Di-, tetra- and polynuclear RhI complexes containing phenylene-1,4-diaminotetra(phosphonite), p-C6H 4[N{P(OC6H4OMe-o)2} 2]2 and their catalytic investigation towards t

Article abstract of DOI:10.1039/b815849e

The reactions of phenylene-1,4-diaminotetra(phosphonite), p-C ₆H₄[N{P(OC₆H₄OMe-o) ₂}₂]₂ (P₂N(Ph)NP₂) (1) with [Rh(COD)Cl]₂ in 1: 2 and 1: 1 molar

Full text of DOI:10.1039/b815849e

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Di-, tetra- and polynuclear RhI complexes containing phenylene-1,4-
diaminotetra(phosphonite), p-C6H4[N{P(OC6H4OMe-o)2}2]2 and their
catalytic investigation towards transfer hydrogenation reactions†
Chelladurai Ganesamoorthy,a Maravanji S. Balakrishna*a and Joel T. Magueb
Received 10th September 2008, Accepted 10th December 2008
First published as an Advance Article on the web 29th January 2009
DOI: 10.1039/b815849e
The reactions of phenylene-1,4-diaminotetra(phosphonite), p-C6H4[N{P(OC6H4OMe-o)2}2]2
(P2N(Ph)NP2) (1) with [Rh(COD)Cl]2 in 1 : 2 and 1 : 1 molar ratio produce tetra- and polymetallic
chelate complexes, [Rh4(COD)2(m-Cl)4(P2N(Ph)NP2)] (2) and [Rh2(m-Cl)2(P2N(Ph)NP2)]n (3),
respectively. Similar reaction of 1 with [Rh(COD)Cl]2 in dichloromethane–acetonitrile mixture
furnishes a dinuclear complex, [Rh2Cl2(CH3CN)2(P2N(Ph)NP2)] (4). The reaction of 3 or 4 with CO
affords a dinuclear carbonyl derivative, [Rh2Cl2(CO)2(P2N(Ph)NP2)] (5). Treatment of 4 with 2
equivalents of pyrazine or 4,4¢-bipyridine produce one-dimensional RhI coordination polymers,
[Rh2Cl2(C4H4N2)(P2N(Ph)NP2)]n (6) and [Rh2Cl2(C10H8N2)(P2N(Ph)NP2)]n (7) in quantitative yields.
The catalytic activity of RhI complexes 2–7 have been investigated in transfer hydrogenation reactions.
bis(diphenylphosphino)hexane] and [Rh(dppa)(CO)Cl]n [dppa =
1,2-bis(diphenylphosphino)acetylene].7 Recently, we have utilized
a “short-bite” aminobis(phosphine), PhN{P(OC6H4OMe-o)2}2 (I)
in combination with various pyridyl ligands to make several
multinuclear mixed ligand complexes including coordination
polymers.8 We have also reported the synthesis of PdII, PtII
and CuI complexes, and catalytic applications of a short-bite
tetraphosphonite, p-C6H4[N{P(OC6H4OMe-o)2}2]2 (hereafter re-
ferred as P2N(Ph)NP2).9 As a part of our interest in the transition
metal chemistry of cyclic and acyclic diphosphazane ligands10
and their catalytic applications,11 we describe herein the coor-
dinating behavior of phenylene-1,4-diaminotetra(phosphonite),
p-C6H4[N{P(OC6H4OMe-o)2}2]2 (1) towards RhI derivatives and
their utility in transfer hydrogenation reactions. The crystal and
molecular structures of a binuclear RhI complex and a RhI
coordination polymer are also described.
