Tetranuclear rhodium(I) macrocycle containing cyclodiphosphazane [Rh 2(μ-Cl)2(CO)2(tBuNP(OC 6H4OMe-o))2-κP]2 and its reversible conversion into trans-[Rh(CO)Cl{(t

Article abstract of DOI:10.1021/om0502537

The 1:1 reaction between cis-[^tBuNP(OC₆H ₄OMe-o)]₂ (2) and [Rh(μ-Cl)(CO)₂] ₂ affords novel tetranuclear rhodium(I) macrocycle (3) containing two cyclodiphosphazanes bridged by two [Rh(μ-Cl)

Full text of DOI:10.1021/om0502537

3780
Organometallics 2005, 24, 3780-3783
Tetranuclear Rhodium(I) Macrocycle Containing
Cyclodiphosphazane
[Rh2(µ-Cl)2(CO)2{(tBuNP(OC6H4OMe-o))2-KP]2 and Its
Reversible Conversion into
trans-[Rh(CO)Cl{(tBuNP(OC6H4OMe-o))2-KP}2]
P. Chandrasekaran,† Joel T. Mague,‡ and Maravanji S. Balakrishna*,†
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076,
India, and Department of Chemistry, Tulane University, New Orleans, Louisiana 70118
Received April 5, 2005
The 1:1 reaction between cis-[tBuNP(OC6H4OMe-o)]2 (2) and [Rh(µ-Cl)(CO)2]2 affords novel
tetranuclear rhodium(I) macrocycle (3) containing two cyclodiphosphazanes bridged by two
[Rh(µ-Cl)(CO)]2 moieties, whereas the corresponding 4:1 reaction affords trans-[Rh(CO)Cl-
{(tBuNP(OC6H4OMe-o))2-κP}2] (4).
Introduction
though the main group chemistry of cyclodiphos-
phazanes has been extensively studied by Chivers’ and
Stahl’s groups,6 their utility in coordination chemistry
is limited7 and their polynuclear transition-metal com-
plexes are even less extensive.8 We report here the
synthesis of a novel tetrarhodium(I) macrocycle contain-
ing two [Rh(µ-Cl)(CO)]2 units bridged by two cyclo-
diphosphazanes and of a trans-mononuclear rhodium(I)
derivative containing two monodentate cyclodiphos-
phazanes.
In recent years, there has been considerable interest
in the construction of supramolecular compounds through
coordination chemistry.1 The metallamacrocycles2 are
one of the most important supramolecular architectures
used in catalysis, sensors, and molecular electronics.3
Nitrogen donor ligands with bis(pyridine) frameworks
have been widely used for constructing macrocycles.4
Macrocycles containing phosphorus centers are less
extensive, mainly due to the lack of availability of
suitable phosphorus(III) frameworks. Diazadiphosphe-
tidines or cyclodiphosphazanes of the type [RNPCl]2
with almost planar N2P2 rings are one such type of
system which can form a variety of macrocycles through
nucleophilic substitutions at phosphorus centers.5 Al-
Results and Discussion
The reaction of cyclodiphosphazane, [tBuNPCl]2 (1),
with 2 equiv of o-methoxyphenol in the presence of
triethylamine afforded cis-[tBuNP(OC6H4OMe-o)]2 (2)
in quantitative yield. Compound 2 is a white solid
and soluble in all common organic solvents. The 31P
NMR spectrum of 2 shows a single resonance at 145.7
ppm indicating the symmetric nature of two phos-
phorus centers. The analytical data, 1H NMR, and mass
spectral data are consistent with the structure proposed
for 2.
In the reaction of [Rh(µ-Cl)(CO)2]2 with 1 equiv of 2,
a tetrarhodium(I) macrocycle, [Rh2(µ-Cl)2(CO)2{(tBuNP-
(OC6H4OMe-o))2-κP}]2 (3), was obtained as shown in
Scheme 1. The 31P NMR spectrum of complex 3 consists
of an AA′XX′ multiplet9 centered at 115.8 ppm with
* To whom correspondence should be addressed. Fax: +91-22-2572-
3480. Tel: +91-22-2576-7181. E-mail: krishna@iitb.ac.in.
† Indian Institute of Technology.
