncorrected.
formed. Multiple measurements of equivalent reflections provided
the basis for empirical absorption corrections as well as corrections
for crystal deterioration during the data collection (SADABS [12a] and
TWINABS [12b]). The structures was solved by Patterson methods and
refined by full-matrix least-squares procedures using the SHELXTL
program package [13]. Hydrogen atoms were placed in calculated
positions and included as riding contributions with isotropic dis-
placement parameters tied to those of the attached non-hydrogen
atoms.
2.3. Synthesis of cis,cis-[{RuCl2(CH3CN)2}2(P2NUNP2)] (2)
A solution of [Ru(g
6-cymene)Cl2]2 (0.023 g, 0.038 mmol) in ace-
tonitrile (5 mL) was added dropwise to a solution of 1 (0.046 g,
0.038 mmol) also in acetonitrile (20 mL). The reaction mixture
was allowed to stir at room temperature for 4 h. The resulting solu-
tion was concentrated to 4 mL and stored at room temperature for
3 days to give pale yellow crystals of 2. Yield: 81% (0.053 g), m.p.:
202–204 °C (dec). 1H NMR (400 MHz, DMSO-d6): d 8.22–6.72 (m,
36H, ArH), 3.50 (s, 24H, OCH3), 2.06 (s, 12H, CH3CN). 31P{1H}
NMR (162 MHz, DMSO-d6): d 101.6 ppm (br s). Anal. Calc. for
C70H72N6O16P4Ru2Cl4 (1721.20): C, 48.85; H, 4.22; N, 4.88. Found:
C, 48.30; H, 3.80; N, 4.20%.
3. Results and discussion
The tetraphosphonite 1 has been prepared by the reaction of p-
C6H4[N(PCl2)2]2 with 4 equiv. of 2-(methoxy)phenol in presence of
triethylamine [5c]. This novel tetradenate ligand can be compared
to two 4,40-bipyridines fused sideways to form a bis-chelating li-
gand yet with four tunable phosphorus atoms. This type of systems
can facilitate the formation of several multinuclear complexes and
we have explored their versatile coordination chemistry. In this pa-
per, we describe the synthesis of di- and tetranuclear RuII com-
plexes of 1 (Scheme 1).
2.4. Synthesis of [{(
g
6-p-cymene)Ru2(
l2-Cl)3Cl}2(P2NUNP2)] (3)
6-cymene)Cl2]2 (0.065 g, 0.106 mmol) and 1
The stoichiometric reaction of 1 with [RuCl2(p-cymene)]2 in
A mixture of [Ru(
g
acetonitrile
afforded
the
dinuclear
complex,
cis,cis-
(0.064 g, 0.053 mmol) in THF (15 mL) was stirred under reflux con-
dition for 5 h. It was cooled to room temperature and concentrated
to 5 mL under vacuum. Keeping this solution at ꢀ30 °C for several
days afforded red crystals of 3. Yield: 76% (0.087 g), m.p.: 198–
200 °C (dec). 1H NMR (400 MHz, CDCl3): d 7.47–6.13 (m, 36H,
ArH), 5.54 (d, JH,H = 5.6 Hz, 4H, cymene Ph), 5.41 (d, 4H, cymene
Ph), 3.81 (s, 24H, OCH3), 2.59 (sep, 2H, CH), 1.69 (s, 6H, CH3),
1.04 ppm (d, JH,H = 7.2 Hz, 12H, C(CH3)2). 31P{1H} NMR (162 MHz,
CDCl3): d 110.1 ppm (s). Anal. Calc. for C82H88N2O16P4Ru4Cl8
(2169.38): C, 45.40; H, 4.09; N, 1.29. Found: C, 45.46; H, 4.58; N,
1.45%.
[{RuCl2(CH3CN)2}2(P2NUNP2)] (2) in good yield. Compound 2 is a
pale yellow micro crystalline solid and partially soluble in di-
methyl sulfoxide. Similarly, the compound
[RuCl2(p-cymene)]2 in 1:2 mole ratio in THF to form a tri-chloro-
bridged tetrametallic complex, [{(
6-p-cymene)Ru2(l2
1 reacts with
g
-
Cl)3Cl}2(P2NUNP2)] (3) as an orange crystalline solid. Recently, we
reported the synthesis and crystal structure of a similar tri-
chloro-bridged bimetallic complex, [(
Cl)3Cl{PhN(P(OC6H4OMe-o)2)2}] with bisphosphonite ligand,
g -
6-p-cymene)Ru2(l2
a
PhN(P(OC6H4OMe-o)2)2 [6d] and this method provides an efficient
way to make this kind of systems without going through multi step
synthesis [14]. The 31P NMR spectra of complexes 2 and 3 show
single resonances at 101.6 and 110.1 ppm, respectively. The 1H
NMR spectrum of complex 2 shows a singlet at 2.06 ppm corre-
sponding to the acetonitrile group and the p-cymene protons of 3
appear as two doublets at 5.41 and 5.54 ppm with a JH,H coupling
of 5.6 Hz. The isopropyl methyl protons appear as a doublet cen-
tered at 1.04 ppm with a JH,H coupling of 7.2 Hz and the CH proton
appears as a multiplet centered at 2.59 ppm. The 1H NMR and ana-
lytical data are consistent with the proposed structures of 2 and 3.
