Novel examples of simultaneous reductive azo cleavage and oxidative aromatic ring amination in rhodium complexes of 2-(arylazo)pyridine

Article abstract of DOI:10.1021/om990617t

The reaction of [AgL¹₂]ClO₄ (L¹ = NH₄C₅N=NC₆H₄(R)) with [RhCl₂L¹₂]ClO₄ (1) in boiling ethanol affords green complexes of the type [RhClL¹L²](ClO₄) (2; L² = NH₄C₅N=NC₆H₃(R)-NC₅H ₄N). This reaction is an unprecedented example wherein the anionic tridentate N,N,N donor L² is formed by the fusion of the pyridyl imide fragment [PyN]^2- to a pendant aromatic ring of the coordinated ligand L¹. The [PyN]^2- originates from the splitting of a diaza function of coordinated L¹. The complexes have been fully characterized, and structures of the two representative complexes la and 2a (R = H) are reported. A reaction pathway based on the reduction potentials of the coordinated ligand L¹ is proposed for the above transformation.

Full text of DOI:10.1021/om990617t

5086
Organometallics 1999, 18, 5086-5090
Novel Exa m p les of Sim u lta n eou s Red u ctive Azo
Clea va ge a n d Oxid a tive Ar om a tic Rin g Am in a tion in
Rh od iu m Com p lexes of 2-(Ar yla zo)p yr id in e
Amit K. Ghosh,† Partha Majumdar,† Larry R. Falvello,‡ Golam Mostafa,§ and
Sreebrata Goswami*,†
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science,
Calcutta 700 032, India, Departamento de Quimica Inorganica, Universidad de Zaragoza,
Zaragoza 50009, Spain, and Department of Physics, Krishnath College,
Berhampur, West Bengal, India
Received August 3, 1999
The reaction of [AgL1 ]ClO4 (L1 ) NH4C5NdNC6H4(R)) with [RhCl2L1 ]ClO4 (1) in boiling
2
2
ethanol affords green complexes of the type [RhClL1L2](ClO4) (2; L2 ) NH4C5NdNC6H3(R)-
NC5H4N). This reaction is an unprecedented example wherein the anionic tridentate N,N,N
donor L2 is formed by the fusion of the pyridyl imide fragment [PyN]2- to a pendant aromatic
ring of the coordinated ligand L1. The [PyN]2- originates from the splitting of a diaza function
of coordinated L1. The complexes have been fully characterized, and structures of the two
representative complexes 1a and 2a (R ) H) are reported. A reaction pathway based on the
reduction potentials of the coordinated ligand L1 is proposed for the above transformation.
In tr od u ction
The examples of reductive cleavage1-4 of a coordinated
diaza function resulting in metal organoimido species
is an important class of chemical transformation. Metal
imido complexes, in turn, have been shown to be
potential intermediates for the metal-promoted organic
transformations5-9 involving the formation of nitrogen-
carbon bonds. Reductive azo cleavage and oxidative
aromatic ring amination occurring in a concerted way
at a single metal site was, however, not known in the
literature. This unusual transformation was observed
when RhCl2(L1)2+ was reacted with Ag(L1)2+ in ethanol
(eq i).
Resu lts a n d Discu ssion
A. Sta r tin g Ma ter ia l. Synthesis of the starting
cationic complex [RhCl2(L1)2](ClO4) (1) was reported by
us10 about a decade ago. Due to the unsymmetric nature
of bidentate L1, there exists five geometrical isomer
possibilities for 1. The structure solution of the repre-
sentative complex 1a indicates a cis,trans,cis geom-
etry.10,11 A view of the cationic part of 1a is shown in
Figure 1. The coordination sphere around rhodium is
approximately octahedral. The metal ion is located at
the crystallographic 2-fold axis; only half of it occupies
the asymmetric unit. The cation Rh(III) is a much poorer
donor than Ru(II)/Os(II), and hence, dπ-pπ interactions
in 1 are unimportant. The N-N distance in 1a is
1.255(5) Å (Table 1), which is almost identical with
that12 (1.258(5) Å) in [L1aH]ClO4. The average N-N
distance in the corresponding Ru(II) and Os(II) com-
* To whom correspondence should be addressed. E-mail: icsg@
mahendra.iacs.res.in. Fax: 91-33-473-2805.
