over P4O10. Yield essentially quantitative (Found: C, 53.05; H,
4.99; N, 13.48. Calc. for C32H36Cl2N7O2Rh: C, 53.00; H, 4.97;
N, 13.53%).
The other two complexes of this type were prepared by simi-
lar procedures and in similar yields (Found: C, 43.87; H, 5.20;
N, 16.40. Calc. for C22H32Cl2N7O2Rh 2a: C, 43.96; H, 5.33; N,
16.32. Found: C, 54.28; H, 5.39; N, 13.12. Calc. for
C34H40Cl2N7O2Rh 2c: C, 54.22; H, 5.32; N, 13.02%).
Triethylammonium cct-dichlorobis[(phenylazo)benzaldoxim-
ato]rhodate(III), [NEt3H][cct-RhCl2L2 ] 3b.
A solution of
2
[NEt3H][tcc-RhCl2L2 ] (0.1 g, 0.138 mmol) in benzene (25 cm3)
2
was heated to reflux for 10 min, during which time it changed
from green to pink. The solution was evaporated to dryness in
vacuo and the desired complex obtained as a pink crystalline
solid in nearly quantitative yield (Found: C, 52.98; H, 4.95; N,
13.58. Calc. for C32H36Cl2N7O2Rh: C, 53.00; H, 4.97; N,
13.53%).
The other two complexes of this family were prepared simi-
larly in similar yields (Found: C, 43.99; H, 5.35; N, 16.24. Calc.
for C22H32Cl2N7O2Rh 3a: C, 43.96; H, 5.33; N, 16.32. Found: C,
54.18; H, 5.32; N, 12.95. Calc. for C34H40Cl2N7O2Rh 3c: C,
54.22; H, 5.32; N, 13.02%).
Fig. 4 Electronic spectra of an isomerising solution of [NEt3H]-
[tcc-RhCl2L2 ] 2b in toluene at 358 K. The arrows indicate the increase
and decrease2of band intensities as the reaction proceeds
Rate measurements
of activation. This is the first example of such isomerisation
resulting from oxime–oximato bridge-proton dissociation.
Isomerisation of complex 2b to 3b was monitored spectro-
photometrically in toluene. A solution (25 cm3) of 2b of known
concentration (5.0 × 10Ϫ4 mol dmϪ3) was taken in a three-
necked flask fitted with a thermometer, a rubber septum and a
water-cooled condenser. The flask was heated in an oil-bath the
temperature of which could be accurately controlled. Aliquots
(0.50 cm3) of solution were withdrawn via the rubber septum at
known intervals and then cooled immediately to 298 K to halt
the reaction. Each was then diluted to 5.00 cm3 and used to
monitor the conversion spectrophotometrically. The absorption
(At) at 412 nm was used. Values of the first-order rate constant
k were obtained from slopes of linear least-squares plots of
Ϫln(|A∞ Ϫ At|) against t. A minimum of 12 data points cover-
ing three half-lives was used for each calculation. The activ-
ation parameters ∆H‡ and ∆S‡ were obtained from Eyring
plots.20
Experimental
Materials
Arylazooximes were prepared by reported methods19 and
RhCl3ؒ3H2O was obtained from Arora-Matthey, Calcutta.
Toluene for rate studies was dried by distilling over sodium–
benzophenone. All other chemicals were used as received.
Physical measurements
Infrared spectra were recorded with a Perkin-Elmer 783 spec-
trophotometer, electronic spectra with a Hitachi 330 spectro-
photometer. A Perkin-Elmer 240C elemental analyser was
used to collect microanalytical data (C, H, N). Conductivity
measurements were carried out in acetonitrile on a Philips
PR9500 bridge.
Crystallography
Single crystals of complexes 1b (0.20 × 0.34 × 0.40 mm) and 2b
(0.26 × 0.46 × 0.50 mm) were grown by slow diffusion of
hexane into dichloromethane solutions and those of 3c (0.20 ×
0.20 × 0.25 mm) by slow diffusion of hexane into acetone,
followed by slow evaporation. Cell parameters were determined
by least-squares fit of 30 machine-centred reflections (2θ =
15–30Њ). Systematic absences afforded the space group P21/c for
1b and P21/n for 3c; 2b could belong either to Pna21 or Pnma
and successful structure solution confirmed the former. Data
were collected by the ω-scan technique in the range of
3 р 2θ р 50Њ for 1b and 2b and of 3 р 2θ р 45Њ for 3c. Two
check reflections measured after every 98 did not show any sig-
nificant change in intensity. Data were corrected for Lorentz-
polarisation effects and absorption (azimuthal scans21). Of the
4556 (1b), 3057 (2b) and 4780 (3c) unique reflections, 3264, 2382
and 2667 respectively with I > 3σ(I), I > 2.5σ(I) and I > 3σ(I)
respectively were used for structure solution (direct method).
All the non-hydrogen atoms were treated anisotropically and in
the case of 1b the oxime H was refined isotropically. All the
hydrogen atoms in 2b and 3c were added at calculated positions
with fixed U (0.08 Å2). Least-squares refinements were per-
formed by full-matrix procedures. All calculations were done on
a Micro-VAXII computer with the SHELXTL PLUS pro-
gram22 and crystal structure plots were drawn using ORTEP.16
Significant crystal data are listed in Table 4.
Syntheses
tcc-Dichloro[(phenylazo)benzaldoximato][(phenylazo)-
benzaldoxime]rhodium(III), tcc-[RhCl2L2(HL2)] 1b. The com-
pound RhCl3ؒ3H2O (0.10 g, 0.38 mmol) was dissolved in hot
dry ethanol (15 cm3). To this HL2 (0.188 g, 0.835 mmol) dis-
solved in the same solvent (10 cm3) was added and the mixture
was heated to reflux for 10 min. The solution was then cooled to
room temperature. The red crystals deposited were filtered off,
washed thoroughly with ethanol and water and then dried in
vacuo over P4O10. Yield 0.130 g (55%) (Found: C, 50.00; H, 3.45;
N, 13.40. Calc. for C26H21Cl2N6O2Rh: C, 50.04; H, 3.37; N,
13.47%).
The other two complexes of this family were synthesized with
similar yields (Found: C, 38.49; H, 3.51; N, 16.90. Calc. for
C16H17Cl2N6O2Rh 1a: C, 38.44; H, 3.40; N, 16.82. Found: C,
51.47; H, 3.86; N, 12.81. Calc. for C28H24Cl2N6O2Rh 1c: C,
51.57; H, 3.84; N, 12.89%).
Triethylammonium tcc-dichlorobis[(phenylazo)benzaldoxim-
ato]rhodate(III), [NEt3H][tcc-RhCl2L22] 2b. To a solution of tcc-
[RhCl2L2(HL2)] (0.1 g, 0.16 mmol) in dichloromethane (20 cm3)
was added Et3N (0.33 g, 0.33 mmol). The solution changed
from red to green and was evaporated to dryness in vacuo. The
green solid obtained was washed with hexane and dried in vacuo
CCDC reference number 186/794.
464
J. Chem. Soc., Dalton Trans., 1998, Pages 461–465
Ganguly, Sanjib
