1776
V. Cˆırcu et al. / Polyhedron 21 (2002) 1775Á1778
/
under a nitrogen atmosphere: the following step was
performed in air. The powder was dissolved in dichlor-
omethane (4 ml), filtered to remove a small amount of
insoluble material, treated with hexane and allowed to
Table 1
Crystal
[Rh(CN)(O2)(PPh3)2(XNC)](CH2Cl2)
data
and
structure
refinement
for
Empirical formula
Formula weight
Temperature (K)
C47H41Cl2N2O2P2Rh
901.57
293(2)
stand for 1 day at r.t. to give redÁbrown crystals. The
/
product was found to be insoluble in chloroform,
dichloromethane, toluene and dimethylsulphoxide
(even with warming). Yield: 0.015 g (22%). IR (KBr)
n(CN) 2160 (s), n(XCN) 2116 (s), n(O2) 863 (m). Anal.
Calc. for C47H41Cl2N2O2P2Rh C, 62.61; H, 4.58; N,
3.11. Found: C, 62.27; H, 4.57; N, 3.13%. The last step
(crystallisation in air) could not be relied upon to give a
product on every occasion.
˚
Wavelength (A)
0.71073
monoclinic
P21/c
Crystal system
Space group
Unit cell dimensions
˚
a (A)
16.569(3)
11.3593 (17)
23.050(4)
90
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
99.947(3)
90
3
˚
2.2. X-ray structure determination
V (A )
4273.1(11)
4
1.401
Z
Dcalc (Mg mꢁ3
Absorption coefficient
)
Intensity data were collected on a Bruker SMART 1K
CCD area detector diffractometer with graphite mono-
chromated Mo Ka radiation (50 kV, 30 mA). The
collection method involved v-scans of width 0.38. Data
0.640
(mmꢁ1
F(000)
)
1848
0.44ꢃ0.15ꢃ0.11
Crystal size (mm)
Range for data collection
Index ranges
1.25Á28.338
/
reduction was carried out using the program SAINTꢂ/
ꢁ215h 522, ꢁ155k 514,
ꢁ225l 530
29 130
[19] and absorption corrections were made using the
program SADABS [20]. The crystal structure was solved
by direct methods using SHELXTL [21]. Non-hydrogen
atoms were first refined isotropically followed by
anistropic refinement by full matrix least-squares calcu-
lation based on F2 using SHELXTL. All hydrogen atoms
were placed geometrically and allowed to ride on their
respective parent atoms. The structure contains a
disordered dichloromethane molecule; the disorder was
resolved by applying a treatment involving three differ-
ently orientated molecules as rigid bodies and summing
their contributions to unity. Diagrams were generated
using SHELXTL and PLATON [22]. Structure and refine-
ment data are given in Table 1.
Reflections collected
Independent reflections
Completeness to umax
Max/min transmission
10 538 [Rintꢀ0.0323]
98.8%
0.9329, 0.7660
Data/restraints/parameters 10 538/1/498
Goodness-of-fit on F2
1.046
Final R indices [I ꢀ2s(I)] R1ꢀ0.0476, wR2ꢀ0.1333
R indices (all data)
Largest difference peaks
R1ꢀ0.0979, wR2ꢀ0.1589
1.238 and ꢁ1.004
ꢁ3
˚
(e A
)
give an Rh(III) peroxo complex [24]), a process favoured
by electron-donating ligands on Rh. The CNꢁ ion,
while carrying a negative charge, is not normally
considered to be strongly electron-donating, certainly
not more so than Clꢁ or N3ꢁ. On two different scales of
electron-donating ability (those of Vaska [25], based on
carbonyl stretching frequencies of complexes
3. Results and discussion
The complex [Rh(CN)(O2)(PPh3)2(XNC)] Fig. 1 has
octahedral geometry with distortions arising from the
[M(Y)(PPh3)2(CO)] (MꢀRh, Ir) and Chatt [26], based
/
on the reversible one-electron oxidation potential of
[Cr(CO)5(Y)]) the CNꢁ ligand is rated as less electron-
donating than Clꢁ, N3ꢁ and NCOꢁ. The ability of
presence of the OÃ
/
O bond, which restricts the OÃ
/
RhÃ
/
O
angle to 41.77(11)8. The RhÃ
/
O and OÃO bond lengths
/
(Table 2) are not significantly different from those
reported for [Rh(O2){PPh2(2-C6H4CHNiPr)}2]BPh4 [9]
and fall towards the middle of the ranges observed for
CNꢁ
to
activate
the
complex
trans-
[Rh(CN)(PPh3)2(XNC)] towards reaction with O2
must, therefore, reside elsewhere, most probably in its
polarisability.
Rh(O2) complexes [3Á15]. The principal intermolecular
/
interactions are a close contact (2.518 A) between a
phenyl hydrogen (attached to C54) and oxygen O1 (of
The cyano ligand differs from Clꢁ, N3ꢁ, NCOꢁ,
˚
NCSꢁ, N(CN)2 and NCBPh3 which, according to
Pearson’s classification [27], are either hard or border-
line, while CNꢁ is soft, i.e. more polarisable. Although
CNBPh3 is also soft it is, in effect, a CNꢁ modified by
attachment of a strong Lewis acid, and its electron-
donating ability and polarisability will consequently be
reduced. From this perspective the four soft ligands of
trans-[Rh(CN)(PPh3)2(XNC)] can be regarded as con-
ꢁ
ꢁ
an adjacent molecule) and several CÃ
actions.
From the series [Rh(Y)(PPh3)2(XNC)] (Yꢀ
/
HÁ Á Áp [23] inter-
/Cl, N3,
NCO, NCS, N(CN)2, NCBPh3, CNBPh3, CN) the only
complex to form an adduct with O2 is the cyano
derivative. The formation of an O2 adduct involves the
transfer of electron density from rhodium to oxygen (to
C?rcu, Viorel