† Indian Association for the Cultivation of Science.
‡ Universidad de Zaragoza.
§ Krishnath College.
(1) Lockwood, M. A.; Fanwick, P. E.; Eisentein, O.; Rothwell, I. P.
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1635.
(11) With consideration of the coordinated atoms in three pairs, viz.
Cl/Cl, N(py)/N(py), and and N(azo)/N(azo) the stereochemistry of the
isomers can be defined by setting the relative positions (cis (c) or trans
(t)) within the pair of identical atoms.
(9) Petillon, F. Y.; Schollhammer, P.; Talarmin, J . Inorg. Chem.
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10.1021/om990617t CCC: $18.00 © 1999 American Chemical Society
Publication on Web 11/22/1999

Rh Complexes of 2-(Arylazo)pyridine
Organometallics, Vol. 18, No. 24, 1999 5087
F igu r e 2. ORTEP plot and atom-numbering scheme for
[RhCl(L1a)(L2a)]+ in [RhCl(L1a)(L2a)]ClO4. Hydrogen atoms
are omitted for clarity.
F igu r e 1. ORTEP plot and atom-numbering scheme for
[RhCl2(L1a)2]+ in [RhCl2(L1a)2]ClO4. Hydrogen atoms are
omitted for clarity.
C. Ch a r a cter iza tion . A view of the cationic part of
the molecule [RhCl(L1a)(L2a)](ClO4) is shown in Figure
2. In this complex, the rhodium center is surrounded
by a distorted-octahedral coordination environment by
one chloride ligand, the bidentate chelating ligand L1a
and the tridentate monoanionic bis-chelating ligand L2a.
The complex as a whole is monocationic, and the
crystallographic asymmetric unit also contains one unit
of perchlorate. The chelate bite angle of L1a, N(28)-
Rh(1)-N(35), is 77.2(3)°, while the corresponding
N(pyridyl)-Rh-N(aza) angle in the tridentate ligand,
viz. N(4)-Rh(1)-N(8), has a value of 79.1(3)°. The
second chelate of L2a, formed by the aza nitrogen N(8)
and the deprotonated amino nitrogen N(15), has a bite
angle of 81.2(3)°.
Ta ble 1. Selected Bon d Dista n ces (Å)
[RhCl2(L1a)2]ClO4 (1a )
Rh-N(1)
Rh-N(3)
Rh-N(4)
Rh-N(6)
2.026(4)
2.035(3)
2.007(3)
2.031(3)
Rh-Cl(1)
Rh-Cl(2)
N(2)-N(3)
N(5)-N(6)
2.3321(14)
2.3104(14)
1.255(5)
1.258(5)
[RhCl(L1a)(L2a)]ClO4 (2a )
Rh(1)-N(8)
Rh(1)-N(15)
Rh(1)-N(28)
Rh(1)-N(35)
Rh(1)-N(4)
Rh(1)-Cl(1)
N(4)-C(5)
1.955(7)
2.037(7)
2.039(7)
2.045(6)
2.051(7)
2.318(2)
1.347(10)
1.396(10)
N(7)-N(8)
1.307(10)
1.348(11)
1.430(12)
1.343(10)
1.256(9)
1.421(11)
1.340(10)
1.418(10)
N(8)-C(9)
C(9)-C(14)
C(14)-N(15)
N(28)-N(29)
N(29)-C(30)
C(30)-N(35)
N(15)-C(16)
C(5)-N(7)
The bond distances (Table 1) along the ligand back-
bones indicate different levels of conjugation in the two
coordinated ligands. For the neutral L1a ligand, the
N-N distance N(28)-N(29) is 1.256(9) Å, while the
corresponding distance in the anionic tridentate ligand,
N(7)-N(8), is 1.307(10) Å. The two bonds on either side
of the aza moiety are shorter in the L2a ligand than they
are in L1a: for L1a, C(27)-N(28) ) 1.430(10) Å and
N(29)-C(30) ) 1.421(11) Å, while the corresponding
distances in the tridentate ligand are N(8)-C(9) )
1.348(11) Å and C(5)-N(7) ) 1.396(10) Å. Taken
together, the lengthening of the aza NdN distance in
L2a and the foreshortening of the N-C distances along-
side the aza moiety, with respect to the corresponding
distances in L1a itself, indicate greater delocalization of
π-electron density in L2a. The central Rh-N bond of the
anionic L2a ligand, Rh(1)-N(8) ) 1.955(7) Å, is signifi-
cantly shorter than the other four Rh-N distances,
which are all near their average value of 2.04 Å.