2.5. General procedure for the transfer hydrogenation reactions
In a dry two-necked round bottom flask under an atmosphere of
nitrogen were placed appropriate amount of catalyst (0.2 or
1 mol%) in 2-propanol (5 mL) and it was stirred at room tempera-
ture for 15 min. Acetophenone (0.1 g, 0.832 mmol) was added to
the mixture and stirred for another 15 min at room temperature.
A 2-propanol solution of sodium isopropoxide (10 mol%) (prepared
by the dissolution of metallic sodium into the hot 2-propanol) was
then added and the resulting mixture was refluxed under an atmo-
sphere of nitrogen and the course of the reaction was monitored by
GC analysis. After completion of the reaction, the solvent was re-
moved. The residual mixture was diluted with H2O and Et2O
(10 mL each), washed with brine and extracted with Et2O
(2 ꢂ 6 mL). The combined organic fractions were dried (MgSO4),
stripped of the solvent and the residue was redissolved in 5 mL
of dichloromethane. An aliquot was taken with a syringe and sub-
jected to GC analysis. Conversions were calculated relative to ace-
tophenone as an internal standard.
3.1. The crystal and molecular structure of 2
Perspective view of the molecular structure of compound 2
with atom numbering scheme is shown in Fig. 1. Crystal data
and the details of the structure determination are given in Table
1, while selected bond lengths and bond angles are given in Table
2. Crystals of 2 suitable for X-ray diffraction analysis were grown
by keeping the saturated acetonitrile solution of 2 at room tem-
perature for several days. Compound 2 is a bimetallic RuII deriv-
ative and ruthenium adopts an approximate octahedral
geometry, with the corners being occupied by two chlorines,
two nitrogens and two phosphorus atoms of tetraphosphazane
1 in cis passion. The P1–N1 and P2–N2 bond distances are
1.694(5) and 1.680(5) Å, respectively, whereas, the Ru1–P1 and
Ru1–P2 distances are 2.218(2) and 2.212(2) Å, respectively. Due
to the formation of strained four-membered chelate ring the P–
N–P angle of the free ligand shrinks from 115.25(9)° to 98.2(3)°
[5c]. The bite angle created by the chelating ligand P1–Ru–P2
with Ru center is 70.27(7)°. In 2, the bridging phenylene ring
makes a dihedral angle of 53.30° (P1–N1–C2–C1) with the plane
of the P–N–P skeletons. Orientation of the phenylene ring with
respect to P–N–P skeleton varies depending upon the choice of
2.6. X-ray crystallography
A crystal of the compound 2 suitable for X-ray crystal analysis
was mounted in a CryoloopTM with a drop of Paratone oil and placed
in the cold nitrogen stream of the KryoflexTM attachment of the Bru-
ker APEX CCD diffractometer. Full spheres of data were collected
using a combination of three sets of 400 scans in
x (0.5° per scan)
at u = 0°, 90° and 180° plus two sets of 800 scans in u (0.45° per
scan) at
x
= ꢀ30° and 210° under the control of the SMART software
package [10]. The raw data were reduced to F2 values using the
SAINT+ software [11] and global refinements of unit cell parameters
using 5662 reflections chosen from the full data sets were per-

3392
C. Ganesamoorthy et al. / Journal of Organometallic Chemistry 694 (2009) 3390–3394
H3CCN
H3CCN
NCCH3
R2
P
R2
P
NCCH3
[RuCl2(p-cym)]2
CH3CN
R u
Cl
N
N
R u
Cl
Cl
PR2
PR2
Cl
R2P
R2P
P
P
R2
R2
2
N
N
R2
R2
P
Cl
Cl
Cl
Cl
1
P
2 [RuCl2(p-cym)]2
THF,
R = -OC6H4OMe-o
N
R u
Cl
R u
R u
R u
N
Cl
Cl
P
P
Cl
R2
R2
3
Scheme 1.