Introduction
A great deal of interest is currently devoted to the synthesis of
multinuclear complexes including coordination polymers using
rigid polydentate phosphine ligands.1 Polyphosphines can readily
form di-, tetra- and/or polynuclear metal complexes with metals in
close proximity to each other, thereby giving rise to strong cooper-
ativity effects in catalytic reactions.2 In addition, conformationally
rigid polyphosphines with extended conjugation in the framework
are potential candidates for designing conducting polymers for
effective electronic coupling through ligands.3 Such materials are
endowed with novel electronic, magnetic and optical properties
and serve as source materials for the production of chemical
sensors and electroluminescent devices.4 Several systems includ-
ing carboxylates, aryl-bridged di-isocyanides and alkyne-bridged
pyridyl ligands have been used for the preparation of various
rhodium polymers which often form porous materials through sec-
ondary interactions.5 The porous network of [Rh2(O2CPh)4(pyz)]n
(pyz = pyrazine) based on benzoate and pyrazine, prepared by
Takamizawa et al., is an efficient system for the inclusion of CO2
molecules inside the molecular channels in the form of molecular
wires.5a However, the polymers reported with these systems
have the metal atoms mostly in higher oxidation states (+2 or
+3)5a,d.e,,6 which limits their utility in applications where significant
metal-based reactivity is desired. Reports on such polymers with
phosphine ligands and also containing RhI are scarce and those
containing polydentate phosphines with pyridyl linkers are not
known in the literature. The only known structurally characterized
RhI coordination polymers are [RhCl(CO)(dpphex)]n [dpphex =
Results and discussion
Rh(I) complexes
The ligand p-C6H4[N{P(OC6H4OMe-o)2}2]2(P2N(Ph)NP2) (1) has
been prepared by the reaction of p-C6H4[N(PCl2)2]2 with four
equivalents of 2-(methoxy)phenol in presence of triethylamine.9
The reactions of 1 with [Rh(COD)Cl]2 in 1 : 2 and 1 : 1 molar ratios
in dichloromethane lead to the successive replacement of the diene
ligands and the formation of chloro-bridged tetra- and polymetal-
lic chelate complexes, [Rh4(COD)2(m-Cl)4(P2N(Ph)NP2)] (2) and
[Rh2(m-Cl)2(P2N(Ph)NP2)]n (3), respectively, as shown in Scheme 1.
Compound 2 is an orange colored crystalline solid, whereas com-
pound 3 is a pale yellow microcrystalline powder insoluble in most
organic solvents. The similar reaction of 1 with [Rh(COD)Cl]2 in
a 1 : 1 ratio in a dichloromethane–acetonitrile mixture (1 : 1)
yielded the chelate complex, [Rh2Cl2(CH3CN)2(P2N(Ph)NP2)] (4)
in good yield. On refluxing complex 3 in acetonitrile the Rh2(m-
Cl)2 bridging units are cleaved to give the binuclear complex 4.
aPhosphorus Laboratory, Department of Chemistry, Indian Institute of
Technology Bombay, Powai, Mumbai, 400 076, India. E-mail: krishna@
chem.iitb.ac.in; Tel: +91 22 2576 7181; Fax: +91 22 2576 7152/2572 3480
bDepartment of Chemistry, Tulane University, New Orleans, Lousiana,
70118, USA
† CCDC reference numbers 701818 and 701819. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/b815849e
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Scheme 1
◦
Interestingly, compound 4 on heating to 120 C under vacuum,
carried out, however, the molecular compositions were confirmed
from elemental analysis and mass spectral data. The spectral and
analytical data support the proposed formulations of complexes
2–7 and the structures of complexes 4 and 6 were confirmed
through single-crystal X-ray diffraction studies. The polymer 6
represents the first structurally characterized RhI polymer having
a rigid tetradentate P–N–P system with pyridyl linkers.
produces the polymeric compound 3 in quantitative yield.
The 31P{ H} NMR spectrum of 2 consists of a doublet centered
1
1
at 106.9 ppm with a JRhP coupling of 240 Hz, whereas complex
4 shows two doublet of doublets centered at 97.3 and 93.1 ppm
with JRhP couplings of 257 and 232 Hz, respectively, with the
1
former corresponding to the phosphorus transto chlorine. The2JPP
coupling is 88 Hz. The slow bubbling of carbon monoxide gas into
a suspension of 3 or 4 in dichloromethane afforded the carbonyl
derivative, [Rh2Cl2(CO)2(P2N(Ph)NP2)] (5) in quantitative yield.
The displacement of coordinated acetonitrile molecules in 4 by
pyrazine or 4,4¢-bipyridine produce one-dimensional zigzag RhI
coordination polymers, [Rh2Cl2(C4H4N2)(P2N(Ph)NP2)]n (6) and
The crystal and molecular structures of 4 and 6
Perspective views of compounds 4 and 6 with atom numbering
schemes are shown in Fig. 1 and 2, respectively. Crystal data and
the details of the structure determinations are given in Table 1,
while selected bond lengths and bond angles are given in Table 2.