The rhodium(III) compounds (2) are diamagnetic
(Rh(III), 4d6). These are 1:1 electrolytes in acetonitrile
and showed intense transitions in the visible region
(Figure 3). The multiple low-energy transitions are
believed to be due to charge transfer transitions involv-
ing both metal and ligand orbitals, while the transitions
occurring in the UV region are assigned to transitions
involving predominantly ligand orbitals. We wish to
note here that such low-energy transitions in rhodium-
(III) complexes are uncommon17 and may have useful-
ness with regard to the development of photocatalysts
active in the long-wavelength region of the visible
plexes of L1 is considerably longer13 due to extensive
π-interactions. The distances between central rhodium
and coordinating atoms are normal.
B. Th e Rea ction . The problems encountered in the
synthesis of halide-free rhodium compounds from a
rhodium(III) starting material are due to its inertness
toward halide substitution reactions. In view of our
recent experience,14 it was anticipated that this problem
of chloride substitution from 1 by another L1 could be
overcome by the use of [Ag(L1)2]+ClO4 as a synthon.15
Unexpectedly, the reaction of 1 with [Ag(L1)2]+ has led
to unusual transformations of coordinated L1 as shown
in eq (i). The formation of the cationic compound 2 (in
65-60% yield) from the above reaction has been au-
thenticated by structural analysis of a representative
example, [RhCl(L1a)(L2a)]ClO4, (2a ). We wish to note
here that we have recently shown16 that amination of
the pendant aryl ring of L1 can be achieved via its
coordination to transition-metal ions due to C-H acti-
vation.
(13) (a) Seal, A.; Ray, S. Acta Crystallogr., Sect. C: Struct. Commun.
1984, 40, 929. (b) Ghosh, B. K.; Mukhopadhyay, A.; Goswami, S.; Ray,
S.; Chakravorty, A. Inorg. Chem. 1984, 23, 4633.
(14) (a) Kakoti, M.; Deb, A. K.; Goswami, S. Inorg. Chem. 1992, 31,
1302. (b) Choudhury, S.; Deb, A. K.; Kharmawphlang, W.; Goswami,
S. Proc. Indian Acad. Sci. 1994, 106, 665. (c) Choudhury, S.; Deb, A.
K.; Goswami, S. J . Chem. Soc., Dalton Trans. 1994, 1305. (d) Khar-
mawphlang, W.; Choudhury, S.; Deb, A. K.; Goswami, S. Inorg. Chem.
1995, 34, 3826. (e) Majumdar, P.; Ghosh, A. K.; Falvello, L. R.; Peng,
S.-M.; Goswami, S. Inorg. Chem. 1998, 37, 1651.
(15) Deb, A. K.; Choudhury, S. Polyhedron 1990, 9, 2251.
(16) Saha, A.; Ghosh, A. K.; Majumdar, P.; Mitra, K. N.; Mondal,
S.; Rajak, K. K.; Falvello, L. R.; Goswami, S. Organometallics 1999,
18, 3772.
