consistent with spectroscopic data. The crystals of the trans,-
mer and cis,mer isomers are almost isomorphous, the structures
being controlled largely by the mer-Ir(PEt2Ph)3 set of atoms
which are almost identical. The structure of the cis,mer isomer
was complicated by some disorder between the arrangement
shown in Fig. 4 and another with the cyanide C(100)N(100)
and Cl(2) with reversed positions. The populations of these
two arrangements were refined and the most abundant
arrangement is that shown in Fig. 4 with a population of
0.796(5). The two mer isomers were completely pure isomeri-
cally and the disorder is not the result of an isomeric mixture.
However, in view of the almost isomorphous nature of these
crystals we would have expected an isomeric mixture to co-
crystallise. This is not the case here. Owing to the disorder in the
cis,mer isomer, it was difficult to obtain an accurate geometry
for the cyanide ligand with population 0.796(5) because it over-
lays a Cl of the minor form with population 0.204(5). To allow
the refinement of a chemically reasonable structure, the
C(100)᎐N(100) distance was constrained to be 1.135 Å. Other
details of the structure, such as the Ir᎐P and Ir᎐Cl distances, are
probably reliable and the thermal parameters for these atoms
are well behaved.
Having these structures allows some comparisons to be made
between the trans influences of the Cl, CN and PEt2Ph ligands.
For example, Ir᎐Cl distances depend upon the ligand trans to
Cl: 2.458(2) (Cltrans to CN), 2.443(2) (Cltrans to PEt2Ph) and
2.384(1), 2.379(1) Å (Cltrans to Cl). The trans influences are in
the order CN > PEt2Ph > Cl. The CN and PEt2Ph ligands also
have trans influences greater than that of Cl in comparing Ir᎐P
distances but it is not possible to separate CN from PEt2Ph in
this case. Thus Ir᎐P distances are 2.310(2) (PEt2Ph trans to Cl),
2.386(1) (PEt2Ph trans to CN) and 2.400(1), 2.374(1), 2.407(2)
and 2.384(2) Å (PEt2Ph trans to PEt2Ph). However, there are
significant differences in the Ir᎐P distances for the two mutually
trans PEt2Ph ligands in both mer complexes so that trans influ-
ences are not the only controlling factors. We believe that the
conformations of the PEt2Ph ligands are also significant. Each
PEt2Ph ligand has two substituents above and one below the
IrP3 plane. The mutually trans PEt2Ph ligands are eclipsed while
the unique PEt2Ph ligand adopts a less symmetrical conform-
ation which is favoured because it allows a close parallel align-
ment of the two Ph substituents (see Figs. 1 and 4). This parallel
alignment is associated with shorter Ir᎐P bond lengths. Thus
for the mutually trans PEt2Ph ligands in these complexes the
Ir᎐P distances are 2.374(1) and 2.384(2) Å for the Ph-aligned
phosphines and significantly longer for the others, 2.400(1) and
2.407(2) Å. We have described earlier how, when iridium
complexes are heavily stacked with tertiary phosphines, these
parallel phenyl alignments have a major effect on the structures
and that barriers to rotation about M᎐P bonds can be large
enough to lead to slow exchange and to separate 31P NMR
signals for the different rotamers.8,9 The complex trans-
[IrCl2(PMe2Ph)4]ϩ exists as three non-interconverting rotamers
at low temperatures.8 In the case of tris-diethylphenylphosphine
mer complexes, crowding is insufficient to prevent rapid
exchange of the trans PEt2Ph ligands by rotation about
Ir᎐P bonds in solution, but sufficient to influence Ir᎐P bond
lengths.