‡ Tulane University.
(1) (a) Lehn, J. M. Chem. Eur. J. 2000, 6, 2097. (b) Leininger, S.;
Olenyuk, B.; Stang, P. J. Chem. Rev. 2000, 100, 853. (c) Fujita, M.
Chem. Soc. Rev. 1998, 417.
(2) (a) Newkome, G. R.; Cho, T. J.; Moorefield, C. N.; Mohapatra,
P. P.; Godinez, L. A. Chem. Eur. J. 2004, 10, 1493. (b) Eisenberg, A.
H.; Dixon, F. M.; Mirkin, C. A.; Stern, C. L.; Incarvito, C. D.; Rheingold,
A. L. Organometallics 2001, 20, 2052. (c) Brasey, T.; Scopelliti, R.;
Severin, K. Inorg. Chem. 2005, 44, 160. (d) Liang, X.; Parkinson, J.
A.; Weishaupl, M.; Gould, R. O.; Paisey, S. J.; Park, H.; Hunter, T. M.;
Blindauer, C. A.; Parsons, S.; Sadler, P. J. J. Am. Chem. Soc. 2002,
124, 9105.
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A.; Zakharov, L. N.; Rheingold, A. L. J. Am. Chem. Soc. 2003, 125,
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Eur. J. 2003, 9, 2845. (c) Schalley, C. A. Angew. Chem., Int. Ed. 2002,
41, 1513.
(4) (a) Yamanoi, Y.; Sakamoto, Y.; Kusukawa, T.; Fujita, M.;
Sakamoto, S.; Yamaguchi, K. J. Am. Chem. Soc. 2001, 123, 980. (b)
Schmitz, M.; Leininger, S.; Fan, J.; Arif, A. M.; Stang, P. J. Organo-
metallics 1999, 18, 4817. (c) Wurthner, F.; Sautter, A. Chem. Commun.
2000, 445.
(5) (a) Gonce, F.; Caminade, A. M.; Boutonnet, F.; Majoral, J. P. J.
Org. Chem. 1992, 57, 970. (b) Kommana, P.; Kumara Swamy, K. C.
Inorg. Chem. 2000, 39, 4384. (c) Garcia, F.; Kowenicki, R. A.; Kuzu, I.;
Riera, L.; McPartlin, M.; Wright, D. S. Dalton Trans. 2004, 2904. (d)
Bashall, A.; Doyle, E. L.; Tubb, C.; Kidd, S. J.; McPartlin, M.; Woods
A. D.; Wright, D. S. Chem. Commun. 2001, 2542. (e) Garcia, F.;
Goodman, J. M.; Kowenicki, R. A.; Kuzu, I.; McPartlin, M.; Silva, M.
A.; Riera, L.; Woods, A. D.; Wright, D. S. Chem. Eur. J. 2004. 10, 6066.
(6) (a) Briand, G. G.; Chivers, T.; Krahn, M. Coord. Chem. Rev. 2002,
233, 237 and references therein. (b) Stahl, L. Coord. Chem. Rev. 2000,
210, 203. and references therein. (c) Chivers, T.; Fedorchuk, C.; Krahn,
M.; Parvez, M.; Schatte, G. Inorg. Chem. 2001, 40, 1936.(d) Chivers,
T.; Krahn, M.; Parvez, M. Chem. Commun. 2000, 463. (e) Chivers, T.;
Krahn, M.; Parvez, M.; Schatte, G. Inorg. Chem. 2001, 40, 2547.