(17) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M.
Advanced Inorganic Chemistry, 6th ed.; Wiley: New York, 1999; p 1048.

5088 Organometallics, Vol. 18, No. 24, 1999
Ta ble 2. Solu tion Sp ectr a l a n d Volta m m etr ic Da ta
Ghosh et al.
cyclic voltammetric datac
compd
absa max, nm (ꢀ, M-1 cm-1
λ
)
oxidn
1.21d
redn
[RhCl(L1a)(L2a)]ClO4
795 (6300), 730 (5700), 660,b 365 (17 400), 280,b 215 (46 100)
795 (5300), 735 (4900), 665,b 365 (14 800), 290,b 215 (40 000)
795 (5300), 735 (5000), 665,b 365 (14 800), 290,b 215 (40 000)
795 (5600), 740 (5450), 665,b 365 (14 000), 280,b 215 (41 600)
-0.04, -0.59e,
-1.40,f -1.78f
-0.06, -0.67e,
-1.47,f -1.83f
-0.06, -0.67e,
-1.47,f -1.83f
-0.10, -0.67e,
-1.51,f -1.85f
[RhCl(L1a)(L2b)]ClO4
[RhCl(L1b)(L2a)]ClO4
[RhCl(L1b)(L2b)]ClO4
1.17d
1.17d
1.13d
Data obtained from absorption spectra: solvent CH3CN. Shoulder. c Experiments were carried out in CH3CN at 298 K using 0.1 M
a
b
NEt4ClO4 as supporting electrolyte: reported data correspond to a scan rate of 50 mV s-1; working electrode, platinum for oxidation
d
processes and glassy carbon for reduction processes; reference electrode,Ag-AgCl; solute concentration, 10-3 M. Irreversible response:
the potential corresponds to Ep,a
.
e Reversible response with current height ca. 2 times larger than a single-electron-transfer process.
f Irreversible response: the potential corresponds to Ep,c
.
these two compounds 2a b and 2ba matches with one
of the methyl resonances for 2bb occurring at a higher
field.
D. Ra tion a le for th e Tr a n sfor m a tion L1 f L2. The
reaction (i) exemplifies an unprecedented chemical
reaction wherein an anionic tridentate N,N,N donor (L2)
is formed by the oxidative fusion16,18 of the pyridyl imide
fragment [PyN]2- to a pendant aromatic ring of a
coordinated diaza ligand. The pyridyl imide fragment
[PyN]2- is presumably formed by the reductive fission
of one of the coordinated diaza ligands. The conversion
L1 f L2 occurs within the coordination sphere.
The reductive NdN cleavage of L1 requires four
electrons, whereas the oxidative fusion C-N bond
formation involves two electrons. In the present context
it may be noted here that the reducible solvent ethanol
is essential19 for this reaction. Important insights into
this NdN cleavage process may be obtained by the
examination of redox properties of the starting com-
pound, 1. It undergoes10 multiple aza reductions: the
first reduction occurs at an anodic potential (+0.02 V),
implying that upon coordination the ligand L1 at a RhIII
center becomes susceptible to reduction. It is also
reasonable14 that the process of [Ag(L1)2]+-assisted
chloride substitution in 1 occurs via an intermediate
where one end of L1 occupies the position of the leaving
Cl-. In this intermediate, the reduction potential of
coordinated L1 is expected to move anodic, which further
facilitates the reduction of the diaza function leading
to NdN cleavage.14,20-22 We wish to note here that even
in the presence of excess [Ag(L1)2]+ reagent (>2 times)
the reaction (i) does not proceed any further and yielded
2 as the only product. Furthermore, this compound is
F igu r e 3. UV-vis spectrum of [RhCl(L1a)(L2a)]ClO4 in
acetonitrile solution. Inset: enlarged spectrum in the range
600-900 nm.
spectrum. The compounds show all characteristic vibra-
tions for the coordinated ligands. The ν(Rh-Cl) band
occurs at 350 cm-1. The spectral characterization data
are collected in Table 2.