Table 4 Crystal data and structure solution and refinement param-
eters for the compounds trans,mer- and cis,mer-[IrCl2(CN)(PEt2Ph)3]a
trans,mer
cis,mer
Crystal size/mm
a/Å
b/Å
0.17 × 0.40 × 0.45
10.719(2)
13.994(1)
22.437(4)
92.50(2)
3362.4(9)
1.56
42.78
0.18 × 0.18 × 0.28
10.555(2)
13.783(2)
22.838(5)
93.58(2)
3316(1)
1.58
43.38
30, 13–27
c/Å
β/Њ
U/Å3
Dc/g cmϪ3
µ(Mo-Kα)/cmϪ1
No. orientation
reflections, 2θ range/Њ
2θ Range/Њ
hkl Range
Total data
Unique data
32, 17–29
5–53
5–50
0,0,Ϫ29 to 14,18,29 0,0,Ϫ28 to 3,17,28
7622
6935
6362
5761
Parameters in refinement 343
336
R (all data)b
0.0413
0.0562
0.0417
0.1100
1.089
0.001
1.75, Ϫ1.11
[I > 2σ(I]b
0.0313
0.0915
1.014
wR2 (all data)c
Goodness of fit
Maximum ∆/σ
Maximum peak,
hole in final difference
Fourier map/e ÅϪ3
0.001
1.33, Ϫ1.00
a
Common to both compounds:colourlesscrystals, formula = C31H45Cl2-
IrNP3, M = 787.78, monoclinic, space group, P21/n, Z = 4, F(000) =
1576, ω scan mode, direct methods structure solution. Graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å), three standard
reflections every 97, no decay, data corrected for absorption empirically
by ψ-scan method, maximum and minimum transmission 1.000 and
0.352 for trans,mer and 0.920 and 0.545 for cis,mer, full-matrix least-
squares refinement of F2. b R = Σ(|Fo| Ϫ |Fc|)/Σ|Fo|. c wR2 = [Σw(Fo2 Ϫ
¹
2
Fc )2/Σw(Fo2)2]² for all data.
the form of [N(PPh3)2]Cl, but this does not alter the course of
the isomerisation of trans,mer-[IrCl2(CN)(PEt2Ph)3] to the fac
and the cis,mer isomers.
Experimental
Materials
Chloroiridic acid, diethylphenylphosphine and K13CN were
used as purchased from Aldrich. The 400 MHz NMR spectra
were obtained on a Varian VXR400 spectrometer and IR
spectra on a Nicolet 280 FTIR spectrometer. The complex mer-
[IrCl3(PEt2Ph)3] was prepared as yellow crystals in 79% yield
from chloroiridic acid and PEt2Ph in refluxing ethanol and HCl
following a reported method.1
Synthesis of trans,mer-[IrCl2(CN)(PEt2Ph)3]
The complex mer-[IrCl3(PEt2Ph)3] (0.200 g) and sodium
cyanide (0.0248 g) were dissolved in methanol (20 cm3) and the
solution refluxed for 2 h. The solution was filtered and the
volume reduced on a Rotavap down to 15 cm3. Bright yellow
crystals (0.142 g, 72%) deposited overnight at room tem-
perature (Found: C, 47.1; H, 5.6; Cl, 9.1; N, 1.85. C31H45Cl2-
IrNP3 requires C, 47.25; H, 5.75; Cl, 9.0; N, 1.8%). The complex
trans,mer-[IrCl2(13CN)(PEt2Ph)3] was prepared similarly using
90%-enriched K13CN.
Conclusion
Whereas yellow mer-[IrCl3(PEt2Ph)3] photoisomerises to the fac
isomer which is extremely insoluble and forms colourless crys-
tals, trans,mer-[IrCl2(CN)(PEt2Ph)3] gives the fac and the cis,-
mer isomers photochemically. All isomers remain in solution so
the isomerisations can be followed straightforwardly and
extended photolysis leads exclusively to the cis,mer isomer.
Formation of the bridged cyanide dinuclear complex fac,fac-
[(PhEt2P)3Cl2Ir(µ-CN)IrCl(CN)(PEt2Ph)3]Cl during the course
of the isomerisation is suppressed by addition of chloride ion in
Photolysis reactions
Reactions were carried out by photolysing dichloromethane
solutions in Pyrex tubes placed next to a fluorescent tube. They
were not carried out quantitatively in terms of light intensities
but care was taken to keep the light intensity constant in a given
experiment. When monitoring by IR spectroscopy, samples
were removed by syringe and IR spectra recorded in 0.1 cm
thickness cell with CaF2 windows. Reactions were carried out in
J. Chem. Soc., Dalton Trans., 1997, Pages 3519–3524
3523
Deeming, Antony J.