Fig. 1. Molecular structure of 2. All hydrogen atoms have been omitted for clarity. Displacement ellipsoids are drawn at the 50% probability level.
Table 1
Table 2
Crystallographic information for compound 2.
Selected bond distances and bond angles for complex 2.
2
Bond distances (Å)
Bond angles (°)
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C70H72Cl4N6O18P4Ru2
1753.16
Complex 2
P1–N1
P2–N1
Ru1–P1
Ru1–P2
Ru1–N2
Ru1–N3
Ru1–Cl1
Ru1–Cl2
P1–O1
1.694(5)
1.680(5)
2.218(2)
2.212(2)
2.034(7)
2.088(9)
2.443(4)
2.384(2)
1.613(5)
1.601(5)
1.604(5)
1.605(5)
1.439(8)
P1–N1–P2
98.2(3)
Triclinic
P1–Ru1–P2
Cl1–Ru1–Cl2
Cl1–Ru1–P1
Cl1–Ru1–P2
Cl2–Ru1–P1
Cl2–Ru1–P2
N2–Ru1–N3
P2–Ru1–N3
P1–Ru1–N3
Cl2–Ru1–N2
Cl2–Ru1–N3
Cl1–Ru1–N2
70.27(7)
86.06(11)
169.01(10)
100.04(9)
88.65(8)
89.69(7)
89.8(4)
173.9(3)
107.9(3)
171.95(16)
84.4(3)
ꢀ
P1 (No. 2)
9.7505(9)
11.9710(10)
17.8465(2)
88.2790(10)
86.3570(10)
88.9130(10)
2077.7(3)
1
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
P1–O3
P2–O5
P2–O7
N1–C2
Z
qcalc (g cmꢀ3
)
1.401
0.635
) (mmꢀ1
)
87.55(19)
l
(Mo K
a
F (0 0 0)
894
Crystal size (mm)
T (K)
0.03 ꢂ 0.07 ꢂ 0.16
100
2h Range (°)
1.1–26.4
16641
8398 [Rint = 0.039]
1.07
0.0727
0.2176
metal to which it is coordinated. In free ligands the bridging phe-
nylene ring is almost perpendicular to the P–N–P skeleton, where
as its platinum and rhodium square planar complexes have al-
most parallel alignment of phenylene ring with the P–N–P skele-
tons [5a,c]. The structurally characterized Group 11 metal
complexes of 1 show perpendicular alignment [5b]. At this mo-
ment, the conformational preference of tetraphosphazane ligand
1 towards different metals is not fully understood.
Total number of reflections
Number of independent reflections
Goodness-of-fit (GOF) (F2)
a
R1
b
wR2
P
P
a
R ¼ kFoj ꢀ jFck= jFoj.
h
i
ꢀ
ꢁ
1=2
P
P
2
2
Rw
¼
wðF2o ꢀFc2Þ= wðFo2Þ
;w¼1=½r2ðF2oÞþðxPÞ ꢃ where P ¼ Fo2 þ2F2c =3.
b

C. Ganesamoorthy et al. / Journal of Organometallic Chemistry 694 (2009) 3390–3394
3393
Table 3
Acknowledgements
Transfer hydrogenation reactions of acetophenone.
We are grateful to the Department of Science and Technology
(DST), New Delhi, for financial support of this work through grant
SR/S1/IC-02/007. C.G. thanks CSIR, New Delhi for Senior Research
Fellowship (SRF). We also thank SAIF, Mumbai, Department of
Chemistry Instrumentation Facilities, Bombay, for spectral and
analytical data and J.T.M. thanks the Louisiana Board of Regents
for purchase of the CCD diffractometer and the Chemistry Depart-
ment of Tulane University for support of the X-ray laboratory.
O
OH
O
OH
Catalyst
iPrONa
+
+
Ph
Ph
Entry
Catalyst
Conditionsa
Conversion (%)b
TONc
1
2
3
2 (1 mol%)
3 (0.2 mol%)
3 (1 mol%)
iPrONa (10 mol%), reflux, 22 h
iPrONa (10 mol%), reflux, 5 h
iPrONa (10 mol%), 30 °C, 24 h
99
100
19
99
500
19
Appendix A. Supplementary material
CCDC 732606 contains the supplementary crystallographic data
for complex 2. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2009.07.002.
a
Acetophenone (0.1 g, 0.832 mmol), iPrONa (10 mol%), catalyst (0.2–1 mol%),
iPrOH (5 mL).
b
Conversion to coupled product determined by GC, based on acetophenone;
average of two runs.
c
Defined as mol product per mol of catalyst.
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