Use of substituted L1 species as reactants also af-
1
forded similar compounds. The H NMR spectra of the
cationic complex 2 contain several overlapping reso-
nances in the aromatic region, owing to the large
numbers of unique protons in these complexes. How-
ever, the methyl resonances for the reactions using
complexes of L1b ligands have been particularly useful
for the confirmation of the pyridyl amide fusion reaction
(eq i). Thus, the reaction product 2bb obtained from the
reaction of [RhCl2(L1b)2]+ with [Ag(L1b)2]+ shows only
two methyl resonances at δ 2.17 and 2.15. The fact that
the reaction product 2ba obtained from the reaction of
[RhCl2(L1b)2]+ and [Ag(L1a)2]+ shows only one methyl
resonance at δ 2.15 confirms the cleavage of one of the
two coordinated ligands L1b present in the starting
rhodium compound. Interestingly, the products obtained
from the reactions of (a) [RhCl2(L1b)2]+ with [Ag(L1a)2]+
and of (b) [RhCl2(L1a)2]+ with [Ag(L1b)2]+ are identical.
The chemical shift of the lone methyl resonance for
(18) (a) Mitra, K. N.; Choudhury, S.; Castin˜eiras, A.; Goswami, S.
J . Chem. Soc., Dalton Trans. 1998, 2901. (b) Mitra, K. N.; Peng, S.-
M.; Goswami, S. Chem. Commun. 1998, 1685. (c) Mitra, K. N.;
Goswami, S. Chem. Commun. 1997, 49; Inorg. Chem. 1997, 36, 1322.
(19) This reaction does not occur in a redox-inert solvent such as
acetonitrile.
(20) Our proposal of reductive NdN bond cleavage is based on
consideration of (i) the high reduction potential of coordinated L1, (ii)
the inability of the reaction of 1 with free ligand L1 to bring about the
transformation 1 f 2, and (iii) the partial (one out of two coordinated
L1) transformation of L1 f L2. Admittedly, the proposal is not a unique
rationalization of the experimental results. It, however, appears to be
the most plausible one.
(21) Similar reactions14 of MX2(L1)2 (M ) Ru(II), Os(II), X ) Cl, Br)
with 2 mol of [Ag(L1)2]+ led to formation of [M(L1)3]2+. A diaza cleavage
process was not observed in the cases of Ru(II) and Os(II). For
comparison, the first reduction potential22 for coordinated L1 in MCl2-
(L1)2 is cathodic by ca. -1.0 V as compared to that in 1.
(22) (a) Goswami, S.; Chakravarty, A. R.; Chakravorty, A. Inorg.
Chem. 1981, 20, 2246. (b) Ghosh, B. K.; Goswami, S.; Chakravorty, A.
Inorg. Chem. 1983, 22, 3358.

Rh Complexes of 2-(Arylazo)pyridine
Organometallics, Vol. 18, No. 24, 1999 5089
Ta ble 3. Cr ysta llogr a p h ic Da ta Collection
P a r a m eter s
unreactive to AgNO3. The above observations taken
together confirm that chloride dissociation and subse-
quent L1 coordination are the two important steps for
L1 f L2 transformation. It has been already shown16
that to promote ortho amination of the activated aro-
matic ring, cis coordination of the amine residue is
essential. The compound 2 is exeptionally inert to
substitution, and further amination of the second L1 was
not observed under the above reaction conditions.
E. Con clu d in g Rem a r k s. The present work further
demonstrates that (aryl)pyridine ligands L1 are suscep-
tible to fascinating metal-mediated chemical transfor-
mations. Earlier it has been demonstrated that the
aromatic -C6H4R moiety of L1 can be hydroxylated,23
thiolated,24 and aminated16 by the C-H activation due
to coordination of L1. Rhenium-mediated aza cleavage
of L1 leading2e to the semibent organoimide function
ReVNC6H4R has also been reported. We now have an
unprecedented example of simultaneous aza cleavage
and ortho amination of the -C6H4R moiety of coordi-
nated L1 mediated by rhodium. The resulting rhodium
complexes show interesting redox as well as optical
properties.