The asymmetric units of 4 and 6 contain half a molecule of
the metal complexes while the rhodium adopts an approximate
square-planar geometry, with the corners occupied by chlorine,
nitrogen and two phosphorus atoms. The core structure of 6
consists of repeating [(P2N(Ph)NP2)(RhCl)2] and pyrazine units
arranged in an alternating fashion to form a one-dimensional
[Rh2Cl2(C10H8N2)(P2N(Ph)NP2)]n (7) (Scheme 2). The 31P{ H}
1
NMR spectrum of 5 also shows two doublet of doublets centered
at 103.2 and 90.4 ppm with the 1JRhP couplings of 223 and 192 Hz,
2
respectively, and JPP coupling of 80 Hz. The high frequency
resonance is assigned to P-atom trans to Cl.12 The IR spectrum of
5 shows nCO at 2048 and 2006 cm-1.13 Because of the poor solubility
of complexes 3, 6 and 7, NMR spectroscopic studies could not be
Scheme 2
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Fig. 1 Molecular structure of 4. All hydrogen atoms have been omitted for clarity. Displacement ellipsoids are drawn at the 50% probability level.
Fig. 2 Molecular structure of 6. All hydrogen atoms and disorder have been omitted for clarity. Displacement ellipsoids are drawn at the 50% probability
level.
zigzag coordination polymer. In 4 and 6, the two independent
Transfer hydrogenation reactions
˚
P–N distances differ only slightly [1.699(2), 1.692(2) A for 4
The catalytic transfer hydrogenation of ketones has emerged as a
useful and convenient method to prepare secondary alcohols by
avoiding the use of molecular hydrogen and pressure apparatus.14
In a preliminary study, complexes 2–7 have been used for the
reduction of acetophenone using 2-propanol as a hydrogen source
in the presence of base. The catalytic reactions were carried out
with 0.1 g of acetophenone in 5 mL of 2-propanol in the presence
of 0.5 mol% of the catalyst and 10 mol% of sodium 2-propoxide
as a promoter (substrate : Ru : base = 200 : 1 : 20) under refluxing
condition. The progress of the reaction was monitored by gas
chromatography and representative catalytic data are given in
Table 3. For example, acetophenone is reduced to 1-phenylethanol
in the presence of sodium 2-propoxide with >99% conversion in
2-propanol at reflux condition with 0.5 mol% of catalyst 2 within
8 h (Table 3, entry 6). The reactions are slow at room temperature
˚
and 1.694(4), 1.701(4) A for 6] with a certain degree of double
bond character while the P–Rh bond lengths display a larger
˚
variation, ranging from 2.141(1) to 2.169(1) A for 4 and 2.135(1)
˚
to 2.179(1) A for 6. The P–Rh bonds trans to chlorine are shorter
than those of trans to nitrogen in both cases. The P–N–P angle
shrinks from 115.25(9) to 94.63(9)◦ (for 4) and 94.74(19)◦ (for 6)
due to the formation of strained four-membered chelate rings.
In both complexes the angles around rhodium atom vary over
a range of 70–101◦, with the smallest being that in the strained,
four-membered chelate ring, indicating the distortion in the square
planar geometry. In 4 and 6, the bridging phenylene rings are
almost parallel to the plane of the P–N–P skeletons with dihedral
angles of 1.4(3)◦ (P2–N–P1 vs. C30–C31 for 4) and 13.0(7)◦
(P1–N1–P2 vs. C15–C16 for 6), respectively.
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Table 1 Crystallographic information for compounds 4 and 6
24 h. Further, the reduction of 4-bromoacetophenone tends to
proceed at significantly lower rate and yield because of the higher
mesomeric effect caused by bromide substitution.15a,16
4
6
Empirical formula
Mr
C66H66Cl2N4O16P4Rh2
1571.83
C66H64Cl2N4O16P4Rh2
1569.81
Crystal system
Space group
Triclinic
Monoclinic
P21/n (no. 14)
16.9519(9)
11.3413(6)
18.325(1)
90
110.072(1)
90
3309.1(3)
2
1.576
0.748
1600
0.09 ¥ 0.12 ¥ 0.13
100
2.0–24.8
23110
Conclusion
¯
P1 (no. 2)
˚
The aminotetra(phosphonite) 1 readily reacts with [Rh(COD)Cl]2
to give di-, tetra- and polymeric complexes depending upon
the reaction conditions and the stoichiometry of the reactants.