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10.1021/om0502537 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 06/22/2005

Tetranuclear Rhodium(I) Macrocycle
Organometallics, Vol. 24, No. 15, 2005 3781
Scheme 1a
Figure 1. Molecular structure of 3 in the crystal (hydrogen
atoms are omitted for clarity). Selected bond lengths (Å)
and angles (deg): Rh(1)-P(1), 2.187(1); Rh(2)-P(2), 2.197-
(1); Rh(1)-Cl(1), 2.353(1); Rh(1)-Cl(2), 2.410(1); Rh(2)-
Cl(1), 2.364(1); Rh(2)-Cl(2), 2.409(1); Rh(1)-C(12), 1.825-
(3); Rh(2)-C(13), 1.820(3); P(1)-N(1), 1.692(3); P(2)-N(2),
1.692(3); Rh(1)‚‚‚Rh(2), 3.365; P(1)-Rh(1)-C(12), 89.47(11);
P(1)-Rh(1)-Cl(1), 96.61(3); Cl(1)-Rh(1)-Cl(2), 84.17(3);
Cl(2)-Rh(1)-C(12), 89.75(11); Rh(1)-Cl(1)-Rh(2), 91.02-
(3); Rh(1)-Cl(2)-Rh(2), 88.60(3).
a Key: (i) 2HOC6H4OMe-o, Et3N/Et2O; (ii) [Rh(µ-Cl)(CO)2]2,
CH3CN; (iii) 0.25[Rh(µ-Cl)(CO)2]2, CH2Cl2; (iv) 6[tBuNPR]2 (2),
CDCl3; (v) 1.5[Rh(µ-Cl)(CO)2]2, CDCl3.
1
| JRhP + 3JRhP| ) 282 Hz and 2JPP ) 47 Hz. This clearly
indicates the magnetic nonequivalence of the two phos-
phorus centers. The noncoordinating nature of the
1
methoxy groups was confirmed by the H NMR spec-
trum which did not show any change in the chemical
shift of the methoxy protons as compared to the same
in the free ligand. The IR spectrum of 3 shows two
absorptions at 2020 and 1992 cm-1 which is consistent
with the cis-related CO/phosphine structures proposed
for similar complexes.10 The reaction of [Rh(µ-Cl)(CO)2]2
with 4 equiv of 2 in dichloromethane afforded bright
yellow crystals of trans-[Rh(CO)Cl{(tBuNP(OC6H4OMe-
o))2-κP}2] (4) in good yield. The 31P NMR spectrum of 4
shows a singlet at 130.8 ppm for uncoordinated phos-
phorus centers and a doublet centered at 112.5 ppm for
1
coordinated phosphorus centers with a JRhP coupling
1
of 187 Hz. The low JRhP is attributed to the trans-
disposition of two phosphorus centers. The IR spectrum
of 4 shows νCO at 2019 cm-1. The mass spectrum of 4
shows a peak at 1031.43, which corresponds to (m/z -
Cl). The structures of compounds 3 and 4 were finally
confirmed by low-temperature single-crystal X-ray dif-
fraction studies.
Perspective views of the molecular structures of
compounds 3 and 4 with atom numbering schemes are
shown in Figures 1 and 2, respectively. Crystal data and
the details of the structure determination are given in
Table 1, while selected bond lengths and bond angles
appear below the corresponding Figures. The complex
3 is the first example of cyclodiphosphazanes forming
a tetranuclear transition metal macrocycle (Figure 1).
The structure consists of two [Rh(µ-Cl)(CO)]2 units
bridged by two cyclodiphosphazanes via P(III) cen-
ters to form a centro-symmetric pentacyclic tetranu-
clear macrocycle with rhodium(I) centers in slightly
distorted square planar environment. The Rh(1)-P(1)
Figure 2. Molecular structure of 4 in the crystal. Selected
bond lengths (Å) and angles (deg): P(1)-Rh, 2.278(1);
P(3)-Rh, 2.286(1); Rh-Cl, 2.364(1); Rh-C(45), 1.825(2);
P(1)-N(1), 1.677(2); P(1)-N(2), 1.680(2); P(2)-N(1), 1.723-
(2); P(2)-N(2), 1.720(2); O(9)-C(45), 1.145(3); P(1)-Rh-
Cl, 88.96(2); P(1)-Rh-C(45), 91.34(7); P(3)-Rh-Cl, 87.84-
(2); P(3)-Rh-C(45), 91.80(7); P(1)-Rh-P(3), 175.73(2);
Cl-Rh-C(45), 178.69(8).
and Rh(2)-P(2) distances are 2.187(1) and 2.197 (1) Å,
respectively. Two planar P2N2 rings are almost orthogo-
nal to the slightly inward puckered [Rh(µ-Cl)]2 rings.