[Rh(L1a)2Cl2]ClO4 [RhCl(L1a)(L2a)]ClO4
(1a )
(2a )
formula
mol wt
cryst syst
space group
a, Å
C
22H18Cl3N6O4Rh
C27H21Cl2N8O4Rh
695.33
triclinic
P1h
8.626(2)
11.434(4)
14.425(5)
104.05(3)
91.99(3)
101.23(2)
1348.6(8)
2
639.68
triclinic
P1h
10.471(2)
11.611(4)
12.666(5)
64.28(4)
69.31(7)
73.56(3)
1282.4(10)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
d
calcd, g/cm3
1.657
1.712
cryst dimens, mm
temp, °C
radiation (λ, Å)
2θ range, deg
total no. of unique
rflns
0.35 × 0.30 × 0.30
0.41 × 0.24 × 0.09
-123 ( 1
Mo KR (0.710 73)
4.0-50.0
4747
20
Mo KR (0.709 30)
1.9-24.9
4490
R1, wR2
0.0321, 0.0862
1.008
0.0703, 0.1800
0.986
GOF
largest diff between 0.731, -0.703
0.98, -1.17
peak and trough,
e/Å3
Ω-1 M-1 cm2 (1 × 10-3 M in CH3CN). IR ν/cm-1 (KBr):
ν(C-N) 1600; ν(ClO4-) 630, 1100; ν(NdN) 1540; ν(Rh-Cl) 350.
P r ep a r a tion of [Rh Cl(L1a )(L2b)](ClO4). A 100 mg (0.156
mmol) portion of the starting complex [RhCl2(L1a)2]ClO4 and
188 mg (0.312 mmol) of [Ag(L1b)2]ClO4 were used and proce-
dures similar to those given above followed to obtain [RhCl-
(L1a)(L2b)]ClO4 in 65% yield. Anal. Found: C, 47.33; H, 3.28;
N, 15.73. Calcd for C28H23Cl2N8O4Rh: C, 47.39; H, 3.24; N,
15.79. ΛM ) 155 Ω-1 M-1 cm2 (1 × 10-3 M in CH3CN). IR
ν/cm-1 (KBr): ν(C-N) 1585; ν(ClO4-) 625, 1100; ν(NdN) 1560;
ν(Rh-Cl) 340.
Exp er im en ta l Section
Ma ter ia ls. The starting rhodium(III) complexes10 [RhCl2-
(L1)2](ClO4) and the silver(I) complexes15 [Ag(L1)2](ClO4) were
synthesized by the reported methods. Chemicals used for
syntheses were of analytical grade. Solvents were dried before
use. Ca u tion ! Perchlorate salts of metal complexes are gener-
ally explosive. Although no detonation tendencies have been
observed, care is advised and handling of only small quantities
recommended.
P h ysica l Mea su r em en ts. A Shimadzu UV 2100 UV/vis
spectrophotometer was used to record electronic spectra in
solutions. 1H NMR spectra were measured in CDCl3 with a
Bruker Avance DPX 300 spectrophotometer and SiMe4 as the
internal standard. A Perkin-Elmer 240C elemental analyzer
was used to collect microanalytical data (C,H,N). Electrochemi-
cal measurements were done under a dry nitrogen atmosphere
on a PAR Model 370-4 electrochemistry system as reported
earlier.12 All potentials reported in this work are referenced
to an Ag-AgCl electrode and are uncorrected for junction
contribution. Electrical conductivities were measured by using
a Systronics 304 direct reading conductivity meter. IR spectra
were recorded with a Perkin-Elmer 783 spectrophotometer.