Displacement of the coordinated solvents from 4 using bridging
bipyridyl linkers produces interesting mixed-ligand RhI coordina-
tion polymers 6 and 7. The RhI derivatives are efficient catalysts
for the transfer hydrogenation of acetophenone. The polymers
produced by rigid polyphosphine of the type 1 have the metals
in conjugation with aromatic p-systems through P–N–P skeletons
with P–N bonds showing multiple bond character. By choosing
appropriate redox-active metals and substituents at the P-centers
it is possible to design efficient conducting polymers. Although,
we do not see any interlink between the p -conjugation and the
catalytic ability of these molecules it is an interesting ligand system
which can be explored in both of these avenues. The work in this
direction is in progress.
a/A
9.2409(5)
11.0859(6)
17.0064(9)
84.207(1)
77.819(1)
88.350(1)
1694.23(16)
1
1.541
0.730
802
0.07 ¥ 0.10 ¥ 0.12
100
1.2–28.3
15149
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
Dc/g cm-3
m(Mo-Ka)/mm-1
F(000)
Crystal size/mm
T/K
2q Range/◦
Total no. reflns
No. indep. reflns
GOF (F2)
7829 (Rint = 0.022)
5711 (Rint = 0.070)
1.07
1.02
a
R1
0.0323
0.0810
0.0467
0.1197
b
wR2
ꢀ
ꢀ
ꢀ
ꢀ
a R = ꢀFo| - |Fcꢀ/ |Fo|. b Rw = {[ w(Fo - Fc2)/ w(Fo2)2]}1/2; w =
2
2
2
1/[s (Fo2) + (xP)2], where P = (Fo + 2Fc2)/3.
Experimental
but proceed at good rates at refluxing conditions. In the absence
of base, no conversion was observed and conversion rates were
increased with increasing concentration of base.15 Although the
reaction conditions were not optimized, all complexes have proven
to be active and efficient catalysts leading to nearly quantitative
conversion of acetophenone into 1-phenylethanol within 8–18 h.
Among them, the tetra-metallic complex 2 appeared to be the most
active precursor for the reduction of acetophenone (8 h, TON =
199) and further it was used for the reduction of ketones other
than acetophenone. The reduction performed with benzophenone
yielded 80% of diphenylmethanol after 24 h with complex 2
(Table 3, entry 13). The complex 2 also shows good activity
in the transfer hydrogenation of six-membered cyclic ketones
(Table 3, entries 14 and 15). Complex 2 catalyzed the transfer
hydrogenation of a-tetralone and cyclohexanone very effectively
but at different rates (Table 3, entries 14 and 15). The reduction of
cyclohexanone yielded less than 1% of the converted product with
10 mol% of base after 24 h under refluxing conditions though a
good conversion has been achieved with 20 mol% of base within
General procedures
All manipulations were performed under rigorously anaerobic
conditions using Schlenk techniques. All the solvents were purified
by conventional procedures and distilled prior to use.17 The com-
11
18
pounds p-C6H4[N{P(OC6H4OMe-o)2}2]2 and [Rh(COD)Cl]2
were prepared according to the published procedures. Pyrazine
and 4,4¢-bipyridine were purchased from Aldrich Chemicals and
used as such without further purification. Other chemicals were
obtained from commercial sources and purified prior to use.