The distances Rh(1)-Cl(1) (2.353(1) Å) and Rh(1)-
Cl(2) (2.410(1) Å) differ significantly. This difference can
most likely be attributed to a greater trans-influence
of the phosphorus ligand as compared to the car-
bonyl ligand. The Rh(1)-Cl(1)-Rh(2) and Rh(1)-Cl(2)-
Rh(2) bond angles are 91.02(3)° and 88.60(3)°, respec-
tively. These differences may be attributed to bond-
strain reduction within the macrocycle.
(9) The 31P NMR spectrum of 3 is best interpreted as the A part of
an AA′XX′ nuclear spin system with JXX′ ) 0.
(10) Balakrishna, M. S.; Santarsiero, B. D.; Cavell, R. G. Inorg.
Chem. 1994, 33, 3079.
The molecular structure of 4 is shown in Figure 2.
The rhodium(I) center is in a slightly distorted square

3782 Organometallics, Vol. 24, No. 15, 2005
Chandrasekaran et al.
31P{1H} NMR (δ in ppm) spectra were recorded using a Varian
spectrometer operating at the appropriate frequencies using
TMS and 85% H3PO4 as internal and external references,
respectively. IR spectra were recorded on a Nicolet Impact 400
FT-IR instrument in KBr disks. Microanalyses were performed
on a Carlo Erba Model 1112 elemental analyzer. Mass spectra
were recorded using Waters Q-Tofmicro-YA-105. Melting
points were recorded in capillary tubes and are uncorrected.
Table 1. Crystallographic Information for
Compounds 3 and 4
3
4
formula
fw
crystal system
space group
a, Å
C
48H64Cl4N4O12P4Rh4
C
45H64ClN4O9P4Rh
1566.36
monoclinic
P21/c (No. 14)
15.642(2)
13.640(1)
14.790(1)
90
1067.24
monoclinic
P21/c (No. 14)
13.774(2)
11.105(1)
32.790(4)
90
Synthesis of cis-[tBuNP(OC6H4OMe-o)]2 (2). A mixture
of 2-methoxyphenol (3.6 g, 3.2 mL, 28.72 mmol) and triethyl-
amine (2.9 g, 4 mL, 28.72 mmol) in 50 mL of diethyl ether
was added dropwise over 30 min to a well-stirred diethyl ether
(125 mL) solution of 1, [tBuNPCl]2 (3.95 g, 14.36 mmol), at 0
°C. The reaction mixture was stirred for 18 h at room
temperature. Et3NHCl was filtered off, and the filtrate was
concentrated to 30 mL under reduced pressure and stored at
-30 °C to afford 2 as a crystalline material. Yield: 96% (6.21
g, 13.7 mmol). Mp: 84-86 °C. 1H NMR (300 MHz, CDCl3): δ
b, Å
c, Å
R, deg
â, deg
γ, deg
112.799(1)
90
96.607(2)
90
V, Å3
Z
2909.0(5)
4
4982.3(10)
4
Dcalc, g cm-3
1.788
1.423
µ (Mo KR), mm-1 1.469
0.581
2224
F (000)
1568
crystal size (mm) 0.02 × 0.11 × 0.19
0.12 × 0.15 × 0.17
t
T (K)
100
100
7.35-6.82 (m, Ph, 8H), 3.83 (s, OMe, 6H), 1.38 (s, Bu, 18H).