P r ep a r a tion of [Rh Cl(L1a )(L2a )](ClO4). A 100 mg (0.156
mmol) portion of the starting complex [RhCl2(L1a)2]ClO4 and
180 mg (0.312 mmol) of [Ag(L1a)2](ClO4) were dissolved in 30
mL of dry ethanol, and the mixture was refluxed over a steam
bath for 4 h. A yellowish green solution resulted, which was
then cooled and filtered through a quantitative filter paper to
remove the insoluble AgCl. The filtrate was then concentrated
to 10 mL, and a solid mass was precipitated out by the addition
of diethyl ether. The precipitate was redissolved in a minimum
volume of dichloromethane and the solution subjected to
column chromatography on a silica gel column (1 × 50 cm). A
green band was eluted with dichloromethane-acetonitrile
(20:1). The solvent was evaporated to dryness under vacuum
and recrystallized from a dichloromethane-hexane mixture.
Yield: 65% Anal. Found: C, 46.41; H, 2.98; N, 16.07. Calcd
for C27H21Cl2N8O4Rh: C, 46.59; H, 3.02; N, 16.10. ΛM ) 140
P r ep a r a tion of [Rh Cl(L1b)(L2a)]ClO4. This compound was
prepared similarly by using [RhCl2(L1b)2]ClO4 and [Ag(L1a)2]-
ClO4 in the proper stoichiometric ratio, and the yield is 60%.
Anal. Found: C, 47.38; H, 3.26; N, 15.76. Calcd for C28H23
-
Cl2N8O4Rh: C, 47.39; H, 3.24; N, 15.79. ΛM ) 155 Ω-1 M-1 cm2
(1 × 10-3 M in CH3CN). IR ν/cm-1 (KBr): ν(C-N) 1580;
ν(ClO4-) 625, 1100; ν(NdN) 1565; ν(Rh-Cl) 340.
P r ep a r a tion of [Rh Cl(L1b)(L2b)]ClO4. A similar procedure
was followed by using [RhCl2(L1b)2]ClO4 and [Ag(L1b)2]ClO4 in
the required stoichiometric ratio, which gave a yield of 65%.
Anal. Found: C, 48.20; H, 3.42; N, 15.46. Calcd for C29H25
-
Cl2N8O4Rh: C, 48.13; H, 3.45; N, 15.49. ΛM ) 140 Ω-1 M-1 cm2
(1 × 10-3 M in CH3CN). IR ν/cm-1 (KBr): ν(C-N) 1595;
ν(ClO4-) 630, 1100; ν(NdN) 1550; ν(Rh-Cl) 350.
X-r a y Cr ysta llogr a p h ic Exp er im en t. Crystallographic
data for RhCl2(L1a)2]ClO4 and [RhCl(L1a)(L2a)]ClO4 together
with their refinement details are collected in Table 3.
[Rh Cl2(L1a )2]ClO4.25 A suitable dark-colored single crystal
of the title compound was mounted on a CAD4 Enraf-Nonius
diffractometer. The unit cell parameters and crystal orienta-
tion matrix were determined by least-squares refinement of
25 accurately centered reflections. Intensity data were col-
lected in the ω-2θ scan mode using graphite-monochromated
Mo KR radiation. The intensity data were corrected for Lorentz
and polarization effects, and spherical absorption corrections
(25) (a) Sheldrick, G. M.; SHELXS 86: Program for the Solution of
Crystal Structure; University of Go¨ttingen, Go¨ttingen, Germany, 1985.
(b) Sheldrick, G. M. SHELXL 93: Program for the Solution of Crystal
Structure; University of Go¨ttingen, Go¨ttingen, Germany, 1993. (c)
Gabe, E. J .; Lepage, Y.; Charland, J . P.; Lee, F. L.; White, P. S.;
NRCVAX. J . Appl. Crystallogr. 1989, 22, 384. (d) Zsolnai, L.; 1994.