Instrumentation
1
1
The H and 31P{ H} NMR (d in ppm) spectra were recorded
using a Varian VXR 400 spectrometer operating at the appro-
priate frequencies using TMS and 85% H3PO4 as internal and
external references, respectively. Infrared spectra were recorded
on a Nicolet Impact 400 FTIR instrument as KBr disks. The
microanalyses were performed using a Carlo Erba Model 1112
◦
˚
Table 2 Selected bond distances (A) and bond angles ( ) for complexes 4 and 6
Complex 4
Complex 6
P1–N1
P2–N1
Rh–P1
Rh–P2
Rh–N2
Rh–Cl
P1–O1
P1–O3
P2–O5
P2–O7
N1–C30
1.6989(19)
1.6921(19)
2.1686(6)
2.1409(6)
2.090(2)
2.3940(6)
1.6042(16)
1.6110(17)
1.6056(17)
1.6146(17)
1.431(3)
P1–N1–P2
P1–Rh–P2
Cl–Rh–P1
P2–Rh–N2
P1–Rh–N2
Cl–Rh–P2
Cl–Rh–N2
Rh–P1–O1
Rh–P1–O3
Rh–P2–O5
Rh–P2–O7
94.63(9)
70.68(2)
101.75(2)
97.78(6)
168.02(6)
172.23(2)
89.88(6)
126.55(6)
124.55(7)
124.74(7)
126.05(6)
P1–N1
P2–N1
Rh1–P1
Rh1–P2
Rh1–N2
Rh1–Cl1
P1–O1
P1–O3
P2–O5
P2–O7
N1–C15
1.694(4)
1.701(4)
2.1791(13)
2.1352(13)
2.165(5)
2.3762(13)
1.607(4)
1.616(3)
1.608(4)
1.611(4)
1.440(6)
P1–N1–P2
94.74(19)
70.75(5)
P1–Rh1–P2
Cl1–Rh1–P1
P2–Rh1–N2
P1–Rh1–N2
Cl1–Rh1–P2
Cl1–Rh1–N2
Rh1–P1–O1
Rh1–P1–O3
Rh1–P2–O5
Rh1–P2–O7
102.14(5)
98.49(13)
167.94(13)
171.22(5)
88.02(13)
125.20(14)
126.14(14)
121.11(15)
129.58(15)
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Table 3 Transfer hydrogenation reactions of acetophenone
Entry
Ketone
Catalyst
Conditionsa
Conv.b (%)
TONc
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Acetophenone
Acetophenone
Acetophenone
Acetophenone
Acetophenone
Acetophenone
Acetophenone
Acetophenone
Acetophenone
Acetophenone
Acetophenone
4-Bromoacetophenone
Benzophenone
a-Tetralone
None
None
None
[Rh(COD)Cl]2
iPrONa (10 mol%), reflux, 24 h
1
50
66
48
61
> 99
83
78
92
100
98
—
—
—
96
122
199
166
156
184
200
98
iPrONa (30 mol%), reflux, 20 h
iPrONa (40 mol%), reflux, 20 h
0.5 mol%. iPrONa (10 mol%), reflux, 10 h
0.5 mol%. iPrONa (10 mol%), reflux, 24 h
0.5 mol%. iPrONa (10 mol%), reflux, 8 h
0.5 mol%. iPrONa (10 mol%), reflux, 7 h
0.5 mol%. iPrONa (10 mol%), reflux, 5 h
0.5 mol%. iPrONa (10 mol%), reflux, 8 h
0.5 mol%. iPrONa (10 mol%), reflux, 18 h
1 mol%. iPrONa (10 mol%), reflux, 8 h
0.5 mol%. iPrONa (10 mol%), reflux, 24 h
0.5 mol%. iPrONa (10 mol%), reflux, 24 h
0.5 mol%. iPrONa (10 mol%), reflux, 24 h
0.5 mol%. iPrONa (20 mol%), reflux, 24 h
[Rh(COD)Cl]2
2
3
4
5
6
7
2
2
2
2
34
80
70
100
68
160
140
200
Cyclohexanone
i
i
a Acetophenone (0.1 g), PrONa (10 mol%), catalyst (0.5 mol%), PrOH (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.
elemental analyzer. The melting points were observed in capillary
tubes and are uncorrected.
NMR (162 MHz, CDCl3): d 97.3 (dd, 1JRhP = 257 Hz), 93.1 (dd,
1JRhP = 232 Hz, 2JPP = 88 Hz).
Synthesis of [Rh4(COD)2(l-Cl)4(P2N(Ph)NP2)] (2). A solution
of 1 (0.037 g, 0.030 mmol) in CH2Cl2 (5 mL) was added dropwise to
a solution of [RhCl(COD)]2 (0.030 g, 0.061 mmol) also in CH2Cl2
(5 mL) with constant stirring. The reaction mixture was allowed
to stir at room temperature for 4 h. The resulting solution was
concentrated to 2 mL, layered with 1 mL of petroleum ether, and
stored at -30 ◦C for 1 day to give analytically pure yellow–orange
crystalline product 2. Yield: 82% (0.050 g); mp 178–180 ◦C. Anal.