31P{1H} NMR (121 MHz, CDCl3): δ 145.6 (s). MS (EI): 451.16
(m/z + 1). Anal. Calcd for C22H32N2O4P2: C, 58.66; H, 7.16; N,
6.21. Found: C, 58.33; H, 7.19; N, 6.15.
2θ range, deg
total no. reflns
1.4-28.4
25324
1.5-28.3
43664
12003 [Rint ) 0.038]
1.04
0.0387
0.0869
no. of indep reflns 6967 [Rint ) 0.036]
GOF (F2)
1.02
0.0369
0.0985
Synthesis of [Rh2(CO)2Cl2{(tBuNP(OC6H4OMe-o))2-KP}]2
(3). A mixture of [Rh(µ-Cl)(CO)2]2 (60 mg, 0.15 mmol) and cis-
[tBuNP(OC6H4OMe-o)]2 (70 mg, 0.15 mmol) in CH3CN (15 mL)
was stirred under reflux conditions for 4 h. The resulting
yellow solution was evaporated under reduced pressure and
twice washed with Et2O (5 mL) to get yellow solid as product
(3). Yield: 92% (112 mg, 0.071 mmol). Mp: 230-232 °C dec.
1H NMR (300 MHz, CDCl3): δ 7.72-6.77 (m, Ph, 16H), 3.80
a
R1
b
wR2
2
2
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) {[∑w(Fo - Fc )/∑w(Fo2)2]}1/2
,
2
2
w ) 1/[σ2(Fo2) + (xP)2] where P ) (Fo + 2Fc )/3.
planar environment with P2N2 rings bending inward
making the angles P(1)-Rh-Cl (88.96(2)°) and
P(3)-Rh-Cl (87.84(2)°) acute. The two trans Rh-P bond
distances in complex 4 are slightly longer than the
equivalent bonds in complex 3 which is expected due to
the weakening of back-bonding. The sum of the angles
around the nitrogen atoms of cyclodiphosphazanes is
∼355°, which shows that the P2N2 rings are slightly
puckered.
In an NMR tube experiment, the reaction of 3 with 6
equiv of the cis-[tBuNP(OC6H4OMe-o)]2 (2) was moni-
tored using 31P NMR spectroscopy in CDCl3. The mac-
rocycle 3 was completely converted into the mononu-
clear complex 4 within 1 h. Likewise, complex 4 was
readily converted into tetranuclear complex 3 when
treated with 1.5 equiv of [Rh(µ-Cl)(CO)2]2 under similar
reaction conditions.
In conclusion, we have reported the first example of
tetranuclear rhodium macrocycle containing cyclodiphos-
phazanes, which act as bridging 4-electron donor ligands.
In the presence of excess cyclodiphosphazane, the
Rh-Cl bridges in the tetranuclear complex 3 cleave to
give the mononuclear complex 4 in a reversible reaction.
The cis-orientation of uncoordinated phosphorus(III)
centers in complex 4 can be used to make the het-
eropolymetallic complexes of high nuclearity. Efforts in
this direction are underway.
t
(s, OMe, 12H), 1.79 (s, Bu, 36H). 31P{1H} NMR (121 MHz,
1
3
2
CDCl3): δ 115.8 (m, | JRhP + JRhP| ) 282 Hz, JPP ) 47 Hz).
FT-IR (KBr disk): νCO 2020 (s) cm-1, 1992 (s) cm-1. Anal. Calcd
for C48H64N4O12P4Rh4Cl4: C, 36.80; H, 4.11; N, 3.57. Found:
C, 36.75; H, 4.12; N, 3.47.
Synthesis of trans-[Rh(CO)Cl{(tBuNP(OC6H4OMe-o))2-
KP}2](4). A dichloromethane (5 mL) solution of [Rh(µ-Cl)-
(CO)2]2 (22 mg, 0.056 mmol) was added dropwise to a
well-stirred dichloromethane solution (10 mL) of cis-[tBuNP-
(OC6H4OMe-o)]2 (0.103 g, 0.227 mmol) at room temperature.