ZORTEP: A Program for the Presentation of Thermal Ellipsoids;
University of Heidelberg, Heidelberg, Germany. (e) Spek, A. L.
PLATON 99; Utrecht University, Utrecht, The Netherlands, 1999.
(23) Bandyopadhyay, P.; Bandyopadhyay, D.; Chakravorty, A.;
Cotton, F. A.; Falvello, L. R.; Han, S. J . Am. Chem. Soc. 1983, 105,
6327.
(24) Santra, B. K.; Thakur, G. A.; Ghosh, P.; Pramanik, A.; Lahiri,
G. K. Inorg Chem. 1996, 35, 3050.

5090 Organometallics, Vol. 18, No. 24, 1999
Ghosh et al.
were carried out using the NRCVAX suite of programs. The
structure was solved by the Patterson method followed by
successive Fourier and difference Fourier syntheses, using
SHELX86 (Sheldrick, 1986). Full-matrix least-squares refine-
ments on F2 were carried out using SHELXL-93, with aniso-
tropic displacement parameters for all non-hydrogen atoms.
Hydrogen atoms were constrained to ride on the respective
carbon atoms with an isotropic displacement parameter equal
to 1.2 times the equivalent isotropic displacement parameter
of their parent atom.
[Rh Cl(L1a )(L2a )]ClO4.26 Geometric and intensity data were
taken from a green platelike crystal of the title compound,
mounted at the end of a glass fiber, using a CAD-4 diffracto-
meter. Data were collected with normal procedures, and the
unit cell was determined from the coordinates of 24 scattering
vectors, each measured at 4 equivalent positions. During
intensity data collection 3 reflections were measured after
every 1/2 h of accumulated X-ray exposure. Data were corrected
for absorption using a posteriori method incorporated in the
program SHELXA. The corrections were applied at the point
of isotropic convergence. The positions of several atoms were
found by direct methods, and the structure was developed and
refined in a series of least-squares cycles and difference Fourier
maps. All hydrogen atoms were placed at calculated positions
and refined as riding atoms, each with an isotropic displace-
ment parameter set to 1.2 times the value of the equivalent
isotropic displacement parameter of its parent carbon atom.
All non-hydrogen atoms were refined anisotropically. In the
2
final refinement, 379 parameters were fitted to all 4747 Fo
data, for a data-to-parameter ratio of 12.5. The refinement
converged with the residuals given in Table 3. The 41
parameters used in the calculation of absorption corrections
were accounted for in the calculation of the esd’s of the
variables refined by least squares.
Ackn owledgm en t. Financial supports received from
the Department of Science and Technology, Council of
Scientific and Industrial Research, New Delhi, India,
and the Spanish Directorate General for Higher Educa-
tion under Grant PB 95-0792 are gratefully acknowl-
edged. We thank the staff at the National Diffractome-
ter Facility at IIT, Kanpur, India, for collecting X-ray
data on compound 1a .
(26) (a) Diffractometer Control Program: CAD4-PC Version 2.0;
Nonius BV, Delft, The Netherlands, 1995. (b) SHELXA (Version
97-1): Fortran program for empirical absorption corrections. (c) Cal-
culations were performed on an Alpha Station 200 4/166 (open VMS/
Alpha V 6.2) using the programs XCAD4B (Harms, 1995) and the
Commercial package SHELXTL (release 5.05/VMS) (Siemens Analyti-
cal X-ray Instruments, Inc., Madison, WI, 1996) and on a Hewlett-
Packard 9000 Model 715/50 (HP-UX V9.05) using public domain
software. (d) Sheldrick, G. M. SHELXL 97, Fortran program for crystal
structure refinement; University of Go¨ttingen, Go¨ttingen, Germany,
1997.
Su p p or tin g In for m a tion Ava ila ble: Text giving com-
plete details of the X-ray analyses of 1a and 2a and tables of
bond distances and angles, atomic coordinated, anisotropic
displacement parameters, and hydrogen atom coordinates for
the two compounds. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM990617T