Calc. for C78H84N2O16P4Rh4Cl4: C, 47.25; H, 4.27; N, 1.41. Found:
C, 47.19; H, 4.23; N, 1.46%. 1H NMR (400 MHz, CDCl3): d 7.79–
6.75 (m, Ph, 36H), 5.50 (br s, CH, 8H), 3.71 (s, OCH3, 24H), 2.01
Synthesis of [Rh2Cl2(CO)2(P2N(Ph)NP2)] (5). Carbon monox-
ide gas was bubbled through a suspension of 3 (0.0626 g,
0.042 mmol) (or 4) in dichloromethane (15 mL) with constant
stirring at room temperature until the solution became clear
(~15 min). The solution was concentrated under reduced pressure,
layered with 2 ml of petroleum ether and stored at -30 ◦C for 1 day
to afford 5 as a yellow crystalline product. Yield: 93% (0.060 g);
mp 218–220 ◦C (decomp.). Anal. Calc. for C64H60N2O18P4Rh2Cl2:
C, 49.73; H, 3.91; N, 1.81. Found: C, 49.62; H, 4.01; N, 1.76%.
1H NMR (400 MHz, CDCl3): d 8.00–6.65 (m, Ph, 36H), 3.50 (s,
1
1
and 1.92 (d, CH2, 16H). 31P{ H} NMR (162 MHz, CDCl3): d
OCH3, 24H). 31P{ H} NMR (162 MHz, CDCl3): d 103.2 (dd,
106.9 (d, 1JRhP = 240 Hz).
1JRhP = 223 Hz), 90.4 (dd, 1JRhP = 192 Hz, 2JPP = 80 Hz). FT-IR
(KBr disc) cm-1: n(CO) 2048 (s), 2006 (s).
Synthesis of [Rh2(l-Cl)2(P2N(Ph)NP2)]n (3). A solution of
[RhCl(COD)]2 (0.031 g, 0.063 mmol) in CH2Cl2 (5 mL) was added
dropwise to a solution of 1 (0.077 g, 0.063 mmol) also in CH2Cl2
(7 mL) with constant stirring. The reaction mixture was allowed to
stir at room temperature for 4 h and the resulting yellow–orange
precipitate was collected by filtration and washed with diethyl ether
twice (5 mL each). Yield: 88% (0.083 g); mp 198–200 ◦C (decomp.).
Anal. Calc. for C62H60N2O16P4Rh2Cl2: C, 49.99; H, 4.06; N, 1.88.
Found: C, 49.93; H, 4.01; N, 1.92%.
Synthesis of [Rh2Cl2(C4H4N2)(P2N(Ph)NP2)]n (6). A solution
of pyrazine (0.001 g, 0.017 mmol) in CH2Cl2 (5 mL) was added
dropwise to a solution of 4 (0.026 g, 0.017 mmol) in acetonitrile
(10 mL) with constant stirring. The reaction mixture was allowed
to stir at room temperature for 4 h to give a red precipitate which
was collected by filtration. Crystals suitable for X-ray analysis were
grown by the slow diffusion of an acetonitrile solution of 4 into
a dichloromethane solution of pyrazine. Yield: 95% (0.025 g); mp
◦
Synthesis of [Rh2Cl2(CH3CN)2(P2N(Ph)NP2)] (4). A solution
of [RhCl(COD)]2 (0.008 g, 0.017 mmol) in acetonitrile (5 mL) was
added dropwise to a solution of 1 (0.021 g, 0.017 mmol) in CH2Cl2
(5 mL) with constant stirring. The reaction mixture was allowed to
stir at room temperature for 15 min and was then stored at room
temperature for 24 h to give analyti◦cally pure yellow crystals of 4.
Yield: 79% (0.022 g); mp 238–240 C (decomp.). Anal. Calc. for
C66H66N4O16P4Rh2Cl2: C, 50.43; H, 4.23; N, 3.56. Found: C, 50.50;
H, 4.26; N, 3.52%. 1H NMR (400 MHz, CDCl3): d 7.74–6.63 (m,
192–194 C (decomp.). Anal. Calc. for C66H64N4O16P4Rh2Cl2: C,
50.50; H, 4.11; N, 3.57. Found: C, 50.48; H, 4.16; N, 3.51%.