The reaction mixture was stirred for 4 h. The solution was
concentrated to 5 mL under reduced pressure, diluted with 3
mL of hexane, and placed at room temperature for a day to
get pale yellow crystals as product. Yield: 87% (0.105 g, 0.098
mmol). Mp: 208-210 °C. 1H NMR (400 MHz, CDCl3):
δ
8.22-6.83 (m, Ph, 16H), 3.85 (s, OMe, 6H), 3.82 (s, OMe,
t
6H), 1.51 (s, Bu, 36H). 31P{1H} NMR (161 MHz, CDCl3): δ
130.8 (s), 112.5 (d, 1JPRh ) 187 Hz). FT-IR (KBr disk): νCO 2019
(s) cm-1. MS (EI): 1031.43 (m/z - Cl). Anal. Calcd for
C45H64N4O9P4RhCl: C, 50.64; H, 6.04; N, 5.24. Found: C;
50.67; H, 5.99; N, 5.28.
X-ray Crystallography. A crystal of 3 or 4 was mounted
in a Cryoloop with a drop of Paratone oil and placed in the
cold nitrogen stream of the Kryoflex attachment of the Bruker
APEX CCD diffractometer. A full sphere of data was collected
using 606 scans in ω (0.3° per scan) at æ ) 0, 120, and 240°
using the SMART software package.14 The raw data were
reduced to F2 values using the SAINT+ software,15 and a
global refinement of unit cell parameters employing 7321-
7383 reflections chosen from the full data set was performed.
Multiple measurements of equivalent reflections provided the
basis for an empirical absorption correction as well as a
correction for any crystal deterioration during the data col-
lection (SADABS16). The structure was solved by direct
methods and refined by full-matrix least-squares procedures
using the SHELXTL program package.17 Hydrogen atoms were
Experimental Section
All manipulations were performed under rigorously anaero-
bic conditions using Schlenk techniques. All the solvents were
purified by conventional procedures and distilled prior to use.11
12
13
The compounds [tBuNPCl]2 (1) and [Rh(µ-Cl)(CO)2]2 were
1
prepared according to the published procedures. The H and
(11) Armarego, W. L. F.; Perrin, D. D. Purification of Laboratory
Chemicals, 4th ed.; Butterworth-Heinemann Linacre House: Jordan
Hill, Oxford, U.K., 1996.
(12) Bashall, A.; Doyle, E. L.; Tubb, C.; Kidd, S. J.; McPartlin, M.;
Woods, A. D.; Wright, D. S. Chem. Commun. 2001, 2542.
(13) McCleverty, J. A.; Wilkinson, G. Inorg. Synth. 1990, 28, 84.
(14) Bruker-AXS. SMART, Version 5.625, Madison, WI, 2000.
(15) Bruker-AXS. SAINT+, Version 6.35A, Madison, WI, 2002.
(16) Sheldrick, G, M. SADABS, Version 2.05, University of Go¨ttin-
gen, Germany, 2002.

Tetranuclear Rhodium(I) Macrocycle
Organometallics, Vol. 24, No. 15, 2005 3783
placed in calculated positions and included as riding contribu-
tions with isotropic displacement parameters tied to those of
the attached non-hydrogen atoms.
J.T.M. thanks the Louisiana Board of Regents for
purchase of the CCD diffractometer under Grant No.
LEQSF (2002-03)-ENH-TR-67. The reviewers’ sugges-
tions at the revision stage were very helpful.
Acknowledgment. We thank the Department of
Science and Technology (DST), New Delhi, for financial
support and CSIR, New Delhi, for JRF and SRF to P.C.
Supporting Information Available: X-ray crystallo-
graphic files (CIF) for the structure determinations of 3 and
4. This material is available free of charge via the Internet at
http://pubs.acs.org.
(17) (a) Bruker-AXS. SHELXTL, Version 6.10, Madison, WI, 2000.
(b) Sheldrick, G. M. SHELXS97 and SHELXL97, University of Go¨t-
tingen, Germany, 1997.
OM0502537