Synthesis of [Rh2Cl2(C10H8N2)(P2N(Ph)NP2)]n (7). This was
synthesized by a procedure similar to that of 6 using two equiv. of
4,4¢-bipyridine (0.003 g, 0.020 mmol) and 4 (0.0157 g, 0.010 mmol).
Yield: 84% (0.0138 g); mp 240–242 ◦C (decomp.). Anal. Calc. for
C72H68N4O16P4Rh2Cl2: C, 52.54; H, 4.16; N, 3.40. Found: C, 52.43;
H, 4.08; N, 3.47%.
1
Ph, 36H), 3.52 (s, OCH3, 24H), 1.95 (s, CH3CN, 6H). 31P{ H}
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General procedure for the transfer hydrogenation reactions
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In a dry two-necked round bottom flask under an atmosphere of
nitrogen were placed appropriate amount of catalyst (0.5 mol%)
in 2-propanol (5 mL) and it was stirred at room temperature for
15 min. The corresponding ketones were 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 atmosphere
of nitrogen and the course of the reaction was monitored by GC
analysis. After completion of the reaction, the solvent was removed
under reduced pressure. The residual mixture was diluted with
H2O and Et2O (10 mL each), washed with brine and extracted
with Et2O (2 ¥ 6 mL). The combined organic fractions were dried
(MgSO4), stripped of the solvent under vacuum and the residue
was redissolved in 5 mL of dichloromethane. An aliquot was taken
with a syringe and subjected to GC analysis. Conversions were
calculated relative to the ketones as an internal standard.
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X-Ray crystallography
A crystal of each of the compounds 4 and 6 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 Bruker APEX CCD diffractome-
ter. Full spheres of data were collected using 606 scans in w
(0.3◦ per scan) at f = 0, 120 and 240◦ under the control of the
APEX2 program suite.19 The raw data were reduced to F2 values
using the SAINT+ software20 and global refinements of unit cell
parameters using 6709 or 7047 reflections chosen from the full
data sets were performed. Multiple measurements of equivalent
reflections provided the basis for empirical absorption corrections
as well as corrections for any crystal deterioration during the data
collection (SADABS21). Both the structures were solved by direct
methods and refined by full-matrix least-squares procedures using
the SHELXTL program package.22 Hydrogen atoms were placed
in calculated positions and included as riding contributions with
isotropic displacement parameters tied to those of the attached
non-hydrogen atoms.
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Acknowledgements
11 (a) B. Punji, J. T. Mague and M. S. Balakrishna, Inorg. Chem.,
2007, 46, 11316–11327; (b) R. Venkateswaran, J. T. Mague and M. S.
Balakrishna, Inorg. Chem., 2007, 46, 809–817; (c) R. Venkateswaran,
M. S. Balakrishna and S. M. Mobin, Eur. J. Inorg. Chem., 2007, 1930–
1938; (d) B. Punji, C. Ganesamoorthy and M. S. Balakrishna, J. Mol.
Catal. A: Chem., 2006, 259, 78–83; (e) B. Punji, J. T. Mague and
M. S. Balakrishna, J. Organomet. Chem., 2006, 691, 4265–4272; (f) B.
Punji, J. T. Mague and M. S. Balakrishna, Dalton Trans., 2006, 1322–
1330.
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1683–1689; (b) E. K. V. D. Beuken, W. G. J. D. Lange, P. W. N. M. V.
Leeuwen, N. Veldman, A. L. Spek and B. L. Feringa, J. Chem. Soc.,
Dalton Trans., 1996, 3561–3569.
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, India, for a
Senior Research Fellowship (SRF). We also thank the Department
of Chemistry Instrumentation Facilities, Bombay, for spectral and
analytical data and J. T. M thanks the Louisiana Board of Regents
through grant LEQSF(2002–03)-ENH-TR-67 for purchase of the
CCD diffractometer and the Chemistry Department of Tulane
University for support of the X-ray Laboratory.
13 B. Punji, J. T. Mague and M. S. Balakrishna, Dalton Trans., 2006,
1322–1330.
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